.. .
.
-_
INTERPRETATION OF GEOPHYSICALDATA FROM THE
COLADO KGRA, PEKSHING COUNTY, NEVADA
bY
Claron E. Mackelprang
April 1982
I
Work performed under contract number DELACOs' 8CID12079
EARTHSCIENCE
LABORATOR
*Univefsity of Utah- Research Institute
Salt L a k e City, Utah
- ,
Prepared
for
U.S. Department of Energy
Division of
Geothermal Energy
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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DOE/ID/12079--56
DE82 019937
I n t e r p r e t a t i o n of Geophysical Data From t h e
GR
JA, Pershing County, Nevada
Colado K
,r..c”’
<-.
+--
/
c
<:
C1 aron E. Mackel prang
A p r i l 1982
0
8
E a r t h Science Laboratory D i v i s i o n
U n i v e r s i t y o f Utah Research I n s t i t u t e
420 Chipeta Way, S u i t e 120
S a l t Lake City, Utah 84108
Prepared for Department o f Energy
D i v i s i o n o f Geothermal Energy
Under C o n t r a c t Number DE-AC07-80ID12079
DOE/ID/12079-58
ESL 71
-
NOTICE
T h i s r e p o r t was prepared t o document work sponsored by t h e U n i t e d S t a t e s
Government.
N e i t h e r t h e U n i t e d S t a t e s n o r i t s agent, t h e U n i t e d S t a t e s
Department o f Energy, n o r any Federal employees, n o r any o f t h e i r c o n t r a c t o r s ,
s u b c o n t r a c t o r s o r t h e i r employees, makes any warranty, express o r imp1 ied, o r
assumes any 1egal 1i a b i 1it y o r responsi b i 1it y f o r t h e accuracy, compl eteness,
o r u s e f u l n e s s o f any i n f o r m a t i o n , apparatus, p r o d u c t o r process d i s c l o s e d , o r
r e p r e s e n t s t h a t i t s use would n o t 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
Reference t o a company o r product name does n o t i m p l y 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
t h e U.S.
0
Q
Department o f Energy t o t h e e x c l u s i o n o f o t h e r s t h a t may be s u i t a b l e .
TABLE OF CONTENTS
Page
................................................................... 1
I n t r o d u c t i o n...............................................................
3
Geologic S e t t i n g ...........................................................
3
Thermal Gradient D r i l l i n g .................................................
~6
Temperature Logs ......................................................
6
Well Log Data f o r D r i l l Holes I G H - 1 and I G H - 2 .............................
15
Surface Geophysical Data ..................................................
18
18
D i s c u s s i o n o f Data Sets ..............................................
G r a v i t y Data .......................................................
19
000.00~0021
Ground Magnetic Data ......................................
MT-AMT and Vector T e l l u r i c Soundings ...............................
21
T e l l u r i c P r o f i l i n g Data ............................................
22
P a r a l l e l E - F i e l d E l e c t r i c a l R e s i s t i v i t y Data .......................
22
Modi f i ed Schl umberger. E q u a t o r i a l and Monopol e Soundings ...........23
23
Time-Domain EM Data ................................................
D i p o l e - D i p o l e E l e c t r i c a l R e s i s t i v i t y Survey ...............................
24
Summary ...................................................................
25
Acknowledgements ..........................................................
26
References ................................................................
26
Abstract
8
Q
ILLUSTRATIONS
Page
IO
8
.....................................................
Fig.
1 . L o c a t i o n Map
Fig.
2
Fig.
3 .Temperature "C @ 100 f e e t
Fig.
4 .Temperatur'e "C
Fig.
5
.Temperature "C @ 500 feet......................................*.9
Fig.
6
.Temperature
Fig.
7 .Temperature Logs P r o f i l e B
Fig.
8
.Temperature
Logs P r o f i l e C.....................~~~~~~~~~~~~~m~~~13
Fig.
9
.Temperature
Logs P r o f i l e D......................................l4
.Thermal
2
G r a d i e n t H o l e Locations...............................*..5
(h
........................................
7
300 feet........................................8
Logs P r o f i l e A.................-..l
......................................
12
F i g . 10 .Temperature Log DH 44~-10.......................................17
0
Fig. 1 1
.G r a v i t y
Profile
Fig. 12
.G r a v i t y
P r o f i l e B-B'.....................................in
F i g . 13
.G r a v i t y
P r o f i l e C-C'.....
A-A~..............................~~~~~~~in
................................
pocket
pocket
i n pocket
PLATES
Plate
11
-
P l a t e I11
-
IV
-
Plate
8
I - Geology Map o f t h e Colado Area, Pershing County, Nevada
Plate
Composite Logs o f Geothermal Wells I G H - 1 and IGH-2, Colado KGRA,
Pershing County, Nevada
Bouguer G r a v i t y Map, Colado Area, Pershing County, Nevada
I n t e r p r e t e d E l e c t r i c a l R e s i s t i v i t y D i s t r i b u t i o n a t a Depth o f
1000 F e e t
Plate
V
-
I n t e r p r e t e d Schematic o f Hydrothermal R e s e r v o i r
ABSTRACT
The Colado geothermal area i s evidenced b y h o t water w e l l s i n a l l u v i u m
along t h e west f l a n k o f t h e West Humboldt Range.
The e x p l o r a t i o n o f t h i s
geothermal system has progressed i n t o advanced stages w i t h completion o f
s h a l l o w thermal g r a d i e n t d r i l l i n g , two i n t e r m e d i a t e - d e p t h e x p l o r a t i o n d r i l l
holes, one deep e x p l o r a t i o n d r i l l hole, d e t a i l e d g e o l o g i c mapping, d i p o l e d i p o l e r e s i s t i v i t y , g r a v i t y , ground magnetics, MT-AMT,
0
TDEM and a s s o r t e d
uncommon e l e c t r i c a l r e s i s t i v i t y techniques.
A thermal anomaly was o u t l i n e d by t h e s h a l l o w d r i l l i n g .
Dipole-dipole
r e s i s t i v i t y and g r a v i t y data along w i t h d e t a i l e d g e o l o g i c mapping have
suggested t h a t t h i s anomaly i s s t r u c t u r a l l y c o n t r o l l e d .
Other geophysical
techniques employed do n o t appear t o c o n t r i b u t e t o an understanding o f t h e
geothermal anomaly.
The two i n t e r m e d i a t e - d e p t h e x p l o r a t i o n h o l e s (IGH-1,
IGH-
2 ) and t h e one deep h o l e (44x-10) may n o t have been l o c a t e d i n t h e most
f a v o r a b l e p o r t i o n s o f t h e geothermal anomaly.
0
The area having t h e g r e a t e s t
e x p l o r a t i o n p o t e n t i a l f o r intermediate-depth d r i l l i n g appears t o be centered
on t h e shal l o w d r i l l h o l e 14-22.
An intermediate-depth d r i l l h o l e l o c a t e d
near DH14-22 i s most l i k e l y t o encounter one o f t h e c o n d u i t s t h a t a l l o w
thermal waters t o r i s e near t h e surface.
1
I
-L---,--.
-
Q
i
Pershing county
i
1
L
-1
STUDY
AREA
Figure
1
INTRODUCTION
The Colado geothermal area ( F i g u r e 1) i s l o c a t e d i n Pershing County,
Nevada approximately 7 m i l e s n o r t h e a s t o f t h e town o f Lovelock.
Getty O i l
Company's 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 was s t i m u l a t e d
when, w h i l e d r i l l i n g on nearby m i n i n g claims, t h e y encountered a l i g h t f l o w o f
steam and thermal waters (Wayne Shaw, personal communication).
