Basem Ahmed Zoheir_Beida_JGE_2012.pdf

Lode-gold mineralization in convergent wrench structures: Examples from South 

Eastern Desert, Egypt 

Basem A. Zoheir 

Department of Geology, Faculty of Science, Benha University, 13518 Benha, Egypt 

article info 

Article history: 

Received 14 July 2011 

Accepted 29 December 2011 

Available online 5 January 2012 

Keywords: 

Lode-gold 

Convergent wrench structures 

Fluid mixing 

Wadi El Beida–Wadi Khashab 

Eastern Desert 

Egypt 

1. Introduction 

abstract 

It is believed that most significant gold deposits throughout the 

world are controlled by major and subsidiary shear zones (e.g., 

Bonnemaison and Marcoux, 1990; Hodgson, 1989; Roberts, 1987). 

Ore fluidmigrationandgolddeposition processes in these deposits 

are attributed to a contrasting fluid-pressure/temperature regime 

between the first and second order structures (Eisenlohr et al., 

E-mail address: basem.zoheir@gmail.com. 

0375-6742/$ – see front matter © 2012 Elsevier B.V. All rights reserved. 

doi:10.1016/j.gexplo.2011.12.005 

Journal of Geochemical Exploration 114 (2012) 82–97 

Contents lists available at SciVerse ScienceDirect 

Journal of Geochemical Exploration 

journal homepage: www.elsevier.com/locate/jgeoexp 

Data from regional- and mine-scale mapping, structural, geochemical and fluid inclusion studies reveal a synkinematic 

genesis of gold in convergent wrench structures that cut the Neoproterozoic greenstone belt in the 

south Eastern Desert of Egypt. Au-quartz lodes in the Wadi El Beida–Wadi Khashab area are associated with 

NNW-trending shear zones in pervasively silicified, ferruginated volcanic/volcaniclastic rocks, or along steeply 

dipping thrust segments bounding allochthonous ophiolitic blocks. Development of the mineralized shear zones 

is attributed to a wrench-dominated transpression assigned to D2 deformation throughout the Pan-African evolution 

of the South Eastern Desert (620–540 Ma?). 

Hydrothermal alteration associated with Au-quartz lodes comprises an inner quartz–sericite–pyrite assemblage 

progressed outwards into an outer quartz–chlorite–calcite assemblage. Mass balance calculations reveal a systematic 

volume- and mass-increase, addition of SiO2, K2O, Fe2O3 t , S and L.O.I. and slight depletion in Na2O in 

the altered wallrocks approaching the Au-quartz lodes. Erratic concentrations of S, MgO and CaO in the altered 

host rocks, however, suggest selective carbonatization, and sulfidation of Fe-rich host rocks proximal to the 

ore bodies. 

Ore bodies include quartz-only and quartz–carbonate lodes with disseminated pyrite, chalcopyrite, chalcocite, 

covellite, marcasite, subordinate pyrrhotite, sphalerite and gold. In addition to free gold inclusions in As-poor 

pyrite, microprobe and LA-ICP-MS spot analyses reveal the presence of traces of Au, Ag (10s to 100s ppmlevels), 

positively correlated with Cu contents (1000s ppm-levels). Analyses of pyrrhotite and marcasite indicate 

a comparable relationship. Chalcopyrite intimately associated with pyrite contains lower levels of refractory 

gold and silver (av. 12 ppm Au and 3 ppm Ag). Solid solution may have been responsible for invisible gold, 

whereas, free gold deposition is a function of remobilization, reconstitution and concentration of the earlier 

phase. 

Primary and pseudosecondary fluid inclusions in the auriferous quartz veins comprise low salinity aqueous– 

carbonic fluids (2–12 eq. wt.% NaCl). Homogenization temperatures of synchronous aqueous-dominant and 

carbonic-dominant (H2O–CO2–NaCl±CH4±N2) fluid inclusions (258–343 °C) correspond to 0.8–2.3 kbars and 

depths of 3 and 9 km (mesothermal conditions). Decreasing gold solubility and segregation from bi-sulfide complexes 

most probably resulted from interplay of dilution and mixing of an evolved carbonic-rich fluid with a 

more oxidized aqueous fluid, pressure fluctuation and wallrock-sulfidation. 

New geochemical data combined with available geophysical information indicate viable gold ore bodies in the 

study area, and suggest similar situation for zones with discernible signs of hydrothermal alteration along the 

major convergent wrench (shear) zones in the Eastern Desert of Egypt. 

© 2012 Elsevier B.V. All rights reserved. 

1989). According to Cox et al. (1991), fluid flow in shear-hosted 

gold deposits is seldom distributed uniformly along individual 

faults or shear zones, but is localized within distinct segments of 

these structures where permeability and/or gradients in hydraulic 

head are highest. Elements that commonly govern ore localization 

and deposit geometry are fault bends, jogs, fault intersections and 

splays (Cox et al., 1991). 

Transpression describes a style of deformation that involves collisional 

orogenesis accompanied by strike–slip shear across a zone 

(Dabo et al., 2008). Wrench-dominated transpression, a characteristic 

feature of obliquely convergent mobile belts, has been suggested to

explain the complex deformation kinematics in the Eastern Desert of 

Egypt (e.g., Abd El-Wahed, 2008; Abd El-wahed and Kamh, 2010; 

Abdeen et al., 2008; Fritz et al., 1996; Fritz et al., 2002; Greiling et 

al., 1994; Loizenbauer et al., 2001; Makroum, 2001; Shalaby, 2010; 

Shalaby et al., 2005; Wallbrecher et al., 1993). In south Eastern Desert 

of Egypt, discrete NW- to NNW-trending, kilometer-scale, shear zones 

cutting the ophioltic and island arc metavolcanic/volcaniclastic assemblages 

in the Wadi El Beida–Wadi Khashab district are likely related to 

the ca. 620–540 Ma, Najd wrench system (de Wall et al., 2001; Kröner 

et al., 1987; Sadek et al., 1996; Stern, 1985; Stern et al., 1989). Transpressional 

wrenching related to the Najd system was consequent to 

thrust-related structures associated with oblique convergence of the 

arc and back-arc assemblage onto the Saharan Metacraton (e.g., Abd 

El-Wahed, 2008 and references therein). 

Gold-bearing quartz veins are widespread in south Eastern Desert 

of Egypt, commonly showing spatial and temporal association with 

shear zones (e.g., Kusky and Ramadan, 2002; Zoheir, 2008, 2011). 

Abundant remnants of ancient gold mining on both flanks of the 

Wadi El Beida and Wadi Khashab, including stopped-out quartz 

veins and tailings, and stone huts likely date back to the Arab times 

(i.e. 11th century AD) or earlier. These mine working ruins could 

have been a part of the big gold rush in the Nubia desert at that 

time. Mine workings are confined to discrete NNW-trending shear 

zones that are associated with shear-band boudins of quartz and 

highly oxidized, ferruginated silicified metavolcanic/volcaniclastic 

rocks (gossan-like bodies). Previous studies (Kontny et al., 1999; 

Obeid et al., 2001; Ramadan, 1994) reported anomalous gold contents 

(10s ppm Au) in the silicified rocks. Significant Au concentrations 

have been reported in gossans, brecciated quartz and quartz carbonate 

veins rich in malachite (Kontny et al., 1999; Nano et al., 2002). Anomalous 

gold concentrations in the gossan-like bodies encouraged a preliminary 

self-potential magnetic and induced polarization surveying 

(Sultan et al., 2009), which revealed the presence of conductor bodies 

(55 to 175 m-across) at ~40–53 m depth in this area. Most magnetic 

and resistivity anomalies coincide with silicified, shear zones, while 

the low-resistivity zones coincide with the altered metavolcanic rocks 

(Sultan et al., 2009). 

Although evolution of this part of the Wadi El Beida–Wadi Khashab 

district is very much affected by the Pan-African Najd wrench system 

(620–540 Ma), no adequate information is available to envisage the 

relationship between gold mineralization and deformation of the 

country rocks in this area. The present contribution is intended to 

provide detailed information on the geological–structural setting 

and genesis of the auriferous silicified shear zones and quartz lodes 

in relation to the regional wrench structures based on field work, 

petrographic and geochemical methods. 

2. Materials and methods 

High-resolution mapping of the lithological units, alteration halos 

and major structures in the study area was aided by using false color 

composite images and color composite ratio satellite images (ETM+ 

and ASTER). Field work encompassed sampling of the mineralized 

shear zones, hydrothermally altered and fresh host rocks. Structural 

measurements, marker sketching and lithological identification have 

been foremost parts of the field work. Petrographic and ore microscopy 

studies are done on 80 polished thin sections of altered/mineralized and 

fresh/un-mineralized quartz lodes and host rocks. Out of these polished 

sections, 31 samples were chosen for electron microprobe studies 

(EMPA). 

Thirty-one representative samples of fresh host rocks, hydrothermally 

altered wallrocks and ore bodies were chosen for geochemical 

studies. Bulk rock analyses for major and trace elements including 

Au were done at the Activation Laboratories Ltd. (Canada) using 

two packages (codes: 4B and 1H) using the simultaneous multielement 

neutron activation INAA and inductive coupled plasma ICP 

B.A. Zoheir / Journal of Geochemical Exploration 114 (2012) 82–97 

(total digestion) techniques. These two packages offer precise detection 

limits for most important elements, e.g. Au (2 ppb), Ag (0.3 ppm), Bi 

(2 ppm), Sb (0.1 ppm) and As (0.5 ppm). 

