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Allanite is a common accessory mineral in igneous rocks. Allanite becomes metamict over geological time-scales as a result of the α-decay of radioactive elements in the crystal structure. This study focuses on the recrystallization of metamict allanite from Savvushka, Russia. The structural recovery produced by annealing was investigated by X-ray powder diffraction, single-crystal synchrotron X-ray diffraction and infrared spectroscopy. A kinetic analysis is presented that shows that the recrystallization process proceeds by at least two different mechanisms.

We have measured the elastic response of radiation-damaged titanite, CaTiSiO5, as a function of thermal annealing. We estimate the bulk modulus of the damaged samples (~24% amorphous) to be 85 GPa, which is much softer than for undamaged crystalline titanite [131.4 GPa; Angel et al. (1999)]. Conversely, the lowest shear modulus of the radiation-damaged material is 52–58 GPa, which is harder that of the undamaged titanite, 46–52 GPa. The bulk and shear moduli of the radiation-damaged materials are close to those of thermal titanite glass, B glass ≈ 75 GPa and G glass ≈ 47 GPa, and are much smaller than expected based on other radiation-damaged materials such as zircon (ZrSiO4). Surprisingly, annealing of the damaged titanite in the range 600 < T < 1000 K leads to additional massive softening of the shear moduli. During annealing the shear modulus of titanite sample 1 softened from 58 to 29 GPa, and sample 2 softened from 52 to 19 GPa. The temperature range for the softening coincides with that found for crystallization of the amorphous regions, as measured previously by diffraction and spectroscopic methods. In contrast to the huge softening of the ultrasonically measured shear modulus, the calorimetrically measured Debye temperature 𝛉D increases by ~5%, suggesting a small intrinsic hardening of the acoustic shear modes. Additional heating to 1473 K leads, in one titanite sample, to a steep increase of the shear modulus to values much larger than that of the initial, radiation-damaged material. Theoretical models are discussed to rationalize the massive softening due to both radiation damage and subsequent anneal.

The electrical properties of annealed, fully metamict gadolinite REEFe2+Be2Si2O10 are studied as a function of annealing temperature. Changes due to annealing are also probed by 57Fe Mossbauer spectroscopy and X-ray diffraction. The electrical conductivity measured at f = 100 Hz between 110 and 750 K varies markedly, ranging from 10−10 to 10−6 S m−1 for untreated samples and 10−9 to 10−3 S m−1 for sample annealed in argon at 1373 K. Average measured activation energies for electrical conduction are 0.47 and 0.63 eV for ranges of 400–450 K and 500–600 K, respectively. The dielectric permittivity shows strong dispersion effects above 235 K. After high temperature annealing, the electrical conductivity shows a marked dispersion below 604 K. The combination of polaron hopping and hydroxyl anion migration is proposed for the electrical conduction mechanism.

Raman spectra of the uranyl titanate mineral brannerite were analysed and related to the mineral structure. A comparison is made with the Raman spectra of uranyl oxyhydroxide hydrates. The observed bands are attributed to the TiO and (UO2)2+ stretching and bending vibrations, UOH bending vibrations, as well as H2O and (OH)− stretching, bending and libration modes. UO bond lengths in uranyls and OH···O bond lengths were calculated from the wavenumbers assigned to the stretching vibrations. Raman bands of brannerite are in harmony with those of the uranyl oxyhydroxides. The mineral brannerite is metamict, as is evidenced by the intensity of the UO stretching and bending modes being of lower intensity than expected and with bands that are significantly broader. Copyright © 2010 John Wiley & Sons, Ltd.

Raman spectra of the uranyl titanate mineral davidite-(La), (La,Ce)(Y,U,Fe2+)(Ti,Fe3+)20(O,OH)38, were analyzed and related to the mineral structure. Observed bands are attributed to the TiO and (UO2)2+ stretching and bending vibrations, U–OH bending vibrations, H2O and (OH)− stretching, bending and libration modes. U–O bond lengths in uranyls and O-H ··· O bond lengths are calculated from the wavenumbers assigned to the stretching vibrations. Raman bands of davidite-(La) are in harmony with those of the uranyl oxyhydroxides. The mineral davidite-(La) is metamict, as is evidenced by the intensity of the UO stretching and bending modes being of lower intensity than expected and with bands that are significantly broader.

U-Pb laser ablation–multicollector–inductively coupled plasma–mass spectrometry (LA-MC-ICP-MS) ages have been determined from large zircon crystals separated from pegmatites of the Adirondack Mountains, New York. Emplacement and metamorphic ages ranging from 949 ± 10 to 1222 ± 12 Ma help constrain the timing of igneous, metamorphic, and deformational history of the region, and are associated with Shawinigan, Ottawan, and Rigolet orogenesis. Geologically reasonable ages were obtained from most zircon separates despite large size, a limited number of grains, high uranium and thorium contents, dark and opaque interiors, high density of fractures, and widespread areas of metamictization and Pb loss. However, few grains show zoning or differences in composition when viewed with the backscattered mode on the scanning electron microscope. Large, clear, internally featureless, U-poor grains yield the best constrained ages. U-Th-Pb monazite ages, determined by electron probe, vary from 874 ± 27 Ma to 297 ± 62; the younger age may reflect the timing of hydrothermal fluid infiltration related to late Acadian events. This study suggests that, with appropriate care, zircons from pegmatites are a reasonable target for LA-MC-ICP-MS geochronology, widening the current arsenal of sampling targets.

The Eastern Segment abutting the Transscandinavian Igneous Belt (TIB) mostly consists of rocks with overlapping igneous ages. In the Eastern Segment west of Lake Vattern, granitoids of clear TIB affinity exhibit strong deformational fabrics. This article presents U–Pb zircon ages from 21 samples spanning the border zone between these deformed TIB rocks in the east, and more thoroughly reworked rocks in the west. Magmatic ages fall in the range 1710–1660 million years, irrespective of the degree of deformation, confirming the overlapping crystallization ages between deformed TIB rocks and orthogneisses of the Eastern Segment. A common history is further supported by leucocratic rocks of similar ages. Prolonged orogenic (magmatic) activity is suggested by continued growth of zircon at 1.66–1.60 Ga. Six of the weakly gneissic rocks show zircons with cathodoluminescence-dark patches and embayments, possibly partly replacing metamict parts of older magmatic crystals, with 207Pb/206Pb ages dominantly between 14...

Raman spectra of the uranyl titanate mineral holfertite Ca x U2−x Ti(O8−x OH4x )·3H2O were analyzed and related to the mineral structure. Observed bands are attributed to the TiO and (UO2)2+ stretching and bending vibrations, U–OH bending vibrations, and H2O stretching and bending. The mineral holfertite is metamict, as is evidenced by the order/disorder of the mineral. Unexpectedly, the Raman spectrum of holfertite does not show any metamictization. The intensities of the UO stretching and bending modes show normal intensity and the bands are sharp.

A fluctuation electron microscopy study of amorphous zircons is reported. A natural metamict zircon sample was compared with amorphous samples prepared by irradiating a gem-quality zircon crystal with a 1.0 MeV beam of N2+ ions over a range of fluences up to 1.5 × 1017 ions/cm2. The two types of amorphous material exhibit similar selected-area diffraction patterns. However, the statistics of the scattering from 1 nm wide volumes indicates that they have significantly different normalised intensity variance plots. Modelling of the variance suggests that the natural metamict zircon consists of paracrystalline grains of zircon embedded within an amorphous ZrSiO4 matrix. The ion-irradiated samples are better modelled as segregated paracrystalline grains of ZrO2 composition within an amorphous SiO2-rich matrix. Although both samples have been rendered disordered by radiation damage, there are two important differences. First, the ion-irradiated materials experience significantly higher fluence rates compared w...

