Gem Diamonds reported a strong end to the year at its Letšeng mine in Lesotho. Full-year production was "above guidance" and prices were "robust", the firm said in a statement.
The miner, which has a half a dozen mines in southern Africa, said the stones from Lesotho achieved an average price per carat of $2,117 in the fourth quarter. But the average price per carat in 2015 was 9 percent down on 2014.
Gem Diamonds reported production of 29,400 carats during the quarter, with full-year output coming to 108,579 carats.
It added that it sold nine rough stones with a value of more than $1 million each, and three diamonds each weighing more than 100 carats.
Gem Diamonds added that it has reduced production at its Ghaghoo operation in Botswana in order to curtail expenditure.