Platinum-Group Element Geochemistry of Igneous Rocks in the Chongjiang Cu–Mo–Au Deposit, Southern Tibet: Implications for the Formation of Post-Collisional Porphyry Cu Deposits.

The article focuses on the timing and extent of sulfide saturation in the post-collisional Chongjiang porphyry Cu–Mo–Au deposit in southern Tibet and its implications for ore formation. It presents geochemical, isotopic, and zircon U–Pb geochronological data showing that the Chongjiang intrusions (14.2–12.8 Ma) are co-magmatic, derived from partial melts of juvenile lower crust mixed with lithospheric mantle melts, and crystallized from oxidized, water-rich magmas. Sulfide saturation occurred early in magma evolution (~3.9 wt % MgO), prior to volatile saturation (~1.4–2.4 wt % MgO), with only a small amount (0.003–0.009 wt %) of magmatic sulfide segregated, which preferentially sequestered highly chalcophile platinum-group elements like Pd but left Cu, Mo, and Au largely in the residual melt. This early but limited sulfide saturation, influenced by thick crustal conditions (~70 km), allowed sufficient Cu–Mo–Au to remain for porphyry mineralization, suggesting that the volume of magmatic sulfide produced is a critical control on the metal endowment and style of post-collisional porphyry deposits in the Gangdese belt.