The composition of hafnium isotopes in zircons iscurrently an important instrument for reconstructionof the source of magmatic rocks. Zircon is stable inmany hypogene and hypergene processes. Metamictization and later processes of alteration practically donot affect the composition of Hf isotopes in zircon[12]. The relative stability of Hf isotopes in zirconsmakes them a powerful instrument for the study of thesource age, as well as the origin and isotopic evolutionof various rocks [6, 11]. The combination of dating ofan individual zircon grain by the U–Pb method withthe study of Hf isotopes of the same grains (with application of local isotopic methods, such as SHRIMP,SIMS, and laser ablation) is the most effective. Such acombination provides important information on therock source even in the case when other isotopic systems are significantly disturbed.We obtained the first Lu–Hf isotopic data (in combination with the U–Pb isotopic data) by the methodof laser ablation for zircons from carbonatite and alkaline rocks of the Il’menoVishnevogorsky Complex inorder to study the age of rocks and the source of theirmaterial. Since the Sm–Nd and Rb–Sr isotopic systems were disturbed to various degrees during the Hercynian collision [5, 9], we considered application ofthe Lu–Hf isotopic system as the most stable andinformative to be especially important.The Il’menoVishnevogorsky Complex occurs atthe boundary between the Middle and Southern Uralsand is located within the Sysert–Ilmeny Precambrianblock, which has a twolevel structure and a long history of the formation. The core of the block is composed of granulitic gneiss and migmatite of the Selyankino Series (the U–Pb age of its zircons is 1820 ±70 Ma), as well as plagiogneiss and amphibolite of theVishnevye Gory Series (PR

Metamict zircon crystals have been thermally annealed between 500 and 1800 K and analyzed using infrared and optical spectroscopy in the spectral region of 1400–7000 cm-1. Recrystallization and dehydroxylation via complex proton/OH diffusion, redistribution, and incorporations of additional hydrogen-related species within the crystal structure of zircon occur at temperatures above 700 K in partially metamict zircon and above 1200 K in heavily amorphized material. Thermally induced changes in O-H stretching spectra are different between E || c and E ⊥ c in weakly metamict zircon. The O-H stretching band near 3342 cm-1 (with E ⊥ c) in an untreated sample shifts to 3277 cm-1 at 1200 K, where the frequency of O-H stretching bands with E || c increases. Conversions of hydrogen-related species were observed and extra OH bands were found at temperatures between 1200 and 1600 K. A dramatic change of OH spectra was recorded between 1600 and 1800 K in partially metamict crystals, resulting in additional absorption features (near 3098 and 2998 cm-1 along E ⊥ c). U4+ and U5+ related spectra are also affected by high-temperature annealing. For highly metamict zircon, the U4+ band near 4830 cm-1 shows an increase in intensity above 1200 K. Additional IRmore » bands at 2146 and 2344 cm-1 appear in the spectra of metamict zircon annealed at high temperatures. Their frequencies are consistent with stretching vibrations of CO and CO2.« less

The kinetics of He migration from zircon of variable degree of metamictization was investigated. The migration parameters of He were experimentally determined, the influence of radiation damage and the degree of metamictization on the stability of the (U-Th)/He isotope system was evaluated, the mechanisms of noble gas escape from zircon were investigated, new data on the kinetics of He migration were obtained and compared with previous results for the kinetics of Xe migration from zircon of the same geologic objects. It was shown that He occurs in two energy positions in the zircon lattice: the main position (more than 80% He) with an activation energy of ∼39 kcal/mol and k 0 = 1011 yr−1 and the second position with an activation energy for migration of 5–10 kcal/mol and k 0 ∼ 106 yr−1. It was concluded that He migration from the main energy position is better described by a single-jump mechanism. The migration of He from the second energy position is consistent with the diffusion mechanism. It was shown that deviations from the linear dependence in the lnln(He0/Het)-1/T coordinates are probably related to the destruction of volume defects containing He atoms at high temperatures (more than 1000°C on the experimental time scale) resulting in a change from the single-jump to diffusion mechanism and the presence of atoms migrating via the diffusion mechanism. It was shown that the peak width in the spectrum of radiogenic He release and the appearance of a second peak also depend on the fraction of atoms migrating in accordance with the diffusion mechanism. It was found that the low activation energy for He release from the second energy position indicates the existence of continuous He loss from the zircon lattice.

The role of fluids during Archaean intra-crustal magmatism has been investigated via integrated SHRIMP U–Pb, δ18O and LA-MC-ICPMS 176Hf isotopic zircon analysis. Six rock samples studied are all from the Nuuk region (southern West Greenland) including two ~3.69 Ga granitic and trondhjemitic gneisses, a 3.64 Ga granitic augen gneiss, a 2.82 Ga granodioritic Ikkattoq gneiss, a migmatite with late Neoarchaean neosome and a homogeneous granite of the 2.56 Ga Qôrqut Granite Complex (QGC). All zircon grains were thoroughly imaged to facilitate analysis of magmatic growth domains. Within the zircon analysed, there is no evidence for metamictization. Initial εHf zircon values (n = 63) are largely sub-chondritic, indicating the granitic host magmas were generated by the remelting of older, un-radiogenic crustal components. Zircon from some granite samples displays more than one 207Pb/206Pb age, and correlated with 176Hf/177Hf compositions can trace multiple phases of remelting or recrystallization during the Archaean. Model ages calculated using Lu/Hf arrays for each sample indicate that the crustal parental rocks to the granites, granodiorites and trondhjemites segregated from a chondrite-like reservoir at an earlier time during the Archaean, corresponding to known formation periods of more primitive tonalite–trondhjemite–granodiorite (TTG) gneisses. Zircon from the ~3.69 Ga granite, the migmatite and QGC granite contains Eoarchaean cores with chondritic 176Hf/177Hf and mantle-like δ18O compositions. The age and geochemical signatures from these inherited components are identical to those of surrounding tonalitic gneisses, further suggesting genesis of these granites by remelting of broadly tonalitic protoliths. Zircon oxygen isotopic compositions (n = 62) over nine age populations (six igneous and three inherited) have weighted mean or mean δ18O values ranging from 5.8 ± 0.6 to 3.7 ± 0.5‰. The 3.64 Ga granitic augen gneiss sample displays the highest δ18O with a mildly supra-mantle composition of 5.8 ± 0.6‰. Inherited Eoarchaean TTG-derived zircon shows mantle-like values. Igneous zircon from all other samples, spanning more than a billion years of Archaean time, record low δ18O sub-mantle compositions. These are the first low δ18O signatures reported from Archaean zircon and represent low δ18O magmas formed by the remelting and metamorphism of older crustal rocks following high-temperature hydrothermal alteration by meteoric water. Meteoric fluid ingress coupled with crustal extension, associated high heat flow and intra-crustal melting are a viable mechanism for the production of the low δ18O granites, granodiorites and trondhjemites reported here. Both high and low δ18O magmas may have been generated in extensional environments and are distinct in composition from Phanerozoic I-type granitic plutonic systems, which are typified by increasing δ18O during intra-crustal reworking. This suggests that Archaean magmatic processes studied here were subtly different from those operating on the modern Earth and involved extensional tectonic regimes and the predominance of remelting of hydrothermally altered crystalline basement.

Titanite, CaTiSiO5, occurs in nature in crystalline and metamict modification. Its structure consists of corner-linked TiO6 octahedra, SiO4 tetrahedra and sevenfold coordinated Ca. Metamictization occurs when a mineral contains impurities like U and Th and is exposed to radioactive irradiation. Recoil processes due to alpha radiation change over geological time scales the structure to a state with persisting short-range order but violated long-range order. Raman and infrared spectra and X-ray diffraction data of metamict as well as crystalline and titanite glass reveal local structural phenomena. Raman spectra of metamict titanite differ from spectra of well-crystalline titanite, indicating the breakdown of selection rules. Raman scattering reveals that anisotropy is preserved upon metamictization and that the structural state of highly metamict titanite should not be considered as quasi-amorphous. The metamict state partially recovers its disorder via heat treatment. Annealing-induced shrinking of unit c...

The results of comparative luminescence investigation of natural and synthetic BeO crystals are presented. Time-resolved luminescence (2.5–8 eV) and luminescence excitation spectra, and the kinetics of glow decay were measured using ultraviolet-vacuum-ultraviolet (VUV) synchrotron radiation (5–22 eV) or x-radiation (50–620 eV or 3–62 keV) ranges. X-ray and thermostimulated luminescence of natural BeO crystals were compared to the glow of additively colored synthetic crystals. The characteristic luminescence of F and F+ centers was found in natural crystals. In synthetic crystals similar luminescence is observed only after additive or radiation coloration by virtue of the creation of F− and F+ centers on anion vacancies. The defects found in the crystal lattice of a natural BeO crystal testify to the degree of mineral metamictization of the given deposit.

