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Sample records for cheralite

  1. Rare earth silicate (Ce, La, Nd, Ca, Th) SiO4 and cheralite (Th, Ca, Ce, La) (Psi)O4 are the responsible minerals for the anomalies of Morro de Ferro

    International Nuclear Information System (INIS)

    The Rare Earth silicate (La, Ce, Nd, Ca, Th)SiO4 and cheralite (identified by Prof. Freeborn on a sample prepared from drilling core) were recognized as the most probable radioactive minerals that gave origin to high radioactive anomaly at Morro do Ferro hill together with coffinite, thorite, pyrochlore, apatite, etc., that are found in small quantity. The acids produced by decomposition of pyrite and fluorite have etched these radioactive minerals giving the high radioactive anomaly caracterized by high grade desiquilibrium of 232Th serie. (Author)

  2. Hydrothermal alteration of monazite-(Ce) from the Santa Maria de Itabira pegmatite district (Minas Gerais, Brazil); Alteration hydrothermale des monazites-(Ce) des pegmatites du district de Santa Maria de Itabira (Minas Gerais, Bresil)

    Energy Technology Data Exchange (ETDEWEB)

    Bilal, E.; Arias Nalini, H.; Nasraoui, M. [Ecole Nationale Superieure des Mines, 42 - Saint-Etienne (France). Dept. de Geochimie, Centre SPIN; Marciano, V.; Neves, J.M.C.; Fernandes, M.L. [Minas Gerais Univ., Belo Horizonte, MG (Brazil). Inst. Geociencias; Fuzikawa, K. [Comissao Nacional de Energia Nuclear (CNEN), Belo Horizonte, MG (Brazil). Centro de Desenvolvimento de Tecnologia Nuclear

    1998-05-01

    Monazite-(Ce) is found in granitic pegmatites in the Santa Maria de Itabira pegmatite district (Minas Gerais, Brazil). During the magmatic stage, monazite-(Ce) seems to have had higher contents of cheralite and buttonite in the solid solution. The Th content in primary monazite-(Ce) is high and characteristic for each pegmatite body. During the late stage (albitisation), the mean LREE content in the altered zone is slightly higher and Th content is very low. The accessory mineral assemblages changed; buttonite and cheralite crystallize together with Th-poor and La-rich monazite-(Ce) at the border of altered crystals. Nd/Sm and U/Pb ratios also changed during the hydrothermal stage. (authors) 13 refs.

  3. Hydrothermal alteration of monazite-(Ce) from the Santa Maria de Itabira pegmatite district (Minas Gerais, Brazil)

    International Nuclear Information System (INIS)

    Monazite-(Ce) is found in granitic pegmatites in the Santa Maria de Itabira pegmatite district (Minas Gerais, Brazil). During the magmatic stage, monazite-(Ce) seems to have had higher contents of cheralite and buttonite in the solid solution. The Th content in primary monazite-(Ce) is high and characteristic for each pegmatite body. During the late stage (albitisation), the mean LREE content in the altered zone is slightly higher and Th content is very low. The accessory mineral assemblages changed; buttonite and cheralite crystallize together with Th-poor and La-rich monazite-(Ce) at the border of altered crystals. Nd/Sm and U/Pb ratios also changed during the hydrothermal stage. (authors)

  4. Uranium- and thorium-rich monazite from a south-alpine pegmatite at Piona, Italy

    International Nuclear Information System (INIS)

    A green pegmatite mineral from Piona, northern Italy, originally described as a phosphate of lanthanum and cerium, has unit-cell parameters a = 6.78, b = 6.96, c = 6.48A, β = 103054', in agreement with monazite. However, the unusual character of this mineral with respect to ''ordinary'' monazite is evident in some physical properties, such as the absorption spectrum in the visible region, which shows bands with their maxima at 640 to 680, 555, and 510 nm, with only weak absorption at 570 to 590 and 522 nm. The refractive indices (α approximately equal to β = 1.78, γ = 1.82) are slightly lower than for most monazite specimens. Electron microprobe analysis indicates a content of uranium (16% UO2) which exceeds any previously-reported figure for members of the monazite group, and a moderately high content of thorium (11% ThO2). A relevant quantity of CaO (4.4%) is also present; silica is nearly absent (0.16%). From these data, relationships to cheralite are evident, and the mineral might be considered as a uranium-rich cheralite, or as its uranium-bearing equivalent; the name monazite is used on acount of the ratio (Ca + U + Th)/(Ce + La + Pr + Nd), which is below unity (0.91 against 1.47 for type cheralite). The rare-earth distribution shows considerable enrichment of La2O3 (40% of the total rare-earth oxides), and depletion of Nd2O3 (7.75%) and Sm2O3 (<< 1%) with respect to the average observed for monazite. As for most well-documented cases of minerals with monazite structure, the substitution Si → P is a relatively minor factor in reestablishing the charge balance when thorium or uranium are present

