-
.... . . .
LA-9966-HDR
UC-66a
Issued: January 1984
LA--9366-NDR
DES4 0 1 0 2 3 3
Petrographic Analysis and Correlation
of Volcanic Rocks in Bostic 1-A Well
near Mountain Home, Idaho
Barbara H. Arney
Jamie N. Gardner
Stephen G. Belluomini’
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.
*Harding-Lawson Associates, 7655 Redwood Boulevard, P.O. Box 578, Novato, CA 94947.
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
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PETROGRAPHIC ANALYSIS AND CORRELATION OF VOLCANIC ROCKS IN
BOSTIC 1 - A WELL NEAR MOUNTAIN HOME, IDAHO
Barbara H. Arney, Jamie N. Gardner, and Stephen G. Belluomini
ABSTRACT
Detailed examination of volcanic rock c u t t i n g s from the Bostic
1 - A well near Mountain Home, Idaho, provides data t h a t c o r r e l a t e the
stratigraphy of the well w i t h the regional s t r a t i g r a p h y of the western
Snake River Plain. The Bostic 1 - A well penetrates b a s a l t of the Middle
Plei stocene Bruneau Formation and underlying sedimentary rocks of the
Upper P1 iocene Glenns Ferry Formation. Basalt u n d e r l y i n g t h e G 1 enns
Ferry Formation i s most l i k e l y Banbury Basalt of Middle Pliocene age o r
Banbury equivalent.
A 350-ft interval of f e l s i c volcanics i s then
i n t e r s e c t e d above another 600 f t of b a s a l t .
The well bottoms i n
a1 t e r e d f e l s i c volcanics.
T h e lowest 600 f t of b a s a l t flows has not been c o r r e l a t e d w i t h
any b a s a l t observed on the surface. From the e s t a b l i shed stratigraphy
of the region, and from petrographic evidence, the s i l i c i c volcanic
rocks occurring b o t h above and below the lowermost basal t s i n the we1 1
a r e probably lower Pliocene Idavada Volcanics. North of the well, i n
the M t . Bennett H i l l s , Idavada Volcanics o v e r l i e c r y s t a l l i n e rocks of
the Idaho b a t h o l i t h . No estimate of depth t o plutonic bedrock can be
made from the well data alone. S t r a t i g r a p h i c comparisons suggest a s
l i t t l e as 0.2 t o 0.3 km more o f Idavada l i e beneath the Bostic 1 - A
well
.
R e s u l t s o f geophysical
studies suggest additional basalt 1 i e s
beneath the Bostic 1 - A rather than g r a n i t i c rocks of the b a t h o l i t h .
I.
INTRODUCTION
T h e Bostic 1 - A well, on the northern margin of the Snake River Plain
near Mountain Home, Idaho (T4S, R 8 E , S25) ( F i g . 1 ) was d r i l l e d as an o i l and
gas wildcat t o 2950 m (9676 f t ) by A1 G r i f f i t h i n 1973. In 1974 Gulf Mineral
Resources Co. took over the well a s a geothermal prospect and ran additional
l i t h o l o g i c and geophysical logs. In e a r l y 1978 the well was acquired by Union
Oil Co., who attempted t o clean i t o u t , then plugged and abandoned i t i n
October 1978.
1
When t h e area e a s t o f Mountain Home, Idaho, was s e l e c t e d f o r study as a
p o t e n t i a l h o t d r y r o c k (HDR) geothermal s i t e (Arney e t a l . 19821, a s t u d y o f
t h e B o s t i c l - A c u t t i n g s was begun.
The study r e v e a l e d t h a t t h e w e l l
i n fact
bottomed i n s i l i c i c v o l c a n i c s o f t h e Idavada Formation r a t h e r t h a n g r a n i t e as
p r e v i o u s l y r e p o r t e d ( G u l f M i n e r a l Resources Co.
,
lithologic log).
t h a t Idaho B a t h o l i t h l a y beneath t h e s i l i c i c v o l c a n i c s ,
Believing
as indeed i t does j u s t
n o r t h of t h e HDR p r o s p e c t (Malde e t a l . 19631, we s t u d i e d , i n more d e t a i l , t h e
volcanic
stratigraphy
i n the well
t o estimate
t h e depth t o g r a n i t e .
The
r e s u l t s o f t h a t work a r e presented i n t h i s r e p o r t .
Subsequent g r a v i t y modeling suggests t h a t no g r a n i t e l i e s beneath t h e
s i l i c i c volcanics a t the Bostic l o c a t i o n .
I n s t e a d , r o c k s beneath t h e bottom
o f t h e B o s t i c l - A w e l l a r e i n t e r p r e t e d t o be b a s a l t s a p p r o x i m a t e l y 3 km t h i c k ,
p r o b a b l y a s s o c i a t e d w i t h t h e opening o f t h e Snake R i v e r P l a i n (Arney e t a l .
1982 1.
I I.
PROCEDURES
Well c u t t i n g s were examined w i t h a b i n o c u l a r microscope
i n t e r v a l s from depths o f 426 t o 536 m (1405
Samples were taken a t 9-m ( 3 0 - f t )
t o 1769 f t ) , and a t 3-m ( 1 0 - f t )
ft).
(Appendix A).
i n t e r v a l s from 1219 t o 2949 m (4023 t o 9676
The small s i z e o f t h e w e l l c u t t i n g s and t h e i r f i n e g r a i n s i z e h i n d e r e d
m i n e r a l i d e n t i f i c a t i o n i n some samples.
C u t t i n g s below 1768 m (5800 f t ) were
mounted on p o s t e r board ( F i g . 2 ) a t 0.5
i n . = 10 f t t o a l l o w a b e t t e r under-
standing o f
the
1ower
vol canic
sequence.
D e t a i 1ed p e t r o g r a p h i c
performed o n l y on c u t t i n g s o f t h e v o l c a n i c r o c k u n i t s .
study was
G r a i n mounts p r e p a r e d
o f samples from depths between 1239 and 2949 m (4090 t o 9676 f t ) were examined
w i t h a p e t r o g r a p h i c microscope t o i d e n t i f y f o r m a t i o n and r o c k t y p e s (Appendix
B)
To a i d i n c o r r e l a t i o n w i t h mapped s u r f a c e u n i t s o f t h e Idavada V o l c a n i c s ,
representative
intervals
from
each
visually
c u t t i n g s were c h e m i c a l l y analyzed u s i n g x - r a y
t h e method of Hagan (1982).
and t h i n
s e c t i o n s made
from
distinct
silicic
unit
i n the
(XRF) , f o l l o w i n g
fluorescence
C u t t i n g s from these i n t e r v a l s were hand-picked,
the
hand-picked
samples
were
examined p e t r o -
graphically.
To i d e n t i f y t h e a1 t e r a t i o n m i n e r a l s p r e s e n t , s e l e c t e d samples were a1 so
analyzed by x - r a y d i f f r a c t i o n
( X R D ) on <400 mesh powders.
When peaks of t h e
a1 t e r a t i o n m i n e r a l s were obscured by t h e o r i g i n a l m i n e r a l o g y ,
2
an a d d i t i o n a l
EXPLANATION
lymbol
Description
Qal
Stream alluvium
QIS
Landslide debris
Qm
Melon gravel, bouiders and cobbles of basalt in basaltic sand matrix.
bouiders commonly 1 m in diatreter and as large as 3 m , late Ple#stocene.
0 sr
Srake River Group, undivided: mainly olivine and/or piagiociase basalt
flows and terrace gravels, late Pleistocene.
Qb
Bruneau formation. caryon fill of undeformed, unconsolidated, detrital
sediments and interbedded basaltic lava flows with marginal deposits Of
pebble and fan graveis, middle Pleistocene.
-
Qbs
Sedimentary material dominated by massive lake beds of white to
light brown fine silt clay and diatomi:e in layers 15 m or more thick,
with subordinate amounts of alluvial silt and sand Lake beds rise to
an elevation of 970 m and merge with alluvial and colluvial deposits
of sand, clay and gravel that rise roughly 91 m Pigher
Qbg
Alluvial deposits of sand and pebble gravel from elevation 970 m to
1000 m. Pebble gravel reworked as beach deposits from contiguous
older gravels
Qbf
Fan gravel, consisting of cobble and pebble sizes in a coarse sandy
matr,x derived from decayed granite Fan deposrt gravels extend
from front of Bennett Hills to 1000 m elevation.
