High Rare Earth Research Articles

REE geochemical characteristics of titanium-rich bauxites: the Permian Kanigorgeh horizon, NW Iran

The Permian Kanigorgeh bauxite horizon is one of the typical titanium-rich bauxite deposits in the northeast of Bukan, West Azerbaijan Province, NW Iran. It is a part of the Irano-Himalayan karst bauxite belt and was developed as discontinuous stratified layers and lenses in Upper Permian carbonates. Mineralogically, diaspore and kaolinite are 2 major mineral phases accompanied by boehmite, smectite, illite, rutile, anatase, hematite, goethite, chlorite, quartz, and plagioclase as minor phases. Geochemical considerations for a selected profile indicate that the concentration values of rare earth elements (REEs) in the bauxite ores range from 8.9 to 200.4 ppm. Eu and Ce anomalies show varying values within the range 0.42-0.65 and 0.12-3.23, respectively. On the basis of Ce behavior, the studied profile can be divided into 2 parts by redox boundary. The most pronounced geochemical characteristics of the studied profile are the occurrences of positive Ce anomalies in the ores of low REE content in the upper part of the profile and negative Ce anomalies in the ores of high REE content in the lower part of the profile. The occurrence of positive and negative Ce anomalies are due to the change of oxidation state of Ce (from Ce3+ to Ce4+) in the upper part and the complexing of Ce4+ with carbonate ligands in the lower part of the profile. The concordance of the analytical values of Na and Ca with those of Eu revealed that the degree of plagioclase alteration is the most important controlling factor for Eu anomalies in the ores. The obtained results revealed that the variations in the chemistry of weathering solutions (e.g., pH), function of carbonate bedrocks as a geochemical barrier, and discrepancy in degree of stability of lanthanide-bearing primary minerals are the major factors influencing the mobilization, distribution, and fractionation of REEs. The correlation coefficients among elements suggest that Mn-oxides are the principal hosts for REEs in the ores at Kanigorgeh.

Kinetics of rare earth pre-loading with 2-ethylhexyl phosphoric acid mono 2-ethylhexyl ester [HEH(EHP)] using rare earth carbonates

A new environment friendly approach for rare earth separation has been developed in this paper. The approach used rare earth carbonates to control the equilibrium acidity during the rare earth loading with HEH(EHP) in chloride system. The kinetics of rare earth pre-loading by the approach was investigated. High rare earth loading of 0.17molL−1 and fast kinetics with about 5min for equilibrium were achieved, which is suitable to the application of conventional rare earth separation process. The approach is free from environmental pollution because no saponification reagent is introduced.

A rare basanite distribution in the northern part of the Izu–Bonin volcanic arc, Japan: Petrological and geochemical constraints

Petrological and geochemical investigations were performed on the uniquely distributed Nanzaki basanite (0.43Ma) in the northern part of the Izu–Bonin volcanic arc, Japan, to clarify its original magma chemistry, and to constrain the source mantle and formation process of the magma. The Nanzaki basanite (monogenetic volcano) is mainly composed of nepheline-bearing basanite lava and scoria. The mineral chemistries are characterized by high forsterite (Fo) contents of olivines, high Mg# (=Mg/(Mg+Fe)) values of clinopyroxenes, and low Cr# (=Cr/(Cr+Al)) values of spinels. Whole-rock major element contents have narrow variation ranges as follows: SiO2 (41.5–44.1%), MgO (10.2–13.1%), CaO (11.9–13.3%), and K2O (0.4–1.9%). Combined with these mineral and whole rock chemistries, the low FeO*/MgO (0.81–1.09) values, high Ni and Cr contents, and narrowly distributed rare earth element (REE) patterns of the Nanzaki basanite represent the primary (undifferentiated) chemical features of the magmas. The incompatible trace element characteristics, especially the high Sr, Ba, and REE contents and low K, Rb, Zr, Hf, and Ti contents, suggest that the basanite magmas were generated from an enriched mantle that was affected by metasomatism with carbonatite magma (or carbonate-melt). In addition, the slight enrichment of Pb, Cs and other alkaline elements in the basanites indicates the close concern of fluids, and the Sr–Nd isotope characteristics of the basanites (low 87Sr/86Sr and 143Nd/144Nd ratios relative to those of basaltic rocks in the volcanic front) are consistent with across arc isotopic variations of the Izu–Bonin volcanic arc.The metasomatism of the source mantle by carbonatite (or carbonate-rich) melt was associated with and potentially facilitated by the infiltration and interaction of some volatile components (CO2, H2O) from the subducting slab. Thus, it is presumed that the enriched and metasomatized mantle parts have been present, ubiquitously in some regions of the mantle wedge, and that the basanitic magma, as in the Nanzaki, has been generated in close association with the unique tectonic regime, as in the northernmost part of the Izu–Bonin volcanic arc where three (or four) plates converged.

