Midcontinent Rift oxide-ultramafic intrusions (OUIs)

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 Small oxide-rich ultramafic intrusions cut troctolite and anorthosite have been encountered along the western margin of the Duluth Complex. These Ti-Fe± PGM±V oxide-bearing ultramafic intrusions are related to the 1.1 Ga Midcontinent Rift System.
Identified resources Identified titanium resources.
Production No known production.
Status Reporting-code-compliant resources established at two sites (Longnose and Titac/Section 34) by Cardero Resources. Resource estimate at Water Hen and bulk sampling conducted at Longnose.
Estimated resources Longnose 58 Mt @16.6% TiO2; Titac 45.1 Mt @ 15.0% TiO2; Water Hen 62 Mt @14% TiO2; deposits have potential for V (http://files.dnr.state.mn.us/lands_minerals/mcc_docs/2016_explore_titanium.pdf).
Geologic maps Miller and others (2001), scale 1:200,000 and 1:500,000.
Geophysical data Adequate aeromagnetic coverage; inadequate aeroradiometric coverage.
Favorable rocks and structures Small late oxide-rich plugs related to faults and large xenoliths of iron-formation.
Deposits Longnose (MRDS dep_id: 10082830), Section 34 deposit (Titac) (MRDS dep_id: 10111326), Waterhen (MRDS dep_id: 10082834).
Evidence from mineral occurrences MRDS.
Geochemical evidence No data.
Geophysical evidence Sharp small round features in aeromagnetic data.
Evidence from other sources Thirteen aeromagnetic/conductive features drilled as contact-type Cu-Ni targets have intercepted Ti-Fe ± PGM ± V oxide-bearing ultramafic intrusions.
Comments Oxide is intergrown coarse-grained ilmenite and titanomagnetite; very low in coproducts such as U, Th, Zr, and REE.
Cover thickness and description Thin to variable (10m +/-10m), 30m encountered in some drill holes near Duluth.
Authors Laurel G. Woodruff, George Hudak, David Dahl, Amy Block.
New data needs Two deposits (Longnose, Titac) have reasonable geological, geochemical, and mineralogical data. Fundamental geologic, geochemical, mineral chemical, structural data need further work in other occurrences.
Geologic mapping and modeling needs more detailed geologic mapping (1:24,000) in areas of known VMS deposits may be a good place to start, especially if supported by high-quality geophysics and lidar.
Geophysical survey and modeling needs Rank 1 aeromagnetic and radiometric data, gravity data, electromagnetic data would all be very helpful.
Digital elevation data needs Lidar variable; adequate, inadequate, and in progress.