Conceptual model of the Şavşat (Artvin/NE Turkey) Geothermal Field developed with hydrogeochemical, isotopic, and geophysical studies

Abstract

The Şavşat (Artvin, Turkey) Geothermal Field (ŞGF) is located on the northeastern border of Turkey. This field is characterized by thermal and mineralized springs and travertine. The temperature of the thermal water is 36 °C, whereas that of the mineralized spring in the area is approximately 11 °C. The Na-HCO 3 -Cl-type thermal water has a pH value of 6.83 and an EC value of 5731 µS/cm. The aim of this study is to characterize the geothermal system by using geological, geophysical, and hydrogeochemical data and to determine its hydrochemical properties. A conceptual hydrogeological model is developed for the hydrogeological flow system in the ŞGF. According to the hydrogeological conceptual model created by geological, geophysical, and hydrogeochemical studies, the reservoir comprises volcanogenic sandstone and volcanic rocks. The cap rock for the geothermal system is composed of turbiditic deposits consisting of mudstone-siltstone-sandstone alternations. An increase in the geothermal gradient is mainly due to Pleistocene volcanic activity in the field. The isotopic values of thermal water (δ 18 O, δ 2 H, δ 3 H) indicate a deeply circulating meteoric origin. The estimated reservoir temperature calculated by silica geothermometers is 100-150 °C, and the mixing rate of cold groundwater with geothermal waters is approximately 70%. It may be possible to obtain warmer fluids from a 300-m-deep borehole cutting through a fracture zone identified by geophysical studies. Heating by conduction via the geothermal gradient resulting from young volcanic activity drives geothermal waters upwards along faults and fractures that act as hydrothermal pathways. The positive δ 13 C VPDB value (+ 4.31‰) indicates a metamorphic origin for the thermal water. The 34 S CDT value (~ 10‰) shows that the sulfur in the geothermal water is derived from volcanic sulfur (SO 2 ). which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made.hydrogeochemical and isotope techniques have been widely used elsewhere to determine the hydrodynamic structure of geothermal systems in recent years (Tarcan et al. 2005;Piscopo et al. 2006; Schaffer and Sass 2014; Yurteri and Şimşek 2017;Uzelli et al. 2017). In this geothermal field, there has not been any study that employs a conceptual approach based on hydrogeological and hydrogeochemical studies, such as hydrochemical facies compositions, isotopic features, water-rock interactions, mixing processes, and reservoir temperature. This study focuses on understanding the mechanism of the geothermal system in the ŞGF for future use, determining the areas with higher temperatures and revealing the hydrogeochemical characteristics of the geothermal water. In accordance with this purpose, geological, geophysical, and hydrogeochemical studies were performed in the area to characterize components such as the reservoir, geothermal fluids, and...

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