In 1895 mining claims were recorded at what would become Sierrita. Underground mining began in 1907 and open-pit development was underway by 1957. In December 2009, Freeport-McMoRan purchased the adjacent Twin Buttes copper mine, providing significant synergies in the Sierrita minerals district. This venture included the potential for expanded mining activities, operations growth for mining copper and molybdenum, and reclamation activity which is currently ongoing.

In 2016, Sierrita curtailed mining and milling operating rates and is operating at 75 percent.

In 2016, copper production at Sierrita amounted to 162 million pounds.

In 2017, copper production amounted to 160 million pounds and more than 920 people were employed here.


Sierrita Operations Fast FactsFreeport McMoRan copper mining in Arizona

  • Sierrita is an open-pit copper and molybdenum mining complex 20 miles southwest of Tucson, Arizona, in Pima County
  • In addition to copper and molybdenum, Sierrita produces rhenium, a rare and highly valued metal
  • In 2016, Sierrita’s direct and indirect economic impact on Arizona totaled $219.1 Million
  • To learn more about the various sustainable development projects in Sierrita, click here
  • Sierrita holds the following operations:
    • A 102,000 metric tons per day (mtd) concentrator that produces copper and molybdenum concentrates
    • A run-of-mine oxide-leaching system and a copper sulfate crystal plant
    • The Twin Buttes electrowinning facility where copper cathode is plated
    • Molybdenum facilities consisting of a leaching circuit, two molybdenum roasters and a packaging facility

Freeport McMoRan copper mining in Arizona