Sulfide S-Zn-Cd isotopes and origin of the Liangyan Zn-Pb deposit in the Sichuan-Yunnan-Guizhou metallogenic province, SW China

Unraveling the metal sources of Zn-Pb deposits is vital to understand the genetic types and ore-forming processes. The Sichuan-Yunnan-Guizhou metallogenic province (SYGMP) hosts abundant Zn-Pb deposits that are variably rich in critical metals such as Ga, Ge, Cd and Tl. However, sources of these critical metals and main metal Zn are still unclear. The Liangyan Cd-rich Zn-Pb deposit as a representative in the SYGMP is hosted in a carbonate sedimentary sequence and controlled by the regional Yadu-Wogong anticline and Yadu-Mangdong thrust fault. SZn-Cd isotopes of sulfide minerals from this deposit are obtained in order to understand the sources of metals and origin of the deposit. Sulfur isotopic results of pyrite and sphalerite reveal that sulfur was produced by thermochemical sulfate reduction (TSR) of sulfates from the Carboniferous dolostone and mudstone and the Ediacaran-Devonian carbonates. Sphalerite grains have δ66ZnJMC values that are negatively correlated with the δ114Cd spex values, implying different sources for both Zn and Cd. The variation trend of δ66ZnJMC and Cd/Zn
suggests that Zn was mainly sourced from the Neoproterozoic basement with minor from the Carboniferous wallrocks. Besides, sphalerite grains show a negative correlation between δ114Cdspex and Zn/Cd, and these values fall in the field close to the Carboniferous carbonates, but away from the Permian Emeishan basalts, indicating that Cd was derived mainly from the Carboniferous wallrocks with minor from the Emeishan basalts. Together with geological evidence, the multi-isotope data suggest that the Liangyan deposit belongs to a thrust-controlled MVT Zn-Pb deposit.