Modern Mining January 2019

DIAMONDS

regarded as the world’s most important source of blue diamonds. These have included the 29,6-carat Blue Moon of Josephine , recovered in 2014; the cut version was sold the follow- ing year for US$48,4 million dollars, equating (based on its polished weight of 12 carats) to a phenomenal US$4 million per carat. Kemp made the comment that given Cullinan’s his- tory of producing large gemstones, a prime consideration in designing the new plant was to maximise the recovery of large diamonds and reduce diamond breakage to a minimum. Since acquiring Cullinan from De Beers in 2008, Petra has transformed the operation, pursuing a modified version of the C-Cut life extension project originally conceived by De Beers but never implemented. As Kemp noted, when Petra acquired the mine it only had sev- eral years of life left without the injection of capital. “It would have closed in 2014,” he said. “We decided to put in a new block cave – which we call C-Cut Phase 1 – on the western side of the orebody, supplemented by a Sub- Level Cave (CC1 East) on the eastern side, and the Life of Mine now extends to 2030.” C-Cut Phase 1 is a 5,7 ha cave with a block height of 200 m. The project has included approximately 27,5 km of development, the deepening of the rock hoisting and man-and- material shafts, a new ground-handling system,

major savings

Left: A view of the new Cullinan plant showing the buildings housing the HPGR, the XRL machines and the final recovery phase. Below: The AG mills at Cullinan. The two medium voltage 6,4 MW, 3,3 kV mill drive packages, were supplied by Shaw Controls.

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January 2019 _ MODERN MINING _ 31