Uraniferous dolomite: a natural source of high groundwater uranium concentrations in northern Bavaria, Germany?

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Steffanowski, Jacqueline
Banning, Andre
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Naturally high uranium (U) concentrations occur in the groundwater of northern Bavaria (southeastern Germany) although the source(s) and geochemical processes controlling its occurrence are poorly understood. An earlier study identified the weathering of uraniferous apatite as responsible for elevated groundwater U in a part of the region. This present study focuses on a uraniferous dolomite facies in the Triassic sandstone aquifer of northern Bavaria as a potential source of dissolved uranium in the regional groundwater. Hydrogeochemical and mineralogical analytical methods (INAA, ICP-OES, SEP, XRD, C/S measurements), in conjunction with existing hydro- and geochemical datasets, as well as hydrogeochemical modeling approaches indicate a strong connection between groundwater U and the dolomitic facies. Highest groundwater concentrations (max 58.3 µg L−1) occur under slightly alkaline and oxic to slightly reducing conditions. Uranium speciation is dominated by mobile U(VI), predominantly in the form of uranyl-carbonate complexes. Groundwater is undersaturated with respect to U mineral phases. In addition, high values in the dolomite extraction step (SEP) and a positive correlation of dolomite (XRD) and Ca with U (INAA) support the assumption of mobilization from the uraniferous dolomite as a potential source for elevated U concentrations, and hence one of the causes for the geogenic groundwater U problem in this region.
Dolcrete , Hydrogeochemistry , Mobility , Sequential extraction , Trace elements , Triassic
Steffanowski, J. and Banning, A. (2017) 'Uraniferous dolomite: a natural source of high groundwater uranium concentrations in northern Bavaria, Germany?'', Environmental Earth Sciences, 76 (15), 508, (11 pp). doi: 10.1007/s12665-017-6848-6
© Springer-Verlag GmbH Germany 2017. This is a post-peer-review, pre-copyedit version of an article published in Environmental Earth Sciences. The final authenticated version is available online at: https://doi.org/10.1007/s12665-017-6848-6