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Experimental results on the growth of cubic diamond on lonsdaleite-bearing diamonds from the Popigai astrobleme at 5.5 GPa and 1450°C in the Fe–Ni–C system are presented. Due to the simultaneous appearance of several crystallization centers, the cubic diamond phase occurred in the form of an aggregate. This is probably due to the specific structure of the paracrystals of impact diamonds from nanosized crystallites (10–100 nm) or polysynthetic twinning inherited from graphite crystals under ultrahigh pressure. The color of the diamond crystals is yellow and is typical of diamonds grown in the Fe–Ni–C system. The predominant morphological shape of diamond crystals is octahedra with additional cubic, rhombic dodecahedron, and tetragonal-trioctahedra faces.

Olivine is the most common rock-forming mineral of the majority of the lithospheric mantle rocks beneath ancient cratons. This study provides the information about an epigenetic olivine in a lherzolite xenolith from the Udachnaya kimberlite pipe (Siberian craton), which is characterized by lower Mg# compared to the rock-forming one (Mg# = 87.4). The iron-rich olivine has been observed in the epigenetic mineral assemblage that forms a kelyphite shell around the rock-forming garnet. Olivine from the kelyphite shell occurs as both homogeneous grains (Mg# = 84.3–85.9) and zoned grains (Mg# = 85.1–87.5). The major and minor elements asymmetric zoning patterns have been found in the rock-forming olivine grains at the contact with the kelyphite shell. These olivine grains have an outer low Mg# (up to 85.9) zone at the contact with the kelyphite shell as the epigenetic olivine grains in the kelyphite shell. We suggest that the iron-rich epigenetic olivine was produced as the result of a reaction between the rock-forming garnet and the primitive kimberlite melt. During this reaction, a hybrid melt was formed in the interstitial space. The hybrid melt was iron-enriched relative to the kimberlite melt. The source of iron for the micro-portions of the interstitial hybrid melt was the rock-forming garnet.

Comprehensive studies of peridotitic xenoliths from the Udachnaya kimberlite (Yakutian diamond province, Siberian craton) confirm that garnet shows inverse correlation of its volumetric percentage with its Cr2O3 contents in refertilizated peridotites, but no such correlation is observed in depleted peridotites. The correlation relationship plots as an isosceles hyperbola, which is consistent with the existing knowledge of origin of refertilized peridotite. The bulk content of aluminum is proportional to the garnet percentage both in depleted and refertilized peridotites, but Al2O3 in the rock correlates with Cr2O3 in garnet only in the refertilized varieties, while the two parameters are independent in depleted mantle rocks. According to the modeling of refertilization-related composition changes in the Udachnaya peridotites, garnet percentages are directly proportional to the amount of clinopyroxene (Gnt = 0.879*Cpx + 0.022, R2 = 0.78) and inversely proportional to that of olivine (Gnt = 0.026/Ol3.141, R2 = 0.79). As the shares of Gnt and Cpx increase from minimum values, orthopyroxene first increases (to 0.16) and then decreases since 0.65 Ol, 0.09 Cpx, and 0.10 Gnt. This model can constrain the place of the parent rock in the refertilization series knowing Cr2O3 contents in separate garnet grains. The average refertilization degree of lithospheric mantle in the region estimated from the compositions of more than 800 garnet xenocrysts in the Udachnaya kimberlite is expressed in the rock modal composition as: Ol = 0.72, Opx = 0.15, Gnt = 0.07, and Cpx = 0.06 (median values).

The experimental results on etching of diamond crystals with octahedral and cubooctahedral habits at a temperature of 1000°С in wet argon are presented. It is found that at a low partial pressure, Н2О can act as an initiator (catalyst) of the surface graphitization of diamonds at the Р–Т-parameters of thermodynamic stability of graphite. The limiting stage of the diamond etching process in the presence of graphite on diamonds is the stage of graphite coating oxidation. Since the outer graphite coating is oxidized, there is no dependence of the etching (oxidation) rate on the morphology of diamond crystals.

