Arkhangelsk Diamondiferous Province Research Articles

PREDICTION OF THE PRIMARY SOURCES OF GIANT CLIPPIR DIAMONDS IN THE NORTH OF YAKUTIA BY THE METHOD OF MINERALOGICAL AND GEOCHEMICAL ANALOGY (METHOD 5E DIAGRAMS)

The finds of giant CLIPPIR-type diamonds in the placers hosted by the Ebelyakh River basin in the north of Yakutia suggest that similar diamonds can be found in the kimberlites of the Anabar region and the nearest northern deposits located within the collisional Khapchan and Daldyn terranes. To predict the discovery of such diamonds, the authors use the 5E diagram method based on the principle of similarity of the compositions of five oxides of satellite minerals (Grt, Cpx, Chr and Ilm) of diamond (DSM) with the reference diagrams for the Karowe pipe (K-6, Botswana) with the composition of those for any other pipe. It was previously shown that the convergence of the DSM compositions of the Karowe and V. Grib (Arkhangelsk diamond province) pipes is 74 %, which might indicate possible presence of CLIPPIR diamonds in the predicted pipe. The application of this technique to two kimberlite pipes of the Anabar region demonstrated that the probability of detecting such diamonds in the Leningrad pipe (Lower Devonian, medium diamond content potential) is 74 %, and in the Malokuonamskaya pipe (Lower Triassic, medium diamond content) is 20 %. A comparison of diagrams 5E and additional PTС – fO2 diagrams of reconstructed sections of the lithospheric mantle showed their efficiency in predicting favorable conditions of CLIPPIR-type diamond crystallization. It is assumed that formation of such diamonds may occur within the proto-kimberlite magmatic chamber located near the boundary of the lithosphere and associated with the asthenospheric source. It should be surrounded by low-oxidized carbon-rich mantle eclogites and dunites with high pressure and temperature, as well as magnesium-rich ilmenite-chromite metasomatites. The use of the 5E diagram method, as the approach to predict giant CLIPPIR diamonds in poorly diamondiferous kimberlites, might attract investing for exploration to audit the industrial potential of a series of such kimberlites in the Anabar region. Its implementation would significantly increase the efficiency of geological exploration and assessment of the potential of poorly diamondiferous pipes that have been suspended as subeconomic.

Thermal State and Thickness of the Lithospheric Mantle Beneath the Northern East-European Platform: Evidence from Clinopyroxene Xenocrysts in Kimberlite Pipes from the Arkhangelsk Region (NW Russia) and Its Applications in Diamond Exploration

This paper presents the reconstruction of the architecture of the lithospheric mantle, including its thermal state and thickness, as well as the scale and efficiency of its sampling by four kimberlites from the Arkhangelsk diamondiferous province: Arkhangelskaya, Lomonosovskaya, V. Grib, and TSNIGRI-Arkhangelskaya. These kimberlites differ in terms of their composition, diamond content, and location. Data presented include the major-element composition of clinopyroxene xenocrysts (>2000 grains), P–T calculations from compositionally filtered Cr-diopside grains, and the reconstruction of local paleogeotherms. Additionally, we used available data on Ni content in peridotitic garnet xenocrysts to calculate their T values and project them onto local Cr-diopside-derived geotherms to reconstruct the vertical distribution of mantle xenocrysts and assess the efficiency of lithospheric mantle sampling by different kimberlites. We identified the presence of a >200 km-thick lithospheric mantle beneath the region at the time of kimberlite emplacement. We also found that the diamond content of the studied pipes was, to some extent, dependent on the following set of factors: (1) the thermal state of the lithospheric mantle; (2) the width of the real “diamond window” marked by mantle xenocrysts, especially by diamond-associated garnets; and (3) the efficiency of lithospheric mantle sampling by kimberlite. The results of this study can be used to inform diamond exploration programs within the region.

