对新疆萨日达拉金矿成矿流体的He、Ar同位素示踪

采用稀有气体同位素质谱方法,通过分析萨日达拉金矿载金黄铁矿中流体包裹体的He、Ar同位素组成,对成矿流体进行示踪研究。结果表明,萨日达拉金矿黄铁矿流体包裹体中He同位素组成变化范围较大,R/Ra值为0.34~1.59,显示壳幔混合特征,二元混合模型计算结果显示以地壳放射性成因氦为主,并有地幔氦的加入;Ar同位素组成较均一,40Ar/36Ar值为305~359,平均336,36Ar/38Ar值为5.34~5.44,平均5.40,显示叠加有部分放射性成因40Ar的大气降水成因氩同位素组成。综合分析结果表明,萨日达拉金矿成矿流体为由大气降水深循环改造而成的地壳流体,其所具有的地幔He同位素组成应继承自下部地壳中隐伏的壳幔混合成因地质体。

Helium and Argon Isotopic Compositions of Fluid Inclusions in Pyrite from Saridala Gold Deposit in Xinjiang

Saridala gold deposit is located within Bing Daban ductile shear zone in the northern margin of Middle Tianshan. After analyzing the subsequent processes that may affect He-Ar original isotopic compositions of ore-forming fluid, the helium and argon isotopic compositions of fluid inclusions in pyrite were analyzed to trace fluid origin by using an inert gas isotopic mass spectrometer.Research results indicate that R/Ra ratios range from 0.34~1.59Ra, which primarily consist of crust-radioactive He with some mantle-derived He; Samples share coincident argon isotopic compositions with 40Ar/36Ar and 36Ar/38Ar ratios ranging from 305 to 359 with an average of 336, and from 5.34 to 5.44 with an average of 5.40, respectively, which yield Ar isotopic compositions of general atmospheric saturated water with some capture of radioactive 40Ar. He and Ar isotopic compositions indicate that ore-forming fluid of the Saridala gold deposit is derived fromcrust, which origin from deep circulation of atmospheric water, and the mantle-derived He means nothing to do with direct mantle process but drops a hint that may existed certain geologic bodies related to the interaction between mantle and crust.