A Cameca SX100 Electron Microprobe at the Institute for Mineralogy 

and Mineral Resources, TU-Clausthal (Germany) was used to determine 

the composition of ore minerals. The operating conditions applied for 

most elements: 30 keV and 2 nA beam current. For analysis of Au, Ag, 

Ni, Co, Bi and Sb, a 100 nA beam current was applied, and count times 

ranged from 10 to 400 s. For high-resolution trace element geochemistry 

of sulfides, some samples were spot-analyzed by a quadrupole LA- 

ICP-MS (Elan 6000) at the US Geological Survey Laser Ablation ICP-MS 

Laboratory, Denver. 

Fluid inclusion microthermometric measurements were carried out 

on ~150 μm-thick doubly-polished wafers using a Linkam TMH-600 

heating/freezing stage at the fluid-inclusion laboratory of the Department 

of Geology and Geochemistry at Stockholm University. Calibrations 

were made against known melting points of pure substances. 

Heating rates of 0.5 and 1 °C/min were applied to record phase changes 

below 30 °C, whereas a heating rate of 5 °C/min was applied for phase 

changes above this temperature. The accuracy is ±0.2 °C for the measured 

melting temperatures and within ±2 °C for the homogenization 

temperatures. Parameters used in fluid inclusion microthermometry include: 

first melting temperatures of CO 2 (T mCO2), freezing depression 

(melting) temperatures of clathrate (Tm clath), ice melting temperatures 

(T mice), partial homogenization temperatures of CO 2 (T hCO2), and total 

homogenization temperatures (Th total). 

3. Geology and structural setting 

The Neoproterozoic greenstone belt exposed in the Wadi El 

Beida–Wadi Khashab area comprises variably deformed ophiolites 

and island-arc volcanic–plutonic rocks. This metamorphic pile is 

cut by extensive syn-orogenic granitoids and discrete intrusions of 

late/post-orogenic gabbros and granites. These Precambrian rocks 

are un-conformably overlain by Cretaceous sandstones (Nubian 

Sandstone) and intruded by Red Sea rift-related, Tertiary basalt 

(Ramadan and Kontny, 2004). 

Metasomatized serpentinite, metagabbro and less common 

pillow metabasalt are overthrusted on the island-arc metavolcanic/ 

volcaniclastic rocks along steeply east-dipping thrust/strike–slip fault 

structures (e.g., Wadi Khashab and Wadi El Beida, Fig. 1). Serpentinite 

and associated talc carbonate rocks form large masses, elongated in a 

NW–SE direction (Gebel Sirsir and parts of Gebel El Beida), or 

occur as irregular slices tectonically incorporated within the volcaniclastic 

terrains. Ophiolitic metagabbro is intimately associated 

with serpentinite and metabasalt and locally exhibits compositional 

layering. Pillowed, amygdaloidal metabasalts associated with discrete, 

stretched chert lenses form a NW–SE belt alternating with 

the ultramafic rocks close to El Beida water well. The island-arc 

metavolcanic/volcaniclastic assemblages are mainly foliated metaandesite/basaltic 

andesite and intermediate to acidic tuffs (i.e., 

mudstones, andesitic tuffs and pyroclastics), forming the NW–SE El 

Beida–Khashab mountainous belt. Arc-related gabbro–diorite intrusions 

cut the metavolcanic/volcaniclastic rocks, forming low-relief hills in the 

western part of the study area (Fig. 1). The syn-orogenic intrusions are 

characterized by a wide compositional range, from tonalite to monzogranite. 

They cut the gabbro–diorite and metavolcanic/volcaniclastic rocks, 

and show variable degrees of shearing and mineral foliation. The Postorogenic 

gabbro forms a small circular intrusion in the southwestern 

part of the mapped area (G. Homraii) cutting metavolcanic rocks and 

syn-orogenic granitoids. Isolated intrusions of post-orogenic granites 

(mainly monzogranite) cut serpentinite and syn-orogenic granitoids in 

the eastern and southwestern parts of the study area, respectively. 

The study area evolved throughout a multistage deformation history 

(e.g., Abdeen et al., 2008; El Amawy et al., 2000; Kontny et al., 

1999; Nano et al., 2002; Obeid et al., 2001). Neoproterozoic terrane 

83

84 B.A. Zoheir / Journal of Geochemical Exploration 114 (2012) 82–97 

Fig. 1. Geological map of the Wadi El Beida–Wadi Khashab region in south Eastern Desert of Egypt. 

Modified from Ashmawy (1987), EGSMA (1992), El Amawy et al. (2000) and Abdeen et al. (2008). 

accretion structures (~720 Ma?), best developed southwest of the study 

area, have been completely obliterated by post-accretionary shortening 

and transpression structures (Table 1). The post-collisional evolution includes 

an early NNE–SSW crustal shortening (D1), which led to the formation 

of WNW–ESE tight intrafolial or overturned folds (F 1) and axial 

planar foliations (S 1). The latter is parallel to the primary (lamination) 

bedding (So) in the island arc metavolcanic/volcaniclastic rocks. 

Southward-vergence is suggested based on the geometry of these 

asymmetrical folds. A subsequent sinistral transpression (D2) was 

likely due to NW-ward nappe stacking led to transpression along

Table 1 

Summary of the deformation events affected the study area based on the observed structures. 

Episode Deformation events Structural elements Kinematics Veins and alteration 

Terrane exhumation 

(e.g., Abdeen et al., 2008) 

Post-collisional transpression 

(Najd fault system; 575–520 Ma; 

Greiling et al., 1994; de Wall 

et al., 2001) 

Post-collisional shortening 

(e.g., Greiling, 1987; de Wall 

et al., 2001) 

Weak brittle deformation, 

which may have a relation 

to the Red Sea opening 

(e.g., Abdeen et al., 2008). 

(D2) Kinematic partitioning 

of ~E–W shortening and 

sinistral transpression 

(e.g., Abd El-Wahed and 

Kamh, 2010). 

(D1) NNE–SSW shortening, 

crustal thickening accompanied 

island-arc accretion and nappe 

stacking resulted in a partitioned 

displacement with northwest 

directed thrusting in the 

internal portions and west to 

southwest directed thrusting in 

the external portions of the 

orogeny (e.g., Stern, 1994). 

thrust segments at the base of the ophiolitic blocks and steeplydipping, 

left lateral NNW–SSE ductile shear zones and major faults 

deformed most of the exposed lithologies and overprinted the preexisting 

lithologic/tectonic contacts. Second-order, sinistral shear 

zones form a positive flower structure (e.g., Clendenin, 1993; 

Waldron et al., 2007). The steeply dipping strike–slip fault segments 

bifurcate into reverse faults and then flatten into moderately dipping 

NNW-trending thrust zones. Related kilometer-scale, NNW–SSE 


—ENE-WSW dextral strike–slip 

faulting affected the syn-orogenic 

granodiorite and pre-existed rocks. 

— Normal faults and joints trending 

invariousdirectionsspreadoverthe 

study area. 

— Intrusion of maficdykeswarms 

in E–WorENE–WSW directions. 

— NNW–SSE left-stepping folds 

— Steeply-dipping, left lateral 

NNW–SSE ductile shear zones and 

major faults 

— Sub-horizontal stretching 

lineations on the steeply-dipping 

NW–SE thrust planes. 

— Conjugate sets of steeply-dipping, 

NW-trending sinistral and 

NE-trending dextral fault zones. 

— Crenulation cleavage (S2) superimposed on S1 in the 

metavolcaniclastic rocks. 

Sketch drawing explaining the 

geometric relationships between 

the different D2 fabrics. 

— WNW–ESE tight intrafolial or 

overturned folds (F1) commonly 

vergent to SW. 

— Axial planar foliations (S1), parallel 

to the primary (lamination) bedding 

So in the island 

arc metavolcanic/volcaniclastic rocks. 

— Less preserved ENE-plunging 

stretching lineation (L1)intheisland 

arc metavolcanic/volcaniclastic rocks 

(e.g., elongate pebbles and stretched 

porphyroblasts), 

developed on or close to the NW–SE 

thrust planes. 

Schematic sketch showing the geometry 

of WNW–ESE striking F1 folds in relation 

to the related foliation and lineation, and 

barren quartz pods. 

— The dextral faults 

may be the conjugate 

shear fractures to the 

NNW–SSE oriented 

sinistral wrench faults 

or are related to a late 

brittle deformation event 

(e.g., Abdeen et al., 2008). 

Crenulation cleavage (S2) imposed upon S1 in the 

metavolcaniclastics. 

Kinematics of the shear 

zones include: 

— S–C fabrics, foliation 

deflection in a NNW–SSE 

direction. 

— en echelon, slightly 

sigmoidal quartz lenses, 

related to progressive 

transpression of the 

NNW–SSE trending, 

sinistral wrench zone. 

