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Hydrogeochemical and Environmental Isotopic Survey in Saraykent (Yozgat) Geothermal Field, Central Anatolia, Turkey

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Saraykent geothermal field is located in Central Anatolia (Yozgat, Turkey). The hydrogeochemical and environmental isotopic data obtained there was used in the assessment of geothermal resource potential and development. According to the extended sampling programme, it included samples of Saraykent precipitation, surface water, geothermal and cold water springs for isotope and hydrogeochemical analyses performed in 2014. In order to identify some chemical and physical properties of water samples, Electrical Conductivity (EC), pH and temperature were measured in-situ. Geothermal fluid from discharged well temperature ranged from 48.2° to 73.6°C in September 2014. The major ion analysis results of geothermal and cold water springs were evaluated by using Schoeller and Piper Diagrams. When these Diagrams assessed origin relationships of waters in the field, cold and geothermal water samples were determined to demonstrate different water type. While water types of cold water samples were classified at Ca-HCO3 and Ca-SO4 type, water types of geothermal water samples were at Na-Cl and Na-SO4 type. Reservoir temperature is calculated as about 108-132 °C from geothermometers. The geothermal waters, which is δ 18 O shifted from local meteoric water line, indicate the meteoric origin and deep circulation system. Tritium content has about zero in geothermal water springs samples in Saraykent, which suggest that the circulation time is more than 60 years. This study was supported by Scientific Research Projects Coordination Unit in Hacettepe University (H.U. BAP).
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Hydrogeochemical and Environmental Isotopic Survey in Saraykent (Yozgat) Geothermal Field, Central
Anatolia, Turkey
Sevim OZULUKALE1, Sakir SIMSEK1
1Hacettepe University, Engineering Faculty, Department of Geological (Hydrogeological) Engineering, 06800,
Beytepe/Ankara
sevimozulukale@hacettepe.edu.tr, ssimsek@hacettepe.edu.tr
Keywords: Geothermal, hydrochemistry,
environmental isotopes, Saraykent, Yozgat, Central
Anatolia, Turkey.
ABSTRACT
Saraykent geothermal field is located in Central
Anatolia (Yozgat, Turkey). The hydrogeochemical
and environmental isotopic data obtained there was
used in the assessment of geothermal resource
potential and development. According to the
extended sampling programme, it included samples
of Saraykent precipitation, surface water,
geothermal and cold water springs for isotope and
hydrogeochemical analyses performed in 2014. In
order to identify some chemical and physical
properties of water samples, Electrical Conductivity
(EC), pH and temperature were measured in-situ.
Geothermal fluid from discharged well temperature
ranged from 48.2° to 73.6°C in September 2014. The
major ion analysis results of geothermal and cold
water springs were evaluated by using Schoeller and
Piper Diagrams. When these Diagrams assessed
origin relationships of waters in the field, cold and
geothermal water samples were determined to
demonstrate different water type. While water types
of cold water samples were classified at Ca-HCO3
and Ca-SO4 type, water types of geothermal water
samples were at Na-Cl and Na-SO4 type. Reservoir
temperature is calculated as about 108-132 °C from
geothermometers. The geothermal waters, which is
δ18O shifted from local meteoric water line, indicate
the meteoric origin and deep circulation system.
Tritium content has about zero in geothermal water
springs samples in Saraykent, which suggest that the
circulation time is more than 60 years. This study
was supported by Scientific Research Projects
Coordination Unit in Hacettepe University (H.U.
BAP).
1. INTRODUCTION
The Saraykent study field is located in nearly
southeast of Yozgat in Central Anatolia, Turkey
(Figure1). This study, water-rock interaction in
geothermal reservoir is used to determine the
possible origin of water in the field with findings
obtained by investigation of physical,
hydrogeochemical and isotopic properties of water
in Saraykent geothermal field.
At the beginning, previous geological works made
by some authors are reviewed (Dalkilic, et al., 2008;
Akcay, et al., 2008; Simsek, 1993; Burcak et al.,
2002).
