Geochemical Barriers Research Articles

Biogeochemical In Situ Barriers in the Aquifers near Uranium Sludge Storages

The long-term operation of uranium sludge storages causes serious problems: it contaminates the neighboring aquifers with dangerous substances (uranium, nitrate, ammonium, and sulfate). To purify the aquifers can be costly and time-consuming; therefore, it is important to use the potential of in situ conditions, e.g., the aboriginal microflora and its ability to biologically remediate water reservoirs. In this work, we study the geological, geochemical, and microbiological characteristics of groundwater contaminated by uranium sludge storages resulting from the production cycles of four Russian chemical plants. All of the sites under consideration were extremely contaminated with nitrate (up to 15 g/L); in each case, we used denitrifying bacteria as a dominant group of microorganisms for purification. Our laboratory studies showed that microbial stimulation of water samples by milk whey promotes O2 and nitrate removal; this, in turn, started the cycle of anaerobic processes of authigenic precipitation caused by the reduction of iron and sulfate in the system. Thus, a mineral geochemical barrier preventing uranium immobilization formed. As a result, the uranium of the liquid phase decreased about 92–98% after 3–6 months (decomposition time depends on the nitrate concentration in the groundwater probe). The resulting amorphous biogenic phases contain sulfur, iron, phosphorus, and uranium.

Ecological and Geochemical State of Soil Cover in Gusinoozersk in the Zone of Influence of Coal Thermal Power Plant

The pollution of the topsoils of the city of Gusinoozersk (Republic of Buryatia) under the influence of emissions from State District Power Plant (SDPP) which used the Okino-Klyuchevskiy brown coal as fuel was studied. The content of 14 elements (Sr, As, Co, Mo, Sb, V, Cu, Ni, Cr, W, Zn, Bi, Cd, Pb) in bulk samples, as well as in the fraction of physical clay (particles with a diameter 10 µm, PM10) and in samples of brown coal and ash from the SDPP. Strontium, As, Co, Mo, Sb, V are the priority pollutants in the soils of Gusinoozersk with higher concentrations of most elements in the PM10 fraction. Soils and the PM10 fraction in the industrial operating subzone are the most polluted with Sr, As, Co, V, Cu, Mo, Ni, Cr, which are contained in the fly ash of the Gusinoozerskaya SDPP. Most of the territory (57% for soils in general and 47% for the PM10 fraction) is characterized by a low level of pollution (Zc = 8–16). Arsenic poses the greatest environmental hazard; in the PM10 fraction, its concentrations exceeded the MPC in 90% of the studied samples. In soils and their PM10 fraction, the leading factors for the accumulation of elements are the content of Fe2O3, organic matter, soil texture, alkaline-acid conditions, and belonging to a functional zone, which determine the formation of various classes of geochemical barriers. The polluting effect of brown coals depends on the content of heavy metals and metalloids in them. Comparison of the chemical composition of the Okino-Klyuchevskii brown coal and ash from the Gusinoozerskaya SDPP and the Kansk-Achinskii coal and ash from the Central Thermal Power Plant of Severobaikalsk showed that the brown coal and ash from Severobaikalsk were slightly enriched in metals and metalloids, which significantly reduced their accumulation in soils.

REE Geochemical Characteristics of the Huri Karst-Type Bauxite Deposit, Irano–Himalayan Belt, Northwestern Iran

The Huri bauxite deposit is located 40 km northwest of Maragheh City, East Azerbaijan province, northwestern Iran. Bauxite horizons at Huri develop within karstic depressions and sinkholes of carbonate footwalls of the Ruteh Formation, overlain by carbonate of the Elika Formation. Powder X-ray diffraction (PXRD) and scanning electron microscope, coupled with energy dispersive X-ray spectroscopy (SEM-EDS) analyses show that the Huri bauxite ores consist of hematite, diaspore, kaolinite, and lesser amounts of halloysite, pyrophyllite, illite, goethite, clinochlore, amesite, rutile, zircon, and monazite. Based on geochemical studies (Eu/Eu* vs. Sm/Nd and U/Th bivariate diagrams), basalt rocks interbedded in limestone of the Ruteh Formation are the possible precursor rocks of the Huri bauxite deposit. The pH variations of weathering solutions, fluctuations in the groundwater table level, the function of carbonate bedrock as a geochemical barrier, simultaneous precipitation of Fe-bearing minerals, and preferential scavenging of light rare earth elements (LREE) by hematite played an important role in the fractionation of LREE from heavy rare earth elements (HREE) in the Huri bauxite ores. Fluctuations in groundwater table level, increasing pH of acidic solutions percolating downward, preferential adsorption of Ce onto hematite at the base of the profile, and the possible presence of Ce-bearing fluorocarbonates played an important role in increasing Ce anomaly from the top of the profile downward.