  5. Crystal chemistry of MIIM′IV(PO4)2 double monophosphates

    International Nuclear Information System (INIS)

    MIIM′IV(PO4)2 compounds have been extensively studied for several decades for their potential applications in the field of several domains such as matrices for actinides conditioning, phosphors etc. In this paper, the relationships between composition and crystal structure of these compounds are established. A review of the various processes used for the synthesis of these compounds is also proposed, as well as their most reported properties. MIIM′IV(PO4)2 structures stem from two different archetypes: the cheralite and the yavapaiite structures, with some exceptions that are also described in this article. The ratio of the cations radii appears to be the most relevant parameter. The high ratio between the ionic radii of the divalent and tetravalent cations in yavapaiite derivates results in the ordering of these cations into well-differentiated polyhedra whereas cheralite is the only non-ordered structure encountered for MIIM′IV(PO4)2 compounds. - Graphical abstract: In this paper, the relationships between composition and crystal structure of MIIM′IV(PO4)2 compounds are established. A review of the various processes used for the synthesis of these compounds is also proposed, as well as their most reported properties. - Highlights: • Crystal structure–composition relationships of MIIM′IV(PO4)2 compounds. • Review of the various processes used for the synthesis of these compounds. • Their most reported properties are described and discussed

  6. Thermodynamic investigation of La1-x (CaTh)x(PO4)1+x(s) (x = 0, 0.25, 0.5, 1) solid solutions

    International Nuclear Information System (INIS)

    Phosphate-based ceramics such as monazites are considered as potential host matrix for immobilization of long-lived trivalent and tetravalent actinides. Monazites are chemically stable with respect to leaching processes and have high radiation stability. These compounds have the unique ability to incorporate a large number of fission products including heavy metals like U4+ and Th4+ in the lattice sites without undergoing structural changes. Monazites have the general formula M2+M4+ (PO4)2 called cheralite. The extent of Ca2+ and Th4+ substitution in monazite and their effect on the thermodynamic stability of the matrix is therefore important for the long term storage of thorium and minor actinides in the matrix. In this work preparation, characterization and stability of Ca2+ and Th4+ substituted monazite is reported

  7. Crystal chemistry of M{sup II}M′{sup IV}(PO{sub 4}){sub 2} double monophosphates

    Energy Technology Data Exchange (ETDEWEB)

    Bregiroux, Damien, E-mail: damien.bregiroux@upmc.fr [Sorbonne Universités, UPMC Univ Paris 06, CNRS, Collège de France, Laboratoire de Chimie de la Matière Condensée de Paris, 11 place Marcelin Berthelot, 75005 Paris (France); Popa, Karin [“Al.I. Cuza” University, Department of Chemistry, 11-Carol I Blvd., 700506 Iasi (Romania); Wallez, Gilles [Institut de Recherche de Chimie Paris (IRCP), CNRS – Chimie ParisTech – Paris Sciences et Lettres PSL UMR8247, 11 rue Pierre et Marie Curie, 75005 Paris (France); Sorbonne Universités, UPMC Univ Paris 06 (France)

    2015-10-15

    M{sup II}M′{sup IV}(PO{sub 4}){sub 2} compounds have been extensively studied for several decades for their potential applications in the field of several domains such as matrices for actinides conditioning, phosphors etc. In this paper, the relationships between composition and crystal structure of these compounds are established. A review of the various processes used for the synthesis of these compounds is also proposed, as well as their most reported properties. M{sup II}M′{sup IV}(PO{sub 4}){sub 2} structures stem from two different archetypes: the cheralite and the yavapaiite structures, with some exceptions that are also described in this article. The ratio of the cations radii appears to be the most relevant parameter. The high ratio between the ionic radii of the divalent and tetravalent cations in yavapaiite derivates results in the ordering of these cations into well-differentiated polyhedra whereas cheralite is the only non-ordered structure encountered for M{sup II}M′{sup IV}(PO{sub 4}){sub 2} compounds. - Graphical abstract: In this paper, the relationships between composition and crystal structure of M{sup II}M′{sup IV}(PO{sub 4}){sub 2} compounds are established. A review of the various processes used for the synthesis of these compounds is also proposed, as well as their most reported properties. - Highlights: • Crystal structure–composition relationships of MIIM′IV(PO4)2 compounds. • Review of the various processes used for the synthesis of these compounds. • Their most reported properties are described and discussed.

