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.
Five map inserts as pdfs with scales between 1 inch = 130 feet to 1 inch = 10 miles.
Harder, E.C.; Johnston, A.W..
Bulletin No. 15. Preliminary Report on the Geology of East Central Minnesota Including the Cuyuna Iron-ore District.
Minnesota Geological Survey.
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