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January 2017
MODERN MINING
49
Top projects
GOLD
A recent photo of the Nkran
pit, the main source of the
Phase 1 ore.
roughly doubling to 470 000 ounces a year. Our
combined resources for Nkran – including sev-
eral satellite deposits – and Esaase amount to
7,94 Moz at a grade of 1,71 g/t and our reserves
are 5,25 Moz at 1,68 g/t. The reserve grade at
Nkran is 2,21 g/t as opposed to 1,41 g/t at Esaase
but Esaase is the larger deposit, accounting for
around 56 % of our total resource ounces.”
Phase 1 is a conventional open-pit, CIL
operation. The mining is in the hands of mining
contractor PW Ghana, highly experienced in
gold mining in the West African region (includ-
ing at Obotan, where it worked for Resolute).
PW’s trucking fleet consists of mainly new
Cat 777s working with a mix of shovels and
excavators, among them a new 300-ton shovel
which arrived on site earlier last year.
Commenting on the mining operation, Truter
says that Asanko was ‘over-mining’ quite sub-
stantially until recently. “We’re currently a
single-pit operation so – to derisk this – we took
the decision to build up a strategic stockpile of
over 1 Mt on the ROM pad. We’ve achieved
this objective, which means that we’ve been
able to cut back the mining rate. We’ve also put
in a twin ramp system to avoid bottlenecks in
the pit and have multiple working faces avail-
able at various elevations to manage water
ingress and any pit slope instability. The maxi-
mum rate at which we can mine at Nkran is
3 Mt/a, so to reach our target of 3,6 Mt/a we
have to bring Dynamite Hill into operation.”
Truter notes that there have been some slope
failures in the Nkran pit. “To counter this, we’ve
now become the first mine in Ghana –- indeed in
West Africa, as far as I know – to install a slope
stability radar (SSR), which we’ve sourced from
an Australian company, GroundProbe. The SSR
monitors movement on a millimetre by milli-
metre basis. The information is transmitted
to our geotechnical office which analyses the
data and can then alert personnel in the pit if
any slippage is expected – and even give a very
accurate estimation of when it might happen
and the volumes involved. We demonstrated
the system recently to Ghana’s Chief inspector
of Mines and he was hugely impressed.”
Moving to the process plant operation, Truter
says the facility – whose basic design was com-
pleted by PMI before Asanko’s involvement
– has performed extraordinarily well and is
now achieving gold recoveries of around 94 %,
which is above feasibility study estimates. “As
I’ve mentioned, the plant is now exceeding its
design capacity,” he observes. “Interestingly,
the mills – which PMI bought and we inherited
– were over-designed and have been more than
capable of keeping up with the higher tonnages
we’ve been putting through the plant. Where
we did have a bottleneck was with the crusher
circuit. So we’ve recently commissioned a
mobile crusher– a Sandvik UJ440i. This can
The SSR monitors
movement on
a millimetre by
millimetre basis.