View
215
Download
0
Category
Preview:
Citation preview
7/24/2019 geologyPlatanares-heiken1991
1/18
Journa l o f Vo lcanology and Geothermal Research
45 (1991) 41 - 58
Elsevier Science Publishers B.V., Amsterda m 41
G eology o f the Platanares geotherm al area D epartam ento de
C o p m H o n d u r a s
G r a nt H e i k e n a N a p o l e o n R a m o s c W e n d e l l D u f f i e ld b J o h n M u s g ra ve a K e n n e t h W o h l e t za Sue Pr ie s t b
J a m e s A l d r i c h a W i l m e r F l o r es c A l e x a n d e r R i t c h i ed F r a s e r G o f f a D e a n E p p l e r a a n d C a r l o s E s c o b a r c
a L os A la m o s N a t io n a l L a b o r a tor y M S 9 6 4 L o s A la m o s N M 8 7 5 4 5 U . S . A .
bU.S . Geolog ica l Survey 2255 N. Gem in i Dr . F lags ta f f A Z 86001 U.S .A .
CEmpresa Na ciona l de Energia Electrica Tegucigalpa Ho ndu ras
aCollege o f Charleston 66 George St. Charleston SC 29424 U .S.A .
(Accepted June 26, 1990)
ABSTRACT
Heiken, G., Ramos, N., Duffield, W., Musgrave, J., Wohletz, K., Priest, S., Aldrich, J., Flores, W., Ritchie, A., Goff, F.,
Eppler, D. a nd Escobar, C., 1991. Geology of the Platanares geothermal area, Depa rtamento de Cop~in, Honduras. In: F. Gof f
(Editor), Honduras - A Geothermal Investigation. J. Volcanol. Geotherm. Res. 45:41 -58.
The Platanares geothermal area, Depar tamento de Cop~in, Honduras, is located within a graben that is complexly faulted. The
graben is bounded on the north by a highland composed of Paleozoic (?) metamorphic rocks in contact with Cretaceous - Tertiary
redbeds of unknown thickness. These are uncon formably overlain by Tertiary andesitic lavas, rhyolitic ignimbrites, and associated
sedimentary rocks. The volcanic rocks are mostly older than 14 Ma, and thus are too old to represent the surface expression of
an active crustal magma body. Thermal fluids that discharge in the area are heated during deep circulation of meteoric water along
faults in a region of somewhat elevated heat flow. Geot hermometry based upon the chemical composition of thermal fluids from
hot springs and from geothermal gradient coreholes suggests that the reservoir equilibrated at temperatures as high as 225 to
240C, within the Cre taceous redbed sequence. Three c, atinuously cored geothermal gradien t holes have been drilled; fluids of
abou t 165C have been produced from two drilled along a NW-trending fault zone, from depths of 250 to 680 m. A conductive
thermal gradient of 139C/km, at a depth of 400 m, was determined from the third well, drilled 0.6 km west of that fault zone.
These data indicate that the Platanares geothermal area holds considerable promise for electrical generation by moderate- to high-
temperature geothermal fluids.
I n t r o d u c t i o n
M o s t h y d r o t h e r m a l s y s t e m s i n C e n t r a l
A m e r ic a s u c h a s t h o se at M o m o t o m b o
N i c a r a g u a ; M i r a v a l le s C o s t a R ic a ; a n d
A h u a c h a p ~ i n E 1 S a l v a d o r a re a s s o c i a te d w i t h
R e c e n t v o l c a n i c f ie l d s w i t h i n te r m e d i a t e t o
s i l i c i c l a v a s a n d p y r o c l a s t i c r o c k s . T h e
n u m e r o u s g e o t h e r m a l m a n i f e s ta t i o n s s c at te r ed
t h r o u g h o u t c e n tr a l a n d w e s t e r n H o n d u r a s a r e
n o t h o w e v e r a s s o c i a te d w i t h s i m i la r y o u n g
v o l c a n o e s . T h e y o u n g e s t r o c k s o f th e s e c o m -
p o s i t i o n s i n H o n d u r a s a r e m i d - to l a te T e r t ia r y .
C e n t r a l H o n d u r a s i s c r o s s e d b y a d i s c o n -
t i n u o u s l i n e o f Q u a t e r n a r y b a s a l t i c c i n d e r
c o n e s a n d la v a f l o w s b u t n o n e o f t h e se y o u n g
v o l c a n i c a r e a s o f f e r t h e p r o m i s e o f h y d r o t h e r -
m a l s y s te m s o f c o m m e r c i a l q u a l i t y.
S u r f a c e m a n i f e s t a t io n s o f t h e h y d r o t h e rm a l
s y s t em s o f H o n d u r a s a re a s s o c i a t e d w i t h la t e
C e n o z o i c f a u lt s a n d c r u s ta l e x t e n s i o n m u c h
l ik e t h o s e o f th e B a s i n - a n d - R a n g e P r o v i n c e o f
0377-0273/91/ 03.50 ( 1991 Elsevier Science Publishers B.V.
7/24/2019 geologyPlatanares-heiken1991
2/18
4 G HEIKEN ET AL
t h e w e s t e r n U n i t e d S t a t e s . M e t e o r i c w a t e r s ,
w h i c h c i r c u l a t e d e e p l y a l o n g f a u l t s y s t e m s , f i ll
i s o l a t e d g e o t h e r m a l r e s e r v o i r s t h a t f e e d h o t
sp r ings and bo i l i ng sp r ings , whe re s i l i c a s i n t e r
a n d c a r b o n a t e t r a v e r ti n e a re d e p o s it e d F l o re s ,
1980; Goff e t a l . , 1987b) .
T e n g e o t h e r m a l s i t e s w e r e i n v e s t i g a t e d i n
H o n d u r a s a s p a r t o f a r e c o n n a i s s a n c e s t u d y b y
L o s A l a m o s , E m p r e s a N a c i o n a l d e E n e r g i a
E l e c t r i c a d e H o n d u r a s , a n d t h e U . S . G e o l o g -
i c al S u r v e y ; t h i s s t u d y i n c l u d e d i n v e s t i g a ti o n s
o f t h e g e o lo g y o f A z a c u a l p a E p p l e r et a l .,
1987b), Pa va na Epp le r e t a l . , 1987a) , P l a t a -
na re s H e ike n e t a l . , 1986, 1987) , an d San Ig -
n a c i o A l d r i c h et a l . , 1 9 87 ), a n d o f t h e h y d r o -
geo che m is t ry o f a l l t en s it es G of f e t a l . , 1987b)
F i g . 1 ). P l a t a n a r e s w a s c h o s e n f o r d e t a i l e d i n -
v e s t i g a t i o n o n t h e b a s i s o f p r e l i m i n a r y g e o l o g i c
m a p p i n g a n d h y d r o g e o c h e m i c a l s t ud i e s, w h i c h
i n d i c a t e d r e s e r v o i r t e m p e r a t u r e s o f 2 25 t o
2 4 0 C , t h e h i g h e s t i n H o n d u r a s . S i n c e 1 9 8 6 ,
a d d i t i o n a l g e o l o g i c a n d g e o c h e m i c a l s t u d i e s
and g rav i t y , s e l f -po t en t i a l , and r e s i s t i v i t y su r -
v e y s H o o v e r a n d P i e r c e , 1 98 8; A n d e r e t a l . ,
1991 - th i s vo lume ; A iken e t a l . , 1991 - th i s
v o l u m e ) h a v e b e e n c o m p l e t e d .
T h e P l a t a n a r e s g e o t h e r m a l a r e a i s l o c a t e d i n
w e s t - c en t r al H o n d u r a s i n t h e D e p a r t a m e n t o d e
C o p ~ n , 3 0 k m e a s t o f t h e b o r d e r w i t h
G u a t e m a l a a n d 16 k m w e s t o f S a n t a R o s a d e
C o p ~ n , w h i c h i s t h e p r o v i n c i a l c a p i t a l . T h e
v i ll a g e o f P l a t a n a r e s is l o c a t e d o n a g r a v e l te r -
r a c e , a f ew te n s o f m e t e r s a b o v e t h e Q u e b r a d a
d e l A g u a C a l ie n t e , a c a n y o n w h o s e n a m e
r e f le c t s t h e p r e s e n c e o f n u m e r o u s h o t s p r i n g s ,
b o i l i n g s p r i n g s , a n d f u m a r o l e s t h a t i s s u e f r o m
t h e b a n k s a n d b e d o f th e q u e b r a d a o v e r a
d i s t a n c e o f a b o u t 3 k m . T h e l o c a l t e r r a i n i s
r u g g e d a n d r a n g e s i n e l e v a t i o n f r o m 7 0 0 t o 1 30 0
m . T h e q u e b r a d a f o l l o w s a f a u l t z o n e , a l o n g
w h i c h t h e f a u l t e d a n d b r e c c i a t e d r o c k s a r e e a s i-
l y e r o d e d .
T h i s w o r k , f u n d e d b y th e U . S . A g e n c y f o r
I n t e r n a t i o n a l D e v e l o p m e n t , f o l l o w e d e a r l i e r
c o u n t r y w i d e r e c o n n a i s s a n c e s t u d i e s b y t h e
U n i t e d N a t i o n s D e v e l o p m e n t P r o g r a m G is -
l a s o n , 1 9 80 ) a n d G e o t h e r m E x , I n c . 1 9 80 ).
g
I s la s d ~ l a B a h ia
::::.::::.:::
' " : ' ~ : : g : ~ , , ~. . . . ' " N
1 k m ]
Fig. 1. Map showinggeothermalareas investigated during the countryw idesurvey by L os Alam os, the U.S. G eological
Survey, and Em presa Nacional de E nergia El6ctrica.
7/24/2019 geologyPlatanares-heiken1991
3/18
GEOLOGY OF THE PLATANARES GEOTHERMAL AREA HONDURAS
4
Regional geologic setting
W e s te r n H o n d u r a s is a h i g h l an d b o u n d e d b y
ma jo r l e f t - l a t e r a l , s t r i ke - s l i p f au l t s on t he
n o r t h , i n c l u d in g t h e M o t a g u a f a u lt z o n e o f
G u a t e m a l a a n d H o n d u r a s , a n d t h e J o c o t a n -
C h a m e l e c 6 n f a u l t z o n e a n d t h e c o n v e r g e n t
p l a te m a r g i n o f t h e C e n t r a l A m e r i c a n v o l c a n ic
f r o n t o n t h e s o u t h w e s t . T h e s e f a u l ts d e f i n e th e
n o r t h w e s t c o r n e r o f t h e C a r i b b e a n p l a t e a n d
f o r m t h e n o r t h e r n b o u n d a r y o f t h e C h o r t i s
B l o c k , a b l o c k o f P a l e o z o i c a n d y o u n g e r c o n -
t i n e n t a l c r u s t ( H o r n e a n d F i n c h , 1 99 0). T o t h e
s o u t h , t h e C h o r t i s b l o c k i s i n c o n t a c t w i t h
y o u n g e r c r u s t a s s o c i a t e d w i t h s u b d u c t i o n o f
t h e C o c o s p l a t e a l o n g t h e M i d d l e A m e r i c a
t r e n c h ( B u r k a r t a n d S e l f , 19 85 ). E x t e n s i o n a n d
c r u s t a l t h i n n i n g w i t h i n t h e C h o r t i s b l o c k a r e
m a n i f e s t e d a s N W - t r e n d i n g g r a b e n s a n d
rh om b g ra ben s ( c f . M i ll s e t a l . , 1967 ; W i l l i ams
a n d M c B i r n e y , 1 9 6 9 ) . T h i s e x t e n s i o n m a y b e
r e l a t e d to
( 1 ) e a s t w a r d m o v e m e n t o f t h e C a r i b b e a n
p l a te w h i l e t h e N W c o r n e r ( w e s t er n H o n d u r a s )
i s p i n n e d b e t w e e n t h e C o c o s a n d A m e r i c a
p l a t e s (P l a fke r , 1976 ) ;
(2 ) r o t a t i o n o f t h e t r a i l in g e d g e o f t h e C a r i b -
b e a n p l a t e a r o u n d a b e n d i n t h e M o t a g u a a n d
J o c o t a n - C h a m e l e c 6 n f a u l t s ( r o t a t i o n o f t h e
Chor t i s b lock ) (Burka r t and Se l f , 1985 ) ; o r
(3 ) e x t e n s i o n o f l i t h o s p h e r e , f o r m i n g N - S
g r a b e n s a n d E N E - t r e n d i n g f r a c tu r e s w i t h l ef t-
l a t e r a l s t ri k e -s l ip m o t i o n t h a t f o r m e d p u l l -
a p a r t b a s i n s ( M a n t o n , 1 98 7) .
