CARLTON COUNTY RECORDER
Commodities (Major) - Uranium
Development Status: Occurrence

The so-called "Arrowhead Mine" at this locality was dug into the Thomson Formation in about 1910 for carbonaceous slate to be used as coal, and possibly also as a gold prospect. Rocks in the immediate vicinity of the mine include thin, alternating beds of fine-grained graywacke, siltstone, and gray slate. However, the dominant lithology in the mine itself appears to be black carbonaceous slate, much fractured and impregnated with pyrite. Although bedding attributes have an easterly trend, the northerly trend of the pyrite-rich zone implies that it is a vein-filling deposit that follows a fracture. In general, the graywacke units at this locality contain various proportions of quartz, feldspar (K-feldspar and oligoclase), muscovite and minor amounts of chlorite and calcite. However, biotite in exposures just to the south of the mine indicates an increase in metamorphic grade in that direction. Carbonaceous material having a disordered graphite mineral structure is present throughout all of the rocks at this locality. Together with the muscovite, it defines a strong foliation in most of the coarser grained beds. It is more abundant and has a massive or globular habit in thin section in the fine-grained pelitic beds. Because the carbonaceous concentrations that embay and surround many silicate minerals are cut by small veinlets of quartz and muscovite, the carbonaceous material appears to be a primary component present before metamorphism. This is one of the two localities in east-central Minnesota known to have anomalously high radioactivity levels. A grab sample from the mine was assayed and found to contain 18 ppm U308 and 0.2 ppm gold (Ojakangas, 1976, p. 140). (Morey)

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Link to USGS MRDS:	10122316

Other Regions, Features and Areas containing this locality

References