Sulfide Rb-Sr and Zircon U-Pb Dating of the similar to 825 Ma Liujiaping Cu-Zn deposit in the Northwestern Yangtze Block (China) and its tectonic implications

摘要

The Neoproterozoic Liujiaping Cu-Zn deposit is a typical VMS (volcanic massive sulfide) deposit in the northwestern Yangtze Block, which is located at the convergent region of different blocks in China. The tectonic setting could provide some implications for the Neoproterozoic tectonic evolution of the Yangtze Block. Both the metallogenic chronology and isotope geochemistry of the Liujiaping deposit are tested. Sulfides and zircons from this deposit were analysed to determine its mineralization age. The sulfide Rb-Sr isotope dating of ores yields an age of 821.0 +/- 5.0 Ma (MSWD = 0.2). The zircon U-Pb SIMS dating of volcanics yields as 825.5 +/- 5.1 Ma (MSWD = 0.3). These dating results indicate that the metallogenesis is synchronous with the volcanic eruption. The Rb contents of the sulfides range from 0.0714 x 10(-6) to 0.7986 x 10(-6), the Sr contents range from 0.6002 x 10(-6) to 15.49 x 10(-6), and the initial Sr isotopic ratios (Sr-87/Sr-86)(i) range from 0.70784 to 0.70911, with an average of 0.70815. The Pb isotopic compositions of the ores and volcanics are (Pb-206/Pb-204) = 16.751-18.051, (Pb-207/Pb-204) = 15.363-15.597 and (Pb-208/Pb-204) = 36.885-38.441. These isotopic geochemical characteristics indicate that the ore-forming materials of the Liujiaping deposit might originate from the mixture of continental crust and mantle. Other Meso-Neoproterozoic VMS deposits along the northwestern Yangtze Block are also summarized. It is concluded that the Liujiaping volcanics and other VMS deposits were formed by the partial melting of lower crust during the subduction of oceanic crust, and the northwestern margin of the Yangtze Block was located in an arc setting at similar to 820 Ma rather than intra-continental rift.