T h e P l a t a n a r e s g e o t h e r m a l a r e a is in t h e m i d -
d l e o f t h is t e c t o n i c a l l y c o m p l e x b l o c k t h a t
/ / , ; o = / . k . / - / . '~ . .. ~ t / / / I
I f > < - -
t / 3 , - q - ~ - J /-' -
O n-
o 7 -
< l v -
g ~
~ e
~o,
Subinal Formation. Red-stained sandstones, sil tstones
sandstones, and conglomerates.
Matagalpa Formation; highly al tered andesi te f lows and
some intarbaddad pyroclastic rocks.
Val le de Angeles Group redbeds, consist ing of hemati te-
stained si l tstones, immature sandstones, pebbly sand-
stones, and conglomerates. Minimum thickness is 1 km.
Total thickness is unknown.
Metamorphic sequence, including highly deformed and
sheared metaquartzi tes, schists, and phyl l ites. This
sequence is only in faul t contact wi th younger rock uni ts.
I t forms the high r idges north of the geothermal a r e a
STRATIGRAPHIC C OLUM N FOR THE PLATANARES GEOT HERM AL AREA
DEPARTAMENTO DE COPAN HOND URAS
F i g 4 C o m p o s i t e s t r a t i g r a p h i c s e c t io n o f l it h o l o g i c u n i t s i n th e P l a t a n a r e s g e o t h e r m a l a r e a
7/24/2019 geologyPlatanares-heiken1991
6/18
6
6 H E I K E N E T A L
m i d - C r e t a c e o u s Y o j o a G r o u p l im e s t o n e s,
s h a l e s , a n d r e d b e d s ) , J u r a s s i c t o E a r l y C r e t a -
c e o us H o n d u r a s G r o u p s a n d st o ne s a n d co n -
g l o m e r a t e s) , a n d J u r a ss i c E1 P l a n F o r m a t i o n
b l a c k s h a l e a n d t h i n - b e d d e d s a n d s t o n e )
F i n c h , 1 9 8 1; H o r n e a n d F i n c h , 1 9 9 0) . N o n e o f
t h e s e o l d e r M e s o z o i c u n i ts c r o p s o u t i n th e a r e a
o f P l a t a n a r e s .
V a l l e d e A n g e l e s r e d b e d s a r e d i f f i c u l t t o
d i s t i n g u i s h f r o m t h e y o u n g e r r e d b e d s o f t h e
S u b i n a l F o r m a t i o n d e s c ri b e d b e lo w ) . B o t h
u n i t s c o n t a i n i m m a t u r e s a n d s t o n e : l i t h a r e n i t e
a s w e l l a s p e b b l y i m m a t u r e s a n d s t o n e s , c o n -
g l o m e r a t e s , a n d s i lt s to n e s . S o m e o f t h e c o a r s e r
c l a s t i c b e d s i n b o t h c o n t a i n c a l c i t e c e m e n t .
T h u s , i n d r i ll c o r e s a n d i n t h e f i e l d , i t is n e a r l y
i m p o s s i b l e t o i d e n t i f y a r e d b e d s e q u e n c e a s
e i th e r V a l l e d e A n g e l e s o r S u b i n a l w i t h o u t i n-
d e p e n d e n t s tr a t ig r a p h i c c o n t r o l . H o w e v e r ,
m o d a l a b u n d a n c e s o f l i t hi c c la s ts t h a t m a k e u p
m o s t o f th e s e c la s ti c r o c k s p r o v i d e a m e a n s o f
d i s c r i m i n a t i o n . T h e V a l l e d e A n g e l e s s a n d -
s t o n e s a n d c o n g l o m e r a t e s c o n t a i n 20-/o t o 9270
b a s a l t c l as ts F ig . 5) . T h e S u b i n a l F o r m a t i o n
c o n t a i n s s a n d s t o n e s c o n s i s t i n g o f 65070 t o 9 37o
m e t a q u a r t z i t e a n d s c h is t c la s ts , w i t h o n l y t r a c e s
o f b a s a l t F i g . 5 ) .
Matagalpa ormation
W i t h t h e e x c e p t io n o f a f e w in t e r b e d d e d , t h i n
t u f f b e d s a n d s a n d s t o n e s , th e M a t a g a l p a F o r -
m a t i o n a t P l a t a n a r e s c o n s i s t s o f m a s s i v e ,
s i li c if i ed a n d e s i t i c l a v a s . T h e s e l a v a s c r o p o u t
a l on g t h e b o t t o m o f t h e u p p e r Q u e b r a d a d e l
A g u a C a l i e n te F i g. 3 ), w h e r e t h e y a r e c u t b y
q u a r t z - a n d c a l ci te - f il le d a n d p a r t l y o p e n f r a c-
t u r e s . T h e a n d e s i t e s w e r e p e n e t r a t e d b y
g e o t h e r m a l g r a d i e n t w e ll s P L T G - 1 a n d - 3 ,
w h e r e t h e y a r e 5 5 6 m a n d 2 6 3 m t h i c k , r e s p e c -
t iv e ly . P L T G - 3 is o n l y 6 8 0 m s o u t h o f P L T G - 1.
T h e l av a s w e r e n o t e n c o u n t e r e d in w e ll P L T G -
2 , w h i c h is a b o u t 1 ,3 6 0 m s o u t h o f P L T G - 1 .
T h i s a b r u p t s o u t h w a r d t h i n n i n g o f t h e la v a s is
r e f l e c t e d i n a s m a l l p o s i t i v e g r a v i t y a n o m a l y
Basalt and
Andes i te
\ \
M e t a q u a r t z i t e / ^
and Schist / LA L3
A
50
LITHICCLASTTYPES,
SANDSTONESlNREDBED
SEQUENCES
~;~ 0/o
/~ SubinalFormation
O Vallede AngelesGroup
\
\
~ Sandstone,
Mudstone
and Che~
Fig. 5. Triangular diagram of l i thic clas t composit ions from sandstone and conglomerate redbe ds w ithin the
Cre taceo us-T ertiary Valle de A ngeles Group and Tert iary Subinal Formation. B ased on 300-point modal analyses
with a spacing of 0.4 m m) of polished thin sections.
7/24/2019 geologyPlatanares-heiken1991
7/18
GEOLOGY OF THE PLATANARES GEOTHERMAL AREA HONDURAS 7
(A iken e t a l . , 1991 - th i s vo lum e) , w h ich i s i n t e r -
p r e t e d a s a s m a l l s t a c k o f l a v a f l o w s ( se e i n t e r -
p r e t i ve c ro s s - sec t i on i n F ig . 3 ) .
Th e l avas a r e po r ph y r i t i c , w i th 1570 t o 25 % ,
0 . 2 - t o 3 - m m - l o n g p h e n o c r y s t s a n d g l o m e r o -
c r y s t s o f p l a g i o c l a s e a n d m a f i c m i n e r a l s i n a
c o a r s e t r a c h y t ic g r o u n d m a s s . A l l o f t h e l a v as
s e e n in o u t c r o p a n d s a m p l e d f r o m d r i ll c o r e a r e
m o d e r a t e l y t o i n t en s e l y h y d r o t h e r m a l l y a l te r e d
a n d t h e r e f o r e d e s c r i p t i o n s o f i g n e o u s t e x t u r e s
a r e i n t e r p r e t a t i v e , b a s e d u p o n r e l i c t t e x t u r e s .
F e l d s p a r s h a v e b e e n r e p l a c e d b y s m e c t i t e ,
a u t h i g e n i c q u a r t z , c h l o r i t e , a n d t r a c e s o f
c a l c i t e ; m a f i c m i n e r a l s h a v e b e e n a l t e r e d t o
c h l o r i t e a n d m a g n e t i t e . V e i n s a r e f i l l e d w i t h
a u t h i g e n i c q u a r t z a n d b i o t i t e , c h l o r i t e , p y r i te ,
s t i b n i t e , c a l c i t e , a n d o t h e r m i n e r a l s ( B a r g a r ,
1991 - th i s vo lume) .
O u r i n t e r p r e t a t i o n t h a t t h e s e a n d e s i t i c l a v a s
a r e p a rt o f t h e m i d - T e r t i a ry M a t a g a l p a F o r m a -
t i o n i s b a s e d o n s i m i l a r i ty t o a d e s c r i p t i o n o f t h e
f o r m a t i o n i n n e a r b y G u a t e m a l a b y W i l l ia m s e t
a l . ( 1964 ) , whe re i t cons i s t s o f h igh ly a l t e r ed
p y r o x e n e - a n d e s i t e f l o w s a n d l a h a r i c b r e c c i a s ,
and l e s se r f l ows o f p l a ty dac i t e . Such a s e -
q u e n c e h as b e e n m a p p e d i n n o rt h w e s t e rn H o n -
d u r a s , w h e r e i t o v e r l i e s t h e V a l l e d e A n g e l e s
G r o u p a n d i s , i n t u r n , o v e r l a i n b y t h e tu f f s o f
t h e P a d r e M i g u e l G r o u p ( W i l l i a m s a n d
M c B i r n e y , 1 9 69 ). I n H o n d u r a s , l o c a l r e l i e f o n
t h e s e r o c k s r a n g e s f r o m 1 00 m t o 3 0 0 m , f o r m -
i n g k n o b b y r i d g e s. N e a r Z a c a p a , 8 0 k m e a st o f
P l a t a n a r e s , t h e M a t a g a l p a F o r m a t i o n i s u p t o
500 m th ick (Finch , 1972) .
