Mafic mineral chemistry as an insight into magma characteristics, tectonic settings and mineralization in three magmatic Ni-Cu deposits in North Xinjiang, NW China

This study utilizes detailed mineral chemistry of mafic phases (clinopyroxene, hornblende, olivine, Cr-spinel) from the Huangshandong (HSD), Huangshanxi (HSX), and Kalatongke Ni-Cu sulfide deposits in the Central Asian Orogenic Belt to elucidate magma characteristics, tectonic settings, and key factors of mineralization. Crystallization conditions (1174–1234 °C; <400 MPa) suggest rapid magma emplacement and imply that regional strike-slip structures facilitated efficient magma ascent and promoted mineralization. The primary magmas were high-Mg tholeiitic melts with moderate H₂O contents (<2.6 wt%), as indicated by: equilibrium melt compositions constrained by Cr-spinel chemistry; trace-element ratios in hornblende (e.g., Sr/Hf<200); and clinopyroxene hygrometry combined with compositional discrimination. Cr-spinel compositions (Cr#=41–64) and clinopyroxene chemical trends (rift-cumulate) reflect a non-arc, post-subduction extensional setting associated with asthenosphere upwelling triggered by slab detachment. The melts in equilibrium with orthopyroxene exhibit LREE enrichment signatures, indicating derivation from subduction-metasomatized lithosphere mantle. The enrichment of U and Pb in the melt equilibrium with hornblende confirms the incorporation of crustal material into the magma source, consistent with metasomatized mantle characteristics. The magma source comprises upwelling asthenosphere mantle and metasomatized mantle. Lower Ce/Pb ratios in the melts relative to arc and back-arc lavas suggest upper crustal contamination. Crustal contamination plays a key role in sulfide saturation.