Tin ores of the Deputatskoye deposit (northeastern Yakut ASSR) were formed during five stages: quartz-tourmaline, cassiterite-silicate-quartz, quartz-sulfide, quartz-carbonate-sulfide, and carbonate. Cassiterite was deposited from solutions of all stages, but its main mass was formed 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.