Plutonic Rocks of the 

Santa Rita Mountains, 

Southeast of Tucson, 

Arizona 

GEOLOGICAL SURVEY PROFESSIONAL PAPER 915 

Plutonic Rocks of the 

Santa Rita Mountains, 

Southeast of Tucson, 

Arizona 

By HARALD DREWES 

GEOLOGICAL SURVEY PROFESSIONAL PAPER 915 

A petrographic description, augmented by 

many modal and chemical analyses and 

radiometric age determinations, of a series of 

plutonic rocks and related hypabyssal 

intrusive rocks, and remarks on 

their relation to some mineral deposits 

UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1976 
UNITED STATES DEPARTMENT OF THE INTERIOR 

THOMAS S. KLEPPE, Secretary 

GEOLOGICAL SURVEY 

V. E. McKelvey, Director 

Library of Congress Cataloging in Publication Data 

Drewes, Harold, 1927-

Plutonic rocks of the Santa Rita Mountains, southeast of Tucson, Arizona. 

(Geological Survey Professional Paper 91 5) 

Bibliography: p. 

Includes index. 

Supt. of Docs. no.: I 19.16:915 

1. Rocks, Igneous. 2. Petrology-Arizona-Santa Rita Mountains. 3. Intrusions (Geology)-Arizona-Santa Rita Mountains. 

I. Title. II. Series: United States Geological Survey Professional Paper 915. 

QE461.D65 552'.3 75-619358 

For sale by the Superintendent of Documents, U.S. Government Printing Office 

Washington, D.C. 20402 

Stock Number 024-001-02865-4 
CONTENTS 

Page 

Metric-English equivalents . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . V 

Page 

Cretaceous rocks-Continued 

Abstract . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 Josephine Canyon Diorite-Continued 

Introduction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 Modal and chemical summary . . . . . . . . . . . . . . . . . . . . . . . 37 

Objectives. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 Age and correlation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39 

Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 Madera Canyon Granodiorite . . . . . . . . . . . . . . . . . . . . . . . . . . . 40 

Geologic setting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 Petrography...................................... 41 

Precambrian rocks. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 Granodiorite . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41 

Pinal Schist . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 Porphyritic granodiorite. . . . . . . . . . . . . . . . . . . . . . . . 42 

Granite gneiss . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 Melanocratic granodiorite . . . . . . . . . . . . . . . . . . . . . . 42 

Continental Granodiorite . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 Modal and chemical summary . . . . . . . . . . . . . . . . . . . . . . . 43 

Petrography . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 Age and correlation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44 

Granodiorite . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 Elephant Head Quartz Monzonite . . . . . . . . . . . . . . . . . . . . . . . 47 

Aplitic rocks. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 1 Petrography . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48 

Lamprophyre . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13 Quantrell stock, coarse-grained quartz monzonite . . 49 

Modal and chemical summary....................... 13 Quantrell stock, fine-grained quartz monzonite . . . . 49 

Age and correlation................................ 15 Yoas stock, coarse-grained quartz monzonite . . . . . . 50 

Triassic and Jurassic rocks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 7 Modal and chemical summary . . . . . . . . . . . . . . . . . . . . . . . 51 

Piper Gulch Monzonite . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 7 Age and correlation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51 

Quartz diorite . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23 Tertiary rocks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54 

Squaw Gulch Granite . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24 Rocks of the Gringo Gulch pluton and other rocks . . . . . . . . . . 55 

Petrography . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25 Granitoid rocks of the Helvetia stock . . . . . . . . . . . . . . . . . . . . . 57 

Granite and quartz monzonite . . . . . . . . . . . . . . . . . . . 26 Petrography . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 58 

Aplite and lamprophyre . . . . . . . . . . . . . . . . . . . . . . . . 27 Modal and chemical summary . . . . . . . . . . . . . . . . . . . . . . . 60 

Modal and chemical summary . . . . . . . . . . . . . . . . . . . . . . . 28 Age and correlation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61 

Age and correlation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28 Quartz latite porphyry of the Greaterville plugs . . . . . . . . . . . . 62 

Cretaceous rocks . . . . . . ... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29 Petrography . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 65 

Granitoid rocks of the Corona stock . . . . . . . . . . . . . . . . . . . . . . 29 Modal and chemical summary . . . . . . . . . . . . . . . . . . . . . . . 66 

Josephine Canyon Diorite . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33 Age and correlation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 67 

Petrography . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34 Granodiorite of the San Cayetano stock. . . . . . . . . . . . . . . . . . . 67 

Dioritic rocks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34 References cited........................................... 71 

Fine-grained quartz monzonite . . . . . . . . . . . . . . . . . . 36 Index.................................................... 73 

ILLUSTRATIONS 

Page 

FIGURE 1. Index map showing location of Sahuarita and Mount Wrightson quadrangles and the Santa Rita Mountains . . . . . . . . . . . . . . . . . . . . . 2 

2. Index map of the Santa Rita Mountains . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 

3. Map showing distribution of Precambrian rocks and specimen collection sites. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 

4. Photograph of specimen 17, Continental Granodiorite . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 

5. Photomicrograph of specimen 19, slightly metamorphosed Continental Granodiorite .................. , . . . . . . . . . . . . . . . . . . . . . 10 

6. Photomicrograph of specimen 12, Continental Granodiorite . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 

7. Photomicrograph of specimen 17, Continental Granodiorite . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 

8. Isometric diagram of a modal tetrahedron...................... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13 

9. Modified triangular diagram showing the modal quartz, potassium feldspar, plagioclase, and fernie minerals of Continental 

Granodiorite . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 

10. Histograms showing average chemical composition of each group of plutonic rocks. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18 

11. Map showing distribution of Triassic rocks and specimen collection sites . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20 

12. Photograph of specimen 37, Piper Gulch Monzonite . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21 

13. Photomicrograph of specimen 37, Piper Gulch Monzonite............................................................... 21 

III 
IV CONTENTS 

Page 

FIGURE ;14. Modified triangular diagram showing the modal quartz, potassium feldspar, plagioclase, and fernie minerals of Piper Gulch 

Monzonite and related rocks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22 

15. Map showing distribution of Squaw Gulch Granite and sample collection sites .............................................. 25 

16. Photograph of specimen 45, Squaw Gulch Granite ...................................................................... 26 

17. Photomicrographs of specimen 45, Squaw Gulch Granite ................................................................ 27 

18. Photomicrograph of specimen 48, Squaw Gulch Granite ............................................................... 28 

19. Modified triangular diagram showing modal quartz, potassium feldspar, plagioclase, and fernie minerals of Squaw Gulch Granite .. 30 

20. Map showing distribution of granitoid rocks of the Corona stock and specimen collection sites . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32 

21. Photomicrograph of sepcimen 64, quartz monzonite of the Corona stock .................................................. 32 

22. Modified triangular diagram showing modal quartz, potassium feldspar, plagioclase, and fernie minerals of granitoid rocks of the 

Corona stock . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33 

23. Map showing distribution of Josephine Canyon Diorite and specimen collection sites ........................................ 35 

24. Photograph of specimen 80, Josephine Canyon Diorite .................................................................. 36 

25. Photomicrographs of specimen 81, Josephine Canyon Diorite . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37 

26. Modified triangular diagram showing modal quartz, potassium feldspar, plagioclase, and fernie minerals of Josephine Canyon 

Diorite ...................................................................................................... 38 

27. Map showing distribution of Madera Canyon Granodiorite and specimen collection sites ..................................... 41 

28. Photograph of specimen 113, nonporphyritic type of Madera Canyon Granodiorite .......................................... 42 

29. Photomicrographs of specimen 113, non porphyritic type of Madera Canyon Granodiorite .................................... 43 

30. Ph~tograph of Specimen 127 of the melanocratic type of Madera Canyon Granodiorite ................................... 44 

31. Modified triangular diagram showing modal quartz, potassium feldspar, plagioclase, and fernie minerals of Madera Canyon 

Granodiorite ................................................................................................. 45 

32. Map showing distribution of Elephant Head Quartz Monzonite and specimen collection sites .................................. 47 

33. Photograph of Elephant Head. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49 

34. Photograph of specimen 134, Elephant Head Quartz Monzonite .......................................................... 50 

35. Photomicrograph of specimen 132, coarse-grained Elephant Head Quartz Monzonite ...................................... 50 

36. Modified triangular diagram showing modal quartz, potassium feldspar, plagioclase, and fernie minerals of Elephant Head Quartz 

Monzonite ........................................................................... _ ........................ 52 

37. Modified triangular d1agram comparing the range of distribution of the modes of the Josephine Canyon Diorite, Madera Canyon 

Granodiorite, and Elephant Head Quartz Monzonite . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53 

38. Map showing distribution of rocks of the Gringo Gulch pluton and other rocks and specimen collection sites ..................... 56 

39. Modified triangular diagram showing modal quartz, potassium feldspar, plagioclase, and fernie minerals of rocks of the Gringo 

Gulch pluton and of the San Cayetano stock ....................................................................... 58 

40. Map showing distribution of granitoid rocks of the Helvetia stocks and porphyry of the Greaterville plugs and specimen collection 

sites ......................................................................................................... 60 

41. Photograph of specimen 174, quartz monzonite of the Helvetia stocks .................................................... 61 

42. PhotomH.:rograph of specimen 174, quartz monzonite of the Helvetia stocks ................................................ 61 

43. Modified triangular diagram showing modal quartz, potassium feldspar, plagioclase, and fernie minerals of the granitoid rocks of 

the Helvetia stocks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63 

44. Photomicrograph of specimen 185, quartz latite porphyry of the Greaterville plugs .......................................... 66 

45. Modified triangular diagram showing modal quartz, potassium feldspar, plagioclase, and fernie minerals of quartz latite porphyry 

of the Greaterville plugs ........................................................................................ 68 

TABLES 

Page 

TABLE 1. Stratigraphic summary of rocks of the Santa Rita Mountains . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 

2. Modes of Continental Granodiorite . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 

3. Chemical and spectrographic analyses and CIPW norms of Continental Granodiorite. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16 

4. Summary of radiometric age determinations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 

5. Modes of Piper Gulch Monzonite . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22 

6. Chemical and spectrographic analyses and CIPW norms of Piper Gulch Monzonite. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23 

7. Modes of Squaw Gulch Granite . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30 

8. Chemical and spectrographic analyses and CIPW norms of Squaw Gulch Granite . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31 

9. Modes of granitoid rocks of the Corona stock . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33 

10. Chemical and spectrographic analyses and CIPW norms of granitoid rocks of the Corona stock . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33 

11. Modes of Josephine Canyon Diorite. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38 

12. Chemical and spectrographic analyses and CIPW norms of Josephine Canyon Diorite . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40 

13. Modes of Madera Canyon Granodiorite . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44 

14. Chemical and spectrographic analyses and CIPW norms of Madera Canyon Granodiorite . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46 

15. Modes of Elephant Head Quartz Monzonite. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52 
CONTENTS v 

Page 

TABLE 16. Chemical and spectrographic analyses and CIPW norms of Elephant Head Quartz Monzonite. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54 

17. Modes of the Gringo Gulch pluton . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59 

18. Chemical and spectrographic analyses and CIPW norms of rocks of the Gringo Gulch pluton . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59 

19. Modes of granitoid rocks of the Helvetia stocks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 62 

20. Chemical and spectrographic analyses and CIPW norms of granitoid rocks of the Helvetia stocks . . . . . . . . . . . . . . . . . . . . . . . . . . . 64 

21. Modes of quartz latite porphyry of the Greaterville plugs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 68 

22. Chemical and spectrographic analyses and CIPW norms of quartz latite porphyry of the Greaterville plugs . . . . . . . . . . . . . . . . . . . . . . 69 

23. Modes of granodiorite of the San Cayetano stock . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 70 

24. Chemical and spectrographic analyses and CIPW norms of granodiorite of the San Cayetano stock . . . . . . . . . . . . . . . . . . . . . . . . . . . . 70 

METRIC-ENGLISH EQUIVALENTS 

Metric unit 

millimetre (mm) metre (m) 

kilometre (km) 

square metre (m2) 

square kilometre (km2) 

hectare (ha) 

cubic centimetre (cm3 ) 

litre (1) 

cubic metre (m3) 

cubic metre cubic hectometre (hma) 

litre 

litre 

litre 

cubic metre 

cubic metre 

gram (g) 

gram 

tonne (t) tonne 

English equivalent 

Length 

0.03937 inch (in) 

3.28 feet (ft) 

.62 mile (mi) 

Area 

10.76 

.386 

2.47 

Volume 

0.061 

61.03 

35.31 

.00081 

=810.7 

2.113 

1.06 

.26 

.00026 

6.290 

Weight 

square feet (ft2) 

square mile (mill) acres 

cubic inch (ina) 

cubic inches 

cubic feet (ft3) 

acre-foot (acre-ft) 

acre-feet 

pints (pt) 

quarts (qt) gallon (gal) million gallons (Mgal or 10a gal) barrels (bbl) (1 bbl=42 gal) 

o.o:m ounce, avoirdupois (oz avdp) .0022 pound, avoirdupois (lb avdp) 

1.1 tons, short (2,000 lb) .98 ton, long (2,240 lb) 

Specific combinations 

kilogram per square centimetre (kg/cm2) 

kilogram per square centimetre 

cubic metre per second 

(m3/s) 

0.96 

.98 

35.3 

atmosphere (atm) 

bar (0.9869 atm) 

cubic feet per second (fts/s) 

Metric unit English equivalent 

Specific combinations-Continued 

litre per second (1/s) 

cubic metre per second 

per square kilometre 

[(m3/s)/km2) 

metre per day (m/d) 

metre per kilometre 

(m/km) kilometre per hour 

(km/h) metre per second (m/s) metre squared per day 

(m2/d) 

cubic metre per second 

(m3js) 

cubic metre per minute 

(mSjmin) 

litre per second (1/s) litre per second per metre [ (1/s) /m] 

kilometre per hour 

(km/h) metre per second (m/s) 

gram per cubic 

centimetre (g/cma) 

gram per square centimetre (g/ctn2) 

gram per square 

centimetre 

degree Celsius (°C) 

degrees Celsius 

(temperature) 

.0353 cubic foot per second 

!Jl.47 cubic feet per second per 

square mile [ (ft3/s) /mill] 

3.28 feet per day (hydraulic conductivity) (ft/d) 

5.28 feet per mile (ft/mi) 

.9113 foot per second (ft/s) 

3.28 feet per second 

10.764 feet squared per day (ft2Jd) 

(transmissivity) 

22.826 million gallons per day (Mgal/d) 

=264.2 gallons per minute (gal/min) 

15.85 gallons per minute 

4.83 gallons per minute per foot 

[(gal/min) /ft] 

.62 mile per hour (ml/h) 

2.237 miles per hour 

62.43 pounds per cubic foot (lb/ft3 ) 

2.048 pounds per square foot (lb/ft2) 

.0142 pound per square inch (lb/ln2) 

Temperature 

1.8 degrees Fahrenheit ( •F) 

= [ (1.8 X •c) + 32] degrees Fahrenheit 

PLUTONIC ROCKS OF THE SANTA RITA MOUNTAINS, 

SOUTHEAST OF TUCSON, ARIZONA 

By HARALD DREWES 

ABSTRACT 

Plutonic masses and some related hypabyssal bodies were intruded into 

the rocks of the Santa Rita Mountains during Precambrian, Triassic, 

Jurassic, Cretaceous (2 episodes), Paleocene (3 episodes), and Oligocene 

times. The plutonic rocks range in composition from diorite to granite; 

most of them are granodiorite or quartz monzonite. The intrusive masses 

range in size from a small batholith to plugs and related dikes; most of 

them underlie areas of I to 10 square miles. Some of the intrusive masses 

are locally associated with contact metamorphic mineral deposits, and 

plugs of quartz latite porphyry of late Paleocene age are closely associated 

with hydrothermal deposits of base and noble metals in the Helvetia and 

Greaterville mining districts. 

