Decades-long slump in copper prices
In production as a working copper mine for more than a century, Utah's Bingham Canyon Mine is so large and so deep — 2 3/4 miles across at the top, and 3/4 of a mile deep — that you could stack two of Chicago's Willis Towers on top of each other inside it. Astronauts aboard the International Space Station can even see it with the naked eye.
Discovered in 1848 by Sanford and Thomas Bingham, who found copper ore on the ground while grazing their family's cattle here in the Oquirrh Mountains outside Salt Lake City, the mine opened in 1906 and has since produced more than 19 million tons of copper -- more than any other mine in the world — as well as millions of ounces of gold, silver and molybdenum, a metal used to strengthen steel.
Bingham Canyon's owner, the giant mining company Rio Tinto, announced in 2001 that it would close the mine by the end of 2013 due to a decades-long slump in copper prices. But they still haven't shut down the mine -- in fact, if you visit today, you'll see fleets of trucks driving down into the mine and carrying loads of rock back out again.
In a reversal, Rio Tinto has decided instead to build a second mine underneath Bingham Canyon, an underground mine 2,000 feet below the floor of today's open pit.
Why? Because the price of copper has rebounded in the 2000s, jumping from about $1 per pound to $5 per pound just before the Great Recession hit in 2007, thanks largely to a dramatic rise in demand from emerging industrial powerhouses like China. Today it hovers around $3 a pound.