THE RICE INSTITUTE
Separation of Zircon and Biotite from
Bentonite for Absolute Dating and
Possibilities for Dating Certain West
Texas Bentonites
by
John H. Terrell
A THESIS
SUBMITTED TO THE FACULTY
IN PARTIAL FULFILLMENT OF THE
REQUIREMENTS FOR THE DEGREE OF
MASTER OF ARTS
Houston, Texas
May, I960
A
ACKNOWLEDGMENT
The writer is grateful to Professor John A. S. Adams
for suggestion of the problem and for guidance in all phases
of the research.
Dr. J. Kenneth Osmond and Dr. Richard
Pliler offered many useful suggestions and assisted with
the laboratory work.
Mary Cornelia Kline kindly processed
the gamma-ray spectrometer samples.
The entire project
was supported by R. A. Welch Foundation Grant C-009.
TABLE OF CONTENTS
Page
Introduction
Definition and Recognition of Bentonite
Importance of Absolute Age Determination
of Bentonite
Necessity for Efficient and Economical
Accessory Mineral Separations
1
3
4
Separation and Analytical Procedures
General Procedures
Quantitative Zircon Separation
Biotite Separation
5
7
12
Results and Discussion of Results
Separation Procedures
Possibilities for Dating
Geochemical Data
14
17
18
Summary and Conclusions
24
List of References
26
Selected Bibliography
Appendix
*
29
35
ILLUSTRATIONS
Some average concentrations of
radioactive elements in certain
igneous rocks.
Relationship between Thorium/
Uranium ratio and potassium con¬
tent of the Bentonite from the
Manzanita limestone member of
the Cherry Canyon formation.
Relationship between Thorium/
Uranium ratio and grit content of
the Bentonite from the Manzanita
limestone member of the Cherry
Canyon formation.
Geographic location of sampling
sites - JHT-1, JHT-2, JHT-4,
JHT-5, JHT-8, JHT-9.
Geographic location of sampling
sites - JHT-3, JHT-6, JHT-7.
Geographic location of sampling
sites - JHT-10 through JHT-15.
TABLE
INTRODUCTION
The major purpose of this investigation was to determine the
most suitable methods for obtaining zircon and biotite crystals
from bentonites for the purpose of isotopic age determinations
and thereby ascertain the possibility of obtaining absolute ages
for certain Permian and Ordovician bentonites from West Texas.
Definition and Recognition of Bentonite.
The Glossary of Geology and Related Sciences (1957) defines
bentonite as:
n
. . . .a clay formed from the decomposition
of volcanic ash and is largely composed of
the clay minerals montmorillonite and
beidellite. The rock must be produced by
the decomposition of volcanic ash and not
from decomposition of other substances.
The color ranges from white to light green
and light blue when fresh. On exposure the
color frequently becomes a light cream and
gradually changes to yellow and in some
cases to red or brown. n (Twenhofel* W.H. ,
Rept. Comm. Sed. , p.99* 1936-37).
The writer wishes to emphasize the volcanic origin of
bentonite rather than the clay mineralogy.
However, it should
be noted that none of the West Texas bentonites investigated
-
2
-
possessed the power to swell greatly in water, as is character¬
istic of montmorillonite, and indeed, some were so highly
altered as to merit the name metabentonite (Ross, 1928: Grim, 1953).
Ross (1928) listed seven features useful in determination of
bentonites:
1. Presence of glass relict structure.
2. Presence of minerals and crystal forms
characteristic of volcanic rocks (euhedral,
zoned, etc.).
3. Absence of minerals that do not have a
volcanic origin (microcline, garnet,
muscovite, calcic and soda plagioclase)
in the same specimen.
4. Waxy luster.
5. Reaction to water.
6. Optical properties.
7. Chemical properties.
In the laboratory, the second and third of these several
criteria were found to be particularly diagnostic of bentonitic beds
when the absence or very low content of rounded or frosted grains,
indicative of detrital contamination, had been established.
In the
field, bentonitic beds could often be identified by color which is
generally green, though occasionally rust-red from ferruginous
stain, texture which is often crinkled or flaky, and uniform thick¬
ness of the bed.
Also, where strata do not dip very steeply,
bentonitic beds are often indicated by distinct re-entrants.
