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Mponeng is a gold mine in South Africa's North West Province. It extends over 4 kilometres below the surface,〔.〕 and is considered to be one of the most substantial gold mines in the world.〔(【引用サイトリンク】url=http://www.mining-technology.com/projects/mponeng/ )〕 It is also currently the world's deepest mine.〔(World's ten deepest mines )〕 The trip from the surface to the bottom of the mine takes over an hour.〔 Over 5400 metric tonnes of rock are excavated from Mponeng each day.〔 At a cost of $19.4 per gram of gold extracted, the mine needs to recover only 10 grams of gold per ton excavated to remain profitable.〔 The mine contains at least two gold reefs, with the deepest one metre thick.〔 The temperature of the rock reaches , and the mine pumps slurry ice underground to cool the tunnel air below .〔 A mixture of concrete, water, and rock is packed into excavated areas, which further acts as an insulator.〔 Tunnel walls are secured by flexible shotcrete reinforced with steel fibers, which is further held in place by diamond-mesh netting.〔 The endemic bacterium ''Desulforudis audaxviator'' was discovered within groundwater samples. Danny Forster visited this mine to do an episode of ''Build It Bigger'' for season number three. ==References== 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Mponeng Gold Mine」の詳細全文を読む スポンサード リンク
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