Greek thermal springs

Contribution to the study of Greek thermal springs: hydrogeologicaland hydrochemical characteristics and origin of thermal waters

Nicolaos Lambrakis · George Kallergis

Abstract A large number of chemical analyses of Greekthermal waters were evaluated in order to investigatespring water origin, water–rock interaction mechanisms,and estimate the thermal potential of the geothermal ar-eas. Four water types were distinguished from geochem-ical diagrams. The relatively fresher waters include sam-ples of Ca–HCO3 and Mg–HCO3 type waters originatingfrom the schistose Rhodope Massif and the Quaternarybasin of Aridea, respectively. Samples of the Na–HCO3water type are typical of springs located in the post-oro-genic basins of northern Greece. These hot, deep-risingNa–HCO3 waters circulate in a CO2-rich environmentthat favours the solubility of alkaline ions such as Nafrom siliceous rocks. Most of the samples belong to theNa–Cl water type and originate from Greek islands andcoastal springs. These are characterized by the mixing ofdeep thermal solutions with seawater and fresh water. Thepresence of CO2 in thermal and mineral springs is due tothe metamorphism of buried marine carbonate horizonswhile H2S is due to both local pyrite oxidation andthe reduction of sulphates. The use of geothermometerssuggested that the investigated geothermal areas havelow enthalpy fluids at depth, while higher temperaturesare likely present in Milos, Lesvos, Nisyros islands andXanthi Basin.

R�sum� Un grand nombre d’analyses chimiques deseaux thermales grecques ont �t� men�es de mani�re �investiguer l’origine des eaux des sources thermales, lesm�canismes d’interaction avec les roches travers�es, etd’estimer le potentiel des zones g�othermiques. Quatretypes d’eau ont �t� distingu�es sur base des diagrammes

g�ochimiques. Les eaux les plus fra�ches correspondentrespectivement aux �chantillons des eaux calco et ma-gn�so carbonat�es du massif schisteux de Rhodope et dubassin quaternaire d’Aridea. Les �chantillons d’eaux sodicarbonat�es proviennent typiquement des sources locali-s�es dans les bassins posts-orog�niques du Nord de laGr�ce. Ces chaudes et tr�s profondes eaux sodi carbona-t�es circulent dans des environnements riches en CO2 quifavorisent la solubilit� des ions alcalins, tel que le sodium,des roches siliceuses. La plus part des �chantillons ont unfacies chlorur� sodique et proviennent des �les grecquesou des environnement c�tier. Ces eaux sont caract�ris�espar des m�langes entre eaux profondes avec des eaux demer et des eaux de surface. La pr�sence de CO2 dans leseaux de sources thermales et min�rales est due au m�ta-morphisme des horizons de calcaires marins et couverts,tandis que la pr�sence de H2S est due � l’oxydation localede la pyrite et � la r�duction des sulfates. L’utilisation deg�othermom�tres sugg�re que les zones g�othermiques�tudi�es contiennent des eaux � faible enthalpie en pro-fondeur, bien que des temp�ratures assez �lev�es soientrencontr�es � Milos, Lesvos, sur les �les Nisyros et dans lebassin de Xanthi.

Resumen Se ha evaluado un gran nfflmero de an�lisisqu�micos de aguas termales griegas con objeto de inves-tigar el origen del agua en los manantiales, los mecanis-mos de interaccin agua-roca, y estimar el potencial ter-mal de las �reas geot�rmicas. Se distinguieron cuatro ti-pos de aguas a partir de diagramas geoqu�micos. Lasaguas relativamente frescas incluyen muestras de aguatipo Ca–HCO3 y Mg–HCO3 que se originan en los es-quistos del Macizo Rhodope y la cuenca Cuaternariade Aridea, respectivamente. Las muestras de agua tipoNa–HCO3 son t�picas de manantiales localizados en lascuencas post-orog�nicas del norte de Grecia. Estas aguascalientes y profundas, de tipo Na–HCO3, circulan en unambiente rico en CO2 que favorece la solubilidad de ionesalcalinos, tal como Na proveniente de rocas sil�cicas. Lamayor�a de las muestras pertenecen al tipo de agua Na–Cly se originan en islas y manantiales costeros griegos.Estas aguas se caracterizan por la mezcla de solucionestermales profundas con agua de mar y agua dulce. Lapresencia de CO2 en manantiales termales y minerales sedebe a el metamorfismo de horizontes carbonatados ma-rinos enterrados mientras que el H2S se debe a oxidacin

Received: 8 March 2003 / Accepted: 17 April 2004Published online: 28 May 2004

Springer-Verlag 2004

N. Lambrakis ()) · G. KallergisDepartment of Geology,Section of Applied Geology and Geophysics,Laboratory of Hydrogeology,University of Patras,26500 Rio-Patras, Greecee-mail: [email protected].: +30-2610-997782Fax: +30-2610-997782

Hydrogeology Journal (2005) 13:506–521 DOI 10.1007/s10040-004-0349-x

local de pirita y reduccin de sulfatos. El uso de geoter-mmetros sugiere que las �reas termales investigadastienen fluidos de baja entalp�a a profundidad, mientrasque las temperaturas m�s elevadas es probable que sepresenten en Milos, Lesvos, islas de Nisyros y la cuencaXanthi.

Keywords Thermal springs · Chemical and isotopiccomposition · Geothermometry · Greece

Introduction

There are many thermal springs in Greece due to thegeology of the country. Magmatic and volcanic processes,the high mountain chains and active fault systems favourthe rise of deep waters that discharge at the surface asthermal springs. The origin of the fluid movement resultsfrom a thermal gradient closely relating to volcanic ac-tivity, leading to convection. Although numerous studieson the origin and quality of thermal waters in territories inGreece have been made during the last 30 years, none ofthem concentrates on the entire country. A large num-ber of chemical analyses of thermal waters exist in manytechnical reports and papers. Their evaluation for thewhole of Greece is not an easy task because (1) the originof the sampling points are not always exactly positioned,(2) the analyses originated from many different labora-tories and their accuracy is not evident, and (3) the anal-yses were made over very different time periods. From1985–1988, the Institute of Geological and Mineral Ex-ploration in Greece (IGME) performed a great number ofchemical analyses on all known Greek thermal springs(Gioni-Stavropoulou 1983; Orfanos 1985; Sfetsos 1988).About 1,300 analyses were evaluated and the most rep-resentative were chosen for each thermal field (Table 1).Chemical patterns of thermal fields resulting from theseanalyses are in agreement with those given in studies onany particular field and therefore are considered to ac-curately reflect the mean chemical composition of ther-mal waters. Similarly, the collected data on isotopic anal-yses are almost the same during different periods. Forexample, stable isotope values of spring 76Le (see Ta-ble 2) do not vary significantly in time despite beingrecorded over a 10-year period. The aim of this paper is todescribe the main hydrogeological and hydrochemicalcharacteristics of geothermal fields and investigate theorigin of thermal waters. Processing of chemical analyseswas made using the Phreeqc program. Saturation indexeswere also simulated and to estimate the thermal waterreservoir temperature all possible geothermometers wereapplied.

