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My. J. E:. G i l b e r t J U R ~ 2 3 , 1971 Page 2

has c o n s i d e r a b l e spade dome. c m a I t h i n k , work very em V! e

Heat Flow Research

and

Explorat ion f o r Geothermal Power

i n t h e

Black Rock Deser t , Nevada

A Report Submitted

t o

Dr.' George W. Berry, Corder0 Mining Company

Edward R.' Decker Assistant Professor

Univers i ty of Wyoming Depte O f Geology

Table of Contents

Page

Introduction....... ....................................... 1

Notation and Units.... ..................................... 1

Heat Flow Determinations on Land .......................... 1

6

7

Resul t s of Recent Cont inental Heat Flow Studies . .......... Hot Springs i n Northwestern Nevada ....................... Heat Flow Research Near Corder0 Mining Company's

Previous Resul t s ................................. 7

Recommendation f o r Future Research....... ....... 10

Cost f o r Future ReseaYeh ........................ 1 6

References ................................................ ' 1 9

Introduction

Measurements of heat flow near the earth's surface provide

the most reliable boundary conditions to be employed in the

calculation of models of subsurface temperatures and the spatial

distribution of crustal sources of heat. The subsurface temperature

and heat source distributions, in turn, have many broad implications

in the explanation of several geologically-observed phenomena and

must be considered in exploration for geothermal power. In this

report, several aspects of modern heat flow research are briefly

summarized and reviewed. These comments are then used as a basis

for a heat flow research project that would provide more definite

data on the geothermal power potential of the Black Rock Desert

area in northwestern Nevada.

Notation and Units @*

Table 1 summarizes the notation and units that are used in ,

this report. More complete discussions of the thermal parameters

and conventions may be found in Roy, Decker, Blackwell and Birch

(1968) and Decker (1969)

Heat Flow Determinations on Land

Determinations of heat flow require the measurement of

temperatures at known positions in underground openings (boreholes,

tunnels, nine shafts, etc.) and the measurement, usually in the

laboratory, of the thermal conductivity or representative samples

of rock from the same openings. Temperatures are frequently measured

with thermistor probes in combination with cables and three-and four- -@bt

\4'

Table 1, Sunmary of n o t a t i o n and u n i t s

Depth - v e r t i c a l depth i n meters ( m ) o r f e e t ( f t ) below the su r face of t h e ground; 1 meterZ3,28 f e e t o

Temperature - OC and OF

Gradient - OC/km, The lezs t - squares grad ien t r e f e r s t o t h e s lope of a leas t - squares s t r a i g h t line f i t t e d t o observed temperatures and depths, The numbers i n parentheses denote t h e depth i n t e r v a l s used.

Thermal Conductivity, K - millical/cm sec OC = loq3 cal/cm sec OC, The numbers i n parentheses i n d i c a t e t h e number of samples determining average conduct iv i tyo

Therm1 R e s i s t i v i t y , €3 - c m sec O C / c a l , The numbers i n parentheses i n d i c a t e t h e number of samples deternknlng average r e s i s t i v i t y ,

C p is s p e c i f i c hea t , andykn density. ';'his pasametler determines t h e changes of temperature w k t h time and dhstacce i n a body and is used i n time-dependent ( t r a n s i e n t ) h e a t conduction ca l cu la t ions ,

For i s o t r o p i c media R = 1 / K ,

Thernal Diffusivkty, k - cm*/seco' k = K/Cp.g where K is conduct iv i ty ,

0 Heat F ow or Heat F l x - 1,O HFU (Heat Flow Unit) = loo rnicrocal/

f low and h e a t f l u x are used interchangibly, In t he theory of h e a t conCuction, hea t f l o w refers t o t h e t r a n s f e r of h e a t per unFt t i m e , whereas heat f l u x r e f e r s t o t he t r a n s f e r of heat per u n i t a r e a 2nd in u n i t t ime,

- In geology, t h e terms heat cm 3 sec = 1,ox1o-z cal/cmZsec,,d

I

Prec i s ion Indices - Standard e r r o r s are used as measures of t h e i n t e r n a l consistency of t h e data, The e r rors are f o r 95% con2idence l i m i t s inclt ldfng a "Students ttl m u l t i p l i e r for (n-1) degrees of freedom,

2

0: lead compensated DC bridges and null-detectors (see Roy, Decker,

Blackwell and Birch, 1.968) . Thermal conductivities are normally measured using divided-bar systems (Birch, 1950). With these

systems and techniques, temperatures may be measured to within

~.C0loC, and thermal conductivities of individual samples can be

reproduced to within *2$.

