Tectono-Magmatic Setting and Distribution of Porphyry Copper Systems in the
Central Tethys Region of Turkey, the Caucasus, Iran, and southern Pakistan
by
Lukas Zurcher
U.S. Geological Survey
The rapidly growing body of geodynamic, geochemical, geochronologic, and ore deposits studies across Turkey, the Caucasus, Iran, and southern Pakistan provided a good opportunity to update and review the time and space constraints of geodynamic processes related to the diverse continental margin, intra-oceanic, and post-collisional tectonic settings that were generated during the sequential rifting of microcontinental fragments from the passive margin of Gondwana in the south, their northward transport across the Neo-Tethys Ocean, and their eventual collision with the active margin of Eurasia in the north.
Integration of geological, geophysical, and remote sensing information with the 41 porphyry deposits undefined including the giant Reko Diq (Pakistan), and the world-class Sar Cheshmeh (Iran), Sungun (Iran), and Kadjaran (Armenia) deposits undefined and 319 porphyry prospects in the region indicate that much of the magmatism and related porphyry copper mineralization can be explained in terms of traditional plate tectonic principles. However, it is also evident that mantle-involved post-subduction processes have also played an important role in localizing world-class porphyry deposits in the region, and that uplift, erosion, subsidence, and burial of mineral deposits, not just their formation, have played a key role in generating the observed distribution of metallogenic patterns.
Twenty five partially overlapping Late Triassic to recent magmatic belts permissive for the occurrence of porphyry copper deposits were identified in the Central Tethys region. Of the 360 known porphyry copper occurrences (the sum of identified deposits and prospects) in the region, about 65% are hosted by the five most favorable belts. 60% are associated with continental arcs; 20% are related to island arcs or back-arcs; and 20% are linked to post-collisional settings. Of the 41 known porphyry copper deposits, roughly comparable fractions are distributed among the different tectonic settings. The most important deposits, however, occur in continental arc (Reko Diq and Sar Cheshmeh) or post-collisional settings (Sungun and Kadjaran).
The level of exposure is an important factor in the observed distribution of porphyry belts. At the regional scale analyzed, the correlation is remarkable because exhumation and burial processes commonly happen at an order of magnitude smaller time and space scales than magmatic events, and what is observed today is the sum product of several partially juxtaposed exhumation and burial events. Permissive magmatic belts with the highest number of porphyry copper occurrences are underlain by comparable areas of coeval permissive volcanic and plutonic rocks, and lesser cover, reflecting adequate levels of preservation and exposure of porphyry systems. These magmatic belts also host most of the known porphyry copper resources in the Central Tethys region. Fewer porphyry systems are known to occur in magmatic belts where the proportion of coeval permissive volcanic-to-plutonic rocks is too high or too low and the fraction of younger cover is high, pointing respectively to crustal levels that are too shallow or too exhumed, and porphyry systems that may be buried.
Overall, formation of the most important porphyry deposits in the Central Tethys region appear to closely precede the high tectonic gradients produced by the final “hard” continent-continent early Oligocene to late Miocene oblique and diachronous collision between the Arabian Platform and the Eurasian margin, and to closely supersede the sudden southward migration and flattening of the subducted slab along the Makran Trench in the latest Miocene. The highest rates of uplift, erosion, and removal of volcanic rocks that are coeval with causative porphyry intrusions also coincide with these tectonic changes.
Lukas Zürcher is a research geologist with the USGS. He received a BS in Geological Engineering from the Colorado School of Mines (1985), and a MS and PhD in Geosciences from the University of Arizona in (1994 and 2002, respectively). He worked as an exploration and consulting geologist for the mining industry in Mexico, Cote d’Ivoire, Bolivia, Argentina, and the US (1985-2010), as a postdoctoral fellow in the Department of Lunar and Planetary Sciences (2002-2005), and as Manager of the Lowell Program in Economic Geology (2002-2011) at the University of Arizona before joining the USGS in 2011. He has 25 years of combined industry and academic experience in geologic, alteration, and mineralization mapping, structural geology, igneous and hydrothermal geochemistry, statistical methods, mineral economics, and GIS-based favorability mapping. His research has included local- to regional-scale geologic, geochemical, and metallogenic studies of intrusion-related, impact-generated, and IOCG hydrothermal systems, as well as comparative analyses of favorability mapping methods. With the USGS, he has contributed to the porphyry copper resource assessments of Mexico, Central America and the Caribbean, and the Central Tethys region.
