Trace-Metal Bearing Sulfides and Oxides in Cambrian Strata of West-Central Wisconsin
What: This Gateway research project will investigate the occurrence of trace metal-bearing sulfides and sulfide weathering products in sandstones from southwestern Wisconsin. This work is significant because these strata serve as a regional groundwater aquifer as well as a source of industrial sand that is mined throughout west-central Wisconsin and are potential sources of groundwater contamination by trace metals.
When: July 7-August 8, 2025
Where: Beloit College, Beloit, WI and the GSA Annual Meeting in San Antonio, TX (October, 2025)
Who: Ten students, a peer mentor, and project directors Dr. Jay Zambito (Beloit College) and Dr. Jim Rougvie (Beloit College).
Prerequisites: Because this experience is a Gateway Project for rising sophomores, there are no specific coursework prerequisites.
Expectations and Obligations:
1. Participation in all project-related work during the summer (5 weeks)
2. Submission of an abstract (individual or in groups) and presentation of a paper (poster or talk) at the Geological Society of America Meeting in San Antonio in October, 2025 (all expenses covered).
PROJECT DESCRIPTION
Mississippi Valley Type (MVT) mineralization is an epigenetic, stratiform replacement of primary sedimentary features, predominantly in carbonate host rock. In one of its type regions, Upper Mississippi Valley Type mineralization is found throughout southwest Wisconsin and extends into Illinois, Iowa, and Minnesota (Fig. 1; see Heyl and West, 1982; Symons et al., 2010). While the most pervasive MVT mineralization in Wisconsin occurs in Ordovician carbonates, the underlying Cambrian quartz sandstone and dolomite-cemented glauconitic sandstone also contain MVT sulfide minerals, some of which bear exceptionally high levels of trace metals (Zambito et al., 2019, 2022a,b). The occurrence of trace metal-bearing MVT sulfides and sulfide weathering product oxides in these sandstones is significant because these strata serve as a regional groundwater aquifer as well as a source of industrial sand that is mined throughout west-central Wisconsin where these strata are well- exposed in the Driftless Area (Parsen and Zambito, 2014; Zambito et al., 2019). Therefore, redox changes resulting from water table fluctuations due to groundwater pumping and sandstone crushing/washing during industrial sand mining (ISM) processes are both potential sources of groundwater contamination by trace metals in the study area (Fig. 2).
Figure 1: Generalized geologic setting and concentration of Mississippi Valley Type (MVT) ore deposits in the study area. Wisconsin state boundary in darker gray and select county boundaries indicated by black lines. Grayscale gradient represents submarine depositional settings with the shallowest areas (pale gray) over the Wisconsin Dome and Arch in northern and central Wisconsin and becoming progressively deeper to the southwest and southeast into the Hollandale Embayment and Michigan Basin, respectively. During deposition of the Wonewoc Formation and Tunnel City Group rocks, the source of siliciclastic sediment (primarily quartz grains) was from modern north and may have included the Wisconsin Arch and Dome (Dott et al., 1986; Runkel et al., 2007, 2012). The blue box denotes both the area of recent previous work (Zambito et al., 2018, 2019, 2022a,b, in prep.; Haas et al., 2024) and this proposed research with a question mark indicating the area of outlying mineralization that will be refined by this study. Modified from Zambito and others (2019).
Figure 2: A) Generalized stratigraphy for the study area. ISM stands for industrial sand mining. B) Conceptual model (not to scale) showing the oxidation (red ‘ox’) of hypothetical sulfide zones (yellow ‘s’) due to water table fluctuations and the formation of a cone of depression in the water table through high-capacity well pumping. Unlabeled stratigraphic units are the same as in parts A, B and C of this figure. C) Conceptual model (not to scale) showing the hypothetical interaction of surface water (unlined storm runoff, process water, and/or settling pond) with groundwater at an industrial mine site through seepage and recharge. Note that strata are oxidized near the exterior of the hill being mined, but sulfides exist further within the hillside. This could be a potential source of groundwater contamination. E.C. stands for Eau Claire Formation. For wells in parts B and C, solid lines of boreholes represent cased portions of wells and dashed lines represent un-lined portions open to the aquitard-aquifer system; in these schematics the borehole in part B is only partially cased, while the borehole in part C is cased to depth. Modified from Zambito et al. (2022a).