Qbu
Undif:erentiated basaltic lava flows ,which erupted episodically from
several vents to form a ser es of lava plateaus and canyon-filling
volcanic dams. Differentiated individual flows in ascending strati-
Qbb
Qbk
graphic
Berry Ranch
orderlava
are flow; olivine-plagioclase basalt, coarse texture;
King Hill lava flows, gray, derse, glassy tex!ure, in three separate
flows:
Morrow Reservoir lava flow; olivine-basalt, moderately coarse texture,
dense,
Cold Springs
glassy: lava flow, plag,oclase-olivlne basalt, gray to black,
Qbr
Qbc
Qbh
Hammett lava flows: plagioclase-olivine basalt of coarse texture. at
least two flows of medium-grained, relatively nonporphyritic basalt
Glenns Ferry formation - Basin fill of poorly consolidated detrital sediments
(Qtg) and minor fava flows of basalt (Qtgb) late Pliocene to early
Pleistocene
QtQ
Qtg
Lake and stream deposits character zed by abrupt lateral changes in
facies Facies include ( 1 ) massive silt beds 12) evenly layered thick
beds of sand ( 3 ) thinly bedded dark clay olive silt and carbonaceos
m a l e (4) rspple-rarked sand and silt k5) granitic sand and f i r e
pebble gravel and ( 6 ) quartzitic cobble gravel Facies 51 and 16)
characterize the Glenns Ferry formation present in the prospect Site
Qtgb
detrital
Lava flows
deposits
of olivire basalt that form sheet1 ke bodies within the
Tb
Banbury Basalt. Lava flows of olivine basalt interbedded locally with minor
amounts of stream and lake deposits middle Pliocene
ldavada Voicanics .Silicic latite chiefly thick layers of devitrified welded tuff
includes
Pliocene some bedded vitric tuff and lava flows late Miocene to early
Tiv
Granitic rocks of Idaho batnolith mainly quartz monzonite and granodiorite
n Composition
I**c
/
Geologic contact dashed where approximately located
hiormal 'ault dashed where approximately located dotted where
concealed bar and ball on downthrown side
-7-
*
e
Strike and dip of beds Barb indicates direction of dsp estimated
Showi vainly i i ldavada voicanics where dips are generally less
[Pan 10Volcanic vent
Bostic 1-A exploratory test well (dry)
Prepared by Harding-Lawson Associates
Geology compiled from and legend modified after ( 1 ) Malde H E and Powers H
A 1972 Geologic Map of the Glenns Ferry-Hagerman Area West-Central Snake
R ver Platn Idaho 12) Malde H E Powers H A and Marshall C H 1963
Fig. 1. Geologic map of prospect area east of Mountain Home,
Idaho showing location of Bostic 1-A well.
F i g . 2.
C u t t i n g s boards of t h e B o s t i c l - A c u t t i n g s from 5800 t o 9676 f t , XRF and XRD
sampling i n t e r v a l s i n d i c a t e d .
5
7400FT
7 8 0 0 FT
F i g . 2. ( c o n t )
6
e 2 0 0 FT
L
hand-picked
sample
powdered f o r XRD.
of
highly
a1 t e r e d c u t t i n g s
from
These samples a r e i n d i c a t e d by " A "
the
same
interval
was
(a1 t e r a t i o n ) f o l l o w i n g
t h e i n t e r v a l depth numbers i n Table C-111.
A1 t e r e d b a s a l t i n t e r v a l s,
chosen f o r f u r t h e r
,
f u n c t i o n o f depth i n t h e w e l l
amygdules
and/or
veins.
The
study o f a1 t e r a t i o n as a
a r e commonly c h a r a c t e r i z e d by z e o l i t e - f i l l e d
l e a s t a1 t e r e d
i n t e r v a l were hand-picked f o r XRF a n a l y s i s .
fragments
from
each
selected
Two a d d i t i o n a l i n t e r v a l s b e l i e v e d
t o be d i k e s by t h e i r apparent freshness were a l s o analyzed by XRF.
Sampling
i n t e r v a l s a r e i n d i c a t e d i n F i g . 2.
Appendix A i s a l i t h o l o g i c d e s c r i p t i o n o f w e l l c u t t i n g s examined w i t h a
b i n o c u l a r microscope.
mounts.
Cuttings
Appendix B c o n t a i n s p e t r o g r a p h i c d e s c r i p t i o n s o f g r a i n
samples
were
taken
at 10-ft
intervals,
r e t a i n e d as t h e u n i t o f measure i n b o t h Appendix A and B.
thus,
feet
are
Appendix C g i v e s
t h e r e s u l t s o f XRD and XRF analyses.
111.
SUMMARY OF BOSTIC 1 - A STRATIGRAPHY
The summary o f B o s t i c 1 - A l i t h o l o g y i s shown i n Table I and F i g . 3 and
focusses on 1 it h o l o g i c f e a t u r e s used f o r s t r a t i g r a p h i c c o r r e l a t i o n s .
Hydro-
thermal a1 t e r a t i o n i s p e r v a s i v e below 1525 m (5000 f t ) , and ranges i n s e v e r i t y
w i t h i n c r e a s i n g depth from z e o l i t e t o g r e e n s c h i s t f a c i e s .
I t i s described i n
more d e t a i l i n Arney, 1982.
IV.
S T R A T I G R A P H I C CORRELATIONS
S t r a t i g r a p h i c c o r r e l a t i o n s a r e shown i n F i g . 3.
The upper 536 m (1769
f t ) o f t h e w e l l p e n e t r a t e s Bruneau Formation o f m i d d l e P l e i s t o c e n e age.
Under-
l y i n g t h e Bruneau Formation a r e sedimentary r o c k s o f t h e Upper P1 iocene Glenns
F e r r y Formation.
of
b a s a l t flows
The i n t e r v a l from 1219 t o 1463 m (4000 t o 4800 f t ) c o n s i s t s
equivalent
t o t h e Banbury B a s a l t o f m i d d l e P l i o c e n e
age.
B a s a l t s from t h e i n t e r v a l 1829 t o 2179 m (6000 t o 7150 f t ) a r e p e t r o g r a p h i c a l l y s i m i l a r t o those from 1219 t o 1463 m (4000 t o 4800 f t ) and a r e c o r r e l a t e d t o t h e Banbury B a s a l t .
report
the
Malde and Powers (1962) and Malde e t a l . (1963)
Banbury B a s a l t c o n t a i n s
a 122-m-thick
(400 f t )
lower
unit
of
a l t e r e d o l i v i n e b a s a l t , which i s separated from a 152-m-thick
(500 f t ) upper
u n i t o f 01 i v i n e basal t and p l a g i o c l ase-ol i v i n e p o r p h y r i t i c basal t by 30 m (100
f t ) o f sedimentary rock.
1219-
a
t o 1463-m
interval
P e t r o g r a p h i c s t u d i e s o f t h e b a s a l t c u t t i n g s from t h e
(4000-
t o 4800-ft)
reveal
o n l y minor
amounts
of
TABLE I
DEPTH INTERVALS AND PRINCIPAL LITHOLOGIES PENETRATED I N BOSTIC l - A WELL
-
0 t o 213 m ( 0 t o 700 f t ) : Not sampled d u r i n g d r i l l i n g ; i t p r o b a b l y
c o n s i s t s of a l l u v i u m u n d e r l a i n by shale w i t h t h i n i n t e r b e d d e d c l a y e y
sandstone and s i 1 t s t o n e .
-
213 t o 417 m (700 t o 1400 f t ) :
sandstone and s i l t s t o n e i n t e r b e d s
t o 381 m (1257 f t ) , and b a s a l t t o
G u l f Energy M i n e r a l s Co. l i t h o l o g y
-
427 t o 536 m (1400 t o 1730 f t ) : M o s t l y dark brown and b l a c k a p h a n i t i c
t o microporphyritic basalt.
1 t o 2 mm z e o l i t e - f i l l e d amygdules occur
between 463 and 509 m (1520 t o 1670 f t ) .
-
536 t o 1219 m (1760 t o 4000 f t ) : M a i n l y sandstone and shale, m i n o r
amounts o f carbonate and p y r i t e .
Minor b a s a l t .
I n f o r m a t i o n from A1
Griffi t h ' s 1 it h o l o g y l o g .
-
1219 t o 1463 m (4000 t o 4800 f t ) :
Basalt flows o f i n t e r s e r t a l t o
s u b o p h i t i c t e x t u r e w i t h m i n o r amounts of o l i v i n e .
Exceedingly f i n e g r a i n e d b a s a l t w i t h v a r i o l i t i c t e x t u r e , p r e s e n t i n t h e i n t e r v a l from
1247 t o 1250 m (4090 t o 4100 f t ) , i s i n t e r p r e t e d t o be fragments o f
p i l l o w s . P i l l o w b a s a l t s a r e mentioned by Malde and Powers (1962) and
Malde e t a l . (1963) o n l y i n t h e i r d e s c r i p t i o n s o f Bruneau and Snake
R i v e r basal t s
L i g h t gray c l a y e y shale w i t h t h i n
t o 350-m ( 1 1 5 5 - f t ) depth, sandstone
427 m (1410 f t ) . I n f o r m a t i o n from
log.
.
-
1463 t o 1829 m (4800 t o 6000 f t ) : M o s t l y shale w i t h some i n t e r b e d d e d
sandstone, c l a y s t o n e , and b a s a l t .
I n f o r m a t i o n from A1 G r i f f i t h ' s
1i t h o l o g y l o g .
-
1829 t o 2179 m (6000 t o 7150 f t ) : B a s a l t and i n t e r b e d d e d sediments,
mostly s i 1tstone.
Only t h e basal t i c i n t e r v a l s were examined i n
detail.
Except f o r an i n c r e a s e i n a l t e r a t i o n , t h e b a s a l t s i n t h i s
i n t e r v a l a r e p e t r o g r a p h i c a l l y v e r y s i m i l a r t o those i n t h e 1219- t o
1463-111 i n t e r v a l (4000 t o 4800 f t ) . Three k i n d s a r e p r e s e n t :
coarseg r a i n e d b a s a l t w i t h s u b o p h i t i c t e x t u r e and o n l y m i n o r o l i v i n e (Type
I ) ,v a r i o l i t i c b a s a l t w i t h quench t e x t u r e s (Type 111, and g l a s s y
p l a g i o c l a s e p o r p h y r i t i c b a s a l t (Type 111).
The Types I 1 and I 1 1
b a s a l t s a r e i n t e r p r e t e d t o be p i l l o w fragments and g l a s s y f l o w tops.
