造山型金矿的地质特征和成矿流体

Geological Characteristics and Ore Forming Fluids of Orogenic Gold Deposits

造山型金矿是全球重要的金矿类型。造山型金矿包含三种类型:产于绿岩带的含金石英碳酸盐脉、产于浊积岩中的含金石英脉和产于条带状铁矿(BIF)中的含金石英脉。造山型金矿的形成受板块构造控制,处于压缩或者转换挤压的造山构造环境。造山型金矿中的绿岩带金矿主要受剪切带、转换断层控制,浊积岩型金矿受褶皱和层间走滑断层控制,而赋存于BIF中的金矿则受剪切带和断层所控制。在这些金矿床中发现了4类流体包裹体:H_2O-CO_2型、富CO_2型、气液包裹体和含Na Cl子矿物的包裹体。所有年代的造山型金矿成矿流体的成分均为低盐度的水溶液和富CO_2的流体,温度在200~400℃范围内。稳定同位素研究表明造山型金矿的成矿流体源自变质流体和岩浆流体。金在成矿流体中的络合物应为Au HS^-或Au H_2S。虽然成矿流体中有丰富的CO_2,但Au在CO_2流体中的溶解度很低,有丰富的CO_2时Au在H_2S中的溶解度增大。流体包裹体研究表明,Au的成矿流体是Na Cl-H_2O-CO_2体系的流体,并在成矿过程中发生了相分离,即Na Cl-H_2O-CO_2流体分成两个流体:H_2O-Na Cl和CO_2-H_2O,Au的沉淀是在这种相分离过程中发生的。

Orogenic gold deposits are one of the most important resources of gold.It could be classified into three types:greenstone-hosted quartz-carbonate vein deposits,turbidite hosted gold deposits and BIF hosted gold deposits of all ages.They are controlled by compressional/transpressional environments and formed within shear zones,anticlines and faults during the post-and syn-tectonic stages.Fluid inclusions studies on orogenic gold deposits indicate 4 types of fluid inclusions:H2O-CO2;CO2-rich;aqueous and halite daughter mineral bearing fluid inclusions.The ore forming fluids are of low salinity(typically less than 10%NaCleqv),CO2-rich(about 10%?25%CO2)and deposition occurred over a temperature range of 200 to 400℃,under lithostatic pressure.Fluid phase separation played an important role in gold deposition.