Geochemical characterization of solid media from three watersheds that transect the basal contact of the Duluth Complex, northeastern Minnesota

To document regional water quality in areas of potential base-metal mining, bedrock, soil, streambed sediment, and surface-water samples were collected and analyzed in three watersheds that cross the basal part of the Duluth Complex (northeastern Minnesota). The three watershed each had different mineral-deposit settings: (1) copper-nickel-platinum group element mineralization (Filson Creek), (2) iron-titanium-oxide mineralization (St. Louis River), and (3) no identified mineralization (Keeley Creek). At least 10 bedrock, 30 soil (two from 15 sites), and up to 13 streambed sediment samples were collected in each watershed and analyzed for 44 major and trace elements by a combined method using a combined inductively coupled plasma atomic emission spectrometry and mass spectrometry method (ICP-AE/MS), total and inorganic carbon, mercury and selenium by individual element methods, and 10 loosely bound metals (when possible). All analyzes were completed at the USGS contract lab using the sample analytical methods. Bedrock sample sites were chosen to provide comprehensive surficial bedrock chemistry within each watershed. Soil sample sites were selected by their proximity to bedrock sites, or to sample a range of glacial landscape features. Streambed sediment sample sites were selected in coordination with water quality sample sites and where surface mineralization was present.