The conditions of genesis of diamondiferous ultrabasic and basic rocks from xenoliths in kimberlite were studied by combining the data from analytical investigations of their mineral phases and experimental results of the study of melting relations in the diamond-forming mineral systems of the upper mantle. The compositions of minerals in some samples of metasomatized diamondiferous eclogite associated with diamond-free eclogite from kimberlite of the Udachnaya pipe (Yakutia) were studied for the first time. The new results obtained in addition to the literature data were applied for generalization of estimates of genetically important characteristics of the chemical compositions of garnets, Ca-clinopyroxenes, and omphacites from diamond-bearing peridotite, pyroxenite, and eclogite. As a result, it was found that quite “fresh” minerals of diamondiferous rocks have typomorphic differences from the same minerals of diamond-free upper-mantle rocks. At the same time, it is significant that the compositions of minerals from diamondiferous rocks and paragenetic inclusions in diamonds are identical. These peculiarities of mineralogy of diamondiferous rocks are genetically significant; based on the mantle–carbonatite theory of the origin of diamond and associated mineral phases, this provides support for the same physicochemical origin of diamonds, minerals of diamondiferous rocks, and paragenetic inclusions in diamonds. Finally, the following genetic conclusions are made. (1) Completely miscible silicate (±oxide)–carbonate melts with dissolved carbon are the parental medium in petrogenesis of diamondiferous ultrabasic and basic rocks. (2) The physicochemically consistent formation of diamondiferous rocks and paragenetic inclusions of peridotitic and eclogitic minerals in diamonds occurred in the common diamond-forming chambers/reservoirs of parental melts; diamond-free peridotite, pyroxenite, and eclogite were the host mantle rocks for such chambers. (3) The origin of continuous series of diamondiferous peridotite–pyroxenite–eclogite rocks is controlled by the fractional ultrabasic–basic evolution of parental melts with exhaustion of olivine and orthorhombic pyroxene via the peritectic reactions. (4) Ascending flows of kimberlite magmas destroyed the parental chambers and captured diamonds with inclusions, individual minerals, their intergrowths, diamondiferous ultrabasic and basic rocks; at the entrance and exit from the chambers, they captured differentiated diamond-free host rocks of the mantle as well. (5) With further ascent from the mantle to the Earth’s crust, the material of diamond-forming chambers and diamond-free mantle was mixed in convecting kimberlite magma and was transported from the mantle to cumulative crustal chambers. (6) Kimberlite magmas were gradually solidified in stationary cumulative chambers with the release of highly compressed fluids; with an increase of pressure up to the critical values, they intruded into the rocks of the roof and ejected kimberlite with xenoliths of diamondiferous and mantle rocks to the surface with the formation of explosion pipes.

Archangelsk kimberlite-picrite Region is world-class source of diamonds, where two large diamond deposits in mining stage presently, with total reserves more than 300 mln carats.Besides that, there is more than a hundred occurrences of non-diamondiferous kimberlites, its convergent rocks and tholeiitic basalts (Fig. 1) (Bogatikov et al., 1999; Garanin, 2006).Within this region based on main petrological characteristics, the largest regional formational taxons have been distinguished: (1) Zimneberezhny Mega-Complex of kimberlites-non-pyroxene alkaline picrites, (2) Nenokso-Chidvinsky Mega-Complex of feldspathic picrites-olivine melilitites (Fig. 2) and (3) Soyana-Pinezhsky dolerite-basalt Complex (Tretyachenko 2008;2015).