Sulfide-bearing polymineralic inclusions in mantle-derived chromium pyrope garnets of lherzolite paragenesis from lamprophyres of the Chompolo field (Aldan shield, southern Siberian craton) have been studied. The inclusions are composed of either only sulfides or sulfides in association with other minerals (carbonates, silicates, oxides, etc.). The sulfide part of the inclusions is represented by up to four minerals. Among the sulfides, minerals rich in Cu and Ni have been found, whereas Fe sulfides (pyrrhotite, troilite) are absent. This distinguishes the inclusions studied from the majority of sulfide inclusions in mantle minerals and diamonds, as well as in mantle xenoliths from kimberlites. The formation of polymineralic inclusions in chromium garnets of the Chompolo field is attributed to the effect of a carbonate–silicate metasomatic melt/fluid on mantle peridotites, as evidenced by the mineral suite associated with the sulfides. The research results indicate significant differences in the nature of metasomatic processes that occurred in the lithospheric mantle of the southern and central parts of the Siberian craton.

Data on the interaction of the Fe–Ni melt with CaCO3 and graphite at 5 GPa and 1400°С under the thermogradient conditions used in experiments on the growth of diamond on the BARS high-pressure apparatus are presented. The phase composition and component composition of the fluid captured by diamonds in the form of inclusions were studied by gas chromatography–mass spectrometry (GC–MS). Diamonds were synthesized from graphite. During the interaction of the Fe–Ni melt with CaCO3, Ca–Fe oxides and (Fe, Ni)3C carbide were formed. The stability of heavy hydrocarbons under the experimental conditions was confirmed. It was established that the composition of the fluid in synthesized diamonds is close to the composition of the fluid from inclusions in some natural diamonds. Nevertheless, it was concluded that crystallization of large diamonds under natural conditions is hardly possible due to the filling of the main crystallization volume with refractory oxide phases.

The first results on diamond growth in the Fe–С–S system with 1 wt % S (relative to Fe) at 6 GPa and 1450°C have been reported. The diamonds obtained contain about 30 ppm N, on average, and belong to the low-N transition diamond group Ib–IIa. It has been suggested that the reduction conditions formed by certain active elements such as S can play an important role in the formation of natural low-N diamonds.

Analysis of diamond grains from placers in the northeastern Siberian craton shows that some diamond varieties (round dodecahedra, varieties II and V-VII in the classification of Orlov) may originate from Precambrian sources. The Precambrian diamonds have different sedimentation histories. Namely, diamonds of varieties V-VII are most strongly rounded though being the most resistant to wear. Therefore, they should have the longest history of dispersal and transport, and thus should be derived from the oldest primary deposits.

Based on a study of diamond grains from placers of the northeastern Siberian Platform, it is shown that certain types of diamonds (rounded dodecahedroids, diamonds of the II and V‒VII varieties, according to the classification by Yu.L. Orlov) could have originated from Precambrian sources. “Ancient” diamonds also differ in terms of their sedimentological history: those of varieties V‒VII, despite the maximum abrasion resistance, have the maximum degree of rounding, reflecting their more long-term sedimentological history, and, therefore, their ore bodies were likely the most ancient.

The enigmatic appearance of cuboctahedral diamonds in ophiolitic and arc volcanic rocks with morphology and infrared characteristics similar to synthetic diamonds that were grown from metal solvent requires a critical reappraisal. We have studied 15 diamond crystals and fragments from Tolbachik volcano lava flows, using Fourier transform infrared spectrometry (FTIR), transmission electron microscopy (TEM), synchrotron X-ray fluorescence (SRXRF) and laser ablation inductively coupled plasma mass-spectrometry (LA-ICP-MS). FTIR spectra of Tolbachik diamonds correspond to typical type Ib patterns of synthetic diamonds. In TEM films prepared using focused ion beam technique, we find Mn-Ni and Mn-Si inclusions in Tolbachik diamonds. SRXRF spectra indicate the presence of Fe-Ni and Fe-Ni-Mn inclusions with Cr, Ti, Cu, and Zn impurities. LA-ICP-MS data show variable but significantly elevated concentrations of Mn, Fe, Ni, and Cu reaching up to 70 ppm. These transition metal concentration levels are comparable with those determined by LA-ICP-MS for similar diamonds from Tibetan ophiolites. Mn-Ni (+Fe) solvent was widely used to produce industrial synthetic diamonds in the former USSR and Russia with very similar proportions of these metals. Hence, it appears highly probable that the cuboctahedral diamonds recovered from Kamchatka arc volcanic rocks represent contamination and are likely derived from drilling tools or other hard instruments. Kinetic data on diamond dissolution in basaltic magma or in fluid phase demonstrate that diamond does not form under the pressures and temperature conditions prevalent within the magmatic system beneath the modern-day Klyuchevskoy group of arc volcanoes. We also considered reference data for inclusions in ophiolitic diamonds and compared them with the composition of solvent used in industrial diamond synthesis in China. The similar inclusion chemistry close to Ni70Mn25Co5 for ophiolitic and synthetic Chinese diamonds scrutinized here suggests that most diamonds recovered from Tibetan and other ophiolites are not natural but instead have a synthetic origin. In order to mitigate further dubious reports of diamonds from unconventional tectonic settings and source rocks, we propose a set of discrimination criteria to better distinguish natural cuboctahedral diamonds from those produced synthetically in industrial environments and found as contaminants in mantle- and crust-derived rocks.

