Geologic units in Beltrami county, Minnesota

Biotite schist of graywacke protolith, and schist-rich migmatite (Neoarchean) at surface, covers 33 % of this area

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

Granitic intrusion (Neoarchean) at surface, covers 20 % 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 metavolcanic rocks (Neoarchean) at surface, covers 14 % 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).

Volcaniclastic rocks of felsic to intermediate composition (Neoarchean) at surface, covers 13 % of this area

Volcaniclastic rocks of felsic to intermediate composition.

Granitoid intrusion (Neoarchean) at surface, covers 7 % of this area

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

Granite-rich migmatite (Neoarchean) at surface, covers 5 % 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.

Undifferentiated (Cenomanian to Campanian) at surface, covers 2 % of this area

Conglomerate, sandstone, mudstone, shale, marlstone, siltstone, and minor lignite, deposited in marine and non-marine settings; likely Cenomanian to Campanian age. Unit outline is the product of contouring the stratigraphic top and base, from which an isopach grid was created. Because the distribution is patchy, unit boundaries were drawn from the gridded data to represent locations where more than 25 feet (8 meters) of thickness occurs. As a result, many areas outside of the unit boundaries may be overlain by thin Cretaceous strata and the unit is depicted without a contact line.

Foliated to gneissic tonalite, granodiorite, and diorite (Neoarchean) at surface, covers 2 % 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.

Gabbro, peridotite, pyroxenite, lamprophyre, and metamorphic equivalents (Neoarchean) at surface, covers 1 % 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.

Granite to granodiorite (Neoarchean) at surface, covers 0.8 % of this area

Granite to granodiorite. Variably magnetic.

Tonalite-leucodiorite plutons (Neoarchean) at surface, covers 0.6 % of this area

Tonalite-leucodiorite plutons. Includes the Grygla, Red Lake Falls, and other plutons having low magnetic and gravity signatures.

Schist of sedimentary protolith (Neoarchean) at surface, covers 0.6 % of this area

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

Magnetic intrusions, undifferentiated (Archean) at surface, covers 0.4 % of this area

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