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Mineral Resources > Online Spatial Data > Geology > by state > Minnesota Geology

Geologic units in Cass county, Minnesota

North Range Group; Mahnomen Formation (Early Proterozoic) at surface, covers < 0.1 % of this area

North Range Group; Mahnomen Formation - Claystone, shale, siltstone, and graywacke metamorphosed to the greenschist facies

Lithology: claystone; shale; siltstone; graywacke

Mille Lacs Group and related rocks of the Penokean fold-and-thrust belt; Slate, argillite, and metasiltstone metamorphosed to the lower greenschist facies (Early Proterozoic) at surface, covers 0.6 % of this area

Mille Lacs Group and related rocks of the Penokean fold-and-thrust belt; Slate, argillite, and metasiltstone metamorphosed to the lower greenschist facies - Includes lesser amounts of mafic hypabyssal intrusions, and fragmental mafic volcanic rocks

Lithology: slate; argillite; metsedimentary rock; metavolcanic rock

Coleraine Formation (Cretaceous) at surface, covers 4 % of this area

Coleraine Formation - Jasper-pebble conglomerate, sandstone, and shale of diverse origin on the Mesabi range of northern Minnesota, and unnamed sandstone and shale of nonmarine to marine origin in east-central Minnesota

Lithology: conglomerate; sandstone; shale

Mafic metavolcanic rocks (Late Archean) at surface, covers 21 % of this area

Mafic metavolcanic rocks - Dominantly basalt that contains thin sedimentary units, including iron-formation. Includes parts of the Ely Greenstone and the Newton Lake Formation in northeastern Minnesota. Also includes metabasalt exposed in the Minnesota River Valley.

Lithology: basalt; sedimentary rock; iron formation; meta-basalt

Animikie Group; Iron-formation - Iron-formation (Early Proterozoic) at surface, covers < 0.1 % of this area

Animikie Group; Iron-formation - Includes the Gunflint Iron Formation in Cook County and the Biwabik Iron Formation and subjacent units of arenite and conglomerate assigned to the Pokegama Quartzite in Itasca, St. Louis, and Lake Counties. Also includes thin lenses of iron-formation (Remer Member) in the Virginia Formation in Itasca County.

Lithology: iron formation; arenite; conglomerate

Mille Lacs Group and related rocks of the Penokean fold-and-thrust belt; Quartz arenite, siltstone, and chert-rich dolostone of the Trout Lake Formation in Crow Wing County (Early Proterozoic) at surface, covers 0.8 % of this area

Mille Lacs Group and related rocks of the Penokean fold-and-thrust belt; Quartz arenite, siltstone, and chert-rich dolostone of the Trout Lake Formation in Crow Wing County

Lithology: arenite; siltstone; dolostone (dolomite)

Multiphase intrusions of hornblende-pyroxene-bearing and biotite-bearing monzonite, monzodiorite, diorite, syenite, and granodiorite (Late Archean) at surface, covers 4 % of this area

Multiphase intrusions of hornblende-pyroxene-bearing and biotite-bearing monzonite, monzodiorite, diorite, syenite, and granodiorite - Typically postdates regional metamorphism and deformation associated with the Algoman orogen.

Lithology: monzonite; monzodiorite; diorite; syenite; granodiorite

Metasedimentary rocks, undivided (Late Archean) at surface, covers 7 % of this area

Metasedimentary rocks, undivided - Graywacke, slate, local units of conglomerate, arenite, graphitic slate, fine-grained felsic volcanogenic, and volcaniclastic rocks, lean oxide iron-formation and its metamorphic equivalents. Includes the Knife Lake Group and the Lake Vermilion Formation in northeastern Minnesota.

Lithology: graywacke; slate; metasedimentary rock; felsic metavolcanic rock; iron formation

Felsic to intermediate volcanic and volcaniclastic rocks, mica schist, phyllite, and granitoid rocks (Late Archean) at surface, covers 11 % of this area

Felsic to intermediate volcanic and volcaniclastic rocks, mica schist, phyllite, and granitoid rocks - Variably and cataclastically deformed. Unit forms aeromagnetic "quiet zone" and probably contains some rocks of Paleoproterozoic age.

Lithology: felsic volcanic rock; intermediate volcanic rock; schist; phyllite; granitoid

Syntectonic to pretectonic granitoid rocks (Late Archean) at surface, covers 28 % of this area

Syntectonic to pretectonic granitoid rocks - Granite and granodiorite of the Vermilion Granitic Complex, the Giants Range and Bemidji batholiths, as well as smaller intrusions of tonalite and monzonite of the Algoman orogen in northern Minnesota. Also includes the Odessa, Sacred Heart, and Fort Ridgely Granites exposed along the Minnesota River Valley in southwestern Minnesota.

Lithology: granite; granodiorite; tonalite; monzonite

Animikie Group; Shale, siltstone, feldspathic graywacke, and associated volcaniclastic rocks (Early Proterozoic) at surface, covers 23 % of this area

Animikie Group; Shale, siltstone, feldspathic graywacke, and associated volcaniclastic rocks - Includes the Rove Formation in Cook County, the Virginia Formation in St. Louis, Itasca, and Lake Counties, and the Thomson Formation in Carlton County

Lithology: shale; siltstone; graywacke; mixed clastic/volcanic