Abstract: He-Ar isotopic compositions of fluid inclusions trapped in pyrites from some representative PGE-polymetallic deposits in Lower Cambrian black rock series in Southern China were analysed by using an inert gas isotopic mass spectrometer．The results show that the ore-forming fluid possesses a low 3He/4He ratio，varying between 0.43×10-8 and 26.39× 10-8，with an R/Ra value of 0.003～0.189．The 40Ar/36Ar are 258～ 287, closing to that of air-saturated water (ASW)．He-At isotopic indicator studies show that the ore-forming fluid was mainly composed of formation water or basinal hot brine an d spa water，while the content of mantle fluid or deep-derived magmatic water might be neglected ．The PGE-polymetallic mineralization might be related to evolution of Caledonian miogeosynclines distributed along southern margin of the South China Craton．In the Early Cambrian Period，the formation water(basinal hot brine)trapped in the Caledonian basins where accumulated extremely thick sediments was expelled and migrated laterally along strata be cause of the pressure generated by overlying sediments．The basinal ho t brine ascended along faults，mixed with sea water and finally deposited ore minerals．