Geochemistry International最新文献

Knowledge of the geochemistry of selenium (Se) is crucial for understanding its behavior in the environment. While numerous studies have explored selenium geochemistry, there is a notable inadequacy, especially in extreme soil conditions such as saline soils, which are widespread globally. This study focuses on characterizing the geochemistry of selenium in saline soils, with a specific focus on the El Hamadna perimeter in Bas-Cheliff, Algeria. This location was chosen due to its diverse salinity levels and selenium content. Utilizing Phreeqc software, the study examines selenium’s chemical speciation. In the arid soils of this region, predicted selenium (IV) concentrations range from 0.19 to 3.05 mg kg^–1, and selenium (VI) concentrations range from 0.54 to 5.58 mg kg^–1. A significant negative correlation was observed between total selenium and Se(VI) concentrations with pH, whereas Se(IV) showed a positive and significant correlation with pH. No correlation was found between selenium concentrations and the salinity gradient in the studied soils. Non-significant correlations were observed between selenium levels and CaCO₃, clay, and organic matter in the soils, suggesting that these soil properties do not influence the distribution of selenium concentrations in the examined soils. Only the pH and the presence of the main form MgSeO₃ control the representation of selenium in the soil profile.

The contemporary scientific investigations delves into the mechanisms of migration, distribution, and fractionation of rare earth elements and yttrium (REE + Y) in aqueous environments characterized by humid and arid sedimentogenesis. This particular facet has been employed to solve numerous fundamental inquiries pertaining to lithology and paleolimnology. The manner in which REE + Y behave in water bodies within the cryolithozone remains largely unexplored. By evaluating the concentration levels and distribution patterns of REE + Y in the waters and sediments of the lakes situated in the Ukok Plateau and the Ulagan depression, under the prevailing conditions of cryolithogenesis as the primary geochemical process transforming rocks, soils, and sediments, we were able to augment the existing comprehension of nival sedimentation. In all the lakes examined, the content of REE + Y in the water exhibits a similar magnitude as that of small lakes in other landscape zones of the southern Western Siberia, while the content level of REE + Y is greater in the bottom sediments. The concentrations, distribution and fractionation of REE + Y vary from lake to lake and are determined by several factors: the chemical properties of REE + Y in solutions, the intensity of transformation of host rocks and the mineral forms of the REE + Y in the rocks (minerals). The concentrations, distribution and fractionation of REE + Y in bottom sediments vary slightly from lake to lake except for the contents of Eu, Y, La. The content of Eu, Y, La in the bottom sediment of the lake is influenced by a combination of factors, including their concentrations in the water, the redox conditions of diagenesis, and the mineral composition of the bottom sediment, particularly the amount of accessory minerals.

The East Qinling Molybdenum Belt (EQMB), which is located on the southern margin of the North China Craton (NCC), is the largest Mo province in the world. This belt hosts a significant number of Mesozoic magmatic-hydrothermal Mo deposits and a small portion of pre-Mesozoic Mo deposits. Understanding the mineralization timing and mechanism of the unique pre-Mesozoic Mo deposits is essential to comprehend the evolution of the EQMB, the pre-Mesozoic Mo enrichment, and the Mesozoic Mo mineralization event. The recently discovered Zhaiwa deposit is a porphyry Mo deposit located in the Xiong’er Terrane of the EQMB. In this study, five molybdenite samples from the Mo-bearing quartz veins were analyzed for Re-Os isotopes composition. These samples yield an isochron age of 1794 ± 45 Ma, which represents the age of mineralization. The mineralization is mostly hosted within the biotite-amphibole plagiogneiss and granite porphyry. LA-ICP-MS U-Pb data of zircons constrain the crystallization age of the granite porphyry to be at 1791 ± 16 Ma. The close spatial and temporal association suggests that the granite porphyry is the causative rocks of the Mo mineralization. The δ³⁴S values of pyrite vary from 5.3 to 6.8‰, suggesting that the S was mainly derived from magmatic source. The intrusion of magmas and associated Mo mineralization are contemporaneous to the regional Xiong’er volcanism that occurred during the late Paleoproterozoic. The Xiong’er volcanism was triggered by partial melting of lithospheric mantle in an extensional setting. The results of our study provide robust evidence for a late Paleoproterozoic Mo metallogenic event along the southern margin of the NCC. Future exploration should also consider the potential of late Paleoproterozoic porphyry Mo mineralization existing in the EQMB, which is closely associated with the Xiong’er volcanism.