Elbrusite-(Zr) Ca 3 (U 6+ Zr)(Fe 3+ 2 Fe 2+ )O 12 , a new uranian garnet ( Ia 3 d , a ≈ 12.55 A, V ≈ 1977 A 3 , Z = 8), within the complex solid solution elbrusite-kimzeyite-toturite Ca 3 (U,Zr,Sn,Ti,Sb,Sc,Nb...) 2 (Fe,Al,Si,Ti) 3 O 12 was discovered in spurrite zones in skarn xenoliths of the Upper Chegem caldera. The empirical formula of holotype elbrusite-(Zr) with 25.14 wt% UO 3 is (Ca 3.040 Th 0.018 Y 0.001 ) ∑3.059 (U 6+ 0.658 Zr 1.040 Sn 0.230 Hf 0.009 Mg 0.004 ) ∑1.941 (Fe 3+ 1.575 Fe 2+ 0.559 Al 0.539 Ti 4+ 0.199 Si 0.099 Sn 0.025 V 5+ 0.004 ) ∑3 O 12 . Associated minerals are spurrite, rondorfite, wadalite, kimzeyite, perovskite, lakargiite, ellestadite-(OH), hillebrandite, afwillite, hydrocalumite, ettringite group minerals, and hydrogrossular. Elbrusite-(Zr) forms grains up to 10–15 μm in size with dominant {110} and minor {211} forms. It often occurs as zones and spots within Fe 3+ -dominant kimzeyite crystals up to 20–30 μm in size. The mineral is dark-brown to black with a brown streak. The density calculated on the basis of the empirical formula is 4.801 g/cm 3 The following broad bands are observed in the Raman spectra of elbrusite-(Zr): 730, 478, 273, 222, and 135 cm −1 . Elbrusite-(Zr) is radioactive and nearly completely metamict. The calculated cumulative dose (α-decay events/mg) of the studied garnets varies from 2.50 × 10 14 [is equivalent to 0.04 displacement per atom (dpa)] for uranian kimzeyite (3.36 wt% UO 3 ), up to 2.05 × 10 15 (0.40 dpa) for elbrusite-(Zr) with 27.09 wt% UO 3 .

Raman spectra of the uranyl titanate mineral betafite were obtained and related to the mineral structure. A comparison is made with the spectra of uranyl oxyhydroxide hydrates. Observed bands are attributed to the (UO2)2+ stretching and bending vibrations, U–OH bending vibrations and H2O and (OH)− stretching, bending and libration modes. U–O bond lengths in uranyls and O−H···O bond lengths are calculated from the wavenumbers assigned to the stretching vibrations. Raman bands of betafite are comparable with those of the uranyl oxyhydroxides. The mineral betafite is metamict as is evidenced by the intensity of the UO stretching and bending modes being of lower intensity than expected and by bands that are significantly broader.

Ti K edge X-ray absorption spectroscopy (XAS) was applied to determine the Ti co-ordination environment in the surface amorphised layer formed on zirconolite ceramics by 2 MeV Kr + irradiation, to a fluence of 5 × 10 15 ions cm −2 . The application of XAS in a grazing angle geometry was demonstrated to be essential in order to probe only the surface damaged layer ( + irradiation induced a change in the Ti co-ordination environment from majority six fold to majority five fold in the amorphised surface layer. This finding is consistent with the formation of five fold Ti in metamict natural zirconolite, as reported previously and confirmed in this study, despite the difference in dose rate of at least 10 12 between ion beam irradiated and naturally metamict materials. This study therefore opens the door to systematic investigation of composition – structure – property relations in materials designed for radioactive waste immobilisation, through the combined application of ion beam irradiation and grazing angle XAS.

Columbite crystals from niobium-yttrium-fluorine (NYF) pegmatites lacking zircon or containing metamict cyrtolite were analyzed for major and minor elements (Electron Microprobe (EMP)), trace elements (Laser Ablation-Inductively Coupled Plasma-Mass Spectrometry (LA-ICP-MS)), and U-Pb geochronology (Laser AblationMulti-Collector-Inductively Coupled Plasma-Mass Spectrometry (LA-MC-ICP-MS)). All four pegmatite localities sampled are hosted by the Proterozoic Fordham gneiss and/or Paleozoic Bedford gneiss (Columbite-(Fe); Kinkel and Baylis localities) and the Manhattan Schist of Lower Paleozoic age (Columbite-(Mn); Fort George and Harlem River Drive localities) and yield Neoacadian ages. The weighted average U-Pb ages are 372.2 ± 8.2 Ma (Baylis Quarry), 371.3 ± 7.3 and 383.4 ± 8.9 Ma (Kinkel Quarry); 383 ± 15 Ma (185th St. and Harlem River Drive); and 372 ± 10 Ma (Fort George). A partial metamict zircon (“cyrtolite”) from the Kinkel Quarry yielded a weighted average U-Pb age of 376.9 ± 4.3 Ma. The Neoacadian ages obtained agree with those determined by thermal ionization mass spectrometry (TIMS) for zircon from Lithium-Cesium-Tantalum (LCT) pegmatites from Connecticut and Maine. No pegmatites temporally associated with the Taconic orogeny were found. The size, lack of common Pb, uniform U concentrations across crystal cross-sections, sufficient but moderate uranium concentrations, lack of metamictization, and consistency in U-Pb isotopic ratios for columbite samples BCB-COL, NYSM #25232, and NYSM #525.8 suggests they show promise as potential standards for oxide mineral LA-MC-ICP-MS geochronological analyses, however, additional characterization using ID-TIMS would be necessary to develop as such.

Heftetjernite, ideally ScTaO 4 , is a new scandium mineral from the Heftetjern pegmatite, Tordal, Telemark, Norway. In the type specimen, it occurs as minute, elongate tabular, very dark brown crystals in a single small void in albite. Other associated minerals are fluorite, muscovite, altered milarite, a metamict, dark greyish brown mineral of the pyrochlore-microlite group, and an unidentified, orange-brown, tabular, nearly X-ray amorphous Ti-Y-Ta-Nb-mineral. Electron-microprobe analysis yielded the empirical formula (Sc 0.64 Sn 0.13 Mn 0.12 Fe 0.08 Ti 0.06 ) ∑1.03 (Ta 0.69 Nb 0.30 ) ∑0.99 O 4 which clearly demonstrates the charge-balanced substitution scheme 2Sc 3+ = (Sn,Ti) 4+ + (Mn,Fe) 2+ . The mineral crystallises in the wolframite structure type, with space group P 2/ c and a = 4.784(1), b = 5.693(1), c = 5.120(1) A, β = 91.15(3)°, V = 139.42(5) A 3 ( Z = 2). A synthetic equivalent is known. Strongest lines in the calculated X-ray powder diffraction pattern of heftetjernite are [ d in A( I ) ( hkl )]: 3.000 (100) (11–1), 2.9570 (97) (111), 3.662 (53) (110), 2.4877 (34) (02–1), 4.783 (33) (100), 3.807 (32) (01–1). The crystal structure was refined to R ( F ) = 1.39 % from single-crystal X-ray diffraction data (293 K). It is based on two types of edge-sharing, distorted octahedra occupied predominantly by Sc and Ta, respectively. Heftetjernite is translucent to transparent, with a dark brownish (with a reddish hue) streak and adamantine lustre. It is brittle, has a perfect {010} cleavage, irregular fracture and a Mohs hardness estimated to be around 4.5 by comparison to ferberite; D x = 6.44 g/cm 3 (from crystal-structure analysis). Optically, the mineral is biaxial with an unknown optical sign, weakly pleochroic (yellowish brown with a reddish tint to reddish brown), with no observable dispersion. A mean refractive index of 2.23 was calculated from the Gladstone-Dale relationship using the X-ray density. Heftetjernite is named after its type locality. The mineral is compared with synthetic ScTaO 4 , ScNbO 4 , iwashiroite-(Y) and formanite-(Y) (both nominally YTaO 4 ), and some comments are made on the relation to Sc-bearing ixiolite.

