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Very primitive ultramafic igneous rocks occur at Mt. La Queglia (Abruzzo, Italy). They form a strongly deformed sill–dyke system now tilted vertically. These rocks were initially classified as alnöite and, subsequently, have been suggested to be a carbonatitic olivine melilitite. However, further investigation and interpretation of these rocks is needed due to the presence of hand-specimen-scale textural variation suggesting a complex petrogenesis. We study the texture, mineral chemistry, and whole-rock geochemistry to define three main rock-types. (1) A brecciated rock with an ocellar texture composed of calcite pseudomorphs after olivine and melilite, plus fresh diopside in a groundmass of mica, aegirine, garnet, calcite, apatite, perovskite, titanate and chlorite. Zoned ocelli in this rock show an amoeboid shape, agglutination, and menisci typical of a plastic state. (2) A quenched rock showing a spinifex texture containing long feathery phenocrysts of cpx and mica suspended in a groundmass of nepheline, aegirine, apatite, Ti–rich magnetite, plus abundant calcite and some K-feldspar and zeolites. (3) A coarse-grained rock is composed of calcite plus intergranular glauconite, a mixture of spinel mineral group and Ti–rich magnetite, accessory barite, pyrite, and chabazite-K. The igneous rocks at Mt. La Queglia show extreme SiO2-undersaturation (33.5–37.3 wt% SiO2), high MgO contents and TiO2/Al2O3 ratios. Rock-type 1 has a lower Mg number Mg# = 100 × [Mg/(Mg + Fe2+)], higher Ca number Ca# = 100 × [Ca/(Ca + Mg)], high Cr (up to 720 ppm) Ni (up to 379 ppm), higher rare earth elements (REE) contents as well as La/Lu ratio, compared to rock-type 2. Perovskite and chromite accumulation seems an important agent during rock differentiation. Rock-type 3 shows REE cross-over with rock-type 2 suggesting light (L)REE concentration in a carbothermal residuum. Mt. La Queglia rocks are an end-member compared to other Upper Cretaceous and Paleogene Italian lamprophyres, suggesting a low degree of melting of a HIMU (a colloquialism for “high-μ”; referring to mantle domains with high 238U/ 204Pb) garnet-bearing mantle source.

Specific features of the crystal chemistry of lamprophyllite-group minerals (LGMs) are discussed using the available literature data and the results of the single-crystal X-ray diffraction and a Raman spectroscopic studies of several samples taken from the Murun alkaline complex (Russia), and Rocky Boy and Gordon Butte pegmatites (USA) presented here. The studied samples are unique in their chemical features and the distribution of cations over structural sites. In particular, the sample from the Gordon Butte pegmatite is a member of the barytolamprophyllite–emmerichite solid solution series, whereas the samples from the Murun alkaline complex and from the Rocky Boy pegmatite are intermediate members of the solid solution series formed by lamprophyllite and a hypothetical Sr analogue of emmerichite. The predominance of O2−over OH−and F−at theXsite is a specific feature of sample Cha-192 from the Murun alkaline complex. New data on the Raman spectra of LGMs obtained in this work show that the wavenumbers of the O—H stretching vibrations depend on the occupancies of theM2 andM3 sites coordinating with (OH)−groups. Cations other than Na+and Ti4+(mainly, Mg and Fe3+) can play a significant role in the coordination of theXsite occupied by (OH)−. Data on polarized Raman spectra of an oriented sample indicate that the OH groups having different local coordinations have similar orientations with respect to the crystal. The calculated measures of similarity (Δ) for lamprophyllite and ericssonite are identical (0.157 and 0.077 for the 2M- and 2O-polytypes, respectively), which indicates that these minerals are crystal-chemically isotypic and probably should be considered within the same mineral group by analogy to the other mineralogical groups which combine isotypic minerals.

Lamprophyric (lamproitic) diatremes in Chompolo field, NE Aldan shield, Siberia dated 132 Ma contain abundant mantle xenocrysts studied by EPMA and LA-ICP-MS. The deepest rocks ~6.5 GPa determined with thermobarometry are phlogopite eclogites. Thermobarometry on pyrope garnets, Cr-diopside and chromites yield a relatively low-temperature geotherm of 35 mW/m2 at the base to 55 mW/m2 at the Moho, while orthopyroxenes give 55 mW/m2. Amphiboles vary from magmatic Cr-hornblendes to metasomatic richterites. Trace element patterns for the host monchiquite are inclined with HFSE minima and are common for all Aldan lamprophyres but there are also more strongly inclined lamproitic varieties with ten times higher LREE contents. The geochemistry of Cr-diopsides, pyrope garnets and phlogopites reveal ancient multistage metasomatism of an originally depleted mantle keel related to both continental subduction and mantle plume activity. The lithospheric mantle is composed of harzburgites, roughly layered with rare dunites. Garnets appear widely at depths from 5.5 to 4.5 GPa. Trace element patterns show four groups from dunites to pyroxenites, related to low degree melting of hydrous and carbonatite melts. Clinopyroxenes reflect various melting degrees and variable trace element contents. The high-temperature orthopyroxene-based branches of the geotherm resulted from the percolation of hydrous plume-related melts. The high temperature 90 mW/m2 geotherm from 2.5 GPa to the Moho reflects fractionation of Fe-rich plume-related siliceous melts. Eclogites and metasomatites melting at the lithosphere base produce lamprophyres rich in LREE (100/C1), LILE, Zr and Ta–Nb minima. The Mg-lamproites are more LREE-enriched to 1000/C1.

We have studied variations in the structure and composition of minerals from the pipes of the Yakutian kimberlite province (YKP) in different mantle terranes of the Siberian craton. The study was based on an extensive database, including the microprobe analysis datasets consolidated by IGM, IG, IEC and IGDNM SB RAS and ALROSA and geochemical analysis of minerals performed by LA‐ICP‐MS (Laser Ablation Inductively Coupled Plasma Mass Spectrometry). The reconstruction shows layering under the tubes, including 6–7 slab that were probably formed due to subduction; the slabs are separated by pyroxenitic, eclogitic and metasomatic layers and dunite lenses. Transects and mantle profiles across kimberlite fields are constructed. Within the limits of the revealed tectonic terranes, we assume a collage of microplates formed in the early – middle Archean. Extended submeridional structures of the tectonic terranes are not always confirmed at the mantle level. Beneath the Anabar and Aldan shields, the mantle sections show more coarse layers and 3–4 large horizons of dunites with garnet and pyroxene nests separated by ilmenite‐ phlogopite metasomatites and pyroxenites. Terranes representing the suture zones between the protocratons (e.g. Khapchan) are often saturated with eclogites and pyroxenites that may occur as leghthy ascending bodies of magmatic eclogites penetrating through the mantle lithosphere structure (ML). A nearly ubiquitous pyroxenite layer at the level of 3.5–4.5 GPa formed probably in the early Archean with a high heat flux during melting of eclogites and was subsequently traced by plume melts. Within the early Archean protocratons – granite‐greenstone terranes (Tungus, Markha, Berekta, and Sharyzhalgai, ~3.8–3.0 Gyr [ Gladkochub et al., 2019 ], the mantle lithosphere is less depleted and largely metasomatized. The ML structure of the Daldyn and Magan granulite‐orthogneiss terranes is layered with folding revealed in the north‐to‐south sections from the Udachnaya pipe to the Krasnopresnenskaya pipe, which is less pronounced in the latitudinal direction. From the Daldyn field to the Alakit field, there is an increase in the degree of metasomatism, and higher alkalinity of pyroxenes and larger amounts of phlogopite are noted. The most productive Aikhal and Yubileinaya pipes are confined to a dunite core, which is accompanied by a change in the specialization of high‐charge elements Ta‐Nb to Zr‐Hf. Within the limits of the Magan terrane, the thin‐layer structure of the middle and upper parts of the craton keel is replaced with a sharply depleted productive horizon at its base. The mantle of the granite‐greenstone Markha terrrein comprises eclogite (often pelitic) horizons, which suggests subduction of the continental lithosphere or sediments. In the central and northern parts of the Siberian craton, most structures in the mantle are sinking to the west at small angles. The geochemistry features of garnets and pyroxenes from various mantle terranes are considered in detail.