The main area
o f geothermal e x p l o r a t i o n t o d a t e i s a l o n g t h e western f l a n k o f t h e West
Humboldt Range, l y i n g between t h e r a i l r o a d s i d i n g s o f Kodak and Woolsey
( P l a t e I ) , a d i s t a n c e o f about 4.5 m i l e s .
T h i s r e p o r t presents an e v a l u a t i o n o f t h e geophysical data package which
8
i n c l u d e s t h e r e s u l t s o f a thermal g r a d i e n t d r i l l i n g program.
The data were
s u b m i t t e d b y G e t t y O i l Company t o t h e E a r t h Science Laboratory, U n i v e r s i t y of
U t a h Research I n s t i t u t e (ESL/UURI), as p a r t o f t h e d a t a due t o t h e U.S.
8
Department o f Energy, D i v i s i o n o f Geothermal Energy t h r o u g h G e t t y ' s
p a r t i c i p a t i o n i n t h e I n d u s t r y Coup1 ed Program.
Results o f a dipol e-dipol e
e l e c t r i c a l r e s i s t i v i t y survey (Mackelprang, 1980) conducted by t h e E a r t h
Science L a b o r a t o r y s u p p o r t i n g our e v a l u a t i o n o f t h i s d a t a package a r e a l s o
i n c l uded i n t h i s r e p o r t .
GEOLOGIC SETTING
Q
The Colado geothermal area i s i n d i c a t e d by h o t water w e l l s i n a l l u v i u m
a l o n g t h e west f l a n k o f t h e West Humboldt Range.
To g a i n a b e t t e r under-
s t a n d i n g o f t h e geothermal environment, S i b b e t t and B u l l e t t (1980) mapped t h e
geology o f t h e West Humboldt Range ( P l a t e I ) a d j a c e n t t o t h e geothermal
area.
The f o l l o w i n g i s t a k e n from t h e a b s t r a c t o f t h e i r r e p o r t .
The West Humboldt Range c o n s i s t s m a i n l y o f T r i a s s i c t o J u r a s s i c s l a t y
Q
3
shal e t o quartzite of the Auld Lang Syne Group.
Carbonate rocks of the
Lovelock Formation have been thrust over the p e l i t i c rocks on the south end of
the area.
Erosional remnants of Tertiary t u f f s and sediments overlay the
metasediments i n the range.
Several thrust f a u l t s are exposed south of Coal Canyon and a structural
break i n the Mesozoic rocks exists under Coal Canyon.
Several low-angle
f a u l t s occur t o the north b u t t h e i r e f f e c t , i f any, on the geothermal occur-
0
rence i s n o t known.
The principal structures are high-angle f a u l t s striking north-northwest,
8
northeast and north-south.
The horst t o graben transition along the range
front consists of several step f a u l t s f o l l owing an irregul ar south-to-north
trend.
0
The structural pattern noted a l o n g the west edge o f the range probably
continues t o the west under the Quaternary a l l u v i u m .
The thermal waters are
thought t o r i s e along a major f a u l t or f a u l t system t o the base of the
a1 1 u v i um.
The surface morphology o f the valley has been strongly affected by the
Pleistocene Lake Lahontan shore features (Morrison, 1964).
Several a l g a l
mounds in the southern part o f the Colado area remain from Lake Lahontan
0
time.
This t u f a i s a typfcal lake deposit and has no geothermal significance
(Morrison, 1964).
A more detailed geologic description of the Colado geothermal area can be
found i n the report by Sibbett and Bullett (1980) which i s an excellent
accompaniment to t h i s report.
Q
4
0
8
0
- ... . . .. . .. . . .. . .... ...
... ... . . . .. . . .. ..
..
THERMAL GRADIENT DRILLING
The Colado geothermal system i s a "blind" hot water system in t h a t no
surface manifestation exists.
Several hot domestic wells have been reported
in the Lovelock area and an industrial well i n alluvium a t Colado has a
reported temperature of 66°C (Garside and Schilling, 1979).
Getty Oil was the f i r s t company t o undertake a serious evaluation of the
a r e a ' s geothermal potential.
This began w i t h the temperature logging of two
holes, R G - 1 and R G - 2 , d r i l l e d for t h e evaluation of mining claims.
The
d r i l l i n g program has progressed t h r o u g h the stage o f d r i l l i n g 18 shallow (<500
Q
f e e t ) thermal gradient holes, two intermediate-depth (1500 feet and 1165 f e e t )
l
holes, and one deep t e s t well (Colado 44x-10) which was d r i l l e d t o a d e p t h o f
7,965 feet.
a
Figure 2 i s a location map for the thermal gradient holes.
Examination of cuttings obtained from the various thermal gradient holes
has identified lithologic changes i n each hole as discussed in detail by
Sibbett and Bul l e t t (1980).
Christensen (1980) performed a mu1 t i e l ement
geochemical analysis of the d r i l l cuttings, and interpretation of the results
out1 i n e d an area o f anomalous geochemistry related t o f l u i d flow and
temperature distribution within the Colado geothermal area.
Temperature Logs
Figures 3, 4 and 5 show temperatures i n "C recorded in the d r i l l holes a t
depths of 100 f e e t , 300 feet and 500 feet respectively.
Quite clearly, the
highest temperatures are encountered a1 ong a northeast-trending zone
encmpassi ng d r i l l holes 16-22, 14-22, 13-26, IGH-1, 10-34, 9-34, and 7-4.
Fluids encountered in these holes have temperatures 60°C or hotter.
It i s
further evident t h a t the thermal fluids are leaking i n t o valley f i l l a t
c3
6-6
15.5
4-16
0
13.8
N
Figure
erature
O
C
3
at a Depth of 1 0 0 Feet
COLADO KGRA, P€RS./NG COUNTY, NEVADA
'8
0
60
16.
4-/6
27.9
N
0
/
I mlle
4
at a Depth of 300 Feet
Figure
Temperature
O
C
COLADO KGRA, PERSMNG COUNTU, IVEVADA
r"
28.0
6-6
I
4 -I6
0
23.2-C
N
i
0
i mile
5
a t a Depth of 500 Feet
Figure
Temperature
O
C
COLADO KGRA, P€RSH/NG COUNTV, NEVADA
re1 a t i v e l y s h a l l o w depths.
8
Temperatures a r e c o o l e r a t t h e g r e a t e r depth shown
by F i g u r e 5, suggesting e i t h e r a m i x i n g o f thermal f l u i d s w i t h ground water o r
a g r e a t e r d i s t a n c e between t h e l e a k i n g c o n d u i t and t h e d r i l l hole.
The
plumbing system f o r t h e thermal f l u i d s i s v e r y l i k e l y f a u l t c o n t r o l l e d w i t h
0
t h e h o t t e s t hole, 14-22, p r o b a b l y b e i n g l o c a t e d v e r y near one o f these
structures.
F i g u r e s 6 through 9 a r e p l o t s o f recorded temperatures o b t a i n e d by G e t t y
0
O i l i n t h e s h a l l o w thermal g r a d i e n t d r i l l holes.
These a r e a l i g n e d as
p r o f i l e s n o r t h t o south across t h e area o f i n t e r e s t .
D r i l l h o l e s 15-21, 17-24
and 18-24 a l l show i n c r e a s i n g temperatures w i t h depth and e x h i b i t thermal
0
g r a d i e n t s o f 65.6"C/km,
75.4"C/km
and 77.8"C/km
respectively.
D r i l l h o l e 16-
22, on t h e o t h e r hand, d i s p l a y s a temperature r e v e r s a l , b u t temperatures
r e c o v e r near t h e bottom o f t h e h o l e and show a thermal g r a d i e n t of 19.7"C/km
0
over t h e f i n a l 50 f e e t .
T h i s g r a d i e n t i s about normal f o r t h e Basin and Range
Province.