Pyrochlore is interpreted as a primary magmatic mineral that appeared in early carbonatite phases at Amba Dongar. Later intrusive phases incorporated this early pyrochlore and caused compositional modification, particularly around the rims, in response to changing magma chemistry. Consequently pyrochlore compositions show wide ranges in Nb, Ta, Ca, Ba, Ti and Ce. The final carbonatite phase was ankeritic and rich in hydrothermal fluids, giving rise to extreme compositional zoning and introduction of diverse elements (Si, U, Sr, Th, Fe), in the contained pyrochlore. Enrichment in radioelements such as U lead to metamictization, alteration and A-site vacancy.

Metamictization and color change in zircons from Cambodia and Tanzania were investigated. Elements analysis to detect radioactivity of elements such as U and Th, and spectroscopic analysis using UV-VIS and Fourier transform infrared spectroscopy were performed. According to the UV-VIS spectroscopic analysis, it was perceived that many and high intense absorption peaks appeared in blue and colorless zircons, while less and low intense absorption peaks appeared in uranium contained green and yellow zircons. It was found that those stones have made progress to the metamictization. After heat treatment, we could detect opposite results. As the results of FTIR spectroscopy analysis, in the metamict green and yellow zircon, it is showed that 3-phonon combination mode bands of internal vibration in the region of 3100~3400 are broad and some of them disappear. However, the disappeared bands are observed again due to restored crystal lattice by the heat treatment. Also, peaks that can detect the uranium content in zircon appears at near 4800 in the green and yellow samples. From this investigation, we could observe the metamictization effect and color change in uranium-bearing zircon by heat treatment using spectroscopic analysis.

Although chemical (non-isotopic) U–Th–Pb dating of monazite by electron microprobe is well-established, dating of zircon by this method is still controversial. Relatively U-rich zircon (up to 2500 ppm of U) from the Třebic Pluton provides a test case for the technique. Zircon grains are commonly partially or completely metamict, and therefore susceptible to Pb loss and common Pb contamination. Using Ca and K contents as indicators of damaged or contaminated zircon, a CHIME (Chemical U–Th–total Pb method) age of 347.8 ± 18 Ma was obtained from data with 0.0062 wt.% of PbO. This age was confirmed by isotopic U–Pb SHRIMP dating (341.6 ± 2.8 Ma). These results are in agreement with previous estimates for the timing of durbachitic intrusions into the root of the Variscan orogen and from the Variscan basement incorporated into Western Alps, between 343 and 332 Ma.

The Zr(Hf)–Th(U)–REE minerals from a subvolcanic A-type granite from Hora Svate Kateřiny, in the Czech Republic, were studied in an effort to distinguish how both magmatic and hydrothermal processes affected the rock system. The primary accessory phases include fluorite, magnetite and zircon, with rare xenotime-(Y), monazite-(Ce), and thorite. Complex solid-solutions with nearly equal contents of (Th+U), (Zr+Hf) and REE components usually form irregular domains within zircon and thorite crystals and are supposedly also primary. The granite was affected by strong reactions with late- to postmagmatic fluids. Pyrite and arsenopyrite crystallized from the first phase of hydrothermal activity, with low fugacity of oxygen. Later, fluid with a higher fugacity of oxygen altered magnetite to hematite, sulfides to Fe hydroxides, and dissolved xenotime. At this stage, Th-and U-bearing zircon and thorite became partially metamict. Arsenic in the fluid phase was oxidized to As 5+ , and intensively metasomatized xenotime, Y-rich zircon and thorite, forming chernovite. Even later, fluid rich in CO 2 dissolved metamict thorite and partially dissolved monazite; after only a short distance of transport, Th-rich bastnasite deposited in contact with fluorite.

Zircon textures, chemistry and microstructures have been characterized in situ within Carboniferous sandstones from the Midland Valley of Scotland using back-scattered electron and cathodoluminescence images, electron backscatter diffraction techniques and chemical analyses. The study of polished thin sections reveals a variety of zircon types including unmodified detrital zircon, zircon outgrowths and different forms of modified zircon that formed in low-temperature conditions within the sedimentary rocks. These rocks have only experienced temperatures of

Electron microprobe analyses are presented of chevkinite-group minerals from Canada, USA, Guatemala, Norway, Scotland, Italy and India. The host rocks are metacarbonates, alkaline and subalkaline granitoids, quartz-bearing pegmatites, carbonatite and an inferred K-rich tuff. The analyses extend slightly the range of compositions in the chevkinite group, e.g. the most MgO-rich phases yet recorded, and we report two further examples where La is the dominant cation in theAsite. Patchily- zoned crystals from Virginia and Guatemala contain both perrierite and chevkinite compositions. The new and published analyses are used to review compositional variation in minerals of the perrierite subgroup, which can form in a wide range of host rock compositions and over a substantial pressure- temperature range. The dominant substitutions in the various cation sites and a generalized substitution scheme are described.

We report the results of 57Fe Mossbauer spectroscopy, gamma-ray spectrometry and X-ray diffraction of two fully metamict samarskites and two partially metamict gadolinites. The absorbed α-dose for these minerals are found to range from 3.6 × 1015 α-decay/mg for one of the gadolinite samples to 7.7 × 1017 α-decay/mg for one of the samarskite samples. The Mossbauer spectra of samarskites and gadolinites show increasing line widths of the Fe2 + doublets with absorbed α-dose. We also observe that the increase in average quadrupole splitting of the Fe2 + cmponents correlates better with absorbed α-dose from 232Th than with total α-dose.

The Portobello granite, which crops out along the littoral in southern Natal is an S-type, red-coloured, foliated, chlorite-biotite granite that preserves evidence of low-temperature alteration. It intruded the 1091 ± 7 Ma Munster Suite quartz monzonorites and has distinctive 1.0 to 1.5 m wide charnockitic margins adjacent to the contacts with the quartz monzonoritic country rock. SHRIMP geochronology on zircon grains from two samples, one taken from the charnockitic margins and the other from the main body of chlorite-biotite granite, produced two statistically distinct ages: 1057 ± 27 Ma for the chlorite-biotite granite and 1093 ± 7 Ma for the charnockitic margin. The age for the charnockitic margins is identical to that of the country rock and, given the previously proposed origin for the margins by way of partial assimilation of the country rock, it is interpreted that the zircons sampled from the charnockitic margins are xenocrystic. The low-precision age of 1057 ± 27 Ma for the chlorite-biotite granite was produced from milky, metamict zircon grains suggestive of low temperature alteration, which may have affected the accuracy of the age. Nevertheless, the age of 1057 ± 27 Ma for the chlorite-biotite granite is statistically similar to the intrusive ages of the Oribi Gorge Suite and to ages recorded by metamorphic overgrowths on zircon grains from the Munster Suite. The ages produced by this study fall within the range of ages thus far acquired for the Margate Terrane of the Natal Metamorphic Belt, and further corroborate the previously proposed continuation of the terrane into the Vardeklettane Terrane of Dronning Maud Land in Antarctica. A zircon core from the charnockitic margins recorded an age of 1800 ± 12 Ma, which is the oldest age thus far recorded in the Margate Terrane.

Outgrowths of zircon and xenotime are abundant on detrital zircon in a greenschist facies regional metamorphic slate from the Scottish Highlands. Back-scattered electron images reveal that ca. 3-μm wide zircon outgrowths are porous, inclusion-rich and contain fine-grained intergrowths with xenotime. Focused ion beam milling, transmission electron microscopy and low-voltage scanning transmission electron microscopy show that the outgrowth microstructure is complex, composed of mis-orientated nano-crystalline zircon and a poorly crystalline zircon–xenotime complex. Well-defined micron-sized xenotime is also present within the outgrowth. Micro-textures show that the outgrowth developed in a polyphase history during cooling and exhumation. Accommodation space for the outgrowth is probably generated by a combination of thermal decompaction and the migration of defects in adjacent quartz driven by the force of crystallisation. Zircon may be unique in its ability to record textural evidence of events during uplift and exhumation that are not recorded in major silicate phases.