Rapid microwave-assisted flux growth of pure β-NaYF4:Yb3+, Ln3+ (Ln = Er, Tm, Ho) microrods with multicolor upconversion luminescence

Pure hexagonal β-NaYF4:Yb3+, Ln3+ (Ln=Er, Tm, Ho) microrods were successfully synthesized for the first time through a rapid microwave-assisted flux cooling method. X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), and photoluminescence (PL) spectra were used to characterize the samples. The results indicate that with the prolonged time, the phase of product transforms from orthorhombic YF3 to hexagonal NaYF4, while the morphology changes from nanoparticles to hollow microtubes then to solid microrods. The microwave (MW) heating technique allows for a reduction of about 90% in preparation time, making it possible to obtain pure β-NaYF4 microrods within only 12min. By changing the dopant’s species, multicolor (yellow, blue, and green) upconversion (UC) emissions can be obtained in β-NaYF4:Yb3+, Ln3+ under 980nm laser diode (LD) excitation. The UC mechanisms in Yb3+/Ln3+ co-doped β-NaYF4 samples were analyzed in detail based on the emission spectra and the plot of luminescence intensity to pump power. Importantly, this synthetic methodology may offer a new alternative in the preparation of high quality rare earth fluorides.

Geochronological and geochemical constraints on the origin of the 304 ± 5 Ma Karamay A-type granites from West Junggar, Northwest China: implications for understanding the Central Asian Orogenic Belt

U–Pb zircon geochronological, geochemical, and whole-rock Sr–Nd isotopic analyses are reported for a suite of Karamay A-type granites from the Central Asian Orogenic Belt (CAOB) in the western Junggar region of northern Xinjiang, Northwest China, with the aim of investigating the sources and petrogenesis of A-type granites. The Karamay pluton includes monzogranite and syenogranite. Laser-ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) zircon U–Pb dating yielded a concordant weighted mean 206Pb/238U age of 304 ± 5 Ma (n = 11), defining a late Carboniferous magmatic event. Geochemically, the rock suite is characterized by high SiO2, FeOt/MgO, total alkalies (K2O + Na2O), Zr, Nb, Y, Ta, Ga/Al, and rare earth elements (REEs) (except for Eu), and low contents of MgO, CaO, and P2O5, with negative Ba, Sr, P, Eu, and Ti anomalies. These features indicate an A-type affinity for the Karamay granitic intrusions. Isotopically, they display consistently depleted Sr–Nd isotopic compositions (initial 87Sr/86Sr = 0.7014–0.7022, ϵNd(t) = +5.6–+7.0). Geochronological, geochemical, and isotopic data suggest that the Karamay A-type granites were derived from remelting juvenile lower crust, followed by fractional crystallization. The Karamay A-type granites as well as widespread late Carboniferous magmatism in the western Junggar region of the southwestern CAOB may have been related to ridge subduction and a resultant slab window. This further demonstrates the importance of the late Palaeozoic granitic magmatism in terms of vertical crustal growth in northern Xinjiang.

Andean Adakite-like high-Mg Andesites on the Northern Margin of the Chilean–Pampean Flat-slab (27–28·5°S) Associated with Frontal Arc Migration and Fore-arc Subduction Erosion

Glassy, plagioclase phenocryst-free, ∼7–3 Ma, andesitic lavas erupted at the southern end of the Andean Central Volcanic Zone (CVZ) at 27–28·5°S are argued to contain a component from continental crust that was incorporated into the sub-arc mantle in a major pulse of fore-arc subduction erosion that removed ∼50 km of fore-arc. The 7–3 Ma amphibole-bearing Pircas Negras (54–64% SiO2) and ∼7·7 Ma pyroxene-bearing Dos Hermanos lavas erupted as the frontal arc was displaced some 50 km eastward over a developing bend in the Wadati–Benioff zone at the northern margin of the Chilean–Pampean flat-slab region. Their chemistry differs from that of older Miocene and younger CVZ arc lavas in the region in having more pronounced high field strength element (La/Ta = 40–100; Ba/Ta = 800–2400) and heavy rare earth element (Sm/Yb ∼ 4–9) depletions and an extreme adakitic-like character (∼600–1400 ppm Sr; Sr/Yb ∼ 400–1350). They also differ from older Miocene lavas in having higher 87Sr/86Sr and lower 143Nd/143Nd at the same wt % SiO2, while still showing trends with increasing wt % SiO2 that are best attributed to contamination in the ∼65–70 km thick crust. Overall, the trace element and isotopic features of the Pircas Negras lavas are consistent with modeling that attributes differences from older and younger lavas to enrichment of the arc mantle wedge by partial melts of tectonically eroded fore-arc crust, with the modeled eroded component being an outcrop and geophysically constrained mixture of 80–90% Jurassic mafic magmatic rocks and 10–20% silicic Paleozoic crust. An adakitic-type partial melt of this eroded crust generated at >2 GPa, reacted with mantle peridotite, can explain the high Mg# values (50–61) and Cr (100–350 ppm) and Ni (40–70 ppm) contents in some 5–3 Ma Pircas Negras lavas. Pre-eruption temperatures over 1060°C, calculated from mineral thermometry and the MELTS program, permit these magmas to subsequently melt and react with overlying eclogitic crust. Magma storage in this thick crust then led to amphibole crystallization and suppression of plagioclase fractionation. Quartz and feldspar xenocrysts were acquired from locally pooled mid-crustal magmas and the silicic upper crustal basement during final rapid ascent to the surface. Given a constant arc–trench gap of 300 km over the last 10 Myr, ∼198 km3 Myr–1 km–1 of fore-arc crust needs to be removed by subduction erosion at 8–3 Ma to account for the material balance of the fore-arc crust.