SW-vergent folds (F1), 

and consistently 

ENE-plunging 

lineations indicating 

top-to-the WSW-tectonic 

transport 

folds (F2), showing en-echelon geometry, verge commonly to the 

WSW and are associated with pervasive axial planar crenulation 

cleavage (S2), which imposes upon S1 in the metavolcaniclastic 

rocks. Boudinaged, stretched gold-bearing, quartz lodes are commonly 

observed where S2 is superimposed on S1. The left-stepping 

folds are consistent with the sinistral sense of wrench motion, and 

have been rotated toward parallelism with the master fault as commonly 

seen in wrench systems (e.g., Harding, et al., 1985; Wilcox 

– 

— Stretched gold-bearing, 

quartz lodes common in 

domains where S 2 is 

imposed upon S 1. 

— Silicified, highly sheared 

metavolcanic and ophiolitic 

rocks along NW and NNW 

shear zones. 

— Highly stretched, 

boudingated quartz 

pockets, with no sulfides 

and barren in gold. 

— Albitization of the 

metavolcanic rocks is 

commonly associated with 

the highly sheared rocks 

alongside the quartz pods. 

85


et al., 1973). Finally, weak brittle deformation led to ENE–WSW dextral 

strike–slip faulting that affected the syn-orogenic granodiorite 

and pre-existing rocks. This deformation event might be related to 

the Red Sea rift (e.g., Abdeen et al., 2008). 

Weathering of the mineralized structures is a striking feature in 

the study area, where zones of bleached wallrocks extend for hundreds 

of meters along the major fault/fracture zones and the splays 

(Fig. 2a). Granophyric dikes are ubiquitous in the altered shear 

zones, commonly associated with quartz veins and disseminated sulfides 

(Fig. 2b). Whereas, aplitic dikes cut less deformed metavolcanic/ 

volcaniclastic rocks in Wadi Khashab (Fig. 2c). Quartz veins are less 

abundant in the shear zones compared to the granophyric dikes 

(Fig. 2d–f). However, networks of quartz veinlets cut the altered 

metavolcanic/volcaniclastic rocks in zones of dense faults/fractures 

intersections. Some quartz veins extend for 40 m and vary in thickness 

from a 2 to 60 cm. Alongside the shear zone, network of quartz 

veinlets cuts pervasively silicified–sericitized–sulfidized metavolcanic/volcaniclastic 

rocks (Fig. 2g). The main ore bodies are made up 

of quartz with subordinate carbonate and ferruginated wallrock 

selvages. Discrete barren quartz lenses are common in brecciated 

granodiorite along the western flank of Wadi Khashab. 

4. Mineralization style and lode characteristics 

Gold-sulfide mineralization is confined to discrete shear zones of 

highly silicified, ferruginated volcanic/volcaniclastic rocks commonly 

associated with sulfide-bearing granophyric dikes and quartz± 

carbonate veins (Tables 2a, 2b and 3). The mineralized shear zones 

form splays off the much larger NNW-trending shear zones, i.e., 

the Wadi Khashab sinistral fault zone. Sub-parallel shear zones 

with disseminated pyrite in variably sheared, silicified metavolcanic/ 

volcaniclastic rocks have been documented for several hundreds of meters 

in the study area (see Fig. 1). This shear zone set occurs within an 

approximately 1000 m-wide envelope of variably strained host rocks; 

individual shears have widths up to 5–10 m, whereas faults are more 

confined. The area between the major shear zones contains a complex 

pattern of anastomosing subvertical shear zones and fabrics wrapping 

around the rigid blocks of the metavolcanic/volcaniclastic rocks. The 

Fig. 2. Field photographs of altered/sheared rocks and quartz lodes in Wadi El Beida–Wadi Khashab area. (a) Extensive pervasively silicified–sericitized NNW-trending alteration 

zone in meta-andesites south of Wadi El Beida. (Photo looking to N). Notice the pervasive kaolinite alteration (1) bounding outer quartz–chlorite–carbonate zone (2) and the inner 

sulfide-bearing quartz–sericite (3) alteration zone, (b) Sulfide-bearing granophyric dike (G) along sheared/altered rock zone south of El Beida water well. (Photo looking to S), (c) 

Barren aplitic granophyric dike (A) cutting meta-agglomerate and breccias along Wadi Khashab. (Photo looking to SW), (d) Mineralized sheared quartz lenses cutting pervasively 

sericitized and furrigenated metavolcaniclastic rocks. (Photo looking N), (e) Bifurcated sheared quartz vein (Q) cutting and enclosing severely altered metavolcaniclastic rocks 

along Wadi Abu Hegleig south of El Beida water well. (Photo looking to NE), (f) Quartz veins cutting foliated gabbro–diorite complex west of Wadi Khashab. (Photo looking to 

NW), (g) Quartz network in highly sericitized metavolcaniclastic rocks next to mineralized quartz lodes in west of Wadi El Beida. (Photo looking to N), (h) Admixed milky and 

grayish quartz and wallrock material in worked quartz lodes from west of Wadi El Beida., (i) Brecciated quartz filling fractures in severely sericitized, sulfidized granophyric 

dikes east of Wadi Khashab. (Photo looking N).

average azimuth of the overall strike of the anastomosing shear network 

is 150°. The ophiolitic metabasalt and arc-related volcanic agglomerate 

and breccias flanking the shear zones are severely 

fragmented and intermixed. Crenulations on the WNW–ESE foliation 

(S1), pervasive NNW–SSE shears are common deformation patterns 

along the altered shear zones. The sense of displacement can be deduced 

unequivocally from several kinematic indicators (e.g. stretched 

objects and stretching lineations, asymptotic schistosity, rotated porphyroclasts, 

etc.), which consistently point toward left-lateral shearing. 

The auriferous quartz veins occur as closely-spaced, parallel or subparallel 

swarms of tabular and subordinate lensoidal veins (3–100 cmthick), 

extending laterally for a few tens of meters. Striations on the vein 

walls are almost invariably plunge steeply to north. Quartz is dominant, 

and carbonate minerals may constitute more than 20% in parts of 

these veins, commonly with disseminated opaque and clay minerals. 

Wallrock materials are present as strongly foliated slivers in quartz 

veins commonly associated with carbonate. Vugs and open-space 

filling textures are mostly absent. Vein quartz textures vary from 

buck (large porphyroblasts), comb (recrystallized grains) and microcrystalline 

(minute subgrains) quartz, and alternating or crosscutting 

bands of different grain size are typical in many veins. Microstructures 

indicate variable degrees of dynamic recrystallization by grain boundary 

migration, subgrain rotation and bulging recrystallization in different 

domains of the individual shear zone. Ribboned, buck quartz is 

dominant in most quartz veins (Fig. 3a), however, the comb quartz variety 

(b20% vol.)±carbonate minerals occupy the interspaces between 

the large quartz ribbons in sulfide-bearing veins (Fig. 3b). A positive 

correlation between well-developed comb textures and disseminated 

sulfide minerals is observed in many samples, given that interstitial 

spaces between comb quartz crystals have everywhere been sealed by 

sulfide minerals and sericite–carbonate±Fe–hydroxide. Laminated 

quartz veins are made up of alternating bands of severely recrystallized 

quartz+wallrock material+sulfide and/or carbonate minerals and 

bands of large less-deformed quartz grains (Fig. 3c). Variations in the 

degree of plastic deformation and in the abundance of microfractures 

are observed between adjacent ribbons and laminae. Some of the mineralized 

lodes are composed mainly of sub-rounded quartz grains with 

highly serrate grain boundaries reflecting significant degrees of bulk recrystallization 

(Fig. 3d). Features of conjugate and progressive shearing 

are common in many of the highly deformed quartz veins (i.e., S–C 

structures; Fig. 3e). In the fragmented parts of the mineralized lodes, 

veinlets of fine-grained, subhedral blocky quartz show drusy growth 

textures normal to the vein wall. Lack of displaced markers and dominance 

of the comb quartz textures (Fig. 3f), clearly imply that these 

late veins occupy true extension fractures (e.g., Simpson and Schmidt, 

1983). 

The analyzed samples of mineralized quartz veins give 2.1– 

6.6 ppm Au, and sulfidized granophyric dikes are also gold-bearing 


(0.2–2.1 ppm Au; Table 2a). Significant correlation coefficient (r) 

values between the analyzed granophyric dikes and quartz lodes 

(Table 2b) indicate a positive correlation between Au, Ag and Cu. 

No discernible correlation occurs between As and either Au or Ag. 

5. Geochemistry of the mineralized shear zones 

Table 2a 

Concentrations of some trace elements in sulfidized granophyre dikes and quartz veins from the Wadi El Beida–Wadi Khashab area. 

Partial to complete destruction of the wallrock textures and 

primary minerals is distinct in the mineralized shear zones. Iron 

oxides/hydroxides fill fractures in the host rocks and replace disseminated 

sulfide grains in quartz veins and in the silicified parts of the 

shear zones. Malachite stains the sheared rocks, vugs and cleavage or 

fracture walls. Based on the dominant hydrothermal alteration phases, 

alteration progressed from outer silicified–chloritized–carbonatized to 

inner silicified–sericitized–pyritized rocks approaching the Au-quartz 

lodes and sulfidized granophyric dikes. In places, alteration is overprinted 

by kaolinite and grayish clay mixtures. 

