Preliminary results of 3D modeling of the Jastraba perlite deposit in the Kremnica Mountains

Perlite occurs in frontal and lower parts of a thick rhyolite lava flow in the Jastraba deposit. 3D modelling based on a net of exploration boreholes and data on expansion ratios shows that the best quality perlite occurs in the central part of the lava flow bellow spherulitic rhyolite cap. Perlite thickness reaches here 90 m and decreases eastward towards front of the lava flow. Results of XRD demonstrate more than 94 % of glass, the rest represented by phenocrysts of plagioclase, sanidine, biotite and minor quartz. Chemical analyses show homogenous composition of perlite with average composition: 72 % SiO₂, 0.1 % TiO₂,13% Al₂O₃ , 1.3 % Fe as Fe₂O₃, 0.05 % MnO, 0.1 % MgO, 0.9 % CaO, 1,8 % Na₂O and 5 % K₂O. Perlite water content determined as loss on ignition is about 5 %. Expansion ratio of perlite varies in the range 8-18. (authors)