CANANEA, SONORA, MEXICO -- In its natural state, Cananea's copper ore is part of a sagebrush-covered mountain in the middle of the Sonora desert 70 miles south of Arizona. To extract the metal indispensable to computers, automobiles, and iPods, the rock is first blown out of the mountainside with explosives and then loaded onto dump trucks so huge the tires would dwarf a basketball player. The trucks then dump their loads -- small boulders, in effect -- into the first crusher on the hilltop overlooking the huge complex. When the crushed rocks pour out down below, into tunnels deep in the hillside, they're still about the size of watermelons. The next crusher breaks them into smaller pieces, and then enormous mills below grind them down even further, until they are no longer rocks at all, or even pebbles, but a steady stream of fine sand. Even though the mine has been still for over 50 days, shut down because its workers are on strike, rock dust in parts of this huge complex, called...