内蒙古哈达门沟金矿成矿流体来源的氦、氩同位素示踪

内蒙古包头市哈达门沟金矿床是华北陆块北缘乌拉山-大青山地区的大型金矿床,矿床赋存于新太古界乌拉山群黑云角闪斜长片麻岩、角闪黑云二长片麻岩和含石榴石黑云斜长片麻岩中,成矿流体性质不明。文章对哈达门沟金矿主要载金矿物黄铁矿开展了流体包裹体中的He、Ar同位素组成研究。研究表明,赋存于黄铁矿流体包裹体中的4He含量为(83.92~606.46)×10-8cm3STP/g,n(3He)/n(4He)值为0.19~0.91Ra,幔源He的含量为2.62%~13.73%,平均为9.95%,表明成矿流体中的He主要来源于地壳,大约10%来源于地幔。~(40)Ar含量为(71.22~308.22)×10~(-8)cm~3STP/g,~(40)Ar/~(36)Ar比值变化于2793.6~7253.5之间,在n(~(40)Ar)/n(~(36)Ar)与R/Ra图解和n(~(40)Ar*)/n(4He)与R/Ra图解中,显示地壳氩和地幔氩的混合来源特征。结合已有的氢、氧、硫同位素研究,认为哈达门沟金矿成矿流体主体为地壳来源,但幔源流体的加入清晰可辨,乌拉特前旗-呼和浩特山前断裂很可能为富钾质壳幔混合流体的运移提供了通道和动力。

Helium and argon isotopic tracing for sources of ore-forming fluid in Hadamen'gou gold deposit, Inner Mongolia

Located in the Wulashan-Daqingshan area on the north margin of the North China Craton, the Hadamen''gou large-sized gold deposit is hosted in the biotite-hornblende-plagioclase gneiss, hornblende-biotite monzonite gneiss and garnet-biotite-plagioclase gneiss of the Wulashan Group. The characteristics of ore-forming fluid are unknown. In this paper, the authors analyzed the helium and argon isotopic compositions of fluid inclusions in pyrite. The ⁴He content ranges from 83.92×10^-8 cm³STP/g to 606.46×10^-8 cm³STP/g, the n(³He)/n(⁴He) ratios are between 0.19 Ra and 0.91 Ra, and the content of He derived from the mantle ranges from 2.62% to 13.73% with an average value of 9.95%;all of these characteristics suggest that the He in ore-forming fluids was mainly derived from the crust with about 10% from the mantle. The ⁴⁰Ar content ranges from 71.22×10^-8 cm³STP/g to 308.22×10^-8 cm³STP/g, the n(⁴⁰Ar)/n(³⁶Ar) ratios are between 2793.6 and 7253.5, and the diagrams of n(⁴⁰Ar)/n(³⁶Ar) versus R/Ra and n(⁴⁰Ar^*)/n(⁴He) versus R/Ra show the mixed source of the crust and the mantle Ar. Based on a comprehensive analysis of hydrogen, oxygen and sulfur isotopic characteristics of the Hadamen''gou gold deposit, it can be concluded that the ore-forming fluid was a mixture of crustal-derived fluid and mantle-derived magmatic fluid, with the former being dominant. In addition, the Urad Front Banner-Hohhot fault probably provided the channel and power for the migration of the K-feldspar-enriched and crust-mantle mixed fluid.