ZrB2 nanoparticle induced nano-LPSO-grain and nano-LPSO-layer reinforced ultra-high strength Mg–RE alloy

ZrB2 nanoparticles were used to modify a selected solidification processed Mg–RE alloy to give it ultrahigh strength (tensile yield strength >400 MPa). This approach did not involve time consuming and therefore cost incurring stages such as (1) ingot solutionizing and quenching prior to hot extrusion as well as (2) thermal aging beyond 24 h after hot extrusion. Rather, the ZrB2 nanoparticle induced finer LPSO phase (nano-LPSO-layer) formation due to nano-surface effects and the consequent nucleating effects of the fibrous LPSO ends during hot extrusion resulted in the formation of nanograins. Alternatively, free zirconium from ZrB2 nanoparticles reacting with the magnesium matrix may have had a significant nanoscale grain refining effect on the alloy. During the 24 h period of lower temperature (200 °C) thermal aging in this study, the LPSO phase formed in nanograins containing sufficient dissolved Gd, Y, and Zn, this being nano-LPSO-grain formation which “auto-locked” the nanoscale grain size during thermal aging due to the thermal stability of the high melting point rare earth containing LPSO phase. Compared to the surrounding alloy matrix, the nano-LPSO-grain cluster with random grain striation orientation was more robust. This was confirmed by the observation of predominantly non-basal or 〈c+a〉 type dislocations requiring higher CRSS around as well as within the room temperature tensile deformed nano-LPSO-grains. The LPSO phase generally constricted the flow of dislocations during deformation. The nano-LPSO-layer also acted as finely divided nanoscale reinforcement for the alloy matrix, including nanoscale strengthening of selected micrograin boundaries by bridging. The higher robustness of the nano-LPSO-grain cluster (and nano-LPSO-layer), good stress transfer characteristics across the nano-LPSO-grain boundary (and nano-LPSO-layer–alloy matrix interface), and nanoscale bridging across selected micrograin boundaries by nano-LPSO-layers contributed to the ultra–high strength characteristic (tensile yield strength >400 MPa) of the selected Mg–RE alloy.

Provenance and tectonic setting of the metapelites deposits in the Bulfat Complex, NE-Iraq

Major and trace elements including rare earth elements (REEs) chemistry of the metapelitic rocks of Bulfat Complex (Iraqi Zagros Suture Zone) indicate their enrichment in large-ion Lithophile, light rare earth (LREE) elements, and relative depletion of high field strength and heavy rare earth (HREE) elements. The linear correlation coefficients between TiO2, K2O, and Al2O3 and total REE reveal that phyllosilicates (e.g., mica) and accessory minerals mainly Ti-bearing phases (e.g., ilmenite) are likely the dominant hosts for REEs. Chondrite-normalized REE patterns typical of continental margin settings with significant enrichment of LREE, prominent negative Eu anomalies, and nearly flat HREE are positively correlated with post-Archean Australian shale (PAAS) and upper continental crust (UCC) patterns. Additionally, their consistent elemental La/Sc, Th/Sc, La/Co, Th/Co, Cr/Th, and Eu/Eu* values suggest that sediments may have been originally derived from an old post-Archean upper continental crust composed chiefly of granitic component. It seems most likely that the felsic source rocks were originated by a process of intra-crustal differentiation such as partial melting and/or fractional crystallization involving fractionation of Ca-plagioclase. The geochemical evidences particularly REEs evaluation show that deposition of clasts occurred in an active continental margin setting during lower–upper Cretaceous period contemporaneous with the igneous activities. It is evident therefore that the clasts source is from the north–northeast side, i.e., from the active margin of Iranian microcontinent (Sanandaj–Sirjan Zone).

