海南岛富文金银多金属矿床成矿流体演化:来自流体包裹体和H-O同位素证据

Evolution of ore-forming fluids in the Fuwen gold-silver polymetallic deposit in Hainan Island:Fluid inclusion and H-O isotope evidence

富文金银多金属矿床位于海南岛雷鸣盆地,为中型高硫化物含金石英脉型金矿床。主要金属矿物有自然金、银金矿、黄铁矿、毒砂、闪锌矿、方铅矿及少量黄铜矿;非金属矿物主要为石英、碳酸盐矿物。金的赋存状态主要以含金矿物形式出现,分布于石英、黄铁矿、毒砂裂隙和被包裹在闪锌矿中。该矿床成矿过程可分为早、中、晚3个阶段,其中,中阶段为主成矿阶段,金主要在中阶段沉淀。早阶段流体包裹体为纯CO_(2)型、富CO_(2)型和少量富液相水溶液包裹体,中阶段为纯CO_(2)型、富CO_(2)型、富液相水溶液型和含子矿物多相包裹体,晚阶段为富液相水溶液包裹体。从早阶段到晚阶段,包裹体均一温度峰值分别为320~330℃、205~225℃和130~140℃,盐度峰值分别为3.50%~5.00%NaCl_(eqv)、2.80%~3.50%NaCl_(eqv)和2.25%~3.00%NaCl_(eqv),指示成矿流体以中温、低盐度为特征。包裹体激光拉曼光谱分析表明,富文矿床的流体包裹体成分以H_(2)O为主,富含CO_(2),并含有少量硫化物。主成矿阶段石英中流体包裹体的δD值为−53.9‰~−45.4‰,δ^(18)OH_(2)O值为1.5‰~7.5‰,反映成矿流体具有岩浆水和大气降水两种来源。进一步利用纯CO_(2)包裹体和纯H_(2)O包裹体等容线相交法,估算主成矿阶段的成矿温度为245~315℃,成矿压力为64~130 MPa。综合研究表明,富文矿床是与侵入岩有关的高硫化物金银多金属矿床,其主成矿阶段发生的流体沸腾和不混溶是金沉淀的主要机制。

The Fuwen gold-silver polymetallic deposit is located in the Leiming Basin of the Cretaceous red rock series in Hainan Island,South China.This is a medium-sized ultra-high sulfide gold-bearing quartz vein type gold deposit.The main ore minerals are natural gold,electrum,pyrite,arsenopyrite,sphalerite,and galena,with a small amount of chalcopyrite,and the gangue minerals are dominated by quartz and carbonate.Gold occurs mainly as Au-bearing minerals distributed in quartz,pyrite,arsenopyrite fissures and encapsulated in sphalerite.Three mineralization stages can be distinguished in the Fuwen deposit:the early,middle,and late stages,with Au precipitation mainly occurring in the middle stage.The fluid inclusions preserved in the early mineralization stage are pure CO_(2)and CO_(2)-rich types,with a small amount of liquid-rich aqueous solution type;fluid inclusions recognized in the middle stage are pure CO_(2),CO_(2)-rich,liquid-rich aqueous solution types with daughter mineral-bearing polyphaser type;and the fluid inclusions identified in the late stage are liquid-rich aqueous solution type.From the early to late stages,the ore-forming inclusions have peak homogenization temperatures of 320–330℃,205–225℃and 130–140℃,and peak salinities of 3.50%–5.00%NaCl_(eqv),2.8%–3.5%NaCl_(eqv)and 2.25%–3.00%NaCl_(eqv),respectively.It indicates that the ore-forming fluid is characterized by middle temperature and low salinity.Laser Raman analysis shows that components of the fluid inclusions in the Fuwen deposit are dominated by H_(2)O,with a large amount of CO_(2)and a small amount of sulfide.TheδD andδ^(18)OH_(2)O values of fluid inclusions in quartz of the main(middle)ore-forming stage range from−53.9‰to−45.4‰and from 1.5‰to 7.5‰,respectively,indicating a derivation from magmatic water and meteoric water.The estimated mineralization temperature and pressure are 245–315℃and 64–130 MPa,respectively,using the isochore line intersection method for pure CO_(2)and H_(2)O inclusions.Hence,the Fuwen deposit is an intrusion-related high-sulfide gold-silver polymetallic deposit,in which the gold precipitation was controlled by fluid boiling and immiscibility during the main mineralization stage.