Sedimentary Uranium Research Articles

Nitrate-Stimulated Release of Naturally Occurring Sedimentary Uranium.

Groundwater uranium (U) concentrations have been measured above the U.S. EPA maximum contaminant level (30 μg/L) in many U.S. aquifers, including in areas not associated with anthropogenic contamination by milling or mining. In addition to carbonate, nitrate has been correlated to uranium groundwater concentrations in two major U.S. aquifers. However, to date, direct evidence that nitrate mobilizes naturally occurring U from aquifer sediments has not been presented. Here, we demonstrate that the influx of high-nitrate porewater through High Plains alluvial aquifer silt sediments bearing naturally occurring U(IV) can stimulate a nitrate-reducing microbial community capable of catalyzing the oxidation and mobilization of U into the porewater. Microbial reduction of nitrate yielded nitrite, a reactive intermediate, which was further demonstrated to abiotically mobilize U from the reduced alluvial aquifer sediments. These results indicate that microbial activity, specifically nitrate reduction to nitrite, is one mechanism driving U mobilization from aquifer sediments in addition to previously described bicarbonate-driven desorption from mineral surfaces, such as Fe(III) oxides.

Marine sedimentary uranium to barium ratios as a potential quantitative proxy for Pleistocene bottom water oxygen concentrations

Oxygen is essential for marine ecosystems, and it is linked by respiration to carbon storage in the deep ocean. Reconstructing oxygen concentrations in the past has been limited by the absence of quantitative, rather than qualitative, proxies, but several new (semi-) quantitative oxygen proxies have recently been developed. In this study we explore the possibility of adding bulk sedimentary uranium (U) to this list by normalizing it to barium (Ba). First, U/Ba and bottom water oxygen concentrations are compared on a global scale, using a core top database, in pelagic environments greater than 200 m water depth. Then, the relationships between U/Ba and bottom water oxygen are examined on smaller spatial scales: within each ocean basin and regionally within the Eastern Equatorial Pacific, the Arabian Sea, and Western Equatorial Atlantic. At this regional scale, where secondary influences on the behavior of both U and Ba may be more spatially uniform, empirical piecewise linear calibrations are developed and subsequently tested on downcore records. U/Ba-based oxygen reconstructions generally agree with those derived from previously published alkenone preservation and benthic foraminiferal surface porosity records. Several limitations to the utility of U/Ba as a proxy for oxygen have also been identified. The proxy should only be applied in the uppermost sedimentary intervals that contain porewater sulfate to minimize barite diagenesis, and phosphorus contents should be monitored for the potential influence of apatite on uranium content. U/Ba is more successful at recording oxygen concentrations during mean glacial and interglacial periods than during climate transitions, when the timing and amplitude may be more sensitive to burndown and smoothing. Conservative errors on the calibrations result in the greatest utility of U/Ba in regions with relatively high oxygen concentrations (e.g., >50 μmol/kg) and large oxygen variability (±10 s of μmol/kg). Even with these caveats, U/Ba is only one of two quantitative oxygen proxies potentially capable of recording variability above 50 μmol/kg, and further investigation into its functionality in different environmental settings is worthwhile in the endeavor to reconstruct the full marine range of oxygen concentrations in the past.

Geochemistry of Mudstones/Silty Mudstones from the Qigequan Formation and Shizigou Formation in Yuejin-II Area, Southwestern Area of the Qaidam Basin: Implications for Sedimentary Environment and Sandstone-Type Uranium Mineralization

