Tectonic setting and mineralization potential of the Zefreh porphyry Cu-Mo deposit, central Iran: Constraints from petrographic and geochemical data

The Zefreh porphyry Cu-Mo deposit is located in the central part of the Cenozoic Urumieh-Dokhtar Magmatic Arc (UDMA), 75 km NE of Isfahan city, central Iran. The Zefreh rocks, ranging from diorite to granodiorite in composition, formed in a subduction-related arc setting, and likely in a pre-plate collisional environment. They are enriched in Th, U, Rb, Pb, light rare earth elements (LREE), but depleted in Ti, Nb, Ta, Ba, Sr, and P. Negative to slightly positive Eu anomalies (0.5–1.1), low to moderate Sr contents, (189–567 ppm), low to moderate Sr/Y ratios (5–23), and low La/Yb ratios (3–8) in the Zefreh magmatic suite rule out considerable amounts of fractionated amphibole from a hydrous magma in the lower crust. Arc crustal thickness in the Zefreh area was probably <40 km at the time of emplacement of the granitoids, under which amphibole did not fractionate considerably from the primitive magma. Melting of garnet-free lower-crustal amphibolites, together with fractional crystallization and crustal assimilation processes may be the main source of the Zefreh granitoids. On the basis of geochemical characteristics of the granitoids (e.g., low to moderate Sr contents, moderate to high contents of Y and Yb, low to moderate ratios of Sr/Y and Dy/Yb, low La/Yb ratios, negative to slightly positive Eu anomalies, and negative anomalies of Sr) and immature arc with thin crust, the Zefreh deposit is likely to be a small, sub-economic porphyry Cu-Mo deposit.