Hydrogeochemicalandhydrogeologicalinvestigationsof...

Hydrogeochemical and hydrogeological investigations ofthermal waters in the Emet area (Kutahya, Turkey)

Unsal Gemici*, Gultekin Tarcan, Mumtaz Colak, Cahit Helvacı

Dokuz Eylul Universitesi, Muhendislik Fakultesi, Jeoloji Muhendisligi Bolumu, 35100-Bornova-I.zmir, Turkey

Received 25 October 2002; accepted 7 May 2003

Editorial handling by R.L. Bassett

Abstract

Metamorphic rocks host the majority of the thermal waters of the Emet area. Only Dereli springs are hosted by non-metamorphic carbonates and ophiolitic rocks. The carbonated rocks of the lower parts of the Neogene sequence arealso secondary reservoir rocks. The measured surface temperatures of thermal waters are between 33 and 54 �C. Mostof the thermal waters are characterized as Ca–Mg–SO4–HCO3 type although there are a few Ca–Na–HCO3, Na–Ca–

SO4 and Ca–Mg–HCO3 waters. Calcium concentrations in the thermal waters are 89–354 mg/kg. High SO4 contents ofthe thermal waters (up to 1309 mg/kg) are related to rocks and minerals in the Red Unit below the Emet boratedeposits. Although the SO4 concentrations are high and SO4 is the major anion, gypsum and anhydrite are under-

saturated for all of the thermal waters indicating that dissolution of SO4 is still taking place in the reservoir. Thermalwaters are oversaturated at outlet conditions with respect to calcite, chalcedony, dolomite and quartz. According to theactivity diagrams thermal waters are likely to form illite as an alteration product in the reservoir and Ca and Mg

contents are controlled by exchange with smectite. Reservoir temperatures obtained by silica geothermometers andassessments of the saturation states of minerals are more appropriate for Emet geothermal waters. Assessments of thevarious geothermometers suggest that reservoir temperature is around 75–87 �C.

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1. Introduction

Emet geothermal field, which includes the thermal

waters of Hamamkoy, Yukarıyoncaagac, Dereli, Gobeland Emet is located in the N–S trending Hisarcık–Emetbasin in the western part of Turkey (Fig. 1). Thermal

waters in the region have been used for balneologicaland, or bathing since the Roman-Byzantine period.They are some of the most famous historical Turkish

spas. Although the thermal springs have been knownsince historical times, only a few undetailed studies of

the Emet geothermal field are available. Geothermalhistories and chemical analyses of these thermal watersare only rarely discussed in books related to thermal

waters of Turkey (Reman, 1942; I.U., 1975; MTA, 1996;Helvacı, 1977).Emet geothermal field and surrounding areas also

include the important borate deposits of Turkey. TheEmet borate deposits are located in the middle of theknown borate deposits of western Anatolia. Borate

minerals (colemanite, ulexite, etc.) are the major sourceof commercial B and are largely concentrated in andaround the Emet basin. Earlier studies in the Emet fieldfocused mainly on the borate deposits to evaluate their

stratigraphy, mineralogy and genesis (Ozpeker, 1969;Helvacı, 1977, 1978, 1984, 1986; Helvacı and Firman,1976; Yalcın, 1984; Dundar et al., 1986; Helvacı et al.,

0883-2927/03/$ - see front matter # 2003 Elsevier Ltd. All rights reserved.

doi:10.1016/S0883-2927(03)00112-4

Applied Geochemistry 19 (2004) 105–117

www.elsevier.com/locate/apgeochem

* Corresponding author. Tel.: +90-232-388-2919; fax: +90-

232-388-78-65.

E-mail address: [email protected] (U. Gemici).

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1993; Kistler and Helvacı, 1994; Colak et al., 2000). The

purpose of this investigation is to determine the hydro-geological and hydrogeochemical properties of the ther-mal waters, their relationships with borate deposits and

the maximum reservoir temperature by application ofchemical geothermometers.Thermal water samples from the study area were col-

lected from springs (samples 1, 2, 3, 4, 5, 7, 8, 9 and 10)

and drilled well (sample 6) (Fig. 1). Two samples werecollected from each and stored in 1000 ml polyethylenebottles. One of the bottles was acidified with 10 ml HCl

for determination of cations and SiO2 analyses. The

unacidified sample was used for anion analyses. Tem-perature, electrical conductivity and pH values weremeasured at spring and, or wellhead conditions. The

remaining chemical constituents and some trace ele-ments were analyzed in the geochemistry laboratory ofDokuz Eylul University, Geological EngineeringDepartment. Sodium, K, Ca, Mg, Li, Al and SiO2 were

determined by atomic absorption spectrophotometry.Chlorine and CO3 and HCO3 (total alkalinity) weredetermined volumetrically and SO4 by a gravimetric

Fig. 1. Geological map (modified from Dubertre et al., 1973) and sampling locations of water samples.