The Ilmeno–Vishnevogorsk (IVC), Buldym, and Chetlassky carbonatite complexes are localized in the folded regions of the Urals and Timan. These complexes differ in geochemical signatures and ore specialization: Nb-deposits of pyrochlore carbonatites are associated with the IVC, while Nb–REE-deposits with the Buldym complex and REE-deposits of bastnäsite carbonatites with the Chetlassky complex. A comparative study of these carbonatite complexes has been conducted in order to establish the reasons for their ore specialization and their sources. The IVC is characterized by low 87Sr/86Sri (0.70336–0.70399) and εNd (+2 to +6), suggesting a single moderately depleted mantle source for rocks and pyrochlore mineralization. The Buldym complex has a higher 87Sr/86Sri (0.70440–0.70513) with negative εNd (−0.2 to −3), which corresponds to enriched mantle source EMI-type. The REE carbonatites of the Chetlassky complex show low 87Sr/86Sri (0.70336–0.70369) and a high εNd (+5–+6), which is close to the DM mantle source with ~5% marine sedimentary component. Based on Sr–Nd isotope signatures, major, and trace element data, we assume that the different ore specialization of Urals and Timan carbonatites may be caused not only by crustal evolution of alkaline-carbonatite magmas, but also by the heterogeneity of their mantle sources associated with different degrees of enrichment in recycled components.

The paper presents data on the chemical composition of pyroxenes from ultrabasic and alkaline rocks of Inagli massif (Aldan Shield). It is found that the composition of pyroxenes of a series of chromium-bearing diopside—diopside—aegirine changes from early to late differentiates in accordance with the evolution of the magmatic melt from which the rocks crystallized as a result of fractional crystallization. It is shown that crystallization differentiation was the main mechanism of dunite formation in the Inagli massif. Separation of the early crystallized phase of dunites led to the accumulation of a more alkaline residual melt from which alkaline-basic and alkaline rocks of the Inagli massif were formed as a result of fraction crystallization. Part of the residual interstitial melt was pressed into cooling cracks or formed in situ as small veins and nests of chromium-bearing diopside. The main series of bodies of chromium-bearing diopside pyroxenites, in some places enriched with phlogopite, was formed by the introduction of pyroxenite residual melt on large cracks formed in dunites after their crystallization. The magmatic scheme of sequential crystallization of rocks of the massif is proposed.

Minerals from mantle xenoliths in the Zapolyarnaya pipe in the Upper Muna field, Russia and from mineral separates from other large diamondiferous kimberlite pipes in this field (Deimos, Novinka and Komsomolskaya-Magnitnaya) were studied with EPMA and LA-ICP-MS. All pipes contain very high proportions of sub-calcic garnets. Zapolyarnaya contains mainly dunitic xenoliths with veinlets of garnets, phlogopites and Fe-rich pyroxenes similar in composition to those from sheared peridotites. PT estimates for the clinopyroxenes trace the convective inflection of the geotherm (40&ndash, 45 mW&middot, m&minus, 2) to 8 GPa, inflected at 6 GPa and overlapping with PT estimates for ilmenites derived from protokimberlites. The Upper Muna mantle lithosphere includes dunite channels from 8 to 2 GPa, which were favorable for melt movement. The primary layering deduced from the fluctuations of CaO in garnets was smoothed by the refertilization events, which formed additional pyroxenes. Clinopyroxenes from the Novinka and Komsomolskaya-Magnitnaya pipes show a more linear geotherm and three branches in the P-Fe# plot from the lithosphere base to the Moho, suggesting several episodes of pervasive melt percolation. Clinopyroxenes from Zapolyarnaya are divided into four groups according to thermobarometry and trace element patterns, which show a stepwise increase of REE and incompatible elements. Lower pressure groups including dunitic garnets have elevated REE with peaks in Rb, Th, Nb, Sr, Zr, and U, suggesting mixing of the parental protokimberlitic melts with partially melted metasomatic veins of ancient subduction origin. At least two stages of melt percolation formed the inclined PT paths: (1) an ancient garnet semi-advective geotherm (35&ndash, 2) formed by volatile-rich melts during the major late Archean event of lithosphere growth, and (2) a hotter megacrystic PT path (Cpx-Ilm) formed by feeding systems for kimberlite eruptions (40&ndash, 2). Ilmenite PT estimates trace three separate PT trajectories, suggesting a multistage process associated with metasomatism and formation of the Cpx-Phl veinlets in dunites. Heating associated with intrusions of protokimberlite caused reactivation of the mantle metasomatites rich in H2O and alkali metals and possibly favored the growth of large megacrystalline diamonds.

The structural model and chemical composition of vlasovite from the Burpala massif (Russia) have been determined using X-ray diffraction methods and electron probe microanalysis. The crystal structure has been refined in the sp. gr. Cc to R = 1.4% (Rw = 1.8%) with the following unit-cell parameters: a = 11.0396(3) A, b = 10.1042(2) A, c = 8.5696(2) A, β = 100.307(1)°, V = 940.48(4) A3, and Z = 4.

Data on mineral-hosted inclusions indicate that the charoite rocks crystallized in a heterogeneous medium of carbonate–silicate and carbonate melts, gaseous and H2O–salt fluids. Our results indicate that the early rock-forming minerals of the charoite rocks started to crystallize at high temperatures (>800°C), and crystallization may have terminated at lower temperatures (600–450°С). Data on the melt and fluid inclusions confirm the conclusion that the charoite rocks are of magmatic origin. The facts that these rocks are typically found as vein- and lens-shaped bodies, the composition of these rocks does not correlate with the composition of the host rocks, and the occurrence of chilled fine-grained domains of the charoite rocks also suggest that these rocks crystallized from magmatic melt.

The concentration and redistribution of ore components from a primary melt to hydrothermal fluids are important for understanding ore formation. The Mushgai-Khudag complex is a typical example of an intrusion where hydrothermal processes are widespread and where we can observe the redistribution of ore components during hydrothermal processes. In this study, we use mineralogical, melt and fluid inclusion data to trace element characteristics of apatite from the Mushgai-Khudag complex to reconstruct the formation of the magnetite-apatite rocks and their magmatic-hydrothermal evolution and to clarify the origin of the REE mineralization. We conclude that the magnetite-apatite rocks crystallized from salt melt with a high content of phosphate and sulfate components at a temperature of approximately 830–850 °C. The origin of magnetite-apatite rocks probably can be explained by the silicate-salt immiscibility that occurred at the alkaline syenite crystallization stage. Further evolution of the salt melt to the brine of the carbonate-(fluoride)-chloride-sulfate composition was accompanied by the barite, celestite and monazite-Ce formation at the temperature of approximately 500–580 °C. The dissolution of apatite and the crystallization of gypsum, phosphosiderite and monazite-Ce pseudomorphs after apatite took place at the hydrothermal stage after a reaction with a fluid that evolved from carbonate-chloride-sulfate (at 250–350 °C) into a predominantly chloride composition (at 150–250 °C). The high activity of the sulfate component and a significant enrichment of the rocks in REE also occurred at the late hydrothermal stage.

The Paleoproterozoic Seligdar magnesiocarbonatite intrusion of the Aldan-Stanovoy shield in Russia underwent extensive postmagmatic hydrothermal alteration and metamorphic events. This study comprises new isotopic (Sr, Nd, C and O) data, whole-rock major and trace element compositions and trace element characteristics of the major minerals to gain a better understanding of the source and the formation process of the carbonatites. The Seligdar carbonatites have high concentrations of P2O5 (up to 18 wt%) and low concentrations of Na, K, Sr and Ba. The chondrite-normalized REE patterns of these carbonatites display significant enrichments of LREE relative to HREE with an average La/Ybcn ratio of 95. Hydrothermal and metamorphic overprints changed the trace element characteristics of the carbonatites and their minerals. These alteration processes were responsible for Sr loss and the shifting of the Sr isotopic compositions towards more radiogenic values. The altered carbonatites are further characterized by distinct 18O- and 13C-enrichments compared to the primary igneous carbonatites. The alteration most likely resulted from both the percolation of crustal-derived hydrothermal fluids and subsequent metamorphic processes accompanied by interaction with limestone-derived CO2. The narrow range of negative eNd(T) values indicates that the Seligdar carbonatites are dominated by a homogenous enriched mantle source component that was separated from the depleted mantle during the Archean.

