The Occurrence of Barium and Strontium in
Typical Nevada Gypsum
A thesis
submitted to the faculty of the University
of Nevada in partial fulfillment of the re quirements for the degree of Master of Science
By
Brent P. Fabbi
Reno, Nevada
June, 1965 Approved by ^ / 2 Department Head
• Ha*- Approved by
11 Acknowledgments
The writer is indebted to Dr. Alex Volborth for suggesting the original problem and for his guidance in the preparation of this paper.
The X-ray spectrograph and associated sample preparation equip ment were made available through the courtesy of the Nevada Mining
Analytical Laboratory.
Without the recent contributions of funds by the Atomic Energy
Commission and the National Science Foundation, especially NSF Grant
No. GP-1987, this project could not have been undertaken.
Sampling of U. S. Gypsum's pit at Gerlach, Nevada was made
possible by Mr. Seeburger. Sampling of the Blue Diamond Mine was
permitted by Marion Brooks. Sampling of Fibreboard's Apex deposit
was through the courtesy of B. G. Long.
Dr. R. Olson provided the geologic information and aided in
selecting the deposits studied in Southern Nevada. C. F. Withington
aided 1n describing the geology of the Gerlach area.
The writer is indebted to Gail Chuba for statistical compilations,
to Or. H. A. Vincent for chemical analyses, and to Hr. P. A. Weyler
for valued advice and assistance.
iii TABLE OF CONTENTS Page
I. Introduction ...... 1
II. Selection of Deposits ...... 4
III. Selection of Analytical Method ...... 4
IV. Sample Collection ...... 6
V. Sample Preparation...... 7
a) Method of Comminution ...... 7
IV. Geology of the Deposits ...... 9
1) Gerlach...... 9
a) Location...... 9
b) G e o l o g y ...... 9
2) Blue D i a m o n d ...... 10
a) Location...... 10
b) G e o l o g y ...... 10
3) Lake M e a d ...... 11
a) Location...... 11
b) G e o l o g y ...... 11
4) Vegas W a s h ...... 13
a) Location...... 13
b) G e o l o g y ...... 13
5) A p e x ...... I3
a) Location...... 13
b) G e o l o g y ...... I3
VII. X-ray Spectrographic Procedure ...... 18
1) Equipment U s e d ...... 18
2) Settings for Barium ...... 18
3) Settings for Strontium ...... 18
1 v Page 4) Settings for Calcium ...... 20
5) Standards ...... 21
VIII. Results of Spectrographic Analysis ...... 21
1) Barium ...... 21
a) Gerlach ...... 22
b) Blue D i a m o n d ...... 22
c) Lake M e a d ...... 22
d) Vegas W a s h ...... 22
e) A p e x ...... 22
f) Discussion...... 27
2) Strontium ...... 31
a) Gerlach...... 31
b) Blue D i a m o n d ...... 31
c) Lake M e a d ...... 31
d) Vegas Wash ...... 32
e) A p e x ...... 32
f) Discussion ...... 38
3) C a l c i u m ...... 39
a) Discussion...... 39
IX. Conclusion...... 44
X. Appendix ...... 46
1) Precision ...... 4?
IX. Bibliography...... 51
v ...... I-IIU IL IM B
LIST OF ILLUSTRATIONS Page
Figure 1 Location of Gypsum Deposits ...... 5
2 Grinding and Pelletizing Equipment . . . 8
3 Photos of Lake Mead Prospect ...... 12
4 Photos of Vegas Wash Quarry ...... 15
5 Photos of Vegas Wash Quarry ...... 16
6 Photos of Apex Deposit ...... 17
7 Photos of X-ray Equipment ...... 19
8 Relative Distribution of BaO ...... 23
9 Similarity in the Slope of Carbonate
and Sulfate Calibration Curves .... 30
10 Relative Distribution of Strontium in
Parts Per M i l l i o n ...... 33
n Relative Distribution of Strontium 1n
Per C e n t ...... 34
12 Distribution Curve for Barium Oxide . . . 49
13 Distribution Curve for Strontium Oxide. . 50
LIST OF TABLES
Table 1 Results of Barium Oxide Analysis. . . 24
2 Results of Strontium Oxide Analysis . 35
3 Results of Calcium Oxide Analysis . . 40
vi It appears there are strontium concentrations in gypsum and the carbonates geologically associated with these gypsum deposits.
Nevada has had in time long past a favorable geological environ ment for the deposition of gypsum. Nevada is an ideal area to deter mine if both barium and strontium do occur with gypsum and associated carbonates since there are extensive gypsum deposits.
In the past few years, notably from 1955 on, much interest in barium and strontium occurring with gypsum has developed abroad.
There are reported occurrences of barium and strontium 1n gypsum rocks, limestone marls, and limestone breccias in the deposits of such varied countries as Italy, Russia, Poland, and Germany. A few of the occurrences are noted below.
One deposit in the Czarkowy region of Poland is reported to contain from 0.06% to 62.19% celestite. The celestite is dispersed throughout the gypsum deposit (Morawiecki, A., and Domaszewska, T., 1957).
A deposit in Thuringia, Germany contains both celestite and strontianlte. An analysis of strontianite at Konitz revealed 1t to be
94.28% SrC03, 4.36% CaC03, and 0.84% BaC03 (Munel, G., 1959).
German Mueller reported that "magascopically, the sediments of the
Upper Malme, Germany are rich in celestite and correspond to the massive anhydrite rocks which are typical of shallow water formation" (Mueller,
6., 1962).
One sample of anhydrite-bearing dolomitic rock in Italy contained
2390 ppm Sr while a white marble had only 190 ppm (Dessau, G., 1962).
The Russians have done more work in this area than any others, for example strontium has been found in the gypsum of the sediments of Northern Kazakstan (Dobrovol'skii, V. V., 1959). A.Allanov found that celestite, gypsum, barite, carbonates, and iron hydroxides are syngenetlc with sediment accumulation in lower Cretaceous strata of South East
Turkmenia (Allanov, A., 1964). Celestite has been found in abundance
in the Dnestr River area. Seven chemical analyses of celestlte-bearing
limestone contained 1.62, 3.01, 5.10, 10.10, 22.83, and 30.10 percent
SrO respectively. Genetically this mineral is associated 1n these de
posits with limestones, marls, dolomites, and gypsum-bearing clays. It
1s paragenetically associated primarily with gypsum, cal cite, native
sulfur, and bituminous matter (Lazarenko, E. K., and SHvko, M. H., 1958).
Kropachev reported an average value of 855 ppm Sr in thirty-seven samples
of anhydrite and 1275 ppm in seventy-five samples of gypsum from the
Kungurian evaporltes in Russia. He concluded that these gypsum deposits
of the fore-Urals were derived by the hydration of anhydrite and strontium
was enriched by 50% (Ham, W. E., 1962).
Work 1n this direction has also been done 1n the United States.
