Composite metallogenesis of sediment-hosted Pb-Zn-Ag-Cu base metal deposits in the Sanjiang Collisional Orogen, SW China, and its deep driving mechanisms

A great number of sediment-hosted Pb-Zn-Ag-Cu deposits occur in the Meso-Cenozoic sedimentary basins within the Sanjiang Tethyan orogeny, SW China, which compose a significant base metal metallogenic belt with an extension over 1000km along the northeastern margin of the Tibetan Plateau. For it is an important type in the continental collision-related deposit spectrum, further study upon these deposits is greatly helpful to understand and improve the theories of the continental collision metallogenesis and guide the exploration. Many studies suggest that these deposits are distinct from the SEDEX and MVT model in terms of ore controls, host rocks and other features, and that multiple sourced fluids associated with mineralization should have been driven by deep processes. However, it is intensively debated on the geotectonic settings of ore formation and spatial-temporal association with the collisional orogeny due to lack of highly resolved chronological data. Some studies indicate that they were resulted from composite mineralization, but these studies did not well document its mechanisms. A comprehensive study has thus been carried out on the geochronology, ore-forming fluids and metal sources, composite metallogenesis and mechanisms for the Pb-Zn-Ag and Cu polymetallic deposits in the Lanping and Changdu basins. The results show that the Cu deposits were mainly formed in 48 similar to 58Ma and the Pb-Zn deposits were formed in 28 similar to 33 Ma. Also, three types of composite mineralization have been recognized: 1) metamorphic fluids and basinal brines or meteoric water, represented by the Jinman-Liancheng Cu deposits; 2) basinal brine and meteoric water, represented by the Jinding deposit; and 3) basinal brine and magmatic fluid with an example of the Lanuoma Pb-Zn-Sb deposit. The Cu deposits happened synchronously with the main collisional compression of the India-Asian continental collision and metamorphic fluids were probably generated by subduction-caused high-pressure metamorphism. The Pb-Zn deposits were formed by basinal brine-dominated fluids driven by orogenic uplift as well as tectonic compression in the stage of the late collisional tectonic transform. Contemporaneous magmatism may have mainly played as heat sources or provided ore materials.