Rare-earth Spectra Research Articles

Geochemical Characteristics of the Pelite Component of Bottom Sediments Deposited Near the Mouths of Modern Major Rivers. How Stable are They Upstream?

The article analyzes a number of geochemical characteristics (values (La/Yb)N and Eu/Eu*, Th content) of fine-grained silty and silty-pelitic gray silts of the Volga, particulate suspended matter of the Lena and silty-pelitic fraction of Yangtze bottom sediments. It has been established that in almost all cases, the indicated parameters of the lanthanide spectra normalized to chondrite and the Th content turn out to be comparable with their values determined for specially prepared (removal of non-terrigenous carriers of rare earth elements – carbonate minerals, Fe-Mn oxyhydroxides and organic components) pelitic fractions of bottom sediments deposited near the mouths of the named major rivers, and remain so thousands of kilometers up from their deltas/mouths. The regulation of the Volga and Yangtze flows does not have a significant impact on the parameters of particulate suspended matter and bottom sediments we are considering.

On the Nature of the Kharamatolou Structure and the Ratio of the Amount of Ultramafic Rocks of the Voykar-Synya Massif to That of the Ray-Iz Massif, Polar Urals

There have been petrographic, geochemical, geochronological (Rb-Sr, Ar-Ar) and isotopic (Sm-Nd) studies done on the metamorphic formations of the Kharamatolou structure of the Polar Urals, which were usually assigned to the Precambrian. The temperatures of metamorphism have been shown to range from 450 to 626 °C, and the pressures – from 3.7–9.1 kbar once PT-conditions reached the amphibolite facies. The amphibolites of the Kharamatolou formation are geochemically divided into two groups. According to the distribution spectra of lanthanides and Nd isotope composition, one group has the characteristics similar to depleted N-MORB basalts εNd(0)=+7.0, and another group – those similar to moderately enriched E-MORB basalts εNd(0)=+(4.5–2.4). It has been found that the Kharamatolou structure is probably composed of the Early to Middle Paleozoic continental rise deposit of the Russian Platform, which passed the main stage of folding and metamorphism in the Late Devonian (Rb-Sr, 366±11 Ma). The gabbro-ultrabasic Ray-Iz and Voykar-Synya massifs have been shown to be one during most of their Pre-Triassic history. Now these ultrabasite massifs are separated by the young (Triassic) Kharamatolou uplift which is an erosive-tectonic semi-window where ultrabasic rocks of the Polar-Ural belt are exposed at the base of the thrust fault. The Kharamatolou structure is one of the transverse uplifts of the Urals which probably resulted from the Middle to Late Triassic compression therealong. As a result of the Middle to Late Triassic uplift of the Haramatolou metamorphites, the overlying ultrabasites were washed away by erosion. The mélange serpentinites observed in the center of the Kharamatolou structure are uneroded remnants of the link that once existed between the Ray-Iz and Voikar-Synya massifs. This significantly increases the metallogenic potential of the Voikar-Synya massif, as the Ray-Iz hosts the largest known chromite deposits in Russia.

THE GENESIS OF GARNET-PYROXENE SYENITES (SVIATONOSSITES) OF THE MALOBYSTRINSKY MASSIF (SLYUDYANKA COMPLEX, SOUTH BAIKAL REGION): RESULTS OF GEOCHEMICAL AND ISOTOPIC STUDIES

