Cadmium isotopic constraints on metal sources in the Huize Zn–Pb deposit, SW China

International audienceThe Sichuan–Yunnan–Guizhou (SYG) Zn–Pb metallogenic zone in SW China contains >400 carbonatehostedhydrothermal Zn–Pb deposits. Some of these, such as the Huize, Tianbaoshan, and Daliangzideposits, are super-large deposits with significant reserves of Cd, Ge, and Ag. However, the sources ofthese metals remain controversial. This study investigated the Cd isotopic geochemistry of the Huizedeposit, the largest Zn–Pb deposit in the SYG area. Sphalerites formed at three stages in the deposit havedifferent colors: black or dark brown (Stage I), red (Stage II), and light-yellow (Stage III). The d114/110Cdvalues of the sphalerites are in the order Stage III < Stage I < Stage II. Kinetic isotopic fractionation is likelythe key factor causing the lower d114/110Cd values in the early formed Stage I sphalerites than in laterformedStage II sphalerites, with cooling of ore-forming fluids being responsible for the still lower valuesof the Stage III sphalerites. In galena, the d114/110Cd values are inversely correlated with Cd contents andtend to be higher in high-Zn galena. We speculate that Cd isotopic fractionation was significant duringthe precipitation of sphalerite and galena, with light Cd isotopes being enriched in galena rather thansphalerite. Comparison of the Cd isotopic signatures and Zn/Cd ratios of different endmembers suggeststhat the d114/110Cd values and Zn/Cd ratios of sphalerite from the Huize deposit, as well as other largescaledeposits from the SYG area, are lie in those range of Emeishan basalts and sedimentary rocks andthe mean d114/110Cd values of these deposits show good negative correlation with 1/Cd, suggesting thatthe ore-forming materials of these deposits were derived from the mixing of Emeishan basalts and sedimentaryrocks. This study demonstrates that Cd isotopes can be useful proxies in elucidating ore genesisin large Zn–Pb deposits