Geographical Distribution of Mineraland Thermal Springs

Figure 1a shows the geographical distribution of the mainthermal springs of Greece, and Fig. 1b shows the coun-

try’s heat flow contour lines (in mW/cm2; Fytikas andKolios 1979). By comparing these maps, it can be easilyseen that most thermal springs are mainly located in areaswith greater heat flow which originated from intensevolcanic activity that took place in recent geologicaltimes. Areas with anomalous geothermal gradients are (1)the slow-moving Tertiary tectonic area of the northernAegean area (Salonica, Migdonia, Anthemus, Strimonas,Drama, Xanthi-Komotini, and Alexandroupolis Basins,the volcanoes of Samothrace, Limnos, Ag. Efstratios andLesvos Islands) (2) the volcanic arc of the southern Ae-gean areas, which is bordered by the volcanic centres ofMicrothiba, Achilion, Lichades, Loutraki, Aigina, Me-thana, Paros, Thira, Nisiros, Ko and others, and, (3) theSperchios depression which is not related with obviousvolcanic activity. To the west of the described regions, thenumber of mineral and thermal springs is small. Theirpresence is always related to that of fault systems.

General Hydrogeological Aspectsof the Main Thermal Fields of Greece

Intense volcanic activity in Greece is known from thepresence of volcanic rocks found in all isopic zones ofcontinental Greece and the islands. From Tertiary times,the Aegean area has been dominated by orogenic vol-canism due to the relative advance of the African plateinto the Eurasian mass. Geochronological and geologicaldata show that volcanic activity has migrated southwardswith time (Fytikas et al. 1984). This volcanic activity isclosely related to fault systems that favour the displace-ment in depth of ground waters and the development ofthermal springs.

According to Fytikas et al. (1984) and Pe-Piper andPiper (1989), volcanic activity in the Aegean Sea com-menced in the Oligocene and continues to the present day.Two major phases took place. The first stage was theOligocene–Miocene volcanic phase during which thevolcanic activity occurred in an East to West orientatedzone from Thrace to the Central Aegean. This activity islocated in many places of the Central Aegean region(Lichades of Euboea Island, Tinos, Sikinos, Samos andPatmos islands). Petrographically, two rock types aremainly observed: the calcareous alkaline type with thedominance of acid members (andesites and dacites) de-veloped mainly in Thrace, and the sosonitic type. Thesecond stage was the Pleistocene to the Quaternary phaseduring which the volcanic centres were arranged into thevolcanic arc of the south Aegean. Petrographically, thecalcareous alkaline series is present with all its membersfrom basalt to ryolithes. Intermediate phases of localvolcanic activity also took place from the Miocene to theQuaternary periods.

Numerous thermal fields are located in the Tertiarybasins of northern Greece. During the Tertiary periodwhen volcanic activity took place, the Rhodope mass (NGreece) shared a long fault of NE–SW, ENE–WSW andNW–SE direction that was active throughout the Neogene

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43.7

17.

2335

5.9

17.9

032

233

0

43M

i-I1

3N

eoge

netu

ffs,

con-

glom

erat

es,

allu

vium

s50

.07.

0028

,638

140.

000.

017

.41

63.4

933

7.48

57.7

94.

6944

4.9

19.5

133

034

1

44M

i-I1

4N

eoge

netu

ffs,

allu

vium

27.0

6.90

3,82

111

8.00

174.

00.

04.

9613

.44

35.3

92.

809.

2941

.19

5.2

244

222

45M

i-I1

5N

eoge

netu

ffs,

pyro

-cl

asti

cs,

allu

vium

s26

.04.

053,

354

152.

0011

1.0

0.0

3.92

12.7

234

.03

4.20

12.2

933

.99

7.63

290

285

46M

i-I1

6N

eoge

netu

ffs,

rhy-

olit

icla

vas,

allu

vium

s40

.66.

708,

433

0.0

25.0

114

.97

96.7

32.

3816

.32

111.

311

.87

152

110

47M

i-I1

7A

lter

edvo

lcan

ics,

mud

flow

s-la

har

24.4

6.50

1,59

40.

03.

547.

3314

.48

0.58

5.43

16.7

72.

5618

615

0

48K

i-I1

8T

uffs

,cl

ays

47.0

36,4

3429

.00

24.0

0.0

98.0

559

.20

456.

9712

.46

1.87

547.

9272

.28

159

118

49K

i-I1

9T

uffs

55.0

7.00

37,1

6027

.00

26.0

0.0

99.4

549

.59

474.

9711

.00

1.94

566.

9269

.50

148

105

50K

i-I2

0T

uffs

48.5

07.

1037

,912

31.0

017

.00

0.0

105.

052

.79

484.

9711

.50

1.67

589.

9260

.70

150

107

51T

hi-I

21C

ryst

alli

zed

lim

esto

nes

32.0

07.

803,

900

32.0

01.

000.

012

.00

5.19

48.3

91.

202.

4355

.24

7.31

153

110

52T

hi-I

22P

hyll

ites

,py

rocl

asti

cs,

pum

ice

34.5

07.

008,

983

75.0

012

.00.

022

.41

10.7

911

4.99

2.50

3.42

124.

4821

.75

144

101

53A

na-I

23M

arbl

es,

clay

s26

.00

7.15

957

18.0

017

.00.

04.

262.

796.

091.

804.

577.

491.

2541

046

854

Ni-

I26

And

esit

icla

va,

tuff

san

dpu

mic

e57

.00

6.80

39,5

2314

0.0

42.0

00.

067

.63

61.5

952

3.97

21.5

12.

