西藏夏垅隐爆角砾岩型铅锌银矿床成矿流体及成矿物质来源  

Characteristics and Source of Ore-Forming Fluids and Source of Metallogenic Materials in the Xialong Cryptoexploseive Breccia Pb-Zn-Ag Deposit,Tibet

作　　者：徐玉涛[1,2] 杨竹森[2] 刘英超[3] 龚雪婧 赵晓燕[1] 费凡[1] 

机构地区：[1]中国地质大学地球科学与资源学院,北京100083 [2]中国地质科学院矿产资源研究所,北京100037 [3]中国地质科学院地质研究所,北京100037

出　　处：《地质学报》2015年第3期618-631,共14页Acta Geologica Sinica

基　　金：国家重点基础发展计划(973计划)"青藏高原南部大陆聚合与成矿作用"(编号:2011CB403104);"十一五"国家科技支撑计划项目(编号:2006BAB01A04)项目资助的成果

摘　　要：夏垅铅锌银矿床位于冈底斯斑岩铜钼成矿带的西端,产于花岗岩基中,属于隐爆角砾岩型矿床。本文对其流体包裹体及H-O-S-Pb同位素组成进行了分析。成矿流体物理性质具有从中高温(240~340℃)、低盐度(2.2%~3.8%NaCl eqv)向低温(160~180℃)、低盐度(0.8%~1.7%NaCl eqv)演化的特征。矿石中石英的δD值为-156‰^-145‰,δ18 O值为-0.4‰~7.1‰,按流体包裹体均一温度换算的δ18 OH2O值为-16.7‰^-3.0‰,表明成矿流体来源于岩浆水和大气降水的混合。金属硫化物的δ34 S值变化范围较小,在-3.0‰^+5.9‰之间,按照同位素平衡系数外推法获得总硫同位素组成δ34SΣ为+9.80‰和+13.13‰,表明硫主要来源于岩浆岩,并反映成矿岩浆演化过程中可能经历了H2S去气作用。方铅矿的206 Pb/204 Pb=18.627~18.758、207 Pb/204Pb=15.598~15.682和208 Pb/204 Pb=38.637~39.298,黄铁矿的206 Pb/204 Pb=18.639~18.678、207 Pb/204 Pb=15.587~15.691和208Pb/204Pb=38.649~38.703,显示部分矿石铅富集放射性成因铅,反映铅的多来源性,即来源于上地幔铅与上地壳铅的混合。反映与夏垅铅锌银矿床成矿相关的岩浆来自于下地壳的部分熔融,并有地幔物质的补给,在岩浆上侵就位过程中又与上地壳中的岩浆房发生了岩浆混合。这也表明该地区可能存在有古老地壳,显示了区域上的独特性,为南拉萨地体区域找矿提供特有的指示意义。The Xialong Pb-Zn-Ag deposit is located in the west of the Gangdise porphyry Cu-Mo metallogenic belt and occurrs within the large granite batholith.It is a cryptoexplosive brecciated Pb-Zn-Ag deposit.In this paper we report the analytical results of the fluid inclusions and H-O-S-Pb isotopes.The ore-forming fluids in the Xialong deposit were evolved from high temperature（240~340℃）,low salinity（2.2% ~3.8% NaCl eqv）to low temperature（160~180℃）,low salinity（0.8% ~1.7% NaCl eqv）.Analytical results of fluid inclusions show very lowδD values.TheδD-δ18 OH2 Odiagram shows that ore-forming fluids originated from the mixing of magmatic and meteoric water.δ34S values of metal sulfides from this deposit range between-3.0‰ ~ ＋5.9‰,with a small change range.According to extrapolation of isotope equilibrium coefficient,δ34S of metal sulfides gives two positive high average values of sulfur isotope,and the values ofΣ34 S are ＋9.80‰ and ＋13.13‰.Two positive-highΣ34 S values reflect that ore-forming magma may have undergone degassing when evolving.The lead isotopic composition of metal sulfide is characterized by enrichment of radiogenic lead isotopic.206Pb/204 Pb,207Pb/204 Pb and 208Pb/204 Pb values of galena are 18.627~18.758,15.598~15.682 and 38.637~39.298.206Pb/204 Pb,207Pb/204 Pb and 208Pb/204 Pb values of pyrite are 18.639~18.678,15.587~15.691 and 38.649~38.703.These data show parts of ore lead enrich radiogenic lead,reflecting the multiple sources of lead and mixing of the upper mantle and upper crust lead.Our study reveals that magma associated with mineralization of Xialong Pb-Zn-Ag deposit comes from the partial melting of the lower crust,with mixing of mantle materials,and in the process of intrusion emplacement,also occurs magma mixing with the magma chamber in the upper crust.These also show that there may exist ancient crust in the area,which provides specific instructions for prospecting in the southern Lhasa terrane.

关 键 词：成矿流体 成矿物质来源 同位素 夏垅铅锌银矿床 西藏冈底斯带 

分 类 号：P618.4[天文地球—矿床学] P618.52[天文地球—地质学]