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

Geologic units in Mille Lacs county, Minnesota

Late-tectonic intrusions of the Penokean orogen (Early Proterozoic) at surface, covers 35 % of this area

Late-tectonic intrusions of the Penokean orogen - Includes the St. Cloud and Rockville Granites and Reformatory granodiorite of east-central Minnesota, the Section 28 granite, the Cedar Mountain Complex, and other unnamed intrusions exposed along the Minnesota River Valley in southwestern Minnesota

Lithology: granite; granodiorite

Unnamed schistose, volcanic, and hypabyssal rocks of mafic composition and volcanic, volcaniclastic, and intrusive rocks of felsic composition (Early Proterozoic) at surface, covers 11 % of this area

Unnamed schistose, volcanic, and hypabyssal rocks of mafic composition and volcanic, volcaniclastic, and intrusive rocks of felsic composition - May be correlative with rocks of the Wisconsin magmatic terranes.

Lithology: schist; felsic volcanic rock; mafic volcanic rock

Denham Formation (Early Proterozoic) at surface, covers 0.1 % of this area

Denham Formation - Quartz arenite and siltstone, oxide iron-formation, marble, mafic hypabyssal intrusions and fragmental volcanic rocks metamorphosed to the staurolite grade of the amphibolite facies

Lithology: sandstone; siltstone; iron formation; marble; metavolcanic rock

Syntectonic intrusions of the Penokean orogen (Early Proterozoic) at surface, covers 5 % of this area

Syntectonic intrusions of the Penokean orogen - Includes the Pierz Granite, the Freedhem and Bradbury Creek Granodiorites, and several unnamed intrusions of granite, granodiorite, tonalite, and gabbro in east-central Minnesota

Lithology: granite; granodiorite; tonalite; gabbro

Mille Lacs Group and related rocks of the Penokean fold-and-thrust belt; Metagraywacke, metasiltstone, and a variety of schistose rocks metamorphosed to the amphibolite facies (Early Proterozoic) at surface, covers 0.4 % of this area

Mille Lacs Group and related rocks of the Penokean fold-and-thrust belt; Metagraywacke, metasiltstone, and a variety of schistose rocks metamorphosed to the amphibolite facies

Lithology: metasedimentary rock; schist

Upper Cambrian, undivided (Late Cambrian) at surface, covers 2 % of this area

Upper Cambrian, undivided - Jordan Sandstone; dolomite, glauconite, and silty glauconite rocks of the St. Lawerence and Franconia Formation; Ironton and Galesville Sandstones; sandy and shaly rocks of the Eau Claire Formation; and the Mt. Simon Sandstone.

Lithology: dolostone (dolomite); sandstone; shale

Migmatitic gneiss, amphibolite, and granite (Middle to Early Archean) at surface, covers 32 % of this area

Migmatitic gneiss, amphibolite, and granite - Montevideo and Morton Gneisses (3600-3000 m.y.) in the Minnesota River Valley, southwestern Minnesota; McGrath Gneiss (2750 m.y.) east of Mille Lacs Lake; components of Hillman Migmatite southwest of Mille Lacs Lake; and Sartell Gneiss in Stearns County. Inferred to include various younger rocks, including granitoid intrusions in the Hillman Migmatite and pillowed basalt in poorly exposed areas of southwestern Minnesota.

Lithology: gneiss; amphibolite; granite; basalt