Cambrian-Ordovician lithostratigraphy, sequence stratigraphy, and depositional environments have previously been described by Runkel and others (2007, 2012) as part of a regional synthesis of Upper Mississippi River Valley (see also Dott et al., 1986). More recent studies primarily focused in Trempealeau County, west-central Wisconsin (Figs. 3, 4, and 5; Zambito et al., 2018, 2019, 2022a,b; Haas et al., 2024) have identified trace-metal bearing sulfide and oxide minerals throughout the Cambrian sandstone succession, including within the aquifer sandstone and aquitard shale of the Mount Simon and Eau Claire formations, respectively, and the ISM target sandstone and overburden dolomitic glauconitic sandstone of the Wonewoc Formation and Tunnel City Group, respectively. In the proposed project the Project Directors and Students will build off this previous work by collecting a dataset of sulfide and oxide occurrence and trace metal composition in neighboring Buffalo County (located just south of Eau Claire, WI, see Fig. 3). The relative simplicity of the system (sulfides interacting with oxygen to become oxides) and the various techniques used on both outcrop and core samples will emphasize a variety of core concepts and skills in the geosciences for these Gateway Students.
Previous work has demonstrated that trace metal-bearing sulfides and oxides in the study area are a potential source of groundwater contamination (Zambito et al., 2019, 2022, a,b); indeed, water samples from private wells near, and process water ponds at, ISM sites show trace metal concentrations above safe levels (Zambito et al., 2019). The results of this project will therefore refine our understanding of not only the extent of MVT mineralization in west-central Wisconsin (Fig. 1) but provide a crucial dataset that will allow local and state government, industry, environmental groups, and private citizens to make more informed decisions regarding locating and permitting extraction of aggregate, industrial sand, and groundwater resources to minimize groundwater impacts. As part of the professional student learning outcomes of this project, the students will interact directly with researchers, environmental regulators, and policy makers in the study area thereby gaining first-hand experience in sharing their societally relevant research with stakeholders while simultaneously learning about potential career paths.
Figure 3: Buffalo County (located just south of Eau Claire, WI) is near the center of large-scale industrial (frac) sand mining (white squares) in west-central Wisconsin, and neighbors Trempealeau County were a large pre-existing data set of sulfide and oxide distribution and trace metal concentration is available from previous studies (Zambito et al., 2018, 2019, 2022a,b; Haas et al., 2024). Black X’s indicate (for the study area) common uses and high extraction rates for the designated purposes, gray X’s indicate less common uses and lower rates of extraction. Modified from Zambito and others (2018).
Figure 4: Photographs of select samples analyzed by XRD (modified from Zambito et al. 2019 and 2022a). A) Hand sample from the Tunnel City Group showing variable iron (hydr)oxide (subsamples a, b, c) and pyrite (subsample d) distribution on a slabbed surface. B, C) Core photograph and single ‘grain’ sample of pyrite, goethite, and hematite from a stratiform, potentially vug- filling rusty sulfide nodule in the Eau Claire Formation. D, E) Core photograph and single ‘grain’ sample of pyrite (in the form of external molds of sand grains) from a sulfide nodule that appears to be associated with Skolithos burrows in in the Mount Simon Formation. Single ‘grain’ samples range in size from ~0.1 to 0.3 mm, and are mounted on the slitted end of an amber-colored, <1 mm diameter tube and attached with vacuum glue. Drill core samples shown are approximately 5.0 to 6.0 cm wide.
Figure 5: Photographs of select core samples from Trempealeau County analyzed by pXRF showing elevated trace metal concentrations in disseminated sulfide cements in the Wonewoc Formation (A) and a stratiform pyrite nodule in the Tunnel City Group (B). Modified from Zambito and others (2019).
Potential Student Projects
The following potential student projects are suitable for rising sophomores and will serve the overall project goals by utilizing a variety of methods to develop a better understanding of sulfide and oxide occurrence and trace metal composition in the study area to constrain MVT mineralization.
Project 1. Mineralogy of outlying MVT mineralization (2-3 students): MVT deposits in the main mineralization (lead-zinc mining) district consist of galena and sphalerite, yet previous work (Zambito et al., 2019, 2022a) found most of the mineralization in the outlying area of MVT mineralization (Fig. 1) consists of trace metal-bearing pyrite. A compilation of new (Buffalo County) and previously published (Trempealeau County) mineralogical data of sulfides and oxides from the region obtained via XRD and SEM analysis will provide insights into regional MVT mineralization.
