Mponeng is a gold mine in South Africa's North West Province. It extends over two miles below the surface,[1] and is considered to be one of the deepest and most substantial gold mines in the world.[2] The trip from the surface to the bottom of the mine takes over an hour.[1]
6,000 tons of rock are excavated from Mponeng each day.[1] At a cost of $550 per ounce of gold extracted, the mine needs to recover only 0.35 ounces of gold per ton excavated to remain profitable.[1] The mine contains at least two gold reefs, with the deepest three feet thick.[1]
The temperature of the rock reaches 140 degrees Fahrenheit (60 Degrees Celsius), and the mine pumps slurry ice underground to cool the tunnel air below 85 degrees Fahrenheit (29.5 degrees Celsius) (.[1] A mixture of concrete, water, and rock is packed into excavated areas, which further acts as an insulator.[1] Tunnel walls are secured by flexible shotcrete reinforced with steel fibers, which is further held in place by diamond-mesh netting.[1]