:f.
:j:'~~---"
-.,. ...
•
"~".....~:.-:-':.
.....::~:.-:~~: -
._.
."
~.
.,.:.£1 aron
...
~L..l1acl<e 1prang
.~~;-~.--~ -~:.-......:":--
_. . .
---....-
-
,...
.
MASTER
September, 1980
•
--_ ..
;2;~,~":':-· ~~
. Prepared for
u.S. Department of Energy
Division
Geothennal Energy .
of
'... . -<. ...;:...
---.--
-...--...::
~~-..:~:=~- .-:.~.-::~~~~
lIl~'rn~~Ufio'~ UF T::;~!:Gct!=;;:-J;T tSulJH~!TU~~:·i
.---;,;;..
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DOE/ 10/ 12079-11
ESL-41
I~TERP~ETATION OF A DIPOLE-DIPOLE ELECTRICAL RESISTIVITY SURVEY,
COLADO liEOTHERMAL AREA. PERSHING COUNTY, NEVADA
by
Claron E. Mackelprang
September, 1980
•
•
EARTH SCIENCE LABORATORY DIVISION
UNIVERSITY OF UTAH RESEARCH INSTITUTE
420 Chipeta Way, Suite 120
Salt Lake City, UT 84108
PREPARED FOR DEPARTMENT OF ENERGY
DIVISION OF GEOTHERMAL ENERGY
UNDER CONTRACT NUMBER DE-AC07-80ID12079
bISCLAIM@R
This oo'ok was prepared as an account of work sponsored by an aQeOcy of the United States Government.
Neither the United States Government nor any ageoc:y thereof, not any of n~i! ,employees. makes any
warranty. express or implied, or assumes ,ny legal liability or responSibility for ~ accurac:;
completeness 01 u.rulness of any information, 8Jlparatus, product, or ~ disclosed, ..
represents th~ its use would not infringe privately owned rights. Reference herem to &nY, specific
commercial product, process. or service by trade name, trade,",fJ<, ~facturer. ,or ome;:se
not necessarily constitute or imply its endorsement, recommendatu)f't, or f.'Ionng by .
States Government or any agency thereof. The views and opinions of authol's expressed herein do not
necessarily state or reflect those of the United Slates Government Of any agency thereof.
u!:
~
l'f'';''';''~a-" ',' , ... ,
:.1/;.) It"all' It!,~ Iii
: .:i'; I1U!..l'I"id
r 13 UliL/MlTfD
NOTICE
This report was prepared to document work sponsored by the United States
Govermnent.
Neither the United States nor its agent, the United States
Department of Energy, nor any Federal employees, nor any of their contractors,
subcontractors or 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.
NOTICE
Reference to a company or product name does not imply approval or
recommendation of the product by the University of Utah Research Institute or
the U.S. Department of Energy to the exclusion of others that may be suitable.
DISCLAIMER
This book. 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 Of implied, or 1SSUm8S any legel liability or responsibility for the accuracy,
completeness. cy usefulness of any information, apparatus, product. 0( process disclosed, Of
represents that its USB would not infringe priY8tely owned rights. Reference herein to any specific
commercial product, process, Of service by trade nllme. trademark. manufacturer. or otherwise, does
not necessarily constitute or imply its endorsement. recommendation. Of favotiog by the United
States Government or any agency thereof. The views and opinions of ....thers expressed herein do not
necessarily state OK reflect thOle of the United States Government or any agency thereof.
--------------~
- _...._ _._.
TABLE OF CONTENTS
ABSTRACT • • • • • • • • • •
INTRODUCTION •
•
• • • • • • • • • • • • • ., • • • • •• 1
• • • • • • • • • • • • • • • • • • • • • • • • • • • •
2
GENERAL GEOLOGY . . . , • • • • • • • • • • • • • • • • • • • • • ••
ELECTRICAL RESISTIVITY SURVEY . . . . . . . . . . . . , . . . . . . .
Survey Procedure • • • • • • • • • • • • • • • • • • • • • • • •
Survey Results • • • • • • • • • • • • • • • • • • • • • • • • •
L;ne D ••••• • • • • • • • • • • • • • • , • • • • • • •
Line A ••• • • • • •• • ••• • •• • ••••• • •• • •
Line C • • • ••• • • • • • • • • • • • • • • • • • • • • •
4
Line E • • • • • • • • • • • • • • • • • • • •
Line S • • • • • • • • • • • • • • • • •
i
•
•
5
5
7
7
9
11
~
• • • • • • 13
•
•
•
•
•
•
•
13
DISCUSSION • • •• • • • • • • • • • • • • • • • • • • • • • • • • • • 17
ACKNOWLEOGEMENTS • • • • • • • • • • • • • • • • • • • • • • • • • • • 18
REFERENCES • • • • • • • • • • • • • • • • • •
• • 19
APPENDIX - Computed Resistivity and Interpreted Sections. • • • • • • 20
ILLUSTRATIONS
· . . . ... . .
..... , .
Figure 1
Location Map ••
Figure 2
Line D Observed Apparent Resistivity/Interpreted Section 8
Figure 3
Line A Observed Apparent Resistivity/Interpreted Section 10
Figure 4
Line C Observed,Apparent Resistivity/Interpreted Section 12
figure 5
line E Observed Apparent Resistivity/Interpreted Section. 14
figure 6
LineS Observed Apparent Resistivity/Interpreted Section 15
Plate I
Resistivity Survey line Location and Geologic Base Map. in pocket
Plate II .
