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Weathering crusts after granites are the most important source of heavy rare-earth elements (HREE) worldwide. Although HREE in these deposits is known to be inherited from parental rocks, the origin of HREE enrichment and the reasons why it is rare outside of China remains unclear. Here, we report the occurrence of variably organized nanoparticles of Ce-poor (<0.2 wt%), Nd-Y-rich bastnäsite-(La), and associated cerianite in parental granites from a HREE deposit, South China. The mineral contains high-HREE abundances (up to 13 wt% Y2O3). Synchrotron radiation-induced X‑ray diffraction and high-resolution transmission electron microscopy analyses suggest that the mineral grew as disordered nanocrystals and (nearly) coaligned nanoparticle aggregations, thus supporting "nonclassical" crystallization mechanisms by particle attachment under hydrothermal conditions. The nanocrystalline Ce-poor, Nd-Y-rich bastnäsite-(La) precipitated at rapidly decreasing temperature related to the influx of externally derived fluids, which caused CO2-H2O immiscibility and REE supersaturation. This interpretation is supported by petrographic data and microthermometric analysis of fluid inclusions in quartz. Unusually high fO2 resulted in Ce oxidation and decoupling from trivalent lanthanides, producing polycrystalline mineralization. [ABSTRACT FROM AUTHOR]

Titanite is a common accessory mineral in silicocarbonatite from the Afrikanda alkaline-ultramafic complex. Kola Peninsula, Russia. In addition to large crystals (described elsewhere), this rock contains microscopic crystals and aggregates of titanite intimately associated with, or mantling, primary Ti minerals (perovskite, ilmenite, magnetite, and garnets). The microcrysts commonly exhibit complex zoning patterns that represent a combination of oscillatory, core-rim, and/or sectorial zoning. Eight varieties of microcrystic titanite, differing in chemical composition, mode of occurrence, and style of zoning, can be distinguished. Most of the compositions have >20% of the Ti site occupied by Al, Fe, Nb, Zr, or a combination thereof, whereas substitutions at the Ca site are limited to [10.sup.-4]. Under these conditions, the earlier-formed Zr minerals zirconolite and zircon were unstable and underwent extensive re-equilibration with the fluid, involving partial removal of Zr. Implications of these data for the sale disposal of nuclear waste are discussed. The structure of zirconian titanite was examined using a synthetic sample of analogous composition (25 mol% CaZrSi[O.sub.5]). Its structure was refined by the Rietveld method from X-ray powder diffraction data in space group A2/a [a 7.1119(7). b. 8.7724(8), and c 6.6007(6) [Angstrom] [beta] 113.569(4)[degrees]]. Reflections violating A centering and/or indicative of Ti-Zr ordering were not observed, and attempts to refine the structure in two alternative space groups (P[2.sub.1]la and P[2.sub.1]) were unsuccessful.

Ivanyuk family gathering on 2016 New Year's Eve: Mikhail (front centre), Gregory, Ayya with grandson Ostap, Viya and Taras (from left to right), Polina with Aglaya (back). Two papers by Dey I et al. i (2021a, b) report the paragenesis and compositional variation of different pyrochlore populations in albitites, dolomite and silicate-rich carbonatites from the Sevattur carbonatite complex, India. Oscillatory- and sector-zoned pyrochlore from carbonatites of the Kerimasi volcano, Gregory rift, Tanzania. Mineralogy and petrology of alkaline rocks and carbonatites: Celebrating the life and work of Gregory Yu. [Extracted from the article]