3963

4.91

36.2

818

815

2

55N

i-I2

7A

ndes

itic

lava

,tu

ffs

and

pum

ice

46.0

06.

9033

,144

11.7

039

.00

0.0

49.2

274

.79

419.

9721

.51

3.19

534.

9327

.93

205

173

56N

i-I2

8A

ndes

itic

lava

,tu

ffs

and

pum

ice

40.0

06.

6018

,153

83.0

057

.00

0.0

38.8

242

.79

219.

988.

503.

7228

5.96

19.3

418

314

7

57K

o-I2

9F

lysc

h,li

mes

tone

42.0

06.

2041

,241

24.0

026

9.0

1.17

96.0

577

.60

506.

9715

.00

21.1

159

3.92

75.7

616

412

458

Ko-

I30

Sch

ists

and

lim

esto

nes,

mes

ozoi

cli

mes

tone

s46

.50

6.5

14,8

5538

.50

258.

00.

025

.21

32.0

017

5.98

5.02

15.7

520

2.97

18.9

916

212

1

59K

o-I3

1F

lysc

hw

ith

lim

esto

nele

nses

22.5

06.

52,

208

14.5

019

5.0

0.0

6.00

19.5

91.

060.

0518

.63

1.24

6.79

199

165

60K

a-I3

4L

imes

tone

san

ddo

lom

ites

37.0

06.

8039

,964

17.0

090

.00.

097

.65

42.0

524.

9715

.00

8.93

612.

4260

.72

162

129

61Ik

-I36

Gne

isse

s,m

arbl

es37

.00

7.05

11,6

9512

.00

16.0

0.0

26.0

115

.59

151.

994.

03.

417

8.97

17.4

015

717

562

Ik-I

37G

neis

ses,

mar

bles

35.0

07.

0026

,871

17.0

019

.50

0.0

60.8

334

.00

353.

9810

.00

3.56

416.

9439

.28

161

120

63Ik

-I38

Gne

isse

s,m

arbl

es35

.00

7.50

20,2

6914

.60

19.0

00.

047

.22

26.0

026

4.98

7.50

3.71

311.

9530

.61

161

120

64Ik

-I39

Gne

isse

s,m

arbl

es,

schi

sts,

cong

lom

erat

es58

.00

6.70

40,0

6525

.00

22.0

00.

073

.64

65.5

952

7.47

15.0

01.

8561

9.91

62.5

816

212

1

65Ik

-I40

Gne

isse

s,m

arbl

es,

schi

sts

54.0

06.

7039

,764

23.0

026

.00

0.0

72.4

364

.40

524.

9515

.00

1.99

614.

8961

.81

162

121

66Ik

-I41

Gne

isse

s,m

arbl

es,

schi

sts

47.8

07.

0037

,705

22.0

017

.00

0.0

66.8

358

.40

531.

4713

.00

2.31

5674

256

.21

152

169

Tab

le1

(con

tinu

ed)

509


Spr

ing

desi

gnat

ions

Lit

holo

gyT

�CP

HT

DS

(mg/

L)

SiO

2(m

g/L

)C

O2

(mg/

L)

H2S

(mg/

L)

Mg2

+

(mg/

L)

Ca2

+

(mg/

L)

Na+

(meq

/L)

K+

(meq

/L)

HC

O3

–

(meq

/L)

Cl–

(meq

/L)

SO

42–

(meq

/L)

Na/

KF

79�C

Na/

KT

r76

�C

67Ik

-I42

Gne

isse

s,m

arbl

es,

schi

sts

54.0

06.

7039

,013

24.0

025

.00

0.0

71.6

365

.00

514.

9713

.00

2.16

604.

9259

.68

154

112

68Ik

-I43

Gne

isse

s,m

arbl

es,

schi

sts

55.0

06.

8039

,828

22.0

025

.00

0.0

71.6

464

.40

524.

9715

.00

2.09

617.

4261

.38

162

121

69Ik

-I44

Gne

isse

s,m

arbl

es40

.00

6.95

26,7

4917

.70

19.0

00.

059

.34

36.7

935

3.98

10.0

02.

9341

1.94

40.3

216

112

070

Ik-I

45G

neis

ses,

mar

bles

40.0

06.

9028

,696

17.0

020

.00

0.0

54.0

245

.20

379.

9710

.00

2.53

442.

444

.39

157

115

71S

a-I4

6G

neis

ses,

mar

bles

,re

cent

depo

sits

30.0

07.

909,

983

50.0

00.

028

.64

14.1

211

7.87

9.05

3.01

147.

8816

.90

241

218

72L

e-I4

7L

avas

30.0

56.

5031

138

.60

1.23

2.19

1.65

0.17

2.98

1.35

1.04

270

257

73L

e-I4

8A

ndes

itic

lava

s43

.00

7.00

5,17

643

.00

2.38

16.2

165

.28

1.73

2.49

74.0

19.

0515

711

574

Le-

I49

And

esit

icla

vas,

rece

ntde

posi

ts65

.00

6.40

12,0

4210

.00

7.24

40.2

115

0.06

5.80

1.80

192.

029.

4518

314

7

75L

e-I5

0Ig

nim

brit

es,

rece

ntde

posi

ts81

.50

6.30

11,4

2364

.00

10.0

426

.79

150.

065.

604.

6718

2.01

6.12

144

144

76L

e-I5

1Ig

nim

brit

es,

rece

ntde

posi

ts37

.00

6.10

12,1

1171

.00

10.2

828

.39

160.

075.

604.

8119

3.04

6.45

176

138

77L

e-I5

2Ig

nim

brit

es,

rece

ntde

posi

ts80

.00

6.30

11,1

6766

.00

9.79

25.9

914

7.06

5.39

4.47

178.

035.

9518

014

2

78L

e-I5

3Ig

nim

brit

es67

.00

5.90

11,1

2079

.00

9.87

25.9

914

7.06

4.80

4.63

177.

025.

7017

113

279

Le-

I54

Mar

bles

,cl

ays

and

sand

ston

es39

.00

6.70

1,53

114

.00

4.11

5.38

16.0

00.

694.

851.

260.

9319

215

7

80L

e-I5

5L

avas

,re

cent

depo

sits

25.0

06.

5034

51.

481.

691.

560.

232.

701.

740.

4531

131

481

Le-

I56

Mar

bles

,sc

hist

s,pe

rido

tite

s44

.00

6.70

24,9

7727

.00

53.2

536

.17

330.