Previous investigations mainly focus on geological,
geochemical and petrographical studies. In the
research field, there are 4 geothermal water wells
with depths ranging between 30-650 m. (YSA13,
YSA14, YSA15 and YSA16). This research utilizes
the diagram approach which is widely used for
hydrogeochemical evaluations. Circulation time of
groundwater in the reservoir is determined by tritium
(T), one of the environmental isotopes. The origin of
geothermal waters and the circulation relationship is
determined by oxygen-18 18O) and deuterium
(δ2H) isotope.
Figure 1: Location map of study field.
2. METHODOLOGY
Hydrogeochemical and isotopic techniques with
geological studies were used to define the
hydrodynamic structures of geothermal systems.
Geologic and hydrogeologic investigations were
performed in the Saraykent geothermal field in order
to establish the local geological structure. Then,
samples from hot and cold-water springs were
collected for hydrochemical, δ18O, δ2H and T
analyses of water in the study field and analyzed to
determine the origin and hydrochemical
characteristics of the geothermal waters.
Stable isotopes 18O and δ2H) were employed to
define hydrological conditions such as the origin of
the geothermal waters and the recharge mechanism
in the geothermal systems.
Tritium (T) data was used to interprete any
contributions of recent cold-water to the geothermal
fluids, and to local groundwater flow systems.
Hydrogeochemical properties in water were
analysed at Hacettepe University Water Chemistry
Laboratory. The field studies were carried out on pH,
temperature (T) and Electrical Conductivity (EC)
measurements at water samples in-situ in September
2014.
Stable isotopes 18O and δ2H) and T in water were
respectively analysed in Hacettepe University (H.U.)
International Research and Application Center
(UKAM) Stable Isotopes Laboratory and H.U.
Geological (Hydrogeological) Engineering
Department Tritium Laboratory.
3. GEOLOGY
Basement rocks of the study field are Paleozoic-
Mesozoic Metamorphics, also called Kirsehir
Metamorphics which are mainly comprised of
marble, schist, gneiss and Upper Cretaceous-
Paleocene ophiolitic unit. Some granite dikes can
also be seen in the study field. Metamorphics are
overlayed by Eocene sedimentary units and volcanic
units (Dalkilic, et al., 2008; Akcay, et al., 2008;
Simsek, 1993; Burcak et al., 2002). This Eocene
units are unconformably overlayed by Middle
Miocene-Pliocene terrestrial sediments, Pliocene
volcanics and Plio-Quaternary clastic unit. Upper
Cretaceous ophiolitic unit (melange) which is at
north of the study field is overlayed as tectonic
contact on the Eocene sedimentary unit. All of them
are unconformably overlayed by Quaternary
alluvium which is the youngest unit in the study field
and located along the Saray Stream in the middle of
the study field (Figure 2).
Figure 2: Geological map of study field (Modified from Dalkilic, et al., 2008 and Akcay, et al., 2008).
4. HYDROGEOCHEMISTRY
In this study, the hydrogoechemical properties of the
geothermal and cold spring water samples taken
from Saraykent district which is located in east of
Yozgat province (Central Anatolia) were examined
(Figure 2).
Geothermal fluid discharge temperature ranged from
48.2° to 73.6 ° C and Electrical Conductivities (EC)
of water samples ranged from 15 to 3870 μs/cm in
the field (Table 1).
The major ion analyses results of geothermal and
cold water springs were evaluated by using Schoeller
and Piper Diagrams.
A semi-logarithmic Schoeller Diagram (Schoeller,
1977), is formed to determine the similarities and
differences of origin between geothermal and cold
water springs. According to this diagram, Saraykent
geothermal water springs have similar compositions
indicating that these waters originate from the same
lithological units and show big differences from the
cold water springs. According to this diagram, the
dominant cation orders of ion contents Geothermal
fluid are Na++K+>Ca+2>Mg+2, anion orders are Cl-
>SO4-2>HCO3- and SO4-2>Cl->HCO3- (Figure 3).