Subinal ormation
A n 8 0 - t o 1 2 0 - m - t h i c k r e d b e d s e q u e n c e ,
w h i c h i s n e a r l y i d e n t i c a l i n a p p e a r a n c e t o t h e
o l d e r r e d b e d s o f t h e V a l le d e A n g e l e s G r o u p ,
u n c o n f o r m a b l y o v e rl ie s a n d e s it i c la v a s o f t h e
M a t a g a l p a F o r m a t i o n . T h e r e d b e d s c o n s i s t o f
r e d a n d g r e e n s a n d s t o n e s , s i lt s to n e s , a n d c o n -
g l o m e r a t e s . A s d i s c u s s e d e a r l i e r , t h e s a n d -
s t on e s a n d c o n g l o m e r a t e s m o s t l y c o ns i st o f
m e t a q u a r t z i t e a n d s c h i s t c l as t s (F i g . 5). M o s t o f
t h e c o a r s e r c l a s t i c r o c k s a r e i m m a t u r e , w i t h
p o o r l y s o r t e d c l a s t s i n a m a t r i x o f g r a y i s h -
p u r p l e s il t. T h i s c l a s t ic r o c k s e q u e n c e , u n d e r l y -
i n g t h e t u f ts o f t h e P a d r e M i g u e l G r o u p , c r o p s
o u t a l o n g t h e w e s t w a l l o f t h e u p p e r Q u e b r a d a
d e A g u a C a l i e n t e a n d i s p e n e t r a t e d b y w e l l s
P L T G - 2 a n d - 3 .
T h e S u b i n a l F o r m a t i o n w a s d e f i n e d fi rs t b y
H i r s c h m a n n (1 96 3) i n t h e M o t a g u a V a l le y o f
G u a t e m a l a a s r e d c l a s t i c s t r a t a b e t w e e n
P a l e o z o i c r o c k s a n d T e r t i a r y v o l c a n i c r o c k s .
W i l l i a m s a n d M c B i r n e y ( 1 9 6 9 ) a p p l i e d t h e
n a m e t o r e d b e d s u n d e r l y i n g t h e P a d r e M i g u e l
G r o u p i n H o n d u r a s ; t h e s e r o c k s a r e c o n t e m -
p o r a n e o u s w i t h t h e t y p e S u b i n a l s e c t i o n , a n d
w e r e d e p o s i te d a f t e r t h e e r u p t i o n s o f
M a t a g a l p a a n d e s it ic la v a s. U s e o f t h e n a m e
S u b i n a l is b a s e d o n st r at i g ra p h i c p o s i t io n
b e t w e e n M a t a g a l p a a n d e s i t i c l a v a s a n d t h e
P a d r e M i g u e l G r o u p t u f t s . A t P l a t a n a r e s ,
r o c k s a s s ig n e d t o t h e S u b i n a l F o r m a t i o n a r e in -
t e r p r e t e d a s a l l u v i a l f a n s d e r i v e d f r o m a
m e t a m o r p h i c h i g h l a n d , w h i c h p a r t l y b u r i e d
d o w n f a u l t e d p i le s o f M a t a g a l p a a n d e s it e s a n d
o l d e r r o ck s . C o r r e l a t i o n o f t h e se r e d b e d s w i th
o t h e rs d e s c ri b e d i n H o n d u r a s a n d G u a t e m a l a ,
on t he ba s i s o f c l a s t t ypes , i s d i f f i cu l t because
e a c h o f t h e s e f a n g l o m e r a t e s o r s m a l l b a s i n -
f i ll in g d e p o s i t s h a s a u n i q u e s o u r c e .
Padre Miguel Group
T h e P a d r e M i g u e l G r o u p c o n s is ts o f m o s t l y
t u f t s a n d t u f f a c e o u s s e d i m e n t a r y r o c k s t h a t
c r o p o u t o v e r m u c h o f w e s te r n H o n d u r a s a n d
s o u t h w e s t e r n G u a t e m a l a ; W i ll ia m s a n d M c B i r-
n e y ( 19 6 9) e s t i m a t e d t h e t h i c k n e s s o f t h e g r o u p
t o b e b e t w e e n 3 0 0 a n d 1 00 0 m . M o s t o f t h e t u f f s
a r e r h y o l i t i c . T h e g r o u p d e s i g n a t i o n r e f e r s t o
i g n i m b r i t e s e q u e n c e s v i s i b l e o v e r m u c h o f
w e s t e r n H o n d u r a s , w h i c h m a y c o m e f r o m
s e v e r a l c a l d e r a s o u r c e s a n d w h o s e d e p o s i t i o n a l
h i s t o r y s p a n s a c o n s i d e r a b l e le n g t h o f t i m e ; K -
A r a g e s f o r t h e P a d r e M i g u e l G r o u p r a n g e f r o m
5 M a t o 3 0 M a ( F . M c D o w e l l , U n i v e r s i t y o f
T e x a s , p e r s. c o m m u n . , 1 9 88 ; W i l l ia m s a n d
M cB i rney , 1969 ; Ep p le r e t a l . , 1987a) . Tu f f s
a n d a s s o c i a t e d m i n o r l a v a s a n d s e d i m e n t a r y
7/24/2019 geologyPlatanares-heiken1991
8/18
48
G H E 1 K E N E T A L
r o c k s o f t h e P a d r e M i g u e l G r o u p c r o p o u t o v e r
m o s t o f t h e P l a ta n a r e s g e o t h e r m a l ar e a . A t
P l a t a n a r e s t h e t h i c k n e s s o f t h i s g r o u p v a r i e s ,
r e a c h in g a m a x i m u m o f 3 10 m .
A l t h o u g h m o s t o f t h e tu f f s a t P l a ta n a r e s a r e
n o n w e l d e d i g n i m b r i t e s , o n e c o n s i s ts o f 1 5/0
w e l d e d , f l a t t e n e d p u m i c e c l a s ts , 5 7o q u a r t z ,
b i o ti te , a n d h o r n b l e n d e p h e n o c r y s t s , a n d 5 %
l i t h i c c l a s t s ( a n d e s i t i c l a v a ) i n a m a t r i x o f
d e v i t r i f i e d s h a r d s . S i m i l a r w e l d e d t u f t s ,
p o s s i b l y c o r r e l a t i v e , w e r e s a m p l e d f o r K - A r
a g e d e t e r m i n a t i o n s f r o m o u t c r o p s a l o n g t h e
Q u e b r a d a d e l as J u n i a p a s a n d a t a d e p t h o f 2 86
m i n w e l l P L T G - 2 . T h e d a t e s , d e t e r m i n e d b y E .
M c K e e , o f t h e U . S . G e o l o g i c a l S u r v e y ar e ,
res pe c t ive ly , 14 .2 +_ 0 .5 M a an d 14 .7 +_ 0 .5
M a ( T a b l e 1 ) .
A b o v e t h e w e ld e d t u f f s a m p l e d i n P L T G - 2
a r e a t l e a s t e i g h t t u f f u n i t s , m o s t o f w h i c h a r e
m a s s i v e , n o n w e l d e d , w h i t e , c r e a m - c o l o r e d , o r
g r e y , f i n e - g r a i n e d i g n i m b r i t e s ; t h e s e u n i t s
r a n g e , i n t h i c k n e s s , f r o m a b o u t 5 m t o 7 0 m .
M o s t a r e v i t r i c o r v i t r i c - l it h i c t u f t s , w i t h 5070 t o
2007o p h e n o c r y s t s o f q u a r t z , s a n i d i n e a n d l e ss e r
p l a g i o c la s e , b i o t it e , h o r n b l e n d e , a n d i l m e n i te ;
p u m i c e la p il li u p t o 1 c m l o n g a r e i n a m a t r i x o f
s h a r d s ( 20 # m t o 5 0 0 ~ m l o n g ) . T h e s e t u f t s a l s o
co n t a i n a t r a ce t o 2 00 70 l i t h ic c l a s t s (m o s t l y
b a s a l t a n d a n d e s i t e l a v a a n d c l a s t s o f o l d e r
t u f f s ) . A c c r e t i o n a r y l a p il li , u p t o 1 c m i n
d i a m e t e r , a r e c o m m o n i n s o m e o f t h e f in e r -
g r a i n e d i g n i m b r i t e s .
B e d s o f n o n w e l d e d t u f f s , w i t h t h ic k n e s s e s o f
0 .5 t o 1 0 m , a r e e x p o s e d a l o n g t h e R i o L a r a ( t o p
o f t h e s e c ti o n s o u t h o f t h e R i o L a r a , m i d d l e o f
t h e s e c t i o n t o t h e n o r t h o f t h e R i o ; F i g . 3 ) a n d
n e a r t h e t o p o f t h e s e c t i o n p e n e t r a t e d b y w e l l
P L T G - 2 . M o s t a re n o r m a l l y g r a d e d , w i t h l a v a
l i t h i c c l a s t s a n d c o a r s e r p u m i c e c l a s t s n e a r t h e
b a s e , g r a d i n g u p in t o f i n e a s h . I n t e r b e d d e d
w i t h t h e s e t u f t s a r e c o n c e n t r a t i o n s o f l i t h i c
c l a s t s a n d m a t r i x - s u p p o r t e d b r e c c i a s , w h i c h
m a y b e v o lc a n ic m u d f l o w d e p o s i ts ; s o m e o f t h e
b r e c c ia s a r e c o n c e n t r a t e d i n 1 - t o 3 - m - d e e p
c h a n n e l s . W i t h i n t h e t u f t s p e n e t r a t e d d u r i n g
d r il li n g , t h e r e a r e i n t e r b e d d e d m u d d y s a n d -
s t o n e s a s s o c i a t e d w i t h s h e a r e d r o c k . I n o u t -
c r o p s a l o n g th e Q u e b r a d a d e A g u a C a l ie n t e ,
s u c h s a n d s t o n e s a r e s e e n t o b e c la s ti c d i k e s
t h a t f o r m e d a l o n g n o r m a l f a u l ts i n th e t u f f s .
P u m i c e f a l l d e p o s i t s a r e r a r e a n d a r e i n -
t e r b e d d e d w i th n o n w e l d e d , f i n e - g r a in e d i g n im -
b r i t e s a l o n g t h e Q u e b r a d a d e A g u a C a l i e n t e .
A l s o i n c lu d e d i n t h e P a d r e M i g u e l G r o u p a r e
p o o r l y b e d d e d , r e d d i s h f a n g l o m e r a t e s a f e w
m e t e r s t h i c k ; t h e s e a r e f o u n d o n l y n e a r f a u l t
c o n t a c t s w i t h t h e m e t a m o r p h i c s e q u e n c e a n d
n o t s o u t h o f t h e R i o L a r a .
T A B L E 1
P o t a s s i u m - a r g o n a g e s o f w e l d e d t u f ts f r o m t h e P l a t a n a r e s g e o th e r m a l a r e a , D e p a r t a m e n t o d e C o p ~ n , H o n d u r a s
S a m p l e R o c k M a t e r i a l K 2 0 4 0 Ar ra d 4 0 Ar ra d A g e
n u m b e r t y p e d a t e d ( w t. ) ( t o o l / g ) ( ) ( M a )
P T L G - 2 R h y o l i t i c w e l d e d t u f f B i o t i t e 8 . 1 9 1 . 73 6 9 1 0 - 1 6 5 . 0 1 4 .7 _+ 0 . 5
J U N I A P A R h y o l i t i c w e l d e d t u f f B i o t i t e 7 .3 1 1 .5 0 17 9 1 0 - 1 4 0 . 5 1 4 .2 _+ 0 . 5
N o t e : a l l s a m p l e p r e p a r a t i o n a n d a n a l y t i c a l w o r k w a s d o n e a t t h e U . S . G e o l o g i c a l S u r v e y l a b o r a t o r i e s i n F l a g s t a f f , A r i z o n a
a n d M e n l o P a r k , u s i n g t h e t e c h n i q u e s d e s c r i b e d i n D a l r y m p l e a n d L a n p h e r e ( 19 6 9 ). W e a n a l y z e d p o t a s s i u m a f t e r l i t h i u m
m e t a b o r a t e f u s i o n , u s i n g a f l a m e p h o t o m e t e r , w i t h t h e l i t h i u m s e r v in g a s th e i n t e r n a l s t a n d a r d ( I n g a m e l l s , 1 97 0). E r r o r ,
s h o w n a s t h e _+ v a l u e , i s t h e e s t i m a t e o f t h e s t a n d a r d d e v i a t i o n o f a n a l y t i c a l p r e c i s io n . K - A r a g e w a s c a l c u l a te d u s i n g t h e
c o n s t a n t s f o r t h e r a d i o a c t i v e d e c a y a n d a b u n d a n c e o f 4 A r r e c o m m e n d e d b y th e I n t e r n a t i o n a l U n i o n o f G e o l o g i c a l
S c i e n c e s S u b c o m m i s i o n o n G e o c h r o n o l o g y ( S t e i g e r a n d J ~ g e r , 1 9 77 ). T h e s e c o n s t a n t s a r e : Y t = 0 . 58 1 1 0 - l 0 y r - 1 ,
Y t = 4 . 9 6 2 1 0 - 10 y r - l , a n d 4 0 K / K t ot a I = 1 .1 6 7 x 1 0 - 4 m o l / m o l . A g e d e t e r m i n a t i o n p r o v i d e d b y E . H . M c K e e , U . S .