148.

002.

3238

8.06

36.9

915

110

9

82L

e-I5

7A

lter

ated

lava

san

dre

cent

depo

sits

27.0

06.

1038

21.

232.

342.

000.

401.

723.

890.

3335

137

3

83L

e-I5

8M

arbl

esan

dsc

hist

s,ba

salt

s,re

cent

depo

sits

36.0

06.

501,

539

14.0

01.

237.

5316

.22

0.35

6.88

19.0

11.

9914

410

0

84L

e-I5

9M

arbl

es,

schi

sts,

rece

ntde

posi

ts47

.00

6.50

35,6

6439

.00

56.8

481

.03

460.

2011

.99

4.09

562.

0943

.41

156

114

85S

a-I6

0G

abbr

o,ba

salt

s,gr

anit

es54

.50

7.00

12,6

191.

8030

.39

164.

5313

.05

6.99

203.

970.

7824

422

3

86S

a-I6

1G

abbr

o,ba

salt

s,gr

anit

es49

.00

7.00

20,4

843.

8054

.20

268.

4417

.92

5.99

339.

941.

3122

820

2

87L

o-P

43M

esoz

oic

lim

esto

nes,

rece

ntde

posi

ts32

.10

7.40

1,73

15.

843.

9217

.75

0.53

5.25

20.6

92.

0516

512

5

88M

e-P

45M

esoz

oic

lim

esto

nes,

rece

ntde

posi

ts27

.50

6.40

27,5

4445

.70

42.6

01.

2269

.23

37.2

034

9.98

10.0

016

.17

406.

9442

.00

162

121

89M

e-P

45a

Mes

ozoi

cli

mes

tone

s,re

cent

depo

sits

30.0

06.

3016

,954

2.00

60.5

026

.00

42.5

023

.52

212.

486.

2512

.32

244.

9627

.32

164

124

90M

e-45

bM

esoz

oic

lim

esto

nes,

rece

ntde

posi

ts28

.00

6.30

9,46

220

.00

43.2

01.

7123

.57

10.2

411

9.99

4.40

7.93

134.

9814

.70

180

142

91M

e-P

46M

esoz

oic

lim

esto

nes,

rece

ntde

posi

ts38

.00

6.40

9,29

112

7.80

59.7

00.

1622

.93

17.2

710

4.49

4.20

18.2

711

5.48

14.6

518

615

0

92M

e-P

46a

Mes

ozoi

cli

mes

tone

s,re

cent

depo

sits

22.5

06.

1539

,670

63.8

057

2.00

0.33

104.

451

.20

499.

9710

.00

27.4

757

7.92

56.0

013

995

93S

p-S

5Ju

rass

icli

mes

tone

s,op

hiol

ites

,qu

ater

nary

depo

sits

32.0

07.

3012

,821

19.1

330

.31

161.

075.

2510

.08

191.

0314

.26

171

132

94S

p-S

7M

esoz

oic

lim

esto

nes,

quat

erna

ryde

posi

ts31

.40

7.70

8,72

213

.81

21.5

910

9.04

3.00

7.23

130.

029.

3016

011

8

95S

p-S

8M

esoz

oic

lim

esto

nes,

quat

erna

ryde

posi

ts33

.00

7.20

10,9

6916

.81

28.2

013

6.06

3.50

10.2

716

2.03

11.7

415

511

3

96S

p-S

9M

esoz

oic

lim

esto

nes,

quat

erna

ryde

posi

ts32

.26.

9010

,747

15.4

129

.20

133.

053.

5010

.11

158.

0311

.65

157

115

97S

p-S

10M

esoz

oic

lim

esto

nes,

quat

erna

ryde

posi

ts28

.20

7.20

6,74

913

.21

16.7

980

.53

2.30

8.83

97.0

16.

9316

212

1

98S

p-S

12M

esoz

oic

lim

esto

nes,

quat

erna

ryde

posi

ts37

.00

7.50

9,22

815

.81

26.5

910

8.04

3.20

14.1

912

9.82

8.87

164

124

99S

p-S

13M

esoz

oic

lim

esto

nes,

quat

erna

ryde

posi

ts40

.00

6.90

9,13

816

.01

27.1

910

5.04

3.80

14.6

912

7.02

9.08

179

141

100S

p-S

14M

esoz

oic

lim

esto

nes,

quat

erna

ryde

posi

ts33

.00

7.40

24,8

1847

.63

51.2

031

2.63

9.00

15.2

937

0.07

33.7

716

312

2

Tab

le1

(con

tinu

ed)

510


Spr

ing

desi

gnat

ions

Lit

holo

gyT

�CP

HT

DS

(mg/

L)

SiO

2(m

g/L

)C

O2

(mg/

L)

H2S

(mg/

L)

Mg2

+

(mg/

L)

Ca2

+

(mg/

L)

Na+

(meq

/L)

K+

(meq

/L)

HC

O3

–

(meq

/L)

Cl–

(meq

/L)

SO

42–

(meq

/L)

Na/

KF

79�C

Na/

KT

r76

�C

101S

p-S

15M

esoz

oic

lim

esto

nes,

quat

erna

ryde

posi

ts38

.00

7.00

19,2

9739

.19

40.0

424

2.10

6.50

11.5

728

8.05

26.6

615

811

6

102S

p-S

18M

esoz

oic

lim

esto

nes,

quat

erna

ryde

posi

ts,

trav

erti

nes

33.2

06.

1010

,514

1850

.04.

2019

.21

41.7

972

.03

4.20

36.6

899

.51

0.08

216

187

103S

p-S

34A

rgil

lite

san

dsa

nd-

ston

esof

flys

ch32

.60

9.15

325

43.4

06.

470.

180.

404.

880.

031.

403.

600.

3878

29

104E

u-S

112

Mes

ozoi

cli

mes

tone

s,ne

ogen

efo

rmat

ions

43.5

06.

5034

,061

24.0

050

.86

79.2

443

7.67

11.5

14.

4952

4.10

51.3

215

711

5

105E

u-S

113

Tra

vert

ines

72.2

06.

2034

,886

1342

0.0

27.6

265

.82

459.

2011

.40

8.81

541.

1024

.28

153

110

106E

-S11

4T

rave

rtin

es59

.00

6.10

33,8

4716

200.

026

.02

79.2

043

4.19

11.0

09.

