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The spread of radioactive contamination in the subsurface medium near Lake Karachai is considered. The complexity of this process requires a comprehensive approach to its study. The source of radioactive contamination is overviewed. The map of faults in subsurface medium is considered in order to determine the prevailing direction of contaminated groundwater flow. Photometry in observation wells has been used for structural geological estimation of transport properties of the shallow aquifer, where contaminated groundwater is moving. This study was carried out along with hydrochemical logging, which makes it possible to estimate the dynamics of contamination of subsurface medium and vertical distribution of groundwater contamination. Special attention is paid to transport of radionuclides in the form of radiocolloid particles. Groundwater samples were taken from various depths corresponding to different contamination levels near Lake Karachai. The depth intervals of sampling were determined from the data of hydrochemical logging. Ultrafiltration through membranes with a specific pore size in combination with gamma spectrometry was used to characterize radionuclide transfer with colloidal particles differing in size. The local elemental composition of the radiocolloid surface was studied by Auger spectroscopy. The chemical composition and structure of radiocolloid particles were determined by X-ray photoelectron spectroscopy with consecutive etching of the particle surface by argon ions for a certain depth. The data obtained indicate that radiocolloid particles are heterogeneous and an organic shell consisting of humic and fulvic acids and technogenic organic compounds coat their surface.  相似文献   
3.
The localization conditions of mineralization at uranium deposits of the Khiagda ore field related to the economic sandstone type in paleovalleys are considered in this paper. These conditions allow different genetic treatments. Uncertainty in genetic estimates is caused by localization of orebodies in both gray sedimentary rocks at the boundary with bleached rocks and in the bleached rocks themselves. The results of mineralogical and geochemical studies have shown that bleaching is related to iron redistribution at the postore stage. Obvious evidence in favor of this conclusion has been obtained from statistical processing of quantitative soluble iron determinations in various geochemical types of host rocks. The postore bleaching is superposed on earlier oxidized and ore-bearing gray rocks, obliterating the coloration inherent to redox ore-controlling zoning.  相似文献   
4.
A cause-and-effect relation is established between historical metallogeny of gold and uranium and extraterrestrial factors (impact events, evolution of the distance between Earth and Moon, rotation geodynamics), which significantly affected the Early Precambrian tectonic evolution of our planet. It is shown by the example of the complex Witwatersrand deposit that the Precambrian polygenetic Au and U deposits of the quartz–pebble type were formed within a near-equatorial epi-Archean supercontinent and were related to extraterrestrial factors under a rotation regime of the plume vertical tectonics. The beginning of breakup of the epi-Archean supercontinent in the Paleo- and Mesoproterozoic (2.0 ± 0.3 Ga) was related to the abrupt decrease in the velocity of the Earth’s axial rotation followed by the dominant regime of subhorizontal plate tectonics and formation of rich U deposits of the nonconformity type (which are structurally related to the horizontal inertial detachments at the contacts of the consolidated crust) and Meso- and Neoproterozoic sedimentary complexes.  相似文献   
5.
The domal structures of the Erzgebirge in Saxony, Germany, which control localization of the Variscan hydrothermal U, Sn, W, and base-metal deposits, started to form in the Late Riphean in the course of folding, regional metamorphism, and granitization and were eventually created at the end of the Paleozoic, when an enormous mass of granitic melts was emplaced and cooled. As is illustrated by the world’s largest Schlema-Alberoda vein uranium deposit, the fractures that determined the localization of ore-bearing veins were formed in the outer contact zones of the Variscan granites related to domal uplifts. Beyond the zones of contact metamorphism, the orientation of ore-bearing fractures changes, their morphology simplifies, the amplitude of displacements decreases, and most fractures pinch out. Such a zoning is explained by development of faults around growing granitic domes.  相似文献   
6.
