July 1980
--
L
>
Um'yersitg of Utah Research Ins
Salt Lake .Ci
9
Division of Geoth
Under Contract No. 0
8
DISTRIBUTION
b
DO E/ ID/ 12079- 3
ch
ESL-39
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GEOCHEMISTRY OF THE COLADO GEOTHERMAL AREA,
PERSH ING COUNTY , NEVADA
bY
Odin D. Christensen
Y
W
July 1980
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.
NOTICE
.
T h i s report was prepared t o document work sponsored by the United States
Government.
Neither the United States nor i t s agent, the United States
Department of Energy, nor any Federal employees, nor any o f t h e i r contractors,
subcontractors or t h e i r employees, makes any warranty, express or implfed, or
assumes any legal l i a b i l i t y or responsibility f o r the accuracy, completeness,
or usefulness of any information, apparatus, product or process disclosed, or
represents t h a t its use would not infringe privately owned rights.
NOT1CE
Reference t o a company or product name does not imply approval or
recommendation of the product by the University of Utah Research I n s t i t u t e or
the U.S.
Department of Energy t o the exclusion o f others t h a t may be suitable.
C
CONTENTS
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... .. .......... ....,....
INTRr>DUCTION . . . . . . . . . . . . . . . . . . . . . . . . . .
ANALYTICAL TECHNIQUES .
. .
. .
DISCUSSION,
. . .. . .. .. .. .. .. ., .. .. .. .. .. .. .. .. .. .. .. .. .. .. . .
Geology..
As,
Li and Be Distributions . . . . . . . . . . . . .
Other Element Distributions . . . . . . . . . . . . . . .
CONCLUSIONS . . . . . . . . . . . . . . . . . . . . . . . . . . .
ACKNOWLEDGEMENTS . . . . . . . . . , . . . . . . .
.* .
REFERENCES.. . . . . . . . . . . . . . . . . . . . . . . . . . .
APPENDIX: Summary o f Geochemical Data . . . . . . . . . . . . . .
ABSTRACT,.
V
v
0
Hg,
Y
*
Gf
FIGURES
u
Figure
Figure 2
4
Generalized geologic cross sections
.. ......
.*.....*
Mercury distribution in d r i l l cuttings . . . . . . . .
Lithium distribution in d r i l l cuttings . . . . . . .
Beryllium distribution in drill cuttings . . . . . . .
2
4
5
5
11
24
26
27
29
31
3
6
8
10
12
Figure 6
13
Figure 8
Figure 9 Temperature distributi
... .........
Mercury distribution in d r i l l cuttings along two
representative cross sections . . .
.... ..
Figure 10 Arsenic distribution i
11 cuttings along two
representative cross sections
Figure 11
Y
...
1
Figure 5 Arsenic distribution in d r i l l cutting
Figure 7
Y
.
........ . . . .
Figure 3 Generalized geology o f the Colado geothermal area
Figure
V
.
An example o f the selection o f threshold values using
probability graphs
Y
.
1 Index map o f gradient hole locations
PAGE
-
14
15
16
17
18
Y'
*
V
F i g u r e 12
F i g u r e 13
V
F i g u r e 14
Lithium, 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 along two
r e p r e s e n t a t i v e cross s e c t i o n s
.............
B e r y l l i u m 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 along two
r e p r e s e n t a t i v e cross sections . . . . . . . . . . . . .
Temperature d i s t r i b u t i o n i n tNo r e p r e s e n t a t i v e
cross s e c t i o n s . . . . . . . . . . . . . . . . . . . .
PAGE
19
20
21
ABSTRACT
;qultielement geochemical analysis of d r i l l cuttings from 18 shallow and 2
intermediate-depth temperature gradient holes outlines an area of anomalous
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geochemistry related t o the fluid flow and temperature d i s t r i b u t i o n within the
Colado geothermal area.
The concentrations of Hg, As, L i , and Re belong t o
more t h a n one s t a t i s t i c a l population and provide the clearest expression of
W
hydrothermal processes.
Enrichments of these four elements define anomalous
zones which are s p a t i a l l y coincident with a measured temperature anomaly.
The
spatial distribution suggests t h a t thermal fluid r i s e s i n t o a l l u v i u m i n the
w
vicinity of a major Basin and Range f a u l t t o depths of 200-400 f e e t (60120 m ) , then flows l a t e r a l l y within shallow alluvial aquifers down the local
hydrologic gradient.
V
As the f l u i d cools, L i , Be, As, and Hg are deposited i n
response t o changing physical and chemical conditions.
As and Be appear t o be
deposited early i n higher temperature zones; L i begins t o deposit early b u t
farms a rather dispersed geochemical anomaly; Hg i s anomalous throughout the
e n t i r e geothermal area b u t i s concentrated i n a shallow halo above the As and
Be anomalies.
The distributions suggest t h a t the entry o f thermal f l u i d s from
depth into t h e alluviuni i s s p a t i a l l y restricted t o a small area and t h a t the
3
larger area of the observed thermal anomaly i s due t o the flow of warm fluid
within shallow aquifers.
