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Aquifer chemistry of thermal waters of the Godavari Valley, India
Journal o f Volcanology and Geothermal Research, 25 (1985) 181--191
181
Elsevier Science Publishers B.V., Amsterdam -- Printed in The Netherlands
AQUIFER CHEMISTRY OF THERMAL WATERS OF THE GODAVARI VALLEY, INDIA V.K. SAXENA and MOHAN L. GUPTA Geothermal Group, National Geophysical Research Institute, Hyderabad -- 500 007, India
(Received March 14, 1984; revised and accepted December 6, 1984)
ABSTRACT Saxena, V.K. and Gupta, M.L., 1985. Aquifer chemistry of thermal waters of the Godavari valley, India. J. Volcanol. Geotherm. Res., 25: 181--191. The results of a chemical study of thermal waters from three hot springs, two water discharges in a mine at 180 m depth, and four wells drilled for exploration of coal and water resources in the Godavari valley indicate: (1) a deep flow path within the Lower Gondwanas (Upper Carboniferous--Lower Triassic) for Agnigundala thermal water which has been found to be in equilibrium with quartz, montmorillonite and kaolinite at 150° C; (2) medium depth circulation also through Lower Gondwana sedimentary rocks and equilibrium with quartz, at 100°C for waters of Buga, Manguru and Bhuttayagudem; and (3) circulation within sedimentary formations for the thermal waters of the Pagdaru and Bhimdole areas. Waters of the last areas show disequilibrium but are within the stability field of kaolinite. The aquifer temperature is most likely to be about 156°C for the Agnigundala, around 100°C for the Buga, and not more than 100°C for the other systems.
INTRODUCTION H o t springs have been k n o w n in the Godavari valley since ancient times. T h e r m a l waters have also been t a p p e d in m a n y r e c e n t e x p l o r a t o r y wells drilled f o r coal a n d g r o u n d w a t e r . The c h e m i s t r y o f some t h e r m a l and cold waters o f t h e valley has been previously p r e s e n t e d (Saxena a n d G u p t a , 1 9 8 2 ; Saxena, 1983). These studies have been f u r t h e r e x t e n d e d t o t w o m o r e areas w h e r e t h e r m a l waters have been e n c o u n t e r e d in g r o u n d w a t e r wells. B o t h t h e previous a n d t h e n e w l y g e n e r a t e d data have been used t o s t u d y the chemical equilibria o f the t h e r m a l waters, to infer their relative d e p t h s o f circulation a n d t h e t y p e o f r o c k s w h i c h have m a i n l y c o n t r i b u t e d to their chemical c o m p o s i t i o n , and to o b t a i n m o r e realistic estimates o f the aquifer t e m p e r a t u r e s . The findings are given a n d discussed in this paper. LOCATION T h e g e o l o g y o f part o f the Godavari valley a n d locations f r o m w h i c h the samples of t h e r m a l waters were collected are s h o w n in Fig. 1.
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Fig. 1. Geological m a p o f a p a r t o f Godavari valley (after GSI, 1975) and l o c a t i o n o f Hot Springs and drill holes. I = Alluvium; II = R a j a h m a n d r y sand s t o n e ( N e o g e n e ) ; III = U p p e r G o n d w a n a s (Middle T r i a s s i c - - L o w e r Cretaceous); IV = K a m t h i , L o w e r G o n d w a n a s ( U p p e r C a r b o n i f e r o u s - - L o w e r Triassic); V = Talchir, L o w e r G o n d w a n a s ( U p p e r Carbonife r o u s - L o w e r Triassic); VI = Pakhal series ( U p p e r P r e c a m b r i a n ) ; VII = Dharwar group ( L o w e r P r e c a m b r i a n ) ; VIII = C h a r n o c k i t e s ( L o w e r P r e c a m b r i a n ) ; IX = K h o n d a l i t e s (Lower P r e c a m b r i a n ) ; X = Alkaline rocks ( P r e c a m b r i a n ) ; XI = Ultra basics ( P r e c a m b r i a n ) ; XII = Archaean.
CHEMISTRY OF THERMAL WATERS
The chemical analyses of thermal waters axe given in Table 1 which shows that these waters axe nearly neutral to mildly alkaline (pH 7.4--7.8). A com-
183
parison summary of the chemical compositions of these thermal waters brings out the following observations: Agnigundala
Buga, Pagdaru, Manguru, B h u t t a y a g u d e m and Bhimdole
More mineralized salinity 1139 p p m 80%, NaCl 7% CaliCO 3 143 p p m SiO~
Less mineralized salinity 4 8 0 - - 8 4 0 ppm 40--55% NaC1 23--35% CaliCO 3 35--67 ppm SiO~
The above observations suggest two different water systems viz. ( 1 ) t h e Agnigundala system, and (2) the Buga, Pagdaru and Manguru system. The waters associated with Bhuttayagudem and Bhimdole are very similar to that of the latter system, thereby reflecting the similarity of the chemical composition of the deep aquifer rocks, namely Gondwanan sediments. The Agnigundala and Bhuttayagudem thermal waters are of the alkali-chloride type, and the others are mixed alkali chloride and bicarbonate. This inference is quite clear from Fig. 2. In addition, there is an indication (Points 4, 5, 8 and 9) in Fig. 2 that the Buga water is altered Manguru water. A detailed classification for distinguishing water groups based on chemical parameters reflecting geological features of reservoirs has been described by Saxena and D'Amore (1984). Using concentrations (meq/1) of the seven major chemical components of the water samples, they have defined six new parameters, normalized between 100 and - 1 0 0 , where ~ (+) and E ( - ) represent the sums of the cations and anions respectively. 100 Parameter A: - -
~(-)
(HCO~ - SO~-)
This parameter mainly distinguishes between waters circulating through calcareous terrains and those flowing through evaporitic rocks. Parameter B: 100 (
SO~-
~(-)
Na ÷ -
r~(+i i
This parameter discriminates between sulphate-enriched waters circulating in evaporitic terrains and sodium-enriched waters found in marly, clayey sedimentary terrains. Parameter C: 100
--
~(+)
~(-)
This parameter tends to distinguish between waters derived from flysch or volcanic rocks and those from earbonate-evaporitic series of from a regional quartzitie-sehistose basement. Both types of water have relatively high Na ÷, but the former have low C1-.