0
• • • • • • • • • • • • .3
Interpreted Electric;:al Resistivity Distribution at a Depth
. of 1000 feet. ••• • • • • • • • o·
in pocket
0
0
•
•
0
•
<II
•
•
•
0
0
•
,0 1n pocket
0
••
Plate III
Interpreted Schemat 1c of Hydrothermal Reservoir
FigureA1
line D. Computed Resistivity/Interpreted Section.
•
0
21
Page
•
Figure A2
Line A Computed Resistivity/Interpreted Section ••••• 22
Figure A3
Line C Computed Resistivity/Interpreted Section ••••• 23
Figure A4
Line £ Computed Resistivity/Interpreted Section ••••• 24
Figure A5
Lirte B Computed Resistivity/Interpreted Section.
• • 25
ABSTRACT
An electrical resistivity survey in the Colado geothermal area, Pershing
County, Nevada has defined areas of low resistivity on each of five lines
surveyed. Some of these areas appear to be fault controlled. Thermal fluids
encountered in several drill holes support the assumption that the hot fluids
may be associated with areas of low resistivity. The evidence of faulting as
interpreted from modeling of the observed. resistivity data is therefore
particularly significant since these structures Inay be the conduits for the
thermal fluids.
Sub-alluvial fault zones are interpreted to occur between stations 0-5
N~
on Line 0 and on Line A·between stations 4 NW and 4 SEe Fault zones are also
interpreted on Line C near stations 1 NW, 1 SE, and 3 SE, and on Line E
between stations 2-4 NW and near 1 SEe
No faulting is evident under the
alluvial cover on the southwest end of Line B.
A deep conductive zone is noted within the mountain range on two
resistivity lines. There is no definite indication that thermal fluids are
associated with this resistivity feature.
1
INTRODUCTION
The Colado geothermal area is located in Pershing County apprQximately 7
miles northeast of Lovelock, Nevada (Figure 1). The main area of geothermal
exploration is alQng the
we~t
flank of the West !1umboldt Range, lying between
the railroad sidings of Kodak and Woolsey (Plate 1), a distance about 4.5
mil es.
The Earth Science Laboratory Division, University of Utah Research
Institute (ESL/UURI) undertook
~n
electrical resistivity survey in April, 1980
to characterize the electrical resistivity distribution of the resource area
in support of the Getty Oil Company geothermal exploration effort. Their
interest in the geothermal potential of the area was stimulated when, while
drilling on mining claims nearby, they encountered a light flow of steam and
thermal waters (Wayne Shaw, personal communication).
An earlier geophysical survey
desi~ned
specifically for the evaluation of
the geothermal potential in the Colado area was performed in 1977 for Getty
Oil Company by Electrodyne Surveys of
~parks,
Nevada. Numerous techniques
(AMT-MT, TDEM, Telluric, Electr1cal Resistivity, Gravity and Ground Magnetic)
were applied with mixed results.
A comparison of this d1pole-dipole resistivity survey with the
Electrodyne resistivity surveys shows the two data sets to be incompatible.
Ill'
The dipole-dipole data are more definitive in delinating not only areas of low
apparent resistivity but structurally controlled areas as well. The data sets
from the survey by Electrodyne are not supportive of each other; technique
application and processing errors are involved, and Electrodyne notes discrepancies in their report.
. 2
r----L ______ ,
Elk"
I
I
Pershing Co
•
•
I
i
.
~STUD
or-
I
•
L__~
~RE~
•
I
L. __ _ 'f,'!.!.••.1!!~J
•
o II
10 10 10 40
«H
FA
i
leALE IN IIILlI
NEVADA·
Figure ,1.
Location Map
3
GENERAL GEOLOGY
The Colado geothermal area is indicated by hot water wells in alluvium
along the west flank of the West
HUI~oldt
Range. Shallow thermal gradient
holes less than 500 feet deep have encountered thermal fluids upwards of
113.50C at a depth of 250 feet.
To gain a better understanding of the geothermal environment, Sibbett
(19HO) recently mapped the geology of the West Humboldt Range (Plate I)
adjacent to the geothermal area. The fo 11 owi ng is taken from the abstract of
•
hi s report •
The West Humboldt Range consists mainly of Triassic to Jurassic slaty
shale to quartzite. of tne Auld Lang Syne Group. Carbonate rocks of the
Lovelock Formation have been thrust over the pelitic rock on the south end of
the area. Erosional remnants of Tertiary tuffs and sediments overlay the
metasediments in the range.
Several thrust faults are exposed south of Coal Canyon and a structural
break in the Mesozoic rocks exists under Coal Canyon. Several low-angle
faults occur to the north but their effect, if any, on the geothermal
occurrence is not known •
. The principal structures are high-angle faults striking north-northwest,
northeast and north-south. The horst-to-graben transition along the range
front consists of several step faults following an irregular south-to-north
4
trend.
The structural pattern noted along the west edge of the range probably
continues to the west under the Quaternary alluviuln. The thermal waters are
thought to rise along a major fault or fault system to the base of the
all uvi um.
A more detailed geologic description of the Colado geothermal area can be
found in Sibbett's (1980) report.
ELECTRICAL RESISTIVITY SURVEY
Survey Procedure
The field survey was conducted by JCW, Inc. of Salt Lake City, Utah
duri ng the peri od April 30 to May 6, 1980. The equi pment used included a
Scintrex Model IPC-7 15 Kw square-wave transrnitter utilizing time-domain mode
current
ge~eration.
The potential field was measured with a Scintrex Model
IPR-10 digital time-domain receiver. When electrical noise was severe, a
Scintrex Model IPR-8A receiver was used in conjunction with a Hewlett Packard
7155B strip chart recorder. Transmitting electrodes were buried aluminum foil
and/or steel stakes driven into the ground. The potential differences were
recorded at the surface using porcelain porous pot electrodes.
