The Letšeng Diamond Mine, found in the landlocked Southern African kingdom of Lesotho, is owned by Gem Diamonds, Ltd. and the government of Lesotho, at an elevation of 3100 m it is the world's highest diamond mine.

Production

It is characterised by extremely low grade ore (less than 2 carat/hundred tons) and is known for producing huge diamonds, having the highest percentage of large diamonds (greater than 10 carat), giving it the highest dollar value per carat of any diamond mine. The world average is roughly US$81 per carat, while Letšeng averaged over US$1,894 per carat for the first six months of 2007. Unusual for Africa, and due to the elevation, temperatures at the mine drop to -20 °C, and snowfalls are common in winter.

Geography

Climate

Letšeng has an alpine tundra climate (Köppen: ET) bordering on a dry-winter subarctic climate (Dwc). This means that Letšeng has a chilly climate with fairly cool temperatures throughout the year, even for Lesotho, and snowfalls can happen as well. The average annual temperature is 5.2 C, the average annual high temperature is 10.4 C and the average annual low temperature is 0.1 C. The warmest month, January, has an average temperature of 9.8 C and an average high temperature of 14.8 C. The coldest month, June, has an average temperature of -0.1 C and an average low temperature of -5.5 C. June is the only month with an average temperature below freezing, although the average temperature of July is exactly 0 C. Letšeng has an average annual precipitation of 881 mm. However, like most of Lesotho and South Africa, this is not evenly distributed throughout the year. Letšeng has a wet season with abundant rainfall from October to March and a dry season with less precipitation from May to August - the coldest time of year. In terms of precipitation April and October serve as transitions between the wet and dry seasons. January is the wettest month, receiving 133 mm of precipitation on average, while July is the driest month, receiving only 8 mm of precipitation on average.

Significant diamond finds

Lesotho Promise

On 4 October 2006 the 603 carat white diamond, the Lesotho Promise was unearthed, which until the January 2018 discovery noted below was the largest reported find this century; at the time it was found it was the 15th largest diamond ever found. The stone is of an exceptional colour, rated D, the top colour for diamonds.

Lesotho Brown

Previously the largest diamond found at Letšeng was the 601 carat Lesotho Brown, recovered in 1967.

Letšeng Legacy

On 13 September 2007 Gem Diamonds, Ltd. announced that it had found a 493.27 carat diamond, making it the 18th largest diamond ever found. It was sold to the Graff-SAFDICO partnership for $10.4 million.

Star of Lesotho

In 2004, Gem Diamonds, Ltd. found a large diamond of 123 carat.

Leseli La Letšeng

On 21 September 2008 Gem Diamonds, Ltd. announced that it found a 478 carat diamond of high quality, making it the 20th largest diamond ever found. It is a type II D colour, with potential to yield a 150 carat cut stone. Chief executive Clifford Elphick said: "Preliminary examination of this remarkable diamond indicates it will yield a record-breaking polished stone of the very best colour and clarity, and has no inclusions visible in its rough form."

November 2010

The discovery of two large rough white diamonds was announced in November 2010. They weighed 196 carat and 184 carat.

Lesotho Legend

In January 2018 Gem Diamonds announced the largest diamond yet discovered at Letšeng, a Type IIa D color stone measured at 910 carat. It sold in March 2018 for $40 million. The same year a light brown diamond of 357.61 carats was discovered.

Letšeng Star

In August 2011 a diamond of 550 carat was found.

Letšeng Dynasty and Letseng Destiny

In May and July 2015, the discovery of two large diamonds was announced : the Letšeng Destiny of 314 carat and the Letšeng dynasty of 357 carat.