Guli Massif Research Articles

Platinum-rhenium-osmium isotope systematics of chromitite and native osmium from the Guli Massif (Maimecha-Kotui Province, Russia)

To gain insight into the source of ore material, this study presents the first Re-Os and Pt-Os isotopic and highly siderophile element (HSE) abundance data for chromitite and osmium minerals from the Guli massif of ultramafic, alkaline rocks and carbonatites located in the Maimecha-Kotui province, Polar Siberia. The study utilized a number of analytical techniques, including electron microprobe analysis, negative thermal ionization mass spectrometry (N-TIMS) and high pressure asher digestion and an isotope dilution-inductively coupled plasma-mass spectrometry. The HSE concentrations in chromitite samples range from 191 to 866 ppb with a predominance of Ir-group platinum-group elements (PGE) (Os, Ir and Ru) over Pt-group PGE (Rh, Pt and Pd) and Re, which is consistent with their platinum-group mineral control (i. e., Os-Ir alloys and laurite, RuS2) within the chromitite. The Re-Os and Pt-Os isotope data indicate that the HSE budget of the chromitite and osmium minerals from the Guli massif was largely controlled by that of the mantle source, which evolved with long-term near-chondritic Re/Os and Pt/Os ratios; this source is within the range of those for the majority of komatiite and abyssal peridotite sources.

Powstawanie polifazowej asamblaży minerałów z grupy platynowców w masywie dunitowo-szonkinitowym Inagli w Aldan Shield na platformie syberyjskiej

The Inagli massif is a concentric-zonal ring massif consisting of a dunite core bordered by a sequential series of peridotites, pyroxenites and shonkinites. In dunites, there are densely disseminated accumulations of chromspinelides, as well as schlieren and veined particles of massive chromitites, to which polyphase growths of platinum-group minerals (PGM) are confined. The Inagli intrusive, like the well-known Konder massif, belongs to an independent "Aldan" type of platinum-bearing deposits. The Aldan type of ring intrusions is a platform analogue of the "Ural-Alaskan" zonal dunite-gabbro massifs of orogenic regions. In placers, dunites and chromitites of the Inagli massif, PGM are mainly represented by isoferroplatinum (Pt3Fe) with an admixture of iridium up to 8 wt %. In isoferroplatinum, symplektitic iridium particles and small inclusions of osmium, laurite, ehrlichmanite, malanite, as well as other sulfides and arsenides of platinum-group elements (PGE) are often observed. The bulk composition of such polymineral aggregates can be calculated based on the volume ratios and chemical composition of individual phases. The results obtained in this way show that the compositions of the initial polycomponent solid solutions vary from Pt-Ir-Fe to Ir-Os-Ru-Rh-Pt-Pd-Fe alloys. Polycomponent homogeneous solid solutions, which composition gradually changes from Ru-Rh-Ir-Os minerals to Fe-Pt alloys, are known in the Witwatersrand placers. A similar series of solid solutions of PGE is identified in the placers of the Guli massif on the Siberian platform. Unlike the placers of the Witwatersrand and Guli massif, where PGM are mainly represented by Os-Ir alloys, Inagli minerals have mainly a Pt-Ir-Fe composition with a low proportion of Os. The structures of most natural polyphase PGM aggregates are similar to those of artificial alloys, therefore, the former are also products of crystallization of multicomponent metal melts and their subsequent solid-phase transformations. The limits of solubility between PGE differ significantly, therefore, depending on the initial composition of metal alloys, both polycomponent solid solutions and polymineral aggregates can be formed. Based on the analysis of combined double and triple diagrams of PGE systems, the author considers possible ways of evolution of phase transformations of alloys of different composition.