B h i m d o l e drill h o l e (b)
Agnigundala hot spring
Buga main hot spring
Buga warm spring
P a g d a r u drill h o l e - 1 (c)
P a g d a r u drill hole-2(c)
M a n g u r u , TW-1 (d)
Manguru, TW-2 (d)
2.
3.
4.
5.
6.
7.
8.
9.
37
38
33
39
40
45
62
52
64
1022
1038
764
774
793
856
1750
499
1280
Temp. 1 Spec. (°C) conduc2
7.8
7.8
7.7
7.7
7.7
7.8
7.5
7.4
7.4
pH 3
766
773
541
542
555
599
1139
341
841
TDS
60
60
35
48
43
67
143
43
63
SiO 2
196
200
95
111
100
95
321
44
142
Na
9.6
8
7A
8.9
8
7.4
23.6
4.4
20.4
K
25
20
50
25
25
50
32.5
41.2
97.5
Ca
in p p m )
3
1.2
7.9
3
18.2
7.9
0.9
4.7
8.8
Mg
6
5
4
5.5
5
4
4
2
3
F
84
84
50
50
50
50
430
100
217
C1
214
214
171
200
171
171
38
64
]43
171
185
121
73
134
147
147
38
150
H C O a SO 4
0.2
0.2
0.1
0.1
0.08
0.08
0.8
0.04
0.2
Li
i Surface temperature. 2 M i c r o m h o s / c m , at 25 ° C. 3 A t 25 ° C. (a) 5 0 0 m drill h o l e d i s c h a r g e s w a t e r 2 7 . 8 1/sec. ( b ) 5 0 0 m drill h o l e d i s c h a r g e s w a t e r 2 2 . 7 1/sec. (c) 3 0 0 m drill h o l e s d i s c h a r g e s w a t e r . (d) H o t w a t e r e m i t t e d in v a r i o u s p l a c e s w i t h a g o o d d i s c h a r g e u n d e r a c o a l m i n e . P r e s e n t s a m p l e s c o l l e c t e d f r o m ] 80 m d e p t h .
Bhuttayagudem drill h o l e ( a )
].
SI. T h e r m a l w a t e r No. a r e a
Chemical analyses of the thermal waters, Godavari valley (concentrations
TABLE 1
0.01
0.01
0.02
0.2
0.2
0.2
2.5
0.1
0.5
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Fig. 2. Piper diagram of the chemical analyses of water samples.
N a + _ Mg2 + Parameter D: 100
~(+)
This parameter characterizes waters that have circulated in dolomitized limestone.
Parameter E: 100
(Ca2+ + Mg 2÷ E(+)
HCO~) ~,(-)
This parameter mainly distinguishes between circulations in carbonate reservoirs and those in sulphate-bearing reservoirs. Parameter F: 100
_( Ca2+ _~_~Na+- K+ )
This parameter reveals the increase of Na ÷ and K+ in the waters.
186
The calculated values of parameters A to F, for the water samples studied have been plotted in rectangular diagrams shown in Fig. 3. These rectangular diagrams suggest a deep circulation of Agnigundala water (through sedimentary rock formations and a near-surface alteration for the waters of Buga, Pagdaru, Bhyttayagudem, Bhimdole and Manguru.
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Fig. 3. Representations of the water samples on the rectangular diagrams defined by the six parameters (see text).
CHEMICAL EQUILIBRIA
Study of the chemical equilibria between minerals and a solution requires the determination of the activities of aqueous species and the identification of minerals found in the associated altered rocks. Calculated Debye-Huckel activity coefficients were used to convert the molalities of the aqueous ionic species into activities. The resultant computer-calculated activity values are given in Table 2. The number of minerals which could participate in reactions with the waters is very large. However, the discussion in this paper is limited to those phases which are inferred to be present in the reservoir; therefore only the following mineral reactions have been considered among phases inferred to be present in the reservoirs. (1) K. feldspar--K, montmorillonite; (2) K. montmorillonite--kaolinite; (3) kaolinite--gibbsite; (4) K. feldspar--illite; (5) K. feldspar--muscovite; (6) K. montmorillonite--illite; (7) muscovite--illite; (8) kaolinite--illite;
187
(9) gibbsite--illite; (10) gibbsite--muscovite; (11) albite--Na, montmorillonite; (12) Na. montmorillonite--kaolinite; (13) Na. montmorillonite--gibbsite; (14) albite--gibbsite. The formulation and solution of the temperature
--log aNa ÷
--log aK+
--log a c a 2 + --logaMg:÷ --logaH4SiO4
1. 2. 3. 4. 5. 6. 7. 8. 9.
2.26 2.77 1.92 2.43 2.41 2.37 2.43 2.11 2.12
3.33 4.00 3.28 3.77 3.74 3.69 3.77 3.74 3.66
2.66 3.04 3.37 3.16 3.25 3.25 3.14 3.35 3.25
B h u t t a y a g u d e m drill-hole B h i m d o l e drill-hole A g n i g u n d a l a H o t Spring Buga Main H o t Spring Buga Warm Spring Pagdaru drill hole-1 Pagdaru drill hole-2 M a n g u r u , TW-1 M a n g u r u , TW-2
3.49 3.76 4.76 5.76 3.17 3.95 3.73 4.35 3.95
3.07 3.28 2.71 3.06 3.27 3.23 3.36 3.11 3.11
LSO~C 8
i I
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150~c
gl
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/~
+o
Z
5'0
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i.3 4.0
F
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g
IW/', 3'3 -2
-3 Log o H4SiO 4
4
1 -2
-3 L og a H 4 Si 0 4
Fig. 4. A c t i v i t y - a c t i v i t y d i a g r a m for t h e K~O-A1203-SiO~-H20 s y s t e m a t 150 ° C for Agnigundala. Fig. 5. A c t i v i t y - a c t i v i t y diagram for t h e Na~O-A1203-SiO2-I-I20 s y s t e m at 150°C for Agnigundala.