The origin of high-Mg melts remains one of the most highly debated questions in igneous petrology. There are two contrasting points of view, namely, (1) melt initiation in a rising high-temperature plume, and (2) mantle melting due to fluxing by water. To address this question we determined H2O, CO2, F, Cl and S concentrations in olivine-hosted melt inclusions of high-Mg volcanic rocks of the Siberian Traps Large Igneous Province that bracket the main pulse of volcanism at about 252–250 Ma, and can be classified as melanephelinites and meimechites. Both rock types belong to the high-Ti rock series. Correcting measured H2O, CO2, F, Cl and S concentrations in homogenized primary meimechite melt inclusions to primary meimechite melt composition using experimental melt compositions resulted in corrected melt-inclusion, volatile compositions of ˜3.88 wt% H2O, ˜1477 ppm CO2, ˜4214 ppm F, ˜2.08 wt% Cl and ˜2490 ppm S. These values are viewed as minimum estimates for the original volatile concentrations in the melt because of the high probability for degassing during melt crystallization and/or during experiment homogenization. Olivine-hosted homogenized melt inclusions from melanephelinites yielded lower corrected concentrations of ˜1.06 wt% H2O, ˜998 ppm CO2, ˜3242 ppm F, ˜607 ppm Cl and ˜2131 ppm S. We also measured water concentrations in clinopyroxenes of melanephelinites by FTIR, obtaining values as high as 133 ppm H2O, which corresponds to 0.91 wt% in the melt, in general agreement with data obtained by SIMS on the olivine-hosted melt inclusions. Olivine grains from melanephelinites are characterized by evolved compositions (Fo 0.80–0.86). Extrapolation to a primitive melanephelinite melt by simple fractional crystallization suggests that it could also contain high H2O concentrations (up to ˜ 3 wt%). Analyzed meimechite and melanephelinite whole-rock samples are characterized by trace-element patterns that are typical of mantle-derived melts and by Sr-Nd isotope ratios that exclude crustal contamination or derivation from ancient lithospheric mantle. Thus, high volatile concentrations can be attributed to sublithospheric mantle source regions. This supports the notion that high-Mg melts form by volatile fluxing of the asthenospheric mantle rather than by decompression melting under relatively dry conditions of a rising abnormally high-temperature mantle plume.

The unique Aldan ore-magmatic province in Yakutia is characterized by Mesozoic alkaline magmatism and related ore deposits (Cu-Au porphyry, gold-quartz vein and gold-brannerite). The Murunskiy alkaline massif occurs in the western part of this province. This massif includes the world's largest volcanic-plutonic complex of potassium-alkaline rocks and has no analogs in the world. High agpaitic indexes are common for all magmatic rocks of the massif. Moreover, the massif is well known for its unique Ba-Sr carbonatite and charoite rocks. We have studied the fluid regime of a post-magmatic formation of rutile and anatase-brookite quartz veins with pyrite, galena, sphalerite, chalcopyrite, native gold and the titanium mineralization. Fluid inclusions study shows that the titanium mineralization was formed at the temperature range of 475–440 °C and pressure between 150 and 125 MPa from heterogeneous chloride-carbonate-sulfate fluid. The immiscible fluid fractions were represented by gaseous phase, low- and middle-concentrated solutions, as well as highly concentrated salt brine. Mineral-forming fluids were characterized by high redox-potential, due to the high concentration of sulfates. The immiscible fluid fractions differ in the content of ore elements. Highly concentrated fluid fractions contain increased concentrations of S, Cu, Mo, Fe, Pb, Zn, U, and Au, and low-concentrated fluid fractions containing U, Th, As, and Au.

Charoite is a unique mineral and a rock of the same name. It is known from the only deposit in the world at the contact with Early Cretaceous syenite and other alkaline rocks of the Malyi Murun massif. The data on 40Ar/39Ar dating of tinaksite, tokkoite, and frankamenite associated with charoite are reported in this paper. All these minerals, except for frankamenite, have shown clear plateau ages overlapping with each other within the analytical errors. The weighted mean of the plateau ages of tinaksite, tokkoite, and microcline is 135.86 ± 0.26 Ma. Considering that these minerals are syngenetic to charoite, this age is the time of charoite crystallization. Frankamenite with an older age (137.55 ± 0.46 Ma) may reflect the polychronous crystallization of the charoite association.

The U–Pb (ID TIMS) geochronological studies of single zircon grains and their fragments have made it possible to establish that rare-metal alkaline granites of the Katugin massif (2055 ± 7‒2066 ± 6 Ma) underwent high-temperature transformations at age levels of ~1921 ± 5 and 1876 ± 7 Ma.

Geochemical and U–Pb geochronological studies have shown that the alkali syenites of the China massif have an age of 311.4 ± 1.8 Ma and potassic specialization in contrast to most massifs of the Vitim alkaline-magmatism zone. The rocks are similar in geochemistry to the nepheline syenites of the Synnyr massif, dated at 289.5 ± 3.5 Ma. The alkali syenites of the China massif formed, most likely, from crustal protoliths.

New versions of the universal Jd-Di exchange clinopyroxene barometer for peridotites, pyroxenites and eclogites, and also garnet barometer for eclogites and peridotites were developed. They were checked using large experimental data sets for eclogitic (∼530) and peridotitic systems (>650). The precision of the universal Cpx barometer for peridotites based on Jd-Di exchange is close to Cr-Tschermakite method produced by Nimis and Taylor (2000). Cpx barometer was transformed by the substitution of major multiplier for KD by the equations dependent from Al-Na-Fe. Obtained equation in combination with the thermometer of Nimis and Taylor (2000) allow to reconstruct position of the magma feeder systems of the alkali basaltic magma within the mantle diapirs in modern platforms like in Vitim plateau and other Southern Siberia localities and several localities worldwide showing good agreement of pressure ranges for black and green suites. These equations allow construct PTX diagrams for the kimberlite localities in Siberia and worldwide calculating simultaneously the PT parameters for different groups of mantle rocks. They give very good results for the concentrates from kimberlite lamproites and placers with mantle minerals. They are useful for PT estimates for diamond inclusions. The positions of eclogite groups in mantle sections are similar to those determined with new Gar–Cpx barometer produced by C. Beyer et al. (2015). The Fe rich eclogites commonly trace the boundary between the lower upper parts of subcontinental lithospheric mantle (SCLM) at 3–4 GPa marking pyroxenite eclogites layer. Ca-rich eclogites and especially grospydites in SCLM beneath Precambrian kimberlites occurs near pyroxenite layer but in younger mantle sections they became common in the lower parts. The diamondiferous Mg Cr-less group eclogites referring to the ancient island arc complexes are also common in the middle part of mantle sections and near 5–6 GPa. Commonly eclogites in lower apart of mantle sections are remelted and trace the high temperature convective branch. The Mg- and Fe-rich pyroxenites also show the extending in pressure trends which suggest the anatexic melting under the influence of volatiles or under the interaction with plums.

