The Won prospect was investigated by the Bureau of Mines in July 1989 and June 1990 as part of an ongoing investigation of the tin resources potential in Alaska. The Won prospect is located 40 miles north of McGrath, Alaska. The tin deposits at the Won Prospect are associated with several northwest-trending, moderately dipping breccia-vein structures developed in tourmaline- and quartz-altered hornfels. Tin occurs in brecciated hornfels with cassiterite matrix, as cassiterite druse on fracture surfaces of open-spaced, crackle breccia, and as disseminated grains in quartz veins containing minor silver, arsenic, copper, antimony, and zinc values. Based upon limited sampling, an estimated combined tin resource of approximately 25.3 M lb tin is indicated for two of the principal breccia structures at the Won Prospect--the Dog Day and south veins. Additionally, 7,700 linear feet of tin-mineralized breccia vein structure can be estimated from projections of other individual breccia vein occurrences.