Crystallization conditions of olivine in dunites the Guli massif, Siberian platform

Crystallization conditions of olivine in dunites of the Guli massif (Siberian Platform) are established using petrological, geochemical, mineralogical and thermobarogeochemical methods. The formation of olivine and chromite from picrite-meimechite ultramafc magmas was followed by the fractionation of clinopyroxenes from basaltic systems with the formation of residual high-alkaline melts. The calculations in PETROLOG and COMAGMAT programs based on the compositions of inclusions and minerals, as well as using olivine-spinel geothermometer, showed that a magmatic system, which was responsible for the formation of dunites of the Guli massif, evolved during the crystallization of olivine in a wide temperature range of 1520–1250 °C in a magma chamber at a depth of about 17 km.

Sources of Ore Material in the Platinum-Group Element Deposits of Polar Siberia and the Middle Urals Based on the Data from Radiogenic (Re–Os, Pt–Os) and Stable (Cu, S) Isotopes

Abstract —Understanding the main events of platinum-group element (PGE) ore formation is impossible without analysis of the sources and behavior of major ore-forming components, namely, platinum, osmium, sulfur, and copper, which are important indicators of magmatic and hydrothermal processes. In contrast to the Re–Os isotope system, the radiogenic Pt–Os isotope system, as well as stable isotopes of Cu and S in PGE deposits, are still relatively understudied. Our comprehensive research is aimed at filling this gap. The paper presents data for the Guli massif of ultramafic and alkaline rocks and carbonatites in Polar Siberia and on the zonal Nizhny Tagil and Svetly Bor clinopyroxenite–dunite massifs in the Middle Urals, which include: (1) the contents of the highly siderophile elements (HSE) in whole rocks and platinum-group minerals (PGM), (2) the Re–Os and Pt–Os isotope systematics of chromitite, Os–Ir alloys, and Ru–Os sulfides, (3) the sulfur isotope composition in Ru–Os and Ir–Rh sulfides in primary and secondary PGM assemblages, and (4) the copper isotope composition in Pt–Fe minerals from chromitites and placers. The research was performed using scanning electron microscopy, electron probe microanalysis, and high-precision isotope-geochemical analysis. The high-precision Re–Os and Pt–Os isotope data show that the HSE contents in chromitites and PGM of the Guli massif were controlled by the composition of the mantle source that evolved with near-chondritic time-integrated Re/Os and Pt/Os ratios, which are also typical of the sources of most komatiites and abyssal peridotites. The δ65Cu values of the studied samples of ferroan platinum and isoferroplatinum are identical within the analytical uncertainty and are close to 0‰, which is typical of high-temperature Cu-containing minerals. The sulfur isotope compositions of the Ir–Rh sulfides of the kashinite–bowieite series and of the Ru–Os sulfides of the laurite–erlichmanite series in the primary PGM assemblages indicate that the source of sulfur has a chondritic isotope composition, which is in agreement with the osmium isotope composition of the Ru–Os sulfides and Os–Ir alloys. The heavy sulfur isotope composition (δ34S = 5.6 ± 1.5‰) of As-containing erlichmanite is consistent with its secondary origin. The new data on the isotope compositions of osmium, copper, and sulfur can be used as new important parameters that characterize the sources of PGE mineralization.

Platinum–Rhenium–Osmium Isotope Systematics of Chromitites and Native Osmium of the Guli Massif, Maimecha–Kotui Province, Russia

Platinum–Rhenium–Osmium Isotope Systematics of Chromitites and Native Osmium of the Guli Massif, Maimecha–Kotui Province, Russia

Sulfur Isotope Composition of Ru–Os Sulfides from the Guli Massif, Maimecha-Kotui Province, Russia: First Results

Sulfur Isotope Composition of Ru–Os Sulfides from the Guli Massif, Maimecha-Kotui Province, Russia: First Results

Assembly method in GIS INTEGRO and its usage for solving
 of magnetic inverse problem

A tool for problem of inversion of geopotential fields has been developed for GIS INTEGRO under the name of “assembly method”, a family of which is currently gaining attention. In the article the capabilities of this specific implementation are being examined in the application to inversion of magnetic fields for regional 3D-modelling of large oil and gas perspective territories. The available methods of control and regularization of minimization of field residual are investigated using synthetic model data in the application to magnetic data and their differences to more well-understood gravity fields. In particular, a value of “depth priority” has the similar effect on model evolution as in the case of gravity problem, but the balanced value is larger. In the last section, an example of the method application is presented: the parameters of lithospheric source of satellite magnetic anomaly associated with Guli massif are investigated.

