Leimengou Mo deposit is one of the classic porphyry Mo deposits in the eastern Qinling molybdenum belt. The oreboides are distributed as lens and layers in the inner and outer contact zones between granite porphyry and Neoarchean Taihua Formation gneiss. Mineralized types contain dissemination and multistage stockworks. Based on intersection and overprinting relationships of veins throughout the deposit, hydrothermal mineralization process at Leimengou can be divided into four stages: (I) K-feldspar stage; (II) quartz-K-feldspar stage; (III) quartz-molybdenum stage; (IV) quartz-carbonate stage. Three types of fluid inclusions have been distinguished as aqueous (type A), CO2-bearing (type B), and daughter mineral-bearing inclusions (type S). Microscopic data (compositions, homogeneity temperature and salinity) of fluid inclusions from different stages demonstrate that the mineralizing fluid of the Leimengou deposits is characterized by a H2O-CO2-NaCl system with medium-high temperatures, medium-low pressures, medium-low salinities, and low density fluids. Hydrogen and oxygen isotopic compositions indicate that magmatic fluid was dominant in early mineralization stage, and meteoric water was involved, to some extent, in mineralization as the mineralization went on. Carbon-oxygen isotope reveals that deep-seated ore-forming fluid was also added. There was no remarkable decreasing of temperature; therefore, fluid immiscibility resulted in precipitation of ore-forming materials. Combined with characteristics of fluid inclusions and paragenesis of mineral assemblages, it is suggested that fluid immiscibility and decreasing of pH and oxygen fugacity were the leading factor for the formation of the deposit.%豫西雷门沟钼矿床位于东秦岭钼矿带东段,是区内典型的斑岩型钼矿床之一.矿体主要分布于花岗斑岩与围岩新太古界太华群片麻岩的内外接触带中,呈透镜状、似层状产出.矿化类型主要有浸染状和细脉-网脉状.根据矿脉穿切关系,将热液成矿过程划分为4个阶段:Ⅰ)面型钾长石化阶段,Ⅱ)石英-钾长石阶段,Ⅲ)石英-辉钼矿-硫化物阶段,Ⅳ)石英-方解石阶段.矿床流体包裹体有3类:H2O包裹体(A型)、含CO2包裹体(B型)及含子矿物多相(S型)包裹体.根据不同阶段流体包裹体显微资料(成分、均一温度、盐度等)综合研究认为,本矿床成矿流体属中低温、中低盐度、低密度的H2O-CO2-NaCl体系,H、O同位素特征显示,成矿早阶段以岩浆水为主,随成矿演化有不同程度大气水的加入,C、O同位素特征表明,成矿流体有深源成分的加入.成矿过程温度降低不明显,流体不混溶作用导致矿质沉淀.结合流体包裹体特征和矿物共生组合关系认为流体不混溶、pH和氧逸度降低是矿床形成的主要因素.
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