Characteristics Of Mineralizing Fluids And Fluid Evolution Of Dabu Porphyry Copper Molybdenum Deposit In Tibet

The Dabu porphyry copper-molybdenum deposit,a large deposit,is formed by continents collision.Its geotectonic position is in the south of the middle Gangdise magmatic rocks belt,30,000 meters close to the south of yarlung zangbo river sature zone.This thesis studied mineralization geological background,ore types,character and structure of ore mineral,wall rock alterations and fluid inclusion,examined the source of mineralizing fluid and the evolution process and dealt with the metallogetic potentiality of porphyry by the methods of fluid inclusion petrography,homogenization temperature and laser Raman analysis.The following conclusions were found.The alterations Dabu ore body have incomplete annuluses on the surface,circled by potassium zone,silicified zone,chlorite-sericite zone and the propylitic zone from center to outside.The strike of the orebody is from north to west.The copper molybedenum mineralization is mainly controlled by the developmental degree of fracture and joint in the rock.The high density of the fracture and joint development has a tendency of better mineralization.The orebody is mainly occurred in the contact zone between granite porphyry and wall rock-granodiorite.The structure of ores is mainly made of subhedral-xenomorphic granular.Its textures are consisted of sta-disseminate,veinlet-disseminated and veinlet,stockwork and breccia.The ores include pyrite as major metal minerals,and chalcopyritef chalcopyrite,bornite,molybdenite as minor ones.The content of ore minerals is accounted for 5%around in the ores.There are mainly five categories of fluid inclusions,namely H₂0-NaCl inclusion size?W?,H₂O and CO₂ inclusion size?C?,Daughter mineral bearing inclusions in aqueous solution?S?,Pure gas phase inclusions?P?and Magma inclusions.Characteristics of inclusions reveal that the mineralizing fluid comes from the porphyry not granodiorite.The mineralizing fluid evolves from the early magmatic hydrothermal,with high temperature and salinity,to the mineralizing one with medium temperature and salinity.In addition,boiling and adiabatic cooling have occurred in the evolution process.Meanwhile,the studies have showed there exists a close relationship between the precipitation of mineralizing materials and fluid boiling.