The survey (Plate I) consisted of four 1000-foot dipole-dipole 7-spreads
(7 transmitting electrodes) trending generally N550W. These are normal to
existing culture (railroad tracks. water lines. power lines, etc.) and mapped
faults.
An effort was also made to keep transmitting electrodes at least 500
feet from the cultural features.
A fifth line was oriented N27 0 E and crossed a bulge in the mountain range
•
5
opposite drill holes having higher recorded temperatures. This line used
20UU-foot dipoles to explore for a potential geothermal reservoir at greater
depth within bedrock.
Data were acquired at n-spacings 1 through 6 on all lines whenever
possible. Voltayes were recorded over several transmitted cycles at each
receiver site. These were averaged together before the computation of
apparent resistivities. A few data pOints are obviously in error in spite of
reasonable field precautions. High noise levels in the electrical signal may
be the cause. The field data are thOUght, however, to be accurate to at least
!lUS exclusive of these questionable points.
'Ii.
6
Survey Results
Plate I shows the location of the resistivity lines, superimposed on a
geologic/topographic base map of the Colado area. The observed data are shown
on Figures 2 through 6 with the interpreted resistivity distribution derived
from modeling the field data. A two-dimensional IP-Resistivlty program
developed at the Earth Science laboratory (Killpack, 1979) was used in the
. numeri ca 1 model i ng. Whil e the computed model s give a good fit to the observed
data, they are non-unique. The resistivity sections on Figures 2 through 6
are from numerical models chosen as best fits to the observed apparent
resistivity field data. Appendix Figures Al through A5 show calculated
resistivities based on these same models for comparison purposes.
Line 0
This line (Figure 2) is at the northernmost end of the geothermal area
and extends west from the range front.
It was located for close proximity to
drill holes 14-22, 13-26, and 1GB-I. these holes have the highest recorded
temperatures, to date, within the geothermal area. The observed data show a
major resistiVity discontinuity, interpreted as a fault, near station 3 NW. A
conductive zone «10 ohm-meters) also lies at depth beneath this station. A
major change in topography south of station 1 SE introduces topographic
effects in the field data.
Mode 11 ng results show that sharp contrasts (greater than a factor of 2)
in resistivity occur between stations 4.. 5 NW, 3-4.NW, 2-3 NW, and 0-:-1 NW.
These resistivity discontinuities are interpreted as faults. Only the
discontinuity near. station
o corresponds
7
to mapped structures.
-
(
"
..
LINE 0
NW8
_500
..:
~ 1000
-•
-
7
DH14-26
6
5
DH13-22
!
4
2!
3
2
I
4
3
6
7
SSE
125
/0.
25
25
125
250
I!:
Q,
Q,
500
'V
I
2000
I
1
25
1
I
780
10- Intrinsic RfJslsf/v/ty (ohm-m)
(/6/000 ft.
APPARENT RESISTIVITY - OBSERVED
NW 5
4
3
2
1
0
I
2
3
4
5 SE
~1--~I--~I~--+I--~I~--+I--~I----~'--~'----~'--~I
D
,~
_
~
P(ohm-m)
•
I
18
17
26 ,-
'.!l13
:(J ~.
-
~,.
_,.
13
II
•
10
12
34
-'IS
-
1 62
43
10
-~
7
•
•
!:)
~
~
f!2 ( 1:3 \
.~
93
-\52 •
10--L-IO
T·
()
14 •
61
20
. . -~
8
II
~6
109
96
• ·""'9~~8'
• #" - -~
• -
9'=-<,
- 9
~'
......
FIGURE 2
-e
-•
-
•
72
53
-
. " " -,31
~
~'"
--38
-
~
42
86
•
58 , -
• 6
82 -
S3
•
/~
I()
50
INTERPRETED RES1STIVITY SECTION AND OBSERVED APPARENT RESISTIVITY
LINE 0 - COLADO GEOTHERMAL AREA
PERSHING COUNTY, NEVADA
Scale 1:24,000
'V
w,
l~orthwest
of station 3 NW is a surface 1ayer about 150 feet thi ck havi ng
a resistivity of 10 ohm-meters. Beneath this lies a much thicker (1500 feet)
and slightly lOore resistive (l!:> ohm-meter) layer. This in turn is underlain
by very conductive material (5 ohm-meter) which extends downward to the limit
of detectability.
Moderately conductive rocks are indicated at depths greater than 2000
feet in the mountain range between stations 0 to 3 SEe Similar rocks, with a
resistivity of about 25 ohm-meters, are within approximately 250 feet of the
surface between stations 5 and 6 SEe
Line A
Line A (Figure 3) was located south of, but still near, drill holes 14-22
and 15-21 so that the transmitting electrodes would cover the inferred hot
zone which trends southwest from DH 14-22. The observed field data show
conductive zones averaging 5-6 ohm-meters at moderate depth overlain by
resistive near-surface rnaterial at both ends of the line. The central part of
the line shows the conductive zone nearer the surface with the resistive zone
beneath and extending to depth.
Modeling results show a thin (100 foot) surface layer with a resistivity
of 10 ohm-meters extending between.stations 1 SE and 2 NW. At 2 NW it
apparently thickens abruptly to the northwest. Directly. beneath this layer
between stations 1 SE and 1 NW is a zone of 4 ohm-meter material with a
variable thickness up to about 1000 feet.
Between stations 1-2 NWthis 4
ohlll-meter material extends down a narrow zone to a depth of approximately 1500
feet where it then continues to the northwest. Similar resistivities occur on
9
•
(
"
LINE A
NW8
0
500
-..
a.•
-
1000
7
6
-l..
