豫西公峪金矿床流体包裹体及其He、Ar、S、H、O同位素组成对成矿流体来源的示踪

Li YF,Mao JW,Hu HB,Bai F J,Li HM,Li MW,Guo BJ and Ye HS.2005.The fluid inclusions and their He-Ar-S-H-O isotopic compositions and tracing to the source of ore-forming fluids for the Gongyu gold deposit,Western Henan.Acta Petrologica Sinic

豫西公峪构造蚀变岩型金矿床位于熊耳山东南缘祁雨沟金矿田内,矿体赋存于北东向断裂破碎带内。为探讨成矿流体的来源,尤其是地幔流体参与成矿的程度,选择13件主成矿期的矿石样品进行了系统研究,测定了公峪构造蚀变岩型金矿床成矿系统的温度及其 S、H、O 同位素和惰性气体 He、Ar 同位素组成。对保存于石英中的原生包裹体进行的详细研究结果表明:公峪构造蚀变岩型金矿床中含有丰富的包裹体,其类型复杂多样,有气体包裹体、气液包裹体、液体包裹体、含 CO_2包裹体四种类型。包裹体的均一温度变化范围较宽,在120℃～440℃之间均有分布,可进一步分为150℃～190℃、210℃～250℃和290～350℃三个区间,但主要集中于150℃～250℃的范围内。结合显微镜下观测载金矿物特点,推测金矿的形成温度区间主要在150℃～250℃之间。冰点变化范围较大,在-0.2℃～-9.6℃之间,对应的盐度在0.53wt%～13.51wt%之间。稳定同位素结果表明:硫化物的δ^(34)S 值变化于-1.7‰～2.2‰之间,与陨石硫的δ^(34)S 值接近,反映为深源;成矿Ⅰ阶段流体的δD 值为-68‰～-86‰,δ^(18)O_(H_2O)为+3.5‰～+4.5‰,Ⅱ阶段流体的δD 值为-67‰～-84‰,δ^(18)O_(H_2O)为-3.7‰～+2.6‰,反映成矿流体主要有两个来源,Ⅰ阶段以深源水为主,Ⅱ阶段有大量大气降水混入。氦氩同位素研究表明:公峪构造蚀变岩型金矿床黄铁矿流体包裹体的~3He/~4He 比值为1.05～3.17R/Ra,高于地壳的~3He/~4He 比值100余倍,但明显低于地幔流体的~3He/~4He 比值;^(40)Ar/^(36)Ar=298～391,略高于大气氩的同位素组成;^(40)Ar/~45He 比值0.08～0.35,平均为0.20,与地壳^(40)Ar/~4He 比值一致。He、Ar 同位素组成特征显示了公峪金矿床成矿流体以大气降水为主,但同时有地幔流体成分,推断金矿床成矿作用与地幔活动有着密切的关系。通过与祁雨沟隐爆角砾岩型金矿床的对比研究,认为虽然祁雨沟金矿和公峪金矿赋存于不同的构造环境中,但是流体包裹体及其同位素研究结果显示了二者的成矿作用具有一致性,他们应属于同一成矿系统的产物,均与燕山晚期岩浆热液活动有关,可能为同源、同期、不同构造空间的演化产物。

Located in the Qiyugou gold ore-field, the south-eastern margin of the Xiong＇ershan area in the western Henan province, the Gongyu altered tectonite-type gold deposit occurs in the NE-trending fracture zones. In this paper the homogenization temperatures and salinity of the fluid inclusions as well as their He-Ar and S-H-O isotopic compositions were systematically measured based on 13 samples from the main phase of gold mineralization. The fluid inclusions in the Gongyu mine can be divided into four types, i. e. vapor-aqueous, aqueous, CO2-bearing inclusions. The fluid inclusion bubbles are 2～20μm in diameter, mostly in the range of 2～4μm. The homogenization temperatures of the fluid inclusions ranges from 120℃～440℃, and dominates by 150℃～250℃ , with three distribution from 150℃～190℃ ,210℃ -250℃ and 290 ～ 350℃. The gold mineralization temperatures vary from 210℃～250℃. Their ice-melting temperatures varies from -2.5℃～-13.5℃, corresponding to a ranges of salinities 4.18wt%～13.51 wt% NaCl equivalent. The S-H-O isotopic analytical results show that δ^34S yalues of sulfide are in the range of -1.7‰～2.2‰ and close to the value of meteorolite, indicating that the ore-forming substance was probably derived from the upper mantle or some deep place. The δD and the δ18OH2O values of the first stage of main phase of gold mineralization are -68‰～-86‰ and ＋3.5‰～＋4.9‰ respectively, implying that the ore-forming fluids were derived mainly from the deep place. The δD and the δ18OH2O values of the second stage of main phase of gold mineralization are -67‰～-84‰ and -3.7‰～＋2.6‰ respectively, suggesting that the oreforming fluids probably came from the deep fluid and the meteoric water. The Ar-He analytical results show that ^3He/^4He ratios of fluid inclusions in pyrite are 1.05～3.17R/Ra, much higher 100 times than that of the crust and lower markedly that of the mantle. ^40Ar/^36Ar ratios are 298～391, slightly higher than that of atmosphere. ^40Ar/^4He ratios of metallogenic fluids are 0.08～0.35 with a mean of 0.20, which are consistent with the value of the crust（0.156）. Helium and argon isotope composition of fluid inclusions suggest that the source of ore-forming fluids is mainly meteoric water, and also have some mantle fluids. Therefore, the above data demonstrate that the Gongyu gold deposit is geneticlly related to mantle fluids. In the Qiyugou orefield, although Qiyugou gold deposit （ cryptoexplosive breccia type） and Gongyu gold deposit （ altered teetonite-type） developed in different types, their fluid inclusions and He-Ar-S-H-O isotopic data show that they originated from the same source and deposited in the same period but at different position, and probably formed in the same metallogenic system which is related to the hydrothermal fluid of Yanshanian period in Qiyugou orefield.