During the Stripa mine experiments (Sweden), the heat-induced transfers of elements in a compacted clay were investigated and related with mineralogical transformations. After four years of experiments, results indicate that Fe, Al and Si moved towards the colder clayey material while Mg and Ca accumulated at the hottest parts of the system. Weathering, dissolution and crystallisation processes were observed at the clay layer scale. Dissolution of kaolinite began from 40°C. The weathering processes led to the formation of largely distributed gels which are able to crystallise depending on the chemical conditions. With increasing temperature, the composition of smectites changed and recorded the chemical environment, comparatively to the parent material. New crystallisation of berthierine-like minerals, saponite and opal were observed in the hottest area. A Si-Al-Fe gel could enable elemental transfers as a support for the migration. The reactivity associating gels-elements-temperature induced sequences of crystallisation which depend on the coupling of Si-Mg and Fe-Al.
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