Graphite in black shales

Region Central, North Central
Mineral systems
Deposit types
Critical minerals
Other minerals

Information leading to the delineation of this focus area

Basis for focus area MRDS records of graphite quarrying.
Identified resources Identified resources and historical production of graphite.
Production Michigan: Quarrying in late 1800s into next century; all closed by 1916; Minnesota: 2 small graphite pits; disseminated graphite of the amorphous type in graywacke.
Status Past mining. Two quarries in Baraga County, Michigan in graphitic slate produced graphite used as paint pigment for battleships; exploration drilling in 1987 by the Michigan Geological Survey and Michigan Technological University.
Estimated resources A ~50 km belt in the lower slate of the Michigamme Formation in Baraga and Marquette counties has more than 3 billion tons of material with carbon contents from 17% to 30% (Taylor, 1988).
Geologic maps Cannon (1986), scale 1:250,000; Jirsa and others (2012), scale 1: 500,000; Miller and others (2001), scale 1:200,000.
Geophysical data Inadequate aeromagnetic and aeroradiometric coverage.
Favorable rocks and structures Minnesota: black slates of the Paleoproterozoic Animikie Group (Rove, Virginia, and Thomson Formations; Michigan/Wisconsin: black slates of the Paleoproterozoic Baraga Group (lower Michigamme Formation). Animikie Group and Baraga Group are time equivalents.
Deposits Detroit Graphite Quarry (MRDS dep_id: 10082848).
Evidence from mineral occurrences MRDS.
Geochemical evidence No data.
Geophysical evidence Black slates are good conductors.
Evidence from other sources No data.
Cover thickness and description Varying glacial cover.
Authors Laurel G. Woodruff.
New data needs New mapping, high resolution geophysics (including EM).
Geologic mapping and modeling needs New 1:24:000 scale mapping in areas of exposure.
Geophysical survey and modeling needs High resolution aeromagnetic and radiometric coverage; EM data.
Digital elevation data needs Lidar adequate over part of focus area, inadequate over others.