Argyle diamond mine of tunnelling, the Argyle underground block cave development was officially completed. In 2013, Argyle is estimated to produce 10.2 million carats with an average per carat price of $25/carat. The Argyle diamond mine is also notable for being the first successful commercial diamond mine exploiting a volcanic pipe of lamproite, rather than the more usual kimberlite pipe; much earlier attempts to mine diamonds from a lamproite pipe in Arkansas, USA were commercially unsuccessful. The Argyle mine is owned by the Rio Tinto Group, a diversified mining company which also owns the Diavik Diamond Mine in Canada and the Murowa Diamond
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