Petrographic descriptions of the plutonic rocks are augmented by 

nearly 200 modal analyses, more than 50 chemical and spectrographic 

analyses, and more than 25 radiometric age determinations. 

The oldest of the plutonic rocks, the Continental Granodiorite, of 

Precambrian Y age, is a coarse-grained, very coarsely porphyritic, partly. 

metamorphosed and much-altered granodiorite and quartz monzonite 

that forms a mass of unknown size. Its host rocks are intensely 

metamorphosed, but they are not mineralized near the intrusive mass. 

During Triassic time, the Piper Gulch Monzonite was intruded, 

probably along a major northwest-trending fault zone. It consists mainly 

of very coarse grained, dark-gray, anorthositic-looking rock in large 

inclusions, septa, and wallrock to younger intrusive masses. Its host rocks 

are metamorphosed and locally mineralized; the mineralization in the 

host is probably related to nearby younger intrusive masses. 

Squaw Gulch Granite forms a partly concealed batholith or very large 

stock of Jurassic age. The rock is coarse grained and pinkish gray, and it 

ranges in composition from granite to quartz monzonite. At least some of 

its host rocks are contact metamorphosed, and those which are Paleozoic 

limestone, near the Glove mine, contain contact metamorphic ore 

deposits, chiefly of base metals and silver. 

Magmatic activity was particularly widespread during the Laramide 

Orogeny extending thn:mgh much of Late Cretaceous time and through 

Paleocene time . Quartz monzonite and granodiorite of the Corona stock 

were intruded into the rocks of the northern end of the Santa Rita 

Mountains about 73 to 74 m.y. (million years) ago. Three composite 

stocks were emplaced in the central and southern part of the mountains 

about 67 to 69 m.y. ago. Of these three, the Josephine Canyon Diorite 

ranges widely in composition from diorite, syenodiorite, and quartz 

diorite to granodiorite and quartz monzonite. It is generally a fine- to 

medium-grained light- to dark-gray rock, and locally it may be 

associated with base-metal mineral deposits. The Madera Canyon 

Granodiorite is a coarse-grained light- to medium-gray porphyritic and 

locally metamorphosed rock not obviously associated with mineral 

deposits. The Elephant Head Quartz Monzonite is also coarse grained, is 

pinkish gray, and is only locally associated with a little mineralization. 

Scattered small stocks and plugs, such as the Gringo Gulch pluton, 

were intruded into rocks of the southern part of the Santa Rita 

Mountains, at least in part during the early Paleocene. They include some 

hypabyssal rocks of uncertain compositiOn, age, and geologic 

association, some hornblende dacite porphyry plugs, and a small microgranodiorite plug. 

During the late Paleocene, one group of small barren stocks and a 

group of ore-associated plugs were intruded into complexly faulted rocks 

of the Helvetia and Greaterville mining districts of the northern part of 

the Santa Rita Mountains. The stocks of Helvetia are mainly of 

granodiorite and quartz monzonite; they are elliptical in plan, their 

position and shape is only slightly controlled by faults, and the host rocks 

are widely metamorphosed. The plugs of Greaterville are of quartz latite 

porphyry, are commonly irregular in plan, and are strongly controlled by 

faults. Hydrothermal fluids associated with these plugs deposited base 

and noble metals in favorable host rocks along faults near the plugs. 

A small stock of granodiorite, of late(?) Oligocene age, was intruded 

into the rocks' of the San Cayetano Mountains. This stock is believed to 

occupy part of a magma chamber associated with an extensive volcanic 

pile in the nearby Grosvenor Hills area. 

INTRODUCTION 

Plutonic rocks and related hypabyssal intrusive rocks 

underlie much of the Santa Rita Mountains and adjacent 

mountains of southeastern Arizona. Significant intrusive 

events are recorded during the Precambrian, Triassic, 

Jurassic, Late Cretaceous, Paleocene, and Oligocene. The 

plutonic rocks intrude sequences of Precambrian 

metamorphic rocks, Paleozoic sedimentary rocks, and 

several sequences of Mesozoic and Cenozoic sedimentary 

and volcanic rocks. As a result of this extensive geologic 

record, the Santa Rita Mountains are the best referencearea 

from which to develop the regional geologic history. The 

plutonic rocks deserve special attention not only because 

they are closely related to the depositional and tectonic 

development of the area, but also because they provide 

most of the radiometrically datable rocks, and because 

some of them seem to be genetically related to mineral 

deposits. 

The Santa Rita Mountains are the first range southeast 

of Tucson (fig. 1). They extend more than 25 miles 

southward from Pantano Wash, along which the main 

railroad and highway east of Tucson lie, to Sonoita Creek, 

about 12 miles from the Mexican border. The mountains 

commonly reach heights of 6,000 to 7,000 feet and the 

highest, Mount Wrightson, is 9,453 feet high. The broad 
2 PLUTONIC ROCKS, SANTA RITA MOUNTAINS, SOUTHEAST OF TUCSON, ARIZONA 

valley east of the mountains lies at an elevation of about 

4,500 feet, whereas the valley west of the mountains is only 

3,000 feet high. The mountains are high enough to receive 

an amount of precipitation adequate to support an 

extensive, though largely scrubby, forest, which contrasts 

strikingly with grasslands in the high valley to the east and 

with the thorn brush and cactus vegetation typical of the 

Sonoran Desert plant assemblage in the low valley to the 

west. 

OBJECTIVES 

A geologic investigation of the Santa Rita Mountains 

was carried out by the U.S. Geological Survey during 

1962-68 to help determine the geologic history of a part 

of southeastern Arizona having the potential of being one 

of the major sources of copper in the country. Several 

mountain ranges were studied during part of the 1950's 

and 1960's by eight geologists, J. R. Cooper, S. C. 

Creasey, T. L. Finnel, P. T. Hayes, E. R. Landis, R. B. 

Raup, F. S. Simons, and the author. The results of the 

investigation in the Santa Rita Mountains are presented 

mainly on two geologic maps (Drewes, 1971b, c) and in a 

report on the structural geology of the area (Drewes, 

1972b). Details on field and laboratory observations and 

analyses that support the main interpretations and the 

results of subordinate studies on particular topical 

problems are presented in separate reports, referred to 

0 10 20 MILES 

0 10 20KILOMETRES 

CONTOUR INTER VAL 1000 FEET 

DATUM IS MEAN SEA LEVEL 

FIGURE I.-Location of the Sahuarita and Mount Wrightson 

quadrangles and the Santa Rita Mountains, southeastern Arizona. 

Major copper mines: 1, Mission-Pima; 2, Twin Buttes; 3, Esperanza; 

4, Sierrita. Published geologic maps: Twin Buttes quadrangle (Cooper, 

1974), Empire Mountains quadrangle (Finnell, 1973), Benson 

quadrangle (Creasey, 1%7), Happy Valley quadrangle (Drewes, 1974), 

Nogales and Lochiel quadrangles (Simons, 1974), Sunnyside quadrangle and parts of Hereford and Fort Huachuca quadrangles (Hayes and 

Raup, 1968), Bisbee quadrangle (Hayes and Landis, 1964), and 

Dragoon quadrangle (Cooper and Silver, 1964). 
INTRODUCTION 3 

herein where pertinent. The objective of the present report 

is to support and augment the study of the structural 

history of the Santa Rita Mountains by presenting 

abundant data on the plutonic and related rocks. 

The petrographic studies of the plutonic rocks of the 

Santa Rita Mountains include both field and laboratory 

observations. Almost 200 modal analyses were made by 

petrographic microscope. More than 50 chemical analyses 

of the major constituents of rocks and spectrographic 

analyses of the trace constituents of the rocks are 

presented, and 27 radiogenic age determinations are 

included. 

This considerable effort in describing and defining the 

plutonic rocks of the area was made for two reasons. First, 

the evidence was clear early during the field investigations 

that the area contained plutonic rocks of many ages, 

among them some new additions to the then-available 

geologic knowledge of the region. Second, some plutonic 

rocks were more closely related to mineralization than 

others, which suggested that distinguishing between the 

plutonic rocks was desirable for purposes of mineral 

exploration. Furthermore, the conditions of emplacement 

of the plutons and their subsequent alteration are also of 

potential economic interest. 

For the purpose of this report, the area referred to as the 

Santa Rita Mountains coincides with the Mount Wrightson 

and Sahuarita 15-minute quadrangles (fig. 2). A small part 

of the northern end of the mountains is therefore omitted; 

it lies in the Empire Mountains quadrangle mapped by T. 

L. Finnell (1971). At the southwest flank of the Santa Rita 

mountains the outlying hills named the Grosvenor Hills 

and the San Cayetano Mountains are included in this 

study. 

Included in this study of plutonic rocks are some 

granitoid rocks believed to be intruded near the surface 

and some fine-grained hypabyssal intrusive rocks believed 

to be genetically related to the plutonic rocks. Precambrian 

regionally metamorphosed rocks are also mentioned herein 

simply for convenience and in order to complete the 

general description of the rocks of the Santa Rita 

Mountains. Hereafter in this report general references to 

plutonic rocks of the area are used in the sense of including 

these few hypabyssal granitoid rocks and aphanitic rocks 

and the Precambrian metamorphic rocks, unless 

specifically stated otherwise. 

ACKNOWLEDGMENTS 

The geologic investigation of the Santa Rita Mountains 

was carried out approximately simultaneously with the 

other studies of the larger program of the U.S. Geological 

Survey, mentioned in the preceding section. As a result, the 

investigation benefited through field consultations and 

from frequent discussions with my colleagues during the 

preparation of all the reports. I am particularly grateful for 

the benefits derived from the colleagues who have worked 

in the adjoining areas (fig. 1)-J. C. Cooper for the 

Sierrita Mountains, T. L. Finnell for the Empire 

Mountains, R. B. Raup for the Canelo Hills, and F. S. 

Simons for the Patagonia Mountains. Undoubtedly some 

geologic interpretations were developed jointly with them, 

yet the following presentation of these ideas and their 

validity in the context of the geology of the Santa Rita 

Mountains remain my own responsibility. 

The success of the field study was facilitated by many 

people. Invaluable assistance in mapping and sampling was 

provided by G. C. Cone, Bruce Hansen, C. W. Norton, F. 

W. Plut, J. R. Riele, R. A. Rohrbacker, F. Sutheimer, and 

W. M. Swartz. Discussions in the field benefited from the 

experience of R. E. Wallace, M. D. Crittenden, Jr., J. H. 

Courtright, and many others. The courtesies of George 

and Sis Bradt, Roy Green, Dewey Kieth, and George 

Yakobian, all residents near the Santa Rita Mountains, 

and those of Professors John Anthony, Evans Mayo, and 

P. E. Damon of the University of Arizona are appreciated. 

Invaluable support was obtained from many 

laboratories. One radiometric age determination was 

obtained from P. E. Damon before its publication, and the 

others were provided by R. F. Marvin, T. W. Stern, Z. E. 

Peterman, S. C. Creasey, and their many colleagues. 

Chemists and spectrographers who have contributed are 

acknowledged in the tables of analytical data. G. C. Cone 

also assisted in many phases of the preparatory work on 

samples. 

Previous geologic studies of the Santa Rita Mountains 

are few, and most of them consider very local areas or 

topical problems. The study by Schrader (1915) represents 

the pioneer effort at geologic mapping in the area and the 

influence of his work is still noticeable on the latest edition 

of the geologic map of Arizona (Wilson and others, 1969). 

Several Master of Science theses on file at the University of 

Arizona were also consulted. The present geologic study is 

thus most accurately viewed as a second-generation effort, 

even though in some respects this is an overstatement. 

GEOLOGIC SETIING 

The geologic setting of the plutonic rocks of the Santa 

Rita Mountains has been extensively described in earlier 

reports (Drewes, 1972a, b), but for convenience of the 

reader, the geologic history is briefly summarized here. 

The names, stratigraphic positions, and ages of the 

plutonic rocks and the other rocks of the area are shown in 

table 1. 

The oldest known rocks of the area are regionally 

metamorphosed rocks conventionally assigned to the Pinal 

Schist. In most nearby areas the formation is a muscovitechlorite or muscovite-biotite schist, but locally this 

formation consists largely of biotite gneiss and granite 

gneiss and of only a small amount of schist, which are 

described in the following section of this report. These 

rocks were deformed, metamorphosed, and intruded, 
4 PLUTONIC ROCKS, SANTA RITA MOUNTAINS, SOUTHEAST OF TUCSON, ARIZONA 

0 

0 

5 10 MILES 

5 10 K ILOMETRES 

CONTOUR INTER VAL 1,000 FEET 

DATUM IS MEAN SEA LEV EL 

CANELO 

HILLS 

FIGURE 2.-The Santa Rita Mountains, showing areas covered by geologic maps in this report: A , figure 3; 8 , 

figure 20; C, figure40; D, figure 27; E, figure 32; F, figure 11; G, figure_23; H, figure 15; I, figure 38. 
INTRODUCTION 

TABLE I.-Stratigraphic summary of rocks of the Santa Rita Mountains, indicating the rocks described 

in this report 

Age Rocks described in this report 

(mainly plutonic rocks) Other rocks 

Quaternary and Tertiary ....................................... Gravel. 

Tertiary: Miocene and Pliocene ................................. Nogales Formation. 1 

Oligocene ..................... Granodiorite of San Cayetano Grosvenor Hills Volcanics, laccoMountains. liths, and dike swarms. I 

Paleocene to Oligocene ........................................ Rhyolite, andesite, and quartz 

Paleocene ..................... Aphanitic rocks, Greaterville intrusives; granitic rocks, Helvetia stocks; rocks of Gringo 

Gulch pluton. 

veins. 1 

Paleocene(?) ................................................. Gringo Gulch Volcanics, volcanics 

of Red Mountain.' 

Tertiary or Cretaceous ......... Quartz latite porphyry intrusives. 

Late Cretaceous ................ Elephant Head Quartz Monzonite. 

Do ....................... Madera Canyon Granodiorite. 

Do ...................... Josephine Canyon Diorite. 

Do ....................... Granitoid rocks of Corona stock. Salero Formation.! 

Do ..................................................... Fort Crittenden Formation.' 

Early Cretaceous ............................................. Bisbee Group. 

Do ..................................................... Bathtub Formation. 1 

Do ..................................................... Temporal Formation.,' 

Jurassic ....................... Squaw Gulch Granite. 

Triassic ....................... Piper Gulch Monzonite. 

Do ..................................................... Gardner Canyon Formation. 1 

Do ..................................................... Mount Wrightson Formation.' 

Permian .................................................... Rainvalley Formation. 

Do ..................................................... Concha Limestone. 

Do ..................................................... Scherrer Formation. 

Do ..................................................... Epitaph Dolomite. 

Do ..................................................... Colina Limestone. 

Permian and Pennsylvanian .................................... Earp Formation. 

Pennsylvanian ............................................... Horquilla Limestone. 

Mississippian ................................................ Escabrosa Limestone. 

Late Devonian ............................................... Martin Formation. 

Late and Middle Cambrian .................................... Abrigo Formation. 