The structures of tokkoite, K2Ca4[Si7O18OH](OH,F) and tinaksite, K2Ca2NaTi[Si7O18OH]O from the Murun massif (Russia) were refined from single-crystal X-ray diffraction data in the triclinic space groupP1̄. Average crystallographic data area≈ 10.423,b≈ 12.477,c≈ 7.112 Å, α ≈ 89.92°, β ≈ 99.68°, γ ≈ 92.97°,V≈ 910.5 Å3for tokkoite;a≈ 10.373,b≈ 12.176,c≈ 7.057 Å, α ≈ 90.82°, β ≈ 99.22°, γ ≈ 92.80°,V≈ 878.5 Å3for tinaksite. The substantial similarities between the geometrical parameters of the tokkoite and tinaksite structures led us to conclude that the two minerals are isostructural. However, major differences of tokkoite with respect to tinaksite are larger lattice constants, especially concerning thebparameter, longer distances, especially ; larger values of the M1–M3 and O20–O2 bond lengths, and a stronger distortion of the M1 polyhedron. Mössbauer analysis showed that significant trivalent iron is present,VIFe3+40.0(7)% in tokkoite and 12.8(3)% in tinaksite. It is confirmed that 2Ca(M1+M2)2++ (F,OH)(O20)–↔ Ti(M1)4++ Na(M2)++ O(O20)–is the exchange reaction that describes the relation between tokkoite and tinaksite. In addition, this exchange reaction causes local stress involving mainly the M1 site and its interaction with the M2 and M3 sites.

Zarnitsa kimberlite pipe in Central Yakutia contains pyrope garnets with Cr2O3 ranging from 9 to 19.3 wt% derived from the asthenospheric mantle. They show mostly S-shaped, inflected rare earth element (REE) patterns for dunitic and harzburgitic, lherzolitic and harzburgitic varieties and all are rich in high field strength elements (HFSE) due to reaction with protokimberlite melts. Lithospheric garnets ( 50 mWm−2) at 6–9 GPa, and a stepped HT geotherm with heated pyroxenite lenses at four levels from 6.5 to 3.5 GPa. Parental melts calculated with KDs suggest that augites and high-Cr garnets in the lithosphere base reacted with essentially carbonatitic melts while garnets from lower pressure show subduction peaks in U, Ba and Pb. The roots of the Zarnitsa pipe served to transfer large portions of deep (>9 GPa) protokimberlite melts to the lithosphere. Smaller diamonds were dissolved due to the elevated oxidation state but in peripheral zones large diamonds could grow.

Three types of carbonatites have been identified based on the analysis of alkaline complexes using geological, petrological, and geochemical data. It has been suggested that for distinguishing carbonatite complexes into these three types, the following criteria should be used: a) the alkalinity type (Na- or K- richer primary magmas) and b) the time when the carbonatite liquid separates from silicate melts in different stages of primary magma differentiation. The first type is genetically related to the kimberlite magmatism and the carbonatite liquid separates from ultramafic magma. The second type is associated with Na-rich alkaline ultramafic rocks and the carbonatite component separates when pyroxenites and ijolites crystallize. The third type is related to K-alkaline complexes and the carbonatite component separates when syenites and granites crystallize. In this article we discuss the geochemical characteristics of all 3 types and outline the difference between them. A model for the formation of carbonatite complexes under the influence of mantle plume processes is given. The geochemistry of C, O, Sr, and Nd isotopes shows that carbonatite complexes, depending on their geotectonic setting (platform surrounding, orogenic areas and rift zones) can originate from three types of mantle sources: depleted mantle, enriched mantle 1 (EM1), and enriched mantle 2 (EM2).

The Arbarastakh Neoproterozoic ultramafic carbonatite complex is located in the southwestern part of the Siberian Craton (Aldan Shield) and contains ore-bearing Zr–Nb (REE) carbonatites and phoscorites. Carbonatites are mainly represented by calcite and silicocarbonatite varieties. The primary minerals composing the carbonatites are calcite and dolomite, as well as phlogopite, clinopyroxene, fluorapatite, amphibole, fluorite, K-feldspar and feldspathoids. Olivine (forsterite), Ti-magnetite, apatite, phlogopite, calcite, dolomite and the minor spinel group minerals form the primary phoscorites. The ore-bearing Zr–Nb mineral assemblages of the phoscorites and carbonatites include accessory zircon, zirconolite, perovskite, pyrochlore and baddeleyite. The Ba–Sr–REE hydrothermal mineralisation consists of ancylite-(Ce), bastnaesite-(Ce) and burbankite, as well as barite-celestite, strontianite, barytocalcite, and rare Cu–Fe sulphides. The silicocarbonatites and carbonatites formed in multiple stages from a single alkaline Ca–Na–K–silicocarbonatite melt, while the phoscorites are products of differentiation of the carbonatitic melt and were crystallised from an Fe-rich phosphate–carbonate melt at temperatures of more than 720 °C. The silicate–phosphate–carbonate melts were responsible for the Zr–Nb mineralisation of the carbonatites at temperatures of more than 540–575 °C; the hydrothermal REE-bearing mineral assemblages crystallised from saline (60–70 wt%) carbonatitic fluids of Na–Ca–Mg–F–carbonate composition at a minimum temperature range of 350–300 °C. The Ca–Sr-carbonate as well as the Na–hydro–carbonate fluids were responsible for the Ba–Sr–REE mineralisation of the phoscorites at ~500–480 and 450–430 °C.

Mantle xenocrysts from early Triassic kimberlite pipes from Kharamai, Ary-Mastakh and Kuranakh fields in the Anabar shield of Siberia revealing similar compositional trends were studied to estimate the superplume influence on the subcratonic lithosphere mantle (SCLM). Pressure-temperature (PT) reconstructions using monomineral thermobarometry for 5 phases show division of the SCLM beneath the Kharamai field into 6 units: pyroxenitic Fe-rich (1–2 GPa) and Mg-rich (2–3 GPa) layers; middle with two levels of Gar-Sp pyroxenites at ∼3 and 4–5 GPa; Gar-dunite–harzburgites ∼4.5–6.5 GPa subjected to Ilm-Px vein metasomatism; and a Mg-rich dunite lower part. In the Anabar shield (Ary-Mastakh, Dyuken and Kuranakh fields) mantle lithosphere is composed of three large units divided into two parts: upper part with amphiboles and phlogopite; two levels of pyroxenites and eclogites at 3 and 4 GPa, and a lower part composed of refertilized dunites. Diagrams showing P-Fe # Gar clusters for garnets and omphacites illustrate the differences between SCLM of these localities. Differences of Triassic SCLM from Devonian SCLM are in simple layering; abundance of Na-Cr-amphiboles and metasomatism in the upper SCLM part, thick pyroxenite-eclogite layer and lower part depletion, heated from SCLM base to 5.0 GPa. Kharamai mantle clinopyroxenes represent three geochemical types: (1) harzburgitic with inclined linear REE, HFSE troughs and elevated Th, U; (2) lherzolitic or pyroxenitic with round TRE patterns and decreasing incompatible elements; (3) eclogitic with Eu troughs, Pb peak and high LILE content. Calculated parental melts for garnets with humped REE patterns suggest dissolution of former Cpx and depression means Cpx and garnets extraction. Clinopyroxenes from Ary-Mastakh fields show less inclined REE patterns with HMREE troughs and an increase of incompatible elements. Clinopyroxenes from Kuranakh field show flatter spoon-like REE patterns and peaks in Ba, U, Pb and Sr, similar to those in ophiolitic harzburgites. The PT diagrams for the mantle sections show high temperature gradients in the uppermost SCLM accompanied by an increase of P-Fe # Ol upward and slightly reduced thickness of the mantle keel of the Siberian craton, resulting from the influence of the Permian–Triassic superplume, but with no signs of delamination.

This paper discusses the genesis of large Siberian alkaline massifs hosting major ore deposits. These reference massifs are grouped based on the predominance of alkalies (K or Na) and their agpaitic index (miaskitic and agpaitic). We proposed new emplacement schemes for the Tomtor, Murun, Burpala, Synnyr, and Bilibino massifs supported by petrochemical and geochemical data, as well as new age estimates. Types of their ore potential and genesis of rare-metal mineralization are discussed. The formational types of carbonatites as the main ore-bearing rocks are given. The depth of magma generation and types of mantle sources are determined using isotopic data from previous studies. A model of plume-related generation of ultramafic alkaline magmas is proposed.

