摘要:
西藏嘎拉勒铜金矿床位于班公湖—怒江成矿带西段,是近年来发现的一个大型镁质矽卡岩型铜金矿床.本文在野外地质调查的基础上,通过S-Pb-C-H-O同位素分析,对嘎拉勒铜金矿床的物质来源进行了探讨.结果表明:①矽卡岩型矿石中黄铜矿的 δ34SV-CDT值在硫同位素直方图上呈塔式分布,变化范围为–4.4‰~6‰,有少许样品值变化范围较大,表明嘎拉勒矿床硫同位素主要以幔源硫为主,有少量壳源的混染;②208Pb/204Pb变化范围为38.427‰~39.008‰,207Pb/204Pb变化范围为15.588‰~15.701‰,206Pb/204Pb变化范围为18.330‰~18.871‰,显示矿区铅同位素来源以造山带铅为主,少量上地壳铅相结合的特征;嘎拉勒矿床形成于碰撞的造山带环境;③含辉钼矿石英脉中 δ18OV-SMOW值范围为12.2‰~12.8‰,平均值12.5‰,δDV-SMOW范围为–103.3‰~–95.3‰,平均值为–99.3‰,δ18OV-PDB值范围为–18.1‰~–17.6‰,平均值为–17.85‰,显示受到大气降水加入明显;④矽卡岩中方解石C-O同位素测试结果δ13CV-PDB为–2‰,δ18OV-PDB为–15.1‰,δ18OV-SMOW为15.4‰,显示嘎拉勒铜金矿床碳酸盐为海相碳酸盐并经历了溶解作用.综合表明,嘎拉勒铜金矿床是由幔源成矿流体作用形成的,成矿过程中有大气降水的加入,成矿流体与碳酸盐岩发生接触交代作用形成矽卡岩型铜金矿床.
Abstract:
The Galale copper and gold deposit in Tibet is located in the western part of the Bangong Co–Nujiang metallogenic belt. It is a large-sized magnesia skarn type copper gold deposit discovered in recent years. Based on field geological survey, the authors investigated the material source of the Galale gold deposit on the basis of S-Pb-C-H-O isotope analysis. Some conclusions have been reached:① Theδ34SV-CDT values of chalcopyrite in skarn-type ore exhibit tower-type distribution on the sulfur isotope histogram, and the variation range is –4.4‰ ~ 6‰, with a few samples showing rather wide variation range. Isotopes are mainly mantle-derived sulfur, with the mixture of a small amount of crustal source.② The variation range of208Pb/204Pb ratios is 38.427‰ ~ 39.008‰,the variation range of207Pb/204Pb ratios is 15.588‰~15.701‰, and the variation range of206Pb/204Pb ratios is 18.330‰~18.871‰, which indicates that the lead isotopic source in the mining area was dominated by orogenic lead. The crustal lead is characterized by the combination; the Galale deposit was formed in a collisional orogenic environment;③ Theδ18OV-SMOW range in the quartz vein is 12.2‰~12.8‰, with an average value of 12.5‰, whereas theδDV-SMOW values vary from –103.3‰ to –95.3‰, with an average of –99.3‰;δ18OV-PDB values vary in the range of –18.1‰ ~ –17.6‰, with an average value of –17.85‰, indicating that the precipitation was significant.④ The isotope analytical results of calcite in skarn areδ13CV-PDBof –2‰,δ18OV-PDBof –15.1‰ andδ18OV-SMOW of 15.4‰, which shows that the carbonate of the Galale copper-gold deposit was marine carbonate and experienced the dissolution. It is shown that the Galale copper-gold deposit was formed by the mantle-derived ore-forming fluid, and the meteorite was added in the mineralization process. The ore-forming fluid interacted with the carbonate rocks to form the skarn-type copper-gold deposit.
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