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GOLD
April 2015
MODERN MINING
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requirements will vary by year as most of the
saprolitic (oxide) material is free-digging, while
all of the unweathered material (sulphide/
fresh) requires drilling and blasting. Loading
will be done with a combination of excavators
and front-end loaders. Material will be loaded
into 50-t to 90-t capacity trucks depending
on the deposit’s location and pit size. Where
possible, material will be taken directly to the
plant but, at satellite deposits, material will be
placed in stockpiles near the pits. This material
will then be reclaimed with front-end loaders
and loaded into 50-t trucks and hauled to the
crushing facility.
Soft run-of-mine ore will initially be crushed
by a mineral sizer and passed through 18 mm
and 180 mm screens. The ball mill will grind
the feed into finer particle size (80 % passing
through a 106 µm screen) to enable gold recov-
ery via gravity concentration or carbon in leach
(CIL). Approximately 40 % of the gold is grav-
ity recoverable.
The main mill product will flow to the
CIL process but a select fraction of the mill
output will be separated and fed into a grav-
ity gold circuit applying centrifugal force to
concentrate heavy, gold bearing particles for
intensive leaching. Once leached, the gold
bearing pregnant leach solution will be piped
into an electrowinning cell. The gravity tails
will be returned to the mill stream.
The gold solids recovered from the gravity
and CIL circuits will be transported into the
secure gold room, where they will be smelted
at a high temperature to produce molten gold,
which will be poured into gold doré bullion
and shipped to a refinery.
The project is estimated to require an initial
2,6 MW of base load power to operate, with
5,6 MW installed power, and Hummingbird
intends contracting out the power generation
on a diesel rental basis. Installation of 1 MW
of solar PV power on a turnkey rental basis is
under consideration to reduce opex.
Summing up the project, Betts describes the
planned mine as being capable of turning a
profit in a varying gold price environment. “The
metallurgy of our resource is excellent, our
power requirement is low and we have a plen-
tiful supply of water. We have an experienced
team ready to start on construction and also
all funding – primarily a US$75 million debt
facility agreed with Taurus Fund Management
– in place. There really is no downside to the
project and we are looking forward to pouring
our first gold next year after a 12-month build
period,” he says.
While Yanfolila will be Hummingbird’s
first mine it is unlikely to be its last. The com-
pany also holds the Dugbe 1 gold project in
south-east Liberia which has the potential to
be bigger than Yanfolila. “Dugbe represents
a virgin discovery by our geologists and now
boasts a resource of just over 4 million ounces
of gold at an average grade of 1,4 g/t,” he says.
“This certainly ranks as Liberia’s biggest gold
deposit and, in fact, is impressive by global
standards. We completed a PEA in 2013 which
demonstrated the viability of a 20-year project
producing up to 125 000 ounces a year in its
early years and we’re now well advanced with
our DFS – which is currently under optimisa-
tion.” He adds that the DFS is being prepared
by a team of consultants led by South Africa’s
MDM Engineering.
In a significant development for Dugbe,
Hummingbird recently announced that it had
signed a collaboration agreement to embark
on the planning and development of a 20 to
30 MW hydro-electric power plant in the Dugbe
area. The agreement is with IFC InfraVentures,
part of the IFC Global Infrastructure Project
Development Fund, and energy company
Aldwych International. To test the viability of
the project, a Pre-Feasibility Study (PFS) is to
be undertaken by Knight Piesold Consulting
(Vancouver) and should be completed by
April next year. The PFS is being funded by
IFC InfraVentures.
Comments Betts: “The hydro-project –
assuming it goes ahead – will not only enhance
the economics of Dugbe 1 by reducing the oper-
ating costs but will also act as a more general
Flowsheet for the Yanfolila
gold project.