Geochemical Characterization of Sulfide Mineralization in Eastern Wisconsin Carbonate Rocks

Much attention has been given to the problem of arsenic contamination in groundwater from northeastern Wisconsin. Previous research by others has detailed a corridor between Oshkosh and Green Bay in which the St. Peter Sandstone aquifer contains arsenic-bearing iron sulfide minerals. Little is known about the potential for arsenic and other metal contamination in Paleozoic rocks in Marinette, Oconto, and Shawano Counties. With parts of northeastern Wisconsin expecting significant population growth over the next 25 years, a better understanding of potential sources of groundwater contamination is needed, especially in rural areas where domestic water wells are prevalent. Research by a principal investigator has shown that many of the Paleozoic rocks throughout eastern Wisconsin contain disseminated sulfide mineralization related to an ancient hydrothermal water-rock system. This ancient system was responsible for precipitation and replacement of a suite of sulfide minerals. Previous work by others regarding arsenic and metals concentrations in rock and ground water has focused on the St. Peter Sandstone over a small area in Winnebago and Outagamie Counties. Little information is known about the trace element signature of the carbonates in the region that host these same sulfide minerals. These rocks are the potential sources for contamination that might impact groundwater or surface water elsewhere in the region. The goal of this project is to characterize the trace element composition of the carbonate rocks from outcrops and quarries in eastern Wisconsin to gain a better understanding of potential sources of arsenic and other metals of concern. This information will improve our understanding of the regional and stratigraphic distribution of these elements in different Paleozoic rocks of eastern Wisconsin. These activities will help to create a baseline for follow-up studies and for determining future impacts of arsenic and other metals in Wisconsin’s groundwater.