Uraniferous Rocks Research Articles

Positive Uranium Anomalies in the Peatlands of Humid Zone: A Review

In recent years, geologists have found peatlands extremely rich in uranium. They can be considered an example of the efficient operation of natural organic geochemical barriers in the humid zone. They also open up the possibility of determining the age of these peatlands by t he isotopic ²³⁰Th/²³⁴U method. The deposition of uranium in peat is due to the U(VI) bioreduction controlled by several geochemical factors: the composition of organic matter and soil solution, the redox potential, and the capacity of uranyl ions to make complexes with organic ligands. By the nature of uranium enrichment, peatlands can be subdivided into two groups: (a) peatlands enriched in uranium carried by soil and groundwater from peripheric sources and (b) peatlands enriched in uranium from underlying uraniferous rocks. The data on geography, genesis, and physicochemical conditions of positive uranium anomalies in peatlands of the humid zone are collected and analyzed in this review.

Geochemical evidence for K-metasomatism related to uranium enrichment in Daejeon granitic rocks near the central Ogcheon Metamorphic Belt, Korea

A new type of uranium occurrence in Korea was identified in pegmatitic and hydrothermally altered granite in the Daejeon area. The U-bearing parts typically include muscovite, pink-feldspar and sericite as alteration minerals. In this study, the geochemical characteristics and alteration age of the granitic rocks were examined to provide evidence for hydrothermally-enriched uranium. The K-Ar ages of muscovite coexisting with U-bearing minerals were determined as 123 and 128 Ma. The U-bearing rocks have relatively low (CaO + Na2O), high K2O contents, and high alteration index values by major element geochemistry. The trace element geochemistry shows that the uraniferous rocks have significantly low Th/U ratios and strongly differentiated features. The rare earth element patterns indicate that the uraniferous rocks have a low total REE and LREE contents with depletion of Eu. Considering the geochemical variation of the granitic rock major, trace and rare earth elements, it can be concluded that uranium enrichment in pegmatites and altered granite should be genetically related to post-magmatic hydrothermal alteration of K-metasomatism after emplacement of the two-mica granite. This is the first report for geochemical characteristics of Mesozoic granite-related U-occurrences in South Korea. This study will help further research for uranium deposits with similarities in geological setting, mineralogy and age data between South China and Korea, and can also be expected to help solve the source problems related to high uranium concentrations in some groundwater occurring in the granitic terrane.

Enacting the substrata: Scientific practice and the political life of uraniferous rocks in Cold War Greenland

In the midst of growing demands for resource based development, Greenland’s uranium has become increasingly entwined with questions of economic sustainability and independent sovereignty for this small island nation. Current geological imaginaries of the substrata inform visions of a prosperous Greenlandic mining future. Yet the political life of Greenland’s radioactive components and rare earths has a history that dates back decades, if not centuries. In order to comprehend how the geological imaginaries that inform current rare earth politics and practices in Greenland came into being, the history of uranium prospecting must be taken into account. Arguing that these imaginaries are not merely an artefact of a recent ‘rush for resources’ or a response to what is simply ‘found’ in nature, this paper explores how the most prominent site of uranium extraction, the Ilímaussaq complex, was first made available to extractive political rationalities. Drawing on archival research in Copenhagen (2015-2016), this article traces the first years of state prompted exploration of Ilímaussaq from 1955 until the conclusion of the first drilling programme in 1958. Unpacking the scientific processes, mechanisms, and practices through which Ilímaussaq was enacted both in the field and in laboratories, this paper interrogates the material and social practices which first brought it into being as a radioactive complex and a space of extraction.