188 Loo"c
, a 0 °C
6
zl
I 7 ÷I
a: I
÷I
+ O Z
5
~6
o
/~.l
I
~
I .~4
-22
-4
Log a H 4 S J 0 4
:(e . 7
I
36 ~2
Log
uH4
'i 0 4
-4
Fig. 6. Activity-activity diagram for the K20-A1203-SiO2-I-~O system at 100~C. Numbers correspond to those in Tables. Fig. 7. Activity-activity diagram for the Na20-A120~-SiO:-H:O system at 100°C. Numbers correspond to those in the tables.
the given reactions have been taken from Helgeson (1969). The activities for various ionic species were calculated for a large number of reactions (Table 2). The most appropriate mineral-water equilibria for the Agnigundala and the Buga, etc. systems have been found at 150°C and 100°C, respectively. The relationships between log aK+/aH+ and log aNa+/aH+ with log aH4SiO4 have been drawn at 150°C for Agnigundala (Figs. 4 and 5) and at 100°C for the Buga, Pagdaru, Manguru, Bhuttayagudem and Bhimdole areas (Figs. 6 and 7). The activity diagrams suggest that the Agnigundala water apparently equilibriates at about 150°C with quartz, montmorillonite and kaolinite. These mineral phases are consistent with water circulation through sedimentary rocks containing quartz and in clay-rich layers with montmorillonite. The inferences are in agreement with local geology and suggest circulation and storage of the Agnigundala thermal waters in Lower Gondwanas (Upper Carb o n i f e r o u s - L o w e r Triassic). In Figs. 6 and 7 we show the Bhuttayagudem, Buga and Manguru waters
189
are near to the quartz saturation line at 100°C, within the stability field of kaolinite, consistent with their sedimentary environment, particularly Rajmahendry sandstone (Neogene), Kamthi, Lower Gondwana (Upper Carboniferous-Lower Triassic). AQUIFER TEMPERATURES
It is well-established that the concentration of certain constituents present in thermal waters and their ionic ratios can act as quantitative indicators of the temperature in the deep aquifers (Fournier and Truesdell, 1973; Truesdell and Singers, 1974; Gupta et al., 1975; Ellis and Mahon, 1977; Fauillac and Michard, 1981; Saxena and Gupta, 1982; Arnorsson et al., 1982; Arnorsson, 1983; Saxena, 1983). The aquifer temperatures calculated from several chemical geothermometers are given in Table 3. The chemical geothermometers differ considerably in the estimated aquifer temperature of a system. A critical examination is required of the various assumptions made in formulating the geothermometers. Our discussions earlier in this paper have shown that the thermal water of Agnigundala is in equilibrium with surrounding minerals with respect to K, Na and Silica. Activity diagrams (Figs. 4--7) show, however, that these waters are not in equilibrium with albite, thereby violating a primary condition for the use of the Na--K--Ca and Na--K, geothermometers (Fournier and Truesdell, 1973; Ellis and Mahon, 1977). Due to lack of proper equilibrium conditions, T(Na/ Li) and T(K-Mg) are also not applicable in such a case (Fauillac and Michard, 1981; W.F. Giggenbach, pers. commun., 1982). Quartz is calculated to be in equilibrium with water at a temperature about 150°C for Agnigundala and 100°C for Buga. The actual calculated TABLE 3 E s t i m a t e d reservoir t e m p e r a t u r e s , in ° C S. T h e r m a l w a t e r area No.
Tsio2 (1) Tsio~ (2) Chalcedony Quartz
TNaKC a (3)
TKMg (4)
1. 2. 3. 4. 5. 6. 7. 8. 9.
82 63 NA 86 63 69 53 80 80
91 51 173 69 86 91 91 100 102
86 58 122 63 56 79 63 88 81
B h u t t a y a g u d e m drill hole B h i m d o l e drill-hole A g n i g u n d a l a H o t spring Buga m a i n H o t spring Buga w a r m spring Pagdaru drill hole-1 Pagdaru drill hole-2 M a n g u r u , TW-1 M a n g u r u , TW-2
NA NA 156 96 NA NA NA NA NA
( 1 ) T = 1 0 1 5 . 1 / ( 4 . 6 5 5 - - 1 o g SiO: ) -- 273 (SiO 2 i n p p m ) (2) T = 1 3 1 5 / ( 5 . 2 0 5 -- log SiO~) -- 273 (SiO 2 in p p m ) (3) F o u r n i e r a n d Truesdell ( 1 9 7 3 ) (4) T = 4 4 1 0 / ( 1 3 . 9 5 - - log K2/Mg) - - 273 (K a n d Mg in p p m ) (5) T = 1 0 0 0 / ( l o g N a / L i + 0 . 3 8 ) -- 273 (Na a n d Li in Molal) N A = N o t applicable. TW = T h e r m a l w a t e r f r o m coal mine.
