Uranium Concentrations In Sediments Research Articles

Holocene Environments of Anomalous Uranium Concentrations in Sediments of Syrytkul Lake (Southern Urals)

The influence of the Holocene sedimentation conditions on uranium accumulation in sediments in Syrytkul Lake has been studied. The comparison of geochemical, palynological, and diatom data has made it possible to reveal the relation between the U concentration (5–89 ppm) in lacustrine sediments and environmental changes over more than 12 cal ka BP. The Late Glacial lake clay is relatively depleted in U. The maximum enrichment in U has been determined for lake sediments accumulated about 11.6–10.3 cal ka BP under climate warming and humidification. It has been concluded that the climate could have affected U accumulation through the catchment vegetation shifts. The dark coniferous forests that spread out after the climate cooling about 4.2 cal ka BP could have contributed to the U decrease.

Dating of U-rich heterogenite: New insights into U deposit genesis and U cycling in the Katanga Copperbelt

The Katanga Copperbelt region of the Democratic Republic of Congo hosts world-class cobalt deposits accounting for ∼50% of the world reserves. Heterogenite (CoOOH) is the most abundant Co-bearing secondary mineral in the region. Its occurrence is the result of oxidation of Cu–Co-sulfides and associated Co reprecipitation in the uppermost part of the deposits, during the Pliocene. In addition to sediment-hosted copper and cobalt ore deposits, the Katanga Copperbelt also hosts numerous uraniferous mineral occurrences and deposits, which can be associated with heterogenite. Within these deposits, heterogenite can have high concentrations of U (up to 3.5%) and Pb (up to ∼4%).In situ SIMS U–Pb ages were obtained for heterogenite samples from the U deposits of Shinkolobwe, Kalongwe and Kambove. These analyses yield distinct Neoproterozoic ages, at ∼876Ma, ∼823Ma and in the ∼720 to ∼670Ma age range. As the geological context prevailing at those times was not favorable for heterogenite formation, these ages most probably record geological events that are not the formation of the mineral itself. For instance, the heterogenites could have inherited the U–Pb signature of a U-rich mineral, most likely uraninite, formed and/or yet reworked at ∼876Ma, ∼823Ma and in the ∼720 to ∼670Ma time interval and spatially associated with primary Co-sulfides. In this hypothesis, the ages obtained in this paper are significant for understanding the cycling and re-deposition of U at given moments in the regional geological history.In such context, the ∼876Ma and the ∼823Ma age are consistent with syn-early diagenetic concentration of uranium in sediments of the Katanga basin. The ∼720 to ∼670Ma ages are interpreted as a phase of U remobilization related to hydrothermal fluid circulation induced by late Nguba proto-oceanic rifting or by early stages of Congo-Kalahari craton convergence, and associated hydrothermal circulation.

Uranium concentrations in sediments of the Suez Canal

Suez Canal bottom sediment samples have been analyzed by alpha-spectrometry for the measurement of uranium. This method is based on the extraction of uranium with trioctylphosphine oxide/cyclohexane (TOPO) followed by reextraction and separation on anion exchange resins, and finally electrodeposition. The α-activity of 238U and 234U were measured by surface barrier detectors, in Bq/kg dry weight. The obtained results were compared with concentrations determined by γ measurements. The results point to a state of disequilibrium between 238U and RaeU (radium equivalent uranium) which is attributed to the escape of radon.

Concentration of uranium in sediments by multiple migration-accretion

The continual expansion of the areas in which uranium finds are being reported in sedimentary rocks makes the hypothesis that the metal was transported by solutions hydrothermal in origin entirely inadequate. Solutions, which originally by their very nature were concentrated, would have had to be dispersed over vast areas with exactly the opposite effect of that necessary to make workable deposits. Weathering and erosion of Precambrian granitic rocks in volumes of many thousands of cubic miles has occurred since Pennsylvanian time in the eight western states which make up our uranium province. If we add to these granites the smaller amounts of volcanic tuffs, the uranium contained in these rocks staggers the imagination, it being at least as large as 400 million tons and probably several times this figure.Under humid conditions and without interior basins with extensive continental sediments the uranium would have been carried to the sea. But given arid or semiarid conditions, continental sediments, and a proper leaching agent, results would be quite different. Such leaching agents, which are also very common in nature, are the bicarbonates of Ca, Mg, and Na. They are able to form with uranium compounds which yield the apparently very stable U-tricarbonate ion [UO 2 (CO 3 ) 3 ] (super -4) in a solution saturated with CO 2 . Because most groundwaters contain large amounts of CO 2 and these bicarbonates, they are considered powerful reagents for the solution of uranium as shown by experiment. They could carry the metal, including also vanadium, long distances through almost neutral environments, always along paths or channels of least resistance until reducing conditions were met when black ores would result. If instead of precipitation the charged solutions regained the surface, the tricarbonate would decompose and the uranium would be precipitated as uranyl minerals only to be redissolved at a later date by the same process.Concentration of large deposits could proceed by several stages of oxidation-solution-migration-accretion, a kind of recycling action as metallurgists would call it. Orogenic movements with resulting new unconformities and new gradients would make more uranium available and, of course, add to the large number of depositional variations encountered in space and time. Whether deposition occurred in the Cutler, the Chinle or Morrison, or much later in the Wasatch or Brown9s Park formations would not alter the principles involved. They would work just as well for the uranium accumulations in the lignites of the western Dakotas as for those in the Todilto limestone.