Geothermal fluids of the Ojo Caliente area discharge from ... Precambrian horst and is in a region of high heat ... depth t o this conductive zone increases steadily.
Geothermal Resources Council, TRANSACTIONS Vol. 6, October 1982
GEOLOGY, RESISTIVITY, AND HYDROGEOCHEMISTRY OF THE OJO CALIENTE HOT SPRINGS AREA, NORTHERN NEW MEXICO
John S t i x , C h r i s Pearson, Francois Vuataz, F r a s e r Goff, J e n n i f e r East*, and Bernhard Hoffers E a r t h and Space S c i e n c e s Division, Los Alamos National Laboratory
Los Alamos, New Mexico 87545 'Geology Department, U n i v e r s i t y of Alaska, Fairbanks, Alaska 99701
ABSTRACT
t h e Santa Fe Group, l i e above t h e Los PiGos and Chama-El Rito. Quaternary pediment and terrace
Geothermal f l u i d s of t h e Ojo C a l i e n t e area d i s c h a r g e from a n o r t h e a s t t r e n d i n g normal f a u l t t h a t j u x t a p o s e s P r e c a m b r i a n m e t a r h y o l l t e and An electrical r e s i s t i v i t y T e r t i a r y sediments. survey shows t h a t the f l u i d s emerge from t h e f a u l t and flow as a plume o f thermal water i n t o cold a q u i f e r s east of t h e f a u l t . Geochemistry of f l u i d s i n d i c a t e s o a maximum r e s e r v o i r temperature a t d e p t h of 80 C w i t h no suggestion o f high temperature i s o t o p i c exchange between water and r e s e r v o i r rocks. From t h i s data, we b e l i e v e t h e Ojo C a l i e n t e s y s t e m i s s u i t a b l e o n l y f o r small-scale direct u s e geothermal a p p l i c a t i o n s .
g r a v e l s , l o e s s , ( s p r i n g ) t r a v e r t i n e , and alluvium unconformably o v e r l i e t h e T e r t i a r y s e c t i o n . The h o t s p r i n g s emanate from alluvium and a s i n g l e o u t c r o p of sheared Precambrian m e t a r h y o l i t e overl a i n by Los PiGos v o l c a n i c pebble conglomerates (Fig. 1 ) . W e found l i t t l e evidence o f exposed Recent f a u l t i n g i n t h e T e r t i a r y and Quaternary d e p o s i t s t o t h e west o f Ojo C a l i e n t e . F a u l t i n g i n t h e Los Pinos i s i n f r e q u e n t ; where it occurs, throw is not more than s e v e r a l meters. Several small, elevated d e p o s i t s o f ( s p r i n g ) t r a v e r t i n e i n d i c a t e more e x t e n s i v e movement of h o t f l u i d s , but no d i r e c t g e o l o g i c evidence proves Quaternary f a u l t i n g i n t h i s area. On t h e o t h e r hand, a major P l i o c e n e f a u l t , t r e n d i n g north-northeast and downthrown t o t h e east, a p p a r e n t l y r u n s beneath t h e alluvium i n t h e Rio Ojo C a l i e n t e v a l l e y . T h i s f a u l t probably o f f s e t s Precambrian m e t a r h y o l i t e i n t h e subsurface. Four l i n e s of evidence point t o t h e e x i s t e n c e o f such a f a u l t . F i r s t , a r e l a t i v e l y l i n e a r r i d g e of exposed m e t a r h y o l i t e t h a t l i e s west of Ojo C a l i e n t e t r e n d s n o r t h - n o r t h e a s t and may be upfaul t e d a g a i n s t buried Los PiGos hidden beneath t h e r i v e r alluvium. Second, t h e Ojo C a l i e n t e f a u l t zone i n t h e T e r t i a r y s e c t i o n 5 km southwest of Ojo C a l i e n t e (May, 1979) strikes north-northeast and i s a l i g n e d w i t h t h e i n f e r r e d f a u l t i n t h e Rio Ojo C a l i e n t e v a l l e y . T h i r d , a f a u l t 8 km n o r t h e a s t of Ojo C a l i e n t e , that down-faults t h e T e r t i a r y t o t h e east a g a i n s t Precambrian q u a r t z i t e t o t h e west, a l s o follows t h i s alignment. These s t r u c t u r e s are major f a u l t s w i t h displacements o f p e r h a p s s e v e r a l h u n d r e d meters. Fourth, the l o c a t i o n o f t h e h o t s p r i n g s appears t o be cont r o l l e d by t h e i n t e r s e c t i o n o f p r e - T e r t i a r y n o r t h e a s t - t r e n d i n g Precambrian shear zones w i t h t h e Pliocene v a l l e y f a u l t (Fig. 1 ) . From t h i s evidence, we p o s t u l a t e t h a t t h e P l i o c e n e v a l l e y f a u l t is a zone of normal f a u l t s downthrown t o t h e east w i t h cumulative o f f s e t o f a t least 100 m. P o s s i b l y , t h i s zone i s a r e a c t i v a t e d Precambrian structure.
