Abstract
The uranium- /fission-xenon systems in eleven samples selected from three occurrences in the Schwarzwald were investigated (Menzenschwand, Wittichen, Mullenbach). Relationships between mineralogical properties, Xe release profiles and Xe-Xe age spectra provide criteria for sample suitability for U-Xe and Xe-Xe dating and interpretation of the Xe-Xe age spectra. U leaching from pitchblendes was demonstrated for three of the Wittichen samples, indicating also disturbed U-Pb relations. The results show that the U-Xe isotopic system is a valuable geochronological tool for studying uranium minerals. In samples of two deposits, fission Xe was well preserved and allowed us to determine Xe-Xe plateau ages: 301 ± 11, 304 ± 9 and 279 ± 10 Ma for Menzenschwand and 244 ± 9 Ma for Wittichen pitchblendes. These ages show the closure times of the U-Xe isotope systems and most probably correspond to the formation of these pitchblendes. They are in accord with published U-Pb data. Four other samples of these two deposits had very irregular spectra. An attempt was made to interpret integrated Xe-Xe ages (U-Xe ages) in these samples in terms of alteration events. Little fission Xe was found in material from Mullenbach. There is a large time gap between the formation of the hosting granites and the U-ore depositions (about 30 and 90 Ma, respectively) in Menzenschwand and Wittichen.
Original language | English |
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Pages (from-to) | 190-205 |
Number of pages | 16 |
Journal | Mineralium Deposita |
Volume | 35 |
Issue number | 2-3 |
DOIs | |
State | Published - Mar 2000 |