Abstract Uranium and vanadium deposits have been mined in the United States since the latter part of the 19th century. Early mining of uranium deposits provided uranium used mainly for coloring glass and ceramic glazes, and associated radium needed in the field of medicine. Development of the atomic bomb by the United States during World War II, and burgeoning energy demands following the war, led to greatly increased production and use of uranium. The high rates of domestic production and use in the late 1950s and early 1960s were due to the need for uranium in nuclear weapons. Production in the United States again increased in the late 1970s owing to the increased development of nuclear power, but it declined sharply after 1980 because of environmental concerns over further use of nuclear power and the availability of cheaper foreign sources (Fig. 1). Vanadium also had early use for coloring glass and glazes. Today, the principal use of vanadium is for toughening and strengthening various steel alloys. Domestic use of vanadium has grown steadily, with surges in war years, to recent time, when economic reversals and the advent of cheaper foreign sources have substantially reduced domestic production of steel. Minor uses of vanadium include alloying with titanium, and as a catalyst. Discussion of the geology of deposits of uranium and/or vanadium in the United States is presented here in the context of the historical discovery and development of the deposits. We first describe deposits, mainly of vein and sandstone types, that

Abstract Uranium ore deposits occur in nearly every major rock type in the earth’s crust, and nearly all igneous, metamorphic, and sedimentary processes are capable of concentrating or dispersing uranium. However, only three types of deposits account for more than 70 percent of known Western World Reasonably Assured Resources (WWRAR): Precambrian quartz-pebble conglomerate type, Proterozoic unconformity type, and Phanerozoic sandstone type. Igneous-related processes in plutonic, volcanic, and magmatic-hydrothermal environments, considered important 25 years ago, now account for less than 10 percent of world resources known at present. The oldest known ore deposits were formed in conglomerates by placer processes under unique anoxic conditions. For the last 2.2 b.y., since oxygenation of the atmosphere, the genesis of both high- and low-temperature deposits has been dominated by three general geochemical processes: (1) oxidation of uranium to soluble U(VI) species permitting aqueous transport, perhaps most commonly as uranyl-carbonate complexes; (2) reduction, principally by C, S −2 , or Fe +2 species, to U(IV) to allow precipitation of uraninite (pitchblende), and coffinite, although the specific reductant commonly cannot be determined because these three tend to be associated geologically; and (3) igneous and metamorphic differentiation caused by exclusion of uranium from crystal structure of most rock-forming minerals. The geochemistry of uranium ore-forming processes has changed in time because of the evolution of life forms and their impact on the earth’s oxygen and carbon budgets. This evolution is reflected in changing predominance of ore types in geologic time: (1) pre-2.8 b.y. ago—no known uranium ore deposits; (2) ca. 2.8 to 2.2 b.y. ago—the first intràcratonic basins and anoxic atmosphere permitted accumulation of placer deposits of uraninite in quartz-pebble conglomerates; these deposits contain about 19 percent of the western world’s resources; (3) ca. 2.2 to 0.4 b.y. ago—following oxygenation of the atmosphere uranium was oxidized and transported as soluble U(VI) complexes to sites of reduction, commonly in organic carbon-rich marginal marine environments. Diagenesis, metamorphism, and near-surface redox enrichment subsequently formed unconformity-type, ultrametamorphic-type, and vein-type ore deposits which together contain more than 25 percent of the western world’s resources; (4) ca. 0.4 b.y. ago to present—after development of land plants the most important ore-forming process was redox-controlled deposition from ground water in continental sediments. Sandstone-type deposits, characteristic of this stage, contain about 40 percent of the western world’s resources.