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The paper presents data on garnets from serpentinized peridotite xenoliths in the Nyurba and Botuoba kimberlite pipes of the Nakyn kimberlite field. The major and trace-element compositions of the garnets were analyzed to determine their compositional specifics and genesis. Based on the REE content and chondrite-normalized distribution patterns, the garnets are divided into two types with sinusoidal ((Sm/Er)n > 1) and normal ((Sm/Er)n < 1) REE distribution patterns. In terms of the Y, Zr, Ti, and Eu relations, and the shape of REE distribution pattern, all the garnets correspond to garnets of metasomatized peridotites, except for one sample falling into the field of depleted garnets of harzburgite–dunite paragenesis. The geochemical characteristics of the garnets record two types of metasomatic agents: carbonatite/fluid for type 1 garnets and silicate/melt for type 2 garnets. The carbonatite metasomatic agent produced harzburgitic garnet and its further transformation into lherzolitic garnet. Silicate metasomatism, which led to the formation of the REE pattern of type 2 garnets, likely overprinted two different types of garnets and, respectively, gave two evolutionary trends. These are depleted residual garnets and type 1 garnets previously subjected to carbonatite metasomatism. The low Y and Th contents in combination with the low Ti/Eu ratios in garnets suggest a moderate reworking of lithospheric peridotites by silicate melts, which is consistent with the high diamond grade of the Nakyn kimberlite field.

—The isotope-geochemical features of diamondiferous metamorphic rocks of the Kokchetav subduction–collision zone (KSCZ) show that both the basement rocks and the sediments of the Kokchetav massif were their protoliths. A whole-rock Sm–Nd isochron from the diamondiferous calc-silicate, garnet–pyroxene rocks and migmatized granite-gneisses of the western block of the KSCZ yielded an age of 1116 ± 14 Ma, while an age of 1.2–1.1 Ga was obtained by U–Pb dating of zircons from the granite-gneiss basement of the Kokchetav microcontinent. Based on these data, we assume that the protoliths of the calc-silicate, garnet–pyroxene rocks and the granite-gneisses of the KSCZ were the basement rocks sharing an initially single Nd source, which was not influenced by high- to ultrahigh-pressure metamorphism (~530 Ma). Therefore, their geochemical features are probably not directly related to ultrahigh-pressure metamorphism. The corresponding rock associations lack isotope-geochemical evidence of partial melting that would occur during ultrahigh-pressure metamorphism, which suggesting that they were metamorphosed under granulite-facies conditions. At the same time, the high-alumina diamondiferous rocks of the Barchi area (garnet–kyanite–mica schists and granofelses), which were depleted to different degrees in light rare-earth elements (REE) and K, have yielded a Sm–Nd whole-rock isochron age of 507 ± 10 Ma indicating partial melting of these rocks during their exhumation stage. The close ɛNd (1100) values of the basement rocks and garnet–kyanite–mica schist with geochemical characteristics arguing against its depletion during high-pressure metamorphism indicate that the basement rocks were a crustal source for high-alumina sediments.

Zircon xenocrysts from two diamond-barren kimberlite pipes (Leningrad and Ruslovaya) in the West Ukukit kimberlite field opened a ‘window’ to the buried crustal basement in the northern Siberian cr...

The data available indicate the complex evolution of deformed peridotites of mantle xenoliths, the P–T parameters of which indicate that they are fragments of the metasomatized lower part of the cratonic lithosphere. The zoning established in garnets from xenoliths in kimberlite pipes is interpreted as a result of metasomatism that occurred shortly before xenoliths reached the surface. Metasomatic alterations in xenoliths of deformed harzburgites were manifested not only in the development of zoning of minerals. The study results show that there is a discrepancy between the data calculated based on the contents of incompatible elements in minerals of xenoliths and those obtained due to direct measurements of the bulk composition of xenoliths. To determine the balance of incompatible elements, we have carried out experiments on leaching xenoliths of deformed lherzolites from the Udachnaya kimberlite pipe. It was established that a significant part of LREEs in the studied xenoliths occurs in the intergranular space. The distribution pattern of incompatible elements and, in particular, the presence of a positive Eu anomaly indicate that the appearance of the intergranular component is not associated with contamination of xenoliths by the kimberlite melt. Quite a few xenoliths demonstrate a positive Eu anomaly, which indicates the influence of the subducted crustal component at one of the modification stages of xenoliths.

The specific features of the mineralogy of SiO 2 inclusions in sublithospheric diamonds are described in this study. Such diamonds are characterized by a complex growth history with stages of growth and dissolution and postgrowth processes of deformation and crushing. The nitrogen content in all studied crystals does not exceed 71 ppm and nitrogen is detected only as B-defects. The carbon isotope composition of diamonds varies widely from -26.5 to -6.7 ‰ of δ 13 С. SiO 2 inclusions associate with omphacitic clinopyroxenes, majoritic garnets, CaSiO 3 , jeffbenite and ferropericlase. All SiO 2 inclusions are coesite, which is often accompanied by micro-blocks of kyanite. These phases are suggested to represent the product of the retrograde transformation of the primary Al-stishovite. Significant internal stresses in the inclusions and deformations around them can be evidence of thise phase transformation. The heavier oxygen isotope composition of SiO 2 inclusions in sublithospheric diamonds (up to 12.9 δ 18 O) indicates the crustal origin of their protoliths. The observed anti-correlation of δ 18 O of SiO 2 inclusions and δ 13 C of their host diamonds reflects the processes of interaction of slab-derived melts with reduced mantle rocks at depths above 270 km.

The paper describes mineralogical characteristics of SiO2 inclusions in sublithospheric diamonds, which typically have complicated growth histories showing alternating episodes of growth, dissolution, and postgrowth deformation and crushing processes. Nitrogen contents in all of the crystals do not exceed 71 ppm, and nitrogen is detected exclusively as B-defects. The carbon isotope composition of the diamonds varies from δ13С = –26.5 to –6.7‰. The SiO2 inclusions occur in association with omphacitic clinopyroxenes, majoritic garnets, CaSiO3, jeffbenite, and ferropericlase. All SiO2 inclusions are coesite, which is often associated with micro-blocks of kyanite in the same inclusions. It was suggested that these phases have been produced by the retrograde dissolution of primary Al-stishovite, which is also evidenced by the significant internal stresses in the inclusions and by deformations around them. The oxygen isotope composition of SiO2 inclusions in sublithospheric diamonds (δ18O up to 12.9‰) indicates a crustal origin of the protoliths. The negative correlation between the δ18O of the SiO2 inclusions and the δ13C of their host diamonds reflects interaction processes between slab-derived melts and reduced mantle rocks at depths greater than 270 km.

