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“三江”中段两类碳酸盐岩容矿铅锌矿化成因的相关性——来自稀土元素地球化学研究的启示
Genetic relationship between the two types of carbonate-hosted Pb-Zn deposits in the middle part of the ‘Sanjiang’ metallogenic belt: Information from REE study
投稿时间:2014-05-23  修订日期:2015-01-19
中文关键词:东莫扎抓铅锌矿床  莫海拉亨铅锌矿床  稀土元素  碳酸盐岩容矿铅锌矿床  "三江"成矿带
英文关键词:Dongmozhazhua Pb-Zn deposit  Mohailaheng Pb-Zn deposit  REE  carbonate-hosted Pb-Zn deposit  'Sanjiang' metallogenic belt
基金项目:中央级公益性基本业务费专项基金(J1314);"973"项目 (2011CB403104); 国家自然科学基金(41403043, 41320104004, 41273050, 41302067); 中国地质调查局项目(1212011220908); 国际地质对比计划(IGCP/SIDA-600)
作者单位E-mail
李玉龙 青海省地质调查院, 青海 西宁 810012  
杨竹森 中国地质科学院 矿产资源研究所, 北京 100037  
田世洪 中国地质科学院 矿产资源研究所, 北京 100037  
赵志逸 青海省地质调查院, 青海 西宁 810012  
卢世银 青海省地质调查院, 青海 西宁 810012  
张尧 青海省地质调查院, 青海 西宁 810012  
刘英超 中国地质科学院 地质研究所, 北京 100037 lychappy@126.com. 
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中文摘要:
      世界范围内的碳酸盐岩容矿铅锌矿带内常在区域上出现以方解石等碳酸盐矿物为主要脉石矿物的富碳酸盐型铅锌矿化和以碳酸盐+萤石为主要脉石矿物的富氟型铅锌矿化这两种矿化形式,但不同元素组合的出现在成因上是否有相关性并不明确.青藏高原"三江"成矿带中段玉树地区同一矿集区内近同时发育了东莫扎抓富碳酸盐型和莫海拉亨富氟型铅锌矿床,二者均为碳酸盐岩赋矿,以逆断层为主要控矿构造,具有层控的矿体产状特征,矿石矿物均为方铅矿+闪锌矿,但是,东莫扎抓矿床以方解石+白云石等碳酸盐矿物为主要脉石矿物,莫海拉亨则以方解石+萤石为主要脉石矿物.研究表明,两个矿区含钙矿物的稀土元素地球化学特征存有差异.东莫扎抓矿区方解石的稀土元素具有轻重稀土元素分馏相对明显、轻稀土元素富集、Eu负异常明显的特征,在球粒陨石标准化配分模式图上呈现右倾或轻微右倾的"V"字形曲线.莫海拉亨矿区方解石及萤石轻重稀土元素分馏不明显,有明显的Eu负异常,球粒陨石标准化配分模式图上呈现轻微的"M"型曲线.稀土元素总量上,东莫扎抓(0.46×10-6~10.79×10-6)较莫海拉亨矿床(0.25×10-6~5.88×10-6)高.稀土元素地球化学特征揭示,两个矿床的含钙矿物都沉淀自与岩浆作用无关的热液流体,伴随硫化物沉淀,流体盐度降低,还原性变弱.莫海拉亨矿床除具有一套和东莫扎抓矿床来源一致的流体外,还具有另一套来自深部变质基底的富氟流体,这套流体控制了富氟型碳酸盐岩容矿铅锌矿床的沉淀位置,使其在区域上更靠近逆冲体系主逆冲带,且多在区域上最底层的碳酸盐岩地层中发育.这一认识解释了世界上多个碳酸盐岩容矿铅锌成矿带内同一空间、时间范围内两套不同类型铅锌矿床型式共同出现的原因.
英文摘要:
      Two kinds of carbonate hosted Pb-Zn deposits, namely carbonate-rich Pb-Zn deposits and fluorite-rich Pb-Zn deposits, extensively exist in the same Pb-Zn metallogenic belt in the world according to the classification based on gangue mineral assemblages. The relationship between the two kinds of deposits remains unclear. In the middle part of the 'Sanjiang' metallogenic belt in the Tibetan Plateau, the Dongmozhazhua carbonate-rich Pb-Zn deposit and the Mohailaheng fluorite-rich Pb-Zn deposit occur in the same carbonate-hosted Pb-Zn ore concentration area. In the two deposits, the carbonate strata are host rocks, the thrust faults are the main ore-controlling structures, the main orebody attitudes are of stratabound type, and sphalerite and galena are the main ore minerals. However, calcite and dolomite are the main gangue minerals in the Dongmozhazhua deposit while calcite and fluorite are the main gangue minerals in the Mohailaheng deposit. The geochemical features of rare earth elements (REE) in calcium-bearing minerals are different in the two deposits. The REE values of calcite in the Dongmozhazhua deposit are mainly characterized by obvious fractionation of LREE and HREE, enrichment of LREE, negative Eu anomalies and 'V'_shaped curves of chondrite-normalized REE patterns with right deviation. In contrast, the REE values of calcite and fluorite in the Mohailaheng deposit are chiefly characterized by no obvious fractionation between LREE and HREE, negative Eu anomalies and 'M'_shaped curves of chondrite-normalized REE patterns with right deviation. The total concentrations of REE (∑REE) of calcite (0.46×10-6~10.79×10-6) in the Dongmozhazhua deposit are higher than those in the Mohailaheng deposit (0.25×10-6~5.88×10-6). The geochemistry of the REE indicates that calcium-bearing minerals in the two deposits were all precipitated from a kind of hydrothermal fluids which had nothing to do with igneous activities. The salinity and reducibility of the fluids decreased with the sulfide precipitation. The two kinds of deposits had similar hydrothermal fluids; nevertheless, there existed another kind of fluid for the Mohailaheng deposit, which was a kind of fluorine-rich fluid from deep metamorphic basement. This fluorine-rich fluid controlled the location of the fluorite-rich carbonate hosted Pb-Zn deposits and could be used to explain the phenomenon why this kind of Pb-Zn deposits were more easily precipitated near the main thrust faults and the lowest carbonate strata in the region. The result achieved by the authors could answer the question why the carbonate-rich Pb-Zn deposit and the fluorite-rich Pb-Zn deposit can occur in the same region and same time in the world.
李玉龙,杨竹森,田世洪,赵志逸,卢世银,张尧,刘英超,2015,“三江”中段两类碳酸盐岩容矿铅锌矿化成因的相关性——来自稀土元素地球化学研究的启示[J].岩石矿物学杂志,34(5):648~664.
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