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At least 109 records · Page 6Linked to original sources
USGS2001

Plant-uptake of uranium: Hydroponic and soil system studies

Limited information is available on screening and selection of terrestrial plants for uptake and translocation of uranium from soil. This article evaluates the removal of uranium from water and soil by selected plants, comparing plant performance in hydroponic systems with that in two soil systems (a sandy-loam soil and an organic-rich soil). Plants selected for this study were Sunflower ( Helianthus giganteus ), Spring Vetch ( Vicia sativa ), Hairy Vetch ( Vicia villosa ), Juniper ( Juniperus monosperma ), Indian Mustard ( Brassica juncea ), and Bush Bean ( Phaseolus nanus ). Plant performance was evaluated both in terms of the percent uranium extracted from the three systems, as well as the biological absorption coefficient (BAC) that normalized uranium uptake to plant biomass. Study results indicate that uranium extraction efficiency decreased sharply across hydroponic, sandy and organic soil systems, indicating that soil organic matter sequestered uranium, rendering it largely unavailable for plant uptake. These results indicate that site-specific soils must be used to screen plants for uranium extraction capability; plant behavior in hydroponic systems does not correlate well with that in soil systems. One plant species, Juniper, exhibited consistent uranium extraction efficiencies and BACs in both sandy and organic soils, suggesting unique uranium extraction capabilities.

International Journal of Phytoremediation↗
USGS1980

Uranium in secondary silica: A possible exploration guide

Study of uraniferous silica precipitates in the Shirley Basin, Wyoming, identified areas where ancient uraniferous ground water once ponded. Chalcedony collected from and directly beneath thick accumulations of rhyolite ash contain as much as 250 ppm uranium in a pre-ash topographic low and lesser concentrations (10 to 160 ppm) elsewhere. Differences in the U concentration of chalcedony collected from approximately the same stratigraphic horizon reflect the enrichment of uranium in ground water as it percolated downward and basinward through the overlying rhyolite ash. Uranium is homogeneously distributed as a uranyl species within the chalcedony and reflects coprecipitation of dissolved uranium and colloidal silica in a uraniferous silica-gel. Laboratory measurements of the partitioning of uranium between various solutions and silica-gel precipitates indicate that, for ranges of pH and dissolved carbonate typical of ground water, dried silica-gel contains about 400 to 1,000 times the uranium concentration of the solution from which it forms. Uranium is postulated to be incorporated as an adsorbed uranyl-silica-hydroxyl complex. A 20-m.y.-minimum apparent age for uraniferous chalcedony was obtained by U-Pb isotope dating. Reported minimum ages for nearby sedimentary uranium deposits generally lie between this age and the age of rhyolite which hosts the silica (32.4 + or - 2.6 m.y.). Leaching of uranium from ash during the period 20 to 32 m.y. is therefore compatible with a volcanic source-rock hypothesis.

Wyoming↗
USGS1954

Summary of investigations of uranium deposits in the Pumpkin Buttes area, Johnson and Campbell Counties, Wyoming

Uranium minerals were discovered in the Pumpkin Buttes area, Campbell and Johnson Counties, Wyo., by the U. S. Geological Survey in October 1951. From June to November 1952, an area of about 750 square miles was examined for uranium deposits, and 211 localities having abnormally high radioactivity were found; uranium minerals are visible at 121 of these localities. All known uranium mineralization in the area is restricted to sandstones of the Wasatch formation, except sparsely disseminated uranium in the sandstone of the White River formation, which caps the Pumpkin Buttes, mid several localities on the Great Pine Ridge southwest of the Pumpkin Buttes where iron-saturated sandstone and clinker in the Fort Union formation have above-normal radioactivity. The uranium occurrences in the Wasatch formation are in a red sandstone zone 450 to 900 feet above the base of the formation and are of two types: small concretionary masses of uranium, iron, manganese and vanadium minerals in sandstone, and irregular zones in which uranium minerals are disseminated in sandstone. The second type is usually larger but of lower grade than the first. Most of the localities at which uranium occurs are in a north-trending belt about 60 miles long and 18 miles in maximum width.

