Geology and Hydrothermal Alteration of the Aydın-Salavatlı Geothermal Field, Western Anatolia, Turkey

Authors: İSMAİL HAKKI KARAMANDERESİ, CAHİT HELVACI

Abstract: The Aydın-Salavatlı geothermal field is located in the middle part of the Büyük Menderes Graben, and is characterized by normal-fault structures. The stratigraphic sequence of the Aydın-Salavatlı geothermal field consists of metamorphic rocks of the Menderes Massif and sedimentary rocks deposited during the rifting period of the Menderes Massif in the Miocene. Geological data suggest that there is a connection between tectonic development and periods of hydrothermal alteration. Hydrothermal alteration in the Aydın-Salavatlı geothermal field occurred in five distinct periods, and all are related to different stages of faulting systems, from the Middle Miocene up to the present. The first period of hydrothermal alteration was characterized by mercury and antimony mineralization related to acidic intrusions, and by the occurrence of rutile mineralization within quartz veins. Gabbros and associated dykes developed in the second period. In this period, gneisses were subjected to hydrothermal alteration. The third period was characterized by granite intrusions. Specularite, talc, calcite, quartz, and aragonite mineralization and travertine formed along the margins of these intrusions. The fourth period was marked by albite and chlorite mineralization that developed during N-S faulting. Hydrothermal alteration zones which developed in the last period are associated with active faults along which hot fluid is circulating. These faults have more than 100 m of downthrow, and formed during the final period of graben formation. Hydrothermal alteration products caused by the circulation of geothermal fluids within these faults in Upper Miocene sediments include kaolinite, illite, montmorillonite, dickite, vermiculite, calcite, pyrite, dolomite and hydrobiotite. These minerals are still precipitating/forming in active circulation zones. Thermal waters of the Aydın-Salavatlı geothermal field are a Na-HCO3 type with high CO2 and B contents that are associated with metamorphic rocks of the Menderes Massif and hydrothermal alteration which developed via water-rock interactions. Geophysical studies were used to outline tectonic structures and frames of the Salavatlı geothermal field.

Keywords: geothermal field, hydrothermal alteration, Büyük Menderes Graben, Salavatlı, western Anatolia, Turkey

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