Journal of Geochemical Exploration 104 (2010) 97–104

Contents lists available at ScienceDirect

Journal of Geochemical Exploration

j o u r n a l h o m e p a g e : w w w. e l s ev i e r. c o m / l o c a t e / j g e o ex p

Fluid geochemistry of the Methana Peninsula and Loutraki geothermal area, Greece
E. Dotsika a,⁎, D. Poutoukis b, B. Raco c
a
National Center for Scientific Research “Demokritos”, I.M.S., 15310 Aghia Paraskevi Attikis, Greece
b
General Secretariat for Research and Technology, Mesogion 14-18, 11510 Athens, Greece
c
Institute of Geosciences and Earth Resources, Via G. Moruzzi 1, 56124 Pisa, Italy

a r t i c l e i n f o a b s t r a c t

Article history: A geochemical survey on the thermal fluids released by the volcanic/geothermal system of Methana Peninsula
Received 25 February 2009 and Loutraki area was undertaken.
Accepted 4 January 2010 The Loutraki area is found in the southern part of Athens and the Methana volcano in the north-eastern part of
Available online 18 January 2010
Peloponnesus, which is characterized by high salinity waters. Chemical and isotopic contents were used for the
investigation of the origin of thermal water, for the estimation of the mixing process between meteoric,
Keywords:
Geochemistry
magmatic and sea water involved in the deep geothermal systems and for the evaluation of the deep aquifer
Stable isotope of water temperature.
Sulfate The chemical and isotopic data of the thermal Cl-rich water springs of Methana suggest that they are fed by
Geothermometry thermal water mixed with local groundwater and seawater respectively. The parent hydrothermal liquid is a
Methana mixture of local groundwater (∼ 43%), seawater (∼ 34%) and arc-type magmatic water (∼ 23%).
Loutraki The chemical and isotopic data of the thermal HCO3-rich water springs of Loutraki samples indicate a purely
Greece meteoric origin.
Assessments from chemical and isotopic geothermometer applied on the thermal waters springs suggest the
probable existence of a deep geothermal reservoir of middle enthalpy (150 °C) a Methana and low enthalpy
(80 °C) in Loutraki area. However, the contribution of marine solutions to the geothermal fluids of Methana
and Loutraki area is one of the main cases for the disturbance of the chemical and isotopic geothermometers
rendering these calculated temperatures questionable.
© 2010 Elsevier B.V. All rights reserved.

1. Introduction 29° to 32 °C. The thermal spring EOT represents the main discharges of
geothermal water at Methana that emerges into pool along the beach.
Methana is found at the north-eastern coast of Peloponnesus in Pausanias thermal water discharges from volcanic rock practically
Greece. It is the westernmost dormant but geodynamically and into the seawater while Agios Nikolas thermal spring (also at
hydrothermally active volcanic system of the South Aegean volcanic Methana) is located on a hill, approximately 200 m from the coast.
arc. The Aegean volcanic arc also comprises, from west to east, Egina, In Methana, the thermal waters (EOT) have been well known since
Loutraki–Soussaki, Milos, Santorini, Kos and Nisyros. In the Aegean antiquity. Scripts by Pausanias, Strabo and Ovid exhibit their presence
Sea, this arc represents the youngest example of volcanism and the and fame during ancient times. The first modern installations operated
only one that is related to the collision between the African and the in 1906.
Eurasian plates (Mckenzie, 1970; Lort et al., 1974). This process takes In Loutraki area, three samples were analyzed (1, 2, and 3). The first
place since the Pliocene and is responsible of volcanism and seismicity reference to Loutraki waters was by Xenophon. These sources mention
(Makris, 1978). Extensive surface hydrothermal and volcanic activity that Sylas was cured with that water and mouth to mouth the secret
is present in all these islands and Methana peninsula. The most recent was spread to everyone in the Roman Empire. “Thermes”, modern
volcanic activity on Methana dates back to 230 BC. Loutraki, is considered the oldest Greek thermal spring city. The first
In general, samples are located in three main sites; Methana, municipal “hot spring store” opened in 1874. The temperature of
Loutraki and Poros. A significant number of thermal water springs thermal water springs emerging a Loutraki is 32–33 °C. Today, the
emerge in Methana area: Agios Nikolas, EOT and Pausanias. The thermal waters at Methana and Loutraki are mainly used for
surface temperature of hot water springs in Methana peninsula (EOT hydrotherapy. Finally, two fresh water samples from Poros area
and Pausanias), which present high salinity at Methana, ranges from were also added in this study. This paper investigates the origin of
thermal waters at Methana and Loutraki and of their mineralization
and the temperatures of deep geothermal reservoirs. This study
⁎ Corresponding author. Tel.: + 30 210 6503305; fax: +30 210 6519430. advances furthermore in relation to the study of Dotsika et al. (2009),
E-mail address: edotsika@ims.demokritos.gr (E. Dotsika). as it has incorporated a complete series of samples for a wider area in

0375-6742/$ – see front matter © 2010 Elsevier B.V. All rights reserved.
doi:10.1016/j.gexplo.2010.01.001
98 E. Dotsika et al. / Journal of Geochemical Exploration 104 (2010) 97–104

Methana. The older publication dealt with only three samples for the peninsula (Fig. 1). 15 samples were collected for chemical analyses
specific region, which also carried a great analytical uncertainty, as and isotopic determination of δ2H and δ18O values of water (in all
mentioned then. Moreover, the present work includes more sampling samples) and tritium, δ13C, δ34S and δ18O (SO4) values of dissolved
sites (23 samples in total), it is based on further analyses (major ions, inorganic carbon and sulfate (in selected samples). The samples of
B, Li, tritium, δ34S, δ18OSO4), geothermometry and also samples from water collected for this study (Tables 1 and 2) are distributed as
close vicinities (Loutraki geothermal area and Poros). follows: 3 from Loutraki (samples 1 to 3), 15 from Methana (4 to 17),
2 from Poros (18 and 19), one from rain water (20) and two from sea
2. Sampling and analysis water (21 and 22).
Temperature, pH, conductivity and alkalinity were measured
Water samples of springs, were collected at Methana and Loutraki directly in the field. Filtered (0.45 µm), acidified (with HNO3 1:1)
and fresh waters from Poros that is situated close to Methana water samples were collected for determination of cations and SiO2.