BTRODUCTION The Ojo C a l i e n t e thermal area is l o c a t e d i n t h e n o r t h w e s t p a r t o f t h e Espan'ola b a s i n o f n o r t h - c e n t r a l New Mexico. The b a s i n is p a r t of t h e Rio Grande r i f t , a major c o n t i n e n t a l rift t h a t
s t r e t c h e s from s o u t h e r n C o l o r a d o t o n o r t h e r n Mexico. The r i f t is characterized by a c t i v e extensional tectonics, Tertiary t o Quaternary volcanism, and high heat flow. The Ojo C a l i e n t e area l i e s on t h e e a s t e r n s i d e o f an exposed Precambrian h o r s t and is i n a r e g i o n o f high heat flow (>2.5 HFU; Reiter e t a l . , 1975). The o b j e c t of t h i s i n v e s t i g a t i o n is t o determine t h e r e l a t i v e s i z e and r e s e r v o i r temperature o f t h e geothermal system a t Ojo C a l i e n t e . GEOLOGY AND STRUCTURE
Metarhyolite, amphibolite, s c h i s t , and subo r d i n a t e g n e i s s of Precambrian age o u t c r o p west of t h e v i l l a g e o f Ojo C a l i e n t e . P a l e o z o i c and Mesozoic sedimentary rocks do not o u t c r o p , b u t u n s e e n r e m n a n t s may e x i s t i n t h e s u b s u r f a c e f l a n k i n g t h e Precambrian h o r s t . Tertiary b a s i n - f i l l sediments are deposited nonconformably over t h e Precambrian basement. Volcanic pebble conglomerates of t h e Cordito Member of t h e Los P i z o s Formation, t r a n s p o r t e d from t h e San Juan, Q u e s t a , and Taos v o l c a n i c c e n t e r s ( n o r t h and east o f Ojo C a l i e n t e ) , u n d e r l i e and i n t e r f i n g e r w i t h n o n v o l c a n i c s a n d s t o n e s o f t h e Chama-El R l t o Member, Tesuque F o r m a t i o n , S a n t a Fe Group. Westerly-derived , q u a r t z o s e , a e o l i a n sands o f t h e Ojo C a l i e n t e Sandstone, Tesuque Formation, a l s o o f
ISTIVITY SOWING S I n o r d e r t o map t h e h o t waters underlying t h e Ojo C a l i e n t e area, we conducted e i g h t Schlumberger D.C. r e s i s t i v i t y soundings i n t h e Rio Ojo C a l i e n t e
55
S t i x e t al. Explanation
Hr
Mecamflne Amphibohta, Uhm, rmbardinalegnasa
36.17s
F i g u r e 1.
