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Geologic units containing iron formation

Arizona

Early Proterozoic metasedimentary rocks (Early Proterozoic)

Metasedimentary rocks, mostly derived from sandstone and shale, with minor conglomerate and carbonate rock. Includes quartz-rich, mostly nonvolcanic Pinal Schist in southeastern Arizona and variably volcanic-lithic sedimentary rocks in the Yavapai and Tonto Basin supergroups in central Arizona. (1600-1800 Ma)

Early Proterozoic metavolcanic rocks (Early Proterozoic)

Weakly to strongly metamorphosed volcanic rocks. Protoliths include basalt, andesite, dacite, and rhyolite deposited as lava or tuff, related sedimentary rock, and shallow intrusive rock. These rocks, widely exposed in several belts in central Arizona, include metavolcanic rocks in the Yavapai and Tonto Basin supergroups. (1650 to 1800 Ma)

Maine

Cambrian Jim Pond Formation (Cambrian)

Cambrian Jim Pond Formation

Ordovician Wassataquoik Chert (Ordovician)

Ordovician Wassataquoik Chert

Michigan

Baraga Group; Tyler Formation (Early Proterozoic)

Baraga Group; Tyler Formation - Light- to dark-gray, feldspathic, fine-grained sandstone, argillaceous siltstone, and argillite. Near base, ferruginous argillite contains beds of cherty sideritic and pyritic iron-formation

Menominee Group; Blair Creek Formation (Early Proterozoic)

Menominee Group; Blair Creek Formation - Dominantly dark-gray, massive, porphyritic tholeiitic basalt. Includes a basal conglomerate and a lean iron-formation in middle of formation

Menominee Group; Ironwood Iron-formation (Early Proterozoic)

Menominee Group; Ironwood Iron-formation - Interbedded cherty and slaty iron-formation. Locally, secondary enrichment has formed "soft ore" bodies. In eastern part of Gogebic Range, Ironwood Iron-formation is intercalated with pyroclastic rocks of Emperor Volcanic Complex, and in eastern half of T. 47 N., R. 43 W. (where mapped within unit Xip) consists entirely of black slate

Menominee Group; Negaunee Iron-formation (Early Proterozoic)

Menominee Group; Negaunee Iron-formation - Highly metamorphosed banded iron-formation. Principal iron-formation in Marquette trough and nearby areas. Includes abundant metadiabase sills.

Menominee Group, undivided (Early Proterozoic)

Menominee Group, undivided - Includes Negaunee Iron-formation, Siamo Slate, and Ajibik Quartzite in areas where units are too thin to map individually.

Menominee Group; unexposed magnetic unit (Early Proterozoic)

Menominee Group; unexposed magnetic unit- Surrounds gneiss domes in Gogebic County, Mich. and Vilas County, Wisc., and occurs in north-central Dickinson County. Probably correlative with part of Blair Creek Formation (unit Xbc). Previously correlated with uppermost unit of Blair Creek Formation (Sims and others, 1984).

Paint River Group; Lower part (Early Proterozoic)

Paint River Group; Lower part - Includes Stambaugh Formation, Hiawatha Graywacke, Riverton Iron-formation, and Dunn Creek Slate (James and others, 1968). Correlated with lower part of Baraga Group

Minnesota

Animikie Group; Iron-formation - Iron-formation (Early Proterozoic)

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.

Denham Formation (Early Proterozoic)

Denham Formation - Quartz arenite and siltstone, oxide iron-formation, marble, mafic hypabyssal intrusions and fragmental volcanic rocks metamorphosed to the staurolite grade of the amphibolite facies

Mafic metavolcanic rocks (Late Archean)

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.

Metabasalt, metadiabase, and metasedimentary rocks metamorphosed to lower greenschist facies (Early Proterozoic)

Metabasalt, metadiabase, and metasedimentary rocks metamorphosed to lower greenschist facies - Includes fragmental volcanic rocks, mafic hypabyssal intrusions, graywacke, graphitic argillite and oxide iron-formation

Metasedimentary rocks, undivided (Late Archean)

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.

Mille Lacs Group and related rocks of the Penokean fold-and-thrust belt; Graphitic schist, slate, and silicate iron-formation metamorphosed to the lower greenschist facies and related conditions (Early Proterozoic)

Mille Lacs Group and related rocks of the Penokean fold-and-thrust belt; Graphitic schist, slate, and silicate iron-formation metamorphosed to the lower greenschist facies and related conditions - Includes substantial quantities of mafic to intermediate igneous rocks

Mille Lacs Group and related rocks of the Penokean fold-and-thrust belt; Metabasalt, metadiabase, and metasedimentary rocks metamorphosed to lower amphibolite facies (Early Proterozoic)

Mille Lacs Group and related rocks of the Penokean fold-and-thrust belt; Metabasalt, metadiabase, and metasedimentary rocks metamorphosed to lower amphibolite facies - Includes fragmental volcanic rocks, mafic hypabyssal intrusions, graphitic argillite, and oxide iron-formation

Mixed metavolcanic rocks (Late Archean)

Mixed metavolcanic rocks - Mafic to felsic volcanic sequences that have variable amounts of felsic volcanogenic and volcaniclastic rocks and lean iron-formation. Includes parts of the Ely Greenstone and the Soudan Iron-formation in northeastern Minnesota.

