for National Geographic News
As gold prices reach near-record highs, South Africa's mining companies are keeping up by drilling to record depths.
The Gold Fields Ltd company intends to set a new record by drilling down 2.5 miles (4 kilometers) at its Driefontein mine, about 37 miles (60 kilometers) southwest of Johannesburg. An estimated 8.5 million ounces (240 million grams) of gold is thought to lie at such depths. (See a map of South Africa.)
Meanwhile, mining firm AngloGold Ashanti, which currently has the world's deepest mine, plans to extend its TauTona, or "Great Lion," mine, west of Johannesburg, to more than 2.4 miles (3.9 kilometers) deep. (See photos of South African mining.)
South Africa is known for having the deepest mines in the world. In comparison, the deepest mine in the United States—the now-defunct Homestake Mine of South Dakota—went down about 8,000 feet (2,438 meters).
Allure of the Ultra-Deep
The ambitious new mining projects are "ultra-deep" mines with shafts that are deeper than 2.2 miles (3.5 kilometers) in the ground, where temperatures rise well over a hundred degrees Fahrenheit (55 degrees Celsius) and rock shatters like glass.
Rocketing gold prices have made ultra-deep mining more attractive in South Africa, the world's largest gold producer.
Recently, gold hit a 28-year high: 770 U.S. dollars per ounce. That means deposits that were once too impure or too deep to mine are now worth prospecting.
"That's all part of the risk ... the investors and the decision-makers have to factor that in," said Ray Durrheim, a seismologist at South Africa's Council for Industrial and Scientific Research who does occasional consulting work for the mining industry.
"New shallow deposits [of gold], aren't easily being discovered around the world," he said. "The resources are at greater depths."
But the gold is dwindling: Analyses of current resources in South Africa suggest that shallow gold reserves have already been tapped.
Ultra-deep miners often have no other choice but to go deeper or look beyond South Africa—and they're doing both.
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