Formation and evolution of multistage ore-forming fluids in the Miocene Bangpu porphyry–skarn deposit, Southern Tibet: insights from LA–ICP–MS trace elements of quartz and fluid inclusions

The large Bangpu Mo–Cu–Pb–Zn deposit, is a Mo-rich (~0.089%), Cu-poor (~0.32%) porphyry–skarn deposit located in the northeastern Gangdese porphyry copper belt (GPCB), Southern Tibet. In this study, LA–ICP–MS data for fluid inclusions and quartz formed during different stages of the mineralization are used to (1) constrain changes in fluid composition during mineralization; (2) infer the origin, transport pathways, and conditions of ore precipitation; and (3) explore the influence of magma chamber on fluid exsolution and shallow mineralization. The Cu content of the vapor-rich (VL) inclusions is higher than that of the halite-bearing (LVH) inclusions, while the Mo, Pb, and Zn contents of the VL and LVH inclusions are similar, indicating that Mo, Cu, Pb, and Zn had a common source, which is inferred to be the intermediate-level magma chamber. The metal contents of fluid inclusions in the early stage potassic alteration-related vein (A vein) and later stage sericitic alteration-related vein (B vein) are similar but variable, implying the intermediate-level magma chamber was too small to form a large stable fluid system. The enrichment of Mo, Pb, and Zn in the Bangpu deposit relative to other porphyry deposits in the GPCB is related to the participation of ancient crustal material. A comparison of our results with those from super-large porphyry Cu deposits elsewhere indicates that metal-rich fluids are not the sole factor to form ore deposits, and the variability of metal contents in the early exsolved fluids is a better predictor of mineralization potential than absolute metal concentrations