The U–Pb ages, REE content, and oxygen isotopic composition of zircon rims developed within a major shear zone in the Kalak Nappe Complex (KNC), Arctic Norway have been determined along with the age of monazite crystals. Different generations of granitic veins have been distinguished based on both field criteria and monazite ages of 446 ± 3 and 424 ± 3 Ma. Within each of these veins, inherited zircon cores are mantled by homogeneous low CL-response zircon rims which yield a range of concordant U–Pb dates of ca. 470–360 Ma. Significant numbers of zircon rims coincide with the timing of monazite crystallization. The zircon rims have moderate light REE enrichment compared to cores, distinctive (Sm/La) n values of less than 12, and La between 0.3 and 10 ppm. This indicates free elemental exchange between newly formed zircon rims and the surrounding matrix. The rims have calculated accumulated alpha-radiation dosages corresponding with a crystalline structure and δ18O values of 1‰. This implies rim crystallization directly from a zirconium-saturated hydrothermal fluid which was modified by some silicate melt. Growth of the zircon rims was prolonged and locally variable due to preferential fluid flow. A third type of zircon can be recognized, forming both rims and cores, with high alpha-radiation doses, and significant enrichment in La, Pr, and Eu. These are interpreted as low-temperature hydrothermally altered metamict zircons. The high volatile input and partial melting in the shear zone favoured prolonged zircon rim growth due to its ability to easily nucleate on inherited seeds. On the other hand, monazite, susceptible to dissolution and re-growth, crystallized in brief episodes, as has been predicted from theoretical phase diagrams. From a regional perspective, these results elucidate cryptic Ar–Ar cooling ages, providing the first record of a Late Ordovician heating and cooling phase within the KNC prior to the climactic Scandian collision.

A granitic pegmatite associated with the Monte Bruffione granodiorite in the Tertiary Adamello Massif, Italy, consists primarily of albite, potassium feldspar, muscovite, quartz, and spessartine (graphic intergrowths with quartz). As accessory minerals, the pegmatite contains magnetite, pyrophanite, monazite-(Ce), uraninite, xenotime-(Y), zircon, and fergusonite-(Y). This yttrium niobate mineral contains inclusions of Th-rich uraninite, and is itself rich in UO 2 (average 7.1 ± 1.1 wt.%, n = 34) and ThO 2 (average 3.5 ± 1.0 wt.%). Many fergusonite crystals display growth zoning, characterized by a general increase towards the rim in the contents of Y and rare earth elements at the expense of U and Th. Irregular or patchy zoning as well as sector zoning are also observed in some of the crystals. Due to the alpha-decay of the U and Th fergusonite is metamict, as documented by transmission electron microscopy (TEM) and micro-Raman spectroscopy. Nevertheless, the mineral could be identified as fergusonite-(Y) on the basis of a canonical discriminant analysis of its chemical composition and on the basis of the close similarity of its Raman spectrum with that of a reference β -fergusonite. The crystalline-to-metamict transformation was associated with macroscopic swelling, as indicated by microfractures that are arranged radially around fergusonite inclusions in pyrophanite. The TEM data revealed that the amorphous fergusonite contains U-rich nanocrystals (5–15 nm across), which in most cases are distributed randomly and which probably nucleated after metamictization. The TEM investigations further revealed the ubiquitous presence of nano-sized (typically 5–25 nm across), nearly circular features, which exhibit a low diffraction contrast and which we interpret as nanopores. We propose that these nanopores represent former bubbles of radiogenic helium. The data presented here allowed us to determine that the critical amorphization dose of fergusonite is ≤ 0.97 × 10 16 alphas/mg, i.e., lower than that of other actinide-rich oxide minerals (e.g., pyrochlore). The presence of the U-rich nanocrystals indicates that fergusonite is able to retain actinides even when it is entirely metamict and even if it is surrounded by microfractures, which represent potential fluid pathways. This result suggests that fergusonite could be a phase suitable to be included in ceramics designed for the immobilization of high-level nuclear waste.

U-Pb systems were examined in samples (ranging from 4 to 10 cm3 in volume) of ore material taken from along a 3.5-m profile across a zone of U mineralization exposed in an underground mine at the Strel’tsovskoe U deposit in eastern Transbaikalia. The behaviors of two isotopic U-Pb systems (238U-206Pb and 235U-207Pb) are principally different in all samples from our profile. While the individual samples are characterized by a vast scatter of their T(206Pb/238U) age values (from 112 to 717 Ma), the corresponding T(207Pb/235U) values vary much less significantly (from 127 to 142 Ma) and are generally close to the true age of the U mineralization. The main reason for the distortion of the U-Pb system is the long-lasting (for tens of million years) migration of intermediate decay products in the 238U-206Pb(RD238U) in the samples. This process resulted in the loss of RD238U from domains with high U concentrations and the subsequent accommodation of RD238U at sites with low U concentrations. The long-term effect of these opposite processes resulted in a deficit or excess of 206Pb as the final product of 238U decay. The loss or migration of RD238U are explained by the occurrence of pitchblende in association with U oxides that have higher Si and OH concentrations than those in the pitchblende and a higher +6U/+4U ratio. The finely dispersed character of the mineralization and the loose or metamict texture of the material are the principal prerequisites for RD238U loss and an excess of 206Pb in adjacent domains with low U concentrations. Domains with low U contents in the zone with U mineralization serve as geochemical barriers (because of sulfides contained in them) at which long-lived RD238U(226Ra, 210Po, 210Bi, and 210Pb) were accommodated and subsequently caused an excess of 206Pb. The 235U-207Pb system remained closed because of the much briefer lifetime of the 235U decay products. This may account for the significant discrepancies between the T(206Pb/238U) and T(207Pb/235U) age values. RD238U was most probably lost via the migration of radioisotopes at the middle part and end of the 238U family (starting with 226Ra). The heavy Th, Pa, and U radioisotopes (234Th, 234Pa, 234U, and 230Th) that occur closer to the beginning of 238U decay, before 226Ra, only relatively insignificantly participated in the process. Our results show that the loss and migration of RD238U are, under certain conditions, the main (or even the only) process responsible for the distortion of the U-Pb system.

Zircon in greenschist-facies metasedimentary rocks from the Scottish Highlands displays a range of complex textures that reflect low-temperature alteration of original detrital grains. In situ back-scattered electron, cathodoluminescence, electron backscatter diffraction and chemical analyses show that altered zircon is porous, weakly luminescent, enriched in non-formula elements such as Al and Fe, and is associated with fractures within the host zircon. The low-temperature zircon appears to be nano-crystalline and to replace U-rich zircon via modification of whole grains or selective alteration of parts of grains, and is linked to the development of zircon outgrowths. The altered zircon is also associated with epitaxial xenotime outgrowths and inclusions. Low-temperature zircon is abundant in slates and other mica-rich samples and its formation is linked to a dissolution–reprecipitation mechanism. Zircon within quartz-rich host rocks typically shows evidence of deformation and the resulting fractures enhance its dissolution, creating rounded embayed morphologies. In contrast, zircon from phyllosilicate-rich rocks contains more new low-temperature growth. Zircon alters during both prograde and retrograde metamorphic events and its development is controlled by both the progressive accumulation of radiation damage in the host grain and the access of metamorphic fluids to the metamict zircon.