The Mushgai-Khudag complex is part of the Late Mesozoic Central Asian carbonatite province. Fluorite mineralization is manifested throughout the province, including the Mushgai-Khudag complex. We have investigated the geochemical features and fluid inclusions of fluorites from different types of fluorite-bearing rocks. Fluorite from quartz-fluorite rocks has rare earth element (REE) concentrations in the range of 10500−144300 ppm and the highest light REE contents, with (La/Yb)N = 56−960. Fluorite from the fluorite-apatite-celestine rocks has slightly lower REE enrichment, especially light REE content, with concentrations of 200−5900 ppm and (La/Yb)N = 18−204. Fluorite from the fluorite-calcite rocks is characterized by REE contents of 22−1100 ppm and a variable (La/Yb)N of 0.6−59. These variations in the fluorite REE composition from different types of rocks were probably caused by the fact that at elevated temperatures, fluorine-containing light REE complexes are more stable than fluorine-containing heavy REE complexes. The progressive enrichment of medium and heavy REEs in the latter fluorite is related to fluid evolution. The homogenization temperature and salinity values of fluid inclusions in the Mushgai-Khudag fluorites vary between 550 and 185 °C and from rather high to 2 wt.%, respectively. The parental fluids of the fluorite-bearing rocks evolved from quartz-fluorite rocks to fluorite-apatite-celestine rocks to fluorite-calcite rocks. The key component was changed from sulfate to carbonate-chloride along with the high to medium temperature decrease (∼500−245 °C).

The Mushgai-Khudag alkaline‑carbonatite complex, located in southern Mongolia within the Central Asian Orogenic Belt (CAOB), comprises a broad range of volcanic and subvolcanic alkaline silicate rocks (melanephelinite-trachyte and shonkinite-alkaline syenite, respectively). Magnetite-apatite rocks, carbonatites, and fluorite mineralization are also manifested in this area. The complex formed between 145 and 133 Ma and is contemporaneous with late Mesozoic alkaline–carbonatite magmatism within the CAOB. Major and trace element characteristics of silicate rocks in the Mushgai-Khudag complex imply that these rocks were formed by the fractional crystallization of alkaline ultramafic parental magma. Magnetite-apatite rocks may be a product of silicate-Ca-Fe-P liquid immiscibility that took place during the alkaline syenite crystallization stage. The Mushgai-Khudag rocks have variable and moderately radiogenic Sr (87Sr/86Sr(i) = 0.70532–0.70614), ƐNd(t) = −1.23 to 1.25) isotopic compositions. LILE/HFSE values and Sr Nd isotope compositions indicate that the parental melts of Mushgai-Khudag were derived from a lithospheric mantle source that was affected by a metasomatic agent in the form a mixture of subducted oceanic crust and its sedimentary components. The δ18OSMOW and δ18CPDB values for calcites in carbonatites range from 16.8‰ to 19.2‰ and from −3.9‰ to 2.0‰, respectively. C O covariations in calcites of the Mushgai-Khudag carbonatites can be explained by the slight host limestone assimilation.

The Malyy (Little) Murun massif of the Aldan Shield of the Siberian Craton has long been a kind of Siberian Mecca for geologists. It has attracted thousands of geologists, prospectors, and mineral collectors despite its remote location. It is famous for a dozen new and rare minerals, including the gemstones charoite and dianite (the latter is the market name for strontian potassicrichrerite), as well as for a range of uncommon alkaline igneous rocks. Despite this, the age of the Malyy Murun igneous complex and associated metasomatic and hydrothermal mineral associations has remained poorly constrained until now. In this paper, we provide extensive 40Ar/39Ar geochronological data to reveal its age and temporal history. It appears that, although unique in terms of rocks and constituent minerals, the Malyy Murun is just one of multiple alkaline massifs and lavas emplaced in the Early Cretaceous (~137&ndash, 128 Ma) within a framework of the extensional setting of the Aldan Shield and nearby Transbaikalian region. The extension took place 40&ndash, 60 million years after the supposed closure of the Mongolia&ndash, Okhotsk Ocean and orogenic peak in the Early&ndash, Middle Jurassic.

Isotope–Geochemical Sm–Nd studies of the Early Proterozoic alkaline granites of the Katugan complex (Aldan shield) were carried out. The unique Katugan rare metals (Ta, Nb, Zr, Y, and REE) deposit is confined to these granites. Parent melts of the granites are of mantle–crustal nature.

The high-temperature behavior of bafertisite was studied by combination of techniques in order to characterize the temperature-induced iron oxidation associated with deprotonation of an octahedral layer. The chemical formula of bafertisite from Darai-Pioz alkaline complex (Tajikistan) determined by electron-microprobe analyzes and Mossbauer spectroscopy is Ba 2.11(Fe ${}_{2.70}^{2+}$ Fe ${}_{0.17}^{3+}$ Mn 1.09Zr 0.04Na 0.03) (Ti 1.96Nb 0.07)(Si 2 O 7)2 O 2(OH 1.29 O 0.65 F 0.06)F 2. In situ high-temperature powder X-ray diffraction revealed abrupt shift of reflections to the high-angle region and reduction of their intensity at T > 525 ∘C. The Mossbauer spectroscopy studies indicated that the crystal structure of bafertisite contains Fe in octahedral sites as predominantly ferric ions with Fe 3+/ ΣFe = 0.06, whereas bafertisite annealed at T = 600 ∘C has Fe in the same position with Fe 3+/ ΣFe up to 0.39. The differential scanning calorimetry and thermogravimetric analyzes reveal the occurrence of a broad exothermic effect at T ∼ 537 ∘C associated with the mass loss corresponding to deprotonation. Since in the studied sample of bafertisite, Fe 2+ apfu strongly prevails over OH apfu, the stoichiometric (charged-balanced) high-temperature oxidized modification cannot be obtained. In the paper, the high-temperature behavior of bafertisite is discussed and compared to that of astrophyllite.

The results of a combined electron probe microanalysis, single-crystal X-ray diffraction, and Fourier transform infrared study of a crystal of armstrongite from Khan Bogdo deposit (Gobi, Mongolia) are reported. Major element analysis provided (wt%): CaO 9.2(1), ZrO2 20.9(2), and SiO2 62.5(2). Significant concentrations of REE (0.45 wt%) were also detected. From single-crystal structural refinement, armstrongite resulted monoclinic [space group C2/m, a = 14.0178(7), b = 14.1289(6), c = 7.8366(3) A, b = 109.436(3)°, V = 1463.6(1) A 3 , Z = 4] and twinned with two individuals rotated around a twin twofold axis parallel to [100]. The analyzed crystal was refined up to R = 3.3% (Rw = 2.9%). The structural refinement showed that the investigated armstrongite has only two water groups per formula unit consistent with the infrared analysis. Indeed, the occurrence in the infrared spectrum of the armstrongite (here reported for the first time) of two bending vibration bands at about 1640 and 1610 cm –1 testifies to the presence of two water groups environments. The results of this integrated approach converged to the following empirical formula (based on Si = 6 atoms per formula unit): (Ca0.96Ce0.01Yb0.01)Zr0.99Si6O14.97·2.02H2O. Finally, the studied mineral shows a framework density (FD = 21.86) lying in the range of zeolites and microporous heterosilicates with tetrahedral-octahedral frameworks. The determined crystal chemical features are relevant for the possible employment of this mineral or of its synthetic analogs for technological applications.