-
2179 t o 2265 m (7150 t o 7430 f t ) : F i n e - g r a i n e d s i l i c i c t u f f c o n t a i n i n g phenocrysts o f p l a g i o c l a s e , potassium f e l d s p a r , m a g n e t i t e , and
pseudomorphs o f c h l o r i t e a f t e r pyroxene.
-
2265 t o 2460 m (7430 t o 8070 f t ) :
2179-111 i n t e r v a l .
-
2460 t o 2949 m (8070 t o 9676 f t ) :
These c u t t i n g s c o n s i s t p r i m a r i l y o f
The few t h i n f r e s h b a s a l t i n t e r h y d r o t h e r m a l l y a1 t e r e d s i l i c i c t u f f s .
v a l s a r e i n t e r p r e t e d as d i k e s .
B a s a l t s i m i l a r t o t h a t i n 1829- t o
9
Shale and Sandstone
Bruneau Formation
Basalt
Shale and Sandstone
Glenns Ferry
Minor Basalt
Basalt with thin Sandstone
near top
Shale, Claystone
Minor Sandstone
Formation
Banbury Basalt
and
lnterbedded
lnterbedded Basalt
and Shale
Sediments
Silicic Volcanics
Basalt
ldaveda Volcanics
Silicic Volcanics
with
some Basalt
Total Depth
F i g . 3.
Bostic 1 - A lithology log.
o l i v i n e and i t i s n o t a d o m i n a n t phenocryst phase.
The sedimentary sequence
between the upper and lower Banbury basal t s observed i n the well a l s o appears
t o be thicker t h a n t h a t described by Malde and Powers.
Hydrothermally a l t e r e d
c a t a c l a s t i c b a s a l t fragments i n the c u t t i n g s a t 1295 m (4250 f t ) suggest the
well i n t e r s e c t s a t l e a s t one f a u l t zone.
The s i l i c i c rocks a t depths of 2179 t o 2949 m (7150 t o 9676 f t ) are
i n t e r p r e t e d as p a r t of the Lower P1 iocene I d a v a d a Volcanics ( s e e below) , w h i c h
a r e exposed i n the M t . Bennett H i l l s 11 kni northeast of the well ( F i g . 1). A
schematic cross-section t h r o u g h the Bostic 1 - A well i s shown i n Fig. 4.
V.
DISCUSSION
Two questions a r i s e concerning the s i l i c i c volcanics i n the Bostic 1 - A
well.
The f i r s t regards Challis Volcanics:
I s Challis encountered i n the
well, and i f n o t , does i t underlie I d a v a d a beneath the well?
Malde e t a1 . (1963) distinguish I d a v a d a from Challis by the absence of
quartz, sanidine, b i o t i t e , a n d hornblende in the I d a v a d a . Our work indicates
t h a t , while s t i l l separable from the Challis by the absence o f hornblende and
b i o t i t e , the I d a v a d a volcanics generally contain plagioclase, two pyroxenes ,
10
The second question concerning the s i l i c i c volcanics i s whether a l l the
s i l i c i c rocks a r e Idavada, even though there i s a thick b a s a l t sequence from
2265- t o 2460-m depth (7430 t o 8070 f t ) .
.
Geologic maps (Malde e t a1 1563; J . Gardner and S. Wood, Los Alamos
National Laboratory , i n prep. ) , show Banbury Basal t overlying the Lower
Pliocene I d a v a d a Volcanics i n nearby areas ( F i g . 1 ) . East of the prospect
area, the Banbury and Idavada a r e l o c a l l y separated by up t o 152 m (500 f t ) O f
densely welded q u a r t z and sanidine phyric r h y o l i t e t u f f o f Lower Pliocene age,
termed the Rhyolite of Magic Reservoir (Malde e t a l . 19631, b u t no b a s a l t l i e s
between t h i s r h y o l i t e and the underlying I d a v a d a Volcanics.
Malde and Powers ( 1 9 6 2 ) describe b a s a l t s underlying and intertonguing
w i t h C h a l l i s equivalents (Miocene age r h y o l i t e s ) i n the Owyhee and Jarbidge
Mountains 80-100 km (50-75 m i ) west of
the prospect area.
Smith
(1966)
reports diktytaxi t i c ol ivine basal t s i n t e r c a l a t e d w i t h Idavada northeast of
the Bostic well i n the eastern M t . Bennett H i l l s .
A1 t h o u g h basal t s a r e commonly interbedded w i t h si1 i c i c volcanic rocks on
the margins o f the Western Snake River P l a i n , none o f the reported occurrences
i n d i c a t e such thick b a s a l t i n t e r v a l s a s seen i n the Bostic well , and no i n t e r bedding of b a s a l t s w i t h Idavada volcanics was mapped i n the western M t .
Bennett H i l l s by Gardner and Wood ( i n p r e p . ) .
Idavada Volcanics
in
the M t .
Bennett H i l l s were erupted d u r i n g
the
f a u l t i n g associated w i t h the opening of the Snake River Plain (Gardner and
Wood, i n p r e p . ) , and the areal extent of each u n i t i s determined by the
topography onto which they were erupted ( S m i t h 1966; Gardner and Wood, i n
prep.).
Since the thick b a s a l t s seen i n the well occur i n the upper p a r t of
the Idavada, they may have been confined t o the lowlands by down-faulting
along the margins of the plain and therefore a r e not seen i n the u p l i f t e d M t .
Bennett H i l l s section.
I t was n o t possible t o c o r r e l a t e various flow units of
the Idavada
Volcanics as mapped on the surface with s p e c i f i c i n t e r v a l s w i t h i n the well.
The chemistry of the surface u n i t s does n o t vary enough t o make them d i s t i n c t i v e , and v a r i a t i o n s i n phenocryst content and composition were ob1 i t e r a t e d i n
the c u t t i n g s by the h i g h degree of a l t e r a t i o n .
Descriptions i n t h i s r e p o r t ,
compared t o the s t r u c t u r a l and s t r a t i g r a p h i c data of Gardner and Wood ( i n
p r e p . ) , suggest there may be as l i t t l e as 0.2 t o 0.3 km more of Idavada
beneath the Bostic l - A well.
12
I d a h o B a t h o l i t h r o c k s occur o n l y as fragments i n sedimentary h o r i z o n s i n
the well.
i n s i t u g r a n i t i c r o c k s below t h e B o s t i c i s n o t p o s s i b l e t o
Depth t o --
e v a l u a t e based on our data.
Geophysical modeling r e p o r t e d i n Arney e t a l .
(1982) suggests a g r e a t t h i c k n e s s o f b a s a l t beneath t h e B o s t i c w e l l , and t h a t
p r o b a b l y no g r a n i t i c r o c k s o f t h e Idaho B a t h o l i t h u n d e r l i e t h i s p o r t i o n o f t h e
Snake R i v e r P l a i n .
REFERENCES
Arney, B. , "Evidence o f Former Higher Temperatures from A1 t e r a t i o n M i n e r a l 5,
B o s t i c l - A Well, Mountain Home, Idaho," GRC Trans, 6 pp. 3-6 (1982).
Arney, B. H., F. E. G o f f , and Harding-Lawson Associates, " E v a l u a t i o n o f t h e
Hot Dry Rock Geothermal P o t e n t i a l o f an Area Near Mountain Home, Idaho," Los
Alamos N a t i o n a l L a b o r a t o r y r e p o r t LA-9365-HDR (May 1981).
Gardner, J . N. and S. H. Wood, "Geologic Map o f t h e Bennett Mountain Area,
Elmore County, Idaho," Los Alamos N a t i o n a l L a b o r a t o r y map, scale 1:62,500 ( i n
preparation).
"X-ray Fluorescence A n a l y s i s Major Elements i n S i l i c i c
Hagan, R. C.,
M i n e r a l s, ' I Los A1 amos N a t i o n a l L a b o r a t o r y r e p o r t LA-9400-MS ( September 1982 1.
Malde, H. E. and H. A. Powers, "Geologic Map o f t h e Glenns Ferry-Hagerman
Area, West-central Snake R i v e r P l a i n , Idaho," US Geol. Surv., Misc. Geol.
I n v e s t . Map No. 1-696, Scale 1:48 000 (1972).
Malde, H. E. and H. A. Powers, "Upper Cenozoic S t r a t i g r a p h y o f Western Snake
73, 1197-1220 (1962).
R i v e r P l a i n , Idaho," Geol. SOC. Am. B u l l . Malde, H. E., H. A. Powers, and C. H. M a r s h a l l , "Reconnaissance Geologic Map
Geol. Surv. Misc.
o f t h e W e s t - c e n t r a l Snake R i v e r P l a i n , I d a h o , " U.S.
G e o l o g i c a l I n v e s t i g a t i o n Map 1-373, s c a l e 1:125,000 (1963).
Smith, C. L., "Geology o f Eastern M t . Bennett H i l l s , Camas, Gooding,
L i n c o l n Counties, Idaho, Ph.D. t h e s i s , Univ. o f Idaho, 129 pp. (1966).
and
13
Uriirsua? features of individual samples from t h i s interval are:
4760-5800
5800-7150
4240-4250
4250-4260
4470-4480
5 1 0 % c a t a c l a s t i c b a s a l t fragments
2-5% quartz and muscovite c r y s t a l s
One fragment of a zeol i te-f i 11ed amygdul e
4680-4690
and 4700-4710
One
percent
of
the
basalt
fragments
a r e coated w i t h sugary green o p a l ( ? ) .
Not examined.
Primarily sedimentary w i t h some b a s a l t i n t e r p r e t e d
as interbedded sediments of Banbury Basalt.
Information from A1
G r i f f i t h ' s d r i l l e r s log.
