Arizona has the distinction of many mine sites that have diverse geology and mineralogy. Located 20 miles southwest of Tucson, the Sierrita Mine, currently operated by Freeport-McMoran, is one of the largest copper molybdenum mining operations worldwide.
It was originally prospected in 1895, however, it was not until 60 years later that its value as a disseminated porphyry copper deposit was determined by Harrison Schmitt, who recommended its development to the Duval Sulphur and Potash Co., which in turn brought it into large scale production in 1959.
Milling operations commenced in 1970. There was noted production of chalcocite and covellite, important secondary copper sulfide minerals, along with molybdenite, which contains 100- and 3,000-parts-per-million of rhenium, a rare element found in less than one-part-per-billion of the earth’s crust.
Milled onsite, the Sierrita Mine is currently the only internal U.S. source of rhenium, a metal used by the aerospace industry as a superalloy in jet and industrial gas turbine engines. Noted for its heat and corrosion resistance, rhenium adds longer engine life coupled with higher performance and operational efficiency as noted in its usage in high-octane lead-free gasoline.