Nb Mineralization Research Articles

Metallogenic Epoch and Tectonic Setting of Saima Niobium Deposit in Fengcheng, Liaoning Province, NE China

The Saima deposit is a newly discovered niobium deposit which is located in the eastern of Liaoning Province, NE China. Its mineralization age and geochemical characteristics are firstly reported in this study. The Nb orebodies are hosted by the grey–brown to grass-green aegirine nepheline syenite. Detailed petrographical studies show that the syenite consists of orthoclase (~50%), nepheline (~30%), biotite (~15%) and minor arfvedsonite (~3%) and aegirine (~2%), with weak hydrothermal alteration dominated by silicification. In situ LA-ICP-MS zircon U-Pb dating indicates that the aegirine nepheline syenite was emplaced in the Late Triassic (229.5 ± 2.2 Ma), which is spatially, temporally and genetically related to Nb mineralization. These aegirine nepheline syenites have SiO2 contents in the range of 55.86–63.80 wt. %, low TiO2 contents of 0.36–0.64 wt. %, P2O5 contents of 0.04–0.11 wt. % and Al2O3 contents of more than 15 wt. %. They are characterized by relatively high (K2O + Na2O) values of 9.72–15.51 wt. %, K2O/Na2O ratios of 2.42–3.64 wt. % and Rittmann indexes (σ = [ω(K2O + Na2O)]2/[ω(SiO2 − 43)]) of 6.84–17.10, belonging to the high-K peralkaline, metaluminous type. These syenites are enriched in large ion lithophile elements (LILEs, e.g., Cs, Rb and Ba) and light rare earth elements (LREEs) and relatively depleted in high field strength elements (HFSEs, e.g., Nb, Zr and Ti) and heavy rare earth elements (HREEs), with transitional elements showing an obvious W-shaped distribution pattern. Based on these geochronological and geochemical features, we propose that the ore-forming intrusion associated with the Nb mineralization was formed under post-collision continental-rift setting, which is consistent with the tectonic regime of post-collision between the North China Craton and Paleo-Asian oceanic plate during the age in Ma for Indosinian (257–205 Ma). Intensive magmatic and metallogenic events resulted from partial melting of lithospheric mantle occurred during the post-collisional rifting, resulting in the development of large-scale Cu–Mo mineralization and rare earth deposits in the eastern part of Liaoning Province.

Boron, carbon, oxygen and radiogenic isotope investigation of carbonatite from the Miaoya complex, central China: Evidences for late-stage REE hydrothermal event and mantle source heterogeneity

The Miaoya carbonatite complex (MCC) is located within the southern edge of the Qinling orogenic belt in central China, and is associated with significant rare earth element (REE) and Nb mineralization. The MCC consists of syenite and carbonatite that were emplaced within Neo- to Mesoproterozoic-aged supracrustal units. The carbonatite intruded the associated syenite as stocks and dikes, and is mainly composed of medium- to fine-grained calcite and abundant REE-bearing minerals. Carbonatite melt generation and emplacement within the MCC occurred during the Silurian (at ~440 Ma), and was subsequently impacted by a late-stage hydrothermal event (~232 Ma) involving REE-rich fluids/melt.This study reports trace element and stable (B, C, and O) and radiogenic (Nd, Pb, and Sr) isotope data for the MCC carbonatite, and these have been subdivided into three groups that represent different REE contents, interpreted as varying degrees of hydrothermal interaction. Overall, the group of carbonatites with the lowest enrichment in LREEs (i.e., least affected by hydrothermal event) is characterized by δ11B values that vary between −7 (typical asthenospheric mantle) and + 4‰; δ11B values and B abundances (~0.2 to ~1 ppm) do not correlate with LREE contents. The Sm-Nd and Pb-Pb isotope systems have both been perturbed by the late-stage, REE-rich hydrothermal activity and corroborate open-system behavior. Contrarily, initial 87Sr/86Sr ratios (vary between ~0.70355 and 0.70385) do not correlate significantly with both LREEs and Sr abundances, nor with initial 143Nd/144Nd ratios. The late-stage hydrothermal event overprinted the Nd and Pb isotope compositions for most of the carbonatite samples examined here, whereas a majority of the samples preserve their variable B and Sr isotope values inherited from their mantle source. The B and Sr isotope data for carbonatites exhibiting the least LREE enrichment correlate positively and suggest carbonatite melt generation from a heterogenous upper mantle source that records the input of recycled crustal material. This finding is consistent with those previously reported for young (<300 Ma old) carbonatites worldwide.

