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Sierrita Mine


Key Facts

Commodity Copper, Molybdenum, Rhenium
Location Arizona, USA
Nearest Landmark: Tucson
Distance:25 miles south of Landmark
Latitude: 31 deg 52 min N
Longitude: 111 deg 6 min W
Satellite Image
Owners Freeport McMoran Copper & Gold Inc
Operator Freeport McMoran
Production 177 Mlbs copper, 23 Mlbs molybdenum (2011)
Deposit Type Porphyry copper & molybdenum deposit
Reserves & Resources 12.1 Bln lbs copper, 1.24 Bln lbs molybdenum (Dec 31, 2011, proven & probable reserves)
Mining Type Surface
Mining Method Open pit
Processing Method Crushing, grinding, glotation, cyanide leaching, SX/EW
Mine Life To 2080
Mining Equipment 235t haul trucks (25); 34 m3 to 56m3 shovels (4)
Processing Equipment Crusher, grinders, flotation circuit, cyanide leaching circuit, SX/EW circuit
Employees N.A.
Contact Information P.O. Box 527
Green Valley, Arizona, USA 85614
Tel:  (520) 648-8500
Fax:  (520) 648-8575

Last updated: July 16, 2012


Sierrita is an open pit copper-molybdenum operation located about 20 miles southwest of Tucson in Pima County, Arizona, USA. The mining complex is part of the Freeport McMoran’s Arizona operations.

The mine has been in operation since 1959 – it processes oxide and sulphide copper mineralization through cyanide leaching and SX/EW process and through flotation methods. In 2004, a copper sulphate crystal plant was also brought into production. Design capacity is 102,000 metric ton-per-day for the concentrator, 50 million pounds cathode copper for the SX/EW facility, and 40 million pounds for the copper sulphate plant.

In 2009, Freeport McMoran (FCX) purchased the adjacent past producer Twin Buttes. The property has potential for the delineation of new copper resources and a feasibility study is expected to commence in 2012.

In 2011, Sierrita produced 177 million pounds copper and 23 million pounds molybdenum.


Sierrita is located in Pima County, Arizona, approximately 20 miles southwest of Tucson and seven miles west of the town of Green Valley and Interstate Highway 19. The site is accessible by a paved highway and by rail.

Arizona is located in the southwest of the United States. Tucson is its second largest city.

Sierrita mine is located in a desert environment with rainfall averaging 12 inches per year.


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.

The company conducted drilling on the Twin Buttes property while metallurgical studies to support a feasibility study were expected to commence in 2012.

As of December 2011, Sierrita’s ore reserves were estimated at 2.78 million tonnes grading 0.23% copper and 0.03% molybdenum for 12.1 billion pounds copper and 1.24 billion pounds molybdenum.

Mining & Operation

The Sierrita operation, including the adjacent Twin Buttes site encompasses approximately 27,000 acres, comprising 13,282 acres of patented mining claims and other fee lands, 11,694 acres of unpatented mining claims and 2,024 acres of leased lands.

Sierita is a conventional open pit mining operation. The highest bench elevation is 1,160 meters above sea level and the ultimate pit bottom is expected to be 440 meters above sea level.

The mining fleet consists of 25 235-metric ton haul trucks loaded by four shovels with bucket sizes ranging from 34 to 56 cubic meters, which are capable of moving an average of 200,000 metric tons of material per day.

The mine uses a number of systems from Modular Mining Systems. These include a wireless communications network; an interactive maintenance management system, and a system that automatically optimizes haul truck assignments.


The Sierrita operation includes a 102,000 metric ton-per-day concentrator that produces copper and molybdenum concentrates. The concentrate gets shipped to FCX’s Miami smelter in Arizona.

Sierrita also produces copper from a ROM oxide-leaching system. Cathode copper is plated at the Twin Buttes EW facility, which has a design capacity of approximately 50 million pounds of copper per year.

There is an in-pit crusher and conveyor system to reduce haulage costs.

In 2004, a copper sulfate crystal plant began production, which has the capacity to produce 40 million pounds of copper sulfate per year. The sulfate has agricultural and industrial applications.

The Sierrita operation also has molybdenum facilities 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.

Sierrita receives electrical power through long-term contracts with the Tucson Electric Power Company.

Sierrita’s production totaled 177 million pounds of copper and 23 million pounds of molybdenum in 2011.

Environment & Community

Freeport McMoran is a party to a litigation that may impact their water rights claims or rights to continued use of currently available water supplies, which could adversely affect the water supply for the Sierrita operation.

Sierrita is one of the safest mines in the United States, having earned the federal government's prestigious Sentinels of Safety award as the safest open-pit mine in the open-pit hard-rock mine category in 1993, '97, '99 and 2001.

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