Direct observations of the analyses (Table 3) indicate higher SiO 2, 

K2O, SO2 and Fe2O3* and lower MgO and CaO contents in the goldbearing, 

hydrothermally altered wallrocks compared to the least altered 

rocks. Loss on ignition (L.O.I.) is considerably high in samples 

displaying intense alteration. Au, Ag, and Cu increase systematically 

from the silicified–chloritized–carbonatized rocks to the inner silicified–sericitized–pyritized 

wallrocks (up to ~3 ppm Au, 2.3 ppm Ag, 

and 236 ppm Cu; Table 3). 

The chemical compositions of fresh and hydrothermally altered 

metavolcanic/volcaniclastic host rocks have been used to infer the 

mass gains and losses of components as a function of hydrothermal 

alteration. In this study, the isocon method of Grant (1986) is used 

to evaluate whether the compositional changes involved significant 

changes in concentrations of components as well as in mass and volume. 

The average values and 1σ errors of samples were used to minimize 

composition heterogeneity of the volcaniclastic rocks. 

Rock forming elements are plotted as oxides in wt.% and trace elements 

in ppm in double-logarithmic plots (Fig. 4). The isocon is defined 

as best fit line through relative immobile elements including Ti, 

P and Y (e.g., Leitch and Lentz, 1994; Selverstone et al., 1991). Elements 

that plot above the isocon have been enriched during alteration, 

whereas elements that plot below the reference isocon are 

depleted with respect to the chosen reference frame (cf. Grant, 

1986). The isocon diagram of the outer quartz–chlorite–calcite alteration 

zone vs. fresh host rocks shows enrichments in most of the elements, 

except K, Na, Co, Zn and Ba, corresponding to chlorite–calcite 

alteration. Gains in S, Cu, Pb, Ag and Au can be attributed to sulfide 

mineralization in the outer parts of the shear zones. The inner 

quartz–sericite–pyrite alteration zone is characterized by gains in K, 

S, Cu, Sb, As Ag and Au vs. relative to the fresh host rocks (Fig. 4). 

ppm Sulfidized granophyric dikes Au-quartz lodes 

be-xx be37 be38 be40 be41 be-18 be-12 kh-21 kh-33 kh-7 kh-16 be-51 be-35 be-34 

Au 0.2 0.9 1.7 2.1 1.5 3.2 6.2 5.5 4.3 2.1 4.9 6.6 5.9 4.8 

Ag b0.3 b0.3 0.7 0.4 0.6 1.8 2.6 2.3 1.7 0.7 3.9 4.5 3.2 2.6 

Cu 167 264 529 333 308 557 711 591 521 272 478 824 630 551 

Pb 13 45 56 32 15 16 11 5 9 8 14 12 5 8 

Zn 104 276 112 38 65 113 133 89 228 112 203 211 109 75 

Ba 630 370 277 300 207 207 110 58 b50 112 b50 b50 b50 122 

Sr 165 208 89 232 93 51 33 26 14 63 12 11 8 27 

As 2 b0.5 8 3 b0.5 b0.5 8 6 b0.5 9 7 5 4 8 

Ni 16 23 28 6 4 b1 8 2 9 11 b1 3 10 12 

Co 10 11 21 b1 b1 2.0 b1 3.0 b1 2.0 b1 b1 2.0 2.3 

V 51 38 31 35 24 3 b2 b2 b2 b2 2 3 6 4 

Cr 11 9 18 23 6 b2 b2 b2 b2 b2 b2 b2 b2 b2 

Sb 0.7 1 2 b0.1 1.2 0.9 1.8 2.3 b0.1 1.6 b0.1 2.4 1.8 1.8 

b0.3 = below detection limit (0.3). 

87


Table 2b 

Correlation coefficients (r) of Au and most trace elements in the ore lodes and sulfidized granophyric dikes. 

Au Ag Cu Pb As Ni Co V Zn Ba Sr 

Au 1.000 

Ag 0.920 1.000 

Cu 0.899 0.834 1.000 

Pb −0.558 −0.506 −0.268 1.000 

As 0.387 0.367 0.328 −0.094 1.000 

Ni −0.524 −0.548 −0.334 0.694 0.092 1.000 

Co −0.543 −0.486 −0.268 0.767 0.080 0.869 1.000 

V −0.811 −0.730 −0.683 0.630 −0.381 0.584 0.606 1.000 

Zn 0.135 0.231 0.140 0.157 −0.216 0.157 0.077 −0.113 1.000 

Ba −0.833 −0.779 −0.711 0.474 −0.331 0.520 0.572 0.907 −0.191 1.000 

Sr −0.791 −0.793 −0.728 0.620 −0.386 0.431 0.376 0.874 −0.117 0.815 1.000 

Bold data indicates significant positive correlation. 

In order to quantify the volume (and mass) changes by hydrothermal 

alteration, Grant's (1986) equations: 

ΔV ¼ ð1=SÞ ρ a =ρ o –1 100; ð1Þ 

ΔM ¼ ðð1=SÞ–1Þ 100; ð2Þ 

where S is the gradient of the isocon, ΔV and ΔM are losses or gains in 

percent and ρ a /ρ o is the ratio for the specific density of altered rock 

and unaltered protolith, respectively. Two isocons were defined for 

each plot using the 1σ error bars of the immobile elements yielding 

a minimum and maximum gradient, defining the minimum and maximum 

values for mass and volume changes. From these, the mean 

values and error bars were calculated. 

Based on the mass balance calculations (Table 3), the inner, silicified–sericitized–pyritized 

wallrocks have experienced considerable 

volume and mass changes, compared to the outer, silicified–chloritized–carbonatized 

wallrocks (Fig. 4a,b). Addition of SiO2, K2O, L.O.I., 

Table 3 

Geochemical data and results of mass balance calculations of hydrothermally altered sheared metavolcanic/volcaniclastic rocks from Wadi El Beida−Wadi Khashab area. 

Least-altered host rocks Quartz (Qtz-chl-carb) alteration Inner (Qtz-Ser-Py) alteration 

n 4 6 7 

average 1σ average 1σ Gain/loss 1σ average 1σ Gain/loss 1σ 

g/100 g 

SiO2 wt.% 62.78 0.67 63.01 0.90 2.95 2.18 69.14 1.24 14.34 3.01 

a 

TiO2 wt.% 0.48 0.06 0.46 0.03 0.00 0.01 0.42 0.07 −0.02 0.01 

a 

Al2O3 wt.% 13.54 0.55 12.79 0.49 −0.20 0.33 11.87 0.53 −0.30 0.49 

t 

Fe2O3 wt.% 5.82 0.44 6.77 0.73 1.24 0.23 6.92 0.55 1.92 0.30 

MnO wt.% 0.07 0.05 0.23 0.06 0.17 0.01 0.19 0.08 0.14 0.01 

MgO wt.% 4.25 0.78 4.97 0.52 0.93 0.17 0.93 0.49 −3.21 0.04 

CaO wt.% 4.28 0.76 6.46 0.41 2.46 0.21 2.01 0.53 −2.04 0.09 

Na2O wt.% 2.73 0.37 2.29 0.12 0.39 0.01 1.65 0.42 −0.89 0.03 

K2O wt.% 3.18 0.58 2.16 0.45 −0.93 0.05 5.14 1.19 2.55 0.22 

a 

P2O5 wt.% 0.29 0.03 0.28 0.05 0.00 0.01 0.26 0.07 0.00 0.01 

L.O.I. wt.% 1.85 0.47 2.66 0.28 0.92 0.10 2.25 0.62 0.66 0.10 

S wt.% 0.08 0.01 0.87 0.43 0.83 0.02 1.03 0.26 1.07 0.04 

g/1000 kg 

Au ppm – – 0.51 0.17 0.53 0.13 2.23 0.96 2.37 0.55 

Ag ppm – – 0.2 0.3 0.21 0.01 1.1 1.2 1.23 0.05 

Cu ppm 29.8 7.2 94.7 82 66.4 31.5 143.3 85.3 108.5 40.89 

Cd ppm 4.0 – – – −4.0 – – – −4.0 – 

Mo ppm – – 12.3 20 12.83 0.41 2.5 1.9 2.79 0.11 

Pb ppm 42.3 5.1 20.2 30 −21.23 0.67 58.6 33.7 23.06 2.56 

Ni ppm 25.8 4.8 22 18 −2.85 0.73 26.3 18.2 3.53 1.15 

Zn ppm 94 18.6 61.3 112 −30.1 2.0 83.9 58.4 −0.42 3.66 

As ppm – – 12.1 9.5 12.62 0.40 5.6 3.81 6.25 0.24 

Ba ppm 591 96.7 627 134 158.2 4.23 61.2 13.1 −522.7 2.67 

Co ppm 23 3.67 21.3 32 −0.78 0.71 14.8 5.80 −6.49 0.65 

Cr ppm 40.8 9.4 34 193 0.1 4.1 46.0 173.4 10.84 10.7 

Eu ppm 0.7 0.00 1.1 1.3 0.45 0.04 0.7 0.60 0.08 0.03 

Sb ppm 0.5 0.00 1.3 2.2 1.29 0.04 1.4 0.7 1.06 0.06 

Sc ppm 17.8 1.48 21.1 2.3 5.25 0.07 9.1 8.08 −7.65 0.40 

Sr ppm 170.3 41.8 310.8 258 208.3 7.01 81.6 50.8 79.28 3.56 

Th ppm 0.63 0.21 0.80 0.2 0.20 0.03 0.53 0.60 −0.04 0.02 

V ppm 129 19.7 107.6 41 −16.7 21.25 92.6 69.2 −25.73 4.04 

W ppm – – 4 4.17 0.13 5 – 5.58 0.22 

Y a 

ppm 26 4.5 24.8 3.7 −0.13 0.00 23.1 3.3 −0.22 0.00 

La ppm 6.2 2.1 8.6 16 2.77 0.27 7.3 2.73 1.94 0.16 

Density gr/cm3 2.80 2.83 2.86 

n = number of analyzed samples. 