TNaILi (5) 96 72 134 68 66 72 80 77 78
190 t e m p e r a t u r e b y TSiO2 ( q u a r t z ) is 1 5 6 ° C f o r A g n i g u n d a l a , a n d 9 6 ° C f o r Buga. CONCLUSIONS T h e p r e s e n t c h e m i c a l studies o f t h e G o d a v a r i valley t h e r m a l waters, have shown that: (1) T h e k n o w n t h e r m a l w a t e r s o f t h e valley b e l o n g to t w o s e p a r a t e s y s t e m s , o n e w h i c h is f o r m e d t h r o u g h d e e p c i r c u l a t i o n in t h e L o w e r G o n d w a n a s e d i m e n t a r y r o c k s a n d is m a n i f e s t in t h e A g n i g u n d a l a area, a n d t h e o t h e r s y s t e m s o f similar c h e m i c a l c h a r a c t e r s , w h i c h are f o r m e d d u e t o shallow c i r c u l a t i o n a n d h e a t i n g o f m e t e o r i c water, also circulate t h r o u g h Lower Gondwana sediments. (2) T h e t h e r m a l w a t e r s o f A g n i g u n d a l a are in e q u i l i b r i u m w i t h t h e inf e r r e d minerals. (3) T h e d e e p a q u i f e r t e m p e r a t u r e o f t h e A g n i g u n d a l a s y s t e m is a p p r o x i m a t e l y 156°C and w h e r e a s t h o s e o f o t h e r s y s t e m s d e p e n d on t h e i r relative d e p t h s o f c i r c u l a t i o n in l o w e r G o n d w a n a s e d i m e n t s , t h e y are n o t likely to e x c e e d 1 0 0 ° C. ACKNOWLEDGEMENTS T h e a u t h o r s are g r a t e f u l to various o f f i c e r s o f Singareni coal m i n e s Ltd., K o t h a g u d e m a n d Central G r o u n d Water B o a r d , H y d e r a b a d f o r t h e i r valuable discussions, suggestions a n d help. T h a n k s are also d u e to Mr. A. Yadagiri for assisting in t h e field w o r k . T h e p e r m i s s i o n to publish this p a p e r f r o m t h e D i r e c t o r , N a t i o n a l G e o p h y s i c a l R e s e a r c h I n s t i t u t e , H y d e r a b a d is g r a t e f u l l y acknowledged. REFERENCES Arnorsson, S., Sigurdsson, S. and Savarsson, H., 1982. The chemistry of geothermal waters in Iceland. Calculation of aqueous speciation from 0 to 370 ° C. Geochim. Cosmochim. Acta, 46: 1513--1532. Arnorsson, S., 1983. Chemical equilibria in Icelandic geothermal systems implications for chemical geothermometry investigations. Geothermics, 12 (2/3): 119--128. Ellis, A.J. and Mahon, W.A.J., 1977. Chemistry and Geothermal systems. Academic Press, New York, N.Y. Fournier, R.O. and Truesdell, A.H., 1973. An empirical Na--K--Ca Geothermometer for natural waters. Geochim. Cosmochim. Acta, 37: 1255--1275. Fauillac, C. and Michard, G., 1981. Sodium-lithium ratio in water applied to geothermometry of geothermal reservoir. Geothermics, 10: 55--70. Gupta, M.L., Saxena, V.K. and Sukhija, B.S., 1975. Analysis of the hot spring activity of the Manikaran area, Himachal Pradesh, India, by Geochemical studies and tritium concentration of spring waters. Proc. 2nd U.N. Symp. Development and Use of Geothermal Resources, San Francisco, U.S. Gov. Printing Office, Washington, DC, pp. 741--744. Helgeson, H.C., 1969. Thermodynamics of hydrothermal systems at elevated temperatures and pressures. Am. J. Sci., 267: 729--804. Saxena, V.K., 1983. Geochemical prospecting for the geothermal resources in the Konkan coast and the Godavari valley, India. Ph.D. thesis, Rewa University, India.
191
Saxena, V.K. and D'Amore, F.D., 1984. Aquifer chemistry of the Puga and Chumatang high temperature geothermal systems in India. J. Volcanol. Geotherm. Res., 21: 333-346. Saxena, V.K. and Gupta, M.L., 1982. Geochemistry of some thermal and cold waters of Godavari valley, India. J. Geol. Soc. India, 23(11) : 551--560. Truesdell, A.H. and Singers, W., 1974. The calculation of aquifer chemistry in hot-water geothermal systems. J. Res. U.S. Geol. Surv., 2(3): 271--278. APPENDIX ( 1 ) log aK+/aH+ (2) log aK+/aH÷ (3) log aH4SiO4 (4) log aK+/aH÷ (5) log aK*/aH÷
= 1.17 log K - p o t a s s i u m felds. - 0.17 log K - p o t a s s i u m m o n t m o . - 1.67 log aH4SiO, = log K - p o t a s s i u m m o n t m . -- 3.5 log K - k a o l i n i t e 4 log aH, SiO4 = log K-gibbsite + 0.5 log K - k a o l i n i t e = 1.35 log K - p o t a s s i u m felds. - 0 . 5 9 log K-illite - 2 log aH,SiO4 + 0.15 log aMg~./aH ÷ = 1.5 log K - p o t a s s i u m felds. - 0.5 log K - m u s c o v i t e 3 log aH, SiO4 = - - 1 . 2 log K - p o t a s s i u m m o n t m . + 3 . 6 8 log K-illite + 0.42 log aH, SiO4 -- 0 . 9 2 log aMg2÷/aH÷ = 4.6 log K m u s c . - 6 log K-illite + 1.5 log aMg2./aH. + 7.2 log aH4SiO, = - - 1 . 9 2 log K-kaol. + 1.67 log K-illite - 2 log aH, SiO, -- 0 . 4 2 log aMg~+/aH+ = - - 3 . 8 3 log K-gibb. + 1.69 log K-illite - 0.42 log aMg2÷/aH+ -- 5.83 log aH,SiO4 3 log K-gibb. + log K - m u s c . - 3 log aH~ SiO, = 1.17 log K-alb. - 0.17 log K - N a . m o n t m . - 1.67 log aH4SiO 4 = - - 3 . 5 log K-kaol. + log K - N a . m o n t m . - 4 log aH,SiO~ = --7 log K-gibb. + log K - N a . m o n t m . - 11 log aH~SiO, = log K-alb. - log K-gibb. - 3 log aH,SiO, -
(6) log aK÷/aH+ (7) log aK÷/aH÷ (8) log aK÷/aH÷ (9) log aK÷/aH÷ (10) log aK÷/aH÷ (11) log aNa÷/aH+ (12) log aNa÷/aH÷ (13) log aNa÷/aH+ (14) log aNa÷/aH÷
Where aNa÷ , aK÷ a n d all÷ are t h e activities o f t h e ions Na ÷, K ÷ a n d H ÷. log K is t h e e q u i l i b r i u m c o n s t a n t o f t h e mineral.