LREE–Nb Mineralization in the South Western Part of Ambadongar Carbonatite Complex, Chhota Udepur District, Gujarat, India

The Ambadongar sub-volcanic carbonatite alkali complex is located about 140 km east of Vadodara, Chhota Udepur district, Gujarat, India and falls in Survey of India Toposheet No. 46 K/1. The complex intrudes Bagh sandstone (Cretaceous) and overlying Deccan basalts (Eocene) and is situated in the Narmada rift zone. The carbonatites came into prominence in the early 1960s with significant discoveries of fluorite and conspicuous radioactivity located near Chhota Udepur, at Ambadongar, the erstwhile Baroda district, Gujarat. Earlier workers have clarified many aspects of the carbonatite complex.

Metallogenic Correlations for the Fe‐Nb‐REE Mineralization in the West Mine of the Bayan Obo Deposit, Inner Mongolia, China

AbstractThe West Mine of the Bayan Obo deposit, located in the northern‐central part of Inner Mongolia, China, is enriched in Nb, rare earth elements and iron (Nb‐REE‐Fe) mineral resources. This paper presents a combined method to explore metallogenic correlation of the Nb‐REE‐Fe mineralization at the Bayan Obo West Mine. The method integrates factor analysis and Back Propagation (BP) neural network technology into processing and modeling of geological data. In this study, the Nb and REE contents of samples were transformed into discrete values to analyze the correlations among the metallogenic elements. The results show weak mineralization correlations between Nb and REEs. Nb and U are closely related in the geochemical patterns, while Fe is closely related to both Th and Mn. LREEs are an important factor for the mineralization of the Bayan Obo deposit, while Fe and Nb can be considered as the results of passive mineralization. On the basis of a metallogenic correlation analysis, the factors affecting the Fe‐REE‐Nb mineralization were extracted, and the Nb mineralization model was established by the BP neural network. Based on the BP neural network data computing, the variability of the Nb concentration displays a coupled multi‐factor nonlinear relationship, which can be used to reveal the inherent metallogenic elemental regularities and predict the degree of element mineralization enrichment in the mining area.

ГРАНИТОЇДИ, РІДКІСНОМЕТАЛІЧНІ ПЕГМАТИТИ ТА ТA-NB МІНЕРАЛІЗАЦІЯ ШПОЛЯНО-ТАШЛИЦЬКОГО РУДНОГО РАЙОНУ (ІНГУЛЬСЬКИЙ МЕГАБЛОК, УКРАЇНСЬКИЙ ЩИТ)

Composition of granites, genetically associated pegmatites and superimposed metasomatites distributed within Shpoliano-Tashlyk ore area (Ingul megablock) is considered. It is established, that on the basis of similarity in their petrographic and petrochemical features granitoids of the area can be related to single complex. Features of ore mineralization are defined by both composition of granitoids (Sgranites) after which rare-metal pegmatites are formed and intensity of superimposed metasomatic alterations. Main minerals-concentrators of Ta and Nb mineralization in granitic pegmatites and metasomatites are represented by minerals of three isomorphic series – columbite-tantalite (Fe,Mn)(Nb,Ta,Ti)2O6, ilmenorutile-struverite (Ti,Nb,Ta)O2 and pyrochlore-microlite (Ca,Na)2Ta2O6(O,B,OH,F). Depending on geological setting such ore minerals as tapiolite, ixiolite, cassiterite, uraninite, nigerite, gahnite are commonly found in association with these minerals. Chemical composion of tantalo-niobates sampled from ore-bearing pegmatites and metasomatites is investigated by microprobe analysis. Most minerals of columbite-tantalite series are characterized by distinct and rhythmic internal zonality and contrasting mosaic structure which are related to considerable heterogeneities of their chemical composition. Within one aggregate mineral phases with wide range of values – from 9,80 to 71,0 % for Ta2O5 and from 10,6 to 70,1 % for Nb2O5 – are established. Among minerals ferruginous varieties which composition relates to Fe-columbite-tantalites (Nb2O5/Ta2O5 = 1–1,2; FeO/MnO = 2,5–6) prevail. Columbite-tantalites are characterised by high contents of admixture elements present (%): TiO2 – to 5,88; WO3 – to 3,70; SnO2 – to 9,20; Sc2O3 – to 5,40. Scandium ores occur as scandium-rich minerals that are mostly confined to the minerals of columbite-tantalite series found in Polohivka ore field. On the Ukrainian Shield high contents of Sc2O3 in tantalo-niobates are established for the first time. Minerals of ilmenorutile-struverite series do not quantitatively yield to minerals of columbite-tantalite series. For minerals of this series Nb2O5/Ta2O5 ratio varies in the range of 0,6-1,4. Among characteristic admixture-elements are prevailed (%): SnO2 – to 3,1, V2O5 – to 5,05; FeO – to 11,51, Cr2O3 – to 1,20. Minerals of pyrochlore-microlite series are of subordinate importance. For the first time by results of U-Pb dating of columbite-tantalites from Mostove ore manifestation (Shpoliano-Tashlyk area) the age of Ta-Nb mineralization is established to be about 1965 ± 25 million years.