The trace element composition of the Onello meteorite is analyzed in detail using SEM and LA-ICP-MS. The following Ni contents of minerals are determined (wt %): 23.0-25.4 in taenite, 5.8-8.8 in kamacite, 22-26 in schreibersite, 44-52 in nickelphosphide, 20.6-21.8 in allabogdanite, and 75-81 in awaruite. In the trace element content, the Onello meteorite corresponds to the IAB group of iron meteorites. Inside this group, it mostly matches the sHH subgroup (with high Au and Ni contents). The presence of allabogdanite in the meteorite indicates the high PT parameters of its formation: >8 GPa and 1000-1400 °C. Thus, the formation of the Onello meteorite is related to impact metamorphism of a parental body of iron meteorites of the IAB group and vinonaites, in which a P- and Ni-rich area underwent melting and further crystallization.

This paper presents the results of a Raman spectroscopic study of shock melt veins in L6 chondritic meteorites Dhofar 717 and 864, and conclusions about the PT-parameters recorded in these meteorites after the impact event. The primary minerals of the host chondrite include olivine, orthopyroxene, clinopyroxene, plagioclase, chromite, phosphates, troilite, and kamasite. Shock melt veins up to 1 cm thick contain fragments of the high- pressure minerals ringwoodite, wadsleyite, majorite, akimotoite, jadeite, lingunite, and tuite and quenched melt consisting of majorite, ringwoodite, troilite, and kamasite. The mineral associations of the Dhofar 717 and 864 chondrites indicate high peak PT-parameters of the impact in the region of stability of majorite (>20 GPa and >2500 K) and bridgmanite (>25 GPa and >2500 K). The presence of lingunite also directly indicates a peak pressure in the area of stability of the bridgmanite.

—Lavas of the Kamchatka volcanoes store cubic-octahedral diamonds identical in morphology and structure to synthetic crystals, and their natural origin is doubted. Judging by published data, the diamonds discovered in the Tolbachik lavas are similar to synthetic diamonds made by different producers, and the analyzed samples rather result from contamination with synthetic material. Ophiolite-hosted diamonds reported from Europe, China, Mongolia, and Polar Urals look like the Tolbachik diamonds and are of the same type. The similarity between crystals coming from geologically dissimilar objects indicates that contamination may occur in those cases as well. Thus, diamonds found in unusual hosts or geologic settings require careful checking. These findings have to be reproduced repeatedly in other in situ samples and approved by independent experts; with all respect to the priority of the first finders, the sampling sites should be open to many researchers, especially the respective specialists. The inevitable disproval of false diamond findings is discouraging and discredits the true discoveries. Possible contamination with synthetic or natural material from cutting tools has to be excluded in all newly found diamonds before claiming their natural origin.

The trace element composition of the Onello meteorite is analyzed in detail using SEM and LA-ICP-MS. The following Ni contents of minerals are determined (wt %): 23.0–25.4 in taenite, 5.8–8.8 in kamacite, 22–26 in schreibersite, 44–52 in nickelphosphide, 20.6–21.8 in allabogdanite, and 75–81 in awaruite. In the trace element content, the Onello meteorite corresponds to the IAB group of iron meteorites. Inside this group, it mostly matches the sHH subgroup (with high Au and Ni contents). The presence of allabogdanite in the meteorite indicates the high PT parameters of its formation: >8 GPa and 1000–1400°C. Thus, the formation of the Onello meteorite is related to impact metamorphism of a parental body of iron meteorites of the IAB group and vinonaites, in which a P- and Ni-rich area underwent melting and further crystallization.