Reconstruction of paleoclimatic facets of sedimentation in Sevastopol Bay based on geochemical data

Data on the abundance of petrogenic and trace elements (including rare earth elements) in the Quaternary deposits of Sevastopol Bay at the pre-technogenic stage of its development were obtained. Anomalies in the enrichment with Ag, Au, Hg, Pb and elevated levels of Cu, Zn, Cd, Sn, Sb in some layers were discovered. These features are apparently due to sulfide mineralization in the denudation area and the emergence of specific geochemical barriers (hydrodynamic and, possibly, saline ones) in the periods of changes in the paleogeographic environment. The ratios of the contents of elements sensitive to the change in the weathering type made it possible to establish the climate characteristics in the source area. During the accumulation of the liman deposits, relative warming and humidization took place, with the boundary strata of this period evidencing drier and colder conditions at the very beginning and completion of the deposit formation. The marine stage begins with warming (the lack of samples in the lower and middle parts does not allow us to trace further the prevailing conditions), but cooling and aridization are observed later on. These constructions fit into the general regional picture of climate change in the southwestern Crimea in the interval of 9.5–3.0thousand years ago.

The World’s Largest Bauxite-Bearing Province, Fouta Djallon–Mandingo (West Africa). Part 4: a Zoning Mechanism in Laterite Bauxite-Bearing Weathering Crust

The results of detailed exploration and year-round observations of the hydrogeological regime at large deposits, as well as special hydrochemical studies of various types of water and changes in the gas composition of the underground atmosphere in the lateritic weathering crust, of the very large bauxite-bearing province, Fouta Djallon–Mandingo, thanks to a reliable factual base, made it possible for the first time to draw a number of important conclusions about the conditions and features of zoning formation in the lateritic weathering profile. The weathering profile consists of two metasomatic columns spatially combined in plan, but vertically separated: an upper one, consisting of hydroxides and oxides of iron and aluminum, and a lower one, composed of clayey eluvium and products of hydration and decomposition of aluminosilicates—polymineral clays and kaolinite. In both columns, the processes of change begin with the same rainwater, but differ in the hydrodynamic parameters in each of the columns. Changes in the weathering profile occur in accordance with the main patterns of low-temperature infiltration metasomatism. The modern hydrogeological and gas regime in bauxite-bearing lateritic covers controls the mineralogical and geochemical zoning. Features of biological and soil processes and hydrodynamics and hydrochemistry in the weathering profile lead to a threshold nature of the change in physicochemical and biochemical conditions, providing the action of geochemical (oxidation, reduction, gley, adsorption) barriers, which is the main mechanism of zonal distribution of matter in lateritic weathering crusts.

Involvement of Bacterial and Fungal Extracellular Products in Transformation of Manganese-Bearing Minerals and Its Environmental Impact.

Manganese oxides are considered an essential component of natural geochemical barriers due to their redox and sorptive reactivity towards essential and potentially toxic trace elements. Despite the perception that they are in a relatively stable phase, microorganisms can actively alter the prevailing conditions in their microenvironment and initiate the dissolution of minerals, a process that is governed by various direct (enzymatic) or indirect mechanisms. Microorganisms are also capable of precipitating the bioavailable manganese ions via redox transformations into biogenic minerals, including manganese oxides (e.g., low-crystalline birnessite) or oxalates. Microbially mediated transformation influences the (bio)geochemistry of manganese and also the environmental chemistry of elements intimately associated with its oxides. Therefore, the biodeterioration of manganese-bearing phases and the subsequent biologically induced precipitation of new biogenic minerals may inevitably and severely impact the environment. This review highlights and discusses the role of microbially induced or catalyzed processes that affect the transformation of manganese oxides in the environment as relevant to the function of geochemical barriers.

