Geologic units in Koochiching county, Minnesota

Additional scientific data in this geographic area

Biotite schist of graywacke protolith, and schist-rich migmatite (Neoarchean) at surface, covers 54 % of this area

Biotite schist of graywacke protolith, and schist-rich migmatite.

Mafic metavolcanic rocks (Neoarchean) at surface, covers 10 % of this area

Mafic metavolcanic rocks. Includes minor volcaniclastic and hypabyssal intrusive rocks metamorphosed to lower greenschist to lower amphibolite facies; includes the Ely Greenstone (~2,722 Ma).

Granite-rich migmatite (Neoarchean) at surface, covers 8 % of this area

Granite-rich migmatite. Contains neosome of variably magnetic biotite granite similar to the Lac La Croix Granite, and paleosome of tonalite to granodiorite gneiss and schist.

Volcaniclastic rocks of felsic to intermediate composition (Neoarchean) at surface, covers 7 % of this area

Volcaniclastic rocks of felsic to intermediate composition.

Foliated to gneissic tonalite, granodiorite, and diorite (Neoarchean) at surface, covers 7 % of this area

Foliated to gneissic tonalite, granodiorite, and diorite. Includes the Lookout Mountain tonalite (~2,718 Ma) of the Giants Range batholith and other intrusions within batholithic complexes defined by a low-to-moderate gravity signature with magnetic foliation apparent from aeromagnetic maps.

Granodiorite to hornblende diorite, locally magmatically foliated (Neoarchean) at surface, covers 4 % of this area

Granodiorite to hornblende diorite, locally magmatically foliated. Includes the Britt Granodiorite (~2,685 Ma) and other intrusions having moderate gravity and magnetic signatures.

Schist of sedimentary protolith (Neoarchean) at surface, covers 4 % of this area

Schist of sedimentary protolith. Metamorphosed to upper greenschist to amphibolite facies.

Granitic intrusion (Neoarchean) at surface, covers 2 % of this area

Granitic intrusion. Includes the Sacred Heart (~2592, 2,603 Ma) and Ortonville granites, the Shannon Lake Granite (~2,674), and other intrusions having low gravity and magnetic signatures.

Mafic to ultramafic hypabyssal intrusive complexes composed of gabbro, pyroxenite, diorite, and anorthosite (Neoarchean) at surface, covers 1.0 % of this area

Mafic to ultramafic hypabyssal intrusive complexes composed of gabbro, pyroxenite, diorite, and anorthosite. Includes the Mentor and Deer Lake complexes, intrusions of the Newton Lake Formation, all within the Wawa subprovince; and the UBD intrusion (~2,685 to 2,695 Ma) in the Wabigoon subprovince.

Migmatite dominated by tonalitic to granodioritic neosome (Neoarchean) at surface, covers 0.8 % of this area

Migmatite dominated by tonalitic to granodioritic neosome.

Syenite, monzodiorite, granodiorite, and diorite (Neoarchean) at surface, covers 0.7 % of this area

Syenite, monzodiorite, granodiorite, and diorite. Commonly hornblende- or pyroxene-bearing; Includes the Coon Lake, Side Lake, and Linden (~2,666 Ma) plutons of north-central Minnesota.

Granite to granodiorite (Neoarchean) at surface, covers 0.6 % of this area

Granite to granodiorite. Variably magnetic.

Granitoid intrusion (Neoarchean) at surface, covers 0.5 % of this area

Granitoid intrusion. Constrained solely by low gravity and magnetic signatures.

Amphibolitic schist and gneiss (Neoarchean) at surface, covers 0.3 % of this area

Amphibolitic schist and gneiss. Both extrusive and intrusive protoliths are likely.

Gabbro, peridotite, pyroxenite, lamprophyre, and metamorphic equivalents (Neoarchean) at surface, covers 0.2 % of this area

Gabbro, peridotite, pyroxenite, lamprophyre, and metamorphic equivalents. Includes the Oaks intrusion (~2,671 Ma) in the Wabigoon subprovince, and a ~2,639 Ma lamprophyre in the western Wawa subprovince; locally defined by variably high gravity and magnetic signatures.

Magnetic intrusions, undifferentiated (Archean) at surface, covers 0.2 % of this area

Magnetic intrusions, undifferentiated. Typically too small to ascertain gravity expression.

Conglomerate, lithic sandstone, and graywacke, undifferentiated (Neoarchean) at surface, covers 0.1 % of this area

Conglomerate, lithic sandstone, and graywacke, undifferentiated. Includes the Midway sequence, Seine Group, and a part of the Knife Lake Group known as the Ogishkemuncie conglomerate that contains clasts of ~2,690 Ma Saganaga Tonalite (unit Ast). Deposition of alluvial fan and fluvial sediments occurred in fault-bounded basins.

Iron-formation (Neoarchean) at surface, covers 0.1 % of this area

Iron-formation. Includes the Soudan Iron Formation and many unnamed units.

Lac La Croix Granite (Neoarchean) at surface, covers < 0.1 % of this area

Pink biotite granite that is variably magnetic and locally pegmatitic (~2,665 to 2,667 Ma).