106 U. Gemici et al. / Applied Geochemistry 19 (2004) 105–117

method. Boron was determined by colorimetric spec-trophotometry using the Carmine Method. Some che-mical analyses of thermal waters from previous studies

were also used. The composition of hot and some cold-water samples are reported in Table 1. Solmineq.88(Kharaka et al., 1988), Aquachem (Calmbach, 1997),

WATCH (Arnorsson et al., 1982; Bjarnason, 1994)computer codes were used to evaluate their geochemicalproperties.

2. Geological and hydrogeological settings

The basement of the study area is Menderes Massifmetamorphic rocks (Dora et al., 1997) and Afyonmetamorphics (Ozcan et al., 1988; Goncuoglu et al.,

1992; Okay et al., 1996). High to low grade meta-morphic rocks (gneiss, mica schists, phyllites, quartzschist and marbles) of the Menderes Massif are theprinciple basement rocks. Afyon metamorphic rocks

outcrop only in the northern parts of the study area(Fig. 1). The non-metamorphic Mesozoic carbonatesand rocks of the I

.zmir-Ankara Zone deposited in flysch

facies rest over the metamorphic rocks along a thrustfault.Lacustrine sediments located in the Hisarcık-Emet

Neogene basin overlie these metamorphic rocks. Paleo-cene Egrigoz granite cuts the metamorphic rocks(Fig. 1). Neogene lacustrine sediments in the Emet area

(Fig. 2) consist of basal conglomerate and sandstone,overlain by alternating thin-bedded lower limestonewith lenses of marl and tuff, and overlain by a red unitthat is composed of conglomerate, sandstone, clay, tuff,

marl, limestone, coal and gypsum bands. A borate-bearing unit of clay with marl, limestone and tuff inter-calations and capping basalts overlies the red unit.

Table 1

Chemical analyses of thermal waters and cold ground waters (Values are in mg/kg, EC: electrical conductivity)

No.
Date T (�C) pH pH
calculated

EC

(mS/cm)
Na+ K+ Ca2+ Mg2+ Cl� HCO3
�
SO42� B Li Al Si Water type
1
2000a 43 7.11 6.34 1350 18.8 5.00 230.8 45.2 11 295.2 541.9 0.1 0.038 0.039 14.1 Ca–Mg–SO4–HCO3 2 2000a 54 7.10 6.39 1041 12.7 3.29 176.8 32.3 11 324.5 319.7 0.26 0.039 0.039 19.5 Ca–Mg–SO4–HCO3 3 2000 43 7.10 6.47 1015 13.1 3.50 166.4 35.5 11 287.9 335.0 0.26 0.048 0.039 22.4 Ca–Mg–SO4–HCO3 4 2000 38 6.90 6.27 1830 14.9 5.36 354.0 62.0 12 292.8 839.5 0.91 0.031 0.053 15.2 Ca–Mg–SO4–HCO3 5 2000a 13 7.25 1606 13.3 4.22 298.8 49.6 13 273.3 749.8 0.91 0.029 <0.025 20.9 Ca–Mg–SO4–HCO3 6 2000 48 7.00 6.63 646 10.1 6.13 89.6 23.3 14 275.7 87.2 0.48 0.013 <0.025 19.5 Ca–Mg–HCO3 7 2000 15 7.20 962 9.2 2 226.8 68.7 50 458.7 433.7 1.44 0.1 9.3 Ca–Mg–SO4–HCO3 8 2000 46 6.47 6.30 1269 6.2 1 288 57.6 17 283.1 772.8 0.5 0.04 15.1 Ca–Mg–SO4–HCO3 9 2000 49 6.45 6.24 1346 7 1 297.2 57.8 17 287.9 792.6 0.5 0.04 15.3 Ca–Mg–SO4–HCO3 10 2000 15 7.09 1636 8.5 0.6 353.6 73.4 20 331.8 1019.3 1.75 0.1 15.0 Ca–Mg–SO4–HCO3 11 1984b 33 7.80 6.63 500 10 1.8 78 21 5.7 348 29 3 – 0.010 4,2 Ca–Mg–HCO3 12 1984b 39 6.70 6.09 1060 110 9.6 139 28 27 756 51 1.6 0.3 0.138 6.0 Ca–Na–HCO3 13 1984b 43 7.10 6.58 2250 340 71 204 61 88 305 1309 5.2 0.2 0.081 14 Na–Ca–SO4
a Gemici and Tarcan (2002b).b MTA (1996).

Fig. 2. Generalized stratigraphic column of Emet area

(Helvacı, 1986).