Fig. 1. Schematic map of Methana and Loutraki area showing the location of sampling sites. Sampling sites include: PA: Pausanias (samples 9–12); AN: Agios Nikolaos (samples 4–8);
EO: EOT (samples 13–16); LO: Loutraki (samples 1–3); PO: Poros (samples 18, 19). ME in the inset picture indicates Methana peninsula. Sample numbers are keyed in Table 1.
 E. Dotsika et al. / Journal of Geochemical Exploration 104 (2010) 97–104 99

Table 1
Chemical compositions (mg/L) of waters from springs and boreholes.

No. Sampling site T pH Cl− Br− HCO3 NO3 SO2−

4 Ca2+ Mg2+ Na+ K+ Li B SiO2
°C mg/L mg/L mg/L mg/L mg/L mg/L mg/L mg/L mg/L mg/L mg/L

1 LOUTRAKI-EOT 1991 32 7.3 750 3.1 305 12 180 121 103 408 17 0.1 0.4 14
2 Karantani 1991 33 7.2 770 3.4 305 5 170 119 103 403 15 0.1 0.3 14
3 Posimo 1991 20 7.6 16 0.1 366 10 2 8 63 20 5 23
4 METHANA Ag. Nikolaos a 35 5.9 4700 7.4 1110 66 610 170 60 2390 85 0.7 1 133
4A Ag. Nikolaosa 35 5.9 4400 7 1150 70 600 230 80 2440 80 130
5 Ag. Nikolaos 1991 35 5.9 3370 7.4 1106 65.7 610 172 58 2385 84 133
6 Ag. Nikolaos 1996 37 6.7 4650 8 1280 63 710 400 320 2690 205 0.6 3 130
7 Ag. Nikolaos 1997 35 6.5 4600 7.8 1140 60 420 375 300 2280 90 0.8 2.6 150
8 Ag. Nikolaos 1998 36 7.8 3950 8 1220 60 770 340 270 2460 180 0.6 1.1 130
9 Pausanias 1991 32 5.6 20,470 70.5 1647 10.6 2730 1480 1690 11,400 380 0.5 7 72
10 Pausanias 1996 33 6.7 21,050 70 1700 0 2700 960 1350 11,900 580 0.6 6.3 72
11 Pausanias 1997 29 6.1 18,500 65 1570 1450 995 1140 9600 340 0.6 7.4 90
12 Pausanias 1998 32 6.1 19,500 65 1650 0 2700 940 1300 11,600 560 0.6 6.2 75
13 EOT 1991 33 5.5 19,300 67 1010 11 2830 1140 1750 10,920 440 2 9.5 44
14 EOT 1996 31 6.1 21,015 70 920 0 2260 890 1790 10,600 470 1.4 9.4 47
15 EOT 1997 31 7 22,000 70 1090 0 3100 950 1300 12,050 750 1.3 8.3 42
16 EOT 1998 32 6 21,580 68 1920 0 2300 950 1270 11,100 470 1.5 9.8 52
17 Posimoa 18 7.5 80 140 12 22 30 10 40 5 23
18 POROS spring 21 7.4 35 460 0 35 120 30 20 0.6 0.02 0 22
19 Borehole 19 7 132 465 0 30 61 85 40 2.5 0.01 0 41
21 Sea water 1991 22,550 70 165 0 2950 485 1540 12,650 450 0.2 4.7 2
22 Sea water 1997 22,950 70 210 0 3050 465 1440 12,800 510 0.2 5 2
a
Dotsika et al. (2009).

Untreated samples were collected for analyses of anions. The major The δ18O values of water in the samples were determined from
chemical constituents were analyzed according to the standard CO2 equilibrated with the water (Epstein and Mayeda, 1953). The δ2H
methods described in Apha (1989). Na+, K+, Ca2+, Mg2+ and SiO2 values of water were measured from H2 generated by the Zn-
contents were determined by atomic absorption. Anions were reduction method (Coleman et al., 1982). The dissolved inorganic
analyzed by ion chromatography. The B content is determined carbon in the water, for the analysis of 13C, was collected as BaCO3
photometrically using the curcumin method. The samples are precipitate. The dissolved SO2−4 in the water samples was precipitated
acidified and evaporated to dryness (at 55 °C) in the presence of as BaSO4 for the analysis of S isotopic compositions (Rafter, 1957). The
curcumin. The precipitate is red in colour and can be dissolved in ethyl measurement of tritium was done by liquid scintillation (IHP-V,
alcohol. The red alcoholic mixture is photometrically determined 2000). Determination of the different isotope ratios has the following
at 540 nm. (404A Method of Standard Methods for the Examination precisions: ±1‰ for δ2H and δ34S; ±0.2‰ for δ18O; and ±0.5‰ for
of Water and Wastewater, APHA-AWWAWPCF, 19th edition, 1995). δ13C. Chemical data and isotopic values are reported in Tables 1 and 2.

