Origin and tectonic setting of the giant Duolong Cu-Au deposit, South Qiangtang Terrane, Tibet: Evidence from geochronology and geochemistry of Early Cretaceous intrusive rocks

We constrain the origin and tectonic setting of the giant Duolong porphyry-epithermal Cu-Au deposit in the South Qiangtang Terrane of northern Tibet, based on new zircon U-Pb ages and Hf isotopic data, as well as whole-rock major and trace element data from poorly studied ore-associated intrusions in the Duolong area. The LA-ICP-MS zircon U-Pb dating indicates that the ore-associated rocks formed between 121 and 126 Ma. These ore-associated rocks are geochemically similar to low-K tholeiitic M-type granitoids and to mid- to high-K, calc-alkaline I-type granitoids. They have variable and predominantly positive zircon epsilon(Hf)(t) values (-1.4 to +15.6) and variable crustal model ages (T-DM(Hf)(C); 176-1122 Ma). Taking into account previous data and the regional geology of the study area, we propose that the ore-associated rocks originated from fractional crystallization of mantle-derived mafic melts and magma mixing of mantle-derived mafic and hybrid lower crust-derived felsic melts, and the hybrid lower crust included a mix of juvenile and older continental material. The Duolong porphyry-epithermal Cu-Au deposit formed within an 'ensialic forearc' of an active continental margin as a result of the northwards subduction of the Bangong-Nujiang Ocean crust beneath the South Qiangtang Terrane. (C) 2016 Elsevier B.V. All rights reserved.