JournalTOCs

Geochemistry International
Journal Prestige (SJR): 0.503

Citation Impact (citeScore): 1
Number of Followers: 1

Hybrid journal (It can contain Open Access articles)
ISSN (Print) 1556-1968 - ISSN (Online) 0016-7029
Published by Springer-Verlag

[2469 journals]

Effect of Acid−Base Interaction at the Evaporation of Alkaline
Components from Chondrule Melts
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  Abstract: — The paper presents experimental data on K2O and Na2O evaporation from melts of various acidity, including the pyroxene chondrules of the Saratov L4 chondrite. The problem of alkali volatility is discussed within the framework of Korzhinskii’s theory of the acid−base interaction of melt components. The main thesis of the theory is confirmed using the examples of evaporation of model compositions and those close to chondrules: the basic parameters of the activity of components are their concentrations and activity coefficients, which control K2O and Na2O behavior in the melt. The reasons for the contradictions between the interpretation of available experimental data on the evaporation of alkalis are considered. It is shown that the acidity−basicity of melt, which is not accounted for in works by foreign authors, should be important factors that determine the comparative volatility of potassium and sodium at chondrule evaporation.
  PubDate: 2022-05-01
Composition of Cosmic Spherules from Ferromanganese Crusts of the Magellan
Seamounts
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  Abstract: — 2720 cosmic spherules extracted from ferromanganese crusts sampled at two guyots of the Magellan Seamounts were studied using a scanning electron microscope. In comparison with collections of modern cosmic spherules, our samples are significantly richer in I-type spherules (consisting of Fe oxides, often with a Fe–Ni metal core). The compositions of 406 metal cores were analyzed. Six spherules with cores significantly enriched in Co (>5 wt %) were found; these were the first spherules of this composition ever found worldwide. Such a high Co content in the cores cannot be explained by the evolution of a micrometeorite of chondrite composition at its melting. Some groups of the spherules have either elevated or lower Co concentrations than those expected according to the evolutionary trend of spherules at oxidation during the atmosphere entry. These groups apparently reflect the composition of the initial micrometeorites. It is proposed to use the composition of the cores of cosmic spherules to reveal the time variation in the composition of cosmic dust entering the Earth. Several spherules were found with small cores compared to the oxide shell; these cores are characterized by the presence of a significant amount of platinum group elements (PGE) (up to 2.4 wt % PGE). The averaged composition of PGE in the high-Ni core, which is the richest in PGE, shows a pattern close to that of chondrite. The collection contains 23 spherules that host PGE nuggets. In three spherules, micrometer-sized nuggets with various PGE were found (one nugget is Os + Ir + Ru, and two others contain all PGE). In 20 spherules, nanometer-sized nuggets of rhodium platinum were found. The largest nugget (3 μm) has PGE ratios close to chondritic, with the exception of a significant depletion in Pd.
  PubDate: 2022-05-01
Magmatic Complexes of the Stalemate Ridge, Northwest Pacific, and Their
Possible Origin
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  Abstract: — An important element in the reconstruction of the geodynamic evolution of the lithosphere in the northwestern Pacific Ocean is the Stalemate Ridge, which is located immediately south of the Aleutian island arc and stretches from southeast to northwest parallel to the Aleutian trench. The collection of our rock samples included rocks dredged along the entire strike of the Stalemate Ridge during cruises 201 and 249 of the German R/V Sonne. This study was focused on peridotites, gabbroids, dolerites, and basalts that fully represent the petrographic diversity of igneous rocks composing segments of the Stalemate Ridge located within a length of 500 km along its strike. The synthesis of all preexisting and newly acquired data on the structure of the Stalemate Ridge and the composition of its rocks led us to the following conclusions of principal importance for developing an adequate geodynamic models for the formation of magmatic complexes and their sources in this area of the northwestern Pacific Ocean: (1) the mafic-ultramafic rock association of the northwestern segment of the Stalemate Ridge was formed at a convergent boundary of lithospheric plates; (2) depleted and enriched sources participated in the formation of magmatic complexes of the Stalemate Ridge; (3) in the area at 170o E within the Stalemate Ridge, a large fault zone occurs, with outcrops of ultramafic rocks found only northwest of this zone and absent southeast of it; and (4) throughout the whole strike of the Stalemate Ridge, magmatic rocks that have no genetic relations to the oceanic lithosphere are sporadically widespread.
