Geochemistry International最新文献

The paper discusses methods for determining the parameters of a spike solution (concentration of the element and its isotope composition) and provides theoretical verification of these methods with reference to strontium as an example. The Sr isotope composition of rocks and minerals is widely used in geochemical and isotope–geochronological research. Earlier theoretically justified techniques for the calibration of a spike of a given chemical element relied on the known isotope composition of the element in the reference solution and the concentrations of the element in both the reference solution and the spike solution. In other words, it was only the isotope composition of the spike that should have been certified. The authors propose a new method for certifying a strontium spike: determining its parameters from results of the isotopic analysis of two mixtures of the spike with a reference solution. In this case, the ratios of the three stable isotopes (⁸⁴Sr, ⁸⁶Sr, and ⁸⁸Sr) are used, and the Sr concentration in the spike solution should not necessarily be precisely known. The isotope composition of one of the mixtures is specified by the geometric mean of the isotope compositions of the reference solution and the spike, and the isotope composition of the other is the arithmetic mean of these indicators. The former is aimed at determining the concentration of the element in the spike, and the latter is used in evaluating the isotope composition of the spike. The combined use of these mixtures makes it possible to obtain all parameters of the spike: its Sr concentration and Sr isotope composition. The authors believe that the most accurate way to determine these parameters is to use all four stable isotopes of Sr. One of the promising ways to determine the parameters of the spike solution is to use a reference solution enriched in the ⁸⁷Sr isotope and with preserved natural ratios of other isotopes. The application of reference solution enriched in the ⁸⁷Sr isotope and a spike enriched in the ⁸⁴Sr isotope enables the parameters to be evaluated.

In this study pyrolysis behaviors, pyrolysis gas evolution and kinetic parameter distribution of marine-continental transitional shale from Shanxi Formation in the Ordos Basin were investigated. To analyze the pyrolysis of kerogen from marine-continental transitional shale of Shanxi Formation at different heating rates TG-FTIR-MS combined technology was used. The weight loss and the evolution of pyrolysis gases of kerogen samples under different heating rates were studied, and the kinetic parameters were calculated. The results showed that the weight loss of kerogen at heating rates of 5, 15 and 25°C/min were 28.08, 25.46 and 26.58 wt %, respectively. With the increase of the pyrolysis temperature, the pyrolysis gases such as H₂O, CO₂, CO, CH₄ and H₂ are successively released. The whole pyrolysis process can be divided into six stages: drying, slow pyrolysis, first fast pyrolysis, second fast pyrolysis, fast polycondensation and slow polycondensation. Among them, in the two fast pyrolysis stages (393.4–589.4°C), the weight loss rate of kerogen was larger. With the increase of conversion rate, the activation energy increases, indicating that the energy required for the fracture of different functional groups is different, and the difficulty of the reaction is also different.

One of the widely discussed issues of genesis of oceanic rises is the possibility of their occurrence due to the interaction of hot spots and mid-ocean ridges. The Crozet Rise (less than 9 million years old) is located in the western Indian Ocean and consists of a group of volcanic islands with alkaline lavas. The paper studies basanites of the largest island of the archipelago, Possession Island. Obtained results of petrological and geochemical studies in combination with available geophysical and numerical models’ data were used to determine the conditions of the formation of the Possession Island lavas, as well as the relationship between the features of the origin of the Crozet Rise and other rises of the western Indian Ocean located near South Africa. The olivine–clinopyroxene–spinel phenocryst assemblage observed in the lavas of Possession Island corresponds to deeper crystallization conditions compared to the typical oceanic magmas, which are usually characterized by the olivine–plagioclase–clinopyroxene assemblage. The fractionation of melts could have occurred in the intermediate chamber as a result of the magma replenishment at pressures of 8–10 kbar and temperatures of 1200–1300°C during the volcanic edifice formation 9 million years ago. The geochemical characteristics of the Possession Island lavas, including the Sr, Nd, and Pb isotopic composition, indicate an enriched source, possibly with an admixture of a HIMU-type component (with the high initial U/Pb and U/Th ratios), and are close to the composition of enriched magmas of the Indian Ocean rises (Crozet, Marion, and Bouvet), but differ from the composition of basalts of the Conrad and Afanasiy Nikitin rises and Mozambique Ridge in the western Indian Ocean. The enriched HIMU-type source is associated mainly with Gondwanan ancient continental mantle. The fragments of continental crust or oceanic mantle enriched at the early evolution stages could be involved in melting, since the Crozet Rise is an intraplate structure recently formed under the influence of a hotspot on a relatively ancient oceanic lithosphere. In this case, the fractionation of alkaline magmas occurred at a depth of ~ 25–30 km. The formation of the eastern part of the Crozet Rise occurred under the influence of the Crozet–Marion hot spot, which can be considered a satellite of the large African plume, which determined the entire evolution of the Southern Ocean.

