Industrial Minerals of Mozambique - InfoMine
Industrial Minerals of Mozambique - InfoMine
Industrial Minerals of Mozambique - InfoMine
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Cilek: Front page<br />
Contents Page <strong>of</strong> the Book<br />
<strong>Industrial</strong> <strong>Minerals</strong> <strong>of</strong> <strong>Mozambique</strong><br />
by Dr. Václav Cílek<br />
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Cilek: Front page<br />
View from Isla <strong>Mozambique</strong> photo by Dr. Václav Cílek (250 kB)<br />
BOOK REVIEW (2 kB)<br />
1. INTRODUCTION (6 kB)<br />
2. GEOLOGICAL REVIEW <strong>of</strong> <strong>Mozambique</strong> (61 kB)<br />
3. DEPOSITS <strong>of</strong> INDUSTRIAL MINERALS<br />
3.1 Andalusite, kyanite, and sillimanite (20 kB)<br />
3.2 Asbestos (23 kB)<br />
3.3 Beryllium minerals (13 kB)<br />
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Cilek: Front page<br />
3.4 Feldspar (44 kB)<br />
3.5 Fluorite (30 kB)<br />
3.6 Graphite (25 kB)<br />
3.7 Lithium minerals (15 kB)<br />
3.8 Magnesite (9 kB)<br />
3.9 Mica (20 kB)<br />
3.10 Rare-earth minerals (41 kB)<br />
3.11 Talc and soapstone (7 kB)<br />
3.12 Titanium and zirconium minerals (46 kB)<br />
3.13 Zeolites (9 kB)<br />
4. DEPOSITS <strong>of</strong> INDUSTRIAL ROCKS<br />
4.1 Bauxite and aluminum laterite (42 kB)<br />
4.2 Bentonite - smectites (28 kB)<br />
4.3 Clays (45 kB)<br />
4.4 Decorative stones (29 kB)<br />
4.5 Diatomite (18 kB)<br />
4.6 Glass sands and foundry sands (20kB)<br />
4.7 Gypsum and anhydrite (20kB)<br />
4.8 Kaolin (37 kB)<br />
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Cilek: Front page<br />
4.9 Limestone and dolomitic limestone (52 kB)<br />
4.10 Mineral pigments (6 kB)<br />
4.11 Nephetine syenite (27 kB)<br />
4.12 Perlite (14 kB)<br />
4.13 Phosphates and apatite (34 kB)<br />
4.14 Quartz raw materials (14 kB)<br />
4.15 Salt (8 kB)<br />
5. DEPOSITS and INDUSTRIAL USE <strong>of</strong> building raw materials (4 kB)<br />
5.1 Raw materials for cement and lime production (10 kB)<br />
5.2 Raw materials for brick production (6 kB)<br />
5.3 Resources and production <strong>of</strong> building stone (7 kB)<br />
5.4 Resources <strong>of</strong> sand and gravel (11 kB)<br />
6. CERAMIC and GLASS INDUSTRY; REFRACTORIES<br />
6.1 Ceramic industry (6 kB)<br />
6.2 Glass industry (6 kB)<br />
6.3 Refractories (9 kB)<br />
7. PROSPECTIVE and POTENTIAL industrial minerals and their uses (7 kB)<br />
8. Minerogenetic provinces and epochs (6 kB)<br />
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Cilek: Front page<br />
9. SELECTED REFERENCES (16 kB)<br />
© Václav Cílek 1989<br />
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Cilek: Bookreview<br />
<strong>Industrial</strong> <strong>Minerals</strong> <strong>of</strong> <strong>Mozambique</strong><br />
By Václav Cílek,<br />
Prague: Czech Geological Office, 1989<br />
Originally Paperback, 250 mm * 174 mm, 326 p.<br />
ISBN 80-7075-027-8<br />
Not for sale<br />
This is a most important landmark book on <strong>Mozambique</strong> coming at a time <strong>of</strong> improving outlook for the<br />
country. The disruptive 15-year civil war between Frelimo government and the Renamo guerrillas has<br />
meant that numerous industrial mineral deposits and prospects have lain dormant and so Dr. Cilek's<br />
review <strong>of</strong> the industrial minerals sector provides a useful plank for the launch <strong>of</strong> renewed interest in<br />
exploration and development.<br />
Surprisingly, the Geological Survey <strong>of</strong> Czechoslovakia opted for publication in English in preference to<br />
Portuguese, the <strong>of</strong>ficial language <strong>of</strong> <strong>Mozambique</strong>. Furthermore, in view <strong>of</strong> the country's tiny output <strong>of</strong><br />
industrial minerals, another surprise is the massive size <strong>of</strong> the publication - 326 pages. Whereas English<br />
language and completeness are very helpful many passages <strong>of</strong> text are poorly edited and detract from the<br />
overall presentation.<br />
The order <strong>of</strong> presenting the principal information adopts the conventional A-Z format, first for industrial<br />
minerals (andalusite to zeolite) then for industrial rocks (bauxite to salt). In the final sections the author<br />
discusses construction materials, manufacturing applications and future prospects. Each commodity is<br />
introduced with background information and a general overview followed by a detailed description <strong>of</strong> all<br />
known deposits and occurrences within <strong>Mozambique</strong> and presentation <strong>of</strong> all the available data. These<br />
commodity sections finish up with appropriate conclusions and summary comments.<br />
The material assembled provides an up-to-date record <strong>of</strong> the current knowledge about <strong>Mozambique</strong><br />
industrial minerals and should be <strong>of</strong> considerable interest to those in the mining industry contemplating<br />
ventures into this underdeveloped and under-explored region.<br />
Book review: D. Nichol, <strong>Minerals</strong> Industry International, March 1991, p. 19.<br />
The idea <strong>of</strong> electronic version <strong>of</strong> the book started when I had read the book with great interest and then<br />
later met Dr. Vaclav Cilek two times. His positive reaction and permission about copyright made it all<br />
possible. The electronic version <strong>of</strong> the book started intensively in winter 2001/2002 when all the text<br />
pages were scanned at VTT with the generous help <strong>of</strong> Mr. Eero Hietalahti. During the spring and<br />
summer 2002 all the figures were scanned and editing work was started by Pr<strong>of</strong>. Veikko Komppa,<br />
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Cilek: Bookreview<br />
originator <strong>of</strong> the project. Digitizing a printed book is not so straightforward business because technical<br />
and chemical text is full <strong>of</strong> errors after scanning. Also the tables do not scan properly. Tables and bad<br />
pages were mainly corrected by myself or by Ms. Mervi Efraimsson.<br />
The purpose <strong>of</strong> this e-version was, and it still is, to be used as a basic reference and training book when<br />
World Bank's <strong>Mozambique</strong> Project will start in the area <strong>of</strong> the <strong>Industrial</strong> <strong>Minerals</strong>. The e-version will be<br />
improved gradually but due to minimal resources allocated at the moment for the work, nothing fancy<br />
will be produced.<br />
Father <strong>of</strong> the e-version:<br />
August 2002, Pr<strong>of</strong>. Veikko Komppa, VTT Processes<br />
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Cilek: 1. Introduction<br />
1. INTRODUCTION<br />
Mozambican resources <strong>of</strong> industrial minerals and rocks are large enough to cover most <strong>of</strong> the<br />
requirements <strong>of</strong> the national industry and to contribute also to the export. The most recent data on more<br />
than forty industrial raw materials <strong>of</strong> <strong>Mozambique</strong> will help the geologist, the mining engineer, the<br />
planners and decision-makers in the government to find the best solution for the present and future<br />
industrial development. This first book on Mozambican resources <strong>of</strong> industrial minerals and rocks<br />
intends to present basic data on non-metallics which are <strong>of</strong> great importance in the development <strong>of</strong> a<br />
number <strong>of</strong> common industrial branches. Economic recovery and development cannot take place without<br />
a progress in the building and silicate industry, chemistry, agriculture and environmental protection. And<br />
just industrial raw materials - known also as non-metallics - are the main basis for this development.<br />
Being bulk materials they must be extracted and utilized locally because are cheap materials and cannot<br />
be imported. Besides the bulk materials, modern industrial minerals include also several valuable raw<br />
materials mined in small quantities and which after the beneficiation can become the most important in<br />
our era <strong>of</strong> the new technical revolution.<br />
The primitive man started to utilize nonmetallic materials in the production <strong>of</strong> stone axes or spears with<br />
stone points, or clay in the pottery production. In the Bronze Age, and later the Iron Age, stone<br />
implements were replaced by metallic ones and this started the industrial revolution which led to a heavy<br />
abuse <strong>of</strong> mineral resources, to economic tremors <strong>of</strong> the present days. The new technological revolution<br />
returns to a utilization <strong>of</strong> industrial minerals and rocks, naturally on much higher level than during the<br />
Stone Age. The new technical revolution is the new era <strong>of</strong> non-metallics. This era substitutes expensive<br />
copper by common silica, special metallic alloys by ceramic masses in the space industry, metallic<br />
engines by the construction <strong>of</strong> ceramic engines that are better than the metallic ones, microelectronics<br />
use structural properties <strong>of</strong> cheep silicate materials, miniaturization is based on the use <strong>of</strong> rare earth<br />
elements and new composite materials display extra ordinary properties by combining metallic and<br />
nonmetallic materials. But even the common products <strong>of</strong> the modern silicate industry, when using<br />
nontraditional processes, can attain special properties - special cements can be used for the production <strong>of</strong><br />
hulls <strong>of</strong> ships, ultra fine ground limestone can substitute kaolin in paper and save about 30% <strong>of</strong> synthetic<br />
material when used as a filler, besides an improvement <strong>of</strong> physical and mechanical properties, smectites<br />
(bentonites) and other absorbing materials can save up to 70% <strong>of</strong> fertilizers in sandy soils which<br />
otherwise could be washed away etc. Most <strong>of</strong> these materials are present in <strong>Mozambique</strong>, but have not<br />
yet been investigated. One <strong>of</strong> the weakest points <strong>of</strong> the utilization <strong>of</strong> Mozambican mineral raw materials<br />
is the low degree <strong>of</strong> technological research both in the field <strong>of</strong> "progressive" materials, and in the<br />
production <strong>of</strong> such common products as bricks and tiles, leaving alone the white ceramic production,<br />
refractory materials etc.<br />
Abundant industrial mineral resources are kaolin, materials for refractories, high quality graphites,<br />
metallurgical grade fluorite, large reserves <strong>of</strong> nepheline syenites, rare-earth minerals, zirconium and<br />
lithium minerals, large reserves <strong>of</strong> gypsum and anhydrite (also for sulphuric acid production), glass<br />
sand, limestone and diatomite. Also building materials are ubiquitous.<br />
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Cilek: 1. Introduction<br />
Missing or in small quantity or <strong>of</strong> a low quality are white ceramic clays (ball and bonding clays),<br />
industrial salts, asbestos, magnesite and dolomite, vermiculite, <strong>of</strong> the chemical materials these are<br />
sodium carbonate and sulphate, borates, bromine, iodine and nitrates; phosphates (apatite) are abundant<br />
but <strong>of</strong> low quality.<br />
The volume is introduced by a brief review <strong>of</strong> the Mozambican geology and mining.While the<br />
knowledge <strong>of</strong> the Archean and Precambrian regions in the W a NW is good and adequate to the needs <strong>of</strong><br />
a mineral exploration, the situation in the NE comprising the provinces Niassa, Nampula and Cabo<br />
Delgado is somehow obscure in spite <strong>of</strong> the fact, that a new geological map, scale 1 :1,000 000, has just<br />
been published. This region needs a detailed geological mapping and further exploration work for<br />
graphite, marble, nepheline syenite, ultrabasic rocks, kimberlites and pegmatites must be supported.<br />
The raw materials are divided in three parts in alphabetic order:<br />
* deposits <strong>of</strong> industrial minerals<br />
* deposits <strong>of</strong> industrial rocks<br />
* building materials.<br />
The last part <strong>of</strong> our short review deals with the production <strong>of</strong> cement and lime, brick industry and a<br />
survey <strong>of</strong> resources <strong>of</strong> building stone, sand and gravel. This is followed by a chapter on ceramic and<br />
glass industries and some proposals for a future production <strong>of</strong> refractories.<br />
The book is concluded by a short review <strong>of</strong> prospective materials and minerogenetic provinces and<br />
epochs.<br />
The selected literature contains just fundament publications and reports.<br />
Several paragraphs dealing with particular raw materials are complemented by conclusion and<br />
recommendation expressing the author's opinion on the subject. It is hoped that some <strong>of</strong> these<br />
conclusions will be changed in the future hand in hand with an increasing knowledge <strong>of</strong> the geology <strong>of</strong><br />
non-metallics and a subsequent industrial development.<br />
<strong>Mozambique</strong> can supply the neighboring countries <strong>of</strong> SADEC (Southern Africa Development and<br />
Economic Cooperation) with a number <strong>of</strong> industrial materials - kaolin, feldspar, diatomite, glass sand,<br />
products <strong>of</strong> nepheline syenite beneficiation, talc, bentonite and materials for refractories. Of the group <strong>of</strong><br />
building materials, the country can export cement and lime <strong>of</strong> the highest quality. It is also hoped, that<br />
sulphuric acid could be produced on the basis <strong>of</strong> anhydrite utilization in addition to a substantial quantity<br />
<strong>of</strong> fertilizers.<br />
© Václav Cílek 1989<br />
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Cilek: 2. Geological Review <strong>of</strong> <strong>Mozambique</strong><br />
2. GEOLOGICAL REVIEW OF MOZAMBIQUE<br />
<strong>Mozambique</strong> - Republica Popular de Moçambique - covers an area <strong>of</strong> 799,380 km2 and extends from 10°27'<br />
northern latitude at the mouth <strong>of</strong> the river Rovuma to 26°52' southern latitude at Ponta d'Ouro. It is bordered in<br />
the N by Tanzania, in the W by Malawi, Zambia and Zimbabwe and the SW by the Republic <strong>of</strong> South Africa<br />
and the Kingdom <strong>of</strong> Swaziland. It has 12,130 000 inhabitants (1980 consensus) with an average density <strong>of</strong> 15<br />
inhabitants per km2 and is divided into ten provinces.<br />
Geomorfological division: this is based on a series <strong>of</strong> belts in decreasing altitude from the interior to the<br />
Indian Ocean coast. <strong>Mozambique</strong> covers mainly the coastal belt fronting on the sea; its important ports serve<br />
the interior African states. There are four principal belts: 1. Interior belt above 1,000 m altitude with several<br />
mountains above 2,000 m near the Zimbabwe border-Precambrian 2. Alto Planalto belt, 1,000 to 600 m<br />
altitude, with an escarpment on the NE - Precambrian-Karroo 3. Medio Planalto belt, 600 to 200 m, Lebombo<br />
Mts. altitude 600 m 4. Planicie -belt <strong>of</strong> lowlands with elevations between 200 and 0 m savanna landscape,<br />
dunes, marshes, lagoons. Good information on Mozambican geomorphology is available from the map "Carta<br />
Geomorfologica", scale 1:2,000 000, elaborated by S. Bondyrev in 1983.<br />
The main rivers, from N to S: Rovuma river fronting on Tanzania in the N, opening in a delta (deposit <strong>of</strong><br />
heavy minerals at Msimbati - Cilek 1976); the Lurio river with a small delta; the Zambezi river, length 850<br />
km. It enters <strong>Mozambique</strong> at Zumbo, narrows to enter an artificial lake at Cabora Bassa, than narrows again<br />
past the town <strong>of</strong> Tete to enter the Lupata Gorge. Then it crosses the East African graben which is traversed<br />
from N-S by the younger Urema-Chire graben which served, originally, for a deviation <strong>of</strong> the flow <strong>of</strong> the<br />
Zambezi along the Cheringoma escarpment to the present port <strong>of</strong> Beira; the Save river with a small delta and,<br />
in the south, the rivers Limpopo and Incomati. The capital is Maputo, former Lourenço Marques, an important<br />
port in the south with railway links to RSA, Swaziland and Zimbabwe. In the centre <strong>of</strong> the country, port Beira<br />
serves the transport to Zimbabwe and interior regions with the town <strong>of</strong> Manica (former Macequece), an old<br />
mining centre with gold production and a geological museum, further the town Tete in the Zambezi valley<br />
with important coal mines at Moatize, with links to Malawi. On the NE side <strong>of</strong> the Zambezi delta the port<br />
Quelimane handles exports <strong>of</strong> the Zambezi Province (tea, copra, lobster and sugar). The main port <strong>of</strong> N-<br />
<strong>Mozambique</strong> is Nacala with railway links to Malawi and the lake Niassa. The division <strong>of</strong> <strong>Mozambique</strong> into<br />
the provinces is shown in Fig. 2.1.<br />
The geological situation <strong>of</strong> <strong>Mozambique</strong> has been described in various comprehensive publications. The first<br />
book on this subject with simple geological map, was published by Andrade (1929); Borges made the similar<br />
compilation in 1940 and 1949, Freitas in 1957. The last geological maps <strong>of</strong> the Mozambican territory were<br />
made by Oberholzer (1966,1968-Carta geologica 1:2,000 000) and Alfonso (1978).<br />
Fig.2.1 Administrative Divisions <strong>of</strong> <strong>Mozambique</strong> (189 kB)<br />
After the independence in 1975 most <strong>of</strong> the country was almost unknown except for the main deposits found<br />
by prospectors and hunters such as pegmatites <strong>of</strong> the Alto Ligonha district, graphite at Angonia and Nampula,<br />
coal at Moatize, gold at Manica and many small deposits <strong>of</strong> semiprecious and precious stones. According to<br />
Jourdan (1986) 66% <strong>of</strong> systematic geological work was done between 1975 and 1983 by experts from<br />
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Cilek: 2. Geological Review <strong>of</strong> <strong>Mozambique</strong><br />
Jugoslavia, USSR, GDR, Sweden, UK, France, Italy, Bulgaria, Czechoslovakia, UN-agencies and, <strong>of</strong> course,<br />
by local Mozambican geological brigades. After 1983, most <strong>of</strong> the field activities was hampered by the actions<br />
<strong>of</strong> antigovernmental forces, but despite this, the geological evaluation programme was started and several<br />
basic geological works originated or were in preparation: Hunting Geology and Geophysics Ltd. edited an<br />
comprehensive report (1984) about the central and southern part (Tete, S<strong>of</strong>ala, Manica Provinces), ENH -<br />
Empresa Nacional de Hidrocarbonetos de Moçambique (1986) concluded the evaluation <strong>of</strong> sedimentary basins<br />
and finally BRGM published a geological map, scale 1 : 1,000 000, with explanations (1986). These three<br />
latter publications were used as a basis <strong>of</strong> the present geological review.<br />
The development <strong>of</strong> the Mozambican Precambrian was depending on the geological evolution <strong>of</strong> E-Africa<br />
and on the origin and the separation <strong>of</strong> the Gondwana continent. The continental fit is presented in Fig. 2.2.<br />
The old Gondwana in the E-African region was built by the continental nuclei - the cratons <strong>of</strong> Dodoma,<br />
Congo, Bangweulu, Zimbabwe and Transvaal <strong>of</strong> the Archean, to the Middle Proterozoic (3,800 - 2,500 m. y.);<br />
around their passive continental margins was deposited the flyshoid facies during the ifumide orogeny (1,800 -<br />
1,300 m. y.). This flyshoid deposits can be traced over a distance <strong>of</strong> 5,000 km and are known as Group Muva<br />
in Zambia and Group Rushinga in <strong>Mozambique</strong>, followed by the development <strong>of</strong> a volcanic arc <strong>of</strong> the Sasare<br />
type and completed by strong granitization around 1,300 m. y. ago. The structural development <strong>of</strong> the<br />
<strong>Mozambique</strong> belt within the Gondwana continent was complicated further during the <strong>Mozambique</strong> orogenic<br />
phase and by the Pan-African orogenic phase along the craton margin as seen in the Group Zambue in the NW<br />
corner <strong>of</strong> <strong>Mozambique</strong>. The central Gondwana in the area <strong>of</strong> today's <strong>Mozambique</strong> was "cut" across by two<br />
distinctive tectonic belts, probably collision zones, which were reactivated during 1,100 - 900 m. y. and<br />
represented in the W by the Mid-Zambezi graben -the Mylonite Zone <strong>of</strong> Hunting (1984) see Fig. 4. 4. 2, and<br />
by the Lurio belt in the E. These zones <strong>of</strong> ENE - WSW direction, which are in fact a continuation <strong>of</strong><br />
Damarides <strong>of</strong> Zimbabwe and Botswana, are at present interrupted in the middle by the East-African rift valley<br />
<strong>of</strong> N - S direction. This prominent rift is the original structural element <strong>of</strong> the Pan-African orogeny (500 ± 100<br />
m. y.) which is represented in <strong>Mozambique</strong> by the deposition <strong>of</strong> the Group Cobue in the extreme NW. On the<br />
border with Tanzania it continues to Malawi and Tanzania and is accompanied by several parallel zones both<br />
W and E. The present and still active East-African rift represents a modern separation <strong>of</strong> the continental plate,<br />
a specific African phenomenon.<br />
Fig.2.2 The continental fit <strong>of</strong> the old Gondwana continent according to Smith and Hallam (1979) (363<br />
kB)<br />
The Mozambican Precambrian was divided into three provinces:<br />
* the Mid-Zambezi Province<br />
* the Niassa Province<br />
* the <strong>Mozambique</strong> Province.<br />
The same division was accepted by BRGM (P. Pinna, 1986), in the description in "Explanations to the new<br />
geological map"<br />
* the southern region, S <strong>of</strong> the Mid-Zambezi Graben and along Zimbabwe<br />
* the northwestern region, N <strong>of</strong> the Mid-Zambezi and W <strong>of</strong> the East-African rift<br />
* the northeastern region, E <strong>of</strong> the East-African rift (see Fig. 2.3.).<br />
Fig.2.3. Structural scheme <strong>of</strong> <strong>Mozambique</strong> and surroundings (BRGM, 1987)<br />
Part 1 (1182 kB)<br />
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Cilek: 2. Geological Review <strong>of</strong> <strong>Mozambique</strong><br />
Part 2 (254 kB)<br />
Structurally, the Precambrian can be divided into four big main units:<br />
1. Archean-Proterozoic Inferior, 3,800-2,500 m. y., covering the border zone with Zimbabwe; it is a<br />
prolongation.<strong>of</strong> the Zimbabwean "greenstone" belts and younger "granitic-gneiss" Complex <strong>of</strong> Archean and<br />
part <strong>of</strong> Proterozoic terrain <strong>of</strong> cratons margin (Group Gairezi)<br />
2. Precambrian B, 1,800 m. y., the Group Umkondo, metasediments and volcanics resting with unconformity<br />
on the craton, the Umkondo cover is almost not folded<br />
3. Precambrian B, beginning <strong>of</strong> PrecambrianA, 1,300-900 m. y., the regions with strong orogeny can be<br />
divided into two principal cycles:<br />
a) continuation <strong>of</strong> the irumidian belt <strong>of</strong> Zambia (Supergroup Muva) into the NW corner <strong>of</strong> <strong>Mozambique</strong><br />
(Group Zambue etc.) and reworking <strong>of</strong> this belt by subsequent orogenies along the craton's margin during<br />
Precambrian B with orogenic phase at about 1,300 m. y.<br />
b) the Mozambican belt which covers the largest part <strong>of</strong> the Precambrian; as a Mozambican orogenic cycle, it<br />
can be divided into three episodes:<br />
1) the depositional epoch called "pre-Mozambican" aged 1,800? - 1,000 m. y. corresponds with the Kibarian<br />
epoch with deposition <strong>of</strong> supracrustal sediments in connection with a stretching <strong>of</strong> the continent - the<br />
Supergroup Chiure in the <strong>Mozambique</strong> Province was deposited as a volcanic-sedimentary sequence on the<br />
crust and Group Mecuburi with deposits <strong>of</strong> an active continental margin (see later)<br />
2) the convergence epoch (1,100 - 900 m.y.) with intense origin <strong>of</strong> igneous material in two zones as:<br />
Granulitic Complex with transformation (from W to E) <strong>of</strong> all igneous rocks <strong>of</strong> charnockite composition s. 1. to<br />
alkaline and tholeiite rocks and granulites, with examples <strong>of</strong> the Luia Group at Angonia in the Niassa Province<br />
and the Unango Group and Supergroup Lurio in the <strong>Mozambique</strong> Province (see the granulitic Mozambican<br />
axis on the structural map Fig 2. 3); as Migmatitic Complex <strong>of</strong> Supergroup Nampula (see structural map) with<br />
migmatites, granitoids, migmatoids <strong>of</strong> calc-alkaline composition<br />
3) the crustal separation epoch according to Pinna (1986) with thrusting accompanied by metamorphosis <strong>of</strong><br />
Supergroup Lurio and Chiure over the Nampula Supergroup over a distance <strong>of</strong> several hundred kilometres<br />
both N and S <strong>of</strong> the Lurio belt. The complexes are granulitic and supposed allochthonic with an upper part <strong>of</strong><br />
gneisses and mylonites <strong>of</strong> supracrustal origin. In my opinion, such orogenic events with "nappes" known for<br />
example from Alpides are hardly to be expected to occur in the Mozambican belt. An overthrusting is, <strong>of</strong><br />
course, common and connected with the zones <strong>of</strong> collision or with doming along the massifs. In neighbouring<br />
Tanzania the corresponding Usagaran System to Lurio and Chire Supergroups is generally divided in twolevel<br />
units, the lower one with granulites and granites overlain by metasediments <strong>of</strong> upper unit. The upper part<br />
<strong>of</strong> the Supergroup Lurio consists <strong>of</strong> gneisses and ultramylonites <strong>of</strong> supracrustal origin <strong>of</strong> an ancient hiatus <strong>of</strong><br />
oceanic deposition and, in my opinion, corresponds with the upper metasedimentary level <strong>of</strong> Usagaran in<br />
Tanzania. The "allochthonous" members-the Supergroups Lurio and Chiure are therefore probably erosion<br />
remnants <strong>of</strong> the upper-level member resting on the Nampula Super group. The process <strong>of</strong> convergence and<br />
crustal separation is accompanied by intense granitization.<br />
4) Pan-African cycle represented by:<br />
a) deposits <strong>of</strong> the Katangan age discordantly overlying the Mozambican granulites in extreme NW (750-500<br />
m. y.) <strong>of</strong> Groups <strong>of</strong> Geci and Cobue. They are <strong>of</strong> periglacial and glacial origin, post-Mozambican and<br />
correspond with the Katangan Supergroup <strong>of</strong> Zaire and Zambia<br />
b) intense tectonic activity on the Mozambican basement with fold axis ENE-WSW and NNE-SSW direction<br />
with intrusive "stocks". The main mobile structures <strong>of</strong> this cycle are the Zambezi and Lurio belts. Several<br />
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granitoid synkynematic massifs developed in the NW, and ring structures in the Lurio belt (500 ± 100 m. y.).<br />
Description <strong>of</strong> Precambrian provinces<br />
A. Mid-Zambezi Province is divided into two geological groups-the Archean craton with its margin and<br />
Precambrian complexes developed between the Craton, Mid-Zambezi graben or the Mylonite Zone <strong>of</strong> Hunting<br />
(1984) and Phanerozoic deposits in the E. The Mylonite Zone as a main structural line divides the southern<br />
province from the northern Niassa Province which is composed largely <strong>of</strong> granite, while the southern province<br />
consists more <strong>of</strong> metasediments. The Archean Zimbabwean craton comprises the Manica belt-group Manica<br />
as a prolongation <strong>of</strong> the Zimbabwean Umtali belt near the town <strong>of</strong> Manica. The Manica group is divided into<br />
the Macequece Formation composed <strong>of</strong> serpentinites, ultrabasic rocks, tremolitic schists and quartzites and the<br />
M'Beza-Vengo Formation consisting <strong>of</strong> conglomerates, sericite-chlorite schists and marbles. South <strong>of</strong> Manica<br />
the greenstone belt corresponds with the Cronley belt <strong>of</strong> Zimbabwe.<br />
Small relicts <strong>of</strong> the greenstone belt are known to occur E <strong>of</strong> the craton in the Barue Formation, e. g., at Honde<br />
with iron deposits or at Mavita with asbestos and talc deposits.<br />
Among younger members <strong>of</strong> the Archean are granitoids and orthogneisses either <strong>of</strong> an oriented or nonoriented<br />
structure. The Archean terrain is known for its gold mineralization in quartzites, banded ironstones and veins,<br />
asbestos and talc and copper.<br />
The marginal formations include the Gairezi and Fronteira Groups and the Group Umkondo.<br />
The Gairezi and Fronteira Groups consist predominantly <strong>of</strong> orthoquartzites and pelitic and semi-pelitic schists<br />
with a widespread occurrence <strong>of</strong> kyanite and staurolite together with andalusite and sillimanite. Both groups<br />
are folded and tectonically disrupted.<br />
The Umkondo Group occurs S <strong>of</strong> Manica overlying the craton in a tabular arrangement, and S <strong>of</strong> the Limpopo<br />
belt. It is composed <strong>of</strong> calc-silicate sediments, gray-wackes, red beds, quartzites and overlain by andesitic<br />
lavas. The age corresponds with the Roan beds <strong>of</strong> Zambia and, together with the Gairezi Group, the Umkondo<br />
is part <strong>of</strong> Irumides (1,800-1,300 m. y.).<br />
The Middle-Upper Proterozoic is represented by irumide orogeny along the margin <strong>of</strong> the craton, with<br />
deposition <strong>of</strong> the Groups Rushinga and Gairezi as an equivalent <strong>of</strong> the Supergroup Muva <strong>of</strong> Zambia dated to<br />
before 1,350 m. y. by the main orogenic phase - Mozambican aged 1,100 - 900 m. y., accompanied also by the<br />
longest depositional phase. Two main groups are developed:<br />
1. Group Rushinga<br />
2. Group Barue<br />
The Rushinga Group is composed <strong>of</strong> metasediments mainly with manganese mineralization represented by the<br />
minerals <strong>of</strong> spessartite, rhodonite, rhodochrosite and by gneisses and migmatites <strong>of</strong> a late Mozambican aqe<br />
(850 ± 40 m.y. )<br />
The Barue Complex is a prominent belt in S-<strong>Mozambique</strong> with typical metaintrusions <strong>of</strong> calcium-alkaline<br />
composition accompanied by crustal granitoids. Most <strong>of</strong> the sequence is probably <strong>of</strong> Mozambican age (1,100 -<br />
800 m. y.), part could be pre-Mozambican (1,800 -1,100 m. y.). The Complex Barue is further divided into<br />
five groups:<br />
Group Matamba <strong>of</strong> gneisses, probably a lateral equivalent <strong>of</strong> the Rushinga Group<br />
Group Changara, charnockites and amphibole gneisses<br />
Group Madzuire with gneisses, granitoid rocks and anatexites: in the E there are typical marbles and quartzites<br />
at Metotola, in the W, alumina-gneisses with sillimanite<br />
Group Canxixe with orthogneisses and migmatites<br />
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Group Nhamatanda with gneisses, micaschists, talcschists and sericite schists with andalusite, metabasites and<br />
iron-quartzites probably <strong>of</strong> Archean age?<br />
B. The Niassa Province or NW region is delimited by the grabens <strong>of</strong> Chire and Zambezi which originated<br />
along the old Precambrian lines and were filled up later by Phanerozoic sediments. Rocks <strong>of</strong> the Mozambican<br />
belt underwent polycyclic and multistructural development during Precambrian B and A. All three orogenic<br />
cycles are traceable: cycle <strong>of</strong> irumide with deposition <strong>of</strong> the Fingoe Group and a small part <strong>of</strong> metasediments<br />
<strong>of</strong> the Group Zambue including metamorphosis, tectogenesis and intrusions <strong>of</strong> Pre-Fingoe granites; in most<br />
parts <strong>of</strong> the region the Mozambican cycle shows a high grade regional metamorphosis and intense<br />
granitization within the groups <strong>of</strong> Zambue, Luia, Angonia together with intrusive massifs <strong>of</strong> anorthosites,<br />
charnockites, granodiorites and granites; the katangan cycle is marked by a discordance inside the Group<br />
Fingoe and other similar units and is terminated by a polyphase tectogenesis and granitization <strong>of</strong> Pan-African<br />
orogeny.<br />
The region is composed <strong>of</strong> five different groups:<br />
1. Zambue, probably Precambrian B<br />
2. Luia and Tete gabbro-anorthosite Complex<br />
3. Angonia<br />
4. Pre-Fingoe granites<br />
5. Fingoe cycle<br />
The Group Zambue covers the NW part <strong>of</strong> the country and is composed <strong>of</strong> gneisses and migmatites with<br />
several layers <strong>of</strong> marbles and quartzites. The age <strong>of</strong> some migmatites is 940 ± 60 m. y. Micaschists with<br />
sillimanite are known from contact zones <strong>of</strong> metadiorites with ironstones at lower levels. Younger Post-Fingoe<br />
granitic massifs extend along the NE-SW axis and are <strong>of</strong> katangan age.<br />
The group originated during the irumide cycle and the deposits are passive margin sediments which later were<br />
substituted by volcano-sedimentary rocks <strong>of</strong> an active margin eventually in the zone <strong>of</strong> subduction at about<br />
1,300 m.y. ago.<br />
The Group Luia is divided into three different lithological units: the Group Luia with highly metamorphosed<br />
gneisses, migmatites, garanulites, cataclasites and blastomylonites is further divided into the Chacocoma<br />
Formation and the Chidua Formation which represent the floor <strong>of</strong> gabbro-anorthosites <strong>of</strong> the Tete Complex.<br />
The Chidue Formation with distinct marbles and ironstones contains W, Cu, Ni and Co. Of importance is the<br />
gabbro-anorthosite Complex <strong>of</strong> Tete with gabbros, norites, anorthosites and pyroxenites with magnetite and<br />
ilmenite with vanadium. Its age is 940 ± 175 m. y., but the main magmatic episode falls into the early<br />
Mozambican cycle <strong>of</strong> (1,100 - 1,000 m. y.).<br />
The last unit is composed <strong>of</strong> old charnockites and granitoids aged about 1,050 +20 / -10 m.y. (orthogneiss <strong>of</strong><br />
the Chipera Complex). To it belongs also brown granites consisting <strong>of</strong> enderbites, mangerites,<br />
leucocharnockites etc.<br />
The Group Angónia situated in the NW <strong>of</strong> the country fronting on Zambia and Malawi, is composed <strong>of</strong><br />
gneisses, metabasites, meta-anorthosites, mangerites and granitoids. The structural pattern is N-S and NW-SE<br />
(area <strong>of</strong> Domue and Zobue) with the large granitic massif <strong>of</strong> Desaranhama. In the Ulongué belt <strong>of</strong> NW-SE<br />
direction the known deposits <strong>of</strong> graphite and limestone have been exploited. Also asbestos is present.<br />
The Pre-Fingoé granites are <strong>of</strong> crustal origin composed <strong>of</strong> damelites and granodiorites, aged 940 ± 60 m.y.<br />
They have been encountered in the groups Luia, Angónia and Zambue.<br />
The Fingóe cycle is composed <strong>of</strong> supracrustal groups <strong>of</strong> Fingóe, Mualadzi and Mchinje. The Group Fingóe is<br />
a belt extending in ENE-WSW direction about 150 km long, from Monte Atchiza to the E <strong>of</strong> town <strong>of</strong> Fingóe.<br />
In the SW end is the Monte Atchiza complex with ultrabasic rocks <strong>of</strong> peridotites, serpentinites, pyroxenites,<br />
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gabbros and norites intruded in Fingóe metasediments and metavolcanics, and both are intruded by Post-<br />
Fingóe granites. The Fingóe Group is a typical <strong>of</strong> cipolinos (marbles and metadolomites), talc, schists and<br />
amphibolites, quartzites and metaconglomerates with skarn deposits in contact zones <strong>of</strong> gold and copper.<br />
The Group Mualadzi continues into Zambia as the Mwani Formation <strong>of</strong> a similar composition to that <strong>of</strong> the<br />
Fingóe Group. The Mchinje Group covers the batholite <strong>of</strong> Desaranhama with schists, gneisses and quartzites.<br />
C. The <strong>Mozambique</strong> Province or NE region is the biggest <strong>of</strong> all Precambrian provinces. In the W, it borders<br />
the East-African rift valley - the Chiré and Niassa graben, in the N the river Rovuma; its remaining eastern<br />
boundary is formed by a coastal strip along the Indian Ocean.<br />
Generally, two structural units can be distinguished:<br />
1. NW region along the eastern shore <strong>of</strong> Lake Niassa represented by extensive granulites and charnockites <strong>of</strong><br />
Mozambican age, 1,100 - 900 m.y., reworked on the western margin during the Pan-African orogeny, 500 ±<br />
100 m.y. The Mozambican granulites originated from a separation <strong>of</strong> the mantle from the crust. The main<br />
representative is the Group Unango composed <strong>of</strong> granulitic othogneisses <strong>of</strong> either an alkaline or tholeiites<br />
composition.<br />
2. Mid- and E region in ENE-WSW direction, divided into two parts by the Lúrio belt. On both the northern<br />
and southern sides, two structural crustal levels can be distinguished: an upper granulitic level represented by<br />
the Supergroup Lúrio (allochthonous according to B. R. G. M., 1986) <strong>of</strong> the subduction zone the Supergroup<br />
Chiure <strong>of</strong> supracrustal origin and the lower granitoid and migmatic Supergroup Nampula on the SE. The<br />
tectonic contact zone between these two structural levels represents a crustal coupling. According to a new<br />
concept suggested by the B. R. G. M. (1986) with regard to a structural development <strong>of</strong> this region and, in<br />
fact, <strong>of</strong> the whole Mozambican belt, the E-W trending Lurio belt is an important collision zone <strong>of</strong> the Central<br />
Gondwana, along which a subduction <strong>of</strong> the plate occurred with a partial melting <strong>of</strong> the mantle. During a<br />
separation <strong>of</strong> the crust, large crustal and supracrustal units were thrown over large distances. However, all this<br />
will have to be confirmed by reliable evidence. The Supergroup Nampula in the SE part <strong>of</strong> N - <strong>Mozambique</strong><br />
has a special structural position as a nucleus <strong>of</strong> antiform outcropping from overlying folded Pan-African units.<br />
It appears to be an old crustal remnant <strong>of</strong> the continent which had later been rejuvenated. It could be<br />
interpreted as an island arc or an active continental margin nowadays made up <strong>of</strong> calc-alkaline igneous rocks<br />
<strong>of</strong> the melted mantle aged 1,100 - 1,030 m. y., calc-alkaline-potassium igneous rocks aged 1,050 - 950 m. y. <strong>of</strong><br />
crustal contamination and <strong>of</strong> synkinematic granites and leucogranites <strong>of</strong> the same composition as previous<br />
ones aged 1,020 - 950 m.y. Some granitoids are probably <strong>of</strong> cratonic origin <strong>of</strong> the Archean or lower<br />
Precambrian age. Typical <strong>of</strong> the whole Nampula Supergroup is the absence <strong>of</strong> alkaline and tholeiitic rocks.<br />
The Mozambican orogeny is the main event <strong>of</strong> 1,100 - 950 m.y. age which represents a crustal convergence<br />
followed by a denudation phase up to 750 m.y. Between 800-and 450 m. y., the Mozambican structures were<br />
reworked with a folds in N-S and NE-SW direction. The structurally important Lurio belt has been active<br />
since the time <strong>of</strong> the Mozambican orogeny, with a subsequent fold overthrusting with vergence direction<br />
towards SSE (B. R. G. M., 1986 - Monapo structure as tectonic remnant on Nampula Supergroup with<br />
transport <strong>of</strong> 150 km?) and new movements with vergence direction towards the NW during the Pan-African<br />
cycle, terminated by the origin <strong>of</strong> the Pan-African granites and Alto Ligonha pegmatites at 500 ± 100 m.y.<br />
The whole Mozambican province is divided into a western structural region and an eastern structural region.<br />
a) The western structural region on the northern side <strong>of</strong> Lake Niassa is composed <strong>of</strong>: Group Meponda <strong>of</strong><br />
highly metamorphosed supracrustal units with a late -magmatic mineralization <strong>of</strong> Monte Naumar (nepheline<br />
syenite, hyperalcaline essexites, carbonatites with U, Nb, RE, Ta in the fracture zone) Group Unango <strong>of</strong><br />
charnockites with mineralization <strong>of</strong> U, Nb, RE apatite in nepheline syenite and carbonatite at Lucuisse N <strong>of</strong><br />
Lichinga -1,070 - 1,020 m.y. Ultramylonites <strong>of</strong> different age Groups Geci and Colue <strong>of</strong> katangan<br />
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metasediments (marble at Malulo)<br />
b) The eastern structural region is typical <strong>of</strong> granulitic complexes overlying migmatitic and granulitic units<br />
("nappes" <strong>of</strong> B. R. G. M., 1986) and divided by the mobile Lurio belt in southern and northern sectors.<br />
i) The southern - Nampula-sector consists mainly <strong>of</strong> granitoids and migmatites with over 50% in the Nampula<br />
Group, nodular sillimanitic rocks in the Mecuburi Group and later synkinematic granitoids in "nappes" <strong>of</strong><br />
several other groups. The Supergroup Lúrio, <strong>of</strong> a granulitic metamorphic grade, is represented by synform<br />
structures <strong>of</strong> Monapo (with apatite deposit <strong>of</strong> Evate) and Mugeba with several lithological units overlying with<br />
disconformity the older Nampula group. Overlying groups contain typical metasediments <strong>of</strong> supracrustal<br />
origin such as cipolinos, graywackes, schists, quartzites together with metabasites, metagranites, granulites<br />
and mylonites <strong>of</strong> a tectonic "melange" composition.<br />
ii) The northern region, N <strong>of</strong> the Lúrio Group along the river Lúrio, has a similar composition to that <strong>of</strong> the<br />
southern sector. It is divided into basement migmaties and granitoids which can be compared with the<br />
Nampula Group. They are present as erosional remnants within the synforms in the Group Marrupa. The<br />
Marrupa Group originated during several phases; first between 1,550 and 1,250 m. y. ago with a deposition <strong>of</strong><br />
original sediments, followed by quartz-diorites and monzonites (1,050 ± 100 m.y.), potassium granites and<br />
syenites (750 ± 150 m.y.) and alkaline granites (500 ± 100 m.y.). There are other groups <strong>of</strong> different<br />
composition.<br />
The superstructural units are composed <strong>of</strong> mylolites and magmatic rocks in several folds represented at<br />
present by synforms such as at Montepuez with marble deposits or by antiforms at Marrupa or Meluco. They<br />
include also the Supergroups Chiúre and Lúrio <strong>of</strong> a regional extension as probable erosional remnants <strong>of</strong> one<br />
original superunit, the pre-Mozambican supracrustal zone <strong>of</strong> granulites. The Group Lúrio s. s. extending from<br />
the mouth <strong>of</strong> the river Lúrio in the E to the village <strong>of</strong> Tepere in the W is made up <strong>of</strong> gralunites and mylonitic<br />
gneisses.<br />
The Pan-African plutonic rocks <strong>of</strong> the Mozambican belt occur at Mocubela NE <strong>of</strong> Quelimane as elipsoidal<br />
massifs <strong>of</strong> monzonitic granites and leucocratic granites <strong>of</strong> 490 ± 21 m.y., in the area <strong>of</strong> Luleia as noritic<br />
gabbros, leucogranites and syenites within the Lurio belt and at Candulo near the river Rovuma <strong>of</strong> 480 m.y.<br />
Of the same age may be also rich pegmatites <strong>of</strong> the Alto Ligonha district.<br />
The Karroo Supergroup<br />
The Precambrian basement rocks are overlain by sediments and lavas <strong>of</strong> the Karroo Supergroup. The coal<br />
seams in the lower part <strong>of</strong> the sequence are among the biggest and most important mineral resources <strong>of</strong><br />
<strong>Mozambique</strong>. The Supergroup is also the oldest sedimentary substratum common to the two main sedimentary<br />
basins in <strong>Mozambique</strong>:<br />
i. e., the S-<strong>Mozambique</strong> basin and the N-Rovuma basin.<br />
In Southern Africa, the Karroo is subdivided into:<br />
Stormberg series - volcanics and sandstones<br />
Beaufort series - sandstones and shales<br />
Ecca series - shales, coal seams, silt and sandstones<br />
Dwyka series - tillites and shales<br />
The age <strong>of</strong> Karroo Supergroup is the Late Carboniferous to the Jurassic, but the lower Karroo - Dwyka, is not<br />
represented in <strong>Mozambique</strong>. The oldest Karroo sediments are <strong>of</strong> the middle Ecca age, followed by upper Ecca,<br />
Beaufort and Stormberg series. In <strong>Mozambique</strong> Karroo outcropping areas occur in five regions:<br />
1. NE <strong>of</strong> Lake Niassa, from Metangula to the river Rovuma - Maniamba basin<br />
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2. scattered outcrops along the Lugenda valley towards the river Rovuma<br />
3. Mid-Zambezi graben, from Zumbo on the Zambian border towards Tete; E <strong>of</strong> it Karroo is covered by<br />
younger sediments up to the Indian Ocean<br />
4. narrow strip between the Lupata Group and the Gorongosa massif and between the rivers Buzi and Save<br />
5. the Lebombo Mts. extending from Pafuri in the N to Swaziland in the S.<br />
The history <strong>of</strong> the development <strong>of</strong> the Mozambican basins, which started already by a deposition <strong>of</strong> Karroo<br />
sediments, is typical <strong>of</strong> the evolution <strong>of</strong> passive continental margins In <strong>Mozambique</strong>, the development is<br />
dominated by rifting and flexural subsidence associated with a continental break-up and a separation <strong>of</strong> parts<br />
<strong>of</strong> the continent in this case the Madagascar plate (S. Lawrence in ENH report, 1986).<br />
During the first "Karroo" phase, a break-up <strong>of</strong> the early Gondwana continent started between the Late<br />
Paleozoic to the Early-Mid Jurassic, followed by second phase up to the Mid-Cretaceous during which the<br />
separation <strong>of</strong> Madagascar occurred by sea-floor spreading and the earliest creation <strong>of</strong> the oceanic crust. On the<br />
continental margin originated the so-called sag basins, while several tectonically bounded fracture basins<br />
developed in the interior-the original East African rift valley system with network <strong>of</strong> a tri-radial basin pattern.<br />
In <strong>Mozambique</strong>, the small Maniamba basin developed as an arm <strong>of</strong> the greater Karroo basin <strong>of</strong> Songea in<br />
Tanzania, but the main sedimentation occurred in the Zambezi graben, which is a part <strong>of</strong> Great Karroo basin<br />
<strong>of</strong> South Africa extending over the sag basins into Antarctica and Madagascar plates.<br />
To conclude this presentation <strong>of</strong> plate tectonic history it should be mentioned that during the third phase<br />
lasting from the late Cretaceous to the present the progressive opening <strong>of</strong> the Indian Ocean continues. On the<br />
continent, a system <strong>of</strong> rift basins has been established across East Africa, some following the fracture zones <strong>of</strong><br />
earlier Karroo basins, some cutting across these grabens such as, for example, the Lake Niassa basin with an<br />
interior fracture basin formation, with a spreading <strong>of</strong> the floor, a thermal flexual subsidence and an injection <strong>of</strong><br />
mantle material.<br />
Karroo in the Maniamba basin is an equivalent <strong>of</strong> the Beaufort and Ecca series - the lower part <strong>of</strong> the Songea<br />
Series <strong>of</strong> Tanzania with coal seams, shales and sandstones in <strong>Mozambique</strong> known as the Lunho series. The<br />
Lunho Series is about 300 m thick composed <strong>of</strong> a lower shale section, a middle limestone section and upper<br />
sandstones. The base is covered with a conglomerate, surrounding the western part <strong>of</strong> the basin.<br />
Karroo <strong>of</strong> the Lugenda valley represents erosional remnants <strong>of</strong> sandstones <strong>of</strong> the upper Ecca to the lower<br />
Beaufort series.<br />
The main Karroo basin is the Mid-Zambezi rift with Karroo sediments over 1 000 m thick split up into several<br />
smaller basins such as Moatize and Condezi near Tete or the Mucanha - Vuzi sector on the north shore <strong>of</strong><br />
Lake Cabora Bassa. Karroo is represented by the middle and upper Ecca with several coal seams exploited at<br />
Moatize followed by Tete sandstones <strong>of</strong> the Beaufort Series overlain by Mpiusa siliceous shales. The<br />
Stormberg series is made up <strong>of</strong> sandstones (Quengene, Batonga, Forest sandstones) overlain by Batoka basalts<br />
about 300 m thick. Towards the E, in the area <strong>of</strong> Lupata Gorge the Stormberg basalts are again overlain by a<br />
conglomerate, sandstones and rhyolites <strong>of</strong> the Post-Karroo age (see Fig. 2. 4.). The economically most<br />
important part <strong>of</strong> the Karroo Supergroup is the Productive Series <strong>of</strong> lower Karroo <strong>of</strong> lower Ecca. In the<br />
Moatize basin it is about 400 m thick, with six coal complexes <strong>of</strong> which the second lowest is mined. Coal<br />
measures consist <strong>of</strong> interbedded coal seams and mudstones with thickness <strong>of</strong> 40 - 1.5 m in ascending order.<br />
The Condesi basin contains a 450 m thick sequence with five coal measures.<br />
Fig.2.4. Stratigraphic Section <strong>of</strong> the Lupata Group at Lupata Gorge on the river Zambezi (ENH, 1986)<br />
(316 kB)<br />
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The narrow belt <strong>of</strong> Karroo outcrops from S <strong>of</strong> the river Zambezi towards the rivers Buzi and Save consists <strong>of</strong><br />
Ecca and Stormberg Series, <strong>of</strong> about 200 m <strong>of</strong> sediments and 200 m <strong>of</strong> basalts, and partly rhyolites, dipping<br />
eastwards below Cretaceous and younger sediments. The belt terminates in <strong>Mozambique</strong> just on river Save<br />
where it rests on the Umkondo System <strong>of</strong> slightly folded low grade metamorphosed Precambrian<br />
metasediments.<br />
The same belt enters again the Mozambican territory at Pafuri and continues for about 800 km to the S along<br />
the frontier building one <strong>of</strong> the most prominent geomorphological and geological feature <strong>of</strong> the whole <strong>of</strong><br />
South Africa - the Lebombo Range, 20 - 30 km wide and <strong>of</strong> about 600 m elevation. The Karroo rocks <strong>of</strong> the<br />
Lebombo Mts. form a monoclinal structure dipping at 10-20°/E; its bottom consists <strong>of</strong> Cave and Bushweld<br />
sandstones <strong>of</strong> the Stormberg series followed by limburgites and basalts. The generalized section is (from top<br />
to bottom):<br />
upper basalt (Movene) -137 m. y. early Cretaceous<br />
rhyolites <strong>of</strong> Pequenos Lebombos<br />
basalts and Goba sandstones<br />
rhyolites and tuffs <strong>of</strong> the Lebombo Range<br />
lower basalts -167 m. y. - Lias (early Jurassic)<br />
Cave Sandstone<br />
In <strong>Mozambique</strong>, the Movene basalt is overlain ununiformly by Lower Cretaceous Maputo sandstone. The<br />
Lebombo Mts. originated along the "rift" fracture zone from eastwards outpouring lavas. Deep boreholes E <strong>of</strong><br />
Lebombo Mts. indicate (ENH, 1986), that the Karroo lavas continue under the sedimentary cover; however<br />
they do not form a continuous sheet <strong>of</strong> effusives, but rather a series <strong>of</strong> parallel, meridionally trending fractures<br />
issueing ever younger magma from W to E.<br />
The Karroo Intrusive rocks are related to the younger post- Karroo (Cretaceous) large alkaline ring<br />
complexes and carbonatite intrusions situated along the rift valleys, not evident in the overlying Cretaceous<br />
sediments. These rocks are <strong>of</strong>ten found very far from the rift zones within the Basement Complex, for<br />
example, they are widespread at Manica in the Archean greenstone belt. Their age span is from Stormberg<br />
(Lower Jurassic) to Cretaceous (Hunting, 1984). Prevailing are swarms <strong>of</strong> dolerite dykes, porphyry and felsite.<br />
In Karroo sediments, both in outcrops and in the boreholes, sills and small stocks <strong>of</strong> microgabbro have been<br />
observed.<br />
The Post-Karroo<br />
The stratigraphy <strong>of</strong> Post-Karroo formations is presented on the generalized stratigraphic column (ENH, 1986).<br />
The sedimentary thickness attains 10 km, the bottom is well marked by the Liassic stage marking an<br />
unconformity between the top <strong>of</strong> the Karroo and generally the Albian -Aptian transgression. The Post-Karroo<br />
strata produce generally a wedge <strong>of</strong> minimum thickness over the exposed Precambrian; their thickness<br />
increases eastwards towards the Indian Ocean.<br />
The ENH (1986) model consists <strong>of</strong> three phases, each with its own litho-tectonic character:<br />
1. Intratectonic basin fill-deposition <strong>of</strong> Karroo<br />
2. Rift Valley fill <strong>of</strong> volcanics and sediments, over the Karroo deposits a deposition <strong>of</strong> continental sediments<br />
with intercalations <strong>of</strong> marine sediments in places in communication with the sea (Jurassic? and Lower<br />
Cretaceous)<br />
3. Break-up basin fill and post break-up transgression and progradation (Upper Cretaceous-Tertiary).<br />
As it is common to passive continental margin zones these phases are separated by unconformities, sediments<br />
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are <strong>of</strong> shallow marine-littoral or paralic origin on the onshore and more on the marine <strong>of</strong>fshore. Features<br />
typical <strong>of</strong> lagoonal and marine deposition <strong>of</strong> evaporites and subsequent salt diapirs known from Tanzania have<br />
not been found in <strong>Mozambique</strong> despite some indications that salt diapirs may have been present in the<br />
Rovuma basin. However, the Miocene Temane Formation <strong>of</strong> evaporites (gypsum and anhydrite) in the<br />
<strong>Mozambique</strong> basin is pro<strong>of</strong> <strong>of</strong> a similar marine influence.<br />
In the <strong>Mozambique</strong> basin, the oldest post-Karroo deposits are <strong>of</strong> Jurassic age (post-Liassic). They are known<br />
from the Lupata Gorge on the Zambezi river (see Fig 2.4) and are composed <strong>of</strong> continental sediments and<br />
volcanics. S <strong>of</strong> the Save river "red beds" <strong>of</strong> continental origin that could be ascribed to the Jurassic (Middle?)<br />
were encountered in several boreholes.<br />
During the Cretaceous, three main transgressions occurred with three cycles <strong>of</strong> deposition, ranging from<br />
Aptian to Albian, from Cenomanian to Turonian and from Senonian to Eocene. Again in the E, open marine<br />
sedimentation conditions prevailed followed by neritic and finally paralic and littoral sedimentation in the W<br />
(see Fig. 2. 5).<br />
Fig.2.5. Stratigraphic Column Karroo-Recent (ENH, 1986) (371 kB)<br />
The Lower Cretaceous is known as the Maputo Formation <strong>of</strong> marine origin <strong>of</strong> sandstones with glauconite and<br />
tuffaceous material exposed in the Maputo river valley. This formation is overlain by a Cenomanian and<br />
Domo Formation <strong>of</strong> sandstones.<br />
The Lower to Middle Cretaceous is represented by the continental Sena Formation overlying with<br />
unconformity Jurassic rhyolites. The formation was built by one or more igneous members (phonolites) and<br />
sandy members. The facies equivalent to the Sena Formation is the Lower Domo shale (ENH, 1986) overlain<br />
by prominent Domo sandstone with gas shows and an upper member <strong>of</strong> the Upper Domo shale.<br />
The marine Grudja Formation <strong>of</strong> Upper Cretaceous-Lower Eocene age consists <strong>of</strong> Lower and Upper Grudja <strong>of</strong><br />
glauconitic sandstones and claystones with a rich fauna. The Grudia sandstone <strong>of</strong> the Paleocene is the main<br />
gas reservoir <strong>of</strong> the Pande gas field and others. In South Africa, the Grudja is known as the Santa Lucia<br />
Formation <strong>of</strong> Zululand.<br />
In outcrops in the area <strong>of</strong> tributaries <strong>of</strong> the Limpopo river the Upper Cretaceous was described as Elefantes<br />
continental Formation, Singuedzi transitional Formation and Uanetze shallow marine Formation. The last<br />
formation shows the presence <strong>of</strong> evaporites.<br />
During the Tertiary, the stretching <strong>of</strong> the continental margin was almost complete but the development <strong>of</strong> rift<br />
basins on the continent, and partly on the shelf, continued. The filling <strong>of</strong> these rift basins was accelerated by<br />
their deepening, and different facies originated from thick delta cones up to reefoidal development. The sea<br />
transgression culminated in the uppermost Eocene and during the Oligocene and Lower Miocene the<br />
regressive stage prevailed (ENH, 1986).<br />
While the transgressive stage was characterized by the development <strong>of</strong> the marine Cheringoma Formation <strong>of</strong><br />
reefoidal limestones, the regressive stage is typical <strong>of</strong> evaporites <strong>of</strong> the Temane Formation. Upper Grudja and<br />
Cheringoma Formations <strong>of</strong> the Paleocene - Eocene age (60 ± m.y. <strong>of</strong> glauconite, ENH, 1986) were observed<br />
in many oil boreholes, but just Cheringoma limestones are about 70 m thick and rest unconformably on the<br />
underlying Grudja (see cross section Fig. 2.6). A deposition <strong>of</strong> Salamanga limestones occurs in the S.<br />
Fig.2.6. Diagrammatic cross-section from the Gorongosa Massif to Inhaminga (ENH, 1986) (347 kB)<br />
The Oligocene starts with a general regresion throughout East Africa. In <strong>Mozambique</strong> Oligocene onshore is<br />
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absent, but it is thick in deltaic sediments <strong>of</strong> the rivers Zambezi and Limpopo (paleodelta <strong>of</strong> Zambezi and<br />
Limpopo - Cilek, 1985); sediments continued to the deposited during the Miocene and Pliocene. Between the<br />
Oligocene and the Miocene there is a slight disconformity and a deposition <strong>of</strong> Inharrime sandy limestones. In<br />
the area S layers <strong>of</strong> gypsum, clay anhydrite and dolomite <strong>of</strong> lagoonal origin (see Fig. 2.7).<br />
Fig.2.7. Miocene Sedimentary Distribution (ENH, 1986) (442 kB)<br />
The tilting <strong>of</strong> the continental margin in the Miocene (King, 1983) resulted in a marine deposition <strong>of</strong> the J<strong>of</strong>ane<br />
Formation outcropping widely along the river Save and S <strong>of</strong> it. J<strong>of</strong>ane deposits are sandy limestones, pure<br />
organic limestones and sandstones uplifted during the Pliocene. Pliocene and Pleistocene deposits are<br />
widespread throughout coastal <strong>Mozambique</strong>. A representative is the Mazama Formation <strong>of</strong> sand, sandstones<br />
and conglomerates overlying the Cheringoma limestones. Widespread sands, cemented sands, gritty<br />
sandstones <strong>of</strong> the Pliocene - Pleistocene can be correlated with the Kalahari System <strong>of</strong> SW Africa (Zimbabwe,<br />
Botswana); here, they are known as proluvial (decksand) sands (Cilek, 1985), a transitional source <strong>of</strong> heavy<br />
minerals in beach deposits. S <strong>of</strong> the river Save, sandy lacustrine limestones are found also in some narrow<br />
grabens - depressions reactivated during the Pleistocene.<br />
Igneous activity <strong>of</strong> the Post-Karroo is complex and rocks <strong>of</strong> different chemical composition are accompanied,<br />
sometimes, by a mineralization <strong>of</strong> rare earths, phosphorus, trace elements and others, thus representing<br />
valuable mineral resources.<br />
They include atractive rocks such as carbonatites, nepheline syenites and gabbros. The magmatic activy during<br />
the Phanerozoic has been illustrated as follow (for a detailed description see Chapters 3 and 4):<br />
Age Magmatic features<br />
Pleistocene-Paleocene vents, extrusions, intercalations in graben<br />
Upper to Lower<br />
Cretaceous<br />
lava flows and volcanic vents, explosive<br />
centers, intrusive domes<br />
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Type <strong>of</strong> rock with<br />
examples<br />
1. basic-ultrabasic:<br />
Mutarara-Sena,<br />
Cheringoma, Gorongosa,<br />
Balama<br />
(augitites, limburgites,<br />
nepheline and olivine<br />
basalts)<br />
2. alkaline: Canxixe,<br />
Gorongosa,<br />
Nhamatanda, W <strong>of</strong> Maputo<br />
1. phonolites-trachytes:<br />
Area <strong>of</strong> Lupata-Doa tuffs,<br />
pyroclastics<br />
2. lavas, trachytes,<br />
carbonatite agglomerates:<br />
Area <strong>of</strong> Lupata, river<br />
Chicongola
Cilek: 2. Geological Review <strong>of</strong> <strong>Mozambique</strong><br />
Lower Cretaceous-Upper<br />
Jurassic<br />
extrussive rocks intrusions<br />
Karroo volcanics <strong>of</strong> Jurassic-Upper Karroo age:<br />
The Post Karroo <strong>of</strong> the Rovuma basin<br />
3. Vents <strong>of</strong> alkaline<br />
syenites: Salambidua,<br />
Morrumbala, Milange<br />
4. Alkaline granites:<br />
Morrumbala<br />
5. Phonolites, Limburgite:<br />
Chandawa, Buzimuana<br />
6. Carbonatites: Mt.<br />
Muambe, Cone Negose,<br />
Mts. uchene (Lupata),<br />
Xiluvo, Cabo Delgado 12°<br />
S, 39° E (R. Muirite),<br />
Milange, Chiperone, Derre<br />
7. Nepheline syenite:<br />
Morrumbala, Mt. Tumbine,<br />
Zanga, Mandimba,<br />
Chandava, Chuare,<br />
Buzimuana<br />
1. basalts: Angoche-llha<br />
<strong>Mozambique</strong> (120-177 ±<br />
m. y.)<br />
2. kimberlites: in Karroo<br />
basin <strong>of</strong> Maniamba<br />
3. gabbros and norites,<br />
hyperites, olivine gabbro,<br />
olivine hyperite: Lichinga<br />
(syenites, monzonites etc.),<br />
Gorongosa massif<br />
rhyolites and ingimbrites <strong>of</strong><br />
Lupata-Doa basalts,<br />
trachytes and rhyolites <strong>of</strong><br />
Rio Luia rhyolites and<br />
basalts <strong>of</strong> Lupata and<br />
Canxixe acid lavas and<br />
basalts <strong>of</strong> river Buzi<br />
volcanics <strong>of</strong> Lebombo<br />
Range<br />
The Jurassic is not known in this border basin, but some beds near Nacala may be <strong>of</strong> Kimmeridgian-Tithonian<br />
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age (ENH, 1986).<br />
The Lower Cretaceous is developed as a thick sequence <strong>of</strong> sandstones first described by Bornhart (1900) as<br />
Makonde beds from Tanzania from Makonde Plateau. They are <strong>of</strong> Aptian age and about 450 m thick (see Fig.<br />
2.8). Near Pemba, coarse sandstones are outcropping with overlying pelagic beds with Megatrigonia schwarzi<br />
<strong>of</strong> Neocomian age. S <strong>of</strong> Pemba there are Aptian - Albian strata, while NE Seonian beds lie directly on<br />
Neocomian beds.<br />
Fig.2.8. Section <strong>of</strong> Rovuma basin sediments <strong>of</strong> <strong>Mozambique</strong> (ENH, 1986) (272 kB)<br />
Makonde beds are represent a well-known transgression <strong>of</strong> the Lower Cretaceous over the Precambrian<br />
basement. The Upper Cretaceous occurs in outcrops near the W margin <strong>of</strong> the basin in the form <strong>of</strong><br />
Globotruncana marls, with limey concretions and Gypsum flakes on the S end <strong>of</strong> the Pemba bay. These marls<br />
are <strong>of</strong> Maestrichtian age. A large part <strong>of</strong> the Upper Cretaceous, i. e., Cenomanian, Turonian and Senonian, is<br />
missing.<br />
The Tertiary-Quaternary is represented by some outcrops <strong>of</strong> Paleocene and Eocene sediments with sandy<br />
limestones as an equivalent <strong>of</strong> the Cheringoma Formation followed by deltaic sediments. Overlying Mikindani<br />
beds <strong>of</strong> Mio-Pliocene age are about 100 m thick.<br />
Quaternary sediments <strong>of</strong> coastal <strong>Mozambique</strong> are <strong>of</strong> considerable extent and thickness. They developed under<br />
unstable conditions <strong>of</strong> glacial and interglacial periods. A description is given <strong>of</strong> a thick sequence <strong>of</strong> sands,<br />
cemented sandstones, clays <strong>of</strong> marshes and mangroves, beach sands and dune sands, located <strong>of</strong> different<br />
elavations above the present sea level. The width <strong>of</strong> Quaternary deposits in the area <strong>of</strong> the Limpopo paleodelta<br />
is over 80 km, with eolian sands sheets reaching sometimes the foot <strong>of</strong> the Lebombo Mts. Important placer<br />
deposits with heavy minerals were found here (Cilek, 1985). These deposits are the only -living1' deposits in<br />
the country, being permanently moved and replenished when ever destroyed.<br />
The mineral resources or <strong>Mozambique</strong> can cover almost all needs <strong>of</strong> the country, but just a few can be used<br />
for export. In the past, the two resources <strong>of</strong> importance were coal and minerals <strong>of</strong> pegmatites, i. e., mainly<br />
columbo-tantatite. The mining industry was small in comparison with other S-African countries such as<br />
Zimbabwe, Zambia, Republic <strong>of</strong> South Africa, Botswana and Angola. This was because, during the partition<br />
<strong>of</strong> Africa, the mineral-rich highlands <strong>of</strong> SE-Africa convenient to European settlers, became part <strong>of</strong> the English<br />
or German empire, while Portugal a small country had to make do with its coastal part.<br />
In 1983, the mining sector <strong>of</strong> <strong>Mozambique</strong> participated with 2% only in the national export earnings and its<br />
futher development was retarded by internal security problems.<br />
The mineral production illustrated in Table 1 shows that concentrates <strong>of</strong> microlite, pollucite and tantalite<br />
together with coal are the main contributors. The development <strong>of</strong> the local industry and the utilization <strong>of</strong> some<br />
minerals is shown in Table 2. Just a few minerals are used in the home industry and, besides a small amount<br />
<strong>of</strong> coal, all are industrial minerals. The original colonial character <strong>of</strong> the country's economy, i. e., a low degree<br />
<strong>of</strong> utilization <strong>of</strong> local mineral resources still prevails.<br />
During the last few years, many new resources have been investigated and reserves <strong>of</strong> different degree <strong>of</strong><br />
verification secured, showing clearly the big potential <strong>of</strong> diversified mineral raw materials. Basing on data<br />
from different sources, the reserves are these:<br />
Apatite 128 Mt Heavy minerals 138.00 Mt<br />
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Asbestos 0.50 Mt Iron ore 64.00 Mt<br />
Bauxite 0.37 Mt Kaolin 2.00 Mt<br />
Bentonite 2.45 Mt Limestone 38.80 Mt<br />
Coal 7,577.52 Mt Marble 29.80 Mm3<br />
Copper 0.10 Mt Mica 0.07 Mt<br />
Diatomite 3.03 Mt Natural gas 120.00 Gm3<br />
Feldspar 1.00 Mt Nepheline syenite 4.30 Gt<br />
Fluorite 1.50 Mt Perlite 0.95 Mt<br />
Gold 47 t Red clay 11.90 Mt<br />
Graphite 40.00 Mt Silica sand 11.50 Mt<br />
Guano 0.76 Mt Tantalum pentoxide 0.007 Mt<br />
White clay 6.40 Mt<br />
The main mineral resources which are being exploited or can play an important rote in the country's economy<br />
are fuels, both coal with several billion tons <strong>of</strong> resources but a higher ash content and low coking properties,<br />
and gas discovered already at Pande, Temane and other localities with an expected discovery <strong>of</strong> oil in the<br />
<strong>of</strong>fshore part<strong>of</strong> the <strong>Mozambique</strong> basin. The next deposits are heavy minerals in beach and dune sands along<br />
the coast containing big reserves <strong>of</strong> world-wide importance apart from a number <strong>of</strong> valuable mineralsilmenite,<br />
rutile, zircon, monazite and others. Next are the pegmatite bodies which have been mined for many<br />
years in the Alto Ligonha district for tantalum, niobium, lithium, rare earths, precious stones and, as a<br />
byproduct <strong>of</strong> kaolin, feldspar, mica, quartz and others.<br />
Recent investigations revealed big resources <strong>of</strong> flake graphite <strong>of</strong> high quality, fluorite in substantial quantities<br />
and metallurgical grade and diatomite <strong>of</strong> filtration grade. The reserves <strong>of</strong> other minerals and mineral raw<br />
materials can ensure both industrial development and export requirements.<br />
There is no doubt that the former underdeveloped mining industry <strong>of</strong> <strong>Mozambique</strong> may turn into a major<br />
contributor to the national income on the basis <strong>of</strong> its present reserves <strong>of</strong> mineral resources.<br />
Table 1<br />
1981: 50 t pollucite<br />
1984: 89 t pollucite<br />
Mineral Production (data Ministry <strong>of</strong> Mineral Resources)<br />
Material unit 1978 1979 1980 1981 1982 1983 1984 1985 1986<br />
microlite<br />
conc.<br />
ton 42 35 25 43 30 23 10 6 2<br />
tantalite conc. ton 40 24 26 34 22 14 7 4 3<br />
mica scrap ton 105 101 226 300 148 39 126 - -<br />
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bismutite ton 5 8 6 4 4 1 1 - 0.08<br />
monazite ton 6 7 9 4 3 4 2 0.16 0.1<br />
beryl indust. ton 16 28 6 7 8 6 7 3 1.4<br />
aquamarine<br />
cut<br />
kg - - 5 3 2 2 3 0.6 0.8<br />
morganite cut kg - - 2 6 4 4 11 17 4<br />
emerald cut kg 18 0.6 0.6 0.7 2 0.03 - - -<br />
tourmaline<br />
cut<br />
kg 12 5 8 3 20 2 0.5 7 1.2<br />
aquamarine<br />
pique<br />
kg 0.5 13 4 3 0.9 0.01 - 7 1.2<br />
morganite<br />
pique<br />
kg - 11 0.9 2 1 - - 0.6 3.4<br />
emerald<br />
pique<br />
kg 3 0.5 0.7 293 94 22 - - -<br />
tourmaline<br />
pique<br />
ton 4 0.7 7 0.2 0.4 0.01 - 3 1<br />
quartz rose<br />
pique<br />
ton - - 12 12 8 5 2 - -<br />
garnet cut ton 2 1 2 2 2 1 1 - -<br />
garnet pique ton 7 9 8 11 9 10 5 - -<br />
feldspar ton 682 585 921 775 696 317 185 67 -<br />
kaolin ton 179 139 216 297 310 292 256 152 -<br />
marble m3 60 304 299 167 561 406 577 715 1137<br />
copper conc. ton 557 1125 691 880 1065 1189 1240 590 1303<br />
asbestos ton 37 789 94 1425 852 - 145 56 -<br />
bentonite ton 1976 1656 848 716 1455 250 413 361 1112<br />
obsidiane ton 78 30<br />
coal natural ton 236,177 319,608 408,543 534,546 66,577 58,713 66,855 20,400 -<br />
coal dressed ton 148,916 197,458 207,263 329,621 200,863 58,122 39,917 39,466 -<br />
External<br />
trade<br />
value in<br />
pounds<br />
M US<br />
$<br />
*) Meticals - 486 m3 marble<br />
1.98 6.27 6.56 7.46 1.83 2.24 2.23 5.81<br />
M £ 35 31 23 24<br />
Table 2 Internal trade <strong>of</strong> mineral raw materials<br />
Name unit 1978 1979 1980 1981 1982 1983 1984 1985<br />
Coal coking ton - - - - 32172 15277 1562 368<br />
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Cilek: 2. Geological Review <strong>of</strong> <strong>Mozambique</strong><br />
Coal steam ton - - - - 51580 21986 7178 9633<br />
Coal total ton 81939 123128 76128 123287 83752 37263 8740 10019<br />
Bentonite ton 200 252 205 632 595 506 830 589<br />
Kaolin ton 200 220 280 377 270 289 210 -<br />
Feldspar ton 400 565 1272 440 858 150 133 122<br />
Asbestos ton - - - 14 136 - 92 7<br />
Marble m3 211 240 223 17 266 243 - 106<br />
Ornamental<br />
stones<br />
million<br />
meticals<br />
*) 1 US $ = 40 Meticals<br />
Data supplied by the Ministry <strong>of</strong> Mineral Resources<br />
© Václav Cílek 1989<br />
64 204 214 300 70 91 115 50<br />
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Cilek: 3.1 Andalysite, kyanite, sillimanite<br />
3. DEPOSITS OF INDUSTRIAL MINERALS<br />
3. 1. Andalusite, kyanite, sillimanite<br />
The chemical composition <strong>of</strong> the main sillimanite minerals andalusite, kyanite and sillimanite is<br />
equivalent to the formula Al2O3 · SiO2, with 62.93% <strong>of</strong> alumina and 37.07% <strong>of</strong> silica. Three other<br />
minerals topaz [Al2Si4O (OH, F)2 ], dumortierite 8 Al2O3 · B203 · 6 SiO2 · H2O and pinite (a mixture<br />
<strong>of</strong> sericite, chlorite and serpentine) are also included in this group. The presence <strong>of</strong> fluorine in topaz, and<br />
boron in dumortierite has in some countries prevented their use due to environmental problems.<br />
Topaz has a typical composition <strong>of</strong> 55-57% <strong>of</strong> alumina, 33% <strong>of</strong> silica and 16-18% <strong>of</strong> fluorine, while<br />
dumortierite as a basic aluminium borosilicate has about 64 to 69% <strong>of</strong> alumina, 28-32% <strong>of</strong> silica and 5%<br />
<strong>of</strong> B2O3.<br />
The most important property <strong>of</strong> sillimanite minerals is their refractoriness, which depends on the<br />
alumina content. It was discovered that the presence <strong>of</strong> sillimanite, andalusite and kyanite in ceramic<br />
materials improves their mechanical resistance and insulating power, but also their refractory properties.<br />
All three minerals when fused are converted to mullite <strong>of</strong> the formula 3 Al2O3 · 2 SiO2, a fibrous<br />
mineral similar to sillimanite. And just mullite is the material sought after by the refractory industry<br />
whereby sillimanite minerals, topaz and dumortierite, are merely acting as "mullite" ore. Mullite is<br />
extremely refractory, has a low coefficient <strong>of</strong> expansion, resists abrasion and slag erosion. Calcination <strong>of</strong><br />
these minerals results in a change to a mixture <strong>of</strong> mullite and silica (88% <strong>of</strong> mullite and 12% <strong>of</strong><br />
cristobalite) at a temperature <strong>of</strong> complete decomposition: 1,410°C for kyanite, 1,500°C for andalusite<br />
and 1,625°C for sillimanite.<br />
Dumortierite breaks down at a temperature <strong>of</strong> 1,250°C and topaz at 1,480°C, giving rise to about 95% <strong>of</strong><br />
mullite.<br />
According to a commercial grading <strong>of</strong> sillimanite minerals, these have to contain a minimum <strong>of</strong> 54 to<br />
56% Al2O3, 42% SiO2, 1.0-1.8% Fe2O3, 0.5% TiO2, 0.1% CaO 0.1-0.2% MgO, 0.4% K2O and 0.4-<br />
0.6% Na2O.<br />
Of mullite refractories, 90% are used chiefly in the metallurgical, glass, ceramic, and cement industries,<br />
being classified as midway between acid silica and basic magnesia refractories with 47 to 90% <strong>of</strong><br />
alumina content. The remaining 10% are used as abrasives, in chemical and electrical industries, as part<br />
<strong>of</strong> glazes and non-slip flooring. The most modern uses are in ceramic mixtures for the production <strong>of</strong><br />
special ceramics and composite materials in such industrial branches as spacecrafts, atomic industry and<br />
as substitutes <strong>of</strong> metals in engineering.<br />
Mullite can be by-produced synthetically by mixing, for example, kaolin and bauxite to reach an<br />
alumina content close to the mullite theoretical value <strong>of</strong> 71.8%. <strong>Minerals</strong> <strong>of</strong> the sillimanite group are<br />
found in deposits and accumulations <strong>of</strong> a different origin. Typical is their occurrence in aluminous<br />
metamorphic rocks in some <strong>of</strong> the metamorphic zones. These zones could be characterized by index<br />
minerals within the progressive regional metamorphism in which sillimanite, kyanite and staurolite<br />
represent the highest grade in descending order.<br />
Physical conditions <strong>of</strong> metamorphism may appear to be less important in the development <strong>of</strong> each<br />
mineral than the chemical composition <strong>of</strong> the rock. The main world deposits <strong>of</strong> sillimanite minerals<br />
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Cilek: 3.1 Andalysite, kyanite, sillimanite<br />
originated during the regional metamorphism <strong>of</strong> aluminous sedimentary rocks.<br />
Andalusite is most commonly found in aluminous shales in contact-metamorphic zones around granitic<br />
or gabbroic intrusions. It is mainly a mineral <strong>of</strong> thermal metamorphism.<br />
Kyanite occurs generally in metamorphic zones <strong>of</strong> high pressure and lower temperature in mica schists,<br />
gneisses and quartzites and could be associated with corundum, garnet and staurolite.<br />
Sillimanite, the most similar to the natural mullite, forms normally in the highest grades in regional<br />
metamorphism, at a raised temperature and a dynamic metamorphism combined with processes <strong>of</strong><br />
metasomatism. It is usually found in metamorphic zones <strong>of</strong> granulite and amphibole facies in micagneisses,<br />
quartz-mica-sillimanite schists and cordierite gneisses. Sillimanite deposits have its origin also<br />
in alumina-rich rocks, but can develop in rocks <strong>of</strong> a low alumina content such as quartzites. It was<br />
proved that metasomatic processes with alumina-rich fluids play a prominent role. But it is clear that<br />
economic deposits could develop from very pure bauxitic or kaolinitic clays or clay-rich sands and silts.<br />
The following types <strong>of</strong> sillimanite group mineral deposits are known:<br />
1. in regionally metamorphosed rocks and contact zones, sillimanite can develop as a dissemmation or<br />
massive concentration <strong>of</strong> prismatic or fibrous aggregates this process normally beginns with the<br />
development <strong>of</strong> quartz-sillimanite-nodules (QSN) and can reach the stage <strong>of</strong> massive sillimanite in<br />
layers and lenses<br />
2. deposits in contact-metamorphosed argillaceous rocks with the development <strong>of</strong> hornfels mainly with<br />
andalusite but also corundum, dumortierite, pyrophyllite and sillimanite<br />
3. occurrences <strong>of</strong> kyanite in bladed disseminated crystals or massive aggregates in quartzites, mica<br />
schists and quartz veins <strong>of</strong> contact zones, hydrothermal veins and pegmatites<br />
4. deposites <strong>of</strong> miscellaneous origin: andalusite, kyanite and dumortierite in secondary quartzites under<br />
the influence <strong>of</strong> hydrothermal and metasomatic solutions, kyanite-sillimanite deposits in mica-gneisses<br />
with graphite or staurolite <strong>of</strong> metasedimentary origin, typical quartz veins etc.<br />
5. placers <strong>of</strong> different origin from fluviatile to beach sand deposits and dunes.<br />
In <strong>Mozambique</strong> no economic deposits <strong>of</strong> sillimanite minerals, dumortierite and topaz have been<br />
discovered as yet. The reason for this is not their absence in <strong>Mozambique</strong> but the little attention given to<br />
these minerals in the past. Their occurrence, either mineralogical or in zones and localities which could<br />
be traced during a geological mapping is known from many places (see Fig. 3.1.1.).<br />
Fig.3.1.1. Occurence <strong>of</strong> andalusite, kyanite, sillimanite, magnesite (336 kB)<br />
Five main areas could be indicated:<br />
1. occurrence <strong>of</strong> argillaceous rocks in contact-metamorphosed zones with andalusite, sillimanite and<br />
staurolite<br />
2. occurrence <strong>of</strong> QSN, fibrous and prismatic sillimanite in high-grade metamorphic zones<br />
3. occurrence <strong>of</strong> kyanite in NW <strong>Mozambique</strong><br />
4. occurrence <strong>of</strong> dumortierite in secondary quartzite<br />
5. placers<br />
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Cilek: 3.1 Andalysite, kyanite, sillimanite<br />
1. Occurrence <strong>of</strong> Archean and Proterozoic Age in the Manica Province<br />
The oldest occurrence <strong>of</strong> andalusite is known from the greenstone belt <strong>of</strong> the Manica Formation <strong>of</strong><br />
Zimbabwe craton. Andatusite is present in the metasediments <strong>of</strong> the "Formacao do Vengo", in beds <strong>of</strong><br />
black argillitic and sericitic schists, argillites and conglomerates. The base <strong>of</strong> the metasediments consists<br />
<strong>of</strong> granodiorites, adametlites and tonalites which are younger and crop out about 1 km northward.<br />
Andalusite is a typical contact-metamorphic mineral. It occurs at about 10 km N the town <strong>of</strong> Manica in<br />
the Serra Vengo range. In the vicinity <strong>of</strong> a Mavita asbestos occurrence, increased content was<br />
discovered: kyanite (0.5-1.0 kg/m3) and sillimanite together with kyanite (150 g/m3) was present in<br />
alluvial deposits.<br />
Another and more extensive occurrence <strong>of</strong> sillimanite minerals is known for a long time from the<br />
Proterozoic "Formacao de Fronteira", which consists <strong>of</strong> metasediments <strong>of</strong> mica-schists, banded<br />
ironstones and quartzites resting with disconformity on granitic rocks <strong>of</strong> the Zimbabwe craton and<br />
granitic gneisses <strong>of</strong> the Barue Formation. Slightly regionally metamorphosed sediments <strong>of</strong> the Fronteira<br />
Formation arranged in narrow S-N ridges, mark the eastern margin <strong>of</strong> the Archean craton. Ideal<br />
conditions for thermal metamorphosis exist in all contact zones made up <strong>of</strong> argillaceous sediments.<br />
Three main localities are known in the vicinity <strong>of</strong> Catandica (former Vila Gouveia) stretching from there<br />
northwards to Senga-Senga over a distance <strong>of</strong> about 50 km (see Fig. 3.1.2.)<br />
Fig.3.1.2. Geological map <strong>of</strong> Catandica area (729 kB)<br />
Serra Choa with kyanite in long-bladed crystals<br />
Barauro with andalusite and kyanite, the latter producing rich eluvial deposits from the decomposition<br />
<strong>of</strong> micaschists<br />
Senga-Senga with presence <strong>of</strong> schists with kyanite, staurolite and garnets. The content <strong>of</strong> kyanite in the<br />
rock is about 10%. Several other sites <strong>of</strong> sillimanite occurrences are marked in the geological map No<br />
1833 (1 : 250,000) S <strong>of</strong> Catandica towards Nova Vanduzi. Some localities are within micaschists, some<br />
in narrow belts <strong>of</strong> orthoquartzites, some even in biotite-amphibole gneisses <strong>of</strong> the Barue Formation. No<br />
analyses and no industrial test are available in spite <strong>of</strong> the fact, that geological conditions for a<br />
development <strong>of</strong> economic deposits are most favourable.<br />
2. Occurrence within the zones <strong>of</strong> high-grade metamorphism<br />
During the geological mapping <strong>of</strong> the whole <strong>Mozambique</strong> belt, sillimanite minerals have been<br />
encountered in many places. Generally, every zone <strong>of</strong> high metamorphism, i. e., the zones <strong>of</strong> granulite<br />
and amphibole facies both in crustal and supracrustal deposits, are suitable for the origin <strong>of</strong> sillimanite<br />
minerals and corundum.<br />
From the genetic point <strong>of</strong> view, the most interesting site <strong>of</strong> occurrence is that near Montepuez in the<br />
Cabo Delgado Province. The highly metamorphosed Precambrian rocks produced two different<br />
lithotogical and structural units: the older Nampula group composed mainly <strong>of</strong> migmatites <strong>of</strong> two<br />
orogenic cycles 1,100-1,300 m. y. and 750-800 m. y. and the younger Lurio group (850-1,000 m. y.)<br />
with migmatites, biotite gneisses, leptinites and crystalline limestones.<br />
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Cilek: 3.1 Andalysite, kyanite, sillimanite<br />
Near the town <strong>of</strong> Namapa, in the proximity <strong>of</strong> the contact with the Lurio group, several zones <strong>of</strong><br />
leptinites and leptinitic gneisses with biotite and garnet contain QSN (quartz-sillimanite-nodules),<br />
which, in my opinion is the first stage <strong>of</strong> a concentration <strong>of</strong> sillimanite into the massive type. Here, the<br />
sillimanite is typically fibrolithic and, together with quartz, displays a "pseudoconglomeratic" texture.<br />
Similar QSN were described also from the Mecuburi Formation in the vicinity <strong>of</strong> Ribaue and Meconta.<br />
In the area <strong>of</strong> Nacala-Memba in the coastal zone, sillimanite-plagioclase gneisses (besides quartz and<br />
biotite) are <strong>of</strong>ten present. Sillimanite is accompanied by kyanite, and both minerals may replace biotite.<br />
Sillimanite is found in finer prismatic crystals and kyanite in elongated crystal forms.<br />
Within the Lurio group in Chiure and the Morrola subgroup, there is a distinctive zone <strong>of</strong> quartzites with<br />
alumina minerals with sillimanite, biotite and muscovite. Around the mouth <strong>of</strong> the river Lurio, E and S<br />
<strong>of</strong> Alua, sillimanite <strong>of</strong>ten occurs together with garnet and graphite, located in the central zones <strong>of</strong><br />
anticlinal structures.<br />
Close to the Monapo structure - a brachysynclinal "ring" structure with apatite, iron and graphite, which<br />
is <strong>of</strong> the same age as the Lurio group-granulites with sillimanite and granitic gneisses contain<br />
sillimanite. All these rocks are apparently <strong>of</strong> a sedimentary origin.<br />
A promising content <strong>of</strong> sillimanite and kyanite was found specially in sillimanitic-zoned quartzites <strong>of</strong><br />
the following composition: quartz 39-80%, sillimanite 7-54% kyanite 6-7%, rutile < 1%, micamuscovite<br />
1%, kaolin 1-4% and Fe-hydroxides 2%.<br />
Quartzites and, in some places, also quartzitic gneisses with sillimanite and kyanite occur in the form <strong>of</strong><br />
prominent horizons throughout the Monapo group, with kyanite anomalies up to 5 g/m3 especially in the<br />
NW part <strong>of</strong> the group and within the Ramiane Formation. Sillimanite is mostly prismatic, in grains up to<br />
5 mm long and without fissures Sillimanite rocks were found in the eastern part <strong>of</strong> the Monapo group<br />
particulary in the Ramiane Formation and in part <strong>of</strong> the Evate Formation. There, near Netia, the content<br />
<strong>of</strong> sillimanite ranges from 10 to 500 g/m3. in the zone between Metocheria and the Evate Forma ion,<br />
NW <strong>of</strong> Naculue the content <strong>of</strong> sillimanite was higher than 50 g/m3. All zones with sillimanite are<br />
somewhat connected with quartzites.<br />
Generally, the high degree <strong>of</strong> metamorphism in the northern part <strong>of</strong> <strong>Mozambique</strong> is characteristic <strong>of</strong><br />
sillimanite, which could also be a good indication <strong>of</strong> graphite deposits.<br />
In NW <strong>Mozambique</strong>, within the Barue Formation, reports are available <strong>of</strong> several localities with quartz<br />
veins with kyanite, and also <strong>of</strong> sillimanite in gneisses from the Gairezi Formation.<br />
3. Occurrence <strong>of</strong> kyanite in NW <strong>Mozambique</strong><br />
In area <strong>of</strong> Muvudzi, about 40 km NNW <strong>of</strong> Tete severa1 pegmatite bodies and quartz dykes were<br />
discovered in the past. The mineralized bodies are situated within the Tete massif and the locality<br />
Mavudzi is known as a now exhausted source <strong>of</strong> radioactive minaral davidite.<br />
Kyanite is present in the veins <strong>of</strong> quartz in massive aggregates several kg in weight with bladed dark<br />
grey sligthly greenish crystals. Apparently its concentration was brought fort under the influence <strong>of</strong><br />
hydrothermal solutions and thermal metamorphism.<br />
Around the northern margin <strong>of</strong> the Tete massif, the development <strong>of</strong> a contact zone with metasediments<br />
<strong>of</strong> the Fingoe Formation - schists and crystalline limestones - coincided probably with the development<br />
<strong>of</strong> andalusite and kyanite.<br />
It is <strong>of</strong> interest that a massive kyanite deposit is being mined in Malawi alonq the border with<br />
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Cilek: 3.1 Andalysite, kyanite, sillimanite<br />
<strong>Mozambique</strong> (NE-part <strong>of</strong> the Tete province), and that disseminated kyanite schists are present in the<br />
district Ncheu, at Kapiridimba, just at 1.5 km NE <strong>of</strong> the border (<strong>of</strong> beacon 22). Malawi rocks (gneisses<br />
and granulites) belong to the Mozambican Angonia Formation, and kyanite-bearing rock is present at<br />
Tsangano on the Mozambican side. In the Satambidwe Hill (Necungas)-a ring structure <strong>of</strong> syenite<br />
intrusion surrounded by Karroo sediments -a contact zone with hornfels was discovered just at the<br />
border with Malawi. About 30% <strong>of</strong> the rock is made up <strong>of</strong> andalusite in short, idiomorphic, prismatic<br />
crystals, accompanied by graphite derived from clay-marl sediments <strong>of</strong> the Karroo. Andalusite occurs in<br />
intergrowth with plagioclase.<br />
4. Dumortierite in secondary quartzite<br />
One locality <strong>of</strong> dumortierite only is known from <strong>Mozambique</strong>; it is situated on the southern side <strong>of</strong> the<br />
Cabora Bassa dam along the road Chicoa-Estima. The dumortierite quartzite is a very distinctive rock <strong>of</strong><br />
cobalt-blue colour, sometimes greyish, hard and massive, occuring in fragments, 10 to 20 cm long,<br />
scattered on the surface. It is commonly used as an ornamental stone. Dumortierite is developed in small<br />
crystals <strong>of</strong> prismatic shape and in aggregates <strong>of</strong> radial structure in fine grained quartzites. The quartzite<br />
forms apparently lenses and irregular bodies along the fault zones between Karroo sediments and<br />
Precambrian rocks <strong>of</strong> granulites, pegmatites and porphyrites. Results <strong>of</strong> the chemical analysis (in %):<br />
SiO2 61.48 CaO 1.75 P2O5 0.01 SiO2 0.71<br />
Al2O3 16.60 Na2O 0.05 TiO2 0.37 B 0.38<br />
Fe2O3+FeO 17.20 K2O 0.08<br />
Reserves were not calculated and the primary deposit under the eluvium is not known.<br />
5. Placers<br />
During the geochemical prospecting <strong>of</strong> the country, andalusite, sillimanite and kyanite were found to be<br />
common minerals <strong>of</strong> heavy mineral concentrates. Higher weight percentages are known, for example,<br />
for river deposits in the Manica province. Owing to the river transport, these minerals are now common<br />
constituents <strong>of</strong> marine placer deposits. In these deposits, they may represent a valuable byproduct.<br />
In <strong>Mozambique</strong>, a higher content <strong>of</strong> andalusite in heavy mineral suite was observed at the mouth <strong>of</strong> the<br />
river Limpopo (5.3%), at Praia Massano and Chidenguele (1.3 and 1.2%), at Ponta Zavora, Guinguane-<br />
Jangamo and Praia T<strong>of</strong>o Miramar (3.8, 1.9, 2.5%), Praia Wor'rungulo and Pomene (3.0, 1.7%) and the<br />
Paradise Islands (2.4%). All these beach sand localities are situated within the Limpopo paleodelta and<br />
the sediments supplied to the sea originate in Transvaal craton, Limpopo zone and Zimbabwe craton<br />
with its platform deposits. The increased amount <strong>of</strong> andalusite indicates clearly a contact-metamorphic<br />
origin <strong>of</strong> the deposits.<br />
Between Beira and the Zambezi delta, one beach sample contained 4.8% <strong>of</strong> kyanite.<br />
The central section <strong>of</strong> the seashore between the river Zambezi and <strong>Mozambique</strong> Island is characteristic<br />
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Cilek: 3.1 Andalysite, kyanite, sillimanite<br />
<strong>of</strong> a prevailing presence <strong>of</strong> kyanite: Gorai, Idugo, Pebane, Melai, Moebase, Moma, Larde, Angoche,<br />
Congolone, Quinga (1.7, 1.2, 1.1, 2.3, 3.4, 1.4, 2.8, 1.3, 2.6, 1.5 % <strong>of</strong> total heavy minerals). Andalusite<br />
in larger quantities is known to occur at Ilha Olinda near the opening <strong>of</strong> the Zambezi river (1.8%),<br />
Pebane (2.1%) and Larde (1.8%). The source rocks are within the <strong>Mozambique</strong> belt.<br />
Higher content <strong>of</strong> kyanite was discovered in scattered sand bodies in the northern section <strong>of</strong> the<br />
Mozambican seashore (1.4-3.0%) with identical source-rocks in the <strong>Mozambique</strong> belt to those within the<br />
central part.<br />
Kyanite forms mostly elongated tabular grains which are transparent or faintly bluish in colour, the<br />
grains <strong>of</strong> andalusite are mostly isometric in form and yellow to yellowish brown in colour; transparent<br />
grains are less frequent. Graphitic pigmentation is common to both minerals. Andalusite is rarely<br />
developed in the form <strong>of</strong> chiastolite. Grain size <strong>of</strong> about 70 to 80% is 0.1 mm, about 2.0 to 15.0% are<br />
below 0.1 mm.<br />
The reserves <strong>of</strong> the sillimanite-group minerals in beach and dune was estimated to about 2 million tons.<br />
Conclusions:<br />
Except the beach and dune deposits with a small content <strong>of</strong> andalusite and kyanite, very little is known<br />
<strong>of</strong> the sillimanite-group minerals in primary deposits. Certainly the most promising area is the extensive<br />
N-S trending zone between the <strong>Mozambique</strong> belt <strong>of</strong> the Baru6 Formation and the Zimbabwean craton<br />
with contact-metamorphic deposits in overlying metasediment <strong>of</strong> the Fronteira Formation.<br />
The contact zone and the aureole <strong>of</strong> pegmatitic and quartzitic dykes around the Tete massif may provide<br />
kyanite accumulations. The sillimanite deposits should be investigated within the high-grade<br />
metamorphic zones, especially in northern <strong>Mozambique</strong>, in the provinces Nampula and Cabo Delgado,<br />
in areas <strong>of</strong> graphite deposits, similarly to that ones in Angonia N <strong>of</strong> Tete.<br />
© Václav Cílek 1989<br />
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Cilek: 3.10. Rare-earth minerals<br />
3.10. Rare-earth minerals<br />
RE-minerals are a source <strong>of</strong> sixteen elements which play the increasing role in modern industry. Without these the present technical<br />
revolution would not be possible.<br />
From a modest beginning <strong>of</strong> utilization in the production <strong>of</strong> gas mantels and flint stones RE-elements found their application in<br />
every branch <strong>of</strong> industry.<br />
The rare-earths group is divided in two subgroups - cerium or light subgroup and yttrium or heavy subgroup.<br />
Cerium subgroup: Yttrium subgroup:<br />
Lanthanum La Yttrium Y<br />
Cerium Ce Terbium Tb<br />
Praseodymium Pr Dysprosium Dy<br />
Neodymium Nd Holmium Ho<br />
Promethium Pm Erbium Er<br />
Samarium Sm Thulium Tm<br />
Europium Eu Ytterbium Yb<br />
Gadolinium Gd Lutetium Lu<br />
included is also Thorium Th included is also Scandium Sc<br />
The cerium subgroup is represented mainly by two minerals - bastnaesite and monazite, while the yttrium subgroup is concentrated<br />
in xenotime. These three minerals are, in fact, the only commercial sources <strong>of</strong> RE.<br />
RE-minerals have generally a complex formula because <strong>of</strong> geochemical affinity. The important RE-minerals:<br />
bastnaesite (Ce,La) (CO3) F<br />
monazite CePO4<br />
xenotime Y PO4<br />
euxenite (Y, Ca, Ce, U, Th) (Nb, Ta, Ti)2 O6<br />
gadolinite Be2 Fe Y2 Si2 O10<br />
cerite Ca Ce6 Si O13<br />
Monazite is <strong>of</strong> a more complex composition, i. e. (Ce, La, Y, Th) PO4 and for RE, the ratio <strong>of</strong> Ce/La is 1:1 (about 30%) and the<br />
content <strong>of</strong> ThO2 up to 12%. Therefore monazite is also an important source <strong>of</strong> thorium. Yttrium occurs in small quantities only.<br />
The content <strong>of</strong> RE is 50-60%.<br />
In bastnaesite, the content <strong>of</strong> the main two cations is 1:1,36% each.<br />
All three main RE-minerals are concentrated in endmembers <strong>of</strong> magmatic rocks, i. e., in granitic and mainly pegmatitic deposits <strong>of</strong><br />
acid composition, and in alkaline end members such as nepheline syenites and pegmatites. At a temperature <strong>of</strong> 800°C, the monazite<br />
crystallizes from magma with prevailing Ce, at 700°C, at an onset <strong>of</strong> separation <strong>of</strong> pegmatitic material, the monazite crystallizes<br />
together with oxides <strong>of</strong> Ti, Nb, Ta and RE, with prevailing Y and Ce. Around 500°C, the last RE mainly as Ce and Y, are separated<br />
in apatites.<br />
All RE-minerals <strong>of</strong> RE accumulate in primary rocks in carbonatites only, which represent a special geochemical cycle.<br />
Exceptional are primary vein deposits <strong>of</strong> bastnaesite and monazite. Accumulations <strong>of</strong> monazite in placers - fluviatile or marine<br />
origin represent the main RE source. A new production <strong>of</strong> bastnaesite as a byproduct <strong>of</strong> iron-ore mining was started in China. In the<br />
Soviet Union, RE are recovered by a processing <strong>of</strong> apatite from the Kola peninsula.<br />
Composition <strong>of</strong> RE-ores (Kuzvart, 1984-Harben-Bates, 1984) (248 kB)<br />
The mining <strong>of</strong> monazite and xenotime is closely related to placer deposits mining, where they are found in commercial quantities<br />