3. Geology

Table 2 The peninsula of Methana is linked to mainland by a narrow isthmus,

Isotopic compositions (‰ V-SMOW) of waters from springs and boreholes.
just 300 m wide. Gray limestone hills are present on the northwest
No. Sampling site δ18O δ 2H δ 13C δ 18O δ 34S T (U. Triassic–L. Jurassic) and on the south (U. Jurassic–Cretaceous). The
(Η2Ο) (Η2Ο) (HCΟ− 3 ) (SΟ2−
4 ) (SΟ2−
4 ) (TU) isthmus is a prolongation of the latter (Dietrich and Gaitanakis, 1995).
‰ ‰ ‰ ‰ ‰
The limestones are the sedimentary basement of Methana, located
SMOW SMOW PDB SMOW CDD
under the volcanic rocks until the depth of 1000 m below sea level
1 LOUTRAKI-EOT − 7.3 − 44.7 9.1 19.8 2 (Volti, 1999). The principle volcanic rocks are andesite and dacite lava
2 L-Karantani − 7.3 − 47.4 9.4 19.8 3
3 L-Posimo − 6.6 − 43.1
domes and flows extending radially from its central part (Pe-Piper
4 METHANA Ag. Nikolaosa − 5.2 −29.0 8.2 18.3 0 and Piper, 2002). The volcanic activity probably started at the Plio-
4A Ag. Nikolaosa − 5.2 −29.0 0 Pleistocene boundary although the oldest dated rocks gave ages of about
5 Ag. Nikolaos −5.1 −28.3 8.2 18.3 0 0.9 Ma. The last volcanic eruption took place at Kammeno Vouno around
6 Ag. Nikolaos − 5.2 − 28.9 0
230 BC and is described by Strabo (Stothers and Rampino, 1983). The
7 Ag. Nikolaos − 5.2 − 28.9 0
8 Ag. Nikolaos −5.3 −30.5 area of Methana is tectonically active (Makris et al., 2004). Many
9 Pausanias 0.2 − 6.2 − 13.0 12.3 22.6 Holocene fault systems are reported (Dietrich and Gaitanakis, 1995) and
10 Pausanias 0.4 − 5.0 0 also active faults of Pleistocene were reactivated during Holocene.
11 Pausanias − 0.2 − 1.0 0 Makris et al. (2004), through microseismicity studies of the Saronikos
12 Pausanias 2007 0.2 − 3.0
gulf, attribute most of the seismic activity in the area to W–E and SW–NE
13 EOT 0.2 − 5.8 −6.0 9.1 20.4 1
14 EOT 1.1 6.0 1 tectonic structures. The geothermal manifestations of Loutra Methana,
15 EOT 1.3 6.0 1 Agios Nikolaos spring are related to a SSW–NNE fault system. The other
16 EOT 1.1 6.0 0 important geothermal manifestation, Pausanias spring on the northern
17 Posimoa − 6.0 −31.4
coast, is found along a WNW–ESE fault system.
18 POROS spring −6.2 −31.4 9.5 20.3
19 Borehole − 5.9 − 31.7 Loutraki is situated between Hellenides externs, represented by
20 Poros, rain water − 6.9 − 34.0 Beotinian zone and inner Hellenides, represented by Pelagonian zone.
21 Sea water 1.4 5.8 9.2 20.5 This last is mainly constituted by ophiolites, sandstones and lime-
22 Sea water 1997 1.1 8.0 stones of Triassic. Dolomitic limestones of Triassic and conglomerates
a
Dotsika et al. (2009). of Pleistocene are also met.
100 E. Dotsika et al. / Journal of Geochemical Exploration 104 (2010) 97–104

4. Hydrochemistry of marine ratio indicating the interaction of the waters with volcanic
formations under high temperatures and CO2 pressures. Ca2+
Water samples have been analyzed for the main constituents, contents of hot springs are probably due to the equilibrium with a
lithium, boron and silica. On the basis of the contents of the seven hydrothermal mineral at high temperatures (>200 °C) and CO2
main ion species, the water samples may be categorized as follows: pressures (Truesdell et al., 1981). In fact, the thermal waters indicate
a relatively high Ca/Na ratio, with respect to all other probably due to
Earth-alkaline-bicarbonate waters: The 3 cold waters belong to limited albitization phenomenon.
this group (samples 3, 17 and 19). Their temperatures range from So, the discrimination of hot waters from the fresh waters and
18 to 21 °C. The relatively low concentration of Cl− in these waters the gradual increase of Cl− content show that these waters are
excludes the marine participation. mixed with a deeper geothermal fluid, that probably contain a marine
Alkaline-chloride waters: This group includes all thermal springs. member.
Their temperatures range from 29 to 36 °C. The TDS of these Over the above this type of water is also rich in Li+ and B and is
waters range from 1.9 to 40 g/L. Based on Cl contents it appears representative of all thermal waters of Loutraki and Methana. The
high B/Cl ratio for the thermal water, Loutraki and Methana, show a
that the marine participation varies between the sampling sites
small variability, 2–3 times that of seawater. Taking into account that
(Loutraki, Agios Nikolaos, Pausanias and EOT).
low B/Cl ratio of seawater and the geological setting of these waters
The positive correlation between Cl− and Na+ indicates that high discharges the excess of B can probably be of marine sedimentary
−
Cl contents of thermal waters arise from the contribution of origin.
seawater and/or a sodium-chloride geothermal liquid. However The observed variations in B/Cl ratios then are likely to reflect the
chloride, bromide (and D), in contrast to Na+, are considered to be participation of seawater and sedimentary material in the formation
conservative ions, even in geothermal environments because their of the rising waters. According to Bebout et al. (1993) B is lost from
contents are not affected by interactions with rocks (in high sediments. The loss of B is strongly dependent of the heating during
temperature environment) and, unless boiling or mixing occurs, subduction. The most likely B removal process is transfer from the
they remain unchanged during deep hydrothermal circulation rock to subducted fluids. Probably the high B/Cl ratio, of these
(Henley and Ellis, 1983). Also the points for Loutraki and Methana thermal waters, over that of seawater, suggests that these thermal
follow different trends on the basis of Cl/Br ratios (Fig. 2A and B). The fluids represent, in varying degree, those fluids. Although B should
trend for Pausanias and EOT thermal waters corresponds to Cl/Br ratio be removed much more easily from sediments, the transfer of Li
of 285–317, approaches closely the ratio for seawater of 322, while the from rock requires intense water–rock interaction at high tempera-
Cl/Br ratios of Agios Nikolaos and Loutraki thermal water are different tures (Goguel, 1983). Li/B ratio of the thermal water shows wide
to that of mean seawater (i.e. about 3.4 * 10− 3, Herrmann et al., 1973). variability: from 0.07 to 0.2 (Pausanias and EOT; 2 to 5 times that of
Also the obtained different cation–chloride ratio is in general higher seawater) and from 0.2 to 0.5 (Loutraki and Agios Nikolaos; 12.5
than that ion–chloride marine ratio indicating the not purely marine times that of seawater) typical of water discharged of the ‘rift-type’
origin for the chemical elements of these waters. A water–rock and ‘arc-type’ systems (Giggenbach et al., 1995) and close to Nisyros
interaction process is approved also by the aggressiveness of thermal ratio (0.05 to 0.18; Marini and Fiebig, 2005). This variation of Li/B
water probably due to the condensation of CO2 geothermal steam. The ratios are likely to reflect the effects of secondary processes such as
influence of CO2 is also confirmed by the relatively high HCO− 3 , which leaching of Li from terrigenous material, in the sediments during
is observed in the hot springs in comparison with the fresh waters. subduction, shifting compositions towards the composition of
The waters, in which the condensation of the geothermal steam took average crustal rocks.
place, have a high composition in bicarbonates i.e. the samples 4 to 16 In Cl–B–Li triagonal diagram, the points representing the deep
(environ 1300 mg/L, from 920 to 1920 mg/L) in relation to the fresh fluids from Milos (Mendrinos, 1988) and Nisyros Islands (Marini and
waters. Also the cation –chloride ratio is in general different than that Fiebig, 2005) have been plotted, as well as a water sample from

