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Genèse du Système Hydrothermal à Fluorine-Barytine-Fer de Chaillac, (Indre, France)

Abstract : The Chaillac hydrothermal system (Indre, France) transects the contact between the Massif Central and the Paris basin. A stratiform deposit (Les Redoutières) connected to a vein (Le Rossignol) composed this system.
The Rossignol vein is hosted by a metamorphic Hercynian basement. This vein is an open structure filled by two successive stages. The first stage is called Fv-v, its paragenesis is green and purple fluorite and quartz with textures of intra vein sediments. A solution with low salinity has formed this stage at 135°C. Isotopic composition of Sr and Nd in fluorite suggests a source linked with acid rocks of the upper crust. The paragenesis of the second stage is made of yellow fluorite, sulfides and barite, three sub-stages are identified: (i) fluorite dominant, (ii) barite dominant, (iii) breccia cemented by fluorite. The substages (i) and (ii) are present in continuum from the root of the system to the horizontal vein of the stratiform deposit. A cold brine (≈ 100°C, 20%wt Eq. NaCl) has formed the whole Fj-Ba stage. Sr, Nd isotopics signatures suggest a source linked with deep basic rocks.
The Redoutières deposit is hosted within Paris basin Hettangian sands (205 – 201). Close to the Rossignol vein the sandstone is cemented by fluorite, which evolved laterally to and vertically to barite and then to an association barite-gœthite. These variations in the cement nature are correlated with the sub-stage (i) and (ii). Above the Rossignol vein, vertical N-S, E-W and horizontal veins form an original barite-gœthite rich sinter. The structure demonstrate an extensional tectonic with opening in E-W and N-S trending. The Hettangian age of the mineralization is attested by the presence of barite pebbles in Hettangian sandstones, modifications in the nature of the Hettangian sediment (i.e. presence of detritic goethite), the sinter texture and the lack of mineralization in the Sinemurian. Anisotropy of Magnetic Susceptibility study of the gœthite rich sandstone and vein, combined with geochemistry, have shown a late lateritic stage superimposed to the hydrothermal formations during Eocene. In addition this study proposes a method based on magnetic fabric to trace paleo-hydrothermal flow.
These observations are integrated in a genetic model based on the deep migration and boiling of a fluid. In that model the vapour condense and give the fluid that formed the Fv-v stage, and then the residual brine precipitate fluorite, barite by mixing with continental waters and iron oxy-hydroxydes.
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Contributor : Nathalie Pothier <>
Submitted on : Wednesday, February 5, 2003 - 10:37:30 AM
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  • HAL Id : tel-00002360, version 1


Stanislas Sizaret. Genèse du Système Hydrothermal à Fluorine-Barytine-Fer de Chaillac, (Indre, France). Minéralogie. Université d'Orléans, 2002. Français. ⟨tel-00002360⟩



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