This paper deals with the study of syenites and sviatonossites (andradite-bearing syenites) of the Malobystrinsky massif of the Slyudyanka complex (South Baikal region, Siberia), and a large monzonite dike similar in age and composition to the rocks of the massif considered. The studied rocks belong to a series of highly ferriferous and metaluminous A-type granitoids (ASI index <1). They are characterized by SiO2 45–65 wt. %, K2O+Na2O up to 12 wt. %, MgO <4 wt. %, TiO2 up to 2.5 wt. %, and Al2O3 up to 17 wt. %. CaO varies in a wide range, from 2.2 to 14.7 wt. %. The rocks are similar to each other in trace element composition and show patterns with troughs for Th-U, Nb-Ta and Ti. Low-amplitude negative Eu anomaly is observed in the distribution spectra of rare earth elements for the entire rock complex. The obtained Sm-Nd age of sviatonossites in the Malobystrinsky massif is 487.1±6.1 Ma (MSWD=0.99). Our results indicate that syenites and monzonites have εNd(t) –1.9…–2.8, at εSr(t) 21–30, and sviatonossites have εNd(t) –3.8…–4.1 at εSr(t) – 26. Model ages TNd(DM) for all rock types are Mesoproterozoic (1.3–1.4 Ga). Based on the chemical and Sr-Nd isotopic composition of the magmatic rocks studied, it can be assumed that they have been generated by partial melting of lower crustal rocks (amphibolites). Crystallization of andradite garnet in syenite magma can occur due to melt contamination with metamorphic host rocks of the Slyudyanka complex.

Rare earth metals detection and recognition based on laser induced breakdown spectroscopy and machine learning.

The rapid detection and identification of the electronic waste (e-waste) containing rare earth (RE) elements is of great significance for the recycling of RE elements. However, the analysis of these materials is extremely challenging due to extreme similarities in appearance or chemical composition. In this research, a new system based on laser induced breakdown spectroscopy (LIBS) and machine learning algorithms is developed for identifying and classifying e-waste of rare-earth phosphors (REPs). Three different kinds of phosphors are selected and the spectra is monitored using this new developed system. The analysis of phosphor spectra shows that there are Gd, Yd, and Y RE element spectra in the phosphor. The results also verify that LIBS could be used to detect RE elements. An unsupervised learning method, principal component analysis (PCA), is used to distinguish the three phosphors and training data set is stored for further identification. Additionally, a supervised learning method, backpropagation artificial neural network (BP-ANN) algorithm is used to establish a neural network model to identify phosphors. The result show that the final phosphor recognition rate reaches 99.9%. The innovative system based on LIBS and machine learning (ML) has the potential to improve rapid in situ detection of RE elements for the classification of e-waste.

Polarization analysis by means of individual soft x-ray absorption spectra of rare earths

X-ray magnetic circular dichroism (XMCD), which by virtue of the sum rules provides element-specific spin and orbital moments, is obtained from the difference between two polarized spectra by reversing the direction of either the light helicity or the applied magnetic field. Usually, it is tacitly assumed that these two spectra are obtained using the same absolute degree of light and magnetic polarization. This is, however, not always possible and depends on circumstances that can be beyond control. First, we recapitulate the conventional XMCD sum rule method to obtain the values of the moments and emphasize some of the complications in the case of the rare-earth ${M}_{4,5}$ edges, such as the presence of strong core-hole $jj$ overlap, linear dichroism, and magnetic dipole term $\ensuremath{\langle}{T}_{z}\ensuremath{\rangle}$. Instead, we propose an alternative method. Using the individual polarized x-ray absorption spectra obtained at the Ho and Dy ${M}_{5}$ edges, where each of the $\mathrm{\ensuremath{\Delta}}J=\ensuremath{-}1,0$, and $+1$ transitions are separated by $\ensuremath{\sim}2$ eV in photon energy, we are able to determine independently the degree of circular dichroism in a single spectrum. Since light is a transverse wave, we need to include, apart from the circular dichroism, also a linear dichroism contribution in order to fit the circularly polarized spectra. In the measurements on paramagnetic rare-earth dopants it was found that reversing the field produces the same degree of circular dichroism, while reversing the helicity yields a $\ensuremath{\sim}$20% difference in the degree of circular dichroism.

GEOLOGIA E GEOQUÍMICA DO STOCK SERRA DO CAPUXU: MAGMATISMO CÁLCIO-ALCALINO DE ALTO-K NO DOMÍNIO RIO PIRANHAS-SERIDÓ, PROVÍNCIA BORBOREMA

