The rocks in the area are mainly Triassic and/or Jurassic basalt flows with minor argillite, limestone, and tuff, intruded by gabbroic sills (Csejtey and others, 1978 [geologic map]; Full Metal Minerals, 2011). These rocks are intruded by an intrusive complex that consists of plugs and dikes of hornblende diorite and a porphyritic diorite to syenite stock. The intrusive complex is exposed for about 1.2 square kilometers but extends under surficial material to the west; the aeromagnetic data suggest it is much larger. The intrusive complex and surrounding rocks are cut by trachyte, felsic, diorite, and andesite dikes. In their regional mapping, Csejtey, Nelson and others (1978 [geologic map]) did not map an intrusive at this prospect although Tertiary granodiorite and a Cretaceous or Tertiary granite are several miles away.

As described by Csejtey and others (1978 [mineral deposits]), a sulfide-bearing felsic dike cuts Triassic metabasalt at the Grizzly Butte prospect. The sulfide minerals are bornite, chalcopyrite, pyrite, and pyrrhotite. Low-grade sulfide veins and disseminated sulfides also occur in silicified metabasalt. A U.S. Geological Survey sample of mineralized volcanic rock contained 0.5 part per million (ppm) gold; a sample of felsic intrusive rock contained 3 ppm silver and 350 ppm copper (Miller and others, 1978). A U.S. Bureau of Mines grab sample of limonitic metabasalt contains 5.17 percent copper, 0.4 parts per million gold, and 550 parts per million tungsten (Kurtak and others, 1992).

Cities Service Minerals Company held 96 claims over the prospect in 1972 and 1973 and Northland Mines held 18 claims in 1974. Kennecott Exploration staked claims in 1998, carried out rock and stream-sediment geochemical surveys, and flew an aeromagnetic survey over the area. Full Metals Minerals optioned the property from Kennecott in 2010 and staked additional claims (Full Metal Minerals, 2011). They began drilling in August 2010.