A version of this story appears in the November 3, 2014 issue of Forbes.
Most of the world’s greatest mines started as a surface outcrop before turning into a big hole in the ground. Australia’s Deep Exploration Technologies Cooperative Research Centre, backed by miners like
The premise is that mineral deposits are evenly scattered across the globe and miners have only found the ones with veins at or near the surface, says Neil Williams, retired chief of government research agency Geoscience Australia. Even the world's deepest mines, like the 2-mile-deep Mponeng gold mine in South Africa, exploit structures that prospectors originally found with conventional methods. Those methods include everything from sophisticated gravity and radiation sensors to old-fashioned panning for gold, where prospectors work upstream until the flakes disappear, then look uphill for the source of the gold.
Most mines "started at the surface, and then by understanding the geology at the surface they said `If it’s here, it ought to be there,'" Williams told me.
Now geologists believe most of the big, company-making mineral deposits have been found. The average depth of so-called "greenfields" discoveries in Australia is still less than 250 feet, Williams said, while even "brownfields" discoveries in known structures average less than 550 feet. But there's no reason to believe there aren't monster discoveries scattered evenly across geologic layers 1,000 feet or lower.
So miners are turning to new methods to find economically viable deposits under the obscuring cover of rock and soil. They're still relying on airborne sensors -- though they could save a lot of money by turning to drones if the government allows it -- paired with high-powered software tuned to find the most likely spots for concentrations of valuable minerals like copper and gold. They then use relatively inexpensive coiled-tubing drilling rigs to punch in exploratory holes for mineral samples and electronic logging.
The model is Australia's Olympic Dam mine, which Williams calls "the most stupendous discovery of the 20th century." It was found under almost 1,000 feet of unrelated rock in the mid-1970s using magnetic and gravity surveys. Current operator BHP believes it contains more than $1 trillion worth of copper and uranium.
At a recent meeting at the Colorado School of Mines in Golden, Williams said, he told students to look east, toward the flatlands.
"There will be Olympic Dams under the Great Plains," he predicted.
Even Olympic Dam's minerals are being dug out of an enormous open pit, and Williams said miners will probably continue to use conventional methods to depths of 1,000 feet. After that, companies are experimenting with a fracking-like technology in which they'd break up the rock layers underground and inject fluids to bring the ore to the surface in solution.