North Range Group; Rabbit Lake Formation (Early Proterozoic)

North Range Group; Rabbit Lake Formation - Mudstone, graywacke, iron-rich strata, and associated mafic metavolcanic rocks metamorphosed to the greenschist facies. Includes thin beds of carbonate-silicate iron-formation

North Range Group; Trommald Formation (Early Proterozoic)

North Range Group; Trommald Formation - Carbonate-silicate iron-formation overlain by hematite iron-formation and associated manganese oxide deposits. Also contains substantial quantities of volcanic and hypabyssal rocks of generally mafic composition. Metamorphosed to greenschist facies.

New Hampshire

Ammonoosuc Volcanics, White quartz-kyanite rock and silicate iron-formation (Middle - Upper Ordovician)

Ammonoosuc Volcanics, White quartz-kyanite rock and silicate iron-formation.

South Dakota

Iron-Formation (Proterozoic | Paleoproterozoic)

Banded, dark-green, reddish-brown, and white iron-formation, ferruginous chert, and minor mica schist. Includes three or more ages of oxide-, carbonate-, silicate-, and sulifide-facies iron-formation and interbedded tuffaceous rocks. Thickness 20-500 ft (6-152 m).

Metabasalt (Proterozoic | Paleoproterozoic)

Dark-green amphibolite, actinolite schist, and greenstone. Interflow units consists of graphitic schist, chert, and carbonate- and silicate-facies iron-formation. Thickness of individual flows 50-400 ft (244-1,524 m).

Metaconglomerate and Metaquartzite (Proterozoic | Paleoproterozoic)

Light-gray to gray, conglomeratic and feldspathic schist, biotite schist, taconite, and phyllite. Individual conglomerate and fanglomerate tongues from 100-500 ft (30-152 m) thick. Total thickness over 10,000 ft (3,048 m).

Metamorphosed Conglomerate (Proterozoic | Paleoproterozoic)

Gray to grayish-brown, conglomeratic biotite phyllite, siliceous biotite phyllite, mica schist, quartzite, and iron-formation. Thickness up to 2,000 ft (610 m).

Wisconsin

Banded iron-formation and associated volcanogenic rocks (Late Archean )

Banded iron-formation and associated volcanogenic rocks - Magnetite-quartz iron-formation and associated talc schist in aluminous quartzofeldspathic schist (unit Wt)

Baraga Group; Michigamme Formation; Banded cherty and slaty iron-formation (Early Proterozoic)

Baraga Group; Michigamme Formation; Banded cherty and slaty iron-formation

Baraga Group; Tyler Formation (Early Proterozoic)

Baraga Group; Tyler Formation - Light- to dark-gray, feldspathic, fine-grained sandstone, argillaceous siltstone, and argillite. Near base, ferruginous argillite contains beds of cherty sideritic and pyritic iron-formation

Ironwood Iron-formation of Menominee Group and Palms Formation of Chocolay Group (Early Proterozoic)

Ironwood Iron-formation of Menominee Group and Palms Formation of Chocolay Group - Mapped where units are too thin to show separately on map (Gogebic Range). Palms Formation includes Bad River Dolomite and Sunday Quartzite of Chocolay Group

Menominee Group; Blair Creek Formation (Early Proterozoic)

Menominee Group; Blair Creek Formation - Dominantly dark-gray, massive, porphyritic tholeiitic basalt. Includes a basal conglomerate and a lean iron-formation in middle of formation

Menominee Group; Ironwood Iron-formation (Early Proterozoic)

Menominee Group; Ironwood Iron-formation- Interbedded cherty and slaty iron-formation. Locally, secondary enrichment has formed "soft ore" bodies. In eastern part of Gogebic Range, Ironwood Iron-formation is intercalated with pyroclastic rocks of Emperor Volcanic Complex, and in eastern half of T. 47 N., R. 43 W. (where mapped within unit Xip) consists entirely of black slate

Menominee Group; unexposed magnetic unit (Early Proterozoic)

Menominee Group; unexposed magnetic unit - Surrounds gneiss domes in Gogebic County, Mich. and Vilas County, Wisc., and occurs in north-central Dickinson County. Probably correlative with part of Blair Creek Formation (unit Xbc). Previously correlated with uppermost unit of Blair Creek Formation (Sims and others, 1984).

Paint River Group; Lower part (Early Proterozoic)

Paint River Group; Lower part- Includes Stambaugh Formation, Hiawatha Graywacke, Riverton Iron-formation, and Dunn Creek Slate (James and others, 1968). Correlated with lower part of Baraga Group

Tuff breccia schist and minor iron-formation (Late Archean)

Tuff breccia schist and minor iron-formation - Pink and gray, layered quartzofeldspathic schist of intermediate volcanic composition and associated thin iron-formation. Felsic gneiss at Arbutus Dam on Black River at Hatfield has U-Pb zircon age of about 2800 Ma (Sims and others, 1989)