Geochemistry International最新文献

The work provides a comprehensive assessment of changes in the intensity of pollution of soils and plants of pine forests with increasing distance from the main sources of pollution. Within the forest-steppe zone of the Chelyabinsk region, zones of environmental tension have been identified based on the summary index of soil contamination with mobile forms of chemical elements and on the level of pine bark contamination. The main polluting elements were Cr, Pb, Zn, Cd, the content of which in soils was tens of times higher than the background values. The same pollutants and Cu were noted for pine bark, but their concentrations were significantly lower and exceeded the background only several times. High values of correlation coefficients between pollution indicators for soils and bark were noted for Pb, Cu, Zn and the summary indices of contamination. The content of most of the studied chemical elements in pine needles does not exceed background values, but the Al and Ni content in some plots near industrial enterprises can be 2–4 times higher than background values.

Abstract—

Petrographic and thermobarometric data obtained on a blastolite lens hosted in sheared rocks of the Gonzhinskii block indicate that the lens contains four mineral assemblages: relict, main, an assemblage corresponding to biotitization, and that of retrograde alterations. The relict assemblage was likely eclogitic. The main mineral assemblage corresponds to zoisite amphibolite developing after eclogite. The P−T metamorphic parameters of this assemblage are P = 13.0−15.0 kbar and T = 580−670°C. However, if the calculations are done using the iron richest outer rim of amphibole 1, the P−T parameters are P = 13.0−17.0 kbar and T = 660−780°C. The mineral assemblage corresponding to the overprinted biotitization is clearly distinct texturally. The lines of the monomineral equilibria of the biotite assemblage plotted using various combinations of the composition of the garnet, biotite, and plagioclase well converge within a compact field of P = 12.5−13.2 kbar and T = 810−830°C. The latest assemblage of retrograde minerals includes low-Al amphibole 2. Our original Sm−Nd isotope date were used to calculate an isochron for a whole-rock sample, garnet, and two amphiboles. The isochron age of the rock is 171 ± 3 Ma and is interpreted as the age of the main mineral assemblage, i.e., its crystallization at the metamorphic peak.

The paper reports the results of U–Pb dating, Nd–Sr–Pb isotope systematics, and geochemical study of quartz diorites associated with ore-bearing (Cu–Pd–Au–Ag) gabbro of the Volkovsky massif, which is localized within the Urals Platinum Belt, at its eastern border with the Silurian–Devonian volcanogenic complexes of the Tagil megazone. The age of the quartz diorites according to U–Pb (TIMS) dating is 429 ± 9 Ma, MSWD = 0.009. Sr–Nd–Pb isotope characteristics (ε_Nd(T) = +5.5…+6.7; (⁸⁷Sr/⁸⁶Sr)_t = 0.70382–0.70392; ²⁰⁶Pb^/204Pb = 18.38–18.57; ²⁰⁷Pb/²⁰⁴Pb = 15.56–15.58; ²⁰⁸Pb/²⁰⁴Pb = 38.14–38.30) indicate a juvenile source with a model age of 570–760 Ma. The obtained data fall within values typical of basalts of ensimatic island arcs. The geochemical features of the granitoids of the Volkovsky massif (low REE concentration, differentiated REE pattern (La/Yb = 8–14) with a weak positive Eu anomaly (Eu/Eu* = 0.9–1.4)) are consistent with the characteristics of melts obtained in experiments on hydrous melting of mafic rocks in equilibrium with amphibole–pyroxene residue. The anomalous concentration of strontium (more than 1000 ppm) in the quartz diorites is due to the high content of this element in a source. Such source could be the oldest rocks of the Urals Platinum Belt—olivine gabbro and metamorphic rocks of their surroundings. The identical ages of the quartz diorites of the Volkovsky massif and monzonitoids of the Kushvinsky massif allow us to consider these rocks as the result of the almost simultaneous mantle and crust melting at the final stage of the formation of the Tagil island-arc system.