Formation of waters of tungsten-ore areas under the influence of natural and anthropogenic factors (Eastern Transbaikalia, Russia)

The industrial development of tungsten deposits in Eastern Transbaikalia contributed to a significant deterioration of the environmental situation in the adjacent territories. Heavy-metal water contamination has become a serious problem in the mining areas. The most dangerous are wastes of sulphide ores, the oxidation of which leads to the formation of acidic drains with abnormally high concentrations of heavy metals. The features of the composition of the waters formed in and around the five tungsten deposits were studied and significant differences in their physical and chemical characteristics were shown. The most saline acidic, sulphate waters with the maximum content of heavy metals are recorded in the drainages of the tailings of beneficiation plants and rock dumps and in the ponds of sludge depositories and deposits with an increased ore sulphide content. The groups of elements posing the greatest danger to aquatic ecosystems were identified as Cd, Cu, Zn, Be, Al, Co, Th, Mn in acidic and slightly acidic waters and W, Mo, U, As, Mn in slightly alkaline and alkaline waters. Based on the Eh-pH water parameter ratio, three types of hydrogeochemical environments formed in the mining areas of tungsten deposits were identified. Metal migration in the waters occurs mainly in the form of simple cations, sulphate, fluoride, hydrocarbonate, carbonate and hydroxyl complexes. Geochemical barriers of oxygen, sorption, acidic and alkaline types were studied in the areas around the deposits. The main factors determining the physical and chemical parameters of the waters are shown, including the regional factor, specifically, the ore and host rock composition, the water exchange intensity, and the technogenic factor, which causes a high level of water pollution.

Assessment of the Impact of Anthropogenic Drainage of Raised Peat-Bog on Changing the Physicochemical Parameters and Migration of Atmospheric Fallout Radioisotopes in Russia’s Subarctic Zone (Subarctic Zone of Russia)

This paper reports on the research results of the radioactivity levels and upward dispersion of radionuclides of atmospheric fallout 210Pb, 137Cs, 241Am and 234,238U as well as key physicochemical parameters in a peat deposit subjected to drainage in 1969–1971. It was found that drainage of the peat bog led the natural moisture content to shrink in the peat. Active aeration in the peat deposit, accompanied by the growth of Eh, raises the strength of oxidative transformation processes of the organic part of the peat, leading to higher levels of peat degradation and major variations in the elemental content. Changes in these parameters affect the behaviour of radionuclides in the peat section. Thus, in contrast to the sites with a natural hydrological regime, within the dried peat deposit a geochemical barrier of sorption type is not formed, capable of retaining a significant proportion of 137Cs. In this connection, there is an acceleration of 137Cs migration. In addition, changes in the hydrological regime led to the predominance of vascular plants with a more developed root system than that of sphagnum, which also contributed to a more intense transfer of 137Cs by the root system up the section. The findings of 210Pb dating of the dried peat bog showed a significantly lower peat accumulation rate compared to the natural bog massif (0.15 ± 0.02 vs. 0.48 ± 0.08 cm/year). A factor examination of the dataset demonstrated that the leading role in the distribution of radionuclides belongs to redox and acid-base conditions, which have changed significantly after draining the peat deposit.

THE WORLD’S LARGEST FOUTA DJALLON–MANDINGO BAUXITE PROVINCE (WEST AFRICA): PART 4. THE MECHANISM OF ZONING FORMATION IN LATERITE BOXITE-BEARING WEATHERING CRUSTS

