Mine excursion
Work on the main drive is progressing steadily. Reliant SPRL is
the mining contractor appointed to develop the first phase.
the main adit, will be connected
to the main drive by means of a
vertical shaft. Currently the team
is advancing at a rate of 1.5m per
day, and blasting takes place every
second day. Work on a second
ventilation shaft is underway.
Mining method
The chosen mining method at
Bisie is sub-level caving. “We
have contracted a consulting team
called Mine Quest, who managed
the transition from conventional
stoping to sub-level caving at the
Trojan Nickel project in Zimbabwe,
to drive the process,” says Faber.
“Sub-level caving is not a true
caving mining method in that the
orebody is still drilled and blasted,
it is best visualised as a long hole
retreat mining method where
the hanging wall is allowed to
cave,” explains Faber. This mining
method is normally suited for
massive ore bodies with a steep
dip where the orebody has higher
rock mass characteristics than the
host rock. In such circumstances
the ore is extracted by drilling,
blasting and loading, allowing
the hanging wall to fracture and
cave under controlled conditions.
It is due to the caving of the
hanging wall that in designing the
mine, the infrastructure is always
placed on the footwall side.
Faber says that the mining
direction will be top-down, with
suitable lead-lags between the
advancing faces to ensure safety of
the people operating on the levels
below. The production drifts will
be developed on the orebody and
slot raises developed between the
levels to initiate the stope mining
face. Blasting rings will be drilled
from the production drift using
mechanised electro-hydraulic
drill rigs. Minimising blasthole
deviation when drilling is crucial
as accuracy of the hole is required
to ensure correct fragmentation,
enhance the flow of ore inside
the cave, and reduce dilution.
“Our biggest concern is dilution.
It is essential that we manage the
dilution, and therefore we brought
in the experts,” says Faber. Some
models on sub-level caving do suggest
dilution of more than 50%, which
could reduce tin production and
negatively impact on profitability at
JANUARY 2018 MINING MIRROR
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