Geologic units in Red Lake county, Minnesota

Biotite schist of graywacke protolith, and schist-rich migmatite (Neoarchean) at surface, covers 36 % of this area

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

Mafic metavolcanic rocks (Neoarchean) at surface, covers 24 % 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).

Tonalite-leucodiorite plutons (Neoarchean) at surface, covers 16 % of this area

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

Granitoid intrusion (Neoarchean) at surface, covers 8 % of this area

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

Schist of sedimentary protolith (Neoarchean) at surface, covers 5 % of this area

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

Volcaniclastic rocks of felsic to intermediate composition (Neoarchean) at surface, covers 5 % of this area

Volcaniclastic rocks of felsic to intermediate composition.

Undifferentiated (Cenomanian to Campanian) at surface, covers 3 % 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.

Granodiorite to hornblende diorite, locally magmatically foliated (Neoarchean) at surface, covers 3 % 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.

Magnetic intrusions, undifferentiated (Archean) at surface, covers 0.9 % of this area

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