湖南瑶岗仙钨矿床成矿流体的氦、氩同位素组成及其意义

Helium and Argon Isotopic Compositions of Ore-Forming Fluid from the Yaogangxian Tungsten Deposit and Their Geological Implications

瑶岗仙钨矿床是南岭地区最典型的石英脉型钨矿床之一。本文对该矿床黄铜矿和黑钨矿中流体包裹体的氦、氩同位素进行了较系统地测定。研究表明,黄铜矿和黑钨矿流体包裹体中3He/4He分别为0.37～0.43Ra和0.05～0.49 Ra,明显高于地壳值;黄铜矿和黑钨矿流体包裹体中的氩同位素分别为673～886和325～903,均明显高于饱和大气雨水的40Ar/36Ar值。这些氦、氩同位素组成揭示该矿床的成矿流体具有壳、幔两端元混合的特点。结合区域地质构造演化和成矿年代学的研究成果,本文认为瑶岗仙钨矿床的成矿流体是由瑶岗仙S型花岗岩浆分异出的含有地幔He的岩浆流体与大气成因地下水的二端元混合产物,S型花岗岩的形成也是壳幔相互作用的结果。

The Yaogangxian tungsten deposit is a typical quart-vein tungsten deposit in the Nanling region, South Chi- na. The helium and argon isotopic compositions of fluid inclusions in chalcopyrite and wolframite collected from this deposit have been analyzed. It is shown that, 3 He/4He ratios of fluid inclusions in chalcopyrite and wolframite fall in the range of 0.37 -0. 43 Ra and 0. 05 -0. 49 Ra, respectively, obviously higher than that of the crust. 40Ar/36Ar ra- tios of these fluid inclusions in above minerals are 673 - 886 and 325 - 903, respectively, which are obviously higher than that of air-saturated meteoric water, indicating that the ore-forming fluid in this deposit is a mixture of mantle- and crustal-derived fluids. Combined with the regional tectonic evolution and geochronological data, the authors con- elude that the ore-forming fluid in this deposit is a mixture of mantle fluid and crustal fluids ; the former is of magmat- ic origin, differentiated from Yaogangxian S-type granite and enriched in helium, the latter is of meteoric origin, and the S-type granite intrusion in the mining district is ascribed to crust-mantle interaction.