Lead isotope ratios in bone ash of blesbok (Damaliscus pygargus phillipsi): A means of screening for the accumulation of contaminants from uraniferous rocks

This study was done to determine whether blesbok (Damaliscus pygargus phillipsi) from the Krugersdorp Game Reserve (KGR) in Gauteng Province, South Africa have higher concentrations of 238U and higher 206Pb/204Pb and 207Pb/204Pb ratios in their bone ash than blesbok from a nearby control reserve that is not exposed to mine water and has no outcrops of uraniferous rocks. Eight blesbok females from the KGR and seven from the control site, all killed with a brain shot, were used. A Thermo X-series 2 quadrupole ICPMS was used to measure the concentrations of 238U and lead and a Nu Instruments NuPlasma HR MC-ICP-MS to measure the lead isotope ratios in the tibial ash from each animal. KGR blesbok had higher mean concentrations of 238U (P = 0.02) and ratios of 206Pb/204Pb and 207Pb/204Pb (P < 0.00001) than the control blesbok. The probability of rejecting the false null hypothesis of no difference in the 206Pb/204Pb or 207Pb/204Pb ratios between KGR and control reserve animals (the power of the test) was 0.999. The blesbok from the KGR accumulated contaminants from an uraniferous environment. The 206Pb/204Pb and 207Pb/204Pb ratios in tibial ash proved effective in confirming accumulation of contaminants from uraniferous rocks.

Determining uraniferous host rocks and minerals as a source of dissolved uranium in granite aquifers near the central Ogcheon metamorphic belt, Korea

Korea has suffered from high U concentrations in some groundwater, especially in Daejeon near the central Ogcheon metamorphic belt. However, clear explanation has not been yet reported for the uranium sources in groundwater. This study is focused on identifying the potential uraniferous host rocks and finding the exact U-minerals serving as uranium sources in groundwater near Daejeon, Korea. For this work, we performed an in situ gamma ray spectrometer survey and a laboratory microscopic study with electron micro-probe analysis. The measurements for radioactive element content did not show any prominent K- and Th-anomaly spots, but they did result in several observations of considerable U-anomalies in pegmatite and hydrothermally altered granite, in which uraninite, coffinite and uranophane were found by electron micro-probe analysis. The occurrences of U-minerals are the first such discovery except in the low-grade U deposits of the Ogcheon metamorphic belt in Korea. All observed U-minerals were intimately associated with hydrothermal alteration. The remarkably low Th/U ratios in the studied uraniferous rocks also suggest that the U enrichment was genetically related to a post-magmatic hydrothermal process. However, many of the uraniferous parts were controlled by a reducing environment and occurred near the border between graphite-rich mica-schist and Jurassic leucocratic granite. The findings on these uraniferous rocks can be used in elucidating the source of highly enriched U groundwater in granite aquifers as well as in understanding the occurrence of igneous U-minerals, which has not been previously reported in Korea.

Structural geometry of uraniferous rocks in the Umra area, Aravalli Supergroup, India

Uranium mineralization occurs in Palaeoproterozoic metasediments of the Aravalli Supergroup in the Umra area, Udaipur district, Rajasthan, India. The host rocks for mineralization were deposited in a shallow marine shelf type environment over an Archaean basement gneiss, the Banded Gneissic Complex. A reducing environment at the depositional site, associated with large-scale biogenic activity, was responsible for precipitation of uranium bearing minerals. Our structural analysis shows that the rocks of the mineralized area have been involved in four phases of deformation. The carbonaceous phyllite unit near Umra shows a ‘mirror-image’ pattern, resulting from the superposition of upright F 2 folds with NE–SW striking axial planes over early ( F 1) isoclinal folds. The exploration block is located on one limb of the regional F 2 fold.

Uranium Provinces in China

Abstract Three uranium provinces are recognized in China, the Southeast China uranium province, the Northeast China‐Inner Mongolia uranium province and the Northwest China (Xinjiang) uranium province. The latter two promise good potential for uranium resources and are major exploration target areas in recent years. There are two major types of uranium deposits: the Phanerozoic hydrothermal type (vein type) and the Meso‐Cenozoic sandstone type in different proportions in the three uranium provinces. The most important reason or prerequisite for the formation of these uranium provinces is that Precambrian uranium‐enriched old basement or its broken parts (median massifs) exists or once existed in these regions, and underwent strong tectonomagmatic activation during Phanerozoic time. Uranium was mobilized from the old basement and migrated upwards to the upper structural level together with the acidic magma originating from anatexis and the primary fluids, which were then mixed with meteoric water and resulted in the formation of Phanerozoic hydrothermal uranium deposits under extensional tectonic environments. Erosion of uraniferous rocks and pre‐existing uranium deposits during the Meso‐Cenozoic brought about the removal of uranium into young sedimentary basins. When those basins were uplifted and slightly deformed by later tectonic activity, roll‐type uranium deposits were formed as a result of redox in permeable sandstone strata.

