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DOE/ID/12079-21
ESL-48
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TRACE-ELEMENT GEOCHEMISTRY OF GRADIENT HOLE CUTTINGS:
BEOWAWE GEOTHERMAL AREA, NEVADA
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Odin D. Christensen
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December 1980
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EARTH SCIENCE LABORATORY
UNIVERSITY OF UTAH RESEARCH INSTITUTE
420 Chipeta Way, S u i t e 120
S a l t Lake City, Utah 84108
Prepared f o r t h e
U. S, Department o f Energy
O i v i s i o n o f Geothermal Energy
3
Under Contract No. DE-AC07-80ID12079
fllS~R~EUnONOF ?HIS DOCUMENT IS UNLIMITED
DISCLAIMER
This report was prepared as an account of work sponsored by an
agency of the United States Government. Neither the United States
Government nor any agency Thereof, nor any of their employees,
makes any warranty, express or implied, or assumes any legal
liability or responsibility for the accuracy, completeness, or
usefulness of any information, apparatus, product, or process
disclosed, or represents that its use would not infringe privately
owned rights. Reference herein to any specific commercial product,
process, or service by trade name, trademark, manufacturer, or
otherwise does not necessarily constitute or imply its endorsement,
recommendation, or favoring by the United States Government or any
agency thereof. The views and opinions of authors expressed herein
do not necessarily state or reflect those of the United States
Government or any agency thereof.
DISCLAIMER
Portions of this document may be illegible in
electronic image products. Images are produced
from the best available original document.
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NOTICE
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T h i s r e p o r t was prepared t o document work sponsored by t h e United States
tiovernment.
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Neither t h e United States nor i t s agent, t h e United States
Department o f Energy, nor any Federal employees, nor any o f t h e i r contractors,
subcontractors o r t h e i r employees, makes any warranty, express o r implied, o r
assumes any l e g a l l i a b i l i t y o r r e s p o n s i b i l i t y f o r t h e accuracy, completeness,
V
o r usefulness o f any information, apparatus, product o r process disclosed, o r
represents t h a t i t s use would not i n f r i n g e p r i v a t e l y owned r i g h t s .
NOTICE
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Keference t o a company o r product name does not imply approval o r
recommendation o f t h e product by t h e U n i v e r s i t y o f Utah Research I n s t i t u t e o r
e
t h e U.S.
Department o f Energy t o t h e exclusion o f o t h e r s t h a t may be s u i t a b l e .
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CONTENTS
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PAGE
-
1
ABSTRACT..............................
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IO
U
............................
ANALYTICAL TECHNIQUES . . . . . . . . . . . . . . . . . . . . . . .
OISCUSSION . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Geology....
........................
Chemistry o f Thermal F l u i d s . . . . . . . . . . . . . . . . . .
Chemistry o f Surface Samples . . . . . . . . . . . . . . . . .
Element D i s t r i b u t i o n s . . . . . . . . . . . . . . . . . . . . .
CONCLUSIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . .
REFERENCES . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
APPENDIX: Sumnary o f Geochemical Data . . . . . . . . . . . . . . .
INTRODUCTION
2
3
4
4
11
13
15
22
26
28
FIGURES
0
Y
Generalized geology o f t h e Beowawe area
Figure 2
Temperature gradient hole l o c a t i o n map
Figure 3
Generalized s t r a t i g r a p h y o f temperature gradient holes
Figure 4
Hg d i s t r i b u t i o n i n d r i l l c u t t i n g s
Figure 5
As d i s t r i b u t i o n i n d r i l l c u t t i n g s
Figure 6
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Figure 7
............
............
............
Mn d i s t r i b u t i o n i n d r i l l c u t t i n g s . . . . . . . . . . . .
L i distribution i n d r i l l cuttings
TABLES
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.........
.........
Figure 1
Table 1
F l u i d compositions from t h e Beowawe area
Table 2
Geochemistry o f selected surface samples
........
........
16
17
18
19
12
14
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ABSTRACT
iqultielement geochemical a n a l y s i s o f d r i l l c u t t i n g s from 26 shallow
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temperature-gradient d r i l l holes and of surface rock samples reveals t r a c e
element d i s t r i b u t i o n s developed w i t h i n these rocks as a consequence o f
chemical i n t e r a c t i o n w i t h thermal f l u i d w i t h i n t h e Beowawe geothermal area.
V
The p r e s e n t l y discharging thermal f l u i d s are d i l u t e i n a l l components except
s i l i c a , suggesting t h a t t h e residence time o f these f l u i d s w i t h i n t h e thermal
r e s e r v o i r has been s h o r t and t h a t chemical i n t e r a c t i o n w i t h t h e r e s e r v o i r rock
v
minimal
.
I n t e r a c t i o n between these d i l u t e f l u i d s and rocks w i t h i n t h e system
has r e s u l t e d i n t h e development o f weak chemical signatures.
The absence of
stronger signatures i n rocks associated w i t h t h e present system suggests t h a t
ti
f l u i d s have had a s i m i l a r d i l u t e chemistry f o r some time.
The s p a t i a l
d i s t r i b u t i o n o f elements commonly associated w i t h geothermal systems, such as
As, Hg and L i s are n e i t h e r l a t e r a l l y nor v e r t i c a l l y continuous.
V
This suggests
t h a t t h e r e i s not now, nor has t h e r e been i n t h e past, pervasive movement of
thermal f l u i d throughout t h e sampled rock but, instead, t h a t i s o l a t e d chemical
u
anomal ies represent d i s t in c t f l u i d - f 1ow channel s.