  PubDate: 2022-05-01
Vertical Distribution of Biomolecules in the Carbonate Sediments and
Bacterial Mat of Steppe Alkaline Lake, Eastern Transbaikalia
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  Abstract: A wide range of lipid biomarkers was identified in the bacterial mat (BM) and carbonate sediment core of Lake Doroninskoe (0–90 cm). The main bioproducers and ecological conditions providing the predominance of definite biota and peculiarities of biochemical processes were determined. The revealed peculiar composition of biomolecules within separate intervals of the bottom sediment (BS) core can be caused by climatic change in Eastern Transbaikalia for the last centuries. Biomolecules produced by bacteria, microalgae, and terrestrial plants were found in variable proportions throughout the studied core. The composition and distribution of steroids, triterpenoids, alkanes, alkanols, alkanones, α-tocopherol, perylene, dihydroactinidiolide, methyl esters of saturated normal and branched, as well as unsaturated fatty acids in BM and BS in combination with mineral and element composition of BS allowed us to divide the studied core section into three intervals. These intervals differ in the content and proportions of some chemical elements and biomolecules, the presence of peculiar organic compounds in the lipophilic extractives, as well as variation trends of some parameters or their groups. The lower oldest part of the sediment contains organic matter (OM) produced mainly by terrestrial plants. Upsection, the fraction of stigmasterol and sitosterol in steroids increases, while that of brassicasterol and cholesterol, steroid ketones, and sigmasterol/sitosterol ratio decreases. At a depth corresponding approximately to the mid-19th century, the OM composition changes. Steroids show an increase of 3-ketone-substituted structures and cholest-5-en-3-ol, with appearance of ergosta-5,7,22-trien-3-ol, stigmasta-5,7,22-trien-3-ol, ergost-7-en-3-ol, and stigmast-7-en-3-ol, in combination with increase of α-tocopherol and dihydroacinidiolide. The content of high molecular weight homologues in n-alkanes and methyl esters of fatty acids decreases. In BS precipitated during 20th century, OM composition and its variation trends are opposite to those observed in the lower part of the section. Obtained data indicate a sequential environmental changes in Transbaikalia for the last ~250 years. Climatic warming during accumulation of the lower part of sediment core of Lake Doroninskoe was replaced by the hot dry period in the second half of 19th century and then by cooling, which lasted up to the last decade. An increase of radiation background by the mid-20th century led to the accumulation of 4-methyl substituted steroids, the intermediate products of sterol biosynthesis, in BS. Our study demonstrates additional approaches to study of the past ecological and climatic changes.
  PubDate: 2022-05-01
Geochemistry of Vendian (') Metasedimentary Rocks of the Byrka Series
of the Argun Superterrane
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  Abstract: This paper presents first geochemical and Sm-Nd isotope-geochemical data on conditionally Vendian metasedimentary rocks of the Byrka Series of the Argun superterrane. Analysis of chemical composition of rocks made it possible to establish that sources of detrital material were both felsic and mafic rocks. This conclusion is consistent with the presence of felsic and mafic metavolcanic intercalations in sequences. The isotope-geochemical studies of metasedimentary rocks of the Byrka Series indicate that their source areas contained rocks with Paleoproterozoic Nd model age. The main sources of clastic material for metasedimentary rocks of the Byrka Series were likely Precambrian magmatic and metamorphic complexes located at the Argun superterrane, within Eastern Transbaikalia, and at the adjacent territory of China.