The use of enhanced Landsat-TM image in the characterization of uraniferous granitic rocks in the Central Eastern Desert of Egypt

Abstract The discovery of uranium deposits is more likely if we can identify favourable setting and target areas on the basis of related geological features, such as favourable host rocks, altered zones and structural lineaments. The synoptic view of the enhanced Landsat-TM imagery covering the Central Eastern Desert enabled the author to recognize and interpret these geological features. The coloured composite ratio image produced from combination of 2/4 × 7 (red), 5/7 × 3 (green) and 5/3 × 7 (blue) band ratios was used to classify the exposed younger granitic masses into three groups, namely Gl, G2 and G3. Each of the granitic groups possesses certain image characteristics, such as colour and surface texture. Moreover, the major tectonic features associated with younger granitic bodies were identified from the Landsat image. Known uranium deposits are recognized to be associated with the youngest granitic group G3. This granite forms circular to elongate shaped, slightly fractured and weathered bodies, ...

Uranium isotopes in the Platte River drainage basin of the North American High plains Region

The North and South Platte Rivers contribute sigficant concentrations of dissolved uranium to the Platte River system from the weathering of uraniferous rocks at their headwaters in Colorado and Wyoming. Uranium isotopes measured in three groups of samples collected from the Platte River and its major tributaries exhibted a wide range of concentrations (0.27–31.7 μg/l) and activity ratios (1.03–1.72) reflecting variations in the contributions of different sources under differing flow conditions. Locally elevated uranium concentrations and higher activity ratios were associated with groundwater sources during low flow periods. Uranium concentrations in surface runoff were lower than in baseflow and correlated significantly with dissolved solids. Uranium activity ratios in runoff were closer to equilibrium values than those in baseflow suggesting that dissolved uranium in runoff is less affected by disequilibrium processes. Mixing calculations using uranium concentrations and activity ratios indicate considerable variations in longitudinal and transverse mixing of tributary water with Plate River water, and temporal variations of groundwater contributions (baseflow and irrigation return flow) in the Plate River system.

Paleontological analysis of a lacustrine carbonaceous uranium deposit at the Anderson mine, Date Creek basin, west-central Arizona (U.S.A.)

The Tertiary sedimentary sequence of the Date Creek basin area of Arizona is composed principally of intertonguing alluvial-fan and lacustrine deposits. The lacustrine rocks contain large intermediate- to, locally, high-grade uranium deposits that form one of the largest uranium resources in the United States (an estimated 670,000 tons of U 3O 8 at an average grade of 0.023% is indicated by drilling to date). At the Anderson mine, about 50,000 tons of U 3O 8 occurs in lacustrine carbonaceous siltstones and mudstones (using a cutoff grade of 0.01%). The Anderson mine constitutes a new class of ore deposit, a lacustrine carbonaceous uranium deposit. Floral and faunal remains at the Anderson mine played a critical role in creating and documenting conditions necessary for uranium mineralization. Organic-rich, uraniferous rocks at the Anderson mine contain plant remains and ostracodes having remarkably detailed preservation of internal features because of infilling by opaline silica. This preservation suggests that the alkaline lake waters in the mine area contained high concentrations of dissolved silica and that silicification occurred rapidly, before compaction or cementation of the enclosing sediment. Uranium coprecipitated with the silica. Thinly laminated, dark-colored, siliceous beds contain centric diatoms preserved with carbonaceous material suggesting that lake waters at the mine were locally deep and anoxic. These alkaline, silica-charged waters and a stagnant, anoxic environment in parts of the lake were necessary conditions for the precipitation of large amounts of uranium in the lake-bottom sediments. Sediments at the Anderson mine contain plant remains and pollen that were derived from diverse vegetative zones suggesting about 1500 m of relief in the area at the time of deposition. The pollen suggests that the valley floor was semiarid and subtropical, whereas nearby mountains supported temperate deciduous forests.