Laser-ICP-MS U–Pb zircon ages and geochemical and Sr–Nd–Pb isotopic compositions of the Niyasar plutonic complex, Iran: constraints on petrogenesis and tectonic evolution

We conducted geochemical and isotopic studies on the Oligocene–Miocene Niyasar plutonic suite in the central Urumieh–Dokhtar magmatic belt, in order better to understand the magma sources and tectonic implications. The Niyasar plutonic suite comprises early Eocene microdiorite, early Oligocene dioritic sills, and middle Miocene tonalite + quartzdiorite and minor diorite assemblages. All samples show a medium-K calc-alkaline, metaluminous affinity and have similar geochemical features, including strong enrichment of large-ion lithophile elements (LILEs, e.g. Rb, Ba, Sr), enrichment of light rare earth elements (LREEs), and depletion in high field strength elements (HFSEs, e.g. Nb, Ta, Ti, P). The chondrite-normalized rare earth element (REE) patterns of microdiorite and dioritic sills are slightly fractionated [(La/Yb)n = 1.1–4] and display weak Eu anomalies (Eu/Eu* = 0.72–1.1). Isotopic data for these mafic mantle-derived rocks display ISr = 0.70604–0.70813, ϵNd (microdiorite: 50 Ma and dioritic sills: 35 Ma, respectively) = +1.6 and −0.4, TDM = 1.3 Ga, and lead isotopic ratios are (206Pb/204Pb) = 18.62–18.57, (207Pb/204Pb) = 15.61–15.66, and (208Pb/204Pb) = 38.65–38.69. The middle Miocene granitoids (18 Ma) are also characterized by relatively high REE and minor Eu anomalies (Eu/Eu* = 0.77–0.98) and have uniform initial 87Sr/86Sr (0.7065–0.7082), a range of initial Nd isotopic ratios [ϵNd(T)] varying from −2.3 to −3.7, and Pb isotopic composition (206Pb/204Pb) = 18.67–18.94, (207Pb/204Pb) = 15.63–15.71, and (208Pb/204Pb) = 38.73–39.01. Geochemical and isotopic evidence for these Eocene–Ologocene mafic rocks suggests that the magmas originated from lithospheric mantle with a large involvement of EMII component during subduction of the Neotethyan ocean slab beneath the Central Iranian plate, and were significantly affected by crustal contamination. Geochemical and isotopic data of the middle Miocene granitoids rule out a purely crustal-derived magma genesis, and suggest a mixed mantle–crustal [MASH (melting, assimilation, storage, and homogenization)] origin in a post-collision extensional setting. Sr–Nd isotope modelling shows that the generation of these magmas involved ∼60% to 70% of a lower crustal-derived melt and ∼30% to 40% of subcontinental lithospheric mantle. All Niyasar plutons exhibit transitional geochemical features, indicating that involvement of an EMII component in the subcontinental mantle and also continental crust beneath the Urumieh–Dokhtar magmatic belt increased from early Eocene to middle Miocene time.

Magmatic and Metamorphic Uraninite Mineralization in the Western Margin of the Trans-Hudson Orogen (Saskatchewan, Canada): A Uranium Source for Unconformity-Related Uranium Deposits?

AbstractThe genetic model for the giant unconformity-related uranium deposits of the Athabasca Basin is still being debated, with one of the main issues being the source of the uranium concentrated by Mesoproterozoic era (ca. 1.60–1.00 Ga) diagenetic-hydrothermal events at the interface between the Athabasca Basin and the underlying Archean/Paleoproterozoic basement rocks. Currently, accessory minerals like monazite, zircon, and/or apatite from the sedimentary basin and basement rocks are proposed as the primary uranium source for these high-grade uranium deposits. Numerous occurrences of U mineralization of Hudsonian age have been documented for decades all around the Athabasca Basin; however, so far these have not been regarded as viable U sources. Here, a systematic and detailed study of two areas of basement rocks near the eastern part of the Athabasca Basin is presented (i.e., the Way Lake property, lying outside the current margin of the basin, and the Moore Lakes property, currently covered by the basin). This study highlights the significant and widespread occurrence of Hudsonian (ca. 1.81–1.76 Ga) uranium oxide (UO2) mineralization in these zones. Two types of mineralization are identified and documented here: magmatic uranium oxides related to granitic pegmatites and leucogranites, which are more common, and high-temperature, vein-hosted uranium oxides, which have the highest grades. The two types were formed during the peak (1.82–1.81 Ga) and/or postthermal peak (1.81–1.72 Ga) events related to the evolution of the Trans-Hudson orogeny. The magmatic uranium oxides formed by partial melting of Wollaston Group metasedimentary rocks. The origin of the vein-type occurrences is unclear, but their high thorium and rare earth element (REE) contents suggest a high-temperature process associated with Ca and/or Na metasomatism. The uranium oxides are associated with other U-, Th-, and REE-bearing accessory minerals like U-rich thorite, thorite, zircon, and/or monazite, adding to the exceptional U contents (100–2,460 ppm) of these UO2-bearing rocks (up to 200 times more primarily enriched in U than other basement or basin rock types). A 3-D model of a 1,300 × 630 × 200-m basement zone from the Way Lake property indicates that uraninite-bearing granitic pegmatites and leucogranites represent 7% of the total volume of crystalline rock. Within this rock volume are approximately 8,121 (assuming a mean U content of 250 ppm) to 16,242 (assuming a mean U content of 500 ppm) tonnes U. The U tonnage of this limited rock volume, contained mainly by the Hudsonian-age UO2, corresponds to between 4% (for McArthur River) and 103% (for Rabbit Lake) of the U tonnage of known unconformity-related U deposits of the basin.Some of the studied rock samples, even macroscopically fresh and located far away from any known unconformity-related U deposit, present clear evidence of alteration, including clay minerals, aluminophosphate-sulfate (APS) minerals, and UO2 dissolution, indicating the percolation of the brines associated with the formation of unconformity-related uranium deposits when the basin was far more geographically extensive. Due to geologic similarities between the studied zones and the basement domains from the eastern part of the Athabasca Basin, i.e., the Hearne province, it is proposed that these domains hosted widespread Hudsonian-age uranium oxide protores. These protores provided easily leachable uranium for the metal enrichment of basinal brines during their percolation within the basement and the formation of the unconformity-related U deposits. These observations bring new insight to the debate about the genetic model of unconformity-related U deposits, and reinforce the metal source potential of the basement compared to that of the sedimentary basin.

