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Geosciences 2016, 6(2), 29; doi:10.3390/geosciences6020029

Geochemical Characterization of Trace MVT Mineralization in Paleozoic Sedimentary Rocks of Northeastern Wisconsin, USA

1
Department of Natural & Applied Sciences (Geoscience), University of Wisconsin-Green Bay, Green Bay, WI 54311, USA
2
Department of Natural & Applied Sciences (Chemistry), University of Wisconsin-Green Bay, Green Bay, WI 54311, USA
3
Department of Natural & Applied Sciences (Statistics), University of Wisconsin-Green Bay, Green Bay, WI 54311, USA
*
Author to whom correspondence should be addressed.
Academic Editor: Michael D. Campbell
Received: 21 March 2016 / Revised: 14 May 2016 / Accepted: 12 June 2016 / Published: 21 June 2016
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Abstract

Disseminated Mississippi Valley-type (MVT) mineralization occurs throughout northeastern Wisconsin, USA, and is recognized as the source of regionally extensive natural groundwater contamination in the form of dissolved arsenic, nickel, and other related metals. Although considerable attention has been given to arsenic contamination of groundwater in the region, limited attention has been focused on characterizing the bedrock sources of these and other metals. A better understanding of the potential sources of groundwater contamination is needed, especially in areas where groundwater is the dominant source of drinking water. This article describes the regional, stratigraphic, and petrographic distribution of MVT mineralization in Paleozoic rocks of northeastern Wisconsin, with a focus on sulfide minerals. Whole-rock geochemical analysis performed on 310 samples of dolomite, sandstone, and shale show detectable levels of arsenic, nickel, cobalt, copper, lead, zinc, and other metals related to various sulfide mineral phases identified using scanning electron microscopy. MVT minerals include pyrite, marcasite, sphalerite, galena, chalcopyrite, fluorite, celestine, barite, and others. We describe the first nickel- and cobalt-bearing sulfide mineral phases known from Paleozoic strata in the region. Arsenic, nickel, and cobalt are sometimes present as isomorphous substitutions in pyrite and marcasite, but discrete mineral phases containing nickel and cobalt elements are also observed, including bravoite and vaesite. Locally abundant stratigraphic zones of sulfide minerals occur across the region, especially in the highly enriched Sulfide Cement Horizon at the top of the Ordovician St. Peter Sandstone. Abundant quantities of sulfides also appear near the contact between the Silurian Mayville Formation and the underlying Maquoketa and Neda formations in certain areas along and east of the Niagara escarpment. This article illustrates how a detailed geochemical and mineralogical investigation can yield a better understanding of groundwater quality problems. View Full-Text
Keywords: Wisconsin; Paleozoic; vaesite; bravoite; sulfide; nickel; cobalt; arsenic Wisconsin; Paleozoic; vaesite; bravoite; sulfide; nickel; cobalt; arsenic
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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. (CC BY 4.0).

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MDPI and ACS Style

Luczaj, J.A.; McIntire, M.J.; Olson Hunt, M.J. Geochemical Characterization of Trace MVT Mineralization in Paleozoic Sedimentary Rocks of Northeastern Wisconsin, USA. Geosciences 2016, 6, 29.

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