四川天宝山铅锌矿床的锌-硫同位素组成及成矿物质来源  

Zb-S isotopic compositions of the Tianbaoshan carbonatehosted Pb-Zn deposit in Sichuan,China:Implications for source of ore components

作　　者：何承真 肖朝益 温汉捷[1] 周汀[1] 朱传威[1] 樊海峰[1] 

机构地区：[1]中国科学院地球化学研究所,矿床地球化学国家重点实验室,贵阳550081 [2]中国科学院大学,北京100049

出　　处：《岩石学报》2016年第11期3394-3406,共13页Acta Petrologica Sinica

基　　金：国家重点基础研究发展计划(“973”)项目(2014CB440906);国家自然科学基金项目(41430315、41573011);中国科学院西部之光项目;中国科学院青年促进会项目;矿床地球化学国家重点实验室“十二·五”项目(SKLOSG-ZY125-07)联合资助

摘　　要：四川天宝山铅锌矿床位于扬子板块西南缘,赋矿地层为上震旦统灯影组白云岩。尽管这个地区已有大量的科研工作,但其成矿物质来源仍然存在争议。本文主要测定了闪锌矿微区样品的锌和硫同位素组成,以及三个中段的闪锌矿单矿物、上震旦统灯影组白云岩和会理群天宝山组砂岩的锌同位素组成。闪锌矿微区样品的δ^(66)Zn值介于0.39‰~0.52‰之间,平均值为0.46‰,δ^(34)SCDT值介于4.24‰~4.87‰之间,平均值为4.59‰。同一块手标本上闪锌矿微区样品具有均一的锌同位素组成表明小尺度上(10×10cm^2)热液流体具有均一的锌同位素组成。在大尺度上(矿体),三个中段的闪锌矿的锌同位素组成范围变化较大,其δ^(66)Zn值介于0.15‰~0.73‰之间。同一块手标本上早期阶段的闪锌矿具有更重的锌同位素组成表明早期阶段的成矿流体可能具有更重的锌同位素组成。三个中段闪锌矿的锌同位素组成变化主要受成矿流体中锌同位素组成和成矿流体的迁移就位途径控制。上震旦统灯影组白云岩的δ^(66)Zn值介于0.06‰~0.35‰之间,平均值为0.21‰,暗示热液淋滤控制了灯影组白云岩的锌同位素组成。会理群天宝山组砂岩的δ^(66)Zn值为0.62‰,可能代表了未经热液淋滤的沉积端元的锌同位素组成。本次研究表明天宝山铅锌矿床的锌主要来源于上震旦统灯影组白云岩,但不能排除白云岩之上的沉积盖层、基底和更深物质的贡献;硫主要来源于上震旦统灯影组地层中的蒸发岩(主要通过热化学还原作用形成还原硫)。The Tianbaoshan Pb-Zn ore deposit, hosted in the Dengying Formation dolostone, is located at the southwestern part of the Yangtze Block. The source of ore components is still controversial, although a lot of studies have been published. In this study, zinc and sulfur isotopic compositions of microdrilled sphalerites, handpicked sphalerites from three adits and the wall rocks are investigated. The microdrilled sphalerite samples exhibit the homogenous Zn isotopic composition （ 866 Zn ： 0. 39‰ to 0. 52‰, on average of 0.46‰） , and the homogenous S isotopic composition （ 834 SCDT = 4. 24‰ to 4. 87‰, on average of 4. 59‰）. These characters indicate that sphalerite may be simultaneously precipitated from a hydrothermal fluids with homogeneous composition at the small scales （ 10 × 10cm2 ）. In contrast, Zn isotopic compositions of handpicked sphalerites from three adits show a wide range from 0. 15‰ to 0. 73‰. The early sphalerites from the same hand specimen are enriched the isotopically heavier Zn, suggesting the heavier zinc isotopic compositions in the early stages ore-forming fluids compared to the late stage ore-forming fluids. Zinc isotopic compositions of sphalerites from three adits are substantially become lighter from 8 to 6 aditat at the large scales, which are controlled by variable zinc isotopic compositions of ore-forming fluids and migratory routes of ore-forming fluids. The 866Zn values of the Dengying Formation dolostone show a narrow range from 0. 06‰ to 0. 35‰ （on the average of 0. 21‰） , which indicates the loss of isotopically heavier Zn during the hydrothermal fluids leaching processes. However, the Tianbaoshan Formation sandstone yield a positive 866 Zn value （0. 62‰） , representing zinc isotopic composition of the primary deposition. Finally, this study indicates that the zinc of Tianbaoshan lead-zinc ore deposit may be derived from the Dengying Formation dolostone, but the contributions of basement and sedimentary covers overlying the Dengying For

关 键 词：天宝山铅锌矿床 闪锌矿 锌同位素 硫同位素 物质来源 

分 类 号：P597.2[天文地球—地球化学] P618.42[天文地球—地质学]