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Hydrogeochemical Investigation of Yerköy (Yozgat-Turkey) Geothermal Waters

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Yerköy geothermal area is located in the Central Anatolia of Turkey. Thermal water springs which have been used for spas for many years have temperatures of 41-45 °C and flow rates of 0.5-2.5 l/s in the area. Geothermal reservoir units are rhyolites, altered granodiorites fractured and faulted zones in the field. Eocene and Oligocene sediments are caprock and overlie unconformably on rhyolites and granodiorites. Quaternary alluvium units overlie unconformably these sediments. Normal slip faults, which are generally NW-SE and NE-SW trending, developed in the region depending on stress tectonics in Neogene and Quaternary. Thermal water springs discharge from the intersection of these faults. Between the years 1992 and 1997, seven shallow wells were drilled ranging from 59 to 262 m with a maximum temperature of 47 °C, in order to the development of spa tourism. For the purpose of investigation of the geothermal potential of the area and development of district heating, two exploration/production wells, YK-2 and YK-3, were drilled ranging from 550 to 750 m, respectively in 2006. The maximum bottom-hole temperatures were measured between 67 and 72°C, respectively in these wells. The thermal waters are alkali sodium chloride type and have high specific electrical conductivities. Hydrothermal alteration minerals, such as chalcedony, quartz, albite, microcline, shows the mineral equilibrium temperature between 60 and 100 °C. According to the isotopic data, thermal waters are meteoric and have a positive δ 18 O shifts because of water-rock interaction. The low tritium values indicate that thermal waters recharged by precipitation before 1952. As a result of these studies, hydrogeochemical model has been evaluated for hydrothermal system of the area.
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European Geothermal Congress 2016
Strasbourg, France, 19-24 Sept 2016
1
Hydrogeochemical Investigation of Yerköy (Yozgat-Turkey) Geothermal
Waters
Elif Yilmaz Turali1, Sakir Simsek1, Kemal Koc1
1Hacettepe University, Engineering Faculty Department of Geological (Hydrogeological) Eng., Beytepe, Ankara
elifylmz@hacettepe.edu.tr
Keywords: Yerköy-Yozgat, Geothermal,
Hydrogeochemistry, Geothermometers, Conceptual
Model.
ABSTRACT
Yerköy geothermal area is located in the Central
Anatolia of Turkey. Thermal water springs which
have been used for spas for many years have
temperatures of 41- 45 °C and flow rates of 0.5-2.5 l/s
in the area. Geothermal reservoir units are rhyolites,
altered granodiorites fractured and faulted zones in the
field. Eocene and Oligocene sediments are caprock
and overlie unconformably on rhyolites and
granodiorites. Quaternary alluvium units overlie
unconformably these sediments. Normal slip faults,
which are generally NW-SE and NE-SW trending,
developed in the region depending on stress tectonics
in Neogene and Quaternary. Thermal water springs
discharge from the intersection of these faults.
Between the years 1992 and 1997, seven shallow
wells were drilled ranging from 59 to 262 m with a
maximum temperature of 47 °C, in order to the
development of spa tourism. For the purpose of
investigation of the geothermal potential of the area
and development of district heating, two
exploration/production wells, YK-2 and YK-3, were
drilled ranging from 550 to 750 m, respectively in
2006. The maximum bottom-hole temperatures were
measured between 67 and 72°C, respectively in these
wells. The thermal waters are alkali sodium chloride
type and have high specific electrical conductivities.
Hydrothermal alteration minerals, such as chalcedony,
quartz, albite, microcline, shows the mineral
equilibrium temperature between 60 and 100 °C.
According to the isotopic data, thermal waters are
meteoric and have a positive δ18O shifts because of
water-rock interaction. The low tritium values indicate
that thermal waters recharged by precipitation before
1952. As a result of these studies, hydrogeochemical
model has been evaluated for hydrothermal system of
the area.
1. INTRODUCTION
The study area is located 34 km SW of the province of
Yozgat and 5 km to Ankara-Yozgat highway (Fig.1).
In the past, there was two thermal springs (Güven and
Camur springs) for spa uses in the area. Güven spring
had a temperature of 41°C with a flowrate of 0.5 l/s.