O Stock Serra do Capuxu (SSC) está situado na porção setentrional da Província Borborema, na porção sudoeste do Domínio Rio Piranhas-Seridó. O stock intrude rochas gnáissicas do Complexo Caicó, dos quais guarda xenólitos, e trunca feições dúcteis prévias. Ocorrem enclaves tipo MME, localmente com feições de coexistência de magmas (mixing e mingling); e schlierens múltiplos e complexos. O SSC caracteriza-se por rochas leucocráticas (ΣMáficos=7,5-13%) de composição monzogranítica, textura equigranular fina/média, ocorrendo localmente fenocristais de K-feldspato (microclina). K-feldspato+plagioclásio+quartzo constituem mais de 85% modal; biotita é o principal máfico (6-10%); titanita, opacos, allanita e zircão são acessórios; e clorita, mica branca e carbonato ocorrem como produtos de transformações tardi-magmáticas. São rochas bastante evoluídas (SiO2=71,80-73,14), com teores de álcalis elevados (Na2O+K2O=8,25-8,77) e baixos teores de cálcio (CaO=1,23-1,69). Os espectros de elementos terras raras (ETR’s) mostram enriquecimento dos ETR’s leves, em relação aos pesados, com pronunciada anomalia negativa de Európio (Eu/Eu*=0,34-0,44). O índice de saturação em alumina do SSC revela um caráter transicional metaluminoso a peraluminoso (A/CNK=0,98-1,03). Diagramas discriminantes de séries magmáticas revelam, na sua maioria, afinidade química com rochas da série subalcalina (cálcio-alcalina de alto-K) e diagramas classificativos de ambiente tectônico associam o SSC a ambiente dominantemente pós-colisional. Esses dados são corroborados pela idade U-Pb em zircão de 579 Ma encontrada para o stock, sugerindo um alojamento tardi-tectônico para o SSC, consonante com os aspectos de campo do pluton. Postula-se uma fonte litosférica, mas diferente dos dioritos associados, para o SSC, possivelmente fusão de gnaisses do embasamento (baixo grau de fusão, face seus elevados e pouco variados teores de SiO2) gerando um magma já de natureza cálcio-alcalina de alto-K. Rochas com assinaturas similares têm sido denominadas de “Granitos Tipo-I Fracionados”

Probing luminescence of rare earth ions in natural pink fluorites using Raman microscopes

AbstractIt is well‐known that many natural fluorite crystals contain rare earth ions. In this work, a series of pink fluorites is studied to demonstrate that the use of Raman microscopes allows to obtain high resolution emission spectra of trivalent rare earth ions. These emission spectra allow in principle to distinguish differences of the local environment related to the charge compensation necessary when the divalent Ca ion is replaced by a trivalent rare earth ion. The pink fluorites from the Alps have grown under hydrothermal conditions, which results in the incorporation of oxygen into the fluorite. In one sample from Juchlistock (Bern, Switzerland), a trigonal Eu3+‐oxygen center is clearly identified. Interestingly, a pink fluorite from China (Huanggang Mine, Inner Mongolia, China) shows a quite different emission spectrum from those of the Alps. In this sample, the emission bands have much lower relative intensity compared with the intensity of the CaF2 Raman peak, indicating a much lower content of Er3+ and Ho3+ which emit around 520–560 nm. Literature examples show that Raman measurements of differently colored fluorite crystals can also present sharp rare earth spectra. By extension, it is thus possible to observe and identify emission spectra of rare earth ions in other mineral crystals using Raman microspectroscopy and avoid misassignments of the corresponding observed Raman spectra.

Rare earth elements in surface waters and sediments of the Mgoua watershed, south western Cameroon

