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In Pennsylvania, uranium deposits occur in sedimentary rocks of Late Devonian to Late Triassic age in the Appalachian Plateaus, Ridge and Valley, and Piedmont provinces. As a result of searches made by prospectors and reconnaissance work by U.S. Geological Survey field parties, uranium occurrences have been discovered in three principal stratigraphic sequences: (1) Upper Devonian rocks, (2) Upper Mississippian and Lower Pennsylvanian rocks, and (3) Upper Triassic rocks. The uranium occurrences in Upper Devonian rocks are commonly associated with gray sandstone or shale that contains copper minerals and carbonaceous plant fossils, but this association is not marked in the largest deposits with the greatest concentration of uranium. The occurrences in the Upper Mississippian and Lower Pennsylvanian beds are in rocks that commonly contain carbonaceous material but do not have megascopically noticeable copper minerals. Those in the Triassic rocks contain small amounts of carbonaceous material, traces of copper, and some pyrite. Uraninite and possibly another black form of uranium oxide probably are primary minerals. Secondary uranium vanadates, phosphates, carbonates, silicates, and possibly arsenates are found in the various deposits. Spectrographic and chemical analyses show that the abundance of uranium is independent of the abundance of any other element. The only relation noted is that lead, vanadium, and selenium are most abundant in rocks in which uranium is also abundant. Some of the uranium occurrences probably formed by syngenetic deposition, others by early epigenetic concentration, and a few by relatively recent leaching and redeposition by ground water. Of the many known uranium occurrences only two, both in Carbon County, seem to be deposits of potential economic value.

Uranium occurrences in sedimentary rocks of Pennsylvania