The first chromatography–mass spectroscopy data on volatiles in diamonds synthesized in the Fe–S–C system with 5 wt % S at 1400–1450°C and 5.0–5.5 GPa indicate the evolution of volatile composition during the diamond growth and, correspondingly, the variation in redox conditions of the reaction cell. A significant role is played by various hydrocarbons (HCs) and their derivatives, the content of which can reach 87%. Our data on possible abiogenic synthesis of HCs (components of natural gas and oil) can result in global recalculations (including climate) related to the global C cycle.

The first data of chromatography—mass spectrometry analysis of volatiles from crystals of synthetic diamonds grown in a Fe—Ni—C system at 1350–1400°С and 5.5–6.0 GPa are presented. The composition of the fluid in equilibrium with the metal-carbon melt is determined, and a comparative estimation for the compounds of different hydrocarbons and their derivatives is made. It is shown that a significant role in these processes is played by high-molecular-weight hydrocarbons; and the total share of hydrocarbons and their derivatives in the fluid compounds can exceed 86%.

A suite of seventeen unique, large, and fresh eclogite xenoliths from the Udachnaya pipe have been studied for their whole-rock and mineral major- and trace-element compositions. Based on their major-element compositions, the Udachnaya eclogites can be subdivided in two groups: high magnesian (Mg# 68.8–81.9) and low magnesian (Mg# 56.8–59). The two eclogite groups are clearly different in the style of correlation between major elements. Positive correlations of FeO and CaO with MgO are observed in the low-magnesian group, whereas these correlations are negative in the high-magnesian group. In terms of trace element composition, the Udachnaya eclogites are enriched over Primitive Mantle, but comparable to mid-ocean-ridge basalt composition, except for significant enrichment in large-ion lithophile elements (LILE; Rb, Ba, K, Sr). Most of the samples show a positive Eu anomaly, irrespective of group. Reconstructed whole-rock composition from clinopyroxene and garnet modal abundances contains much less incompatible elements (LILE, light rare earth elements, high field strength elements) than measured composition. Approximately 60 to 100% of the middle rare earth elements, Zr, and Hf, and nearly 100% of the heavy rare earth elements, Co, V, and Sc of the whole-rock budget are concentrated in Gar and Cpx. Variations in major element compositions cover a full section of the modern and Archaean oceanic crust, from troctolite, through gabbroic rocks, to basalts. The low-Mg# eclogites could have formed from upper oceanic crust protoliths, being a mixture of basalts and gabbro, whereas the high-Mg# eclogites are originated from gabbro-troctolite section of the lower oceanic crust. Concordant variations of Eu anomaly with the Lu/Sr ratio and the V and Ni contents in the eclogite compositions are in agreement with the fractionation of plagioclase, clinopyroxene, and olivine in their low-pressure precursor rocks. Negative correlations of SiO2 and MgO, and a low Nd/YbNMORB ratio, in the low-Mg# eclogites are in agreement with partial melt loss, but the presence of accessory quartz limits the degree of melting to 13%. Major and trace element compositions suggest that the high-Mg# eclogites, and, consequently, the lower oceanic crust, could not have experienced significant melt loss, and subduction in the Archaean may have been essentially dry, compared to the present day.

A complete microelement analysis of the Chinga meteorite was performed, and the possibility of attributing it together with a number of other iron meteorites into the IVC subgroup, which is transition between IVA and IVB is proposed.

The results of experimental modeling of the conditions of crystallization of high-Ca chromium garnets in the system serpentine–chromite–Ca-Cr-bearing hydrous fluid at a pressure of 5 GPa and temperature of 1300°С are reported. The mineral association including quantitatively predominant high-Mg olivine and diopside-rich clinopyroxene, bright-green garnet, and newly formed chrome spinel was formed. Garnet mostly crystallized around primary chromite grains and was characterized by a high concentration of CaO and Cr2O3. According to the chemical composition, garnets obtained are close to the uvarovite–pyrope varieties, which enter the composition of relatively rare natural paragenesis of garnet wehrlite. The experimental data obtained clearly show that high-Ca chromium garnets are formed in the reaction of chromite-bearing peridotite and Ca-rich fluid at high P–T parameters.