Since 1964, the Center for Geochronological Research - CPGeo, one of the interdepartmental centers of the Instituto de Geociências (IG) of São Paulo University, has developed studies related to several geological processes associated with different rock types. Thermal Ionization Mass Spectrometry Isotopic Dilution (ID-TIMS) has been the technique widely used in the CPGeo U-Pb Laboratory. It provides reliable and accurate results in age determination of superposed events. However, the open-system behavior such as Pb-loss, the inheritance problem and metamictization processes allow and impel us to a much richer understanding of the power and limitations of U-Pb geochronology and thermochronology. In this article, we present the current methodology used at the CPGeo-IGc-USP U-Pb laboratory, the improvements on ID-TIMS method, and report high-precision U-Pb data from zircon, monazite, epidote, titanite, baddeleyite and rutile from different rock types of several domains of the Brazilian south-southeast area, Argentina and Uruguay.O Centro de Pesquisas Geocronológicas (CPGeo), um dos centros interdepartamentais do Instituto de Geociências (IG) da Universidade de São Paulo (USP), desde 1964 desenvolve estudos relacionados a diversos processos geológicos que se associam a diferentes tipos de rochas. A técnica amplamente utilizada no Laboratório U-Pb é a diluição isotópica por espectrometria de massa termo ionizada (ID-TIMS). Esta sistemática proporciona resultados bastante confiáveis e precisos na determinação das idades de eventos geológicos superpostos. Entretanto, o comportamento de sistema aberto como perda de Pb, problemas de herança isotópica e processos de metamictização, nos permite o entendimento do poder e limitação da geocronologia e termocronologia U-Pb. Neste artigo apresentamos a metodologia atualmente utilizada no Laboratório U-Pb do CPGeo-IGc-USP, as melhorias atingidas na técnica ID-TIMS e alguns dados obtidos em zircão, epídoto, titanita, baddeleyita e rutilo de diferentes tipos de rochas de alguns domínios da região sul-sudeste brasileira e da Argentina e Uruguai.

Dark-brownish, euhedral crystals of an “allanite-like” mineral occur in a hematite-impregnated Mn-silicate rock at Kesebol, Vastra Gotaland, Sweden, associated with gasparite-(Ce), chernovite-(Y), rhodonite, andradite, manganoan calcite, and quartz. A structural study was carried out on single crystals—untreated, heated in air, and heated under inert atmosphere—combined with Mossbauer spectroscopy and TEM investigation. In all the untreated crystals the mean distance indicates that Me 2+ (Me = Mn, Fe) prevails at this site ( in the range 2.169–2.180 A), in contrast with chemical data obtained by EPMA that yield a simplified formula Ca(REE 2/3 3+ □ 1/3 )Me 3 3+ (SiO 4 )(Si 2 O 7 ) O(OH), when normalized to Si = 3.00 apfu. Moreover, when a crystal is heated in air, all geometrical and structural variations indicate the development of an oxidation-dehydrogenation reaction, thus confirming that M3 is occupied by divalent cations before heating. The corresponding dehydrogenation is confirmed by a dramatic lengthening of the donor-acceptor distance. A crystal was annealed under inert atmosphere to verify possible effects of radiation damage on the polyhedral volumes. After prolonged annealing at 700 °C, a slight decrease of the unit-cell parameters is observed, suggesting restoring of crystallinity from a “partially metamict” state. Nonetheless, even in the annealed crystal, the distance is still consistent with a dominance of divalent cations at the M3 site. For all the examined crystals, structural data point to an octahedral cation population as follows: M1 = (Me 3+ , Al); M2 = (Al, Me 3+ ); M3 = (Me 2+ , Me 3+ ). This assumption is also in agreement with the Mossbauer spectrum, which was fitted to two Lorentzian quadrupole doublets for Fe 3+ and one for Fe 2+ . Values of the isomer shifts (0.36 and 0.37 mm/s for Fe 3+ ; 1.11 mm/s for Fe 2+ ) and the quadrupole splitting (1.96 and 1.02 for Fe 3+ ; 1.90 for Fe 2+ ) show that Fe 2+ (~12% of the total iron) is located in M3, while Fe 3+ occupies M1 and, to lesser extent, M2. TEM-EDS investigations have revealed chemical heterogeneities related to different degree of radiation damage. In particular, areas showing poor crystallinity are relatively enriched in Si and O with respect to the highly crystalline areas, thus suggesting that EPMA chemical data are biased by the presence of metamict areas enriched in SiO 2 and likely in H 2 O. EPMA data were therefore corrected for the excess of silica. The cation population after correction is in keeping with the structural and spectroscopic data. Disregarding minor substitutions, the ideal chemical formula for the epidote-group mineral from Kesebol is CaREEFe 3+ AlMn 2+ (Si 2 O 7 )(SiO 4 )O(OH), which is related to ferriallanite-(Ce) by the substitutional vector M3 (Mn 2+ ) → M3 (Fe 2+ ).

The line profile form of Raman spectra can be analyzed using the very same approach and software used for diffractogram deconvolution via the Rietveld approach. In both cases the ‘true’ profile containing information about the sample must be separated from the instrument's profile function (and potentially from the emission profile) which can be achieved by deconvolution. In this first part of a two-part study we demonstrate how the instrument's function can be described via a Gaussian function profile (yielding the very same result as several convoluted hat functions) using several examples (diamond, calcite, silicon and silicon carbide) for which true Raman bandwidth values are presented (assuming the true band profile to be Lorentzian). Also, asymmetrical bands can be described and analyzed via the presented deconvolution approach. The second part of this study will discuss and apply this method for studying the radiation-induced damage in zircon grains (metamictization). Copyright © 2008 John Wiley & Sons, Ltd.

abst R a C t An eclogite facies meta-plagiogranite from the Lanzo massif (western Alps, Italy) contains crystals of zircon intimately associated with allanite. Zircon displays different microtextures ranging from pristine, euhedral, and magmatic to fractured, porous varieties with mosaic zoning, and pervasive recrystallization into euhedral microcrystals. Fractures and voids in the recrystallized zircon microcrystals are mainly filled by high-pressure Na-rich pyroxene. Electron backscattered diffraction analysis revealed a similar crystallographic orientation for primary magmatic zircon crystals and microcrystals, with less than 2° misorientation among neighboring microdomains. The textural change is coupled with chemical and isotopic modifications: recrystallized zircon domains contain significantly less Th and light- to mid-REE, but are richer in Sr than magmatic zircon crystals. Magmatic zircon preserves the protolith U-Pb age of 163.5 ± 1.7 Ma, whereas zircon microcrystals have a mean age of 55 ± 1 Ma. The coexisting allanite also contains inclusions of Na-rich pyroxene and has chemical features (elevated Sr and Ni contents and lack of Eu anomaly) indicating formation at high pressure. Despite being associated texturally with zircon, allanite yields a younger Th-Pb age of 46.5 ± 3.0 Ma, suggesting that the Lanzo unit remained at relatively high pressure conditions for ~8 m.y. Zircon recrystallization proceeded with volume reduction and loss of material to an alkaline metamorphic fluid that acted as the agent for a coupled dissolution-reprecipitation process. Recrystallization occurred with minimum transport, in a low-strain environment, and was not significantly enhanced by metamictization. The source of the fluid for zircon recrystallization is most probably related to prograde devolatilization reactions in the surrounding serpentinite.

We report the preliminary results of 57Fe Mossbauer spectroscopy, gamma-ray spectrometry and X-ray diffraction (XRD) analysis of five complex metamict minerals: brannerite, cerite, columbite, perrierite and samarskite The absorbed α-dose for these minerals vary widely, ranging from 1.3 × 1015 α-decay/mg (cerite) to as high as 2.0 × 1018 α-decay/mg (brannerite). The Mossbauer spectra show decreasing isomer shift values for Fe2 + components with absorbed α-dose. One unexpected result of these spectra is a nearly complete crystallinity of the columbite sample despite its high absorbed α-dose of 1.9 × 1016 α-decay/mg.

The structural variations of synthetic zircon (ZrSiO4) single crystals irradiated at room temperature by 280 keV Pb+ ions (with fluences up to 1 × 1015 ions/cm2) were investigated using infrared (IR) spectroscopy. Like metamict zircon whose crystal structure is damaged and amorphized by naturally occurring α-decay events, the Pb+-irradiated zircon crystals show a dramatic decrease in reflectivity. However, no significant decrease in wavenumbers of the stretching vibrations of SiO4 tetrahedra in zircon was detected. The Pb+-implanted zircon exhibits new IR bands, indicating irradiation-induced new vibrations or domains, clusters or phases in addition to SiO2 and ZrO2. IR features consistent with those of Pb silicates (with a divalent state, i.e., Pb2+) are also found in the irradiated sample. This finding implies that some of the radiogenic Pb in natural zircon might not actually reside in the zircon lattice or in ZrSiO4 phases, but form new local domains or clusters. Infrared bands of OH-stretching vibrations were also detected in the irradiated synthetic zircon, which was originally free from OH features prior to the irradiation. These results indicate that H can easily diffuse into the irradiated layer or into irradiated-induced phases to form OH or and hydrous species after the irradiated material is damaged. The type and content of hydrous species vary with irradiation fluences.