A human health risk assessment of rare earth elements in soil and vegetables from a mining area in Fujian Province, Southeast China

Contaminated food through dietary intake has become the main potential risk impacts on human health. This study investigated concentrations of rare earth elements (REEs) in soil, vegetables, human hair and blood, and assessed human health risk through vegetables consumption in the vicinity of a large-scale mining area located in Hetian Town of Changting County, Fujian Province, Southeast China. The results of the study included the following mean concentrations for total and bio-available REEs of 242.92±68.98 (135.85–327.56)μgg−1 and 118.59±38.49 (57.89–158.96)μgg−1 dry weight (dw) in agricultural soil, respectively, and total REEs of 3.58±5.28 (0.07–64.42)μgg−1 dw in vegetable samples. Concentrations of total REEs in blood and hair collected from the local residents ranged from 424.76 to 1274.80μgL−1 with an average of 689.74±254.25μgL−1 and from 0.06 to 1.59μgg−1 with an average of 0.48±0.59μgg−1 of the study, respectively. In addition, a significant correlation was observed between REEs in blood and corresponding soil samples (R2=0.6556, p<0.05), however there was no correlation between REEs in hair and corresponding soils (p>0.05). Mean concentrations of REEs of 2.85 (0.59–10.24)μgL−1 in well water from the local households was 53-fold than that in the drinking water of Fuzhou city (0.054μgL−1). The health risk assessment indicated that vegetable consumption would not result in exceeding the safe values of estimate daily intake (EDI) REEs (100−110μgkg−1d−1) for adults and children, but attention should be paid to monitoring human beings health in such rare earth mining areas due to long-term exposure to high dose REEs from food consumptions.

Enrichment of Rare Earth Elements during magmatic and post-magmatic processes: a case study from the Loch Loyal Syenite Complex, northern Scotland

Concern about security of supply of critical elements used in new technologies, such as the Rare Earth Elements (REE), means that it is increasingly important to understand the processes by which they are enriched in crustal settings. High REE contents are found in syenite-dominated alkaline complexes intruded along the Moine Thrust Zone, a major collisional zone in north-west Scotland. The most northerly of these is the Loch Loyal Syenite Complex, which comprises three separate intrusions. One of these, the Cnoc nan Cuilean intrusion, contains two mappable zones: a Mixed Syenite Zone in which mafic melasyenite is mixed and mingled with leucosyenite and a Massive Leucosyenite Zone. Within the Mixed Syenite Zone, hydrothermal activity is evident in the form of narrow altered veins dominated by biotite and magnetite; these are poorly exposed and their lateral extent is uncertain. The REE mineral allanite is relatively abundant in the melasyenite and is extremely enriched in the biotite–magnetite veins, which have up to 2 % total rare earth oxides in bulk rock analyses. An overall model for development of this intrusion can be divided into three episodes: (1) generation of a Light Rare Earth Element (LREE)-enriched parental magma due to enrichment of the mantle source by subduction of pelagic carbonates; (2) early crystallisation of allanite in melasyenite, due to the saturation of the magma in the LREE; and (3) hydrothermal alteration, in three different episodes identified by petrography and mineral chemistry, generating the intense enrichment of REE in the biotite–magnetite veins. Dating of allanite and titanite in the biotite–magnetite veins gives ages of c. 426 Ma, overlapping with previously published crystallisation ages for zircon in the syenite.

