Three miles into Buick Mine, Joe Vaughn points his flashlight at a rock wall. A vein of silvery-grey ore sparkles in the light. “That’s the lead,” says Vaughn, mine superintendent at Doe Run’s Buick and Brushy Creek Mines. “That’s what we’re after.” Vaughn is 1,200 feet underground, nearly a quarter-mile down. The wall in front of him is pocked with