Home – Home – Jornals – Advanced Search

On the territory of the Egor’evsk district, 3500 results of probe microanalyses of surface gold particles taken from 17 placers, weathering crusts, and orebodies were processed and summarized. High-fineness and mercury-containing gold is predominantly found within mother lodes and placers, and medium- and low-fineness gold is distributed in subordinate and dramatically subordinate quantities, especially in the placers. A unique feature of the gold composition, rarely occurring in other districts, is the constant and commonly simultaneous presence of mercury and copper impurities. Analysis of Ag, Hg, and Cu content variations has enabled us to identify five main grades of gold. The mother lodes of the predominant gold grades are metasomatites with beresite and listwaenite compositions, which are developed primarily after lower Cambrian volcanoterrigenous-carbonate rocks and ore-bearing mafic dikes. Mercury-containing gold is characteristic of beresites, but copper-bearing gold is typical of listwaenites. The relationship between corresponding grades of surface and ore gold is confirmed by the presence of microinclusions in the gold grains. Nonconformity between the content of gold from mother loads, weathering crusts, and placers is explained by the losses of Hg and Ag impurities by endogenous gold under subsurface hypergene conditions. Identification of mineral-geochemical properties of surface gold is of exceptional practical importance in ore-grade gold mineralization prediction.

Integrated geological and geochemical studies were performed for lignite from the Yenisei middle reaches, represented by carbonized fragments of trees with high germanium contents. Geochemical characteristics of terrigenous sediments with Ge-bearing lignite are determined. The chemical and mineral compositions, textures, and structures of carbonized wood fragments were studied. Scanning of individual cross sections of lignite fragments has revealed a regular distribution of germanium and impurity elements. Consistent patterns of the formation of Ge-containing lignites have been established, as well as the processes of their posthydrothermal transformation, which led to the impoverishment of the primary contents of the valuable component and to the input of a number of impurity elements. The latter formed rims over the lignite fragments and microveinlets with sulfide mineralization. The hypothesis has been put forward that germanium mineralization formed in lignites of the Kas basin, in particular, the Serchanskoe deposit.

One of the main objectives of geoelectric prospecting is mapping of the consolidated low-conductivity basement geometry. To resolve the issue, it will be equally important to delineate local structures at the bottom of the sedimentary complex and to estimate the misinterpretation of results due to the presence of areas with nonuniform conductivity in the stratified geologic cross section. Another relevant objective of EM sounding is to resolve the problem of delineation of anticlinal oil and gas traps. The horizontally layered model with a local inclusion of 3D abnormal areas is certain to fit for the above-mentioned objectives. The study is concerned with the technique of nonstationary EM sounding. When applied to the solution of structural problems, this technique considers the uniform distribution of fields within relatively large volume units of the space explored. Consequently, it results in the more efficient application of the perturbation technique (Born approximation) to the solution of the forward electrodynamics problem. The study presents the findings of 3D tomographic inversion with the use of synthetic and physical modeling data. They definitely allow us to acknowledge that the proposed mathematical apparatus for 3D inversion based on Born linearization of the forward problem has proved to be quite applicable.

Results of profile magnetotelluric (MT) and magnetovariational (MV) soundings of the Pamir-Alai zone are presented. The problems of construction of a 2D geoelectric model of the lithosphere of the Pamir-Alai zone and its characteristics are considered. The results of the MT sounding inversion indicate the existence of a zone of lateral plastic flow in the Earth’s crust beneath the Alai depression, which manifested itself as a conductive lower-crust structure traced for at least 200 km in the E-W direction along the strike of the Alai depression. Analysis of the relationship between the parameters of the geoelectric structure and the seismicity distribution in the study region has revealed a spatial correlation between the location of the hypocenters of K > 11 earthquakes that occurred in the Pamir-Alai territory and the geoelectric structure of the Earth’s crust in this region. New data on the tectonic stratification of the Earth’s crust have been obtained, which permits us to supplement and refine the existing geological and geophysical data on the deep structure of the Pamir-Tien Shan junction zone. Conclusions about the nature of anomalous crustal conductivity in the Alai basin have been drawn.

