Geological, rare earth elemental and isotopic constraints on the origin of the Banbanqiao Zn–Pb deposit, southwest China

Abstract

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 0.26–10.32wt.% Pb and 0.81–28.8wt.% Zn have been controlled until now. δ13CPDB and δ18OSMOW values of calcite separates range from −2.8‰ to −0.7‰ (average −1.1‰) and +14.1‰ to +17.0‰ (average +15.5‰), respectively. The δ13CPDB 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 δ18OSMOW values are among those of mantle, marine carbonate rocks and sedimentary organic matter. δ34SCDT values of sulfide separates range from +3.2‰ to +9.9‰ (average +6.5‰), unlike mantle-derived sulfur (0±3‰), whilst lower than evaporites (+22‰ to +28‰) within host strata. 206Pb/204Pb, 207Pb/204Pb and 208Pb/204Pb 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 206Pb/204Pb, 207Pb/204Pb and 208Pb/204Pb 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 207Pb/204Pb vs. 206Pb/204Pb. Total REE (ΣREE) contents of country shale and dolostone whole-rock samples are 2.63ppm and 0.72–86.2ppm with δEu values are 2.79 and 0.34–0.70, respectively. Pyrite, sphalerite, galena and calcite samples have ΣREE contents of 5.3–36.4ppm, 0.29–3.39ppm, 0.52ppm and 22.0–41.1ppm, respectively, and δEu 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 18O-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.