URAN A THORIUM V GRANITICKÝCH PEGMATITECH A APLITECH SILEZIKA

Abstract

Contents of uranium and thorium were measured using a laboratory gamma-ray spectrometer in 575 samples of granitic pegmatites and aplites from Silesicum. Very low contents of the both elements were found in metapegmatites occurring in metagranitoids and blastomylonites of the Desná Group, in pre-Variscan muscovite pegmatites with tourmaline, and in Variscan beryl-columbite pegmatites. Very high uranium and thorium contents are in some pegmatite dykes occurring on the Kluč Hill near Kociánov. The pegmatites are composed mainly of feldspars, quartz and mica (biotite and/or muscovite), and contain accessory minerals of uranium and thorium such as uraninite, coffi nite and thorite. The Kluč Hill pegmatites are spatially and genetically bound to a small I-type Variscan granitoid body (so-called Rudná hora Intrusion). Highest average uranium contents were found in pyroxenic pegmatites occurring in the Žulová Massif mantle (its marbles can be considered the main source of uranium).