Modern Mining January 2018

DIAMONDS

and high pressure grinding rolls (HPGRs) which promote inter-particle crushing; this equipment was supplied by thyssenkrupp Industrial Solutions South Africa – formerly thyssenkrupp Polysius. There is also a top- cut of 75 mm to cater for diamonds of over 3 000 carats – an important consideration for the mine that produced, up to Petra’s acquisi- tion in 2008, a quarter of the world’s diamonds over 400 carats in size. The plant also makes use of X-ray lumines- cence (XRL) to replace dense media separation – with only the -12 mm material reporting to the DMS circuit. The XRL machines have been supplied by Russia’s Bourevestnik, one of the pioneers in this field. There are already signs that the new plant is delivering value, according to Johan Dippenaar, Petra Diamonds’ CEO, with the XRL modules of the plant put into operation during September 2017. “Encouragingly, two plus-200 carat stones have already been recovered, proving the effi- cacy of the large diamond recovery circuit,” said Dippenaar in his October 2017 trading update. “However, both these stones were of poor quality and low value.” Since Petra acquired the mine, Cullinan has produced a number of large, high-value stones including a 507,5 carat white diamond – the

Left: A view of Cullinan dia- mond mine’s new buildings housing its high pressure grinding rolls (HPGRs), X-ray luminescence (XRL) machines and final recovery phase. Below: The mill recycling belt in the new Cullinan plant’s compact configura- tion, which has reduced the length of conveyors from 15 km to just 3 km.

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