Obtained as a result of detailed exploration and year-round observations of the hydrogeological regime at large deposits, as well as special hydrochemical studies of various types of water and changes in the gas composition of the underground atmosphere in the lateritic weathering crust of the largest bauxite-bearing province FDM, thanks to a reliable factual base, allowed us to draw a number of important conclusions on the conditions and features of the formation of zoning in the lateritic weathering profile for the first time. The weathering profile consists of two metasomatic columns spatially combined in plan, but vertically separated: the upper, lateritic cover, composed mainly of the products of the final hydrolysis of lateritic weathering, that is, hydroxides and oxides of iron and aluminum; the lower one, composed of clayey eluvium, products of hydration and decomposition of aluminosilicates - polymineral clays and kaolinite. In both columns, the processes of changing begin with the same rainwater, but differ in hydrodynamic parameters in each of the columns. Changes in the weathering profile occur in accordance with the main patterns of low-temperature infiltration metasomatism. The modern hydrogeological and gas regime in the bauxite-bearing lateritic covers controls the mineralogical and geochemical zoning. Peculiarities of biological and soil processes, hydrodynamics and hydrochemistry in the weathering profile lead to the threshold nature of the change in physicochemical and biochemical conditions, providing the action of geochemical (oxidative, reducing, gley, adsorption) barriers - the main mechanism of zonal distribution of matter in lateritic crusts.

Origin of ironstones of the Udokan Cu deposit (Siberia, Russia): A key study using SEM and LA-ICP-MS

Iron is an important element involved in the formation of sedimentary-hosted copper deposits. Its accumulation in sedimentary basins and subsequent redistribution ultimately affect the position of copper mineralization. The Udokan copperstone deposit contains considerable Fe reserves as magnetite and hematite. The Fe oxides form disseminated and layered aggregates in both Cu-bearing horizons and host metasandstones. The layered aggregates of Fe oxides contain detrital (zircon, chromite and apatite) and authigenic (a Th silicate) components. The ironstones bear chemical features both of clastic and chemical sediments. The enrichment of ironstones in Cr, Zr and Hf is due to the presence of relics of detrital chromite and zircon. The presence of rare earth elements (REEs), U, and Th in composition of ironstones is a result of chemical precipitation/sorption.According to the LA-ICP-MS data, Al, Mg, and V are the most significant trace elements of magnetite, whereas Ti and V are hosted in hematite. The extremely high Ti, Cr and Cu contents of magnetite are associated with inclusions of minerals of these elements. In hematite, the high Ti contents are due to inclusions of rutile or titanite. The correlations between the trace elements in Fe oxides reflect the mineral assemblages characteristic of two stages of sediment transformation: (i) earlier diagenetic with the formation of a hematite-rutile assemblage and early Cu sulphides and Th and REE mineralization and (ii) later metamorphic, which is related to the formation of magnetite metacrysts and recrystallization of Cu sulphides.The Fe-rich sediments formed at a river–sea geochemical barrier as a result both of sedimentation of clastic Fe oxides and flocculation of dissolved iron. The maturation of gel and lithification of sediments were accompanied by desorption of metals that accumulated in the ferruginous sediments. Some of them formed the authigenic phases (like Th), while others were isomorphically incorporated in other authigenic minerals (e.g., Nb, Ta and Sn in rutile).

Soil pH change induced by smelting activities affects secondary carbonate production and long-term Cd activity in subsoils

Cadmium (Cd) is a typical element with contamination risk caused by anthropogenic sources. Cd is known to associate with Fe (hydr)oxides in pH-neutral to slightly acidic soils. However, field evidence on the effects of high pH on the long-term migration and redistribution of Cd in the soil is lacking. In this study, a comprehensive investigation of Cd, Pb, and Zn distribution in soils was performed at a Pb–Zn smelter site to unravel the pH control of long-term Cd activity in soils contaminated by non-ferrous metal smelting. Atmospheric deposition caused widespread contamination of the surface soil. In contrast, the discharge of heavy metals and alkaline waste liquid from two separate pollutant sources inside the smelter resulted in severe pollution migrating from the deeper layers up to a depth of 10 m. Elemental analysis showed that the Cd/Zn ratio in soil increased as the pH value increased, indicating that Cd was progressively decoupled from Zn and accumulated in the solid phase. Chemical extraction, SEM-EDS mapping, and micro-FTIR mapping analysis of soil particles revealed that most of the Cd were correlated with calcite, which formed as a secondary mineral at a higher pH. The production of secondary carbonate as a geochemical barrier enhanced the natural attenuation of Cd, which provides a reference for remediating Cd pollution. Overall, the results provide information for studying the transport and accumulation of heavy metals in deep soil layers. On the other hand, as carbonate is an unstable sink compared to other carriers, this mechanism should be considered in future studies on health and ecological risk assessment criteria for heavy metal pollutants in alkaline environments.

