Midcontinent Rift mafic-ultramafic satellite intrusions: record NC2018

Region	Central, North Central
States	Michigan Wisconsin
Mineral systems	Mafic magmatic
Deposit types	Iron-titanium oxide Nickel-copper-PGE sulfide
Commodities	copper gold iron phosphorus selenium silver
Critical minerals	vanadium
Other minerals	cobalt graphite nickel PGE REE tellurium titanium vanadium

Information leading to the delineation of this focus area

Basis for focus area	Mapped extent of mafic and ultramafic satellite intrusions related to the 1.1 Ga Midcontinent Rift System.
Identified resources	Identified vanadium resources.
Production	No known production.
Status	Unknown.
Estimated resources	Round Lake intrusion (Wisconsin) has a reported resource potential of 50 millions tons of 1.5% V in rock consisting of 72% titaniferous magnetite.
Geologic maps	Sims (1992), scale 1:500,000; Jirsa and others (2012), scale 1:500,000.
Geophysical data	Inadequate aeromagnetic and aeroradiometric coverage.
Favorable rocks and structures	Small mafic and ultramafic intrusions related to the early, magnetically reversed stage of the 1.1 Ga Midcontinent Rift System. Emplaced into country rock outside of the central rift area, and recognized by their geophysical attributes.
Deposits	Round Lake intrusion.
Evidence from mineral occurrences	Mudrey and others (2003).
Geochemical evidence	Geochemical analyses in Schulz, Woodruff and Nicholson (2014).
Geophysical evidence	Intrusions typically have strong magnetically reversed signatures, and are small and plug-like shape. Can sometimes be identified in poor quality aeromagnetic data against a background of Archean and Paleoproterozoic country rock.
Evidence from other sources	No data.
Cover thickness and description	Glacial cover ~ 25 m over the Round Lake intrusion.
Authors	Laurel G. Woodruff.
New data needs	New mapping, high resolution geophysics.
Geologic mapping and modeling needs	At present, OUIs are presented as single lithological units on state maps. More detailed mapping and analysis to further understand lithological relationships to mineralization in the OUI is needed to form the basis for further geological/mineralogical/geochemical/structural/geophysical/mineral potential studies and associated modeling.
Geophysical survey and modeling needs	Rank 1 aeromagnetic coverage may reveal additional OUIs, delineate intrusive geometry, and identify structural controls on discovered and undiscovered OUIs.
Digital elevation data needs	Lidar adequate.