This paper reports isotopic and geochemical studies of eclogites from the western ultrahigh pressure (UHP) and eastern high-pressure (HP) blocks of the Kokchetav subduction–collision zone. These HP and UHP eclogites exhumed in two stages: (1) The rocks of the western block metamorphosed within the field of diamond stability (e.g., Kumdy-Kol and Barchy); (2) In contrast, the metamorphic evolution of the eastern block reached the pressure peak within the stability field of coesite (e.g., Kulet, Chaglinka, Sulu-Tyube, Daulet, and Borovoe). The eclogites vary widely in the ratios of incompatible elements and in the isotope ratios of Nd (143Nd/144Nd = 0.51137–0.513180) and Sr (87Sr/86Sr = 0.70393–0.78447). The Sulu-Tyube eclogites display isotope-geochemical features close to N-MORB, while those from the other sites are compositionally similar to E-type MORB or island arc basalts (IAB). The model ages TNd(DM) of eclogites vary between 1.95 and 0.67 Ga. The Sulu-Tyube eclogite yields the youngest age; it has the values of εNd(T) (7.2) and 87Sr/86Sr (0.70393) close to the depleted mantle values. The crustal input to the protolith of the Kokchetav eclogites is evident on the εNd(T)–86Sr/87Sr and εNd(T)–T plots. The eclogites make up a trend from DM to country rocks. Some eclogites from the Kulet, Kumdy-Kol, and Barchy localities display signs of partial melting, such as high Sm/Nd (0.65–0.51) and low (La/Sm)N (0.34–0.58) values. The equilibrium temperatures of these eclogites are higher than 850 °C. The geochemical features of eclogites testify to the possibility of the eclogite protolith formation in the tectonic setting of passive continental rift margin subducted to depths over 120 km.

Olivine from the deep mantle-derived rocks, such as ultramafic lamprophyres, carries important information about the composition of the mantle source, the processes of mantle metasomatism, the origin of specific silicate-carbonate melts, as well as the composition and mechanisms of crystallization of these rocks. Textures and compositions of olivine from the carbonate-rich ultramafic lamprophyres (aillikites) of the Terina complex, along with their mineral and melt inclusions, exposed that olivines have different sources. Two populations of olivines were considered: macrocrysts (&gt, 1 mm) and groundmass olivines (&lt, 1 mm). Groundmass olivines are phenocrysts and characterized by weak variations in Mg# (84–86.5), a sharp increase in Ca and Ti contents, and a decrease in Ni and Cr from core to rim. They have higher concentrations of Li, Cu, Ti, and Na compared to macrocrysts. Among the macrocrysts, the following populations are observed: (1) high-Mg olivines (Mg# 89–91) with high Ni and low Ti contents, which are interpreted as xenocrysts from the slightly depleted lherzolite mantle, (2) high-Ca olivines (Mg# 84–88, CaO 0.13–0.21 wt %), which have patterns similar to groundmass olivines and are interpreted as cumulates of early portions of aillikite melt, (3) macrocrysts with wide variations in Mg# (73–88), low CaO contents (0.04–0.11 wt %), and positive slope in Ca vs. Al and negative slope in Ca vs. Mn, which are interpreted as disintegrated megacrysts from the Cr-poor megacryst suite. The megacryst suite could have been formed in the pre-trap period during the melting of the metasomatized subcontinental lithospheric mantle (SCLM). The aillikite melt evolution is traced by secondary melt inclusions in olivine macrocrysts: early phlogopite-diopside-calcite-apatite association, containing Ti-magnetite and ilmenite, is followed by an association with magnetite and sulfides (pyrrhotite and pentlandite), finally, at a late stage, inclusions with a predominance of Ca-Na-carbonates and sulfates and enriched in U, Th, Y, REEs, Sr, and Ba were captured.

We present a new dataset on the composition of high-density fluids (HDFs) in cloudy (n = 25), coated (n = 10) and cuboid (n = 10) diamonds from the Nyurbinskaya kimberlite pipe. These diamonds represent different populations each showing distinct growth histories. The cores of coated diamonds display multiple growth stages and contrasting sources of carbon. Fibrous coats and cuboid diamonds have similar carbon isotopes and nitrogen systematics, suggesting their formation in the last metasomatic events related to kimberlite magmatism, as is common for most such diamonds worldwide. The HDFs in most of these diamonds span a wide range from low-Mg carbonatitic to hydrous silicic compositions. The major- and trace-element variations suggest that the sources for such HDFs range in composition between the depleted mantle and more fertile mantle reservoirs. Hydrous-silicic HDFs could originate from a 13C-enriched source, which originates through subduction of crustal metasedimentary material. Percolation of such HDFs through carbonated eclogites and peridotites facilitates the formation of cuboid diamonds and fibrous coats in the mantle section beneath the corresponding area of the Siberian craton. Cloudy diamonds represent an apparently older population, reflecting continuous diamond formation predominantly from high-Mg carbonatitic HDFs that caused discrete episodes of diamond precipitation. Their high Mg# and enrichment in incompatible elements support a metasomatized peridotitic source for these HDFs.

The 35 paired diamond intergrowths of rounded colorless transparent and gray opaque crystals from the placers of northeastern Siberian Platform were investigated. Mineral inclusions (KFsp, Coe, E-Grt, Po) detected in studied samples belong to eclogitic paragenesis. The majority of studied samples have uniform ranges of nitrogen content (1126–1982 at. ppm) and carbon isotope composition (− 16.8 to − 23.2 ‰). These characteristics pointing towards subducted material are possible sources for their genesis. Two samples consist of a gray opaque crystal with the subduction-related characteristics (δ13C ca. − 21‰ and N ca. 1300 at. ppm) and a transparent crystal with low nitrogen content (412 and 29 at. ppm) and a heavy carbon isotopic composition (δ13C − 4.2 and − 4.6‰) common for primary mantle range. The higher degree of nitrogen aggregation in the crystals with mantle-like characteristics testifies their longer storage in the mantle conditions. These samples reflect multistage diamond growth history and directly indicate the mixing of mantle and subduction carbon sources at the basement of subcontinental lithospheric mantle of northeastern Siberian Platform.

