Mineralization Regularity And Ore Genesis Of Duocaima Pb-Zn Deposit In Tuotuohe Area

Duocaima lead-zinc deposit is the new discovered superlarge deposit in Tuotuohe region in recent years.According to the latest report,the orebody reserves of more than 6 million tons,which is believed to have a great prospecting potential.But the controversial ore deposit type and the unknown mineralization enrichment regularity have seriously restrict ore-search breakthrough.So it is necessary to do research comprehensively and deeply,to provide some new information for ore-search in Tuotuohe region.The paper is based on field investigation,combining with the regional geological background of the Tuotuohe area,studying geological characteristics and ore bodies features.The paper study the structural geology,fluid geology and geochemical;ascertain the characteristics and evolution of orebody characteristics,fluid mineralization regularities and the ore genesis.The geotectonic position of Duocaima lead-zinc deposit is in the northeast of the qiangtang block on the Tibetan plateau,among the songpan-ganzi block,the north Lhasa block.The distribution and form of ore boides controls by strucures which stretch NWW.The ore bodies of Duocaima lead-zinc deposit occur in Jiushidaoban Formation,next came Tuotuohe Formation and Wudaoliang Formation,mainly exist in clastic limestone,micrite and siltstone.The vein and lenticular ore bodies are originated in the north of extensional tectonic fracture zone.North-south fault cut off the ore body,causing the difference rise phenomenon.The ore minerals of Duocaima lead-zinc deposit consist mainly galena,sphalerite,pyrite and chalcopyrite,the gangue minerals are mainly composed of calcite,quartz and barite,the structure of the ore is mainly granular structure,cataclastic texture and metasomatic structure.Wall rock alteration mainly have carbonation,silicide and barite,reflecting the characteristics of low temperature liquid alteration.Mineralization can be broadly divided into the following three stages:pyrite quartz-stage,chalcedony-barite-carbonate-galena-stage,carbonate-gypsum stage.Fluid inclusion temperature measurement results show that the ore-forming fluid is in low temperature(108?423.6?),low salinity(1.2?17.1%),low density(0.58 g/cm3?1.03 g/cm3).Temperature,pressure and salinity gradually reduced from morning till night.Atmospheric precipitation participate ore-forming fluid in the late mineralization.Metallogenic pressure range of 9.87?26.03 MPa,metallogenic depth range of 0.99?2.60 km.Carbon and oxygen isotope results show that the fluid originated from deep react with surrounding rock in the process of rising.Sulfur isotopic features indicate that ore-forming fluid mainly come from magmatic hydrothermal and bacteria reduction of the formation of sulfur.Lead isotope results show that the lead has the characteristics of mixed lead,give priority to with shell source lead mixed a small amount of deep mantle source of lead.Basied on the results,Duocaima lead-zinc deposit belong to the vein type deposit in low temperature.The metallogenic time is between 40 to 20M,which is later than the formation of the thrust nappe,and the metallogenic tectonic setting is late collision stage in India-Asian continent.