Recycling of palaeo-Pacific subducted oceanic crust related to a Fe-Cu-Au mineralization in the Xu-Huai region of North Anhui-Jiangsu, East China: Geochronological and geochemical constraints

摘要

In this study, Early Cretaceous skarn deposits and genesis of their host diorite/monzodiorite porphyry in the Xuzhou-Huaibei (Xu-Huai) region, northern Anhui-Jiangsu have been discussed by detailed geochemical work. In-situ zircon U-Pb dating of the diorites related to Fe-Cu-Au deposits shows that they were formed between 131.4 +/- 1.5Ma and 130.8 +/- 1.8Ma. Geochemical data indicate a depletion of high field strength elements (HFSE) in the diorite porphyry with similarity to that of arc-related igneous rocks. The diorite porphyry was probably derived from typical arc magmas related to continental margin subduction characterized by light rare earth elements (LREEs) enrichment and HFSE depletion. REEs compositions of apatite in the diorite porphyry indicate that the dioritic magma was produced from the metasomatized subcontinental mantle by slab-derived fluids. The magma was proven to be a high oxygen fugacity; thus, it was particularly conducive to the precipitation of Fe, Cu, Au and other ore-forming elements. The S-34 values of pyrite and chalcopyrite of Fe-Cu-Au ores range from -0.2 parts per thousand to 2.8 parts per thousand, indicating that the sulphur in the ore was probably derived from deep-seated magmas. Integrated with geochronological and geochemical analyses, we suggest that the Early Cretaceous igneous suites associated with Fe-Cu-Au deposits in the Xu-Huai region are related to recycling subduction of Pacific oceanic crust.