(about 1% <strong>of</strong> total heavy minerals) as a byproduct <strong>of</strong> titanium and zirconium extraction. As a result, the production level <strong>of</strong><br />
monazite (xenotime is quite rare in placers) is dependent mainly on the market demands for titanium minerals. In fact, the content<br />
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<strong>of</strong> monazite is low, but it is present in many placer deposits and the large volumes <strong>of</strong> sand treated secure a constant supply and<br />
<strong>of</strong>ten oversupply <strong>of</strong> monazite on the world market.<br />
Bastnaesite in just one commercial deposit at the Mountain Pass area <strong>of</strong> the San Bernardino County in carbonatite, averages 5-15%<br />
<strong>of</strong> the carbonate rock. Another exception is the monazite deposit <strong>of</strong> the vein type Van Rhynsdorp in the Republic <strong>of</strong> South Africa<br />
which produces an RE-concentrate <strong>of</strong> 50-80% purity with 2-10% ThO2. In the Soviet Union, an important source <strong>of</strong> RE are apatites<br />
with an RE-content <strong>of</strong> 0.6-0.8%.<br />
The production <strong>of</strong> a RE-concentrate from crude ore and ore mining are cheap in comparison with a separation <strong>of</strong> RE (such as<br />
chlorides, Ce-RE carbonates and La-RE carbonates) from the concentrate which could be 1000 times more expensive. Two<br />
technological processes are used in the treatment <strong>of</strong> RE concentrate-monazite:<br />
1. acid-using H2SO4 up to 180-200°C (1.5 t <strong>of</strong> sulphuric acid for 1 t <strong>of</strong> concentrate)<br />
2. alkali-explained by the equation: (RE)PO4 + 3 NaOH ===> RE(OH)3 + Na3PO4 (1.5 kg NaOH on 1 kg <strong>of</strong> monazite).<br />
The result is RE as sulphate or hydroxide and separated Th. Then follows a separation <strong>of</strong> each RE-element by liquid-liquid solvent<br />
extraction and ion exchange.<br />
Few countries only export a natural concentrate <strong>of</strong> RE, most produce intermediate products such as RE-chloride and only a few<br />
REO <strong>of</strong> 99.9% purity.<br />
From RE-chloride, the so-called mish-metal is produced, i. e., an intermediate product <strong>of</strong> this composition: 51-53% Ce, 15-17%<br />
Nd, 3-4% Pr, 22-25% La, 2-3% Sm, 3% Tb, 3% Y and about 5% iron. Mish-metal is a compound representing the first utilization<br />
<strong>of</strong> an RE-mixed alloy used in the production <strong>of</strong> flints for lighters, later in that <strong>of</strong> docile iron and, nowadays, HSLA (high strength -<br />
low alloy) steels. It is necessary to stress that 0.01% <strong>of</strong> mish metal substantially increases the steel quality and can substitute several<br />
expensive alloying metals. Mish metal found other uses in the production <strong>of</strong> strong permanent magnets substituting expensive<br />
samarium. Cerium plays an important role in the polishing <strong>of</strong> glass, lenses, mirrors, TV-screens, but also as a colouring agent for<br />
TV-tubes and in a decolourization <strong>of</strong> glass. In electronics, RE are used in computers for memory films in GGG (galium-gadoliniumgarnet),<br />
in the production <strong>of</strong> special ceramics. Yttrium is essential in the production <strong>of</strong> YAG (yttrium-aluminium-garnet) for<br />
magnetic information storage, in an imitation <strong>of</strong> diamonds and crystals in lasers. In the atomic industry, yttrium secures the<br />
production <strong>of</strong> special stainless steels, gadolinium and europium in active zones <strong>of</strong> reactors as neutron absorbents.<br />
Main uses <strong>of</strong> REO: 40% as catalysts, 35% in the iron and steel industry, 18% in glass and ceramics and others. In the last group, the<br />
greatest future development is expected in control rods in atomic powerstations, phosphors and luminophors, super-alloys, magnets,<br />
catalysts, military applications and fiber optics.<br />
<strong>Mozambique</strong> is one <strong>of</strong> the few African countries where RE were extracted and exported.<br />
A unique deposit is the Guilherme pegmatite near Ribaue from where euxenite ore was transported to a dressing plant at the Boa<br />
Esperanca mine. Euxenite was exported to England for some years, but owing to unfavourable market conditions, production was<br />
discontinued sometimes in 1966.<br />
In <strong>Mozambique</strong> sites <strong>of</strong> RE occurrence are numerous and cover all genetic types <strong>of</strong><br />
known deposits:<br />
1. deposits in pegmatites and granitic rocks<br />
2. deposits in alkaline rocks<br />
3. deposits in carbonatites<br />
4. accumulations in apatites<br />
5. placer deposits.<br />
Of all these five genetic types, the placer deposits in beach and dune deposits in the coastal zone are the most important and<br />
economically most feasible ones (see Fig. 3.6.1).<br />
1. Pegmatite deposits<br />
RE are concentrated within the group <strong>of</strong> rare earths and radioactive minerals-pegmatites arranged in certain zones generally <strong>of</strong> NW-<br />
SE direction, crossing the zones <strong>of</strong> pegmatites with rare metals in NE-SW direction.<br />
Fig. 3.10.1 Alto Ligonha pegmatite district (Zambezi Province, Aquater, 1983). (63 kB)<br />
<strong>Minerals</strong> with RE:<br />
fergusonite Y, Er, Ce, U, ... (Nb, Ta) O4<br />
samarskite Fe, Ca, UO2 • Ce, Y (Nb, Ta)6<br />
euxenite -niobite and titanite <strong>of</strong> Y, Er, Ce, U<br />
polycrase - niobite and titanite <strong>of</strong> Y, Er, Ce, U<br />
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betafite - hydrous titanite and columbate <strong>of</strong> Ca, U, Y, Er, Ce<br />
monazite-(Ce, La, Nd) PO4<br />
xenotime-Y2O3 • P2O5<br />
rabdophanite - hydrated phosphate <strong>of</strong> Y, Ce<br />
pollucite- H2O • 2CS2O • 2Al2O3 • 9SiO2<br />
According to Barros-Vicente (1963) fergusonite was discovered in pegmatites <strong>of</strong> Enluma I. and Jlodo, in the shape <strong>of</strong> small<br />
spindles, 1 to 5 cm long, associated with quartz and zircon. On the surface, the crystals are covered by a yellowish alteration zone.<br />
Samarskite -is present in the area <strong>of</strong> Ribaue, in the mine Boa Esperanca, at Macotaia, Ingelo, Nahia and elsewhere. It is associated<br />
with muscovite, rarely with columbite. The crystals <strong>of</strong> samarskite are <strong>of</strong>ten arranged fanlike, <strong>of</strong> a distinctive violet-blue colour<br />
covered with a yellow layer, probably from uranium alteration. The aggregates are big, 25 cm length, over 2 kg.<br />
Samarskite from pegmatite Nahia: %<br />
SiO2 1.24 ThO2 1.94<br />
SnO2 1.48 Ce2O3 2.62<br />
PbO 0.47 Y2O3 12.16<br />
TiO2 1.59 U3O8 10.04<br />
Ta2O5 + Nb2O5 52.43 CaO 2.20<br />
Fe2O3 9.72 MgO traces<br />
MnO 0.90 H2O 2.16<br />
Al2O3 1.54<br />
Many other sites <strong>of</strong> samarskite occurrence had been discovered in the past. Bulgargeomin (1983) found a pegmatite in the area at<br />
the mouth <strong>of</strong> the river Lurio 5 km NW <strong>of</strong> Taquinha, with beryl, quartz, tourmaline and another pegmatite <strong>of</strong> small dimension (5 m ·<br />
0.5 m) 32 km SW <strong>of</strong> Taquinha with samarskite. It was also reported from pegmatites <strong>of</strong> Serra Meluli near Nipepe, in about 10 cm<br />
long masses (Geol. Inst. Beograd, 1984).<br />
Euxenite is well-known from several pegmatites <strong>of</strong> the Alto Ligonha district s. l. Often, it was found at Nauela and Ile, Mucharro,<br />
Nampoca, Nahavarra etc. It was mined at Guilherme and Muetia (Nauela region) and concentrated at the Boa Esperanca mine at<br />
Ribaue.<br />
Two samples were analysed by de Ledoux Co. (Barros-Vicente, 1963):<br />
% Guilherme Mucharro % Guilherme Mucharro<br />
TiO2 27.89 23.36 Pr6O11 0.06 0.24<br />
ZrO2 1.53 1.35 Nd2O3 0.30 0.85<br />
Fe2O3 3.42 4.18 Sm2O3 0.29 0.53<br />
U3O8 11.99 9.58 Eu2O3 0.01 0.02<br />
Nb2O5 26.87 24.13 Gd2O3 0.037 0.84<br />
Ta2O5 4.53 4.08 Tb4O7 0.01 0.02<br />
P2O5 0.33 1.48 Dy2O3 0.72 1.32<br />
Al2O3 1.05 1.05 Ho2O3 0.015 0.27<br />
CaO 0.76 0.87 Er2O3 0.61 1.02<br />
PbO 1.18 0.96 Tu2O3 0.13 1.90<br />
SiO2 1.23 2.08 Yb2O3 1.03 1.90<br />
BaO 0.07 0.04 Lu2O3 0.15 0.27<br />
MgO 0.02 0.15 Sc2O3 0.01 0.02<br />
MnO 0.07 0.15 ThO2 2.52 2.56<br />
SnO2 0.16 0.04 S 0.005 0.008<br />
Y2O3 5.30 10.72 C 0.072 0.064<br />
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La2O3 0.04 0.18 L. i. 6.68 4.09<br />
CeO2 0.07 1.23<br />
Euxenite is associated with columbite in tubular crystals, <strong>of</strong>ten altered.<br />
Polycrase or euxenite-polycrase occurs in pegmatites <strong>of</strong> Boa Esperanca and Giline. It is quite rare and generally covered with a<br />
yellow alteration zone similarly to euxenite and samarskite.<br />
Betafite is present just at the Boa Esperanca mine, in small massive aggregates <strong>of</strong> black-greenish colour.<br />
Moçambiquite was introduced as a new mineral by J. M. Cotelo Neiva and J. M. Correia Neves on the international Geological<br />
Congress (1960) at Copenhagen (Barros - Vicente, 1963). It is a mineral composed mainly <strong>of</strong> thorium occurring in one locality only<br />
- the mine Muiane, where forms octahedrons <strong>of</strong> yellow-brownish colour and specific gravity 5.24. Spectrographic analysis: Thdominant;<br />
Si, U, Zr, Y abundant; Pb, Er, Cd, Sa, Mn in traces.<br />
Chemical analysis <strong>of</strong> Mocambiquite from the Muiane mine (University <strong>of</strong> Coimbra by Neiva-Neves) (in %):<br />
SiO2 11.00<br />
ThO2 58.80<br />
U3O8 6.04<br />
CaO 0.59<br />
Fe2O3 0.22<br />
Al2O3 4.40<br />
RE<br />
H2O<br />
8.60<br />
Monazite is frequent in pegmatites <strong>of</strong> Alto Ligonha and surroundings and is the mineral that occurs not only in RE-radioactive<br />
minerals-pegmatites but <strong>of</strong>ten also in the group <strong>of</strong> rare metals pegmatites.<br />
Its crystals are generally tabular or elongate and in aggregates <strong>of</strong> prismatic crystals usually about 1 cm long. Some crystals are even<br />
5 cm long, and aggregates may attain a weight <strong>of</strong> more than 2 kg. The colour <strong>of</strong> the mineral depends on the thorium content, when<br />
strongly radioactive (20% <strong>of</strong> ThO) it is greenish (areas <strong>of</strong> Ingela, Naquissupa, Namacotche), when weakly radioactive it is <strong>of</strong><br />
brownish-green colour. Main pegmatite localities with monazite are the mine Morrua and an area <strong>of</strong> Ribaue.<br />
Apart from the Alto Ligonha district, monazite occurs in many other localities throughout the Mozambican belt in connection with<br />
granitic pegmatites.<br />
Two chemical analyses are known (de Ledoux Co.):<br />
% Muetia Guilherme<br />
P2O5 32.80 31.42<br />
Ce2O3 23.80 22.45<br />
ThO2 7.1 7.8<br />
Y2O3 etc. 35.0 36.25<br />
Xenotime<br />
Barros-Vicente (1963) reported it from one locality only - pegmatite Namivo - where it is in intergrowth with zircon.<br />
Later, the author visited the mine Boa Esperanca (1980) and learned that xenotime was produced and processed in the Ribaue area.<br />
The concentrate was exported to England in this composition (minimum 53% RE) (in %):<br />
CeO2 11.2 Sm2O3 2 Ho2O3 < 1<br />
Y2O3 46.3 Eu2O3 < 1 Er2O3 6<br />
La2O3 5 Gd2O3 3 Tm2O3 1<br />
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Pr6O11 1 Tb4O7 1 Yb2O3 8<br />
Ne12O3 6 Dy2O3 7 Lu2O3 < 1<br />
Rabdophanite - reported from Nuaparra, in close intergrowth with thorite.<br />
Pollucite, a mineral <strong>of</strong> cesium, occurs in several, especially zoned pegmatites, in the zone <strong>of</strong> lithium minerals, commonly with<br />
petalite at Namacotche, Nahora, Muiane, Morrua etc. Its main producer was the pegmatite mine Namacotche, in a quality <strong>of</strong> Cs<br />
33.45%, Rb 0.48%.<br />
RE minerals are concentrated in zoned pegmatites in the internal zone, within the zone <strong>of</strong> big feldspars. Monazite, euxenite,<br />
samarskite and xenotime are the main RE-minerals. In the central and SW part <strong>of</strong> the Alto Ligonha pegmatite field, there occur<br />
both mineralization <strong>of</strong> RE with rare metals. Some pegmatites <strong>of</strong> a microcline variety display a simple zoning with vein-type<br />
pegmatite bodies up to a length <strong>of</strong> 250 m. Mineralization is represented by beryl, columbite-tantalite, bismute, monazite, euxenite,<br />
zircon and xenotime.<br />
Another known area <strong>of</strong> its occurrence lies 10 km NE <strong>of</strong> Alto Molucue, with the group <strong>of</strong> pegmatites <strong>of</strong> Guilherme, Muetia and<br />
Conua. Veins are about 150 m long, 15 m wide and almost subvertical. They occur in granitized host rocks with a simple zoning <strong>of</strong><br />
quartz core, block microcline and external homogeneous pegmatite. Mineral assemblage is represented by euxenite, monazite,<br />
bismutite, beryl within the zones <strong>of</strong> albitization.<br />
The Boa Esperanca mine near Ribaue is not known only for its kaolin and feldspar production, but also for the presence <strong>of</strong> a<br />
number <strong>of</strong> other minerals - samarskite, zircon, monazite, xenotime and others. The pegmatite with a quartz nucleus has a zonal<br />
structure with oligoclase-microcline block pegmatite, muscovite and a homogeneous external zone.<br />
Perhaps the best example <strong>of</strong> RE-pegmatites is present in the Zambezia Province, between Mocuba and Gurue, and its NE extension<br />
to Alto Ligonha towards Nacala. Host rocks are biolite-amphibole and pyroxene-biotite gneisses, rarely granitoid massifs. The<br />
pegmatites can be classified as microcline with a zonal structure. Mineralization occurs with monazite, euxenite, samarskite,<br />
ilmenite, magnetite, columbo-tantalite and beryl.<br />
One <strong>of</strong> the most important areas is that at Moala, on the right bank <strong>of</strong> Lurio river, 47 km NE <strong>of</strong> Gurue. The veins are 500 m long or<br />
more, 3-5 m wide. Zonal structure is well developed. Mineralization occurs in the form <strong>of</strong> veins and disseminations with<br />
samarskite, monazite, itmenite, magnetite, and a minor content <strong>of</strong> columbite, tantalite and zircon. Spectroscopic analyses disclosed<br />
significant quantities <strong>of</strong> Nb, U, Sc. Other pegmatites <strong>of</strong> this area contain thorite, davidite and uraninites. Total extension <strong>of</strong> REpegmatites<br />
is about 400 km2.<br />
Numerous pegmatites are known to occur near the port <strong>of</strong> Nacala. Generally, they exhibit a simple zoning and are about 8-10 m<br />
wide. There are two main areas - one 9 km SW <strong>of</strong> Nacala (Tulua, Equesa, Namiope), the other around Vila Cabo-Comane. The<br />
Tulua vein, at present the main supplier <strong>of</strong> feldspar and amazonite, is 250 m long, 10-15 m wide, dipping 50-55°SE. It is <strong>of</strong> zonal<br />
structure with a quartz nucleus, a sodalithic zone, a microcline zone and a quartz-microcline zone. Mineralogical assemblage:<br />
samarskite, monazite, zircon, garnet, microlite, tantalite, cassiterite, bismutite and uraninite.<br />
The Equesa and Namiope veins are 100 m long, 10 m wide, dipping 40-50°. Zonal structure is similar to that <strong>of</strong> Tulua,<br />
mineralization is represented by black, green and pink tourmaline, monazite, xenotime, zircon, ilmenite, garnet and rarely<br />
columbite, microlite, bismutite and cassiterite.<br />
At Vila Cabo-Comane, the small pegmatite is <strong>of</strong> the microcline variety with a quartz nucleus. <strong>Minerals</strong> present are tourmaline,<br />
monazite, zircon, xenotime, rutile, ilmenite, magnetite and garnet.<br />
Three RE-minerals <strong>of</strong> pegmatites were produced in <strong>Mozambique</strong> (Barros-Vicente, 1963): euxenite, samarskite and monazite. Their<br />
production started in 1937, with 17.5 t <strong>of</strong> samarskite, dropping to 0.4-0.06 t (except for 1.25 t 1948) and stopped in 1953 due to<br />
unfavourable market conditions. Euxenite was produced in a small quantity only (total 1944-1960: 1.66 t). Monazite started to be<br />
produced in 1937 with 13.04 t, dropping to 250 kg and ceasing in 1961 with 243 kg (Barros-Vicente, 1963). Pollucite was also<br />
produced; in 1961, 5 t were exported to the USA.<br />
The only mineral still produced and exported is monazite-2.1 t produced in 1974, 12 t in 1975, 9 t in 1980 going down to 0.16 t in<br />
1985, from three pegmatite-producing mines, Morrua, Marropino and Muiane.<br />
2. Deposits in alkaline rocks<br />
Several nepheline syenites and alkaline syenites bodies known to occur in <strong>Mozambique</strong> have been investigated for different<br />
minerals. Some <strong>of</strong> these contained RE.<br />
In the massif Conguene at the southern end <strong>of</strong>-Malawi, on the E side <strong>of</strong> the Niassa rift valley, nepheline syenites with biotite are<br />
developed. RE were found within the type <strong>of</strong> alkaline metasomes-fenites. They concentrate in the contact zone <strong>of</strong> the nonnephelinic<br />
syenites with nepheline syenites, with Rb2O (300 g/t), Nb2O5 (400-2,000 g/t) and Ta2O5 (100-400 g/t).<br />
Trace elements (VAMI, Leningrad, 1981) (in g/t):<br />
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Sample Ga Rb2O V2O5 Li2O Ta2O5 Nb2O5 Tr2O3 Zr Cr2O3 TiO2 Cl F Sr Ba<br />
B-1 33 230 30 20 12 240 68 835 tr. 1,200 120 360 370 700<br />
B-2 32 130 10 10 5 108 118 263 30 3,400 280 490 900 -<br />
Both samples have an interestingly increased content <strong>of</strong> gallium and rubidium, both are <strong>of</strong> high value and could be economically<br />
recovered as byproducts, thus improving overall economic parametres <strong>of</strong> syenites, which could be used in the alumina production<br />
(see chapter alkaline rocks).<br />
Besides the reserves <strong>of</strong> alumina raw materials, possible reserves <strong>of</strong> niobium pentaoxide were calculated in the order <strong>of</strong> 25,000 t,<br />
content 0.1%. Similar reserves <strong>of</strong> rubidium oxide can be estimated in the order <strong>of</strong> 30,000 t.<br />
In the northern part <strong>of</strong> <strong>Mozambique</strong>, in the Province Niassa in the vicinity <strong>of</strong> Unango (N <strong>of</strong> Lichinga), over a area <strong>of</strong> about 5,000<br />
km2 several alkaline complexes were discovered during geochemical prospecting, with mineralizations <strong>of</strong> uranium, niobium,<br />
tantalum and RE connected with anomalies <strong>of</strong> phosphorus.<br />
In the same province, just near the bank <strong>of</strong> lake Niassa, around Meponda in Precambrian gneisses, several intrusions <strong>of</strong> granites,<br />
monzonites, syenites and alkaline syenites were discovered. On Monte Tchonde (Geol. Institute, Beograd -1984) a circular structure<br />
composed <strong>of</strong> these rocks is cut by several dykes <strong>of</strong> rhyolite. Several radioactive anomalies were detected, with three types <strong>of</strong><br />
mineralization:<br />
a) in relation with red granites and quartzitic monzonites <strong>of</strong> Mt. Tchonde<br />
b) in rhyolitic dykes<br />
c) in alkaline rocks<br />
The first two anomalies are characterized by a high content <strong>of</strong> K, U, Th, their value is small. The third type contained an increased<br />
quantity <strong>of</strong> V, Th, Ta, Nb and RE. These accumulations are regarded as promising. Some preliminary work deliniated the<br />
anomalies which extend for about 8 km, 100-200 m width, in altered alkaline syenites, subalkaline metadiorites and nepheline<br />
syenites. Trenching revealed that several lenses <strong>of</strong> highly altered rocks <strong>of</strong> this belt, measuring 10 to 1 000 m in length and several m<br />
width, contain U -0.05% to 0.16%, thorium up to 1.3% with niobium, tantalum and RE.<br />
3. Deposits in carbonatites<br />
Generally, all carbonatites display a higher amount <strong>of</strong> phosphorus and RE. All carbonatites <strong>of</strong> <strong>Mozambique</strong> are connected with<br />
deep-seated fractures <strong>of</strong> rift valley systems. The main localities <strong>of</strong> volcanic vents with carbonatite are: Monte Xiluvo in the S,<br />
Monte Muamba on the N near Tete and Cone Negose near the Zambeze river in the W. Other bodies, originally supposed to be<br />
carbonatites such as Salambidwe at the Malawian border or Serra Morrumbala E <strong>of</strong> the Niassa rift valley, are syenite intrusions<br />
without a carbonatite vent.<br />
Monte Xiluvo has not yet been explored substantially; Monte Muambe is an important fluorite deposit (see chapter-fluorites) with<br />
an increased amount <strong>of</strong> niobium and RE, the latter being included most probably in monazite and partly in pyrochlore (?).<br />
A spectroscopic analysis <strong>of</strong> carbonatite revealed the presence <strong>of</strong> Y, Ce, Nb and Sr.<br />
Cone Negose is a carbonatite intrusion close to the N boundary fault system <strong>of</strong> the mid-Zambezi trough. The country rocks to the N<br />
<strong>of</strong> the main fault are metasediments <strong>of</strong> the Fingoe Formation intruded by granites and cut by porphyry and dolerite dykes (Hunting,<br />
1984).<br />
Karroo sediments occur S <strong>of</strong> the fault. Cone Negose is situated N <strong>of</strong> the main fault; all other small satellite Cretaceous intrusions<br />
occur to the S in the Karroo area.<br />
Cone Negose consists <strong>of</strong> a central core <strong>of</strong> carbonatite surrounded by a ring <strong>of</strong> trachytic and carbonate breccia or vent agglomerate.<br />
All satellite stocks and plugs to the S consist <strong>of</strong> similar trachytic vent agglomerates.<br />
Carbonatites are developed in various successive stages (Carvalho, 1977):<br />
A. grey carbonatite with pyrochlore and monazite (RE)<br />
B. red veins and buff carbonatite with bastnaesite and baryte (RE)<br />
C. phosphatic carbonatite with brookite and barytes<br />
D. silicified carbonatite with fluorapatite, pyrochlore and baryte<br />
F. fluorapatite<br />
Buff carbonatite is characterized by an increased content <strong>of</strong> baryte and a high content <strong>of</strong> bastnaesite with RE; red vein stage has<br />
high content <strong>of</strong> niobium bearing TiO2.<br />
Carbonatites <strong>of</strong> Cone Negose are <strong>of</strong> the magnesium type i. e. "rauhaugites".<br />
New discoveries <strong>of</strong> RE in carbonatites were made in the northern part <strong>of</strong> <strong>Mozambique</strong>. The site is called Luicuisse after the river<br />
Luicuisse; it lies in the Province Niassa, near the settlement Navago, about 240 km NE <strong>of</strong> Lichinga.<br />
In Precambrian rocks, several alkaline intrusions <strong>of</strong> nepheline syenites and syenites were discovered with fracture zones filled up<br />
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Cilek: 3.10. Rare-earth minerals<br />
by mineralized carbonatites with RE, U and Th and apatite. The superficial zone <strong>of</strong> weathering is 7-8 m thick, its mineral content is<br />
increased.<br />
The Luicuisse finding is, in fact, a large circular structure with complex mineralization.<br />
In the weathering zone in many pits, columbite, pyrochlore, apatite, monazite and magnetite were determined. Over an area <strong>of</strong> 0.66<br />
km2, an eluvial deposit <strong>of</strong> 30 m thickness was delineated; it contained columbite and zircon (in 90% <strong>of</strong> samples), pyrochlore (78%<br />
<strong>of</strong> samples) and apatite (in 33.8% <strong>of</strong> samples). RE, Nb, Ta, Cs, La, Y, Zr are ten-times higher than their clarke. The content <strong>of</strong><br />
P2O5 averages 2.34%, in some samples 6.77%.<br />
4. Accumulations in apatites<br />
Apatite deposit in crystalline limestones <strong>of</strong> the Mozambican belt at Evate in the Province Nampula contains partly also fluorapatite<br />
Ca5 (F (PO4)3), rarely hydroxyde apatite (Ca5 (PO4)3 (OH)) with an increased amount <strong>of</strong> SrO (0.25%) and RE (0.59% max.). RE<br />
are represented by Ce predominant over La and a minor Y and Yb. The content <strong>of</strong> almost 0.6% RE in some sections <strong>of</strong> the deposits,<br />
with an average <strong>of</strong> 0.3%, is very similar to the average content <strong>of</strong> apatite from the Kola peninsula in the Soviet Union (0.6 - 0.8 %<br />
RE). The technological process <strong>of</strong> recovering RE from Kola apatite has been known for many years and apatite is an important<br />
source <strong>of</strong> RE. If the Evate apatite were to be mined also RE could be recovered as a byproduct.<br />
5. Placer deposits<br />
Heavy mineral accumulations are known to occur along the whole Mozambican seashore. They are both in beach-and dune deposits<br />
with heavy minerals (HM) represented by ilmenite, rutile, zircon, monazite, kyanite and andalusite. The main accumulations <strong>of</strong> HM<br />
are in Mid-<strong>Mozambique</strong>, in a section <strong>of</strong> the seashore between Beira and Quinga. In southern <strong>Mozambique</strong>, huge beach- and dune<br />
deposits developed during the Quaternary with an inland extension <strong>of</strong> about 80 km from present seashore. The HM assemblage<br />
consists <strong>of</strong> economic HM (see above) and waste silicate minerals.<br />
In N- <strong>Mozambique</strong> from <strong>Mozambique</strong> Island to the Rovuma river, just few and small sand bodies with HM were found on the<br />
coralline seashore.<br />
The content <strong>of</strong> monazite in an assemblage <strong>of</strong> economic HM is usually less than 1%. Within the whole HM assemblage, a minimum<br />
content <strong>of</strong> 0.5% <strong>of</strong> monazite is regarded as an economic accumulation.<br />
List <strong>of</strong> localities:<br />
Marracuene - 1.0%<br />
fossil placer on an old beach hurried under eolian sands and eroded on the bank<br />
<strong>of</strong> river Incomati<br />
Inhambane Bay - 0.5% old dunes on the W side <strong>of</strong> the peninsula bordering the E side <strong>of</strong> the bay<br />
Beira - 1.5%, beaches NE <strong>of</strong> Beria towards the delta <strong>of</strong> the river Zambezi, transgressive sands<br />
Deia - 5.8%<br />
beach sand on Deia deposit with altered HM near Quelimane, samples <strong>of</strong><br />
Nöldeke (1978)<br />
Deia - 0.5% beach sand -Deia deposit, modern beach with silicate HM<br />
Raraga - 1.8% beach sand from retention ridge with economic minerals<br />
Gorai - 0.5% beach sand, 3 km long beach with high concentration <strong>of</strong> HM<br />
Idugo - 0.8% beach and dunes, deposits <strong>of</strong> old concession<br />
Pebane - 0.6% beach with high content <strong>of</strong> HM concentrate produced contained 3% monazite<br />
Melai - 0.5% beach, part <strong>of</strong> Pebane deposit<br />
Moebase - 0.7% beach, 50 km long seashore, surveyed beach 13 km, HM also in dunes<br />
Moma - 1.7% beach, 15 km long, beach and dune ridges<br />
Angoche - 1.7% beach NE <strong>of</strong> town with several ridges<br />
Congolone - 1.2% huge dune deposit NE <strong>of</strong> Angoche, dune Congolone is complex dune<br />
Quinga - 0.9% last stretch <strong>of</strong> beach and dune deposits <strong>of</strong> middle <strong>Mozambique</strong><br />
Palma - 0.7% thin layer <strong>of</strong> sand over coral platform<br />
Monazite forms usually round oval grains <strong>of</strong> yellow-brown colour. Also a small amount <strong>of</strong> xenotime was found, but it could not be<br />
separated.<br />
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Cilek: 3.10. Rare-earth minerals<br />
Monazite contains elements <strong>of</strong> the cerium group - mainly La, Ce, Nd and Sm. The average <strong>of</strong> REO is usually 50-60% and 2-10%<br />
Th. Mozambican monazite has about 38-45% <strong>of</strong> RE with prevailing La, Ce, Nd 36-43%, but even the Sm content is interesting.<br />
Average U and Th content is above 5%; the mineral can indeed be classified as a strategic one (see Table 5).<br />
Table 5. Instrumental neutron activation analysis <strong>of</strong> Monazite made at IMRM-Czechoslovakia: (in %) (262 kB)<br />
Estimated reserves <strong>of</strong> monazite in selected beach - and dune deposits represented about 500,000 t. The world annual production is<br />
about 25,000 t/y, a production unit needs about 5,000 t <strong>of</strong> monazite annually and this amount could be extracted just from a few<br />
deposits. An example <strong>of</strong> a possible future source <strong>of</strong> monazite is the Congolone-dune deposit from which about 1,500 t <strong>of</strong> monazite<br />
could be recovered as a byproduct at an annual production <strong>of</strong> about 100,000 t <strong>of</strong> ilmenite.<br />
Conclusions:<br />
Mozambican rare-earths resources are both big and diversified. Again, the well-known pegmatite district <strong>of</strong> Alto Ligonha proved its<br />
extraordinary properties in that not only columbite-tantalite ores are extracted at present but in the also commercial quantities <strong>of</strong> REminerals<br />
euxenite, samarskite and monazite. There are large possibilities to produce monazite as a byproduct <strong>of</strong> rare-metals mining<br />
and to start a new production <strong>of</strong> RE and radioactive materials from several promising pegmatites both in the Alto Ligonha district s.<br />
l. or outside it.<br />
Futher resources in alkaline rocks-nepheline syenites are feasible as soon as these are put into production either for ceramics or the<br />
alumina industry. The content <strong>of</strong> rubidium is promising.<br />
A similar situation can be envisaged with the production <strong>of</strong> apatite which contains, for example at the Evate deposit, a maximum <strong>of</strong><br />
0.6% RE.<br />
The most feasible are deposits <strong>of</strong> monazite from beach - and dune sands known to be present in many places on the seashore.<br />
Several thousand tons could be recovered annualy and processed directly in <strong>Mozambique</strong> either as a chloride or a mishmetal, which<br />
finally could be used locally in the production <strong>of</strong> special alloys and high-strength steel.<br />
© Václav Cílek 1989<br />
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Cilek: 3.11. Talc and soapstone<br />
3.11. Talc and soapstone<br />
Talc is a hydrous magnesium silicate Mg3(Si4O10) (OH), originating as secondary mineral from an<br />
alteration <strong>of</strong> magnesium silicates such as olivine, pyroxenes or amphiboles. Commonly it is white or<br />
green, in pearly foliated masses. The massive variety is called steatite. Talc is very s<strong>of</strong>t; number 1 on the<br />
Mohs hardness scale, greasy, with a perfect basal cleavage, <strong>of</strong>ten in foliated structure. Admixtures with<br />
some elements give talc a special colour: chromium deep green with violet spots in serpentinites, nickel<br />
or Fe2+ - apple-green, copper-bluish green. In deposits, talc is accompanied by several minerals such as<br />
serpentine, dolomite, magnesite, tremolite, anthophyllite, quartz and others. Commercial-grade talc is<br />
rock composed predominantly <strong>of</strong> talc (from 60 to 98%), calcite (1-12%), tremolite (30-40%) and<br />
anthophyllite (5%). Rock composed <strong>of</strong> at least 35% talc and 25% <strong>of</strong> the mentioned minerals, is called<br />
soapstone.<br />
Chemical and physical properties <strong>of</strong> talc and steatite are used in many industrial branches. Talc is a<br />
mineral used with still increasing intensity for the s<strong>of</strong>tness <strong>of</strong> its powder, its high coating ability, high<br />
melting point, low electric conductivity, high absorption capacity and white colour. Talc found its use in<br />
the textile industry, production <strong>of</strong> soap, tooth-paste, in the cosmetic and the rubber industry, in chemistry<br />
in catalysis. Other applications are in the pharmaceutical industry, as a lubricant, oil absorbent, filler in<br />
paint (important in white-pigment TiO, dispersion), plastics and paper.<br />
Electroceramic talc must contain less than 0.7% Fe2O3 and also steatite can be used as refractory<br />
material. Mixed with 25-40% <strong>of</strong> clay it is used in the production <strong>of</strong> earthenware. It can replace kaolin as<br />
a paper-coating product and several materials in refractory products. Soapstone can be cut in quarries<br />
into structural units for the use as refractory bricks in metallurgical, glass and cement furnaces. Its oldest<br />
and still popular use is in soapstone carvings.<br />
Two genetic types <strong>of</strong> deposits are known:<br />
1. in ultrabasic rocks and serpentinites<br />
2. hydrothermal deposits in dolomitic and silicate rocks<br />
1. Deposits developed similarly to deposits <strong>of</strong> asbestos. Talc rock can replace whole<br />
bodies <strong>of</strong> serpentinite, but more commonly forms a rind around serpentinite with asbestos. Often, several<br />
zones are developed: unaltered serpentinite - zone <strong>of</strong> talc - carbonate serpentinite - talc zone - actinolite<br />
and chlorite zone - granitic rock. Talc is an alteration <strong>of</strong> serpentinite by hydrothermal solutions with<br />
SiO, and CO, during regional or contact metamorphism according to the equations (Kuzvart, 1984):<br />
H4Mg2Si2O9 (serpentinite) + 2SiO2 ===>H2Mg3Si4O12 + H2O (talc or steatite)<br />
2 H4 (Mg, Fe)3 Si2O9 + 3CO2 ===> H2Mg3Si4O12 + (Mg, Fe) CO3 + 3 H2O (soapstone)<br />
2. Deposits <strong>of</strong> talc in magnesites, dolomites and dolomitic limestones are formed by hydrothermal<br />
influence <strong>of</strong> nearby intrusions according to the equations (Kuzvart, 1984):<br />
3 MgCO3 + 4SiO2 + H2O ===> H2Mg3Si4O12 + 3 CO2<br />
3 MgCa (CO3)2 + 4SiO2 + H20 ===> H2Mg3Si4O12 + 3 CaCO3 + 3 CO2<br />
In both cases, SiO2 is supplied by granitic intrusions.<br />
In <strong>Mozambique</strong>, talc is not being produced, despite the fact that several deposits <strong>of</strong> talc may be present<br />
in mined asbestos deposits (see chapter "asbestos"). Knowledge is available just <strong>of</strong> deposits <strong>of</strong> the first<br />
type in ultrabasites and serpentinites, while an absence <strong>of</strong> dolomites and a scarcity <strong>of</strong> dolomitic<br />
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Cilek: 3.11. Talc and soapstone<br />
limestones prevented a development <strong>of</strong> the second type <strong>of</strong> deposit (see Fig. 3.2.1).<br />
a) The Serra Mangota asbestos deposit also contains talc and talc schists. In the W- part originated the<br />
carbonate-talc zone <strong>of</strong> serpentinite while in the E- part prevail talc schists. Because good quality<br />
asbestos is connected mainly with carbonate serpentinite, talc deposits, presumably best-developed in<br />
the E part <strong>of</strong> the ridge, should be explored and mined here.<br />
b) Small findings <strong>of</strong> reworked greenstone belts <strong>of</strong> the Mozambican belt include a continuation <strong>of</strong><br />
"Cronley greenstones" from Zimbabwe to <strong>Mozambique</strong> with a possible occurrence <strong>of</strong> talc in areas <strong>of</strong><br />
Maravia near Fingoe and the ultrabasic complex <strong>of</strong> Monte Atchiza. In the latter, an alteration <strong>of</strong><br />
peridotites and pyroxenites into serpentinite and further into actinolite and anthophyllite is common. The<br />
presence <strong>of</strong> talc may be possible.<br />
c) The asbestos deposit Mavita is the best example <strong>of</strong> a first-type deposit with the development <strong>of</strong> a<br />
different zone between the unaltered serpentinite and intrusive rocks. The rind structure <strong>of</strong> talc, talcschists<br />
and chlorite and mica schists around the serpentinite and asbestos was observed on many partial<br />
asbestos deposits. Talc-schists are apple-green, mainly steatite-schists, pearly and greasy. They form<br />
belts ranging from several to several tens <strong>of</strong> m width, with reserves estimated to more than several<br />
million t. No tests for talc materials were made despite the fact, that this material could improved<br />
substantially the mining for asbestos.<br />
d) The Mulatala deposit is a large zone <strong>of</strong> altered ultrabasic rocks, with a presence <strong>of</strong> talc in harzburgitic<br />
serpentinites. The rock <strong>of</strong> asbestos is composed <strong>of</strong> talc, vermiculite, anthophyllite, chlorite and probably<br />
quartz.<br />
Other localities with talc, tremolite, actinolite and chloritic rocks were discovered by Bulgargeomin<br />
(1983) in ultrabasites at Monte Nicuculo, 50 km W <strong>of</strong> Pemba and 7 km S <strong>of</strong> M. Nicuculo.<br />
Conclusions:<br />
Promising talc deposits are connected with ultrabasic mainly serpentinite bodies containing asbestos. No<br />
talc tests were made.<br />
Two deposits should be explored for talc in <strong>Mozambique</strong>: Serra Mangota near Manica and anthophyllite<br />
deposits at Mavita S <strong>of</strong> Chimoio.<br />
A utilization <strong>of</strong> talc and soapstone could be beneficial mainly to the local industry: as refractory material<br />
in glass, cement and future metallurgical industry, in several other industrial branches such as the<br />
production <strong>of</strong> earthenware-porcelain and tiles, in textiles, tooth-paste, soap, rubber and as a filler.<br />
© Václav Cílek 1989<br />
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Cilek: 3.12. Titanium and zirconium minerals<br />
3.12. Titanium and zirconium minerals<br />
Common titanium minerals are ilmenite, rutile, anatase, brookite, leucoxene. Among the oxides, the most abundant is<br />
rutile with a content <strong>of</strong> 89.5 to 99% TiO2, followed by anatase (98.4-99.8 % TiO2), brookite, ilmenite-rutile, tantalumrutile<br />
and ulvospinel.<br />
Other mineral groups include ilmenite FeTiO3 and titanite CaTiSiO5. The content <strong>of</strong> TiO2 in ilmenite varies between 48.6<br />
and 57.3%. A higher content <strong>of</strong> iron is caused by an intergrowth <strong>of</strong> hematite or magnetite. Some ilmenites possess a<br />
higher content <strong>of</strong> TiO2 than theoretically acceptable, i. e. 52.7%, because <strong>of</strong> the presence <strong>of</strong> fine pheno crystallites <strong>of</strong><br />
rutile or spinel. V, Nb, Cr and Ta are present as impurities. The TiO2 content in a commercial product should not fall<br />
below 50%, the maximum content <strong>of</strong> vanadium 0.5%, that <strong>of</strong> chromium 0.1%, manganese 0.5%, niobium 0.5% and<br />
copper 0.1%. In rutile, a minimum content <strong>of</strong> TiO2 <strong>of</strong> 92% is acceptable.<br />
Zirconium minerals include zircon and baddeleyite. Zircon is silicate ZrSiO4 and baddeleyite oxide ZrO2. Zircon supplies<br />
98% <strong>of</strong> world demand for zirconium and contains 67% ZrO2 and about 2% <strong>of</strong> hafnium. Baddeleyite is almost pure<br />
zirconium oxide with 96.5-98.9% ZrO2 and is mined in primary deposits in a few places only.<br />
The most important <strong>of</strong> titanium minerals is ilmenite which accounts for almost 85% <strong>of</strong> the minerals used in titanium<br />
products. Leucoxene called "altered ilmenite" is an accompanying mineral in placer deposits, in which a minimal content<br />
<strong>of</strong> at least 68% TiO2, had been upgraded by oxidation and partial removal <strong>of</strong> iron.<br />
Rutile is the most important <strong>of</strong> Ti-oxides.<br />
The most important <strong>of</strong> all zirconium minerals, is zircon, followed by quite rare baddeleyite. In both minerals, common<br />
impurities include thorium, uranium, rare earths and yttrium, calcium, magnesium, iron and hafnium. Hafnium is very<br />
similar to zirconium in chemical and physical properties, but must be removed in certain applications <strong>of</strong> zirconium.<br />
More than 90% <strong>of</strong> titanium minerals are used in the production <strong>of</strong> titanium dioxide, TiO2, a pigment known as white<br />
pigment, used also in plastics, paper, rubber, additive in frits, glazes and titanium ceramics mixtures. The remaining 10%<br />
are used mainly as titanium metal, which is light, strong and anticorrosive and finds increasing use in the aircraft industry,<br />
rocket and satellite construction, atomic industry, in submarines, special machinery for chemical, textile and metallurgical<br />
industries and also in medical appliances. Two methods are used in a production <strong>of</strong> titanium dioxide-the older, nowadays<br />
seldom used sulfate route and the modern chloride route.<br />
The sulfate route requires either simple ilmenite with 45-55% <strong>of</strong> TiO2 or titanium slag with 70-80% TiO2. This material is<br />
dissolved in sulphuric acid and titania is then precipitated by hydrolysis, filtered, washed and calcined to produce TiO2. A<br />
problem arises from waste disposal (ferrous-sulfate) harmful to the environment. In Czechoslovakia, ferrous-sulfate is<br />
used partly in the pigment industry.<br />
The chloride route is more complicated, more expensive, requires a feedstock with a higher TiO2 content, but is<br />
environmentally harmless. The material is usually made-up <strong>of</strong> rutile or, nowadays, different products <strong>of</strong> upgraded ilmenitesynthetic<br />
rutile or titanium slags with 85% TiO2 or more, chlorinated at 850-950°C in the presence <strong>of</strong> petroleum coke to<br />
produce TiCl4. This is oxidised to produce TiO2. Titanium tetrachloride is the basic material for the production <strong>of</strong> metal<br />
using a reduction process with metallic magnesium.<br />
Zircon displays high mechanical strength, it is refractory and resistant to corrosion and has a low neutron absorption.<br />
Thus, over 90% are consumed in special refractories and ceramics to produce refractory bricks, refractory sand and<br />
foundry sand. Zirconia ZrO2 is produced by reacting zircon and dolomite resulting in still higher refractory products,<br />
melting point 2,700°C (200°C higher than that <strong>of</strong> zircon). Zirconium is applied also as casings <strong>of</strong> atomic fuel rods, in<br />
ferroalloys, as abrasives, in the chemical industry, enamels and glazes. As a part <strong>of</strong> alloys it is used in special steels and as<br />
zirconium boride, melting point 3,300°C.<br />
Zircon is admixed with hafnium, which is difficult to separate from zirconium. The presence <strong>of</strong> Hf is harmful in an<br />
utilization <strong>of</strong> zirconium in the atomic industry because it diminishes the permeability <strong>of</strong> Zr for neutrons.<br />
Titanium minerals are concentrated in magmatic rocks and their derivates. The most important are basic magmatic rocks<br />
with ilmenite mainly. In most cases, ilmenite is not separated, but developed as titanium-magnetite. This type <strong>of</strong> deposits<br />
bound on anorthosites, gabbros, pyroxenites and amphibolites are residual liquid segregation deposits usually injected in<br />
zones <strong>of</strong> weakness. The most important in an economic utilization <strong>of</strong> titanium-magnetites is the degree <strong>of</strong> separation <strong>of</strong><br />
ilmenite and magnetite. At a temperature <strong>of</strong> 800°C, a mixing <strong>of</strong> magnetite and ilmenite is continuous, at 700-600°C the<br />
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Cilek: 3.12. Titanium and zirconium minerals<br />
isomorphic mixture disintegrates and an intergrowth <strong>of</strong> crystals <strong>of</strong> ilmenite and magnetite originates. The degree <strong>of</strong><br />
separation <strong>of</strong> ilmenite crystals is decisive for a treatment <strong>of</strong> iron ore. Two types <strong>of</strong> deposits <strong>of</strong> Ti-magnetite occur - one<br />
with a high content <strong>of</strong> Ti (over 20%) connected with anorthosites and gabbros, the other with 5-8% TiO2 bound to<br />
pyroxenites and peridotites.<br />
By contrast, rutile minerals are concentrated in acid magmas, as accessories in pegmatites, in contact deposits and vein<br />
deposits <strong>of</strong> the alpine type.<br />
Zirconium minerals with a hafnium admixture are quite common minerals to almost all types <strong>of</strong> rocks but, substantially,<br />
occur as accessories in granitic rocks and their pegmatites, in some granodiorites and badeleyite especially in syenites with<br />
a high alkali content.<br />
Both titanium and zirconium minerals are hard, with a specific gravity <strong>of</strong> 4 or more and can easily accumulate as heavy<br />
minerals in placer deposits. Placers are first fluviatile and finally marine either in beach or dune accumulations. A heavy<br />
minerals assemblage on the seashore normally includes ilmenite, rutile, magnetite, zircon, monazite and many others such<br />
as andalusite, kyanite, garnets, leucoxene. The assemblage composition varies according to the extension <strong>of</strong> mineralogical<br />
provinces <strong>of</strong> the hinterland. The presence <strong>of</strong> some minerals depends also on the cyclic development <strong>of</strong> a sand body, while<br />
a polycyclic development can eliminate less resistant heavy minerals such as magnetite or, during a temporary deposition<br />
and subsequent transport, the iron in titanium-magnetite may be removed leaving ilmenite only. There are several<br />
developmental stages <strong>of</strong> heavy minerals accumulations in economic beach and dune deposits:<br />
suitable parent rock containing heavy minerals<br />
a period <strong>of</strong> long and deep weathering and the origin <strong>of</strong> a weathering pr<strong>of</strong>ile<br />
uplift and destruction <strong>of</strong> weathered land surface<br />
stream transport <strong>of</strong> resistant heavy minerals<br />
deposition on the seashore in one or rather more cycles<br />
sufficient sea-energy, energy <strong>of</strong> currents and waves on an emergent seashore.<br />
A deposition <strong>of</strong> sand with heavy minerals on beaches occurs generally in narrow strips, sometimes at a high concentration;<br />
these may be carried by wind action to form subsequently large dune deposits thereby decreasing frequently the original<br />
higher concentration <strong>of</strong> heavy minerals.<br />
All placer deposits are mined in the same manner i. e. as an extraction <strong>of</strong> building sand using front-end loaders, excavators<br />
or dredges. Big floating dredges are used on beach - and dune deposits and heavy minerals are concentrated on the board<br />
using gravity methods - spirals, shaking tables, magnetic and high-intensity electromagnetic separation <strong>of</strong> magnetic and<br />
non-magnetic and low and high conductive minerals. These placers are mined for an extraction <strong>of</strong> ilmenite and rutile,<br />
zircon is a byproduct.<br />
The mining <strong>of</strong> primary titanium minerals is confined to a few large deposits in the world: titania-ferrous magnetite<br />
(ilmenite in anorthosite) gabbro body in Quebec, Canada, ilmenite deposits in anorthosites in Norway and ilmenitemagnetite<br />
and titanomagnetite in the Ural, Soviet Union. A special method, known as QIT process has been developed by<br />
Quebec Iron and Titanium to produce titanium slag and pig iron in electric furnaces. The same process is used for low<br />
quality S-African ilmenite at Richard's Bay.<br />
Baddeleyite in primary deposits is mined on the Kola peninsula from ultrabasic igneous complex and from Palabora, an<br />
igneous complex in Transvaal. Very pure concentrates <strong>of</strong> zirconia are obtained (96-99% ZrO2).<br />
In <strong>Mozambique</strong> there are present both primary and secondary titanium deposits. Descriptions are available <strong>of</strong> many zircon<br />
localities both in primary and placer deposits. Types <strong>of</strong> titanium mineral deposits (see Fig. 3.2.1):<br />
1. Primary deposits <strong>of</strong> ilmenite:<br />
a) titanium-magnetite deposits in gabbro-anorthosites<br />
b) ilmenite, magnetite, rutile in pyroxenite and alkaline rocks in Precambrian<br />
c) ilmenite-rutile in pegmatites<br />
2. Primary deposits <strong>of</strong> rutile:<br />
a) in quartz veins or pegmatites<br />
b) in metasomatic deposits<br />
3. Primary zirconium:<br />
in pegmatites and alkaline rocks<br />
4. Secondary deposits:<br />
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Cilek: 3.12. Titanium and zirconium minerals<br />
in placer <strong>of</strong> fluviatile and marine origin.<br />
la) Primary deposits <strong>of</strong> magmatic origin <strong>of</strong> Upper Precambrian rocks are connected with the Tete gabbro-anorthosite<br />
Complex (see Fig. 3.12.1) which extends for almost 120 km in an irregularly E-W trending massif N <strong>of</strong> the town <strong>of</strong> Tete.<br />
According to Hunting (1984) it is a large sheet or monolith between 10 to 20 km thick composed <strong>of</strong> basic igneous rocks. It<br />
consists <strong>of</strong> gabbro, norite and anorthosite with minor ultrabasic rock types. It also contains plenty <strong>of</strong> opaque minerals<br />
(ilmenite, magnetite, sulphides) enriched in titanium and vanadium, impoverished in chromium and cobalt when<br />
compared to those <strong>of</strong> layered intrusions such as the Bushveld Complex. It is a rigid body which resisted deformation and<br />
could be compared with the Allard Lake in Canada, the Adirondacks area in the U. S. A. or the Tellnes deposit in Norway.<br />
Fig. 3.12.1 Schematic cross section <strong>of</strong> the Tete Complex (Hunting, 1984) (295 kB)<br />
Gabbro-anorthosites are associated with titanium-magnetite deposits, which result from a magmatic segregation and later<br />
injection into the zones <strong>of</strong> weakness. These ilmenite-magnetite segregations are widespread in the form <strong>of</strong> individually<br />
small very irregular dykes, sheets and lenses. Sometimes, they contain base metals-copper, nickel and cobalt.<br />
The Tete gabbro-anorthosite Complex covers an area <strong>of</strong> about 6,000 km2 and is <strong>of</strong> Upper Precambrian age. The<br />
mineralogical assemblage is composed <strong>of</strong> magnetite and ilmenite intergrown with subordinate minerals <strong>of</strong> titanospinel,<br />
ulvospinel, anatase, pyrite, chalcopyrite and pyrrhotite. Titanomagnetite deposits stretch over 140 km in NW-SE direction<br />
along the N- bank <strong>of</strong> the river Zambezi. The main deposits, from NW to SE, are these:<br />
Massamba<br />
Inhantipissa (Singere)<br />
Txizita<br />
Machedua<br />
Antigo Caldas Xavier<br />
Lupata<br />
The average composition <strong>of</strong> titanomagnetites is: 20% TiO2, 50% Fe2O3, 18% FeO, 0.60% V2O5.<br />
The maximum content <strong>of</strong> TiO2 - 32.9% was discovered in the deposit Txizita. Also rutile is <strong>of</strong>ten present in magnetites.<br />
Mineralogically, the ore contains 20% ilmenite, 30% magnetite and 50% hematite. Ilmenite occurs in grains <strong>of</strong> about 0.2<br />
mm in size, exceptionally 0.6-2 mm in diameter, in some places in laminae and needles intergrown with magnetite and<br />
hematite.<br />
Ore composition (in %):<br />
Locality TiO2 Fe V2O5<br />
Deposit Machedua 14.40 - 18.50 49.07 - 50.89 0.51 - 0.71<br />
Mt. Txizita 32.76 44.98 -<br />
Mawili 9.75 - 13.29 50.86 - 52.10 - Mg 0.90 - 2.0<br />
Pilot tests performed with Tete titanomagnetite showed that the content <strong>of</strong> TiO2 was low and Ti-slag, as a byproduct <strong>of</strong><br />
iron, <strong>of</strong> a low grade.<br />
1b) Titanium minerals in pyroxenites and alkaline rocks <strong>of</strong> the Precambrian<br />
Two localities were found in metamorphic rocks <strong>of</strong> the Mozambican belt: Ulongue in the Tete Province and the deposit<br />
Mazua near Memba in the Nampula Province.<br />
The Ulongue ilmenite prospect was discovered by a UN project (1982) as a small hill 8 km SE <strong>of</strong> the village. The deposit<br />
is located in the Ulongue metallogenic zone <strong>of</strong> NW-SE direction containing graphite, iron ore, ilmenite, asbestos,<br />
vanadium minerals and limestone. The zone is underlain mostly by paragneisses, migmatites and granulites, which are<br />
intruded by basic, acid and alkaline rocks.<br />
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Cilek: 3.12. Titanium and zirconium minerals<br />
Three ilmenite localities coincide with the eastern graphite-bearing zone, two at Chiziro with three ilmenite dykes, 200 m<br />
long and 0.75 to 2.5 m wide with 53% TiO2, one at the river Mepassadoze about 1,800 m NW <strong>of</strong> Chiziro with an ilmenite<br />
dyke in a wide zone <strong>of</strong> kaolinized granulite, 600 m long and 2.5 to 3.0 m thick.<br />
The deposit Flazua is situated 40 km NW <strong>of</strong> Memba in the Nampula Province and was discovered by Geol. Institute -<br />
Beograd during an exploration for asbestos. The ilmenite body is 10 km long, average width 20 m, and reserves <strong>of</strong><br />
ilmenite calculated up to a depth <strong>of</strong> 5 m are 2,700 000 t. The ore body is part <strong>of</strong> the pyroxenite-amphibolite zone and<br />
contains also rutile. It needs further exploration. The deposit appears to be promising, and probably <strong>of</strong> the intrusive type<br />
connected with as yet unknown anorthosite-gabbro bodies.<br />
1c) Ilmenite (rutile) in pegmatites<br />
Ilmenite together with magnetite is found very <strong>of</strong>ten in pegmatites <strong>of</strong> the Alto Ligonha district s. l.<br />
In zonal pegmatites in the areas <strong>of</strong> Mocuba, Nauela and Morrua ilmenite is concentrated in external zones and especially<br />
in the contact zone with andalusite, rutile, beryl, hornblende etc. and in the zones <strong>of</strong> homogeneous and "book" mica.<br />
Ilmenite and rutile are absent in the internal zone, but rutile could again be found in the contact zone between the quarzitic<br />
nucleus and the quartz-mica zone. Ilmenite occurs normally in grains, without a crystalographic habitus, in fragments up<br />
to 7.4 cm (Barros-Vicente, 1963). Ilmenite-rutile (estruverite) is rare in pegmatites <strong>of</strong> Nampoca and Morrua.<br />
Rutile, generally in quartz crystals, occurs in pegmatites <strong>of</strong> Muiane and Nahora. At Morrua, it is grained and found <strong>of</strong>ten<br />
in the inner zone with microlite.<br />
2a) Rutile in quartz veins and pegmatites<br />
In the Tete Province, NW <strong>of</strong> the town and around the river Zambezi, several rutile locaties were discovered in the past.<br />
Along the road Tete-Estima, on the river M'Tetadzi, there are outcrops <strong>of</strong> quartzitic gneisses with several veins <strong>of</strong> quartz<br />
and pegmatite with abundant rutile. Rutile in quartz builds remnants <strong>of</strong> up to 5 cm in diameter and some loose crystals in<br />
alluvial deposits may attain 8 cm length (Real, 1959 in Godinho, 1970). The zone with rutile is 4 km long. Another large<br />
site <strong>of</strong> its occurrence lies on the river Mulato in quartz veins and pegmatites and in eluvial deposits. Near river Zambezi,<br />
in quarries <strong>of</strong> Boroma, rutile can be encountered in pegmatites within the contact zone <strong>of</strong> gneiss and gabbro.<br />
2b) Rutile in metasomatic deposits<br />
In the same area as 2a, rutile was found at Zumbo on the Zambian border, in crystalline limestones with inclusions <strong>of</strong><br />
pyroxene, mica, graphite. In the locality Cacame near the road Tete-Furancungo, a metasomatic deposit with abundant<br />
rutile developed in limestone near its contact with diorite. The content <strong>of</strong> rutile averages 60.42%, with 1.05% iron and<br />
2.85% ilmenite; small amount <strong>of</strong> chalcopyrite and pyrite is present.<br />
3. Primary zirconium occurrence<br />
Zircon is represented in several pegmatites <strong>of</strong> the Alto Ligonha district s. l., for example at Boa Esperanca, Namecuna,<br />
Nuaparra, Nampoca, Macochaia, Namacotche, Muiane, Muhano, Namirrapo etc. (Barros-Vicente, 1963). Some crystals <strong>of</strong><br />
zircon are 2 cm long with one exception measuring 6.5 x 3.5 x 3.5 cm (at Namecuna). The mineral is generally<br />
radioactive. Zircon is associated with quartz, bismuthite and columbo-tantalite in the inner zone, in some pegmatites as an<br />
intergrowth with xenotime or microlite.<br />
The variety naegite -zircon with yttrium, niobium-tantalum, thorium and uranium associated with quartz, bismuthite,<br />
thorite, rhabdophanite and metatorbernite, was found in Nuaparra pegmatite.<br />
Another variety cirtolite with uranium, thorium, RE was found at Morrua.<br />
Some zircons have a greatly increased HfO2 content <strong>of</strong> 32% at Namacotche.<br />
Altered zircon <strong>of</strong> the brownish vitreous variety known as malaconite was found in the area <strong>of</strong> Ribaue.<br />
Chemical analysis from pegmatite Namecuna: %<br />
SiO2 28.91<br />
ZrO2 + HfO2 66.21<br />
TiO2 0.14<br />
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Cilek: 3.12. Titanium and zirconium minerals<br />
Fe2O3 0.64<br />
Al2O3 1.02<br />
MnO Tr.<br />
U3O8 0.97<br />
ThO2 + REO 0.55<br />
CaO 1.22<br />
MgO 0.23<br />
L. i. 0.27<br />
residue 0.64<br />
Total 100.80<br />
In the Niassa Province, within the sedimentary basins <strong>of</strong> the rivers Lunho and Fugue, several bodies <strong>of</strong> kimbertitic rocks<br />
were discovered in 1982-83. Kimberlites and its breccia form several dykes with a typical mineralogical assemblage <strong>of</strong><br />
ilmenite, zircon and rutile; they are developed in the Maniamba graben.<br />
4. Secondary deposits-placers<br />
The description <strong>of</strong> localities <strong>of</strong> a primary occurence <strong>of</strong> Ti-Zr minerals was intended to point out possible primary<br />
resources-parent rocks <strong>of</strong> these mineral in the hinterland <strong>of</strong> the seashore, where the most important and economic deposits<br />
<strong>of</strong> these minerals occur. Naturally, some <strong>of</strong> these primary deposits may gain in economic importance if the concentrated<br />
minerals were present in large quantity and in good quality, but these cases are an exception. However, for a development<br />
<strong>of</strong> secondary accumulations, minerals <strong>of</strong> a rock-forming nature or accessory minerals in igneous and sedimentary<br />
formations are more important. An example <strong>of</strong> small-scale accumulations heavy minerals (HM) are alluvial deposits, for<br />
example those <strong>of</strong> the river Zambezi basin, with a concentration <strong>of</strong> ilmenite, rutile, or zircon. These placers represent, in<br />
fact the direct source for marine accumulations around the mouth <strong>of</strong> the Zambezi river. Similar situation exists around the<br />
estuaries and deltas <strong>of</strong> other big Mozambican rivers as the Limpopo, Save, Ligonha, Lurio and Rovuma.<br />
The origin <strong>of</strong>-HM accumulations is a complicated process which passes through several stages. A sorting <strong>of</strong> HM occurs<br />
gradually along with a destruction <strong>of</strong> resistant minerals, and the longer this process (weathering-transport-sorting) the<br />
higher the degree <strong>of</strong> sorting and the higher the content <strong>of</strong> HM remnants within the mineralogical assemblage.<br />
The parent rocks <strong>of</strong> HM in <strong>Mozambique</strong> are present in various Precambrian formations: with regard to the catchment<br />
areas <strong>of</strong> big rivers they are far inside the African continent.<br />
Along the Mozambican coast HM accumulations could be found either on beaches or in dunes.<br />
In the past, titanium minerals were mined at Pebane (1959), and several other deposits were explored. The main useful<br />
minerals were: ilmenite, leucoxene, rutile, zircon, monazite, kyanite, andalusite and magnetite.<br />
The titanium group is the most useful and predominant one. The main mineral is ilmenite, FeTiO3 <strong>of</strong> 48.6 - 57.3% TiO2<br />
with the presence <strong>of</strong> MgO and up to 6% Fe2O3. Leucoxenized ilmenite is typical <strong>of</strong> all Mozambican deposits. Unaltered<br />
ilmenite grains hardly ever occur. The process <strong>of</strong> leucoxenization represents a removal <strong>of</strong> some iron and the<br />
recrystallization to an anatase - rutile mixture: it leads to an increase in TiO2 over the theoretical content. On the other<br />
hand, ilmenite does not reach even this level in some deposits. This might be due to the fact that there are some magnetite<br />
inclusions which change the Ti: Fe ratio in favour <strong>of</strong> Fe.<br />
The results show, that the TiO2 content is below 50% in the whole area, from South African border to Xai-Xai up to the<br />
river Save, to an area which is called the Limpopo paleodelta.<br />
In some places, is the content <strong>of</strong> Cr2O3 higher, up to 1%. Deposits NE <strong>of</strong> the mouth <strong>of</strong> the river Zambezi also contain lowgrade<br />
ilmenite. At Pebane the TiO2 content is high, but the content <strong>of</strong> impurities is increased. The commercial product<br />
from Pebane contains 0.15% Cr2O3 and 53% TiO2. A spinel was discovered to contain about 25% <strong>of</strong> Cr. Good-quality<br />
ilmenite can be found in Angoche and the Quinga area, but also at Gorai, Idugo, Moma and Moebase.<br />
It is believed that "old concentrates" <strong>of</strong> multi-cycle origin contain a higher-quality ilmenite.<br />
The reason could be a prolonged weathering process and a partial removal <strong>of</strong> iron.<br />
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Cilek: 3.12. Titanium and zirconium minerals<br />
Rutile TiO2 is the best titanium mineral, with a TiO2 content between 89.5 and 99.0%. Zircon Zr SiO4 is a byproduct <strong>of</strong><br />
ilmenite mining. Chemical analyses show a ZrO2 content from 46 to 60%.<br />
HM deposits in coastal <strong>Mozambique</strong> (from south to the north):<br />
Ponta d'Ouro-Maputo<br />
Marracuene<br />
Around Limpopo river mouth<br />
Xai-Xai<br />
Ponta Zavora-Jangamo<br />
Praia Morrungulo<br />
Inhassoro<br />
Beira<br />
Deia<br />
Ilha Olinda<br />
Zalala<br />
Pebane (Idugo, Gorai, Raraga)<br />
Moebase<br />
Moma<br />
Angoche<br />
Congolone<br />
Quinga<br />
small local incidence N <strong>of</strong> Ilha Moçambique.<br />
The most promising deposits are those between Quelimane and Quinga. The deposits <strong>of</strong> southern <strong>Mozambique</strong> are not<br />
well-known, but widely extended beach- and dune deposits <strong>of</strong> the Quaternary in an 80 km wide belt and an occurence <strong>of</strong><br />
HM on modern beaches suggest a large potential <strong>of</strong> these low-grade deposits.<br />
In 1983, Aquater <strong>of</strong> Italy made a detailed exploration in the Quelimane area and its estimate <strong>of</strong> reserves was 24.9 Mt <strong>of</strong><br />
HM sand i.e. 2.5 Mt <strong>of</strong> HM, <strong>of</strong> which 2 million t was ilmenite. The quality <strong>of</strong> ilmenite was 48.5-50% TiO2 (its content in<br />
mineral sand 9.61%), 65.5% ZrO2 for zircon with reserves <strong>of</strong> about 200,000 t.<br />
At Angoche, the Jugoslav Team explored the biggest dune in <strong>Mozambique</strong> called Congolone and surroundings and<br />
discovered over 14 Mt <strong>of</strong> HM in the area. The Congolone dune contained 2.2 Mt <strong>of</strong> HM in grade over 8% in the sand and<br />
2.8 Mt <strong>of</strong> HM 4-8% HM in sand.<br />
Ilmenite represents over 81%, leucoxene 1.3%, zircon 5.2%, rutile 2.8% and monazite 1.2% <strong>of</strong> HM suite.<br />
Chemical analyses <strong>of</strong> ilmenite: %<br />
Area TiO2 FeO Fe2O3 Cr2O3 P2O5 V<br />
Ponta d'Ouro 49.67 35.96 13.05 0.22 0.042 0.04<br />
Marracuene 51.16 27.62 17.99 1.04 0.033 0.12<br />
Limpopo 47.60 31.99 18.75 tr. 0.054 0.075<br />
Xai-Xai 47.13 32.71 17.55 0.41 0.061 0.11<br />
Zavora 48.83 33.86 15.72 tr. 0.036 0.093<br />
Morrungulo 49.93 31.97 15.29 tr. 0.023 0.099<br />
Inhassoro 49.70 27.97 20.12 0.93 0.037 0.13<br />
Zalala 46.13 27.91 21.79 0.80 0.34 0.098<br />
Pebane 52.76 22.15 20.27 0.21 0.120 0.073<br />
Moebase 53.75 20.14 23.86 0.26 0.042 0.081<br />
Angoche 54.41 22.47 23.09 0.23 0.078 0.063<br />
Congolone 55.36 16.34 25.71 0.18 0.072 0.063<br />
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Cilek: 3.12. Titanium and zirconium minerals<br />
Quinga 56.80 14.43 25.06 0.17 0.120 0.052<br />
The quality <strong>of</strong> ilmenite is low in most localities, but may be improved by treatment. Clearly, the best-quality ilmenite is<br />
found in the NE part <strong>of</strong> Mid- <strong>Mozambique</strong> between Pebane and Quinga.<br />
Chemical analyses <strong>of</strong> rutile: %<br />
Area Cr V Fe2O3 TiO2<br />
Ponta d'Ouro 0.076 0.226 0.67 99.0<br />
Xai-Xai 0.210 0.093 1.36 08.3<br />
Macuse 0.101 0.211 0.77 98.9<br />
Idugo 0.118 0.223 0.82 98.8<br />
Pebane 0.104 0.236 1.32 98.3<br />
Angoche 0.102 0.204 1.40 98.3<br />
Quinga 0.074 0.225 0.70 99.0<br />
A true picture <strong>of</strong> mineral assemblage in a HM concentrate <strong>of</strong> Mozambican beach sands, from which several economic<br />
minerals mentioned above are being recovered is shown by the following analysis:<br />
Praia Zalala - beach concentrate, analysis by Geoindustria, Prague: g/m3<br />
Magnetite* 5.5 spinel black tr.<br />
Scheelite tr. spinel green tr.<br />
Gold 1 grain garnet 50<br />
Titanite 1.5 rutile 5.50<br />
Tourmaline upto 1 brookite tr.<br />
Andalusite tr. anatase upto 1<br />
Kyanite 1.5 limonite tr.<br />
Monazite tr. leucoxene upto 1<br />
Sillimanite 1.5 martite tr.<br />
Staurolite 1.5 apatite upto 1<br />
Zircon 1.5 zoisite tr.<br />
Epidote 5.50 carbonates (org.) tr.<br />
Pyroxene tr.<br />
Ilmenite tr.<br />
Remark: Magnetite including titanomagnetite and chromite.<br />
On the deposit Quelimane three control analyses <strong>of</strong> HM concentrate were made in 1987 in U. S. A. at Rice University and<br />
the University <strong>of</strong> Georgia.<br />
First the size analysis and sink/float analysis were performed with these results:<br />
Sample + 14 mesh - 14 mesh floating - 14 mesh sinking<br />
1. 0.7 86.3 13.0<br />
2. 1.3 82.9 15.8<br />
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Cilek: 3.12. Titanium and zirconium minerals<br />
3. 0.2 83.6 16.2<br />
The -14 mesh sink fraction represents the HM suite, which in this case is composed <strong>of</strong> different heavy minerals, in<br />
<strong>Mozambique</strong> divided into two groups: economic HM and waste silicate (non-economic) HM. The Quelimane deposit<br />
therefore represents a mineralogical suite rich in non-economic HM which is common to fluviatile sediments, here<br />
sediments transported by the river Zambezi and deposited on the beach in very short distances.<br />
Analysis <strong>of</strong> sink fraction:<br />
Sample 1 2 3<br />
Rice U U <strong>of</strong> GA Avg Rice U U <strong>of</strong> GA Avg Rice U U <strong>of</strong> GA Avg<br />
- Ilmenite 24.3 30.3 27.3 23.6 30.6 27.1 34.0 34.3 34.2<br />
Economic<br />
HM<br />
Rutile<br />
Zircon<br />
Monazite<br />
0.8<br />
1.7<br />
0.4<br />
0.7<br />
1.2<br />
0.4<br />
0.7<br />
1.5<br />
0.4<br />
3.1<br />
0.4<br />
0.4<br />
1.0<br />
1.9<br />
0.4<br />
2.0<br />
1.1<br />
0.4<br />
1.9<br />
5.1<br />
N.D.<br />
0.7<br />
3.1<br />
0.4<br />
1.3<br />
4.1<br />
0.2<br />
- Iron oxide 10.1 1.3 5.7 9.8 2.5 6.2 12.2 2.5 7.4<br />
- Amphibole 18.6 32.2 25.4 30.1 37.0 33.5 19.1 31.4 25.2<br />
Garnet 10.9 0.3 5.6 16.4 1.8 9.1 14.5 6.5 10.5<br />
Pyroxene 8.6 3.4 6.0 8.6 3.6 6.1 5.8 4.3 5.0<br />
Sphene 3.5 4.1 3.8 2.1 4.2 3.2 2.3 2.5 2.4<br />
Noneconomic<br />
HM<br />
Apatite<br />
Spinel<br />
2.0<br />
1.2<br />
1.1<br />
N.D.<br />
1.6<br />
0.6<br />
2.3<br />
N.D.<br />
1.6<br />
N.D.<br />
2.0<br />
N.D.<br />
0.8<br />
0.7<br />
2.1<br />
N.D.<br />
1.5<br />
0.4<br />
Al-Sil 1.8 1.9 1.8 0.9 2.4 1.7 0.8 N.D. 0.4<br />
Feldspar 4.2 1.1 2.6 0.4 0.4 0.4 N.D. N.D. N.D.<br />
Biotite N.D. N.D. N.D. 0.2 N.D. 0.1 0.5 N.D. 0.2<br />
Quartz 11.9 7.7 9.8 1.7 0.9 1.3 2.3 1.0 1.7<br />
Iron silicates N.D. 14.3 7.2 N.D. 11.3 5.6 N.D. 10.8 5.4<br />
- Chromite N.D. N.D. N.D. N.D. 0.4 0.2 N.D. 0.4 0.2<br />
Total 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0<br />
The table shows, that ilmenite represents just about 30 to 55% <strong>of</strong> total HM i. e. its actual content in sand is 3.9 to 5.5%.<br />
Because the commercial product <strong>of</strong> ilmenite requires a minimum <strong>of</strong> 45% TiO2, but normally about 60% TiO2, the quality<br />
<strong>of</strong> ilmenite was this:<br />
Sample<br />
Rice U<br />
1<br />
U <strong>of</strong> GA Avg Rice U<br />
2<br />
U <strong>of</strong> GA Avg Rice U<br />
3<br />
U <strong>of</strong> GA Avg<br />
TiO2 content % Distribution <strong>of</strong> grains<br />
< 45 %<br />
3.6 20.7 12.1 1.8 13.8 7.8 2.3 9.3 5.8<br />
45-50%<br />
41.1 44.4 42.8 30.4 38.4 34.4 37.2 35.8 36.5<br />
50-55%<br />
30.4 19.8 25.1 57.1 28.5 42.8 38.4 29.9 34.1<br />
>50%<br />
25.0 15.1 20.0 10.7 19.3 15.0 22.1 25.0 23.6<br />
No. <strong>of</strong> grains<br />
counted<br />
300 300 - 300 300 - 300 300 -<br />
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Cilek: 3.12. Titanium and zirconium minerals<br />
Avg TiO2 content<br />
(wt % in ilmenite)<br />
No. <strong>of</strong> grains for<br />
avg TiO2 content<br />
52.0 49.0 50.5 51.7 50.5 51.1 52.0 49.0 50.5<br />
56 63 - 56 68 - 86 77 -<br />
Conclusion: The above data indicate that the maximum TiO2 content that could be produced as an ilmenite product from the three<br />
(3) samples examined will be 49-50% TiO2 assuming standard extraction techniques and recovery factors.<br />
The estimated reserves <strong>of</strong> HM in dune- and beach deposits are substantial in <strong>Mozambique</strong> - over 120 Mt, <strong>of</strong> which about<br />
95 Mt is ilmenite, 3.6 Mt futile and 6 Mt zircon. Futher HM reserves, <strong>of</strong> an order <strong>of</strong> about 60 Mt, were discovered on the<br />
shelf in the Zambezi delta by the research vessel Valdivia (1971).<br />
Conclusions:<br />
Primary deposits <strong>of</strong> titanium minerals are present in the Tete gabbro-anorthosite Complex in the form <strong>of</strong> titanomagnetites,<br />
with about 20% <strong>of</strong> TiO2. The treatment <strong>of</strong> this ore yields low-quality titania slag. More promising are some sites <strong>of</strong><br />
ilmenite occurrence in Precambrian basic rocks, especially at Mazua near Memba in the Nampula Province. Such deposit<br />
should be worth further exploration. Long before an exploitation <strong>of</strong> all possible primary deposits <strong>of</strong> titanium and<br />
zirconium minerals, huge reserves in beach and dune deposits should be utilized. These deposits place <strong>Mozambique</strong> in the<br />
position <strong>of</strong> a potential world producer <strong>of</strong> ilmenite, rutile, zircon and monazite.<br />
© Václav Cílek 1989<br />
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Cilek: 3.13. Zeolites<br />
3.13. Zeolites<br />
Comprise a large group <strong>of</strong> related minerals, usually well-crystallized and found in cavernes <strong>of</strong> lavas,<br />
mainly basalts. They are hydrated aluminium silicates <strong>of</strong> alkaline elements with the structure <strong>of</strong> an open<br />
aluminosilicate framework composed <strong>of</strong> (Si, Al)O4 tetrahedra. Wide channels inside the structure<br />
contain molecules <strong>of</strong> water and cations <strong>of</strong> Na K and Ca which balance the negative charge <strong>of</strong> the<br />
framework. The name zeolite-boiling-stone - is due to their intumescence (bubbling) when heated. The<br />
water is released continuously in increasing temperatures and dehydrated zeolites can absorb other<br />
liquids without disrupting the strong bonded framework structure.<br />
Zeolites with different framework topologies are found in nature (about 30 varieties) and are also<br />
produced synthetically (about 150).<br />
Economically important natural zeolites:<br />
analcime Na16 [(AlO2)16 (SiO2)32] • 16H2O<br />
clinoptiolite Na6 [(AlO2)6 (SiO2)30] • 24H2O<br />
chabasite Ca2 [(AlO2)4 (SiO2)8] • 13H2O<br />
mordenite Na8 [(AlO2)8 (SiO2)40] • 24H2O<br />
phillipsite (K, Na)10 [(AlO2) (SiO2)22] • 20H2O<br />
laumontite Ca4 [(AlO2)8 (SiO2)46] • 16H2O<br />
erionite 4.5(Ca, Mg, K2, Na2)4.5 [(AlO2)9 (SiO2)27] • 27H2O<br />
natrolite Na16 [(AlO2)16 (SiO2)24] • 16H2O<br />
The zeolite structure is used in the industry for its special properties:<br />
a) adsorption<br />
b) molecular sieve<br />
c) ion-exchange<br />
The first two properties are used when water is removed by heating and the zeolite can then adsorb other<br />
molecules. The channel diameter range from 2 to 7 Å therefore selected molecules only are accepted.<br />
This property is used in a separation <strong>of</strong> hydrocarbons, adsorption <strong>of</strong> H2S, CO2, SO2, cleaning<br />
radioactive waste <strong>of</strong> Cs, Sr. The ion exchange property is used in agriculture in a similar way to<br />
bentonite, to bind fertilizer elements and release them slowly, in animals aid nutrition and as a carrier <strong>of</strong><br />
herbicides, pesticides and fungicides. Natural zeolites are used in hydraulic cement productions, as a<br />
filler in the paper industry, as a polishing agent, a catalyst and others.<br />
Knowledge <strong>of</strong> zeolite deposits is fairly recent, just about twenty years, but they are widespread and<br />
found in different types <strong>of</strong> deposits <strong>of</strong> saline alkaline lakes, deep sea sediments, in volcanic glass altered<br />
by meteoric water, hydrothermal deposits and initial metamorphic stages.<br />
Generally zeolites originate from a reaction <strong>of</strong> pore water with other materials such as volcanic glass,<br />
clay or silica. They alter further by a reaction <strong>of</strong> pore water.<br />
Clinoptiolite is altered to analcime, which may be replaced by laumontite etc. and this results in a<br />
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Cilek: 3.13. Zeolites<br />
reduction <strong>of</strong> a number <strong>of</strong> zeolite varieties in older rocks (no zeolites occur in the Early Precambrian).<br />
The process <strong>of</strong> zeolite genesis - zeolitization - is rapid, they originate from basaltic or rhyolitic glasses in<br />
a few days or years. Zeolite deposits may attain several tens to hundreds <strong>of</strong> meters and, in many<br />
deposits, especially those developed in open hydrologic systems they occur together with smectites<br />
(upper zone); the lower zones have a higher pH and contain dissolved solids. Important deposits are<br />
present in places <strong>of</strong> hydrothermal alteration <strong>of</strong> volcanic rocks by intrusive massifs and under the effect<br />
<strong>of</strong> fossil or modern geothermal water.<br />
Generally, zeolite deposits may be expected in areas <strong>of</strong> volcanic activity owing to an alteration <strong>of</strong><br />
volcanic glasses, tuffs and tuffites by the action <strong>of</strong> hot waters or meteoric waters and in connection with<br />
smectites.<br />
In <strong>Mozambique</strong>, an occurrence <strong>of</strong> zeolites, well-developed crystals in cavity, was described by Carvalho<br />
(1944) from Mossurize in Karroo basalts. In 1969, zeolites from Corumana Mountain in the Lebombo<br />
Range (NW <strong>of</strong> Maputo at the town <strong>of</strong> Sabie) were described by Neves and Nunes from the contact zone<br />
<strong>of</strong> rhyolites and basalts. Big crystals <strong>of</strong> quartz, stilbite, laumontite, scolecite and natrolite measuring 10 x<br />
30 cm, are found in cavities.<br />
Stilbite occurs in typical larger-sized sheaf-like aggregates, white or light reddish in colour, in a thin<br />
tabular habit. The theoretical formula is<br />
4 • [Ca (Al2Si7O18) • 7H2O] which differs in a substitution <strong>of</strong> Na Al - Si and Ca Al2 - Si2.<br />
Chemical composition (in %) Cell content<br />
SiO2 56.18 Si 26.19<br />
Al2O3 15.26 Al 8.39<br />
Fe2O3 0.80 Fe 0.27<br />
CaO 8.32 Ca 4.14<br />
Na2O 0.70 Na 0.61<br />
K2O 0.05 - -<br />
H2O 18.64 H 57.77<br />
total 99.95 O 98.75<br />
Laumontite occurs in two phases - fully hydrated laumontite and the less hydrated leonhardite. The<br />
mineral is milky white and occurs both in a prismatic habit over stilbite, and in veins. Comparing the<br />
cell content with a theoretical value corresponding to formula 4 [Ca (AlSi2O6)2 • 4H2O] a good fit<br />
exists except for a lower value <strong>of</strong> hydrogen.<br />
Natrolite and scolecite <strong>of</strong> a light reddish colour are developed either in veins <strong>of</strong> a fibrous habit or in<br />
close associated parallel layers.<br />
The chemical analysis revealed: SiO2 - 46.94%, Al2O3 - 26.11%, CaO - 4.07%, Na2O - 12.60%, K2O -<br />
0.01% and H2O - 10.50%. Aggregates are made up <strong>of</strong> about 23 to 35% scolecite and 76 to 63% natrolite.<br />
The paragenesis <strong>of</strong> minerals at Corumana in cavities <strong>of</strong> basalt begins with saccharoid quartz, then white<br />
stilbite in crystals and finally laumontite. Fibrous zeolites - natrolite and scolecite - are intimately<br />
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Cilek: 3.13. Zeolites<br />
associated and crystallized simultaneously.<br />
Zeolites in crystals in cavities and veins in Karroo basalts <strong>of</strong> a late-hydrothermal origin will probably be<br />
more widely distributed than described for the above mentioned two localities. Microcrystalline zeolites,<br />
<strong>of</strong> economic importance in the country, can be expected in thick layers <strong>of</strong> rhyolitic and basaltic ash-tuffs<br />
and tuffites altered either directly in shallow basins during or shortly after the deposition or by<br />
underwater action. The zeolites could be found below the bentonite layers or in the zones <strong>of</strong> higher<br />
tectonic movements influenced by hydrothermal or meteoric waters.<br />
The importance <strong>of</strong> zeolites discovery for the Mozambican agriculture and industry is not in need to be<br />
stressed. A potential source <strong>of</strong> zeolites are Karroo volcanics from the Lebombo Mts. range to the area <strong>of</strong><br />
Chibabava <strong>of</strong> Karroo volcanics in the Tete Province.<br />
© Václav Cílek 1989<br />
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Cilek: 3.2. Asbestos<br />
3.2. Asbestos<br />
The term asbestos is generally used for the group <strong>of</strong> minerals which consist <strong>of</strong> flexible fibers - closely<br />
packed crystals, or fibrils that can be spun or are resistant to heat andchemical attack. The longer fibers<br />
"spinning" - blended with cotton, rayon or other fibers are used in yarn or cloth; "nonspinning" fibers are<br />
valuable for different types <strong>of</strong> firepro<strong>of</strong>ing and insulation materials.<br />
Asbestos minerals fall into two groups:<br />
i) serpentine, which is represented by chrysotile - Mg6[(OH)4Si2O5]2<br />
ii) amphibole,which is represented by anthophyllite - (Mg, Fe2+)7 (Si8O22) (OH, F)2, amosite,<br />
crocidolite.<br />
The asbestos minerals are products <strong>of</strong> metamorphism and occur as "cross fibers" ex-tending from wall to<br />
wall, "slip fibers" roughly parallel to the vein walls and "mass" fibers as an aggregate <strong>of</strong> non-oriented<br />
fibers.<br />
Asbestos deposits originated by alteration processes in four types <strong>of</strong> rocks:<br />
1. ultramafic rocks <strong>of</strong> alpine-type with chrysotile mainly<br />
2. ultramafic rocks-stratiform deposits with chrysotile mainly<br />
3. banded ironstones with amosite, crocidolite, anthophyllite<br />
4. dolomitic limestones-contact deposits with chrysolite<br />
About 95% <strong>of</strong> the world production is chrysotile or "white asbestos", fusion point 1,521°C.<br />
Chrysotile is found in fillings <strong>of</strong> veinlets in serpentine producing largely a complex stockwork. The rock<br />
is mined in bulk, crushed and asbestos is separated in the mill.<br />
Amphibole asbestos varies greatly in its chemical composition, with several impurities and chemical<br />
substitution. Crocidolite known as "blue asbestos", has generally a good development <strong>of</strong> long fibres, low<br />
fusion point 1,193°C, but a high resistance to acids and alkalies. Amosite "brown asbestos" is <strong>of</strong> coarse<br />
texture and resistant to acids and alkalies and also heat. Anthophyllite is well-resistant both to heat<br />
(melting point 1,468°C) and chemicals, but has short harsh fibres <strong>of</strong> poor flexibility. Its present<br />
economic utilization is negligible.<br />
The most abundant are asbestos deposits with chrysotile in serpentinites. They originate by the process<br />
<strong>of</strong> serpentinization (autometamorphic) <strong>of</strong> ultrabasic rocks which probably represent the rocks <strong>of</strong> the<br />
upper mantle. The majority <strong>of</strong> chrysotile is formed,most probably, after serpentinization by the action <strong>of</strong><br />
solutions associated with granitoid intrusions. According to the temperature and pressure in different<br />
zones, these minerals developed:<br />
650°C - biotite zone near the granites<br />
550-600°C - amphibole zone (anthophyllite)<br />
500°C - talc zone<br />
450°C - antigorite zone<br />
400°C - chrysotile zone ultrabasic rock<br />
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Cilek: 3.2. Asbestos<br />
Autometamorphic serpentinization may have affected 40-80% <strong>of</strong> rock such as peridotite or pyroxenite;<br />
serpentinite could further be altered by hydrothermal solutions associated with granitic veins and massifs<br />
intruding the body <strong>of</strong> mafic rocks already fractured during the orogenesis.<br />
Asbestos minerals are used mainly in the manufacture <strong>of</strong> asbestos-cement products(sheet, pipe), in<br />
flooring products and in friction products (brake linings etc.). Their utilization in asbestos textiles, paints<br />
production, insulation and as filler is small.<br />
Asbestos mining, treatment and end uses represent health hazards such as lung disease, cancer <strong>of</strong> the<br />
lung etc. Therefore, there is a considerable pressure for a replacement <strong>of</strong> asbestos fibre. This results in a<br />
year by year reduction in the consumption <strong>of</strong> asbestos and at present the quantity <strong>of</strong> asbestos fibre<br />
available exceeds world demands.<br />
In <strong>Mozambique</strong>, two genetic types <strong>of</strong> asbestos could be found in four areas (see Fig.3.2.1):<br />
1. chrysotile asbestos in serpentinite body originating from a metamorphosis <strong>of</strong> Archean greenstones <strong>of</strong><br />
the Zimbabwe craton - deposit Serra Mangota near Manica<br />
2. small chrysotile asbestos bodies as clusters <strong>of</strong> reworked old greenstone belts within the Mozambican<br />
belt - Manica, S<strong>of</strong>ala, Upper Zambezi provinces<br />
3. anthophyllite asbestos originating from a serpentinization by the action <strong>of</strong> solutions associated with<br />
granitic intrusions-mixed type <strong>of</strong> stratiform ultramafic intrusion and partly probably <strong>of</strong> banded ironstone<br />
type - deposit Mavita S <strong>of</strong> Manica<br />
4. anthophyllite asbestos in glimmerites <strong>of</strong> ultrabasic rocks <strong>of</strong> the Mulatela - Nampula Province.<br />
Fig.3.2.1 Occurences <strong>of</strong> asbestos, beryl, talc and soapstone, titanium minerals, rutile, zircon (471<br />
kB)<br />
1. Serra Mangota<br />
In 1930, a small exploitation <strong>of</strong> chrysotile asbestos was in progress at Serra Mangota about 10 km NNE<br />
<strong>of</strong> Manica. In 1951, mining was not reported. Serra Mangota is a ridge <strong>of</strong> E-W extension composed <strong>of</strong><br />
serpentinite and schists. It is a part <strong>of</strong> Archaic rocks - greenstones belt <strong>of</strong> the Upper zone <strong>of</strong> the<br />
Zimbabwe craton. In <strong>Mozambique</strong>, just accross the border with Zimbabwe, these archaic<br />
metasedimentary and volcanic rocks <strong>of</strong> the Manica (Macequece) Formation produced an E-W trending<br />
belt resting on granitic rocks. They are composed mainly <strong>of</strong> serpentinites with subordinary inclusions <strong>of</strong><br />
metasediments. Serpentinites build extensive bodies within the Manica Formation and also outside it<br />
resting on the surrounding granitic shield. They are supposed to be either meta- morphosed lavas or<br />
intrusive rocks with intercalations <strong>of</strong> talc schists, chloritic and sericitic schists and banded ironstones<br />
(see Fig. 3.2.2). The Manica Formation is famous for its gold mineralization.<br />
Fig. 3.2.2 Geological map <strong>of</strong> Serra Mangota (Obretenov, 1984) (629 kB)<br />
The Serra Mangota s. s. is a steeply dipping serpentinite body with two petrological varieties: a hard,<br />
green serpentinite and lighter green carbonated one. The hard green variety forms the highest parts <strong>of</strong> the<br />
ridge, while the s<strong>of</strong>ter, carbonated serpentinite forms the levelled plateaus. Furthermore are present talc<br />
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Cilek: 3.2. Asbestos<br />
schists, young intrusives <strong>of</strong> microgranites and dolerites, ferruginous quartzites and metasediments.<br />
Several faults <strong>of</strong> NE-SW direction traverse the range. Separated asbestos outcrops are present over a<br />
strike <strong>of</strong> about 5 km. Eastwards, the amout <strong>of</strong> carbonated serpentinite decreases and talc schists become<br />
apparent. Towards the west, carbonated serpentinite with short good-quality fibers is predominant. In the<br />
east, two areas were exploited before World War 2 (with long fibres). Long, rich fibers were not <strong>of</strong> great<br />
interest, because they occurred invery small serpentine lenses surrounded by talc schists. The mining<br />
area was in thewestern part mainly, with carbonate serpentinite with good amount <strong>of</strong> fiber over a distance<br />
<strong>of</strong> 1,200 m and width <strong>of</strong> the zone 200 m, dipping steeply (see Fig. 3.2.3) The favourable host rock<br />
<strong>of</strong> chrysotile is a carbonate serpentinite variety with a fiber content arround 2 %. Asbestos extracted<br />
from open pits was <strong>of</strong> good quality but small in quantity (some samples can still be seen in the museum<br />
in Manica). Mining was abandoned before 1940 and later prospection revealed that the bulk <strong>of</strong><br />
serpentinized bodies have the oreexhausted. Only some ore with more than 1% <strong>of</strong> fiber remained. No<br />
talc evaluation was made.<br />
Fig. 3.2.3 Cross-section <strong>of</strong> Serra Mangota asbestos-talc deposit (311 kB)<br />
2. Small occurrence or chrysolite asbestos<br />
Many small sites <strong>of</strong> occurrence <strong>of</strong> asbestos were observed in Manica, S<strong>of</strong>ala and theUpper Zambezia<br />
provinces. They developed within clusters <strong>of</strong> reworked old greenstonesbelts in many parts <strong>of</strong> the<br />
Mozambican belt. The greenstones are represented by serpen-finite bodies surrounded by metasediments<br />
and included in gneisses, migmatites andgranitic rocks at quite a big distance eastwards from the eastern<br />
margin <strong>of</strong> the Zimbabwecraton. Within the Zimbabwe craton, in the area <strong>of</strong> the rivers Bonde and Zonue,<br />
"Cronleygreenstones" were observed by Hunting (1984); they extended from Zimbabwe, with sev-eral<br />
tenses <strong>of</strong> serpentinites and banded ironstones with possible asbestos occurrences(see Mavita deposit).<br />
Chrysotile was found in the Maravia area near Fingoe and in the Monte Atchiza area.Especially Monte<br />
Atchiza with its ultrabasic complex and chrysolite occurrence has beenin the centre <strong>of</strong> interest for a long<br />
time. It consists <strong>of</strong> bodies <strong>of</strong> serpentinites, gabbros andnorites, with minor peridotites and pyroxenites.<br />
This ultrabasic complex intruded themetasedimentary Fingoe Formation and later was intruded itself by<br />
post-Fingoe granites.<br />
Monte Atchiza complex was regarded as the northern extension <strong>of</strong> the Great Dyke <strong>of</strong>Zimbabwe, but it is<br />
younger and differs from it mainly in a dominance <strong>of</strong> olivine over orto-pyroxene in peridotites and<br />
pyroxenites. It seems, that ultrabasic rocks are in a stratiformarrangement with serpentinites with patches<br />
<strong>of</strong> chrysolite. Peridotites and pyroxeniteshave also partly been altered into serpentine, actinolite,<br />
anth<strong>of</strong>yllite and opaque minerals. No significant mineralization <strong>of</strong> chromium, nickel, platinum as that <strong>of</strong><br />
the Great Dyke and the Bushveldt Complex, was observed there (Hunting, 1984). Some<br />
inextensiveoccurrences were found <strong>of</strong> chromite and asbestos only. According to Real (1960) the asbestos<br />
at Monte Atchiza occurs in two different varieties - in veins and veinlets (in thenortheastern part)<br />
<strong>of</strong> picrolite and antigorite associated with accumulations <strong>of</strong> garnierite(Atchiza-Nhantreze) and highly<br />
silicified in hard- and long fibres - amphibole asbestos (up to 50 cm long) (N <strong>of</strong> Mt. Atchiza) within the<br />
metamorphic rocks <strong>of</strong> the Formation Fingoe.<br />
Results <strong>of</strong> analyses <strong>of</strong> two samples <strong>of</strong> serpentinites <strong>of</strong> Monte Atchiza (in %):<br />
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Cilek: 3.2. Asbestos<br />
SiO2 38.40 40.25<br />
Al2O3 2.09 2.61<br />
FeO 1.69 1.46<br />
Fe2O3 5.32 4.36<br />
Fe2O3 + FeO (7.01) (5.82)<br />
MgO 38.87 38.85<br />
CaO 0.45 -<br />
Na2O 0.14 0.18<br />
K2O 0.24 0.16<br />
TiO2 0.05 -<br />
P2O5 - 0.08<br />
Cr2O3 0.34 0.35<br />
MnO 0.12 0.02<br />
NiO 0.57 0.08<br />
Near the Malawi border, about 120 km N <strong>of</strong> Tete and 1.5 km W <strong>of</strong> the village <strong>of</strong> Tzangano, an ultrabasic<br />
body, partly serpentinized was encountered. The body is some 2.4 km long and 200-400 m wide. Tough,<br />
initially, only tremolite and actinolite were found, also long fibre-asbestos was present in lenses and<br />
veins. The lenses <strong>of</strong> asbestos are 20-40cm wide, that <strong>of</strong> long fibre-anthophyllite attain a thickness <strong>of</strong> 2.6<br />
m. Magnetite is ubiquitous, in the ultrabasic body. The enclosing rocks are biotite gneisses. No analyses<br />
<strong>of</strong> asbestos were made, only one sample <strong>of</strong> serpentinite was analyzed for the presence <strong>of</strong> metals: 80 ppm<br />
Co, 15 ppm Cu, 30 ppm Pt, 0.26% Cr and 0.81% Ni. On the footwall there is a outcrop <strong>of</strong> grey-green<br />
talcose mica schists.<br />
River Ualadze asbestos<br />
Hunting (1984) reports a small occurrence <strong>of</strong> asbestos on the river Ualadze near Chicoa at the Cabora<br />
Bassa dam. The asbestos is associated with a pair <strong>of</strong> basaltic dykes which intruded coarse, mesocratic,<br />
unfoliated granite with feldspar phenocrysts in a groundmass <strong>of</strong> hornblende, quartz and biotite. The<br />
dykes are cut by a sub-horizontal shear plane along which the asbestos occurs. It can be inferred from<br />
the occurrence <strong>of</strong> thicker sheets <strong>of</strong> asbestos where the shear plane cut the earlier dykes, that asbestos<br />
developed probably during shearing and hydration <strong>of</strong> the basaltic dyke rock. The bodies <strong>of</strong> asbestos<br />
appear to have been very small and are <strong>of</strong> no economic interest.<br />
3. Deposit Mavita<br />
The first research work performed during 1943-46 in the Mavita area, about 60 kmSSE <strong>of</strong> Manica,<br />
revealed small scattered deposits <strong>of</strong> anthophyllite. Exploitation started in the sixties. The following data<br />
are available on production:<br />
1967 - 507 t<br />
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Cilek: 3.2. Asbestos<br />
1968 - 120 t<br />
1972 - 600 t<br />
1973 - 624 t<br />
The deposit was the property <strong>of</strong> Minas Gerais de Moçambique Lda. In 1973, the production was<br />
interrupted and a rehabilitation program was started in 1978 with the assistance <strong>of</strong> the German<br />
Democratic Republic. Small production was obtained from a pilot plant <strong>of</strong> anthophyllite <strong>of</strong> about 25,000<br />
t <strong>of</strong> ore up to the end <strong>of</strong> 1980. No futher mining continued.<br />
The Mavita deposit area, similarly to the Serra Mangota deposit, is situated within the greenstones belt<br />
<strong>of</strong> Archean age-Zimbabwean craton. Asbestos occurs in serpentinized ultrabasic rocks or in association<br />
with these. The rocks belong to the Manica Formation, but here they display a general structural NNE-<br />
SSW trend. Serpentinites, probably <strong>of</strong> the"alpine-type", were tectonically injected and later reworked.<br />
Metasediments include sericitic and chloritic schists, quartzites and iron-banded formation.<br />
Metavolcanics are represented by the greenstones group (see Fig. 3.2.4).<br />
Associated with serpentinites are talc, talc-schists and mica-schists.<br />
Intrusive rocks include granites, pegmatites and basic dykes. Migmatization is ubiquitous.<br />
Asbestos occurs over an area <strong>of</strong> about 300 km2, with some 160 asbestos bodies acknowleged so far.<br />
The reserves are: 325,000 t proved and 237,000 t probable<br />
Geophysical exploration <strong>of</strong> 48 km2 by the GDR in 1978 and 1980, and some drilling revealed about<br />
36,000 t <strong>of</strong> reserves.<br />
Anthophyllite is found in lenses <strong>of</strong> a 2 x 3 m range, few are 10 m long, with a maximum length <strong>of</strong> 45 m.<br />
Asbestos is associated with talc-schist lenses within the granitic rocks and migmatites, or gneiss, with a<br />
biotite-enriched zone at the contact.<br />
The content <strong>of</strong> asbestos in the rock is about 30%.<br />
Anthophyllite is usually <strong>of</strong> the long fiber type, hard and is not amendable to fiber separation which is<br />
also due to the widespread phenomenon <strong>of</strong> silicification. Weathering affects greatly the migmatites and<br />
lowers the quality <strong>of</strong> the fibres.<br />
Talc and talc-schists with tremolite are common in the deposit zone, but their quality is not known.<br />
Mavita's anthophyllite is unsuitable for asbestos-cement products and for making woven material. It can<br />
be used in the production <strong>of</strong> insulation bars, seals, acid-resistant filtres (results <strong>of</strong> the Laboratory<br />
Dresden, GDR, 1980).<br />
According to Eternit S. A. <strong>of</strong> Switzerland, the mineral cannot be used in their products.<br />
4. Deposit <strong>of</strong> Mulatala<br />
Within the whole <strong>Mozambique</strong> belt, small massifs <strong>of</strong> ultrabasic rocks with asbestos are found in many<br />
places. Some are serpentinites with small veins and pockets <strong>of</strong> asbestos and layers <strong>of</strong> talc schists, some<br />
simply just slightly altered ultrabasic rocks. They are generally <strong>of</strong> small economic importance. One <strong>of</strong><br />
these deposits in the Province Cabo Delgado was described by the Belgrade Geological Institute (1984).<br />
It is situated between the rivers Mulatala and Nacala in the coastal zone near the port <strong>of</strong> Nacala. Most <strong>of</strong><br />
the area is made up <strong>of</strong> biotite gneiss with gneiss-granite building intrusions up to 30 m thick The zone<br />
with asbestos is 6 km long and 70 to 100 m wide, with the old pegmatite mine <strong>of</strong> Gerais Minas in its<br />
central part.<br />
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Cilek: 3.2. Asbestos<br />
Ultrabasic rocks originated along the fracture zone 60-240°, 2 to 100 m thick. It consisted <strong>of</strong> brecciated<br />
greenish altered serpentinite, which is, in fact, completely silicified consisting <strong>of</strong> harzburgite, enstatite<br />
and dunite. The original rock was rich in olivine and enstatite-pendotites which underwent<br />
serpentinization, carbonitization, talcozation and silicification. This resulted in an almost complete<br />
serpentinization with few relics <strong>of</strong> enstatite and chromite.<br />
The zone is composed at random <strong>of</strong> talcized harburgitic serpentinites, enstatite-duniteserpentinites and<br />
dunitic serpentinites. The original ultrabasic rocks were altered meta-somatically during the<br />
hydrothermal phase which is in connection with the origin <strong>of</strong> granitoid rocks nearby.<br />
The zone contains also metagabbro in veins, gedriric schists, cumingtonite schists and mainly beds <strong>of</strong><br />
glimmerites. And precisely within the glimmerite are the bodies <strong>of</strong> asbestos. The asbestos zone is<br />
composed <strong>of</strong> anthophyllite, vermiculite, chlorite, quartz and talc.<br />
The cumulative content <strong>of</strong> asbestos is (Geol. Inst. Beograd -1984):<br />
+1mm +0.5 mm +0.2 mm +0.1 mm<br />
0.76 % 8.30 % 8.68 % 2.74 %<br />
The chemical analysis <strong>of</strong> asbestos and asbestos rock (talc, vermiculite, anthophyllite, chlorite, quartz?)<br />
in %:<br />
SiO2 58.88 60.51<br />
Al2O3 1.59 1.27<br />
Fe2O3 5.39 3.50<br />
FeO 2.54 2.70<br />
CaO 3.35 3.65<br />
MgO 22.92 22.83<br />
MnO 0.21 0.14<br />
TiO2 0.08 0.07<br />
Na2O 0.28 0.33<br />
K2O 0.15 0.09<br />
Cr2O3 0.152 0.143<br />
NiO 0.122 0.122<br />
A physico-mechanical test revealed these properties <strong>of</strong> asbestos rock:<br />
* loose dyke mass 0.410 g/cm3<br />
* compact dyke mass 0.732 g/cm3<br />
* specific mass <strong>of</strong> asbestos 2.94 g/cm3<br />
Other small anthophyllite bodies were found also in enstatite-dunite serpentinites.<br />
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Cilek: 3.2. Asbestos<br />
Generally, asbestos bodies are very irregular in shape, <strong>of</strong>ten oval, along the foliation planes, as a result<br />
<strong>of</strong> tectonic movement. The content <strong>of</strong> asbestos is a complex fiber aggregate mainly <strong>of</strong> variable quality<br />
with a small proportion <strong>of</strong> elongate fiber (fiber length below 1 mm). Large bodies <strong>of</strong> asbestos were not<br />
found.<br />
Conclusions:<br />
Only areas <strong>of</strong> greenstones belt <strong>of</strong> the eastern extension <strong>of</strong> the Zimbabwe craton into <strong>Mozambique</strong> can be<br />
envisaged as promising for a future exploration <strong>of</strong> asbestos. A possible extraction <strong>of</strong> asbestos should be<br />
accompanied by the utilization <strong>of</strong> other mineral products, mainly talc. Other asbestos occurrences within<br />
