Challis fluorspar

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

Information leading to the delineation of this focus area

Basis for focus area Outline of ~20 fluorspar prospects and occurrences associated with the Bayhorse fluorite deposit.
Identified resources Estimated resources for fluorite; historical production of fluorite, lead, and zinc.
Production Byproduct fluorite production from Pb-Zn deposits in the area. Production from the Chalspar No. 1 deposit was 475 tons of metallurgical-grade fluorspar and 245 tons of lower grade material.
Status Historical small-scale mining; no development at the Bayhorse mine (largest fluorspar deposit in the area).
Estimated resources Measured reserves in excess of 3.2 million short tons of 36% CaF2 at the Bayhorse deposit (Snyder, 1978).
Geologic maps Brennan and others (2020), scale 1:24,000; Hobbs and others (1991), scale 1:62,500.
Geophysical data Inadequate Rank 3 to 4 aeromagnetic and Rank 4 aeroradiometric coverage.
Favorable rocks and structures Bayhorse Formation; Garden Creek dolomite; Bayhorse anticline; along faults, in breccia zones.
Deposits Bayhorse fluorite deposit, Keystone mine, Kraken Hill mine (MRDS dep_id: 10071072), Pacific mine (MRDS dep_id: 10071113), Chalspar No.1 mine (MRDS dep_id: 10071073), Chalspar No. 5 prospect (MRDS dep_id: 10071075).
Evidence from mineral occurrences MRDS.
Geochemical evidence Deposits contain fluorite with minor quartz and calcite. Analysis of hand-picked material from the Pacific mine contained 50-60% Pb, 60-80 oz Ag/ton, and 2-3% Zn; some samples had 30-60% CaF2.
Geophysical evidence Unknown.
Evidence from other sources Unknown.
Comments Bayhorse deposit: Metallurgical pilot plant testing indicated that either acid-grade or metallurgical grade spar could be produced (Snyder, 1978). These are hydrothermal replacements of carbonate associated with heat and fluids from the Challis Volcanic Group. Described by Worl and others (1989) as: "Fluorspar breccia manto deposits; formed by hydrothermal solutions reacting with limestone and dolostone in stratiform breccia zones; fluorspar is main commodity, but barite, gold, silver, lead, and zinc are also present. Area of high resource potential is on Keystone Mountain west of Challis.
Cover thickness and description Outcropping stratabound fluorite and vein-type fluorite encountered in drill core throughout the area.
Authors Virginia S. Gillerman, Reed S. Lewis, Christopher A. Tate, Jane M. Hammarstrom, Joshua M. Rosera.
New data needs Geochemical sampling.
Geologic mapping and modeling needs None requested at this time.
Geophysical survey and modeling needs High resolution, Rank 1 aeromagnetic and aeroradiometric coverage.
Digital elevation data needs Lidar in progress.