Sulfide and oxide mineralization occurs along the western and northern footwall contacts of the 1.1-Ga Duluth Complex (Complex) in northeastern Minnesota, which was emplaced during the formation of the Midcontinent Rift System. Platinum-group element mineralization is known to occur only along the western contact. The Duluth Complex is composed of troctolitic, gabbroic, and anorthositic rocks that form a series of individual intrusions that make up the Complex. These were emplaced into footwall rocks of Archean granite-greenstone terranes and Lower Proterozoic metasedimentary rocks (Biwabik and Gunflint Iron-Formations; Rove, Virginia, and Thomson Formations) and into the penecontemporaneous North Shore Volcanic Group basalts, which form the hanging wall, and, in some areas, the footwall. Development of riftrelated structures, both extensional and contractional, affected development of mineralization. Structural discontinuities provided conduits for emplacement of late-stage granophyric and pegmatitic iron-rich ultramafic rocks. Faults and folds were responsible for localizing massive sulfide mineralization, as well as, for providing conduits for later syn-to post-magmatic hydrothermal fluids.On the northern margin of the Complex, 81.6 million tons of low-grade titaniferous magnetite ore (approximately 12 to 14% TiO 2 ) occur in 14 bodies that range in size from 1 to 19 million tons. Oxide mineralization along the western contact contains 245 million tons of ≥10% TiO 2 . These include the Wyman Creek area, Longnose, Longear, and Section 17 bodies of the Partridge River Intrusion, and the Water Hen Intrusion of the southern Duluth Complex. Overall three types of oxide mineralization occur in the Duluth Complex: (1) oxide-rich metasedimentary inclusions in mafic or ultramafic rocks that exhibit metasedimentary textures and/or can be traced laterally into footwall iron-formation; (2) banded or layered oxide segregations that include cumulus oxide-rich horizons; and (3) late discordant oxide-bearing ultra-

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Geochemical analyses applied to lake sedimentary records can reveal the history of pollution by metals and the effects of remedial efforts. Lakes provide ideal environments for geochemical studies because they have steady deposition of fine grained material suitable for fixation of pollutants. The Laurentian Great Lakes are the most studied system in this field, and they have well-preserved chronological profiles. To date, this important system has been considered in parts for inorganic geochemistry, hampering basin-wide conclusions regarding metal contamination. We filled spatial and temporal gaps in a comprehensive geochemical analysis of 11 sediment cores collected from all five Great Lakes. Hierarchical cluster analysis of all Great Lakes samples divided the metal analytes into five functional groups: (1) carbonate elements; (2) metals and oxides with diverse natural sources, including a subgroup of analytes known to be anthropogenically enriched (Cd, Pb, Sn, Zn, and Sb); (3) common crustal elements; (4) metals related to coal and nuclear power generation; and (5) all of the co-occurring rare earth elements. Two contamination indices (Igeo and EF) applied to sedimentary metals indicated that Na, Co, Mn, Cd, Pb, Ta, and Cu were each, at some point during the Anthropocene, the most enriched metal pollutants in Great Lakes sediments. Land uses correlated with the metal analytes, such as increases in contaminant metals with the rise in catchment population and increases in carbonate elements (e.g. Ca) with agriculture. Certain contamination trends were observed basin-wide, such as for the atmospheric pollutant Pb, which followed a rise associated with fossil fuel combustion and a decline following the ban of leaded gasoline. Other trends were lake-specific, such as recent high concentrations of Na in Lake Superior, likely due to road salt applications, and a late-20th-century peak in Ca associated with algal whiting events in Lake Ontario. Some metals exceeded guidelines for sediment quality, in some cases prior to European settlement of the basin, indicating that a paleolimnological context is important for appropriate management of sediment contamination. The Great Lakes are sensitive to environmental changes such as pollution by metals, and it is clear that while there has been remedial success, results from the uppermost intervals of cores indicate ongoing problems.

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