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June 2015
MODERN MINING
47
MINING IN AFRICA
feature
Machines belonging to
mining contractor PW
Ghana in action at the mine.
Asanko Gold announced
in November last year that
it had selected PW for the
Nkran pre-strip – Nkran
is the main pit at Obotan
– plus the first year of
mining operations. The
prestrip operations are well
underway with the first
ore having being already
intercepted and stockpiled.
Genser Energy Ghana to build Asanko power plant
Asanko Gold Inc announced in
early June the signing of a binding
Power Purchase Agreement (PPA)
with Genser Energy Ghana Limited
(Genser) for the supply of all the
power required for Phase 1 of the
Asanko Gold Mine. Genser is an es-
tablished independent power pro-
ducer and power plant operator in
Ghana that provides power to large
industrial and parastatal clients.
Under the agreement, Genser
will build and operate a 19,2 MW
liquid fuel power plant adjacent
to the mine site and supply 17 MW
of nominal power to Phase 1 on a
fixed-price, life-of-mine contract.
The initial contracted rates for the
first two years (2016 and 2017) are
slightly below the rates that were
published in the Phase 1 Definitive
Project Plan in November 2014. In
2018 and 2019 the contracted tar-
iffs decrease in each year providing
a benefit to the long term operat-
ing cost profile of the mine.
Permitting and construction of
the 19,2 MW plant will begin im-
mediately, with power expected
to be available in Q4 2015 in ad-
vance of commissioning Phase 1 in
early 2016.
million when compared to a standalone Esaase
plant and associated infrastructure. These sav-
ings include a shared and expanded tailings
storage facility (US$23 million), utilisation
of the current power supply line being con-
structed for Phase 1 (US$7 million), buildings
such as workshops and offices (US$7 million),
civils works and plant terraces (US$7 million)
and savings in construction accommodation
and facilities (US$9 million).
An industry standard, troughed overland
conveyor has been chosen as the ore trans-
port method with a low operating cost of
US$0,71 per tonne. The conveyor represents
the most optimal method when compared to
the various other options that were reviewed
including trucking, rail or piping. Although
the capital cost of the conveyor is significant,
this is more than offset by the other savings
that have been achieved, as well as its low
operating costs, providing a net capital saving
of US$17 million compared to the standalone
2013 PFS for Esaase.
The Phase 2 study will be advanced to a full
Definitive Feasibility Study (DFS), which will
also seek to optimise the mining operations by
more efficiently sequencing the six open pit
deposits into one integrated mining schedule,
as well as achieve process synergies and opti-
misations. The DFS will commence during the
current quarter, with an investment decision
planned for Q2 2016.
The US$270 million, Phase 2 expansion will
take approximately 18 months to build, with
production from Esaase targeted to come on
stream in Q1 2018. This timetable is predicated
on a positive investment decision from Asanko
Gold’s board in Q2 2016.
The Phase 1 processing plant is currently
around 50 % complete. It includes single stage
jaw crushing with reclaim from a live stockpile
and open circuit SAG mill, feeding cyclones
that in turn operate in a closed circuit with a
ball mill. A pebble crusher will receive scats
from the SAG mill, crush them and return
them to the SAG for further grinding. The
hydrocyclones will achieve the final product
size of P80 106 µm. A gravity circuit will be
utilised to treat a portion of the cyclone under-
flow stream to recover coarse free gold, around
40 %, from the recirculating load. The milled
product will gravitate to a trash screen before
entering a pre-leach thickener followed by a
conditioning tank.
A seven-stage CIL circuit will be used to
leach and adsorb gold from the milled ore onto
activated carbon. An AARL elution circuit will
be used to recover gold from loaded carbon.
Cyanide in the CIL tailings will be detoxified
using the SO
2
/air method.
The Phase 2 expansion project will expand
the central processing facility with the addi-
tion of a 5 Mt/a ball mill, gravity concentrator
followed by a flotation circuit. The concentrate
from the float circuit at a mass pull of plus/
minus 10 % will be reground and then trans-
ferred to a new CIL circuit for leaching and then
final gold production.
Phase 2 further makes provision for the
opportunity to optimise feed material streams
to either the flotation or whole ore leach circuit
via interlinking conveyors between the respec-
tive mill feed circuits. In doing this, there is an
opportunity to optimise recoveries and oper-
ating costs depending on the ore types being