The observed temperatures provide 8 measure of the uncorrected

gradient. Uncorrected values of heat flow combine the observed

temperatures and conductivities and are usually calculated by one

of three nethods, If the gradient profile is linear, the heat

flow may be calculated as the product of mean conductivity multiplied

by the least-squares gradient (GK); otherwise, the flux should be

calculated from the resistance integral (RI) (after Bullard, 1939,

p. 481) , or as the mean value of several heat flows determined over

I

I

@ several separate intervals of depth (I) ,, The results obtained after

these methods were applied to geothermal data collected in four

different drill holes are summarized in Table 2. The temperature-

I

: I depth profiles for these holes are shown in Figures 1 through 4. I

The gradient is very uniform i n DDH#CH3 at C e r r i l l o s , N e w Mexico

(Fig, 1) ; therefore, heat flow was calculated as the simple product

of least-squares gradient times mean conductivity. At DDH#l and

DDH#2 near Santa Rita, New Mexico and DDH#N-55 near White Pine,

Michigan, however, the gradients significantly varied with depth

and heat flows were calculated using t h e interval and the resistance

integralmethsds, respectively (see Figures 2, 3 and 4; also Table 2) , _.. '

The high precision (standard errors < +5%) of the calculations !id ..-.

Table 2. Xethods f o r heat f low calculationso

GK Y ~ t ~ h o d -

Qz = Gradient O K Q Cerrillos, N. Flex,

White P i m , Mich, DDH C H # 3 f? rJpf :Lj3 '

0 cm sec C C d .

m

,,

G r a d i m t : (90-280m) 24, 422°C/lim

Conductivit!:: 5, OLZ ( 4.2) ~ lO- - ' cz l

cm sec %

H e s t Flow: w

7 0 65 B O O B 80 58 9.08

Heat Flow = 1,040 2 .003 HFU

i+ ( a f t e r R.F. Roy, unpublished)

1

0 Table 2 continued

I Method

Z Q

Santa R i t a , N o Mexo

DDH #1 DDH #2

Depth Gradient Averzge Heat Depth Gradient Average Heat Conduc- Flow Conduc- Flow

m I_ OC t i v i t y m - OC t i v i t y km 10-3cal HFU km 10'3cal HFU

cm sec% CIR set%

26 22 20 2 4 22 20 28 22 22 22 22

Heat Flow = l.$:l HFU Corrected Heat Flow = 2 , 0 0 ~ , 0 2 HFU

Corrected Heat Flow = l . 8 k e l HFU

TEMPERATURE, OC

Figure 1, Temperature vso depth in. drill hole CH-3, Cerrillos, N e w Mexico (Decker, unpublished) e

, ..- . .

20

40

60

EO

120

v)

6- w 5 uo z

2a

2a

.

.

.

.

. ,

Figure 2** Temperature vso depth in drill hole #1, Santa Rita, New Mexico (Decker, unpublished)

cn G eiJ I- w z

r -r

I= a w c)

20

40

60

80

100

120

140

160

180

200

220

240

13 '11 IS 16 17 18 19 b I I I b I I 1

Figure 30h Temperature VS. depth in drill hole #2, Santa Rita, New Mexico (Decker, unpublished).

1

W I

I

I

I

. . I

'. I

Figure 4,, Temperature, gradient, conductivity, and heat flow vso depth in drill hole N-55, White Pine, Michigan ( RoF Roy, unpublished)

3

demonstrates that the temperature and conductivity data are internally Grs consistent at all four sites and clearly illustrates the need for

different calculation methods in the analyses of geothermal

measurements at different localities.

The geothermal data from Santa Rita, New Mexico also illustrate

the value of heat flow in the determination of deep temperature

and heat source distributions, In particular, the gradient in

DDH#2 systematically increases ( 34-58'C/km) with depth below 180

meters, but the conductivity varies inversely such that the vertical

component of flux is uniform (2.002.02 HFU) throughout the 180-to

240-meter interval (see Figure 3: also, Table 2). The gradient is

significantly lower ( 22,7f.2°C/km) in DDH#l about two miles distant,

but the "topographically correctedtt flux at this site is l . 8 o k l

@: HFU, a value close to that obtained in DDH#2. . The good agreement

between the heat flows obtained in the two different drill holes

shows that high and uniform regional flux is characteristic of the

Santa Rita areao

in the Santa Rita area, and if the inverse correlation between

temperatures and conductivity had not been observed in DDH#2,

it would have been reasonable to speculate that the increasing

and higher gradients in DDH#2 provided evidence for anomalous heat

If the regional flux were not known to be uniform

sources (hot waters, etc.) closer to the surface near this site.

