Hydrogeochemical and isotopic investigation of the Bursa-Oylat thermal waters, Turkey

The Oylat spa is located 80 km southeast of Bursa and 30 km south of Ineg?l in the Marmara region. With temperature of 40°C and discharge of 45 l/s, the Oylat main spring is the most important hot water spring of the area. Southeast of the spa the Forest Management spring has a temperature of 39.4°C and discharge of 2 l/s. The G?z spring 2 km north of the spa, which is used for therapy of eye disease, and cold waters of the Saadet village springs with an acidic character are the further important water sources of the area. EC values of Main spring and Forest Management hot spring (750–780 μS/cm) are lower than those of Saadet and G?z spring waters (2,070–1,280 μS/cm) and ionic abundances are Ca > Na + K > Mg and SO₄ > HCO₃ > Cl. The Oylat and Sızı springs have low Na and K contents but high Ca and HCO₃ concentrations. According to AIH classification, these are Ca–SO₄–HCO₃ waters. Based on the results of δ¹⁸O, ²H and ³H isotope analyses, the thermal waters have a meteoric origin. The meteoric water infiltrates along fractures and faults, gets heated, and then returns to surface through hydrothermal conduits. Oylat waters do not have high reservoir temperatures. They are deep, circulating recharge waters from higher enhanced elevations. δ¹³C_DIC values of the Main spring and Forest Management hot spring are −6.31 and −4.45‰, respectively, indicating that δ¹³C is derived from dissolution of limestones. The neutral pH thermal waters are about +18.7‰ in δ³⁴S while the sulfate in the cold waters is about +17‰ (practically identical to the value for the neutral pH thermal waters). However, the G?z and Saadet springs (acid sulfate waters) have much lower δ³⁴S values (~+4‰).