Recent studies of microcrystalline (< 100 μm) oxide minerals from the groundmass of Yakutian and Arkhangelsk diamondiferous provinces kimberlites showed that these minerals are sensitive to the origination, evolution and formation conditions of the kimberlitic rocks. Therefore, their compositional peculiarities and mineral ratios could be used potentially as indirect criteria for express-evaluation of kimberlites as potential diamond host (Garanin V.K. et al., 2009). It was found that indirect criteria for potential diamond-content of kimberlite rocks, reflects the formation depth of kimberlite melts and the possibility of removal of the diamond to the surface, is microcrystalline picrochromites (contain >40-42 wt.% Cr2O3, and less than 6 wt.% TiO2) and/or microcrystalline chromium picroilmenites (> 10 wt.% MgO and an average 2.3-3.5 wt.% Cr2O3) presence in groundmass, depending on the specialization of microcrystalline oxides. Indicators of reducing the original diamond grade, reflecting the length of occurrence the diamond in the transporting kimberlite melt and aggressiveness degree of the latter, are the extensive crystallization trends of microspinellides with successively forming varied composition ulvospinels and titanomagnetites, a large perovskite number (> 30-40% microoxide phases), etc. This study’s aim was to establish the possibility of using previously identified relationship between microcrystalline oxides and diamond grade for African kimberlites. In this regard, microcrystalline oxides from kimberlitic groundmass were investigated. Kimberlites differ by diamond grade and presented well-known and recently discovered pipes: Marsfontein (South Africa), Camachia, Catoca and other north-eastern

pipes with diamond grade; pipes and others pipes with low diamond grade, Grenada pipe non-diamond-bearing), in which in heavy mineral concentrates are widely submitted chromites and ilmenite, are allocated two equal trends: spinelic and ilmenitic ones. The spinelic trend begins from midium-chromium picroferrochromites with 49-52% Cr203 and 2,5-5,5 % Ti02 for diamondiferous pipes; from midium-chromium picroferrichromites with 42-44% Cr203 and 5-7% Ti02 for low diamond bearing pipes; from magnesian Cr-bearing ulvospinel (37-38% Cr203 and 9-10% Ti02) for non-diamond-bearing pipes. All these trends are completed by titanomagnetite crystallization for picritic pipes (Velikan, Montichellitovaya) are typical Cr-bearing ulvospinels with 21-24% Cr203 and 10-13% Ti02 are typical. Ilmenitic trend begins from picroilmenites for diamondiferous pipes. For non¬ diamond-bearing pipes is only characteristic Mn-containing ilmenite. Only one ilmenitic trend with predominantly distribution of Mn-containing ilmenite is established for magnesian ferrriferous-titanian non-diamond-bearing kimberlites with low contents pyropes and chromespinels and with high content of ilmenite (Morkokka

The collections of 55 diamond crystals from Timan placers was studied by method of scan¬ ning electron microscopy on SEM JSM -T20 (JEOL, Japan) and spectroscopic method on absor¬ ption spectra in visible and ultraviolet ranges on the MPS -2000 spectrophotometer (Shimadzu, Japan).Morphological discription was done on the basic Yu.L. Orlov classification (1984). MorphologyDiamonds of the I morphological type prevail (52.7 %).Rombododecahedron are widely distributed among investigated crystals.Usually they are colorless crystals and have clear

The mineralogical and petrogeochemical features of the Neoproterozoic kimberlite rocks of the Lahtojoki and Niilonsuo pipes of the Kaavi cluster (Kaavi-Kuopio, Finland) have been studied, differences in their petrogeochemical composition, quantitative and chemical composition of oxide minerals of deep (mantle) and kimberlite genesis have been revealed. The kimberlites of the pipes are moderately titanic, but the TiO2 content in the kimberlites of Niilonsuo is higher (2.11 wt.%) than in the kimberlites from the breccia of the Lahtojoki pipe (1.07 wt.%). The kimberlites of the Niilonsuo pipe also differ in higher concentrations of Fe2 O3 , Ca, P, K, Rb, V, Nb, Ba, Th, U, Ta and REE. In the Lahtojoki kimberlite breccias the main TiO2 concentrator mineral is magnesian ilmenite (13,3—15,2 wt.% MgO; 0,5—4,4 wt.% Cr2 O3 ), (macrocrysts up to 4 mm); the fine-grained matrix of rocks contains small grains of rutile, chromespinelides, Mn-ilmenite and sometimes titanomagnetite. Macrocrystals of magnesian ilmenite have been not found in the kimberlites of the Niilonsuo pipe, perovskite acts as the main mineral of titanium, and chromespinelids and titanomagnetite are less common. Long-term crystallization of relatively large (up to 200 μm) perovskite grains proceeded according to estimates using an Nb-Fe-perovskite oxybarometer under a wide range of oxygen fugacity (fо2 ) of the kimberlite melt (NNO from -3,8 to 5,1). Chromespinelids from the groundmass of kimberlite pipe rocks differ in composition, but have the same specific zonality — enrichment of Al and Mg in the edge zones of crystals, which is possibly due to the dissolution of phlogopite phenocrysts in the rising kimberlite melt. In addition to oxide minerals, djerfisherite is widely distributed in the groundmass of kimberlites of the Niilonsuo pipe, the composition of which for the rocks of the body has been described for the first time. The combination of features of oxide mineralization indicates unfavorable conditions for the preservation of diamonds during their transportation by kimberlite melt.