G e o l o g i c a l S u r v e y .
7/24/2019 geologyPlatanares-heiken1991
9/18
GEOLOGY OF THE PLATANARES GEOTHERMAL AREA HONDURAS 9
M a n y o f t h e t u f f s a r e s i li ci fi ed a lo n g m a j o r
f a u l t s . T h e s e r o c k s a r e b r i t t l e a n d c r o s s e d b y
a b u n d a n t o p e n a n d c a l ci te - f il le d f r a c t u r e s .
S i l i c i f i e d t u f f s l o c a l l y f o r m e r o s i o n - r e s i s t a n t
r id g e s. M a n y o f t h e t u f f s p e n e t r a t e d d u r i n g
d r il li n g o f w e ll s P L T G - 2 a n d P L T G - 3 a r e
s i l i c i f i e d , a n d o n l y r e l i c t t e x t u r e s r e m a i n .
A f e w l a v a f l o w s h a v e b e e n i d e n t i f i e d a t
P l a t a n a r e s w i th i n t h e P a d r e M i g u e l G r o u p ;
r h y o l i ti c la v a f l o w b r e c c i a c r o p s o u t a l o n g a n d
n e a r t h e Q u e b r a d a d e la s J u n i a p a s a n d b a s a l ti c
l a v a c r o p s o u t a l o n g t h e R i o L a r a . N o v e n t
a r e a s h a v e b e e n i d e n t i f ie d f o r t h e s e la v a s .
S o u r c e s f o r t h e t u f fs o f t h e P a d r e M i g u e l
G r o u p a t P la t a n a r e s a r e n o t k n o w n . H o w e v e r ,
t h e m a s s i v e , n o n w e l d e d i g n i m b r i t e s e x t e n d
s o u t h w a r d t o t h e C o r d i l le r a d e C e l a q u e , a p r o -
p a b l e c a l d er a c o m p l e x 2 0 k m s o u t h o f P l a t a n -
a r e s . T h e t u f f s a t C e l a q u e a r e l i t h o l o g i c a l l y
s i m i la r t o t h o s e a t P l a t a n a r e s , s u g g e s t in g th a t
t h is c a l d e r a c o m p l e x m a y b e t h e s o u r c e f o r t h e
i g n i m b r i t e s a t P l a t a n a r e s . I f th i s i n t e r p r e t a t i o n
is c o r r e c t, t h e n p y r o c l a s t i c fl o w s f r o m t h e C e l a-
q u e a r e a f l o w e d n o r t h , b u r y i n g a c o m p l e x t er -
r a i n a t P l a t a n a r e s t h a t c o n s i s t e d o f a h i g h l a n d
o f P a l e o z o ic m e t a m o r p h i c r o ck s a n d M e s o z o ic
r e d b e d s o v e r l a i n b y m i d - T e r t i a r y a n d e s i t e
f l o w s a n d a l l u v ia l f a n s. A s m e n t i o n e d a b o v e ,
t h e P a d r e M i g u el G r o u p i n w e st er n H o n d u r a s
a n d e a s t e rn G u a t e m a l a r a n g e s in a g e f r o m 5 t o
3 0 M a ; t h e r a n g e o f a g es a t P l a t a n a r e s is
u n k n o w n , b u t t u f f s w e d a t e d n e a r th e b a s e o f
t h e s e c t io n h a v e ag e s o f a b o u t 1 4.5 M a . T h e r e
m a y b e m u l t i p l e so u r c es f o r t h e P a d r e M i g u e l
t u f f s , s u c h a s a n e a r b y s i l i c i c l a v a f i e l d o f
u n k n o w n l o c a t io n , b u t f i e ld w o r k is n e e d e d to
i d e n t i f y a ll p o s s i b l e s o u r c e s , i n c l u d i n g c a l d e r a s
o t h e r t h a n t h a t i n f e r r e d a t t h e C o r d i l l e r a d e
C e l a qu e . I m p o r t a n t t o g e o t h e r m a l m o d e l s o f
P l a t a n a r e s , h o w e v e r , is t h e f a c t t h a t t h e s e
v o l c a n i c r o c k s a r e r e l a ti v e ly o l d a n d t h u s t h e i r
s o u r c e m a g m a b o d i e s h a v e s o l i d i f i e d a n d
p r e s u m a b l y c o o l e d t o b a c k g r o u n d c r u s t a l
t e m p e r a t u r e s , w h e t h e r t h e y a r e l o c a te d b e n e a t h
P l a t a n a r e s o r s o m e d i s ta n c e a w a y S m i t h a n d
S h aw , 1 9 7 5 ) .
Terrace gravels
T h e v i ll a g e o f P l a t a n a r e s is l o c a t e d o n a 1 .0 -
b y 1 .2 5 k m s t r e a m t e r r a c e , w h i c h f o r m s t h e u p -
p e r p a r t o f t h e s o u t h w e s t e r n s l o p e s o f t h e
Q u e b r a d a d e l A g u a C a l ie n t e. T h e t e rr a c e
s l o p es a b o u t 3 .5 t o t h e s o u t h e a s t f r o m a n
e l e v a t i o n o f 8 0 0 m t o 7 4 0 m . T e r r a c e g r a v e l s
f o r m a n i r r e g u l a r d e p o s i t , u p t o 6 0 m t h i c k ,
w h i c h o v e r l i e s a s u r f a c e o f m o d e r a t e r e l i e f
e r o d e d i n t o tu f f s o f t h e P a d r e M i g u e l G r o u p .
T h e g r av e ls a r e p o o r l y b e d d e d a n d c o n s is t o f
a n g u l a r t o s u b a n g u l a r c o b b l e s a n d p e b b l e s ,
m o s t l y q u a r t z it e , s c h i s t, a n d e s i t e a n d t u f f . T h e
u p p e r t h i r d o f t h e d e p o s i t i s s t a i n e d r e d b y
h e m a t i t e .
A l o w e r - e l e v a t i o n t e r r a c e i s p r e s e n t i n t h e
s o u t h e a s t p a r t o f t h e m a p p e d a r e a, n e a r t h e
c o n f l u e n c e o f t h e Q u e b r a d a d e l A g u a C a l ie n t e
w i t h t h e R i o H i g u i t o . T h i s t e r r a c e s l o p e s g e n t ly
t o t h e s o u t h e a s t a t a n a v e r a g e e l e v a t i o n o f
a b o u t 7 0 0 m .
Silica sinter dep osits
D e p o s i t s o f s i l i c e o u s s i n t e r a n d c o n g l o m e r -
a t e s c e m e n t e d b y si li ca si n te r u n c o n f o r m a b l y
o v e r li e t u f f s a n d l a v a s a lo n g t h e Q u e b r a d a d e l
A g u a C a l i e n t e . T h e c o n g l o m e r a t e s a re l it h o g i-
c a ll y s i m i la r t o m o d e r n s t r e a m g r a v e l s a n d c o n -
s is t o f c o b b le s a n d p e b b le s f r o m m e t a m o r p h i c ,
v o l c a n i c l a v a ), a n d r e d b e d c l a s ti c s o u r c e s . T h e
s i n t e r d e p o s i t s f o r m o v e r h a n g i n g l e d g e s a n d
l o c a l l y f o r m i m p e r m e a b l e c a p r o c k s o v e r h o t
s p r in g s . M o d e r n s t r ea m g r av e ls i n th e m a i n h o t
s p r i n g a r e a a r e n o w b e i n g c e m e n t e d b y s i li ca
f r o m h o t s p r i n g s . O n e o f th e s i n t e r d e p o s i t s is
c u t b y a f a u l t in th e u p p e r Q u e b r a d a d e l A g u a
C a l i e n t e .
ot spr ings and fuma roles
M o s t h o t s p r i n g s a n d a l l o f t h e b o i l i n g
s p r i n g s a t P l a t a n a r e s l i e w i t h i n a 0 . 5 - 1 . 0 - k m -
w i d e , N W - t r e n d i n g f a u l t a n d f r a c t u r e z o n e
w h o s e p r i n c i p a l p h y s i o g r a p h i c e x p r e s s i o n i s
Q u e b r a d a d e A g u a C a l i e n te . A f ew w a r m
s p r i n g s d i s c h a r g e f r o m s i l i c i f i e d , f r a c t u r e d
7/24/2019 geologyPlatanares-heiken1991
10/18
50 G HEIKEN ET AL
t u f f s a l o n g t h e R i o L a r a . M o s t s p r i n g s v e n t a t
t h e b o t t o m o f t h e q u e b r a d a b u t s o m e d i s c ha r ge
o c c u r s f r o m f r a c t u r e d t u f f s a s h i g h a s 3 5 m
a b o v e s t r e a m l e v e l. A t a w a t e r f a l l , w h i c h f l o w s
o v e r a f a u l t s c a r p , h o t s p r i n g s f lo w a l o n g b e d -
d i n g p l a n e s i n s i li c if ie d t u f f . F o r m a p s a n d
d e t a i l e d d e s c r i p t i o n s o f t h e s p r i n g s , s e e H e i k e n
e t a l. ( 1 9 8 6 ) a n d G o f f e t a l. ( 1 9 8 7 b ) ; ( J a n i k e t
a l . , 1 9 9 1 - t h is v o l u m e ) .
tructural framework
M o s t s t r a t i f i c a t io n i n th e t u f f s o f t h e P a d r e
M i g u e l G r o u p d i p s 1 5 t o 3 0 t o t h e s o u t h ; a t -
t i t u d e s d i v e r g e f r o m t h i s r e g i o n a l d i p n e a r
f a u l t s a n d l a n d s l id e s . B e d d i n g w i t h in t h e V a l l e
d e A n g e l e s r e d b e d s d i p s g e n e r a l ly t o t h e s o u t h
o r s o u t h w e s t , a t 15 t o n e a r l y v e r t i c a l .
