1. College of Earth Sciences��Jilin University��Changchun 130061��China; 2. Faculty of Prospecting and Surveying Engineering��Changchun Institute of Technology��Changchun 130021��China

Noble gas isotopic compositions of fluid inclusions in sulfides from Naozhi Cu- - Au deposit were ana- lyzed by using an inert gas isotopic mass spectrometer based on the study of the deposit geology and material compo- sitions of fluid inclusions�� The experimental data show that fluid inclusions in pyrite and chalcopyrite have 3 He/ 4 He ratios of 0. 033 ��0. 104 ��a with an average of 0. 061 ��a�� The 20 Ne/ 22 Ne and 21 Ne/ 22 Ne ratios range in 9. 817 �� 9. 960 and 0. 029 0 ��0. 029 5�� respectively�� which is similar to the composition of the atmosphere�� whereas 40 Ar/ 36 Ar ratios range from 324 to 349 with an average of 341 which are slightly higher than the ratio of air- saturated water (295. 5)�� The 3 He/ 4 He composition of fluid inclusions implies that ore- forming fluid of the Naozhi Cu - - Au deposit was crust- derived��and the mantle- derived He might be neglected�� Except for crustal radiogenic Ar ( 40 Ar* )��at- mospheric Ar was involved in the ore- forming fluids�� The content of the radiogenic Ar varies from 8. 8% to 15. 5%�� averaging 13. 4%�� while the atmospheric Ar is 84. 5% ��91. 2%�� averaging 86. 6%�� Combining with stable isotope data and the chronology of diagenesis and metallogenesis��we suggest that the Naozhi Cu - - Au deposit is a medium- sulphidation epithermal Cu - - Au deposit�� The ore- forming fluids originated from melting of the lower crust�� Minerali- zing fluids were strongly contaminated by meteoric water during ascent��and the mineral precipitation occurred at a shallow crustal level associated with the decrease of temperature and pressure��