Southwest Montana graphite

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

Information leading to the delineation of this focus area

Basis for focus area Multipart focus area composed of graphite mineral sites surrounded by a 5 km buffer. In Robinson and others (2017), two past producers (from north to south) are Black Diamond Carbon Graphitic and Crystal Graphite mine. Black Diamond Carbon Graphitic is listed as flake and Crystal Graphite mine is listed as lump or flake. In MRDS, several additional past producers (United Minerals Co. Mill, Birds Nest Graphite Deposit), prospects, occurrences, and unknowns are listed. Associated with metamorphic rocks in Montana on state geologic map compilation (Horton and others, 2017).
Identified resources Historical production of graphite.
Production The Crystal Graphite mine (lump) began operation in 1902, total production was about 2,200 tons graphite, and no production after 1948 (Cameron and Weis, 1960; Weis, 1963).
Status Past mining.
Estimated resources Unknown.
Geologic maps Raines and Johnson (1996), scale 1:500,000.
Geophysical data Inadequate aeromagnetic and aeroradiometric coverage.
Favorable rocks and structures Shear zones in lower Paleozoic gneiss.
Deposits Black Diamond Carbon Graphitic (MRDS dep_id: 10173269), Crystal Graphite mine (MRDS dep_id: 10070489; USMIN Site_ID: MT00008), Birds Nest Graphite (MRDS dep_id: 10010811).
Evidence from mineral occurrences MRDS; USMIN; Robinson and others (2017).
Geochemical evidence Unknown.
Geophysical evidence Unknown.
Evidence from other sources Unknown.
Comments The Black Diamond graphite deposit is a metamorphosed coal seam at the top of the Morrison Formation, overlain by the Kootenai Formation. The metamorphosed coal seam is black, earthy, internally contorted with numerous metallic-lustered slickensides. The seam is underlain by hard, sheared claystone and overlain by hard, black, shattered and sheared shale and mudstone. At the Crystal Graphite mine, graphite occurs in veins in gneiss and disseminations in pegmatite.
Cover thickness and description Metamorphic and Mesozoic granitic rocks (Horton and others, 2017).
Authors David A. Ponce.
New data needs Re-evaluate deposit, geological mapping, lidar.
Geologic mapping and modeling needs Detailed geologic mapping.
Geophysical survey and modeling needs High resolution aeromagnetic and radiometric coverage. Graphite is unusually highly conductive and magnetotelluric surveys may be useful.
Digital elevation data needs Lidar incomplete.