Recent Data on the Isotope–Geochemical Composition of Kimberlites in the TSNIGRI-Arkhangelskaya Pipe, Arkhangelsk Diamondiferous Province (Northern East European Platform)

Recent Data on the Isotope–Geochemical Composition of Kimberlites in the TSNIGRI-Arkhangelskaya Pipe, Arkhangelsk Diamondiferous Province (Northern East European Platform)

Reconstruction of the composition and structure of the lithospheric mantle based on the major element composition of garnet and chromium diopside xenocrysts from rocks of the crater part of a kimberlite pipe (the example of the V. Grib pipe, Arkhangelsk diamondiferous province)

The article reports data on the concentrations of the major elements in garnet (1104 grains) and clinopyroxene (238 grains) xenocrysts extracted from rocks of the crater part of the highly diamondiferous V. Grib kimberlite pipe, located within the Arkhangelsk diamondiferous province. All garnet grains were divided into five color groups: violet (35% of the total sample), orange (40%), red (23%), red-orange (<1%) and dichroic (1.3%). The composition of garnets indicates the presence in the lithospheric mantle of lherzolites (39 %), harzburgite-dunites (up to 8 %, including 4 % of potentially diamond-bearing), as well as a significant amount of megacrysts (23 %), low-chromium pyroxenites (up to 19 %), and eclogites (11 %). The temperature varies from 900 to 1200 °С, which is the most common temperature range of diamond stability in the lithospheric mantle rocks, corresponds to 78 % of lherzolite garnets and 88 % of garnets of the harzburgite-dunite paragenesis, including 95 % of “diamond association” garnets. The bestfit geotherm was determined using the software "Gtherm" according to the calculated P-T values of chrome diopside xenocrysts and was consistent with 36.8 mW/m2 surface heat flux. Reconstruction of the structure of the lithospheric mantle indicates the location of garnets of lherzolite paragenesis throughout the entire section of the lithospheric mantle from ~ 80 to ~ 205 km, harzburgite-dunites, including potentially diamond-bearing varieties, mainly in its central and lower parts from ~ 130 to ~ 180 km. The lower boundary of the lithospheric mantle was established at a depth of ~ 230 km. The thickness of the “diamond window” is ~ 85 km. The results of the study showed that kimberlite indicator minerals from the crater parts could be suitable to predict the potential diamond content of kimberlite objects at the drilling stage.

Contrasting Diamond Potentials of Kimberlites of the V. Grib and TsNIGRI-Arkhangelskaya Pipes (Arkhangelsk Diamondiferous Province) as a Result of the Different Compositions and Evolution of the Lithospheric Mantle: Data on the Contents of Major and Trace Elements in Garnet Xenocrysts

Abstract —The paper presents data on the contents of major and trace elements in garnet xenocrysts from kimberlites of the highly diamondiferous V. Grib pipe (1100 grains) and weakly diamondiferous TsNIGRI-Arkhangelskaya pipe (446 grains). We have established that the high diamond potential of the V. Grib kimberlite pipe is due to several factors related to the composition and structure of the lithospheric mantle represented by kimberlite: (1) a “cold” regime, with a heat flow of 36–38 mW/m2; (2) a thick “diamond window” (70–102 km), with the depth level of the lower boundary of the lithospheric mantle estimated at >200 km; (3) the high degree of preservation of diamondbearing peridotites under the P–T conditions of diamond stability despite the high degree of impregnation of the lithospheric-mantle rocks by high-temperature silicate melts. The low diamond content of the TsNIGRI-Arkhangelskaya kimberlite pipe as compared with the V. Grib pipe is due to the following factors: (1) a more intense heat flow in the lithospheric mantle, 38–42 mW/m2; (2) a thinner “diamond window”, 10–60 km, with the depth level of the lower boundary of the lithospheric mantle estimated at <200 km; (3) weak impregnation of the rocks of the middle and lower lithospheric mantle by CHO fluid/melt, which might have induced diamond formation; (4) minimum preservation of diamond-bearing peridotites in the lower lithospheric mantle, partly because of the possible impregnation of this zone by high-temperature silicate melts.