Mantle-derived carbonatites emplaced in orogenic belts and some extensional settings are hypothesized to contain recycled crustal material. However, these carbonatites are typically composed of calcite showing a typical mantle range of C–O isotopic values devoid of recognizable sedimentary fingerprints. Here, we report the first known instance of C–Sr isotope decoupling between intimately associated dolomite carbonatites and magnetite–forsterite–calcite carbonatites from the northern Qinling orogen, central China. The calcite-dominant variety is developed at the contact between the dolomite carbonatite and metasomatized wall-rock gneiss. The two types of carbonatites have similar δ18OVSMOW (6·98‰ to 9·96‰), εNd(i) (-3·01 to -6·47) and Pb (206Pb/204Pb(i) = 17·369–17·584, 207Pb/204Pb(i) = 15·443–15·466) isotopic compositions, but significantly different C and Sr isotopic signatures (δ13CVPDB = -3·09 to -3·58‰ and -6·11 to -7·19‰; 87Sr/86Sr(i) = 0·70373 to 0·70565 vs 0·70565 to 0·70624 for the dolomite and calcite rocks, respectively). The relative enrichment of the early-crystallizing dolomite carbonatite in 13C and its depletion in 87Sr are primary isotopic characteristics inherited from its mantle source. The observed field relations, petrographic and geochemical characteristics of the Caotan dolomite and calcite carbonatites imply that the strong C–Sr isotopic decoupling between them could not result from mixing of different mantle reservoirs (e.g. HIMU and EM1), or from magma fractionation processes. We propose that the calcite carbonatites were a by-product of metasomatic reactions between primary dolomitic melts and felsic wall-rock. These reactions involved the loss of Mg and CO2 from the magma, leading to depletion of the evolved calcite-saturated liquid in 13C and its enrichment in radiogenic Sr. We conclude that calcite carbonatites in plate-collision zones may not represent primary melts even if their isotopic signature is recognizably 'mantle-like'. [ABSTRACT FROM AUTHOR]

The high-pressure perovskite [K.sub.2/3][Th.sub.1/3][TiO.sub.3] was synthesized at P = 6 GPa and T = 1200 [degrees] C. This compound does not form at ambient pressures, as both solid-state reaction and synthesis from the melt yield a mixture of thorianite ([ThO.sub.2]) and jeppeite ([K.sub2][Ti.sub.6][O.sub.13]). [K.sub.2/3][Th.sub.1/3][TiO.sub.3] is a partially ordered derivative of the ideal perovskite structure, which crystallizes with tetragonal symmetry, in space group P4/mmm, a = 3.9007(2), c = 7.8099(7) [Angstrom], V = 118.83(2) [[Angstrom].sup.3], Z = 2. The structure of this compound was refined by the Rietveld method from the X-ray diffraction powder data. The degree of disorder calculated from the refined cation occupancies of the 1a and 1b sites is 58%. The [K.sup.1+] cations preferentially enter the 1a site, whereas most [Th.sup.4+] is accommodated in the comparatively smaller 1b site (polyhedral volumes are 53 and 46 [[Angstrom].sup.3], respectively). In response to this two-dimensional (planar) ordering, the [Ti.sup.4+] cations are displaced by about 0.1 [Angstrom] toward the planes populated by the lower-charged cations. [K.sub.2/3][Th.sub.1/3][TiO.sub.3] and related structures may be a viable repository for Th in Ti-rich alkali metasomatites in the lithospheric upper mantle.