– Below detection limit. 

Gains/losses are given as g/100 g for major elements, as g/10 3 kg for trace elements, and as g/10 6 kg for Au. 

a 

Immobile elements chosen for the definition of the isocon.

Fe2O3* and S, and loss of CaO, MgO, and Na2O characterize the major 

chemical changes in the inner wallrocks. On the other hand, the silicified–chloritized–carbonatized 

rocks showed addition of most major 

and trace elements and depletion in K2O, V and Co (Table 3). Addition 

of SiO2, K2O, and S in the altered wallrocks that are relative to the 

fresh (unaltered) host rocks coincides with the pervasive silicification, 

sericitization and pyritization (Table 3). As chlorite and carbonate 

replaced most of the protolith mineralogy, addition of CaO, Fe 2O 3* 

and MgO occurred at the expense of K2O and Na2O in the carbonatized–chloritized 

wallrocks. The uniformity of element mobility and 

the relatively low error of the average values indicate that geochemical 

changes due to wall rock alteration were relatively homogenous 

on the deposit scale, with mass and volume increase towards the 

ore bodies. 


Fig. 3. Photomicrographs of microstructures in quartz veins from Wadi El Beida–Wadi Khashab area (crossed polarized light). (a) Ribbon-dominant vein specimen of preferably 

oriented large quartz crystals (qtz) and interstitial carbonate (cc), (b) Sheared large quartz ribbons. Fine-grained recrystallized grains developed along grain boundaries and 

along the shear planes indicative of grain-boundary migration/recrystallization in quartz veins, (c) Large quartz ribbons with serrate boundaries filled with sulfide minerals 

(dark) and cut by conjugate fracture sets locally with fine subgrains, (d) Bulging recrystallization of large quartz crystals, where grain boundaries are filled with sulfide minerals 

and wallrock material. Primary isolated and clustered fluid inclusions are abundant in the large quartz crystals, (e) Intensely re-crystallized quartz ribbons with fine-grained polygonal 

subgrains defining the C and S-planes. The gray quartz along S–C planes was likely derived by progressive resorption and recrystallization of the comb and buck quartz. 

Microscopic sulfide inclusions are ubiquitous, possibly contributing to the gray color of this quartz type, (f) texturally zoned extensional (syntaxial) veinlet with internal elongated 

blocky microstructures cutting the sheared mineralized quartz veins. 

6. Ore minerals 

Disseminated sulfides are common in the quartz veins, granophyric 

dikes and altered host rocks in shear zones. Principal ore minerals include 

pyrite, chalcopyrite, chalcocite, covellite, marcasite, and gold. Pyrite 

is ubiquitous, commonly as discrete and aggregated grains of 

variable size (from specks up to 3 mm-across). Inclusions of chalcopyrite, 

sphalerite, pyrrhotite and gold, less than 50 μm-across are common 

in many of the large pyrite crystals in the mineralized quartz veins and 

granophyric dikes (Fig. 5a,b). Pyrite is partly overgrown by chalcopyrite 

and/or chalcocite (Fig. 5c,d). Alteration of pyrite to goethite is common. 

Electron microprobe analyses (Table 4) reveal the presence of traces of 

Cu and Ni in pyrite and marcasite (up to 0.12 and 0.16, respectively). 

The analyzed pyrite is As-poor or barren and oscillatory zoning of As 

89


Fig. 4. Isocon diagram after Grant (1986) for: (a) the outer quartz–chlorite–carbonate 

alteration, and (b) the inner quartz–sericite–pyrite alteration, plotted against the unaltered 

host rock metavolcanics. 

in pyrite in the back-scattered electron (BSE) images is totally absent. 

Chalcopyrite forms patchy intergrowths with sphalerite and pyrite. Locally, 

chalcopyrite is variably replaced by chalcocite, covellite and 

digenite (Fig. 5d). A few grains of chalcocite were observed associated 

with chalcopyrite. Also, chalcocite intergrows with pyrite and marcasite 

in many samples. Sphalerite occurs as dark gray (Fe-rich), irregular and 

anhedral masses ranging in size from tiny specks to crystals more than 

1 mm across. The mineral is intimately intergrown with pyrite, chalcopyrite, 

and pyrrhotite. Large sphalerite patches show abundant chalcopyrite 

blebs ‘chalcopyrite disease’. Marcasite is locally associated with 

pyrite as irregularly-formed discrete grains or fine-grained aggregates. 

Marcasite, locally colloform, replaces pyrite and chalcopyrite in many 

samples (Fig. 5e,f). Gold forms small inclusions in pyrite, or disseminated 

in fine-grained quartz, sericite and calcite matrix in the intensively 

altered wallrocks. Gold occurs also as thin wires rimming pyrite crystals 

(Fig. 5g). The analyzed gold grains show, generally b10 wt.% Ag, and 

consistently high fineness levels (1000 *Au/Au+Ag>900). Hematite 

forms veinlets commonly associated with quartz (quartz–hematite 

stockwork) or occurs as foliation-parallel laminations of acicular laths 

in the basaltic andesite host rocks. The hematite laminations contain 

abundant relict magnetite inclusions, likely of pre-mineralization/alteration 

origin. Hematite associated with micro-crystalline quartz in 

quartz veins, however, contains no magnetite inclusions. Discrete gold 

inclusions can be found in the hematite veins where carbonate and supergene 

Cu-hydroxides are common (Fig. 5h). 

Goethite and malachite are supergene phases associated with sulfide 

minerals in voids or along micro-fractures. Ramadan and Kontny (2004) 

described a complex alteration of chalcopyrite to anilite (Cu 6.7Fe 0.3S 4) 

and covellite (CuS), and finally to delafossite (CuFeO2) basedonSEM 

and electron microprobe studies of the samples collected from El 

Beida mineralization. 

Analysis by LA-ICP-MS of several pyrite grains (Table 5a) revealed 

the presence of trace amounts of Au (8.5–120.1 ppm), Ag (2.2– 

57.8 ppm), As (42–468 ppm), Sb (up to 4.7 ppm), Ni (66–415 ppm), 

Co (218–701 ppm), Cu (120–6442 ppm), and Pb (26–121 ppm). Au 

values positively correlate with Ag and Cu, whereas, no correlation was 

observed between Au and As. Pyrrhotite contains traces of Au (26– 

35 ppm), Ag (2–27 ppm), As (23–45 ppm), Ni (29–1009 ppm), Co (54– 

339 ppm), Cu (47–129 ppm), Zn (24–31 ppm). Au positively correlates 

with Ag, and no distinct correlation has been observed between Au and 

the other elements. LA-ICP-MS measurements on marcasite reveal the 

presence of Au (up to 36 ppm), Ag (up to 3.3 ppm), As (up to 22 ppm), 

Ni (up to 34 ppm), Co (11–79 ppm), Cu (up to 263 ppm). Chalcopyrite 

contains traces of Au (9.3–18.4 ppm) and Ag (1.5–4.2 ppm) that do not 

show correlation with any other trace element (i.e., 357–611 ppm Pb, 

1345–899 ppm Zn; Table 5b). 

7. Fluid inclusions 

Upon a petrographic study, thirteen double-polished thick sections 

(~150 μm thick) that represent all types of the mineralized 

quartz veins were selected for microthermometric measurements. 

Selection of these samples was based on the availability of workable 

inclusions in synchronous groups (cf. Touret, 2001). Solitary inclusions 

and those that occur in clusters, or along intra-granular planar 

arrays (pseudosecondary inclusions) in less deformed quartz grains 

were considered for detailed petrography and microthermometric 

studies. Fluid inclusions on trails crossing grain boundaries are interpreted 

as secondary inclusions, and are discarded from further investigation. 

From each fluid inclusion assemblage (FIA: Goldstein 

and Reynolds, 1994), more than five representative inclusions with 

substantial size are measured for better reliability of the microthermometric 

results. 

Fluid inclusions in the mineralized quartz veins belong to the H 2O– 

CO2–NaCl±CH4(±N2) system. On the basis of their phase contents at 

ambient laboratory temperature, the observed fluid inclusions are 

grouped into three types, namely: type-I: bi-phase aqueous inclusions 

(liquid+vapor aqueous), type-II: bi-phase aqueous–carbonic (liquid 

CO2 bubble surrounded by liquid H2O), and type-III tri-phase, carbonicrich 

aqueous–carbonic inclusions (liquid H 2O–liquid CO 2–vapor CO 2), 

generally with no daughter minerals (Fig. 6a–d). The liquid CO2 bubbles 

in type-II inclusions have typically dark boundaries (meniscus) against 

the liquid H2O fraction, and show a characteristic phase change on 

both cooling and warming runs. Most of the observed fluid inclusions 

are 2–10 μm across, but a few ones measure up to 20 μm-across. The 

type-I inclusions are relatively large in size compared to other inclusion 

types in a single trail. Most of the type-I and type-II inclusions are elliptical 

or oval in shape, whereas inclusions of type-III commonly exhibit a 

negative crystal habit. The liquid to vapor ratios are used to discriminate 

between type-I and type-II inclusions. Whereas, proportions of the 

aqueous and carbonic phases are used to classify inclusions of type-II 

and type-III. The type-III inclusions show consistently small aqueous 

fraction (20–30%). 