S i m p l i f i e d g e o l o g i c map of t h e Ojo C a l i e n t e area, New Mexico showing l o c a t i o n s o f r e s i s t i v i t y
stations. v a l l e y w i t h i n a few k i l o m e t e r s o f t h e h o t s p r i n g s . F i g u r e 1 shows t h e l o c a t i o n o f t h e survey p o i n t s . When i n t e r p r e t e d , these soundings a l l o w u s t o i n f e r the earth's r e s i s t i v i t y as a f u n c t i o n of depth underneath t h e s u r v e y p o i n t . These surveys are e f f e c t i v e i n l o c a t i n g hot water because sediments s a t u r a t e d w i t h geothermal f l u i d s are much more c o n d u c t i v e t h a n s e d i m e n t s s a t u r a t e d w i t h cold, fresh water. Methods o f data a c q u i s i t i o n and i n t e r p r e t a t i o n have been described i n a prev i o u s paper of similar scope (Pearson and Goff,
Ojo C a l i e n t e . The r e s i s t i v e sediments t h a t overl i e the conducting zones r e p r e s e n t sediments saturated w i t h c o o l fresh ground water fed by t h e Rio Ojo C a l i e n t e . Line O J 8 (Fig. 21, r u n a t t h e h o t s p r i n g s s e v e r a l hundred meters west of O J 4, a l s o detected t h e geothermal plume. However, t h e s l i g h t l y h i g h e r r e s i s t i v i t i e s detected by O J 8 may i n d i c a t e calcite deposition i n the underlying sediments. T h i s reduces t h e p o r o s i t y and t h u s i n c r e a s e s t h e formation r e s i s t i v i t y .
1981).
GEOCHEMISTRY OF THE THERMAL WATEM
We f o u n d a n e l e c t r i c a l l y c o n d u c t i v e zone u n d e r n e a t h t h e Rio O j o C a l i e n t e v a l l e y w i t h r e s i s t i v i t i e s o f less t h a n 10 n m . T h i s zone is c e n t e r e d a t l i n e O J 4 n e a r t h e hot s p r i n g s where it comes w i t h i n 10 m of t h e s u r f a c e ( F i g . 2). The d e p t h t o t h i s conductive zone i n c r e a s e s s t e a d i l y t o t h e n o r t h and s o u t h , d i s a p p e a r i n g 1 lam t o t h e n o r t h o f t h e hot s p r i n g s and 2 laa t o t h e south. The s o u r c e o f t h e geothermal waters a p p a r e n t l y u n d e r l i e s t h e Ojo C a l i e n t e r e s o r t a d j a c e n t t o t h e h o t s p r i n g s , s i n c e t h e low (>lo n-m) r e s i s t i v i t i e s are c l o s e s t t o t h e s u r f a c e here. Thus, we i n t e r p r e t t h e geothermal f l u i d s t o rise as a plume from a s h o r t segment of t h e P l i o c e n e v a l l e y f a u l t and t h e n d i s p e r s e eastward i n t o t h e v a l l e y alluvium.
On t h e s i t e of t h e resort i t s e l f , f i v e h o t s p r i n g s have been used f o r a very long time. Cold b u t m i n e r a l i z e d water a l s o flows from a s e e p located a few t e n s o f meters west o f t h e s p r i n g s . Four shallow wells have been d r i l l e d d u r i n g t h e past 40 y e a r s i n t h e alluvium for water supply (Summers, 1976). A l l of them d i s p l a y e v i d e n c e o f m i x t u r e between thermal waters and cold ground water. One of t h e s e wells ( t h e c l o s e s t t o t h e s p r i n g s ) , which i s n o t used and has no n a t u r a l discharge, has a recorded bottom-hole t e m p e r a t u r e of 55OC a t a d e p t h o f 26 m (J. Hunter, Los Alamos N a t i o n a l Laboratory, unpublished data, 1982). The hot sproings h p e a s u r f a c e temperature ranging from 32 t o 45 C and t h e i r t o t a l discharge v a r i e s from 200 t o 1300 l/min, according t o h i s t o r i c a l data (Summers, 1976).
zone of moderately conductive sediments k m ) is found a t i n t e r m e d i a t e d e p t h s ( i . e . , 10-40 m) s o u t h o f t h e hot s p r i n g s . T h i s r e p r e s e n t s an o u t f l o w zone where geothermal waters i n the v a l l e y mix w i t h fresh c o o l water. T h i s zone o f mixing also may extend s l i g h t l y t o t h e n o r t h o f A
( 13-20
A l l the emergences have t h e same t y p e o f c h e m i s t r y and c a n b e c l a s s i f i e d a s sodiumbicarbo;ate waters w i t h s u b s t a n t i a l amounts o f silica, f l u o r i d e , l i t h i u m and boron (Table 1).
56
Stix e t al.