U. Gemici et al. / Applied Geochemistry 19 (2004) 105–117 107

Borate deposits were formed during the Miocene inclosed lacustrine basins with abnormally high salinityand alkalinity (Helvacı and Firman, 1976; Helvacı et al.,1993). Borates of commercial grade are represented by

colemanite with minor amounts of ulexite in the Emetdeposit (Helvacı et al., 1993). Upper limestone withalternating clay and calcareous clay overlie the borate

bearing clay unit (Helvacı, 1984; 1986; Colak, 1995).Overlying volcanic rocks consist of calc-alkaline flowsand abundant pyroclastic layers. Volcanic activity

occurred in the Emet area from Early Miocene to LateMiocene (Helvacı, 1984). Basalts that overlie the Upperlimestones are the last products of volcanic activity

about 15.4 Ma (Helvacı and Alonso, 2000).Most of the thermal waters discharge along the N–S

trending faults that form the Hisarcık-Emet basin. Thecirculation of thermal waters is closely related to major

fault and fractured zones. Fractured metamorphic rocksof the Menderes Massif and Afyon metamorphics suchas gneiss, metaquartzite, various schists and especially

marbles are assumed to be the main reservoir rocks forthe Emet thermal waters. Reservoir rocks for the Derelisprings (sample 12) are the carbonate and the ophiolitic

rocks. The fractures and faults in these rocks provide ameans for circulation to depth and return of the heatedwaters to the surface. The lower parts of the Neogene

sequence (especially lower limestone and red units)(Fig. 2) may also act as a secondary reservoir for theEmet geothermal waters. Hamamkoy (samples 1, 2, 3,4), Yoncaagac (samples 8, 9), Emet spa (sample 6) and

Yenicekoy (sample 13) emerge from the springs whereRed unit rocks outcrops. Gobel (sample 11) springsissue from the marbles of the Afyon metamorphics

along the E–W trending normal fault. Relativelyimpermeable Neogene rocks cap the Emet geothermalsystem. Plate movements were important in the forma-

tion of western Anatolia. The subduction of the African-Arabian plate beneath the Anatolian plate caused thefusion of the lithosphere. The melting plumes, emplacedat shallow depths in the crust, supply the heat in the

thinning of the rift structure (Kocak, 1990). The esti-mated thickness of the lithosphere in western Turkey isabout 30–40 km indicating that the asthenosphere is

rather shallow, and a high mantle contribution to sur-face heat flow is suggested (Alptekin et al., 1990). TheGediz earthquake (1970) and historical earthquakes are

evidence of tectonic activity in and around the studyarea. An increased geothermal gradient due to the gra-ben tectonism could be the heat source for the Emet

geothermal field.

3. Field characteristics of thermal waters

Thermal waters are obtained from wells and are usedto heat hotels and spa facilities, for bathing, swimming

pools and balneological purposes in the Emet geother-mal areas. In Emet spa (sample 6) several closely spacedsprings were present within tens of meters of each other(Reman, 1942). However, most of the thermal springs

have disappeared due to the over pumping of residentialwells. A well with a temperature of 48 �C (sample 6)now feeds the baths at Emet spa. Thermal water from

Gobel Spring (sample 11) discharges along a NW–SEtrending fault with a temperature of 38 �C at approxi-mately 10 l/s discharge rate. There are 4 springs (tem-

peratures 439 �C) along an E–W trending fault with atotal discharge of 200 l/s in the Dereli springs area(sample 12). Thermal waters also discharge at Yenice

(sample 13) with a temperature of 43 �C at approxi-mately 10 l/s. A N–S trending fault controls the locationof the thermal springs. Yoncaagac consists of twosprings with temperatures of 46 and 49 �C (samples 8

and 9, respectively) and no mineral deposition occursaround these springs. Hamamkoy thermal waters (sam-ples 1, 2, 3 and 4) range from 43 and 45 �C and are

depositing travertine. Thermal waters around Hamam-koy village have been used for bathing and balneo-logical purposes for many years (Hamamkoy spa).

The locations of some thermal waters in the studyarea were affected by an earthquake on 30 March 1970(I..U., 1975). This earthquake affected the field char-

acteristics of thermal springs in Hamamkoy. The dis-charge rate of water at site 2 decreased and a new spring(sample 1) appeared a day after the earthquake (I

..U.,

1975). The chemical properties of the new spring are

similar to the old spring but its temperature is lower.

4. Water chemistry

Table 1 lists the chemical composition of water sam-

ples. Trace element data are also shown in Table 3 forsome selected water samples. A series of diagramsshowing the relative concentrations of the thermal fluidswere used to investigate the relations between the ions,

to classify the water samples and water–rock processes.Solmineq.88 (Kharaka et al., 1988) and Aquachem(Calmbach, 1997) computer codes were used to evaluate

mineral speciation and to construct the diagrams. Clas-sifications of the water samples in Table 1 were madeaccording to principles of IAH (1979). Total equivalents

of cations and anions separately were accepted as 100%and ions with more than 20% (meq/l) were taken intoconsideration in this classification.