Middle Cambrian ............................................ Bolsa Quartzite. 

Precambrian Y ................. Continental Granodiorite. 

Precambrian X ................ Pinal Schist and granite geneiss. 

1 Formation that contains volcanic rocks. 

5 

either during one geologic event or separately in the given 

sequence, by a large pluton of Continental Granodiorite 

(Drewes, 1968). The rocks were uplifted and deeply eroded 

before the deposition of a sequence of Paleozoic rocks; 

indeed, considering evidence from the Rincon Mountains 

(fig. 1) 10 miles north of the Santa Rita Mountains, this 

uplift predates the deposition of the Apache Group of 

Precambrian Y age. 

with the Rainvalley Formation, of late Early Permian or 

slightly younger age. Nearby areas have no Permian rocks 

younger than the Rainvalley Formation. This marine 

sequence was deposited in a shallow continental sea and its 

mternal disconformities mark a succession of epeirogenic 

fluctuations of an otherwise tectonically stable region. 

The Paleozoic rocks of the Santa Rita Mountains are 

believed to have lain unconformably on the Precambrian 

crystalline rocks, although they are now invariably faulted 

upon them. The Paleozoic rocks form a concordant marine 

sequence that begins with the Bolsa Quartzite of Middle 

Cambrian age, contains several disconformities, and ends 

Moderate tectonic activity marked the interval between 

the deposition of Permian rocks and the onset of the 

Laramide orogeny in mid-Cretaceous time. Toward the 

end of the Permian the region was uplifted and· the sea 

retreated; in Early Triassic time, the area now occupied by 

the Santa Rita Mountains was faulted, an uplifted block 

was deeply eroded, and a thick pile of volcanic and 

sedimentary rocks of the Mount Wrightson and Gardner 
6 PLUTONIC ROCKS, SANTA RITA MOUNTAINS, SOUTHEAST OF TUCSON, ARIZONA 

Canyon Formations were deposited in a fault-block basin 

(Drewes, 1971a). Near the end of Triassic time a stock of 

the Piper Gulch Monzonite was intruded, perhaps along an 

old fault zone, the Santa Rita fault scar (Drewes, 1972b). 

During the Jurassic Period a large stock or small batholith 

of granite intruded the southern part of the area. Faulting 

and erosion followed, and during Early Cretaceous time 

the Temporal Formation, Bathtub Formation and Bisbee 

Group were deposited in a continental environment. Both 

the local relief and tectonic activity decreased during this 

interval and, before its close, a shallow sea briefly 

encroached upon the area for the last time. 

The initial impulse of the Laramide orogeny occurred 

during mid-Cretaceous time, for the Upper Cretaceous 

Fort Crittenden Formation was deposited unconformably 

upon the Lower Cretaceous Bisbee. The deposition of 

coarse clastic rocks and resumption of volcanism mark the 

upper part of the Fort Crittenden and widespread 

volcanism is recorded in the succeeding Salero Formation. 

During this time, the Corona stock was emplaced in the 

northern part of what is now the Santa Rita Mountains. 

Major northeastward-directed thrust faulting marked the 

tectonic climax of the Piman phase of the Laramide 

orogeny during the time of deposition of the Salero 

Formation (probably Campanian time). The Piman phase 

culminated a few million years later with a series of 

multiple intrusions of rocks known as the Josephine 

Canyon Diorite, Madera Canyon Granodiorite, and 

Elephant Head Quartz Monzonite. 

During early Paleocene time, about 63 to 58 m.y. 

(million years) ago, the area was tectonically fairly quiet. 

The Josephine Canyon stock, a large epizonal body, was 

partly exposed by erosion and the volcanic and 

sedimentary rocks of the Gringo Gulch Volcanics and the 

volcanic rocks of Red Mountain were deposited in the 

southern part of the area. The Gringo Gulch pluton and 

other small bodies were probably emplaced during that 

time. 

In late Paleocene time, tectonic and volcanic ~ctivity was 

renewed in the northern part of the area to record the 

Helvetian phase of the Laramide orogeny (Drewes, 1972b). 

Minor northwestward-directed thrust faulting was 

penecontemporaneous with the emplacement of a group of 

small stocks named the Helvetia stocks. Quartz latite 

porphyry intrusives that are locally referred to as "ore 

porphyry'' because of their association with mineralization 

(Drewes, 1970) were intruded at the close of the Helvetian 

phase of the Laramide orogeny. 

During the time between the Paleocene and Oligocene 

the local geologic record is fragmentary. Mineralized 

quartz veins were emplaced in the southern part of the area 

and some rhyolite volcanic rocks and andesitic intrusive 

rocks were emplaced in the northern part. The area was 

strongly eroded and possibly block faulted to form the 

ancestral Santa Rita Mountains. 

During late Oligocene time magmatic activity was 

renewed in the southern part of the area. Rhyolite and 

rhyodacite of the Grosvenor Hills Volcanics were extruded 

as flows and tuffs. Vitric laccoliths and dikes were intruded 

into these tuffs (Drewes, 1972a), and at a considerably 

greater depth the feeder dikes of the volcanic rocks and 

hypabyssal intrusive rocks are believed to have emanated 

from small stocks such as that of the granodiorite of the 

San Cayetano Mountains, the youngest pluton of the area. 

The area was block faulted several times during the late 

Tertiary and Quaternary, and gravel of several formations 

filled the basins next to the raised and gently 

southeastward tilted Santa Rita Mountains. The latest 

magmatic activity is recorded by basalt flows, of Miocene 

or Pliocene age that are intercalated in the oldest unit of 

gravel along the Santa Cruz River a few miles south and 

west of the Mount Wrightson quadrangle. 

In the above review of the geologic setting of the 

plutonic rocks, as well as in the summary in table 1, the 

association of plutonic events with volcanic and tectonic 

events seems clear. Likewise, some of the magmatic events 

are shown to be related, at least in time if not also in origin, 

to mineralization. 

PRECAMBRIAN ROCKS 

Rocks of Precambrian age compose an older group of 

regionally metamorphosed granite, gneiss, and schist and 

a younger granodiorite pluton. As mentioned before, the 

metamorphic rocks are described with the plutonic rocks 

because they have not been previously described in the 

topical papers on the Mesozoic or Cenozoic rocks of the 

area. The metamorphic rocks include rocks assigned to the 

Pinal Schist and to an associated granite gneiss, and they 

are intruded by the Precambrian Continental Granodiorite. 

PINAL SCHIST 

The oldest rocks of the Santa Rita Mountains are 

foliated rocks that sufficiently resemble the Pinal Schist of 

some nearby areas to be assigned to that formation. The 

Pinal Schist, as it has been used in southeastern Arizona in 

recent decades, includes a wide variety of metasedimen~­

tary, metavolcanic, and other metaigneous rock types, 

probably of significantly different ages from place to 

place. Cooper and Silver (1964, p. 23, 24) described in 

detail a variety of these rocks that are extensively exposed 

30 miles east-northeast of the north end of the Santa Rita 

Mountains. Somewhat more gneissic varieties are being 

studied in the Rincon Mountains (Drewes, 1974). 

In the Santa Rita Mountains, Pinal Schist appears in a 

few small widely scattered areas, shown in detail on the 

geologic map of the Sahuarita quadrangle (Drewes, 1971 b) 

and shown in a more general way, as rocks older than the 

Continental Granodiorite, in figure 3 of this report. Biotite 

gneiss and schist are the most common lithology, and 
PRECAMBRIAN ROCKS 7 

chlorite schist and phyllite appear in a few localities. The 

Pinal Schist in the large outcrop areas, lying athwart the 

crest of the mountains west of Greaterville, is biotite gneiss 

and schist that is intruded to the north and east by the 

Continental Granodiorite and is faulted against younger 

rocks to the southwest. The intrusive contact is broad and 

gradational, and inclusions of Pinal Schist occur in the 

granodiorite as far north as Box Canyon (fig. 3). 

The rocks of the main outcrop areas consist of 

alternating layers, typically a half an inch to many inches 

thick, of biotite gneiss or biotite schist and of feldspathic 

rock. Less commonly the rocks also include hornblendebiotite gneiss and some pegmatite bodies and lamprophyre 

dikes that may be related to the Continental Granodiorite. 

Weathered outcrops of biotite gneiss are dark grayish 

brown and have the sheen of a micaceous surface. The 

relatively unweathered outcrops, such as those along the 

bottom of Sawmill Canyon, are medium dark gray and the 

gnessic layers are more conspicuous. In places these layers 

are strongly deformed on a small scale, in the manner of 

ptygmatic folds. Elsewhere the layers are cut by many 

small faults and intrusives that are internal features of the 

formation which may be related to the emplacement of the 

nearby Continental Granodiorite. Locally the attitude of 

the foliation appears to be erratic, but over the outcrop 

area foliation strikes northwesterly and dips steeply 

southwest. 

Under the microscope, the grains of a typical dark or 

micaceous layer are seen to be about 0.5 mm long and 

those of the adjacent light-colored felsic layers 0.5 to 1.5 

mm. Alined grains of biotite control the strong schistosity 

of the rock; grain alinement is fairly subtle in the felsic 

layers. Dark layers have an estimated mode of: quartz, 5; 

andesine plagioclase, 65; biotite, 30; ilmenitic magnetite, 3; 

and traces each of sphene, apatite, zircon, and allanite(?). 

Light layers have an estimated mocle of: quartz, 50; 

andesine, 40; biotite, 5; and traces each of magnetite, 

sphene, and apatite. Alteration minerals are scarce and 

they consist of a little chlorite and epidote. The anorthite 

content of plagioclase ranges from 38 to 42 percent. Biotite 

is pleochroic in pale yellow brown to moderate brown. 

Chlorite schist and phyllite are mapped (Drewes, 1971b) 

as small slivers along a northwest-trending tear fault about 

half a mile east of Helvetia. The rocks crop out on 

dark-gray low knolls or ledges in many places surrounded 

by slopes of light-brownish-gray Continental Granodiorite. The schist consists of microscopic layers of alined 

mica and of quartz and feldspar with a cataclastic texture. 

Biotite, plagioclase, and quartz each make up about 30 

percent of the rock, sericite and chlorite each almost 5 

percent of the rock, and ilmenitic magnetite, zircon, and 

apatite trace amounts. The chlorite- and biotite-rich layers 

have a felty texture, indicative of recrystallization after 

shearing. The quartz forms mosaic-textured or 

interlocking aggregates of crystals, also indicative of 

postcataclasis recrystallization. 

The origin and metamorphic development of the biotite 

gneiss and schist and of the chlorite schist and phyllite are 

uncertain. The biotite gneiss may have been a sedimentary 

rock, whose alternating beds of siltstone and arkosic 

sandstone were transformed by dynamothermal (load?) 

metamorphism into a rock in the biotite-chlorite subfacies 

of the greenschist facies (Turner and Verhoogen, 1951, p. 

446). Many of the aplitic sheets intruded subparallel to the 

foliation could be orogenic features, perhaps related to 

metamorphism itself. These events may have occurred 

during the Mazatzal Revolution (Wilson, 1939, p. 1161). 

The chlorite schist and phyllite were tectcmically deformed 

by movement along the tear faults in which the slivers lie. 

These faults were active during the Helvetian phase of the 

Laramide orogeny (Drewes, 1972b). The posttectonic 

recrystallization was probably concomitant with the 

emplacement of the youngest quartz latite porphyry plugs 

toward the end of the Paleocene. Alternatively, the 

recrystallization may be still younger and related to the 

mid-Tertiary thermal event recorded mainly in the Rincon 

Mountains. 

GRANITE GNEISS 

Granite gneiss crops out over an area of about 3 square 

miles near Cottonwood Canyon on the west flank of the 

southern part of the Santa Rita Mountains; it is shown as 

schist and granite gneiss in figure 3 and is shown in greater 

detail on the geologic map of the Mount Wrightson 

quadrangle (Drewes, 1971c). The gneiss is intruded by 

granitoid rocks that resemble the Continental Granodiorite 

or a strongly metamorphosed equivalent of that 

granodiorite. The foliation of the gneiss and the geologic 

relation with the granodiorite suggest that the gneiss is 

probably of the same general age as the Pinal Schist. Rocks 

of Paleozoic or younger age overlie, or are faulted against, 

the granite gneiss. 

The granite gneiss underlies low hills, which are 

uniformly colored a pale brownish gray, that contrast 

subtly with the more varicolored hills of volcanic rocks to 

the east and west. A northwest-trending grain, reflecting 

the strike of the foliation, helps to distinguish this terrain 

from the nearby hills of Jurassic granite. Although 

generally striking northwestward, the foliation of the 

gneiss is arcuate, concave to the northeast, and dips 

moderately to the southwest. 

In detail, the lithology of the granite gneiss varies as 

much as does that of the Pinal Schist. In the northeastern 

part of the outcrop area the rock is a faintly gneissic quartz 

monzonite. The central part of the area contains the typical 

granite gneiss, and the southwestern part contains a 

biotite-granite gneiss. Shearing and chemical alteration of 

the rocks increases toward the north and northeast, where 

faults bound the gneiss. 
8 PLUTONIC ROCKS, SANTA RITA MOUNTAINS, SOUTHEAST OF TUCSON, ARIZONA 

EXPLANATION 

Younger rocks 

l!;neous and sedimentary rocks 

of Phanerozoic age 

Continental Granodiorite and related 

rocks of Precambrian Y age 

Yc, granodiorit e, quartz monzonite, 

and aplite 

Ycc, Continental Granodiorite, concealed heneath pediment gravel 

Older rocks 

Schi.<t and granite gneiss of 

Precamhrian age 

-----------------

Contact 

Dolled where concealed 

----------------- Fault 

Dnlled where concealed 

. 9 

Moded 

Q 11 

Chemically 

analyzed 

*1 

Radiometrically 

dated 

Specimen collection sites and numbers 

0 

0 2 

31 

3 4 

3 

X Mount 

Wrightson 

4 

5 K l LOMETRES 

yr 

yr 

5 M I LES 

FIGURE 3.-Distribution of Precambrian rocks and specimen collection sites. 
PRECAMBRIAN ROCKS 9 

The granite gneiss has a hypidiomorphic-granular to 

tabular microscopic texture that is modified by an 

alinement of mineral grains and by a slight zoning of lightand dark-colored grains. In this section, some specimens 

show a seriate texture. Mineral grains are commonly 

0.2-3.0 mm long, and in some specimens the grain size 

distribution is bimodal with the smaller grains included in 

larger poikilitic grains. 

Essential minerals of the gneiss typically are quartz, 

microcline, plagioclase, and biotite, but some rocks have 

only one of the feldspars. The microcline contains very fine 

perthitic intergrowths and indistinct grid twinning that 

appears to be partly obliterated. The plagioclase 

commonly has a calcic oligoclase composition, but in some 

rocks it has an albite composition, presumable as a result 

of albitization. Biotite forms discrete subhedral plates that 

are pleochroic in yellowish brown to moderate brown and 

that are partly chloritized. In addition, the rock contains 

0.5 to 3 percent each of ilmenitic magnetite and apatite and 

trace amounts of sphene and zircon. This entire mineral 

assemblage is slightly to moderately altered to epidote, 

chlorite, sericite, kaolinite, and leucoxene. 

The granite gneiss presumably was formed by the 

metamorphism of granitoid rock. This metamorphism 

probably is part of the regional metamorphism affecting 

the Pinal Schist, for it is associated with a well-developed 

foliation and shows no increase in intensity near the 

contact with younger plutonic rocks. This rock, then, may 

well be the oldest plutonic rock of the Santa Rita 

Mountains. 