Coherent near-surface
enrichments o f As and Mn are consistent w i t h a system i n which f l u i d s
discharge from along t h e Malpais F a u l t and f l o w downslope w i t h i n shallow
permeable horizons, d e p o s i t i n g As near t h e discharge p o i n t and Mn more
0
distally.
Discontinuous As, L i and Hg concentrations near White Canyon t o t h e
east o f t h e p r e s e n t l y a c t i v e surface features record t h e e f f e c t s o f chemical
i n t e r a c t i o n o f rocks w i t h f l u i d s chemically u n l i k e t h e p r e s e n t l y discharging
3
fluids.
The observed t r a c e element d i s t r i b u t i
s suggest t h a t h i s t o r i c a l l y
the Beowawe area has been t h e center o f more than one hydrothermal event and
t h a t t h e near-surfa
p o r t i o n o f t h e pres
t hot-water geothermal system i s
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c o n t r o l l e d by a s i n g l e source f r a c t u r e , t h e Malpais F a u l t , o r an i n t e r s e c t i o n
o f f a u l t s a t t h e s i n t e r terrace.
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INTRODUCTION
The Beowawe geothermal area l i e s i n northern Nevada along t h e Lander and
Eureka county l i n e , approximately 30 km southeast o f B a t t l e Mountain (Figure
1).
The geothermal p o t e n t i a l o f t h e area i s c u r r e n t l y being evaluated by
Chevron Resources Company and Getty O i l Company.
This study i s p a r t o f a
comprehensive ongoing case study o f t h e area being prepared by t h e E a r t h
Science Laboratory D i v i s i o n o f t h e U n i v e r s i t y o f Utah Research I n s t i t u t e
(ESL/UUHI ) i n cooperati on w i t h these companies through t h e I n d u s t r y Coup1ed
Program o f t h e D i v i s i o n of Geothermal Energy of t h e U. S. Department o f Energy
(DOEDGE)
.
Multielement geochemical a n a l y s i s o f d r i l l c u t t i n g s from 26 shallow
temperature-gradient holes d r i l l e d by Chevron has been performed i n an attempt
t o more c l o s e l y d e f i n e t h e near-surface geometry o f t h e geothermal resource.
Recent s t u d i e s demonstrate t h a t t h e t r a c e element geochemistry o f we1 1
c u t t i n g s from geothermal systems can be a useful e x p l o r a t i o n guide (Bamford
and others, 1980; Christensen and others, 1980b; Christensen, 1980 a,b)
.
Trace element d i s t r i b u t i o n s , devel oped as a consequence o f temperature
gradients and f l u i d flow w i t h i n a geothermal system, place c o n s t r a i n t s on t h e
p o s s i b l e geometry o f t h e present system and may provide i n s i g h t i n t o i t s
thermal and convective h i s t o r y .
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ANALYTICAL TECHNIQUES
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D r i l l c u t t i n g s were prepared f o r a n a l y s i s by compositing i n d i v i d u a l
washed 10-foot i n t e r v a l samples over 100-foot i n t e r v a l s (Bamford, 1978) and
Y
p u l v e r i z i n g t o l e s s than 270 mesh i n a tungsten carbide shatterbox.
Pulverized samples were dissolved by a f o u r - a c i d d i g e s t i o n procedure
(Chri stensen and others, 1980a).
Q$
Samples were analyzed f o r 37 elements by in d u c t i v e l y coup1ed
plasma-atomic emission spectroscopy (ICP-AES) using an Appl i e d Research
Laboratories i n d u c t i v e l y coupled plasma quantometer (ICPQ) i n t h e ESL
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geochemical laboratory.
Elements determined by ICP-AES were Na, K, Ca, Mg,
Fe, A l , S i , T i , P, S r , Ba, V, C r , Mn, Co, N i , Cu, Mo, Pb, Zn, Cd, Ag, Au, As,
w
Sb, B i , U, Te, Sn, W, L i , Be, B, Z r , La, Ce, and Th.
S p e c i f i c s of t h e
a n a l y t i c a l instrumentation and procedures, as w e l l as an evaluation o f t h e
q u a l i t y o f analyses a r e summarized i n Christensen and o t h e r s (1980a).
Y
In
a d d i t i o n , As was determined on each sample s o l u t i o n by a c o l o r i m e t r i c
procedure and Hg was determined on s o l i d samples by g o l d f i l m mercury
detector
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I n order t o d i s t i n g u i s h chemical v a r i a t i a n s r e s u l t i n g from geothermal
processes from t h e numerical dispersion o f a n a l y t i c a l values expected i n
n a t u r a l normal o r lognormal geochemical populations, elemental a n a l y t i c a l
V
values were eval uated graphical l y through t h e use o f cumulative probabi 1it y
pl o t s fa1 1owing t h e procedures d e s c r i b i d by S i n c l a i r (1974, 1976) and
Lepel t i e r (1969).
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The method permits estimation o f population parameters and
s e l e c t i o n o f d i s c r i m i n a t i o n thresholds f o r mixed d i s t r i b u t i o n s o f two o r more
3
r
numerical populations.
An example o f the a p p l i c a t i o n o f t h i s technique i s
Y
presented i n Chri stensen (1980b).
O f the elements investigated, t h e d i s t r i b u t i o n s o f Hg, As, L i and Mn are
Y
most p e r t i n e n t t o t h e f o l l o w i n g discussion o f t h e geochemistry o f t h e Beowawe
geothermal area.