The chemistry of the thermal and cold waters in thestudy area are similar. Based on their chemical compo-sition, the waters can be divided into three groups: 1)Ca–Mg–SO4–HCO3 type waters (samples 1, 2, 3, 4, 5, 6,

7, 8, 9 and 10). 2) Ca–Mg–HCO3 type waters (samples11 and 12). 3) Na–Ca–SO4 (sample 13). The thermalwaters have temperatures between 33 and 54 �C with


electrical conductivity values of 500–2250 mS/cm. Cal-cium and SO4 concentrations of the thermal watersrange from 89.6 to 354 mg/kg and 29 to 1309 mg/kg,respectively. The second and third groups of waters

have relatively lower values of dissolved solids. Calciumand Mg are still the dominant cations but their con-centrations are lower than those of the first group. Theyvary between 78–139 mg/kg and 21–28 mg/kg, respec-

tively. However, HCO3 values are significantly higheraround 348–756 mg/kg, and SO4 concentrations aresignificantly lower about 29–51 mg/kg. The third type of

water (sample 13) is high in Na, Ca and SO4 (SO4 con-centration of 1309 mg/kg).Calcium is the dominant cation in first and second

type waters indicating that carbonate rocks are the mainreservoir rocks for these waters. The main process thatcontrols the chemical properties of water is the dissolu-tion of limestone and dolomite. Magnesium contents of

the thermal waters from the study area range from 21 to62 mg/kg indicating water rock reactions at low tem-peratures and/or mixing with cold ground waters.

Fig. 3a shows the relative concentrations of Na+K,Ca and Mg of waters. All of the waters plot in the Caarea with the exception of sample 13 in which Na is the

dominant cation. The relative Cl, HCO3 and SO4 con-centrations of the waters are shown on Fig. 3b. The firstand third group of samples plot in the SO4-rich part of

the diagram. The remainder (Samples 6, 11 and 12) plotin HCO3 dominant part of the diagram.Sulfate concentrations are very high in the thermal

and cold waters with the exception of sample 6. Relative

concentrations of Ca, SO4 and HCO3 are shown in Fig. 4(after Giggenbach et al., 1988; Kavouridis et al., 1999).The graph indicates the dissolution and deposition of

calcite and gypsum. Water samples show a trend sug-

gesting that dissolution of CaSO4 is an important pro-cess in water–rock interaction for Emet waters. Watersfrom the first and third groups dissolve CaSO4 in var-

ious amounts during circulation in the reservoir. Alongthe trend line the Ca/SO4 ratio decreases due to theincreasing CaSO4 dissolution. As CaSO4 dissolves, SO4/HCO3 values increase, changing the water from HCO3-

dominant to SO4-dominant (Fig. 3b). Correlation coeffi-cients of some major ions were computed by AquaChemcomputer code and the relationships of the constituents

in the water samples are denoted on Fig. 5 in which therelation between silica and temperature is also pre-sented. The correlation coefficients of SO4 with Ca and

Fig. 3. Relative Na+K, Mg, Ca (a) and Cl, SO4, HCO3 (b) concentrations (mg/kg) of waters from the study area.

Fig. 4. Relative Ca, HCO3 and SO4 concentrations (mg/kg) of

thermal waters from the study area.


Mg are about 0.97 and 0.88, respectively. Similarly, Caand Mg show a close correlation (r=0.86). The closepositive linear correlation between Ca, Mg, SO4 and

some of the other ions (Fig. 5) corroborates the dis-solution of gypsum and the mixing.Geological and hydrogeochemical investigations

showed that there are 2 reservoirs for the thermal watersfrom the Emet geothermal area. Paleozoic metamorphicrocks and non-metamorphic rocks of I

.zmir-Ankara

Zone from which, samples 11 and 12 discharge form the

deeper one. The rest of the thermal waters also circulatethrough the Neogene terrestrial rocks of the second reser-voir (Fig. 1). The thermal waters of western Anatolia are

mainly Na–HCO3 type. They are produced by rock dis-solution and ion exchange reactions in deep aquifers athigh temperatures. Although the expected type of ther-

mal waters in the deep thermal aquifers is initially Na–HCO3, mixing during the upflow, and re-equilibrationprocesses causes Na–HCO3 type waters to turn into

various types (Gemici and Tarcan, 2002a,b). Samples 11and 12 issuing from the rocks of the deeper reservoir areHCO3 type waters The higher SO4 of the other watersare directly related to dissolution of gypsum in the sec-

ond reservoir.The Emet borate deposits are characterized by high

Ca borate (colemanite), very low Na and relatively high

Fig. 5. Relations of some major ions for waters from the study area (values in mg/l).


Mg, Sr, As and S concentrations (Helvacı and Firman,1976). Realgar, celestite and native S are almost ubi-quitous in borates and sediments, and appear to have

formed at all stages during deposition and diagenesis.The unit of clay, tuff, tuffite and marl containing theborate deposits has abundant realgar and orpiment insome horizons (Helvacı, 1984). The elements Mg, Sr, As

and S are present both in the evaporite and in the clayfractions but mainly in the latter. Major oxide compo-sitions of tuffs and clays are given in Table 2. Bicarbonate-

type thermal waters penetrate through to the secondaquifer along the faults and fractures from the deeperaquifer and volcanic rocks, mainly tuffs, borate and

non-borate minerals (gypsum, celestite) and native Sresult in an increase in the SO4 contents of thermalwaters due to dissolution processes.Similar to the SO4 enrichment in the second reservoir