A coesite-bearing diamondiferous eclogite from the Udachnaya kimberlite (Daldyn field, Siberian craton) has been studied to trace its complex evolution recorded in rock-forming and minor mineral constituents. The eclogite sample is composed of rock-forming omphacite (60 vol%), garnet (35 vol%) and quartz/coesite (5 vol%) and contains intergranular euhedral zoned olivine crystals, up to 200 &micro, m long, coexisting with phlogopite, orthopyroxene, clinopyroxene (secondary), K-feldspar, plagioclase, spinel, sodalite and djerfisherite. Garnet grains are zoned, with a relatively homogeneous core and a more magnesian overgrowth rim. The rim zones further differ from the core in having higher Zr/Y (6 times that in the cores), ascribed to interaction with, or precipitation from, a kimberlite-related melt. Judging by pressure-temperature estimates (~1200 &deg, C, 6.2 GPa), the xenolith originated at depths of ~180&ndash, 200 km at the base of the continental lithosphere. The spatial coexistence of olivine, orthopyroxene and coesite/quartz with K-Na-Cl minerals in the xenolith indicates that eclogite reacted with a deep-seated kimberlite melt. However, Fe-rich olivine, orthopyroxene and low-pressure minerals (sodalite and djerfisherite) likely result from metasomatic reaction at shallower depths during transport of the eclogite by the erupting kimberlite melt. Our results demonstrate that a mixed eclogitic-peridotitic paragenesis, reported previously from inclusions in diamond, can form by interaction of eclogite and a kimberlite-related 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 paper presents new data on the internal structure of super-deep (sublithospheric) diamonds from Sa&otilde, Luiz river placers (Brazil) and from alluvial placers of the northeastern Siberian platform (Yakutia). The sublithospheric origin of these diamonds is supported by the presence of mineral inclusions corresponding to associations of the transition zone and lower mantle. The features of morphology and internal structure have been studied by optical and scanning electron microscopy (SEM), cathodoluminescence topography (CL), and electron backscatter diffraction (EBSD) techniques. Diamonds typically have complicated growth histories displaying alternating episodes of growth, dissolution, and post-growth deformation and crushing processes. Most crystals have endured both plastic and brittle deformation during the growth history. Abundant deformation and resorption/growth features suggest a highly dynamic growth environment for super-deep diamonds. High temperatures expected in the transition zone and lower mantle could explain the plastic deformations of super-deep diamonds with low nitrogen content.

Mosaic diamonds from the Zarnitsa kimberlite (Daldyn field, Yakutian diamondiferous province) are morphologicaly and structurally similar to dark gray mosaic diamonds of varieties V and VII found frequently in placers of the northeastern Siberian craton. However, although being similar in microstructure, the two groups of diamonds differ in formation mechanism: splitting of crystals in the case of placer diamonds (V and VII) and growth by geometric selection in the Zarnitsa kimberlite diamonds. Selective growth on originally polycrystalline substrates in the latter has produced radial microstructures with grains coarsening rimward from distinctly polycrystalline cores. Besides the formation mechanisms, diamonds of the two groups differ in origin of mineral inclusions, distribution of defects and nitrogen impurity, and carbon isotope composition. Unlike the placer diamonds of varieties V and VII, the analyzed crystals from the Zarnitsa kimberlite enclose peridotitic minerals (olivines and subcalcic Cr-bearing pyropes) and have total nitrogen contents common to natural kimberlitic diamonds (0 to 1761 ppm) and typical mantle carbon isotope compositions (–1.9 to –6.2‰ δ13C; –4.2‰ on average). The distribution of defect centers in the Zarnitsa diamond samples fits the annealing model implying that nitrogen aggregation decreases from core to rim.

In the present paper, the results of our isotope–geochemical studies on eclogites of the ultrahighpressure metamorphic complex of the Kokchetav massif are reported. The fact that the distribution of nonmobile elements in most of the samples was close to that of E-type MORB basalts is shown by using geochemical multielement diagrams normalized to N-MORB. Six samples were found to have a negative anomaly over niobium that may have resulted from contamination with crustal material. For eclogites of the Kokchetav massif, the 147Sm/144Nd ratio was found to range widely from 0.143 to 0.367. The eNd-values calculated for the age of the highly barometric stage of metamorphism (530 million years) varied from–10.3 to +8.1. Eclogites show a dispersion of model ages from 1.95 billion years to 670 million years. On the graphs in the eNd(T)–87Sr/86Sr and eNd(T)–T coordinates, eclogites were shown to form trends that can be interpreted as a result of contamination of the eclogite protolith by the host rocks. Based on the data obtained, it is proposed that the basalts of rift zones that may have geochemical characteristics of N-MORB basalts and at the same time may be contaminated by the continental crust may have served as proxies for eclogite protoliths of the Kokchetav massif.

According to present views, the crustal terranes of the Anabar province of the Siberian craton were initially independent blocks, separated from the convecting mantle at 3.1 (Daldyn terrane), 2.9 (Magan terrane) and 2.5 Ga (Markha terrane) (Rosen, 2003, 2004; Rosen et al., 1994, 2005, 2009). Previous studies of zircons in a suite of crustal xenoliths from kimberlite pipes of the Markha terrane concluded that the evolution of the crust of the Markha terrane is very similar to that of the Daldyn terrane. To test this conclusion we present results of U-Pb and Hf-isotope studies on zircons in crustal xenoliths from the Zapolyarnaya kimberlite pipe (Upper Muna kimberlite field), located within the Daldyn terrane, and the Botuobinskaya pipe (Nakyn kimberlite field) in the center of the Markha terrane. The data on xenoliths from the Botuobinskaya kimberlite pipe record tectonothermal events at 2.94, 2.8, 2.7 and 2 Ga. The event at 2 Ga caused Pb loss in zircons from a mafic granulite. U-Pb dating of zircons from the Zapolyarnaya pipe gives an age of 2.7 Ga. All zircons from the studied crustal xenoliths have Archean Hf model ages ranging from 3.65 to 3.11 Ga. This relatively narrow range suggests that reworking of the ancient crust beneath the Nakyn and Upper Muna kimberlite fields was minor, compared with the Daldyn and Alakit-Markha fields (Shatsky et al., 2016). This study, when combined with dating of detrital zircons, implies that tectonic-thermal events at 2.9–2.85, 2.75–2.7 and 2.0–1.95 Ga occurred everywhere on the Anabar tectonic province, and could reflect the upwelling of superplumes at 2.9, 2.7 and 2 Ga. The presence of the same tectonic-thermal events in the Daldyn and Markha terranes (Rosen et al., 2006a,b) supports the conclusion that the identification of the Markha terrane as a separate unit is not valid.

