Modern Mining March 2019

feature DIAMOND MINING Layout of the Liqhobong mine. “The mine was built without a single LTI being recorded throughout the development phase and well into the operating phase.”

has at least another two years available before it has to take a decision on whether to pro- ceed with Cut 3. Discussing the current performance of Liqhobong, Bosma says the mine is func- tioning extremely efficiently. “This is a very low cost opera- tion run by a very experienced team that has a good under- standing of the orebody,” he says. “Most metrics are improving from quarter to quarter and we’re on track to meet guidance of 820 000 to 870 000 carats during FY-2019 from the treatment of between 3,6 and 3,8 Mt of ore. The pro- cessing plant is exceeding its nameplate capacity of 500 t/h or 3,5 Mt/a on a consistent

basis and we believe we can extract even bet- ter performance from it in future. Our target on utilisation is 81 % and we’ve exceeded this on a number of occasions. “Our safety record continues to be exem- plary. The mine was built without a single LTI being recorded throughout the development phase and well into the operating phase. In fact, we only experienced our first – and, thus far, only – LTI in Q3-2018, at which point we had worked 6,7 million injury-free man hours since the start of the project in mid-2014, which is a truly excellent performance.” The Liqhobong processing plant uses a con- ventional flowsheet comprising scrubbing, screening, crushing, concentration via DMS and final recovery using Flowsort X-ray machines. The design has proved to be efficient requiring only minor modifications – mainly to reduce the incidence of diamond breakage – since commissioning. Firestone is, however, looking at a six-month trial of an X-Ray Transmission (XRT) unit. As Bosma explains: “Some types of Type II diamonds don’t fluoresce and therefore our current X-ray machines would not pick them up. So we’re considering renting an XRT sorter. The plan is to run our tailings through this which would allow us to determine whether we’ve missed any non-fluorescing stones. If this proves to be the case, then obviously we would consider installing a permanent XRT circuit at the mine.” While Firestone operates the plant directly, the mining is outsourced to Basil Read Mining. Excavators include three 80-tonne machines

He took over as CEO of the company in July 2018, succeeding Stuart Brown. He holds BSc (Honours) and MSc degrees as well as an MBA from the University of Cape Town’s Graduate School of Business. He points out that Liqhobong has not yet produced as many large, high-value stones as had been hoped. “Stones of this type can really swing the dial so this is disappoint- ing,” he says. “Having said this, we had some notable recoveries during FY-2018 includ- ing a 4-carat fancy pink that achieved a sale price of US$112 781/carat and 45-carat white that sold for US$1,2 million. More recently, we recovered a 46-carat gem diamond which sold for more than US$1 million. The largest stone we’ve ever recovered is a 311-carat yel- low makeable which sold for US$0,23 million recently.” Since Modern Mining spoke to Bosma during the Mining Indaba, Firestone has announced the recovery of 70-carat white, makeable dia- mond, which was mined from the northern, low-grade part of the pit where the bulk of min- ing will take place in the coming months. To adjust to the lower-than-expected price obtained for its diamonds, Firestone adopted a revised mine plan in December 2017 which envisages a mine life of nine years instead of 14 and the execution of two cuts rather than three, with a significant reduction in waste stripping. “This plan delivers the best results over the medium-term at low risk but we still have the option of implementing a third cut should market conditions change for the bet- ter,” observes Bosma. He adds that Firestone

30  MODERN MINING  March 2019