Major and trace element variations in picroilmenites from Late Devonian kimberlite pipes in Siberia reveal similarities within the region in general, but show individual features for ilmenites from different fields and pipes. Empirical ilmenite thermobarometry (Ashchepkov et al., 2010), as well as common methods of mantle thermobarometry and trace element geochemical modeling, shows long compositional trends for the ilmenites. These are a result of complex processes of polybaric fractionation of protokimberlite melts, accompanied by the interaction with mantle wall rocks and dissolution of previous wall rock and metasomatic associations. Evolution of the parental magmas for the picroilmenites was determined for the three distinct phases of kimberlite activity from Yubileynaya and nearby Aprelskaya pipes, showing heating and an increase of Fe# (Fe# = Fe / (Fe + Mg) a.u.) of mantle peridotite minerals from stage to stage and splitting of the magmatic system in the final stages. High-pressure (5.5–7.0 GPa) Cr-bearing Mg-rich ilmenites (group 1) reflect the conditions of high-temperature metasomatic rocks at the base of the mantle lithosphere. Trace element patterns are enriched to 0.1–10/relative to primitive mantle (PM) and have flattened, spoon-like or S- or W-shaped rare earth element (REE) patterns with Pb > 1. These result from melting and crystallization in melt-feeding channels in the base of the lithosphere, where high-temperature dunites, harzburgites and pyroxenites were formed. Cr-poor ilmenite megacrysts (group 2) trace the high-temperature path of protokimberlites developed as result of fractional crystallization and wall rock assimilation during the creation of the feeder systems prior to the main kimberlite eruption. Inflections in ilmenite compositional trends probably reflect the mantle layering and pulsing melt intrusion during melt migration within the channels. Group 2 ilmenites have inclined REE enriched patterns (10–100)/PM with La / Ybn ~ 10–25, similar to those derived from kimberlites, with high-field-strength elements (HFSE) peaks (typical megacrysts). A series of similar patterns results from polybaric Assimilation + fractional crystallization (AFC) crystallization of protokimberlite melts which also precipitated sulfides (Pb < 1) and mixed with partial melts from garnet peridotites. Relatively low-Ti ilmenites with high-Cr content (group 3) probably crystallized in the metasomatic front under the rising protokimberlite source and represent the product of crystallization of segregated partial melts from metasomatic rocks. Cr-rich ilmenites are typical of veins and veinlets in peridotites crystallized from highly contaminated magma intruded into wall rocks in different levels within the mantle columns. Ilmenites which have the highest trace element contents (1000/PM) have REE patterns similar to those of perovskites. Low Cr contents suggest relatively closed system fractionation which occurred from the base of the lithosphere up to the garnet–spinel transition, according to monomineral thermobarometry for Mir and Dachnaya pipes. Restricted trends were detected for ilmenites from Udachnaya and most other pipes from the Daldyn–Alakit fields and other regions (Nakyn, Upper Muna and Prianabarie), where ilmenite trends extend from the base of the lithosphere mainly up to 4.0 GPa. Interaction of the megacryst forming melts with the mantle lithosphere caused heating and HFSE metasomatism prior to kimberlite eruption.

Textural, mineralogical and geochemical data on F-rich rhyolite (ongonite) from the Ary-Bulak massif of eastern Transbaikalia help constrain the formation of magmatic topaz. In these rocks, topaz occurs as phenocrysts, thus providing compelling evidence for crystallisation at the orthomagmatic stage. Cathodoluminescence images of topaz and quartz reveal growth textures with multiple truncation events in single grains, indicative of a dynamic system that shifted from saturated to undersaturated conditions with respect to topaz and quartz. Electron microprobe and Raman analyses of topaz indicate near-pure F composition [Al2SiO4F2], with very limited OH replacement. Laser ablation ICP-MS traverses revealed the presence of a large number of trace elements present at sub-ppm to hundreds of ppm levels. The chemical zoning of topaz records trace element fluctuations in the coexisting melt. Concentrations of some trace elements (Li, Ga, Nb, Ta and W) are correlated with cathodoluminescence intensity, thus suggesting that some of these elements act as CL activators in topaz. The study of melt inclusions indicates that melts with different F contents were trapped at different stages during formation of quartz and topaz phenocrysts, respectively. Electron microprobe analyses of glass in subhedral quartz-hosted melt inclusions indicate F ≤ 1.2 wt.%, whereas irregular-shaped melt inclusions hosted in both topaz and quartz have F ≤ 9 wt.%. Cryolithionite [Na3Li3Al2F12] coexists with glass in irregular inclusions, implying high Li contents in the melt. The very high F contents would have increased the solubility of Nb, Ta and W in the melt, thus allowing progressive concentration of these elements during magma evolution. Crystallisation of Nb–Ta–W-oxides (W-ixiolite and tantalite–columbite) may have been triggered by separation of cryolithionite, which would have caused F and Li depletion and consequent drop in the solubility of these elements.

The Burpala alkaline massif is a unique geological object. More than 50 Zr, Nb, Ti, Th, Be, and REE minerals have been identified in rare-metal syenite of this massif. Their contents often reach tens of percent, and concentrations of rare elements in rocks are as high as 3.6% REE, 4% Zr, 0.5% Y, 0.5% Nb, 0.5% Th, and 0.1% U. Geological and geochemical data show that all rocks in the Burpala massif are derivatives of alkaline magma initially enriched in rare elements. These rocks vary in composition from shonkinite, melanocratic syenite, nepheline and alkali syenites to alaskite and alkali granite. The extreme products of magma fractionation are rare-metal pegmatites, apatite-fluorite rocks, and carbonatites. The primary melts were related to the enriched EM-2 mantle source. The U-Pb zircon ages of pulaskite (main intrusive phase) and rare-metal syenite (vein phase) are estimated at 294 ± 1 and 283 ± 8 Ma, respectively. The massif was formed as a result of impact of the mantle plume on the active continental margin of the Siberian paleocontinent.

This paper presents the results of geochronological studies of the Tomtor alkaline-ultramafic pluton, one of the largest Nb, Y, Sc, and TR deposits. A new scheme of its magmatism is given. The current K-Ar and Rb-Sr ages of different igneous rocks of the Tomtor pluton range from 800 to 250 Ma [Zaitsev et al., 1992; Frolov et al., 2003]. Such dispersion is probably related to the intense carbonatization of the rocks. The U-Pb zircon and 40Ar/39Ar mica ages indicate two stages of the formation of the pluton (700 and 400 Ma), which agrees well with the age of cycles of rift-related tectonogenesis of the Siberian platform.

This paper presents the U-Pb zircon age of pulaskite of the main phase (294 ± 1 Ma) and the rare metal syenite (283 ± 8 Ma) of the Burpala alkaline pluton. The geochronological data show that it was formed in the Early Permian. By age, it is comparable with the Synnyr pluton of the Synnyr rift zone, alkaline granitic rocks and bimodal volcanic associations of the Uda-Vitim rift zone, and carbonatites of the Saizhen rift zone of the Central Asian foldbelt. These intraplate igneous complexes were formed almost simultaneously with crustal granitic rocks of the Angara-Vitim batholite. All of this gives ground to suppose that the origination of their parental melts is a result of the influence of the mantle hot spot or mantle plume on the lithosphere that led to extensive crustal anatexis.

The structure, structural disorder and chemistry of miserite from the charoite-bearing rocks of the Murun massif (Russia) and from alkaline-syenite pegmatitic rocks of the Dara-i-Pioz massif (Tajikistan) were investigated employing a combination of electron microprobe, single crystal diffraction and micro-Fourier transform infrared spectroscopy analysis. Chemical analysis of the sample investigated by X-ray diffraction evidenced that Dara-i-Pioz miserite has a greater REE concentration than Murun miserite (~0.22 vs. 0.05 apfu, respectively) and also contains Y (0.14 apfu), which is absent in Murun miserite. The occurrence of a band at about 1,600 cm−1 testified to the presence of H2O in miserite at hand. Structural analyses yielded average cell parameters of a = 10.092, b = 16.016, c = 7.356 A, α = 96.60°, β = 111.27° and γ = 76.34°. Anisotropic structural refinement in space group P $$\bar{1}$$ converged at similar values for the analyzed samples (R ~3.4, R w ~3.8 %). An interesting feature shown by both the miserite specimen is the presence, revealed by difference Fourier analysis, of a disordered part of the structure. This turned out to be due to the flipping of the tetrahedra belonging to the isolated [Si2O7]6− diorthogroups, one of the two radicals (the other is [Si12O30]12−) characterizing the miserite structure. The sixfold and seven-vertex Ca polyhedra linked to the inverted diorthogroups show variation in coordination number with respect to those of the ordered structure.

