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
Williamson diamond mine years of operation, average ore grade was about per hundred tons (60 mg/t); in the first few years of full operation grades were as high as per hundred tons (124 mg/t), or 10 times the ore realized today. Production in the 1950s and 1960s was usually between 500,000 and 750,000 carats (100 and 150 kg) per year; the peak year of production was 1966, when 924,984 carats (185 kg) were produced. Today production levels for all Williamson mine diamond recovery activities is about 300,000 carats (60 kg) per year. Notable stones produced at the Williamson mine include the Williamson pink