Fig. 2. Relative Cl–Br–B (A) and Cl–Li–B (B) contents in waters from Methana, Loutraki and Poros areas, in mg/L. Black triangle: Sea water; Crosses: Loutraki waters (samples 1–3);
black diamonds: Agios Nikolaos waters (samples 4–8); squares: Pausanias waters (samples 9–12); triangles: EOT waters (samples 13–16); diamonds: Poros waters (samples 18, 19);
star: Warakei sample (from Giggenbach et al., 1995); black star: Broadlands sample (from Giggenbach et al., 1995); del: Nisyros samples; black del: Milos samples.
 E. Dotsika et al. / Journal of Geochemical Exploration 104 (2010) 97–104 101

Warakei (‘rift-type’) and one from Broadlands (‘arc-type’) reservoir 1992). The water samples from 1986 (Barnes et al., 1986) are also
(Giggenbach et al., 1995). shown in Fig. 3.
All the samples appear that occupy distinct positions from the line The points representative of cold waters from Poros fall between
representing the Li/B ratio of seawater of 0.04. On the other hand the global meteoric water line and the Eastern Mediterranean
the trend observed may be indicated the participation of a deep meteoric water line. Agios Nikolaos thermal springs are slightly
geothermal liquid in the geothermal reservoir of Methana. The trend shifted to the right of the local meteoric water (Poros) and to the right
observed may also be explained in terms of mixing between a low-Li+ of the line that represents an ideal mixing between seawater and local
and B component and a high-Li+ and B component. The first is fresh water. This is probably originated through dilution, addition of
probably marine water or dilute groundwater, like Poros, while the local groundwater to a deep, hot geothermal liquid, whereas seawater
latter may be deep geothermal reservoir suggesting that B and Li+ do does not appear to entrain in this thermal water flow. The isotopic
not derive only from seawater but come from a thermal member data of water from EOT and Pausanias (samples 9, 10, 11, 12 and 13)
which is more or less diluted by fresh water and marine water and shows δ18O similar to seawater, but δ2H different from seawater
that the supply of these ions by rock leaching is significant. suggesting mixing with deep thermal fluid. On the contrary, the
In general, it appears that there is a unique source of Li+ and B in isotopic data of the EOT waters (samples 14, 15 and 16), sampled in
both water EOT/Pausanias and Agios Nikolaos hot water springs. The 1996, 1997 and 1998, show similar isotopic composition with that of
characteristics of this unique geothermal source appear to be the unaltered sea water. This fact is attributed to sea water intrusion,
same with those of the geothermal field of Milos and Nisyros Islands. taking into account the works that took place in the area in 1991,
This unique source seems to produce the Li+ and B contents in Agios which also caused a decrease in output temperature. A sample from
Nikolaos and Loutraki spring water through dilution with local cold 1986 (Barnes et al., 1986) shows also Cl− (21,800 mg/L) and δ18O
ground waters and Li+ and B in EOT/Pausanias thermal liquid through enrichment (1.4‰) similar to seawater, but a depletion in δ2H
mixing with marine water. (−5.2‰) in relation to that of seawater. It is therefore believed that
the older samples better represent the deep geothermal system.
5. Isotope analyses However, the mixing between the hot water of EOT and Pausanias
thermal water and seawater is favoured by the location of the thermal
5.1. Stable isotopes spring on the shoreline. The occurrence of this process is also
confirmed by chemical data (Br/Cl ratios in EOT and Pausanias–
Analyses of δD, δ18O and tritium have been performed on all Methana thermal water are similar to that of mean seawater).
samples. Moreover, δ18O and δ34S in dissolved sulfates and bicarbon- Therefore, the pure geothermal liquid is situated along the extension
ate have been determined on selected samples. Data are reported in (Fig. 3), towards lower δD and δ18O values, of the mixing line passing
Table 2. The tritium content of the hot springs is indicative of the through seawater and the EOT and Pausanias samples.
significant underground transit time. The EOT and Pausanias mixing line and the Agios Nikolaos dilution
The stable isotope contents from Methana and Poros show quite line could be extrapolated to define (through their intersection) the
large variations of δ18O ranging from −6.9 to 1.3‰ and δD from − 34 isotopic composition of the parent geothermal liquid (PGL), possibly
to 6‰. The maximum values are observed for samples EOT and involved in the origin of both waters. The δ2H and δ18O contents and the
Pausanias thermal springs and the minimum value is observed for Cl− concentration obtained for the pure geothermal liquid are also
sample 18 and 19 Poros fresh spring. The samples EOT and Pausania reported in the δ2H versus Cl− plot (Fig. 4). In this way, the values
thermal springs show an isotopic enrichment in relation with the obtained for the PGL of Methana are: δ2H = −17.22‰, δ18O = −0.95‰
Agios Nikolaos thermal waters (4, 4a, 5, 6, 7 and 8). and Cl− = 16,000 mg/L. These values are a bit different from those
The stable isotopic composition (δ2H versus δ18O) of the waters of proposed by Dotsika et al. (2009). However, in that study, the samples
Methana, Poros and Loutraki is shown in Fig. 3. In the same figure, from the area of Methana were only three. Again, it can be concluded
the arc-type magmatic water (ATMW) is also reported (Giggenbach,

