Natural radioactivity of metamorphic and igneous rocks and pre-Cenozoic sedimentary rocks on the map sheet 15-13 Vrbno pod PradědemArticle PDF
Natural radioactivity of metamorphic and igneous rocks and pre-Cenozoic sedimentary rocks on the map sheet 15-13 Vrbno pod Pradědem
The aim of the paper is to inform about natural radioactivity of metamorphic and igneous rocks and pre-Cenozoic sedimentary rocks on the map sheet 15-13 Vrbno pod Pradědem. Crystalline rocks outcropping on the western edge of the map sheet belong to the Silesicum, namely to the Desná Group (metagranitoids and blastomylonites prevail) and to the Vrbno Group (phyllites, quartzites, metadolerites, green schists, marbles and metamorphosed acid to intermediate volcanites and pyroclastics). Unmetamorphosed or anchimetamorfosed siliciclastics (greywackes, quartzolithic and quartzofeldspathic sandstones, siltstones, silty shales, clay shales and sporadic polymict conglomerates) belonging to three Variscan flyschoid formations (Andělská Hora Fm., Horní Benešov Fm., Moravice Fm.) are exposed in most areas of the map sheet in the so-called Nízký Jeseník Culm Basin. Potassium, uranium and thorium contents were measured using a laboratory gamma–ray spectrometer in 1015 rock samples. Data are tabled and discussed. From calculated values of mass activity of 226Ra equivalent it is evident that natural radioactivity of the studied rocks is low. Increased mass activity values (249 Bq.kg-1 in average) were found in metamorphosed acid to intermediate volcanites (metakeratophyres) outcropping in the northernmost part of the Vrbno Group.
Jiří Zimák, Department of Geology, Faculty of Science, Palacký University, 17. listopadu 12, 771 46 Olomouc; e-mail: email@example.com