20-6 Investigating the Origin and Water Contamination Potential of Trace-Metal Bearing Sulfides and Oxides in the Cambrian St. Lawrence Formation, Western Wisconsin​

Session: Undergraduate Research

Presenting Author:

Simone de Montigny

Authors:

de Montigny, Simone¹, Diesl, Madeleine², Goldstein, Arin³, Hueper, Samantha⁴, Rougvie, James R.⁵, Zambito, James Joseph⁶

(1) Beloit College, Beloit, WI, USA, (2) Mount Holyoke College, South Hadley, MA, , (3) Amherst College, Amherst, MA, USA, (4) Pennsylvania State University, University Park, PA, USA, (5) Beloit College, Beloit, WI, , (6) Beloit College, Beloit, WI, USA,

Abstract:

Sulfide and oxide minerals have been identified throughout the Cambrian sandstone succession in west-central Wisconsin. This study characterizes sulfide and oxide mineral occurrences in outcrop and core from the St. Lawrence Formation in Buffalo and Trempealeau County, WI. The occurrence of trace metal-bearing sulfides and sulfide weathering product oxides may contribute to high trace metal concentrations in groundwater from the underlying strata, which are a regional groundwater aquifer.​ Mineralogical and trace metal analysis of sulfides and oxides in the St. Lawrence help to determine how changing redox conditions may cause them to be a source of groundwater contamination, and whether they represent Cambrian diagenetic mineral growth or post-Cambrian Mississippi Valley Type (MVT) lead-zinc (Pb-Zn) mineralization outlying the main Upper Mississippi Valley Pb-Zn district.

St. Lawrence outcrop localities and core samples contain scattered iron oxide- and sulfide-bearing vugs and concretions, which were evaluated using XRD, SEM, ICP-MS and pXRF analyses. Trace metal concentrations in these minerals are variable. Some vugs and concretions display low trace metal values, whereas other samples show elevated (>1000 ppm) trace metal concentrations, particularly of lead, zinc, arsenic, copper, and nickel. Iron oxide and sulfide-filled vugs are relatively higher in lead, zinc, arsenic, and nickel as compared with iron oxide and sulfide concretions. Sulfide concretions show elevated levels of arsenic (As) and nickel (Ni), but lack the Zn and Pb concentrations indicative of MVT mineralization. The trace metal composition in both concretions and vugs could be indicative of MVT mineralization, extending the known distribution of outlying MVT mineralization. Thin-section analysis using reflected light and SEM will be used to further understand the mineralogy of these features and how reduction and oxidation may cause them to release trace metals. MVT mineralizing fluids likely moved through basement fractures and aquifer strata to reach the St. Lawrence Formation. Because similar mineralization likely occurs throughout underlying aquifer units, the presence of elevated trace metals in oxides and sulfides in this unit within Buffalo County provides insight into potential impacts on groundwater resources. As oxidation of sulfide minerals occurs, trace metals may be liberated; therefore, redox condition changes due to water table fluctuations are possible sources of groundwater contamination. This information can be used to inform best practices for well owners.

Geological Society of America Abstracts with Programs. Vol. 58, No. 1, 2026

doi: 10.1130/abs/2026SE-12775

© Copyright 2026 The Geological Society of America (GSA), all rights reserved.