Role of vein-phases in nanoscale sequestration of U, Nb, Ti, and Pb during the alteration of pyrochlore

Deditius, Artur P.; Smith, Frances N.; Utsunomiya, Satoshi; Ewing, Rodney C.

doi:10.1016/j.gca.2014.11.024

Cited by 15 publications

(3 citation statements)

References 73 publications

(133 reference statements)

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“…Moreover, TEM results show that U and Pb leached out of uraninite are transported along fractures over several tens to several hundreds of microns and redeposited locally as a U-Pb-rich silicate or U-Pb-rich oxide phase (Figure 9a,c). Specifically, in Fe-Pb-O-S system, when T= 100 • C, the stability field changing from Fe 2+ -Pb-sulfide to Fe 3+ -Pb-oxide implies the drop of log(ƒS 2 ) to below −40 log units and the rise log(ƒO 2 ) to above -55 log units, respectively [78,79], but it is still unable to trigger the large-scale remobilization of uranium as soluble ions. Temperature constraints from monazite-xenotime thermometry suggest low temperature conditions (85-174 • C) for local coffinitization after uraninite.…”

Section: Processes Responsible For Uraninite Alteration and Radiohalo Formationmentioning

confidence: 99%

Uraninite from the Guangshigou Pegmatite-Type Uranium Deposit in the North Qinling Orogen, Central China: Its Occurrence, Alteration and Implications for Post-Caledonian Uranium Circulation

Bonnetti

Liu

et al. 2021

Minerals

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The Guangshigou deposit is the largest pegmatite-type uranium deposit in the Shangdan domain of the North Qinling Orogenic Belt, which is characterized by the enrichment of uraninite hosted in biotite granitic pegmatites. At Guangshigou, uraninite commonly occurs as mineral inclusions in quartz, K-feldspar and biotite or in interstices of these rock-forming minerals with magmatic characteristics (e.g., U/Th < 100, high ThO2, Y2O3 and REE2O3 contents and low concentrations of CaO, FeO and SiO2). It crystallized at 407.6 ± 2.9 Ma from fractionated calc-alkaline high-K pegmatitic melts under conditions of 470–700 °C and 2.4–3.4 kbar as deduced by the compositions of coexisting peritectic biotite. The primary uranium mineralization took place during the Late Caledonian post-collisional extension in the North Qinling Orogen. After this magmatic event, uraninite has experienced multiple episodes of fluid-assisted metasomatism, which generated an alteration halo of mineral assemblages. The alteration halo (or radiohalo) was the result of the combined effects of metamictization and metasomatism characterized by an assemblage of goethite, coffinite and an unidentified aluminosilicate (probably clay minerals) around altered uraninite. This fluid-assisted alteration was concomitant with the albitization of K-feldspar subsequently followed by the coffinitization of uraninite during the major period of 84.9–143.6 Ma, as determined by U-Th-Pb chemical ages. Further investigations revealed that the metasomatic overprinting on uraninite initially and preferentially took place along microcracks or cavities induced by metamictization and promoted their amorphization, followed by the release of U and Pb from structure and the incorporation of K, Ca and Si from the fluids, finally resulting in various degrees of uraninite coffinitization. The released U and Pb were transported by alkali-rich, relatively oxidizing fluids and then re-precipitated locally as coffinite and an amorphous U-Pb-rich silicate under low to moderate temperature conditions (85–174 °C). The compositional changes in primary uraninite, its structure amorphization together with the paragenetic sequence of secondary phases, therefore, corroborate a combined result of intense metamictization of uraninite and an influx of alkali–metasomatic fluids during the Late Mesozoic Yanshanian magmatic event in the region. Hence, the remobilization and circulation of uranium in the North Qinling Orogen was most likely driven by post-Caledonian magmatism and hydrothermal activities related to large-scale tectonic events. In this regards, Paleozoic pegmatite-type uranium mineralization may represent a significant uranium source for Mesozoic hydrothermal mineralization identified in the Qinling Orogenic Belt.

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Section: Processes Responsible For Uraninite Alteration and Radiohalo Formationmentioning

confidence: 99%

Uraninite from the Guangshigou Pegmatite-Type Uranium Deposit in the North Qinling Orogen, Central China: Its Occurrence, Alteration and Implications for Post-Caledonian Uranium Circulation

Bonnetti

Liu

et al. 2021

Minerals

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“…For many ceramic systems, natural analogues have confirmed the suitability to immobilize radionuclides for several million years (6)(7)(8). Besides monazite (9)(10)(11)(12)(13)(14)(15), apatite (16)(17), thorium phosphate diphosphate (18)(19)(20), perovskite (21)(22), and zirconolite (21,23), a particular interest was dedicated to pyrochlore (24)(25). Due to their high aqueous durability (26)(27)(28)(29), chemical flexibility and radiation tolerance (8,30), zirconate pyrochlores with the general chemical composition A 2 B 2 O 7 seem to be highly promising candidates for the immobilization of plutonium (25,(31)(32).…”

Section: Introductionmentioning

confidence: 99%

Monitoring the microstructural evolution of Nd 2 Zr 2 O 7 pyrochlore during dissolution at 90 °C in 4 M HCl: Implications regarding the evaluation of the chemical durability

Szenknect

Finkeldei

Brandt

et al. 2017

Journal of Nuclear Materials

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Understanding the dissolution mechanism at the solid/solution interface of Nd 2 Zr 2 O 7 pyrochlore is a critical step to evaluate its suitability to immobilize radionuclides. In this aim, the chemical durability of Nd 2 Zr 2 O 7 pyrochlore sintered samples in 4 M HCl was examined by several complementary techniques. Microstructural and structural changes were evidenced at the solid/solution interface. Environmental Scanning Electron Microscopy (ESEM), Atomic Force Microscopy (AFM) and X-Ray Reflectivity (XRR) showed that the dissolution occurs heterogeneously at the surface with a complex interplay of several dissolution rate contributors. The most important process observed is the chemo-mechanical corrosion of the pyrochlore as a consequence of the grain boundaries dissolution. The evolution of the crystal structure at the solid/solution interface was also

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“…They are a wellknown source of tantalum and niobium, and some old specimens also contain thorium or uranium [1]. The synthetic counterparts may accommodate a very broad spectrum of tri-and tetravalent cations in the A 2 B 2 O 7 structure [2].…”

Section: Introductionmentioning

confidence: 99%

Microstructure, electrical and humidity sensing properties of light rare earths zirconates

Petrila

Popa

Tudorache

2016

Sensors and Actuators A: Physical

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Role of vein-phases in nanoscale sequestration of U, Nb, Ti, and Pb during the alteration of pyrochlore

Cited by 15 publications

References 73 publications

Uraninite from the Guangshigou Pegmatite-Type Uranium Deposit in the North Qinling Orogen, Central China: Its Occurrence, Alteration and Implications for Post-Caledonian Uranium Circulation

Uraninite from the Guangshigou Pegmatite-Type Uranium Deposit in the North Qinling Orogen, Central China: Its Occurrence, Alteration and Implications for Post-Caledonian Uranium Circulation

Monitoring the microstructural evolution of Nd 2 Zr 2 O 7 pyrochlore during dissolution at 90 °C in 4 M HCl: Implications regarding the evaluation of the chemical durability

Microstructure, electrical and humidity sensing properties of light rare earths zirconates

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