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DIAMONDS
October 2015
MODERN MINING
31
Toe of the new slimes dam
wall (September 2015).
assortment (US$/carat/sieve
size). The resultant revenue
estimate was increased to
align to the BCO of the new
treatment plant of 1,25 mm.
Furthermore, the large stone
potential was investigated
by extrapolation of assort-
ment and SFD data beyond
+10,8 ct/stone.
Applying the latest rev-
enue estimates in the mine
plan resulted in a weighted
un-escalated average diamond
price of US$131/ct, which has
equated to an average esca-
lated diamond price over the
life of mine of US$165/ct,
representing an increase of
approximately 13 % from the
2013 DFS. Given the current market condi-
tions, the 2014 revenue estimate has not been
escalated until 2017 in the financial model.
The first stage in producing the new mine
plan involved the appointment of an inde-
pendent consultant to update the SAMREC
compliant 2009 diamond resource estimate for
Liqhobong.
This process started with a detailed re-log-
ging of the main pipe borehole core, enabling
the construction of a new 3D geological solid
model for the project. As part of the re-logging
exercise, new density measurements were also
collected which allowed for a local block esti-
mate of density for the first time. The previous
grade estimate was also based on the wide
diameter holes drilled during 2008 but has
now been updated to exclude the boart com-
ponent. The independent work, undertaken in
accordance with SAMREC guidelines (2009),
estimated that the Liqhobong main pipe con-
tains: an indicated diamond resource to a depth
of 2 467 m above sea level or masl (183 m below
surface) estimated to comprise 9,5 Mct in 35 Mt
of kimberlite at an average grade of 27 cpht;
and an inferred diamond resource below
2 467 masl, estimated to contain 13,5 Mct in 48
Mt at an average grade of 28 cpht.
The 22 % carat reduction in the total dia-
mond resource from 2009, says Firestone, is
mainly a result of the reduced volume due to
the new geological model and the pipe tapering
at depth, the removal of the boart carats, the
increase in the BCO to 1,25 mm from 1,0 mm
and depletions due to the pilot plant.
The Liqhobong project is being built under
the direction an owner’s team led by Glenn
Black, Firestone’s Chief Project Officer. The
EPCM contractor is DRA with the other major
contractors being Turnkey Civils Lesotho
(Residue Storage Facility), Stefanutti Stocks
(civils and earthworks) and SMEI (structural,
mechanical, platework and piping). The total
workforce currently numbers around 680 and
the site had recorded zero lost time injuries
(with over 1,3 million man hours worked) to
the end of September.
Photos courtesy of Firestone Diamonds
french sa