Earlier, a belt of alkali-granite plutons and a carbonatite province were discovered in the South Gobi Desert, Mongolia. The Lugingol pluton of pseudoleucitic syenites with carbonatites was assigned to the alkali-granite belt. However, new dating showed that it is 40 Myr younger than the Khan-Bogdo pluton and a large fault separates it from the alkali-granite belt. In the same part of the South Gobi Desert, a dike series of alkaline K-shonkinites with a rare-metal carbonatite vein was found by V.I. Kovalenko west of the Lugingol pluton, near Mt. Baruun Hasar Uula, and a dike series of alkali and nepheline syenites was found by us northeast of the Lugingol pluton. These data give grounds to distinguish an intrusive complex of K-alkaline shonkinites and leucitic syenites with Late Paleozoic REE-bearing carbonatites. Thus, three alkaline-rock complexes of different ages are distinguished in the South Gobi Desert. We present refined geological maps of these complexes. The plutons of all three complexes are deposits of trace elements (REE, Nb, Zr, Y, P). The chemical composition of the silicate rocks of the complex, rare-metal agpaitic pegmatites, and carbonatite and apatite rare-metal ores was considered in detail. Shonkinites from Mt. Baruun Hasar Uula and the Mountain Pass mine (United States) and their carbonatites, along with the Lugingol carbonatites, belong to a single association of K-alkaline rocks and carbonatites, as evidenced by their identical chemical, mineral, and geochemical rare-metal compositions. Rare-earth element patterns and spidergrams show similarities and differences between the rare-metal rocks of three complexes as well as paragenetic differences between their rare-metal minerals. A rare process is described—the amorphization of rare-metal minerals, related to their high-temperature crystallization in a medium with abnormal silica contents of the Khan-Bogdo pegmatites. The parental magmas of the alkali-carbonatite complexes were generated from the EM-2 contaminated mantle that had undergone recycling, whereas the parental magmas of the Khan-Bogdo agpaitic alkali granites were produced from depleted mantle.

Regularities of the mantle structure beneath the Siberian Craton were determined using the monomineral thermobarometry and common Opx-Gar methods. Samples were taken from 80 pipes from the Siberian Craton and in comparison 70 pipes from worldwide kimberlites. The largest pipes contain several dunite layers in the lower part of lithospheric mantle which are responsible for the diamond grade. The lithospheric mantle consists of two major parts divided at a depth of 4.0 GPa by a pyroxenite layer. Major intervals determined for the mantle beneath Udachnaya and Mir are: 1) 8.0–6.5 GPa harzburgites, eclogites and dunitic veins; 2) 6.5–5.5 GPa sheared peridotites, low-Cr pyroxenites, dunites; 3)in 5.5–4.0 GPa interval there are 4–6 layers of harzburgitic paleoslabs; 4) 4.0–3.5 GPa the pyroxenites lens; 5) upper layered Sp-Gar peridotite sequence including a trap of basaltic and other silicate melt cumulates at 3.0–2.0 GPa. The lithospheric mantle beneath seven different tectonic terrains in Siberia is characterized by TRE geochemistry and major elements of peridotitic clinopyroxenes. The mantle in Magan terrain contains more fertile peridotites in the South (Mir pipe) than in North (Alakit) which were metasomatized by subduction-related melts producing Phl and Cpx about 500–800 Ma ago. Daldyn terrain is essentially harzburgitic in the west part (abyssal peridotite) but in the east in Upper Muna (East Daldyn terrain) the mantle is more differentiated and in general more oxidized. The Markha terrain (Nakyn) contains depleted but partly refertilized harzburgites, subducted pelitic material and abundant eclogites. Circum-Anabar mantle is ultradepleted in the lower part but in the upper regions it has been fertilized by fluid-rich melts very enriched in incompatible elements. The P-Fe# diagrams (and other components) reveal different structure of mantle columns in each terrain. They are subvertical for the mantle sampled by Devonian pipes. Beneath Mesozoic pipes the mantle has been affected by melt percolation caused by the Siberian Superplume which created continuous Fe-enrichment in the upper part. The models of continent growth and evolution are briefly discussed. In general the geothermal regime and mantle heating is negatively correlated with the thickness of lithosphere. The sheared peridotites under Udachnaya and other kimberlite pipe are likely to have formed after the intrusion of protokimberlite volatile rich (hydrous) melts and hydraulic fracturing. This mechanism is responsible for the origin of asthenospheric lenses. Progressive melting especially in the pervasive zones may be responsible for the creation of 3-4 upper asthenospheric lens near mostly before 4.0 GPa which may be accompanied by mantle diapirism. Such a lens is the trap for the kimberlites in Siberia in Mesozoic time and in rifted intracontinental areas and margins.

Garnet, clinopyroxene and ilmenite xenocrysts from three Angolan kimberlite pipes belonging to the Catoca cluster (Angola Caquele, Camitongo I and II, and Catoca) from the SW part of the Congo–Kasai craton, reveal similar features which suggest a similarity of mantle structure. PT estimates for pyropes, Cr-diopsides and picroilmenites reveal similar geothermal conditions of ~ 37–40 mW/m 2 . This is slightly higher than the values determined for the Catoca pipe. Higher temperature conditions ~ 45 mW/m 2 were determined for low-Cr pyroxenes and omphacites. The similar general mineralogy and suggested mantle lithology, as well as reconstructed layering of the sub-continental lithospheric mantle (SCLM), are similar for Camitongo I–II as well as for Caquele and Catoca pipes. Heating at depths of 7.5–4.5 GPa (240–140 km) is a general feature of the SCLM beneath the field. The high temperature trend for low-Cr and hybrid pyroxenes from the base of the SCLM up to 30 GPa (100 km) represents the PT path of the protokimberlite melts. PT conditions for ilmenites mainly correspond to colder conditions of crystallization in wall rocks and the outer parts of magmatic channels. Individual geochemical features of the minerals for each SCLM suggest pervasive metasomatism in lower part of the SCLM. Clinopyroxene trace element patterns from the Caquele pipe reveal a lherzolitic affinity; they are LILE-enriched with Ba peaks due to phlogopite melting, while those from Camitongo I–II show Ta–Nb enrichment and Pb troughs. The ilmenite trends trace the mantle column from deep to shallow mantle, evolving to Fe-ilmenites due to advanced AFC of protokimberlite magma that also produced abundant Fe-rich clinopyroxenes. The rise of calculated f O 2 correlates with the position of protokimberlites. Comparison with the thermal gradient derived from peridotitic inclusions from Catoca cluster is lower than for Lesotho possibly related to the thicker lithospheric roots beneath the Congo–Kasai craton.

New major and trace element and Nd-Sr isotope results are reported for the carbonatites of the Veseloe and Pogranichnoe occurrences, Northern Transbaikalia. The carbonatites from both these occurrences are enriched in Sr, Ba, LREE, Th, U, and depleted in Ti, Cr, and V relative to primitive mantle. As compared to the “average dolomite carbonatite”, the rocks from the Northern Transbaikalia have higher contents of Ni, Cr, and low contents of Ba, Ti, and V. The rocks are characterized by 87Sr/86S in the range of 0.7037–0.7043 and ɛNd from + 0.6 to + 2.05. Obtained geochemical and isotope data indicate that the carbonatites were derived from moderately depleted source with a contribution of enriched component.

Lower crustal xenoliths from the Udachnaya and Komsomolskaya kimberlite pipes in Siberia are mainly meta-igneous mafic garnet granulites, with subordinate feldspar-rich garnet granulites. Pressure and temperature estimates are interpreted as the conditions in the lower crust at the time of the last granulite-facies metamorphic event (800–890°C) followed by cooling to 610–720°C with a pressure decrease from 1·2 to 0·8 GPa. Most of the xenoliths show minor alteration. Leaching experiments demonstrate that their isotopic, major and trace element compositions have been affected by interaction not only with the host kimberlite but also with a fluid mobilized from local sedimentary country rocks. To obtain unambiguous compositional data we have calculated the composition of selected samples using modal analyses, electron microprobe and laser ablation inductively coupled plasma mass spectrometry data for constituent minerals. The reconstructed protoliths of most of the xenoliths were Fe-tholeiites of intraplate affinity, similar to some Archean basalts, whereas the others show characteristics of subduction-related magmas. However, the mafic granulites are strongly depleted in Rb, Th and U, which were removed by a small-degree partial melt. A protolith age of c. 3 Ga is supported by a disturbed Sm–Nd isochron, Nd and Hf model ages, and published U–Pb ages of zircon cores.

