Insights from Molybdenum Isotopes into Rhenium Enrichment in Porphyry Mo Deposits: Evidence from the Shapinggou Deposit, Eastern China

Rhenium (Re) is a critical metal indispensable to high-technology manufacturing, defense, and new energy industries. Molybdenite in porphyry deposits is one of the most important hosts of economically recoverable Re. However, the mechanisms controlling Re enrichment in molybdenite remain debated. Ore-forming fluids in Dabie-type porphyry Mo deposits are CO₂-rich and commonly occur as coexisting vapor and brine phases, favoring phase separation and boiling. Recent work on the Jinduicheng Dabie-type porphyry Mo deposit in the East Qinling–Dabie Mo metallogenic belt suggested that fluid boiling plays an important role in Re enrichment, but whether this mechanism also applies to other Dabie-type porphyry Mo deposits remains unclear. In this study, Mo and S isotopes of molybdenite from the Shapinggou porphyry Mo deposit were employed to investigate Re enrichment in Dabie-type porphyry Mo deposits. The results show that molybdenite contains 1.13–23.56 ppm Re, has δ^98/95Mo values of −0.28‰ to +1.02‰, and shows a negative correlation between δ^98/95Mo and δ³⁴S. From early- to late-stage molybdenite, δ^98/95Mo values decrease systematically. The systematic decrease in Mo isotopic compositions during mineralization indicates that fluid boiling was the key factor controlling their variation. The negative correlation between Re contents and Mo isotopic compositions further suggests that Re enrichment was also controlled by fluid boiling. During boiling, lighter Mo isotopes and Re partitioned into the vapor phase, whereas delayed vapor-phase Re precipitation and increased residual-fluid salinity enhanced Re mobility in the liquid phase, producing late-stage molybdenite with high Re contents and light Mo isotopic compositions. This study demonstrates that fluid boiling was an important process during mineralization at Shapinggou and may represent one of the factors controlling Re contents in Dabie-type porphyry Mo deposits.