The concentrations and distribution spectra of 14 stable rare earth elements (REE) were studied for surface waters (n = 30) and sediments (n = 30) of the tropical zone Mgoua watershed in southwest of Cameroon. Samples were analyzed using the inductively coupled plasma mass spectrometer (ICP-MS) method. The ∑REE concentrations of the surface waters vary from 0.11 to 6.60 µg/L with an average value of 1.18 µg/L. This average is 150 times lower than the average values of the Post-Archean Australian Average Shale (PAAS). In the sediments, the concentrations range from 282.12 to 727.67 ppm with an average value of 550.05 ppm, making it 2.5 times higher than the PAAS. Rare earth spectra normalized to PAAS are spread out and show heavy rare earth enrichment; positive Eu anomalies; negative, low, or no Ce anomalies; and a gradual decrease in heavy earths in river and well waters and sediments, but are sawtooth with strong negative Ce anomalies in effluent waters and sediments. A low rare earth fractionation is noted in river and well waters [(La/Yb)N ~ 0.35–1.19], while it is high in effluent waters [(La/Yb)N ~ 0.42–56.99]; a slight depletion of rare earths in all environments [(La/Sm)N ~ 0.69–2.35], as well as a depletion of heavy rare earths [(Gd/Yb)N ~ 0.58–1.94]. In the sediments, the same characteristics are found with elemental ratio values differing slightly [(La/Yb)N ~ 1.15–1.99]; [(La/Sm)N ~ 0.75–1.36]; and [(Gd/Yb)N ~ 1.15–2.01]. This study shows that the Mgoua watershed does not have a high concentration of REE, although in the sediments they are well above the average PASS value while they are insignificant in the waters.

Marine diagenesis of ikaite: Implications from the isotopic and geochemical composition of glendonites and host concretions (Palaeogene–Neogene sediments, Sakhalin Island)

AbstractGlendonites represent pseudomorphs after calcium carbonate hexahydrate (ikaite) and can be used as indicators of past cold climates, because ikaite only naturally occurs in cold environments (<7°C) in the modern. The results of a multi‐proxy study of 11 glendonite and host concretion samples from Palaeogene (Gennoishi Formation) and Neogene (Bora and Vengeri formations) sediments from Sakhalin Island, Russian Far East are reported here. Petrographic, cathodoluminescence, powder X‐ray diffraction and scanning electron microscope analyses reveal that glendonites are composed of several successive mineralogical phases: low‐magnesium ikaite‐derived calcite, high‐magnesium acicular cement (calcite and dolomite) and blocky calcite or authigenic quartz filling the remaining pore space. Host concretions comprise sandy limestones cemented by high‐magnesium calcite. The δ13C and δ18O values for host concretions and enclosed glendonites are very similar, with δ13C ranging from –20.3 to +1.9‰ Vienna Pee‐Dee Belemnite and δ18O ranging from –3.4 to +3.4‰ Vienna Pee‐Dee Belemnite. Such isotopic values suggest that seawater was the main source of oxygen, while dissolved inorganic carbon and decaying organic matter were the main carbon sources for ikaite growth, concretion and glendonite cementation. The 87Sr/86Sr values within the glendonites and host concretions are significantly lower compared with coeval Palaeogene–Neogene marine carbonates, suggesting an influence of continental runoff on their isotopic composition. Post Archean Australian Shale normalized rare earth element patterns display negative Ce anomalies and positive Eu anomalies, with a depletion in light rare earth elements or bulge in middle rare earth elements. Such spectra of rare earth elements indicate that ikaite growth and replacement occurred very close to the aerobic–anaerobic boundary, with pore waters derived from trapped seawater and/or ikaite dehydration. Since Mg/Ca ratios and alkalinity increase with depth below the sediment–water interface, subsequent mineral phases show enrichment in Mg, while the lack of diagenetic alteration by basinal fluids enabled preservation of the primary isotopic and geochemical characteristics of ikaite within the recrystallized pseudomorph.