The Qaidam Basin has been the focus of sandstone-type uranium prospecting since the 1950s. In recent years, relying on the uranium geological survey project supported by the China Geological Survey, and the cooperation with the Qinhai oil company, drilling work at the Yuejin-II area in this basin has achieved breakthroughs on industrial-level sandstone-type uranium exploration. In this study, we present major, trace and REE geochemical analysis of the Qigequan Formation and the Shizigou Formation mudstones/silty mudstones collected from an industrial uranium ore drillholes in the Yuejin-II area. The Shizigou and Qigequan Formations exhibit signatures of non-intense alteration, low rock maturity and proximal provenance. The overall arid paleoclimatic conditions controlled the sedimentation of large volume of uranium rich materials. The period of relative humidity prompted the sedimentation of reduced agents. Aided by the neotectonic-induced slopes and tectonic windows, oxygenated fluids migrated along permeable layers and extracted the hexavalent uranium, transported in the form of uranyl ion (UO22+). When the oxygen–uranium-rich fluids finally infiltrated into the reductive sand body, the hexavalent uranium was reduced to tetravalent uranium and deposited in the form of uranium compounds. Large-scale and centrally distributed reductive sand bodies provided favorable ore storage space for the sandstone-type uranium mineralization in the Yuejin-II area.

Southern Ocean Oxygenation Changes Inferred From Redox‐Sensitive Trace Metals Across Marine Isotope Stage 11

AbstractChanges in the circulation of the Southern Ocean are known to have impacted global nutrient, heat, and carbon cycles during the glacial and interglacial periods of the late Pleistocene. Proxy‐based records of these changes deserve continued scrutiny as the implications may be important for constraining future change. A record of authigenic uranium from the South Atlantic has been used to infer changes in deep‐sea oxygenation and organic matter export over the past 0.5 million years. Since sedimentary uranium has the possible complication of remobilization, it is prudent to investigate the behavior of other redox‐sensitive trace metals to confidently interpret temporal changes in oxygenation. Focusing here on the exceptionally long interglacial warm period, Marine Isotope Stage (MIS) 11, we found concurrent authigenic enrichments of uranium (U) and rhenium (Re) throughout MIS 12 to 10, overall supporting prior interpretations of low‐oxygen periods. However, there are differential responses of Re and U to oxygen changes and some evidence of small‐scale Re remobilization, which may involve differences in molecular‐level reduction mechanisms. Peaks in authigenic manganese (Mn) intervening with peaks in Re and U indicate increases in porewater oxygenation which likely relate to increased Antarctic Bottom Water circulation at the onset of MIS11c and during the peak warmth of the interglacial around 400 ka.

Uranium in animals, vegetables and minerals: landscape geochemical and biogeochemical expressions of the Four Mile West sedimentary uranium deposit, South Australia

The sediment-hosted uranium deposit at Four Mile West is buried by 130–150 m of sediments yet has a landscape as well as a surficial geochemical and biogeochemical expression of the mineral system. The landscape expression includes exposure of stratigraphy with now-oxidised redox overprinting (including ‘roll-fronts’) equivalent to those in the buried mineralisation. The landscape also includes morpho-tectonic expressions of faults that have been responsible for the development and preservation of mineralisation. Most importantly, this faulting has produced an embayment in the range front corresponding to a down-faulted area on the plains that has hosted throughflow of surface and groundwater and preservation of underlying, chemically reduced, ore-hosting Mesozoic and Cenozoic sediments. Landscape geochemical and biogeochemical expressions of buried mineralisation are best represented in U2/Th and selected trace elements, rather than simply elevated U contents in isolation. These associations are especially important for distinguishing between the U-rich expressions of buried, sediment-hosted mineralisation and laterally transported U-rich detritus from the adjacent ranges. The surficial geochemical and biogeochemical expression of the underlying mineralised substrate, with higher U2/Th, is best expressed in regolith carbonates, river red gums and potentially ants and macropod droppings. The mechanism proposed for this vertical geochemical transfer is in part tree-root depth penetration (or burrowing in the case of ants) but most importantly upward groundwater flux. Important groundwater fluctuations are connected to low-frequency–high-intensity rainfall periods that drive groundwater recharge and significantly raises the water-table towards the land surface, especially along faults and fractures near the range front and the immediately adjacent plains. During seasons with high rainfall, this groundwater rise may even express itself as water discharge at springs along the range front. Other media, such as stream sediments, soils and inland tea tree are more closely associated with expressing lateral physical dispersion and re-accumulation of U within the landscape. This study shows that surficial mapping, geochemistry and biogeochemistry within a landscape processes/landscape system context can be invaluable for the detection of, and exploration for, buried sediment-hosted uranium mineral systems, and most especially understanding more about the behaviour of chemical elements in the Australian landscape.

