鄂西北构家河金矿床成矿流体特征

摘要

构家河金矿床位于南秦岭武当山西缘,产于绢云绿泥石英片岩和变石英砂岩之中,受韧性滑脱剪切构造带控制.矿化类型主要有破碎带蚀变岩型和石英脉型,其中前者形成了破碎带蚀变岩型主矿体,呈似层状或透镜状分布于近南北向断裂中,次矿体分布在北西和北东向次级断裂中,为石英脉型矿体.成矿作用包括3个阶段:石英-硫化物阶段、石英-硫化物-金银矿化阶段和石英-碳酸盐阶段.对主矿体石英-硫化物-金银矿化阶段和石英-碳酸盐阶段的流体包裹体进行了显微观察和测温,同时对不同阶段的石英和方解石、白云石等进行了D、O、C同位素测试.结果显示,包裹体以原生气液两相包裹体为主,且主要为富液相包裹体;石英-硫化物-金银矿化阶段包裹体均一温度集中于180～270℃,峰值为220℃,盐度和密度分别为1.40％ ～14.46％和0.60～0.97 g/cm3;石英-碳酸盐阶段均一温度峰值为170℃,盐度和密度分别为1.34％ ～7.31％和0.86～0.96 g/cm3;石英-硫化物-金银矿化阶段和石英-碳酸盐阶段石英的δDV SMOW值分别为-93.3％‰～-70.9‰和-91.6％‰～-67.2‰,δ18OV-SMOW值为12.9‰～14.5‰和11.9‰～13.8‰;方解石和白云石的δ13CV-PDB值为-12.4‰～-12.0‰,δ18OvPDB值为-18.4‰～-18.1‰.成矿流体特征显示该矿床初始成矿流体为中温、低盐度的变质热液,再结合区域成矿地质与成矿构造背景,认为构家河金矿为造山型金矿床.%The Goujiahe gold deposit is located in the western Wudang Mountain of South Qinling,which is controlled by ductile slip-shear belt and occurs in sericite chlorite-quartz schist and metamorphic quartz sandstone.The mineralization type is mainly composed of fracture alteration type and quartz vein type mineralization,in which the former formed the main orebody.The main fracture alteration type orebody is distributed in nearly NS-trending fault in stratoid or lenticular form,and the secondary orebodies were filled in NW-and NE-trending secondary faults,forming quartz vein ore bodies.Three metallogenic phases were recognized:the early quartzsulfide stage,the middle quartz-sulfide-gold and silver stage and the late quartz-carbonate stage.The fluid inclusions of the quartz-sulfide-gold and the silver stage and the quartz-carbonate stage of the main orebody were observed and measured,the D,O,C isotope analysis of different stages of quartz and calcite and dolomite was conducted.The results show that most of fluid inclusions are enriched in liquid primary inclusions in crowded random distribution.The homogeneous temperature peak is rn~tly 220℃ and 170℃,the salinity is 1.40％ to 14.46％ and 1.34 ％ to 7.31％,the density is 0.60～0.97 g/cm3 and 0.86～0.96 g/cm3 for the quartz-sulfide-gold and silver stage and the quartz-carbonate stage respectively.The hydrogen and oxygen isotope study of the two phase yielded 12.9‰～ 14.5‰ and 11.9％～ 13.8‰,and the carbon and oxygen isotope study of calcite and dolomite yielded the values of δ13CV-PDB=-12.4‰～-12.0‰,δ18OV-PDB =-18.4‰～-18.1‰,suggesting that the original ore-forming fluids were metamorphic in genesis,characterized by mesothermal and low-salinity nature.Geological and fluid features and metallogenic tectonic background suggest that the Goujiahe gold deposit may be of the orogenic-type mineralization system.