Trace element and isotopic evidence for REE migration and fractionation in salts next to a basalt dyke |
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| Institution: | 1. ULP-EOST-CNRS, Centre de Géochimie de la Surface UMR 7517, 1 rue Blessig, F-67084, Strasbourg, Cedex, France;2. IMMR, Technische Universität Clausthal, Adolph-Roemer-Strasse 2 A, D-38670, Clausthal-Zellerfeld, Germany;1. Center for Environmental Studies, National Central University, Taiwan;2. Department of Earth Sciences, National Central University, Taiwan;3. Department of Geosciences, National Taiwan University, Taiwan;4. Institute of Earth Sciences, Academia Sinica, Taiwan;1. Dipartimento di Scienze della Terra e dell’Ambiente, Università degli Studi di Pavia, Via A. Ferrata 1, I-27100 Pavia, Italy;2. C.N.R. – Istituto di Geoscienze e Georisorse (IGG), Unità Operativa di Pavia, Via A. Ferrata 1, I-27100 Pavia, Italy;3. Japan Agency for Marine-Earth Science and Technology (JAMSTEC), 2-15 Natsushimacho, Yokosuka, Kanagawa Prefecture 237‑0061, Japan;1. 28A Lenton Road, The Park, Nottingham NG7 1DT, UK;2. NCB Naturalis, P. O. Box 9517, 2300 RA Leiden, The Netherlands;3. Center for Geological Survey (CGS) (Pusat Survei Geologi), Jl. Diponegoro, 57, Bandung, Indonesia;1. Deep Exploration Technologies Cooperative Research Centre (DET CRC), Future Industries Institute (FII), X Building, University of South Australia, Mawson Lakes SA 5095, South Australia, Australia;2. Geological Survey of South Australia, 11 Waymouth Street, Adelaide 5000, South Australia, Australia |
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| Abstract: | Neodymium and Sr isotopic compositions and the rare earth elements (REE) distribution patterns have been determined in salts adjacent to a basaltic dyke along 2 parallel horizontal profiles. The salts, originally consisting of carnallite (KMgCl3 · 6H2O), have been transformed during basalt intrusion mainly into halite (NaCl) and sylvite (KCl) by fluids saturated in NaCl. The Sr isotope data suggests that much more fluid penetrated the upper than the lower horizon. The Nd isotope data shows that in the upper horizon, where fluid flow was stronger, Nd is essentially derived from the basalt. In contrast, in the lower horizon a strong salt Nd component is present.The REE data document in both horizons is a strong depletion of Ce, Pr, Nd, Sm and Eu with increasing distance from the basalt. This depletion of the light rare earths (LREE) is stronger in the upper horizon where fluid flow was stronger. The authors suggest that this REE fractionation is more likely due to precipitation of LREE-enriched accessory minerals such as apatite, than to differential REE solubility caused by selective REE complexation. This finding is of interest for REE behaviour in brines in general, and for the behaviour of radioactive REE and actinides in a salt repository for high-level nuclear waste in particular. |
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