Columbitization of fluorcalciopyrochlore by hydrothermalism at the Saint-Honoré alkaline complex, Québec (Canada): New insights on halite in carbonatites

Niobium (Nb) in carbonatite is mainly hosted in fluorcalciopyrochlore and columbite-(Fe). Information related to Nb petrogenesis is useful for understanding the processes related to Nb mineralization and carbonatite evolution. The Saint-Honoré, Quebec, alkaline complex offers a rare opportunity for studying these processes as the complex is not affected by post-emplacement deformation, metamorphism nor weathering. Columbite-(Fe) is shown to be an alteration product of fluorcalciopyrochlore (columbitization). Columbitization is characterized by the leaching of Na and F from the A- and Y-sites of the pyrochlore crystal structure. As alteration increases, Fe and Mn are slowly introduced while Ca is simultaneously leached. Leached Ca and F then crystallize as inclusions of calcite and fluorite within the columbite-(Fe). A-site cations and vacancies in the crystal structure of fresh and altered pyrochlores demonstrate that pyrochlore alteration is hydrothermal in origin. Moreover, halite is a ubiquitous mineral in the Saint-Honoré alkaline complex. Petrographic evidence shows that halite forms in weakly altered pyrochlores, suggesting halite has a secondary origin. As alteration increases, halite is expelled by the hydrothermal fluid and is carried farther into the complex, filling factures throughout the carbonatite. The hydrothermal hypothesis is strengthened by significant enrichments in Cl and HREEs in columbite-(Fe). Chlorine is most likely introduced by a hydrothermal fluid that increases the solubility of REEs.

Nitrobenzene degradation in aqueous solution using ozone/cobalt supported activated carbon coupling process: A kinetic approach

Abstract In this study, a new supported catalyst (Co/OSAC) based on olive stones activated carbon (OSAC) was developed using the wetness impregnation method. A kinetic study was performed to investigate the effect of ozone/supported catalyst coupling process on nitrobenzene degradation in aqueous solution. Several analytical techniques, such as Nitrogen adsorption-desorption at 77 K, XRD, XPS and SEM-EDX analyses were used to characterize the new catalyst. The effect of adding t-BuOH as radical scavengers was also investigated. Characterization results showed that a highly distribution of cobalt nanoparticles on the surface of OSCA was obtained by using impregnation method. Results were modelled by a global first-order model (R2 > 0.99). Co/OSAC exhibited a high activity in oxidation of NB compared to ozone alone and OSAC. The total organic carbon (TOC) removal proved that Co/AC/O3 combined process increases significantly the mineralization of NB with about 65% in 20 min compared to 45% and 24% using O3/OSAC and ozonation alone respectively. The kinetic contribution of radical mechanisms was estimated by using tertbutanol as radical scavenger. It was demonstrated that NB degradation is mainly due to radical generation promoted on the surface of the catalyst.

Late Paleozoic and Early Mesozoic rare-metal granites in Central Mongolia and Baikal region: review of geochemistry, possible magma sources and related mineralization