浅析贝尔凹陷伊敏组砂体沉积特征及铀矿成矿潜力

浅析贝尔凹陷伊敏组砂体沉积特征及铀矿成矿潜力

Crustal fluid flow in hot continental extension: tectonic framework of geothermal areas and mineral deposits in western Anatolia

Abstract Lithospheric thinning and crustal extension have shaped the Alpine orogen in western Anatolia since the late Oligocene, resulting in the denudation of one of Earth's largest metamorphic core complexes, the Menderes Massif. We review locations and characteristics of geothermal fields and of Miocene mineral deposits in the context of crustal structure and geodynamic processes. Thermal spring locations show a close spatial association with active fault zones; the largest geothermal areas are located in the widest graben and at fault intersections, but show little relation to volcanic activity. During the first stage of tectonic denudation in the Miocene, epithermal, porphyry-type gold and structurally controlled base-metal deposits formed synchronously with K-rich volcanic and plutonic complexes in the northern Menderes Massif. Depositional environments favoured the formation of lignite, sedimentary uranium and borate deposits. Throughout this phase of extension in a hot continental setting, secondary porosity caused by brittle faulting of metamorphic basement rocks provided the key pathways for fluids and magmas. Although the Menderes Massif has remained in a similar position relative to active plate boundaries from the Miocene to the present, three significant changes in subcontinental mantle dynamics affected the nature of hydrothermal flow. First, the partial removal of lithospheric mantle changed the primary source component of magmatic rocks and metals from metasomatized lithosphere mantle to asthenospheric mantle. Secondly, surface uplift and progressive crustal extension led to segmentation of the Miocene land surface along NNE–SSW- and east–west-orientated fault zones, which changed the overall structural control on crustal permeability. Finally, hydrothermal flow changed from locally magmatic driven, to focused flow of topographically and thermally driven fluids in the crust, with high background heat flow caused by regional upwelling of the asthenosphere. The Menderes Massif is a continental tectonic domain that has experienced rapid thinning of lithospheric mantle and crustal extension in an overall convergent plate tectonic setting. The tectonic and geodynamic framework for evolving hydrothermal activity in western Anatolia may be applicable to other ore-forming systems in hot, extending continental crust in Earth's history.

First experimental determination of the solubility constant of coffinite

Dissolution experiments have been performed in order to determine the solubility constant of coffinite, USiO4. Several assemblages of phases were used in under-saturated experiments performed in 0.1molL−1 HCl under Ar atmosphere, as well as in air. These samples were fully-characterized and were composed of either USiO4, solely, or USiO4 and additional oxide byproducts that resulted from the synthesis procedure. The solubility constant of coffinite was determined at 25°C and 1bar (log*KS°(USiO4, cr)=−5.25±0.05), as well as the standard free energy of formation of coffinite (ΔfG°(298K)=−1867.6±3.2kJmol−1), which enables one to infer the relative stability of coffinite and uraninite as a function of groundwater composition. Geochemical simulations using PHREEQC 2 software and the Thermochimie data base indicate that coffinite precipitates at 25°C under reducing conditions, at pH=6, for H4SiO4(aq) concentration of 7 × 10−5molL−1 and U(OH)4(aq) concentration of 10−11molL−1. The ΔfG° value determined was used to calculate the standard free energy associated with the formation of coffinite from a mixture of uraninite and quartz. The value obtained (Δr,oxG°=20.6±5.2kJmol−1) indicates unambiguously that coffinite is less stable than the quartz+uraninite mixture at 25°C. Geochemical simulations using PHREEQC 2 software indicate that coffinite precipitates in solutions supersaturated with respect to UO2(cr), but undersaturated with respect to UO2(am) in aqueous solutions with silica concentrations typical of groundwater. These favorable conditions during the formation of sedimentary uranium ore deposits, as well as slow dissolution kinetics, explain the common occurrence of coffinite.