Ca and Mg contents of thermal waters (groups 1 and 3)show an increase as well. Calcium contents are around78 and 139 mg/kg for samples 11 and 12, which are not

affected by Neogene sediments. Thermal waters issuing

from the second reservoir in the Neogene sedimentshave Ca concentrations of 89.6 and 354 mg/kg.Table 3 shows the trace element concentrations of

some selected thermal waters. Compared with sample 5,trace element concentrations are relatively higher forthermal waters because of the leaching of the reservoirrocks. While Sb, Zn and Fe values show remarkable

increases, Pb, Li, Cd, Ni, Cr, Mn and Al concentrationsincrease slightly relative to the cold water sample.Some ionic ratios of thermal waters are presented in

Table 4. Ca–Mg–SO4–HCO3 type waters (samples 1–10)have generally lower ionic ratios than those of Ca–Mg–HCO3 (samples 11 and 12) and Na–Ca–SO4 (sample 13)

type waters. The higher ratios of Na/Ca, Na/Mg, Na/Cl,(Na+K)/Cl and (Na+K)/(Ca+Mg) for samples 11–13indicate relatively prolonged water–rock interactiontime. Ca/SO4 ionic ratios for samples 11 and 12 (group

2) are significantly higher indicating that dissolution ofgypsum has an important effect in the final compositionof the thermal waters of group 1. High Na/Ca ratios

(>50) are indicative of direct feed from the reservoir

Table 3

Trace element values for some selected water samples (mg/kg)

No
Sb Pb Li Zn Cd Fe Ni Cr Mn Sr As
1
0.87 0.10 0.038 0.05 0.006 0.148 0.050 0.042 0.024 0.181 0.02
2
0.68 0.07 0.039 0.13 0.004 0.217 0.025 0.030 0.007 0.117 0.01
3
0.54 0.05 0.048 0.23 0.003 0.103 0.025 0.042 0.003 0.088 0.01
4
0.87 0.11 0.031 0.03 0.006 0.331 0.044 0.055 0.025 0.193 0.02
5
0.31 0.06 0.029 0.01 0.002 0.002 0.019 0.030 0.003 0.059 0.02
6
0.68 0.07 0.013 0.06 0.004 0.432 0.038 0.017 0.019 0.052 0.03
Table 2

Summary statistics for a) tuff samples (n=8) and b) clay samples (n=7) (Helvacı, 1977)

Oxide %
(a) (b)
Mean
S.D. Maximum Minimum Range Mean S.D. Maximum Minimum Range
SiO2
58.65 7.33 67.50 48.02 19.48 49.11 2.82 52.50 44.64 7.86
Al2O3
15.17 1.62 17.76 13.15 4.61 16.03 6.43 21.03 11.35 9.68
TiO2
0.51 0.13 0.70 0.38 0.32 0.53 0.14 9.82 0.34 0.48
Fe2O3
2.22 0.82 3.75 1.26 2.49 3.88 1.11 5.62 1.82 3.80
FeO
0.80 0.65 2.06 0.36 1.70 0.79 0.27 1.18 0.46 0.72
MgO
4.89 1.26 6.16 2.53 3.63 7.54 3.34 14.59 4.12 10.07
CaO
2.96 2.48 7.91 1.25 6.74 2.74 2.37 7.40 0.28 7.12
Na2O
0.42 0.24 0.85 0.17 0.68 0.70 1.27 4.08 0.16 3.92
K2O
8.27 0.70 9.66 7.38 2.28 4.28 1.85 6.01 0.09 5.92
MnO
0.05 0.03 0.10 0.03 0.07 0.08 0.04 0.15 0.03 0.12
P2O5
0.11 0.04 0.16 0.07 0.09 0.19 0.13 0.47 0.00 3.57
H2O
2.44 2.96 5.69 0.00 5.69 10.51 2.36 15.41 7.66 7.75
CO2
0.03 0.09 0.24 0.00 0.24 0.98 1.37 3.57 0.00 3.57
B2O3
0.18 0.20 0.58 0.00 0.58 0.60 0.37 1.09 0.18 0.91
SO3
1.56 1.32 4.12 0.43 3.69 0.46 0.21 0.97 0.25 0.72

and less cold groundwater contribution (Nicholson,1993). Na/Ca ratios of thermal waters from the studyarea are significantly low with values of generally less

than 1 (Table 4) indicating that reservoir temperature isnot very high.

5. Geothermometer applications

Chemical analyses of geothermal fluids can be used toestimate subsurface reservoir temperature under certainconditions. Chemical analyses of thermal waters

(Table 1) from the study area were used to estimate thereservoir temperature of Emet geothermal area by sev-eral solute geothermometers. The degree of water–rockequilibrium attained in the reservoir was evaluated by

determining the Maturity Index (MI) of thermal watersproposed by Giggenbach (1988). MI values of thermalwaters from the study area are presented in Table 5. MI

values less than 2.0 are found in immature waters thatdo not attain equilibrium with their associated rocks.All the thermal waters in the study area have MI values

less than 2.0 indicating that none of these thermalwaters have attained water–rock equilibrium. Therefore,cation geothermometers are not considered.