-3-
King (1948) determined the volcanic nature o£ some of the
Permian bentonites to be described, but the Ordovician bentonites
have not been reported previously.
Importance of Absolute Age Determinations of Bentonite.
Bentonite beds indicate peaks of volcanic activity (Weaver,
1953) which span only brief moments in the geologic sense.
The
bentonite beds, however, may cover broad geographic areas.
Bentonite, produced by the alteration of ash which has fallen and
accumulated in bodies of water, is sedimentary in its manner of
occurrence.
This feature is important in two respects.
First,
bentonite layers form distinctive beds very useful as key horizons
for stratigraphic correlation (Ross, 1925).
Second, absolute
dating of a bentonite provides an internal age useful for relating
the absolute time scale to the relative paleontological time scale.
Satisfactory age determinations from bentonites can be made
utilizing the uranium 238 - lead 206 ratio (Edwards, et al, 1959)
or the uranium 235 - lead 207 ratio (Adams, et al, I960) from
accessory zircon, and the strontium - rubidium ratio (Adams
et al, 1958) or the potassium 40 -- argon 40 ratio (Faul and Thomas,
1959) from accessory biotite.
For zircon, radiation damage and total
-4-
lead-alpha count methods may be employed.
In addition, the
thorium-lead method may be used for zircons of sufficient age.
Necessity for Efficient and Economical Accessory Mineral
Separations.
It seems very likely that bentonites are more prevalent in
the geologic column than has previously been recognized.
Because
of the current interest in absolute dating (Adams et al, 1959; Faul
and Thomas, 1959; Mayne, Lambert, and York, 1959; Davidson,
1959; Kulp, 1959; Carroll, 1959) and owing to the particular
advantages offered in dating bentonites, many occurrences of
bentonites should become known.
A bentonite sample weighing at least 20 kilograms is required
to obtain sufficient zircon for isotopic age dating (Hamill, 1957).
Thus, to make practical use of bentonite for this purpose, the
laboratory preparation of the zircon concentrates should be
accomplished as efficiently and economically as possible.
For this
reason, the decision was made to determine the apparatus and
techniques best suited for preparing zircon and biotite separates.
The equipment and methods deemed most suitable were utilized
to examine some Ordovician and Permian bentonites from West
Texas , an Ordovician bentonite from Norway, and a Chattanooga
- 5 -
(Mississippian-Devonian) bentonite from Tennessee.
SEPARATION AND ANALYTICAL PROCEDURES
Storage: Bentonite samples of four or five kilogram weight
were collected and stored in ordinary boxes, or if they were to
be kept for some time, in polyethylene -lined burlap bags.
Gamma-ray spectrometry: About one-half kilogram of
sample was dried (if necessary), and ground in a ball mill until
the material would pass a 100 mesh sieve (sieve openings .147
millimeter in diameter).
The sample was then mixed for 30
minutes in a Fisher-Kendall mixer and 350 grams of the material
packed into a canister devised for that purpose.
Gamma-ray
spectrometry subsequently was used by Miss Cornelia Kline to
determine the thorium, uranium and potassium concentrations
of the samples.
Disaggregation: A 500 gram test sample of each bentonite
was disaggregated.
Disaggregation of the non-indurated samples
was accomplished by agitation in water, using an ordinary house¬
hold blender.
In some instances, small amounts of sodium
carbonate were used as a deflocculant to disperse the sample.
Full-scale samples were dispersed in 20-liter polyethylene
6-
-
buckets with the aid of a "Lightnin" mixer.
The few indurated samples were prepared by processing
with a jaw-crusher, a rotary disc pulverizer, and a ball mill.
Elutriation: Bentonites contain some 50-90 percent clay,
the remainder or "grit" consisting of sand and silt-sized particles
of quartz, feldspar, zircon, biotite and other minerals.
A
valuable concentration of the zircon and biotite was made by
water elutriation, which removed the clay fraction.
Tap water
was tested and found to cause no significant lead contamination,
and therefore, was used for elutriating all of the samples.
Various apparatus for elutriation have been described by
Hutton (1950), Milner (1952), Tickell (1947) and others, but most
of the devices were not suitable for processing very large samples.