Geology and geochemistry of Zn-Pb(-Ge-Ag) deposits in the Sichuan-Yunnan-Guizhou Triangle area, China: A review and a new type

Mississippi Valley Type (MVT)1 deposits represent the majority of carbonate-hosted Zn–Pb deposits globally. They typically form in an extensional tectonic setting along passive margins. However, studies on carbonate-hosted Zn–Pb deposits in the Sichuan–Yunnan–Guizhou Triangle area (SYGT) reveal differences in terms of the essential features of typical MVT deposits. We discuss the main features of these deposits, controlled by folds and faults, high-grade Zn–Pb ores and symbiotic or associated elements (i.e., abundant Ag and dispersed amounts of Ge, Ga, and Cd) of significant economic value. Based on a comparison of Pb-Zn deposits in SYGT and classical MVT deposits formed in an extensional tectonic setting, as well as a subsequent discussion on deposit classification, we propose that the Huize-style Zn–Pb deposits are a new deposit style, whose basic features can guide future ore exploration. We define the Huize-style deposits based on four factors: i) Hierarchical ore-controlling system of strike-slip fault-fold structures, ii) litho-facies associated with typical alternation and mineralisation, iii) ore-forming geochemical features revealed by typical mineral assemblages, mineralisation alteration zoning, fluid-inclusion, isotope geochemistry and metallogenic acid–alkali geochemical barriers, and iv) different prospecting methods to those typically used for MVT deposits. The Huize-style and typical MVT deposits constitute the carbonate-hosted non-magmatic epigenetic hydrothermal-type (CNHT) Zn–Pb deposits.

Geochemical Characteristics of the Vertical Distribution of Heavy Metals in the Hummocky Peatlands of the Cryolithozone.

One of the main reservoirs depositing various classes of pollutants in high latitude regions are wetland ecosystems. Climate warming trends result in the degradation of permafrost in cryolitic peatlands, which exposes the hydrological network to risks of heavy metal (HM) ingress and its subsequent migration to the Arctic Ocean basin. The objectives included: (1) carrying out a quantitative analysis of the content of HMs and As across the profile of Histosols in background and technogenic landscapes of the Subarctic region, (2) evaluating the contribution of the anthropogenic impact to the accumulation of trace elements in the seasonally thawed layer (STL) of peat deposits, (3) discovering the effect of biogeochemical barriers on the vertical distribution of HMs and As. The analyses of elements were conducted by atom emission spectroscopy with inductively coupled plasma, atomic absorption spectroscopy and scanning electron microscopy with an energy-dispersive X-ray detecting. The study focused on the characteristics of the layer-by-layer accumulation of HMs and As in hummocky peatlands of the extreme northern taiga. It revealed the upper level of microelement accumulation to be associated with the STL as a result of aerogenic pollution. Specifically composed spheroidal microparticles found in the upper layer of peat may serve as indicators of the area polluted by power plants. The accumulation of water-soluble forms of most of the pollutants studied on the upper boundary of the permafrost layer (PL) is explained by the high mobility of elements in an acidic environment. In the STL, humic acids act as a significant sorption geochemical barrier for elements with a high stability constant value. In the PL, the accumulation of pollutants is associated with their sorption on aluminum-iron complexes and interaction with the sulfide barrier. A significant contribution of biogenic element accumulation was shown by statistical analysis.

Geochemical barriers in the technogenic zone of tungsten deposits in Eastern Transbaikalia (Russia)

The relevance of the study is due to the need to protect the environment in mining regions in connection with the pollution of surface and groundwater. The conditions of the formation and influence of technogenic geochemical barriers on the physicochemical parameters of water developed in the areas of tungsten deposits in Eastern Transbaikalia have been studied. Locations of oxygen, sorption, alkaline, acidic and hydrodynamic type geochemical barriers have been identified. It has been shown that the most widespread barriers are complex geochemical barriers formed as a result of the superposition of several barriers.

