Gem Diamonds has unearthed its sixth diamond of more than 100 carats this year from its Letseng mine in Lesotho, southern Africa.
Shares in the London-listed miner lifted 1.37 per cent to 71.97p in morning trading after it unveiled its high-quality 115 carat, D-colour, or near colourless, Type IIa diamond.
Gem Diamonds owns 70 per cent of the Letseng mine, which it said is the highest dollar-per-carat kimberlite diamond mine in the world. The government of Lesotho owns the rest of the mine.
Earlier this year, Gem Diamonds warned the market for rough and polished diamonds was "cautious", but strong demand for Letseng's large, high-quality, white rough diamonds continued.
The company's revenue fell 14 per cent in the first half of the year due to lower production and a decline in average diamond prices.