矿床地球化学国家重点实验室知识库

The newly discovered Banbanqiao Zn-Pb deposit in the southeastern part of the Sichuan-Yunnan-Guizhou (SYG) Pb-Zn metallogenic province is located on the western Yangtze Block, southwest China. Ore bodies of the Banbanqiao deposit are stratiform type, host in dolomitic limestone and dolostone of the Lower Carboniferous Dapu Formation and occur within the NNE-trending Banbanqiao anticline. More than 1.5 million tones (Mt) Zn-Pb ores at grades of 0.26-1032 wt.% Pb and 0.81-28.8 wt.% Zn have been controlled until now. delta C-13(PDB) and delta(18) O-SMOW values of calcite separates range from -2.8 parts per thousand to -0.7 parts per thousand (average -1.1 parts per thousand) and +14.1 parts per thousand to +17.0 parts per thousand (average +15.5 parts per thousand), respectively. The delta C-13(PDB) values are similar to those of marine carbonate rocks, but higher than those of mantle and significantly different from those of sedimentary organic matter. However, the delta O-18(SMOW) values are among those of mantle, marine carbonate rocks and sedimentary organic matter. delta S-34(CDT) values of sulfide separates range from +3.2 parts per thousand to +9.9 parts per thousand (average +6.5 parts per thousand), unlike mantle-derived sulfur (0 +/- 3 parts per thousand), whilst lower than evaporites (+22 parts per thousand to +28 parts per thousand) within host strata. Pb-206/Pb-204, Pb-207/Pb-204 and Pb-208/Pb-204 values of country shale and dolostone whole-rock samples are 18.47, 15.66 and 38.70, and 18.44-18.60, 15.66-15.85 and 38.70-39.14, respectively. Sulfide separates have Pb-206/Pb-204, Pb-207/Pb-204 and Pb-208/Pb-204 values ranging from 18.03 to 18.73, 15.65 to 15.78 and 38.15 to 39.14, respectively. These Pb isotopic data indicate a clearly crustal source of Pb in the plot of Pb-207/Pb-204 vs. Pb-206/Pb-204. Total REE (Sigma REE) contents of country shale and dolostone whole-rock samples are 2.63 ppm and 0.72-86.2 ppm with delta Eu values are 2.79 and 0.34-0.70, respectively. Pyrite, sphalerite, galena and calcite samples have Sigma REE contents of 5.3-36.4 ppm, 0.29-3.39 ppm, 0.52 ppm and 22.0-41.1 ppm, respectively, and 8Eu values of 0.64-0.86, 0.94-2.86, 0.32 and 0.21-0.45, respectively. These rare earth elemental and isotopic data suggest that the REE, C and S in the ore-forming fluids of the Banbanqiao deposit were mainly originated from the carbonate host rocks, while the Pb and O were primarily derived from radiogenic Pb- and O-18-depleted sources, which are most likely to be the underlying Proterozoic basement rocks. Studies on the geology, rare earth elements and isotope geochemistry indicate that the Banbanqiao deposit is a carbonate-hosted, stratiform, anticline-controlled, epigenetic and high grade Zn-Pb deposit formed by elemental compositions of mixed origin, and is a typical SYG-type deposit in the western Yangtze Block, southwest China.