Trace element investigation of the Turkey Track porphyry ......Acknowledgments This work was conducted under the direction and guidance of Dr. P. E. Damon and was financed in part

Trace element investigation of the "TurkeyTrack" porphyry, southeastern Arizona

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TRACE ELEMENT INVESTIGATION OF THE "TURKEY TRACK" PORPHYRY, SOUTHEASTERN ARIZONA

byJames Edward Mlelke

A Thesis Submitted to the Faculty of theDEPARTMENT OF GEOLOGY

In Partial Fulfillment of the Requirements For the Degree ofMASTER OF SCIENCE

In the Graduate CollegeTHE UNIVERSITY OF ARIZONA

1965

STATEMENT BY AUTHOR

This thesis has been submitted in partial fulfillment of requirements for an advanced degree at the University of Arizona and is deposited in the University Library to be made available to borrowers under rules of the Library.

Brief quotations from this thesis are allowable without special permission, provided that accurate acknowledgment of source is made. Requests for permission for extended quotation from or reproduction of this manuscript in whole or in part may be granted by the head of the major department or the Dean of the Graduate College when in his judgment the proposed use of the material is in the interests of scholarship. In all other instances, however, permission must be obtained from the author.

SIGNED:

APPROVAL BY THESIS DIRECTOR

This thesis has been approved on the date shown below:

Pau1 E. Damon Professor of Geology

>rv><

Acknowledgments

This work was conducted under the direction and guidance of Dr. P. E. Damon and was financed in part by A.E.C. contract AT (11-1) - 689. I wish to express my gratitude to Dr. Damon for his many helpful suggestionsand advice throughout. In addition I wish to thank Mr./Robert O'Hare of the Arizona Bureau of Mines who permitted the investigator to use the emission spectrograph and facilities of the Bureau of Mines, and who made many helpful suggestions concerning the emission spectrographlc work.Mr. Robert Palmer, research technician of the geochemistry laboratories contributed greatly in maintaining and repairing the electronic equipment, and I am grateful for his instruction in this area.

I also wish to express my appreciation to Mr. Richard Bennett who ran the flame photometer and offered many helpful suggestions in this work. The members of the geochemistry laboratories contributed greatly with timely suggestions and helpful criticisms of this investigation.

ill

Table of Contents

List of Illustrations . viList of Tables ......................................viiA b s t r a c t ....................................... viiiChapter I - Introduction 1

1.1 Purpose of the Investigation............ 1

1 .2 Location of the Area of Investigation . . 21.3 Past Investigations ..................... 5

1.4 Present Investigation .................. 7

Chapter II - Porphyry Occurrences Investigated . 3in this S t u d y ............... ...2.1 Sample Locations and Petrology . . . . Q

Sawtooth Mountains .................. 8

Desert Museum ............... 9

Sentinel Peak ..................... 10

Tumamoc Hill ..................... 11

Black M o u n t a i n ..................... 11

San Xavier M i s s i o n .................. 12

Pima District ..................... 13

Saguaro National Monument ............ 14Clenega G a p ........................ 15

Mine t a Ridge ..................... 16Dos Cabezas Mountains . . . . . . 18

Page

iv

VPage

Fisher Hills ..................... 19Chapter III - Radiometric Analyses ............ 20

3.1 Alpha C o u n t i n g .................. ... . 203.2 Beta Counting ............... 243 .3 Gamma C o u n t i n g ............................35

Chapter IV - Nonradiometric Chemical Analyses . . 604.1 Fluorlmetrlc Analyses .................. 60

4.2 Flame Photometry ........................ 6l4.3 Emission Spectroscopy .................. 6l

Chapter V - Conclusions............................77Appendix A - Data on Rock Standards used 82

In this Investigation ........................Appendix B - Equations for the Determination 83

of U, Th, and K In Common Rocks by Gamma Scintillation Counting ........................

Selected Bibliography ........................... 88

List of Illustrations

1 Location of Area Under Study ............ 3

2 Index Map of "Turkey Track" and Related 4Porphyries . . . . ...............

3 Alphas/hour versus alphas/mg hour . . . 254 Alphas/mg hour versus % K (beta counting) 285 Alphas/mg hour versus % K for "Turkey

Track” Localities ..................... 326 Uranium and Thorium Series Spectra . . . 36

7 Gamma Scintillation SpectrometerDrift versus T i m e .................. 39

8 Determination of Optimum Channel Width. . 409 Uranium Expected versus Uranium

Determined by Gamma Counting . . . . 4210 Thorium Expected versus Thorium

Determined by Gamma Counting . . . . 43!11 Potassium Expected versus Potassium

Determined by Gamma Counting . . . . 4412 Th/U Expected versus Th/U Determined

by Gamma Counting.................. 4513 Typical Working Curve for Cobalt in

Silicate Rocks ........................ 69

14 Potassium Content versus Cobalt plusNickel Content ........................ 72

15 Potassium Content versus Scandium . . . 73

16 Potassium Content versus Cesium . . . . ?417 Cesium Content versus Chromium . . . . 75

vl

Figure Page

List of Tables

Table Page1 Comparison of Chemical Analyses of

Rock Types with the "Turkey Track" 62 Alpha and Beta Counting Data3 Radiometric Variations Within a Single

Locality .....................

21

344 Comparisons of Uranium Determinations 485 Comparisons of Thorium Determinations 516 Comparisons of Potassium Determinations 547 Comparisons of Th/U Ratios 578 Emission Spectrographic Analyses 639 Comparison of Trace Element Content of

the "Turkey Track" with W-l and G-l . . 76

vii

Abstract

A rock unit of unusual composition, the "Turkey Track" porphyry, occurs In several localities over a wide spread although limited area In southern Arizona. The "Turkey Track" has been proposed as a correlative guide; however. It has been questioned whether all "Turkey Track" localities represent one rock unit. The "Turkey Track" dould be a useful correlation guide If It could be established that all "Turkey Track" localities represent one rock unit, formed during a short Interval of time. This Investigation attempts to demonstrate by uniformity In trace element content coupled with similarities In chemical and mlneraloglcal composition that the "Turkey Track" localities probably do have a common parent and were erupted or Intruded penecontemporaneously. Concurrent K-Ar age dating Indicates apparent ages of around 28 million years among various "Turkey Track" localities.

Samples were collected from "Turkey Track" localities and subjected to alpha, beta, and gamma counting, flame photometry, fluorlmetry, emission spectroscopy, and petrographic analysis. Plots of <tf/mg hr versus for severalvolcanic porphyries show a definite grouping of "Turkey Track" samples. Uranium analysis by gamma counting agreed quite well with fluorlmetrlc uranium determinations, Indicating the

value of the gamma method. Use of larger samples and avlil

lxlarger "well" scintillation crystal would greatly improve the precision.

Emission spectroscopy showed little variation in trace element content among "Turkey Track" samples. In addition the "Turkey Track" appeared higher In Cs, Na, and K than normal rocks of similar Si and Al content. All "Turkey Track" samples have similar petrographic characteristics. Most distinctive are the large unzoned plagloclase laths, and commonly two pyroxenes in an aphanltlc groundmass.

Chapter I

Introduction

1.1 Purpose of the InvestigationA volcanic rock unit known as the "Turkey Track"

porphyry has been proposed as a correlation guide over a large area in southeastern Arizona. According to Cooper (1961) the "Turkey Track" is characterized petrographlcally by large weakly zoned plagioclase laths and commonly two pyroxenes in a gray to reddish-brown, fine-grained to glassy groundmass. Whether or not all volcanic rocks having these characteristics are cogenet1c is open to question. Porphy- ritlc andesites with different characteristics have been correlated with the "Turkey Track". The "Turkey Track" is an easily recognizable unit and could be used as a correlation guide if it were well defined, and if all such well defined "Turkey Track" porphyries in southern Arizona were contemporaneous. Consequently, a more complete chemical and petrographic definition of the unit is desired.

Previous geochemical investigations of volcanic rocks in southern Arizona have shown that radiometric analyses may be useful in distinguishing a particular rock unit. One rock unit, the "Turkey Track" porphyry, shows a characteristic grouping of points when plotted as cC activity versus

1

2yS activity. A distinctive radiometric criterion such as this is particularly useful as it is relatively easy to subject questionable samples to oL , and y counting techniques.

One purpose of the following work is to determine whether the concept is valid that similar volcanic porphyries are correlative and oogenetic over a great distance - 100 miles or more. The validity of this concept will be established for the "Turkey Track" porphyry by numerous chemical and petrographic analyses coupled with concurrent K-Ar age determinations. On the basis of the validity of this concept, an attempt will be made to correlate various "Turkey Track" localities using chemical and petrographic data.

1 .2 Location of the Area of InvestigationThe sample area covered by this Investigation lies

within the Basin and Range Province in southeastern Arizona. It extends from the Tucson Mountains, Pima County, 100 miles eastward to the Dos Cabezas and Fisher Hills, Cochise and Graham Counties (Figure 1). Andesite porphyries which are, or are similar to, the unit nicknamed the "Turkey Track" are found in at least eighteen localities within this district. These localities include the Desert Museum area, Tumamoc Hill, Sentinel Peek, Black Mountain, San Xavier Mission, Pima District, Mineta Ridge, Happy Valley quadrangle, Saguaro National Monument, Cienega Gap,

3

FIGURE I

ARIZONA

LOCATION OF AREA UNDER STUDY

Key to Figure 2

1. Sawtooth Mountains2. Desert Museum3. Tumamoc Hill and Sentinel Peak4. Black Mountain5. San Xavier Mission6. Pima District7. Fresnal Canyon8. Cienega Gap and Davidson Canyon9. Saguaro National Monument10. Mlneta Ridge11. Happy Valley Quadrangle12. Kelsey Canyon13. Winchester Mountains14. Steele Hills15. Dos Cabezas Mountains16. Fisher Hills and southern Graham Mountains17. Little Table Mountain and northern Galiuro Mountains

SOUTHEAST ARIZONA

SCALEGRAHAMPINAL

25 M ILES

PIMA

COCHISE

SANTACRUZ

FIGURE 2 INDEX MAP 'TURKEY TRACK AND' RELATED PORPHYRIES

GR

EE

NLE

E

5Davidson Canyon, Kelsey Canyon, Winchester Mountains,Little Table Mountain, Steele Hills, Dos Cabezas Mountains, Fisher Hills, and Fresnal Canyon (Figure 2 ).

1.3 Past InvestigationsThe term, "Turkey Track",was first applied to the

porphyry unit in a descriptive sense. Since then it has become commonly accepted as the name of the porphyry and appears in the literature as such (Denton 194?, Cooper 1961, Fair 1961, Mayo 1961, McColly 1961).

Cooper proposed use of the porphyry as a correlation guide and presented a fairly comprehensive petrographic and chemical study of several "Turkey Track" localities. Petrographlcally he was able to distinguish two separate types of "Turkey Track", one with two pyroxenes, augite and hypersthene, and the other having augite and olivine which has been largely altered to red ferruginous material. Both types are quite similar in other characteristics.