Although modern techniques allow very precise (*lo$) determin-

ations of flux over short intervals of depth (20-50 meters) in

drill holes, the experience of much logging has shown that various

disturbances (climatic changes, culture, ground water circulation,

4

u' etc.) are likely to affect temperatures in the first few tens of

meters beneath the earth's surface. As a result, values of thermal

gradient representative of the heat flow from below are usually

not obtainable at depths of less than 100 meters. For example,

the highly irregular gradients in the upper portions of DDH#2 at

Santa Rita, New Mexico (Figure 3) and the drill holes near Hesperus

and Colorado Springs, Colorado (Figures 5 and 6) represent the disturbing effects of circulating waters that are entering the holes

at various locations. The heat flows calculated in these zones

are significantly different (A10 to &loof%, Decker, 1966 and 1971, unpublished) from those obtained in the lower, undisturbed intervals.

Tho effect of circulating water is more regular at the site near

Colorado Springs, Colorado (Figure 6), but the flux also is variable and inaccurate for a distance of 800 feet above the point (~2300 feet)

where water enters the hole,,

Figure 7 illustrates the effect of transient changes of culture and climate on near-surface temperatures. The linear portions

of the deep (below 100 meters, or so) temperature curves represent

thermal equilibrium established when the surface temperature was

different (higher and lower) throughout the areas . The curvature i n the shallower profiles, however, represents the adjustment of

near-surface temperatures to recent changes of mean surface

temperatures associated with climatic variation and changes of

vegetation or construction (see, for examples, Lachenbruch and

Marshall, 1969; Roy, Blackwell, and Decker, 1971, in press). If

the magnitudes and durations of the surface temperature fluctuations

I

0.

,

'

' I WELL TEMPERATURES ' F I REO CREEK ANTICLINE I

Figure 60 Temperature vso depth i n a d r i l l h o l e near Colorado Springs, Colorado (after Birch, 1947)

. , '

. .

I I t M P t K A L U K t ('C) I

I

!

; 5c

1OC

n

E U

150 I- Q w Q

200

' 250

300

9 10 1 1 - 12 13 14 15 I I I I I

I

. I

. .

. . .

. CAMBR/.DE, MASS o OBSERVED TEMPERATUUE 4

50 YEARS, TWO LAYERS,

GRAVEL BEDROCK k = 0.009 0.01 cm7sec K = 5.0 7.0 m c o k m secOC AT = 5°C

1 I I I 1 . (a )

TEMPERATURE ('C)

Figure 7. Effect of c u l t u r e and c l i m a t i c change on subsurface g rad ien t so (a ) Ef fec t of nearby )Q

bui ld ings a t s i t e i n Cambridge, Masso (from Royo Blackwell and Decker, 1971, i n press) , . Open - c i r c l e s are observed t empera tu resz 1 ~ 0 .

S o l i d squares zapqesent temper-. - .$E atures obtained a f t e r CO%re6tiOn

conduct lv i t iesd (b) Effec t of ~

shown dfffuslvities an& _.

c l ima t i c change a t t h r e e s i t e s 0

i n t he Alaskan Arc t i c (after Lachenbruch and Marshall , 1969) .*

I

sz

-

900.

i

I ( b )

I 1 - -

/

I I

5

--. are known in a quantitative sense, corrections (after Birch, 1948;

Roy, Blackwell, and Decker, 1971: also, Figure 7a) may be applied to the near-surface temperatures to obtain corrected values for

the geothermal gradient; otherwise, as is usually the case, any

attempts to use uncorrected nonlinear near-surface temperature

profiles would obviously lead to unreliable estimates for the

heat flow from below, or the true regional flux.

The disturbing affect of circulating ground water can be of

the transient type and, at drill sites where it is economically

feasible, may be greatly reduced or alleviated by grouting (AM-9,

or cement) casing in place at the termination of drilling,

technique has been used with good success in drill holes in the

New York-New England area (see, for example, Figure 8) , also could have been used to alleviate the water disturbance shown

in Figure 6.

culturally induced disturbances, it does reduce those related to

circulating water and should be done at all sites drilled specifically

for heat flow research,

This

Grouting

@ Although grouting does not remove climatically or

Like measurements of gravity at the earth's surface, observations

of underground temperature obtain their full significance only

after certain kinds of topographic reduction, In general, the

I

temperatures follow the topography such that the isothermal surfaces

are more widely separated beneath peaks than under valleys. As a

result, more heat is conducted out through the valley floors than

through the sides of adjacent h i l l s or mountains,

Birch (1950) (see also Bullard, 1938: Jeffreys, 1938: Carslaw @

50

100 P t

150 Q

200

!

i 250

7 TEMPERATURE, OC

8 9 10

.. . , . . . ~ _.

i . . -

11 12 13:

Figure 8, Temperatures. vso depth before and after grouting in drill hole at Londonderry, Vermont (from Roy, Blackwell and Decker, 1971, in press)o

.

and Jaegers 1959; Jaeger, 1965) has developed a method for

calculating the first order effects of two-and three-dimensional

topography,

Blackwell, and Birch, 1968, Table 5 ; Decker, 1969; Blackwell, 1969).

clearly demonstrate that uncorrected heat flows in deep (100-1000

H i s results, together with those of others (Roy, Decker,

meters) drill holes or tunnels may be 10-40$ different from those

obtained after correction for steady-state topography.

correction may be 2 5 O - 2 O O $ at localities where the depth of

The terrain

measurement (shallow drill holes) is small relative to the distance

to moderate relief (Lachenbruch, 1969)~ Thus the distorting effects of local topography must be considered at each temperature station,'

if regional heat flow surveys are to provide reliable quantitative

information on the subsurface temperature and heat source regimes.

