Source of arsenic based on geological and hydrogeochemical properties of geothermal systems in Western Turkey

Turkey is an area of complex geology with active tectonics and high geothermal potential. Especially, the western part of Turkey is a region of abundant geothermal activity. Faults accommodating the deep circulation of hydrothermal fluids of meteoric origin are the primary means by which of geothermal systems are controlled in this region. Many of the thermal activities are related to the improved dilation on the ~ E–W-strikes of the graben faults. This situation serves as a suitable environment for the presence of high levels of arsenic in geothermal water resources. The highest concentrations of naturally occurring aqueous arsenic (As) are found in certain types of geothermal waters, generally those related to major graben faults. In this regard, high arsenic concentrations in geothermal resources have been detected in Western Turkey, including but not limited to Biga Peninsulla, Gediz Graben, Kucuk, and Buyuk Menderes Graben with values ranging from 1 to 1419 ppb in geothermal fluids. The thermal waters have surface temperatures of up to 100 °C and reservoir temperatures range from 150 to 248 °C in the Menderes Graben, from 120 to 287 °C in the Gediz Graben, and from 153 to 174 °C in Biga Peninsula. Hydrogeochemically, the Menderes graben and Gediz Graben thermal waters are of the Na-HCO3, Ca-HCO3, and Na-SO4 types, whereas some geothermal fluids such as those of Tuzla and Kestanbol in the Biga Peninsula, Çeşme, and Urla are of the Na-Cl type.

► We investigate the potential sources and levels of arsenic in geothermal resources of western Turkey.
► High arsenic content is attributed to deep water circulation from a deeply seated magma body.
► Elevated levels of arsenic are correlated with various altered rock types in geothermal resources.
► As is attributed to the dissolution of ferromanganese minerals within the Miocene sediments in Western Turkey.