The Central Asian Orogenic Belt (CAOB) was a scene of intense granitoid magmatism during the Phanerozoic with formation of vast batholiths: Angara-Vitim and Daurian-Khentei. In the Late Paleozoic and Early Mesozoic times, the peripheral zones of batholiths underwent granitic magmatism associated with rare-metal mineralization. Petrological and geochemical studies show that the rare-metal Li–F granites formed, with a gap about 100 My, large igneous provinces of the Mongol-Okhotsk Belt. Late Paleozoic rare-metal granites build a series of multiphase plutons in the Baikal region (e.g. Kharagul 318 ± 7 Ma, Bitu-Dzhida 311 ± 10 Ma and Urugudei 321 ± 5 Ma). The early medium-grained biotite granites and leucogranites were followed by topaz-bearing microclineand amazonite–albite granites and a series of dikes. The Early Mesozoic epoch was marked by the formation of the Daurian-Khentei Batholith (230–190 Ma) in the center of area and rifting zones with alkaline and rare-metal granite plutons on the peripheries. In contrast to the Late Paleozoic, small Early Mesozoic intrusions (e.g., Avdar Pluton ~10 km2, 212–209 Ma) of rare-metal Li–F granites within the Avdar-Khoshutul series of granitoids coexisted with sizable plutons (e.g., Janchivlan Pluton ~70 km2, 227–195.3 Ma). Rare-metal Li–F granites of the Janchivlan Pluton produced small domal intrusions composed of microcline–albite, amazonite–albite and albite–lepidolite granites. The Sn–Ta–Nb mineralization is associated with albite–lepidolite granites. The rare-metal granites of the Baikal region and Central Mongolia of contrasting ages show an identical geochemical signature of Li–F granites. It is expressed by increase in F, Li, Rb, Cs, Sn, Be, Ta and Pb and decrease in Sr, Ba, Zn, Zr, Th and U contents in course of multiphase intrusions formation. The geochemical data confirm the magmatic model for genesis of the studied rare-metal Li–F granites. However, this process of magma differentiation was terminated with formation of albitites, microclinites and muscovite greisens. The whole-rock geochemistry and isotopic composition of the granites points to the Precambrian crust of the Baikal region (T2DМ = 1.0–1.3 Ga) as the most likely source. We propose the formation of the initial granitic melts due to anatexis of the higher levels of the continental crust, with fluids released during granulite-facies metamorphism in the lower crust. The rare-metal Li–F granites of the studied provinces are intraplate formations geochemically different from the Early Paleozoic collisional granitoids. This could be caused by the influence of deep-seated source on the occurrence of rare-metal magmatism.

Polymetallic mineralised veins in ferroan/A-type Cretaceous leucogranite, Stewart Island, New Zealand

ABSTRACTThe 140 ± 1 Ma hypersolvus, ferroan, weakly peralkaline to weakly peraluminous North Red Head leucogranite in northwest Stewart Island is cut by quartz-pyrite-rich veins that contain a wide variety of Mo, Ag, Te, Bi, Au, Co, Cu, Pb, Zn, REE, Nb, Y, Th, U, Zr, Ti, Be and F-bearing minerals. Patchy hematite-pyrite alteration locally overprints leucogranite in the vicinity of the mineralised veins. Individual veins are up to 5 m thick and 200+ m long. U–Pb dating and trace-element geochemistry indicate a direct link between leucogranite crystallisation and exsolution of the vein-forming hydrothermal fluid. Mineralised veins developed along transpressional faults within the leucogranite soon after emplacement. Incipiently mineralised quartz ± pyrite veins at Waituna Bay and the northern end of West Ruggedy Beach several kilometres from North Red Head are probably part of the same hydrothermal system as the veins at North Red Head. Metal and alteration assemblages at North Red Head most closely resemble those in rare hydrothermal systems associated with oxidised fluorine-rich A-type granites.

Stable isotope composition of minerals in the Belaya Zima plutonic complex, Russia: Implications for the sources of the parental magma and metasomatizing fluids

The Belaya Zima alkaline–carbonatite complex in the East Sayan Mountains, Russia, is a multiphase concentric intrusion, which comprises diverse alkaline silicate rocks and carbonatites. Melteigites are the earliest products of crystallization and they are followed by ijolites–urtites, nepheline syenites, and finally, calcite, calcite–dolomite and ankerite carbonatites. In this paper, we present new geochronological data (Ar–Ar method), chemical and stable isotope (H, C and O) compositions of the main rock-forming minerals in carbonatites and the silicate rocks of the complex. The Ar–Ar dating of phlogopite from ankerite carbonatites is consistent with the age of syenite emplacement and implies that the silicate rocks and carbonatites are likely to be comagmatic. The evolutionary trends of pyroxene, fluorapatite, amphibole and phlogopite are consistent with fractional crystallization from a single parental magma. Primary Nb mineralization is represented by pyrochlore, whereas columbite-(Fe) is a replacement product of pyrochlore at the post magmatic, hydrothermal stage. At that stage, interaction of calcite carbonatites with hydrothermal fluids resulted in the formation of hydrothermal paragenesis comprising dolomite–ankerite, monazite-(Ce), ancylite-(Ce), minerals of burbankite group and Ca–REE fluorcarbonates. The hydrothermal processes were also responsible for cation leaching from pyrochlore, the replacements of phlogopite by tetraferriphlogopite and early Ca-rich pyroxene by aegirine. The stable isotope data suggest that the rocks crystallized from a 18O-depleted magma. Shifts toward higher δ18O values relative to the primary compositions are commonly observed in minerals from carbonatites, which is attributed to hydrothermal processes.

