04/06/2025
A first investigation on the presence of lithium in sedimentary rocks of Soultz-sous-Forêts wells
The Upper Rhine Graben (URG) is a promising area for geothermal lithium (Li) extraction, with concentrations in deep geothermal brine exceeding 150 mg/L. They often come accompanied by significant flowrates suitable for geothermal power and heat production. Despite this richness, we still cannot identify with precision the mechanisms leading to the brine enrichment in Li.
ÉS-Géothermie (ÉS-G) researchers characterised the major and trace elements, including Li content, of 34 samples collected from both the Triassic limestone and the sandstone from the Soultz-sous-Forêts wells. They analysed them according to their depth and lithostratigraphy, correlating the Li content with eventual mineralogical changes induced by fluid-rock interactions during diagenesis or hydrothermal circulations. The study suggests that water-rock interactions in both Variscan and Triassic rocks release lithium from phyllosilicates into the brine, which is then trapped in permeable zones, particularly in deep-seated granite.
While lithium concentrations in Muschelkalk and Buntsandstein vary between 1 and 90 ppm, they reach up to 1938 ppm in granite, indicating higher lithium content in Triassic formations. These findings refine the understanding of high lithium concentration in URG brine and highlight specific reservoir zones where lithium enrichment occurs. Future studies will aim to correlate lithium concentrations with fracture characteristics, such as density and aperture, to better understand the relationship between permeability and structural occurrence.
If the subject interests you, ÉS-G researchers will present the findings of their investigations at the European Geothermal Congress, between 6 and 10 October 2025.