Zoned crystals of carbocernaite occur in hydrothermally reworked burbankite-fluorapatite-bearing calcite carbonatite at Bear Lodge, Wyoming. The mineral is paragenetically associated with pyrite, strontianite, barite, ancylite-(Ce), and late-stage calcite, and is interpreted to have precipitated from sulfate-bearing fluids derived from an external source and enriched in Na, Ca, Sr, Ba, and rare-earth elements (REE) through dissolution of the primary calcite and burbankite. The crystals of carbocernaite show a complex juxtaposition of core-rim, sectoral, and oscillatory zoning patterns arising from significant variations in the content of all major cations, which can be expressed by the empirical formula (Ca0.43-0.91Sr0.40-0.69REE0.18-0.59Na0.18-0.53Ba0-0.08)Σ1.96-2.00(CO3)2. Interelement correlations indicate that the examined crystals can be viewed as a solid solution between two hypothetical end-members, CaSr(CO3)2 and NaREE(CO3)2, with the most Na-REE-rich areas in pyramidal (morphologically speaking) growth sectors representing a probable new mineral species. Although the Bear Lodge carbocernaite is consistently enriched in light REE relative to heavy REE and Y (chondrite-normalized La/Er = 500-4200), the pyramidal sectors exhibit a greater degree of fractionation between these two groups of elements relative to their associated prismatic sectors. A sample approaching the solid-solution midline [(Ca0.57Na0.42)Σ0.99(Sr0.50REE0.47Ba0.01)Σ0.98(CO3)2] was studied by single-crystal X-ray diffraction and shown to have a monoclinic symmetry [space group P11 m, a = 6.434(4), b = 7.266(5), c = 5.220(3) Å, γ = 89.979(17)°, Z = 2] as opposed to the orthorhombic symmetry (space group Pb21 m) proposed in earlier studies. The symmetry reduction is due to partial cation order in sevenfold-coordinated sites occupied predominantly by Ca and Na, and in tenfold-coordinated sites hosting Sr, REE, and Ba. The ordering also causes splitting of carbonate vibrational modes at 690-740 and 1080-1100 cm−1 in Raman spectra. Using Raman micro-spectroscopy, carbocernaite can be readily distinguished from burbankite- and ancylite-group carbonates characterized by similar energy-dispersive spectra. [ABSTRACT FROM AUTHOR]

Apatite-group phosphates are nearly ubiquitous in carbonatites, but our understanding of these minerals is inadequate, particularly in the areas of element partitioning and petrogenetic interpretation of their compositional variation among spatially associated rocks and within individual crystals. In the present work, the mode of occurrence, and major- and trace-element chemistry of apatite (sensu lato) from calcite and dolomite carbonatites, their associated cumulate rocks (including phoscorites) and hydrothermal parageneses were studied using a set of 80 samples from 50 localities worldwide. The majority of this set represents material for which no analytical data are available in the literature. Electron-microprobe and laser-ablation mass-spectrometry data (~ 600 and 400 analyses, respectively), accompanied by back-scattered-electron and cathodoluminescence images and Raman spectra, were used to identify the key compositional characteristics and zoning patterns of carbonatitic apatite. These data are placed in the context of phosphorus geochemistry in carbonatitic systems and carbonatite evolution, and compared to the models proposed by previous workers. The documented variations in apatite morphology and zoning represent a detailed record of a wide range of evolutionary processes, both magmatic and fluid-driven. The majority of igneous apatite from the examined rocks is Cl-poor fluorapatite or F-rich hydroxylapatite (≥ 0.3 apfu F) with 0.2–2.7 wt.% SrO, 0–4.5 wt.% LREE 2 O 3 , 0–0.8 wt.% Na 2 O, and low levels of other cations accommodated in the Ca site (up to 1000 ppm Mn, 2300 ppm Fe, 200 ppm Ba, 150 ppm Pb, 700 ppm Th and 150 ppm U), none of which show meaningful correlation with the host-rock type. Silicate, (SO 4 ) 2 − and (VO 4 ) 3 − anions, substituting for (PO 4 ) 3 − , tend to occur in greater abundance in crystals from calcite carbonatites (up to 4.2 wt.% SiO 2 , 1.5 wt.% SO 3 and 660 ppm V). Although (CO 3 ) 2 − groups are very likely present in some samples, Raman micro-spectroscopy proved inconclusive for apatites with small P-site deficiencies and other substituent elements in this site. Indicator REE ratios sensitive to redox conditions (δCe, δEu) and hydrothermal overprint (δY) form a fairly tight cluster of values (0.8–1.3, 0.8–1.1 and 0.6–0.9, respectively) and may be used in combination with trace-element abundances for the development of geochemical exploration tools. Hydrothermal apatite forms in carbonatites as the product of replacement of primary apatite, or is deposited in fractures and interstices as euhedral crystals and aggregates associated with typical late-stage minerals (e.g., quartz and chlorite). Hydrothermal apatite is typically depleted in Sr, REE, Mn and Th, but enriched in F (up to 4.8 wt.%) relative to its igneous precursor, and also differs from the latter in at least some of key REE ratios [e.g., shows (La/Yb) cn ≤ 25, or a negative Ce anomaly]. The only significant exception is Sr(± REE,Na)-rich replacement zones and overgrowths on igneous apatite from some dolomite(-bearing) carbonatites. Their crystallization conditions and source fluid appear to be very different from the more common Sr-REE-depleted variety. Based on the new evidence presented in this work, trace-element partitioning between apatite and carbonatitic magmas, phosphate solubility in these magmas, and compositional variation of apatite-group minerals from spatially associated carbonatitic rocks are critically re-evaluated. [ABSTRACT FROM AUTHOR]