Редкие и редкоземельные элементы в Cu-Ni рудах Норильского района

The deposits of the Norilsk region are confined to the marginal northwestern part of the Siberian platform and are associated with the manifestation of the Early Mesozoic trap volcanism. Sulfide mineralization is concentrated in the intrusive facies of the volcano-intrusive complex. Four main types of Cu-Ni ores are distinguished according to textural features: massive, vein-disseminated, brecciated, and disseminated. The main types of Cu-Ni ores differ significantly from each other in the chemical composition and content of rock- and ore-forming components. The enrichment ratios of ore trace elements in the Oktyabrskaya and Talnakhskaya vein-disseminated ore mainly reach hundreds (S, Pt, Au, Se,Te, Pb, As, Sn, Mo) and thousands (Ni, Cu, Ag, Pd) times. A rather high enrichment of all types of Bi, Re and Cd ores has been revealed, which are potentially industrially significant as high-tech metals, and can be promising for associated mining. The amount of rare-earth elements (REE) in ores is several times less than in the upper crust and more than in the primitive mantle. The concentration of rare earths in the main types of ores, with the exception of massive ones, exceeds the level of the chondrite standard, and REE fractionation is weak. The distribution spectra of chondrite-normalized REEs have a slight negative slope: the total content of light REEs is higher than that of heavy ones. The similarity of the geometry of the REE spectra of massive, vein-disseminated, brecciated and disseminated types of ores containing a significant admixture of host rocks indicates the inheritance of the REE composition in ores from the host rocks. In the disseminated ores of common taxite gabbro-dolerites, the Eu anomaly is present in the Kharaelakhsky (Oktyabrskoye Deposit) and Talnakhsky (Talnakhskoye Deposit) intrusions, it is positive, and in the Norilsk I Intrusive (in the same rocks), it is negative. Higher concentrations of REEs and significant fractionation of light and heavy rare elements are typical for host contact-metamorphic and metasomatic rocks with vein-disseminated (exocontact) ores. For olivine-free hornfels and skarns in brecciated ores, as well as for vein-disseminated ores, significant fractionation of light REEs with relatively heavy ones and a pronounced Eu minimum are characteristic. In massive ores, the distribution of REEs is determined by the composition of xenoliths.

The distribution of Rare Earth Elements discriminates the growth substrate of Vitis vinifera L.

Sustainable agricultural, food-related strategies and geographic traceability require understanding of the plant physiological response to stress potentially generated by contaminated soils. Here, we have investigated the effect of contaminated substrate on growth of Vitis vinifera L. plants analysing the distribution of full Rare Earth Elements (REE) spectra in different parts of the plant. Experiments were carried out using pristine plants growing in a handmade substrate (blank experiment) and in REE artificially-enriched soil (spiked experiment). Our results show that both plant mass and REE amount in leaves are not influenced by the substrate enrichment while roots are by one-order of magnitude enriched for three-orders of magnitude enhancement of the soil substrate. This clearly indicates that soil contamination does not significantly influence the REE amount in the aerial parts. However, the spectra of REE normalized changes when the soil is enriched. We found that Light-REE (from La to Gd) are by more than one order of magnitude enriched compared to Heavy-REE (from Tb to Lu plus Y) in spiked experiment showing the specific response of Vitis vinifera L. to the stress generated by soil contamination. We propose that REE distribution spectra is a marker of Vitis vinifera L. substrate of growth and providing a new tool for tracing the geographical origin of agri-food products.

Europium-Doped Ceria-Gadolinium Mixed Oxides: PARAFAC Analysis and High-Resolution Emission Spectroscopy under Cryogenic Conditions for Structural Analysis.

Gadolinium-doped ceria or gadolinium-stabilized ceria (GDC) is an important technical material due to its ability to conduct O2- ions, e.g., used in solid oxide fuel cells operated at intermediate temperature as an electrolyte, diffusion barrier, and electrode component. We have synthesized Ce1-xGdxO2-y:Eu3+ (0 ≤ x ≤ 0.4) nanoparticles (11-15 nm) using a scalable spray pyrolysis method, which allows the continuous large-scale technical production of such materials. Introducing Eu3+ ions in small amounts into ceria and GDC as spectroscopic probes can provide detailed information about the atomic structure and local environments and allows us to monitor small structural changes. This study presents a novel approach to structurally elucidate europium-doped Ce1-xGdxO2-y:Eu3+ nanoparticles by way of Eu3+ spectroscopy, processing the spectroscopic data with the multiway decomposition method parallel factor (PARAFAC) analysis. In order to perform the deconvolution of spectra, data sets of excitation wavelength, emission wavelength, and time are required. Room temperature, time-resolved emission spectra recorded at λex = 464 nm show that Gd3+ doping results in significantly altered emission spectra compared to pure ceria. The PARAFAC analysis for the pure ceria samples reveals a high-symmetry species (which can also be probed directly via the CeO2 charge transfer band) and a low-symmetry species. The GDC samples yield two low-symmetry spectra in the same experiment. High-resolution emission spectra recorded under cryogenic conditions after probing the 5D0-7F0 transition at λex = 575-583 nm revealed additional variation in the low-symmetry Eu3+ sites in pure ceria and GDC. The total luminescence spectra of CeO2-y:Eu3+ showed Eu3+ ions located in at least three slightly different coordination environments with the same fundamental symmetry, whereas the overall hypsochromic shift and increased broadening of the 5D0-7F0 excitation in the GDC samples, as well as the broadened spectra after deconvolution point to less homogeneous environments. The data of the Gd3+-containing samples indicates that the average charge density around the Eu3+ ions in the lattice is decreased with increasing Gd3+ and oxygen vacancy concentration. For reference, the Judd-Ofelt parameters of all spectra were calculated. PARAFAC proves to be a powerful tool to analyze lanthanide spectra in crystalline solid materials, which are characterized by numerous Stark transitions and where measurements usually yield a superposition of different contributions to any given spectrum.

