Inside the Billion-Dollar Dig to America’s Biggest Copper Deposit – by Matthew Philips (Bloomberg News – March 14, 2016)

Miners are 7,000 feet down and they aren’t turning back.

The entrance to America’s deepest mine shaft sits on a plateau high above the Arizona desert, about an hour east of Phoenix. Tucked against the base of a ridge of steep cliffs, it looks southeast over miles of ragged boulder fields. What looks like a large capital A rises above its entrance. It’s the steel headframe used to hoist equipment in and out of the shaft, a concrete tube 30 feet wide that goes 6,943 feet straight down.

The No. 10 mine shaft, as it’s called, is on the southern edge of an old underground mine. For 86 years, the Magma Superior mine pulled copper and silver out of the surrounding mountains before closing in 1996 when the minerals ran out. Over its lifetime, Magma grew to include nine separate shafts, some of them miles apart.

The final shaft, No. 9, was finished in the 1970s. After Magma closed, No. 9 sat abandoned for nearly 20 years before becoming part of the new Resolution Copper mine. It’s now the ventilation shaft for its younger, deeper cousin, No. 10, just a few hundred feet away.

Visited on a chilly day in December, the area around the top of the mine, the “collar” in mining terms, doesn’t look inviting. Steam clouds pour from the mouth of No. 9. It’s the hot air being drawn from the cave dug at the bottom of No. 10. That far down, rocks formed billions of years ago still carry heat from the molten core of the earth.

Without the elaborate refrigeration system that pumps chilled air down No. 10, the bottom of the mine would be 180F, far too hot for a human to withstand. “You’d cook,” says Randy Seppala, 60, project manager for shaft development. Miners have long called this heat the “hand of the devil,” reaching up from the depths.

Seppala works for Resolution Copper Mining, a venture between the two largest mining companies in the world, Rio Tinto and BHP Billiton. Together they’ve spent more than $1 billion, including $350 million sinking the No. 10 mine shaft, in hopes of tapping nearly 2 billion metric tons of ore. Less than 2 percent of it is believed to be copper. It might not sound like much, but that’s considered dense, making it the fourth-largest undeveloped copper deposit in the world.

Resolution Copper plans to dig four more shafts over the next 15 years. At peak production, this will be the biggest copper mine in the U.S., producing 100,000 tons of rock a day, and enough copper to meet a quarter of the country’s demand.

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