W. E. Ham has observed celestite 1n the Cloud Chief formation occurring
with gypsum in Oklahoma (Ham, W. E., 1961), Ham also noted that normal
anhydrite of evaporite origin contains abundant strontium as an 1so-
morphous substitution of strontium for calcium in the Blaine formation
which showed a range of 865 to 3165 ppm. The average strontium 1n
anhydrite amounts to 1475 ppm in 22 samples while the average strontium
present in gypsum 1s 970 ppm in 38 samples of that deposit. Ham observed
that all of the strontium appeared to substitute within the anhydrite
space lattice and does not occur as a separate phase in the form of
celestite. On changing by hydration to gypsum the anhydrite lattice is
destroyed and a new lattice is formed, thus SrSO^ is formed as celestite
-2- in the gypsum (Ham, U. E., 1962). Only small amounts of barium and strontium were found in the gypsum and associated carbonates of the
Colorado Plateau (Newman, W. L., 1962).
As the mining of gypsum and its subsequent treatment to form a variety of gypsum products is a major mining industry in Nevada, the abundance of barium and strontium in gypsum and associated carbonates is also important from a geochemical standpoint. Strontium minerals may also form an important by-product for the mining industry 1f dis covered in large enough quantities. Mineralogical identification of these minerals is however difficult, and therefore the logical approach is chemical analysis.
In order to investigate the occurrence of barium and strontium in
Nevada, five typical deposits have been sampled. The samples were analyzed using an X-ray spectrograph.
The strontium and barium minerals associated with sulfates and carbonates are celestite (SrSO^), strontianite (SrC03), barite (BaSO^), witherite (BaC03), and bromlite (Ca,Ba)C03.
-3- II. Selection of Deposits
Gypsum occurs in an area that encompasses over 4000 square miles in Southern Nevada. Many gypsum deposits and associated carbonates are to be found in this area.
The shape of the deposit and the amount of exposed gypsum was a factor considered 1n the selection of deposits. Since many deposits existed, only those that appeared typical were chosen. Four deposits were finally selected as being typical of Southern Nevada.
A fifth deposit at Gerlach in Northern Nevada was also chosen.
This deposit 1s well exposed and 1s one of the very few deposits in the northern part of the state. (See Fig. 1).
III. Selection of Analytical Method
The need for faster means of chemical analysis became critical in the last 20 years. The classical chemical methods were too laborious, required much time, and were costly (Shapiro, L., and Brannock, W., 1956).
The use of the flame photometer, spectrophotometer, colorimeter,
X-ray spectrograph, and X-ray diffractometer were highly successful in the fields of instrumental analysis to which they were applied, because these methods permitted a rapid analysis of many samples and were precise (Baird, A. K., and others, 1962).
The following are excerpts from the findings of several scientists who highly recommend the use of the X-ray spectrograph: "X-ray fluores cent spectrographlc analysis 1s a rapid and reliable means for the analysis of large numbers of samples", (Chodos, A. A., and Engel, C. G., 1961).
"The method is comparable in accuracy, is much faster than chemical analy sis..." (Stever, K. R., and others, 1960). "X-ray spectrography is a
-4- 5
T
HUMBOLDT
ELKO
"n
-- !I._____I Gerlach 'A PERSHING I J
LANDER EUREKA \ WASHOE \ (
_ , . < r >1 \ CHURCHILL / y'''"IR S T OR E E4 ^ WHITE PINE ) M' \ b^ORJMSBY \ s \ LDOUGLAS' f r' \ \ / \ \ I .YON1 \ ------^ \\L \ V | MINERAL \ r / \ NYE \ 7 \ / \ r ESMERALDA j N LINCOLN \ \ \
Figure I \ INDEX MAP \ \ CLARK \ v.eas*,Washr Location of Gypsum Lake / ' \ _ s ■ N Blue Me*dl Deposits Diamond \ \ l I \ \ \ \
\ r 3 O 5 10 20 30 40 50 60 Miles V, rapid and precise method for quantitative analysis of major elements in granitic rocks", (Baird, MacColl, and McIntyre, 1961). "The advantages of fluorescent X-ray analysis H e in the versatility and speed of analy sis. Sample preparation techniques were similar to, and as lengthy as, those for conventional methods. However, after one preparation many elements could be determined easily and in a short time from the same sample", (Seim, H. J., Lytle, F. W., and Dye, W. B., 1961). "Comparison of the statistical results with corresponding figures of other conven tional methods shows that this X-ray method 1s superior," (Volborth, A.,
1963).
The X-ray spectrograph combines several advantages over other methods. It is accurate and precise, and 1t is also fast and nondestruc tive. The selection of the X-ray spectrograph as an Instrumental analy tical method of determining barium and strontium was based on its inherent advantages over both chemical and other instrumental methods. Efficient excitation the strontium-K and barium-L spectra is possible with the
X-ray spectrograph.
IV. Sample Collection
Inasmuch as this thesis is primarily concerned with the general distribution of barium and strontium and not with a detailed study or mine examination, only a few samples were collected from each deposit.
These samples are only indicative of the variation of barium and stron tium in each deposit.
In one instance the samples from Apex were drill cuttings. In another, as at Blue Diamond, the samples were provided by the company.
The samples from the other deposits were surface samples.
-6- V. Sample Preparation
Sample preparation is highly important, since any errors which occur during sample preparation will diminish the accuracy of the X-ray spectro- graphic analysis. Errors can be caused by dilution of the sample with bakelite if care is not taken in preparing the pellet, contamination of the sample by the grinding apparatus if it is not thoroughly clean, a difference in the particle size of one sample as compared to another, a change in the density of the compacted particles due to a difference in the pressure applied to the pelletizing die, and a lack of homogeneity in the sample.
A large particle size causes a matrix effect (Campbell, W. J., and
Thatcher, J. W., 1958; Claisse, F., 1957). Bernstein's investigations show that particle size is one of the most important factors to consider in X-ray spectrography and that the fluorescent intensity and sensitivity increase as the particle size decreases up to a certain point (Bernstein,
F., 1951). Then, any further reduction in particle size does not increase intensity. Between 20 and 65 micron particle size range, the intensity
is not affected by further grinding. All of the samples of gypsum and
carbonates were ground to 95% minus 400 mesh or 37 microns.
A satisfactory method of comminution similar to the one found
successful by the Nevada Mining Analytical Laboratory was employed. Care
fully handled samples, upwards of five pounds were reduced to about 1/2
inch size in the jaw crusher. This coarse material was further reduced
to about 1/8 inch in a cone crusher. A Braun pulverizer was used to grind
the 1/8 inch material down to about 80% minus 100 mesh. The samples were
then split on a Jones splitter and the 2 pound portion which was kept was
homogenized in an automatic blender for fifteen minutes. A Pica mill with
-7- Pelletizing die under 12,500 lb per square inch pressure Figure 2. - Grinding and Pelletizing Equipment
- 8- tungsten steel balls ground the 100 mesh material to 95% minus 400 mesh.
A 10 gram sample of the 100 mesh material was ground 3 minutes. This was repeated three times and yielded a 30 gram powder. The 30 gram powder sample was homogenized on the Pica mill for 5 minutes, using the blender.