Geochemistry of Rare Earth Metals in the Ore Eudialyte Complex of the Lovozero Rare Earth Deposit

Rare earth elements belong to the category of strategic metals. The largest deposits of these strategic raw materials are associated with alkali-carbonatite formations. The largest alkali-carbonatite complexes of the world are located on the Kola Peninsula and in Polar Siberia. These complexes have great potential for strategic raw materials, including rare earths. The purpose of this work was to estimate the rare earth potential for ore eudialyte in the Lovozero deposit. Thus, 120 eudialyte grains from eudialyte ores were studied by inductively coupled plasma mass spectrometry. In the ore eudialyte-bearing complex, the average value of the total amount of rare earths in eudialytes is 12 566 g/t, which is significantly higher than the total amount of rare earths in apatite from five deposits of the Khibiny Massif. Considering the many millions of tons of nepheline syenites of the eudialyte-bearing complex and the almost linear trend of rare-earth spectra for eudialyte, it can be concluded that the eudialyte deposit of the Lovozero Massif is extremely valuable.

Klimovskii Metasomatic Complex of the Belomorian Mobile Belt: Composition, Age, Geological Position

Metasomatites of the White Sea mobile belt of the Fennoscandian (Baltic) shield are considered. Metasomatites are traced from southeast to northwest for a distance of ≥550 km. In mineral composition, metasomatites correspond to the paragenesis of amphibolite facies of regional high-pressure metamorphism. To determine the tectonic position of metasomatites and their place in the sequence of geological events, we carried out isotope-geochemical studies of zircons, isolated both from metasomatites and their enclosing gneisses. It was established that the host metamorphic formations formed in the Neoarchean and metasomatites formed in the Late Paleoproterozoic (≈1.9 Ga). The rare-earth spectra of the studied zircons indicate that they formed from a fluid in a retrograde branch of regional metamorphism. Fluids were discharged along the deep thrust planes, thereby marking the zones of their exits to the modern surface. The results obtained indicate tectonothermal reworking of Archean complexes in the Late Paleoproterozoic.

Advanced computational approach to studying Rydberg and autoionization resonances in spectra of lanthanides: Ytterbium

We present the results of computing the Rydberg autoionization resonances in spectra of the ytterbium atom, in particular, data on the energies and widths of the autoionization resonances 4f13 [2F7/2]6s2np[5/2]2, 4f13 [2F7/2]6s2nf[5/2]2, which are arisen in result of excitation of the 4f-shell electrons. For some values of the principal quantum number the presented data are compared with the corresponding available experimental data by Jong-Hoon Yi et al, which are obtained by method of three-photon laser polarization spectroscopy. As the method of computing we apply the method of a relativistic many-body perturbation theory with the Dirac-Kohn-Sham zeroth approximation combined with the generalized relativistic energy approach. This approach takes effectively into account the important exchange-correlation corrections as the corrections of the perturbation theory second and higher orders (for example, the polarization interaction, quasiparticles screening corrections) and effect of the non-Coulomb grouping levels in the Rydberg spectra etc.