Study on the exploration and mining order of continental sedimentary uranium and coal mine in Xinjiang

Study on the exploration and mining order of continental sedimentary uranium and coal mine in Xinjiang

Geophysics and Uranium in the Curnamona and Billeroo Palaeochannel Systems, Frome Embayment, South Australia

SUMMARY Tectonism is believed to have exerted a strong control on the current disposition of sedimentary hosted uranium mineral deposits in the Frome Embayment, in South Australia. However the extent of this control has not been well understood, nor documented. Here, we examine the combined use of regional and finer-scale TEMPEST AEM data sets, linked to a structural interpretation of airborne magnetics and ground gravity, to extend our understanding of the evolution, geometry and variability of sediment packages associated with sedimentary uranium mineralisation in the Curnamona and Billeroo Palaeochannel systems. Through the analysis of both smooth and blocky model LEI inversions of these AEM data, we contend that structural control was critical in determining the initial orientation of the palaeovalleys and the location of basal sequences of the Eyre Formation, the host to known uranium mineralisation. We examine this influence in the context of the Goulds Dam uranium deposit. The presence of reactivated basement faults which controlled the initial orientation of the palaeovalley systems may also have a role in providing the loci for mobile reductants from underlying basin sequences, although this requires further investigation.

Fixed wing vs. helicopter airborne EM for mapping fine scale conductivity variations in transported sedimentary cover associated with sedimentary uranium mineralisation

SUMMARY Comparing AEM data from different systems is always an interesting exercise. Differences, some minor, some major, are almost always observed. Some are caused by system characteristics while others arise in the interpretation, including by settings employed in inversion. In this paper differences resulting from varying regularization parameters, specifically those associated with vertical constraints, when inverting are examined with respect to the detail resolved in transported sediments. These sediments are host to sedimentary uranium mineralisation in the Frome Embayment of South Australia. Subtle changes in ground conductivity linked to changes in the character of cover has significance for a variety of reasons, including the definition of layers or boundaries that could be employed in geochemical sampling as part of an exploration programme, or for defining aquifers, their character, and groundwater they contain. Hence an understanding of approaches to better resolve subsurface conductivity variation is important. Coincident lines of TEMPEST and SkyTEM data along with induction conductivity logs have made it possible to make direct comparisons of inversion results. Individual soundings of AEM data have been inverted and the results compared against borehole conductivity logs to establish appropriate inversion settings. This has also been extended to a flight line of data. Borehole lithological logs have been used to verify that the optimisation of the vertical constraints resulted in improved conductivitydepth sections for TEMPEST AEM data acquired for both fine and regional-scale studies. This study confirms the importance of carefully considering the optimisation of inversion parameters for a particular survey.

A combined chemical, isotopic and microstructural study of pyrite from roll-front uranium deposits, Lake Eyre Basin, South Australia

