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

Geologic units in Saint Louis county, Minnesota

[Additional scientific data in this geographic area]

Syntectonic to pretectonic granitoid rocks (Late Archean) at surface, covers 17 % 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

Duluth Complex; Troctolitic and gabbroic cumulate rocks (Middle Proterozoic) at surface, covers 8 % of this area

Duluth Complex; Troctolitic and gabbroic cumulate rocks - Constitute at least nine named and several unnamed intrusions

Lithology: troctolite; gabbro

Bayfield Group; Orienta Sandstone (Middle Proterozoic) at surface, covers < 0.1 % of this area

Bayfield Group; Orienta Sandstone - Poorly sorted arkosic sandstone

Lithology: arkose

Metasedimentary rocks, undivided (Late Archean) at surface, covers 9 % 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

Paragneiss, schist, and amphibolite (Late Archean) at surface, covers 1 % of this area

Paragneiss, schist, and amphibolite - Amphibolite-facies equivalent of units Amv and Ams; locally includes abundant intrusions of unit Agr.

Lithology: paragneiss; schist; amphibolite

Fond du Lac Formation (Middle Proterozoic) at surface, covers < 0.1 % of this area

Fond du Lac Formation - Red to dark-brown shale, feldspathic sandstone, and arkose of fluvial origin. Includes the Oldenberg Point Member, a pronounced basal unit of quartz-pebble conglomerate in the Duluth area.

Lithology: shale; sandstone; arkose; conglomerate

Animikie Group; Shale, siltstone, feldspathic graywacke, and associated volcaniclastic rocks (Early Proterozoic) at surface, covers 29 % 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

Duluth Complex; Felsic series (Middle Proterozoic) at surface, covers 0.2 % of this area

Duluth Complex; Felsic series - Granophyric granite and related felsic rocks

Lithology: granite

Subvolcanic mafic rocks, undivided; Beaver Bay Complex and other named and unnamed gabbroic-troctolitic intrusions (Middle Proterozoic) at surface, covers 1 % of this area

Subvolcanic mafic rocks, undivided; Beaver Bay Complex and other named and unnamed gabbroic-troctolitic intrusions - Includes a number of other intrusions in a variety of dikes and sills such the Endion sill and the Pigeon River intrusions.

Lithology: gabbro; troctolite

Duluth Complex; Anorthositic series (Middle Proterozoic) at surface, covers 3 % of this area

Duluth Complex; Anorthositic series - Plagioclase-rich gabbroic cumulates and related rocks

Lithology: anorthosite; gabbro

Paragneiss and schist-rich migmatite (Late Archean) at surface, covers 6 % of this area

Paragneiss and schist-rich migmatite - Grades into undivided metasedimentary rocks (unit Ams).

Lithology: paragneiss; migmatite

Mixed metavolcanic rocks (Late Archean) at surface, covers 1 % of this area

Mixed metavolcanic rocks - Mafic to felsic volcanic sequences that have variable amounts of felsic volcanogenic and volcaniclastic rocks and lean iron-formation. Includes parts of the Ely Greenstone and the Soudan Iron-formation in northeastern Minnesota.

Lithology: mafic metavolcanic rock; felsic metavolcanic rock; iron formation

North Shore Volcanic Group; Reversely polarized volcanic rocks, undivided (Middle Proterozoic) at surface, covers < 0.1 % of this area

North Shore Volcanic Group; Reversely polarized volcanic rocks, undivided - Mixed tholeiitic diabasic and porphyritic basalt, trachybasalt, and rhyolite in far northeastern Minnesota and porphyritic and diabasic basalt near Duluth. Includes units of a basal quartz arenite, Puckwunge Sandstone and Nopeming Formation, in northeastern Minnesota and near Duluth, respectively.

Lithology: basalt; trachybasalt; rhyolite; arenite; sandstone

Granite-rich migmatite (Late Archean) at surface, covers 13 % of this area

Granite-rich migmatite - Granitic gneiss, paragneiss, schist, and migmatite in the Vermillion Granitic Complex, and other parts of extreme northern Minnesota. Grades into granitoid rocks.

Lithology: gneiss; schist; migmatite

North Shore Volcanic Group; Normally polarized volcanic rocks, undivided (Middle Proterozoic) at surface, covers 2 % of this area

North Shore Volcanic Group; Normally polarized volcanic rocks, undivided - Basalt, andesitic basalt, rhyolite and related volcanogenic interflow sedimentary rocks along and inland from the North Shore of Lake Superior.

Lithology: basalt; rhyolite; clastic

Coleraine Formation (Cretaceous) at surface, covers 1 % 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

Animikie Group; Iron-formation - Iron-formation (Early Proterozoic) at surface, covers 2 % 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

Multiphase intrusions of hornblende-pyroxene-bearing and biotite-bearing monzonite, monzodiorite, diorite, syenite, and granodiorite (Late Archean) at surface, covers 1 % 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

Gabbro, diorite, peridotite, and associated komatiitic flows of the Deer Lake sequence in Itasca County and the upper part of the Newton Lake Formation in Lake and St. Louis Counties (Late Archean) at surface, covers 0.1 % of this area

Gabbro, diorite, peridotite, and associated komatiitic flows of the Deer Lake sequence in Itasca County and the upper part of the Newton Lake Formation in Lake and St. Louis Counties

Lithology: gabbro; diorite; peridotite; ultramafitite (komatiite)

Mafic metavolcanic rocks (Late Archean) at surface, covers 3 % 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