  PubDate: 2022-05-01
Migration of Elements in Soil Waters of the Valday Hills
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  Abstract: — The paper presents data on the chemical composition of lysimetric waters of the northern part of the Valday Hills and on natural geochemical and anthropogenic factors that control the composition of the lysimetric water. The influence of the type of elementary landscape and soil characteristics (mineral, granulometric, and chemical composition) on the formation of soil water on a seasonal basis is considered. Features of the accumulation and transport of elements during the passage of atmospheric precipitation through the soil horizon are estimated. Statistical methods are applied to identify factors that determine the migration activity of elements during different seasons of the year, and the effects of soil mineral composition, biogeochemical processes, and anthropogenic precipitation on the chemical composition of water in the aeration zone are estimated.
  PubDate: 2022-05-01
Sedimentary and Geochemical Responses to the End Ordovician Glaciation in
the Guanyinqiao Formation (Late Ordovician-Early Silurian Period) in the
Sichuan Basin
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  Abstract: During the Late Ordovician-Early Silurian period, Gondwanan glaciation has affected around the world. To infer the geologic record of the glaciation across the Ordovician-Silurian transition in South China, we measured the petrological and geochemical characteristics of 60 samples of Wufeng-Longmaxi Formations taken from four sections and Huadi no. 1 well in the Sichuan Basin. Petrologically, the Guanyinqiao Formation is composed of argillaceous sandstone, argillaceous siltstone, silty bioclastic limestone and silty limestone, combing with their sedimentary structures and fossils, which verifies a shallow water environment between the two sets of black shales in the Wufeng and Longmaxi Formations. Geochemically, the Chemical Index of Alteration (CIA) and Sr/Cu ratios indicate that palaeoclimate transformed from warm to cold and then to warm again during the Late Ordovician-Early Silurian period. The low CIA values of Guanyinqiao Formation, suggesting a short-cold climate which is consistent with Gondwana glaciation in Hirnantian period. In addition, the fluctuations of V/(V + Ni), V/Cr, V/Sc, Sr/Ba and Zr/Rb ratios from Wufeng-Longmaxi Formations implied that sea water had experienced an anoxic-oxic-anoxic process, the paleosalinity changed from sea water to brackish-marine and then to sea water, and the hydrodynamic condition had shown low-high-low characteristic. All these results indicate that because of the end Ordovician Glaciation, the area of the ice sheet increased, the climate changed and sea level fell during the Hirnantian period.
  PubDate: 2022-04-11
Identification of the Organic Matter of Peat for Field Testing of the
Oxithermography Technique for Carbon Content Evaluation
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  Abstract: The technique of oxihtermography is proposed as a method for determining organic carbon concentration (total organic carbon, TOC) in eutrophic peat. The peat samples were collected in the vicinities of the village of Nenashkino, Ryazan oblast, and in bogs in Tyumen oblast. The organic constituents of the peats were compared with samples of humic acids (HA) for using the latter as standard references samples. This approach enables correlating the analytical signal with the organic carbon (TOC) concentration by using a calibration plot.