Data f o r these elements are presented g r a p h i c a l l y i n t h i s
r e p o r t as Figures 4 through 7.
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A data summary f o r a l l elements i s included i n
t h e appendix; complete data i s a v a i l a b l e on open f i l e a t ESL/UURI.
DISCUSS I O N
01
Geology
A comprehensive geologic study o f t h e Beowawe area has r e c e n t l y been
completed by Struhsacker (1980).
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The f o l l o w i n g discussion o f t h e geology of
Beowawe i s l a r g e l y abstracted from t h i s work.
The t3eowawe geothermal system l i e s n e w t h e a x i s o f t h e Basin and Range
I
,
physiographic province w i t h i n the B a t t l e Mountain heat flow h i g h (Figure 1).
Y
The geothermal system i s marked by t h e presence o f hot springs and fumaroles
associated w i t h a l a r g e opaline s i n t e r terrace.
'a
along t h e f a u l t - c o n t r o l l e d Malpais R i m which bounds t h e southeast margin o f
Whirlwind Valley (Figure 1).
r,
w
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The t e r r a c e has developed
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ita,
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FIGURE 2
TEMPERATURE GRADIENT HOLE
LOCATION MAP
[PiiD Quaternary allurlum
Quaternary SIUCOOUS sinter
Quatarnary I r n d o
Lato Miocono an4, Plloconr
volaanics (basaltlo andrsltr,
dacltr, basam, and minor
redimonh and tuffs)
lzzd pre-Late
M k e m Rocks
(Ordorlcion Volmy quartrlhr,
ahorts, ord olltstonos; ond
Tortlory )rfhmor? rodlmonta,
tuffs and ktnbkndo andeslt.)
&fault
(hfornd whom doshd)
/-cantoo? (Infwnd whrro bosh.dl
lo
9
rtrlh. a n l a p d tlwr
U Chevron toe+ ~ t o a
OWMU
bp
#.a am m m k r
The Beowawe geothermal system appears t o be a high-temperature, hot-water
Y
system, l o c a l i z e d w i t h i n an area o f s t r u c t u r a l complexity.
Major f a u l t
systems a c t i ve from p r e - T e r t i ary t o the present have c o n t r o l 1ed t h e d e p o s i t i o n
Y
of volcanic rocks, t h e topography, and, apparently, t h e present geothermal
f l u i d flow.
Rocks exposed w i t h i n t h e geothermal area i n c l u d e s i l i c e o u s
Ordovician eugeosynclinal rocks, T e r t i a r y volcanic rocks ranging i n
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composition from b a s a l t t o dacite, and T e r t i a r y and Quaternary gravels.
Three major episodes o f s t r u c t u r a l development are evident from t h e
s t r u c t u r e s mapped w i t h i n t h e geothermal area (Figure 1): a Paleozoic t h r u s t
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f a u l t i n g event, a NW-trending graben developed d u r i n g mid-Miocene time, and
NE-trending Basin and Range f a u l t i n g .
I n t h e v i c i n i t y o f t h e geothermal area, t h e allochthonous s i l i c e o u s rocks
o f t h e Ordovician Valmy Formation l i e i n exposed f a u l t c o n t a c t upon t h e
subjacent autochthonous carbonates along t h e Roberts Mountain Thrust o f t h e
upper Devonian t o lower M i s s i s s i p p i a n A n t l e r Orogeny.
The main t h r u s t and t h e
many subsidi-ary f a u l t s have severely f r a c t u r e d and f o l d e d t h e upper p l a t e
rocks, c o n t r i b u t i n g t o t h e i r e f f e c t i v e permeability.
Although t h e carbonates
have not y e t been penetrated by d r i l l holes, i t i s presumed t h a t they occur a t
g r e a t e r depths throughout t h e area.
Horizons o f sandstone i n t e r s e c t e d w i t h i n
two deep d r i l l holes i n the area have been i n t e r p r e t e d as t e c t o n i c s l i c e s of
v
allochthonous S i l u r i a n E l d e r sandstone.
Major north-northwest-trending f r a c t u r e s o c c u r r i n g w i t h i n t h e study area
l a t e r a l l y c o n f i n e a t h i c k sequence o f middle-Miocene c a l c - a l k a l i n e t o a l k a l i n e
0
Y
flows.
These flows accumulated i n a graben produced by r i f t i n g along t h e
7
Oregon-Nevada lineament.
The numerous north-trending splays o f t h e Dunphy
Pass F a u l t Zone (Figure 1) formed t h e eastern boundary o f t h i s graben.
Continued a c t i v i t y on t h i s f a u l t zone a f t e r cessation o f volcanism has
r e s u l t e d i n measurable v e r t i c a l displacement o f volcanic u n i t s i n t h e v i c i n i t y
o f Whi t e Canyon.
The east-northeast and east-trending f a u l t s o f t h e Malpais f a u l t zone
(Figure 1) represent t h e f i n a l p e r i o d o f Basin and Range f a u l t i n g .
These
post-date a l l volcanic u n i t s , suggesting a maximum age o f 15.5 m.y.
In
yeneral, north-northeast-trending Basin and Range normal f a u l t s doininate t h e
r e g i o n a l s t r u c t u r a l t e r r a i n o f north-central Nevada and g i v e r i s e t o t h e major
ranges and valleys.
The regional f a u l t t r e n d w i t h i n t h e mapped area, however,
i s a b r u p t l y d e f l e c t e d eastward, producing t h e zone o f s t r u c t u r a l comp e x i t y a t
t h e Beowawe area.