9351

3.10

23.2

215

411

210

7Eu-

S11

5T

rave

rtin

es73

.00

6.15

33,7

4110

440.

027

.22

83.2

043

5.19

10.6

010

.73

521.

1023

.96

152

109

108E

-S11

6T

rave

rtin

es35

.80

6.10

30,4

8413

400.

025

.09

72.3

939

0.54

10.1

28.

8246

3.57

21.8

015

611

410

9Eu-

S11

7M

etam

orph

icro

cks

39.0

6.40

23,0

7659

.00

50.0

453

.20

306.

137.

008.

5737

7.07

2.93

147

104

110P

w-P

4M

esoz

oic

lim

esto

nes

28.0

07.

0032

,709

11.0

02.

800.

1763

.65

44.7

944

3.19

10.0

03.

1750

6.09

48.0

714

710

311

1Pw

-P9

Neo

gene

lim

esto

nes

and

sand

ston

es28

.00

7.90

1,05

119

.30.

203.

126.

0010

.80

0.02

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Table 2 Isotopic composition of thermal-waters from the main thermal fields of Greece

Locations Springs d18O%o dD%o Locations Springs d18O%o dD%o

Gennisea (Xanthi Basin) 3X10 –6.24 –49.06 Lesvos 84Le9 +0.5 –0.6Eleytheres 11S10 –7.09 –49.82 Methana 88Me6 –4.80 –26.1Nigrita (Strimon Basin) 15S10 –8.71 –62.48 89Me5 –5.69 –30.2

25M8 –9.5 –67.3 Loutraki 87Lo5 –7.64 –44.7Volvi (Migdonia Basin)Lagadas (Migdonia Basin)

25M10 –9.35 –66.35 104Eu3 –0.37 +0.326M8 –9.3 –67.7 Edipsos (Euboea) 105Eu3 0.00 –0.927M8 –8.4 –59.6 106Eu3 –0.26 +2.2

Kynthos 40Ky7 –0.08 –1.2 Kamena Vourla (SperchiosBasin)Thermopyles (SperchiosBasin)Hypati (Sperchios Basin)

93Sp2 –4.91 –27.1Milos 43Mi7 +1.5 +6.5 95Sp –8.40 –48.6

42Mi7 –4.91 –24.6 96Sp2 –5.76 –31.3Ikaria 64Ik10 1.4 10.1 98Sp5 –7.30 –55.5Lesvos 76Le1 –4.94 –33.1 102Sp4 –7.90 –50.5

76Le6 –5.49 –32.7 Kyllini 112P10 –5.99 –33.276Le9 –5.3 –38.5 Kaiafas 114P10 –2.63 –11.174Le9 –4.7 –32.9

1 Papastamataki and Leonis 1982a, 1985 2 Papastamataki and Leonis 1982b 3 Papastamataki and Leonis 1982c4 Papastamataki and Leonis 1982d 5 Anonymous 1984 6 Barnes et al. 1986 7 Lohnert 19888 Poutoukis and Dotsika 1993 9 Michelot at al. 1993 10 Mitropoulos and Kita 1997

Fig. 1 Distribution map of the principal thermal waters of Greece

512


period. The area was shaped by strike-slip faulting andrelated extension processes. Tertiary basins are relatedand controlled by these faults that are associated with adifferent basin type and are parallel to the long axes of thebasins (Koukouvelas and Aydin 2002). In this way, theTertiary basins of northern Greece were formed. Thesefaults played a very significant role in allowing the ther-mal fluids to rise from their storage zones (reservoirs), toregional aquifers (Dimopoulos and Aggelidis 1986; An-dronopoulos 1967; Kolios 1985, 1986; Dimopoulos 1989;Traganos 1991). In these aquifers, thermal waters are lo-calized in neogene sediments such as sandstone, calcar-eous sandstone, and conglomerates with depths of over200 m (Kolios 1985; Karydakis and Kavouridis 1983;1989).

Deep thermal waters rising in western Peloponnesus,where volcanic manifestations are unknown, are also lo-

calized in sands and conglomerate intercalations of neo-gene formations (Kallergis and Lambrakis 1992, 1993).The tectonic formation of west Peloponnesus played asignificant role in the appearance of thermal springs. Thesprings are located on an axis parallel to WNS–ESE faults(Kiskyras 1962).

Thermal waters of the Loutraki-Sousaki area springsbelonging to the volcanic Aegean Island arc, which ex-perienced recent volcanic activity, are localized in Pleis-tocene conglomerates (Schroeder 1985; Fytikas and Ka-vouridis 1985). The rise of thermal water in the region isrelated to an active E–W trending fault system located inthe eastern part of the Golf of Corinth, which was levelbefore the deposition of the neogene sediments in thebasin of Corinth (Fytikas and Kavouridis 1985).

Apart from the above-mentioned springs, very impor-tant thermal fields of Methana and the islands of Milos,

Fig. 2 Classification of thethermal-water springs using theexpanded Durov diagram

Fig. 3 Logarithmic plots of relationships between concentration (meq/L) of chloride vs. sodium (a) and calcium (b) in Na–HCO3 typeGreek thermal waters

513


514


Serifos, Syros, Paros, Thira, Ios, Naxos, Syfnos, Amor-gos, Kos, Nisiros and Euboea belong to the volcanicAegean island arc. Volcanic rocks are very commonabove a crystalline substratum that characterised all is-lands of the central Aegean (Durr et al. 1978; Boronkayand Doutsos 1994). During the Pleistocene, extensiveandesitic volcanism with different kinds of calc–alkalinepyroclastic products and lavas (Fytikas 1977) took placeon Lesvos, Milos, Thira and Nisyros. This volcanism,caused by thermal anomalies at relatively shallow depth,is proved by the presence of fumaroles on Milos andNisyros (Fytikas et al. 1989; Chiodini et al. 1993). Ther-mal waters rise to the surface either directly from thecrystalline substratum and volcanic rocks, or to smallalluvial aquifers in Quaternary deposits.

Quaternary deposits of the Sperchios Valley, very closeto Euboea Island, host the thermal waters of Ypati Springin conglomerates (Marinos and Frangopoulos 1973), as atKammena Vourla and Thermopyles (Orfanos and Sfetsos1975). The valley is delimited by WNW–ESE orientedfaults that relay thermal fields with the sea (Georgalas andPapakis 1966). Thermal waters also rise to the alluvialaquifers in the areas of Aridea (Tzimourtas 1986), Thermaof Xanthi, and the volcanic islands of the Aegean Sea.

