Abstract
A specific, radium bearing type of barites has been known from the Ohře (Eger) Rift, a region of Cenozoic volcanic activity in northwestern Bohemia, Czech Republic, since 1904. Barites from Karlovy Vary, Teplice and Děcin areas have been studied to elucidate geochemical history of these specific samples. Low background radiometric method using high-resolution gamma-ray spectrometry has shown that radioactivity of these barites (up to 8 Bq g−1) is carried by 226Ra, which is not in equilibrium with the parent 238U. In all samples, uranium activity was below 0.005 Bq g−1––the detection limit achieved by instrumental neutron activation analysis. The alpha track method on a crystal plate has shown that 226Ra is accumulated in surface layers or crystal cracks, therefore, the crystal rims must be relatively young, not older than 10–15 thousand years. In a lead fraction isolated from the barites, concentration and isotopic composition of lead were determined by photon activation analysis and ICP MS, respectively.
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