HYDROTERMÁLNÍ ASOCIACE NA ŽILÁCH V KLASTICKÝCH HORNINÁCH SPODNÍHO KARBONU DRAHANSKÉ A ZÁBŘEŽSKÉ VRCHOVINY: GENETICKÉ ASPEKTY
Roč.12,(2005)
Hydrothermal veins occurred in the Lower Carboniferous siliciclastics of the Drahany and Zábřeh Upland and have been investigated by several methods: optic, structural and petrography, geochemistry and microthermometry. The principal aim of the study was to reveal the main precipitation conditions and to distinguish different generations of veins. The attention was concentrated on post-Variscan veins and their gangue minerals, especially on carbonates (calcites). Their optical and chemical characteristics, stable isotope signature and fluid inclusions have been studied. Only few samples contained hydrothermal sulphides. The older vein system, most likely late Variscan, has mineral assemblage: quartz ± calcite ± chlorite ± sulphides (pyrite). Minerals display a severe deformation and calcites are fine grained with a low intensity of cathodoluminescence. Post-Variscan generations of veins have the mineral assemblage with calcite - barite - sulphides (sphalerite, galena, chalcopyrite, pyrite-markazite) ± quartz ± fluorite ± siderite. Hydrothermal phases are coarser grained and the vein direction coincide with regional faults (NW-SE, NNE-SSW, NE-SW). The main post-Variscan population of calcites precipitated from solutions of H2O - NaCl ± CaCl2 ± KCl ± MgCl2 ± FeCl2 type under low temperatures within a range of 60-90°C. One of the younger aqueous hydrothermal systems contain also higher liquid hydrocarbons displaying light blue fluorescence. Isotopic composition of parent fluids were about values of d18O from 0 to 10 SMOW, what is indicative for transformed basinal brines originated from sea or partly meteoric waters.
Drahany Upland; Lower Carboniferous; hydrothermal veins; carbonates; stable isotopes; fluid systems
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