0
D r i l l h o l e s 11-36 and 12-26 ( F i g u r e 7 ) a1 so show i n c r e a s i n g temperature
w i t h depth and thermal g r a d i e n t s o f 60.7"C/km
D r i l l holes RG-1 and RG-2,
0
and 69.6"C/km
respectively.
which a r e t h e mineral assessment holes, show v e r y
h i g h thermal g r a d i e n t s w i t h o u t encountering a temperature maximum.
The
i s o t h e r m a l i n t e r v a l i n t h e bottom o f these h o l e s i s i n t e r p r e t e d t o be due t o a
c l o s i n g o f f o r b r i d g i n g over i n t h e holes.
c)
The h o t t e s t shallow thermal
g r a d i e n t h o l e d r i l l e d i s DH14-22 w i t h a maximum recorded temperature of
113.5"C a t a depth o f 250 feet.
D r i l l h o l e 13-26 a l s o shows a h i g h thermal
g r a d i e n t , b u t b o t h t h i s h o l e and DH14-22 a r e e x h i b i t i n g a temperature r e v e r s a l
8
i n t h e deeper p o r t i o n o f t h e holes.
10
"
7
8
(3
18
0
8
8
5.4 OC/km
0
-OH
16-22
19.7 OC/km
DH 18-24
77.8 OC0km
0
65.6 OC/ km
8
I
3.20
1
I
1
I
Z70
12.20
16.70
21.20
T€MP€RATUff€ IN
Figure
O f
6
I
25.70
X IO
Temperature Logs Profile A
I
30.20
0
DH 12-26
69.6 %/km
O H 15-21
65.6 .C/km
OH 13-266
R
R
-22
I
11-36
60.7OC/km
OH
1
I
I
I
I
7.70
12.20
16.70
21.20
I
25.70
TEMPERATUR€ /N OF X /O
Figure 7
Temperature L o g s Profile I3
I
30.20
T€MP€UATUU€ IN OC
DH 1-12
43.5 OC/km
I
I
I
7.70
12.20
16.70
I
1
I
21.20
25.70
7EMPERATUU€ Iff OF X 10
Figure
8
mperature Logs Profile C
I
30.20
T€MP€RAWf?€ IN
Q
8
0
SOTHERM
0
77.9 OC/km
O H 6-6
53.3 OC/km
I
3.20
Z70
I
12.20
I
21.20
I
16.70
T€MPERATUR€ lN
Figure
Temprature
O F
1
25.70
X IO
9
Logs Profile D
I
30.20
The d r i l l h o l e s shown on F i g u r e 8 show temperatures i n DH1-12 and DH2-2
t o have g r a d i e n t s about t w i c e t h e Basin and Range average (20-30°C/km)
i n t e r v a l between 50 f e e t and 500 f e e t .
for the
The upper p o r t i o n o f h o l e s 8-34,
9-34
and 10-34 e x h i b i t h i g h g r a d i e n t s b u t t h e s e a l l decrease t o g r a d i e n t s o f 5065"C/km,
a t l e a s t i n 9-34 and 10-34.
The temperature g r a d i e n t i n h o l e 8-34
may have r e v e r s e d a t i t s deepest p o i n t .
The remaining h o l e s on F i g u r e 9 a r e s i m i l a r t o those p r e v i o u s l y d i s -
0
cussed.
Thermal g r a d i e n t s r o u g h l y double t h e Basin and Range average occur i n
DH3-10 and DH6-6 from a depth o f 50 f e e t t o t o t a l depth.
D r i l l h o l e 4-16
s t a r t e d o u t n e a r l y i s o t h e r m a l b u t p i c k e d up about 150 f e e t w i t h t h e
temperature maximum being a t t h e bottom o f t h e hole.
i n d i c a t i o n s o f a t u r n o v e r s t a r t i n g t o develop.
There are, however,
DH5-8 and DH7-4 b o t h s t a r t e d
o u t w i t h h i g h e r g r a d i e n t s , b u t a t a depth o f 300 f e e t DH5-8 went i s o t h e r m a l
0
w h i l e DH7-4 had a r e v e r s a l .
WELL LOG DATA FOR DRILL HOLES I G H - 1 AND IGH-2
Q
P l a t e I 1 i s a composite o f t h e v a r i o u s l o g s recorded i n t h e i n t e r m e d i a t e depth d r i l l holes.
Inc.,
8
D r i l l h o l e I G H - 1 was d r i l l e d by K. 0. B u r t D r i l l i n g Co.,
S p r i n g v i l l e , Utah, d u r i n g March 4-18,
1980.
T o t a l depth was 1500 f e e t .
D r i l l h o l e IGH-2 was d r i l l e d by Southwest D r i l l i n g and E x p l o r a t i o n Inc.,
Rig
#7, d u r i n g Oct. 30-Nov. 18, 1979, t o a t o t a l depth o f 1165 f e e t .
H o l e I G H - 1 s t a r t e d i n a r g i l l a c e o u s s i 1 t s t o n e , p e n e t r a t e d q u a r t z i t e and
bottomed i n a t h i c k sequence o f s l a t e o r s l a t y shale.
The f i r s t c h a r a c t e r -
i s t i c f e a t u r e i n t h e l o g s o f t h i s h o l e occurs a t a depth o f 425 f e e t , r o u g h l y
c o i n c i d i n g w i t h t h e water t a b l e .
C a l i p e r , p o r o s i t y ( n e u t r o n and d e n s i t y ) and
gamma ray 1 ogs show an i n c r e a s e a t t h i s depth whereas b u l k d e n s i t y , r e s i s - -
15
t i v i t y and spontaneous p o t e n t i a l l o g s show decreases.
IO
A p o s s i b l e f a u l t zone
i s a l s o shown on t h e l i t h o l o g i c l o g a t t h i s horizon.
The s l a t e o r s l a t y s h a l e l a y e r shown i n t h e 500-540 f o o t i n t e r v a l i s a l s o
i n d i c a t e d i n t h e v a r i o u s l o g s b u t a t a s l i g h t l y g r e a t e r depth w i t h a l l t h e
I
I
IQ
l o g s showing increases i n t h e i r measured parameters.
An i n d i c a t i o n o f severe
h o l e enlargement occurs i n t h e 900-1200 f o o t i n t e r v a l .
This i n t e r v a l i s
e v i d e n t i n t h e v a r i o u s l o g s as a general, b u t i r r e g u l a r , zone of s l i g h t l y
c3
h i g h e r p o r o s i t y and l o w e r b u l k d e n s i t y , r e s i s t i v i t y , spontaneous p o t e n t i a l and
gamma ray response.
These e f f e c t s have n o t , however, been c o r r e l a t e d t o any
diagnostic c h a r a c t e r i s t i c s o f t h e l i t h o l o g i c log.
D r i l 1 h o l e IGH-2 p e n e t r a t e d approximately 1100 f e e t o f a1 t e r n a t i n g 1 ayers
o f coarse and f i n e g r a v e l b e f o r e b o t t o m i n g i n 65 f e e t o f s l a t e o r s l a t y
0
shale.
The temperature l o g was r u n by U n i t e d W i r e l i n e Surveys, Inc.,
January 9, 1980.
200 f e e t
8
-
on
It shows a pronounced i n c r e a s e i n temperature a t a d e p t h of
t h e depth t o t h e water t a b l e .
The temperature g r a d i e n t below
200 f e e t t o t o t a l depth o f t h e h o l e i s a c o n s t a n t 114'C/km
(7.2"F/100
The o t h e r l o g s t a k e n i n t h i s h o l e a r e shown t o be v e r y e r r a t i c .
ft).
There i s ,
however, a pronounced increase in h o l e r u g o s i t y , n e u t r o n p o r o s i t y and b u l k
0
d e n s i t y along w i t h a decrease i n sonic v e l o c i t y , r e s i s t i v i t y and gamma r a y
response i n t h e depth i n t e r v a l 960-1140 f e e t .