(7125 f t on e l e c t r i c logs, lag correction would make c u t t i n g s depth
7140 f t )
Basalt w i t h interbedded sediments. Apparently several
flows separated by sedimentary i n t e r v a l s .
The i n t e r i o r of each
.
flow i s a l t e r e d and z e o l i t i z e d , b u t the tops and bottoms a r e general l y fresher.
5800-5950
Basal t w i t h
pl a g i o c l a s e a n d
pyroxene
phenocrysts.
A1 t e r e d , c o n t a i n s zeol i t e s a n d / o r c a l c i t e .
c u t t i n g s appear brownish and s o i l covered.
Rounded
Base of u n i t
i s fine-grained, blue-gray b a s a l t .
5950-6040
Sedimentary l a y e r , upper p a r t i s c o a r s e - g r a i n e d a n d
c u t t i n g s look l i k e a l t e r e d g r a n i t e , b u t t h i n section
shows them t o be wacke consisting of quartz and a l t e r e d
With
feldspar i n a pale greenish gray clay m a t r i x .
g r e a t e r d e p t h , fine-grained volcanics, b a s a l t , and a
6040-6050
f i n e r grained v a r i e t y of the green wacke appear.
Fresh glassy b a s a l t - possibly a dike.
6050-6070
Si1 t s t o n e , mixed w i t h fine-grained basal ts.
6070-6350
S e v e r a l b a s a l t f l o w s . Vary from very black c o a r s e grained fresh rock, t o a l t e r e d gray-green o r oxidized
red rocks w i t h z e o l i t e s and green c l a y s ( ? ) .
Top and bottom of t h i s i n t e r v a l a r e s i l t s t o n e s , and
s i 1 t s t o n e comprises a t l e a s t 30% of c u t t i n g s throughout
the i n t e r v a l .
Beneath the upper s i l t s t o n e i s a fineg r a i n e d green wacke, s i m i l a r t o t h a t a t 5950 f t .
6350-6620
Coarse-grained,
below the wacke.
fresh,
black,
basalt
cuttings
appear
Basalt i s mixed w i t h s i l t s t o n e and
15
lost
circulation
materials
and
so
is
not a
clearly
defined u n i t .
6620-7150
B a s a l t f l o w s w i t h t h i n sedimentary i n t e r b e d s .
Thickest
sedimentary bed i s s i l t s t o n e between 7020-7050 f t .
argillite
varies
appears
between 7100
from v e r y
abundant t i n y
fresh
feldspar
black
laths,
ft.
and 7130
Basalt
and c o a r s e - g r a i n e d
to
a1 t e r e d ,
Red
with
zeol i t i z e d ,
r e d d i s h , o r green-gray.
7150-7420
(7380 f t on e l e c t r i c l o g s ,
7400 f t ) .
l a g c o r r e c t i o n f o r c u t t i n g s would make
P a l e l a v e n d e r - g r a y a p h a n i t i c s i l i c i c t u f f w i t h sparse
p h e n o c r y s t s o f f e l d s p a r and dark green c h l o r i t e a f t e r p y r o x e n e ( ? ) .
Top 20 f t a r e a l t e r e d c h a l k y green.
increases
appears
with
depth.
Some
toward base o f
unit.
Red s t a i n i n g and m o t t l i n g
brick-red
fragments.
A t 7230-7240
Green
clay
f t abundant c a l c i t e
and/or z e o l i t e , m a t r i x t o t a l l y a1 t e r e d b r i c k red.
7420-7460
Dark gray a p h a n i t i c s i l i c i c t u f f , and i n c r e a s i n g amounts o f b a s a l t .
A t 7430-7440 f t f r e s h dark b l a c k p l a g i o c l a s e p h y r i c b a s a l t .
Below
7440, p l a g i o c l a s e i s s m a l l e r b u t more d i s t i n c t because b a s a l t i s so
altered.
7460-8070
M o s t l y red, w i t h z e o l i t e - f i l l e d amygdules.
M o s t l y b a s a l t w i t h one p o s s i b l e sedimentary i n t e r v a l (7520-7570 f t )
which c o n t a i n s s i l t s t o n e , dark brown s h a l e and abundant d r i l l p i p e
No i n d i c a t i o n on l o g o f change i n d r i l l i n g , c i r c u l a t i o n
fragments.
or electrical
greenish
p r o p e r t i e s over t h a t i n t e r v a l .
plagioclase
laths
in a
r e d d i s h m a t r i x become g r e e n i s h
p l a g i o c l a s e l a t h s and g r e e n c l a y
in c r e a s i ng depth.
B a s a l t i s a1 t e r e d ;
i n a purplish matrix with
Zeol it e amygdule f i11 ings s c a t t e r e d t h r o u g h o u t .
Abundant z e o l i t e s a t 7790-7810, 7830-7850, and 7870-7880 f t .
B a s a l t a t base o f i n t e r v a l (8030-8070 f t ) , i s f r e s h and b l a c k and
appears a l m o s t g l a s s y from t h e i n t e r g r o w t h o f f r e s h pyroxene and
plagioclase.
8070-8080
I n t e r p r e t e d as d i k e because o f t h e l a c k o f a l t e r a t i o n .
A1 t e r e d s i 1 i c i c t u f f w i t h
abundant q u a r t z ,
and c h a l k y
feldspar.
Some t e r m i n a t e d q u a r t z c r y s t a l s up t o 2 mm l o n g .
8080-8190
Very
fine-grained,
dark
r e d t o medium gray t o p a l e p i n k ,
c l a y s t o n e o r s h a l e comprise 30-40% o f t h e c u t t i n g s .
in c l udes c u t t i ngs o f
basal t , p l a g i o c l ase
16
Interval also
porphyri t i c
s i l i c i c t u f f , s i 1 t s t o n e , and m i n o r z e o l i t e s and q u a r t z .
baked
pal e
green
8 190-8430
S i 1 i c i c t u f f , mostly p a l e
green a p h a n i t i c m a t r i x ,
but
with
plagioclase and abundant magnetite i n c r y s t a l c l u s t e r s u p t o 1 mm
i n diameter.
Green c’lay a1 t e r a t i o n increases w i t h depth.
Green
f l u o r i t e ( ? ) veins and f i l l i n g s above 8300 f t .
Fragments of l i g h t
p i n k t o red claystone appear a t 8270-8290 f t . Yellow-green (mostly
euhedral) epidote c r y s t a l s f i r s t appear a t 8390-8400 f t . Traces of
epidote coatings appear as h i g h as 8260 f t .
A few fragments of
d a r k red-brown vitrophyre w i t h c l e a r feldspar c r y s t a l s appear a t
8430 f e e t .
8430-8630
(8380-8605 on gamma log)
l i t e s and minor epidote.
Fine-grained d a r k gray b a s a l t w i t h zeoS i l t s t o n e fragments a t 8510-8530 f t may
be from a t h i n sediment interbed or may be downhole contaminants.
Alteration of b a s a l t t o white plagioclase and green clay i n a
reddish matrix i s most intense between 8510 and 8580 f t .
Pink
a p h a n i t i c ( s i 1 i c i c ? ) v o l c a n i c rock comprises a b o u t ha1 f t h e
c u t t i n g s a t 8610-8620 f t , b u t the 10 f t interval below t h i s i s
b a s a l t . No returns from 8630-8650 f t .
8650-8670
Predominantly s i l t s t o n e w i t h some b a s a l t , a1 tered s i l i c i c t u f f , and
v i trophyre.
8670-8710
Altered and s i l i c i f i e d t u f f , pale green and chalky-white.
colored staining i s intense toward base of i n t e r v a l .
8710-8720
8720-8730
8730-8820
SalmonEuhedral
p y r i t e i n the m a t r i x . Chlorite pseudomorphs.
Fine-grai ned d a r k gray basal t.
Mostly s i l t s t o n e , w i t h some b a s a l t t u f f or minor vitrophyre.
(-8780 on gamma l o g ) .
Pale gray, green t o lavender s i l i c i c t u f f
w i t h f i n e veining.
P y r i t e occurs i n small euhedral c r y s t a l s . One
fragment of massive p y r i t e i n the 8730-8740 f t i n t e r v a l . Salmon t o
red s t a i n i n g predominates down t o 8780 f t , green clay o r c h l o r i t e
a1 t e r a t i o n t o 8820 f t .
Chalky white material occurs throughout
interval ( f r e e and i n green matrix). No epidote i n t h i s i n t e r v a l .
Trace of green f l u o r i t e ( ? ) .
8820-8840
(8780-8801 on gamma l o g ) .
8840-8890
Mostly white or very l i g h t green s i l i c i f i e d t u f f .
8890-8900
appear veined or brecciated. Minor disseminated p y r i t e .
Fresh fine-grained b a s a l t as i n 8820-8840 f t .
Fresh fine-grained b a s a l t , possibly dike.
Many fragments
17
REFERENCES
Belluomini , S. G. and G. Van Houten, "Petrographic and S t r a t i g r a p h i c Correlat i o n of the Bostic 1 A Well," Harding-Lawson Associates r e p o r t t o Los Alamos
National Laboratory (1981).
APPENDIX B
GRAIN-MOUNT PETROGRAPHY
(Some descriptions modified from Belluomini and Van Houten, 1981.)
I n t e r v a l s selected f o r XRF a n a l y s i s indicated by " ( X R F ) " i n " I n t e r v a l " column.
( See "Procedures" f o r c r i t e r i a f o r sel ec t i on) .
