Actinides in Geology, Energy, and the Environment. Remobilization of U and REE and the formation of secondary minerals in oxidized U deposits
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Susanne Göb
Abstract
The hydrothermal uranium vein-type deposits of Menzenschwand and Wittichen in the Schwarzwald in southwestern Germany have been investigated with regards to their primary and secondary mineralization. Primary magmatic uraninite I from the host granite of Menzenschwand, primary hydrothermal uraninite II and secondary (supergene) uranyl silicates (uranophane and cuprosklodowskite), uranyl phosphates (torbernite and uranocircite), and uranyl arsenates (zeunerite, heinrichite, nováčekite, walpurgite, and uranospinite) were analyzed for their REE contents by LA-ICP-MS together with uraninite II samples from other known Schwarzwald uraninite II occurrences for comparison. Water samples were taken from drillings and abandoned mines and were analyzed for their major and trace element composition including U and REE.
The REE patterns of uraninite show significant Eu anomaly variations: negative Eu anomalies are related to granitic host rocks, whereas positive Eu anomalies imply a gneissic REE source. This is in agreement with the observation of Eu anomalies in granite and gneiss derived waters, which display negative and positive Eu anomalies, respectively.
Rare earth element distributions in the secondary uranyl minerals provide information about the sequence of mineral precipitation and the degree of remobilization of U. Cerium anomalies (or their absence) imply that uranyl silicates formed during an earlier stage of weathering under more reduced conditions than the uranyl arsenates and phosphates. The REE patterns of the uranyl silicates in Wittichen are similar to those of uraninite II, suggesting a very local redistribution on the millimeter- to centimeter-scale. In contrast, the REE patterns of uranyl arsenates and phosphates are different from uraninite II patterns and resemble those of the waters. This shows that the uranyl phosphates and arsenates are formed not only by redistribution of U in the hydrothermal veins but are influenced by waters from the host rock implying that U was probably transported over a greater distance. These conclusions are supported by field observations, where uranyl silicates are often found in the vicinity of uraninite II, whereas uranyl phosphates and arsenates are commonly found on fissures in the host rock.
To explain specific features in the sulfide-rich (pyrite, chalcopyrite) Menzenschwand deposit, we conducted thermodynamic reaction modeling using the PHREEQC computer code. Sulfide oxidation was modeled by reaction of a U-rich water in equilibrium with atmospheric oxygen with FeS2 and CuFeS2. A water that initially precipitates uranophane gradually evolves to more acidic pH values, thereby reaching torbernite saturation. This is in agreement with observed paragenetic sequences. Ongoing reaction results in a further decrease of pH and in the destabilization of uranophane and torbernite. Since goethite precipitates even at low-pH values, these calculations can explain observed pseudomorphs of goethite after both uranophane and torbernite, which are frequently observed at Menzenschwand. If the reaction proceeds and fO2 in the system is buffered by the surrounding minerals, U6+ can be reduced to U4+ and uraninite can form and replace pyrite and earlier formed secondary uranium minerals such as ianthinite. Also these textures have been observed. We show that the combination of REE geochemistry, careful paragenetic observations and thermodynamic modeling allows to reconstruct the formation and weathering of uranium deposits in great detail.