Fig. 3. 18O and 2H contents of water [PGL: Parent geothermal liquid; EMMWL: East
Mediterranean Meteoric Water Line (Craig, 1961); GMWL: Global Meteoric Water Line
(Craig, 1961)]. Symbols same as in Fig. 2. black circles: from Barnes et al. (1986). Fig. 4. 2H contents of water versus Cl− contents. Symbols same as in Figs. 2 and 3.
102 E. Dotsika et al. / Journal of Geochemical Exploration 104 (2010) 97–104

−
that a unique PGL feeds both systems: EOT–Pausanias and Agios SO2−4 /Cl ratio, could be due to a mixing of marine sulfate with “light”
Nikolaos thermal waters. sulfate. This “light” sulfate, provided by the meteoric component,
As mentioned before a unique parent geothermal liquid (PGL) is suggests probably dissolution of sulfur or sulfate of deep rocks or
involved in the origin of A. Nikolaos and EOT–Pausanias thermal mixing of sulfate that coming by sulfur oxidation. These sulfur minerals
waters. Possible origins of this deep water to Methana geothermal have different isotopic values in the volcanic rocks (δ34S = 0 ± 5‰) and
system could be local ground water, seawater or magmatic water. in the sedimentary rocks (average value δ34S = −12‰) (Rafter and
δ2H contents of PGL aquifer water differs from that of local ground Mizutani, 1967). When the depletion of δ34S, relative to marine sulfate,
water, seawater and volcanic or magmatic water but on the basis of is correlated to an increase of the 1/SO2−
4 ratio, the contribution of sulfur
chlorinity and Cl/Br ratio, the best candidate for PGL origin is oxidation is confirmed. In fact, in the case of Agios Nikolaos water, the
seawater. Also the Cl− contents of Methana waters are very different depletion of δ34S is accompanied by the increase of 1/SO2− 4 ratio.
to that of volcanic or magmatic water because the Cl contents of these According to the values of δ18O in water and sulfate of thermal water, it
waters not exceed 3 g/L before flashing (Ellis and Mahon, 1977). In is estimated that the main part of oxygen, which is incorporated in
Fig. 3 (δ2H–δ18O) it is shown that the origin of the PGL of Methana can the sulfate formed by oxidation, comes from atmospheric oxygen. This
be: a mixture made up of local groundwater (∼ 43%) and diluted arc- suggests that the oxidation reactions took place in the soils and/or in
type magmatic water (DATMW) (∼ 57%). The values obtained for the the shallow aquifers.
DATMW of Methana are: δ2H = −4.55‰, δ18O = 3.6‰. This DATMW The δ34S value of the sample corresponding to the water of the
is a mixing between seawater (∼ 60%) and arc-type magmatic water source of Pausanias (δ34S = 22.6‰) is slightly higher than that of the
(∼40%). Therefore, the origin of the PGL could be ascribed to mixing marine SO2− 4 . Probably this enrichment is due to the reduction
between local groundwater (∼43%), seawater (∼ 34%) and ATMW processes confirming by the smell of H2S in the water of the spring.
(∼23%). The δ34S value of the sample corresponding to the water of the
He isotopic compositions, corrected for air contamination, range source of ΕΟΤ (δ34S = 20.4‰) is similar to the SO2− 4 in seawater,
from 2.18 to 2.57 R/Ra (D'Alessandro et al., 2008) indicating a indicating the seawater origin of these anions in the water of the
substantial contribution from a mantle component. The latter can be spring. The slightly diminished δ18O value of the SO2− 4 in the water
estimated in 34– 40% considering a composition of 8 R/Ra of the He of of the spring (9.1‰) in comparison to the one of the SO2− 4 of sea water
the mantle end-member. The maximum 3He/4He ratios in the Aegean origin (9.5 ± 0.2‰) may be attributed to isotopic exchange between
arc were found at Nisyros and are almost identical to the Sub the oxygen of the water molecules and the one of the sulfate ions.
Continental Lithospheric Mantle value (Shimizu et al., 2005; Dotsika
et al., 2009). 6. Geothermometry
A mixture constituted by local groundwater, which has experi-
enced oxygen isotope exchange (∼ 6‰) most likely through interac- The sulfate–water isotopic geothermometer (Loyd, 1968; Mizutani
tion with rocks at high temperature is discarded as the origin of the and Rafter, 1969), which is based on the equilibrium exchange of
PGL because a shift of 6‰ at least is more than what water–rock oxygen isotopes between aqueous SO2− 4 and H2O, was utilized. The
interaction could cause (O'Neil and Taylor, 1967; Bottinga, 1969) at calculated temperatures for the wider sampling region varied,
temperatures close to 300 °C. None of the used geothermometers depending on each location (TLoutraki = 110 °C < TMethana) and from
permits the acceptance of such high temperatures at Methana. spring to spring (TAgios Nikolaos = 140 °C, TPasuanias = 150 °C, and
So, the main source of recharge water of Methana can be TEOT = 200 °C).
