ABSTRACTMicro‐Raman spectroscopy was employed to analyze apatite‐containing samples from the Tomtor complex of ultrabasic rocks and carbonatites, located in the sharply continental region of Yakutia, Russia. Raman spectra excited at a wavelength of 532 nm revealed the characteristic vibrational bands of apatite, as well as bands attributed to carotenoid‐type cyanobacteria. Additionally, as an artifact, the spectra exhibited bands resulting from the laser‐induced photoluminescence of trivalent rare earth elements (REEs). Preresonance Raman spectra recorded at least two distinct C=C stretching modes of the β‐carotene polyene chain, indicating the presence of this carotenoid component associated with apatite. Furthermore, three characteristic carotenoid bands were recorded in samples from the specific weathering crust on carbonatites that lacked apatite‐related bands. These findings provide direct evidence of cyanobacteria in the studied samples, suggesting the likely involvement of microorganisms in the formation of Nb‐REE‐rich ores within the Tomtor field in Russia.

Carbonaceous materials (CMs) in black-shale rock specimens from the Kular Range, Sakha Republic, Yakutia, Russia, were investigated by micro-Raman spectroscopy. Studies of CM in Permian rock samples from the Ulakhan-Sis anticline collected from various boreholes in the Kular gold-bearing area, and CM in nodular monazite (NM) samples from alluvial sediments of different creeks of the Yana River basin revealed similar spectral features. Micro-Raman spectra excited at a wavelength of 532 nm exhibited characteristic CM bands together with bands of quartz, muscovite, anatase, rutile, carbonate, and pyrite. In the first-order Raman spectra of CM, G-bands were observed in the wavenumber range of similar to 1584-1597 cm(-1), and D1 bands at similar to 1347-1351 cm(-1) for black shale specimens, whereas for NM, G bands appeared between similar to 1572 cm(-1) and 1594 cm(-1), and D1 bands between similar to 1340 cm(-1) and 1351 cm(-1). NM grains consist of monazite containing numerous mineral inclusions of various sizes (from several to 10-20 mu m). The Raman spectral characteristics of these associated minerals are discussed. Temperature ranges for metamorphic transformations derived from the Raman data are estimated to be 300-360 degrees C for CM bedrock and 346-430 degrees C for CM NM.

Data indicating the important role of microorganisms in the formation of nodular monazite (NM) (kularite) of the Kular Range, Republic of Sakha (Yakutia), are presented. The NM contains microorganisms (cyanobacteria) replaced by REE-bearing phosphate (monazite) in the form of stromatolitic microedifices, as well as framboidal Fe sulfides in monazite. The Corg isotopic composition of kularite corresponds to biogenic carbon: the δ13С values vary from –22.2 to –22.3‰.

Samples of siliceous rocks of the Southern Kambalny Central Thermal Field (SKC) containing a unique ore mineralization were studied. Optical microscopy, scanning electron microscopy, X-ray microanalysis, X-ray diffraction, ICP-MS, and Raman spectroscopy were used in this study. High concentrations and a wide range of rare and rare-earth elements were found in siliceous rocks. Silicates (quartz, moganite, and opal-crystobalite/tridymite opal), oxides (hematite and anatase), hydroxides (goethite), carbonates (calcite with Fe and Mn impurities), sulfates (barite with Sr impurity and gypsum), sulfides (pyrite, marcasite, chalcopyrite, and chalcocite), phosphates (xenotime-Y, YPO4 with impurities of lanthanides, S, Ca, and As; berlinite, AlPO4 with the V impurity), and apatite were identified. Structures of anatase replacement by quartz often in association with pyrite were identified. The mineralization of SKC siliceous rocks reflects the physicochemical specificity of deep metal-bearing solutions.

