Johannesburg-based engineering and project delivery company DRA Global’s “innovative” process plant designs assisted in the recent recovery of very large diamonds at Southern Africa-focused diamond miner Lucara’s Karowe mine, in Botswana.

In November, a 1 111 ct diamond was recovered from the mine in north-central Botswana. It is the biggest diamond to be discovered in Botswana and the largest find in more than a century.

“The significance of the recovery of a gem-quality stone larger than 1 000 ct, the largest for more than a century . . . cannot be overstated,” says Lucara CEO William Lamb.

In the same month, Lucara also recovered two “exceptional” white diamonds: a 813 ct stone and a 374 ct stone, which were also found at the Karowe mine.

Meanwhile, DRA notes that, following on from the successful greenfield Karowe AK06 diamond project, in Botswana, completed and commissioned in April 2012, DRA was awarded the brownfield Phase 2 Karowe plant upgrade project in March 2014 by Boteti Mining, a 100%-owned subsidiary of Lucara.

The company says that, as part of the Phase 2 upgrade, the need for a large diamond recovery circuit was identified. The inclusion of the circuit at Karowe using X-ray transmissive (XRT)technology enabled an increase in the top size of material treated in the diamond recovery process.

DRA explains that the selective nature of XRT sorting, combined with the larger particle size treated, allows for the recovery of larger diamonds, compared with traditional processes.

“This approach provides for the early detection and recovery of large diamonds, thereby minimising diamond breakage associated with additional crushing and materials handling circuits in the downstream processes,” the company states.

DRA MD Africa Johann de Bruin comments that, since the commissioning of the Karowe upgrade project and the associated large- diamond recovery circuit in mid- 2015, the DRA design has proven to be as effective as envisaged.

“The plant recently recovered both the largest and second- largest diamonds ever recovered in Botswana, with the massive 1 111 ct stone being the largest diamond recovered so far this century,” he enthuses.

In conclusion, De Bruin states that the project and its performance clearly prove that DRA continues to be the technical leader in the design and delivery of diamond recovery plants, and confirms its position at the forefront of efforts to incorporate and use leading-edge and innovative process technologies.