Hamill (1957) has assembled a hydrocyclonic separator that will
handle large samples, and the writer has used the equipment with
a fair degree of success.
The latter device, however, has the
disadvantage of requiring more than one person to operate it.
Large scale elutriation was accomplished most successfully
using a 20-liter-capacity translucent plastic bucket.
One-half
liter or less of disaggregated material was placed in the bucket,
- 7 -
the bucket filled about three-quarters full of water, and the mix¬
ture allowed to settle for approximately 90 seconds.
Following
the settling period, most of the supernatant fluid was decanted
slowly, care being taken not to pour off any grit.
This process
was repeated two or three times or until the supernatant liquid
was clear following the waiting period.
The clean grit was then
removed for drying, and new material added to the bucket for
elutriation.
This method permitted very close operator control.
On some samples, a method of continuous elutriation was
employed.
Two or three liters of disaggregated material were
added to the large bucket, and then the bucket was filled with water.
The bucket was placed in a sink to catch the over-flow and water
was slowly introduced at the bottom of the bucket via a section
of rubber tubing attached to a water tap.
The water in-flow was
adjusted very carefully to prevent the grit from being washed
out of the bucket.
The only attention required was an occasional
stirring of the grit at the bottom of the bucket to release the en¬
trapped clay.
This method had the advantage of requiring little
time from the operator.
QUANTITATIVE ZIRCON SEPARATION
Sizing: Zircons in all the samples were found to possess
-
8
-
an intermediate diameter of less than .147 millimeter; in some
samples the zircons were all smaller than . 074 millimeter.
For this reason, all samples were sieved through a 100 mesh
screen (sieve opening .147 millimeter in diameter) for the zircon
concentration.
Sieves were of nylon bolting cloth held in cardboard or
plexiglas frames.
There was a possibility of some lead con¬
tamination from the bolting cloth (Waring and Worthing, 1953)
and perhaps stainless steel sieves would have been better.
Brass
sieves, which might be soldered, were avoided as possible lead
contaminant s.
Density Separation;
Further large sample volume re¬
ductions were made by means of heavy liquid separations.
Bromoform (specific gravity 2.7/) was used rather than
tetrabromethane (specific gravity 2. 96) because of its lower
cost and because of its lower viscosity.
Samples with a grain size less than . 074 millimeter were
best separated with the aid of a centrifuge utilizing four 125
milliliter separatory funnels.
Funnels were filled approximately
half full with bromoform, 10—15 grams of sample were added to
- 9 each, and then the counterbalancing pairs of funnels were brought
to equal weight by adding bromoform to the lighter ones.
The
bromoform sample mixture was thoroughly agitated, and then
centrifuged for five or six minutes at 500 rpm.
Samples that were sized to -100 mesh (less than
147 milli¬
meter grain size) were separated in a large separatory funnel
or in a four liter beaker.
Several hundred grams of material
were processed at one time by this method.
Separation was
greatly hastened by gently and continuously agitating the mixture.
The agitation was accomplished by bubbling air, from a small
air pump, through the mixture.
Petrographic Study: After the heavy liquid separation of the
500 gram samples, the heavy fractions were examined to deter¬
mine the general mineralogy and to determine the zircon (specific
gravity 4. 7) content.
The zircon determination was made with a
petrographic microscope possessing a mechanical stage and a
cross-hair ocular.
For each sample, a slide with several hundred
heavy grains was prepared.
A grain count of 100-200 grains was
performed for each slide, and the percentage of zircon was then
calculated.
This method is not very accurate but is satisfactory
for the present purpose.
The light fraction was also examined to determine its general
-
10
-
mineralogy and to see if there was any appreciable biotite con¬
tent.
Magnetic Susceptibility Separation: A Frantz Isodynamic
Magnetic Separator was used to obtain a non-magnetic separate
from the heavy fraction.
The highly magnetic content was re¬
moved with a hand magnet.
The remaining material was then run
through the separator, utilizing settings of 15-20 degrees for the
side angle, 30-35 degrees for the forward angle, and 1.2-1.4
for the amperage.
In every case, the material had to be re¬
cycled several times to obtain a clean fractionation.
In a few samples, the major portion of the zircon was
separated into the magnetic fraction, owing to an extensive iron
oxide coating on the zircon grains.