  8. Monazite-(Ce in Hercynian granites and pegmatites of the Bratislava massif, Western Carpathians: compositional variations and Th-U-Pb electron-microprobe dating

    Directory of Open Access Journals (Sweden)

    Pavel Uher

    2014-12-01

    Full Text Available Monazite-(Ce represents a characteristic magmatic accessory mineral of the Hercynian peraluminous S-type granites to granodiorites and related granitic pegmatites of the Bratislava Granitic Massif (BGM, Malé Karpaty Mountains, Central Western Carpathians, SW Slovakia. Monazite forms euhedral to subhedral crystals, up to 200 μm in size, usually it is unzoned in BSE, rarely it reveals oscillatory or sector zoning. Thorium concentrations of 2 to 9 wt. % ThO2 (≤0.09 apfu and local elevated uranium contents (≤4.3 wt. % UO2, ≤0.04 apfu are characteristic for the pegmatite monazites. Both huttonite ThSiREE-1P-1 and cheralite Ca(Th,UREE-2 substitutions took place in the studied monazite. Electron-microprobe Th-U-Pb monazite dating of the granites and pegmatites gave an isochron age of 353±2 Ma (MSWD = 0.88, n = 290, which confirmed the meso-Hercynian, Carboniferous, Lower Mississipian magmatic crystallization. An analogous age (359±11 Ma was obtained from monazite from adjacent paragneiss, corresponding to the age of the Hercynian contact thermal metamorphism related to the granite intrusion of BGM. Monazite in some granite shows also older clastic or authigenic grains or zones (~505 to 400 Ma, with maximum of 420±7 Ma which probably represents inherited material from the Lower Paleozoic metapelitic to metapsammitic protolith of BGM.

  9. Age Dating from Electron Microprobe Analyses of U, Th, and Pb: Geological Advantages and Analytical Difficulties.

    Science.gov (United States)

    Bowles, John F W

    2015-10-01

    Electron microprobe analysis of U, Th, and Pb in naturally occurring minerals can indicate their age. Where the Pb is entirely due to the radioactive decay of U and Th, the time since mineral formation or equilibration can be calculated. Uraninite (UO2), monazite (REE PO4), zircon (ZrSiO4), and xenotime (YPO4) have been used, the latter containing U and/or Th in minor proportions. Any stable U- or Th-bearing phase can be considered. Careful analysis is required with attention to interferences, background measurement, detection limits, and Pb-free sample preparation. Extended counting times (600 s) at a probe current >200 nA are recommended. Ages can be determined from uraninite older than 2 Ma for a Pb detection limit of 0.02% and up to 700-1,000 Ma, after which Pb can be lost from the structure. The youngest monazite ages permitted by the Pb detection limit are 50-100 Ma and ages greater than 3,000 Ma have been determined. The method does not provide the detail of isotopic methods, but results can be obtained more readily. Examples show dating of cheralite ((Ca,Ce)(Th,Ce)(PO4)2), a rock containing primary and secondary UO2, and a suite of detrital uraninite grains that formed a part of a mineral exploration program. PMID:25936439

  10. Surface features and alteration products of natural zirconolite leached in silica-saturated solutions

    International Nuclear Information System (INIS)

    Zirconolite, CaZrTi2P7, has been proposed as an immobilization phase for the disposition of excess weapons Pu and other actinides (e.g., 235U). Due to actinide incorporation, zirconolite is expected to sustain α-decay event damage and become aperiodic (=metamict) over time. The leaching behavior of metamict zirconolite is, therefore, of interest. Because groundwater in a variety of geologic settings contains up to saturation concentrations of silicic acid, H4SiO4, silica-saturated solutions were used. Natural, metamict (>1026 α-decay events per m3) zirconolite grains, nominally (Ca,Th)ZrTi2O7 (US National Museum sample No. B20392, Walawada, Sri Lanka) were leached in two separate silica-saturated solutions at 150 C for 60 days. Surface features and alteration products were examined using scanning electron microscopy (SEM) and quantitative energy dispersive X-ray spectroscopy (EDS). Secondary electron (SEI) images of the surfaces of the leached grains from both experiments revealed pores, probably due to the accumulation of He-bubbles from α-decay events, of approximately 4% as estimated by contrast enhanced gray-scale analysis of digital images. SEI of the zirconolite surface before leaching showed a smooth surface. The pores not only increase the surface area of the metamict zirconolite, but also act as nucleation sites for alteration phase growth. One experiment was conducted in a silica-saturated solution containing approximately 100 ppm P as measured by atomic absorption spectroscopy (AAS). The main alteration phase was euhedral, monoclinic cheralite, (Th,Ca,Ce)(P,Si)O4 (monazite group). The second experiment was conducted in the absence of P. The main alteration phase was subhedral cubic thorianite, ThO2