CONTINENTAL GRANODIORITE 

The Continental Granodiorite is a coarse-grained and 

coarsely porphyritic rock that forms part of a single large 

stock (or batholith?) in the northern part of the Santa Rita 

Mountains; it also forms some small intrusive bodies on 

the southwest flank of the mountains (fig. 3). The 

formation was defined and was briefly described by 

Drewes (1968); further details on its distribution are shown 

on the geologic maps of the area (Drewes, 1971b and 

1971c). The granodiorite is generally massive, but locally it 

is faintly foliated. Dark minerals are fairly abundant in this 

rock, and they typically form aggregates that form a 

meshwork around the light-colored minerals. 

The Continental Granodiorite intrudes the Pinal Schist, 

which forms roof pendants or remnants of wallrock, as 

well as some scattered inclusions. Small bodies of 

granodiorite also intrude the granite gneiss of the 

southwestern flank of the mountains. Balsa Quartzite, of 

Cambrian age, is the oldest rock overlying the 

granodiorite, but, inasmuch as these rocks seem to be 

separated everywhere by a fault, the geologic relations 

have been variously interpreted as a depositional contact 

and as an intrusive one. The fault separating the 

granodiorite from the Balsa is believed to be a regional 

thrust fault of the Piman phase of the Laramide orogeny 

(Drewes, 1972b), which followed a major unconformity. 

The complexities of this contact led to conflicting 

interpretations on the age of the granodiorite, as reviewed 

in the section on the age of that rock. 

PETROGRAPHY 

The Continental Granodiorite is made up mainly of 

granodiorite, but it includes small aplitic dikes and sills and 

small lamprophyre dikes. These small intrusive bodies 

presumably are genetically related to the granodiorite 

pluton because they are virtually coextensive with it and 

are absent in the younger rocks around it. The included 

dikes and sills are too small to be shown in figure 3 but the 

distribution of some of the larger aplitic masses are shown 

on the geologic maps of the northern part of the mountains 

(Drewes, 1971b; 1972b, pl. 5). 

GRANODIORITE 

The dominant rock type of the Continental Granodiorite 

is mostly biotite granodiorite, but in places it grades into 

biotite quartz monzonite, and it includes some 

biotite-hornblende granodiorite. The rock of the main 

outcrop area in the northern part of the mountains (fig. 3) 

is almost free of hornblende and grades, seemingly at 

random, from the biotite granodiorite to the biotite quartz 

monzonite. The rock of the small outcrop areas, to the 

southwest, contains several percent of hornblende. 

Slopes underlain by the granodiorite are somber colored 

and mostly a light brownish gray. Outcrops are small and 

irregular; even in the deepest canyons, such as Box 

Canyon, they rarely form extensive cliffs because the rock 

is abundantly fractured and disaggregates readily. As a 

result of these internal weaknesses, the local relief on 

slopes underlain by granodiorite is generally more subdued 

than that on nearby slopes underlain by Paleozoic rocks or 

by some of the younger plutonic rocks. In areas of low 

relief the granodiorite is covered thickly by grus and in all 

areas the freshest exposures are in the narrowest and 

deepest gullies or canyons. The one exception to this weak 

weathering habit occurs along the crest of the mountains 

southeast of Helvetia, where the granodiorite is very 

massive and less friable than elsewhere, and so it forms 

large rounded knobs and bosses which dominate the 

landscape. 

Unweathered specimens of granodiorite (fig. 4) are dark 

gray, commonly with a slight greenish tinge in rocks having 

perhaps as much as 20 percent dark minerals, but with a 

pinkish cast in rocks having only about 10 percent dark 

minerals. Biotite and chlorite, most abundant of the dark 

minerals, form clusters between or around the quartz and 

feldspars. Phenocrysts, which in part are actually 

porphyroblasts, are of potassium feldspar and are as much 
10 PLUTONIC ROCKS, SANTA RITA MOUNTAINS, SOUTHEAST OF TUCSON, ARIZONA 

as 4 em long. In most rocks they make up about 5 percent 

of the volume, but they are scarce or absent in some of the 

small intrusive masses on the southwest flank of the 

mountains. Compared to the phenocrysts in the younger 

plutonic rocks, they are mostly smaller and less abundant. 

The large phenocrysts of the Continental Granodiorite are 

found in the grus mantle on weathered terrane, and they 

persist as clasts in some Mesozoic conglomerates that 

overlie the granodiorite. 

The granodiorite locally contains small widely scattered 

xenoliths that are mostly of uncertain origin. A few of 

them shown in the areas of Box Canyon and Enzenberg 

Canyon (Drewes, 1971c; and about 1 mile south of 

collection site 3, fig. 3, this report) are from the Pinal 

Schist. Elsewhere the granodiorite contains smaller 

xenoliths that resemble the granite gneiss unit. Still others 

may be remnants of a hornblende gneiss or an amphibolite 

not known at the surface. 

Zones of sheared rock and veinlets of aplitic material 

and of quartz are also common features of the 

granodiorite. Some of the sheared zones are obviously 

related to mapped faults, but most of them are small and 

so widely scattered and randomly oriented as to indicate 

little more than that the rocks apparently have had a long 

and involved geologic history. The aplitic veinlets may be 

genetically related to the larger mapped bodies of aplite, 

which are described in the following section of this report. 

In thin section, the granodiorite is seen to have a 

hypidiomorphic-granular texture in which the groundmass 

FIGURE 4.- Specimen 17. Continental Granodiorite, showing porphyritic 

texture and clustered dark minerals. 

grains are 3 to 7 mm in diameter. A cataclastic texture is 

superposed on the hypidiomorhpic-granular texture of 

those specimens from the eastern bodies of hornblendebiotite granodiorite, which occur near the fault that 

bounds the Precambrian rocks. The samples from in, and 

north of, the Box Canyon area have a mosaic to sutured or 

seriate texture superposed on the granular one. Traces of 

microgranophyric texture appear in some specimens and 

the rims of many large crystals are poikilitic. Poikilitic 

grains and a bimodal distribution of groundmass grain size 

are particularly common in the southern part of the 

outcrop area of hornblende-biotite granodiorite, which 

appears to be metamorphosed by the nearby pluton of 

Squaw Gulch Granite. 

Modes of 24 samples of Continental Granodiorite, 

grouped to show the mineral composition of the 

unmetamorphosed and slightly metamorphosed rocks of 

the main granodiorite stock separately from the other 

rocks, are listed in table 2. The collection sites of the 

FIGURE 5.- Specimen 19. Slightly metamorphosed Continental Granodiorite showing indistinct grid twinning in microcline. Crystals: microcline (M), microcline or orthoclase (mo), plagioclase ( P ), quartz (Q), 

biotite (B); ilmenitic magnetite CimJ, and sphene ( S ). Crossed nicols; 

X20. 
PRECAMBRIAN ROCKS 11 

samples are shown in figure 3; and additional data in field 

notes and maps, filed in the U.S. Geological Survey 

Records Center in Denver, are keyed to this report through 

the field numbers. 

Standard techniques were used in moding the plutonic 

rocks of the area; many thin sections were preferred to a 

few rock slabs. In such coarsely porphyritic rocks as the 

Continental Granodiorite modal data involving potassium 

feldspar are most reliably obtained by using the mean of 

many counts, and even then the relatively large value of the 

standard deviation suggests that the data are insufficient. 

Point counting, using an 0.5-mm grid, was done on thin 

sections that were stained with sodium cobaltinitrate, as 

needed. Separate counts of 1,000 points each were made of 

the top and bottom halves of thin sections in an attempt to 

check the modal uniformity over a thin section area of 7 to 

8 square centimetres. The relative abundance of quartz 

between the halves of a moded thin section, reported as the 

quartz index, gives an approximate measure of the 

mineralogic uniformity of a rock at this scale. Thus, a 

quartz index of 1 implies perfect mixing, and the smaller 

the value of the index, the poorer the mixing. To some 

extent, of course, variations in grain size between rock 

types interfere with this attempt, the finer grained rocks 

giving the visual impression of being better mixed. 

However, the mean quartz index of rock types having 

similar grain size varies sufficiently to suggest that the 

degree of mixing is an intrinsic feature of the rock. 

The main mineral constituents of the granodiorite are 

quartz, two feldspars, biotite, and, in some specimens, 

hornblende. Among the light-colored grains, quartz is 

anhedral and bimodally sized in those rocks which have the 

mosaic or seriate texture. Its undulatory extinction is 

commonly large, but that of quartz of the strongly 

metamorphosed granodiorite of the southwest flank of the 

mountains is faint or absent. Plagioclase forms subhedral 

tabular crystals. The anorthite content of plagioclase from 

the biotite granodiorite is 0 to 30 percent; in about half the 

specimens crystal cores are of oligoclase and the rims 

albite, whereas in the other specimens only albite is 

present, suggesting that the granodiorite is incompletely 

albitized. The anorthite content of plagioclase from the 

hornblende-biotite granodiorite is 35 to 50 percent, in the 

range of andesine. The plagioclase of most specimens is 

moderately to intensely altered to sericite and clay 

minerals, which are stained by some iron oxide; the 

specimens from the strongly metamorphosed hornblendebiotite granodiorite are relatively unaltered. The 

potassium feldspar of most specimens forms anhedral 

subequant grains. In the unmetamorphosed rocks the 

potassium feldspar is microcline; in the other rocks it is 

either orthoclase or microcline or possibly both. Typically 

the microcline grid twinning is indistinct or blurred and 

discontinuous through a crystal (fig. 5) of the slightly 

metamorphosed rock. Most orthoclase and micro.cline is 

perthitic, with lace and patch perthite types and coarse and 

fine perthite sizes equally common (fig. 6). The albite 

phase of the perthitic crystals are moded separately; in this 

report such albite is considered to be part of the plagioclase 

component, but its abundance is tabulated independently 

to permit an alternate grouping. Albite in perthitic grains 

makes up only 2 to 3 percent of most specimens but ranges 

from 0.8 to 8.4. percent. Kaolinite alteration of potassium 

feldspar is ubiquitous and in many specimens is intense. 

Dark minerals are more abundant in the Continental 

Granodiorite than in most other plutonic rocks of the area; 

the color index of the rock ranges from 10 to 20 percent. 

Biotite, or its chlorite alteration mineral, is the most 

abundant dark mineral. It forms clusters of relatively large 

subequant grains in unmetamorphosed rocks (fig. 6) or 

felty aggregates of relatively small tabular grains in 

metamorphosed rocks (fig. 7). Biotite is pleochroic in 

yellowish brown to moderate brown. The alteration of 

biotite to chlorite is a common feature; relatively unaltered 

biotite is most common in the metamorphosed rocks, and 

the more intense the metamorphism, the more abundant 

the biotite seems to be, no doubt as recrystallized or 

secondary micas. Hornblende is pleochroic in pale 

yellowish green to pale olive green to pale bluish green. 

Some hornblende grains are poikilitic, containing quartz 

and biotite. Magnetite is invariably ilmenitic and 

commonly is clustered with biotite and sphene. The 

abundance of zircon is generally greater in this 

granodiorite than in other plutonic rocks of the area, and 

the zircon of specimen 19 (fig. 5) is probaoly hyacinth 

zircon. 

Alteration minerals are chiefly sericite, clay minerals, 

and chlorite; epidote, uralite, calcite, iron oxide, 

leucoxene, and penninite are also present in smaller 

amounts and in various combinations. 

APLITIC ROCKS 

Aplite, alaskite, and fine-grained leucocratic quartz 

monzonite bodies in the Continental Granodiorite are 

hereinafter collectively referred to as aplitic rocks of the 

granodiorite. The aplitic rocks form many intrusive masses 

too small to be shown either in figure 3 of this report or on 

the geologic maps, but the larger masses are shown on the 

map of the Sahuarita quadrangle (Drewes, 1971b). The 

quartz veinlets that were mentioned in the preceding 

section of this report as being scattered throughout the 

granodiorite may be related to the aplitic rocks but are 

unmapped because of their small size. 

The intrusive masses of aplitic rocks commonly are 

lenticular or tabular, a few feet to a few tens of feet thick, 

and hundreds of feet long. Some of the masses are 

pluglike(?) and are irregular in plan; others resemble 

closely spaced dikelets. Many of the tabular intrusive 
12 PLUTONIC ROCKS, SANTA RITA MOUNTAINS, SOUTHEAST OF TUCSON, ARIZONA 

FIGURE 6.-Specimen 12. Continental Granodiorite showing a cluster of 

large chloritized biotite crystals and part of a perthitic microcline phenocryst that has a coarse-textured lace to patch perthite. Crystals: 

microcline (M) and altered albite (a b) of the perthitic phenocryst, 

quartz (Q), chloritized biotite (cb), ilmenitic magnetite (im), calcite 

(ca) derived from alteration of biotite, apatite (ap) leucoxene ( L) 

derived from sphene, and possible zircon ( z ). Crossed nicols; X 20. 

masses are clustered in belts of subparallel-striking sheets 

in which gently inclined masses are as abundant as steeply 

inclined ones. The contact of most of the aplitic rocks with 

the granodiorite is sharp, but in a few places, such as the 

hills a mile southwest of the cemetery below Helvetia and 

around the large aplitic mass 1 to 1.5 miles south of Box 

Canyon (Drewes, 1971b), the contact is apparently 

gradational. 

The aplitic rocks weather yellowish gray rather than the 

more somber brownish gray of the granodiorite, and 

outcrops of aplitic rocks are more resistant to weathering 

and hence are more abundant and somewhat more rugged 

than those of the granodiorite. Outcrops of aplitic rocks 

commonly form narrows and falls where they cross the 

bottoms of canyons. Small angular blocks of aplitic rocks 

are strewn around the outcrops, along with a grus that does 

not contain large chips of feldspar phenocrysts. 

, • ~ ,J 1 I T 

FIGURE 7 .- Specimen 17. Continental Granodiorite showing part of a 

phenocryst or porphyroblast and small felly-textured recrystallized 

biotite. Crystals: orthoclase or microcline (om), quartz (Q), plagioclase ( P), biotite (B), and altered albite (a b) in fine lacy perthitic 

intergrowths, ilmenitic magnetite (im), sphene ( S ), apatite (a p), and 

zircon ( Z ). Crossed nicols; X 25. 

Mineral grains of the aplitic rocks are mostly 1 to 2 mm 

in diameter and are arranged in an idiomorphic-granular 

texture. Most of the aplitic masses have a felty or granular 

nonporphyritic texture; some have a few phenocrysts, 

which are generally less than 7 mm long. 

The assemblage and abundance of minerals in the aplitic 

rocks differ slightly from those of its granodiorite host. 

Modal analyses of two rocks, specimens 23 and 24, are 

given in table 2. Estimated modes of three addition~! 

rocks, not presented in the table, show some variations 

from the tabulated modes; the mica of one rock is biotite, 

that of another is muscovite, and the third contains both 

micas. Likewise, apatite and zircon are in only some of the 

rocks and not consistently together. And finally, the 

potassium feldspar is orthoclase in some rocks and 

microcline in others. Throughout the aplitic rocks, though, 

the plagioclase is either albite or oligoclase. The albite in 

perthitic grains is finely lacy and rarely exceeds a few 
PRECAMBRIAN ROCKS 

percent by volume. Biotite occurs either as widely scattered Quartz 

0 

13 

chloritized flakes or as unaltered inclusions in quartz. Felty 

aggregates of small biotite crystals, typical of recrystallized 

rocks, are found in the aplitic rocks 1 to 2 miles southwest 

of Helvetia. Sericite and clay minerals are abundant 

alteration products in the aplitic rocks. 