Only t h e b u l k d e n s i t y can n o t
be e x p l a i n e d by w a t e r - f i l l e d open f r a c t u r e s .
D r i l l h o l e 44X-10 was r e c e n t l y (1981) completed a t an i n t e r m e d i a t e depth
o f 7965 f e e t .
T h i s h o l e was l o c a t e d near d r i l l h o l e IGH-2.
The predominant
r o c k s p e n e t r a t e d were p h y l l i t e w i t h i n t e r v a l s o f q u a r t z and s e r i c i t e t o t h e
bottom o f t h e hole.
The temperature l o g ( F i g u r e 10) showed a f a i r l y normal
Basin and Range g r a d i e n t t o a depth o f 4600'.
16
The temperature p i c k s up a t
TEMPERATURE
D€G.
C
)
0
0.
915
305
1830
610,
17.8S°C/KM
0.98O F A 0 0 FT
2 745
915
2;
8L
3660h
2
%
12
ru
h
L 1220
X
h
%a
25.65OC/KM
1.40° F/ 100FT
X
1
4575 Q
1525
5490
1830
38.84OC/K M
2.13O WlOOFT
6405
2135
7320
2440
T..MPERATLJRE
DEG.
Figure 10
F
Temperature Log
Drill Hole 44X-10
Muy
5,1981
5900 f e e t
0
nd c o n t i n u e s t o increase t o t o t a l depth o f 7965 f e e t .
Therm 1
g r a d i e n t s a r e h i g h o v e r t h i s i n t e r v a l w i t h t h e b o t t o m 65 f e e t b e i n g about
263"C/km.
T h i s g r a d i e n t was o b t a i n e d from a temperature l o g taken t h e day
a f t e r c o m p l e t i o n o f t h e d r i l l hole, hence i t may be i n e r r o r because
0
i n s u f f i c i e n t t i m e had passed f o r t h e h o l e t o e q u i l i b r a t e .
SURFACE GEOPHYSICAL DATA
Q
I n mid-1977, G e t t y O i l Company c o n t r a c t e d several geophysical surveys o f
t h e Colado area t o Electrodyne Surveys o f Sparks, Nevada.
The purpose o f
these surveys was t o d e l i n e a t e s t r u c t u r e and anomalous areas w i t h i n o r below
Q
a l l u v i a l cover t h a t c o u l d be r e l a t e d t o t h e geothermal occurrence noted on
G e t t y ' s m i n i n g claims.
D i s c u s s i o n o f D a t a Sets
Several geophysical techniques were appl i e d by E l ectrodyne Surveys t o
determine t h e r e s i s t i v i t y s t r u c t u r e o f t h e geothermal area.
0
I n addition,
E l ectrodyne subcontracted g r a v i t y and ground magnetic surveys t o Lanton Survey
Company o f V a l l e j o , C a l i f o r n i a .
E l e c t r o d y n e ' s approach was t o use what t h e y
c a l l e d "reconnaissance" t y p e surveys, namely M -AMT soundings, r o v i n g V e c t o r
8
T e l l u r i c soundings, and i n - l i n e T e l l u r i c p r o f i i n g i n c o n j u n c t i o n w i t h t h e
g r a v i t y and ground magnetic d a t a t o d e f i n e t h e s t r u c t u r a l make-up and anoma1 ous 1ow apparent r e s i s t i v i t y zones.
0
Subsequent areas i n t e r p r e t e d by
E l e c t r o d y n e t o be o f i n t e r e s t were t h e n " d e t a i l e d " u s i n g (DC) g a l v a n i c
e l e c t r i c a l r e s i s t i v i t y soundings, para1 l e 1 e l e c t r i c - f i e l d (DC) measurements,
time-domain electromagnetic (TDEM) soundings and combined e l e c t r i c - f i e l d
8
TDEM soundings.
-
Two techniques, MT-AMT and a s e c o n d - d e r i v a t i v e map of t h e
g r a v i t y d a t a c o n s t r u c t e d by E l ectrodyne, form t h e r e f e r e n c e base used by
E l e c t r o d y n e t o i n t e r p r e t t h e data s e t s from t h e o t h e r surveys.
18
Observations
1
8
r e g a r d i n g t h e v a r i o u s techniques and t h e i r i n t e r p r e t a t i o n by E l ectrodyne
follow.
T h i s data s e t obtained by Lanton Survey Company c o n s t i -
G r a v i t y Data:
t u t e s a r e g i o n a l s u r v e y over t h e general geothermal area.
b
Copies of t h e f i e l d
d a t a were o b t a i n e d from G e t t y O i l , checked f o r p r o c e s s i n g e r r o r s and were
found t o be o f good q u a l i t y .
Lanton o b t a i n e d e l e v a t i o n s w i t h t r a n s i t and
s t a d i a and t e r r a i n c o r r e c t i o n s were made a t each s t a t i o n t h r o u g h zone D ( o u t e r
c3
radius of 558').
Our (ESL) r e v i s e d Bouguer g r a v i t y map i s shown as P l a t e 111.
E l ectrodyne computed a s e c o n d - d e r i v a t i v e g r a v i t y map from which t h e y
0
i n t e r p r e t e d a complex s t r u c t u r a l p i c t u r e .
Our review, however, suggests t h a t
t e r r a i n c o r r e c t i o n s were n o t cunputed f o r an adequate area around each s t a t i o n
n o r were s t a t i o n s o f s u f f i c i e n t a r e a l d e n s i t y t o j u s t i f y a q u a n t i t a t i v e
i n t e r p r e t a t i o n based upon t h e s e c o n d - d e r i v a t i v e technique.
T h e i r second-
d e r i v a t i v e map i s t h e r e f o r e thought t o be v e r y s p e c u l a t i v e .
It i s p o s s i b l e , however, t o p r e s e n t an i n t e r p r e t a t i o n based upon t h e
Bouguer g r a v i t y data.
G r a v i t y data from t h e Carson Sink Area (Wahl , 1965
show a p r o n o u n c e d low n o r t h o f L o v e l o c k along the west f l a n k o f t h e West
Humboldt Range which has been i n t e r p r e t e d as due t o 7100 f e e t o f down-fau t ed
Cenozoic sediments.
The d e n s i t y c o n t r a s t between these sediments and t h e Pre-
T e r t i a r y r o c k s o f t h e range i s r o u g h l y -0.6
gm/cc.
The g r a v i t y d a t a obta ned
by Lanton Survey Company e s s e n t i a l l y d u p l i c a t e d t h e g r a v i t y l o w n o r t h of
Lovelock and gave a d d i t i o n a l d e t a i l along t h e west f l a n k o f t h e West Humboldt
Range ( P l a t e 111).
These data g i v e s t r o n g evidence f o r f a u l t i n g along t h e
western f l a n k o f t h e range.
South o f Coal Canyon t h e g r a v i t y d a t a suggest a
NE-SW s t r i k e t o t h e b o r d e r i n g s t r u c t u r e s .
A s t r u c t u r a l break i n t h e Mesozoic
r o c k s f o l l o w s Coal Canyon ( S i b b e t t and B u l l e t t , 1980).
19
T h i s break a p p a r e n t l y
-. .
. . ..
. ..-
. ..- . . . ... .
. . . . . .. .
. .
.. . .
. . ..-.. .
.
-- . -
- - .. - . .
forms a hinge l i n e allowing f o r the deflection of the border f a u l t s t o the
north.
This north-trending f a u l t system can be traced i n the gravity d a t a
across the valley, passing between the range f r o n t and DH15-21 and along the
eastern side o f the gravity h i g h located a t the extreme north end of the
gravity survey area ( C ) .
This northern gravity h i g h i s caused by bedrock i n
the mountain range t h a t forms the western border to the Humboldt River Valley
i n the Rye Patch area, Rye Patch being located on Highway 40 approximately 15
miles north of Colado.
