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
Argyle diamond mine of the open pit; these reserves would be mined underground (by block caving), rather than the open pit method currently used. In late 2005, Rio Tinto Ltd concluded that the operation was economically feasible. Pre-production construction of the underground mine commenced in early to mid 2006 The Argyle diamond mine is economically feasible because its large reserves and high-grade ore offset a low average diamond value. The estimated value of Argyle diamond production is only US$7 per carat ($35/g); this compares to values of $70 per carat ($350/g) for diamonds produced at the Diavik mine and US$170 per carat ($850/g)