This paper presents new major and trace element data from 150 garnet xenocrysts from the V. Grib kimberlite pipe located in the central part of the Arkhangelsk diamondiferous province (ADP). Based on the concentrations of Cr 2 O 3 , CaO, TiO 2 and rare earth elements (REE) the garnets were divided into seven groups: (1) lherzolitic “depleted” garnets (“Lz 1”), (2) lherzolitic garnets with normal REE patterns (“Lz 2”), (3) lherzolitic garnets with weakly sinusoidal REE patterns (“Lz 3”), (4) lherzolitic garnets with strongly sinusoidal REE patterns (“Lz 4”), (5) harzburgitic garnets with sinusoidal REE patterns (“Hz”), (6) wehrlitic garnets with weakly sinusoidal REE patterns (“W”), (7) garnets of megacryst paragenesis with normal REE patterns (“Meg”). Detailed mineralogical and geochemical garnet studies and modeling results suggest several stages of mantle metasomatism influenced by carbonatite and silicate melts. Carbonatitic metasomatism at the first stage resulted in refertilization of the lithospheric mantle, which is evidenced by a nearly vertical CaO-Cr 2 O 3 trend from harzburgitic (“Hz”) to lherzolitic (“Lz 4”) garnet composition. Harzburgitic garnets (“Hz”) have probably been formed by interactions between carbonatite melts and exsolved garnets in high-degree melt extraction residues. At the second stage of metasomatism, garnets with weakly sinusoidal REE patterns (“Lz 3”, “W”) were affected by a silicate melt possessing a REE composition similar to that of ADP alkaline mica-poor picrites. At the last stage, the garnets interacted with basaltic melts, which resulted in the decrease CaO-Cr 2 O 3 trend of “Lz 2” garnet composition. Cr-poor garnets of megacryst paragenesis (“Meg”) could crystallize directly from the silicate melt which has a REE composition close to that of ADP alkaline mica-poor picrites. P - T estimates of the garnet xenocrysts indicate that the interval of ∼60–110 km of the lithospheric mantle beneath the V. Grib pipe was predominantly affected by the silicate melts, whereas the lithospheric mantle deeper than 150 km was influenced by the carbonatite melts.

The results of integrated studies of inclusion-containing diamonds from kimberlites of the Snap Lake dike complex (Canada) are presented. Features of the morphology, defect–impurity composition, and internal structure of the diamonds were determined by optic and scanning microscopy. The chemical composition of crystalline inclusions (olivine, garnet, and pyroxene) in diamonds was studied using a microanalyzer with an electronic probe. The inclusions of ultramafic paragenesis in the diamond (87%) are predominant. Carbonates, sulfide and hydrated silicate phases were found only in multiphase microinclusions. The large phlogopite inclusion studied was similar in composition to earlier studied nanosize inclusions of high-silica mica in diamonds from Snap Lake kimberlites. Revealed features of studied diamonds and presence of high-silica mica suggest that diamonds from Snap Lake have formed as the result of interaction between enriched in volatile and titanium high-potassium carbonate–silicate melts and peridotitic substrate at the base of thick lithospheric mantle.

Although kimberlite magma carries large amounts of mantle-derived xenocrysts and xenoliths (with sizes up to meters), this magma ascends from the Earth's mantle (> 150–250 km) to the surface in a matter of hours or days, which enables diamonds to survive. The recently proposed assimilation-fuelled buoyancy model for kimberlite magma ascent emphasizes the importance of fluid CO2 that is produced via the reactive dissolution of mantle-derived orthopyroxene xenocrysts into kimberlite melt, which initially has carbonatitic composition. Here, we use a series of high-pressure experiments to test this model by studying the interaction of orthopyroxene (Opx) with an alkali-dolomitic melt (simplified to 0.7Na2CO3 + 0.3K2CO3 + 2CaMg(CO3)2), which is close to the melt that is produced by the partial melting of a kimberlite source, at P = 3.1–6.5 GPa and T = 1200–1600 °C, i.e., up to pressures that correspond to depths (~ 200 km) from where the ascent of kimberlite magma would start. During the first set of experiments, we study the reaction between powdered Opx and model carbonate melt in a homogeneous mixture. During the second set of experiments, we investigate the mechanism and kinetics of the dissolution of Opx crystals in alkali-dolomitic melt. Depending on the P-T conditions, Opx dissolves in the alkali-dolomitic melt (CL) either congruently or incongruently via the following reactions: Mg2Si2O6 (Opx) + CaMg(CO3)2 (CL) = CaMgSi2O6 (clinopyroxene) + 2MgCO3 (CL) and Mg2Si2O6 (Opx) = Mg2SiO4 (olivine) + SiO2 (CL). The experiments confirm that the dissolution of Opx causes gradual SiO2 enrichment in the initial carbonate melt, as previously suggested. However, the assimilation of Opx by carbonate melt does not produce fluid CO2 in the experiments because the CO2 is totally dissolved in the evolved melt. Thus, our results clearly demonstrate the absence of exsolved CO2 fluid at 3.1–6.5 GPa in ascending kimberlite magma and disprove the assimilation-fuelled buoyancy model for kimberlite magma ascent in the lithospheric mantle. We alternatively suggest that the extreme buoyancy of kimberlite magma at depths of 100–250 km is an exclusive consequence of the unique physical properties (i.e., low density, ultra-low viscosity and, thus, high mobility) of the kimberlite melt, which are dictated by its carbonatitic composition.

