Petrogenesis and metallogenic setting of the Habo porphyry Cu–(Mo–Au) deposit, Yunnan, China

Abstract

Although most porphyry-type deposits are associated with subduction-related magmas within magmatic arc settings, recent research has identified a number of porphyry-type deposits that formed in post-subduction tectonic settings. The newly discovered Habo porphyry Cu–(Mo–Au) deposit in Yunnan, China, formed in a post-subduction tectonic setting and is located in the southwest of the Cenozoic Ailao Shan–Red River continental collision zone. The deposit is associated with the Habo South granite pluton, which consists of three mineralization-related quartz monzonite porphyries and a post-mineralization diorite porphyry. Zircons from the Habo South granite and quartz monzonite porphyries were analyzed by in situ U–Pb LA-ICP-MS, yielding a similiar age of 36Ma, with molybdenite Re–Os isotope dating indicating that the Habo porphyry deposit formed at 35.5Ma. Both magmatism and the associated mineralization at Habo are coeval with porphyry copper deposits in the Yulong metallogenic belt of Eastern Tibet. The Habo South granite and porphyries have SiO2 concentrations of 67.28–73.44wt.%, MgO concentrations of <1.5wt.%, Al2O3 concentrations around 15wt.%, Al2O3/(CaO+Na2O+K2O) (A/CNK) ratios of >1.1, K2O+Na2O concentrations generally between 7 and 9wt.%, and K2O/Na2O ratios of >1.4, showing indicative of high-K magmas. The Habo South granite and quartz monzonite porphyries are enriched in light rare earth elements (LREE) and large ion lithophile elements (LILE), and depleted in heavy rare earth elements (HREE) and high field strength elements (HFSE), with high Sr and low Y concentrations. They have initial 87Sr/86Sr values of 0.7071–0.7083, with εNd(t) values from −5.3 to −3.7. These features are indicative of lower-crust derived adakitic magmas, and are similar to those of mineralized porphyries in the Yulong copper belt in Eastern Tibet. This mineralogical, geochemical, and isotope evidence strongly suggests that the magmas that formed both porphyries and the Habo South granite were derived by partial melting of a region of thickened lower crust, with assimilation of components generated from a region of phlogopite-bearing lithospheric mantle involved during intrusion. The Habo porphyry deposit represents an extension of the Yulong metallogenic belt and formed in response to regional tectonic activity in Eastern Tibet.