0
F a u l t i n g i s present a l o n g the eastern side of this
northern g r a v i t y h i g h and , w i t h 1 i t t l e imagination, can be projected s o u t h
across the valley i n t o the north-trending f a u l t system located just n o r t h of
Coal Canyon.
The north-trending f a u l t system t o the north of Coal Canyon has been open
t o f l u i d movement i n the past a s evidenced by the intense hematite s t a i n i n g i n
0
the Tertiary and Mesozoic rocks near t h i s zone.
The andesite lava flows
nearby have been strongly altered t o s e r i c i t e , c a l c i t e , chlorite, q u a r t z , clay
and hematite (Sibbett and BuTlett, 1980).
0
I t i s quite possible t h a t the
extension of t h i s f a u l t zone t o the n o r t h beneath the gravel cover i s also
similarly a1 tered.
Another f a u l t system apparent1 y extends northeast from DH16-22 a1 ong the
0
range front and essentially duplicates the trend for the segment south of Coal
Canyon.
There i s evidence i n the gravity d a t a t h a t this f a u l t system extends
southwest i n t o the vicinity of Colado and i s separate from the faulting along
8
the range front south of Coal Canyon.
Sibbett (personal communication) notes
t h a t the alteration along the NE-SW trending f a u l t segments i s considerably
8
less intense as i n the intervening area d i r e c t l y north o f Coal Canyon.
The
projected f a u l t intersection i n the vicinity of DH14-22 may cause a zone of
20
i n t e n s e f r a c t u r i n g , increased p e r m e a b i l i t y and f l u i d movement, and may be t h e
main c o n d u i t f o r h o t f l u i d s noted i n DH14-22.
F i g u r e s 11-13 a r e computed 2 1/2-dimensional
g r a v i t y models across t h e
Colado area, t h e i r l o c a t i o n s being shown on P l a t e 111.
A -0.6 gm/cc bedrock-
a l l u v i u m d e n s i t y c o n t r a s t was used i n computing these models.
While non-
unique, these models g i v e a good approximation t o t h e t h i c k n e s s o f v a l l e y f i l l
(<6000 f e e t ) as w e l l as general l o c a t i o n s of b u r i e d f a u l t s which may be t h e
0
c o n d u i t s f o r thermal f l u i d s
Ground Magnetic Data:
d u r i n g t h e g r a v i t y survey.
Total - f i e l d ground magnetic data were a c q u i r e d
These s t a t i o n s appear t o be l o c a t e d along roads
c o n t a i n i n g b u r i e d water l i n e s , p o w e r l i n e s and metal fences.
The data
presented appear t o have s t r o n g c u l t u r a l i n t e r f e r e n c e s as a r e s u l t and a r e n o t
included i n t h i s report.
MT-AMT and Vector T e l l u r i c Soundings:
T h i r t y - o n e MT-AMT and seventeen
r o v i n g v e c t o r t e l l u r i c soundings were made a t Colado by Electrodyne.
0
The data
p r e s e n t a t i o n they p r o v i d e d t o DOE c o n s i s t s o f t a b u l a t e d apparent r e s i s t i v i t i e s
(Tables 11-1 and 111-1, Vol.
11, ESL Open-File Release NV/COL/GOC-1) f o r t h e
s t a t i o n s i t e s d e r i v e d from f r e q u e n c i e s o f 14 Hz and 0.045 Hz.
The source d a t a
f o r t h e s e r e s u l t s a r e n o t a v a i l a b l e , hence, i t i s n o t p o s s i b l e t o e v a l u a t e t h e
apparent r e s i s t i v i t y d a t a presented.
The d e s c r i p t i o n of t h e method and
a c q u i s i t i o n techniques presented i n Volume II o f E l ectrodyne's r e p o r t ,
however, lends some i n s i g h t i n t o data q u a l i t y .
Electrodyne appears t o have gathered t h e i r f i e l d data b y measuring t h e
e l e c t r i c f i e 1 d w i t h orthogonal p o t e n t i a l e l e c t r o d e s and t h e magnetic f i e l d
w i t h a d u a l - a x i s f l u x g a t e magnetometer.
21
T h i s magnetometer had a s e n s i t i v i t y
'0
usual case f o r m i d d l e l a t i t u d e s , t h e median a m p l i t u d e v a l u e f o r magnetic
v a r i a t i o n s w i t h i n t h e frequency range 0.03 t o 0.2 cps i s about 0.02 gammas
(Yungul, 1966; Campbell, 1959).
Based on t h i s r a t h e r c i r c u m s t a n t i a l evidence,
T y p i c a l l y , i t i s necessary t o know t h e apparent one-dimensional
r e s i s t i v i t y a t a base s i t e i n o r d e r t o r e l a t e t h e r e s u l t s o f t e l l u r i c
8
soundings a t o t h e r s i t e s t o apparent r e s i s t i v i t y .
The apparent r e s i s t i v i t y a t
t h e base s i t e can b e determined p r e f e r a b l y from a r e s i s t i v i t y l o g i n a d r i l l
h o l e o r a l t e r n a t i v e l y from a sounding t e c h n i q u e such as MT.
Due t o t h e l o w
s e n s i t i v i t y o f t h e magnetometer used i n t h e MT soundings and s i n c e no
r e s i s t i v i t y l o g s were a v a i l a b l e , none o f t h e necessary requirements f o r a base
c3
s i t e have been met.
Hence, t h e apparent r e s i s t i v i t i e s determined from t h e
t e l l u r i c surveys a t Colado appear t o be suspect a l s o .
T e l l u r i c P r o f i l i n g Data:
0
The d a t a a c q u i s i t i o n f o r t h i s t e c h n i q u e i s
s i m i l a r t o r o v i n g t e l l u r i c soundings except t h a t t h e p o t e n t i a l d i f f e r e n c e i s
compared between e l e c t r o d e s from a p r e v i o u s s i t e and a new s i t e , p l a c e d i n l i n e , using a multichannel receiver.
9
i n conductance between t h e two s i t e s .
The d a t a should d i s p l a y r e l a t i v e changes
Several d i s c r e p a n c i e s were noted
between contoured apparent r e s i s t i v i t y maps ( E l ectrodyne' s P1a t e s V I I and
V I I I ) and t a b u l a t e d apparent r e s i s t i v i t y v a l u e s shown i n Volume 11, Table I V
o f E l ectrodyne' s r e p o r t (ESL OFR NV/COL/GOC-l).
These d i screpancies cons1 s t s
o f d a t a omissions, p l o t t i n g o f s e l e c t e d v a l u e s r a t h e r t h a n a l l v a l u e s a l o n g
t h e p r o f i l e s , and p l o t t i n g o f values n o t l i s t e d i n t h e t a b l e .
Para1 l e 1 E-Fie1 d E l e c t r i c a l R e s i s t i v i t y Data:
t h i s t e c h n i q u e i s r e l a t i v e l y unknown.
As E l ectrodyne s t a t e s ,
There i s no r e f e r e n c e t o i t b e i n g used
22
f o r d e t e r m i n a t i o n o f apparent r e s i s t i v i t y e i t h e r as a general geophysical
survey technique o r as a method t o prospect f o r geothermal f l u i d s i n t h e U.S.
geophysical 1 it e r a t u r e .
The E l ectrodyne d e s c r i p t i o n o f t h e technique does n o t
go i n t o s u f f i c i e n t d e t a i l t o make an a n a l y s i s o f t h e data p o s s i b l e .
One o f
E l ectrodyne' s p r o f i l es was repeated by them w i t h r e s u l t a n t apparent
r e s i s t i v i t i e s v a r y i n g by as much as a f a c t o r o f 7.