The coating was easily re¬
moved by boiling the sample in a ten percent solution of oxalic
acid for thirty minutes, using a piece of aluminum metal to
collect the precipitate (Leith, 1950).
After treating the sample,
the zircon could be obtained in the non-magnetic fraction.
In no case could a satisfactory diamagnetic separation be
made.
This failure is probably caused by magnetic inclusions
in a large number of the zircons, rather than by magnetic
coatings .
-11
-
Additional Density Separation: For most samples, an
additional heavy liquid separation was found necessary.
Methylene iodide (specific gravity 3. 33) was used for that pur¬
pose.
Clerici solution (specific gravity approximately 5.0)
was not used because zircon takes some of the thallium from
the solution, and thallium masks the lead in mass spectrographic analysis.
Heavy salt-melts were rejected because of
their high viscosity,
in many cases, the methylene iodide
separation was sufficient to obtain a 99 / percent pure zircon
concentrate.
Miscellaneous Techniques: Panning of the elutriated
grit was avoided because the method is not sufficiently
quantitative.
If some zircon loss could have been tolerated,
the method would have been effective for sample-volume
reduction.
Some impurities, if they were soft, were removed in the
following manner.
The sample was placed in a glass vial
which allowed ample space for agitation and movement, and
then shaken vigorously.
The resistant zircon was unaffected
while the soft material was powdered and subsequently removed
by elutriation.
-
12
-
Pyrite, which was a major impurity in two samples, was
removed in part by magnetic separation after the material had
been heated to 450 degrees Centigrade for a few minutes, and
in part by leaching with concentrated nitric acid.
The latter
method involves some risk of lead contamination from the
possible lead content of the pyrite.
Dielectric separation was attempted to remove the pyrite
from the zircon concentrate, but was found to be ineffective
for large scale operation.
The method would probably be pre¬
ferable to hand picking in other cases, however.
BIOTITE SEPARATION
Sizing: Biotite grains were found to be variable in size,
but in some samples a degree of concentration was obtained by
sieving the grit through a nest of sieves ranging in size from
about 40 mesh to 200 mesh (. 417 to . 074 millimeter sieve
openings) and collecting the size fraction enriched in biotite.
For samples containing only small amounts of biotite, a
considerable concentration was obtained with the Frantz
separator.
The biotite was found to be magnetically susceptible
- 13 -
over a range of . 4 to .8 amperes, the susceptibility varying from
sample to sample.
The sample was run through the separator
at an amperage setting just les s than that at which the biotite was
magnetic, to remove the more magnetic grains.
The non¬
magnetic fraction, containing the biotite, was then run through
the separator at a setting just greater than that at which the
biotite was magnetic, to remove the less magnetic grains.
Occasionally, this procedure, with each of its two steps re¬
peated several times, was sufficient to obtain a 99/ percent
pure separate.
This technique is particularly useful for
separating biotite from chlorite, when chlorite is present.
From samples containing abundant biotite, the biotite was
concentrated most effectively by the cardboard technique.
A small amount of sample was sprinkled onto a piece of smooth
surfaced bristol board, the board tipped to an angle of 10-30
degrees (the greater the grain size, the less the angle), and
the board gently and continuously tapped on one edge.
The
more equant grains rolled down and off the board, while the
flat micaceous grains were displaced only slightly.
The
biotite thus collected was set aside, and additional sample was
processed until sufficient biotite had been obtained.
The
14
-
apparatus could probably be mechanized profitably for larger
t
operations than performed here (Faul and Davis, 1959).
This method was a useful adjunct to magnetic separation.
RESULTS AND DISCUSSION OF RESULTS
Separation. Procedures: The methods and apparatus
described under Separation and Analytical Procedures were
found adequate for samples up to 100 kilograms raw weight.
Various physical measurements (see Table I) were made
on each sample to determine whether some simple laboratory
test could indicate which samples would be mechanically suit¬
ed for age-determinations.
The results indicate that the best
criterion is the percentage of zircon in the bromoform heavy
fraction.
The most suitable samples are those containing the
highest percentage of zircon, providing the tptal yield of
heavy minerals is reasonably high.
The next samples are
those that have a lower zircon percentage due to a pre¬
ponderance of a single contaminating mineral.
