The mineralogical-petrological analysis of 12 core samples from the exploration well B3/17 has shown that 7 of the examined rocks classify as basaltic andesite, 2 as breccia, 2 as extremely calcitised rocks that could not have been unambiguously determined and 1 as hyaloclastite. The rocks have an amygdaloidal texture, porphyritic/glomeroporphyritic structure and are strongly altered. Their colour varies from olive and greyish-green to brownish-purple. The groundmass of the effusive varieties is intersertal (4 samples), vitrophyric/intersertal (3 samples), hypohyaline (2 samples) and hyalopilitic (1 sample) and consists of chlorite, sericite, calcite and volcanic glass. The phenocrysts that were found were recognised as completely altered, sericitised, calcitised and chloritised feldspars. The amygdules are composed of calcite, chlorite and chalcedony/opal and the cracks are filled by secondary carbonate. The XRD analysis has confirmed the microstructural composition of the samples. Three different varieties of the examined rocks were chosen for the chemical analysis of major, minor, trace and rare earth elements. According to the chemical classification of effusive rocks based on the TAS diagram, the samples correspond to phonotephrite and basaltic trachyandesite, and one sample is on the border between the two mentioned fields. Based on the Na2O and K2O content, two of the samples classify as shoshonites, while according to the Nb/Y-Zr/TiO2 element ratios they are representative of basaltic andesite to andesite.