Gem Diamonds (LON:GEMD) said it recovered two white diamonds of around 160 carat (ct) each from its Letšeng mine at the end of January.
The two rough diamonds - a 162.06ct type II diamond and a 161.74ct type I diamond - are expected to achieve top prices at Letšeng's February tender, the company said.
Both diamonds were recovered in a largely undamaged condition, said Gem which has taken measures to reduce diamond damage at the mine in Lesotho.
Last December, a 78.69ct white diamond from the mine sold for US$5.2mln, or US$65,954 per carat, and a 55.57ct white diamond sold for US$3.1mln, equivalent to US$57,228 per carat.
Letšeng has produced four of the top 20 largest white gem quality diamonds since Gem Diamonds acquired the mine in 2006.
"We are pleased to see the Letšeng mine continue to deliver such large high quality white diamonds as the mine confirms its position as the world's foremost source of exceptional large diamonds,” said the chief executive Clifford Elphick.