Typomorphic features of garnet xenocrysts from the crater and diatreme parts of the high diamondiferous V. Grib kimberlite pipe (Arkhangelsk diamondiferous province): application in prospecting and exploration for diamonds in the north of the East European platform

Research subject. Morphology of garnet xenocryst grains from the crater and diatreme parts of the highly diamondiferous V. Grib kimberlite pipe of the Arkhangelsk diamondiferous province. Aim. To reconstruct the main stages of endogenous and exogenous morphogenesis of garnet xenocrysts from the crater and diatreme parts of the kimberlite pipe based on a detailed study of their morphological features. To demonstrate the applicability of the data obtained in the interpretation of the morphology of grains of kimberlite indicator minerals from modern alluvial sediments during prospecting and exploration for diamonds in the north of the East European Platform. Materials and methods. A detailed study of the morphology of 655 garnet grains was carried using the methods of optical and electron-scanning microscopy. Garnet grains were selected from the heavy mineral concentrate of crushed rocks, representing the crater (sandstones) and diatreme (kimberlite) parts of the V. Grib pipe. All visually diagnosed garnet grains were handpicked selected from the rocks of the crater part, extracted from the core of one borehole and representing an interval from 70 to 174 m from the surface. For comparison, out of 1100 grains of garnet xenocrysts, selected by random sampling from the concentrate of minerals of the heavy fraction of kimberlite of the diatreme part, 180 garnet grains were selected, representing four-color groups: purple, red, red-orange and orange. Results. The majority of garnets from the crater (96%) and diatreme (89%) parts of the V. Grib kimberlite pipe were shown to exhibit the “primary” magmatic morphology. Nevertheless, the garnet grains with well-developed pyramidal shingle-like (3% in the crater and 11% in the diatreme) and drop-shaped (1% in the crater) reliefs have been identified. These types of garnets were formed under the influence of postmagmatic processes. For the first time, in the deep diatreme part of the pipe (more than 200 m from the surface), composed of dense kimberlite, garnets with a well-developed pyramidal shingle-like relief were found, which had been previously interpreted for the East European Platform only as components of the secondary deposits or the upper horizons of the crater parts of the pipes. Conclusions. Garnets with a well-developed pyramidal shingle-like relief, found in modern alluvial sediments, can be interpreted as from a secondary deposit only if they show signs of mechanical abrasion; the absence of traces of mechanical abrasion on such grains does not allow us to exclude the proximity of the primary source. The presence of drop-shaped relief garnets in the crater of the V. Grib pipe (150-168 m from the surface) also calls into question the unambiguous interpretation of such grains as a sign of secondary deposits: only the maximum degree of chemical abrasion of garnets with the formation of cuboids grains can indicate their redeposited nature. The results confirm the need to improve the method of prospecting for diamond deposits according to the typomorphic features of kimberlite indicator minerals recovered from the modern sediments, sampled in the north of the East European Platform.

U-Pb (LA-ICP-MS) age of detrital zircons from sandstones of the crater part of the V. Grib kimberlite pipe and KL-01 magmatic object, Arkhangelsk diamondiferous province (north of the East European Platform)

Research subject. Detrital zircons from sandstones that contain no admixtures of magmatic material, sampled from the crater parts of the highly diamondiferous V. Grib kimberlite pipe and KL-01 magmatic object. Both objects are located in the north of the East European Platform, within the Arkhangelsk diamondiferous province, at a distance of ≈100 km from each other. Aim. To obtain the first data on the composition of the U-Pb isotope system of detrital zircons from sandstones of magmatic objects of the Arkhangelsk diamondiferous province in order to evaluate the ages of their sources and reveal correlations with known tectono-thermal events in the continental crust of the region. Materials and methods. Using the LA-ICP-MS method, data were obtained on the composition of the U-Pb isotopic system of 52 zircon grains from the sandstones of the V. Grib pipe and 143 zircon grains from the KL-01 sandstones. Results. Sources of various ages from Archean to Neoproterozoic were established for the studied zircons. However, the majority zircons have Mesoproterozoic age, namely 63 and 65% of grains from the V. Grib pipe and KL-01 object, respectively. The sandstones of the V. Grib pipe contain a larger amount of Meso- and Neo-Archean zircons (≈15%) and a smaller amount of Paleoproterozoic grains (≈14%) compared to those from the KL-01 object ≈7 and 20%, respectively. The population of zircons with the U-Pb ages of 900-700 Ma is absent in the two objects. The minimum age of zircons from sandstones of the crater of the V. Grib pipe (557 ± ± 9 Ma) and KL-01 object (609 ± 9 Ma) is consistent with that of formation of the Vendian sandstones in the area of the pipes of the Arkhangelsk diamondiferous province. Conclusions. The obtained U-Pb age for the studied detrital zircons generally correlate with the previously identified stages of tectono-thermal events in the continental crust of the northern territories of the East European Platform, with the exception of the Mesoproterozoic period 1.7-1.4 and 1.3-1.0 Ga ago, which corresponds to the predominant part U-Pb age values of the studied zircons.

