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Overview

Scientific Issue and Relevance

Platinum-group elements (PGE) are critical commodities. They are essential for the U.S. economy; however the U.S. imports about 90 percent of the platinum-group elements that we need to use. There are no available substitutes.

Previous work done in the U.S. show that the areas with the greatest potential for these commodities are in south-central Montana (Stillwater Complex) and the Great Lakes Region (igneous rocks associated with Keweenawan magmatic event). Igneous rocks associated with the Keweenawan large-igneous province cover more than 160,000 km2 and include flood basalts, mafic intrusions, and minor rhyolite lava flows. Platinum-group elements occur in magmatic contact-type deposits found in two layered intrusions that crop out along the western margin of the Mesoproterozoic Duluth Complex, Minnesota. The Duluth Complex, related to Keweenawan large-igneous province and the Midcontinent Rift, is composed of several discrete intrusions formed from mafic to felsic magmas that were emplaced between 1,108 and 1,098 Ma into older rocks. Contact-type mineralization of interest (few percent of sulfide minerals) is found in the South Kawishiwi and the Partirdge River intrusions of the Duluth Complex.

Research Activities

Our current activities focus on two Keweenawan igneous intrusions (South Kawsishiwi, MN, and the Mellen Complex, WI) to determine how much platinum-group elements are present, how much could be found, and how it formed. Our first objective is to study the magmatic processes that lead to the formation of the compositionally zoned contact-type deposits in the South Kawishiwi intrusion and to probabilistically estimate the amount of undiscovered resource near the identified mineral occurrences. Our second objective is to document the contact-type mineralized occurrences at the Mellen Complex and complete a lithogeochemical survey that might provide insight on reef-type potential. Our three main tasks are listed below.

  1. Lithogeochemical and sulfur isotopic studies of the Maturi and Birch Lake mineral occurrences, South Kawishiwi Intrusion, Minnesota (Contact: Mike Zientek, mzientek@usgs.gov)
  2. Gaussian geostatistical simulation of contact-type mineralization in the South Kawishiwi Intrusion, Minnesota (Contact: Josh Coyan, jcoyan@usgs.gov)
  3. Platinum-Group Element (PGE) potential of the Mellen Complex, Wisconsin (Klaus Schulz, kschulz@usgs.gov)
core warehouse
Core warehouse in Ely, MN. Photo by M. Zientek, USGS.
scientists examining cores
USGS scientists Josh Coyan and Heather Parks examining drill core through the Maturi deposit. Photo by M. Zientek, USGS.
core textures
Textures of rock in drill core. Photo by M. Zientek, USGS.

Completed Activities

Assessment of the Platinum-Group Element Resources in Mafic-Ultramafic Igneous Intrusions of the Midcontinent Rift System, Lake Superior Region

Contacts: Michael Zientek, mzientek@usgs.gov, and Klaus Schulz, kschulz@usgs.gov

An earlier phase (2012-2016) of our project focused on conducting and publishing an assessment of the Duluth Complex and related mafic-ultramafic intrusions in the 1.1 Ga Midcontinent Rift System in the Lake Superior region. The research was conducted in coordination with the Minnesota Geological Survey, the Minnesota Department of Natural Resources, the Natural Resources Research Institute, academia, and industry.

Our work focused on:

  • preparing deposit models for reef-type and contact-type platinum-group element (PGE) deposits,
  • preparing the economic filter that will be used with the assessment,
  • acquiring and compiling publicly available data for the Duluth Complex and related mafic and ultramafic intrusions,
  • establishing relationships with partners, and
  • evaluating and selecting software to use for 3-D visualization and geostatistical resource estimation.

Products

Reports

Schulz, K.J., Woodruff, L.G., Nicholson, S.W., Seal, R.R., II, Piatak, N.M., Chandler, V.W., and Mars, J.L., 2014, Occurrence model for magmatic sulfide-rich nickel-copper-(platinum-group element) deposits related to mafic and ultramafic dike-sill complexes: U.S. Geological Survey Scientific Investigations Report 2010–5070–I, 80 p., https://doi.org/10.3133/sir20105070I.

Abstracts

Schulz, K.J., Woodruff, L.G., and Nicholson, S.W., 2014, Midcontinent Rift-related satellite mafic-ultramafic intrusions hosting Fe-Ti-V oxide deposits: Institute on Lake Superior Geology Annual Meeting Proceedings Volume 60, Part 1 - Program and Abstracts, p. 111-112. View ILSG 2014 Proceedings Volume. [PDF file, 19.5 MB]

Zientek, M.L., Schulz, K.J., Woodruff, L.G., Cannon, W.F., Nicholson, S.W., Zürcher, L., Parks, H.L., and Dicken, C., 2016, Assessment of Undiscovered Nickel-Copper-Platinum Group Element (Ni-Cu-PGE) Resources Related to Conduit-Type Mineralization in the Midcontinent Rift System, Michigan, Minnesota, Ontario, and Wisconsin: Institute on Lake Superior Geology Annual Meeting Proceedings Volume 62, Part 1 - Program and Abstracts, p. 155-156. View ILSG 2016 Proceedings Volume. [PDF file, 13.8 MB]

Partners

Indiana University Bloomington (Dr. Edward Ripley)

Natural Resources Research Institute, University of Minnesota (Dr. Dean Peterson)

Twin Metals Minnesota (Kevin Boerst and Nicole Hoffman)

The use of firm, trade, and brand names is for identification purposes only and does not constitute endorsement by the U.S. government.

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