Chemically these two types seem to be identical and show an average composition close to that of a doreite in Nockolds1 classification system (Nockolds 1954).Notable in the chemical composition of the "Turkey Track" is the low iron content and high alkali content compared to a doreite (Table 1).

6

Table 1 Comparison of Rock Types

% 1 2 3 4 5 6

S1° 2 57.55 — — 52.45 56 .00 5 3 .0 58.96

A12°3 13.36 — — 16.99 16 .81 16 .4 13 .02

3.45 — — 6 .1 1 3.74 -- 2.77FeO 1.36 6 .50 2 .8 8 4.36 7 .02 5.49MgO 1.4? 2.17 3 .1 0 3.39 5.17 4.74CaO 6 .32 3.70 7 .0 2 6 .8? 4.69 7.44Na20 4.13 3.29 3.79 3.56 2 .6 1 .92

k2o 3 .28 3 .0 6 2.71 2 .60 2 .7 2.03H2(^ 0 .60 —— 0 .8 6 0 .9 2 1.13h 20- 0 .92 —— 1 .0 8 — —— 0.63t i o2 1 .50 —— 1.79 1.29 —— 1.32p205 0.43 —— 0.67 0.33 —— 0.31MnO 0.05 —— 0.13 0 .1 3 0.07

O O f\) 0.44 0.13 —— —— 0.05Cl 0 .0 1 — — 0 .0 1 — —F 0 .0 6 0.07 __ __

Total 99.93 99.79 100.00 99.96

1. "Turkey Track'; Twin Buttes Quad., Cooper (196l)2. "Turkey Track", San Xavier Mission, Halva (1961)3. "Turkey Track", L. Table Mtn., Klondyke Quad., Cooper

(1961)4. Average Doreite, Nockolds (1954)5. Average southern Arizona "basalt", Halva (1961)6. Basaltic Andesite, Faust and Callaghan (1948)

Halva (1961) In working with basalts In southern Arizona noticed a tight grouping of the porphyry samples when plotted as alpha activity versus % K. This grouping appeared distinct from other volcanic units in the area which spread diffusely over the graph and in general had a lower ratio of alpha ray activity to beta ray activity from radioactive elements in the rock.

1.4 Present InvestigationThe present investigation is an attempt to verify

the findings of Cooper and Halve and present additional data on the trace element content of the NTurkey Track" porphyry. Chemical and petrographic data have been obtained from samples of verlous porphyritic andesites. Uranium, thorium, and potassium have been determined radiometrlcally and by flame photometry and fluorimetry. Other trace elements were determined by emission spectroscopy.

Chapter II

Porphyry Occurrences Investigated In this Study

2.1 Sample Localities and PetrologySeveral localities were sampled In this Investi

gation In an attempt to determine the range In trace element content of the "Turkey Track" and establish whether the distinct radiochemical grouping of the "Turkey Track"Is typical over a wide sample area. The following areas were Investigated, and, while the list probably Is not complete, It represents fairly well the range of known "Turkey Track" occurrences.

Sawtooth MountainsThe porphyry unit exposed In the west flank of

the Sawtooth Mountains (Halva 1961) does not have the same characteristics as the "Turkey Track". Macroscop- Ically, the plagloclase phenocrysts are much smaller and there Is much more blotlte In proportion to pyroxene.The radiometric data Indicate that this locality does not comply with most other "Turkey Track" localities.Chemically the * emission Is low (1 .0 6 a/mg hr) and the potassium content Is slightly lower (2 .25^).

8

9Desert Museum

A number of small Intrusive bodies are known to lie In the vicinity of the Arizona Sonora Desert Museum, located on the west side of the Tucson Mountains 12 miles west of Tucson. Two of these Intruslves are characterized by large plagloclase phenocrysts In a reddish-brown to brownish-gray aphanltlc matrix. The outcrop area of the larger body, located just south of the museum, covers a little over an acre. A smaller lens-shaped body lies to the north. These bodies Intrude Cretaceous (?) mudstones, slltstones, and sandstones of the Recreation red beds and appear to lie on the core of an asymmetrical anticline locally overturned to the east. Mayo (1961) suggests that the moist sediments were fluidized to a minor extent by the hot porphyry mass and tended to flow around It. Sedimentary Inclusions within the porphyry are Interpreted as roof pendants, Indicating that the exposure Is near the top of the Intrusion. The outcrop Is highly weathered.

Petrographlcally, the porphyry consists of about 40$ feldspar phenocrysts of labradorlte composition.These phenocrysts are up to one Inch In length and very highly, altered. One-eighth Inch phenocrysts of auglte altered to magnetite and chlorite form about 15# of the rock, and one-eighth Inch phenocrysts of magnetIte-llmenlte

10comprise about 5^* the rest being groundmass. The groundmass contains magnetite, feldspar and auglte with their alteration products, and some glassy material partially devltrified. Small quartz crystals are present some containing elongated crystals of ilmenite.

Sentinel PeakA wedge of "Turkey Track" resting on the Shorts

Ranch andesite and overlain by olivine basalt flows is

found in the side of Sentinel Peak or "A" Mountain, located on the west side of Tucson. The "Turkey Track" here appears to be a flow as indicated by the general association of the unit and the numerous vugs it contains. This area was first mapped in detail by Tolman (1909). The porphyry unit is thickest in the east where it becomes covered by alluvium and pinches out to the west in less than one-half mile. The geochemistry laboratory of the University of Arizona has obtained a number of K-Ar ages from the volcanic series exposed on Sentinel Peak and Tumamoc Hill (Bikerman and Demon 1964). These indicate an apparent age of 28.0 ± 2 .6 million years for plagloclase from the "Turkey Track" porphyry unit.

11The feldspar phenocrysts average three-quarter

Inch In diameter and are slightly zoned. Extinctionangles on alblte twinning Indicate an approximatecomposition of An . Anhedral blotlte phenocrysts

50 15.up to one-quarter Inch In diameter containing magnetite Inclusions are present. Reddish-brown ferruginous material possibly altered from olivine Is found. Auglte Is found In phenocrysts up to one-quarter Inch In diameter and as a constituent of the groundmass. Other constituents of the groundmass Include minute grains of magnetite, feldspar, and glass material.

Tumamoc HillTumamoc Hill is located on the west side of Tucson

Just west of "A" Mountain. The "Turkey Track" occurs as the lowermost unit of a sequence of basalt flows overlying andesite Intruslves. The surrounding area is covered by recent alluvium. The porphyry here Is very similar to that found on "A" Mountain and is probably from the same parent magma.

Black MountainBlack Mountain Is located 12 miles southwest of

Tucson near the San Xavier Mission. A 150 foot section (Helndl 1959) of "Turkey Track" is exposed on the north

12side of the mountain lying conformably on the San Xavier conglomerate and overlain by andesitic basalt flows. A thick dike of "Turkey Track" porphyry crosscuts the alluvial conglomerate at the west end of the mountain. Andesite porphyry crops out In the hills east of Black Mountain and small Intrusions Into granitic rocks are found to the south. Outcrops are generally highly fractured and badly weathered.

The porphyry Is reddish-gray In color with plagloclase, An ^ + , found In large tabular phenocrystscommonly In Intergrowths resembling bird tracks. Because alteration Is extensive compositions are only approximate. Sericite and clay minerals are commonly developed in the feldspar roughly parallel to twin planes. About 5$ of the rock consists of subhedral phenocrysts of augite and hypersthene extensively altered and bordered by magnetite and brown iron-rich material. Tiny segregations of magnetite are common throughout the groundmass and as inclusions In phenocrysts. The groundmass consists of microscopicplagloclase laths— the larger ones being An in

38 t 5composition, augite, glassy material, and magnetite or hematite dust.

San Xavier Mission

"Turkey Track" flows are found in the Del Bac Hills on the Ssn Xavier Indian Reservation about 10 miles

13southwest of Tucson. These flows appear to be closely related to the section exposed three miles to the southwest on Black Mountain. The flows are generally light gray In color and contain numerous vugs. The outcrops are extensively fractured and weathered.

Large tabular plagloclase phenocrysts, some having

undulatory extinction, average An ^ 4. ^ in composition. Pyroxene phenocrysts up to one-quarter inch diameter compose approximately 5^ of the rock. Thepyroxene Is augite showing alteration to chlorite. Some vugs are coated with calcite. The groundmass consists of mlcrolites of plagloclase and augite, magnetite, and partially devltrl- fied glass.

Pima DistrictThe Pima district is a mining area located 20

miles southwest of Tucson in the vicinity of Twin Buttes. The "Turkey Track" exposed here is generally brownish-gray in color ranging from light gray to brownish-red. Cooper (1960a) has recently presented an excellent report on the geology of this area.

A K-Ar date has been obtained on plagloclase from a flow in the Helmet fanglomerate (Mauger 1964). This gave an apparent age of 37 i 17 million years but the atmospheric correction was large causing the large margin of error. A blotite from a tuff in the fanglomerate has

recently been run yielding an apparent age of 27 .9 t 2 .6

million years (Mauger personal communication). A dacite dike cutting the Helmet fanglomerate has been dated at 24 million years (Creasy and Kistler 19&2 ).

Plagioclase laths up to 1 inch in length constitute 35 - 4($ of the bulk composition. These laths range from An and some are weakly zoned. Many containinclusions of magnetite-ilmenite and glassy material. Smaller phenocrysts of auglte and hypersthene are found commonly altered to brown iron-rich material and a green serpentinous mineral, possibly antlgorlte. The groundmass contains mlcrolltes of pyroxene and feldspar, magnetite, and glassy material. Vugs contain a green mineral, possibly celadonlte.

Saguaro National MonumentSaguaro National Monument is located 10 miles

east of Tucson in the western foothills of the Bineon Mountains. Plugs of "Turkey Track" ranging in size from 100 to nearly 1000 feet in diameter intrude the granite pediment flanking the Rincons (McColly 1961). Locations of the porphyry intrusives are closely related to prominent faults. The porphyry is gray to reddish-brown and outcrops of the smaller intrusives appear badly weathered.

15The porphyry contains subhedral plagioclase

crystals up to an inch in length, commonly fractured, and altered to kaoUnite and serlcite. The plagioclase is labradorlte about An ^ in composition. Smalleuhedral to subhedral olive blotite phenocrysts compose about 5% of the rock. Pyroxene is altered to reddish- brown ferruginous material and a greenish chlorltic mineral. Fractures in the large plagioclase laths are stained by a bright red to pale yellow material. The groundmass appears to be glassy and partly opaque, probably containing submicroscoplc feldspar and auglte crystals, magnetite, and glass.