Mineral Assemblage of Olivine-Hosted Melt Inclusions in a Mantle Xenolith from the V. Grib Kimberlite Pipe: Direct Evidence for the Presence of an Alkali-Rich Carbonate Melt in the Mantle Beneath the Baltic Super-Craton

This report deals with the first mineralogical examination of secondary crystallized melt inclusions (CMIs) in healed cracks within olivine in a mantle peridotite xenolith from the V. Grib kimberlite pipe (Arkhangelsk diamondiferous province). In contrast to micro/nano-inclusions in diamonds, the studied CMIs are quite large (up to 50 µm), so that the mineral composition of the CMIs can be determined via conventional analytical approaches, e.g., Raman spectroscopy and scanning electron microscopy. Garnet peridotite is a coarse-grained mantle rock that equilibrates at 3.3 GPa and 750 °C (corresponding to a depth of ~100 km). The CMIs are therefore tiny snapshots of melt that existed in the shallow lithospheric mantle and were entrapped in olivine. In total, nineteen mineral species were identified among the daughter magmatic minerals of the CMIs. Various Na-K-Ca-, Na-Ca-, Na-Mg-, Ca-Mg-, Mg- and Ca-carbonates; Na-Mg-carbonates with the additional anions Cl−, SO42− and PO43−; alkali sulfates; chlorides; phosphates; sulfides; oxides; and silicates were established. Within the mineral assemblage, carbonates were predominant, with their abundance being more than 62 vol.%. The CMIs contained twelve alkali-rich minerals; nine of them were Na-bearing and showed bulk molar (Na + K)/Ca ≥ 1. The CMIs’ parental melt was an alkali-rich carbonate liquid that contained low amounts of SiO2 (≤9.6 wt%) and H2O (≤2.6 wt%). According to our estimates, the time of complete equilibration between olivine within the healed cracks and host olivine in the mantle at the calculated P-T parameters for the studied xenolith should be no more than several years. Based on this geologically short time span, a genetic link between the studied CMIs and the magmatism that formed the V. Grib kimberlite pipe is suggested.

Deep structure of the Verkhnetovskaya kimberlite pipe in the Arkhangelsk diamondiferous province according to passive seismic and radiological methods

AbstractThe exploration of kimberlite pipes is difficult. However, information about their deep structure is necessary for tasks such as prospecting, exploration and development of kimberlite pipes. Therefore, it is necessary to increase the efficiency of deep structure research. In addition, pipes in different territories differ in their properties. The latter requires the study of the peculiarities of the manifestation of pipes in various areas. The Verkhnetovskaya pipe is the only kimberlite object currently known in the Chernoozerskaya area of the Arkhangelsk diamondiferous province. This indicates the need for a comprehensive study of this pipe. The main reason it is difficult to study the pipes of the Arkhangelsk diamondiferous province is the large overburden thickness. In order to increase the efficiency of prospecting, we used a set of methods: microseismic sounding method, passive seismic interferometry, H/V method, gamma spectrometry and emanation mapping. The analysis showed that a new field measurement technique was tested in this research, resulting in more stable data. The main improvement in field measurements is the determination of the optimal accumulation time of microseism when implementing the microseismic sounding method. In addition, the location of the stations in the implementation of passive interferometry made it possible to minimize the influence of the azimuthal distribution of ambient noise sources. The studies made it possible to construct the geophysical image of the investigated pipe and the surrounding medium. As a result, it was shown that the northwestern side has a vertical structure, while according to the drilling data, the side has a uniform slope. In particular, the presence of previously unknown lateral channels was shown. The proposed methodology made it possible to obtain important information with minimal time and technical costs, confirming the applicability of the proposed methodology in the Chernoozerskaya area.