Shallow forearc mantle dynamics and geochemistry: New insights from IODP Expedition 366

The Mariana forearc is a unique setting on Earth where serpentinite mud volcanoes exhume clasts originating from depths of 15 km and more from the forearc mantle. These peridotite clasts are variably serpentinized by interaction with slab derived fluid, and provide a record of forearc mantle dynamics and changes in geochemistry with depth. During International Oceanic Discovery Program (IODP) Expedition 366, we recovered serpentinized ultramafic clasts contained within serpentinite muds of three different mud volcanoes located at increasing distance from the Mariana trench and at increasing depth to the slab/mantle interface: Yinazao (distance to the trench: 55 km / depth to the slab/mantle interface: 13 km), Fantangisña (62 km / 14 km) and Asùt Tesoru (72 km / 18 km). Four different types of ultramafic clasts were recovered: blue serpentinites, lizardite-serpentinites, antigorite/lizardite- and antigorite-serpentinites. Lizardite-serpentinites are primarily composed of orange serpentine, forming mesh and bastite textures. Raman and microprobe analyses revealed that these textures contain a mixture of Fe-rich brucite (XMg ~ 0.84) and lizardite/chrysotile. Antigorite/lizardite- and antigorite-serpentinites record the progressive recrystallization of mesh and bastite textures to antigorite, magnetite and pure Fe-poor brucite (XMg ~ 0.92). Oxygen isotope compositions of clasts and pore fluids showed that the transition from lizardite to antigorite is due to the increase in temperature from 200 °C to about 400 °C within the forearc area above the slab/mantle interface. Lizardite-, antigorite/lizardite- and antigorite-serpentinites displayed U-shaped chondrite normalized Rare Earth Element (REE) patterns and are characterized by high fluid mobile element concentrations (Cs, Li, Sr, As, Sb, B, Li) relative to abyssal peridotites and/or primitive mantle. The recrystallization of lizardite to antigorite is accompanied by a decrease in Cs, Li and Sr, and an increase in As and Sb concentrations in the bulk clasts, whereas B concentrations are relatively constant. Some clasts are overprinted by blue serpentine, often in association with sulfides. Most of these blue serpentinites were recovered at Yinazao and the uppermost units of Fantangisña and Asùt Tesoru suggesting alteration in the shallower portions of the forearc, possibly during exhumation of the clasts. This episode of alteration resulted in a flattening of REE spectra and an increase of Zn concentrations in serpentinites. Otherwise, no systematic changes of ultramafic clasts chemistry or mineralogy were observed with increasing depth to the slab. The samples document previously undescribed prograde metamorphic events in the shallow portions of the Mariana subduction zone, consistent with a continuous burial of the serpentinized forearc mantle during subduction. Similar processes, induced by the interaction with fluids released from the downgoing slab, likely occur in subduction zones worldwide. At greater depth, breakdown of brucite and antigorite will result in the massive transfer of fluids and fluid mobile elements, such as As, Sb and B, to the source of arc magmas.

Fractionation of Rare-Earth Elements in the Processes of Hydrothermal Ore Formation

The data on the distribution of elements in the Pb–Zn cross-section of the Gatsirovskaya vein (the Upper Zgid deposit, North Ossetia, Russia) have shown that the spectra of rare-earth elements (REEs) changed significantly in the ore samples during the vein formation. The sharp growth of the LaN/YbN, LaN/NdN, GdN/HoN, and GdN/YbN ratios is confined to the vein intervals, where the maximum amount of ore components is deposited. The comparison of the REE spectra of ores to the characteristics of the spectra of the rocks surrounding the vein and the host rocks suggests that the vein material deposited from the solutions in which the REE ratio changed with time. REE fractionation occurred due to the mobilization of components by hydrothermal solutions during their interaction with the Paleozoic host granites.

Fractionation of rare-earth elements in the processes of hydrothermal ore formation

Data on the distribution of elements across the Pb-Zn section of the Gatsyrovskaya vein (Upper Zgid, North Ossetia, Russia) showed that during the formation of the vein significant changes in the spectra of rare-earth elements (REE) occur in ore samples. The sharp growth of ratios LaN/YbN, LaN/NdN, GdN/HoN, and GdN/YbN is confined to the vein intervals, where the maximum amount of ore components is deposited. A comparison of the REE spectra of ores with the characteristics of the spectra of the near-vein and host rocks suggests that the deposition of the vein material occurred from solutions whose compositions with respect to the REE varied with time. REE fractionation occurred due to the mobilization of components by hydrothermal solutions during their reaction with the host Paleozoic granites.