Degradation and mineralization of aqueous nitrobenzene using ETS-4 photocatalysis

The microporous Engelhard titanosilicate ETS-4 is synthesized with the photocatalytic active –Ti–O–Ti– quantum wires in its framework. The transition metal cations are ion exchanged from their metal salt solutions to give M-ETS-4 (M = Fe, Co, Ni, Cu and Ag). The synthesized materials are extensively characterized by XRD, FT-IR, TGA, SEM and UV–vis-DRS. The photocatalytic activity of these synthesized samples is investigated for the degradation and mineralization of aqueous solution of nitrobenzene as a model pollutant compound. Decrease in chemical oxygen demand (COD) and absorbance of photodegraded NB revealed mineralization of NB. The photocatalytic activity of ETS-4 is attributed to the active –Ti–O–Ti– wires in its framework. Transition metal ions present in ETS-4 enhance the photocatalytic activity by the separating photogenerated charge carriers in ETS-4. Ag ions are found to show pronounced improvement in the photocatalytic activity compared to other transition metal ions. COD study reveals ~59% mineralization in 240 min of irradiation with Ag-ETS-4.

Hf isotopes and trace elements as indicators of zircon genesis in the evolution of the alkaline-carbonatite magmatic system (Il’meno-Vishnevogorskii Complex, Urals, Russia)

384 The methods of local analysis in the study of the isotope composition and isomorphic admixture in zir� con stimulated treatment of this mineral as a widely applied instrument for rock dating, as well as for origin of substance sources and geochemical evolution of rocks. The geochemical data (the concentration and trace and rareearth elemen t patterns in zircon), as well as the study of the U-Th-Pb and Lu-Hf isotope systems, currently may be applied for these in addition to the morphology and cathode luminescent proper� ties of zircon. Using laser ablation (LA-ICP-MS), we studied the Hf isotope composition in combination with the U-Pb age and trace elements content in zircons of the Il'meno-Vishnevogorskii alkaline-carbonatite com� plex (Uralian foldbelt, Russia). The Il'meno-Vishnevogorskii Complex (IVC) composed of nepheline syenite (miaskite), fenite, miaskitic pegmatite, and carbonatite with REE-Zr- Nb mineralization is located in the South Urals, in the axial part of the Sysertsko-Il'menogorskii anticlino� rium and includes two large miaskite massifs (Vish�

New data of the Bayan Obo Fe–REE–Nb deposit, Inner Mongolia: Implications for ore genesis

The Bayan Obo deposit in the Inner Mongolia, North China Craton, is the largest rare-earth element (REE) resource in the world. The deposit is hosted in Mesoproterozoic sediments of the Bayan Obo Group, the lithological sequence of which has been divided into seventeen units (H1–H17). The REE mineralization is mainly concentrated in the H8 dolomite unit, and therefore the depositional age of this unit is important in addressing the debate over the genesis of the REE–Fe–Nb ore deposit. Here we present U–Pb and Hf model ages of zircons from the adjacent H9 slate. Our data suggest that the H9 slate formed at 1505±12Ma and the H8 dolomite was deposited during the Mesoproterozoic. We also present Ar–Ar ages of riebeckite in veins cutting the H8 dolomite and biotite in the ore bodies which show 389.5±3.0Ma and 289.1±1.8Ma, respectively. The U–Pb measurements from overgrowth zircon in H9 slate give an age of 518.8±7.5Ma. These new age data indicate that the Bayan Obo deposit was disturbed during thermal events at 520Ma to 390Ma, generating a second phase of REE–Nb mineralization. The δ7Li values of the REE mineralized dolomite are similar to those of carbonatite dykes. Combined with ɛNd features, we provide geochemical evidences that REE mineralized dolomite has undergone fluid interaction. Results reveal that the carbonatite magmatism occurred within the Bayan Obo rift at ca. 1.2 Ga, provided the primary source for REE–Nb mineralization or to fertilize the Bayan Obo crust, and the later was remobilized during the Caledonian to generate the second phase of mineralization within a convergent plate margin regime.

