新疆阿希低硫型金矿稀有气体同位素地球化学及其成矿意义

Noble gas isotopic geochemistry of Axi gold deposit,and its metallogenic implications,Xinjiang,China.

阿希是一个赋存在新疆西天山古生代陆相火山岩中的大型低硫型(冰长石-绢云母型)浅成低温热液金矿床.本文利用高真空惰性气体同位素质谱仪测定了阿希金矿黄铁矿中流体包裹体的稀有气体同位素组成,结果显示其~3He/~4He 比值为0.0218～0.138R_a,平均为0.044R_a;^(40)Ar/^(36)Ar 为317.7～866.0,平均为467.3,略高于大气中^(40)Ar/^(36)Ar 比值(295.5);^(20)Ne/^(22)Ne 和^(21)Ne/^(22)Ne 的比值分别为8.08～13.00和0.028～0.063,^(82)Kr/^(84)kr、^(83)Kr/^(84)kr、^(86)Kr/^(84) Kr 的比值分别为0.159～0.278、0.171～0.238、0.280～0.348,^(129)Xe/^(132)Xe 和^(134)XP/^(132)Xe 分别为0.96～1.017、0.401～0.443。流体包裹体~3He/~4He 显示成矿流体来自壳源,不舍幔源 He;流体中除壳源放射性成因^(40)Ar~*外,有大气 Ar 的参与,放射性成因^(40)Ar~*的含量为7.0%～65.9%,平均为29.0%,大气^(40)Ar 的贡献为43.0～93 0%,平均为71.0%,稀有气体同位素组成反映出阿希金矿成矿流体为循环的大气降水。F^(84)Ke 和 F^(129)Xe 值显示流体在成矿作用过程中曾发生过沸腾作用。

Axi gold deposit is a typical low-sulfidation （adularia-sericite） type large-scale epithermal gold deposit, which is hosted in the Lower Carboniferous andesitic volcanic rocks and pyroclastics in western Tianshan, Xinjiang, Noble gas isotopic compositions of inclusion fluids in pyrites from Axi gold deposit were analyzed by using an inert gas isotopic mass spectrometer, and the results indicate that ^ 3He/^4 He and ^40 Ar/^36 Ar are 0. 0218 -0. 138R with an average of 0. 044R, and 317.7 -866 with an average of 467.3 respectively. The later is a little higher than that of the air（295.5 ）. Besides, the ^20Ne/^22 Ne and ^21 Ne/^22 Ne are 8.08 - 13.00 and 0. 028 -0. 063, ^82Kr/^84Kr, ^83Kr/^84Kr and ^86Kr/^84Kr are 0. 159 -0. 278, 0. 171 -0. 238 and 0. 280 -0. 348,^129Xe/^132Xe and ^134Xe/^132Xe are 0. 96 - 1. 017 are 0. 401 -0. 443 respectively. ^3He/^4He composition of fluid inclusions implies that ore-forming fluid of the Axi gold deposit was crust-derived, and the mantle-derived He might be neglected. Excepting for crustal radiogenic At（^40 Ar^＊ ）, atmospheric Ar was involved in the ore-forming fluids. The content of the radiogenic Ar varies between 7.0% to 65.9% , averaging 29.0% , while the atmospheric Ar is 43.0 -93.0% ,averaging 71.0%. Noble gas isotopic composition indicates that the ore-forming fluids of Axi gold deposit was recycled meteoric water. F^84Ke and F^129Xe show that boiling might have occurred during gold mineralizaion of this deposit.