Composition, Structure, and Thermal Regime of the Lithospheric Mantle in the Area of the Highly Diamondiferous V. Grib Kimberlite Pipe, Arkhangelsk Diamondiferous Province: Data on the Chemical Composition of Garnet and Chrome-Diopside Xenocrysts

Composition, Structure, and Thermal Regime of the Lithospheric Mantle in the Area of the Highly Diamondiferous V. Grib Kimberlite Pipe, Arkhangelsk Diamondiferous Province: Data on the Chemical Composition of Garnet and Chrome-Diopside Xenocrysts

Garnet composition from kimberlites of the Arkhangelsk region as a proxy for diamond prospectivity

We showed the effectiveness of the various existing methods applied for the determination of the diamond prospectivity of kimberlite pipes based on the composition of garnets on the examples of high-grade diamond-bearing kimberlite pipes V. Grib and Arkhangelsk and low-grade kimberlite pipe TsNIGRI-Arkhangelsk, located in the Arkhangelsk diamondiferous province. The reasons for the low diamond grade of the TsNIGRI-Arkhangelskaya pipe are revealed. The results of this work allowed us to determine the analytical procedure for studying the garnet grains extracted from panned samples and magmatic bodies in order to assess the potential diamond grade of prospected areas in order to plan subsequent exploration and appraisal work in the Arkhangelsk region.

Radon over Kimberlite Pipes: Surface Field Experiments and Calculations of Vertical Diffusion (Arkhangelsk Diamondiferous Province, NW Russia)

We present the results of field and experimental studies to assess the influence on the formation of the radon field over the kimberlite pipes of the Arkhangelsk diamondiferous province. Measurements were made in the field to establish the radon radiation in the soil air and the gas permeability of soils in the area of the Chidvinskaya pipe. Experimental work was aimed at determining the radiation and physical parameters of the rocks occurring within the kimberlite field. Based on a set of field and experimental data, a model of the diffusion transfer of radon in the area of the Chidvinskaya pipe was calculated for three profiles, represented by the rocks of the pipe, sedimentary rocks of the exocontacts of the pipe, and host sandy and clay sedimentary rocks. The results of the calculations show that the rocks of the exocontacts of the pipe have the greatest potential for increased radon radiation. The calculated values of the radon radiation produced by these rocks exceeded 9000 Bq·m−3. The diatreme kimberlites produced the lowest radon radiation. We showed that the source of the increased values of radon radiation is the rocks of the pipe’s exocontacts. This fact will make it possible to use the emanation method as an additional one for the search for kimberlite pipes.

Titanium-rich metasomatism in the lithospheric mantle beneath the Arkhangelsk Diamond Province, Russia: insights from ilmenite-bearing xenoliths and HP–HT reaction experiments

Titanium-rich metasomatism in the lithospheric mantle beneath the Arkhangelsk Diamond Province, Russia: insights from ilmenite-bearing xenoliths and HP–HT reaction experiments

Radiation and physical parameters of kimberlites and host rocks of the Lomonosov diamond deposit (Russian North-West)

In this paper, experimental studies of rocks were carried out to assess the main radiation and physical factors affecting the formation of the radon field over the kimberlite pipes of the Arkhangelsk diamondiferous province (for example, the Lomonosov diamond deposit). For various types of rocks, the following was studied: porosity, density, radium-226 activity, free radon activity, radon production rate, emanation coefficient. The research results showed that the main factors in the formation of the radon field are porosity and the coefficient of emanation. These parameters directly affect the amount of free radon. In addition, we calculated the radon production by various types of rocks, represented by vent kimberlites, tuffaceous-sedimentary rocks of the crater, enclosing and overlying sediments. Regression analysis showed that the radon production rate in rocks reflects the formation of a radon field under conditions of occurrence of a kimberlite body. The studied radiation and physical parameters showed that the greatest amount of radon in a free state is produced by rocks of the near-pipe space, represented by the enclosing Vendian V2 deposits and characterized by high values of the emanation coefficient, specific activity of radium, the radon production rate, and porosity. At the same time, the formation of free radon in the tube body is limited due to the low values of porosity, emanation coefficient, and the radon production rate.