Magnetoplumbite-group minerals from various paragenetic assemblages, including a xenolith of altered garnet lherzolite from the Obnazhennaya kimberlite pipe in Yakutia, sulfide-free metasomatic Pb–Zn–Sb ore from the Pelagonian massif in the Republic of North Macedonia, and some other metasomatic occurrences have been studied with electron microprobe, as well as using IR and Raman spectroscopy. New data on isomorphic substitutions and crystal chemistry of the magnetoplumbite-group minerals have been obtained. Three potentially new mineral species belonging to this group have been identified: Al-dominant analogue of yimengite, Ba-dominant analogue of nežilovite, and Mn-dominant analogue of plumboferrite.

The garnet nodules from the enrichment concentrate of the Mir kimberlite pipe, which have different saturation levels of regularly oriented mineral and primary polyphase fluid inclusions, are investigated. The garnets that contain inclusions are classified in the grossular-almandine-pyrope series and are usually characterized by an increased content of Si, Mg, Al, and the absence of Fe 3+ . The polyphase fluid inclusions are studied using IR-Fourier- and Raman spectroscopy. The presence of polyaromatic hydrocarbons, H 2 O and CO 2 is established in their structure, which indicates the hydrocarbon specific character of fluids that participate in the processes of deep mineral formation.

The mineralogical and petrogeochemical features of the Neoproterozoic kimberlite rocks of the Lahtojoki and Niilonsuo pipes of the Kaavi cluster (Kaavi-Kuopio, Finland) have been studied, differences in their petrogeochemical composition, quantitative and chemical composition of oxide minerals of deep (mantle) and kimberlite genesis have been revealed. The kimberlites of the pipes are moderately titanic, but the TiO2 content in the kimberlites of Niilonsuo is higher (2.11 wt.%) than in the kimberlites from the breccia of the Lahtojoki pipe (1.07 wt.%). The kimberlites of the Niilonsuo pipe also differ in higher concentrations of Fe2 O3 , Ca, P, K, Rb, V, Nb, Ba, Th, U, Ta and REE. In the Lahtojoki kimberlite breccias the main TiO2 concentrator mineral is magnesian ilmenite (13,3—15,2 wt.% MgO; 0,5—4,4 wt.% Cr2 O3 ), (macrocrysts up to 4 mm); the fine-grained matrix of rocks contains small grains of rutile, chromespinelides, Mn-ilmenite and sometimes titanomagnetite. Macrocrystals of magnesian ilmenite have been not found in the kimberlites of the Niilonsuo pipe, perovskite acts as the main mineral of titanium, and chromespinelids and titanomagnetite are less common. Long-term crystallization of relatively large (up to 200 μm) perovskite grains proceeded according to estimates using an Nb-Fe-perovskite oxybarometer under a wide range of oxygen fugacity (fо2 ) of the kimberlite melt (NNO from -3,8 to 5,1). Chromespinelids from the groundmass of kimberlite pipe rocks differ in composition, but have the same specific zonality — enrichment of Al and Mg in the edge zones of crystals, which is possibly due to the dissolution of phlogopite phenocrysts in the rising kimberlite melt. In addition to oxide minerals, djerfisherite is widely distributed in the groundmass of kimberlites of the Niilonsuo pipe, the composition of which for the rocks of the body has been described for the first time. The combination of features of oxide mineralization indicates unfavorable conditions for the preservation of diamonds during their transportation by kimberlite melt.