Project 2. Trace metal composition of sulfide and oxide minerals (2-3 students): Portable X-Ray Fluorescence Analysis (pXRF) offers a relatively cheap and fast tool for collecting large elemental datasets. The relatively small analysis window (8mm) also allows acquisition of data from mineralogically variable subsamples (see Fig. 4A). Students will collect data on trace metal composition across sulfide-oxide phase changes in samples from outcrop and core to document the mineral phases in which trace metals are present and develop a model for trace metal liberation through redox reactions. Subsequent ICP-MS analysis will be used to better constrain trace elemental concentrations.
Project 3. Lithostratigraphy of the Cambrian Succession, Buffalo County (2-3 students): To date, there has been no detailed lithostratigraphic work on the succession in Buffalo County. Previous work in neighboring Trempealeau County (Zambito et al., 2018, 2019, 2022, a,b) will serve as a reference for students to recognize stratigraphic units in the study area and interpret environmental changes that may represent a depositional depth gradient from the Wisconsin Arch to Hollandale Embayment (Fig. 1).
Project 4. Magnetic Susceptibility and the Stratigraphic Distribution of Sulfides and Oxides (2-3 students): Magnetic Susceptibility (MS) analysis provides information on the presence of magnetic minerals either in the iron-titanium oxygen (FeTiO) group or the iron-sulfur (FeS) group; each mineral or rock has a different average susceptibility value based on its composition. MS data is also a relatively cheap and fast tool for collecting large datasets. Systematic collection of MS data from cores in the study region will provide a stratigraphic dataset from which students can estimate if some sandstone units are more ‘mineralized’ than others and with which to compare to lithologic observations
Project Logistics
This Gateway Project includes a project introduction at Beloit College; field work in west-central Wisconsin (Buffalo County); core measuring and sampling at the Wisconsin Geological and Natural History Survey (WGNHS) core repository; laboratory analyses at Beloit College laboratories; and participation and presentation at the Geological Society of America National Meeting in San Antonio, TX. A tentative timeline for core repository/fieldwork, laboratory work, conference travel, and resulting products is outlined in Figure 6 and text below.
Figure 6: Gantt chart outlining tentative 5-week Keck project plan. See text below for details that include post-summer activities.
Pre-Project Planning
June 2025: At least 2 group Zoom meetings will cover personal introductions as well as travel and project logistics.
5-Week Keck Project
July 7: Students arrive at Chicago O’Hare Airport (ORD), travel by shuttle bus to Beloit College.
July 8-11: Project Intro: safety training and mini-lectures focused on mineralogy, sedimentology, etc.
July 12-13: Days off; students will have access to discount/thrift stores and pharmacies.
July 14-15: Project Intro: Discussion of previous literature and geologic maps.
July 16: Travel to field area in Buffalo County, Wisconsin by van.
July 17-21:Field work (outcrop sampling) and professional development (WI DNR, county officials, industry).
July 22: Travel back to Beloit College by van.
July 23-25: Day trips to WGNHS (core sampling) and professional development (WGNHS).
July 26-27: Days off.
July 28- Aug 1: Laboratory Analysis.
August 2-3: Days off.
August 4-5: Laboratory Analysis.
August 6-7: Prepare Poster for National GSA Meeting.
August 8: Students return home via travel by shuttle bus to Chicago O’Hare Airport (ORD).
Academic-Year Professional Development
August 2025: Students begin fall semester; Project Directors communicate GSA preparations.
October 2025: Students present group poster at National GSA Meeting (San Antonio, TX).
References
Dott, R.H., Byers, C.W., Fielder, G.W., Stenzel, S.R., Winfree, K.E., 1986. Aeolian to marine transition in Cambro-Ordovician cratonic sheet sandstones of the northern Mississippi Valley, U.S.A. Sedimentology. 33, 345–367. https://doi.org/10.1111/j.1365-3091.1986.tb00541.x.
