| 二长石地质温度计在估算乌拉山金矿碱性长石形成温度中的应用 |
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| 引用本文： | 胡萍,赵令湖,边秋娟.二长石地质温度计在估算乌拉山金矿碱性长石形成温度中的应用[J].岩石矿物学杂志,2004,23(4):327-336. |
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| 作者姓名： | 胡萍 赵令湖 边秋娟 |
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| 作者单位： | 1. 中国地质大学,湖北,武汉,430074;Northeastern Illinois University Chicago,IL 60625,USA
2. 中国地质大学,湖北,武汉,430074 |
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| 基金项目： | 教育部科学技术研究基金资助项目 (95 491 1 5 ) |
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| 摘 要： | 内蒙古乌拉山金矿田内主要出露晚太古代乌拉山群区域变质岩和规模不一的花岗岩体以及不同时代、不同种类的脉状地质体。含金矿脉中主要矿物共生组合为碱性长石、石英、斜长石、碳酸盐矿物(方解石、白云石)和少量金属硫化物。矿床的显著特征为碱性长石交代作用强烈，碱性长石也广泛产于该地区其他各种类型的岩石中。本文采用电子显微探针分析了共生碱性长石和斜长石的化学成分，并采用三元二长石温度模型估计了碱性长石的平衡温度。结果表明，第一成矿阶段的碱性长石一石英含金矿脉中碱性长石的形成温度为353℃，第二成矿阶段石英含金矿脉中碱性长石的形成温度为281℃，矿脉碱性长石形成压力约为5kbar。这些结果与同类矿石中平衡共生的碳酸盐矿物和云母类矿物的地质温度计估计的形成温度以及共生石英中流体包裹体的均一温度非常一致。因此，乌拉山金矿床形成和富集的温度可估测为260～380℃，压力约为5kbar。此外，应用二长石温度计计算了本地区区域变质片麻岩和花岗岩中碱性长石的平衡温度，所得温度比采用共生铁铝榴石和黑云母温度计估计的温度要低约250℃。这表明共生的铁铝榴石和黑云母的平衡温度可能代表其寄主变质岩变质期温度及寄主花岗岩原生温度，而区域变质岩和花岗岩中的碱性长石在经历了随后多次热液作用后，可能重新平衡再生，这也与前人对乌拉山金矿的矿床地质和同位素研究的结果一致。
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| 关 键 词： | 碱性长石 形成温度 二长石温度计 乌拉山金矿床 内蒙古 |
Formation temperaturesof alkali feldspars from the Wulashan gold deposit:an estimate by two-feldspar thermometry |
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| Abstract.Formation temperaturesof alkali feldspars from the Wulashan gold deposit:an estimate by two-feldspar thermometry[J].Acta Petrologica Et Mineralogica,2004,23(4):327-336. |
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| Authors: | Abstract |
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| Abstract: | The Wulashan gold deposit, Inner Mongolia, China, which is characterized by intensive alkali feldspar metasomati, is hosted by the late Archean gneiss, amphibolite, migmatite, and marble of the Wulashan Group and surrounded by several intrusions. The general mineral assemblage of mineralized lodes is alkali feldspar + quartz + plagioclase + carbonate (calcite and Fe-dolomite etc). Alkali feldspar is also present as a major component within country rocks. On the basis of the microprobe analyses for coexisting alkali feldspar and plagioclase, the equilibrium temperatures of the alkali feldspars are calculated using several ternary two-feldspar geothermometers. The obtained temperatures at 5 kbar are 353℃ for alkali feldspars from gold-bearing veins I (K-feldspar-quartz veins), and 281℃ for alkali feldspars from gold-bearing veins Ⅱ (quartz veins), in good agreement with the estimated temperatures for coexisting carbonates, mica minerals and gold, and with the homogeneous temperatures of fluid inclusions in quartz and alkali feldspars. Therefore, the gold mineralization in the Wulashan gold deposit formed at the temperatures ranging from 280～360℃ and the pressure of 5 kbar. On the other hand, the temperatures of alkali feldspars from regional metamorphic gneiss and granite are lower than the equilibration temperatures of coexisting almandine and biotite, indicating that the temperatures of almandine and biotite may represent the peak temperature of metamorphi and alkali feldspars in metamorphic rocks and granite may re-equilibrate after experiencing numerous overprinting thermal / magmatic events. |
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| Keywords: | alkali feldspar formation temperature two-feldspar thermometer the Wulashan gold deposit Inner Mongolia |
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