The single
mineral can generally be removed by one process which raises
the relative zircon content considerably.
Samples containing
less than one percent zircon in the bromoform heavy fraction
-15-
TABLE
Grit From
Sample
Num per
Gram
Bromoform Heavies
Sample
(Weight in
JHT-I
500
grams)
From
Grit
Zircon From
Bromoform Heavies
(Weight in grams)
( Percent)
92.0
.01
13
JHT-2
135.5
.29
< 1
JHT-3
185.5
.02
< 1
JHT-4
240.0
3.39
< 1
168.5
.03
107.5
2.00
< 1
63.5
.02
< 1
JHT-8
172.0
.20
2-3
JHT-9
308.0
.50
2
JHT-IO
76.5
1.26
< 1
JHT-I 1
158.0
.19
<1
JHT-12
191.5
.31
<1
JHT-13
231.5
.09
< 1
JHT-15
125.5
1.60
<1
K
*
JHT-5
7
#
JHT-6
#
•JHT-7
*
-16-
TABLE
Sample
Thorium Metal
Numbers
(Continued)
Uranium Metal
Concentrations
Concentrations
(parts per
(parts per
million)
million )
Potassium Metal
Thorium /Uranium
Controtions
Ratios
(parts per
hundred )
*
JHT-2
37.3
6.7
4.7
5.6
JHT-3
30.5
5.6
1.8
5.5
5.9
1.6
1.5
3.7
16.2
4.3
3.0
3.8
22.4
2.9
7.6
7.7
17.6
1.9
6.7
9.3
31.3
64
3.8
4.9
*
JHT-4
*
JHT-5
*
JHT-6
«
JHT-7
*
JHT-8
Geochemical data for
JHT-I, JHT-9 through JHT-13, and JHT-15
not available.
*
Samples from the bentonite layer located within the Manzanita limestone member
of the
The
Cherry
Canyon
formation.
bentonites from Norway and Tennessee are to be reported
at a later date
- 17 -
were not found suitable for the methods and apparatus described
herein.
Biotite separations were generally found to be dependent
upon the biotite concentration in the bromoform light fraction.
Where biotite was readily detectable with a hand lens, a biotite
concentrate could be made with reasonable ease.
Possibilities for Dating: Sample JHT-8 appears satis¬
factory for dating, possessing an unambiguous mineral
assemblage and fine euhedral zircons.
Though the sample
contains only 8-12 milligrams of zircon per kilogram, the radio¬
activity of the zircon (as determined by alpha count) is quite
high, and approximately 150 kilograms of sample should suffice
(see Summary and Conclusions).
Mechanically and petrographically, sample JHT-9 is
suitable for a zircon age-determination.
Not more than 200
kilograms of sample should be required; however, the
bentonite layer is only one inch thick, and obtaining a sufficient
quantity of material would be difficult.
Samples JHT-5 and JHT-1 would be the next possibilities
for dating, but more efficient laboratory apparatus for
separation will be required to make them practicable.
- 18 -
A small amount of biotite of large grain size, very fresh,
and so black as to be almost opaque is contained in sample
JHT-6, and should be eminently suited for dating.
A few
kilograms of sample should provide an adequate concentrate.
Sample JHT-9 contains abundant biotite, of fairly large
grain size, which appears to be somewhat bleached.
This
biotite may be satisfactory for dating or might give an
anomalous value as was the case for a "golden" biotite report¬
ed by Adams and others (1958).
Less than one-half kilogram
of raw sample should provide sufficient biotite.
Because this
bentonite also contains sufficient zircon for dating, it might be
the best sample to date first, so that a comparison of the biotite
and zircon ages could be made.
Geochemical Data: The geochemical data on each bentonite
are presented in Table I.
The potassium metal concentrations
range from 1. 5 to 7. 6 parts per hundred, averaging 4. 2 parts
per hundred.
Thorium metal concentrations range from 5.9
to 37.3 parts per million, and average 23.0 parts per million.
Uranium metal concentrations average 4. 2 parts per million,
with a range of 1. 6 to 6.7 parts per million.
The thorium-
uranium ratios average 5. 8 with a range of 3.7 to 9.3.
- 19 -
The average values obtained compare closely with those re¬
corded by Hamill (1957) for a number of Ordovician bentonites,
using gamma ray spectrometry.