I n terval
(ft)
4090-4100
Description
Ninety percent basal t , f i v e
percent
claystone , r e s t
individual
c r y s t a l s o f p l a g i o c l a s e ( p l a g ) , q u a r t z ( some show undual t o r y
e x t i n c t i o n ) , clinopyroxene ( c p x ) , minor ol i v i n e (01 1 , and a few
fragments of palagonite.
Claystone:
Fragments a r e massive and
composed predominantly of subequal amounts of exceedingly f i n e grained clay and fine angular t o subrounded quartz g r a i n s w i t h
minor amounts o f carbonate, opaques, and mafic minerals.
Basalt:
Texture mainly i n t e r s e r t a l
t o subophitic, l o c a l l y hyaloophitic o r amygdaloidal ( f i l l e d w i t h
Cpx and plag w i t h g l a s s and minor 01.
c l a y and carbonate).
Glass, 75% of which i s palagonitized,
l a r g e l y dark red t o red-brown,
r a r e l y pale brown.
colored i n plane-polarized l i g h t ( P P L )
Cpx i s tan-
and commonly zoned, some-
01 i s e i t h e r p a r t i a l l y
t i n i z e d o r marginally a l t e r e d t o iddingsite.
Opaques
s k e l e t a l h a b i t . Plag l a t h s show very l i t t l e o r no zoning.
dozen fragments of exceedingly fine-grained b a s a l t a r e a1 so
w i t h very long, narrow plag l a t h s (length-to-width r a t i o s
times i n an hourglass p a t t e r n .
is
serpenhave a
Half a
present
of 10-
2 0 : l ) t h a t a r e usually randomly oriented o r l o c a l l y show a weakly
developed v a r i o l i t i c texture s e t i n an a1 t e r e d groundmass of green
c l a y and granular opaques.
4150-4160
V i r t u a l l y i d e n t i c a l t o the above sample.
19
4240-4250
Lithology and percentage of various components i d e n t i c a l t o the
above two samples except for the addition of 5-10% hydrothermallya l t e r e d c a t a c l a s t i c b a s a l t and minor amounts of s i n g l e c r y s t a l s of
A1 so present a r e s i n g l e cryso x y b i o t i t e , carbonate, and quartz.
t a l s of cpx and unoxidized b i o t i t e t h a t show undulatory e x t i n c t i o n
and bent cleavage planes. C a t a c l a s t i c b a s a l t : Elongate fragments
w i t h a streaked f a b r i c .
Cpx completely granulated and generally
t o t a l l y converted t o epidote.
Plag has survived granulation much
b e t t e r than the cpx and t h u s occurs a s crudely developed augens
4400-4410
with undulose e x t i n c t i o n .
Very similar t o the above samples.
Tan color i n cpx more promin-
ent; a higher percent of the g l a s s i s palagonitized. Minute hopper
c r y s t a l s of plag occur i n some of the palagonite.
Stubby
4450-4470 Coarse-grained i n t e r s e r t a l t o subophi t i c f r e s h b a s a l t .
p l a g s t a i n e d yellow-brown a l o n g f r a c t u r e s , and p a l e t a n cpx
(XRF)
fractured along cleavage b u t unaltered, i n a groundmass of brown
pal agoni t i z e d gl a s s w i t h skel eta1 pl ag and t i n y magnetite. Opaque
minerals a r e l a r g e blocky, some s k e l e t a l ; magnetite and ilmenite.
Sparse serpentinized 01 c r y s t a l s . Tiny a c i c u l a r a p a t i t e inclusions
i n plag.
D i f f e r s from the above i n having l e s s
4540-4550 Almost t o t a l l y b a s a l t i c .
o r i g i n a l g l a s s , s l i g h t l y codrser grain s i z e , and s l i g h t l y more 01.
One fragment of dark red-black g l a s s w i t h a s i n g l e plag c r y s t a l .
Most g l a s s f r e s h , and
4720-4730 Basalt noticeably f r e s h e r than above.
contains abundant a p a t i t e needles, plag hopper c r y s t a l s , and minute
5890-5900
pl umose cpx c r y s t a l 1 i t e s .
Not a t r u l y homogeneous sample.
( X R F1
palagonitized g l a s s , 30% fine- t o medium-grained b a s a l t .
6050-6060
Largely subophi t i c plagioclase phyric b a s a l t w i t h l o c a l l y devel oped
Predominantly (870%) d e v i t r i f i e d
o p h i t i c t e x t u r e . Plag i s f r e s h , cpx l o c a l l y rimmed and/or veined
w i t h hematite , groundmass enti r e l y pal agoni t e , green cl ay, and/or
Cpx strongly tandark-bl ack , red-bl ack g l a s s (chl orophaei t e ? )
Five percent claystone
as
colored in plane-polarized 1 i g h t .
above, b u t s l i g h t l y coarser grained and r i c h e r i n carbonate. One
percent t o t a l s i n g l e c r y s t a l s of plag, red-black g l a s s conta n i n g
.
scattered
20
plag
laths
l o c a l l y converted
to c l a y ( ? ) , devitr fied
g l a s s , a n d fragments o f chi1 1 ed basal t w i t h weakly devel oped
variol i t i c texture ( s e e sample 4090-4200 f t ) .
6130-6140
Largely subophi t i c t o i n t e r s e r t a l pyroxene phyric ( r a r e l y o p h i t i c )
b a s a l t w i t h l a r g e amounts of c l a y i n t h e groundmass a n d i n
amygdul e s .
Mi nor devel opment of zeol i t e s i n amygdul e s .
Five
6220-6230
(XRF)
percent t o t a l d e v i t r i f i e d g l a s s ( s p h e r u l i t i c ) , s i n g l e c r y s t a l s of
plag and cpx, black g l a s s w i t h v a r i o l e s of green c l a y , and c h i l l e d ,
weakly variol i t i c b a s a l t .
Homogeneous b u t very a1 tered sample.
F i ne-grai ned t o variol i t i c
b a s a l t w i t h plag phenocrysts and sparse 01 r e l i c t s , now heavily
outlined by opaques.
Groundmass choked w i t h tiny (<0.02 mm)
opaques , rendering g r a i n s nearly opaque.
I n t e r s t i t i a1 pyroxene
<0.01 mm, and a l t e r e d green g l a s s .
Some of the coarser plag has
green clay replacement, and c h l o r i t e f i l l s v e s i c l e s .
have b r i g h t o r a n g e - r e d
a1 t e r a t i o n of
Some grains
pyroxene and p l a g
and
s e r p e n t i n i z e d ( ? ) 01.
6250-6260
6320-6330
Basalt w i t h minor claystone and d e v i t r i f i e d g l a s s .
above. Basalt fragments 1 oca1 l y peppered
zeol i t e s .
The bulk of t h i s sample i s composed of two
Type I S u b o p h i t i c plag p h y r i c ( a s
interval )
Type I1 - Very long, narrow plagioclase
.
Lithologies as
w i t h equant opaques.
No
types of b a s a l t :
d e s c r i b e d i n 6050-6060
l a t h s usually s e t i n a
dark brown, nearly opaque groundmass.
The plag i n Type I1 i s often v a r i o l i t i c ; a few hopper c r y s t a l s are
usually present.
Some of the groundmass i s a l t e r e d t o green c l a y
and there a r e a few amygdaloidal z e o l i t e s .
Cpx occurs only as
6370-6380
minute granules. Approximately 2% d e v i t r i f i e d g l a s s ( s p h e r u l i t i c )
and t r a c e s of red-black vitrophyre w i t h a few plag l a t h s .
Seventy percent sedimentary, r a n g i n g from cl aystone ( a s above)
t o fine-grained sandstone w i t h a clay m a t r i x and angular quartz
grains.
Thirty percent b a s a l t , both Type I and I1 ( s e e above).
Minor amounts of individual c r y s t a l s o f cpx, carbonate , zeol i t e s ,
serpentinized 01 , and d e v i t r i f i e d g l a s s .
6560-6570
Mixture of claystone and Type I and 11 b a s a l t s w i t h t r a c e amounts
of d e v i t r i f i e d g l a s s and orange palagonite.
The Type I b a s a l t
21
contains minor amounts of 01 and z e o l i t e s .
Five percent b a s a l t .
fragments w i t h fresh g l a s s and skeletal opaques ( s i m i l a r t o 40004800 f t ) . This Type I b a s a l t seems t o grade i n t o another type of
basalt:
Type I11 - Dark red-black g l a s s p a r t i a l l y converted t o green clay
and enveloping cloudy plag l a t h s , with minor cpx.
6630-6640
Largely Type I b a s a l t w i t h lesser amounts of Type I11 b a s a l t and
only minor amounts of Type I 1 b a s a l t , claystone, and d e v i t r i f i e d
g l a s s . Type I b a s a l t groundmass i s l a r g e l y dark red t o red-black
.
It a1 so contains abundant green clay
and zeol i t e s , and i s 1oca1 l y vei ned w i t h hemati t e .
glass or chl orophaei t e ( ? )
6750-6760
(XRF)
Mixture of 30% Type I , 20% Type 11, and 50% Type I11 b a s a l t .
Abundant z e o l i t e s i n a l l three b a s a l t types. The groundmass of the
Type I11 b a s a l t i s almost opaque dark brown-black from oxidation
and peppered w i t h opaques.
Trace amounts of catacl a s t i c b a s a l t .
Hand-picked XRF sample:
not homogeneous sample.
Mostly ( ~ 6 0 % )
o p h i t i c t o subophitic b a s a l t .