Results of Recent Continental Heat Flow Studies @

and Birch, 1968; Lachenbruch, 1968; Roy, Blackwell and Decker,

1971, in press) suggest that the earth's thermal field may be

subdivided into "heat f l o w provincos,Il within which there are

local basement radioactivity (U, Th, K).

form

where Qs is the flux where radioactive heat generation is A,, Q0

is the heat flow where As = 0, and H, with the dimension of thickness,

These lines are of the

. Qs = Qo + ASH

is the slope of. the line, The intercept Q is considered to provide

a meaure of the heat from the lower crust and/or upper mantle,

and it can be analytically shown that the steady-state heat from

a layer with vertically uniform heat production As and thickness

H would be the excess flux (Qs- Qo = As H) at a given site.

A list of well-determined "heat flow provinces" and the

parameters of their respective heat flow - heat production l i f ies

is given in Table 3,

of the lines imply that crustal radioactivity has undergone extreme

upward differentiation and readily accounts for 1.0 to 1.5

YFU variations of heat flow at the surface, The significantly

different Qo values (.4 to 1,4 HFU), on the other harid, provide

the first reliable demonstration that heat flows from the lower

crust and upper mantle are the characteristic thermal parameters

The similar slopes (total range 5 to 10 km)

I .

_.

of the provinces,

uniform throughout

flux (109 -201 HFU)

Rocky Mountains is

anomalies at depth

of flux ( > 3 0 0 HFU)

Moreover, the intercepts (ao) appear to be. each province. Thus the average high surface

in the Basin and Range province and Southern

probably due to heat sources and temperature

(,H) beneath each region, The very high values

observed in these areas suggest that anonalous

heat sources and temperatures are locally closer to the surfaceo

Heat Flow Research Near Corder0

Mlnir,g Company8 s Hot Springs In Northwestern Nevada .- . . . _

-

Previous Results, Hadsell, Grose and Berry (1967) summarized flow

rates and mean water temperatures for the hot springs at Soldier

Meadows, Fly Rancho Gerlach and the Pinto Mountalns (Table 4) , and calculated heat flows in seven shallow (65-385 ft, deep) drill

holes at the Pinto Plountain Prospect (Figures 9-15). Their data

c

Table 3.’ Summary of hea t f low provinces . _ -

.Data a f t e r Roy, Blackwell and B i r c h (19681, Roy, Slackwell and Decker (1971, i n p r e s s ) , and Jaeger (1970) .

Average Range of Range of In t e rcep t - Flux -- Flux Radioact ivi ty Slope Province

km lO”6cal 10’6cal 10-6ca1 10-l3Ca1 3 cm2sec cm sec 2 cm see 2 c m sec

Continental U.S.

Basin and Range Province 9.4 1,4 109-2.1 106-3.7 3.0-10,o

Eas te rn U.S. 7.5 08 102 0 81-2 3 0 4-21 0 2

Sierra Nevada 1001 04 0 94 06-1.3 1e8-9.6

Southern Rocky Mtns. 10 1.2 1.9-2.1 1.5-3.7 3 0 ~ - 1 6 0 ~

A u s t r a l i a

Western 4.5 .6 1.6 7-2 o 3 1.2-21.9

Table 4;1Summary of flow rates and mean temperatures of

not spr ings in northwestern Nevada (from Badsell, Grose

and Berry, 1967)0

Locality

Soldier Meadows

Fly Ranch

Gerlach

Pinto Mountains

Flow Rate gal/min

2 8k2 -, .

. -

1472

253 142

-.

Temperature O F

. - __. __. .. .. . . .. . . , . .. . . . .. . .- ... . -..~ . . . .. . .. . .-.-" __ . ~. . ~- ~. ~..

- ._ - _.

TEMPERATURE I N O F

RO 130

c3'

8C

120

I60

9

24

I 280

i

320

360. -4;

400 I ~

Figure 9* Geothermal data from r o t r d r i l l hole i n the Pinto Mountains' (from Hadsel l , Grose and Berry, 19a67ye ;* ,

. '

r . , ..

_. . .

* ~-

( fFon Hadsell , Grose and Berry, 1967)o* -- -- ._ _-I-_.