7.1. Microthermometric results 

Microthermometric data of measured inclusions are summarized in 

Table 6 and Fig. 7. Composition and density of H2O–CO2 phases were estimated 

using the H 2O–CO 2–CH 4 ternary system (Jacobs and Kerrick, 

1981). Salinities of the aqueous inclusions (type-I) were calculated 

from the final ice melting temperatures (T mice) using the equation of 

Bodnar (1993). Whereas, salinities of the aqueous–carbonic inclusions 

(type-II and type-III) were based on the final melting temperatures of 

clathrate (in the presence of liquid CO2) using the computer program

package “clathrates” of Bakker (1997) and Bakker and Brown (2003). 

The equations of state of Brown and Lamb (1989) have been used to calculate 

the isochores for selected aqueous–carbonic inclusions. 

Total freezing was achieved by cooling down to −110 °C. Because of 

the difficulty of viewing phase changes in small inclusions, clathrate and 

ice melting measurements could not be performed on all inclusions for 

which T htotwas measured. Melting of CO 2 (T mCO2)intheaqueous– 

carbonic inclusions (type-II and type-III) occurred at −56.6 to 

−61.9 °C, but commonly between −57 and −59 °C (Fig. 7a). Melting 

of ice (Tm ice) in type-I inclusions occurred between −1.5 and −8.9 °C, 

but mostly clustered between −4 and−7 °C. In the aqueous-carbonic 


Fig. 5. Photomicrographs of the ore minerals of Wadi El Beida–Wadi Khashab mineralization (a) irregular relict patches of pyrrhotite (po) and sphalerite (sph) in a large pyrite (py) 

grain, (b) Disseminated gold blebs in carbonate horizon and associated with fine grains of pyrite (py), (C) Chalcopyrite (cpy) intergrown with pyrite and replaced by rhythmic covellite 

(cov) and chalcocite (cc), (D) Chalcopyrite intergrown with sphalerite (sph) and replaced by chalcocite (cc) and digenite (dig). Note development of malachite (mal) into a 

void, (e) collorform marcasite pseudomorphs pyrite (Backscattered Electron image, BSE), (f) Marcasite replacing pyrite–chalcopyrite intergrowth. (BSE), (g) Gold grain associated 

with a subhedral pyrite crystal. (BSE), (h) Malachite (mal) and calcite grains and veins cutting hematite lamination in the host metavolcanic rocks. Notice the dispersed gold speck 

(Au) in hematite (close up view given). (BSE). 

inclusions (type-II and type-III), clathrate melting varied from 8.2 to 

2.7 °C, but mostly between 7 and 5.5 °C (Fig. 7b). Inclusions of type-II 

showed clathrate melting at a wider temperature range (3.6–8.2 °C) 

relative to those of type-III (6.2–8.4 °C). Partial homogenization of CO2 

in type II and type III occurred commonly to liquid, but a few inclusions 

of type III displayed vapor bubble expansion and homogenization into 

the vapor phase (at 9.8–17.2 °C). A few two-phase aqueous inclusions 

exhibited H2O–CO2 clathrate melting upon warning, although no separate 

CO 2 phase is present. The presence of clathrate indicates that these 

inclusions contain a small amount of CO2, though melting points are 

barely observed (measured at ~7 °C in two inclusions). In the type II 

91


Table 4 

Representative EMPA data of sulfide minerals disseminated quartz veins from Wadi El Beida–Wadi Khashab area. 

Wt.% Pyrite Marcasite 

Fe 46.01 46.25 45.86 44.90 46.53 46.20 46.42 45.86 45.60 46.17 46.10 46.09 44.49 44.85 44.91 

S 52.66 52.92 52.66 52.83 52.23 52.80 52.71 52.73 52.39 52.71 52.62 52.52 53.75 53.54 53.81 

As – – – – – – – – – – – – – – – 

Cu – 0.07 0.09 0.04 – – 0.12 0.05 – – 0.09 – 0.09 – 0.11 

Ni 0.04 0.04 – 0.07 – 0.07 0.06 – 0.04 0.16 0.07 0.08 0.12 – 0.09 

Sum 98.71 99.21 98.52 97.94 98.76 99.07 99.31 98.64 98.03 99.04 98.88 98.69 98.41 98.39 98.92 

Chalcopyrite Sphalerite 

Fe 30.83 29.72 30.26 30.92 30.60 30.77 29.93 29.98 30.74 7.39 6.95 6.08 6.81 6.61 6.50 

S 33.86 34.33 34.02 35.13 34.25 34.79 35.27 34.29 34.84 34.04 33.88 34.54 34.53 34.19 34.29 

Cu 34.30 34.94 34.17 33.52 33.90 33.07 33.81 33.95 33.55 

Zn 0.03 0.05 0.15 0.11 0.15 0.03 0.23 0.11 0.03 57.64 58.29 58.79 57.64 58.44 58.49 

Sum 99.02 99.04 98.6 99.68 99.25 98.90 99.24 98.33 99.16 99.1 99.12 99.41 98.98 99.24 99.32 

Chalcocite Covellite Digenite Pyrrhotite Gold 

Fe 0.32 0.26 0.41 0.81 0.43 0.51 0.29 0.12 0.15 60.89 60.32 60.38 

S 21.32 22.09 22.19 32.17 31.98 32.24 22.15 23.23 22.87 38.65 38.42 37.96 

As 0.13 0.21 0.25 

Ni 0.16 0.12 0.09 

Cu 78.45 77.08 77.14 66.71 66.23 67.01 76.46 76.48 76.55 – – – 

Ag 0.12 – – 5.69 7.27 3.11 

Au 0.09 0.16 0.12 93.89 92.31 96.65 

Sum 100.16 99.43 99.74 99.73 98.64 99.79 98.9 99.83 99.57 100. 4 99.23 98.8 99.58 99.58 99.76 

– Below detection limit. 

Blank cells refer to unmeasured elements. 

aqueous–carbonic inclusions, Th CO2ranges between 29.2 and 8.7 °C, 

whereas type III inclusions showed T h CO2 between 3.4 and 20.2 °C 

(Fig. 7c). The total homogenization of all inclusion types (I, II and II) occurred 

commonly into liquid. In a few inclusions of type-III, homogenization 

does not involve the disappearance of the vapor bubble into the 

liquid phase, but the meniscus disappeared at higher temperatures and 

decrepitation is common. Decrepitation of the large H2O–CO2 fluid inclusions 

(>15um-long) at critical temperatures during measurement 

of total homogenization temperatures (Th total) was sporadic. The decrepitation 

temperatures varied from sample to sample, but mostly initiated 

around 330 °C. The undecrepitated aqueous–carbonic (type-II 

and type-III) and aqueous (type-I) inclusions showed comparable 

Table 5a 

Representative LA-ICP-MS measurements on some sulfides disseminated in the auriferous 

lodes in W. El-Beida-Khashab area. 

Spot Au Ag Sb Te Pb Bi As Ni Co Cu Zn 

be-Py01 – – – – 13 – 95 – 103 – – 

be-Py03 22.1 8.5 2.9 – 50 – 206 66 240 1022 – 

be-Py01 34.9 22.6 4.7 – – – – – 701 1225 48.1 

be-Py07 – – – – 26 – 468 103 – 335 – 

be-Py01 9.8 2.2 2.7 – 42 – – 190 308 120 – 

kh-Py05 120.1 57.8 – – 40 – 295 415 322 6442 43.5 

kh-Py06 17.2 36.4 2.6 – 75 – 42 – – 3228 – 

kh-Py09 8.5 11.7 – – 121 – 55 762 218 1119 – 

kh-Py11 24.6 13.6 – – – – – 297 – 139 23.9 

be-Po01 34.8 26.7 – – – – 45 1009 339 47 – 

be-Po03 25.7 5.9 – – 5 – 29 29 184 – 24.4 

be-Po15 30.5 24.0 – – – – – 111 254 – – 

be-Po07 – 7.9 – – – – 23 – 54 – 31.1 

be-Po01 28.0 16.3 – – – – – 37 95 129 – 

kh-Po05 – 1.8 – – – – – 109 58 – – 

kh-Mc6 – – – – 10 1.1 22 – 79 – – 

be-Mc9 20.6 2.4 – – 7 1.0 – 34 – 51 – 

kh-Mc2 12.9 1.6 2.7 – – – 16 – 11 – – 

be-Mc8 35.8 3.3 – – – – – 7 19 263 – 

kh-Cpy02 18.4 3.2 – – 602 – – 112 12 >>>> 1212 

kh-Cpy04 11.2 2.9 – – 441 – 24 24 – >>>> 903 

be-Cpy8 9.3 4.2 2.1 – 611 – – 53 7 >>>> 1345 

be-Cpy11 9.7 1.5 – – 357 – – 38 – >>>> 899 

Det. limit 0.1 0.6 1.8 16 2 0.2 10 6 1.6 17 20.8 

Py = pyrite, Po = pyrrhotite, Mc = marcasite, Cpy = chalcopyrite. 

total homogenization temperatures (Th total), broadly established on a 

considerable number of inclusions between 258 and 343 °C (Fig. 7d). 

