Acta Musei Moraviae

Natural radioactivity of metamorphic and igneous rocks and pre-Cenozoic sedimentary rocks on the map sheet 14-43 Mohelnice

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 14-43 Mohelnice. Metamorphic and igneous rocks belou to three geological units: Svinov-Vranová Crystalline Complex (mainly mica schists), Zábřeh Group (gneisses, phyllites, mica schists, amphibolites, acid to intermediate metavolcanites, marbles, granitoids, and metagranitoids) and Desná Group (blastomylonites and metagranitoids are dominant). Unmetamorphosed pre-Cenozoic sedimentary rocks are represented by Givetian flysch sediments (Mohelnice Fm.) and Visean flysch formations (Protivanov Fm., Andělská Hora Fm.), Permian siliciclastics of the Orlice Basin, and siliciclastic sediments of the Bohemian Cretaceous Basin (Peruc-Korycany, Bílá Hora, Jizera, Teplice, and Březno Fms.). Contents of potassium, uranium and thorium were measured using a laboratory gamma-ray spectrometer in 998 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. Slightly increased mass activity values (199 Bq.kg^-1 in average) were found in metagranitoids (so-called “Libina granite”) outcropping in the Rohle Dome.