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
Yellowknife came from gold mining, and later government; however, because of falling gold prices and increased operating costs, the final gold mine closed in 2004, marking a turning point for Yellowknife's economy. After a downturn in the 1990s during the closure of the gold mines and the downsizing of the government workforce in 1999, Yellowknife's economy has recovered, largely because of the diamond boom; the Ekati Diamond Mine, owned and operated by BHP Billiton (sold to Dominion Diamond Corporation in 2013), opened in 1998. A second mine, Diavik Diamond Mine, began production in 2003. Production from the two operating mines in