Hydrothermal Alteration Of Soultz-Sous-Forêts Granite Near The Granite-Sediment Interface In Geothermal Context

Abstract

The cover--?basement interface is an important issue for the geothermal resource in the rhine graben. Geothermal drilling such as those in soultz--?sous--?forêts (Bas--?rhin) Revealed the presence of numerous fractures in granite and in its triassic sedimentary cover filled by secondary minerals. Most studies on the alteration of the granite have been conducted between 2 and 5 km deep. Few studies have been conducted on the top of the granite near the basement--?sediment interface at 1.5km. However, the flow of brine through the network of fractures in the upper part of the granite reservoir caused successive penetrative mineralogical transformations. Therefore, this study focused on alteration products over the first 200 meters of highly altered granite. 40 core samples were studied using different methods: Optical microscopy, x--?ray diffraction, sem, electron microprobe, major and trace element chemical analysis.