1
I NTR OD UC T I 0
FiI
The Colado geothermal area l i e s i n south-central Pershing County, Nevada,
approximately 8 miles northeast of Lovelock (Figure 1). The geothermal
potential of the area f o r e l e c t r i c pgwer production i s currently being
evaluated by Getty Oil Company i n cooperation w i t h the Division o f Geothermal
Energy of the U. S. Department of Energy.
D u r i n g 1979-80, 18 shallow and 2 intermediate-depth temperature-gradient
'
w
holes were d r i l l e d w i t h i n the area ( F i g . 1 ) . C u t t i n g s from these holes were
subsequently released for study t o the University o f U t a h Research I n s t i t u t e ,
Earth Science Laboratory Division ESL) t h r o u g h the DOE/DCE Industry Coup1 ed
Program.
V
T h i s study i s p a r t of a n ongoing case study o f the Col ado geothermal
area by ESL.
Multielement geochemical analysis of the d r i l l cuttings has been
performed i n order t o more closely define the p o s i t i o n and extent of the
Y
geothermal resource.
Recent studies demonstrate t h a t the trace element
geochemistry o f well cuttings from geothermal systems can be a useful
exploration guide, particularly i n the early stages of geothermal development
u
(Bamford, 1978; Eamford and others, 1980; Bamford and Chri stensen, 1979;
sen and others, 1980b).
Trace element distributions developed as a
consequence of temperature gradients and f l u i d flow w i t h i n a geothermal system
Y
place constraints on the possible geometry of the present system and may
provide insight i n t o i t s thermal and convective history.
P
3
2
el'
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br'
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7.
.:
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4.
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ANALYTICAL TECHNIQUES
Samples were p r e p a r e d , f o r a n a l y s i s by washing a l l i n d i v i d u a l 1 0 - f o o t
d
i n t e r v a l samples, compositing samples over 100-foot i n t e r v a l s , and p u l v e r i z i n g
t o l e s s t h a n 270 mesh i n a SPEX tungsten c a r b i d e shatterbox.
Pulverized
samples were d i s s o l v e d b y a f o u r a c i d d i g e s t i o n procedure (Christensen and
W
o t h e r s , 1980a).
Samples were analyzed f o r 37 elements by i n d u c t i v e l y coupled plasma-
v
atomic emi s s i on spectroscopy ( ICP-AES) u s i ng an Appl i e d Research' L a b o r a t o r i e s
i n d u c t i v e l y coupled plasma quantometer (ICPQ) Model QA-137 i n t h e ESL
geochemical l a b o r a t o r y .
u
Elements determined by ICP-AES were Na, K , Ca, Mg,
Fe, A l , S i , T i , P, S r , Ba, V , C r y Mn, Co, N i , Cu, Mo, Pb, Zn, Cd, Ag, Au, As,
Sb, B i , U, Te, Sn, W, L i , Be, B, Z r , La, Ce, and Th.
Specifics o f the
a n a l y t i c a l i n s t r u m e n t a t i o n and procedures, as w e l l as an e v a l u a t i o n o f t h e
V
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).
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 i n s o l i d samples by g o l d f i l m mercury
@
!
d e t e c t or,
I n o r d e r t o d i s t i n g u i s h chemical
processes f r o m t h e d i s p e r s i o n o f anal
r e s u l t i n g from
es expected i n n a t u r a l normal
3
o r lognormal background geochemical
i c a l values were
partitioned graphically thro
r o b a b i 1it y p l o t s
f o l 1owing t h e procedures des
l a i r (1974, 1976) and L e p e l t i e r
b,
(1969).
The method p e r m i t s e s t i m a t i o n o f p o p u l a t i o n parameters f o r mixed
d i s t r i b u t i o n s o f two o r more populations.
rr
4
It i n v o l v e s d i s s e c t i o n o f t h e
Y
cumulative frequency d i s t r i b u t i o n curve u s i n g p r o b a b i l i t y graph paper.
For
t h i s t y p e o f graph, t h e cumulative frequency d i s t r i b u t i o n c u r v e o f a normal
d i s t r i b u t i o n i s a s t r a i g h t l i n e from vihich t h e mean and standard d e v i a t i o n o f
v
t h e d i s t r i b u t i o n can be estimated.
For polymodal d i s t r i b u t i o n s , t h e
c u m u l a t i v e frequency d i s t r i b u t i o n curve can be d i s s e c t e d i n t o two o r more
l i n e s f r o m which t h e parameters o f each d i s t r i b u t i o n can be estimated.
U
An
example o f t h i s procedure f o r Colado a r s e n i c data i s presented as F i g u r e 2.
B o l d c o n t o u r values presented i n F i g u r e s 5 through 8 and 10 through 13 have
been determined by t h i s method, and thus represent s t a t i s t i c a l l y determined
w
t h r e s h o l d s s e p a r a t i n g d i s t i n c t geochemical populations.
Other contours have
been added f o r c l a r i t y .
