青海玉树东莫扎抓铅锌矿床S、Pb、Sr-Nd同位素组成:对成矿物质来源的指示  

Sulfur, lead, strontium and neodymium isotope compositions of the Dongmozhazhua lead-zinc ore deposit in the Yushu area, southern Qinghai: Implications for the sources of ore-forming material in the deposit

作　　者：田世洪[1] 杨竹森[1] 侯增谦[2] 刘英超[2] 宋玉财[2] 王富春[3] 薛万文[3] 

机构地区：[1]中国地质科学院矿产资源研究所国土资源部成矿作用与资源评价重点实验室,北京100037 [2]中国地质科学院地质研究所,北京100037 [3]青海省地质调查院,西宁810012

出　　处：《岩石学报》2011年第7期2173-2183,共11页Acta Petrologica Sinica

基　　金：国家973项目(2011CB403104;2009CB421007;2009CB421008);"十一五"国家科技支撑计划重大项目(2006BAB01A08);国土资源大调查项目(1212010818096);国家自然科学联合基金(U09336051);中央级公益性科研院所基本科研业务费专项资金(K0802)联合资助

摘　　要：青海玉树地区东莫扎抓铅锌矿床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典型代表。在野外地质观察基础上,本文对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。结果表明,硫化物δ34S值为-29‰~6‰,峰值为-8‰^-6‰,反映了总体富轻硫的特征,而重晶石δ34S值为18·3‰^+22·8‰,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18·387~18·703、15·391~15·768、38·372~38·809,而脉石矿物的206Pb/204Pb、207Pb/204Pb和208Pb/204Pb分别为18·423~18·612、15·491~15·701、38·497~38·612。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0·70855~0·70928、58·0~68·4、0·512273~0·512353、-6·2^-4·7。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。The Dongmozhazhua Pb-Zn deposit 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, is the typical Pb-Zn deposit in the Cu-Pb-Zn polymetallic mineralization belt for the northern part of the Nujiang-Lancangjiang-Jinshajiang area. On the basis of geological field observations, the authors 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 -29‰-6‰, and show peaks at -8‰--6‰, reflecting the characteristic of light sulfur. δ34S values of barite are 18.3‰-＋22.8‰, 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 18.387-18.703, 15.391-15.768 and 38.372-38.809, respectively. The 206Pb/204Pb, 207Pb/204Pb and 208Pb/204Pb ratios for gangue minerals are between 18.423-18.612, 15.491-15.701 and 38.497-38.612, 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 c

关 键 词：成矿物质来源 S同位素 PB同位素 SR-ND同位素 东莫扎抓铅锌矿床 青海玉树 

分 类 号：P618.42[天文地球—矿床学] P618.43[天文地球—地质学]