Free Republic

One of the world’s largest untapped copper deposits sits 7,000 feet below the Earth’s surface. It is a lode that operator Rio Tinto RIO 0.68% PLC wouldn’t have touched—until now. Not that long ago, an abundance of high-grade copper could be mined out of shallower open pits. But as those deposits are depleted and high-grade copper becomes tougher to find, firms such as Rio have been compelled to mine deeper underground.

Silver King Mine (1875-1920) In 1873, a soldier named Sullivan, who had been involved in the construction of the road that had become the main route between the Globe area and valleys of the Salt and Gila rivers was returning to camp one evening, when he found several heavy, black nuggets of metallic material near the base of Stoneman’s Grade (Short et al, 1943). Although he had little knowledge of minerals, he figured that he must have found something unusual. He kept the black nuggets and returned to camp without saying any- thing about his discovery to the other soldiers....

Shaft #10 at the Resolution Copper mine in Superior reached its final depth of 6,943 feet (2,116 m). The 28-foot diameter shaft is the deepest single lift shaft in North America, according to the company. [Right top, bottom of shaft #10. Photo credit, Resolution Copper] The Resolution mine would produce an estimated 25% of the nation's copper for the next 40 years once it's completed. [Right bottom, headframe for shaft #10. Photo credit, Nyal Niemuth] "The completion of this 1.3 mile deep vertical shaft is truly unprecedented in North America,” said Tom Goodell, General Manager of Shaft Development for the...