Re-Os isotope system of sulfide from the Fule carbonate-hosted Pb-Zn deposit, SW China: implications for Re-Os dating of Pb-Zn mineralization
Re-Os isotope system of sulfide from the Fule carbonate-hosted Pb-Zn deposit, SW China: implications for Re-Os dating of Pb-Zn mineralization
复制标题
中国西南富乐碳酸盐岩铅锌矿床硫化物铼锇同位素系统：对铅锌矿化铼锇测年的意义
DOI：
10.1016/j.oregeorev.2020.103558
复制
发表时间：
2020
影响因子：
3.3
通讯作者：
Xiao-Wen Huang
中科院分区：
文献类型：
--
作者：
Chuan Lyu;Jian-Feng Gao;Liang Qi;Xiao-Wen Huang
富乐存款是中国西南川滇黔成矿省东南部碳酸盐岩型铅锌矿床之一。该存款是由阳新组的钠长石灰岩和白云岩，锌铅矿石储量超过2000万吨（Mt）。矿石矿物主要有闪锌矿、方铅矿和黄铁矿。根据矿体产状、矿石结构和矿物组合特征，将热液成矿阶段划分为3个世代：（1）浅棕色闪锌矿与少量方铅矿在白云岩角砾岩中共生，（2）深棕色至棕色闪锌矿与方铅矿、白云岩和少量石膏共生，（3）浅棕色闪锌矿与少量方铅矿在白云岩角砾岩中共生，（4）浅棕色闪锌矿与少量方铅矿在白云岩角砾岩中共生。（3）方解石脉中浸染状红棕色至浅黄色闪锌矿，三个阶段硫化物的主量、微量元素、Re-Os和S同位素组成基本相同。闪锌矿中的铼和锇分别为7-58 ppb和3-56 ppt，方铅矿中的铼和锇分别为13-30 ppb和1- 5 ppt，闪锌矿中的187 Re/188 Os和187 Os/188 Os分别为387-16193和1.29-12.0，方铅矿中的Re/188 Os和187 Os/188 Os分别为5449-27180和0.35-5.0。黄铁矿、方铅矿和闪锌矿的δ 34 S值分别为+14.69‰ ~+20.64‰、+6.26‰ ~+12.39‰和+12.01‰ ~+16.03‰。闪锌矿和方铅矿的Re-Os同位素组成具有1 ~ 500 Ma的Os模式年龄，表明为不封闭的Re-Os体系，同一样品中不同硫化物的硫同位素组成呈（δ 34黄铁矿≥）δ 34闪锌矿> δ 34方铅矿的趋势，表明不同硫化物之间硫同位素具有依附平衡。闪锌矿中流体包裹体均一温度为135 ~ 235 ℃，有220-235 ℃和135-160 ℃两个峰值，与计算的闪锌矿-方铅矿对均一温度（99 ~ 202 ℃）吻合较好。硫化物中硫同位素组成较高（+6.3‰ ~+16.6 ‰），表明硫主要来源于石炭纪石膏的还原作用。SYG成矿域碳酸盐岩型矿床硫化物矿石中的闪锌矿和方铅矿在氧化性流体作用下经历了矿后热液蚀变，形成了石膏、菱锌矿和角闪石等氧化矿物。这种氧化流体的活性可能持续很长时间。在这种氧化环境中，硫化物中的铼比Os具有更强的移动的性，因此在硫化物与流体之间的相互作用停止之前，铼-锇同位素体系保持开放状态。因此，碳酸盐岩的氧化还原条件对碳酸盐岩型铅锌矿床中硫化物Re-Os同位素体系的封闭性有重要影响。含氧化性矿物碳酸盐岩型铅锌矿床中的硫化物不适合作Re-Os定年。而Re-Os同位素体系则可用于还原碳酸盐岩中铅锌矿化的年龄测定。
The Fule deposit is one of the carbonate-hosted Pb-Zn deposits in southeastern part of the Sichuan-Yunnan-Guizhou (SYG) metallogenic province, SW China. This deposit is hosted by dolomitic limestone and dolomite of the Yangxin Formation with Zn-Pb ore reserves of more than 20 million tons (Mt). Ore minerals mainly include sphalerite, galena and pyrite. According to the occurrence of orebodies, ore textures, and mineral assemblages, the hydrothermal Zn-Pb mineralization stage could be subdivided into three generations: (1) light brown sphalerite associated with minor galena in dolomite breccias; (2) dark brown to brown sphalerite associated with galena, dolomite and minor gypsum; (3) disseminated reddish-brown to light yellow sphalerite in calcite vein.Sulfides from three stages have similar major, trace elements, Re-Os and S isotopic compositions. Rhenium and Os in sphalerite are 7–58 ppb and 3–56 ppt, respectively, and in galena of 13–30 ppb and 1-5ppt, respectively.187Re/188Os and187Os/188Os ratios in sphalerite are 387–16193 and 1.29–12.0, respectively, and in galena of 5449–27180 and 0.35–5.0, respectively. Pyrite, galena, and sphalerite have δ34S values of +14.69‰ to +20.64‰, +6.26‰ to +12.39‰, and +12.01‰ to +16.03‰, respectively. Re-Os isotopic compositions of sphalerite and galena have Os model ages from 1 Ma to 500 Ma, indicating an unclosed Re-Os system.Different sulfides from the same sample follow the trend of (δ34Spyrite≥ ) δ34Ssphalterite> δ34Sgalena,indicating that sulfur isotopes between different sulfides have attached equilibrium. Fluid inclusions in sphalerite have homogenization temperatures ranging from 135 ℃ to 235 ℃ with two peaks of 220–235 ℃ and 135–160 ℃, which agree well with calculated temperatures of sphalerite-galena pairs (99 ℃–202 ℃). A relatively high sulfur isotope composition (+6.3‰ to + 16.6‰) in sulfides, indicating that sulfur was mainly derived from the reduction of gypsum in Carboniferous strata. Sphalerite and galena in sulfide ores of carbonate-hosted deposits in SYG metallogenic province have experienced post-ore hydrothermal alteration by oxidizing fluids, forming oxidized minerals including gypsum, smithsonite, and anglesite. The activity of such oxidized fluids might last for a long time. Rhenium in sulfides is more mobile than Os in such an oxidizing environment and thus Re-Os isotope system remains open until the interaction between sulfide and fluids stops. Therefore, redox condition of hosting carbonates can highly influence the closure of Re-Os isotope system of sulfide in carbonate-hosted Pb-Zn deposits. Sulfide in oxidizing mineral bearing carbonate-hosted Pb-Zn deposits is not suitable for Re-Os dating. In contrast, Re-Os isotope system is possible to be used for dating the age of Pb-Zn mineralization within reduced carbonates.