LIU Yang1, GAO Zhi-wu2, YANG Chen-yu2, DENG Ming-guo1*, LIU Jin-kang1, ZHAO Fa3
(1. Faculty of Land Resource Engineering, Kunming University of Science and Technology, Kunming 650093, China;
2. School of Engineering, Zunyi Normal College, Zunyi 563000, China;
3. Yunnan Yongchang Lead & Zinc Co. Ltd.，Baoshan 678307, China)
Abstract: The Mengxing lead-zinc deposit is one of the most representative epithermal lead-zinc deposits in the Baoshan Block. However, but the source and evolution of ore-forming fluids of the deposit has been relative weakly studied. As the calcite, most important gangue mineral, has a close relationship with the mineralization, so the C and O isotopic compositions of calcites of stage Ⅰ and stage Ⅱ have been analyzed. The theoretical modelings of the fluid-rock interaction, CO2 degassing, and fluid mixing have also been undertaken.The results show that the calcite precipitation in the deposit was mainly resulted from the fluid-rock interaction. The ore-forming fluid could be mainly sourced from the H2CO3-rich fluid in the ore-hosted strata in the Mengxing deposit, with the average δ13C and δ18O data of 1.0‰ and 10.5‰ for Stage Ⅰ calcite and those of -0.8‰ and 7.5‰ for StageⅡcalcite, respectively. The Stage Ⅰ and Stage Ⅱ calcites were precipitated at temperatures ranging from 270 ℃ to 315 ℃ and from 182 ℃ to 230 ℃, respectively. The decrease of δ13C and δ18O values from Stage I calcite to Stage II calcite shows that the CO2 degassing had already occurred before the fluid-rock interaction of Stage II.
Keywords: Calcite; C-O isotopes; fluid-rock interaction; CO2 degassing; fluid mixing; ore-forming fluid
ACTA MINERALOGICA SINICA Vol. 41, No.1, 2021, page 57-68