The radiogenic isotope signature of strontium as an environmental tracer of the dynamics of geothermal reservoirs (Podhale Basin, southern Poland)

Abstract

The intensive development of geothermal energy in Poland provides new opportunities to study the occurrence and circulation of thermal waters. We have analysed the isotopic variability of thermal waters in the Podhale Basin, using 87Sr/86Sr ratios to characterize their hydrodynamic behaviour. Strontium isotopic signatures in the geothermal water samples analysed range from 0.70835 to 0.70877. Extreme 87Sr/86Sr values were observed along the western and eastern margins of the Podhale Basin, while other chemical parameters showed extreme values in the southern and northern parts of the area. Contrary to expectations based on recharge and circulation patterns and the negative Spearman correlation, a clear northwards decrease in 87Sr/86Sr values was not confirmed. Waters from the Chochołów and Bukowina Tatrzanska wells were found to differ from the other samples, consistent with previous observations that classify these wells as containing mixed waters, recharged during the Holocene and pre-Holocene. The 87Sr/86Sr values in Phanerozoic carbonate rocks and the Tatra crystalline core indicate that both lithological units may contribute strontium to the geothermal waters. These results highlight the need for further quantitative assessment of strontium mixing, for example using a two-component mixing model, along with a broader geological interpretation.