Classification and Hydrochemical Characteristicsof Thermal SpringsThe expanded Durov diagram (Fig. 2; Lloyd 1965), whichis congener to the Langelier and Ludwig (1942) diagram,is used for a first classification of Greek thermal waters. Itis clear from the diagram that the waters can be groupedinto four main water types: Ca–HCO3 type, Mg–HCO3type, Na–HCO3 type, and the Na–Cl type.

Springs originating directly from crystalline rocks innorthern Greece (Aridea internal basin and the Rhodopemassif) belong to the first two types of thermal water(Ca–HCO3 and Ca–Mg–HCO3 type waters). These wa-ters have a small concentration of total dissolved solids(TDS; Table 1). After Ellis and Machon (1977) HCO3

�

waters are considered to occur in volcanic areas wheresteam containing CO2 condenses into the liquid phase.Giggenbach (1991) indicates that HCO3

� waters can alsoreflect interaction of CO2 charged fluids at lower tem-peratures as well as mixing with local groundwater.

Samples from the post-orogenic basins (Alexandrou-polis, Xanthi, Strimonas, Migdonia Basins) belong mainlyto the Na–HCO3 water type. Their content in TDS islower than that of the next type of Na–Cl waters in whichNa is considered to be derived from mixing with seawa-ter. The dominance of Na in these springs (see Fig. 3a,where the dotted line is the seawater mixing line) could becaused by the water’s increased alteration capacity due to

the high CO2 concentration that favours the solubility ofalkaline elements from silicic rocks (Ellis and Mahon1977). However, in some cases, ion exchange phenomenabetween Na and Ca could also be responsible for sodiumand calcium concentrations (samples from Alexandrou-polis-Xanthi Basin, Sperchios Basin, western Pelopon-nesus; Fig. 3b). The above-mentioned hydrochemicalprocess is also encountered in other geothermal areas withhigh CO2 levels as in the inner basin of Rhodope, inAnthemous Basin, in Lesvos Island and in SperchiosBasin.

Most of the samples were classified into the Na–Clwater type and are characterised by high TDS values anda Na/Cl ionic report of about 0.85, very close to that ofseawater (for seawater Na/Cl=0.84; Fig. 4a). This wa-ter type comprises almost all the samples from islandgeothermal fields and from coastal springs. Their chem-ical composition seems to be strongly affected by water ofsodium-chloride composition as Minissale et al. (1989;1997) have also shown.

Na–Cl type waters could be potentially equivalent toseawater mixing with meteoric water or waters havingdissolute marine evaporites or deep circulation of recentseawater. Aquilina et al. (2002), demonstrated that in theBalaruc thermal fluids, which are a mixture of karst wa-ters and waters of marine origin, the thermal end-memberis itself a mixture of seawater and meteoric palaeowater.Assuming that deep circulation of seawater was thesource of the dissolved salts, one would expect the waterto have the geochemical characteristics of seawater assuggested by the correlation between Na and Br in theislands (r>98%) (Fig. 4b).

Figure 4c exhibits two groups of samples with goodcorrelation between Cl and SO4 (r>98%). Most of thewater samples belong to the first group. The concordancebetween the thermal fluid regression line and the seawa-ter–rainwater mixing line, suggests the same origin ofthese ions: seawater. However, the small discrepancybetween the two lines, especially for the more salinesamples, could be attributed to increased amounts ofsulphates caused by the dilution of anhydride if brinesexist at depth, or to the oxidation of pyrite according tothe reaction, FeS2+4.75 O2+1.5 H2O+4e�$Fe(OH)3+2SO4

2� (Appelo and Postma 1993). Samples from Milos,Nisiros and Euboea Islands belong to the second watergroup, which presents a lack of SO4 in relation to the firstgroup. Divergences from the seawater–rainwater mixingline suggest modification of the original seawater bywater–rock interactions.

The depletion of magnesium (Fig. 4d) could be at-tributed to the ion exchange process at high temperaturein several calcium-magnesium silicate minerals (Ellis1971; Giggenbach 1988) or to the following reactionsthat, according to Schoeller and Schoeller (1985), couldbe taking place in crystalline rocks.

The first is that magnesium concentrations decreasewith temperature, and chlorite is formed from the fol-lowing reaction:

Fig. 4 Logarithmic plots of relationships between concentration(meq/L) of chemical species a chloride vs. Na/Cl, b chloride vs.bromide, c chloride vs. sulphates d chloride vs. magnesium, ecalcium vs. sulphates, f Mg/Ca vs. SO4/Ca, g chloride vs. boron, hchlorides vs. nitrates in Na–Cl type Greek thermal waters

515


KAl3Si3O10 OHð Þ2 þ 7:5Mgþ2 þ 1:5H4SiO4

þ9H2O$ 1:5MgAl2Si3O10 OHð Þ8 þ 14HþþKþ

Laumonite or prenite also are formed. The second re-action is that calcium concentrations should increase withdepth as a result of anorthite dilution via the reaction,CaAl2Si2O8+H2O+2H+$Ca+2+Al2Si2O5(OH)4. Hence, sea-water brings almost the totality of dissolved Cl, Br andSO4. In order to evaluate whether anhydride is diluted, thecorrelation line between Ca and SO4 is drawn.

In Fig. 4e, several groups of samples could be distin-guished. One group, suggesting a Ca/SO4 ratio of 1:1 as inthe dilution of anhydrite, comprises samples mainly fromIkaria Island where the above-mentioned mineral does notexist. Other groups suggesting Ca/SO4 ratios of 1.33:1 or3:1, comprise samples from Sperchios Basin or Euboeaand Milos islands respectively. Not having a clear imageabout these relationships, Fig. 4f with normalized con-centrations of SO4 and Mg to Ca, was drawn to differen-tiate the seawater and evaporate end-members (Aquilina etal. 2002). The regression line (r>98%) for the majority ofthe samples is almost in concordance with the seawater–rainwater mixing-line. A few samples from western Pelo-ponnesus and the Anthemous Basin where anhydrite exists,are in discrepancy with the line towards the anhydritecorner, and suggest that dissolution of this mineral may beresponsible for the sulphate enrichment of thermal water.

