西秦岭铧厂沟金矿床流体包裹体特征研究及矿床成因

摘要

铧厂沟金矿位于西秦岭勉略缝合带南侧,其产出受韧脆性剪切带控制,赋矿围岩为泥盆系细碧岩、凝灰质绢云千枚岩和灰岩.根据脉体穿切关系和矿物交代关系,可以将铧厂沟金矿分为早、中、晚3个成矿阶段.在铧厂沟金矿的石英中发育了CO2-H2O型、纯CO2型、H2O溶液型和含子矿物型四种类型流体包裹体.早期石英中原生包裹体主要是CO2-H2O型和纯CO2型,其成分为CO2+H2O±N2±CH4±H2S,均一温度集中在320～360℃,盐度为0.43%～5.14%NaCleqv;中阶段为主成矿阶段,该阶段石英中包含了所有四种类型的包裹体,其中H2O溶液型包襄体占了大多数,CO2-H2O和水溶液包裹体均一温度集中在240～320℃,盐度为0.43%～11.19%NaCleqv;晚阶段石英仅发育水溶液型包裹体,具有较低的均一温度(118～228℃)和盐度(0.18%～6.59%NaCleqv).根据CO2-H2O型包裹体计算主成矿阶段压力为70～195MPa,成矿深度为5～7km.总体而言,铧厂沟金矿的初始流体具有中高温、富CO2、低盐度的变质流体特征,晚成矿阶段流体演化为低温、低盐度水溶液流体,流体的不混溶导致了主成矿期的矿质的大量沉淀,铧厂金矿为中浅成的造山型矿床.%The Huachanggou gold deposit, Shaanxi Province, is located in the southern edge of Mianlue suture zone of the West Qinling Orogen. It is controlled by a ductile-brittle shear zone and hosted in the Devonian spilite, tuffaceous sericitized phyllite and limestone. The crosscutting relationships and mineral replacement suggest that the ore forming process includes the early, middle and late stages. In the quartz of Huachanggou gold deposit, four types of fluid inclusions (Fis) are identified as CO2-H2O, pure CO2, H2O-solution and daughter mineral-bearing. The early-stage quartz contains primary pure CO2 and CO2-H2O with homogenization temperatures clustering 320-360X1 and the salinity of 0. 43% -5.14% NaCleqv. Vapor bubbles are composed of CO2 + H2O ± N2 ± CH3 ± H2S. The middle-stage quartz trapped all the four types of Fis, the H2O-solution Fis account for the majority. Most of CO2-H2O and the H2O-solution Fis homogenized betwwen 240 ~320t, and with the salinities 0.43% -11.19% NaCleqv. Fluid inclusions in late-stage quartz are H2O-solution with low homogenization temperatures (118 - 2281) and low salinities (0. 18% - 6.59% NaCleqv). Minimum trapping pressures estimated from CO2-H2O inclusions are 70 - 195MPa for middle stages, suggesting that gold mineralization occurred at the depths of 5 ~7km. In general, the ore fluids in the early and middle stages are characterized by meso- to hypothermal, CO2-rich and low salinity, which are considered as the nature of metamorphic fluids, whereas the late-stage fluids are low temperature, low salinity and CO2-poor. Fluid immiscibility caused gold precipitation in the middle-stage. The ore-forming fluid-system of the Huachanggou gold deposit is same to the orogenic-type. The Huachanggou gold deposit is a mesozonal to epizonal orogenic gold deposit.