However, the median homogenization temperatures from each cluster 

occur in relatively small ranges (mostly less than 30 °C). 

7.2. Fluid inclusions composition 

Data of fluid inclusion microthermometry indicate that chief components 

of the mineralizing fluids are H 2O and CO 2. Based on the ice 

melting temperatures, the aqueous inclusions (type-I) have salinities 

of 2.6–12.7 wt.% eq. NaCl. Based on the clathrate melting temperatures, 

type-II and type-III fluid inclusions have salinities between 2 

and 8.5 wt.% eq. NaCl, (Fig. 7e). Typically, the vapor-dominant inclusions 

(type-III) have lower salinities compared to the type-II inclusions. 

The aqueous inclusions (type-I) have a typical composition of 0.96– 

0.99 mol% H2O+0.04–0.01 mol% NaCl. Based on the Tm CO 2 and Th CO 2 

data of type-II and type-III inclusions, CO 2 density ranges between 

0.28 and 0.87 g/cm 3 . The bulk composition of measured fluid inclusions 

was estimated on the basis of volume percent of CO 2 and H 2O phases 

“degree of fill” at room temperature (Roedder and Bodnar, 1980). The 

volume percent of CO 2 in type-II inclusions ranges from 30 to 60%, 

which corresponds to XCO 2 (mole %) between 10 and 30. Whereas, 

most type-III inclusions have 70–90 vol.% CO 2, corresponding to 19– 

38 mol% of CO2. Melting below the typical melting temperature of 

pure CO 2 (−56.6 °C) implies the presence of dissolved gasses other 

than CO2. IfCH4 is assumed, approximately 6–14 mol% CH4 in the 

CO 2-bearing inclusions is estimated by applying the graphical method 

of mole composition of CO2–CH4 mixtures (Shepherd et al., 1985). 

7.3. Fluid mixing versus immiscibility 

The highly variable CO 2/H 2O ratios have been used as evidence of 

phase separation and heterogeneous trapping (Ramboz et al., 1982), 

fluid mixing (Anderson et al., 1992; Cassidy and Bennett, 1993; 

Pichavant et al., 1982), or post-entrapment modifications with variable 

loss of H 2O(Crawford and Hollister, 1986). The regular morphology 

(i.e., absence of necking-down) of the measured fluid inclusions 

and absence of vertical tendencies on the salinity–T h total diagram 

(Fig. 7f) and/or density variation from core to rim in a single quartz

grain (e.g., Huizenga and Touret, 1999) discards significant postentrapment 

modifications in the measured inclusions. Variable CO 2/ 

H2O ratios in the measured inclusions may, therefore, be attributed 

to immiscibility or heterogeneous entrapment, likely attained by mixing 

or unmixing (phase separation). 

Slight changes in ambient physical conditions (e.g., pressure) during 

the development of a shear zone can result in separation of CO2 

and H 2O phases from a parent, homogeneous aqueous–carbonic 

fluid. Trapping of immiscible fluids will result in coexisting vaporrich 

inclusions, and liquid-rich inclusions that show opposite modes 

of total homogenization over the same temperature range (e.g., 

Ramboz et al., 1982). This criterion is not met by the measured inclusions, 

where both liquid-rich and vapor-rich CO2-bearing fluid inclusions 

homogenize commonly to the liquid phase over a wide range of 

temperature, and without an obvious correlation between L:V ratio. 

Therefore, type-II and type-III inclusions cannot represent separated 

phases by immiscibility. Instead, heterogeneous trapping of two 

fluids is another possible mechanism that can result in preservation 

of CO2-rich fluid inclusions. Ramboz et al. (1982) outlined four criteria 

for determination of heterogeneous trapping of two fluids in 

the same inclusion: (1) simultaneous trapping of inclusions, (2) no 

evidence of leakage or necking, (3) scattered degree of fill, T h tot and 

bulk compositions, and (4) Th tot histogram that is non-symmetrical 


Table 5b 

Correlation coefficients (r) between gold and other trace elements in sulfide minerals disseminated in quartz veins. 

Au Ag Sb Pb As Ni Co Cu Zn 

Au 1.000 

Ag 0.800 1.000 

Sb −0.078 0.112 1.000 

Pb −0.208 −0.217 −0.019 1.000 

As 0.319 0.222 0.075 −0.165 1.000 

Ni 0.253 0.394 −0.228 −0.097 0.120 1.000 

Co 0.391 0.463 0.486 −0.319 0.040 0.327 1.000 

Cu 0.788 0.847 0.146 −0.123 0.446 0.201 0.298 1.000 

Zn −0.190 −0.241 −0.033 0.983 −0.207 −0.157 −0.318 −0.177 1.000 

and flattened. In the present study, type-II and type-III inclusions 

meet most of these four criteria. The type-I inclusions are mostly 

aqueous-only, but a few of them contain non-virtual fraction of CO2. 

This may imply incomplete mixing of originally aqueous and carbonic 

fluids. Linear “mixing trends” on Th total versus eq. wt.% NaCl plot are 

commonly used to test mixing of two fluids (Fig. 7f; Shepherd et al., 

1985). Heterogeneous mechanical trapping of varying proportions 

of the two end-member fluids (i.e., H 2O and CO 2±CH 4) is likely to result 

in poorly defined mixing trends (Shepherd et al., 1985), so this 

test may constrain the measured type-II and type-III inclusions. It is 

therefore, concluded that the investigated fluid inclusions are best 

explained by heterogeneous trapping of fluids during gold mineralization 

and vein growth. While type-II represent mixed aqueous and 

carbonic fluids, fluid mixing (miscibility) in the mineralized quartz 

veins might have been incomplete or succeeded by partial phase separation 

to generate the aqueous-only (type-I) and carbonic-dominant 

(type-III) fluid inclusions, due to pressure fluctuation throughout 

evolution of the shear zones. 

7.4. Conditions of gold deposition 

The measured fluid inclusions are considered primary or pseudosecondary 

in the sense of Roedder (1984). Combination of some features 

Fig. 6. Photomicrographs showing different types, shapes, and compositions of fluid inclusions in the mineralized quartz lodes at room temperature. (a) and (b) Mixture of H 2O-rich 

(type I) and CO 2-bearing (type-II, type-III) fluid inclusions, (c) and (d) variable degree of filling in three-phase CO 2-rich inclusions (type-III). 

93


Table 6 

Characteristics and microthermometric data of the different fluid inclusion types in mineralized quartz veins. 

Type I: H2O–NaCl inclusions (aqueous) Type II: H2O–NaCl–CO2±CH4±N2 inclusions 

(aqueous-rich) 

Abundance: ~25% of the bulk fluid inclusion population 

Mode of occurrence: isolated, clustered or trail-bound 

in association other incl. types 

Shape: sub-rounded, oval, elongate 

Size: ~4–20 μm 

Occurrence: isolated, in clusters, or on trails 

Vol.% H 2O vapor=5–20 

T m ice =−1.5 to −8.9 °C 

T h total=262 to 337 °C 

Salinity =2.7–12.7 wt.% NaCl eq. 

dH 2 O (g/cm 3 )=1.01–1.08 g/cm 3 

The used equations of state are given in the text. 

including: (i) the simple ore mineralogy, (ii) occurrence of gold specks 

and sulfide grains in cores of the less-deformed quartz crystals, and 

(iii) absence of severe post-entrapment modifications, suggests that 

gold introduction was coeval with formation of the quartz veins, typical 

for shear-related orogenic gold quartz vein systems (e.g., Dubé and 

Gosselin, 2007 and references therein). Association of the three inclusion 

types in primary/pseudosecondary sites in the mineralized quartz 

veins suggests gold deposition through fluid mixing (miscibility). The 

aqueous-rich and carbonic-rich fluid inclusions (type-II and type-III) 

have, therefore, inherently variable bulk compositions and densities. 

The entire range of Th totalof the aqueous (type-I) and aqueous– 

carbonic inclusions (type-II and type-III) is comparable with temperature 

conditions inferred from quartz textures of the mineralized lodes 

(e.g., Stipp et al., 2002). The total homogenization temperatures of the 

measured inclusions (258–343 °C), correspond to 0.8 to 2.3 kbars 

using isochores for the aqueous–carbonic inclusions. The calculations 

of pressure assuming that entrapment of fluids occurred under lithostatic 

conditions indicate depths of 3 and 9 km. Variations in the estimated 

P–T conditions could have been the result of exhumation and 

pressure fluctuation when the fluid straddled the brittle–ductile transition. 

The brittle–ductile deformation is consistent with vein-quartz textures 

that vary from brecciated to ribboned. 

