Arthur A. Bookstrom

Undiscovered Phanerozoic Porphyry Copper Deposits—A Global Assessment

Porphyry copper deposits represent the principal source of global copper supply. To address the questions of where future copper supplies are likely to come from and how much copper could exist within the upper kilometer of the earth’s crust, the USGS led a cooperative international effort to assess the world’s undiscovered Phanerozoic porphyry copper deposits using a geologybased, probabilistic form of mineral resource assessment (Singer and Menzie, 2010). Globally, 175 tracts permissive for porphyry copper deposits were defined to include volcanic and intrusive rocks of specified ranges of age and composition. The rocks represent: (1) magmatic arcs that developed on continental crust above subducting oceanic plates, (2) island arcs that formed on oceanic crust, and(or) (3) postconvergent magmatic belts within continents. Quantitative assessments of undiscovered resources were done for 155 of those permissive tracts.

Relationship between Porphyry Copper Occurrences, Crustal Preservation Levels, and Amount of Exploration in Magmatic Belts of the Central Tethys Region

A probabilistic assessment of undiscovered resources in porphyry copper deposits in the Central Tethys region of Turkey, the Caucasus, Iran, western Pakistan, and southern Afghanistan was conducted as part of a U.S.G.S. global mineral resource assessment. The purpose was to delineate areas as permissive tracts for the occurrence of porphyry Cu-Mo and Cu-Au deposits, and to provide estimates of amounts of Cu, Mo, and Au likely to be contained in undiscovered porphyry deposits (Zürcher et al., 2013; Zürcher et al., in review). Tectonic, geologic, geochemical, geochronologic, and ore deposits data compiled and analyzed for this assessment show that magmatism in the region can be rationalized in terms of fundamental plate tectonic principles, including mantle-involved post-subduction processes. However, uplift, erosion, subsidence, and burial of porphyry copper deposits also played an important role in shaping the observed metallogenic patterns.