A one gram powdered sample was then pressed into a pellet in the pressure die developed by Baird and improved by Volborth (Baird, A. K., 1961;
Volborth, A., 1962). A one gram powdered sample was carefully placed in the die on top of a glass disc. Bueller Bakellte was placed on top of the powdered sample. A piston was inserted into the die and a pressure of
12,500 psi was exerted upon the system. This pressure caused the loose bakellte to form a strong casting around the pressed powder.
The finished, circular, one square inch pellet had a smooth surface and was strong enough to endure the numerous handlings required by each analysis.
VI. Geology of the Deposits
Since detailed mapping of the deposits was not a problem of this thesis, only a general description of the deposits is Included.
GERLACH
Location
U. S. Gypsum Company's deposit 1n northwestern Nevada 1s about 10 miles south of Gerlach at the western base of Luxor Peak in the SW 1/4 of unsurveyed section 31, T. 31 N., R. 24 E.
Geology
"The gypsum crops out on a low terrace at an elevation of about
5000 feet, in beds that are nearly vertical. The beds are bounded on
the north, west, and east by white to light gray limestone, and on the
-9- south by alluvium. The deposit is a wedge-shaped mass, 3500 feet long trending slightly east of north. It ranges from 1600 feet wide at the north end to only a few feet wide at the south end. The age of the gypsum has been given as Trlassic.
The gypsum 1s white, massive, and pure. The deposit 1s cut by brown fine-grained diabase dikes that are probably related to the
Tertiary volcanic rocks to the east. Anhydrite occurs with the gypsum near the surface, and the deposit becomes predominantly anhydritic at about 100 feet below the surface", C. F. Wlthington, in a personal communication (Stone, R. W., and others, 1920; Wlthington, C. F., 1964).
BLUE DIAMOND
Location
The Blue Diamond Mine is about 15 miles southwest of Las Vegas on the western slope of Blue Diamond Hill in section 32, T. 21 S., R. 59 E.
Geology
The bedrock gypsum deposit being mined by the Blue Diamond Division of the FUntkote Company is intercalated Into the youngest Permian strata in the area, which H e immediately beneath a profound Pem.ian-Triassic unconformity.
The Kaibab Formation as previously described by field workers has recently been divided into two formations: a) the Toroweap Formation, which has a gray limestone between two red bed members, and b) the overlying strati graphically redefined Kaibab Formation which has a brownish cherty cl iff-forming limestone at the base overlain by the
Harrisburg member (approximately 150' thick) of gypsum, anhydrite, red beds, and carbonate strata.
-10- Although the two red bed members of the Toroweap Formation contain laterally persistent ledges of rock gypsum, only the Harrisburg member of the Kaibab Formation is or has been mined. The Harrisburg member has four gypsum ledges of which the basal two are consistently mined. The upper two are thinner, laterally discontinuous, and relatively impure.
In ascending order the following is a typical section of the Harris burg: rock gypsum (Bed #4) which lies on top of basal cherty limestone of the redefined Kaibab Formation, limestone, rock gypsum (Bed #3), red beds, rock gypsum (Bed #2), red beds, rock gypsum (Bed #1), red beds, and finally a dolomitic limestone caprock which has protected the Harrisburg members from being completely eroded from the dip slope which forms the western flank of Blue Diamond Hill.
The regional structure is homoclinal and the regional strike is northerly with dips ranging from 20 to 30 degrees westerly (Olson, R. H.,
1964).
LAKE MEAD
Location
This prospect is on the north western slope of Frenchman's Mountain about 7-1/2 miles east of North Las Vegas on Lake Mead Boulevard 1n the
NW1/4 of section 24, T. 20 S., R. 62 E.
Geology
All of the gypsum here is in the Toroweap Formation. There is no
Kaibab or Harrisburg gypsum in this immediate vicinity. The lowermost occurrence is in the lowest of three Permian Thumb members and the upper most is in the highest of the three Permian Thumb members (Olson, R. H.,
1964). m am
Lake Head Prospect workings looking east
Exposed east face of Lake Mead Prospect
Figure 3. - Photo of Lake Mead Prospect VFGAS WASH
Locati on
This old quarry is in northerly to northeasterly trending strike valleys in the southern structural block of Frenchman-Sunrise Mountain.
It is 13 miles east of Las Vegas and 7 miles north of Henderson 1n the
NW1/4 of section 16 and the El/2 of sections 4 and 9, T. 21 S., R. 63 E.
Geology
This deposit lies in the Thumb formation and is classed as Cre taceous^). Yellow siltstone lies above and below the gypsum. Fresh water limestone lies below the gypsum and siltstone. Coarse conglomerate lies above the bedded siltstone and gypsum. Higher grade rock gypsum lies consistently strati graphically above the lower grade gypsum-bearing siltstone and argillaceous units. The structure dips at about 50 degrees easterly (Olson, R. H., 1964; Longwell, C. R., 1963).
APEX
Location
Fibreboard's deposit at Apex is about 12 miles east of North Las
Vegas and 3 miles west of the Muddy Mountains in section 7, T. 20 S.,
R. 64 E.
Geology
The Apex gypsum deposit currently being mined and processed by the
Fibreboard Paper Products Corporation covers approximately seven square miles.
In this Immediate area gypsiferous continental Cretaceous(?) red beds have been homocllnally tilted southward at an average dip angle of
30 degrees, subsequently pedimented, and finally overlapped by continen tal fine-grained elastics of the Muddy Creek Formation (Pliocene?), the
-13- Uj.j -most portion of which is host to the gypsum deposit.
Field investigations suggest that little of the gypsum of the cap rock which forms this mesa-like deposit is indigenous and that most of it has probably been derived from the underlying Mesozoic gypsiferous strata.
This deposit is a classic example of a secondary gypsum deposit formed by the upward percolation of gypsiferous ground waters and their subsequent dessication at the surface in a desert environment. The gypsum deposit, which is concordant with the present erosion surface, ranges from an average thickness of 10 feet at the extreme southeastern comer to 50 feet and more at the extreme northwestern corner.
The ore is selenite with ferrugenous, argillaceous, and silty material as included impurities. Neither the texture nor the cementa tion resembles in the slightest the granular, non-selenitic, friable
"gypsite" cappings so common in the outlying areas around this deposit and throughout the desert regions of the southwestern United States.
(Olson, R. H., 1964).
-14- Vegas Wash Quarry looking south west
Figure 4. - Photos of Vegas Wash Quarry Vegas Wash Quarry looking north
Figure 5. - Photos of Vegas Wash Quarry Apex deposit looking south west
Apex deposit looking west
Apex deposit looking west north west (Photos courtesy of Fibreboard Paper Products Corp.)
-17- VII. X-ray Spectrograph!c Procedure
Barium, strontium, and calcium were determined and reported as oxides.
Each of the elements required different settings and adjustments on the
X-ray spectrograph.
Equipment Used:
1. Universal Vacuum Spectrograph with 5 mil collimator.
2. X-ray Generator, type PW 1010.
a) voltage regulator.
b) current regulator.