© 2015 by Walter de Gruyter Berlin/Boston
Articles in the same Issue
- Highlight and Breakthrough. A fresh look at crystals in the Bishop Tuff
- Actinides in Geology, Energy, and the Environment. Remobilization of U and REE and the formation of secondary minerals in oxidized U deposits
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- Redox systematics of martian magmas with implications for magnetite stability
- Hydrogen incorporation and the oxidation state of iron in ringwoodite: A spectroscopic study
- Hydrous ringwoodite to 5 K and 35 GPa: Multiple hydrogen bonding sites resolved with FTIR spectroscopy
- Calibration of zircon as a Raman spectroscopic pressure sensor to high temperatures and application to water-silicate melt systems
- Computational study of the elastic behavior of the 2M1 muscovite-paragonite series
- Vanadium L2,3 XANES experiments and first-principles multielectron calculations: Impact of second-nearest neighboring cations on vanadium-bearing fresnoites
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- Static disorders of atoms and experimental determination of Debye temperature in pyrope: Low- and high-temperature single-crystal X-ray diffraction study—Reply
Articles in the same Issue
- Highlight and Breakthrough. A fresh look at crystals in the Bishop Tuff
- Actinides in Geology, Energy, and the Environment. Remobilization of U and REE and the formation of secondary minerals in oxidized U deposits
- Actinides in Geology, Energy, and the Environment. Revision of the symmetry and the crystal structure of čejkaite, Na4(UO2)(CO3)3
- Characterization of ferric arsenate-sulfate compounds: Implications for arsenic control in refractory gold processing residues
- Crystal structure and chemistry of skarn-associated bismuthian vesuvianite
- Transformation of graphite to lonsdaleite and diamond in the Goalpara ureilite directly observed by TEM
- Quartz nanocrystals in the 2.48 Ga Dales Gorge banded iron formation of Hamersley, Western Australia: Evidence for a change from submarine to subaerial volcanism at the end of the Archean
- Synthesis and characterization of amphiboles along the tremolite–glaucophane join
- Elasticity of franklinite and trends for transition-metal oxide spinels
- Redox systematics of martian magmas with implications for magnetite stability
- Hydrogen incorporation and the oxidation state of iron in ringwoodite: A spectroscopic study
- Hydrous ringwoodite to 5 K and 35 GPa: Multiple hydrogen bonding sites resolved with FTIR spectroscopy
- Calibration of zircon as a Raman spectroscopic pressure sensor to high temperatures and application to water-silicate melt systems
- Computational study of the elastic behavior of the 2M1 muscovite-paragonite series
- Vanadium L2,3 XANES experiments and first-principles multielectron calculations: Impact of second-nearest neighboring cations on vanadium-bearing fresnoites
- A time-resolved X-ray diffraction study of Cs exchange into hexagonal H-birnessite
- Grain-boundary diffusion rates inferred from grain-size variations of quartz in metacherts from a contact aureole
- On the use of unpolarized infrared spectroscopy for quantitative analysis of absorbing species in birefringent crystals
- A computational model of cation ordering in the magnesioferrite-qandilite (MgFe2O4- Mg2TiO4) solid solution and its potential application to titanomagnetite (Fe3O4-Fe2TiO4)
- 3T-phlogopite from Kasenyi kamafugite (SW Uganda): EPMA, XPS, FTIR, and SCXRD study
- Revision of the crystal structure and chemical formula of haiweeite, Ca(UO2)2(Si5O12)(OH)2·6H2O
- Cation arrangement in the octahedral and tetrahedral sheets of cis-vacant polymorph of dioctahedral 2:1 phyllosilicates by quantum mechanical calculations
- High-pressure phase transitions of Fe3–xTixO4 solid solution up to 60 GPa correlated with electronic spin transition
- Hydrogen incorporation in crystalline zircon: Insight from ab initio calculations
- The vibrational features of hydroxylapatite and type A carbonated apatite: A first principle contribution
- STEM investigation of exsolution lamellae and “c” reflections in Ca-rich dolomite from the Platteville Formation, western Wisconsin
- Karenwebberite, Na(Fe2+,Mn2+)PO4, a new member of the triphylite group from the Malpensata pegmatite, Lecco Province, Italy
- The crystal structure of ramdohrite, Pb5.9Fe0.1Mn0.1In0.1Cd0.2Ag2.8Sb10.8S24: A new refinement
- Static disorders of atoms and experimental determination of Debye temperature in pyrope: Low- and high-temperature single-crystal X-ray diffraction study—Discussion
- Static disorders of atoms and experimental determination of Debye temperature in pyrope: Low- and high-temperature single-crystal X-ray diffraction study—Reply