181
Elsevier Science Publishers B.V., Amsterdam -- Printed in The Netherlands
AQUIFER CHEMISTRY OF THERMAL WATERS OF THE GODAVARI VALLEY, INDIA V.K. SAXENA and MOHAN L. GUPTA Geothermal Group, National Geophysical Research Institute, Hyderabad -- 500 007, India
(Received March 14, 1984; revised and accepted December 6, 1984)
ABSTRACT Saxena, V.K. and Gupta, M.L., 1985. Aquifer chemistry of thermal waters of the Godavari valley, India. J. Volcanol. Geotherm. Res., 25: 181--191. The results of a chemical study of thermal waters from three hot springs, two water discharges in a mine at 180 m depth, and four wells drilled for exploration of coal and water resources in the Godavari valley indicate: (1) a deep flow path within the Lower Gondwanas (Upper Carboniferous--Lower Triassic) for Agnigundala thermal water which has been found to be in equilibrium with quartz, montmorillonite and kaolinite at 150° C; (2) medium depth circulation also through Lower Gondwana sedimentary rocks and equilibrium with quartz, at 100°C for waters of Buga, Manguru and Bhuttayagudem; and (3) circulation within sedimentary formations for the thermal waters of the Pagdaru and Bhimdole areas. Waters of the last areas show disequilibrium but are within the stability field of kaolinite. The aquifer temperature is most likely to be about 156°C for the Agnigundala, around 100°C for the Buga, and not more than 100°C for the other systems.
INTRODUCTION H o t springs have been k n o w n in the Godavari valley since ancient times. T h e r m a l waters have also been t a p p e d in m a n y r e c e n t e x p l o r a t o r y wells drilled f o r coal a n d g r o u n d w a t e r . The c h e m i s t r y o f some t h e r m a l and cold waters o f t h e valley has been previously p r e s e n t e d (Saxena a n d G u p t a , 1 9 8 2 ; Saxena, 1983). These studies have been f u r t h e r e x t e n d e d t o t w o m o r e areas w h e r e t h e r m a l waters have been e n c o u n t e r e d in g r o u n d w a t e r wells. B o t h t h e previous a n d t h e n e w l y g e n e r a t e d data have been used t o s t u d y the chemical equilibria o f the t h e r m a l waters, to infer their relative d e p t h s o f circulation a n d t h e t y p e o f r o c k s w h i c h have m a i n l y c o n t r i b u t e d to their chemical c o m p o s i t i o n , and to o b t a i n m o r e realistic estimates o f the aquifer t e m p e r a t u r e s . The findings are given a n d discussed in this paper. LOCATION T h e g e o l o g y o f part o f the Godavari valley a n d locations f r o m w h i c h the samples of t h e r m a l waters were collected are s h o w n in Fig. 1.
182
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Fig. 1. Geological m a p o f a p a r t o f Godavari valley (after GSI, 1975) and l o c a t i o n o f Hot Springs and drill holes. I = Alluvium; II = R a j a h m a n d r y sand s t o n e ( N e o g e n e ) ; III = U p p e r G o n d w a n a s (Middle T r i a s s i c - - L o w e r Cretaceous); IV = K a m t h i , L o w e r G o n d w a n a s ( U p p e r C a r b o n i f e r o u s - - L o w e r Triassic); V = Talchir, L o w e r G o n d w a n a s ( U p p e r Carbonife r o u s - L o w e r Triassic); VI = Pakhal series ( U p p e r P r e c a m b r i a n ) ; VII = Dharwar group ( L o w e r P r e c a m b r i a n ) ; VIII = C h a r n o c k i t e s ( L o w e r P r e c a m b r i a n ) ; IX = K h o n d a l i t e s (Lower P r e c a m b r i a n ) ; X = Alkaline rocks ( P r e c a m b r i a n ) ; XI = Ultra basics ( P r e c a m b r i a n ) ; XII = Archaean.
CHEMISTRY OF THERMAL WATERS
The chemical analyses of thermal waters axe given in Table 1 which shows that these waters axe nearly neutral to mildly alkaline (pH 7.4--7.8). A com-
183
parison summary of the chemical compositions of these thermal waters brings out the following observations: Agnigundala
Buga, Pagdaru, Manguru, B h u t t a y a g u d e m and Bhimdole
More mineralized salinity 1139 p p m 80%, NaCl 7% CaliCO 3 143 p p m SiO~
Less mineralized salinity 4 8 0 - - 8 4 0 ppm 40--55% NaC1 23--35% CaliCO 3 35--67 ppm SiO~
The above observations suggest two different water systems viz. ( 1 ) t h e Agnigundala system, and (2) the Buga, Pagdaru and Manguru system. The waters associated with Bhuttayagudem and Bhimdole are very similar to that of the latter system, thereby reflecting the similarity of the chemical composition of the deep aquifer rocks, namely Gondwanan sediments. The Agnigundala and Bhuttayagudem thermal waters are of the alkali-chloride type, and the others are mixed alkali chloride and bicarbonate. This inference is quite clear from Fig. 2. In addition, there is an indication (Points 4, 5, 8 and 9) in Fig. 2 that the Buga water is altered Manguru water. A detailed classification for distinguishing water groups based on chemical parameters reflecting geological features of reservoirs has been described by Saxena and D'Amore (1984). Using concentrations (meq/1) of the seven major chemical components of the water samples, they have defined six new parameters, normalized between 100 and - 1 0 0 , where ~ (+) and E ( - ) represent the sums of the cations and anions respectively. 100 Parameter A: - -
~(-)
(HCO~ - SO~-)
This parameter mainly distinguishes between waters circulating through calcareous terrains and those flowing through evaporitic rocks. Parameter B: 100 (
SO~-
~(-)
Na ÷ -
r~(+i i
This parameter discriminates between sulphate-enriched waters circulating in evaporitic terrains and sodium-enriched waters found in marly, clayey sedimentary terrains. Parameter C: 100
--
~(+)
~(-)
This parameter tends to distinguish between waters derived from flysch or volcanic rocks and those from earbonate-evaporitic series of from a regional quartzitie-sehistose basement. Both types of water have relatively high Na ÷, but the former have low C1-.