L i t t l e confidence i n t h e
technique appears warranted s i n c e b e t t e r DC and AC s u r v e y i n g methods w i t h w e l l
e s t a b l i s h e d i n t e r p r e t a t i o n procedures a r e a v a i l a b l e .
M o d i f i e d Schl umberger, E q u a t o r i a l and Monopole Soundings:
DC e l e c t r i c a l
r e s i s t i v i t y soundi ngs were a1 so obtained i n t h e Col ado area by E l e c t r o d y n e
0
through t h e use o f l o n g c r o s s e d - b i p o l e sources.
Supposedly t h i s technique
enables b o t h l a t e r a l and v e r t i c a l d e f i n i t i o n o f apparent r e s i s t i v i t y t h r o u g h
t h e canbined use o f m o d i f i e d Schlumberger, e q u a t o r i a l , o r monopole soundings
a t a single site.
Apparently, curve matching was used t o d e r i v e t h e d i s p l a y e d
one-dimensional v e r t i c a l r e s i s t i v i t y s e c t i o n s .
2.3,
With t h e e x c e p t i o n o f s i t e s
10.1 and 10.2 (ESL OFR NV/COL/GOC-1 P l a t e X ) , which used monopole and
modified Schl umberger a r r a y s , a1 1 soundings a r e ambiguous r e g a r d i n g t h e a r r a y
used.
The sounding r e s u l t s were smoothed because t h e data themselves were
highly erratic.
Q
I n general, t h e r e s u l t s o f t h i s survey a r e open t o
conjecture.
Time-Domain EM Data:
0
Because t h e t i m e - d m a i n EM sounding l o c a t i o n s do
n o t c o i n c i d e w i t h t h o s e o f t h e DC e l e c t r i c a l r e s i s t i v i t y soundings, i t i s n o t
p o s s i b l e t o compare d i r e c t l y apparent r e s i s t i v i t y v a l u e s obtained.
It would
seem l o g i c a l t o expect a t l e a s t near-surface apparent r e s i s t i v i t i e s t o be
Q
s i m i l a r between t h e two techniques.
The r e s u l t s obtained w i t h DC and TDEM
soundings show gross d i f f e r e n c e s i n t h e i n t e r p r e t e d apparent r e s i s t i v i t y
8
23
distribution.
0
T h i s appears t o r e s u l t from t h e use o f one-dimensional modeling
The E a r t h Science Laboratory D i v i s i o n , U n i v e r s i t y o f Utah Research
I n s t i t u t e (ESL/UURI) undertook a d i p o l e - d i p o l e e l e c t r i c a l r e s i s t i v i t y survey
(Mackelprang, 1980) t o c h a r a c t e r i z e t h e e l e c t r i c a l r e s i s t i v i t y d i s t r i b u t i o n o f
0
t h e resource area i n support o f t h e G e t t y O i l Company geothermal e x p l o r a t i o n
effort.
T h i s survey i s adequately described i n t h e ESL/UURI r e p o r t
referenced
0
.
A comparison o f t h e d i p o l e - d i p o l e r e s i s t i v i t y survey w i t h t h e E l e c t r o d y n e
r e s i s t i v i t y surveys shows t h e two data s e t s t o have major d i f f e r e n c e s .
The
d i p o l e - d i p o l e data appear t o be more d e f i n i t i v e i n d e l i n e a t i n g n o t o n l y areas
o f 1ow apparent r e s i s t i v i t y b u t s t r u c t u r a l l y c o n t r o l 1ed areas as we1 1.
P l a t e I V i s an o v e r l a y t o P l a t e I and shows l o c a t i o n o f r e s i s t i v i t y l i n e s
Q
and t h e e l e c t r i c a l r e s i s t i v i t y d i s t r i b u t i o n a t a depth o f approximately 1000
f e e t f o r each o f t h e f i v e ESL d i p o l e - d i p o l e l i n e s .
T h i s p l a t e shows t h e sharp
r e s i s t i v i t y c o n t r a s t s and t h e i r l o c a t i o n s from which t h e f a u l t i n g i s i n f e r r e d .
Q
The data source f o r P l a t e I V i s t h e computed models shown as F i g u r e A 1 t h r o u g h
A5 i n t h e r e p o r t by Mackelprang (1980).
s t r u c t u r e s w i t h i n t h e mountain range.
Q
There i s good c o r r e l a t i o n w i t h mapped
The d e t e c t i o n o f subal l u v i a l f a u l t s
away from t h e mountain f r o n t i s o f p a r t i c u l a r importance f o r , w h i l e these
f a u l t s may have been suspected, t h e i r l o c a t i o n was n o t known.
8
24
Although shown
as separate f a u l t s , several could be p a r t of a single f a u l t zone and i t must
be understood t h a t the locations of these f a u l t s as shown on Plate V are t o be
considered as close approximations only.
They a r e necessarily subject t o the
s e n s i t i v i t y of the dipole spacing used as well as the non-uniqueness of the
lo
computer model i n g technique.
Plate V shows an interpreted schematic of the hydrothermal reservoir
based upon r e s i s t i v i t y contrasts shown on Plate IV.
Areas interpreted t o
contain gravel saturated w i t h thermal waters as well as areas containing the
conduits f o r these waters have been denoted.
Thermal waters encountered i n
several shal low d r i l l holes support the assumption t h a t the h o t f l u i d s may be
associated w i t h areas of low apparent r e s i s t i v i t y .
The evidence of faulting
a s interpreted from model i n g of the dipole-dipole observed apparent resist i v i t y d a t a i s therefore particularly significant since these structures may
be the conduits f o r the thermal fluids.
Shown also on t h i s Plate are loca-
tions of interpreted f a u l t s taken from evaluation of the Bouguer gravity d a t a .
SUMMARY
8
T h i s r e p o r t presents an i n t e r p r e t a t i o n o f t h e geophysical d a t a gathered
i n the Colado geothermal area.
fran several sources.
The d a t a package described herein was acquired
A t this point i t i s f e l t t h a t a d d i t i o n a l testing of the
geothermal potential i n the Colado area will require additional intermediatedepth d r i l l i n g .
8
Judicious selection of these d r i l l s i t e s can be made through
evaluation of the many d a t a sets a v a i l a b l e , not only i n this report b u t those
previously evaluated and released under separate cover.
There can be l i t t l e
doubt t h a t the thermal f l u i d s noted i n the Colado geothermal area are rising
fran great depths along structurally controlled conduits.
Because d r i l l hole
14-22 i s i n the center of the thermal anomaly and since structural
25
,
i n t e r s e c t i o n s based on i n t e r p r e t a t i o n o f g r a v i t y and d i p o l e - d i p o l e r e s i s t i v i t y
I
data occur near t h i s d r i l l hole, i t i s concluded t h a t t h i s area p r o v i d e s t h e
g r e a t e s t p o t e n t i a l f o r i n t e r s e c t i n g one o f t h e s e c o n d u i t s w i t h an
i n t e r m e d i a t e - d e p t h d r i l l hole.
i
ACKNOW LE DGEME NTS
The e v a l u a t i o n o f t h e geophysical data c o n t a i n e d i n t h i s r e p o r t was made
a v a i l a b l e w i t h funds p r o v i d e d by t h e Department o f 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 D i v i s i o n , U n i v e r s i t y of
Utah Research I n s t i t u t e under c o n t r a c t number DE-AC07-80ID12079,
0
as p a r t o f
t h e I n d u s t r y Coupled Case Study Program.
Special thanks a r e given t o Dawnetta B o l a r i s and K i e t h N. Thompson who
0
p r o v i d e d d r a f t i n g e x p e r t i s e and t o H o l l y Baker and Karen Wallwork who
p a t i e n t l y typed t h i s r e p o r t and i t s r e v i s i o n s .
