Modern Mining November 2016

DIAMONDS

Cullinan’s C-Cut starts its Development of one of the deepest mechanised kimberlite block caves in the world – the C-Cut at Petra Diamonds’ Cullinan Diamond Mine (CDM) near Pretoria – is now at an advanced stage, with the project over 80 % complete and already delivering its first ore. Modern Mining recently went un- derground at Cullinan in the company of Petra management and personnel fromMurray & Roberts Cementation, the biggest contractor on the project, to view the progress being made on the new cave, which by 2019 will be producing ore at a steady-state rate of around 3,7 Mt/a.

T he C-Cut project forms part of Petra’s overall strategy to shift pro- duction at its underground mines in South Africa from mature, diluted caves to new undiluted production blocks. As Andre Cloete, Petra’s Project Manager for the C-Cut points out, the intention is not to increase ROM production levels but to achieve grade (higher diamond content per tonne mined). “The problem with mature caves is that they become increasingly diluted with waste rock,” he explains. “This dilution is now quite severe at mines such as Cullinan, Finsch and Koffiefontein and has negatively impacted on ROM grades. In the

case of Cullinan, the C-Cut will see the ROM grade – presently running at around 33 cpht – increase to approximately 50 cpht by 2019.” He adds that the move to new production blocks will have additional benefits, over and above the undiluted ore and resultant increase in grades. “The reduced amount of waste rock to be handled will lead to reduced wear and tear on machinery, as the waste rock is typically much harder than the kimberlite ore, while the overall product mix will also improve.” The C-Cut is a project first proposed by De Beers, the previous owner of Cullinan, back in the 1990s. De Beers took the project to an advanced study stage and (in 2002) estimated its

Crusher 1 South, which was commissioned in July 2016.

30  MODERN MINING  November 2016