The Bear Lodge alkaline complex in northeastern Wyoming (USA) is host to potentially economic rare-earth mineralization in carbonatite and carbonatite-related veins and dikes that intrude heterolithic diatreme breccias in the Bull Hill area of the Bear Lodge Mountains. The deposit is zoned and consists of pervasively oxidized material at and near the surface, which passes through a thin transitional zone at a depth of ~ 120–183 m, and grades into unaltered carbonatites at depths greater than ~ 183–190 m. Carbonatites in the unoxidized zone consist of coarse and fine-grained calcite that is Sr-, Mn- and inclusion-rich and are characterized by the presence of primary burbankite, early-stage parisite and synchysite with minor bastnäsite that have high (La/Nd) cn and (La/Ce) cn values. The early minerals are replaced with polycrystalline pseudomorphs consisting of secondary rare-earth fluorocarbonates and ancylite with minor monazite. Different secondary parageneses can be distinguished on the basis of the relative abundances and composition of individual minerals. Variations in key element ratios, such as (La/Nd) cn , and chondrite-normalized profiles of the rare-earth minerals and calcite record multiple stages of hydrothermal deposition involving fluids of different chemistry. A single sample of primary calcite shows mantle-like δ 18 O V-SMOW and δ 13 C V-PDB values, whereas most other samples are somewhat depleted in 13 C (δ 13 C V-PDB ≈ − 8 to − 10‰) and show a small positive shift in δ 18 O V-SMOW due to degassing and wall-rock interaction. Isotopic re-equilibration is more pronounced in the transitional and oxidized zones; large shifts in δ 18 O V-SMOW (to ~ 18‰) reflect the input of meteoric water during pervasive hydrothermal reworking and supergene oxidation. The textural relations, mineral chemistry and C and O stable-isotopic variations record a polygenetic sequence of rare-earth mineralization in the deposit. With the exception of one Pb-poor sample showing an appreciable positive shift in 208 Pb/ 204 Pb value (~ 39.2), the Bear Lodge carbonatites are remarkably uniform in their Nd, Sr and Pb isotopic composition: 143 Nd/ 144 Nd t = 0.512591–0.512608; εNd t = 0.2–0.6; 87 Sr/ 86 Sr t = 0.704555–0.704639; εSr t = − 1.5–2.7; 206 Pb/ 204 Pb t = 18.071–18.320; 207 Pb/ 204 Pb t = 15.543–15.593; and 208 Pb/ 204 Pb t = 38.045–39.165. These isotopic characteristics indicate that the source of the carbonatitic magma was in the subcontinental lithospheric mantle, and modified by subduction-related metasomatism. Carbonatites are interpreted to be generated from small degrees of partial melt that may have been produced via interaction of upwelling asthenosphere giving a small depleted MORB component, with an EM1 component likely derived from subducted Farallon crust. [ABSTRACT FROM AUTHOR]

The relative criticality of mineral commodities is evaluated using a wide range of parameters and in different contexts (e.g., from the standpoint of their importance to national security, or to a specific industrial application), which explains the multiplicity of classification schemes and variations in terminology applied to these commodities in the literature, media and government reports. The core group of critical metals, listed alphabetically, includes: antimony, beryllium, chromium, cobalt, gallium, germanium, indium, lithium, niobium, platinoids, rare-earth elements (REE, including yttrium), tantalum and tungsten. The present retrospect briefly describes the emergence of critical metals as a distinct resource type and the evolution of society's perception of these commodities over the past 100 years. [ABSTRACT FROM AUTHOR]