The influence of corrosion products of metal structures of a repository on the sorption behavior of long-lived radionuclides in the environment of the host crystalline rocks should be taken into account during modeling aimed at confirming the safety of deep disposal of radioactive waste (RW). This study focuses on the influence of iron(II/III) on the sorption and spatial distribution of ²³⁷Np, ²³⁹Pu, and ²⁴¹Am on the minerals of a fractured gneiss sample from the Yeniseisky site of the Nizhnekansky massif (Krasnoyarsk krai). Kinetic dependencies and quantitative parameters were obtained for actinide sorption in the presence of iron in model solutions, including solution affected by contact with steel ST3. It was shown that the presence of iron (oxy)hydroxide increases the rate of actinide sorption by the rock, whereas ionic iron species have practically no effect on this process. Digital radiography demonstrated that the preferential actinide retention phase was formed by iron(III) precipitation on the calcite surface. The Raman spectrum of this phase corresponds to the iron-bearing mineral lepidocrocite.

A nine-year experimental study of the uptake of dissolved fluorine by calcite, aragonite, and dolomite from seawater has shown that the occurrence of magnesium in sedimentary carbonate minerals is favorable for their enrichment in fluorine. According to the intensity of dissolved fluorine removal from seawater by carbonate minerals, these minerals are arranged in the following succession: dolomite ( gg ) calcite > aragonite, and the fluorine uptake by dolomite is 40–60 times higher than by calcite and aragonite. It was concluded that the magnesiality of sedimentary carbonate rocks is an important factor controlling their fluorine content, along with the fluorine concentration in the waters of the sedimentation basins.

The West Transbaikal rift region was formed in a continental setting in the Late Jurassic and has been developed until the Early Cenozoic. The Uda sector is one of its central fragments and includes the Uda, Eravnoe and Zaza depressions. New Sr, Nd, Pb, O isotopic data reported in this study in combination with geochemical signatures of Cretaceous basaltic rocks of each depression allowed us to estimate the compositions of mantle- and crustal-derived magmas and to propose their mixing model. During the formation of volcanics of the Uda sector within the age range of ∼143–71 Ma, the isotopic sources successively changed from enriched (EMI and EMII) to moderately depleted PREMA types. The Early Cretaceous primary magmas were derived from mantle sources that included subduction-enriched mantle, which resulted in the depletion of the basaltic rocks in Ta, Nb, Ti and in high (La/Ta)_N (2.2–4.9) and (La/Nb)_N (2.1–4.2) ratios at high contents of incompatible trace elements. Mantle magmas of the Uda depression were contaminated with a lower crustal component, which is characterized by the moderate or lowered contents of Zr and La, and low La/Yb and Rb/Sr ratios compared to the composition of basaltic melt. Compositions of basaltic rocks from the Eravnoe and Zaza depressions reflect the interaction of mantle magmas with upper crustal granitoids of the Angara–Vitim batholith. Mantle-crust interaction least affected the composition of Late Cretaceous volcanics, the geochemical characteristics of which are consistent with the dynamics of temporal isotope variations of mantle sources.

Widespread granites in the Wuzhuerhada area within the Tataleng granitic batholith in NW China show notable U, F, W, B, Rb, Be, and Sn geochemical anomalies. However, the petrogenesis and mineralization potential for them are unexamined for now. This study investigated the major and trace element compositions, zircon U–Pb ages, and zircon Hf isotope and trace element compositions for the Wuzhuerhada rapakivi granite and the granite dyke in it. Two samples for the rapakivi granite yielded weighted mean ²⁰⁶Pb/²³⁸U zircon ages of 430 ± 2 and 433 ± 4 Ma, respectively, and one sample for the granite dyke yielded a weighted mean ²⁰⁶Pb/²³⁸U zircon age of 433 ± 4 Ma, indicating comparable emplacement ages of the Early Silurian granites. Geochemically, the Wuzhuerhada rapakivi granite and the granite dyke are slightly peraluminous, with relatively high ASI values, high alkali contents, and negative Eu anomalies, suggesting I-type granites. Geochemistry and zircon ε_Hf(t) values of –14.2 to –4.9 for them suggest that they were all derived from the partial melting of igneous rocks within the Paleoproterozoic relatively shallow mafic reworked lower crust in a typical syn-collisional setting. Minus ΔFMQ value, low quantitative oxygen fugacity (fO₂), and low Ce⁴⁺/Ce³⁺ ratios for zircons suggest that the studied granites have relatively reduced redox states. But the granite dyke shows fractionated whole-rock geochemistry and contains some hydrothermal-affected zircons, indicating that the granite dyke has more Sn–W–(U) mineralization potential than the rapakivi granite or other neighbour granites. Our contributions would help delineate possible Sn–W–(U) ore-prospecting areas where fractionated granite was emplaced in the South Qilian belt.