Exposed r e s e r v o i r rocks w i t h i n t h e Beowawe area i n c l u d e t h e Pale z o i c
s i l i c e o u s eugeosynclinal rocks o f t h e Valmy Formation and o v e r l y i n g T e r t i a r y
volcanic u n i t s .
The Valmy Formation consists o f s i l i c e o u s s i l t s t o n e w i t h
s i g n i f i c a n t amounts o f q u a r t z i t e , sandstone, bedded chert, s i l i c e o u s
conglomerate, and l o c a l l y bedded nodular b a r i t e .
Tectonism has severely
f r a c t u r e d t h e Valmy rocks t o produce c a t a c l a s t i c textures.
T e r t i a r y volcanic
rocks i n c l u d e dikes, flows, and t u f f s l o c a l l y interbedded w i t h i n t e r f l o w
tuffaceous and a l l u v i a l horizons.
The generalized s t r a t i g r a p h y o f t h e d r i l l
holes i s s u n a r i z e d i n Figure 3.
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8
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w
w
W
W
c,
v
Y
3
W
cu
cu
-N
v)
cu
9
,,
L
a
cn
0
c,
a
L
aJ
G
Q
c,
3
cc
W
a
L
LL
*r
'0,
Surface hydrothermal a1t e r a t i o n i s c l o s e l y associated w i t h t h e Mal pai s
F a u l t , extending from t h e s i n t e r t e r r a c e t o t h e town o f Beowawe.
The modern
hydrothermal a c t i v i t y i s centered on t h e s i n t e r t e r r a c e a t t h e western end of
t h i s zone along t h e Terrace Fault.
Erosion along t h e Malpais Scarp has
exposed areas o f s i l i c a veining, a r g i l l i z a t i o n , p y r i t i z a t i o n , and
limonitization.
The i n t e n s i t y o f a l t e r a t i o n v a r i e s g r e a t l y due, apparently,
t o t h e i n f l u e n c e o f cross f r a c t u r e s and l i t h o l o g i c c o n t r o l w i t h i n t h e Malpais
I W
I
F a u l t Zone d u r i n g hydrothermal a c t i v i t y .
I
The i n t e r s e c t i o n o f t h e Malpais F a u l t w i t h t h e Dunphy Pass F a u l t zone a t
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t h e mouth o f White Canyon has been t h e center o f i n t e n s e hydrothermal a c t i v i t y
i n t h e past.
A dense swarm o f east-trending chalcedony veins cuts T e r t i a r y
d a c i t e and h i g h l y f r a c t u r e d rocks of t h e Valmy Formation,
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A r g i l l i c alteration
o f t h e volcanic rock i n t h e vein swarm increases toward t h e i n d i v i d u a l veins.
Primary d i ssemi nated magnetite and secondary p y r i t e are rep1 aced by abundant
limonite.
rr
Displacement o f t h e a l t e r a t i o n zone across White Canyon i n d i c a t e s
motion on t h e Dunphy Pass F a u l t zone subsequent t o t h e d e p o s i t i o n of t h e
chal cedony vei ns.
A t t h e Red D e v i l Mine near t h e northeast end o f t h e a l t e r a t i o n zone, a
northeast-trending v e r t i c a l f r a c t u r e zone c o n t r o l s a 30 m-wide f a u l t b r e c c i a
i n Valmy
formation^
q u a r t z i t e , s i l t s t o n e , and conglomerate.
The b r e c c i a i s
characterized by q u a r t z - p y r i t e veins and cinnabar f i l m s along f r a c t u r e
3
surfaces,
The r e l a t i v e age o f t h i s m i n e r a l i z a t i o n i s uncertain.
The Ginn and Rossi w e l l s d r i l l e d by Chevron (Figure 1) penetrate a p o o r l y
Y
V
def ined zonal sequence o f hydrothermal a1t e r a t i on products (Struhsacker ,
10
1980).
I n general , t h e pervasive a l t e r a t i o n through t h e Miocene volcanic
s e c t i o n changes with depth from a c l ay-cal c i te-quartz-pyri t e assembl age t o a
c h l o r i t e - c a l c i t e - c l ay-pyri t e assembl age.
A quartz-cal c i t e - p y r i te-chl o r i t e -
s e r i c i t e - e p i d o t e assembl age i s c h a r a c t e r i s t i c below t h e Tertiary-Ordovician
contact.
Chemistry o f Thermal F l u i d s
The thermal f l u i d s discharging a t t h e surface and obtained from w e l l s i n
t h e t3eowawe area a r e anomalous compared t o many other p r e v i o u s l y studied
hydrothermal systems (Bamford , 1978; Bamford and others, 1980; Chri stensen,
1980a, b) because o f t h e i r low concentrations o f dissolved m a t e r i a l .
These
d i l u t e f l u i d s , however, are very s i m i l a r t o those obtained from many other
Basin and Range geothermal systems o f s i m i l a r temperature (Mariner and others,
1974; Sanders and Miles, 1974).
Selected f l u i d compositions from t h e Beowawe
area are summarized i n Table 1.
I n general, t h e f l u i d s a r e a l k a l i n e (pH =
8-9) and have t o t a l dissolved s o l i d s l e s s than 1400 mg/l
.
Sodium i s t h e
p r i n c i p a l cation; chloride, s u l f a t e , and carbonate species are a l l s i g n i f i c a n t
anions.
Trace elements which are f r e q u e n t l y enr ched i n thermal f l u i d s
( E l l i s , 1979), such as As, Sb, W, B y L i , Rb, Cs, F and Br, a r e a l l present a t
r e l a t i v e l y low concentrations.