the <strong>Mozambique</strong> belt, similar to other East-African countries, are generally small and <strong>of</strong> low economic<br />
importance.<br />
At present, two units produce asbestos-cement in the country - Beira and Maputo. They use annually<br />
about 4000 t <strong>of</strong> asbestos fibres, which are imported, but could be produced locally. The formely mined<br />
Mavita anthophyllite, could have been used locally as a filler,coating material and in acid-alkali resistant<br />
products.<br />
© Václav Cílek 1989<br />
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Cilek: 3.3. Beryllium minerals<br />
3.3. Beryllium minerals<br />
The content <strong>of</strong> beryllium in earth crust ranges from 1 to 3.5 ppm and about 40 minerals contain a substancial quantity <strong>of</strong><br />
beryllium. A major portion <strong>of</strong> beryllium minerals are binded on granite pegmatites, especially on the type <strong>of</strong> albite-pegmatite,<br />
albite-microcline pegmatite, less microline and albite-spodumene pegmatites (about 20 minerals).<br />
A smaller part, about 11 minerals, are known from alkali pegmatites, followed by hydrothermal-pneumatolytic deposits,<br />
skarns, metasomatic deposits etc.<br />
Two minerals only bear economic significance - beryl and bertrandite. The list below contains the main beryllium minerals<br />
(the last three minerals occur in <strong>Mozambique</strong>: they are <strong>of</strong> little importance):<br />
Mineral Formula % BeO Remarks<br />
Beryl Be3 Al2 (Si6 O18) 14.0 - gem varieties: emerald, aquamarine, morganite, heliodor<br />
Bertrandite Be4 Si2 O4 (OH)2 42.0 - the only commercial source: USA - Utah<br />
Chrysoberyl Be Al2 O4 19.8 - in pegmatites, with Fe, Cr, - gem variety alexandrite<br />
Phenakite Be2 Si O4 45.0 - in quartz veins<br />
Helvite 3 (Mn, Fe) Be SiO4 · MnS 11-14 - in ore veins and skarns<br />
Barylite Ba Be2 Si2O7 16<br />
Euclase H Be Al SiO5 in pegmatites and veins<br />
Gadolinite Be2 Fe Y2 Si2O10 in granite pegmatites<br />
Herderite Ca Be (F, OH) PO4 in pegmatites<br />
Beryllium is an element <strong>of</strong> a rapidly increasing importance in our modern technological age. About 75% <strong>of</strong> total consumption<br />
is used in special alloys Be-Cu, Be-Al, Be-Ni, Be-Co which are hard, elastic, refractory, have nonsparking properties, thermal<br />
and electrical conductivity and they are used in aircraft, missiles, spacecraft industries, solid rocket fuels, computer parts etc.<br />
About 15% <strong>of</strong> total consumption is used in the form <strong>of</strong> beryllium oxide (BeO) with a melting point <strong>of</strong> 2,750 °C in specialty<br />
refractory ceramics as sparking plugs, aircraft engine parts, high frequency insulators, together with beryllium carbide (BeC).<br />
The beryllium metal production uses about 10% <strong>of</strong> the total annual output; the metal is used in the atomic industry, as neutron<br />
deflector etc. A small admixture <strong>of</strong> a few 0.X % even improves substantially the properties <strong>of</strong> steel for special purposes as<br />
noncorrosive, high-heat resistant, for special surgical instruments etc. An increased industrial consumption is impeded by<br />
limited resources.<br />
The traditional source <strong>of</strong> beryllium is beryl, with typical content <strong>of</strong> 12 - 13.5% <strong>of</strong> BeO (theoretical 14.0%). A lower content <strong>of</strong><br />
BeO is accounted to impurities and substitutions such as Na, Li, Cs, Rb, K (maximum 1%), and minor amounts <strong>of</strong> Ca, Mg,<br />
Mn, Fe, Cr, H2O and CO2 (carbonate). Chemically pure beryl is colourless, but in nature it is blue or greenish-blue<br />
(aquamarine), yellow (heliodor) in a mixture with Fe, emerald green with Cr or V. Morganite is pink because it contains Li<br />
and Cs. The BeO content varies between 10 and 15%.<br />
Beryl crystals occuring mainly in pegmatites may attain a spectacular size with crystals weighting <strong>of</strong> several tons. Berylliumbearing<br />
pegmatites are principally <strong>of</strong> Precambrian age (50%) or <strong>of</strong> Paleozoic age (37%). In pegmatites, beryl is concentrated<br />
usually near the quartz core.<br />
The actual ore grades contain about 3-4% BeO with crystals <strong>of</strong> about a few cm to a few mm long, but some deposits <strong>of</strong> beryl,<br />
with a content <strong>of</strong> 0.3-1.0% <strong>of</strong> mineral, could also be mined economically.<br />
In <strong>Mozambique</strong>, all beryllium resources occur in pegmatite deposits. Apart from coal Mozambican pegmatites are the most<br />
significant mineral resources <strong>of</strong> the country and, within the pegmatite deposits, beryllium minerals and columbo-tantalite ores<br />
are the most important ones (see Fig. 3.2.1.) at present.<br />
Pegmatites developed practically in all areas <strong>of</strong> the Precambrian in connection with granites <strong>of</strong> two orogenies-an older less<br />
important one <strong>of</strong> 1,100-800 m. y. -Mozambican and Pan-African orogeny <strong>of</strong> 500 - 450 m. y. Pegmatites can develop on<br />
granitic plutons without any visible connection, but, generally, are connected with certain types <strong>of</strong> metasediments in old<br />
lineaments.<br />
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Cilek: 3.3. Beryllium minerals<br />
The known pegmatite areas are these (see Fig. 3.3.1):<br />
* Alto Ligonha, Zambeze Province<br />
* Monapo-Nacala, Nampula Province<br />
* Ribaue - Malema - Nipepe in Nampula - Niassa provinces<br />
* Balama-Montepuez-Mueda-Rio Rovuma in the Cabo Delgado Province<br />
* Zumbo-Zambue in the Tete Province and others.<br />
Pegmatites are economically important in an extraction <strong>of</strong> rare-metals, rare-earths, radioactive minerals, in semiprecious and<br />
precious stones and industrial minerals.<br />
The group <strong>of</strong> industrial minerals comprises beryllium and lithium minerals, mica, feldspar, kaolin, quartz and others.<br />
Fig.3.3.1 Pegmatites <strong>of</strong> the Alto Ligonha district Zambézia (Barros-Vicente, 1963) (554 kB)<br />
Pegmatite group 5<br />
A - Pegmatite field <strong>of</strong> Alto Ligonha (Murropoce, Nuaparra, Muhano, Marige, Muiane, Tarupe, Naquissupa (Namuaca),<br />
Ingela, Piteia, Nahia, Mirrucue, Merrapane, Macula<br />
B - Pegmatite field <strong>of</strong> Alto Molócué (Namacotche, Mutala, Namarrela, Mecossa)<br />
C - Pegmatite field <strong>of</strong> Gilé (Famalicão, Nahora, Namivo, Nampoça)<br />
D - Pegmatite field <strong>of</strong> Meleta (Morrua, Melela, Namarripo, Marropino)<br />
E - Pegmatite field <strong>of</strong> Mucubela (Ginamo, Ilodo)<br />
Pegmatite group 6<br />
A - Pegmatite field <strong>of</strong> Ribaue (Boa Esperança)<br />
B - Pegmatite field <strong>of</strong> Nauela (Guilherme, Muetia, Comua)<br />
C - Pegmatite field <strong>of</strong> Erego (Ile)<br />
D - Pegmatite field <strong>of</strong> Mugeba (Mugema, Bere, Minhote, Maria, Nigule)<br />
E - Pegmatite field <strong>of</strong> Naburi (Nalume)<br />
F - Pegmatite field <strong>of</strong> Murrupula (Mtomoti, Mocotaia)<br />
Pegmatite group 7<br />
A - Pegmatite field <strong>of</strong> Mocuba (Namagoa, Munhamade, Licungo, Munhiba)<br />
Beryllium minerals were mined in pegmatites <strong>of</strong> the Alto Ligonha area. It was started in 1936; the first prospecting for gold<br />
and mica in the area dates back to the year 1930. First data on beryl recovery are from 1938 (see also Table 3.).<br />
Table 3 <strong>Minerals</strong> and concentrates <strong>of</strong> pegmatites extracted in the Alto Ligonha 1957-1963 (377 kB)<br />
The known beryllium minerals are these: Beryl industrial, in gem-quality: aquamarine, heliodor, morganite, emerald,<br />
gadolinite, euclase, herderite.<br />
Beryllium minerals were mined on a small scale in many pegmatite bodies; only a few bigger pegmatite mines produced beryl<br />
in larger quantity: the mines Morrua, Muiane, Ilodo, Naipa, Namivo, Murropoce and Nuaparra. In the last years, the sole<br />
producers were Muiane, Morrua and Nuaparra.<br />
In the production <strong>of</strong> industrial beryl <strong>Mozambique</strong> always ranked among the principal world producers. Here are some figures<br />
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Cilek: 3.3. Beryllium minerals<br />
on beryl production (examples for certain years only):<br />
1938 5,000 kg 1947 61,000 kg 1960 1,495 634 kg<br />
1942 9,200 kg 1949 135,547 kg 1961 973,067 kg<br />
1943 15,000 kg 1953 218,474 kg 1963 556,362 kg<br />
1945 3,608 kg 1954 909,140 kg 1973 6,000 kg<br />
1946 28,000 kg 1957 1,696 723 kg 1978 16,000 kg<br />
In 1979, after the independence beryl production reached the top with 28,000 kg; it decreased to 3,000 kg in 1985. Since then,<br />
the production ceased.<br />
Beryl is encountered in pegmatites within the zones <strong>of</strong> big feldspars and lithium minerals, in connection with albite. Smaller<br />
quantities are to be found also in the inner zone <strong>of</strong> mica-quartz and near the quartz core.<br />
Beryl differs in colour, volume and shape. Minimum grain size is slightly above 0.5 cm, the mineral is handpicked. Some<br />
crystals produce perfect hexagonal forms in a prism with rare pyramidal faces. Some attain a spectacular size such as the<br />
crystal from Muiane weighting 14 tons and measuring 1 x 4 m, that from Nihir with 22 tons and Munhamala I - with 50 tons.<br />
Crystals <strong>of</strong> 400 kg weight are not infrequent.<br />
The colour is white, green, blue, brown and black -the latter a speciality <strong>of</strong> <strong>Mozambique</strong>. Black beryl is found in pegmatites <strong>of</strong><br />
Moneia, Munhamala, Muiane, Muhano and Naipa. It is worth knowing, that this variety has been zoned.<br />
The content <strong>of</strong> BeO generally is >10.5 %, <strong>of</strong>ten surpassing 13.0 %.<br />
BeO content (average <strong>of</strong> 114 samples) in a commercial product (1963):<br />
maximum 13.32 %, minimum 9.10 %, average 11.76 %.<br />
Impurities include quite commonly quartz, microcline and muscovite; rarely tourmaline, zircon, chromite, tremolite, garnet.<br />
Some crystals display a zonation with white beryl surrounded by green beryl, rarely vice versa.<br />
Beryl in gem quality is <strong>of</strong>ten found in the form <strong>of</strong> aquamarine, in irregular bands within industrial beryl crystals. At Muiane, a<br />
piece <strong>of</strong> aquamarine measured 40 x 20 cm, a piece <strong>of</strong> morganite from Marropino measured 25 x 13 cm.<br />
Chemical analyses <strong>of</strong> beryl:<br />
1. Alto Ligonha (Campos J.-1948) % 2. Muiane (Barros-Vicente, 1963) %<br />
SiO2 64.26 62.99<br />
Al2O3 20.69 18.65<br />
Fe2O3 0.36 4.29<br />
BeO 12.45 13.02<br />
MnO2 tr. -<br />
CaO 0.12 0.10<br />
MgO 0.00 tr.<br />
Na2O + K2O 0.66 0.30<br />
Li 1.46 0.59<br />
P2O5 - 0.05<br />
Total 100.00 99.99<br />
Chrysoberyl was found at Muiane, but appears to be very rare in general.<br />
Gadolinite is known from two localities - Muiane and Macotaia.<br />
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Cilek: 3.3. Beryllium minerals<br />
Chemical composition: %<br />
SiO2 30.03 MgO 1.10<br />
(Er,Y)2O3 38.94 Fe2O3 0.65<br />
(Ce, La, Di)2O3 2.82 FeO 13.35<br />
Density: 4.470<br />
ThO2 0.76 H2O 0.60<br />
BeO 10.98 rest. 0.29<br />
CaO 0.48 100.0<br />
Euctase occurs in pegmatites <strong>of</strong> Muiane and Nahora in the form <strong>of</strong> small prismatic crystals only.<br />
Chemical composition: Muiane %<br />
SiO2 41.10 H2O- 0.09<br />
Al2O3 35.00 99.94<br />
BeO 17.25 Ga2O 0.013<br />
H2O+ 6.40 GeO2 0.026<br />
Herderite is more frequent in the area <strong>of</strong> Alto Ligonha and was identified in the Muiane mine.<br />
It has the form <strong>of</strong> crystalline aggregates <strong>of</strong> greenish-blue colour.<br />
Conclusions:<br />
Beryl is the only beryllium mineral <strong>of</strong> <strong>Mozambique</strong> that bears economic importance. It is found in pegmatites together with<br />
columbo-tantalite, microlite and lithium minerals for example at Nuaparra, Muiane, Morrua and Ribaue within the Alto<br />
Ligonha area. Outside this area, occurs in Tulua pegmatite near Nacala, Nacala-Mamba and near the Tanzanian border. Futher<br />
localities favourable for beryl development could be the tectonically active zones with pegmatite, and intrusive massifs <strong>of</strong><br />
granitic and syenitic rocks at the Morrola shear zones, in the vicinity <strong>of</strong> Montepuéz and Muéda, Cabo Delgado Province and<br />
elsewhere.<br />
The present importance <strong>of</strong> beryllium and its limited natural resources place <strong>Mozambique</strong> in very favourable world position.<br />
Small-scale mining operations for beryl look upon a very long and successful history in <strong>Mozambique</strong> and this experience<br />
could be renewed.<br />
© Václav Cílek 1989<br />
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Cilek: 3.4. Feldspar<br />
3.4. Feldspar<br />
Feldspars contsitute one <strong>of</strong> the most important groups <strong>of</strong> rock-forming minerals. All are aluminum silicates and<br />
move over a range <strong>of</strong> potassium sodium and calcium contents (rarely barium). Feldspars are divided in two<br />
subgroups:<br />
a) potash feldspars-orthoclase, microcline, sanidine, adularia<br />
b) sodium calcium feldspars or plagioclase series albite, oligoclase, andesine, labradorite, bytownite, anorthite.<br />
Orthoclase K(AlSi308) is monoclinic and <strong>of</strong>ten associated with quartz and mica. Often it is found as twinned<br />
crystals (Carlsbad-, Baveno, Manebach twins). When potassium is replaced by sodium the high-temperature<br />
polymorph <strong>of</strong> sanidine originates (50% Na). Varieties <strong>of</strong> orthoclase, adularia, sanidine or albite with a bluish<br />
opalescent display <strong>of</strong> colours are called moonstone. Orthoclase commonly changes to kaolinite or sericite.<br />
Microcline K(Al Si308) is triclinic and occurs frequently in pegmatites in the form <strong>of</strong> large crystals and<br />
cleavable masses. It grades <strong>of</strong>ten into albite Na(Al Si3O8) through a microscopic intergrowth termed perthite.<br />
Perthite also displays a coarse perthitic structure.<br />
Microcline is the only bright green feldspar which is called amazonite or amazonstone.<br />
Both orthoclase and microcline are used in ceramics, ceramic glazes and glass. Amazonite is used as a<br />
ornamental stone and in jewellry.<br />
The Plagioclase Series starts from sodium rich end member <strong>of</strong> albite to calcium rich end member <strong>of</strong> anorthite.<br />
Albite Na (Al Si3 O8)<br />
% <strong>of</strong> albite<br />
100 - 90<br />
Oligoclase a 90 - 70<br />
Andesine continuous 70 - 50<br />
Labradorite change 50 - 30<br />
Bytownite to 30 - 10<br />
Anorthite Ca (Al2 Si2 O8) 10 - 0<br />
Labradorite is marked by an iridescent colour display <strong>of</strong> blue and green; aventurine is either an albite, oligoclase<br />
or labradorite with a golden sparkle due to hematite inclusions.<br />
Plagioclase feldspars alter into sericite, kaolinite and calcite.<br />
Commercially used feldspars are potash-feldspars (orthoclase, microcline), albite as soda feldspar and their<br />
grades perthite-albite-oligoclase.<br />
More than 90% are used in the glass and ceramic industries, the rest serves as fillers in plastics, paint, rubber,<br />
and as mild abrasives in grinding wheels and powder.<br />
In the glass production feldspar preferably natrium feldspar introduces aluminium (1-3%,
Cilek: 3.4. Feldspar<br />
Potash feldspars, even at a higher cost <strong>of</strong> energy, produce ceramic ware <strong>of</strong> lower porosity, a better electric<br />
resistivity and strength. Porcelain ware is coated with a glassy glaze, in which K-feldspar <strong>of</strong> highest quality is<br />
used. The amount used is twice that <strong>of</strong> its content in the ceramic body.<br />
Feldspars are divided into several groups in different countries according to their quality and the mode <strong>of</strong> use.<br />
The best quality feldspar is K-feldspar with 85% <strong>of</strong> feldspar mass, at a ratio <strong>of</strong> K2O/(K2O + Na2O) 0.75 to 1.0%<br />
and with contents <strong>of</strong> Fe2O3
Cilek: 3.4. Feldspar<br />
mineral income was derived from pegmatites.<br />
Pegmatites are innumerous, and hundreds or perhaps thousands <strong>of</strong> these have not been explored as yet. A typical<br />
feature <strong>of</strong> most <strong>of</strong> the bigger pegmatite bodies is deep superficial weathering in some pegmatites up to a depth <strong>of</strong><br />
50 m which alters feldspars and the whole parent rock into kaolin and unaltered remnants <strong>of</strong> feldspar, quartz and<br />
mica with economic minerals, which could be easily extracted. However this is not favourable for the production<br />
<strong>of</strong> feldspar and most <strong>of</strong> the kaolin and feldspar is lost as waste during the separation <strong>of</strong> valuable economic<br />
minerals by washing and screening. That the production <strong>of</strong> these "waste" materials is possible shows the mine<br />
Boa Esperanca at Ribaue.<br />
The pegmatite extending from N-S, is about 130 m long and 60 to 70 m wide, with a core <strong>of</strong> quartz about 90 m<br />
long and 30 m wide. Along this core are zones <strong>of</strong> feldspar with mica, beryl, amazonite, with economic minerals<br />
<strong>of</strong> euxenite, samarskite, tourmaline and bismutite (see Fig. 3.4.1).<br />
Fig. 3.4.1. Cross-section <strong>of</strong> Ribaue pegmatite (Geol.Institute, Beograd, 1984) (435 kB)<br />
The most <strong>of</strong> feldspar is altered to kaolin with feldspar in relics only. The deposit was originally mined for beryl,<br />
mica, amazonite and rare-earth minerals. A small beneficiation plant treated the kaolinized pegmatite to produce<br />
washed kaolin (10-20% <strong>of</strong> material) and another dressing unit produced the feldspar. In 1982, for example, the<br />
annual production was 1,790 t <strong>of</strong> raw kaolin, 310 t <strong>of</strong> washed kaolin, 7,420 t <strong>of</strong> raw feldspar and 635 t <strong>of</strong> ground<br />
feldspar. The deposit is almost exhausted; a team <strong>of</strong> the Geological Institute <strong>of</strong> Belgrade (1984) calculated about<br />
23,400 t <strong>of</strong> raw kaolin and 820 t <strong>of</strong> feldspar. Unfortunatelly the reserves <strong>of</strong> 390 kt <strong>of</strong> kaolinized pegmatite were<br />
not evaluated. The feldspar is orthoclase-microcline, very pure, in lenses near quartz core.<br />
The chemical analyses show this composition (in %):<br />
Sample No. 110038 110038 110039<br />
SiO2 61.05 62.98 63.67<br />
TiO2 0.03 - 0.25<br />
Al2O3 22.47 19.83 20.40<br />
Fe2O3 3.19 0.41 0.28<br />
FeO 0.07 - -<br />
MgO - 0.02 0.06<br />
CaO 0.84 0.42 0.35<br />
Na2O 0.39 0.46 0.68<br />
K2O 8.00 13.25 12.88<br />
LOI 3.00 2.42 1.30<br />
The grain size <strong>of</strong> processed feldspar is 0.8 mm and it is sold in two grades-white and pink. Part <strong>of</strong> it is exported,<br />
part is used locally. The iron content is somehow increased, the potassium content is high. The feldspar is used<br />
in the ceramic industry.<br />
Nuaparra pegmatite in the pegmatite district <strong>of</strong> Alto Ligonha is an example <strong>of</strong> an unaltered pegmatite body with<br />
very well preserved feldspars <strong>of</strong> high quality. The quarry is connected by a dirt track <strong>of</strong> about 33 km with the<br />
mine Muiane, the most important one producing rare metals. In the vicinity <strong>of</strong> the Nuaparra mine, which<br />
produced originally beryl-aquamarine and later mica, are numerous other pegmatites (see Fig. 3.4.2.). Generally,<br />
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these pegmatites are different from the pegmatites <strong>of</strong> the Alto Ligonha district s. s., they are poor in columbotantalite<br />
and gemstones contents, but rich in mica, which has been mined here over 20 years. Big crystals <strong>of</strong><br />
beryl are found near the quartz core. The pegmatite is mined from both sides <strong>of</strong> Namiroe river in four small<br />
quarries.<br />
The Nuaparra pegmatite and its vicinity was surveyed by Intergeo-Praque (Duda et al., 1986) and this resulted in<br />
an estimate <strong>of</strong> reserves:<br />
1,373 kt <strong>of</strong> feldspar, <strong>of</strong> which 540 kt corresponds to rich potassium-sodium feldspar with 65-85% <strong>of</strong> feldspar<br />
mass, 0.6 to 0.75 <strong>of</strong> ratio <strong>of</strong> alkalies,
Cilek: 3.4. Feldspar<br />
hand, they are characterized by a low degree <strong>of</strong> kaolinization <strong>of</strong> feldspar, although Na is never completely absent.<br />
Zonation in Nuaparra 1/1 pegmatite (Fig. 3.4.3):<br />
1. Marginal pegmatite zone<br />
2. Small block zone<br />
3. Large block zone<br />
4. Metasomatic zone<br />
Fig. 3.4.3. Cross-section <strong>of</strong> Nuaparra pegmatite (Duda, 1986) (283 kB)<br />
Result <strong>of</strong> analyses <strong>of</strong> feldspar samples from Nuaparra:<br />
Jung 1978 Obretenov 1978 Ivanicka et al. 1981<br />
I. A I. B I. A I. B I. A I. B<br />
sample weight<br />
kg<br />
20 20 2000 20 5 5<br />
% SiO2 65.5 64.4 65.5 65.0 64.96 65.40<br />
Al2O3 18.4 19.2 18.5 18.7 17.82 18.73<br />
Fe2O3 0.12 0.10 0.10 0.06 0.04 0.02<br />
TiO2 0.005 0.01 0.06 0.01 0.02 0.01<br />
CaO 0.07 0.07 0.07 0.09 0.01 0.01<br />
MgO 0.09 0.09 0.22 0.06 0.04 0.02<br />
MnO - - - - 0.01 0.001<br />
P2O5 - - - - 0.085 0.090<br />
K2O 13.1 13.2 13.2 13.6 12.50 10.80<br />
Na2O 1.8 2.5 2.2 2.1 2.24 3.56<br />
H2O - - - - 0.60 0.06<br />
L. I. 0.7 0.4 0.3 - 1.36 1.13<br />
Content <strong>of</strong><br />
feldspar mass<br />
92.6 99.1 96.6 98.1 92.8 93.9<br />
K2O/(K2O + Na2O) 0.88 0.84 0.86 0.87 0.85 0.75<br />
colour after<br />
firing<br />
pure<br />
white<br />
pure<br />
white<br />
pure<br />
white<br />
pure<br />
white<br />
white<br />
greyish<br />
white<br />
Temperature<br />
<strong>of</strong> firing °C<br />
1,465<br />
1,465<br />
without<br />
1,465<br />
fissures and<br />
1,320<br />
rests<br />
1,250 1,250<br />
volume weight<br />
kg/cm3<br />
- - - - 2.512 2.495<br />
Nuaparra feldspar belongs to the very rich potassium natrium grade and can be used in the porcelain mass. Its<br />
whitness at 1,410 °C is 71.88%, tensile strength 808 kp/cm , good transparency; all this indicated its suitability<br />
in fine ceramic ware, sanitary ware and glazes.<br />
Duda et al. (1986) describe different types <strong>of</strong> feldspars, <strong>of</strong> which the main variety was potassium feldspar with a<br />
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variable component <strong>of</strong> Na due to the presence <strong>of</strong> perthitic albite. The content <strong>of</strong> Fe was below 0.1%, if higher it<br />
is due to weathering.<br />
Four samples were analysed (in %): Sample<br />
No. SiO2 Al2O3 K2O Na2O MgO CaO MnO<br />
Fe2O3<br />
-FeO<br />
P2O5 L.I. Total<br />
39 64.12 18.17 13.58 1.76 0.11 0.01 0.04 0.18 0.03 1.20 99.20<br />
43 64.40 18.40 13.28 2.25 0.02 0.03 0.01 0.08 0.01 0.74 99.20<br />
46 64.47 18.48 14.09 0.52 0.02 0.05 0.02 0.05 0.08 1.80 99.54<br />
64 64.47 18.56 13.06 2.88 0.03 0.04 0.02 0.08 0.03 0.65 99.64<br />
The plagioclase group is represented by albite - oligoclase, which originated from the albitisation process<br />
similar to albite-cleavelandite and albite-perthite. Spectral analysis <strong>of</strong> cleavelandite: content <strong>of</strong> elements >10% -<br />
Al, Si, | 10-1% - Na |1-0.1% - Ca, Fe, B, Bi, K, Mg, Ti | 0.1-0.01% - Ba, Be, Cr, Li, Mn, Nb, Zr | < 0.01% - Ag,<br />
Co, Cu, Ga, Ni, Pb, Sn, Sr, V.<br />
The mineralogical composition <strong>of</strong> feldspars and other minerals shows that pegmatite <strong>of</strong> Nuaparra represents an<br />
intermediate type between feldspathic - muscovitic pegmatites with a low mineralization <strong>of</strong> Be (Ta, Nb) and<br />
microclinic pegmatite with a mineralization <strong>of</strong> rare metals in microcline zone. The latter zone is represented by<br />
green beryl, columbo-tantaline and sometines by the development <strong>of</strong> a complex <strong>of</strong> quartz-albite-lepidolite.<br />
The Nuaparra pegmatite probably originated in the granitic massif Muacomuane nearby.<br />
As to a zonal chemical composition and structural features <strong>of</strong> feldspars, two main zones can be distinguished:<br />
1. pegmatite <strong>of</strong> the large block zone<br />
2. Pegmatite <strong>of</strong> the small block zone<br />
Feldspar in big blocks is an industrial material <strong>of</strong> high quality which consists <strong>of</strong> feldspatic material 75-85% and<br />
a low content <strong>of</strong> coloured oxides (<strong>of</strong>ten above 0.15%).<br />
Major elements <strong>of</strong> feldspar: (in %)<br />
Sample Na2O K2O Fe2O3 TiO2 CaO<br />
A section 2.16 11.98 0.14 0.01 0.03<br />
B section 1.00 12.82 0.15 0.01 0.02<br />
Borehole F-4 3.5-34.7 m 1.80 11.56 0.25 0.01 0.04<br />
Borehole F-4 38.4-43.9 m 9.91 0.39 0.20 0.01 0.22<br />
Average 1.57 12.01 0.16 0.01 0.03<br />
SiO2 average 58.82%, Al2O3 19.84%, FeO 0.06%, MgO 0.003%, Li2O 0.008%, BeO 0.0012%, Bi2O3 0.004%,<br />
Nb 0.0002%.<br />
Feldspar <strong>of</strong> the small block zone is generally low in content, irregularly developed and <strong>of</strong> medium quality.The<br />
recovery ratio is 49.8% only with 75% <strong>of</strong> potassium feldspar, 12% <strong>of</strong> plagioclase and 4% <strong>of</strong> calcite, mica and<br />
kaolin.<br />
Chemical composition: Na2O 4.18%, K2O 6.13%, Fe2O3 0.28%, TiO2 0.03%, CaO 0.26%.<br />
The content <strong>of</strong> coloured oxides is 0.17 - 0.40% (maximum 0.60%), SiO2 63.48%, Al2O3 18.88%, MgO 0.007%,<br />
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Li2O 0.006%, BeO 0.0032%, Bi2O3 0.003% and Nb 0.0006%.<br />
Besides the main pegmatite body at Nuaparra (1/1), with reserves <strong>of</strong> about 1,072 kt in the large block zone and<br />
860 kt in the small block zone in category C-2, five other pegmatite areas N outside Nuaparra (1/4) were<br />
explored which disclosed these reserves in D-2 category:<br />
1/3 ........... 1,200 kt<br />
1/4 ........... 1,080 kt<br />
1/5 ........... 1,117 kt<br />
1/6 ........... 2,331 kt<br />
1/7 ........... 1,010 kt<br />
total ......... 5,700 kt<br />
The Nuaparra deposits and pegmatites in the vicinity represent very high quality feldspars suitable for export and<br />
easily marketable. The reserves could be augmented.<br />
Pegmatites <strong>of</strong> the Alto Ligonha district, with vast reserves <strong>of</strong> feldspars, can be divided in four types:<br />
A. Natrium pegmatites zonal, with beryl, columbo-tantalite, microlite, tourmaline, lithium-minerals, cassiterite<br />
etc. Typical examples are Mocuba, Muiane, Marige, Naipa, Nahira, Murropoa, Nauro, Morrua, Moneia. This<br />
type is not the best for the recovery <strong>of</strong> feldspars which are mainly albites or other feldspars in several small<br />
zones. An example <strong>of</strong> such zonal pegmatite was described by GDR geologists from Marropino (1983):<br />
1. zone <strong>of</strong> quartz nucleus, thickness 0-15 m<br />
2. zone <strong>of</strong> lithium minerals with albite <strong>of</strong> medium to very big size 0-35 m<br />
3. zone almost without lithium minerals, with albite-pegmatite <strong>of</strong> medium size, 0-30 m<br />
4. pegmatite with quartz-muscovite<br />
5. homogeneous pegmatite <strong>of</strong> saccharoid texture, with albite and muscovite, 0-20 m<br />
6. greisen with lepidolite, 0-1 m<br />
7. greisen with phlogopite, 0-0.07 m<br />
8. albite-microcline pegmatite with muscovite, 0-10 m<br />
9. microcline-pegmatite with or without muscovite, 0-3 m<br />
10. granitoid pegmatite with muscovite and biotite, 0-3 m;<br />
granite migmatitic, 0-2 m<br />
parent rock <strong>of</strong> granite, syenitic to monzonitic<br />
B. Potassium pegmatites zonal, with an ill-developed potash zone. The principal minerals are K-feldspar, beryl<br />
and mica. Examples are Nuaparra, Mugeba, Nauro, Igaro. These pegmatites are the best source <strong>of</strong> feldspars (see<br />
Nuaparra).<br />
C. Potassium pegmatites zonal, rich in radioactive minerals and rare-earths; for example at Boa Esperanca and<br />
Gurrue. They are suitable for feldspar recovery with valuable byproducts.<br />
D. Heterogeneous pegmatites with amazonite and tourmaline, e. g. the Monapo structure.<br />
The main potash-feldspar is microcline, <strong>of</strong>ten perthitic, which is probably the original feldspar <strong>of</strong> most<br />
pegmatites <strong>of</strong> the area. It is found mainly within the zone <strong>of</strong> grand feldspars in big masses <strong>of</strong>ten altered. A close<br />
connection with other economic minerals such as beryl and columbo-tantalite is common. Microcline can also be<br />
found in external zones. Usually, crystal forms are not developed and, in few localities only, the Carlsbad and<br />
Baveno twins were found (Muiane, Naipa, Munhamola).<br />
The amazonite variety occurs outside the Alto Ligonha district.<br />
Orthoclase is less frequent than microcline and <strong>of</strong>ten replaced by albite. It is more common in external zones<br />
(Muiane), less in the zone <strong>of</strong> grand feldspars. Orthoclase originated under conditions <strong>of</strong> higher temperature and<br />
pressure and its remnants are found in microcline.<br />
Albite is most common to the group <strong>of</strong> plagioclase. Generally, it occurs within the lithium-minerals zone with<br />
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lepidolite and spodumene. It is indicative <strong>of</strong> mineralization <strong>of</strong> niobium-tantalum and beryllium. Cleavelandite,<br />
its lamellar variety, is known, for example, from Nahia, Namacotche and Munhamola. Albite is commonly<br />
altered and in intergrowth with tantalite and gem-tourmaline (Muiane, Morrua).<br />
Oligoclase is bound to the homogeneous zone <strong>of</strong> pegmatites and, in some places, is the first mineral to crystalize.<br />
It is quite frequent in pegmatites <strong>of</strong> Muiane, Naipa, Moneia and Namiro. The distribution and description <strong>of</strong><br />
feldspar in different pegmatite mines (Barros et Vicente, 1963) see above, is <strong>of</strong> historical value. Feldspar is<br />
produced in four pegmatite mines at present: Muiane, Morrua, Marropino and Nuaparra.<br />
At the Muiane mine, a big body <strong>of</strong> pegmatite is mined for recovery <strong>of</strong> columbo-tantalite, beryl, mica and<br />
precious stones. The pegmatite is almost completely kaolinized and small amount <strong>of</strong> feldspar remnants persist<br />
within the inner zones mainly the lithium zone. Feldspar grains together with kaolin represent the waste material<br />
which is deposited in a nearby depression. Reserves <strong>of</strong> kaolin are substantial, but so far not used in industry. An<br />
estimate <strong>of</strong> feldspar reserves was made by Zuberec et al. (1981) at a range <strong>of</strong> 80,000 t, with additional reserves<br />
<strong>of</strong> 200,000 t in pegmatite deposits. No analyses were made <strong>of</strong> feldspar.<br />
At the Morrua mine, the most important in columbo-tantalite production, the situation is simitar to that at<br />
Muiane. All altered pegmatitic materials <strong>of</strong> kaolin and feldspar are regarded as a waste and dumped without<br />
futher use. Zuberec et al. (1981) analyzed chemically sample <strong>of</strong> feldspar from the quarry and obtained these<br />
results.<br />
SiO2 64.71 P2O5 0.072<br />
Fe2O3 0.02 MnO 0.001<br />
Al2O3 16.99 Na2O 3.24<br />
CaO 0.56 K2O 9.40<br />
MgO 0.02 H2O 0.40<br />
TiO2<br />
The content <strong>of</strong><br />
0.08 L. I. 4.39<br />
feldspathic<br />
mass:<br />
82.9 % Ratio K2O/(K2O+Na2O) 0.74<br />
Colour after firing at 1,250 °C: white with small rests.<br />
It is a sodium - potassium feldspar which could be used in the ceramic industry. It is supposed that about 5,000 t<br />
<strong>of</strong> feldspar per year could be extracted from Morrua. However, at present, the project cannot be realized for a<br />
very poor conditions <strong>of</strong> the roads.<br />
At the Marropino mine, no feldspar samples were analysed. The mine produced tantalite, microlite, lepidolite,<br />
bismutite, but feldspars <strong>of</strong> the potassium - sodium type within the zone <strong>of</strong> grand feldspars have never been<br />
utilized, because <strong>of</strong> their almost total alteration to kaolin.<br />
Since 1984, all feldspar production has come from the Tutua deposit 30 km SW <strong>of</strong> the port <strong>of</strong> Nacala. Opencast<br />
manual mining started in mid-1984. Due to the security situation it has not been possible to survey the deposit.<br />
In 1985,66.7 tons <strong>of</strong> crushed feldspar were produced for the glass industry. The projected milling capacity is<br />
2,500 t/year.<br />
The Tulua pegmatite is composed <strong>of</strong> quartz and perthitic microcline, which are the ceramic materials <strong>of</strong> the<br />
deposit. In addition, amazonite, mica, beryl and transparent tourmaline are found in the vicinity.<br />
Other feldspar-pegmatite localities were described in the provinces <strong>of</strong> Nampula, Niassa and Cabo Delgado. The<br />
Yugoslav team (1984) studied several localities NW <strong>of</strong> Ribaue, in the vicinity <strong>of</strong> the villages <strong>of</strong> Nipepe and<br />
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Metarica. Pegmatite with amazonite was found in Serra Nhoto about 5 km SW od Munjaveni: dominant is<br />
microcline with smaller lenses <strong>of</strong> quartz, zones <strong>of</strong> mica and tourmaline. The pegmatite is 155 m long and up to<br />
13 m wide and during colonial times, was exploited for amazonite, occurring in irregular zones and lenses <strong>of</strong><br />
light green to dark green colour with white microcline. The reserves <strong>of</strong> ornamental amazonite are estimated to<br />
about 15 m3. Samarskite in 10 cm masses is also present.<br />
Another pegmatite, 160 m long and up to 60 m wide, is located 4 km N <strong>of</strong> Metarica. Again microcline is<br />
dominant with light green amazonite in lenses <strong>of</strong> dcm to 0.5 m thickness. Arithmetic mean <strong>of</strong> 30 samples <strong>of</strong><br />
Serra Meluli feldspar (in %):<br />
SiO2 66.60 MgO 0.23<br />
FeO 0.17 Na2O 1.44<br />
Fe2O3 2.02 K2O 7.94<br />
Al2O3 19.72 TiO2 0.04<br />
CaO 0.64 L. I. 4.24<br />
Potassium feldspar is dominant, but a hight iron content, probably due to weathering, renders these feldspars<br />
uneconomic.<br />
In the vicinity <strong>of</strong> Ribaue, a small pegmatite body 100-150 m long was explored (1 km SW <strong>of</strong> the Boa Esperanca<br />
mine). The feldspars <strong>of</strong> pegmatite show a high content <strong>of</strong> iron, silica and a low content <strong>of</strong> alkalies. It is an<br />
example <strong>of</strong> uneconomic pegmatite.<br />
Two analyses were made (in %):<br />
SiO2 72.18 73.84 CaO 1.82 0.70<br />
Al2O3 16.10 16.87 MgO tr. tr.<br />
Fe2O3 3.19 3.40 K2O 3.73 2.64<br />
FeO 0.29 0.22 Na2O 1.71 0.33<br />
TiO2 0.05 0.50 L.i. 0.73 1.56<br />
In the past, kaolinized granite, 6 km NE <strong>of</strong> the railway station Japala near Nampula, was used for the production<br />
<strong>of</strong> ceramic ware in Nampula. Weathered granite forms about 10 m high outrops <strong>of</strong> reddish colour representing<br />
the lower kaolin zone. The reserves <strong>of</strong> this material are big, the estimate is 4-5 million t.<br />
Weathered kaolinized granite has a high alumina content (average 21%), an iron and titanium content <strong>of</strong> up to<br />
5.76% and is unsuitable for the commercial use.<br />
One sample No. 110 005 is presented here (in %):<br />
SiO2 69.08 CaO 0.79<br />
Al203 17.76 MgO 0.08<br />
Fe2O3 3.89 K20 5.83<br />
FeO 0.22 Na2O 0.32<br />
TiO2 0.15 L. i. 4.24<br />
Halfway between Nampula and Ribaue, near the Namina railway station, one pegmatite body, about 3.5 m thick,<br />
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was discovered. It is potassium feldspar with a relatively high alkali content, but with an increased iron content.<br />
Chemical analyses (in %):<br />
SiO2 58.46 58.33 CaO 0.80 0.56<br />
Al2O3 24.20 24.63 K2O 8.50 8.79<br />
Fe2O3 1.68 1.20 Na2O 0.96 0.48<br />
FeO 0.24 0.07 L. i. 4.72 5.49<br />
TiO2 0.10 -<br />
Also other pegmatite bodies have been described from between Nacala-Memba, with a homogeneous zone and a<br />
zone <strong>of</strong> grand feldspars, and at Bacia de Msauize, with pegmatites <strong>of</strong> the C-type.<br />
Information on the quality <strong>of</strong> feldspars in pegmatite from other areas such as Inchope Doeroi in the Manica<br />
Province or Zambue in the Tete Province, is not available.<br />
Eluvial and alluvial deposits with feldspar are known from the vicinity <strong>of</strong> Nacala port. Zuberec et al (1981)<br />
described kaolinitic sands with a considerable content <strong>of</strong> feldspar grains i.e. 48% <strong>of</strong> feldspar within the fraction<br />
0.208 - 2.0 mm and about 21% <strong>of</strong> feldspar within the fraction 0.053 - 0.208 mm. These sands are the result <strong>of</strong><br />
weathering <strong>of</strong> some granites and pegmatites, with a subsequent transport over a short distance.<br />
Gula (1981) describes typical sedimentary deposits <strong>of</strong> sand with 7% <strong>of</strong> orthoclase and albite from Maconde<br />
beds. These beds are <strong>of</strong> Cretaceous age (Neocomian-Aptian), fairly large in extension, overlying Precambrian<br />
rocks in an about 400 m thick sequence, from the estuary <strong>of</strong> the river Lurio to the Tanzanian border. They build<br />
up the margin <strong>of</strong> the Rovuma basin and, generally, are cemented into quartzitic-feldspathic sandstone, finely to<br />
coarsely grained with conglomerate intercalations. No technological tests have been made. The feldspar content<br />
<strong>of</strong> these deposits is to low to be <strong>of</strong> economic value but a utilization <strong>of</strong> quartz could make it pr<strong>of</strong>itable.<br />
During the exploration <strong>of</strong> beach and dune sands along the coast, no feldspar accumulations were found in the<br />
quartzitic, generally well sorted, sands.<br />
Conclusions:<br />
<strong>Mozambique</strong>, with regard to feldspar resources, has not yet reached the stage <strong>of</strong> a developing country. The<br />
production and internal consumption <strong>of</strong> feldspar is more than marginal. The famous Alto Ligonha district and<br />
many other less known pegmatite fields <strong>of</strong>fer huge possibilities for a future mining <strong>of</strong> pegmatites just for<br />
feldspar or as a byproduct <strong>of</strong> mining for other minerals. Pegmatites could provide first-grade feldspar<br />
concentrates both for export and the local market.<br />
Also other feldspar resources such as aplites, some granitic rocks, rocks with feldspathoids and sedimentary<br />
deposits could be mined, but not for the reason <strong>of</strong> a shortage <strong>of</strong> first-grade material, but from an economic point<br />
<strong>of</strong> view, i.e., because <strong>of</strong> transport difficulties or a cheaper substitute material on the local market. An example<br />
could be the use <strong>of</strong> rhyolites, phonolites or nepheline syenites, close to the site <strong>of</strong> production.<br />
© Václav Cílek 1989<br />
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Cilek: 3.5. Fluorite (fluorspar)<br />
3.5. Fluorite (fluorspar)<br />
The element fluorine is widespread within the crust and its minerals originated in range from high temperature magmatic<br />
minerals to minerals <strong>of</strong> low temperature in sedimentary deposits. One <strong>of</strong> the first minerals which crystalizes from the magma<br />
is fluorapatite Ca5(PO4)3 F. The content <strong>of</strong> fluorine is 3.78%, but the content <strong>of</strong> apatite, especially in alkaline rocks, is low,<br />
about 2-3%, and rarely could build economic accumulations. The main mass <strong>of</strong> fluorine during the magma crystallization is<br />
concentrated in ore veins and pegmatites. Here, fluorine is found in independent minerals or as an isomorphic admixture in<br />
many silicate minerals, owing to a strong affinity between fluorine and many elements. The ionic radius <strong>of</strong> fluorine (1.33 Å)<br />
corresponds practically with that <strong>of</strong> hydroxyl (1.33,1.40 Å) and oxygen (1.36 Å). Therefore, fluorine is found in a combined<br />
form, or as a substitute for other ions.<br />
During the magma derivation the main part <strong>of</strong> fluorine migrated into various deposits, i. e., hydrothermal, hypothermal,<br />
mesothermal and epithermal. All these deposits represent also the main economic accumulations.<br />
Selected fluorine-bearing minerals:<br />
Fluorite CaF2 - ore veins and metasomatic deposits below 300 °C, rarely in pegmatites below 400 °C, in sediments at low<br />
temperature<br />
Cryolite Na3 Al F6 - in pegmatites <strong>of</strong> alkali magma, a sole economic deposit at Ivigtut which ceased mining<br />
Villiaumite NaF - in miarolitic cavities <strong>of</strong> nepheline syenites<br />
Sellaite Mg F2 - ore veins, fumaroles, salt paragenesis<br />
Topaz Al2 SiO4 (F, OH) - prominent mineral <strong>of</strong> granite pegmatites<br />
Chondrodide 2 Mg2 SiO4 • Mg (F, OH)2 - contact-zone mineral, in crystalline limestones<br />
Fluorapatite Ca3 (PO4)3 • (F, Cl) - pegmatites, ore veins, alkaline rocks, metamorphic rocks.<br />
The most common and also the most important is fluorite. Theoretically, it contains 51.1% calcium and 48.9 fluorine. The<br />
colour ranges from colourless, white, yellow, green, purple to deep blue and violet. Originally, fluorite crystals were used as<br />
ornamental stones for carving pearls, cups, vases and slabs and in China and Korea <strong>of</strong> today, they are used for statuttes and<br />
different complicatelly carved ornamental utensils.<br />
Fluorite <strong>of</strong> commercial value is called fluorspar. According to Harben-Bates (1984) flourspar is produced in three grades:<br />
acid, ceramic and metallurgical.<br />
1. Acid - grade fluorspar is <strong>of</strong> highest quality; it is used in the chemical industry (more than 60% <strong>of</strong> total consumption and<br />
should contain 95-97% CaF2, maximum 1% SiO2, 0.03 to 0.10% sulphur and 0.00x % Ba, Pb etc.).<br />
Other limitations are, for example, the content <strong>of</strong> CaC03 which should not be higher than 1%, moisture and grain size.<br />
Fluorite is used in the production <strong>of</strong> hydr<strong>of</strong>luoric acid (HF-aqueous), the starting point in the production <strong>of</strong> various organic<br />
and inorganic fluoride chemicals, elemental fluorine and synthetic cryolite.<br />
The acid is used as an etching agent on glass, sulphur hexafluoride as a gaseous insulator in high-voltage installations,<br />
elemental flourine as the most important fluorating agent in organic synthesis. In nuclear industry fluorine is applied in<br />
separation <strong>of</strong> 235 U from abundant 238 U, as refrigerant aerosol propellent and solvent.<br />
Very important is the production <strong>of</strong> synthetic cryolite which is prepared from HF, Na2CO3 and Al(OH)3 ===> AlF3 • 3 NaF.<br />
Synthetic cryolite is a molten electrolyte used in the Hall-Heroult process <strong>of</strong> aluminum production, and about 55 kg are<br />
required for the production <strong>of</strong> 1 t <strong>of</strong> Al. Other uses are: part <strong>of</strong> high-octane petrol, production <strong>of</strong> Teflon, glass polishing,<br />
enamel stripping, electroplating etc.<br />
2. Ceramic grade fluorspar includes several grades with about 95% CaF2 maximum 1% CaCO3, 3.0% SiO2 and 0.15%<br />
Fe2O3. This grade is used in the production <strong>of</strong> flint and opal glasses, enamels as coatings <strong>of</strong> steel parts, for example, <strong>of</strong><br />
refrigerators, cooking ware etc. Lower grades are nowadays used in the glass-fiber production for insulating and building<br />
purposes, in cement production (minimum 50% CaF,) where it decreases the temperature <strong>of</strong> clinker from 1,250 °C to 800 °C,<br />
in the plastic industry and in different building materials.<br />
3. Metallurgical grade fluorspar in the manufacture <strong>of</strong> steel is used to lower the melting point, improve the fluidity <strong>of</strong> stag<br />
and absorb impurities such as S and P from the iron ore. In open-hearth furnaces, electric furnaces and oxygen converters, the<br />
minimum content <strong>of</strong> CaF2, is 75%, with maximally 10% <strong>of</strong> SiO2 and 6% BaSO4. The grain size must be above 3 mm (the<br />
prevalent grain size 30 mm), without presence <strong>of</strong> Pb and Zn. A minimum <strong>of</strong> 60 effective percent <strong>of</strong> fluorspar is required (=<br />
SiO2 % x 2.5 substracted from CaF2 %). The amount <strong>of</strong> fluorspar needed for producing 1 t <strong>of</strong> steel is 1.6 to 6.0 kg.<br />
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Cilek: 3.5. Fluorite (fluorspar)<br />
Fluorite is found in a wide range <strong>of</strong> ore deposits: in greisen within the ro<strong>of</strong> zone <strong>of</strong> granitic intrusions, in skarn within the<br />
contact zone <strong>of</strong> limestone, quartz-fluorite veins with Cu-Pb-Zn mineralization, in nepheline syenites with RE and uranium<br />
minerals, in fluorite-barite-quartz veins, in stockworks and impregnation deposits, filling <strong>of</strong> brecciated zones, in residual<br />
fragmentary deposits and small accumulations in pegmatites.<br />
Important concentrations coincide with regions <strong>of</strong> low gravity and high heat flow such as the rift valley continental zones<br />
accompanied, in the vicinity, by igneous activity <strong>of</strong> alkalic or carbonatite composition and hydrothermal postorogenic effects.<br />
The deep-seated fault zones <strong>of</strong> regional structure are the main pathways for a liberation <strong>of</strong> fluorine from the upper mantle.<br />
Fluorine then reacts with surrounding rocks: with limestone to produce CaF2 and different silicates.<br />
Replacement deposits occur in carbonates, they are stratabound and ought to be associated with adjacent structural breaks.<br />
Fluorite is also common in contact deposits, in alkalic rock complexes and in carbonatites.<br />
In <strong>Mozambique</strong>, fluorite mineralization is associated with Mesozoic magmatism, with deep-seated faults connected with the<br />
East-African rift valley, with hydrothermal solutions.<br />
Two large genetic groups <strong>of</strong> fluorite deposits can be distinguished (see Fig. 3.1.1):<br />
1. hydrothermal deposits on fracture zones in veins and fissures<br />
2. hydrothermal deposits <strong>of</strong> the metasomatic type with the stages hypothermal, mesothermal to epithermal, connected with<br />
magmatic rocks (alkaline and carbonate).<br />
The first type <strong>of</strong> deposits is represented by massive fluorite <strong>of</strong> a crystalline arrangement, with concretions in parallel layers<br />
and <strong>of</strong> a radial structure, <strong>of</strong> greenish and violet colour; in small pockets disseminated with brecciated quartz and chalcedony.<br />
The second type <strong>of</strong> deposits connected with alkaline rocks and carbonatites is represented either by irregular aggregates <strong>of</strong><br />
radial arrangement <strong>of</strong> yellow colour or as impregnation <strong>of</strong> ftuorite <strong>of</strong> a blue colour.<br />
From the regional point <strong>of</strong> view <strong>of</strong> distribution, all main deposits are found either on the E or W side <strong>of</strong> the East-African rift<br />
valey (Niassa rift), <strong>of</strong> N-S extension or along the Mid-Zambezi rift valley branching from the main rift westwards along the<br />
river Zambezi.<br />
On the E side <strong>of</strong> the Niassa rift, there are several nepheline syenite massifs <strong>of</strong> Cretaceous age, with fluorite mineralization, e.<br />
g., at Morrumbala, Tumbine and Mauzo; a presence <strong>of</strong> other fluorite was indicated in trachytic lavas <strong>of</strong> Lupata bordering on<br />
the NW the Cretaceous sediments <strong>of</strong> the Zambeze depression. There, fluorite is developed as a dissemination, in small<br />
cavities inside the lavas and as a cementation agent in porous trachytic breccia.<br />
On the W side <strong>of</strong> the Niassa rift, all known carbonatite intrusions display a certain content <strong>of</strong> fluorite: Monte Xiluvo on the<br />
southern end, Monte Muambe near the river Zambeze and Monte Salambidwe with syenite in the outer ring and with inner<br />
carbonatite on the Malawi side. Some <strong>of</strong> these localities are richer in apatite and rare earths.<br />
The best known and recently explored fluorite deposit is Monte Muambe (Geol. Institute, Beograd 1984). An extract <strong>of</strong> the<br />
report was published in "Summary <strong>of</strong> World Congress <strong>of</strong> non-metallic minerals" (1985). Mt. Muambe is a ring-shaped hill<br />
(see Fig. 3.5.1) situated on the southern margin <strong>of</strong> the Tete Complex, in a depression filled with Mesozoic sediments and<br />
volcanics <strong>of</strong> Karroo. The ring consists <strong>of</strong> Upper Karroo arcositic sandstones, the diameter <strong>of</strong> the external ring is 6 km with a<br />
crater about 200 m lower. The floor <strong>of</strong> the crater is <strong>of</strong> highly dissected carbonatite, which is strongly karstified and covered<br />
with laterite. Carbonatites-carbonatite s. s., agglomerate tuff, feldspathic rocks and basic dykes cover about 40% <strong>of</strong> the<br />
caldera. The typical carbonatite is a hard, compact rock, grey or brown in colour, with knots <strong>of</strong> silicified material. Prevalent<br />
are calcitic carbonatites-sovites, less abundant are sideritic carbonatites. According to texture, these types <strong>of</strong> carbonatite can<br />
be distinquished:<br />
hypidiomorphic granular<br />
medium grained<br />
fine grained<br />
pseudoporphyric<br />
trachytic.<br />
Fig.3.5.1. Geological map <strong>of</strong> Monte Muambe (Geol.Institute, Beograd, 1981) (538 kB)<br />
Pure carbonatite may contain over 80% CaCO3, 0.2-6.15% dolomite; carbonate-silicate rock contains about 40% CaCO3.<br />
Carbonatite fills the vent and is also injected into adjacent rocks and then altered.<br />
Chemical composition <strong>of</strong> carbonatite (1 = mean chem. content, 2 = minimum and 3 = maximum content (in %).<br />
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Cilek: 3.5. Fluorite (fluorspar)<br />
1 2 3<br />
SiO2 - 0.8 5.48 Carbonatite occurs <strong>of</strong>ten<br />
TiO2 0.29 - 0.44 in veins and postvolcanic<br />
Al2O3 1.54 0.12 6.37 dykes some as hydrothermal<br />
Fe2O3 5.87 1.08 10.83 flurite solutions with<br />
FeO 0.08 0.01 0.12 an increased content <strong>of</strong><br />
MnO 0.84 - 2.28 rare earths such as Y, La,<br />
MgO 0.42 - 0.95 Ce.<br />
CaO 49.29 42.05 54.70<br />
Na2O 0.11 0.02 0.31<br />
K2O 0.23 0.02 0.75<br />
P2O5 0.64 0.01 2.73<br />
H2O- 0.16 - 0.54<br />
H2O+ 0.09 - 0.13<br />
CO2 38.37 31.29 41.65<br />
Spectrochemical analysis (ppm-arithmetic mean):<br />
Cu Ti Mo Y La Ce V Be Nb Sr CaF2<br />
5.65 21.21 2.73 85.15 263.73 380.30 19.33 94.24 47.27 2898.40 4.29<br />
Surroundind carbonatites on the outer side build-up a ring <strong>of</strong> rocks very rich in alkaline feldspars. These rocks are products <strong>of</strong><br />
fenitization, a process typical <strong>of</strong> changes in adjacent country rocks during syenite alkaline melt intrusions. Chemical analyses<br />
<strong>of</strong> samples <strong>of</strong> syenite-fenite: 90% <strong>of</strong> K-feldspar, accessory minerals 1 - 10% (apatite, zircon, pyrite, martite, potash feldsparsanidine,<br />
monazite) - texture: hypidiomorphic granular<br />
% 1 2 3<br />
SiO2 41.21 44.32 45.35<br />
TiO2 0.36 0.39 0.35<br />
Al2O3 18.80 15.39 17.07<br />
Fe2O3 6.57 15.50 8.45<br />
FeO 1.55 0.01 0.01<br />
MnO 0.46 1.47 0.99<br />
MgO 0.61 1.82 0.81<br />
CaO 8.41 3.65 8.41<br />
Na2O 0.40 0.48 0.95<br />
K2O 13.70 12.05 12.68<br />
P2O5 0.98 0.52 0.43<br />
H2O 0.10 0.36 0.14<br />
CO2 5.32 4.70 4.79<br />
Fluorite mineralization was formed by postvolcanic activity, i. e., after the emplacement <strong>of</strong> carbonatite. Mineralization is<br />
found in permeable and fractures zones One such zone is the contact betwen fenites and carbonatite. In the field, fluorite was<br />
observed on the W and S margins <strong>of</strong> the carbonatite intrusion. Electrical prospecting revealed a resistivity anomaly near the<br />
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Cilek: 3.5. Fluorite (fluorspar)<br />
eastern part that could be linked to fluorite mineralization. The whole contact length <strong>of</strong> 9 km should be investigated in detail<br />
to determine the extent <strong>of</strong> the mineralized area.<br />
Although the primary dissemination halo <strong>of</strong> fluorite veins within the carbonatite is small, i.e. seldom more than 1 cm, it can be<br />
as wide as 50 metres in fenite.<br />
Fractured zones related to a collapse <strong>of</strong> the central part <strong>of</strong> the caldera, are sometimes mineralized and fluorite occurs as a crust<br />
around brecciated fragments and as a fracture filling <strong>of</strong> smaller "en echelon" fractures.<br />
Two types <strong>of</strong> fluorite mineralizations are found:<br />
a) Blue fluorite, composed <strong>of</strong> fine-grained aggregates <strong>of</strong> hypidiomorphic-idiomorphic cubic crystals.<br />
Inclusions (gas, fluid, calcite) are <strong>of</strong>ten present. Metallic minerals constitute an average <strong>of</strong> 6-10% by volume, sometimes 20%.<br />
An analysis <strong>of</strong> a typical sample is given below. Blue fluorite is rich in beryllium, strontium, yttrium and lathanum. Be<br />
concentration was recorded to be as high as 10,000 ppm.<br />
b) Yellow fluorite consists <strong>of</strong> two types:<br />
(i) Massive yellowish-white fluorite<br />
(ii) Transparent yellow fluorite, <strong>of</strong>ten occurring in "kidney shaped" structures.<br />
Inclusions are far less common to this variety. Concentrations <strong>of</strong> Be, Y, La and Nb are lower, while the concentration <strong>of</strong> Sr is<br />
higher than that in blue fluorite.<br />
Analysis (in %) Yellow Fluorite Blue Fluorite<br />
SiO2 2.06 1.86<br />
Fe2O3 8.80 15.95<br />
Al2O3 1.10 2.67<br />
TiO2 0.21 0.65<br />
MnO 0.006 0.010<br />
CaCO3 1.16 2.11<br />
CaF2 85.11 74.49<br />
MgCO3 0.86 1.53<br />
Na2O 0.05 0.12<br />
K2O 0.08 0.10<br />
S 0.02 0.01<br />
Pb 0.03 0.03<br />
Zn 0.05 0.08<br />
Sb 0.016 0.004<br />
Cu - -<br />
Ba 0.05 0.08<br />
Sr 0.23 0.27<br />
L. i. 1.22 0.02<br />
(Analyses <strong>of</strong> two representative fluorite samples).<br />
The reserves are substantial and it is necessary to stress that in some trenches, massive fluorite <strong>of</strong> a thickness <strong>of</strong> about 20 m<br />
has been encountered. The average width <strong>of</strong> veins is 10-20 m, length 100-250 m, reserves are calculated to 50 m depth with<br />
specific gravity 2.7. It ought to be remembered, that just a small part <strong>of</strong> the Muambe deposit was explored.<br />
Following reserves are calculated:<br />
Prospective: 699,849 t <strong>of</strong> fluorite ore with 81% <strong>of</strong> fluorite 567,457 t pure fluorite<br />
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Cilek: 3.5. Fluorite (fluorspar)<br />
Possible: 723,057 t <strong>of</strong> fluorite ore with 75% <strong>of</strong> fluorite 552,631 t pure fluorite<br />
Total: 1,422,906 t <strong>of</strong> fluorite ore 79% <strong>of</strong> fluorite 1,120,088 t pure fluorite<br />
Apart from caldera, residual deposits contain 1,510,375 t <strong>of</strong> martite without TiO2, with an increased value <strong>of</strong> Ba, Nb, Sr and<br />
probably RE. The deposit covers about 200 ha, its average thickness is 0.8 m.<br />
Fenites can serve as potash-rich rocks, for example, in the ceramic or glass industry and part <strong>of</strong> the carbonatites in cement or<br />
lime production (with a low phosphorus content).<br />
Preliminary dressing tests indicate that fluorspar <strong>of</strong> the metallurgical grade can be obtained (partly even without dressing)<br />
with CaF2 74-85%, SiO2 2%, Fe2O3 9-15%, and acid fluorspar with CaF2 92-98% prepared by flotation for use in the<br />
chemical industry.<br />
The Muambe fluorite deposit is <strong>of</strong> extreme economic value and future exploration will increase the reserves. Mineralization<br />
and ore emplacement are the results <strong>of</strong> post-volcanic hydrothermal activity.<br />
South-west <strong>of</strong> the river Zambeze, and appreciably remote from the deep-seated faults <strong>of</strong> the East-African rift are two<br />
important areas with fluorite mineralization:<br />
1. the zone <strong>of</strong> Macossa-Maringoe-Canxixe<br />
2. the zone <strong>of</strong> Djanguire-Monte Domba<br />
1. This zone is about 100 km long and 20 km wide, with several veins <strong>of</strong> fluorite along the contact-line between the<br />
Precambrian Barue Formation and sedimentary and volcanic rocks <strong>of</strong> the Karroo and Cretaceous. The boundary is tectonic, as<br />
common to a development <strong>of</strong> Karroo troughts, it represents the tectonic margin <strong>of</strong> the Mid-Zambeze rift which deviates here<br />
from a N-S to a NW direction. Fluorite mineralization is bound to faults in N-S (15 °E or W) direction, richer deposits<br />
developed in sites <strong>of</strong> an intersection with NW-SE fractures.<br />
Alves (1961-64) recognized ten areas <strong>of</strong> fluorite veins:<br />
Rio Nhamafunda thickness 0.02 m<br />
Djalira Sul 0.6 - 5.1 m, inclination 50° to vertical<br />
Rio Nhanzamba 0.01 - 16.5 m, vertical<br />
Djalira-Rio M'Bahate 6.15 - 7.00 m, 65° to vertical<br />
Djalira Norte 0.10 - 1.60 m, 30° to vertical<br />
Sambza Sul 0.10 - 1.35 m, 40° to vertical<br />
Entre os rios Samba e Nhatsapo small mineralizations<br />
Monte Geramo brecciated quartz veins<br />
Povoacao de Joni 2.70 m<br />
Monte Chizumba -<br />
Some <strong>of</strong> the deposits have been known for quite a long time; about 2,000 t <strong>of</strong> fluorite were extracted from the surface to a<br />
depth <strong>of</strong> 25 m from deposit Geramo.<br />
In the whole area, fluorite is closely connected with chalcedony-quartz in veins which are concordant to the general foliation<br />
<strong>of</strong> surrounding metamorphic rocks. The length <strong>of</strong> veins is about 20 to 600 m, with a thickness <strong>of</strong> 1-3 m. Some veins may<br />
attain a length <strong>of</strong> 2-4 km and thickness <strong>of</strong> 10-15 m. The inclination <strong>of</strong> veins is from steep to vertical. Drilling disclosed<br />
fluorite up to the depth <strong>of</strong> 80 m. In the southern part, the veins can be followed for about 40 km; the width <strong>of</strong> the zone is about<br />
2-4 km, exceptionally 10 km. About forty interrupted veins are present. Fluorite developed either in a disseminated or massive<br />
form. The disseminated type forms inclusions and amygdaloidal fillings in strongly fractured quartz, or as a cemented<br />
material in breccias. Massive fluorite occurs in veins and lenses up to 8 m thick. The colour <strong>of</strong> fluorite is violet and green,<br />
seldom yellow, with an ore content averaging 24.0-38.9% CaF2.<br />
Technological tests made with Djalira (Maringue) fluorite confirmed that metallurgical fluorspar can be produced with a CaF2<br />
content <strong>of</strong> 85%, and acid fluorspar with 97% CaF2. Fluorite from Geramo (Canxixe) was tested by the Mitsubishi Shoji<br />
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Cilek: 3.5. Fluorite (fluorspar)<br />
Kaisha Company (1972), and the concentrate <strong>of</strong> 97% CaF2 was produced.<br />
According to new tests (1982) two types <strong>of</strong> fluorite can be produced from the original concentrate <strong>of</strong> 82-84% CaF2:<br />
acid fluorspar with 96% CaF2, with 16% recovery<br />
metallurgical fluorspar with 92% CaF2, with 5-6% recovery.<br />
The reserves <strong>of</strong> the Maringue deposit are estimated to 43,000 t, those <strong>of</strong> Canxixe to 160,000 t <strong>of</strong> fluorite in three veins. Other<br />
fluorite veins represent estimated reserves <strong>of</strong> 500,000 t.<br />
2. The deposit Djanguire is situated at 154 km from the town <strong>of</strong> Tete on the Tete-Changara road. It was first examined in<br />
1963/64. It is composed <strong>of</strong> zones with different degree <strong>of</strong> fluorite mineralization <strong>of</strong> which the zone "Inter Luia" is the most<br />
important one. This zone is about 2,000 m long with a maximum width <strong>of</strong> 750 m. The thickness <strong>of</strong> the veins is 0.10 to 3.0m.<br />
Composition <strong>of</strong> some veins <strong>of</strong> the Djanguire deposit:<br />
Name <strong>of</strong> vein CaF2 SiO2 CaCO3 BaSO4 F S<br />
Inter-Luia F.1 22.7-82.8 13.74-57.28 0.51-1.92 0 0.34-1.4 0.01<br />
Inter-Luia F.2 71.8-83.8 14.81-27.33 0.79-0.95 0 0.47-0.68 0.01<br />
Inter-Luia F.3 65.9 28.92 0.61 0 0.36 0.01<br />
Mt. Nhambadula F.8 80.8 14.08 0.69 0 0.58 0.01<br />
The reserves <strong>of</strong> fluorite in the Djanguire area (Alves, 1961-64):<br />
70,000 t proved<br />
110,000 t probable<br />
600,000 t possible<br />
total 780,000 t<br />
The Monte Domba deposit is situated near Changara and fluorite with quartz in veins <strong>of</strong> NW-SE direction developed in a<br />
number <strong>of</strong> veins with two types <strong>of</strong> mineralization - disseminated and massive.<br />
The length <strong>of</strong> one vein is about 70 m with thickness between 1.70 and 2.25 m, the others are shorter and less thick. Fluorite is<br />
incrusted on quartz and, sometimes, <strong>of</strong> a cockade texture. Baryte is present, but rare.<br />
Alves (1961-64) described the genesis <strong>of</strong> the deposit:<br />
phase <strong>of</strong> crustal fracturing with a development <strong>of</strong> oriented fractures<br />
filling up <strong>of</strong> fractures by massive milky quartz<br />
new phase <strong>of</strong> fracturing resulting in crushing <strong>of</strong> massive quartz<br />
deposition <strong>of</strong> fluorite and chalcedony<br />
formation <strong>of</strong> crust <strong>of</strong> hialine and euhedral quartz.<br />
Fluorite occurs generally in small crystals <strong>of</strong> green colour, sometimes banded. The genesis is in connection with faults <strong>of</strong> the<br />
rift-valley, but also with a post-volcanic activity and the origin <strong>of</strong> ring structures <strong>of</strong> alkaline rocks.<br />
Especially Monte Domba originated on fault lines connected with a regional fault system known here as the Metangua Rift.<br />
The age <strong>of</strong> mineralization is Jurassic or Cretaceous.<br />
Further to the NW, within the E-W section <strong>of</strong> the Mid-Zambeze rift valley, and on the northern bank <strong>of</strong> the Cabora Bassa<br />
dam, is the prominent area <strong>of</strong> Cone Negose with a carbonatite intrusion and a complex mineralization with apatite, fluorite,<br />
rare earths and metals.<br />
In some places the content <strong>of</strong> fluorite is 20%, but generally is low and <strong>of</strong> no economic interest.<br />
Conclusions:<br />
The most important fluorite deposit is that <strong>of</strong> hydrothermal and metasomatic origin on the Monte Muambe carbonatite<br />
intrusion. Untreated fluorspar is <strong>of</strong> metallurgical grade, acid fluorspar can be obtained by flotation. Reserves are big and could<br />
be increased by futher exploration. Together with fluorite some reserves <strong>of</strong> rare earths, beryllium, niobium and strontium can<br />
be expected. The weathering crust on the caldera carbonatite deposit <strong>of</strong>fers some reserves <strong>of</strong> good-quality martite. Classical<br />
deposits <strong>of</strong> fluorite are connected with deep-seated faults <strong>of</strong> the Niassa and Mid-Zambeze rift and are developed mainly on the<br />
western or southern side <strong>of</strong> the rift-valley, in the area <strong>of</strong> Djanguire-Mt. Domba and Macossa-Maringoe-Canxixe. The deposits<br />
are fluorite-chalcedony-quartz veins on fractures within the Precambrian rocks but close to the troughs <strong>of</strong> Karroo or<br />
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Cilek: 3.5. Fluorite (fluorspar)<br />
Cretaceous filling. They are <strong>of</strong> Jurassic-Cretaceous age.<br />
Some accumulations <strong>of</strong> fluorite are to be found also on the eastern side <strong>of</strong> the rift valley, in intrusive carbonatite or alkaline<br />
rocks and over an extensive area Lupata alkaline lavas <strong>of</strong> Karroo.<br />
It is almost certain that future exploration will substantially increase these reserves together with reserves <strong>of</strong> other elements<br />
and rare earths.<br />
In this field, <strong>Mozambique</strong> has indeed a bright future.<br />
© Václav Cílek 1989<br />
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Cilek: 3.6. Graphite<br />
3.6. Graphite<br />
Graphite is a mineral <strong>of</strong> a hexagonal modification <strong>of</strong> carbon, black to steel-gray in colour, hardness 1 to 2, specific gravity 2.1<br />
to 2.3. In nature, it is found in igneous, sedimentary and mainly metamorphic rocks. Graphite in igneous rocks is primary<br />
crystallized carbon in veins or bands; in metamorphic rocks, it is the result <strong>of</strong> organic matter transformation. Graphite is plastic<br />
due to a perfect basal cleavage with weakly bond layers allowing them to slide over one another. The plasticity <strong>of</strong> graphite is<br />
responsible for easy tectonic movements on fault planes. Graphite is also a good heat conductor, it has a metallic lustre and it is<br />
resistant to weathering.<br />
According to its structure, graphite is divided into "flake graphite" or crystalline graphite (flakes 0.1-X mm in size),<br />
microcrystalline or massive (crystals 0.001-0.1 mm) and cryptocrystalline or amorphous (crystals below 0.001 mm). The term<br />
amorphous refers to the s<strong>of</strong>t black earthy appearance <strong>of</strong> graphite in metamorphic rocks, while crystalline graphite displays<br />
metallic luster.<br />
The minimum content <strong>of</strong> crystalline graphite in rock should be at least 3% <strong>of</strong> carbon for massive graphite about 10% C in rock<br />
is needed for economic mining. The three largest industries are steelmaking, foundries and refractories. A mixture <strong>of</strong> clay and<br />
graphite is used for refractory crucibles and retorts for melting nonferrous metals and alloys. The last innovation <strong>of</strong> use <strong>of</strong> flake<br />
graphite is in the production <strong>of</strong> magnesite carbon refractory bricks. For smelting crucibles, amorphous or flake graphite can be<br />
used. A minimum 95% C graphite is required for use as a lubricant, which is applied, for example, in textile machines or in<br />
places with an increased temperature. Specifically, it is used as moderator in atomic reactors, rocket components, turbines,<br />
military machines etc. Other uses include dry-cell batteries, carbon brushes in electrical motors, in paints and pigments and, <strong>of</strong><br />
course, in pencils. Many small uses are in carbon paper, chinese ink, lining <strong>of</strong> foundry moulds, in shoe polishes and rubber.<br />
The quality requirements <strong>of</strong> graphite differ in each country and in fact, in each factoty, although some general norms have been<br />
accepted internationally.<br />
For casting: ash content 18 - 25%, moisture up to 1.5%, important is the fineness <strong>of</strong> ground material: +0.25 mm < 5%, -0.053<br />
mm maximum to 25%<br />
For ceramic crucible: ash content 8.5 - 11.0%, volatile matter at 300°C up to 2%, moisture up to 1% and Fe2O3 up to 1.7%<br />
Galvanic elements and basic accumulators: ash content 10-14%, volatile matter up to 1%, moisture up to 1%, Cu maximum<br />
0.05%, total Co Ni Pb As in traces, fineness <strong>of</strong> ground material +0.16 mm up to 10%, - 0.063 mm minimum 45%<br />
Electrodes: crystalline graphite with ash content up to 20% for anthracite electrodes and 6-10% for coke electrode, volatile<br />
matter not measured, moisture up to 1% and fineness <strong>of</strong> ground material - 0.063 mm up to 20%<br />
Pencils: ash content up to 3%, or to 5%, volatile matter up to 1%, moisture up to 1%, fineness <strong>of</strong> ground material - 0.063 mm<br />
up to 1%<br />
Lubricants: ash content up to 7-9%, moisture up to 1%, volatile matter up to 1% pH neutral, sulphur up to 0.2%, fineness<br />
100% up to 0.2 mm.<br />
The origin <strong>of</strong> graphite is still a controversial issue. However most graphite deposits are <strong>of</strong> metamorphic origin. All types <strong>of</strong><br />
organic matter such as dispersed carbonaceous matter, hydrocarbons, anthracite, anthraxolite and slightly metamorphosed coal<br />
sedimentary layers may be converted to graphite by contact and mainly regional metamorphism. The carbonaceous material<br />
changes from amorphous graphite to crystalline graphite with regard to the grade <strong>of</strong> metamorphic processes, reaching the<br />
amphibolite facies <strong>of</strong> ultrametamorphic stage with well-developed graphite crystals. The degree <strong>of</strong> graphitization depends<br />
mainly on temperature, pressure conditions are less important. It is believed that graphite needs a minimum <strong>of</strong> 400°C for its<br />
origin. This metamorphic process is valid for most Phanerozoic deposits with either disseminated graphite in metasedimentary<br />
formations or in concentrated graphite layers on foliation on schistose planes.<br />
Controversal is the origin <strong>of</strong> secondary-epigenetic graphite. This graphite is common to Precambrian schists and gneisses <strong>of</strong><br />
medium but mainly high-grade metamorphism. Graphite occurs in veins, fracture fillings, replacement and seggregation<br />
concentrations.<br />
It is clear that part <strong>of</strong> the graphite can crystallize in situ from the present organic matter, but part <strong>of</strong> it must be redeposited.<br />
Harben et Bates (1984) suggest (viz Weis et al., 1981) that epigenetic graphite is derived from syngenetic graphite or<br />
carbonaceous detritus by a process that converts carbon to a fluid. It is a reaction <strong>of</strong> superheated water vapour and<br />
carbonaceous compounds (but not carbonates!) at 700-900°C:<br />
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Cilek: 3.6. Graphite<br />
C + H2O ===> CO + H2<br />
which produces the only mobile carbon compound. Under geological conditions the precipitation <strong>of</strong> carbon starts at about 600-<br />
750°C:<br />
CO + CO ===> C + CO2<br />
A basic condition for this process is the presence <strong>of</strong> the original organic matter in a sedimentary sequence. Where this matter<br />
does not exist, graphite accumulations can not develop. Genetic types <strong>of</strong> graphite deposits according to Kužvart (1984).<br />
1. Early magmatic graphite develops during an intrusion <strong>of</strong> alkali rocks-granites, syenites, into a metasedimentary formation.<br />
Graphite crystallizes synchronously with the intrusive rocks in the form <strong>of</strong> stocks and nests. Its quality is high, but deposits <strong>of</strong><br />
this type are rare.<br />
2. Contact-metasomatic (skarn) deposits develop at the contact <strong>of</strong> carbonate rocks with plutonic magmatites such as<br />
pegmatites and aplites causing a crystallization <strong>of</strong> organic carbon. The graphite is flaky in the form <strong>of</strong> stockwork and veins.<br />
3. Vein deposits formed from postmagmatic solutions with graphite in veins and lenses <strong>of</strong> few mm to 2-5 m. This development<br />
occurs in crystalline rocks with pure graphite <strong>of</strong> 80-98% C, coarsely flaky (see previous discussion on epigenetic graphite) in<br />
veins stockworks, pockets, cavity fillings in Precambrian gneisses, granulites, quartzites etc.<br />
4. Metamorphogenic deposits formed by a concentration and crystallization <strong>of</strong> organic matter during predominantly regional<br />
metamorphism. Kužvart (1984) divides these deposits into:<br />
a) metamorphic graphite deposits in layers and lenses in crystalline rocks with disseminated graphite flakes, with a graphite<br />
content in the rock between 1 and 15% in series about 15-210 m thick<br />
b) metamorphosed graphite deposits are generated by contact or regional metamorphism from sediments rich in organic matter<br />
such as coal etc. Metamorphosed coal seams attain several m in thickness with graphite <strong>of</strong> the massive type (80-85% C) on the<br />
contact with granitic rocks.<br />
Regionally metamorphosed shales, sandstones and limestones with organic matter are transferred to gneisses, marbles and<br />
quartzites with crystalline or amorphous graphite, <strong>of</strong>ten with sulphur, vanadium and phosphorus (biogenic origin). Later<br />
tectonic stresses can change the disseminated graphite in stringers, swelled lenses and bizarrely scaled structures <strong>of</strong> higher<br />
purity graphite.<br />
Into this group fall the biggest world deposits. Weathering-resistant graphite is <strong>of</strong>ten mined in superficial deposits <strong>of</strong> wholly or<br />
partly decomposed parent rocks with a low graphite content <strong>of</strong> 3-5%, enriched in residual deposits to about 10-15% (see<br />
Madagascar deposits).<br />
In <strong>Mozambique</strong>, the mining <strong>of</strong> graphite started as early as 1911 in the Tete Province - Angónia and, in 1927, after the<br />
discovery <strong>of</strong> the Itotone deposits near Nacala by Europeans. Nunes (1952) mentions that graphite from the latter locality called<br />
"itoto" by the local population, was known several centuries ago and used for ornamental painting <strong>of</strong> pots known as "muapas".<br />
Beside the Itotone deposit, other deposits nearby a Metocheria and Jagaia, Otaco-Ancone and Evate were also exploited. This<br />
graphite was exported from the port <strong>of</strong> Nacala; was never treated mechanically, but just handpicked. Fereira da Silva (1953)<br />
presents some mining data and states that about 2,500 t <strong>of</strong> graphite with a C content <strong>of</strong> 70-74% was exported from Itotone in<br />
1953. Sometimes, it contained even more than 80% C. At that time, also the mine Otaco-Ancone was in production, the deposit<br />
Nacoto (Netia) was explored and big bed <strong>of</strong> disseminated graphite with a content <strong>of</strong> 18% C was discovered (see Fig. 3.6.1). On<br />
the Evate deposit, mining started in 1951, and soon the mine reached an annual production <strong>of</strong> 300 t.<br />
The quality <strong>of</strong> exported graphite as given by Nunes (1952):<br />
% C volatile C graphite Ash<br />
Otaco-Ancone 1.40 49.00 47.82<br />
Itotone 1.87 91.79 6.18<br />
Angónia 5.84 80.72 12.60<br />
The second historical area <strong>of</strong> graphite exploitation is at Angónia in the Tete Province near the Malawian border. First, graphite<br />
occurrence was reported in 1912, although actual mining had started in 1911. In 1944, about 50 t <strong>of</strong> graphite had been exported<br />
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Cilek: 3.6. Graphite<br />
from the port <strong>of</strong> Beira. Mining operations ceased in 1955. The quality <strong>of</strong> graphite is mentioned above. The mines in operation<br />
were situated in the zone NW-SE <strong>of</strong> Ulongue towards the Malawian border: Metengo-Balama, Chiziro (Satemua) and the<br />
nearby mine Maue.<br />
Other sites <strong>of</strong> graphite occurence were discovered in the Niassa province at Juluti (Mogovolas) and Catur near Lichinga;<br />
Balame near Montepuez, between Chiure and the river Lúrio, near Macondes, Muecate and Ancuabe near Pemba in the Cabo<br />
Delgado Province.<br />
In the Manica and S<strong>of</strong>ala provinces, a small occurrence <strong>of</strong> graphite was found at Barue, Gorongosa, Mossurize, Mombane and<br />
in the Province Zambezia at Serra Chiperone and Morrumbala (Nunes, 1952).<br />
Mozambican graphite deposits can be divided into these main areas (see Fig. 3.6.1):<br />
a) Angónia<br />
b) Monapo structural unit<br />
c) Lúrio belt<br />
d) Morrola structural unit<br />
Fig. 3.6.1. Occurence <strong>of</strong> graphite, mica, rare-earth minerals (328 kB)<br />
The dominant genetical type <strong>of</strong> graphite deposits is represented by metamorphosed deposits in zones <strong>of</strong> high grade<br />
metamorphism <strong>of</strong> amphibole or granulite facies in metasedimentary graphitic rocks. Quite common is a secondary enrichment<br />
<strong>of</strong> graphite in veins, fractures and fillings due to a regional ultrametamorphism, or in contact zones.<br />
Rare is an occurence <strong>of</strong> epigenetic graphite and graphite <strong>of</strong> magmatic origin.<br />
Lächelt (1985) divides graphite deposits into five groups:<br />
1. disseminated graphite in graphitic gneisses, biotite-amphibole and amphibole-pyroxene gneisses<br />
2. graphite along the zones and boundaries <strong>of</strong> migmatization and inside the migmatites<br />
3. graphite (fuchsite) in crystalline limestones and other metasediments near the zones <strong>of</strong> graphitic rocks<br />
4. graphite in stockworks, veins etc. <strong>of</strong> epigenetic origin (<strong>of</strong>ten in magmatic but also in gneissic rocks); this includes also<br />
graphite in a kaolinized cover <strong>of</strong> basic magmaticrocks as, for example, anorthosites <strong>of</strong> Angónia<br />
5. Graphite in the weathering crust <strong>of</strong> primary deposits.<br />
a) Angónia<br />
The Angónia Formation is composed <strong>of</strong> different rocks <strong>of</strong> the Precambrian <strong>Mozambique</strong> belt, mainly metasediments -<br />
paragneisses, crystalline limestones and quartzites. The general structural trends is NW - SE and the graphitic zone follows this<br />
direction from Vila Coutinho Velha through Ulongoe to Metengo Balama in the SE <strong>of</strong> the Malawian border. The graphitic zone<br />
is highly metamorphosed in granulitic-charnockitic facies with several areas with an incereased content <strong>of</strong> both primary and<br />
epigenetic graphite (see Fig. 3.6.2.)<br />
Fig. 3.6.2. Geological map <strong>of</strong> the Ulongue zone - Angónia (Huntington, 1984 - Geol.Intitute, Beograd, 1982) (435 kB)<br />
Primary graphite in metasediments is <strong>of</strong> metamorphogenic origin, normally disseminated within leucocratic gneisses,<br />
amphibole-pyroxene gneisses, garnet gneisses, quartzites and crystalline limestones with apatite and pyrhotine. Graphite<br />
accumulations follow the plane <strong>of</strong> foliation with an inclination <strong>of</strong> above 45°/NE.<br />
According to Lächelt (1985), also the margins <strong>of</strong> vast areas <strong>of</strong> migmatitization are richer in graphite content but always in<br />
gneisses and not in migmatites.<br />
Epigenetic graphite present in stockworks and veins <strong>of</strong> hydrothermal origin, developed in crystals well known in this area<br />
which attain up to 15 cm. Graphite occurs within massifs <strong>of</strong> metaanorthosites, seldom syenites, which intrude the<br />
metasediments. Some graphite is found in gneisses. The veins <strong>of</strong> graphite are well preserved in the superficial, partly<br />
kaolinized zone on meta anorthosites. Deposits within the graphitic zone (from NW to SE):<br />
1. Vila Coutinho Velha (Ulongoe Velha) - graphite in gneisses and lateritic deposits<br />
2. Nhankar - graphite in two layers in gneisses and also in crystalline limestone<br />
3. Rio Maue and Chiziro, grapite in stockwork and veins in anorthosite and kaolin<br />
4. Satemua (Mouzinho), graphite in gneisses and laterites<br />
5. Metengo Balama, graphite in stockwork and veins in anorthosite.<br />
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Cilek: 3.6. Graphite<br />
The occurence <strong>of</strong> graphite at Vila Coutinho Velha is <strong>of</strong> small importance. Graphite is present in gneisses rich in biotite, which<br />
are enclosed in migmatites and granulites with almandine, partly is in lateritic crust.<br />
Nhankar deposit, situated about 14 km NW <strong>of</strong> Ulongoe, is <strong>of</strong> dissimenated type, in biotite-amphibole gneisses following the<br />
zone <strong>of</strong> granulites. Mineralized graphite developed in two layers separated by the zone <strong>of</strong> migmatites. Also here crystalline<br />
limestone is developed.<br />
An estimate <strong>of</strong> reserves in steep dipping strata, made in 1950, suggested 234,000 t <strong>of</strong> rock with 17,200 t <strong>of</strong> extractable graphite.<br />
The most important and best known deposit is Satemua. In 1983, the deposit was investigated by the Geological Institute <strong>of</strong><br />
Beograd. It is situated about 10 km SE <strong>of</strong> Ulongoe. Graphite is disseminated in laminae and veins <strong>of</strong> different thickness. The<br />
deposit is about 1,200 m long, with an average thickness <strong>of</strong> 40 m and an incline <strong>of</strong> 40-60° to the NE. It consists <strong>of</strong> two<br />
mineralized zones <strong>of</strong> graphitic gneisses surrounded by migmatites and granulites. Also crystalline limestones and carbonatic<br />
rocks contain graphite.<br />
The reserves were calculated in different levels:<br />
at 20 m depth with 6% C - 67,000 t <strong>of</strong> graphite<br />
at 30 m, with 6% C - 338,000 t graphite<br />
at 100 m - 650,000 t <strong>of</strong> graphite.<br />
The technological test using flotation indicated that crystalline graphite <strong>of</strong> the flakey type, with 94% C, 1% <strong>of</strong> moisture and 5%<br />
<strong>of</strong> ash can be obtained. Opencast mining is feasible. Some parts <strong>of</strong> deposits contain about 10% <strong>of</strong> graphite, part <strong>of</strong> it in lateritic<br />
deposits and an increased content <strong>of</strong> V2O5 0.10-0.54% bound in mineral essentially muscovite-roscoelite.<br />
The deposits <strong>of</strong> Rio Maue-Chiziro and Metengo Balama are <strong>of</strong> the stockwork and vein type, with pure graphite in cm<br />
thickness, which was mined in the past. They are mineralogically attractive, with big graphite crystals but <strong>of</strong> small economic<br />
importance.<br />
The geologists <strong>of</strong> the Beograd Geological Institute collected several samples from Angónia graphite deposits: their content <strong>of</strong><br />
carbon varied between 10.03-11.12%, SiO2 43.03-48.32% and ash content 78.74-85.94%.<br />
Two main types <strong>of</strong> graphite zones can be distinguished: disseminated in flakes in gneisses and massive in veins and lenses in<br />
granulites.<br />
Some laminae are 0.5 to 3.0 mm thick.<br />
The flotation product is <strong>of</strong> the metallurgical grade and can have many other uses, except in the pencil manufacture. Results <strong>of</strong><br />
chemical tests: Sample No.:<br />
1. Rio Maue-epigenetic graphite<br />
2. Satemua-primary graphite<br />
3. Nhanhar Zone I-primary graphite<br />
4. Nhanhar Zone II-primary graphite<br />
% sample 1. 2. 3. 4.<br />
SiO2 43.3 46.34 48.32 48.11<br />
TiO2 0.47 1.20 0.95 1.20<br />
Al2O3 22.62 18.23 17.40 18.46<br />
Fe2O3 6.93 10.67 9.56 9.28<br />
MgO 3.09 3.80 4.67 2.19<br />
CaO 3.08 4.77 3.91 4.03<br />
Na2O 1.50 1.15 1.10 1.41<br />
K2O 1.40 1.45 1.80 2.75<br />
S 0.09 0.17 0.26 0.14<br />
V2O5 0.04 0.10 0.10 0.08<br />
C 11.12 10.22 10.21 10.03<br />
Ash 85.55 78.74 83.29 85.94<br />
Moisture 2.47 3.01 2.99 2.71<br />
b) The Monapo structural unit<br />
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Cilek: 3.6. Graphite<br />
is situated in the Nampula Province between the towns <strong>of</strong> Nampula and Nacala. It is interpreted as an "overthrust", a tectonic<br />
unit thrust from the northern Lúrio belt to above the older Nampula Formation. Another interpretation is that <strong>of</strong> a synclinal<br />
structure, ringshaped, lying with discomformity on the older Precambrian. In my opinion, this is the upper part <strong>of</strong> the<br />
Precambrian known in Tanzania as Usagaran; its upper unit which is mainly metasedimentary is represented as an erosional<br />
remnant.<br />
The grade <strong>of</strong> metamorphism corresponds to that <strong>of</strong> the Lúrio belt; most <strong>of</strong> the rocks are metamorphosed to granulite facies or<br />
even ultrametamorphosed. Dominant are granite gneisses, granite-migmatites, paragneisses, amphibolites, carbonatic<br />
metasediments with intrusive basic and acidic rocks.<br />
Within the Monapo structure are several old graphite mines <strong>of</strong> which the oldest and also best known is the mine itotone. The<br />
Geological Institute Beograd (1984) explored the whole area <strong>of</strong> Monapo. The average C content <strong>of</strong> the itotone deposit was 70-<br />
74%, <strong>of</strong> the Evate-Utoca deposit 68% (with 3,000 t <strong>of</strong> graphite extracted), and 18% only in the mine Nacota with "black"<br />
graphite.<br />
Around the itotone mine there are several other graphite deposits. The graphite occurrence is associated with fillings <strong>of</strong><br />
fractures in granite gneiss, coarse-grained granite and also pegmatites few cm thick or in small nest-like clots. Granite seems to<br />
have been injected migmatically into the gneisses. Veins <strong>of</strong> graphite are very steep in NE-SW direction. It was determined<br />
microscopically that graphite occurs in veins and veinlets or impregranations with 25-95% content, its thickness ranges<br />
between several mm and several cm. A thickness <strong>of</strong> 25 cm is known from an older report. Generally it is thought, that the<br />
graphite content in the graphite zone is about 1%.<br />
Of the analyses <strong>of</strong> graphite from Itotone made, here are three control analyses (in %):<br />
Sample 3. 14. 26.<br />
SiO2 38.83 28.45 35.24<br />
Al2O3 9.67 7.24 7.87<br />
Fe2O3 1.51 3.85 2.82<br />
CaO 0.33 0.23 0.44<br />
MgO 0.09 0.16 0.67<br />
TiO2 0.35 0.27 0.86<br />
P2O5 0.07 0.27 0.34<br />
MnO 0.008 0.023 0.056<br />
Na2O 0.81 0.21 1.86<br />
K2O 3.85 2.10 3.10<br />
V ppm 30 30 30<br />
S 0.05 0.05 0.05<br />
H2O 0.27 0.43 0.77<br />
L.i. 44.04 56.69 45.69<br />
Content <strong>of</strong> carbon is expressed by the loss <strong>of</strong> ignition. Several general rules in the development <strong>of</strong> vein-type graphite deposits<br />
have been determined at the Monapo structural unit: graphite is connected with very high degree <strong>of</strong> metamorphic rocks <strong>of</strong><br />
granulite facies with typical mineral <strong>of</strong> sillimanite. There exist two types <strong>of</strong> mineralization - first with graphite in granitegneisses<br />
disseminated or as impregnations or in pockets with average 25%; secondly in typically vein or swarm <strong>of</strong> veins within<br />
fractures, locally <strong>of</strong> pegmatitic origin, accompanied by quartz and siliceous impregnations. The content <strong>of</strong> graphite could attain<br />
even 94% <strong>of</strong> flaky crystalline variety.<br />
c) Lúrio belt<br />
forms the northern boundary <strong>of</strong> the so-called Nampula block, and is composed <strong>of</strong> several different formations. Lächelt (1985)<br />
suggests that it is <strong>of</strong> geosynclinal origin with regard to its present degree <strong>of</strong> metamorphism <strong>of</strong> amphibole and granulite facies.<br />
The most distinctive feature <strong>of</strong> the belt is its structural development. Within the generally trending Mozambican belt in N-S<br />
direction, the Lúrio belt proceeds generally E-W or ENE-WSW along the river Lúrio. Some rocks are metasediments<br />
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Cilek: 3.6. Graphite<br />
composed <strong>of</strong> garnet gneisses, graphitic gneisses and crystalline limestones with intrusive rocks <strong>of</strong> granodioritic to syenitic<br />
composition. Within the Lúrio belt, the occurrence <strong>of</strong> metamorphic graphite has been known for a long time (Noticia<br />
Explicativa, 1974) from Nipepe, Nicomissore and Mequice located in the central part <strong>of</strong> this belt, from Nipepe to the S.<br />
However, no data are available on these sites as yet.<br />
At the E-end <strong>of</strong> the Lúrio belt, just near the boundary between Precambrian rocks and the coastal sedimentary basin, an<br />
occurrence <strong>of</strong> graphite at Mazeze was observed long ago. The entire crystalline area around the mouth <strong>of</strong> the Lúrio river was<br />
explored by Bulgar Geomin in 1983. They discovered several tens <strong>of</strong> graphite deposits and regarded this area as one <strong>of</strong> the<br />
most promising graphite districts <strong>of</strong> Southern Africa. The main deposits extend from the N <strong>of</strong> river to the SW, close to the port<br />
<strong>of</strong> Pemba. The advantage <strong>of</strong> the area is its close proximity <strong>of</strong> the port and good tarmac roads, with concentrations <strong>of</strong> deposits<br />
over an area <strong>of</strong> about 5,000 km2. Of about thirty deposits, the more important are these:<br />
1. Rio Uanapula, at about 12 km S <strong>of</strong> the road Pemba-Montepuez. The graphite zone is 8 km long, its thickness ranges from<br />
20-70 m, with massive graphite with C content <strong>of</strong> 15-22%. About 1.2 million t <strong>of</strong> graphite can be extracted to the depth <strong>of</strong> 20<br />
m in opencast.<br />
2. Taquinha, at 9 km NE <strong>of</strong> the river Megaruma. The graphite zone consists <strong>of</strong> gneisses <strong>of</strong> the Metoro Formation, 3 km long,<br />
50-70 m thick, trending E-W, inclination 25-30°C, massive flaky graphite with a C content <strong>of</strong> 15-20%. The reserves, up to a<br />
depth <strong>of</strong> 20 m, have been estimated to 6,490 000 t <strong>of</strong> graphite ore.<br />
3. Rio Megaruma, at 10 km N <strong>of</strong> Mazeze, is an important graphite deposit. It is part <strong>of</strong> the subformation Matasse, with<br />
massive, large-flake graphite. This is the original deposit Mazeze, which had been mined intermittently in the past. The<br />
graphitic zone <strong>of</strong> E-W direction with 30° inclination is 9-10 km long, 10-20 m thick with a C content <strong>of</strong> 10-17%. The reserves,<br />
up to a depth <strong>of</strong> 20 m, have been estimated to 3,870 000 t <strong>of</strong> graphite ore.<br />
4. Mazeze, 13 km E <strong>of</strong> Mazeze and N <strong>of</strong> the main road Mazeze-Pemba; the deposit was discovered in the 1970ties by BRGM<br />
searching for uranium. The deposit is very promising, with a graphitic zone <strong>of</strong> the subformation Namiropa, about 3 km long,<br />
thickness <strong>of</strong> graphitic gneisses from 15-20 m to 50-60 m, C content 15-20%. The massive graphite is <strong>of</strong> the large-flake variety.<br />
Estimated reserves, up to a depth <strong>of</strong> 20m, are 3,600 000 t <strong>of</strong> graphite ore.<br />
5. Monte Nipacue represents a zone <strong>of</strong> 3-5 km length, thickness 15-60 m, C content 17.15%. The reserves up to a depth <strong>of</strong> 10<br />
m, are estimated to 10,750 000 t <strong>of</strong> graphite ore.<br />
6. Rio Muaguide - Ivanca, at 17 km NE <strong>of</strong> Metoro and near the road Pemba-Ancuabe. Graphitic gneisses <strong>of</strong> the subformation<br />
Namiropa form a zone 3,000 m long 40-60 m wide, C content 15-20%. The zone trends NW-SE with inclination <strong>of</strong> 5°. The<br />
reserves estimated to a depth <strong>of</strong> 20 m, are 5,160 000 t <strong>of</strong> graphite ore. 7. Monte Jocolo, is situated W <strong>of</strong> a mountain <strong>of</strong> the same<br />
name (695.8 m above sea level), and 5 km E <strong>of</strong> the deposit Rio Uanapula. The zone is 4 km long, 10-20 m wide, 110° strike<br />
and 35° inclination, C content 10%. The estimated reserves <strong>of</strong> graphite ore are 1,720 000 t.<br />
8. The Ancuabe deposit near the road Pemba-Montepuez with graphite content 3-10% <strong>of</strong> the large-flake variety. For the whole<br />
district, the estimate <strong>of</strong> graphite ore reserves is about 35 million t.<br />
Bulgargeomin collected several bulk samples <strong>of</strong> graphite ore from which they obtained pure concentrates <strong>of</strong> high quality flake<br />
graphite. Pilot tests as well as a processing unit are being prepared. Graphite deposits around the mouth <strong>of</strong> the river Lúrio are<br />
certainly <strong>of</strong> greatest importance in <strong>Mozambique</strong> and will add further reserves.<br />
d) Morrola structural unit<br />
is part <strong>of</strong> the Lichinga block, the most northern part <strong>of</strong> <strong>Mozambique</strong>. It is interpreted as a sinform structure with structural<br />
trends from N-S to NE-SW. It is named after a small village SW <strong>of</strong> Montepuez. The only known site <strong>of</strong> graphite occurrence is<br />
at Montepuez (in Map <strong>of</strong> Deposits No. 125, 1974), in graphitic shists closely connected with well-known crystalline limestones<br />
deposits-marbles <strong>of</strong> Montepuez. Graphite with fuchsite is part <strong>of</strong> the marble sequence. The Morrola Formation consists <strong>of</strong><br />
paragneisses, carbonatic rocks and quartzites with ilmenite, garnets and epidote. Graphitic gneisses are common. The<br />
metamorphic sequence with magmatic rocks, mainly pyroxenites, is metamorphosed to granulite facies. No exploration work<br />
has been performed as yet.<br />
Conclusions:<br />
<strong>Mozambique</strong> has an old tradition in graphite mining. The quality <strong>of</strong> exported graphite from Angónia and Monapo areas was<br />
derived, in the past from an extraction <strong>of</strong> best-quality graphite without any treatment. Despite this setback, the quality <strong>of</strong><br />
Mozambican graphite was high, <strong>of</strong> metallurgical type. New discoveries around the mouth <strong>of</strong> the river Lúrio place Mozambican<br />
graphite deposits, with regard the reserves and quality, among the potential and biggest producers <strong>of</strong> this mineral in the world.<br />
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Cilek: 3.6. Graphite<br />
© Václav Cílek 1989<br />
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Cilek: 3.7. Lithium minerals<br />
3. 7. Lithium minerals<br />
Lithium is a white s<strong>of</strong>t metal, and one <strong>of</strong> the lightest <strong>of</strong> all metals, atomic weight 6.938.<br />
Its average content in the earth crust is 20 ppm, and it had been concentrating mainly in residual magma<br />
during magma crystallization. Granite pegmatites are the main lithium source together with beryllium,<br />
tantalum, tin, cesium, rubidium and others. Within zonal pegmatites, lithium minerals belong to a later<br />
phase <strong>of</strong> crystallization during which commence metasomatic processes <strong>of</strong> albitization. Therefore,<br />
lithium zones are best developed in sodalitic-albite-spodumene pegmatites.<br />
Besides granitic pegmatites, the main source <strong>of</strong> lithium are lithium-rich brines.<br />
Although lithium occurs in substabtial amount in some 20 minerals, just three <strong>of</strong> these are <strong>of</strong> commercial<br />
value.<br />
Spodumene LiAl (SiO3)2 composed <strong>of</strong> 64.6% SiO2, 27.4% Al2O3 and 8.0% Li2O. The average Li20<br />
content is usually 4 to 7.5% (from 2.91 to 7.66%) due to a substitution <strong>of</strong> lithium by natrium or<br />
potassium. In pegmatites spodumene is <strong>of</strong>ten developed in big crystals which can easily alternate in a<br />
mixture <strong>of</strong> eucryptite LiAl SiO4 and albite NaAl Si3O8. Spodumene is the most important source <strong>of</strong><br />
lithium for direct use in the glass industry but its Fe2O3 content should not be higher than 0.1%, and<br />
Li2O about 6-7%. A lower Li2O content indicates an intergrowth with quartz. Transparent spodumene is<br />
<strong>of</strong> gem quality: greenish-hiddenite, yellow-triphanite and pinkish-kunzite.<br />
Petatite LiAl (Si2O5)2, is composed <strong>of</strong> 78.4% SiO2, 16.7% Al2O3 and 4.9% Li2O. The actual range <strong>of</strong><br />
Li2O is 3.0 to 4.9%. The mineral is mostly massive, colourless and friable. It is accompanied in<br />
pegmatites by spodumene, lepidolite, eucryptite and tourmaline. Its industrial use is similar to that <strong>of</strong><br />
spodumene, i. e., mainly in the glass industry.<br />
Lepidolite (OH, F)2 KLi Al2Si3O10 is a monoclinic mica <strong>of</strong> varying composition due to isomorphic<br />
mixing. Its chemical and structural properties change according to the lithium content. Lepidolite occurs<br />
in the form <strong>of</strong> small crystals and blades, but mainly as a massive flake-grained variety. It is <strong>of</strong> purplish<br />
colour. Its theoretical Li2O content is 7.74%, but the range <strong>of</strong> the ore is mainly 3.0-4.7%. Lepidolite is<br />
commonly enriched by rubidium (0.91-3.80 Rb2O) and cesium (0.16-1.90 Cs2O). Fluorine and<br />
rubidium contents (sometimes up to 4%) render the ore more suitable for melting which is favourable<br />
for use in the glass industry and enamel production. Since fluorine content is environmentally harmful,<br />
lepidolite is substituted nowadays by other materials. Two other important lithium bearing pegmatite<br />
minerals are eucryptite and amblygonite.<br />
Eucryptite LiAl SiO4, is a mineral <strong>of</strong> the nepheline group and its theoretical Li2O content is 11.88%. It<br />
occurs commonly in pegamtites where its crystals are <strong>of</strong>ten enclosed in albite. It originates from an<br />
alteration <strong>of</strong> spodumene by the action <strong>of</strong> sodium-rich solutions. Eucryptite is a rare mineral and could<br />
be mined as a byproduct only. The only commercial world deposit is Bikita in Zimbabwe.<br />
Amblygonite LiAl (PO4) (F, OH), the only lithium non-silicate mineral, represents the last member <strong>of</strong><br />
the group with high fluorine content. It forms big crystals or is massive, with high Li2O content <strong>of</strong><br />
10.2%. The ore grades usually have 7.5-9.0% Li2O, but the mineral is rare.<br />
Deposits <strong>of</strong> lithium minerals can be divided into:<br />
1. Lithium granites<br />
2. Granite-pegmatites<br />
3. Pneumatolytic deposits<br />
