61 / 82
January 2015
MODERN MINING
59
DIAMONDS
Top projects
Left:
Plant and infrastruc-
ture layout post 15 years of
phase 1 mining.
Below:
Layout of the new
plant, which will have a
capacity of 3,6 Mt/a.
grade – approximately 2 to 6 cpht. This low
grade is offset, at least in the case of Letšeng, by
the consistency with which large high-quality
stones are produced – in fact, Letšeng typically
gets an average of well over US$2 000/carat for
its diamonds.
“Liqhobong, by contrast, has an exception-
ally high grade by Lesotho standards of 33 cpht
but its diamonds have generally been regarded
as low value,” he explains. “The base case price
per carat used in the revised DFS is a relatively
modest US$107 and the project, of course, is
highly viable on this basis. We do believe, how-
ever, that Liqhobong – like its neighbours – has
the ability to produce large stones. The figure
of US$107 is based on the recovery and sale
of the diamonds from the pilot plant operation
but does not take into account breakage of large
stones in the plant which – due to shortfalls in
its design – was a persistent problem.
“We estimate that over the 22 months we
operated the pilot plant nine large 100 carat
plus stones were crushed. Based on an analysis
of the fragments, three of them were calculated
to be over 200 carats, with the biggest being
an approximately 430 carat yellow diamond.
Taking large stones into account, our expec-
tation is that the average price could rise to
US$156 per carat – hence the upside case in
the revised DFS.”
The DFS envisages open-pit mining of the
main pipe down to 393 m over 15 years –
exploiting a reserve of over 11 million carats at
a grade of 32,07 cpht – at an average strip ratio
of waste to ore of 2,28. The ore will be treated in
the Main Treatment Plant (MTP) which utilises
a conventional flowsheet comprising scrub-
bing, screening, crushing, concentration via
DMS, and final recovery using X-ray machines.
The plant will have 2 x 250 t/h streams. The
mining cost is estimated at R21,5/t and the pro-
cessing cost at R57,8/t. The total cost per tonne
of ore processed is projected at R140,92/t. The
mine will have a power draw of approximately
5 MW, to be supplied from the Lesotho grid.
With the funding under its belt and avail-
able in the second quarter of 2014, Firestone
was able to award the key contracts and
launch the construction phase of the project
in May/June 2014 and by 20 June over R1 bil-
lion of the project budget had been committed.
DRA was appointed as the EPCM contractor
while other awards include the residue storage
facility or RSF (Turnkey Civils Lesotho), the
civils and earthworks (Stefanutti Stocks), the
structural, mechanical, piping and platework
or SMPP (SMEI Projects) and the overhead
power line required to connect the site to the
Lesotho grid (Infrastructure Projects). Some of
these elements are substantial with the RSF
contract being worth R330 million, the civil
and earthworks R263 million and the SMPP
R327 million.
In addition, the contracts for the supply of
long-lead items such as the crushers, scrubbers,
apron feeder, vibrating screens and primary
rock breaker have all been placed. The fact that
the mining industry globally is in a subdued
state has assisted Firestone inasmuch as suppli-
ers generally have capacity and have submitted
competitive prices. The escalation risk has
“We estimate
that over the
22 months we
operated the
pilot plant nine
large 100 carat
plus stones were
crushed.”
Stuart Brown, CEO,
Firestone Diamonds