The ambiguity of genetic interpretations of uranium ore formation at Mo-U deposits of the Strel’tsovka ore field led us to perform additional geochemical, mineralogical, and thermobarogeochemical studies. As a result, it has been established that closely related U and F were progressively gained in the Late Mesozoic volcanic rocks from the older basic volcanics (170 Ma) to the younger silicic igneous rocks (140 Ma). The Early Cretaceous postmagmatic hydrothermal epoch (140–125 Ma) is subdivided into preore, uranium ore, and first and second postore stages. The primary brannerite-pitchblende ore was formed in association with fluorite. At the first postore stage, this assemblage was replaced by a U-Si metagel, which was previously identified as coffinite. The metagel shows a wide compositional variation; its fine structure has been studied. The preore metasomatic alteration and related veined mineralization were formed under the effect of sodium (bicarbonate)-chloride solution at a temperature of 250–200°C. The uranium ore formation began with albitization and hematitization of rocks affected by supercritical fluid at 530–500°C; brannerite and pitchblende precipitated at 350–300°C. The chondrite-normalized REE patterns of pitchblende hosted in trachybasalt, trachydacite, and granite demonstrate a pronounced Sm-Nd discontinuity and a statistically significant tetrad effect of W type. These attributes were not established in REE patterns of rhyolites derived from the upper crustal magma chamber. This circumstance and a chronological gap of 5 Ma between silicic volcanism and ore formation do not allow us to suggest that uranium was derived from this magma chamber. According to the proposed model, the evolved silicic Li-F magma was a source of uranium. U4+, together with REE, was fractionated into the fluid phase as complex fluoride compounds. The uranium mineralization was deposited at a temperature barrier. It is suggested that hydromica alteration and the formation of molybdenum mineralization were genetically unrelated to the uranium ore formation.  相似文献   
7.
The paper concerns the geological–structural conditions of ore localization, mineralogy and chemistry of ore, and geochemical features of the ore-bearing medium at exogenic–epigenetic paleovalley deposits of the Hiagda ore field. The general localization regularities and ore control factors of uranium mineralization can be used for mining, exploration, and refining the prospecting criteria and indications of this type of deposits.  相似文献   
8.
This paper reports the results of a study of the geochemistry of bottom sediments from the zones of mixing between the freshwater of the Ob and Yenisei rivers and the saline water of the Kara Sea by means of neutron activation analysis. Using separate datasets for the sediments of the Ob and Yenisei estuaries accumulated under identical facies conditions, some characteristic features of the distribution of a number of chemical elements (mostly lithophile group elements) were established. The differences between them were attributed to distinctive regional geological and geochemical features of the catchments of the Ob and Yenisei, which are inherited by the geochemical characteristics of terrigenous material transported to the sea. The choice of the most informative indicator elements and their grouping on the basis of the character of behavior demonstrated that bottom sediments of the Ob or Yenisei origin can be identified in the marine region studied using the geochemical characteristics of a small group of samples.  相似文献   
9.
The convective transfer of 137Cs and 90Sr by groundwater on the territory of the Russian Research Centre Kurchatov Institute (RRCKI) was modeled. Geological data on the RRCKI site and possible sources of radionuclides show that the uppermost aquifer, composed of Quaternary sediments, is the most probable region of spreading of radioactive contamination. Since the lateral migration of radionuclides is predominant, a 2D horizontal model was used for the forecasting of spreading of radioactive contaminants in the subsurface medium. Transient or long-term repositories of radioactive materials at the RRCKI site (concentrated sources) and aquifer rocks contaminated in the course of removal of radionuclides from these repositories (distributed source) are responsible for groundwater pollution. The initial 137Cs and 90Sr distributions used in the forecasting of radionuclide migration were determined from their contents in core samples taken from wells drilled in contaminated areas of the RRCKI site. The zone of radionuclide migration is limited by poorly permeable moraine loam from below and by the water table from above. To determine the upper and lower boundaries, these surfaces were mapped in plan view. The data of meteorological observations over a long period were used to map the intensity of precipitation in the studied territory. The density of rocks in the uppermost aquifer and partition coefficients of radionuclides between rocks and groundwater were estimated from the data of laboratory examination of the core samples. The available data on the permeability of rock samples and the results of test pumping out of some wells were involved in the consideration. The results obtained and the data on the water table allowed us to define a gauge problem for determining the distribution of the filtration coefficient in the uppermost aquifer. This problem was solved taking the intensity of precipitation into account. The properties of the uppermost aquifer and the initial radionuclide distribution therein were used as initial data for modeling 137Cs and 90Sr migration on the territory of the RRCKI over 50 years.  相似文献   
10.
The density of global radioactive contamination was the most reliable estimated in marine regions and less accurate for intracontinental areas with semi-arid and arid climatic conditions. This work presents the results of using a new method developed for estimating the density of global radioactive contamination based on the calculation of 137Cs concentration in closed lake catchments. An average density of of 137Cs contamination in the model closed lake catchments of southwestern Siberian steppe landscapes is 0.80 ± 0.24 kBq m–2 that is 2–3 times lower than the levels calculated on the basis of the published data.  相似文献   
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