Critical raw materials from geothermal fluids: Potential in the North German Basin

Abstract

The EU-funded CRM-geothermal project aims to integrate the extraction of critical raw materials and geothermal heat from deep geothermal reservoirs. Within the project, extraction technologies and their economic and environmental feasibility are tested and evaluated across several geological regions in Europe and East Africa.   The focus of this study is the North German Basin, a typical sedimentary basin that initiated rifting in the late Carboniferous period, accumulating various sediments to a thickness of up to 10–12 km. Located in central Europe it stretches over an area from Poland to the Netherlands, traversing across North Germany. The succession is beginning with Permian volcanic rocks at the base, and overlain by alternating layers of mud-, silt- sandstones and evaporates; some of which have already been identified for geothermal energy extraction (e.g. Neustadt-Glewe, Schwerin, and Potsdam). Up to now, the extraction of lithium (Li) has not been explored, despite the existence of elevated Li concentrations occurring in formation fluids of the Rotliegend and Bunter sandstone. In this study the potential content of selected critical and valuable elements (Li, Sr, Cu) and their availability in various formations of the North German Basin was assessed. For this purpose, cuttings from different formation rocks from one deep well (GrSk04/05; 4000 m depth) were first analyzed for bulk concentrations of these elements. Most promising samples (with Li up to 74 ppm, Cu up to 214 ppm, and Sr with up to 2334 ppm) were selected from Muschelkalk, Bunter sandstone (Dethfurt), Zechstein (Ohre), Permian Rotliegend sandstone (Hannover), and volcanic rocks)  for a sequential extraction. This method provides indication on the type of elemental bonding within minerals, allowing to estimate the availability and sustainability of the CRM in the respective formation fluids.