The Aley Nb deposit in northern British Columbia, Canada, is hosted by metamorphosed calcite and dolomite carbonatites of anorogenic affinity emplaced in Lower Paleozoic sedimentary carbonate rocks in the Devonian. Primary Nb mineralization consists of pyrochlore (commonly comprising a U–Ta-rich and F-poor core) and ferrocolumbite developed as discrete crystals and replacement products after the pyrochlore. These phases and associated heavy minerals (apatite ± magnetite ± zircon ± baddeleyite) precipitated early in the magmatic history and probably formed laterally extensive cumulate layers up to at least 1.5 m in thickness. Fractionation of copious amounts of pyrochlore is reflected in the chemical composition of the carbonatites and their constituent minerals, which show large variations in Nb/Ta value, but a near-chondritic Zr/Hf ratio. Alkali-rich metasomatic rocks (in particular, fenites and glimmerites) associated with the carbonatites are barren; the bulk of Nb in these rocks is contained in rutile, phlogopite and, to a much lesser extent, amphibole. When the passive margin of North America became the zone of plate convergence in the Cretaceous, the host carbonatites were strongly deformed, which is manifested in structures and textures indicative of grain comminution, ductile flow, folding and, locally, brecciation. The structure and continuity of the cumulate units enriched in Nb minerals were profoundly affected by these processes. Interaction of the carbonatites with crustal fluids of complex chemistry resulted in extensive dolomitization, replacement of the pyrochlore and ferrocolumbite by fersmite, and development of hydrothermal parageneses consistent with the lower greenschist-facies conditions. At these late evolutionary stages, Nb was mobilized only to a very limited extent and sequestered in a variety of minerals (fersmite, euxenite, Mg-rich ferrocolumbite and Nb-bearing rutile) typically occurring as scarce minute crystals associated with hydrothermal dolomite, quartz and chlorite. Progressive enrichment of the deformed dolomite carbonatites in heavy C and O isotopes relative to primary calcite, coupled with changes in the trace-element composition of Nb phases, indicate that the fluids were equilibrated with the wall-rock sedimentary rocks hosting the Aley deposit and were capable of transporting F − , (PO 4 ) 3 − , U, Th and rare-earth elements, but not Nb. [ABSTRACT FROM AUTHOR]

Most studies of compositional heterogeneities in the mantle, related to recycling of crustal sediments or delaminated subcontinental lithosphere, come from oceanic setting basalts. In this work, we present direct geochronological and geochemical evidence for the incorporation of recycled crustal materials in collision-related carbonatites of the South Qinling orogenic belt (SQ), which merges with the Lesser Qinling orogen (LQ) to separate the South and North China Blocks. The SQ carbonatites occur mainly as stock associated with syenites. The data presented here show that zircon from the syenites yields an age of 766 ± 25 Ma, which differs significantly from the age of primary monazite from the carbonatites (233.6 ± 1.7 Ma). The syenites contain lower initial 87 Sr/ 86 Sr and higher ε Nd values. This indicates that the carbonatites do not have genetically related with the silicate rocks, and were directly derived from a primary carbonate magma generated in the mantle. The carbonatites show a Sr–Nd isotopic signature similar to that of the chondritic uniform reservoir (CHUR), and parallel Sm–Nd model ages ( T CHUR ) of 190–300 Ma. However, the rocks have extremely variable Pb isotopic values straddling between the HIMU and EM1 mantle end-members. Most carbon and oxygen isotopic compositions of the SQ carbonatites plot outside the field for primary igneous carbonates. Their δ 13 C shows higher value than a ‘normal’ mantle, which implies an incorporation of recycled inorganic carbon. The carbonatites were emplaced close to the Mianlue suture, and followed the closure of the Mianlue ocean and Triassic collision of the South and North China Blocks. However, direct melting of the subducted Mianlue oceanic crust characterized by high ε Nd and low (EM1-like) 206 Pb/ 204 Pb values cannot explain the CHUR-like Nd signature and the Pb isotopic trend toward HIMU in the SQ carbonatites. We conclude that their parental magma was derived from a source incorporating the Mianlue oceanic crust mixed with an asthenospheric (or deeper) material characterized by high Pb and low Nd isotopic values. This material represents a deep-seated Proterozoic carbonate component recycled via mantle convection or localized upwelling. Notably, this model cannot explain the isotopic compositions of the Late Triassic (209–221 Ma) carbonatites in the LQ, characterized by a mantle-derived δ 13 C, but EM1-like Sr–Nd–Pb isotopic compositions. This signature is best explained in terms of delamination of the lower continental crust thickened during the collision of the South and North China Blocks, and partial incorporation of the delaminated material into the LQ mantle source. Modeling of the measured Sr–Nd–Pb isotopic variations suggests that the source of the LQ carbonatites could be produced by mixing of 80–85% of mantle material and 15–20% of delaminated lower continental crust. The emplacement of the SQ and LQ carbonatites marked a gradual transition from a compressional tectonic regime, brought about by the collision of the South and North China Blocks to intra-orogenic extension in the waning stages of the Triassic orogeny. [ABSTRACT FROM AUTHOR]