B h i m d o l e drill h o l e (b)
Agnigundala hot spring
Buga main hot spring
Buga warm spring
P a g d a r u drill h o l e - 1 (c)
P a g d a r u drill hole-2(c)
M a n g u r u , TW-1 (d)
Manguru, TW-2 (d)
2.
3.
4.
5.
6.
7.
8.
9.
37
38
33
39
40
45
62
52
64
1022
1038
764
774
793
856
1750
499
1280
Temp. 1 Spec. (°C) conduc2
7.8
7.8
7.7
7.7
7.7
7.8
7.5
7.4
7.4
pH 3
766
773
541
542
555
599
1139
341
841
TDS
60
60
35
48
43
67
143
43
63
SiO 2
196
200
95
111
100
95
321
44
142
Na
9.6
8
7A
8.9
8
7.4
23.6
4.4
20.4
K
25
20
50
25
25
50
32.5
41.2
97.5
Ca
in p p m )
3
1.2
7.9
3
18.2
7.9
0.9
4.7
8.8
Mg
6
5
4
5.5
5
4
4
2
3
F
84
84
50
50
50
50
430
100
217
C1
214
214
171
200
171
171
38
64
]43
171
185
121
73
134
147
147
38
150
H C O a SO 4
0.2
0.2
0.1
0.1
0.08
0.08
0.8
0.04
0.2
Li
i Surface temperature. 2 M i c r o m h o s / c m , at 25 ° C. 3 A t 25 ° C. (a) 5 0 0 m drill h o l e d i s c h a r g e s w a t e r 2 7 . 8 1/sec. ( b ) 5 0 0 m drill h o l e d i s c h a r g e s w a t e r 2 2 . 7 1/sec. (c) 3 0 0 m drill h o l e s d i s c h a r g e s w a t e r . (d) H o t w a t e r e m i t t e d in v a r i o u s p l a c e s w i t h a g o o d d i s c h a r g e u n d e r a c o a l m i n e . P r e s e n t s a m p l e s c o l l e c t e d f r o m ] 80 m d e p t h .
Bhuttayagudem drill h o l e ( a )
].
SI. T h e r m a l w a t e r No. a r e a
Chemical analyses of the thermal waters, Godavari valley (concentrations
TABLE 1
0.01
0.01
0.02
0.2
0.2
0.2
2.5
0.1
0.5
B
185
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Fig. 2. Piper diagram of the chemical analyses of water samples.
N a + _ Mg2 + Parameter D: 100
~(+)
This parameter characterizes waters that have circulated in dolomitized limestone.
Parameter E: 100
(Ca2+ + Mg 2÷ E(+)
HCO~) ~,(-)
This parameter mainly distinguishes between circulations in carbonate reservoirs and those in sulphate-bearing reservoirs. Parameter F: 100
_( Ca2+ _~_~Na+- K+ )
This parameter reveals the increase of Na ÷ and K+ in the waters.
186
The calculated values of parameters A to F, for the water samples studied have been plotted in rectangular diagrams shown in Fig. 3. These rectangular diagrams suggest a deep circulation of Agnigundala water (through sedimentary rock formations and a near-surface alteration for the waters of Buga, Pagdaru, Bhyttayagudem, Bhimdole and Manguru.
'°°1
oo;
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E
(d)
Fig. 3. Representations of the water samples on the rectangular diagrams defined by the six parameters (see text).
CHEMICAL EQUILIBRIA
Study of the chemical equilibria between minerals and a solution requires the determination of the activities of aqueous species and the identification of minerals found in the associated altered rocks. Calculated Debye-Huckel activity coefficients were used to convert the molalities of the aqueous ionic species into activities. The resultant computer-calculated activity values are given in Table 2. The number of minerals which could participate in reactions with the waters is very large. However, the discussion in this paper is limited to those phases which are inferred to be present in the reservoir; therefore only the following mineral reactions have been considered among phases inferred to be present in the reservoirs. (1) K. feldspar--K, montmorillonite; (2) K. montmorillonite--kaolinite; (3) kaolinite--gibbsite; (4) K. feldspar--illite; (5) K. feldspar--muscovite; (6) K. montmorillonite--illite; (7) muscovite--illite; (8) kaolinite--illite;
187
(9) gibbsite--illite; (10) gibbsite--muscovite; (11) albite--Na, montmorillonite; (12) Na. montmorillonite--kaolinite; (13) Na. montmorillonite--gibbsite; (14) albite--gibbsite. The formulation and solution of the temperature
--log aNa ÷
--log aK+
--log a c a 2 + --logaMg:÷ --logaH4SiO4
1. 2. 3. 4. 5. 6. 7. 8. 9.
2.26 2.77 1.92 2.43 2.41 2.37 2.43 2.11 2.12
3.33 4.00 3.28 3.77 3.74 3.69 3.77 3.74 3.66
2.66 3.04 3.37 3.16 3.25 3.25 3.14 3.35 3.25
B h u t t a y a g u d e m drill-hole B h i m d o l e drill-hole A g n i g u n d a l a H o t Spring Buga Main H o t Spring Buga Warm Spring Pagdaru drill hole-1 Pagdaru drill hole-2 M a n g u r u , TW-1 M a n g u r u , TW-2
3.49 3.76 4.76 5.76 3.17 3.95 3.73 4.35 3.95
3.07 3.28 2.71 3.06 3.27 3.23 3.36 3.11 3.11
LSO~C 8
i I
J
zl
?,
~t 7-
150~c
gl
/
I
_oi
+I o
~.~
/~
+o
Z
5'0
Q
I
o
+I
.z. o
i.3 4.0
F
~
g
IW/', 3'3 -2
-3 Log o H4SiO 4
4
1 -2
-3 L og a H 4 Si 0 4
Fig. 4. A c t i v i t y - a c t i v i t y d i a g r a m for t h e K~O-A1203-SiO~-H20 s y s t e m a t 150 ° C for Agnigundala. Fig. 5. A c t i v i t y - a c t i v i t y diagram for t h e Na~O-A1203-SiO2-I-I20 s y s t e m at 150°C for Agnigundala.