3. Electronic circuit panel.
4. Pulse Height Analyzer.
5. X-ray spectrographic tube with tungsten target.
Settings for barium:
1. Pulse Height Analyzer base line of 3.6 volts and window of
8.4 volts. See appendix for discussion of discrimination using base
line and window adjustments.
2. 50 KV and 35 mA for target excitation.
3. Detector - flow proportional counter with 0.75 SCFH of P-10 gas.
4. Flow proportional counter tube voltage 1420 v.
5. Goniometer Setting: 36.8 degrees of 29 at La .
6. Analyzing crystal EDDT: d * 8.808.
7. Scale factor of 1 x 100 x 32.
8. Vacuum path.
9. Counting with fixed time.
Settings for strontium: (Initial 100-1000 ppm)
pulse Height Analyzer base line of 2.4 volts and a window of
9.6 volts.
-18- X-ray Generator, Universal Vacuum Spectrograph, and Electronic
Circuit Panel Z. 50 KV and 35 mA for target excitation.
3. Detector - scintillation counter.
4. Scintillation counter tube voltage 680 v.
5. 24.725 degrees of 29 at K^.
6. LiF analyzing crystal: d = 4.028.
7. Scale factor of 100 x 8 x 128.
8. Vacuum path.
9. Counting with fixed count.
The above settings were satisfactory for values of strontium between
100 and 1000 ppm. The settings had to be changed for higher values due to the Increased intensity associated with a broadening of the peak. The pulse height analyzer settings were changed to a base line of 1.8 volts and a window of 6.0 volts, 22.05 degrees of 29 at K& was the new setting on the goniometer. A lower target excitation amperage of 33 mA and no vacuum also reduced the Intensity of X-rays being emitted so that the counter would not be flooded with too many counts.
Settings for calcium:
1. Pulse Height Analyzer base line of 1.9 volts and window of
vol ts.
2. 50 KV and 35 mA for target excitation.
3. Detector - flow proportional counter with 0.25 SCFH of P-10 gas
4. Flow proportional counter tube voltage at 1460 v.
5. 44.90 degrees of 29 at Kq.
6. EDDT analyzing crystal: d = 8.808.
7. Scale factor of 100 x 128 x 8.
8. No vacuum.
9. Counting with fixed time.
-20- Standards:
Artificial standards of 0.01, 0.10, 1.00, 5.00, and 10.00% barium oxide were prepared by combining appropriate weighed amounts of BaO to a
C. P. matrix of calcium sulfate. These samples were all blended for 5 minutes on the Pica mill, ground for 3 minutes on the Pica mill, and then blended again for 5 minutes on the Pica mill. The method for preparing the pellet has already been outlined.
Artificial standards of strontium oxide were prepared 1n the same manner as were the barium oxide standards.
Because carbonates were to be analyzed also, standards of barium oxide and strontium oxide in a C. P. matrix of calcium carbonate were prepared 1n the same fashion.
Artificial standards of calcium sulfate were prepared by diluting the C. P. sample of calcium sulfate with C. P. sodium sulfate. Then the sample was homogenized, ground, and re-homogenized as was previously described.
Artificial standards of calcium carbonate were also prepared by diluting the C. P. calcium carbonate with sodium carbonate, homogenizing, grinding, homogenizing, and pelletizing.
VIII. Results of X-ray Spectrographlc Analysis
BARIUM
Barium occurred only 1n trace amounts 1n all of the deposits.
Figure 8 shows the relative distribution of barium oxide 1n each of the deposits and 1s not Intended to compare one deposit with another. Only the overall scope of the results 1s shown. The ratio figures shown on the left side of Figure 8 were derived by dividing the number of counts
-21- obtained in the analysis of the standard, in this case the standard was
100 ppm BaO, by the number of counts obtained in the analysis of each
unknown. The ratio 1s inversely proportional to the amount of BaO present
1n each sample. The analysis of the samples for BaO is in Table 1.
Gerl ach
The values ranged between less than 100 ppm to 1070 ppm BaO at the
Gerlach deposit. Samples 14 and 15, which were taken in alluvium, have
fairly high values of BaO. Most of the gypsum samples do not have as
much BaO as the carbonate samples.
Blue Diamond
The amount of BaO in the Blue Diamond deposit is rather low as most
of the samples contain less than 100 ppm BaO. The sample of gypsum that
contains 365 ppm BaO lies between two red beds, the lower one having
100 ppm BaO and the upper one less than 100 ppm BaO.
Lake Mead
Except for three samples the amount of BaO present was 100 ppm BaO
or less. BaO is present in both the sulfates and carbonates.
Vegas Wash
A wide range of BaO occurs at the Vegas Wash quarry, the values
being from less than 100 ppm BaO to 930 ppm BaO. More BaO is in the
siltstones than in the sulfates or carbonates.
Apex
The deposit at Apex is unusual in that it does not have high purity
gypsum, yet it 1s being commercially mined. This deposit has a low range
of BaO values, but most of the samples do contain in excess of 100 ppm BaO.
-22- Intensity Ratio 5 4.0 3.0 2.0 .0 0.0 1.0 200 eaie itiuin f aim Oxide Barium of Distribution Relative 0 0 4 n at Pr Million Per Parts in iue 8 Figure 0 0 6 0 0 8
1000 _i_ 1200 Vo IV) Table 1
Bari um 1 0 Sample No. ppm BaO V* S Predominant Rock Type
6-1 < 100 3.6 .0434 Sulfate
G-2 435 3.0 .0216 Carbonate
6-3 < 100 5.7 .7410 Sulfate
G-3a 1000 0.2 .0005 Carbonate
6-4 < 100 0.4 .0056 Sul fate
G-5 < 100 2.2 .0293 Sulfate
G-6a < 100 3.9 .0635 Sulfate
G-6b 80 1.9 .0188 Sulfate
G-6c 270 0.2 .0019 Sulfate
6-7 < 100 2.2 .0322 Sulfate
6-8 < 100 2.0 .0291 Sul fate
6-9 < 100 2.4 .0253 Sul fate Sulfate 6-10 < 100 5.3 .0747 Sulfate G-ll < 100 2.4 .0349 Sulfate 6-12 < 100 2.4 .0336 Sulfate G-13 < 100 5.8 .0915 .0073 Carbonate 6-14 995 2.6 .0025 Carbonate G-15 1070 1.1 .0356 Sul fate G—16 < 100 2.7 .0613 Sul fate 6-17 < 100 4.2 .0130 Sul fate G-18 < 100 1.0 .0221 Sulfate 6-19 655 4.0 4.2 .0613 Sul fate G-20 < 100
-24- Table 1. - Cont.