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Cilek: 3.7. Lithium minerals<br />
4. Hydrothermal deposits<br />
5. Lithium-rich sediments<br />
6. Evaporites<br />
7. Brines, mineral waters, sea water<br />
Of all these types, just types 2 and 7 are <strong>of</strong> commercial interest at the present.<br />
Pegmatites with lithium minerals are either zonal or homogeneous, unzoned, mainly <strong>of</strong> the albitespodumene<br />
type. They range from early-stage minerals like iron-rich spodumene <strong>of</strong> green colour<br />
through the intermediate stage with spodumene-petalite-lepidolite-amblygonite to the last stage <strong>of</strong><br />
hydrothermal alteration with eucryptite, cookeite and bikitaite.<br />
The minimum content <strong>of</strong> lithium minerals to be economically extractable is about 1% in hard rocks and<br />
about 0.03% in brines.<br />
Natural ore <strong>of</strong> spodumene and petalite is used in the ceramic industry, glass-ceramics, enamels, frits and<br />
lithium salts production. Lepidolite is used mainly in the glass pro- duction, amblygonite as raw material<br />
in lithium-chemicals.<br />
Lithium represents an excellent flux in glass batch, because it lowers viscosity and melting point,<br />
improves chemical resistivity, surface strength etc. Its main use is in the production <strong>of</strong> TV tubes and<br />
glass-ceramics and also in special whire ceramics and refractories. In the chemical industry, lithium<br />
compounds are used as special lubricants (greases in motor-cars, military), lithium hydroxide as an<br />
absorbent <strong>of</strong> carbon dioxide in submarines and spacecrafts, buthylene-lithium in the production <strong>of</strong><br />
synthetic rubber and polymers.<br />
Large quantities are used in aluminium and metal industry for the production <strong>of</strong> batteries in civil and<br />
military fields.<br />
Future applications include new technologies in glass products using minor amounts <strong>of</strong> 0.075 to 0.15%<br />
<strong>of</strong> Li2O, better quality glass <strong>of</strong> some borosilicate glasses, production <strong>of</strong> aluminium-lithium alloys for<br />
aerospace industry (1.5-3.0% <strong>of</strong> Li2O) and moilten carbonate fuel cells.<br />
Its main future use is envisaged in the atomic industry in thermo-nuclear reactors where lithium can<br />
serve as an atomic combustion and cooling agent.<br />
In thermonuclear reactors, the energy source will be a mixture <strong>of</strong> deuterium-tritium, part will be<br />
produced inside the reactor by the bombardment <strong>of</strong> isotope Li-6 by neutrons released during the<br />
reaction: see the equation - 6Li (n, alpha) T.<br />
Another future use is in batteries for the storage <strong>of</strong> electrical energy produced for example from solar<br />
energy or wind energy, which is very important for many developing countries. These batteries should<br />
serve also as a source <strong>of</strong> electricity in future automobiles.<br />
From these points, lithium resource may constitute, in the near future, a bigger source <strong>of</strong> energy than<br />
present solid and liquid fuels.<br />
In every country lithium resources require special attention and a careful evaluation <strong>of</strong> reverves. World<br />
production in 1973 was 6,400 t <strong>of</strong> contained lithium. In 1986 it increased to 8,400 t. Two major<br />
applications for lithium during these years concern additions <strong>of</strong> lithium carbonate to aluminium potlines<br />
and its use as a constituent in glass and ceramics.<br />
In <strong>Mozambique</strong>,three lithium-bearing minerals have been produced: lepidolite, amblygonite and<br />
petalite. All <strong>of</strong> these are pegmatite minerals, obtained generall as byproducts in columbo-tantalite<br />
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Cilek: 3.7. Lithium minerals<br />
mining. Lithium minerals are concentrated in zonal pegmatites in the lithium zone near the quartz core<br />
with albite, locally with spodumene and always with lepidolite (see Fig. 3.7.1.). In some pegmatites such<br />
as Marropino, another lithium zone has been developed with lepidolite-greisen <strong>of</strong> a small thickness.<br />
Lithium minerals are concentrated in peqmatites <strong>of</strong> the sodium-lithium type with beryl, columbotantalite,<br />
microlite and typically with tourmaline. The zones differ in thickness from 1 to 40 m.<br />
Fig. 3.7.1. Structural scheme <strong>of</strong> the zonal pegmatite <strong>of</strong> Zambezia (Barros-Vicente, 1963) (314 kB)<br />
Lepidolite is a typical mineral <strong>of</strong> sodium-pegmatites and, in <strong>Mozambique</strong>, it develops <strong>of</strong>ten in<br />
aggregates <strong>of</strong> columnar shape with a spherical top and a diameter about 15-20 cm. The spheroidal<br />
columns are usually 30-40 cm long with pink mica flakes on the surface, inside with massive radial<br />
aggregates. Besides in these typical columns, lepidolite is found in massive medium-grained layers<br />
commonly mixed with quartz. The columnar shape is characteristic <strong>of</strong> the lithium zone near the quartzcore,<br />
the massive form <strong>of</strong>ten <strong>of</strong> greisen zones. Owing to a deep weathering <strong>of</strong> pegmatites <strong>of</strong> Alto<br />
Ligonha area, the lepidolite in different aggregates is easily released from the kaolinitic groundmass.<br />
The colour <strong>of</strong> lepidolite is lilac or pink not depending on the lithium content but on the presence <strong>of</strong><br />
manganese and iron. The Li-content varies between 1.82 and 4.92% (Marropino). Generally, the content<br />
<strong>of</strong> lithium in Alto Ligonha area is lower than expected and this could be the result <strong>of</strong> a mining <strong>of</strong><br />
lepodolite with muscovite and quartz. In the past, a major portion <strong>of</strong> lepidolite was unsalable because <strong>of</strong><br />
its low Li-content.<br />
The content <strong>of</strong> rubidium in Alto Ligonha area is 0.23-0.35% Rb2O, that <strong>of</strong> cesium 0.78-1.68% Ce2O.<br />
Lepidolite is connected with the development <strong>of</strong> tourmalines <strong>of</strong> gem quality, with verdelite and rubelite.<br />
In addition, lepidolite is associated with microlite and with some radioactive minerals - mainly monazite<br />
or zircon as it is known from mines <strong>of</strong> Morrua, Muiane, Marige, Namivo and Ilovo.<br />
Cookeite is a product <strong>of</strong> alteration <strong>of</strong> spodumene and this lithium-mica occurs in the form <strong>of</strong> small<br />
aggregates at Muiane, Marige, Morrua and Marropino.<br />
Spodumene is found in all sodium-lithium pegmatites with lepidolite and albite usually in big massive<br />
forms, always altered and difficult to identify. Prismatic crystals occur together with albite and quartz in<br />
irregular bands in pegmatites <strong>of</strong> Morrua, Moneia, Muiane, Namivo, Nahora and Maipa. Some <strong>of</strong> these<br />
crystals are 5-50 cm long, 2-10 cm in diameter and fibrous. When altered, they are commonly <strong>of</strong> a<br />
reddish colour.<br />
In some mines such as Morrua, Marropino and Nahora, the gem variety <strong>of</strong> violet kunzite is extracted;<br />
hiddenite <strong>of</strong> yellow to greenish colour was mined at Namacotche, Munhamola I., Muiane and Nahora.<br />
Chemical analysis <strong>of</strong> spodumene (pegmatite Ilodo, Barros-Vicente 1963) in %<br />
SiO2 61.12<br />
Al2O3 + Fe2O3 30.00<br />
CaO 0.24<br />
MgO 0.07<br />
P2O5 tr.<br />
Li2O 5.0<br />
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Cilek: 3.7. Lithium minerals<br />
Petallite has been reported from the lithium-zone <strong>of</strong> a few pegmatite mines only: Morrua, Marropino,<br />
Ginamo, Nahora and Moneia. Usually, it is in close connection with lepidolite in those parts <strong>of</strong> the<br />
lithium-zone, in which spodumene is less developed.<br />
Eucryptite is a rare mineral usually in intergrowth with albite, and derived probably from spodumene. It<br />
was found at Morrua and Marropino.<br />
Amblygonite is common to the lithium-zone <strong>of</strong> many pegmatites such as Nanro Napa, Namacotche,<br />
Moneia, Nahora, Morrua, Marropino, Ginamo and Ilodo. It is present in blocks <strong>of</strong> different shape and<br />
small veins which cut accross the lepido- lite, its colour is white, sometimes greyish. Chemical analysispegmatite<br />
Nanro; Barros-Vicente 1963: %<br />
SiO2 1.00 Li2O 5.91<br />
P2O5 47.33 Na2O 1.39<br />
Al2O3 34.98 K2O 0.45<br />
Fe2O3 0.52 F 1.07<br />
CaO 0.48 L. i. 8.00<br />
101.13<br />
Pollucite is a cesium mineral, formula H2O • 2Cs20 • 2 Al2O3 • 9 SiO2. It is mentioned here because <strong>of</strong><br />
its intimate connection with petalite within the lithium zone <strong>of</strong> some pegmatites such as those from<br />
Namacotche, Nahora, Muiane, Moneia, Morrua and others.<br />
In <strong>Mozambique</strong> the production <strong>of</strong> lithium minerals started after World War 2. The first figures on<br />
production were given in 1949, about 510 t <strong>of</strong> Li-minerals, 1951 - 278 t, 1952 1,000 t, 1953 - 1,462 t,<br />
1956 - 1,002 t, 1959 - 90 t, 1963 - 104 t.<br />
Lepidolite was <strong>of</strong>ten <strong>of</strong> poor quality and some tonnages were not salable. According to Barros-Vicente<br />
(1963), the average composition is 4.15 % Li2O (3,9 - 4.92 %) and 0.99 % Fe2O3 (0.15-2.23 %).<br />
Lepidolite was exported from 1957 - 50 t with maximum <strong>of</strong> 274 t in 1962. At present Li minerals are<br />
stockpiled for a shortage <strong>of</strong> markets, - pollucite stockpile is about 55.9 t (P. Jourdan, 1986). Petallite was<br />
produced in small quantities (in 1956 - 25 t and amblygonite 35-40 t ?). From the port <strong>of</strong> Beira, petallite<br />
(minimum 3.8% Li2O), lepidolite (min. 7.5% Li2O), spodumene (3.8% Li2O) and ambligonite (min.<br />
7.5% Li2O) were exported (Barros-Vicente, 1963).<br />
Conclusions:<br />
Lithium minerals, despite <strong>of</strong> present lack <strong>of</strong> market, will become very important potential resources in<br />
the near future. A complex utilization <strong>of</strong> pegmatitic material could improve also the quality <strong>of</strong> each<br />
lithium mineral to a marketable product. With the development <strong>of</strong> glass, ceramic and alumina industry in<br />
<strong>Mozambique</strong> big internal market for lithium could be established.<br />
© Václav Cílek 1989<br />
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Cilek: 3.8. Magnesite<br />
3.8. Magnesite<br />
Magnesite, magnesium carbonate, MgCO3 (47.8% MgO, 52.2% CO2) is the end member <strong>of</strong> an<br />
isomorphous series <strong>of</strong> carbonates. The complete substitutional series extends up to siderite FeCO3 as a<br />
result <strong>of</strong> a substitution <strong>of</strong> ferrous iron by magnesium. Manganese, calcium, cobalt, Al2O3 and SiO2 may<br />
substitute magnesium or are common admixtures.<br />
Magnesite is the most important magnesium mineral. It occurs in two physical forms: cryptocrystalline<br />
or amorphous in dull white compact porcelain-like masses with a conchoidal fracture, and crystalline,<br />
which is s<strong>of</strong>ter <strong>of</strong> higher specific gravity, coarse, cleavable and marble-like masses.<br />
Magnesite is found as:<br />
1. infiltration deposits <strong>of</strong> amorphous magnesite originating from an alteration <strong>of</strong> magnesium-rich rocks<br />
such as serpentine, dunite, peridotite-by the action <strong>of</strong> waters carrying carbon dioxide<br />
2. hydrotermal deposits <strong>of</strong> amorphous magnesite in ultrabasic rocks due to the leaching <strong>of</strong> magnesium<br />
from serpentine by hydrothermal solutions<br />
3. replacement hydrothermal-metasomatic deposits <strong>of</strong> crystalline magnesite <strong>of</strong> dolomite, limestone,<br />
shales by magnesium-bearing solutions<br />
4. sedimentary deposits <strong>of</strong> massive magnesite developed in salt lakes, around hot springs and in lagoons;<br />
magnesite forms with high concentration <strong>of</strong> MgSO4 in an alkalic environment.<br />
Coarse, cleavable masses <strong>of</strong> magnesite are <strong>of</strong> metamorphic origin and commonly associated with talc,<br />
chlorite and mica schists. Two main commercial grades <strong>of</strong> magnesia are produced from crude<br />
magnesite: caustic magnesite clinker-calcined magnesia produced at 700-1,000°C from both crystalline<br />
and amorphous magnesite; deadburnt magnesia produced at 1,450 - 1,750°C from crystalline magnesite<br />
only. The latter is the main refractory grade with mineral periclase as main constituent, and other<br />
minerals such as forsterite, spinellides and monticellite. The higher the content <strong>of</strong> periclase, the higher<br />
the quality <strong>of</strong> the product.<br />
Magnesia - MgO produced from magnesite is inert and has a high melting point; therefore it is used as<br />
refractory in steel fournaces. Production increased substantially with an introduction <strong>of</strong> an oxygen<br />
furnace, which needs a basic-refractory lining such as magnesite. Other uses are in nonferrous metalprocessing<br />
units, cement kilns and sulphuric acid manufacture. About four fifhts <strong>of</strong> magnesite goes into<br />
the production <strong>of</strong> refractories. The remaining part is used in fertilizers, special oxychloride cement, as a<br />
source <strong>of</strong> carbon dioxide, production <strong>of</strong> magnesium compounds and magnesium metal, and in medicine.<br />
Two thirds <strong>of</strong> commercial supplies are derived from magnesite and, at present, an increasing volume is<br />
produced from seawater.<br />
The introduction <strong>of</strong> new refractory products based on magnesia and flake graphite (magnesia-carbon or<br />
mag-carbon refractories) changed the situation in the consumption <strong>of</strong> magnesite.<br />
Mag-carbon refractories originally developed for use in electric-arc steelmaking, are used in an<br />
increasing rate as linings in basic oxygen steel production. The use <strong>of</strong> deadburned magnesia requires a<br />
higher-quality material: over 97% MgO, low iron and boron content, lime and silica ratio 2:1, bulk<br />
density 3.4 g/cc or above, crystallite size over 100 microns. It means that supply is restricted to the<br />
seawater product and to a few top-quality magnesite deposits.<br />
Caustic grade magnesia <strong>of</strong> medium and lower grade is less used, and new methods <strong>of</strong> beneficiation <strong>of</strong><br />
natural magnesite have been developed.<br />
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Cilek: 3.8. Magnesite<br />
In <strong>Mozambique</strong>, the occurrence <strong>of</strong> magnesite is limited to a few localities (see Fig. 3.1.1), and these had<br />
not been investigated. Of these, the most important is situated at Monte Atchiza, a complex in the Tete<br />
Province just on the northern bank <strong>of</strong> the Cabora Bassa dam. The complex consists <strong>of</strong> basic and<br />
ultrabasic rocks within the drainage basin <strong>of</strong> the river Mecucoe. It intruded the fold belt <strong>of</strong> the Fingoe<br />
Group after the main deformation <strong>of</strong> the latter rocks. It itself has been intruded by Post-Fingoe granites.<br />
The complex was maped during the 1960ies by Real (1962) and, recently, by Hunting (1984). It consists<br />
<strong>of</strong> serpentinite, gabbro and norite with minor peridotite and pyroxenite.<br />
Real (1962) observed big, almost white, veins <strong>of</strong> magnesite within the black rocks <strong>of</strong> serpentinite. Some<br />
<strong>of</strong> these veins are 20 to 30 cm thick and traverse the basic rocks. Many concretions <strong>of</strong> magnesite could<br />
be found also in river alluvia. The presence <strong>of</strong> opal is typical <strong>of</strong> hydrothermal origin. Hunting reports<br />
magnesite float which is plentiful in the eluvium and colluvium overlying and surrounding the<br />
serpentinites. Bed rock occurrence found by Real does not appear to represent concentrations <strong>of</strong><br />
magnesite veins <strong>of</strong> any significance. According to the above description it could be concluded that<br />
amorphous magnesite originating from weathering and a hydrothermal alteration <strong>of</strong> serpentinites occurs<br />
in serpentinites <strong>of</strong> Monte Atchiza. The presence <strong>of</strong> CO2-containing water is possible, common are<br />
thermal waters on faults bordering the rift valley. The process could be explained as follows: H4 Mg3<br />
Si2 O9 + 2 H2O + 3 CO2 ===> 3 MgCO3 + 4 H2O + 2 SiO2 (opal, chalcedony, quartz).<br />
An extension <strong>of</strong> the Monte Atchiza massif into a combination with fault lines and thermal waters could<br />
be very favourable for the development <strong>of</strong> magnesite deposits. It should be noted that these deposits are<br />
developed to the maximum depth <strong>of</strong> about 200 m and the economic content <strong>of</strong> magnesite within the rock<br />
complex should be minimum 20%.<br />
The second site <strong>of</strong> occurrence <strong>of</strong> magnesite is connected with serpentinites and asbestos deposits. In<br />
Serra Mangota near Manica in an Archean greenstones-belt these are <strong>of</strong> a similar origin to those at<br />
Monte Atchiza. No details are available <strong>of</strong> this occurrence. A small deposit <strong>of</strong> magnesite was discovered<br />
by Gouveia (1967) in the Cabo Delgado Province near Pemba on Monte Namalasse. Here the ultrabasic<br />
rocks-dunites - are developed with fractures filled up by magnesite. On the surface the blocks <strong>of</strong> 20-50<br />
cm <strong>of</strong> white magnesite can be found. The magnesite again originated from ultrabasic rocks alteration<br />
with amorphous magnesite.<br />
Carvalho (1944) presents a description <strong>of</strong> magnesite occurrence near the railway at Chimoio in the<br />
Manica Province. The occurrence is supposed to be big (?) and the magnesite in the rock has a 92%<br />
purity. Analysis (in %):<br />
MgO 43.77 SiO2 1.78<br />
Fe2O3 + Al2O3 0.50 CO2 + H2O 51.03<br />
CaO 2.92<br />
Conclusions:<br />
In <strong>Mozambique</strong>, just deposits <strong>of</strong> the serpentine alteration type are developed. Their occurrence should<br />
have an economic importance, if the ultrabasic complexes were larger in extension, the grade <strong>of</strong><br />
amorphous magnesite high and the content <strong>of</strong> ore over 20%. From this point <strong>of</strong> view, the Atchiza<br />
complex is promising and should be explored. Otherwise, basic type refractories could be produced from<br />
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Cilek: 3.8. Magnesite<br />
serpentinites or dolomitic limestones <strong>of</strong> crystalline origin.<br />
The presence <strong>of</strong> flake graphite in large quantities, together with periclase materials may represent a basis<br />
for the production <strong>of</strong> magnesium-carbon refractories. Lower-grade refractories (up to 1,500°C), could be<br />
produced from available dolomitic or serpentinitic raw materials.<br />
© Václav Cílek 1989<br />
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Cilek: 3.9. Mica<br />
3.9. Mica<br />
Mica represents a group <strong>of</strong> minerals with common physical properties to those <strong>of</strong> muscovite, biotite, phlogopite, lepidolite and zinnwaldite.<br />
Micas are common rock-forming minerals, but muscovite and phlogopite only, due to their physical properties, and lepidolite and zinnwaldite,<br />
as a source <strong>of</strong> lithium, are economically important.<br />
Muscovite K Al2 (Al Si3 O10) (OH)2, specific gravity 2.77-2.88, is called common or white mica, monoclinic; it occurs in small flakes or<br />
foliated masses, or large hexagonal crystals known as "mica books" from pegmatites. Muscovite contains isomorphous admixtures <strong>of</strong> Fe3+ (up<br />
to 4%), Fe2+ (up to 1.2%), Mg, Na, Rb, Cs, Ba, Cr.<br />
Phlogopite K Mg3 (Al Si3 O10) (OH)2, specific gravity 2.76-2.90 known as bronze mica, is commonly found in hexagonal tapering elongated<br />
"mica books", usually in dolomite marbles. It contains iron, fluorine or manganese. If the ratio <strong>of</strong> Mg : Fe is less than 2 :1, it is called biotite.<br />
In the old days muscovite was used as window panes in Moscow, hence its name and exported from Russia to the West. Because it splits<br />
readilly into thin, flexible, but tough sheets, muscovite found its application in the electroinsulation industry. It is electricity resistant,<br />
mechanically, chemically and thermally stable. The colour is one <strong>of</strong> the main properties for grading: muscovite with tints <strong>of</strong> ruby is called ruby<br />
mica and is regarded as superior in respect to electrical properties, green mica as superior for optical uses.<br />
Muscovite is a primary constituent <strong>of</strong> acid igneous rocks such as granite or pegmatite, in a variety <strong>of</strong> metamorphosed rocks and in clastic<br />
sedimentary rocks. Much <strong>of</strong> the commercial muscovite comes from pegmatites as sheet mica or as a byproduct <strong>of</strong> feldspar mining or kaolin<br />
dressing. Sericite - a fine-grained muscovite is used as a cement - binding material. Phlogopite is regarded as inferior to muscovite, but is<br />
superior to muscovite in heat resistance (muscovite breaks up at 800°C, phlogopite at 1,000°C). It is associated with crystalline limestones or<br />
ultrabasic rocks.<br />
High-quality mica, known as sheet mica, is found in "books" in pegmatites and is mined and sorted by hand. After cleaning it <strong>of</strong> impurities<br />
such as quartz, feldspar, it is split into block mica <strong>of</strong> a minimum dimension <strong>of</strong> 4 cm2. Quality-sheet mica is divided into eight groups: above<br />
150 cm2 up to 4-6 cm2 with sheets <strong>of</strong> rectangle <strong>of</strong> sides 3 :1.<br />
The minimum content <strong>of</strong> mica in pegmatites is about 20 kg/m3, but high-quality mica containing 3-5 kg/m3 can be mined economically. A low<br />
content <strong>of</strong> mica is acceptable also when mica is a byproduct <strong>of</strong> feldspar or quartz mining.<br />
Sheet mica is usefull because <strong>of</strong> its electrical properties; during World War 2, became a strategic mineral for aircraft and tank engines<br />
production. It is used in condensers, as an insulating material, in furnaces windows, as a nonconducting element in electrical appliances, radio<br />
and TV, radar, fillers <strong>of</strong> plastics, in the paper industry, but also in the building industry as an admixture <strong>of</strong> plaster.<br />
About 10% <strong>of</strong> mined mica only can be used as sheet mica, therefore, the wastes <strong>of</strong> sheet mica are nowadays cemented together, layer by layer<br />
to form a "mica-sandwich" for use in electronics, substituting much <strong>of</strong> the sheet mica. Ground mica is processed waste mica both from sheet<br />
mica waste and flake mica from mining <strong>of</strong> pegmatite and kaolin as a byproduct. Mica is ground in a dry or wet process and used in plasterboard<br />
joint cement, as a dusting agent in ro<strong>of</strong>ing and <strong>of</strong>ten as lost-circulation material in drilling, and also in paint and rubber industry (less<br />
than 40 micron).<br />
Table 4. Mineralization <strong>of</strong> zonal pegmatites <strong>of</strong> Zambezia (Barros-Vicente, 1963) (588 kB)<br />
In <strong>Mozambique</strong>, mica mining is restricted to pegmatite mining. No other mica resources have been used as far. Scrap mica could be obtained<br />
as a byproduct <strong>of</strong> columbo-tantalite mining and mining for other economic minerals in pegmatites (see Fig. 3.6.1). Barros-Vicente (1963)<br />
published some information on the history <strong>of</strong> mica mining in the pegmatite district <strong>of</strong> Alto Ligonha. Around 1934, the interest in mica mining<br />
was started by Portuguese settlers; earlier, mica was extracted at Ribaue and at Naipa and Merrapane. During a search for other mica deposits,<br />
together with gold rush in this region, important localities <strong>of</strong> columbo-tantalite, beryl, topaz and semiprecious stones were discovered.<br />
Two grades <strong>of</strong> mica - black spotted and ruby, were exported from pegmatites <strong>of</strong> Zambezia. Later, also natural mica - scrap mica <strong>of</strong> a small size,<br />
has been produced. There were certain doubts expressed even by Barros-Vicente (1963) whether split - sheet mica <strong>of</strong> commercial size was<br />
produced in <strong>Mozambique</strong>, as this was common to the former British colonies in the neighbouring Zimbabwe and Tanzania. The production,<br />
according to these authors, was as follows:<br />
Year Production (kg) Export (kg)<br />
1956 12,164 233<br />
1957 30,170 1,711<br />
1958 2,074 50<br />
1959 5,518 2,470<br />
1960 1,051 1,297<br />
1961 1,522 1,528<br />
1962 551 -<br />
1963 - -<br />
Total 53,050 7,279kg<br />
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Cilek: 3.9. Mica<br />
The main producer <strong>of</strong> black-spotted mica was the Naipa mine, while Intocha (Intxotxa) produced the bulk <strong>of</strong> ruby mica. Only a small part <strong>of</strong><br />
mined mica was <strong>of</strong> commercial grade (10-15%), a major portion <strong>of</strong> mica was sold directly at the mining site to different foreign companies at a<br />
lower price. This trend in production <strong>of</strong> scrap mica continued even after independence, when annual production reached the peak <strong>of</strong> 300 t in<br />
1981.<br />
Mica in pegmatites is very common and abundant. In zoned pegmatites, it is concentrated mainly in the external zone, or near the quartz core<br />
(see Table 4.).<br />
Different types <strong>of</strong> mica are known to occur in pegmatites: muscovite, sericite, gilbertite, lepidolite, cookeite, biotite, vermiculite and<br />
phlogopite.<br />
Ruby mica <strong>of</strong> the Gile district is concentrated in pegmatites <strong>of</strong> Nahora, Intocha, Mocachaia and Namacala, while black-spotted mica occurs<br />
and is mined in the Alto Ligonha district mainly from pegmatites <strong>of</strong> Murropoce, Muchuloni, Nuaparra, Muiane and Naipa. More favourable for<br />
the development <strong>of</strong> mica are pegmatites either unzoned or <strong>of</strong> simple zonation, when compared with complicatelly zoned pegmatites <strong>of</strong> the<br />
columbo-tantalite and sodium-lithium type (muscovite <strong>of</strong> a larger dimension in "books"). Also pegmatites in mica-gneisses, with a welldeveloped<br />
marginal zone, and xenoliths <strong>of</strong> the surrounding rock, display better-developed mica crystals.<br />
In the past, mica was extracted either as a main - or a byproduct (the latter is more common) from these pegmatites:<br />
1. Alto Ligonha district:<br />
Naquissupa<br />
15°39' S mica with beryl<br />
38°21' E Ta-Nb<br />
Merrapane<br />
15°52' S ruby mica with beryl<br />
38°22' E Ta-Nb, Bi, cassiterite<br />
2. Gile district<br />
3. Ribaue district<br />
4. Mugeba district<br />
Murropoce<br />
Mucholoni<br />
Nuaparra<br />
Nahia<br />
Muiane<br />
Naipa<br />
Nahora<br />
Intocha<br />
Namacala<br />
Boa<br />
Esperanca<br />
Enluma<br />
Maria<br />
Muagotaia<br />
5. Mocuba district Munhida<br />
6. Alto Molocue district<br />
Namcotche<br />
Munhamola<br />
15°40' S<br />
30°05' E<br />
15°46' S<br />
38°03' E<br />
15°46' S<br />
38°28' E<br />
15°45' S<br />
38°15' E<br />
15°57' S<br />
38°19' E<br />
15°05' S<br />
38°19' E<br />
16°37' S<br />
37°18' E<br />
16°36' S<br />
37°23' E<br />
16°58' S<br />
36°55' E<br />
15°57' S<br />
37°55' E<br />
spotted mica with beryl, morganite,<br />
aquamarine, Bi, Ta-Nb<br />
scrap mica with beryl, rose qurtz,<br />
aquamarine, Ta-Nb, Bi<br />
mica with beryl, Ta-Nb, Bi, monazite<br />
mica with quartz, lepidolite, amblygonite,<br />
beryl, Ta-Nb, Bi, kaolin<br />
spotted mica<br />
ruby mica, exported block mica<br />
ruby mica (upto 30x50cm) with beryl,<br />
monazite, quartz, Ta-Nb, Bi<br />
scrap mica with feldspar, kaolin<br />
samarskite, zircon, beryl, monazite, Ta-Nb<br />
mica with beryl, Ta-Nb, Bi, monazite<br />
mica with beryl, Ta-Nb, Bi<br />
mica with beryl, Ta-Nb, Bi<br />
green splitting mica with beryl, polucite,<br />
microlite, tantalite, columbite,<br />
monazite, cassiterite, bismutite<br />
The pegmatites outside the Alto Ligonha distriuct s. l. are <strong>of</strong> less economic importance, the zonation is simple, pegmatites are less<br />
differentiated, a typical feature is the presence <strong>of</strong> rare earths. These pegmatites contain tourmalines, beryl, feldspars and mica as major<br />
constituents. Some contain radioactive minerals.<br />
These pegmatites are present in the Monapo structural unit, in the area <strong>of</strong> Nacala-Memba and around the Msauize basin, in the vicinity <strong>of</strong><br />
Metarica, in the area <strong>of</strong> Chimoio near Gondola and in many other places within the whole Mozambican belt, in sites with smaller and bigger<br />
occurence <strong>of</strong> pegmatites.<br />
In 1978, experts from the GDR-Dresden, investigated the mica occurrence in <strong>Mozambique</strong>.They visited several localities <strong>of</strong> previous mining:<br />
mines <strong>of</strong> Merrapane, Namacala and Intocha with ruby mica. A very important deposit <strong>of</strong> ruby mica was Merrapane from which big quantities<br />
<strong>of</strong> sheet mica were exported as block mica during the World War 2. The deposit Intocha was also in production till 1971 for splitting mica<br />
(about 950 t), later just scrap mica was exported from both mines to Great Britain and other countries as a source <strong>of</strong> mica powder. Although a<br />
grinding plant for the production <strong>of</strong> ground mica for oil-well boreholes had been projected, this plan was not realized.<br />
Four samples were investigated:<br />
No. 1607 - Nuaparra I, green muscovite, unsuitable as splitting and scrap mica<br />
No. 2302 - Namacotcha, green muscovite, to be used as splitting mica (sheet mica)<br />
No. 2401 - Munhamola, muscovite, suitable as sheet mica<br />
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Cilek: 3.9. Mica<br />
No. 2801 - Intocha, ruby mica, exported as block mica.<br />
Other pegmatite mines were also evaluated: Boa Esperance with muscovite unsuitable for sheet-and block mica, Muiane producing mica as a<br />
byproduct and useable as ground mica only, Naipa with impurities and unsuitable as block mica, and Murropoce with black-spotted mica.<br />
The results obtained from the samples:<br />
Desintegration:<br />
Sample No<br />
loss in<br />
calcination<br />
%<br />
yields<br />
%<br />
volume<br />
cm3<br />
thickness<br />
micron<br />
g/cm3<br />
force rupture<br />
kp/cm<br />
resist. to<br />
rupture<br />
kp/mm2<br />
Temperature <strong>of</strong><br />
calcination<br />
1607 2.57 68.8 35.0 53 1.16 0.315 0.167 796°C<br />
2302 2.05 83.6 33.0 44 1.39 0.244 0.119 824°C<br />
2401 3.26 81.9 31.0 42 1.44 0.255 0.112 776°C<br />
2801 2.22 90.9 33.5 41 1.48 0.726 0.302 900°C<br />
For the muscovite, the temperature <strong>of</strong> breakdown is between 600 and 800 °C; calcination starts at almost 800 °C and is effective at 900°C<br />
(Sample No. 2801). Loss <strong>of</strong> water is normal except for sample 2401. Sample 1607 from Nuaparra: mica <strong>of</strong> low quality demonstrated by a low<br />
yield, large volume, big thickness <strong>of</strong> the fine product and, therefore, small specific gravity.<br />
Samples 2302 and 2401 are almost identical, <strong>of</strong> good quality, but even here the yield is somewhat low. Sample 2801 from Intocha is the best,<br />
with good resistivity to rupture and good material recovery. This mica ranged in grade from "fair stained" to "spotted", but has traces <strong>of</strong><br />
impurities represented by ilmenite, hematite and magnetite. It can be used as sheet mica up to sheet size <strong>of</strong> 5 to 20 cm2.<br />
The green mica from Nuaparra is suitable as scrap mica only in the production <strong>of</strong> mica paper.<br />
Green micas from Namacotcha and Munhamola can partly be used as sheet mica, while ruby mica from Intocha is suitable both for splitting<br />
and electroinsulation purposes.<br />
The only approved reserves <strong>of</strong> mica in <strong>Mozambique</strong> are those from the mine Muiane. Thieke (1980) calculated 72,000 t <strong>of</strong> mica reserves<br />
(content 1.1% in kaolinized pegmatite in a fraction above 6.35 mm), but no qualitative tests were made. Previous results <strong>of</strong> GDR experts<br />
(1978) indicated that this mica is suitable as ground mica (oil-wells, filler?).<br />
In 1986, Duda et al. described the Nuaparra pegmatite deposit. The exploration was aimed at an evaluation <strong>of</strong> feldspar reserves, but some data<br />
on mica properties were also gained. It is necessary to stress, that this deposit, besides some semiprecious stones and a small amount <strong>of</strong> Ta-Nb<br />
and Bi, served as a source <strong>of</strong> mica. This mica was exported as natural mica without beneficiation.<br />
According to Duda (1986), the muscovite <strong>of</strong> Nuaparra is developed in two types:<br />
1) in the zone <strong>of</strong> quartz-muscovite with mica in books and<br />
2) in the middle zone with big microcline.<br />
Spectral analyses Content <strong>of</strong> elements in descending order<br />
1. muscovite Si, Al K, Fe Li, Mg, Mn Ba, B, Cr, Ga, Nb, Pb Ag, Cu<br />
Ca, Bi Na, Ti, Be Sb, Sc, Sn, Sr, W, Zr Mo, Ni, V, Y<br />
2. muscovite Si, Al K, Fe Li, Mg, Mn B, Ba, Be, Ga, Nb, Sn Ag, Cu<br />
Ca Na, Ti, Bi Sr, W, Zn, Zr Mo, Ni, Pb, Cr, V<br />
In both cases, the muscovite is <strong>of</strong> normal composition with a low content <strong>of</strong> lithium but an increased content <strong>of</strong> Be, Ti, Sn, Ga. Quite new is<br />
the determination <strong>of</strong> Bi, Nb, Zr, Mo, Ni.<br />
Conclusion:<br />
The estimated reserves <strong>of</strong> mica in <strong>Mozambique</strong> are 72 kt. Reserves from the pegmatite mine Muiane represent a byproduct <strong>of</strong> columbotantalite<br />
mining mixed with kaolin, feldspar and quartz. The quality <strong>of</strong> mica is low and is suitable for the production <strong>of</strong> ground mica only.<br />
<strong>Mozambique</strong> has an old history <strong>of</strong> mica mining in pegmatites, some deposits have been supplying high quality ruby mica, some scrap mica,<br />
but better commercial grades <strong>of</strong> sheet mica were never produced. Local manpower was used for the extraction, but skilled manpower necessary<br />
for the splitting and cutting was not introduced. Two ways exist to develop huge mica resources in <strong>Mozambique</strong>:<br />
1. special mining for mica on less zonal or unzonal pegmatites<br />
2. to utilize mica byproducts in an mining <strong>of</strong> other minerals and produce scrap and ground mica.<br />
The emphasis should be put on high-quality scrap mica-mica without impurities - in small flakes and for different industrial branches.<br />
Substantial reserves exist already in the present pegmatite mines.<br />
© Václav Cílek 1989<br />
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Cilek: 4.1. Bauxite and aluminum laterite<br />
4. DEPOSITS OF INDUSTRIAL ROCKS<br />
4.1. Bauxite and aluminium laterite<br />
Bauxite is a group name for a mixture <strong>of</strong> hydrous aluminium oxides composed mainly <strong>of</strong> trihydrate gibbsite Al(OH)3<br />
with 65.35% Al2O3 and 34.65% H2O, and monohydrates AlO(OH) diaspore with 85% Al2O3 and 15% H2O and<br />
boehmite with 84.97% Al2O3 and 15.03% H2O and finally <strong>of</strong> amorphous cliachite Al2O3 • n H2O. Bauxite is a rock<br />
name and also a commercial name commonly applied to aluminum ore.<br />
Bauxite is generally the endproduct <strong>of</strong> a complicated alteration process <strong>of</strong> aluminium-rich rocks undergoing several<br />
stages <strong>of</strong> weathering which include:<br />
a) kaolinization in which aluminium-silicate minerals <strong>of</strong> the parent rocks (plagioclase feldspar is probably the best<br />
altered mineral) are transferred to hydrated silicates <strong>of</strong> alumina, or kaolinite minerals<br />
b) lateritization - laterite and aluminum laterite is a mixture <strong>of</strong> hydroxides <strong>of</strong> iron and alumina and other residual<br />
materials such as alkalies, lime, titania, magnesia and silica. Aluminum laterite is the endproduct towards the last stage<br />
<strong>of</strong><br />
c) bauxitization with prevailing hydrated aluminum oxides, some iron oxides and impuri- ties including remaining silica.<br />
In nature, these three-stage products and zones are not allways developed. Bauxite can rest directly on the parent rock,<br />
the process can stop at the kaolin zone, the kaolin zone with bauxite zone only is developed or, and this is true in most<br />
cases, aluminum laterite is the end product.<br />
Bauxite development requires certain chemical, physical and geological conditions:<br />
* tropical climate above 20°C<br />
* alternating wet and dry seasons<br />
* high-porosity rock with high alumina content<br />
* vegetation cover with bacterial activity<br />
* low topographical relief on higher ground<br />
* long periods <strong>of</strong> stability and weathering.<br />
Under these conditions, the chemical leaching is possible, silica is removed and alumina oxides and iron are<br />
concentrated. The movement <strong>of</strong> the water table and porosity <strong>of</strong> parent rocks make it easier. The result is a bauxite<br />
residual deposit. From there eluvial and detrital bauxite deposits are derived. Main genetical types <strong>of</strong> bauxite and Allaterites<br />
deposits:<br />
a) "terra rossa" or limestone bauxite, also called karst bauxite<br />
b) lateritic or silicate bauxite, Al-laterites.<br />
Karst bauxite deposits occur in sinkholes <strong>of</strong> a recent surface or a fossil surface. Some <strong>of</strong> these can be folded and<br />
disrupted tectonically. These deposits cannot be regarded as a limestone weathering residue, because some deposits are<br />
<strong>of</strong> the thick blanket-type and, therefore, rewashed or entrapped Al-laterites had to undergone further desilification in an<br />
alkaline environment. Evidence <strong>of</strong> postdepositional changes is a sharp boundary between different bauxite facies. Allaterites<br />
can develop on different parent rocks, from sedimentary to metamorphic ones, and, therefore, the resulting<br />
lateritic bauxite is extremely variable. The best deposits developed by lateritization <strong>of</strong> high alumina and low silica and<br />
iron are leucocratic rocks as for example syenites and anorthosites. The quality <strong>of</strong> the bauxitic horizon can be improved<br />
by organic substances made available from an overlying peat horizon, to increase deferrization. On the surface <strong>of</strong> the<br />
pr<strong>of</strong>ile, a hard iron-rich zone - hardpan develops, followed by a spotted horizon underlain by a kaolin zone.<br />
Resulting from a destruction <strong>of</strong> lateritic or bauxitic pr<strong>of</strong>iles, rewashed deposits originate-conglomerate and slope<br />
deposits, deposits transported over short distances and deposits in sedimentary formations either as fillings <strong>of</strong> valley and<br />
other depressions, or stratiform deposits.<br />
Bauxites and lateritic bauxites contain several admixtures: kaolinite, chlorite, illite, quartz, <strong>of</strong>ten a substantial amount <strong>of</strong><br />
titanium minerals, iron oxides, rare-earths, uranium and thorium and some metals. When metamorphosed they give rise<br />
to deposits <strong>of</strong> the sillimanite-group minerals, corundum and emery. About 95% <strong>of</strong> all mined bauxite is used in the Bayer<br />
process to produce alumina and from this about 90% is then used in metal production. The Bayer process consists <strong>of</strong> a<br />
conversion <strong>of</strong> bauxite to soluble sodium aluminate by mixing it with soda, the insoluble SiO2, TiO2, and Fe2O3 are then<br />
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removed. Alumina trihydrate, after calcination, is prepared for an electrolytic production <strong>of</strong> Al-metal. The requirements<br />
for the quality <strong>of</strong> bauxite is minimally 40% Al2O3, maximally SiO2 5%.<br />
For low-grade bauxite ore the sintering process (LSS method) is used. The use <strong>of</strong> different processes depends directly on<br />
moduli Al2O3/SiO2 and the content <strong>of</strong> calcium (see following table):<br />
Technology Al2O3 % modulus Al2O3/SiO2 CaO %<br />
Bayer - high grade minimum 40 minimum 10 maximum 3<br />
Bayer minimum 40 - maximum 3<br />
LSS - high grade - minimum 10 over 3<br />
LSS - minimum 3 -<br />
Bauxite for nonmetallic uses, when calcined or fused, requires a specific composition: Al2O3 above 58%, less than 2%<br />
Fe2O3, maximum 5% SiO2, 3% TiO2, and 0.2% Na2O + K2O.<br />
This material is used in a production <strong>of</strong> calcined ware with a mixture <strong>of</strong> mullite and corundum (Al2O3 is 80-90%) or<br />
after heating, to produce fused alumina-pure corundum with almost 100% Al2O3. Refractory bricks, crucibles and<br />
cement are produced for blast furnaces and cement killns. Futher uses are abrasives in grinding wheels and cements.<br />
In chemical industry, the bauxite composition required is this: 56-60% Al2O3, 4-9% SiO2, up to 3.5% TiO2, 3% Fe2O3.<br />
Bauxite is also used as an admixture in special cement production. The byproducts <strong>of</strong> aluminium are cast iron, Fe2O3, V,<br />
Cr, Ga recovery, red-mud for manufacturing <strong>of</strong> cement and pigments and titanium recovery.<br />
Owing to a scarcity <strong>of</strong> high-quality bauxite several countries started to use subtitute-raw materials, such as kaolinic or<br />
illitic shales, kaolinic clays, nepheline syenites, alunite, anorthosite etc. The Al2O3 content <strong>of</strong> these materials is 20 to<br />
30%. During World War 2, kaolinic clays for alumina production were used in Japan, Germany, Poland; the nepheline<br />
syenite is still used in Soviet Union, with cement as a byproduct.<br />
In <strong>Mozambique</strong>, the development <strong>of</strong> bauxite and Al-laterites is known to occur in a few localities only and, in fact, all<br />
these are situated in high attitudes (over 1,600 m above sea level), and originated by an alteration <strong>of</strong> alkaline rocks (see<br />
Fig. 4.1.1).<br />
Fig. 4.1.1. Occurences <strong>of</strong> bauxite and aluminium laterite; bentonite, perlite. (380 kB)<br />
The only deposit in production is Serra de Moriangane, also known as Alumen or Monte Snuta in the Province Manica<br />
just on the Zimbabwean border. It was discovered in 1911.<br />
Other areas with some bauxite occurence are:<br />
Monte Salambidua and others in the Province Tete,<br />
Monte Mauzo and others in the Province Zambezia.<br />
The deposit Alumen was the property <strong>of</strong> the former Rhodesian company Wankie Collieries (from 1935) and was and is<br />
still mined by John Meikles Co. The production started in 1938 with 382 t, 1940 - 180 t and, during the period 1940-<br />
1950, total production was 5,799 t used in refractory bricks and 21,408 t in the production <strong>of</strong> alumina sulphate by<br />
African Explosives Co. Later, the production stabilized on 4,000 t/year and continued with about 2,000 t/year up to the<br />
present.<br />
Three claims are situated just ENE from the border. In Zimbabwe the bauxite is <strong>of</strong> low quality (about 40% Al2O3) and<br />
also in the E part which was explored by "Companhia de <strong>Mozambique</strong>" it is <strong>of</strong> a lower quality with a high content <strong>of</strong><br />
SiO2 (15-46%) and a low content <strong>of</strong> Al2O3 (40-45%). The Alumen claims produced bauxite with SiO2 - 11-12%,<br />
Al2O3 - 58-60% and Fe2O3 - 2.0% (1940-1950).<br />
Analyses <strong>of</strong> selected samples (in %)-Borges (1950):<br />
1940 - production 1,030 t 1941 - production 1,351 t<br />
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humidity 0.68 1.13 0.57 0.073 0.6 0.7 0.87 0.63<br />
SiO2 5.86 10.61 7.86 8.54 10.68 9.52 - -<br />
Al2O3 64.91 64.56 60.32 60.86 59.85 60.81 62.98 59.16<br />
Fe 1.09 1.19 1.11 1.21 0.83 0.78 0.78 0.81<br />
insolubles 8.15 13.15 17.66 16.32 - - - -<br />
Quality <strong>of</strong> mined bauxite and gibbsite in 1961 was as follows: %<br />
Bauxite Gibbsite<br />
Al2O3 62.36 58.08<br />
SiO2 3.14 12.62<br />
Fe2O3 2.18 1.82<br />
H2O 30.53 26.29<br />
The Alumen deposit represents an alteration zone <strong>of</strong> about 1 m thick, with bauxite containing nodules <strong>of</strong> gibbsite and<br />
overlaid by a kaolinitic horizon. The mined zone is very irregular, bauxite developed in lenses or pockets with an<br />
irregular thickness <strong>of</strong> overburden. Bauxite originated from an alteration <strong>of</strong> hornblende syenite which follows a narrow<br />
zone <strong>of</strong> contact betwen gabbroic and gneissic rocks.<br />
Reserves (Real, 1963) are small: 85-115,000 t <strong>of</strong> bauxite, 3,000 t <strong>of</strong> gibbsite nodules and 600,000 t kaolin, which<br />
represents the waste.<br />
A low content <strong>of</strong> iron oxides enables a utilization <strong>of</strong> bauxite as refractory and chemical materials, the high silica content<br />
(over 5%) is unfavourable for metal production.<br />
The deposit is small but has established the local market. In the vicinity, new exploration started with the aim to increase<br />
the reserves. P. Knup gave this description <strong>of</strong> the area:<br />
"The bauxite ore bodies occur in the N part <strong>of</strong> the lower Precambrian Odzi-Umtali greenstone belt, close to a contact<br />
with the Zimbabwean granite-gneiss complex. N <strong>of</strong> the deposits is an outcrop <strong>of</strong> granite-gneisses and talc-schists. SW <strong>of</strong><br />
these, chlorite-schists and felsites were observed. The ore bodies themselves overlie mainly intrusive rocks <strong>of</strong> saturated<br />
to undersaturated composition such as a gabbro-anorthosite rock sequence, diorites and mafic volcanic rocks. The rock<br />
units are folded and regionally epimetamorphosed. Their dips attain 50° to 60°, and they strike in E-NE direction.<br />
Moderate faulting with relatively small displacements occurs in some places (Fig. 4.1.2).<br />
Fig 4.1.2. Area <strong>of</strong> Alumen bauxite mine (Knup, 1987) (385 kB)<br />
The deposits are residual. They occupy predominantly an E- directed escarpment <strong>of</strong> the watershed where precipitation is<br />
much higher than on the W slopes. Deep bauxitization by weathering and leaching developed on slightly inclined,<br />
plateau-shaped, old erosion surfaces which are mostly SE oriented.<br />
Subsequently, the surfaces became dissected into stream valleys causing erosion along their courses in incised river beds<br />
and on the slopes. Therefore, just remnants <strong>of</strong> different sizes representing the once coherent plateau, are now present and<br />
contain ore bodies. These are rare in altitudes below 1,500 m.<br />
Four main ore types exist:<br />
A. White saprolitic bauxite. It is friable, texturally light and porous, and <strong>of</strong>ten retains characteristics <strong>of</strong> the primary<br />
parent rock, notably joints.<br />
B. Light brown saprolitic bauxite <strong>of</strong> similar physical nature to A.<br />
C. Brown, ferruginous, saprolitic bauxite. It is mainly fine-textured, friable and rich in iron.<br />
D. White kaolinitic clay with concretionary, white bauxite. The contents <strong>of</strong> gibbsite nodules are very variable and so are<br />
their sizes and shapes. Diameters from 1 to tens <strong>of</strong> cm are observable. Both silex and anothosite nodules are, however,<br />
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Cilek: 4.1. Bauxite and aluminum laterite<br />
also present. The clay is sticky when wet, and, on the other hand, extremely fine and friable when dry.<br />
There is a conspicuous relationship between bauxite and the parent rock. White bauxites - types A and D - derived from<br />
anorthosites, light brown bauxite - type B - derived from diorites and intermediate <strong>of</strong> the gabbro-anorthosite series, and<br />
ferruginous bauxite type C-derived from gabbros and basic volcanic rocks. The variety <strong>of</strong> source rocks, and their<br />
complex interrelationship contributed greatly to a considerable degree <strong>of</strong> ore grade variation over even very short<br />
distances. They are also responsible, together with erosion, for the lens-shaped nature and restricted size <strong>of</strong> the bauxite<br />
ore bodies. These vary in lengths from 100 to a maximum <strong>of</strong> 500 m, in width from 25 to 150 m. Their thickness varies<br />
from a few metres to over 20 metres in some places. Since intensity <strong>of</strong> weathering and leaching differ locally, the depth<br />
<strong>of</strong> the unaltered bedrock are irregular and <strong>of</strong>ten unpredictable.<br />
For practical purposes, both white-ore types A and D are regarded as first quality, high grade ore. Type B is regarded as<br />
second quality bauxite, whereas type C as third quality (Al2O3 < 45%), and deemed to be waste. White kaolinitic clay,<br />
having been liberated from gibbsite nodules by wet screening and /or scrubbing must be considered to be another raw<br />
material usable, for instance, in the building industry. At present, however, it is dumped. Reserve estimates for ore types<br />
A, B and D, and kaolinitic clay in the Alumen Mine and Morondo areas range between 3 and 5 million tons.<br />
Analytical results <strong>of</strong> representative ore type samples:<br />
Location<br />
Ore type (%)<br />
Quarry 3<br />
A<br />
P 39/2-3<br />
Quarry 10<br />
B<br />
P 81/0-1<br />
Quarry 8<br />
C<br />
P 32/3-4<br />
Quarry 7<br />
D<br />
F 21/7-8<br />
Quarry 7<br />
Kaolinitic<br />
Clay<br />
Al2O3 58.83 49.65 44.01 57.16 39.60<br />
Fe2O3 1.55 13.81 17.78 0.64 0.91<br />
TiO2 0.27 0.84 3.07 0.00 0.01<br />
SiO2 9.00 9.19 9.92 16.92 43.90<br />
L. i. 28.62 23.96 24.12 24.05 15.00<br />
Na2O 0.04 0.04 0.07 0.11 0.09<br />
K2O 1.65 1.20 0.10 0.58 0.19<br />
CaO 0.02 0.08 0.00 0.03 0.00<br />
MgO 0.27 0.09 0.00 0.00 0.00<br />
P2O5 0.01 0.04 0.21 0.02 0.00<br />
MnO 0.06 0.03 0.07 0.06 0.02<br />
Total 99.92 98.93 99.36 99.57 99.72<br />
In the past (Real, 1963) several other areas were checked in the vicinity <strong>of</strong> Serra Moriangane:<br />
Rio Inhamucarara<br />
Monte Vumba<br />
Chimanimani - Rotanda<br />
Around the tributaries <strong>of</strong> the Rio Inhamucara, an alteration <strong>of</strong> granite-gneiss occurred, with the development <strong>of</strong> 0.4-1.4 m<br />
thick horizon <strong>of</strong> kaolin and bauxite with about 0.3 m <strong>of</strong> gibbsite. The silicate bauxite contains Al2O3 54%, SiO2 10%<br />
and Fe2O3 5.6%. On the Vumba mountain, well-known in <strong>Mozambique</strong> for its popular mineral water, just a small<br />
kaolinized zone was discovered on the contact between gabbro and granite.<br />
In the Chimanimani area a few zones with kaolin-bauxite are connected with intrusive dolerite dykes.<br />
Other small areas are Serra Zuira with laterites (41.70% Al2O3, 10.60% SiO2, 21.56% Fe2O3) and E <strong>of</strong> Alumen claims,<br />
within the Serra Moriangane (1,823 m) there is a lateritic crust and bauxite. Real (1963) analysed one trench with this<br />
pr<strong>of</strong>ile (in %):<br />
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Depth SiO2 Fe2O3 Al2O3<br />
1.8m 6.04 24.53 49.93<br />
2.3m 17.84 3.19 54.95<br />
2.8m 17.78 1.98 58.40<br />
3.0m 17.68 1.21 52.11<br />
Judging from these observations bauxite horizons may have developed in several places under mountainous conditions,<br />
if suitable parent rocks were present. Generally speaking, deposits in this area will be inextensive and variable in quality.<br />
Most <strong>of</strong> these may be as inaccessible as the deposit Alumen, accessible just from the Zimbabwean side only.<br />
Within the Tete Province, several localities with a possible bauxite occurences had been explored in the past (Real,<br />
1963) and during 1980-81 (Samokhvalov, 1981). They found just laterites with an increased quartz content and an<br />
insignificant alumina content (localities near Zobue, Vila Coutinho).<br />
The most prominent syenite intrusions <strong>of</strong> the region are Salambidua NE <strong>of</strong> Tete on the Malawian border, and Cheneca<br />
composed <strong>of</strong> three massif: Domue, Cheneca and Macangue, NE <strong>of</strong> Furancungo on the Malawian border. Here the<br />
margins consist <strong>of</strong> gneisses and migmatites, but the central part <strong>of</strong> syenites with hornblende. The top levels are about<br />
1,300-1,400 m high surrounded by sharp slopes. There are two types <strong>of</strong> weathering zones: clayey sand zone 2 m thick N<br />
<strong>of</strong> Domue and in the border zone, and a zone <strong>of</strong> kaolinitic-clays reddish, 4.5 m thick, with about 15-20% <strong>of</strong> quartz, in S<br />
and SE part <strong>of</strong> the massif. Bauxite was not discovered.<br />
The Lupata massif <strong>of</strong> Cretaceous age developed as a brachysynclinal closure <strong>of</strong> the Mid-Zambeze basin was also<br />
examined. Trachytes, phonolites and amygdoidal effusives are covered with a weathering zone <strong>of</strong> thickness 1.5 m<br />
without laterite.<br />
In the Province Zambezia, several localities were checked, but only two <strong>of</strong> these Mauzo and probably Milange, have<br />
better conditions for the development <strong>of</strong> bauxite horizon, but certainly not <strong>of</strong> significant economic value. The exploration<br />
work provided some valuable data on the development <strong>of</strong> weathering pr<strong>of</strong>iles - mainly lateritic - on different parent rocks<br />
and on different elevation levels and is worth to be included here (Samokhvalov et al., 1981). The best known locality is<br />
Mauzo. It is situated 40 km N <strong>of</strong> the town <strong>of</strong> Milange on the Malawian border. The mountain is composed <strong>of</strong> nepheline<br />
syenites which are <strong>of</strong> an intermediate composition between foiatites and luiavrites with pyroxene. The main components<br />
are: orthoclase-perthite, nepheline, heguirine, heguirine-augite. Accessory components are: hornblende, biotite, albite<br />
and sodalite. The height <strong>of</strong> Mauzo is 1,472 m and the elevation above the surrounding plain composed <strong>of</strong> biotiteplagioclase<br />
gneisses is about 800 m. The top <strong>of</strong> the mountain is flat, more than 2 km long and more than half a km wide,<br />
at level 1,400-1,472 m. About 30% <strong>of</strong> the plain is occupied by outcrops <strong>of</strong> syenite or by rock debris. The rest is a lateritic<br />
cover, eroded in many places, because it lacks a superficial hard ferruginous horizon.<br />
In 1963, Real described this locality and analyzed rocks and bauxite. According to him, the parent rock is nepheline<br />
syenite with aegirine-augite (foiatite) <strong>of</strong> this composition (in %):<br />
SiO2 55.28 CaO 3.78 TiO2 0.69<br />
Al2O3 20.77 Na2O 7.69 P2O5 0.20<br />
Fe2O3 2.22 K2O 7.38 MnO 0.11<br />
FeO 1.45 H2O+ 0.33<br />
MgO 0.29 H2O- 0.25<br />
Real also described the weathering pr<strong>of</strong>ile:<br />
0.15-0.20 m -horizon <strong>of</strong> black soil with gibbsite nodules<br />
1.40 m - blocks <strong>of</strong> kaolinized syenites<br />
1.0 m - blocks <strong>of</strong> yellowish bauxite<br />
At the depth <strong>of</strong> 1.6 m, he analyzed a sample <strong>of</strong> bauxite (in %):<br />
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H2O 0.68 Fe2O3 7.59 TiO2 1.23<br />
SiO2 4.21 P2O5 0.34 K2O 0.17<br />
Al2O3 56.94 MgO 0.78<br />
Thus, the presence <strong>of</strong> bauxite with gibbsite was confirmed and futher explored in 1967.<br />
From trenches made at that time channel samples (1980) were taken by a Russian team. Established pr<strong>of</strong>ile:<br />
0.25 m - soil with humus<br />
1.20 m - clay yellowish - reddish with concentrations <strong>of</strong> gibbsite or kaolinized syenites<br />
2.25 m - clay yellowish - reddish with gibbsite,syenites nepheline highly weathered<br />
Five selected samples some <strong>of</strong> good quality <strong>of</strong> Mauzo correspond to the composition <strong>of</strong> bauxite (in %):<br />
Sample Al2O3 SiO2 Fe2O3 TiO2 L. i. Total gibbsite kaolin<br />
Ma - 1 (4.5 m) 50.31 20.28 4.65 1.04 24.00 100.28 63.74 22.19<br />
Ma - 3 (1.5 m) 47.82 14.93 7.58 1.34 28.58 100.25 66.06 13.59<br />
Ma - 5 (2.5 m) 37.82 44.80 7.70 0.68 20.10 100.50 14.60 72.68<br />
Ma - 6 (0.4 m) 44.46 23.08 6.69 0.86 24.88 99.97 40.90 45.56<br />
Ma - 6 (3.0 m) 60.40 1.23 5.99 0.73 32.07 100.42 91.15 2.08<br />
Complete chemical analyses showing a similar composition (USSR, 1981): %<br />
Sample SiO2<br />
quartz<br />
SiO2<br />
bound<br />
Al2O3 Fe2O3 FeO TiO2 CaO MgO P2O5 K2O Na2O SO3 H2O CO2<br />
P-71-1 40.07 0.28 36.06 5.35 0.53 1.03 0.45 0.05 0.117 0.86 0.05 0.09 1.12 0.05<br />
P-71-2 44.01 1.00 34.89 4.85 0.27 0.91 0.38 0.41 0.043 3.09 0.13 0.04 1.13 0.05<br />
P-71-3 32.66 0.12 39.73 6.72 0.72 1.29 0.51 0.05 0.237 0.21 0.05 0.11 0.89 0.06<br />
These analyses <strong>of</strong> channel samples indicate the presence <strong>of</strong> Al-laterites. The higher content <strong>of</strong> alumina and a low content<br />
<strong>of</strong> silica in previous research work was probably due to the selected material. A detailed exploration <strong>of</strong> Monte Mauzo,<br />
may disclose small reserves <strong>of</strong> bauxite, say in the order <strong>of</strong> 150-200,000 t with Al content 43-50% with silica modulus 2-<br />
3, but hardly an economic deposit.<br />
S <strong>of</strong> Monte Mauzo are the Milange Mts. consisting <strong>of</strong> Serra de Tumbine (1,524 m) and Monte Tundo (1,274m).<br />
The Tumbine massif is composed in its central part, <strong>of</strong> nepheline syenites (aegirine-biotite), in NE-part <strong>of</strong> leucocratic<br />
syenites, on the margins <strong>of</strong> quartzitic syenites. The intrusion is surrounded by different gneisses. The top is flat over a<br />
small part only and therefore the development <strong>of</strong> a weathering pr<strong>of</strong>ile is difficult to assess. Tumbine is a continuation and<br />
a small extension <strong>of</strong> the big massif Milange, which is situated mainly in Malawi with the well-known "planalto" <strong>of</strong><br />
Lichineya with Al-laterite. The deposit was discovered in 1924 by Dixley and explored in 1939 confirming 60 million t<br />
<strong>of</strong> Al-laterite <strong>of</strong> this average composition: Al2O3 - 42.73%, SiO2 (quartz) - 15.65%, SiO2 (bound) - 2.22%, Fe2O3 -<br />
13.93%, TiO2 - 1,57% and loss <strong>of</strong> ignition 23.46%. This discovery was the main reason for starting exploration work at<br />
Tumbine. According to the first results only the content <strong>of</strong> alumina reached seldom 40%, with a high content <strong>of</strong> silica 20<br />
- 40%. Samokhvalov (1981) and his group made several pits to a depth <strong>of</strong> 8 m and discovered that the lateritic pr<strong>of</strong>ile is<br />
mainly kaolinitic. Gibbsite was developed just locally and usually below 20%, maximum value 26%. These laterites are<br />
<strong>of</strong> no economic interest.<br />
Some analyses <strong>of</strong> laterite Tumbine (USSR, 1981) (in %):<br />
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Sample Al2O3 SiO2 Fe2O3 FeO TiO2 L.i. Gibbsite Kaolin<br />
T-3 (0,46 m) 36.92 33.09 8.88 - 1.22 18.91 25.99 51.12<br />
T-3 (4,00 m) 32.87 41.68 1.67 - 0.56 16.07 23.17 45.55<br />
T-17 (1,10 m) 39.49 39.26 4.86 - 0.89 15.60 10.26 84.27<br />
T-17 (3,10 m) 35.10 46.96 4.41 - 0.48 12.48 18.05 59.90<br />
P-2 (0,10-2,00 m) 37.10 33.40 8.90 0.29 - 20.60 - -<br />
P-2 (0,10-2,00 m) 37.38 33.68 8.80 0.63 1.95 16.42 13.69 72.00<br />
P-4 (0,50-3,00 m) 30.80 33.70 9.20 0.65 - 16.10 - -<br />
A complete analysis (USSR, 1981) Tumbine (in %):<br />
Sample<br />
SiO2<br />
quartz<br />
SiO2<br />
bound<br />
Al2O3 Fe2O3 FeO TiO2 CaO MgO<br />
P-3 (1,5-3,2 m) 45.45 0.32 27.47 7.19 1.17 0.82 0.58 0.32<br />
P-3 (3,25 m) 52.00 0.44 21.53 6.77 2.06 1.01 0.67 0.64<br />
Sample<br />
P2O5 K2O Na2O SO3 L.i. H2O CO2<br />
P-3 (1,5-3,2 m) 0.149 5.13 1.62 0.05 9.70 0.69 0.05<br />
P-3 (3,25 m) 0.167 6.38 3.39 0.03 5.37 0.45 0.17<br />
The results <strong>of</strong> these analyses suggest a laterite-kaolin composition. The upper part <strong>of</strong> the pr<strong>of</strong>ile with gibbsite and a<br />
hardpan-ferruginous crust had probably been removed by erosion.<br />
In other nepheline syenites areas two localities only were checked: Monte Derre in Serra Chiperone and Serra<br />
Morrumbala in the S near the river Zambezi. In both cases, only kaolinitic pr<strong>of</strong>iles with laterites were found.<br />
The following analyses (Afonso-Pinto, 1967) show this composition (in %):<br />
Sample L.i. Al2O3 SiO2 Fe2O3 TiO2 Gibbsite etc.<br />
Monte Derre 107/SP (1,0 m) 14.54 35.34 33.56 11.03 0.97 10.55<br />
Monte Derre 104/SP (4,5 m) 13.74 35.03 30.23 7.81 0.56 16.43<br />
Serra Morrumbala R1/RA (1,0 m) 10.50 18.45 22.50 5.40 0.65 -<br />
136SP (3,0 m) 11.08 27.63 30.03 7.50 0.40 3.21<br />
It can generally be said about the bauxite occurrence on nepheline syenites in the Tete and Zambezia provinces, that just<br />
the Mauzo hill could yield some bauxite with an Al2O3 content over 40%, an elevated silica content and iron between 4-<br />
8%.<br />
The large group <strong>of</strong> nepheline syenites in this area can be utilized in ceramics and in a production <strong>of</strong> alumina. This<br />
problem is discussed in Chapter 4.11.<br />
The following description is dealing with an exploration <strong>of</strong> lateritic pr<strong>of</strong>iles and presented here, because little is known<br />
<strong>of</strong> these residual deposits; widespread in tropical countries.<br />
An example <strong>of</strong> lateritic pr<strong>of</strong>ile development in the Province Zambezia is an area SE <strong>of</strong> Milange, with parent rocks <strong>of</strong><br />
migmatites at the level <strong>of</strong> 660-700 m (Samokhvalov, 1981)-area <strong>of</strong> Macassania.<br />
The weathering pr<strong>of</strong>ile, common to many other areas <strong>of</strong> <strong>Mozambique</strong>, is composed basically <strong>of</strong> kaolin, oxides and<br />
hydroxides <strong>of</strong> iron, quartz and little gibbsite developed just within the horizon <strong>of</strong> pisolithic argillite. Interesting is an<br />
icreased content <strong>of</strong> P2O5 (0.28-1.206 %).<br />
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Cilek: 4.1. Bauxite and aluminum laterite<br />
Pr<strong>of</strong>ile established (elements in average %):<br />
Horizon<br />
Thickness<br />
m<br />
SiO2 Al2O3 Fe2O3 FeO TiO2 L.i.<br />
humus soil 0.3 - - - - - -<br />
agrillite pisolithic cemented 1.4 29.76 21.66 25.60 0.73 3.79 14.77<br />
agrillite reddish with pisoliths 1.2 31.53 20.16 21.90 1.29 2.10 14.90<br />
agrillite reddish with sand 1.0 42.08 25.15 14.3 0.42 2.32 13.58<br />
agrillite dark red 1.4 33.11 22.06 18.39 1.14 1.96 13.31<br />
buff argillite massive 1.1 42.41 20.67 13.86 0.92 1.92 12.22<br />
argillite bedded 1.7 32.26 21.91 20.23 1.57 0.87 13.77<br />
In the past, during an investigation <strong>of</strong> soil pr<strong>of</strong>iles at Gurue, two samples <strong>of</strong> a clay component were analyzed. They<br />
contained: Al2O3 37.92% and 38.87%, SiO2 15.42% and 17.89%. A mineralogical analysis disclosed 38% and 38.5% <strong>of</strong><br />
gibbsite respectively in these samples. Samokhvalov (1981) examined the weathering pr<strong>of</strong>iles over amphibole and biotite<br />
gneisses in several trenches in an area 5-12 km WNW <strong>of</strong> the town <strong>of</strong> Gurue. The altitude <strong>of</strong> the area ranges between 670<br />
and 750 m.<br />
General pr<strong>of</strong>ile (average chemical composition in %):<br />
Horizon<br />
Thickness<br />
m<br />
SiO2 Al2O3 Fe2O3 TiO2 L.i.<br />
humus soil 0.75 - - - - -<br />
argillite pisolithic 1.1 39.18 22.57 17.84 2.87 15.77<br />
argillite reddish sandy 4.4 38.80 35.24 15.04 2.15 13.34<br />
argillite reddish 1.9 38.57 25.45 13.51 3.14 15.89<br />
argillite kaolinitic 3.0 37.90 25.61 14.98 2.09 14.61<br />
argillite kaolinitic bedded 2.7 45.46 20.92 14.61 1.94 13.61<br />
Some samples were washed to remove big grains <strong>of</strong> quartz, an improvement <strong>of</strong> Al2O3 content was about 2%. The clay<br />
consisted mainly <strong>of</strong> kaolin with oxides and hydroxides <strong>of</strong> iron, with a small amout <strong>of</strong> dispersed gibbsite which cannot be<br />
concentrated. In two cases only, the content <strong>of</strong> gibbsite attained 7-24%.<br />
In the Province Nampula, two areas were examined: in the vicinity <strong>of</strong> Nacala and Angoche, both in the coastal strip.<br />
Near Nampula and close to Mossuril, a belt <strong>of</strong> basalts <strong>of</strong> Cretaceous - Jurassic age was found and on it a thick alteration<br />
cover. The basalts were amygdaloid and porphyric, with up to 20% <strong>of</strong> opal, chalcedony and quartz.<br />
The lateritic zone was more than 10 m thick and consisted, in 70-75% <strong>of</strong> laterite and ferruginous and kaolinitic material.<br />
Iron compounds attained 19-23%, gibbsite was not detected. Only in two cases, layers <strong>of</strong> allites were found with Al2O3<br />
27.94 and 33.10%, SiO2 16.22 and 24.80%; gibbsite accouned for 18.0 and 21.7%, respectively.<br />
General pr<strong>of</strong>ile (with average chemical composition) (in %):<br />
Horizon<br />
Thickness<br />
m<br />
SiO2 Al2O3 Fe2O3 FeO TiO2 L.i.<br />
humus soil 0.4 - - - - - -<br />
argillite sandy with pisoliths 2.7 33.66 24.10 14.70 0.93 1.39 17.18<br />
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Cilek: 4.1. Bauxite and aluminum laterite<br />
argillite reddish pisolithic 6.5 36.70 25.79 16.36 0.51 1.15 17.13<br />
argillite kaolinitic 0.95 38.38 19.42 14.06 0.53 1.18 19.78<br />
argillite kaolinitic bedded 1.2 37.65 21.11 13.18 - 1.04 18.72<br />
Also near the village <strong>of</strong> Boila, 4.5 km NW <strong>of</strong> Port Angoche, the weathered crust above Cretaceous-Jurassic basalts was<br />
examined (Samokhvalov, 1981). The elevation was similar to that at Nacala (30-40 m above s. l.) with groundwater near<br />
the surface. At sites <strong>of</strong> outcropping basalts, a hard crust, 0.5-1.0 m in thickness, with dominant iron pisoliths was<br />
developed. In places, where the basalts were covered with Quaternary sediments, the alteration zone is thicker.<br />
An example <strong>of</strong> weathered pr<strong>of</strong>ile near Angoche:<br />
Horizon<br />
Thickness<br />
m<br />
SiO2 Al2O3 Fe2O3 FeO TiO2 L.i.<br />
soil humus 0.5 - - - - - -<br />
sand clayey 5.6 - - - - - -<br />
argillite pisolithic 5.0 36.21 22.7 22.48 0.36 0.90 14.92<br />
argillite kaolinitic 3.2 44.70 16.27 21.30 - 1.44 12.55<br />
argillite kaolinitic bedded 1.5 41.89 24.24 13.81 1.22 1.16 15.50<br />
Here and in other localities kaolinitic-ferruginous lateritic clays only were encountered with kaolin content <strong>of</strong> 47-64%,<br />
iron 27.6-32.5%, silica 3.2-20.3% and gibbsite 1.7%. The superficial cemented crust was composed <strong>of</strong> oxides and<br />
hydroxides <strong>of</strong> iron (50-58%) and kaolin (26-35%). The composition <strong>of</strong> argillites with pisoliths was kaolinic-ferric with<br />
fragments <strong>of</strong> not fully dissintegrated rocks. No bauxites were found. In the Province Niassa, two genetically different<br />
weathering pr<strong>of</strong>iles were studied by Samokhvalov (1981):<br />
a) a fossil horizon at the base <strong>of</strong> Karroo Formation<br />
b) recent and subrecent pr<strong>of</strong>iles on Precambrian rocks in altitudes between 1100 and 1300 m.<br />
a) In borehole no. 9., in the area Lufutize, basal sediments <strong>of</strong> the Karroo basin consisted <strong>of</strong> gabbroic rocks strongly<br />
altered in a kaolinic mass; the upper part <strong>of</strong> the weathered horizon was rich in apatite (10%) and ilmenite-magnetite<br />
(20%). Overlying were conglomerates and ateurites <strong>of</strong> red colour <strong>of</strong> K-3 horizon. On some outcrops near the river<br />
Matonda, crystalline rocks had been deeply weathered in pre-Karroo times, partly transported and mixed with basal<br />
Karroo sediments in a transitional zone.<br />
b) Lateritic cover <strong>of</strong> crystalline rocks in the surroundings <strong>of</strong> Lichinga (70-100 km around), about 1 to 6 m thick, <strong>of</strong> a<br />
lateritic-ferruginous composition with quartz grains. In some places, a lateritic crust with abundant pisoliths was<br />
encountered, with under- lying sediments <strong>of</strong> argillitic-pisolithic composition:<br />
SiO2 48.6, 57.6%; Al2O3 22.5, 25.3%; Fe2O3 11.0, 11.4%. The presence <strong>of</strong> bauxites was not detected.<br />
Conclusions:<br />
As in many African countries <strong>of</strong> tropical zone, widespread weathering crusts are developed over the biggest part <strong>of</strong> the<br />
region. A reddish lateritic, mostly kaolinic and partly ferruginous horizon is developed. The content <strong>of</strong> gibbsite in these<br />
lateritic horizons attains even 38%, as in the area <strong>of</strong> Gurue, but is much lower in other areas <strong>of</strong> the coastal plain (30 m<br />
above s. l.) up to an elevation <strong>of</strong> over 1,000 m (1.7% at Angoche, 24% at Gurue, 20% at Milange). In some <strong>of</strong> these<br />
lateritic horizons, the content <strong>of</strong> some trace elements such gallium, yttrium, zirconium and niobium is <strong>of</strong> interest.<br />
Bauxite with content <strong>of</strong> more than 60% Al2O3, about 2% <strong>of</strong> Fe2O3 and 3% SiO2 <strong>of</strong> refractory and chemical grade has<br />
been mined near Manica since 1938 and exported by the Zimbabwean company E. C. Meikles Ltd. The annual amount<br />
<strong>of</strong> ore extracted is small, ranging between 2,000 and 3,000 t in the last years. Reserves are small and not fit for big<br />
operations. The deposit is accessible from the Zimbabwean side only.<br />
Another very small source (about 200kt <strong>of</strong> reserves) was found on Monte Mauzo, this time on the Malawian borders.<br />
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Cilek: 4.1. Bauxite and aluminum laterite<br />
Both deposits developed by an alteration <strong>of</strong> nepheline syenites at an altitude <strong>of</strong> about 1,400 m on flat surface, as<br />
erosional remnants.<br />
Several other sites with nepheline syenite in <strong>Mozambique</strong> do not contain bauxite despite favourable geological and<br />
geomorphological conditions such as at Serra Morrumbala. A refractory-grade bauxite from Manica should be used in<br />
the production <strong>of</strong> refractory bricks for the Mozambican industry.<br />
Present exploration programme in the surroundings <strong>of</strong> Manica revealed promising reserves <strong>of</strong> 3 to 5 million tons <strong>of</strong><br />
bauxite ore.<br />
© Václav Cílek 1989<br />
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Cilek: 4.10. Mineral pigments<br />
4.10. Mineral pigments<br />
Mineral pigments or inorganic pigments are used in paints according the their covering power, suitable<br />
colour, sorbing capacity for oil, neutral pH and opacity. The chemical composition is <strong>of</strong> minor<br />
importance. These pigments are used in plaster, cement, mortar, rubber, plastics, in foodstuff, "old"<br />
cosmetics, ceramics and glass, floor and wall tiles, linoleum etc.<br />
Bateman (1951) divides pigments into three classes:<br />
* natural mineral pigments<br />
* pigments made by burning or subliming natural pigments<br />
* manufactured paints.<br />
Natural pigments contain usually iron as the main colouring agent in minerals <strong>of</strong> limonite, hematite,<br />
magnetite with admixture <strong>of</strong> clay and rarely manganese minerals.<br />
These minerals form natural ochres, umbers and siennas <strong>of</strong> yellow, brown and red colours and have been<br />
used by primeval man in decorations and drawnings (rock paintings common to E-Africa). They have<br />
been employed in many industrial branches and at home both in the past and the present.<br />
Mineral red is composed <strong>of</strong> hematite which underwent residual weathering. Other iron -bearing minerals<br />
produced similar reds. The content <strong>of</strong> Fe2O3 ranges between 60 and almost 90%, whereby the purest<br />
paints are almost pure red hematites.<br />
Ochres and bolus (smectite clay with limonite) are neutral in character and widely accepted as a<br />
component part <strong>of</strong> wall paints, in a number <strong>of</strong> plastic products, oil paints etc. They are mixtures <strong>of</strong><br />
hematite, limonite and clay <strong>of</strong> yellow to brown colours. They require fineness (remnants on sieve mesh<br />
size 0.09 mm maximally 0.5-2.0%) Fe2O3 in a dry state around 16% to 40% (exceptionally up to 80%),<br />
clear colour, consumption <strong>of</strong> oil 60% etc. Roasted ochres give a reddish brown colour.<br />
Manganese oxide (11-25%) in ochre gives a typical brown colour and is known as umber; less<br />
manganese oxide and more limonite is known as sienna.<br />
Green-coloured materials originate in nature in rocks rich in chlorite, greenstones and glauconite.<br />
Ground shales are responsible for the particular colour <strong>of</strong> the original material - red, black, grey etc.<br />
Whites are obtained from kaolin, baryte, talc, white clay and other rocks and minerals.<br />
Malachite gives a green colour, azurite a blue, pyrolusite a black colour, etc.<br />
Different paints can be produced even from carbon materials - for example oxyhumolites, weathered<br />
coals from the outcrops, are used in the production <strong>of</strong> brown or grey pigments.<br />
Manufactured pigments are prepared by roasting ochres using iron ore, copper ore and other compounds<br />
<strong>of</strong> lead, zinc, barium, chromium etc. Various combinations <strong>of</strong> colour are prepared by mixing different<br />
materials.<br />
In <strong>Mozambique</strong>, mineral pigments have been used since the stone age. In the Manica Province, for<br />
example at Serra Vumba, very nice rock paintings made <strong>of</strong> reddish and brown ochres were discovered.<br />
In the Nampula-Nacala area, graphite was used (Nupes, 1952) several centuries ago for ornamental<br />
paintings <strong>of</strong> pots known in the region as "muapas". In the area <strong>of</strong> nepheline syenite massifs (Martins,<br />
1940), the weathered clay cover <strong>of</strong> a reddish colour-in fact reddish kaolin, was used as paint by the local<br />
people.<br />
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Cilek: 4.10. Mineral pigments<br />
White paint for ornamental purposes has been used in many villages where limestone was burned in<br />
furnaces to produce lime. White skin paint based on kaolin is used by the women <strong>of</strong> N-coastal<br />
<strong>Mozambique</strong>.<br />
There existed certainly in the past many other paints and pigments in different regions <strong>of</strong> <strong>Mozambique</strong>.<br />
And mineral raw material could have provided a number <strong>of</strong> mineral pigments both in the past and again<br />
at present. Here are several suggestions:<br />
Red and brown ochres - in all localities <strong>of</strong> residual weathering on banded ironstones, iron deposits with<br />
hematite and magnetite, on ultrabasic rocks (Tete, Manica, Barue, Niassa)<br />
Whites - on kaolin pr<strong>of</strong>iles, on bauxite pr<strong>of</strong>iles (Manica, Nampula, Cabo Delgado)<br />
Pink and red - on weathered kaolin pr<strong>of</strong>iles, on lateritic soils and laterites on weathered syenites and<br />
anorthosites, on rhyolites and basalts<br />
Grey and black - graphites <strong>of</strong> Angonia, Monapo, Nacala and Lurio, weathered coal outcrops in Karroo<br />
in Tete Province and Niassa Province<br />
Green - copper mineralization, greenstones <strong>of</strong> the Archean and Precambrian, glauconite <strong>of</strong> the<br />
Cretaceous<br />
Greenish-white - talc <strong>of</strong> the Manica, Tete and Nampula Provinces<br />
Carbon-black - natural gas soot from gas deposits at Buzi, Pande, Temane<br />
Conclusions:<br />
No natural pigments are industrially used in <strong>Mozambique</strong> and therefore, recommendations have been<br />
made only for future research on these generally cheap materials. These materials will come into the<br />
industrial stream as soon as the country starts to develop industrial minerals and rocks and to economize<br />
on imported raw materials. A utilization <strong>of</strong> these very different materials with low tonnage consumption<br />
is a case for small-scale mining enterprises.<br />
© Václav Cílek 1989<br />
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Cilek: 4.11. Nepheline syenite<br />
4.11. Nepheline syenite<br />
Nepheline syenite is a new modern rock introduced by the U. S. A. and Canada after World War 2 which competes with feldspar and aplite as a source <strong>of</strong><br />
alumina and alkalies in the production <strong>of</strong> glass, ceramics, the production <strong>of</strong> alumina, cement and caustic soda, potassium sulphate, as filler and in the<br />
production <strong>of</strong> chemicals.<br />
Nepheline syenite is a silica-deficient, crystalline rock resembling granite in appearance but <strong>of</strong> a different composition. It consists essentially <strong>of</strong> feldspar (both<br />
albite and microcline), nepheline and varying amounts <strong>of</strong> mafic and accesory minerals.<br />
Nepheline Na3 K (Al4Si4O16) is usually massive or occurs as embedded grains in syenites, phonolites, some basalts and pegmatites. The nepheline content <strong>of</strong><br />
nepheline syenites is over 20%, no quartz is present and apart from a few % <strong>of</strong> accessory minerals, the remaining rock is made up <strong>of</strong> feldspars.<br />
The few producers <strong>of</strong> nepheline syenite in the world are these: in Europe Norway with a deposit on Stjernoy Island, USSR with deposits <strong>of</strong> apatite on the Kola<br />
Peninsula and in America at Blue Mountain in Canada, and the Canaan deposit in Brazil.<br />
The production from Stjernoy deposit is a good example <strong>of</strong> a utilization <strong>of</strong> the ore in glass, ceramic and filler industries, that <strong>of</strong> Kola an example <strong>of</strong> a<br />
successful complex utilization <strong>of</strong> this rock for alumina, alkalies and cement products.<br />
The Stjernoy deposit started production in 1961 (Bull-Miksch, 1985). The crude ore contains: 56% <strong>of</strong> perthite, 34% <strong>of</strong> nepheline and other minerals such as<br />
magnetite, biotite, amphibole, pyroxene, calcite and sphene. Two types <strong>of</strong> nepheline syenite facies have been identified -a biotite and a hornblende-pyroxene<br />
type. The latter is the main commercial source. The deposit in Caledonian crystalline rocks is part <strong>of</strong> a ring structure with gabbros and carbonatites, lensshaped<br />
about 2 km long and 250 m wide. The ore is crushed, screened, dressed in low- and high- intensity magnetic separators and air classifiers. Three<br />
commercial grades are produced:<br />
* glass grade<br />
* amber grade<br />
* ceramic grade <strong>of</strong> this chemical composition (in %):<br />
Oxide Glass grade Amber grade Ceramic grade<br />
SiO2 57 56.5 57<br />
Al2O3 23.8 22.5 23.8<br />
Fe2O3 0.10 0.4 0.12<br />
Na2O 7.9 7.5 7.8<br />
K2O 9.0 8.2 9.1<br />
CaO 1.3 2.5 1.1<br />
L. i. 1.2 no mention 1.1<br />
Nepheline syenite is valuable mainly for its high alkali and alumina content, high fluxing power <strong>of</strong> nepheline and perthite and a common hardness and<br />
whiteness. The glass industry uses nepheline syenite in the production <strong>of</strong> glass containers, sheet glass, float glass and fibreglass. The iron content required has<br />
to be low and the ratio Fe2O3 : Al2O3 should be 0.0004. The ratio alkalies/silica i. e. Na2O + K2O : SiO2 should be 1 : 3 - 4. Nepheline with the ratio Na2O :<br />
SiO2 = 1 : 2 has a high alkaline content when compared, for example, with albite (1 : 6). This means that in flint glass production the melting time is 11<br />
minutes for nepheline and 103 minutes for albite, which is self-explanatory.<br />
Glass, which is a mixture <strong>of</strong> silica (sand), soda ash and limestone mainly, has to be complemented with alumina, which induces high strength and prevents<br />
devitrification. The nepheline syenite replaces alumina and part <strong>of</strong> the expensive soda ash.<br />
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Cilek: 4.11. Nepheline syenite<br />
The foam and fibreglass production, the popularity <strong>of</strong> which is rapidly increasing, welcomes the amber grade as a cheap raw material (0.4% <strong>of</strong> Fe2O3 is<br />
acceptable).<br />
In the ceramic industry for which the chemical components and fluxing agents <strong>of</strong> nepheline syenite (i.e., reactivity in the mass, rheology and whiteness after<br />
firing) are decisive is used in a production <strong>of</strong> hotel china, sanitary ware, enamel, electrical and dental appliances.<br />
It is used less frequently as a filler and extender for its durability, acid-resistance and low vehicle absorption.<br />
Demands for nepheline syenite are expected to increase in the future because the glass industry will be introducing new types <strong>of</strong> glass containers.<br />
Nepheline syenite <strong>of</strong> the Kola Peninsula is a raw material for the production <strong>of</strong> alumina, sodium and potassium chemicals and the waste, red mud, is part <strong>of</strong><br />
the cement clinker.<br />
The deposit is, in fact, a source <strong>of</strong> apatite developed in two zones, the upper one containing 65% apatite, 20% nepheline and 10% aegirine-amphibole, the<br />
lower zone with 30% nepheline and 45% apatite. 150 t <strong>of</strong> nepheline concentrate produces 40 t <strong>of</strong> alumina and another 30 t <strong>of</strong> potash and soda. Apart from rare<br />
earths, also gallium and rubidium were recovered.<br />
Average composition <strong>of</strong> Kola nepheline syenite for alumina production:<br />
27-29% Al2O3, maximum 17.5% <strong>of</strong> alkalies, 40-44% SiO2, 1.3-7.5% CaO, 0.4-1.2% Mg, Na2O 11.3-12.8% and iron oxides are almost absent.<br />
Moduluses are used in an evaluation <strong>of</strong> the reserves <strong>of</strong> syenites:<br />
Alkaline Calcic Silica Alumina<br />
Na2O + K2O CaO SiO2 Al2O3<br />
___________ _____ ______ _________________<br />
Al2O3 Al2O3 Al2O3 Fe2O3 + FeO + MgO<br />
Other ratios like between Na2O and K2O are also important. Exact specifications do not exist, each deposit is evaluated under special specifications.<br />
Canadian nepheline syenite (Harben-Bates, 1984) is composed essentially <strong>of</strong> 20-25% nepheline, 48-54% albite and 18-23% microcline. The accessory<br />
minerals totalling 6% include 0.2-0.6% magnetite, 0-4% biotite, 0-3% hastingsite and 0-2% muscovite and aegirine.<br />
The Brazilian nepheline syenite is composed <strong>of</strong> 55% microcline and microcline-perthite, 20% nepheline and 15% albite.<br />
In <strong>Mozambique</strong>, nepheline syenites are concentrated mainly along the East African rift valley, at the border with S-Malawi. These massifs intrude into a<br />
Precambrian basement and their age is 116 -138 m.y., i.e. Upper Jurassic-Lower Cretaceous. This determination <strong>of</strong> age was made for the Chilwa alkaline<br />
province in Malawi (Afonso-Pinto, 1967), no data are available for the Mozambican side.<br />
Apart from the Chilwa alkaline province (Fig. 4.11.1) syenite was found in many parts <strong>of</strong> <strong>Mozambique</strong>: syenites-gabbros without nepheline syenites in the<br />
SW part <strong>of</strong> the Lurio belt, in the Niassa Province, ring structures in the northern continuation <strong>of</strong> the Lake Chirua graben, Monte Tchonde near Meponda on the<br />
bank <strong>of</strong> Lake Niassa, massifs <strong>of</strong> Mecula and Lugenda, nepheline gneisses within the ring structures <strong>of</strong> Monapo and Mocuba, and others. All these sites are<br />
situated around or at a certain distance from the rift structures and deliminate in fact these tectonic features.<br />
Fig. 4.11.1. Schematic map <strong>of</strong> Southern Malawi-Chilva Alkaline Province (Cilek, 1987) (493 kB)<br />
The best known sites <strong>of</strong> syenite and nepheline syenite occurrence in <strong>Mozambique</strong> are in the Chilwa alkaline province, and represent there the biggest<br />
accumulation <strong>of</strong> these rocks. On the Malawian side, syenitic intrusions are accompanied by carbonatites, which are dominant in many areas. All these<br />
intrusions are in close connection with deep-seated fractures <strong>of</strong> different sections <strong>of</strong> the East African rift: in the S, the Urema graben, Shire graben and in the<br />
N Niassa-Rukwa rift.<br />
The genesis <strong>of</strong> syenite massifs (carbonatites are clearly <strong>of</strong> explosive origin) is explained by a magma stopping. The massifs are epizonal and many are <strong>of</strong> a<br />
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Cilek: 4.11. Nepheline syenite<br />
typical oval shape with sharp boundaries, some are quasi concordant and follow the foliation planes <strong>of</strong> Precambrian rocks, but all are epizonal stocks and<br />
developed as follows (Afonso-Pinto, 1967):<br />
a) phase <strong>of</strong> collapse - destabilization <strong>of</strong> the magmatic chamber and origin <strong>of</strong> fractures<br />
b) phase <strong>of</strong> passive magma ascent - the cover <strong>of</strong> the chamber is fragmented and blocks fall into the magma from surrounding rocks and are melted and<br />
absorbed<br />
c) phase <strong>of</strong> consolidation - the upper part <strong>of</strong> the magma solidifies and its subsidence starts with the development <strong>of</strong> fractures, ring-dykes and cone-sheets.<br />
Generally, the initial phase is triggered by an explosive phase which causes the first magma movement known as "updoming". Erosion will uncover the<br />
massif, remove the cone-sheets and flatten the intrusive rocks to a certain geomorphological level here probably to the Pan-African land surface (Tertiary age).<br />
Syenite massifs <strong>of</strong> <strong>Mozambique</strong> (from S to N) on the eastern margin <strong>of</strong> the Rift Valley)-<br />
Monte Mauzo<br />
Serra Tumbine<br />
Serra Chiperone (Conguene, Derre, Pandibue, Muembili)<br />
Serra Morrumbala<br />
Western margin <strong>of</strong> the Rift Valley:<br />
Salambidua<br />
Cheneca (see fig. 4.11.1)<br />
On the Mozambican side Monte Mauzo is composed <strong>of</strong> nepheline syenites with aegirine, on the Malawian side, the central part consists <strong>of</strong> carbonatites<br />
feldspathic breccia and agglomerates and syenites. Mauzo (and Tumbine in the S) are <strong>of</strong> a typical oval shape, in SE-NW direction.<br />
According to Afonso-Pinto (1967) this hill is composed <strong>of</strong> nepheline syenite with foids with a fenitization ring around the syenite, with dykes and intrusions<br />
<strong>of</strong> microgranites and phonolites.<br />
Residual deposits <strong>of</strong> bauxite and Al-laterite are described in Chapter "Bauxites"<br />
Chemical analyses:<br />
1. Nepheline syenite-<strong>Mozambique</strong> (Real, 1965)<br />
2. Foiate with aegirine-augite, Malawi (Dixey, 1955)<br />
3. Phonolite from the Malawian side (Dixey, 1955), which may also serve as glass or ceramic material.<br />
% 1 2 3<br />
SiO2 55.28 54.37 56.83<br />
TiO2 0.69 0.77 0.12<br />
Al2O3 20.77 23.22 20.78<br />
Fe2O3 2.22 1.62 3.57<br />
FeO 1.45 1.32 0.41<br />
MnO 0.11 0.07 0.40<br />
MgO 0.29 0.57 0.02<br />
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Cilek: 4.11. Nepheline syenite<br />
CaO 3.78 1.60 0.65<br />
Na2O 7.69 8.25 10.73<br />
K2O 7.38 7.35 4.72<br />
P2O5 0.20 0.08 0.001<br />
H2O+ 0.33 0.50 0.32<br />
H2O- 0.25 0.20 0.07<br />
SUM 100.44 99.92 98.621<br />
Another additional analysis: ZrO2 - 0.50%, BaO - 0.01% and SrO - 0.07%. The phonolite contains orthoclase and sodium pyroxene.<br />
Nepheline syenite is typical and can be compared with that <strong>of</strong> Chiperone.<br />
Serra Tumbine is almost circular measuring 8 km in diameter. It is a typical intrusion in gneisses and granites <strong>of</strong> a basement <strong>of</strong> alkaline syenite and syenite<br />
sub-alkaline with dykes <strong>of</strong> microsyenites and trachyte. Residual deposits <strong>of</strong> Al-laterites and kaolin are restricted. Alkaline syenites are predominant, they are<br />
microperthitic with biotite, amphibole and sphene. Quartz in small quantities was found in the border zone <strong>of</strong> syenites.<br />
Subalkaline syenites are greenish, medium-grained rocks with mirmequilite, perthitic orthoclase, some quartz and apatite. Mafic minerals are represented by<br />
aegirine-augite, biotite, sodium amphibole and nuclei <strong>of</strong> pyroxene. The rocks could be classified as subalkaline syenite, biotitic and amphibolitic, with apatite.<br />
Two analyses were:<br />
1. Syenite microperthitic with augite, riebeckite and aegirine-augite (Coelho, 1959)<br />
2. Syenite microperthitic with augite, acnite and riebeckite (Coelho, 1959)<br />
% 1 2 % 1 2<br />
SiO2 60.18 61.18 CaO 2.00 1.34<br />
TiO2 0.68 0.88 Na2O 8.75 6.77<br />
Al2O3 18.50 17.80 K2O 5.99 6.33<br />
Fe2O3 1.18 1.01 P2O5 0.20 0.09<br />
FeO 1.84 2.44 H2O+ 0.23 0.11<br />
MnO 0.03 0.10 H2O- 0.42 0.51<br />
MgO 0.30 1.19<br />
Total 100.30 99.75<br />
Serra Chiperone s.s. is composed <strong>of</strong> nepheline syenite with some pegmatites <strong>of</strong> nepheline syenite and some younger dolerite dykes. An oval intrusion<br />
penetrates the basement rocks <strong>of</strong> gneisses, migmatites and granulites. The massif extends in NW-SE direction for 12 km with an elevation <strong>of</strong> 2,065 m. Serra<br />
Chiperone is part <strong>of</strong> the mountain range, which includes also the morphologically separated hills Derre, Pandilue, Muembili and Congene (Conguene) in SE<br />
direction, and the hills Missouge, Missecue, Langoma and Mongoe in W direction.<br />
Analyses <strong>of</strong> syenite microperthitic, nephelinic with biotite (Coelho, 1959): %<br />
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SiO2 53.76 54.44 CaO 1.85 1.26<br />
TiO2 0.47 0.33 Na2O 8.29 7.59<br />
Al2O3 23.93 22.05 K2O 6.74 6.92<br />
Fe2O3 2.10 2.91 P2O5 tr. 0.04<br />
FeO 1.91 2.82 H2O+ 0.46 0.33<br />
MnO 0.03 0.10 H2O- 0.26 0.27<br />
MgO - 0.14<br />
Total 99.80 100.15<br />
Nepheline syenites <strong>of</strong> Serra Chiperone are chemically similar to those <strong>of</strong> Mauzo and Tumbine.<br />
The mountains Derre, Pandibue and Muembili are massifs <strong>of</strong> nepheline syenite, elongated in NE direction, with axes 9.5 and 5.7 km long and 1.3 and 2.4 km<br />
wide. The basement consists <strong>of</strong> gneisses and migmatites, which underwent a fenitization around the contact zones. The main rock, i. e., nepheline syenite, is<br />
medium - to coarse - grained composed <strong>of</strong> abundant microperthite, microcline, albite, nepheline (some crystals are on margins altered to calcite and<br />
cancrinite), very rare quartz, biotite, epidote, magnetite, sphene and alanite. It can be classified as syenite microperthitic nephelinic with biotite.<br />
Monte Conguene is the only locality, explored recently by a Russian team as a possible source <strong>of</strong> alumina (see Barmine-Tveriankine, 1982 and technological<br />
research by VAMI - Leningrad, 1981). All data presented here are excerptions <strong>of</strong> these reports and <strong>of</strong> a report by Afonso-Pinto, 1967.<br />
The massif is composed <strong>of</strong> two hills, Conguene and Chissindo, covering an area <strong>of</strong> 14 km2, in elongated oval shape in NE direction. Similar to other syenite<br />
massifs, it is a typical intrusion into Precambrian schists and gneisses, <strong>of</strong> Cretaceous age. The main part consists <strong>of</strong> nepheline syenite <strong>of</strong> the miaskite series,<br />
which is a potential source <strong>of</strong> alumina and a subsequent metal production. From the N to the NE and the NW, nepheline syenite borders a belt <strong>of</strong> alkaline<br />
biotite - feldspar syenite which extends in a belt <strong>of</strong> 200 to 1000 m in width. Nepheline syenites are <strong>of</strong> leucocratic and mesocratic medium-grained varieties and<br />
have a gneiss-like texture.<br />
They contain:<br />
55 - 75 % microcline-perthite<br />
15 - 20 % nepheline<br />
accessory minerals: biotite, magnetite, ilmenite, titanite, zircon, pyrochlore<br />
Non-nepheline syenite occurs in the biotite-hornblende and the biotite-pyroxene-hornblende varieties: there are also hybridic rocks with amphibole-feldspars,<br />
with quartz up to 5% presenting another variety <strong>of</strong> quartzitic syenites. Over 102 samples were collected and analysed.<br />
Results <strong>of</strong> sample analyses:<br />
Content: SiO2 Al2O3 CaO Na2O K2O R2O Fe total R2O/ Al2O3 CaO/ SiO2 SiO2/ Al2O3<br />
minimum 50.08 18.12 0.01 4.65 3.85 8.27 2.21 0.60 0.0001 3.38<br />
maximum 61.50 25.33 2.72 10.80 7.26 14.83 9.69 1.08 0.0555 5.79<br />
average 55.63 22.03 0.73 8.22 5.88 12.08 4.29 0.90 0.0149 4.30<br />
From these 162 samples, 101 samples were selected covering the area <strong>of</strong> suitable rock for reserves calculation. The results <strong>of</strong> analyses <strong>of</strong> 101 samples are as<br />
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follows:<br />
Content SiO2 TiO2 Al2O3 Fe2O3 FeO MnO2 MgO CaO Na2O K2O P2O5 R2O Fe2O3<br />
minimum 51.0 0.01 19.51 0.97 0.01 0.01 0.01 3.26 3.13 0.01 0.33 5.32 1.81<br />
maximum 59.3 0.77 27.0 4.45 2.63 0.19 1.18 2.72 10.8 7.26 5.32 14.48 5.96<br />
average 52.23 0.27 22.57 2.57 1.26 0.09 0.15 0.70 8.31 5.99 0.08 12.26 3.97<br />
The moduluses are: R2O/Al2O3 CaO/SiO2 SiO2/Al2O3<br />
0.36 0.0001 3.45<br />
1.08 0.0555 5.16<br />
average 0.90 0.0137 4.16<br />
Two bulk samples were collected for technological tests, using the soviet method for producing alumina, sodium and potassium carbonates and high grade<br />
portland cement together with recovery <strong>of</strong> gallium and rubidium.<br />
It was clear from the very beginning that the Mozambican samples (B-1 Conguene, B-2 Chissindo) are different from soviet Kola material in that they have a<br />
lower Al content (22%) and a higher Si content (57%).<br />
Average chemical composition (in %):<br />
1 (Sample B-1) 2 1 (Sample B-2) 2<br />
Al2O3 25.3 21.9 22.3 22.0<br />
Na2O 7.95 8.4 10.5 9.3<br />
K2O 4.64 5.64 3.75 4.7<br />
CaO 0.35 0.7 2.1 0.8<br />
SiO2 56.9 57.0 54.8 56.6<br />
Fe2O3 1.40 1.9 4.85 1.2<br />
FeO 0.30 1.6 3.57 2.2<br />
MgO 0.08 0.17 0.1 0.15<br />
TiO2 - 0.12 0.24 0.25<br />
MnO 0.05 0.09 0.13 0.13<br />
P2O5 0.05 0.02 0.1 0.07<br />
H2O 0.28 - 0.39 -<br />
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Cilek: 4.11. Nepheline syenite<br />
L.i. 1.82 0.53 - 0.92<br />
Samples "2" are controlled analyses performed by VAMI.<br />
Fluctuation <strong>of</strong> the major components was considerable: Al2O3 19.2-25.8%, Na2O 8.0-15.3%, K2O 2.5-5.0%, Fe2O3 2.7-6.6%, FeO 1.9-5.0%.<br />
In a selected area measuring 1.6 km2, nepheline syenite has a alumina content <strong>of</strong> 23.6-27.0%, alumina modulus 5.9-6.0, alkaline modulus 0.91 and Na2O/<br />
K2O ratio 1.5-1.9.<br />
Quantitative mineralogical composition:<br />
B-1 B-2 B-1 B-2<br />
nepheline 18.9 18.0<br />
natrolite - 1.6 orthoclase (microcline) 28.2 26.9<br />
analcite 1.6 - plagioclase 42.5 40.1<br />
liebernite 1.2 2.2 biotite 5.9 8.3<br />
cancrinite - 1.1 apatite - 0.2<br />
sodalite - 0.5 sphene - 0.1<br />
calcite 0.2 0.4 zircon 0.1 -<br />
feldspars total 70.7 67.0 titano-magnetite 1.4 0.6<br />
total 100.0 100.0<br />
Distribution <strong>of</strong> main chemical components in minerals (% <strong>of</strong> total content):<br />
<strong>Minerals</strong><br />
Al2O3 Na2O<br />
B-1<br />
K2O SiO2 Al2O3 Na2O<br />
B-2<br />
K2O SiO2<br />
nepheline 30.2 40.4 15.0 13.7 28.2 36.7 14.0 13.0<br />
nepheline alteration 3.7 2.2 1.7 2.3 7.9 6.7 4.0 4.2<br />
feldspars 62.3 57.4 75.0 80.5 58.3 56.0 72.0 77.7<br />
mafic and opaque minerals 3.8 - 8.3 3.5 5.6 0.6 10.0 5.1<br />
total 100 100 100 100 100 100 100 100<br />
The main minerals <strong>of</strong> nepheline syenite are feldspars (microcline, orthoclase, microcline-perthite) <strong>of</strong> the soda-potash variety and calcium-soda feldspars<br />
(placioclase-albite); in sample B-1 28.2 and 42.5%, in sample B-2 26.9 and 40.1%. The quantity <strong>of</strong> nepheline is below 20%. A favourable feature <strong>of</strong><br />
Mozambican ore is its high alkaline ratio (0.91-0.93) and its high CaO content which ensure a high yield <strong>of</strong> potash; a negative feature is its lower alumina<br />
content (22%) and its higher silica content (57%) when compared with Kola ore.<br />
Generally, this nepheline syenite belongs to the high-alumina type, <strong>of</strong> miaskites <strong>of</strong> the Na-K branch. According to VAMI-Leningrad, the specification grade is<br />
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Cilek: 4.11. Nepheline syenite<br />
to category III and, therefore, it is suitable for a production <strong>of</strong> alumina sodium and potassium compounds and portland cement.<br />
The reserves estimated from the samples are 1,200 000 t (specific gravity 2.5 t/m3), prognostic reserves <strong>of</strong> the whole nepheline syenite body 290 million t.<br />
As a result <strong>of</strong> alkali metasomatosis and albitization, higher amounts <strong>of</strong> Nb2O5 with content 0.1%, Ta2O5, Rb20 (100-400 g and 300 g/t respectivelly) have<br />
developed with possible reserves.<br />
Serra Morrumballa is a huge intrusive massif N <strong>of</strong> the river Zambezi (see Fig. 4. 11. 2), <strong>of</strong> irregular oval shape, N-S direction, 15 km in length and about 5<br />
km in width. The structure <strong>of</strong> the massif is fairly complicated and different from other syenite massifs.<br />
Fig. 4.11.2. Geological map <strong>of</strong> Serra Morrumbala syenite massif (Geol. Inst. Beograd, 1981) (403 kB)<br />
It is a plutonic body intruded in Precambrian gneisses composed <strong>of</strong> syenites, granites, granulosyenites and rhyolitic lavas and breccias.<br />
Alkali granites occupy the NE part, alkali syenites the S part. Several veins <strong>of</strong> syenitic and granitic composition cut through the massif. They are alkali syenite<br />