Clenega Gap"Turkey Track" porphyry flows are exposed in

Clenega Gap and Davidson Canyon located about 30 miles east of Tucson along the Benson Highway. The porphyry unit occurs within and is concordant with the bedding of the Pantano formation, an alluvial and lacustrine deposit possibly correlative with the Helmet fanglomerate of the Pima district. Lower contacts show baking and alteration while the overlying sediments are unaltered and appear to

rest on an erosion surface. According to Brennan (1957) individual outcropings are from 3 to 50 feet thick and contain small xenoliths of limestone, quartzite, and mudstone.

16Two dates have been obtained by the Geochemistry

Laboratory, University of Arizona, from an associated ash flow In the Pantano formation exposed at Davidson Canyon and the Benson Highway. Sanldlne yielded an apparent age of 3 6 .7 4 1 .1 million years and blotlte 3 2 .8 t 2 .7 million years (Damon and Blkerman, In preparation). This unit Is lower In the sequence of the Pantano formation than Is the "Turkey Track"'.

Tabular plagloclase phenocrysts average three- quarter Inch In length and are In about the middle of the labradorlte range In composition. The feldspar laths are altered to clay minerals occasionally In fuzzy bands perpendicular to the twinning. Auglte and possibly hypersthene are present In small phenocrysts altered to green serpentIncus and brown ferruginous material. Magnetite Is present In tiny segregations throughout the groundmass and as Inclusions In the phenocrysts. The groundmass Is brownish-gray containing feldspar, auglte, magnetite, and some partly devltrlfled glassy material. Calclte and quartz are found In vugs.

Mineta RidgeThe Mineta Ridge area Is located 25 miles east of

Tucson In the foothills on the northeast flank of the Rincon Mountains. Reddish-purple "Turkey Track" porphyry representing either a flow or sill Is found resting on

17the late Oligocene and early Miocene age Mineta formation of Chew (1952). This age for the Mineta formation has been assigned on the basis of a fossil rhinoceros found within it (Lance i960). Furthermore, the “Turkey Track" here predates the Catalina uplift which is thought to be 6 .8 1 1.7 million years (Damon , Erickson, and Livingston 1963). The Mineta formation consists of freshwater limestone, siltstone, sandstone, and conglomerate.The porphyry is concordant with the underlying beds except where the beds are locally disturbed. According to Chew the top of the section is eroded off so that the complete thickness is unknown,although a maximum thickness of 150

feet is exposed. Four samples were collected from scattered localities in this area.

The feldspar phenocrysts average one-half inch in length and although highly altered appear close to An^ 0

in composition. Augite is present in small euhedral to subhedral phenocrysts highly altered to urallte (?) and brown ferruginous material. Opaque inclusions of magnetite are found in the phenocrysts. The groundmass is composed of augite, feldspar laths of indetermlnant composition, magnetite, clay minerals, and some glass. Tiny fractures cutting through some specimens are filled with calcite.The composition of the rock is about 40/& andesine- labradorlte, 14# auglte-urallte, 5# magnetite, 20# groundmass feldspar, 20# glass and clay minerals, and less than 1# calcite vein filling.

18Dos Cabezas

The Dos Cabezas Mountains are located about 75 miles east of Tucson on the east side of the Sulfur Springs Valley. A ten mile long dike of "Turkey Track" crops out along the trend of the range. This dike was sampled In two places to determine the range In composition.Relatively little variation in alpha and beta emission was observed over the length of this dike. The dike is generally gray to brownish-gray in color. The feldspar phenocrysts are up to l£ inches in length and comprise a major portion of the bulk composition. The feldspar shows some alteration to clay minerals. Extinction angles of

the plagioclase indicate a composition of An 52 + 4 which is in the labradorite or andeslne-labradorlte range.Smaller phenocrysts of augite are present which have a low optic angle (40° - 45°) but somewhat higher than plgeonite. The pyroxene has altered to chlorite in fractures and around the margins of the grains. Small euhedral to subhedral biotite-chlorite phenocrysts are also present. Magnetite is disseminated in small grains throughout the groundmass and as inclusions in the phenocrysts. The groundmass contains augite and feldspar microlltes in hyalopilitic texture.

19Fisher Hills

The Fisher Hills are located north of the Dos Cabezas Mountains and south of the Graham Mountains about 75 miles east of Tucson. The "Turkey Track" exhibits good flow structure here and overlies Pre-Cambrian (?) granite in the sample area. Elsewhere in the vicinity, according to Cooper (1960b), the porphyry rests on older volcanics and interfingers with dark-red rhyolite to the north. The flows are reddish-purple and outcrops appear much fresher and more angular than most exposures of the "Turkey Track" in other localities.

Plagloclase from a flow in the southern part of the area averaged An^0_^Q in composition. In addition to the large laths, numerous tiny stumpy euhedral feldspar phenocrysts are present. Typical "bird track" Intergrowths of feldspar are common. Some of the plagloclase laths have strong undulatory extinction. Small phenocrysts of augite are altered to brown ferruginous material and green highly birefrigent material probably after serpentine. Tiny euhedral to subhedral biotlte phenocrysts are present. The groundmass contains feldspar, augite, hematite dust, glass, and green serpentinous material.

Chapter III

Radiometric Analyses

3.1 Alpha CountingThe samples were subjected to radiometric analyses

by alpha and beta counting. Samples were prepared for counting by crushing and sieving to minus 60 mesh. Fines below 300 mesh were not counted.

The samples were placed In a 5 Inch thick source planchette for alpha counting, and counted for periods up to 12 hours. Standards were counted at frequent Intervals as a constant check on the counting efficiency. The apparent count rates of samples were then adjusted by efficiency correction factors determined from slight changes In the count rates of the standards. Starch was counted frequently as a check on the background. The background was considerably reduced by phosphering the photomultiplier tube under a nitrogen atmosphere and sealing It off with mylar. This procedure lowered the actual background to around 16 counts per hour although a higher apparent background of 40 counts per hour was normally recorded with starch. The difference Is thought to be activity Inherent In the detector and planchettes as empty planchettes produced the same apparent background.

20

21Table 2 Alpha and Beta Counting Data

Sample (Ref) No. <xYhr Location

a/mg hr $s.d. /s/hr 2 K #8.d

JEM 1 63 (ITT)San Xavier Mission

391 2.59 3 .13 312 2.99 3.95

JEM 2 63 (2TT)San Xavier Mission

481 3.36 2 .66 321 2.45 3.46

B 42 60 (3TT)San Xavier Mission

534 3.46 2 .98 310 2 .5 0 3.10

B 41 60 (4TT)Black Mountain

338 2.24 3 .2 6 290 2.94 3.71

RM 2 64 (5TT)Pima District

598 4.07 2.18 205 0 .5 2 2.77

JEM 3 63 (6TT)Cienega Gap

374 2.48 3.16 240 1.99 4.47

JEM 11 63 (?TT) Davidson Canyon

634 4.25 2.49 270 1.46 2.45

B 50 60 (8TT)Davidson Canyon

354 2.48 2.37 204 2.82 3.69

JEM 4 63 (9TT)Mineta Ridge

350 2.34 3.03 24? 2 .2 6 4.35


273 1.95 3.55 311 3.17 3 .6 0


304 2,13 3.57 265 2.42 4.15

JEM ? 63 (12TT)Mineta Ridge

313 2.13 3.03 250 2.43 4.14

JEM 10 64 (13TT) Saguaro Nat. Mon.

383 2 .8 0 2 .63 200 2 .5 2 2.87

JEM 11 64 (14TT) Saguaro Nat, Mon.

505 3.36 2.77 311 2.59 2.79

22Table 2 (Continued)

Sample (Ref) No.JaAYtat 4 f&Yt

cv/hr <*/mg hr #s.d. f/hr * K £s.d

CJH 1 2B (15TT) Tumamoc Hill

397 2 .5 6 3.24 363 2 .3 6 2 .9 0

FED 16 63 (16TT) Sentinel Peak

307 2.04 3.32 245 2.41 3.74

FED 2 64 (17TT) Desert Museum

443 2.94 2.45 289 2.51 3.36

B 55 61 (18TT)Desert Museum

467 3 .0 2 2 .2 1 312 2.80 3.93

JEM 6 64 (19TT) Dos Cabezas Mtns.

290 2.74 3.45 189 2.13 3 .6 2

JEM 7 64 (20TT) Dos Cabezas Mtns.

478 3 .2 0 2.48 278 2 .2 1 3.70

JEM 8 64 (21TT) Fisher Hills

799 5.32 2.41 388 2.54 3.46

JEM 9 64 (22TT) Kelsey Canyon

290 1.84 2 .58 257 2.65 3 .0 2

JEM 12 64 (23TT) Happy Valley Quad

-3-r\CM 1.56 3.46 253 2.83 1.15

B49 60 (24 A) Sawtooth Mtns.

164 1 .0 6 3.45 194 2.25 4.13

B 53 60 (25 B) San Bernardino

68 0.48 2 .9 8 85 1 .52 2.19

JEM 8 63 (26 R) Desert Museum

63 0.43 2.82 145 2 .3 0 2.32

JEM 13 64 (31 A) Empire Mtns.

92 0.65 2.18 54 0.39 2.19

USES 4978 60Columbia River basalt

0.42 1.51 68 1.03 2.73


Sample Number Location

o</hr e/mg hr #s.d. /s/hr jfs.d.

USES 4?84 Triass16 Diabase

51 0 .3 6 1.99 29 0.45 4.67

USES 4981 639Granltevllle Granite

4.47 1.63 328 4.77 2 .10

G-lWesterly Granite

1172 8 .20 0.65 317 1 .96 2.04

W-lDiabase

53 0.37 2 .2 1 44 0 .6 1 3.75

USES 4985 Deccan Trap

60 0.42 1 .92 54 0.77 2.65

USES 4983 Milford Granite

139 1.32 1.39 225 3.48 1 .92

BP-102Smithwick Shale

226 1 .5 8 1.03 104 1.33 3.55

BP-113Surinam Bauxite

2271 15.90 0.74 306 4.67

USES 4979 461Chelmsford Granite

3.23 1.83 428 7.54 1.85

24Alpha and beta counting results are presented

In Table 2 . In this and all subsequent tables and figures samples are reference numbered and classified by rock type as Indicated by hand specimen description. For example, A = andesite, B = basalt, KB z potassium basalt,B z rhyolite, T z tuff, QL z quartz latite, and TT = "Turkey Track" classification. Raw data in a/hr was converted to the more meaningful units of «/mg hr by a factor calculated from standards. Seven standards were run several times and a line of least squares was calculated to fit the data. A conversion factor of 0.0070/mg i 18/to s.d. was found. It should be noted, however, that the conversion factor affects only the absolute accuracy but not the relative error between analyses. The raw data from the standards was also used to determine the actual background which was 15.7 <x/hr. This data is plotted in Figure 3 .

Alpha activity is an indirect measure of uranium and thorium content in a rock. Other alpha emitters exist in nature but their normal concentrations are so low that their emission Is assumed to be negligible.

