Where were the Metal, Sulfur and Water from in the Postcollisional Porphyry Cu Deposit at Qulong in South Tibet

Objective Most porphyry Cu deposits （PCDs） were formed in association with subduction-related calc-alkaline magmas, which occurred widely in magmatic arcs worldwide. A widely accepted model is that such deposits were formed from hydrothermal fluids exsolved from hydrous, high oxygen fugacity, sulfur-rich arc magmas, derived from a mantle wedge metasomatized by subduction-slab fluids. Recent studies have documented that such deposits may also occur in post-collisional settings, e.g., the Gangdese porphyry Cu belts in Tibet. The formation of such PCDs is very difficult to be explained by the classic PCDs model, which results in an alternative model to be proposed to interpret the genesis of PCDs in such settings. In this alternative model, metals and sulfur of the post-collisional PCDs were generally thought to be derived from a subduction-modified thickened lower crust, rather than a metasomatized mantle wedge. However, our detailed analysis suggests that the sources of metals and sulfur for the PCDs in post-collisional settings still cannot be well explained by the lower-crust melting model.