Geologic units in Saint Louis county, Minnesota

Additional scientific data in this geographic area

Slate and graywacke (Paleoproterozoic) at surface, covers 29 % of this area

Slate and graywacke. Includes the Rove (~1,836 to 1,777 Ma), Virginia (~1,832 Ma near base), and Thompson Formations (youngest zircons in the Thompson Formation ~1,790 Ma).

Biotite schist of graywacke protolith, and schist-rich migmatite (Neoarchean) at surface, covers 13 % of this area

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

Granite-rich migmatite (Neoarchean) at surface, covers 10 % 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.

Lac La Croix Granite (Neoarchean) at surface, covers 7 % of this area

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

Troctolite (Mesoproterozoic) at surface, covers 5 % of this area

Troctolite. Includes the Boulder Lake, Tuscarora (~1,099 Ma), Partridge River (~1,098 Ma), South Kawishiwi, and part of the Western Margin intrusions.

Anorthositic intrusions and inclusions, undifferentiated (Mesoproterozoic) at surface, covers 4 % of this area

Anorthositic intrusions and inclusions, undifferentiated (~1,099 Ma).

Granite to granodiorite (Neoarchean) at surface, covers 3 % of this area

Granite to granodiorite. Variably magnetic.

Gabbro (Mesoproterozoic) at surface, covers 3 % of this area

Gabbro. Includes the Western Margin, Greenwood Lake, Bald Eagle (~1,098), Lake One, Lake Three, Wilder Lake, and Osier Lake intrusions.

Volcanogenic graywacke and mudstone (Neoarchean) at surface, covers 3 % of this area

Volcanogenic graywacke and mudstone. Includes the Lake Vermilion Formation.

Volcaniclastic rocks of felsic to intermediate composition (Neoarchean) at surface, covers 3 % of this area

Volcaniclastic rocks of felsic to intermediate composition.

Mafic metavolcanic rocks (Neoarchean) at surface, covers 2 % 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).

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.

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.

Gunflint (~1,878 Ma), Biwabik, and Emily Iron Formations (Paleoproterozoic) at surface, covers 2 % of this area

Locally includes thin basal sandstone and conglomerate. Capped by an irregular layer of brecciated iron-formation and ejecta derived from the 1,850 Ma Sudbury meteorite impact.

Syenite, monzodiorite, granodiorite, and diorite (Neoarchean) at surface, covers 1 % 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.

Monzonite, quartz monzonite, and granodiorite (Neoarchean) at surface, covers 1 % of this area

Monzonite, quartz monzonite, and granodiorite. Includes the Farm Lake phase of the Giants Range batholith.

Coleraine Formation (Late Cenomanian) at surface, covers 1 % of this area

Conglomerate, lignite, sandstone, and shale; shallow marine and non-marine. Late Cenomanian age is inferred. Despite exposures in mines on the Mesabi Iron Range, the position of much of the unit contact is highly speculative.

Granodiorite to hornblende diorite, locally magmatically foliated (Neoarchean) at surface, covers 1 % 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.

Migmatite dominated by tonalitic to granodioritic neosome (Neoarchean) at surface, covers 1 % of this area

Migmatite dominated by tonalitic to granodioritic neosome.

Basalt and basaltic andesite (Mesoproterozoic) at surface, covers 1.0 % of this area

Basalt and basaltic andesite. Includes the Leif Erickson, Lakeside (~1,098 Ma), Sucker River, Larsmont, Two Harbors, Crow Creek, Gooseberry River, Gustafson Hill, Baptism River, Good Harbor Bay, Cascade River, Croftville, Red Cliff, and Marr Island lavas.

Calc-alkalic volcanic and volcaniclastic rocks (Neoarchean) at surface, covers 0.7 % of this area

Calc-alkalic volcanic and volcaniclastic rocks.

Amphibolitic schist and gneiss (Neoarchean) at surface, covers 0.7 % of this area

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

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

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

Diabase, gabbro, and ferromonzodiorite (Mesoproterozoic) at surface, covers 0.5 % of this area

Diabase, gabbro, and ferromonzodiorite. Primarily sills including the Endion, Lester River, Silver Cliff, Stony Point, Split Rock, Lafayette Bluff, Lake Clara–Lichen Lake, Pigeon River, and Reservation River intrusions.

Gabbroic intrusions (Mesoproterozoic) at surface, covers 0.5 % of this area

Gabbroic intrusions. Including the Sawmill, London, Brule River, Hovland, and Pigeon Point intrusions.