3 .2 Beta CountingBeta counts were detected in a low level lead

shielded anticoincidence counter using three-quarter inch

25

y SURtMAM BAUXITE

2000

1000

V INTfflCBFT * ffc * / h f

SLOFt s /SB

J H I t M W I C K SHALE

MILFOAD QRANI7E/ COLUMBIA RIVER BASALT

g b DECCAN TAAA p W -1T A IA H IC t lA IA S B

a /m g h rFigure 3 Determination of alpha/mg hour conversion

factor

diameter planchettes. Beta emission results primarily from the decay of K^O; however, beta decay from other isotopes is also detected. Interference from uranium and thorium is corrected by alpha counting after the technique developed by Damon et al (i960). Beta emission from Rb®^ was not‘ taken into account. However, the contribution from normal amounts of rubidium in rocks would be within counting error.

Samples were counted alternately with starch and potassium dichromate with occasional check runs of Columbia River Basalt. Percent potassium was determined from net count rates by the following equation:

*KX : KsNx/Nb - CNa

whereNx is the beta cph of the sampleNg is the average beta count of potassium dichromateKg is the potassium content of the dichromate (2 6.57%)C is a constant correction factor for the counter based on alpha and beta counts of standards

Na is the alpha cph of the sample

The value of C, the alpha correction factor, was calculated from the above equation using counting data from runs of ten rock standards. The standards used were G-l, W-l, Milford Granite, Columbia River Basalt,

26

27Trlassie Diabase, Deccan Trap, Saithwlck Shale, Surinam Bauxite, Chelmsford Granite, and Granltevllle Granite.The value computed for C was 0.0043.

Figure 4 is a plot of alpha activity in a/mg hr versus percent potassium by beta counting for several volcanic rocks in southern Arizona. Figure 5 is the same plot for only the "Turkey Track" showing overlap of the localities. In addition to data from this investigation radiometric data from Taylor (i960), Bikerman (1962), and Halva (1961) are included in the graph. It should be pointed out that although each set of data is consistent within Itself intercomparisons of data are a little rough. Several problems arise in trying to bring together radiometric data from different investigations. These problems become apparent when comparisons are made of different sources of data on the same rock unit. The discrepancies that arise are primarily among the cc/mg hr values. Some of the discrepancies may be attributed to the following: the location of samples is sometimes vaguesingle units may tend to vary somewhat in composition; uranium and thorium are contained in no common minerals, hence, their distribution may be erratic; differences in the nature and efficiency of the detection system; and slight differences in sample preparation.

23

?o« Q

*»r0U k KB Q

O87"71 R

F I G U R E 4„9

4'

rr"Q OetReo*0 Os$"10 A o71 eG 0 G 7»R•*'G .rgO-

Otz*

Q J O R O id i

o

oHQLO

O

H8 *8oM ilFORO GRANiTf

G ©°IZO KB

O'?* Q1IK../0 ,'o>T.

P3^ 0 ",Ke n*0 o .lOt HB ' GT ITT

K

it* o

| . ? K 8 y " G 0 " , X ' ' x

<Ofc K# G Gl61*8' 111 K8 1tK| pT i9t 0 X0 ISTT '

J 7 *

OZZTt\ 0 ovlZTF- 0 »Z,K8 >311 |7TT«»?®"TT G

\ l » T7

QWO*

GI O I K B

""ooji117 KB

CJkd

(5.177d.JTT

^ t/

U2o.ATT

,§TT

0too KB .9. •8- -

0Hint oH Z k »

oiie o18KB

G'** BO i l KB

• O.ZBKB ©oUA&OSO DIOHITC

© ioi *111 KB

Q 1 .KBOSMI TH w ICK5 H R L £

o

d5 N& O QlZZKt

«BcPi7BJfcfl

0

i«B101

O O C O L U M e i R R I V 6 K B A S A L T

I t s B

O O C C C A D T R 8 R

0 W-IO TKlASilt 0 l* 8*3 t

,'*0 /,

Figure 4Alpha activity versus beta activity of southern Arizona volcanic rocks

2a /m g h r

os r T

3, 4,

Key to Figure 4

A = andesite, B = basalt, KB = potassium basalt, R = rhyolite,

T » tuff, QL « quartz latite, TO * probable "Turkey Track" Numbers 1 - 3 2 are identified in Table 2, 35 - 69 refer toTaylor's data, 70 - 89 refer to Blkerman1s data, 90 - 126

refer to Halva's data.Reference Location Number35 B36 B37 B 33 B39 B40 B41 B42 KB43 KB44 A45 A46 A 4? A 43 R49 QL50 R51 T52 T53 T54 R55 B56 R57 B58 R59 B60 R61 R62 R63 A64 A65 QL

Atascosa Mtns. basalt Atascosa Mtns. basalt Atascosa Mtns. basalt Atascosa Mtns. basalt Atascosa Mtns.

BottomBottomBottomTopTopTop

basaltAtascosa Mtns. basalt Santa Rita Mtns. basalt Tucson Mtns. basalt Composite Tucson Mtns. basalt Top Atascosa Mtns. upper andesite Sycamore andesite Santa Rita Mtns. upper andesite Shorts Ranch andesite Sycamore spherulltic rhyolite Quartz latite porphyry Blotite rhyolite Atascosa Mtns. tuff Santa Rita Mtns. tuff Safford tuffMontana Pk. fm. 1 Bottom Montana Pk. fm. 2 Bottom Montana Pk. fm. 3 Bottom Montana Pk. fm. 1 Top Montana Pk. fm. 2 Top Montana Pk. fm. 3 Top Santa Rita Mtns. rhyolite Mustang Mtns. rhyolite Cat Mountain rhyolite Ruby Road fm.Santa Rita Mtns. older andesite Santa Rita Mtns. older latite

29

Key to Figure 4 (Continued)

Reference Location SampleNumber Number

66 A Tucson Mtns. older andesite6? B Pajarito lavas68 A Santa Rita Mtns. Cret. andesite69 A Tucson Mtns. Cret. andesite

70 H Ajo Way section 27-J-l71 B Ajo Way section 27-J-372 R Ajo Way section 27-J-I573 R Ajo Way section 25-S-674 R Ajo Way section 2-0-5a75 B Ajo Way section 2-0-6a76 R Cat Mountain section 10-F-277 R Cat Mountain section 10-F-6a78 R Cat Mountain section 10-F-1 079 B Bren Mountain section 15-N-T80 R Bren Mountain section 15-N-881 R Bren Mountain section 15-N-1482 R East of Cat Mountain 2-N-283 a Near Sweetwater Drive 18-J-284 R Near Sweetwater Drive 18-J-485 R Twin Hills section 17-M-l86 R Twin Hills section 17-M-387 T Twin Hills, Safford tuff 17-M-oa88 T Twin Hills, Safford tuff 17-M-789 R Gates Pass 3-J-l

90 A Sasco andesite91 KB Sasco basalt92 A Sawtooth andesite93 A Sawtooth andesite94 A Sawtooth andesite95 KB Plcacho intrusive96 KB Tombstone basalt97 KB Tombstone basalt98 KB Sawtooth basalt99 A Tortolita andesite100 KB Tortollta basalt101 KB Galiuro basalt102 KB Black Mesa Top flow103 KB Black Mesa Fifth flow104 KB Black Mesa Fourth flow105 KB Black Mesa Third flow

Key to Figure 4 (Continued)

ReferenceNumber106 KB 10? A108 T109 T110 T111 KB112 KB113 kb114 KB115 KB116 KB117 KB118 KB119 KB120 KB121 KB122 KB123 KB124 KB125 B126 KB

Location

Black Mesa Second flow Tumamoc andesite Tomamoc tuff #1 Tumamoc tuff #2 Tumamoc tuff #3 Tumamoc basalt Top flow Tumamoc basalt Fourth flow Tumamoc basalt Third flow Tumamoc basalt Intrusive 2 Tumamoc basalt Intrusive 1 White Mtns. basalt #1 White Mtns. basalt #2 White Mtns. basalt #3 White Mtns. basalt #4 Mlnetta basalt Beddlngton basalt San Bernardino basalt #1 San Bernardino basalt #2 San Bernardino basalt #3 Carrlzo basalt Catalina Wash #1

M I NE TTA RID6E

H I L L J O U T H w e S T OF SAN XAVIER MISSI ONHAPPY VALLEY QUADRANGLE —D A VIDSON CANYON AT B E N S O N HIGHWAY

, — ^-DESERT MUSEUM

/o rr

S A G U A R O NA T i O/VAL M O N U M E N T

<e i t

) x < i r x / S A N X A V I E R M I S S I O N

F I SH E R MILLS

li TTSEN T I N E . PEAR

— DOS CADEZA5 MTNS.M TT

T U M A M O C WI LL

— C l EIN EGA GAP

D A V I D S O N C A N Y O N A T

C I E N E G A C R E E K

\ P l M A D I S T R I C T

F/GU/^5 5 "Turkey Track" Localities

or/mg hr

33An attempt was made to plot the bulk of the

data from Halva1s "Geochemical Investigation of Basalts in Southern Arizona" although the alpha emission was reported in */hr. Using the conversion factor suggested by Halva produced rather high values of a/mg hr. Actually, the values of or/hr for the "Turkey Track" are fairly similar in both investigations and a/mg hr values would conform quite well using the same conversion factor for both. Consequently, the conversion factor determined in this investigation was used to plot this data. Intercomparisons of potassium percentages are generally in good agreement among all radiometric investigations.

The low potassium values of the Davidson Canyon at Clenega Gap sample end the Pima District sample perhaps are not representative. Both samples appeared highly altered and K could easily have been removed. Other samples from the Clenega Gap - Davidson Canyon area plotted within the "Turkey Track" grouping. The Pima District sample showed a very high atmospheric correction when age dated.

In addition to the overall attempt to determine the range in activity of the "Turkey Track" over a very large area incorporating several separate localities, an attempt was made to determine the variance in alpha and beta activity of a single unit in one locality. Two localities are presented in Table 3 to serve as indications.

