Alteration geochemistry of the Nopal I uranium deposit (Sierra Peña Blanca,Mexico), a natural analogue for a radioactive waste repository in volcanic tuffs |
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| Authors: | Georges Calas Pierre Agrinier Thierry Allard Philippe Ildefonse |
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| Affiliation: | 1. Institut de Minéralogie et de Physique des Milieux Condensés, Université Paris 6, Université Paris 7, Institut de Physique du Globe de Paris, CNRS, 140 rue de Lourmel, 75015 Paris, France;2. Laboratoire de Géochimie des Isotopes Stables, Institut de Physique du Globe de Paris, Université Paris 7, CNRS, 2, place Jussieu, 75251 Paris Cedex 05, France;3. Deceased. |
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| Abstract: | Natural analogues provide an approach to characterize and test the long‐term modelling of a repository performance. This article presents geochemical information about the alteration conditions of the Nopal I uranium deposit, Mexico, an analogue for the proposed Yucca Mountain radioactive waste repository. Mineralization and hydrothermal alteration of volcanic tuffs are contemporaneous, according to petrographic observations. Trace element geochemistry (U, Th, REE) provides evidence for local mobilization of uranium under oxidizing conditions and further precipitation under reducing conditions. O‐ and H‐isotope geochemistry of kaolinite, smectite, opal and calcite suggests that argillic alteration proceeded at shallow depth with meteoric water at 25–75 °C, a low‐temperature context, unusual for volcanic‐hosted uranium deposits. This temperature range is compatible with some post‐closure evolution models of the proposed Yucca Mountain repository. |
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