1. MINING
To define the ore from the
waste rock,
samples are taken
at set intervals along surveyed lines within the pit. These samples
are assayed. Assay
results are used to mark out areas of ore and waste rock, which are
mined separately. Some of the harder areas require blasting to
loosen the rock prior to excavation by hydraulic diggers. Dump
trucks haul the rock to the primary crushers.
2. CRUSHING
The primary crushers - two
Stamlers and a
jaw crusher -
located at the mine site, receive ore and waste at separate times.
They break the larger rocks down to a size suitable for transport on
the conveyor.
3. TRANSPORT
A rubber belted conveyor transports the ore and waste rock to the
mill and waste
disposal area. Large electromagnets remove any steel debris
excavated from the old workings.
4. GRINDING AND SIZING Ore is
stockpiled at the mill before being fed into a
S.A.G. mill with
lime, water and steel balls. The larger particles from this mill are
returned to the S.A.G. mill for more
grinding. The
finer particles receive more grinding in a
ball mill, and
are size classified to give a final product of 80% <70 microns.
5. LEACHING & ADSORPTION
A slurry of ground ore, water and a weak
cyanide solution
is fed into large steel
leach tanks
where the gold and silver are dissolved. Following this leaching
process the slurry passes through six adsorption tanks containing
carbon
granules which adsorb the gold and silver. This process removes 93%
of the gold and 70% of the silver.
6. ELUTION & ELECTROWINNING The loaded carbon is fed into an elution column where the
bullion is washed off. The barren carbon is recycled. The wash
solution—pregnant electrolyte—is passed through electrowinning cells
where gold & silver is won onto stainless steel cathodes.
7. BULLION PRODUCTION
The loaded cathodes are rinsed to yield a gold and silver bearing
sludge which is dried, mixed with fluxes and put into the furnace.
After several hours the molten material is poured into a cascade of
moulds producing bars of
doré bullion.
8. WATER TREATMENT
Some water from dewatering the mine, from the embankment underdrains
and decantation from the
tailings pond is
recycled for use in the grinding circuit. Excess water is pumped to
the Water Treatment Plant and treated to the required standards
before discharge into the River.
9. TAILINGS DISPOSAL Waste rock from the
mine is used to build the embankment structure. The embankment
retains the tailings slurry in a pond where solids settle and
compact. Water is decanted off and used in the process plant or
treated before it is discharged.
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