甘肃干沙鄂博稀土矿床成矿介质演化过程:来自包裹体的信息

在矿床地质研究基础上,通过对石英、萤石、方解石中流体包裹体岩相学、显微测温分析,对甘肃省干沙鄂博稀土矿床成矿流体的特征、演化及成矿机理进行了讨论.结果表明:矿床中发育大量包裹体,按室温下的成分相态特征,将其分为熔体包裹体、流体-熔体包裹体、气液H2O包裹体、气液CO2包裹体、CO2-H2O包裹体和含子矿物的气液H2O包裹体、含子矿物的CO2-H2O包裹体等7种类型.在成矿过程中,包裹体组合从熔体包裹体→流体-熔体包裹体+流体包裹体→流体包裹体的变化,反映了成矿介质经历了从岩浆→岩浆+热液→热液的演化过程.在岩浆-热液成矿期,流体-熔体包裹体大量存在,以及富H2O相CO2-H2O包裹体与富cO2相CO2-H2O包裹体密切共生,表明成矿时曾经发生两次不混溶作用,早期岩浆-热液不混溶作用导致萤石和REE-氟碳酸盐的晶出,而CO2-H2O不混溶作用引起了硫化物的沉淀.

Research on evolution process of ore-forming medium in Ganshaebo REE deposit,Gansu, China: Information from inclusions

The characteristics,evolution of the ore-forming medium and precipitation mechanism of the Ganshaebo REE deposit are studied based on geological investigation and petrography and research of micro-thermometry of fluid inclusions in quartz,fluorite and calcite.A large amount of inclusions have been found in the ore of the deposit and according to the characteristics of composition and phase behavior at room temperature,seven types of the inclusions have been recognized,including melt inclusions,fluid-melt inclusions,H2O inclusions,CO2 inclusions,CO2-H2O inclusions,daughterbearing H2O inclusions and daughter-bearing CO2-H2O inclusions.During the ore-forming process,the inclusion types change from melt inclusion into fluid-melt inclusion+ fluid inclusion,and then to fluid inclusion.It imply that the ore-forming medium varied from magma to magma+hydrothermal,and then to hydrothermal solution.Two types of immiscibility took place during the magmahydrothermal metallogenic period,the early magma-hydrothermal immiscibility is characterized by the occurrence of abundant fluid-melt inclusions,resulting in the precipitation of fluorite and REEfluorine carbonates,and the late CO2-H2O immiscibility is characterized by the coexistence of H2O-rich CO2-H2O inclusions and CO2-rich CO2-H2O inclusions,leading to the precipitation of sulfides.