Abstract: The source of sulfur is vital to understand the ore-forming process and genesis of IOCG deposits. We summarize the data of sulfur isotope from the Lala deposit in Sichuan Province, and discuss sulfur isotope compositions of sulfide and their sources on the basis of geologic and ore microscopic studies. The large variability in sulfur isotope indicates that the ore-forming sulfur was multi-sourced. The δ34S value of pyrite ranges from -1.4‰ to 4.9‰ with a mean value of 1.8‰ and the δ34S value of chalcopyrite ranges from -5.9‰ to 9‰ with a mean value of 1.5‰. Together with sulfide formation analysis and comparison with some type IOCG deposits worldwide, these data demonstrate that sulfur from seawater evaporate is important to precipitation of pyrite and chalcopyrite. But there is no evidence to support that the variation of sulfur isotope composition is reduced during metamorphism in the Lala deposit.

Key words: sulfur isotope, IOCG deposit, source of sulfur, Lala copper deposit