Wyoming↗
USGS2026

Uranium—Deposits, production and resources, market dynamics, and supply chain risks

Introduction Interest in nuclear power for the generation of electricity has risen with the increase in the need for more diverse baseload power, enhanced energy security, and the development of new technologies, such as small modular reactors (SMRs), which could provide power for remote areas, industrial applications, and artificial intelligence (AI) data centers. In 2024, the U.S. Department of Energy received $2.7 billion in congressional funding to bolster the domestic uranium production and nuclear fuel supply chain and address reliance on imports from foreign suppliers. In 2025, the U.S. Government issued several Executive and Secretary’s orders aimed at revitalizing the U.S. nuclear sector. If SMRs are to be as widely deployed in the United States and worldwide as envisioned, demand for uranium (nuclear reactor fuel) will likely increase. After the Fukushima nuclear accident in 2011, the market spot price of uranium began a decline, followed by a decrease in U.S. and global uranium exploration and mine development expenditures that led to a uranium supply deficit until 2020, when prices started to recover, prompting a resurgence in uranium exploration and development. In January of 2024, the uranium spot price rose to a 17-year high $106 (U.S. dollars) per pound of U3O8 (triuranium oxide, commonly known as “yellowcake”), which is expected to increase uranium exploration, mine development, and uranium production domestically and worldwide.

Fact Sheet↗
USGS2015

Uranium in the Wyoming Landscape Conservation Initiative study area, southwestern Wyoming

Wyoming has led the nation as the producer of uranium ore since 1995 and contains the largest reserves of any state. Approximately one third of Wyoming’s total production came from deposits in, or immediately adjacent to, the Wyoming Landscape Conservation Initiative (WLCI) study area in the southwestern corner of the state including all of Carbon, Lincoln, Sublette, Sweetwater, Uinta, and parts of southern Fremont Counties. Conventional open-pit and underground mining methods were employed in the study area until the early 1990s. Since the early 1990s, all uranium mining has been by in-situ recovery (also called in-situ leach). It is estimated that statewide remaining resources of 141,000 tonnes of uranium are about twice the 84,000 tonnes of uranium that the state has already produced. An evaluation of the mineral commodities present in the WLCI study area that may have a role in the development of southwest Wyoming includes uranium. The WLCI study area contains five uranium mineralized areas: Ketchum Buttes, Poison Basin, Shirley Basin, the southern part of Crooks Gap–Green Mountain, and most of Great Divide Basin. Mineralized areas described in the report and outlined on an accompanying map are based on the presence of either contiguous claim blocks, continuous mineralization adjacent to prospective uranium properties, suggestions of mineralization based on site entries in the U.S. Geological Survey’s Mineral Resources Data System (MRDS), or extension of geologic host units or structures. Mineralized areas are not the same as mining districts: the latter have defined administrative boundaries. In the WLCI study area, all uranium areas except Poison Basin and Ketchum Buttes contain roll-front deposits in Eocene (56–34 Ma) sedimentary rocks. Tabular sandstone-hosted uranium deposits are also recognized within the study area.

Wyoming↗
USGS1979

Radium and uranium concentrations and associated hydrogeochemistry in ground water in southwestern Pueblo County, Colorado