The Tevinskoye agate deposit is located in the North of the Kamchatka peninsula (Russia) and represented by agate-bearing Eocene basaltic and andesitic rocks of the Kinkilsk complex. Agate mineralization occurs in lavas and tuffs as amygdales, geodes, lenses and veins, which are the main sources of the resupply of coastal agate placers. The present study aimed to perform a comprehensive mineralogical, geochemical, and O-isotope investigation of amethyst-bearing agates, and to evaluate data concerning the origin of mineralization and the conditions for amethyst formation. Agates exhibit spectacular textures, with variation in the sequence of silica filling of amygdales and geodes. The mineral composition of the agates is mainly represented by micro- and macro-crystalline quartz, amethyst, length-fast and zebraic chalcedony, moganite, goethite, and clinoptilolite. Carbonate forms individual bands in the outer zones of some agates. The presence of small amounts of native copper, covellite, chalcopyrite and pyrite is a feature of these agates. Copper and iron mineralization are probably typomorphic features related to the host rock composition. The measured values of crystallite size (525–560 Å) and the high moganite content (up to 50%) of agate with amethyst are evidenced by the young age (~45 Ma) of agate-hosting rocks. Agate formation temperatures (21–229 °C) were calculated from the O-isotope composition of chalcedony (+19.6 to +25.5‰), quartz (+18.1 to +22.3‰), and amethyst (+18.2 to +21.5‰). The cold-water monophase fluid inclusions revealed in amethyst crystals suggest that the mineralizing fluids have low temperatures (<100 °C) and low salinity. Magnetite grains in host rock, together with goethite inclusions identified within the amethyst crystals, point to a change in redox conditions and the presence of iron in the agate-forming fluids, which entered the quartz lattice during crystallization and influenced the formation of the violet color.

A rare gold–telluride montbrayite from the large Svetlinsk gold–telluride deposit (South Urals, Russia) was comprehensively studied using optical microscopy, scanning electron microscopy, electron microprobe analysis, reflectance measurements, electron backscatter diffraction, and Raman spectroscopy. Significant variations in the composition of the mineral were revealed (in wt%): Au 36.98–48.66, Te 43.35–56.53, Sb 2.49–8.10, Ag up to 4.56, Pb up to 2.04, Bi up to 0.33, Cu up to 1.42. There are two distinct groups with much more-limited variation within the observed compositional interval (in wt%): (1) Au 36.98–41.22, Te 49.35–56.53, Sb 2.49–5.57; (2) Au 47.86–48.66, Te 43.35–44.92, Sb 7.15–8.10. The empirical formula calculated on the basis of 61 apfu is Au16.43–23.28Sb1.79–6.09Te32.01–38.89Ag0–3.69Bi0–0.14Pb0–0.90Cu0–1.96. Two substitution mechanisms for antimony are proposed in the studied montbrayite grains: Sb→Au (2.5–5.6 wt% Sb) and Sb→Te (7–8 wt% Sb). The dependence of the reflection spectra and Raman spectra on the antimony content and its substitution mechanism, respectively, was found in the mineral. The slope of the reflectance spectra decreases and the curve in the blue–green region of the spectrum disappears with increasing Sb content in montbrayite. Raman spectra are reported for the first time for this mineral. The average positions of the peak with high-intensity are ~64 cm−1 and ~90 cm−1 for montbrayite with Sb→Te and Sb→Au, respectively. Two grains of montbrayite demonstrate decomposition according to two schemes: (1) montbrayite (7 wt% Sb) → native gold + calaverite ± altaite, and (2) montbrayite (5 wt% Sb) → native gold + tellurantimony ± altaite. A combination of melting and dissolution–precipitation processes may be responsible for the formation of these decomposition textures.

