新疆西准噶尔苏云河钼矿床成矿流体和成矿时代

The ore-forming fluid and geochronology of the Suyunhe Mo deposit,West Junggar,Xinjiang

苏云河钼矿位于新疆北部西准噶尔巴尔鲁克山西段,隶属于巴尔鲁克山成矿带,由3个花岗岩体组成,矿体主要位于与岩体接触的凝灰岩地层中。辉钼矿的Re-Os模式年龄为293.3±4.0Ma^296.8±4.3Ma,等时线年龄为294.4±1.7Ma,加权平均年龄为295.0±1.5Ma,表明矿化发生于早二叠世。苏云河钼矿床的石英脉中发育3种类型的包裹体:富液相包裹体、富气相包裹体和含子晶多相包裹体。研究表明,与3个岩体矿化有关的流体具有类似特征,均可以分为3个阶段。早阶段三种类型的包裹体均发育,均一温度>491℃,盐度>58.6%Na Cleqv,密度>1.15g/cm3,具有高温、高盐度、高密度的特征,属Na Cl-CO2-H2O体系。中阶段发育富液相包裹体和富气相包裹体,均一温度为240~443℃,盐度为1.7%~21.0%Na Cleqv,密度为0.38~1.03g/cm3,为中高温、中低盐度、中低密度流体,属Na Cl-CO2-CH4-H2O体系。晚阶段仅发育富液相包裹体,均一温度为153~239℃,盐度为<9.6%Na Cleqv,密度为0.81~0.94g/cm3,为中低温、低盐度、中低密度流体,属Na Cl-H2O体系。石英包裹体中水的氢氧同位素研究表明早阶段的成矿流体以岩浆水为主,中阶段和晚阶段为岩浆水和大气水的混合水,并且随着流体演化,大气水所占的比例逐渐升高。除此之外,综合流体包裹体和氢氧同位素地球化学特征表明流体沸腾作用和混合作用是引起苏云河钼矿床矿质沉淀的主要因素。

The Suyunhe Mo deposit,in the western part of the Barluk Mountain, West Junggar, northern Xinjiang, belongs to the Barluk metallogenic belt and consists of three granitic bodies. The orebodies are mainly located in the tuff which contacts with granitic bodies. Mo mineralization occurred in the Early Permain, with the Re-Os model ages of molybdenites being 293.3±4. 0Ma - 296. 8 ± 4. 3Ma, the isochron age of molybdenites being 294.4 ± 1.7Ma and the weighted average age of molybdenites being 295.0 ± 1.5Ma. Three types of fluid inclusions, i.e. , liquid-rich two phases, vapor-rich two phases, and daughter mineral-bearing polyphase inclusions, are present in the Suyunhe Mo deposit. The research indicates that the ore-forming fluids in different granitoids are similar and can be divided into three stages. The early stage, belonging to NaC1-CO2-H2 O system, develops all three types of inclusions and is characterized by high temperature, high salinity and high density, with the homogenization temperatures being above 491℃, the salinites being above 58. 6% NaCleqv and the densities being above 1.15g/cm^3. The middle stage, belonging to NaC1-CO2-H20 system, develops liquid-rich two phases and vapor-rich two phases inclusions and is characterized by high-middle temperature, middle- low salinity and middle-low density, with the homogenization temperatures being 240 N 443℃, the salinities being 1.7% N 21.0% NaCleqv, and the densities being 0. 38 - 1.03g/cm^3. The late stage, belonging to NaC1-H20 system, only develops liquid-rich two phases inclusions and is characterized by middle-low temperature, low salinity and middle-low density, with the homogenization temperatures being 153 - 239℃, the salinities being below 9. 6% NaCleqv, and the densities being 0. 81 - 0. 9dg/cm^3. The hydrogen and oxygen isotopes of water in quartz inclusions indicate that the early stage fluids were mainly made up of magmatic water, and the middle and late stage fluids consisted of magmatic water and meteoric water. Moreover, the proportion of meteoric water rose with the evolution of fluids. Besides, both the fluid inclusions and hydrogen-oxygen isotopes studies indicate that the boiling and mixing of fluids are the main factors that lead to the deposition of ore-forming substances.