Strontium hydrogeochemistry of thermal groundwaters from Baikal and Xinzhou

Abstract

This paper reports our work on the strontium hydrogeochemistry of thermal groundwaters in the Baikal Rift System (BRS) in Russia and Mongolia and the Xinzhou basin of the Shanxi Rift System (SRS) in northern China. Though similar in geological background, groundwaters from the BRS and the Xinzhou basin have different strontium isotope compositions. Both the strontium contents and the⁸⁷Sr/⁸⁶Sr ratios of thermal water samples from Xinzhou are higher than those of most samples from Baikal. The major reason is the difference in hostrock geochemistry. The hostrocks of the Xinzhou waters are Archaean metamorphic rocks, while those of the Baikal waters except the Kejielikov spring are Proterozoic or younger rocks. In the study areas, cold groundwaters usually show lower⁸⁷Sr/⁸⁶Sr ratio due to shorter water-rock interaction history and lower equilibration degree. Strontium hydrogeochemistry often provides important information about mixing processes. Ca/Sr ratio can be used as an important hydrogeochemical parameter. Case studies at Xinzhou show that thermal waters with lowest Ca/Sr ratios are most weakly affected by mixing with shallow groundwaters, as supported by our hydrochemical and sulfur isotope studies.