Geochemical Characterization of Sulfide Mineralization in Eastern Wisconsin Carbonate Rocks

Background/Need:
Characterization of geologic factors affecting groundwater movement, contamination, and aquifer recharge was a stated research priority by the University of Wisconsin System in the Joint Solicitation for Groundwater Research & Monitoring Proposals document for fiscal year 2008. The chemistry of groundwater systems is controlled in part by the composition of the host rock. Groundwater in eastern Wisconsin carbonate rocks has the potential to be in direct contact with significant quantities of sulfide minerals because of their petrographic location in the host rocks. Sulfide minerals are often found coating the walls of joints, faults, and interconnected vugs in these dolostones. Oxidation of these sulfide minerals has been shown to be the major source of arsenic and other metals of concern in eastern Wisconsin (e.g., Thornburg and Sahai, 2004; Johnson and Riewe, 2006). Because interconnected fractures and bedding planes are important groundwater conduits in carbonate aquifers, the composition of minerals coating these fractures is an important control on groundwater quality.
Objectives:
The objective of the project was to characterize the trace metal composition of the carbonate (and other) rocks from outcrops, quarries, and drill cores in northeastern 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, stratigraphic, and petrographic distribution of these elements in the different Paleozoic strata of eastern Wisconsin. These activities will help to create a baseline for follow-up studies and help determine future impacts of arsenic and other metals in Wisconsin’s groundwater.