Strontium isotopic geochemistry of Tianqiao Pb-Zn deposit,Southwest China

Tianqiao carbonate-hosted Pb-Zn deposit, controlled by NW-trending F₃₇ thrust fault and NW-trending Tianqiao anticline, is located in the eastern part of Sichuan-Yunnan-Guizhou (SYG) Pb-Zn metallogenic province, southwestern Yangtze Block, southwest China. Ore bodies in this deposit are hosted in the Devonian-Carboniferous carbonate rocks, and ore minerals include sphalerite, galena and pyrite, while the gangue minerals are dominated by calcite and dolomite. Using high-precision solid thermal ionization mass spectrometry (TIMS), this paper reports the strontium isotopic compositions (0.7119 to 0.7167) of sulfide samples from the Tianqiao deposit in order to trace the origin of hydrothermal fluids. Compared with the country rocks, the calculated ⁸⁷Sr/⁸⁶Sr_{200 Ma} values of sulfide range from 0.7118 to 0.7130, higher than those of the age-corrected Devonian to Permian sedimentary rocks (0.7073 to 0.7101) and the Middle Permian Emeishan flood basalts (0.7078 to 0.7039), but lower than those of the age-corrected Proterozoic basement rocks (such as the Kunyang and Huili Groups, ⁸⁷Sr/⁸⁶Sr_{200 Ma}=0.7243 to 0.7288). This implies a mixed strontium source between the older basement rocks and the younger cover sequences. Together with geologic and previous isotopic evidences, we considered that the fluids’ mixing is a possible mechanism for sulfide precipitation in the Tianqiao deposit.