Anika Thomas investigated during an internship and her Master Thesis the rocks of the North German Basin regarding the abundance of the critical elements lithium, strontium and copper.
Anika is a Master student from the Martin-Luther-University Halle-Wittenberg where she studied Applied Geosciences. For her Master Thesis, she joined the GFZ Potsdam and the CRM-geothermal project.
If you are interested in the full thesis, please find it here (in German): https://crm-geothermal.eu/go/thesis-anika-thomas
The North German Basin is a sedimentary basin that opened up due to rift processes and was subsequently filled with various sediments. It extends in the north of Germany with outcrops as far as the Netherlands and Poland. For her analysis, Anika selected 23 samples of cuttings from the geothermal well in Groß Schönebeck, which is 4400 m deep. In a first step, a total digestion of the samples was made to determine the total content of lithium, strontium and copper in the rocks.
Figure 1: Overview of the total digestion of all samples for the elements lithium, copper (element content on the left y-axis) and strontium (element content on the right y-axis).
Based on the results of this step, five samples from the Muschelkalk, the Buntsandstein (Detfurth), the Zechstein (Ohre), the Rotliegend and the volcanic rocks were selected. These samples were dissolved phase by phase using sequential extraction (according to Müller et al. (2017[1])) to identify which mineral phases the critical elements lithium, strontium and copper are bound to and how they are mobilised from the rock and released into the fluid.
Figure 2: Schematic illustration of sequential extraction with 50 ml solution each, according to Müller et al. (2017).
In addition, the samples are analysed before and after sequential extraction using Powder-X-ray diffraction in order to analyse the mineral composition and determine any changes in it. Finally, Anika compared the results of her work with previous fluid analyses and an initial rough estimate of the total element content in the North German Basin is made in order to draw conclusions about the extraction potential.
Additional to the work of her Master thesis, Anika has also conducted leaching experiments on selected samples to investigate the kinetics of element dissolution from the rocks in depleted brine. Once the fully analysis of the samples is completed, the results will be brought together with leaching experiments on other geothermal systems considered in the CRM-geothermal project: Rock samples from Cornwall (UK) and Tuzla (Turkey).
The results of Anika’s work provide insight into the source of the elements in the brines of the North German Basin to predict the sustainability of extraction and to provide guidance for future exploration for new CRM-rich geothermal systems.
—-
[1] Müller, D. R., Friedland, G. & Regenspurg, S. (2017). An improved sequential extraction method to determine element mobility in pyrite-bearing siliciclastic rocks. Interna-tional Journal of Environmental Analytical Chemistry, 97(2), 168–188. https://doi.org/10.1080/03067319.2017.1294166
