The Kingdom of Lesotho, a landlocked enclave within South Africa, is one of Africa's smaller diamond producers by volume but among the world's most distinguished by value per carat. The country's diamond geology is unusual: high-altitude (above 3,000 metres) kimberlite pipes in the Maluti Mountains have produced a disproportionate share of plus-100-carat gem stones over the past sixty years, and the in-situ value per carat at the principal Letseng mine is the highest of any kimberlite operation in the world.

Geology and principal deposits

Lesotho's diamonds are sourced from kimberlite pipes intruded into the Karoo Supergroup basalts of the Drakensberg-Maluti highlands. The pipes are small in diameter and low in grade compared with the giants of South Africa and Botswana, but produce an exceptional proportion of large, gem-quality Type IIa stones - the chemically pure, nitrogen-free diamonds that yield the highest D-colour, highest-clarity polished goods.

The principal active mines are:

• Letseng-La-Terae - Africa's highest mine, at 3,100 metres in the Maluti Mountains, operated by Letseng Diamonds (currently Letseng Diamonds Ltd. with majority Gem Diamonds Ltd. ownership and Government of Lesotho 30%). Letseng has produced multiple plus-100-carat diamonds including the Lesotho Promise (603 ct, 2006), the Letseng Legacy (493 ct, 2007), the Lesotho Brown (601 ct, 1967, predating the Letseng modern operation but from the same area), the Lesotho Star (550 ct, 2018) and others.
• Mothae - operated by Mothae Diamonds, a subsidiary of the Australian-listed Lucapa Diamond Co.
• Kao - operated by Storm Mountain Diamonds (Namakwa Diamonds parentage), known for high-quality Type IIa goods.
• Liqhobong - operated by Firestone Diamonds.

Trade significance

Lesotho's combined output is small - in the order of one to two million carats per year - but the value per carat at Letseng has historically been the highest of any major kimberlite operation in the world, frequently exceeding U.S. $1,500 per carat at the mine and occasionally several thousand. This reflects the unusual size and quality distribution: while average grade is low, the rare plus-100-carat Type IIa stones drive disproportionate revenue, and Letseng has produced some of the most important rough diamonds of the past two decades.

The country joined the Kimberley Process Certification Scheme at its inception, and Lesotho diamonds carry KPCS documentation. Lesotho is a member of the Common Monetary Area with South Africa, and most rough is exported through Antwerp tenders and through De Beers and Sotheby's specialist large-stone auctions. The government's 30% Letseng stake provides a significant revenue stream and royalty income to the Treasury, and the diamond industry is one of the country's principal foreign-exchange earners alongside textiles and migrant remittances.