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Article Dans Une Revue Chemical Geology Année : 2007

Recent mobilization of U-series radionuclides in the Bernardan U deposit (French Massif Central)

Patricia Patrier Mas

Résumé

Several nuclides of the ;238;U (;234;U, ;230;Th, ;226;Ra, ;210;Pb) and ;235;U (;231;Pa, ;227;Ac) decay series have been measured through gamma spectrometry in the U-bearing episyenites of the Bernardan mine (northwest Massif Central, France), in order to study recent mobilizations in the U-deposit and their time-scales. (;230;Th/;238;U) and (;231;Pa/;235;U) ratios show that U has been little affected during the last 350 ky, especially in the U-rich samples. In contrast, ;226;Ra was subjected to a general redistribution, with a clear tendency for Ra to be lost from the U-rich samples and added to U-poor samples. The highest Ra excesses are present in low-U samples, and are related to adsorption onto iron hydroxides. Ra appears to have been redistributed within the mineralised episyenitic bodies, which seem to remain in ;226;Ra–;238;U radioactive equilibrium, a result consistent with the earlier study of Leroy [1984. Episyénitisation dans le gisement d'uranium du Bernardan (Marche): Comparaison avec des gisements similaires du Nord-Ouest du Massif Central français. Miner. Depos. 19, 26–35]. As shown by the ;226;Ra and ;210;Pb data, the Ra redistribution was very active between 8 and 0.1 ky, and this might be a consequence of the hydrological changes in groundwater circulation accompanying the Holocene climate warming.

Dates et versions

hal-00407600 , version 1 (27-07-2009)

Identifiants

Citer

Michel Condomines, O. Loubeau, Patricia Patrier Mas. Recent mobilization of U-series radionuclides in the Bernardan U deposit (French Massif Central). Chemical Geology, 2007, 244 (1-2), pp.304-315,. ⟨10.1016/j.chemgeo.2007.06.020⟩. ⟨hal-00407600⟩
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