Silica geothermometers give reservoir temperaturesranging from 50 to 99 �C. The temperatures obtained bysilica geothermometers vary between 50 and 70 �C for

the chalcedony geothermometer and 79–99 �C for thequartz geothermometer (Table 6). However, geothermo-metry based on amorphous silica, alpha-cristobalite and

beta-cristobalite give temperatures below those mea-sured at the surface. The existing silica vs temperaturerelation of waters from the study area is presented in

Fig. 6. A least square line through a plot of dissolvedsilica and measured temperatures for the Hisarcık springand well waters produces the equation (silica=5.94+

(0.632*t�C). This relation can be used to estimate theaquifer-temperature of the secondary reservoir. Thesilica vs temperature curve for chalcedony (Fournier,1977) and the silica versus temperature line for the

Hisarcık waters were plotted in Fig. 6. The intersectionof the curve and line at 75 �C gives the temperature ofthe secondary reservoir. It is concluded that the reser-

Table 4

Some ionic ratios of the thermal waters (in meq/l)

Samples
1 2 3 4 5 6 7 8 9 10 11 12 13
Na/Ca
0.07 0.06 0.07 0.04 0.04 0.10 0.04 0.02 0.02 0.02 0.11 0.69 1.45
Na/Mg
0.22 0.21 0.20 0.13 0.14 0.23 0.07 0.06 0.06 0.06 0.25 2.08 2.95
Na/K
6.38 6.55 6.35 4.72 5.35 2.80 7.80 10.52 11.87 24.03 9.42 19.44 8.12
Na/Cl
2.64 1.78 1.84 1.92 1.58 1.11 0.28 0.56 0.64 0.66 2.71 6.29 5.96
Ca/SO4
1.02 1.32 1.19 1.01 0.95 2.46 1.25 0.89 0.90 0.83 6.44 6.53 0.37
(Na+K)/(Cl
3.05 2.05 2.13 2.32 1.87 1.51 0.32 0.62 0.69 0.68 2.99 6.61 6.70
(Na+K)/(Ca+Mg)
0.06 0.06 0.06 0.03 0.04 0.09 0.03 0.02 0.02 0.02 0.09 0.54 1.09
(Cl+SO4)/HCO3
2.40 1.31 1.54 3.71 3.57 0.49 1.39 3.57 3.60 4.01 0.13 0.15 5.95
Ca/SO4
1.02 1.32 1.19 1.01 0.95 2.46 1.25 0.89 0.90 0.83 6.44 6.53 0.37
Table 5

Maturity index values of the thermal waters

Sample
1 2 3 4 5 6 8 9 11 12 13
MI
0.49 0.44 0.43 0.34 0.36 0.28 0.24 0.29 0.49 1.22 1.28
Table 6

Geothermometry results (�C) of hot water samples from the

study area

1 2
3 4 6 8 9 11 12 13 Ref.
SiO2 (quartz)
79 93 99 82 93 82 8 3 38 48 79 a
SiO2 (chalcedony, no steam loss)
51 65 70 53 64 53 5 5 10 20 51 b
SiO2 (quartz no steam loss)
67 82 87 70 81 70 7 1 24 34 67 b
a Fournier (1977).b Arnorsson et al. (1983).
Fig. 6. Silica versus temperature diagram.

voir temperatures of the Emet geothermal area do notexceed 100 �C.

6. Mineral saturation states

Mineral equilibrium calculations are useful in pre-dicting the presence of reactive minerals and estimatingmineral reactivity in a groundwater system. By using thesaturation index approach it is possible to predict the

reactive minerals in host rocks from the groundwaterdata without examining samples of the solid phases(Deutsch, 1997), and which minerals may precipitate

during the extraction and use of thermal fluids. Mineralsaturation indices of hydrothermal minerals that arelikely to be present in the reservoir of the geothermal

system were calculated at outlet temperature and pH bythe Solmineq.88 computer code (Kharaka et al., 1988).Results are presented in Table 7. Adularia, aragonite,calcite, chalcedony, dolomite, laumontite, microcline

and quartz are supersaturated at outlet temperature andpH values for most of the thermal waters. All thermalwaters in the study are supersaturated with respect to

calcite at sampling temperatures suggesting that CO2degassing may have occurred. Only samples 8 and 9have negative values but they are also nearly in equili-

brium with calcite. Similarly samples 11 and 12 arenearly in equilibrium with respect to chalcedony. Scal-ing of the carbonate minerals with the exception of

samples 8 and 9 is expected for the thermal waters.Travertine deposits are observed in a wide area wherethermal springs of samples 2–4 and 13 issue. When deepwells are drilled to obtain more thermal fluids for bal-

neological and heating purposes, scaling problems canbe anticipated. Gypsum and anhydrite are under-saturated at the discharge temperature for all of the

thermal waters. The rest of the minerals in Table 7 havevarious saturation indices.The state of equilibrium between water and mineral

phases is a function of temperature. Therefore satura-tion indices can be used as geothermometers (Reed andSpycher, 1984; D’Amore and Mejia, 1998). If the equi-

librium lines of a group of minerals converge this indicatesthe most likely reservoir temperature (Tole et al., 1993).To construct the log (Q/K) versus temperature graphs,saturation indices were calculated at outlet pH for var-

ious temperatures to evaluate the equilibrium states ofsome hydrothermal minerals at different temperatures(Figs. 7 and 8). A temperature interval between 25 and

