| Weilasituo Pb-Zn deposit,situated in Baiyinchagan,Chifeng City,Inner Mongolia,is developed in the western slope of the southern Great Xing'an Range(SGXR).Based on the previous studies,the geological characteristics of Weilasituo Pb-Zn deposit are summarized and the characteristics of the fluid inclusions are studied in detail.By studying the petrography,thermodynamics and geochemical properties of the fluid inclusions,the origin of the ore-forming fluids,geochemical characteristics and evolution of ore-forming fluids are discussed,and the genesis of deposits is summarized in this thesis.The mining area is relatively simple in terms of the exposed strata,mainly Baoyintu group,a small amount of Carboniferous quartz diorite and widely developed Quaternary.The structural features in the study area are distinctively controlled by the regional tectonic,folds and faults are developed,and it is obvious that the ore bodies are controlled by the faults.The main ore body is strictly controlled by the east and west direction "S" type pressure-torsional fault.The magmatic rocks in the mining area are mainly intrusive rocks and the Carboniferous quartz diorite veins.According to the ore-body structures,ore structures and paregenetic association of minerals,the hydrothermal mineralization of Weilasituo Pb-Zn deposit can be divided into three stages:? quartz-arsenopyrite-pyrite stage;? polymetallic sulphide-quartz stage;? quartz-carbonate stage.Through the analysis of the type and distribution of alteration,there are many types of wall rock in Weilasituo Pb-Zn deposit.The common alteration types of surrounding rock of mesothermal deposits can be found in the deposit,such as silicification,choritization,beresitization,kaolinization,etc.,of which silicification and choritization are related to ore formation.Systematic study on fluid inclusions reveals that there are three types of primary fluid inclusions existed in the ores,which are two-phase aqueous,CH4 rich and CH4-CO2 bearing fluid inclusions,respectively.Homogenization temperatures of fluid inclusions in Stage ? ranges from 243.1? to 398.5?,with salinities of 4.8% ~12% NaCleqv;for stage ?,homogenization temperatures decrease to 190.0?~331.1?,salinities change to3.5%~9.1 % NaCleqv and those in stage ? have homogenized at temperature of 180.0?~240.0 ?,with salinities of 3.7%~6.7 % NaCleqv,which yield characteristics of intermediate temperate and low salinity.The analytic results through Laser Laman Spectroscopy suggest that the gas phases are rich in CH4,CO2 and H2 O.The analytic results from H,O isotope indicate that the mineralizing fluids derived from magmatic water and accompanied with participation of meteoric water.Based on the analysis of sulfur,lead and canbon isotopes in sulfide,it is believed that the ore-forming materials are mainly from magma.Weilasituo ?34S is mainly concentrated in the vicinity of 0,which is consistent with the characteristics of magmatic sulfur,so that the mineralization materials has a deep source characteristic;Weilasituo ore lead isotope projection points are in the orogenic belt growth line or below the trend line,which is considered to be a feature of the orogenic model,which imply that the ore lead is derived from the mantle or lower crust,and has the characteristics of the mixed source of each repository.The ?13C in ores ranges from-19.7‰~-19.1‰,which between magmatic CO2 and reduced carbon in sedimentary or metamorphic rocks.It is believed that this is the result of a mix source.Weilasituo Pb-Zn deposit is a typical mesothermal vein deposit,combined with the tectonic evolution history of the Early Cretaceous in the southern part of the Great Xing'an Range,we can conclude that in the orogenic environment magma genuine from the mantle(lower crust)magma differentiation,and the process of continuous invasion with the surrounding rock when the raised along the fracture structure of the cracks,than formed mineral hydrothermal fluids.The meteoric water joint in the later stage,and the organic matter such as CH4 was generated during the reaction.With the change of the external conditions such as the temperature and pressure,the ore-forming elements in the ore-bearing hydrothermal fluids were enriched in the mineralization area. |
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