内蒙古克什克腾旗长岭子铅锌矿床流体包裹体及矿床成因类型研究

Study of fluid inclusions and ore genetic type of the Changlingzi deposit,Keshiketeng County,Inner Mongolia

内蒙古克什克腾旗长岭子铅锌矿床是大兴安岭南段新发现的一个矿床,矿体赋存于下二叠统大石寨组海相火山岩建造中,矿体受夕卡岩控制。根据手标本中脉体穿插关系和岩石薄片中观察的矿物共生组合特征,文中将长岭子铅锌矿的成矿过程划分为4个阶段:干夕卡岩阶段、湿夕卡岩-磁铁矿阶段、石英-硫化物阶段和石英-碳酸盐阶段,分别以石榴子石±透辉石±硅灰石、石英+绿帘石+电气石+磁铁矿、石英+黄铁矿±磁黄铁矿±黄铜矿±方铅矿±闪锌矿和石英±方解石的矿物组合为标志。长岭子矿床主要发育水溶液包裹体(W型)和含子矿物多相包裹体(S型),前者可进一步划分为富液相(WL型)和富气相(WV型)两个亚类。干夕卡岩阶段辉石中主要发育S型和WL型包裹体,湿夕卡岩-磁铁矿阶段绿帘石和石英中主要发育WL型、WV型和S型包裹体,石英-硫化物阶段石英中可见所有类型的包裹体,石英-碳酸盐阶段的石英±方解石脉中仅见WL型包裹体。干夕卡岩阶段辉石中流体包裹体的均一温度和盐度分别为387~524℃和10.7%~52%(NaCleqv.);湿夕卡岩-磁铁矿阶段包裹体均一温度为312~533℃,盐度为11.3%~60%(NaCleqv.);石英-硫化物阶段包裹体均一温度介于182~329℃,盐度介于4.7%~38%(NaCleqv.);石英-碳酸盐阶段包裹体均一温度为124~199℃,盐度介于3.1%~22.4%(NaCleqv.)。上述矿床地质和成矿流体特征表明长岭子铅锌矿为夕卡岩型矿床。成矿流体经历了自夕卡岩阶段高温、高盐度岩浆热液向石英-碳酸盐阶段低温、低盐度大气降水热液的转变。石英-硫化物阶段发育沸腾包裹体组合,表明成矿流体发生了沸腾作用,这可能是成矿物质沉淀的主要机制。

The Changlingzi Pb-Zn deposit in Keshiketeng County,Inner Mongolia,China,was recently discovered in the southern Great Hinggan Range.Ore bodies occur as veins in the Early Permian Dashizhai Formation with skarn alteration.The Early Permian Dashizhai Formation consists of marine intermediateacid volcanic rocks and spilites interbeded with sandstones and slates.Based on the mineral assemblages and crosscutting relations of vein lets,the mineralization process can be divided into four stages（from early to late）：the dry skarn stage,wet skarn-magnetite stage,quartz-sulfide stage and quartz-carbonate stage characterized by the mineral assemblages of garnet±diopside±wollastonite,quartz＋epidote＋tourmaline＋magnetite,quartz＋pyrite±pyrrhotite±chalcopyrite±galena±sphalerite,and quartz±calcite,respectively.Two types of fluid inclusions（FIs）,including aqueous（W-type）and daughter mineral-bearing polyphase（S-type）fluid inclusions,occur in the Changlingzi deposit.And the W-type can be subdivided into the liquidrich（WL-type）and vapor-rich（WV-type）types.The diopside grains contain S-and WL-type FIs.The epidote and quartz grains of the wet skarn-magnetite stage contain WL-,WV-and S-type FIs.Quartzes of the quartz-sulfide stage include all types of FIs.Only WL-type FIs are present in the quartz-carbonate stage quartz±calcite veins.FIs in the diopside were homogenized at 387-524℃,with salinities ranging from 10.7 to 52 wt.%（NaCleqv.）.FIs of the wet skarn-magnetite,quartz-sulfides and quartz-carbonate stages attained homogenization temperatures of 312-533℃,182-329℃,124-199℃ and salinities of 11.3-60,4.7-38 and 3.1-22.4 wt.%（NaCleqv.）,respectively.The above characteristics of ore geology and ore-forming fluids indicated that the Changlingzi Pb-Zn deposit is a typical skarn-type deposit.The ore-forming fluids experienced an evolutionary transformation from the high-temperature,high-salinity magmatic fluids of the skarn stage to the low-temperature,low-salinity meteoric waters of the quartz-carbonate stage.The occurrence of ebullition in the quartz-sulfide stage was recognized as an important mechanism for ore-metals precipitation.