Gem Raises Values at Mine Where Big Diamond Found

Gem Diamonds Ltd. rose the most in more than 18 months in London trading after it raised the value of the precious stones buried at its Letseng mine in Lesotho and said the operation contains more than previously thought.

Gem increased the average price of its so-called probable reserves of the stones 19 percent to $2,045 a carat, the London-based company said in a statement today. It also boosted the probable reserves at the mine by 64 percent to 2.26 million carats.

The shares climbed as much as 5.7 percent to 185 pence, the highest intraday level since Oct. 9, 2012 and were 3.9 percent higher at 181.75 pence at 8:42 a.m.

Letseng, once operated by De Beers, was bought by Gem in 2006 for $118.5 million and is famous for the size and value of its stones. The mine has produced some of the world’s biggest diamonds including the 603-carat Lesotho Promise, the largest unearthed this century, and a 550-carat rock that was discovered in 2011.

Gem, which is set to open a new mine in Botswana later this year, is seeking to benefit from rising prices. Rough-diamond prices are up about 10 percent this year, data compiled by WWW International Diamond Consultants Ltd. shows, after more than doubling in the past five as the U.S. economy recovered and China’s rising middle class bought more.

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