10
5
4
DH14-22
I
0
2
3
2
3
4
15
.:
I:
2000
4
4
I
"0
35
25
I
'I
1
3000
500
4
0.
"0
I
1
1000
10= Intrinsic Resistivity (ohm-m)
a= 1000 ft.
.....
o
APPARENT RESISTIVITY - OBSERVED
NW5
4
3
2
I
0
•
2
3
4
59E
I~--~I----+I~~I~~+I--~I~--~J----~J--~I----~I--~I
_ /1 0
I\V'
•
1c0
•
10~
to--et'" •
•
P(ohm-m) 4
•
5
•
5
•
FIGURE 3
•5
6
•
7
•
6
•
6• •5 --JJI•
.
7
.
•
•
1;
"&~~
t2
889
~.
IV
t8
•
12
•15•
19
• (33) • 9
. ... •
13
.../
10~
;(.
.
5
6
\0 .
4
•
17
13 •
•
!5
5
•
6
•
•
6
•
5
•
14-- 15
.~IO
8.-"'r 6
•
(9)
6
•
•
•
INTERPRETED RESISTIVITY SECTION AND OBSERVED APPARENT RESISTIVITY
LINE A - COLADO GEOTHERMAL AREA
PERSHING COUNTY, NEVADA
Scale I: 24pOO
-E
f
-•
the southeast
end~
coming to within approximately 600 feet of the surface
between stations 3-4· SEe A more resistive material (15-35 ohm-meter) occurs
near surface between stations 1 and a SEe
A 15 ohm-meter body also extends to
depth beneath and adjacent to the 4 ohm-meter zone noted on the northwest end
of the line.
Because the projected trend of high temperatures between drill holes
14-22 and lU-34 crosses Line A near station 0, it could be inferred that the
conductive (4 ohm-meter) near-surface layer is indicative of shallow thermal
fluids.
Lending support to this interpretation is the shallow hot water
aquifer shown on a log of drill hole IGH-l (Getty Oil Co., personal letter).
The conduit for these fluids appears to lie between stations 1-2 NW.
line C
Tnis line (Figure 4) extends northwest from Coal Canyon and passes near
drill holes 8-34, 9-34 and 10-34. The field data show a conductive « 5
ohm-meter) zone enclosed by slightly more resistive (5-10 ohm-meter) material
at depth beneath stations 0-3 SEe DH 9-34 is located just south of Line C
between stations 0-1 SE and is centered on the conductive zone.
Model results show a
cond~ctive,
approximately 2 ohm-meter, zone at depth
which is enclosed by 10 ohm-meter.materia1.
depth of approximately 1000 feet.
This conductive zone occurs at a
The temperature log of DH 9-34 suggests a
possible heat source nearby •. Thus, the 2 ohm-meter zone may indicate the
presence of conductive thermal fluids.
No faults are indicated by sharp
resistivity contrasts in the data however, so the high temperatures noted are
likely due to a pluming effect of thermal fluids· down the hydraulic gradient
11
.c
(
(
LINE C
NW 8
7,
6
5
4
3
DH10-34
2
DH9-34
DH8-34
3
2
6
7
8 SE
o~--~--~~--9---~--~--~~--~~r&--~~--e---~-L~~~&---~---&---eo
eoo
10
1000
10
-•
soo
.:
: 2000
e-
I
Go
V
-..
Ii
2
I:
Go
-
2
rJ
3
1000 .
10= Infrln6ic R.6i6tlvlfy (ohm-m)
0= 1000" .
....
N
APPARENT RESISTIVITY - OBSERVED
N W !5
4
3
2
0
2
3
4
!5 SE
~I--~'----~'--~'~--+---~'~--+----rl--~I----~I--~I
1~ 1~
6
7.59
10- 11
•
9
FIGURE 4
1.;
.'
•
_i
6
7
'
rK s
6 ''''', 8
5'-:'5) 0 1
8
'
9
;:..
6
9y,·.
. . .
9
0yO
,0-'
P(ohm-m)
'
:/,8
•
~
3
4
•
I
8
'7'
0-;-0
10
s -!....
6
•
2
4 • ~O\ 9
•
3 • !5 ~ 6 -
2
•
34'S
. . . . . ."'"
•
3
4
•
•
'
2
3
•
!
~
•
:
•
:
7. 5
•
~
INTERPRETED RESISTIVITY SECTION AND OBSERVED APPARENT RESISTIVITY
LINE C - COLADO GEOTHERMAL AREA
PERSHING COUNTY, NEVADA
Scale 1:24,000
within an aquifer.
line E
This line (Figure 5) is the southernmost line of the survey. Station 0
lies just north of drill hole IGH-2 (formerly DH 3-10). The field data
indicate a resistive surface layer extending approxilMtely from stations 3 NW
to 5 Sf and appearing thickest in the station interval 1 to 2 SEe Very
conductive material is present at a depth of approximately 2000 feet and
extends the entire length of the line.
to the surface
on
This conductive material
COil~S
closer
the northeast end of the line. Faulting is suggested by the
field data between stations 5 and 6 SE and is supported by geologie mappiny.
The model results show 25 ohm-meter material at the surface between
stations 1 to 3 SEe This resi.stive body is overlain by material more
conductive (10 ohm-meter) both to the northwest and southeast. A conductive
(2.S ohm-meter) layer occurs ata depth of about 2000 feet and extends both
laterally and downward to the limits of detectability. The very conductive
zone between stations 5 a.nd 6 SE is interpreted as higher porosity and/or
alteration probably
associat~d
with faulting.
line B
This line (Figure 6) differs from the other lines in that lOOO-foot
dipoles are used.
