Letseng-La-Terae Mine (Letseng Mine; Lets'eng Mine), Maluti Mts., Mokhotlong District, Lesotho

A diamond mine, currently owned by African Gem Diamonds. The deposit consists of several kimberlite pipes intruded through 1500 m of Karoo (Stormberg) basalt. Two of the pipes, referred to as the Main and Satellite pipes respectively, have economic grades. They were discovered in 1957 as a weathered outcrop in a stream. In 1959, it was declared a "government digging" and hundreds of small-scale miners started to excavate the near-surface weathered kimberlite. In 1968, the property was acquired by Rio Tinto and explored through a series of underground tunnels, but the prospect was abandoned in 1972. De Beers subsequently acquired the deposit and mined the Main Pipe from 1975 until 1982. During this time, only little work was done on the Satellite Pipe. In 1999, the mining rights were obtained by Letseng Diamonds, who focussed their activities on the Satellite Pipe. In 2007, the mine was aquired by African Gem Diamonds.

During mining operations in the Satellite Pipe, a high number of large diamonds of exceptional quality were recovered, among them stones of 72, 76, 106 and 112 carats within a single week. The 603 ct "Lesotho Promise", discovered in 2006, ranks as the world's 15th largest diamond. It is said that 15% of the production is larger than 10 carats, and 1% is larger than 100 carats, per stone.

The Letseng pipes also contain abundant mantle and lower crustal xenoliths, including garnet-bearing gneisses and granulites, eclogites, lherzolites, harzburgites and dunites.


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By THABO THAKALEKOALA, Associated Press, September 13, 2007:

A 494-carat diamond, believed to be the 18th largest in the world, has been found at this mine in Lesotho.

The stone was an exceptional quality white diamond, said Natural Resources Minister Monyane Moleleki. "This recovery adds more to the chapter of excellence for this mine internationally," said a visibly elated Moleleki.

The Lesotho Promise, a 603-carat stone, was uncovered last year (2006) at the same mine and sold for $12.3 million. A 215-carat flawless diamond found in January 2007 brought $8.3 million.
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References:
- Field, M., Stiefenhofer, J., Robey, J., and Kurszlaukis, S. (2008): Kimberlite-hosted diamond deposits of southern Africa: A review. Ore Geology Reviews 34, 33-75.