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Item Bulletin No. 15. Preliminary Report on the Geology of East Central Minnesota Including the Cuyuna Iron-ore District(Minnesota Geological Survey, 1918) Harder, E.C.; Johnston, A.W.The geologic work in the Cuyuna iron-ore district is being done jointly by the Minnesota Geological Survey and the United States Geological Survey. Since only a few outcrops of bed rock occur in the district or in the region adjacent to it, the study has been based largely on the results of exploration and mining work. Many drill cores and records of diamond drilling from various parts of the district have been examined, and in addition the occurrence and structure of the rocks as shown in the underground and open pit workings of various mines have been studied in detail, and detailed geologic and topographic maps have been made of several of the open pit mines. In order to gain a more comprehensive idea of the major structure of the rocks of east central Minnesota. and particularly to note if possible the relation of the rocks of the Cuyuna district to such major structure, a careful study of the rock outcrops of the region lying west, south, and east of the Cuyuna district was made. This included the detailed mapping of most of the rock exposures lying nearest to the Cuyuna district in Cass, Todd, Morrison, Mille Lacs, Kanabec, Pine, Carlton, and Aitkin counties, and a more general study of the outlying exposures in these counties and also in Stearns, Benton, and Sherburne counties. North of the Cuyuna district, in the region lying between it and the Mesabi district, no rock outcrops are known and the relation between the rock formations of these two districts will have to be determined by underground exploration.Item Guidebook 9. Field Trip Guidebook for Stratigraphy, Structure and Mineral Resources of East-Central Minnesota(Minnesota Geological Survey, 1979) Morey, G.B.; Davidson, D.M. JrEarly in the 20th century, east-central Minnesota became the source of appreciable quantities of iron and ferromanganese, and even earlier, the source of a variety of granite products (Morey, 1977). Because of the obvious economic importance of the commodities to the state, most of the geologic work in east-central Minnesota focused on the Cuyuna iron-mining district or on the St. Cloud area where there are numerous granite quarries. Less attention was given to the geology of other parts of east-central Minnesota and to the possible presence of other mineral resources. This was true mainly because a fairly ubiquitous mantle of Quaternary materials made it difficult, time consuming and expensive for a company to establish the basic geologic information necessary to a successful exploration program. However, recent geologic work (Morey, 1978) has led to the recognition of several geologic environments that are similar to mineral-producing districts elsewhere in the world (Morey, 1977). Although these studies have shown that a variety of mineral occurrences may exist, most attention to date has focused on environments that may contain uranium. This road log starts at the Minnesota-Wisconsin border along the st. Louis River near Fond du Lac, the westernmost suburb of Duluth, Minnesota, and terminates near Sturgeon Lake on U.S. Interstate Highway 35 some 50 miles southwest of Duluth. Note that the mileages in this road log are approximate.Item Information Circular 28. Graphite in Early Proterozoic Rocks of East-Central Minnesota(Minnesota Geological Survey, 1989) McSwiggen, Peter L.; Morey, G.B.The Penokean orogen and southern Animikie basin of cast-central Minnesota contain numerous carbonaceous units. The carbon content of these units ranges from as little as 1-2 wt.% to as much as 44 wt.%; the thickness of these units ranges from a few inches to over 500 feet. By using published values for the energy content of some Finnish and Swedish carbonaceous rocks, it is possible to estimate the energy content in samples from this study. These values indicate that a ton of rock with 44 wt.% graphite contains approximately as much energy as one ton of lignite or a half ton of bituminous coal. This suggests that such a rock contains roughly $13.50-19.00/ton worth of energy. In certain localities, the carbonaceous units also contain significant precious and base metal concentrations. Values of as much as 350 ppb gold and 6 ppm silver were recorded.Item Information Circular 32. Geology and Manganese Resources of the Cuyuna Iron Range, East-Central Minnesota(Minnesota Geological Survey, 1990) Morey, G.B.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.