Archean gneiss terranes

Region Central, North Central
Mineral systems
Deposit types
Other minerals

Information leading to the delineation of this focus area

Basis for focus area Archean gneiss terrane of the Southern Complex (Wisconsin/Michigan) and the Minnesota River Valley terrane (Minnesota). Minnesota: bedrock constrained by the Great Lakes Tectonic Zone north) and the Spirit Lake discontinuity (south), and the Midcontinent Rift System (east); Michigan/Wisconsin: bedrock bounded by the Great Lakes Tectonic Zone (north) and Niagara fault zone (south), and the Midcontinent Rift System (east and west).
Identified resources Unknown.
Production Unknown.
Status Unknown.
Estimated resources Unknown.
Geologic maps Jirsa and others (2012), scale 1: 500,000; Cannon and Ottke (1999), compilation scale 1:100,000.
Geophysical data Adequate aeromagnetic coverage in Minnesota, inadequate elsewhere; inadequate aeroradiometric coverage.
Favorable rocks and structures Archean granites with some known pegmatites, also some Paleoproterozoic granites.
Deposits No data.
Evidence from mineral occurrences Reported occurrences of enrichment in LREE and HREE, as well as Ta and F in pegmatites.
Geochemical evidence No data.
Geophysical evidence No data.
Evidence from other sources No data.
Comments No reported mineralization, but rock type is permissive for possible critical mineral deposits.
Cover thickness and description Some surface exposures; glacial cover (<50 m).
Authors Benjamin J. Drenth, Klaus Schulz.
New data needs New mapping, high resolution geophysics.
Geologic mapping and modeling needs Need new geologic mapping.
Geophysical survey and modeling needs Need aeromagnetic, radiometric, and gravity data collection.
Digital elevation data needs Lidar adequate.