314
M171VRIC W A I l l l
-
-39
CAI C l l F
CEM€NrCO m s
56
MININbl
GrUIMCRhlAl WArlH
Table 1
Chemical a n a l y s e s (mg/l) , f i e l d pH, s u r f a c e temperature of selected samples from Ojo C a l i e n t e , New Mexico. Li
Sample' Iron Spring Lithia Spring Hot Yell Yell I1
2.2 2.7 5.5
-
TDS~
Sample' Iron Spring Lithia Spring Hot Yell Well #1
3576 3474 3343 1787
Na
953 1167 927 496 pH
6.40 6.55 6.115 7.80
Ms
K
6.60
29.0 28.5 27.11 16 Temp.
43 38 54 32
8.70 2.90 16
Ca
HCOl
21.0 23.6
2090 2070 1870 907
7.3 40 T
T 110 109 95
-
(OC)
SO4
195 155
80
-
29
13
c1
F
229 227 242 149
14.2 13.5 20.8 7.5
171
173
R
-
and chemical geothermometry B 1.53 1.47 1.54
-
(OC)
sio* 58.9 58.4 43.4
-
T
T
110 65
-
s#NfW.
CALCITE SA TURATEO SEOIMENTS>
127 149 206
-
133 137 132 136
149 150 156
137
73 61 92 42
'The f i r s t three samples were collected in December 1979, while Yell I1 was obtained in August 1965 (Summers, 1976). total dissolved solids equals the sun of the constituents listed above.
2TDS:
Extensive t r a v e r t i n e d e p o s i t s are known i n t h e area and t h e thermal water may n o t only d i s s o l v e s i l i c a t e s of Precambrian c r y s t a l l i n e r o c k s , b u t a l s o limestone from buried Paleozoic o r Mesozoic sedimentary r o c k s during its a s c e n t . Except d i s charge, t h e o t h e r physical and chemical parameters do not seem t o go through s e v e r e s e a s o n a l v a r i a t i o n s and i f one can deduce whether mixing and/or d i l u t i o n between thermal and nonthermal waters occur, it should be q u i t e c o n s t a n t . The first conclusion of t h e i s o t o p i c s t u d y shows t h a t t h e warm waters of Ojo C a l i e n t e do not f i t e x a c t l y on t h e g e n e r a l meteoric water l i n e b u t on a kind of evaporation l i n e w i t h a s l i g h t enrichment o f both oxygen-18 and deuterium (Fig. 3).
shown by s e v e r a l o t h e r h o t water systems (Vuataz, i n prep.). A mixing model h a s been e s t a b l i s h e d f o r t h e s p r i n g s and wells, u s i n g t h e data of t h e p r e s e n t s t u d y and a l l t h e h i s t o r i c a l d a t a (Summers, 1976; T r a i n e r and Lyford, 1979). The b e s t - f i t l i n e of t h e magnesium v e r s u s c h l o r i d e ( F i g . 4A) may be e x t r a p o l a t e d t o a v e r y small mWnesium c o n c e n t r a t i o n , which could r e p r e s e n t t h e unmixed thermal water a t depth. The l i n e i n t e r sects t h e c h l o r i d e a x i s a t a maximum v a l u e o f 290 mg/l. A r e l a t i o n between temperature and c h l o r i d e shows a good p o s i t i v e t r e n d f o r t h e wells, w p l e t h e s p r i n g s d i s p l a y a conductive c o o l i n g of 8 t o 23OC ( F i g . 4B). Reporting t h e e x t r a p o l a t e d c h l o r i d e c o n c e n t r a t i o n on t h i s diagram, a temperature o f 68OC is obtained f o r t h e h o t end-member. T h i s temperature, around 13OC more than t h e maximum recorded should correspond t o t h e thermal water a t r e l a t i v e l y shallow depth b u t before any mixing w i t h t h e cold a q u i f e r .
OF THE RESERVOIR TEMPThe magnesium c o n c e n t r a t i o n of thermal waters o f t e n c o r r e l a t e s i n i n v e r s e r a t i o t o t h e concent r a t i o n of a non-reactive a n i o n , l i k e c h l o r i d e , as
57
er ai.
Stlx
water r e s e r v o i r is believed t o reach a temperature o f 8OoC (&lo0), by t h e chalcedony and t h e Na-K-Ca (Mg-corrected) geothermogeters. T h i s temperature i s not far from t h e 68 C found w i t h t h e mixing model. The h o t water r e s e r v o i r is probably fed by l o c a l g r o u n d waters i n f i l t r a t i n g down t h r o u g h f r a c t u r e s and f a u l t s , and warmed by t h e r e g i o n a l heat-flow o f t h e Rio Grande rift.
