Argyle diamond mine at the Ekati mine, both in Canada. However, Argyle has two to four times the concentration of diamonds (ore grade) of these mines. This makes extraction economically feasible, as mine costs are mostly related to the amount of ore processed, not the amount of diamond extracted. In 2005, Rio Tinto was given the go-ahead to a future expansion project, moving it from an open pit to an underground mine. This plan was postponed; in September 2010 Rio Tinto announced fresh plans to develop an underground mine beneath the existing pit, increasing annual production to 9 million tonnes of ore. The
Letseng diamond mine Letseng diamond mine The Letseng diamond mine, found in the landlocked Southern African kingdom of Lesotho, is owned by Gem Diamonds, Ltd. and the government of Lesotho, and at an elevation of 3,100 m (10,000 ft) it is the world's highest diamond mine. It is characterised by extremely low grade ore (less than /hundred tons) and is known for producing huge diamonds, having the highest percentage of large diamonds (greater than ), giving it the highest dollar value per carat of any diamond mine. The world average is roughly US$81 per carat, while Letseng averaged over US$1,894 per carat for