摘要
劳家沟钼矿是西拉木伦成矿带东段阿鲁科尔沁旗天山镇新发现的一个斑岩型钼矿床。矿床赋矿岩石为中细粒斑状二长花岗岩,矿化类型以细脉状和浸染状辉钼矿为主。成矿过程包括早阶段(石英-辉钼矿-黄铁矿组合)、中阶段(石英-多金属硫化物组合)和晚阶段(石英-方解石组合)三个阶段。早阶段的石英细脉中发育气相水包裹体(PV)、液相水包裹体(PL)、CO2-H2O三相包裹体(C)、富液相水溶液包裹体(L)、富气相水溶液包裹体(V)和含子矿物多相包裹体(S),子矿物包括石盐、硬石膏及其它不明矿物;中阶段较早阶段除缺少CO2三相包裹体外,其它相似;而晚阶段的石英-方解石细脉中流体包裹体发育较少,且类型单一,只有L类和少量V类。流体包裹体岩相学、显微测温及单个包裹体激光拉曼光谱分析结果表明劳家沟斑岩钼矿的成矿流体是以高温、高盐度、高氧逸度和含CO2为特征的岩浆热液型流体,从早到晚其演化规律为:早阶段高温(320～>550℃)、高盐度(6～16wt%Na-Cleqv、52.89～>66.75wt%NaCleqv)、高氧逸度、富CO2→中阶段中高温(280～>550℃)、高盐度(5～>15wt%NaCleqv、>66.75wt%NaCleqv)、含CO2→晚阶段中低温(160～250℃)、低盐度(0.5～5wt%Na-Cleqv)、贫CO2。利用含石盐子晶包裹体的气液均一温度ThL-V、石盐消失温度Tmhalite和压力三者之间的关系对其最小捕获压力进行估算,结果显示成矿深度大约为5～7km。根据区域成矿规律推测劳家沟斑岩钼矿的成矿时间大致为早白垩世,成矿构造背景对应于中国东部岩石圈强烈减薄。本文将劳家沟斑岩钼矿的成矿机制大致概括为:岩石圈强烈减薄诱发岩浆侵入活动,岩浆在侵入晚期发生液态不混溶作用形成高温、高盐度、高氧逸度、含CO2的含矿气水热液,在地壳快速抬升期间流体多次减压沸腾,导致成矿物质沉淀。
The Laojiagou deposit,which has been recently found at Tianshan town,Ar Horqin Banner,east of the Xilamulun metallogenic belt,is a porphyry Mo deposit.It is hosted in the fine-grained porphiric monzogranite,dominated by veinlet-disseminated molybdenite mineralization.There were three stages involved in the ore-forming process：early stage（quartz-molybdenite-pyrite assemblage）,middle stage（quartz-polymetallic sulfide assemblage） and late stage（quartz-calcite assemblage）.The early stage-related quartz veins contain abundant fluid inclusions（FI）,including pure gas FI,pure liquid FI,CO2-bearing three-phase FI,liquid-rich FI,gas-rich FI and daughter mineral-bearing multiphase FI,in which halite,anhydrite and other unknown minerals are contained.Compared with the early stage,the middle stage lacks of C-type FI.The number and diversity of the late stage fluid inclusions decreases dramatically,with a small amount of L-type and V-type FI.Petrography,microthermometry and laser Raman analysis on FI indicate the ore-bearing fluid is magmatic hydrothermal fluid characterized by high-temperature,hypersaline,high-oxygen and CO2-bearing.From the early stage to late stage,it evolved regularly from high-temperature（320~〉550℃）,hypersaline（6~16wt%NaCleqv,52.89~〉66.75wt%NaCleqv）,high-oxygen fugacity and CO2-rich,then high-medium-temperature（280~〉550℃）,hypersaline（5~15wt%NaCleqv,〉66.75wt%NaCleqv）,CO2-bearing,to medium-low temperature（160~250℃）,low salinity（0.5~5wt%NaCleqv） and CO2-barren.Based on the relationship among the liquid-vapor homogenization（ThL-V）,halite dissolution temperature（Tmhalite） and pressure,the minimum trapped pressure has been estimated,which suggests that the mineralization depth is approximately 5~7km.The ore-forming mechanism of the Laojiagou porphyry Mo deposit is inferred as follows：immiscibility occurred in the process of magmatic intrusion,causing the escape of ore-bearing hydrothermal fluid from magma.Then,boiling extensively took place during the period of the crustal uplifting,resulting in the precipitation of metal in the hydrothermal fluid.According to regional metallogenic regularity,the mineralization age of the Laojiagou porphyry Mo deposit is most likely to be the early Cretaceous,when the lithospheric of Eastern China was greatly thinning.
出处
《地质与勘探》
CAS
CSCD
北大核心
2012年第4期663-676,共14页
Geology and Exploration
基金
国家自然科学基金项目(40972065)
关键词
斑岩钼矿
流体包裹体
劳家沟
西拉木伦成矿带
porphyry Mo deposit； fluid inclusion； Laojiagou； Xilamulun metallogenic belt
