Information Circular 32. Geology and Manganese Resources of the Cuyuna Iron Range, East-Central Minnesota

Abstract

Ever since their discovery in 1904, it has been recognized that the iron-formations and associated ore deposits of the Cuyuna iron range in east-central Minnesota contained appreciable quantities of manganese which was extracted as ferromanganese ores from several mines on the North range from 1911 to 1984. The presence of this manganese resource sets the Cuyuna range apart from other iron-mining districts of the Lake Superior region. The emphasis of this report is on the geologic factors that seem to control how the manganese is distributed on the Cuyuna range. However because the range was exploited principally for its iron ores, much of the available information is fragmentary. Although the manganese is closely associated with the iron ores, it was carefully evaluated by only a few of the companies operating on the range. Other companies examined the manganese-bearing material in only a cursory manner, and therefore in spite of what appears to be an extensive data base, our knowledge of the geology of the manganese resources is fragmentary and in part confusing. It is not yet possible to construct a coherent, detailed picture of the primary origin of the manganese-bearing strata, the structure and stratigraphic positions of these strata, and the precise tenor, extent, and localization of the several different kinds of manganese-bearing material that have been recognized. The ultimate utilization of the Cuyuna manganese deposits will require new metallurgical and beneficiation techniques that must be designed specifically for the different kinds of ores, and this report, if nothing else, should call attention to the deficiencies of the present geological data base.