The Nature and Development of the Wyoming Uranium Province
W.W. Boberg, 2010. "The Nature and Development of the Wyoming Uranium Province", The Challenge of Finding New Mineral Resources: Global Metallogeny, Innovative Exploration, and New Discoveries, Richard J. Goldfarb, Erin E. Marsh, Thomas Monecke
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Although the Wyoming uranium province has no individual deposits that can be considered giant deposits, it is nevertheless a major uranium province with occurrences in nearly all rock units. Significant uranium has been mined from geologic units of various ages from Cretaceous to the Oligocene. Approximately 91,000 metric tons (t) of U3O8 have been produced since the early 1950s and approximately 165,000 t U3O8 "forward-cost" reserves are recognized in the region.
The formation of the Wyoming uranium province most likely started during the Archean with the formation of granitic and metamorphic rocks of the Granite Mountains of central Wyoming. This is supported by the observation that the major uranium deposits within Cenozoic sedimentary rocks are generally in clusters that surround the Precambrian core complexes of central Wyoming.
Crustal deformation during the Laramide orogeny initiated formation of the uplifts and basins that characterize present-day Wyoming. Continued development of these structures throughout the early Tertiary resulted in Eocene breaching of the Precambrian cores of the uplifts and the creation of major basins containing significant volumes of Tertiary sediments. Extensive physical and chemical weathering of the Precambrian cores of the uplifts took place during early Tertiary due to the subtropical climate with high rainfall. The central Wyoming Precambrian granitic rocks lost 50 to 75 percent of their uranium content during the Laramide events.
Volcanism in the western United States affected the Wyoming region starting with the Challis-Absaroka volcanism in the middle to late Eocene, followed by extensive periods of volcanism from various centers that continued sporadically through the Pliocene and into the Quaternary. This span of more than 45 m.y. of volcanism resulted in extensive deposition of thick rhyolitic tuff sequences throughout the region. Some of the tuffs incorporated the weathered debris from the Precambrian highlands and this uranium-rich material was included in thick beds of tuffaceous sediments. Such uranium was readily leached by the dissolution of glassy ash and given the huge volumes of ash deposited across the region; additional uranium resources likely remain to be discovered.
Uranium-Pb age measurements demonstrate that formation of many major uranium districts in the province occurred in the late Eocene and throughout the Oligocene. However, in contrast, the southern Powder River basin deposits were formed during the Pliocene. The major deposits in the Wyoming uranium province occur in fluvial sedimentary units of both Paleocene and Eocene age, whereas other economic deposits in the province occur in Cretaceous sedimentary rocks and brecciated rocks of Precambrian age. Regardless of the age or type of host rock, it is likely that many of the deposits have a common genesis.
The ore-forming fluid for the roll-front and related deposits was uranium-enriched surficial water leaching ash fall tuffs and deeply weathered Precambrian rocks. Paleodrainage systems that shifted across the landscape in response to various regional and local tectonic events transported the uranium in surficial waters which, in turn, recharged the ground water below the paleodrainage systems. Permeable rock capable of transmitting significant quantities of the ground water were favorable locations for the deposition of uranium deposits. Precipitation of the uranium in sandstone host rocks was primarily due to reducing conditions caused by organic carbon buried with the original sediments or by the leakage of hydrocarbons into the sediments. Precipitation in karst regions in carbonate rocks was the result of acid neutralization.
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The Challenge of Finding New Mineral Resources: Global Metallogeny, Innovative Exploration, and New Discoveries
VOLCANIC-ASSOCIATED and sedimentary-exhalative massive sulfide deposits on land account for more than one-half of the world's total past production and current reserves of zinc and lead, 7 percent of the copper, 18 percent of the silver, and a significant amount of gold and other by-product metals (Singer, 1995). A new source of these metals is now being considered for exploitation from deep-sea massive sulfide deposits. Because the oceans cover more than 70 percent of the Earth's surface, many expect the ocean floor to host a proportionately large number of these deposits. However, there have been few attempts to estimate the global mineral potential. Significant accumulations of metals from hydrothermal vents have been documented at some locations (e.g., 91.7 Mt of 2.06% Zn, 0.46% Cu, 58.5 g/t Co, 40.95 g/t Ag, and 0.51 g/t Au in the Atlantis II Deep of the Red Sea: Mustafa et al., 1984; Nawab, 1984; Guney et al., 1988). Even more metal is contained in deep-sea manganese nodules. Current estimates in the U.S. Geological Survey (USGS) mineral commodities summaries indicate a global resource of copper in deep-sea nodules of about 700 Mt. In the Pacific "high-grade" area, an estimated 34,000 Mt of nodules contain 7,500 Mt of Mn, 340 Mt of Ni, 265 Mt of Cu, and 78 Mt of Co (Morgan, 2000; Rona, 2003). A number of countries, including China, Japan, Korea, Russia, France, and Germany, are actively exploring this area.