The indoor radon problem: Studies in the Albuquerque, New Mexico area

Radon buildup in homes is now recognized throughout the world as a potentially major health hazard. The U.S. Nuclear Regulatory Commission and the U.S. Environmental Protection Agency estimate 8,000–30,000 fatalities per year in the United States due to indoor radon. The Albuquerque, New Mexico area was chosen for study because it is representative of metropolitan areas in the southwestern United States where slightly uraniferous source rocks (Sandia granite) have provided the very immature soil for much of the area. The granite contains 4.7 ppm U, and limestone capping the granite 5.7 ppm U. Soils in the area average 4.24 ppm U, and Th/U ratios average 3.2. These data suggest some removal of U from the source rocks, but fixation of the U in the soils (that is, as opposed to widespread removal of the U by solution), thus providing a ready source for soil radon. A pilot study of soil radon in the area in winter of 1983–1984 shows high values, 180 pCi/l, relative to the U.S. average (about 100 pCi/l). In the winter of 1986–1987, 180 dwellings were surveyed for their indoor radon levels, including 20 that had been surveyed in summer of 1986. Twenty-eight percent of those in the winter study yielded indoor radon above the EPA suggested maximum permissible level of 4 pCi/l air, well above the EPA estimate of 10–15 dwellings for the U.S. The indoor radon levels show positive correlation with closeness to the Sandia Mountains, to soil radon, to excess insulation, to homes with solar capacities, and other factors. Building materials may provide a very minor source of some indoor radon. Summer readings are lower than winter readings except when the houses possess refrigerated air conditioning.

Multielement analysis of uraniferous rocks by INAA: Special reference to interferences due to uranium and fission of uranium

The presence of uranium in a sample enhances the true values of La, Ce, Nd, Sm determined by INAA if appropriate corrections are not made for the interference. The enhancement of the true values comes about because the (n, γ) activation products of these elements, viz.140La,141Ce,147Nd,153Sm, are also produced from the fission of235U (∼0.72% natural isotopic abundance) even when La, Ce, Nd, Sm are totally absent in the given sample. In a 5 hour irradiation 1 μg of U is found to be equal to 0.28 μg of Ce and 0.23 μg of Nd while the equivalent La is found to be dependent upon the delay from end of irradiation to sample counting time. A numerical procedure is given to correct for these interferences. Spectral interferences from fission and (n, γ) β products of uranium in the determination of other trace elements by INAA is also investigated. Uranium is found to be determined best using the 278 keV gamma-ray of239Np.

The time related occurrence of uranium deposits

Plotting of the main types of uranium deposits in a diagram according to their time related occurrence reveals a characteristic qualitative and quantitative distribution of the deposits to distinct epochs, and a grouping into five principle generations of deposits. Furtheron, most of the deposits show an obvious geographic affinity to uraniferous source rocks of also distinct geological ages.

Elemental Analysis of Uraniferous Rocks and Ores by X-Ray Spectrometry

Large-scale uranium exploration programs and industrial mine development require rapid and accurate analytical determinations of uranium and associated elements, at concentration levels ranging from a few parts-per-million to the per-cent range. The analytical requirements for associated suites of elements vary with application, but quality control and production practices in U.S. uranium mines and mills commonly require determinations of calcium, iron, copper, molybdenum, and vanadium, in addition to uranium. Previous work has demonstrated the capabilities of wavelength-dispersive x-ray spectrometric methods for many exploration applications. The purpose of this investigation is to assess the accuracy of x-ray determinations of uranium at ore-grade levels, utilizing both wavelength-dispersive and energy-dispersive spectrometers, and to discuss the acquistion of multi-element data.

Geological, geochemical and ecological research in the Ilímaussaq region, South Greenland

In 1977 field work was concerned with the lujavrites and kakortokites of the south-eastern part of the Ilimaussaq alkaline intrusion (see Andersen &amp; Bohse, this report), pegmatites and veins within the intrusion, the Narssaq intrusion situated to the west of the Ilimaussaq intrusion, and the environmental geochemistry and the ecology of the Narssaq region. Preliminary results of the field work and of some of the laboratory investigations are reported below. It should also be mentioned that a diamond drilling programme was carried out in the uraniferous rocks of the Kvanefjeld area in the northern part of the Ilimaussaq intrusion (see Nyegaard, this report).