Sample No. ppm BaO c - % S Predominant Rock Type
Carbonate 8D-1 < 100 0.2 .0030 Sulfate BD-2 < 100 0.6 .0075 Carbonate BD-3 < 100 2.0 .0247
ED-4 365 1.2 .0099 Sulfate Cherty carbonate BD-5 100 2.7 .0264 Sulfate BD-6 < 100 2.6 .0356 Carbonate BD-7 < 100 2.5 .0302 Sulfate BD-8 < 100 1.1 .0164 .0565 Carbonate BD-9 < 100 4.4 .1136 Carbonate LM-1 < 100 9.0 .0321 Carbonate LM-la < 100 2.6 .0251 Sulfate LM-2 < 100 2.3 .0205 Sul fate LM-3 < 100 1.9 .0535 Carbonate LM-4 < 100 4.1 2.9 .0410 Sulfate LM-5 < 100 Carbonate 2.2 .0288 LM-5a < 100 Carbonate 2.4 .0319 LM-6 < 100 Carbonate 0.2 .0032 LM-7 < 100 Carbonate 6.2 .0794 LM-8 < 100 Carbonate 1.5 .0202 LM-9 < 100 Sulfate 0.8 .0060 LM-9a 435 Sulfate .04 .0058 LM-10 < 100 Sul fate 1.3 .0117 LM-11 240 Sul fate 1.0 .0143 LM-12 < 100 Carbonate 5.0 .0472 LM-12a 170
-25- Table 1. - Cont.
Sample No. ppm BaO C - % S Predominant Rock Type
VW-1-1 905 0.5 .0018 Si 1i cate
VW-1-2 745 1.2 .0057 Sulfate
VW-1-3 < 100 1.3 .0168 Sulfate
,It ini'**#-’■ O ft■ / < 100 5.3 .0674 Sulfate
VW-2-5 930 1.4 .0046 Si 1i cate
VW-2-6 390 1.5 .0115 Carbonate
VW-2-7 < 100 1.1 .0136 Sulfate
VW-3-8 330 0.6 .0052 Sul fate
VW-3-9 425 1.7 .0124 Sulfate
VW-3-10 395 2.3 .0174 Sulfate
VW—3-11 100 3.6 .0429 Sul fate
VW-4-12 175 0.9 .0083 Sulfate
VW-4-13 < 100 1.7 .0212 Sulfate Sulfate VW-4-14 80 2.5 .0254 Sulfate VW-4-15 < 100 0.2 .0024 Sul fate VW-4-16 < 100 1.2 .0135 .0758 Sulfate A-l < 100 7.3 .0165 Sulfate A-2 305 2.0 .0265 Sul fate A-3 < 100 2.5 .0511 Sul fate A-4 < 100 4.9 .0734 Sul fate A-5 < 100 6.1 .0155 Sulfate A-6 100 1.6 .0169 Sulfate A-7 145 1.7 .0175 Sulfate A-8 140 1.8 4.2 .0429 Sulfate A-9 80
26- Table 1. - Cont. 1 0 Sample No. ppm BaO 5^ S Predominant Rock Type
A-10 < 100 2.7 .0305 Sulfate
A-11 85 0.4 .0040 Sulfate
A-12 545 2.7 .0174 Sulfate
A~ i -S 200 2.7 .0251 Sulfate
A-14 230 2.0 .0179 Sulfate Sulfate A-15 225 1.4 .0128
A-16 105 3.6 .0359 Sul fate Sulfate A-17 < 100 3.8 .0428 Sul fate A-18 90 1.7 .0167
Discussion
Barium as was expected, 1s only present In trace amounts. This 1s
1n part due to the 1on1c size of barlun, 1.34 8, which 1s too large to
permit 1t to readily replace the calcium of 1on1c radius 0.99 A (Mason,
B., 1958). Barium sulfate 1s characteristically found 1n metalliferous veins
rather than bedded formations. Barium 1s also found In feldspars and
micas. During the process of weathering barium 1s dissolved out of
these minerals (Clark, F. W., 1924). The barium migrates 1n fresh water
as BaCl2 until It reaches sea water where It 1s converted to BaS04. It
rapidly precipitates In the coastal zone of the basin due to the sulfur
Ions which are present In sea water (Katchenkov, S. M., 1962). Barium
constitutes 0.006 grams per ton of sea water (Mason, B., 1958).
Calcium sulfate 1s deposited as gypsum when the salinity of sea
water 1s 3.5 times the normal salinity, therefore a large amount of sea
-27- water must first be evaporated (Bateman, A. M., 1959). This would mean that the edge of the water would recede toward the center of the basin which entraps or holds the water. Any barium which had initially precipi tated in the coastal zone would remain there. Unless new influxes of barium in fresh water entered the basin, any gypsum which formed as an evaporite should be nearly barren of barium, since the deposition of gypsum as an evaporite would be far removed from the original area of barium precipitation.
The question of whether or not a carbonate rock could be analyzed
using a standard with a sulfate matrix was raised 1n the course of
these analyses.
Because of Compton scattering by atoms of low atomic number such as
oxygen, carbon, hydrogen, sulfur, etc., the X-ray quantum may be inelastic-
ally scattered and lose its energy. This Compton scattering will interfere
with measurements of low concentrations of elements (B1rks, L. S., 1959).
Carbon 1s a lower atomic number element than sulfur, therefore one
can expect a higher background and therefore a greater relative intensity
In carbonate rock analysis. Figure 9 is a calibration curve depicting the similarity in the slope
of the carbonate and sulfate lines under two different circumstances.
First, when the background is not subtracted, and secondly, when the back
ground is subtracted from the total counts taken during an analysis. For
example, a count for a barium oxide standard of 0.10% in a calcium sulfate
matrix which would include the background might be 48.66 counts per minute.
A count for a barium oxide blank sample might be 8.14 counts per minute.
The calibration curve which included the background would be the same as
line 1, and if the background were subtracted, (8.14), the resulting
-28- curve would be line 3. The same reasoning holds true for a carbonate rock and this is shown in lines 2 and 4. The background was not sub tracted in either the barium oxide analysis or later In the strontium oxide analysis as an exacting precision 1n the analyses was not war ranted. However, for high precision geochemical work, the background must be subtracted.
The variance 1n the slope of lines 1 and 2 is due to the difference in the mass number between carbon and sulfur. Carbon, being the lighter element, scatters the X-ray quantum more than does the sulfur. This scat tering causes a higher background in the carbonates than in the sulfates.
The intensity ratio difference between the two rocks results in a deeper pitch to the carbonate number two line when a calibration curve is drawn.
The same holds true for lines 3 and 4 where the background has been sub tracted.
If the background is not subtracted there is a seemingly 50 ppm difference between the sulfate and carbonate analysis. This is minor since values of less than 100 ppm are not included in this work.
If on the other hand, the background is subtracted as 1n lines 3 and
4, there is an apparent difference amounting to 110 ppm barium oxide be tween the sulfate and carbonate analysis. This greater precision would of course be warranted 1n precision geochemical work.
One can therefore conclude, on the basis of the above observations, that it would be possible to analyze a carbonate using a sulfate standard, and vice versa, if absolute values were not essential to the work being done. A brief discussion of the method used to determine the precision of the analysis is given in the Appendix.
-29- Intensity Ratio 1 .0 0 8.0 6.0 4.0 2.0 0.0 +- 0 0 40 0 10 1200 1000 800 0 0 6 400 200 iiaiy nte lp o .abnt ancf Sulfate .Carbonate of Slope inthe Similarity itiuin Curves Distribution iue 9 Figure 1 1400 STRONTIUM
The deposits at Gerlach, Blue Diamond, and Lake Mead contained
small amounts of strontium. Figure 10 shows the relative distribution
of strontium oxide in the Lake Mead, Gerlach, and Blue Diamond deposits.