188 Loo"c
, a 0 °C
6
zl
I 7 ÷I
a: I
÷I
+ O Z
5
~6
o
/~.l
I
~
I .~4
-22
-4
Log a H 4 S J 0 4
:(e . 7
I
36 ~2
Log
uH4
'i 0 4
-4
Fig. 6. Activity-activity diagram for the K20-A1203-SiO2-I-~O system at 100~C. Numbers correspond to those in Tables. Fig. 7. Activity-activity diagram for the Na20-A120~-SiO:-H:O system at 100°C. Numbers correspond to those in the tables.
the given reactions have been taken from Helgeson (1969). The activities for various ionic species were calculated for a large number of reactions (Table 2). The most appropriate mineral-water equilibria for the Agnigundala and the Buga, etc. systems have been found at 150°C and 100°C, respectively. The relationships between log aK+/aH+ and log aNa+/aH+ with log aH4SiO4 have been drawn at 150°C for Agnigundala (Figs. 4 and 5) and at 100°C for the Buga, Pagdaru, Manguru, Bhuttayagudem and Bhimdole areas (Figs. 6 and 7). The activity diagrams suggest that the Agnigundala water apparently equilibriates at about 150°C with quartz, montmorillonite and kaolinite. These mineral phases are consistent with water circulation through sedimentary rocks containing quartz and in clay-rich layers with montmorillonite. The inferences are in agreement with local geology and suggest circulation and storage of the Agnigundala thermal waters in Lower Gondwanas (Upper Carb o n i f e r o u s - L o w e r Triassic). In Figs. 6 and 7 we show the Bhuttayagudem, Buga and Manguru waters
189
are near to the quartz saturation line at 100°C, within the stability field of kaolinite, consistent with their sedimentary environment, particularly Rajmahendry sandstone (Neogene), Kamthi, Lower Gondwana (Upper Carboniferous-Lower Triassic). AQUIFER TEMPERATURES
It is well-established that the concentration of certain constituents present in thermal waters and their ionic ratios can act as quantitative indicators of the temperature in the deep aquifers (Fournier and Truesdell, 1973; Truesdell and Singers, 1974; Gupta et al., 1975; Ellis and Mahon, 1977; Fauillac and Michard, 1981; Saxena and Gupta, 1982; Arnorsson et al., 1982; Arnorsson, 1983; Saxena, 1983). The aquifer temperatures calculated from several chemical geothermometers are given in Table 3. The chemical geothermometers differ considerably in the estimated aquifer temperature of a system. A critical examination is required of the various assumptions made in formulating the geothermometers. Our discussions earlier in this paper have shown that the thermal water of Agnigundala is in equilibrium with surrounding minerals with respect to K, Na and Silica. Activity diagrams (Figs. 4--7) show, however, that these waters are not in equilibrium with albite, thereby violating a primary condition for the use of the Na--K--Ca and Na--K, geothermometers (Fournier and Truesdell, 1973; Ellis and Mahon, 1977). Due to lack of proper equilibrium conditions, T(Na/ Li) and T(K-Mg) are also not applicable in such a case (Fauillac and Michard, 1981; W.F. Giggenbach, pers. commun., 1982). Quartz is calculated to be in equilibrium with water at a temperature about 150°C for Agnigundala and 100°C for Buga. The actual calculated TABLE 3 E s t i m a t e d reservoir t e m p e r a t u r e s , in ° C S. T h e r m a l w a t e r area No.
Tsio2 (1) Tsio~ (2) Chalcedony Quartz
TNaKC a (3)
TKMg (4)
1. 2. 3. 4. 5. 6. 7. 8. 9.
82 63 NA 86 63 69 53 80 80
91 51 173 69 86 91 91 100 102
86 58 122 63 56 79 63 88 81
B h u t t a y a g u d e m drill hole B h i m d o l e drill-hole A g n i g u n d a l a H o t spring Buga m a i n H o t spring Buga w a r m spring Pagdaru drill hole-1 Pagdaru drill hole-2 M a n g u r u , TW-1 M a n g u r u , TW-2
NA NA 156 96 NA NA NA NA NA
( 1 ) T = 1 0 1 5 . 1 / ( 4 . 6 5 5 - - 1 o g SiO: ) -- 273 (SiO 2 i n p p m ) (2) T = 1 3 1 5 / ( 5 . 2 0 5 -- log SiO~) -- 273 (SiO 2 in p p m ) (3) F o u r n i e r a n d Truesdell ( 1 9 7 3 ) (4) T = 4 4 1 0 / ( 1 3 . 9 5 - - log K2/Mg) - - 273 (K a n d Mg in p p m ) (5) T = 1 0 0 0 / ( l o g N a / L i + 0 . 3 8 ) -- 273 (Na a n d Li in Molal) N A = N o t applicable. TW = T h e r m a l w a t e r f r o m coal mine.