34

of the variation. One, representing a single although large feature Is a dike 10 miles long in the Dos Cabezas Mountains. The other locality chosen for its large outcrop area is Mineta Ridge. The results of four widely spaced samples are also shown in Table 3. It is interesting to note that the statistical error in >o K by beta counting and a/mg hr values is about 5/» for each sample, whereas the standard deviation of each group is about 10^ or twice as high. Furthermore, the standard deviation of samples within one locality is roughly half that of all localities combined which is about 20#. This compares favorably with the data presented by Blkerman in which the standard deviation of alpha activity over several localities of the Cat Mountain rhyolite is about 15#. Table 3 Radiometric Variations within a Single Locality

Sample (Ref.) No. */hr “/mg hr ,0/hr # KDike in the Dos Cabezas Mountains

JEM 6 64 (19TT) 391 2.74 271 2.13JEM 7 64 (20TT) 478 3.20 278 2.21

Mineta RldeeJEM 4 63 (9TT) 350 2.34 247 2 .2 6

JEM 5 63 (10TT) 278 1.95 3 H 3.17JEM 6 63 (11TT) 304 2.13 265 2.42JEM 7 63 (12TT) 318 2 .1 3 250 2.43

353.3 Gamma Scintillation Spectroscopy

A need exists for a quick accurate method of analyzing separately for uranium and thorium In common rocks. A method of 3 channel gamma scintillation counting was used to enable simultaneous determination of K, U, and Th. Such techniques were first proposed by Hurley (1956) and by Adams, Richardson, and Templeton (1958). Hurley proposed use of the 0 .238 Mev. Pb^lZ peak from the thorium series and the adjacent valley in the composite spectrum which lies on a rough plateau in the uranium series at 0.180 Mev (Figure 6 ). This method has the advantage of a relatively high count rate by using low energy gammas. However, unless potassium could otherwise be accounted for (as it is in a third channel centered on the potassium photopeak at 1.46 Mev), it would generally require greater than 100 ppm equivalent uranium to overcome potassium interference.Adams, Richardson, and Templeton used the high energy end of the spectrum counting the 1 .76 Mev Bi peak in the uranium series and the 2.62 Mev Tl^°® peak in the thorium series. This method has the advantage of being free from potassium interference but has the disadvantage of a low count rate. Both of these methods require that the uranium and thorium series be in secular equilibrium. To circumvent this restriction Damon and Freely (1957) developed a technique for analysis of uranium by measurement of the

0.093 Mev gamma ray of Th234 using a thin scintillation

36

Pb212

fp-^228

CM i—i CMm

Monazite Thorium Series

fji 208lllrrnyyTrrTTTTH-rrfT^

Th234 Energy

Pitchblende Uranium Series

1 Ba226Th234

1 Th230 Pb2l4

i U~h~K->

Energy

B1214

Figure 6 Gamma spectra of uranium and thorium series showing locations of counting channels

37crystal and copper and lead absorbers. Copper absorbers reduce the counting efficiency of gammas below 0 .070 Mev. Combining this effect with a thin crystal further limits the region of good detection to below 0.120. Lead is then used to distinguish emission of 0.093 Mev Th^^ gammas by

critical absorption. Since Th23^ is the first daughter of U238 and its half life is only 24 days, equilibrium with its parent is almost assured.

Primarily, Baird Atomic gamma counting equipment was used in this investigation and consisted of a well type Nal (T1 activated) solid scintillation crystal detector, Model 810B; a linear nonoverloading amplifier model 215; and three

single channel pulse height analyzers model 510. Each pulse height analyzer was connected to a separate scaler and the counts from each channel were recorded simultaneously. Samples were crushed and weighed to fill small plastic vials. Since the geometry of the detection system influences the count rate, a constant volume of sample was used and the weight corrected to 25 grams. This was the maximum amount that would fit into the well. Being thus limited to a relatively small amount of material, the total activity of the sample was not very great. Consequently, attempts to work in the high energy range (2.62 Mev of Tl203 and 1 .7 6 Mev of Bi2!^) proved fruitless. Working with the O .606 Mev gamma of Bi2!^ was also attempted but again the net count rates proved too low to produce accurate results.

33The primary difficulty in counting for 24 hours, as was necessary in the high energy raqge, was that the channels drifted slightly. While the actual drift was low, so also was the net count rate resulting in rather large error. Figure 7 is a plot of the channel drift as indicated by the change in count rate over a period of several days.

The method finally adopted is essentially the same as that proposed by Hurley. Potassium is determined from a channel set at the 1.46 Mev peak, thorium from the 0.238 Mev Pb2* 2 peak in the thorium series, and uranium from a channel centered at 0,180 Mev which is plateau in the uranium series. In the composite spectrum the uranium channel falls in a relative valley from which the Pb rises; thus, maximum contrast between uranium and thorium is obtained. An additional advantage in using these neighboring channels is that contributions to the gross count rate from potassium is fairly uniform in this region. For convenience voltage settings on the pulse height analyzers were calibrated in terras of energy by using isotopes with peaks at known energies. Optimum channel width for thorium and uranium was determined by plotting the peak plateau width in percent range of base-line settings versus channel width (Figure 8 ). The peak plateau width was defined by a 3# change in count rate. It was found that a 30 kev channel width will have 97# or more of the

39

FIGURE 7 tw o cases showing d r i f t fo llow ing shutdown

K channel

U channel

Th channel

K channel

U channel

Th channel

rdnq

e in

b

ase

line

-/O FIGURE 8

0

0

20 40 GO 80 IOO_ j------------------- 1-------------------- 1--------------------1--------------------1 channe l w id th ke v

Figure 8 Determination of optimum channel width O

41peak maximum count rate within ± 1 .5^ of the base-line setting. Consequently, a channel width of 30 kev was used. A"channel width of 100 kev was used for potassium.

The net count rate of the Pb2-1-2 peak was used to determine the thorium content after contributions from uranium and potassium were subtracted. The same was done for each of the other two elements, forming in effect three equations with three unknowns. These can be solved simultaneously provided the counts/g min ppm from uranium and thorium and counts/g min % from potassium are known for each of the three channels. Using standards these constants can be determined.

Potassium dlchromate was used as the pure potassium standard. Unfortunately uranium free thorium and thorium free uranium standards were not available. Consequently, constants were calculated on the simultaneous solution of equations based on the standards W-l and G-l. This method does not have the accuracy of using pure standards as it makes the uranium and thorium constants dependent on one another to some extent. Furthermore, the activity of G-l and W-l is not great, especially in the case of W-l. Standards of higher activity would have helped in decreasing counting error. Figures 9, 1 0, 1 1, and 12

indicate the relative accuracy of the method.

42

FIGURE 9

4

M ILFORD GRANITE

DECCAN TRAP

W -1

GABBRO DIORITE

TRIASSIC DIABASE COLUMBIA RIVER BASALT

ppm U expectedFigure 9 Uranium content expected versus uranium

determined by gamma counting

ppm

I h

d

eie

rmm

cd

43

FIGURE 1C

- 7 0

- 50

-4 0

60

■30

/

//

G-,,-r/

/•z

/X

/Z

-20 /

/

-10 !Z/MILFORD GRANITE

/-COLOMBIA RIVER BASALT

K Z x - t r m s i ic DIABASE |>V/D£.I^ V > D £ C C A N TRAP

10GRBBRO DIORIlTC

20j_ppm 1 h

Gamma counting

3 0 4 0 50I_________ J__________L_expected

/<

de

term

ine

d

44

FIGURE II

MILFORD e M N IT t

Gamma counting() COLUMBIA AIVCA BASAL?

BABBBO PIOAITLDICC ANTMP

! h/U

de

ter m

ined

45

FIGURE 12

O GflBBRO DIORITC

() DECCAN TRAP

Gamma counting

/ h / U expec ted

46

It can be seen from the above figures that the error of the method Is slightly greater for uranium than for thorium. Several explanations are possible. The most likely cause Is the low uranium activity of the standards W-l and 0-1 upon which the constants of counts/g min ppm are based. This is not so evident for thorium as 0-1 is relatively high In thorium and thus makes a fairly good thorium standard. Potassium determinations are in fair agreement with expected results even though the gamma activity from potassium is low. The fairly good agreement may partly be the result of the standard in that a pure potassium standard was available.

Two standards, Triassic Diabase and Columbia River Basalt, indicate no uranium due to their relatively low activity. This may be an indication of the useful detection limit of the method at least in the case of Triassic Diabase. This explanation breaks down somewhat in the case of Columbia River Basalt which is reported to have a higher uranium content of 1 ppm. These same two standards show higher than expected thorium because the actual counts due to uranium are not being subtracted. Fortunately, the gamma emission from U, Th, and K for the "Turkey Track" was significantly higher than most of the standards which were basalts and other basic rocks.

Part of the data In Tables: 4, 5» 6, and 7 were obtained by the above method. Counting time per run was from one to three hours and each sample was counted at least three times with the results being averaged.Before and after each sample run drift was determined by counting an active uranium and potassium source for 10 minutes. The average of a great many such checks provided a norm to which sample count rates could be corrected. Equations for the gamma calculations are presented in appendix "B".

48Table 4 Comparisons of Uranium Determinations

Sample (Ref) No. Location

U(r)ppm

Counting$s.d.

U(fluor)ppm

%Differ


1.8 4.9 4.2 57


3.2 5.1 3.3 3.0


3.3 3.8 3.2 3.0

B 41 60 (4TT) Black Mountain

3.9 3.9 3.4 13

RM 2 64 (5TT) Pima District

1.2 8.9 --

JEM 3 63 (6TT) Cienega Gap

2.5 6.6 3.7 32


4.0 4.8 2.9 27

B 50 60 (8TT) Davidson Canyon

3.1 4.6 4.1 24

JEM 4 63 (9TT) Mlneta Ridge

2.7 5.1 2.9 6.9


2.7 4.9 —— ——*


3.2 4.7 — —

JEM 7.63 (12TT) Mlneta Ridge

1.3 7.8 2.3 43


2.8 ' 5.1 2.6 7.1


2.4 4.5 2.4 0

Table 4 (Continued)49

Sample (Bef) No. Location

U(r)ppm

Counting%s.d.

U(fluor)ppm %Differ


2.1 5.2 3.5 40

FED 2 64 (17TT)Desert Museum

5.8 2.9 5.8 0

B 55 6l (18TT)Desert Museum

5.4 3.3 —

JEM 6 64 (19TT)Dos Cabezas Mtns.

2.8 4.4 2.9 3.4

JEM 7 64 (20TT)Dos Cabeza s Mtns.

2.0 5.4 3.2 37

JEM 8 64 (21TT)Fisher Hills

3.9 4.1 4.0 2.5

JEM 9 64 (22TT)Kelsey Canyon

3.2 4.7 3.3 3.0

JEM 12 64 (23TT) Happy Valley Quad.

2.3 5.3 2.6 11

B 49 60 (24 A)Sawtooth Mtns.

1 .1 8.6 1.7 35

B 53 6o (25KB) San Bernardino

.26 16 O .65 60

JEM 8 63 (26 B) Desert Museum .35 18 ——

JEM 9 63 (27 B) Desert Museum

2.2 5.0 ——

JEM 1 64 (28 KB) Black Mountain

• 00 00 9.9 —— ——

JEM 4 64 (29KB) Del Bac Hills

3.6 7.5 — — — —



U(x)PPm

Counting#s.d.

U(fluor)Ppm

%Differ

JEM 6 64 (30KB) Plcacho Peak

2.5 5.0 — — -


0 .0 30 — —

USES 4978 0.0Columbia River basalt

23 1 .00.94

100

USES 4934 Triassic Diabase

0 .0 44 — —

0 -1Westerly Granite

3.7 1.9 3.2 14

W-lDiabase

0 .5 2 18 0 .5 6 7.3


0.87 17 —— —


0 .9 6 7.0 0 .4 5 53

USES 4982 Gabbro-Dlorite

0 .2 1 26 0 .6 7 69

Data on standards from Independent sources are presented in Appendix "A".

