内蒙古哈什吐钼矿床熔融-流体包裹体特征及硫同位素组成

Characteristics of Melt-Fluid Inclusions and Sulfur Isotopic Compositions of the Hashitu Molybdenum Deposit,Inner Mongolia

哈什吐钼矿床是近年来在大兴安岭中段地区新发现的矿床,矿体产出于花岗岩体内,是一个与酸性岩浆作用密切相关的内生金属矿床.矿床金属矿物组成主要为辉钼矿、黄铜矿、黄铁矿、磁黄铁矿、闪锌矿、方铅矿、毒砂等.包裹体研究表明包裹体类型主要为液体包裹体(Ia型)、气体包裹体(Ib型)、含子晶包裹体(Ic型)及熔融包裹体(II型)构成.不同类型包裹体共存产出表明这些包裹体大都经历了流体沸腾作用.包裹体均一测温表明流体包裹体均一温度主要变化于250～500℃,熔融包裹体均一温度集中变化于750～950℃.计算得到流体盐度、压力和密度变化范围分别为1%～49%NaCl eqv、5～100MPa、0.7～1.1g/cm3.包裹体研究表明哈什吐钼矿床成矿流体为一种高温度、高盐度、高压力、中高密度且含一定量CO2的流体,该流体可归属为H2O-NaCl-CO2-SO42-体系.硫化物的δ34Sv-cdt(‰)变化范围为0.4‰～3.8‰,计算得到成矿流体的δ34SH2S(‰)变化范围为1.1‰～4.7‰,硫同位素组成表明成矿作用与深部岩浆作用有密切联系.矿床成矿流体演化过程发生了流体沸腾和混合作用,显著的减压沸腾作用是造成成矿体系发生大量硫化物沉淀的主要机制.哈什吐钼矿床的发现对该区寻找岩浆热液型的内生多金属矿床具有重要的启示意义.该区找矿勘探应重视岩体与不同岩性岩石及构造带的接触部位以及岩体与构造断裂交汇的部位.

The Hashitu Mo deposit was discovered recently in the middle section of the Da Hinggan Montain district.The ore body occurs in granite intrusion and this deposit is regarded as an endogenic metallic ore deposit related to acid magmatism.The metallic minerals are composed of molybdenite,chalcopyrite,pyrite,sphalerite,galena,and arsenopyrite,etc.The fluid inclusions study demonstrates that inclusion types mainly involve liquid inclusion（Ia type）,gaseous inclusion（Ib type）,daughter crystal inclusion（Ic type）and melt inclusion（II type）.Co-existence of different inclusion types indicates the fluid boiling.The heating and freezing study shows that homogenization temperature of fluid and melt inclusions ranges 250～500℃and 750～ 950℃,respectively.The calculation of fluid salinity,pressure and density indicates that these values range 1%～49% NaCl eqv,5～100MPa and 0.7～1.1g/cm3,respectively.The fluid inclusion study indicates that ore forming fluid are characterized by high temperature,high salinity,high pressure,high-moderate density and CO2bearing,which can be classified as H2ONaCl-CO2-SO42-system.δ34Sv-cdt（‰）values of sulfides and δ34 SH2S（‰）values of ore forming fluid range from 0.4‰ to 3.8‰and 1.1‰ to 4.7‰,respectively.These isotopic values indicate that mineralization is related with magmatism in this region.Both fluid boiling and mixing are identified in ore forming fluid evolution and fluid boiling resulting in pressure decrease was the mainly mechanism for sulfide minerals deposition form hydrothermal fluid.Discovery of the Hashitu Mo deposit in this region is helpful to the exploration of other magmatic-hydrothermal Mo-W-Cu-Pb-Zn-Au deposits.More attention should be paid to the contact and intersection parts between intrusions and other host rocks,intrusions and structural zones in future mining exploration.