porphyry, nepheline syenite porphyry, trachyte and solvsbergite, <strong>of</strong> alkali province.<br />
Alkali granite is pink, medium - to coarse - grained, with alkali amphibole (10%), orthoclase-perthite (60%) and quartz (20-30%). Alkali syenite with quartz<br />
(3-10%) contains about 10% <strong>of</strong> mafic minerals and orthoclase-perthite.<br />
Alkali syenites <strong>of</strong> Morrumbala are composed <strong>of</strong> microperthite and orthoclase, aegirine, augite, sodium amphibole, biotite, sphene and zircon. Syenite alkali:<br />
microperthitic with pyroxene, amphibole and rare riebeckite (Coelho 1959):<br />
1 2 1 2<br />
SiO2 57.68 52.04 MgO 1.03 0.75<br />
TiO2 1.03 0.53 CaO 3.61 1.19<br />
Al2O3 18.08 21.07 Na2O 7.22 11.82<br />
Fe2O3 1.48 3.72 P2O5 0.49 0.24<br />
FeO 3.80 1.90 H2O+ 0.19 0.09<br />
MnO 0.07 0.12 H2O- 0.30 0.87<br />
In general, its chemical composition is similar to that <strong>of</strong> other massifs <strong>of</strong> the Chilwa Alkaline province, but at Morrumbala the structure <strong>of</strong> the massif is more<br />
complex with migrating centres or different plutonic rocks and a different degree <strong>of</strong> magma contamination. From an economic point <strong>of</strong> view, just some vein<br />
rocks with a higher alkali content could be <strong>of</strong> interest, the alumina content is low, the silica content high.<br />
Alkaline massifs west <strong>of</strong> the Rift Valley<br />
The W- part <strong>of</strong> the massif Salambidua is situated in <strong>Mozambique</strong>. It is composed <strong>of</strong> hornblende syenites without nepheline; the central part on the Malawian<br />
side is made up <strong>of</strong> carbonatite. The massif is a circular plutonic intrusion (see Fig. 4.11.3). The chemical composition <strong>of</strong> microperthitic syenite with amphibole<br />
and pyroxene (Coelho 1956) is this (in %):<br />
SiO2 58.96 MnO 0.11 P2O5 tr.<br />
TiO2 0.62 MgO 0.83 H2O+ 0.23<br />
Al2O3 17.27 CaO 3.08 H2O- 0.35<br />
Fe2O3 1.93 Na2O 7.47<br />
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FeO 3.95 K2O 5.09<br />
Fig. 4.11.3. Geological map <strong>of</strong> Monte Salambidwe syenite massif (Geol.Inst., Beograd, 1981) (426 kB)<br />
The massif Cheneca, not explored into detail, consists <strong>of</strong> hornblende-syenites. Minor alkaline intrusions occur also at Monte Buzimuana (Chuare) located<br />
between the carbonatite ring structure <strong>of</strong> Muambe in the S and Salambidua in the N. From these radiate dykes <strong>of</strong> solvsbergite and other alkaline rocks.<br />
The largest Cretaceous intrusion <strong>of</strong> the whole region is the Serra de Gorongosa, which rises 2,000 m above the surrounding plain. The complex consists <strong>of</strong> a<br />
central core <strong>of</strong> micropegmatite granite which intruded an earlier gabbroic intrusion comprising tholeiitic gabbros with labradorite and clinopyroxene and some<br />
norite and olivine gabbros.<br />
These rocks are, naturally, out <strong>of</strong> use even as substitutes for nepheline syenites, but are <strong>of</strong> an identical alkaline province. Often, they are accompanied by a<br />
swarm <strong>of</strong> dykes extending from Gorongosa complex over 60 km (Hunting, 1984).<br />
Some <strong>of</strong> these alkaline complexes with phonolites, trachytes and affinite derivates may provide alkalies and alumina for the glass industry in order to<br />
substitute soda ash and add alumina to the batch. In many countries, phonolites, trachytes and rhyolites are used in a production <strong>of</strong> coloured container glass.<br />
An example is trachyte <strong>of</strong> Monte Nharuchonga which belongs to the Xiluvo carbonatite ring structure and lies W <strong>of</strong> Beira.<br />
Composition is this (in %): SiO2 - 50.66, Al2O3 - 17.20, Fe2O3 - 7.19, FeO - 1.60, CaO - 1.75, Na2O - 7.50, K2O - 6.03, P2O5 - 0.09, SO3 - 0.65 and L. i.<br />
3.69%.<br />
In 1984, the Geological Institute <strong>of</strong> Beograd explored a complex <strong>of</strong> alkaline rocks in central <strong>Mozambique</strong>.<br />
They examined two groups <strong>of</strong> rocks:<br />
Alkaline rocks <strong>of</strong> the Lupata Series <strong>of</strong> the Lower Cretaceous, similar rocks to those <strong>of</strong> the Sena Formation, Mio-Pliocene age. The Lupata series is composed,<br />
at its base, by several different alkaline rocks, which form an extensive sickel-shaped outcrop in mid-Zambezi, at the Lupata rapids. Rocks <strong>of</strong> the Lupata<br />
Series are mostly trachytic, they include phonolites, analcite kenyites and blairmorites, with different agglomerates. The lavas are potash-enriched,<br />
undersaturated and <strong>of</strong> alkaline affinity. The age <strong>of</strong> the rocks spans over 130 to 100 million years (Hunting, 1984).<br />
Phonolites <strong>of</strong> the Lupata Series contain abundant nepheline, alkali-feldspar, clinopyroxene and are <strong>of</strong> a trachytoid and nephelinoid texture.<br />
Overlying unconformly Cretaceous sediments and volcanics the Sena Formation is composed mainly <strong>of</strong> pebbly calcareous muddy grit and several volcanic<br />
vents. The volcanic rocks <strong>of</strong> the Sena Formation are phonolites, trachytes with nepheline basalts, olivine basalts, augitites and limburgites.<br />
Analysis <strong>of</strong> phonolites samples from the Sena Formation by Geol. Inst. Beograd (1984):<br />
Sample 1 2 3<br />
SiO2 53.99 53.90 53.63<br />
TiO2 0.25 0.17 0.17<br />
Al2O3 19.37 22.52 21.67<br />
Fe2O3 3.02 3.74 1.32<br />
FeO 1.50 0.44 3.07<br />
MnO 0.13 0.08 0.11<br />
MgO 1.56 0.86 0.86<br />
CaO 1.62 0.25 1.35<br />
Na2O 7.20 10.20 10.40<br />
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K2O 5.64 4.80 5.32<br />
P2O5 - - 0.02<br />
H2O+ 5.46 3.77 1.77<br />
H2O- 0.49 0.10 0.29<br />
Total 100.23 100.83 99.98<br />
Samples 1, 2 were obtained from a phonolite plug penetrating Precambrian rocks, sample 3 from a volcanic vent into the Sena Formation.<br />
Other alkaline rocks occurring in <strong>Mozambique</strong> are these: nepheline syenites, trachytes and phonolites - ready sources <strong>of</strong> raw materials needed in the glass and<br />
ceramic industry. Pegmatites <strong>of</strong> nepheline and other types <strong>of</strong> syenites may represent a source <strong>of</strong> corrundum, rare metals and earths and other minerals.<br />
Apparently, they are to be found along all rift valleys and grabens filled with Karroo and younger sequences or in deep faults and ring structures within the<br />
whole Mozambican belt.<br />
Conclusions:<br />
There are such quantities <strong>of</strong> nepheline syenites in <strong>Mozambique</strong> that, if mined, they could easily surpass the world production <strong>of</strong> nepheline syenite for glass and<br />
ceramic industry. In addition they may represent a resource in a production <strong>of</strong> alumina, sodium and potassium compouds, rare earths and metals. Nepheline<br />
syenites are concentrated in the Chilwa alkaline province covering the East African rift valley in the form <strong>of</strong> several isolated epizonal plutonic massifs -<br />
intrusions mainly <strong>of</strong> Cretaceous age.<br />
Nepheline syenites may serve as a source <strong>of</strong> nepheline feldspars and, generally, may be a valuable flux -and alumina component <strong>of</strong> glass and part <strong>of</strong> ceramic<br />
mixtures in porcelain, sanitary ware etc. Although it has not been tested along these lines, several chemical and mineralogical analyses confirmed, that a<br />
production <strong>of</strong> commercial products depended on the dressing method <strong>of</strong> each petrological type <strong>of</strong> syenite in question.<br />
Technological tests made <strong>of</strong> nepheline syenite from Monte Conguene proved that it is suitable for alumina production.<br />
Reserves were estimated to 290 million t with 1,200 000 t <strong>of</strong> checked reserves. Considering other nepheline syenite massifs described in the text, estimated<br />
reserves suggest several thousands <strong>of</strong> million tons and are, in fact, inexhaustive.<br />
© Václav Cílek 1989<br />
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Cilek: 4.12. Perlite<br />
4.12. Perlite<br />
Perlite is a volcanic glass <strong>of</strong> a typical concentric globular "pearl-like" structure, commonly light grey<br />
and <strong>of</strong> rhyolitic or rhyolite-dacite composition. The "pearl-like" or onion-like structure with macro- and<br />
microscopic cracks is the result <strong>of</strong> shrinkage by cooling <strong>of</strong> volcanic glass. The commercial product,<br />
however, is glass, that at about 760-1,100°C will expand and form a lightweight frothy material. The<br />
expanding properties are caused by molecular water and loosely contained water (1-10%). During<br />
sintering water in the glass is converted to steam which cannot escape through the viscous walls <strong>of</strong> glass<br />
and thus glassy foam is produced. It is somewhat similar to natural pumice. The volume <strong>of</strong> the original<br />
glass increases 10 to 20 times and its density decreases from about 1.0 to 0.02. In nature, this process is<br />
repressed by the weight <strong>of</strong> overburden or by a quick cooling <strong>of</strong> the outer parts <strong>of</strong> lava flows, lava domes<br />
or at the contact with the water basin.<br />
The composition <strong>of</strong> expanded perlite is identical to that <strong>of</strong> the parent rock - about 70% SiO2, 12%<br />
Al2O3, 3% coloured oxides and up to 8% <strong>of</strong> alkalies. The water content varies from 1-10%. Apparently<br />
most perlite deposits originate by a hydration <strong>of</strong> obsidian (< 2% water), which contains magmatic water<br />
only. Therefore the presence <strong>of</strong> meteoric water from groundwater resources decides probably upon the<br />
expanding properties <strong>of</strong> perlite. In the U. S. A., some perlites contain rounded bodies <strong>of</strong> obsidian nuclei -<br />
drops <strong>of</strong> black glass known as Apache tears (Harben, Bates -1984), confirming the hydratation process<br />
in obsidian.<br />
Perlite displays significant physical properties - it is light, highly porous and stabile; its thermal and<br />
acoustic properties are utilized in lightweight concrete, in insulation in foundries for the transport <strong>of</strong><br />
ingots, in the transport <strong>of</strong> liquified natural gas, as a filler in paints, plastics, for filtering water etc. Perlite<br />
is usually pretreated at the deposit site, it is crushed and sieved to the required grain size (0.3 to 1.5<br />
mm), and transported to the place <strong>of</strong> consumption where it is expanded. Competitive material is pumice,<br />
which is stronger in concrete and naturally expanded, but it has to be transported in large volumes.<br />
Another competitive material is vermiculite with similar or even better properties.<br />
In nature, perlite is found in lava domes, lava flows, dikes and sills, in rhyolites, andesites and dacites<br />
layers originating from hydrothermal alteration. In the geological past, "old" perlites changed from a<br />
vitreous to a crystalline texture, whereby the devitrified or recrystallized material lost its expanding<br />
properties. The age <strong>of</strong> commercial perlites is rarely older than the Oligocene (Harben-Bates, 1984). The<br />
minimum-sized economic deposit should contain 100-300,000 t <strong>of</strong> ore.<br />
In <strong>Mozambique</strong>, perlite (see Fig. 4. 1. 1) was discovered by L. Mallac during the prospection <strong>of</strong> the<br />
Pequenos Lebombos Mts. in 1953-1960. The sites are located S <strong>of</strong> bentonite deposits and layers <strong>of</strong><br />
obsidian and perlite in rhyolites are fairly slender. The two major deposits explored were: Muguene<br />
South and Muguene North. On Muguene South, proved reserves were 100,000 t, probable reserves<br />
400,000 t, while on deposit Muguene North the reserves <strong>of</strong> vitrified rhyolite glass achieved 250,000 t <strong>of</strong><br />
proved and 1 million t <strong>of</strong> probable reserves. Several other claims in the vicinity - Ali, Lona, Cris, Ursula<br />
were laid down. Before 1961 (Mallac, 1962) one furnace for perlite heating was errected there and small<br />
amounts <strong>of</strong> perlite were produced. However not every volcanic glass was suitable for a production <strong>of</strong><br />
expanded perlite.<br />
A sample <strong>of</strong> perlite was sent to the South African Portland Cement Institute in Johannesburg and tests<br />
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Cilek: 4.12. Perlite<br />
were made with the following results:<br />
loose bulk density lb/cu. ft. 8.77 - USA perlite 6.84<br />
consolidated bulk density lb/cu. ft. 12.03 -USA perlite 8.46<br />
A low density is essential for the quality <strong>of</strong> perlite and perlite from Muguene has a bulk weight <strong>of</strong><br />
aproximately 30% higher than the American sample.<br />
The grading analysis gave these results:<br />
BS Sieve No. Muguene sample USA comp. sample<br />
7 99.5 100<br />
14 95.1 87<br />
25 62.7 51.1<br />
52 39.0 28.9<br />
100 25.0 16.0<br />
The Muguene sample has an excess <strong>of</strong> fine material, when compared with the American product. The<br />
material is acceptable for use as a concrete or plaster aggregate, but could be improved by reducing the<br />
amount -100 mesh material to about 15%.<br />
In 1978-79, the vicinity <strong>of</strong> Muguene was again explored and 28 boreholes were sunk. The overlying<br />
strata are rhyolites <strong>of</strong> brownish colour and a fluvial structure which are altered and partly bentonized.<br />
Below the rhyolite is a layer <strong>of</strong> bentonized rhyolite (thickness about 3 m) overlying dark grey obsidian<br />
(about 2 m thick). This is followed by a layer <strong>of</strong> greenish perlite, about 1 m thick. The lowest layer<br />
above the basalts is fine-grained grey aleurite, about 2 m thick. In places where the obsidian layer is thin,<br />
it is completely altered into bentonite (Kouzmine-Akimidze, 1981). Maximum thickness <strong>of</strong> obsidian in<br />
borehole 28 was 3.34 m.<br />
Chemical analysis (Laboratories ING):<br />
SiO2 72.90 MgO 1.71<br />
Al2O3 11.47 P2O5 0.025<br />
Fe2O3 2.35 Na2O 5.95<br />
CaO 0.56 K2O 4.55<br />
Reserves were calculated for two sectors:<br />
sector A - average thickness <strong>of</strong> obsidian 1.45 m<br />
specific gravity 2.33-2.41 g/m3<br />
reserves 32,370 t.<br />
sector B - average thickness <strong>of</strong> obsidian 2.12 m<br />
specific gravity 2.35 g/cm3<br />
reserves 22,090 t.<br />
Acceptable are just the reserves <strong>of</strong> sector A with an overburden <strong>of</strong> rhyolite <strong>of</strong> a maximum thickness <strong>of</strong><br />
15 m. An interesting observation is an alteration in the texture <strong>of</strong> perlite, the material is devitrified and<br />
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Cilek: 4.12. Perlite<br />
rhyolitic glass is recrystallized; it is composed <strong>of</strong> a number <strong>of</strong> oolitic and spheric nuclei with grains <strong>of</strong><br />
quartz.<br />
In 1982, the new exploration stage <strong>of</strong> the whole area <strong>of</strong> Pequenos and Grandes Lebombos made by<br />
Ivanicka-Sykora resulted in the discovery <strong>of</strong> a deposit <strong>of</strong> obsidian close to the town <strong>of</strong> Ressano Garcia.<br />
The deposit extends just N and S <strong>of</strong> the main road Maputo-South Africa, about 20 km E <strong>of</strong> Ressano<br />
Garcia (Fig. 4.12.1).<br />
Fig. 4.12.1. Geological map <strong>of</strong> a part <strong>of</strong> the Lebombo Mts. (Compiled by Ivanicka, 1982) (563 kB)<br />
The volcanic complex <strong>of</strong> the "Grandes Lebombos" forms a 20 km wide chain, oriented from N to S. The<br />
rocks belong to the Jurasic Stormberg Series (Upper Karroo), and consist <strong>of</strong> rhyolites, basalts and<br />
doleritic dykes. In the study area, rhyolites are in tectonic contact with younger basalts. They contain<br />
intercalations <strong>of</strong> porphyrites, rhyodacites and volcanic breccias. The thickness <strong>of</strong> the complex is up to<br />
500 m: volcanic glass is developed in its upper part.<br />
The deposit, studied at length, has a N-S trend extending over 600 m, with an average width <strong>of</strong> 60 m and<br />
a depth between 3.5 m and 25.0 m.<br />
Volcanic glass is <strong>of</strong> a rhyodacitic composition, it is dark greyish to black in colour, which changes<br />
locally into greenish brown and green.<br />
It is compact and strongly recrystallized, and has a perlite texture. This volcanic glass was transformed<br />
to bentonite along faulted contact faults.<br />
Basalts occupy the low-lying parts and are seldom seen in outcrops. The fresh rock has a dark grey<br />
colour and is finely grained. Dolerite sills are prominent in the landscape and are <strong>of</strong> a dark green,<br />
compact variety.<br />
Volcanic glass is part <strong>of</strong> a volcanic sequence composed <strong>of</strong> rhyolites, rhyodacites and tuffs, all <strong>of</strong> effusive<br />
origin. Part <strong>of</strong> the lava flow emerged from rhyolite copulas and a substantial cooling <strong>of</strong> their outher part<br />
occurred probably in water environment. The composition <strong>of</strong> glass corresponds to that <strong>of</strong> rhyodacite<br />
(Fig. 4.12.2).<br />
Fig. 4.12.2. Cross section <strong>of</strong> volcanic glass occurences at Ressano Garcia (Ivanicka, 1982) (293 kB)<br />
Similarly to the Muguene deposit in Pequenos Lebombos, altered rhyolites and tuffs developed in the<br />
ro<strong>of</strong> <strong>of</strong> the obsidian layer.<br />
The thickness <strong>of</strong> bentonized material is 2-3 m, its composition (in %) is this:<br />
A minimum maximum<br />
SiO2 54.86 60.64<br />
Al2O3 14.42 15.11<br />
Fe2O3 5.22 6.91<br />
CaO 0.42 0.86<br />
MgO 0.81 1.99<br />
Na2O 0.92 1.47<br />
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Cilek: 4.12. Perlite<br />
K2O 0.98 3.04<br />
TiO2 0.24 0.53<br />
H2O- (105°C) 8.08 14.40<br />
H2O+ (1,100°C) 3.32 6.37<br />
The ion exchange is high:<br />
Na+ mval/100g 1.11- 2.72<br />
K+ mval/100g 0.44- 1.52<br />
Ca2+ mval/100g 12.50-30.00<br />
Mg2+ mval/100g 33.71-41.91<br />
The composition <strong>of</strong> volcanic glass is similar to that <strong>of</strong> the analyzed bentonitic material which proves that<br />
bentonites originated from an alteration <strong>of</strong> volcanic glass. Apparently the development was this:<br />
obsidian ===> hydratation ===> perlite ===> recrystallized and devitrified perlite ===> bentonite.<br />
Part <strong>of</strong> perlite may be absent.<br />
Chemical composition <strong>of</strong> volcanic glass:<br />
mimimum % maximum % minimum % maximum %<br />
SiO2 66.19 67.80 P2O5 0.03 0.06<br />
Al2O3 13.73 14.89 MnO 0.05 0.09<br />
Fe2O3 3.13 4.05 Na2O 2.81 3.85<br />
CaO 0.27 0.34 K2O 2.08 3.32<br />
MgO 0.28 0.36 SO3 0.11 0.41<br />
FeO 0.55 2.90 H2O- (105°C) 1.76 2.62<br />
TiO2 0.13 0.44 H2O+ (1,100°C) 3.17 4.08<br />
The absorption coefficient <strong>of</strong> most <strong>of</strong> the samples is lower than 1%, specific weight between 2.38 and<br />
2.75 g/cm3 (more commonly between 2.3 g and 2.45 g/cm3), porosity low, ranging from 0.1% to 2.5%.<br />
The Los Angeles test resulted mostly in value exceeding 35%, but below 80%.<br />
Compression tests were carried out just with 9 samples and values differed considerably. The minimum<br />
value was 335 kg/cm2, the maximum 1,197 kg/cm2.<br />
Estimated reserves:<br />
Category C1 585,792 t<br />
Category C2 322,388 t<br />
Total 908,180 t<br />
Overburden is negligible.<br />
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Cilek: 4.12. Perlite<br />
The Ressano Garcia deposit was chosen for its favourable location and expansion tests were made <strong>of</strong><br />
representative samples after drilling. For each <strong>of</strong> these samples, the fractions 4.75-10.00 mm and 0.20-<br />
1.18 mm <strong>of</strong> crushed rock were heated from 1,000°C through 1,100°C to 1,200°C, but expansion<br />
characteristic were not observed at any <strong>of</strong> these temperatures. Fractions between 0.20-1.18 mm were<br />
tested in Czechoslovakia in an expansion oven but no expansion occured. The results indicated that the<br />
material could not be used as expanded perlite, although its chemical composition, i.e. a high<br />
concentration <strong>of</strong> H2O+ at 1,100 °C and it as an expandable type. However, it can be used in road<br />
construction or concrete production. This exploration <strong>of</strong> volcanic glass - a possible source <strong>of</strong> expanded<br />
perlite-serves as an example <strong>of</strong> an underestimation <strong>of</strong> the importance <strong>of</strong> technological testing <strong>of</strong> the<br />
investigated material before the start <strong>of</strong> the main exploration. The result is, that expensive exploration<br />
programme was the disclosure <strong>of</strong> a "deposit" <strong>of</strong> volcanic glass, which could possibly be utilized as<br />
ornamental stone or as a doubtful building material in an area, in which high-quality building stone is<br />
plentifull.<br />
Other perlite occurence may possibly be found within other areas <strong>of</strong> Karroo volcanics <strong>of</strong> Jurassic-<br />
Cretaceous age. Their commercial utilization will depend on the degree <strong>of</strong> subsequent alteration and<br />
devitrification.<br />
Conclusions:<br />
Perlite is a very useful material for the building industry, as a thermic and acustic insulation, for<br />
filtration and as a filler. Perlite deposits in Karroo volcanics <strong>of</strong> Cretaceous age are either too small -<br />
layers <strong>of</strong> 1.3 m thick, or the degree <strong>of</strong> alteration, in this case the process <strong>of</strong> bentonization and<br />
devitrification is so high that commercially important deposits could hardly be expected in <strong>Mozambique</strong>.<br />
If the common rule that deposit older than the Otigocene could hardly contain expanded perlite were to<br />
be valid throughout the world, the Karroo volcanic glasses in <strong>Mozambique</strong> would yield only remnants <strong>of</strong><br />
commercially suitable material even if found in a bigger quantity.<br />
In my opinion, other sources <strong>of</strong> expanded material could be used in the country such as Karroo<br />
claystones or other younger clays <strong>of</strong> the Tertiary age.<br />
© Václav Cílek 1989<br />
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Cilek: 4.13. Phosphates and apatite<br />
4.13. Phosphates and apatite<br />
Phosphorus is one <strong>of</strong> the most essential elements for life, and beside nitrogene and potassium, a primary material<br />
in fertilizer production. The importance <strong>of</strong> phosphorus compounds increases directly with an increase in the<br />
world population and still higher demands for food, more soil and higher crop yields. Therefore, phosphates are<br />
in the centre <strong>of</strong> attention <strong>of</strong> all countries, both developed and developing, because it can secure the food supply<br />
for the population. More than 90% <strong>of</strong> phosphates are used in the production <strong>of</strong> fertilizers.<br />
A useful phosphorus mineral <strong>of</strong> phosphates is apatite, which may be present in magmatic rocks and in<br />
sedimentary formations, where the rock is called phosphorite.<br />
Apatite is a calcium fluorine-chlorine-hydrozyl phosphate <strong>of</strong> the formula Ca5(PO4)3 (F, Cl, OH). Apatites in<br />
magmatic and metamorphic rocks are crystalline fluorapatite Ca5(PO4)3F and chlorapatite Ca5(PO4)3Cl with a<br />
content <strong>of</strong> P2O5 42.3 and 41.0%. The hydroxy-fluorapatite Ca5(PO4)3 (OH, F) is also the main constituent in<br />
most igneous rocks and carbonatites.<br />
In sedimentary deposits, apatites are not as structurally stable as are crystalline apatites. Besides Cl and F in a<br />
complex anion, the groups OH, O or CO3 are always present and the resulting rock is a mixture <strong>of</strong> several main<br />
components, which is known as francolite or cellophane <strong>of</strong> an amorphus structure, the essential part <strong>of</strong><br />
sedimentary apatites <strong>of</strong> a formula identical to that <strong>of</strong> fluorapatite Ca5(PO4, CO3, OH) (F, OH). One <strong>of</strong> the<br />
isomorphic component <strong>of</strong> sedimentary phosphorites is also carbonateapatite Ca10(PO4)6 (CO3).<br />
Apatite <strong>of</strong> igneous origin occurs in typical hexagonal prismatic crystals <strong>of</strong> greenish, yellow, violet colour or<br />
colourless, with a vitreous luster <strong>of</strong> specific gravity 3.1-3.2; by contrast, sedimentary apatite occurs in granular to<br />
dense masses, in coll<strong>of</strong>orm or botryoidal crusts, cryptocrystalline (francolite).<br />
Besides normal phosphates, also aluminous phosphates can serve as a source <strong>of</strong> phosphorus. Three minerals in<br />
this group are <strong>of</strong> some importance: wavellite, crandallite and miltisite.<br />
Phosphates in sedimentary rocks appear in the form <strong>of</strong> cement in sandstones and sand, grains in clays, part <strong>of</strong><br />
fossil shells (content 10-25% P2O5) and in oolites (mm diameter) and concretions. Commercial "phosphate rock"<br />
should contain at least 20% <strong>of</strong> P2O5 despite the fact that some deposits have a P2O5 amount <strong>of</strong> 5% and are still<br />
economic (carbonatites with byproducts <strong>of</strong> magnetite, pyrochlore, rare earths, monazite, anatase, vermiculite).<br />
The content <strong>of</strong> P2O5 is the main criterium used in quality grading, the P content is rarely used. The old American<br />
grades <strong>of</strong> PBL (bone phosphate <strong>of</strong> lime) still survive from the time when phosphates were produced from bones.<br />
The main use <strong>of</strong> phosphate is in the fertilizer production. Mainly readily soluble carbonate phosphates are applied<br />
after grinding directly to the soil, but most <strong>of</strong> the phosphates - both crystalline and amorphous need to be<br />
beneficiated. First, the impurities such as chert, clay, sand, limestone, dolomite, must be removed, by crushing,<br />
sieving, washing and flotation to increase the P2O5 content to about 30%. The phosphate is then treated in a dry<br />
or wet process. The first process - production <strong>of</strong> the so-called thermophosphate, involves heating in an electric<br />
furnace to produce elementar P, which is converted to pure phosphoric acid used in chemical and food-grade<br />
products.<br />
The wet process includes the action <strong>of</strong> sulphuric acid on beneficiated phosphate to produce superphosphate CaH2<br />
(PO4)2 • H2O + CaSO4 • 2H2O with 16-21% P2O5. In this process, roughly 5 t <strong>of</strong> impure gypsum is obtained<br />
from 1 t <strong>of</strong> P2O5 and most <strong>of</strong> it is waste. Superphosphate can further be treated to triple superphosphate with<br />
about 45% P2O5, the final member <strong>of</strong> which is phoshoric acid. This acid or superphosphoric acid is preferred in<br />
the industry, because it can easily be transported by tankers.<br />
Not all natural phosphates are suitable for fertilizer production, because some cannot be beneficiated. The high<br />
content <strong>of</strong> CaO needs an extra amount <strong>of</strong> sulphuric acid, also harmful is an increased amount <strong>of</strong> Fe, Mg and Al.<br />
This applies also to Cl and F.<br />
The remaining 10% <strong>of</strong> phosphate (90% fertilizer) are utilized by various industries foodstuff, fodder, detergents,<br />
drinks, surface metal treatment etc.<br />
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Cilek: 4.13. Phosphates and apatite<br />
A division <strong>of</strong> the genetic types <strong>of</strong> apatite and phosphate deposits is this:<br />
1. crystalline apatite in late magmatic deposits <strong>of</strong> magnetite-apatite and nepheline-apatite type<br />
2. skarn deposits<br />
3. metasomatic deposits in carbonate rocks<br />
4. carbonatite deposits<br />
5. hydrothermal and mesothermal veins and sills<br />
6. metamorphosed sedimentary deposits<br />
Types 1-5 are primary deposits <strong>of</strong> apatite in relation to igneous rocks <strong>of</strong> alkaline composition or in carbonatites<br />
volcanic bodies. An accumulation <strong>of</strong> apatite is brought about by magma separation, hot fluids and gases in the<br />
way <strong>of</strong> metasomatic replacement, hydrothermal solutions or simple injection.<br />
Sedimentary deposits originate from these primary sources. They constitute about 85% <strong>of</strong> commercial production<br />
<strong>of</strong> phosphates and can be divided into:<br />
1 sedimentary phosphate deposits <strong>of</strong> geosynclinal and epicontinental seas originate during biochemical process<br />
bringing forth concretionally and oolithic phosphates. The development <strong>of</strong> these deposits is usually multicyclic<br />
process which requires specific structural conditions, chemical system, transport <strong>of</strong> elements, reworking <strong>of</strong><br />
deposits, residual enrichment and additional new phosphorus material<br />
2 phosphate gravel or land pebble or river pebble deposits originate by reworking <strong>of</strong> older deposits<br />
3 residual and infiltration deposits originate from a dissolution <strong>of</strong> carbonates by phosphate, mainly in karst areas,<br />
and a deposition in blanket deposits or in cavities and fissures<br />
4 guano deposits <strong>of</strong> two types, birds excrements and bats excrements, originate from an interaction with<br />
underlying limestone<br />
5 wavellite, a alumina phosphate, may be concentrated in a phosphate deposit<br />
The Mozambican phosphate deposits are essentially primary deposits <strong>of</strong> apatite in<br />
1 crystalline limestones <strong>of</strong> the Precambrian originated from a replacement and metasomatism together with<br />
injection; apatite-carbonate, apatite-magnetite and apatite-silicate types <strong>of</strong> mineralization occur.<br />
The two deposits are: Monte Muande-Monte Fema near Tete and Evate deposit near Nampula<br />
2 Occurence in carbonatites with apatite <strong>of</strong> a low content, dispersed or in thin hydrothermal veins; three volcanic<br />
massifs are known: Monte Xiluvo near Beira, Monte Muamba SE <strong>of</strong> Tete and Cone Negose on the bank <strong>of</strong> the<br />
Cabora Bassa dam, <strong>of</strong> Jurrasic -Cretaceous age; small sill bodies <strong>of</strong> carbonatite at Luicuisse in the Niassa<br />
Province.<br />
Sedimentary deposits can also be divided into two groups:<br />
3 Phosphorites <strong>of</strong> hypothetical presence, supposed to be developed in coastal sedimentary basins: in the S-<br />
Mozambican basin and in the N-Rovuma basin, <strong>of</strong> Cretaceous-Tertiary age<br />
4 Deposits <strong>of</strong> guano <strong>of</strong> bats in karst cavities <strong>of</strong> Cheringoma and J<strong>of</strong>ane limestones <strong>of</strong> Eocene and Miocene age;<br />
the only phosphates used by the local population. The guano is <strong>of</strong> Quaternary age (Fig. 4.13.1).<br />
Fig. 4.13.1. Occurences <strong>of</strong> phosphate and apatite (323 kB)<br />
The best known magnetite-apatite deposit is Monte Muande. The iron ore mined will be used in the production<br />
<strong>of</strong> sponge iron in the first Mozambican iron and steel factory. Apatite as a byproduct will be concentrated and<br />
futher treated.<br />
The Monte Muande deposit is situated about 30 km NW <strong>of</strong> Tete on the N- bank <strong>of</strong> the river Zambezi and<br />
continues as the Monte Fema deposits in SW direction across the river on its S- bank. It is part <strong>of</strong> hills called<br />
Serra Muande which lies in the zone <strong>of</strong> uranium mineralization <strong>of</strong> Mavudzi type (davidite). In the past, interest<br />
was centered mainly on magnetite deposits, investigated by the Nissho company in 1960 and by the Yugoslav<br />
team in 1984 (Fig. 4.13.2).<br />
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Fig. 4.13.2. Schematic geological map <strong>of</strong> Monte Muande (Geol.Inst., Beograd, 1984) (429 kB)<br />
The deposit Muande consists <strong>of</strong> medium grained crystalline marble belonging to the Chidue Group, with<br />
abundant bands and crystals <strong>of</strong> magnetite, and interlayers <strong>of</strong> gneisses. The marbles overlie biotite and augen<br />
gneisses and, in the contact zones, remobilized marbles penetrate in the gneiss in a thin layers (Hunting, 1984).<br />
Marbles <strong>of</strong> the Chidue Group are overlain by igneous rocks <strong>of</strong> the Tete Complex, mainly gabbro, with some<br />
pyroxenites and hornblendites intruding the marbles. All rocks <strong>of</strong> the region are intruded by late granite, aplite,<br />
syenite and pegmatite dykes.<br />
Magnetite and apatite concentrations <strong>of</strong> economic importance located around the top <strong>of</strong> Monte Muande, occur<br />
within the marble massif (4.5 km long) as stratiform bodies concordant with the foliation. While magnetite forms<br />
different sills or is disseminated in marbles in very variable concentration, the distribution <strong>of</strong> apatite is more<br />
homogeneous.<br />
The ore zones are <strong>of</strong> NE-SW direction; the mineralization is concentrated in three zones <strong>of</strong> which the central is<br />
the richest. The marble beds could be several 100 m thick and biotite marbles with apatite and none or little<br />
magnetite, but with a characteristic presence <strong>of</strong> flint nodules, alternate with magnetite-mineralized marbles. The<br />
main magnetite zone is 3,500 m long and 800 m thick (see Fig. 4.13.3).<br />
Fig. 4.13.3. Cross sections through the central zone <strong>of</strong> Monte Muande (Geol.Inst., Beograd, 1984) (482 kB)<br />
The process <strong>of</strong> mineralization starts with apatite at a pneumatolytic phase <strong>of</strong> the Tete igneous complex, with<br />
coarse grains and, sometimes, concentrated layers, followed by magnetite ore injection <strong>of</strong> residual liquids after<br />
magma differentiation into an adjacent area <strong>of</strong> ductile crystalline limestones.<br />
The apatite <strong>of</strong> the pneumatolytic phase is accompanied by rare-earth mineralization, the magnetite injection with<br />
ilmenite.<br />
Analysis <strong>of</strong> a composite sample (in %):<br />
Fe (total) 17.68<br />
Fe (sol.) 15.54<br />
P2O5 4.03<br />
SiO2 4.19<br />
Al2O3 1.45<br />
TiO2 1.99<br />
CaO 35.29<br />
MgO 6.24<br />
S 0.30<br />
Mn 0.13<br />
This composition corresponds to the mineralogy <strong>of</strong> biotite and chlorite 13%, apatite 11 % which contains about<br />
4% P2O5, ratio apatite: carbonate = 1:5.1, difficult to separate; opaque minerals 20% (magnetite, hematite,<br />
goethite, pyrite, small pyrrhotite and chalco pyrite). Magnetite easily separable at 0.3 mm .<br />
Average content <strong>of</strong> total<br />
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Fe 3 - 67 %<br />
FeO 2 - 28 %<br />
TiO2 0.8 - 5.6 %<br />
P2O5 0.2 -11.4 % (mainly 4.4 - 5.6 %)<br />
CaO 1.0-46.0 %<br />
The deposit was divided by the Yugoslav team into these primary zones:<br />
1 high-grade Fe deposit- average thickness 5.15 m<br />
Fe 3.59 - 60.08 % - av. 34.52 %<br />
P2O5 0.06 -11.51 % - av. 5.12%<br />
2 moderate - grade Fe deposit - average thickness 8.75 m<br />
Fe 4.05-56.19 %, av. 21. 11%<br />
P2O5 0.45-11.41 %-av. 5.25%<br />
3 low-grade Fe deposit - average thickness 29.0 m<br />
Fe 2.00-28.50 %-av. 9.95%<br />
P2O5 0.89- 7.56 %-av. 4.02%<br />
In addition an eluvial deposit covers the marble area at an average thickness <strong>of</strong> 2.52 m and an Fe content <strong>of</strong> 1.55-<br />
66.50%-average 45.52%, P2O5 0.25-13.40%, average 5.01%.<br />
The eluvial deposits are <strong>of</strong> a typical residual origin on marbles with karst phenomena.<br />
Therefore, reserves were calculated<br />
in eluvial deposit: 2,680 000 t Fe 295,000 t P2O5<br />
in primary deposit: 14,620 000 t Fe 3,855 000 t P2O5<br />
total 17,300 000 t Fe 4,150 000 t P2O5<br />
Reserves were calculated to a depth <strong>of</strong> 140 m only. Futher reserves may be delineated in the Monte Fema area on<br />
the S-bank <strong>of</strong> the river Zambezi.<br />
The Evate deposit within the Monapo structure is situated about 100 km <strong>of</strong> Nampula and close to the port <strong>of</strong><br />
Nacala. The deposit was discovered during a geophysical investigation for graphite by the Russian team (1975),<br />
later explored by Bulgarian (1983) and finally by Czechoslovakian geologists (1985) (Fig. 4.13.4 eastern part <strong>of</strong><br />
Evate).<br />
Fig. 4.13.4 Geological map <strong>of</strong> E - Evate deposit (Bulgargeomin -1983, Intergeo - 1985) (810 kB)<br />
Two regional geological units <strong>of</strong> the area are the older Nampula Group and the younger Lurio Group. The<br />
Monapo structure and also the formation are supposed to be an isolated plate <strong>of</strong> the younger Lurio Group shifted<br />
from the N and resting on the older Nampula Group. The shape <strong>of</strong> the structure is brachysynctinal, oval, with its<br />
axis in NNE-SSW direction. It is divided into four units, from the bottom upwards: Namialo, Ramiane,<br />
Metocheria and Evate. The deposit <strong>of</strong> apatite-magnetite within the Evate unit is composed <strong>of</strong> biotite gneisses,<br />
sillimanite- monzonitic- and graphitic gneisses with two different marble horizons.<br />
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According to Yourde-Wolf (1974) the age <strong>of</strong> the Monapo Formation is 970 ± 23 m.y. for granulites in the upper<br />
part <strong>of</strong> the sequence, 1,035 and 1,175 m.y. for leptinites and granulites-charnoquites, 860 m.y. for the phase <strong>of</strong><br />
anatexis, for the Katangan orogeny 500 m.y., terminating the orogenic activities in the region.<br />
The Evate deposit consists <strong>of</strong> a lens <strong>of</strong> marbles, about 3 km long and a maximum width <strong>of</strong> 850 m, which<br />
constitutes about 70% <strong>of</strong> the area, the remaining part are gneisses, 2 to 40 m thick. The mineralized apatite zones<br />
are 5-100 m thick. The marbles contain as their main constituents apatite, magnetite, forsterite, phlogopite and<br />
graphite, and minor proportion <strong>of</strong> diopside, amphibole, wollastonite, tremolite, scapolite, serpentine, garnets,<br />
spinele, microcline, plagioclase, quartz, rutile, sulphides, zeolites, cancrinite and anhydrite (Intergeo, 1985).<br />
In the past, graphite was mined in the Monapo Formation (see Chap. graphite), marble was burned to produce<br />
lime and some pegmatites were exploited for amazonite.<br />
Magnetite <strong>of</strong> Evate, similar to that <strong>of</strong> Muande, developed very irregularly throughout the deposit; its content<br />
ranges from 0 to 10% and is quite independent <strong>of</strong> the distribution <strong>of</strong> apatite. The central part <strong>of</strong> the deposit, where<br />
magnetite was first discovered, is the richest, with layers <strong>of</strong> magnetite <strong>of</strong> a disseminated type. The chemical<br />
composition <strong>of</strong> magnetite is this: Fe2O3 - 67.33%, FeO - 27.95%, TiO2 - 2.24%, MgO - 1.58%, Al2O3 - 0.79%,<br />
MnO - 0.0%.<br />
Apatite <strong>of</strong> Evate is <strong>of</strong> the fluorapatite variety Ca5(PO4)3F , an occurence <strong>of</strong> hydroxy-apatite Ca5(PO4)3 OH<br />
with an increased content <strong>of</strong> strontium, and RE is fairly rare.<br />
The apatite content in marbles is 15-30% with richer and poorer layers; their content increases to 40-50% just in<br />
the contact zones with gneisses. In the eluvial part, an enrichment zone <strong>of</strong> P2O5, 14-18%, represents about one<br />
fourth <strong>of</strong> the reserves.<br />
A chemical analysis revealed this composition: 0.05-19.7% P2O5 in marbles, 7-8% only in isolated marbles<br />
surrounded by gneisses and 0.00-1.5% in intrusive rocks.<br />
Beltchev (1983) analysed two composite samples, one with P2O5 above 8% (sample 1), the second below 8%<br />
(sample 2).<br />
% sample 1 sample 2<br />
P2O5 10.96 6.29<br />
Fe2O3 + FeO 7.8 2.86<br />
CaO 46.25 47.17<br />
MgO 4.26 2.90<br />
TiO2 1.63 0.52<br />
SiO2 1.50 0.67<br />
Al2O3 0.70 0.37<br />
Calculation <strong>of</strong> the reserves (Bulgargeomin, 1983):<br />
Apatite<br />
ore<br />
Iron<br />
ore<br />
category C2 92 million t<br />
category C1<br />
category C2 1.25 million t<br />
32 million t <strong>of</strong> this composition:<br />
9.59% P2O5, 3.80% Fe2O3, 3.59% MgO, 0.53% TiO2, 5.14% Fe2O3 + FeO<br />
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category C1<br />
3.45 million t <strong>of</strong> this composition:<br />
0.98% P2O5, 27.86% Fe2O3, 30.71% CaO, 7.76% MgO, 2.58% TiO2<br />
Having regard to all complexities <strong>of</strong> a dressing <strong>of</strong> Evate ore, the results <strong>of</strong> a new stage <strong>of</strong> this exploration by<br />
Intergeo (1985) indicated considerably larger reserves <strong>of</strong> this composition:<br />
155.413 000 t <strong>of</strong> apatite ore <strong>of</strong> 9.32% P2O5, 5.76% Fe, 1.21% TiO2, 47.69% CaO.<br />
The reserves were calculated at 100 m above sea level.<br />
A geochemical prospection made <strong>of</strong> the whole Monapo structure revealed very interesting results (Zacek-Duda,<br />
1986).<br />
An evaluation <strong>of</strong> an interaction <strong>of</strong> each geological field with a display <strong>of</strong> materials and energies in each section,<br />
revealed dislocation zones <strong>of</strong> a different age. The most important fracture zones are directed from N-S, W-E and<br />
NW-SE. These interpreted lines, probably deep-seated fractures, helped to clarify accumulations <strong>of</strong> some<br />
elements and minerals. Apparently fluids with phosphorus and other elements ascended along these zones and<br />
processes <strong>of</strong> metasomatosis together with infiltration-diffusion occurred there. At a contact <strong>of</strong> silicate and<br />
carbonate rocks, metasomatic degradation <strong>of</strong> carbonates by forsterite, enstatite, apatite and wollastonite took<br />
place, and the process <strong>of</strong> apatite and badeleyite deposition continued during the postmagmatic phase.<br />
The authors are <strong>of</strong> the opinion that further apatite mineralization may be discovered in the Metocheria unit<br />
(apatite-martite-silicate mineralization) in connection with basic and ultrabasic intrusive rocks. This type <strong>of</strong><br />
mineralization is highly promising.<br />
An occurence <strong>of</strong> apatite in carbonatites <strong>of</strong> Jurassic-Cretaceous age originates in volcanic massifs connected with<br />
deep-seated fractures along the rift. Usually, the central part <strong>of</strong> the crater is filled with carbonatite, while the outer<br />
ring is made up <strong>of</strong> alkaline rocks. This can be seen in the Xiluvo carbonatite massif by a carbonatite centre<br />
surrounded by volcanic breccia and accompanied by trachyte volcanic cones. Xiluvo carbonatite is extracted and<br />
used as a building stone in three quarries. Chemical composition <strong>of</strong> some samples <strong>of</strong> carbonatite (in %):<br />
Sample % SiO2 Al2O3 Fe2O3 FeO CaO Na2O K2O P2O5<br />
Xiluvo 1 17.86 2.29 5.00 2.76 35.23 1.23 1.25 3.60<br />
Xiluvo 5 28.35 5.35 11.00 1.45 27.69 0.49 6.87 1.39<br />
Xiluvo 9 10.5 4.84 2.80 2.76 22.43 0.23 0.01 6.08<br />
Xiluvo 10 13.48 5.86 12.28 4.50 24.88 0.32 1.92 2.56<br />
Some <strong>of</strong> the samples have an increased content <strong>of</strong> P2O5, but mainly in hydrothermally affected zones. Very little<br />
is known about apatite mineralization, or a possible occurrences <strong>of</strong> fluorite. In my opinion, the best utilization <strong>of</strong><br />
Xiluvo carbonatite is in agriculture, in the production <strong>of</strong> lime, in which an increased content <strong>of</strong> phosphorus<br />
should be <strong>of</strong> advantage (see Fig. 4.13.5).<br />
Fig. 4.13.5. Geological scheme <strong>of</strong> Monte Xiluvo carbonatite (Hunting, 1984) (287 kB)<br />
The next site <strong>of</strong> carbonatite occurrence is caldera <strong>of</strong> Monte Muambe (see Chap. fluorite). The carbonatite<br />
contains from 0.01 to 2.73% P2O5 (in apatite). A higher phosphorus content may be found in residual deposits <strong>of</strong><br />
caldera with karst phenomena.<br />
Cone Negose carbonatite situated near the Mid- Zambezi rift, is a stock-like intrusion measuring 2 km in<br />
diameter, associated with alkaline volcanic activity <strong>of</strong> Mesozoic age (Middle Jurassic-Upper Cretaceous). The<br />
central intrusion is accompanied by a number <strong>of</strong> small volcanoes situated mainly in the Karroo Formation<br />
disrupted by several fault lines (Fig. 4.13. 6). Prior to carbonatite intrusion, intense alkaline metasomatism<br />
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occurred around the vent.<br />
Fig. 4.13.6. Geological sketch map <strong>of</strong> Cone Negose carbonatite and surroundings (Hunting, 1984) (759 kB)<br />
Carbonatites were deposited in various succesive stages <strong>of</strong> dome development (Geol. Inst., Beograd, 1984):<br />
grey carbonatite - first stage<br />
buff carbonatite - second stage<br />
red-vein stage with hematite, baryte, quartz with TiO2 and Nb<br />
metasomatically altered carbonatite with grains <strong>of</strong> apatite<br />
silicified carbonatite zones - last stage.<br />
Apatite mineralization occurs in metasomatic rocks altered during the final action <strong>of</strong> fluids, with a phosphorus<br />
and silica enrichment.<br />
Carvalho (1977) described a phosphate enrichment also in the last stages <strong>of</strong> carbonatite deposition - as phosphatic<br />
carbonatite with brookite and baryte (red-vein stage), as silicified carbonatites with fluorapatite, pyrochlore,<br />
baryte and finally as fluorapatite, probably during the postmagmatic stage.<br />
Carbonatites <strong>of</strong> the magnesium type "rauhaugites" located in the central part <strong>of</strong> the dome contain phosphates.<br />
Metasomatic mineralization <strong>of</strong> phosphate occurs in two stages:<br />
I stage <strong>of</strong> microcrystalline apatite with cellophane<br />
II stage with recrystallized apatite<br />
Phosphate is disseminated in carbonatite, but also layers 1 m thick occur in buff carbonatite with more that 60%<br />
<strong>of</strong> apatite. However, an average content <strong>of</strong> P2O5 is generally 1-2%.<br />
If apatite were to be economically recovered, other minerals with Nb-Ta, Sr and RE should be extracted as the<br />
main product.<br />
Carbonatite deposits with apatite and uranium minerals at Luicuisse are situated 240 km NE <strong>of</strong> the town <strong>of</strong><br />
Lichinga in the Niassa Province. There are many fracture zones with carbonatites within the big ring structure.<br />
Along these zones carbonatites are mineralized with RE, uranium and apatite. Residual deposits <strong>of</strong> a thickness <strong>of</strong><br />
7-8 m are present and developed throughout the area and contain columbite, pyrochlore, apatite, monazite,<br />
magnetite, concentrated by weathering <strong>of</strong> underlying carbonatites, granites, syenites and metapyroxenites.<br />
In some sectors, the eluvial deposit is more than 30 m thick. Apatite was determined in 33.8% <strong>of</strong> samples. The<br />
content <strong>of</strong> P2O5 varies, being 2.34% on the average (in 84.4% out <strong>of</strong> all analysed samples), in 26 samples it was<br />
increased up to 6.77% P2O5.<br />
In <strong>Mozambique</strong>, hydrothermal phosphate minerals, some very rare, were described by Neves and Nunes (1968)<br />
from pegmatites <strong>of</strong> the Alto Ligonha district. They are just <strong>of</strong> mineratogical importance.<br />
Amblygonite, formula (Li, Na) Al [(PO4) (F, OH)], quite frequent in occurrence, was obtained from Nahora<br />
pegmatite NNW <strong>of</strong> Gile. It is milky white with a brown film (lithium crust). Elsewhere it was found in Morrua<br />
pegmatite and at a site near Mutala.<br />
Composition <strong>of</strong> the Nahora sample: % P2O5 47.5, Al2O3 34.6, Li2O 9.48, Na2O 0.73, F 5.4 and H2O 4.6. X-ray<br />
determination disclosed also Rb, Sr, Sn and Fe.<br />
Montebrasite (Li, Na) Al [(PO4) (OH, F)] again from Nahora occured in an intimate association with hureaulite,<br />
eosphorite, variscite, quartz and zircon.<br />
Triplite was found in pegmatites E <strong>of</strong> Nuaparra. It is allotriomorphic, brownish in colour, formula (Mn, Fe2+),<br />
[F / PO4] composition: % P2O5 32.58, MnO 52.90, FeO 8.77, K2O 0.17, Na2O 0.06, H2O 0.40, F 8.51. Triplite<br />
occurs in association with quartz and is enveloped by supergene hydroxides <strong>of</strong> Fe and Mn.<br />
Apatite occurs commonly in many pegmatites, at Nahora and Morrua, it is <strong>of</strong> a blue grey colour, and associated<br />
with quartz, clevelandite and lepidolite. Ilodo pegmatite contains also apatite associated with beryl, mica and<br />
green tourmaline.<br />
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Chemical analyses <strong>of</strong> apatite (in %):<br />
Nahora Morrua Ilodo<br />
P2O5 40.80 41.84 41.52<br />
CaO 52.80 53.70 50.96<br />
Fe2O3 0.15 tr. tr.<br />
MnO 2.79 1.99 5.41<br />
F 2.00 3.37 3.40<br />
H2O 1.50 0.50 0.90<br />
Total 100.04 101.40 102.19<br />
X-ray analyses disclosed in Nahora apatite Cd - 0.21% and traces <strong>of</strong> Th and Fe, in that <strong>of</strong> Morrua traces <strong>of</strong> Y -<br />
0.05%, Sr, Th and Fe, in Ilodo apatite Y - 0.35%, and traces <strong>of</strong> Ce, Sr, Fe, Ho and Gd.<br />
Hureaulite, formula (Mn, Fe2+)5 H2(PO4)4 • 4H2O is a rare mineral which occurs normally as a product <strong>of</strong><br />
hydrothermal alteration <strong>of</strong> lithiophylite. The Nahora hureaulite is light rose, enveloped in a black mass <strong>of</strong><br />
cryptomelane, Mn-oxides and phosphosiderite and associated with earthy phosphosiderite.<br />
Chemical analysis (in %): P2O5 39.16, MnO 33.96, FeO 13.98, H2O 13.10.<br />
Phosphosiderite is composed <strong>of</strong> Fe3+ (PO4) • 2H2O, and is a alteration <strong>of</strong> primary phosphates. It was found in<br />
pegmatites <strong>of</strong> Nahora and Nuaparra. Nahora phosphosiderite contains 36.8% P2O5, 43.3% Fe2O3 and 19.8%<br />
H2O. It is <strong>of</strong> supergene origin.<br />
Variscite Al (PO4) • 2H2O from Nahora is <strong>of</strong> a rosy colour forming fine films over montebrasite <strong>of</strong> which it is a<br />
supergene alteration. It is found in association with saccharoid quartz.<br />
Bermanite Mn2+ Mn3+ [(PO4)(OH)] • 4H2O from Nuaparra pegmatite is a product <strong>of</strong> alteration <strong>of</strong> triplite.<br />
Eosphorite (Mn, Fe2+ Al [(OH)2, PO4] • H2O is very rare. It was described from Nahora associated with<br />
montebrasite and zircon.<br />
Chemical composition (in %): P2O5 31.18, FeO 7.70, MnO 23.99, Al2O3 22.67, H2O 14.46.<br />
Sedimentary deposits <strong>of</strong> phosphorites were found near Magude (2.7-3.1% P2O5 only), thickness 25-50 m and<br />
50% <strong>of</strong> glauconite are presumed. Their presence in the N <strong>of</strong> the Rovuma basin has been anticipated on the basis<br />
<strong>of</strong> the fact that phosphate layers are developed in the Majunga basin on the W coast <strong>of</strong> Madagascar, i. e., in a<br />
geologically similar environment within the <strong>Mozambique</strong> geosyncline. The recent borehole Mocimboa 1, situated<br />
14 km SW <strong>of</strong> the town <strong>of</strong> Mocimboa da Praia was completed in 1986. It was drilled to a depth <strong>of</strong> 11 240 feet<br />
going through the Oligocene, Paleocene, Lower Senonian, Turonian, Cenomanian up to the Albo-Aptian. No<br />
traces <strong>of</strong> gypsum, salt, glauconite and phosphates are presented on the drilling log.<br />
Geophysical exploration revealed anomalies <strong>of</strong> gama radiation in the S- Mozambican basin. Together with certain<br />
doubtfull traces <strong>of</strong> phosphates in outcrops these formations appear promising:<br />
Grudja Formation - Paleocene<br />
Cheringoma Formation - Eocene<br />
J<strong>of</strong>ane Formation - Miocene.<br />
The following areas within these formations should be investigated: Cheringoma plateau, River Buzi bay, River<br />
Save bay, bays <strong>of</strong> the rivers Rio Elefantes and Incomati and the S- part <strong>of</strong> the Mozambican basin. The most<br />
promising are those sections in the sedimentary sequence which contain transgressive sediments <strong>of</strong> the<br />
Cretaceous and Tertiary with a possible uranium mineralization (see Fig. 4.13.7).<br />
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Fig. 4.13.7. Probable phosphorite occurences in some deep oil-wells (ENH, 1986) (429 kB)<br />
Deposits <strong>of</strong> bat guano were investigated in all karst areas <strong>of</strong> <strong>Mozambique</strong> in which cavities were present - J<strong>of</strong>ane<br />
Formation near Vilanculos, Cheringoma Formation <strong>of</strong> the river Buzi area and the Cherimgoma plateau, and along<br />
the Urema through.<br />
In 1953, Bettencourt Dias described deposits <strong>of</strong> guano in seven caves about 60 km NW <strong>of</strong> Vilanculos. The caves<br />
are located near the village Chefe Buchane at the road to Nhacolo. They have usually a surface entrance <strong>of</strong> oval<br />
shape <strong>of</strong> sinkholes and an irregular underground plan (Fig. 4.13. 8). The floor <strong>of</strong> the cave is covered with a layer<br />
<strong>of</strong> bat guano about 1 m thick <strong>of</strong> ununiform quality. Reserves estimated for seven caves amount to 14,000 m3 <strong>of</strong><br />
guano.<br />
Fig. 4.13.8. Example <strong>of</strong> two caves near Vilanculos with guano <strong>of</strong> bates (Bettencourt Dias, 1953) (329 kB)<br />
Simplified analyses:<br />
Samples % humidity N P2O5 K2O<br />
surface - 1 13.31 3.73 9.80 0.61<br />
surface - 2 15.50 7.71 7.21 1.05<br />
1 m depth - 1 8.43 1.19 8.34 0.86<br />
1 m depth - 2 8.34 2.85 12.80 0.65<br />
Guano for local use is hand extracted, which is dangerous because some caves may be filled by gas.<br />
Lächelt (1985) presents a survey both <strong>of</strong> guano reserves and its quality.<br />
Composition % Vilaculos Area <strong>of</strong> Búzi Area <strong>of</strong> Cheringoma<br />
NO3 5.22 3.26 2.74<br />
P2O5 3.32 3.88 5.14<br />
K2O 2.95 1.52 1.37<br />
Reserves 30,000 t 132,700 t 600,000 t<br />
In the caves guano covers an area ranging between 25 and 65 m2, in depths <strong>of</strong> 1 to 17 m, thickness <strong>of</strong> guano layer<br />
1 to 10 m. Total guano reserves represent 762,700 t. In 1953 - 1960, about 6,000 t <strong>of</strong> guano were extracted at<br />
Vilanculos, 100 t at Buzi.<br />
Conclusions:<br />
Reserves <strong>of</strong> apatite in the Monte Muande deposit are 4,150 000 t P2O5 with 5.00%, as an average content in ore;<br />
in the Evate deposit, 155,413 000 t ore with an average content <strong>of</strong> 9.32% P2O5, i.e., 14.5 million t <strong>of</strong> P2O5.<br />
Reserves <strong>of</strong> carbonatite deposits are not yet known, but the content <strong>of</strong> apatite is low and irregular. Phosphates<br />
from this type <strong>of</strong> deposits can be extracted as a part <strong>of</strong> agricultural lime.<br />
Guano deposits in caves may just cover local agricultural needs.<br />
The two commercially interesting deposits <strong>of</strong> apatite - Muande and Evate - are low-grade phosphate deposits.<br />
Muande apatite may be utilize economically together with an extraction <strong>of</strong> iron ore; apatite from Evate will need<br />
further technological testing.<br />
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Cilek: 4.13. Phosphates and apatite<br />
© Václav Cílek 1989<br />
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Cilek: 4.14. Quartz<br />
4.14. Quartz raw materials<br />
Quartz raw materials include these varieties:<br />
quartz crystal<br />
quartz vein, pegmatite, segregation<br />
quartzites<br />
flint, chert<br />
quartz sand and pebble.<br />
All these materials are composed <strong>of</strong> quartz with a minimum content <strong>of</strong> SiO2 96%.<br />
Quartz is a mineral composed <strong>of</strong> SiO2, normally close to 100% SiO2, with trace amounts <strong>of</strong> Fe, Mg, Al, Ca, Li, Na, K, Ti ,(46.7% Si<br />
and 53.3% O), specific gravity 2.65 g/cm3. Quartz is a very common mineral <strong>of</strong> widespread occurrence and is found in nature as<br />
coarse crystallized variety (quartz with well-formed crystals or in irregular masses) and <strong>of</strong> a microcrystalline variety (chalcedony).<br />
Ordinary quartz (alpha type) transforms at about 573°C to beta quartz or high quartz, at 876°C to tridymite and at 1, 470°C to<br />
cristoballite, which is the main constituent <strong>of</strong> refractory silica material. At about 1, 730°C quartz melts to silica glass. During the<br />
development <strong>of</strong> polymorphs <strong>of</strong> quartz changes occur in volume weight and volume and structural water is released. Of commercial<br />
interest are pure quartz varieties without any impurities.<br />
Quartz crystal. Clear colourless quartz in monocrystals, twinning is not acceptable, without bubles, vacuoles, mineral particles and<br />
colour variations is the only grade which is accepted in a production <strong>of</strong> prisms, lenses in microscopes, electronics (main consumer),<br />
radio oscillator circuits, watches and as filter plates. Electronics utilize quartz as a dielectric material and for its piezoelectric<br />
properties. In comparison with other similar materials, quartz has the advantage <strong>of</strong> a chemical and physical stability, high elasticity<br />
and its relative abundance (Harben, Bates -1984).<br />
Owing to numerous defects <strong>of</strong> natural quartz crystals piezoelectric-grade crystals are produced nowadays by a laboratory synthesis<br />
which, on the other hand, needs a feedstock <strong>of</strong> crushed pure quartz known as lascas from which saturated solutions <strong>of</strong> quartz are<br />
obtained and left to crystallize on a natural quartz chips-seed plates. These seed plates are made <strong>of</strong> clear quartz in crystals <strong>of</strong> cavity<br />
fillings and should contain Fe2O3, TiO2 and others in amounts <strong>of</strong> 1 or 2 ppm, alkalies in a similar amount and about 30 ppm <strong>of</strong> Al2O3.<br />
In <strong>Mozambique</strong>, quartz crystal is only known from pegmatite deposits. In the past, small quantities were exported for piezoelectric<br />
purposes (200-600 kg a year) as an ocassional byproduct. Quartz crystals occur in several pegmatite mines, in the quartz core <strong>of</strong><br />
pegmatites at Monea, Munhamola, Nuaparra, Namacotche, Nahia, Naipa and Muiane. Some crystals are really museum specimens,<br />
almost 1 m long, <strong>of</strong> a perfect crystal form. Barros-Vicente (1963) described crystallization <strong>of</strong> quartz at a temperature <strong>of</strong> about less than<br />
600°C with grey, and then violet quartz, white milky, hyaline, and as the last stage, as an amethyst below 400°C. Quartz is almost the<br />
last mineral <strong>of</strong> the crystallization sequence.<br />
Quartz in vein, pegmatite and segregation. This includes massive milky and hyaline varieties <strong>of</strong> high purity. Vein quartz is usually<br />
found in fracture zones in the form <strong>of</strong> tabular bodies or lenses in several generations and varieties, from coarse to fine-grained<br />
crystalline. Some vein deposits are <strong>of</strong> regional importance owing to their extension <strong>of</strong> several km and thickness <strong>of</strong> more than 100 m.<br />
They are usually <strong>of</strong> a lower purity than quartz crystals containing about 96-97% SiO2. Quartz is found also in many hydrothermal<br />
veins, <strong>of</strong>ten mineralized, for which some parts only, mainly the central ones, contain pure quartz.<br />
Large quantities <strong>of</strong> massive quartz are present in central and marginal pegmatite zones. The pegmatite quartz nucleus is composed <strong>of</strong><br />
pure massive quartz, <strong>of</strong>ten with an admixture <strong>of</strong> some minerals and therefore <strong>of</strong> a lower quality.<br />
Segregated quartz is generally metamorphosed quartz developing during the regional metamorphism, both with irregular bodies and<br />
grain, but the "reworked" variety with a small amount <strong>of</strong> gaseous and liquid inclusions - is suitable for production <strong>of</strong> quartz glass.<br />
This quartz is used in ceramics (minimum SiO2 95-99, 97%, maximum 0.03-0.7% Fe2O3, 1.5-3.0% Al2O3 and 0.2-0.4% TiO2), in<br />
the production <strong>of</strong> quartz glass which is in fact, pure melted quartz with more than 99.2% SiO2, 0.02% Fe2O3, 0.1% TiO2 and 0.2%<br />
Al2O3; futher utilization is in metal silicon (minimum SiO2 99.0%, maximum 0.35% Al2O3, 0.05% Fe2O3, 0.4% CaO + MgO),<br />
ferrosilicon (minimum 97% SiO2) and silicon carbide SiC (over 99% SiO2).<br />
Special attention must be paid to the quality <strong>of</strong> quartz for quartz glass and only the production <strong>of</strong> testing glass ingots can prove which<br />
quartz is suitable (the absence <strong>of</strong> bubbles from gaseous and water inclusions).<br />
In <strong>Mozambique</strong>, descriptions are available <strong>of</strong> many localities with vein -and segregation - quartz, but analyses were not made. The<br />
only quartz deposits tested are <strong>of</strong> pegmatite origin.<br />
The pegmatite core <strong>of</strong> the kaolin deposit Boa Esperanca, at Ribaue was also tested with these results (Geol. Institute, Beograd, 1984):<br />
%<br />
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Cilek: 4.14. Quartz<br />
Sample No. 0036 N. 110036<br />
SiO2 97.24 96.04<br />
Al2O3 0.18 -<br />
Fe2O3 0.71 2.61<br />
FeO 0.09 0.14<br />
MgO 0.02 -<br />
CaO 1.26 0.36<br />
Na2O 0.04 0.36<br />
K2O 0.02 -<br />
TiO2 - -<br />
The guality <strong>of</strong> quartz is low and the material may be used in the metallurgy <strong>of</strong> basic ores.<br />
Another quartz pegmatite was tested during a feldspar exploration on the Nuaparra deposit (Duda, 1986). The pegmatite does not<br />
possess a distinctive quartz core, but consists <strong>of</strong> three zones: marginal zone <strong>of</strong> graphic texture, pegmatite with small crystals and<br />
quartz in grains from 1-10 cm and an inner zone with feldspar and quartz in block <strong>of</strong> > 1 m in diameter.<br />
Quartz is white, greyish, rose and smoky. Spectrometric analyses revealed an interesting composition <strong>of</strong> each quartz variety:<br />
Mineral 10% 10-1% 1-0.1% 0.1-0.01% quartz <strong>of</strong> graphic zone ===> quartz smoky ===> quartz white greyish ===> quartz rose ===><br />
quartz crystal.<br />
Three composite samples were prepared from drilling cores:<br />
Composition % Borehole F-4 (0-3.5 m)<br />
F-4 (20.4-20.7<br />
23.2-33.4 m)<br />
F-7 (5.15-6.6 m)<br />
SiO2 97.23 95.85 98.00<br />
Al2O3 0.51 1.02 0.25<br />
Fe2O3 0.33 0.30 0.51<br />
FeO 0.27 0.16 0.38<br />
TiO2 0.01 0.01 0.01<br />
CaO 0.03 0.03 0.06<br />
MgO 0.09 0.004 0.02<br />
Na2O 0.09 0.13 0.06<br />
K2O 0.27 0.10 0.09<br />
Li2O 0.004 0.046 0.005<br />
BeO 0.0007 0.0649 0.0007<br />
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Cilek: 4.14. Quartz<br />
Bi2O3 0.003 0.003 0.003<br />
All quartz samples do not comply to the requirements for the production <strong>of</strong> quartz glass, metal silicon or glass. It could be used in<br />
ceramics or lower-quality glass after beneficiation. Pegmatite quartz, if not concentrated in the core or even in quartz crystals, contains<br />
a certain quantity <strong>of</strong> mineral impurities. Therefore, a small part only complies to the requirements.<br />
Quartzites are rocks composed mainly <strong>of</strong> quartz with an admixture <strong>of</strong> micas, feldspar, clay minerals etc., <strong>of</strong> sedimentary origin and<br />
also metamorphic. They originate from a silicification <strong>of</strong> sandstones, a cementation <strong>of</strong> quartzitic sandstone by siliceous cement and<br />
also from an alteration <strong>of</strong> siltstones. There are several transitional stages between quartzites and sandstones; limnoquartzite is a special<br />
type <strong>of</strong> freshwater rock composed <strong>of</strong> opal or cryptocrystalline silicon.<br />
<strong>Industrial</strong> grades <strong>of</strong> quartzite:<br />
amorphous<br />
crystalline<br />
Amorphous quartzite is a sedimentary rock - ganister quartzite - composed <strong>of</strong> quartz grains (0.04-0.08 mm) cemented by a very fine<br />
material, probably recrystallized opal (grain size 0.0003-0.002 mm) which originates during a superficial kaolinization at which the<br />
colloidal silica is precipitated and deposited in sandstones. The composition <strong>of</strong> this quartzite is 96-99% SiO2, 1.5-0.3% Al2O3, 0.3-<br />
0.5% CaO and 0.01-0.02% P. It is a very important material in the production <strong>of</strong> acid refractories-silica bricks or dinas (used in<br />
temperature over 1, 550°C), in metallurgy for metal silicon and ferrosilicon.<br />
Crystalline quartzites are also <strong>of</strong> sedimentary origin formed by a silicification <strong>of</strong> sand stones with bigger quartz grains. It is used<br />
mainly in the production <strong>of</strong> ferrosilicon.<br />
In <strong>Mozambique</strong>, analogous sedimentary quartzites have neither been found nor tested. These materials may probably occur in a lower<br />
sequence <strong>of</strong> the Karroo Formation, in the Lupata Formation <strong>of</strong> Cretaceous age and in Tertiary beds. In order to discover quartzites <strong>of</strong><br />
an appropriate quality sections ought to be examined in which sedimentation was interrupted and the sandstone was exposed and<br />
influenced by superficial weathering.<br />
In Precambrian formations, thick beds were found <strong>of</strong> metamorphosed quartzites although, generally, these rocks are impure and<br />
seldom only fit for industrial use. However, some areas <strong>of</strong> metamorphic quartzites may be found suitable:<br />
1 Chidue Group with impure quartzites within the metasedimentary complex (banded quartzites)<br />
2 Zambue Group with extensive pure quartzites around the Aruangua valley. Quartzites are grey, glassy, medium - to coarse - grained,<br />
with a minor proportion <strong>of</strong> feldspar, biotite, sillimanite and muscovite.Pure quartzites enclosed in gneiss occur in the region <strong>of</strong><br />
Cassenga and Chingoa. Some quartzites contain feldspar, sulphides, garnets and pass into banded ironstones.<br />
3 Fingoe Group-widespread are siliceous granular metasediments ranging from very fine-grained rocks-cherts-to medium-and coarsegrained<br />
quartzites. They build the prominent Fingoe ridge, are grey, pinkish or cream, composed <strong>of</strong> quartz, plagioclase, epidote,<br />
biotite. <strong>Industrial</strong>ly promising may be the very fine-grained siliceous metasediments which might be metamorphosed cherts or<br />
siliceous oozes, or well sorted fine-grained sandstones (Hunting, 1984).<br />
4 Barue Group contains upstanding sinuous ridges <strong>of</strong> quartzites N <strong>of</strong> Nhacainga, W <strong>of</strong> Canxixe, NW <strong>of</strong> Guro and in the Serra<br />
Nhandrura. The quartzite areas correspond partly with the marble extension.<br />
5 Gairezi and Fronteira Groups consist predominantly <strong>of</strong> white orthoquartzite and pelitic schist. Quartzites dominate in the<br />
Chimanimani Mts. and the Serra Sitatonga. They are sugary granular recrystallized rocks composed <strong>of</strong> quartz with a small amount <strong>of</strong><br />
zircon, magnetite and sericite.<br />
6 Umkondo Group <strong>of</strong> almost unfolded metasediments contains quartzites in a sequence <strong>of</strong> phyllites, siliceous dolomites and<br />
metasiltstones.<br />
7 <strong>Mozambique</strong> belt s.l., in N- <strong>Mozambique</strong>, is divided into a number <strong>of</strong> units <strong>of</strong> which the geosynclinal and platform deposits contain<br />
metasediments-crystalline limestones, schists and quartzites scattered over the higher degree metamorphosed rocks. Quartzites occur<br />
in the Lurio belt, the Morrola structure and the Niassa Province.<br />
Flint, chert, forms concretions <strong>of</strong> opal-chalcedony composition and, when pure, could be used in silica bricks production. In<br />
<strong>Mozambique</strong>, chert may be found in Karroo volcanics and if redeposited, in younger sedimentary formations such as Lupata or Sena.<br />
Quartz sand and pebble are nowadays widely used to replace quartzites. Sands <strong>of</strong> the glass - and foundry - grade have been described<br />
already. Pebbles <strong>of</strong> pure quartz from alluvial river deposits in terraces or in deltas are, in some countries, the basic material for dinas<br />
and ferrosilicon production. In <strong>Mozambique</strong>, thick river deposits if properly sorted may also supply pure quartz pebbles.<br />
Some quartzites or quartzitic sandstones are used as grinding wheels, could be hardly replaceable by artificial abrasives. Spheric<br />
concretions <strong>of</strong> chert are used at ball mills in a preparation <strong>of</strong> the ceramic mass. Quartzites may be also used as a slag-forming<br />
admixture in metallurgy. Special high-purity quartz is used in optoelectronics in a production <strong>of</strong> silicon wires, which are replacing<br />
expensive metals.<br />
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Cilek: 4.14. Quartz<br />
© Václav Cílek 1989<br />
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Cilek: 4.15. Salt<br />
4.15. Salt<br />
Common salt or rock salt is composed <strong>of</strong> mineral halite, formula NaCI, hardness 2.5 and specific gravity<br />
2.16. The chemical composition is sodium chloride with 39.3% Na and 60.7% Cl. It is <strong>of</strong>ten mixed with<br />
calcium and magnesium sulphate and chlorite, most common is anhydrite. Salt as a sedimentary rock<br />
occurs with shale, dolomite, anhydrite and other sediments together with other halides such as sylvite,<br />
polyhalite, carnallite, kainite and clay minerals.<br />
Salt has been used from time immemorial for direct human consumption and transported from the<br />
deposits along the well - known salt - paths for distances <strong>of</strong> hundreds <strong>of</strong> km. In Africa such famous salt<br />
localities are in the Taoudeni basin in the S <strong>of</strong> the Sahara or in the Danakil depression on the Red Sea.<br />
Nowadays the largest proportion <strong>of</strong> salt-about two thirds -is used in the chemical industry as a basic<br />
material in a production <strong>of</strong> chlorine and caustic soda, with limestone in the Solvay process to produce<br />
soda ash, with sulphuric acid to produce hydrochloric acid and sodium sulphate (see glass industry) and<br />
in many other products such as soap, herbicides, food seasoning, glazes in ceramics, in textiles and as a<br />
dye. In many countries it is used in a defrosting <strong>of</strong> roads in winter, which causes severe environmental<br />
damage.<br />
Salt is a very common mineral originating in large beds from an evaporation <strong>of</strong> seawater in restricted<br />
basins. As the sea water evaporates the concentration <strong>of</strong> salt increases up to the point <strong>of</strong> supersaturation -<br />
halite, gypsum, anhydrite, sylvite and other salts precipitate. It has been suggested that thick layers <strong>of</strong><br />
pure salt may originated in partially separated bays with a limited intake <strong>of</strong> seawater, or in deep-water<br />
basins with layers <strong>of</strong> brine, and on supratidal mud flats <strong>of</strong> the type "sabhka". Because salt is a weak<br />
crystalline solid and is mobile within the crust, it can be pushed under compressional stress into the<br />
zones <strong>of</strong> lower pressure thus building salt domes-diapirs.<br />
Common salt occurs in several basins, gypsum-anhydrite beds in others and potassium salts in a few<br />
beds only.<br />
Salt is mined either by means <strong>of</strong> the room-and-pillar method, if deposited near the surface, or, with the<br />
help <strong>of</strong> boreholes, by pumping water down the hole to the salt horizon and precipitating the artificial<br />
brine under pressure.<br />
Salt deposits are salt beds <strong>of</strong> marine origin which developed in shallow basins along the passive<br />
continental margin or in grabens on continental platforms covering several thousand km2. Under a<br />
lateral pressure or simply by a higher specific gravity <strong>of</strong> the surrounding sediments these salt beds are<br />
transformed into diapirs, diapiric folds or salt domes <strong>of</strong> regular shape.<br />
The biggest salt reserves are contained in seawater (18 million km3) from which probably salt was first<br />
recovered by the primeval man by boiling the water. In warm and dry climatic zones, salt is produced in<br />
artificial ponds along the coast <strong>of</strong> the oceans using the tide to fill or empty these salinas and solar energy<br />
to evaporite the seawater.<br />
Other type <strong>of</strong> salt deposits are either salt lakes <strong>of</strong> the playa type in arid areas, or salt lakes as relics <strong>of</strong><br />
marine basins after regression, and continental lakes supplied with salt solutions from surrounding salt<br />
deposits. A special case are salt deposits with dissolved Na, Mg, Ca and K chlorides, sulphates and<br />
carbonates in rift valley basins to which salts are delivered by hot springs on fracture zones. Such<br />
deposits occur at Lake Rukwa and Lake Natron in Tanzania, Lake Magadi in Kenya and several other<br />
localities within the African Rift System.<br />
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Cilek: 4.15. Salt<br />
Finally, salt may be recovered from salt springs or boreholes containing brine either from buried "fossil"<br />
seawater or from water with dissolved salts collected en route from rocks and weathered rock layers.<br />
In <strong>Mozambique</strong>, the only source <strong>of</strong> salt are the salinas on the seashore <strong>of</strong> the Indian Ocean. Several are<br />
situated at Maputo, at Nova Mambone near the river Save, at Beira and between Quelimane to<br />
Quissanga N <strong>of</strong> Pemba. The best conditions are, <strong>of</strong> course, in the N, where the weather is warmer and<br />
the dry season is distinctive (see the map-Fig. 4.15.1).<br />
Fig. 4.15.1 Occurences <strong>of</strong> salt (304 kB)<br />
The salinas cover generally several hectars in the mangrove belt, where the bottom is clayey and flat and<br />
the establishment <strong>of</strong> partial rectangular basins separated from each other by low bariers is easy. Oblong<br />
bigger basins are divided by channels suplied with seawater from the main channel closed with a sluice<br />
at the side facing the sea. The evaporation cycle depends on weather conditions. From a partially divided<br />
oblong basin, water with an increased concentration <strong>of</strong> salts is transferred to a second pond and finally to<br />
the production pond where CaSO4 and then NaCl precipitate and common salt is collected.<br />
Total production capacity <strong>of</strong> the Mozambican salinas is more than 120,000 t/year, although, owing to -<br />
the internal situation, about 22% only is produced and table salt is imported.<br />
Salt deposits <strong>of</strong> the country have never been seriously investigated. In my opinion, there are three other<br />
types <strong>of</strong> salt deposit:<br />
1 bedded salt within the Temane Formation in the Mozambican basin. There are geological indications,<br />
that salt may be present along with anhydrite (gypsum), dolomite in this lagoonal (sebhka) deposit<br />
which covers an area <strong>of</strong> 30,000 km2; salt may be present in the centre <strong>of</strong> the basin.<br />
2 salt in diapir in the Rovuma basin at Pemba, where Flores (see ENH report, 1986) suggests that the<br />
Pemba bay originates from a dissolution and collapse <strong>of</strong> the salt dome. The nearest salt diapir is in the<br />
Tanzanian part <strong>of</strong> the Rovuma basin at Mandawa, about 180 km N <strong>of</strong> Rovuma. The thickness <strong>of</strong> salt is<br />
over 2,000 m.<br />
3 salt in Tertiary - Quaternary (?) beds on the floor or slopes <strong>of</strong> the Niassa Rift Valley, at northwards <strong>of</strong><br />
the Lake Chilwa.<br />
Brines with salt occurring in the neighbouring Tanzania may be present in <strong>Mozambique</strong> along the<br />
fracture zones both in the rift valley, N-S direction, and in regional faults <strong>of</strong> the Mid-Zambezi-Lurio<br />
belt, W-E direction. According to A. Babij (personal communication) mineralized waters <strong>of</strong> natural<br />
springs, with higher content <strong>of</strong> salt, were found in several places. Near Mossuril in the Nampula<br />
Province, a spring <strong>of</strong> 46°C has the following chemical composition with mineralization<br />
8.0<br />
Cl 90 . SO4 10<br />
Ca 67 . Na 33<br />
Si 97<br />
Another spring is at Namacurra, water temperature 73 to 80°C, with mineralization<br />
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Cilek: 4.15. Salt<br />
8.1<br />
Cl 96<br />
Ca 46 . Na 53<br />
Si 87<br />
Very interesting is the group <strong>of</strong> springs along the Zambezi rift valley, between Zumbo and Mt. Atchiza,<br />
with mineralized waters with NaCl, indicating a connection with deep-seated fractures. Artificial<br />
"springs"-artesian waters (?) occur in the area <strong>of</strong> the Temane Formation, with high content <strong>of</strong> salt from<br />
several oil exploration boreholes.<br />
List <strong>of</strong> salinas in <strong>Mozambique</strong> (366 kB)<br />
© Václav Cílek 1989<br />
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Cilek: 4.2. Bentonite-smectites<br />
4.2. Bentonite-smectites<br />
The modern term smectites introduced to the literature in 1970 (Millot) includes several varieties <strong>of</strong> clays, similar to micas<br />
with pyrophyllite structure (gibbsite sheets between two sheets <strong>of</strong> silica layers). The general chemical formula is (Na)0.7<br />
(Al3.3 Mg 0.7) Si8O20 (OH) • n H2O, which is usually different in nature owing to a substitution <strong>of</strong> Al for Si in a<br />
tetrahedral structure or Mg, Fe, Zn, Ni, Li for Al in an octahedral structure. The three-layered structure with water and ions<br />
<strong>of</strong> Ca, Na and K are loosely bound to each other to form an expanding-lattice structure.<br />
The group <strong>of</strong> smectite minerals includes montmorillonite, saponite, hectorite, palygorskite and beidellite.<br />
The name bentonite refers to a clayey rock characterized by a mixture <strong>of</strong> different clay minerals in which montmorillonite<br />
prevails which account for the typical properties <strong>of</strong> the rock such as a high absorption capacity, high cation exchange<br />
capability, swelling, plasticity and bonding power. The two most important smectites are sodium montmorillonite known as<br />
sodium bentonite, which is swelling, and calcium montmorillonite called calcium bentonite which is nonswelling.<br />
Magnesium montmorillonite is a saponite and an armargosite, potassium montmorillonite a metabentonite and lithium<br />
montmorillonite a hectorite.<br />
The principal admixtures <strong>of</strong> bentonite are kaolinite, illite, feldspar, quartz, biotite, pyroxene, remnants <strong>of</strong> parent rocks,<br />
calcite and aragonite in younger fissure fillings, opal, zeolites and cristobalite, and fragments <strong>of</strong> different rocks.<br />
Bentonite is used in many industrial branches - in refining, filtration and decolourization <strong>of</strong> vegetable oils, wine and<br />
drinking water, in cosmetics, pharmaceutical products, as fillers and extenders in paints, fodder and removal <strong>of</strong> radioactive<br />
waste-fixation <strong>of</strong> radioactive cations are by sintering at 1,000°C, in the paper industry. In the building industry, bentonite is<br />
used for its impermeability properties in grouting and lining canals, ponds, dams and everywhere, where the stability <strong>of</strong> the<br />
soil needs to be improved.<br />
The biggest part <strong>of</strong> bentonite is used in foundry sands (about 3-5% as binding agent) and in rotary drilling as a lubricant and<br />
coating material for an uncased wall <strong>of</strong> hole, and to increase viscosity <strong>of</strong> the drilling mud.<br />
The binding properties <strong>of</strong> bentonite are used in the production <strong>of</strong> iron ore pellets and molding sands.<br />
Requirements for foundries:<br />
ion exchange capacity 45 at a minimum<br />
green compressive strength 300-600 kpa<br />
permeability 120 min.<br />
shatter index 42-44 min.<br />
Fe2O3 max. 14%<br />
CaCO3 max. 2.5%<br />
Rheological properties are used both in drilling muds, and ceramics in a production <strong>of</strong> china ware.<br />
Adsorption capacity <strong>of</strong> bentonite is used in refining sugar-cane juice, beer, oils and recently <strong>of</strong>ten in agriculture as a carrier<br />
<strong>of</strong> fertilizers, pesticides and hazardous chemicals. In animal food, bentonite acts as a binder and filler, it improves the<br />
efficiency <strong>of</strong> food and prevents disease.<br />
In several countries, it is used as a sorbent to improve the fertility <strong>of</strong> sandy soils, prevents wash-out fertilizers from the<br />
upper layer to the groundwater or into watercourses, to enhance water retention and add several trace elements as important<br />
nutrients directly to the soil.<br />
The amount <strong>of</strong> bentonite required for one hectar <strong>of</strong> sandy soil is 20 to 40 t and the crop yield increase, for several years, is<br />
15 to 30% depending on the crop.<br />
Agricultural use <strong>of</strong> smectites:<br />
a) as a fertilizer mineral to supply directly N, P, K, Ca, Mg, S and micro- and trace elements such as B, Fe, Mn, Cu, Mo, Cl,<br />
Co<br />
b) as a sorbent in crop plant production in sandy soils<br />
c) as a sorbent in animal husbandry<br />
d) as a carrier <strong>of</strong> chemicals to protect plants against insects<br />
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Cilek: 4.2. Bentonite-smectites<br />
Bentonite for agricultural purposes requires:<br />
ion exchange capacity, minimum 25 mg/100 g<br />
minimum 25% <strong>of</strong> montmorillonite<br />
the amount <strong>of</strong> remnants on the sieve depends on the type <strong>of</strong> machine used for dispersion; content <strong>of</strong> iron, fragments <strong>of</strong> rocks<br />
not important.<br />
Bentonite is used also in ceramics: the accepted maximum for coarse ceramics is 2.5% Fe2O3, for sanitary ceramics 1.8%<br />
and for fine ceramics 1.2% Fe2O3. The grain size <strong>of</strong> material below 1 micron minimally 30%.<br />
To improve the quality <strong>of</strong> natural Ca or Mg-bentonites for foundry, drilling and generally binding purposes, activatednatrified-bentonite<br />
is processed by adding sodium chemical, usually soda ash.<br />
On the other hand properties <strong>of</strong> nonswelling bentonite <strong>of</strong> the calcium type are used for its absorption ability, for which it<br />
can replace "Fuller's earth" (attapulgite, sepiolite) or bleaching clays.<br />
Synthetic bentonite is <strong>of</strong> the alumina type and is used for catalytic cracking, hydrogeneration and dehydrogeneration by a<br />
treatment <strong>of</strong> smectite clay with sulfuric and hydrochloric acid, followed by calcination to remove adsorbed alkalies, alkaline<br />
earths etc. in petroleum refining (Harben-Bates, 1984).<br />
Very important in an exploration <strong>of</strong> smectites is an exact knowledge <strong>of</strong> the genetic type <strong>of</strong> the deposit. Some bentonite<br />
layers in sedimentary and volcanic sequences are indistinct, and their contact with surrounding beds may be gradual.<br />
Sharp boundaries are typical <strong>of</strong> the genetic types:<br />
a) layers <strong>of</strong> volcanic ash altered in a marine or lacustrine environment immediatelly after eruption, during which under<br />
alkaline condition hot ash and warm water <strong>of</strong> a shallow basin was altered into bentonite<br />
b) during a prolonged groundwater effect, the layers <strong>of</strong> volcanic tuffs and tuffites can be altered in an alkaline environment<br />
<strong>of</strong> the sedimentary basin under conditions <strong>of</strong> good porosity <strong>of</strong> volcanic material and an unpermeable layer beneath it; <strong>of</strong>ten,<br />
a lower silica-rich horizon developed from a leached upper layer. The irregular shape <strong>of</strong> a bentonite body is typical <strong>of</strong>:<br />
c) hydrothermal bentonite deposits either on hydrothermal veins, or as bottom layers in alkaline lakes with hot springs (see<br />
bentonite and magnesite deposits on Lake Natron - Tanzania or the hectorite deposit in California).<br />
The most common origin <strong>of</strong> bentonite:<br />
d) surface weathering <strong>of</strong> tuffs, agglomerates, porous volcanic rocks and glass; towards the bottom, an increased amount <strong>of</strong><br />
remnants <strong>of</strong> parent rock, silica and alkalies is evident. Some <strong>of</strong> these deposits are very thick (several 10 m) and large in<br />
extent.<br />
e) redeposition and mixing with other clayey material account for an origin <strong>of</strong> bentonitic clays.<br />
Some bentonite layers <strong>of</strong> type a) and e) may be enormously extended over hundreds km2 and could mark either a prominent<br />
volcanic explosive phase or stable sedimentary conditions. Often, these bentonite layers serve as "marker" beds in oil<br />
geology.<br />
In <strong>Mozambique</strong>, bentonite deposits are connected with volcanic rocks <strong>of</strong> Karroo Formation (see Fig. 4.1.1). These rocks<br />
accumulated in the upper part <strong>of</strong> Karroo <strong>of</strong> Triassic and Jurassic age in the Stormberg Series, which is composed <strong>of</strong> basalts<br />
and younger rhyolites and ignimbrites. Karroo volcanics form several prominent ridges and massifs. One <strong>of</strong> the most<br />
prominent structural units, even within the African continent is the Lebombo Mountains chain that runs along the border<br />
with South Africa for a distance <strong>of</strong> some 500 km, between 25°45' and 26°15' South. Average altitude is about 450 m and its<br />
width is 35km.<br />
Another Karroo volcanic chain extends along the S-African border, from Nuanetsi syncline to the Xiluvo carbonatite<br />
structure, for about 250 km in SW-NE direction; the Chibabawa rhyolites and other volcanic belts border the Cretaceous<br />
Zambezi basin in roughly N-S direction on the W side up to the brachysynclinat closure <strong>of</strong> the Cretaceous Lupata alkaline<br />
sequence. The last prominent massif <strong>of</strong> Karroo volcanics is the Massif Luia S <strong>of</strong> the Cabora Bassa Dam on the Zimbabwean<br />
border.<br />
The main and best known bentonite deposits have been located at about 40 km SW <strong>of</strong> Maputo in the Boane area on the<br />
slope <strong>of</strong> the Little Lebombo Mts. (see Fig. 4.2.1).<br />
Fig. 4.2.1 Geological map <strong>of</strong> the bentonite deposit near Boane (different sources) (1012 kB)<br />
This ridge forms an escarpment that can be traced over some 60 kilometres and has a general N-S trend. Several sites <strong>of</strong><br />
occurence and deposits <strong>of</strong> bentonite were found in it. The bentonite areas are characteristic by a rather flat topography and<br />
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Cilek: 4.2. Bentonite-smectites<br />
are <strong>of</strong>ten covered by swamps, with prominent rhyolitic rocks.<br />
The main river in the area is the Umbeluzi, fed mostly by perennial tributaries. During the rainy season, the freatic water<br />
table rises considerably and floods the low lying parts.<br />
Various deposits and old quarries <strong>of</strong> bentonite are situated in an area around Boane.<br />
Most <strong>of</strong> these deposits are easily accessible, within short reach <strong>of</strong> both the Maputo-Namaacha tarmac road and Maputo-<br />
Ressano Garcia road. A bentonite factory processing 12,000 t/y is situated near the Maputo-Namaacha road, about 6 km<br />
from the crossing near Boane (Luzinada factory and deposits in former reports).<br />
Regionally, rocks vary in age from Karroo to Quaternary. The Karroo is limited to the Stormberg Series and consists<br />
completely <strong>of</strong> volcanic rocks. They form an eastwards dipping monocline. To the W <strong>of</strong> Lebombo are Karroo sediments.<br />
Eastwards occur younger rocks, ranging from Cretaceous to Quaternary.<br />
The Stormberg Series can be subdivided into a basalt and rhyolite complex.<br />
-The basalts are interbedded between rhyolites and are also found in the plain on the E side <strong>of</strong> the rhyolite where they are<br />
covered by younger rocks. They are strongly eroded and occupy topographically low areas.<br />
-The rhyolites occupy higher ground and form ridges parallel to the Lebombo mountains.<br />
Cretaceous rocks consist <strong>of</strong> calcareous sandstones limited to a narrow belt E <strong>of</strong> the Lebombo hills.<br />
Tertiary rocks are siliceous limestones and calcareous sandstones and are found above the surface where the overlying<br />
Quaternary had been eroded by major rivers such as Maputo and Tembe.<br />
The Quaternary consits mainly <strong>of</strong> Pleistocene and Holocene dune fields. Terraces and alluvial deposits are found along the<br />
major rivers.<br />
In the Boane area, the Karroo consists almost entirely <strong>of</strong> volcanic rocks.<br />
Two volcanic phases can be distinguished in the field: a phase 1 consisting <strong>of</strong> rhyolites and porphyritic rocks and phase 2,<br />
including rhyolites, volcanic breccia and basalts. Younger rhyolitic intrusives <strong>of</strong> Cretaceous age occur locally, rare<br />
Quaternary alluvial deposits consist <strong>of</strong> clayey sediments (see Fig. 4.2.2).<br />
Fig. 4.2.2. Cross section <strong>of</strong> bentonite deposit Luzinada-Cooperativa II. (Zuberec-Ivanicka, 1981) (410 kB)<br />
Faulting occurred in Post-Karroo times and may be linked with a rift system. The faults have mostly N-S trend and are<br />
almost vertical.<br />
The first exploration for bentonite started in 1962 just close to the present Luzinada factory. Actual production at the factory<br />
begun in 1967. Its capacity is 12,000 t/year <strong>of</strong> proccesing <strong>of</strong> raw material with an output <strong>of</strong> natrified bentonite (2% <strong>of</strong> soda<br />
ash) <strong>of</strong> about 5-6,000 t/y. Raw bentonite is extracted from an open pit about 3 km from factory, from an area known as<br />
Cooperativa I. The bentonite originated from an alteration <strong>of</strong> rhyolitic rocks-rhyolites and tuffites with volcanic glass <strong>of</strong> the<br />
second eruptive phase, which is typical <strong>of</strong> the development <strong>of</strong> obsidian <strong>of</strong> a perlitic texture at the base. Practically the whole<br />
perlite seam, throughout its course has been altered into bentonite. Rhyolitic rocks overlay the perlite while Quaternary<br />
sediments are found on the top <strong>of</strong> the sequence. The bentonite layer has a N-S strike and is bounded by N-S trending faults.<br />
Due to faulting, the whole area is subdivided into smaller blocks with different thickness <strong>of</strong> bentonite. The layer <strong>of</strong><br />
bentonite varies from 2.1 to 10 m, while overburden thickness ranges from 0.9 to 3.8m.<br />
Composition <strong>of</strong> treated bentonite from the factory (Noticia explicativa, Carta de Jazigos,1974):%<br />
SiO2 73.18 Colour-white<br />
Al2O3 13.79 pH 9.6<br />
Fe2O3 1.03 viscosity-15 cp c/7% suspension<br />
TiO2 0.13 Green resistance-8 to 8.5 pounds/inch2<br />
CaO 1.73 Resistace after drying-40 to 50 pounds/inch2<br />
MgO 2.50 Filtration loss -16 to 100 cm3<br />
KaO 0.12 Durability-very good<br />
Na2O 1.93 Fusion point 1,240°C<br />
L.i. 5.38 The main impurity is cristobalite<br />
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Cilek: 4.2. Bentonite-smectites<br />
In the surroundings <strong>of</strong> Cooperativa I, in a belt stretching northwards, several other small bentonite pits have been opened<br />
such as Mina Ceramica, Ultra, Verga, Movene, Maro and Portella, over a distance <strong>of</strong> about 40 km.<br />
From the mine Portella, bentonite was mined from a depth <strong>of</strong> 4 to 31 m <strong>of</strong> clean montmorillonite clay with reserves over<br />
500,000 t and <strong>of</strong> this quality: %<br />
SiO2 66.28<br />
Al2O3 13.10<br />
Fe2O3 2.38<br />
TiO2 0.95<br />
CaO 4.68<br />
MgO 3.38<br />
Na2O 0.45<br />
This bentonite <strong>of</strong> the calcium type was activated by soda ash (2-3%) and about 3,000 t/year were exported to Europe. In<br />
other mines, the thickness <strong>of</strong> the bentonite layer, under a Quaternary cover <strong>of</strong> several m, was 6 m at Ceramica with white<br />
bentonite, 9 m at Verga and over 20 m at Movene.<br />
It was observed, that the thickness <strong>of</strong> the bentonite layer depended on the presence and density <strong>of</strong> faulting. The bentonite<br />
horizon, stretching for many km along the foot <strong>of</strong> Little Lebombos could therefore be interrupted by blocks <strong>of</strong> less altered<br />
rhyolitic material with inferior bentonite properties. Several bentonite bodies at all stages <strong>of</strong> alteration were discovered<br />
during prospecting.<br />
In some instances, the bentonite may grade over a very wide range <strong>of</strong> intermediate stages into fresh unaltered rock, in other<br />
instances, there may be a sharp contact with the parent rock. In some places, the clay may contain a very large number <strong>of</strong><br />
calcareous concretions. The appearance <strong>of</strong> bentonite varies from a wax-like material, yellow-green in colour through a stage<br />
<strong>of</strong> green clay (a green or blue colour is caused by Fe3+ in a reducing environment) <strong>of</strong> an almost granular appearance to<br />
ultimately a pale yellow clay, which is streaked with red and alters in parent rocks <strong>of</strong> the lower red tuffs and agglomerates.<br />
Throughout the bentonitic layer, relicts <strong>of</strong> rhyolite with some fresh rock fragments can be found in all altitudes and<br />
positions.<br />
The estimated reserves <strong>of</strong> the whole belt calculated during this first prospecting stage amounted to 15 million t.<br />
Several chemical analyses <strong>of</strong> different rock types showed clearly the degree <strong>of</strong> alteration into a bentonite mass (Zimro<br />
(PTY) Ltd., 1977): %<br />
Rhyolite (base)<br />
Weathered<br />
tuff rhyolite<br />
Perlite<br />
Welded tuff<br />
rhyolite<br />
Karroo basalt<br />
(Goba)<br />
SiO2 76.64 74.33 67.82 70.34 46.10<br />
Al2O3 17.14 17.95 16.20 17.69 22.25<br />
Fe2O3 1.84 1.23 0.41 0.65 10.12<br />
TiO2 0.10 0.01 0.01 0.11 2.51<br />
CaO 0.35 0.49 0.78 0.20 5.60<br />
MgO 0.19 0.28 0.50 0.48 2.90<br />
K2O 0.23 0.37 5.91 7.98 1.53<br />
Na2O 0.18 0.28 1.85 1.84 3.41<br />
L.i. 3.88 4.53 6.10 1.05 H2O 2.30<br />
Total 100.60 99.47 99.58 100.34 100.40<br />
The analyses indicate, that all rhyolitic rocks have a very similar composition, but differ mainly in the content <strong>of</strong> alkalies.<br />
The best material for an alteration to bentonite is volcanic glass. The example <strong>of</strong> the other volcanic Karroo rock-basalt from<br />
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Cilek: 4.2. Bentonite-smectites<br />
Goba shows clearly, that this rock is an unsuitable parent rock for bentonite origin and in that the degree <strong>of</strong> the alteration<br />
process is low - rhyolitic parent material, just sligthly altered, may be favourable for the genesis <strong>of</strong> these bentonites. In<br />
1981, the geology <strong>of</strong> the deposit Cooperativa I. was re-evaluated by a new exploration programme and additional reserves<br />
were discovered (Cooperativa II)-Zuberec et al., 1981):<br />
Bentonite <strong>of</strong> the area contains generally<br />
45-70% montmorillonite<br />
26-52% cristobalite<br />
3- 6% feldspar, oxides Fe,Ti, others<br />
Results <strong>of</strong> an analysis performed by XRD:<br />
54% montmorillonite (96% < 0.063 mm, 4% above 0.063 mm)<br />
35% cristobalite<br />
5% kaolinite<br />
3% calcite<br />
2% quartz<br />
1% dolomite<br />
Chemical composition <strong>of</strong> Cooperativa II (average <strong>of</strong> samples from boreholes):<br />
maximum % minimum %<br />
most commonly<br />
occurring average %<br />
GDR<br />
SiO2 55.10 64.30 58-63 68.8<br />
Al2O3 6.95 14.60 8-11 11.8<br />
Fe2O3 1.38 5.92 3-5 2.6<br />
CaO 0.98 9.39 1-6 3.8<br />
MgO 0.71 3.88 1-3 2.2<br />
TiO2 0.12 0.35 0.15-0.25 0.3<br />
K2O 0.03 1.28 less than 0.3 0.1<br />
Na2O 0.43 1.72 0.7-1.4 1.1<br />
H2O (105°C) 1.90 15.32 7-11 -<br />
L.i. (1,100°C) 5.70 17.99 7-12 -<br />
MnO 0.01 0.06 less than 0.1 _<br />
P2O5 0.007 0.015 0.07-0.08 -<br />
SO3 - 0.14 0.01 0.1<br />
This material can be beneficiated to a commercial bentonite grade.<br />
The Fe2O3 content <strong>of</strong> most samples is above 3%, which is the limit for use in ceramics, glass and the foodstuff industries.<br />
The ion-exchange capacity which should minimally be 40 mval/100 g (except for some uses, e. g. in agriculture) is 39.9-<br />
75.71 mval, with a prevailing value <strong>of</strong> 40-60 mval/100 g in Cooperativa I. The lower value <strong>of</strong> exchange capacity than<br />
expected in this type <strong>of</strong> bentonite, is due to a high content <strong>of</strong> cristobalite. Results <strong>of</strong> cation-exchange tests and grain-size<br />
analysis (Cooperativa II):<br />
Core<br />
Sm 4<br />
Cation-exchange analysis Mval/100 g Screen analysis (%)<br />
sample<br />
interval (m)<br />
0.15 N NH4Cl<br />
from to Ca2+ Mg2+ Na+ K+ Tot.<br />
4/1 5.90 6.40 22.20 13.06 1.96 0.52 35.74 8.30 12.82 13.15 3.63 5.45 4.35 47.7<br />
2.00<br />
mm<br />
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1.00<br />
mm<br />
0.325<br />
mm<br />
0.208<br />
mm<br />
0.105<br />
mm<br />
0.053<br />
mm<br />
Tot.