11
TABLE 1
FLUID COMPOSITIONS FROM THE BEOWAWE AREA
Y
U
1
2
Hot Spring
Hot Spring
3
Blowing
We1 1
4
6
5
Blowing
We1 1
Ginn 1-13
We1 1
Rossi 21-19
We1 1
261
27
<.25
<.5
210
8
1 .o
260
41
16
.3
<.025
<.07
154
180
18
30
8.9
2.0
*
c3
Na
K
Ca
My
Fe
Si
Sr
LI
w
Ba
Mn
Mo
As
Sb
W
Li
B
Rb
234
15
<.25
280
40
1.5
<.5
<.025
124
.02
<.625
<.25
<1.25
<.625
<.75
< 125
1.25
.
2.0
---
cs
<.09
229
167
06
<.625
<.25
<1.25
<.625
.
---
.05
< .003
0011
.033
0011
.135
< e 7 5
<.125
1.5
2.2
-320
.220
-----
----Steam
1129
9.8-.2
95
---
-I-
---
---
---
.05
< .003
..019
04
-013
---
---
---
1.8
2.2
1.1
1.1
----88'
1390
8.6
570
8.1
-150
---
..200
145
J
J
TDS
pH &20°C)
T, c
v
* a l l a n a l y t i c values i n mg/l
**dash (---) i n d i c a t e s Val ue n o t determined
***the f o l l o w i n g elements were analyzed f o r i n samples 1 and 3 b u t are present- i n
concentrations below t h e a n a l y t i c a l l i m i t s o f detection: A l , T i , P, V, C r , Co,
Cd, Ag, Au, B i , U, Te, Sn, B
d
U
906,
8.$-.2
95
---
b e l ow s i n t e r
01 1ected 6-24-8
2. Hot s p r i n g below s i n t e r terrace; from Wollenberg and others, 1977.
3. Blowing w e l l brine. Collected 6-24-80. Analyzed by ESL, 7-1980.
4. Blowing w e l l b r i n e ; from Wollenberg and others, 1977.
5. Ginn 1-13 d r i l l stem t e s t a t t o t a l depth, 6-28-74; from Chevron, 1979.
6. Rossi 21-19 f l o w t e s t , 12-76; from Chevron, 1979.
12
---
Although t h e s a l i n i t i e s and t r a c e element concentrations are low, s i 1i c a
Y
contents are unusually high, suggesting t h a t t h e f l u i d s have had short
residence times w i t h i n t h e system and have undergone r e l a t i v e l y l i t t l e
w
chemical i n t e r a c t i o n w i t h t h e r e s e r v o i r rocks.
Several o t h e r processes could
These
produce t h i s p a r t i c u l a r chemistry, however, and can not be neglected.
i n c l u d e f l u i d t r a n s i t through a low surface area environment, e q u i l i b r a t i o n
Y
w i t h s i l i c e o u s r e s e r v o i r rocks, o r l o s s o f elements t o d e p o s i t i o n a l phases.
Chemistry o f Surface Samples
The chemistry o f a number o f surface rock samples from t h e Beowawe area
v'
i s summarized i n Table 2 and t h e i r l o c a t i o n s i n d i c a t e d on Figure 2.
These
samples c o n s i s t o f m a t e r i a l s which have c l e a r l y been a f f e c t e d by i n t e r a c t i o n
w i t h thermal f l u i d s .
J
Samples 1 through 4, c o l l e c t e d near t h e mouth o f White
Canyon, document t h e t r a c e element signature associated w i t h t h e o l d e r
chalcedonic v e i n i n g present along t h e Malpais F a u l t i n t h a t area.
c o n s i s t e n t enrichment i s t h a t of
V
As.
The o n l y
The copper concentration i n sample 1 i s
c o n s i s t e n t w i t h r e l a t i v e l y h i g h l e v e l s o f Cu measured i n o t h e r unaltered Valmy
Formation samples and i s a t t r i b u t e d t o a primary l i t h o l o g i c concentration i n
these eugeosyncli.na1 sediments,
Y
Samples o f opal i n e s i n t e r (sample 5) and
a l t e r e d b a s a l t i c andesite (sample 6) from t h e a c t i v e geothermal area are
d e f i c i e n t i n As and L i when compared t o a l t e r e d rocks i n t h e Roosevelt system
(Bamford and others, 1980; Chri stensen and others, 1980b), r e f l e c t i n g t h e
Y
d i l u t e f l u i d s a t Beowawe.
samples are those o f Mn.
The o n l y notably higher concentrations i n these
As might be expected from t h e d i l u t e thermal f l u i d s ,
t h e t r a c e element signature o f s o l i d s a f f e c t e d by these f l u i d s i s a l s o very
w
weak
.