In situ analyses of micas in the Yashan granite, South China: Constraints on magmatic and hydrothermal evolutions of W and Ta–Nb bearing granites

Most rare-metal granites in South China host major W deposits with few or without Ta–Nb mineralization. However, the Yashan granitic pluton, located in the Yichun area of western Jiangxi province, South China, hosts a major Nb–Ta deposit with minor W mineralization. It is thus important for understanding the diversity of W and Nb–Ta mineralization associated with rare-metal granites. The Yashan pluton consists of multi-stage intrusive units, including the protolithionite (-muscovite) granite, Li-mica granite and topaz–lepidolite granite from the early to late stages. Bulk-rock REE contents and La/Yb ratios decrease from protolithionite granite to Li-mica granite to topaz–lepidolite granite, suggesting the dominant plagioclase fractionation. This variation, together with increasing Li, Rb, Cs and Ta but decreasing Nb/Ta and Zr/Hf ratios, is consistent with the magmatic evolution. In the Yashan pluton, micas are protolithionite, muscovite, Li-mica and lepidolite, and zircons show wide concentration ranges of ZrO2, HfO2, UO2, ThO2, Y2O3 and P2O5. Compositional variations of minerals, such as increasing F, Rb and Li in mica and increasing Hf, U and P in zircon are also in concert with the magmatic evolution from protolithionite granite to Li-mica granite to topaz–lepidolite granite. The most evolved topaz–lepidolite granite has the highest bulk-rock Li, Rb, Cs, F and P contents, consistent with the highest contents of these elements and the lowest Nb/Ta ratio in mica and the lowest Zr/Hf ratio in zircon. Ta–Nb enrichment was closely related to the enrichment of volatile elements (i.e. Li, F and P) in the melt during magmatic evolution, which raised the proportion of non-bridging oxygens (NBOs) in the melt. The rims of zoned micas in the Li-mica and topaz–lepidolite granites contain lower Rb, Cs, Nb and Ta and much lower F and W than the cores and/or mantles, indicating an exotic aqueous fluid during hydrothermal evolution. Some columbite-group minerals may have formed from exotic aqueous fluids which were originally depleted in F, Rb, Cs, Nb, Ta and W, but such fluids were not responsible for Ta–Nb enrichment in the Yashan granite. The interaction of hydrothermal fluids with previously existing micas may have played an important role in leaching, concentrating and transporting W, Fe and Ti. Ta–Nb enrichment was associated with highly evolved magmas, but W mineralization is closely related to hydrothermal fluid. Thus these magmatic and hydrothermal processes explain the diversity of W and Ta–Nb mineralizations in the rare-metal granites.

The key role of mica during igneous concentration of tantalum

Igneous rocks with high Ta concentrations share a number of similarities such as high Ta/Nb, low Ti, LREE and Zr concentrations and granitic compositions. These features can be traced through fractionated granitic series. Formation of Ta-rich melts begins with anatexis in the presence of residual biotite, followed by magmatic crystallization of biotite and muscovite. Crystallization of biotite and muscovite increases Ta/Nb and reduces the Ti content of the melt. Titanium-bearing oxides such as rutile and titanite are enriched in Ta and have the potential to deplete Ta at early stages of fractionation. However, mica crystallization suppresses their saturation and allows Ta to increase in the melt. Saturation with respect to Ta and Nb minerals occurs at the latest stages of magmatic crystallization, and columbite can originate from recrystallization of mica. We propose a model for prediction of intrusion fertility for Ta.

Carbonatite-hosted niobium deposit at Aley, northern British Columbia (Canada): Mineralogy, geochemistry and petrogenesis

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 1.5m 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−, (PO4)3−, U, Th and rare-earth elements, but not Nb.

