滇西勐兴铅锌矿床热液方解石碳氧同位素组成及其意义

Carbon and oxygen isotopic compositions of hydrothermal calcites from the Mengxing Pb-Zn deposit,western Yunnan and their significances

勐兴铅锌矿床是保山地块内浅成热液铅锌矿床中极具代表性的矿床,但有关成矿流体来源及演化方面的研究较为薄弱。因方解石与矿化关系密切,故对其C、O同位素组成进行了水岩反应、CO_(2)去气、流体混合作用的理论模拟。结果表明,该矿床方解石的形成主要是由于水岩反应引起的,成矿流体可能来自赋矿地层中富含H2CO3的流体,其中阶段Ⅰ和阶段Ⅱ初始流体的δ^(13)C、δ^(18)O值分别为1.0‰和10.5‰、-0.8‰和7.5‰,方解石的形成温度分别集中于270~315℃和182~230℃之间,δ^(13)C和δ^(18)O值的降低表明在阶段Ⅱ成矿流体与围岩反应之前已经发生了CO_(2)热液去气作用。

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 stageⅠand stageⅡhave been analyzed.The theoretical modelings of the fluid-rock interaction,CO_(2) 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 averageδ^(13)C andδ^(18)O data of 1.0‰and 10.5‰for StageⅠcalcite and those of-0.8‰and 7.5‰for StageⅡcalcite,respectively.The StageⅠand StageⅡcalcites were precipitated at temperatures ranging from 270℃to 315℃and from 182℃to 230℃,respectively.The decrease ofδ^(13)C andδ^(18)O values from StageⅠcalcite to StageⅡcalcite shows that the CO_(2) degassing had already occurred before the fluid-rock interaction of StageⅡ.