considered to be approximately 40–60 mixture of local groundwater In particular, if the δ18O content of aqueous sulfate on sample
and diluted arc-type magmatic water. EOT is only controlled by equilibration with water, and if isotopic
Mixing of arc-type magmatic water and seawater is observed in equilibrium is reached, the δ18O (SO2−4 –H2O) temperature would be
Nisyros Island in Greece (Chiodini et al., 1993; Dotsika and Michelot, close to 200 °C. The aqueous sulfate in Agios Nikolaos water sample is
1993; Brombach et al., 2003), Milos, Santorini and Sousaki area also of marine origin, but the original δ18O content of the water was
(Dotsika et al., 2009). modified by mixing between sea water and meteoric water (dilution).
Thus, two temperatures are obtained, depending on whether dilution
5.2. Stable isotope of sulfate is considered to have occurred before (∼ 140 °C) or after (∼ 200 °C)
equilibration. Regarding the aqueous sulfate of Pausanias sample, it is
The 34S and 18O contents of the samples (Table 2) are compared to partially reduced and therefore the suggested temperature (∼ 150 °C)
those of marine sulfate (δ34S = 20.1‰ CD and δ18O = 9.3‰ SMOW), is under-estimated.
which is very constant over the world (δ34S = 20‰ CD and Regarding the samples from Loutraki, the isotopic geothermometer
δ18O = 9.5‰ SMOW) (Longinelli, 1989). The δ34S and δ18O values of was estimated but it was not used, because this sulfate is of shallow
Loutraki and Poros waters are very close to those of marine sulfate. origin and not at equilibrium with water.
The water sample from Poros is purely meteoric, without any Regarding the chemical geothermometers, in the square plot of
participation of sea water, while Loutraki waters show a marine 10 Mg / (10 Mg + Ca) versus 10 K / (10 K + Na) (Fig. 5), which was
participation lower than 4%. The isotopic ratios of sulfates in rain proposed by Giggenbach (1988), the thermal springs of Methana
water are dependent on their origin. If their origin is marine, then the distribute close to the seawater point, with limited shifts towards
isotopic ratios would be similar to those of sea water. However, the either the field of rock dissolution or the full-equilibrium line.
more far away from the sea coast, the higher the SO4/Cl ratio of Consequently, application of chemical geothermometers to these
meteoric waters will be, in relation to sea water. Hence, the isotopic thermal waters is not expected to provide meaningful results.
ratios of rain water vary: δ18Ο = 5 to 17‰ (Rafter and Mizutani, Nevertheless, it cannot be excluded that the three samples 4, 4A,
1967) δ34S = − 2.5 to 19.5‰ (Cortecci and Longinelli, 1970). The δ34S and 5, which are those most shifted towards full-equilibrium
and δ18O values of Loutraki and Poros waters indicate the marine compositions, are representative of fully equilibrated waters which
origin of the diluted sulfate and the SO4/Cl ratio probably indicates have suffered either dilution or addition of seawater. Therefore, it
the participation of aerosols in the meteoric waters of the region. seems that the contribution of marine solutions to the geothermal
The δ34S and δ18O values of the thermal waters, except for ΕΟΤ fluids of Methana and Loutraki area is one of the main causes for the
sample, are different to those of marine sulfate. Samples 4 and 5 (Agios disturbance of the chemical and isotopic geothermometer.
Nikolaos) contains sulfate that is depleted in heavy isotopes, relative to To gain more insights into the possible effects of dilution, they have
marine sulfate. This depletion, which is correlated to an increase of the been modelled following the approach of Chiodini et al. (1996). First,
 E. Dotsika et al. / Journal of Geochemical Exploration 104 (2010) 97–104 103

provide apparent mineral–solution equilibrium temperatures and Cl−

concentration of the pure geothermal liquid. This geothermometric-
mixing model shows the convergence of Na–K and K–Mg equilibrium
temperatures at ∼140 °C, for a Cl concentration slightly lower than
9500 mg/L, whereas the two silica functions provide equilibrium
temperatures which appear to be somewhat too high (α-cristobalite)
or somewhat too low (β-cristobalite). Temperatures even higher are
provided by the solubilities of quartz and chalcedony, whereas
temperatures even lower are given by the solubility of amorphous
silica.
The dilution line is also shown in Fig. 5. The computed equilibrium
temperature for the geothermal end-member possibly involved in
samples 1, 2, 4, 4A and 5 is very similar to the apparent Na–K
equilibrium temperature of seawater, a fact which casts some doubts
on its reliability.
According to D'Alessandro et al. (2008), gas geothermometry
indicates temperatures maybe as high as 210 °C but this temperature
is not confirmed by the chemical geothermometers.

