吉林永吉县大黑山斑岩型钼矿床成矿流体地球化学特征及成矿机制

Characteristics of Ore-Forming Fluids and Metallogenic Mechanism of the Daheishan Porphyry Mo Deposit in Yongji Area,Jilin Province

大黑山钼矿床位于张广才岭—小兴安岭成矿带南段,矿体主要赋存在花岗闪长岩和花岗闪长斑岩内。含矿石英脉中主要发育气液两相包裹体(W型)和含子矿物三相包裹体(S型),偶见含CO2包裹体。成矿早阶段含矿石英脉中主要发育W型、S型包裹体和少量含CO2包裹体,均一温度为208～443℃,盐度(w(NaCl))为2.9%～49.8%,流体密度为0.5～1.2g·cm-3;主成矿阶段含矿石英脉中发育W型、S型包裹体和少量含CO2包裹体,子矿物为石盐和金属硫化物,均一温度为197～398℃,盐度为1.6%～43.9%,流体密度为0.5～1.1g·cm-3;成矿晚阶段仅见气液两相包裹体(W型),均一温度为171～301℃、盐度为1.6%～19.8%,流体密度为0.6～0.9g·cm-3。主成矿阶段流体包裹体类型多样,且具有相似的均一温度,压力范围为30～100MPa,成矿深度约为4km。成矿阶段早期流体沸腾作用和晚期流体混合作用是金属硫化物沉淀的主要机制。

The Daheishan Mo deposit is located in the south segment of the Xiao Hinggan Mountains-Zhangguangcai Mountains metallogenic belt.Ore bodies are mainly hosted in granodiorite and granodiorite porphyry.Fluid inclusions in ore-bearing quartz veins can be classified into aqueous two-phase（W-type）and daughter mineral-bearing multiphase（S-type） occasional containing CO2 inclusion.Fluid inclusions formed in the early stage are W-type,S-type and a small amount of containing CO2 inclusions,and the homogenization temperature of this type of inclusion change from 208℃ to 443℃,salinities from 2.9% to 49.8% NaCl equivalent and the density from 0.5 g·cm-3 to 1.2g·cm-3;The quartz-molybdenite veins from the main ore-forming stage contain W-type and S-type inclusions with homogenization temperatures from 197℃ to 398℃,salinities from 1.6% to 43.9% NaCl equivalent and density from 0.5 g·cm-3 to 1.1 g·cm-3.The daughter minerals in fluid inclusions from the main ore-forming stage include salt daughter mineral and metallic sulfide daughter mineral.Fluid inclusions of the late stage are major W-type inclusions,with homogenization temperatures from 171℃ to 301℃,salinities from 1.6% to 19.8% NaCl equivalent and the density from 0.6 g·cm-3 to 0.9 g·cm-3.Fluid boiling in the main stage is evidenced by the co-existence of different types of fluid inclusions with similar homogenization temperatures.The pressures of fluid inclusions formed in main stage change from 30 MPa to 100 MPa,corresponding to depths of about 4 km.The fluid boiling in the early ore-forming stage and fluid miscibility in late stage played very important roles in the precipitation of metal sulfides.