Ar and N Isotopic Composition and Elemental Ratios of Ar, N, He, and C in Fluid Inclusions in Ultramafic Rocks of the Guli Massif (Polar Siberia)

The first data on the isotopic composition and elemental ratios of nitrogen, carbon, and noble gases in samples from the early stages of the formation of the Guli Complex (Maimecha-Kotui igneous province, Polar Siberia), obtained using the method of stepwise crushing, are reported. The 40Ar/36Ar ratios in the crushing steps vary from the values close to atmospheric (~296) in the meimechite sample to 5000–6000 in pyroxenite and melilitolite; the latter correspond to the estimate for the mantle source of carbonatite from the Guli massif, according to the Ne–Ar systematics. The bulk nitrogen isotopic composition (δ15N) in the studied rocks varies from +3.7 to –5.9‰, showing a regular increase in δ15N with increasing nitrogen concentration; the range of δ15N variations in crushing steps is even wider: from +6.7‰ in pyroxenite to –15.4‰ in meimechite. The data obtained for the ultrabasic rocks of the Guli Massif suggest a significantly lower contribution of the subducted nitrogen of organic origin in comparison with the alkaline–ultramafic rocks of the Kola alkaline province and associated carbonatite, as well as with the Guli carbonatite and some Indian alkaline–ultramafic complexes with carbonatite. The N/36Ar ratios in the trapped mantle component of the ultramafic rocks are 4–8 times lower than that in the associated carbonatite. This, most likely, indicates different fluid sources, or the preferred escape of nitrogen from the fluid phase at the early stages of the formation of the Guli Massif.

Correlation high-calc undersaturated earth silicon complex of Maymecha-Kotuy province with Siberian flood basalts. New age data of massif Kugda (Polar Siberia)

Perovskite crystals from ore-bearing olivinite and phoscorite of Kugda Massif were analyzed by LA-ICP-MS. Age obtained for alkaline rocks of Kugda Massif is 2576 Ma. It means that Kugda massif was formed simultaneously with the Siberian flood basalts and Guli Massif (2509 Ma) which is the largest pluton in the Maymecha-Kotuy Province and is highly differentiated. The melilite-bearing Kugda Complex was formed synchronously with Siberian Trapps and Guli Massif, which suggests that these rocks might be genetically related.

Sulfide mineralization of phoscorites and carbonatites of the guli massif (Polar Siberia) and potential of these rocks on noble metals

A first complex investigation of mineral forms of Au and Ag and distribution of noble metals in sulfide-containing phoscorites and carbonatites, their magnetite and sulfide concentrates of alkaline ultrabasic massif Guli (Polar Siberia) was made by neutron activation method, XRF and microprobe analyses. Sulfide concentrates of carbonatites are enriched with Pt up to 2.93, Au up to 61.6 and Ag up to 3.61 (ppm).
 The main sulfides are pyrrhotite, djerfisherite, chalcopyrite and pyrite. Silver is accumulated in the late chalcopyrite, Ag- djerfisherite, later ― lenaite, sternbergite or argentopyrite and native silver. Wide dissemination of djerfisherite in phoscorites and carbonatites and defined inclusions of rasvumite, K-Na-Ca carbonates, carbocernaite and strontianite in pyrrhotite, is the evidence of of high activity of K, Na, Sr, LREE, F, Cl and S during the sulfides crystallization. Chlorine has a high capacity for the formation of chlorine-silver complexes and is probably an agent for the transfer of noble metals in carbonatites.
 The comparison of surveyed associations with published experimental data shows that formation of sulfides starts at the temperature no lower than 500С (early pyrrhotite) and lasts till 150C (argentopyrite). The late carbonatite assemblages may can be enriched with Au and Ag and be a potential source of formation of alluvial gold.