  11. Multi-stage evolution of xenotime-(Y) from Písek pegmatites, Czech Republic: an electron probe micro-analysis and Raman spectroscopy study

    Science.gov (United States)

    Švecová, E.; Čopjaková, R.; Losos, Z.; Škoda, R.; Nasdala, L.; Cícha, J.

    2016-04-01

    The chemical variability, degree of radiation damage, and alteration of xenotime from the Písek granitic pegmatites (Czech Republic) were investigated by micro-chemical analysis and Raman spectroscopy. Dominant large xenotime-(Y) grains enriched in U, Th and Zr crystallized from a melt almost simultaneously with zircon, monazite and tourmaline. Xenotime is well to poorly crystalline depending on its U and Th contents. It shows complex secondary textures cutting magmatic growth zones as a result of its interaction with F,Ca,alkali-rich fluids during the hydrothermal stage of the pegmatite evolution. The magmatic xenotime underwent intense secondary alteration, from rims inwards, resulting in the formation of inclusion-rich well crystalline xenotime domains of near end-member composition. Two types of recrystallization were distinguished in relation to the type of inclusions: i) xenotime with coffinite-thorite, cheralite and monazite inclusions and ii) xenotime with zirconcheralite and zircon inclusions. Additionally, inner poorly crystalline U,Th-rich xenotime domains were locally altered, hydrated, depleted in P, Y, HREE, U, Si and radiogenic Pb, and enriched in fluid-borne cations (mainly Ca, F, Th, Zr, Fe). Interaction of radiation-damaged xenotime with hydrothermal fluids resulted in the disturbance of the U-Th-Pb system. Alteration of radiation-damaged xenotime was followed by intensive recrystallization indicating the presence of fluids >200 °C. Subsequently other types of xenotime formed as a consequence of fluid-driven alteration of magmatic monazite, and Y,REE,Ti,Nb-oxides or crystallized from hydrothermal fluids along cracks in magmatic monazite and xenotime.

  12. Mobility of thorium from the Morro do Ferro

    International Nuclear Information System (INIS)

    An estimated 20,000 metric ton (MT) deposit of Th is located near the summit of the Morro do Ferro, a hill near the center of the Pocos de Caldas plateau in the State of Minas Gerais, Brazil. Most of the Th is contained in microscopic crystals of cheralite, monazite and zircon in a matrix of highly weathered alkalic igneous rock interlaced by a stockwork of magnetite dikes. Because of similarities in the chemistries of Th and Pu under many environmental conditions, a study of the rate of mobilization of Th from this deposit is being undertaken to improve our understanding of how rapidly Pu would be mobilized from a nuclear waste repository that has been breached. The deposit also contains appreciable quantities of U and rare earth elements, and their mobilization rates are being investigated, but only the Th data are presented here. Mobilization is being studied: a) by measuring the rate of Th transport by a stream that drains the hill, and b) by analysis of dated cores from sedimentary deposits in the drainage basin. The mean total Th concentration (dissolved plus suspended particulates)in samples of stream water collected during the past year was 0.39 μg/l. The standard error of the mean was 0.07 μg/l. To a first approximation, the estimated annual mobilization rate of the Th deposit has been calculated to be 4 x 10-8 per year. If this rate of mobilization persists, the life of the Th deposit would thus be about 25 million years. (Author)

  13. Versatile Monazite: Resolving geological records and solving challenges in materials science: Monazite as a promising long-term radioactive waste matrix: benefits of high-structural flexibility and chemical durability

    International Nuclear Information System (INIS)