  PubDate: 2022-04-01
Physicochemical Study of Titanium-Bearing Garnets
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  Abstract: — Four samples of natural Ti-bearing garnets from Odihincha, Maimecha-Kotui alkaline province, Krasnoyarsk Krai, Russia, were studied using electron microprobe analysis, X-ray powder diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), Raman and Mössbauer spectroscopy, and thermal analysis. The enthalpies of formation from elements were determined with a high-temperature heat-flux Tian–Calvet microcalorimeter by means of the melt solution calorimetry. The first ever values of \({{\Delta }_{{\text{f}}}}H_{{{\text{el}}}}^{0}\) (298.15 K) were determined as follows: −5861.1 ± 11.3 kJ/mol for (Ca3.00Na0.02Fe2+0.01) ( \({\text{Fe}}_{{1.42}}^{{3 + }}{\text{Ti}}_{{0.26}}^{{4 + }}\) Al0.21Mg0.04 \({\text{Fe}}_{{0.03}}^{{2 + }}{\text{Mn}}_{{0.01}}^{{2 + }}\) )[(Si2.85 \({\text{Fe}}_{{0.13}}^{{3 + }}\) )O11.92(OH)0.08]; −5915.2 ± 9.0 kJ/mol for Ca3.01( \({\text{Fe}}_{{1.27}}^{{3 + }}{\text{Ti}}_{{0.57}}^{{4 + }}\) Mg0.05 \({\text{Fe}}_{{0.03}}^{{2 + }}{\text{Mn}}_{{0.01}}^{{2 + }}\) )[(Si2.69Al0.16 \({\text{Fe}}_{{{\text{0}}{\text{.13}}}}^{{{\text{3 + }}}}{\text{Ti}}_{{{\text{0}}{\text{.01}}}}^{{{\text{4 + }}}}\) )O11.96(OH)0.04]; −5902.5 ± 9.1 kJ/mol for (Ca2.97 \({\text{Mn}}_{{{\text{0}}{\text{.02}}}}^{{{\text{2 + }}}}{\text{Fe}}_{{{\text{0}}{\text{.01}}}}^{{{\text{2 + }}}}\) )( \({\text{Fe}}_{{{\text{1}}{\text{.20}}}}^{{{\text{3 + }}}}{\text{Ti}}_{{{\text{0}}{\text{.64}}}}^{{{\text{4 + }}}}\) Mg0.05 \({\text{Fe}}_{{0.04}}^{{2 + }}\) )[(Si2.64 \({\text{Fe}}_{{{\text{0}}{\text{.23}}}}^{{{\text{3 + }}}}\) Al0.11 \({\text{Ti}}_{{0.01}}^{{4 + }}\) )O11.96(OH)0.04]; and −5945.7 ± 10.2 kJ/mol for (Ca2.90Na0.04 \({\text{Fe}}_{{{\text{0}}{\text{.03}}}}^{{{\text{2 + }}}}{\text{Mn}}_{{{\text{0}}{\text{.02}}}}^{{{\text{2 + }}}}\) Mg0.01)( \({\text{Fe}}_{{{\text{0}}{\text{.97}}}}^{{{\text{3 + }}}}{\text{Ti}}_{{{\text{0}}{\text{.71}}}}^{{{\text{4 + }}}}\) Mg0.13Zr0.08 \({\text{Fe}}_{{{\text{0}}{\text{.05}}}}^{{{\text{2 + }}}}\) ) [(Si2.33 \({\text{Fe}}_{{{\text{0}}{\text{.32}}}}^{{{\text{3 + }}}}{\text{Ti}}_{{{\text{0}}{\text{.24}}}}^{{{\text{4 + }}}}\) Al0.07)O11.84(OH)0.16]. The standard Gibbs free energies of formation of these garnets were calculated using the values obtained for the formation enthalpies and estimated for the entropies. Also, the enthalpies of formation of the end-members of the isomorphic schorlomite–morimotoite series were derived. The thermodynamic constants were used in quantitative modeling of the stability fields of these minerals.
  PubDate: 2022-04-01
Comparative Analysis of Pleistocene Sedimentation Parameters in the
Pelagic Zone and at Submarine Continental Margins of the Indian Ocean
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  Abstract: Abstract We have done a comparative analysis of quantitative parameters for Pleistocene sediments from pelagic zone of the Indian Ocean and submarine parts of its continental margins (for five key areas). The distribution areas, thicknesses, and volumes of main lithological types and groups have been analyzed. Dry sediment masses and their accumulation rates have been calculated. In the Neopleistocene compared to Eopleistocene, the fluxes (absolute masses) of all components of bottom sediments have been increased both in the pelagic zone and on the continental margins. Biogenic sedimentation was more important for facies structure of pelagic zone than (on average) for continental margins.