51Table 5 Comparisons of Thorium Determinations

Sample (Ref) No. TY Location

1 (r) ppm

Counting£e.d.

Th («-U) ppm

%Differ.


18 3.1 12 33


17 3.5 24 29


19 2 .6 26 27

B 41 60 (4TT) Pima District

18 2.9 11 39

RM 2 64 (5TT) Pima District

13 5.1 2 .1 85

JEM 3 63 (6TT) Clenega Gap

14 4.4 17 18

JEM 11 63 (7TT) Davidson Canyon

18 3.4 23 22

B 50 60 (8TT) Davidson Canyon

22 3.5 11 50

JEM 4 63 (9TT) Mineta Ridge

16 3.4 15 6.3


18 3.3 11 39


18 3.2 11 39


15 4.7 14 6.7


18 3.4 27 33

CJH-l_2b (15TT) Tumamoc Hill

17 2.9 19 11

52

Table 5 (Continued)


Th (r) PPm

Counting /6s.d.

Th (* -U) PPm

%Differ.

PED 16 63 (l6TT) Sentinel Peak

17 3.3 14 18

PED 2 64 (17TT)Desert Museum*

31 2 .0 8.9 71


32 2 .2 12 62


19 2.7 19 0


15 3.4 24 37


25 2.7 43 42


13 3.0 8 .2 54

JEM 12 64 (23TT) Happy Valley Quad

15 3.6 7.0 53


7.2 7.1 4.9 32

B 53 60 (25KB)San Bernardino

3.3 13 2.7 15

JEM 8 63 (26 B)Desert Museum

3.7 14 3.4 8 .1

JEM 9 63 (2? B)Desert Museum

23 2.9 —— —-

JEM 1 64 (28KB) Black Mountain

8.5 6.7 —- —-

JEM 4 64 (29KB) Dos Bac Hills

7.7 5.0 — — — -



Th (r) ppm

Counting£s.d.

Th («-U) ppm

%Differ.

JEM 5 64 (20 KB) Plcacho Peak

13 3.9 ■ —


5.6 14 — — — —

USES 4978 4.5Columbia River Basalt

9.9 0.57 86

USES 4984 Trlassic Diabase

3.3 14 — — —

0-1Westerly Granite

52 1.0 79 34

w-lDiabase

2.4 15 1.8 25


2.4 15 1.1 54


9.6 4.5 12 20

USES 49.82 Gabbro Dlorite

1.4 18 —

54Table 6 Comparisons of K Determinations

Sample (Ref) No. K M%

K(/3)%

K(f.Phot)%

(y,f) *Differ. (Af>2Differ.


4.0 2.99 2.24 25 25


1.8 2.54 — 28 — —

B 42 60 (3TT)B 42 60 (-140 mesh) San Xavier Mission

2.5 2 .5 03.17 2.90

08.5

B 41 60 (4TT)B 41 60 (-140 mesh) Black Mountain '

1.3

\

2.943.12 3.15

540.95

EM 2 64 (5TT)Pima District

2.1 0 .5 2 — — 76 —

JEM 3 63 (6TT)Clenega Gap

1.7 1.99 2.24 66 11


0 .65 1.46 — 55 —


2.7 2.82 2.79 3.6 1.1


1.9 2 .26 2.20 16 2.7


3.4 3.25 3.20 4.4 1.5


1.4 2.4? — — 44 — —


3.0 2.43 2.44 19 0,41


2.4 2.59 3.01 7.3 14

CJH 1 2B (15TT) 1.8CJH 1 2B (-140 mesh) Tumamoc Hill

2.362.68 2.72

251.5



K(r)%

K(P)%

K(f.phot)%

(r,P);%Differ.

(/8,f)£Differ,


2 .0 2.41 — — 1.7 —


0.87 2.51 2.17 65 14

B 55 61 (18TT)B 55 61 (-140 mesh) Desert Museum

0.55 2.802.89 2 .92

801 .1


1.3 2.64 2.43 50 7.9


2.5 2 .2 1 2 .3 6 12 6.4


2 .1 2.54 3.46 16 27


0.76 2.65 1.93 71 25


2.4 2.83 2.77 14 21

B 49 60 (24 A) Sawtooth Mtns.

2 .6 2.25 2 .20 13 2 .2

B 53 60 (25KB) San Bernardino

1.5 1.52 1 .16 0 24

JEM 8 63 (26 R) Desert Museum

2 .6 2 .3 0 —— 12 ——

JEM 9 63 (27 B) Desert Museum

2 .6 —— —— —— —-

JEM 1 64 (28 KB) Black Mountain

3.7 “ —— —— ——

JEM 4 64 (29 KB) Del Bac Hills

2.7 — — — — — — — —

56

Table 6 (Continued)

Sample (Hef) No. Location

K(r)%

K(/3)%

K(f.Phot)% Differ.

(P,F)2Differ

JEM 5 64 (30 KB) Plcacho Peak

5.3 — — —— — — — —


0 .00 0.39 —- 100

USES 4978 0.72Columbia Elver basalt

1.03 —— 30 — —

G-lWesterly Granite

4.5 1 .9 6 — — 56 ——

USES 4984 Triassic Diabase

0 .00 0.45 — — 100

W-lDiabase

0 .5 6 0 .6 1 — — 82 — —


0.46 0.77 —— 40 ——


3.3 3.48 — — 52 — —

USES 4982 Gabbro Dlorlte

0.45 — — — ——

RP-102Smlthwick Shale

1.33 — — — — — —

USES 4981 — * » 4.77 m m «m mm mm

Granltevllle Granite

Data on standards from Independent sources are presented In appendix "A".

57Table 7 Comparisons of Th/U Ratios


Th/U M Th/U (“-U) Weighted average (3 :1 )

JEN 1 63 (ITT)San Xavier Mission

9.9 2.9 8 .2


5.3 7.2 5.8


5.8 7.9 6.3


4.6 3.3 4.0


11 1.7 8.7


5.5 6.9 5.8


4.5 7.8 5.3


7.2 2 .8 6 .1

JEM 4 63 (9TT)Mlneta Ridge

6 .1 5.1 5.9


6.4 3.9 5.8


5.7 .3.4 5.1


12 6.3 11


6.3 10 7.2

CJH 1 2B (15TT) Tumamoc Hill 7.1 7.7 7.2



Th/U M Th/U («-U) Weighted aver age (3:1)


8 .2 6 .8 7.9

FED 2 64 (1?TT)Desert Museum

5.3 1.5 4.4


5.9 2 .2 5.0


6.7 6 .6 6.7


7.8 7.4 7.7


6.5 11 7.6


5.7 2 .6 4.9


6.3 2 .7 5.4


6 .8 2 .8 5.8

B 53 60 (25 KB)San Bernardino

13 4.2 11

JEM 8 63 (26 B)Desert Museum

7.8 , 9.7 8.3

JEM 9 63 (27 R)Desert Museum

10 —— —

JEM 1 64 (28 KB)Black Mountain

9.6 —— ——

JEM 4 64 (29 KB) Del Bac Hills

2 .1 — — --



Th/U (r) Th/U («-U) Weightedaverage (3 :1)

JEM 5 64 (30 KB) Picacho Peak

5.3 — — ——

USES 4979Columbia River basalt

— 0.59 --

G-lWesterly Granite

14 25 17

W-lDiabase 4.7 3.2 4.3


2.7 1.3 2.4


10 27 14

USES 4982 Gabbro Diorlte

6.5 —— —

Data on standards from independent sources are presented in appendix "A".

Chapter IV

Nonradiometric Chemical Analyses

4.1 Fluorimetric AnalysesAs an independent check on the gamma counting

and to provide a means of calculating thorium content from total alpha activity, uranium was determined by fluorimetry. One gram of sample was digested in HF-HNO^ taken to incipient dryness and brought back into solution

in 50 ml 5$ HNO^. Uranium was then extracted from a 2 ml aliquot into exactly 10 ml of ethyl acetate using 15 ml of A1(N0^)^ as a buffer. The extraction was necessary to reduce the quenching effect of iron in the samples. Six drops of the acetate solution were then dried onto a Fluoroflux pellet of 98^ NaF and 2$> LlF. Samples were spiked with 0 .1 ppm uranium. In addition a blank was prepared and extracted under the same conditions as the samples. Samples, spiked samples, and blank were run in duplicate on the, pellets. The pellets were fused in small platinum crucibles for two minutes at about 1000°C and allowed to cool slowly for 15 minutes before analyzing in the fluorimeter. Samples were analyzed in a Jarrel-Ash Model Galvanek-Morrisen Fluorimeter. This data is included in Table 4.

60

61

4.2 Flame PhotometryIn addition to potassium analysis by beta counting,

samples were subjected to flame photometry. The samples were prepared by digestion in HF using 3 ml of concentrated H2SO4 , After all the HF was fumed off at 6o°C, the temper

ature was Increased to 120°C until S0^ began to evolve.

The solutions were then allowed to cool and stored concentrated in polyethylene bottles for not more than two weeks until they could be diluted to 200 ml and run by Mr.Bichard Bennett on a modified Perkin Elmer flame photometer using an internal standard and sodium buffer. This data is included in the comparison shown in Table 6 . The standard deviation of the best radiometric method is 2 -5%. The precision of the flame photometric method is about 1 1$ s.d.

4.3 Emission SpectroscopySeveral trace elements were determined by emission

spectroscopy using the 3 .5 meter grating spectrograph of the Arizona Bureau of Mines. The analytical procedure briefly was as follows; electrodes were cut and shaped from 3 /1 6 inch diameter carbon rod to the following dimensions; o.d. 3.5mm, l.d. 2mm, depth 2mm. Electrodes were pre-arced for 5 seconds before loading. Samples were arced to completion using a slit width of 0 ,03 microns and anode excitation. Strontium carbonate was used as an internal standard in a 1:1 mixture with sample. A rock standard and

62a step-sectored Iron spectrum were placed on each film.Line Intensities were read on a Jarrell-Ash Microphotometer.The following lines were read: Ba 455^.0, Co 3453.5* Cr 4274.8, Cs 4555.4, Cu 3274.0, Ga 4033.0, K 4044.1, Mg 2352.1,Mn 4034.5, Na 3303.0, N1 3414.8, Sc 3911.8, Tl 4296.0, and V 4379.2 .