The sample analysis may be found in Table 2. The deposit at Apex and
Vegas Wash indicated some relatively high values which are shown in
Figure 11 and Table 2.
Gerlach
Strontium was found to be present in the samples from Gerlach.
The values ranged from 300 ppm to 0.14% in sulfates and from 733 ppm
to 0.12% in the two carbonate samples. Apparently the SrO is equally
distributed, as all of the samples whether sulfates or carbonates con
tained in excess of 100 ppm.
Blue Diamond
Blue Diamond Company's gypsum deposit also contained strontium.
One of the samples had less than 100 ppm while three others were in the
0.10% range. The rest of the samples lay somewhere between these two
values. Because only nine samples were analyzed from this deposit,
the values of strontium can only Indicate the presence of strontium.
Lake Mead
Once again no preference was shown for either carbonates or sulfates
as strontium was present in both at the Lake Mead prospect. From less
than 100 ppm to over 800 ppm strontium oxide were present i«. the car
bonates, and concurrently from less than 100 ppm to over 900 ppm stron
tium oxide were found in the sulfates.
Although the above deposits gave an indication to the presence of
strontium in gypsum and associated carbonates, none of the samples analyzed contained over 0.14% SrO.
Vegas Wash
High amounts of strontium were found 1n the Vegas Wash deposit.
One sample contained over 10.0% SrO. Several samples from this deposit, which is an old quarry, contained over 0.50% SrO. This deposit is quite extensive and all but three of the samples were taken in the gypsum. Two samples were siltstones and one was a carbonate. Both slltstone samples showed an indication of strontium oxide. The carbonate sample had 2.92%
SrO.
The high value of 10.42% was found 1n a white seam in the third bench or working that was sampled. See Figure 5. It will be noted that the pink seam contained 1.87% SrO and the hanging wall adjacent to it contained 1.70% SrO.
Further and more detailed sampling and analysis of this deposit is warranted on the basis of the above findings. The carbonates which under lie this deposit should also be sampled in greater detail. Naturally the single carbonate sample can only indicate that strontium oxide does occur in the limestone.
Apex
The deposit at Apex has been described by Dr. R. H. Olson as being very nearly homogenous. A quick look at Table 2 will confirm this. The amount of strontium oxide present varies only from 0.47% to 1.00% and averages 0.70%. It would be difficult to predict the source or the host for the SrO since the deposit has a lime content of 2% to 5%.
Because barium 1s less soluble than strontium it did not appreciably accompany strontium in the upward percolation of gypsiferous waters which tended to enrich the strontium in the gypsum.
-32- Intensity Ratio 1 1.00 0.90 0.60 0.40 .20 0.20 0 . 00 - 0 200 eaie itiuin f totu Oxide Strontium of Distribution Relative ae ead M Lake 0 60 0 1000 800 600 400 / n at Pr Million Per Parts in le Diamond Blue iue 10 Figure Gerlach
1200 1400 vw Table 2
Strontium
Sample No. % SrO ppm SrO ; - % S Predominant Rock Type
6-1 - 832 0.0 .0000 Sulfate
G-2 0.12 1231 0.5 .0055 Carbonate
G-3 - 1076 0.4 .0040 Sul fate
G-3a - 733 0.7 .0060 Carbonate
G-4 - 303 0.3 .0017 Sulfate
G-5 - 989 0.6 .0058 Sulfate
G-6a - 833 0.2 .0019 Sulfate
G-6b 0.11 1166 0.3 .0033 Sulfate
G-6c - 530 0.2 .0011 Sulfate
G-7 - 521 0.5 .0035 Sulfate
G-8 - 390 0.2 .0013 Sulfate
G-9 - 400 0.3 .0017 Sulfate
G-10 0.10 - 0.4 .0037 Sulfate
G-ll - 741 0.3 .0024 Sulfate
G-12 - 818 0.3 .0027 Sul fate
G-13 0.14 1407 0.3 .0038 Sulfate
G-14 - 477 0.1 .0006 Carbonate
G-15 - 836 0.7 .0059 Carbonate
G-16 - 836 0.1 .0010 Sulfate
G-17 0.12 1236 0.5 .0054 Sulfate Sulfate G-18 0.12 1220 0.3 .0035 Sulfate G-19 0.12 1232 0.5 .0055 Sulfate G-20 - 1357 0.0 .0000 Sulfate BD-1 - 419 0.2 .0014
-35- Table 2. - Cont.
Sample No. % SrO ppm SrO C - % S Predominant Rock Type
BD-2 0.10 1020 0.3 .0028 Sulfate
BD-3 0.12 1159 0.4 .0043 Carbonate
BD-4 - 211 0.3 .0014 Sulfate
BD-5 - < 100 0.9 .0029 Sulfate
BD-6 0.10 1005 0.8 .0082 Sulfate
BD-7 - 313 0.8 .0059 Carbonate
BD-8 - 966 0.5 .0052 Sulfate
BD-9 - 286 0.9 .0066 Carbonate
LM-1 - 260 0.4 .0020 Carbonate
LM-la - < 100 0.4 .0012 Carbonate
LM—2 - < 100 0.0 .0004 Sulfate
LM-3 - < 100 0.3 .0012 Sulfate
LM-4 - 544 0.7 .0056 Carbonate
LM-5 - 438 0.3 .0019 Sulfate
LM-5a - < 100 0.3 .0011 Carbonate
LM-6 - < 100 0.7 .0020 Carbonate
LM-7 - < 100 0,7 .0024 Carbonate
LM-8 - < 100 0.2 .0009 Carbonate
LM-9 - 139 0.3 .0013 Sulfate
LM-9a - 416 0.2 .0014 Sulfate
LM-10 - < 100 0.9 .0034 Sulfate
LM-11 - 918 0.5 .0044 Sulfate
LM-12 - 681 0.4 .0030 Sulfate Carbonate LM-12a - 805 0.0 .0004 Silicate VW-1-1 — 456 0.4 .0025
- 36- Table 2. - Cont.
