Information Circular 19. Geologic Terranes of Minnesota and Their Uranium Potential

Abstract

The geology of Minnesota is exceedingly complex (fig. 1). It is characterized by a wide diversity of superposed rock types ranging in age from about 3,600 million years (m.y.) before present to less than 10,000 years before present. Although complex, the rock record can be subdivided into seven bedrock units, or terranes, each having characteristic lithic and structural attributes (fig. 2). One additional terrane, consisting of unconsolidated glacial deposits of Pleistocene age, that overlies all of the bedrock terranes also is recognized. Uranium occurs in relatively small quantities, widely disseminated. in each of the geologic terranes in Minnesota. However, the formation of an ore deposit from which uranium can be profitably extracted requires a unique combination of geological conditions that occur at only a very few places in the world. Although exploration interest in a region may stem from the more or less random discovery of traces of mineralization, it more commonly begins with the knowledge that the geology of an area is comparable to the geology of areas where mineral deposits are known to occur. Evaluation of a region's mineral potential always starts with an evaluation of whatever information is available about the geology of the region.