The observed resistivity values represent the integrated
effect of a larger volume of earth,. both horizontally and vertically, while
. the spatial resolution of the interpreted section is only half that of the.
lOOO-foot dipole lines.
13
(
(
(
.,c
(
(
(
LINE E
DH7-4
5
NW8
0
4
2
3
aSE
2
0
~oo
..
-.: 1000
5
If:
.-
a.
;2000
10
15
-"--
1
2.5
2.5
j
I
I
L_
~o
-
10 -Intrinsic Resistivity (ohm-m)
0=/000 It.
APPARENT RES1STIVITY - OBSERVED
3
2
0
2
3
4
~
1~--~1----+1--~'~--+---~1~--~---+'--~1~--+1--~1
4
10 ___ 9
.• 5 •
5
.~.
~.
!>
.
FIGURE 5
~
8
•
•
tz,O
~8 \... 23
21 . / 19
•
•
...
• .
U
18
I~
18
~.
•
•
~,.
SE
If)
17
I~ ,.
• 10
/
~
. ,'4-./11
. - - y /3
. .
.
:1,
y~
10
.
.
.
.-----. . . . . .
•
•
•
•
•
•
4
.
~
.8~"
-
10-·~·
8
8
.
11
..
4
3
•
~~
4
~
6
•
-~ ~
~ ~
#~'.
8
-
6
•
4"").
2
(13)
'.~.'\.
)0.-"'<'
..
~
4
)-~
6
i
•
5
INTERPRETED RESISTIVITY SECTION AND OBSERVED APPARENT RESISTIVITY
LINE E - COLADO GEOTHERMAL AREA
PERSHING COUNTY, NEVADA
Scale 1:24,000
6:
ca.
1000
NW ~
-..e
•
"
tL __ JI
LJ
3000
10
(
(
(
•
(
OJ
LINE B
1
DHIGH2
SW8 .
7
6
1
OH8-34
0
4
3
2
0
3
4
.5
6
7
8NE
o~~:d~~~=c~~~--~~=r~~~~,~.,~i--~-+~~~O
w
~
~
"" 1000
::~ZOOO
.....a 3000
eo<)
A
5
25
25
'-----~
~~----------------------------------------------------------------------~
10= Intrinsic Resistivity (ohm-m)
t
....
1000 -3
2000
a=2000ft
APPARENT RESISTIVITY - OBSERVED
.....
U1
SW5
4
I
3
I
2
I
I
I
I
0
I
2
I
I
,-...~--
3
I
,51~O~
4
I
.
.
.,
".'
.
.
.
.
.
.
.
.
.
.
. . . . . .,. . . .
0 171
8
4t01
::
~.
5~~
6
(48)
, 5~
•
p(ohm-m)
2
4
3
2
•
3
•
3
2
•
•
FIGURE 6
I
.
~
2
5NE
I
•
3
3
4
6·
3
4
•
5
It,·
;J
• 0
""
•
~
4
2·
'49
II
II
118
'26
115
82
112
98
~ ·'29~·
-;; •
• 10t·,~NR •
•
183
'45"142_146--.'1'5
13
~~..
5..v-!
13 •
164
•I-
(;)
.....
o·
23
•
•
<'~
..,
52
150
III
67· 100
•
"'0
INTERPRETED RESISTIVITY SECTION AND OBSERVED APPARENT RESISTIVITY
LINE B - COLA DO GEOTHERMAL AREA
PERSHING COUNTY, NEVADA
Scale 1:24,000
E
This profile trends
northeast-southwes~,
subparallel to the dominant
structure, and is more influenced by lateral (and non-two-diinensional)
yeometrywithin the earth. The line passes close to drill holes IGH .. 2 and
8-34, and between
stat i on
0
17~24
and 18-24. The range front is encountered at about
and the enti re northeast end of the l; ne crosses the range.
Topographic effects are. therefore present in the field data on this end of the
1ine •.
The model results show a major resistivity contrast, interpreted as a
fault, bet\-/e.en stations 0 and 1 SW. This appears tobe the range front fault
that separates the conductive valley fill with resistivities of 5-10
Ohm-meters from the rocks of the range which have resistivitjes upwards of
'lUG-3UU ohm-meters. The valley fill is very uniform in resistivity wit" no
anomalous contrasts indicative of buried faulting. The data of this
resistivity line do not suggest the presence of a fault extending NW out of
Coal Canyon into the valley_
Several resistivity contrasts, interpreted as faults, are noted on the
northeast end of the line.
Near-surface rocks in this area have
resistivities averaging .about.200 ()hm-meters for the most part. The presence
of fairly conductive (25 ohm-meters)
a~eas
in the mountain range is of
interest •. The area at depth between stations 0-2 NE is coincident with the
conductive area noted at depth on Line 0 between stations 1 to 3 Sf; the
significance of this conductive area is not presently known. - The 25
. 'P,
ohm-meter body between stations 4-:-SNE maybe due in part to latera 1 .effects
of alluvium !=lose to the line.
16
DISCUSSION
Plate II is an overlay to Plate I and shows the electrical resistivity
distribution at the depth of approximately lUOO feet for each of the five
lines.
This plate shows the sharpresistivity contrasts and their locations
from which the faulting is inferred.
The data source for Plate II is the
computed mOdels shown as Figures Al through AS.
with mapped structures within the mountain range.
There is good correlation
The detection of
suballuvial faults away from the mountain front is of particular importance,
for, while these faults may have been suspected, their approximate location
was not known.