125 �C was considered to apply this method for micro-cline, zoisite, laumontite, quartz, adularia and chalced-ony. Calcite, dolomite and gypsum are present in the

reservoir but are not included in the log (Q/K) graphssince they do not give reasonable results. Calcite anddolomite are always supersaturated at the investigatedtemperature interval. Another alterationmineral, kaolinite

is also supersaturated for all of the thermal waters withthe exception of sample Gobel (11). Gypsum is alwaysundersaturated for thermal waters in the study area for

the temperature range of 25–125 �C. However, some ofthe Hisarcık waters are saturated with respect to anhy-drite in the temperature range of 87–123 �C. Samples 1,

4, 8 and 9 are saturated with respect to anhydrite at 110,87, 95 and 93 �C, respectively. It could be concludedthat temperature in the secondary reservoir is between

54 �C, the highest measured spring temperature, and87 �C, the lowest anhydrite saturation temperature.Anhydrite is less soluble at higher temperatures so watercoming from depth would be undersaturated in the

cooler temperatures of the secondary reservoir.For sample 1 microcline, zoisite, laumontite and

quartz minerals tend to be near to zero (SI=0) between

Table 7

Mineral saturation index values of thermal waters at outlet conditions

1
2 3 4 6 8 9 11 12 13
Adularia
1.15 0.04 1.61 1.67 0.80 �0.67 1.08 1.80
Albite
0.17 �0.98 0.63 0.54 �0.52 �1.51 0.57 0.88
Analcime
0.69 �0.35 0.96 0.98 �0.06 0.61 1.41 1.53
Anhydrite
�0.76 �1.14 �1.01 �0.55 �1.65 �0.61 �0.52 �2.32 �1.93 �0.86
Aragonite
0.37 0.34 0.27 0.22 0.06 0.75 0.19 0.04
Calcite
0.50 0.43 0.39 0.35 0.18 �0.13 �0.06 0.88 0.32 0.14
Chalcedony
0.24 0.18 0.44 0.34 0.32 0.24 0.20 �0.12 �0.07 0.18
Diopside
�2.00 �1.42 �1.78 �2.91 �2.22 �4.25 �4.07 �1.44 �4.88 �2.47
Dolomite
1.78 1.79 1.61 1.37 1.33 0.62 0.75 2.59 1.42 1.28
Gypsum
�0.61 �1.03 �0.87 �0.36 �1.54 �0.49 �0.42 �2.10 �1.75 �0.66
Laumontite
3.26 1.57 3.98 4.12 1.99 0.69 2.94 2.34
Microcline
2.76 1.49 3.22 3.33 2.36 1.05 2.73 3.42
Quartz
0.49 0.43 0.67 0.58 0.57 0.48 0.45 0.11 0.17 0.42
Zoisite
1.19 �0.77 1.62 1.82 �0.95 �1.53 0.97 �0.18

90 and 95 �C (Fig. 7a). In Fig. 7b (sample 2) and c(sample 3) adularia, analcime and chalcedony are satu-rated at temperatures of 70–80 �C. Saturation occurs forlaumontite, quartz and microcline in the temperature

interval of 85–95 �C for sample 4 (Fig. 8a). Log Q/Kcurves of the same minerals for sample 11 intersectbetween 40 and 55 �C (Fig. 8b). However the intersec-

tions for all of the water samples in Figs. 7 and 8 occurslightly below the zero line. Intersection of curvesslightly below Q/K=0 can indicate dilution (Reed andSpycher, 1984; Palandri and Reed, 2001). Alternatively,

the Al value may be lower as suggested by Pang and Reed(1998). Dilution or low Al causes the log Q/K curves toshift downward but the intersection still shows the reser-

Fig. 7. Mineral equilibrium diagrams of samples 1, 2 and 3.
Fig. 8. Mineral equilibrium diagrams of samples 4, 11 and 12.

voir temperature. The estimated reservoir temperature ofabout 45 �C is the lowest of the samples investigated inthis study. Fig. 8c refers to the saturation indices of

sample 12 with respect to analcime, diopside, micro-cline, anhydrite, laumontite and quartz minerals. SIvalues for these minerals intersect between 90 and

105 �C. This is the highest estimated temperature forthermal waters from the study area. Saturation indexlines intersect below zero probably indicating dilution.Saturation indices of some selected alteration minerals

(Figs. 7 and 8) gave a wide temperature interval of40�105 �C. This wide temperature range may resultfrom mixing of geothermal waters with cold ground

waters.

