The Xiongcun Cu-Zn-Au deposit in the western segment of the Gangdese, Tibet: A Mesozoic VHMS-type deposit cut by late veins

The Xiongcun Cu-Zn-Au deposit lies in the western segment of the Gangdese porphyry copper belt and in the forearc basin of the Southern Gangdese volcanic arc. The deposit is hosted by Cretaceous marine intermediate and basic volcanic clastic rocks that filled a supra-subduction forearc basin. The mineralized alteration zone is 2 km in length and varies in width from 100 m to 400 m with an average of about 200 m. The mineralized horizon is divided into a lower stringer mineralization and upper massive, sub-massive and banded mineralization. Laminated and banded mineralization lies in the hanging wall. Weak sulfidation is documented in the footwall. In addition, some late veins and lenticular sulfide bodies cut the early formed sulfide horizons. The most prospective ore bodies are developed in the upper mineralization horizon. Alteration is zoned with distal propylitization and proximal silicification, sericitization ± chrolitization in the ore body. Fluid inclusion analysis, sulphur isotopes, and trace elements of sulfides reveal that the deposit has the similar features compared with ancient volcanic-hosted massive sulfide deposits (VHMS) and modern active chimney. Based on these characteristics, we propose the deposit is a deformed VHMS-type deposit that formed in the forearc of the Gangdese volcanomagmatic arc during Mesozoic subduction. Second stage veins, inferred to form during collision between the India subcontinent and Eurasia cut the VHMS deposit prior to or simultaneous with intrusion of a post-mineral Himalayan-age diorite porphyries.