Schlüsselwörter
(Englisch)
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Lithium, geothermal brines, exploration, geology, energy transition.
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Kurzbeschreibung
(Englisch)
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Geothermal energy is one of the important energy sources contemplated in the Swiss Energy Strategy 2050. Since (deep) drilling projects are associated with a high capital expense, their realization requires a careful selection of the promising drilling site(s) and a robust business case. Depending on the geological setting, some geothermal fluids are known to contain metals of importance for the energy transition, which can be of economic interest for the geothermal project itself and at large for the manufacturing of batteries, conductors or other high-tech products.
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Abstract
(Englisch)
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The production of geothermal energy coupled with the extraction of lithium or other critical metals from deep aquifers could provide an important economic incentive to scale up geothermal exploration and production in Switzerland. A review of the literature reveals that lithium, globally, has become one of the key critical raw materials needed for the energy transition, especially for the storage of energy. Therefore, the focus of lithium exploration has recently expanded to include geothermal brines, as an alternative to conventionally exploited hard rock occurrences or salar brines. Deep geothermal aquifers are known to occasionally contain significant concentrations of lithium. Although research pilot wells are well advanced (e.g. in Germany or the USA), no lithium is commercially produced from a geothermal well at industrial scale yet.
We have compiled 79 lithium concentrations from the publicly accessible wells in Switzerland deeper than 100 m. Lithium concentrations in the aquifers encountered are, with two exceptions, below 33 mg/l. Two wells in the Swiss Molasse Basin, at Pfaffnau and Berlingen, have elevated lithium concentrations of 82 mg/l and 144 mg/l, respectively. Both measurements originate from the Upper Muschelkalk aquifer. These concentrations are lower than the highest concentrations recorded so far in the Upper Rhine Graben (100-210 mg/l) or in several regions of Italy (up to 480 mg/l). The process of lithium enrichment in geothermal fluids at depth is yet poorly understood. Our data reveal that geothermal fluids with high TDS (total dissolved solids) values also have elevated lithium concentrations and are predominantly located in areas with high heat flow. In Switzerland, areas with high heat flow are located in the Basel and Lower Aare Valley regions as well as in the area of Lake Constance. An up-to-date heat flow map could provide useful indications for the exploration of metal-rich geothermal brines.
To better understand the spatial distribution and key parameters controlling the concentration of critical raw materials such as lithium in deep aquifers, and to provide a robust basis for further investigations, we propose the following measures: (i) update the data base with recent and not publicly available well data, (ii) repeat lithium concentration measurements at key sites with high concentrations but low confidence (if the well data or water samples are still accessible), (iii) analyse the geological setting (stratigraphy, reservoir properties, regional heat flow, local tectonics) in areas with high lithium concentrations to enhance the understanding of the process of lithium enrichment, (iv) establish a sampling and well testing protocol to guide the permitting authorities at Canton level and the operators of the future, federally-subsidised geothermal projects, to obtain comprehensive hydrochemical analyses of the deep fluids.
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