Correlation of High-Calcium Silica-Undersaturated Complex of the Maymecha–Kotuy Province with Siberian Flood Basalts: New Age Data on the Kugda Massif (Polar Siberia)

Abstract—Perovskite crystals from the ore-bearing olivinite and phoscorite of the Kugda massif were analyzed by LA-ICP-MS. Age obtained for the alkaline rocks of the Kugda massif is 257 ± 6 Ma. This implies that the Kugda massif was formed simultaneously with the Siberian flood basalts and Guli Massif (250 ± 9 Ma), which is the largest and highly differentiated pluton in the Maymecha–Kotuy Province. The simultaneous formation of the melilite-bearing Kugda Complex, Siberian flood basalts, and Guli Massif suggests the possible genetic relation of these rocks.

In situ LA-ICPMS Isotopic and Geochronological Studies on Carbonatites and Phoscorites from the Guli Massif, Maymecha-Kotuy, Polar Siberia

In this study we present a fresh isotopic data, as well as U–Pb ages from different REE-minerals in carbonatites and phoscorites of Guli massif using in situ LA-ICPMS technique. The analyses were conducted on apatites and perovskites from calcio-carbonatite and phoscorite units, as well as on pyrochlores and baddeleyites from the carbonatites. The 87Sr/86Sr ratios obtained from apatites and perovskites from the phoscorites are 0.70308–0.70314 and 0.70306–0.70313, respectively; and 0.70310–0.70325 and 0.70314–0.70327, for the pyrochlores and apatites from the carbonatites, respectively. Furthermore, the in situ laser ablation analyses of apatites and perovskites from the phoscorite yield eNd from 3.6 (±1) to 5.1 (±0.5) and from 3.8 (±0.5) to 4.9 (±0.5), respectively; eNd of apatites, perovskites and pyrochlores from carbonatite ranges from 3.2 (±0.7) to 4.9 (±0.9), 3.9 (±0.6) to 4.5 (±0.8) and 3.2 (±0.4) to 4.4 (±0.8), respectively. Laser ablation analyses of baddeleyites yielded an eHf(t)d of +8.5 (± 0.18); prior to this study Hf isotopic characteristic of Guli massif was not known. Our new in situ eNd, 87Sr/86Sr and eHf data on minerals in the Guli carbonatites imply a depleted source with a long time integrated high Lu/Hf, Sm/Nd, Sr/Rb ratios. In situ U–Pb age determination was performed on perovskites from the carbonatites and phoscorites and also on pyrochlores and baddeleyites from carbonatites. The co-existing pyrochlores, perovskites and baddeleyites in carbonatites yielded ages of 252.3 ± 1.9, 252.5 ± 1.5 and 250.8 ± 1.4 Ma, respectively. The perovskites from the phoscorites yielded an age of 253.8 ± 1.9 Ma. The obtained age for Guli carbonatites and phoscorites lies within the range of ages previously reported for the Siberian Flood Basalts and suggest essentially synchronous emplacement with the Permian-Triassic boundary.

Hafnium–Neodymium Isotope Systematics of Carbonatites from the Guli Massif (Maimecha–Kotui Province, Russia)

This work presents new data on the Hf-isotope systematics of baddeleyite and the Nd-isotope compositions of calcite carbonatites of the Guli massif, located within the Maimecha–Kotui province. The Hf–Nd isotope signatures of carbonatites (eHf ~ 10.4, eNd ~ 5.8) indicate that depleted mantle material was involved during magma generation. The application of the Hf–Nd isotope systematics provided an essential tracer for the depleted mantle contribution into the source of carbonatites from the Guli Massif.