The common sulfide mineral pyrite is abundant throughout sedimentary uranium systems at Pepegoona, Pepegoona West and Pannikan, Lake Eyre Basin, South Australia. Combined chemical, isotopic and microstructural analysis of pyrite indicates variation in fluid composition, sulfur source and precipitation conditions during a protracted mineralization event. The results show the significant role played by pyrite as a metal scavenger and monitor of fluid changes in low-temperature hydrothermal systems.In-situ micrometer-scale sulfur isotope analyses of pyrite demonstrated broad-scale isotopic heterogeneity (δ34S=−43.9 to +32.4‰VCDT), indicative of complex, multi-faceted pyrite evolution, and sulfur derived from more than a single source. Preserved textures support this assertion and indicate a genetic model involving more than one phase of pyrite formation. Authigenic pyrite underwent prolonged evolution and recrystallization, evidenced by a genetic relationship between archetypal framboidal aggregates and pyrite euhedra. Secondary hydrothermal pyrite commonly displays hyper-enrichment of several trace elements (Mn, Co, Ni, As, Se, Mo, Sb, W and Tl) in ore-bearing horizons. Hydrothermal fluids of magmatic and meteoric origins supplied metals to the system but the geochemical signature of pyrite suggests a dominantly granitic source and also the influence of mafic rock types. Irregular variation in δ34S, coupled with oscillatory trace element zonation in secondary pyrite, is interpreted in terms of continuous variations in fluid composition and cycles of diagenetic recrystallization. A late-stage oxidizing fluid may have mobilized selenium from pre-existing pyrite. Subsequent restoration of reduced conditions within the aquifer caused ongoing pyrite re-crystallization and precipitation of selenium as native selenium.These results provide the first qualitative constraints on the formation mechanisms of the uranium deposits at Beverley North. Insights into depositional conditions and sources of both sulfide and uranium mineralization and an improved understanding of pyrite geochemistry can also underpin an effective vector for uranium exploration at Beverley North and other sedimentary systems of the Lake Eyre Basin, as well as in comparable geological environments elsewhere.

X-Ray Crystallography of Uraninites Associated with the Albitite Belt of Western India: Evidence for the High-Temperature Origin of Uranium and Associated Mineralisation

Abstract X-ray diffraction (XRD) studies on the radioactive ore samples from various parts of Rajasthan and Haryana have revealed the presence of several uranium and other atomic mineral occurrences in the albitite belt of western India. The primary uranium minerals (PUMs) are uraninite and brannerite, whereas, the secondary uranium minerals (SUMs) show considerable speciations: phosphate, silicate, hydrous oxide hydrate, and vanadate. Multiple oxides (MOs) are davidite, fergusonite, aeschynite-(Y), microlite, samarskite, euxenite, betafite, and columbite-tantalite. The thorium minerals are huttonite, thorite, uranoan-thorite, thorianite, thorutite, and brabantite. The yttrium and REE-bearing minerals are xenotime, britholite, allanite, chevkinite, tritomite, and monazite. It is noted that the measured unit cell dimension (a0) of the investigated uraninites ranges from 5.4110 Å to 5.4646 Å. The highest unit cell dimension (5.4646 Å) represents a composition (or oxidation grade) of UO2.05, whereas, the lowest one (5.4110 Å) corresponds to a composition of UO2.54. Furthermore, it is also apparent that, with increase in oxidation grade, there is a concomitant decrease in unit cell dimension. As most of the values of ao of uraninites from the albitite belt are high (> 5.45 Å), it may be inferred that the overall temperature of formation of uraninites of the albitite belt was higher (ca. 400°C). However, the low values of a0 in certain localities could be due to the prevalence of relatively low and fluctuating temperature regimes locally (ca. 400° - 100° C). Numerous occurrences of refractory, multiple oxides, and REE minerals, in association with uranium mineralisation, also support a high-temperature origin for the investigated uraninites. Binary data plots of unit cell dimension (a0) versus oxidation grade/composition (UO2+x) of uraninites (n = 36) suggest that the gross uranium mineralisation in the albitite belt of western India is mainly linked to regional metamorphism, anatexis, granitic intrusion, metasomatism, and contact metamorphosed granite-pegmatite aureoles and granite-related vein type with hydrothermal overprints, including redistribution of intrinsic sedimentary uranium and its concentration along suitable structural locales. These interpretations are consistent with the known gross geologic features of the albitite belt. Furthermore, the presence of marialite (calcian) in many places in the albitite belt also supports such a contention, as this mineral is known to be restricted to metamorphic and metasomatic environments. The speciation of secondary uranium minerals could be due to the higher oxidation of U4+ to U6+ in surface to near-surface conditions and its (U6+) remobilisation as uranyl ions. The combination of moving uranyl ions with available cations and anions en route caused re-precipitation of U as diversified assemblages of low-temperature uranyl minerals under suitable physicochemical conditions.