The paper presents quantitative analyses (ICP-MS) of surface, snowmelt, and rainfall waters for 30 elements and analyses of the bottom silts for 49 elements for mountain lakes in the Iolgo Range, Altai Mountains; and data on physicochemical characteristics of the water bodies (pH, redox potential (RP), and electrical conductivity). The surface waters are ultrafresh (mineralization (total dissolved solids, TDS) 5.7–43 mg/L) and slightly alkaline to alkaline (pH 7.6–9.0), and their RP corresponds to an oxidizing geochemical environment (166–225 mV). The water of all the lakes belongs to the calcic group. The predominant cations in the snowfield are Na, K, and Ca, and those in the rainfall are K, Si, and Ca. The characteristics of the water bodies are assumed as background ones for the territory. The content of pollutants does not exceed the maximum allowable concentration (MAC) in drinking water. The low concentrations of humic acids in the lean stony soils, long-lasting contact of the waters with Na-rich weathering products of the underlying sedimentary–volcanic rocks, and low CO₂ concentrations in the regional atmosphere are favorable for the formation of alkaline lake waters in the upper part of the Karakol valley. The main factors in the formation of the most alkaline and mineralized waters of all of the lakes studied in the upper Karakol valley are geochemical features of the bottom silts of these lakes and their stagnant nature, which facilitates the accumulation of elements over a long period of time. The lake silts inherit geochemical markers from the underlying volcanics, indicating the geodynamic setting of their formation. The PM-normalized multielemental patterns of the bottom silts show enrichment in LREE and LILE, depletion in HREE, and clearly discernible Nb, Ta, and Ti minima, which indicates that they contain weathering products of subduction-related rocks (which formed on an active continental margin). The study area is located within the Saganyy-Kylay Pb–Zn ore region with Pb and Cu ore occurrences and with W and Zn lithochemical anomalies. Elevated contents of these and associated metals are found both in the watercourses of the Tura and Ugul river basins and in the bottom silts of the lakes. Contents of Ni, Zn, and Pb in the surface waters and concentrations Be, V, Cu, Zn, Mo, W, and Pb in the lake silts exceed the Clarke values for lacustrine waters and the Earth’s crust, respectively, which corresponds to the metallogenic specifics of this region.

Halogens play an essential role in mantle petrology, but no data on halogen content in diamonds are available to date. Concentrations of fluorine and chlorine in diamond were determined quantitative for the first time, using quantitative SIMS analysis based on external standards prepared by the ion-implantation of halogens. Fluorine concentrations in diamond vary from 0.018 to 0.036 at ppm (3.2‒6.3 × 10¹⁵ at/cm³); chlorine concentrations are similar, from 0.014 to 0.034 at ppm (2.4‒4.5 × 10¹⁵ at/cm³). Most likely, F and Cl are related to microinclusions in diamonds, although one cannot exclude their position in the diamond lattice. The source of halogens in the studied diamonds is complex. A part of F and Cl is juvenile, remained from their primary concentrations. Another part, forming the halogen repository in the deep Earth, comes to the mantle via subduction. Fluorine may form the fluorine–vacancy (F–V) complex in the diamond structure, F and Cl may be compositional parts of microinclusions in diamonds as well. The F/Cl ratio in the studied diamonds (1.00–1.82) is similar to F/Cl ratios in kimberlites (0.38‒1.68). It differs from the estimates for the Earth’s mantle (0.62–0.68) but is close to enstatite chondrite values (1.16–2.77).

The results of our studies of iron-bearing phases in various meteorites using Mössbauer spectroscopy with a high velocity resolution were briefly reviewed. Examples of obtained Mössbauer spectra of meteorites and their fitting were considered and demonstrated advantages of this technique for revealing spectral components related to various iron-bearing phases that could not be observed in the spectra recorded by conventional Mössbauer spectroscopy. It was shown that the obtained results can be used for the phase identification, phase analysis, estimation of variations in the local microenvironment and parameters of ⁵⁷Fe hyperfine interactions, determination of cation ordering in silicate crystals, and calculation of the temperatures of equilibrium cation distribution as well as for the systematization of ordinary chondrites.