| 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. |
