The mine also contains silver, gold and molybdenum (used in steel alloys)--a common combination found in the Peruvian Andes.

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Sales of molybdenum, which is used to make steel and iron alloys, should increase to 90 million this year, from 83 million in 2012.

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Phelps said that on a pro forma basis for 2006, its production combined with Freeport s would be approximately 1.9 million tons of copper, 1.8 million ounces of gold and 69 million pounds of molybdenum, a metal used for hardening steel.

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At one point, the nearby Climax mine produced close to 75 percent of the world's molybdenum, which is used as a hardening agent for steel in cars, as well as in computer chips and monitors.

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