However, these values are quite
different from those obtained by Osmond (1954), who used an
alpha-count method on some Ordovician bentonites (See Figure I).
Figure I shows the greater content of thorium and uranium
in bentonites than in some other igneous rocks (Richardson,
1957; Rankama and Sahama, 1950; Whitfield, 1958).
The values
for an average felsic ash are worthy of note, inasmuch as
bentonites are probably derived therefrom.
In comparison to
the ash, the bentonites described here show an average five
percent increase in uranium and 64. 3 percent increase in
thorium.
The relative increase in thorium can be explained by
the net loss in mass during the alteration of the ash to bentonite,
little or no thorium being added or removed in the process.
Considering that thorium is immobile owing to its insolubility,
a loss of uranium is thus implied.
Uranium is insoluble in its reduced tetravalent state but is
soluble in its oxidized hexavalent form as the uranyl ion,
Thus, the thorium-uranium ratio is affected both by loss in mass
20
FIGURE
I.
-
21
-
from alteration of the ash to bentonite and by the redox potential
of the environment.
Though a loss of uranium has been previous¬
ly implied, it would seem possible for the uranium removed
from one point of a bentonite layer to be added at another point,
producing a decreased thorium-uranium ratio.
In Figure 2, the plot of thorium-uranium ratio against
potassium content indicates an inverse relationship between
uranium and potassium in a bentonite bed.
Apparently, the more
favorable the conditions for removing uranium, the less favorable
are the conditions for removing potassium.
The plot of thorium-uranium ratio against grit content in
Figure 3 indicates a direct relationship between uranium content
and grit content.
A significant proportion of the uranium is
apparently held in the 15-48 percent grit content of the bentonites.
More specifically, the most probable location of the uranium is
within the zircon and some other resistate minerals of the grit.
Potassium
Member of the Cherry Canyon Formation .
(parts per hundred)
22
FIGURE
2
FIGURE
3.
- 24 -
SUMMARY AND CONCLUSIONS
The apparatus and procedures described under Separation
and Analytical Procedures were found adequate for quantitative
separation of zircon and biotite grains from bentonite samples up
to 100-kilogram size.
Equipment of larger volume for elutriation
and heavy liquid separation would permit samples possibly twice
as large.
However, the greater need is for a magnetic separator
of larger sample capacity and greater processing speed.
In
addition, an inert heavy liquid of about 4. 8 specific gravity would
be highly desirable.
Samples JHT-8 and JHT-9 were found satisfactory for ob¬
taining zircon concentrates for isotopic age-determinations.
Samples JHT-1 and JHT-5 would be satisfactory for obtaining
zircon concentrates if more efficient equipment were available.
Samples JHT-6 and JHT-9 were found to contain sufficient
biotite for age dates.
The bentonites reported in this study were found to contain the
following average concentrations and ranges of concentration of
potassium, uranium and thorium metals:
- 25 -
Average Concentrations
Ranges of Concentration
K . 4.17 pph
1. 48 - 6. 73 pph
U
4. 62 ppm
2.33 - 7.12 ppm
Th
24. 04 ppm
7. 92 - 37. 80 ppm
Th/U 5.01
3. 26 - 8.50
These data are interpreted in terms of net loss in mass in
the alteration of ash to bentonite, redox potential of the environ¬
ment, and the mineralogic content of the bentonites.
-
26
-
LIST OF REFERENCES
Adams, J. A. S., Edwards, G. , Henle, W. and Osmond, J. K. ,
(1958), Absolute dating of bentonites by strontiumrubidium isotopes. Program of the Geol. Soc.
Am. , 71st Annual Meeting, Los Angeles, 1958.
p. 23.
Adams, J.A. S., Edwards, G. , Henle, W. and Osmond, J. K.,
(in press), The absolute dating of the Ordovician
and the geologic time scale.
Carroll, D. , (1959), Zircon from a bentonite bed in
Martinsburg shale (Ordovician) at Fisher's Hill,
Virginia, Bull. Geol. Soc. Am., V. 70,
pp. 223-224.
Davidson, C. F., (1959), How old is the Cambrian system?
Nature, V. 183, pp. 768-769.