Based on study of fluid and melt inclusions in minerals from igneous rocks and associated ore-metasomatic objects, we consider the formation conditions of oxidized fluids produced at the final stages of differentiation of alkali-basic, alkaline, lamproitic, and some granitoid melts. These fluids are characterized by wide variations in composition, concentrations, and physicochemical parameters (P, T, Eh, pH, etc.) and are of sulfate-chloride, sulfate-carbonate, sulfate-fluoride, fluoride-sulfate, essentially sulfate, and other types. The specific composition of these magmatogene fluids showing a high extractive power favors the effective removal of ore-forming elements (Fe, Mn, Co, N, Ag, Cu, Pb, Zn, Mo, W, Bi, U, REE, etc.) from melt and their trapping from the host rocks. The set of these elements is determined by P-T-X-parameters, conditions of fluid separation from melts, composition of fluid-generating magmas, and geochemical composition and metal-bearing capacity of rocks through which the fluids migrate. These factors significantly determine the metallogeny of alkaline, alkali-basic, and some granitoid complexes and associated mineralization.

This paper studies the petrology of K-alkaline lamproite-carbonatite complexes, which are widespread in Siberia. They are exemplified by the Murun and Bilibino massifs in West and Central Aldan. In these massifs, the entire range of differentiates was first found, from K-ultrabasic-alkalic rocks through basic and intermediate ones to alkali granites and unique residual calc-silicate rocks (benstonite Ba-Sr carbonatites and charoite rocks). Also, intrusive equivalents of lamproites occur in these massifs, and the Murun massif was probably formed from highly differentiated lamproite magmas. In many K-alkaline complexes, silicate and silicate-carbonate magma layering takes place. Stages of magmatism are described for both massifs. Binary and ternary petrochemical diagrams exhibit the same compositional trend from early to late rocks. In this paper, lamproites are considered from the chemical point of view; their diagnostic properties are described in terms of chemical and mineral composition. From geological, petrological, and geochemical data, formational analysis of alkaline complexes was performed, four formational types of world lamproites were first identified, and diamond content criteria were developed for them. The carbonatite problem was studied from the petrological point of view, and four formational types of carbonatites were identified using geological, geochemical, and genetic criteria. It has been suggested that for dividing carbonatite complexes into four formational types the following criteria be used: the alkalinity type (Na or K) of alkalic rocks in the complex and the time when the carbonatite liquid separates from silicate melts in different stages of primary magma differentiation. These linked parameters influence the ore content type of carbonatite complexes. A formation model for K-alkaline carbonatite complexes is given, and the Tomtor alkaline carbonatite massif with tuffaceous rare-metal ores is described to prove that they have ore reserves. The geochemistry of C, O, Sr, and Nd isotopes shows that K-alkaline complexes, depending on their geotectonic setting, can originate from three types of mantle sources: depleted mantle, enriched mantle 1 (EM1), and enriched mantle 2 (EM2). It is concluded that ore-bearing ultrabasic-alkaline complexes of lamproites and carbonatites can melt out of different types of mantle, whose composition only slightly influences their ore content. Apparently, the main factors are the low degree of selective mantle melting (less than 1%) and plumes supplying fluid and alkaline components, which stimulate this melting. Later on, the processes important for the accumulation of ore and trace elements are long-term magma differentiation and its layering during crystallization.

Several spindle-shaped grains of zircon, which have a small size (

Trace element and SHRIMP U–Pb geochronological data are presented for zircons from granulite xenoliths from the Devonian Udachnaya kimberlite pipe, situated in the central part of the Siberian craton (66°05′N, 110°45′ E). The xenoliths include three two-pyroxene garnet granulites, one garnet granulite lacking orthopyroxene, three felsic garnet granulites, one kinzigite and one amphibolized garnet granulite. Most of them are clearly distinct from the local upper crustal lithologies and have pressure and temperature estimates indicative of derivation from the lower crust. Zircons from these granulites show a record of several magmatic and metamorphic events, with different domains revealed by CL imaging and variations in REE content and Th/U ratios. The first event is shown by magmatic zircon in the cores of some grains that yield discordant Archaean to Proterozoic ages. All other domains of the studied zircons have textures typical for metamorphic zircons. They have Proterozoic ages and were formed by subsolidus growth or as a result of solid-state recrystallization of pre-existing zircon. They give a range of concordant ages from 1.94 to 1.81 Ga, in which several distinct episodes can be distinguished that relate to the collision of terranes during the accretion of the Siberian craton, accompanied by formation of granite melts. During these events the xenolith protoliths were metamorphosed under granulite-facies conditions at pressures corresponding to lower crustal depths, except for the kinzigite that is probably derived from shallower depths.

The Arshan carbonatites in the Transbaikalia region of Siberia consist of sovite with high concentrations of the REE, Sr, Ba, and SO 3 , and low concentrations of Nb and P 2 O 5 . There was a high fugacity of oxygen and fluid activity at the time of formation of these carbonatites, and they were later altered by hydrothermal solutions. Bastnasite formed as a magmatic mineral in the carbonatites, on the basis of petrographic evidence and fluid-inclusion data. The recrystallization of calcite, the replacement of bastnasite and phlogopite, and the formation of secondary sulfates, strontianite, calcite and fluorite resulted from a hydrothermal process. The 87 Sr/ 86 Sr values of minerals in the Arshan carbonatites are higher than in many other carbonatites, but are similar to those in the continental basalts of Transbaikalia. The δ 34 S CDT values resemble those of other Transbaikalia carbonatites and alkaline rocks. The δ 13 C V–PDB isotopic values in the carbonatite plot within the field defined for primary igneous carbonatites. On the other hand, δ 18 O V–SMOW values for the Arshan bastnasite is only partially within the usual range of mantle values. The altered carbonatites are characterized by lighter δ 18 O values, probably because of the influence of meteoric water. The carbonatites were formed from an enriched source in the mantle and crystallized rapidly at shallow depth.

Four original monomineral methods for mantle peridotite associations are used to reconstruct P – T conditions beneath the kimberlite pipes of Yakutia. The clinopyroxene Jd–Di method gives the closest coincidence with Opx barometry in accord with all physico-chemical boundaries. Garnet thermometers calibrated using Opx, Gar–Cpx and Ni-garnet thermometers and two variants of barometers were developed separately for pyroxenites and peridotites. A Cr–Sp thermobarometer uses the monomineralic version of the Ol–Sp thermometer and a newly calibrated Cr–Sp barometer. A picroilmenite method uses the Ol–Sp thermometer and a pressure-calibration of the geikielite component. Each mantle column is divided into two (upper and lower) sections by a pyroxenite layer located near 40 kbar. Below the pyroxenite layer, the lower section comprises 3–4 lithologically distinct horizons, with a thermally perturbed layer at the base. Above the pyroxenite layer are 3–5 lithologically distinct horizons, which are more fertile than the lower sections. Splitting of the geotherms characterizes most P – T diagrams and is ascribed to multistage melt percolation processes typical for the mantle beneath kimberlite pipes. The largest pipes are diamond-bearing and have a highly depleted peridotite lens above the asthenospheric layer.

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

The list of authors and their affiliations should read as follows: A. Gerdes a , Academician L. N. Kogarkob,*, and N. V. Vladykin c a Institute of Earth Sciences, Goethe University, Frankfurt, Germany b Vernadsky Institute of Geochemistry and Analytical Chemistry, Russian Academy of Sciences, Moscow, 119991 Russia c Vinogradov Institute of Geochemistry, Siberian Branch, Russian Academy of Sciences, Irkutsk, 664033 Russia *e-mail: kogarko@geochi.ru