O f t h e elements i n v e s t i g a t e d , Hg, As, L i , and Be appear t o belong t o more
w
t
16'
.-.
si
28-
7 E-
I
I
.
pa# 16-
8 12-
!t
*,
V
04-
O I
21
41
1
61
91
a
151
121
i
181
f
1
J
221
251
281
Y
v
'
j'?
log ppm As+
Y
w
Y
Y
r3
F i g u r e 2. An example o f t h e s e l e c t i o n o f t h r e s h o l d values u s i n g probab i l i t y graphs: ( a j ' d i s t r i b u t i o n histogram, a r i t h m e t i c scale; ( b ) d i s t r i b u t i o n histogram, l o g a r i t h m i c scale; ( c ) cumulative frequency d i s t r i but i o n on l o g a r i t h m i c p r o b a b i l i t y scale. Threshold values o f 35 ppm and
140 ppm e f f e c t i v e l y separate t h r e e p o p u l a t i m of As a n a l y t i c ' values.
W
6
cally.
Y
D e t a i l e d g e o l o g i c mapping and o t h e r i n v e s t i g a t i o n s w i t h i n t h e Colado
geothermal area a r e c u r r e n t l y i n progress by Bruce S i b b e t t o f ESL i n
c o n j u n c t i o n w i t h t h e DOE/DGE I n d u s t r y Coupled Program.
Irs
The Colado geothermal area s t r a d d l e s t h e western f l a n k o f t h e West
Huinboldt Range adjacent t o t h e Humboldt R i v e r V a l l e y ( F i g u r e 1).
Rocks
exposed w i t h i n t h e thermal area a r e predominantly c l a s t i c Mesozoic sedimentary
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rocks, T e r t i a r y r h y o l i t i c t o d a c i t i c t u f f s and flows,
d e p o s i t s ( F i g u r e 3).
and Quaternary a l l u v i a l
The rocks have been subjected t o severpl p e r i o d s o f
deformation c h a r a c t e r i z e d by l a r g e - s c a l e f o l d i n g , t h r u s t f a u l t i n g , and Basin
w
and Range normal f a u l t i n g .
Antimony, copper, and p r e c i o u s metal d e p o s i t s o f
t h e W i l l a r d D i s t r i c t were mined i n t h e e a s t e r n p o r t i o n o f t h e area.
Indeed,
h i g h temperatures and steam encountered i n p r e c i o u s m e t a l e x p l o r a t i o n d r i l l
w
holes and trenches were i n p a r t r e s p o n s i b l e f o r arousing i n i t i a l i n t e r e s t i n
t h e geothermal p o t e n t i a l o f t h e area.
The e a s t e r n p o r t i o n o f t h e geothermal prospect i s l a r g e l y u n d e r l a i n b y
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sedimentary rocks o f T r i a s s i c and J u r a s s i c age assigned t o t h e Auld Lang Syne
Group.
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Predominant l i t h o l o g i e s a r e shale, sandstone, q u a r t z i t e , and limestone
To t h e south, J u r a s s i c
t h a t i n general s t r i k e n o r
e s t and d i p southwest.
gypsum sequences cover t h e
a s t i c sediments i n a s e r i e s o f i m b r i c a t e t h r u s t
sheets.
T e r t i a r y v o l c a n i c and p
l a s t i c rocks o v e r l i e t h e sedimentary rocks
throughout t h e d i s t r i c t .
Y
Antimony, go1 d, and copper d e p o s i t s a r e devel oped a1 ong numerous
n o r t h e a s t - and n o r t h w e s t - s t r i k i n g q u a r t z v e i n s and s i 1 i c i f i e d zones w i t h i n t h e
w
od
metasedimentary rocks.
The most e x t e n s i v e m i n i n g development has been a t t h e
7
c
c
e
e
e
c
*
c
c
c
EXPLANATION
QUATERNARY
=-Humbold?
rlver channel and flood plain depaslts
m - A l l u v l a l tans and mlluvlum
[pU-Eollan sand and sllt, active and lnactlve
m - L a k o tahontan depaslts
I1lZlhj-Laks shorn deposits * beach, spits, deltas
TERTIARY
El-Allwi urn
fID-Tuft
~ - F t h ~ l tm
e ,M v e d ~ mplug
~
MESOZOIC
CBID- Limestone
m - s l a t e , argillite
#-Thrust
--Fault,
fautt, teeth on upper plate
dashed where Inferred
c--Contact,
dashed where Inferred
e -Drill hole location
R
(after S i bbqtt and Bul l e t t , 1930)
PERSHING COUNTY, NEVADA
northern body of the Johnson-Heizer mine (S19, T28N, R33E) along a vein
striking N45W and dipping 60' SW.
Northeast and east-weit-trending structures
I
control mineralization a t the Willard group o f gold mines (S25-26, T28N, R32E)
(Osterl i n g , 1960).
Most of the area i s covered by unconsolidated alluvial f a n , lake bottom,
eolian, and flood plain deposits (Figure 3).
Shoreline features o f Pleisto-
cene Lake Lahontan, including calcareous t u f a deposits, were developed along
the f l a n k s of the West Humboldt Range.
Much of the alluvial material i s
porous and serves as aquifers f o r shallow groundwater i n the Humboldt giver
Val 1 ey (Cohen, 1964, 1966 )
.
Basin and Range block faulting is represented by normal f a u l t s along the
margins o f the West Humboldt Range.
The inferred positions of some of these
f a u l t s are indicated on Figure 3 a f t e r Osterling (1960), Johnson (1977),
S i b b e t t (1980, personal communication), and Mackel prang (1980, personal
communication).
