矿床地球化学国家重点实验室知识库

Located on the western Yangtze Block, SW China, the Sichuan–Yunnan–Guizhou Pb–Zn metallogenic (SYG) province, contains known total Pb and Zn metals more than 20 million tons (Mt) grading > 10% Pb + Zn and is a well known producer of base metals in China. The Shaojiwan carbonate-hosted Pb–Zn deposit is a representative deposit in this province with 0.5 Mt metals of 0.71 to 10.56% Pb and 2.09 to 30.27% Zn. Its ore bodies are hosted in Devonian and Permian carbonate rocks and structurally controlled by the Yadu–Mangdong thrust fault. Lead–zinc ores composed of pyrite, sphalerite, galena, calcite and dolomite occur as brecciated, veinlets and disseminations in dolomitized limestone rocks.

The S–Pb–Sr isotope compositions of sulfide minerals have been analyzed to trace the sources of sulfur and metals for the Shaojiwan Pb–Zn deposit. δ³⁴S values of sulfide minerals range from + 8.4 to + 11.6‰, suggesting that sulfur in the hydrothermal fluids was derived predominantly from evaporite rocks in the host strata. Sulfide minerals have a small range of Pb isotope compositions (²⁰⁶Pb/²⁰⁴Pb = 18.616 to 18.686, ²⁰⁷Pb/²⁰⁴Pb = 15.682 to 15.728 and ²⁰⁸Pb/²⁰⁴Pb = 39.067 to 39.181) that are close to upper crust Pb evolution curve and similar to Proterozoic basement in the SYG province. This implies that the lead metal originated mainly from the basement rocks. ⁸⁷Sr/⁸⁶Sr ratios of sphalerite range from 0.7114 to 0.7130, and ⁸⁷Sr/⁸⁶Sr_200 Ma ratios range from 0.7113 to 0.7129, higher than Sinian to Permian sedimentary rocks and Permian Emeishan flood basalts, but lower than basement rocks. This implies a mixed strontium source between the older basement rocks and the younger cover sequences. Therefore, the fluids' mixing is a possible mechanism for sulfide precipitation in the Shaojiwan Pb–Zn deposit.