Yellowish-brown a1 t e r a t i o n o f
pyroxene especially a t edges of g r a i n , some green clay replacing
f e l dspar. Opaques a r e magnetite and ilmeni t e . 30% coarser grained
One piece fine-grained si1 tstone.
plag i n opaque g l a s s matrix.
Vein c h l o r i t e , carbonate and quartz 5 feldspar.
6840-6850
Roughly equal amounts of Type I and I 1 b a s a l t s and dark orangebrown pal agoni t e ; minor amounts of Type I I1 basal t. Most pal ogoni t e
contains plag l a t h s and shows local r e l i c t p e r l i t i c cracks.
c l aystone.
Minor
6960-6970
Type I b a s a l t twice a s abundant a s Type 11.
Minor amounts of
marginally serpentinized 01 i n Type I .
Some fragments have f r e s h
glass.
Minor amounts of claystone, d e v i t r i f i e d g l a s s , and orange
pal agoni t e .
7020-7030
Thirty percent carbonate-rich claystone, 25% Type I b a s a l t , and 40%
7160-7170
Type I 1 b a s a l t .
Type I b a s a l t groundmass has abundant clay and
pal agoni t e . M i nor c a l c i t e c r y s t a l s , zeol i t e , and Type I I I basal t .
Three t o f i v e percent t o t a l claystone and Type I b a s a l t . Rest i s
devitrified tuff.
R e l i c t shards can be recognized i n a few
fragments.
22
fied s i l i c i c volcanic ( t u f f ? ) and claystone.
8020-8030
Sixty percent Type I b a s a l t w i t h a clay-rich groundmass, 20% Type
Minor amounts of
d e v i t r i f i e d s i l i c i c v o l c a n i c , Type I 1 b a s a l t , a n d c l a y - f i l l e d
amygdules, some of which contain intergrown z e o l i t e s .
Mainly fresh subophi t i c basal t w i t h some groundmass cl ay
Mi nor
amounts of a l l three b a s a l t types, d e v i t r i f i e d s i l i c i c volcanic
( l o c a l l y s p h e r u l i t i c ) , and claystone.
Two b a s a l t types.
Predominantly ( ~ . 8 0 % )coarse-grained (0.5-1.0
mm) fresh subophitic to i n t e r s e r t a l b a s a l t .
Sparse opaques are
mostly blocky magnetite. Minor c h l o r i t e a1 t e r a t i o n of feldspar and
pyroxene.
Fragment of vein epidote.
Rest of grains are opaque
g l a s s , most containing t h i n skeletal feldspar l a t h s .
I11 b a s a l t ,
8030-8040
8050-8060
( XRF 1
8070-8080
and 20% carbonate-poor claystone.
.
Sixty percent d e v i t r i f i e d s i l i c i c volcanic w i t h large r e l i c t cryst a l s of embayed q u a r t z and f e l d s p a r a n d minor a l t e r a t i o n t o
epidote; r a r e g r a n i t i c fragments exhibiting p e r t h i t e ; l a r g e f r e e
microcline c r y s t a l s ; 20% each of Type I and I 1 b a s a l t . Traces of
cl aystone and opaque bl ack g l a s s (without c r y s t a l s )
Five-ten percent b a s a l t ; subequal amounts of Type I and 11. Rest
i s d e v i t r i f i e d s i l i c i c volcanic; minute epidote i s a b u n d a n t i n the
groundmass.
.
8240-8250
8260-8270
Coarsely d e v i t r i f i e d t u f f .
Original s h a r d s t r u c t u r e l o s t . Small
(XRF)
patches of brown clay and c h l o r i t e and minor epidote a l t e r a t i o n i n
groundmass. Larger patches of carbonate replacement. Voids f i l l e d
w i t h chl ori t e t potassium feldspar and q u a r t z .
P1 ag phenocrysts
8430-8440
a r e abundant and very a l t e r e d .
Rounded opaques are probably
magnetite. No pseudomorphs a f t e r pyroxene or 01. Rare sphene.
Seventy-five percent d e v i t r i f i e d si1 i c i c volcanic ( t u f f ) as i n
8070-8080 f t , strongly epidotized. About 5% of the fragments show
evidence of re1 i c t welded t e x t u r e s ; d e v i t r i f i e d t u f f a1 so contains
several bl ocky pseudomorphs of chl o r i t e a f t e r pyroxene and 01 ; 20%
Type I a n d 5% Type I 1 b a s a l t .
Traces of calcareous claystone and
opaque red-bl ack gl ass.
8530-8540
(XRF 1
24
Mostly homogeneous sample of medium-grained subophi t i c b a s a l t w i t h
a b u n d a n t blocky m a g n e t i t e 0 . 0 5 mm diam.
C h l o r i t e i s mostly
interstitial.
Some grains very f r e s h , some have c h l o r i t e a1 t e r a -
tion of plag and pyroxene. Two grains of plag l a t h s enclosed i n
red-black opaque g l a s s ; a few grains f i n e r grained without subo p h i t i c texture.
No 01.
Prehnite and epidote which appeared i n
XRD p a t t e r n do not appear i n t h i s hand-picked sample.
8600-86 10 Largely b a s a l t , 80% Type I w i t h t r a c e s o f 01, groundmass w i t h
abundant hematite.
Rest i s Type 11.
One percent t o t a l c a l c i t e
c r y s t a l s , s e r p e n t i n i z e d 01 c r y s t a l s , z e o l i t e , c l a y - f i l l e d
amygdules, claystone, and d e v i t r i f i e d t u f f ( l o c a l l y s p h e r u l i t i c ) .
8670-8680
F o r t y p e r c e n t d e v i t r i f i e d s i l i c i c t u f f ( l o c a l l y developed
welding?); 40% Type I b a s a l t w i t h abundant clay. Minor palagonite
and s k e l e t a l opaques i n the groundmass, 15%, carbonate-rich claystone. Rest i s Type I 1 and I11 b a s a l t .
8750-8760
(XRF 1
Coarsely d e v i t r i f i e d t u f f , some plumose d e v i t r i f i c a t i o n . Original
texture ob1 i t e r a t e d .
Green clay a n d carbonate rep1 acement of
Sparse phenocrysts.
Rare
f e l d s p a r s extensive i n some grains.
quartz
phenocrysts w i t h
secondary
c h l o r i t e pseudomorphs a f t e r pyroxene.
bi-pyrami dal
overgrowths
and
Opaques sparse and sharply
euhedral ( c u b i c ) .
Some p e r l i t i c cracks s t i l l
8800-88 10 Medium t o f i n e l y d e v i t r i f i e d t u f f .
apparent.
Some plumose d e v i t r i f i c a t i o n .
F a i r l y homogeneous
(XRF)
sample, s t r o n g l y a1 t e r e d w i t h e x t e n s i v e chl o r i t e and c a l c i t e
replacement of groundmass.
Spray of p r e h n i t e ( ? ) i n one grain.
Sparse phenocrysts of very a1 t e r e d pl ag.
Sparse , usual l y small
opaques, surrounded by rounded a l t e r a t i o n rims.
8830-8840
Seventy-five percent b a s a l t , (50% Type I 1 and 25% Type I ) . Rest i s
claystone and d e v i t r i f i e d s i 1 i c i c volcanic.
Minor amounts of
cal c i t e , zeol i t e c r y s t a l s , and pal agoni t e .
8970-8980
Coarsely d e v i t r i f i e d t u f f , f a i r l y homogeneous sample. Groundmass
(XRF)
contains some clay.
C h l o r i t e occurs i n the groundmass and f i l l s
voids.
Small carbonate veins occur i n a few grains. Phenocrysts
-(10% of the rock and a r e extremely a l t e r e d . Plag contains abundant
opaque spots, small c l u s t e r s of epidote c r y s t a l s and c l e a r patches
of a l b i t e .
The s i n g l e pyroxene has been a1 tered t o c h l o r i t e .
Sparse opaques appear resorbed and embayed. Sphene i s associated
w i t h some ooaeues.
25
9060-9070 S i x t y p e r c e n t d e v i t r i f i e d s i l i c i c v o l c a n i c w i t h r e l i c t p l a g c r y s t a l s and pseudomorphs o f c h l o r i t e a f t e r c p x ( ? ) o r o l ( ? ) ;
s t r o n g l y s p h e r u l i t i c w i t h abundant c l a y i n t h e groundmass;
locally
30% Type
I I b a s a l t , 5% Type I b a s a l t w i t h m i n o r 01 and green c l a y i n groundmass.
Minor
claystone,
clay-filled
amygdules,
and
cataclastic
basalt.
9110-9120 Subequal
amounts
of
I and I 1 b a s a l t s .
Type
Abundant
amygdules and v e i n s o f c a l c i t e , q u a r t z , and e p i d o t e .
calcite
M i n o r amounts
o f c a t a c l a s t i c b a s a l t , c l a y s t o n e , and d e v i t r i f i e d s i l i c i c v o l c a n i c .
9130-9150 Coarse-grained a1 t e r e d b a s a l t .
(XRF)
and a r e i l m e n i t e and b l ocky
some c h l o r i t e a f t e r
mass.
and skel e t a 1 magnetite.
Grey-green
e p i d o t e and m i n o r c a l c i t e rep1 acement i n
a1 t e r a t i o n of groundmass,
plag,
Opaques comprise 5-7% o f t h e r o c k
pyroxene.
Some e p i d o t e i n t h e ground-
Fragment o f c h l o r i t e and p r e h n i t e v e i n o r amygdule ( w i t h
some e p i d o t e ? )
.