Кашпарский кембро-ордовикский габбро-диорит-кварцмонцодиорит-сиенитовый комплекс - новое петрографическое подразделение на восточном склоне Кузнецкого Алатау

On the basis of material obtained during the geological survey works on the state GDP-200 on the territory of two nomenclature sheets (N-45-XXIV и N-46-XIX) substantiated of the allocation of a new for the region three-phase Kashpar gabbro-diorite-quartz monodiodite-syenitic complex with the author's U-Pb dating in the range from 472 to 487 Ma (£ 3 -Oi). Previously, these formations preceding the formation of Tigertysh granitoids were included in the composition of the Kogtach gabbro-montsodiorite-syenite complex with an absolute age of more than 500 Ma (C 2 ). It has been shown that the permanent presence of normative, and sometimes modal nepheline is characteristic of the rocks of the Kogtakh complex, while Kashpar magmatites are distinguished by a noticeable content of not only normative, but also modal quartz in dioritoids and syenites, which indicates a different degree of saturation with silicic acid and alkalis of the initial magmatic melts. In the study area was attested 33 intrusions of the Kashpar complex with a total area of more than 1,600 km 2 with the dominance of dioritoidov second phase (1,340 km 2 ) and the more modest role of early gabbroids (250 km 2 ) and late syenite (23,3 km 2 ). Brief descriptions of five representative arrays, including the petrotypic Kashpar intrusive, are given. The common mineralogical and petrographic features were identified, namely: the absence of modal olivine in the rocks of all three phases, the frequent predominance of magnesian hornblende over clinopyroxene, the appearance of small amounts of modal orthorhombic pyroxene (hypersthene) in dioritoids (up to 5 %), the presence of quartz in the second rocks and third intrusive phases. For the first time, the author's data on the contents of petrogenic, rare and rare-earth elements in the rocks of the complex are introduced into scientific circulation. Revealed a distinct high-potassium bias of the chemism of almost all of the formations in the framework of the calc-alkaline potassium-sodium petrochemical series. It was established that with an increase in the degree of differentiation from gabbroids to syenites, there is a decrease in concentrations CaO, MgO, FeO^^., TiO 2 , P 2 O 5 with parallel growth of contents of Rb, Zr, Nb, Th, U и £REE. In the rare-earth spectra light dominates REE (La/Yb N =9-21), a weak europium anomaly is characteristic of the second phase rocks (Eu/Eu*=0,77). It is shown that the intrusive rocks of the complex on the spider-diagrams exhibit intermediate geochemical characteristics between intraplate basalts of the type OIB and marginal continental type IAB, which is evidence in favor of the assumption of the formation of magmatic differentiates in a complex geodynamic setting. Metallogenic specialization is determined by the confinement to some of the massifs (Balakhchin, Maganak, Syra group) of gold deposits and manifestations of gold-sulfide-quartz type.

Spectroscopy and energy transfer in Tb3+/Sm3+ co-doped lead borate glasses

In this work, luminescence properties of Tb3+/Sm3+ co-doped lead borate glasses are examined in details. Luminescence spectra of rare earths were measured under different excitation wavelengths. Characteristic luminescence bands corresponding to electronic transitions of terbium and samarium ions were detected under direct excitation of Tb3+. The energy transfer from Tb3+ to Sm3+ ions in lead borate glass occurs through a nonradiative process with an efficiency from 0.6% to 16%, depending on samarium concentration. Luminescence decay curves for the 4G5/2 state of Sm3+ ions in lead borate glasses were fitted using the Inokuti-Hirayama model. The concentration-dependent luminescence quenching was explained by the non-radiative energy transfer process between the Sm3+ ions through the cross-relaxation mechanism. The CIE chromaticity coordinates and correlated color temperatures for Tb3+/Sm3+ co-doped lead borate glasses are also presented and discussed.