-

TEMPERATURE I N OF

4c

I - - ,

80

120

I

I L

60 EO 100 ' 120 140

@-THERMOCOUPLE BE M P E R AT U R E

G-AVERAGE GEOTHERMAL

ASSUMED COMDUCTlVlTIES IN 10-3 cal/cm s e c OC AND STABILIZED BOTTOM HOLE TEMPERATURE IN O F . W.T-ASSUMED WATER TABLE

PROSPEC? MOLE

TEMPERATURE IN OF

6 0 80 IO0 120 I40

. .

ins

TEMPERATURE IN OF 4

* 40

80

I20

60 80 IO0 120 ,140

WEIGHTED AVERAGE TEM PE RAT U R E CURW E

TEMP E R AT U RE @-Y HERMOCOUPLE

G -AVERAGE GEOTHERMAL

HF-HEAT FLOW IN IO+ c a ~ / c r n ~ sec

ASSU RA ED CON DUCTIV ITiES

STABILIZED EOTTOM HOLE TEMPERATURE IN O F .

IN 10-3 cQi/Cm sec UC AND

PINTO M'OUNTAIMS

PROSPECT HOLE

- . . ., -.-. __ , . _^__I_.__^...__. ,. . ... _ ,___- -.- - .___ ___-. -

40

f "

80

W E I G HT E D AVER AG E TEMPERATURE CURVE,

o-THERMOCOUPLE I 2 O k TEMPERATURE

it"]!J&J+ G-AVERAGE GEOTHERMAL b'[;!iiy;,

1 . d LL I , GRADIENT I N "F/IOO FT

I N -r 3 '120 140

IN caI/crn sec OC AND STABILIZED BOTTOM HOLE TEMPERATURE I N O F .

W.T,-ASSUMED WATER TABLE

Figure 15, Geothermal data from z-otary drill !?.ole in t h e Pinto Mountains (from Hadsell, Grose and 5 m r y p 19670)

3

T

e ble 5.Base temp r a t u r e h e a t f l u x a t ho t springs

Heat Flux = Tf/A

i n northwestern Nevadao Method a f t e r White (1968)

= ( F / A ) ,xodoCp ( B t - St) where Tf = heat f low ( c a l / s e c ) , A is area, x = 63.1 c m h n , F = flow rate (gal/min), d = densi ty ( l o o ~ f t ! ) , c p = s p e c i f i c heat

(1.0 cal ) , V t = base temperature (OC), and S t = sur face temperature (OC) . gal sec em 3

- - g c ' _ _

. _ U

St Local i ty - Rate - Bt - gal/min OC OC

Flow

-

Pin to Mountains 142 48.9 12.2 142 71.1 12.2 142 87a2 12.2

J

F l y Ranch 14-72 58.9 1202

Gerlach 253 7g04 1202

S o l d i e r Meadows 2 842 43.3 12,2

Surface** T o t a l Area Heat Flow km2 105ca1

s ec

1.08 '3.3 1008 5.3 1.08 6.7

094 4304

a 02 10.7

4307 55.8

* A f t e r Hadsell , Grose and Berry (1967). ** Estimated from maps by Berry and Downs 1966a,b,c, 1969) + Normal Continental Flux = 105x10-6cal/~m h sec:

Average Basin and Range Flux = 2,OxlO" cal/cm2seco

Heat Flux

cmzsec 10-5ca1

2:; 6.2

46.4

535 103

Rat io of Calculated Flux t o Normal Cont inental and Basin and Range Flux.+

Normal Basin & Range

20.3 3z06 41.0

10

known and the surface temperatures can not be reliably

continued downward,

Recommendation for Future Research, Future evaluation of Cordero8 s

geothermal prospects should be directed toward the acquisition of

reliable heat flow data and a better knowledge of the deep subsurface

temperature regimes at each area,

futuro research are outlined below,

A few recommendations for

1) Since most of the springs crop out near or along obvious

or postulated faults or fault systemss the tempemtures

measured near and in them undoubtedly represent the end

result of a complex history of heat transfer between host

rock and circulating fluids migrating upward and along

fault planes or fractures.

transfer will depend upon the undisturbed regional gradient,

the flow rate of the fluids, the thermal diffusivfties of

The actual amount of heat

t h e host rocks, and the orientation of the fault planes o r

systems, but the general effect i s that hot waters from depth

lose heat to the lower temperature surroundings and the

temperatures measured in springs at the surface do provide

direct measures of the true magnitude of the underlying thermal

anomaly,’ Moreover, If the above mentioned parameters are

1, Seeo f o r example, Figure 6, 2300 and 2400 feet and flows to the surfaceo The flow rate (1 gal/min) is low enough such that the water l o ses heat to the rock during upward migration. If a fast flow occurred, the water temperature could be 83OP all of the way to the surfacea the low flow rateo

Water enters the hole between

The temperature at the surface is 20* lower f o r

11

known, the reduction of water temperature can be analytically

determined by approximating the springs and fault planes

as line, cylindrical or plane sources of heat (see Birch,

1947; Carslaw and Jaeger, 1959, Chandrasekhar, 1961; Levich, 1962; Jakob, 1957) Therefore additional exploration near

the hot spring areas should include more extensive gravity

and magnetic surveys to determine the subsurface geology and

the extent and orientation of folding and faulting at depth.

