Climax Molybdenum Mine, Colorado

The Climax Mine is one of the largest molybdenum mines in the world, and was the origin of the company that is now called Climax Molybdenum, owned by Freeport-McMoRan. The mine is directly on the Continental Divide, and got its name from railroad engineers who built a line to the top of the pass—the climax—in the late 1880s, connecting it to the boomtown of Leadville in the valley below. The mine opened as an underground operation, starting in 1915. By 1926, three fourths of all the molybdenum in the world came from here. Block-cave mining started in 1927, an excavation technique that was pioneered at the mine. The process uses explosives to cause controlled cave-ins in massive vertical cavernous voids. Under its own weight, the broken material spills into pre-constructed funnels and is hauled off over time by train cars that line up under the funnels in a tunnel below. This technique enabled production to increase dramatically. In World War Two, molybdenum was considered an important strategic resource, as it was used to make hardened steel for everything from aircraft engines to armor plating. Most of the nation’s supply at that time came from this mine. By 1957, Climax claimed to be the largest underground mine in the world. A company town, built here in 1936, had as many as 2,000 people in the 1950s. In the 1960s, as open pit mining expanded, the town was in the way, and was removed. Many of the town’s buildings, and people, moved to Leadville, joining the rest of the workforce, which surpassed 3,000 employees by 1979. In 1976, the company opened a major underground operation at the Henderson Mine, 40 miles away, which has surpassed the Climax mine in output.