A n a r e a o f a b o u t 5 k m 2, b o u n d e d b y L a
B u f a f a u l t o n t h e n o r t h w e s t , a p o s s i b l e f a u l t
p a r a ll e l t o th e R i o L a r a o n t h e s o u t h , u n n a m e d
f a u lt s o n t h e w e s t, a n d t h e Q u e b r a d a d e l A g u a
C a l i e n t e f a u l t o n t h e e a s t is h i g h l y d i s r u p t e d b y
n o r m a l f a u l t s ( F ig . 3 ); s li c k e n s i d e o r i e n t a t i o n s
i n d i c a t e t h a t a n u m b e r o f h i g h - a n g l e f a u l t s
h a v e p r e d o m i n a n t l y s t r i k e - s l i p m o t i o n . T h e
T e r t i a r y v o l c a n i c r o c k s , i n c l u d i n g t h e a n d e s i t ic
l av a s o f th e M a t a g a l p a F o r m a t i o n a n d t h e tu f f s
o f th e P a d r e M i g u e l G r o u p , a r e d o w n f a u l t e d
a g a i n s t C r e t a c e o u s - T e r t ia r y r e d b e d s o f t h e
V a ll e d e A n g e l e s G r o u p , d e f i n in g a N W -
t r e n d i n g g r a b e n . T h e g r a b e n is t e r m i n a t e d o n
t h e n o r t h b y t h e E - W t o N E - t r e n d i n g L a B u f a
f a u l t . A l l h o t s p r i n g s o f t h e P l a t a n a r e s a r e a l ie
s o u t h o f th i s fa u l t . A d e t a i l e d s tr u c t u r a l m a p o f
t h e c e n t e r o f t h i s a r e a h a s b e e n p r e p a r e d b y
A l d r i c h e t a l . ( 1 9 9 1 - t h i s v o l u m e ) .
A l t h o u g h p o o r l y e x p o s e d i n o u t c r o p , a m a -
j o r E - t r e n d i n g f a u l t m a y p a r a l le l th e R i o L a r a
( R i o L a r a F a u l t o n F i g. 3 ). N o r t h o f t h e R i o
L a r a , t h e r e a r e n u m e r o u s f a u l t s a n d h o t
s p r i n g s , w h e r e a s t o t h e s o u t h t h e r e i s l i t t l e
d e f o r m a t i o n o t h e r t h a n t h e g e n t le r e g io n a l d i p
a n d n o h o t s p r i n g s a r e v i s i b l e . E a s t w a r d f r o m
t h e m o u t h o f t h e R i o L a r a , t h e R i o H i g u i t o
t a k e s a 9 0 b e n d a n d f o l lo w s t h e e x t e n s i o n o f
t h e a p p a r e n t R i o L a r a f a u l t ( F i g . 2 ) . W e l l
P L T G - 2 , d r il le d 0 .5 k m n o r t h o f th e R i o L a r a ,
p e n e t r a t e s a s e q u e n c e o f h e a v i ly f r a c t u r e d a n d
f a u l t e d r o c k s a n d c l a s t i c d i k e s .
T h e m a i n tr a c e o f t h e Q u e b r a d a d e l A g u a
C a l i e n t e f a u l t is p a ra l le l t o t h e q u e b r a d a o f t h e
s a m e n a m e a n d h a s a s t r o n g p h y s i o g r a p h i c e x-
p r e s s i o n , i n c l u d i n g e s c a r p m e n t s a l o n g a l l u v i al
t er r ac e s a t t h e m o u t h o f th e q u e b r a d a . T w e n t y -
e i g h t g r o u p s o f h o t a n d b o i l i n g s p r i n g s r i s e
a l o n g N W - t r e n d i n g f a u l t s a n d f r a c t u r e s o f t h is
f a u l t z o n e .
N e a r l y a l l o f t h e r o c k u n i t s s a m p l e d b y d r i l-
l in g a r e f r a c t u r e d a n d f a u l t e d . T h e c h a r a c t e r i s -
t ic s o f a l l f r a c t u r e s e t s w i t h i n r o c k u n i t s s a m p l -
e d b y d r i l li n g a r e c o n t r o l l e d b y l it h o l o g y . S t e e p -
l y d i p p i n g f r a c t u r e s ( d i p = 6 0 t o 9 0 ) a r e
f o u n d w i th i n h y d r o t h e r m a l l y a lt e re d l a va s a n d
w e l d e d t u f f o n l y , w h e r e a s t h o s e w i th l o w d i p s
a r e f o u n d i n a ll r o c k t y p e s , a n d a r e m o s t a b u n -
d a n t i n s i lt s t o n e s . F r a c t u r e s f i ll e d w i t h
a u t h ig e n i c m i n er a l s a r e m o s t c o m m o n i n s u c h
c o m p e t e n t r o c k u n i t s a s t h e a n d e s i t ic l a v as .
ydrotherm al alteration
T h r e e e x p l o r a t i o n c o r e h o l e s ( P L T G - 1 ,
P L T G - 2 , a n d P L T G - 3 ) w e r e d r il le d t o d e p t h s
o f 6 5 0 m , 4 2 8 m , a n d 6 7 9 m , r e s p e c ti v e ly a t
P l a t a n a r e s t o p r o v i d e d a t a o n l i th o l o g i e s ,
t e m p e r a t u r e g r a d i e n t s , p h y s i c a l p r o p e r t i e s ,
a n d c h e m i c a l c o m p o s i t i o n o f f l u i d s (F ig s . 3 a n d
6 ) (S . G o f f e t a l . , 1 9 8 7 , 1 9 8 8 ; G o f f e t a l . , 1 9 9 1 -
t h is v o l u m e ) .
P L T G - 1 a n d P L T G - 3 a r e lo c a t e d w i t h in t h e
m a i n N W - t r e n d i n g f a u l t z o n e c l o s e t o t h e
Q u e b r a d a d e A g u a C a l ie n t e (F ig . 3 ). P L T G - 1
e n c o u n t e r e d h o t w a t e r a t 2 5 2 m a n d f r o m 6 25
m t o 6 4 4 m . P L T G - 3 , l o c a t e d 65 0 m S E o f
P L T G - 1 , e n c o u n t e r e d h o t w a t e r at d e p t h s o f
4 5 9 m a n d 6 2 2 m t o 6 3 5 m ( F i g . 7 ). R o c k u n i t s
s a m p l e d b y c o r i n g i n b o t h w e ll s 1 a n d 3 a re
h y d r o t h e r m a l l y a l te r e d .
P L T G - 2 , l o c a te d 1 k m s o u t h o f P L T G - 1 a n d
a w a y f r o m t h e m a i n h o t s p r i n g a re a , s h o w s a
c o n d u c t i v e g e o t h e r m a l g r a d i e n t o f 13 9 C / k m
7/24/2019 geologyPlatanares-heiken1991
11/18
G E O L O G Y O F T H E P L A T A N A R E S G E O T H E R M A L A R E A , H O N D U RA S 5
C O R R E L A T I O N S - P L A T A N A R E S G E O T H E R M A L A R E A
E l e v . = 7 1 0 m )
\
\ ~ PLTG
2 4 0 m + \ ~ ] ~
\~(Elev. = 760m)
E l e v = 7 1 0 m ) /
\
C O M P O S I T E S T R A T I G R A P H I C ~ 3 0 ~ C - 'a e z e i? O e /
S E C T I O N , 1 0C 1 3 0 C \ ~ ~ - ' O ~ 2 '
Q U E B R A D A d e ~ ' , ~ H ~ /
A G U A C A L I E N T E , ~
\ \
20C / /
3
~at~g 1
- . .
o o o c
150oC
' ( ? ) .U
1 1 0 C
5 0 0 - _ J ~ J - - - - 1 65 oc . . . . . . . . . ?)
6( )~C
G~upo de q]
6 0 0 , a e A n g e~es
M E T E R S H X t a e r e d b e 6 e
1 6 0 C 0 0 . 5
I I I I I I I r
V e r t ic a l e x a g g e r a t i o n = 2 . 5 x
/
/
I
200m +
/ C O M P O S I T E S T R A T I G R A P H I C
S E C T I O N ,
R I O L A R A
1. 0 km
I i
F i g . 6 . F e n c e d i a g r a m o f s t r a t i g r a p h y o f t h e P l a t a n a r e s g e o t h e r m a l a r e a , b a s e d u p o n c o m p o s i t e s t r a ti g r a p h i c s e c t io n s
o u t c r o p s ) a n d t h r e e g e o t h e r m a l g r a d i e n t c o r eh o l e s . P a t t e r n s w i t h in t h e M a t a g a l p a F o r m a t i o n : w h i t e = l a v a s a n d
s t i p p l e d = i n t e r b e d d e d t u f t s . P a t t e r n s w i t h i n th e P a d r e M i g u e l G r o u p ; w a v y p a t t e r n = w e l d e d t u f f, l i g h t s ti p -
p l e = m a s s i v e , n o n w e l d e d t u f t s , a n d c o a r s e s t i p p le = b e d d e d t u f t s .
a t a d e p t h o f 4 0 0 m ( l i n e a r g r a d i e n t s o f
2 3 9 C / k m f r o m 0 t o 1 50 m a n d 1 3 9 C f r o m
1 7 0 t o 4 0 0 m ; M e e r t a n d S m i t h , 1 9 9 1 - t h i s
v o l u m e ) ( F ig . 7 ). T h e r o c k u n i t s p e n e t r a t e d b y
t h is w e l l s h o w l it tl e h y d r o t h e r m a l a l t e r a t i o n .
ethods and procedure
C o r e s f r o m P L T G - 1 w e r e sa m p l e d e v e ry 1 0
m a n d t h o se f r o m P L T G - 2 a n d P L T G - 3 w e r e
s a m p l e d e v e r y 20 m ( m o s t w e r e r e p r e s e n t a t iv e
o f t h e w h o l e r o c k a n d s o m e s a m p l e s a re o f
v e i ns ) . T h i n s e c t i o n s w e r e c u t f r o m e a c h s a m p l e
a n d i o n - e tc h e d b e f o r e p e t r o g r a p h i c , E D S
a n a l y s e s o n a s c a n n i n g e l e c t r o n m i c r o s c o p e a n d
e l e c t r o n m i c r o p r o b e a n a l y s e s . B u l k r o c k
s a m p l e s f r o m e a c h i n te r v a l w e r e c r u s h e d a n d
t h e p o w d e r s g r o u n d to 5 m b e f o r e an a ly s is o n
a S i e m e n s D 5 0 0 a u t o m a t e d X - r a y d i ff r a c -
t o m e t e r a t a s t e p o f 0 .0 2 , a r a t e o f 1 .0 s / s t e p ,
s c a n n e d f r o m 2 t o 3 7 2 -t h e t a , u n d e r C u K a
r a d i a t i o n . I n s t r u m e n t s e t t i n g s w e r e 5 0 k V a c -
c e l e r a t i n g v o l t a g e a n d 4 0 m A t u b e c u r r e n t .
M i n e r a l p h a s e s w e r e i d e n t i f i e d b y o p t i c a l
m e t h o d s , X R D , a n d e n e r g y -d i sp e r s iv e X - r a y
s p e c t r o m e t r y d u r i n g e x a m i n a t i o n w i th a s c an -
n i n g e l e c t r o n m i c r o s c o p e . T h e w e i g h t p e r c e n -
t a g e s o f m i n e r a l p h a s e s i n F i g u r e 7 a r e s e m i -
q u a n t i t a t i v e a n d w e r e c a l c u l a t e d u s i n g a p r o -
g r a m ( Q u a n t v ) t h a t u s e s p e a k i n te n s it ie s o f t h e
s a m p l e , c o m p a r e d w i t h t h o s e o f s t a n d a r d s .