9220-9250 Homogeneous sample o f f i n e - g r a i ned ((0.25
mm 1ong ) p l ag i n a1 t e r e d
(XRF 1
and
nearly
opaque
g l assy
matrix.
i n c l u d e b l o c k y m a g n e t i t e and
Fragments
of
fracture
Opaques
ilmenite.
filling
barely
Epidote
quartz
discernible,
filling
epidote.
2
voids.
Strained
e x t i n c t i o n i n granular vein quartz.
9380-9390 S u b e q u a l
amounts
of
devitrified
silicic
s p h e r u l i t i c w i t h abundant groundmass e p i d o t e )
basalt.
volcanic
and l a r g e l y Type I
Ten p e r c e n t o f t h e b a s a l t i s u n a l t e r e d ,
cpx-plag
phyric.
Silicic
volcanic
(locally
contains
subophitic,
relict
and
feldspar
phenocrysts, and pseudomorphs o f c h l o r i t e a f t e r cpx and o l ( ? ) .
9420-9460 C o a r s e l y d e v i t r i f i e d t u f f ,
(XRF 1
brown spherul ites.
a1 t e r e d ( ? ) dark
Original
brown.
Some l i g h t e r
t e x t u r e s ob1 i t e r a t e d .
m i n o r and o c c u r s m o s t l y as v o i d and f r a c t u r e f i l l i n g s .
-<lo%.
C h l o r i t e is
Phenocrysts
P l a g c o n t a i n s many t i n y e l o n g a t e opaques, perhaps t h e r e s u l t
o f e x c l u s i o n o f opaque m a t t e r a l o n g cleavage p l a n e s on r e c r y s t a l lization.
Small patches o f green c l a y replacement and small c l e a r
a1 b i t e ( ? ) patches occur i n p l ag.
Some phenocrysts appear resorbed.
Sparse opaques rounded and resorbed.
Sparse c h l o r i t e pseudomorphs
a f t e r pyroxene(?).
9500-9510 N i n e t y - f i v e p e r c e n t d e v i t r i f i e d s i 1 i c i c v o l c a n i c
r e l i c t p l a g phenocrysts.
26
\
( a s above) w i t h
F i v e p e r c e n t Type I and Type I 1 b a s a l t s .
Seventy p e r c e n t d e v i t r i f i e d s i l i c i c v o l c a n i c , 30% b a s a l t ( a l l t h r e e
9590-9600
types).
M i nor c l aystone.
9676 (TD)
Some v a r i a t i o n i n d e v i t r i f i c a t i o n g r a i n s i z e ,
(XRF)
devitrified.
F a i n t r e 1 i c t per1 i t i c c r a c k s ,
random o u t l i n e d w i t h c h l o r i t e .
spread throughout
but mostly
finely
b o t h c o n c e n t r i c and
Patchy c h l o r i t e and e p i d o t e wide-
t h e groundmass.
Phenocrysts >lo%.
P1 ag v i r -
t u a l l y u n d i s t i n g u i s h a b l e i n p l a n e l i g h t because o f r e c r y s t a l 1 i z a t i o n t o a l b i t e w i t h abundant opaque e x c l u s i o n s .
i n plag.
Opaques a r e rounded.
Minor epidote
A c l u s t e r o f small q u a r t z may be
r e c r y s t a l l i z e d from l a r g e r g r a i n .
REFERENCES
B e l l u o m i n i , S. G. and G. Van Houten, " P e t r o g r a p h i c and S t r a t i g r a p h i c C o r r e l a t i o n o f t h e B o s t i c 1 A Well," Harding-Lawson A s s o c i a t e s r e p o r t t o Los Alamos
N a t i o n a l L a b o r a t o r y (1981).
APPENDIX C
CHEMICAL ANALYSES AND X-RAY DIFFRACTION DATA
TABLE C - I
CHEMICAL
ANALYSES OF S E L E C T E D ~BASALT SAMPLES FROM THE BOSTIC
85308540
ft
91309150
ft
O i ke
92309250
ft
45.62
48.13
48.89
44.06
2.51
1.88
3.13
3.61
13.98
13.65
14.47
13.29
13.21
11.60
12.02
11.04
13.02
14.83
44504470
ft
58805900
ft
62206230
ft
67506760
ft
77907800
ft
Si02
Ti02
46.00
45.59
45.00
45.24
46.67
3.48
3.09
2.81
2.65
2.06
A1203
FeO
13.29
15.06
13.45
14.42
14.79
12.77
13.63
12.64
(Dike?)
80508060
ft
HgO
6.47
6.37
6. a7
5.25
6.74
8.04
7.31
4.69
5.97
MnO
0.23
0.20
0.23
0.18
0.19
0.21
0.19
0.20
0. 23
CaO
8.90
9. 37
9.42
10.45
9.64
11.20
9.17
6.27
9.46
Na20
2.22
2.62
2.50
1.53
3.11
2.08
2. 95
3.04
1.95
0.67
0.41
0.38
0.26
0.39
0.14
0.54
1.96
0.74
0. 56
0. 38
0. 34
0.40
0. 33
0.63
K20
0. 72
p205
-
Totalb
97.04
0. 75
94.62
95.82
93.37
- 94.72
95.87
96.01
95.12
LA
WELL
0. 7 1
94.77
a See t e x t f o r discussion o f s e l e c t i o n c r i t e r i a .
T o t a l s a r e b e l i e v e d low because o f water contained i n a l t e r a t i o n m i n e r a l s .
Loss on i g n i t i o n performed i n a i r r e s u l t s i n gains due t o o x i d a t i o n of i r o n ,
so a c t u a l water content has n o t been determined.
27
APPENDIX C ( c o n t )
TABLE C-I1
ANALYSES OF S E L E C T E D ~ SAMPLES OF IDAVADA
CHEMICAL
72107220
ft
- - Si02
72.61
Ti02
0.55
68.05
0. 71
87508760
ft
_ _
-
88008810
ft
89708980
ft
94409460
ft
9676
(TO)
ft
73.49
69.11
72.44
71.93
73.22
0.41
0.59
0.50
0.56
0.50
13.73
11.36
13.14
12.11
11.67
11. 81
FeO
2. 79
3.84
2.61
3. 7 1
3.51
3.31
3.04
Mil0
0.35
0.72
0.34
0.91
0.37
0.46
0.30
MnO
0.04
0.07
0.04
0.06
0.06
0.05
0.05
A1203
CaO
1.03
2.33
1.21
2. 56
1. 14
1.25
1.56
Na20
2.79
2.90
1.82
4.49
2.37
2. 18
2.89
K20
5. 34
0.06
4.23
5.74
1.87
5.40
5.86
0.11
0.05
0.06
0.05
0.05
4.34
0.06
2. 1 7
1. 36
2. 51
2.47
0. 79
0.82
'2'5
.LO1
Total
a
28
12.04
82508270
ft
- - _
FROM THE BOSTIC LA
0. 75
98.35
98.86
98.43
99.01
See t e x t f o r d i s c u s s i o n o f s e l e c t i o n c r i t e r i a .
100.42
98.11
98.59
WELL
APPENDIX C ( c o n t )
TABLE C - I 1 1
AL.T E RAT I ON MINERAL.S DETERMINED BY XRD OF SELECTED U N I T S
v)
w
L-
-
w-
x o
5880-5900
v
x
6220-6230
x
6750-6760
x
X
V
h.S
x
x
x
p
t?
h
f
x
p
t
=
=
=
=
=
p
X
X
X
P
P
X
P
x
X
x
P
X
X
P
X
x
x
t?
8250-8270
p?
8750-8760 A
x
8800-8910
P
X
x
7210-7220 A
P
x
X
t
9130-9150
x
P
X
J
V
t
x
x
a
X
X
8530-8540
e
0
n
X
7790-7800
W
-i
L
t
J
L
0,
x
a
c,
c
7
O N
w
c)
c
l=
u a ~m
Basalt
-
w
w
c,c,
X
8970-3980
9420-9460
x
x
x
x
X
x
x
x?
p
9676 A
heulandite
stilbite
abundant
present
trace
29
~
z
--
HYDROCARBON LOG *
D U A L INDUCTION-LATEROLOG*
SHALE
TUFF
W
.....
SANDSTONE
I'"."'(]
VOLCANIC
FLOW
LITHOLOGY
0 - 700'
NO SAMPLES O B T A I N E D FROM T H E UPPER
213111 (700ft) OF T H E WELL.
100
SP
SPONTANEOUS
POTENTIAL
MILLIMHOS/M=
MILLIVOLTS
HYDROCARBON
loo0
0 HMS ,M 2 /M
EQUIPMENT D A T A :
Refer to S c h l u m b e r g e r Manual
or o r i g i n a l logs.
700 - 1150'
CLAY-SHALE; L I G H T GRAY, S L I G H T L Y
S I L T Y ; VERY T O MODERATELY CALCAREOUS,
WITH T H I N SANDSTONE A N D S I L T S T O N E BEDS.
SOME O F T H E SANDSTONE A N D SHALE
C O N T A I N S ALTERED V O L C A N I C GLASS.
00
CONDUCTIVITY
Hydrocarbon Log
bY
Continental Laboratories
B i t Size 8-314"
T y p e FJuid in Hole:
F r e s h M u d (FGM)
00
DEEP I N D U C T I O N LOG
5 00
IO00
0
I
RESIST I V l T Y
H)O
OHM& H'/H
DEZP INDUCTION LOG
10
MV
300
000
-
NO SAMPLES I N T H I S N T E R V A L
bl+
AVERAGED IATEROLOC-I
AMP. A Y E : LATEROLOC- I
I
Z
100
0
-
).
cy:
2 00
a
IO0
W
z
W
Z
u
cy:
0
W
30 0
I-
U
E
cy:
0
u.