Discovery of the REE minerals in the Wulong–Nanchuan bauxite deposits, Chongqing, China: Insights on conditions of formation and processes

The karstic bauxite deposits in the south Chongqing–north Guizhou Province bauxite belt are enriched in rare earth elements (REEs). REEs in this belt have been considered to be adsorbed on the surface of clay or diaspore minerals in the ion state. However, extracting tests have demonstrated that the amount of REE adsorption in bauxite ore is very low. In order to comprehensively understand the occurrence of REE in bauxite ores, the chemical and mineralogical compositions of Wulong–Nanchuan karst bauxites and their textural components have been studied. The bulk samples are composed of diaspore, boehmite, kaolinite, illite, hematite, anatase, and pyrite. The ∑REE concentrations vary widely, from 17 to 3610ppm REE, in the bauxite ores and most of the ores show an obvious positive Ce anomaly.Many kinds of REE minerals were identified in these bauxite ores including synchysite, bastnaesite, cerianite, and churchite. These minerals seldom occur in the same sample (with the exception of synchysite and bastnaesite). Synchysite occurs rarely as homogeneously single crystals, but typically contains a microfine phase of bastnaesite. Cerianite occurs mainly as framboidal clusters among chamosite or as fracture or micro-crack fillings. The existence of REE mineral phases is responsible for the high REE content and positive Ce anomaly in the ores. The compositions of the REE minerals show that the Eu anomaly can change subtly during the weathering. The REE compositions of the bauxite ores suggest that the REE mainly derives from the weathered remnants of the underlying Hanjiadian Formation shales and probably, a minor fraction derives from the Huanglong carbonates.The formation processes of these REE minerals can be explained assuming: (1) Ce oxidation and cerianite precipitation in the uppermost part of the deposits; (2) the mobile phosphates combined with the Y-enriched sediments and the HREE-enriched solutions under an acidic environment allow the precipitation of churchite-(Y); and (3) remobilization of cerium as fluoride complex, as a consequence of more acidic conditions in the uppermost part of the deposit, and precipitation of Ce3+ as fluorocarbonate mineral toward the carbonate bedrock barrier, at alkaline pH.

Production of High Purity Mg-X Rare Earth Binary Alloys Using Zr

An Fe content lower than the tolerance limit is critical in controlling corrosion rates of Mg alloys. The possibility of reducing Fe below the tolerance in Mg melts was studied using Zr as a precipitating agent. The experiments were carried out on Mg-X binary alloys with rare-earths, X = Y, Ce, Gd, Nd, and La. The laboratory scale results show that Zr is effective in reducing the Fe content from the Mg melt for Mg-X binary alloys. Purification occurs by the precipitation from the melt of Fe rich precipitates, and the settling of the precipitates to the bottom of the melt. Any desired Fe content down to one wt ppm can in principle be achieved by appropriate melt treatment. The experimental results are discussed with respect to calculated phase diagrams.

Luminescent properties of hybrid materials prepared by the polymeric precursor method

Abstract Rare earth complexes (RE) can be incorporated in silica matrixes, originating organic/inorganic hybrid materials with good thermal stability and high rare earth emission lines. In this work, the hybrid material was obtained by the polymeric precursor method and ultrasonic dispersed with spherical silica particles prepared by the Stober Method. The Raman spectra indicated that the Eu3+ ions are involved in a polymeric structure formed as consequence of the chelation and polyesterification reactions of this ion with citric acid and ethylene glycol. After the ultrasonic stirring, 2-hydroxynicotinic ligand will also compose this polymeric rigid structure. The TGA/DTA analysis showed that this polymeric material was thermal decomposed at 300 °C. Moreover, this process allows the chelating process of the 2-hydroxynicotinic acid ligand to the Eu3+ ions. The 29Si NMR showed that the ultrasonic dispersion of the reactants was not able to promote the functionalization of the silica particles with the 2-hydroxynicotinic acid ligand. Moreover, heat treatment promotes the [Eu(HnicO2)3] complex particles incorporation into silica pores. At this temperature, the TGA curve showed that only the thermal degradation of ethylene glycol and citric acid used during the experimental procedure occurs. The silica and hybrid materials are composed by spherical and aggregated particles with particle size of approximately 450 nm, which can be influenced by the heat treatment. These materials also present an absorption band located at 337 nm. The photoluminescent study showed that when the hybrid samples were excited at 337 nm wavelength, the ligand absorbs the excitation light. Part of this energy is transferred to the Eu3+ ion, which main emission, 5D0 → 7F2, is observed in the emission spectrum at 612 nm. As the heating temperature increases to 300 °C, the energy transfer is more favorable. The lifetime values showed that the Eu3+ emission is enhanced due to the energy transfer process in the powders.

