[en] The argillaceous materials properties could be favourable to the radioelements confinement in high activity and thermogenic nuclear waste disposal. This study relates to the transformations induced on these materials under thermal stress and the impact on their properties. The samples were collected in the vicinity of a natural analogue: a basaltic intrusion in an argillaceous formation (argillites of Laumiere, Aveyron, France). This volcanic event has functioned for an unreachable time in a laboratory. The study of the mixed-layered illite-smectite minerals (I-S), major minerals of these argillites, shows an illitisation at the basaltic intrusion contact. The thin and disturbed variation of an index of crystallinity of the I-S corresponds to the influence of the geological context. Laumiere highlighted determining parameters (smectite formation during hydrothermal alteration) which has influenced the evolution of argillaceous materials in thermal context. (author)