Pages: 377 - 387
Abstract: Three alteration zones are recognized in hydrothermally altered granitoid rocks at the Dubrava Sb-Au deposit, Nizke Tatry Mts., Western Carpathians: the outermost chlorite zone, muscovite zone and the innermost illite-carbonate zone. Chlorite replacing biotite originated at temperature about 320 ± 40 °C (according to Cathelineau 1988) and the frequency distribution of AlIV in chlorite suggests its re-equilibration during later hydrothermal events. The muscovite and illite-carbonate zones are superimposed on the chlorite zone. Muscovite appears to be of both magmatic and hydrothermal origin, as deciphered from its TiO2 content. Hydrothermal muscovite replaces plagioclase and chlorite. In the innermost zone, carbonates and sulphides become abundant, muscovite and feldspars are replaced by illite. Measurements of crystallinity index values of illite gave an estimate of 180–200 °C for the illite-carbonate zone. The altered rocks were enriched in K2O, H2O, CO2, Sb and S and depleted in CaO, MgO, Fe2O3, and Na2O. Minor changes in Al2O3 and SiO2 content are ascribed either to the variations of the composition of the primary magmatic precursor or local redistribution of these elements. Limited data on alteration of amphibole gneisses and migmatites suggest that the main processes were chloritization and illititation; SiO2 and Na2O were removed and K2O added to these rocks.
Keywords: Nizke Tatry Mts., granitoids, hydrothermal alteration, illite, muscoviteDownload PDF document