Vladykinite, ideally Na3Sr4(Fe2+Fe3+)Si8O24, is a new complex sheet silicate occurring as abundant prismatic crystals in a dike of coarse-grained peralkaline feldspathoid syenite in the north-central part of the Murun complex in eastern Siberia, Russia (Lat. 58° 22' 48" N; Long. 119° 03' 44" E). The new mineral is an early magmatic phase associated with aegirine, potassium feldspar, eudialyte, lamprophyllite, and nepheline; strontianite (as pseudomorphs after vladykinite) and K-rich vishnevite are found in the same assemblage, but represent products of late hydrothermal reworking. Vladykinite is brittle, has a Mohs hardness of 5, and distinct cleavage on {100}. In thin section, it is colorless, biaxial negative [α = 1.624(2), β = 1.652(2), γ = 1.657(2), 2Vmeas = 44(1)°, 2Vcalc = 45(1)°] and shows an optic orientation consistent with its structural characteristics (X^a = 5.1° in β obtuse, Z^c = 4.7° in β acute, Y = b). The Raman spectrum of vladykinite consists of the following vibration modes (listed in order of decreasing intensity): 401, 203, 465, 991, 968, 915, 348, 167, 129, 264, 1039, and 681 cm-1; O-H signals were not detected. The Mössbauer spectrum indicates that both Fe2+ and Fe3+ are present in the mineral (Fe3+/Fe∑ = 0.47), and that both cations occur in a tetrahedral coordination. The mean chemical composition of vladykinite (acquired by wavelength-dispersive X-ray spectrometry and laser-ablation inductively-coupled-plasma mass-spectrometry), with FeΣ recast into Fe2+ and Fe3+ in accord with the Mössbauer data, gives the following empirical formula calculated to 24 O atoms: (Na2.45Ca0.56)Σ3.01(Sr3.81K0.04Ba0.02La0.02Ce0.01)Σ3.90(Fe0.752+Fe0.663+Mn0.26Zn0.16Al0.12Mg0.05Ti0.01)γ2.01(Si7.81Al0.19)Σ8.00O24. The mineral is monoclinic, space group P21/c, a = 5.21381(13), b = 7.9143(2), c = 26.0888(7) Å, β = 90.3556(7)°, V = 1076.50(5) ų, Z = 2. The ten strongest lines in the powder X-ray diffraction pattern are [dobs in Å (I) (hkl)]: 2.957 (100) (123, 123); 2.826 (100) (117, 117); 3.612 (58) (114, 114); 3.146 (37) (120); 2.470 (32) (210, 01.10); 4.290 (30) (111, 111); 3.339 (30) (106, 115, 106); 2.604 (28) (200); 2.437 (25) (034); 1.785 (25) (21.10, 234). The structure of vladykinite, refined by single-crystal techniques on the basis of 3032 reflections with F0 > 4σF0 to R1 = 1.6%, consists of tetrahedral sheets parallel to (100) and consisting of (Si8O24)16- units incorporating four-membered silicate rings and joined into five- and eight-membered rings by sharing vertices with larger tetrahedra hosting Fe2+, Fe3+, Mn, Zn, Al, Mg, and Ti. Larger cations (predominantly Na, Sr, and Ca) are accommodated in octahedral and square-antiprismatic interlayer sites sandwiched between the tetrahedral sheets. Structural relations between vladykinite and other sheet silicates incorporating four-, five-, and eight-membered rings are discussed. The name vladykinite is in honor of Nikolay V. Vladykin (Vinogradov Institute of Geochemistry, Russia), in recognition of his contribution to the study of alkaline rocks. Holotype and co-type specimens of the mineral were deposited in the Robert B. Ferguson Museum of Mineralogy in Winnipeg, Canada. [ABSTRACT FROM AUTHOR]