  PubDate: 2022-04-01
Post-Spinel Phases in the Earth’s Mantle
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  Abstract: — The post-spinel phases include compounds with stoichiometry \({{A}^{{2 + }}}B_{2}^{{3 + }}{{{\text{O}}}_{4}}\) \(\left( {A_{2}^{{2 + }}{{B}^{{4 + }}}{{{\text{O}}}_{4}}} \right)\) and structures of the calcium ferrite CaFe2O4, calcium titanate CaTi2O4, and marokite CaMn2O4 types. The structures with a centered Cmcm (Bbmm) and primitive Pnma (Pmcn) and Pbcm (Pmab) cells are distinguished in this family of topologically related compounds with a “marokite” channel formed by six octahedra. The sites A and B are occupied by various cations, in particular, Cr, Al, Mg, Fe, Ca, Ti, Fe, Na, and Si, which implies the formation of solid solutions of a wide compositional range. In nature, such high-pressure phases were found in meteorites, as inclusions in diamond crystals, and in rocks from some metamorphic complexes. This review provides a characterization of natural mineralogical finds, the results of an experimental study of post-spinel phases of various compositions and their solid solutions, as well as crystal chemical simulation and assessment of likely compositions and the areas of stability of compounds with a “marokite” channel. The discrepancy between the results of individual studies indicates the necessity to clarify the stability parameters and probable isostructural transitions, and, ultimately, to improve the classification of post-spinel phases.
  PubDate: 2022-04-01
Geochemistry of Oils in the Middle Devonian–Lower Frasnian Terrigenous
Petroleum System of the Timan–Pechora Basin
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  Abstract: — The paper presents original data on the composition of hydrocarbon biomarkers and the carbon isotope composition of fractions of some oils in the Middle Devonian–lower Frasnian terrigenous rock complex in the Timan–Pechora basin. The oils typically contain high concentrations of paraffin hydrocarbons. The oils of hydrocarbon systems were generated at the catagenesis of terrigenous organic matter in the host rocks. The complex of hydrocarbon biomarkers of the oils shows features indicating that the paraffin-rich dominant component of the oils mixed with oils from other hydrocarbon systems, namely, from the Domanik–Tournaisian and Lower Paleozoic carbonate rock complexes.
  PubDate: 2022-04-01
Volatile, Trace, and Ore Elements in Magmatic Melts and Natural Fluids:
Evidence from Mineral-Hosted Inclusions. I. Mean Concentrations of 45
Elements in the Main Geodynamic Settings of the Earth
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  Abstract: — Published data on the composition of mineral-hosted inclusions and quenched glasses of rocks were used to estimate the mean concentrations of 45 volatile, trace, and ore elements in silicate igneous melts from the main geodynamic settings of the Earth and in natural fluids. The following geodynamic settings were distinguished according to the conditions of formation and evolution of the igneous melts: (I) oceanic spreading zones (mid-oceanic ridges), (II) oceanic mantle-plume zones (oceanic islands and lava plateaus); (III and IV) subduction-related settings (III is island-arc zones, and IV is active continental margins); (V) continental rifts and hotspot zones; and (VI) backarc spreading basins related to subduction. The contents of the elements in basic and felsic melts were compared in settings III, IV and V. It was shown that differences in the enrichment factors of ore elements between the geodynamic settings could be caused by variations in the contribution of fluids to element transport and accumulation. Ratios of element contents in each of the geodynamic environments to the global mean values were calculated.