7/24/2019 geologyPlatanares-heiken1991
12/18
5 2
G. HEI KEN ET AL.
E3
0
1 0 0 -
2 0 0 -
3 0 0
4 0 0 - - -
5 0 0 - - -
6 0 0 -
7 0 0 _
O
1 0 0 -
2 0 0 -
3 0 0 -
4 0 0 -
5 0 0 -
I
D
m
_ b
6 0 0 - m
7 0 0 _
0 -
1 0 0 -
2 0 0 -
3 0 0
~ 4170-
Q
7 0 0 _ 0 1 0 0 6 0 0 2 0 0 3 0 1 0 0
Q t z F e l d S m C c K a
2 2 0 0 3 8 8
I I C h C I C r O p
10
20
~ ao(
0 400
500
600
7O0
0
10C
20C
1
~ 40
50(
60(
70(
01
~ 4 ~
5o@
6oo[
7ool
P L T G - 1
I I L
i i
P L T G - 3
I I
P L T G - 2
510 100 150
T E M P E R A T U R E C )
200
F i g . 7 . V a r i a t io n o f m i n e r a l s f r o m b u l k r oc k s a m p l e s w i t h d e p t h in th r e e g e o t h e r m a l g r a d i e n t c o r e h o l e s ( h o s t r o c k
s a m p l e s ) . Q t z = q u a r t z , F e l d = f e l d s p a r , S m = s m e c t i t e , C c - - c a l c i t e , K a = k a o l i n i t e , I1 = i l l i te , C h = c h l o r i t e ,
C 1 = c l i n o p t i lo l i t e , C r = c r i s to b a l i te , a n d O p = o p a l C - T . V a l u e s a re i n w e i g h t p e r c e n t . T e m p e r a t u r e m e a s u r e m e n t s
( f r o m D . S m i t h , U n i v e r s i t y o f F l o r i d a a n d o n s i t e d r i ll in g te a m s , u n p u b l i s h e d r e p o r ts ) w e r e m a d e a t 3 0 - m i n t e r v al s , b o t h
d u r i n g d e s c e n t a n d a s c e n t o f t h e p r o b e . S a m p l e s r e p r e s e n t a ti v e o f t h e m a j o r l i t h o i o g i c u n i t s w e r e c o ll e c t ed f o r t h e r m a l
c o n d u c t i v i t y v a l u e s .
7/24/2019 geologyPlatanares-heiken1991
13/18
GEOLOGY OF THE PLATANARES GEOTHERMAL AREA HONDURAS 53
S e l e c te d , h o m o g e n i z e d r o c k p o w d e r s ( 17 7 t o 4 0
m ) o f v o l c a n i c r o c k s w e r e a n a l y z e d b y X - r a y
f l u o r e s c e n c e , f o l l o w i n g t h e p r o c e d u r e s o f
V a l e n t i n e ( 1 98 3 ); t h e d a t a a p p e a r i n T a b l e 2 .
H y d r o t h e r m a l m i n e r a lo g y P L T G 1
P r i n c i p a l h y d r o t h e r m a l m i n e r a l s i n c l u d e
q u a r t z , s m e c t i t e , m i x e d - l a y e r i l li t e -s m e c t i t e , il-
l i t e , k ao l i n i t e , p y r i t e , m a rca s i t e , c a l c i t e ,
f l u o ri te , a n d m i n o r to t r a ce a m o u n t s o f
l a u m o n t i t e , r u t i l e , s t i b n i t e , a n d s p h a l e r i t e .
P h e n o c r y s t s w i t h i n a n d e s it i c la v a s a r e p a r t l y t o
c o m p l e t e l y a lt e r e d t o s m e c t it e , m i x e d - l a y e r
i l l i t e - s m e c t i t e , i l l i t e , a n d t r a c e a m o u n t s o f
k a o l i n i t e . T h e g r o u n d m a s s m i n e r a l s o f l a v a
s a m p l e s a r e a l t e r e d t o q u a r t z , s m e c t i t e , i l l i t e ,
a n d k a o l i n i t e ( a l s o i d e n t i f i e d b y B a r g a r , t h i s
v o l u m e ) . S m e c t i t e i s m o r e o r l e s s e v e n l y
d i s t r i b u t e d t h r o u g h o u t t h e g r o u n d m a s s ,
w h e r e a s k a o l i n i t e a n d i l l i t e o c c u r a s s m a l l
c l u m p s . C h l o r i t e a n d b a r i t e a r e p r e s e n t a s
d i s c o n t i n u o u s v e in l e ts , a n d r e p l a ce s m a f i c
m i n e r a l s ; i t i s m o s t a b u n d a n t f r o m d e p t h s o f
3 9 0 m t o 5 4 0 m (F i g . 7 ) . T h e re i s a w ea k v e r t i c a l
z o n a t i o n o f a l t e r a t i o n m i n e r a l s , w i t h d e c r e a s -
i n g s m e c t i t e a n d i n c r e a s i n g c h l o r it e w i t h d e p t h .
A l l o p h a n e i s p r e s e n t at a ll d e p t h s a n d m a k e s u p
a s m u c h a s 5 v o l u m e p e r ce n t. N e a r a m a j o r
t h e r m a l - w a t e r e n t r y a t a d e p t h o f 2 5 2 m , t h e r e
is a n i n c r e a s e i n t h e v o l u m e o f k a o l i n i te a n d il-
l it e (1 5 a n d 2 0 w t . 70 ). I n s u f f i c i e n t t i m e f o r
w o r k o n a l t e r a t i o n a g e s p r e c l u d e s a n y d i s c u s -
s i o n o n w h i c h o f t h e a l t e r a t i o n p r o d u c t s a r e
r e la t e d to a n o l d e r o r p r e s e n t - d a y h y d r o t h e r -
m a l s y s t e m . T h e k a o l i n i t e - i l l i t e i n t h e
2 0 0 - 3 0 0 - m i n t e r v a l s u g g e s t s t h a t a t le a s t s o m e
o f t h e a l t e r a t i o n w a s c a u s e d b y t h e p r e s e n t
h y d r o t h e r m a l s y s t e m . T h e s e v e r i t y o f a l t e r a -
t i o n i s e v i d e n t i n t h e c h e m i c a l a n a l y s e s
p r e s e n t e d i n T a b l e 2 . A l t h o u g h t h e e n t i r e
v o l c a n i c s e q u e n c e in P L T G - 1 is a n d e s i t ic , c o n -
t e n ts o f d i v a le n t a n d m o n o v a l e n t m e t a ls a r e
v a r i ab l e an d t h e t o t a l s a r e < 9 4 w t . 70 , r e f l e c -
t i n g a l t e r a t i o n w i t h h y d r o u s m i n e r a l s .
P y r i t e o c c u r s t h r o u g h o u t t h e e n ti re 6 5 0 - m -
t h i c k s e c t i o n , p r i n c i p a l ly a s v e in l e ts u p t o 1 m m
w i d e . T y p i c a l l y i t f o r m s l o o s e , i r r e g u l a r a g -
g r e g a t e s o f f i n e - g r a i n e d , e u h e d r a l c r y s t a l s ; i n
t h e u p p e r m o s t 1 00 m o f t h e s e c t io n , p y r i t e is in -
t e r g r o w n w i t h m a r c a s i t e . O p e n f r a c t u r e s a t a
d e p t h o f 7 0 m a r e l i n e d w i th s m e c t it e , q u a r t z ,
p y r i t e , m a r c a s i t e , a n d s t i b n i t e . T h e m a r c a s i t e
o c c u r s a s c lu s t er s o f c o c k s c o m b c r y s ta l s a n d t h e
s t i b n i t e f o r m s s p r a y s o f a c i c u l a r c r y s t a ls u p t o
1 8 m m l o n g .
V e i n s o f q u a r t z , c a l c i te , a n d f l u o r i t e a r e p r e -
s e n t a t a ll d e p t h s u p t o 3 c m w i d e . A 2 - c m - t h i c k
q u a r t z v e i n a t a d e p t h o f 1 50 m c o n t a i n s v u g s
0
1 0 0
PLTG 1
0 5 10
N U M B E R O F F R A C T U R E S
P E R m O F E P T H
PL T G 3
P L T G 2
15 0 5 10 15 0 10 20
30 40
2 0 0
3 0 0
t~ 400
500
6 0 0
7 0 0
F i g . 8 . V a r i a t i o n o f o p e n f r a c t u r e d e n s i t y , w i t h d e p t h , i n t h r e e g e o t h e r m a l g r a d i e n t c o r e h o l e s , P l a t a n a r e s G e o t h e r m a l
S i te . F r a c t u r e s w e r e m e a s u r e d a l o n g a l l o f t h e c o r e s c o l le c t e d c o n t i n u o u s c o r i n g ) a n d a v e r a g e d a t 2 - m i n t e r v a l s .
7/24/2019 geologyPlatanares-heiken1991
14/18
T
A
2
W
h
e
o
c
m
c
a
y
o
s
e
e
c
e
s
m
e
o
v
c
c
o
P
a
a
e
H
a
m
o
e
e
m
s
n
w
a
a
e
e
m
s
n
p
m
a
S
m
e
N
b
P
G
1
0
P
G
2
0
P
G
1
5
0
P
G
2
7
5
P
G
2
1
0
P
G
2
2
0
P
G
3
2
0
P
G
3
4
5
F
m
o
:
M
a
a
p
M
a
a
p
M
a
a
p
P
e
M
g
P
e
M
g
P
e
M
g
P
e
M
g
M
a
a
p
R
y
~
A
e
A
e
A
e
l
g
m
e
I
g
m
e
l
g
m
e
I
g
m
e
A
e
P
G
3
4
9
M
a
a
p
A
e
P
G
3
5
1
M
a
a
p
A
e
S
O
2
6
0
6
7
6
2
8
4
6
8
7
0
7
1
6
1
T
O
2
0
4
0
6
0
6
0
3
0
2
0
3
8
0
3
0
6
A
1
0
1
5
1
7
9
3
1
4
1
8
1
0
1
0
F
1
2
3
3
3
6
1
9
2
5
I
3
1
4
3
7
M
n
O
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
M
g
O
0
3
0
8
1
2
0
1
0
1
0
1
0
1
1
0
C
O
9
2
4
7
2
2
0
9
1
4
0
2
1
4
4
3
K
2
5
2
9
2
5
1
8
5
1
8
2
3
6
3
1
N
0
2
1
0
4
9
1
3
2
0
0
7
3
2
3
1
P
0
2
0
2
0
2
0
0
0
0
0
0
0
1
0
2
T
a
s
9
4
9
0
9
0
9
3
9
8
9
3
9
7
9
5
B
2
8
8
8
6
7
8
8
R
8
7
6
6
1
2
8
1
S
4
2
4
1
1
5
1
3
V
3
4
4
9
1
1
3
5
C
9
9
1
2
1
1
1
N
1
4
9
5
1
1
2
1
Z
4
6
7
4
9
4
3
6
Y
1
1
1
2
5
3
1
1
Z
1
2
2
1
2
2
1
2
N
2
2
2
1
2
1
2
2
6
6
0
6
1
5
3
9
0
0
1
2
5
2
3
2
5
5
0
0
2
9
1
7
6
3
3
8
7
7
1
2
2
6
3
0
6
1
8
3
6
0
0
0
7
5
0
2
4
4
0
0
2
9
0
1
5
4
6
5
6
5
2
2
a
A
y
G
L
m
L
A
X
s
p
o
b
S
m
e
n
m
s
h
w
d
h
c
A
s
m
e
e
b
v
y
n
d
e
o
a
e
a
o
7/24/2019 geologyPlatanares-heiken1991
15/18
GEOLOGY OF THE PLATANARES GEOTHERMA L AREA HONDURAS 55
l i n e d w i t h f l u o r i t e c r y s t a l s . O t h e r v e i n s c o n -
t a i n i n g c a l c i t e a n d f l u o r i t e a r e t y p i c a l l y n a r -
r o w e r , le ss t h a n 5 m m w i d e .