Zircon macrocrysts in (sub)volcanic silica-undersaturated rocks are an important source of information about mantle processes and their relative timing with respect to magmatism. The present work describes variations in trace element (Sc, Ti, Y, Nb, lanthanides, Hf, Ta, Pb, Th, and U) and isotopic (U-Pb) composition of zircon from the Drybones Bay kimberlite, Northwest Territories, Canada. These data were acquired at a spatial resolution of ≤100 µm and correlated to the internal characteristics of macrocrysts (imaged using cathodoluminescence, CL). Six types of zircon were distinguished on the basis of its luminescence characteristics, with the majority of grains exhibiting more than one type of CL response. The oscillatory-zoned core and growth sectors of Drybones Bay zircon show consistent variations in rare-earth elements (REE), Hf, Th, and U. Their chondrite-normalized REE patterns are typical of macrocrystic zircon and exhibit extreme enrichment in heavy lanthanides and a positive Ce anomaly. Their Ti content decreases slightly from the core into growth sectors, but the Ti-in-zircon thermometry gives overlapping average crystallization temperatures (820 ± 26 °C to 781 ± 19 °C, respectively). There is no trace element or CL evidence for Pb loss or other forms of chemical re-equilibration. All distinct zircon types are concordant and give a U-Pb age of 445.6 ± 0.8 Ma. We interpret the examined macrocrysts as products of interaction between a shallow (<100 km) mantle source and transient kimberlitic melt. [ABSTRACT FROM AUTHOR]

Abstract: Carbonatites are known to contain the highest concentrations of rare-earth elements (REE) among all igneous rocks. The REE distribution of carbonatites is commonly believed to be controlled by that of the rock-forming Ca minerals (i.e., calcite, dolomite, and ankerite) and apatite because of their high modal content and tolerance for the substitution of Ca by light REE (LREE). Contrary to this conjecture, calcite from the Miaoya carbonatite (China), analyzed in situ by laser-ablation inductively-coupled-plasma mass-spectrometry, is characterized by low REE contents (100–260ppm) and relatively flat chondrite-normalized REE distribution patterns [average (La/Yb)CN =1.6]. The carbonatite contains abundant REE-rich minerals, including monazite and fluorapatite, both precipitated earlier than the REE-poor calcite, and REE-fluorocarbonates that postdated the calcite. Hydrothermal REE-bearing fluorite and barite veins are not observed at Miaoya. The textural and analytical evidence indicates that the initially high concentrations of REE and P in the carbonatitic magma facilitated early precipitation of REE-rich phosphates. Subsequent crystallization of REE-poor calcite led to enrichment of the residual liquid in REE, particularly LREE. This implies that REE are generally incompatible with respect to calcite and the calcite/melt partition coefficients for heavy REE (HREE) are significantly greater than those for LREE. Precipitation of REE-fluorocarbonates late in the evolutionary history resulted in depletion of the residual liquid in LREE, as manifested by the development of HREE-enriched late-stage calcite [(La/Yb)CN ≈0.7] in syenites associated with the carbonatite. The observed variations of REE distribution between calcite and whole rocks are interpreted to arise from multistage fractional crystallization (phosphates⇒calcite⇒REE-fluorocarbonates) from an initially REE-rich carbonatitic liquid. [Copyright &y& Elsevier]