Intensified water–rock interactions are obvious in is-lands thermal waters for which boron determinations areavailable. In Fig. 4g, samples from Nisyros, Milos, Les-vos, Kythnos and Euboea Islands with an excess of Brelative to Cl could be attributed to intensified water–rockinteractions. Additionally, nitrate concentrations that existin most of the samples (Fig. 4h), indicates the participa-tion of fresh water.

It should be noted that in addition to the mixing ofthermal with cold, fresh and seawater, cases of fractionalmagmatic water participation should not be ruled out. Forexample, while drilling on the island of Thira, thermaland mineral water was located which had a TDS contentof 53.223 gr/L (Kavouridis et al. 1982), higher than thatof seawater. According to Chiodini et al. (1994), the in-creased values of TDS may be due to the presence ofmantle fluids in Thira Island (Palea and Nea Kameni).

Isotopic Composition of Thermal and Mineral Waters

Table 2 presents values of the stable isotopes in water(d18O and dD) for the main geothermal fields in Greece.The d18O and dD diagram in Fig. 5 has been drawn usingdata where Greek rainfall areas have also been drawnaccording to Chiodini et al. (1994).

The position of many thermal waters from Euboea,Kynthos, Milos and Lesvos Islands are very close to meansea water (SMOW) indicating their purely marine origin.Thermal waters from Sperchios, Migdonia, Loutraki Ba-sins, Methana and West Peloponnesus area are close to

the meteoric rainfall area. Thermal waters from Komoti-ni-Xanthi, Srimonas, Sperchios Basins and Lesvos Island,show strong meteoric contribution while their positionunder the meteoric water area could mean mixing withseawater.

The above results are in accordance with observationin the previous section where it is mentioned that thermalsprings rising close to the sea are strongly affected byseawater that enters the hydrological circuit.

Diluted CO2 and H2S Gases in Thermaland Mineral Waters

From Table 1 it can be seen that many thermal andmineral waters contain increased amounts of dissolvedCO2 and H2S gases. Springs with high CO2 concentra-tions are located in the basins of Strimonas, Aridea, An-themous and Sperchios. The majority of these springshave CO2 levels varying between 200 to 1,850 mg L�1.After Barnes et al. (1986), according to stable d13C inCO2 isotope data, the origin of CO2 in thermal fields ofGreece is the result of the thermometamorphism of ma-rine limestones. This process also occurs in other similargeothermal areas (Nuti et al. 1980).

Thermal and mineral waters containing H2S are en-countered in the basins of Strimonas, Migdonia andSperchios, the area of Methana, the western Pelopon-nesus, and Epirus. Hydrogen sulphate (H2S) results fromthe reduction of sulphate ions under suitable conditionsand in the presence of bacteria. It may also derive fromthe oxidation of pyrite and the anaerobic alteration of

Fig. 5 d18O and d2H composition of thermal and mineral waters ofthe main geothermal springs in Greece. Hellenic rainfall area afterChiodini et al. (1994)

516


organic matter. In the western Peloponnesus, H2S is pro-duced from the reduction of sulphates present in thegypsum of Trias (Kallergis and Lambrakis 1992). Thiscould also be the case in the areas of Methana andSperchios. According to Poutoukis and Dotsika (1993), inthe Migdonia Basin, H2S is produced from the reductionof pyrite-derived sulphate, although it is much more likelythat CO2 produces a solution that is acid, and pyrite isaltered according to the following type of reaction:

FeS2 þ Hþ ! Feþ2 þ H2S

Geothermometry

As made clear in the previous paragraphs, groundwatersof Greek thermal springs acquire their chemical compo-sition at depth by interacting with silicic rocks bearingalkaline elements and some carbonates (mainly marbles).However, they also interact with shallow aquifers orseawaters. In most cases, except for the islands, theseshallow aquifers are located in the neogene sediments.

The degree of water–rock interaction in all sampleswas determined by calculating the saturation index of theminerals calcite (SIC), dolomite (SId), gypsum (SIg), chal-cedony (SICh) and quartz (SIQ) using the Phreeqc pro-gram. The above saturation frequency index diagramsshow that most Greek thermal waters are over-saturated incalcite and dolomite (Fig. 6). The only negative values areencountered in samples of Lesvos and Milos Islandswhere the contribution of Ca and Mg bearing minerals isnot significant due to the dominating volcanic rocks inthe islands. Almost all thermal waters are unsaturated ingypsum while the majority are saturated in quartz and lesssaturated in chalcedony. Thermal waters unsaturated inchalcedony are encountered in samples from the westernPeloponnesus and Epirus, Strimonas Basin and the islandsof Nisyros, Ikaria, and Lesvos. Consequently, chemicalgeothermometers are presented, based on the mineralswith the highest grades of saturation. Moreover, as seenfrom Table 3, several geothermometers lead to unac-cepted temperature values.

Table 3 and Fig. 7 show statistics from the applicationof selected geothermometers. Fig. 7 shows that whendifferent geothermometers are applied, the estimated tem-

Fig. 6 Frequency diagrams for calcite, dolomite, gypsum, chalcedony and quartz saturation indexes

517


peratures differ. The mean estimated temperatures for allthe thermal springs as calculated by the Na, K and Cabased geothermometers, are similar and vary between 149and 187 �C (Table 3). The geothermometers of Truesdell1975 and Fournier 1979 (Table 4) provided the closesttemperature compared to that measured in wells drilled inMilos Island at 1,000–1,400-m depth that is greater than

300 �C (Fytikas 1978). According to Liakopoulos et al.(1991), that temperature is 318 �C. This could be taken asevidence that in Milos thermal water, a full equilibriumhas been achieved between rocks and water in the storagezone. The geothermometers based on SiO2 and Mg cor-rection show values that differ from previous values. It isknown that the Na–K–Ca–Mg geothermometer can be

Table 3 Statistical parametersfrom geothermometer applica-tion concerning the estimatedtemperature of thermal waters.SD standard deviation