Tracing low‐temperature fluid flow on ridge flanks with sedimentary uranium distribution

The uranium content of sediments and pore fluids along a ridge axis to ridge flank transect perpendicular to the southern East‐Pacific Rise is used to assess the impact of low‐temperature fluid flow on U distribution. Two distinct regions are identified: (1) a young crustal site (0.36 Ma crust) where significant solid phase U enrichments occur and (2) the ridge flank (1.9–4.6 Ma crust) with uniform U association with hydrothermal Fe oxide phases in the solid phases. Upward advection and diffusion of cool, U‐depleted basement fluids occurs at many coring sites. At the 0.36 Ma site the oxic basal‐fluids strip the plume derived sediment of the excess U, effectively migrating the U upwards through the sediment into the overlying water column. At the ridge flank sites the pore fluid advection rates are highest at bathymetric/basement highs and advection velocities of up to 7.5 mm yr−1 are inferred from the pore fluid profiles. These estimates are consistent with previous calculations based on fluoride pore fluid distributions. The basal‐fluid U depletions are in the range 10–70% relative to seawater depending on temperature and redox state. Low‐temperature uptake of U during basalt alteration is a significant sink from seawater in the global seawater U budget (6.7–29 Mmol yr−1). Pore fluid U content is a sensitive tracer of extremely low‐temperature (<5°C) and low‐velocity (<10 mm yr−1) advection through ridge flank systems and the basal sediment U/Fe ratio is potentially a useful proxy for basement alteration history where low ratios indicate extensive oxic alteration of basal‐sediments during fluid flow.

Occurrences and distributions of branched alkylbenzenes in the Dongsheng sedimentary uranium ore deposits, China

A series of branched alkylbenzene ranging from C 15 to C 19 with several isomers (2–5) at each carbon number were identified in sediments from the Dongsheng sedimentary uranium ore deposits, Ordos Basin, China. The distribution patterns of the branched alkylbenzenes show significant differences in the sample extracts. The branched alkylbenzenes from organic-rich argillites and coals range from C 15 to C 19 homologues, in which the C 17 or C 18 dominated. On the other hand, the C 19 branched alkylbenzenes dominated in the sandstone/siltstone extracts. The obvious differences of the branched alkylbenzene distributions between the uranium-host sandstones/siltstones and the interbedded barren organic-rich mudstones/coals probably indicate their potential use as biological markers associated with particular depositional environments and/or maturity diagenetic processes. Possible origins for these branched alkylbenzenes include interaction of simple aromatic compounds with, or cyclization and aromatization reactions of, these linear lipid precursors such as fatty acids, methyl alkanoates, wax esters or alkanes/alkenes that occur naturally in carbonaceous sediments. The possible simple aromatic compounds may include substituted benzenes, functionalized compounds such as phenols that are bound to kerogen at the benzyl position, and phenols that are decomposition products derived from aquatic and terrestrial sources. The distributions of methyl alkanoates and n-alkanes were found to be different between organic-rich mudstone/coal and sandstone/siltstone. From this result, it can be concluded that such differences of the alkylbenzene distributions were mainly resulting from the differences of organic precursors, although maturity effect and radiolytic alteration cannot be completely excluded.