Radium and uranium concentrations in water from 37 wells tapping the aquifer system of the Dakota Sandstone and Purgatoire Formation in southwestern Pueblo County, Colorado, have a wide range of values and define several areas of high radioactivity in the ground water. Radium ranges from 0.3 to 420 picocuries per liter and has a median value of 8.8, and uranium ranges from 0.02 to 180 micrograms per liter and has a median value of 2.4. Radon concentrations, measured in 32 of the 37 wells, range from less than 100 picocuries per liter to as much as 27,000 and have a median value of 580. Relationships among the radioactive elements and 28 other geochemical parameters were studied by using correlation coefficients and R-mode factor analysis. Five factor groups were determined to represent major influences on water chemistry: (1) short-term solution reactions, (2) oxidation reactions, (3) hydrolysis reactions, (4) uranium distribution, and (5) long-term solution reactions. Uranium concentrations are most strongly influenced by oxidation reactions but also are affected by solution reactions and distribution of uranium in the rocks of the aquifer system. Radon and radium concentrations are mostly controlled by uranium distribution; radium also shows a moderate negative relationship with oxidation. To explain the statistical and spatial relationships among the parameters, a model was developed involving the selective leaching of uranium-bearing phases and metal sulfides which occur in discontinuous zones in sandstone and shale. When reducing conditions prevail, uranium is immobile, but radium can be taken into solution. When faults and associated fractured rocks allow oxidizing conditions to dominate, uranium can be taken into solution; radium can also be taken into solution, or it may become immobilized by coprecipitation with iron and manganese oxides or with barite. Several areas within the study area are discussed in terms of the model.

Open-File Report↗
USGS1953

Occurrences of uranium-bearing minerals in the St. Kevin District, Lake County, Colorado

Two hundred and seventy-one prospect pits, mine dumps, or mine workings within the Sugar Loaf-St. Kevin mining districts and vicinity were tested for radioactivity by the U.S. Geological Survey in 1951 during six weeks of investigation on behalf of the Division of Raw Materials of the U.S. Atomic Energy Commission. One hundred and twenty-two weak radioactivity anomalies were found in the St. Kevin district and vicinity, and eight slight anomalies were noted in the Sugar Loaf district, which adjoins the St. Kevin district on the south. Most of the radioactivity anomalies were found in igneous and metamorphic rocks of pre-Cambrian age, but some were found in metalliferous veins of Tertiary age. Samples of altered granite or schist contain as much as 0.065 percent uranium, probably in the form of secondary uranium minerals. Samples of vein material contain as much as 0.013 percent uranium, also probably in the form of secondary uranium minerals. At only a few localities has the identity of the uranium-bearing minerals been determined. Torbernite, associated with turquoise, malachite, and chrysocolla, occurs as disseminations and fracture coatings in altered granite at the Josie May turquoise mine; metatobernite is disseminated in granite at the Turquoise Chief mine. Commonly the limonite-stained fractures in the altered granite and schist are radioactive; metatorbernite has been identified in limonite stain at one locality. A uranium-variety of florencite, a hydrous cerium aluminum phosphate, is disseminated in the granite on the dump of a mine just west of the St. Kevin district, and autunite (?) is disseminated in fine-grained, highly silicified rock in the northeastern part of the St. Kevin district. None of the uranium occurrences are of commercial importance. They are for the most part in non-glaciated terrane, which has been subjected to a very long period of weathering. Thus, chemical leaching within the zone of weathering may have greatly reduced the uranium content of material near the surface, and occurrences of even small quantities of secondary uranium minerals might be related to stronger, primary concentrations at depth.

Colorado↗
USGS1955

Radioactivity and uranium content of some Cretaceous shales, central Great Plains