Study of Deep Structure of the Kimberlite Pipe Named After M. Lomonosov of the Arkhangelsk Diamondiferous Province Obtained by Joint Using of Passive Seismic and Radiometric Methods

Study of Deep Structure of the Kimberlite Pipe Named After M. Lomonosov of the Arkhangelsk Diamondiferous Province Obtained by Joint Using of Passive Seismic and Radiometric Methods

Radon over Kimberlite Pipes: Estimation of the Emanation Properties of Rocks (Lomonosov Diamond Deposit, NW Russia)

In this paper, using the example of the Lomonosov diamond deposit, experimental studies of rocks were carried out to assess the main radiation and physical factors affecting the formation of the radon field over the kimberlite pipes of the Arkhangelsk diamondiferous province. For various types of rocks, represented by vent kimberlites, tuffaceous-sedimentary rocks of the crater and enclosing and overlying sediments, the following were studied: porosity, density, activity of radium-226, activity of radon in a free state, level of radon production, and emanation coefficient. The research results showed that the greatest amount of radon in a free state is produced by rocks of the near-pipe space, represented by the enclosing Vendian V2 deposits and characterized by high values of the emanation coefficient, radium activity, radon production level and porosity. This fact is associated with the structural and geological features of the near-pipe space, which was exposed to the impact of kimberlite magma on the host rocks. The lowest values of these parameters are characteristic of the kimberlites of the vent facies, which limits the formation of free radon in the body of the pipe. The results of the experimental studies create prospects for the development of emanation methods for searching for kimberlite pipes in the conditions of the Arkhangelsk diamondiferous province.

Origin of Water in Mantle Eclogites from the V. Grib Kimberlite Pipe, NW Russia

Abstract The water content in the garnet and clinopyroxene in the mantle eclogites from the V. Grib kimberlite pipe (Arkhangelsk Diamondiferous Province, NW Russia) was analysed using Fourier transform infrared spectrometry. The results show that all clinopyroxene grains contained structural water at concentrations of 39 to 247 ppm, whereas two garnet samples contained detectable water at concentrations of 211 and 337 ppm. The low-MgO eclogites with oceanic gabbro precursors contained significantly higher water concentrations in the omphacites (70–247 ppm) and whole rock (35–224 ppm) compared to those with oceanic basalt protoliths (49–73 ppm and 20–36 ppm, respectively). The incorporation of water into the clinopyroxene may be associated with vacancies at the M2 site, Al in the tetrahedral position, and the elements that filled the M2 site (mostly Na and Ca). The highest water content in the omphacite was detected in a nonmetasomatised sample and was assumed to represent residual water that survived during subduction. Other eclogite samples showed signs of modal and/or cryptic metasomatism and contained less water in the omphacites compared to the nonmetasomatised sample. The water content was heterogeneous within the eclogite section of the sampled lithospheric mantle. The lack of distinct and uniform correlations between the indices of eclogite modification and their water content indicated that the saturation with water was disturbed during their residence within the lithospheric mantle.

Magmatic Material in Sandstone Shows Prospects for New Diamond Deposits within the Northern East European Platform

A detailed study of sandstones recovered from the upper part of the recently discovered KL-01 magmatic pipe in the southern part of the Arkhangelsk diamondiferous province (ADP), containing magmatic material and rare kimberlite indicator minerals, is presented in this paper. Results are compared to the composition of crater samples of the highly diamondiferous Vladimir Grib kimberlite pipe and several poorly to non-diamondiferous ADP pipes. To identify the type of magmatic material admixture, a model of binary mixing between country Vendian sandstones and typical ADP magmatic rocks based on correlations of La/Yb and Zr/Nb ratios and Ni contents is proposed. The modeling results show that the type of magmatic component in the KL-01 samples can be identified as kimberlite, with a maximum admixture of 20 vol.%. Kimberlite indicator mineral geochemistry did not exclude the interpretation that the composition, structure, thermal state and metasomatic enrichment of the lithospheric mantle sampled by the KL-01 pipe were suitable for the formation and preservation of diamonds. The lower boundary of the sampled lithospheric mantle could be in the depth range of 175–190 km, with a diamond window width of 55–70 km. Thus, the sandstones could represent the upper level of the crater of a new kimberlite pipe.

