Uranium Isotope Fractionation

Andersen, Morten B.; Stirling, Claudine H.; Weyer, Stefan

doi:10.2138/rmg.2017.82.19

Cited by 160 publications

(210 citation statements)

References 207 publications

Supporting

Mentioning

172

Contrasting

Unclassified

Order By: Relevance

“…Thus, sediment δ 238 U can serve as a signature for past or present biological activity in sedimentary rocks. In three out of four samples, the sandstone of the roll-front deposit investigated here displays higher δ 238 U than those typically observed for the continental crust (δ 238 U∼−0.3‰)41424344 consistent with a predominantly biotic reduction mechanism (Fig. 3 and Supplementary Table 5).…”

Section: Resultssupporting

confidence: 62%

Biogenic non-crystalline U(IV) revealed as major component in uranium ore deposits

Bhattacharyya

Campbell

Kelly³

et al. 2017

Nat Commun

Self Cite

View full text Add to dashboard Cite

Historically, it is believed that crystalline uraninite, produced via the abiotic reduction of hexavalent uranium (U(VI)) is the dominant reduced U species formed in low-temperature uranium roll-front ore deposits. Here we show that non-crystalline U(IV) generated through biologically mediated U(VI) reduction is the predominant U(IV) species in an undisturbed U roll-front ore deposit in Wyoming, USA. Characterization of U species revealed that the majority (∼58-89%) of U is bound as U(IV) to C-containing organic functional groups or inorganic carbonate, while uraninite and U(VI) represent only minor components. The uranium deposit exhibited mostly 238U-enriched isotope signatures, consistent with largely biotic reduction of U(VI) to U(IV). This finding implies that biogenic processes are more important to uranium ore genesis than previously understood. The predominance of a relatively labile form of U(IV) also provides an opportunity for a more economical and environmentally benign mining process, as well as the design of more effective post-mining restoration strategies and human health-risk assessment.

show abstract

Section: Resultssupporting

confidence: 62%

Biogenic non-crystalline U(IV) revealed as major component in uranium ore deposits

Bhattacharyya

Campbell

Kelly³

et al. 2017

Nat Commun

Self Cite

View full text Add to dashboard Cite

show abstract

“…[2016], 20.28&, 2r 5 0.07, n 5 3 by Lau et al [2017]). In addition, CRM-129a was analyzed at 21.54& (2r 5 0.11, n 5 10), within error of previously published values (-1.54& in Brennecka et al [2010]; 21.52& in Lau et al [2017]; 21.53& in Lau et al [2017]), though previous studies have suggested that CRM-129a solutions may be heterogeneous [Andersen et al, 2017]. Mean 2r within an individual analysis was 0.08&.…”

Section: Geochemical Methodssupporting

confidence: 66%

“…[]; −1.53‰ in Lau et al . []), though previous studies have suggested that CRM‐129a solutions may be heterogeneous [ Andersen et al ., ]. Mean 2 σ within an individual analysis was 0.08‰.…”

Section: Geochemical Methodsmentioning

confidence: 97%

Uranium isotope evidence for an expansion of marine anoxia during the end‐Triassic extinction

Jost

Bachan

Schootbrugge

et al. 2017

Geochem Geophys Geosyst

View full text Add to dashboard Cite

The end‐Triassic extinction coincided with an increase in marine black shale deposition and biomarkers for photic zone euxinia, suggesting that anoxia played a role in suppressing marine biodiversity. However, global changes in ocean anoxia are difficult to quantify using proxies for local anoxia. Uranium isotopes (δ238U) in CaCO3 sediments deposited under locally well‐oxygenated bottom waters can passively track seawater δ238U, which is sensitive to the global areal extent of seafloor anoxia due to preferential reduction of 238U(VI) relative to 235U(VI) in anoxic marine sediments. We measured δ238U in shallow‐marine limestones from two stratigraphic sections in the Lombardy Basin, northern Italy, spanning over 400 m. We observe a ∼0.7‰ negative excursion in δ238U beginning in the lowermost Jurassic, coeval with the onset of the initial negative δ13C excursion and persisting for the duration of subsequent high δ13C values in the lower‐middle Hettangian stage. The δ238U excursion cannot be realistically explained by local mixing of uranium in primary marine carbonate and reduced authigenic uranium. Based on output from a forward model of the uranium cycle, the excursion is consistent with a 40–100‐fold increase in the extent of anoxic deposition occurring worldwide. Additionally, relatively constant uranium concentrations point toward increased uranium delivery to the oceans from continental weathering, which is consistent with weathering‐induced eutrophication following the rapid increase in pCO2 during emplacement of the Central Atlantic Magmatic Province. The relative timing and duration of the excursion in δ238U implies that anoxia could have delayed biotic recovery well into the Hettangian stage.

show abstract

“…Metamorphite deposits involve fluids characterized by higher temperatures, 200 to 400 • C [24], and these are variable in grade, size, and tonnage. Metamorphite deposits that are structure-bound (examined here) occur as monometallic veins associated with traces of other metallic minerals, or as polymetallic veins found with Co, Cu, Fe, Mo, Ni, Pb, Zn, Ag, and As metallics [2].…”

Section: Uranium Depositsmentioning

confidence: 99%

“…Natural variations in the 238 U/ 235 U ratio are attributed to several factors, such as nuclear field shift, temperature, oxidation state, and source rock composition. Nuclear field shift is a mass-independent effect used to predict the dependence of isotopic fractionation on temperature and is particularly important for heavy elements [23,24]. It has been argued previously that the difference in 238 U/ 235 U ratios between low-and high-temperature U ore deposits is related to the temperature dependence of the nuclear field shift [25,26].…”

mentioning

confidence: 99%

The Role of Continental Crust in the Formation of Uraninite-Based Ore Deposits

et al. 2020

View full text Add to dashboard Cite

This study reports trace element abundances and Pb, Sr, and U isotopic signatures of uraninite from a variety of ore deposits in order to establish baseline forensic information for source attribution of raw, natural U-rich samples. Trace element concentrations, reported here, provide insights into uraninite crystal substitution mechanisms and possible crustal sources of U, including mobility of trace elements between pristine versus altered fractions. Spatially resolved laser ablation (LA) multicollector (MC) inductively coupled plasma mass spectrometry (ICP-MS) analyses were used to determine secondary 207Pb-206Pb isochron ages, and these were validated by corroborative results obtained by solution mode (SM) MC-ICP-MS for the same sample. Secondary Pb-Pb isochron ages obtained, in this study, indicate that uraninite alteration occurs shortly after ore mineralization. Initial 87Sr/86Sr values correlate in general with host craton age, and therefore suggest that uraninite ore formation is closely linked to the nature of the bedrock geology. The δ238U values are explained by invoking multiple physicochemical conditions and parameters such as temperature, nuclear field shift, oxidation, and source rock composition. The δ234U values indicate that the uraninites, investigated here, have undergone recent alteration, but the latter has not perturbed the Pb-Pb secondary isochron ages.

show abstract

Uranium Isotope Fractionation

Cited by 160 publications

References 207 publications

Biogenic non-crystalline U(IV) revealed as major component in uranium ore deposits

Biogenic non-crystalline U(IV) revealed as major component in uranium ore deposits

Uranium isotope evidence for an expansion of marine anoxia during the end‐Triassic extinction

The Role of Continental Crust in the Formation of Uraninite-Based Ore Deposits

Contact Info

Product

Resources

About