Nioboaeschynite-(Y), with ideal chemical formula [(Y, Ln), Ca, Th](Nb, Ta, Ti, Fe)2O6, is a new member of the aeschynite group. It was discovered at the Bear Lake Diggings, Lot 9, conc. X, Monmouth Township, Haliburton County, near Gooderham, Ontario, Canada. It occurs as subhedral crystals up to 1 cm in size, in association with apatite, amphibole, feldspar, biotite, calcite, quartz, monazite, pyrite, and uranian thorite. The mineral is translucent, deep brownish-red with grayish-brown streak, with a vitreous luster. It is brittle with a Mohs hardness of 5-6, and its measured micro-hardness VHN100 is 922. It shows no discernable cleavage and has conchoidal fracture. Reflectance values for the COM wavelengths [%, Roil, Rair]: 470 nm (3.4, 14.6), 546 nm (3.3, 14.1), 589 nm (3.2, 13.8), and 650 nm (3.2, 13.7). Microscopic color is dark brown. Pleochroism, bireflectance and anisotropy are absent. It is naturally metamict, and after heating at 1000°C it re-crystallizes orthorhombically, space group Pbnm, with a=5.279(3) Å , b=10.966 (5) Å , c=7.443(3) Å , V=430.9(3) Å 3, Z=4. The eight strongest X-ray powder diffraction lines for nioboaeschynite-(Y) [d in Å (I)(hkl)] are: 3.009(100)(130), 2.931(69)(112), 3.079(20)(022), 1.580(16)(134), 1.863(14)(004), 2.783(12)(131), 2.636(12)(200) and 2.006(11)(222). The electron microprobe analysis gave CaO 4.34, MnO 0.11, Fe2O3 2.16, Y2O3 5.34, La2O3 0.84, Ce2O3 4.50, Pr2O3 0.65, Nd2O3 4.47, Sm2O3 1.21, Eu2O3 0.10, Gd2O3 0.91, Dy2O3 0.60, Er2O3 0.42, Tm2O3 0.05, Yb2O3 0.57, ThO2 12.10, UO2 0.59, TiO2 18.41, Nb2O5 31.46, Ta2O5 3.97, H2O 2.61, total 95.41 wt %. Water content was determined by TGA. The empirical formula of nioboaeschynite-(Y), based on 6 oxygen atoms, (and without H2O) is [(Y0.19Ln0.34)Ca0.31Th0.18U0.009Mn0.006] 1.04(Nb0.94Ti0.92Ta0.07Fe3+0.11) 2.04O6. Dmeas. = 5.34 g/cm3, Dcalc. = 5.33 g/cm3. Crystal structure is not refined, but it is the same type as for the other minerals of this group. The new mineral is named after the dominant cations. Nioboaeschynite-(Y) was approved by the IMA Commission on New Minerals and Mineral Names (2003-038a).

The ion beam (IBL) and thermally stimulated luminescence (TL) of a zircon megacryst (ZrSiO 4 ) from Brazil are here studied. The sample has been characterized by X-ray fluorescence, back scattered electrons in scanning electron microscopy and alpha spectrometry. The radioactive content suggests that this zircon is not in secular equilibrium. Such disequilibrium can be attributed to an increase in 234 U content. The IBL spectra exhibit broad bands, common to other silicates at 240, 260, 290, 340, 400, 560 and 750 nm and sharp emission peaks due to REE such as Dy 3 + or Yb 3 + , at 480, 580 and 980 nm. The 240 and 260 nm waveband could be linked to non-bridging oxygen hole centers and the thermolabile 290 nm emission to the presence of OH - ions in the lattice. The universal 340 nm emission, also observed in stressed silicates, could be linked to Si–O bond breakings and the broad 400 nm emission with [ AlO 4 / M + ] 0 centers; the sharp 480 and 580 nm peaks with Dy 3 + point defects, assuming that the broad bands at 560 and 750 nm are attributed to Mn 2 + and Fe 3 + point defects finally the sharp waveband at 980 nm could be assigned to Yb 3 + centers. The thermal stability tests of the blue TL emission of zircon confirm a continuum in the trap structure probably associated with successive dehydroxylation process. Both IBL and TL modify the OH bonds giving rise to strong ultraviolet luminescence centers.

The structure and composition of metamict zircon from the Georgeville epizonal A-type granite in the Antigonish Highlands, Nova Scotia, were determined using EMPA, SXRF, LA–ICP–MS, Raman microspectroscopy and TEM data. Individual crystals of zircon are variably altered and consist of four domains distinguished on the basis of texture and composition. Domain A consists of zircon and zirconium oxide nanocrystals in an amorphous matrix and is trace-element-enriched. Replacement of domain A in proximity to microfractures produced a porous and relatively trace-element-poor zircon (domain B) with disseminated Th–U- and Y-enriched inclusions (domain C). Domain D consists of amorphous zirconium silicate that is depleted in trace elements but enriched in Hf. It is found in fractures, together with minor amounts of thorite and thorianite. It Domain D is anhydrous and free of inclusions and pore spaces and has a composition similar to highly crystalline zircon. Micro- and nanoscale element-distribution maps indicate that high-field-strength trace elements in metamict zircon were redistributed during alteration by diffusion and by dissolution-and-reprecipitation processes near microfractures and other fluid channelways. The anomalous chondrite-normalized rare-earth-element patterns and Nd isotopic signature of the granite is attributed largely to the preferential transport and deposition of rare-earth elements during subsolidus re-equilibration of metamict zircon. Hydrothermally deposited zirconium silicate (domain D) has a composition similar to that of highly crystalline Hf-rich zircon but is completely amorphous. This observation emphasizes the need to verify the structural integrity and aqueous durability of hydrothermally deposited zircon before it is used to reconstruct hydrothermal processes.

The Lovozero pluton (Kola Peninsula, Russia) is an unique object from the standpoint of the abundance, diversity, and originality of Th mineralization. In contrast to other igneous rocks and to such chemical elements as Ca, REE, U, and Na, Th in the hyperalkaline pegmatites and hydrothermalites of the Lovozero pluton commonly occurs as its own mineral phases. Umbozerite Na3Sr4Th(Mn,Zn,Fe,Mg)[Si8O24](OH) (7 samples), Ti-Th silicate Na0–7Sr0–1ThTi1–2Si8O22–23(OH) · nH2O (8 samples), Na-Th silicate (Na,K)4Th3[Si8(O,OH)24] · nH2O (6 samples), thorite (2 samples), steenstrupine-(Ce)-thorosteenstrupine series minerals (5 samples), and Th phosphate (Th,Na,K,Ca,Mg,U,Sr,Ba)[(P,Si, Al)1O4] · nH2O (1 sample) were investigated in this study. Ti-Th silicates and Th phosphate have been described for the first time. All of the above-mentioned minerals have been examined with electron microprobe, IR spectroscopy, powder diffraction, thermogravimetric and optical methods. High-Th minerals such as steenstrupine, umbozerite, Th phosphate, and Na-Th silicates crystallized mainly during the ussingite stage of the pegmatite-forming process. At the early hydrothermal high-alkaline stage, steenstrupine was replaced with REE and Th aggregates (belovite, vitusite, seidite, Na-Th silicates, Ti-Th silicates, etc.). Thorite, Ti-Th silicates, and minerals of the rhabdophane and monazite groups were formed at the late hydrothermal low-alkaline stage. Despite the metamict features of almost all samples, stoichiometric ratios of cations in umbozerites and Ti-Th silicates remain stable. Clear relationships have been revealed between umbozerites and Ti-Th silicates, on the one hand, and seidite-(Ce), a Ti-silicate that has a zeolite-like structure, on the other. This implies that, under certain conditions, these minerals may be regarded as potential suppliers of Th to the environment due to the leaching of Th from zeolite channels.