Picroilmenite from Kimberlite Pipes of Central Yakutia

Picroilmenite is one of the most important indicator minerals of kimberlite rocks, which can be used in solving petrological problems and in the search for diamond deposits. The present study shows the results of studying picroilmenite grains from the Manchary and Aprelskaya pipes within the Khompu-May kimberlite field (Central Yakutia). The rocks composing the pipes are represented by porphyritic kimberlite and kimberlite breccia, between which there are gradual transitions. Rocks forming the upper pipe horizons are highly carbonatized and supergenetically altered. Porphyritic segregations are represented by carbonatized serpentine pseudomorphs from macro-, megacrysts and olivine phenocrysts. Pyrope, picroilmenite mega-, macrocrysts and chromospinellide macrocrysts are found in both pipes. Most weakly altered parts of mesostasis are microgranular and formed mostly by phlogopite, with xenomorphic segregations of calcite and serpentine. Picroilmenite in both kimberlite bodies occurs as irregular and rounded macrorysts ranging from 0.7 to 10 mm and megacrysts ranging from 10 to 25 mm. Micrograins of this mineral were not diagnosed in the mesostasis. Individual grains of picroilmenite from the Manchary pipe are surrounded by a polymineral rim composed of either ferrospinel and magnetite, or perovskite and magnetite. High-and low-chromium varieties which correspond to two parageneses are identified among the picroilmenite grains from the Manchary pipe. Crystallization trend of high-chromium ilmenites from the Manchary pipe is clearly seen in the diagram in the coordinates Fe2O3-FeTiO3-MgTiO3 and associated with the presence of Cr-rich phlogopite from lherzolites xenoliths. Picroilmenite grains from the Aprelskaya kimberlite pipe are more magnesian in comparison with similar grains from the Manchary pipe. Picroilmenite from both pipes in the coordinates Fe2O3-FeTiO3-MgTiO3 is characterized by a magmatic kimberlite trend of the mineral composition evolution. The distribution of mineral composition points from the studied pipes in the diagram in the coordinates MgO - Cr2O3 has form of the “Haggerty parabola” (Haggerty, 1975) - typical for picroilmenites from kimberlites of industrial diamond-bearing middle Paleozoic pipes of Yakutia (Aikhal, Mir, Udachnaya). In general, picroilmenite of Central Yakutia pipes differs from picroilmenite of the Aikhal, Mir and Udachnaya pipes by the presence of the parabola right branch in the Haggerty diagram and an indistinct left branch. The Aikhal, Mir, and Udachnaya pipes are characterized by a clear demonstration of the left branch and a weak right. At the same time, the composition points of the high-chromium picroilmenite variety from the Manchary pipe in the Haggerty diagram coincide with the high-chromium picroilmenite from the Grib kimberlite pipe (Arkhangelsk diamondiferous province). Thus, the study showed the genetic polygeny of picroilmenite from the Manchary and Aprelskaya kimberlite pipes, and also the correlation with mineralogical diamond potential of both pipes traced by comparison with the known industrial ilmenite diamondiferous pipes of Yakutia and Arkhangelsk region.

Using Resource-P (Geoton) High Resolution Satellite Imagery to Predict the Locations of Diamond-Bearing Kimberlites in the Wintercoast Mineragenic Zone (Arkhangelsk Region)

Satellite imaging is interpreted to reveal deep faults that mark the boundaries of structural blocks and hidden basement faults with feathering of the N-NE strike that govern the localization of diamondiferous kimberlite pipes in the central part of the Arkhangelsk diamondiferous province. Space-based imaging shows that the reference region of the Zolotitsky ore field is characterized by a dense network of faults in northeastern and northwestern strikes. The ring structure located at the junction of the Ruchevsky Ledge and the Chubal Step is of greatest interest in the northern part of the considered area. As in the reference Zolotitsky field, the high density of lineaments of different orientations, the values of the magnetic field, and the thickness of the sedimentary cover make this structure a priority for ground-based prospecting.