Electronic Sorters prove their worth

It is a shame that the world's largest uncut diamond, which was expected to sell for more than £52 million at Sotheby's last month failed to make its reserve price, the highest bid being £45 million.

The rough diamond, of 1,109 carats and believed to be more than 2.5 billion years old is the Lesedi la Rona, almost the size of a tennis ball, which was unearthed in Botswana in November at the Lucara Diamond Mine Corp's Kaowe mine.

The Lesedi la Rona which means "our light" in the Tswana language, wasn't the only big gem discovered that week - two other huge diamonds were found from the same mine within 72 hours, a 374 carat diamond which hasn't been named and an 812.77 carat diamond called The Constellation.

ROMRA Sorters at Kaowe

I'll bet the company is pleased that it installed six TOMRA electronic sorters last May (posting of 27 November 2015), which recovered these huge stones prior to crushing. The TOMRA XRT sorters replaced conventional Dense Media Separation technology in the -60+8mm size range. Each sorter can treat up to 150 tons per hour at over 8,000 hours per year. There is no need to further process the sorter’s concentrate before final hand sorting, and congratulations to Tiroyaone Mathaba who was sorting when he spotted what turned out to be the 1,109 carat diamond. His boss William Lamb said that all of the mine's 804 employees and contractors received a bonus, but he didn't reveal how much.

A further congratulation to Lucra- as part of the plan for the auction at Sotheby's, the company put 3 small stones up for sale, fetching a total of US$104,000 for charities in Botswana.