7. Activity diagrams

Activity diagrams that are based on the estimation ofthe alteration minerals formed as a result of water–rock

interaction were used to estimate the fluid mineral equi-librium and water–rock interaction of the thermalwaters. Illustrations of phase relations were investigated

in diagrams constructed by Grasby et al. (2000) (Fig. 9).Since pH and temperature largely affect water rockinteraction, pH and the temperature measured at the

surface may not reflect the equilibrium conditions in thereservoir. The reservoir pH (Table 1) was calculated bySolmineq.88 computer code from the Ca and HCO3values assuming that the thermal waters are in equili-brium with calcite in the reservoir conditions and thatno Ca or HCO3 was lost from solution. Reservoir tem-peratures obtained in Figs. 8 and 9 were used. Activity

ratios calculated by Solmineq.88 computer code fromwater composition at estimated pH and temperaturesare plotted in Fig. 9a and b. As shown in Fig. 9a activity

data for these thermal springs plot parallel to the phaseboundary with a strong trend. Calcium and Mg con-centrations of thermal waters are also controlled by

exchange with smectite that is abundant in sedimentaryrocks (mostly as Li-bearing saponite in the borate zone)in the study area. Smectites are the dominant clay

minerals in Neogene units at the south part of Emet.The most important feature of the smectite family is thecapacity to accept and exchange hydrated cations andother polar molecules within the interlayer position. The

type of molecule present is determined by the chemicalactivity of the molecule in the environment around thesmectite (Velde, 1992). Possible reaction boundaries are

shown on a plot of (aNa/aH) versus (aK/aH) (Fig. 9b).The scatter in the data is probably due to the lack of Naand K minerals in the reservoir. Evidence of circulation

through the deeper reservoir rocks of the Emet geo-thermal field has been obliterated. Metamorphic rocksare rich in minerals containing Na and K. Processes inthe upper aquifer, composed of Neogene sediments and

carbonate rocks is dominant in determining the finalcomposition of the geothermal waters. The thermalwaters from the study area fall into the illite stability

field (Fig. 9b). Based on this figure, thermal waters arelikely to form illite in the reservoir. Field observationsshow that illites are common in the Neogene units in the

northern part of Emet. Illites that are a low-temperatureclay mineral are close to the muscovite structure andcomposition, KAl2(Si3,Al)O10(OH)2. There is some Mg

and Fe2+ in the illites due to Al substitution (Velde, 1992).

8. Conclusions

Thermal waters from the study area can be dividedinto 3 distinct types. Most of the thermal waters are Ca–

Fig. 9. Distribution of the thermal waters in activity diagrams: (a) plot of log [aCa2+/a(H+)2] versus log [aMg2+/a(H+)2]; (b) plot of

log aNa+/aH+) versus log (aK+/aH+) (constructed by Grasby et al., 2000) at 300 bar and 100 �C.


Mg–SO4–HCO3 type. Ca–Mg–HCO3 and Na–Ca–SO4type waters form the second and third groups. Geologi-cal and hydrogeochemical investigations showed thatthere are 2 reservoirs for the thermal waters from the

Emet geothermal area. Paleozoic metamorphic rocksand non-metamorphic rocks of the I

.zmir–Ankara Zone

form the deeper one. The Neogene terrestrial rocks are

the second reservoir.High SO4 contents of the thermal waters are related

to rocks and minerals in the Red Unit below the Emet

borate deposits. Dissolution of CaSO4 is an importantprocess in water–rock interaction for Emet waters. AsCaSO4 dissolves, SO4/HCO3 values increase, changing

the water from HCO3-dominant to SO4-dominant.Gypsum in the Red Unit is the likely source for the Caand SO4 of the Hisarcık waters.Aragonite, calcite, chalcedony, dolomite, laumontite,

microcline and quartz minerals are supersaturated atspring conditions. When deep wells are drilled to obtainmore thermal fluids for balneological and heating pur-

poses, calcite scaling problems will be encountered.Saturation temperatures for selected alteration mineralsrange from 40 to 105 �C. Gypsum is always under-

saturated for thermal waters in the study area for thetemperature range 25–125 �C. However, some of theHisarcık waters are saturated with respect to anhydrite

in the temperature range 87–123 �C. It could be con-cluded that temperature in the secondary reservoir isbetween 54 �C, the highest measured spring temperature,and 87 �C, the lowest anhydrite saturation temperature.

Silica geothermometers give reservoir temperaturesranging from of 50 to 99 �C. Although chalcedony andquartz geothermometers give reasonable results, amor-

phous silica, alpha-cristobalite and beta-cristobalite givetemperatures below those measured at the spring. Silicaconcentrations are controlled by more stable phases like

chalcedony and quartz. The silica versus temperaturegraph for the Hisarcık waters gives a temperature of75 �C for the secondary reservoir. This is a possibletemperature based on the anhydrite saturation calcula-

tion that requires the secondary reservoir temperatureto be 487 �C. Various geothermometers suggest thatreservoir temperatures are around 75–87 �C.

Acknowledgements

The authors acknowledge the support of Dokuz EylulUniversity Research Fund (03.KB.FEN.085). The authorswould like to thank two anonymous reviewers for thought-

ful reviews of and suggestions for the manuscript.

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