Marinette County contains very diverse bedrock. The southeastern portion consists of Cambrian and Ordovician sedimentary rocks dipping monoclinally gently to the east, off the Wisconsin Arch. The Cambrian rocks are mostly clastic sandstones, while the Ordovician rocks are carbonate dominated. The northwestern portion of the county contains diverse Proterozoic metamorphic and igneous rocks. These are dominated by granites, meta-volcanic and meta-sedimentary rocks deformed during the 1.80 – 1.85 billion year old Penokean Orogeny. The Penokean orogeny was a continent-continent collision, with the rocks seen in the county being ocean crust and island arc materials caught up in the collision. Quartzite outcrops at McCaslin and Thunder Mountains, and can yield nice quartz crystals. Several small molydbenite deposits are known from the county. Locally ultramafic rocks host magnesite and chromite deposits. To date, none of the deposits have proved of major economic value. Thick glacial drift, lakes and forests make outcrops scarce, but these deposits can yield interesting glacially transported rocks and minerals.
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49 entries listed. 33 valid minerals.
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Olson, J. (1984) The Geology of the Lower Proterozoic Mc Caslin Formation, northeastern Wisconsin: Geoscience Wisconsin 9: 1-19.
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