Magnetic and gravity d a t a suggest the presence o f several
additional parallel f a u l t s beneath the alluvial cover t o the west o f the range
(Mackelprang, personal communication).
structures serve as imp0
I t seems 1 i k e l y that these deep
controls on the hydr
y of the geothermal
system,
The presence of anomalously w m temperatures
Colado area has been
hot a t a depth o f 10 m
time.
Christe
a s h a f t (NE 1/4 SEI
hallow depths i n the
20) reported water so
7 , T28N, R32E) t h a t the
s h a f t had t o be abandoned (Osterling, 1960) and Getty Oil Company encountered
steam i n a shallow mineral exploration d r i l l hole i n Section 26, T28N, R32E.
9
z
c
a
c
--
c
c
c
c
2
S
A
0
Figure 4. Generalized geologic c r o s s
s e c t i o n s o f the Colado geothermal a r e a
( a f t e r S i b b e t t and Bullett, 1979)
A l t e r a t i o n , a p p a r e n t l y r e l a t e d t o thermal f l u i d s , occurs i n t h e s e c t i o n
v
p e n e t r a t e d by t h e 500-foot g r a d i e n t h o l e 14-22 (Figures 1,4) where a l l u v i u m i s
s i l i c i f i e d a t depths froin 100 f e e t t o t o t a l depth (30-150 m) and p y r i t i z e d i n
t h e approximate i n t e r v a l 300 t o 400 f e e t (90-120 in).
As, Hg, L i , and Be D i s t r i b u t i o n
As, Hg, L i , and Be a r e commonly enriched i n thermal f l u i d s ( E l l i s and
Mahon, 1977; Weissberg and o t h e r s , 1979) and have been shown t o f o r m
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c h a r a c t e r i s t i c d i s p e r s i o n p a t t e r n s about o t h e r hot-water geothermal systems
(Bamford, 1978; Capuano and Moore, 1980; f3arnford and others, 1980, Christensen
The d i s t r i b u t i o n s o f these elements i n p l a n s e c t i o n s a t
and o t h e r s , 1980b).
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f i v e 1 0 0 - f o o t (30 m) depth i n t e r v a l s (Figures 5-8), and i n t w o r e p r e s e n t a t i v e
c r o s s s e c t i o n s (Figures 10-13) can be compared w i t h t h e measured temperatures
i n t h e same s e c t i o n s ( F i g u r e s 9 and 14).
The g r e a t e s t temperatures observed
V
i n t h e 20 g r a d i e n t holes, up t o 113OC, were measured i n h o l e 14-22.
hole, as w e l l as i n several o t h e r s (5-8,
In this
7-4, 13-26, and 16-22), t h e maximum
temperatures a r e encountered a t l e s s than t o t a l depth, s t r o n g l y suggesting
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t h a t thermal f l u i d s a r e r i s i n g i n t o t h e a l l u v i u m and f l o w i n g l a t e r a l l y t h r o u g h
shallow a q u i f e r s a t depths o f 200-400 f e e
d i s t r i b u t i o n s o f several
W
(60-120 m>.
The s p a t i a l
lements bear c l
temperature p r o f i1e.
The numerical and s p a t i a l d i s t r i b u t i o n s o f As an
w
instructive.
The
umerical d i s t r i b u t
suggests the presence o f t h r e e
c o n c e n t r a t i o n s between them
of
35 and 140 ppm (Fig. 2 ) .
3
3
11
The g r e a t e s t concen-
.
w
13
*12
0
22
w
v
*9
W
F i g u r e 5. Arsenic 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 ( a ) 0-100 f e e t , ( b ) 100-200
f e e t , ( c ) 200-300 f e e t , ( d ) 300-400 f e e t ,
( e ) 400-500 f e e t .
3
Y
12
.I60
0120
rgg
I
)
Figure 60 Mercury distribution in drill
cuttings ( a ) 0-100 feet, ( b ) 100-200
feet, ( c ) 200-300 f e e t , ( d ) 300-400
f e e t , ( e ) 400-500 feet.
'
13
u
060
046
0%
v
3
3
W
u
9
J
J
3
Figure 7. ,ithiurn 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 ( a ) 0-100 f e e t , ( b ) 100-200
f e e t , ( c ) 200-300 f e e t , ( d ) 300-400
f e e t , (e) 400-500 f e e t .
"Gl.7 -0\2.0
\
0
1
9
*@
-1.9
O1.9
o2J
01.9
OL8
1.6
18
0
0
OI.9
1.7
1.9
1.6
Figure 8. Beryllium d i s t r i b u t i o n i n d r i l l
cuttings ( a ) 0-100 f e e t , (b) 100-200
f e e t , ( c ) 200-300 f e e t , ( d ) 300-400
f e e t , ( e ) 400-500 feet.
J
3
u
'
u
1
3l.d
w
F i g u r e 9. Temperature d i s t r i b u t i o n i n
temperature g r a d i e n t holes ( a ) 100
f e e t , ( b ) 200 f e e t , ( c ) 300 f e e t
( d ) 400 f e e t , (e) 500 feet.