The paper presents new petrographic, major element and Fourier transform infrared (FTIR) spectroscopy data and PT-estimates of whole-rock samples and minerals of a collection of 19 relatively fresh peridotite xenoliths from the Udachnaya kimberlite pipe, which were recovered from its deeper levels. The xenoliths are non-deformed (granular), medium-deformed and highly deformed (porphyroclastic, mosaic-porphyroclastic, mylonitic) lherzolites, harzburgite and dunite. The lherzolites yielded equilibration temperatures (T) and pressures (P) ranging from 913 to 1324 °C and from 4.6 to 6.3 GPa, respectively. The non-deformed and medium-deformed peridotites match the 35 mW/m2 conductive continental geotherm, whereas the highly deformed varieties match the 45 mW/m2 geotherm. The content of water spans 2 ± 1–95 ± 52 ppm in olivine, 1 ± 0.5–61 ± 9 ppm in orthopyroxene, and 7 ± 2–71 ± 30 ppm in clinopyroxene. The amount of water in garnets is negligible. Based on the modal proportions of mineral phases in the xenoliths, the water contents in peridotites were estimated to vary over a wide range from

Microinclusions of high-density fluids (HDFs) were studied in coated diamonds from the Udachnaya kimberlite pipe (Siberian craton, Russia). The presence of C-centers in the coats testifies to their formation shortly before kimberlite eruption, whereas the cores have much longer mantle residence in chemically different mantle substrates, i.e., peridotite-type (P-type) and eclogite-type (E-type). The carbon isotope composition indicates an isotopically homogeneous carbon source for coats and a heterogeneous source for cores. Microinclusions in the coats belong to two groups: high-Mg carbonatitic and low-Mg carbonatitic to silicic. A relationship was found between high-Mg carbonatitic HDFs and peridotitic host rocks and between low-Mg carbonatitic to silicic and eclogites. The composition of high-Mg carbonatitic HDFs with a &ldquo, planed&rdquo, trace-element pattern can evolve to low-Mg carbonatitic to silicic during percolation through different mantle rocks. The compositional variations of microinclusions in the coats reflect this evolution.

New findings of silicate-melt inclusions in two alluvial diamonds (from the Kholomolokh placer, northeastern Siberian Platform) are reported. Both diamonds exhibit a high degree of N aggregation state (60&ndash, 70% B) suggesting their long residence in the mantle. Raman spectral analysis revealed that the composite inclusions consist of clinopyroxene and silicate glass. Hopper crystals of clinopyroxene were observed using scanning electron microscopy and energy-dispersive spectroscopic analyses, these are different in composition from the omphacite inclusions that co-exist in the same diamonds. The glasses in these inclusions contain relatively high SiO2, Al2O3, Na2O and, K2O. These composite inclusions are primary melt that partially crystallised at the cooling stage. Hopper crystals of clinopyroxene imply rapid cooling rates, likely related to the uplift of crystals in the kimberlite melt. The reconstructed composition of such primary melts suggests that they were formed as the product of metasomatised mantle. One of the most likely source of melts/fluids metasomatising the mantle could be a subducted slab.

Polycrystalline diamond aggregates (boart, framesites, diamondites) have been widely studied but their origin is poorly understood. We report the results of a study in situ of two polished fragments of fine-grained (40–400 μm size of individual diamond grains) dense polycrystalline diamond aggregates from the Mir pipe containing visible multiple interstitial garnet inclusions. They were analyzed for major and trace elements of inclusions and one of them — for δ 13 C and N abundance and isotopic composition of host diamonds. These aggregates are classified as variety IX by Orlov (1977). No cavities were observed in these samples. Sixty two irregular garnet grains and one clinopyroxene inclusion were detected and analyzed in sample Mr 832. Garnets are homogeneous within single grains but variable in Mg# [100Mg/(Mg + Fe)] from 60 up to 87 and CaO contents (3.3–5.3 wt.%) among grains with a trend to negative correlation. Low Cr (550–640 ppm) confirms eclogitic (E-type) paragenesis. High Na 2 O contents (5.2 wt.%) of a single pyroxene inclusion are additional evidence of eclogitic nature of this sample. Wide variations in trace elements (ppm) are characteristic for garnet grains: Sr (2.7–25.6), Y (9.7–14.1), Zr (15.6–38.7) and positive Eu anomaly is present. The δ 13 C of diamonds within studied sample is variable (− 6.4 ÷− 9.8 ‰) as well as N abundance (75–1150 ppm) and δ 15 N − 27, − 38, − 58 ‰. The second peridotitic (U/P-type) sample Mr 838 contains eight inclusions of Mg-rich Cr-pyropes (Mg# ~ 85, Cr 2 O 3 3.2–3.4 wt.%) and magnesite inclusion with 4.35 wt.% FeO and 1.73 wt.% CaO. Trace element content in pyropes is relatively uniform (ppm): Sr (0.4–1.6), Y (13.2–13.4) and Zr (13.0). We conclude that heterogeneous distribution of the trace elements among garnet grains in Mr 832 and magnesite presence in Mr 838 are indicative of the effects of mantle metasomatism and rapid crystallization shortly before the eruption of the kimberlite.

The staged high-pressure annealing of natural cubic diamonds with numerous melt microinclusions from the Internatsional’naya kimberlite pipe was studied experimentally. The results mainly show that the carbonate phases, the daughter phases in partially crystallized microinclusions in diamonds, may undergo phase transformations under the mantle P–T conditions. Most likely, partial melting and further dissolution of dolomite in the carbonate–silicate melt (homogenization of inclusions) occur in inclusions. The experimental data on the staged high-pressure annealing of diamonds with melt microinclusions allow us to estimate the temperature of their homogenization as 1400–1500°C. Thus, cubic diamonds from the Internatsional’naya pipe could have been formed under quite high temperatures corresponding to the lithosphere/asthenosphere boundary. However, it should be noted that the effect of selective capture of inclusions with partial loss of volatiles in relation to the composition of the crystallization medium is not excluded during the growth. This may increase the temperature of their homogenization significantly between 1400 and 1500°C.