Lake Peyungda contains annually layered bottom sediments (varves), which make it possible to build a reliable age model for the entire depth of the core. An age model was refined over the last century based on the presence of a layer of anomalous thickness associated with the fall of the Tunguska cosmic body (TCB) in June 1908. The results of scanning µXRF-SI (elemental analysis along core depth) were used for comparison with regional average annual weather observation data over the time span of 1895–2000 to create a transfer function: average annual temperature as a function of the elemental composition of the dated layer of bottom sediment. Approximation of the obtained function to the depth of core sampling made it possible to reconstruct changes in regional temperature over the time interval of the last millennium with an annual time resolution. Comparison of the obtained reconstruction with literature data on reconstructions for the Arctic region over the past 1000 years shows the presence of general trends and extremes, which confirms the reliability of the obtained results.

The paper discusses the melt sources and formation parameters of the Khokhol-Repyevka granitoid batholith that compose the Don terrane of the Volga–Don orogen in the East European craton. The batholith consists of three granitoid types: Pavlovsk granitoids (quartz monzonites–granites, mostly without pyroxenes), Potudan granitoids (quartz monzogabbro–granodiorites containing pyroxene), and hybrid ones (quartz monzodiorites, monzonites, and quartz monzonites). These three types of rocks occur together and have a similar age of 2050–2080 Ma, similar geochemical characteristics (high contents of Ba, Sr, and highly fractionated REE patterns with Gd_N/Yb_N = 2–11), but differ in petrographic and isotopic geochemical parameters. The initial isotope characteristics of the sources of the Pavlovsk-type rocks are ε_Nd(t) = +0.2 to ‒3.7 and Sr_i = 0.70335, those of the Potudan type are ε_Nd(t) = –1.7 to –3.8, Sr_i = 0.70381–0.70910, and the hybrid rocks have ε_Nd(t) = –8.8, Sr_i = 0.70596. In addition to granitoids, the batholith was found out to host two types of leucogranite dikes. One of them is characterized by ε_Nd(t) = –3.8 and fractionated HREE patterns (Gd_N/Yb_N = 2.1–3.8) and could be formed as a result of the deep differentiation of Pavlovsk-type magma. The other type has ε_Nd(t) = –7.8 and less fractionated HREE patterns (Gd_N/Yb_N = 1.1–1.6), which likely resulted from the melting of a crustal source at shallow depths. The Rb–Sr isotope-geochemical characteristics of rocks of the Pavlovsk and Potudan types indicate that their melts were derived from different sources. Therefore the melts of the Khokhol–Repyevka batholith were derived from at least three sources: (1) lower (or buried oceanic) crust of predominantly mafic composition and/or enriched mantle, which was metasomatized in the Proterozoic, whose involvement is reflected in the composition of the Pavlovsk granitoids; (2) an enriched mantle source, which was likely subcontinental lithospheric mantle (SCLM) that had been metasomatized during an earlier stage of the geological development of the region, specific of the Potudan-type monzonitoids; and (3) Archean crust consisting mostly of TTG gneisses and metasediments, which underwent melting and participated in the formation of some of the leucogranite dikes and hybrid rocks. The results of thermodynamic modeling indicate that the mixing of two melts contrasting in composition (Potudan-type mafic and Pavlovsk-type intermediate–felsic) could form only some of the hybrid rocks. The others could be formed by mafic melt contaminated with anatectic melts derived from the Archean crust of the Kursk block.

