MULLAN, Idaho – At the Lucky Friday Mine, a descent of nearly a mile takes only 2 1/2 minutes. You climb aboard the “cage” on the Silver Shaft, which operates like a high-speed elevator. Rock walls, encased in concrete, whiz by. When the cage stops with a rattle and a shake, you’re 4,900 feet below the Earth’s surface, deep in the Bitterroot Mountains, where the rock is shot through with silver veins.