This paper discusses mineralogy of Ca-rich inclusions in ultra-deep (sublithospheric) diamonds. It was shown that most of the Ca-rich majoritic garnets are of metabasic (eclogitic) affinity. The observed variation in major and trace element composition is consistent with variations in the composition of the protolith and the degree of enrichment or depletion during interaction with melts. Major and trace element compositions of the inclusions of Ca minerals in ultra-deep diamonds indicate that they crystallized from Ca-carbonatite melts that were derived from partial melting of eclogite bodies in deeply subducted oceanic crust in the transition zone or even the lower mantle. The occurrence of merwinite or CAS inclusions in ultra-deep diamonds can serve as mineralogical indicators of the interaction of metaperidotitic and metabasic mantle lithologies with alkaline carbonatite melts. The discovery of the inclusions of carbonates in association with ultra-deep Ca minerals can not only provide additional support for their role in the diamond formation process but also help to define additional mantle reservoirs involved in global carbon cycle.

U–Pb age and Hf-isotope data were collected on zircons from crustal xenoliths from the Late Devonian kimberlite pipes of Markha terrane. The xenoliths include mafic garnet granulites (Gt+Pl+Cpx±Opx±Amp±Bt±Scp) and garnet–biotite gneisses (Grt+Bt+Pl+Kfs+Qtz±Scp). The data from this study demonstrate that the crust of the Markha terrane experienced several tectonothermal events. Zircons with Archean Hf model ages (TDM = 3.13–2.5 Ga) are predominant in all xenoliths with one exception. These data imply that most of the lower and middle crust beneath the Markha terrane was produced in the Archean time. Later this Paleoarchean crust was significantly reworked in several tectonothermal events, including a Neoarchean stage (2.9–2.5 Ga), and several Paleoproterozoic metamorphic stages (1.98, 1.9 and 1.8 Ga). There is very little evidence for generation of juvenile crust associated with these metamorphic events. Importantly, crustal xenoliths from kimberlite pipes of the Markha terrane record all the same events that occurred in the adjacent Daldyn and Magan terranes.

The specific gray to almost black diamonds of rounded morphology are especially typical in alluvial placers of the northeastern part of the Siberian platform. The results of study of internal structure of these diamonds are presented. X-ray topography and birefringence patterns of polished plates of studied diamonds show their radial mosaic structure. Diamonds consists of slightly misorientated (up to 20′) subindividuals which are combined to mosaic wedge-shaped sectors. Electron back-scatter diffraction technique has demonstrated that subindividuals are often combined in the single large blocks (subgrains). The whole crystals commonly consist of several large subgrains misoriented up to 5° to one another. The total nitrogen content of these diamonds vary in the range 900–3300 ppm and nitrogen aggregation state (NB/(NB + NA)*100) from 25 to 64 %. Rounded diamond crystals of variety V are suggested to have been formed at the high growth rate caused by the high oversaturation of carbon in the crystallization medium. It may result in the splitting of growing crystal and their radial mosaic structure as a sequence. High content of structural nitrogen defects and the great number of mechanical impurities – various mineral and fluid inclusions may also favor to generation of this structure.

Diamonds of eclogitic assemblages are dominant in the placer diamond deposits of the northeastern Siberian platform. In this study we present new trace elements and stable isotopes (δ13C and δ18O) data for alluvial diamonds and their garnet inclusions from this locality. Cr-rich garnets of peridotitic affinity in the studied diamonds have a narrow range of δ18O values from 5.7‰ to 6.2‰, which is largely overlapping with the accepted mantle range. This narrow range suggests that the garnet inclusions showing different REE patterns and little variations in oxygen isotopes may have formed by different processes involving fluid/melts that, however, were in oxygen isotopic equilibrium with the mantle. The trace element composition of the eclogitic garnet inclusions supports a crustal origin for at least the high-Ca garnets, which show flat HREE patterns and in some cases a positive Eu-anomaly. High-Ca eclogitic garnets generally show heavier oxygen isotope compositions (δ18O 6.5–9.6‰) than what is observed in low-Ca garnets (δ18O 5.7–7.4‰). The variability in oxygen isotopes and trace elements is suggested to be inherited from contrasting crustal protoliths. The relationship between the high δ18O values of inclusions and the low δ13C values of the host diamonds implies that the high-Ca garnet inclusions were derived from intensely hydrated (e.g., δ18O > 7‰) and typically oxidised basaltic rock close to the seawater interface, and that the carbon for diamonds was closely associated with this protolith.

Evidence for the involvement of a subduction component in diamond formation is analyzed based on literature data and our studies. Examination of xenoliths of diamondiferous eclogites, including X-ray tomography analysis, testifies to the superposed character of most diamonds. Diamond generation is accompanied by the serious modification of eclogite substratum. Isotope–geochemical data show that the eclogites originated from oceanic-crust rocks. The oxygen isotope compositions of garnets and clinopyroxenes from websterite xenoliths are similar to the mantle average (5.3–5.6‰). The eclogite minerals vary considerably in oxygen isotope composition (δ18O of 5.3 to 12.4‰). Diamonds of eclogitic paragenesis predominate dramatically in the placers of the northeastern Yakutian diamondiferous province. In placer eclogitic diamonds, δ13C varies from − 27.2 to − 3‰ (n = 28). In diamonds of ultrabasic paragenesis, the range of δ13C values is much narrower (from − 7.1 to − 0.5‰). All diamonds of variety V have a lighter carbon isotope composition (from − 24.1 to − 17.4‰). In a wide range of crystals with a contrasting carbon isotope composition, the isotope composition of the rim tends toward the average mantle value. This suggests that the eclogitic diamonds grew first with the participation of carbon from subducted continental crust and finally with the involvement of mantle carbon.

We demonstrate for the first time the presence of iron carbides in placer diamonds from the northeastern region of the Siberian craton. It was found that the inclusions are polycrystalline aggregates, and iron carbides filling the fissures in the diamonds, thus providing clear evidence that the iron melts were captured first. Iron carbides were identified in diamonds containing mineral inclusions of eclogitic (Kfs, sulfide) and peridotitc (olivine) paragenesis. Iron carbides with minor amounts of admixed nickel were detected in a diamond sample containing an olivine inclusion (0.3 wt% Ni), indicating that the iron melt was not in equilibrium with the mantle peridotite.The low nickel contents of the iron carbides provide the best evidence that the subducted crust is a likely source of the iron melt. Diamonds containing carbide inclusions are characterised by a relatively low nitrogen aggregation state (5–35%), which is not consistent with the high temperature of the transition zone. Therefore, we have reason to assume that the studied diamonds are from the lower regions of the lithosphere. Considering all factors, the model for the interaction of the ascending asthenospheric mantle with the subducting slab seems to be more realistic.