A s a m p l e o f a n d e s i ti c w a l l r o c k a d j a c e n t t o
o p e n f r a c t u r e s p a r t l y f i l l e d w i t h s t i b n i t e ,
p y r i t e , a n d m a r c a s i t e ( d e p t h = 75 m ) c o n -
t a in s < 6 p p b A u , 1 8.3 p p m Sb , 91 p p m Z n , 4 2
p p m A s a n d < 3 p p m A g . V e i n q u a r t z f r o m a
d e p t h o f 2 52 m ( a m a j o r w a t e r e n t r y ) c o n t a i n s
3 .1 p p m A u , 3 7 4 p p m S b , 2 6 p p m Z n , 2 9 0 0 p p m
A s , 8 .5 p p m A g , 1 . 8 B a , 3 00 0 p p m M o , a n d
1 7 p p m S e ( i n s t r u m e n t a l n e u t r o n a c t i v a t i o n
a n a l y s e s b y S . G a r c i a , L o s A l a m o s ) . A
l i m o n i t i c j a s p e r o i d f r o m a f a u l t S E o f t h e
Q u e b r a d a d e la s J u n i a p a s c o n t a i n s < 6 p p b
A u b u t 47 p p m A s a n d 11 p p m S b .
H y d r o t h e r m a l m i n er a lo g y P L T G 2
H y d r o t h e r m a l m i n e r a l s i d e n t i f i e d i n t h e
r o c k s o f P L T G - 2 c o n t a i n s m e c t it e , m i x e d - la y e r
i l l i t e - s m e c t i t e , q u a r t z , c r i s t o b a l i t e , o p a l - C T ,
c l i n o p t i l o l i t e , a n d m i n o r c a l c i t e , k a o l i n i t e , i l -
l it e, a n d c h l o r i te . T h e u p p e r m o s t 1 50 m o f t h e
s e c ti o n c o n t a i n s o p a l C - T a n d v a r y in g a m o u n t s
o f c r i s t o b a l it e a n d c l in o p t i lo l i te . F r o m d e p t h s
o f 1 5 0 m t o 3 1 0 m , t h e r e i s a n a r g i l l i c
a s s e m b l a g e c o n s i s t in g o f s m e c t i te , q u a r t z , a n d
s p a r s e k a o l i n i t e . T h e a r g i l l i c a s s e m b l a g e i s
b e t t e r- d e v e l o p e d w it h d e p t h a n d p r e d o m i n a t e s
b e l o w 1 80 m . A t a d e p t h o f 2 71 m t h e r e is m i n o r
c h l o r i t e , a n d b e l o w 3 2 0 m i l l i t e i s m o r e a b u n -
d a n t , s u g g e s t in g a t r a n s i t io n t o a m o r e p h y l l ic
a s s e m b l ag e . C h e m i c a l ly , t h e tu f f s o f P L T G - 2
s h o w w e a k t o m o d e r a t e a l t e r a t i o n . T h e l e a s t
a l t e r e d s a m p l e ( d e p t h = 1 50 m ) m i g h t b e c la s -
s e d a s a r h y o d a c i t e ( 6 7 S i O 2 ). T h e o t h e r
s a m p l e s s h o w s i l i c if i c a t io n a n d p o t a s s i c a l t e r a -
t i o n ( T a b l e 2 ) .
H y d r o t h e r m a l m i n e r a lo g y P L T G 3
W i t h i n t h e t h i r d a n d d e e p e s t c o r e h o l e t h e
p r i n c i p a l h y d r o t h e r m a l a l t e r a t io n m i n e r a l s a r e
q u a r t z , s m e c t i t e , m i x e d - l a y e r i l li t e -s m e c t i t e ,
a n d m i n o r t o t r ac e a m o u n t s o f k a o l in i te ,
c a l c i t e , i l l i t e , a n d c h l o r i t e . T h e u p p e r m o s t 2 1 0
m i s s i li c if i e d a n d w e a k l y a l t e r e d t o a n a r g i ll ic
a s s e m b l a g e. A t u f f s a m p l e f r o m t h e b o t t o m o f
t h e P a d r e M i g u e l s e c t i o n s h o w s l i tt le a l t e r a t io n
a n d h a s a r h y o l i t ic c o m p o s i t i o n ( T a b l e 2) .
B e l o w t h i s d e p t h , q u a r t z , s m e c t i t e , i l l i t e , a n d
r a r e k a o l i n i t e a r e t h e d o m i n a n t p h a s e s ;
h o w e v e r , t h i s a s s e m b l a g e c o n t i n u e s o n l y t o 2 5 0
m w h e r e s m e c t i t e a n d m i n o r k a o l i n i t e a r e o n c e
a g a i n d o m i n a n t to t h e b o t t o m o f t h e h o le a t 6 79
m . T h e r e is a tr a c e o f c h l o r i t e a t a d e p t h o f 4 0 0
m . T h e a n d e s i t e s o f P L T G - 3 s h o w l es s a l te r a -
t i o n t h a n t h o s e i n P L T G - 1 .
P y r i t e i s l a c k i n g i n t h e t u f t s ( s u r f a c e t o a
d e p t h o f 2 71 m ) b u t i s p r e s e n t i n a n d e s i t i c la v a s
( d e p t h = 3 6 2 m t o 6 22 m ) , w h e r e i t o c c u r s as
d i s s e m i n a t e d c r y s ta l s a n d d i s c o n t i n u o u s
v e i n l e t s . A t a d e p t h o f 3 8 0 . 5 m , a q u a r t z v e i n
c o n t a i n e d a c i c u l a r c r y s t a l s o f b e r t h i e r i t e
( F e S b z S 4 ) . T h e w a l l r o c k a d j a c e n t t o t h i s v e i n
c o n t a i n s 49 0 p p b A u , 5 50 p p m A s , 17 p p m S b ,
8 00 p p m B a , 13 0 p p m Z n , a n d 2 p p m A g ( I N -
A A a n a l y s i s ) .
V e i n l e ts o f a n h y d r i t e a r e p r e s e n t i n t h e u p p e r
3 0 m o f P L T G - 3 , b u t t h e r e m a i n d e r o f th e t u f f
s e c t i o n (3 0 - 2 71 m ) l a c k s a n h y d r i t e v e i n s . T h e
a n d e s i t ic la v a s ( 36 4 - 6 2 2 m ) c o n t a i n n u m e r o u s
v e i n s, u p t o 5 m m w i d e , o f q u a r t z , c a lc i te , a n d
c l a y . C a l c i t e v e i n s , u p t o 2 c m w i d e , o c c u r a t
d e p t h s o f 5 65 a n d 6 4 5 m .
S u r f a c e h y d r o t h e r m a l a l te r a ti o n
A r e a s o f s u r f a c e a l t e r a ti o n a r e s i m i la r to t h e
a l t e r a t io n e n c o u n t e r e d i n t h e c o r e h o l e s ; m o s t l y
s i l ic i f i c a t io n a n d a r g i ll ic in c h a r a c t e r . T h e r e a r e
t w o m i n e s n e a r th e P l a t a n a r e s g e o t h e r m a l a re a ;
t h e S a n A n d r 6 s g o l d m i n e a n d t h e E l Q u e t za l
a n t i m o n y m i n e (R o b e r t s a n d I r v i n g , 1 9 57 ). T h e
S a n A n d r 6 s m i n e is p r o d u c i n g f r o m o r e h o s t e d
i n q u a r t z v e i n s t h a t a r e f o u n d i n la v a s a n d t u f t s
o f th e P a d r e M i g u el G r o u p a n d M a t a g a l p a F o r -
m a t i o n . A s a m p l e f r o m t h e o r e h o r i z o n c o n -
t a i n e d q u a r t z , c i n n a b a r , a n d p y r i t e ( X R D
an a l y s i s ) a s w e l l a s v i s i b l e g o l d f l ak e s .
T h e E 1 Q u e t z a l m i n e is l o c a t e d a b o u t 3 . 2 k m
N N W o f t h e v il la g e o f S a n A n d r 6 s . T h e o r e i s
h o s t e d i n c a lc i te a n d q u a r t z v e i n s , w h i c h a p p e a r
t o b e a s s o c i a t e d w i t h T e r t i a r y ( ? ) d i o r i t e s i l l s
7/24/2019 geologyPlatanares-heiken1991
16/18
56
G H E I K E N E T A L
and dikes that intrude the Paleozoic schists
Gof f et al., 1991-this volume). The hydro the r-
mal system responsible for these deposits ap-
pears to have been volca nogenic and related to
the Matagalpa andesitic composite cones; it
does not appear to be related in any way to the
present-day hydrothermal system, which is
related to extensional and strike-slip faults.
Di s cu s s i on
The Platanares geothermal area is located
near the intersection of major structural
elements of western Honduras, a group of
ENE-trending, sinistral strike-slip faults that
form the northern boundary of the Chortis
block and NW-trending normal faults formed
during the extension that has thinned this block
dur ing the past 10 m.y . Mills et al., 1967).
Cretaceous and Tertiary redbeds of unknown
thickness overlie metamorphic basement and
appear to serve as the major geothe rmal reser-
voir rock. They, in turn, are overlain by a se-
quence o f Oligocene to Miocene volcanic and
sedimen tary rocks, including andesitic lavas, a
thin fanglomerate, and a group of nonwelded
and welded ignimbrites. Normal faults offset
all of the Tertiary rocks and appear to offset
terrace gravels of probable Quaternary age.
Boiling springs are located along fractures of
the NW-trending fault system. Most hot
springs, surface patches of intense hydro ther-
mal alt eration, and siliceous sinter deposits oc-
cur within an area of abo ut 5 km 2. Beneath this
area, a geothermal reservoir is inferred to be
located in redbeds of the Valle de Angeles
Group, at a depth of 1.2 to 1.5 km, and at a
temp erat ure o f 225 oC Goff et al. , 1987a, 1991-
this issue). Two of the three coreholes en-
countered a 165C reservoir at shallower
depths.
None of the volcanic rocks within this area
appear to be Quaternary; two welded tuffs
from the lower part of the Padre Miguel Group
were dated at 14.2 and 14.7 Ma and the
andesitic lavas are older. There is no evidence
for a magmati c heat source for this geothermal
system. The volcanic rocks, including the
rhyolitic ignimbrites, are all over 14 m.y. old,
precluding a magmatic heat source interpreta-
tion based on thermal models by Smith and
Shaw, 1975). All thermal springs are located
along normal faults in a region of extensional
tectonics, suggesting that the system is similar
to those of the Basin-and-Range province of
the United States. The geothermal gradient
hole drilling at Pla tanares indicates that there is
a considerable geothermal resource there and
that it should be developed by production dril-
ling.
c know l e d g emen t s
The work within Hondur as has been funded
by the United States Agency for International
Development, through the Regional Office,
Central American Project and the Honduran
office and was done under the auspices of the
U.S. De part ment of Energy. We wish to tha nk
Lynn Sheldon and Carl Duisberg, USAID and
Rod Saubers, Inter Ameri can Geodetic Survey,
for their continued support. The paper was
greatly improved during reviews by T. Donnel-
ly State University of New York) and G.
