Geologic units in Florence county, Wisconsin

Mafic metavolcanic rocks (Early Proterozoic) at surface, covers 33 % of this area

Dominantly tholeiitic basalt and basaltic andesite flows and tuffs; associated with sheet dikes, massive and layered metagabbro, and ultramafic rocks. In northeastern Wisconsin, rocks have been named the Quinnesec Formation.

Granite-tonalite (Early Proterozoic) at surface, covers 27 % of this area

Gray to pinkish-gray, medium-grained, generally equigranular granite to tonalite and granitoid gneiss; locally includes diorite. Intrudes older metavolcanic rocks. Zircon ages range from 1852 +/- 15 to 1862 +/- 5 Ma

Baraga Group; Michigamme Formation, undivided (Early Proterozoic) at surface, covers 18 % of this area

Thick and stratigraphically varied formation of sedimentary and less abundant volcanic rocks. Metamorphosed graywacke is predominant rock of Michigamme Formation. Calcareous concretions common. Metamorphosed from cholorite to sillimanite grade (Cannon, 1986). Mapped undivided in poorly exposed areas

Badwater Greenstone (Early Proterozoic) at surface, covers 6 % of this area

Dark-greenish-gray, pillowed to massive tholeiitic basalt and pyroclastic rocks. Correlated with the Hemlock Formation on basis of geology and similarity in chemical composition.

Spikehorn Granite and Bush Lake Granites, undivided (Early Proterozoic) at surface, covers 4 % of this area

Gray to pinkish-gray, fine- to medium-grained, massive granite containing scattered phenocrysts of potassium feldspar. Exposed in northeastern Wisconsin

Paint River Group; Upper part (Early Proterozoic) at surface, covers 4 % of this area

Dominantly Fortune Lakes Slate, but includes other rocks in poorly exposed areas. Correlated with upper part of Baraga Group.

Paint River Group; Lower part (Early Proterozoic) at surface, covers 2 % of this area

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

Quartz diorite (Early Proterozoic) at surface, covers 2 % of this area

Includes Marinette Quartz Diorite of Dunbar Dome (Sims and others, 1985a) and nearby Twelve Foot Falls Quartz Diorite

Dacite and volcanogenic graywacke (Early Proterozoic) at surface, covers 1 % of this area

Includes andesite tuff. Occurs in northeastern Wisconsin. Dacite has age of 1866 +/- 39 Ma.

Metagabbro (Early Proterozoic) at surface, covers 0.9 % of this area

Mafic to ultramafic bodies defined and delineated principally by positive magnetic and gravity anomalies; includes diorite bodies. Comagmatic with unit Xmi

Chocolay Group, undivided (Early Proterozoic) at surface, covers 0.9 % of this area

In Dickinson County, Mich., includes Randville Dolomite, Sturgeon Quartzite, and Fern Creek Formation. In Marquette range, between Marquette Bay and Champion, includes Wewe Slate, Kona Dolomite, Mesnard Quartzite, and Enchantment Lake Formation

Paint River Group; Upper part (Early Proterozoic) at surface, covers 0.3 % of this area

Dominantly Fortune Lakes Slate, but includes other rocks in poorly exposed areas. Correlated with upper part of Baraga Group.

Badwater Greenstone (Early Proterozoic) at surface, covers 0.1 % of this area

Dark-greenish-gray, pillowed to massive tholeiitic basalt and pyroclastic rocks. Correlated with the Hemlock Formation on basis of geology and similarity in chemical composition.

Mafic metavolcanic rocks (Early Proterozoic) at surface, covers 0.1 % of this area

Dominantly tholeiitic basalt and basaltic andesite flows and tuffs; associated with sheet dikes, massive and layered metagabbro, and ultramafic rocks. In northeastern Wisconsin, rocks have been named the Quinnesec Formation.

Baraga Group; Michigamme Formation, undivided (Early Proterozoic) at surface, covers < 0.1 % of this area

Thick and stratigraphically varied formation of sedimentary and less abundant volcanic rocks. Metamorphosed graywacke is predominant rock of Michigamme Formation. Calcareous concretions common. Metamorphosed from cholorite to sillimanite grade (Cannon, 1986). Mapped undivided in poorly exposed areas

Chocolay Group, undivided (Early Proterozoic) at surface, covers < 0.1 % of this area

In Dickinson County, Mich., includes Randville Dolomite, Sturgeon Quartzite, and Fern Creek Formation. In Marquette range, between Marquette Bay and Champion, includes Wewe Slate, Kona Dolomite, Mesnard Quartzite, and Enchantment Lake Formation

Menominee and Chocolay Groups, undivided (Early Proterozoic) at surface, covers < 0.1 % of this area

Mapped where units are too thin to show separately on map