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Abstract

The midcontinent of the United States hosts some of the world's largest, economically most valuable mineral districts and metallogenic provinces. The Precambrian iron deposits of the Lake Superior region include both Algoma- and Lake Superior-type Fe and Fe-Mn ores. Native cu and Cu-Ni sulfides occur in the mafic igneous rocks of the Keweenawan rift, and in the Late Precambrian Nonesuch Shale. The largest Au producer in the Western Hemisphere, the Homestake Mine in the Black Hills, yields its gold from cummingtonite schist, a metamorphosed iron-carbonate formation. (The most famous ores of this region, however, are not Precambrian; they are the Mississippi-Valley type Pb, Zn, fluorite, and barite deposits in the Paleozoic platform carbonates.)

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