13
z
E
cli
c
Q
t
e
c
c
t
TABLE 2
GEOCHEMISTRY OF SELECTED SURFACE SAMPLES
1
Valmy Chert:
Breccia & s i 1icahematite v e i n i n g
3
S i 1i c i f i e d , a r g i 11i z e d A r g i 11ized
vol cani c b r e c c i a
volcanic b r e c c i a
4
Chal cedoni c
vein material
5
6
Opa i n e s i n t e r
@ The Geyser
terrace
Arg
ized, b a s a l t i c
andes it e
Na
K
Ca
Mg
Fe
279'
4120
822
644
12200
957
53000
1690
523
16400
6600
35606
3680
638
32600
317
1390
29000
4220
4240
7560
10500
3130
970
28100
6540
11400
1760
801
48300
A1
Ti
Sr
Ba
261
1310
356
78
882
38500
2530
458
81
1090
55100
3790
903
136
1390
4610
107
94
51
460
37500
2640
468
202
971
97600
4870
868
275
1530
Mn
co
cu
Pb
Zn
43
<1
17
<10
<5
42
(1
6
15
c5
60
2
9
22
39
80
<1
7
<10
<5
123
2
7
17
22
139
1
5
33
42
A9
<2
30
16
1.3
<2
145
36
5.4
4
65
15
4.4
2
23
52
6.1
<2
7
42
3.4
<2
8
50
1.9
39
13
20
250
34
59
314
50
96
8
5
<10
219
40
64
398
64
127
SP
'
2
AS
Li
Be
Zr
La
Ce
*
I
a l l values i n mg/kg
** The f o l l o w i n g elements were analyzed f o r b u t are present a t o r below a n a l y t i c a l l i m i t s o f detections:
V, C r , N i , Mo, Cd,
Au, Sb, B i , U, Te, Sn, and Th. S i , W, and 6 a r e 1o s t o r contaminated d u r i n g sample preparation o r analysis.
Element D i s t r i b u t i o n s
Y
The d i s t r i b u t i o n s o f Hg,
As, L i , and Mn a r e presented i n map sections for
f i v e depth i n t e r v a l s i n Figures 4 through 7.
These elements have been found
t o be r e a d i l y d i s t r i b u t e d by thermal f l u i d s i n o t h e r systems (Bamford and
J
others, 1980; Christensen, 1980 a,b).
W
md
V
Y
15
r
1
J
U
3
d
Y
ld
v
:
f
?
I
f
'
\
5
X
16
P
B
s
e
4
e
\ s
\
ef8
t
e
a
?
\
I
i
c
c
t
I[
c
' 0
04
*3
*I
'
'.
Figure 5 . Arsenic distribution i n
drill cuttings: ( A ) 0-100 feet
(B) 100-200 feet
(C) 200-300 feet
(D) 300-400 feet
( E ) 400-500 feet
Dark 1 nes i n d cate the location
of the Mal pai s Faul t.
3
3
rr
3
3
r3
Y
3
J
d
v
f
f
e
e
t
?
E
c
18
f
?
e
\
?
c
3
Y
Y
u3
Y
J
V
u3
W
c
\;
3
19
6 0 0 0 3
C,ccoooou
aJ
a
'F
3
I
I
LdOOOOQ,
I
nocu m e a,V - O I
n
..
U
n
U
n
U
n
.
C
n
c,
U L
.-
e m o o w c U, a
J
~
U
c, I O O O O t
v)O.-ccUmbC,.
.t-
~
ai
Q ,
v)
. U
I
\ . f
a
~
~
S t a t i s t i c a l l y , Hg a n a l y t i c a l values belong t o two lognormal populations
w i t h a threshold value between them o f 110 ppb.
r e s t r i c t e d t o d r i l l holes 48 and 9 (Figure 4).
The anomalous values are
Hole 35, located between these
two, has concentrations c o n s i s t e n t l y greater than t h e mean.
sample i n t e r v a l s have two common f a c t o r s :
The anomalous
they are located east o f t h e
p r e s e n t l y a c t i v e thermal area near t h e t r a c e o f t h e Dunphy Pass F a u l t zone and
are composed p r i m a r i l y o f tuffaceous sediments,
The anomalous concentrations
are apparently not associated s p a t i a l l y w i t h t h e present geothermal system and
are not l a t e r a l l y o r v e r t i c a l l y continous.
rc'
Two i n t e r p r e t a t i o n s are plausible.
The Dunphy Pass F a u l t zone may represent a s t r u c t u r e along which f l u i d s have
r i s e n and migrated l a t e r a l l y through permeable tuffaceous sediments, a model
c o n s i s t e n t w i t h t h e anomalous temperature gradient observed i n hole 48
c,
Struhsacker, personal communication).
(E.
A1t e r n a t i vely, t h e coincidence o f
anomalous Hy concentrations and tuffaceous horizons may be a consequence o f
primary enrichment of Hg i n these rocks.
W
Arsenic concentrations are generally g r e a t e r and i t s d i s t r i b u t i o n
S p a t i a l l y coherent i n t h e upper sample l e v e l (Figure 5).
S t a t i s t i c a l l y , the
a n a l y t i c a l values c o n s t i t u t e a s i n g l e numerical population.
3
Comparison w i t h
analyses o f surface samples (Table 2) shows t h a t these concentrations are
s i g n i f i c a n t l y lower than i n m a t e r i a l s a f f e c t e d by t h e e a r l i e r a l t e r a t i o n
event.
W
The l a t e r a l l y and v e r t i c a l l y discontinuous d i s t r i b u t i o n o f higher
values and t h e c o n s i s t e n t l y low concentrations
imply t h a t t h e r e
never been a pervasive f l
i t h i n t h e lower two l e v e l s
o f As-enriched thermal - f l u i d
through t h e area, but r a t h e r t h a t f l u i d f l o w has apparently been r e s t r i c t e d t o
d i s c r e t e s t r u c t u r e s o r permeable zones.
20
The c l u s t e r i n g o f s l i g h t l y higher As
Y
concentrations a t t h e shallowest l e v e l t o the west o f t h e s i n t e r t e r r a c e i s
believed t o be a consequence o f surface o r near-surface discharge o f thermal
f l u i d s from d i s c r e t e f l u i d channels followed by downslope movement o f t h e
J
c o o l i n g f l u i d s w i t h i n shallow aquifers.
