Modern Mining October 2015

DIAMONDS

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

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

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

Toe of the new slimes dam wall (September 2015).

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October 2015  MODERN MINING  31