Although shown as separate faults, several could be part of a
single fault zone and it must be understood that the locations of these faults
as shown on Plate II are to be considered as close approximations only.
They
are necessarily subject to the sensitivity of the dipole spacing used as well
as the non-uniqueness of the computer modeling technique.
Plate III is an overlay to Plates I and II.
It shows an interpreted
schematic of the hydrothermal reservoir based upon resistivity contrasts.
Areas interpreted to contain gravels saturated with thermal waters as well as
areas containing the conduits for· these waters have been denoted •
..
17
ACKi~OWLEOGEMENTS
This survey was completed with funds provided by the Department of
Energy, Division of Geothermal Energy, to the Earth Science laboratory
Uivision, University of Utah Research Institute under contract number
UE-ACU7-tmIU12079, as part of the Industry Coupled Case Study Progra:n.
Special thanks are given to Dawnetta Bolaris who provided drafting
expertise and to Holly Baker who patiently typed this report and its
revisions.
Thanks are also given to those Inembers of ESl staff who provided a
careful review of this report's contents.
18
REFERENCES
Electrodyne Surveys, 1978, An Electrical Resistivity Survey of the Colado Hot
Springs Prospect, Pershing County, Nevada: Volumes I & II submitted to
Getty Oil. Company: Earth Science Laboratory open-file release
(NV ICOl IGOC-l ) •
betty Oil Company, 1979, Tetnjlerature Logs fro:n Shal1m1 Depth Drill Holes:
Earth Science Laboratory open-file release (NV/COL/GOC-3).
Killpack, Terry J.,Hohmann, Gerald W., 1979, Interactive Dipole-Dipole
Resistivity and IP Modeling of Arbitrary Two-Dimensional Structures:
Univ. of Utah Res. Inst., Earth Science Laboratory report 15, 120 p.
Siboett, Bruce So, Bullett, Michael J., 1980, Geology of the Colado Geothermal
area, Pershing County, Nevada: Univ. of Utah Res. Inst., Earth Science
laooratory report 38, 34 p.
19
APPENUIX
Computed Resistivity and Interpreted Sections
20
(
(
(
(
t
(
"
NW
8
o
.... 500
...,
~
DH 14-26
6
7
~ 1000
./
'J
r.~
I ~
1.1! ~
.?t
V.1! '!l
...
'0
~.:
.5
4
&
_
6
7
8
~~~_o
rio ....
~, ",;
2 50 ~
.e.
...,
~~6
I.~~
I
'17 ,-
SE
3
2
I~
II. ~~
~
2000
a
5
<i_
-
LINE 0
DH11-22 ~IGH 1
~
i.5
t-5 00
I,~~
12~
750
10 =Intrinsic
Re~istivity
(ohm-m)
o =1000 ff.
APPARENT RESISTIVITY - COMPUTED
NW-5
I
-
-4
,
-3
,
-2
I
.
N
19
19
)(
34
11
·10
.)(
16
.)(
10
)(
ro
e
.~
42~
.31
)(
)(
11
15
lC)(
39
1
;8"
)(
-
)(
lC
11
)(
77
)(
9Z~108
91
)(
)(
70
64
~
35
lC"')(
~~
~
lC
109
lC
66
•
35
)(
5SE
I
,
(85
)(
48
51
70
)( ~
~
FIGURE Ai
~
4
,
lC
73'
11)(
3
'
133
lC
lC
16
)(
10
74 \
59
lC
2
~
lC
10
12
11
)(
10)(
11)(
)(
1
d
,.
)( )( :<)( )( )(
17
20
-1
I
60
)(
)(
73
60
lC
lC
'57
61
lC
~6~ ~
)(
\
59 .
lC
Ie
~
o
INTERPRETED RESISTIVITY SECTION AND COMPUTED APPARENT RESISTIVITY
LINE 0 - COLADa GEOTHERMAL AREA
PERSHING COUNTY, NEVADA
Scale 1:24,000
:s
8
500
-
7
6
5
4
3
~O
2
ID
2
~
4
3
/';J
I';;;
I,p
P
~
5
6
7
~
~~
I" ~.5
1000
I~
I~ ~
I;,
...
~
.~.:
E
I- 500 ~
..
II!
:2000
It
'V
4
~~
4
0-
::.15
'V
4
3000
I- 1000
10 =Intrinsic Resistivity (ohm-m)
o=/OOOff.
APPARENT RESISTIVITY - COMPUTED
N
N
NW-5
-4
-3
-2
-1
0
1
2
3
4
SSE
l~--+'--~J~--rJ----~I------~I---+J~--t~----+'----~I~~1
.
l(
<s:
"""0
6
5
K
"9
9
x~J
gY 16
14 " 1 5
~x ~i·
J2
11
7
IC K XIjK X 6 IC
18
x
13
K
IC
9
XC)
IC
X
7
x--15
x7~9'>-... Jl
5
9~
19
6 x
6
X
X
X
5
6
X
X
10
10 /
~
JC
X
5
;<10
B
6
)(
7
x
8
IC 5
"
FIGURE A 2
.«
t
LINE A
DH14-22
NW
o
«
(
(
(
(
INTERPRETED
RESISTIV1TY SECTION AND COMPUTED APPARENT RES1STIVITY
LINE A - COLADO GEOTHERMAL AREA
PERSHING COUNTY, NEVADA
Scale I: 24,000
DH 10-34
1
2,
NW
1
8
o
5
6
3
4
LINE C
DH9-34
0
DH8-34
3
4
l
2
1
1
SE
8
o
I")·
~
!.
..:
a 2000
•
.....
,.
