Ore-forming material sources of the Jurassic Cu-Pb-Zn mineralization in the Qin-Hang ore belt, South China: Constraints from S-Pb isotopes

摘要

The Qin-Hang ore belt in South China, which serves as the boundary between the Yangtze and Cathaysia blocks, is marked by extensive Jurassic porphyry-skarn-metasomatic Cu-Pb-Zn polymetallic mineralization. In this contribution, S and Pb isotopic compositions of the Baoshan Cu-Pb-Zn deposit in the western portion of the Qin-Hang ore belt were analyzed to determine the ore-forming material sources in the area. This is coupled by the first systematic collection, compilation and interpretation of previously published S and Pb isotopic data of multiple sulfide minerals to reveal the metal origin and accumulation mechanism of the Cu-Pb-Zn mineralization from the significant deposits in the region (i.e., Dexing, Qibaoshan, Shuikoushan, Baoshan, Huangshaping, Tongshanling and Dabaoshan). The results show that Cu mineralization is characterized by low 208 , and narrow delta S-34 (parts per thousand) range of values (-5 to 6) and Pb isotopic ratios (Pb-208/Pb-204 = 38.0-39.0, Pb-207/Pb-204 = 15.4-15.8, and Pb-206/Pb-204 = 17.7-18.7), which are consistent with those of local porphyries. In contrast, the Pb-Zn mineralization reveals higher and more variable delta S-34 (parts per thousand) values (-4 to 18) and Pb isotopic ratios (Pb-208/Pb-204 = 38.0-39.5, Pb-207/Pb-204 = 15.3-16.0, and Pb-206/Pb-204 = 18.0-19.0) that correspond to wall-rock and basement rock compositions in the region. This indicates that the sulfur and lead that formed the Cu mineralization in the Qin-Hang ore belt was mainly sourced from regional magmatism with mantle contributions, whereas the sulfur and lead for the Pb-Zn mineralization was likely derived from the host sedimentary rocks and Proterozoic metamorphic basement rocks, respectively. The S and Pb isotopic data, combined with the geochemical signatures of mineralization-related porphyries, suggest that the Cu was sourced from the deeper levels along with mantle-derived magmas. In contrast, the Pb-Zn probably originated from the crust, with partial melting of the crystalline basement in the Cathaysia Block. Consequently, a three-stage genetic model is proposed to explain the ore-forming processes of the Qin-Hang Cu-polymetallic belt in South China.