A calibration curve was prepared from the step- sectored iron spectrum on each film. This curve relates galvanometer deflections to relative line intensity.Working curves then relate the relative line intensity to concentration. Working curves for each element were prepared from numerous arcings of rock standards. Only rock standards were used in order to decrease matrix effects. Some rock standards for which trace element data Is available are W-l and G-l (Stevens, et al i960); Chelmsford Granite, Granltevllle Granite, Canadian Syenite, and USES Plastic Clay (Taylor and Kolbe 1964). All but the syenite were used in this investigation. In addition to the above USES Opal Glass and USES Pb-Ba Glass were arced. Precision among repeated runs was about 10$ for each element. Estimated error in the method is about 25$ and is lower for some elements than others. Data are presented in Table 8 and in most cases should be treated only as a general indication of the order of magnitude.

This is especially true for barium and manganese for which the results are only very general. Lead was detected in all

63Table 8 Emission spectrographic analyses

Sample (Ref) No. Ba Cs K Na GaLocation ppm ppm % % ppm

JEM 1 63 (ITT) 1600 2.7 2 .6 1.7 12San Xavier MissionJEM 2 63 (2TT)San Xavier Mission

1600


1600


1600

JEM 7 63 (12TT)Mineta. Ridge

1600


1600


1600

JEM 7 64 (20 TT)Dos Cabezas Mtns.

1600


1600


1600


1600


220


1600

PED 2 64 (17TT)Desert Museum

1600

3.7 2 .6 3.3 12

3.7 2 .6 2 .2 12

6 .2 2 .6 2 .2 12

3.7 2 .6 3.3 18

2.7 • 2 .6 2 .2 18

6 .2 2 .6 2 .2 12

6 .2 1 .1 2 .2 12

3.7 2 .6 2 .2 12

3.7 2 .6 2 .2 12

2.7 2 .6 3.3 18

2.7 0 .5 6 2 .2 9

3.7 2 .6 3.3 12

2.3 2 .6 3.3 12

64Table 8 (Continued.)


Bappm

Csppm

K%

Na%

Gappm


1600 3.7 2 .6 3.3 18

JEM 11 63 (7TT)Davidson Canyon

1600 3.7 2.6 2.2 13


1600 2.7 2.6 3.3 18


220 2.7 2.6 2.2 12


1600 3.7 2.6 3.3 12

B 49 60 (24A)Sawtooth Mountains (andesite porphyry)

1600 1.9 2.6 2.2 12

B 53 60 (25 KB)San Bernardino (basalt porphyry)

1600 3.7 2.6 3.3 18

G-lWesterly Granite

1220 1.5 4 .5 1 2.46 18

W-lDiabase

220 1.1 0 .5 6 1.54 16


2000 —— — —— —

USES 4981Graniteville Granite

180 — — —— —— ——

USES 98 Plastic Cloy

6?0 2.5 2.64 -- . w—'

USES 91 Opal Glass

70 — — 2.77 --

USES 89 Fb-Ba Glass 6.97



tjs%

Coppm

Nippm

Scppm

Mnppm

JEM 1 63 (ITT)San Xavier tiisslon

1 .2 28 30 16 135


3.1 38 43 43 135


0 .6 18 30 16 135


1 .2 38 48 21 135


1 .2 38 30 21 1300

JEM 12 64 (23TT)Happy Valley Quad. 3 .1 12 12 4 1300


3.1 38 48 29 135


1 .2 38 30 29 135

JEM 8 64 (2%TT)Fisher Hills

1 .2 22 5 29 135


1 .2 28 30 16 135

JEM 11 64 (14TT)Saguaro Nat. Mon.

1 .2 28 48 13 1300

CJH 1 2B (15TT)Tumamoc Hill

0 .6 38 48 13 83

FED 16 63 (16TT)Sentinel Peak

3.1 22 82 21 135


1 .2 12 4.3 13 135



Mg%

Coppm

Nippm

Scppm

Mnppm


3.1 22 30 16 1300


0 .6 28 30 21 1300


1 .2 18 21 13 1300


0 .6 33 48 16 135

RM 2 64 (5TT)Pima District

1 .2 28 30 43 135

B 49 60 (24A)Sawtooth Mountains andesite porphyry

1 .2 22 21 13 135

B 53 60 (25 KB)Sen Bernardino basalt porphyry

1 .2 166 82 13 1300

G-lWesterly Granite

0.24 2 .2 1 .2 4 210

W-lDiabase

3.96 51 82 43 1300


0.056 nd 4.8 10 530

USES 4981Granlteville Granite

0.023 — — nd tr 44

USES 98 Plastic Clay

0 .60 12 ' 50 20 60

USES 91 Opal Glass

—— 5 nd nd 60

USES 39 Pb-Ba Glass

— — nd nd nd 680



Cuppm

Crppm

T1ppm

VPPm


nd 37 4800 680


54 37 9500 630


77 53 4800 70


77 92 9500 170

JEM 7 63 (12 TT)Mineta Ridge

42 92 9500 680


8 18 3000 170


tr 92 9500 630


tr 53 9500 170


tr 53 9500 170


77 92 9500 170


20 92 9500 70


54 28 2100 34


100 92 9500 630


nd 22 4300 19


Sample (Bef) No. Location

Cuppm

Crppm

Tippm

Vppm

JEM 3 63 (6TT)Cienega Gap

42 92 9500 680


54 53 9500 170


77 53 9500 170


54 37 4800 34

BM 2 64 (5TT)Pima District

140 53 9500 170

B 49 60 (24A)Sawtooth Mountains andesite porphyry

16 92 4300 170

B 53 60 (25 KBSan Bernardino basalt porphyry

72 220 9500 170

G-lWesterly Granite

13 22 1400 21

W-lDiabase

110 120 7400 240


9 6 600 nd

USES 4981Granlteville Granite

9 — — 290 nd

USES 98 Plastic Clay

66 130 8000 150

USES 91 Opal Glass

16 30 130 nd

USES 89Pb-Ba Glass ......

15 9 130 nd(nd, not detected; t)?, trace; —— > not looked for)

69

Plastic Clay

Opal Glass

I Sr 3465

Figure 13 Typical working curve for cobalt In silicates

samples but the value of the working curve for this element was negligible due to the high background in the Pb 4057.8 region. Figure 13 is a typical working curve for cobalt in silicate rocks.

Although the above spectroscopic method provided reasonable results, its potential value could be considerably improved by reducing the error. One source of error was that the spectroscopic laboratory had been undergoing reconstruction. Despite efforts to thoroughly clean the room, contamination was probably at a high level. Furthermore at the time the only film available for quantitative analysis was slightly fogged; thus, the sensitivity was reduced. The electrodes available were not "Spec Pure" although no significant contamination was detected in the pre-arced blanks. This may have been removed by the pre-arcing. Background could have been greatly reduced by arcing under a nitrogen-free atmosphere if these facilities had been available. This would have improved determinations of all reported elements, Pb, and would probably have allowed detection of other elements masked by the CN bands.

The generally uniform and somewhat unusual trace element content ofthe "Turkey Track" prophyry is brought out in figures 14 - 17. Included in these figures for purposes of contrast are a granite, G-l; a diabase; W-l; an andesite porphyry, 24A; and a potassium basalt, 25 KB.

70

The average trace element content of the "Turkey Track* as determined In this investigation is compared with 0-1 and W-l m Table 9.

71

72

G-l FIGURE 14

O m i l f o r d g r a n i t e

O OBTT 25TT

2ITT O

)I4T T

Q t T T

O E TT

O17 TT ef.

” ;;°s,,C T o 'tTT’OGirr

Q 2 Z T T

O „ 2$ KB

100,QW-l 200.

Ni + Co ppm •Figure 14 Potassium versus nickel plus cobalt content

73

o6-1

4

O MILFORD GRANITE

-3

1377

-2

I tT T

.?7

oHTT

I IT T

I fT T3?T I t T T 0

0 HTT0 l*TT i s r r 0

21A toil

8ITT 0O

17 T TITT

ifrr

2TT

OZ5 KB

ppm Sc10 20 30 40 «" 50I I i I O i

Figure 15 Scandium versus potassium

74

v

o a - i

-4.

-

-3 0 I tTTO ITT

S m r

QlfcTTq i s t t

» " % Z,T, T

& T ," T T g

£OTT 0

r 0 ITT0ITTT

G 6TTITT 0

-2 0 Z 2 TT

O l f K #

*-

- /

ppm C s/ p1 OW- I ^ 3

141

5I

61

Figure 16 Potassium versus cesium content

75

0 2 5 KB

HTT 01 TT

ppm Cs

Figure 17 . Cesium versus chromium content

76

Table 9 Comparison of Trace Element Content

Element 0 -1 w-l "Turkey Track" average

Ba 1220 225 1500

Cs 1.5 1.08 3.7K* 4.51 0 .5 6 2 .52

Na# 2.46 1.54 2 .6

Ga 18 16 14

Mg* 0.24 3.96 1 .6

Co 2 .2 120 28Ml 2 .1 82 30Sc 4 43 18Mn 210 1300 500

Cu 13 110 42

Cr 22 120 60

Tl 1400 7400 8100

V 21 240 300

Th 3.7 0 .5 2 19U 52 2.4 3.3

Values are In ppm unless otherwise noted.

Chapter V

Conclusions

Radlometrically, most samples of the "Turkey Track" from widely separated areas fall within a fairly well defined region when plotted as ^ K versus of/mg hr. Although this region of the <*, p plot is not completely unique among all porphyrltlc rocks in the area, it is a significant feature. Most other porphyries fall well outside this region or overlap only its margins. The field in which "Turkey Track" samples plot is definitely distinct from most "basalts" in southern Arizona which have lower alpha activity. Rocks which overlap the "Turkey Track" field are primarily rhyolitic and andesitic in composition. Rocks of this composition are found to have a wide variation in radiometric characteristics and tend to scatter over much of the graph area. However, as a rough generalization most rhyolite and andesite porphyries have a lower <x/yd ratio than the "Turkey Track". Previous Investigations have shown that the radiometric variation within a single flow is within or equal to counting error (Sabels i960, Halva 1961). Bikerman's (1962) data indicate that the variation in of/mg hr over a single large outcrop area is 2 or 3 times counting error. This investigation

77

confirms that of the others and further shows that the variation over several wide spread localities of the same or similar rock is again only 2 or 3 times greater. It is not at all unreasonable to expect a more widespread radiometric variation over a geographically large area, but the fact that the variation is still not excessive strongly suggests that the "Turkey Track" is all one unit.

Slight differences in petrography of the various "Turkey Track" localities Is not reflected In the radiometric or chemical analyses. For example the presence of quartz grains in the Desert Museum locality or the alteration after olivine at Sentinel Peak do not indicate significant chemical differences. These differences in mineralogy more likely reflect local differences in pressure and temperature during crystallization of magma bodies of similar chemical compositions. Any apparent differences in chemistry resulting from different mineral assemblages is probably compensated by slight adjustments in the composition of the groundoass. As much of the rock is groundmass however, its mineralogy is difficult to

determine.The composition of the "Turkey Track" while some

what unusual is not unrelated to the associated volcanic rocks. Most middle Tertiary "basalts" in southern Arizona which are even more widespread than the "Turkey Track"

78

have many of the same chemical peculiarities. For example both of these rock types have a high potassium content and a composition similar to a doreite, with the "Turkey Track" being more felsic them the "basalts". Furthermore, the "Turkey Track" commonly forms the base of the volcanic sequence. Consequently the stratigraphic relationships, similar radiochemical and chemical composition, and similar mineralogy all tend to support the suggestion that the "basalts" and the "Turkey Track" originated in the one magma chamber or source area.

