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Assessing the Influence of Natural Copper-Nickel-Bearing Bedrocks of the Duluth Complex on Water Quality in Minnesota, 2013–15

Scientific Investigations Report 2020-5039
Prepared in cooperation with the University of Minnesota-Duluth Natural Resources Research Institute
By: , , , , , and 
https://doi.org/10.3133/sir20205039

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Abstract

The U.S. Geological Survey, in cooperation with the University of Minnesota-Duluth Natural Resources Research Institute, completed an assessment of regional water quality in areas of potential base-metal mining in Minnesota. Bedrock, soil, streambed sediment, and surface-water samples were collected in three watersheds that cross the basal part of the Duluth Complex with different mineral-deposit settings: (1) copper-nickel-platinum group element mineralization (Filson Creek), (2) iron-titanium-oxide mineralization (headwaters of the St. Louis River), and (3) no identified mineralization (Keeley Creek). At least 10 bedrock, 30 soil (2 each from 15 sites), and as many as 13 streambed sediment samples were collected in each watershed and analyzed for 44 major and trace elements, total and inorganic carbon, and 10 loosely bound metals (when possible). Surface-water samples were collected at four to nine locations in each watershed three to four times per year for 2 years (total of 141 environmental samples). Surface-water samples were analyzed for 10 trace metals (total and dissolved concentrations), 8 trace elements, 8 major ions (dissolved concentrations), alkalinity, and total and dissolved organic carbon.

Metal and element concentrations in solid media varied by watershed, representing local geology. Copper-nickel sulfide mineralization in the Filson Creek watershed was evidenced in bedrock, soil, and streambed sediments. In the Keeley Creek watershed, silicate mineralogy of underlying bedrock contributed metals to streambed sediments. Thick glacial cover masked potential bedrock contributions to solid media in the St. Louis River watershed. Water-quality data indicate that waters in all three watersheds are dilute. Water quality is more similar between the Filson and Keeley Creek watersheds, compared to the St. Louis River watershed, because of the difference in glacial cover. Metal concentrations (copper and nickel, in particular) in surface-water samples follow similar patterns of concentrations in solid media, indicating the influence of bedrock on water quality in Filson and Keeley Creeks. Data from this study provide a baseline of metal concentrations and general water quality within an area of active mineral exploration.

Suggested Citation

Elliott, S.M., Jones, P.M., Woodruff, L.G., Jennings, C.E., Krall, A.L., and Morel, D.L., 2020, Assessing the influence of natural copper-nickel-bearing bedrocks of the Duluth Complex on water quality in Minnesota, 2013–15: U.S. Geological Survey Scientific Investigations Report 2020–5039, 51 p., https://doi.org/10.3133/sir20205039.

ISSN: 2328-0328 (online)

Study Area

Table of Contents

  • Acknowledgments
  • Abstract
  • Introduction
  • Purpose and Scope
  • Description of Study Areas
  • Methods of Study
  • Solid Media Geochemistry and Water Quality near the Basal Part of the Duluth Complex
  • Summary
  • References Cited
Publication type Report
Publication Subtype USGS Numbered Series
Title Assessing the influence of natural copper-nickel-bearing bedrocks of the Duluth Complex on water quality in Minnesota, 2013–15
Series title Scientific Investigations Report
Series number 2020-5039
DOI 10.3133/sir20205039
Year Published 2020
Language English
Publisher U.S. Geological Survey
Publisher location Reston, VA
Contributing office(s) Upper Midwest Water Science Center
Description Report: x, 51 p.; 1 Table; 2 Appendices; Data Release
Country United States
State Minnesota
Other Geospatial Duluth Complex, Filson Creek, Keeley Creek, headwaters of the St. Louis River watersheds
Online Only (Y/N) Y
Google Analytic Metrics Metrics page
Additional publication details