The Sharon Springs member of the Pierre shale of Cretaceous age, a hard black organic-rich shale similar to the Chattanooga shale, is radioactive throughout central and western South Dakota, most of Nebraska, northern Kansas, and northeastern Colorado. In the Missouri River valley, thin beds of the shale contain as much as 0.01 percent uranium. Beds as much as 20 feet thick or more have a radioactivity of about 0.01 percent equivalent uranium in southwestern Nebraska according to interpretation of gamma-ray well logs. The radioactivity and uranium content is highest in the Missouri River valley in South Dakota and in southwestern Nebraska where the shale rests disconformably on the underlying Niobrara formation of Cretaceous age. Near the Black Hills, and in the area to the north, the shale of the Sharon Springs member rests on a wedge of the Gammon ferruginous member of the Pierre, which is represented by a disonformity to the east and south, and the radioactivity of the shale is low although greater than that of over-lying strata. The shale also contains a suite of trace elements in which arsenic, boron, chromium, copper, molybdenum, nickel, selenium, and vanadium are conspicuous. Molybdenum and tin are less abundant in the Sharon Springs than in similar shales of Palezoic age and silver and selenium are more abundant. In the Great Plains region, the upper 30-50 feet of Cretaceous shales overlain unconformably by the White River group of Oligocene age has been altered to bright-colored material. This altered zone is chiefly the result of pre-Oligocene weathering although post-Oligocene ground water conditions also have affected the zone. The greatest radioactivity occurs in masses of unaltered shale measuring about 1 x 4 feet in cross section included in the lower part of the altered zone. Where the zone is developed on shale and marl of the Niobrara formation, parts of the included unaltered shale contains as much as 0.1 percent equivalent uranium and 0.03 percent uranium. The disequalibrium between equivalent uranium (radioactivity) and the uranium content of the shales is believed to be a surface feature caused by relatively recent leaching of uranium from the present outcrops. The co-extensive distribution of the altered zone of Cretaceous shales and strata of the overlying White River group suggest that most of the uranium in the small masses of unaltered marl in the altered zone has been derived from the White River group.

Colorado;Kansas;Nebraska;Wyoming↗
USGS1953

Summary of investigations of uranium deposits in the Pumpkin Buttes area, Johnson and Campbell Counties, Wyoming

Uranium minerals were discovered in the Pumpkin Buttes area Campbell and Johnson Counties by the U.S. Geological Survey in October 1951 From June to November 1952 an area of about 750 square miles was examined for uranium deposits, and 211 localities with abnormally high radioactivity were found uranium minerals are visible at 121 of these localities. All known uranium mineralization is restricted to sandstones of the Wasatch formation exclusive of sparsely disseminated uranium in the White River sandstone which caps the Pumpkin Buttes and several localities on the Great Pine Ridge southwest of the Pumpkin Buttes where ironstone and clinker in the Fort Union formation have above normal radioactivity. The uranium occurrences in the Wasatch formation are in a red sandstone zone 450 to 900 feet above the base of formation and are of two types. (1) small concretionary masses of uranium, iron, and manganese minerals in sandstone and (2) irregular zones in which uranium minerals are disseminated in sandstone The second type is usually larger but lower grade than the first type. Most of the localities at which uranium occurs are in a north -trending belt approximately 60 miles long with a maximum width of 18 miles,