Metallogeny of the Northwestern and Central Dinarides and Southern Tisia

The Dinaridic metallogenic province is a part of the Alpine–Himalayan orogenic system, developed as a result of opening and closure of the Tethys Ocean by convergence of the African and Eurasian plates. The northern boundary of the Dinarides is related to the northern African margin (Adria–Apulia). The Tisia mega-unit, a small continental block, positioned between the Dinarides and the Carpathians, is genetically related to the South Eurasian edge. The geology of the Dinarides is constrained by the Alpine Wilson cycle. The major stages of the cycle are: (a) Permian early intra-continental rifting; (b) Triassic advanced rifting; (c) Jurassic oceanization; (d) Cretaceous subduction; (e) Paleogene collision; and (f) Neogene post-collision and extension followed by orogenic collapse. Each stage creates characteristic ore deposits related to the specific geological environments. Stage (a) bears hydrothermal siderite–barite–polysulphide deposits, epigenetic sedimentary uranium deposits, red bed-type, sabkha-type copper and barite deposits and evaporites. Stage (b) favored SEDEX and hydrothermal iron–polysulphide–barite–mercury and MVT deposits. Stage (c) developed chromites, asbestos, talc and magnesite deposits. The spatial position of stage (d) remains poorly constrained. The Southern Tisia unit might be a possible candidate for the Tethyan active continental margin with the Cretaceous subduction zone positioned beneath. Absence of voluminous subduction-related magmatism and mineral deposits, however, favors subduction within the Vardar zone (the easternmost Dinarides), adjoined to the Serbomacedonian ensialic terrain with its large Cu-porphyry deposits. Stage (e) was a prelude to the prolific phase (f) with its numerous hydrothermal Pb, Zn and Sb deposits that mostly occur in the western Vardar zone. The geology and metallogeny of Southern Tisia, with medium/high grade metamorphics, I-type, S-type granites, resembles the Middle Austro-Alpine unit, formed during the main Carboniferous collisional stage. This contribution provides a review of the metallogenic characteristics of the Northwestern and Central Dinarides and Southern Tisia mega-units, based on recently-gained knowledge on the regional geology, petrology and genesis of mineral deposits. Establishment of the plate tectonic model several decades ago greatly contributed to an integrated interpretation of ore deposit genesis. In turn, basic research in the field of ore genesis generated new data that can be used to improve the plate tectonic model.

Sedimentary uranium in South Australia: a history of early exploration and discovery in the Lake Frome region

The potential for sedimentary uranium in South Australia was substantively overlooked for more than 60 years following the discovery of the Radium Hill uranium deposit in 1906, despite local knowledge of, and several expert visits to sedimentary uranium deposits in the Colorado Plateau region of the United States during subsequent years. In the late 1960s, a combination of factors including the commercial opportunity for nuclear power generation and the removal of Government export controls on uranium, coupled with increasing demand for mineral commodities generally, changed the situation, and led the US based Kerr McGee group to take an interest in uranium in South Australia in 1967. Their exploration quickly revealed anomalous uranium in Cenozoic sediments. Soon after, South Australian geologist Brian Fitzpatrick visited the Wyoming sedimentary uranium region on behalf of the OTP group, which then quickly secured exploration acreage over the sedimentary region, adjacent to the long-known Mount Painter uranium deposits in South Australia. Within 18 months, the Beverley uranium resource was discovered and a new sedimentary uranium province was revealed. Further discoveries followed at Honeymoon in 1972, Gould's Dam in 1974 and Oban in 1982. Critical factors in these subsequent discoveries were the joint venture arrangements including up to four separate parties and the inspiration provided by Professor Eric Rudd (University of Adelaide). Close liaison by explorers with the Geological Survey of South Australia also provided regional mapping, regional stratigraphic drilling, experimental geophysics and spore-pollen dating.

