The assessment of origin and sustainable use of the Hudai (Sandikli- Afyonkarahisar) geothermal waters of Turkey

In this study, geothermal waters in The Hudai Geothermal Field (HJA) and its vicinity have been investigated for geological, hydrogeological, hydrochemical, isotopic purposes. Potantial geothermal energy of the field has been evaluated by the reservoir temperatures of the geothermal waters.HJF is located in southwestern of Sandıklı, Afyonkarahisar. In the investigation area, the oldest geologic units are schist of Precambrian age. Paleozoic rocks consist of quartzite, schist limestone, and dolomite. Mesozoic is represented by conglomerate, marly sandstone, siltstone and limestone which is karstic and blocky. Tuff, pillow lava, andesite, alternation of conglomerate, sand, silt, clay and travertine, and alluvium of Quaternary age forms of Senozoic units. Alluvium, travertine, conglomerate, sandstone and limestone levels are permeable; quartzite and dolomite levels are semi-permeable units. However shale, siltstone, claystone and marl levels are impermeable. To determine hydrochemical and isotopic features of both geothermal and cold waters, samples were taken from the locations in the study area. Generally, the waters have assembled in three different hydrochemical facies, such as Ca-Mg-HCO3, Ca-Mg-SO4 and Na-Ca-SO4-HCO3, respectively. All waters are of meteoric origin to the isotope results. The ?18O and ?2H values range from -7.45 to -10.81 and -54 to -75.22, respectively. Geothermal waters have long residence time and deep circulation. whereas cold waters have short residence time and shallow circulation. The reservoir tempeatures of the geothermal waters are between from 24 to 107 °C. ?13C (?PDB) values of all cold waters (-22.1- 15.1) are lower than geothermal waters (-0.6-0.2). The high 14C apperant ages of geothermal waters may imply the modern biogenic carbon contribution. According to the ?34S values, there are coal, limestone, volcanic sulfur contribution to geothermal waters.The Hudai Geothermal Field has been in used for several purposes such as balneotherapy, heating and thermal tourism in recent years.