The presence of xenon isotopes from in-situ spontaneous fission of short-lived 244 Pu has been confirmed in a suite of 16 Hadean detrital zircons from Western Australia. In order to investigate the effects of xenon loss on estimates of the inferred Pu/U ratio we have irradiated the zircons with thermal neutrons to generate Xe from 235 U neutron fission. 131 Xe/ 134 Xe and 132 Xe/ 134 Xe ratios have been used to calculate the relative contributions from spontaneous fission of 244 Pu and 238 U and neutron fission of 235 U and hence compare nominal Pu/U ratios and xenon retention ages. U–Xe ages are typically lower than the Pb–Pb ages, indicating that xenon loss is common. We show how the ternary mixing diagram can be used to place constraints on the timing and extent of this loss and to generate a corresponding Pu–U–Xe isochron. Although the zircons investigated in this study were extracted from the same metasedimentary unit, the timing of xenon loss is variable. This suggests that the loss may be the result of variable degrees of metamictization from grain to grain. Inferred (Pu/U)o ratios show a general decrease with the discordancy between Pb–Pb and U– Xe ages. For the least discordant samples we infer (Pu/U)o ∼0.008 which is close to the widely adopted chondritic value. While we cannot completely exclude the effects of Pu/U fractionation in magmatic and other processes between formation of the Earth and crystallisation of the zircons we conclude that they have been relatively small (bfactor 2?) and reflect the compatible behaviour of Pu and U in the 4+ valence state. © 2007 Elsevier B.V. All rights reserved.

We have investigated the zircon from granites of the Spanish Central System (SCS) batholith. This batholith is composed of plutons of both I- and S-type granite, with different degrees of fractionation. The association provides a natural laboratory for the study of compositional evolution of zircon. We recognize two types of magmatic zircon. Type-1 zircon consists of euhedral and elongate crystals showing an oscillatory zoning, usually hosted in the early major minerals, being more abundant in granodiorite and monzogranite plutons. Type-2 zircon is characterized by smaller and more equant crystals, unzoned, or irregularly zoned, and usually interstitial to the rock-forming minerals, and forming clusters with other accessory minerals. This second type is more abundant in leucogranites, aplites and pegmatites. Type-2 zircon shows the highest concentrations of Hf (16.58 wt.% HfO 2 ), U (4.83% UO 2 ), Th (4.87% ThO 2 ), Y (8.51% Y 2 O 3 ), and HREE (3.78% HREE 2 O 3 ), and the lowest analytical totals (down to 91.2%). The replacement of Zr by tetravalent cations (Th, U and Hf) is favored in the most evolved granites. Micro-areas of zircon with low analytical totals (91–98 wt.%) have a high level of cation substitution. Moreover, their high Th–U contents induce elevated levels of radiation damage. Disturbances in the original structure, combined with severe metamictization of U–Th-rich micro-areas, may have caused an enhanced susceptibility to secondary alteration. This process, in turn, is believed to have formed the observed strongly damaged and cation-deficient zircon. The range of Zr/Hf values in zircon crystals of the granites studied and those of related metamorphic rocks (as possible crustal sources) are similar. The composition of zircon from SCS granulite xenoliths overlaps with the compositional field of zircon from granite, supporting previous models of crustal recycling for the origin of the SCS batholith.

Interaction of metamict zircon with solutions of various composition (H2O, 1 m NaCl + 0.5 m HCl, 1 m NaCl, 1 m NaHCO3, 0.1 m Na2CO3, 1 m Na2CO3, 2 m Na2CO3, and 1 m NaOH) was examined at temperatures of 25–800°C, pressures of 1 and 5 kbar, and exposure times of 3, 7, and 14 days. The choice of fluid compositions was determined by the fact that aqueous, chloride, and carbonate solutions are the principal components of postmagmatic, metamorphic, and metasomatic fluids that can affect zircon in nature. Occurring in contact with these solutions, metamict zircon congruently and incongruently dissolves competing with the sorption of elements, crystallization of newly formed phases, and the restoration of the crystal structure. The intensities of these processes are controlled by the temperature, pressure, exposure time, and the pH and composition of the solution.

The ideal formula for chevkinite can be expressed as A 4 BC 2 D 2 Si 4 O 22 . It is important to determine the valence state and site occupation proportions for Fe among the B, C, and D octahedral sites as it may help to identify different species in the chevkinite group. Non-metamict chevkinite-(Ce) from Mianxi alkali feldspar-granite, Sichuan Province, China, was investigated using Mossbauer spectroscopy. The Fe 3+ /ΣFe ratio was 39.2%. A significant increase of Fe 3+ occured during metamictization and annealing for chevkinite-group minerals. In metamict samples Fe tended to lower coordination. According to the correlation between bond length and isomer shift ( IS ), the quadrupole doublets with IS = 1.10 and 0.94 mm·s −1 can be assigned to Fe 2+ in the B and C octahedral sites, respectively. Based on the correlation between octahedral distortion and quadrupole splitting ( QS ), the quadrupole doublets with QS = 0.86 and 0.77 mm·s −1 can be assigned to Fe 3+ in the C and D sites, respectively. The simplified formula can be revised as: Ce 4 Fe 2+ (Ti, Fe 2+ , Fe 3+ ) 2 (Ti, Fe 3+ ) 2 Si 4 (O, OH) 22 . It indicated that the non-metamict chevkinite-(Ce) belonged to Fe 2+ end member of the chevkinite group because Fe 2+ was the predominant component in the B site.

After a decade of studies and development, it is now accepted that reliable U–Th–total Pb isochron ages can be calculated for monazite using an electron microprobe at μm scale, either directly on thin sections or on separated grains mounted in polished section. The potential for determining U–Th–Pb chemical ages from other U- and Th-enriched phases has been investigated compared to chemical monazite-dating results for which individual spot-age precisions of 20 to 100 Ma can be achieved from individual spot analyses. Using isochron plots for monazite, the age homogeneity of a given population of data can be assessed and, depending upon the number of analyses ( n ∼ 50), a precision of 5 to 10 Ma can be obtained. The U content in xenotime widely varies from less than 0.1 wt.% up to 3 wt.%, but Th rarely exceeds 1 wt.%. As a consequence, the amount of radiogenic Pb produced during a given period remains significantly lower for xenotime than for monazite, leading to a lower precision (± 20 Ma) on the mean ages. Xenotime, however, appears to remain as a closed system, but common Pb must be carefully checked. Furthermore, the electron-microprobe technique (EPMA) allows controlling any age discrepancy on xenotime grains as small as 10–20 μm that cannot be dated by other isotopic methods. Such xenotime ages can be useful when studying the monazite–xenotime equilibrium. The electron microprobe is not the most reliable method for dating zircon since U and Th concentrations are generally low and common Pb is not negligible. Nevertheless, the spatial resolution of EPMA coupled with isotope methods allows conclusive in situ studies about radiogenic Pb mobility and metamictization. Thorite does not seem suitable for dating with either isotope methods or EPMA because of continuous radiogenic Pb loss. Conversely, the oxide phases, thorianite and baddeleyite are robust minerals with closed systems. They are rather rare and seem to incorporate negligible common Pb, making EPMA a method of choice for dating them. For thorianite, the precision on the mean age can be similar as that obtained for monazite, or even better, while the precision for baddeleyite cannot be significantly better than 20 to 50 Ma due to the limited amount of U (∼ 0.1%) and the lack of Th.

The activity ratios of 224Ra/228Ra and 228Th/232Th in leachate from euxenite increased with increasing pH, while the activity ratio of 230Th/232Th decreased. The leaching behavior of 224Ra which is formed through four decay processes of232Th, was different from that of 228Ra which is formed by a single decay of 232Th. Thorium-228, decay products of232Th, was also leached more effectively than 232Th. However, 230Th which is formed through four decay processes of 238U showed different leaching behavior from 224Ra and 228Th. Variation in the activity ratio of 228Ra/226Ra in leachate from euxenite sample in metamict state with pH of the solution in contact showed no apparent tendency and was observed to be almost as same as that in the euxenite sample partly because of so small activity ratio in the sample. The leaching efficiency of Ra isotopes and 228Th was estimated to be mainly dependent on the difference in the history of decay processes which have formed the nuclides. This estimation was consistent with the observation with the monazite sample reported previously.