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Variations in the mouth areas of the Yenisei and Pur rivers over the period of 50 years were revealed on the basis of comparison of topographic maps prepared in the 1950s and space images made from the Landsat satellite in 1973 (MSS System) and 1999, 2000 (ETM System). Maps of the drainage network dynamics were compiled; they show that, over a period of many years, mouth areas of northern rivers undergo slow but steady changes, which are indicative of the continuing protrusion of deltas into bays at a rate up to 20 m/year, the increment in mouth areas reaching 0.05–0.07% a year. As noted, secondary water streams die off under the condition of flow concentration in main branches, and small islands get integrated. It was found that, over the period under study, natural variations in the level of the receiving water body and human-induced changes in river basins (construction of a chain of reservoirs) did not have considerable impact on dynamic processes occurring in deltas. 相似文献
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V. L. Tauson R. G. Kravtsova S. V. Lipko A. S. Makshakov K. Yu. Arsentev 《Doklady Earth Sciences》2018,480(1):624-630
Using the methods of electron spectroscopy of the surface and SEM–EDS, it is shown that native gold of the deposit related to the epithermal Au–Ag ore formation contains oxidized gold with an oxidation degree of Au (I) or higher on the surface. A thin layer (~15 nm) with high concentrations of Ag and S and an underlying SiO2-bearing layer with a thickness of ~30–60 nm play a protective role providing preservation of Ag and Au sulfides in the surface parts of the Au–Ag grains under the oxidizing conditions. S-rich marginal parts of native gold particles may be represented by solid solutions Ag2–xAu x S or (with a lack of S) by agglomerates of Ag n Au m S clusters. The formation of surface zoning in the nanoscale on the surface of native Au is abundant in nature and may be applied in prospecting. 相似文献
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The first bryolithochemical studies have been carried out within the Dukat ore field (Balygychan-Sugoi trough, northeastern Russia), in its northeast (Dukat Au-Ag deposit, Chaika site) and on its eastern flank (Au-Ag ore occurrence, Piritovyi site). Sampling was made along primary water streams draining Au-Ag ore zones, because the headstreams localized in the permafrost zone are poor in alluvial sediments or lack them, whereas the stream banks and beds are overgrown with aquatic and semiaquatic mosses. We examined samples of moss cushions with loose sediments (fine silt suspension and sand-silt material). The study has shown that moss cushions are an effective natural trap extracting finely dispersed, ultradisperse, and colloid-dispersed particles, including ore ones, from water stream suspension. The contents of major elements indicating Au-Ag mineralization (Au, Ag, Hg, Sb, As, Pb, and Zn) in the bryolithochemical and lithochemical samples were compared. The highest contents of these elements have been revealed in the bryolithochemical samples. Scintillation analysis shows a predominance of finely dispersed Au and Ag particles. The chemical composition of lithoparticles and probable species of elements indicating mineralization were studied by energy-dispersive X-ray microanalysis. It has been concluded that the bryolithochemical stream sediments are an integral part of the lithochemical ones and can also be effectively used to reveal geochemical anomalies and identify the corresponding ores. It is shown that the bryolithochemical sediment streams bear important information about the chemical composition of primary ores, as they have the same major indicator elements (Au, Ag, Hg, Sb, As, Pb, and Zn) and nearly the same mineral composition (finely dispersed gold and silver, electrum, silver sulfosalts, and simple sulfides). The proposed bryolithochemical research is promising not only for northeastern Russia but also for other areas with similar landscapes, primarily areas where lithochemical and bryolithochemical stream sediments form in the northern subarctic and arctic environments. 相似文献
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V.L. Tauson S.V. Lipko N.V. Smagunov R.G. Kravtsova K.Yu. Arsent’ev 《Russian Geology and Geophysics》2018,59(12):1718-1732
The interfacial crystal layer of poorly soluble mineral grown under hydrothermal conditions is modified chemically into a surficial nonautonomous phase (SNAP) and, in this capacity, takes part in growth process, doing several important functions. This paper considers some of them related to geochemistry and mineralogy. The new interpretation is given to the following phenomena: (1) selection of components during crystal growth in multiphase associations; (2) stability of multiphase parageneses having a common chemical component; (3) dual character of the distribution coefficients due to different properties of the crystal volume and SNAP; (4) formation of nano- and microinclusions of unusual composition different from the basic mineral phase; (5) spatial ordering of nano- and microparticles during their directed aggregation at the growing crystal face; (6) accumulation of valuable components (primarily noble metals), incompatible in most of mineral matrixes, in the surficial layer; and (7) effect of “hidden” metal content, associated with the presence of noble metals in the SNAP or of nano- and microinclusions formed during the SNAP evolution. 相似文献
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Astronomy Reports - We present the first high accuracy UBV RI(RI)c light curves of poor investigated eclipsing star V1103 Cas = GSC 3682 736 ( $$P{{ = 6.18}^{d}}$$ , $$V = {{11.16}^{m}}$$ , $$e =... 相似文献
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Astronomy Reports - We present the first high accuracy UBVRI(RI)c CCD light curves of the poorly investigated eclipsing system V680 Mon = GSC 7428 218 (P = 8.54d, V = 10.02m). They were used to... 相似文献
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Astronomy Reports - We found that the known spectroscopic binary and variable BU CMi = HD65241 ( $$V = 6.4{-} {{6.7}^{{\text{m}}}}$$ , A0 V) is a quadruple doubly eclipsing 2+2 system. Both... 相似文献
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The Niger River delta, one of the largest deltas of the world, is characterized in this article. The geographic features, including the delta hydrographic system, natural and territorial complexes, hydrological regime, and the dynamics of the coastline, are discussed. Special emphasis is given to the assessment of the impact of the following factors on the delta structure and regime: river flow regulation, tides, the ocean level rise, sea waves, natural and human-induced land subsidence. 相似文献
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Water Resources - Ground (expedition) and remote (space-based) methods have been used to carry out detail studies of variations of Danube delta coastline (DC). The displacements of the DC (the... 相似文献