  PubDate: 2022-04-01
Geochemistry and Radioecology of Waters and Bottom Sediments of the Mzymta
River, the Black Sea Coast
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  Abstract: Abstract The geochemical composition of waters of the Mzymta River is subjected to sharp seasonal changes. In summer, the waters are enriched in 34 elements (mainly REE, Fe, Mn, Cs, Al, and Cd) relative to their average contents in river waters. REEs in the waters show steady relations MREE > HREE > LREE with a general positive trend to the mouth. In spring, they are enriched only in 14 elements. They have the poorer REE composition and less fractionated REE patterns. In summer, their contamination significantly increase relative to MPC, with growth from the upper reaches to the river mouth. A general geochemical specialization of bottom sediments is determined by 27 elements, contents of which insignificantly exceed their average contents in rocks exposed in the basin for the upper continental crust. Disagreement between the high level of water contamination in summer and a weak contamination of the bottom sediments of the river is related to the low contents of finely dispersed mineral and organic matter in the latters. It was determined that chemical elements are supplied in water from three main sources: natural, natural–technogenic, and anthropogenic–technogenic. The maximum contribution to the water contamination over the entire river extent is provided by natural sources: rocks that compose the basin. The anomalous increase of concentrations of chemical elements, including Th and Y, in the middle and lower reaches of the river is related to the natural–technogenic sources at the adjacent slopes of the valley. These are technogenic areas and talus, as well as highway and railway roads, and sometimes building embankments, which are made up of disintegrated rocks devoid of soil–vegetation layer. The anthropogenic–technogenic factors make only a limited contribution to the contamination of water and bottom sediments of the river. The radioecological state of waters and bottom sediments of the Mzymta River is safe.
  PubDate: 2022-04-01
Molybdenum Isotopes Behavior in the Dolomite-Terra Rossa Weathering System
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  Abstract: The assumption that the composition of continental input can be characterized from crustal rock types is the prerequisite for the application of the molybdenum (Mo) isotopic composition as an agent to determine variations in the redox state of the paleo-oceans. The Mo isotopes’ behavior in the weathered profile of basalt and granite had been studied in pervious works (Pearce et al., 2010, Voegelin et al., 2012 and Wang et al., 2018). However, the Mo isotopes’ behavior in the weathered profile of carbonate rock is unknown. In this work, the Mo concentration and Mo isotopic composition in a weathered profile from Guizhou province, China, are investigated for the first time to understand the behavior of Mo isotopes during carbonate rock chemical weathering. The profile is developed on Early Triassic dolomite. According to the field observation and element ratios, the weathered profile is divided into intensely weathered zone (IWZ), weekly weathered zone (WWZ) and fresh bedrock. The clear correlation between Hf and Zr concentration suggests that the dolomite is the parental material for the terra rossa. The τMo of weather soil ranging from ‒1.37 to –0.14 indicates the significant loose of Mo. The δ98Mo of the soil varies from –0.66 to 0.12‰, markedly lighter than the fresh bedrocks (1.82 to 1.97‰). The difference between soils and fresh bedrocks in δ98Mo suggests that Mo isotopes are fractionated during carbonate rock chemical weathering and heavy Mo isotopes are preferentially released, similar to the weathered profile of basalt and granite. According to the coupling relationship between Mo/Al2O3 and δ98Mo, the weathered model of dolomite was established: (1) the carbonate component is firstly dissolved, releasing most Mo with heavy Mo isotope composition. (2) The detrital component then is weathered to form secondary minerals, which adsorb the Mo from weathering fluid. Thus, the Mo/Al2O3 and δ98Mo of samples from IWZ are greater than that of WWZ.
  PubDate: 2022-03-02
  DOI: 10.1134/S0016702922060106
Heavy Metal Species in the Bottom Sediments of the Aquatic System of Lake
Gusinoe (Buryatia)
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  Abstract: Abstract Pollution of bottom sediments of Lake Gusinoe by heavy metals (cadmium, chromium, copper, zinc, and lead) is considered. The exchangeable, reducible, and oxidized species of the elements were distinguished in bottom sediments, which were sampled in the central part of the lake and near mouths of main rivers and water discharge sites from SDPP (State District Power Plant), sewage treatment plant of Gusinoozersk, and Kholboldzha coal mine. Analysis of obtained data showed that Ni, Cr, Mn, and Fe occur in bottom sediments in hardly accessible form and in absorbed form on the surface of iron, manganese, and aluminum hydroxides. The high content of biologically available Cu, Zn, and Pb forms in the Zagustai and Tsagan-gol rivers creates a serious threat for the ecological state of the lake. The fractionation of heavy metal forms in the area of eliminated source of pollution related to the water disposal from the Kholboldzha coal mine showed that the content of heavy metals strictly bound with sample matrix is higher than that of the exchangeable fraction of elements.
