Fluorspar Deposits Near Meyers Cove, Lemhi County, Idaho

The fluorspar deposits near Meyers Cove, Lemhi County, Idaho, are localized along three groups of shear zones: one group strikes northeast and dips steeply northwestward, another strikes northeast and dips gently northwestward, and the third strikes northwest and dips gently southwestward. The country rocks are tuffs and flows of the Casto volcanics of Permian (?) age and the Challis volcanics of late Oligocene or early Miocene age. The known deposits are in a belt about 3 miles long and 2 miles wide and crop out at altitudes between 5,100 feet and 7,200 feet above sea level. The principal vein minerals are fluorite, chalcedony, and barite. The fluorite occurs as lodes, crusts around fragments of rock, and replacements of fine breccia. The lodes range in size from veinlets to vein zones several hundred feet long and as much as 20 feet wide and contain ore that ranges in grade from 40 percent to 85 percent CaF2; the average grade is about 50 percent CaF2.