Modern Mining January 2018

DIAMONDS

electrical motors required is now only 84 – compared to the 589 motors in the old installation. Water saving – an imperative of grow- ing concern in South Africa – has also been decisively addressed in the new plant; the amount of water consumed by the plant per tonne of material processed will be 0,06 m 3 – a 65 % improvement on the 0,17 m 3 /t previously. It is expected that the plant will increase liberation of diamonds across the total spectrum, leading to a grade improvement of about 10 %. The amount of +1 mm unliberated kimber- lite particles in the tailings will reduce from 60 % to 40 %, while the -1 mm slimes will do the reverse – rising from 40 % to 60 %. Security has been enhanced through a totally ‘hands-off’ final recovery system; new final recovery sorting machines now concentrate load reduction from 50 t/h to 25 t/h. Improved liberation (and hence reduced tonnes in ciruculation), less material reporting to DMS, reduced need for step-wise crush- ing (due to AG milling) and higher levels of automation are expected to lead to savings in operating expenditure of R20-R25 per tonne. The new Cullinan plant will certainly be a useful test for AG milling in South Africa; this technology is well proven by Russia’s Alrosa in the processing of kimberlite ore, but has only in recent years been applied in African countries such as Angola and Botswana. Report by Paul Crankshaw, photos courtesy of Petra

Cullinan’s final recovery building and sort house, showing the tailings belt in the centre.

Cullinan mine – Quick facts Location: Gauteng Province, South Africa Mine start date: 1903 Total resources and reserves: 192,7 Mct Mining method: Block cave. FY2017 saw the first significant producton of undiluted ore from the new block cave (C-Cut Phase 1). Depth of current mining: 880 m Employees: 1 220 Contractors: 1 944 Mine plan: To 2030 Ownership: Petra Diamonds Limited: 74 %; Kago Diamonds (Pty) Ltd: 14 %; Itumeleng Petra Diamonds Employee Trust: 12 %. 

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January 2018  MODERN MINING  61