Mineral potential and geology of Paleozoic and Mesozoic rocks in Minnesota

In southeastern Minnesota, essentially undeformed Ordovician carbonate rocks host scattered calcite- or dolomite-filled veins and breccia zones in which marcasite, sphalerite, and galena locally occur. These represent the outer fringes of the regional hydrothermal system that produced the Mississippi Valley type (MVT) lead-zinc deposits farther south, in southwestern Wisconsin and eastern Iowa. As a result of recent refinements in the MVT deposit model, some interest has been rekindled in the lead-zinc potential of southeastern Minnesota.

Geoterranes map

Undeformed carbonaceous shale and siltstone of Late Cretaceous age lie unconformably on Precambrian rocks in much of southwestern Minnesota. Although some Cretaceous strata are currently being mined for industrial clay, greater potential may exist. The rocks have stratigraphic and compositional attributes that suggest the possibility for shallow-marine sedimentary manganese concentration according to the Cannon-Force depositional model. Reconnaissance exploration has determined that some manganese enrichment did occur in these rocks, but no economic Mn deposits have been identified.

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