  PubDate: 2022-03-01
  DOI: 10.1134/S0016702922010037
Advanced Instruments for Identifying Geochemical Dependences of
Radionuclide Migration in Natural Waters
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  Abstract: Abstract The geochemical dependences of the migration of natural radionuclides (U and Th) in different species are analyzed for the Semipalatinsk test site using methods of multivariate statistics. The region is distinguished by the wide diversity of geochemical environments and a large number of water bodies. A brief study of water geochemistry of the studied water bodies of the Semipalatinsk test site is reported, and the contents of natural radionuclides and proportions of their forms (suspended, colloidal and dissolved) are established. Differences in the migration of thorium and uranium in water bodies, streams, and minor water streams have been determined. It was found that the Ca/Mg, \({{{\text{SO}}_{4}^{{2 - }}} \mathord{\left/ {\vphantom {{{\text{SO}}_{4}^{{2 - }}} {{\text{C}}{{{\text{l}}}^{ - }}}}} \right. \kern-0em} {{\text{C}}{{{\text{l}}}^{ - }}}},\) and Th/U ratios serve as markers of geochemical processes in the studied waters. Non-parametric correlation analysis indicates that the major component ratios are good to use as a geochemical descriptors of thorium and uranium speciation. According to the discriminant analysis data, the suspended and colloid thorium species are indicators of colloidal transport. Factor and cluster analyses have revealed the paragenetic associations of major and trace components related to the uranium and thorium speciation.
  PubDate: 2022-03-01
  DOI: 10.1134/S0016702922010116
Geochemistry and Petrology of Protosulfide Melts in an Ore-Bearing
Apophysis of the Yoko-Dovyren Intrusion
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  Abstract: — The paper presents results of petrological and geochemical studies of sulfide-bearing rocks from a bottom apophysis in the central part of the Yoko-Dovyren massif, northern Transbaikalia, Russia. It is composed of plagioperidotite and was sampled in a bulge up to 300 m thick throughout the whole vertical section, from its upper to lower contact. The observed diversity of sulfide-bearing rocks is subdivided into four types: (1) picrodolerite with droplet-shaped sulfides, (2) olivine gabbronorite with sulfides varying from droplet-shaped to irregular globules, (3) olivine gabbronorite with larger globules and patchy net-textured domains, and (4) net-textured ores. These varieties occur in the basal zone of the apophysis, in the interval up to 30 m inward from the lower contact. Petrographic features of these rocks correspond to olivine ortho- and mesocumulates, with the only exception of the quenched picrodolerite with an ophitic groundmass. The association of sulfides (pyrrhotite, chalcopyrite, pentlandite, and cubanite) has a pretty little varying composition, except only a relative decrease in the proportion of chalcopyrite in samples with more than 5% sulfides. The results of X-ray computed tomography show an increase in the sulfide connectivity in the rocks (from 25 to 95%) with increasing sulfide abundance. These characteristics, supported by visualized 3D models, allowed us to identify a morpho-structural trend tended from the rocks with sulfide droplets to the net-textured ores. The first ever data were obtained on the chemostratigraphy (PGE and tellurium) of rocks composing this apophysis. Covariations of Au, Pt and Pd with S and Te indicate that the precious metals have a single sulfide precursor. The 100%-sulfide compositions calculated for these rocks indicate that the most primitive and PGE rich sulfides correspond to droplets it the lowerest part of the apophysis, whereas the net-textured ores are depleted in these elements. The geochemical estimates are supported with COMAGMAT-5 modeling which made it possible to calculate the average Au, PGE, and Te contents in the protosulfide melt (in ppm): 2.9 Au, 14.4 Pt, 25.1 Pd, and 44.3 Te. Results of the geochemical studies of different fragments of the net-textured ores reveal a heterogeneity in the form of domains relatively enriched in copper, PGE, and tellurium, whose characteristic size is a few dozen centimeters. This can be considered as a signature of the porous migration and accumulation of the crystallization products of the original sulfide liquid at the subsolidus stage of cooling down the ore-bearing cumulates.