II
1000
z:
6
5
~oo
--
«
(
(
f
f.
(
~
Ie
..
'~
~ 500
I~
3000
fo 1000
10= Intrinsic Resistivity (ohm-m)
0=/000 ft. .
N
(.oJ
APPARENT RESISTIVITY - COMPUTED
NW -5
";4
-3
-2
-1
0
1
2
3
4
5 SE
~1---+l--~l--~l~--~I---4f--~I~--~I---+I--~I---4I
x
x
~.
~--a
7.
. 7
9
.""
K
9
l0
~
10_
x
X
X
10
""",-
/x~
x
7 If:
I(
9
FIGURE A3
5
.......7.
)( 4
x
x
4
4)( S
S)( S
x
8
x,~
)(
S
)(
'-ct......... S 7'.5
4
)()()(
x
5'
4
x
4
4 )( 4
9
5
4
x
10
/
7
I(...,...-.-~'"
5
1
~J0
,0
4
X .
l(
J0 1 ) '
p(ohm.;.m)
7
)( xX
?'$.
~5
'·""9
x
S
S)( S
X
5
x
5
S)( S
)(
".
fj
INTERPRETED RESISTIVITY SECTION AND COMPUTED APPARENT RESISTIVITY
LINE C - COLADO GEOTHERMAL AREA
PERSHING COUNTY, NEVADA
Scale 1:24,000
0..
-•
."
I~
."
z:
(
('
(
(
•
(
"
LINE E
NW OH7';'4
0
8
7
6
OHIGH2
o
2
3
4
5
I
~
..
-
.J:!
tJ
i.e: '!]
:?;~
_ I nnn.
..:
Ie;: 10
.
~;;
I~
7
!) II:;
,t.
~
'I"
i/W
500
6
5
4
2
"
I~
D.
i~
....~2000
E
~oo .J:!
D.
...•
L ~.
~~.
'U
;
3 000
1000
10~ Intrinsic Resistivity
(ohm-m) ,
0=/000 ft.
APPARENT RESISTIVITY - COMPUTED
NW -5
-3
-4
-1
-2
0
1
2
3
4,
5 SE
I~~---+I--~I~--rl--~I--~'~I~-+I--~I~--+I--~I~--;1
~
J8\....
o
J(
1(
5
_J(
J(
P(Ohm-m)
4
9
6
4
J(
J(
)C
9
6
~5
J(
J(
9 \
9
12
)(
lC
8
X
~
J(
J(
4
J(
..
x
J(
5
,
J(
'"
FIGURE A4 INTERPRETED RESISTIVITY
8
)(
~
10 ~
9,
,x'"" ~
8
457
J(
x2
1 8/;'9 ; ; 6
'
J(
0
~12
5
p
:
,
2
'\
J(
J(
lC
18
9 _ x10,
x
8
y .~.
~1
lC
J(\)(
0
~yq;
rz
10
776
v
n
5-,(
~
rA
8
3
lC,
J(
lC
J(
lC
2
SECTION AND COMPUTED APPARENT RESISTIVITY
LINE E-COLADO GEOTHERMAL AREA
PERSHING COUNTY, NEVADA
Scale I: 24,000
(
(
(
(
..
l
LINE B
SW
8
DHIGH2
7
~6
DHS-34
o..
3
~
o
2
. I0
~D
500
_1000
-
4
5
I~ ~
..:
.
1!3
f;:2000I·
.:J 3000,.
0.
-
.
4000
5000I-
2
3
6
7
e
0
?( ~,
500
?rJl~
1000 ~
0.
~~
2000
APPARENT RESISTIVITY - COMPUTED
SW-5
-4
-3
-2
-1
0
1
3
4
5 NE
~1---4I--~I~·---+I--~----~--4---~---4f----I~~I
U'I
-.::~___::.--150
FIGURE A5
INTERPRETED RESISTIVITY SECTION AND COMPUTED APPARENT RESISTIVITY
LINE 8-COLADO GEOTHERMAL AREA
PERSHING COUNTY. NEVADA
Scole 1:24,000
-r.
10= Intrinsic Resistivity (ohm-m)
0=2000ff.
N
1
1.3 Pit)
4r~
I
NE
5
51 t7
~I ')
.
4-
Plate I
R. 32 E.
CORRELATION OF HAP UNITS
01
9
/
I I
Qr
/
7
QoI
Q1s
~
~
Ouaternary
Unconformi ty
~
Unconfomi ty
1
i<"..
/
~#-·rfl.,.~_'~_-"_''-'-_-_-,-
r-T-r-b'
EB
T!
~
Tertiary
rrd
01
Tal
I \"
Unconform'lty
I
I
~
Unconformity
_ _ ---,.~_
~
Jd
ravel Pft '-,J/I,-.,f:'.;r::f,.//
JI
T.
28
Jliw
N.
I J~s
T
JliQ
Jlil
ffiJ
28
N.
I >Mesozoic
~Isb
~
DESCRIPTION OF MAP UNITS
Humboldt River channel and flood plain.
Landslide deposits.
Alluvial fans and colluvium.
Wind-deposited sand and si1t9 active and inactive, fills valleys
in Humboldt Range and reworks Lahontan sediments.
Lake Lahontan deep water deposits.
Lake Lahontan shore deposits, beach and deltas.
Tertiary units north of Coal Canyon
~
Tuffaceous mudstone and minor sand and qravel.
~
Lacustrine limestone Irrith interbedded clastic sediments.
Pink non-welded ash-flow containing a fe"'l altered feldspar
phenocrysts, devitrified glass shards, and fine-Qrainerl
secondary quartz between the shards.