1 -120
The geophysics and geology suggest t h a t t h e thermal r e s e r v o i r a t Ojo C a l i e n t e is s t r u c t u r a l l y c o n t r o l l e d and o f l i m i t e d e x t e n t . The thermal waters emerge from a b u r i e d n o r t h - n o r t h e a s t
1
mI
-15
-14
-12
-13
t r e n d i n g P l i o c e n e f a u l t t h a t is p a r t o f t h e Ojo C a l i e n t e f a u l t zone. Thermal f l u i d s are confined t o deposits o f alluvium i n t h e Rio Ojo C a l i e n t e v a l l e y and mix w i t h c o o l meteoric waters w i t h i n t h e v a l l e y . Geochemistry o f t h e f l g i d s i n d i c a t e a maximum r e s e r v o i r temperature of 80 C, t h u s , i t is our belief t h a t t h e Ojo C a l i e n t e system is s u i t able only f o r small-scale direct use geothermal applications.
p o (%I Figure 3. Oxygen-18 and deuterium i n t h e thermal waters from Ojo C a l i e n t e . Symbols: diamond, unused hot well; s o l i d circles, warm s p r i n g s ; open circles, shallow a q u i f e r . I
1
1
I
I
1
I
A
ACKNOWLEDGMENTS
30-
George Mauro of Ojo C a l i e n t e Resort k i n d l y helped and advised us throughout t h i s p r o j e c t . T h i s i n v e s t i g a t i o n was supported by U.S. Depart-
T
-F
ment o f Energy, Office o f Basic Energy Sciences and Division o f Geothermal Energy.
P 10-
REFERENCES
0
60
lM1
150
200
May, S. J., 1979, Neogene s t r a t i g r a p h y and s t r u c t u r e o f t h e Ojo Caliente-Rio Chama area, Espanola b a s i n , New Mexico, New Mexico Geol. SOC. Guidebook, 30th F i e l d Conf., p. 83-88.
260
CI (rng/l)
Figure 4A. Mixing model between magnesium and chloride. Symbols: box, e x t r a p o l a t e d deep hot end-member; o t h e r s same as Fig. 3. 1
I
Pearson, C. and Goff, F., 1981, A. Schlumberger r e s i s t i v i t y s t u d y of t h e Jemez Springs r e g i o n of n o r t h w e s t e r n N e w Mexico, Geotherm. Resources Council Trans., v. 5 , p. 119-122.
I
1
0 ///
/I
1
a
I
60
1m
I
160
I
200
Reiter, M., Edwards, C. L., Hartman, H., and Weidman, C., 1975, T e r r e s t r i a l heat f l o w along t h e Rio Grande rift, New Mexico and southern Colorado, Geol. SOC. Am. Bull., v. 86, p. 811-818.
1
I
/ O 0
-
1
2w
Summers, W. K., 1976, Catalog of thermal waters i n New Mexico, New Mexico Bur. Mines and Miner. Resour. Hydrol. Report 4: 80 p.
iI
Trainer, F. W. and Lyford, F. P., 1979, Geothermal hydrology i n the Rio Grande r i f t , Northc e n t r a l New Mexico, New Mexico Geol. SOC. Guidebook, 3 0 t h F i e l d Conf., S a n t a Fe Country, 1979: p. 229-306.
CI h g / I
Figure 48. P l o t of temperature a g a i n s t c h l o r i d e . The best-fit l i n e is Symbols same as Fig. 4A. c a l c u l a t e d o n l y w i t h t h e d a t a of t h e w e l l s , because t h e s p r i n g s undergo conductive cooling.
Vuataz, F. D., i n prep., Hydrology, geochemistry and geothermal aspects of t h e thermal waters from Switzerland and a d j a c e n t a l p i n e r e g i o n s , Submitted t o J. Volc. Geotherm. Res.
The chemical geothermometry c a l c u l a t i o n s do n o t g i v e a clear p i c t u r e of t h e r e s e r v o i r temperat u r e as y e t (Table 1 ) . A t t h i s p o i n t , t h e deep
58
