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Diamond mining

Hauling kimberlitic ore from the Letšeng Mine in Lesotho, with the newly-discovered 442-carat rough stone in the foreground.



The Letšeng Mine in the mountainous southern African Kingdom of Lesotho has produced another massive diamond, with its owner, Gem Diamonds, announcing that a 442-carat stone was recently recovered at the site.

Located in the Maluti Mountains of Lesotho, Letšeng is renowned for its production of large, top-color white diamonds, and is ranked as the highest average dollar-per-carat kimberlite mine in the world.

“The recovery of this remarkable 442 carat diamond, one of the world’s largest gem quality diamonds to be recovered this year, is further confirmation of the caliber of the Letšeng mine and its ability to consistently produce large, high quality diamonds,” said Clifford Elphick, the company’s CEO. “It is also a fitting testament to the dedication of the employees in the group to have recovered such an extraordinary diamond, whilst at the same time maintaining strict adherence to health and safety precautions during the global COVID pandemic.”

While Gem Diamonds has still not declared how the stone will be sold, market pundits believe that it could achieve a price in excess of $25 million. Elphick said that part of the expected income would be earmarked for financing a community project in Lesotho.

On the news of the latest discovery, the company’s share price jumped by 10.7 percent on the london Stock Exchange.



The two diamondiferous kimberlite pipes that comprise the Letšeng Mine were discovered in 1957, but the remote location of the site and the grade of 0.88 carats per hundred metric tons of ore in the main in pipe, which accounts for accounts for 75 percent of the mine’s output, and 2.6 carats per hundred metric tons of ore in the satellite pipe, made it the lowest grade for any diamond mine in the world. Economic grades are considered to range from 5 to 400 carats per hundred metric tons of ore.

It’s fair to believe that Letšeng would have never been developed, were it not for a local digger, Ernestine Ramaboa, who in 1967 unearthed a brown colored diamond weighing 601.26 carats at the site. At the time it was reported to be the world’s 11th largest gem-quality diamond and was named the Lesotho Brown. First sold to a South African dealer, in 1968 it was purchased at auction by Harry Winston. The rough diamond yielded 18 polished stones, including the Lesotho I, a flawless 71.73-carat diamond, and the Lesotho III, a 40.42 carat marquise-shaped stone, which was purchased by Aristotle Onassis and given to Jacqueline Kennedy as an engagement ring.

The 910-carat Lesotho Legend, discovered in 2018 and sold for $40 million.

The discovery of a large diamond provided enough incentive for Rio Tinto to conduct an in-depth examination of the Letšeng, but in the end it declined the opportunity of building a mine. The country’s government then invited De Beers to make an offer, which it took up. In November 1977 an open pit mine was officially opened.

To make the project viable a $3.7 million road was built through the mountains, connecting the mine to both Johannesburg, South Africa, and also to Maseru, Lesotho’s capital. A primary sorting and washing facility was built at the mine. It included an X-ray machine to identify larger diamonds.

But despite some large stones being recovered, including a 130-carat stone in 1978, when diamond prices crashed in the early 1980s De Beers halted operations after just five years. Total production at that stage equaled 272,840 carats, with about 65 percent being gem quality. Some 7.6 percent of the production involved stones of larger than larger than 14.7 carats, and they accounted for 62 percent of the mine’s revenue.

The 26 D-flawless diamonds fashioned from the 603-carat Lesotho Promise, made into a single necklace by Graff.


When Gem Diamonds acquired the right to mine the concession in 2006, Letšeng had resumed active mining for just over a year. Its annual production at the time was 55,000 carats.

The mine today ranks in the top 15 global diamond producers by revenue., but that is almost entirely due to it production of large high-value stones, which account for 70 percent to 80 percent of Gem Diamonds’ annual revenue.

Among the diamond produced are the 910-carat Lesotho Legend, an exceptional D-color stone discovered in 2018, which sold for $40 million. It was the fifth largest gem-quality rough diamond ever discovered, and the largest ever mined in Lesotho.

In 2003 the 603-carat Lesotho Promise was discovered and is still ranked in the top 20 of the world’s largest white diamonds. Sold for $12.4 million that October, it yielded 26 D-flawless diamonds, the largest of which was a 76-carat pear-shaped stone. All were fashioned into a single necklace by Graff.

In August 2011 the 550-carat Letšeng Star was discovered. Sold for an undisclosed amount, it yielded more than 165 carats of D-color stones, including a 33-carat diamond and 12 pairs of pear-shaped diamonds.