3
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Y
Y
0
V
ol
3
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/
/
rc,
o m
c
aJcn
v)c
L O
<';;;
e
c
c
e
i
c
n
MERCURY
R
J >75Oppb
ead 250-750ppb
80-250ppb
0 <80ppb
Figure 11. Mercury d i s t r i bution i n d r i 11
cuttings along two representative cross
sections.
V
V
Y
c
e
t
c
c
c
f
c
ru
0
BERYLLIUM
m
>2Sppm
El 2.0-2.5ppm
<2.0ppm
a
Figure 13, Beryllium distribution i n d r i l l
cuttings along two representative cross
secti ons.
V
U
V
c
aJ
>
*C
c
v
t r a t i o n s occur i n t h e deepest samples from holes 14-22, 16-22, and 18-24.
Hg
c o n c e n t r a t i o n s throughout t h e e n t i r e prospect area a r e s i g n i f i c a n t l y g r e a t e r
t h a n those observed about nongeothermal areas o r w i d e l y p e r i p h e r a l t o these
V
areas (Capuano and !loore,
Statistical
1980; Sllann and others, 1980).
e v a l u a t i o n shows t h a t M g data s i m i l a r l y belong t o two o v e r l a p p i n g lognarinal
p o p u l a t i o n s w i t h d i f f e r e n t dispersions.
V
A t h r e s h o l d v a l u e o f 250 ppb
e f f e c t i v e l y separates values o f a h i g h e r , inore w i d e l y dispersed, p o p u l a t i o n
f r o m values r e p r e s e n t i n g a m i x t u r e o f t h e two p o p u l a t i o n s below.
Spatially,
these anomalous Hy values occur above and around t h e h i g h e s t As values and t h e
Y
h i g h e s t measured temperatures.
A s i m i l a r d i s t r i b u t i o n p a t t e r n of As and Hg i s observed a t Roosevelt Hot
Springs, Utah.
w
The observed d i s t r i b u t i o n s and h e a t i n g experiinents i n d i c a t e
t h a t Hg r e m o b i l i z a t i o n occurs a t temperatures as l o w
as 20Oot25O0C and t h a t
t h e d i s t r i b u t i o n o f Hg p e r i p h e r a l t o t h e thermal c e n t e r
i s l a r g e l y produced by
t h e present thermal c o n f i g u r a t i o n (Christensen and others, 198Ob).
r3
The
r e s t r i c t e d p e r i p h e r a l c o n c e n t r a t i o n o f tlg observed a t Colado i s a1 so probably
temperature c o n t r o l 1ed and suggests t h a t temperatures present a t t h e base o f
t h e Hg anomaly a t t h e t i m e o f I t s development may have approached 200°C.
Y
V
how l e s s c o n c l u s i v e e v i
ce o f d i s t i n c t s t a t i s t i c a l popula-
ess d e f i n i t i v e s p a t i a l
tribution.
i n general l o c a t e d
Higher c o n c e n t r a t i o n s a r e
h i n t h e a l l u v i u m , and may, e s p e c i a l l y i n the 200-300
f o o t (60-90 m) depth i n t e r v a l , r e f l e c t t h e l a t e r a l Plow o f thermal f l u i d
toward t h e southwest w i t h i n a shallow.groundwater a q u i f e r .
Y
3
t r a t i o n s observed i n the a l l u v i u m could
also i n part reflect
The h i g h L i concenthe contribution
I
o f d e t r i t a l s i 1 iceous volcanic materal
.
The cqnsi stently greater concentra-
tioris a b o u t the higher temperature locations t h o u g h strongly support t h e
relationship between thermal fluid flow and L i enrichment.
Be concentration values similarly appear t o belong t o two overlapping b u t
d i s t i n c t lognornal populations.
The greater concentrations occur in holes
13-26 and 14-22, and i n the two i ntertnediatadepth gradient hol gs , coincident
Y
w i t h the thermal anomaly a t shelllaw Igvels and apparently increasing w i t h
depth.
The distributions of these four elements appear t o be remarkably w i n c i -
3
dent.
All gre enriched w i t h i n the $rea
near d r i l l hole
systematic reduction away from t h i s area.
u
d a t a froin 200-400 f t . (60-120 m) (Figs.
1 4 4 2 and exhibit
This i s especially evident i n the
5-8). Thesg patterns are completely
consistent with the measured temperature d I S t r i b u t j o n a t Coledo and r e f l e c t
the configuration of ‘active, near-surface f l u i d pathways in a hot-water
0
geothermal system.
These data suggest t h a t thermal f l u i d s r i s e through the
alluviun i n the vicinity of gradient hole 14-22 t g depths of 200-400 feet
(60-120 m), then flow l a t e r a l l y t o the w u t h
Ird
process.
As the f l u i d s c
the changing physical and
U
w
groundwaters i n the
the hydrologic gradient, probab
, and Hg are
nditiom.
deposited i n response t o
As and
Be
ap
deposited i n higher temperature tones; L i begins t o deposit
t o be
b u t forms a
rather dispersed geochemical anomaly a b q u t
i s anomalously h i g h
throughout the e n t i r e geothe
i n a shallow halo
above the As and Be anomalies.
T h i s configuratian i s similar t o t h a t observed
I
W
about the Rooseve t Hot S p r i n g s thermal area, U t a h (Christensen and others,
1980b).
