166-4 Characterization of Manganese Mineralization at the Cuyuna Range, Central Minnesota

Session: Mineralogical Characterization of Economic Resources: From Critical Minerals to Gemstones

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Abstract:

The Paleoproterozoic Cuyuna Range of central Minnesota contains elevated levels of manganese when compared to other Iron Formations of the Lake Superior Region. It consists of a Penokean fold-and-thrust belt divided into the Emily District, North Range, and South Range which are separated by structural and stratigraphic discontinuities making each area geologically distinct. Although prior work has documented a variety of textural and mineralogical associations, this study provides new lithogeochemical data to further characterize the manganese-bearing lithologies across the Cuyuna Range in support of ongoing research for manganese and other critical minerals in Minnesota as part of the USGS Earth MRI program.

A total of 201 drill core samples of iron formation and country rocks were collected from 37 drill holes across the Emily District, North Range, and South Range. Core samples have been studied petrographically, compared to historic logs, and assessed geochemically. Preliminary results show both granular and banded types with variable levels of Mn enrichment with respect to average crust for both iron formation and country rocks across the range. Mn contents range from below average (< 0.1 %), above average (0.1-1 %), elevated (1-5 %), enriched (5-10 %), mangniferous (10-35 %), and highly manganiferous (>35%) - extending up to 50% Mn.

Iron formations of the Emily District contain some of the most elevated Mn contents and encompass varieties such as hematite and quartz-bearing granular and banded carbonate-silicate iron formation with chlorite and magnetite. Rock and mineral textures also show a variety of silica and oxide replacement features and relict sedimentary structures such as algal and oolitic-like concentric rims. Further mineralogical analyses via XRD and SEM, combined with new lithogeochemical results will aid in characterizing the nature of manganese mineralization regionally across the Cuyuna Range and better constrain lithologic groupings within each area.

Geological Society of America Abstracts with Program. Vol. 57, No. 6, 2025

doi: 10.1130/abs/2025AM-9229

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