Geochronology, petrology, and geochemistry of the Yaojiazhuang ultramafic-syenitic complex from the North China Craton

The Yaojiazhuang ultramafic-syenitic complex is one of the representative Triassic alkaline plutons on the northern margin of the North China Craton (NCC). Based on detailed study of the zircon U-Pb age, petrological, mineralogical, and geochemical data of the complex, the characteristics of the magmas system, the petrogenesis of different rock types, and the nature of the mantle source were discussed to provide new constraints on the origin and tectonic setting of the Triassic alkaline belt. Cumulus ultramafic rocks, clinopyroxene-syenites and syenites are the main rock types of the complex. The zircons from the syenites yielded a U-Pb age of 209 Ma. Diopside-augite, biotite, and sanidine-orthoclase are the major minerals, with subordinate apatite and magnetite. Rocks from the complex are enriched in large ion lithophile elements (LILE) and light rare earth elements (LREE), depleted in high field strength elements (HFSE) and heavy rare earth elements (HREE), and the initial 87Sr/86Sr ranges from 0.7057 to 0.7061 and ɛ Nd(t) from −9.4 to −11.4. Mineralogy and geochemical data demonstrate that the parent magma of the complex is SiO2-undersaturated ultrapotassic alkaline-peralkaline, and is characterized by high CaO content and fluid compositions (P2O5, CO2, H2O), and by high oxygen fugacity and high temperature. The complex was originated from a phlogopite-clinopyroxenite-rich lithospheric mantle source in the garnet-stable area (> 80 km) that had previously been metasomatized by melts/fluids from altered oceanic crust. The parent magma has been contaminated by little ancient TTG gneisses during magma emplacement. The development of the Yaojiazhuang complex indicates that the northern margin of the NCC has entered into an extensively extensional regime in the Late Triassic.

Within plate, arc, and collisional Neoproterozoic granitic magmatism in the Araxá Group, Southern Brasília belt, Minas Gerais, Brazil

Three Neoproterozoic granitic episodes associated with the Araxa Group, in Southern Brasilia Belt between the cities of Araxa and Cascalho Rico, Minas Gerais State, Brazil, are characterized from the geologic, geochemical, and geochronological points of view. The earliest episode, of 833 Ma, generated in a within-plate environment, is represented by the Quebra Anzol Granite, which has: low 87Sr/86Sr = 0.706 ratios and eNd(833) = -3.98; high levels of SiO2, Na2O, MnO, Nb, Y and Co; and low concentrations of Sr and Ba, with the absence of anorthite and presence of diopside, acmite, and positive Eu anomaly, therefore it may have been originated from mantle sources with small crustal contamination. The second episode, of 790 Ma, is represented by the pre-collisional Monte Carmelo Granitic Complex, which was partially remobilized in a collisional event around 630 Ma. It is metaluminous to peraluminous with low 87Sr/86Sr ratios of 0.706, high light rare earth elements fractionation relative to heavy rare earth elements, and negative Nb, Ta, Sr, P, and Ti anomalies. Their eNd(790) = -2.218, with T DM = 1.29 Ga, indicate an origin from juvenile sources and reveal the existence of a late Mesoproterozoic magmatic arc in this region. The last granitic episode has taken place in a collisional tectonic environment between 642 and 630 Ma, generating peraluminous granites with muscovite, garnet, and tourmaline denominated Serra Velha, Tamandua, Pirapetinga, Galheirinho, Perdizes, Estrela do Sul, and Cascalho Rico. They have negative eNdt, Nd model ages from Neo to Mesoproterozoic, and variable rare Earth elements enrichment patterns, with strong negative Eu anomalies.

Eocene–Oligocene post-collisional magmatism in the Lut–Sistan region, eastern Iran: Magma genesis and tectonic implications

