|
|||||
|
|
| 河南省栾川县西沟铅锌银矿床单矿物铷-锶同位素组成特征 | |
| 引用本文： | 祁进平,宋要武,李双庆,陈福坤.河南省栾川县西沟铅锌银矿床单矿物铷-锶同位素组成特征[J].岩石学报,2009,25(11):2843-2854. |
| 作者姓名： | 祁进平 宋要武 李双庆 陈福坤 |
| 作者单位： | 1. 中国科学院广州地球化学研究所成矿动力学重点实验室,广州,510640;北京大学造山带与地壳演化实验室,北京,100871 2. 河南省地质调查院,郑州,450007 3. 中国科学技术大学中科院壳幔物质与环境重点实验室,合肥,230026 |
| 基金项目： | 国家973项目2006CB403500;国家自然科学基金项目，中国博士后科学基金，中国科学院百人计划项目 |
| 摘 要： | 河南栾川西沟铅锌银矿床位于华北克拉通南缘栾川断裂北侧,为赋存于中-晚元古代浅变质碳酸盐建造中的层控矿床,被认为是晚元古代的热水沉积型矿床.从成矿早阶段至晚阶段,矿物共生组合依次为;细粒黄铁矿、粗粒黄铁矿-闪锌矿-白云石-石英组合、多金属硫化物-白云石-石英组合、黄铁矿-石英-碳酸盐组合.本文对其矿石硫化物和黑云母进行了单颗粒矿物Rb-Sr同位素分析和研究.1件赋矿钙质二云片岩样品的5个黑云母颗粒样品给出Rb-Sr等时线年龄为366.0±10Ma,代表赋矿围岩的区域变质年龄.由于黄铁矿-碳酸盐细脉切穿了钙质二云片岩的片理,闪锌矿细脉切穿大理岩条带,矿体未遭受区域变质作用,可推断矿化发生于366Ma之后.考虑到区域内的构造变形事件和大规模花岗岩类侵入和成矿作用的年龄数据集中在156～134Ma,峰值在138 Ma左右,认为西沟铅锌银矿床形成于晚侏罗世-早白垩世.5件成矿早阶段细粒黄铁矿具有较低的I_(Sr-138Ma0值(按138Ma计算的锶同位素初始比值),变化范围为0.7100～0.7151,平均0.7127,该值略高于晚侏罗-早白垩斑岩类和花岗岩基,明显低于太古代太华群变质基底、中元古代熊耳群安山质火山盖层和中-晚元古代栾川群和官道口群的片岩地层,但与赋矿围岩栾川群大理岩地层接近,表明碳酸盐地层变质脱水和晚侏罗-早白垩岩浆岩均有可能为早阶段成矿提供成矿流体.相比之下,主成矿阶段硫化物则更加富含放射成因锶;14个主成矿阶段粗粒黄铁矿测点的I_(Sr-138Ma)值范围为0.7152～0.7344,平均0.7247,13个闪锌矿测点的I_(Sr-138Ma)值范围为0.7108～0.7398,平均0.7283,这些硫化物I_(Sr-138Ma)值接近于或低于太古宙太华群、中元古代熊耳群和中-晚元古代官道口群和栾川群,表明这些地层的锶都有可能混入成矿流体.因此,上述研究表明成矿早阶段流体主要为壳源岩石的变质脱水流体或燕山期岩浆热液,而在主成矿阶段,通过水岩相互作用与浅源循环的大气水或建造水的混入,浅部盖层栾川群地层的成分较多地加入了成矿系统. |
| 关 键 词： | 西沟铅锌银矿床 单颗粒矿物Rb-Sr定年 硫化物 锶同位素 |
Single-grain Rb-Sr isotopic composition of the Xigou Pb-Zn-Ag deposit, Luanchuan, Henan province. |
|
| QI JinPing,SONG YaoWu,LI ShuangQing,CHEN FuKun.Single-grain Rb-Sr isotopic composition of the Xigou Pb-Zn-Ag deposit, Luanchuan, Henan province.[J].Acta Petrologica Sinica,2009,25(11):2843-2854. | |
| Authors: | QI JinPing SONG YaoWu LI ShuangQing CHEN FuKun |
| Abstract: | The Xigou Pb-Zn-Ag deposit in Luanchuan,Henan Province is located north of the Luanchuan fault which occurs along the southern margin of the North China Craton.This deposit is of stratabound and hosted in Neoproterozoic carbonate strata and was considered as Neoproterozoic SEDEX-type deposit.The paragenesis,from early to late ore stage,includes:fine-grained pyrite,coarsegrained pyrite-sphalerite-dolomite-quartz assemblage,polymetallic sulfides-dolomite-quartz assemblage,and pyrite-quartz-carbonate assemblage,respectively.In this study,the single-grain Rb-Sr analytical technique is employed on sulfides and biotite to date the Pb-Zn-Ag mineralization of the deposit.Five biotite grains from a host-rock calcic two-mica schist sample yield a Rb-Sr isochron age of 366.0±10 Ma,which is interpreted as metamorphic time of the host rocks.Field observations show that mineralization most probably postdated the metamorphism of the host rocks,as pyrite-bearing carbonates or sphalerite veinlets crosscut the schistosity or band of the metamorphic rocks and the orebodies did not undergo regional metamorphism.Considering that the tectonic deformation,massive granitic magmatism and mineralizations of Mo,Pb,Zn and Ag cluster in the period of 156～134 Ma with a peak at 138 Ma in the adjacent areas,it is reasonable to assume that the Xigou Pb-Zn-Ag deposit formed at ca.138 Ma.Fine-grained pyrite of the early ore stage,coarse-grained pyrite and sphalerite of the main ore stage fail to give reasonable Rb-Sr isochron ages,probably due to overprint of later hydrothermal processes.Five fine-grained pyrite grains of the early ore stage give low I_(Sr-138Ma)values(the initial ~(87)Sr/~(86)Sr values at 138Ma)of 0.7100～0.7151,with an average of O.7127,slightly higher than those of late Jurassic to early Cretaceous intermediate-felsic porphyries and granite plutons,significantly lower than those of the Archean Taihua Group(metamorphic basement rocks),the Mesoproterozoic Xiong' er Group(andesitic volcanic rocks),and overlying schists of Meso-Neoproterozoic Luanchuan and Guandaokou groups,but close to those of hosting marble of the Luanchuan Group,indicating that metamorphic devolatilization of carbonate rocks and magmatic fluids are possible sources of ore fluids.In contrast,sulfides in main ore stages show higher and variable radiogenic Sr isotope contents:fourteen coarse-grained pyrite grains show I_(Sr-138Ma) values of 0.7152-O.7344,with an average of 0.7247.Thirteen sphalerite grains give I_(Sr-138Ma) values between 0.7108～0.7398,with an average of 0.7283.These I_(Sr-138Ma) values are significantly higher than those of late Jurassic to early Cretaceous intermediate-felsic porphyries and granite plutons but close to or lower than those of the Taihua Group,the Xiong' er Group,and the Luanchuan and Guandaokou groups.Thus,it can be deduced that the early ore stage was probably dominated by metamorphic or magmatic fluids,and in the main ore stage,involvement of the overlying strata(the Luanchuan Group)was significant,tlarough water-rock interaction and/or input of meteoric or formation water. |
| Keywords: | Xigou Pb-Zn-Ag deposit Single-grain Rb-Sr dating Sulfide Sr isotope |
| 本文献已被 万方数据 等数据库收录！ | |
| 点击此处可从《岩石学报》浏览原始摘要信息 | |
| 点击此处可从《岩石学报》下载免费的PDF全文 | |