大兴安岭北段旁开门金(银)矿床地球化学特征及成因

Geochemistry and Genesis of Pangkaimen Gold-Silver Deposit in Northern Segment of Da Xing'an Mountains

旁开门金(银)矿床地处爱辉—呼玛成矿带,矿床主体赋存于侏罗系甘河组火山岩中,矿体主要以脉状形式产出,严格受硅化角砾岩带控制。区内甘河组玄武安山岩、安山岩、流纹岩属过铝高钾钙碱性系列,玄武岩和石英斑岩属过铝质钾玄系列,它们均来源于地幔岩浆,为同源岩浆分异的产物。矿石中流体包裹体发育较差,以气液两相包裹体为主,仅见少量含子矿物三相包裹体。气液两相包裹体均一温度为268.8～331.6℃,盐度(w(NaCl))为8.67%～13.11%,含子矿物三相包裹体均一温度为288.8～313.3℃,盐度为37.32%～39.23%;表明成矿流体为中温、中—高盐度的热液体系。根据流体包裹体氢、氧同位素分析结果推断其为岩浆流体与大气降水混合热液。矿床形成于早白垩世由挤压转变为伸展环境,成矿物质来源于深部岩浆及火山岩地层,成矿温度为中温,成矿深度属浅成,其成因类型为浅成中温热液矿床。

Pangkaimen gold-silver deposit is located in Aihui-Huma metallogenic belt,and the main ore bodies are hosted by Jurassic volcanic rocks in Ganhe Formation.The ore body formed as veins which are under strict control of silicified breccia zone.The basaltic andesite,andesite,and rhyolite in Ganhe Formation are the peraluminous high-K calc-alkaline series,and basalt and quartz porphyry are shoshonite series.They derived from mantle and formed as products of co-genetic magma.The fluid inclusions are poorly developed with main type of gas-liquid two-phase inclusions and minor three-phase inclusions with daughter crystals.The homogenization temperature for gas-liquid two-phase inclusion is from 268.8℃ to 331.6℃,and the salinity（contents of NaCl） from 8.67% to 13.11%.The homogenization temperature for three-phase inclusions is from 288.8℃ to 313.3℃,and the salinity from 37.32% to 39.23%.Therefore,the ore-forming fluids are the hydrothermal system with medium temperature,medium to high salinity.According to the analytical results of hydrogen and oxygen isotope,we infer that the hydrothermal system is a mixed fluid of magmatic hydrothermal fluid with atmospheric water.The tectonic setting for this deposit was changed from compress to extension in the Early Cretaceous.The ore-forming material is mainly from deep-seated magma and volcanic rocks,and the mineralization conditions are medium temperature and shallow depth.The genetic type for this deposit is medium temperature epithermal ore deposit.