Primary and secondary niobium mineral deposits associated with carbonatites

This work reviews the character and origin of primary and supergene economic deposits of niobium associated with carbonatites. The Brazilian supergene deposits account for about 92% of the total worldwide production of Nb, with the primary St. Honoré carbonatite and other sources accounting for only for 7 and 1%, respectively. The emphasis of the review is upon the styles of Nb mineralization and the geological factors which lead to economic concentrations of Nb-bearing minerals. Primary economic deposits of Nb are associated principally with carbonatites found in diverse types of plutonic alkaline rock complexes. Primary magmas are principally those of the melilitite, nephelinite and aillikite clans. Although many primary niobium deposits are associated with carbonatites, ijolites and syenites in the same alkaline complexes can also contain significant Nb mineralization in the form of niobian titanite and diverse Nb–Zr-silicates (marianoite-wöhlerite); these potential sources of Nb have not as yet been explored or exploited. Primary Nb deposits can be regarded as large tonnage, low grade (typically <1wt.% Nb2O5) disseminated ore deposits. Niobium is hosted principally by diverse Na–Ca–U-pyrochlores, ferrocolumbite and fersmite. Every actual, and potential, primary Nb deposit is unique with respect to the varieties of pyrochlore present; extent of replacement by other minerals; and degree of alteration by deuteric/hydrothermal fluids. Within a given occurrence individual petrographically-defined units of carbonatite contain distinct suites of pyrochlore. Bulk rock analysis for Nb gives no indication of the style of mineralization and provides no information of use regarding beneficiation of the ore. Evaluation of any Nb deposit requires extensive definition drilling and detailed mineralogical studies. Primary Nb deposits result from the early crystallization of Nb-bearing minerals in magma chambers followed by crystal fractionation, magma mixing, and redistribution of Nb-minerals by density currents. Supergene Nb deposits occur in laterites formed by extensive weathering of primary carbonatites. The process results in the decomposition of apatite and magnetite, removal of soluble carbonates and physical concentration of resistant primary pyrochlore. Intense lateritization results initially in the replacement of primary pyrochlores by supergene, commonly Ba, Sr, K or Pb-bearing pyrochlores, and ultimately complete decomposition of pyrochlore and formation of Nb-bearing rutile, brookite, and anatase. The Nb contents of the laterites can be enriched up to 10 times or more above those of the primary carbonatite. Commonly, pyrochlores in laterites are fine grained and intimately intergrown with hematite, goethite and minerals of the crandallite group. The different styles of mineralization of primary and secondary Nb deposits require different methods of ore beneficiation.

A review of the genesis of the world class Bayan Obo Fe–REE–Nb deposits, Inner Mongolia, China: Multistage processes and outstanding questions

The Bayan Obo Fe–REE–Nb deposit is the world's largest rare earth element (REE) resource and with the increasing focus on critical metal resources has become a focus of global interest. The deposit is hosted in the Palaeoproterozoic Bayan Obo Group, mainly concentrated in the H8 dolomite marble. The ores consist of light REE enriched monazite and bastnäsite, with a wide array of other REE minerals. Niobium mineralisation is hosted primarily in aeschynite and pyrochlore, although there are a wide range of other Nb-minerals. The origin of the host dolomite and ore bodies has been a subject of intense debate. The host dolomite has been proposed to be both of sedimentary origin and an igneous carbonatite. Carbonatite dykes do occur widely in the area, and consideration of the textural, geochemical and isotopic composition of the dolomite suggests an origin via intrusion of magmatic carbonatite into meta-sedimentary marble, accompanied by metasomatism. The origin of the ore bodies is complex, indicated most strongly by an ~1Ga range in radiometric age determinations. Compilation of available data suggests that the ores were originally formed around 1.3Ga (Sm–Nd isochron ages; Th–Pb ages of zircon), close in time to the intrusion of the carbonatite dykes. The ores were subsequently subjected to several stages of deformation and hydrothermal overprint, culminating in deformation, metamorphism and fluid flow related to the Caledonian subduction of the Mongolian Plate under the North China Craton from ~450 to 420Ma (Th–Pb ages of monazite). This stage resulted in the formation of the strong foliation (‘banding’) of the ore. The presence of undeformed veins with alkali mineral fills, and the overprinting of the foliation by Nb minerals suggest that secondary fluid flow events may also have contributed to the metal endowment of the deposits, as well as remobilising the original Fe and REE mineralisation. The alteration mineralogy and geochemistry of the ores are comparable to those of many REE mineralised carbonatites. Initial Nd isotope ratios at 450Ma, however, suggest crustal sources for the metals. These conflicting lines of evidence can be reconciled if a (at least) two stage isotopic evolution is accepted for the deposits, with an original mantle-sourced, carbonatite-related metal accumulation forming around 1.3Ga with εNd close to 0. The ore was remobilised, with associated re-equilibration of Th–Pb isotope systematics during deformation at ~450Ma. A further stage of alkaline hydrothermal fluid was responsible for Nb mineralisation at this stage. The complex geological history, with multiple stages of alkaline, high field strength element-rich, metasomatic fluid flow, is probably the main reason for the exceptional metal endowment of the Bayan Obo area.

