The Characteristics And Formation Mechanism Of Ore Deposit In Eastern Margin Of Gangdise Metallogenic Belt

BangPu and DongZhongla polymetallic deposits will be chosen and discussed in this paper which as the typical deposits in Gangdise metallogenic belt, and research on fluid inclusion which record a lot of metallogenic information, through testing and computing, comparing other same typical deposits fluid information in this area, to view the ore-forming material sources, ore-forming fluid origin evolution and metallogenic mechanism in different deposits of Gangdise belt, providing a scientific basis for intra-continent orogeny copper polymetallic deposit and lead zinc ore metallogenic model.The stratum mainly exposure in BangPu Mo-Cu polymetallic deposit is lower permian series LuoBadui group (P1l) and palaeogene DianZhongzu group (E1d) in this area, and they contact as faults. Ore body mainly as a hidden and semi-hidden one. The structure of ore is mainly formed by hydrothermal solution metasomatism and crystallization. The composition of ore mineral is rather complex. BangPu Mo-Cu polymetallic deposit has typical alteration zoning characteristics no matter in plane or profile. Epoch of mineralization can be marked off three phases and three stages. BangPu Mo-Cu polymetallic deposit fluid inclusion mainly present as groups, scattered far and wide or many forms. Each ore mineral inclusion type is rather complex. Homogenization temperature range of temperature is 133.7～488.0℃, mineralize stress is low. Salinity of fluid belongs to middle-high and high-medium density fluid, from the early stage of Metallogenic to late stage of sulphide and carbonate minerals content increase successively. Deep source fluid could be as the BangPu Mo-Cu polymetallic deposit ore-forming fluid mainly source. In later period as the evolution of fluid, the proportion of meteoric waters gradually increase, which we can also draw the conclusion by testing He and Ar isotope. Mo migrates in ore-forming fluid mainly as HMoO4- form. From Mo-Cu phase to Pb-Zn phase to Gyp-Cal phase show high to low change rule. The total Cu activity reduces gradually.The stratum mainly exposure in DongZhongla lead and zinc deposit are lower permian series LuoBadui group (P1l) and Quaternary system. The orefield mainly structures are north-west and transmeridional fractures, and exposure mid-acidic intrusive rock. The number of Ⅰ、Ⅱ、Ⅲ、Ⅳ ore body can zone in DongZhongla lead and zinc deposit, and structure of ores mainly formed by hydatogenesis, the deposit metallogenic epochs can be divided into 2 stages and 4 phases.The quantity of Ore deposit inclusion is much, large and types are complete. Inclusion forms are complex. Totally, homogenization temperature of quartz is higher than calcite. Uniform pressure from Ⅰ phase�'Ⅱ phase�'Ⅲ phase has depressed characteristic in total. The deposit ore-forming fluid is low salinity and Low density; the ore-forming process fugacity is reducing gradually. Mineralization environments changed from reducing environment to Weak reduction environment. Sulfide content increased successively; carbonate minerals content reduced successively. In combination with the test values of He,Ar isotope, the fluid in DongZhongla lead and zinc deposit are mainly from meteoric waters and magmatic water combined, meteoric waters is the main source. The hydrochemical type in DongZhongla lead and zinc deposit fluid in Ⅰ�'Ⅱ�'Ⅲ phase, and the evolution is SO42--Cl--K+-Na+ type�'SO42--Cl--Na+ type�'SO42--Cl--Mg2+-Na+ type in total.In the whole stage of mineralization Pb form exists in Pb(HS)20 and PbS(H2S)20, secondly is Pb(HS)3- and PbCl20 form. Zn form exists in Zn(HS)3- and ZnS(H2S)20, secondly is ZnCl3- ZnCl20 and ZnCl+ form.By testing and computing, comparing the other same types deposit fluid information in eastern margin of Gangdise belt. We think fluid inclusion mainly presents as scattered specks and group-distribution, and mostly are in 60μm. The types of inclusion is gas-liquid, a few of them are pure liquid and pure gaseous phase inclusion. The crystal Halite has gas-liquid-solid three phase inclusion in copper mine. The inclusion forms are irregularity, oval and negative form. The range of homogenization temperature in copper ore deposit is large, lead zinc ore inclusion has lower temperature, and range of variation is small. For fluid salinity and density, copper mine is higher than lead zinc ore, range of variation is large, but the pressure is in opposite rightly. Copper deposit and lead and zinc deposit fluid inclusion gas phase composition familiar character in eastern margin of Gangdise belt, that is gas phase composition mostly are H2O, ore-forming fluid combine meteoric waters and magmatic water, meteoric waters is mostly. liquid phase ingredient characteristic show that copper types deposit ore-forming fluid mainly are SO42--Cl--K+-Na+, lead and zinc deposit type mainly are SO42--Cl--Na+.