| The massive ore in magmatic copper-nickel sulfide deposits holds significant economic value. In the Jinchuan copper-nickel deposit, massive ore is primarily enriched in the No. 2 orebody of the II mining area. Research into its genesis is of great importance for guiding regional prospecting. [Methods] This study conducted systematic research on the massive ore of this orebody by integrating mineral liberation analysis (TIMA), platinum group element (PGE) geochemistry, and in-situ sulfur isotope analysis. [Results] The results indicate that the massive ore is dominated by pyrite + pentlandite, which differs from the pyrrhotite + pentlandite assemblage found in net-textured ore. The total PGE content is low, with a chondrite-normalized pattern showing enrichment in PPGE, depletion in IPGE, and a left-leaning trend. Pt exhibits a strong negative anomaly and is decoupled from Pd. The sulfur isotope composition (δ3?S = -2.64‰ ~ -0.61‰) is close to the mantle value, while the Δ33S values (-2.56‰ ~ 0.9‰) reveal contamination by Archean crustal sulfur. Rayleigh fractionation modeling indicates that the massive ore was formed by the accumulation of monosulfide solid solution (MSS) after the initial sulfide melt underwent approximately 40% to 70% fractional crystallization. [Conclusion] The genesis of the massive ore in the No. 2 orebody of the Jinchuan II mining area can be summarized as follows: Mantle-derived parental magma experienced high-degree fractional crystallization and crustal sulfur contamination at depth, triggering sulfide immiscibility. The early differentiated, Pt- and Pd-rich intermediate solid solution (ISS) magma formed disseminated and net-textured ores. Subsequently, the late-stage, residual MSS-rich cumulate magma was emplaced under tectonic stress, ultimately crystallizing to form the massive ore characterized by the pyrite + pentlandite assemblage. |
