【摘要】 青海玉树地区莫海拉亨铅锌矿床和东莫扎抓铅锌矿床均位于青藏高原金沙江缝合带和班公湖-怒江缝合带夹持的羌塘地体东北缘,是"三江"北段铜铅锌多金属成矿带铅锌矿床的2个典型代表。笔者曾通过对东莫扎抓铅锌矿床的S-Pb-Sr-Nd同位素组成特征研究,认为其成矿物质来源于沉积地层。本文在野外地质观察基础上,亦对莫海拉亨铅锌矿床的矿石矿物和重晶石进行了S同位素组成分析,对矿石矿物、脉石矿物和区域地层进行了Pb同位素组成分析,对脉石矿物进行了Sr-Nd同位素组成分析。分析结果表明,硫化物δ34S值为-30.0‰～7.4‰,峰值为-18‰～-2‰,反映了总体富轻硫的特征,而重晶石δ34S值为20.2‰～+24.2‰,来自于第三纪陆相盆地。宽的δ34S变化可以解释为流体在盆地内活动期间与不同地层单元发生相互作用,从而继承了不同物质单元的S同位素特点,还原硫应主要来自于硫酸盐的细菌还原或者含硫有机质的热还原,反映硫来自沉积盆地。矿石矿物的206Pb/204Pb、207Pb/204Pb和208Pb/204Pb分别为18.298～18.694、15.298～15.721、38.169～38.894,而脉石矿物的206Pb/204Pb、207Pb/204Pb和208Pb/204Pb分别为18.418～18.672、15.418～15.719、38.403～38.845。矿石矿物和脉石矿物的Pb同位素组成介于区域上地壳Pb组成范围内,总体类似于MVT矿床,显示Pb等金属元素来源于上地壳岩石。脉石矿物的(87Sr/86Sr)i、εSr(t)、(143Nd/144Nd)i和εNd(t)分别为0.70851～0.70906、57.4～65.2、0.512265～0.512361、-6.5～-4.6。Sr-Nd同位素特征亦显示脉石矿物的物质来源于上地壳岩石。总体来说,莫海拉亨铅锌矿床的S-Pb-Sr-Nd同位素特征均与东莫扎抓铅锌矿床的一样,显示均来自沉积地层。并结合矿床地质特征和地球化学特征,讨论了莫海拉亨铅锌矿床和东莫扎抓铅锌矿床形成的动力学背景。更多还原

【Abstract】 The Mohailaheng and Dongmozhazhua Pb-Zn deposits in the Yushu area of Qinghai Province,located in the northeast margin of Qiangtang terrane which is between Jinshajiang suture zone and Bangonghu-Nujiang suture zone,are the two typical Pb-Zn deposits in the Cu-Pb-Zn polymetallic mineralization belt for the northern part of the Nujiang-Lancangjiang-Jinshajiang area.The authors thought the sources of ore-froming material were derived from the sedimentary strata by the research of sulfur,lead,strontium and neodymium isotope compositions of the Dongmozhazhua lead-zinc ore deposit.On the basis of geological field observations,the authors also made the research on the Mohailaheng lead-zinc ore deposit and selected sulfide minerals and barite for S isotope compositions analyses,sulfide minerals,gangue minerals and regional strata for Pb isotope compositions analyses,and gangue minerals for Sr-Nd isotope compositions.δ34S values of sulfide minerals are-30.0‰~+7.4‰,and show peaks at-18‰~-2‰,reflecting the characteristic of light sulfur.δ34S values of barite are 20.2‰~+24.2‰,implying the derivation of Tertiary continental facies basin.The ore deposit displays wide variations in sulfide δ34S values,indicating multiple sulfur sources.On account of the lack of magmatic activity,it is realistic to view the rocks in the basin as the source of sulfur.Sulfur in the rocks was transferred into hydrothermal fluids via fluid-rock interaction.Therefore,the variation in rock types across the basin is likely to influence the variation of sulfur isotopic compositions.Reduced sulfurs were mainly derived from the biogenic sulfate reduction or the thermochemical reduction of sulfur-bearing organic matter,implying that sulfur came from the sedimentary basin.The 206Pb/204Pb,207Pb/204Pb and 208Pb/204Pb ratios for sulfide minerals vary in ranges of 18.298~18.694,15.298~15.721 and 38.169~38.894,respectively.The 206Pb/204Pb,207Pb/204Pb and 208Pb/204Pb ratios for gangue minerals are between 18.418~18.672,15.418~15.719 and 38.403~38.845,respectively.In the diagrams of 207Pb/204Pb-206Pb/204Pb and 208Pb/204Pb-206Pb/204Pb,the Pb isotope compositions of the sulfide minerals and gangue minerals fall into the regional upper crust lead zone,similar to MVT deposit,implying that Pb might have come from the upper crust rocks.The(87Sr/86Sr)i,εSr(t),(143Nd/144Nd)i and εNd(t) ratios for gangue minerals vary in ranges of 0.70851~0.70906,57.4~65.2,0.512265~0.512361 and-6.5~-4.6,respectively.The Sr-Nd isotope compositions of the gangue minerals indicate that their matter sources also came from the upper crust rocks.On the whole,the characters of sulfur,lead,strontium and neodymium isotope compositions of the Mohailaheng lead-zinc ore deposit in the Yushu area are the same as those of the Dongmozhazhua lead-zinc ore deposit,implying that they both derived from the sedimentary strata.Together with the geological and geochemical features of the Mohailaheng and Dongmozhazhua Pb-Zn deposits,the authors discussed their dynamical settings.更多还原