IVI
p?
-
a
W
3
-.I
0
a
400
1150 - 1250'
SANDSTONE
I-
3
a
W
z
1400 - 1760'
B A S A L T ; FRESH, B L A C K , GROUNDMASS I S
A P H A N I T I C T O GLASSY WITH FINE-GRAINED
PLAGIOCLASE A N D O L I V I N E . SMALL (1-2mm)
2 EO L I T E -F I L L E D AMY GD ULES OCCUR M I NOR
AMOUNTS OF CLAYSTONE A N D Q U A R T Z
C R Y S T A L S ARE ALSO PRESENT
3
.
p?
m
500
600
500
700
1760 - 2050'
SANDSTONE WITH TRACES O F P Y R I T E ,
BASALT, AND CARBONATE
2
80C
C
I-
I90(
d
IC
-7.
60(
- ?-
0
>
1001
C
L
p?
!lo(
!201
70(
>.
w
tY
cy:
z
w
U
W
LL
-
u
I-
0
-
VI
cy:
W
-.I
I-
a
z
z
-
2050
-
2990'
S H A L E : ARGILLACEOUS, WITH SOME
SANDSTONE AND B A S A L T ; S L I G H T L Y
CALCAREOUS, TUFFACEOUS.
w
V
* A I G r i f f i t h , MaY-JulY 1973
** G u l f M i n e r a l Resources Co.,September
UII I
1974
WELL L O C A T I O N : SW$, SW+, SEC: 25, T45, R8E
I
I
I
I
I
I
-I
I
I
I
I
I
I
I
I
Fig. A-1.
L i t h o l o g i c and g e o p h y s i c a l l o g s o f t h e B o s t i c l - A w e l l ,
and Van Houten 1981).
Idaho ( f r o m Belluomini
I
I
DUAL INDUCTION-LATEROLOG
H Y D R O C A R B O N LOG
w
E
.
DEPTH
a
Z
LITHOLOGY
I
SPONTANEOUS
POTENTIAL
I I
CONDUCTIVITY
I 1%
I I I I
~n I
I
I
HYDROCARBON
J
11
I
*.
'
.-
.*-
.-
"-
, I
'
I
I (
-.
. . . . . . . . . . .
~
2 400
1
. . * ..
. ,
.
.
--1r---, t
'. '
.
1
I
..
. .
r4-24-n
I
.
-- ..
. . . -. .
,
.
,
'
'-I
2500
'I
. . . . . . . . . .. . . .,
.-
2600
800 -
2700
I .-:
----.
2800
2900
900-
3000
'
2 990-4000'
SANDSTONE AND MINOR SHALE, WITH T R A C E S
OF P Y R I T E , B A S A L T A N D C A R B O N A T E
t/a
etj*
#
,
I
____-_
*_.
.......
m
L
IO
IO
W
0.I
I
.
.
.
. . . . . .
..
3200
.
1000.
. .
_.
.- . . . . .
3100
- . . -
. . .
. . . .
...
3300
3400
I
.
.
.
.m
,
-
0.1
I
-4-21-n
.
..__..-.-,-
3500
I
,
,
,
t--
_ - . I .
---
I
',
1
+. . . . . . . . .
--.-
1
I
11 00.
- 360(
,
,
8 ,
3700
4
.
, . /
8
,
.-.. . . . . . . .
I
....
I
-4-nyrr
I
I
/
,3800
'
390C
.---.
...
_-..
..I..
1200.
.-
F i g . A-1. ( c o n t )
.
-.
-1
,
._
I
1
D U A L INDUC'TION-LATEROLOG
HYDROCARBON LOG
HYDROCARBON
L ITHOLOGY
i
4000 - 4800'
B A S A L T : I N T E R S E R T A L T O SUBOPHITIC, WITH
CLINOPYROXENE, PLAGIOCLASE, A N D MINOR
O L I V I N E . L O C A L L Y C O N T A I N S AMYGDULES
F I L L E D WITH C L A Y A N D C A R B O N T A T E .
B A S A L T BECOMES COARSER GRAINED WITH
DEPTH. ALSO C O N T A I N S 5 T O 20% WEAKLY
T O MODERATELY CALCAREOUS C L A Y STONE
A N D UP T O 5 % Q U A R T Z C R Y S T A L S .
41 00
I
1
. -
4200
1 2 W - 44 10'
S I M I L A R T O A B O V E EXCEPT C O N T A I N S
5 T O 10% HYDROTHERMALLY ALTERED
C A T A C L A S T I C B A S A L T . PYROXENE IS
COMPLETELY G R A N U L A T E D A N D
CONVERTED T O EPIDOTE; MUCH OF
T H E GLASS IS P A L A G O N I T I Z E D , A N D
CRUDE AUCEN S T R U C T U R E IS DEVELOPED
IN PLAGIOCLASE,
1300-
4300
'd
I
I
.
j
1
I
6- 2-7s
I-
4400
4500
1400
4600
...
470C
. . . . .
- . _ .
,
.
-.
.
.
. .
t
t
4800
:
I
4800 - 5750'
SHALE : A R G l LLACEOUS, WITH SANDSTON E
AND B A S A L T , S L I G H T L Y CALCAREOUS,
TUFFACEOUS.
480
.'-
3 .'
3
~
. . . . . . .
......
. . .
. . . . . .
....
3
3 .... : . . . . . . . . . . .
490C
4-6-73
~
1500
5ooc
51 O (
520(
1600
5x
,5301
I
g
... . . . _ :-.:
IT..
3-6-73
...:_.
.
. . .
.
,540
I
-
550(
g---
1700
.__
,560
.
:.
F i g . A-1. ( c o n t )
'
.....
- -
+
76-0-13
!
. T . .
. . . . . . . . .
,
--
T - .
I
---
. . .-
. -
I
.
jJ
COMPENSATED FORMATION D E N S I T Y LOG
**
1
BOREHOLE COMPENSATED SONIC LOG
**
W
U.
INTERVAL
TRANSIT
TIME
DEPTH
L ITH0LOGY
1
SPONTANEOUS
POTENTIAL
I
HYDROCARBON
CONDUCTIVITY
BULK DENSITY
GAMMA R A Y
9 / 1 3 / 7 4 B i t Size: 8-314''
T y p e F l u i d in Hole: FGM
Fluid Level: Full
7480 - 7600'
T U F F W I T H MINOR B A S A L T A N D C L A Y S T O N E .
HEMATITE STAINING AND EXTENSIVE
ALTERATION TO C L A Y . TRACES OF
M U S C O V I T E A N D ZEOLITES.
750C
GAMMA R A Y
1
TEMP**@)
I
J
U.
DEPTH
9/13/74
B i t Size: 8-314"
T y p e F l u i d in Hole: FGM
7500
2300
230C
7601
7600
770C
7700
-.25
0
t.25
CORRECTION
grams lcc
7800
w
IYP
HOLE D I A M E T E R
(INCHES)
2400
20
-
,
790C
API UNITS
I
.
,
.
15
.o
30
.o
111-73
10
HOLE D I A M E T E R
(INCHES)
SANDSTONE P O R O S I T Y - %
1
,
8000 -9002'
D E V I T R I F I E D T U F F W I T H M I N O R AMOUNTS
OF SUBOPHITIC A N D V A R l O L l T l C BASALT,
R E D - B L A C K V I T R O P H Y R E (t P L A G I O C L A S E ) ,
A N D SMALLER AMOUNTS O F C L A Y S T O N E .
E P I D O T E PRESENT I N GROUNDMASS O F B O T H
TIJFF A Q D B A S A L T . E V I D E N C E O F WELDING
IN SOME T U F F SAMPLES.
8001
7800
CALIPER
CALIPER
,
,
,
,
I
10
.
2 400
0
3
3
I
8
1
- 2.65 G M I C C
Fluid Density - 1.00 G M i C C
tiraio Density
GRAMS C .C.
2.5
1.5
1
,
7900
API UNITS
2.(
MICROSECONDS PER FOOT
,40
3. 0
90
I
! 40
190
111
1uc
8000
810C
-I- I2 -13
2500
820C
IT
8200
8301
il
8300
i.
W
2500
. .
z
8400
W
0
-
8500
J
a
2600
8400
W
8430 - 8500'
D A R K RED, G R A Y , OR L A V E N D E R T U F F
APPEARS A T 8430' ( 3 0 P E R C E N T ) . I N T H E
N E X T 70 FEET T H E Y G R A D U A L L Y INCREASE
I N A B U N D A N C E A T T H E EXPENSE O F T H E
WHITE T U F F , WHICH DISAPPEARS E N T I R E L Y
A T 8500 FEET.
8500
2600
cz
W
8600
8600
3
0
-I
8700
8700
H
8800
8800
2701
2700
8900
9000
9002 - 9676'
D E V I T R I F I E D G R A Y T O GREEN T U F F W I T H
SUBORDINATE INTERBEDDED SUBOPHITIC
OR V A R l O L l T l C B A S A L T FLOWS. T U F F IS
OFTEN EXTENSIVELY ALTERED T O CLAY
AND LOCALLY SPHERULITIC.
H
8900
-I -
9000
.R
91 00
9100
280C
2800
2 mu
9200
i
9200
9300
f
B300
9400
I
9400
H
9500
9500
!&s
'Ik
I
9600
9600
F i g . A-1. ( c o n t )
*AI G r i f f i t h , M a y - J u l y 1973
* * G u l f Mineral Resources Co. ,September 1974
2 mt