Considered with direct observations of regional flux, thermal

conductivity, and presently available water-flow rates (Table 4;

and Berry, personal communication, 1970 and 1971), detailed

analyses for the thermal effects of the local geology could

lead to better estimates for the highest subsurface temperatures

and the depths at which large quantities of dry steam might be

produced.

2 ) The thermal affects of local geology can be significant,

but many studies of hot springs indicate that the flows

a t the surface consist l a rge ly of meteoric water (Toulmin

and Clark, 1967; White, 1.967)~ As a result, the temperatures

measured in hot springs at the surface also may be abnormally

low due to mixing with lower temperature ground water, Thus

future exploration should: a) obtain reliable knowledge of

each regional -ground water regime; b) arrive at estimates

for the age and volumes, etc, of meteoric and primary waters;

and c) use background heat flow data to obtain estimates

for the temperatures of meteoric waters before mixing with

hotter waters from belowo

.,

The thermal consequences of a

12

mixing of meteoric and primary waters are complex, but may

be treated analytically if local hydrology, water ages, and

regional heat flow are known in a quantitative senseo Studies

of this type could be especially pertinent in Soldier

Meadows where the low temperatures of the springs (Table 4)

suggest quenching by colder near-surface waters.

This research would require chemical analyses and

additional geologic mapping, It would be desirable also

to conduct deep electrical surveys ( > lOOO', DC resistivity

and EM) in each area since changes in resistivity can

reflect the degree of saturation in subsurface rock (Keller

and Frischkneckt, 1966; Grant and West, 1965), Moreover,

electrical surveys provide information on subsurface structure

and subsurface temperature anomalies (Keller and ?rktchard, 1966).

Thus the electrical surveys could yield data on regional

hydrology, geologic structure, and subsurface temperature

models that could be compared with those based on heat flow

studfes to arrive at additional estimates for the depths at

which high temperatures might occuro

3) Deep rotary and core drilling to deternine reliable values

of heat flow near the hot springso The holes should be at

least 200 meters deep, penetrate competent rock units

(not just aiiuvi&) in. the bottoms of the holes, and be

continuously coredI(NX or BX size) for the bottom 30 to 50

meters, The holes should be cased and left accessible for

subsequent temperature loggings. The casing should be grouted

A

in place with cement or chemical grout (Am-9, American

Cyanamide CO:) to alleviate disturbances associated with

circulating water, Because the primary objective is to use

the heat flow measurements to determine the deep temperature

regimes and estimate the depths appropriate for the production

of dry steam, the holes should - not be drilled near individual

hot springs; temperatures close to the springs obviously

would be anomalous and'provide little information on. the ,

flux at depth,'

Although the final selection of hole locations would

require further consultations with Cordero's Geologists,

existing maps (Berry and Downs, 1966a, b, c, 1969) and a brief visit to each property in July, 1970 suggest the following numbers and distribution of sites:

A,. Pinto Mountain Hot Springs, Two drill holes would be

needede2 One should be drilled in the granodiorite

about half way between West and East Spring,

should be 3OOO-to 4000-feet west of the West Spring,

The other I

Secause the granodiorite#appears.to be compositionally

and texturally uniform, excellent background heat flow I

should be obtained at this site, The other site would

provide data away from the springs and detect deep

temperature anomalies associated with circulating waters , etc, along the north-south trending fault very near

West Spring, Since there is 3OO'-to 400 feet of relief

in the area, terrain corrections would be needed at / \

14

a l l s i t e s . The T e r t i a r y volcanics and sediments near the

su r face a l s o should be sampled f o r s t u d l e s of their

tnermnl p r o p e r t i e s , and t o determfne i f r e f r a c t i o n

.. .

- - .

models should be ca lcu la ted . Although only t w o sp r ing

systems are evident a t t h e P i n t o iYountnin prospec t , 'the

r e l a t i v e l y simple geology and exposures, t h e h igh

temperatures of t h e spr ings (Table 4). and t h e e a r l i e r

shallow d r i l l i n g (F igures 9-15) make it an e x c e l l e n t

t e s t a rea .