Geological structure of Ustuk ore field features of mining

The article provides information on mineralization of the Ustuk mineral field with uranium and other rare metals.The distribution of radioactive elements in rocks was studied in field studies. As a result of the research, it was found that uranium-rich vanadium mineralization and secondary minerals of carnotite-tyuyamunite series were formed. Also, the primary minerals of uranium and rare earth elements were enriched with uranium and rare earth elements in the metamorphic quartzization front. A favorable environment (geochemical barrier) for quartzization of skarnoids was created and mineral deposition took place.Carriers of uranium and rare earth elements in primary minerals, consisting of 91.25% cerium, lanthanum, praseodymium and neodymium oxides, were identified as: yttrotitanite, apatite, rutile, leucoxen, orthite, uraninite, monazite, xenotime. Quartz ore deposits with iron sulfides and hydroxides have been exposed in the area.

К вопросу обеспечения безопасности труда при проектировании технологии подземной добычи руд

The article is devoted to the issue of optimizing the operating mode of a mining enterprise according to the criterion of improving the safety of miners in the development of an ore deposit by an underground method. The problems of mining production solved at the design stage of mining enterprises are designated as derivatives of the efficiency function depending on the performance of the system, the total costs of development and operation, the amount of damage due to unreliability, time, etc. It is shown that one of the methods for optimizing the design support of mining operations is the modeling of the main mining processes. The purpose of the study is formulated as detailing the concept of ensuring occupational safety when engaging in the production of substandard metal-containing mineral raw materials. It is noted that the underground mines are among the most complex objects for which it is advisable to use multi-variant design with step-by-step optimization of intermediate design solutions. The extraction of mineral raw materials is characterized by an increase in volumes and accumulation of aggressive processing waste with a dangerous impact on the environment. It is noted that technogenic deposits are formed without considering the subsequent use of tailings, for example, storage with the creation of geochemical barriers. A new area of metal leaching into a disintegrator was proposed, which allows to produce products from substandard raw materials with less energy consumption. The characteristic of innovations in mining is given. A mathematical model is recommended that allows considering the features of technologies taking into account the costs of ensuring the safety of employees. It is concluded that the optimization of mining production is characterized by the extraction of metals using technologies with a combined mechanochemical effect.

АКТУАЛЬНЫЕ АСПЕКТЫ ИЗУЧЕНИЯ ПЕРИОДИЧЕСКИ ПЕРЕСЫХАЮЩИХ АКВАТОРИЙ В КОНТЕКСТЕ УГЛЕРОДНОГО ЦИКЛА (НА ПРИМЕРЕ БАССЕЙНА НИЖНЕГО ДОНА)

Investigations were carried out in the reservoirs of the Don delta and Western Manych to study the biogeochemical cycles of elements, mainly carbon, in the transition zones between land and water. The main physical and geographical processes that determine the supply, transfer and transformation of organic matter and the connectivity of aquatic and terrestrial ecosystems are identified. A decrease of the surface area, based on a comparison of remote sensing data in ArcGIS for the period 1985–2021, of the water surface of reservoirs in average of 15– 16 % was established (in the Don delta, mainly due to the destruction of man-made ponds, in Manych – due to a decrease in the water level). It is possible to slow down biogeochemical processes in drained areas and change one type of process to another as a result of the absence of a hydrological flow. A shift of geochemical barriers towards the river during surges and an increase of mineralized underground runoff during negative surges was recorded under the influence of surge phenomena in the Don Delta. For the system of reservoirs of the Western Manych, the presence of salinity gradients between its individual parts was noted. Investigations have established that the mixing zones of fresh and salt water – biogeochemical “hot spots”, are characterized by a contrasting chemical composition and very different concentrations of organic and suspended matter. A tendency to a significant change in the structure of the upper part of the profile of alluvial soils of the river delta was noted with the continuing low water in the Lower Don. Areas with varying degrees of manifestation of soil-forming processes, as well as the main natural and anthropogenic factors that control these processes, have been identified.