Organic geochemistry of the Dongsheng sedimentary uranium ore deposits, China

Organic matter (OM) associated with the Dongsheng sedimentary U ore hosting sandstone/siltstone was characterized by Rock-Eval, gas chromatography–mass spectrometry and stable C isotope analysis and compared to other OM in the sandstone/siltstone interbedded organic matter-rich strata. The OM in all of the analyzed samples is Type III with Ro less than 0.6%, indicating that the OM associated with these U ore deposits can be classified as a poor hydrocarbon source potential for oil and gas. n-Alkanes in the organic-rich strata are characterized by a higher relative abundance of high-molecular-weight (HMW) homologues and are dominated by C 25, C 27 or C 29 with distinct odd-to-even C number predominances from C 23 to C 29. In contrast, in the sandstone/siltstone samples, the n-alkanes have a higher relative abundance of medium-molecular-weight homologues and are dominated by C 22 with no or only slight odd-to-even C number predominances from C 23 to C 29. Methyl alkanoates in the sandstone/siltstone extracts range from C 14 to C 30, maximizing at C 16, with a strong even C number predominance, but in the organic-rich layers the HMW homologues are higher, maximizing at C 24, C 26 or C 28, also with an even predominance above C 22. n-Alkanes in the sandstone/siltstone sequence are significantly depleted in 13C relative to n-alkanes in most of the organic-rich strata. Diasterenes, ββ-hopanes and hopenes are present in nearly all the organic-rich sediments but in the sandstone/siltstone samples they occur as the geologically mature isomers. All the results indicate that the OM in the Dongsheng U ore body is derived from different kinds of source materials. The organic compounds in the organic-rich strata are mainly terrestrial, whereas, in the sand/siltstones, they are derived mainly from aquatic biota. Similar distribution patterns and consistent δ 13C variations between n-alkanes and methyl alkanoates in corresponding samples suggest they are derived from the same precursors. The OM in the organic-rich strata does not appear to have a direct role in the precipitation of the U ore in the sandstone, but an indirect role cannot be excluded. The OM in the U hosting sandstone shows a relatively low hydrogen index, presumably due to oxidation or radiolytic damage.

Palaeochannel uranium signatures and exploration models, South Australia

Sedimentary uranium mineralisation in South Australia is mostly in Cainozoic basinal palaeochannels developed on or proximal to Precambrian cratons. Precambrian basement of the Gawler and Curnamona cratons have uranium contents in the range 10-100 ppm, well above the crustal average of 2.8 ppm U. Deeply weathered basement rocks in these regions were incised during early Tertiary times and the sediments in these palaeodrainage networks now form several significant uranium provinces. The palaeochannel uranium deposits are typically hosted by medium to coarse-grained sandstone deposited in a continental fluvial, latchstring, alluvial, or marginal marine sedimentary environment. Impermeable clay units are intercalated in the sedimentary sequence and often occur immediately above and below the mineralised sandstone. Uranium mineralisation is associated with reduced conditions, and similar to elsewhere in the world, the host sediments to the Tertiary uranium mineralisation often contain pyrite and organic (plant) matter that is either disseminated or forms lignite seams. Tabular or roll-front shaped mineralised bodies formed along the contact with clay horizons and also along the palaeochannel margins. Tertiary continental sediments in SA are important favourable hosts because of the high organic content in channel sediments due to widespread colonisation by land plants during this time. The precise geometric definition of a palaeochannel is important in the selection of exploration targets for sandstone uranium. This often requires the integration of various geoscientific data sets in order to define targets and to improve the effectiveness of drilling. Refinements in remote sensing and geophysical techniques, data processing, sedimentology and computer-aided interpretations provide an effective, economic and efficient method of outlining the principal drainage patterns and channel dimensions. An improved understanding of sedimentary models and their relationship to uranium distribution will assist the effectiveness of exploration industry to explore for uranium in buried channel systems.

The chemical behavior of sedimentary uranium in Authie Bay (France)

A general study on uranium present at trace levels in anoxic sediments derived from Authie Bay (in northern France) has been undertaken. For that purpose, concentrations of various uranium species in pore waters and recovered solutions (after mineralization of sediments) were determined by ICP-AES and ICP-MS. To access the extent of early diagenesis occurring in these sediments, reduced solid sulfur species were determined after their conversion into H2S gas following sequential extraction procedures. Our preliminary findings reveal that dissolved U(VI) precipitates rapidly with depth in pore waters certainly in the form of insoluble U(IV). Under stronger reducing conditions, new aqueous species [mostly and ] in which uranium is in oxidation state IV are formed in the pore water. Valuable interpretation of these particular properties of sedimentary U has necessitated a global examination of sediment biochemistry because of the influence of bacterial activities on the chemistry of Fe, Mn, S and more particularly U by metal-reducing bacteria.