Mining_Methods_UnderGround_Mining - Mining and Blasting

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