Proceedings World Geothermal Congress 2010 Bali, Indonesia, 25-29 April 2010 Geochemical and Isotopic Characteristics of the Balıkesir Thermal Waters, Turkey Halim Mutlu and Ahmet Kılıç Eskisehir Osmangazi University, Department of Geological Engineering, Eskisehir, 26480, Turkey [email protected] Keywords: Water-rock interaction, stable isotope, In this study geochemical characteristics of the Balıkesir geothermometry, Balikesir thermal waters, Turkey. thermal waters are investigated on the basis of various water-rock interaction models and the equilibrium states of ABSTRACT geothermal minerals and reservoir temperatures of thermal waters are examined. Moreover, the source of water and its The Balıkesir geothermal waters in northwestern Turkey are dissolved constituents are discussed. represented by discharge temperatures in the range of 32- 99ºC and TDS contents between 327 and 2578 mg/l. The 2. WATER CHEMISTRY waters in the region are of Na-SO4, Na-HCO3 and Ca-HCO3 type character. It was determined that the solubility of silica A total of 21 thermal water samples were collected from the in most of waters is controlled by the chalcedony phase. geothermal wells and springs in the Balıkesir region in Equilibrium states of the Balıkesir thermal waters studied by August 2005. Locations of the water samples are shown in means of the Na-K-Mg-Ca diagram, mineral saturation Figure 1. Waters of the Gönen, Manyas, Pamukçu, Bigadiç calculations and activity diagrams approximate a reservoir and Edremit areas are collected from wells while those of temperature of about 120ºC. Most waters are found to be the Ekşidere, Sındırgı, Balya and Susurluk fields are equilibrated with calcite, chalcedony±quartz and muscovite sampled from hot springs. at predicted temperature ranges similar to those calculated from the chemical geothermometers. δ18O-δD compositions Results of chemical analyses illustrated in the Langelier and clearly indicate a meteoric origin for these waters. δ34S Ludwig (1942) diagram indicate that waters from the Gönen, contents of sulfate in thermal waters ranging from -5.5 to Pamukçu, Edremit and Balya areas are Na-SO4 type waters +25.2‰ correspond to nonmarine evaporates while sulfur in (Figure 2). some others is derived from the sulfate reduction process. 50 0 13 SO 4 +Cl δ C composition of dissolved inorganic carbonate in waters 50 0 BALYA GÖNEN SLK-2 WATERS is between -17.7 and +0.7‰. Carbon in high-temperature WATERS BİGADİÇ waters is thought to have originated from dissolution of WATERS SINDIRGI marine carbonates. On the contrary, carbon in low- PAMUKÇU WATERS temperature waters is derived from an organic source. WATERS EDREMİT 1. INTRODUCTION WATERS MK-1 Turkey, situated on a tectonically and magmatically active EKS-2 part of the eastern Mediterranean region, is represented by Ca+Mg extensive geothermal activity which is noticeable with numerous geothermal areas throughout the country (Mutlu Na+K and Güleç, 1998). The Balıkesir region in northwestern MK-2 Anatolia is one of the promising geothermal provinces in SLK-1 Turkey (Figure 1). Thermal waters in this region with discharge rates ranging from 1.5 to 75 l/sec and temperatures up to 98ºC are used for greenhouse, house heating and EKS-1 therapeutic purposes. In the region, application of central heating was initiated in the Gönen area in 1984 and has been expanded to include the Edremit and Bigadiç areas (Mutlu, 50 2007). 0 050HCO 3 +CO3 Figure 2: Langelier-Ludwig diagram for the Balıkesir thermal waters. The Bigadiç and Sındırgı areas are characterized by Na- HCO3 type waters. The Ekşidere thermal water is of Ca- HCO3 type and, the Manyas and Susurluk fields are represented with Na-Ca-HCO3 type waters. Low chloride concentrations in hot waters may indicate that water circulation in most of geothermal areas is shallow. Surprisingly, cold waters from Ekşidere (EKS-2 and EKS-3) in the Gönen area also yield SO4-enriched trends. At first glance, the SO4-rich nature of waters may be attributed to steam-heated process (e.g. oxidation of H S), however, since Figure 1: Geological map of the Balıkesir region showing 2 pH values of most of the samples are well above 7, this may studied geothermal areas (simplified from Mutlu, not to be the case. Alternatively, dissolution of Neogene 2007). 1 Mutlu and Kılıç evaporates (e.g., borate and gypsum) which widely occur in maximum temperature of around 120ºC better reflects the the northwest Turkey is probably the main source of sulfate reservoir temperatures for the Balıkesir region. in the waters (Palmer et al., 2004). 