B.' F l y Ranch Hot Springs, Two holes should be d r i l l e d -

i n t h e high r e s i s t i v i t y l a y e r ( 3 5 ohm-meters) t h a t

K e l l e r and P r i t c h a r d (1966) mapped w i t h electromagnetic

and DC r e s i s t i v i t y surveys. T h i s u n i t should provide

t h e b e s t deep geothermal data because it appears t o

have low poros i ty and reduced water conten t ; tnus t h e r e

should be fewer t r a n s i e n t d i s turbances due t o c i r c u l a t i n g

water, I t would be d e s i r a b l e t o have data on t h e

downthrown s i d e of t h e f a u l t bordering t h e e a s t s i d e of

t h e sp r ing system, bu t a hea t flow s i t e i n t h i s area

should no t be s e l e c t e d without b e t t e r es t imates for

t h e depth t o basement,.

C o s Gerlach Hot Springs, One d r i l l ho le i n the g ranod io r i t e

c roping o u t t o t h e north and west of Mud and Great Bo i l ing

Springs, r e spec t ive ly , should provide an e x c e l l e n t va lue

f o r t h e undisturbed flux, A t e r r a i n c o r r e c t i o n would . - .

_ - be needed a t t h i s s i t e , A s i t e 2000-to 3000-feet e a s t

of Great Boi l ing Spr ings should provide data on the

underlying, deep temperature anomalyo D r i l l i n g i n

t h e a l l u v i a l va l l ey should be delayed u n t i l geophysical

techniques a r e employed t o determine the subsurface geology.

Do Soldier Mendows. Because of t he large areal ex ten t ,

t h e l a r g e t o t a l flow r a t e (Table Lk), and t h e low temperatures

of t h e sp r ings (Table 4) , thorough research should be

conducted t o determine the deep f l u x i n t h i s a r e a o A very

comprehensive survey would r e q u i r e t h e d r i l l i n g of f i v e

ho le s a t t h e fol lowing rough l o c a t i o n s ( s e e Berry and

Downso 1969): t h e western boundary of S27, T4ON, R24E;

t h e northwest quarter of S25, T40N, R24E; t h e c e n t r a l

po r t ion of Sl3, TLCON, R24E: t h e northwest q u a r t e r of

Sl9, TbON, R25E; and t h e e a s t e r n po r t ions of S17 o r S6

(Sl& Gul l ion Creek) , TMN, R25E.

would r e q u i r e f o u r d r i l l holes, w i t h t h e s i t e i n Sl3,

A less thorough survey

TltON, R24E being de le t ed , and t h e l o c a t i o n on Sl9, T4ON,

R2JE being s u b s t i t u t e d f o r by a site roughly halfvaay

between Springs E and F and B and C. I n e i t h e r case,

t h e s i t e s off t he e a s t e r n and western boundaries of t h e

Meadows should provide hea t flow data f o r t he a r e a s away

from t h e spr ingsd Those i n t h e Meadows should l e a d t o

accu ra t e es t imates for t h e magnitudes of t h e underlying

thermai-anomaly.* A study of t h e ha l f -wid ths , etc,, of

. . . I

\

t h e h e a t flow anomaly a c r o s s t h e meadows would provide

data on t h e depths t o anomalously high subsurface

temperatures:

16

@ Cost f o r F u t u r e Resezrc.,. The approximate expense for c:ravity and

deep electrical surveys i n each area are summarized in the excellent I

report by Keller and Pritchard (1966, pa 12-13) With the

exception of t he proposed shallow drilling, it is my opinion that

their proposals have great merit and could be of special value

at the Gerlach and Soldier Meadows prospects, where more subsurface

I

I

control (geologic, hydrologic, and temperature) is needed, I also

believe that the final evaluation of a l l of the hot spring areas

should include a comparison of subsurface temperature models

arrived at f rom heat f low and resistivity surveys.

Heat flow measursmnts would involve expenses f o r contract

drilling, casing and grouting, preparation of thermal conductivity

samples, field support f o r temperature logging, ar,d costs for data

@ reduction and interpretation,\ The average expenses that would be

Gus

incurred if the work were done using equipmen% and personnel at the

University of Wyoming as summarized below:

Drilling, Casing and Grouting. Rotary and core drilling is

estimted at $7 to $8 per linear foot of drill hole. whereas experience shows that casing (with l i l t black iron pipe) ar,d

grouting costs about $.'75 per foot of hole, including materials

and rig-time,. Therefore a 200 meter hole would cost $4900

to $5600, A lower cost might be incurred at Soldier Meadows,

if four to five holes were drilled,*

Thermal Conductivity.' Commercial grinding and edging of

conductivity samples averages about $' j0o0 to $30450 per sample,

Approximately 150 to 200 samples would be needed at a total

cost of $525 to $7500:

is not included, because our laboratory could handle 20-to

A cost for laboratory measurements

30-additional samples per day without interrupting the usual

routine;

F i e l d Support for Temperature Measurements. A 200 meter hole

may be readily logged in two hours using portable equipment;

Therefore one day, including travel from the nearest base,

would be required to measure temperatures at any prospect.

