Suitability of the rocks from Pezinok-Pernek crystalline complex as a building material from viewpoint of 238U, 232Th and 40K content

Spatial radionuclides distribution in main rock types: granodiorites, biotite-gneisses, black shales and amphibolite at the investigated locality (Pezinok - Kolarsky vrch) was studied in samples from two bore holes. Concentrations of 238U, 232Th and 40K in samples were analysed by gamma-spectrometry (a concentrations: 238U 0.091 - 37.800; 232Th 0.534 - 13.234; 40K 0.116 - 5.162 mg kg-1). The highest average 238U concentrations were in black shales, highest average 232Th concentrations in granodiorite and highest average 40K concentrations in granodiorite. Activities of 238U were found in the range of 1,092 - 48,960 Bq kg-1 (with exception of one anomalous value - 453,6 Bq kg-1), activities of 232Th in range of 2,189 - 54,298 Bq kg-1 and activities of 40K in range of 30,933 - 1376,499. The source of 238U and 232Th (and partially also of 40K) is in the granodiorite intrusion. The U was during the metamorphic process mobilised to the black shales. The Pb isotope study proved, that the source of the Pb is not homogenous and is of crustal - upper crustal (orogenic) origin. The concentrations and consequently the total activities of 238U, 232Th and 40K in investigated rock samples exceed the permitted limit for building material. It is possible to recommend their utilisation only for external purposes. (authors)