— Interaction between a melt of kimberlite from the Nyurbinskaya pipe (Yakutia) and natural monocrystalline diamonds was studied experimentally at 0.15 GPa and 1200–1250°C in high-pressure and high-temperature Ar gas “bombs.” The loss of diamond weight with slight surface dissolution of diamonds in a Ca carbonate-bearing kimberlite melt over the course of 2 h (the period of kimberlite transport from upper-mantle diamond-forming chambers to the crustal cumulative centers) is 3–4.5%. In 4 and 7–8 days (under the conditions of crustal cumulative centers), the weight of diamond decreases with remarkable bulk dissolution by 13.5 and 24.5–27.5%, respectively. In the run at 0.15 GPa and 1200°C kimberlite and ilmenite (added) melts interact to produce perovskite melt. Both of the melts, rich in titanium minerals, are immiscible with kimberlite melt and therefore cannot influence the diamond dissolution kinetics in the kimberlite melt. The experimental results suggest that precisely the dissolution processes for thermodynamically metastable diamonds in silicate–carbonate kimberlitic magmas are responsible for the effective decrease in the diamond potential of kimberlite deposits. The paper discusses the physicochemical reasons for the decrease in the kimberlite diamond potential during the chemically active history of diamond genesis: from upper-mantle chambers to the explosive release of diamonds and kimberlite material from cumulative centers to the Earth’s surface. The data on experimental physicochemical studies of the origin, analytical mineralogy of inclusions, and isotope geochemistry of diamonds are correlated.

Melting relations in the multicomponent diamond-forming systems of the upper mantle with a boundary of K–Na–Mg–Fe–Ca carbonate, phases of the model peridotite and eclogite, carbon, and titanium minerals from kimberlite (ilmenite FeTiO3, perovskite CaTiO3, and rutile TiO2) were studied experimentally at 7–8 GPa and 1600–1650°C. Perovskite reacts with the formation of rutile in the diamond-forming silicate–carbonate melts. We discovered liquid immiscibility between melts of titanium minerals, on the one hand, and carbonate–carbon, peridotite–carbonate–carbon, and eclogite–carbonate–carbon diamond-forming melts, on the other. The solubility of titanium mineral in diamond-forming melts is negligible independent of their concentration in the experimental systems. Growth melts retain high diamond-forming efficiency. In general, the experimental results are evident for the xenogenic nature of titanium minerals in inclusions in diamond and, therefore, in diamond-forming melts. It is shown that the physicochemical factors that may correlate the diamond content with the concentration of Ti in kimberlite do not occur during the diamond genesis in silicate–carbonate–carbon parental melts containing titanium minerals and their melts.

The M.V. Lomonosov diamond deposit, Arkhangelsk region, NW Russia consists of six kimberlite pipes, forming 9.5 km length cluster within the Zolotitskoe Kimberlitic Field. These pipes are composed of the same type petrography varieties of kimberlitic rocks, but based on a number of geological and diamond features this cluster divided into Northern (M.V. Lomonosova, Pomorskaya, Pionerskaya and Karpinskogo-2 pipes) and Southern (Karpinskogo-1, Archangelskaya) Groups (Fig. 1a). The diamond grade in main types of ore – tuffisitic (autolithic) kimberlites of the Southern Group kimberlite pipes is higher (1.2-1.5 ct/t) than in the Northern Group (0.4-0.7 ct/t). Pomorskaya pipe reserves with low diamond grade ores (<0.1 ct/t) estimated as resources presently, because the mining of this pipe is unecomical presently.

Experimental studies of melting relations in the system ilmenite–K–Na–Mg–Fe–Ca carbonatite–carbon at 8 GPa and 1600°C provide evidence for the effect of liquid immiscibility between ilmenite and carbonatite melts. It is shown that the solubility of ilmenite in carbonatitic melts is negligible and does not depend on its concentration in experimental samples within 25–75 wt %. However, carbonatite–carbon melts are characterized by a high diamond-forming efficiency. This means that the correlation between the concentration of TiO2 and diamond content is problematic for mantle chambers and requires further, more complex, experimental studies.