Thanks a r e a l s o g i v e n t o those
members o f ESL s t a f f who p r o v i d e d a c a r e f u l r e v i e w o f t h i s r e p o r t ' s contents.
REFERENCES
Campbell, W. H., 1959, Studies o f magnetic f i e l d m i c r o p u l s a t i o n s w i t h p e r i o d s
o f 5-30 seconds: Jour. Geophys. Research, v. 64, p. 1819-1826.
Christensen, 0. D., 1980, Geochemistry o f t h e Colado geothermal area, Pershing
County, Nevada: Univ. o f Utah Res. Inst., E a r t h Science L a b o r a t o r y
r e p o r t 39, 31 p.
c3
E l ectrodyne Surveys, 1978, An E l e c t r i c a l R e s i s t i v i t y Survey o f Col ado Hot
Springs Prospect, Pershing County, Nevada: Volumes I 81 I 1 submitted t o
G e t t y O i l Company: E a r t h Science Laboratory o p e n - f i l e re1 ease
(NV/COL/GOC-1)
Garside, L. J . , and S c h i l l i n g , J. H., 1979, Thermal Waters o f Nevada:
Bur. Mines and Geol., B u l l . 89, 115 p.
8
Nev.
G e t t y O i l Company, 1979, Temperature Logs from Shallow Depth D r i l l Holes:
E a r t h Science Laboratory o p e n - f i l e r e l e a s e (NV/COL/GOC-3)
26
K i l l p a c k , T. J. and Hohmann, G. W., 1979, I n t e r a c t i v e d i p o l e - d i p o l e
r e s i s t i v i t y and I P modeling o f a r b i t r a r y two-dimensional s t r u c t u r e s :
Univ. o f Utah Res. Inst., E a r t h Science L a b o r a t o r y r e p o r t 15, 120 p .
Mackelprang, C. E., 1980, I n t e r p r e t a t i o n of a D i p o l e - D i p o l e E l e c t r i c a l
R e s i s t i v i t y Survey, Colado Geothermal area, Pershing County, Nevada:
Univ. o f Utah Res. I n s t . , E a r t h Science L a b o r a t o r y r e p o r t 41, 25 p.
M o r r i s o n , R. B., 1964, Lake Lahontan: Geology o f Southern Carson Desert,
NV: U.S. Geol Survey, Prof. Paper 401, 156 p.
.
Schlumberger, 1972, Log I n t e r p r e t a t i o n , Vol. I - P r i n c i p l e s ; 113 p.
S i b b e t t , B. S., and B u l l e t t , M. J., 1980, Geology o f t h e Colado geothermal
area, Pershing County, Nevada: Univ. o f Utah Res. I n s t . , E a r t h Science
L a b o r a t o r y r e p o r t 38, 34 p.
Wahl, R. R., 1965, An i n t e r p r e t a t i o n o f g r a v i t y d a t a from t h e Carson Sink
Area, Nevada: Rept on Student Research P r o j e c t , Dept o f Geophysics,
School o f E a r t h Sciences, S t a n f o r d U n i v e r s i t y .
.
8
.
Yungul, S. H., 1966, T e l l u r i c sounding - A m a g n e t o t e l l u r i c method w i t h o u t
magnetic measurements: Geophysics, Vol. X X X I , No. 1, Feb., p. 185-191.
27
SE
NW
400
8.00
12.00
16.00
20.00
24.00
28.00
32.00
36.00
40.00
FT ( X IO3)
OBSERVEO=O
CALCULATED= X
A'
A
n
AP- - 0 . 6 g m k c
X
U
I-
LL
FT
(x
Figure
103)
11
GRAVITY PROFILE A-A'
COLADO KGRA, PERSHING COUNTY, NEVADA
44.00
NW
SE
0
0-
w
8-
cri
a
- $-
- 0
x
W
-J
Q:
8z*
0
2L
8.
oi 0.00
I
400
I
. 0.00
I
I
I
I
I
1
I
I
I
I
I
1
I
12.00
16.00
20.00
24.00
28.00
32.00
36.00
40.00
44.00
48.00
52.00
56.00
60.00
1
60.00
OBSERVED=O
C A LCUL AT€ O=X
0
9
QD
A P = -0.6gm /CC
0
4
yo.00
I
I
I
1
I
I
I
I
I
I
1
I
I
I
4.00
8.00
12.00
16.00
20.00
24.00
28.00
32.00
36.00
40.00
44.00
48.00
52.00
56.00
FT
.
(x
Figure
103)
12
GRAVITY PROFILE B-B'
COLADO KGRA, PERSHING COUNTY, NEVADA
NW
S€
OBSERVED=O
CALCULATED=X
C'
C
#
n
M
0
SURFACE
9
0
-t
AP=-0.6gm/cc
X
v
I-
LL
0
8
0 0.00
4.00
8.00
12.00
16.00
FT
20.00
( x to3)
Figure
24.00
28.00
32.00
13
GRAVITY PROFILE C-C'
COLADO KGRA, PERSHI"
COUNTY, NEVADA
36.00
Plate I
CORRELATION OF MAP UNITS
, /TIb,
1-TpKpF]Quaternary
-
Unconformi t y
!
;
.I'
Tertiary
Unconformi t y
El
Unconfonni t y
,A;
T.
28
N.
Mesozoic
T.
!8
N.
DESCRIPTION OF MAP UNITS
-
[TI
Humboldt R i v e r channel and flood p l a i n .
F]
Landslide deposits.
,
F
l
A l l u v i a l fans and colluvium,
Fl
Wind-deposited sand and s i l t , a c t i v e and i n a c t i v e , f i l l s v a l l e y s
i n Humboldt Range and reworks Lahontan sediments.
Lake Lahontan deep water deposits.
Fl
-
Lake Lahontan shore deposits, beach and deltas.
T e r t i a r y u n i t s n o r t h o f Coal Canyon
i
I
Ts
I
Tuffaceous mudstone and minor sand and gravel.
I
Tlr
I
Lacustrine limestone w i t h interbedded c l a s t i c sediments.
Pink non-welded ash-flow c o n t a i n i n g a few a l t e r e d f e l d s p a r
phenocrysts, d e v i t r i f i e d glass shards, and fine-grained
secondary q u a r t z between t h e shards.
F]
F
I
Alluvium, c o n t a i n i n g cobbles o f ash-flow t u f f i n a c l a y and
s i l t matrix.
R h y o l i t e breccia dikes
contain
[TIa glassy m a t r i x and c u t T t .
F
l
fragments o f ash-flow t u f f i n
White,
phenocrysts.
welded ash-flow t u f f , c r y s t a l poor w i t h a few q u a r t z
R h y o l i t e s i l l s and dikes, c r y s t a l poor, s t r o n g l y f l o w banded.
Some dikes are feeders t o T t and grade i n t o p y r o c l a s t i c dikes.
..
F l
Fl
F]
Coarse conglomerate c o n t a i n i n g c l a s t s o f 1imestone, q u a r t z i t e
and andesite i n a sandy matrix.
Andesite lava flows which c o n t a i n small p l a g i o c l a s e and a l t e r e d
mafic phenocrysts. The flows are dark g r a y t o o l i v e .
Uasalt s i l l w i t h a diabasic texture.
b u t i t s age i s unknown.
The s i l l i n t r u d e s J R s
T e r t i a r y u n i t s south o f Coal Canyon.
R h y o l i t e lava flow, c r y s t a l poor, d e v i t r i f i e d .
p]
l
-F
R h y o l i t e i n t r u s i v e dome o r plug, y e l l o w i s h brown, f l o w banded
felsite.
P y r o c l a s t i c deposits, i n c l u d e p e r l i t e s , minor ash-flow tuff, and
t u f f o r ash a l t e r e d t o clay.
-
r
l
D i o r i t e , greenish gray and medium-grained.