Camur spring temperature were 45 °C (Simsek, 1993;
Gündüz, 1993). Between the years 1992 and 1997,
seven shallow wells were drilled ranging from 59 to
262 m. After the drilling study, Güven thermal spring
was dry (Gündüz, and Özten, 1994).
In 1992, two shallow wells were drilled by State
Hydraulic Works (DSI-1 and DSI-2) with an average
temperature of 41 °C and flowrate of 2 l/s, for
increasing the water flowrate for thermal spas. In
1993, YK-1 well was drilled by General Directorate of
Mineral Research and Exploration (MTA) at the depth
of 250 m with a 47°C temperature and 10 l/s artesian
flowrate (Gündüz, 1993; Gündüz, and Özten, 1994).
Also, there are four production wells in the area for a
privately operated Koyunbasoglu spa, which have an
average temperature of 40.3 °C and flowrate of 2.5 l/s
(Canik, 2004). This spa is located 600 m west of
Güven spring. Two deep wells YK-2 and YK-3 were
drilled by Yozgat Governorship to supply hot water
for bathing and determine potential of district heating,
in 2006. Depths of the YK-2 and YK-3 wells are
between 550 and 750 m, flowrates are 45 and 55 l/s
and temperatures are 54.5 and 56.5 °C, respectively.
The maximum bottom-hole temperatures were
measured between 67 and 72°C in YK-2 and YK-3
wells, respectively (Simsek et al., 2006).
There is a hot water spring and spa in Cicekdag-
Bulamacli, located about 3 km SW of Yerköy
geothermal area. This spring has a temperature of 43.8
°C and flowrate of 2.5 l/s. Its water chemistry was
compared with Yerköy geothermal waters.
In this study, water samples of cold and thermal
waters were collected and analysed for major ion
constituents, isotopic composition and tritium activity.
Chemical analyses and 3H isotopes were analyzed in
Hacettepe University (HU) Water Chemistry
Laboratory in Hydrogeology Engineering Department
and environmental isotopes of deuterium (δ2H) and
oxygen-18 (δ18O) were analyzed in the Scientific and
Technological Research Council of Turkey
(TUBITAK) Marmara Research Center (MAM).
Based on these data, it was carried out to present a
conceptual hydrothermal model of Yerköy geothermal
area.
2. GEOLOGY AND HYDROGEOLOGY
2.1 Geological settings
Yilmaz Turali et al.
2
The basement rocks in the field are granites and
rhyolites (Figure 1). Granites known as Yozgat
granitoid (Ky), refer to intrusives of Central Anatolia,
have calc-alkaline compound and is outcrop as
batholith, pluton, vein in the field. Rhyolites are a
member of Kotudag Volcanics (Kyk) that consist of
rhyolites, rhyodacites, granite porphyry etc. Kotudag
Volcanics outcrop south and east of study area
(Sarikaya Hill) and contact with Yozgat granitoid in
the southeast of the area. The formation of intrusive
rocks is between early Cretaceous-Late Eocene (Ketin,
1955, Büyükönal, 1977).
Eocene sediments (Te) consisting of alternation of
conglomerate, sandstone, marl with sand and marl
overlie unconformity with Kotudag Volcanics.
Oligocene unit (Deliceirmak Formation, Td) that
covers conformably Eocene sediments consists of
evaporitic (gypsum and halite) and terrestrial
sediments (alternation of conglomerate, sandstone)
and is outcrop north of the area which covers wide
portions.
Quaternary terrace, alluvium and travertine are the
youngest rocks in the study area. Terrace covers in the
south-eastern part of Yerkoy. Travertines are located
around hot and mineral water springs in the area that
is a little portions.
Yerköy geothermal area is controlled by mainly NW-
SE and NE-SW trending faults which normal and step.
Thermal waters emerge from location that these faults
closer each other.
2.2 Hydrogeological settings
Basement rock rhyolites and altered granodiorites
which have secondary porosity with tectonic
movements are permeable. These rocks are the hot
water reservoir in the field. Eocene, Oligocene,
Pliocene sediments which are alternation of
evaporates, limestone, marl, limestone with clay and
sandstone, are cap rock with low permeability. Also,
limestone, sedimentary rocks (mainly limestone) in
fault zone and alluviums in the Delice Stream bed
consisting of conglomerate, sand and clay are
important aquifer for cold water.