The observed d i s t r i b u t i o n s o f temperature, A S , Hg, L i and Be reflect the
V
forn of f l u i d flow paths, and appear t o be largely independent of lithochemical effects.
The prominent Hg concentration (750 ppb) occurring i n the
lowermost interval i n IGH-2 may reflect Hg deposition from therval waters
V
f l o w i n g along a permeable zone a t the base of t h e alluvial section,
Structurally, the area between d r i l l holes 13T-26 an# 14-22 appears t o be
w
a c r i t i c a l area.
The mapped geology (Johnson, 1977; Sibbett and P u l l e t t ,
1980) and available gravity d a t a (Claren Mackelprang, personal comnunication)
suggest t h a t one of the Basin and Range f a u l t s bounding the western margin o f
V
the West Humboldt Range passes between the two holes and abruptly changes
trend in t h i s area.
The apparent structural intersection may form a favorable
conduit f o r the conduction of thermal fluids i n t o the shallow permeable
rd
alluvium.
Prominent As and Be concentrations mark the position of shallow
thermal f l u i d flow i n the vicinity of d r i l l hole 14-22.
anomalous Hg concentrations eastward from
3
The extension o f the
e most prominent As anomaly
suggests t h a t the thermal anomaly may extend t h i s direction a$ well.
Other Element Distributions
w
.
There are a n
are known t o be mo
of elements i n addition t o As, Hg, L i , and Be which
i n geothermal f l u i d s ( E l l i s and Mahan, 1977; E l l i s ,
1979; Weisberg and others, 1979) and can be
w
system t h r o u g h water-rock interaction.
istributed w i t h i n a geothermal
I t i s e n t i r e l y possible and expected
t h a t one or more other elements could prove useful i n other geothermal areas.
Irr'
.
U
I n the Colado area, however, other poss ble elemental distributiotls related t o
geothermal processes e i t h e r are obscured by geochemical distributions formed
duri ng other geol ogic events, or are devel oped a t concentration 1 eve1 s bel ow
w
the detection limits of the analytical methods employed.
Although several of the major elements, particularly the qlkali and
w
alkaline earth metals, are comiionly present in s i g n i f i c m t conceqtratians in
thermal f l u i d s , t h e i r redistribution within the rock3 resulting from
interaction with these f l u i d s i s riiasked by the greater variability due t o
lithologic differences between samples.
Elements for which t h i s i s true i n
c3
the Colado area include Na, K , e a , Mg, Fe, Al, S i , Ti, P , Sr,
and
Another group of elements are of limited value i n t h i s area due t o t h e i r
v
low concentrations and uncertainties associated with the preparation and
analysis o f samples.
Elements present largely or entirely a t concentratiom
lower t h a n the limits o f determination of the ICPQ (Christsnsen and Qthers,
Y
d
1980a) include: V , Mo, Pb, Th, Ag, Au, Bi, U, and Te.
Three other elernents of
limited value due t o loss or c
ation during preparation and analysis
include Si ( l o s t during HF sam
estion) W (cmtamination introduced from
WC mill used f o r sample commin
and P (contami nation i ntroduced f rorfi
borosilicate glass i n the ICPQ).
Eva1 uation of g
cumul a t i ve probabi 1 it y plats perrni t s
V
rapid discrimination
s t a t i s t i c a l population and mixed distri
cy
n g i n g t g a Simple
wo or more populations.
The numerical v a r i a b i l i t y o f a number o f elements i n t h i $ study, when
evaluated in this manner, i s found t o be cansistent w i t h the variability
rJ
expected w i t h i n a s i n g l e lognormal population.
The a p p a r e n t l y random s p a t i a l
d i s t r i b u t i o n o f extreme h i g h and low values f o r these elements f u r t h e r
supports t h i s suggestion.
Elements i n t h e Colada area which belong t s a
s i n g l e background geochemical p o p u l a t i o n and a r e e v i d e n t l y n o t s j g n i f i c a n t l y
W
r e d i s t r i b u t e d by geothermal processes i n c l u d e Ra, Cu,
Mn, S r , F e r C r , N i , Pb,
Sn, La, and Ce.
The numerical d i s t r i b u t i o n s o f g number o f a t h e r elqmcnts a r e polymodal.
Y
T h e i r d i s t r i b u t i o n s , however, a r e c l e a r l y r e l a t e d t o
the; 1 i t h o l o g i c
v a r i a b i l i t y o f samples and t h e i n f l u e n c e o f ather geolngic proces$es.
and Cd i n p a r t i c u l a r a r e present i n g r e a t e r c o n c e n t r a t i o n s i n
W
Mesozoic a r g i l l i t e s and s l a t e s , whereas Z r
Zn, Cu,
the dark-colored
i s r e l a t i v q l y l e $ s abundant i n
these rocks than i n t h e overlying a l l u v i a l nlqteriql.
Apparent s p a t i a l zoning
o f these elements i s due s i m p l y t o the d i s t r i b u t i o n of l i t h o l o g i e s i n t e r s e c t e d
W
i n t h e d r i l l holes.
