Rare earth elements, yttrium and Pb isotope ratios in thermal spring and well waters of West Anatolia, Turkey: a hydrochemical study of their origin

Rare earth elements (REE), yttrium, major elements and Pb isotope ratios were determined in thermal well and spring waters, and rocks of the Büyük Menderes and Gediz grabens, Turkey, which includes the geothermal fields of Kizildere, Salavatli, Germencik, Kula and Salihli. Together with the results of short- and long-time leaching of local rocks, REE and Y and Pb isotope ratios indicate that the Palaeozoic mica schists dominantly control the REE and Y signatures of the deep-seated Na–HCO3 waters. Marbles may also be involved, but their low REE contribution is overridden by the much higher REE and Y abundances in the mica schists. Palaeozoic gneisses can be excluded as source rocks by both Pb isotope ratios and REE leaching behaviour. The deep-seated waters either ascend rapidly in production wells and precipitate carbonate-silica scales at temperatures of about 200 °C or these waters ascend slowly to springs, become enriched in Ca2+, Cl− and SO42−, and discharge with temperatures up to 100 °C as fumaroles or hot springs. Some of these spring waters precipitate large amounts of travertine upon exsolution of CO2. In contrast, the thermal Ca–HCO3-type of water from Pamukkale has its source in the regional Pliocene limestones.