Cilek: 4.2. Bentonite-smectites<br />
4/2 6.40 9.00 22.57 24.93 0 0.64 48.14 1.47 2.38 4.46 1.72 2.55 1.78 14.3<br />
4/3 9.00 12.20 21.39 28.50 0.44 9.46 59.79 0.60 1.25 4.48 3.83 6.47 3.32 20.3<br />
4/4 12.20 15.95 17.82 24.34 6.96 0.71 49.83 0.25 0.78 1.38 1.04 3.00 2.25 8.7<br />
4/5 15.95 16.15 9.50 24.93 13.92 18.26 66.61 3.30 3.70 5.70 2.20 4.80 6.32 26.0<br />
4/6 16.15 17.70 17.23 27.90 8.35 0.96 54.44 0.27 0.12 0.40 0.23 0.41 0.36 1.7<br />
4/7 17.70 19.30 26.14 29.68 6.84 0.81 63.47 1.00 1.25 3.00 2.66 4.21 1.61 13.7<br />
4/8 19.30 21.95 24.95 23.75 5.00 1.02 54.72 8.74 7.53 7.93 3.43 830 3.20 37.1<br />
The main bearers <strong>of</strong> ion-exchange properties are Ca2+ and Mg2+ followed by Na+ and K+.<br />
A maximum <strong>of</strong> 30% <strong>of</strong> grains on sieve 0.053 mm is fulfilled according to requirements because the value is between 1.79<br />
and 28.70%. Firing tests at temperature 1,150°C disclosing a brownish, greenish and brown colour, point to a high Fe2O3<br />
content which excludes this bentonite from use in ceramics.<br />
Bentonite suitability in foundry sands was tested in the GDR (the norm requires a minimum <strong>of</strong> 5.39 N/cm2 at 3%<br />
humidity): the results <strong>of</strong> samples <strong>of</strong> bentonite - 6.26 and 6.28 N/cm2 obtained in 1979 fullfilled the requirements for<br />
foundry sand.<br />
Generally, it was confirmed that bentonite from the new deposit Cooperativa II could be used in foundries, as drilling mud,<br />
in the building industry and agriculture.<br />
Calculated reserves: north <strong>of</strong> Cooperativa I/old pit 64,600 t<br />
north <strong>of</strong> Cooperativa I/old pit 356,565 t<br />
north <strong>of</strong> Cooperativa II 163,395 t<br />
Further prognostic reserves N <strong>of</strong> these deposits 4,100 000 t.<br />
Before independence <strong>Mozambique</strong> produced annually some 4.000 t.<br />
Figures <strong>of</strong> production and export:<br />
Year Production t Export t Internal use<br />
1971 6,373 4,820<br />
1972 3,722 2,153<br />
1973 4,421 3,216<br />
1974 4,699 4,218<br />
1975 1,400 -<br />
1976 1,610<br />
1977 2,643<br />
1978 1,976 1,542 200<br />
1979 1,656 1,007 252<br />
1980 848 606 205<br />
1981 716 180 632<br />
1982 1,455 20 595<br />
1983 250 20 506<br />
1984 414 58 830<br />
1985 361 - 589<br />
1986 1,112 40 515<br />
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Cilek: 4.2. Bentonite-smectites<br />
Additional tests for bentonite from the factory Luzinada (deposit Cooperativa I) made in 1983 by Cullinan <strong>Minerals</strong> Ltd.<br />
indicated a declining quality <strong>of</strong> the product.<br />
The foundry tests non-activated activated bentonite (2% <strong>of</strong> Na2CO3)<br />
moisture % 13.5 11.4<br />
initial viscosity sec 23 24.1<br />
base exchange 50 68<br />
grit on + 53 micron % 2 -<br />
permeability 120.5 112<br />
green compr. strength (kPa) 94.9 103.2<br />
dry compr. strength (kPa) 267 132.8<br />
Shatter index % 32.5 31.5<br />
The tests showed a poor compactness and, therefore a high water demand as well as a low shatter and dry strenghts. Base<br />
exchange and viscosity was low. According to Cullinan, this bentonite should be mixed with a good-quality bentonite and<br />
used in iron foundries making castings. On the other hand, the quality requirements were much higher than European<br />
demands (here, for example, the foundry grade bentonite required 80 mval/100 g ion-exchange).<br />
Drilling tests by Cullinan showed that viscosity and filter loss were very low and therefore not fit as a drilling grade.<br />
Also other Karroo volcanic ranges may be potential areas for bentonite discovery:<br />
Chibabawa rhyolites<br />
Rhyolites and andesites on the western side <strong>of</strong> Zambezi basin<br />
Rhyolites <strong>of</strong> Luia massif<br />
The most important problem to be solved for a future exploration is the genesis <strong>of</strong> Mozambican bentonite deposits, whether<br />
deposits <strong>of</strong> the Little Lembombo Mts. originated:<br />
a) from a surface weathering <strong>of</strong> tuffs, tuffites and volcanic glass or<br />
b) from an alteration in the alkaline lacustrine environment or<br />
c) from hydrothermal action with the aid <strong>of</strong> hot springs<br />
Remnants <strong>of</strong> parent rocks in bentonite are in favour <strong>of</strong> a) point while irregular shape, no evidence <strong>of</strong> chemical changes<br />
towards the bottom, great thickness <strong>of</strong> the bentonite layer and sharp boundaries are in favour <strong>of</strong> b) and c) points. In my<br />
opinion, there is evidence <strong>of</strong> some action <strong>of</strong> hot waters in the alkaline environment. This possibility-almost syngenetic<br />
alterations <strong>of</strong> volcanic material in lakes and hot waters on the fractures as a postvolcanic agent, may bring forth a much<br />
wider extension <strong>of</strong> bentonite deposits than surface weathering.<br />
Conclusions:<br />
The Mozambican bentonite deposits are connected with rhyolitic parent rocks <strong>of</strong> Triassic Karroo volcanics (Stormberg<br />
Formation) and originated either by surface weathering and/or hydrothermal action <strong>of</strong> low temperature waters in an alkaline<br />
environment. Bentonite deposits have been explored in the vicinity <strong>of</strong> Boane on the dipslope <strong>of</strong> Little Lebombo Mts. and<br />
bentonite has been mined since 1967. Bentonite is <strong>of</strong> the calcium type and is activated - natrified. The high content <strong>of</strong><br />
cristobalite lowers the quality and the utilization is as a foundry sand, in the building industry and agriculture. Further<br />
research on beneficiation <strong>of</strong> this bentonite will be necessary and will be justified by big reserves, attaining possibly a<br />
minimum 15-25 million t.<br />
© Václav Cílek 1989<br />
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Cilek: 4.3. Clays<br />
4.3. Clays<br />
Clays are very fine-grained sediments consisting <strong>of</strong> a single or several clay minerals in addition to non-clay<br />
materials. Clay minerals as the main constituents <strong>of</strong> clay can gen- erally be divided into three groups: kaolinite,<br />
montmorillonite and illite minerals.<br />
Clays are sediments with more than 50% <strong>of</strong> clay, the composition <strong>of</strong> which depends on the chemical properties <strong>of</strong><br />
the parent rock, weathering conditions and the sedimentary environment.<br />
Classification <strong>of</strong> clays is based on<br />
1) their origin - residual and transported (fluviatile, lacustrine, marine, lagoonar etc.)<br />
2) their composition - monomineral (kaolinitic, montmoritlonitic, illitic)<br />
3) their utilization - refractory, plastic, earthen - and stoneware clays<br />
Clay minerals originate under hypergenic conditions, rarely under hydrothermal con- ditions, and display specific<br />
physical and chemical properties. They are divided with re- gard to their mineralogical structure into those with<br />
molecules <strong>of</strong> (H2O) or ions (OH+). The clay particles are usually below 2 microns with colloidal properties<br />
(sorption capacity, coagulation from suspension, electrophoresis, tixotropic properties, rheology etc.). During<br />
firing clay minerals display characteristic endothermic and exothermic reactions, caused by an escape <strong>of</strong> water or<br />
structural changes (see, for example, DTA).<br />
The main clay mineral is kaolinite with a composition <strong>of</strong> HAl2Si2O9, or Al2O2 • 2 SiO2 • 2 H20. Besides<br />
kaolinite, two other modifications are known - nacrite and dickite.<br />
The main structural unit is a silica-tetrahedral sheet which is similar to micas <strong>of</strong> the total composition (Si2O5)<br />
combined with octahedral groups <strong>of</strong> a total composition [Al2(O, OH)6]. Both layers are bound by oxygens and<br />
the structure does not expand with added water, their cation-exchange capacity is low. Kaolinite particles are<br />
flaky, <strong>of</strong> hexagonal shape, <strong>of</strong>ten well arranged; sometimes the stacking <strong>of</strong> these layers may be disordered as this is<br />
common to refractory clays.<br />
Smectites have already been described in the chapter "Bentonite".<br />
Illite is a clay mineral <strong>of</strong> a structure very similar to that <strong>of</strong> mica, with few interlayer cations, resulting in weak<br />
binding forces between layers and disordered stacking. The illite group <strong>of</strong>ten called hydromicas, has a varying<br />
chemical composition with less alkalies and more SiO2 than micas. The general composition is that <strong>of</strong> mineral<br />
phengite: from 3 Al2O3 • 6 SiO2 • K2O • 2 H2O to 2.5 Al2O3 • 7 SiO2 • 0.5 K2O • 2 H2O • n H2O. Illite has a<br />
good sorption capacity and therefore, if substantially concentrated, may become a valuable ceramic material.<br />
Other clay minerals include halloysite, chemically similar to kaolinite, attapulgite (also known as palygorskite),<br />
composed <strong>of</strong> (Mg, Al)2Si4O10(OH) • 4 H2O and sepiolite, a magnesium silicate <strong>of</strong> a theoretical formula (Si12)<br />
Mg9O30 (OH)6 (OH)2 • 6 H2O.<br />
In terms <strong>of</strong> their utilization, the main kaolinitic clays are divided into four big groups:<br />
1. Refractory clays<br />
2. Ball clays (plastic clays, earthen - and white ceramic clays)<br />
3. Stoneware clays<br />
4. Common clays<br />
1. Refractory clays or fire clays are composed mainly <strong>of</strong> kaolinite and are resistant to temperatures <strong>of</strong> more than<br />
1,580°C (equivalent to No. 26 Seger pyrometric cone). These clays are used in the production <strong>of</strong> refractory bricks<br />
or monoliths for a lining <strong>of</strong> blast furnaces, metallurgical furnaces, cement and lime kilns, in alloys metallurgy etc.<br />
A big portion (30% or more) <strong>of</strong> fire clays is used in the production <strong>of</strong> chamotte - a refractory aggregate which is<br />
crushed after firing, then cemented with refractory bond clay, moulted into required shape and fired anew. The<br />
result are chamotte bricks or monoliths used as medium-quality refractory material. The fire clays, due to a<br />
competition with magnesite, bauxite, sillimanite and the like, have a declining market and therefore, are more<br />
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Cilek: 4.3. Clays<br />
<strong>of</strong>ten used in non-refractory products formerly the domain <strong>of</strong> ball- and stoneware clays.<br />
Various requirements for refractory clays in the different countries, (Polak, 1972).<br />
Property<br />
Refractoriness<br />
Seger cone<br />
Temperature °C<br />
Sintering<br />
Temperature °C<br />
range <strong>of</strong> sintering °C<br />
Plasticity (bonding)<br />
% <strong>of</strong> opening material<br />
Chemical characteristics<br />
content <strong>of</strong> Al2O3 after<br />
firing at 1000 °C<br />
Classes<br />
1 2 3 4<br />
34<br />
1750<br />
easily sintered<br />
1250<br />
300<br />
highly bonding<br />
60<br />
extra high<br />
aluminous<br />
40<br />
33-34<br />
1730-1750<br />
sintered<br />
1250-1350<br />
300<br />
bonding<br />
60-30<br />
highly aluminous<br />
32-33<br />
1710-1730<br />
difficult sintered<br />
1350-1410<br />
200<br />
little bonding<br />
30-10<br />
31-32<br />
1690-1710<br />
very diff.sintered<br />
1410<br />
100<br />
non-bonding<br />
10<br />
medium aluminous weakly aluminous<br />
40-37<br />
37-34<br />
34-30<br />
Fe2O3 % Maximum 1.5-2.0 1.5-3.0 1.5-6.0 6.0<br />
Grain size > 0.09 mm<br />
max. %<br />
0-2 1-5 1-10 1-20<br />
2. Ball clays or plastic clays contain about 70% <strong>of</strong> kaolinite (disordered), some illite, quartz, smectite, chlorite and<br />
carbonaceous material. Organic matter in ball clays darkens the material, sometimes even to black colour, but<br />
disappears during the firing. Ball clays are highly plastic, <strong>of</strong> a high green strength, and are refractory. Plastic clays<br />
are highly regarded in the ceramic industry for their long vitrification range and are used in vitreous china,<br />
sanitary ware, stoneware and wall tiles. A specific utilization have earthenware clays in the production <strong>of</strong> porousbiscuit-unglazed<br />
porcelain, in sintered porcelain and heavy china. Special ceramics are made <strong>of</strong> earthenware clay<br />
such as majolica or faience. They sinter in a whitish colour at 1,250-1,300°C.<br />
General requirements for plastic clays (Polak, 1972):<br />
Property<br />
Whiteness<br />
After firing at 1250 °C<br />
Grain size<br />
0.09 - 2 mm max. %<br />
0.06 mm max. %<br />
Fe2O3 %<br />
TiO2 %<br />
Sintering<br />
Temperature °C<br />
range <strong>of</strong> sintering °C<br />
Plasticity<br />
% <strong>of</strong> opening material<br />
Classes<br />
1 2 3 4<br />
snow white white less white whitish<br />
80<br />
80-75<br />
75-65<br />
65-50<br />
very fine<br />
2<br />
fine<br />
5 - 5<br />
fine to medium<br />
2-10<br />
medium<br />
10<br />
20-10<br />
0-20<br />
1.0-1.5<br />
1.0<br />
1.0<br />
-<br />
0.4-0.8 0.4-1.2 0.8-1.6<br />
-<br />
easily sintered sintered difficult sintered very diff.sintered<br />
1250 1250-1350 1350-1410 1410<br />
300<br />
300<br />
200<br />
100<br />
highly bonding bonding little bonding -<br />
60<br />
60-30<br />
30-10<br />
-<br />
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Cilek: 4.3. Clays<br />
Water absorption, weight % 19 12-19 8-12 2-8<br />
Shrinkage at 1250 °C 6 6-12 12-15 15<br />
3. Stoneware clays are partly plastic clays <strong>of</strong> a lower grade used in heavy products such as sintered ceramic<br />
products, pipes, bricks and floor tiles. The fusion point is below 1,280°C (Seger cone below 26) and the<br />
vitrification range - i. e. the difference between sintering and deformation temperatures should be at least 100°C.<br />
Also lower-grade fire clays can be included in stoneware clays.<br />
General requirements for stoneware clays (Polak, 1972):<br />
Property<br />
1 2<br />
Classes<br />
3 4<br />
Sintering<br />
easily sintered sintered<br />
-<br />
-<br />
Sintering Temperature °C<br />
1250 1250-1350<br />
-<br />
-<br />
vitrification range °C<br />
100<br />
10<br />
-<br />
-<br />
Plasticity<br />
highly bonding bonding little bonding<br />
-<br />
% <strong>of</strong> opening material<br />
60<br />
60-30<br />
30-10<br />
-<br />
Acid resistance<br />
highly resistant sufficiently resist. little resist.<br />
-<br />
resistivity %<br />
97<br />
97-95<br />
95<br />
-<br />
Refractoriness<br />
highly refractory medium refractory low or non-refract. -<br />
Seger cone<br />
32<br />
29-32<br />
29<br />
-<br />
Temperature °C<br />
1710 1650-1710 1650<br />
-<br />
Grain size<br />
very fine<br />
fine fine to medium coarse<br />
>2.00-7.00 mm max. %<br />
0<br />
1<br />
1<br />
1<br />
>0.09 mm max. %<br />
2<br />
5<br />
10<br />
20<br />
Shrinkage during sintering % 10 10-14 14 -<br />
In the practice, stoneware clays should sinter at 1,250°C, refractoriness should be below 1,350°C and vitrification<br />
ought to range between 200 and 300°C. High-quality stoneware clays are highly plastic with a good refractoriness<br />
and could be used as low-grade refractory clays. In the manufacture, two types <strong>of</strong> ware can be distinguished: fine<br />
and coarse stoneware. The first group comprises fine floor tiles and sintered wall tiles, the second group<br />
agriculture ware, pipes, chemical and highly acid-resistant stoneware. Stoneware is either glazed or unglazed. A<br />
lot <strong>of</strong> it is used in the household and as ornamental stoneware.<br />
Both stoneware clays and ball clays with a high plasticity are used in heavy and fine ceramic uses, a high amount<br />
<strong>of</strong> ball clays together with kaolin, feldspar and quartz for the production <strong>of</strong> porcelain, pottery, tiles, earthenware,<br />
sanitary ware and different technical ceramic products. The clays used in ceramics must be processed to remove<br />
numerous impurities-admixtures such as quartz, mica, rock fragments, calcite, dolomite, siderite, gypsum, opal,<br />
sulphides, heavy minerals, organic matter etc.<br />
The industry utilizes these distinctive physical properties <strong>of</strong> clays:<br />
plasticity - enables the preparation <strong>of</strong> mass by adding water<br />
swelling - increase in volume by absorbing water<br />
shrinkage - loss <strong>of</strong> water by drying at about 110°C and firing at about 1,250°C<br />
sintering - partial melting at temperature betwen 450 and 1,400°C depending on clay<br />
composition colour - ceramic clays-whitish colour after firing, other tints by coloured clays<br />
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Cilek: 4.3. Clays<br />
4. Common clays usually coloured are widespread clays which do not require a particular specifications and<br />
processing; they are for local consumption. They are structural clays used in the production <strong>of</strong> building bricks,<br />
ro<strong>of</strong>ing tiles, drain tiles, sewer pipes and different structural units <strong>of</strong> either red or other colour depending on the<br />
raw material. These clays are plastic enough for molding and vitrification below 1,100°C. They are composed<br />
mainly <strong>of</strong> illite, kaolinite, smectite, different mixed layered clays, chlorite, mica etc. Some contain more quartz<br />
and must be corrected by adding plastic materials, some are highly plastic and are corrected by adding quartz or<br />
other hard material such as shales, weathered crystalline rocks etc.<br />
About 50% <strong>of</strong> common clay is used in the production <strong>of</strong> building bricks and aggregates, ro<strong>of</strong>ing tiles etc., 20% is<br />
used in portland cement as a source <strong>of</strong> alumina and silica and the remaining part in different other branches <strong>of</strong> the<br />
building industry such as lightweight aggregates (expandite, keramzite), small household - and agricultural<br />
products, even in the wall tile production etc. In Europe, the brick factories are located at many strategic points so<br />
that the distance <strong>of</strong> transport does not extend more than 100 km.<br />
Clays for building bricks and similar products should fulfil these requirements (Polak,<br />
1972):<br />
Quality Class 1 2 3 4<br />
Plasticity highly plastic plastic medium plastic lean<br />
Strength after drying<br />
modulus minimum<br />
50<br />
25<br />
15<br />
6<br />
<strong>of</strong> rupture after firing<br />
kp/cm2 at 950 °C<br />
90<br />
150-40 40-20 below 25<br />
Liquid limit minnimum % 40 25 20 below 20<br />
Drying shrinkage %<br />
Sintering shrinkage %<br />
12 7 4.5 below 4.5<br />
850 °C<br />
>13 7.2-13.5 4-7.5 below 4.6<br />
950 °C<br />
>14<br />
7-14.5 4.5-8.0 below 4.8<br />
1050 °C<br />
>15 8.5-15.5 4.7-9.0 below 4.9<br />
Water absorption, weight %<br />
after firing at 850-1050 °C<br />
8 12 15 15<br />
Grain size > 7 mm maximum 0 2 5 20<br />
Grain size > 2 mm maximum 1 15 35 70<br />
Besides the composition clay should posses:<br />
total fineness 65-75% with clay content 30-40%, salts not more than 1%, iron content<br />
not more than 5%,<br />
CaO and MgO content up to 1.5%.<br />
Winkler diagram <strong>of</strong> requirements for different building - brick products based on grain size dustribution (Fig.<br />
4.3.1):<br />
Fig. 4.3.1. Winkler diagramme for classification <strong>of</strong> brick materails with regard to grain size distribution<br />
(231 kB)<br />
The genesis <strong>of</strong> all clays in connected with alteration processes due to weathering <strong>of</strong> alumosilicate rocks and<br />
transport with subsequent deposition.<br />
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Cilek: 4.3. Clays<br />
Types <strong>of</strong> clay deposits suggested by Kuzvart (1984):<br />
1. eluvial clay deposits - weathering <strong>of</strong> carbonate rocks with an origin <strong>of</strong> smectites<br />
2. proluvial clay deposits - poorly sorted, sandy<br />
3. collucial clay deposits - on slopes<br />
4. alluvial (river) deposits - unsorted clays<br />
5. lacustrine deposits - first-rate refractory clays wilth organic matter<br />
6. salty lakes deposits - hydromicas, smectites, chlorite, admixtures <strong>of</strong> salt, gypsum etc.<br />
7. glacial, morainic or boulder clays - poorly sorted, hydromicas for solid bricks<br />
8. glaci<strong>of</strong>luvial clays - rewashed clays <strong>of</strong> type 7, typical varves<br />
9. eolian clayey-silty rocks - loesses, for bricks and as a corrective component <strong>of</strong> cement<br />
10. clays <strong>of</strong> brackish lagoons - low refractory, mixture <strong>of</strong> clay minerals<br />
11. clays <strong>of</strong> salty lagoons - alternate with salt and carbonates<br />
12. shallow-water shelf marine clays - < 50 m, in bays<br />
13. shelf deep-water (50-200 m) hydromica-beidellite clays - highly dispersive<br />
14. volcanogenic marine clays - smectites by halmyrolysis <strong>of</strong> tuffs<br />
Also glauconite belongs to the group <strong>of</strong> clay minerals; it is a hydrous silicate <strong>of</strong> iron and potassium, but, usually,<br />
being a mixture, it varies in composition.Potash ranges from 2.2 to 7.9%. Glauconite is known as green sand,<br />
because <strong>of</strong> its dark green to blueish green colour. Usually glauconite occurs in an admixture with sands and marls<br />
<strong>of</strong> marine origin <strong>of</strong> the Mesozoic or Tertiary age. For its potassium and kalium content, it is used as a fertilizer in<br />
agriculture and as a water s<strong>of</strong>tening agent. When mixed with sand it is also used in foundry sands.<br />
Other material <strong>of</strong> this group are claystones <strong>of</strong> various genesis. Some claystones from older sedimentary<br />
formations <strong>of</strong> the Paleozoic or the Mesozoic are valuable ceramic materials, mainly refractory, known, for<br />
example, from productive Karroo beds <strong>of</strong> the Ecca Formation.<br />
In <strong>Mozambique</strong> there are many deposits <strong>of</strong> different clays and their distribution is apparently widespread. Most <strong>of</strong><br />
Mozambican clays are <strong>of</strong> a low quality, the dominant type is common clay <strong>of</strong> a reddish colour, less <strong>of</strong>ten plastic<br />
clay with a whitish tint. In the past, clays, mainly reddish clays, were used in local pottery, and some areas were<br />
famous, for example, the coastal area <strong>of</strong> Xai-Xai and Inharrime, in the N an area in the vicinity <strong>of</strong> Pemba, inland<br />
the area Nacala and some places on the shore <strong>of</strong> Lake Niassa. While a Portuguese colony, many brick factories<br />
were built in different localities using clay from the neighbourhood. Usually, no laboratory tests were made<br />
because the experience and estimate <strong>of</strong> the material were sufficient.<br />
With a few exceptions, the only clays used were <strong>of</strong> Quaternary age-residual or alluvial in origin, mainly highly<br />
plastic which needed sandy corrections. All clays <strong>of</strong> reddish, brownish, yellowish, whitish and greyish colour are<br />
common clays. In <strong>Mozambique</strong>, common clays, even those for brick making, are called "ceramica<br />
vermelha" (reddish ceramic), and white plastic clays may, sometimes, be even <strong>of</strong> a refractory grade. The testing <strong>of</strong><br />
these clays started a few years ago and is decribed below.<br />
Almost no data are avaiable on clays <strong>of</strong> sedimentary formations from the Karroo up to present. It has been<br />
anticipated, that lower Karroo formations may contain ceramic-grade clays and refractory clays. Cretaceous clays<br />
are used at Nacala in an alumina-silica correction <strong>of</strong> pure limestones in the cement production. Tertiary clays were<br />
tested at Sabie near Maputo, but were found to be calcitic. The main source <strong>of</strong> clays for local production are<br />
Quaternarydeposits.<br />
Calculation <strong>of</strong> reserves <strong>of</strong> several explored localities:<br />
Ar 1 Namaacha reserves <strong>of</strong> 9,985 t for white ceramics<br />
Ar 2 Umbeluzi reserves C1 + C2 <strong>of</strong> 972,400 t for white ceramics<br />
Umbeluzi reserves prognostic <strong>of</strong> 529,520 t for white ceramics<br />
Umbeluzi reserves C1 + C2 <strong>of</strong> 3,081 210 t for coloured ceramics<br />
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Cilek: 4.3. Clays<br />
Umbeluzi reserves prognostic <strong>of</strong> 1,960 050 t for coloured ceramics<br />
Ar 9 Xai-Xai reserves B + C1 <strong>of</strong> 1,889 400 t for coloured ceramics<br />
Ar 11 Inharrime reserves C1 <strong>of</strong> 747 000 t for coloured ceramics<br />
Inharrime reserves C2 <strong>of</strong> 210,000 t for coloured ceramics<br />
Ar 18 Dondo-Inhamizua reserves C1 + C2 <strong>of</strong> 648,280 t for coloured ceramics<br />
Ar 20 Quelimane reserves C2 <strong>of</strong> 2,950 000 t for coloured ceramics<br />
Ar 23 Namacurra reserves prognostic above 15,000 t for coloured ceramics<br />
Ar 32 Nampula reserves C2 <strong>of</strong> 81,990 t for coloured ceramics<br />
Ar 35 Pemba reserves A <strong>of</strong> 1,360 000 t for coloured ceramics<br />
Ar 37 Lichinga reserves C2 <strong>of</strong> 479,400 t for coloured ceramics<br />
Ar 38 Area <strong>of</strong> N'guri-Diaca with reserves A <strong>of</strong> 709,400 t for coloured ceramics<br />
Area <strong>of</strong> N'guri-Diaca with reserves prognostic <strong>of</strong> 867,000 t <strong>of</strong> coloured ceramics<br />
Selected clay localities are shown in the attached map (Fig. 4.3.2).<br />
Fig. 4.3.2. Occurences <strong>of</strong> clay and kaolin (413 kB)<br />
Fig. 4.3.3. Cross section <strong>of</strong> clay deposits in Maputo valley (Geol.Institute, Beograd, 1982) Bela Vista,<br />
Salamanga (506 kB)<br />
In order to obtain a better understanding <strong>of</strong> the situation in the ceramic industry <strong>of</strong> <strong>Mozambique</strong> data are present<br />
on some more recently investigated clay localities (from S-N). In the vicinity <strong>of</strong> Maputo, the locality Salamanga<br />
(Bela Vista) was examined in 1979 and again in 1985. The clay deposit is <strong>of</strong> Quaternary age, and <strong>of</strong> sedimentary<br />
origin, the clays were deposited in a marine environment. Diallo (1979) estimated reserves <strong>of</strong> 2,093 023 t <strong>of</strong> clay<br />
suitable for the production <strong>of</strong> bricks and tiles. The belt <strong>of</strong> clayey sediments is about 300-500 m wide and stretches<br />
over 25 km in N-S direction. The thickness <strong>of</strong> the clay layer is 6 m and below it interlayers <strong>of</strong> sandy clay and sand<br />
with marine shells were intersected (see Fig. 4.3.3). Technological tests disclosed that the clay is very fine and<br />
highly plastic, with a high liquid limit and linear shrinkage. Its colour after firing is red and some samples have a<br />
unidimensional expansion similar to vermiculite (by 1,000°C). The plasticity limit is very low and the clay must<br />
be corrected by sand or ash to be used as brick material, with a maximum firing temperature below 1,000°C.<br />
Chemical analyses <strong>of</strong> some samples (in %):<br />
% SiO2 Al2O3 Fe2O3 CaO MgO SO3 K2O Na2O Cl L.i.<br />
1583-D 53.0 19.5 7.1 0.9 - 2.1 0.15 0.18 0.8 18.4<br />
1586-D 56.9 16.8 6.4 0.6 1.7 4.1 0.14 0.13 1.6 18.4<br />
1591-D 52.2 21.1 11.2 0.7 - - 0.12 0.8 - 10.9<br />
1592-D 48.8 22.5 12.8 0.6 - - 0.12 0.12 - 10.4<br />
1583 - D 1586 - D 1591 - D 1592 - D<br />
Liquid limit in %<br />
38.9 30.4 48.2 48.2<br />
Linear shrinkage % 11 7 13 13.1<br />
after 800 °C 11.3 - - -<br />
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after 900 °C 12.3 13.4 15.8 16.0<br />
after 1000 °C 13.3 - - -<br />
after 1100 °C - - - -<br />
Water absorption % after 800 °C 16.8 19.0 - -<br />
after 900 °C 17.9 19.1 18.0 17.0<br />
after 1000 °C 14.0 21.7 - -<br />
after 1100 °C - 17.6 - -<br />
Plasticity limit (MPa) dried in air 1.97 3.94 1.37 0.96<br />
after 900 °C 9.01 - 0.56 -<br />
after 1000 °C - 1,87 - -<br />
In 1985, the Geological Institute, Beograd checked the same area with the result that the extension <strong>of</strong> clay deposit<br />
is much smaller and the clay is hardly suitable for brick making. An area <strong>of</strong> 1.5 km in length and 350-950 m width<br />
was explored up to the underground water table.<br />
Average chemical analysis (in %):<br />
SiO2 51.30 TiO2 0.99<br />
Al2O3 16.80 P2O5 0.99<br />
Fe2O3 7.64 MnO 0.02<br />
FeO 0.64 Na2O 1.39<br />
CaO 0.24 K2O 1.64<br />
MgO 0.99<br />
The clay shows a low alumina content, a high iron and an increased alkalies content.<br />
The only ceramic factory in <strong>Mozambique</strong> producing wall tiles is situated at Umbeluzi about 30 km W <strong>of</strong> Maputo.<br />
Until 1972, the factory had been supplied with a ceramic mixture imported from Portugal, but afterward<br />
production ceased due to a lack <strong>of</strong> material.<br />
Repeated efforts were made to replace imported material and <strong>of</strong> course first area to be explored for possible clay<br />
deposit was the vicinity <strong>of</strong> the ceramic factory.<br />
The areas at Goba Fronteira, Changalave, Resano Garcia, Muamba, Sabie and at Namaacha were explored for<br />
white clays.<br />
Assenov and Diallo (1982) described the exploration at Namaacha. The deposit near the Anglican church in the<br />
town <strong>of</strong> Namaacha on the border with Swaziland is <strong>of</strong> eluvial origin; it developed in two weathering zones, the<br />
upper one <strong>of</strong> reddish clay with remnants <strong>of</strong> rhyolites, the lower one <strong>of</strong> greyish clay - the zone <strong>of</strong> removal <strong>of</strong><br />
sequioxides over the underlying rhyolite body. The thickness <strong>of</strong> clay is maximally 5 m. The grey clay displays a<br />
higher silica content, a lower alumina and iron content. But it is <strong>of</strong> low plasticity, and possesses average<br />
mechanical properties and is reddish in colour after firing. It could be used in the production <strong>of</strong> tiles and bricks,<br />
but not in the production <strong>of</strong> wall tiles.<br />
Results <strong>of</strong> an analysis <strong>of</strong> selected samples:<br />
Sample % 2134-C 2262-C 247-D 203-D<br />
SiO2 72.7 77.9 73.9 71.1<br />
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Cilek: 4.3. Clays<br />
Al2O3 11.4 10.9 13.1 15.7<br />
Fe2O3 8.5 3.8 4.8 2.5<br />
CaO 0.3 0.4 0.6 0.2<br />
MgO 0.3 - - -<br />
L.i. 4.2 - - -<br />
Liquid limit 28 31 34 33<br />
Plasticity limit 18 19 19 15<br />
Shrinkage limit 9.6 9.9 9.8 9.1<br />
< 2 micron 11 - 22 18<br />
3-20 micron 26 - 28 28<br />
> 20 micron 63 - 50 54<br />
> 74 micron 30 - 15 21<br />
Firing temperature oC 1,100 1,100 1,100 1,200<br />
Shrinkage linear % 6 4 3 7.5<br />
Colour after firing reddish yellowish orange dark yellow<br />
Water absorption % 20 17 18 14<br />
Plasticity limit MPa - 6.4 6.4 8.9<br />
Compression strength - 20.6 14.9 21.8<br />
About 150 km N <strong>of</strong> Maputo, at the confluence <strong>of</strong> the rivers Sabie and Incomati, the area was investigated for<br />
limestones by Italian geologists. In Tertiary sediments, they discovered a bed, 5 m thick, <strong>of</strong> clay overlying<br />
calcarenites and several smaller beds <strong>of</strong> marls and calcitic clays (Zuberec et. al., 1981). Macroscopically, the clays<br />
are calcitic, <strong>of</strong> medium grain and <strong>of</strong> a yellow to brown colour.<br />
Analysis <strong>of</strong> two samples (in %):<br />
% Sabie - 1 Sabie - 2<br />
SiO2 61.66 63.46<br />
Al2O3 5.09 4.88<br />
Fe2O3 4.19 4.26<br />
CaO 6.44 1.46<br />
MgO 3.42 1.85<br />
L. i. 16.33 -<br />
Granulometric analysis <strong>of</strong> sample Sabie 2:<br />
3.27 mm - 13.85%, 2 mm -13.62%, 1 mm - 10.0%, 0.707 mm -3.20%, 0.5 mm -2.16%, 0.305 mm - 2.02%, 0.208<br />
mm - 3.20%, 0.105 mm - 13.95%, 0.074 mm - 8.50% and 0.053 mm - 2.70%.<br />
After firing at 1,250°C, the colour <strong>of</strong> the clay fraction below 0.074 mm is buff with brown spots. The clay can be<br />
classified as arenite calcitic-argillitic with a high iron content unsuitable for ceramics.<br />
Other clay localities nearby are situated along the river Incomati at the village Xinavane, E <strong>of</strong> the town <strong>of</strong><br />
Magude. Two brick factories were in operation at Xinavane and at Maholela exploiting extensive clay deposits <strong>of</strong><br />
alluvial origin <strong>of</strong> the river Incomati. The thickness <strong>of</strong> clay is minimally 5 m, it is plastic, fine-grained and greyish<br />
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Cilek: 4.3. Clays<br />
in colour. It was used for a production <strong>of</strong> bricks and tiles, and it is still used in pottery at Maholela (Diallo, 1980).<br />
Other clay localities are N <strong>of</strong> Inharrime, where the brick factory at the Muramba river about 23 km SWS <strong>of</strong><br />
Inhambane is in production. The clays are again <strong>of</strong> alluvial origin, stretching along the river for the distance <strong>of</strong> 20<br />
km and a width about 2 km. On both sides, the area is covered by high older coastal dunes.<br />
The clay used in the factory is grey, locally reddish, sandy and calcitic, plastic to semiplastic, yellowish to dark<br />
reddish after firing. After mixing with sand it is suitable for a production <strong>of</strong> bricks and blocks.<br />
The reserves are 747,000 t <strong>of</strong> category C1 and 210,000 t C2.<br />
In order to build a brick factory in the area Xai-Xai, two localities were examined (Tzonev et Dimitrov,1982):<br />
clay-deposit 1. -12 km N <strong>of</strong> the town Xai-Xai, deposit 2.-1 km out <strong>of</strong> town, near the road to Inhambane. In<br />
addition, one sand locality was examined during the investigation. Both clay localities are alluvial deposits <strong>of</strong> the<br />
river Limpopo. In deposit 1, clay is typically dark grey, humic, very well sorted and plastic, <strong>of</strong> a type common to<br />
the alluvial plain <strong>of</strong> Limpopo, where big rice plantations are being established. The clay <strong>of</strong> deposit 2 is brown,<br />
very plastic clay at a higher elevation, locally sandy, developed in a swampy river bay. Clay <strong>of</strong> deposit 1 contains<br />
about 20% <strong>of</strong> volatiles and 70% <strong>of</strong> particles below 2 micron. It is highly plastic even if mixed with 15-20% <strong>of</strong><br />
sand and ash, and can be used for a production <strong>of</strong> bricks <strong>of</strong> low mechanical strength suitable in inner walls. The<br />
clay <strong>of</strong> deposit 2 is more suitable for brick production, if mixed with 15% sand and 5% ash. In both samples, DTA<br />
determinations disclosed more illite than kaolinite.<br />
Some results <strong>of</strong> analyses are following:<br />
% SiO2 Al2O3 Fe2O3 CaO MgO TiO2 K2O Na2O SO3 L. i.<br />
Deposit 1 45.44 16.69 10.38 0.56 1.16 0.61 1.03 0.83 0.52 19.89<br />
Deposit 2 43.40 16.34 8.80 2.10 1.93 0.96 1.03 0.90 0.40 21.10<br />
Reserves <strong>of</strong> deposit 1 are 790,312 m3 <strong>of</strong> category B + C1 and estimated 230,000 m3, in deposit 2 - 321,100 m3.<br />
The technological tests indicate that the firing temperature must be below 900°C, the clay must be mixed with 15-<br />
20% <strong>of</strong> sand and ash for brick production, and with ash only for a production <strong>of</strong> tiles; the mixture must be slowly<br />
and carefully dried before firing. Several tests were performed with natural material (also with different mixtures):<br />
Granulometry: % (average values) Deposit 1 Deposit 2<br />
< 2 micron 52.17 55.28<br />
2-20 micron 36.22 21.71<br />
20-200 micron 9.56 19.00<br />
> 200 micron 2.50 3.33<br />
1 - 3 mm 0.00 0.11<br />
> 3 mm 0.00 0.00<br />
Liquid limit 79.92 64.00<br />
Plasticity limit 36.92 30.00<br />
Shinkage limit 4.67 6.97<br />
Total shrinkage occurs <strong>of</strong> clay 2 at 850°C with values <strong>of</strong> 14.26%, liquid limit 13.36% and plasticity limit 6.84<br />
MPa.<br />
The mineralogical determination <strong>of</strong> the composition by X-rays:<br />
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Cilek: 4.3. Clays<br />
Sample 828 - B 835 - B 844 - B 848 - B<br />
Montmorillonite + + + +<br />
Kaolinite + + + +<br />
Montmorillonite-illite + + + +<br />
Quartz + + + +<br />
Tridymite - - - -<br />
Cristobalite - - - -<br />
K-feldspar - - - -<br />
Plagioclase + + + +<br />
Carbonates - - + +<br />
No muscovite and Fe-minerals are present.<br />
An example <strong>of</strong> the suitability <strong>of</strong> clays for different ceramic end-uses is presented in the Winkler and Avgustinik<br />
diagrams.<br />
According to Winkler's diagram, some clay samples may be suitable for a production <strong>of</strong> solid bricks, holed bricks<br />
and tiles; the Avgustinik diagram indicates a suitability for stoneware (one sample), tiles (one sample), clinker<br />
(one sample) and brick production (Fig. 4.3.4 a, b).<br />
Fig. 4.3.4.<br />
a. Triaxial diagramme <strong>of</strong> grain distribution <strong>of</strong> Winkler: Deposit 2. Xai-Xai<br />
b. Avgustinik's diagramme <strong>of</strong> clay utilization and chemical composition: Deposit 2. Xai-Xai (506 kB)<br />
A brick factory and the clay deposit Inhamizua are located at about 30 km NW <strong>of</strong> Beira. The deposit is <strong>of</strong> alluvial<br />
origin, marine-fluviatile developed on the bank <strong>of</strong> the river Pungoe near its estuary. The tide <strong>of</strong> the sea<br />
conditioned the growth <strong>of</strong> mangroves and a swampy environment.<br />
The clay is grey or greenish grey, very plastic (see granulometry and skrinkage limit) with a high content <strong>of</strong><br />
lignitic material, sometimes with intercalations <strong>of</strong> sand, remnants <strong>of</strong> roots and brackish water shells. The thickness<br />
is about 3 m up to the ground-water level, and widely extended.<br />
This mangrove clay, in fact, the mangrove soil deposited under reduction conditions, very common to coastal<br />
areas, is unsuitable for brick production. It is more convenient for the production <strong>of</strong> light-weight aggregates,<br />
because it is expandable - swelling, when properly fired.<br />
For brick production it must be corrected by adding about 30% <strong>of</strong> sand to minimize the high degree <strong>of</strong> shrinkage;<br />
a higher amount <strong>of</strong> sand lowers futher its mechanical properties. A better corrective material would be ash or<br />
milled slag, but these materials are not avaiable. Thonen (1981) calculated reserves <strong>of</strong> the clay to be 447,000 t <strong>of</strong><br />
C1, and 220,000 t <strong>of</strong> category C2.<br />
Chemical composition and mechanical properties <strong>of</strong> several samples:<br />
Samples % 1 (0,3 m) 6 (0,4-2,0 m) 8 (0,3-1,9 m) 18 (0,2-1,5 m)<br />
SiO2 54.76 54.96 54.15 62.00<br />
Al2O3 23.22 24.56 21.77 18.69<br />
Fe2O3 6.39 5.56 6.77 4.44<br />
CaO 0.98 0.85 2.15 2.15<br />
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Cilek: 4.3. Clays<br />
MgO 2.26 2.36 2.49 1.76<br />
SO3 0.59 0.75 0.46 0.32<br />
L.i. 9.78 9.40 10.86 8.67<br />
< 2 micron 53 43 60 28<br />
2-20 micron 21 28 22 15<br />
20-200 micron 16 15 16 32<br />
> 20 micron 10 14 2 25<br />
1-3 mm 1 1 0 6<br />
> 3 mm 0 0 0 0<br />
Liquid limit 80 78 71 54<br />
Plasticity limit 34 33 37 20<br />
Shrinkage limit 8.89 8.64 8.55 8.74<br />
Total shrinkage after firing 15.0 15.9 18.4 10.7<br />
Good-quality clay is known from Pemba, where the brick factory is situated between the harbour and the airport.<br />
The deposit developed as residual clay over Tertiary clays and limestones. Three samples only were collected<br />
around the factory.<br />
The clay is suitable for the production <strong>of</strong> bricks and tiles; some sections <strong>of</strong> the deposit may provide clay <strong>of</strong> a<br />
better quality usable in the production <strong>of</strong> glazed sewer pipes.<br />
This lateritic red clay is <strong>of</strong> medium plasticity, has a satisfactory value <strong>of</strong> shrinkage and is dark red after firing. A<br />
negative property is its high calcium content, responsible for a development <strong>of</strong> concretions inside and on the<br />
surface <strong>of</strong> the body.<br />
Chemical composition and results <strong>of</strong> mechanical tests (Laboratorio de Engenharia de <strong>Mozambique</strong> -1982, Estudo<br />
da Aptidao de Argila de Pemba):<br />
Sample % 1 2 3<br />
SiO2 58.8 59.8 58.2<br />
Al2O3 16.1 17.4 20.4<br />
Fe2O3 4.7 4.9 1.9<br />
CaO 5.1 3.9 4.3<br />
MgO 1.9 2.1 3.9<br />
SO3 0.0 0.1 0.1<br />
L.i. 10.2 7.6 7.7<br />
< 2 micron 28 35 35<br />
2-20 micron 28 17 18<br />
20-200 micron 26 28 37<br />
> 200 micron 18 20 10<br />
1-3 mm 1 1 1<br />
> 3 mm 0 0 0<br />
Liquid limit 58 67 62<br />
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Cilek: 4.3. Clays<br />
Plasticity limit 24 24 24<br />
Shrinkage limit 8.66 9.20 9.14<br />
Samples 1 and 2<br />
tested after firing at<br />
920°C 965°C 1,000°C<br />
Water absorption 25.5 27.4 25.5 27.4 25.5 27.4<br />
Total shrinkage 11.4 11.3 11.1 11.2 11.5 11.6<br />
Plasticity limit MPa 6.8 5.1 5.4 4.9 6.7 6.3<br />
Compression strength MPa 11.6 8.3 10.4 12.7 12.4 17.6<br />
Shrinkage limit<br />
10**(-10) MPa<br />
2.36 2.64 - - - -<br />
In the vicinity <strong>of</strong> Nampula, there are two brick factories, one in the town, one at Momola, 14 km outside the town.<br />
The clay deposit was investigated S <strong>of</strong> Nampula on the bank <strong>of</strong> river Muapelume. It is a residual deposit with<br />
about a 1.5 m thick layer <strong>of</strong> brownish sandy clay underlain by an about 2.0-2.5 m thick layer <strong>of</strong> compact grey<br />
clay. Calculated reserves were 82,000 t <strong>of</strong> C2 category, but results <strong>of</strong> the tests are not known. A bulk sample<br />
tested at the brick factory Liberdade in Nampula showed a good quality for brick making (Tzonev, 1981).<br />
Widespread in <strong>Mozambique</strong> are residual deposits <strong>of</strong> laterite, lateritic clays and lateritic-kaolinitic clays <strong>of</strong> a<br />
different development. One locality near Gurue W <strong>of</strong> Nampula and N <strong>of</strong> Quelimane was investigated by Italian<br />
geologists as a possible source <strong>of</strong> clay for brick making.<br />
In the area <strong>of</strong> tea plantations, about 15 km S <strong>of</strong> the town, an investigation <strong>of</strong> weathering pr<strong>of</strong>iles in morphological<br />
depressions disclosed a thickness <strong>of</strong> about 1.5 m, overlying Precambrian granites-monzonites and migmatites<br />
(Bascia-Mariani, 1982).<br />
Three samples from different localities:<br />
1 - 0.3 to 0.8 m - white clay<br />
2 - 1.1 to 1.6m - white clay<br />
3 - 0.3 to 1.4 m - weathered clayey rock horizon<br />
Results <strong>of</strong> chemical analysis:<br />
Sample% 1 2 3<br />
SiO2 48.2 48.46 58.70<br />
Al2O3 30.07 31.12 23.61<br />
Fe2O3 2.00 1.92 5.45<br />
CaO 0.85 0.57 0.01<br />
MgO 1.20 1.10 1.17<br />
SO3 0.00 0.01 0.10<br />
L.i. 12.44 11.96 9.35<br />
< 2 micron 37 50 48<br />
2-20 micron 15 14 9<br />
20-200 micron 15 23 8<br />
> 200 micron 33 13 35<br />
1-3 mm 10 5 10<br />
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Cilek: 4.3. Clays<br />
> 3 mm 0 0 0<br />
Liquid limit % 43 49 55<br />
Plasticity limit % 20 24 35<br />
Shrinkage limit % 9.27 9.02 10.9<br />
The results show a high content <strong>of</strong> particles below 2 micron, small plasticity and low mechanical strength. The<br />
clay is probably kaolin in the upper part <strong>of</strong> the pr<strong>of</strong>ile. It is not suitable for brick production.<br />
Conclusions:<br />
Exploited clay deposits <strong>of</strong> <strong>Mozambique</strong> are mostly Quaternary alluvial or residual clays <strong>of</strong> reddish or greyish<br />
colour and high plasticity, which need to be corrected by sand or ash to be suitable for a production <strong>of</strong> bricks, tiles<br />
and pottery. Some deposits could probably be used in the production <strong>of</strong> stoneware and heavy technical and<br />
agricultural ceramic products. Ball clays or refractory clays have not been found, but may possibly exist within<br />
the sedimentary formations from Karroo to Quaternary. They may be discovered in systematic search for these<br />
formations. Fire clay should be developed in the Beaufort Formation <strong>of</strong> Karroo in the Tete Province.<br />
© Václav Cílek 1989<br />
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Cilek: 4.4. Decorative stones<br />
4.4. Decorative stones<br />
This group <strong>of</strong> stones includes a vast variety <strong>of</strong> commercially valuable stones <strong>of</strong> igneous, sedimentary<br />
and metamorphic origin which can be cut, polished and sculptured and give striking effects with regard<br />
to their texture and colour. The value <strong>of</strong> decorative stone is much higher than that <strong>of</strong> a common building<br />
stone and the products made include such articles as ashtrays, fireplaces, wainscoting material,<br />
baseboards, souvenirs, art objects, but mainly slabs, columns, steps, gravestones, monuments, memorials<br />
etc.<br />
Decorative stones can be used either for exterior or interior purposes. Most <strong>of</strong> the stones are used in the<br />
production <strong>of</strong> slabs in the exterior using hard resistant igneous rocks, and mainly marbles in the interior.<br />
At present, a large number <strong>of</strong> polished decorative stones are replaced by cheaper crushed ones used in<br />
artifical stone and terazzo flooring.<br />
Generally, the extraction <strong>of</strong> decorative stones applies to the minimum volume <strong>of</strong> 0.5 m3, with a yield <strong>of</strong><br />
about 25% <strong>of</strong> total rock volume (normally 30-50%), but in the case <strong>of</strong> rare decorative stone, even the<br />
blocks <strong>of</strong> several cm3 are extracted.<br />
From a genetical point <strong>of</strong> view, these groups <strong>of</strong> decorative stone are known:<br />
1. igneous rocks:<br />
dark colour such as gabbro, dolerites, serpentinites, diabase;<br />
light colour such as granite, anorthosite, syenite, labradorite<br />
2. metamorphic rocks:<br />
marbles (crystalline limestones) and its varieties<br />
3. sedimentary rocks: limestones, travertine<br />
Decorative stones encompass also a group <strong>of</strong> rare decorative stones such as dumortierite, amazonite,<br />
rhodonite, silicified wood, anyolite etc. In case <strong>of</strong> rare decorative stones even very small deposits with<br />
reserves <strong>of</strong> several m3 and a size <strong>of</strong> several cm3 can successfully be mined.<br />
Acceptive specifications for an extraction <strong>of</strong> decorative stones:<br />
compressive strength minimum 40 MPa, normally 80 to 110 MPa<br />
flexibility strength, dry or water saturated, 10 MPa<br />
resistance to scrub wear (abrasion) 0.55 % loss <strong>of</strong> rock/cm2<br />
porosity up to 3%<br />
water absorption < 0.5%<br />
specific gravity for marble 2.4<br />
the rock must be easy to polish, resistant to weathering, with small thermal dilatation and conductivity<br />
etc.<br />
In nature, decorative rock should have certain uniform properties-texture and colour to be able to secure<br />
the delivery for many years ahead. An important property for mining is a development <strong>of</strong> joints and<br />
fractures; a high density be deterrent to their utilization as dimension blocks, while a proper system <strong>of</strong><br />
joints facilitates extraction. Generally, three systems <strong>of</strong> joints are present in igneous rocks: sheet joints,<br />
in subparallel or parallel direction to the surface structure (on small massifs like onion sheets) separating<br />
the rock into sheets or beds; "headers", almost vertical joints, which traverse the rock mass and divide it<br />
into blocks; rift or "run" joints, also grain joints are vertical and transverse. In igneous decorative stones,<br />
these joints marked L, Q and S, are <strong>of</strong>ten at right angles and are essential in an extraction <strong>of</strong> blocks.<br />
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Cilek: 4.4. Decorative stones<br />
In sedimentary rocks, the bedding planes are <strong>of</strong> greatest importance, whereas in metamorphic rocks the<br />
fotiation planes play the decisive role in that they divide the rock mass into small blocks and slabs, <strong>of</strong>ten<br />
not marketable.<br />
Also <strong>of</strong> importance is the mineralogical composition <strong>of</strong> decorative stone: in marbles, the presence <strong>of</strong><br />
hard minerals or s<strong>of</strong>t and porous particles can cause difficulties in polishing; prevailing minerals <strong>of</strong> good<br />
cleavage, minerals with sheet structure are ill polishable and may cause discontinuous polished surface.<br />
The durability <strong>of</strong> polish under climatic conditions depends on the rock - marbles are excellent in a dry<br />
climate, but desintegrate under wet conditions. Typical is damage <strong>of</strong> soluble decorative stones <strong>of</strong> calcitic<br />
composition - dull polish surface and disintegration into thin layers in the aggresive acid environment <strong>of</strong><br />
modern cities. Therefore natural stones in the form <strong>of</strong> slabs for a cladding <strong>of</strong> buildings is less <strong>of</strong>ten used<br />
and interior applications prevail. Marble slabs <strong>of</strong> a very small thickness and hence, cheaper, substitute<br />
the former thick slabs.<br />
In <strong>Mozambique</strong> almost all decorative stones used on buildings, such as slabs, interior and exterior,<br />
steps, small decorative articles and monuments were imported mainly from Portugal in the past. A very<br />
small quantity was produced locally using marble from Montepuez in the Province <strong>of</strong> Cabo Degado.<br />
The country is extremelly rich in many types <strong>of</strong> decorative rocks ready for exploitation and processing.<br />
Small workshops were and still are active in Maputo, processing marbles from Montepuez and small<br />
scale production <strong>of</strong> rare decorative stones in art objects and jewellerly is part <strong>of</strong> the semiprecious and<br />
precious stone industry (see Fig. 4.4.1).<br />
Decorative stones <strong>of</strong> <strong>Mozambique</strong> can be divided into:<br />
a) igneous rocks<br />
dark coloured "black granites" (gabbros), serpentinites<br />
red granites, syenites and brown granites, light coloured "granites"-anorthosites, norites, diorites,<br />
granites, rhyolites<br />
b) metamorphic rocks<br />
marbles (crystalline limestones), lamboanite<br />
c) rare decorative stones<br />
dumortierite quartzite, amazonite, rhodonite<br />
Sedimentary decorative stones have not been investigated as yet in <strong>Mozambique</strong>.<br />
Fig. 4.4.1. Occurences <strong>of</strong> marbles and ornamental stones (398 kB)<br />
a) Igneous decorative stones<br />
Dark coloured "black granites" are, in fact, gabbros and serpentinites developed in many small massifs<br />
and sheet-like bodies from Archean to post-Karroo times.<br />
So far, this rock has not been extracted in <strong>Mozambique</strong>. One small locality was explored near Chimoio<br />
in the Beira corridor (Geol. Inst. Beograd, 1982). It is a dioritic gabbro intrusion divided into three<br />
different outcrops <strong>of</strong> which the most extensive is on Monte Mecatacata. The hill, NW <strong>of</strong> the village <strong>of</strong><br />
Gondola and just 29 km N <strong>of</strong> the main tarmac road, arises about 80 m above the surrounding plateau<br />
built by the Barue Formation-Precambrian gneisses and migmatitic gneisses. Quartz veins and lenses are<br />
frequent and run in NE-SW direction. Around the gabbro plutons are large slope debris deposits and<br />
many spheroidal blocks up to 15 m3 in size. These blocks represent a part <strong>of</strong> the reserves.<br />
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Gabbro is dark grey and contains hornblende, little quartz and biotite, and plagioclase. It can be<br />
classified as a gabbro-metadiorite. The weathered cover on Monte Mecatacata is about 10 m thick with<br />
typical rounded blocks <strong>of</strong> gabbro inside. The area <strong>of</strong> pluton is small-about 2 km2.<br />
Results <strong>of</strong> physico-mechanical tests <strong>of</strong> four samples:<br />
Compression strength<br />
maximum 2,591 - 2,428 kg/cm2<br />
minimum 2,264 - 1,816 kg/cm2<br />
Compression strength-water-saturared samples:<br />
maximum 2,489 - 2,295 kg/cm2<br />
minimum 1,989 - 1,795 kg/cm2<br />
Compression strength after freezing:<br />
maximum 2,438 - 2,244 kg/cm2<br />
minimum 2,338 - 1,734 kg/cm2<br />
Water absorption at N. P. conditions 0.10-0.07%<br />
Apparent porosity 0.02 %<br />
No colour or structural changes were noticed after a freeze-defreezing test and Na2SO4 treatment. The<br />
gabbro is <strong>of</strong> very good quality and has decorative properties. It can be used in exterior horizontal and<br />
vertical linings, monuments, curbs, naturally in the form <strong>of</strong> a crushed aggregate. It can easily be cut,<br />
dressed and polished.<br />
Reserves calculated for three gabbro outcrops:<br />
800,000 m3 probable<br />
1,153 000 m3 prognostic<br />
1,953 000 m3 total<br />
Another locality <strong>of</strong> olivine gabbro was investigated at Monre Mesa NW <strong>of</strong> Memba, N <strong>of</strong> Nacala port<br />
and near the seashore. Monte Mesa is a prominent inselberg about 120 m high, 1.5 km wide and 2.1 km<br />
long. The rock is almost black, compact, disintegrating into blocks <strong>of</strong> 2-10 m3. It is <strong>of</strong> kelyphite texture<br />
and is composed <strong>of</strong> plagioclase, rhombic and monoclinic pyroxene, olivine, amphibole and blades <strong>of</strong><br />
biotite. It lends itself well to cutting, polishing and possesses highly decorative properties. It is an<br />
ornamental stone which can be used both for small decorative objects and monuments, gravestones and<br />
slabs.<br />
Its properties are these (Research Institute <strong>of</strong> Materials and Structures, Beograd, 1984):<br />
Resistance to pressure:<br />
dry maximum 250 MPa<br />
minimum 230 MPa<br />
water-saturated<br />
maximum 235 MPa<br />
minimum 230 MPa<br />
after freezing<br />
maximum 226 MPa<br />
minimum 217 MPa<br />
Resistance to scrub wear 7.68 cm3/50 cm2<br />
mass volume gp 2.97 Mg/m3<br />
porosity 0.020 %<br />
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persisting resistance to Na2SO4<br />
One <strong>of</strong> the biggest sites <strong>of</strong> gabbro occurrence in <strong>Mozambique</strong> is the post-Karroo ring complex <strong>of</strong><br />
Gorongosa situated W <strong>of</strong> the Urema trough. It is about 30 km long (N-S) and 25 km wide. On the E side<br />
it is composed <strong>of</strong> syenites and granites, the W-part <strong>of</strong> the ring is <strong>of</strong> gabbroic composition. It rises 2,000<br />
m above the surrounding plateau. The gabbros have intruded first, probably in the form <strong>of</strong> a flattened<br />
lopolithic body. This was later intruded by a granitic diapir and finally, a narrow subvertical sheet <strong>of</strong><br />
gabbroic rocks intruded the central granitic core.<br />
The gabbro is a compact dark rock with good mechanical properties; it consists <strong>of</strong> tholeiitic gabbros<br />
with labradorite and clinopyroxene and some norites and olivine gabbros. An interesting rock with<br />
probable decorative properties is micropegmatite granite (graphic granite) with albite, orthoclase, quartz,<br />
clinopyroxene, hornblende, chlorite and biotite forming the central core <strong>of</strong> the complex (Hunting, 1984).<br />
Many other gabbroic massifs occur within the Mozambican belt. Just recently, a small massif <strong>of</strong> gabbro<br />
was investigated at Machipanda on the Zimbabwean border. The gabbro is almost black, very finegrained,<br />
with alternating green and black minerals <strong>of</strong> about 1 mm. It disintegrated into blocks <strong>of</strong><br />
different size. It is an excellent rock for a production <strong>of</strong> polished stabs. The extension <strong>of</strong> the massif is 2 x<br />
1 km.<br />
Several types <strong>of</strong> dark rocks are present in the Tete gabbro-anorthosite Complex. Ultramafic rocks are<br />
poorly represented, but occur in some localities. Pyroxenites form green, granular medium-grained rocks<br />
with augite, hypersthene and plagioclase with olivine which, if predominant, produces peridotites.<br />
Numerous basic dykes <strong>of</strong> dark grey dolerite composed <strong>of</strong> plagioclase, augite and less pyroxene cut<br />
through the massif Some are 10 m thick (see Fig. 4.4.2).<br />
Fig. 4.4.2. Schematic Map <strong>of</strong> Mid-Zambezi Province with Zambezi rift and "the Mylonite<br />
Zone" (Hunting, 1984) (607 kB)<br />
In the Manica Province, many thick and long dolerite dykes cut the Archean rocks. One <strong>of</strong> this dyke is in<br />
fact diabase composed mainly <strong>of</strong> serpentinite and amphibole.<br />
Serpentinite-metamorphic product <strong>of</strong> peridotite and related rocks was known to the old Greeks and<br />
Romans as verd antique. It is a beautifull rock <strong>of</strong> deep green colour <strong>of</strong>ten with streaks <strong>of</strong> light-colour<br />
calcite. This rock is <strong>of</strong>ten too much jointed and therefore unsuitable for use as dimension stone.<br />
In <strong>Mozambique</strong>, serpentinites are connected with deposits <strong>of</strong> asbestos and talc and are found at Manica<br />
(Serra Morrumbala and several other belts <strong>of</strong> the so-called green schists), in the area <strong>of</strong> Mavita, in small<br />
localities <strong>of</strong> the Cabo Delgado Province and in bigger accumulation in the Monte Atchiza Complex in<br />
the Tete Province. The complex consists <strong>of</strong> serpentinite, gabbro and norite with minor peridotite and<br />
pyroxenite (Real, 1962). All these rocks may represent a nice decorative material.<br />
The second group <strong>of</strong> igneous decorative rocks include red granites, syenites and brown granites. The<br />
only locality <strong>of</strong> red granite, resembling the Scandinavian rapakivi red granite was discovered on the<br />
bank <strong>of</strong> Lake Niassa at Monte Tchonde E <strong>of</strong> the village <strong>of</strong> Meponda in the Niassa Province. The massif<br />
covers about 12 km2 <strong>of</strong> ring-like structure which penetrated the surrounding Precambrian migmatites,<br />
which were uplifted and deformed. Over an area <strong>of</strong> 12 km2, 95% <strong>of</strong> the massif consists <strong>of</strong> granite.<br />
Several facial changes were observed in the size <strong>of</strong> phenocrysts, the colour <strong>of</strong> feldspars and the quartz<br />
content. Red granite covers an area <strong>of</strong> about 6 km2, blocks <strong>of</strong> extractable dimension attained up to 10 x<br />
5 x 5 m and the reserves <strong>of</strong> 60 million m3 were calculated (Fig. 4.4.3).<br />
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Fig. 4.4.3. Monte Tchonde - red granite (615 kB)<br />
The rock <strong>of</strong> interest is <strong>of</strong> pink colour from K-feldspar, coarsely grained. It contains also white grey<br />
plagioclase and glassy quartz, biotite, traces <strong>of</strong> zircon, epidote, apatite and muscovite. The texture is<br />
allotriomorphically granular.<br />
Result <strong>of</strong> physico-mechanical tests:<br />
volume weight g/cm3<br />
dry particles 2.51-2.64<br />
saturated 2.60-2.65<br />
water absorption % 0.4 - 0.6<br />
aggregate impact value % 24.9 - 29.5<br />
aggregate abrasion value % 20.0 - 39.5<br />
Syenites <strong>of</strong> <strong>Mozambique</strong> form several young massifs connected with movements along the East-African<br />
rift valley. Nepheline syenites have been already described. Apart from these there are several other<br />
syenite facies. A typical example is Monte Morrumbala a big massif N <strong>of</strong> river Zambezi composed <strong>of</strong><br />
syenite, granite and minor feldspathoid syenite.<br />
Alkali granite is pink, medium-to coarse-grained, with 10% <strong>of</strong> alkali amphibole, 60% <strong>of</strong> orthoclaseperthite<br />
and 20-30% <strong>of</strong> quartz.<br />
Alkali syenite with quartz contains 10% <strong>of</strong> mafic minerals, 3-10% <strong>of</strong> quartz and orthoclase-perthite.<br />
Alkali syenites from Morrumbala contain 10-20% <strong>of</strong> coloured constituents (augite, riebeckite) and are <strong>of</strong><br />
a light pink colour.<br />
Other massifs such as Chiperone, Tumbine, Mauzo consist mainly <strong>of</strong> nepheline syenites, an excellent<br />
ornamental stone for slabs, sculptures, monuments etc. Other massifs such Salambidua with hornblendesyenite<br />
(Conguene, Chiperone etc.) and with part <strong>of</strong> the massif composed <strong>of</strong> syenites, cannot be used as<br />
ceramic raw material but, could serve as a source <strong>of</strong> decorative stones.<br />
Brown granite called "granito castanho" in <strong>Mozambique</strong> known from the provinces <strong>of</strong> Tete, Manica,<br />
S<strong>of</strong>ala and Zambezia is, petrographically, a charnockitic granite. It is a dense, brown, tough rock,<br />
medium to coarse grained, <strong>of</strong> equigranular or porphyritic texture. Fresh surface is mainly dark grey or<br />
black and quartz and feldspars have a characteristic dark grey colour with a greasy lustre (Hunting,<br />
1984).<br />
They are composed <strong>of</strong> quartz, alkali feldspar, plagioclase, hypersthene, augite, biotite, hornblende, with<br />
abundant opaque minerals. In composition, they range from true granite and syenite to granodiorite and<br />
quartz monzonite.<br />
The textures <strong>of</strong> the rocks are either even-grained or porphyritic. They form masses or conformable<br />
sheets and are developed as mountains and ranges NW <strong>of</strong> Tete and near Furancungo. They are mainly<br />
conform to the country rocks but intrude in fact, the Chiperone complex and the Luia Group. The age <strong>of</strong><br />
brown granites is 1,050 + 20 -10 m.y. (Hunting, 1984, pg. 128).<br />
These granites could certainly be used as decorative stones, but nobody checked their properties as yet.<br />
The last group <strong>of</strong> igneous origin are light-coloured rocks. These rocks are well known from the Tete<br />
gabbro-anorthosite Complex, which is composed predominantly <strong>of</strong> light-coloured gabbro and norite<br />
with subordinate anorthosite in layers or later intrusions. The textures are medium -to very coarse -<br />
grained, with a widespread replacement <strong>of</strong> original minerals, in places, zones <strong>of</strong> cataclasis and shearing<br />
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are common.<br />
Fresh gabbro and norite is light grey, homogeneous, unfoliated granular rock composed <strong>of</strong> plagiclase,<br />
pyroxene and iron-titanium oxides. The plagioclase is sodic labradorite. The pyroxene is either augite or<br />
hypersthene (Hunting, 1984).<br />
Anorthosite is light grey or white composed <strong>of</strong> andesine or sodic labradorite, with a minor proportion <strong>of</strong><br />
pyroxene and opaque minerals. Alkali feldspar, biotite, sphene, sulphides and garnet occur as accessory<br />
minerals. The textures are granular and, similar to the gabbros, plagioclase is replaced in some places by<br />
scapolite and pyroxene by hornblende.<br />
Some localities <strong>of</strong> the Tete complex were investigated by the Geol. Inst. Beograd (1982), which<br />
described an anorthosite massif <strong>of</strong> the Monies Inhangoma and Sicarabo with labradorite <strong>of</strong> grey to<br />
purple colour, fine grained with huge reserves and <strong>of</strong> ornamental quality (near Moatize).<br />
Another site <strong>of</strong> occurrence <strong>of</strong> ornamental stone has been described from a norite massif at Necungas<br />
close to a railroad in the SE corner <strong>of</strong> the Tete complex, with good quality stone.<br />
Light-coloured decorative stones can also be found in big lava layers and intrusive bodies <strong>of</strong> rhyolites <strong>of</strong><br />
the Stormberg Formation <strong>of</strong> the Upper Karroo in the Lebombo Mts., and in other volcanic rock areas <strong>of</strong><br />
the Karroo. The rhyolites are greyish to whitish in colour, dense and compact and, generally, <strong>of</strong> high<br />
mechanical strength. Rhyolites and trachytes are part <strong>of</strong> light-grey, acid lavas group forming several lava<br />
flows interlayered with amygdaloid basalts, tuffs and pyroclastics stretching from the Lebombo Mts. to<br />
Chibabava, Lupata and the Mid-Zambezi rift.<br />
b) Decorative rocks <strong>of</strong> metamorphic origin<br />
The only locality in <strong>Mozambique</strong> which produces marbles <strong>of</strong> decorative quality is Montepuez in the<br />
Cabo Delgado Province. There are several deposits within the belt <strong>of</strong> crystalline rocks stretching over 30<br />
km at a width <strong>of</strong> 1.5 km. The main quarries are situated 3 km N <strong>of</strong> village. The deposit is connected with<br />
the port <strong>of</strong> Pemba by a tarmac road <strong>of</strong> 215 km.<br />
The deposit is part <strong>of</strong> the Supergroup Chiure <strong>of</strong> sedimentary origin and 780 m. y. Apart from marbles<br />
the productive belt includes amphibolites, gneisses, quartzites and some intrusive granitic massifs. The<br />
belt is highly folded and tectonically disturbed by the grade <strong>of</strong> metamorphism diminishing in SW<br />
direction. Several isoclinal structures are developed, with monoclinal folds <strong>of</strong> NE-SW direction and<br />
inclination in the quarry area <strong>of</strong> 55°.<br />
The marbles are macrocrystalline with quartz, feldspar, pyrite, chalcopyrite and rutile in some places<br />
with wollastonite. The genesis <strong>of</strong> marbles is a marine deposition <strong>of</strong> limestone with some intercalations<br />
<strong>of</strong> silt, sand and clay followed by regional metamorphosis <strong>of</strong> thermal type and concluded by contact<br />
metamorphosis and hydrothermal alteration with the origin <strong>of</strong> sulphides, recrystallization <strong>of</strong> calcite (big<br />
crystals) and an origin <strong>of</strong> druzes <strong>of</strong> quartz.<br />
The marble contains about 50% <strong>of</strong> calcite and 50% <strong>of</strong> dolomite with layers <strong>of</strong> amphibolites, gneisses and<br />
schists 5 to 50 cm long and 2-6 cm thick. The weathered surface zone is 4-5 m thick, with iron<br />
hydroxides and hematite.<br />
There are three systems <strong>of</strong> joints which enable an extraction <strong>of</strong> blocks averaging a volume <strong>of</strong> about 1<br />
m3. Types <strong>of</strong> marbles produced (according to their classification at the Montepuez quarries and<br />
workshops in Maputo):<br />
marmore branco - MB - white marble<br />
marmore branco de neve - MBN - snow white<br />
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marmore branco cinzento claro - MBC - white to light grey<br />
marmore branco com amphibolite - MBA - white with amphibolite<br />
marmore cinzento - MC - grey<br />
marmore cinzento claro - MCC - light grey<br />
marmore cinzento escuro - MCE - dark grey<br />
marmore tipo magram MM.<br />
The most interesting is the magram type marble representing a mixture <strong>of</strong> all marbles described above<br />
with a higher content <strong>of</strong> silicates, feldspar, amphibole, schists and secondary calcite in big crystals.<br />
Generally, the Montepuez marbles are high-quality ornamental stones except for layers with hard<br />
minerals such as quartz and rocks with quartzites and pegmatites. The best-quality marble is expected to<br />
be snow-white saccharoidal.<br />
The marbles are used in small artistic objects, souvenirs, monuments, sculptures. Naturally, they can be<br />
used as building material (impure layers), in metallurgy, a refining <strong>of</strong> sugar, soda production, in<br />
foodstuff and agriculture. Their possible exploitation has been known to local inhabitants for many<br />
centuries, however small-scale mining was started as late as after World War 2 by the company<br />
Monteiro Lda. Systematic exploration started in 1981.<br />
The production <strong>of</strong> blocks (1.3 - 1.5 m3) is fairly small:<br />
1979 304.5m3 1982 562.7m3 1985 2241m3<br />
1980 295.5m3 1983 406.0m3 1986 11372m3<br />
1981 126.8m3 1984 574.0m3<br />
Reserves calculated by Bulgargeomin (1983):<br />
White marble category C1 3,800 000 m3 category C2 2,360 000 m3<br />
Light grey category 2,400 000 m3 category 870 000 m3<br />
Grey category 7,650 000 m3 category 4,000 000 m3<br />
Magram category 2,150 000 m3 category 2,600 000 m3<br />
Total reserves 25,844 000 m3. Estimated block recovery is between 40 and 50%.<br />
Technology properties:<br />
porosity 0.58%<br />
water absorption 0.21%<br />
density 2.85 g/cm3<br />
Compression strength dry 2.839 kg/cm2<br />
Compression strength saturated 2.893 kg/cm2<br />
Hardness coefficient Kb very high = 1<br />
Many other marble deposits are known to occur within the Mozambican belt <strong>of</strong> which some may<br />
represent decorative stones <strong>of</strong> high quality such as in the Formation Barúe, Fingoe, locaties in Angónia,<br />
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near Lichinga, E <strong>of</strong> the Chiré trought and others.<br />
Another metamorphic decorative rock discovered in 1983 by the Jugoslav geological team is<br />
lamboanite, a variety <strong>of</strong> migmatite <strong>of</strong> extraordinary quality (see Fig. 4.4.4).<br />
Fig. 4.4.4. Geological map <strong>of</strong> the lamboanite occurence - Namiola area (Geol. Institute, Beograd,<br />
1984) (474 kB)<br />
It occurs in the quarry at Monte Xica 35 km W on Monapo and at about 100 km from Nampula.<br />
The quarry produces crushed stone. A lens <strong>of</strong> lamboanite 500 m long and 80 m wide directed from<br />
NNW to SSE occurs at the bottom <strong>of</strong> the hill (Fig. 4.4.5).<br />
Fig. 4.4.5. Lamboanite quarry on Monte Xica-Namialo (Geol. Institute, Beograd, 1984) (268 kB)<br />
Lamboanite is a rock <strong>of</strong> light grey colour with a greenish shade, medium-grained, containing microcline<br />
perthite, plagioclase, quartz, amphibole and biotite. The face <strong>of</strong> the quarry is 100 m long and 20 m high.<br />
The estimated volume <strong>of</strong> dimension blocks is about 30%. Ornamental qualities <strong>of</strong> the rock are obvious<br />
and its extraordinary pattern is due to a succesion <strong>of</strong> dark and light-coloured mineral concentrations. The<br />
rock is tough, difficult to cut and polish. Isometric grains prevail over platy minerals and this is reflected<br />
in its indistinct foliation. It can be used as a facing and building stone in civil engineering, and a<br />
production <strong>of</strong> slabs both for the interior and the exterior.<br />
Reserves amount to 1,530 000 m3 <strong>of</strong> which about 500,000 m3 can be extracted in dimension blocks.<br />
Compression strength in a dry state<br />
minimum 132 MPa<br />
maximum 143 MPa<br />
Compression in a water saturated state<br />
minimum 131 MPa<br />
maximum 140 MPa<br />
Bonding strength<br />
maximum 12.5 MPa<br />
minimum 10.8 MPa<br />
Resistance to abrasion at machine cutting As 8.28 cm3/50 cm2<br />
Water absorption 0.26%<br />
volume mass 2.61 Mg/m3<br />
porosity 0.019<br />
Generally the compressive strength is moderately high, bonding strength good and abrasion very good.<br />
c) Rare decorative stones include these varieties:<br />
dumortierite<br />
amazonite<br />
rhodonite, rhodochrosite<br />
others<br />
Dumortierite is, in fact, quartzite with dumortierite known to occur in one locality only, i. e., at Chicoa<br />
in the Tete Province near the Cabora Bassa dam. The rock is extremely distinctive in colour, a cobalt-to<br />
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greyish blue and is collected from the surface <strong>of</strong> the eluvial deposit as pieces measuring several 10 cm3.<br />
It is used in the production <strong>of</strong> small ornamental articles.<br />
Amazonite is a green feldspar <strong>of</strong> very distinctive colour, with excellent cleavage found in many<br />
pegmatite deposits <strong>of</strong> the Alto Ligonha district, in the Monapo structure, Tulua pegmatite near Nacala,<br />
Nipepe in the Niassa Province and other places. It is mined in small blocks and used in the production <strong>of</strong><br />
small articles <strong>of</strong> cheap jewellry such as bracelets, necklaces, pendants etc. Reserves are difficult to<br />
calculate, in some pegmatites they range in volume between 10-50 m3.<br />
Rhodonite is a brownish-reddish, and also pink manganese silicate with typical black veins <strong>of</strong><br />
manganese <strong>of</strong> the formula Mn(Si03). It is used as an ornamental stone for small-size objects and<br />
souvenirs such as ash trays, stone eggs, book supports, pendants etc. In <strong>Mozambique</strong>, it occurs at the<br />
Tete Province in the form <strong>of</strong> nodules in manganese mineralization zones <strong>of</strong> the Formation Rushinga near<br />
the Zimbabwean border. According to Alves (1961,1964) it is found in four zones:<br />
Mazoe N<br />
Mazoe S<br />
Catambula<br />
Blaundi Bonga<br />
Manganese mineralization with Mn-oxides and Mn-silicates and carbonates (the latter at Mazoe N)<br />
occurs in gneisses in the form <strong>of</strong> lenses associated with Mn-garnets.<br />
The thickness <strong>of</strong> zones is a few meters (2-5m) at a length <strong>of</strong> a few km. In terms <strong>of</strong> its genesis it<br />
originated from metamorphosed sediments in contact zones, giving rise especially to the origin <strong>of</strong><br />
rhodonite. Rhodonite occurs mainly at Catambula-Serra de Inhandendje inside nodular gneisses<br />
measuring between several cm and one m. Mn-minerals are pyrolusite and rhodonite accompanied by<br />
spessartite, rhodochrosite, hematite, magnetite and Mn-garnets.<br />
Composition <strong>of</strong> rhodonite (Real, 1966): 44.69% Mn, 24.30% SiO2 and 0.006% P.<br />
Rhodonite can serve exceptionally as manganese ore in small quantities in steel production.<br />
Other decorative stones used in jewelry and small decorative articles in <strong>Mozambique</strong> include banded<br />
ironstones found in many iron deposits, or iron-titanium oxides <strong>of</strong> the Tete anorthosite complex which<br />
may have very interesting colour after polishing.<br />
Conclusions:<br />
Mozambican decorative stones include large-volume rocks such as marbles, gabbros, serpentinites, red<br />
granites, syenites, anorthosites and lamboanite and, rarely, decorative stones <strong>of</strong> a small volume such as<br />
dumortierite, amazonite, rhodonite and others. The desire <strong>of</strong> mankind for natural stones <strong>of</strong> distinctive<br />
decorative properties at present and in the future will certainly secure the development <strong>of</strong> the<br />
manufacture <strong>of</strong> slabs, dimension blocks for monuments, decorative objects and souvenirs. The recent<br />
discovery <strong>of</strong> exotic migmatite-lamboanite will be certainly followed by discovery <strong>of</strong> other interesting<br />
decorative stones.<br />
© Václav Cílek 1989<br />
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Cilek: 4.5. Diatomite<br />
4.5. Diatomite<br />
Diatomite or diatomaceous earth or kieselguhr is a lightweight, white to gray coloured friable<br />
sedimentary rock composed mainly <strong>of</strong> shells or frustules <strong>of</strong> diatoms. The algae Diatomaceae - are<br />
unicellular floating plants living in fresh, brakesh or marine environment <strong>of</strong> shallow water. The shells<br />
are made up <strong>of</strong> silica extracted from the water and, therefore, the biggest accumulations <strong>of</strong> diatoms are<br />
present in basins near the volcanic centres with a high supply <strong>of</strong> dissolved inorganic salts. The cell<br />
measures 5 to 1,000 micron, but mostly within a range <strong>of</strong> 50 - 100 micron. One cubic meter <strong>of</strong> water<br />
may contain one billion diatoms and their reproduction is so fast that a layer <strong>of</strong> several mm can develop<br />
during one year.<br />
Diatomite deposits range in thickness <strong>of</strong> several to several ten and hundred <strong>of</strong> meters. They contain clay,<br />
silt, volcanic ash and other impurities and grade into diatomaceous shales after diagenetic changes.<br />
Commercial diatomite contains over 80% <strong>of</strong> silica, the remaining compounds are Al2O3 and Fe2O3.<br />
Bulk density <strong>of</strong> diatomite is about 0.5 to 0.9 kg/cm3, bulk specific gravity 2.1 and more. The porosity is<br />
extremely high reaching 90% with up to 30 millions <strong>of</strong> shells in 1 cm3.<br />
They are used mainly (60-70%) as a filtering aid in clarifying liquids. The principal requirements are<br />
diatom skeletal constitution, density and soluble impurites. Their main application is in a purification <strong>of</strong><br />
water, wine, beer, juices, mineral oils, filtration <strong>of</strong> dry-cleaning fluids and separation <strong>of</strong> oils and<br />
chemicals.<br />
Another major use is that <strong>of</strong> a filler, a flatting agent in paints, anti-blocking agent in polyethylene<br />
production, reinforcing agent in silicone rubber and paper filler. In addition they are used as pesticide<br />
carriers, storage and transportation <strong>of</strong> hazardous liquids, as a mild abrasive and in polishes. They used to<br />
be <strong>of</strong> importance in the production <strong>of</strong> dynamite. A large proportion <strong>of</strong> impure or low-quality diatomite is<br />
used in the building industry, e. g., for thermal and acoustic insulations.<br />
The main increase is expected in their application as filters where diatomite is by far superior to other<br />
materials.<br />
Although raw diatomite was used in the early days <strong>of</strong> the filtration industry, nowadays most material is<br />
calcined in order to burn all organic matter and render it less susceptible to chemical attack by acids and<br />
alkalies. Furthermore, calcination converts all impurities to fused slags which can be removed at a later<br />
stage. Flux calcination is applied to obtain grades with the biggest filtration speed, using mostly soda ash<br />
as fluxing agent.<br />
Chemical composition <strong>of</strong> diatomite:<br />
% 1 dicalite USA 2 Idaho USA 3 Kenya Soysambu 4 USSR Kamyslov<br />
SiO2 86.8 89.82 84.50 79.22<br />
Al2O3 4.1 1.82 3.06 6.58<br />
Fe2O3 1.6 0.44 1.86 3.56<br />
TiO2 - 0.07 0.17 0.48<br />
CaO 1.7 1.26 1.80 1.43<br />
MgO 0.4 0.54 0.39 0.98<br />
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Cilek: 4.5. Diatomite<br />
Na2O<br />
K2O<br />
0.8<br />
1.03<br />
0.22<br />
1.19<br />
0.91<br />
0.65<br />
0.72<br />
L. i. 4.6 4.02 6.08 4.91<br />
In <strong>Mozambique</strong>, several promising deposits <strong>of</strong> diatomite are present in the coastal belt. All these<br />
deposits are <strong>of</strong> Pleistocene - Holocene age and probably originated in lagoons, river depressions and<br />
lakes on different elevation levels. In my opinion, the best conditions for an origin <strong>of</strong> these deposits must<br />
have been available in interglacial times <strong>of</strong> the Pleistocene, when a rise in the water table <strong>of</strong> the sea level<br />
chocked the openings <strong>of</strong> the rivers and extensive inner lakes (ria lakes) originated along the river beds.<br />
Nowadays, many sites <strong>of</strong> diatomite occurrence, which may probably have been eroded with prograding<br />
denudation during glacial times are covered by dune sands. Several still unknown deposits may be<br />
discovered in sedimentary sequences <strong>of</strong> the Tertiary or Cretaceous especially in the S- part <strong>of</strong> the<br />
country formed during the development <strong>of</strong> the Limpopo paleodelta, in the Zambezi paleodelta, Mid-<br />
<strong>Mozambique</strong> and in depressions <strong>of</strong> the rift valleys, i. e., Shire and Urema troughts, Niassa rift and in a<br />
sedimentary basin on the coast <strong>of</strong> N-<strong>Mozambique</strong>.<br />
Diatomite areas from S to N (see Fig. 4.5.1):<br />
1. South <strong>of</strong> Maputo-Bela Vista, Boane 6. Panda<br />
2. Marracuene-Manhica 7. Inhambane<br />
3. Macia-Ch6kwe-Magude 8. Nova Mambone<br />
4. Chicomo-Manjacaze<br />
5. Inharrime-Chidenguele<br />
9. Pemba<br />
Fig. 4.5.1. Occurences <strong>of</strong> diatomite, glass and foundry sand, building sand-gravel (392 kB)<br />
Diatomite deposits have been known since 1940, detailed exploration started in 1960. In 1970 the<br />
deposit Diana at Manhica was explored.<br />
The deposit Beta Vista contains diatomite <strong>of</strong> no economic importance. It developed in occasional<br />
swamps and marshes <strong>of</strong> the younger Quaternary at the elevation <strong>of</strong> 140 m above sea level. Nowadays<br />
the whole area is covered by dunes underlaid by silt, clay <strong>of</strong> dark colour and clayey sand with some<br />
diatomite. It is expected that diatomite layers may be found in deeper layers <strong>of</strong> Pleistocene deposits.<br />
Around Boane, 30 km W <strong>of</strong> Maputo, diatomite layers <strong>of</strong> 0.25 to 0.80 m are known overlying Pleistocene<br />
sands <strong>of</strong> the dune. Diatomite is directly on the surface and part <strong>of</strong> the deposit may be eroded already. Its<br />
bulk density is 0.6 g/cm3, average thickness 0.5 m, and it covers an area <strong>of</strong> about 1 km2. Estimated<br />
reserves are 300,000 t, but futher reserves in the vicinity may be up to 1 and 2 million tons.<br />
Chemical analyses <strong>of</strong> diatomite Boane deposit (Geol. Inst., Beograd -1984):<br />
Sample 2010 2021 2014<br />
SiO2 % 92.09 87.42 88.84<br />
Fe2O3 0.60 1.59 0.79<br />
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Cilek: 4.5. Diatomite<br />
Al2O3 2.49 4.86 1.01<br />
CaO tr. 0.16 0.17<br />
MgO 0.20 0.23 0.41<br />
P2O5 0.03 0.0.02 0.11<br />
TiO2 0.33 0.35 0.16<br />
Na2O 0.30 0.21 0.18<br />
K2O 0.12 0.09 0.20<br />
L.i. 3.73 5.02 8.22<br />
The investigation at Boane (1982-84) disclosed a greatly erratic incidence, diatomite had not been<br />
deposited in situ, but transported and later eroded. The area, about 280 km2, is not very promising.<br />
The best deposits <strong>of</strong> diatomite are located in the vicinity <strong>of</strong> Manhica, where in 1970 the beneficiation<br />
plant should be constructed. The probable area with ditomite layers covers about 1,100 km2 (see Fig.<br />
4.5.2). Another area known as Alvor investigated already is situated at about 15 km NW <strong>of</strong> Manhica.<br />
There 2,600 m2 were stripped <strong>of</strong> overburden and a diatomite layer <strong>of</strong> 1 m thickness was uncovered. The<br />
deposit is <strong>of</strong> elongated shape in N-S direction, 550 m long and 200 m wide. Estimated reserves on 2 km2<br />
are 960,000 t (average thickness 0.8 m).<br />
Fig. 4.5.2. Block diagramme <strong>of</strong> trench on Manica diatomite deposit (Geol.Inst., Beograd, 1984) (211<br />
kB)<br />
In the area <strong>of</strong> Manhica the deposits <strong>of</strong> Diana and Marina were investigated.<br />
The Diana deposit is located at about 20 km NW <strong>of</strong> the village <strong>of</strong> Manhica. There are both a tarmac road<br />
and a railroad between Manhica and Maputo. The deposit is roughtly oblong in shape, 3.6 km long and<br />
450 m wide, oriented in a N-S direction (Fig. 4.5.3). It consists <strong>of</strong> three layers <strong>of</strong> diatomite:<br />
* The upper section is a compact material <strong>of</strong> about 0.5 m in thickness which should be regarded as<br />
overburden.<br />
* The central part is separated from the upper section by a 1.5 m thick sand bed.<br />
* The lowest section is represented by the oldest diatomite bed, separated from the central part by a 0.5<br />
to 1.0 m thick layer, and continues to a depth <strong>of</strong> more than 9 m.<br />
The middle layer is fairly sand-contaminated. The lower layer consists <strong>of</strong> almost pure diatomite. A study<br />
<strong>of</strong> this lower layer disclosed the presence <strong>of</strong> about 27 genera and 100 different species.<br />
The diatomite is <strong>of</strong> Upper Pleistocene age and was deposited in brackish to freshwater environment (pH<br />
6).<br />
The total thickness <strong>of</strong> the deposit is not known but an assumed depth <strong>of</strong> just 3 m and a bulk density <strong>of</strong><br />
0.32 kg/cm3 estimated resources are 1,500 000 t. Taking into consideration a loss <strong>of</strong> 50% due to<br />
processing, there should still be at least some 750,000 t <strong>of</strong> saleable diatomite which gives a mine life <strong>of</strong><br />
25 years at an annual production <strong>of</strong> 30,000 t.<br />
Fig. 4.5.3. Typical section <strong>of</strong> diatomite deposit Diana (202 kB)<br />
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Cilek: 4.5. Diatomite<br />
A second area known as the Marina deposit is, in fact, an extension <strong>of</strong> the Diana deposit to the S. A<br />
concession for this deposit was requested in 1974. Total reserves for this deposit should also be in the<br />
order <strong>of</strong> 1.5 million t <strong>of</strong> dry diatomite.<br />
Three representative samples from the Diana deposit were subjected to extensive chemical and<br />
technologial testing. Sample A was taken from the middle layer, sample B from the uppermost layer <strong>of</strong><br />
the boottom bed and sample C near the water table in the middle <strong>of</strong> bottom bed.<br />
A B C<br />
Diatomite content after elutriation test (%)<br />
Sieve analysis<br />
56 48.5 77<br />
+ 30 mesh<br />
1.6<br />
2.2<br />
1.0<br />
- 30 + 100 mesh<br />
26.8<br />
51.6<br />
14.4<br />
- 100 + 200 mesh<br />
16.2<br />
5.4<br />
7.6<br />
- 200 mesh<br />
Percentage <strong>of</strong> sand in each fraction<br />
55.4<br />
40.8<br />
77.0<br />
+ 30 mesh<br />
1.6<br />
2.2<br />
1.0<br />
- 30 + 100 mesh<br />
25.6<br />
47.2<br />
14.2<br />
- 100 + 200 mesh<br />
15.4<br />
5.4<br />
7.0<br />
- 200 mesh<br />
13.2<br />
5.6<br />
8.0<br />
According to these figures most <strong>of</strong> the raw material could be used without processing in a sandseparation<br />
plant.<br />
Bulk density g/cm3 A B C<br />
- 8 mesh raw<br />
- 200 mesh raw<br />
- 200 mesh calcined<br />
Chemical composition <strong>of</strong> the Diana samples:<br />
0.72<br />
0.26<br />
-<br />
0.88<br />
0.34<br />
-<br />
0.44<br />
0.163<br />
0.160<br />
Constituent A B C<br />
SiO2 % 79.38 78.23 85.97<br />
Al2O3 7.24 8.27 3.77<br />
Fe2O3 0.88 0.92 0.43<br />
TiO2 0.38 0.32 0.18<br />
CaO 0.17 0.24 0.13<br />
MgO
Cilek: 4.5. Diatomite<br />
K2O 0.80 0.74 0.59<br />
L.i. 9.04 9.08 6.56<br />
Total 99.27 99.60 98.86<br />
In 1983, the area was resampled; a total 22 samples were taken. Arithmetic mean and standard<br />
devitations <strong>of</strong> 22 samples:<br />
Constituent Mean Standard deviation (22 samples)<br />
SiO2 86.36 3.85<br />
Al2O3 4.21 1.25<br />
Fe2O3 1.18 0.35<br />
TiO2 0.46 0.09<br />
CaO 0.5 0.47<br />
MgO 0.2 0.08<br />
Na2O 0.11 0.03<br />
K2O 0.81 0.17<br />
L.i. 6.56 1.62<br />
Total 100.39<br />
N <strong>of</strong> Macia near the main coastal road the group <strong>of</strong> Santa Fe diatomite deposits were investigated. The<br />
area is also known as Mazivila.<br />
Deposits:<br />
a) Muduaine, about 700 m N <strong>of</strong> Mazivila with diatomite layers up to 1 m thick<br />
b) Lagoa Ramo, 5 km SW <strong>of</strong> Mazivila<br />
c) The zone N <strong>of</strong> the area Mabiele<br />
d) The zone <strong>of</strong> Chicomo about 35 km E <strong>of</strong> Chicomo covering an area <strong>of</strong> 11 km2<br />
Important localities are Buana, Lagoa Mayuana, Maculuva and Lagoa Maticuana.<br />
The diatomite occurrence is known superficially only and the thickness <strong>of</strong> these Quaternary diatomite<br />
deposits ranges between 0.3 and 1 m.<br />
Several old claims were made in this area. For three <strong>of</strong> these claims, i. e. Nachene, Mazibila and<br />
Pequene, resources were evaluated. The claims are situated in an area situated basically within the<br />
coordinates 33°00'E and 33°10'E and 24°50'S and 25°00'S. Road connections are good with the main<br />
tarmac road from Maputo to the N running 5 km to the E <strong>of</strong> the area.<br />
The diatomite had probably been deposited during the Pleistocene by floodwaters from tributaries <strong>of</strong> the<br />
Nkomati river.<br />
Resource estimates for the three deposits:<br />
Deposit Length (m) Width (m) Thickness (m) Tonnage (t)<br />
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Cilek: 4.5. Diatomite<br />
Nachene 150 13,000 0.5 300,000<br />
Mazibila 2,160 360 0.5 125,000<br />
Pequene 900 720 2.0 415,000<br />
Total 840,000<br />
These results were obtained in 1965. In 1974, a concession was requested for the Pequene deposit. At<br />
that time, the applicants estimated total reserves in the order <strong>of</strong> 3.5 million t <strong>of</strong> dry diatomite.<br />
Chemical analysis <strong>of</strong> the Pequene deposit (1984):<br />
SiO2<br />
Al2O3<br />
Fe2O3<br />
CaO<br />
MgO<br />
L. i.<br />
Humidity<br />
83.84<br />
-<br />
4.72<br />
1.00<br />
0.92<br />
8.92<br />
1.08<br />
Total 100.48<br />
During the mapping, several sites <strong>of</strong> diatomite occurrence were discovered; however, samples are not<br />
available for testing and analyses.<br />
Promising is the whole coastal belt from Macia to Inharrime and from there to Inhambane up to Nova<br />
Mambone on the river Save.<br />
The depression between the river Save and Beira, which is part <strong>of</strong> the East-African rift valley, may also<br />
contain diatomite, but it does not occur on the surface.<br />
The presence <strong>of</strong> diatomite was suggested by an observation near Pemba (SiO2 - 87.28%, Fe2O3 -<br />
0.71%, CaO + MgO - 1.30%) and indicating some diatomite sites in the Rovuma basin on the Tanzanian<br />
border.<br />
Conclusions:<br />
Among the industrial minerals, diatomite represents a very valuable material <strong>of</strong> a wide range uses, the<br />
importance <strong>of</strong> which is permanently increasing. Apart from its role as a filter agent and filler, it increases<br />
in importance in the field <strong>of</strong> environmental protection.<br />
<strong>Mozambique</strong>, especially its southern low-lying coastal plain with sandy soil and little economic<br />
importance, is very rich in diatomite deposits. Although the reserves are not substantial, owing to the<br />
few localities investigated in the past, extensive areas may provide vast reserves <strong>of</strong> diatomite.<br />
The area near Manhica is, at present best prepared for exploitation and a beneficiation factory is in<br />
preparation with an annual production <strong>of</strong> 30,000 t <strong>of</strong> calcined diatomite (65-75% <strong>of</strong> the capacity) and 25-<br />
35% <strong>of</strong> flux-calcined diatomite. Minor quantities <strong>of</strong> dry product could be sold as additives. The present<br />
estimates <strong>of</strong> diatomite reserves surpass 3 million tons.<br />
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Cilek: 4.5. Diatomite<br />
© Václav Cílek 1989<br />
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Cilek: 4.6. Glass sands and foundry sands<br />
4.6. Glass sands and foundry sands<br />
Glass sand is a type <strong>of</strong> normal sand, which is either selectively mined or treated in such a way to comply<br />
with the requirements. A basic requirement for glass sand is its chemical composition-the main<br />
constituent is quartz with about 99% <strong>of</strong> SiO2 and 0.05% <strong>of</strong> Fe2O3 as the principal harmful ingredient,<br />
and the grain size <strong>of</strong> the sand required mainly within the range 0.1- 0.3 mm. The grain size affects<br />
directly the melting <strong>of</strong> the batch, the iron content is responsible for the colour <strong>of</strong> the glass.<br />
Economically acceptable are just psammitic rocks such as sandstones and sands, which can easily be<br />
washed, sorted, chemically treated and prepared in agreement with the requirements for each final<br />
product.<br />
Required chemical composition <strong>of</strong> glass sands (Polak, 1972):<br />
Quality class A B C D E<br />
SiO2 min. % 98.5 99.0 99.0 99.2 99.3<br />
Fe2O3 max. % 0.040 0.025 0.021 0.020 0.016<br />
TiO2 max. % 0.15 0.10 0.10 0.10 0.05<br />
Al2O3 max. % 0.40 0.30 0.20 0.20 0.20<br />
Requirement for grain size distribution (Polak, 1972):<br />
Quality class A B C D E<br />
< 0.100 mm max. 1.5 max. 1.5 max. 1.5<br />
max. 1.0<br />
0.100 - 0.315<br />
max. 5.0<br />
0.315 - 0.500 min. 90.0 min. 93.0 min.94.0 min. 84.0<br />
0.500 - 0.630<br />
min. 85.0<br />
0.630 - 0.800<br />
0.800 - 1.00<br />
max. 8.0 max. 5.0 max. 5.0<br />
max. 10.0<br />
max. 15.0<br />
1.00 - 1.25 max. 0.2 max. 0.2 - max. 0.2 -<br />
Class<br />
A - sheet glass, container glass and certain technical sorts<br />
B - sheet, container, technical glass<br />
C - sheet, container, household and some special technical glass<br />
D - silica opaque glass<br />
E - crystal, semioptic and special technical glass<br />
Glass-sand raw materials normally contain clay and silt which fill the grains interstices. This material<br />
can be removed by washing. The next harmfull constituents are particles <strong>of</strong> feldspar, mica, dark silicate<br />
minerals etc. which usually are present in negligible quantities and are almost absent in well-sorted sand.<br />
The problem <strong>of</strong> a purity <strong>of</strong> quartz sand for glass can be interfered with by a presence <strong>of</strong> heavy minerals<br />
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Cilek: 4.6. Glass sands and foundry sands<br />
such as ilmenite, magnetite, rutile, titano-magnetite and others. These constituents must be removed by<br />
magnetic and high-tension electro-magnetic separation, because they are not only the source <strong>of</strong> a high<br />
iron content in glass melt but responsible for the presence <strong>of</strong> the so-called "black stones" in the glass.<br />
After removing all these impurities either totally or partly, the quality <strong>of</strong> the glass sand will depend on<br />
the character <strong>of</strong> the quartz grains. Well-sorted quartz sand <strong>of</strong> the so-called polycyclic development is<br />
composed <strong>of</strong> isometric, well-worn rounded grains on which a surface layer <strong>of</strong> limonite and clay minerals<br />
is almost absent. But if present, a special treatment using abrasion or chemical removal methods must be<br />
applied. The presence <strong>of</strong> iron and titanium, besides chromium, vanadium and other elements, can be in<br />
connection with an intergrowth <strong>of</strong> these minerals with quartz (a typical example are spinelides) or in the<br />
form <strong>of</strong> a hematite - and limonite - coatings in deep minute cracks in quartz grains. These impurities<br />
cannot be removed by dressing.<br />
In the past, other glass raw materials were used - mainly vein quartz, quartzites and quartz pebbles. Pure<br />
vein quartz is still being used in the production <strong>of</strong> high-quality silica glass.<br />
Foundry sands are nowadays principally glass sands <strong>of</strong> a lower quality mixed with a binding agent such<br />
as bentonite or organic compounds to attain the required green and dry strength, permeability <strong>of</strong> the<br />
moulds and stability under certain temperature. Quartz sand must sometimes be replaced by chromium<br />
sand, when its resistance to high temperature is required. Natural foundry sands are <strong>of</strong>ten reddish, with a<br />
clay content <strong>of</strong> up to 30% for which they are called either lean or fat sands.<br />
Requirements for foundry sands (for steel castings) -an example (Polak, 1972):<br />
Sand sort Clay binding agent %<br />
Harmfull components in quartz mass diam. > 0.01 mm<br />
K2O + Na2O CaO + MgO Fe2O3<br />
quartzitic max. 1 0.5 1.0 1.0<br />
quartzitic 1-2 0.5 1.0 1.0<br />
lean 2-8 0.5 1.0 1.2<br />
semi-fattish 8-115-305 0.5 1.0 1.2<br />
fattish 0.5 1.0 1.5<br />
Very important is grain size distribution, which should be <strong>of</strong> a medium-size range and the content <strong>of</strong> fine<br />
sand (0.20-0.10 mm) should not be more than 5%, with maximally 1% <strong>of</strong> grains over 3 mm. Organic<br />
natural impurities are not acceptable. The average SiO2 content should be 90-95%, sulphur content<br />
below 0.025%.<br />
In <strong>Mozambique</strong>, glass sand deposits have been investigated in the vicinity <strong>of</strong> Maputo in order to supply<br />
a glass factory in Machava (industrial zone <strong>of</strong> Maputo).<br />
Glass sand resources are enormous in <strong>Mozambique</strong> (see Fig. 4.5.1). They include recent beach sands,<br />
dune sands <strong>of</strong> several zones from the so-called interior dunes to inland dunes, thick alluvial deposits<br />
around water courses, a filling <strong>of</strong> wide and extensive river valleys <strong>of</strong> interglacial phases development,<br />
vast proluvial sand deposits covering the whole coastal belt, cones and fans <strong>of</strong> sand around the<br />
escarpments, psammitic deposits within the grabens <strong>of</strong> rift valleys, older marine and fluviatile terraces<br />
etc. Of an older sedimentary sequence are sandstones <strong>of</strong> Karroo Formation, sands and conglomerates <strong>of</strong><br />
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Cilek: 4.6. Glass sands and foundry sands<br />
the Lupata group <strong>of</strong> Lower and Upper Cretaceous, the Sena Formation <strong>of</strong> the Upper Cretaceous and<br />
several sandy sequences <strong>of</strong> the Tertiary. Weathered pr<strong>of</strong>iles <strong>of</strong> crystalline rocks are generally too clayey,<br />
but are the parent material for the sand bodies when worked up in river streams and on the seashore.<br />
Within the coastal belt, the biggest reserves <strong>of</strong> sand are concentrated either in dunes or in thick deposits<br />
<strong>of</strong> river valleys, which were deepened during the glacial periods and filled up during interglacial periods.<br />
Some boreholes indicated a thickness <strong>of</strong> these deposits surpassing 50 m. Dune deposits are either white<br />
quartzitic sands, mainly in zone near the seashore, or older dunes <strong>of</strong> a reddish colour in inland zones.<br />
Glass-sand deposits can be found in white sands which are generally pure quartz sands with heavy<br />
minerals as the main source <strong>of</strong> impurities. Therefore, the main treatment <strong>of</strong> these sands should include<br />
washing to remove clay material and electro-magnetic separation to eliminate heavy minerals. The grain<br />
size <strong>of</strong> these sands is acceptable being mainly within the range <strong>of</strong> 0.1-0.3 mm; prevalent are fine-grained<br />
sands, medium-grained and coarse sands can be found around the mouths <strong>of</strong> rivers, derived from<br />
fluviatite sands.<br />
Natural foundry sands <strong>of</strong> an inexhaustible quantity can be found in red sands <strong>of</strong> older dunes, on which<br />
for example the City <strong>of</strong> Maputo was built. These extend from the S-African border through the<br />
provinces Maputo, Gaza and Inhambane to the provinces Zambezia, Nampula and Cabo Delgado. Red<br />
sands are naturally a semifattish or fattish variety <strong>of</strong> foundry sands.<br />
The reserves <strong>of</strong> sand are extremelly large, but mostly unfit for a direct use in the industry. However,<br />
various steps <strong>of</strong> sand treatment may provide all required sorts <strong>of</strong> sand for glass production and foundries.<br />
a) In the glass production, the sand from the deposit Marracuene is used. This deposit is situated at 5<br />
km SW <strong>of</strong> Marracuene on the main coastal road, about 25 km N <strong>of</strong> Maputo. The sands are white, fine to<br />
medium grained and more than 4 m thick. They developed as marine sands <strong>of</strong> the Pleistocene age and<br />
are covered by 1 m thick red layer <strong>of</strong> argillaceous sand. The reserves are estimated to more than 1<br />
million tons. Sands from this deposit are transported to the glass factory in Maputo.<br />
Analyses <strong>of</strong> sand (Zuberec et al., 1981):<br />
% %<br />
SiO2 97.78 97.84<br />
Al2O3 0.16 0.18<br />
Fe2O3 0.03 0.14<br />
Cao 0.08 0.34<br />
MgO 0.01 0.40<br />
Na2O 0.16 -<br />
K2O 0.20 -<br />
SO3 0.34 -<br />
TiO2 0.17 -<br />
L.i. 0.34 -<br />
Grain-size distribution (in % on sieves):<br />
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Cilek: 4.6. Glass sands and foundry sands<br />
1 mm 0.707 0.50 0.315 0.208 0.105 0.074 0.053 total<br />
0.01 0.88 10.10 28.22 36.12 20.04 0.42 0.18 95.97<br />
0.02 0.60 4.25 16.98 39.87 30.46 1.81 0.48 94.47<br />
Weight volume = 1.530 kg/m3<br />
According to the mineralogical analysis the fraction 0.028 mm - 1.0 mm contains 95% <strong>of</strong> pure quartz,<br />
3% <strong>of</strong> tourmaline and 2% <strong>of</strong> reddish-brown limonite; the fraction 0.053 - 0.208 mm has 95% <strong>of</strong> pure<br />
quartz, 3% <strong>of</strong> tourmaline, 1.5% <strong>of</strong> limonite and 0.5% <strong>of</strong> calcite.<br />
This sand used in the glass production without any treatment gives the glass a greenish tint. According<br />
to the requirements it could be used for container glass, but ought to be dressed before use in the batch in<br />
a production <strong>of</strong> household utility glass.<br />