A melt inclusion study was carried out in the leucite-bearing tephriphonolite and phonolite lavas of the Bolsena complex in order to obtain direct data on the chemical composition of initial melts, their evolution, and their crystallization temperatures. It has been found that the initial melt for the considered rocks was of tephrite-basanite composition. Its crystallization began with the formation of clinopyroxene phenocrysts at 1205-1100 °C, then leucite and plagioclase crystallization took place at about 1120 °C and 1080-1060 °C, respectively. The initial tephrite-basanite melt was slightly enriched in volatile components (H₂O, F, SO₃, and Cl). During the crystallization of clinopyroxene, leucite, and plagioclase, the composition of the initial magma changed toward an increase in the contents of SiO₂, Al₂O₃, and K₂O and a decrease in the contents of FeO, MgO, and CaO, i.e., evolved toward phonolite. A similar evolution trend is typical of alkaline basic systems. The tephrite-basanite melt was probably the product of the crystallization differentiation of the parental mantle magma similar in composition to the leucite-bearing tephrite-basanite of the Montefiascone complex.

The distribution and fractionation of rare-earth elements (REE) in the Northwestern Pacific surface sediments are studied. The REE contents in the sediments were 30-106 ppm, and the Y contents ranged from 9.34 to 24.5 ppm. The bottom sediments located near the Kuril-Kamchatka arc were depleted in REE as compared with the sediments of the abyssal plain of the Pacific, the Kuril basin of the Sea of Okhotsk, and the northwestern Bering Sea. The effect of distributive provinces and lithodynamic setting on the REE composition and REE contents in the sediments was expressed as a positive correlation of the LREE/HREE ratio with the grain composition, Rb/Sr, and Nb/Y and its negative correlation with Zr/Rb. The variations in the bulk REE composition were due to the variations in LREE contents.

The evolution of peat deposits of the Vydrino bog (southern Baikal region) and concentration of elements in them are discussed. The bog peat massif more than 4 m in thickness formed mostly during the Holocene. The beginning of peat formation dates back to the late Allerød (13.1 ka). At present, the Vydrino bog is a biogeocoenosis of the high-moor type with a transitional peat deposit. We have established that the bog nonuniformly accumulated chemical elements during its formation. Concentration of Pb, Sn, Cd, Zn, and Sb in recent vegetation and in the upper layer of the peat bog is mainly due to forest fires and anthropogenic air pollution. The anomalous enrichment of peat with Zn and Cu in the Early Holocene (12.1-8.8 ka) horizons proceeded through the periodic inflow of thermal groundwater into the bottom part of the peat deposit. Authigenic Zn and Cu sulfides formed on the inner membrane of the cell wall of sphagnum moss. Geochemical modeling has shown that Zn and Cu sulfides can form abiotically.

The paper considers present-day rock temperature distribution in the top of the Tyumen and Malyshevka Formations throughout the West Siberian sedimentary basin. A temperature variations map based on earlier and newly obtained data has been compiled for regional hydrocarbon reservoir Yu2. A forecast of the temperature variations in the Malyshevka Formation top has been made for the Arctic regions that have not been well studied with deep drilling. Analysis of hydrocarbon pools distribution within the Bathonian reservoir is presented.

The paper considers the results of a series of laboratory experiments (more than 100) on the formation of synthetic sand samples containing water/ice and methane or tetrahydrofuran hydrates in the pore space and of the measurement of their acoustic properties (velocities and attenuation of acoustic waves). The main aim of the experiments was to establish the relationship between the velocities of acoustic waves and the ice or hydrate saturation of the samples. An increase in the content of ice and hydrates always leads to a velocity increase. However, the rate of the velocity increase is determined by the localization of ice and hydrates in the samples: at the contacts between the sand grains (“cementing” model) or in the pore space (“filling” model). It has been established that the “cementing” model, characterized by a drastic initial increase in velocities, works for ice or gas hydrates formed from free methane and localized in the pores. On the contrary, tetrahydrofuran hydrates form by the “filling” model and cause a slow increase in velocities.

Examples of two geodynamically active regions in Central Mongolia are used to demonstrate the radon and tectonic activities of faults and find out how their individual parameters affect the radon field. In general, the radon activity of faults increases with the higher contribution of extension in dynamic faulting conditions, with stronger seismic activity, and also in concentrated disjunctive structures at their late evolution stages compared to wide rupture zones at the initial formation stages of their internal structure. Nonuniform structure is an intrinsic property of near-fault radon anomalies, which is defined primarily by nonuniform disruptions of the substrate in the fault zone by ruptures and by spatial variations in the displacement amplitude. Taking the established regularities into account will facilitate a higher efficiency of emanation surveys in studies of seismic hazard associated with crustal faults.