Wyoming↗
USGS1956

Summary of the mineralogy of the Colorado Plateau uranium ores

In the Colorado Plateau uranium has been produced chiefly from very shallow mines in carnotite ores (oxidized vanadiferous uranium ores) until recent deeper mining penetrated black unoxidized ores in water-saturated rocks and extensive exploration has discovered many deposits of low to nonvanadiferous ores. The uranium ores include a wide range from highly vanadiferous and from as much as one percent to a trace of copper, and contain a small amount of iron and traces of lead, zinc, molybdenum, cobalt, nickel, silver, manganese, and other metals. Recent investigation indicates that the carnotite ores have been derived by progressive oxidation of primary (unoxidized) black ores that contain low-valent uranium and vanadium oxides and silicates. The uranium minerals, uraninite and coffinite, are associated with coalified wood or other carbonaceous material. The vanadium minerals, chiefly montroseite, roscoelite, and other vanadium silicates, occur in the interstices of the sandstone and in siltstone and clay pellets as well as associated with fossil wood. Calcite, dolomite, barite and minor amounts of sulfides, arsenides, and selenides occur in the unoxidized ore. Partially oxidized vanadiferous ore is blue black, purplish brown, or greenish black in contrast to the black or dark gray unoxidized ore. Vanadium combines with uranium to form rauvite. The excess vanadium is present in corvusite, fernandinite, melanovanadite and many other quadrivalent and quinquevalent vanadium minerals as well as in vanadium silicates. Pyrite and part or all of the calcite are replaced by iron oxides and gypsum. In oxidized vanadiferous uranium ores the uranium is fixed in the relatively insoluble minerals carnotite and tyuyamunite, and the excess vanadium commonly combines with one or more of the following: calcium, sodium, potassium, magnesium, aluminum, iron, copper, manganese, or barium, or rarely it forms the hydrated pentoxide. The relatively stable vanadium silicates are little affected by oxidation. The unoxidized nonvanadiferous ores contain uraninite and coffinite in close association with coalified wood and iron and copper sulfides, and traces of many other sulfides, arsenides and selenides. The oxidized nonvanadiferous ores differ from the vanadiferous ores because, in the absence of vanadium to complex the uranium, a great variety of secondary yellow and greenish-yellow uranyl minerals are formed. The uranyl sulfates and carbonates are more common than the oxides, phosphates, arsenates, and silicates. Because the sulfates and carbonates are much less stable that carnotite, the oxidized nonvanadiferous ores occure only as halos around cores of unoxidized ore and do not form large oxidized deposits close to the surface of the ground as carnotite ores. Oxidation has taken place since the lowering of the water table in the present erosion cycle. Because of local structures and the highly lenticular character of the fluviatile host rocks perched water tables and water-saturated lenses of sandstone are common high above the regional water table. Unoxidized ore has been preserved in these water-saturated rocks and the boundary between oxidized and unoxidized ore is very irregular.

Utah↗
USGS1956

Host rocks and their alterations as related to uranium-bearing veins in the United States

This paper, dealing with the different kinds of host rocks and their alterations associated with uranium-bearing veins in the United States, is a chapter of a comprehensive report entitled , "Geology of uranium-bearing vein deposits in the United States," in preparation by George W. Walker, Frank W. Osterwald, and others. The comprehensive report will include detailed information on tectonic and structural setting, kinds of host rocks, wall-rock alteration, mineralogy, physical characteristics, processes of deposition, and concepts of origin of uraniferous veins; but, because it will not be completed until sometime in the future, some chapters of the report are being transmitted as they are finished. Part of an introductory chapter to the comprehensive report entitled, "Classification and distribution of uranium-bearing veins in the United States" (Walker and Osterwald, 1956) has already been transmitted; several of the terms used herein are defined in the introductory chapter. Data included in this chapter demonstrate that uranium-bearing veins are: 1) in rocks of nearly all textural, chemical, and mineralogic types; 2) most abundant in holocrystalline, commonly equigranular, igeneous and metamorphic rocks characterized by a moderate to high silica content and and by similar physical properties. Although some of the physiochemical properties of the host rocks are discussed in terms of favorability or nonfavoribility for uranium deposition, the principal purpose of this chapter is to establish the petroloic environment in which uranium-bearing veins have been found. Because favorability or nonfavorability of host rocks is related complexly to the chemistry of ore solutions and to methods or uranium transport and deposition, several hypothetical processes of transport and deposition have been referred to briefly; these and other hypotheses will be outlines and discussed in greater detail in a subsequent chapter. The compilation of data leading to this report and its preparation by a member of the Uranium Research and Resource Section, U.S. Geological Survey, was done on behalf of the Division of Raw Materials, U.S. Atomic Energy Commission. The report is based on both published and unpublished information collected principally by personnel of the U.S. Geological Survey, the U.S. Atomic Energy Commission or its predecessor organization, the Manhattan Engineer District, and to a lesser extent by staff members of other Federal or State agencies and by geologists in private industry. Information concerning foreign uranium-bearing vein deposits has been extracted almost exclusively from published reports; references to these and other data are included at appropriate places.