LAMPROPHYRE 

Small dikes of dark-greenish-gray rock are sparsely 

scattered throughout the Continental Granodiorite. Some 

dikes occupy dilation fractures as much as 3 feet wide and 

are a fine-grained dioritic rock. Other dikes form short 

tabular bodies as much as 10 feet wide and are a finely 

porphyritic dacite or andesite. The outcrops of both rock 

types are inconspicuous and generally lie in small sags and 

low areas. 

A few specimens of lamprophyre have an ophitic to 

subophitic texture, with crystals 0.1 to 0.3 mm long. A few 

acicular crystals and rare phenocrysts are as much as 4 mm 

long. Plagioclase, potassium feldspar, and an amphibole 

are the most abundant minerals; quartz and pyroxene(?) 

are present in small amounts, and magnetite, apatite, and 

zircon occur in trace amounts. The plagioclase has a 

composition of albite, probably as a result of diagenetic(?) 

albitization. Alteration minerals, such as sericite, clay 

mineralsl, chlorite, and epidote, are abundant. 

In the Santa Rita Mountains, many of the plutons and 

their host rocks contain lamprophyre dikes. Although 

slightly variable in habit, texture, and phenocryst 

mineralogy from dike to dike, the lamprophyre dikes of 

some plutons are uniform. In the absence of a considerably 

more detailed study of these dikes, they are considered 

simply as lamprophyres from late-phase magmas of the 

plutons with which they are associatied, rather than as the 

result of distinctly later and genetically unassociated 

magmatic events. 

MODAL AND CHEMICAL SUMMARY 

For ease of comparison of the abundant analytical data 

on the plutonic rocks, the tables of analyses are augmented 

by a series of modified triangular diagrams summarizing 

the modes and by a series of histograms summarizing the 

chemical analyses. 

The triangular diagram summarizing the modes consists 

of two parts (fig. 9): the left half is part of a standard 

quartz-potassium feldspar-plagioclase diagram, following 

the general method of Johannsen (1939, p. 152) and as 

used by Bateman (1961, p. 1524) and by Ross (1969, p. 7). 

The quartz-rich corner is eliminated, as it is unoccupied by 

analyses of the plutonic rocks of the Santa Rita Mountains 

suite; and the right half is a similar but smaller segment of 

a quartz-plagioclase-fernie mineral triangular diagram. 

Together, these two parts of the diagram represent the 

front and right side of a tetrahedron (fig. 8) showing the 

Potassium K 

feldspar 

p 

Plagioclase 

FIGURE 8.-Isometric diagram of a modal tetrahedron whose apices 

QK P F represent, respectively, the quartz, potassium feldspar, plagioclase, and fernie minerals. The solid A B C D K P is a hemitetrahedron. The solid E G H J K P is the body whose front face, E K P J , 

and right side, J PH, are projected into the plane of the modified triangular diagrams, such as that of figure 9. The true mode of hypothetical specimen, s, (having 16 percent quartz, 16 percent orthoclase, 48 

percent plagioclase, and 20 percent fernie minerals) is first plotted as 

s ' on the leucocratic face, QK P, of the tetrahedron in the usual 

manner, the fernie component having been subtracted and the others 

recalculated to 100 percent. The projection of the true mode on the 

right face, Q P F, of the tetrahedron is then plotted as s along the 

edge, L F, of plane L F M, on which s, s ', and s" all lie. 

three major leucocratic components of granitoid rocks plus 

the combined fernie mineral component. The method of 

plotting the fernie component is illustrated in figure 8; the 

resulting diagram slightly exceeds in size a hemitetrahedron 

in the example shown in figure 9 but equals a 

hemitetrahedron in all following examples. In figure 9 the 

right side of the oversized hemitetrahedron is rotated into 

the plane of its front face. Each mode is represented by two 

points on the diagram, one showing the relative abundance 

of the leucocratic components and the other the actual 

abundance of the fernie component. The true composition, 

in terms of these four components, must be visualized as a 

projection within the tetrahedron controlled by the two 

points shown. The method of projection shown in figure 8 

gives both the recomputed data shown on the conventional 

triangular diagram plus actual data on the fernie 

component, which the recomputed data on a triangular 

diagram showing quartz, plagioclase, and fernie end 

members would not. 

A composite of the modal analyses of the Continental 

Granodiorite (fig. 9) shows the unmetamorphosed rocks to 

be scattered in a fairly compact subspherical body centered 
14 PLUTONIC ROCKS, SANTA RITA MOUNTAINS, SOUTHEAST OF TUCSON, ARIZONA 

Rock type ............... 

Specimen No ............. I 2 

Field No ................ 914 1034 

Quartz .................. 15.8 28.1 

Plagiclase, total .......... 32.8 35.1 

(plagioclase in perthite) (8.4) (1.0) 

Microcline .............. 36.0 19.8 

Orthoclase . . . . . . . . . . . . .. 0 0 

Biotite .................. 12.4 12.8 

Hornblende ............. 0 0 

Magnetite ............... 1.5 2.0 

Apatite ................. . 6 .4 

Sphene ............. .... .7 1.8 

Zircon ............... ... 0 . 05 

Allanite .............. ... 0 0 

Rutile .... . . . . . . . . . . . . . . .05 0 

Muscovite ............ ... 0 0 

Pyrite .. . . . . . . . . . . . ... .I 0 

Total ... ... .. ····· 99.95 100.05 

Fernie .... ... ..... 15.4 17.0 

Percent anthoritc 

in plagioclase ... ....... 5-10 0-10 

Quart/ mixing 

index (sec text) .. ... .81! .79 

TABLE 2.-Mode(inpercent) 

[Field numbers are abbreviated, symbols showing year of collection and collector's initial omitted. Full field number of specimen 1 thus 

Granodiorite (includes quartz monzonite) Slightly (regionally?) 

metamorphosed 

granodiorite 

and quartz monzonite 

3 4 5 6 7 8 9 10 II 12 113 1-13 14 15 16 

1014 997 1022 913 994 899b 898 100 897 104 627 Mean s 1220 1191 1142: 

19.9 30.5 21.5 24.4 24.5 22.8 29.0 32.2 25.1 16.4 20.5 23.9 5.1 28.2 32.8 46.3 

52.6 43.4 46.9 41.0 45.8 42.2 39.6 39.4 42.8 26.7 56.5 41.9 7.9 35.4 32.9 27.6 

(0.2) 0 (1.2) (0.8) (0.8) (3.5) (2.6) 0 (1.5) 0 0 (1.5) (2.3) 0 (5.1) (2.0) 

12.4 8.1 19.1 25.0 12.7 21.8 15.3 13.7 II. I 38.6 9.0 18.7 9.7 0 17.5 17.4 

0 0 0 0 0 0 0 0 0 0 0 0 . .. 15.2 0 0 

13.2 13.0 9.1 7.8 13.2 9.8 12.1 10.7 16.2 11.7 10.1 11.7 2.2 15.4 14.0 6.6 

0 0 0 0 0 0 0 0 0 0 .2 Tr. ... 0 0 0 

1.7 3.9 1.4 .4 1.5 1.7 .9 3.0 2.4 2.9 2.2 2.0 .9 4.4 1.9 1.6 

Tr . .6 .4 .4 .5 .4 .6 .8 1.0 1.0 .4 .5 .3 1.0 .9 .IS 

0 Tr. 1.6 .5 1.8 1.2 2.4 0 1.4 0 .9 .9 .8 .05 Tr. .4 

.2 .05 .05 Tr. Tr. .05 .05 .I .05 .2 .2 .I . I .4 Tr . Tr . 

0 0 0 .5 0 0 .05 0 0 0 0 Tr. ... 0 0 0 

0 0 0 0 0 0 0 0 0 0 0 Tr. ... 0 0 0 

0 .5 0 0 0 0 0 0 0 0 0 Tr. 0 0 0 0 

0 0 0 0 0 0 0 0 0 0 0 Tr. ... 0 0 0 

100.0 100.05 100.05 100.0 100.0 99.95 100.0 99.9 100.05 97.5 100.0 99.7 ... 100.05 100.0 100.05 

15.1 18.1 12.5 9.6 17.0 13.2 16.1 14.6 21.0 16.8 14.0 15.2 2.9 21.2 16.8 8.7 

5-10 5-10 0 0 0-5 0-5 0 0-5 5-10 3 27-30 0-10 ... 0 0-5 . .. 

.92 .86 .77 .89 .91 .93 .91 .82 .95 ... .92 .88 .06 .89 .86 .77 

I Mode of specimen 13 has affinity to metagranodiontc. 

POTASSIUM 

FELDSPAR EXPLANATION 

~ 

Granodiorite and quartz 

monzonite, unmetamorphosed 

and weakly metamorphosed 

~ 

Granodiorite and quartz 

monzonite, strongly metamorphosed 

El 

Fine-grained quartz monzonite 

and aplite 

Estimated shift in composition 

resulting from adjustment of 

phenocryst abundance 

FIGURE 9.-Modified triangular diagram showing modal quartz, potassium feldspar, plagioclase, and fernie minerals of Continental Granodiorite. 

Abundance of quartz in specimen 16 may be anomalously large. 

near a point about 15 percent of the distance from the 

granodiorite field toward the fernie point of the 

tetrahedron. The body circumscribing the modal analyses 

of the metamorphosed rocks is larger and less regular. In 

.subsequent sections of this report the skewness of the 

modal bodies thus represented will vary considerably. 
PRECAMBRIAN ROCKS 15 

of Continental Granodiorite 

is 650914. Symbols s, standard deviation; Tr., trace; ... , not determined] 

Slightly (regionally?) metamorphosed Strongly contact Fine-grained granodionte and quartz metamorphosed quartz monzonite monzonite-Continued metagranodiorite and aplite phase 

17 18 19 14-19 l-19 20 21 22 23 24 

1152 1043 1046 Mean s Mean s 620 611,686 614 1106 1104 

31.0 27.7 27.8 32.3 6.8 26.8 6.8 10.2 4.3 15.8 21.8 36.0 

42.8 41.5 31.0 35.2 7.8 39.8 7.8 36.3 55.4 42.4 46.4 19.8 

(1.2) (Tr.) (4.9) (2.2) (2.3) (1.7) (2.3) (2.4) 0 (2.5) (5.4) (9.0) 

9.4 0 7.6 8.7 10.1 15.5 10.1 42.0 0 0 27.5 42.7 

0 18.0 18.0 8.5 6.4 2.7 6.4 0 .5 29.4 0 0 

13.0 9.4 11.6 11.7 2.5 11.7 2.5 9.3 5.6 7.5 3.5 .7 

0 0 0 0 ... Tr. . .. .9 29.2 .I 0 0 

1.9 1.8 1.9 2.3 1.0 2.1 1.0 1.0 2.5 3.4 .4 .5 

. 9 .6 .9 .7 .3 .6 .3 Tr . .7 .6 .2 Tr . 1.0 .9 1.1 .6 . 7 .8 .7 .I 1.8 .8 .2 .I 

.05 .I .I .I . 2 .I .2 .I 0 Tr. .05 Tr. 0 0 Tr. Tr. Tr. Tr. ... 0 0 0 0 .15 

0 0 0 0 ... 0 . .. 0 0 0 0 0 

0 0 0 0 ... 0 0 0 0 0 0 0 0 0 0 0 ... 0 . .. 0 0 0 0 0 

100.05 100.0 100.0 100.1 ... 100.1 ... 99.9 100.0 100.0 100.05 99.95 16.8 12.8 15.6 15.4 4.2 15.3 3.2 11.4 39.8 12.4 4.3 1.5 

5-15 0-5 5-1(1 0-10 ... 0-10 ... 37-40 28-31 5-35 0-5 0 

.93 .92 .98 .89 .06 .88 .05 .67 .58 .98 .83 .84 

The chemical and spectrographic analyses and calculated 

CIPW norms are listed in table 3 and the chemical analyses 

of the Continental Granodiorite and of the other plutonic 

rocks are summarized in figure 10. Inasmuch as this study 

was part of a general geological investigation, rapid rock 

analytic techniques and semiquantitative spectrographic 

methods were used. Chemically, the Continental 

Granodiorite closely resembles the average granodiorites 

reported by Johannsen (1932, p. 344) and by Nockolds 

(1954, p. 1014). Most noteworthy of the spectrographic 

results is the decrease in the abundance of copper and lead 

in the metamorphosed granodiorite near Helvetia 

compared to the content in unmetamorphosed 

granodiorite near Greaterville. This change reflects the 

variations in the copper content of mica, described by 

Lovering and others, (1970), and studied in greater detail 

in some rocks of the nearby Sierrita Mountains by Banks 

(1974). 

AGE AND CORRELATION 

The Continental Granodiorite has not been precisely 

dated by radiometric means. Lead-alpha dates indicate an 

age of at least 1,450 m.y. (Drewes, 1968, p. C5); rubidiumstrontium and potassium-argon dates are discordant with 

the lead-alpha date, and they suggest that later thermal 

events have modified at least many of the available 

radiometric ages. The granodiorite is thus considered to be 

at least 1,450 m.y. old and it may be 1,600 to 1,700 m.y. 

old. 

Geologic means do not permit the dating of the 

granodiorite with complete confidence either, but the field 

relations also suggest a Precambrian age. The fault 

separating the Cambrian Bolsa Quartzite from the 

granodiorite has been described in the introductory section 

on the Continental Granodiorite as following an 

unconformity. In addition, cobbles of granodiorite 

resembling the Continental occur in conglomerate lenses 

intercalated in the Triassic Mount Wrightson Formation 

(Drewes, 1971a, p. 12); if the cobbles are derived from the 

Continental, the pluton must be at least as old as Triassic. 

Furthermore, the granodiorite has a distinctly older 

appearance through its alteration, shear zones, and local 

areas of faint foliation, than the plutonic rocks of Triassic 

and younger ages in the Santa Rita Mountains . 

Radiometric ages of 11 plutonic rocks of the Santa Rita 

Mountains are listed in table 4. The general locations from 

which the dated samples were collected are shown in figure 

3; and detailed locations of two sample sites are shown on 

the geologic map of the Sahuarita quadrangle (Drewes, 

1971 b). The detailed collection site of the third sample is 

not shown on the geologic map of the Mount Wrightson 

quadrangle (Drewes, 1971c); it lies in the Mavis Wash area, 

just east of the middle one of three small areas mapped as 

Bolsa (?) Quartzite, in the larger outcrop area of contactmetamorphosed Continental(?) Granodiorite. 

Three samples of granodiorite are radiometrically dated, 

two of them by two methods each. Sample 21 is probably 

thoroughly recrystallized and sample 19 is slightly 

recrystallized, features which were not initially recognized 

in the field. The lead-alpha ages of zircons of specimens 1 

and 19, 1,360 m.y. and 1,450 m.y., are probably nearest to 

the true age of the rock, for the zircon would be among the 

minerals most refractory to change by thermal 

metamorphism. The rubidium-strontium whole-rock age, 

800 m.y., only corroborates a Precambrian age of 

specimen 1; perhaps a very mild metamorphism, 

petrographically not noticeable and so not considered in 

tables 2-4, has resulted in loss of radiogenic strontium 

from this rock. The potassium-argon age of 55 m.y. of 

specimen 19 coincides closely with the ages of the Helvetia 

stocks, the nearest of which lies 2Y2 miles to the north, and 

the biotite of the rock of the intervening area is subtly 

recrystallized. The other potassium-argon age, 159 m.y. 