We carried out a comprehensive study of native gold (morphology, composition, intergrowths, and microinclusions) from alluvial deposits of the Kamenny stream (Ozerninsky ore cluster, Western Transbaikalia, Russia). The study showed that there were four types of native gold, which differed significantly in their characteristics and probably had different primary sources from which placers were formed: gold–quartz, oxidized gold–sulfide, gold–silver, and zones of listvenites with copper–gold and gold–brannerite (Elkon-type). Particular attention was paid to the study of unique, both in size and in composition, gold–brannerite nuggets of the Kamenny stream. It was established that the gold in the gold–brannerite nuggets (GBNs) had wide variations in chemical composition and mineral features. According to them, there were five different fineness types of native gold: 750–800‰; 850–880‰; 880–920‰; 930–960‰; and 980–1000‰. The data obtained indicated a multistage, possibly polygenic, and probably polychronous formation of GBN gold–uranium mineralization. The first stage was the formation of early quartz–nasturanium–gold–W–rutile–magnetite association (Middle–Late Paleozoic age). The second was the crystallization of brannerite and the replacement of an earlier pitchblende with brannerite (Late Triassic (T3)–Early Jurassic (J1) age). The third was the formation of the hematite–barite–rutile–gold association as a result of deformation–hydrothermal processes, which was associated with the appearance of zones of alteration in brannerite in contact with native gold with 8–15 wt.% Ag. The fourth was hypergene or the low-temperature hydrothermal alteration of minerals of early stages with the development of iron hydroxides (goethite) with impurities of manganese, tellurium, arsenic, phosphorus, and other elements. The carbon isotopic composition of an organic substance indicates the involvement of a biogenic carbon source. In the OOC area, there were signs that the composition of the GBNs and the quartz–chlorite–K–feldspar-containing rocks corresponded to Elkon-type deposits.

Electron microprobe analysis (EMPA), X-ray powder diffraction (XRD), and Raman spectroscopy (RS) were applied to characterize the synthetic gold chalcogenides of the Au-Te-Se-S system and natural analogs from the Gaching deposit (Central Kamchatka, Russia). The EPMA results showed that the synthetic chalcogenides have different Te/Se/S and Au/X (X = Te + Se + S) ratios: AuX2, Au3X10, and AuX. They are similar in composition to natural compounds - calaverite (AuTe2), maletoyvayamite (Au3Te6Se4), and unnamed minerals AuTe0.7Se0.3 and AuSe0.7S0.3. It was established that chalcogenides AuX, Au3X10, and AuX2 have a specific Raman spectra with characteristic peaks. The position of the peaks and the character of the spectra of the synthetic phases and their natural analogs from the Gaching deposit coincide within the limits of accuracy. Different ratios of chalcogenes Te/Se/S in compounds influence the Raman peak positions. The positions of the peaks for natural compounds AuX differ depending on the predominance of Te (AuTe0.7Se0.3) or Se (AuSe0.7S0.3). AuSe synthetic phases consist of a mixture of alpha- and beta-polymorphs. Raman spectroscopy can be used for the identification of natural gold chalcogenides worldwide, which are difficult to diagnose by other methods due to the microscopic grain sizes and close intergrowths with other ore minerals. The similarity of the Raman spectra upon changing the concentrations of Se and S suggests identical structures and possible isomorphism in the composition range of AuTe0.7Se0.3- AuTe0.7Se0.2S0.1, AuTe1.9Se0.1- AuTe1.8Se0.1S0.1, and Au3Te6Se4- Au3Te6S3Se.

As a result of comprehensive study and laser 40Ar/39Ar dating of sanidines from the rocks of the Talakhtakh diatreme (TD) (Arctic Siberia), it has been found that the formation time of sanidine trachytes (lamproites) corresponds to the isochronous age value of 1497 ± 40 Ma or the weighted average age (as more accurate) of 1476 ± 17 Ma. The obtained age of the TD rocks is fully consistent with the formation time of the main rocks from the Kuonamka large igneous province (LIP). Thus, the Talakhtakh diatreme should be considered as an integral part of the Kuonamka LIP together with widely distributed basaltic sills, dikes, and covers on the Anabar Shield and within the Riphean sedimentary cover.

An analysis of a number of samples from the Tomtor deposit of Nb and rare-earth elements (Republic of Saha (Yakutia)) by X-ray diffractometry, IR spectroscopy, and Raman spectroscopy makes it possible to cover the structural organization of minerals and their components from the long-range to the mid- and short-range orders. The apatites present in the samples are characterized by a large variety of anion and cation substitutions (including rare-earth elements) in various structural sites. Raman microspectroscopy revealed some specific features, inherent in molecular biomarkers (specifically, a band due to double bonds –C=C– in the central part of the polyene chain of carotenoids, which characterize cyanobacteria associated with apatite), which is a direct proof of participation of microorganisms in the formation of apatites in rocks of this deposit.

