Natural radioactivity of metamorphic and igneous rocks and pre-Cenozoic sedimentary rocks on the map sheet 14–42 RýmařovArticle PDF
Natural radioactivity of metamorphic and igneous rocks and pre-Cenozoic sedimentary rocks on the map sheet 14–42 Rýmařov
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 14-42 Rýmařov in the northeastern part of the Bohemian Massif. Crystalline rocks belong to Silesicum, namely to the Keprník Group (orthogneisses and blastomylonites prevail), the Desná Group (mainly paragneisses, metagranitoids, orthogneisses, blastomylonites, phyllonites and amphibolites) and the Vrbno Group (phyllites, quartzites, metakeratophyres, felsic metatuffs, greenschists and metadolerites). Metapegmatites and Variscan granitic pegmatites are abundant in Silesicum. Variscan I-type granitoid bodies are represented by the Mt. Rudná Intrusion. Variscan flyschoid siliciclastics (anchimetamorphosed greywackes, sandstones, siltstones and shales) belong to the Andělská Hora Formation. Contents of potassium, uranium and thorium were measured using a laboratoř gamma–ray spectrometer in 2163 rock samples. Data are tabled and discussed. Most rocks outcropping on the map sheet show low values of mass activity of 226Ra equivalent, lower than that for average Earth crust (about 180 Bq.kg-1). Increased values of mass activity were found in three types of rocks: metakeratophyres of the Vrbno Group (214 Bq.kg-1 on average), felsic metatuffs of the Vrbno Group (191 Bq.kg-1) and granitoids of the Mt. Rudná Intrusion (207 Bq.kg-1).
Jiří Zimák, Department of Geology, Faculty of Science, Palacký University, 17. Listopadu 12, 77146 Olomouc, Czech Republic, e-mail: email@example.com