Minimum Maximum Average SD Var%

SiO2 Am1 –114.0 20.0 –43.774 26.645 670.0SiO2 CriA2 –64.0 96.0 20.86 31.391 167.0SiO2 CriB3 –100.0 47.0 –23.538 29.059 313.0SiO2 Chalc4 –53.0 120.0 38.538 34.243 144.0SiO2 Qz5 –21.0 146.0 69.86 32.513 114.0Na/K FOUR736 –30.0 505.0 149.081 81.664 106.0Na/K TR757 –18.0 468.0 154.306 74.989 104.0Na/K FOUR798 32.0 410.0 187.427 59.454 92.0K/Mg GIG839 –26.0 85.0 43.726 13.684 131.0Na–K–Ca10 6.0 292.0 169.065 38.238 98.0Na–K–Ca–Mg11 17.0 204.0 72.862 46.744 92.01 Fournier 1977 2 Fournier 1977 3 Fournier 1977 4 Fournier 19735 Fournier and Rowe 1966 6 Fournier 1973 7 Truesdell 1975 8 Fournier 19799 Giggenbach et al. 1983 10 Fournier and Truesdell 1973 11Fournier and Potter 1979

Fig. 7 Frequency diagrams for the estimated temperatures using the quartz, Na/K, N/Mg, Na–K–Ca and Na–K–Ca–Mg geothermometers

518


used in cases where thermal waters mix with cold freshwaters, which is the case for all neogene and tertiarybasins. Saline water contribution, however, greatly re-duces the reliability of this geothermometer. The lowvalues obtained by the SiO2 geothermometers could beexplained by low silicate contents in the storage zone(metamorphosed carbonates rocks in many cases) and/orby partial equilibration of water–rock due to short contacttimes.

Using the above six geothermometers (Table 4), theareas with the highest estimated temperatures are Milos,Lesvos, and Nisyros Islands, and Xanti geothermal field.

Conclusions

In this paper, the basic hydrogeological and hydrochem-ical characteristics of the Greek geothermal areas are pre-sented and the origin of thermal and mineral spring watersis investigated. These springs occur mainly in the post-orogenic basins of the northern Aegean and the Aegeanisland arc. Geothermal areas are related to recent volcanicactivity and active tectonics. Fluid movement is due tovolcanic activity and a thermal gradient leading to con-vection. This is the case for the majority of springs withinareas of Tertiary basins of northern Greece and the Ae-gean island arc. In western Greece, where volcanic ac-tivity does not exist, the thermal gradient is due only todepth.

Spring waters in islands and coastal areas are typical ofmarine solutions and result from the mixing of deep ther-mal reservoir water and with meteoric water. In conti-nental areas, thermal water rising from deep reservoirs isfrequently localized in aquifers of neogene sedimentssuch as conglomerates and sandstones, while in somecases it is mixed with karst surface water.

Chemical data combined with isotopic data classifiedthermal springs into four types of water that originatefrom marine and non-marine sources. The most importanttype that belong to marine sources, has a Na/Cl ratio ofabout 0.85, comprises the spring waters of island andcoastal regions, and is of the Na–Cl type. In some cases(e.g. Euboea and Lesvos Islands), it seems that thermalwaters are due to direct seawater infiltration. However,the contribution of mantle fluids should not be excludedat least in the more recent volcanic islands (Chiodini et al.1994). The other three water types originate from non-

marine sources. The Na–HCO3 type occurs in the internalareas of post-orogenic basins (e.g. Strimonas, Migdonia,etc.). High amounts of CO2 contribute to the chemicalcomposition of these waters and favour the solubility ofalkaline elements such as Na, from siliciceous rocks. Ionexchange phenomena between Ca of the waters and Nafrom clay minerals should not be excluded, and con-tributes to the increase of Na content. The two remainingwater types, Ca–HCO3 and Mg–HCO3, are considered tobe associated with local groundwater.

The presence of CO2 in the thermal and mineral watersstudied is due to the metamorphism of marine carbonates.The occurrence of H2S in spring waters of the MigdoniaBasin is due to the alteration of pyrite, while in thePeloponnesus it is due to the reduction of sulphates orig-inating from dissolved gypsum.

Geothermometric analysis is related to mean temper-atures between 149 and 187 �C. These temperatures areprobably due to a normal gradient, given that the depth ofthe post-orogenic basin of Greece is thought to be greaterthan 4,000 m. The most promising geothermal fields ofGreece are encountered in the Milos, Lesvos, and NisyrosIslands and Xanthi Basin.

Acknowledgments The authors wish to express their gratitude tothe Editor and the referees for their careful readings of the manu-scripts. Their comments, suggestions, and remarks proved indis-pensable in helping us improve the style and presentation of thispaper.

References

Anonymous (1984) Methana-Poros, Loutraki-Sousaki, Platystomo:Aidipsos geothermal projects. Final report, Geothermica Ital-iana Sr 1, ENEL, Italy

Andronopoulos B (1967) The mineralisation of the Therma area,Xanthi, northern Greece (in Greek). Geological reconnaissanceReport No. 40, IGSR, Athens

Appelo CAJ, Postma D (1993) Geochemistry, groundwater andpollution. Balkema, Rotterdam

Aquilina L, Ladouche B, Doerfliger N, Seidel JL, Bakalowicz M,Dupuy C, Le Strat P (2002) Origin, evolution and residencetime of thermal fluids (Balaruc Springs, southern France): im-plications for fluid transfer across the continental shelf. ChemGeol 192:1–24

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Table 4 The maximum estimated temperatures (in paranthesis) using the six selected geothermometers

Geothermometers Springs with higher estimate temperatures (�C)

SiO2 Qz 45Mi (146), 42Mi(138), 9R (130), 74Le (123), 32Ai (120) 56Ni (114), 78Le (111), 76Le (106)Na/K (Fournier 1973) 53Ana (460), 83Le (390), 43Mi (366), 42Mi (357), 5X (299), 72Le (298), 6,7R (281), 55Ni (225), 54Ni (205)Na/K (Truesdell 1975) 82Le (373), 43Mi (341), 80Le (314), 21S (298), 45Mi (285), 5X (258), 72Le (257), 17S (244)Na/K (Fournier 1979) 82Le (351), 43Mi (330), 42Mi (322), 80Le (311), 21S (299), 45Mi (290), 21S (283), 5X (271), 54Ni (188),

55Ni (205)Na–K–Ca (Fournier 1973) 43Mi (292), 42Mi (283), 53Ana (270), 45Mi (230), 71Sa (225), 17S (213), 4X (210), 55Ni (209), 54Ni (202)Na–K–Ca–Mg (Fournierand Potter 1979)

42Mi (176), 43Mi (176), 5X (160), 12S (149), 13S (153), 7R (152), 6R (149), 11S (149), 8R (136), 14S (130)

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