Alteration Zoning And Geochemical Elements Migration Characteristics Associated With Sinongduo Ag-Pb-Zn Deposit,Tibet

The tectonic location of the Sinongduo Ag-Pb-Zn deposit is located on the arc fault uplift belt in the southern margin of the Gangdise metallogenic belt,Tibet.It is occurred in the Linzizong volcanic rocks.The method of shortwave infrared and rock geochemical survey was comprehenly used in the research,measurement of the typical drill holes in the different types of orebody in the mining area,determined alteration combination charactics,Systematic analysised of the migration characteristics of elements during alteration,explored mineralizational medanism.In the field through drill hole cataloguing found that the orebody was strongly silicified,and cryptocrystalline,quartz veins and quartz in different occurrence states in the form of quartz aggregate were found in the drill hole.According to the two metallogenic mechanisms of volcanism and hydrothermal fluid in the mining area,the orebody in the mining area are also divided into two main types: cryptoexplosive breccia type and hydrothermal vein type.The author choose two different ore-forming mechanism under typical drill hole BZK0022 and BZK0101 carried on the detailed field logging,found under the influence of volcanism,drill hole BZK0022 occurrence of orebody and cryptoexplosive breccia formation of the breccia,is close to the size of the orebody mainly occurs in the breccia 1-3 cm in size of cryptoexplosive breccia,breccia progressively smaller size to the periphery of the process,the orebody pinchout and thus determine the detonation center position,breccia,size distribution and formation has a close relationship between the ore bodies,There is no obvious hidden explosion breccia in the hydrothermal vein type ore body,and the ore body is mainly found in the rhyolite porphyry.Short-wave infrared measurement results show that the main alteration minerals developed in the mining area are sericite,illite and montmorillonite.However,under different mineralization mechanisms,the three main altered minerals have significant differences in spatial location and content.The altered mineral assemblage of cryptoexplosive breccia type ore body from top to bottom is as follows: Sericite ?Sericite + Illite?Sericite?Sericite + Illite + Montmorillonite?Sericite?Sericite + Illite + Montmorillonite ?Sericite?Sericite + Illite?Sericite?Sericite + Illite ?Sericite?Illite + Montmorillonite;The alteration mineral assemblage of hydrothermal vein type ore body from top to bottom is as follows: Sericite + Illite + Montmorillonite ?Sericite?Sericite + Illite?Sericite?Sericite + Illite?Sericite + Illite?Sericite + Illite?Sericite?Sericite + Illite?Sericite?Sericite + Illite?Sericite?Sericite + Illite?Sericite?Sericite + Illite?Sericite?Sericite + Illite? Sericite?Sericite+Illite?Sericite.In drilling BZK0022,there are relatively few montmorillonite minerals,mainly illite.In BZK0101,a large amount of montmorillonite is contained in the borehole.It is speculated that the sericite formed by hydrothermal action is affected by external precipitation irrigation,and Tschermak reaction occurs to form a large amount of sodium mica,and a large amount of altered mineral assemblage of sodium mica + montmorillonite is formed on the top of the borehole.There is relatively little sodium mica in the wall rock alteration minerals of the cryptoexplosive breccia type ore body,and a large amount of illite may be produced by fluid metasomatic crystalline tuff,or it may be a reaction of illite montmorillonite.Different geochemical elements in rocks have different migration characteristics in each alteration zone,which reflects certain regular changes in spatial distribution and combination of elements,indicating that the changes of metallogenic environment such as temperature,pressure,pH value and oxidization-reductivity have certain influence on the occurrence of ore bodies during the formation process.Comprehensive analysis of the mining area of surrounding rock alteration mineral assemblages,rock geochemical characteristics,combined with the analysis of the existing fluid inclusions in the mining area,think,get more silver lead-zinc mine bed early in the hydrothermal mineralization period of ore-forming fluid contains a large amount of Ag,Pb,ore-forming elements such as zinc,low salinity,low density,low pressure,low temperature characteristics.Among them,the changes of Cu and Mo migration also indicate that the fluid comes from deep hydrothermal fluid,which is completely different from the ore body under the volcanism mechanism.The mineral association characteristics of illite and montmorillonite in the mining area,as well as the formation of a large amount of sodium mica fully explain the miscibility mechanism of deep hydrothermal fluid and atmospheric precipitation,and further elaborate the formation mechanism of epithermal deposits.