Trace Elements Investigations↗
USGS1950

The Leyden uranium prospect, Jefferson County, Colorado

The Leyden uranium prospect is in sec. 28, T, 2 S., R. 70 W, Jefferson County, Cplo, Examination of the property was made in February 1950. Uranium was first reported in this locality in 1875 by Captain E. L. Berthoud, who noted uranium minerals associated with the main coal bed. The Old Leyden coal mine workings have long been abandoned and caved, but specimens of the uranium-bearing rock can be seen on the old dump 700 feet to the south. The mineralized coal bed is 10 to 12 feet thick and occurs near the base of the Laramie formation of Upper Cretaceous age. Uranium minerals are present in the form of yellow incrustations and inclusions in fractured and partly silicified coal. Petrographic studies indicate that the silica and uranium minerals were deposited after deposition and carbonization of the coal. Secondary uranium minerals also were found by C. R. Butler along the outcrop of the sandstones in the Laramie formation. No uranium minerals were found in place by the writer, but four samples from the dump contained 0.001, 0,005, 0.17 and 0.69 percent uranium.

Colorado↗
USGS2022

A methodology to assess the historical environmental footprint of in-situ recovery (ISR) of uranium: A demonstration in the Goliad Sand in the Texas Coastal Plain, USA

In-situ recovery (ISR) has been the only technique used to extract uranium from sandstone-hosted uranium deposits in the Pliocene Goliad Sand in the Texas Coastal Plain. Water plays a crucial role throughout the ISR lifecycle of production and groundwater restoration yet neither the water use nor other environmental footprints have been well documented. The goal of this study is to examine historical records for all six ISR operations completed in the Goliad Sand to identify and quantify parameters that indicate the surface and aquifer disturbances, water use, and radon emissions. Overall, the average mine area was 0.00023 ± 0.00006 acres per pound (ac/lb) U 3 O 8 . The average mine pore volume was 48.9 ± 50 gal/lb U 3 O 8 with a minimum affected aquifer volume of 0.51 ± 0.08 cubic feet per pound (cu ft/lb) U 3 O 8. An average of 258 ± 40 gallons (gal) of fluid were disposed per pound (lb) U 3 O 8 , with an average of 169 ± 26 gal/lb U 3 O 8 attributed to restoration and 89 ± 36 gal/lb U 3 O 8 attributed to the uranium production phase. The average radon emitted was 1.06 × 10 −3 ± 7.4 × 10 −4 curies per pound (Ci/lb) U 3 O 8 . Goodness-of-fit ( R 2 ) values are ≥0.79 for linear regressions of the amount of uranium produced versus mine area, mine pore volumes, mine aquifer volumes, water pumped, and total water disposed. The R 2 value for radon emitted was 0.68. However, the water disposed only during the uranium production phase is more strongly correlated to the number of production days ( R 2 = 0.96) than to uranium production ( R 2 = 0.84), whereas the volume of water disposed during restoration is more strongly correlated to the “pore volume” ( R 2 = 0.97) than to uranium production ( R 2 = 0.90). Pore volume is an industry term used to describe the amount of fluid circulated through the aquifer during the uranium production period and stipulated in bond agreements in order to satisfy groundwater restoration requirements. Models constructed in this study can be used to estimate probable water use and the extent of surface and aquifer disturbances associated with ISR-amenable undiscovered uranium resources in the Goliad Sand. The historical perspective offered by the data compiled and correlations may prove useful to both industry and regulators.

