Fluid Inclusion And Stable Isotopes Study Of Luobuzhen Pb-Zn Deposit In The Gangdese Belt,Southern Tibet

The Luobuzhen Pb-Zn deposit in the western Gangdese is hosted in the dacite of Linzizong Group and porphyritic monzogranite and controlled by fault.The ore minerals consist mainly of pyrite,chalcopyrite,galena and sphalerite,gangue minerals are composed of quartz,sericite and clay mineral etc.There are euhedral-subhedral granular,emulsion,replacement remnant,rimmed and corrugation textures,and disseminated,veined,star point and mass structures.Its ore-forming processes can be divided into early quartz-pyrite stage(Stage ?)and late quartz-polymetallic sulfide stage(Stage ?).Three major types of fluid inclusions are identified in quartzs of Stage ?,i.e.pure gaseous inclusions(components are CO2 or CH4),aqueous inclusions(liquid components are mainly composed of H2O with minor amount of CO2,and vapor components are mainly composed of H2O and CO2)and daughter mineral-bearing inclusions.Types and the corresponding components of fluid inclusions in quartzs of Stage ? are similar to those in quartzs of Stage ?.However,both liquid and gas components of some of the aqueous inclusions in stage? quartzs are H2O.Two types of fluid inclusions are recognized in sphalerite of Stage?,i.e.aqueous inclusions and daughter mineral-bearing inclusions.Their liquid and gas components are dominated by H2O and the daughter mineral is calcite.The inclusions of Stage ? are homogenized at temperatures concentrating at 200?320?with salinities concentrating at 8 to 16 wt%NaCleqv.Inclusions of Stage ? are homogenized at temperatures concentrating at 180?240? and 280?320?,with salinities concentrating at 6 to 12 wt%NaCleqv.The metallogenic fluid is characterized by a H2O-NaCl±CO2 system with medium temperature and medium to low salinity.The ?DH2O values of metallogenic fluid vary from-9‰ to-125‰,while the ?18OH2O values are between 3.9‰ and 6.6‰.These features suggest that the metallogenic fluid was mainly originated from magmatic water.Analysed sulphur-isotope compositions(?34SV-CDT)of sulfide minerals,porphyritic monzogranite and dacite range from-5.1‰ to 0.1‰,from 3.8‰ to 5.5‰,from-2.6‰to 0.9‰,respectively.?34SV-CDT of sulfide minerals are in accordance with the expected fractionation trends(?34Sgalena<?34Schalcopyrite<?34Ssphalerite<?34Spyrite),suggesting that they were form in equilibrium.These isotopic values suggest that magmatic sulphur dominates in sulphides,sulphur was leached from dacite.Lead-isotope compositions of sulfide minerals display a narrow range of values(208Pb/204Pb=39.068?39.560,207Pb/204Pb=15.640?15.785,206Pb/204Pb=18.722?18.849),which define steep linear arrays in conventional isotope plots,it can be invoked by mixing of crustal and mantle sources with distinct Pb isotopes.Immiscibility is the major mechanism for deposition of sulfides.