The chemical and D, O, S, and Sr isotopic composition of 26 thermal waters (>25 °C) and 25 cold waters from springs and wells in Okayama Prefecture were investigated to examine the geochemical characteristics of the geothermal resources in a non-volcanic region. No clear geochemical difference was noted between the thermal and cold waters. Some of these waters were formed by mixing of fossil seawater and meteoric water; however, most with low salt concentrations are of meteoric origin and are presumed to have flowed out with a residence time of several months. The waters studied were classified as Ca²⁺−HCO₃⁻ and Na⁺−HCO₃⁻ types, with ⁸⁷Sr/⁸⁶Sr values close to those of the granite base. These thermal and cold waters were formed by an infiltration of meteoric water into the granite layer that subsequently reacted with carbonate and clay minerals. Considering the main chemical components of the waters, the estimated maximum underground temperature was approximately 100 °C. Therefore, the utilization of these geothermal resources for geothermal heat pumps was judged to be effective even though calcium carbonate scale could precipitate in the heat exchanger.

研究了冈山县泉水和泉水中26个温泉水（> 25°C）和25个冷水的化学和D，O，S和Sr同位素组成，以研究非火山岩地热资源的地球化学特征。地区。在热水和冷水之间没有发现明显的地球化学差异。其中一些水是由化石海水和陨石水混合而成的。但是，大多数盐浓度低的都是流星状的，并且假定已经流失了几个月的停留时间。研究了水被归类为的Ca ²⁺ -HCO ₃ ^-和Na ⁺ -HCO ₃ ^-类型，与⁸⁷锶/ ⁸⁶Sr值接近花岗岩基底的Sr值。这些热水和冷水是由陨石水渗入花岗岩层形成的，花岗岩层随后与碳酸盐和粘土矿物发生反应。考虑到水的主要化学成分，估计的最高地下温度约为100°C。因此，即使碳酸钙垢可能在热交换器中沉淀，也认为将这些地热资源用于地热热泵是有效的。