15'
Alluvium, containing cobbles of ash-flow tuff in a clay and
silt matrix.
32
Rhyolite breccia dikes contain
a glassy matrix and cut Tt.
4081/ "
White, \·Jelded ash-flO\oJ tuff. crystal poor with a few quartz
phenocrysts.
,
.
7-4
/
Rhyolite sills and dikes, crystal poor, strongly flow banded.
Some dikes are feeders to Tt and grade into pyroclastic dikes.
Coarse conglomerate containing clasts of limestone, quartzite
and andesite in a sandy matrix.
"
Andesite lava flows which contain small plagioclase and altered
mafic phenocrysts. The flows are dark qray to olive.
//'/4
./,
)~
fragments of ash-flow tuff in
,
Basalt sill with a diahasic texture.
but its age is unknown.
The sill intrudes JR s
Tertiary units south of Coal Canyon.
Rhyolite lava flow, crystal poor, devitrifiedo
,
•
\\
8
Rhyolite intrusive dome or plug, yellowish brown. flow banded
felsite.
,
Pyroclastic deposits, include perlites, minor ash-flow tuff, and
tuff or ash altered to clay.
9
Diorite, greenish gray and medium-grained. It is tentatively
assiqned a Jurassic age based on lithologic similarity to
age dated rocks to the south (Speed, 1976) •
,.
,
Lovelock
Fonnation~
thick beds of gray lime<;tone
l ...
ith Tilinor
shale beds (Speed, 1974).
Auld
Lan~
Syne Group
Thick beds of light gray to tan limestone, gray orthoquartzite,
and brown mudstone. The 50 to 100 feet thick limestone beds
distinquish the sequence from the thin limestone beds in the
T.
27
N.
,
,,
,
,,
pelite
T
sequence (Jli s, JR 1, JTo q).
(J~
Dark qray lenses of limestone within the pelite
27
N.
Orthoquartzite~
gray "to olive or reddish
brown~
s) ..
fine-grained
quartzite.
Slaty-shale, mudstone and minor siltstone bpds. ThP. shale which
grades to slate is thinly bedded and weathprs tan. The mudstone
is medium-to dark-brown and poorly bedded. Thin argillaceous
siltstone beds of limited extent are present within the slates.
"'~"
Siltstone~ clean, wpll sorted siltstone to very fine sandstone,
weathers to yellow rtnd tan tones, occurs only in detached thrust
plate.
Assigned a Triassic age by Speed (1976),
Limestone solution breccia exposed at the base of thrust sheets.
The upper zone is an o1ive IJray collapse breccia. The lower
zone contains large blocks of folded gray limestone. The age of
the limestone is unknown but it seems to underly the Triassic
siltstone.
EXPLANATION OF HAP SYMBOLS
~20
Contact, dashed where approximate
Fault, dashed ...there inferred, dotted where covered
~
6
N
SCALE 124,000
Eo~c=~===c==~~'~/2==~==~==~~===0E=~~~~==================~~~=3IMILE
IOEggDH"'C:"F3=l0,====,oiO"O":="",2,,O.,O=O==,30~O:¥O==~40~OC0'==='=050~O~"",603'0,:"O,==~7?OO 0 FE ET
E===E'"'="=EE'"'="i5~=="==E'=iO===========~=,="",1 KILOMETER
§CJIJENCJE
•'~ JEARTH
lLAlRORATORY
,
\.Y
rflSL
•
UNIVERSITY of UTAH
RESEARCH INSTITUTE
..
6
Breccia zone
CV
Calcite vein
QV
Quartz vein
•
/5-2/
x
GEOLOGY MAP OF THE COLADO AREA
GEOLOGY BY BRUCE 5, SIBBETT. 1980
,
.')
Thermal
grad;en~
Prospect pit
Adit
APPROXIMATE MEAN
DECLINATION, 1970
PERSHING COUNTY, NEVADA
Thrust fault, dashed where inferred
Strike and dip of bedding or compaction fo1iation
Plate I
\
'
~.
Shaft
hole
R. 32 E.
R. 33 E.
PLATE IT
T.
28
N.
T.
28
N.
40· 1:1'
40· 15'
EXPLANATION
(ohm-m)
. . P<' 5
W}.f;i%,!il 5 <. P < 10
D
o
10<PS 25
25<P:::: 50
D50<P~ /25
T.
27
DP>125
N.
T.
27
N.
PLATE II
INTERPRETED
ELECTRICAL RESISTIVITY DISTRIBUTION
at a DEPTH of 1000 FEET
COLADO GEOTHERMAL AREA
EARTH §ClIENCE
LABORATORY
PERSHING COUNTY, NEVADA
UNIVERSITY of UTAH
RESEARCH INSTITUTE
N
•
IX)
R. 32 E.
SCALE I: 24,000
R. 33 E.
R. 32 E.
R. 33 E.
PLATEm
-
'"co
o
T.
28
N.
T.
28
N.
40 0 15'
40°15'
EXPLANATION
•
~
T.
27
§§II
N.
Oeep low resistivity zone
(Possible deep reservoir area)
Shallow low resistivity zone
(Possible shallow plume)
Probable feeder zones for
thermal fluids
PLATE ill
INTERPRETED SCHEMATIC
of HYDROTHERMAL RESERVOIR
(FROM RESISTIVITY DATA)
COLADO GEOTHERMAL AREA
EARTH §ClIENCE
LABORATORY
PERSHING COUNTY, NEVADA
UNIVERSITY of UTAH
RESEARCH INSTITUTE
•co'"
R.32 E.
SCALE I: 24,000
R.33 E.
T.
27
N.