Physicochemical Conditions of Crystallization of Rocks from Ultrabasic Massifs of the Siberian Platform

A great volume of original information on the formation of the ultrabasic rocks of the Siberian Platform has been accumulated owing to the study of melt inclusions in Cr-spinels. The inclusions show the general tendencies in the behavior of the magmatic systems during the formation of the ultrabasic massifs of the Siberian Platform, tracing the main evolution trend of decreasing Mg number with SiO2 increase in the melts with subsequent transition from picrites through picrobasalts to basalts. The compositions of the melt inclusions indicate that the crystallization conditions of the rocks of the concentrically zoned massifs (Konder, Inagli, Chad) sharply differ from those of the Guli massif. Numerical modeling using the PETROLOG and PLUTON softwares and data on the composition of inclusions in Cr-spinels yielded maximum crystallization temperatures of the olivines from the dunites of the Konder (1545–1430°C), Inagli (1530–1430°C), Chad (1460–1420°C), and Guli (1520–1420°C) massifs, and those of Cr-spinels from the Konder (1420–1380°C), Inagli (up to 1430°C), Chad (1430–1330°C), and Guli (1410–1370°C) massifs. Modeling of the Guli massif with the PLUTON software using the compositions of the melt inclusions revealed the possible formation of the alkaline rocks at the final reverse stage of the evolution of the picritic magmas (with decrease of SiO2 and alkali accumulation) after termination of olivine crystallization with temperature decrease from 1240–1230°C to 1200–1090°C. Modeling with the PLUTON software showed that the dunites of the Guli massif coexisted with Fe-rich (with moderate TiO2 contents) melts, the crystallization of which led (beginning from 1210°C) to the formation of pyroxenes between cumulate olivine. Further temperature decrease (from 1125°C) with decreasing FeO and TiO2 contents provided the formation of clinopyroxenes of pyroxenites. For the Konder massif, modeling with the PLUTON software indicates the possible formation of kosvites from picrobasaltic magmas beginning from 1350°C and the formation of clinopyroxenites and olivine–diopside rocks from olivine basaltic melts from 1250°C.

Light noble gas data in Guli massif carbonatites reveal the subcontinental lithospheric mantle as primary fluid source

For better understanding of the fluid phase sources of carbonatites of Guli alkaline-ultrabasic intrusion (Maymecha-Kotuy complex) we have studied isotope composition of He and Ne in the carbonatites of different formation stages. The data definitely point to the subcontinental lithospheric mantle (SCLM) as a primary source of fluid phase of Guli carbonatites. The absence of plume signature in such a plume-like object (from petrological point of view) could be explained in terms that Guli carbonatites have been formed at the waning stage of plume magmatic activity with an essential input of SCLM components.

Petrogenesis of dunites of the Guli ultrabasic massif (northern Siberian Platform)

New data on silicate melt inclusions in accessory Cr-spinel have given an insight into the physicochemical conditions of petrogenesis of dunites of the Guli massif (northern Siberian Platform). Studies of the inclusions demonstrate the contribution of high-Mg (16-22 wt.% MgO) alkali-picritic and picrobasaltic melts to the crystallization of these ultrabasic rocks. During the intrachamber crystallization of the Guli massif dunites, the composition of magmatic systems evolved from picrite-meimechite (with olivine forming at 1500-1380 °C and Cr-spinel forming at 1420-1360 °C) to picrobasalt. Comparison with well-known associations of ultrabasic igneous rocks has shown that melt inclusions in Cr-spinel from the Guli massif dunites are similar to inclusions in olivine phenocrysts from meimechites in the contents of most petrochemical components and in the distribution of indicator trace and rare-earth elements. In general, the new information on melt inclusions testifies that the Guli massif dunites formed with the participation of high-temperature high-Mg melts similar in composition to meimechite magmas.