The possible c o n t r i b u t i o n of
mechanical o r hydrologic dispersion o f As from t h e o l d e r a l t e r a t i o n ,
p a r t i c u l a r l y w i t h i n a1 l u v i a l i n t e r v a l s , cannot be evaluated from t h e a v a i l a b l e
W
data.
L i t h i u m i s an element t h a t i s c h a r a c t e r i s t i c a l l y enriched i n thermal
J
f l u i d s (Brondi and others, 1973) and may form dispersion patterns i n rocks
a f f e c t e d by f l u i d i n t e r a c t i o n s (Barnford and others, 1980; Christensen and
others, 1980b).
W
A t Beowawe, L i forms two lognormal numerical populations w i t h
a threshold concentration value o f 65 ppm.
The d i s t r i b u t i o n o f L i i n samples
(Figure 6), l i k e t h a t o f As and Hg, i s not l a t e r a l l y o r v e r t i c a l l y continuous.
Anomalously high values are located near t h e t r a c e o f t h e Dunphy Pass F a u l t
W
zone and near Whirlwind B u t t e j u s t west o f t h e s i n t e r terrace.
As w i t h t h e As
values, there appears t o be a coherent p a t t e r n o n l y a t t h e shallowest l e v e l
(0-100 ' ) o f sampl ing
cri
depth.
.
Anomal ous L i concentrat ions , h
ever, continue t o
The extremely high concentration o f L i (626 ppm) occurring i n t h e
shallowest l e v e l o f d r i l l hole 48, i s associated w i t h unaltered T e r t i a r y
b a s a l t and an o v e r l y i n g c a l c i t e - b e a r i n g tuffaceous 1ake deposit, suggesting
V
the l i k e l i h o o d o f l i t h o l o g i c control.
S t a t i s t i c a l l y , Mn concentrations appear t o form a s i n g l e normal
population with a mean o f about 700 ppm.
rr
Contours o f Mn concentrations
(Figure 7), however, o u t l i n e an area o f Mn enrichment w i t h i n c u t t i n g s samples
21
3
w
t o t h e n o r t h and west o f t h e Malpais escarpment, peripheral and downslope from
t h e p o i n t o f p r e s e n t l y discharging Mn-bearing f l u i d s .
Generally,
concentrations are greater near t h e surface than a t depth.
u3
The geometry
suggests t h a t Mn has been enriched by surface o r near-surface discharge and
f l o w o f f l u i d downslope away from t h e system.
The d i s t r i b u t i o n s o f other elements do not seem t o be r e l a t e d t o
geothermal r e d i s t r i b u t i o n s .
Some elements, p a r t i c u l a r l y Ba, S r , Na, K, Cay
Mg, Fe, A l , and T i are c l e a r l y l i t h o l o g i c a l l y c o n t r o l l e d .
Copper appears t o
possess a normal numerical and s p a t i a l d i s t r i b u t i o n except f o r anomalous
rrt
concentrations i n hole 9, w i t h i n a l l u v i u m a t t h e mouth o f White Canyon.
This
area i s downslope from exposures o f r e l a t i v e l y Cu-rich metasediments o f t h e
Valmy Formation.
S i m i l a r l y , unusually h i g h Ba concentrations w i t h i n a1 u v i a1
sediments are undoubtedly re1ated t o c l a s t s o f Valmy-deri ved b a r i t e .
Conclusions
The t r a c e element geochemistry o f t h e Beowawe geothermal system, a1though
not as s t r o n g l y developed and d i a g n o s t i c as a t o t h e r areas (Christensen,
1980a; Christensen and others, 1980b), does provide i n s i g h t i n t o t h e geometry
3
and chemical h i s t o r y o f t h e Beowawe system.
The present thermal f l u i d s a t Beowawe are d i l u t e i n a l l components except
SiO,,
W
L
suggesting t h a t t h e i r residence time w i t h i n t h e geothermal system has
been short and chemical i n t e r a c t i o n w i t h t h e r e s e r v o i r rock minimal.
I n t e r a c t i o n between these d i l u t e f l u i d s and rocks w i t h i n t h e system has
r e s u l t e d i n weak geochemical signatures which are not c l e a r l y d i s t i n g u i s h a b l e
from t h e normal chemical v a r i a b i l i t y w i t h i n t h e rocks.
22
The absence o f
stronger geochemical signatures in rocks associated w i t h the present system
suggests t h a t the fluids have had a similar dilute chemistry f o r some time.
The more pronounced chemical signature of the older alteration and intense
veining localized near the mouth of White Canyon indicates a different fluid
chemistry or different physical conditions.
The spatial distributions of elements commonly associated w i t h geothermal
systems, such as As, L i and Hg, are neither laterally nor vertically coherent
b u t rather are marked by restricted p o i n t anomalies.
T h i s overall pattern
suggests t h a t there i s not now, nor has there been in the past, pervasive
movement o f fluid t h r o u g h o u t the sampled rocks.
Isolated chemical
concentrations probably represent the intersection of the d r i l l holes w i t h
The
fracture zones or permeable horizons t h r o u g h which fluids have coursed.
coherent near-surface enrichment of As immediately t o the west of the active
system and the peripheral Mn enrichment downslope are consistent w i t h a system
i n which fluids slightly enriched in Mn and As discharge from along the
Malpais F a u l t and flow downslope within alluvium or permeable bedrock.
