Tin ores of the Deputatskoye deposit (North-East Yakut ASSR) were formed during five stages: quartz-tourmaline, cassiterite-silicate-quartz, quartz-sulfide, quartz-carbonate-sulfide and carbonate. Cassiterite was isolated from solutions of all stages, but its main mass appeared in the second stage in close association with vein quartz, tourmaline, fluorite, chlorite and wolframite. Cassiterites of the second (main productive) stage were the subject of our study.