This work was financially supported though a JSPS international research fellowship PE 14721 (to MWB) and JSPS KAKENHI grant numbers JP 26287139 and JP15KK0150 (to HS). The work of DAZ and ALR was supported by Russian science foundation (16-17-10067). RB acknowledges funding from the NERC (NE/M000427/1). SM acknowledges funding from the NERC (NE/PO12167/1). Fluid inclusions in diamond provide otherwise inaccessible information on the origin and nature of carbonaceous fluid(s) in the mantle. Here we evaluate the role of subducted volatiles in diamond formation within the Siberian cratonic lithosphere. Specifically, we focus on the halogen (Cl, Br and I) and noble gas (He, Ne and Ar) geochemistry of fluids trapped within cubic, coated and cloudy fibrous diamonds from the Nyurbinskaya kimberlite, Siberia. Our data show Br/Cl and I/Cl ratios consistent with involvement of altered oceanic crust, suggesting subduction-derived fluids have infiltrated the Siberian lithosphere. 3He/4He ranging from 2 to 11 RA, indicates the addition of a primordial mantle component to the SCLM. Mantle plumes may therefore act as a trigger to re-mobilise subducted carbon-rich fluids from the sub-continental lithospheric mantle, and we argue this may be an essential process in the formation of fluid-rich diamonds, and kimberlitic magmatism. Publisher PDF

A xenolith of bimineralic eclogite from the Udachnaya kimberlite pipe provides a snapshot of interaction between mantle rocks and diamond-forming fluids/melts. The major-element composition of the eclogite is similar to that of N-MORB and/or oceanic gabbros, but its trace-element pattern shows the effects of mantle metasomatism, which resulted in diamond formation. The diamonds are clustered in alteration veins that crosscut primary garnet and clinopyroxene. The diamonds contain microinclusions of a fluid/melt dominated by carbonate and KCl. Compared to the worldwide dataset, the microinclusions in these diamonds fall in middle of the range between saline fluids and low-Mg carbonatitic melts. The fluid/melt acted as a metasomatic agent that percolated through ancient eclogitic rocks stored in the mantle. This interaction is consistent with calculated partition coefficients between the rock-forming minerals and diamond-forming fluid/melt, which are similar to experimentally-determined values. Some differences between the calculated and experimental values may be due to the low contents of water and silicates in the chloride-carbonate melt observed in this study, and in particular its high contents of K and LILE. The lack of nitrogen aggregation in the diamonds implies that the diamond-forming metasomatism took place shortly before the eruption of the kimberlite, and that the microinclusions thus represent saline carbonate-rich fluids circulating in the basement of lithospheric mantle (150–170 km depth).

Headless placer diamond deposits occur in Cenozoic alluvium within the Paleoproterozoic Khapchan fold belt of the Olenek province in the northeastern part of the Siberian Platform, yet the known kimberlite pipes from this region are low-grade or non-diamondiferous. To characterise the subcontinental diamondiferous lithospheric mantle of this region, the mineral inclusions in 265 diamonds were exposed and analysed. Inclusions of the eclogite suite are predominant (> 72%): garnet, omphacitic clinopyroxene, coesite, K-feldspar, rutile and corundum. The garnet and Cpx inclusions are within the range of eclogitic inclusions worldwide. Diamonds of the peridotitic contain olivine, Сr-pyrope garnet, ortopyroxene and chromite. The olivines have Fo contents between 89.7 and 93.8 mol. % (average – 92.4). Majoritic garnets of both peridotitic and eclogitic parageneses were identified in four diamonds. Most eclogitic diamonds display positive Eu anomalies. High-Ca garnets are LREE-depleted, show strong positive Eu (up to 4.25) and Sr anomalies and have HREE contents lower than those of the lowand intermediate-Ca garnets. The presence of majorite inclusions indicates that some of the diamonds may have sublithospheric origins. Although diamonds with peridotitic-suite garnets constitute a minor percentage of the volume, the composition of these diamonds indicates a depleted composition for the peridotitic mantle. Diamonds of harzburgitic paragenesis compose 57% of the peridotitic suite, which is close to the world average. For an assumed pressure of 5 GPa, eclogitic garnet and clinopyroxene gave temperatures in the range of 1028–1290 oC. The composition of mineral inclusions of the peridotitic suite and the equilibrium temperatures of the eclogitic suite suggest that the lithospheric mantle of the Olenek province had a composition and thermal regime that was similar to those of the Archean cratonic mantle at the time the diamonds were brought to the surface.

We studied clastics of high-alumina garnet–kyanite–mica schists and garnet–kyanite–quartz granofelses, including diamond-bearing ones, found in the eluvial sediments near Lake Barchi. In contents of major elements the studied rocks correspond to argillaceous shales. The garnet–kyanite–quartz granofelses are poorer in K (0.49–1.35 wt.% K2O) than the garnet–kyanite–mica schists (4.9–2.2 wt.% K2O) but have the same contents of other major components. The REE patterns of most of the garnet–kyanite–phengite schists are similar to those of the Post-Archean Australian Shale (PAAS) (x¯La/Yb=13). All garnet–kyanite–quartz rocks are much stronger depleted in LREE (x¯La/Yb=1.4) and other incompatible elements. Our studies show that allanite and monazite are the main concentrators of LREE and Th in the garnet–kyanite–phengite rocks of the Barchi site. Monazite, occurring as inclusions in garnet, contains not only LREE but also Th, U, and Pb. Rutile of the nondepleted rocks is enriched in Fe and Nb impurities only. The garnet–kyanite–quartz granofelses bear rutile, apatite, and xenotime as accessory phases. Rutile of the depleted rocks shows wide variations in contents of Nb, Ta, and V impurities. In places, the contents of Nb and Ta reach 10.5 and 2.3 wt.%, respectively. The rutile decomposes into rutile with Nb (1.4 wt.%) and Fe (0.87 wt.%) impurities and titanium oxide rich in Fe (6.61 wt.%), Nb (up to 20.8 wt.%), and Ta (up to 2.81%) impurities. Based on the measured contents of incompatible elements in differently depleted high-alumina rocks, the following series of element mobility during UHP metamorphism has been established: Th > Ce > La > Pr > Nd > K > Ba > Rb > Cs > Sm > Eu. The contents of U, P, and Zr in the depleted rocks are similar to those in the nondepleted rocks. The studies have shown that metapelites subducted to the depths with diamond stability conditions can be depleted to different degrees. This might be either due to their exhumation from different depths of the subduction zone or to the presence of an external source of water controlling the temperature of dissolution of phengite and the formation of supercritical fluid/melt.

