Note on the First Discovery of Vanadinite in Idaho¹

Vanadinite was discovered by the writer in a small prospect near the tunnel of the Iron Mask Mine in the Spring Mountain Mining District, Lemhi County, Idaho. This is the first reported occurrence of vanadinite in Idaho. It occurs as yellow-brown tabular crystals 2 millimeters wide and ½ millimeter thick in clusters on manganiferous limonite. All of the crystals are hexagonal prisms with base and first order pyramidal faces well developed. The mineral was identified by qualitative wet methods. The Iron Mask Mine is owned by William Clark, of Gilmore, Idaho, and was at one time in operation for its lead-silver values. The rocks of the Spring Mountain Mining District are described by Umpleby² as being late Devonian or early Carboniferous sedimentary rocks which were mineralized in late Cretaceous or early Eocene time. The vein of the Iron Mask Mine is in blue-gray limestone and is probably a contact phenomenon caused by one of the numerous quartz diorite intrusions.