内蒙古东山湾钨钼多金属矿床成矿流体地球化学特征及成因

东山湾钨钼多金属矿床为大兴安岭南段新发现的一斑岩型矿床,产于燕山晚期花岗斑岩体与二叠系的接触带附近。该矿床主要发育细脉、微细脉浸染型矿化,其钨钼银多金属热液成矿作用划分为黑钨矿-锡石-毒砂-石英阶段(Ⅰ)、毒砂-辉钼矿-石英阶段(Ⅱ)、银多金属硫化物-石英阶段(Ⅲ)3个阶段。为了系统研究该矿床不同成矿阶段成矿流体的来源、性质及其演化特点,对不同成矿阶段样品进行了流体包裹体岩相学、显微测温学及碳、氢、氧同位素研究。结果表明:Ⅰ、Ⅱ阶段石英中流体包裹体的均一温度分别为232.7~321.7℃和201.2~352.7℃,盐度(w(NaCl))分别为3.4%~9.8%和4.1%~10.4%,成矿流体属中温、中等盐度不均匀的NaCl-H2O体系型热液;Ⅲ阶段石英中流体包裹体的均一温度变化范围为198.6~273.5℃,盐度为5.0%~8.4%,成矿流体属中低温、中低盐度均匀的NaCl-H2O体系型热液;Ⅱ阶段石英样品的δ18 O值为7.5‰~9.0‰,石英中流体包裹体的δDH2O-SMOW值与δ13 CPDB值分别为-175.6‰~-160.3‰与-23.5‰~-20.1‰。成矿流体具有岩浆分异热液的特点,并伴随大气降水的大量加入,流体运移过程中地层有机质的加入导致了成矿流体具有较低的δDH2O-SMOW值、δ13 CPDB值;成矿流体的不混容作用、大气降水的加入是导致区内钨钼沉淀、成矿的主要机制,而银多金属矿化则可能由成矿流体的降温冷却所引起。

Geochemical Characteristics of Ore-Forming Fluids and Genesis of Dongshanwan Tungsten-Molybdenum Polymetallic Deposit in Inner Mongolia

Dongshanwan W Mo poly-metallic deposit is a newly discovered porphyry type deposit in the southern Great Xing’an Range.It occurs in the contact zone of the Late Yanshanian granitoids and Permian strata. It mainly develops as vein-let type and fine vein disseminated type in terms of mineralization.The formation of Dongshanwan deposit can be divided into three stages:I.wolframite-arsenopyrite-quartz,Ⅱ.arsenopyrite-molybdenite-quartz,and Ⅲ.silver polymetallic-quartz.For the purpose of getting the origin,nature,and evolution characteristics of the ore-forming fluids of the different mineralization stages,we discuss the petrography,micro-thermometry,and carbon-hydrogen-oxygen isotope of the fluid inclusions.The results show that:the aqueous two-phase and vapor-rich two-phase fluid inclusions developed in stage I and II,their homogenization temperature ranges 232.7 321.7 ℃ and 201.2 352.7 ℃,the salinity values of ranges 3.4% 9.8% and 4.1% 10.4%,and the ore-forming fluid belongs to medium temperature and medium salinity NaCl H 2 O hydrothermal system. The aqueous two-phase fluid inclusions developed in stage III,their homogenization temperature ranges from 1 98.6 to 273.5℃,the salinity values ranges from 5.0% 8.4%,and the ore-forming fluid belongs to low temperature and low salinity NaCl H 2 O hydrothermal system.Theδ1 8 O value of quartz sample ranges from 7.5‰ 9.0‰,theδDH2 O SMOW value andδ1 3 CPDB value of the fluid inclusions in quartz are -175.6‰ - 1 60.3‰ and - 23.5‰ - 20.1‰.The ore-forming fluid has the characteristics of hydrothermal magma,which is accompanied by adding of meteoric water and organic matter in the formation,this led to a lower value of δDH 2 O SMOW and δ1 3 CPDB value of ore-forming fluid. The immiscibility and adding of meteoric water led to the mineralization of tungsten and tin,and the silver poly-metallic mineralization might be caused mainly by cooling of the ore-forming fluid.