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    内蒙古十八倾壕金矿床铅同位素组成的构造学意义

    Structural significance of the lead isotopic composition of the Shibaqinghao gold deposit, Central Inner Mongolia

    • 摘要: 提要:十八倾壕金矿有两种类型矿体:糜棱岩型矿体和石英脉型矿体。糜棱岩型矿石Pb同位素组成以低放射性成因铅为特点:206Pb/204Pb为 16.63~17.45,207Pb/204Pb 为 15.31~15.48,208Pb/204Pb 为 36.52~38.85;在铅的动力学演化曲线上非常接近幔源铅演化模式曲线;与区域上典型的韧性剪切带型金矿——后石花金矿的铅同位素组成一致,是早元古代晚期(2 040 Ma)韧性剪切变质变形作用的产物。石英脉型矿石Pb同位素组成以高放射性成因铅为特点:206Pb/204Pb为18.23~19.74,207Pb/204Pb 为 15.69~15.89,208Pb/204Pb 为 38.64~40.13;在铅的动力学演化曲线上非常接近上地壳铅演化的模式曲线;与区域上典型的燕山期岩浆热液型金矿——东伙房金矿以及燕山期花岗岩的铅同位素组成一致,是燕山期岩浆热液型金矿化。十八倾壕金矿是两次不同性质成矿作用叠加的结果。这从Pb同位素组成上证明了笔者曾经提出的关于该矿床叠加构造控矿的观点。

       

      Abstract: Abstract:There are two types of gold orebody in the Shibaqinghao gold deposit:mylonite ore and quartz vein ore.The Pb isotopic composition for mylonite ore is characterized by lower Pb isotope ratios, with 206Pb/204Pb=16.63 to 17.45, 206Pb/204Pb=15.31 to15.48 and 206Pb/204Pb=36.52 to 38.85, and its lead dynamic evolution curve is very close to the model curve of the mantle lead evolution and consistent with the lead isotopic composition of the typical ductile shear zone gold deposit——the Houshihua gold deposit in the area. These suggest that gold in the mylonite ore might be derived from country rocks, and that the ore is the product of late Paleoproterozoic (2040 Ma) ductile shear metamorphism-deformation. The Pb isotopic composition of quartz vein ore is characterized by higher Pb isotope ratios, with 206Pb/204Pb=18.23 to 19.74, 206Pb/204Pb=15.69 to 15.89 and 206Pb/204Pb=38.64 to 40.13, and its lead dynamic evolution curve is very close to the model curve of the upper crust lead evolution and consistent with the lead isotopic composition of the typical Yangshanian magmatic-hydrothermal gold deposit——the Donghuofang gold deposit in the area, suggesting that it is magmatic-hydrothermal gold mineralization. The Donghuofang gold deposit resulted from overlapping of two mineralizations of different natures. This supports the view proposed by the author that the deposit was controlled by overlapping structure.

       

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