Modern Mining March 2016

DIAMONDS

Lerala on the brink of production

Botswana’s Lerala diamond mine near the border post of Martin’s Drift – which was originally commissioned in 2008 but placed on care and maintenance early in 2009 – is on the brink of recommissioning, with first diamond production expected in April. The owner, ASX-listed, Kimberley Diamonds Limited (KDL), has all but completed an extensive refurbishment and upgrade of the process plant designed to allow it to achieve a reliable throughput of 200 t/h and enhanced diamond recovery.

T he deposit at Lerala comprises a cluster of five diamond-bearing kimberlites – designated K2 to K6 – which were originally dis- covered by De Beers in the early 1990s. KDL will be the fourth company to mine at the site. De Beers undertook a trial mining programme starting in 1997 but decided that the Tswapong project – as it was then known – did not meet its economic criteria. ASX-listed DiamonEx later picked up the project and built the present mine infrastructure but had the misfortune to bring the mine on line when the global resources market was in disarray follow- ing the global financial crash of 2008. A third company, Mantle Diamonds, oper- ated the mine for a few months in 2012 producing approximately 73 000 carats. A range of technical issues in the processing plant, however, resulted in poor recovery and led to the mine once again being put on care and maintenance. KDL acquired the project in early 2014 and is confident that it can succeed where its prede- cessors have failed. It announced in September 2014 that South African engineering company Consulmet had been appointed to design mod- ifications to the plant intended to facilitate dramatically improved diamond recovery and throughput reliability. Consulmet was subse- quently engaged to execute the plant upgrade and refurbishment on an LSTK basis. The upgrade and reopening of Lerala is costing A$14 million (with the plant modifica- tions accounting for A$9,4 million). The mine – which has a 20,1 Mt resource with an average grade of 24,2 cpht – will have a life of nine years and is expected to generate a net cash flow of A$165 million over this period. Average annual production is estimated at 336 000 carats. Approximately 1,4 Mt of ore will be

produced annually with the mining being handled by a mining contrac- t o r, Ba s i l Re a d Botswana. The con-

tract covers the initial five years of mining and its value is around A$47 million at current exchange rates. Basil Read Botswana was due to start mining this month (March), starting in the dewatered K3 pit. The upgraded plant is a conventional dia- mond processing facility incorporating primary, secondary and tertiary crushing and associated screening; primary and secondary scrubbing and screening; and gravity concentration via a DMS module with dual cyclones which are fed fines (+1 mm/-6 mm) and coarse (+ 6 mm/-18 mm) product streams. Sink screen concentrate is pumped to a new recovery module which will classify and dry the concentrate prior to X-ray sorting and final recovery by hand sorting, all within a new secure recovery facility. The completely new recovery section is designed to enhance first pass diamond recov- ery and minimise diamond loss while the new secondary crusher is expected to improve dia- mond liberation and processing reliability. A scrubber and trommel have been added to the plant to handle wet ore and maintain through- put while additional surge capacity will decouple sections of the plant, reduce down- time and maintain head feed rates. Automated thickener control will ensure a consistent and optimised tailings treatment philosophy. The mine and processing plant are powered by diesel gensets and source excess water via a pipeline from the Seleka wellfield. Labour and services will be sourced from the local villages including the Lerala village, located 10 km south-west of the 21,86 km 2 mining licence. 

The new platform for the primary scrubber (left fore- ground) ready to accept the scrubber shell, the primary crusher (rear) and the re- furbished conveyor (photo: Kimberley Diamonds)

KDL acquired the project in early 2014 and is confident that it can succeed where its predecessors have failed.

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March 2016  MODERN MINING  39