Abstract

Three variably old groups of banded iron formation (BIF) are known in the Kostomuksha Greenstone Belt (KGB) of the Karelian Craton. This paper deals with the earliest of them, Mesoarchean (2.87–2.81 Ga) BIF-1. BIF-1 occurs among the komatiite–basalt unit of the KGB. BIF-1 consists mainly of quartz and magnetite, with varying amounts of amphibole, biotite, and garnet; the variations of SiO₂ (48.3–58.6 wt %) and ({text{F}}{{{text{e}}}_{{text{2}}}}{text{O}}_{{text{3}}}^{{text{T}}}) (21.34–33.82 wt %) suggest that the rocks are BIF. BIF-1 of the KGB, as well as most Archean BIFs, contain high ({text{F}}{{{text{e}}}_{{text{2}}}}{text{O}}_{{text{3}}}^{{text{T}}}) concentration, display a contrasting positive Eu anomaly, lack of Ce anomaly, and the depletion of LREE relative to HREE. However, they differ from other BIFs in the higher Al₂O₃, TiO₂, MgO, K₂O, Cr, Ni, Zr, Ba, Cu and Zn concentrations. BIF-1 was formed in a marine basin at an anoxic atmosphere due to hydrothermal fluids, the proportion of which varies from 20 to 80%, and a terrigenous component derived mainly from basalts, komatiites, and dacites of host rocks. Mesoarchean BIF-1 of the KGB was accumulated in a small rift structures within an oceanic volcanic plateau, the formation of which is associated with the influence of a mantle plume on the oceanic lithosphere.

Abstract

The solubility of crystalline MoO₃ in HCl solutions with variable concentration was investigated at 100, 155, 200, 250, 300, 350°C and saturated vapor pressure. The results showed that the MoO₃ solubility increases with increasing HCl concentration. Using the OptimA program, the Gibbs energies of MoO₂Cl₂ complex have been determined. The stability constants of MoO₂Cl₂ are calculated according to the reaction:

$${text{Mo}}{{{text{O}}}_{{{text{3(c)}}}}} + 2{text{HC}}{{{text{l}}}_{{{text{(aq)}}}}} to {text{Mo}}{{{text{O}}}_{{text{2}}}}{text{Cl}}_{{2{text{(aq)}}}}^{^circ } + {{{text{H}}}_{{text{2}}}}{{{text{O}}}_{{{text{(l)}}}}}.$$

The pK values are 1.07 ± 0.29; 1.06 ± 0.49; 1.74 ± 0.71; 1.83 ± 0.47; 1.50 ± 0.28; 0.95 ± 0.57, respectively, at 100, 155, 200, 250, 300, 350°C (saturated vapor pressure).

Abstract

The Shangyun area is classified as a medium-high temperature geothermal region situated in western Yunnan, inside the tropical zone of Yunnan and Tibet. Granites exhibit a wide distribution, while active faults demonstrate a rather advanced state of development. Consequently, the geological conditions are favourable for the creation of geothermal resources. Drawing upon previous research findings and geothermal drilling data, this study undertakes an analysis of the principal geological factors contributing to the development of the Shangyun geothermal system in Yunnan. The investigation reveals several noteworthy characteristics of geothermal activity within the granite region, including proximity to heat sources, substantial thermal gradients, water accumulation within fractures, the coexistence of deep and shallow geothermal phenomena, and the occurrence of hot springs along extensive and profound fault lines. The determined ground heat flow value in the Shangyun area is 142.74 mW/m², with its primary heat source being predominantly influenced by high mantle heat flow and the radioactive heat generation of the Lincang granite located in the eastern region with the mean rate of radioactive heat generation of 7.6 μW/m³. The reservoir space mostly consists of weathered crust and fracture type heat storage. Additionally, the upper Jurassic mudstone, which has a thickness ranging from 500 to 1000 m and a thermal conductivity of 2.39 W/(m K), serves as an effective regional cap layer. The dissolution of silicate has a significant impact on the composition of geothermal water, with the primary type being HCO₃–Na. The process of atmospheric precipitation infiltration and recharge contributes significantly to the availability of ample water resources for geothermal systems. Based on an analysis of the electrical data pertaining to the region, it can be inferred that the primary source of the water supply originates from the eastern mountain. Furthermore, it is seen that the active fault serves as the conduit for the deep circulation of geothermal water. This study presents a comprehensive examination of several geothermal geological features, including heat source, heat storage, hot channel, and geothermal water, in order to build a geothermal model specific to the Shangyun region.