Sample No. % SrO ppm SrO C - % S Predominant Rock Type
VW-1-2 - 458 0.4 .0027 Sulfate
VW-1-3 0.69 6944 0.0 .0000 Sulfate
VW-2-4 0.57 5678 2.3 .0957 Sulfate
VW-2-5 0.13 1265 0.3 .0038 Silicate
VW-2-6 2.92 - 0.4 .0394 Carbonate
VW-2-7 0.87 8735 0.4 .0036 Sulfate
VW-3-8 0.95 9547 0.4 .0039 Sulfate
VW-3-9 10.42 - 0.7 .0500 Sulfate
VW-3-10 1.87 - 0.7 .0114 Sulfate Sulfate VW-3-11 1.70 - 0.7 .0096 Sulfate VW-4-12 0.72 7155 0.1 .0006 .0014 Sulfate VW-4-13 0.86 8574 0.2 Sulfate VW-4-14 1.04 - 0.5 .0050 .0008 Sulfate VW-4-15 0.41 4061 0.2 .0215 Sulfate VW-4-16 0.83 8323 0.6 .0019 Sulfate A-l 0.58 5833 0.3 .0006 Sulfate A-2 0.67 6708 0.1 0.4 .0022 Sulfate A-3 0.47 4665 .0026 Sulfate A-4 1.00 - 0.3 0.2 .0017 Sulfate A-5 1.00 - 0.4 .0023 Su'l fate A-6 0.48 4807 0.3 .0023 Sulfate A-7 0.64 6375 0.2 .0015 Sulfate A-8 0.93 9273 0.3 .0028 Sul fate A-9 0.88 8778 0.1 .0010 Sulfate A-10 0.63 6306
-37- Table 2. - Cont. 1 Sample No. % SrO ppm SrO 0 S Predominant Rock Type
A-11 0.62 6169 0.1 .0010 Sulfate
A-12 0.51 5111 0.4 .0022 Sulfate
A-13 0.75 7452 0.5 .0042 Sulfate
A-14 0.70 7009 0.5 .0037 Sulfate
A-15 0.73 7293 0.2 .0018 Sulfate
A-16 0.97 9652 0.2 .0019 Sulfate
A-17 0.55 5466 0.5 .0031 Sulfate
A-18 0.64 6397 0.2 .0017 Sulfate
Discussion
By assuming that sufficient sulfate is present one can estimate the
amount of celestite that would be formed by the Sr present in the samples.
The sample from Vegas Wash which has over 10% SrO can be estimated
to contain about 21% celestite, the balance being gypsum and impurities.
The samples which contain 1.87% and 1.70% SrO would be equivalent to
3.6% and 3.3% celestite, respectively.
The two samples from Apex which contain 1% SrO could be expected
to be composed of almost 2% celestite.
The carbonate sample at Vegas Wash contains 2.92% SrO. This
sample may contain strontianite as an accessory mineral up to about
4.1% of the sample. Igneous rocks are the original source of strontium which is a
minor element (Clark, F. W., 1924). Strontium follows the same path to the sea that barium does. Often
U r g e amounts of strontium remain dissolved 1. the sea because strontium
-38- is soluble and because sea water must become saterated with strontium before it will precipitate out.
In coastal zones and in warm basins, calcium is deposited as a sedi ment by chemical precipitation (Katchenkov, S. M., 1962). About one half of the calcium sulfate is deposited as gypsum before anhydrite is depos ited (Bateman, A. M., 1959).
Strontium occurs with calcium because of the similarity in ionic o o size, 1.12 A and 0.99 A respectively, and the electrical charge. Accumu lation of celestite indicates a high salt concentration in the sea basin due to tectonic activity where large sections of the oceans have been cut off during movement of the land (Katchenkov, S. M., 1959).
Calcium and strontium precipitate in a certain sequence: CaC03,
CaC03 + MgC03, SrS04 , CaS04, 2H20, and CaSC>4. This usually occurs 1n lagoonal parts of the basin in temperate to hot arid regions (Katchenkov,
S. M., 1962; Rankama, K., and Sahama, Th. G., 1960).
CALCIUM
All of the samples were also analyzed for calcium oxide. Lower values of calcium oxide were found 1n some samples than might be expected theoretically. This is of course due to the many impurities present in each sample. See Table 3.
Discussion
The calcium oxide analysis of the samples from the five deposits is
fairly typical of the amount of the calcium oxide that would be expected
in these samples. Examining the deposit at Apex which has several in
cluded impurities, one can readily understand why such low values of
calcium oxide were found. The low calcium oxide content of 19.46% in
- 39- sample VW-3-9 corresponds with the strontium oxide content of 10.42%.
Therefore the estimated percentage of gypsum would be 60% and the esti mated percentage of celestite would be 21%, the balance being impurities.
The carbonate sample, VW-2-6, based on a calcium oxide content of 29.08%
could have an estimated 53% calcium carbonate content and an estimated
10% strontianite (SrS04) content, the balance again being impurities.
The range of calcium oxide values for the samples of the other deposits
lies somewhere between having many impurities, which have not been
analyzed for, to high purity.
Table 3.
Calcium
Sample No. % CaO C - % S Predominant Rock Type
G-l 32.50 0.38 .0038 Sulfate
G-2 47.10 0.00 .0000 Carbonate
G-3 35.15 0.23 .0024 Sulfate
G-3a 28.90 0.32 .0016 Carbonate
G-4 33.49 0.06 .0006 Sulfate
G-5 32.18 0.12 .0012 Sulfate
G-6a 32.62 0.18 .0018 Sulfate
G-6b 30.18 0.20 .0019 Sulfate
G-6c 39.62 0.18 .0021 Sulfate Sulfate G-7 32.66 0.13 .0013 Sulfate G-8 35.75 0.26 .0028 Sulfate G-9 38.69 0.14 .0016 Sulfate G-10 34.77 0.19 .0020 Sulfate G-l 1 33.27 0.13 .0013
-40- Table 3. - Cont.