As the
fluids cool, As i s deposited near the discharge p o i n t and Mn more d i s t a l l y .
Mn may a l s o be redistributed by supergene processes, being locally leached
from rocks by warm discharging f l ui d s , mobi 1 i zed downs1ope, and deposited i n
cooler zones away from the active discharge area.
Similar zoning of As and Mn
i s observed i n soils a t the Roosevelt Hot Springs thermal area, Utah.
These
chemical distributions suggest t h a t the near-surface portion of the Beowawe
system i s controlled by a single-source fracture, the Malpais Fault or an
intersection of faults near The Geysers, and t h a t t h i s portion of the thermal
area has been affected by dilute fluids throughout i t s history.
23
Concentrations o f Hg,
As, and L i and anomalous temperature gradients
along t h e t r e n d o f White Canyon suggest t h a t t h i s may be a zone o f f l u i d
leakage o v e r l y i n g a zone o f thermal f l u i d convection.
The chemical
differences between samples from t h e White Canyon area and t h e samples near
d
t h e present f l u i d discharge area, however, may i n d i c a t e t h a t t h e element
enrichments a r e t h e consequence o f i n t e r a c t i o n w i t h chemically d i f f e r e n t
fluids.
I f thermal f l u i d s occur a t depth along t h e Dunphy Pass F a u l t zone and
3
t h e observed chemical anomalies are r e l a t e d t o t h e present f l u i d s , i t i s
l i k e l y t h a t t h e f r a c t u r e s c o n t r o l l i n g f l u i d f l o w are not connected w i t h those
o f t h e Malpais F a u l t , and t h a t two separate convection systems e x i s t .
More
J
l i k e l y , t h e chemical signatures i n t h e White Canyon area r e c o r d t h e e f f e c t s of
water-rock i n t e r a c t i o n d u r i n g an o l d e r hydrothermal event characterized by
f l u i d s much d i f f e r e n t from t h e present d i l u t e waters.
I f so, t h e Dunphy Pass
lr3
F a u l t zone may w e l l represent a deep conduit t o t h e Beowawe system, as
proposed by Struhsacker and Smith (1980).
w
This geochemical model i s based upon t h e known geochemistry o f 26
g r a d i e n t holes c o v e r i ng some 13 squa
depth o f 150 meters.
The observed g
kilometers and penetrating t o a maximum
chemistry a t t h i s l e v e l places some
1 i m i t s upon t h e possible near-surface geometry and a c t i v i t y o f t h e geothermal
system b u t cannot unambiguously o u t l i n e i t s dimensions.
Continuing work w i l l
evaluate t h e chemistry o f c u t t i n g s from t h e t h r e e deep d r i l l holes within t h e
U
system (Struhsacker, 1980) and may more p r e c i s e l y d e f i n e t h e system.
3
3
24
,3
i
ACKNOWLEDGEMENTS
Analytical work was performed by R u t h Kroneman w i t h the assistance of
As director o f the ESL geochemical program,
Tina Cerliny and Beverly Miller.
Joe Moore provided encouragement and constructive suggestions and criticism
t h r o u g h o u t the study.
Discussions w i t h Eric Struhsacker clarified
interpretations of the geology.
Critical reviews by Joe Moore, Dave Cole,
Howard Ross, and Dennis Nielson are appreciated.
The patient support of the
ESL secretarial and drafting staffs are gratefully acknowledged.
Funding for this work was provided by the United States Department of
rp
Energy, Division of Geothermal Energy t o the Earth Science Laboratory under
contract number DE-AC07-80ID12079.
25
7
1
REFERENCES
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I n s t i t u t e , E a r t h Science Laboratory Report 6, 196 p.
3
3
Barnford, R. W., Christensen, 0. D., and Capuano, R. M., 1980, Multielement
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3
Chevron Resources Co., 1979: Open-file data released by E a r t h Science
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ud
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u
u3
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IJ
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”
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crr
J
in Barnes,
26
3
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and Miles, J. F., 1974, Mineral content o f selected geothermal
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3
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.
rs
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3
Struhsacker, E. M., and Smith, C h r i s t i a n , 1980, Model f o r a deep conduit t o
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'
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6808
I
s3
J
.
27
.
3
APPENDIX
.c,
SUMMARY OF GEOCHEMICAL DATA
E 1ement
J
3
r3
Minimum
5340
14600
10700
1640
13700
47900
1810
218
165
840
<150
<2
240
11
<5
r3
5
<50
10
32
<5
<2
(4
<1
<30
&J
3
3
<loo
<2000
<50
<5
17
1.5
161
15
28
<150
(5
Maxi mum
Mean Standard D e v i a t i o n
28700
41600
130000
32200
68000
80300
8010
2020
507
2420
214
37
1080
145
17
24
<50
38
137
<5
2.5
24100
27200
27600
6710
50300
71100
5440
1100
245
1440
-0-
688
25
--
10
<51)
24
108
<5
<2
<4
<4
<30
<4
12
<30
<lo0
<2000
<50
<loo
<2000
<50
<5
8
626
5.1
521
36
3.8
,392
53
105
<150
<289
71
149
<150
550
--
--
186
17
---4
5
13
--
-------
--
-58
0.7
89
10
24
--0
As determined c o l o r i m e t r i c a l l y , Hg by gold f i l m detector, a l l - other elements
by ICPQe
S i l o s t d u r i n g digestion; W and B con
i n a t e d d u r i n g sample preparation and
analysi s.
cy
U
3520
7320
16300
4790
10100
4960
1410
422
44
284
28