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Sierrita Mine

Description: Sierrita is an open-pit copper and molybdenum mining complex.

Did you know? In addition to copper and molybdenum, the mine produces rhenium, a rare and highly valued metal.

Location: 20 miles southwest of Tucson, Arizona.

Ores: The Sierrita mine is a porphyry copper deposit that has oxide and secondary sulfide mineralization, and primary sulfide mineralization. The predominant oxide copper minerals are malachite, azurite and chrysocolla. Chalcocite is the most important secondary copper sulfide mineral, and chalcopyrite and molybdenite are the dominant primary sulfides.

Processes and facilities: The Sierrita operation includes a 102,000 metric ton-per-day concentrator that produces copper and molybdenum concentrates. Sierrita also produces copper from a run-of-mine oxide-leaching system. Copper cathode is plated at the Twin Buttes electrowinning facility. The Sierrita operation has a molybdenum facility consisting of a leaching circuit, two molybdenum roasters and a packaging facility. The molybdenum facilities process molybdenum concentrate produced by Sierrita, from our other mines, and from third-party sources.

In response to low copper and molybdenum prices, during December 2015, we announced plans to suspend production at the Sierrita mine. The plan consists of putting the mine and concentrator operations on care-and maintenance status and producing copper through the oxide-leaching system. Additionally, Sierrita's molybdenum processing facility will continue to process material from our other mines.

Background: First claims recorded in 1895. First worked as an underground mine beginning in 1907; open-pit development began in 1957. In 2009, FCX purchased the Twin Buttes copper mine, which ceased operations in 1994 and is adjacent to the Sierrita mine. The purchase provides significant synergies in the Sierrita minerals district, including the potential for expanded mining activities and access to material that can be used for Sierrita tailings and stockpile reclamation purposes.

Ownership: 100%.

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