Horn e Wesleyan University).
References
Aldrich, M.J., Heiken, G., Flores, W., Ramos, N. and
Ritchie, A., 1987. San Ignacio La Tembladera)
geothermal site , Departamento de Francisco
Moraz~n, Honduras, Central America. Los Alamos
National Laboratory Rpt. LA-10696-MS, 27 pp.
Aldrich, M.J., Adams,A.I. and Escobar, C., 1991. Struc-
tural geology and stress history of the Platanares
geothermal site, Honduras: implications on the tec-
tonics of the northwesternCaribbean plate boundary.
J. Volcanol. Geotherm. Res., 45: 59-69.
Ander, M.E., Aiken, C.L. and De la Fuente, M.F., 1991.
Regional gravity investigation of Honduras, Central
America. J. Volcanol. Geotherm. Res., 45:11 -27.
Aiken, C.L., Ander, M.E. and de la Fuente, M.F., 1991.
Geophysical investigations of the platanares geother-
mal site. J. Volcanol. Geotherm. Res., 45:71 - 90.
Bargar, K.E., 1991. Fluid inclusions and preliminary
7/24/2019 geologyPlatanares-heiken1991
17/18
GEOLOGY OF THE PLATANARES GEOTHERMAL AREA HONDURAS 7
studies of hydrothermal alteration in core hole PLTG-
l, Platanares geothermal area, Honduras. J.
Volcanol. Geotherm. Res., 45: 147- 160.
Burkart, B. and Self, S., 1985. Extension and rotation of
crustal blocks in northern Central America and effect
on volcanic arc. Geology, 13: 22-36.
Dalrymple, G. and Lanphere, M., 1969. Potassium-
Argon Dating. W.H. Freeman, San Fancisco, Calif.,
248 pp.
Eppler, D., Duffield, W.A. , Heiken, G., Wohletz, K.,
Flores, W. and Paredes, J.R., 1987a. Geology of the
Pavana Geothermal Area, Departamento de
Choluteca, Honduras, Central America. Los Alamos
National Laboratory Rpt. LA-10864-MS, 17 pp.
Eppler, D., Baldridge, S., Perry, F., Flores, W., Paredes,
J.R. and Finch, R., 1987b. Geology of the Azacualpa
Geothermal Site, Departamento de Comayagua, Hon-
duras, Central America. Los Alamos National
Laboratory Rpt. LA-10687-MS, 32 pp.
Fakundiny, R.H. and Everett, J.E., 1976 . Re-
examination of the stratigraphy of the E1 Rosario and
Comayagua Quadrangles. In: G. Dengo, and O.
Samayoa, Editors), Informe de la IV Reuni6n de
Ge61ogos de America Central. Publ. Geol. del ICAITI
No. V.
Finch, R.C., 1972. Geology of the San Pedro Zacapa
Quadrangle. Ph.D. thesis, University of Texas,
Austin, 238 pp.
Finch, R., 1981. Mesozoic stratigraphy of Central Hon-
duras. Bull. Am. Assoc. Pet. Geol., 65: 1320- 1333.
Flores, W., 1980. Geology of the Platanares area. Annex
V, in Report of the activities and interpretation of
results of the geothermal project of Honduras
1979-1980: Energy Programme of the Central
America isthmus, Dept. RLA/76/012 ENEE), v. 1.
GeothermEx, 1980. Report of the activities and inter-
pretation of results of the geothermal project of Hon-
duras 1979-1980, vol. 1. Consulting report
RLA/76/012, Berkeley, Calif. unpubl.).
Gislason, G., 1980. Report o f the activities and interpreta-
tion of results of the Geothermal Project of Honduras
1979-1980. Energy Programme of the Central
American Isthmus, v. 1, Empresa Nacional de Energia
E16ctric v. 1, RLA/76/012, 85 pp.
Goff, F., Shevenell, L., Kelkar, S., Smith, D., Meert, J.,
Heiken, G., Bargar, K., Ramos, N., Truesdell, A.,
Stallard, M. and Musgrave, J., 1987a. Stratigraphy,
temperature profiles, and flow test data from the
PLTG-1 and PLTG-2 coreholes, Platanares geother-
mal system, Honduras. Geotherm. Res. Council
Trans., ll: 253-259.
Goff, F.E., Truesdell, A., Grigsby, C., Janik, K.,
Shevenall, L., Paredes, J., Gutierrez, J., Trujillo, P.
and Counce, D., 1987b. Hydrogeochemical investiga-
tion of six geothermal sites in Honduras, Central
America. Los Alamos National Laboratory Rpt. LA-
10785-MS, 170 pp.
Goff, S., Rtifenacht, H., Laughlin, A., Adams, A., Plan-
ner, H. and Ramos, N., 1987. Geothermal corehole
drilling and operations, Platanares, Honduras, Cen-
tral America. Geotherm. Res. Council Trans., 11:
37 - 40.
Goff , S., Laughlin, A., Riifenacht, F., Goff, Heiken, G.,
Adams, A., Musgrave, J., Planner, H. and Ramos,
N., 1988. Exploration geothermal gradient drilling,
Platanares, Honduras, Central America. Los Alamos
National Laboratory Report, LA-11349-MS, 29 pp.
Goff, F., Goff, S., Kelkar, S., Shevenell, L., Truesdell,
A., Musgrave, J., Rtifenacht, H. and Flores, W.,
1991. Exploration drilling and reservoir model of the
Platanares geothermal system, Honduras, Central
America. J. Volcanol. Geotherm. Res., 45:101 - 123.
Heiken, G., Eppler, D., Wohletz, K., Flores, W., Ramos,
N. and Ritchie, A., 1986. Geology of the Platanares
geothermal site, Cop~n, Honduras . Los Alamos Na-
tional Laboratory Rpt. LA-10634-MS, 24 pp.
Heiken, G., Duffield, W., Wohletz, K., Priest, S.,
Ramos, N., Flores, W., Eppler, D., Ritchie, A. and
Escobar, C., 1987. Geology of the Platanares geother-
mal area, Cop~n, Honduras. Geotherm. Res. Council
Trans., 11: 263 - 266.
Hirschmann, T., 1963. Reconnaissance geology and
stratigraphy of the Subinal formation of the E1 Pro-
greso area, Guatemala. M.S. thesis, University of In-
diana.
Hoover, D. and Pierce, H., 1988. Electrical Geophysical
Studies of the Platanares Geothermal Area, Hon-
duras. Unpubl. Report to the Los Alamos National
Laboratory, 22 pp.
Horne, G.S., Clark, G.S. and Pushkar, P., 1976. Pre-
Cretaceous rocks in northwestern Honduras : base-
ment terrane in Sierra de Omoa. Bull. Am. Assoc. Pet.
Geol., 60: 566-583.
Horne, G.S. and Finch, R.C., 1990. Mesozoic
stratigraphy of the Chortis block of northern Central
America. Geol. Soc. Am. Series on Decade of North
American Geol ogy -Geology of the Caribbean in
press).
Ingamells, C., 1970. Lithium metaborate flux in silicate
analysis. Anal. Chim. Acta, 52: 323-334.
Janik, C.J., Goff, F., Truesdell, A., Shevenell, L.,
Stallard, M., Trujillo, P. and Counce, D., 1991. A
geochemical model of the Platanares geothermal
system, Honduras. J. Volcanol. Geotherm. Res., 45:
125- 147.
Manton, W.I., 1987. Tectonic interpretation of the mot-
7/24/2019 geologyPlatanares-heiken1991
18/18
58 G HEIKEN ET AI
p h o l o g y o f H o n d u r a s . T e c to n i cs , 6: 6 3 3 - 6 5 1 .
M e e r t , J . G . a n d S m i t h , D . L . , 1 99 1 . H e a t f l o w a t t h e
P l a t a n a r e s , H o n d u r a s , g e o t h e r m a l s i t e . J . V o l c a n o l .
G e o t h e r m . R e s . , 4 5: 9 1 - 9 9 .
M i l l s , R . A . , H u g h , K . E . , F e r a y , D . E . a n d S w o l f s , H . C . ,
1 9 67 . M e s o z o i c s t r a t i g r a p h y o f H o n d u r a s . A m .
As soc . Pe t . Geo l . Bu l l. , 51 :171 1 - 1786.
P l a f k e r , G . , 1 9 76 . T e c t o n i c a s p e c ts o f th e G u a t e m a l a
e a r t h q u a k e o f 4 F e b r u a r y , 1 9 76 . S c ie n c e , 9 3 :
1201 - 1208.
R o b e r t s , R . J . a n d I r v i n g , E . M . , 1 9 57 . M i n e r a l d e p o s i ts o f
Cen t ra l Amer i ca . U.S . Geo l . Surv . Bu l l . , 1034 , 205
p p .
S m i t h , R . L . a n d S h a w , H . , 1 9 7 5 . I g n e o u s - r e l a t e d
g e o t h e r m a l s y s t e m s . I n : D . W h i t e a n d D . W i l l i a m s
E d i t o r s ) , A s s e s s m e n t o f G e o t h e r m a l R e s o u r c e s o f t h e
U n i t e d S t a t e s . U . S . G e o l . S u r v . , C i r c . , 7 2 6 : 5 8 - 8 3 .
S t e ige r , R . and J / i ge r , E . , 1977 . Sub com mis ion on
g e o c h r o n o l o g y : C o n v e n t i o n o n t h e u s e o f d e c a y c o n -
s t a n ts i n g eo - a n d c o s m o - c h r o n o l o g y . E a r t h P l a n e t .
Sc i . Le t t . , 36 : 349- 362 .
U n i t e d N a t i o n s D e v e l o p m e n t P r o g r a m U N D P ) , 1 97 2.
Inves t i gac i6n de l os r ecu r sos mine ra l e s en ~rea s se l ec -
c i o n a d e s , H o n d u r a s : g e o l o g i a d e l a r e g i 6 n n o r o e s t e d e
H o n d u r a s . U n i t e d N a t i o n s D e v e l o p m e n t P r o g r a m I n -
f o r m e T 6 c ni co D P / S F / U N / 9 6 , N e w Y o r k , 28 p p.
Va len t i ne , G . , 1983. Proced ure s f o r ana lys i s o f s i li c a te
r o c k s a n d m i n e ra l s a t L o s A l a m o s N a t i o n a l L a b o r a t o r y
b y X - r a y f l u o r e s c e n c e . L o s A l a m o s N a t i o n a l
L a b o r a t o r y R p t . , L A - 9 6 6 3 - M S , 3 3 p p .
W i l l i a m s , H . a n d M c B i r n e y , A . R . , 1 9 6 9 . V o l c a n i c
H i s t o r y o f H o n d u r a s . U n i v . C a l i f. P u b l . G e o l . S c i ., 8 5 :
1 101.
W i l l ia m s , H . , M c B i r n e y , A . R . a n d D e n g o , G . , 1 9 64 .
G e o l o g i c r e c o n n a i s s a n c e o f s o u t h e a s t e r n G u a t e m a l a .
Un iv . Ca l i f . Pub l . G eo l . Sc i . , 50 : 1 - 62 .
Recommended