Sb and Au a r e l a r g e l y p r e s e n t i n c m c e n t r a t i o n s w e l l
below t h e l i m i t s o f t h e a n a l y t i c a l procedure b u t Occur i n 4nomalously g r e a t
c o n c e n t r a t i o n s i n a few i s o l a t e d a l l u v i a l sample i n t e r v a l s .
W
This i s
a t t r i b u t a b l e t o t h e l i k e l y presence o f d e t r i t a l m a t e r i a l w i t h i n a l l u v i u m from
t h e Sb and Au dep s i t s i n t h e West Humboldt Range t o t h e east.
13
i s i r r e g u l a r l y en i c h e d i n samples
.as w e l l as i n dlluvium.
The polymodal d i s t r i b u t i o n s of t h e s e elements a r e
r e l a t e d t o t h e combined e f f e c t s o f
eochemical gnd g e o l o g i c events
geothermal System.
d not apparently t o r e d i s t r i b u t i o n
o$
%
CONCLUSIONS
A n a l y s i s of c u t t i n g s from 18
low
temperatyre g r a d i e n t d r i l l h o l e s and
from two i n t e r m e d i a t e depth g r a d i e n t holes w i t h i n t h e Colado geothermal area
Y
W
out1 ines an area of anomalous geochemistry spatially coincident w i t h an area
clr
of anomalously h i g h measured temperatures. Both are apparently related t o the
shallow flow of geothermal f l u i d s , As these thermal fluids interact w i t h rock
iuaterial, L i s As, Be, and Hg deposit i n a characteristically zoned sequence,
W
I n the Colado area, fluids appear t o rise t o shallow levels near d r i l l
hole 14-22, perhaps along permeable zones resulting from the intersection of
deep structures. As the fluids enter the alluvium, they apparently flow
W
southwestward w i t h i n shallow aquifers down the local hydrologic slope.
Increased temperatures and enhanced concentration$ o f As, L i s Be, and Hg mark
the course of f l u i d flow.
v
Anomalously h i g h concentrations o f Hg a t the base
of the alluvium suggest t h a t significant flow occurs along this interface.
The d i s t r i b u t i o n s observed suggest t h a t the discharge of thermal f l u i d s
Y
froin depth i n t o the a l l u v i u m i s s p a t i a l l y restricted t p a small area i n the
v i c i n i t y of gradient hole 14-22 (S22, T28N, R32E).
The larger area of the
observed thermal anomaly and of known thermal wells is due t o pluming of warm
d
f l u i d w i t h i n shallow aquifers.
ACKNOWLEDGEMENTS
3
Analytical work was performed by R u t h Kroneman w i t h the assistance of
Tina Cerl i n g and Bev Mil ler.
f the ESL geochemical program, Joe
Moore provided encouragement and constructive cri ticism throughout the study.
Y
Discussions w i t h Bruce Si bbett
d Claren Mackel
o f the geology and geophysics o f the Co do area.
by Joe Moore, Howard Ros
ng clarified
terpretati on
Critical manuscri p t reviews
n , and Jim Stringfellow are appreciated.
a
Funding f o r t h i s work was provided by t h e U n i t e d $ t a t e s Department
of
L
Energy, D i v i s i o n o f Geothermal Energy t o t h e E a r t h Science Laboratory under
c o n t r a c t number DE-AC07-801012079.
3
REFERENCES
'W
Banford, 3. W., 1978, Geochemistry of solid rnaterials from two U.S. geothermal systems and i t s application t o exploration: Univ. of Utah Research
I n s t i t u t e , Earth Science Laboratory Rept. 6 , 196 p.
w
3
J
Bamford, R. W., and Christensen, 0. D., 1979, Multielernent geochemical
exploration data for the Cove Fort-Sul phurdal e Known Geothermal Resource
Area, Beaver and Millard Counties, Utah: Univ. o f Utah Research Inst,,
Earth Science Laboratory Rept. 19, 17 p.
Bamford, R. W., Christensen, 0. D., and Capuano, R., M., 1980, Multielement
geochemistry o f sol i d materials i n geothermal systems and i t s applicat i o n s P a r t I : The hot-water system a t the Roosevelt Hot Springs KGRA,
Utah: Univ. of Utah Research Inst., Earth Science laboratory Rept. 30,
168 p.
Capuano, R. M. and Moore, J. N., 1980, Hg and As soil geochemistry as a
technique f o r mapping permeable structures over a hot-water geothermal
system: Geol. SOC. America Abstracts w i t h Programs, V. 1 2 , p. 269.
Christen, 0. G., 1920, Report of land examiner on Sec. 27, T. 28N, R. 32E,
MDM: Southern Pacific Company report (unpubl ished).
L,
Christensen, 0. D., Kroneman, R. L., and Capuano, R. M., 1980a, Multielement
analysis of geologic materials by inductively coupled plasma-atomic
emission spectroscopy: Univ. o f U t a h Research Inst., Earth Science
Laboratory Rept. 32, 33 p.
0
Christensen, 0. D o , Moore, J. N., and Capuano, R. M., 1980b, Trace element
geochemical zoning in the Roosevelt Hot Sprirlgs thermal area, Utah:
Geothermal Resources Counci 1 Transactions , v 4 ( in prep )
.
..
