河南祁雨沟金矿床成矿流体演化特征

Fluid evolution of Qiyugou cryptoexplosive breccia type gold deposit, Henan

祁雨沟隐爆角砾岩金矿床产于太古宇太华群中,金矿化分为6个成矿阶段,其中第Ⅰ,Ⅲ,Ⅴ阶段石英39Ar 40Ar坪年龄分别为130 31±0 86,122 61±0 61和(109 20±0 70)Ma。对各成矿阶段石英、方解石中流体包裹体均一温度、盐度、化学成分、氢氧同位素组成分析结果表明,早阶段流体为岩浆水,其后逐渐有大气降水的混合;第Ⅰ阶段高温(301 2～465 4℃)、中等盐度(9 1%～18 6%)的流体曾发生沸腾,形成较多以气相为主的包裹体;从第Ⅱ成矿阶段开始,流体沸腾减弱而出现不混溶现象;在第Ⅲ成矿阶段,不混溶作用增强,形成富CO2的低盐度流体与富H2O高盐度流体;在第Ⅳ—Ⅴ成矿阶段,大气降水的混合作用趋于增强,流体总体盐度降低。流体包裹体气相成分以CO2,H2S,CH4为主,含少量CO,N2,H2等,并且早阶段流体CO2含量较高,在第Ⅲ—Ⅴ成矿阶段,H2S,CH4,CO浓度增高,金属矿物大量出现。减压作用造成初始高温流体沸腾,其后温度降低以及盐析效应可能造成富CO2流体与富H2O流体的不混溶,而Au的大量沉淀则主要与大气降水的混合作用有关。

The Qiyugou cryptoexplosive breccia type gold deposit is hosted by Archean Taihua Group. Six stages of mineralization were distinguished, and the ()^(39)Ar-^(40)Ar plateau ages for quartz from I, III,V stage quartz veins are 130.31±0.86,122.61±0.61 and (109.20±0.70) Ma respectively. Homogenization temperature, salinity, chemical and isotopic composition of fluid inclusions in quartz and calcite from different mineralization stages indicate that the ore fluid of early occurred when the high tempture(301.2～465.4 ℃), middle salinity (9.1%～18.6%) fluid of stage I moved upward, forming vapor-dominated fluid inclusions. From mineralization stage II, fluid boiling declined and fluid unmixing presented. In stage III, the activitu of fluid unmixing increased, resulting in the coexistence of CO_2-rich fluid inclusions with low salinity and H_2O-rich inclusions of high salinity. In stage IV and V, the mixing of magmatic water with meteoric water developed intensively, so the salinity of the fluid decreased. The vapor phase component of the fluid inclusions are mainly CO_2, H_2S, CH_4 with minor CO, N_2, H_2. In early mineralization stage, the fluid contains more CO_2; while in the main mineralization stages, a great amount of ore minerals occured, and the fluid contains more CO_2, H_2S, CH_4. The decompression has made for fluid boiling, later the salting-out effect and the fall of tempreture might have lead unmixing between CO_2-rich fluid and H_2O-rich fluid, and that fluid mixing caused gold precipitation.