CRM-geothermal - geochemical results of drill core material, scaling and salt precipitates at Tuzla, Seferihisar and Dikili geothermal sites, Eastern Turkey

The EU funded project CRM-geothermal aims to establish an overview of the potential for critical raw materials (CRM) in geothermal fluids across the EU and third countries (Ref). Within this framework, the geothermal sites of Tuzla, Seferihisar and Dikili in eastern Turkey have been visited in March 2023. To estimate the potential of CRM at these sites, a comprehensive sampling program was performed. Rock samples (drill gravel) of the production borehole and scaling from gas-water separators were obtained. Furthermore, sampling of geothermal fluids (gas and brine) and precipitates (salt) along the production line was performed. Here, the results of the geochemical analyses of solid sample materials (drill gravel, scales and salt) are presented. All analyses were performed in the ElMiE-Lab (Elements and Minerals of the Earth Laboratory) at German Research Centre for Geosciences Potsdam, Germany (https://labinfrastructure.geo-x.net/laboratories/8). For their major and minor element compositions, bulk samples of drill gravel and scales were analyzed with XRF and ICP-MS, respectively. Salt precipitates were analyzed for dry loss and mineral composition using XRD.

Sampling of drill gravel: Drill core gravel from Tuzla geothermal site was obtained from existing samples taken during drilling in 2010. For the analyses, three samples of the geothermal reservoir horizon at different depth and from two different drill holes were chosen. Sampling of scales: Scales were sampled during geothermal power plant maintenance in 2023 in Tuzla and in 2022 in Seferihisar. It was analyzed from all water-gas separators from the three drill holes in Tuzla. For Seferihisar, fresh scales were obtained from inside a tube, a pump and a fitter. Sampling of salt precipitates: During the visits, fresh salt precipitates were taken from outside the pipeline that transports geothermal brine to the power plant. The sampling points were located near the production well. Here, few connectors were slightly leaking which is negligible for the geothermal power production. Over time, the small amounts of brine release causes salt precipitation, due to brine cooling and evaporation. The residual salts occurs in form of fine crystalline precipitations around the pipe connectors or, stalactite-like salt tubings. Sampling of fresh, slightly moist material was performed by either scratching material off the precipitate deposit or breaking off juvenile stalactite outgrowth. The sample were stored and transported in air-tight zipper plastic bags to avoid sample alteration by atmospheric air.