This sand can also be used as ceramic grade in ceramic mixtures and as a foundry sand.<br />
b) Chemical composition <strong>of</strong> dune sand: %<br />
SiO2 92.28 MgO 0.16<br />
Al2O3 3.56 Na2O 0.40<br />
Fe2O3 0.75 K2O 0.54<br />
CaO 1.18<br />
The dune sands are generally not pure in that they contain remnants <strong>of</strong> shells, feldspar and heavy<br />
minerals. Without dressing they represent a source <strong>of</strong> container glass grade only.<br />
c) Near Nacala, Zuberec et al. (1981) discovered kaolinitic sand, which could serve as kaolin, and the<br />
sands, after treatment, could-probably be used as glass or ceramic sands.<br />
One sample <strong>of</strong> treated sand: %<br />
SiO2 98.18 MgO 0.01<br />
Al2O3 0.05 Na2O 0.11<br />
Fe2O3 0.78 K2O 0.10<br />
CaO 0.01 TiO2 0.01<br />
d) Mineralogical composition <strong>of</strong> samples from the town <strong>of</strong> Beira (in % weight). (Exploration <strong>of</strong> the<br />
Beira corridor for building materials), % <strong>of</strong> weight:<br />
Sample 1<br />
(from the river<br />
Pungwe-channel)<br />
Sample 2<br />
(beach)<br />
Sample 3<br />
(beach and dune)<br />
Shells 1.78 - -<br />
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Cilek: 4.6. Glass sands and foundry sands<br />
Quartz 95.86 98.51 98.02<br />
Feldspar 2.12 1.39 1.66<br />
Garnet ind. - -<br />
Mica ind. - -<br />
Limonite ind. - -<br />
Amphibole-pyroxene 0.08 - -<br />
Ilmenite ind. - 0.08<br />
Epidote ind. - -<br />
Kyanite ind. - -<br />
Silimanite 0.09 0.10 0.24<br />
Andalusite 0.08 - -<br />
Grain-size distribution <strong>of</strong> these sands is shown <strong>of</strong> Fig. 4.6.1. Also other minerals such as rutile,<br />
tourmaline, staurolite, leucoxene, magnetite, zircon and biotite are present (ind. = indicated, in grains<br />
below 10, i. e. 0.01%).<br />
Fig. 4.6.1 Example <strong>of</strong> grain-size distribution <strong>of</strong> sand from Beira (sample from channel dredging)<br />
Laboratorio de Engenharia, Maputo (223 kB)<br />
e) Highly promising in a production <strong>of</strong> glass and foundry sands is the mining <strong>of</strong> heavy minerals <strong>of</strong> beach<br />
and dune sands. Waste-washed and electromagnetically treated sand presents a high-quality quartz sand.<br />
If 100,000 tons <strong>of</strong> heavy minerals a year were to be recovered, and this is a modest enterprice, about 1<br />
million t <strong>of</strong> quartz sand should be available to cover the needs <strong>of</strong> several Mozambican provinces for<br />
building sand and sands for the glass and ceramic industry.<br />
f) The foundry sands used in the only foundry in Maputo are white glass sands and reddish dune sands<br />
which are mixed and to which bentonite is added as a bonding agent. The quantity used is very small,<br />
hundreds <strong>of</strong> tons a year. Natural foundry sands are plentiful in Maputo: red dune sands, partly cemented<br />
into sandstones from Ponta Vermelha were used when building the old Maputo fortress and many old<br />
houses at the Baixa-suburb. Their properties have not been examined as yet.<br />
Conclusions:<br />
Reserves <strong>of</strong> glass sand <strong>of</strong> the investigated locality near Marracuene amount to 1-3 million tons. The sand<br />
is suitable for the production <strong>of</strong> container glass, but should be treated for the production <strong>of</strong> higherquality<br />
glass. The foundry sand is either glass sand or clayey red sand <strong>of</strong> older reddish dunes, mixed<br />
with bentonite for use in foundry. The reserves <strong>of</strong> sand, expecially in the coastal belt, are inexhaustible,<br />
but the sand needs a particular treatment to be used in required industrial grades.<br />
© Václav Cílek 1989<br />
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Cilek: 4.7. Gypsum and anhydrite<br />
4.7. Gypsum and anhydrite<br />
Gypsum is a s<strong>of</strong>t, transparent to translucent mineral, commonly in elongated tabular crystals <strong>of</strong> the formula CaSO4 • 2<br />
H2O, hardness 2 and specific gravity 2.3. Common are "fish-tail" contact twins, the fibrous variety is known as "satin spar",<br />
the transparent variety as selenite and the massive fine-grained variety as alabaster. Theoretically, it contains 32.6% CaO,<br />
46.5% SO3 and 20.9% K2O.<br />
Anhydrite is more widespread than gypsum and is supposed to be a primary mineral. It is the anhydrous form <strong>of</strong> gypsum,<br />
formula CaSO4, hardness 3.5 and specific gravity 2.98-3.00. Usually it occurs in cleavable masses <strong>of</strong> a vitreous or pearly<br />
lusture. Theoretically, it contains 41.2% CaO and 58.8% SO3.<br />
Gypsum and anhydrite are evaporites accompanied by limestone, dolomite and shale. A mixture <strong>of</strong> gypsum, sand and soil is<br />
known as gypsite. Artificial gypsum is a byproduct <strong>of</strong> the production <strong>of</strong> phosphoric acid from phosphate rock. About 4.5 t<br />
<strong>of</strong> calcium sulfate is contained in the production <strong>of</strong> 1 t <strong>of</strong> phosphoric acid. This byproduct known as "phosphogypsum" is<br />
produced each year in a larger quantity than whole gypsum-anhydrite, but is considered as waste because <strong>of</strong> its less suitable<br />
physical properties and impurities. Some countries developed a technology for the use <strong>of</strong> phosphogypsum in cement and<br />
building industries.<br />
Anhydrite has a limited industrial use; mixed with coke, shale and siliceous rock, sulphuric acid and cement clinker are<br />
produced. Futher uses are in artificial marbles and anhydrite cement. Gypsum is more useful, when heated it loses threequarters<br />
<strong>of</strong> its water (at 107°C) and changes into the hemihydrate CaSO4 • 1/2 H2O known as plaster <strong>of</strong> paris. When mixed<br />
with water, it hardens into stucco. Plaster can be spread, cast, molded and used in the production <strong>of</strong> plasterboard - several<br />
plies <strong>of</strong> fiberboard, paper, etc. bonded to a hardened plaster core. For this purpose 40-60% <strong>of</strong> gypsum is used. Another 40%<br />
is used in the cement industry as a retarding agent (3-5% <strong>of</strong> clinker), in medicine, as a filler in paint and paper, the<br />
production <strong>of</strong> ceramic casting forms, as fertilizer in agriculture (expecially in peanut plantations), in toothpaste and drilling<br />
mud.<br />
Gypsum and anhydrite are evaporites which originate:<br />
1) in shallow basins and salt flats under arid conditions with an inflow <strong>of</strong> water which evaporates forming a sequence <strong>of</strong><br />
calcium carbonate, calcium sulfate and salts. From these shallow basins, a part or the whole gypsum/anhydrite sequence<br />
was leached, transported and deposited in deeper basin. This explains the development <strong>of</strong> several m to several 10m thick<br />
gypsum deposits.<br />
2) in lagoons and sabkhas along the periphery <strong>of</strong> deeper basins with a sequence <strong>of</strong> lagoonal limestone, gypsum and<br />
dolomitic limestone and dolomite.<br />
3) as a "caprock" <strong>of</strong> salt domes, overlying sharply the top <strong>of</strong> the dome and originating from a leaching <strong>of</strong> salt through watersaturated<br />
layers.<br />
Commercial deposits <strong>of</strong> gypsum are mainly flat-lying beds <strong>of</strong> a thickness <strong>of</strong> several m on the surface or near the surface. An<br />
alteration <strong>of</strong> anhydrite into gypsum is common, occurring from below the surface to a depth <strong>of</strong> 150 m by hydration whereby<br />
the volume increases by 30%. At a greater depth, gypsum loses water and changes into anhydrite.<br />
Most <strong>of</strong> the gypsum deposits originated just by a hydration <strong>of</strong> anhydrite, when the deposits were denuded.<br />
Gypsum is mined with conventional means using the room-and pillar method. After extraction, when still containing some<br />
impurities, it is dressed by washing or in heavy-media separation plants to obtain minimally a gypsum concentrate, <strong>of</strong> 80%,<br />
usable in a plaster production <strong>of</strong> wallboards or when <strong>of</strong> a higher grade, in medicine etc.<br />
In <strong>Mozambique</strong> literary data refer to five gypsum sites:<br />
1 Porto Henrique Maputo Province<br />
2 Divinhe S<strong>of</strong>ala Province<br />
3 Vendas Gaza Province<br />
4 Pemba Cabo Delgado Province<br />
5 Bilibiza Cabo Delgado Province<br />
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Cilek: 4.7. Gypsum and anhydrite<br />
In the area <strong>of</strong> Porto Henrique several boreholes were drilled and layers <strong>of</strong> gypsum about 0.5 m thick were discovered at a<br />
depth <strong>of</strong> 29 m. The gypsum was connected with limestone beds outcropping onto the bank <strong>of</strong> the river Tembe. The possible<br />
age <strong>of</strong> the deposit is Tertiary.<br />
In the province Gaza, several small outcrops <strong>of</strong> gypsum were found, but not evaluated. Even in the Province S<strong>of</strong>ala, a few<br />
remarks only inform on a gypsum occurrence. Lachelt (1985) described gypsum <strong>of</strong> a thickness <strong>of</strong> about 15m from<br />
evaporites <strong>of</strong> Temane called gypsum <strong>of</strong> Divinhe. He describes also sites in the province <strong>of</strong> Cabo Delgado stretching from<br />
the mouth <strong>of</strong> the river Lurio to the Tanzanian border. Particular gypsum sites were found in the vicinity <strong>of</strong> the ports Nacala<br />
and Pemba. The age <strong>of</strong> these gypsum deposits is supposed to be Tertiary to Quaternary.<br />
Many years <strong>of</strong> exploration, drilling for oil and gas in coastal <strong>Mozambique</strong>, revealed important data on the lithological<br />
development <strong>of</strong> post-Karroo formations, which were brought to light also by the discovery <strong>of</strong> extensive evaporite deposits<br />
(ENH, 1986).<br />
In <strong>Mozambique</strong>, two pericontinental sedimentary basins have developed, the S- <strong>Mozambique</strong> and the N- Rovuma basins.<br />
There are several interior rift basins, the Maniamba, Middle Zambezi and Lake Niassa.<br />
The most important are the two coastal basins. The <strong>Mozambique</strong> basin is composed <strong>of</strong> Cenozoic and Cretaceous marine,<br />
continental and deltaic sediments, with a maximum thickness <strong>of</strong> 12 km in the deepest part-the Zambezi depression. These<br />
sediments rest unconformably on Karroo sediments and volcanics. Cretaceous shales with sandstones and glauconitic sands<br />
contain commercial gas accumulations in three gas fields- Buzi, Temane and Pande.<br />
Gypsum and anhydrite were discovered by means <strong>of</strong> boreholes in the sedimentary cover <strong>of</strong> many localities. The oldest<br />
anhydrite deposit lies in the S- part <strong>of</strong> the <strong>Mozambique</strong> basin near Xai-Xai in an Upper Jurassic? (Lower Cretaceous/<br />
Cenomanian) sequence.<br />
Sedimentary layers called "Red Beds" are formation <strong>of</strong> continental origin, represented by red claystones with interbedding<br />
limestone, dolomite and red-brown anhydrite (?). These sediments extend apparently up to the outcrops <strong>of</strong> the Lebombo<br />
Mts. volcanics and fill up the S- grabens, discordantly resting on Stromberg basalts ( ENH, 1986). They are overlapped by<br />
marine sands <strong>of</strong> the Maputo Formation-Lower Cretaceous, cenomanian sediments.<br />
The extensive development <strong>of</strong> gypsum and anhydrite occurred in the Oligocene/Miocene sequence. The Oligocene marks<br />
the beginning <strong>of</strong> a general regression common to all <strong>of</strong> East-Africa with a marked unconformity between Eocene/<br />
Oligocene. The regression resulted in a local erosion or very reduced deposition mainly in the area S <strong>of</strong> Beira. A subsurface<br />
Buzi Formation consisting <strong>of</strong> marine sands and shales <strong>of</strong> Oligocene age is passing into the Lower Miocene in Buzi area.<br />
The Inharrime sandy limestone Formation is an equivalent facies and crops out in the coastal area. During the transition<br />
from Oligocene to Miocene a particular facies developed over a limited area mainly S <strong>of</strong> the river Save - the Temane<br />
Formation (Fig. 4.7.1). This formation consists <strong>of</strong> dark grey, red-brown shales, sandstones and layers <strong>of</strong> gypsum and<br />
anhydrite, stringers <strong>of</strong> gypsiferrous limestone and sand. The evaporite basin is confined to the central part <strong>of</strong> the<br />
<strong>Mozambique</strong> basin S <strong>of</strong> the river Save, to the E <strong>of</strong> the borehole Balane-1 and the S to the borehole Funhalouro 1.<br />
Southwards the evaporites are laterally displaced by red sediments <strong>of</strong> the Inharrime Formation. The thickness <strong>of</strong> the<br />
Temane Formation is 130-230 m. No detailed descriptions are available, the layers <strong>of</strong> gypsum and anhydrite are several m<br />
to 15 m thick, gypsum nodules and crystals are present in limestones and marls. Calcium sulphate may attain a total<br />
thickness over 50 m (Fig. 4.7.2).<br />
Fig. 4.7.1. The map and list <strong>of</strong> wells in which the Temane evaporates are present (ENH, 1986) (342 kB)<br />
Fig. 4.7.2. Sedimentary Column - Pande Gas Field (ENH, 1986) (363 kB)<br />
List <strong>of</strong> well pr<strong>of</strong>iles in Temane evaporites:<br />
No. <strong>of</strong><br />
ENH<br />
Name<br />
Temane Formation<br />
depth (m) thickness (m)<br />
17 Mambone 1. 267-449 181<br />
19 North Pande 1. 181-367 186<br />
20 Pande 5. 192-364 172<br />
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22 Pande 1. 183-342 159<br />
23 Lambo 1. 166-364 198<br />
26 Chicuir 1. 155-387 232<br />
27 Macovane 1. 163-392 229<br />
31 Columbila 1. 207-460 253<br />
32 Cherimira 1. 217-454 237<br />
33 Zualane 1.<br />
201-398<br />
398-523<br />
197<br />
125<br />
36 Inhassoro 1. 228-457 229<br />
37 Temane 1. 168-403 235<br />
38 Chaimel 1. 175-384 209<br />
43 Funhalouro 1. 536-679 143<br />
Of Inharrime Formation with evaporites<br />
Description <strong>of</strong> Temane evaporites as a subsurface unit (ENH, 1986, appendix):<br />
Type Locality: Temane well no. 1,640' - 1,240' (first observed) - ' denotes feet<br />
Paratype(s): Mambone well no. 1, 1,020' - 1,290' Unknown in outcrops<br />
Lithology: Gypsum, milky-white crystalline with inclusions and bands <strong>of</strong> dark green claystones. With stringers <strong>of</strong><br />
gypsiferous limestone, and medium grained, poorly sorted gypsiferous sandstones.<br />
Paleontology: The calcarenites in Temane (gypsiferous) include Rotalidae and tracks <strong>of</strong> Molluscs<br />
Age: Upper Oligocene, based on evidence <strong>of</strong> fossils in over-and-underlying formations.<br />
Environment and Equivalents: Evaporitic, closed basin, more closed in Mambone then in Temane (the latter having<br />
limestone stringers and oolites).<br />
Equivalents: A Temane evaporite Equivalent (Otve) in Balane 1,200'- 2,100' in shaley, euxinic facies with small<br />
nummulites, ostracoda and fish 201 teeth, radiolaria and echinoidea. This section is marginal with regard <strong>of</strong> the evaporitic<br />
basin <strong>of</strong> Temane-Mambone. (This unit is in part corresponding to the one previously called Dark coloured shales in Final<br />
Report Balane 1)."<br />
The area covered by the Temane evaporites is shown on the map (Fig. 4.7.1) and extends over <strong>of</strong> about 35,000 km2. Part <strong>of</strong><br />
the area is built by two elevated blocks - Pande-Temane high (No. IX <strong>of</strong> ENH) and southern high Nhachengue-Domo (No.<br />
43 <strong>of</strong> ENH), the southernmost locality <strong>of</strong> Temane evaporites, lies inside the Mazenga graben bordering the gypsum area on<br />
the W; evaporites occur at great depth (top 536 m - Fig. 4.7.3).<br />
Fig. 4.7.3 Lithological pr<strong>of</strong>ile <strong>of</strong> Temane Formation in Pande-1 borehole (Legelt, 1987) (209 kB)<br />
The most promising mining area, i.e., in shallow depth, should be in the Temane-Pande gas field or in ist close vicinity, on<br />
the top <strong>of</strong> the structural elevation (about 150 m deep - Fig. 4.7.4).<br />
Fig. 4.7.4. Geological cross section <strong>of</strong> the Pande Gas Field (version 3, ENH, 1986) (297 kB)<br />
The reserves <strong>of</strong> Temane evaporites are prognostic only; neither detailed descriptions <strong>of</strong> beds or analyses are available. The<br />
average thickness <strong>of</strong> gypsum /anhydrite is roughly 10 m only and a reduction in the extension <strong>of</strong> gypsiferrous sediments is<br />
calculated on 20% only. Estimated reserves are still huge - 140 billion t.<br />
In 1978, Masson and Ulpiu evaluated evaporite deposits <strong>of</strong> two gas-fields at Pande and Temane. Quaternary deposits are<br />
about 10m thick overlying a J<strong>of</strong>ane Formation <strong>of</strong> Miocene age. This formation rests on the escarpment <strong>of</strong> river Save at the<br />
village J<strong>of</strong>ane, where the sandy calcarenites and limestones, oolithic limestones and sandy marls crop out at a thickness <strong>of</strong><br />
115 m. In wells, this formation is composed <strong>of</strong> hard microcrystalline limestones <strong>of</strong>ten dolomitic and locally oolithic. In the<br />
well Temane I, olive-grey clay with intercalations <strong>of</strong> limestone and an occasional layer <strong>of</strong> gypsum are present in the lower<br />
part <strong>of</strong> the J<strong>of</strong>ane Formation (thickness 30 m).<br />
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Cilek: 4.7. Gypsum and anhydrite<br />
The underlying Temane Formation contains gypsum, pockets <strong>of</strong> anhydrite and gypsiferrous limestone. According to the<br />
authors, the gypsum <strong>of</strong> some wells, represents more than 50% <strong>of</strong> the Formation sediments. In most wells the thickness <strong>of</strong><br />
particular evaporite layers attains about 15 m, in boreholes Pande 1 and Temane 1 more than 20 m.<br />
Unfortunatelly, just two cores were taken in the whole area. In well Mambone-1 a 3 m long core from a depth <strong>of</strong> 363 m;<br />
"70% <strong>of</strong> rock is made up <strong>of</strong> milky white hard gypsum, crystalline, almost pure, with several layers <strong>of</strong> dark-green compact<br />
clay (30%); in the well Temane 1, 2.4 m long core from a depth <strong>of</strong> 275 m: olive-grey sandy compact marl (0.3 m) and<br />
alternation <strong>of</strong> sandy gypsum with anhydrite and organogenic limestone."<br />
The reserves were calculated for an area <strong>of</strong> 25 km2 only, with an average thickness <strong>of</strong> 10 m <strong>of</strong> the gypsum layer, which<br />
may equal 500 million t <strong>of</strong> gypsum with a 50% <strong>of</strong> ore reduction = 250 million t <strong>of</strong> gypsum.<br />
Two areas recommended for exploration are: Pande and Temane-Columbila, in the stretch <strong>of</strong> 25 km only.<br />
The N- Rovuma basin, <strong>of</strong> a maximum width <strong>of</strong> 120 km, contains sediments, probably from Jurrasic? to the Recent age. The<br />
Lower Cretaceous consists <strong>of</strong> continental sandstones <strong>of</strong> Makonde beds <strong>of</strong> a thickness <strong>of</strong> about 450 m (probably Aptian).<br />
Overlying strata <strong>of</strong> marine origin <strong>of</strong> the Lower Cretaceous developed in a belt E <strong>of</strong> Makonde beds. They crop out, for<br />
example, at Pemba Bay, where they consist <strong>of</strong> different sandstones with Megatrigonia schwarzi indicating the Neocomian<br />
age. The thickness is about 100-150 m.<br />
In 1986, an exploratory well was drilled by the Exon Comp., International at Mocimboa 1, situated 14 km SW <strong>of</strong><br />
Mocimboa; its depth was 3,522 m, penetrating the Tertiary to a depth <strong>of</strong> 2,303 m (Burdigalian, Oligocene, Paleocene), and<br />
the Lower Senonian, Turonian and Cenomanian up to the Albo-Aptian. No evaporite formation was intersected. However<br />
gypsum and anhydrite may still be found either near the basins margin, in a Tertiary-Quaternary formation, or as a caprock<br />
on a possible salt dome. This idea is supported by the presence <strong>of</strong> salt domes (Mandawa) in the N part <strong>of</strong> the Rovuma basin<br />
in S- Tanzania.<br />
The Upper Cretaceous is particularly well developed in a narrow belt running almost parallel to the coast at distances<br />
ranging from several km at Pemba to tens <strong>of</strong> km at Mocimboa da Praia in the N. Globotruncana marls are present at Pemba,<br />
at the base <strong>of</strong> the cliff and on the S- side <strong>of</strong> the bay. The marls are gypsiferrous, greyish-brown to brownish yellow, in<br />
places silty with typical limey concretions and gypsum flakes. They are <strong>of</strong> Maestrichtian age and 230 m thick. The same<br />
marls crop out at the N <strong>of</strong> the bay. Of great interest is a suggestion by Flores (in ENH report, 1986) that the physiography <strong>of</strong><br />
the bay and the attitude <strong>of</strong> surrounding rocks indicate the presence <strong>of</strong> a salt diapir in the subsurface, originating probably in<br />
the bay and later influenced by a solution <strong>of</strong> salt and subsequent collapse. Mio-Pliocene beds (e. g. Mikindani beds) are <strong>of</strong><br />
little thickness.<br />
Conclusions:<br />
The rich gypsum deposits are still wholy untouched. They are <strong>of</strong> substantial importance in the building industry - cement<br />
production and plaster, and in other industrial branches. The deposits S <strong>of</strong> the river Save are traceable over an area <strong>of</strong> about<br />
35,000 km2 in the Temane Formation with a gypsum (anhydrite) layer, 10-15 m thick. They originated from a chemical<br />
precipitation in lagoons during the regression stage <strong>of</strong> the Oligocene-Lower Miocene. The gypsum /anhydrite resources<br />
may be estimated to 140 billion tons, prognostic reserves in the area <strong>of</strong> the Pande-Temane gas fields to 250 million tons.<br />
The deposits are at a depth <strong>of</strong> 150-200 m, but may be nearer to the surface in some places. Underground mining using room<br />
and pilar method is envisaged. Other sites <strong>of</strong> gypsum occurence are known from wells in "red beds", Xai-Xai area, in Upper<br />
Jurassic-Lower Cretaceous (anhydrite), in the Upper Cretaceous <strong>of</strong> the Rovuma basin near Pemba and probably in younger<br />
Tertiary - Quaternary sediments in S- <strong>Mozambique</strong>.<br />
© Václav Cílek 1989<br />
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Cilek: 4.8. Kaolin<br />
4.8. Kaolin<br />
Kaolin is a clayey material, white or light in colour, plastic, composed mainly <strong>of</strong> clay-mineral kaolinite,<br />
formula Al2 (Si2O5)(OH)4 and a theoretical composition <strong>of</strong> 46.54% SiO2, 39.5% Al2O3 and 13.96%<br />
H2O. The structure <strong>of</strong> kaolinite is an indefinitely repeated silica tetrahedral sheet and a gibbsite sheet.<br />
The mineral does not expand, has a low cation-exchange capacity, forms flaky pseudohexagonal crystals,<br />
which may occur either in piles or be disordered. The crystal structure with flat platelets gives it an<br />
excellent covering power and together with whiteness, chemical inertness, nonabrasiveness, makes kaolin<br />
a very good filler and coating agent.<br />
Apart from kaolinite, kaolin contains other clay-minerals such as illite, montmorillonite, haloysite and<br />
others, futher quartz, feldspars, micas, heavy minerals, organic matter etc.<br />
Therefore raw kaolin is treated and beneficiated to remove all harmfull particles and to increase its clay<br />
content. Generally, kaolin after extraction is washed in troughs, in hydrocyclons and centrifuges, then<br />
treated with various chemical and physical methods such as flotation, flocculation, bleaching to remove<br />
coloured oxides, high-intensity magnetic separation and finally delamination to break down larger crystal<br />
units into individual flakes.<br />
Originally, kaolin was used in ceramics for the production <strong>of</strong> porcelain in China in the third century B.<br />
C., later, also in China, in the manufacture <strong>of</strong> paper. Its use in these fields <strong>of</strong> production continued up to<br />
the present.<br />
Other uses <strong>of</strong> kaolin are as filler in rubber, plastics, paints, cosmetics, catalysts, food additives and filter<br />
aids.<br />
In the ceramic industry, requirements for kaolin quality depend on its use for example, in fine ceramics,<br />
the content <strong>of</strong> Al2O3 should be a minimum <strong>of</strong> 34%, Fe2O3 + TiO2 maximum 1.6%, with good<br />
rheological properties, tension strength in bending minimum 6 kp/cm2, refractoriness minimum 32 SC. In<br />
the production <strong>of</strong> sanitary ware, white wall tiles and acid chamottes, kaolin <strong>of</strong> lower quality may be used:<br />
Al2O3 + TiO2 maximum 34%, Fe2O3 maximum 2.0%, fluxing agents (K, Na, Ca, Mg) maximum 3.0%,<br />
minimum refractoriness 33 SC and humidity maximum 13%.<br />
The paper industry requires the highest-quality coating kaolin <strong>of</strong> specific properties. The whiteness must<br />
be higher than 70%, usually over 80%, its viscosity very high and size particles very low (about 80% <strong>of</strong><br />
particles < 1 micron). With regard to the type <strong>of</strong> paper produced, a different amount <strong>of</strong> kaolin is<br />
consumed, for example, in writing paper about 30% <strong>of</strong> the material.<br />
Kaolin used as a filler in the rubber industry should correspond to the grade <strong>of</strong> ceramic or paper kaolin,<br />
but the so-called "rubber poisons" should be:0.002% Mn at a maximum, 0.001% Cu and 0.05-0.15% Fe,<br />
SO3 < 0.20%.<br />
Kaolin for cosmetics can contain up to 1.5% FeO, it must be very fine and <strong>of</strong> a whiteness <strong>of</strong> more than<br />
80%.<br />
With regard to the limited reserves <strong>of</strong> bauxite for alumina production, the use <strong>of</strong> kaolin or kaolinitic clays<br />
was tested. It was discovered that kaolin for alumina production should contain a minimum <strong>of</strong> 32%<br />
Al2O3 a maximum <strong>of</strong> 3% Fe2O3 maximum 47% SiO2, 0.6% CaO + MgO and 0.5% K2O + Na2O.<br />
The deposits <strong>of</strong> kaolin may contain 10 to 90% <strong>of</strong> kaolinite depending on the type <strong>of</strong> the deposit and the<br />
composition <strong>of</strong> the parent rock. Economic deposits <strong>of</strong> kaolin should have a minimum (10-15%) content <strong>of</strong><br />
the useable fraction provided that, for example, kaolin sands can also be utilized. Normally, commercial<br />
kaolin deposits contain over 15% <strong>of</strong> clay. Raw kaolin has a limited use, in a production <strong>of</strong> building<br />
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Cilek: 4.8. Kaolin<br />
ceramics, acid chamotte, stoneware etc. Waste removed by washing is mainly silt, sand and mica. All<br />
these materials can be used: sand in ceramic mixtures, silt, for example, in wall tiles mixtures and fine<br />
mica in the building industry in ornamental mortars.<br />
Washed kaolin cleared <strong>of</strong> sand and impure clay, is used in different industries. In ceramics, the ceramic<br />
mass requires about 50% <strong>of</strong> kaolin, 25% <strong>of</strong> quartz and 25% <strong>of</strong> feldspar. In cement production, about 20%<br />
is used in a mixture for the production <strong>of</strong> white cement, a large amount <strong>of</strong> kaolin is used in the production<br />
<strong>of</strong> refractory ware as chamotte or synthetic mullite (withstanding 1,550°C).<br />
Synthetic mullite replaces high alumina refractory minerals such as kyanite, andalusite and sillimanite.<br />
The mixture has to contain up to 73% Al2O3, which is accomplished by mixing kaolin with pure Al2O3<br />
and using catalysts to help the crystallization <strong>of</strong> mullite.<br />
Kaolin deposits can be divided into three types:<br />
1 weathering<br />
2 hydrothermal<br />
3 secondary<br />
The weathering type kaolin deposits are most common and originate by weathering-kaolinization <strong>of</strong><br />
feldspar-rich rocks such as granites, gneisses, arkosic sandstones etc. The process <strong>of</strong> kaolinization does<br />
not depend on climatic zones, but on the environment: kaolinite originates mainly at the ratio Al2O3 :<br />
SiO2 = 1 : 2 and pH 4-5 (i. e. acid conditions). Kaolinization is supported also by the presence <strong>of</strong> humic<br />
acids, thermal waters containing CO2 and other agents. During the kaolinization process orthoclase (K Al<br />
Si4O8), which contains 64.63% SiO2, 18.49% Al2O3 and 16.88% K2O, loses all K2O and part <strong>of</strong> silica.<br />
In this case kaolinite contains more Al2O3 - 39.56%, less silica 46.50% and more water -13.94%.<br />
Weathered kaolinic pr<strong>of</strong>iles can attain the thickness <strong>of</strong> several tens <strong>of</strong> meters, exceptionally over 100 m.<br />
The white kaoline zone is usually underlain by a brown - red zone <strong>of</strong> partially altered parent rock, from<br />
which iron and alkalies had not been removed completely. Kaolin horizons also underlay the lateritic<br />
horizons crusts.<br />
The hydrothermal type <strong>of</strong> a kaolin deposit is common to hydrothermal vein deposits and occurs<br />
expecially in Cornwall, England and in solfatara areas <strong>of</strong> Mexico. Secondary kaolin deposits are<br />
widespread and, in fact, the largest world deposits are <strong>of</strong> this type. An example is the Pugu Hills deposit<br />
in Tanzania, where several hundred m thick sandstones with kaolin were deposited as Tertiary deltaic<br />
sediments on the Indian ocean seashore. The origin <strong>of</strong> kaolin can be explained in two ways:<br />
as a transport <strong>of</strong> kaolin and sand into the delta from primary kaolin pr<strong>of</strong>iles<br />
or by a weathering <strong>of</strong> feldspar containing sands within the delta and above the water table.<br />
In <strong>Mozambique</strong>, all three genetical types <strong>of</strong> kaolin deposits are present (see Fig. 4. 3. 2). The most<br />
important is the first type - weathering, known from several pegmatite deposits <strong>of</strong> the Alto Ligonha<br />
district; the second type - hydrothermal - has just a theoretical value and is known to occur in goldbearing<br />
veins; the third type - secondary kaolin <strong>of</strong> sedimentary origin was discovered recently at Nacala<br />
and similar deposits may exist within the paleodeltas in <strong>Mozambique</strong> and the Rovuma basins.<br />
The only deposit in production is the Ribaue pegmatite mine. This mine known as Boa Esperanca<br />
produces also feldspar, besides a small amount <strong>of</strong> other economic minerals (see Chap.-feldspar). In the<br />
past, part <strong>of</strong> the kaolinized pegmatite was mined opencast, part underground by driving galleries. The<br />
greatest part <strong>of</strong> pegmatite is altered into kaolin, either white, which is utilized; or coloured, which is<br />
waste. The main pegmatite body around the quartz core is about 130 m long and 60 to 70 m wide. Altered<br />
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Cilek: 4.8. Kaolin<br />
pegmatite is treated at a small plant directly at the mine, sieving (3 mm sieve) and about 20 - 40% <strong>of</strong><br />
material is rejected. The rest is used as untreated raw kaolin and sold as such, 10 - 15% is sold after<br />
washing. The Geol. Institute, Beograd (1984) evaluated the whole deposit; a major part <strong>of</strong> it is mined out<br />
and the reserves <strong>of</strong> raw kaolin in category C 1 are 23,400 t only, <strong>of</strong> which the washed kaolin (15%)<br />
represents 3,500 t, i. e. a 7 year-life for the mine with 500 t/annual production. The main reserves <strong>of</strong><br />
kaolinized pegmatite <strong>of</strong> 390,000 t were not tested, but could certainly be used in ceramics.<br />
The Yugoslav team tested in detail three samples <strong>of</strong> raw kaolin (Results in %):<br />
SiO2 49.69 48.92 49.73<br />
Al2O3 35.27 33.26 32.81<br />
Fe2O3 0.28 2.38 1.09<br />
FeO 0.03 0.22 0.19<br />
MgO 0.09 - -<br />
CaO 0.69 0.72 0.28<br />
Na2O 1.44 1.58 0.19<br />
K2O 0.65 0.58 3.67<br />
L.i. 12.32 12.22 12.32<br />
X-ray analyses have shown mineral composition <strong>of</strong> kaolinite (at a medium degree <strong>of</strong> crystallization), Kfeldspar,<br />
Na-feldspar, quartz and mica. A differential - thermic and thermogravimetric - analysis is<br />
presented in Fig. 4.8.1. The DTA curve illustrates a distinct smaller endothermal effect at about 100 °C,<br />
which can be contributed to the presence <strong>of</strong> a clay-mineral <strong>of</strong> the illitic type. At 530°C, a large<br />
endothermal peak becames apparent and this is typical <strong>of</strong> kaolinite, similar to the very distinctive peak at<br />
970°C. The TG curve illustrates clearly an original loss <strong>of</strong> water and a further loss at 470-550°C, <strong>of</strong><br />
which the first can be attributed to the presence <strong>of</strong> illite; the latter to the presence <strong>of</strong> kaolinite. Total mass<br />
loss amounts to 9.5%. According to the Yugoslav evaluation, Ribaue kaolin can be used in ceramics, as<br />
filler and in the paper industry.<br />
Fig. 4.8.1. DTA and TG curves <strong>of</strong> sample No. 110058 - kaolin from Ribaue (113 kB)<br />
In 1977, the Institute <strong>of</strong> economy for raw materials in Dresden - GDR tested two samples from Ribaue -<br />
raw and washed kaolin.<br />
Composition <strong>of</strong> raw kaolin: 90% kaolinite 1% feldspar<br />
5% muscovite 1% anatase<br />
3% quartz<br />
The chemical analysis corresponds to this mineralogical composition and shows 43% Al2O3 and 1.3%<br />
K20 + Na2O. It is remarkable that raw kaolin does not contain Fe2O3. The volume <strong>of</strong> fraction > 63<br />
micron is 10.1% and consists <strong>of</strong> 20% <strong>of</strong> kaolinite, 22% <strong>of</strong> feldspar and about 30% <strong>of</strong> quartz. The fraction<br />
< 2 micron is small in volume -15%.<br />
The quality <strong>of</strong> kaolin in ceramic mass is characterized by a high amount <strong>of</strong> water to cause fluidity <strong>of</strong><br />
33%, a 3% shrinkage after drying and a small degree <strong>of</strong> sintering at 1,300°C. The water absorption is<br />
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Cilek: 4.8. Kaolin<br />
26% and the colour after firing is white. Washed kaolin displays almost the same properties as unwashed<br />
one, but the content <strong>of</strong> Fe2O3 is 0.8%.<br />
Rational analyses recalculated on the basis <strong>of</strong> chemical composition:<br />
Raw kaolin washed kaolin Raw kaolin washed kaolin<br />
clay% 91.3 91.5 feldspar % 7.7 4.9<br />
quartz % 1.3 2.3 oxides % 0.5 1.1<br />
The large quantity <strong>of</strong> kaolinite is causing a high uptake <strong>of</strong> water for fluidity and poor sintering is due to a<br />
small amount <strong>of</strong> alkalies, but otherwise kaolin can be used in the ceramic industry - fine - and coarseware<br />
production.<br />
Analytical results (Dresden, 1977):<br />
Type <strong>of</strong> testing<br />
Sample No2902 kaolin raw<br />
(unwashed)<br />
Sample No2904<br />
kaolin washed<br />
1 2 3<br />
1. weight volume (g/l) 1100 200<br />
2. granulometry (%) fraction rest on sieve fraction rest on sieve<br />
>63 micron 10.1 100 0.6 100<br />
31.5-63 micron 1.3 89.9 1.9 99.4<br />
20.0-31.5 micron 10.3 88.6 2.2 97.5<br />
12.5-20.0 micron 11.1 73.3 8.7 95.3<br />
6.3-12.5 micron 20.1 67.2 17.2 86.6<br />
3.15-6.3 micron 21.1 47.1 23.6 89.4<br />
2.0-3.15 micron 11.2 26.0 15.8 45.8<br />
1.5-2.0 micron 2.9 14.8 5.6 30.0<br />
>1,5 micron 11.9 11.9 24.4 24.4<br />
3. mineralogical<br />
composition<br />
X-ray analysis<br />
microscopy <strong>of</strong><br />
>0.063 mm<br />
fraction<br />
kaolinite (%) 90 20<br />
muscovite (%) 5 5<br />
quartz (%) 3 52<br />
feldspar (%) 1 22<br />
others (%) 1 1<br />
4. chemical composition before firing after firing before firing after firing<br />
L.i. (%) 12.0 - 13.0 -<br />
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Cilek: 4.8. Kaolin<br />
SiO2 (%) 48.9 55.5 48.1 55.4<br />
Al2O3 (%) 37.5 42.1 37.1 42.6<br />
Fe2O3 (%) 0 0 0.7 0.8<br />
TiO2 (%) 0 0.1 0.1 0.1<br />
CaO (%) 0.4 0.5 0.4 0.5<br />
MgO (%) 0.1 0.1 0.1 0.1<br />
K2O (%) 0.7 0.8 0.5 0.6<br />
Na2O (%) 0.4 0.5 0.2 0.2<br />
5. ceramic properties<br />
moisture plasticity (%) 33.4 33.1<br />
shrinkage after drying<br />
(%)<br />
3.0 5.2<br />
firing temperature (°C) 1300 1300<br />
shrinkage after firing (%) 8.7 11.6<br />
shrinkage total (%) 11.4 16.2<br />
water absorption (%) 25.8 18.0<br />
colour after firing white whitish<br />
The largest kaolin "producer" in the country is the Nb-Ta pegmatite deposit and the mine Muiane<br />
situated in the Alto Ligonha pegmatite district S <strong>of</strong> Alto Ligonha and 115 km from Nampula. The<br />
pegmatite body builds a distinctive hill above the surrounding plateau due to the resistance <strong>of</strong> the hard<br />
quartzitic core. The morphological position enabled kaolinization and at present the weathered zone is<br />
about 30 m thick. Pegmatite is <strong>of</strong> an oval shape with longer axis <strong>of</strong> 350 m in NNE-SSW direction and a<br />
shorter axis measuring 250 m. Pegmatite intruded Precambrian gneisses, schists and amphibolites and<br />
several zones developed around the quartz zone. Towards the centre, kaolinization diminishes. Kaolinized<br />
pegmatite is mined from around the quartz core and the material is slipped down to the dressing station,<br />
where quartz, kaolin and unaltered milled pegmatite, representing the waste, are pumped into a pond and<br />
deposited there. Mica, several precious stones, Nb-Ta minerals and beryl are the main products <strong>of</strong> mining.<br />
In my opinion, annual production <strong>of</strong> kaolin may reach about 10,000 t apart from a certain amount <strong>of</strong><br />
feldspar and silty kaolin, which could be used also in the ceramic industry.<br />
In 1980, Thieke evaluated kaolin reserves in three zones - lithium zone, inner and outer zones in category<br />
C1 to 2,687 060 t and C2 628 282 t which makes a total <strong>of</strong> 3,315 342 t kaolin (50% kaolin content in<br />
kaolinized pegmatite). The content <strong>of</strong> mica is 1.1% <strong>of</strong> pegmatite. In the German Democratic Republic<br />
(1978) at the Institute <strong>of</strong> economy for raw materials in Dresden, three samples from Muiane were tested,<br />
one <strong>of</strong> raw kaolinized pegmatite from feldspathic zone (channel sample) and two samples <strong>of</strong> waste<br />
material - kaolin from the waste pond (0.0-0.4 m and 0.4-2.0 m), in which about 100,000 t <strong>of</strong> material are<br />
deposited. It may be possible to extract from it kaolin <strong>of</strong> commercial value.<br />
Mineralogical composition <strong>of</strong> kaolinized pegmatite:<br />
60 % K-feldspar, 35% kaolinite, 5% quartz and mica<br />
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Cilek: 4.8. Kaolin<br />
Chemical composition (%):<br />
SiO2 58.5 TiO2 0.1 Na2O 0.5<br />
Al2O3 24.1 CaO 0.6 K2O 10.4<br />
Fe2O3 0.3 MgO 0.1 L. i. 4.7<br />
The clay content < 0.063 mm is about 20%. It follows from these data that kaolinized pegmatite is poor<br />
on coloured oxides, it is coarse-grained and, in fact, has a high content <strong>of</strong> unaltered feldspar grains<br />
(microcline) and represents a mixture <strong>of</strong> kaolinite and feldspar <strong>of</strong> a very fine grain. The content <strong>of</strong><br />
washed kaolin processed in two-phase hydrocyclones is 19-20% and in three-phase hydrocyclones 15%.<br />
The latter product has these properties (results from Amberger Kaolinwerke GmbH Hirshau, FRG):<br />
fraction < 0.002 mm 68% kaolinite 46.5 %<br />
K-feldspar (microcline) 52% Fe2O3 0.37%<br />
Na-feldspar 1.5% whiteness (Eirepho) 87.3 %<br />
These results show, that washed kaolin suitable for both the ceramic (fine ceramics) and the paper<br />
industry, can be produced from kaolinized pegmatite from Muiane. The content <strong>of</strong> kaolin-clay is<br />
somewhat low (15-20%), but the economy <strong>of</strong> kaolin recovery could be improved by utilizing the<br />
hydrocyclone product <strong>of</strong> fine feldspar.<br />
In 1981, several pegmatite and kaolin samples were tested in Czechoslovakia. The analyses showed a<br />
composition <strong>of</strong> kaolinized pegmatite which indicated a possibility <strong>of</strong> recovering kaolin-clay <strong>of</strong> high<br />
purity, whiteness and content.<br />
Sample <strong>of</strong> altered pegmatite - Muiane<br />
Original sample (%)<br />
fraction below<br />
0.053 mm<br />
above 0.053 mm 0.020-0.053 mm 0.0-0.20 mm<br />
SiO2 45.09 43.93 46.90 43.85 42.88<br />
Fe2O3 1.12 0.55 1.80 1.86 0.28<br />
Al2O3 33.64 35.96 28.95 35.67 36.35<br />
CaO 0.46 0.50 0.40 0.54 0.42<br />
MgO 0.043 0.05 0.09 0.04 0.10<br />
TiO2 0.09 0.09 0.09 0.05 0.18<br />
P2O5 0.01 0.01 0.017 0.045 0.019<br />
MnO 0.046 - - - -<br />
Na2O 0.42 0.13 0.07 0.35 0.94<br />
K2O 1.23 1.29 1.14 1.22 1.45<br />
H2O 1.76 0.18 2.21 0.32 0.12<br />
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Cilek: 4.8. Kaolin<br />
L. i. 16.22 17.05 16.86 16.48 16.72<br />
Further tests showed clearly that a major portion <strong>of</strong> the sample consisted <strong>of</strong> kaolinized feldspar and<br />
quartz, in addition to muscovite and lepidolite, about 10% each. Granulometry above 0.053 mm was<br />
50.09%, below 0.053 mm 27.72% , kaolin content 22.19%.<br />
The perfectly altered pegmatite <strong>of</strong> Muiane has contained less <strong>of</strong> particles above 0.053 mm - 43.96%,<br />
more particles below 0.053 mm - 39.47% and a kaolin content 16.57%.<br />
Chemical composition (in %):<br />
Original sample (%)<br />
fraction below<br />
0.053 mm<br />
above 0.053<br />
mm<br />
0.020-0.053 mm 0.0-0.20 mm<br />
SiO2 46.66 44.58 47.66 45.18 42.70<br />
Fe2O3 0.39 0.09 0.80 0.10 0.08<br />
Al2O3 33.97 36.96 31.40 36.29 37.74<br />
CaO 0.14 0.07 0.60 0.06 0.08<br />
MgO 0.20 0.16 0.30 0.40 0.16<br />
TiO2 0.19 0.22 0.16 0.27 0.10<br />
P2O5 0.027 0.030 0.021 0.095 0.018<br />
MnO 0.01 0.001 - - -<br />
Na2O 0.16 0.16 0.21 0.20 0.11<br />
K2O 0.38 0.14 0.43 0.06 0.24<br />
H2O 0.62 0.24 2.33 0.98 0.79<br />
L. i. 17.34 17.26 15.32 16.05 17.80<br />
Interest in an investigation <strong>of</strong> Muiane kaolin was focused also on a utilization <strong>of</strong> waste in the waste pond<br />
composed <strong>of</strong> a mixture <strong>of</strong> kaolin clay and sandy material.<br />
The two samples collected from the upper layer (0.0-0.4 m) and the lower layer (0.4-2.0 m) were both <strong>of</strong><br />
a similar composition (Dresden, GDR, 1978): 80% kaolinite, 10% muscovite and 5% quartz. The amount<br />
<strong>of</strong> quartz and feldspar was very low. This is understandable, because the "sandy" fraction had been<br />
removed together with heavy minerals for the treatment <strong>of</strong> Nb-Ta and precious stones, while the clay<br />
fraction, without grains <strong>of</strong> economic minerals, had been separated as waste.<br />
Rational analysis based on a chemical analysis showing composition <strong>of</strong> samples:<br />
substance % sample 0.0-0.4 m sample 0.4-2.0 m<br />
clay 87.5 85.2<br />
quartz 1.3 2.1<br />
feldspar 8.0 9.1<br />
oxides 2.4 2.6<br />
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Cilek: 4.8. Kaolin<br />
The average chemical composition was about 54% SiO2, 41% Al2O3, 1.8% Fe2O3 and 1.4% K2O. The<br />
high kaolinite content corresponded to the high loss <strong>of</strong> ignition -13%.<br />
The grain size was also typical: just 1-2% > 63 micron and 63-72% < 2 micron, and the fraction above 63<br />
micron, consisted mainly <strong>of</strong> muscovite flakes, besides a very small amount <strong>of</strong> biotite, anatase, magnetite,<br />
quartz and rock remnants.<br />
Ceramic properties <strong>of</strong> this waste kaolin were characterized by a high volume <strong>of</strong> water needed for<br />
plasticity - 25% and a shrinkage <strong>of</strong> 5% after drying. These high values are typical <strong>of</strong> pure kaolinite and,<br />
together with K2O, Fe2O3 and CaO in minerals <strong>of</strong> biotite, feldspar and muscovite, cause a strong<br />
sintering just at 1,100°C, shrinkage 11-12% and water absorption 2-6%; the colour after firing is rose to<br />
grey. Very fine cracks in fired material are typical <strong>of</strong> plastic materials, can be corrected by adding 10-<br />
20% <strong>of</strong> quartz sand grain size 0.06-2.0 mm. Hence, it may be conduced that waste kaolin from Muiane,<br />
although hardly treatable for a removal <strong>of</strong> coloured oxides and alkalies to improve its quality, could be<br />
used directly, after adding corrective sand, in the production <strong>of</strong> special hard and light colour bricks fired<br />
at a maximum temperature <strong>of</strong> 1,300°C which could, in fact, serve as low-quality refractory material.<br />
Another important pegmatite mine - Marropino produces Nb-Ta minerals, whereby kaolin is again a<br />
waste. The ore-bearing pegmatite is deeply kaolinized, similar to other pegmatites <strong>of</strong> the Alto Ligonha<br />
district which crop out to the surface. In 1978, geologists <strong>of</strong> BRGM made technological tests <strong>of</strong> the<br />
kaolin. The investigation was intended both to determine the quality <strong>of</strong> kaolin and to check a possible<br />
content <strong>of</strong> Nb-Ta in the clayey fraction for recovery, which normally is lost in kaolin waste.<br />
Separation in hydrocyclone has shown a - 40 micron kaolin fraction in the order <strong>of</strong> 18.30% <strong>of</strong> which the<br />
part below 10 micron is 9.59% and above 10 micron 8.71%.<br />
X-ray and diffractometry analyses <strong>of</strong> Marropino pegmatite:<br />
35% quartz<br />
31 % feldspar (albite)<br />
19% micas<br />
12% kaolinite<br />
According to the results, the content <strong>of</strong> kaolin is fairly low; other economic minerals the main product <strong>of</strong><br />
the mine - are these:<br />
SnO2 21 g/t<br />
Nb2O5 < 715 g/t = < 0.05 % Nb<br />
Ta2O5 < 610 g/t =< 0.05 % Ta<br />
BeO 505 g/t = 0.36 % beryl<br />
Gibbsite was not detected in the kaolin fraction. Very interesting is the presence <strong>of</strong> 0.13% Li2O, in the<br />
fraction - 40 micron, which improves the vitrification. This property may be common to all kaolins <strong>of</strong><br />
albite type pegmatites with rare metals and lithium minerals in the Alto Ligonha district.<br />
Mineralogical composition <strong>of</strong> pegmatite and kaolin fractions (in %):<br />
Pegmatite Fraction < 40 micron Fraction 10 micron<br />
kaolinite 12 65 ~80<br />
micas 19 4 -<br />
albite 31 29 ~20<br />
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Cilek: 4.8. Kaolin<br />
quartz 35 0 -<br />
organic matter n.d. ~0.45 -<br />
water hydroscopic 1.6 0.9 -<br />
The chemical analyses include also Nb and Ta contents: the content <strong>of</strong> iron and titanium is low.<br />
Pegmatite<br />
%<br />
Fraction < 40<br />
micron<br />
%<br />
Pegmatite<br />
%<br />
Fraction < 40<br />
micron<br />
%<br />
SiO2 69.90 51.90 K2O 1.05 0.47<br />
Al2O3 18.30 32.25 Li2O 0.22 0.13<br />
Fe2O3 0.26 0.12 P2O5 0.03 0.21<br />
FeO 0.45 0.26 H2O- 0.30 0.25<br />
MnO 0.20 0.15 H2O+ 3.85 10.55<br />
TiO2 0.06 0.04 C organic n.d. 0.27<br />
CaO 0.25 0.20 SO3 0.02 0.05<br />
MgO 0.35 0.10 Nb
Cilek: 4.8. Kaolin<br />
Technologial tests on - 40 micron kaolin indicated very good properties for a utilization in ceramics - fine<br />
ceramics, in the production <strong>of</strong> faiance and procelain: humidity pasticity after drying - 36.1%, shrinkage<br />
after drying 3.1%, shrinkage after firing 3.14% (1,100°C), 11.50% (1,300°C), 12.55% (1,400°C), and<br />
water absorption 37.04% (1,100°C), 7.49% (1,300°C) and 3.25% (1,400°C). The colour after firing at<br />
1,100 - 1,400°C is white, the mass is homogeneous - porous - and has a porcelain-like aspect. Tests made<br />
for a utilization in the paper industry disclosed its low suitability - an increased content <strong>of</strong> abrasive<br />
minerals mainly feldspars, low rheological properties and an insufficient whiteness in the green stage,<br />
82.5% (required are 87%).<br />
The example <strong>of</strong> Marropino pegmatite provides clear evidence for an inadequate treatment <strong>of</strong> the ore; the<br />
extraction <strong>of</strong> Nb-Ta minerals is a half-way process, part <strong>of</strong> these minerals get lost together with a number<br />
<strong>of</strong> trace elements, a big amount <strong>of</strong> high-quality kaolin, feldspar, quartz, mica, minerals <strong>of</strong> lithium and<br />
berylium. Undoubtedly, a better recovery <strong>of</strong> Nb-Ta minerals must go hand in hand with a utilization <strong>of</strong><br />
the kaolin component <strong>of</strong> the pegmatite to improve the economy <strong>of</strong> mining.<br />
The only investigated deposit <strong>of</strong> sedimentary kaolin is situated near Nacala about 15 km to the S. The<br />
deposit consists <strong>of</strong> beds <strong>of</strong> kaolin sand with this pr<strong>of</strong>ile: 1.4 - 1.6 m top soil with dark grey sand and<br />
little or no kaolin<br />
1.6 - 12.0 m fine grey sand, with little or no kaolin; white kaolin sand and grey with a high content <strong>of</strong><br />
kaolin; fine - to medium - grained sand with little kaolin; fine grey sand and yellow kaolin sand with a<br />
high content <strong>of</strong> kaolin.<br />
On an average, kaolin-bearing sands have a thickness <strong>of</strong> 12.5 m at a maximum overburden thickness <strong>of</strong><br />
2.2 m. The origin <strong>of</strong> these sands can be attributed to the transport <strong>of</strong> fluvio-alluvial sediments over a short<br />
distance. The kaolin comes from weathered crystalline rocks which are about 5 km W. In 1981, Zuberec<br />
et al. discovered the deposit and collected several samples, some <strong>of</strong> which were tested in Czechoslovakia.<br />
Results <strong>of</strong> chemical analyses showing this composition:<br />
% Kaolin sand<br />
Fraction below<br />
0.053 mm<br />
Above 0.053<br />
mm<br />
0.020-0.052 mm 0.00-0.02 mm<br />
SiO2 76.17 49.75 92.20 58.20 48.57<br />
Fe2O3 1.22 1.29 1.20 0.20 1.20<br />
Al2O3 12.93 30.79 1.76 27.88 33.67<br />
CaO 0.61 0.10 0.98 0.18 0.06<br />
MgO 0.66 0.23 0.90 0.30 0.20<br />
TiO2 0.18 0.27 0.06 0.20 0.32<br />
P2O5 0.01 0.01 0.005 0.005 0.045<br />
MnO 0.001 0.01 - - -<br />
Na2O 0.30 0.27 0.46 0.38 1.16<br />
K2O 2.30 2.08 2.23 1.89 2.23<br />
H2O(105oC) 0.70 0.02 0.18 0.26 0.57<br />
L.i. 4.53 15.07 0.50 9.19 13.66<br />
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Cilek: 4.8. Kaolin<br />
The clay content <strong>of</strong> kaolin sand is below 0.053 mm: 25-30% and 20-25% in fraction 0.00-0.020 mm. The<br />
main clay-mineral is kaolinite; quartz sand >0.053 mm can be used in the ceramic industry.<br />
Later, the deposit was explored in detail (Zuberec et al. 1984) and 51 boreholes were drilled. The results<br />
revealed that kaolin sands were not just <strong>of</strong> a lower quality than anticipated, but there was also a difference<br />
in both a lateral and vertical deposition.<br />
Average composition <strong>of</strong> sands composed <strong>of</strong> quartz grains, kaolin and K-feldspar (in %):<br />
% Composition from - to Composition - prevailing Composition - Average<br />
SiO2 51-84 60-71.5 64<br />
Al2O3 9.6-31.5 15-23 21<br />
Fe2O3 0.6-3.3 0.9-2.6 1.6<br />
K2O 1.5-7.7 2.4-5.7 4<br />
TiO2 0.02-0.6 0.1-0.3 0.17<br />
CaO 0.08-1.8 0.1-0.2 0.15<br />
MgO 0.05-0.5 0.1-0.2 0.17<br />
Na2O 0.08-0.5 0.1-0.4 0.18<br />
L.i. 0.08-0.5 4.5-7.5 7<br />
MnO below 0.008 %<br />
A granulometric evaluation revealed that the content <strong>of</strong> sand was 60-70%, while remaining 40-30% were<br />
silt and clay. The fraction below - 20 micron contains less than 10% <strong>of</strong> kaolin and is thus considered to be<br />
a poor kaolin deposit. From the economic point <strong>of</strong> view the production <strong>of</strong> washed kaolin is not to be<br />
recommended, both for a low clay content, and a low quality <strong>of</strong> kaolin.<br />
Its low quality was indicated by a separation <strong>of</strong> kaolin below 38 micron, a higher content <strong>of</strong> Al2O3, a<br />
lower amount <strong>of</strong> SiO2, but a high content Fe2O3 1.4-2.5%, exceptionally up to 4%. A higher amount <strong>of</strong><br />
alkalies, mainly K2O, comes from unaltered remnants <strong>of</strong> feldspars.<br />
Also technological tests confirmed, that washed kaolin could not be used in better quality ceramic ware:<br />
the colour after firing at 900°C is yellow-pink, at 1,200°C clear pink and at 1,360°C light grey. The<br />
shrinkage <strong>of</strong> 6% is medium, bending strength 3 MPa.<br />
According to chemical, granulometric, mineratogical and technological tests, the raw material <strong>of</strong> Nacala<br />
deposit can be denominated as kaolinic feldspar sand. These basic properties are typical:<br />
65-70% <strong>of</strong> sand<br />
35-30% <strong>of</strong> clay with prevailing content <strong>of</strong> silt<br />
10% and below <strong>of</strong> kaolin - 20 micron.<br />
After the treatment, i. e., a separation <strong>of</strong> coarse-grained particles and extraction <strong>of</strong> white kaolinic sand<br />
only, the composition is this:<br />
SiO2 75.30 %<br />
Al2O3 15.81 %<br />
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Cilek: 4.8. Kaolin<br />
TiO2 0.15%<br />
Fe2O3 0.66 %<br />
CaO -<br />
MgO 0.20 %<br />
K2O 3.65 %<br />
Na2O 0.10%<br />
L. i. 3.97 %<br />
It was suggested to use this kaolin sand in the production <strong>of</strong> tiles made <strong>of</strong> a ceramic mass containing 20-<br />
30% kaolin sand.<br />
The reserves were calculated with strong emphasis on specifications for kaolin sands suitable as part <strong>of</strong><br />
the ceramic mass, <strong>of</strong> these basic requirements:<br />
Al2O3 over 15%<br />
Fe2O3 maximum 3 %<br />
Fraction below 0.06 mm (containing silt and clay) with a minimum content in raw material, i.e., 28%.<br />
The reserves <strong>of</strong> this "corrective ceramic material" are substantial:<br />
category<br />
C1 - 1,462 589 t<br />
C2 - 2,044 125 t<br />
total: 3,506 714 t<br />
Other sites <strong>of</strong> kaolin occurrence in <strong>Mozambique</strong> are not adequatelly known, many kaolinic weathered<br />
zones were encountered in many places during the geological mapping. Around Nampula, the lower kolin<br />
zones with coloured oxides and slightly altered granites were used in ceramics (see Chap.-feldspar) <strong>of</strong> an<br />
inferior quality. Many kaolin deposits may still be discovered in feldspar-rich massifs such as syenites,<br />
anorthosites or in sedimentary arkosic sandstones. The altered pr<strong>of</strong>ile on syenite discovered near Manica<br />
on claimes <strong>of</strong> bauxite contains kaolin <strong>of</strong> this quality:<br />
% SiO2 45.81 combined<br />
SiO2 1.49 free<br />
Al2O3 38.94<br />
Fe2O3 0.06<br />
H2O 13.70<br />
Its analysis was published by P. Carvalho (1944) and the material was described as a kaolin "vein" in<br />
bauxite, with 98.5% <strong>of</strong> kaolin.<br />
In neighbouring Tanzania (Cilek, 1979), one <strong>of</strong> the biggest kaolin deposit in the world was described<br />
from the Pugu Hills near Dar-es-Salaam as Tertiary deltaic kaolin sands and sandstones. The Pugu Hills<br />
kaolin deposit is an uplifted delta, but such deltas do not occur in <strong>Mozambique</strong>. Nevertheless, kaolinic<br />
sands may be present in deeper layers within the paleodeltas <strong>of</strong> the rivers Limpopo, Zambezi or Rovuma.<br />
In the Rovuma basin, the Cretaceous Makonde beds or Neogene Mikindani beds contain sandstones with<br />
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Cilek: 4.8. Kaolin<br />
cementing kaolinic material.<br />
Another kaolinic layer may be found within the Karroo sequence, mainly in coal measures, where<br />
refractory clays are known to occur in Zimbabwe.<br />
A small occurrence <strong>of</strong> kaolin <strong>of</strong> hydrothermal origin was found in gold veins <strong>of</strong> the Manica gold district<br />
and it will certainly be present on tin deposits around Inchope. Larger accumulations <strong>of</strong> kaolin may also<br />
be found in pegmatite subsurface bodies undergoing a slight hydrothermal alteration and albitization<br />
connected with pegmatite development.<br />
Conclusions:<br />
Kaolin deposits <strong>of</strong> <strong>Mozambique</strong> are concentrated in the N part <strong>of</strong> the country in the form <strong>of</strong> an alteration<br />
product <strong>of</strong> pegmatite deposits. Outcropping feldspar-rich pegmatites, in a morphologically raised position<br />
underwent weathering with kaolin zones development. The only very small kaolin deposit in production<br />
is Boa Esperanca in Ribaue, W <strong>of</strong> Nampula. Other big deposits are on Nb-Ta-bearing pegmatites, kaolins<br />
are regarded a waste material and therefore not utilized. Reserves <strong>of</strong> these sites are large and a simple<br />
treatment <strong>of</strong> kaolin waste may result both in a kaolin recovery and a recovery <strong>of</strong> additional Nb-Ta<br />
minerals. Pegmatite deposits in production may yield several tens <strong>of</strong> thousand tons <strong>of</strong> kaolin a year <strong>of</strong><br />
ceramic and partly paper grade quality, besides feldspar, quartz and other economic minerals. The only<br />
deposit <strong>of</strong> kaolinic sands <strong>of</strong> sedimentary origin near Nacala may yield the "corrective" sand with kaolin<br />
and feldspar in the ceramic mass.<br />
An investigation <strong>of</strong> kaolin deposits in the country is just in its first stage, but it is certain, that a permanent<br />
utilization <strong>of</strong> kaolin material on pegmatite mines should cover the entire need <strong>of</strong> the country and therefore<br />
there is no necessity to explore new localities.<br />
© Václav Cílek 1989<br />
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Cilek: 4.9 Limestone and dolomitic limestone<br />
4.9. Limestone and dolomitic limestone<br />
Limestone is a sedimentary rock containing mineral calcite as its main component. Calcite <strong>of</strong> a formula CaCO3,<br />
hardness 3 and specific gravity 2.71, is a s<strong>of</strong>t, vitreous, transparent to translucent mineral <strong>of</strong> a perfect rhombohedral<br />
cleavage. It is composed <strong>of</strong> 56.0% CaO and 44.0% CO2 whereby part <strong>of</strong> the calcium may be substituted by Mn, Zn,<br />
Fe and Co.<br />
Calcite develops in several varieties known as Iceland spar (<strong>of</strong> a strong double refraction), satin spar (silky luster),<br />
Mexican onyx (banded calcite and aragonite), travertine, chalk and particularly in limestones, it is a dull compact<br />
rock, in marble a metamorphic equivalent <strong>of</strong> limestone.<br />
Besides calcite limestone may contain different admixtures, <strong>of</strong> which the most common is dolomite <strong>of</strong> the formula Ca<br />
Mg(CO3)2, the main constituent <strong>of</strong> dolomite rock ("dolostone"). On one end <strong>of</strong> the spectrum, is limestone with a high<br />
calcium content <strong>of</strong> 95%, on the other end dolomite with a high dolomite mineral content <strong>of</strong> 94% (43% MgCO3).<br />
Other admixtures are clay, sand, chert, organic matter, glauconite, pyrite etc. The colour <strong>of</strong> pure limestone is usually<br />
white, but it is commonly grey, reddish, greenish and black in nature. According to different admixtures in limestone,<br />
in quantities <strong>of</strong> about 10% and more, the rock is known as clayey, sandy, bituminous, glauconitic, etc. Similarly,<br />
differences in the classification <strong>of</strong> limestone are derived from its morphology, structure, texture, genesis and its use.<br />
According to the clay content, the spectrum accepted for commercial products is this (Polak, 1972):<br />
high-quality limestone 98-100% CaCO3 clay content 0-2 %<br />
pure limestone 98-95 % CaCO3 clay content 2-5 %<br />
limestone 95-90% CaCO3 clay content 5-10 %<br />
marly limestone 90-75% CaCO3 clay content 10-25 %<br />
calciticmarl 75-40% CaCO3 clay cantent 25-60 %<br />
marl 40-15% CaCO3 clay content 60-85 %<br />
calciticclay 15-5% CaCO3 clay content 85-95 %<br />
clay 5-0% CaCO3 clay content 95-100%<br />
According to the dolomite content, this spectrum was accepted (Kuzvart, 1984):<br />
limestone - up to 10% <strong>of</strong> CaMg(CO3)2<br />
dolomitic limestone - 10 - 50 % <strong>of</strong> CaMg (CO3)2<br />
calcitic dolomite - 50 - 90 % <strong>of</strong> CaMg (CO3)2<br />
dolomite - up to 10 % <strong>of</strong> CaCO3<br />
Limestones display also different degree <strong>of</strong> crystalinity, bed thickness, content <strong>of</strong> fossils, diagenesis, silicification etc.<br />
and, therefore, it is advisable to use proper adjectives.<br />
Most limestones originated as shallow marine water sediments composed <strong>of</strong> shells, skeleton remnants <strong>of</strong> corals,<br />
bryozoans, algae etc., which were fragmented to even a small size and cemented together by very fine grains <strong>of</strong><br />
calcitic sand, limy mud calcite ooze. Many limestones are <strong>of</strong> coralline origin and these fossil reefs represent very pure<br />
limestones <strong>of</strong> high commercial value. Often, calcite precipitates directly onto the surface <strong>of</strong> small shell particles in the<br />
form <strong>of</strong> ooids and, in the zone <strong>of</strong> high energy and active water circulation ooids "grainstones" are made up <strong>of</strong> pure<br />
limestone, because the mud had been swept away by turbulent waters.<br />
In a lagoonal environment, micritic limestone <strong>of</strong> a high quality originates from deposited calcareous mud. The<br />
admixture <strong>of</strong> quartz grains usually does not surpass 5%. Part <strong>of</strong> the limestone, mainly coral-algal reefs, can be<br />
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Cilek: 4.9 Limestone and dolomitic limestone<br />
replaced by dolomite by metasomatism or a direct growth <strong>of</strong> dolomite crystals in fossils.<br />
Chalk is a variety <strong>of</strong> organogenic limestone or micrite, it is white and s<strong>of</strong>t and used as normal limestone or for writing<br />
on blackboards.<br />
Oolitic limestone or aragonite sand (aragonite is dimorphous with calcite but is less stable) is formed by a<br />
precipitation from seawater and consists <strong>of</strong> extremely small particles with a nucleus <strong>of</strong> shell fragments and laminae <strong>of</strong><br />
calcite and aragonite. Its CaCO3 content is 96-97% (Harben-Bates, 1984), the lower layer is usually diagenetically<br />
consolidated in beds.<br />
Limestone is used in almost every branch <strong>of</strong> the industry. If the rock is compact, it can be used as crushed stone for<br />
the aggregate, and as a building stone for many other purposes depending on its physico-mechanical properties.<br />
Because limestone and dolomitic limestone (chemical composition is immaterial) deposits occur generally in many<br />
places, their use in the building industry is widespread. Some coloured limestones are also used as dimension stones,<br />
they can easily be cut and polished and were used in several monumental buildings, especially churches. Today, slabs<br />
<strong>of</strong> selected limestones are produced for inner linings. In some countries, over 50% <strong>of</strong> recovered limestone rocks are<br />
used as crushed stone.<br />
Owing to its chemical properties, limestone is an essential part <strong>of</strong> cement raw materials (75-80%). All types <strong>of</strong><br />
limestones are used, from pure limestone and crystalline limestone to marls, chalk, calcitic sand, marine shells and<br />
limestone waste, and are supplemented by clay, shale, pyrite, slag and other silica-containing materials, alumina and<br />
iron. Exceptionally natural cement rock corresponds to the type "calcitic marl".<br />
Another important use is in the production <strong>of</strong> lime, at a calcination <strong>of</strong> calcium carbonate at 1,000-1,100°C<br />
(CaCO3 + heat ===> CaO + CO2).<br />
High-quality material is required, because each portion <strong>of</strong> silica and other impurities will double the loss <strong>of</strong> lime (44%<br />
<strong>of</strong> limestone weight is lost in the process).<br />
Part <strong>of</strong> the lime is converted to hydrated lime, but an essential amount is used in many industries; in a production <strong>of</strong><br />
soda ash in Solvay process, as filler, as flux in metallurgy, in alkalies, in glass and ceramic industries, in water<br />
treatment; micr<strong>of</strong>ine-grained limestone is used as a specific filler in plastics, in treating pulp for paper production, in<br />
refining sugar, an extender in paint and finally in mortar and plaster. The last use was very important in the past, but<br />
nowadays, lime in mortar is replaced by cement. A demand for pulverized limestone or lime is increasing in<br />
agriculture to neutralize acid rain, correct soil acidity and support the growth <strong>of</strong> plants.<br />
During the past ten years, the calcium carbonate market underwent substantial changes. In the paper industry calcium<br />
carbonate (products 325 mesh and below) replaces kaolin, the use in plastics and paint is overwhelming. In all<br />
countries, in which limestone is available, it is used in these industries on the account <strong>of</strong> other more expensive<br />
materials. Because limestone is one <strong>of</strong> the most plentiful <strong>of</strong> the mineral <strong>of</strong> the earth - about 15% <strong>of</strong> its sedimentary<br />
crust-fine-ground products <strong>of</strong> calcium carbonate have the advantage both in terms <strong>of</strong> their geographical location and a<br />
good product performance. Remarkable is the utilization <strong>of</strong> calcium carbonate in plastics. An overall increase over the<br />
last 10 years averages 8% per year mainly in polyesters and polyvinyl chloride (PVC). Glass-reinforced polyester is<br />
composed <strong>of</strong> about 35-40% <strong>of</strong> resin, 20% <strong>of</strong> chopped glass and 40-45% <strong>of</strong> calcium carbonate, with a small amount <strong>of</strong><br />
additives. The best example <strong>of</strong> the use <strong>of</strong> polyester is in automobile industry, nowadays every car contains calcium<br />
carbonate - in plastic door panels, front - end panel etc.<br />
Polyvinyl chloride is a thermoplastic material which is either flexible or rigid. Calcium carbonate <strong>of</strong> 3.0 micron grade<br />
participates in 15-20% in the plastic body. The main produce are pipes, mouldings, furniture, and the market is<br />
growing steadily. Calcium carbonate has been used for years in matte paper coatings and as a base coat pigment in<br />
card board, but just marginally as a filler. In Europe, the use <strong>of</strong> "whitings" is common and calcium carbonate is used<br />
at levels as high as 20% or more <strong>of</strong> the paper. Required grades for ultrafine material are 1.5-2.0 micron as a filler and<br />
0.6-0.8 micron for coatings.<br />
To compile with the requirements for ultrafine-grade material, the very pure limestone deposits must be explored.<br />
For a classical utilization <strong>of</strong> limestone, some general requirements adopted in the past are these:<br />
Limestone for lime production: used in a production<br />
<strong>of</strong> burnt (pure) lime<br />
hydraulic lime<br />
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Cilek: 4.9 Limestone and dolomitic limestone<br />
hydrated lime.<br />
Burnt lime (CaO) is produced by firing <strong>of</strong> limestone or dolomitic limestone at a temperature below the sintering point.<br />
The required CaO + MgO content is 80-85%, <strong>of</strong> which MgO should be below 7%, maximum loss <strong>of</strong> ignition 8% and<br />
CO2 5%.<br />
Hydraulic lime for mortar is produced by firing <strong>of</strong> limestones with hydraulic components (oxides <strong>of</strong> Si, Al, Fe) at a<br />
sintering temperature. It hardens in water.<br />
Hydraulic lime should contain a minimally 90% CaO + MgO (<strong>of</strong> which maximally 3% <strong>of</strong> MgO), maximum SiO2 5%<br />
and R2O3 4.5%. Both compression strength and dilatation strengh are also tested.<br />
Hydrated lime should have a CaO content <strong>of</strong> 64-70%, MgO maximum 5.5-2.0%, SiO2 and acid-insoluble remnants<br />
maximum 2.5%, humidity 3%.<br />
Accepted requirement for cement production:<br />
CaCO3 minimum 80 %<br />
MgCO3 maximum 7 %<br />
MnO maximum 0.3 %<br />
Sulphur maximum 1.0%<br />
P2O5 maximum 0.1 %<br />
K2O + Na2O maximum 0.5 %<br />
quartz and chert maximum 3 %<br />
Metallurgical limestone (used in blast furnaces, electrical furnaces for iron, production <strong>of</strong> steel, foundries) requires the<br />
highest possible content <strong>of</strong> CaCO3 and the possibly lowest content <strong>of</strong> SiO2, because every 1% SiO2 binds 2%<br />
CaCO3 (for example 100 kg CaCO3 = 103 kg limestone with 1% <strong>of</strong> SiO2 + Al2O3 or 106 kg limestone with 2%<br />
SiO2 + Al2O3 etc.).<br />
The minimum content <strong>of</strong> CaCO3 + MgCO3 should not fall below 95% (MgCO3 maximum 16%), Al2O3 maximum<br />
1.5%, CaSO4 maximum 0.5%, SiO2 up to 3% and P maximum 0.07%. The limestone for alumina foundries requires<br />
an even better quality - over 96% CaCO3 and MgCO3 below 2%. Limestones for chemical industries must be pure<br />
with 96-98% CaCO3 + MgCO3 (MgCO3 up to 1%), SiO2 maximum 0.5%, Al2O3 + Fe2O3 maximum 0.3% etc.).<br />
Limestones for saturation in sugar plants should have 94% CaCO3, 3% MgCO3, 2% SiO2 + insolubles, Al2O3 +<br />
Fe2O3 up to 2%, alkalies 0.2% and SO3 maximum 0.25% (aggregate 80 to 200 mm).<br />
Glass factories use pure limestones with an Fe2O3 content up to 0.01%, a content above 0.5% gives the glass a<br />
greenish tint. The presence <strong>of</strong> TiO2, ZrO2 and other refractory oxides is also harmfull.<br />
Limestones for agriculture either for soil improvement or as feedstuff for animals, are <strong>of</strong> a different quality. For soil<br />
purposes even low-quality limestones (80% <strong>of</strong> carbonates), but finelly pulverized are used, for animals, the content <strong>of</strong><br />
carbonates should be over 92%, a higher P2O5 content, trace elements except As, Zn, Pb and Cu, are welcomed.<br />
The group <strong>of</strong> limestones includes other rocks containing calcite, generally marbles and carbonatites known under the<br />
common name calcitic materials.<br />
In <strong>Mozambique</strong>, the types <strong>of</strong> calcitic rocks are these (see Fig. 4.9.1):<br />
1. sedimentary -limestones, dolomitic limestones, marls, lacustrine limestones -the most important deposits<br />
2. crystalline - marbles <strong>of</strong> different composition, used locally in the past for lime production<br />
3. volcanic - carbonatites, mostly mineralized (apatite, rare earths etc.)<br />
Fig. 4.9.1. Occurence <strong>of</strong> limestone (435 kB)<br />
1. Sedimentary limestones and marls are present at different levels in the sedimentary sequence <strong>of</strong> coastal<br />
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Cilek: 4.9 Limestone and dolomitic limestone<br />
<strong>Mozambique</strong>. The two sedimentary basins are: <strong>Mozambique</strong> basin in the S <strong>of</strong> the country from the border with South<br />
Africa up to the N margin <strong>of</strong> the Zambezi delta; the Rovuma basin on the border with Tanzania and finally, a narrow<br />
coastal sedimentary belt between both basins.<br />
Main limestone layers and some marls <strong>of</strong> the Cretaceous occur in Red Beds <strong>of</strong> the Neocomian overlying with<br />
disconformity Karroo volcanics, in the Sena Formation <strong>of</strong> Aptian-Albian. The Upper Cretaceous is mainly marly<br />
(Lower Grudja). The main accumulation <strong>of</strong> calcitic sediments occurs within the Tertiary. In the Upper Grudja<br />
Formation <strong>of</strong> Paleocene age are marls and calcitic shales. Limestones with a high carbonate content occur in the<br />
Eocene S <strong>of</strong> Maputo in the Salamanga Formation, and in the Cheringoma Formation in two areas - W <strong>of</strong> Beira along<br />
the river Buzi and in the type locality N <strong>of</strong> Beira on the Cheringoma plateau. The second important accumulation <strong>of</strong><br />
limestones is in the Miocene, in the J<strong>of</strong>ane Formation (Fig. 4. 9. 2). A large area with outcrops <strong>of</strong> limestone extends<br />
from S <strong>of</strong> the river Save to the Inhambane.<br />
Fig 4.9.2. Generalized Stratigraphy <strong>of</strong> the <strong>Mozambique</strong> Basin and Global Cycles <strong>of</strong> the Sea Level Changes<br />
(ENH, 1986) (612 kB)<br />
In the Rovuma basin, calcitic marls and marly limestones occur in the Cretaceous beds Conducia and Megatrigonia,<br />
in Globotruncana marls and again mainly in the Eocene <strong>of</strong> the Cheringoma Formation. Coral limestones were found<br />
over an area from Pebane in the S to Tanzania in the N. They are <strong>of</strong> Pliocene to Quaternary age (see general pr<strong>of</strong>ile,<br />
Cilek, 1985). The coral reefs form platforms raised + 30 m, + 15 m and + 5 m above the sea level on the shore. Many<br />
coral islands on the shelf are + 5 m elevated and surrounded by coral platforms exposed during low tide, with living<br />
coral and algal colonies on the margin. Wide coral platforms fringe the whole seashore, from the llha <strong>Mozambique</strong> to<br />
the Rovuma river, except for small section influenced by fresh water. Scattered coral reefs could be traced from llha<br />
Inhaca in the Maputo bay to the Paradise Islands at Vilanculos. The coral reefs are a source <strong>of</strong> excellent pure<br />
limestone; around them wide layers <strong>of</strong> coral sand and mud are developing on the shelf.<br />
Lacustrine Quaternary limestone deposits are known to occur in several places <strong>of</strong> the <strong>Mozambique</strong> basin, between<br />
Maputo and the river Save as sediments <strong>of</strong> inland lakes originating during the interglacial periods within the older<br />
grabens.<br />
2. Crystalline limestones - marbles are present in almost all crystalline complexes <strong>of</strong> <strong>Mozambique</strong> including<br />
Archean and Precambrian rocks. They are originally sedimentary rocks metamorphosed during several orogenetic<br />
phases and deposited either as a platform or geosynclinal sediments. The latter case is more common. There are still<br />
vast areas in which crystalline limestone deposits may be found. Primary attention should be given to mobile belts <strong>of</strong><br />
the Precambrian with carbonatic sediments, to greenstones belts and generally to the upper structural level <strong>of</strong> the<br />
Mozambican belt with prevailing metasediments.<br />
The oldest crystalline limestones <strong>of</strong> <strong>Mozambique</strong> are those <strong>of</strong> the Archean Greenstone Belt - <strong>of</strong> the Zimbabwean<br />
craton. Of the three formations - Macequece, Mbeza and Vengo, the last consists <strong>of</strong> a band <strong>of</strong> sericite-chlorite schists<br />
and phyllites including black schists with minor bands <strong>of</strong> marble and conglomerate. The marble was used for lime<br />
production near the town <strong>of</strong> Manica.<br />
In other Archean rocks - in the Luia Group <strong>of</strong> the central Tete Province narrow bands <strong>of</strong> marble and banded<br />
ironstones are enclosed in granulites <strong>of</strong> acid composition. The marbles are coarsely granular, white or grey rocks,<br />
almost pure calcite, but also contain laminae <strong>of</strong> calc-silicate minerals. In part, they are dolomitic and always closely<br />
associated with the marbles. They occur mainly around the river Luatize NE <strong>of</strong> Fingoe and around Chiputo near the<br />
Zambian border.<br />
Precambrian formations are divided into several groups. The Chidue Group situated on the periphery <strong>of</strong> the Tete<br />
Complex over an area extending from Massamba to Estima represents metasediments outcropping as marbles, schists,<br />
quartzites and associated metasediments. Marbles <strong>of</strong> the Mufa-Boroma area are white or cream, medium-grained<br />
forming usually distinctive structural ridges such as Chacocoma marbles Near Tete, marbles were used in lime<br />
production.<br />
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Cilek: 4.9 Limestone and dolomitic limestone<br />
In the NW part <strong>of</strong> the Tete Province, the Zambue Group was distinguished between the towns <strong>of</strong> Zumbo and<br />
Malowera, just in the corner frontering with Zambia. It consists <strong>of</strong> impure coarse-grained dolomitic marbles in a<br />
metasedimentary sequence with thin siliceous bands, known as Mvuvye marbles. In the Fingoe Group, a widely<br />
varied belt <strong>of</strong> predominantly metasedimentary rocks developed just E <strong>of</strong> the Zambue Group, in which marbles and<br />
metadolomites are abundant (see Chap. ornamental stones). The marbles are cream or white, medium-to fine-grained,<br />
<strong>of</strong>ten in dolomitic varieties. The main accumulations occur in the area Monte Mancupiti - Monte Manga.<br />
The extensive Barue Group stretching from the river Zambezi almost up to the river Save, E <strong>of</strong> the Zimbabwean<br />
craton, contains numerous bands <strong>of</strong> marble in the S<strong>of</strong>ala Province. The marbles are cream or grey, medium-grained,<br />
banded rocks with or without calc-silicate minerals, <strong>of</strong>ten with disseminated graphite. They occur at Meteme in the<br />
Tete Province and in many other localities <strong>of</strong> the S<strong>of</strong>ala Province N <strong>of</strong> Gorongosa, S <strong>of</strong> Canxixe and in an extensive<br />
belt <strong>of</strong> SW-NE direction between Meteme and N <strong>of</strong> Canxixe.<br />
The Umkondo Group lies at the border with Zimbabwe, near the towns <strong>of</strong> Rotanda and Espungabera. The group<br />
consists <strong>of</strong> slightly deformed phyllites, metasiltstones and quartzites with siliceous dolomite and limestones bands<br />
developed near the base <strong>of</strong> the sequence.<br />
The Rushinga Group is situated in the N part <strong>of</strong> the Luenha river along the road Tete Harare, just at the Zimbabwean<br />
border; it consists <strong>of</strong> banded gneisses and metasediments. The area had been prospected for manganese. According to<br />
Hunting (1984) the group is a Pan-African sequence <strong>of</strong> metasediments <strong>of</strong> a younger age than the Umkondo and<br />
Gairezi Groups. The calc-silicate gneisses form finely banded units up to 20 m thick in which occur thin<br />
discontinuous lenses <strong>of</strong> medium-grained calcite marble. The locality is known as Masanga and is situated WSW <strong>of</strong><br />
Changara. Remnants <strong>of</strong> lime furnaces can still be seen in several places. Big, but less well-known sites <strong>of</strong> crystalline<br />
limestone occurrence have been mapped in the whole <strong>of</strong> N-<strong>Mozambique</strong>, in the provinces Nampula, Cabo Delgado<br />
and Niassa.<br />
The well-known marbles <strong>of</strong> Montepuez have already been described. Many other bodies within the Lurio belt were<br />
investigated, such as the locality Marese. Near the Tanzanian border, marble is known to occur at Negomano S <strong>of</strong> the<br />
river Rovuma and in other localities in the structure <strong>of</strong> Morrola (see graphite). During an investigation for graphite,<br />
several limestone deposits were discovered N <strong>of</strong> the mouth <strong>of</strong> the river Lurio. Other sites marble occurrence in<br />
connection with deposits <strong>of</strong> apatite, magnetite and graphite, are known from the Monapo structure.<br />
In the Niassa Province, where the deposit Malulo had been exploited in the past, an investigation <strong>of</strong> the Formation<br />
Geci disclosed marble in several sites.<br />
Reserves <strong>of</strong> crystalline limestones are substantial in the deposit Muande near Tete and in its neighbourhood, on Monte<br />
Fema, where iron ore and apatite were discovered. Small marble quarries for lime production were established at the<br />
genetically similar deposit Evate near Nampula situated within the Monapo structure.<br />
3. Carbonatites in small volcanic massifs may yield an acceptable cement material. In <strong>Mozambique</strong>, carbonatite<br />
localities are these (from S to N): Monte Xiluvo NW <strong>of</strong> Beira, Monte Muambe, Buzimuna and Chandava E <strong>of</strong> Tete,<br />
Salambidua N <strong>of</strong> latter localities, but with central carbonatite on the Malawian side <strong>of</strong> border and finally Cone Negose<br />
on northern bank <strong>of</strong> Cabora Bassa dam.<br />
Several deposits were investigated in detail:<br />
The most southern limestone deposit is situated at Salamanga near the village <strong>of</strong> Boa Vista. In a narrow zone, 1.5-2.0<br />
km, extending in N-S direction calcareous rocks are present which display typical karst phenomena such as sinkholes,<br />
small cavities, etc. The calcareous sequence is <strong>of</strong> Eocene age and is known as the Salamanga Formation. The<br />
limestone attains a thickness <strong>of</strong> about 10-15 m and is composed <strong>of</strong> heterogeneous layers with an admixture <strong>of</strong> sand,<br />
and underlain by distinctive greenish glauconitic sandstone. Overburden, 1 to 13 m thick, consists <strong>of</strong> sands, locally<br />
calcareous, <strong>of</strong> the Quaternary. A limestone quarry supplies limestone to a cement factory at Matola on the outskirts <strong>of</strong><br />
Maputo, whereby lime furnaces are operating directly on the locality.<br />
The last exploration was performed by the Yugoslav team in 1985. They confirmed a great variability <strong>of</strong> limestone;<br />
the dip <strong>of</strong> strata was subhorizontal 3-5°/E. In the NE area, the thickness <strong>of</strong> carbonate rocks was 55.6 m, in the SW just<br />
11.35 m. The average thickness was calculated on 31 m with the purest limestone composed on the top <strong>of</strong> an<br />
organogeneous layer with shells <strong>of</strong> Gastropoda and Lamellibranchiata (1.4-6.0 m). Most <strong>of</strong> the sequence is made up<br />
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Cilek: 4.9 Limestone and dolomitic limestone<br />
<strong>of</strong> sandy limestone and carbonatic sandstone with glauconite up to 3%.<br />
Sandy limestone is organogenic-detrital with a carbonate component <strong>of</strong> 50-70% in the very sandy variety; a normal<br />
content is 70-87% <strong>of</strong> calcium carbonate.<br />
Average values for 19 boreholes:<br />
% SiO2 10.60 MgO 2.55 Na2O 0.38 H2O 350°C 0.71<br />
Al2O3 0.99 TiO2 0.095 K2O 0.40 H2O 105°C 0.83<br />
Fe2O3 1.16 P2O5 0.26 SO3 0.12 CaCO3 78.55<br />
CaO 44.44 MnO 0.44 L. i. 37.15 MgCO3 5.00<br />
Average composition was asessed also from several trenches. Mean content <strong>of</strong> boreholes and trenches (in %):<br />
SiO2 17.48 (10.60 and 26.95)<br />
Al2O3 1.16 (0.99 and 1.40)<br />
Fe2O3 1.17 (0.58 and 1.59)<br />
CaO 41.45 (26.1 and 51.09)<br />
Average <strong>of</strong> carbonates CaCO3 + MgCO3 is 78.13% (57.23 and 91.79%)<br />
MgO 2.03 (2.55 and 1.30)<br />
SO3 0.11 (0.04 and 0.33)<br />
The mining conditions are very favourable, the quarry is situated on an escarpment along the bank <strong>of</strong> the river Maputo.<br />
Results <strong>of</strong> control analyses <strong>of</strong> sample composition: %<br />
% SiO2 Al2O3 Fe2O3 CaO MgO TiO2 P2O5 Na2O K2O CaCO3 MgCO3<br />
Boreholes F-9 3.18 0.98 1.14 51.16 1.33 tr. 0.36 0.56 0.25 91.35 2.79<br />
F-13 3.88 1.09 1.27 50.34 1.66 tr. 0.26 0.68 0.20 89.89 3.48<br />
Trenches TR-23 36.22 1.88 1.36 32.07 0.90 tr. tr. 0.90 0.36 57.26 2.07<br />
TR-39 21.34 1.21 0.67 40.87 1.33 tr. 0.40 0.70 0.19 72.96 2.94<br />
The reserves <strong>of</strong> carbonate material suitable for a production <strong>of</strong> portland cement and hydraulic lime amount to<br />
1,198,985 845 t (557,667 835 m3).<br />
In the Maputo and Gaza provinces, sandy limestones or marly limestones together with calcitic and glauconitic<br />
sandstones are present in outcrops on the E - slopes <strong>of</strong> the Lebombo Mts. They generally belong to the Lower<br />
Cretaceous-Aptian Maputo Formation, which begins at the base <strong>of</strong> the transgressive cycle with lagoonar sediments <strong>of</strong><br />
black saline marls.<br />
The Upper Cretaceous consists mainly <strong>of</strong> continental facies, sandstones transgress over Karroo basalts in an area<br />
between Sabie and Rio dos Elefantes and from there to Singuedzi, followed by marine sandstones <strong>of</strong> Uanetze and<br />
Mahel outcroping about 25 km N <strong>of</strong> the river Incomati, E <strong>of</strong> older formations.<br />
Therefore, Cretaceous sediments are less important with regard to their carbonate content.<br />
Extensive limestone deposits are developed in the Tertiary. An equivalent <strong>of</strong> the Eocene Salamanga Formation in the<br />
S is the Eocene Cheringoma Formation in the N surfacing in two important areas: around the river Buzi W <strong>of</strong> Beira in<br />
the S<strong>of</strong>ala Province and in the type locality on the Cheringoma plateau and escarpment bordering the E- side <strong>of</strong> the<br />
rift valley- the Urema Trough. The Cheringoma Formation extend for about 100 km in NNE-SSW direction from<br />
Muanza in the S to the N <strong>of</strong> Inhaminga. The Cheringoma Formation along the river Buzi is not well known. One<br />
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Cilek: 4.9 Limestone and dolomitic limestone<br />
analysis <strong>of</strong> limestone from the locality Inhaboa was made in London (1944). Outcrops <strong>of</strong> limestones occur over a<br />
distance <strong>of</strong> more than 50 km just E <strong>of</strong> the confluence <strong>of</strong> the rivers Buzi and Revue.<br />
Limestone quality (in %):<br />
CaO 54.80 CaCO3 content<br />
MgO 0.49 97.76% is similar.<br />
SiO2 0.92 to that <strong>of</strong> the<br />
Fe2O3 0.23 Cheringoma<br />
Al2O3 0.33 plateau<br />
L. i. 43.34<br />
Similar results <strong>of</strong> another analysis <strong>of</strong> Campos (1961) (in %):<br />
Limestone quality (in %):<br />
CaO 54.52 CaCO3 content<br />
MgO 0.28 97.25<br />
SiO2 1.43<br />
Fe2O3 0.36<br />
Al2O3 0.22<br />
L. i. 43.19<br />
Drilling for oil and gas in the S<strong>of</strong>ala Province revealed the basic stratigraphy <strong>of</strong> Tertiary formations. In term <strong>of</strong><br />
carbonate, the Upper Grudja Formation <strong>of</strong> the Paleocene and partly Eocene may be promising just in some parts<br />
owing to decrease in some layers <strong>of</strong> limestone and dolomitic limestone. Sandstones with glauconite are dominant and<br />
according to a K/Ar determination <strong>of</strong> the Upper Grudja their age may be 60.0 ± m. y. (ENH, 1986). There is an<br />
angular unconformity on the top <strong>of</strong> the Upper Grudja and the Cheringoma Formation. Just the upper part <strong>of</strong> the<br />
Eocene system is present in outcrops both at Buzi and the Cheringoma plateau and this represents the carbonatic part.<br />
At the type locality, in quarries on the plateau near Muanza, the Formation is about 70 m thick and rests discordantly<br />
on the underlying Grudja Formation. The limestone is pure to sandy, whitish in colour with extremely abundant<br />
fossils - Nummulites atacicus, numerous Camerina sp., Operculina sp., gastropods and coral and echinoid remnants.<br />
The environment was warm clear water <strong>of</strong> neritic-bathyal depths. Changes <strong>of</strong> facies into marly limestones and marls<br />
proceed up to the present shoreline. The whole Cheringoma plateau is a typical karst area - deep sinkholes, extensive<br />
caves, steep canyons and subterraneous rivers are abundant.<br />
In 1944 (Carvalho), two analyses <strong>of</strong> limestones <strong>of</strong> the Cheringoma Formation were made in London on (in %):<br />
Oxide Nhindini valley W slope <strong>of</strong> the scarp<br />
CaO 51.0 49.90<br />
MgO 0.84 0.92<br />
SiO2 4.59 5.30<br />
Al2O3 + Fe2O3 1.30 2.98<br />
L. i. 41.48 39.65<br />
CaCO3 90.98 89.02<br />
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Cilek: 4.9 Limestone and dolomitic limestone<br />
First, the area was explored in 1952 by Bettencourt Dias by drilling boreholes over the area <strong>of</strong> the Urema trough<br />
escarpment to detect the best limestone deposits for the cement factory at Dondo near Beira. Unsuitable for cement<br />
production were limestone deposits S <strong>of</strong> the road Muanza-Urema but N <strong>of</strong> it good-quality limestone was discovered<br />
in the localities Codzo, Nhangatua, Condue, Massiquidze, Muanza and Mueredzi (from N to S). The last three<br />
deposits are the best, with a stable thickness and quality, while from other deposits, limestone <strong>of</strong> the best quality had<br />
partially been removed by erosion.<br />
The deposits Mueredzi, Muanza and Massiquidze fringe the escarpment, which originated in the last stage <strong>of</strong> rift<br />
valley development in the Pleistocene. All these deposits are about 25 km W <strong>of</strong> the Trans-Zambezian railway line and<br />
at 110.98 and 80 km respectively from the cement factory at Dondo.<br />
The Codzo deposit is made up <strong>of</strong> nummulithic limestone, 40 m thick, around the rapids <strong>of</strong> the river Codzo, which is<br />
partly subterraneous, partly flowing through a canyon and caves. On the surface, the limestone contains 90-95%<br />
CaCO3, in the borehole the carbonate content diminishes from 80 to 40% at a depth <strong>of</strong> 20 m (see Fig. 4.9.3).<br />
Fig 4.9.3. Cross section <strong>of</strong> Rio Codzo limestone deposit (Bettencourt Dias, 1952)<br />
Fig 4.9.4. Geological pr<strong>of</strong>ile <strong>of</strong> Rio Muanza limestone deposit (Bettencourt Dias, 1952) (521 kB)<br />
The deposit <strong>of</strong> the river Condue is similar to that <strong>of</strong> the Codzo, the CaCO3 content is higher on the surface and<br />
diminishing towards the depth (90% on the surface, 85% CaCO3 in 40% <strong>of</strong> samples, below 76% CaCO3 in 60% <strong>of</strong><br />
samples). The Cheringoma Formation is intruded by a younger basalt vent forming the hill Nhaguere. In several<br />
samples, the content <strong>of</strong> CaCO3 was as high as 97.50%.<br />
The deposit Nhangatua located between Codzo and Condue displays variation in the content <strong>of</strong> CaCO3.<br />
The northernmost <strong>of</strong> the three deposits is Massinquize, with limestone outcropping over 7 km at a height <strong>of</strong> about<br />
10m. The white fossiliferous limestone has a high CaCO3 content. Bettencourt Dias explored the deposit in 17<br />
traverse sections. Examples <strong>of</strong> the limestone quality in some sections (CaCO3 in %):<br />
Section 1 - 98.88 %<br />
Section 2 - 97.88%<br />
Section 5 - 98.10%<br />
Section 7 - 89.30%<br />
Section 17- 95.45%<br />
The deposit Muanza is located on the river <strong>of</strong> the same name. The scarp is about 12 m high, part <strong>of</strong> the area is covered<br />
by reddish sand. About half <strong>of</strong> the area represents good-quality limestone, as evident in the sections (section 11 is the<br />
first with limestone, section 22 the last (in % CaCO3)):<br />
Section 11 - 88.00 %<br />
Section 12 - 95.94%<br />
Section 14 - 100 % CaCO3 in one sample, 98.00 % in the others<br />
Section 18 - 94.75%<br />
Section 22 - 93.11%<br />
The development <strong>of</strong> the Cheringoma Formation within the whole area is best demonstrated on the stratigraphical<br />
section (Bettencourt Dias, 1953 Fig. 4.9.4).<br />
The southernmost deposit on the river Mueredzi is the best investigated deposit <strong>of</strong> the lot. The regular development <strong>of</strong><br />
the limestone bed is extraordinary, the section <strong>of</strong> calcareous rock <strong>of</strong> the Cheringoma Formation is uncovered and<br />
extensive outcrops are present in karst area. The river Mueredzi builds a canyon 16 m deep and over 600 m long, with<br />
a CaCO3 content in limestones <strong>of</strong> over 85%. About 60% <strong>of</strong> limestone samples contain 90-100% <strong>of</strong> CaCO3, 35% 85-<br />
90% <strong>of</strong> CaCO3. The reserves <strong>of</strong> limestone on both banks <strong>of</strong> the river amount to 10,230 000 t. In the whole area, there<br />
may be possible reserves <strong>of</strong> several hundred million tons.<br />
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Cilek: 4.9 Limestone and dolomitic limestone<br />
In the Inhambane Province, near the seashore, extensive outcrops <strong>of</strong> Miocene limestone exist within the J<strong>of</strong>ane<br />
Formation. However, the size <strong>of</strong> the actual deposit is much bigger, but most <strong>of</strong> it is obscured by a Quaternary cover.<br />
The thickness <strong>of</strong> limestones is more than 100 m and the best outcrops developed near Urrongos and J<strong>of</strong>ane around the<br />
river Save. The whole area displays karst phenomena such as caves, sinkholes, chimneys and differently steep<br />
depressions which may be covered partially by Quaternary sand and clay. The caves originate usually from sinkholes<br />
<strong>of</strong> which some are filled by bat guano. The depth <strong>of</strong> the karst phenomena is not known, their surface elevations is 100-<br />
150 m above the sea and, taking into the account the water table <strong>of</strong> the sea <strong>of</strong> about - 70 m during glacial times, the<br />
whole carbonatic sequence <strong>of</strong> J<strong>of</strong>ane limestones could have been influenced by calcite dissolution.<br />
In the past there must have been some local lime production judging from the name <strong>of</strong> a village "Fornos" (furnaces) in<br />
the centre <strong>of</strong> the limestone area. The area has not been investigated in terms <strong>of</strong> its potential for cement and lime<br />
production. Few analyses were made <strong>of</strong> surface samples from these localities (Campos, 1961): %<br />
% Massinga Mabote Macovane Vilanculos<br />
SiO2 0.82 0.81 1.09 0.47<br />
Fe2O3 0.27 0.07 0.04 0.30<br />
Al2O3 0.11 0.17 0.22 0.22<br />
CaO 52.12 55.46 54.94 54.24<br />
MgO 0.36 0.06 0.17 1.10<br />
L.i. 43.32 43.43 43.54 43.67<br />
The sample <strong>of</strong> Mabote (on the parallel 20°S) is probably lacustrine limestone.<br />
Lächelt (1985) analyzed 9 samples <strong>of</strong> white, yellowish and rose limestones from Vilanculos:<br />
Samples 33DP 43DP 143DP 143C 23G 238B 18G 132C 15DP 20G<br />
CaO % 53.65 53.65 55.27 51.24 54.43 54.32 53.26 53.42 18.42 52.25<br />
MgO tr. tr. tr. tr. tr. - tr. - 12.51 tr.<br />
SiO2 1.76 2.26 0.63 5.21 1.00 0.76 1.92 1.44 36.80 4.05<br />
Fe2O3+Al2O3 1.15 0.91 0.31 2.35 1.18 1.15 1.48 1.51 0.90 1.47<br />
P2O5 - tr. tr. tr. tr. 0.02 0.02 tr. tr. tr.<br />
SO3 - tr. tr. tr. tr. 0.02 0.02 tr. tr. tr.<br />
Reserves were not calculated, but from the surface area <strong>of</strong> limestone (8,000 km2), the resources for cement and lime<br />
production and agriculture can be estimated to be 1,120 million tons.<br />
In the vicinity <strong>of</strong> the Nacala port, Pliocene - Pleistocene coral limestones from a raised coral platform, 5-10 m above<br />
sea level, are used and mixed with clays <strong>of</strong> Cretaceous age near the boundary <strong>of</strong> crystalline rocks. A cement factory at<br />
Nacala is quarrying coral limestone, thickness about 15 m, from the E- part <strong>of</strong> the Nacala peninsula, and clay <strong>of</strong> the<br />
Nacala bay (Fig. 4.9.5).<br />
A coral limestone deposit is at Relanzapo, clays are available from two localities: Quissimanlujo from Tertiary clays<br />
and Natimanga (Cretaceous).<br />
Average analyses, K. Legelt:<br />
1 surface layer<br />
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Cilek: 4.9 Limestone and dolomitic limestone<br />
2 coral limestone loose (Relanzapo )<br />
3 coral limestone compact (Relanzapo )<br />
4 control analyses <strong>of</strong> Relanzapo limestones<br />
5 clays from Quissimajulo (Tertiary)<br />
6 clays from Natimanga (Cretaceous)<br />
1 (n=2) 2 (n=16) 3 (n=3) 4 (n=7) 5 (n=15) 6 (n=55)<br />
SiO2 2.53 0.79 0.94 0.61 59.17 63.92<br />
Al2O3 1.46 1.65 1.15 1.55 12.73 12.58<br />
Fe2O3 1.40 1.15 1.33 0.57 4.84 3.10<br />
FeO 0.94 0.52 0.53 0.12 0.72 0.69<br />
CaO 53.25 50.07 50.53 49.34 6.93 2.66<br />
Na2O 0.26 0.32 0.17 0.47 1.20 2.01<br />
K2O 0.05 0.06 0.05 0.03 2.35 3.78<br />
SO3 - 1.11 - 0.22 0.001 1.65<br />
P2O5 - 0.06 - 0.09 0.06 0.16<br />
L.i. - 43.58 - 43.48 11.66 8.70<br />
SUM - 99.31 - 96.48 99.66 99.25<br />
CaCO3 95.32 90.31 90.44 88.07<br />
Fig. 4.9.5. Cross section <strong>of</strong> area Nacala port (Cilek, 1987)<br />
Fig. 4.9.6. Schematic cross section illustrating the facies changes in the Fingoe Group (Hunting, 1984)(375 kB)<br />
Miocene calcarenites (loose limestone composed <strong>of</strong> small fragments) were investigated for possible lime production<br />
W <strong>of</strong> Pemba. The thickness is about 2-3 m, with underlying Cretaceous beds <strong>of</strong> Megatrigonia Schwartzi. Two<br />
localities checked were - locality B with calcitic rocks <strong>of</strong> 78-80% CaCO3 and 14-16% SiO2 without substantial<br />
reserves, and the locality Plantacao Pinto where, in the past, lime was produced in a local furnace. However reserves<br />
are too small to be <strong>of</strong> economic value for industrial production.<br />
The analyses presented below show the composition <strong>of</strong> these sandy limestones and indicate the risk <strong>of</strong> an inadequate<br />
preparation for an investigation <strong>of</strong> these common materials:<br />
% Locality B Locality Plantacao Pinto<br />
SiO2 14.14-23.31 10.37-21.72<br />
Al2O3 2.20-4.23 2.83-4.16<br />
Fe2O3 0.01-0.21 0.13-0.30<br />
CaO 38.46-45.34 41.18-48.47<br />
MgO 0.64-1.30 0.44-1.36<br />
SO3 0.01-0.06 0.00-0.06<br />
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Cilek: 4.9 Limestone and dolomitic limestone<br />
Na2O 0.48-0.98 0.40-1.00<br />
K2O 0.48-0.80 0.32-1.14<br />
R2O3 2.28-4.44 CO2 21.40-24.80<br />
R.l. 3.28-6.10 2.20-4.98<br />
L.i. 30.02-34.83 30.03-37.26<br />
CaCO3 68.45-80.70 73.50-86.60<br />
The quality <strong>of</strong> calcarenites is low, but suitable for a production <strong>of</strong> hydraulic lime.<br />
Crystalline limestones <strong>of</strong> the Chidue Group build whole ridges <strong>of</strong> saccharoid marble around Chidue and Massamba,<br />
with a grain size <strong>of</strong> 0.8-4.0 mm, with calcite dominated by dolomite. Fine-grained quartz and green fibrous aggregates<br />
<strong>of</strong> malachite are present in some carbonates thus forming a nice ornamental rock. In the neighbouring Fingoe<br />
Formation, numerous small lenses or larger masses <strong>of</strong> crystalline limestones originated at different structural levels<br />
(see Fig. 4.9.6).<br />
Included in the Chidue Group is also the area <strong>of</strong> Monte Muande situated NW <strong>of</strong> Tete on the N bank <strong>of</strong> the river<br />
Zambezi. The same geological structure continues in the Monte Fema area S <strong>of</strong> the river. The whole region is known<br />
for its uranium mineralization, with centres at Mavudzi and Chacocoma. Mineralized zones are concentrated just in<br />
the Chidue contact zone <strong>of</strong> carbonate rocks with Tete gabbro and the norite complex. Davidite or mavudzite mined in<br />
the Mavudzi mine occurs in calc-quartz veins in shear zones. The crystalline limestones <strong>of</strong> Chidue are also bearers <strong>of</strong><br />
tungsten, rare earths, copper and gold mineralizations.<br />
On Monte Muande, thorium anomalies were discovered by Hunting (1984). However, the locality is known as a<br />
deposit <strong>of</strong> iron and apatite (see Chapt. phosphates), and therefore, carbonate rocks only are described below.<br />
Marbles <strong>of</strong> Muande vary in thickness in a range <strong>of</strong> several hundred m (500 m and more) and can be divided in biotite<br />
marbles and magnetite-bearing marbles.<br />
Biotite marble with apatite contains 36.60% calcite, 18.30% dolomite, 26.70 biotite, 14.70% apatite and 3.70%<br />
metallic minerals. Another variety <strong>of</strong> dolomitic-calcitic marble is composed <strong>of</strong> 69.50% calcite, 16.90% dolomite,<br />
0.40% magnetite, 11.60% apatite, 0.50% quartz and 1.10% orthite (Geol. Inst., Beograd, 1984).<br />
The crystalline limestones <strong>of</strong> the Barue Formation in S<strong>of</strong>ala and the Manica Provinces around Canxixe and<br />
Maringue were investigated by the Geol. Inst., Beograd (1984). In samples from the NW part <strong>of</strong> the area large lenses<br />
<strong>of</strong> coarse granular marble contained calcite grains up to 5 mm, forsterite, muscovite, quartz and metallic minerals.<br />
Two types were analysed - 1) pure calcitic marble - 2) impure marble with about 30% <strong>of</strong> quartz, muscovite and<br />
feldspar (between Canxixe-Mtene).<br />
Sample 1 2<br />
SiO2 % 0.02 26.68<br />
TiO2 0.02 0.05<br />
Al2O3 0.03 6.19<br />
Fe2O3 0.27 1.12<br />
FeO - -<br />
MnO 0.05 0.03<br />
MgO 0.31 1.00<br />
CaO 56.20 34.77<br />
P2O5 0.05 0.13<br />
L.i. 43.15 28.78<br />
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Cilek: 4.9 Limestone and dolomitic limestone<br />
Very pure limestones were detected in the northern part near Buzua (Geol. Inst. Beograd):<br />