The paper assesses the chemical transformation of surface waters in the southeastern part of the Khibiny Mountainous Massif after launching the Oleniy Ruchey apatite–nepheline ore deposit in 2012. The influence of the Oleniy Ruchey Mine was reflected in an increase in water mineralization (by an order of magnitude) and in a change in the basic ion ratios in water objects receiving runoff from mines, rock, and tailing dumps compared to the watercourses unaffected by the mining enterprise’s activities. Natural hydrocarbonate–sodium water with a mineralization of 10 mg/L was transformed into the nitrate–sodium or sulfate–calcium water. The content of nitrogen group compounds in the Lake Komarinoe water, which receives wastewater from the tailing dumps over the ten-year history of the mining and processing plant, has increased by two orders of magnitude, and the nitrate became basic ion. The concentrations of other basic ions and mineralization in this lake increased by an order of magnitude, as the content of trace elements (Sr, F, Mo), which belong to the main rock-forming minerals of apatite–nepheline deposits. Compared to the background water bodies, the mine wastewaters have the elevated mineralization (up to 260 mg/L), pH value (up to 10), and a modified chemical composition. They are characterized by a hydrocarbonate–sodium composition with a large proportion of nitrates and sulfates. Mine wastewaters have elevated contents of nutrient compounds, organic matter, and some trace elements (Al, Fe, Sr, Cu, Mn, Zn, and Cr). It has been established that the geochemical modifications in the quality of surface water are locally developed, being typical of water bodies receiving wastewater from a mining enterprise, in contrast to metallurgical plants, the atmospheric emissions of which caused pollution over tens and hundreds km.

The processes of albite ordering were experimentally studied in the temperature range of 500–150°C at a pressure of 0.5–1 kbar in alkaline solutions of sodium hydroxide with excess silica. Our original experimental and literature data on the ordering of albite and sodic plagioclase were used to derive dependences for evaluating the temperature based on the degree of feldspar structural ordering. Temperatures were determined for plagioclase-bearing mineral assemblages of rocks from various greenschist-facies metamorphic complexes.

The problem of identifying scarce PGE–Cu–Ni-bearing intrusions among the huge array of barren mafic bodies in the northwestern Siberian Platform has been faced by researchers for several decades. Its solution is usually based on the geological and geophysical methods. Geochemical studies including modern elemental and isotopic analytical data are much less frequently applied for this purpose. We applied such an approach to some Norilsk complex bodies containing sulfide mineralization. Using the Maslovsky deposit located in the Norilsk syncline as an example, we have demonstrated the characteristic features of ore-bearing rocks that can be used in the search for new promising targets. The rocks of the Maslovsky deposit were studied in two sections from boreholes OM-4 and OM-24. Their geochemical parameters fall within the ranges of ε_Nd = 1.0 ± 1.0 and (La/Lu)_n = 2.3 ± 0.8, which differ the magmatic bodies of the Norilsk district with unique sulfide ores from barren massifs. The ⁸⁷Sr/⁸⁶Sr ratios in the representative gabbroic rocks from the vertical cross-sections of the Maslovsky deposit vary from 0.7056 to 0.7069. As PGEs are accumulated in the rocks, the Pd/Pt ratio increases from ~1 at clarke contents to ~3 in rich ores. No evidence of in situ assimilation by melts of silicate rocks was found.

The layer-by-layer analysis of the variation dynamics of chemical parameters of snow at one of the observation sites (at the village of Yaksha) in the Pechora–Ilych state biosphere reserve in the winter of 2019–2020 has shown that the chemical composition of atmospheric precipitation is affected dominantly by long-range material transport. Features of the atmospheric circulation and the regions from which air masses are transferred control the saturation of the precipitation with certain chemical components. The calculation of the trajectories of reverse transport of air masses allowed us to identify regions where the air masses can be formed that come to the study area and carry material that potentially affects the chemical composition of the precipitation. The calculation of trajectories is demonstrated to make it possible to identify source regions of pollutants entering the atmosphere. This method of studying the chemical composition of snow is generally very informative and enables better understanding its formation factors.

Important problems of magma differentiation, formation of native metals, and ore-forming processes in the Earth’s crust are often related to participation of hydrogen. In this paper, new experimental data on the crystallization of andesite melts at high temperatures (900–1250°C) and hydrogen pressures (10–100 MPa) have been obtained, which clarify the possible role of hydrogen in the processes occurring in andesite melts in the Earth’s crust and during volcanism under strongly reduced conditions ((f{text{O}}_{2}) = 10^–17–10^–18). In the crystallization experiments, it was found out that the compositions of the crystals (pyroxenes and plagioclases) formed in experiments on crystallization of andesite melt under hydrogen pressure closely correspond to the crystal compositions of lava flows of Avacha volcano in Kamchatka. This result can be considered as an experimental confirmation of the participation of hydrogen in the volcanic process.