Edwards, G., Henle, W. , Osmond, J. K. , and Adams, J.A. S. ,
(1959), Further progress in absolute dating of
the middle Ordovician. Program of the Geol.
Soc. Am. , 72nd Annual Meeting, Pittsburgh,
1958, p. 38A.
Faul, H. , and Davis, G. L., (1959), Mineral separation with
asymmetric vibrators, Am. Min., V. 40,
No. 10, pp. 1076-1081.
Faul, H. , and Thomas, H. , (1959), Argon ages of the great ash
bed from the Ordovician of Alabama and of the
bentonite marker in the Chattanooga shale from
Tennessee, Program of the Geol. Soc. Am.,
72nd Annual Meeting, Pittsburgh, 1959, pp.
42A-43A.
Glossary of Geology and Related Sciences, (1957).
Am. Geol. Inst., N. A. S.-N. R. C., Pub. 501,
Wash., D. C., p. 31.
Grim, R. E. , (1953), Clay Mineralogy, McGraw-Hill Book Co. ,
New York, pp. 361-362.
- 27 -
Hamill, G. S., (1957), The radioactivity, accessory minerals
and possibilities for absolute dating of bentonites,
Master's Dissertation, The Rice Institute, May,
1957.
Hutton, C. O. , (1950), Studies of heavy detrital minerals, Bull.
Geol. Soc. Am., V. 61, pp. 635-716.
King, P. B., (1948), Geology of the southern Guadalupe
Mountains, U. S. Geol. Surv. Prof. Paper No.
215.
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APPENDIX
- 35 -
SAMPLE LOCALITIES AND STRATIGRAPHY
Samples JHT-1 through JHT-9 were collected from the Dela¬
ware Mountain Group, Guadalupe Series of the Permian, in the
Guadalupe Mountains of West Texas (See Figures 4 and 5).
Samples JHT-3, JHT-4 and samples JHT-6 through JHT-8
were collected from sections described by King (1948).
Samples JHT-10 through JHT-13 and JHT-15 were collected
from new road cuts in the Hueco Mountains of West Texas and
have not been reported previously (See Figure 6).
The ben¬
tonites here have been assigned a tentative middle or late Ordo¬
vician age.
Sample JHT-1
Locality: The exposure occurs in a road cut facing southeast
on U. S. Highway 62, five miles northeast of Pine Spring Camp.
Stratigraphy: The bentonite bed forms a distinct re-entrant
between two impure limestone layers in the Hegler limestone
member of the Bell Canyon formation.
The bentonite is about
ten inches thick, generally grayish-green, flaky and rather dry.
-36-
Geographic
c-ocation of
Sampling
Sites
FIGURE
J HT-I , JHT-2, JHT-4, JHT-5, JHT-8,and JHT-9.
4.
-37-
Geographic
Location of
Sampling Sites JHT-3, JHT-6, and JHT-7.
FIGURE
5.
-38-
Geographic Location of Sampling Sites
FIGURE
JHT-IO Through JHT-15.
6.
- 39 -
Sample JHT-2
L»ocality: The sample was collected from the same road cut
as JHT-1, but from a horizon approximately twelve feet lower in
the section.
Stratigraphy: The bentonite forms a re-entrant between two
sandy limestone layers in the Manzanita limestone member of the
Cherry Canyon formation.
The bed is six inches thick, medium
green, dry and flaky.
Sample JHT-3
Locality: The exposure occurs about one quarter of a mile
east of U. S. Highway 62, five and three-quarter miles north of
the intersection of U. S. Highway 62 and State Highway 54.
Stratigraphy: The bentonite layer occurs between two sand¬
stone layers in the Brushy Canyon formation.
The layer is about
three inches thick, uniformly olive-green, finely banded, well
indurated and shale-like.
Sample JHT-4
Locality: The bentonite occurs approximately three quarters
of a mile northwest on the road leading to the Liggin Ranch which
- 40 -
is about four and one-half miles northeast of Pine Spring Camp
on U. S. Highway 62.
The exposure sampled was about 500 feet
northeast from the Liggin Ranch headquarters.
Stratigraphy: This bentonite occurs between two sandy lime¬
stone beds in the Manzanita limestone member of the Cherry
Canyon formation.
