Midcontinent Rift 'reef'-type PGE

Region Central, North Central
Mineral systems
Deposit types
Other minerals

Information leading to the delineation of this focus area

Basis for focus area PGE enrichment in the Sonju Lake Intrusion (Beaver Bay Complex) and rocks along the eastern side of the South Kawishiwi intrusion (Duluth Complex) ; Potato River Intrusion in the Mellen Complex has a similar magmatic style. Intrusions part of the 1.1 Ga Midcontinent Rift System.
Identified resources Unknown.
Production Unknown.
Status Sonju Lake intrusion (Minnesota) had reconnaissance exploration by Franconia Minerals; currently inactive. No exploration in the Potato River complex (Wisconsin).
Estimated resources Unknown.
Geologic maps Sonju Lake Intrusion: Miller, Brown and others (1993), scale 1:24,000; Potato River Intrusion: Cannon and others (1996), scale 1:100,000.
Geophysical data Adequate aeromagnetic coverage; inadequate aeroradiometric coverage.
Favorable rocks and structures Tholeiitic layered intrusions in the Duluth (Layered Series at Duluth-DLS) and Beaver Bay (Sonju Lake Intrusion) Complexes; Potato River Intrusion (part of Mellen Complex) in Wisconsin has similarities.
Deposits No data.
Evidence from mineral occurrences No data.
Geochemical evidence Multiple geochemical analyses through Sonju Lake Intrusion reported in Miller (1999).
Geophysical evidence No data.
Evidence from other sources No data.
Comments Deposit type compared to Skaergaard Intrusion; tholeiitic composition somewhat unusual for this type of deposit.
Cover thickness and description Thin glacial cover.
Authors Laurel G. Woodruff.
New data needs New mapping, high resolution geophysics.
Geologic mapping and modeling needs Mapping at 1:24,000 scale over Sonju Lake Intrusion; mapping over Potato River Intrusion of 1:100,000 scale.
Geophysical survey and modeling needs Need rank 1 aeromagnetic data in Minnesota and Wisconsin.
Digital elevation data needs Lidar in progress.