8. Discussion and conclusions 

It has been established that numerous en-echelon sinistral NNWtrending 

Riedel shear zones in the Eastern Desert of Egypt are related 

to positive flower structures associated with the (620–540 Ma) Najd 

transcurrent shear system (e.g., Abdeen and Greiling, 2005; Fritz et al., 

1996). Formation of the NNW-trending, sinistral shear zones in the 

Wadi El Beida–Wadi Khashab area is attributed to a regional NNW– 

SSE folding and transpression (D2), during which extensive shear 

zones and conjugate fault systems were developed. The mineralized 

shear zones in the study area are part of the high-angle convergent 

wrench structure, namely Wadi Kharit–Wadi Hodein zone (e.g., 

Abdeen et al., 2008; de Wall et al., 2001; Greiling et al., 1994; Zoheir, 

2011). Spatial association of the investigated auriferous shear zones 

and regional convergent structures is typical for the orogenic, lodegold 

setting (e.g., Goldfarb et al., 2001; Huston et al., 2007). 

Within the shear zones, quartz veins, quartz network and granophyric 

dikes with disseminated sulfides are gold-bearing (~0.2–7ppm 

Abundance: ~45% of the bulk inclusions population 

Shape: equant, elongate, irregular 

Size: b2–15 μm 

Occurrence: isolated or on intra-granular trails 

DF=0.4–0.7 

T mCO2 =−57.3 to −62.4 °C 

T hCO2 =8.7 to 29.2 °C (to liquid) 

T m Clath=3.6 to 8.2 °C 


d CO2 (g/cm 3 )=0.62–0.87 g/cm 3 

Salinity =3.6–12.3 wt.% NaCl eq. 

XCO 2 (mol%)=10–30 

Bulk density =0.83–0.99 g/cm 3 

Type III: H2O–NaCl–CO2±CH4±N2 inclusions 

(carbonic-rich) 

Abundance: ~30% of the bulk inclusions population 

Shape: oval, oblate, negative crystal 

Size: b2–10 μm 

Occurrence: isolated, along intra-granular trails 

DF= b0.2–0.3 

T mCO2 =−56.7 to −59.6 °C 

T hCO2 =3.4 to 20.2 °C (into liquid) 

T hCO2 =9.8 to 17.2 °C (into vapor) 

T m Clath=5.0 to 8.9 °C 


dCO 2 (g/cm 3 )=0.12–0.91 g/cm 3 

Salinity =~2–9 wt.% NaCl eq. 

X CO2 (mol%)=12–77 

Bulk density =0.27–0.94 g/cm 3 

Au). The bulk gold-sulfide mineralization in the quartz lodes is confined 

to comb quartz mixed with ferruginated domains of sericite and carbonate. 

Incorporation of foliated wallrock slivers into the quartz veins 

and replacement of foliation seams adjacent to veins by hydrothermal 

minerals suggest that the mineralized quartz veins have developed coeval 

with formation of the shear zones (e.g., Robert and Brown, 1986). 

Structural control on mineralization is further evident by anisotropy 

of magnetic susceptibility measurements (Nano et al., 2002). 

Association of gold and pyrite is observed in all mineralized quartz 

samples. However, occurrence of gold specks in the hematite veins in 

the altered host rocks points toward the possible contribution of sulfidation 

of iron-rich rocks as a gold deposition mechanism. Presence 

of invisible gold in pyrrhotite and pyrite is evident from the electron 

microprobe data and LA-ICP-MS. The LA-ICP-MS data demonstrated 

that the elevated contents of As in Fe-sulfides are not coupled with 

an increase in their Au and Ag contents. A correlation exists between 

Au and Cu values in the measured pyrites. Similar to hydrothermal 

pyrites in orogenic and Carlin-style gold deposits (e.g., Large et al., 

2009), pyrite from the in the investigated samples shows simple 

trace element geochemistry, including only low values of Au, As, Ni, 

Cu, Zn, Co and Pb. The presence of (10s–100s ppm-levels) refractory 

gold in sulfides disseminated in gold-quartz lodes was described in 

other gold deposits in the Eastern Desert of Egypt (Hilmy and 

Osman, 1989; Zoheir, 2008), elsewhere in important orogenic gold 

deposits in the greenstone belts (e.g., Hutti deposit in India, Saha 

and Venkatesh, 2002). Solid solution may have been responsible for 

invisible gold, whereas, free gold deposition is a function of remobilization, 

reconstitution and concentration of the earlier phase. Thus, scarcity 

of visible gold in the quartz lodes in Wadi El Beida–Wadi Khashab area 

may be explained by the relatively low contents of invisible gold in 

sulfides. 

Infiltration of gold-bearing hydrothermal fluids into the shear zones 

led to pervasive alteration progressed from a quartz–sericite–pyrite 

assemblage in the vicinity of Au-quartz lodes, outwards to a quartz– 

chlorite–calcite assemblage. In places, both alteration assemblages have 

later been partly obliterated by argillic alteration (kaolinite + clay 

minerals). The systematic increase in SiO 2,K 2O and 3 K/Al and depletion 

in Na2O is suggestive of pervasive silicification and sericitization during 

evolution of the alteration. While, the erratic distribution of S in the 

wallrocks and granophyric dikes implies that sulfidation was selectively 

intense in the Fe-rich rocks. Phillips and Groves (1983) argued that the


Fig. 7. Histogram presentations of microthermometric data from fluid inclusions in mineralized quartz veins from Wadi El Beida–Wadi Khashab area. (a) Melting temperatures of 

CO 2 in CO 2-bearing inclusions type-II and type-III, (b) partial homogenization temperatures of CO 2 (T hCO2 )inCO 2-bearing inclusions, (c) clathrate melting temperatures (T m clath)in 

CO 2-bearing inclusions, (d) total homogenization temperatures (T h total) of all inclusion types measured, (e) calculated salinities of the three types of inclusions, (f) T h total versus 

salinity (eq. wt.% NaCl) plot of the fluid inclusions in the mineralized quartz veins used to test for fluid mixing. Notice the arbitrary trends of all inclusion types meet at the high 

temperature, low salinity area. 

95


depositional mechanism for gold in lode deposits hosted by iron-rich 

rocks was sulfidation of the host rock. Removal of S from the ore fluid 

destabilizes gold-thio complexes and leads to gold deposition. The frequent 

association of hematite and variably oxidized Fe–Cu-sulfides 

(i.e. pyrite, chalcopyrite) with gold specks suggests that sulfidation 

was important for gold deposition at the Wadi El Beida–Wadi Khashab 

area. Removal of S from the ore fluid through fluid–wallrock interaction 

could have destabilized gold-thio complexes and contributed significantly 

in gold deposition (e.g., Cox et al., 1995). 

The distribution and compositional characteristics of the different 

aqueous and aqueous–carbonic fluid inclusions (types-I, II and III) are 

best explained by mixing of H2O- with CO2-rich fluids. The fact that 

most fluid inclusions homogenize to the liquid phase and have overlapping 

salinity values excludes the possibility that unmixing of H2O– 

CO 2–NaCl occurred during trapping or that significant reworking of 

the fluid inclusions subsequent to trapping has occurred (e.g., 

Ramboz et al., 1982). Heterogeneous entrapment and fluid mixing 

in the investigated Au-quartz lodes occurred at depths of 3–9km 

(i.e. T h total vs. eq. wt.% NaCl plot, Fig. 7f). Mixing with aqueous fluid 

enriched the ore fluids in oxygen and decreased sulfur activity (e.g., 

Loucks and Mavrogenes, 1999). Fluid mixing as a gold-deposition 

mechanism in lode-gold deposits is described in the Eastern Desert 

Au deposits (e.g., Harraz, 2000) and elsewhere in important gold deposits 

worldwide (e.g., Boiron et al., 2003; Olivo et al, 2006, and references 

therein). 

Unlike the genetic model proposed by Arehart (1996) for Carlintype 

deposits, emplacement of orogenic lode gold mineralization generally 

occurs at crustal depths in excess of several kilometers. This 

makes direct interaction of a hot and reduced fluid with a more oxidized 

fluid of purely meteoric origin is less likely and requires an alternative 

process to initiate fluid mixing, such as the fault valve 

mechanism (e.g., Sibson and Scott, 1998). In this model, repeated 

lock-up and failure of second-order faults result in fluid migration 

into the surrounding wallrocks during cyclic pressure built-up, followed 

by fault failure and reversal of the pressure head, and hydrothermal 

sealing of the dilational zone. During penetration of, and 

interaction with the wallrock, the hydrothermal auriferous fluid 

evolves toward more reduced conditions before reacting with more 

oxidized fluids within the active fault zone, causing destabilization 

of gold complexes and gold precipitation (e.g., Cox et al., 1995). 

The new geochemical and mineralogical data presented in this 

study combined with the extensive gossan along the shear zones, together 

with the available geophysical data (Sultan et al., 2009) most 

likely indicate potential gold ore bodies. Accordingly, this area and 

areas of discernible hydrothermal alteration along major convergent 

wrench structures in the Eastern Desert of Egypt warrant extensive 

assay and pitting programs for commercial evaluation. 

Acknowledgments 

This work is financed by Egyptian Science and Technology Development 

Fund (STDF), grant no. 150. The author highly appreciates 

the intimate cooperation between the STDF team and Benha 

University. Professors B. Lehmann (TU-Clausthal, Germany), P. 

Weihed (Lulea University of Technology, Sweden) and Richard 

Goldfarb (US Geological Survey, Denver) are thanked for allowing 

the different laboratory faculties during the course of undertaking 

this study. The manuscript was much improved by reviews of Dr. 

Agustin Martin-Izard (JGE Associate Editor) and two anonymous 

reviewers. 

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