Cyclic zone (Mesoproterozoic) at surface, covers 0.4 % of this area

Gabbro to troctolite (~1,099 Ma).

Undifferentiated mafic to felsic lava flows (Mesoproterozoic) at surface, covers 0.3 % of this area

Undifferentiated mafic to felsic lava flows. Includes the Lakeside, Lakewood, and Cross River lavas.

Undifferentiated volcanic rocks and volcanic hornfels (Mesoproterozoic) at surface, covers 0.3 % of this area

Undifferentiated volcanic rocks and volcanic hornfels.

Felsic intrusive rocks, granophyre (Mesoproterozoic) at surface, covers 0.2 % of this area

Felsic intrusive rocks, granophyre. Includes parts of the Eagle Mountain (~1,098 Ma) and Pine Mountain (~1,095 to 1,098 Ma) intrusions.

Mafic to ultramafic hypabyssal intrusive complexes composed of gabbro, pyroxenite, diorite, and anorthosite (Neoarchean) at surface, covers 0.2 % 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.

Conglomerate, lithic sandstone, and graywacke, undifferentiated (Neoarchean) at surface, covers 0.2 % 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.

Mafic to ultramafic (komatiitic) volcanic rocks (Neoarchean) at surface, covers 0.2 % of this area

Mafic to ultramafic (komatiitic) volcanic rocks. Includes the Newton Lake Formation and Deer Lake sequence.

Ferromonzodiorite forming the upper contact zone (Mesoproterozoic) at surface, covers 0.2 % of this area

Ferromonzodiorite forming the upper contact zone.

Granitoid intrusion (Neoarchean) at surface, covers 0.2 % of this area

Granitoid intrusion. Constrained solely by low 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.

Granophyre, ferromonzodiorite, and leucogabbro (Mesoproterozoic) at surface, covers 0.1 % of this area

Granophyre, ferromonzodiorite, and leucogabbro. Includes the Mt. Weber (~1,106 Ma), Whitefish Lake (~1,109 Ma), Beth Lake, Misquah Hills (~1,106 Ma), and Cucumber Lake (~1,106 Ma) granophyres, and Wine Lake monzodiorite.

Sandstone, siltstone, and local conglomerate (Mesoproterozoic) at surface, covers 0.1 % of this area

Sandstone, siltstone, and local conglomerate. Includes the Hinckley Sandstone and Fond du Lac (youngest detrital zircons ~1,000 Ma) and Solar Church Formations; deposition in eolian, fluvial, and lacustrine environments.

Interlayered metavolcanic, volcaniclastic, and hypabyssal intrusive rocks (Neoarchean) at surface, covers 0.1 % of this area

Interlayered metavolcanic, volcaniclastic, and hypabyssal intrusive rocks. Metamorphosed to amphibolite facies.

Pokegama Quartzite (Paleoproterozoic) at surface, covers 0.1 % of this area

Includes conglomerate and siliceous mudstone.

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

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

Knife Lake Group volcanogenic lithic sandstone, conglomerate, siltstone, graywacke, and slate (Neoarchean) at surface, covers < 0.1 % of this area

Volcanogenic lithic sandstone, conglomerate, siltstone, graywacke, and slate.

Lower sequence, primarily basalt (Mesoproterozoic) at surface, covers < 0.1 % of this area

Lower sequence, primarily basalt. Includes the Ely's Peak and Grand Portage basalts and Hovland lavas (~1,108 Ma).

Porphyritic quartzofeldspathic dikes (Neoarchean) at surface, covers < 0.1 % of this area

Porphyritic quartzofeldspathic dikes. Typically hypabyssal intrusions associated with felsic volcanic sequences.

Granitic to granodioritic orthogneiss (Neoarchean) at surface, covers < 0.1 % of this area

Granitic to granodioritic orthogneiss. Includes the McGrath Gneiss (~2,752 ± 15, 2,557 Ma) and unnamed units.

Gabbro, peridotite, pyroxenite, lamprophyre, and metamorphic equivalents (Neoarchean) at surface, covers < 0.1 % 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.

Knife Lake Group, hornblende-phyric volcanic flows, breccia, and tuff. (Neoarchean) at surface, covers < 0.1 % of this area

Hornblende-phyric volcanic flows, breccia, and tuff.

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

Poorly sorted arkosic sandstone

Puckwunge and Nopeming Sandstones (Mesoproterozoic) at surface, covers < 0.1 % of this area

Puckwunge and Nopeming Sandstones.