Pembine-Wausau and Minnesota Paleoproterozoic

Region Central, North Central
Mineral systems
Deposit types
Critical minerals
Other minerals

Information leading to the delineation of this focus area

Basis for focus area The ~1.89-1.83 Ga Pembine Wausau island arc terrane (Schulz and Cannon, 2007) hosts multiple VMS deposits, including Crandon, Back Forty, Flambeau, Bend, Pelican, and Lynne. Only the oxide zone of the Flambeau deposit has been mined for Cu, Au, and Ag. Focus area is drawn to include all volcanic rocks of the Pembine-Wausau terrane as shown by Horton and others (2017), and age equivalent volcanic rocks in Minnesota.
Identified resources Identified resources of copper, gold, lead, and silver. Historical production of copper, gold, and silver (Flambeau Mine, Wisconsin).
Production Flambeau mine (1993-1997): 1.8 million tons of ore, producing 181,000 tons Cu, 334,000 oz Au, 3.3 million oz Ag.
Status Past mining; planned future production dependent on permitting (Back Forty, Michigan), and ongoing exploration in Wisconsin for VMS deposits for Au, Cu, Zn, Ag, and Pb.
Estimated resources Michigan: The Back Forty deposit has an estimated 16.6 Mt of Measured and Indicated mineral resources of over 1.0 million oz Au, 13.2 million oz Ag, 1.1 billion lbs Zn, 116 million lbs Cu, and 94 million lbs Pb (Puritch and others, 2018). Wisconsin: The Crandon deposit in Wisconsin, the largest deposit in the Pembine-Wausau terrane of Wisconsin, is estimated to contain 61.1 Mt of ore grading 1.04% Cu, 5.56% Zn, 0.48% Pb, 1.2 g/t Au, and 43 g/t Ag (Erickson and Cȏté, 1996; Lambe and Rowe, 1987).
Geologic maps Sims (1989, 1990), scale 1:250,000; Sims and Schulz (1993), scale 1:100,000.
Geophysical data Mostly inadequate (Rank 4) aeromagnetic coverage and inadequate aeroradiometric coverage.
Favorable rocks and structures Volcanic rocks associated with volcanic seafloor mineral systems.
Deposits Flambeau/Ladysmith mine (MRDS dep_id: 10302641), Crandon Zn-Cu deposit (MRDS dep_id: 10097436), Pelican River Zn-Cu deposit (MRDS dep_id: 10073160), Lynne deposit (MRDS dep_id: 10082574), Back Forty deposit.
Evidence from mineral occurrences MRDS.
Geochemical evidence No data.
Geophysical evidence No data.
Evidence from other sources No data.
Cover thickness and description Partially exposed; glacial cover in most areas.
Authors Benjamin J. Drenth, Laurel G. Woodruff.
New data needs Geological mapping, high resolution geophysics.
Geologic mapping and modeling needs Modern 1:24,000 scale geologic maps, drill core logs, and 3-D geologic model.
Geophysical survey and modeling needs High-resolution, Rank 1 aeromagnetic and aeroradiometric surveys.
Digital elevation data needs Lidar quality variable; adequate in much of Wisconsin, inadequate in much of Minnesota.