(sample 21), dates the age of crystallization of an 

anomalously fresh-looking granodiorite variety as 

Jurassic, in an area of rock otherwise resembling the 

Continental Granodiorite. The granodiorite lies within a 

few hundred feet of a concealed contact of Squaw Gulch 

Granite, of Jurassic age, and apparently was contact 

metamorphosed by that granite. 

The laboratory measurements and constants used in 

calculating the ages shown in table 4 are listed by Marvin 

and others (1973). 

Plutonic rocks resembling the Continental Granodiorite 

occur in the Rincon and Sierrita Mountains and possibly 
16 PLUTONIC ROCKS, SANTA RITA MOUNTAINS, SOUTHEAST OF TUCSON, ARIZONA 

TABLE 3.-Chemica/ and spectrographic analyses and CIPW norms of Continental Granodiorite 

[Chemical analyses by rapid rock method (Shapiro and Brannock, 1962), with analyses of specimens I, II, 14, and 19 supplemented by atomic absorption method and others supplemented by X-ray 

fluorescence method. Chemical analyses by Lowell Artis, S. D. Botts, G. W. Chloe, P. L. D. Elmore, John Glenn, J. Kelsey, H. Smith, and Dwight Taylor. Spectrographic analyses 

(semiquantitative method) by W. B. Crandell, J. L. Finley, J. C. Hamilton, and A. L. Sutton. Elements looked for but not found: As, Au, B, Bi, Cd, Eu, Ge, Hf, Hg, In, Li, 

Pd, Pr, Pt, Re, Sb, Sm, Sn, Ta, Te, Th, Tl, U, W, and Zn. Symbols: s, standard deviation:<, less than; .... , not determined; Tr., trace; N, not detected] 

Rock type. 

Slighty Granodiorite Strongly contact Granodiorite and quartz monzonite metamorphose<i and metamorphosed 

granodioritr quartz monzonite metagranodiorite 

Specimen No .. .... .... . ...... I II 12 13 14 I 1- 14 19 1- 19 20 21 

Field No. 914 897 104 Mean s Mean s 6)) 1

....... ......... .. 627 1220 1046 • I 620 

Chemical analyses (weight percent) 

Si02. 59.0 67.4 69.4 64.6 67.8 65.6 4.1 67.4 65.9 3.7 64.3 59.7 

AI203 17.4 14.4 12.4 17.6 14.0 15.2 2.3 14.3 15.0 2.1 17.4 17.4 

Fe203. 3.4 2.2 3.6 1.0 1.8 2.4 1.1 3.0 2.5 1.0 2.1 3.3 

FeO ..... 3.0 2.1 1.3 1.2 3.0 2.1 .9 2.0 2.1 .8 2.3 3.3 

MgO .... ...... ... 1.2 1.2 .61 1.2 1.3 1.1 .3 .91 1.1 .3 .90 2.0 

CaO ..... ...... .. ....... .... 2.9 2.7 1.7 5.2 2.0 2.9 1.4 3.3 3.0 1.2 4.5 4.9 Na2o. 3. 7 2.8 3.8 4.2 2.3 3.4 .8 3.1 3.3 .7 4.6 3.8 

K20 . 6.9 4.1 4.5 2.2 5.3 4.6 1.7 2.8 4.3 1.7 2.2 2.9 

H20-. .08 .II .13 .33 .08 .15 .II .14 .15 .09 .08 .16 

H20+ 1.0 1.2 1.2 1.0 .42 1.0 .32 .82 .95 .29 .70 .76 

Ti02. .46 .18 .92 .74 .83 .63 .30 1.0 .69 .31 .52 1.0 

P205. .42 .29 .34 .28 .27 .32 .06 .43 .34 .07 .22 .47 MaO. ······· .12 .12 .12 .08 .13 .II .02 .08 .II .02 .12 .13 C02. <.05 .36 .34 .II .05 .16 .18 .05 .14 .17 .05 .08 

Total ................. 100 99 100 100 99 100 ... 99 100 . .. 100 100 

Spectrographic analyses (weight percent) 

Ag .......... ············ .. 0 0 0.0005 0 0 Tr. . .. 0 Tr. . .. 0 0 

Ba ········ .. ············ .. .2 .15 .2 .2 .I .17 .04 .07 .15 .06 .2 .15 

Be ······· ... . . . . . . . . . . . . .0001 .0002 0 .0002 .0003 .0002 .0001 0 .0001 .0007 .0002 0 

Ce .... ... ... ············ .02 .02 .015 0 .05 .02 .02 N N N 0 .02 

Co ..... ... ... .. . ... .. .... .002 .001 .001 .0007 .001 .001 .0004 .007 .002 .002 .001 .0015 

Cr .... ..... ..... .... ... .0015 .002 .001 .0005 .01 .003 .004 .002 .003 .004 .0003 .001 

Cu. ······ ... ....... . ..... .003 .02 .I .00015 .005 .03 .04 .007 .02 .04 .0005 .002 

Ga .. ..... .. ... . .. ... .. .0015 .0015 .003 .002 .0015 .002 .001 N N N .002 .001 

La ······· ..... ....... ... .. .02 .01 .005 0 .01 .009 .007 .007 .009 .007 .01 .005 

Mo. ······· ..... .. ........ .. 0 0 0 0 .0003 Tr. N 0 Tr. N 0 .0003 

Nb. ········ .... .. ........ .0005 .0007 .0015 0 .002 .0009 .0008 0 .0008 .0008 0 0 

Nd. ... ..... ... .. .02 .015 .007 0 0 .008 .009 N N N .005 0 

Ni ..... ........ .... ... ..... <.003 < .003 .0007 .0015 .002 .002 .003 .003 .002 .001 .0005 <.003 Pb. ..... .... ... .. .007 .007 .07 .0015 .002 .02 .03 .0015 .01 .03 .0015 .001 

Sc. ·········· .... ......... .002 .001 .001 .0015 .002 .0015 .0005 .007 .002 .002 .002 .002 

Sn ..... ...... ...... ... .0005 .0007 0 0 0 .0001 .015 0 .0002 .0003 0 0 Sr .. ... ... ...... . .. ...... ... .03 .02 .03 .I .02 .04 .03 .003 .03 .03 .01 .07 

V. ... ... ... .007 .007 .007 .01 .007 .008 .001 .02 .01 .005 .007 .015 

Y. .... ... ... ... .005 .005 .005 .002 .01 .005 .003 .0015 .005 .003 .003 .003 

Yb. .... ...... .0005 .0005 N .0003 .001 .0005 .0003 N N N .0007 .0003 

Zr ··········· ..... .... .03 .05 .03 .015 .03 .03 .01 .007 .03 .01 .015 .03 

CIPW norms 

Q 3.6 29.0 27.6 19.9 27.7 

c 0 2.0 0 0 1.6 

or. 40.9 24.4 26.6 13.0 31.5 

ab 31.4 23.9 32.1 35.5 19.6 

an 

r~ 10.5 9.3 3.5 22.7 7.9 

.35 0 .23 .24 0 

di en .... .19 0 .20 .19 0 

f'··· .II 0 0 .02 0 

hy en ... 2.8 3.0 1.3 2.8 3.3 

r, .. 2.0 2.0 0 .28 2.9 

mt 4.9 3.2 1.9 1.5 2.6 

hm 0 0 2.3 0 0 

il .87 .34 1.7 1.4 1.6 

ap 1.0 .69 .80 .66 .64 

cc .II . 82 .77 .25 .II 

Total 98.7 98.7 99.0 98.4 99.5 

Fernie 12.3 10.1 9.2 7.3 11.2 

also in the Empire and Patagonia Mountains (fig. 1). In the 

Rincon Mountains (Drewes, 1974) a gneissic granodiorite 

porphyry that intrudes Pinal Schist and is intruded by 

other less foliated rock of probable Precambrian age is 

believed to be a strongly metamorphosed equivalent of the 

Continental Granodiorite. In the Sierrita Mountains, rocks 

originally mapped by J. R. Cooper (written commun., 

············ .. .......... 31.8 ..................... 18.1 13.7 

······················· 1.3 ····················· 0 .4 

························ 16.7 ····················· 13.0 17.1 

···················· ... 26.4 ····················· 38.9 32.1 

······················· 13.3 ..................... 20.3 20.7 

················· ...... 0 ····················· .23 0 

....... ................ 0 ····················· .12 0 

······················· 0 ..... ················ .10 0 

..... . . . . . . . . . . ......... 2.3 ····················· 2.1 5.0 

······················· 0 ····················· 1.8 1.9 

.... ···················· 3.8 . .................... 3.0 4.8 

························ .38 ····················· 0 0 .............. .......... 1.9 ······ ··············· 1.0 1.9 

························ 1.0 ······· .............. .52 1.1 

...... ·················· .11 ····················· 0 .18 

.. ·········· . . . . . . . . . . . . 99.0 ····················· 99.2 98.9 

························ 9 . .5 ····················· 8.9 14.9 

1970) as granite and diorite of Precambrian age, and 

schist and gneiss of undetermined age resemble, 

respectively, the unfoliated and the foliated varieties of the 

Continental Granodiorite, with which I have correlated 

them (Cooper, 1974). On the northern flank of the Empire 

Mountains T. L. Finnell (pral commun., 1972:) has mapped 

Precambrian plutonic rocks, some of which resemble a 
TRIASSIC AND JURASSIC ROCKS 17 

TABLE 4.-Summary of radiometric age determinations of plutonic rocks of the Santa Rita Mountains 

Specimen Field Formation Geologic 

No. No. (pluton) age 

197 650687 Granodiorite of the San (late?) Oligocene .. 

Cayetano Mountains. 

189 6601185l 192 6701245 

(2) 6801472 

Aphanitic rocks (late?) Paleocene .... 

(Greaterville plugs). 

163 

163 6601051 66D1051 ! 174 70DI612 

Granitoid rocks (late?) Paleocene .... 

(Helvetia stocks). 

160 63D281 } 

158 364D660 (Gringo Gulch pluton) .. Paleocene .. 

132 6507S4 ~ 

139 650876 

Elephant Head Quartz Late Cretaceous .... 

Monzonite (Quantrell 

stock). 

(2) RM-6-63 Madera Canyon Late Cretaceous ..... 

Granodiorite. 

80 

610316} 

83 63R292 

101 5630507 (2) F-33-68 

Josephine Canyon Late Cretaceous ... 

Diorite. 

Granitic rock (Corona Late Cretaceous ..... 

stock). 

. 54 64D605} 

45 63D282 

Squaw Gulch Granite ... Jurassic ........... 

34 630280 Piper Gulch Monzonite Triassic ............ 

65D914 } 

19 65DI046 Continental Grano- Precambrian ...... 

diorite. 

21 665D686 Continental Grano- Precambrian(?) ..... 

diorite(?). 

I Map 1-614 (Drewes, 197lc); map·l-613 (Drewes, 1971b). 

2 Not given a specimen number; no modal or chemical analyses available. 

3 Specimens 64D660 and 64D661 were collected from nearly the same outcrops; the dated 

rock has coarser phenocrysts than the moded one. 

nonporphyritic and finer grained variety of Continental 

Granodiorite and others of which resemble different 

plutonic rocks like ones found in the Rincon and 

Whetstone Mountains. Precambrian plutonic rocks of the 

Patagonia Mountains (Simons, 1974) also include coarsely 

porphyritic granodiorite with a general resemblance to the 

Continental. Although rocks similar to the Continental 

Granodiorite seem. to be fairly widespread, there is no 

evidence to suggest that all known occurrences are from 

the same pluton, or indeed are of identical age. 

TRIASSIC AND JURASSIC ROCKS 

Plutonic masses were intruded into the area of the Santa 

Rita Mountains during the Triassic and Jurassic Periods, 

approximately coinciding with times of abundant volcanic 

activity. This magmatic activity followed a long quiescent 

interval that began after the emplacement of the 

Continental Granodiorite in the Precambrian. The 

magmatic activity of the early Mesozoic began with the 

Dating Radiometric Comment Collection method age(m.y.) siteshownl 

K-Ar 27.6 ± 0.8 Genetically related to Map 1-614. Grosvenor Hills Volcanics (Drewes, 1972). 

l t•± ''! Map 1-613. K-Ar 56.3 ± 2.1 "Ore porphyry" quartz Map 1-613. latite porphyry. 

55.7± 1.9 Fig. 40, this report. 

t'± "! l M•p 1-613. K-Ar 53.5 ± 2.0 Barren stocks, geologi- Map 1-613. cally older than "ore 

53.9± 2.0 porphyry." Fig. 40, this report. 

{60.3 ± 6.0 Microgranodiorite ..... Map 1-614. K-Ar 

60.4 ± 6.0 Hornblende dacite porphyry ............... Map 1-614. 

rA· Ph-alpha 170 ~.2± ± 20 '"} {Map 1-614. Rock without recrystalli- K-Ar 69.0 ± 2.9 zation texture. Pb- Map 1-614. Ph-alpha 188 ± 40 alpha ages may reflect 

a Jurassic history, now 

nearly obliterated. K-Ar 67.9± 2.1 Collected and dated by Map 1-614. 

P. E. Damon (written 

467.1 ± 7.0} 

commun., 1964). 

rA· Quartz diorite phase .... Map 1-614. Ph-alpha 62 ± 10 

Ph-alpha 63 ± 10 Map 1-614. 

Ph-alpha 61 ±20 Quartz monzonite phase ..... Map 1-614. 

K-Ar 73.8± 2.6 Quartz diorite collected Open-file map. 

and correlated byT. L. 

145±4 Finnell. 

{K-Ar Ph-alpha 160±20 } ························· .... Map 1-614. 

Ph-alpha 161 ±20 Map 1-614. 

Ph-alpha 184± 20 Map 1-614. r .. ~ ... 14SO± 100 ~ { Map 1-613. 

Rb-Sr 8oo± 80 Biotite has recrystalliza- K-Ar 55± 1.7 tion texture; nearby Map 1-613. 

Pb-alpha 1360 ± 270 stocks 53-55 m.y. 

old. K-Ar 159± 5 Nearby stock 145-161 Map 1-614. 

m.y. 

4 Reported as 67± 3 by Marvin and others (1973, table I, no. 3). 5 Specimen 63D507 and 63D276, referred to in other tables, from same outcrop. 6 Specimens 650686 and 64D611, referred to in other tables, from same outcrop. 

locally prolific volcanism that formed the Mount 

Wrightson pile (Drewes, 1971a) and followed near the end 

of the Triassic with the intrusion of a stock of the Piper 

Gulch Monzonite and smaller masses of quartz diorite. 

About this time, or slightly later, volcanism is again 

recorded, in the Upper Triassic and Lower Jurassic Canelo 

Hills Volcanics. Near the middle of Jurassic time a 

batholith of Squaw Gulch Granite was emplaced in the 

southern part of the area. Finally, between the Middle 

Jurassic and the onset of the Laramide orogenic events in 

the mid-Cretaceous, magmatic activity dwindled; of three 

formations, only the oldest two contain volcanic rocks. 

PIPER GULCH MONZONITE 

The Piper Gulch Monzonite, defined by Drewes (1968), 

is a very coarse grained dark-gray rock almost unique in its 

Triassic age and monzonite to syenodiorite composition to 

this part of Arizona. The monzonite underlies many small 

areas and a larger one, together not exceeding 4 square 
18 PLUTONIC ROCKS, SANTA RITA MOUNTAINS, SOUTHEAST OF TUCSON, ARIZONA 

60 

55 

fz 

w 

u 

a: 

w 

~ 15 I 

(!) 