The fluid phase evolution during the formation of carbonatite of the Guli massif: Evidence from the isotope (C, N, Ar) data

The first data on variations of the isotope composition and element ratios of carbon, nitrogen, and argon in carbonatites of different generations and ultrabasic rocks of the Guli massif obtained by the method of step crushing are reported. It is shown that early carbonatite differs significantly from the later ones by the concentration of highly volatile components, as well as by the isotope compositions of carbon (CO2), argon, and hydrogen (H2O). The data obtained allow us to conclude that the mantle component predominated in the fluid at the early stages of formation of rocks of the Guli massif, whereas the late stages of carbonatite formation were characterized by an additional fluid source, which introduced atmospheric argon, and most likely a high portion of carbon dioxide with isotopically heavy carbon.

Solid Inclusions in Au-nuggets, genesis and derivation from alkaline rocks of the Guli Massif, Northern Siberia

AbstractA total of 112 Au-nuggets, collected from alluvial placer deposits of the Ingarinda River from the Guli massif, located in northem Siberia, Russia, were investigated. The Guli massif consists of a huge dunite-clinopyroxenite complex (the largest complex in the world), an alkaline to highly alkaline rock suite (melilite, nephelinite, ijolite) enveloping the dunite and carbonatite intrusions, associated with disseminated schlieren type chromitite and Au-Ag, Pt placer deposits. The nuggets are characterized by various sizes and shapes and show chemical compositions Au, Au-Ag and AuCu, typical for a derivate of carbon-atites and/or ultramafic complexes. A great variety of oxide, silicate, REE-minerals, carbonate and sulphide inclusions have been detected in the nuggets, which are identical in mineralogy and chemical composition to mineral constituents of the alkaline to highly alkaline rock suite surrounding the Guli dunite core complex thus, considered as the source for Au-nuggets.

Results of dating of thorianite and baddeleyite from carbonatites of the Guli massif, Russia

The isotopic–geochronological features of thorianite and baddeleyite from carbonatites of the Guli massif, located within Maimecha–Kotui province in the north of the Siberian Platform, are characterized for the first time. The economic complex platinum-group element (PGE) and gold placer deposits are closely related to the Guli massif. Similar geochronological data for thorianite (250.1 ± 2.9 Ma, MSWD = 0.09, n = 36) and baddeleyite (250.8 ± 1.2 Ma, MSWD = 0.2, n = 6) obtained by two different methods indicate that carbonatites were formed close to the Permian–Triassic boundary and are synchronous with tholeiitic flood basalts of the Siberian Platform.

Composition and sources of volatiles and noble gases in fluid inclusions in pyroxenites and carbonatites of the Seblyavr Massif, Kola Peninsula

Carbonatites and related pyroxenites from the Seblyavr alkaline-ultramafic massif were analyzed for isotopic composition and concentrations of carbon (in carbon dioxide), nitrogen, and noble gases using the stepwise crushing technique. The C isotopic composition in crushing steps of calcite from the carbonatite varies from −6.6 to −15.0‰ (PDB) with average values from −8.5 to −10.5‰, which is lower than the mantle range for $\delta ^{13} C_{(CO_2 )} $ (from −3 to −5‰) and can likely be explained by long-term isotopic exchange between the carbon of CO2 in inclusions and their host Ca carbonate. The 40Ar/36Ar ratios in the crushing extractions of the calcites vary from the atmospheric value of 296 to 3200. Diopside from the pyroxenite has these ratios as high as 26000–33000 (such high values for pyroxenite in the Kola alkaline-ultramafic province have been obtained for the first time), which corresponds to the values obtained for MORB chilled glasses. Nitrogen in the samples is isotopically heavy, δ15N from +1 to +2 on average, which is consistent with earlier data on carbonatite massifs in the Kola alkaline province (Dauphas and Marty, 1999) and carbonatites of the Guli Massif (Buikin et al., 2011). The N2 content in the crushing extractions is correlated with the 36Ar concentration, which is an indicator of atmospheric contamination and suggests the dominance of the crustal N component in the samples, likely as a result of subduction or penetration of the ancient meteoric water into the magma chamber or a metasomatic source. The variations in the isotopic and elemental composition of the gas components between crushing steps suggest that the investigated samples contain inclusions of at least two populations.