Compared to xenoliths, kimberlite xenocrysts provide, although less accurate, more complete information about the deep structure and processes in the subcratonic lithospheric mantle (SCLM). This work is devoted to the study the composition of xenogenic olivine from kimberlites as the main mineral constituting SCLM. Olivine in kimberlites has a different origin, including those not related to depleted rocks of the lithosphere. It can crystallize directly from kimberlite or belong to the so-called Cr-poor megacryst association. In this regard, for the correct interpretation of data on its composition, it is necessary to have sufficiently clear criteria for the separation of olivine xenocrysts from kimberlites into various genetic types. In order to remove olivines crystallizing directly from kimberlite from consideration, in our study we used only central homogeneous parts of crystals larger than 0.5 mm in size [Giuliani, 2018].Based on unique and literature data on the composition of olivines from 230 xenoliths of peridotites from 12 kimberlites of the North American, South African and Siberian cratons we proposed a general division into 4 genetic types: olivines of ultrahigh-temperature (HTP-1), high-temperature (HTP-2), low-temperature (LTP) peridotites, olivines of low-chromium megacrystal association (MCA). The separation scheme uses the CaO content as an indicator of the temperature of formation and the ratio Mg/Mg+Fe as an indicator of the degree of enrichment.A study of more than 1,500 olivines from a number of kimberlite bodies of the Siberian platform according to this scheme revealed three characteristic distributions of olivine types in kimberlite bodies: 1) without high-temperature differences (Obnazhennaya pipe), 2) with significant development of HTP-2 (Olivinovaya and Vtorogodnitsa pipes) and 3) with significant development of HTP-1 (Dianga pipe). Only the latter type is characterized by the presence of a noticeable amount of olivines of the megaryst association.In general, variations in the composition of LTP olivines correspond to granular ones, while HTP-1 and HTP-2 correspond to deformed (shared) peridotites. Interestingly, the enrichment of olivines with incompatible components in these three types does not correlate directly with the formation temperature. Olivines of ultrahigh-temperature peridotites (HTP-1) have unexpectedly small compositional variations and occupy an intermediate position between low-temperature and high-temperature in content of incompatible elements.A study of the content of impurity elements (TiO2, NiO) in olivines made it possible to propose the way of formation of two different types of high-temperature olivines. It belongs to the model [Harte et al., 1993; Burgess and Harte, 1999; Burgess and Harte, 2004] where megacrystal melt of various stages of fractionation [Moore et al., 1992] effects depleted rocks of lithospheric mantle. According to it, HTP-2 olivines arose upon exposure to a fractionated melt characteristic of late crystallization stages, and HTP-1 olivines due to unfractionated (less enriched with incompatible components) megacrystal melt at higher temperatures characteristic of the initial crystallization stage.Funded by RFBR grant 18-05-01143, T.V.A. was supported by RSF grant 16-17-10067.

Moissanites were found in tagamites of the Popigai meteorite crater along with impact diamonds. We have studied 55 samples including 49 individual polytypes and six intergrowths. The numbers of 6H, 15R, 4H, 6H/15R, and 6H/4H polytypes are 82, 7, 5, 4, and 2%, respectively. By the assemblage of polytypes, the moissanites of the Popigai astrobleme are distinct from kimberlite moissanites, as well as from synthetic SiC, which is characterized by the absence of the 4H polytype and the presence of more diverse inclusions (including Fe-bearing). The Popigai astrobleme is one of few objects with reliable natural moissanite. Technogenic contamination is excluded, since any researcher can find this mineral in tagamites.

