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

Geologic units in Cook county, Minnesota

North Shore Volcanic Group; Normally polarized volcanic rocks, undivided (Middle Proterozoic) at surface, covers 27 % 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

Logan Intrusions (Middle Proterozoic) at surface, covers 3 % of this area

Logan Intrusions - Diabase, porphyritic diabase, gabbro, and related felsic sills and dikes.

Lithology: diabase; gabbro; felsic volcanic rock

North Shore Volcanic Group; Reversely polarized volcanic rocks, undivided (Middle Proterozoic) at surface, covers 8 % 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

North Shore Volcanic Group; Schroeder-Lutsen basalts (Middle Proterozoic) at surface, covers 2 % of this area

North Shore Volcanic Group; Schroeder-Lutsen basalts - Predominantly ophitic olivine tholeiitic basalt unconformably over older, normally polarized volcanic rocks. Based on its stratigraphic position and geochemical affinities, the unit may be correlative with the Lake Shore traps of northern Michigan

Lithology: basalt

Mafic metavolcanic rocks (Late Archean) at surface, covers 0.8 % 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 0.8 % 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

Metasedimentary rocks, undivided (Late Archean) at surface, covers 0.7 % 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

Duluth Complex; Early gabbros (Middle Proterozoic) at surface, covers 5 % of this area

Duluth Complex; Early gabbros - Gabbro and related rocks in northeastern Minnesota that have petrologic affinities to the Logan Intrusions

Lithology: gabbro

Duluth Complex; Troctolitic and gabbroic cumulate rocks (Middle Proterozoic) at surface, covers 2 % of this area

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

Lithology: troctolite; gabbro

Saganaga Tonalite of northeastern Minnesota (Late Archean) at surface, covers 5 % of this area

Saganaga Tonalite of northeastern Minnesota - Emplaced more-or-less contemporaneously with deposition of metasedimentary and metavolcanic rocks

Lithology: tonalite

Animikie Group; Shale, siltstone, feldspathic graywacke, and associated volcaniclastic rocks (Early Proterozoic) at surface, covers 7 % 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 11 % 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 21 % 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 5 % of this area

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

Lithology: anorthosite; gabbro