Anhydrite–gypsum transition in the argillites of flooded salt workings in eastern France |
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| Authors: | Elie Boidin Françoise Homand Fabien Thomas Jacques Yvon |
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| Institution: | (1) LAEGO, Nancy-Université, Rue du Doyen Marcel Roubault, BP 40, 54501 Vandoeuvre-lès-Nancy Cedex, France;(2) Laboratoire Environnement et Minéralurgie, UMR 7569 CNRS/Nancy-Université, BP 40, 54501 Vandœuvre-lès-Nancy Cedex, France |
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| Abstract: | This study aims at understanding the physico-chemical interactions between the saturated brine and the rocks enclosing the
underground salt workings in Lorraine (eastern France). These anhydrite-rich and argillaceous rocks were characterized in
terms of mineralogy, micro-texture and connected porosity. Then, the two main lithofacies, massive anhydrite and anhydrite-rich
argillite, were immersed in brine during more than 1 year. During this batch experiment, the argillites were affected by macroscopic
splitting, contrarily to the massive anhydrite. Micro-texture and brine chemical analyses clearly show the swelling due to
the hydration of anhydrite into gypsum inside the argillites, whereas hydration occurs superficially on the massive anhydrite,
due to its very low permeability. Anhydrite–gypsum transformation is promoted by the presence of dissolved strontium and potassium
in saturated brine. The low activity of water in saturated brine does not allow the clay fraction to swell significantly during
the experiment. Thus, the expansion resulting from the hydration of anhydrite into gypsum might be responsible of the splitting
of argillite in a saturated brine environment. The superficial anhydrite hydration on massive anhydrite can be explained by
the low amount of connected porosity (less than 1%). |
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| Keywords: | Sulphates Experimental petrography Mineralogy Microtexture Precipitation– dissolution |
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