Raman spectroscopy and infrared (IR) spectroscopy can be used in the determination of the structural organization of crystals from the short-range order (IR) to the mid- and far-range orders (Raman). Among the 230 possible crystal space groups, only 61 can unambiguously be determined by X-ray diffraction. In other cases, from two to five space groups are characterized by unified diffraction extinction rules. The symmetry of the active irreducible representations of vibrations in IR, Raman, and hyper-Raman (HR) spectra for all crystallographic systems are systematized, and cases are indicated where the ambiguity in the assignment of crystal structures to the space groups with unified diffraction extinction rules can be overcome. The refinement of a space group of a mineral by analyzing the selection rules from IR and Raman spectra is discussed, and some examples are considered, including nontronite, kladnoite, and ugrandite.

Rippite K2(Nb,Ti)2(Si4O12)(O,F)2, a new K-Nb-cyclosilicate, has been discovered in calciocarbonatites from the Chuktukon massif (Chadobets upland, SW Siberian Platform, Krasnoyarsk Territory, Russia). It was found in a primary mineral assemblage, which also includes calcite, fluorcalciopyrochlore, tainiolite, fluorapatite, fluorite, Nb-rich rutile, olekminskite, K-feldspar, Fe-Mn–dolomite and quartz. Goethite, francolite (Sr-rich carbonate–fluorapatite) and psilomelane (romanèchite ± hollandite) aggregates as well as barite, monazite-(Ce), parisite-(Ce), synchysite-(Ce) and Sr-Ba-Pb-rich keno-/hydropyrochlore are related to a stage of metasomatic (hydrothermal) alteration of carbonatites. The calcite–dolomite coexistence assumes crystallization temperature near 837 °C for the primary carbonatite paragenesis. Rippite is tetragonal: P4bm, a = 8.73885(16), c = 8.1277(2) Å, V = 620.69(2) Å3, Z = 2. It is closely identical in the structure and cell parameters to synthetic K2Nb2(Si4O12)O2 (or KNbSi2O7). Similar to synthetic phase, the mineral has nonlinear properties. Some optical and physical properties for rippite are: colorless; Mohs’ hardness—4–5; cleavage—(001) very perfect, (100) perfect to distinct; density (meas.)—3.17(2) g/cm3; density (calc.)—3.198 g/cm3; optically uniaxial (+); ω = 1.737-1.739; ε = 1.747 (589 nm). The empirical formula of the holotype rippite (mean of 120 analyses) is K2(Nb1.90Ti0.09Zr0.01)[Si4O12](O1.78OH0.12F0.10). Majority of rippite prismatic crystals are weakly zoned and show Ti-poor composition K2(Nb1.93Ti0.05Zr0.02)[Si4O12](O1.93F0.07). Raman and IR spectroscopy, and SIMS data indicate very low H2O content (0.09–0.23 wt %). Some grains may contain an outermost zone, which is enriched in Ti (+Zr) and F, up to K2(Nb1.67Ti0.32Zr0.01)[Si4O12](O1.67F0.33). It strongly suggests the incorporation of (Ti,Zr) and F in the structure of rippite via the isomorphism Nb5+ + O2− → (Ti,Zr)4+ + F1−. The content of a hypothetical end-member K2Ti2[Si4O12]F2 may be up to 17 mol. %. Rippite represents a new structural type among [Si4O12]-cyclosilicates because of specific type of connection of the octahedral chains and [Si4O12]8− rings. In structural and chemical aspects it seems to be in close with the labuntsovite-supergroup minerals, namely with vuoriyarvite-(K), K2(Nb,Ti)2(Si4O12)(O,OH)2∙4H2O.

