Orogenic gold mineralization constrained by sphalerite geochemistry: evidence from the Bangbu deposit, Tibet, SW China

• The Bangbu sphalerite records medium- to low-temperature, CO 2 -rich fluids. • Multivariate analysis distinguishes the Bangbu sphalerite from magmatic-hydrothermal deposits. • Sulfur isotopes reveal significant sub-crustal fluid involvement. • Two stage model: subduction pre-enrichment and metamorphic remobilization. Located in the eastern segment of the Yarlung–Tsangpo suture zone (YTSZ), the Bangbu deposit formed during the subduction–collision evolution of the Himalayan–Tibetan orogen and constitutes a significant example of hydrothermal gold mineralization in this tectonic setting. Pyrite has commonly been employed to trace ore-forming processes in orogenic gold systems, but the role of coexisting sphalerite as an additional tracer mineral remains insufficiently investigated. This study presents a comprehensive geochemical characterization of sphalerite occurring with ore-stage pyrite in quartz–sulfide veins from the Bangbu deposit, and places these results in the context of a global dataset covering sphalerite from diverse mineralization environments. Compared with sphalerite from other deposit types, the Bangbu sphalerite is characterized by elevated Cd but depleted Ga, Mn and Sn. Both PLS-DA and its orthogonal variant (OPLS-DA) show that sphalerite from Bangbu represents a distinct geochemical cluster that is readily separable from typical magmatic–hydrothermal systems. Application of the GGIMFis geothermometer to the Bangbu sphalerite yields temperatures of 230–260 °C (peak at ∼250 °C), while the corresponding lg f S 2 values of –14.5 to –12.4 point to intermediate- to low-sulfidation conditions. These parameters are consistent with medium to low temperature, low salinity, CO 2 -rich fluids and show no clear evidence for a significant magmatic or mantle-derived fluid component, and instead pointing to a predominantly metamorphic fluid origin. Coexisting sphalerite and pyrite display narrowly distributed δ 34 S values of ∼+2‰ and near-equilibrium isotopic fractionation, and their sulfur isotope compositions are lighter than those of sulfides in the surrounding low-grade metamorphic strata. This discrepancy with a simple metamorphic devolatilization model, together with the observation that δ 34 S values fall within the range expected for sulfur released by slab-derived fluids, supports a significant sub-crustal fluid contribution and indicates that a single metamorphic devolatilization model cannot fully explain the gold mineralization. Integrating constraints from trace element compositions, temperature estimates, sulfur fugacity and sulfur isotopes, this study proposes a two-stage genetic model for the Bangbu deposit, including subduction-related devolatilization pre-enrichment and metamorphic reactivation. The results demonstrate that ore-stage sphalerite provides independent constraints on the ore-forming conditions and fluid sources of orogenic gold deposits, and represents an important complement to traditional pyrite-based tracer systems.