Gem Diamonds Limited is a London Stock Exchange-listed diamond mining company whose principal asset is the Letseng mine in the Maluti Mountains of Lesotho, southern Africa. The company is notable within the gem trade not for volume of production but for the extraordinary calibre of rough it recovers: Letseng consistently ranks among the world's highest-value diamond mines by average revenue per carat, a distinction driven by the regular appearance of large, exceptional-quality stones rather than by tonnage processed.

The Letseng Mine

Situated at an elevation of approximately 3,100 metres in the Lesotho highlands, Letseng is one of the highest-altitude diamond mines in operation. The kimberlite pipes at Letseng — the Main and Satellite pipes — are characterised by low diamond grades measured in carats per hundred tonnes, yet the stones recovered are disproportionately large and of high gem quality. This counter-intuitive combination of low grade and high value per carat defines the mine's economic logic and its significance to the upper end of the rough diamond market.

A substantial proportion of Letseng's production consists of Type IIa diamonds — stones chemically pure in nitrogen, often colourless to the highest degree, and frequently of D colour under GIA grading. Type IIa material of this scale is exceptionally rare globally, and Letseng's consistent delivery of such goods has established it as a benchmark source for the finest colourless rough.

Notable Recoveries

Letseng has yielded some of the most significant rough diamonds of the modern era. Among the most documented:

• The Lesotho Promise (603 carats), recovered in 2006, was at the time one of the largest gem-quality rough diamonds found in decades and was subsequently cut into a suite of D-colour, internally flawless polished stones.
• The Letšeng Legacy (910 carats), recovered in 2018, ranked among the largest gem-quality diamonds ever found.
• The Sewelô (1,758 carats), recovered in 2019, is the largest diamond discovered in Botswana and one of the largest ever found globally — though this stone came from Lucara Diamond Corp's Karowe mine, not Letseng. Letseng's own record stones remain among the most commercially significant in recent history.

Recoveries exceeding 100 carats at Letseng are sufficiently frequent that the mine maintains a documented track record of such stones, which Gem Diamonds reports publicly through quarterly production releases filed with the London Stock Exchange.

Sales Methodology and Market Transparency

Gem Diamonds sells its rough primarily through a tender process, in which qualified buyers submit sealed bids for parcels and individual exceptional stones. This method, common among producers of high-value rough, allows price discovery in a competitive environment and is considered appropriate for goods where individual stone value can vary enormously. Direct sales to specific buyers are also conducted for certain categories of production.

Because Gem Diamonds is a publicly listed company subject to London Stock Exchange disclosure requirements, it publishes quarterly production and sales reports detailing carats recovered, average per-carat values achieved, and notable individual stones sold. This reporting cadence provides the gem trade with a degree of transparency into the high-end rough market that is unusual among diamond producers, making Gem Diamonds' results a watched indicator of conditions at the top of the rough market.

Significance to the Trade

For gemmologists, dealers, and auction specialists, Gem Diamonds and Letseng represent a reliable source of the large, high-clarity, D-colour Type IIa rough that underpins the most important polished diamonds offered at major auction houses. Stones with documented Letseng provenance carry a degree of narrative and traceable origin that adds to their appeal in an era of increasing demand for supply-chain transparency. The mine's output, though modest in total carat weight, exerts an influence on the top tier of the polished diamond market disproportionate to its volume.