Modern Mining July 2015

COUNTRY FOCUS – BOTSWANA

machines. The selection of XRT was based on extensive testwork on the Karowe ore which indicated that the XRT route was superior to other concentration methods examined. The entire upgrade and optimisation project at Karowe was covered in our January issue this year but, to briefly recap, the work – carried out by DRA as EPCM contractor – has encompassed modifications to the autogenous mill (which, incidentally, was the first mill of its type to be installed at a diamond mine in Africa outside of Angola), the installation of new secondary and tertiary crushers, and the construction of an XRT building housing five high-capacity Tomra XRT machines. The process route for all ore now is for the +1,5 x 8 mm ore fraction to go to DMS and XRF (X-ray Fluorescence) recovery with the

to allow it to treat harder and higher yield material, particularly in the south lobe of the kimberlite, and its design allowed for this,” he explains. “As it became clear, however, that the mine was emerging as a prodigious producer of large diamonds, we decided that we would also need to incorporate a facility to avoid breakage of large stones and allow Lucara to realise their full value. So the entire project has had two ele- ments to it – the upgrade, which was always planned, and a ‘Large Diamond Recovery’ cir- cuit able to treat material up to 60 mm in size.” To cater for both the anticipated increase in DMS yield and assist with the recovery of large stones, Lucara elected not to increase the DMS capacity, but to go for new technology that represents a ‘first’ in the diamond mining industry – the use of X-ray Transmission (XRT)

Left: The coarse (14 – 32 mm) XRT feed fraction. Right: These four stones of 270 ct, 196 ct, 142 ct and 342 ct were recently recovered at Karowe. The 342 ct diamond was recovered prior to the commissioning of the XRT machines but the others represent the first significant recoveries from the XRT circuit.

The XRT building houses five high-capacity Tomra XRT machines.

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July 2015  MODERN MINING  29