TNaILi (5) 96 72 134 68 66 72 80 77 78
190 t e m p e r a t u r e b y TSiO2 ( q u a r t z ) is 1 5 6 ° C f o r A g n i g u n d a l a , a n d 9 6 ° C f o r Buga. CONCLUSIONS T h e p r e s e n t c h e m i c a l studies o f t h e G o d a v a r i valley t h e r m a l waters, have shown that: (1) T h e k n o w n t h e r m a l w a t e r s o f t h e valley b e l o n g to t w o s e p a r a t e s y s t e m s , o n e w h i c h is f o r m e d t h r o u g h d e e p c i r c u l a t i o n in t h e L o w e r G o n d w a n a s e d i m e n t a r y r o c k s a n d is m a n i f e s t in t h e A g n i g u n d a l a area, a n d t h e o t h e r s y s t e m s o f similar c h e m i c a l c h a r a c t e r s , w h i c h are f o r m e d d u e t o shallow c i r c u l a t i o n a n d h e a t i n g o f m e t e o r i c water, also circulate t h r o u g h Lower Gondwana sediments. (2) T h e t h e r m a l w a t e r s o f A g n i g u n d a l a are in e q u i l i b r i u m w i t h t h e inf e r r e d minerals. (3) T h e d e e p a q u i f e r t e m p e r a t u r e o f t h e A g n i g u n d a l a s y s t e m is a p p r o x i m a t e l y 156°C and w h e r e a s t h o s e o f o t h e r s y s t e m s d e p e n d on t h e i r relative d e p t h s o f c i r c u l a t i o n in l o w e r G o n d w a n a s e d i m e n t s , t h e y are n o t likely to e x c e e d 1 0 0 ° C. ACKNOWLEDGEMENTS T h e a u t h o r s are g r a t e f u l to various o f f i c e r s o f Singareni coal m i n e s Ltd., K o t h a g u d e m a n d Central G r o u n d Water B o a r d , H y d e r a b a d f o r t h e i r valuable discussions, suggestions a n d help. T h a n k s are also d u e to Mr. A. Yadagiri for assisting in t h e field w o r k . T h e p e r m i s s i o n to publish this p a p e r f r o m t h e D i r e c t o r , N a t i o n a l G e o p h y s i c a l R e s e a r c h I n s t i t u t e , H y d e r a b a d is g r a t e f u l l y acknowledged. REFERENCES Arnorsson, S., Sigurdsson, S. and Savarsson, H., 1982. The chemistry of geothermal waters in Iceland. Calculation of aqueous speciation from 0 to 370 ° C. Geochim. Cosmochim. Acta, 46: 1513--1532. Arnorsson, S., 1983. Chemical equilibria in Icelandic geothermal systems implications for chemical geothermometry investigations. Geothermics, 12 (2/3): 119--128. Ellis, A.J. and Mahon, W.A.J., 1977. Chemistry and Geothermal systems. Academic Press, New York, N.Y. Fournier, R.O. and Truesdell, A.H., 1973. An empirical Na--K--Ca Geothermometer for natural waters. Geochim. Cosmochim. Acta, 37: 1255--1275. Fauillac, C. and Michard, G., 1981. Sodium-lithium ratio in water applied to geothermometry of geothermal reservoir. Geothermics, 10: 55--70. Gupta, M.L., Saxena, V.K. and Sukhija, B.S., 1975. Analysis of the hot spring activity of the Manikaran area, Himachal Pradesh, India, by Geochemical studies and tritium concentration of spring waters. Proc. 2nd U.N. Symp. Development and Use of Geothermal Resources, San Francisco, U.S. Gov. Printing Office, Washington, DC, pp. 741--744. Helgeson, H.C., 1969. Thermodynamics of hydrothermal systems at elevated temperatures and pressures. Am. J. Sci., 267: 729--804. Saxena, V.K., 1983. Geochemical prospecting for the geothermal resources in the Konkan coast and the Godavari valley, India. Ph.D. thesis, Rewa University, India.
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Saxena, V.K. and D'Amore, F.D., 1984. Aquifer chemistry of the Puga and Chumatang high temperature geothermal systems in India. J. Volcanol. Geotherm. Res., 21: 333-346. Saxena, V.K. and Gupta, M.L., 1982. Geochemistry of some thermal and cold waters of Godavari valley, India. J. Geol. Soc. India, 23(11) : 551--560. Truesdell, A.H. and Singers, W., 1974. The calculation of aquifer chemistry in hot-water geothermal systems. J. Res. U.S. Geol. Surv., 2(3): 271--278. APPENDIX ( 1 ) log aK+/aH+ (2) log aK+/aH÷ (3) log aH4SiO4 (4) log aK+/aH÷ (5) log aK*/aH÷
= 1.17 log K - p o t a s s i u m felds. - 0.17 log K - p o t a s s i u m m o n t m o . - 1.67 log aH4SiO, = log K - p o t a s s i u m m o n t m . -- 3.5 log K - k a o l i n i t e 4 log aH, SiO4 = log K-gibbsite + 0.5 log K - k a o l i n i t e = 1.35 log K - p o t a s s i u m felds. - 0 . 5 9 log K-illite - 2 log aH,SiO4 + 0.15 log aMg~./aH ÷ = 1.5 log K - p o t a s s i u m felds. - 0.5 log K - m u s c o v i t e 3 log aH, SiO4 = - - 1 . 2 log K - p o t a s s i u m m o n t m . + 3 . 6 8 log K-illite + 0.42 log aH, SiO4 -- 0 . 9 2 log aMg2÷/aH÷ = 4.6 log K m u s c . - 6 log K-illite + 1.5 log aMg2./aH. + 7.2 log aH4SiO, = - - 1 . 9 2 log K-kaol. + 1.67 log K-illite - 2 log aH, SiO, -- 0 . 4 2 log aMg~+/aH+ = - - 3 . 8 3 log K-gibb. + 1.69 log K-illite - 0.42 log aMg2÷/aH+ -- 5.83 log aH,SiO4 3 log K-gibb. + log K - m u s c . - 3 log aH~ SiO, = 1.17 log K-alb. - 0.17 log K - N a . m o n t m . - 1.67 log aH4SiO 4 = - - 3 . 5 log K-kaol. + log K - N a . m o n t m . - 4 log aH,SiO~ = --7 log K-gibb. + log K - N a . m o n t m . - 11 log aH~SiO, = log K-alb. - log K-gibb. - 3 log aH,SiO, -
(6) log aK÷/aH+ (7) log aK÷/aH÷ (8) log aK÷/aH÷ (9) log aK÷/aH÷ (10) log aK÷/aH÷ (11) log aNa÷/aH+ (12) log aNa÷/aH÷ (13) log aNa÷/aH+ (14) log aNa÷/aH÷
Where aNa÷ , aK÷ a n d all÷ are t h e activities o f t h e ions Na ÷, K ÷ a n d H ÷. log K is t h e e q u i l i b r i u m c o n s t a n t o f t h e mineral.