The Piper Diagram has been used widely to classify
water type by major cation and anion concentrations
for tracing hydrogeochemical process of water
caused by interaction between water with reservoir
rocks (Piper, 1944). The relationship between
geothermal water springs and hydrogeochemical
evolution processes through circulation systems is
explained using the Piper Diagram. Geothermal
water and cold water samples are shown in the Piper
Diagram (Figure 4). This diagram indicates that the
same origin waters are same group with together in
the same part of the diagram.
Table 1: Analyses results of sampling points
*No analysis conducted.
As it is explained above for ion arrangements,
geothermal waters are classified as NaCl and NaSO4
type waters and these springs show the deep
circulation in the field. Cold water springs are
classified as CaHCO3 type water and these springs
show the shallow circulation in the field.
Field
Code
Explanations
Date
T
(°C)
EC
(μS/cm,
25 °C)
Concentration
Ca+2
(ppm)
Mg+2
(ppm)
Na+
(ppm)
K+
(ppm)
HCO3-
(ppm)
CO3-2
(ppm)
SO4-2
(ppm)
Cl-
(ppm)
SiO2
(ppm)
Saraykent
YSA13
Geothermal
Well
10.09.2014
73.6
3020
139.31
8.15
569.91
42.79
273.76
0.0
508.44
550.90
131.52
YSA14
Geothermal
Well
10.09.2014
68.0
3870
142.19
7.15
607.56
47.01
244.00
0.0
555.22
590.77
139.32
YSA15
Geothermal
Well
10.09.2014
67.6
3690
143.11
6.90
600.57
45.73
244.00
0.0
551.90
580.55
129.00
YSA16
Geothermal
Well
10.09.2014
48.2
2950
179.32
8.25
458.82
29.44
249.95
0.0
631.35
374.63
98.04
YSA17
Stream
10.09.2014
19.5
1071
118.95
27.39
43.92
16.08
499.90
0.0
51.96
25.43
26.81
YSA18
Spring
10.09.2014
22.1
787
128.84
18.54
33.97
4.05
398.73
0.0
81.23
10.71
55.61
Precipitation
Precipitation
Sept. 2014
15.6
15
4.03
0.19
0.22
0.29
15.25
0.0
0.41
0.25
*
Figure 3: Chemical analysis of waters in the study field plotted on the Schoeller Diagram (Sampling: September 2014).
Geothermal waters have heat transfer in contact with
rocks until coming to surface and thus have lower
temperatures than the reservoir temperature. Thus,
reservoir temperatures of geothermal waters are
calculated by geothermometer methods.
Reservoir temperature of Saraykent geothermal field
was estimated by geothermometer equations
proposed by some authors. Position of geothermal
waters in Na-K-Mg diagram proposed for cation
geothermometers by Giggenbach (1988) indicate
immature waters. For that reason, more reliable
results for prediction of reservoir temperature are
assumed to be silica geothermometers than cation
geothermometers. Possible reservoir temperature
according to Fournier (1977) and Arnórsson et al.
(1983) is calculated as about 108 - 132°C based on
chalcedony geothermometers for Saraykent
geothermal spring.
Figure 4: Piper Diagram showing the chemical compositions of waters (Sampling: September 2014).
Cold Waters
Geothermal
Waters
5. EVALUATION OF THE ENVIRONMENTAL
ISOTOPE ANALYSIS RESULTS
Hot and cold water samples were collected for δ18O,
δ2H and T analyses of water in the study field (Table
2). Stable isotopic analyses δ18O and δ2H of water
were carried out to determine the origin of
geothermal waters. While cold water sample points
are located along this Local Meteoric Water Line
(LMWL), geothermal waters have apparent δ18O
shift from LMWL (Figure 5). This shows that
geothermal system is fed by meteoric precipitations
and has a deep circulation of groundwater with high
temperature in the study field.
T contents of Saraykent geothermal waters ranged
from 0.00 to 0.40 TU. Saraykent geothermal waters
have almost zero tritium content. Low tritium
contents of geothermal waters show that the springs
are fed by groundwater having a relatively long term
passing time and have a deep circulation of
groundwater flow system in the study field (Figure
6).
