Sponsored by:
Freeport-McMoRan Copper & Gold, Inc.
Abstract
The Safford district located in southeastern Arizona is a linear trending group of porphyry copper deposits. Production in the Safford district began with the Dos Pobres deposit in 2007 and the San Juan deposit in 2011. The Safford mine is currently a crushed leach operation. Ore and gangue minerals unique to different porphyry deposits have a profound effect on the processes and production of copper from the mine; hence, understanding of the geology can help fine tune recovery of copper. Since mining began our understanding of the structure, alteration and mineralogical distribution, and genesis of the Dos Pobres and San Juan deposits has increased. Structures within the mining area have been mapped to aid in blasting and slope stability. Mineralogical distributions have been mapped to better determine ore types and blending of ores in the leach pad. Genesis of the deposits is better understood. Tonalite to quartz monzonite magmas (57.2 Ma) intruded into a Cretaceous andesitic volcanic package. These various intrusions had their own hydrothermal systems that produced the initial hypogene mineralization. Subsequent erosion and oxidation of the deposits occurred; followed by Tertiary volcanic flows (24-31 Ma), faulting and additional erosion and oxidation. Initial hypogene alteration consisted of early sodic-calcic followed by various expressions of potassic, sericitic and later propolytic alteration. This hypogene alteration was overprinted by an in situ oxidation of the system that has produced the current ore body at Safford. Oxide mineralization is complicated but generally follows the following trends with depth – leached cap, copper bearing limonite, black oxides, chrysocolla, chalcocite. Chalcocite is above the hypogene sulfides comprised of pyrite, chalcopyrite and bornite.
Bill Stavast is a Senior Geologist with Freeport-McMoRan. He received a B.S. and M.S. in Geology from Brigham Young University (2000 and 2002, respectively) and a PhD in Geosciences from the University of Arizona (2006). He has worked with Phelps Dodge and Freeport-McMoRan since 2006. Projects he has worked on are Safford, Tenke-Fungurume, Twin Buttes and Ajo.