    Monazite (Ln3+PO4) and related solid solutions are a well-known source of rare earth elements on earth. They may also accommodate large amounts of thorium and uranium without sustaining damage to the structure by self-irradiation. Such observations led to monazite-type structures being proposed as a potential host matrix for sequestering long-lived radionuclides produced during the nuclear fuel cycle and/or plutonium and americium from dismantled nuclear weapons. Monazite has two main advantages as a matrix for the containment of radioactive waste (or 'radwaste'). The first is a highly flexible structure that permits accommodation of high concentrations of actinides. The incorporation of trivalent elements may be achieved by direct synthesis of An3+PO4 (An3+ = plutonium, Pu to einsteinium, Es), while tetravalent cation incorporation requires coupled substitutions, either on the anionic site (leading to monazite-huttonite solid solution) or on the cationic site (monazite-cheralite solid solution). Various methods developed for the preparation of such compounds are summarized here, as well as the experimental conditions required for the production of sintered pellets, with a particular focus on plutonium-bearing compositions. The second highly favorable property of monazite is its high chemical durability. Several experimental procedures developed to determine normalized leaching rates are reviewed, as well as results obtained from natural and synthetic monazite. Potential phases formed during dissolution were considered because they also partially control the concentration of actinides in the media. A preliminary list for such phases of interest, as well as corresponding thermodynamic data, is presented. (authors)

  14. The Nolans Bore rare-earth element-phosphorus-uranium mineral system: geology, origin and post-depositional modifications

    Science.gov (United States)

    Huston, David L.; Maas, Roland; Cross, Andrew; Hussey, Kelvin J.; Mernagh, Terrence P.; Fraser, Geoff; Champion, David C.

    2016-08-01

    Orogeny. Surface exposure and weathering of fluorapatite produced acidic fluids and intense, near-surface kaolinitised zones that include high-grade, supergene-enriched cheralite-rich ores.

  15. The Nolans Bore rare-earth element-phosphorus-uranium mineral system: geology, origin and post-depositional modifications

    Science.gov (United States)

    Huston, David L.; Maas, Roland; Cross, Andrew; Hussey, Kelvin J.; Mernagh, Terrence P.; Fraser, Geoff; Champion, David C.

    2016-01-01

    Orogeny. Surface exposure and weathering of fluorapatite produced acidic fluids and intense, near-surface kaolinitised zones that include high-grade, supergene-enriched cheralite-rich ores.

  16. Timing and duration of ultra-high temperature metamorphism in sapphirine-bearing metapelite granulite from Kodaikanal, Madurai block, South India: constraints from mineral chemistry and U-Th - total Pb EPMA age of monazite

    International Nuclear Information System (INIS)

    The southern part of Peninsular India, popularly known as the Southern Granulite Terrane (SGT) witnessed a pervasive granulite faces metamorphism, ductile shearing and widespread migmatization during Pan-African orogeny, which marks the final assembly of the Gondwanaland during Cambrian (ca 500 Mu). The tectonic evolution of SGT, irrespective of its Gondwana connection, is far-reaching due to occurrences of ultra-high temperature (UHT) granulites in different parts of the SGT. In the present study, dynamics of melting and temporal evolution of sapphirine-bearing metapelite granulite, hosted within the Kodaikanal charnockite massif, during syn - to post - UHT metamorphic conditions are examined. The onset of UHT metamorphism in the rock is marked by the growth of Al-rich orthopyroxene (Al2O3 ∼8 wt%) porphyroblast, sapphirine-cordierite symplectite via biotite dehydration melting. Embayment of orthopyroxene porphyroblast and accumulation of melt, now preserved as mesoperthites, in the pressure shadow region around the porphyroblast attest to syn-tectonic melting and crystallization. Monazites of varying sizes (40 to 100 mm) occur pervasively, either as inclusion in peritectic phases or in the biotite-mesoperthite rich matrix. Diagnostic chemical variation diagram, such as 4 (REE + Y + P) versus 4 (Th + U + Si), (Si + Y + REE) versus (Ca + P) suggests that the core and rims domains are linked by dominantly huttonitic (Th4+ - Si4+ = REE3+ P5+) and cheralite (Th4+ + Ca2+ = 2 REE4+) substitutions. An increase in partitioning of Th towards the rim is also accompanied with a decrease in La/Sm ratio towards the rim. This together with core to rim chemical variation in monazite attests to monazite growth (core) and overgrowth (rim) during peak UHT metamorphism and subsequent cooling. U - Th - total Pb monazite ages constrain the timing of dehydration melting as well as peak UHT metamorphism at - 560 Ma and post-peak cooling at ∼510 Ma. This establishes a time span of