Samples 154 053 057 209 211/1<br />
SiO2 0.89 0.37 0.02 2.53 1.13<br />
Al2O3 0.24 0.23 0.03 0.45 0.56<br />
Fe2O3 0.65 0.19 0.27 0.26 0.51<br />
CaO 53.84 55.24 56.20 54.12 49.63<br />
MgO 1.24 0.41 0.31 0.35 2.52<br />
TiO2 0.02 0.04 0.02 0.02 0.04<br />
P2O5 0.06 0.10 0.05 0.01 0.06<br />
MnO 0.01 0.01 0.05 0.05 0.01<br />
CO2+H2O+ 43.35 43.14 43.14 41.87 41.32<br />
Total 100.03 99.73 100.09 99.66 95.78<br />
% X-ray fluorescence <strong>of</strong> Sample 209: 10 ppm Nb2O5, 20 ppm Rb2O, 15 ppm Ta2O5 30 ppm Cs2O.<br />
The limestones are very pure with MgO + Fe2O3 content 0.4-0.5% and may be used in the glass industry (some<br />
bands), cement and lime production and as a metallurgical grade.<br />
Small sites <strong>of</strong> an occurrence <strong>of</strong> crystalline limestone were found at Angonia, in the Ulongoe metallogenic zone in<br />
which marbles coincide with the W graphite zones (see Chap. graphite). The locality is named Fornos and remnants<br />
<strong>of</strong> old lime furnaces confirm the use <strong>of</strong> marble by the local population.<br />
The marbles at Chire in the Zambezian Province E <strong>of</strong> the Malawian border were and still are used in a production <strong>of</strong><br />
lime for saturation in sugar refineries. The lime furnace is situated between the towns <strong>of</strong> Chire and Marire and utilizes<br />
several small marble lenses, 35 to 50m thick.<br />
In the surroundings are about 22 major bodies <strong>of</strong> marbles <strong>of</strong> which several had been investigated by a Russian team in<br />
connection with a possible utilization <strong>of</strong> nepheline syenite in the alumina production (Barmine, Tveriankine, 1982).<br />
The marbles are from 0.5 to 300 m thick, greatly variable in their composition, in conformity to both biotitic and<br />
granitic gneisses and quartzites in their vicinity.<br />
Marbles are commonly dolomitized with a MgO content ranging between 0.25 and 20.56% (dolomites) always with<br />
quartz, muscovite, biotite, hornblende, feldspar and graphite. Some sections are iron -impregnated up to 25% <strong>of</strong> their<br />
content. Two bigger deposits - Monte Chifuso and Bonesse, both in the area <strong>of</strong> Amosse were selected for a detailed<br />
investigation.<br />
The deposit Chifuso is a ridge <strong>of</strong> NNE direction, dipping E, 3 km long and maximally 300 m thick. It contains light,<br />
reddish and greyish calcite, fine graphite, biotite, quartz, feldspar, with lenses <strong>of</strong> biotite gneiss, 0.4 to 0.5 m thick with<br />
gradual changes in the phases. Locally, it is cut by dolerite dykes <strong>of</strong> 1 m thickness. The Bonesse marble is similar, it<br />
contains lenses <strong>of</strong> gneisses and quartzites.<br />
Composition % SiO2 CaO MgO Fe2O3 FeO CaCO3 MgCO3<br />
Chifuso<br />
(34 samples)<br />
Bonesse<br />
(6 samples)<br />
min 0.16<br />
max 15.6<br />
avg 3.43<br />
min 2.58<br />
max 5.44<br />
42.63<br />
54.42<br />
50.26<br />
26.78<br />
44.95<br />
0.55<br />
4.84<br />
1.62<br />
5.64<br />
20.32<br />
0.07<br />
2.77<br />
0.35<br />
0.18<br />
0.78<br />
0.1<br />
1.65<br />
0.42<br />
0.14<br />
1.22<br />
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76.07<br />
97.13<br />
89.76<br />
47.96<br />
80.22<br />
1.36<br />
12.1<br />
4.03<br />
14.0<br />
50.42<br />
Fe2O3<br />
total<br />
0.18<br />
4.21<br />
0.82<br />
0.67<br />
1.79
Cilek: 4.9 Limestone and dolomitic limestone<br />
avg<br />
4.21 36.58 12.84 0.46 0.54 65.31 31.85 1.06<br />
Although these marbles do not answer the requirements for alumina production which are CaO minimum 53%, SiO2<br />
maximum 2%, MgO maximum 1% and Fe2O3 maximum 0.6%; they may <strong>of</strong> course, be used in the production <strong>of</strong> lime<br />
or cement.<br />
In the Monapo structure, the Evate deposits <strong>of</strong> iron and apatite were investigated. Both economic minerals are present<br />
in crystalline limestone layers, which constitute about 70% <strong>of</strong> the deposit. The thickness <strong>of</strong> mineralized marbles is 5<br />
to 100 m. In the area is a small quarry, which extracts pure marbles for the production <strong>of</strong> lime in a furnace. The<br />
content <strong>of</strong> CaO in marbles varies from 20 to 55% (average 35-45%) while the MgO content is regular in all types <strong>of</strong><br />
rocks, in marbles 2.5-4.5%, in impure marbles even up to 22.7%. The reserves <strong>of</strong> marble are big, and certainly several<br />
times higher than the calculated reserves <strong>of</strong> 125 million t <strong>of</strong> apatite ore.<br />
Large areas with marble were discovered around and N <strong>of</strong> the river Lurio. The Namapa and Monote Formations<br />
around the mouth <strong>of</strong> the river Lurio contain many lenses <strong>of</strong> white and grey marbles with phlogopite and graphite;<br />
whitish marbles are mapped in the Metoro Formation around Jocolo belts: length 5 to 15 km, width 400-500 m.<br />
In the vicinity <strong>of</strong> Chiure, about 25 km N <strong>of</strong> the river Lurio, there are several older marble quarries.<br />
The marbles <strong>of</strong> Montepuez are extracted as ornamental stone. The waste <strong>of</strong> this production, together with an<br />
utilization <strong>of</strong> many other sites <strong>of</strong> marble occurrence in the whole region may serve as a base for lime and cement<br />
production. However, it ought to be considered that coral limestones <strong>of</strong> Pemba on the coast are a better and<br />
economically more feasible material than hard and <strong>of</strong>ten impure crystalline limestones.<br />
For the landlocked Niassa Province there is no other way than to use the local crystalline limestones in lime<br />
production. Jourdan and Paulis (1979) investigated the marble deposit <strong>of</strong> Malula 50 km N <strong>of</strong> Lichinga. The first<br />
utilization <strong>of</strong> this marble was in lime furnaces before World War 1 and it is believed that it was used by the local<br />
population many centuries ago. Five furnaces were still in production in the fifties and lime was used in mortars and<br />
tints. The Malula marbles are very variable in composition, with lenses and layers <strong>of</strong> phyllites, gneisses and graphite.<br />
Some are <strong>of</strong> a breccia structure with grains <strong>of</strong> dolomite and calcite as a result <strong>of</strong> a "solution and collapse" genesis<br />
(Fig. 4.9.7).<br />
The reserves are these:<br />
E - deposit with CaO content over 50% 32,880 000 t<br />
W- deposit with CaO content 46-55% about 10,000000 t<br />
Fig. 4.9.7. Geological map <strong>of</strong> limestone deposit Malula-Niassa Province (Jourdan-Paulis, 1979) (374 kB)<br />
Reserves were not calculated for the NE part, containing low-quality limestone with 20-27% CaO content.<br />
The authors divided carbonate rocks into grades:<br />
limestone 0.0 - 1.1 %MgO<br />
magnesium limestone 1.1 - 2.1 %MgO<br />
dolomitic limestone 2.1 - 10.8 %MgO<br />
calcitic dolomite 10.8 - 19.5 %MgO<br />
dolomite 19.5 - 21.6 % MgO (one sample)<br />
Chemical analysis <strong>of</strong> selected samples (in %) (total <strong>of</strong> 73 samples):<br />
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Cilek: 4.9 Limestone and dolomitic limestone<br />
Type <strong>of</strong><br />
rock<br />
Sample SiO2 Al2O3 Fe2O3 CaO MgO L.i. R.I. CO2<br />
37 1.1 1.1 0.1 55.3 0.8 41.6 1.2 32.2<br />
limestone<br />
38<br />
39<br />
1.1<br />
1.4<br />
1.5<br />
1.6<br />
0.5<br />
0.1<br />
54.5<br />
54.5<br />
0.7<br />
0.8<br />
42.1<br />
41.2<br />
0.5<br />
0.2<br />
32.3<br />
33.0<br />
40 0.9 0.6 0.1 55.1 0.5 40.4 0.1 32.7<br />
magnesium 32 0.8 0.7 0.2 54.6 1.2 42.7 0.4 31.8<br />
limestone 33 1.5 1.8 0.2 54.1 1.2 41.2 0.3 33.1<br />
dolomitic 19 5.0 1.8 0.4 44.2 8.3 41.6 0.6 32.1<br />
20 1.8 1.7 0.3 53.1 4.2 42.5 0.5 32.6<br />
limestone 21 2.4 1.4 0.3 48.6 6.5 37.1 0.9 29.9<br />
calcitic 1 1.3 1.3 0.5 34.0 18.9 44.9 0.3 32.4<br />
2 2.5 3.8 0.4 35.0 17.8 43.4 7.8 31.9<br />
dolomite 3 1.6 2.8 0.4 39.0 13.3 43.1 7.6 32.3<br />
dolomite 58 0.6 1.2 0.1 32.7 20.9 46.1 0.7 32.7<br />
Some portion <strong>of</strong> the Malula carbonate rock may be used as dolomites in refractory products. Its major use is in the<br />
production <strong>of</strong> hydraulic lime and cement.<br />
The last group <strong>of</strong> calcium carbonate rocks are carbonatites. On Monte Xiluvo, a carbonatite massif, a big quarry has<br />
been in operation for many years; it produces crushed stone for aggregates and other building purposes.<br />
Results <strong>of</strong> tests and analyses <strong>of</strong> carbonatite (Cilek, 1987) in %:<br />
Sample SiO2 Al2O3 Fe2O3 FeO CaO Na2O K2O P2O5 SO3 L.i. CaCO3<br />
1. 17.86 2.29 5.00 2.76 35.23 1.23 1.25 3.60 0.95 25.15 62.89<br />
2. 4.15 2.42 4.00 2.32 36.86 0.05 0.04
Cilek: 4.9 Limestone and dolomitic limestone<br />
The carbonatites contain phosphorus and rare earths in small quantities. If these minerals were to be mined<br />
economically, calcitic waste could be used in cement production, e. g., as a high calcium carbonate correction <strong>of</strong><br />
marbles <strong>of</strong> the Fingoe Formation for example.<br />
Conclusions:<br />
Limestones and marls <strong>of</strong> sedimentary origin should cover the entire demands for calcium carbonate both in a<br />
production <strong>of</strong> cement and lime, and in other industrial branches such as ceramics and glass. Very pure limestones<br />
occur in the Cheringoma and J<strong>of</strong>fane Formations and should be used as filler in paper, plastics, rubber, foodstuff,<br />
paint, in ultrafine ground products.<br />
Estimated reserves are thousands million tons. Additional large reserves exist in coral limestones along the shore.<br />
Crystalline limestones can be used in a local production <strong>of</strong> lime as this was done in the past, and utilized locally in the<br />
cement production; some <strong>of</strong> it may be used even in the ceramic and glass industry and small portion as a source <strong>of</strong><br />
magnesium.<br />
© Václav Cílek 1989<br />
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Cilek: 5. DEPOSITS and INDUSTRIAL USE <strong>of</strong> building raw materials<br />
5. DEPOSITS and INDUSTRIAL USE <strong>of</strong> building raw materials<br />
Undoubtedly building materials are essential for every country. They are bulk materials, cheep and<br />
locally used. The degree <strong>of</strong> production and industrial utilization <strong>of</strong> these materials points directly to the<br />
state <strong>of</strong> development <strong>of</strong> the national economy. Developing countries with an undeveloped utilization <strong>of</strong><br />
building materials, despite the high amount <strong>of</strong> extracting industry in ores, demonstrate clearly the<br />
industrial backwardness, low cultural development and colonial dependence.<br />
In <strong>Mozambique</strong>, the building industry was quite well developed even before the independence in 1975.<br />
The country was able both to construct big, modern cities and villages and an adequate system <strong>of</strong> roads<br />
and railway lines. In spite <strong>of</strong> this a typical colonial policy surfaced several times. A good example is the<br />
ceramic factory at Umbeluzi, supplied with ceramic mass from Portugal, or the import <strong>of</strong> marble slabs<br />
and blocks from different European countries despite an availability <strong>of</strong> these materials in <strong>Mozambique</strong>.<br />
On the other hand, several plants were established for an extraction <strong>of</strong> building materials, a number <strong>of</strong><br />
big and small quarries flourished in the vicinity <strong>of</strong> towns, along the roads and railways, small sand pits<br />
were everywhere, and sand and crushed stone were the main materials in concrete. The utilization <strong>of</strong><br />
gravel was scarce and so was the use <strong>of</strong> lime in mortar and, generally, in the construction industry.<br />
Three cement factories served the needs <strong>of</strong> some provinces, a number <strong>of</strong> small and big brick factories<br />
near the towns served the population, and small indigenous furnaces near limestone deposits produced<br />
lime since time immemorial. As an example I should like to present a short extract from a book by J.<br />
Romero (1860) in which he describes the coastal zone <strong>of</strong> Cabo Delgado Province:<br />
"On the seashore there are numerous quarries, also on the islands, and the building stone is used in the<br />
construction <strong>of</strong> houses and lime production. Vila do Ibo is extracting large quantity <strong>of</strong> rock for lime both<br />
for the population and the government. Near Pemba, grey massive rock is extracted. In different places<br />
exist more than 140 workshops for pottery, and 27 furnaces for lime production. The manufacture <strong>of</strong><br />
very good quality bricks and tiles is common. For the Governor at Ibo, the house was built and 1,200<br />
barrels <strong>of</strong> lime were supplied ...."<br />
The construction <strong>of</strong> modern cities, small towns and villages, private houses and villas, naturally for the<br />
Portuguese "colons" mainly, all this was possible because <strong>of</strong> an adequate extracting industry <strong>of</strong> building<br />
raw materials.<br />
The raw materials used were these:<br />
1. materials for cement and lime production<br />
2. materials for brick production<br />
3. resources and production <strong>of</strong> building stone<br />
4. resources <strong>of</strong> sand and gravel<br />
© Václav Cílek 1989<br />
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Cilek: 5.1.Raw materials for cement and lime production<br />
5.1. Raw materials for cement and lime production<br />
The term <strong>of</strong> cement raw materials includes various natural and artificial materials, suitable for cement production.<br />
Cements are a powdery material, which when mixed with water hardens in the air or below the water. Several types <strong>of</strong> cements<br />
can be distinquished on the basis <strong>of</strong> their mineralogical composition: silicate, aluminous, portland (slag and blast-furnace<br />
subtypes), pozzolan, white and lime cements.<br />
Cement is produced from a mixture <strong>of</strong> raw materials ground to powder (10-15% remain on the sieve 4,900 openings/cm2), either<br />
in the form <strong>of</strong> dense mud (an older, so-called wet process <strong>of</strong> cement production) or dry (dry process, most modern because it<br />
saves energy). The grinded material is burned in a furnace at a sintering temperature <strong>of</strong> 1,400-1,450°C to a product known as<br />
clinker, which is ground, mixed with additional materials (mainly gypsum) and bagged.<br />
In the furnace, chemical reactions occur between the main components (usually 80% <strong>of</strong> lime, 20% <strong>of</strong> clay) <strong>of</strong> SiO2, Al2O3,<br />
Fe2O3, CaO and new minerals originate: tricalcium silicate about 50%, dicalcium silicate about 25%, tricalcium aluminate about<br />
10%, tetracalcium alumin<strong>of</strong>errite about 15%, and other minerals in small amount.<br />
The raw material for cement production must contain all components needed in the composition <strong>of</strong> clinkers mentioned above and<br />
besides these other compounds are present - FeO, TiO2, MgO, SrO, Na2O, K2O, P2O5, CO2, SO3. Some <strong>of</strong> these components<br />
are harmfull and must be limited (MgO maximum 5%, P2O5 up to 2%, K2O + Na2O up to 0.5%, heavy metals etc.).<br />
The main components <strong>of</strong> cement CaO, Fe2O3, Al2O3, SiO2 must be present in a certain amount and at a reciprocal ratio<br />
expressed by cement moduli:<br />
1 Hydraulic modulus = CaO /(SiO2 + Al2O3 + Fe2O3) good quality cement has 1.7-2.3<br />
2 Silicate modulus = SiO2 /(Al2O3 + Fe2O3) good quality cement has 1.8-3.3<br />
3 Alumina modulus = Al2O3 / Fe2O3 this ratio lies between 1.5-2.5, but may reach even 12 in quick hardened cements.<br />
By burning the cement mixture, all CaO must be converted into silicate and alumina compounds, because free CaO in cement<br />
causes a volume instability.<br />
The content <strong>of</strong> CaO is controlled by the lime saturation factor "LSF" which can be expressed by the formula<br />
100 CaO / (2.8 SiO2 + 1.18 Al2O3 + 0.65 Fe2O3)<br />
and should be 85-100 after Lea-Parker.<br />
LSF is also calculated using the formula suggested by Kind-Jung<br />
[CaO - (1.65 Al2O3 + 0.35 Fe2O3 + 0.7 SiO2)] / (2.8 SiO2)<br />
which should be 0.92-0.95.<br />
Natural raw materials rarely correspond to these moduli (some clayey or marly limestones) and, therefore, the mixtures must be<br />
prepared from several components. One component is known as the "basic" one, usually limestone, the remaining are called<br />
"corrective" as for example, clay, shale, soil, quartz sand, bauxite, pyrite, slag etc. A corrective material could be also pure<br />
limestone, if marl or impure limestone were used as the basic material.<br />
General requirements for cement raw materials may vary from place to place and depend directly on the components locally<br />
available. Special grades <strong>of</strong> cement require also special corrective materials: for Portland cement, the content <strong>of</strong> MgO must be<br />
below 6%, the gypsum which is added to the clinker generally in 3-5% weight volume and serves as a retardant during the<br />
hardening <strong>of</strong> concrete, must be minimal, the physical properties <strong>of</strong> Portland cement concrete must be high and concrete must be<br />
resistant to aggressive solutions. Slag cements, using besides Portland clinker the slag <strong>of</strong> blast furnaces, must comply in the slag<br />
to the ratio (CaO + MgO) : (SiO2 + Al2O3) = 0.95; SO3 content maximum 3% etc. White cement mixed with raw kaolin to<br />
obtain the white colour, should contain maximally 2.0% MgCO3, 0.25% Fe2O3, 0.03% MnO and 1.5%SO3.<br />
In <strong>Mozambique</strong>, three cement factories, built before the indenpendence, were established in Matola near Maputo, at Dondo 30<br />
km from Beira and at the port <strong>of</strong> Nacala (see Fig. 5.1). All factories are situated near the sea ports and have railway links at the<br />
site, except Nacala. The Matola cement factory operated originally three furnaces on the wet process, which were replaced in<br />
1973 by one furnace on the dry process, with a daily production <strong>of</strong> 2,000 t clinker i.e. 600,000 t <strong>of</strong> clinker a year. The Dondo<br />
cement factory is situated on the railway line from Beira to Harare and is equipped with one furnace <strong>of</strong> wet process, with a daily<br />
production <strong>of</strong> 1,000 t clinker i.e. 300,000 t <strong>of</strong> clinker a year. The Nacala cement factory is situated directly at the port, it is the<br />
smallest one using a semidry process with a daily production <strong>of</strong> 300 t <strong>of</strong> clinker, i.e. 90,000 t annually.<br />
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Cilek: 5.1.Raw materials for cement and lime production<br />
The total capacity <strong>of</strong> clinker is 990,000 t, i.e. roughly 1 million t <strong>of</strong> the cement production capacity. The raw materials for the<br />
Matola factory are obtained mainly from the Salamanga limestone deposit, for the Dondo factory from the Muanza deposit and<br />
for the Nacala factory from the Nacala peninsula.<br />
Fig. 5.1. Cement and lime production localities (367 kB)<br />
The example is given <strong>of</strong> the composition <strong>of</strong> cement raw materials for Matola factory.<br />
Its components are these:<br />
limestone <strong>of</strong> Eocene age from the Salamanga deposit (85-87%)<br />
clay from the Boane deposit (5-6%)<br />
sand from the Umbeluzi river<br />
fly ash and slag from the Sonefe Power Plant (3-4%).<br />
The following data are presented by the Geol. Institute, Beograd (1985). Quality criteria for raw material composition are:<br />
CaO 38-40 %<br />
MgO > 3.2 %<br />
Na2O < 1.0%<br />
Cl < 0.04 %<br />
In 1981, in the last year <strong>of</strong> full information, the Salamanga limestone was analyzed with these results:<br />
Variation interval %<br />
x min. - x max.<br />
Mean composition %<br />
CaO 45.8-52.36 49.69<br />
SiO2 4.01-12.50 7.24<br />
Al2O3 0.51-1.91 1.00<br />
Fe2O3 0.92-1.84 1.19<br />
MgO 0.62-0.86 0.72<br />
The table shows a higher CaO content than required by standards and, therefore, limestone is mixed with other materials:<br />
Salamanga limestone has LSF 2.35 or 2.23, silicate modulus 3.31 and alumina modulus 0.84.<br />
In 1982, the limestone used in the Matola factory had this composition:<br />
average minimum maximum<br />
L.i. 37.34 36.31 37.87<br />
SiO2 9.97 5.28 12.09<br />
Al2O3 1.71 1.28 2.29<br />
Fe2O3 1.61 1.28 2.44<br />
CaO 47.07 45.64 50.96<br />
MgO 0.66 0.60 1.01<br />
Clay (C) composition and ash (A) composition (in %):<br />
average C average A minimum C minimum A maximum C maximum A<br />
L.i. 14.28 21.51 13.13 20.44 16.18 22.95<br />
SiO2 44.96 43.36 41.63 40.89 49.81 47.01<br />
Al2O3 18.23 19.27 16.70 17.46 21.16 20.39<br />
Fe2O3 13.95 4.11 12.06 3.87 16.04 4.27<br />
CaO 5.76 9.24 1,68 7.00 8.40 12.60<br />
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Cilek: 5.1.Raw materials for cement and lime production<br />
MgO 0.96 1.36 0.60 1.01 1.41 2.02<br />
SO3 - 0.69 - 0.32 - 1.19<br />
Sand composition from 1985 (in %):<br />
SiO2 78.64<br />
Al2O3 9.69<br />
Fe2O3 2.48<br />
CaO 0.56<br />
MgO 0.40<br />
L. i. 4.88<br />
The annual consumption <strong>of</strong> gypsum for all cement factories is about 40,000 t with a required SO3 content 41-43%. All gypsum<br />
is imported despite the fact, that huge reserves exist in the Temane Formation near Vilanculos. The last bulk <strong>of</strong> gypsum comes<br />
from the Palabora deposit in S-Africa, where it is a waste from phosphoric acid production.<br />
Gypsum composition (1986 import) (in %):<br />
SiO2 3.00 CaO 36.40 insolubles 2.39<br />
Al2O3 0.51 MgO 0.40 L. i. 12.25<br />
Fe2O3 0.16 SO3 46.37<br />
The cement factory at Nacala produces good-quality portland cement from a mixture <strong>of</strong> about 77.5% <strong>of</strong> limestone, 21% <strong>of</strong> clay<br />
and 1.5% <strong>of</strong> roasted imported pyrite (+ 5% <strong>of</strong> gypsum). The limestone is quarried at about 20 km E <strong>of</strong> the factory from<br />
Pleistocene coral limestone at Relanzapo, the clay, <strong>of</strong> the Cretaceous, from Natimanga, at about 10 km S <strong>of</strong> the factory or from<br />
Quissimanjulo S <strong>of</strong> Relanzapo. The silicate modulus is 2.33, that <strong>of</strong> alumina 1.54, lime saturation factor is 105.<br />
Average analyses show this composition (in %):<br />
Mixture Limestone Clay Pyrite Gypsum<br />
SiO2 12.51 2.59 50.24 3.40 0.7<br />
Al2O3 3.31 0.38 14.50 2.93 0.3<br />
Fe2O3 2.08 0.24 5.99 71.99 0.2<br />
CaO 42.28 52.08 10.64 1.96 33.0<br />
MgO 0.60 0.80 1.61 - 0.6<br />
H2O - - 7.00 13.19 43.97 SO3<br />
L.i. 35.60 42.87 13.22 - 14.7<br />
Total 96.38 98.96 102.72 93.47 93.47<br />
The lime produced in <strong>Mozambique</strong> is used just marginally in the building industry, in agriculture and mainly for saturation<br />
purposes in sugar cane factories.<br />
Two lime production units operate on an industrial basis -the biggest unit is established in the Dondo cement factory, where one<br />
rotary kiln for cement was reconstructed for lime production. The kiln is heated by oil and has an annual production capacity <strong>of</strong><br />
35-40,000 t <strong>of</strong> lime. The raw material is pure Cheringoma limestone. The whole production goes to the sugar factories and it is<br />
envisaged its export to Malavi and Zimbabwe.<br />
The second unit is at Salamanga, S <strong>of</strong> Maputo, with two vertical kilns electrically heated, with an annual production capacity <strong>of</strong><br />
9,000 t. The raw material is Satamanga limestone mined at the spot, and the production goes also to sugar factories in S<br />
<strong>Mozambique</strong>. The hydraulic modulus was calculated and its mean value is 3.49 which shows that the lime is highly hydraulic. A<br />
proposed production <strong>of</strong> hydraulic lime and its utilization for construction purposes could therefore be established just at<br />
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Cilek: 5.1.Raw materials for cement and lime production<br />
Salamanga.<br />
Review <strong>of</strong> lime production units in <strong>Mozambique</strong> (see also Fig 5.1):<br />
No Locality Province Company<br />
Installed<br />
capacity<br />
t/year<br />
1 Salamanga Maputo C. <strong>Mozambique</strong> 9,000<br />
2 Dondo S<strong>of</strong>ala C. <strong>Mozambique</strong> 40,000<br />
3 Buzi-Estaquinha S<strong>of</strong>ala Acucar Buzi 800<br />
4 Boroma Tete C. I. Tete 3,000<br />
5 Chire Zambezia C. I. Zambezia 2,000<br />
6 Corrane Nampula C. I. Nampula 800<br />
7 Pemba (7 km) Cabo Delgado Cooperativa 200<br />
8 Malulu Niassa C. I. Niassa 800<br />
Total annual lime production capacity 56,600 t<br />
Besides these lime furnaces operated on an <strong>of</strong>ficial basis, small local furnaces are used and operated in many areas with an<br />
occurrence <strong>of</strong> limestone. The localities are these:<br />
9 Morrumbene Imhambane, using J<strong>of</strong>ane Formation limestone<br />
10 Fornos Inhambane, in the centre <strong>of</strong> the J<strong>of</strong>ane Formation area<br />
11 Zamulanlomba Manica, crystalline limestone <strong>of</strong> Barué Formation<br />
12 Malona Manica, crystalline limestone <strong>of</strong> Barué Formation<br />
13 Muchanga Cado Delgado, Tertiary limestone<br />
14 Namuno Cabo Delgado, crystalline limestone<br />
© Václav Cílek 1989<br />
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Cilek: 5.2. Raw materials for brick production<br />
5.2. Raw materials for brick production<br />
These include all products <strong>of</strong> a natural decomposition <strong>of</strong> rocks which can be used in the brick production<br />
either in their natural state or after a necessary beneficiation.<br />
Brick materials are generally plastic and have the ability to be shaped into desired forms; they possess<br />
low sintering properties, burning below 1,100°C. Two main components in brickmaking materials can<br />
be distinguished-the plastic one and the nonplastic one. These two components may be present in<br />
desired proportions in natural clays, but usually the necessary blend must be prepared by adding either a<br />
plastic component (clay) or a nonplastic, opening component (sand, silt, ash, slag, fly ash etc.). The main<br />
brickmaking materials are clays and claystones, loam, marls, weathered schists etc.<br />
Harmful to the final products are calcitic concretions, fragments <strong>of</strong> rock, gypsum, siderite, organic<br />
matter etc.; can cause irregularites in the mass during the burning.<br />
Bricks are burnt at different temperature ranges - high temperature is used for a mass with a low alkali<br />
content, low iron content and high alumina and silica content, and hard-burnt products are obtained<br />
which can substitute even stone in buildings or roads pavements. The high content <strong>of</strong> alkalies, iron and<br />
organic substances may cause a premature melting <strong>of</strong> the brick and its deformation, and the burning<br />
temperature must be lowered. Unburnt bricks-adobe-are produced <strong>of</strong> brickloam, dried in the sun. Bricks<br />
have been used since time immemorial everywhere where stone was not available.<br />
Brick products fall into several groups:<br />
1 wall materials - bricks common, massive, holed, light-weight, thin-waited, vitrified, enameled etc.<br />
2 bricks and structural elements for chimneys<br />
3 ro<strong>of</strong>ing material-tiles<br />
4 ceiling structural units<br />
5 sewer pipes and drain tiles<br />
6 others - wall and floor tiles, paving bricks, crushed bricks etc.<br />
In <strong>Mozambique</strong>, as in many other countries, bricks are produced <strong>of</strong> different clays, loams and weathered<br />
natural materials such as lateritic clays, kaolinitic and illitic clays, alluvial clays and even clays <strong>of</strong><br />
swamps and mangrove soil. In S- <strong>Mozambique</strong>, many clayey raw materials contain a high proportion <strong>of</strong><br />
smectite from weathered Karroo volcanics and must be corrected by adding sand or ash, in the coastal<br />
zone <strong>of</strong>ten swamp deposits are used-which yield dark-grey organic clays <strong>of</strong> a very high plasticity. In<br />
higher elevated zones and within the crystalline rock zones, reddish lateritic clays are used <strong>of</strong> which<br />
good-quality bricks, tiles and pottery can be produced (see Fig. 5.2).<br />
In the past, many brick workshops and factories were built without any preliminary testing, by visual<br />
experience only, resulting in the production <strong>of</strong> low-quality bricks and tiles. When the production <strong>of</strong> lightweight<br />
bricks, holed bricks and tiles was started, the low quality <strong>of</strong> the raw material was reflected in a<br />
big amount <strong>of</strong> waste. In some brick factories waste is very high not just for the low quality <strong>of</strong> the raw<br />
material, but also for a lack <strong>of</strong> beneficiation <strong>of</strong> the material-diminishing the plasticity by using an<br />
opening material or by washing the clay to remove rock particles and sand to increase the plasticity.<br />
To supplement industrial brick products, small-scale brick units were established experimentally to be<br />
used by the population for building houses. Such experimental units using a mixer, shapper and a small<br />
kiln for 200 bricks have now been in production at Chimoio for several years.<br />
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Cilek: 5.2. Raw materials for brick production<br />
Fig. 5.2 Brick factories - locality map (303 kB)<br />
TABLE: Brick factories in <strong>Mozambique</strong> (340 kB)<br />
The total production capacity (planned or installed) <strong>of</strong> <strong>Mozambique</strong> in units (bricks, tiles, pipes) is about<br />
32 million, the recent or possible output is 10 million units less.<br />
The main products are bricks, usually holed, exceptionally massive, full. One brick factory produces<br />
also coloured pottery (Maholela), sewer pipes are produced in Maputo and Nampula. Other small brick<br />
factories are situated at Chokwe and Massingir in the Gaza Province, at Caia in the S<strong>of</strong>ala Province, at<br />
Moatize and Ulongue in the Tete Province and at Montepuez and Mueda in the Cabo Delgado Province,<br />
at Mocuba and Molocue in the Zambezia Province. How many other brick factories had been in<br />
production in the past is not known.<br />
Small pottery workshops using brick clay are scattered throughout the country, one is near Chimoio.<br />
The biggest accumulation <strong>of</strong> brick - and tile factories is naturally near Maputo, other factories are almost<br />
regularly distributed throughout other provinces in places <strong>of</strong> population concentration.<br />
© Václav Cílek 1989<br />
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Cilek: 5.3. Resources and production <strong>of</strong> building stone<br />
5.3. Resources and production <strong>of</strong> building stone<br />
Building stone is the most common building material used in two main fields, as a dimension stone and a crushed<br />
aggregate. According to the utilization and the degree <strong>of</strong> dressing, the grades <strong>of</strong> dimension stone are these:<br />
rough stone or quarry stone, not dressed<br />
stone for rough products - paving blocks, vergas, ashlar, kerbs and coarsely worked elements for construction<br />
cut stone products shaped into building plates, paving stones, covering plates etc.<br />
dimension stone for statues and monuments<br />
curtain-wall panels and slabs for special purposes<br />
The rock for dimension stone should be "sound", unweathered, resistant to mechanical effects and chemical<br />
corrosion, with a compression strength <strong>of</strong> 40-180 MPa, an absorption capacity below 5%, with a surface <strong>of</strong><br />
uniform composition. The requirements for each type <strong>of</strong> product have been established by standards.<br />
Crushed aggregate production is prevailing and in immense quantity when compared with dimension stone<br />
production. Crushed stone is handled in bulk and its value is low. The main cost <strong>of</strong> crushed stone is in the<br />
consumption <strong>of</strong> energy and transport charges. Therefore, the stone, besides toughness-resistance to impact,<br />
hardness-resistance to abrasion and soundness-resistance to climate and environmental impacts, should also easily<br />
be extracted with a dense network <strong>of</strong> cracks and joints and <strong>of</strong> appropriate hardness. Gabbro or amphibolite, for<br />
example, are expensive to crush when used for ordinary purposes, limestone or dolomite are s<strong>of</strong>ter and the energy<br />
consumption for crushing is low. Transport costs <strong>of</strong> a crushed aggregate are generally high and the transport<br />
distance should not exceed 50 km. Also the quarry capacity should not exceed the market needs within an<br />
economic transport distance, i. e. usually more than 1 million t per year. An exception are large railway quarries<br />
established at the railway lines, and using railway lines and railway trucks for a long-distance transportation <strong>of</strong><br />
crushed aggregate. Therefore modern crushing units are mobile or semimobile, with a capacity <strong>of</strong> several hundred<br />
t/hr and moving from place to place in accord with the demands <strong>of</strong> the market.<br />
Building stone includes all possible types <strong>of</strong> rock <strong>of</strong> appropriate properties: granites diorites, gabbrodiorites and<br />
gabbros, amphibolites, trachytes, basalts, phonolites, andesites, rhyolites, quartzites, limestones, dolomites,<br />
gneisses, sandstones etc.<br />
The best-quality dimension stones are fine - to medium - grained granites and their varieties <strong>of</strong> the igneous rock<br />
group, limestones <strong>of</strong> sedimentary rocks and marbles <strong>of</strong> the metamorphic group. Excellent mechanical properties<br />
when crushed display basalts, dolerites, trachytes and fine grained granites. A crushed aggregate should be<br />
replaced everywhere by a natural aggregate - sand and gravel, because the latter is almost 50% cheaper and <strong>of</strong>ten<br />
<strong>of</strong> a higher quality in concrete.<br />
The establishment <strong>of</strong> quarries for building stone is determined both by local consumption and geological and<br />
geomorphological conditions. In Africa, the best places for a quarry are usually inselbergs, which represent<br />
remnants <strong>of</strong> an older peneplain and are generally rocks <strong>of</strong> a higher resistance to weathering. Inselbergs are<br />
composed <strong>of</strong> granitic intrusion or their composition is identical to that <strong>of</strong> surrounding rocks. An overburden is<br />
nonexistent on steep slopes, the top is slightly weathered. Convenient places for quarries are also steep slopes <strong>of</strong><br />
lava flows and intrusive massifs <strong>of</strong> volcanic rocks. Dolerite dykes can form distinctive morphological ridges as<br />
well as quartzite beds.<br />
Young tectonic escarpments and surroundings <strong>of</strong> rift valleys <strong>of</strong>fer excellent examples <strong>of</strong> different rock outcrops<br />
and extraction <strong>of</strong> stone.<br />
In <strong>Mozambique</strong>, deposits <strong>of</strong> building stone are immense and every place <strong>of</strong> consumption could be supplied from<br />
quarries located nearby. An exception is coastal S-<strong>Mozambique</strong> made up <strong>of</strong> young sedimentary formations, where<br />
the only building stone is represented by s<strong>of</strong>t Tertiary limestone. A similar situation exist within the Zambezi<br />
delta, futher N the coastal belt is narrow with outcropping crystalline rocks close to it. Coral limestone-the<br />
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Cilek: 5.3. Resources and production <strong>of</strong> building stone<br />
principal building stone <strong>of</strong> old swahili towns-is present both on the seashore and the islands (see Fig. 5.3).<br />
Fig. 5.3. Building stone-quarries (according to the Ministry <strong>of</strong> Construction and Water) (395 kB)<br />
Many small and big quarries have been opened for a shorter or longer periods when even the need arouse. Few<br />
quarries are still in operation and several localities have been investigated to secure industrial reserves <strong>of</strong> building<br />
stones. Many are <strong>of</strong> ornamental stone quality, like the newly discovered labradorites at Moatize near Tete, black<br />
granites near Gondola and Lurio area, brown and red granites <strong>of</strong> the Tete Province and many others.<br />
It is impossible to present a complete lists <strong>of</strong> localities in <strong>Mozambique</strong> in which building stone occurs. The general<br />
review shows the distribution <strong>of</strong> the main rock types in the provinces:<br />
Province Type <strong>of</strong> rock Area Remarks<br />
Maputo<br />
Gaza<br />
Inhambane<br />
Manica<br />
S<strong>of</strong>ala<br />
rhyolites and basalts<br />
limestones<br />
red sandstones<br />
rhyolites and andesites, basalts<br />
limestones<br />
limestones<br />
beach rocks<br />
dirrerent magmatic and<br />
metamorphic rocks - granites,<br />
gabbros, diorites, gneisses,<br />
marbles, quartzites, schists<br />
sandstones <strong>of</strong> Karroo basalt,<br />
andesitic basalts<br />
dolerites and rhyolites<br />
dolerites, serpentinites, gabbro<br />
metamorphic and magmatic<br />
rocks<br />
<strong>of</strong> Archean (Vila Machado<br />
Formation)<br />
and Precambrian gneisses,<br />
anatexites, granites,<br />
quartzites and marbles, basalts<br />
and rhyolites,<br />
gabbro and syenites<br />
trachytes, limburgites and<br />
augitites<br />
carbonatite<br />
sandstones<br />
limestones<br />
Lebombo Mts.<br />
Salamanga and S Maputo-Ponta<br />
Vermelha<br />
Lebombo Mts.<br />
Mapulanguene and Massingir<br />
Rio Save-Vilanculos,<br />
Inhambane<br />
coastal zone<br />
the whole province<br />
northern part<br />
SE part <strong>of</strong> Chibabawa<br />
near Manica<br />
western and northwestern part<br />
along the rift valley<br />
Gorogosa massif<br />
margins <strong>of</strong> rift valley<br />
nearZambezi<br />
MonteXiluvo<br />
Sena Formation<br />
Cheringoma Formation<br />
near Buzi-Cheringoma plateau<br />
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also perlites, tuffs, tuffites,<br />
obsidian<br />
inferior quality,<br />
Pleistocene cemented sands<br />
Cretaceous<br />
Miocene J<strong>of</strong>ane Formation<br />
Quaternary sandstones<br />
concretional limestones<br />
Arhaic and Precambrian<br />
Karroo<br />
Karroo<br />
post-Karroo<br />
Karroo<br />
Post-Karroo<br />
Post-Cretaceous<br />
Cretaceous<br />
Tertiary
Cilek: 5.3. Resources and production <strong>of</strong> building stone<br />
Tete<br />
Zambézia<br />
Nampula<br />
Cabo<br />
Delgado<br />
Niassa<br />
big variety <strong>of</strong> rocks<br />
gabbro-anorthosites<br />
granitic gneisses, charnockites<br />
brown granites, labradorites<br />
serpentinites<br />
marbles and quartzites<br />
marbles<br />
alkaline lavas<br />
rhyolites and andesites<br />
carbonatites<br />
granites, gneisses, syenites<br />
nepheline syenites<br />
marbles<br />
quartzites, schists<br />
gneisses and granite-gneisses<br />
granites, charnockites,<br />
migmatites<br />
marbles, quartzites, schists<br />
amphibolites, serpentinites<br />
basalts and thoileites<br />
coral limestones<br />
granites, granite-gneisses<br />
migmatites<br />
gneisses<br />
marbles<br />
ultrabasic rocks and gabbroic<br />
massifs<br />
volcanic vents<br />
sandstones<br />
coral limestones<br />
granites, granite-gneisses<br />
red granites and syenites<br />
carbonatites<br />
charnockites<br />
marbles<br />
sandstones<br />
Tete Complex<br />
Angonia<br />
Monte Atchiza<br />
Fingoe Formation<br />
Chidue<br />
Bandur<br />
Tambara, Changara<br />
near E <strong>of</strong> Tete<br />
Cone Negose<br />
along the E margin<br />
<strong>of</strong> East-African<br />
Rift Valley<br />
coastal belt near Angoche<br />
on the coast<br />
Montepuéz and river Lúrio belt<br />
within S <strong>of</strong> Rovuma river<br />
Rovuma basin<br />
coastal belt<br />
degree <strong>of</strong> knowledge is low<br />
NE <strong>of</strong> Metangula<br />
Angonia, Fingoe<br />
arround Tete Complex<br />
Lubata on Zambezi river<br />
Lupata, L. Cretaceous<br />
Mid-Zambezi rift<br />
marbles also for<br />
lime production<br />
igneous massifs<br />
Precambrian, amphibolite and<br />
granulite facies,<br />
Jurassic-Cretaceous<br />
Pliocene-Holocene, old towns<br />
<strong>of</strong><br />
Mossuril and <strong>Mozambique</strong><br />
tectonic graben<br />
grits and conglomerates <strong>of</strong><br />
Cretaceous elevated coral<br />
platforms<br />
Holocene coastal and island<br />
reefs<br />
red granite near lake Niassa<br />
Karroo<br />
Quarries <strong>of</strong> building stone are scattered throught <strong>Mozambique</strong>. A few <strong>of</strong> these which are still in operation are<br />
marked in the attached map. Many other quarries around settlements, roads and railways have been abandoned, but<br />
could easily be reopened if the machinery were again newly installed.<br />
Typical is the situation in the Beira corridor where only two quarries, Xiluvo and Matsinho near Chimoio, operate.<br />
However, an other big railway quarry E <strong>of</strong> Matsinho called Garuzo could immediately be put into operation.<br />
In the following table, 26 localities are listed with an installed capacity <strong>of</strong> 1,625 m3/h representing an annual<br />
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Cilek: 5.3. Resources and production <strong>of</strong> building stone<br />
capacity <strong>of</strong> about 6 million m3. With the start <strong>of</strong> new construction projects, the geological situation <strong>of</strong> the country<br />
can easily secure an additional production <strong>of</strong> building stone close to the construction sites as this had been<br />
arranged in the past, for example, at the Cabora Bassa dam, a recently errected dam in the Little Lebombos Mts.<br />
near Maputo and others.<br />
Province Name Organization Capacity installed m3/h<br />
Maputo<br />
Estevel I.<br />
Estevel II.<br />
Movene I.<br />
M.C.A.Prosul<br />
Gaza Mabalane M.C.A.-C.I.G. 30<br />
Inhambane Unguana M.C.A.-C.I.I. 20<br />
120<br />
150<br />
45<br />
S<strong>of</strong>ala Xiluvo I.,II.,III. M.C.A.-Promoc 45 (100, 10 no production)<br />
Manica Chimoio M.C.A.-C.I.M. 45<br />
Zambezia<br />
Tete<br />
Nampula<br />
Cabo<br />
Naciaia Móvel M.C.A.-CETA 30<br />
Naciaia I. M.C.A.-CIZAM 20<br />
Naciaia II. M.C.A.-CIZAM 20<br />
Longoze M.C.A.-CETA 20 destroyed<br />
Longoze Movel M.C.A.-CETA 20 destroyed<br />
Mocuba M.C.A.-CETA 15<br />
Mocuba M.C.A.-C.I.S.-C.T. 50<br />
Gurué M.C.A.-C.I.S.-C.T. 50<br />
Mugulamo M.C.A.-C.I.S.-C.T. 70<br />
Alto Ligonha M.C.A.-C.I.S.-C.T. 70<br />
Revuboe M.C.A.-C.I.T. 50<br />
Aqua-Boa M.C.A.-CETA 10<br />
Aqua-Boa M.C.A.-CETA 30<br />
Ulonque M.C.A.-CETA 50<br />
Songo M.C.B. 350 for the Cabora Bassa dam<br />
Namialo CFM M.I.S.-C.F.M. 70<br />
Naguema M.C.A.-C.I.N. 30<br />
Barragem M.C.A.-C.I.N. 20<br />
Murrupula M.C.A.-CETA 30<br />
Km 50 (Pemba) M.C.A.-C.I.C.D. 50<br />
Montepuez M.C.A.-C.I.C.D. 10<br />
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Cilek: 5.3. Resources and production <strong>of</strong> building stone<br />
Delgado Mueda M.C.A.-TAMEGA 25<br />
Niassa<br />
© Václav Cílek 1989<br />
Bagarila M.C.A.-C.I.N. 50<br />
Cuamba M.C.A.-C.I.N. 30<br />
26 localities Total 1,625 m3/h<br />
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Cilek: 5.4. Resources <strong>of</strong> sand and gravel<br />
5.4. Resources <strong>of</strong> sand and gravel<br />
Among the world resources, both metallic and nonmetallic, the tonnage and value <strong>of</strong> sand and gravel highly outrank all other<br />
substances. Neither gold nor copper, neither diamonds nor iron ore, but common building sand and gravel <strong>of</strong> a value <strong>of</strong> 2.5-<br />
3.0 US $ per ton represent the biggest mineral value. Millions <strong>of</strong> tons are produced annually in every country with a<br />
developed industry and billions <strong>of</strong> dolars are spent on these materials. Gravel and sand are used in the building industry as a<br />
natural aggregate in the production <strong>of</strong> concrete (in a mixture with 10-15% <strong>of</strong> cement), drainage and road base layers,<br />
stabilization layers etc.<br />
Sand is a elastic sediment, grain size 0.063 to 2 mm, below is silt and clay, above it gravel. Sand is usually divided into three<br />
classes<br />
fine-grained 0.063-0.25 mm<br />
medium-grained 0.25-1.0 mm<br />
coarse-grained 1.0-2.0 mm.<br />
Sand is dominantly quartz with more or less feldspar, mica, silt and clay and rock fragments, well-sorted with different range<br />
<strong>of</strong> grain size. The grains <strong>of</strong> a sand body that had undergone a polycyclic development are always uniform, e. g., beach-sand<br />
deposits. River deposits, alluvial and terrace accumulation are less sorted, in the upper reaches <strong>of</strong> streams ill-sorted, in the<br />
lower reaches and matured rivers well-sorted. The genesis <strong>of</strong> sand is reflected in some typical features such as degree <strong>of</strong><br />
rounding, sphericity, surface-grain coatings, etc.<br />
By contrast, gravel, when compared with sand, is <strong>of</strong> a very variable composition, with grains and pebbles <strong>of</strong> different rocks<br />
reflecting the original geological environment - the source area. The granules <strong>of</strong> gravel have to be composed <strong>of</strong> sound<br />
resistant rocks, should be free <strong>of</strong> mica, clay, silt and flat grains and s<strong>of</strong>t rocks. Gravel varies in grain size from 2 to 128 mm<br />
and again can be divided in three classes:<br />
fine-grained gravel 2.0- 8.0 mm<br />
medium-grained 8.0- 32.0 mm<br />
coarse-grained 32.0-128.0 mm<br />
Gravel and sand are usually mixed together and according to the ratio gravel/sand these classes are distinguished (Kuzvart,<br />
1984):<br />
grain >2 mm 100% 50% 25% 0%<br />
gravel sandy gravel sand with gravel sand<br />
grain
Cilek: 5.4. Resources <strong>of</strong> sand and gravel<br />
In <strong>Mozambique</strong>, huge accumulations <strong>of</strong> building sand and gravel developed in the coastal zone: on beaches, in the dune belt<br />
and on the shelf. The development <strong>of</strong> sand-gravel deposits is connected with the geomorphological development <strong>of</strong> the<br />
African continent. Late Cretaceous - Mid Tertiary African land surface with a widespread and deep weathering crust<br />
supplied detritus to the basins until the Pliocene during the Post-African land surface phases. The Late-Tertiary, mainly post-<br />
Miocene movements connected with the Niassa-Shire rift and finally the Pleistocene upheaval (Cilek, 1985) caused the<br />
transport <strong>of</strong> huge detrital masses from the African interior by streams to the shore. It is estimated that from then to the<br />
present, the continent at the Limpopo paleodelta (Cilek, 1985) spread for about 80 km over the shelf. The main sand and<br />
gravel accumulations exceeding 1,000 m are present in the Limpopo paleodelta, the Zambezi river paleodelta - first from the<br />
area <strong>of</strong> the present mouth <strong>of</strong> the river Buzi, later from the Quelimane area and recently from the Zambezi mouth -and from<br />
several other rivers. During the Quaternary, from the Main Glacial period before about 100,000 years till the Last Glacial<br />
Period (18,000-10,000 years), the streams straightened their courses while the seawater table was lowering, cut deep into the<br />
floor depositing sand and gravel on the shelf far from the present seashore line. Several distinctive canyons on the shelf are<br />
in support <strong>of</strong> this development. During interglacial periods with a higher sea level, the rivers lost theirs transporting power,<br />
their mouths become chocked with sediments and rivers started to meander.<br />
The present river valleys are extremaly wide, the river Buzi has about 8 km width at Beira, the river Lurio 6 km and the river<br />
Zambezi has shallows in its lower reaches <strong>of</strong> several km and sand bars. The thickness <strong>of</strong> sand and gravel deposits in these<br />
old river valleys attains sometimes 50-70 m, the thickness on river terraces is not known.<br />
Subrecent and recent tectonic movements along the rift valley formed different sand and gravel accumulations in different<br />
zones <strong>of</strong> the stream. For example, the river Zambezi, when leaving the narrow pass at Lupata volcanics near Tambara,<br />
discharges coarse grained sediments and widens its bed. When reaching the delta proper, the stream is slow, the river bed<br />
narrow with several channels and only fine silt with a high amount <strong>of</strong> mica is deposited on the shelf. The mouth <strong>of</strong> some<br />
rivers is chocked and are flowing over long distances parallel to the shoreline before entering the sea. This phenomenon is<br />
due to a rising sea level and a diminishing stream gradient in the lower reaches. The Limpopo river forms wide alluvial flats<br />
<strong>of</strong> dark clay soil near its mouth; other rivers e. g. the Save, Buzi etc. are surrounded by mangrove swamps with clay deposits.<br />
Besides alluvial sand and gravel, huge reserves <strong>of</strong> sand are on the beach and in the dunes. These sands are generally wellsorted,<br />
grain size mostly 0.1-0.2 mm. Sand and gravel with a grain size <strong>of</strong> more than 2 mm are present at the mouth <strong>of</strong> rivers<br />
in which a sorting by sea energy had not yet taken place. Eolian sands occur either in recent or subrecent dunes in a belt near<br />
beach - these sands are white or grey contrary to interior dunes which are generally <strong>of</strong> a red colour and underwent<br />
weathering. Red-dune sands are slightly clayey and useable as a 'building sand in stabilization layers and for other purposes<br />
(some <strong>of</strong> these may be natural foundry sands), but cannot be used as a part <strong>of</strong> aggregate.<br />
Other sand and gravel accumulations occur in river terraces and in local geomorphological depressions - in East Africa<br />
known as mbuga basins - where layers <strong>of</strong> detrial sediments alternate with argillaceous beds.<br />
Generally, coastal <strong>Mozambique</strong> may provide inexhaustible reserves <strong>of</strong> sand and gravel, the interior <strong>of</strong> the country has<br />
substantial deposits <strong>of</strong> sand and gravel in alluvial deposits (many are auriferrous).<br />
Localities <strong>of</strong> gravel and sand in the provinces <strong>of</strong> <strong>Mozambique</strong>:<br />
Province Maputo: Rio Muira, Rio Umbeluzi, Rio Incomati, Goba, Marracuene and river terraces and coastal dunes<br />
Province Gaza:<br />
Chokwe, Massingir, Macia, interior dunes and river terraces along the river Save, J<strong>of</strong>ane,<br />
Madindze, Divinhe, Vilanculos, Nova Mambone, beach and dune sands<br />
Province Inhambane:<br />
along rivers Revue and others near Manica (with gold), Rio Muda, Pungoe, and tributaries <strong>of</strong> Rio<br />
Zambeze, Tambara, Dombe etc.<br />
Province Manica: Rio Zambeze and tributaries, Rio Pungoe and Save, Chemba, Caia, Marromeu<br />
Province S<strong>of</strong>ala:<br />
Rio Revuboe (with gold), depression at Rio Condedezi, weathered sandstones <strong>of</strong> Karroo and Post-<br />
Karroo<br />
Province Tete:<br />
Rio Zambeze, Licuare, Raraga, Ligonha, belt <strong>of</strong> coastal beach ridges and eotian sands at Quelimane<br />
- Pebane - Moebase<br />
Province Zambezia: Rio Lurio and tributaries, small sand bodies on the seashore, proluvial sands<br />
Province Nampula: Rio Lugenda and Rio Rovuma, small streams and beach deposits beach deposits<br />
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Cilek: 5.4. Resources <strong>of</strong> sand and gravel<br />
Province Cabo<br />
Delgado: Province<br />
Niassa:<br />
© Václav Cílek 1989<br />
on Lake Niassa, Rio Lugenda and Lurio, Karroo sediments near Metangula<br />
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Cilek: 6.1. Ceramic industry<br />
6. CERAMIC and GLASS INDUSTRY; REFRACTORIES<br />
6.1. Ceramic industry<br />
The group <strong>of</strong> ceramic raw materials for the production <strong>of</strong> white-ware ceramic products includes three components:<br />
quartz, feldspar, kaolin or clay. Other materials that can be added to the ceramic mass are limestone, dolomite,<br />
bentonite, etc. depending on the technology <strong>of</strong> production and on the required properties <strong>of</strong> the final product.<br />
The old practice using "classical" materials for the ceramic batch, i. e., a silica-alumina composition, has changed<br />
and more flux materials are used nowadays -illitic clays with dispersed iron, alkalic rocks <strong>of</strong> which nepheline syenite<br />
is a typical representative, tuffs, lithium compounds and more feldspar and limestone. This results in a shift from<br />
silicate ceramic mass to calc-silicate composition. An increased portion <strong>of</strong> Na2O, K2O, CaO and MgO in the batch<br />
reduces the content <strong>of</strong> Al2O3, and SiO2 - minerals which need high sintering temperature - which means a saving <strong>of</strong><br />
energy.<br />
The production <strong>of</strong> different ceramic products requires a large variety <strong>of</strong> ceramic mass composition:<br />
1. hard porcelain - sintering temperature 1,400-1,450°C composition: kaolin clay, ball clay, quartz, feldspar<br />
2. s<strong>of</strong>t porcelain - sintering temperature 1,250°C<br />
3. sanitary ware - sintering temperature 1,230°C<br />
4. earthenware - sintering temperature 800-950°C<br />
5. wall tiles - sintering temperature 1,050°C<br />
6. white floor tiles-sintering temperature 1,300°C<br />
The content <strong>of</strong> kaolin clay in group 1 is about 40-65%, in group 3 20-30% only. Ball clay or other ceramic clay<br />
amounts to 5-10% in hard porcelain and is increasing towards lower temperature sintering products. Quartz<br />
constitutes about 10-20% <strong>of</strong> the body, feldspar about 20-40% in groups 1, 2, 3 but has a reduced content in groups 4,<br />
5, 6. In the production <strong>of</strong> earthenware and tiles, dolomite and limestone are added in amounts ranging from several<br />
% to 15%.<br />
In fact, each ceramic factory uses different raw materials for different products and the mixture <strong>of</strong>ten depends on the<br />
availability <strong>of</strong> these materials in each particular country. However, basic requirements have to be observed such as<br />
SiO2 content, Al2O3 content and others - mainly coloured oxides, which may cause a colouring <strong>of</strong> the ceramic body<br />
after firing. The diagram shows relationships <strong>of</strong> different components (basic ones only) in different ceramic products<br />
(Fig. 6.1).<br />
Fig. 6.1 The composition <strong>of</strong> different ceramic products (88 kB)<br />
Several auxiliary materials in the ceramic industry include opacifiers in sanitary ware such as tin oxide, zircon,<br />
rutile, apatite and glazes in porcelain such as feldspar, dolomite, limestone, talc, wollastonite and several other<br />
synthetic ones. Another important auxiliary material is gypsum used in a preparation <strong>of</strong> moulds.<br />
In <strong>Mozambique</strong>, the only "pure" white ceramics, i. e., wall tiles and minor production <strong>of</strong> ceramic table-ware were<br />
produced by the Umbeluzi ceramic factory situated about 30 km W <strong>of</strong> Maputo. The factory "rarity" is in that it lacks<br />
a section for the preparation <strong>of</strong> the ceramic mixture, because it used a ready-made ceramic batch imported from<br />
Portugal.<br />
A recent investigation revealed different sites <strong>of</strong> an occurrence <strong>of</strong> ceramic materials in <strong>Mozambique</strong> which can be<br />
used in the ceramic body for wall tiles production (see Fig 6.2).<br />
Fig. 6.2. Map <strong>of</strong> raw materials for white ceramics (389 kB)<br />
Zuberec-Lacko-Novysedlak (1984) present the results <strong>of</strong> some tests made for the Umbeluzi factory. In 1981, the first<br />
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Cilek: 6.1. Ceramic industry<br />
bench test was made in Czechoslovakia with this mixture for wall tiles production:<br />
1. clay from Umbeluzi deposit near the factory - 30%<br />
2. limestone <strong>of</strong> Eocene age from Salamanga near Maputo - 20%<br />
3. kaolin from the pegmatite mine Muiane, Nampula Province - 13%<br />
4. kaolin - feldsphatic sand from Nacala, Nampula Province - 20%<br />
5. sand from Marracuene N <strong>of</strong> Maputo - 17%.<br />
The composition <strong>of</strong> the mixture was calculated on the basis <strong>of</strong> the content <strong>of</strong> 68% SiO2 and 10% Al2O3.<br />
Results <strong>of</strong> chemical tests <strong>of</strong> above materials:<br />
% SiO2 Fe2O3 Al2O3 CaO MgO TiO2 Na2O K2O<br />
1 76.17 1.22 12.93 0.61 0.66 0.18 0.30 2.30<br />
2 7.42 3.15 1.97 43.88 0.71 0.11 0.67 0.19<br />
3 61.17 5.94 16.22 0.70 1.36 1.36 1.26 2.14<br />
4 46.66 0.39 33.97 0.14 0.20 0.19 0.16 0.38<br />
5 97.78 0.03 0.16 0.08 0.01 0.17 0.16 0.20<br />
The bending strength after drying is 1.57 MPa, after 45 hours <strong>of</strong> burning at 1,200°C 16.7 MPa, shrinkage 0.80%,<br />
water absorption 24.7% and volume weight 1,611 kg/m3. The tiles are <strong>of</strong> a white, slightly greenish colour, with<br />
water absorption <strong>of</strong> 21.3%, volume weight 1,609 kg/m3 and bending strength 19.1 MPa. They represent a product <strong>of</strong><br />
good quality.<br />
The second bench test used a reduced number <strong>of</strong> raw materials in the ceramic body:<br />
1. clay from Umbeluzi - 39%<br />
2. kaolin - feldspathic sand from Nacala - 28%<br />
3. limestone <strong>of</strong> Salamanga - 18%<br />
4. sand from Marracuene - 15%.<br />
The same calculation and chemical analyses were made in Czechoslovakia:<br />
% L.i. SiO2 Al2O3 TiO2 Fe2O3 CaO MgO K2O Na2O<br />
1 7.56 61.80 16.57 1.16 7.20 1.68 1.31 1.68 0.89<br />
2 3.97 75.30 15.81 0.14 0.66 - 0.20 3.65 0.10<br />
3 41.0 7.25 1.27 0.10 1.50 47.95 0.25 0.34 0.23<br />
4 0.33 96.90 1.78 0.25 0.20 - 0.15 0.30 0.01<br />
The analysis <strong>of</strong> sintered ceramic mass has revealed 68.9% SiO2, 10.6% CaO and 12.8% Al2O3. The colour <strong>of</strong> tiles<br />
is red, due to a high content <strong>of</strong> iron from Umbeluzi clay. The sintering temperature must not surpass 1,050°C. The<br />
ceramic mass may be improved by adding 0.2% <strong>of</strong> soda ash and 0.1% <strong>of</strong> sodium silicate.<br />
The second test proved that tiles can be produced without kaolin from Muiane. However, a variation in the quality <strong>of</strong><br />
Umbeluzi clay may cause some problems in final products and the red colour body (at the level <strong>of</strong> brick or pottery<br />
quality) in wall tiles has to be covered up by a strong opacifier.<br />
© Václav Cílek 1989<br />
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Cilek: 6.2. Glass industry<br />
6.2. Glass industry<br />
Glass is made substantially by melting silica sand and fluxes in a glass-melting furnace. Batch materials<br />
for glass production are <strong>of</strong> a soda-lime-silica composition: pure silica sand as glass forming oxide, soda -<br />
Na2O as fluxing agent, lime - CaO or CaO + MgO as stabilizing material to provide chemical durability,<br />
Al2O3 and B2O3 as auxiliary materials for high strength and prevention <strong>of</strong> devitrification, and others -<br />
sulphur or sulphur oxides to improve melting and the refining process. Silica sand should be very pure<br />
(see chap. glass sand) with about 99% SiO2 and low in iron, alumina, chromium, titanium etc. Soda ash<br />
with Na2CO3 over 99%, with maximum 0.5% NaCl and 0.1% Fe2O3. Limestone content should have<br />
more than 54% CaO + MgO and maximally 0.1 % Fe2O3. Feldspar more than 19% Al2O3, alkalies<br />
more than 11%, and maximally 0.1 % Fe2O3.<br />
Soda ash produced in the Solvay process or from natural trona ore accounts for more than 50% <strong>of</strong> the<br />
cost <strong>of</strong> the raw material per ton <strong>of</strong> glass. Therefore, it is <strong>of</strong>ten substitued by cheaper materials such as<br />
nepheline syenite (potash feldspar and nepheline). The dissolution rate <strong>of</strong> silicate minerals in the glass<br />
melt depends on the ratio alkalies: silica and is in favour <strong>of</strong> nepheline with Na2O - SiO2 ratio 1: 2 which<br />
enables melting within 11 minutes at 1,350°C. When using albite, with Na2O - SiO2 ratio 1 : 6, melting<br />
requires 103 minutes at the same temperature.<br />
Other materials include aplite (Al2O3 more than 22%, Fe2O3 0.1-0.4%), sodium sulphate - salt cake<br />
(Na2SO4 more than 99%, NaCl 0.002%, Fe2O3 0.2%), gypsum and anhydrite, some decolouring and<br />
colouring agents etc.<br />
Part <strong>of</strong> the glass batch is broken glass - cullet (up to 35%) which melts at 800°C and, therefore, can<br />
accelerate the melting <strong>of</strong> the batch. All products <strong>of</strong> the glass batch must be 100% below 0.4 mm passing<br />
the 30 mesh screen.<br />
Fluxes are very important agents both in the glass and ceramic production because they<br />
a) facilitate reactions in the solid phase during sintering and hardening<br />
b) are a substantial part <strong>of</strong> the batch in glass production<br />
c) lower the energy consumption, the melting temperature, quicken the process <strong>of</strong> sintering and melting<br />
and enable to use shorter melting times.<br />
Modern fluxes include a number <strong>of</strong> raw materials:<br />
rocks with nepheline (perthite, nepheline)<br />
rocks with albite (higher SiO2)<br />
alkali-feldspar syenites (low-coloured oxides)<br />
rhyolites/phonolites: K2O/Na2O ratio = 7.5 - 51/0.6 - 0.7 only in coloured glass products<br />
wollastonite<br />
lithium minerals.<br />
An increased production <strong>of</strong> container glass, better, thinner and cheaper, fiber glass and foam glass (for<br />
insulating purposes) requires an increased use <strong>of</strong> cheap fluxes, represented by the above mentioned<br />
materials, <strong>of</strong> which the most used are nepheline syenite, phonolite, rhyolite, trachyte and Li-minerals.<br />
The production <strong>of</strong> the glass industry can be divided in these groups:<br />
1 Containers glass (bottles and jars)<br />
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Cilek: 6.2. Glass industry<br />
2 Pressed and blown glass (table, kitchen, art, novelty glass, lighting ware, glass fiber)<br />
3 Flat glass (sheet or window glass, plate, laminated, safety glass)<br />
In <strong>Mozambique</strong>, container glass only was produced, when its production started in the Machava glass<br />
factory in Maputo in 1957, with a daily production <strong>of</strong> 4 t. Later, the production increased to 59 t per day<br />
(1972) including an automatic production <strong>of</strong> transparent and coloured bottles (brown and green).<br />
Nowadays, a reconstruction is under way for a production <strong>of</strong> 125 t per day <strong>of</strong> glass containers. Apart<br />
from this, furnaces produce daily 20 t <strong>of</strong> container glass, pressed and blown glass (cups, plates, lighting<br />
ware etc.) <strong>of</strong> natural colour (the glass has a greenish tint) and coloured glass using colouring agents such<br />
as amber, sulphur, coal minerals or charcoal, sodium bisulphate, chromite etc.<br />
Composition <strong>of</strong> the batch:<br />
55-58% sand<br />
18-20% soda<br />
15-18% limestone<br />
5- 6% feldspar<br />
cutlet, auxiliary materials.<br />
Sand is extracted at Marracuene, but is not dressed, limestone comes from Salamanga. Both materials<br />
are at about 40 km from the factory. Feldspar is normally obtained from N-<strong>Mozambique</strong>, from Ribaue or<br />
Tulua: other materials are imported - soda, sodium sulphate, sodium nitrate, arsenic and cobalt oxide.<br />
The main problem in the production <strong>of</strong> glass is the use <strong>of</strong> natural sand from Marracuene and limestone<br />
from Salamanga, <strong>of</strong> this composition: %<br />
Sand Limestone<br />
SiO2 89.6 89.9 10.4<br />
Al2O3 5.3 6.2 3.6<br />
Fe2O3 0.7 0.7 1.1<br />
CaO 0.1 0.1 46.6<br />
MgO 0.1 0.1 0.5<br />
Na2O 0.2 0.2 -<br />
K2O 1.8 1.7 -<br />
Both sand and limestone have a high content <strong>of</strong> iron, limestone a low content <strong>of</strong> CaO and MgO. The<br />
quality <strong>of</strong> the glass batch could correspond to requirements <strong>of</strong> container glass, but barely to that <strong>of</strong><br />
pressed and blown glass. The dressing <strong>of</strong> sand and limestone would be necessary.<br />
© Václav Cílek 1989<br />
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Cilek: 6.3. Refractories<br />
6.3. Refractories<br />
Classification <strong>of</strong> refractory materials is based on their general composition and, to lesser degree, on the physical properties,<br />
which must be heat-resistant (minimum 1,500°C), thermal shock resistant-capable to withstand different ranges <strong>of</strong><br />
temperatures, resistant to mechanical stress and chemical attack.<br />
Refractory materials can be divided into three groups:<br />
1 Acid refractory clays or fire clays melting point °C<br />
kaolin - Al2O3, SiO2 1,785<br />
silica-SiO2, as quartz sand, crushed quartz, quartzite, diatomite 1,700-1,615<br />
2 Basic magnesia, MgO as magnesite 2,800<br />
lime-magnesia (CaO • MgO) from dolomite 2,370<br />
limestone CaO, CO2 2,485<br />
zirconium oxide ZrO2 2,700<br />
from zircon ZrO2, SiO2 2,303<br />
barium oxide BaO from baryte BaSO4 1,920<br />
3 Inert aluminium oxide Al2O3 2,050<br />
between acid silica - bauxite or sillimanite, andalusite<br />
basic magnesia kyanite, dumortierite<br />
chromium oxide Cr2O3 2,430<br />
chromite Cr2O3 • FeO 2,050<br />
graphite (no oxigen or air) 3,700<br />
In the past, fine clay and kaolin made up the bulk <strong>of</strong> refractories - aluminosilicate bricks, usually as a combination <strong>of</strong> flint<br />
refractory clay, some plastic clay and high-alumina clay or bauxite. These bricks were used in furnaces, boilers and for many<br />
other purposes. Modern high-alumina bricks <strong>of</strong> group 3 or alumina-silica refractories containing more than 50% <strong>of</strong> alumina<br />
consist predominantly <strong>of</strong> mullite (3 Al2O3 • 2 SiO2) crystals. The raw materials used are bauxite (Al(OH)3), diaspore (Al2O3<br />
• H2O), kyanite, sillimanite, andalusite (Al2O3 • SiO2) and fused and sintered alumina (Al2O3). There is a steady trend<br />
towards the use <strong>of</strong> high-alumina brick and tile to replace fire clay. These modern mullite products are used in rotary kilns in<br />
the production <strong>of</strong> cement and lime, ro<strong>of</strong> bricks for electric steel-melting furnaces, blast furnace lining and blast furnace stove<br />
bricks, ladle bricks and bricks for Al-melting furnaces.<br />
Basic bricks, mainly magnesia and chrome, are used for basic slags in metallurgical furnaces such as steel, nickel and copper,<br />
zirconia bricks as special refractories in electrical furnaces for refining precious metals.<br />
Silica bricks are acid bricks made mainly from ganister, a true quartzite, also from silica sand and diatomite. The bricks have<br />
the advantage <strong>of</strong> a common availability <strong>of</strong> the material and low price, they are resistant to the attack <strong>of</strong> iron oxides and have<br />
an excellent hot-load resistance at temperatures close to their melting point. They are still used in coke ovens, ceramic kilns<br />
and glass tank crowns, but minimally at present in electric furnaces for melting steel and ro<strong>of</strong> brick for open hearth, because<br />
<strong>of</strong> raised operating temperatures and a reduced open-hearths use. Silica bricks tend to crack when heated rapidly at low<br />
temperatures.<br />
Special refractories are produced by a combination <strong>of</strong> graphite, silica carbide, zircon, borides, nitrides etc. Insulating bricks<br />
capable to withstand high temperatures, and but retaining their insulating properties are produced by adding, for example,<br />
diatomite as a light-weight aggregate.<br />
Several other raw materials are used in the production <strong>of</strong> refractories. Talc <strong>of</strong> white colour, with a low content <strong>of</strong> coloured<br />
oxides, is used in a production <strong>of</strong> insulators <strong>of</strong> high voltage, sparking plugs and in ceramic masses. Dunite is a basic material<br />
in the production <strong>of</strong> forsterite, refractory material such as serpentinite.<br />
In <strong>Mozambique</strong>, refractory materials are used in cement and lime factories, in brick and ceramic factories, in metallurgy and<br />
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Cilek: 6.3. Refractories<br />
for steam boilers in power stations etc. Besides low-quality refractory materials are used in the production <strong>of</strong> small household<br />
appliances, linings <strong>of</strong> ovens and elsewhere in the building trade.<br />
Of the two production units in the country one is at Quelimane, one in Maputo. Both produce low-quality chamotte bricks and<br />
other products such as cooking plates and small electrotechnical elements.<br />
The cement and lime industry uses imported magnesite and chrome - magnesite bricks for temperatures <strong>of</strong> more than 1,500°C<br />
and high alumina shapes for temperature <strong>of</strong> more than 1,000°C. The small foundry industry imports magnesite bricks and<br />
rammed dolomite for refractory lining and heavy duty magnesite bricks, chrome-magnesite bricks and silica (dinas) bricks.<br />
Raw materials for refractories available in <strong>Mozambique</strong> or those that may be discovered are these:<br />
1 fireclay<br />
most probably in the Karroo Formation in Beaufort member <strong>of</strong> productive sequence; in the coal fields<br />
<strong>of</strong> the Tete Province (Moatize, Mecuco-Chicoa) and the Niassa Province<br />
2 kaolin huge reserves in altered pegmatites <strong>of</strong> the Alto Ligonha district (Muiane, Ribaue etc.)<br />
3 silica<br />
in hydrothermal quartz <strong>of</strong> pegmatite cores <strong>of</strong> the Alto Ligonha district; in vein quartz; in quartzites <strong>of</strong><br />
Precambrian formations; in quartz sand and diatomite<br />
4 magnesite at the Monte Atchiza ultrabasic Complex, at Serra Mangota near Manica together with serpentinites<br />
5 dolomite<br />
in the crystalline limestone deposit Malulu in the Niassa Province; underground deposits <strong>of</strong><br />
precipitated dolomite <strong>of</strong> the Temane Formation in the Inhambane Province<br />
6 limestone many sites <strong>of</strong> occurrence both crystalline and sedimentary<br />
7 zircon in beach sands <strong>of</strong> coastal <strong>Mozambique</strong> together with kyanite and andalusite<br />
8 bauxite from claims Alumen near Manica, refractory, where bauxite is mined, kaolin is dispersed<br />
9 sillimanite, kyanite,<br />
large deposits in the Manica Province; the Tete Province and other localities, need to be investigated<br />
andalusite<br />
10 graphite<br />
recently discovered, substantial reserves <strong>of</strong> flake graphite in the Cabo Delgado Province, other<br />
deposits were mined near Nampula, Nacala and in Angonia in the Tete Province<br />
The production <strong>of</strong> refractories could be started in the existing factories at Quelimane and Maputo using bauxite <strong>of</strong> Manica and<br />
kaolin from Ribaue or Muiane. Binding clay in chamotte should be imported, otherwise local low-quality plastic clays must<br />
be used. Other raw materials for refractories will be made available as soon as the mining <strong>of</strong> heavy minerals is started -<br />
especially zircon may provide extra-quality special refractory products. Special high-temperature refractories could be<br />
produced from graphite, others from magnesite, sillimanite group minerals, serpentinite and talc.<br />
© Václav Cílek 1989<br />
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Cilek: 7. PROSPECTIVE and POTENTIAL industrial minerals and their uses<br />
7. PROSPECTIVE and POTENTIAL industrial minerals and their uses<br />
In <strong>Mozambique</strong>, it would be not appropriate to talk about exhausted resources <strong>of</strong> industrial minerals<br />
which should be replaced by unconventional industrial raw materials because a major part <strong>of</strong> these<br />
resources has not even been touched as yet and it is to be expected that these materials-prospective and<br />
potential from the present point <strong>of</strong> view, will be utilized as soon as the particular industrial branches are<br />
going to be developed.<br />
Owing to a large variety <strong>of</strong> different industrial materials, both classical and prospective it will be<br />
advisable to select the most promising <strong>of</strong> these materials to the benefit <strong>of</strong> industrial growth.<br />
Three groups have been chosen to be discussed in this chapter:<br />
1 potential industrial materials <strong>of</strong> big reserves with substantial present and future demands<br />
2 prospective raw materials with a possible use in future industrial development<br />
3 minor industrially interesting minerals.<br />
1 The present review <strong>of</strong> industrial minerals and rocks indicates both strong and weak points in the<br />
development <strong>of</strong> these resources for industrial development. The weakness is in an absence <strong>of</strong> highquality<br />
ceramic clays, in the low quality and small resources <strong>of</strong> asbestos and unknown reserves <strong>of</strong><br />
magnesite, the absence <strong>of</strong> sulphur and pyrite, the lack <strong>of</strong> metallurgical bauxite and dolomite, the lack <strong>of</strong><br />
phosphorites and a low content <strong>of</strong> apatite and finally the absence <strong>of</strong> common and industrial salts. The<br />
strength and advantage <strong>of</strong> industrial materials surpasses many times the lack <strong>of</strong> some <strong>of</strong> these resouces.<br />
Substantial industrial resources are these:<br />
Ceramic raw materials - big reserves <strong>of</strong> kaolin and feldspar as a waste material in the mining <strong>of</strong><br />
columbo-tantalite <strong>of</strong> pegmatites <strong>of</strong> the Alto Ligonha district;<br />
Glass Materials - huge reserves <strong>of</strong> quartz sands in the coastal zone, feldspar and limestones <strong>of</strong> different<br />
quality, fluxes are available to secure the production <strong>of</strong> container-and pressed glass; flat glass and fibrefoam<br />
glass can also be produced;<br />
Cement-lime production - rich deposits <strong>of</strong> pure limestones for portland cement and lime production,<br />
limestones and marls <strong>of</strong> sedimentary origin for hydraulic lime and saturation lime, high quality<br />
limestones for ceramics and glass;<br />
Gypsum and anhydrite -huge reserves in the Temane Formation can cover, first, the needs <strong>of</strong> the cement<br />
industry, later the needs <strong>of</strong> the building industry (plaster and plasterboards) and, because <strong>of</strong> a lack <strong>of</strong><br />
sulphur and pyrite, anhydrite can be used as a basic material for sulphuric acid production, and also in<br />
the glass production to replace sulphur and limestone;<br />
Graphite - <strong>of</strong> flake quality and amorphous grade for export and production <strong>of</strong> special refractories;<br />
Sillimanite, andalusite, kyanite - potential raw materials for refractories <strong>of</strong> mullite composition, big<br />
reserves are envisaged in the Fronteira Formation, lucrative export material;<br />
Fertilizers - apatites <strong>of</strong> Monte Muande and Evate, futher industrial rocks to improve the soil; utilization<br />
<strong>of</strong> fertilizer such as smectites (bentonite <strong>of</strong> Karroo volcanics), probably zeolites, tuffs and tuffites, lime<br />
and glauconite; can be used also as an aid in animal nutrition;<br />
Nepheline syenite-inexhaustible reserves for nepheline-feldspar production, RE as byproduct, for<br />
ceramic and glass production, alumina and cement production (with limestone);<br />
Diatomite - big reserves and good-quality material for filtration, as filler, light-weight building elements<br />
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Cilek: 7. PROSPECTIVE and POTENTIAL industrial minerals and their uses<br />
etc.;<br />
Materials for metallurgy - big reserves <strong>of</strong> fluorite, limestone, ganister for refractory bricks, foundry<br />
sands and bentonite;<br />
Bauxite and kaolin -for the production <strong>of</strong> chamotte and other refractories;<br />
Protection <strong>of</strong> the natural environment materials - absorbtion materials such as smectites, zeolites, lime<br />
and ground limestone, diatomite, filtration sand etc.<br />
2 Prospective raw materials, some <strong>of</strong> these unconventional, can be used when industrial development<br />
has mastered the technology <strong>of</strong> common raw materials utilization.<br />
Several proposals for the use <strong>of</strong> these materials:<br />
Rare-earths from monazite <strong>of</strong> beach and dune deposits, <strong>of</strong> alkaline rocks and pegmatites can be utilized<br />
as mixed compounds or, in a later stage, as pure elementar RE. A simple technology in producing mixed<br />
RE as mischmetal may result in a production <strong>of</strong> high-strength, low-alloy steels and ductile iron and<br />
increase several times the value <strong>of</strong> future steel production in <strong>Mozambique</strong>. RE could also be used in<br />
ceramics and glass industry and as petroleumcracking catalysts. As byproduct <strong>of</strong> monazite processing,<br />
thorium is obtained which can be used in the production <strong>of</strong> alloys with magnesia and in the future, as<br />
fuel in atomic reactors.<br />
Zircon from beach sands for special high-temperature refractories, but also, for a quite common<br />
utilization, as foundry sand.<br />
Lithium minerals are typical raw materials <strong>of</strong> the near future, at present they are used as lubricants, as air<br />
regeneration agent in submarines and satellites, in the glass industry as enamels and glazes, as an<br />
admixture in white ceramic mass and refractories; future uses are as fuel in thermonuclear reactors and<br />
as cooling agent and for storage <strong>of</strong> electric energy. Are available in pegmatites.<br />
Alkaline rocks, mainly nepheline syenites, as a source <strong>of</strong> alumina, cement and RE and trace elements.<br />
Talc as a filler, in ceramics and refractories. Glauconite as a fertilizer, in foundry sands and in water<br />
treatment; it occurs at Mague-Sabie in the Maputo Province in Cretaceous sandstones, 20 to 50 m thick,<br />
with 2.7-3.1% P2O5 and 4.1% K2O with a glauconite content up to 50%.<br />
3 Minor raw materials include, for example, corundum which was mined near Tete as an abrasive<br />
material and exported; olivine in ultrabasic rocks as slag conditioner and a fluxing agent in blast<br />
furnaces, in refractories and heat-storage units, as abrasive; mica sheet and ground mica in electrical<br />
industry and as filler; quartz crystals in electronics; vermiculite as thermal and acustic insulator, in lightweight<br />
aggregate and in agriculture; garnet as abrasive material etc.<br />
© Václav Cílek 1989<br />
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Cilek: 8. Minerogenetic provinces and epochs<br />
8. Minerogenetic provinces and epochs<br />
The described minerogenetic provinces and epochs <strong>of</strong> industrial minerals and rocks in <strong>Mozambique</strong> indicate that our<br />
knownledge decreases with an increasing age <strong>of</strong> geological formations. In the Precambrian, there are still large regions,<br />
mainly in N- <strong>Mozambique</strong>, which will have to be futher investigated and where a discovery <strong>of</strong> new mineral deposits will be<br />
probable as suggested by recent findings <strong>of</strong> kimberlites, alkaline rocks with phosphate, RE and in many new localities, <strong>of</strong><br />
pegmatites, marbles, zones <strong>of</strong> ultrabasic rocks with asbestos, talc, rich deposits <strong>of</strong> graphite, ilmenite rich zones and others.<br />
Minerogenetic epochs are limited periods <strong>of</strong> industrial minerals and rocks connected with one cycle <strong>of</strong> orogenesis or<br />
sedimentation either during plate tectonic development or geosynclinal or epicontinental phases. These epochs can be<br />
determined quite accurately in sedimentary deposits or young volcanic epochs, but just roughly deliminated within the<br />
Precambrian and the minerals and rocks represent quite common materials, because the exact minerals are hardly known.<br />
Minerogenetic units are represented by groups <strong>of</strong> minerals <strong>of</strong> related genesis and <strong>of</strong> similar history; some are welldetermined,<br />
some are wide-range common materials. Building materials are generally not mentioned, because they could<br />
include most <strong>of</strong> crystalline rock materials and thus render the review very confused.<br />
The development <strong>of</strong> industrial minerals and rocks in geological epochs and units is shown in table below.<br />
Minerogenetic<br />
Epoch<br />
Recent-Subrecent -<br />
100,000 years<br />
Miocene<br />
Eocene<br />
Mid Tertiary -<br />
Late Cretaceous<br />
Pleistocene-Jurassic<br />
- 150 m.y.<br />
Karroo Formation<br />
150-300 m. y.<br />
Upper Precambrian<br />
450-700 m. y.<br />
Middle Precambrian<br />
900-1,100m.y.<br />
Characteristics Minerogenetic unit<br />
oscillation <strong>of</strong> sea level<br />
formation <strong>of</strong> bays, lagoons and<br />
epicontinental basins<br />
Post-African Land Surface (mid-Late<br />
Miocene)<br />
African Land Surface period <strong>of</strong><br />
peneplainisation and sedimentation<br />
post-Karroo volcanic vents, volcanoes,<br />
ascending massifs in connection with zones<br />
<strong>of</strong> fractures along the East-African rift<br />
valley<br />
era <strong>of</strong> tectonic activity along the reactived<br />
fractures; era <strong>of</strong> deposition in tectonic<br />
depressions on continental platform<br />
Pan-African (500±100 m. y.) - Katangan<br />
orogenies (700-500 m. y.) last metamorphic<br />
phase, reactivation <strong>of</strong> older tectonic zones;<br />
katangan deposits <strong>of</strong> small extent pan-<br />
African granitoids and pegmatites<br />
denudation 900-700 m. y., main orogeny<br />
mozambican, multiphase metamorphism<br />
accompanied by granitic intrusions,<br />
granulites over granite and migmatites<br />
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placers with heavy minerals: ilmenite, rutile, zircon,<br />
monazite, kyanite, gravel-sand, diatomite<br />
limestones <strong>of</strong> J<strong>of</strong>ane Formation, evaporites: gypsum,<br />
anhydrite, salt, dolomite <strong>of</strong> Temane F., limestones <strong>of</strong><br />
Cheringoma F., Salamanga<br />
heavy minerals in transitional source, kaolin, clay,<br />
taterite, bentonite, kaolin, clay, bauxite, laterites<br />
basic and alkaline rocks, nepheline syenite with Al, P,<br />
Fe, RE; carbonatites with P, F; fluorite in veins and<br />
stockwork<br />
rhyolites, basalts, tuffs, bentonite, fireclay?, perlite,<br />
zeolites, agates<br />
apatite, magnetite in crystalline limestone, sillimanite,<br />
andalusite, kyanite, graphite, pegmatites: RE, mica,<br />
feldspar, quartz, beryl, lithium, precious stones RE in<br />
intrusive alkaline rocks<br />
apatite, Nb, U, RE; pegmatites: RE, gems, mica,<br />
fedspar; graphite in contact and high grade;<br />
metamorphic deposits, marbles
Cilek: 8. Minerogenetic provinces and epochs<br />
Middle-Lower<br />
Precambrian<br />
1,350-1,800 m.y.<br />
Lower Precambrian<br />
1,800-2,500 m. y.<br />
Archean<br />
2,500-3,800 m. y.<br />
© Václav Cílek 1989<br />
Irumide orogeny and intercratonic; basin fill<br />
on active margin, metamorphism; Groups<br />
Gairezi, Zambue, Fronteira<br />
geosynclinal deposition on Archean<br />
basement<br />
cratons <strong>of</strong> Zimbabwe and Transvaal;<br />
shallow water deposits, origin <strong>of</strong> nuclei <strong>of</strong><br />
shield with greenstone belts<br />
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quartzites; (ganister)?; sillimanite, andalusite, kyanite;<br />
asbestos and talc<br />
quartzites, marbles<br />
graphite, asbestos and talc<br />
serpentinite, talc, asbestos, magnesite
Cilek: 9. SELECTED REFERENCES<br />
9. SELECTED REFERENCES<br />
AfonsoR.S.(1978):<br />
A geologia de <strong>Mozambique</strong>. Noticia Explicativa da Carta Geol. Moc., 1 : 2,000 000, Imprensa Nac.<br />
Moc., pg. 1-191, Maputo.<br />
Afonso R. S. -Pinto M. (1967):<br />
Macicos alcalinos de Milange e Morrumbala. Pesquisa de bauxites. Inter. Rep., Institute Nacional de<br />
Geologia (ING), pg. 1-53, Maputo.<br />
Andrade C.F.(1929):<br />
Esboco geologico de <strong>Mozambique</strong>. Imprensa Nac. de Lisboa, pg. 1-232, Lisboa.<br />
Assenov B. - Diallo 0. F. (1982):<br />
Relatorio sobre as argilas da regiao de Namaacha. Inter. Rep., ING, pg. 1-22, Maputo.<br />
Bandet G.-Beauville J. L. (1978):<br />
Etude du kaolin de Marropino (<strong>Mozambique</strong>). BRGM, Inter. Rep., ING, pg. 1-21, Maputo.<br />
Barmine V. -Tveriankine J. (1982):<br />
Relatorio sobre os trabalhos de prospeccao e evaliacao dos sienitos nefelinicos do mocico Conguene e<br />
rochas calcarias de area Chire. Inter. Rep., ING, pg. 1-15, Maputo.<br />
Barros R. M. F.-Vicente C. A. M. (1963):<br />
Estudo dos campos pegmatiticos da Zambezia. Campanha de 1963. Inter. Rep., ING, pg. 1-133 I., 134-<br />
290 II., 291-439 III., Maputo.<br />
Bascia G.-Mariani F. (1982):<br />
Relatorio sobre a investigacao de depositos argilosos na zona de Gurue em Zambezia. Inter. Rep., ING,<br />
pg. 1-4, Maputo.<br />
Bateman A.(1951):<br />
Economic Mineral Deposits. Sec. Ed., John Willey & Sons, Inc., New York, pg. 1-916.<br />
Beltchev M.(1983):<br />
Relatorio sobre apatite de Evate, provincia Nampula. Bulgargeomin, Inter. Rep., ING, pg. 1-71, Maputo.<br />
Bettencourt Dias M. (1952):<br />
Depositos de calcareo nacircunsricao de Cheringoma, Inter. Rep., ING, pg. 1-41, Maputo.<br />
Bettencourt Dias M. (1953):<br />
Acumulacoes de "guano morcego" em cavernas nos calcareos da circunscricao de Vilanculos. Inter.<br />
Rep., ING, pg. 1-20, Maputo.<br />
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Cilek: 9. SELECTED REFERENCES<br />
Bloomfield K.(1961):<br />
The Age <strong>of</strong> Chilwa Alkaline Province. Rec. Geol. Sur. Nyasaland, 1., 1959, pg. 20-45, Zomba.<br />
Borges A.(1950):<br />
O jazigo de bauxite da Serra de Mariangane. Inter. Rep., ING, pg. 1-21, Maputo.<br />
Bornhardt W.(1900):<br />
Zur Oberflachengestaltung und Geologie Deutsch-Ostafrika. Bd. VII., pg. 1-490, Berlin.<br />
BRGM(1986):<br />
Notice explicative de la carte geologique a 1:1,000 000 de la Republique populaire du <strong>Mozambique</strong><br />
(1986), ING-BRGM, pg. 1-261, Maputo.<br />
Bulgargeomin(1983):<br />
Trabalhos desenvolvidos durante o ano de 1982 sobre pesquisa geologica de jazigo de marmore em<br />
Montepuez e o calculo de reservas. Inter. Rep., ING, pg. 1-25, Maputo.<br />
Bulgargeomin(1983):<br />
Geologia da Foz do Rio Lurio. Inter. Rep., ING, pg. 1-171, Maputo.<br />
Campos J.(1948):<br />
Ensaios de semimicroanalize qualitativa dalguns minerais raros de <strong>Mozambique</strong>. Inter. Rep., ING, pg. 1-<br />
14, Maputo.<br />
Campos J.(1961):<br />
Notas sobre alguns calcareos de Mocambique. Boll. Invest. Cient. Moc., Vol. 2., No. 1., pg. 31-37,<br />
Maputo.<br />
Carvalho P.(1944):<br />
Estudo dos jazigos mineiros da Colonia de Mocambique. Inter. Rep., ING, pg. 1-49, Maputo.<br />
Carvalho L.H.B.(1971):<br />
Formacoes vulcanicas de Carinde (Tete-Mocambique). Unpubl. PHD. Thesis, Univ. Aveiro, pg. 1-120,<br />
Portugal.<br />
Cilek V. (1985):<br />
Heavy Mineral Accumulations in Coastal <strong>Mozambique</strong>. Rozpr. CSAV, roc. 95, s. 1., pg. 1-91,<br />
Academia, Prague.<br />
Cilek V.(1987):<br />
Corredor da Beira. A Review <strong>of</strong> the building raw materials. Inter. Rep., ING, pg. 1-36, Maputo.<br />
Civitelli G.-Mariani F. (1984):<br />
Estudo geologico do sedimentar da provincia de Cabo Delgado finalizado a pesquisa de gesso. Inter.<br />
Rep., ING, pg. 1-44, Maputo.<br />
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Cilek: 9. SELECTED REFERENCES<br />
Diallo O.R.(1979):<br />
Relatorio sobre a prospeccao pormenorizada das argitas de Bela Vista. Inter. Rep., ING, pg. 1-7, Maputo.<br />
Diallo O.R.(1980):<br />
Relatorio sobre a prospeccao pormenorizada das argilas para a ceramica vermelha na regiao de<br />
Inharrime (provincia de Inhambane) area de Ravene-Muhamba. Inter. Rep., ING, pg. 1-14, Maputo.<br />
Diallo O.R.(1980):<br />
Relatorio sobre visita de estudo das argilas de Xinavane. Inter. Rep., ING, pg. 1-3, Maputo.<br />
Duda J.et. al.(1986):<br />
Pegmatitos de Nuaparra (feldspato e mica). Inter. Rep., pg. 1-133, Maputo.<br />
ENH (1986):<br />
The Petroleum Geology and Hydrocarbon Prospectivity <strong>of</strong> <strong>Mozambique</strong>. Vol. I. pg. 1-132, Vol. II. pg. 1-<br />
321, Inter. Rep. <strong>of</strong> Empressa National de Hidrocarbonetos de Mocambique, Maputo.<br />
Ferrari J.H.(1981):<br />
Iron ore in the Peoples Republic <strong>of</strong> <strong>Mozambique</strong>. Inter. Rep., ING, pg. 1-83, Maputo.<br />
Ferrari J.H.(1981):<br />
Asbestos in the P. R. <strong>of</strong> <strong>Mozambique</strong>-evaluation and perspectives. Inter. Rep., ING, pg. 28-59, Maputo.<br />
Franken R.B.(1982):<br />
Asbestos prospect near Tzangano, Moatize-Angonia. Inter. Rep., ING, pg. 1-7, Maputo.<br />
Freitas F.(1950):<br />
Asbestos de Manica. Inter. Rep., ING, pg. 34-52, Maputo.<br />
Geological Institute Beograd (1982):<br />
Annual Report-Geol. Prospecting and Investigation in Manica, S<strong>of</strong>ala, Zambezia and Tete Provinces.<br />
Inter. Rep., ING, pg. 1-64, Maputo.<br />
Geological Institute Beograd (1982):<br />
Annual Report on works performed by Jugoslav expert team in 1981 (Report on investigations <strong>of</strong> "black<br />
granites" section. Inter. Rep., ING, pg. 58-64, Maputo.<br />
Geological Institute Beograd (1982):<br />
Prefeasibility Study on graphite exploitation Angonia deposit-<strong>Mozambique</strong>. Inter. Rep., ING, pg. 1-55,<br />
Maputo.<br />
Geological Institute Beograd (1982):<br />
Final Report on geol. investigation <strong>of</strong> asbestos, iron minerals, apatite and amazonite in Nampula<br />
Province. Inter. Rep., ING, pg. 1-62, Maputo.<br />
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Cilek: 9. SELECTED REFERENCES<br />
Geological Institute Beograd (1984):<br />
Final Report on geol. investigation <strong>of</strong> ornamental stone in provinces Tete, Niassa, Nampula and Maputolocality<br />
Namialo. Inter. Rep., ING, pg. 1-14, Maputo.<br />
Geological Institute Beograd (1984);<br />
Final Report on geol. prospection and exploration works in alkaline rocks complex <strong>of</strong> Chemba. Inter.<br />
Rep., ING, pg. 1-56, Maputo.<br />
Geological Institute Beograd (1984):<br />
Final Report on geol. investigation <strong>of</strong> magnetite and apatite mineralisation at Monte Muande, Tete<br />
Province. Inter. Rep., ING, pg. 1-214, Maputo.<br />
Geological Institute Beograd (1984):<br />
Final Report-Geol. Investigations <strong>of</strong> diatomite occurences and deposits in Bela Vista-Marracuene-<br />
Manhica, Magude-Chicano and Macia Xai-Xai areas, Maputo Provinces. Inter. Rep., ING, pg. 1-62,<br />
Maputo.<br />
Geological Institute Beograd (1984):<br />
Final Report on the geol. research <strong>of</strong> pegmatite in the region <strong>of</strong> the Ribaue mine. Inter. Rep., ING, pg. 1-<br />
48, Maputo.<br />
Geological Institute Beograd (1984):<br />
Final Report-geol. investigation <strong>of</strong> graphite deposits in the area Monapo-Itotone-Nampula. Inter. Rep.,<br />
ING, pg. 1-15, Maputo.<br />
Geological Institute Beograd (1985):<br />
Final Report on geol. investigation <strong>of</strong> limestone in the Maputo Valley, Maputo Province. Inter. Rep.,<br />
ING, pg. 1-81, Maputo.<br />
Geological Institute Beograd (1985):<br />
Final Report on the geol. research <strong>of</strong> ornamental stones in the Province <strong>of</strong> Niassa (Red Granite). Inter.<br />
Rep., ING, pg. 1-16, Maputo.<br />
Geological Institute Beograd (1985):<br />
Final Report on geol. investigation <strong>of</strong> limestone and clay in the Maputo valley. Inter. Rep., ING, pg. 1-<br />
35, Maputo.<br />
Godinho J. (1970):<br />
Relatorio sobre as possibilidades de exploracao de titanio no distrito de Tete. Inter. Rep., ING, pg. 1-19,<br />
Maputo.<br />
Gouveia J.C. (1967):<br />
Relatorio da visita a alguns locais do distrito de Cabo Delgado. Inter. Rep., ING, pg. 1-6, Maputo.<br />
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Cilek: 9. SELECTED REFERENCES<br />
Gouveia J.C. (1974):<br />
Carta de jazigos e ocorrencias minerais (escala 1 : 2,000 000) com noticia explicativa. Direccao dos<br />
Servicos de Geologia e Minas, Maputo.<br />
Gula J. (1981):<br />
Report about non-metallic minerals in <strong>Mozambique</strong>. Inter. Rep., ING, pg. 1-45, Maputo.<br />
Harben P.-Bates R. (1984):<br />
Geology <strong>of</strong> Nonmetallics. R. Hartnoll Ltd., U. K., pg. 1-392, Cornwale.<br />
Haslar O. et.al. (1985):<br />
Relatorio final Evate-da jaziga de apatite. Intergeo-Geoindustria, pg. 1-133, ING-Maputo.<br />
Hunting Geology & Geophysics Ltd. (1984):<br />
Mineral Inventory Project. Final Report. Inter. Rep., ING, pg. 1-329, Maputo.<br />
Institute for economy <strong>of</strong> raw materials, Dresden (1978):<br />
Relatorio sobre resultados de investigacoes tecnologicas de mat. prim. em amostras de caulino,<br />
procedentes do jazigo de Muiane na zona pegmatitica de Alto Ligonha na Rep. P. do <strong>Mozambique</strong>.<br />
Inter. Rep., ING, pg. 1-13, Maputo.<br />
Intergeo, Prague (1985):<br />
Relatorio Final - Monapo, Prospeccao Regional Geoquimica, <strong>Mozambique</strong>. Inter. Rep., ING, pg. 1-105,<br />
Maputo.<br />
Ivanicka J. -Sykora J. (1982):<br />
Relatorio final e calculo de reservas no jazigo de Ressano Garcia (Vidro vulcanico). Inter. Rep., ING,<br />
pg. 1-34, Maputo.<br />
Jourdan P.(1986):<br />
The Mineral Industry <strong>of</strong> <strong>Mozambique</strong>. Raw Materials Report, Vol. 4., No 4., pg. 31-45, Lusaka.<br />
Jourdan P.-Paulis R. (1979):<br />
Avaliacao preliminar do jazigo de calcario de Malulu-Niassa. Inter. Rep., ING, pg. 1-14, Maputo.<br />
Jourde G.-WoIff J. P. (1970):<br />
Contribuicao para o conhecimento da geologia da area de Montepuez. BRGM au <strong>Mozambique</strong>. Inter.<br />
Rep., ING, pg. 1-45, Maputo.<br />
Kaspar J.-Pristoupil V. (1970):<br />
<strong>Industrial</strong> raw materials (Surovinove zdroje prumyslu), SNTL, pg. 1-382, Prague.<br />
Kimambo R.H. (1986):<br />
Development <strong>of</strong> the non-metallic minerals and the silicate industry in Tanzania. Vol. I, pg. 1-100, East<br />
Africa Publ. Ltd., Dar es Salaam.<br />
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Cilek: 9. SELECTED REFERENCES<br />
King L.C. (1983):<br />
Wandering continents and spreading sea floors on an expanding earth. John Willeys and Sons, pg. 1-<br />
205,1983.<br />
Koscal M.-Kachamila J.-Stefanovic M.-Janjic M. (1985):<br />
Fluorite mineralisation <strong>of</strong> Monte Muambe carbonatite complex, <strong>Mozambique</strong>. Summary, World Congr.<br />
Non-Met. Min., pg. 103-114, Beograd.<br />
Kouzmine G. -Akimidze A. (1981):<br />
Obsidiana dos Pequenos Libombos. Inter. Rep., ING, pg. 1-18, Maputo.<br />
Kraft E. (1980):<br />
Relatorio sintesse sobre as ocorrencias de grafite na regiao de Angonia (provincia de Tete). Inter. Rep.,<br />
ING, pg. 1-5, Maputo.<br />
Kuzvart M. (1984):<br />
<strong>Industrial</strong> <strong>Minerals</strong> and Rocks. Elsevier, pg. 1-454, Academia, Prague.<br />
Lamey C.A. (1966):<br />
Metallic and <strong>Industrial</strong> Mineral Deposits. Mc Graw-Hill, pg. 1-567, New York.<br />
Lachelt S. (1985):<br />
Contribuicao para o estudo geologico, tectonico e metalogenico de <strong>Mozambique</strong>. Inter. Rep., ING, pg. 1-<br />
362, Maputo.<br />
Ledder H. (1987):<br />
Noticia explicativa da carta de jazigos e ocorrencias de minerios nao metalicos. Inter. Rep., ING, pg. 1-<br />
55, Maputo.<br />
Lefond S. J. (1975):<br />
<strong>Industrial</strong> minerals and rocks (non-metallics other than fuels). 4th. ed., Am. Inst. <strong>of</strong> Mining, Metall. and<br />
Petroleum Eng., pg. 1-1360, New York.<br />
Mariani F. - Ballara G. - Uamusse M. (1984):<br />
Relatorio sobre a pesquisa de calcareos para cal em Pemba. Inter. Rep., ING, pg. 1-33, Maputo.<br />
Martins R. (1940):<br />
Reconhecimento geologico do Monte Chiperone. Rel. inedito, 45., Serv. Geol. Min. Moc., pg. 1-8,<br />
Maputo.<br />
Masson G.-Ulpiu S. (1978):<br />
Geological Report concerning perspectives and researches for gypsum in the Sul Save region (Pande-<br />
Temane). Inter. Rep., ENH, pg. 1-11, Maputo.<br />
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Cilek: 9. SELECTED REFERENCES<br />
Millot G. (1970):<br />
Geology <strong>of</strong> Clays. Springer Verlag, pg. 1-429.<br />
Mullac L. (1962):<br />
Physical properties <strong>of</strong> perlite sample-Lourenco Marques. Inter. Rep., ING, pg. 1-6, Maputo.<br />
Neves C. -Nunes L. (1968):<br />
Pegmatitic Phosphates <strong>of</strong> Alto-Ligonha Region (<strong>Mozambique</strong>), Rev. Cienc. Geol., Lour. Marq., Vol. 1.,<br />
serie A, pg. 1-48, Maputo.<br />
Neves C. -Nunes L. (1969):<br />
Zeolites from Corumana Mountain (Lebombo Range, <strong>Mozambique</strong>-Portuguese East Africa). Rev.<br />
cienc., Geol., Ser. A. I., pg. 73-92, Maputo.<br />
Nunes A.F. (1952):<br />
Minerais uteis de Mocambique-grafite. Extr. Bol. No. 74, Soc. Est. Moc., pg. 101-105, Maputo.<br />
Pinto A.S. (1934):<br />
Relatorio sobre os trabalhos de prospeccao no distrito de <strong>Mozambique</strong>. (Importancia de jazigos de mica<br />
no distrito de <strong>Mozambique</strong>), Inter. Rep., ING, pg. 1-61, Maputo.<br />
Polak A. (1972):<br />
Non-metallic raw materials (Nerudne nerostne suroviny), SNTL, pg. 1-390, Prague.<br />
Real F. (1960):<br />
Relatorio da Campanha de 1959. Inter. Rep., ING, pg. 1-103, Maputo.<br />
Real F. (1962):<br />
O macico ultrabasico de Monte Atchiza (<strong>Mozambique</strong>). Reconhecimento geol.-mineiro. Junta de<br />
Investigacoes do Ultramar. Inter. Rep., ING, pg. 1-55, Maputo.<br />
Real F. (1963):<br />
Ocorrencias de aluminio. Inter. Rep., ING, pg. 1-50, Maputo.<br />
Real F. (1965):<br />
Ocorrencias de aluminio. In "Vale do Zambeze". Elementos de estudio Rel. Res. Brig. Geol. Prosp. Min.<br />
1961-1964. M. F. P. Z., Lisboa, ING, pg. 24-47, Maputo.<br />
RibeiroS. (1952):<br />
Grafites de Angonia. Inter. Rep., ING, pg. 1-51, Maputo.<br />
Samokhvalov M. (1981):<br />
Crostas lateriticas de alteracao da parte norte de <strong>Mozambique</strong>. Inter. Rep., ING pg 1-32 Maputo.<br />
Silva L. C.-Godinho J.-Quadrado R. (1968):<br />
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Cilek: 9. SELECTED REFERENCES<br />
Nota sobre a existencia de dumortierite em Cabora-Bassa (<strong>Mozambique</strong>). Garcia de Orta (Lisboa), Vol.<br />
16., No. 2, pg. 243-248, Lisboa.<br />
Smirnov V.I. (1975):<br />
Geology <strong>of</strong> Mineral deposits. Mir., pg. 1-687, Moscow.<br />
Thieke H.U. (1980):<br />
Relatorio sobre a situacao das reservas de caulino e mica (moscovita) de jazigo pegmati'tico de Muiane.<br />
Inter. Rep., ING, pg. 1-12, Maputo.<br />
Tzonev O. (1981):<br />
Prospeccao preliminar de argilas Inhamizua-Beira. Inter. Rep., ING, pg. 1-25, Maputo.<br />
Tzonev O. (1981):<br />
Pesquisa preliminar de argila Nampula-Rio Muapelume. Inter. Rep., ING, pg. 1-9, Maputo.<br />
Tzonev O. - Dimitrov D. (1982):<br />
Relatorio da pesquisa de argila e areia da regiao de Xai-Xai. Inter. Rep., ING, pg. 1-46, Maputo.<br />
UN-TCD (1983):<br />
Geophysical Exploration in the Tete area. Inter. Rep., ING, proj. MOZ 80/013, pg. 1-9, Maputo.<br />
VAMI-Leningrad (1981):<br />
Mineralogical and technological study <strong>of</strong> <strong>Mozambique</strong> nepheline ores. Inter. Rep., ING, pg. 1-92,<br />
Maputo.<br />
Varley E. R. (1965):<br />
Sillimanite-andalusite, kyanite, sillimanite. Overseas Geol. Sur., Min. Res. Div., Her Maj. Stat. Off., pg.<br />
1-165, London.<br />
VEB Kombinat Geol. Forsch. Halle (1983):<br />
Relatorio final-projecto pegmatito Marropino. Inter. Rep., ING, pg. 1-102, Maputo.<br />
Zuberec J.-Ivanicka J.-Sykora J. (1981):<br />
O estudo geologico e tecnologico das materias primas de ceramica nas localidades escolhidas na R. P.<br />
<strong>Mozambique</strong>. Inter. Rep., ING, pg. 1-30, Maputo.<br />
Zuberec J. -Ivanifcka J.-Sykora J. (1981):<br />
A Situacao geologico-tecnologica e o calculo das reservas da zona de bentonite Luzinada. Inter. Rep.,<br />
ING, pg. 1-42, Maputo.<br />
Zuberec J.-Ivanicka J.-Sykora J. (1981):<br />
Prospeccao e pesquisa geol. das areias caulinicas na regiao de Nacala. Inter. Rep., ING, pg. 1-11,<br />
Maputo.<br />
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Cilek: 9. SELECTED REFERENCES<br />
Zuberec J. - Lacko L. - Novysedlak J. (1984):<br />
Relatorio-pesquisa detalhada do jazigo de areia caulinica-Nacala. Inter. Rep., ING, pg. 1-30, Maputo.<br />
Zacek M.-Duda J. (1986):<br />
Prognostic evaluation <strong>of</strong> Monapo Group in <strong>Mozambique</strong> by method Kombi (Prognozni ocenenf serie<br />
Monapo v Mos. metodou Kombi). Geol. Pruzkum 8-9, pg. 249-252, Prague.<br />
© Václav Cílek 1989<br />
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