Petrogenesis and metallogenic implications of Late Mesozoic intrusive rocks in the Tongling region, eastern China: a case study and perspective review

Large-scale Cu-Au mineralization is associated with Late Mesozoic intrusive rocks in the Tongling region of eastern China, which mainly comprise pyroxene monzodiorite, quartz monzodiorite, and granodiorite. To constrain the petrogenesis of the intrusive rocks and Cu-Au mineralization, detailed analyses of the geochronology, apatite in situ geochemistry, whole-rock geochemistry, and zircon Hf isotopic compositions were performed. Magmatic zircons from pyroxene monzodiorites, quartz monzodiorites, and granodiorites yield U-Pb ages of 136-149Ma, 136-146Ma, and 138-152Ma, respectively, indicating that their formation ages are contemporaneous. Quartz monzodiorites and granodiorites (SiO2=57.9-69.5wt.%) are highly potassic calc-alkaline rocks with adakitic affinity and have low MgO and Y contents, low zircon epsilon(Hf)(t) values (-11.7 to -39.0), high apatite Cl contents (>0.2wt.%), and log fO(2) values (-23.2 to -8.23), indicating that they may have formed when metasomatized mantle-derived magmas mixed with slab-derived magmas before undergoing crustal assimilation and fractional crystallization. Pyroxene monzodiorites (SiO2=48.4-53.0wt.%) are shoshonitic and record high MgO, P2O5, and Y contents, high zircon epsilon(Hf)(t) values (1.55 to -7.87), high oxygen fugacity, low Nb and Ta contents, and low apatite Cl contents (mainly <0.2wt.%), suggesting that they were primarily derived from a metasomatized lithospheric mantle-derived magma that experienced the assimilation of lower crustal materials. The results indicate that the intrusive rocks and associated large-scale Cu-Au mineralization of the Tongling region resulted from the partial melting of the subducted oceanic slab in an oxidizing environment.