The Letseng diamond mine, found in the landlocked Southern African kingdom of Lesotho, is owned by Gem Diamonds, Ltd. and the government of Lesotho, and at an elevation of 3,100 m (10,000 ft) it is the world's highest diamond mine.
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It is characterised by extremely low grade ore (less than 2 carats (400 mg)/hundred tons) and is well known for producing huge diamonds, having the highest percentage of large diamonds (greater than 10 carats (2.0 g)), giving it the highest dollar value per carat of any diamond mine. The world average is roughly US$81 per carat, while Letseng averaged over US$1,894 per carat for the first six months of 2007.[1]
Unusual for Africa, and due to the elevation, temperatures at the mine drop to -20 °C, and snowfalls are common in winter.
On the 4th of October 2006 the 603 carat (121 g) white diamond, the Lesotho Promise was unearthed, and is the largest reported find this century and the 15th largest diamond ever found. The stone is an exceptional colour, rated D, the top colour for diamonds.
Previously the largest diamond found at Letseng was the 601 carat (120 g) Lesotho Brown, recovered in 1967.
On September 13, 2007 Gem Diamonds, Ltd. announced that it found a 493 carats (99 g) diamond, making it the 18th largest diamond ever found. It was sold to the Graff-SAFDICO partnership for $10 million.[1]
In 2004, Gem Diamonds, Ltd. found a large diamond of 123 carats (25 g).[2]
On September 21, 2008 Gem Diamonds, Ltd. announced that it found a 478 carats (96 g) 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 carats (30 g) 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."[3][4] [5]
The discovery of two large rough white diamonds was announced in November 2010.[6] They weighed 196ct and 184ct.[7]