The spatial coexistence and synchronous formation of magmatogene porphyry Cu–Mo mineralization and epithermal gold mineralization are due to the genetic relationship between their formation processes. This relationship might be due to the generation of metal-bearing fluids of different geochemical compositions by the porphyry ore-magmatic system, which then participate in the formation of magmatogene porphyry Cu–Mo(Au) and associated epithermal gold deposits. Synthesis of fluid inclusions in quartz was performed for experimental study of the behavior of Cu, Mo, W, Sn, Au, As, Sb, Te, Ag, and Bi in heterophase fluids similar in composition and aggregate state to natural ore-forming fluids of porphyry Cu–Mo(Au) deposits. We have established that at 700 ºC, a pressure decrease from 117 to 106 MPa leads to a significant enrichment of the gas phase of heterophase chloride fluid with Au, As, Sb, and Bi. The heterophase state of carbonate–chloride–sulfate fluids is observed at 600 ºC and 100–90 MPa. It characterizes the highly concentrated liquid carbonate–sulfide phase–liquid chloride phase–low-density gas phase equilibrium. A decrease in the pressure of heterophase carbonate–chloride–sulfate fluid leads to a noticeable enrichment of its chloride phase with Cu, Mo, Fe, W, Ag, Sn, Sb, and Zn relative to the carbonate–sulfate phase. The processes of redistribution of ore elements between the phases of heterophase fluids can be considered a model of generation of metal-bearing chloride fluids, which occurs in nature during the formation of porphyry Cu–Mo(Au) deposits, as well as a model of generation of gas fluids supplying Au, Te, As, and other ore elements to the place of formation of epithermal Au–Cu and Au–Ag mineralization. © 2015, V.S. Sobolev IGM, Siberian Branch of the RAS. Published by Elsevier B.V. All rights reserved.

Evidence for phase transitions in mineral inclusions in superdeep diamonds of alluvial placers in the Sao Luiz River deposits (Brazil) is obtained by the electron backscatter diffraction technique. It has been shown that the crystal structure of superdeep diamonds is significantly deformed around inclusions of MgSi-, CaSi-, and CaTiSi-perovskites, SiO2 (stishovite?), and Mg2SiO4 (ringwoodite?). On the contrary, significant deformations around inclusions of olivine, ferropericlase, and majoritic garnet are not detected. The absence of deformation near these minerals reveals the lack of phase transitions with dramatic volume changes. The present study suggests that the formation of superdeep diamonds proceeds at different levels of the sublithospheric mantle, transition zone, and lower mantle. © 2015, V.S. Sobolev IGM, Siberian Branch of the RAS. Published by Elsevier B.V. All rights reserved.

The Zarnitsa kimberlite pipe is one of the largest pipes of the Yakutian diamondiferous province. Currently, some limited published data exists on the diamonds from this deposit. Among the diamond population of this pipe there is a specific series of dark gray to black diamonds with transition morphologies between octahedron and rounded rhombic dodecahedron. These diamonds have specific zonal and sectorial mosaic-block internal structures. The inner parts of these crystals have polycrystalline structure with significant misorientations between sub-individuals. The high consistency of the mechanical admixtures (inclusions) in the diamonds cores can cause a high grid stress of the crystal structure and promote the block (polycrystalline) structure of the core components. These diamond crystals have subsequently been formed due to crystallization of bigger sub-individuals on the polycrystalline cores according to the geometric selection law.

The results of isotope-geochemical studies of eclogits and host rocks of the North-Muya block are presented. The studies showed broad variations both in the character of distribution of incompatible elements and in the Nd and Sr isotope composition of eclogits from the North-Muya block. The Nd isotope composition of eclogits is characterized by broad variations, which is reflected in the value of ɛNd(T), which has both positive (from +0.3 to +6.9) and negative values (from −0.5 to −16.8). The isotope characteristics for the both samples of eclogits (Mu 12-11, 12-12) with the lowest values of ɛNd(T) clearly indicate protolith contamination by an ancient source of Meso- or Paleoarchean age. Consequently, the melts of the protoliths of the eclogites intruded into the continental crust, and the eclogite-gneiss complex of the North-Muya block may be considered as a paleozone of the continental subduction.

861 The Udachnaya kimberlite pipe in the Daldyn kimberlite field (Daldyn–Alakit region) of the central part of the Yakutian diamond province is the largest diamond deposit in Russia and one of the largest in the world. The pipe consists of two conjugate bodies: Udachnaya East and Udachnaya West. As is evident from the U–Pb dating of perovskites from kimberlites, the ages of the Udachnaya pipe formation are 367 ± 3 and 367 ± 5 Ma (Udachnaya East); 361 ± 4 and 353 ± 5 Ma (Udachnaya West) [1]. Deep seated xenoliths of mantle rocks in kimber lite pipes are represented by a wide spectrum of ultra basic rocks, as well as pyroxenites and eclogites. Eclogites are coarse granular rocks mostly composed of garnet and clinopyroxene with accessory rutile. In addition to bimineral eclogites, the most abundant among xenoliths of the basic composition, there are corundum and kyanite eclogites [2]. Numerous stud ies of eclogite xenoliths from the Udachnaya kimber lite pipe have provided evidence for the influence of mantle metasomatism on the upper mantle rocks and have distinguished some signs of metasomatic origin of diamonds [3, 4]. However, the age of these processes has been not determined to date. Because of this, we have performed the dating of rutiles from the eclogite xenolith (Sample UD 208 05) entering the composi tion of the secondary mineral association. Eclogite xenolith from the Udachnaya pipe (Sam ple UD 208 05) is bimineral eclogite composed of dark green xenomorphic clinopyroxene (3–6 mm) and round garnet (2–5 mm) grains reaching ~55 and ~44 vol %, respectively. The xenolith contains the areas of partial melting including veins crossing rock forming omphacite and garnet, which consist of amor phous material (silicate glass) and products of its replacement (chlorite and quartz). These areas are surrounded by replaced omphacite with the typical “sponged textures” (symplectites) [3]. Among the accessory minerals are rutile, ilmenite, and pyrrhotite. The chemical composition of minerals was analyzed by energy dispersive spectrometry on a Tescan MYRA 3 LMU electron microscope with an EDS detector (Oxford Instruments) and using a JEOL JXA 8100 X ray microanalyzer at the Institute of Geology and Mineralogy, Siberian Branch, Russian Academy of Sciences.