Yerköy geothermal area is located in Delice basin
covers an area of approximately 9160 km2. The
average annual air temperature within the basin is 9.6
ºC and average rainfall within the basin is 408.16
mm/year. Evapotransporation within the basin were
determined to be 337 mm/year (Yilmaz, 2007).
Figure 1: Geological map of Yerköy and its vicinity and locations of wells, springs and water sampling
Yilmaz Turali et al.
3
3. HYDROGEOCHEMISTRY
Geothermal and cold water samples were collected in
the geothermal area to determine the physical,
chemical, and isotopic compositions of waters. The
sample locations are shown in Figure 1. Temperature,
pH and EC were carried out on site. The physical and
chemical parameters are provided in Table 1.
3.1 Sampling points
Geothermal water samples were collected from wells.
These wells are Koyunbasoglu spa well (S-1),
Bulamacli spa well (S-2) and the last drilled
geothermal wells of YK-2 and YK-3. Present, hot and
mineral water springs do not observed in the field due
to drilling works. However, these two old springs
(Güven (S-3) and Camur (S-4) springs) have been
examined with thermal well samples (Gündüz, 1993).
Cold waters were collected from three springs (C-1,
C-3 and C-4), two shallow wells (C-2 and C-5) and
Delice Stream (C-6).
3.2 Chemical and physical characteristics of waters
In situ measured temperatures of geothermal waters
are between 40.3 and 56.2 °C and electrical
conductivities (EC) are between 6470 and 17320
µS/cm, pH are between 6.93 and 8.51 (Table 1).
Measured temperatures of cold waters are between 13
and 19.9 °C, electrical conductivities are between 678
and 6970 µS/cm and pH are between 7.28 and 7.94.
According to the ionic compound, sodium the most
abundant cation and chloride is the most important
anion in thermal waters. Geothermal waters are type
of Na-Cl.
Cold waters have three subgroups, including types of
Na-Cl (C-1), Na-HCO3 (C-3, C-4 and C-6), and Na-
SO4 (C-2 and C-5). The relations of waters were
examined by semi-logarithmic and triangular diagrams
(Fig.2). According to the diagrams, the waters are
three different types, including Yerköy thermal waters
(S-1, S-3, S-4, YK-2, YK-3), Bulamacli water (S-2),
and cold waters (C-2, C-3, C-4, C-5 and C-6). Cold
water spring of C-1, which has highly salinity, differs
from other cold waters. This sample and Bulamacli
spring shows a mixing between cold and thermal
water (Figure 2a).
Chloride and boron relationship of thermal and cold
waters were examined with a log-log diagram (Figure
3). According to the Figure 3, the chlorides and boron
are well correlated on a linear trend and S-2 and C-1
samples indicate a mixing between cold and thermal
waters.
The diagrams indicate that Yerköy geothermal waters
are highly salinity sodium-chloride type and have
different composition from Bulamacli thermal water.
Table 1: Chemical and physical properties of Yerköy waters
* Wellhead temperatures; ** Gündüz, 1993
Samp
No
Sample
Date
T
(ºC)
EC
(µS/cm)
Na
K
Ca
Mg
HCO3
Cl
SO4
SiO2
B
C-1
Mineral spring
July
2006
19.9
6970
1095.6
17.5
460.2
10.9
101.9
2048.6
792.6
16.4
3.5
C-2
Cold spring
July
2006
15.7
2360
282.3
6.5
174.9
56.3
279.8
293.3
684.8
20.0
1.0
C-3
Cold spring
July
2006
18.9
678
70.9
1.0
60.8
14.4
254.8
21.3
46.8
15.3
0.2
C-4
Cold spring
July
2006
19.0
860
101.3
1.3
68.1
19.7
410.7
18.7
66.4
13.8
0.3
C-5
Cold well
July
2006
13.0
1470
187.8
2.9
76.3
56.8
353.5
69.6
402.6
19.3
0.4
C-6
Delice Stream
July
2006
22.0
1130
116.8
7.01
81.3
33.0
222.9
136.7
163.7
12.2
0.4
S-1
Koyunbasoglu
Spa well
July
2006
41.2*
19440
3745.4
102.5
1673.8
2.5
38.2
9380.1
270.6
22.8
9.2
S-2
Bulamacli Spa
well
July
2006
43.8
7160
1357.5
91.7
220.9
10.3
817.4
2062.3
365.9
80.4
3.9
S-3**
Güven Spa
spring
June
1993
47
11760
2100
60
821
61
55
4418
428
30
6.6
S-4**
Camur Spa
spring
June
1993
45
17100
2900
70
1222
12.2
43
6700
359
22
7.4
YK-2
Geothermal
well
March
2006
54.5*
16660
2905.9
77.9
1334.2
3.3
11.5
6812.3
316.4
19.9
7.0
YK-3
Geothermal
well
July
2006
56.2*
13610
2243.0
63.9
929.9
3.9
60.5
5332.1
407.7
26.8
5.6
Yilmaz Turali et al.