Texas↗
USGS1980

Research on interactive genetic-geological models to evaluate favourability for undiscovered uranium resources

Current methods of evaluating favourability for undiscovered uranium resources are unduly subjective, quite possibly inconsistent and, as a consequence, of questionable reliability. This research is aimed at reducing the subjectivity and increasing the reliability by designing an improved method that depends largely on geological data and their statistical frequency of occurrence. This progress report outlines a genetic approach to modelling the geological factors that controlled uranium mineralization in order to evaluate the favourability for the occurrence of undiscovered uranium deposits of the type modeled. A genetic model is constructed from all the factors that describe the processes, in chronological sequence, that formed uranium deposits thought to have a common origin. The field and laboratory evidence for the processes constitute a geologic occurrence base that parallels the chronological sequence of events. The genetic model and the geologic-occurrence base are portrayed as two columns of an interactive matrix called the "genetic-geologic model". For each column, eight chronological stages are used to describe the overall formation of the uranium deposits. These stages consist of (1) precursor processes; (2) host-rock formation; (3) preparation of host-rock; (4) uranium-source development; (5) transport of uranium; (6) primary uranium deposition; (7) post-deposition modification; and (8) preservation. To apply the genetic-geological model to evaluate favourability, a question is posed that determines the presence or absence of each attribute listed under the geologic-occurrence base. By building a logic circuit of the attributes according to either their essential or non-essential nature, the resultant match between a well-documented control area and the test area may be determined. The degree of match is a measure of favourability for uranium occurrence as hypothesized in the genetic model. This process of geological decision analysis results in a series of favourability maps that can be combined into a final composite favourability map.

Conference Paper↗
USGS1978

Uranium in waters and aquifer rocks at the Nevada Test Site, Nye County, Nevada

Previous chemical, geological, and hydrological information describing the physical and chemical environment of the Nevada Test Site (a Federal reserve for the testing of nuclear explosive devices) has been combined with new radiochemical and isotope data for water and rock samples in order to explain the behavior of uranium during alteration of thick sequences of rhyolitic volcanic rocks and associated volcaniclastic sediments. A model is proposed in which uranium mobility is controlled by two competing processes. Uranium is liberated from the volcanic rocks through dissolution of the glassy constituents and is carried in solution as a uranyl carbonate complex. Uranium is subsequently removed from solution by adsorption on secondary oxides of iron, titanium, and manganese, as observed in fission-track maps of aquifer rocks. The model explains the poor correlation of dissolved uranium with depth within tuffaceous sequences in which percolation of ground water is predominantly downward. Good positive correlation of dissolved uranium with dissolved Na, total dissolved solids, and total carbonate supports the glass dissolution model, while inverse correlation of dissolved uranium with U 234 /U 238 ratios of waters implies uranium is being absorbed by a relatively insoluble, surficial phase. Alpha radioactivity of Test Site water is primarily caused by high U 234 contents, and beta activity is highly correlated with dissolved K (K 40 ). Small amounts of dissolved radium, Pb 210 , and Po 210 are present but no evidence was found for alpha activity sources related to nuclear testing (Pu, U 235 ). A filtered but unacidified carbonate solution of uranium was found to be stable (± 10 percent of original U concentration) for years when stored in acid-washed polyethylene bottles.

Nevada↗
USGS2015

Persistent U(IV) and U(VI) following in-situ recovery (ISR) mining of a sandstone uranium deposit, Wyoming, USA

Drill-core samples from a sandstone-hosted uranium (U) deposit in Wyoming were characterized to determine the abundance and distribution of uranium following in-situ recovery (ISR) mining with oxygen- and carbon dioxide-enriched water. Concentrations of uranium, collected from ten depth intervals, ranged from 5 to 1920 ppm. A composite sample contained 750 ppm uranium with an average oxidation state of 54% U(VI) and 46% U(IV). Scanning electron microscopy (SEM) indicated rare high uranium (&sim;1000 ppm U) in spatial association with P/Ca and Si/O attributed to relict uranium minerals, possibly coffinite, uraninite, and autunite, trapped within low permeability layers bypassed during ISR mining. Fission track analysis revealed lower but still elevated concentrations of U in the clay/silica matrix and organic matter (several 10 s ppm) and yet higher concentrations associated with Fe-rich/S-poor sites, likely iron oxides, on altered chlorite or euhedral pyrite surfaces (but not on framboidal pyrite). Organic C (<1.62%), total S (<0.31%), and P (<0.03%) were in low abundance relative to the overall bulk composition. Microbial community analysis showed a diverse group of bacteria present with a wide range of putative metabolisms, and provides evidence for a variety of redox microenvironments co-existing in core samples. Although the uranium minerals persisting in low permeability areas in association with organic carbon were less affected by oxidizing solutions during mining, the likely sequestration of uranium within labile iron oxides following mining and sensitivity to changes in redox conditions requires careful attention during groundwater restoration.