6.CONCLUSIONS AND RECOMMENDATION
The result of hydrogeochemical and environmental
isotope analysis performed for determining
properties of the Saraykent geothermal field are
listed below:
Cold water springs are classified as CaHCO3 type
water and these springs show the shallow
circulation in the field.
Geothermal waters are classified as NaCl and
NaSO4 type waters and these springs show the
deep circulation in the field.
Reservoir temperature is calculated as about 108-
132 °C based on chalcedony geothermometers
for Saraykent geothermal waters.
Geothermal waters have apparent δ18O shift
from LMWL. This shows that geothermal
system is fed by meteoric precipitations and has
a deep circulation of groundwater with high
temperature in the study field.
Low tritium contents (0.00 to 0.40 TU) of
geothermal waters are shown that the springs are
fed by groundwater having a relatively long-
term circulation time and have a deep
circulation of groundwater flow system in the
study field.
The geothermal waters could be utilized
widespread for spas and other integrated
geothermal applications (balneology, thermal
tourism, heating etc.) to provide healthy, clean
and sustainable use of geothermal waters in the
study field.
Table 2: Environmental Isotope Analyses Results
* Sampling: August 2015.
Field
Code
Explanations
Date
T (°C)
pH
EC
(μS/cm,
25 °C)
T (TU)
δ18O
δ2H
Saraykent
YSA13
Geothermal Well
10.09.2014
73.6
7.16
3020
-10.35
-91.15
0.00
YSA14
Geothermal Well
10.09.2014
68.0
7.16
3870
-9.85
-93.45
0.40
YSA15
Geothermal Well
10.09.2014
67.6
7.50
3690
-9.86
-93.73
0.00
YSA16
Geothermal Well
10.09.2014
48.2
7.67
2950
-10.91
-95.06
0.00
YSA17
Saray Stream
10.09.2014
19.5
7.89
1071
-10.3
-77.67
6.67
YSA18
Spring
10.09.2014
22.1
7.40
787
-11.36
-79.37
7.16
Precipitation
Precipitation
Sept. 2014
15.6*
7.84
15
-8.71
-52.18
7.83*
Figure 5: Plot of δ18O and δ2H for geothermal and cold waters of the Saraykent field (Sampling: September 2014; GW:
Geothermal Well).
Figure 6: Hydrogeological cross section along A-A’and A'-A’’ (Sampling: September 2014; * Sampling: August 2015).
REFERENCES
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ACKNOWLEDGEMENTS
This study was supported by Scientific Research
Projects Coordination Unit in Hacettepe University
(H.U. BAP Project ID: 014D09602007). The authors
wish to thank MTA General Directorate, Yozgat
Governorate, Saraykent District Governor, and the
isotopic and hydrochemical analysis of water
samples carried out Prof. Dr. M. Ekmekci at UKAM
Stable Isotopes Laboratory of Hacettepe University,
Hydrogeology Laboratory staffs of Hacettepe
University Prof. Dr. S. Bayari and Hydrogeology
Laboratory staffs of Hacettepe University. The
authors also would like to thank K. Koc for his help
in some drawings and D. Ozbek and M. Ozulukale
for their help in the field.
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Isotope survey of geothermal systems of Central Anatolia
  • S Simsek
Simsek, S.: Isotope survey of geothermal systems of Central Anatolia, Hacettepe University International Research and Application Center for Karst Water Resources. Ankara, HU-IAEA Report-Research Contract 6716/RB, (1993).
Geological Maps of Turkey in 1: 100.000 scale, Yozgat I-34 Sheet
  • A E Akcay
  • M Donmez
  • H Kara
  • A F Yergok
  • K Esenturk
Akcay, A. E., Donmez, M., Kara, H., Yergok, A. F. and Esenturk, K.: Geological Maps of Turkey in 1: 100.000 scale, Yozgat I-34 Sheet, MTA Publ., Ankara, No. 81 (2008) [in Turkish].