内蒙古鸡冠山斑岩钼矿床成矿时代和成矿流体研究  

Geochronology and fluid inclusion study of the Jiguanshan porphyry Mo deposit,Inner Mongolia

作　　者：陈伟军[1,2] 刘建明[1] 刘红涛[1] 孙兴国[1,2] 张瑞斌[1,2] 张作伦[1,2] 覃锋[1,2] 

机构地区：[1]中国科学院地质与地球物理研究所中国科学院矿产资源重点实验室,北京100029 [2]中国科学院研究生院,北京100039

出　　处：《岩石学报》2010年第5期1423-1436,共14页Acta Petrologica Sinica

基　　金：国家重点基础研究项目(2006CB403507);国家自然科学基金项目(40972065)联合资助

摘　　要：内蒙古鸡冠山钼矿床是西拉沐伦钼成矿带上的典型斑岩矿床。矿床产于火山侵入杂岩中,矿化类型以细脉浸染状矿化为主。对矿床5件辉钼矿样品进行了铼-锇同位素分析,获得了151.1±1.3Ma的等时线年龄,表明成矿作用发生在晚侏罗世。成矿作用可划分为三个阶段:早阶段为石英-黄铁矿阶段,发育乳白色石英和粗粒浸染状黄铁矿;中阶段包括早期石英-多金属硫化物亚阶段和晚期石英-萤石-金属硫化物亚阶段;晚阶段为石英-碳酸盐细脉,穿切早、中阶段脉体和矿物组合。鸡冠山钼矿床流体包裹体岩相学研究表明,与成矿有关的包裹体主要有六种类型:富液相、富气相、含子晶多相、含CO2三相、纯CO2及纯液相包裹体。其中,早阶段以富气和富CO2包裹体为主,中阶段多种包裹体共存,晚阶段则主要为富液包裹体。冷热台显微测温和激光拉曼显微探针(LRM)成分分析结果表明,早阶段石英中原生包裹体的均一温度>480℃,盐度最高>66.75%NaCleqv,包裹体气相成分富含水和CO2,液相成分则以水为主,子晶矿物有石盐、黄铜矿以及指示氧化条件的赤铁矿等,同时也说明成矿流体是富含成矿金属元素的。中阶段早期石英中的流体包裹体均一温度为320～480℃,晚期石英和萤石中的流体包裹体的均一温度为180～320℃。中阶段流体盐度介于4.65%～56.76%NaCleqv。中阶段包裹体含石盐、方解石、黄铜矿、赤铁矿等子矿物,富气相、富液相与含子晶多相包裹体共存,且具有相近的均一温度,而盐度相差悬殊,指示流体发生了沸腾。晚阶段流体的温度降低至100～180℃,盐度则低于10.86%NaCleqv,流体包裹体成分主要为水。鸡冠山钼矿成矿流体演化从早至晚为:从早阶段高温、高盐度、高氧逸度、富CO2、富成矿物质以岩浆热液为主成矿流体,演化至晚期低温、低盐度、无子晶、贫CO2、以大气降水为主的流体。沸腾The Jiguanshan Mo deposit is a very typical porphyry deposit hosted in the Xilamulun molybdenum metallogenic belt.The deposit occurs within the volcanic-intrusive complex.Re-Os isotope dating from five molybdenite samples gives an isochron age of 151.1 ± 1.3Ma,which indicates the deposit formed in the late Jurassic.The Mo mineralization is characterized by a variety of veinlets and disseminated styles.The hydrothermal ore-forming processes can be divided into three stages:stage I-ore-in poor stage,it is characterized by ivory-white quartz veins and minor disseminated pyrites;stage II-the primary Mo mineralization stage,it can be subdivided into two substages:quartz-polymetallic sulfide and fluorite-quartz-polymetallic sulfide substages;stage III-barren stage,it consists of quartzs and carbonates,and it overprints the minerals of the former two stages.Petrographic observation suggests that six major types of fluid inclusion related to mineralization are present in this deposit:gas-rich,liquid-rich,daughter-mineral bearing polyphase,CO2-bearing three-phase,pure CO2 phase and liquid phase inclusions.Fluid inclusions in stage I are mainly gas-rich ones with small amount of CO2 phase ones,while stage II are multiform inclusions including gas-rich,liquid-rich and daughter-mineral bearing poly-phase inclusions.However,none but liquid-rich fluid inclusions can be observed in stage III.Microthermometric and laser Raman spectroscopic studies indicate that homogenization temperatures of fluid inclusions in quartz-veins from stage I are above 480℃,with the high salinities of above 66.75% NaCleqv.Liquid components are dominated by H2O and vapor bubbles mainly composed of CO2 and H2O.Daughter minerals of the poly-phase fluid inclusions include halite,chalcopyrite and hematite representing an oxidizing condition,which indicates the ore-forming fluid is metal-rich magmatic fluid.The stage II fluid inclusions with the temperature range of 320 ～ 480℃ in early phase and 180 ～ 320℃ in late phase,respectively,and fluid sal

关 键 词：斑岩钼矿 Re-Os等时线年龄 流体包裹体 内蒙古鸡冠山 西拉沐伦钼矿带 

分 类 号：P618.65[天文地球—矿床学]