7. Conclusions

Water samples from springs and boreholes were collected during

this investigation in Loutraki and Methana. Interpretation of geo-
Fig. 5. Relative Na, K, Mg and Ca contents of Methana and Loutraki water samples. chemical data and isotopic ratios of waters show that the fluids
emerging at Loutraki represent geothermal system in their waning
stage, while the fluids from Methana proceed from active geothermal
systems. The chemical and isotopic data of the thermal water of
the concentrations of the chemical components of geothermometric
Loutraki samples indicate a purely meteoric origin.
interest (SiO2, Na+, K+, Mg2+, and Ca2+) of water were regressed
Based on the Li, B and Cl contents of the samples, it appears that
against chloride, for the 5 considered samples with codes 1, 2, 4, 4A
there is a unique source of Li+ and B in both water EOT/Pausanias and
and 5.
Agios Nikolaos hot water springs. This unique source seems to
Then these linear relations have been inserted into the geother-
produce the Li+ and B contents in Agios Nikolaos and Loutraki spring
mometric functions Na–K (Fournier, 1979), K–Mg (Giggenbach,
water through dilution with local cold ground waters and Li+ and B
1988), α-cristobalite and β-cristobalite (Fournier, 1973) and the
in EOT/Pausanias thermal liquid through mixing with marine water.
corresponding equilibrium temperatures have been computed for
The general characteristics of this unique geothermal source indicate
varying Cl concentrations, up to 10,000 mg/L. Obtained results are
its similarity with those from Milos and Nisyros geothermal fields.
displayed in Fig. 6, where the intersections of two or more curves
The relations between the δ2H and δ18O values of water and Cl−
content of the thermal Cl-rich water springs of Methana suggest that
they are fed by thermal water mixed with local groundwater and
seawater respectively. The parent hydrothermal liquid is a mixture of
local groundwater (∼ 43%), seawater (∼34%) and arc-type magmatic
water (∼ 23%). It is likely that the magmatic contribution to the deep
geothermal system in Methana is not very high like to Nisyros and
Milos Islands (Dotsika et al., 2009).
Assessments from chemical and isotopic geothermometers ap-
plied on the thermal waters springs suggest the probable existence of
a deep geothermal reservoir of middle enthalpy (150 °C) at Methana
and low enthalpy (80 °C) in Loutraki area. However, the contribution
of marine solutions to the geothermal fluids of Methana and Loutraki
area is one of the main causes for the disturbance of the chemical and
isotopic geothermometers rendering these calculated temperatures
questionable.

Acknowledgments

The authors would like to express their gratitude to L. Marini for

his vital advice, as well as the two unknown reviewers and the editor-
in-chief for their fruitful remarks and recommendations, which
essentially contributed to the improvement of the manuscript.

References
Apha, 1989. Standard Methods for the Examination of Water and Wastewater, 19th
end. American Public Health Association, Washington, DC.
Fig. 6. Variations of Na–K, K–Mg, α-cristobalite and β-cristobalite temperatures versus APHA, AWWA, WEF, Eaton, A.D., Clesceri, L.S., Greenberg, A.E., 1995. Standard Methods
Cl− contents for the thermal waters of Methana and Loutraki areas. for the Determination of Water and Wastewater, 19th edition.
104 E. Dotsika et al. / Journal of Geochemical Exploration 104 (2010) 97–104