Samples of rock from the Tomtor Nb - REE (rare-earth elements) deposit (Russia) have been investigated by Raman micro-spectroscopy using visible 532 nm wavelength excitation. Raman spectra of different samples of this rock confirm their composition as calcites and other carbonates such as rhodochrosite, and mixed solid solution phases (Ca, Mn, Fe, Mg, Ba, Sr, REE)(CO3). An association between cyanobacteria and the apatite crystals has been noted Cyanobacteria exhibited Raman modes at 1520-1517 cm(-1) located in the double bonds of the central part of the polyene chain of carotenoids. A slight shift of this mode in the apatite-containing samples are dependent upon the compositions of carotenoids, the ratio of the rare earth elements adsorbed by cyanobacteria as well as their interaction with the environment. Laser-induced photoluminescence of REE andMn+2, obtained as an analytical artifact in the Raman spectra, has been observed in most cases with significant spectral intensity. The luminescence emission ofMn(2+), Sm3+, Eu3+, Pr3+, Ho3+, Er3+ in the spectra of the apatite-containing samples obtained with 532 nm excitation can be attributed both to apatite and to other mineral phases with a low concentration which contain these elemental ions. The results obtained in this study allowed us to confirm that the biogenic presence of the cyanobacterial mat had a significant impact on the formation of the unique Nb-REE Tomtor deposit. (C) 2020 Elsevier B.V. All rights reserved.

Sorption of uranyl ions from uranyl nitrate UO2(NO3)2 · 6H2O solutions by natural and synthetic layered silicates was studied by X-ray diffraction, IR spectroscopy, and high-resolution inductively coupled plasma mass spectrometry. The modifications of some structural parameters of the studied species after they were reacted with uranyl ions are due to a partial incorporation of uranyls into the interlayer spaces of the smectite structure, or the rotation of the tetrahedra of a tetrahedral network and the distortion of octahedra in an octahedral layer. The natural bottom clay samples from the Pacific Ocean and the Sea of Okhotsk have the best sorption properties. This is due to structural defects and the formation of uranium complexes with the iron ions of the smectite structure. Iron present in clay minerals improves their sorption potentials.

The N-S trending Central-Aldan magnesiocarbonatite province is located in the Aldan-Stanovoy shield (South Yakutia, Russia). Several apatite-dolomitic carbonatite occurrences were studied: Seligdar, Muostalaah, Ust-Chulman and Birikeen. Mineralogical and petrographic investigations indicate intense hydrothermal-metasomatic alteration and metamorphism, which are reflected in the evolution of the mineral parageneses. The primary minerals are fluorapatite, magnetite, ilmenite, dolomite, K-feldspar, phlogopite and accessory zircon, titanite, baddeleyite and thorite. The hydrothermal-metasomatic minerals are quartz, calcite and siderite aggregates with haematite, monazite-(Ce), xenotime-(Y), rutile-(Nb), barite-(Sr), anhydrite, ancylite-(Ce) and rare sulphide mineral phases. Alkaline rocks associated with the Muostalaah complex, were also studied. The following U-Pb ages have been obtained (Ma): 1930 ± 7 for Muostalaah alkaline basic rocks, 1906 ± 6 for Muostalaah carbonatites, and 1880 ± 13 and 1878 ± 17 for Seligdar and Ust-Chulman carbonatites, respectively.

The graphite in marbles from Oltrek, an uninhabited island on Lake Baikal, has been investigated by micro-Raman spectroscopy using visible and near-ultraviolet wavelength excitation. All graphite samples exhibit a sharp first-order Raman band at about 1,580 cm(-1) with a width from 10 to 19 cm(-1), and sometimes a D1 band with very low intensity, which is occasionally absent. Using Raman spectra data it was estimated that the temperature of graphite formation in the Oltrek marbles is about 530-650 degrees C and possibly even higher. This evaluation is in good agreement with the temperatures (about 700 degrees C) determined by a graphite isotope geothermometer of the graphite-calcite pair. Scanning electron microscopy images have recorded a conical graphite morphology on the surface of plate crystals of graphite. Raman spectra of samples with cones about 200-400 nm sizes showed that the graphite was associated with nontronite in the specimens studied. Natural nontronite, a clay mineral of the smectite group, has not been well characterized using Raman spectroscopy. Here, the Raman spectra of the Oltrek nontronite were compared with the spectrum of nontronite from the weathered crust of the Salair Ridge, Russia. The formation of hexagonal-pyramidal structures on the surface of graphite with the participation of clay and bio-organic matter in marble is discussed.