New 40Ar/39Ar, geochemical and SrNd isotopic analyses of Eocene–Oligocene magmatic rocks in the Lut–Sistan region, eastern Iran shed light on their origin and the regional geodynamic evolution. Samples were collected from outcrops in the Sistan suture zone and to the west on the Lut block, which together constitute a diffuse magmatic province with an estimated size of ~300km×400km. Magmatism was active from the Middle Eocene (~46Ma) to the Late Oligocene (~25Ma). The studied rocks are dominated by volcanic and sub-volcanic rocks with minor intrusive rocks, ranging from basaltic to rhyolitic compositions with a peak in intermediate compositions. Most of them have calc-alkaline to high-K calc-alkaline affinity, although shoshonitic rocks are also present. The rocks are characterized by (i) E-MORB-like ratios involving high field strength and heavy rare earth elements, and (ii) an orogenic signature including enrichments of large ion lithophile elements and Th, Nb-Ta-Ti-P troughs and a positive Pb spike on MORB-normalized trace element variation diagrams. A juvenile mantle origin is apparent from the dominance of positive εNd(t) values for the studied rocks. The SrNd isotopic compositions [(87Sr/86Sr)i=0.7042 to 0.7065; εNd(t)=−4.9 to +5.5] do not form parallel arrays with SiO2, Nb/La, Nb/U and Ce/Pb as would be expected for crustal contamination. Since the magmatism post-dated the Lut–Sistan collision and cannot be related directly to subduction, the orogenic signature is likely inherited from the mantle source, presumably modified by sediment partial melt and fluid released from subducted slab during the Late Cretaceous Sistan subduction. We propose that the magmatism was triggered by convective removal of the lithosphere and resultant asthenospheric upwelling during extensional collapse of the east Iranian ranges in the Eocene–Oligocene.

Petrogenesis of adamellites from eastern Shandong Province: geochronological, geochemical, and Sr–Nd–Pb isotopic evidence

Geochronology, geochemistry, and whole-rock Sr–Nd–Pb isotopes were studied on a suite of Mesozoic adamellites from eastern China to characterize their ages and petrogenesis. Sensitive high-resolution ion microprobe U–Pb zircon analyses were done, yielding consistent ages of 123.2 ± 1.8 to 122.1 ± 2.1 Ma for the samples. These rocks belong to the alkaline magma series in terms of K2O + Na2O contents (8.45–9.58 wt.%) and to the shoshonitic series based on their high K2O contents (5.23–5.79 wt.%). The adamellites are further characterized by high light rare earth element contents [(La/Yb)N = 14.96–45.99]; negative Eu anomalies (δEu = 0.46–0.75); positive anomalies in Rb, Th, Pb, and U; and negative anomalies in Sr, Ba, and high field-strength elements (i.e. Nb, Ta, P, and Ti). In addition, all of the adamellites in this study display relatively low radiogenic Sr [(87Sr/86Sr)i = 0.7081–0.7089] and negative ϵNd(t) values from –16.70 to –17.80. These results suggest that the adamellites were derived from low-degree partial melting of an enriched lithospheric mantle below the North China Craton (NCC). The parent magmas likely experienced fractional crystallization of potassium feldspar, plagioclase and Fe–Ti oxides (e.g. rutile, ilmenite, and titanite), apatite, and zircon during the ascent of alkaline rocks without crustal contamination.

The Demir Kapija Ophiolite, Macedonia (FYROM): a Snapshot of Subduction Initiation within a Back-arc

The Demir Kapija ophiolitic complex in southern Macedonia–FYROM (Former Yugoslav Republic of Macedonia) represents the southernmost exposure of the Tethyan Eastern Vardar ophiolitic unit in the Eastern Mediterranean. It consists of a mafic volcanic sequence (pillow basalts, sheeted dyke diabases and gabbros) that was subsequently intruded by island arc magmas with and without adakitic affinity. The mafic volcanic sequence is characterized by slightly increased ratios of large ion lithophile elements to high field strength elements (LILE/HFSE), flat rare earth element (REE) patterns, radiogenic 143Nd/144Nd (up to 0·51272) and high TiO2 contents (which reflect Pl + Ol + Cpx fractionation). The relationship between TiO2 and MgO contents indicates that Ti saturation was eventually reached and that Ti-magnetite fractionated. The mafic volcanic sequence of the ophiolite complex formed around 166·4 Ma in a short-lived intra-oceanic back-arc basin by slab roll-back of the Western Vardar Ocean. The rocks with and without adakitic affinity are spatially and temporally closely related. Their crystallization age is around 164 Ma. Our data suggest that two subgroups of arc lavas evolved as discrete volcanic lineages that are not related by fractional crystallization of a common parental magma, and that two different parental magmas are required. The arc lavas with adakitic affinity show some of the typical features of adakites; that is, low heavy REE, elevated Sr/Y, high LILE and high light REE. Major and trace element compositions of clinopyroxene phenocrysts resemble those of typical adakite-derived clinopyroxene. The very high Th/La, Th/Yb and Ba/Yb ratios and the reduced 143Nd/144Nd values (around 0·51245) of the rocks with adakitic affinity are considered to reflect contributions of sedimentary material to their mantle source. By analogy with adakites, these rocks are interpreted as the product of slab + sediment melting in an unusually hot subduction zone (subduction of young oceanic crust). In contrast, the arc lavas without adakitic affinity are related to a different parental melt, similar to common arc magmas. The Demir Kapija ophiolite formed in a short-lived intra-oceanic back-arc basin during subduction initiation within a back-arc. The arc intrusions are related to the change from an extensional to a compressional regime.