Geologic settings in central and eastern Montana and in a few places in southwestern Montana are similar to the settings in areas favorable for the occurrence of uranium deposits. Several areas in Montana seem especially favorable for the occurrence of uranium.The alkalic igneous rock province of central Montana is similar to the one of the Colorado Plateau. On the basis of this analogy, certain areas in Montana, where the lithology and (or) structure are considered favorable for the occurrence of uranium, are suggested for prospecting. Seleniferous plants, similar to those that are uranium indicators on the Colorado Plateau, might be used as an aid in prospecting for uranium provided that the seleniferous shale areas are taken into account.Uranium deposits, similar to those in North and South Dakota, may be found in Cretaceous and Tertiary sandstones, lignites, and low-grade coals of eastern Montana; also, the magnetite-bearing beds of certain Cretaceoussandstones may contain fossil placer deposits of radioactive black minerals. Theoccurrence of uranium in basal conglomerates, quartzites, and sandstones in Africa and Ontario suggests that similar basal sedimentary rocks in central Montana may contain uranium.Many of the radioactivity anomalies in Montana found from the air are closely associated with the Eagle sandstone; others are associated with Precambrian basement rocks, Upper Cretaceous and Lower Tertiary igneous rocks, or sedimentary rocks of Jurassic and Cretaceous age. Glacial cover and lack of outcrops locally may hinder prospecting for uranium.