130 120 (120) 140 ) C 3. MINERAL EQUILIBRIUM CALCULATIONS 110 ( s r Equilibrium states of common hydrothermal minerals which e 100 (110) t 130 e are likely to be precipitated in the thermal waters of 11 m 90 .8 o 0 2 = m Balıkesir region were investigated on the saturation diagram (100) r 80 R e h 120 t (Figure 3). The WATSPEC program (Wigley, 1977) was o 70 (90) e G ) used to compute the saturation index (SI) of various 2 60 110 y (80) n o carbonate, sulfate, silica and silicate minerals at discharge SiO (mg/l) d 50 e (70) c 100 l temperatures of waters. Results yield that most waters are a 40 (60) h 90 C ( slightly oversaturated with respect to calcite and slightly (50) 30 & 80 z undersaturated with respect to aragonite and dolomite. (40) t r 20 70 a Although most samples are sulfate-enriched, none of them is u Q oversaturated or equilibrated with gypsum and anhydrite. 10 0 This may imply that SO4 concentration in waters is 30 40 50 60 70 80 90 100 controlled by steady state dissolution process (Grasby et al., Discharge T ( C) 2000). Calcite Dolomite Anhydrite Quartz Microcline Adularia Illite Figure 4: Silica-temperature relations for the Balıkesir 7 Aragonite Gypsum Chalcedony Albite Kaolinite Goethite thermal waters. 6 The reservoir temperatures computed from the cation 5 geothermometers for each sample are generally greater than 4 those of silica geothermometers. Na-K geothermometer of 3 Tonani (1980) and K-Mg geothermometer of Giggenbach 2 (1988) yield temperature ranges of about 50-260ºC and 30- LogSI 1 120ºC, respectively. Because Na/K ratios of waters are more 0 sensible to changes in temperature compared to K/Mg ratios (Giggenbach, 1988), the temperature range obtained from -1 the Na-K geothermometer is significantly wider than that -2 from the K-Mg geothermometer (Figure 5a and b). -3 70 G-7 G-16 MK-1 PMK-1 BHS-1 SHS-1 EDR-1 GDR-1 SLK-1 A G-8 EKS-1 MK-2 PMK-2 BHS-2 SHS-2 EDR-2 BLY-1 SLK-2 60 Figure 3: Mineral equilibrium diagram for the Balıkesir 60 ) C 50 ( thermal waters. r e t e 40 m 80 o m Microcline, albite and partly adularia show over saturation r e h Na / K Na / t trends, but the degree of saturation is always higher for the 30 o 100 e G former. Quartz and chalcedony are also supersaturated in all K - 120 waters. Saturation indices computed for goethite and 20 a kaolinite are the highest among the minerals of interest. Illite 140 N 160 displays strong under saturation behavior except for the 180 10 200 Susurluk waters (Figure 3). 260 0 4. GEOTHERMOMETRY APPLICATIONS 20 30 40 50 60 70 80 90 100 In this section, reservoir temperatures of Balıkesir thermal Discharge T ( C) 550 waters are estimated with various geochemical methods 120 including chemical geothermometers and mineral saturation 500 B calculations and, the results obtained from these techniques 450 are discussed. ) 400 C ( r e 350 t 4.1 Chemical Geothermometers e m 300 o m In order to estimate reservoir temperatures of the Balıkesir r 110 e 2 h t thermal waters, various chemical geothermometers were / K Mg 250 o e G used. In Figure 4, silica contents of waters are plotted vs. 200 g M their discharge temperatures. The trend between these two - 150 2 K parameters shows a broad positive correlation (R =0.811). 100 Also displayed in this figure is the range of quartz and 100 90 chalcedony geothermometers. In general, reservoir 50 80 70 temperatures computed from the quartz geothermometer 0 (Arnórsson, 1985) are about 20-30ºC higher than those of 20 30 40 50 60 70 80 90 100 chalcedony geothermometer (Fournier and Potter, 1982). Discharge T ( C) Since chalcedony, rather than quartz, controls the silica solubility at temperatures less than 180ºC (Fournier, 1991), Figure 5: Cation temperatures for the Balıkesir thermal it seems that chalcedony geothermometer attaining a waters: A) Na-K and B) K-Mg geothermometers. 2 Mutlu and Kılıç Given that correlation between K-Mg and chalcedony The WATSPEC program (Wigley, 1977) was used to geothermometers (R2=0.494) is much greater than that calculate saturation indices (SI) of 15 most common between Na-K and chalcedony geothermometers geothermal minerals (adularia, albite, analcime, aragonite, (R2=0.005), K-Mg geothermometer gives more suitable calcite, chalcedony, dolomite, goethite, kaolinite, reservoir temperatures (maximum 118ºC) for the region. laumontite, microcline, K-mica, quartz, Ca-montmorillonite and Na-montmorillonite). It is important to note that not all 4.2 Na-K-Mg-Ca Diagram the minerals but those shifting closer to the equilibrium line (log SI=0) are plotted in the diagrams in Figure 7. The In Figure 6, 10Mg/(10Mg+Ca) vs. 10K/(10K+Na) ratios measured temperatures and temperatures computed from the (Giggenbach, 1988) of the Balıkesir thermal waters are chalcedony and K-Mg geothermometers are also shown in plotted. The trend of samples does not suggest any the figures for comparison. Possible reservoir temperatures equilibrium between the reservoir rock and thermal waters. of the selected thermal waters of the Balıkesir region, The diagram in Figure 6 also implies that the solutes in the estimated with the mineral equilibrium calculations, are Balıkesir waters are not derived from the dissolution of presented in Figure 7a and b (SHS-1: ~120ºC and SLK-2: average crustal rock or they have gained their TDS by ~125ºC).