Results 1 - 10 of 2014
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[en] This paper presents the results of U–Pb (LA-ICP-MS) and Lu–Hf isotope studies of detrital zircons from the presumably Permian meta sedimentary rocks of the Tokur terrane. It has been established that the grains of detrital zircons from the meta sedimentary rocks of the Tokur and Ekimchan formations have a similar age distribution, which indicates the similar (or equal) age of these formations. The youngest zircons in these rocks has a U–Pb age of 326–323 Ma, which determines the lower age limit of the protolith of the rocks. The upper age limit of the formations corresponds to 254–251 Ma, which is the age of the Late Permian granitoids intruded into these formations. The main sources of zircon in the meta sedimentary rocks of the Tokur terrane are the igneous and metamorphic massifs of the southeast framing of the North Asian Craton. The Tokur terrane can be considered as a fragment of the Paleozoic accretionary complex, formed near the southeastern margin of the North Asian Craton.
[en] Regional exploration for uranium was carried out in South Greenland in 1979 and 1980. From the planning stage the area between the fjords Tasermiut and Soendre Sermilik was considered a favourable target because deposits from geological environments of similar age, structure and lithology are known, e.g. the Makkovik Bay area in Labrador. The deposits sought were mainly pegmatitic or vein type deposits related to a Proterozoic unconformity. During the South Greenland uranium exploration project the area was covered in 1979 by a regional reconnaissance gamma-spectrometric survey and by drainage geochemistry (stream sediments and stream waters). Several areas of anomalous radioactivity were recorded, and on the basis of this and short field visit in 1979 it was decided to undertake a more systematic follow-up in 1980. The preliminary results of this work are reported below. (author)
[en] The source of uranium in Gondwana sediments appears to be uraniferous crystalline rocks of Surguja comprising quartzo-feldspathic cataclasite, biotite schist, sheared granite-gneiss and pink granite, in which established deposits of uranium, viz. Jajawal and Dumhath are already known in nearby areas. Uranium was most likely remobilized from Surguja crystalline into the sediments and then precipitated in feldspathic sandstone of the Talchir Formation in reducing environment caused due to hematitization of pyrites. Post-Gondwana fractures and faults have facilitated remobilization of uranium from the basement rocks. Uranium mineralization in this area may not occur in isolation and is expected to be widespread in Talchir sandstone. Thus, this discovery has opened a new target area for future exploration for uranium mineralization within the Lower Gondwana sedimentary rocks
[en] Uranium behaviour in the process of sulfide-gley catagenesis is described. The investigations were carried out using f- radiography and electron microscopy. Samples of sandstones and aleurolites from the contact zone of gleyed and non-gleyed (red colour) Riphean rocks were studied. It has been found that in the course of rock gleying by supergene solutions uranium (its major part) accumulates in aggregates of neogenic hydromica in the form of uniform and finely dispersed uranium minerals (mainly beta-uranotil), and to a lesser extent - in the sorbed form in neogenic and relic auxiliary minerals (leucoxene, iron oxides, sphene, orthite)
[en] Presented are the analysis results on distribution and interaction of uranium concentrations in sedimentary rocks in the process of ore formation. It is shown that they are realized in the form of a series of genetic types, which are positioned zonely relatively to the feeding source. The space placing of uranium mineralization relatively to the feeding regions is determined mainly by the way of movement of waters carrying uranium. Theoretically a lateral series of regional metallogenic zonation of exogenous uranium ore and uranium-bearing formations includes local uranium concentration in paleovalleys, soil-infiltrational manifestations in crusts of weathering, crack-infiltrational ones in root rocks, soil-infiltrational ones in edge parts of mantle, bed-infiltrational ones within the limits of depression and, at last, syngenetic accumulations of uranium in lakes and seas at the level of the regional erosion basis. Incomplete lateral series are connected with the local peculiarities of the tectonical regime, of the lithology-facies sediment content, and with the dynamics of underground waters and with the amplitude of vertical movements
[en] The potentiality of application Rb-Sr method in argillous sediments, using samples from paleozoic and mesozoic formation in brazilian sedimentaries basin was tested. Physical, chemistry and isotopic analysis of thirty eight samples were made in the laboratories of geochronology Research Center from the University of Sao Paulo. Four isochronic diagrams for the argillous sedimentary rocks were also proposed. (author)
[en] This work was presented, in the second phase of sands prospecting for construction program.This project have been as purpose, to assure the supply of Montevideo with this long term material. The study was carried out in framework of the project of Geologic Collaboration Uruguayan-German. A detail cartography was made in an area of 435 km2 in the low course of the River Santa Lucia (from 20 to 50 km West of Montevideo).