Biogeochemical Permeable Barrier Based on Zeolite and Expanded Clay for Immobilization of Metals in Groundwater

Groundwater samples contaminated with potentially toxic elements (PTE), including metals and nitrate ions, were collected at a depth of 8–10 m from the Siberian Chemical Plant multicomponent waste storage. The possibility of developing a permeable biogeochemical barrier with zeolite and lightweight expanded clay aggregate (LECA) was investigated. The mass fraction and properties of several metals (Mn, Fe, Co, Ni, Cu, Zn, Cd, Hg and Pb) were determined to investigate their fixation on the chosen materials at the given experimental conditions. It was established that metals in sulfide or phosphate forms can be effectively immobilized via biomineralization on LECA, whereas metals from the non-chalcogen group are primarily retained in the form of phosphates. The formation of biogenic deposits of iron sulfide, which serve as a sorption–precipitation phase during the immobilization of the majority of metals, is an important aspect of the LECA loading process. The use of LECA and zeolite in the form of a two-component barrier is feasible based on the data obtained. It is assumed that metal immobilization processes occur due to sorption mechanisms in the zone of zeolite loading. Microbial nitrate removal and the formation of iron sulfide phases under reducing conditions, which form a geochemical barrier for metals, are expected in the LECA zone.

Soil-archaeological studies of Koy-Gunzhar Scythian tumuli (Kazakhstan): building materials and techniques, diagenetic transformations of buried paleosols

The tumuli of the Koy-Gunzhar burial ground (2400-2000 cal years BP) in the North Kazakhstan are monumental earthen mounds, built in honour of the Scythian elite. The tumuli, besides representing the diversity of the building techniques for such earth burial mounds, also provide a unique opportunity to study the direction and character of the paleosol diagenesis for nearly 2400 years. This soil-archaeological study aimed to reveal mound building techniques, the characteristics of materials used for construction, and diagenetic changes of the buried paleosols. The comparative analysis of tumulus embankments and buried soils (their genesis and diagenetic transformations) provided the opportunity to establish the source of the building material and to reconstruct some details of the building technologies. For instance, the Calcic Someric Kastanozem (Arenic, Protosodic), buried by loam-sandy and sandy substrate of the tumulus 3, corresponds to dry steppe conditions and has no considerable signs of diagenetic transformations, whereas the paleosol under the tumulus 1 was affected by strong diagenetic transformation supposedly due to acid drainage from the embankment which originally contained sulfidic material being subjected to oxidation and acidification after the tumulus construction. Diagenesis was manifested in the redistribution of pedogenic carbonates and enrichment in iron, magnesium, manganese, and aluminum compounds in the upper 32 cm of the buried soil. These elements were partially accumulated at the carbonate geochemical barrier (over Bk horizon of the buried soil). This soil was transformed by diagenesis from Kasrtanozem to Mollic Cambic Umbrisol (Epiloamic, Katoarenic). The builders of the tumulus 1 used a loamier substrate to construct the mound, different from the parent material for adjacent soils (loamy sands and sands). The loamier substrate ensured the firmness of the mound construction. The builders employed an uncommon technique to produce a mound with defined properties and used foreign building materials brought from the distance.

Геохимическая активность снега и послойная изменчивость изотопного состава кислорода (δ18О) в снежной толще в условиях разной запыленности приземной атмосферы

The layered distribution of the isotopic composition (18O) in the snow mass under conditions of different dust pollution of the near-surface atmosphere was studied on the territory of two scientific test sites of the IAO SB RAS: the Fonovaya observatory and the suburban BEK test site (Tomsk). Interlayer differences in isotopic characteristics and the activity of snow chemical reactions were evaluated in conjunction with the analysis of the dispersed composition of the precipitated aerosol substance, the radiation transparency of snow in the UV range, and taking into account reverse trajectories of air mass transfer. Interlayer fluctuations in 18O values were established, the variability of which increased in layers confined to the thermal diffusion geochemical barrier. We suggested that due to the geochemical activity of snow and its ultraviolet transparency, as well as the presence of iron-containing dust-aerosol particles in the snow mass, conditions arose that initiated photoactivated snow-chemical reactions. Their occurrence may be accompanied by free radical oxidation of the precipitated aerosol matter and the formation of stable photoreaction products, which may be evidenced by the established post-sedimentary interlayer differences in the isotope stratification of the snow mass.