Wyoming↗
USGS2021

Elemental and radionuclide exposures and uptakes by small rodents, invertebrates, and vegetation at active and post-production uranium mines in the Grand Canyon watershed

The effects of breccia pipe uranium mining in the Grand Canyon watershed (Arizona) on ecological and cultural resources are largely unknown. We characterized the exposure of biota to uranium and co-occurring ore body elements during active ore production and at a site where ore production had recently concluded. Our results indicate that biota have taken up uranium and other elements (e.g., arsenic, cadmium, copper, molybdenum, uranium) from exposure to ore and surficial contamination, like blowing dust. Results indicate the potential for prolonged exposure to elements and radionuclides upon conclusion of active ore production. Mean radium-226 in deer mice was up to 4 times greater than uranium-234 and uranium-238 in those same samples; this may indicate a potential for, but does not necessarily imply, radium-226 toxicity. Soil screening benchmarks for uranium and molybdenum and other toxicity thresholds for arsenic, copper, selenium, uranium (e.g., growth effects) were exceeded in vegetation, invertebrates, and rodents ( Peromyscus spp. , Thomomys bottae, Tamias dorsalis, Dipodomys deserti ). However, the prevalence and severity of microscopic lesions in rodent tissues (as direct evidence of biological effects of uptake and exposure) could not be definitively linked to mining. Our data indicate that land managers might consider factors like species, seasonal changes in environmental concentrations, and bioavailability, when determining mine permitting and remediation in the Grand Canyon watershed. Ultimately, our results will be useful for site-specific ecological risk analysis and can support future decisions regarding the mineral extraction withdrawal in the Grand Canyon watershed and elsewhere.

Arizona↗
USGS2013

Uranium redox transition pathways in acetate-amended sediments

Redox transitions of uranium [from U(VI) to U(IV)] in low-temperature sediments govern the mobility of uranium in the environment and the accumulation of uranium in ore bodies, and inform our understanding of Earth’s geochemical history. The molecular-scale mechanistic pathways of these transitions determine the U(IV) products formed, thus influencing uranium isotope fractionation, reoxidation, and transport in sediments. Studies that improve our understanding of these pathways have the potential to substantially advance process understanding across a number of earth sciences disciplines. Detailed mechanistic information regarding uranium redox transitions in field sediments is largely nonexistent, owing to the difficulty of directly observing molecular-scale processes in the subsurface and the compositional/physical complexity of subsurface systems. Here, we present results from an in situ study of uranium redox transitions occurring in aquifer sediments under sulfate-reducing conditions. Based on molecular-scale spectroscopic, pore-scale geochemical, and macroscale aqueous evidence, we propose a biotic–abiotic transition pathway in which biomass-hosted mackinawite (FeS) is an electron source to reduce U(VI) to U(IV), which subsequently reacts with biomass to produce monomeric U(IV) species. A species resembling nanoscale uraninite is also present, implying the operation of at least two redox transition pathways. The presence of multiple pathways in low-temperature sediments unifies apparently contrasting prior observations and helps to explain sustained uranium reduction under disparate biogeochemical conditions. These findings have direct implications for our understanding of uranium bioremediation, ore formation, and global geochemical processes.

PNAS↗