The Little Commonwealth exploration in northeastern Florence County, Wisconsin, is underlain by highly ferruginous clastic rocks that are stratigraphically equivalent to vitreous quartzite. The relationship between these rocks is one of abrupt facies change, with complete gradation between facies. This stratigraphic unit is conformably underlain by sericitic phyllite and unconformably overlain by slate and graywacke of the lower part of the Dunn Creek formation of upper Animikie age.
The strata are vertical and minor structures due to tectonic movement are present. Some of the deformation may be of pre-diagenetic origin.
Metamorphism of the Little Commonwealth rocks has developed abundant stilpnomelane, garnet, and martite. Metasomatism is indicated by the occurrence of tourmaline, pyrite, chalcopyrite, and arsenopyrite. The area is probably in the biotite zone of regional metamorphism.
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USGS Numbered Series
Geology of the Little Commonwealth area, Florence County, Wisconsin