Geochemistry of magmatic and hydrothermal zircon from the highly evolved Baerzhe alkaline granite: implications for Zr–REE–Nb mineralization

The Baerzhe alkaline granite pluton hosts one of the largest rare metal (Zr, rare earth elements, and Nb) deposits in Asia. It contains a geological resource of about 100 Mt at 1.84 % ZrO2, 0.30 % Ce2O3, and 0.26 % Nb2O5. Zirconium, rare earth elements (REE), and Nb are primarily hosted by zircon, yttroceberysite, fergusonite, ferrocolumbite, and pyrochlore. Three types of zircon can be identified in the deposit: magmatic, metamict, and hydrothermal. Primary magmatic zircon grains occur in the barren hypersolvus granite and are commonly prismatic, with oscillatory zones and abundant melt and mineral inclusions. The occurrence of aegirine and fluorite in the recrystallized melt inclusions hosted in the magmatic zircon indicates that the parental magma of the Baerzhe pluton is alkali- and F-rich. Metamict zircon grains occur in the mineralized subsolvus granite and are commonly prismatic and murky with cracks, pores, and mineral inclusions. They commonly show dissolution textures, indicating a magmatic origin with later metamictization due to deuteric hydrothermal alteration. Hydrothermal zircon grains occur in mineralized subsolvus granite and are dipyramidal with quartz inclusions, with murky CL images. They have 608 to 2,502 ppm light REE and 787 to 2,521 ppm Nb, much higher than magmatic zircon. The texture and composition of the three types of zircon indicate that they experienced remobilization and recrystallization during the transition from a magmatic to a hydrothermal system. Large amounts of Zr, REE, and Nb were enriched and precipitated during the transitional period to form the giant low-grade Baerzhe Zr–REE–Nb deposit.

Age and substance sources of the Ilmeno-Vishnevogorsky Alkaline Complex (South Urals): Rb-Sr, Sm-Nd, U-Pb, and Lu-Hf isotope data

) ofmiaskites, fenites, and carbonatites with REE–Zr–Nb mineralization located in the Uralian foldbelt.Although the IVC is well studied, a number of important genesis and geochronological problems are currently debatable. Thus, because of the wide dispersionof datings obtained by the different isotope–geochronological methods on various rocks and minerals, ofcritical concern are the problems of geochronology ofalkaline rocks and carbonatites of the IVC. The keyquestion of the IVC genesis is the role of mantle andcrustal sources for rock and ore formation. Theseproblems may be solved on the basis of the complexand systematic study of the Rb–Sr, Sm–Nd, U–Pb,and Lu–Hf isotope systems of rocks and minerals,which currently have become an important and indispensable instrument for reconstruction of the sourceof magmatic rocks and solution of the problems oftheir origin.We applied the isochron methods based on theSm–Nd and Rb–Sr isotope systems of bulk samplesand rockforming minerals of miaskites and carbonatites (TIMS method, Institute of Geology andGeochemistry, Yekaterinburg; Institute of Precambrian Geology and Geochronology, Saint Petersburg;Institute of Geology, Apatity), as well as the local U–Pb isotope dating of zircons from carbonatites andmiaskites from Vishnevogorsky and Buldym massifs(ion microprobe SHRIMPII, Russian GeologicalResearch Institute, Saint Petersburg; laser ablationLaICPMS, GEMOC, Sydney) for dating of themain rock types of the IVC. The U–Pb isotope systems of pyrochlores from the IVC (TIMS, AllRussianGeological Research Institute, SaintPetersburg) wereused for dating as well. The initial isotope characteristics of rocks and minerals of the IVC were obtained inorder to establish the sources of substances for magmatic rocks and ores and the role of mantle in theirformation.The Ilmeno–Vishnevogorsky Complex is locatedat the boundary between the South and Middle Uralsin the Sysertsko–Ilmenogorsky block of Precambrianrocks occurring in the Uralian paleooceanic complexes. The core of this block is composed of granuliticgneisses and migmatites of the Selyankinskaya Series,as well as plagiogneisses and amphibolites of the Vishnevogorskaya Series (