4
Figure 2: Semi-logarithmic Schoeller (a) and Triangular diagram (b) for cold and thermal water samples in
Yerköy geothermal area
Figure 3: The chlorideboron relationship in
thermal and cold water in Yerköy
geothermal area
3.2 Geothermometers
The Na-K-Mg triangular diagram of Giggenbach
(1988) indicates the equilibrium temperatures of
minerals containing these elements (Fig. 4). According
to the diagram, sample S-1 is as fully equilibrated
waters, the other samples (S-2, S-3, S-4, YK-2 and
YK-3) are as partially equilibrated waters and
indicating reservoir temperature between 77 and 214
ºC. But, it was considered that reservoir temperature,
which estimates with cation geothermometers, give
relatively higher value because of high salinity
solution.
According to the quartz and chalcedony equations of
Fournier (1977), Fournier and Potter (1982),
Arnorsson et al. (1983), D’Amore and Arnorsson
(2000), reservoir temperatures were calculated up to
92 ºC by chalcedony and 85 ºC by quartz
geothermometers.
3.3 Solution-mineral equilibrium
Mineral equilibrium diagrams were formed by
calculating saturation indexes of minerals at various
temperatures. The mineral equilibrium calculations
were performed using Watch computer program of
Bjarnason (1994). The mineral equilibrium diagrams
represent saturation indexes (log (Q/K)) versus
temperature of thermal waters of S-1, S-2, YK-2, and
YK-3 for main secondary minerals (Fig.5). According
to the diagram, equilibrium temperatures are between
80 and 100 °C for S-1 water, 60 and 80 °C for YK-2,
60 and 100 °C for YK-3, and 100 and 140 °C for
Bulamacli spring (S-2). As it can be seen in Figure 5,
the saturations of albite (NaAlSi3O8), K-feldspar, and
quartz minerals, which are main rock forming
minerals in igneous rocks, indicate that the aquifer
rock is possibly granite or rhyolites. Thermal waters
are close to the equilibrium with chalcedony, quartz
minerals and feldspar such as albite and microcline.
Figure 4: Na-K-Mg ternary diagram of Yerköy
thermal waters
Yilmaz Turali et al.
5
Figure 5: Diagrams showing the change in
calculated saturation indexes (log Q/K) of
various minerals as a function of
temperature.
3.4 Isotopic characteristics of waters
Environmental isotopes of deuterium (δ2H) and
oxygen-18 18O) ratios are good indicators of water
origins. The isotope analyses were performed by
TUBITAK, MAM. The oxygen-18 values of waters are
between -11.63 and -9.34 ‰. The deuterium values of
these waters are between -83.95 and -67.56 (Table
2).
According to this environmental isotopic analysis, hot
waters are of meteoric origin and recharged by
precipitation from higher elevations in accordance
with cold water samples (Figure 6). An oxygen-18
shift is observed as 2.4 δ18O in YK-3 geothermal
well water. This shift indicates a deep circulation and
water-rock interactions. Also, Figure 5 shows that
Bulamacli thermal water (S-2) is recharged by
precipitation from higher elevations in accordance
with Yerköy thermal waters.
