Mineralogical evolution of argillites in dehydrated-oxidised zones: the example of the argillitic walls from Tournemire tunnel.

Digging of underground work such as that of the Tournemire tunnel in a Toar cian argillite formation, has an impact on the surface mineralogy of the ro ck blocks. In spite of its very low water content, the argillite is reactiv e as a consequence of the modification of the redox conditions. Thus, atmos pheric oxygen in presence of adsorbed water induces pyrite corrosion and fo rmation of secondary mineral phases such as gypsum, celestite, jarosite and Fe-hydroxides, which play a significant role on the water-rock equilibria of the mechanically disturbed zone. (C) 2001 Academie des sciences / Editio ns scientifiques et medicales Elsevier SAS.