Gem Diamonds Ltd. rose the most in more than nine months in London trading after discovering a 100-carat white diamond at its Letseng mine in Lesotho.
Gem rose as much as 7.7 percent, the steepest intraday gain since Sept. 6, and traded at 121.5 pence at 8:13 a.m. The diamond is the third stone larger than 100 carats found at Letseng since May, Gem said in a statement today.
“Following recent sales, we believe that this stone could fetch offers greater than $5 million,” Numis Securities Ltd. said in a note to investors.
Letseng, once operated by De Beers, was bought by Gem in 2006 for $118.5 million. The mine has produced some of the world’s biggest diamonds including the 603-carat Lesotho Promise, the largest diamond unearthed this century, and a 550-carat stone that was discovered in 2011.
Gem said that its average selling price was $2,087 a carat in June compared with $1,599 a carat in its first three tenders of 2013.