Coeur d'Alene Mining District (Silver Valley antimony)

Region West, Northwest
Mineral systems
Deposit types
Critical minerals
Other minerals

Information leading to the delineation of this focus area

Basis for focus area Focus area for the greater Coeur d'Alene mining district in Idaho and Montana encompasses an area with MRDS records for silver+tetrahedrite and antimony+stibnite as well as areas with potential for mesothermal polymetallic veins in the Wallace 2 degree sheet (Harrison, Leach and Kleinkopf, 1986).
Identified resources Historical production of antimony, cadmium, cobalt, copper, lead, silver, and zinc.
Production The Coeur d'Alene district has produced about 34 000 t Ag, 7.2 Mt Pb, 2.8 Mt Zn, 15 t Au, and smaller amounts of Sb and Cd (Leach and others, 1998; Long 1998). Sunshine mine produced >10,000 t Ag and byproduct Sb (from Ag-rich tetrahedrite); Sb recovery ceased in 2001 (Carlin, 2003). Cobalt recovered from Zn concentrates.
Status Past and current mining. Active exploration in Idaho in main Coeur d'Alene district at two operating mines. Includes discovery of new tetrahedrite-bearing veins (Gillerman, on Idaho Geological Survey, 2020).
Estimated resources Unknown.
Geologic maps Lewis and others (2002), scale 1:100,000; Lewis and Derkey (1999), scale 1:100,000; Hobbs and others (1965), scale 1:24,000; Derkey and others (1996), scale 1:62,500.
Geophysical data See: U.S. Geological Survey (1969), scale 1:62,500.
Favorable rocks and structures Idaho: The richest tetrahedrite veins are in the Sunshine mine hosted in the Revett-St. Regis Formations. Montana: In the Belt Supergroup antimony veins are restricted to upper parts of the Prichard Formation. The US Antimony deposit is located on the north side of a major east-west-trending wrench fault system (the Lewis and Clark line). The quartz-stibnite veins occur near the contact between quartzite and phyllite in the uppermost Prichard Formation. The veins can be as large as 1 km long and 1 m wide and contain 60 percent stibnite; accessory sulfide minerals include arsenopyrite, pyrite, sphalerite, and chalcopyrite (Hofstra and others, 2013a).
Deposits Idaho: Sunshine mine (MRDS dep_id: 10241626; USMIN Site_ID: ID00050) (also antimony veins as tetrahedrite at Galena, Coeur and Lucky Friday mines); Montana: US Antimony mine (Stibnite Hill mine, MRDS dep_id: 10070483).
Evidence from mineral occurrences MRDS; USMIN.
Geochemical evidence See: Gott and Cathrall (1979), Harrison, Leach and Kleinkopf (1986), Leach (1989).
Geophysical evidence Unknown.
Evidence from other sources Unknown.
Comments Within the Coeur d'Alene (CDA) district, Sb occurs in tetrahedrite and stibnite. Polybasite, pyrargyrite, bournonite, meneghinite, boulangerite, and jamesonite reported on levels of a few mines below the zone of oxidation. Antimony also contained in galena. After galena and sphalerite, tetrahedrite is the third most abundant ore mineral and, therefore, constitutes the most important Sb source within the district. Five samples, mostly from the Sunshine mine, show that Sb in Coeur d'Alene tetrahedrite probably ranges between 20 and 30% (Fryklund and Weis, 1964, p. 18). US Antimony mine (closed in 1983) is a simple quartz-stibnite vein deposit; the second largest US example after Yellow Pine mine in Idaho. Mineral system for CDA has Sb as critical mineral plus world-class production of Ag, Pb, and Zn from quartz-siderite-sulfide veins hosted in Precambrian Belt metasedimentary rocks. Base metals and unknown amount of Ag and Sb probably enriched in Proterozoic stratiform syngenetic mineralization with vein formation and likely addition of Sb during Cretaceous metamorphism and deformation. Antimony in tetrahedrite is byproduct of Ag and Cu production. For the CDA Sb and As are only critical commodities. Two large operating mines in CDA plus exploration work. No current Sb production but tetrahedrite is in resource.
Cover thickness and description Unknown.
Authors Albert H. Hofstra, Virginia S. Gillerman, Reed S. Lewis, Christopher A. Tate, Jane M. Hammarstrom.
New data needs Compilation of information from current mine operators in the Coeur d'Alene district for tetrahedrite veins, geologic mapping, high resolution geophysics, lidar.
Geologic mapping and modeling needs No mapping at larger scale than 1:100:000 scale available.
Geophysical survey and modeling needs High-resolution, Rank 1 aeromagnetic and aeroradiometric surveys.
Digital elevation data needs Lidar in progress over part of the focus area; not available in the rest.