Sample No. % CaO C - % S Predominant Rock Type
G-12 33.38 0.06 .0006 Sulfate
8-13 35.99 0.26 .0028 Sulfate
6-14 6.84 0.30 .0014 Carbonate
G-15 14.61 0.11 .0007 Carbonate
G-16 34.70 0.12 .0013 Sulfate
G-17 33.31 0.06 .0006 Sulfate
G-18 39.88 0.24 .0028 Sulfate Sulfate G-19 26.69 0.09 .0008 Sulfate G-20 33.69 0.34 .0035 Sulfate BD-1 31.20 0.20 .0020 .0032 Sul fate BD-2 32.78 0.32 .0034 Carbonate 3D-3 37.41 0.31 .0012 S u lfa te BD-4 17.02 0.18 .0000 Mixture, Silica BD-5 - 0.00 .0037 Sulfate BD-6 32.10 0.37 .0009 Carbonate 3D-7 38.80 0.13 .0016 Sulfate BD-8 33.22 0.16 .0020 Carbonate BD-S 39.30 0.11 .0029 Mixture, Carbonate LM-l 48.20 0.22 .0014 Carbonate LM-la 29.80 0.27 .0043 Sulfate LM-2 34.80 0.41 Sulfate 0.14 .0012 LM-3 25.92 .0016 Carbonate LM-4 28.30 0.32 .0000 Sul fate LM-5 38.20 0.00 Mixture, Carbonate 0.16 .0021 LM-5a 49.40
-41- Table 3. - Cont
Sample No. % CaO C - % S Predominant ______Rock Type
LM-6 49.60 0.02 .0003 Mixture, Carbonate
LM-7 44.70 0.13 .0016 Mixture, Carbonate
LM-8 48.00 0.14 .0018 Mixture, Carbonate
LM-9 34.04 0.17 .0018 Sulfate
LM-9a 26.91 0.25 .0022 Sulfate
LM-10 36.53 0.19 .0021 Sulfate
LM-11 34.54 0.40 .0043 Sulfate
LM-12 32.77 0.00 .0000 Sulfate Carbonate LM-12a 39.00 0.24 .0017 Silicate VW-1-1 12.08 0.96 .0056
VW-1-2 37.18 0.41 .0045 Sulfate Sulfate VW-1-3 30.61 0.26 .0025 Sulfate VW-2-4 30.84 0.25 .0024 Silicate VW-2-5 2.21 0.29 .0011 .0018 Carbonate VW-2-6 29.80 0.35 .0030 Sulfate VW-2-7 32.99 0.30 .0016 Sulfate VW-3-8 20.61 0.21 .0005 Sulfate VW-3-9 19.46 0.08 .0005 Sulfate VW-3-10 25.59 0.06 ' .0069 Sulfate VW-3-11 29.75 0.73 .0019 Sulfate VW-4-12 24.85 0.22 o o —a
o Sul fate VW-4-13 30.25 0.10 • .0020 Sulfate VW-4-14 30.61 0.21 .0025 Sulfate VW-4-15 23.32 0.25 .0000 Sulfate VW-4-16 30.81 0.00
42 Table 3. - Cont. 1 Sample No. % CaO 0 S Predominant Rock Type
A-l 26.60 0.28 .0025 Sulfate ) ) A-2 26.43 0.18 .0016 Sulfate ) ) A-3 26.43 0.18 .0016 Sulfate ) ) A-4 26.89 0.19 .0017 Sulfate )
A-5 28.03 0.28 .0026 Sulfate )
A-6 26.14 0.10 .0009 Sulfate ) ) A-7 26.15 0.37 .0037 Sulfate ) ) A-8 26.42 0.23 .0020 Sulfate ) ) Sulfate ) 2-5% 1 A-9 26.46 0.11 .0010 ) Sulfate ) A-10 28.10 0.14 .0013 ) Sulfate ) A—11 27.32 0.14 .0013 ) .0013 Sulfate ) A-12 14.74 0.20 ) .0017 Sulfate ) A-l 3 26.75 0.19 ) Sulfate ) 24.14 0.22 .0018 A-14 ) Sulfate ) 21.61 0.30 .0023 A-l 5 ) .0015 Sulfate ) A-16 25.49 0.17 ) Sulfate ) 27.97 0.00 .0000 A-l 7 ) .0008 Sulfate ) A-18 26.12 0.09 IX, Conclusion
It can be concluded that the original assumption that barium and strontium would be found with gypsum and associated carbonates 1n Nevada has been proven to be true. The barium is only present 1n trace amounts.
Strontium was found to be present 1n both carbonates and sulfates 1n con siderable amounts.
Greater than trace amounts of barium oxide were not found with gypsum or carbonates because of barium's large Ionic radius, its immedi ate precipitation near coastal areas of the sea, and the regression of the sea away from the coastal areas to lagoonal areas of the basin as water evaporated.
Significant amounts of strontium oxide were found associated with gypsum and carbonates. This is attributed to strontium's similarity in ionic radius and its co-prec1pitation with calcium under the same environmental conditions, i.e., high salinity and warm climate.
Although not enough data 1s as yet available, it may be possible to analyze a carbonate and a sulfate with a single standard made up of a mixture of the sulfate and carbonate. Referring to Figure 9, one can see how the calibration curve of the sulfate and carbonate of lines 3 and
4 almost coincide showing that the maximum difference is 110 ppm over the composition range studied. By using a mixture to produce the standard, the new calibration line should fall between the sulfate and carbonate lines and the corresponding intensity ratios should fall within acceptable limits that would give acceptable or reasonably accurate results.
In this case it was again possible to demonstrate the advantages of a non-destructive method for fast and accurate analytical work using the
X-ray spectrograph.
-44- The most time consuming portion of the procedure was not the analysis, but the sample preparation. Each time a piece of equipment was used it had to be cleaned thoroughly. Control of particle size in samples was highly important because 1t directly affected the intensity ratios.
The actual analysis was fairly rapid since 48 pellets or 16 samples could be analyzed in an 8 hour day. The samples were analyzed in trip licate so as to obtain the precision that this method warrants.
Unlike a wet chemical analysis, no fusions or separations are re quired by this method. Nothing is either added or deleted from the sample to change its composition. The pellets made by pressing the finely ground powder with a bakellte backing can be stored permanently after the analysis. As such they may be used as secondary standards in the future.
On the basis of the above findings, a more detailed study of the
Vegas Wash deposit may be warranted 1n order to determine the extent, pattern, frequency and amount of strontium present throughout the deposit.
In as much as only five deposits have been sampled, a further inquiry into many other gypsum deposits may reveal the presence of strontium.
Certainly such possibilities of future sources of minerals should not be overlooked.
By using the X-ray spectrograph!c technique, it may be possible to broaden the field of analytical methods that can be successfully used
1n mining exploration. The search for new ore bodies and for new methods of analysis, although dissimilar in approach, is a never ending one.
-45- X. Appendix
-46- Precision
The precision of the analytical results was determined by using 1 ^~2 the statistical equation S j j — ----, where S equals standard ^ n - 1 deviation of a single observation; n equals the number of observations or analyses; d equals deviation of an observation from an arithmetic mean, x. The relative deviation or coefficient of variation, C, is 100 S equal to x
Each of the samples was analyzed 1n triplicate by preparing three pellets from each sample. Each pellet was counted four times and an average count for each pellet was determined. An Intensity ratio for each pellet was then computed from the average count of each pellet.
The standard deviation, S, 1s determined from the Intensity ratios.
The following is an example of a standard deviation, S, and a relative deviation, C, determination for a sample analyzed for barium;
.2 Intensity Ratio______d______d_
1.2043 -112 12544 S s 0.0434 1.2634 +479 229441
1.1788 -367 134689 c „ ,100 x 0.0434 « 3 .5 7 % 1.2155 x » 1.2155 376674
-47- Explanation of Figures 12 and 13
Figure 12 is the distribution curve for the X-ray spectrographlc analysis of barium oxide. This curve allows one to determine final voltages and count only that portion of the curve that is the result of pulses from the element being analyzed. It is possible to cut off the low amplitude electrical noise pulses using the base adjustment discriminator which allows only the pulses above the noise to be counted.
Pulses of higher amplitude are also reflected at the same 29 setting as the desired wave length of the element being analyzed.
These higher unwanted amplitude pulses are caused by characteristic
wave lengths of higher atomic number elements and by higher order
scattered radiation. These X-rays are being emitted simultaneously
with the X-rays of barium and strontium. These high amplitude pulses
can also be discriminated by using the window adjustment which allows
only those pulses from the sample to be counted.
Figure 13 1s the distribution curve for the X-ray spectrographlc
analysis of strontium oxide. This curve performs the same functions
as the curve for barium oxide does and the same methods of eliminating
unwanted pulses are applicable.
-48- ? VOLTS/6 TJo C
Figure 12
Distribution Curve of INTENSITY n itiuin uv of Curve Distribution totu Oxide Strontium iue 13 Figure 'y 5 0 XI. Bibliography
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