Geothermal-lithium co-production from subsurface brines: comparing technological and policy pathways across the Leduc Formation (Canada) and the Buntsandstein (Germany/France)

Co-producing geothermal energy and critical elements (notably lithium, Li) from deep subsurface brines is emerging as a “two-for-one” subsurface use^[1,2]: renewable heat/power plus domestic supply of battery materials. Yet, the feasibility of geothermal-Li co-development is shaped by coupled constraints spanning reservoir deliverability, fluid chemistry, process integration, and permitting regimes^[3,4]. Here we compare technological and policy designs of geothermal-Li co-development using two representative deep saline aquifer systems: (1) the Devonian Leduc Formation in the Western Canadian Sedimentary Basin (Alberta, Canada), and (2) the Triassic Buntsandstein (Bunter Sandstone) reservoirs of the Upper Rhine Graben (Germany/France).

For the Leduc Formation, we expand on our prior feasibility work^[1,2] focused on deep (>1.5 km) aquifers and regulatory pathways that already combine geothermal development and brine-hosted mineral considerations within Alberta’s existing energy and injection governance (e.g., Directives 089 and 090). A Python-based, multi-criteria geospatial screening analysis^[1] integrated temperature, Li occurrence, geologic constraints, proximity to recorded seismicity, and Indigenous rights-holder considerations to narrow to a preferred candidate locality near Whitecourt/Fox Creek region. This quantitative screening analysis first targeted areas where modeled subsurface temperatures exceed 100 °C and then intersected these “hot spots” with formation-water datasets indicating elevated dissolved Li, through a basin-scale mapping approach^[2]. Among the candidate areas, there were regions that fall within multiple Indigenous territories (e.g., Treaty 6 and 8), located within 10s km radius of nearby First Nations reserves (e.g., Alexander 134A), highlighting stakeholder engagement as an operational constraint alongside technical screening.

For the Buntsandstein of the Upper Rhine Graben (Germany/France), we build on existing works, targeting deep (~2.5–5 km) Triassic sandstone reservoirs^[5]. Published datasets indicate geothermal brines with Li concentrations in the ~160–200 mg/L range, hosted in settings where the Buntsandstein can form a principal reservoir unit^[6,7]. Lithium enrichment is linked to a complex hydrothermal history and interaction with sedimentary and evaporitic components of the rift fill, implying that resource sustainability cannot be inferred from “static” brine grades alone. Recent reservoir-scale modeling based on Upper Rhine Graben stratigraphy indicates that, under plausible reinjection–production connectivity, Li concentrations may decline over multi-decadal operation (order-tens of percent), even while heat production remains comparatively stable, making flow rate, reinjection strategy, and extraction efficiency the dominant levers for long-run performance^[5,7]. On the German side, this co-development is governed through state mining authorities by issuing exploration titles explicitly covering “Erdwärme, Sole und Lithium” under the Federal Mining Act (BBergG)^[8,9], with project execution governed parallel with water-law permissions for brine handling/reinjection.

Across both regions, we identify a practical policy design lesson: geothermal-li projects would benefit under integrated regulation as “closed-loop” subsurface systems, with adaptive monitoring triggers tied to (a) reservoir pressure, (b) reinjection breakthrough and Li decline trajectories, and (c) scaling/corrosion and waste streams from direct lithium extraction process. By aligning and comparing subsurface governance with coupled thermo-hydro-chemical characteristics of these resources globally, regulators can better capture synergies (energy + minerals) while containing shared risks, accelerating responsible deployment in both mature hydrocarbon basins and geothermal provinces.