Mining_Methods_UnderGround_Mining - Mining and Blasting
Mining_Methods_UnderGround_Mining - Mining and Blasting
Mining_Methods_UnderGround_Mining - Mining and Blasting
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CaMPO FOrMOSO, Brazil<br />
Sub level caving for chromite<br />
in search of<br />
excellence<br />
Cia de Ferro Ligas da Bahia (Ferbasa)<br />
is a private capital group,<br />
which produces chromite, silicon<br />
<strong>and</strong> limestone. One of Brazil’s most<br />
important metallurgical companies,<br />
Ferbasa has surface <strong>and</strong> underground<br />
mining operations in<br />
the state of Bahia in north-eastern<br />
Brazil, where their Pedrinhas open<br />
pit chrome mine, located in Campo<br />
Formoso, has been in operation<br />
since 1961. Pedrinhas currently pro-<br />
duces about 2,400,000 cu m/year<br />
of chromite ore <strong>and</strong> waste, yielding<br />
54,000 t/year of hard lump chromite<br />
<strong>and</strong> 114,000 t/year of chromite<br />
concentrate. At the Medrado<br />
<strong>and</strong> Ipueira underground mines,<br />
lump chromite is produced using<br />
primarily sublevel caving techniques<br />
with raises opened using slot<br />
drilling, where a fleet of Atlas<br />
Copco equipment offers key support<br />
in exploration, development<br />
<strong>and</strong> production.<br />
underground geology<br />
Located in the city of Andorinha, around<br />
100 km from the Pedrinhas mine, the<br />
company’s underground operations have<br />
been developed within the Medrado/<br />
Ipueira deposit.<br />
This is one of several chromite-mineralized<br />
intrusions in the Jacurici Valley<br />
in the north-east of the São Francisco<br />
Craton, which hosts Brazil’s largest<br />
chromite deposits. Being irregular <strong>and</strong><br />
fractured with numerous faults, the deposit<br />
presents a considerable geological<br />
<strong>and</strong> mining challenge.<br />
The Medrado/Ipueira deposit is divided<br />
into several mining areas. There<br />
are the Medrado mine <strong>and</strong> the Ipueira<br />
mine, the latter of which is divided into<br />
five working areas: Ipueira II, III, IV,<br />
V <strong>and</strong> VI. Currently, besides Medrado,<br />
only Ipueira II, III, IV <strong>and</strong> V are operational,<br />
whereas Ipueira VI is a future<br />
expansion project. The underground mi-<br />
nes have been in steady operation since<br />
1977. In 2004, Ipueira produced 450,000 t<br />
Entrance to the Ipueira mine.<br />
of run-of-mine ore for a final produc-<br />
tion of 127,000 t of hard lump. In the<br />
same year Medrado produced 192,000 t<br />
of ROM ore for a final production of<br />
48,000 t of hard lump. Current target<br />
is a total of 216,000 t of hard lump.<br />
underground exploration<br />
The company is always looking for the<br />
best way of doing things in consultation<br />
with workers, technical consultants <strong>and</strong><br />
through visits to other mines. The consultation<br />
process also includes manufacturers<br />
of mining equipment, with which<br />
Ferbasa discusses the best technological<br />
options for its operations. This consultation<br />
process is very important for the<br />
mine, in order to help maintain a high<br />
level of modernization.<br />
From a geological point of view, the<br />
Medrado/Ipueira orebody represents a<br />
challenge. With an average thickness of<br />
8 m, <strong>and</strong> 500 m-long panels, the orebody<br />
is irregular <strong>and</strong> fractured with numerous<br />
faults. The accurate delineation of<br />
the orebody is very important, <strong>and</strong> to<br />
this end the geology department has to<br />
carry out a great deal of exploration<br />
drilling. The main machine employed in<br />
this key task is an Atlas Copco Diamec<br />
U6 exploration drill rig equipped with<br />
an operator’s panel. This machine is<br />
used in all situations at the underground<br />
mine, to drill holes of up to 150 m-deep.<br />
The decision to acquire this machine<br />
took into account the fact that it is equipped<br />
with a wire line system. This<br />
feature makes possible to conduct core<br />
drilling in the worst rock conditions,<br />
such as the faulted <strong>and</strong> fractured rock<br />
at Ferbasa.<br />
Ferbasa carries out about 7,200 m/y<br />
of drift development. The fleet of deve-<br />
lopment rigs includes two Atlas Copco<br />
electro-hydraulic units. One is a Rocket<br />
Boomer H 252 rig equipped with COP<br />
1238 rock drill which drills 3.9 m-long<br />
holes to achieve 6,000 drilled metres/<br />
month at a productivity of 55 m/hour.<br />
There is also a Rocket Boomer M2 D<br />
rig equipped with COP 1838ME rock<br />
drill which drills 4.5 m holes to achieve<br />
12,000 drilled metres/month at an average<br />
rate of 70 m/hour.<br />
Sublevel caving<br />
The main underground mining method<br />
employed is longitudinal sublevel caving,<br />
though open stoping is also used<br />
in some areas of Ipueira, depending on<br />
the layout of the orebody. When the orebody<br />
is vertical, sublevel caving is used<br />
underground mining methods 129