Barnes, I., Leonis, G., Papastamataki, A., 1986. Stable isotope tracing of the origin of CO2 Goguel, R., 1983. The rare alkalies in hydrothermal alteration at Wairakei and Broadlands,
discharges in Greece. Intern. Symposium on underground water tracing, Athens, geothermal fields. Geochim. Cosmochim. Acta 47 (3), 429–437.
1986, pp. 29–43. Henley, R.W., Ellis, A.J., 1983. Geothermal systems ancient and modern: a geochemical
Bebout, G.E., Ryan, J.G., Leeman, W.P., 1993. B–Be systematics in subduction-related review. Earth-Sci. Rev. 19, 1–50.
metamorphic rocks: characterization of the subducted component. Geochim. Herrmann, A.G., Knate, D., Schneider, J., Peters, H., 1973. Geochemistry of modern
Cosmochim. Acta 57 (10), 2227–2237. seawater and brines from saltpans: main components and bromine distribution.
Bottinga, Y., 1969. Calculated fractionation factors for carbon and hydrogen isotope Contrib. Mineral. Petrol. 40, 1–24.
exchange in the system calcite–carbon dioxide–graphite–methane–hydrogen– International Hydrological Programme (IHP-V), 2000. Environmental isotopes in the
water vapour. Geochim. Cosmochim. Acta 33, 49–64. hydrological cycle. Principles and Applications: In: Mook, W.G. (Ed.), Introduction.
Brombach, T., Caliro, S., Chiodini, G., Fiebig, J., Hunziker, J., Raco, B., 2003. Geochemical Theory Methods Review, vol. 1. Paris.
evidence for mixing of magmatic fluids with seawater, Nisyros hydrothermal Longinelli, A., 1989. Oxygen-18 and sulphur-34 in dissolved oceanic sulphate and
system, Greece. Bull. Volcanol. 65, 505–516. phosphate. In: Fritz, P., Fontes, J.Ch. (Eds.), Chapter 7 in Handbook of Environmental
Chiodini, G., Cioni, R., Leonis, C., Marini, L. And, Raco, B., 1993. Fluid geochemistry of Isotope Geochemistry, vol. 3. Elsevier, Amsterdam, pp. 219–255.
Nisyros Island, Dodecanese, Greece. Volcanol. Geotherm. Res. 56, 95–112. Lort, J.M., Limond, W.Q., Gray, F., 1974. Preliminary seismic studies in the eastern
Chiodini, G., Cioni, R., Frullani, A., Guidi, M., Marini, L., Prati, F., Raco, B., 1996. Fluid Mediterranean. Earth Planet. Sci. Lett. 21, 355–366.
geochemistry of Montserrat Island, West Indies. Bull. Volcanol. 58, 380–392. Loyd, R.M., 1968. Oxygen isotope behaviour in the sulfate–water system. J. Geophys.
Coleman, M.L., Shepherd, T.J., Durham, J.J., Rouse, J.E., Moore, G.R., 1982. Reduction of Res. 73, 6099–6110.
water with zinc for hydrogen isotope analysis. Anal. Chem. 54 (6), 993–995. Makris, J., 1978. The crust and upper mantle of the Aegean region from deep seismic
Cortecci, G., Longinelli, A., 1970. Isotopic composition of sulphate in rain water, Pisa, soundings. Tectonophysics 46, 269–284.
Italy. Earth Planet. Sci. Lett. 8 (1), 36–40. Makris, J., Papoulia, J., Drakatos, G., 2004. Tectonic deformation and microseismicity of
Craig, H., 1961. Isotopic variations in meteoric waters. Science 133, 1702–1703. the Saronikos Gulf, Greece. Bull. Seismol. Soc. Am. 94 (3), 920–929.
D'Alessandro, W., Brusca, L., Kyriakopoulos, K., Michas, G., Papadakis, G., 2008. Methana, Marini, L., Fiebig, J., 2005. Fluid geochemistry of the magmatic-hydrothermal system of
the westernmost active volcanic system of the south Aegean arc (Greece): insight Nisyros (Greece). In: Hunziker, J.C., Marini, L. (Eds.), The Geology, Geochemistry
from fluids geochemistry. J. Volcanol. Geoth. Res. 178, 818–828. and Evolution of Nisyros Volcano (Greece). Implications for the Volcanic Hazards,
Dietrich, V., Gaitanakis, P., 1995. Geological Map of Methana Peninsula (Greece). ETH vol. 44, pp. 121–163. Memoires de Géologie (Lausanne).
Zürich, Switzerland. McKenzie, D., 1970. Plate tectonics of the Mediterranean region. Nature 226.
Dotsika, E., Michelot, J.L., 1993. Hydrochemistry, isotope contents and origin of Mendrinos, 1988. Modelling of Milos Geothermal Field in Greece. Master in
geothermal fluids at Nisyros (Dodecanese). Bull. Geol. Soc. Greece XXVIII/2, Engineering, Univ. of Auckland, School of Engineering, p. 176.
293–304. Mizutani, H., Rafter, T.A., 1969. Oxygen isotopic composition of sulfates, 3. Oxygen
Dotsika, E., Poutoukis, D., Michelot, J.L., Raco, B., 2009. Natural tracers for identifying the isotopic fractionation in the disulfate–water system. N. Z. J. Sci. 12, 54–59.
origin of the thermal fluids emerging along the Aegean Volcanic arc (Greece): O'Neil, J.R., Taylor Jr., H.P., 1967. The oxygen isotope and cation exchange chemistry of
evidence of Arc-Type Magmatic Water (ATMW) participation. J. Volcanol. Geoth. feldspars. Am. Mineral. 52, 1414–1437.
Res. 179, 19–32. Pe-Piper, G., Piper, D.J.W., 2002. The Igneous Rocks of Greece. Bornträger, Berlin.
Ellis, A.J., Mahon, W.A.J., 1977. Chemistry and Geothermal Systems. Academic Press, Rafter, T.A., 1957. Sulphur isotopic variations in nature, P 1: the preparation of sulphur
New York. 392 pp. dioxide for mass spectrometer examination. N. Z. J. Sci. Tech. B38, 849.
Epstein, S., Mayeda, T., 1953. Variation of 18O content of waters from natural sources. Rafter, T.A., Mizutani, H., 1967. Oxygen isotopic composition of sulfates, 2. Preliminary
Geochim. Cosmochim. Acta 4 (5), 213–224. results on oxygen isotopic variation in sulphates and relationship of the environment
Fournier, R.O., 1973. Silica in thermal waters: laboratory and field investigations. Proc. and to their δ34S values. N. Z. J. Sci. 10, 816.
Int.l Symp. Hydrogeochemistry and Biogeochemistry, Tokyo. pp. 122–139. Shimizu, A., Sumino, H., Nagao, K., Notsu, K., Mitropoulos, P., 2005. Variation in noble
Fournier, R.O., 1979. A revised equation for the Na/K geothermometer. Geotherm. Res. gas isotopic composition of gas samples from Aegean arc, Greece. J. Volcanol. Geoth.
Counc. Trans. 5, 1–16. Res. 140, 321–339.
Giggenbach, W.F., 1988. Geothermal solute equilibria. Derivation of Na–K–Mg–Ca Stothers, R.B., Rampino, M.R., 1983. Volcanic eruptions in the Mediterranean before A.D.
geoindicators. Geochim. Cosmochim. Acta 52, 2749–2765. 630 from written and archeological sources. J. Geophys. Res. 88, 6357–6371.
Giggenbach, W.F., 1992. Isotopic shifts in waters from geothermal and volcanic systems Truesdell, A.H., Thompson, J.M., Coplen, T.B., Nehring, N.L., Janick, C.J., 1981. The origin
along convergent plate boundaries and their origin. Earth Planet. Sci. Lett. 113, of the Cerro Prieto geothermal brine. Geothermics 10 (3/4), 225–238.
495–510. Volti, T.K., 1999. Magnetotelluric measurements on the Methana peninsula (Greece):
Giggenbach, W.F., Stewart, M.K., Sano, Y., Goguel, R.L., Lyon, G.L., 1995. Isotope and modelling and interpretation. Tectonophysics 301, 111–132.
geochemical techniques applied to geothermal investigations. IAEA-TECDOC 788,
209–231.