~ 

10 

15 

10 

A 

Continental Granodiorite, 

exclusive of strongly 

metamorphosed granadiorite (6) 

G 

Granitoid stocks of 

Helvetia stocks, exclusive 

of Sycamore stock (9); 

broken line, quartz diorite 

of Sycamore stock (2) 

55iJ 

15 

10 

70~ 

15 

10 

5 

B 

Piper Gulch 

Monzonite (3) 

H 

Quartz latite porphyry 

of Greaterville plugs (6) 

65 

60 

c Joseph me Canyon 

D1orite, exclusive of 

55 fine-grained quartz 

monzonite (6); broken 

line, fine-gramed quartz 

monzonite (3) 

15 

10 

70~ Squaw Gulch Granite (4) 

15 

10 

5 

60 

55 

15 

10 

70~ 

15 

10 

D 

Madera Canyon 

Granodiorite (5) 

J 

Quartz monzonite 

of Corona stock ( 1) 

FIGURE 10.-Histograms showing average chemical composition of each group of plutonic rocks. Parenthetic figures 

miles. These outcrop areas lie mainly in a belt that extends 

from the middle reaches of Temporal Gulch 

northwestward to the west wall of Madera Canyon, shown 

in general fashion in figure 11 and shown in greater detail 

on the geologic map of the Mount Wrightson quadrangle 

(Drewes, 1971c). Monzonite underlies part of the east wall 

of Madera Canyon, and very small masses of monzonite lie 

well southwest of the main belt of outcrops. The 

monzonite intrudes the Mount Wrightson Formation and 

is extensively intruded by the Squaw Gulch Granite and 

some younger rocks. The masses of monzonite included 

within the younger intrusive bodies are elongated and 

oriented parallel to the northwest-trending belt of 

outcrops. Where the monzonite inclusions are abundant, 

as between specimen collection sites 38 and 30 in figure 11, 

they may once have formed a single elongate stock. 

Indeed, that stock may have extended the length of the 

outcrop belt to site 25. 

The intrusive contact of the monzonite with older rocks 

if; fairly sharp, but that of the younger rocks with the 
TRIASSIC AND JURASSIC ROCKS 19 

70l 

~ 15 w 

u 

a: 

g: 

>--

I 

810 

;: 

>-

z 

w 

u 

a: 

w 

0. 

5 

15 

!;: 10 

"' iij 

;: 

701J 

£ 15 Microgranodiorite of 

Gringo Gulch stock ( 1); 

broken line, dacite porphyry of Gringo Gu lch 

stock (1) 

10 

5 

K 

Elephant Head 

Quartz Monzonite (4) 15 

10 

show number of analyses averaged. 

F 

Granodiorite of San 

Cayetano stock ( 1) 

L 

Composite of Squaw Gulch 

Granite (patterned), quart z 

monzonite of Corona stock 

(heavy line), and Elephant 

Head Quartz Monzoriite 

(dashed line) (9) 

Quartz 

monzonite 

of Corona 

monzonite is broadly gradational in many places. For 

example, west of Madera Canyon the monzonite is 

gradually assimilated over a zone hundreds of feet wide. 

The attitudes of the monzonite contact with the host rocks 

is gentle along the upper reaches of Temporal Gulch and 

farther north, but it is steep to the southeast. The caps of 

host rock on the higher hills west of the upper reaches of 

Temporal Gulch even suggest that the top of this part of 

the monzonite stock lies at the level of the tops of these 

hills. The host rock near the contact with the monzonite is 

strongly contact metamorphosed to a sugary-textured 

metavolcanic rock with intercalated quartzite. Secondary 

minerals, such as schorlite tourmaline, are fairly abundant 

in pockets and in rosettes along fractures in the 

metamorphosed rock. Mineralization of the host rock, 

such as that evident in the Mansfield Canyon area (Drewes, 

1973), is probably related to younger intrusive rocks 

although some pyrite in and near the Piper Gulch could be 

related to the monzonite. Younger rocks not only intrude 

the monzonite, but, toward the south, rocks of Early 

Cretaceous age unconformably overlie it. 

The appearance of the Piper Gulch Monzonite in 

outcrops varies, apparently largely as the result of a 

difference in the friability of the rock. In many of the 

southwestern areas the rock forms but few and small 

outcrops, and these typically occur in topographically low 

positions in which grus forms a fairly thick, though 

discontinuous, veneer. The grus that formed on a 

monzonite parent rock is distinctly darker than that 

formed on the neighboring granite. In many of the 

northern outcrop areas the monzonite underlies 

grayish-brown rounded outcrops and some fairly 

prominent bosses, as well as steep slopes strewn with 

coarse residual blocks and grus. A train of monzonite 

blocks that are as much as 20 feet long and 10 feet wide and 

thick lie along the Montosa Canyon at least as far as 5 

miles from their source on Mount Hopkins. The dark-gray 

color, derived from both the calcic plagioclase and the 

abundance of fernie minerals, and the very coarse grained 

texture distinguish the Piper Gulch Monzonite from the 

other plutonic rocks in the area (fig. 12). Superficially the 

rock resembles anorthosite, but on fresh surfaces a small 

amount of light-colored interstitial material is visible. 

The prevalent texture of the monzonite is idiomorphic to 

hypidiomorphic tabular, but east of Madera Canyon the 

texture is porphyritic. Much of the rock is made up of 

plagioclase laths 7-15 mm long; the other minerals are 

considerably smaller. The phenocrysts of the one body of 

porphyritic monzonite east of Madera Canyon are also in 

the 10-mm-size range, but the groundmass has a grain size 

less than 5 mm. Much myrmekitic texture and some 

granophyric texture is superposed on the general 

idiomorphic tabular texture. Most rocks that are not 

obviously hybrid contain a very fine grained, nearly 

submicroscopic, fingerprintlike myrmekitic intergrowth of 

quartz in feldspar (fig. 13). These normal rock textures 

have been modified by recrystallization in specimens from 

near the contacts with the younger stocks. Recrystallization produces a bimodal distribution of grain size, seriate 

grain boundaries, bent and partly resorbed edges of 

plagioclase crystals, and it may enhance the development 

of poikilitic grains; granophyric and myrmekitic textures, 

however, seem to be unaffected. 

The Piper Gulch Monzonite is made up of plagioclase 
20 PLUTONIC ROCKS, SANTA RITA MOUNTAINS, SOUTHEAST OF TUCSON, ARIZONA 

31 r-----------------~-----r----.-~~~~~------~~~--------~~ 

o37 

Moded 

45' 

r ,.Jfip 

29 

EXPLANATION 

Younger rocks 

Igneous and sedimentary rocks 

Piper Gulch 

Monzonite 

~ <( 

Quartz (( 

diorite fOlder rocks 

Igneous and sedimentary rocks 

Contact 

Dotted where projected through 

younger intrusive rocks 

-----·········· Fault 

Dotted where projected through 

younger intrusive rocks 

o3B 

Chemically 

analyzed 

*34 

Radiometrically 

dated 

Specimen collection sites and numbers 

X Mount Wrightson 

or 

0 2 3 MILES 

0 2 3 K ILOMETRES 

FIGURE !I.-Distribution of Triassic rocks and specimen collection sites. 

(30- 55 percent by estimate), orthoclase (10- 40 percent), 

amphibole (2- 20 percent), less than 10 percent each of 

quartz, pyroxene, biotite, and magnetite, and trace 

amounts of apatite, sphene, zircon, rutile(?), and 

tourmaline. A few rocks, not including those moded (table 

5), also contain primary(?) pyrite. Modal plagioclase, 
TRIASSIC AND JURASSIC ROCKS 21 

FIGURE 12.-Specimen 37. Piper Gulch Monzonite, showing abundant 

very coarse grained dark-gray plagioclase. 

biotite, and sphene decrease in abundance southeastward 

and orthoclase and pyroxene increase. Most of the moded 

specimens contain insufficient quartz to bring the rock out 

of the monzonite or syenodiorite fields of the modified 

triangular diagram of figure 14, but the quartz content of 

specimen 34 is sufficient to place the analysis in the 

quartz-poor end of the granodiorite field. The solid figure 

circumscribed around the modes in figure 14 forms a 

highly flattened oblate spheroid centered roughly 20 

percent of the way from the right-hand side of the 

monzonite field toward the fernie apex. 

Plagioclase forms large subhedral grains that are . 

moderately to strongly altered to clay minerals and sericite, 

giving them a finely mottled gray to pale-brownish-gray 

appearance in clear transmitted light. The anorthite 

content of plagioclase of most specimens is 40 to 60 

percent, placing it with calcic oligoclase or sodic 

labradorite. The plagioclase of a few specimens from near 

the contacts of monzonite masses is apparently albitized. 

The plagioclase crystals of a few other specimens are so 

severely altered that their estimated anorthite content of 0 

to 40 percent is as likely to be unreliable as it is to be the 

results of incomplete albitization. 

Orthoclase and quartz are generally anhedral and 

FIGURE 13.- Specimen 37. Piper Gulch Monzonite, showing fingerprintlike myrmekitic texture (my). Crystals: orthoclase ( 0), plagioclase ( P). amphibole (A), ilmenitic magnetite (im), and apatite (ap), 

pyroxene (PX), and quartz (Q). Crossed nicols; X 20. 

interstitial to the other grains; only in the porphyritic 

variety of monzonite east of Madera Canyon does the 

orthoclase form subhedral grains in the groundmass. 

Strong kaolinite alteration gives orthoclase a smooth very 

pale brown appearance. The orthoclase is commonly finely 

perthitic with albite which forms lacy or banded patterns 

that make up only a few percent of the grains. Some 

orthoclase grains are poikilitic. Quartz grains show little or 

no undulatory extinction. The amphibole, probably a 

hornblende, forms subhedral to anhedral crystals which in 

most specimens are pleochroic in pale yellowish green to 

pale greenish gray but in some specimens are pleochroic in 

light green to pale olive green. It commonly is strongly 

altered to uralite and chlorite or penninitic chlorite. The 

clinopyroxene, possibly augite, is present in about half the 

specimens, generally those with scant amphibole. The 

biotite forms subhedral crystals that are pleochroic in pale 

yellowish brown to moderate brown and are strongly 

altered to chlorite and iron oxide. The magnetite is 

ilmenitic and in many specimens it is sheathed by sphene. 
22 PLUTONIC ROCKS, SANTA RITA MOUNTAINS, SOUTHEAST OF TUCSON, ARIZONA 

TABLE 5.-Modes of Piper Gulch Monzonite and related rocks 

[Field numbers arc abbreviated; yea r of collectio n and collec tor's initia l omilled. Full field number of specimen 25 thus is 650840, etc. (except R21 , which was collected independently by 

R. Rohrbacher). s, standard deviation, Tr., trace; ... , not determined] 

Rock type Monzonite and syenodiorite Quartz diorite ... . .. and diorite 

Specimen No . . ... . 25 26 27 28 29 30 31 32 33 34 35 36 37 38 25-38 39 40 

Field No . 840 725 779 578 470 144 151 148 R21 280 160 156 Mean s 18o8 854 . . . . . . . . . . 185 212 

Quartz. 2.8 1.9 3.3 209 5.6 0.8 2.7 3.1 4.8 8.6 4.2 6.1 1.3 7.3 3.8 2.4 0.7 3.5 

Plagioclase, total . 62 .8 55.8 43.2 52 .9 38 . 51.0 57.4 55 .9 29.5 57 .8 42.4 40.5 46. 7 49. 3 48.9 9.2 54.9 71.2 

(plagioclase in perthite). 0 (2.0) (4.5) 0 (4.1) (0.6) 0 (2.0) 0 0 0 0 0 0 (0.9) (1.6) (1.9) 0 

Orthoclase . 13.1 26.3 31.7 29.2 26.4 35.0 22.2 21.4 39.7 14.5 31.4 27 .6 34.6 24.4 27.0 7.6 27 .0 9.2 

Hornblende . 310.3 7.6 3.8 11.4 17.6 7.8 12.9 7.8 21.5 14.4 11.0 11.6 2.8 9.8 10.7 5.0 8.7 11.6 

Pyroxene . .. .. .... . .. 0 0 5.7 0 0 0 0 0 0 0 4.8 3.9 6.7 4.8 1.9 2.6 0 0 

Biotite . .. . .. . .. . . 36.3 .8 4.4 .5 6.2 .5 .6 8.2 0 Tr. l.l 2.7 2.2 0 2.4 2.8 .5 0 

Magnetite. .. .... .. 2.7 3.9 5.9 3.8 4.6 3.9 3.3 2.5 3.3 4.0 3.8 6.3 3.9 3.7 4.0 I. I 6.9 3.7 

Apat ite. .. .... 1.0 1.1 1.2 1.0 .5 .6 .4 .8 1.2 .7 1.1 .8 .9 .4 .8 .3 1.0 .5 

Sphene . .. .. . . .. . .9 .8 .6 .3 .4 .3 .4 .3 0 0 Tr. .05 0 .05 .3 .3 .3 .3 

Rutile. • • • • • • 0 • • • • • • • • 0 0 0 0 0 0 0 0 0 0 .I .3 .I 0 Tr. .08 0 0 

Tourmaline . . I 1.8 .2 0 0 .05 0 .05 0 Tr. .05 .2 . 8 .I .2 .5 Tr . 0 

Zircon . . . . . . . . . . . . . . .05 0 0 0 0 0 0 0 0 Tr. 0 0 Tr. 0 Tr. 0 Tr. 

Total . .... . ... . 100.05 100.0 100.0 100.0 100.0 99 .95 99.9 100.05 100.0 100.0 99.95 100.05 100.0 99.85 100.0 100.0 100.0 

Fernie. 21.3 16.0 21.8 17.0 29.3 13.2 17.6 19.6 26.0 19. 1 22.0 25 .8 17.4 18.9 20.3 17.4 16.1 

Percem plagioclase Common range 

in anorthite. 47-55 45 -56 50-55 50-55 0 - 5 45 - 50 45-50 0 38 - 50 60 38-39 47-55 20 - 56 48 - 50 35-55 37- 41 0-5 

Quartz mixing 

index (see text) . .85 .90 .97 .80 .93 1.00 .50 . 79 .62 .85 .45 .53 .55 .36 .72 .21 .30 .87 

I Rock is metamo rphosed. · 2 Quartz content may be as much as 0. 5 percent higher, owing to presence of uncounted mic rogranophyre . 

3 Modal sum of hornblende and biotite, 16.6 percent, is more reliable than these reported values. 

FEMIC 

MINERALS 

QUARTZ QUARTZ 

~A----- ra ite------.-~~~~~~~ -- ~----~ 

POTASSIUM 

FELDSPAR 

EXPLANATION 

.-:-- Monzonite and 

syenodiorite 

<i> 

Dioritic rocks 

(modal syenodiorite) 

FIGURE 14.-Mod.ified triangular diagram showing modal quartz, potassium feldspar, plagioclase, and fernie minerals of Piper Gulch Monzonite 

and related rocks. 

Of the trace minerals, apatite forms crystals that range 

in shape from stubby prismatic to highly acicular. Sphene 

is notably less abundant in the monzonite than in other 

rocks in the area that have a high color index, such as the 

Josephine Canyon Diorite. Rutile(?) forms acicular 

crystals along the cleavage planes of the orthoclase of 

several specimens. Schorlite tourmaline is a secondary 

mineral in the border rocks, and it may be a primary 

mineral elsewhere in the monzonite. 

