Freeport-McMoRan's Sierrita Mine

Freeport-McMoRan's Sierrita Mine

When: Thursday, October 24, 8:30 AM – 12:15 PM
Where: FMI’s Sierrita Mine, 20 Miles south of Tucson
To register: Contact Emma Loiselle,


Sierrita is an open-pit copper and molybdenum mining complex. In addition to copper and molybdenum, the mine produces rhenium, a rare and highly valued metal.


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 100,000 metric ton-per day concentrator that produces copper and molybdenum concentrate. 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. 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.


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.