Distribution of water among the main rock-forming nominally anhydrous minerals of mantle xenoliths of peridotitic and eclogitic parageneses from the Udachnaya kimberlite pipe, Yakutia, has been studied by IR spectroscopy. The spectra of all minerals exhibit vibrations attributed to hydroxyl structural defects. The content of H2O (ppm) in minerals of peridotites is as follows: 23–75 in olivine, 52–317 in orthopyroxene, 29–126 in clinopyroxene, and 0–95 in garnet. In eclogites, garnet contains up to 833 ppm H2O, and clinopyroxene, up to 1898 ppm (~ 0.19 wt.%). The obtained data and the results of previous studies of minerals of mantle xenoliths show wide variations in H2O contents both within different kimberlite provinces and within the Udachnaya kimberlite pipe. Judging from the volume ratios of mineral phases in the studied xenoliths, the water content varies over narrow ranges of values, 38–126 ppm. At the same time, the water content in the studied eclogite xenoliths is much higher and varies widely, 391–1112 ppm.

Diamonds from placer deposits in the northeastern Siberian platform were examined for variations in the isotopic composition of carbon and concentrations of nitrogen. The diamonds display large variability in N concentrations, ranging from below detection to 3500 ppm. Nitrogen levels in diamonds with eclogitic inclusions are generally high (average of 950 ppm) compared to diamonds of the ultramafic suite (average of 513 ppm). Diamonds belonging to variety V (classification scheme of Orlov, 1977) have relatively high N levels (from 1500 to 3500 ppm, average of 2549 ppm). The average nitrogen level is five times higher than the worldwide average. Values of δ 13 C in the diamonds range from −27.2 to −3‰ ( n = 28) in eclogitic diamonds and from −7.1 to −0.5‰ ( n = 16) in peridotitic diamonds. Diamonds of variety V range in δ 13 C from −24.1 to −17.4‰. The distributions of nitrogen and its aggregation state in some diamond crystals imply the occurrence of multiple growth events. This is especially evident in the nitrogen content, which decreases and then increases from core to rim. The results indicate that there is no correlation between local variations in the isotopic composition of carbon and either the content or degree of aggregation of nitrogen. The diamonds of variety V differ from most diamonds worldwide in their high N content and light C-isotope composition. The large ranges of δ 13 C and the lack of correlation with nitrogen levels are inconsistent with the open-system Rayleigh isotopic fractionation of carbon species. The nature of the variations in the carbon isotope composition and the nitrogen concentrations indicate that the diamond growth medium had at least two sources of fluids/melts (mantle and recycled Earth crust via subduction). Mantle carbon was involved in the process of diamond formation during the final stages of diamond growth.

Diamonds from Juina province, Brazil, and some others localities reveal the existence of a deep, Ca-rich carbonate-silicate source different from ultramafic and eclogite compositions. In this study, we describe the first observation of merwinite (Ca 2.85 Mg 0.96 Fe 0.11 Si 2.04 O 8 ) in a diamond; it occurs as an inclusion in the central growth domain of a diamond from the Sao Luiz river alluvial deposits (Juina, Brazil). In addition, the diamond contains inclusions of walstromite-structured CaSiO 3 in the core and (Mg 0.86 Fe 0.14 ) 2 SiO 4 olivine in the rim. According to available experimental data, under mantle conditions, merwinite can only be formed in a specific Ca-rich and Mg- and Si-depleted enviroment that differs from any known mantle lithology (peridotitic or eclogitic). We suggest that such chemical conditions can occur during the interaction of subduction-derived calcium carbonatite melt with peridotitic mantle. The partial reduction of the melt could cause the simultaneous crystallization of Ca-rich silicates (CaSiO 3 and merwinite) and diamond at an early stage, and (Mg 0.86 Fe 0.14 ) 2 SiO 4 olivine and diamond at a later stage, after the Ca-Mg exchange between carbonatite melt and peridotite has ceased. This scenario is supported by the presence of calcite microinclusions within merwinite.

Taking advantage of the common occurrence of superdeep mineral inclusion assemblages, we examined core-to-rim primary zonation in 69 diamonds from the alluvial deposits of the Sao-Luis River (Juina, Brazil). Syngenetic inclusions were represented by phases of superdeep paragenesis. The dominant inclusions are majoritic garnets, ferropericlases and CaSi- and CaSiTi-perovskites. Rare inclusions of MgSi-perovskites, olivines, clinopyroxenes, TAPP, phases of SiO2, kyanites, AlSi-phases, KFsp (K-hollandite?), CF, NAL, grossular, merwinite, native iron, Fe-sulphides, magnesite and CaCO3 + CaMgSi2O6 (composite inclusions) were also found. The diamonds from Sao-Luis display wide variations in carbon isotopic compositions (δ13C), from +2.7 to −25.3‰. The diamonds with inclusions of ferropericlase have a very narrow range of δ13C values, from −2.1 to −7.7‰, which are close to the “normal” mantle values. In many cases, diamonds with inclusions of calcic majoritic garnet and CaSi- and CaSiTi-perovskites display marked differences from this range. Low δ13C values (−10 to −25 ‰) were observed exclusively in a series of diamonds with majorite garnets, Ca-silicates, aluminous silicates and SiO2. The δ13C values from the cores to rims in certain individual crystals varied substantially, indicating multiple stages of growth. The highly negative δ13C values in the cores (−20 to −25 ‰) potentially represent organic matter in metasediments of altered oceanic crust, and the lower δ13C values may represent mixing trends towards “normal” mantle compositions. In this study, we also found a set of diamonds that display an opposite trend of change of the carbon source, from primordial mantle to subducted/crust (either biotic or abiotic carbon).

The variety of morphology and properties of natural diamonds reflects variations in the conditions of their formation in different mantle environments. This study presents new data on the distribution of impurity centers in diamond type Ib-IaA from xenolith of bimineral eclogite from the Udachnaya kimberlite pipe. The high content of non-aggregated nitrogen C defects in the studied diamonds indicates their formation shortly before the stage of transportation to the surface by the kimberlite melt. The observed sectorial heterogeneity of the distribution of C- and A-defects indicates that aggregation of nitrogen in the octahedral sectors occurs faster than in the cuboid sectors.