Cohen, P., 1964, Preliminary results o f hydrogeologic investigations in
Valley o f the Humboldt River near Winnemucca, Nevada: United States
Geological Survey Water Supply Paper 1754, 59 p.
Y
1966, Water in the Humboldt River Valley near Winnemucca, Nevada:
United States Geological Survey Water Supply Paper 1816, 69 p.
Cohen, P.,
Coonrad, W. L., 1957, Geology and mineral resources o f Township 27 North,
Ranges 31, 32 and 33 East, Mount Diablo Meridian, Pershing County,
J
Nevada: Southern Pacific Company Report (unpublished), 43 p.
E l l i s , A. J., 1979, Explored Geothermal Systems i n Barnes, H, L., Geochemi s t r y of Hydrothermal Ore Deposits: New YorG John W
3
E l l i s , A. J., and Mahon, W. A. J., 1977, Chemistry and Geothermal Systems:
New York, Academic Press, 392 pages.
.
w
e,
w
Glenn, W. E., Chapman, 0. S., Foley, D., Capuano, !?.
M., S i b b e t t , B , S., C l e ,
D., and Ward, S , , 1980, Geothermal e x p l o r a t i o n a t Hi1 1 A i r Force Rase,
Ogden, Utah: 'Jniv. o f Utah Research Inst., Earth Science Laboratory
liept. 34, 77 p.
Johnson, M. G., 1977, Geology and mineral deposits o f Pershing County, Nevqda:
Nevada Bureau o f Mines and Geology B u l l e t i n 89, 115 p.
L e p e l t i e r , C. , 1969, A s i m p l i f i e d s t a t i s t i c a l treatment o f geochemical data
by graphical representation: Economic Geology, v. 64, p . 538-550.
W
O s t e r l i n g , W. A., 1960, Geology and mineral resources o f Township 28 North,
Ranges 31 and 32 East, Mount D i a b l o Meridian, Pershing County, Nevada:
Southern P a c i f i c Company r e p o r t (unpublished), 23 p.
S i b b e t t , 0. S., and B u l l e t t , M. J., 1979, L i t h o l Q g y o f 18 shallow thermal
g r a d i e n t holes, Colado area, Nevada: Univ. o f Utah Research Inst., E a r t h
Science Labordtory o p e n - f i l e release, 7 p.
"3
Y
S i b b e t t , B. S. and B u l l e t t , 14. J., 1980, Geology o f t h e Colado geothermal
-area, Pershing County, Nevada: Univ. o f Utah Research Ipst., E a r t h
Science L a b o r a t w y Report ( i n prep.).
S i n c l a i r , A. J., 1974, S e l e c t i o n o f t h r e s h o l d values i n geochemical data u s i n g
p r o b a b i l i t y graphs: Jour. Geochemical E x p l o r a t i o n , v. 3, p. 129-149.
.
S i n c l a i r , A. J , 1976, Appl ic a t i o n s o f probabi 1 ity graphs i n mineral expl orat i o n : Association o f E x p l o r a t i o n Geochemists Special Volume no. 4, 95 p.
b
3
Weissberg, 8. G., Brown, P. R. L., and Seward, T. M,, 1979, Ore metals i n
a c t i v e geothermal systems i n Barnes, H. L. , Geochemistry o f Hydrothermal
Ore Deposits: New York, J x n Wiley and Sons.
APPENDIX
b
Summary o f Geochemical Data
Element
Na, P P
K , PPm
Ca, PPm
MgY PPm
Fe, P P
A1 9 PPm
T i s ppm
p, P W
S r , ppm
Ba, ppm
v, PPm
Cr, ppm
Mn, P P
c o , ppm
Ni, PPm
cu, ppm
Mo, ppm
Pb, ppm
Z n , ppm
Cd, ppm
Ag, PPm
Au, ppm
As, PPm
Sb, ppm
Bi, PPm
u, PPm
Te, P P
Irs
w
3
?v
%
Sn, ppm
Li
.
Be,
Zr,
La,
Ce,
Th,
Hg,
3
3
9
'
M i n i mum
~
~
340
9120
2190
1830
9970
32500
1260
413
19
262
<150
12
45
~
-
~
ppm
PPm
PPm
ppm
ppm
P P ~
PPb
13
8
9
<50
<10
33
(5
<2
<4
9
<30
Maxi mum
29800
34600
132000
59900
40500
84700
3250
3420
428
2890
<150
72
1180
875
50
279
<50
37
2000
10
20
7
275.
Mean Standard Deviation
8410
6670
21000
6220
52400
25200
10300
8010
22600
6550
56400
11000
2180
443
956
563
189
111
969
-786
<150
38
12
388
173
41
83
24
8
28
26
<50
-
150
-
c
-
47
-
173
<loo
<loo
<loo
(2000
<50
<5
20
1.5
11
14
<2000
(50
25
96
3.0
107
33
<2000
23
57
(150
10
<150
3300
<50
-
48
2.1
56
22
40
<150
265
-
219
7
-49
-
-
c
32
0.3
25
11
-4179
As determined c o l o r i m e t r i c a l l y , Hg by gold film d e t e c t o r , a l l other elements
by ICPQ.
W and B contamination during sample preparaS i lost during sample d i g e s t
t i o n and a n a l y s i s .
3
-&
-
31