The country rocks on southeastern Gravina Island are Upper Jurassic or Cretaceous marine andesitic or basaltic volcanic rocks that are gradationally interbedded with subordinate flyschlike sedimentary rocks (Berg, 1973; Berg and others, 1988). The strata were regionally metamorphosed to greenschist-grade phyllite and semischist in Late Cretaceous time. The country rocks are cut by intermediate or mafic dikes that apparently postdate the regional metamorphism.Wright and Wright (1908, p. 179) describe the deposit as two parallel 'veins' that strike northwest, parallel to the foliation of altered greenschist hostrock. They do not describe the ore minerals, but the deposits probably contain basemetal sulfides and were prospected in the early 1900s chiefly for gold. The deposits are 6 and 18 feet thick and are separated by 50 feet of relatively barren rock. Although Wright and Wright do not mention quartz at the Moonshine, Elliott and others (1978) infer that the deposits are quartz veins. However, Wright and Wright's description, the geologic setting of the Moonshine prospect, and its proximity to other lode deposits on southeastern Gravina Island (KC073, 074), suggest instead that the Moonshine is mainly a stratiform deposit, comprising sulfide bands or disseminations parallel to the foliation of the schist hostrock. If so, the Moonshine may be a metamorphosed Besshi massive sulfide deposit of Late Jurassic age.