延边地区闹枝浅成热液铜金矿床稀有气体同位素地球化学特征及其成矿意义

在矿床地质和矿物流体包裹体研究的基础上,利用高真空惰性气体同位素质谱仪测定了闹枝铜金矿床硫化物中流体包裹体的稀有气体同位素组成。实验数据表明:3He/4He比值为0.033~0.104Ra,平均为0.061 Ra;20Ne/22Ne和21Ne/22Ne值分别为9.817~9.960和0.029 0~0.029 5,具有以大气组成为主的特征;40Ar/36Ar为324~349,平均为341,略高于饱和大气水(40Ar/36Ar=295.5)。流体包裹体3He/4He显示成矿流体来自壳源,不含幔源He;流体中除壳源放射性成因40Ar*外,有大气Ar的参与,放射性成因40Ar*的含量为8.8%~15.5%,平均为13.4%,大气40Ar的贡献为84.5%~91.2%,平均86.6%。结合稳定同位素特征和成岩成矿年代学研究成果,进一步厘定该矿床为相对独立的浅成中硫化型铜金矿床,成矿流体来自于年轻的大陆地壳流体,含矿流体上升过程中受到循环大气降水强烈混染作用,伴随温压条件的降低,成矿流体卸载有用元素,最终沉淀成矿。

Noble gas isotopic geochemistry of Naozhi epithermal Cu-Au deposit in Yanbian of China and its metallogenic implications

Noble gas isotopic compositions of fluid inclusions in sulfides from Naozhi Cu- - Au deposit were ana- lyzed by using an inert gas isotopic mass spectrometer based on the study of the deposit geology and material compo- sitions of fluid inclusions． The experimental data show that fluid inclusions in pyrite and chalcopyrite have 3 He/ 4 He ratios of 0. 033 ～0. 104 Ｒa with an average of 0. 061 Ｒa． The 20 Ne/ 22 Ne and 21 Ne/ 22 Ne ratios range in 9. 817 ～ 9. 960 and 0. 029 0 ～0. 029 5， respectively， which is similar to the composition of the atmosphere， whereas 40 Ar/ 36 Ar ratios range from 324 to 349 with an average of 341 which are slightly higher than the ratio of air- saturated water (295. 5)． The 3 He/ 4 He composition of fluid inclusions implies that ore- forming fluid of the Naozhi Cu - - Au deposit was crust- derived，and the mantle- derived He might be neglected． Except for crustal radiogenic Ar ( 40 Ar* )，at- mospheric Ar was involved in the ore- forming fluids． The content of the radiogenic Ar varies from 8. 8% to 15. 5%， averaging 13. 4%， while the atmospheric Ar is 84. 5% ～91. 2%， averaging 86. 6%． Combining with stable isotope data and the chronology of diagenesis and metallogenesis，we suggest that the Naozhi Cu - - Au deposit is a medium- sulphidation epithermal Cu - - Au deposit． The ore- forming fluids originated from melting of the lower crust． Minerali- zing fluids were strongly contaminated by meteoric water during ascent，and the mineral precipitation occurred at a shallow crustal level associated with the decrease of temperature and pressure．