陕西凤县左家庄金矿床流体包裹体地球化学特征与成因

Geochemical characteristics of fluid inclusions and their implications for the genesis of the Zuojiazhuang gold deposit in Fengxian County,Shaanxi Province,China

左家庄金矿位于西秦岭凤太矿集区西北角的何家庄岩体西端南侧与上石炭统侵入接触的内接触带。矿体受构造与岩体双重控制,主要发育于东西向构造内充填的石英脉中。区内中粒二长花岗岩与粉砂质绢云板岩接触带是金矿化的有利部位。本文对左家庄金矿床成矿流体的成分、来源、物理化学条件及演化特征进行了研究,认为左家庄金矿流体包裹体类型可以分为气液两相包裹体、纯液相包裹体和纯气相包裹体3类,包裹体多以水溶液包裹体(L_(H_(2)O)-V_(H_(2)O))为主、并有CO_(2)-H_(2)O包裹体(LCO_(2)-L_(H_(2)O)),流体包裹体液相成分主要为水,气相成分主要为CO_(2)及少量N_(2)和H_(2)。成矿流体为中低温(229~320℃)-低盐度(7.31%~12.28%Na Cl.eq)以变质热液为主后期混入大气降水的混合流体,矿床中硫化物形成于富重硫(黄铁矿δ^(34)S=11.4‰~13.77‰)环境。左家庄金矿具有典型造山型金矿床特征。

The Zuojiazhuang gold deposit is located in the inner contact zone between the southwestern part of the Hejiazhuang intrusion and Upper Carboniferous stratum in the northwestern Fengtai ore-concentrated area in the West Qinling.Its ore bodies,controlled by both the structure and intrusion,are mainly developed in form of quartz veins filled in the east-westward structures.The contact zone between medium-grained monzogranite and silty sericite slate in the deposit is a favorable zone for gold mineralization.The composition,source,physicochemical conditions and evolution characteristics of ore-forming fluids of the Zuojiazhuang gold deposit have been studied in this paper.The fluid inclusions can be classified into three types including the gas-liquid two-phase inclusion,pure liquid inclusion,and pure gas-phase inclusion.They are mostly aqueous inclusions(L_(H_(2)O)-V_(H_(2)O)),with minor CO_(2)-H_(2)O inclusions(LCO_(2)-L_(H_(2)O)).They have liquid phase of water,and gas phase of major CO_(2) and minor N_(2) and H_(2).They have medium to low homogenization temperatures(229-320℃)and low salinities(7.31%-12.28%Na Cleq.).The ore-forming fluid was mainly sourced from metamorphic hydrothermal fluid,and was mixed with meteoric water in the late ore-forming stage.The sulfides of the dposit were formed in an environment enriched with heavy sulfur(with δ^(34)S values of 11.4‰-13.77‰for pyrites).The Zuojiazhuang gold deposit has characteristics of the typical orogenic gold deposit.