The results of experiments on dissolution of diamond in a Fe melt with variable concentrations of S at high P–T parameters are presented. It is established that the maximal degree of diamond dissolution occurs at a sulfur concentration of 15 wt %. With decreasing or increasing S content, dissolution of diamond slows down and almost does not occur during the period of the experiment (60 min), when the “eutectic” composition is gained. In contrast to a pure Fe melt, the presence of S decreases the carbon solubility and, therefore, reduces the aggressiveness of metal melt in relation to diamonds, thus, stimulating their preservation in the Earth’s mantle, especially if the concentration of S exceeds that in the “eutectic” composition.

The first results are presented for the synthesis of diamond at 6.5 GPa and 1600°C during migration of molten iron through a silicate matrix, which is composed of olivine crystals with interstitial graphite. The experiment shows that diamonds in the Earth’s mantle and the terrestrial planets could have formed during differentiation. Diamond crystals, which were formed during iron segregation of the Earth’s differentiation, could be centers for further crystallization of mantle diamonds.

New results of Rb–Sr and Sm–Nd isotope analyses have been obtained on samples of deformed peridotite xenoliths collected from the Udachnaya kimberlite pipe (Yakutia). The data obtained imply two main stages of metasomatic alteration of the lithospheric mantle base matter in the central part of the Siberian Craton. Elevated ratios of Sr isotopes may be considered as evidence of an ancient stage of metasomatic enrichment by a carbonatite melt. The acquired Nd isotope composition together with the geochemistry of the deformed peridotite xenoliths suggests that the second stage of metasomatic alteration took place shortly before formation of the kimberlite melt. The metasomatic agent of this stage had a silicate character and arrived from an asthenosphere source, common for the normal OIB type (PREMA) and the Group-I kimberlite.

40Ar/39Ar dating of phlogopite from kelyphitic rims around garnet grains from the Udachnaya–Vostochnaya kimberlite pipe in the Sakha (Yakutia) Republic (Russia) revealed that when this mineral has contact with a kimberlite melt its age corresponds (within error limits) to that of the formation of the kimberlite pipe, thus indicating that the method may be used for dating kimberlites and related rocks. In mantle xenoliths, kelyphitic phlogopites rimming garnet grains partially lose radiogenic Ar, which results in a complex age spectrum. Rejuvenation of the K/Ar system in them is determined by the thermal impact of the kimberlite melt on captured rocks.

The results of morphological examination and the character of the structural orientation and estimation of residual pressure calculated from spectra of combination dispersion in olivine inclusions within diamonds of the Ebelyakh placer and kimberlite pipes of the Yakutian Diamondiferous Province are presented. The data analysis aimed at revealing indications of similarity and/or differences between diamonds from the pipes and the placer. Differences in the structural orientation and spectra of combination dispersion of the inclusions of olivine in dodecahedroids of placers of the northeastern part of the Siberian Platform support the assumption of their non-kimberlite nature.

The results of the first study of the PGE distribution in deformed lherzolites of the Udachnaya kimberlite pipe (Yakutia) are presented here. The complex character of evolution of the PGE composition in the Deformed lherzolites is assumed to be the result of silicate metasomatism. At the first stage, growth in the amount of clinopyroxene and garnet in the rock is accompanied by a decrease in the concentration of the compatible PGE (Os, Ir). During the final stage, the rock is enriched with incompatible PGE (Pt, Pd) and Re possible due to precipitation of submicron-sized particles of sulfides in the interstitial space of these mantle rocks.

Data are presented on the discovery of altaite in the Maslyanino iron meteorite with silicate inclusions (IAB group), the interrelations of altaite and other minerals are shown, and models of altaite petrogenesis are proposed.

Study of the magmatics in the Nakyn kimberlite field, with consideration of the isotope dating results, allowed us to establish a sequence of their formation. First, 368.5–374.4 Ma ago intrusions of the Vilyui–Markha dike belt formed. Then (363–364 Ma) intrusion of kimberlites took place. In the Early Carboniferous (338.2–345.6 Ma), alkaline basaltic magma intruded through faults controlling the kimberlites. The magmatic activity finished 331–324.9 Ma ago with the formation of explosive breccias. It has been found that the Nyurba kimberlite pipe consists of two bodies: their kimberlite melts have successively intruded through independent channels.

The authors wish to make the following erratum to this paper [...]