Table 2: Tritium and stable isotope content of
samples in the study area
Sample
No
Sampling
Date
δ18O
(‰SMOW)
δ2H
(‰SMOW)
Tritium
(TU)
C-1
July 2006
-9.49
-76.84
3.81
C-2
July 2006
-8.73
-64.22
6.48
C-3
July 2006
-9.61
-67.56
5.54
S-1
July 2006
-10.43
-78.09
0.39
S-2
July 2006
-11.63
-90.02
0.81
YK-3
July 2006
-9.34
-83.95
1.1
Figure 6: δ18O - δ2H diagram of Yerköy waters
Tritium values of cold waters (C-1, C-2, C-3, C-4, and
C-5, and C-6) are an average 5.53 tritium units. These
waters are modern water. The tritium values of
thermal waters are about zero and indicate that thermal
waters recharged by precipitation before 1952 (Clark
and Fritz, 1997).
4. CONCLUSIONS
In this study, a hydrothermal conceptual model of the
geothermal field has been developed by
hydrogeochemical study (Figure 7).
According to the hydrogeochemistry study, three main
water types were determined based on their chemical
composition in Yerköy geothermal area. Thermal
waters are Na-Cl type. However, Yerköy geothermal
water chemistry is different from Bulamacli
geothermal water. Bulamacli water is more diluted
with cold water. Cold water types are Na-Cl, Na-
HCO3, and Na-SO4 type.
According to the silica geothermometers and mineral
equilibrium calculations, temperatures have been
estimated up to 100 ºC, which are closer to the
measured as 72 ºC at the bottom hole (750 m) in YK-3
Yilmaz Turali et al.
6
well, drilled in 2006 m. δ18O-δ2H values show that
positive δ18O shifts because of water-rock interaction
and it is indicates a deep circulating system. The low
tritium values indicate that thermal waters recharged
by precipitation before 1952.
Yerköy hydrothermal system mainly recharged from
the Kotudag volcanic (Sarikaya Hill) and Eocene,
Oligocene, Pliocene formations. Meteoric waters are
infiltrated from these units into underground and
heated by heat flux and thermal gradient, and rises by
convection. These waters rise along the main faults
and fractures and stored in the Cretaceous Kotudag
Volcanic member and Yozgat granitoid rocks and
also, Eocene limestone that are assumed as the
shallow geothermal reservoir (Fig. 7).
When thermal water outcrops, it is mixed by cold
water in Eocene conglomerate and limestone.
Volcanic units like rhyolites, tuff, and agglomerate
that no fault and fractures zones and Eocene,
Oligocene, Pliocene sediments, which are alternation
of limestone, marl, limestone with clay and sandstone,
are cap rocks with low permeability. Thermal waters
in the study area have highly salinity due to these
waters are acquired Na-Cl by water-rock interactions
during infiltrating and rising into Eocene, Oligocene,
Pliocene formations consisting of gypsum and halite.
A large-scale utilization is carried out for the
greenhouse, tourism and balneological uses in the
field. In case of using the thermal water for
greenhouse heating, it is certainly should be reinjected
because of high salinity.
Figure 7: Schematic conceptual model of Yerköy hydrothermal system
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Acknowledgements
The authors wish to thank the Governorship of Yozgat
and District Governorship of Yerköy Staffs for their
support and thank for analyses of water samples to
Hacettepe University Laboratory and TUBITAK
MAM Laboratory Staffs and chemists.
ResearchGate has not been able to resolve any citations for this publication.
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Geology, Hydrogeology, Drilling and Testing Consultancy Report of YK-2 and YK-3 Wells in Yerköy
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  • K Koc
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Simsek, S., Koc, K., Yilmaz E.: Geology, Hydrogeology, Drilling and Testing Consultancy Report of YK-2 and YK-3 Wells in Yerköy, Hacettepe University, Yozgat Governorship Office and District Governorship of Yerkoy, (2006), (in Turkish).
Report of Geology-Hydrogeology and Geophysics Study of Yerköy Güven Spa
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Canik, B.: Report of Geology-Hydrogeology and Geophysics Study of Yerköy Güven Spa (Uyuz Bath), District Governorship of Yerkoy, (2004) (in Turkish).
Isotope Survey of Geothermal Systems of Central Anatolia
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Simsek, S.: Isotope Survey of Geothermal Systems of Central Anatolia, Hacettepe University International Research and Application Center for Karst Water Resources, HU-IAEA Research Contract 6716/RB Final Report, Ankara, (1993).