Two loggings on differer.t days, separated by a month, or so,

would be needed. Excluding costs for air travel, etc, to

and from the nearest base, temperature logging would cost

about $100/day plus a $15-$16 per d l e n per man (one or two),

If temperatures were logged with equipment already in existence, ..

no cost for equipment would be incurred; new equipment would

cost $2000 to $2500 for cable, (teflon insulated), thermistors,

construction ar,d calibration of probes, and DC circuitry for

resistance measurements at the surface (bridges and null-

detectors).

Intermetation, This would involve data reduction and

interpretation, and the preparation of reports. Since most

of the necessary computer programs are in existence, only

6 to 7 man-days would be needed for rather complete inter-

pretations in- each areao The rr,aximum cost for interpretation

at each prospect is estimated to be $800, including computer

time,

18

The above discussion demonstrates that heat flow measurements crs at Cordero*s Geothermal Power prospects would be costly, For

example,the proposed, reszarch at all four prospects

would cost $60,000 to $70,000; However, without reliable h e a t

flow datr; and hence more reliable subsurface tenperature modelsp

drilling for geothermal power in these areas would be very

speculative, as is strongly suggested by the deep (lOOO-5000 ft.),

non-producing holes near the anomalous springs at Beowafve and /

Bradie Hot Spr ings , Nevadao*

References

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Humboldt County Nevada, Sun . O i l CO., August 2 5 , 196673, Geologic map of P in to Mountaim Hot Spring2 Area,

, Geologic map of Fly Ranch Hot Springs, Washoe County, Nevada, August 25, 1 9 6 6 ~ .

Geologic map of the S o l d i e r Meadows Area, Humboldt County, Nevada, Corder0 Mining Company, Revised map, May 1, 1969,

Blackwell , D.D., Heat flow determinations i n t h e northwestern United S t a t e s , J. Geophys, Res,, 74, 992-1007, 1969.

Birch, F ranc i s , Temperature and h e a t flow in EL w e l l near Colorado Springs, Am. Jour . S c i , , 245, 733-753,, 1947.

The e f f e c t s of P le i s tocene c l ima t i c v a r i a t i o n s upo; geothermal g rad ien t s , Am; Jour, S c i , , 246, 729-760, 1948,

, Flow of h e a t i n t h e Front Range, Colorado, B u l l . Geol. soc. A m o , 61, 567-630, 19300

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Bul la rd , E,C., The d is t rubance of t h e temperature g rad ien t i n t h e e a r t h ' s c r u s t by i n e q u a l i t i e s of he igh t , Monthly Notices Roy, Astrom. Socor Geophys. Suppl. , ,4, 360-362, 1938.

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C a r s l a w , H,S., and Jaegero J.Cos Conduction of Heat i n S o l i d s , 2nd Edi t ion, Oxford Universi ty Press, 1959.

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20

Hadsell , Frank, Grose, LOTo, and Berryo G , W o , Thermal d q t a o f t he Black Rock Desert Areao IIumboldt and Washoe Cou~ties, Nevada, Report submitted t o Sun O i l Company, Apr i l , 1967*

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Ke l l e r , G.V,, and Frischknecht, F.C., E l e c t r i c a l Methods i n Geophysical Prospectinq, Pergamon P>ess, New York, 1966.

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Lachenbruch. A.H, P r e l i z i I ~ ~ a r y g e o t h e ~ ~ d . model f o r the S i e r r a Nevadla, Jour. Geaphys.' 3es, , 73, 6977-6989, 1968.

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Lachenbruch, A a I l p , and Marshall, BoV., H e a t f low i n t h e Arc t i c , Joure A r c t i c I n s t , North Am,, 22, 3 , 300-311, 1969.

Levich, V,G., Physiochemical Hydrodynamics, Prent ice-Hal l , Englewood C l i f f s , New Hersey ,* l962 ,

Roy, R,F., Blackwell, D.D., and Birch, F , , Heat genera t ion of p lu tonic rocks and con t inen ta l h e a t f low provincesp E a r t h . P lan t . S c i , L e t t e r s , 5, 1, p. 1-12, 1968.

Boy, R.F. , Blackwell, D.D., and Decker, E,R. flow, i n volume Th,e na tu re of t h e S o l i d E a r t h , i n honor of Fe S r i c h , McGraw H i l l , i n p re s s , 1971.

Cont inental h e a t

Roy, R,F., Decker, E.R., Blackwell , D.D., and Birch, F., Heat flow i n t h e United S t a t e s , Jour. Geophys. Bes., 73 , 5207-5221, 1968.

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t h e r m 1 and mineral w a t e r s , in Geochemistry of Hydrothermal Ore Deposits, ed i t ed by Hubert Lloyd Barnes, H o l t , Rinehart and Winston, Into, New York, p. 575-631, 1967.

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