  PubDate: 2022-03-01
  DOI: 10.1134/S0016702922030065
Demagnetization of Ordinary Chondrites under Hydrostatic Pressure up to
1.8 GPa
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  Abstract: We present here the results of hydrostatic pressure demagnetization experiments up to 1.8 GPa on LL, L and H ordinary chondrites—the most common type of meteorites with Fe-Ni alloys being the main magnetic carrier. We used a non-magnetic high-pressure cell of piston-cylinder type made of “Russian” alloy (NiCrAl) together with a liquid pressure transmitting medium PES-1 (polyethylsiloxane) to ensure purely hydrostatic pressure. This technique allowed measuring magnetic remanence of investigated samples directly under pressure as well as upon decompression. Pressure was always applied in near-zero magnetic field (<5 μT). The experiments revealed that under hydrostatic pressure up to 1.8 GPa, ordinary chondrites lose up to 51% of their initial saturation isothermal remanent magnetization. Pressure demagnetization degree is proportional to the coercivity of remanence (Bcr), which reflects the magnetic hardness of the samples. This is similar to what was observed for ferrimagnetic minerals others than Fe–Ni alloys. In addition, pressure of 1.8 GPa does not demagnetize samples with Bcr > 80 mT, i.e. whose main metal phase is tetrataenite (Fe0.5Ni0.5). This study gives an overview of pressure sensitivity of ordinary chondrites up to 1.8 GPa and has implications for extraterrestrial paleomagnetism as it can help to interpret remanent magnetization of ordinary chondrites that suffered shock metamorphism processes.
  PubDate: 2022-02-09
  DOI: 10.1134/S0016702922050032
Sorption-Desorption Behavior of Zn in Common Soil Diagnostic Horizons from
Southwestern Iran
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  Abstract: A full understanding of the nature of sorption/desorption reactions of Zn in soils is crucial for the interpretation and prediction of its chemical behavior in soils. Therefore, to identify the kinetics of zinc (Zn) adsorption in selected common diagnostic horizons of soils in southwestern Iran, 30 ml of solutions containing 10 mg Zn/L was added to 3 g of each of mollic, calcic, and salic diagnostic horizons (in triplicate) and at specified times (5 to 2880 minutes) the residual concentration of Zn in the supernatant was measured by an atomic absorption spectrometer. The results indicated that the Zn adsorption process in the soils studied was a three-stage process. Accordingly, by end of the first step (120 minutes from the beginning of the experiment) 65.7, 57.8, and 26.7% of the total amount of Zn was adsorbed in mollic, calcic and salic horizons, respectively. The Zn adsorption capacity of mollic, calcic, and salic diagnostic horizons were 58.20, 63.57, and 79.50 mg g−1, respectively. Excellent agreement was found between the pseudo-second-order kinetic model and the experimental data (R2 ≈ 0.994–0.999). The Zn sorption/desorption isotherms were also derived with 0.1 M Ca (NO3)2 solutions containing varying concentrations of Zn (0 to 10 mg L−1) for 24 h. Accordingly, comparing with the Langmuir model (0.888 < R2 sorption < 0.956; 0.896 < R2 desorption < 0.984), Freundlich isotherm model (0.987 < R2 sorption < 0.999; 0.963 < R2 desorption < 0.994) could better explain Zn sorption/desorption data in the soils studied. The Zn adsorption data on all three soils followed an L-shaped isotherm. Besides, Zn adsorption isotherms showed greater values than desorption isotherms, suggesting that the Zn adsorption process is irreversible. Results obtained from hysteresis calculations indicated that the desorption of freshly sorbed Zn was less hysteretic in calcic and mollic horizons relative to salic horizon. This suggests low mobility and leaching potential of freshly sorbed Zn can be expected from these soils.
  PubDate: 2022-02-09
  DOI: 10.1134/S001670292205007X