Post‐Collisional Lithospheric Delamination and Magmatic Ni–Cu Sulphide Mineralisation in the Cangjinyu Prospect, Southern Central Asian Orogenic Belt

ABSTRACT This study presents petrological, geochemical and geochronological data from the Cangjinyu mafic–ultramafic complex in the Beishan Terrane, northwestern China, aiming to clarify the origin of its Ni–Cu sulphide mineralisation and the regional tectonic evolution. LA–ICP–MS zircon U–Pb dating of olivine gabbro and gabbro reveals crystallisation ages of 278 and 276 Ma, respectively, indicating the emplacement timing of the complex. Re–Os isotopic dating of pentlandite gives an isochron age of 277 Ma, consistent with the host rock ages, suggesting a magmatic sulphide liquid immiscibility origin for the deposit. Geochemical analyses show that the rocks have tholeiitic affinities, low SiO 2 (41.33–50.79 wt.%), enriched heavy rare earth elements and depletions in high‐field‐strength elements, with negative Nb–Ta–Ti anomalies typical of arc‐related magmatism. High La/Nb (2.40–7.37) and low La/Ba (0.03–0.13) ratios indicate a subduction‐modified lithospheric mantle source metasomatised by fluids from ancient subducted plates. The complex formed in a post‐subduction extensional setting after the closure of the Paleo‐Asian Ocean, with magmatic evolution driven by fractional crystallisation and crustal contamination (1%–10%), leading to sulphide saturation and mineralisation.