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Uranium mineralisation of the Lugian orthogneiss as a precursor of the radioactive springs genesis
Fatková, Karolína ; Goliáš, Viktor (advisor) ; Škoda, Radek (referee)
The Lugian area is known for the occurrence of springs of radioactive radon mineral waters in areas formed by orthogneisses. Samples of mineralized orthogneisses (Sněžník, Krkonoše and Jizera) found by field radiometry were examined. By the laboratory gamma spectrometry of 28 samples, it was discovered that K and Th have background concentrations, in contrast U-Ra is increased up to 108,5 ppm. The distribution of radionuclides was determined by the alpha autoradiography method in eight selected samples with the highest uranium concentrations. According to optical and electron microscopy with ED analysis, radionuclides are present in the following mineralization stages: Common accessory minerals (zircon, monazite, xenotime, apatite, thorite) occur in the primary magmatic association. The primary magmatic uraninite s.s., associated with zircon, was found in two samples. Its presence is probably the main reason for the high fertility of lugian orthogneisses. Uraninite s.s. also occurs in the form of inclusions in pyrite in the metamorphic (syndeformative) period. Symptoms of greisenization (fluorite, fluorine-rich zircon) can be observed in the Jizera orthogneiss. The hydrothermal stage with comb-like quartz and hematite in the cavities and veinlets is evident in the Krkonoše orthogneiss. The...
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Petrogenesis and evolution of the Davle Volcanic Complex
Santolík, Václav ; Ackerman, Lukáš (advisor) ; Krmíček, Lukáš (referee)
The Davle Volcanic Complex (DVC) situated in the Teplá-Barrandian unit (TBU) of the Bohemian Massif, is considered as a Neoproterozoic-Cambrian magmatic arc that developed on the northern active margin of Gondwana supercontinent during Cadomian accretionary orogeny. This study combines data obtained from fieldwork, petrography, rock-forming mineral microanalysis, major and trace element analysis, Sr-Nd-Pb isotopic systematics and U-Pb zircon geochronology in order to reveal the petrogenesis and evolution of the DVC. At least three-stage metamorphism including Cadomian seafloor alteration, Variscan regional metamorphism as well as contact metamorphism related to the emplacement of the Central Bohemian Plutonic Complex affected the DVC. The studied rocks follow calc-alkaline trend whereas tholeiitic trend previously reported is rather related to younger magmatic events. The northern part of the DVC is dominated by felsic subvolcanic (plagiogranite), volcanic (dacite- rhyolite) and pyroclastic (dacitic-rhyolitic tuffs and breccias) rocks with a few outcrops of basaltic andesite-andesite pillow lavas documenting the subaqueous activity of the DVC. These rocks are Na-rich, but K-poor, the plagiogranite contains albite most likely primary in origin, and exhibit highly radiogenic εNd values (~ +6 to +11),...
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