| The west ore district of Barendaba(i.e.Bairen ore district) is located in the silver polymetallic metallogenic belt of the west slope of Greater Khingan Mountains,where the ore deposit is super large hydrothermal type silver polymetallic deposit. By doing the research about geological characteristics and geochemical characteristics of rock and deposit in the Bairen ore district,the main understanding can be achieved:(1) Research has shown that,by using technical means such as basic geological data analysis,field geological investigation,polished and thin section microscopic observation,etc.,EW-trending compresso-shear faul is the main ore control structure,and the main orebodies are formed within the faults in the direction of EW;quartz diorite and biotite plagioclase gneiss are the main ore-bearing wall rocks.Ore types are mainly primary sulfide ores,and ore textures are mainly automorphic, hypidiomorphic, xenomorphic, metasomatic, cataclastic, emulsion and milk drop.Ore structures are mainly block,disseminated,vein,stockwork,breccia and gelatineous.(2) Geochemical study of the rock indicates that quartz diorite belongs to poor-K calc-alkaline series.It is obviously rich in LILE such as Rb,Ba and U,etc.,and poor in HFSE such as Nb,Ta,Zr and Hf,etc.;these results suggest that there is less influence of mantle source material in the process of formation and evolution of quartz diorite,which probably comes from partial melting of the lower crust.At the same time,quartz diorite is rich in light rare earth elements and has positive anomaly of U parameters,which suggests there is maybe cumulate plagioclase during the process of magma evolution. Biotite plagioclase gneiss is rich in K,and its protolith is mainly sedimentary rock(the sedimentary rock is probably sandstone) which is maybe mixed with some volcaniclastic rocks.(3) The studies of H,O isotope and fluid inclusions suggest that the ore forming process has a continuous evolution from high temperature to low temperature,and mineralization is mainly in the middle and low temperature range.The ore-forming fluids come from magmatic water and meteoric water.During the main metallogenic epoch,it is mainly magmatic water,and during the later period,it is mainly meteoric water. Pressure and depth decrease gradually from the early stage to the late stage of mineralization.The resault reflects that the direction of fluids move to the shallow part,and the fluieds are sedimented and Enriched in suitable tectonic environment such as along the fracture zones and fracture.That means the metallogenic system may be gradually transformed from closure to open.The study of sulfur isotope indicates that ?34S is close to zero.That means the sulfur mainly comes from magma. The Pb isotopic is related to the intrusion of granite in Yanshan, which is concealed in the deep part or the periphery of the mining area.(4) Combining regional tectonic setting,metallogenic epoch and characteristics of fluid geochemistry,we think the ore deposit in the west ore district of Barendaba is a medium-low temperature hydrothermal type deposit,which is formed in Yanshanian period,controlled by fault structures,and related to magmatic hydrothermal fluids.Some geological features,geophysical and geochemical characteristics can be used as important prospecting marks in the ore district. There may be some concealed orebodie buried deeply in the north of ore district.This area can be regarded as the key area of the next step prospecting work,and it has great potential for looking for high temperature mineral elements such as W and Sn. |
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