The exposed bentonite is possibly six inches
thick, very light bluish green, finely granular, and very poorly
laminated.
Sample JHT-5
Locality: A bentonite is exposed in both sides of a road cut
on U. S. Highway 62, about three and three-quarter miles north¬
east of Pine Spring Camp.
The exposure was sampled from the
west-facing slope.
Stratigraphy: This bentonite occurs within the Manzanita
limestone member of the Cherry Canyon formation, and probably
correlates with JHT-2 and JHT-4.
thick.
The bed is four to six inches
The fresh material is unctuous, light bluish-green, faintly
banded, and stained irregularly with iron oxide.
On weathered
surfaces, it appears earthy and buff-gray in coloration.
- 41 Sample JHT-6
Locality: This exposure is located near a ranch house
approximately three quarters of a mile northwest of Pine Spring
Camp, on a slope of Pine Spring Valley.
Stratigraphy: Occurring within the Manzanita limestone
member of the Cherry Canyon formation, this bentonite appears
to correlate with JHT-2, JHT-4 and JHT-5. ‘ The bentonite layer
is 10 to 12 inches thick, bright green and flaggy.
The material is
greatly silicified and forms a slightly projecting ledge.
Sample JHT-7
Locality: On the southeast slope of El Capitan about 1500
feet from the summit, is an occurrence of bentonite.
Stratigraphy: The bentonite seems to correlate with JHT-2
and JHT-4 through JHT-6, occurring within the Manzanita lime¬
stone member of the Cherry Canyon formation.
The bed is
possibly four inches thick, and crops out irregularly due to ex¬
tensive slumping of the overlying strata.
The bentonite is bright
bluish-green, locally stained brown by iron oxide, and is great¬
ly silicified.
42 -
Sample JHT-8
Locality: The bentonite is exposed near the base of a small
valley approximately one and one-half miles north of the
n
D,f
Ranch headquarters.
Stratigraphy: The bentonite occurs within the Manzanita
limestone member of the Cherry Canyon formation, and thus
appears to correlate with JHT-2 and JHT-4 through JHT-7.
The
thickness is not certain owing to slumping of the overlying strata
and the extensive soil cover but is possibly 10-12 inches thick.
The material is moist, medium green with some white streaks,
and has a granular texture.
Sample JHT-9
Locality: This exposure occurs in a road cut facing southeast
on U. S. Highway 62, five miles northeast of Pine Spring Camp.
The layer is about seven feet higher in the section than is JHT-1.
Stratigraphy: The bentonite is located between impure lime¬
stone layers of the Hegler limestone member of the Bell Canyon
formation.
The stratum is approximately one inch thick, platy,
and green.
The abundance of megascopically visible light brown
biotite in the bentonite bed is noteworthy.
- 43 -
Samples JHT-10, JHT-11,
JHT-15
Locality: Approximately four tenths of a mile west of bench
mark 41118 on U. S. Highways 62 and 180 occur two bentonite
layers.
The exposures in the north-facing cut were sampled.
Stratigraphy: One bentonite layer, approximately three feet
thick, is overlain by a massive gray fossiliferous limestone layer.
This bentonite contains zones of abundant calcite nodules, and is
weathered to an earthy brown.
Sample JHT-10 was taken from the
upper three or four inches of the bed, which was unctuous and
green to bluish green where not stained rust-red from iron oxide.
JHT-11 was collected from a few inches thickness of dark green
unctuous material near the middle of the bed.
A second bentonite
layer, a few inches thick, slightly lower in the section, was
sampled from its full thickness to obtain JHT-15.
Samples JHT-12, JHT-13,
JHT-14
Locality: Several bentonitic beds are exposed in a road cut
approximately one and three tenths miles east of bench mark
211118 on Highways 62 and 180.
Stratigraphy: Sample JHT-12 was obtained about 150 feet
from the west end of the south-facing cut from a sixteen inch
- 44 -
thick bed.
The layer was sampled from its full thickness, the
upper ten inches of which were grayish-green streaked with brown,
and the lower six inches rust brown, dry and flaky.
Sample JHT-13 was collected from the lower three or four
inches of an eighteen inch thick bed, 120 feet from the east end
of the north-facing cut.
The material is brown with some green
streaks and has an earthy appearance.