Haas, L.D., Ginder-Vogel, M., Zambito, J.J., Hart, D., and Roden, E., 2024. Microbially-mediated oxidation of trace element-bearing pyrite in sandstone aquifer sediments, Environmental Science: Advances, Royal Society of Chemistry, https://doi.org/10.1039/d3va00399j
Heyl, A.V., West, W.S., 1982. Outlying mineral occurrences related to the upper Mississippi Valley mineral district, Wisconsin, Iowa, Illinois, and Minnesota. Econ. Geol. 77, 1803–1817. https://doi.org/10.2113/gsecongeo.77.8.1803.
Parsen, M.J., Zambito, J.J., 2014. Frac sand in Wisconsin. In: Wisconsin Geological and Natural History Survey Factsheet 05. https://wgnhs.wisc.edu/pubs/fs05/.
Runkel, A.C., Miller, J.F., McKay, R.M., Palmer, A.R., Taylor, J.F., 2007. High-resolution sequence stratigraphy of lower Paleozoic sheet sandstones in Central North America: the role of special conditions of cratonic interiors in development of stratal architecture. Geol. Soc. Am. Bull. 119 (7–8), 860–881. https://doi.org/10.1130/B26117.1.
Runkel, A.C., McKay, R.M., Cowan, C.A., Miller, J.F., Taylor, J.F., 2012. The Sauk megasequence in the cratonic interior of North America: Interplay between a fully developed inner detrital belt and the central great American carbonate bank. In: Derby, J.R., Fritz, R.D., Longacre, S.A., Morgan, W.A., Sternbach, C.A. (Eds.), The Great American Carbonate Bank: The Geology and Economic Resources of the Cambrian – Ordovician Sauk Megasequence of Laurentia, AAPG Memoir 98, pp. 1001–1011. https://doi.org/10.1306/13331526M983522.
Shonnard, C., Currano, E., Foreman, B., and Zambito, J.J., 2019. Early Paleogene overbank depositional patterns in the Hanna Basin and comparison with coeval strata in the Bighorn Basin (Wyoming, U.S.A.), Keck Geology Consortium Short Contributions 32:1-11.
Symons, D.T.A., Kawasaki, K., Pannalal, S.J., 2010. Paleomagnetic mapping of the regional fluid flow event that mineralized the upper Mississippi Valley Zn–Pb ore district, Wisconsin, U.S.A. J. Geochem. Explor. 106, 188–196. https://doi.org/10.1016/j.gexplo.2009.11.004.
Zambito, J.J., McLaughlin, P.I., Haas, L.D., Stewart, E.K., Hurth, M.J., and Bremmer, S.E., 2016, Sampling Methodologies and Data Analysis Techniques for Geologic Materials Using Portable X-Ray Fluorescence (pXRF) Elemental Analysis: Wisconsin Geological and Natural History Survey, Open- File Report WOFR2016-02, 5 appendices, 12 p.
Zambito, J.J., Mauel, S.W., Haas, L.D., Batten, W.G., Streiff, C.M., Chase, P.M., Niemisto, E.N., Heyrman, E.J., 2018. Preliminary bedrock geology of southern Trempealeau County, Wisconsin. In: Wisconsin Geological and Natural History Survey Open-File Report 2018-01, 29 p., 2 plates. https://wgnhs.wisc.edu/pubs/000954/.
Zambito, J.J., Haas, L.D., Parsen, M.J., McLaughlin, P.I., 2019. Preliminary geochemistry and mineralogy of the Wonewoc Formation and Tunnel City Group contact interval strata: implications for water quality. In: Wisconsin Geological and Natural History Survey Open-File Report 2019-01, 28 p., 5 appendices. https://wgnhs.wisc.edu/pubs/wofr201901/.
Zambito IV, J.J., Haas, L.D., Parsen, M.J., 2022a. Identifying the source of groundwater contaminants in west-central Wiscon- sin, U.S.A.: geochemical and mineralogical characterization of the Cambrian sandstone aquifer, J. Contam. Hydrol. 247: 103966, doi: 10.1016/j.jconhyd.2022.103966 .
Zambito, J., Haas, L., and Parsen, M., 2022b. A portable x-ray fluorescence (pXRF) elemental dataset collected from Cambrian-age sandstone aquifer material, Wisconsin, U.S.A., Data in Brief. https://doi.org/10.1016/j.dib.2022.108411 & https://doi.org/10.26022/IEDA/112311