Within the magma chamber gravitational differentiation could have created a less dense more felsic fraction of "Turkey Track" composition in the upper portions of the chamber. This material would have been tapped off first followed by the more basaltic fraction. Within the "Turkey Track" slight differentiation is suggested by the mineralogy. Cooper (1961) suggests that the slightly more mafic "Turkey Track" localities represent an original magma from which, by crystal settling in the magma chamber, the more felsic varieties could form.

Although the "Turkey Track" localities appear to be from the same parent, they probably do not represent one eruption from one vent. Rather they may represent a series of eruptions from several vents, or intrusions into several areas all within the span of a few million years. Evidence for this comes from Damon et al AEC Progress Report

79

80Coo-699-42, 1964, unpublished, which shows that a great number of volcanic and plutonlc rocks in southern Arizona formed around the Paleogene-Neogene boundary, 25-30 million years ago.

Emission spectroscopic analyses indicated that there is very little real variation in trace element content among the "Turkey Track" localities. Most of the minor differences that do show up could be attributed to normal variation in the analyses. One element, cesium, does tend to show an abnormally high concentration in most "Turkey Track" samples. This is reasonable as cesium is an alkali metal, as are potassium and sodium which are also high.

Agreement of the uranium analyses by fluorimetic and gamma counting is fairly good. In most cases agreement is within the limits of error. Considering the effort involved in sample preparation for fluorimetric analysis this certainly emphasizes the potential value of gamma counting for uranium and thorium.

Thorium concentrations were calculated from a/mg hr values by subtracting the a/mg hr contribution from uranium. The values used were 1 ppm U equals 0.3674 <v/mg hr and 1 ppm Th equals 0.08853 tf/mg hr. Values for uranium were determined by fluorimetry or gamma counting when fluorimetric analyses had not been run. Comparisons of thorium by gamma counting and the of, U method are fairly good.

Flame photometric potassium analyses generally agreed quite well with the beta counting but much less s with gamma counting. This is probably due to the low gamma activity of K^° and the generally high background.

In general the value of radiometric methods of analysis has been demonstrated. Coupled with chemical and petrographic studies these can be useful aids for correlation of volcanic rocks.

APPENDIX "A"

Data on Bock Standards used in this Investigation

NumberDescription

Uppm

Thppm

. Th/U K%

<*/mg hr (calculate

USES 4984 a *c Triassic Diabase

0 .60 1.5 2.5 0.48 0.35

USES 4982 a»c Gabbro Diorite

0.53

VOH 3.0 1.29 0.34

USES 4978 0 1.0Columbia River Basalt

1 .9 1.9 0.82 0.54

USES 4985 c Deccan Trap

0.66 2 .8 4.3 0.65 0 .5 0

W-l d Diabase

O .52 2 .4 4.6 0.56 0.40

0-1 dWesterly Granite

3.7 52 14.0 4.51 6.0

USES 4933 b >c Milford Granite

0 .67 9 .0 13.4 3.33 1.0

BP-102 e Smlthwick Shale

2.3 8 .7 3.8 1.6 1 .62

RP-113 e Surlum Bauxite

6.1 132 21.6 0.5 13.94

USES 4979 c Chelmsford Granite

8.8 —- — 4.61 — —

USES 4981 0 9.2Graniteville Granite

— — -- 3.81

a - Evans and Goodman 1941 b - Hurley 1956 c * USES analyses d • Stevens et al i960e ■ Adams, Richardson, and Templeton, 1953

82

APPENDIX "B"

The simultaneous determination of uranium, thorium, and potassium by gamma scintillation spectroscopy requires the use of three channels. From each channel a total count rate is obtained. This is first corrected for drift and efficiency as mentioned in the text, then corrected for background, and finally for a sample weight for 25 grams.The net count rate per channel still represents the total gamma emission from uranium, thorium, and potassium. To solve for these individually the following method was used.

Let the subscripts 1, 2, and 3 Indicate respectively the channels centered at 0.180, 0.238, and 1.46 Mev. The standards 0-1, W-l, and KgCrgOy were used to determine the counting coefficients.

Uq , Tq , Kq = uranium, thorium, and potassiumcontent respectively of 0-1 in ppm

Uw , Ty, Ky = uranium, thorium, and potassiumcontent respectively of W-l in ppm

K = potassium content of potassium standard in per cent Gi> g2> g3 = count rate from 0-1 in channels 1, 2, and 3 wl» w2> w3 = count rate from W-l in channels 1, 2, and 3 KK- , KKg, KK-j ™ count rate from potassium standard in

channels 1, 2, and 3

83

34Rl, Rg, R3 = count rate from unknown sample in

channels 1 , 2, and 3

, Ug, U3 = count rate from uranium only in0 -1 and W-l in channels 1 , 2 , and 3

in cpm per ppmTg, Tj - count rate from thorium only in

0-1 and W-l in channels 1, 2, and 3

K2, * count rate from potassium standardin channels 1 , 2, and 3 in cpm per #= KK(1.2.3)

KSince the potassium standard is free from uranium

and thorium, the count rates for 0 -1 can immediately be

corrected for potassium by subtracting KqK^, kq^2* an<KqK^ from O^, 02, and 0^ respectively. In the same manner

count rates from W-l can be corrected for potassium. From the corrected values of 0 , G2, Gj and W^, W2, W^ values for U-p U2, and T p T2, can now be calculated by

solution of three pairs of equations involving two unknowns each. Thus

UGUi TqT^ = (corrected)UwUi TyT^ = W]_ (corrected)

and similarly for U2, U^, and T2, .

Letting X, Y, and Z equal the counts per minute from uranium, thorium, and potassium respectively in R^

the following equations can be solved for the final results.

85X + Y + Z - Si(u2/ Ui)X (T2/T1)Y + (k2/k1)z - s2 (U3/U1)X + (T3/T1)Y (K3/Ki)Z « S3

Solving as a determinant1 1

R2 T2/T1 Kg/Kj,R3 13/T1 K3/Ki

X = _______ ______________ _ = aSi + bB2 + cS31 1 1U2/Ui T2/Ti K2/KiU3/U1 t3A i K3/Ki

where a » T2/T^-. K3/K - K2/Ki . T3/Tib — T3/Ti- K3/Ki

c = ^2^1”d * a + (U2/U1)b > (U3/U1)c

likewiseX = eB-) + f BP + gB?

d

where e — Kg/K^ , U^/U^ — Ug/U^ . K^/K^

f * K3/Ki - U3/Ui S = U2/Ui - K2/Ki

Uranium * X/U^ ppm Thorium ■ Y/Ti ppmPotassium = JL (B3 - X(U3/Ui) “ %(T3/Ti)) percent

86In the spectrometer used the following values

were determined.Ug/Ui = 0.382 U3/U1 = 0.389 T2/Ti x 2.814 T3/Ti = 0.634 K2/Ki = 0.636 K3/K1 ■ 2.047

U]_ = 1.840 ppm U per cpra T]_ - 0.235 ppm Th per cpm K3* 1.697 per cent K per cpm

From these values a - 5 .2 9, b * -1.3 6, c * -2.13, d = 3.94,

e * -0 .5 2, f x 1.6 6, and g = -0 .3 0.Error In the method Is dependent on the proportion

of uranium or thorium In the sample. Error In the potassium determination will have the same effect on both uranium and thorium channels and thus will not effect the ratio significantly. Statistical counting error for "Turkey Track" samples varied from 3 - 8/5 in the uranium channel, 2 - 5^ in the thorium channel, and 6 - 13# In the potassium channel. Estimated total error in the uranium determination would vary from over 3# to Infinity depending on the percent of t he total activity due to uranium. Instrument drift contributes to the total error.

87Maximum instrument drift observed for this Instrument is 5^ over a period of several days after allowing seven days for the Instrument to stabilize.

An average "Turkey Track” sample counted 30 - 50$ above background In the uranium and thorium channels and about 15$ above background in the potassium channel. However, high gross count rates improved the statistics.

Selected Bibliography

Adams, J.A.S., Richardson, J.E., and Templeton, C.C.,1958, Determination of Thorium and Uranium in Sedimentary Rocks by Two Independent Methods, Geochim. et Cos. Acta 11. pp 270, 1958.

Ahrens, L.H., and Taylor, S.R., 1961, Spectrochemical Analysis, 2nd Ed. Addison Wesley.

Bikerman, M., 1962, A Geologic - Geochemical Study of the Cat Mountain Rhyolite/University of Arizona unpublished Masters Thesis.

Blkerman, M., and Damon, Paul E., 1964, K-Ar Dating of the Tucson Mountains, Pima County, Arizona: unpublished U, S. Atomic Energy Comm. Progress Report Coo-689-42 Appendix A II.

Brennan, D.J., 1957, Geological Reconnaissance of Clenega Gap, Pima County, Arizona, University of Arizona unpublished Ph. D. Thesis.

Brown, W*H., 1939, Tucson Mountains - An Arizona Basin- Range Type, Bull. O.S.A pp 697 - 760.

Centanni, Frederick A., Ross, Arthur M., and DeSesa,Michael A., 1956, Fluorimetrlc Determination of Uranium, Analytical Chemistry £2,, pp 1651.

Cherry, R.D., 1963, The Determination of Th and U inGeological Samples by an alpha counting technique, Geochim. et Cos. Acta PP 183 - 190.

Chew, R.T.,111, 1953, The Geology of the Mineta Ridge Area Pima and Cochise Counties, Arizona, University of Arizona unpublished Masters Thesis, pp 53.

Cooper, John R., 1960a, Some Geologic Features of the Pima Mining District, Pima County, Arizona, U.S.G.S.Bull. 1112-C, pp 63 - 103.

Cooper, John R., 1960b, Reconnaissance Map of the Wilicox, Fisher Hills, Cochise, and Dos Cabezas quadrangles, Cochise, and Graham Counties, Arizona, U.S.G.S. Mineral Inv. Field Studies Map MF 231.

88

Cooper, John H., 1961, Turkey Track Porphyry - A Possible Guide for Correlation of Miocene Hocks in southeastern Arizona, Arizona Geol. Soc. Digest 4,,PP 17 - 34.

Damon, Paul E., and Feely, H.W,, 1957, Radiometric Analysis of Uranium Content in Ores, U.S.Atomic Energy Commission BME - 3153.

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Documents

Trace element investigation of the Turkey Track porphyry ......Acknowledgments This work was conducted under the direction and guidance of Dr. P. E. Damon and was financed in part