The role of preexisting geologic architecture in the formation of giant porphyry-related Cu+ or -Au deposits; examples from New Guinea and Chile

Development of giant porphyry-related copper and/or gold deposits in New Guinea and N and central Chile occurred during Tertiary magmatic events that overprinted earlier extensional tectonic settings. The earlier tectonic settings consisted of a Mesozoic passive margin in New Guinea, a Jurassic-Cretaceous back-arc basin in N Chile, and an Oligocene intra-arc basin in central Chile. The pre-existing architecture of the basement rocks, the fault systems, and the stratigraphic packages associated with these settings played a strong role in controlling development of the giant deposits. Although the extensional tectonic settings in these terrains were different, they share a number of elements that were used during formation of the Tertiary ore deposits. These were the presence of coupled systems of deeply detached, listric synsedimentary faults and steep transverse faults, and the presence of a relatively flat-lying heterogeneous volcano-sedimentary rock package. During Tertiary collision the deeply detached listric faults were inverted and strongly focused uplift, exhumation, and associated overpressuring-induced failure and fluid flow. In addition, steep transverse faults were activated to form wrench systems, with attendant steep, deeply tapping pathways for magma and/or fluid associated with dilatant jogs, flexures, or fault intersections. Ore deposits are commonly located in the hanging wall of the thrust faults. From the example terrains, a set of exploration indicators have been constructed to highlight belts that are prospective for giant porphyry Cu systems.