It i s tentatively
assigned a Jurassic age based on l i t h o l o g i c s i m i l a r i t y t o
age dated rocks t o t h e south (Speed, 1976).
Lovclock Formation, t h i c k beds o f gray limestone w i t h minor
shale beds (Speed, 1974).
Auld Lang Syne Group
Thick beds o f l i g h t gray t o t a n limestone, gray o r t h o q u a r t z i t e ,
and brown mudstone. The 50 t o 100 feet t h i c k limestone beds
d i s t i n g u i s h t h e sequence from t h e t h i n limestone beds i n t h e
p e l i t e sequence (J'A s, JT? 1, JT?4).
I=]
T.
27
N.
'I
2
N
Dark gray lenses o f limestone w i t h i n t h e p e l i t e
(JR 5 ) .
1J)lqJ
Orthoquartzite, gray t o o l i v e o r reddish brown, fine-grained
quartzite.
IJ..I
Slaty-shale, mudstone and minor s i l t s t o n e beds. The shale which
grades t o s l a t e i s t h i n l y bedded and weathers tan. The mudstone
i s medium-to dark-brown and p o o r l y bedded. Thin a r g i l l a c e o u s
s i l t s t o n e beds o f l i m i t e d e x t e n t a r e present w i t h i n t h e slates.
/,
[
T
I
-I.I.b]
S i l t s t o n e , clean, well sorted s i l t s t o n e t o very f i n e sandstone,
weathers t o y e l l o w and t a n tones, occurs o n l y i n detached t h r u s t
p l a t e . Assigned a T r i a s s i c age by Speed (1976).
Limestone s o l u t i o n b r e c c i a exposed a t the base o f t h r u s t sheets.
The upper zone i s an o l i v e gray c o l l a p s e breccia. The lower
zone contains l a r g e blocks of f o l d e d gray limestone. The age o f
t h e limestone i s unknown b u t i t seems t o underly t h e T r i a s s i c
s i 1 tstone.
EXPLANATION OF MAP SYMBOLS
0
/
,/
/
Fault, dashed where i n f e r r e d , d o t t e d where covered
/)*
Thrust f a u l t , dashed where i n f e r r e d
b
Breccia zone
b
A&
h
SCALE 1:24,000
EARTH SCIIIENCE
LABORATORY
'
..
I
--~~
io00
I /2
0
I MILE
1
1000
2000
3000
4000
5000
WOO
7000 FEET
0
c.-
I
.5
0
Contact, dashed where approximate
0
'
cv
Calcite vein
qv
Quartz v e i n
I KILOMETER
4
5s
UNIVERSITY of UTAH
RESEARCH INS TI TU TE
Plate I
GEOLOGY MAP OF THE COLADO AREA
PERSHING COUNTY, NEVADA
GEOLOGY B Y BRUCE S. SIBBETT, 1980
S t r i k e and d i p o f bedding o r compaction f o l i a t i o n
0
15-21
X
r
APPROAIMATE MEAN
DECLINATION, 1970
E
Thermal g r a d i e n t h o l e
Prospect p i t
Adit
Shaft
PLATE I
E X P L A N A T I O N
IGH- 1
CALIPER
NEUTRON POROSITY
DENSITY POROSITY
INCHES
K LIMESTONE
X LIMESTONE
I5
30
0
0
45
SCHLUMlERGE@LOO
100
RESISTIVITY
SPONTANEOUS
POTENTIAL
GAMMA RAY
GRAMS/CC
2.0
2.5
OHM-M
MILLIVOLTS
API UNITS
60
3.0
SCo&UYIERGfRCOMPENSATED
DENSITY LOG
L
200
BULK DENSITY
10
1000
100
SCHLUMIEROE@DUAL INDUCTION
SPHERICALLY FOCUSED LOG
-
400
rr:
w
2;
bl
I
No sample
SCHLUMIERGtR LOG
Argillaceous siltstone
400
4
I
200-
zl
.-a
E
PI
E
t
SCHLUMIE@Gt@
LOG
200
-
v1
2;"
w
100
GEOLOGY
.-0
800
EPI
w
n
300
IO00
-_
-
1200
400
-
1400
V
-
161 2
DRILL RATE
TEMPERATURE
FT/HR
100
'F
200
0
NEUTRON POROSITY
K SANDSTONE
INCHES
100
0
20
40
METERS/ HR
CALIPER
200
IS
1
60
50
100
I P SYllH LOO
400
600
800
MICROSECONDS/METER
UNIlEO WIRELINE
LOG
SCMLUMIC@O€RIO@EHOLE
COMPENIAlEO SONIC LOO
llPII0
400
I-
w
w
h
a
E
PI
600
W
PI
n
w
800
I
1000
1200
MICROSECONDS/ FT
100
200
?&a
BULK DENSITY
RESISTIVITY
GRAMSICC
OHM-M
1.5
SPONTANEOUS
POTENTIAL
GAMMA RAY
MILLIVOLTS
; 100
API UNITS
100
I
GEOLOGY
200
200
*C
200
SONIC
300
I
L
t
SCHLUMIE@GE@
COMPENSATED
DCNSITV LOG
t
SCHLUYIE@OE@
DUAL
INDUCTION SPHE@ICALLV
FOCUSED LOG
ii
L
L
SCULUMIt@G€@
LOG
RSF
PLATE II
h
EARTH SCIENCE
LABORATORY
UNlVEffSIlY of U l A n
MSEARCH I N S l I l U l E
COMPOSITE
of
LOG
GEOTHERMAL WELLS ICH-1 and IGH-2
COLADOILGRA
?ershhg County Nevada
JANUARY, 1901
111: 31Vld
r,oc
009
'3€ € 'tl
I
'3Z€:'CI
I
'3CE'CI
lob
0
°
*
1
4
-L
a,
0
0.
"
BZ
E
1
+
- ,oz 009
,oz 009
"
62
1
4
-L
a,
0
-.
N
0,
0
13lVld
\
R, 32 E .
R. 33 E .
PLATE E
b
T.
28
N.
e78-24
T.
28
N.
'40° IS'
~
--
40' 15'-
71-36
*5-8
* 7-12
EXPLANAITIOF\J
(OHM-M)
4-16.
PSS
5 1 PSlO
THHMAL GRADIENT HOLE
f.
27
N.
T.
27
N.
7-4
PLATE ISl
INTE R'PRETED
ELECTRICAL RES ISTlVlTY 01STRIBUTION
at a DEPTH of 1000 FEET
h
COLADO GEOTHERMAL AREA
EARTH S(CHIEN<CE
LABORATORY
PERSHING COUNTY, NEVADA
UNIVERSITY of UTAH
RESEARCH INSTITUTE
SCALE 1:24,000
I
R.32 E.
R. 33 E.
-.IC'
->
-
12 3"9--5-l
\
I
R. 3 3 E .
R. 32 E.
I
I
PLATE 9:
17-24.
r.
18
N.
- 40O15'
40' 15'
0
17-36
5-8
0 1-12
EXPLA N A ~ O N
Deep low resistivity zone
...I(Possible
deep reservoir area)
..................
..........
...........
.............
..........
.......
...........
..........
..........
.......
Shu//ow low resistivity zone
4-?6
(Possible shallow plume)
Probable feeder zones for
thermal fluids
8
9-34
a
TH€RMAL GRADKNT HOLE
x<
PLATE I
NTERPRETED SCHEMATIC
of HYDROTHERMAL RESERVOIR
(FROM RESISTIVITY AND GRAVITY DATA)
h
COLADO GEOTHERMAL AREA
EARTH SCIENCE
LABORATORY
PERSHING COUNTY, NEVADA
UNIVERSITY o f UTAH
RESEARCH INSTITUTE
SCALE I: 24,000
1
R . 3 2 E.
R . 3 3 E.
T.
27
N.