Abstract: The Qinling molybdenum belt is a prominent metallogenic structure in central China hosting several significant porphyry- and porphyry–skarn-type deposits. The Huanglongpu Mo deposit in the north-western part of the belt is unique in that it is associated with carbonatite dykes, rather than felsic magmatism. The carbonatites are composed largely of Sr–Mn-rich calcite and characterized by high concentrations of Sr and rare-earth elements (REE), and stable-isotope values indicative of a mantle source (δ 13CPDB =−6.7±0.2‰ and δ 18OSMOW =8.2±1.0‰). Molybdenite is associated with galena and REE minerals (parisite, bastnäsite and monazite). Both molybdenite and galena are characterized by high Re contents (up to 0.4 and 0.2wt.%, respectively) and Re/(Mo, Pb) ratios approaching the primitive-mantle values. In contrast to the rock-forming calcite, the REE minerals are enriched in light REE, whose relative proportion increases from parisite-(Ce) [average (La/Nd)n =2.1] to bastnäsite-(Ce) and monazite-(Ce) [average (La/Nd)n =3.1, 4.6, respectively]. The whole-rock compositions are characterized by some of the highest Mo and heavy REE abundances reported for carbonatites to date: up to 1010ppm Mo, 1130ppm Y+Gd…Lu and (La/Yb)n =1.2–2.7. The unusual trace-element geochemistry of the Huanglongpu rocks may ultimately reflect the composition of their mantle source, but their enrichment in Mo+Re was undoubtedly enhanced through preferential partitioning of these elements into a light REE–Pb–S-rich fluid derived from the carbonatitic magma modified by calcite fractionation. The present work shows that Mo can be retained, transported and deposited by carbonatitic fluids capable of generating economic Mo deposits. [Copyright &y& Elsevier]

The structure of the synthetic fluoroperovskite, Na2LiAlF6 (simmonsite), has been determined by powder X-ray diffraction using the Rietveld method of structure refinement. The compound adopts space group P21/n [#14; a=5.2842(1); b=5.3698(1); c=7.5063(2) A˚; β=89.98(1)°; Z=4), and is a member of the cryolite (Na2NaAlF6) structural group characterized by ordering of the B-site cations (Li, Al) and tilting of the BF6 octahedra according to the tilt scheme a−b−c+. Rotations of the B-site polyhedra are less (ΦLi=14.9°; ΦAl=17.0°) than those found in cryolite (ΦNa=18.6; ΦAl=23.5°) because of the larger difference in the ionic radii of the B-site cations in cryolite as compared to those in simmonsite. Na at the A-site is displaced from the special position resulting in 10- and 8-fold coordination in simmonsite and cryolite, respectively. By analogy with the synthetic compound, naturally occurring simmonsite is considered to adopt space group P21/n (#14) and not the P21(#4) or P21/m(#11) space groups. [Copyright &y& Elsevier]

The unique, giant, rare earth element (REE) deposit at Bayan Obo, northern China, is the world's largest REE deposit. It is geologically complex, and its genesis is still debated. Here, we report in situ Th-Pb dating and Nd isotope ratios for monazite and Sr isotope ratios for dolomite and apatite from fresh drill cores. The measured monazite ages (361-913 Ma) and previously reported whole-rock Sm-Nd data show a linear relationship with the initial Nd isotope ratio, suggesting a single-stage evolution from a Sm-Nd source that was formed before 913 Ma. All monazites show consistent εNd(1.3Ga) values (0.3 ± 0.6) close to those of the adjacent 1.3 Ga carbonatite and mafic dikes. The primary dolomite and apatite show lower 87Sr/86Sr ratios (0.7024-0.7030) than the recrystallized dolomite (0.7038-0.7097). The REE ores at Bayan Obo are interpreted to have originally formed as products of ca. 1.3 Ga carbonatitic magmatism and to have undergone subsequent thermal perturbations induced by Sr-rich, but REE-poor, metamorphic fluids derived from nearby sedimentary rocks. [ABSTRACT FROM AUTHOR]