The alteration minerals are, in addition to those already 

mentioned, epidote, leucoxene, and calcite. 

Chemical and spectrographic analyses and calculated 

CIPW norms of three specimens are shown in table 6. The 

mean composition of these specimens is similar to the 
TRIASSIC AND JURASSIC ROCKS 23 

TABLE 6.-Chemical and spectrographic analyses and CIPW norms of 

Piper Gulch Monzonite and related rocks 

[Chemical analyses by rapid rock method (Shapiro and Brannock, 1962), with sample 40 supplemented by atomic absorption method and all other specimens supplemented by X-ray 

nuorescence method. Chemical analysts: Lowell Artis, S.D. Botts, G. W. Chloe, P. L. D. Elmore, John Glenn, H. Smith, and Dwight Taylor. Spectrographic analyses by semiquantitative method. Spectrographic analysts: W. B. Crandell, J. L. Finley, and J. C. Hamilton. Elements looked for but not found: Ag, As, Au, Bi, Cd, Eu, Ge, Hf, Hg, In, Li, Pd, Pr, Pt, Re, 

Sb, Sm, Ta, Te, Th, Tl, U, W, and Zn. Symbols: s, standard deviation; <, less than; N, not 

detected; ... , not determined] 

Rock type, ............ . 

Specimen No .. . 

Field No ........ . 

Si02 .. .... .. ...... 

AI203 .. .. ...... 

Fe203 ..... ... . ..... 

FeO ... ..... ······· MgO ..... . ' . . . ······· CaO .... ...... ....... 

Na20 ... .... ... ..... 

K20 .. ......... ······· H20- ........ ........ 

H20+ ..... ... ... 

Ti02 .. .... ..... 

P205 ... .... . .... 

MnO. ....... ..... 

C02 .. ........ . ...... 

Total ...... ...... 

B ··········· Ba ··················· Be ... .. .. ...... . .. 

Ce ... ... ········ .... 

Co. .... ··········· Cr ..... .......... 

Cu .. .. . . ············ Ga .... ..... ······· La ...... ·········· Mo. ...... ············ Nb. ........ .. ······· Nd. .... ·············· Ni ......... ........... 

Pb ... ················· Sc ...................... 

Sn . . . . . . . . . . . . . . . . . . . . . Sr ...................... 

v ······················ y ..... ················ Yb .... ... ·········· Zr ............... ...... 

Q 

c 

or. 

ab 

an 

t di en ...... 

fs ...... 

hy rn. fs. 

mt 

hm 

il 

ap 

cc. 

Total 

Fernie 

Monzonite and syenodiorite 

27 

779 

34 

280 

38 I 27- 38 

212 Mean 

Chemical analyses (weight percent) 

55.4 56.0 56.0 55.8 0.3 

18.2 15.8 17.2 17.1 1.2 

4.2 5.0 4.5 4.6 .4 

3.0 3.8 3.3 3.4 .4 

3.1 2.7 3.0 2.9 .2 

5.0 5.3 5.0 5.1 .2 

3.8 3.0 3.4 3.4 .4 

4.3 4.2 4.5 4.3 .2 

.30 .19 .19 .23 .06 

.80 1.4 1.1 1.1 .3 

.97 1.2 1.2 1.12 .I 

.57 .53 .42 .51 .08 

.14 .33 .18 .22 .I 

.II .16 <.05 .09 .08 

100 100 100 100 . .. 

Spectrographic analyses (weight percent) 

0.007 0.005 0.003 0.005 0.002 

.I .15 .01 .09 .07 

.0001 .0002 .0003 .0002 .0001 

.01 0 N .005 .007 

.002 .002 .003 .003 .0006 

.001 .002 .0007 .001 .0007 

.03 .015 .03 .03 .009 

.001 .003 N .002 .001 

.007 .005 .005 .006 .001 

.0005 0 0 .0002 .0002 

0 .0015 0 .0005 .0008 

0 .007 N .004 .005 

<.003 .0015 .003 .002 .0008 

.0015 .0015 .001 .001 .0003 

.005 .002 .007 .004 .003 

.0003 0 0 .0001 .0002 

.I .I .015 .07 .05 

.02 .015 .015 .02 .003 

.003 .003 .015 .007 .007 

.0003 N N .0003 . .. .03 .02 .005 .02 .01 

CIPWnorms 

3.2 9.4 5.5 

0 0 0 

25.4 24.8 26.6 

32.1 25.4 28.8 

19.9 17.2 18.4 

.20 1.9 1.5 

.16 1.4 1.2 

.01 .31 .12 

7.6 5.3 6.2 

.68 1.2 .58 

6.1 7.3 6.5 

0 0 0 .. .. ... . . 1.8 2.3 2.3 

1.4 1.3 1.0 

.25 .36 0 

98.8 98.2 98.7 

18.2 21.4 19.4 

Quartz 

diorite 

40 

854 

64.1 

16.8 

2.8 

2.1 

1.1 

4.3 

4.0 

2.0 

.15 

1.3 

.78 

.29 

.13 

<.05 

100 

0 

.I 

0 

.01 

.0005 

0 

.0005 

.0015 

.007 

0 

0 

.01 

0 

.0007 

.0005 

.07 

.002 

.002 

.0002 

.02 

23.1 

1.0 

11.8 

33.9 

19.1 

0 

0 

0 

2.7 

.50 

4.1 

0 

1.5 

.69 

.II 

98.5 

9.6 

composition of the hornblende-biotite monzonite of 

Nockolds (1954, p. 1017). 

The Piper Gulch Monzonite is dated as Triassic by one 

lead-alpha age determination (table 4; specimen 34). A 

Late Triassic or Early Jurassic age of this formation was 

also surmised from its geologic relations to other rocks: it 

postdates the Triassic Mount Wrightson Formation and 

predates the Jurassic Squaw Gulch Granite. The reliability 

of the lead-alpha age determination, which would be low if 

taken by itself, is considerably increased because that age 

determination is part of a series of determinations on 

Mesozoic rocks which are internally consistent with the 

geologic relations between the rocks. 

Monzonite that resembles precisely the composition and 

age of the Piper Gulch is not known in other parts of 

southeastern Arizona. However, roc~ that resemble the 

Piper Gulch in a general way include the Harris Ranch 

Monzonite of Damon (1965), in the Sierrita Mountains 

(fig. 1) and the Copper Belle Monzonite Porphyry (Gilluly, 

1956, p. 63- 65) in the Courtland area (fig. 1 ), 50 miles 

east of the Santa Rita Mountains. Neither of these 

formations is radiometrically dated, and the restraints in 

age imposed by the geologic relations of the Copper Belle 

to surrounding formations are fewer than those on the 

Piper Gulch or the Harris Ranch. 

QUARTZ DIORITE 

Two masses of strongly altered quartz diorite and other 

dioritic rocks underlie an area of about 2 square miles of 

the high central part of the Santa Rita Mountains (fig. 11) 

and are provisionally mapped as intrusive masses of 

Triassic age. One of these intrusive masses underlies a 

broadly arcuate area about 3 Yz miles long and ~ mile wide 

between Cave Creek and Florida Canyon. The elongate 

shape of this mass and its parallelism to some faults 1-3 

miles east of the mass (Drewes, 1971c) suggest that its 

emplacement was structurally controlled, but direct 

evidence supporting this notion has not been found in the 

thick and uniform pile of volcanic rocks into which the 

quartz diorite was intruded. The other intrusive mass of 

quartz diorite crops out in an irregular area high on the 

east wall of Madera C'...anyon. 

The Triassic quartz diorite is generally a greenish-gray to 

bluish-gray rock that is poorly exposed because it is more 

friable than the Mount Wrightson volcanic host rocks. The 

quartz diorite typically underlies benches, saddles, and 

steep slopes thickly covered by colluvium derived from the 

volcanics. The available outcrops are small except along 

the bottom of a tributary on the south side of Cave Creek 

where the rock is an atypically fine grained border phase. 

The contact was not seen and the intrusive relations are 

inferred from the shapes of the masses and the suggestions 

of chilled fine-grained textures of rocks near some of the 

margins of the masses. Along the western side of the 

irregular-shaped mass the quartz diorite and its andesitic 

border-phase contain some small inclusions of hybridized 
24 PLUTONIC ROCKS, SANTA RITA MOUNTAINS, SOUTHEAST OF TUCSON, ARIZONA 

porphyritic rock resembling the nearby body of Piper 

Gulch Monzonite. Toward the northern part of this 

contact area the quartz diorite itself appears to be 

recrystallized by the adjacent stock of Madera Canyon 

Granodiorite. 

The quartz diorite has a sparsely porphyritic felty to 

granular texture and a mineral assemblage that is largely 

obscured by alteration. The felty laths of the groundmass 

are 0.1 -2.0 mm long and the few phenocrysts are only 

about 4 mm long. The major mineral constituents and their 

estimated abundance are andesine plagioclase (50 -75 

percent), amphibole (8- 20 percent) and quartz (0.5 -15 

percent). Some specimens contain potassium feldspar, 

pyroxene, and biotite in unknown but probably small 

quantities. Trace amounts of magnetite, zircon, apatite, 

and sphene are generally also present. The secondary 

minerals are very abundant and include chlorite, epidote, 

zoisite, leucoxene, penninite, calcite, sericite, iron oxide, 

and clay minerals. The plagioclase of most specimens is 

albitized. 

The relatively large variation in the content of quartz 

among specimens and within a specimen suggests that 

quartz may be in part recrystallized or a secondary 

mineral. Note that the quartz content of the two moded 

specimens in table 5, the least altered rocks available, is as 

low as any recorded (0.5 -15 percent), and the specimens 

are modal syenodiorites. The mixing index of specimen 39 

(table 5) is also unusually small. Furthermore, that 

specimen has unusually large amounts of orthoclase, 

magnetite, and apatite. Other specimens too altered to be 

moded seem to be quartz diorites, which designation is 

applied to the entire suite of specimens. Assembling modal 

data on the Triassic quartz diorite will require additional 

detailed study. 

Chemical and spectrographic analyses of a single 

specimen are listed in table 6. In view of the modal 

uncertainties, these analytical results must be evaluated 

cautiously. 

The quartz diorite masses are dated only through their 

geologic relations to other rocks; it seems unlikely that the 

rock can be dated by radiometric methods because it is so 

strongly altered. Both dioritic masses intrude the Mount 

Wrightson Formation of Triassic age. The inclusions in 

one mass may be penecontemporaneous with, or younger 

than, the Piper Gulch Monzonite, which, in turn, appears 

to be altered by the Madera Canyon Granodiorite of Late 

Cretaceous age. The intensive alteration of the rock, which 

is so unlike that of the Jurassic and Cretaceous intrusive 

bodies, and the dioritic composition, which is also unlike 

that of the Jurassic body, are the reasons for assigning the 

quartz diorite to the older part (Triassic) of the age range 

available for the rock. Correlation of the quartz diorite is 

precluded by the uncertain age and original composition. 

SQUAW GULCH GRANITE 

Squaw Gulch Granite, defined by Drewes (1968), is a 

coarse-grained pink rock, mainly of granitic composition, 

that forms an intrusive mass almost batholithic in size. It 

underlies an outcrop area of only 12 square miles in the 

southern part of the Santa Rita Mountains (fig. 15), but at 

shallow depths the granite mass probably extends over an 

area of 40 square miles. About 3 miles south of the Squaw 

Gulch area, granite of similar appearance underlies a 

substantial part of the upfaulted block of the northern 

Patagonia Mountains (Simons, 1974). The granite of the 

Patagonia Mountains may be a direct extension of the 

Squaw Gulch Granite batholith, or it may be a separate 

cupola of that batholith. In addition, a shred of evidence, 

to be discussed in the section on the Elephant Head Quartz 

Monzonite, suggests that the Squaw Gulch Granite may 

have extended northwestward where it was thoroughly 

recrystallized during Late Cretaceous time. 

In the Santa Rita Mountains the granite intruded 

igneous, sedimentary, and metamorphic rocks of 

Precambrian, Paleozoic, and Triassic ages. The contact 

with the Triassic Mount Wrightson is typically steep, and 

the nearby volcanic rocks are contact metamorphosed. 

(See geologic map, Drewes, 1971c.) Near the Glove mine 

(fig. 15) the granite intruded contact-metamorphosed 

Paleozoic formations along another steep contact. Some of 

the Continental Granodiorite immediately north of the 

collection site of specimen 54 was also recrystallized by the 

granite, and the concealed contact there is inferred to be 

steep and regular. The contact of the granite with other 

rocks, such as the Triassic Piper Gulch Monzonite and a 

few small masses of Paleozoic rock south of the Glove 

mine, is short and dips irregularly; there the host rock 

forms inclusions, roof pendants, or septa, rather than 

wallrock, to the batholith. Most of the intrusive contacts 

are fairly sharp, but the contacts with some of the 

inclusions of Piper Gulch Monzonite are gradational over 

distances of tens to hundreds of feet. The rocks in the 

transition zone are mottled and consist of patches of 

dark-gray monzonite surrounded by pinkish-gray granitic 

material. 

Rocks of Early Cretaceous and younger ages 

unconformably overlie the granite. The oldest of these 

formations is the Temporal, a pre-Bisbee Group volcanic 

and sedimentary formation that contains wedges of 

granite-boulder conglomerate and that was deposited on a 

surface of rugged local relief carved on the granite as 

described by Drewes (1971a, figs. 18 and 19, and p. C35). 

Along the west flank of the mountains, the Upper 

Cretaceous Salero Formation overlies an extensive area of 

granite on a surface of moderate local relief, and some 

members of the Salero consist mainly of sediment derived 

from weathered Squaw Gulch Granite. 
TRIASSIC AND JURASSIC ROCKS 25 

yr 

Js ""2'---- __ / ------------------.. ------ --?------ --- -----?--

yr 

EXPLANATION 

Younger rocks 

Igneous and sedimentary rocks 

Jurassic Squaw Gulch Granite 

a. aplite 

Older rocks 

Igneous and sedimentary ro cks 

• 44 

Moded 

Q46 

Chemically 

analyzed 

Contact 

Dotted where projected through 

younger intrusive rocks 

---···········- Fault 

Dolled where concealed or projected through younger intrusive rocks 

*45 

Radiometrically 

dated 

110° 45' 

0 

C.... or 

yr 

" r 

Js 

0 2 3 4MILES 

0 2 3 4 KILOMETRES 

FIGURE 15.-Distribution of Squaw Gulch Granite and specimen collection sites. 

PETROGRAPHY 

The Squaw Gulch Granite is made up mainly of 

coarse-grained granitic rock intruded by some small masses 

of aplite and lamprophyre. In composition and appearance 

the granitic rock is uniform over a distance of a mile or so 

but varies from a pinkish rock of granite composition in 

the southeast to a grayish rock of sodic quartz monzonite 

composition in the northwest. The term "granite" is 

emphasized in the name of the formation in order to 
26 PLUTONIC ROCKS, SANTA RITA MOUNTAINS, SOUTHEAST OF TUCSON, ARIZONA 

distinguish it from other formations whose composition is 

entirely of quartz monzonite. Aplite generally fills dilation 

fractures, forms small irregular bodies within the 

batholith, or has accumulated along parts of the 

northeastern margin of the batholith where it forms a 

sill-like tongue into the host rock. A few lamprophyre 

dikes that were plotted on the field sheets are too small to 

be shown on the published geologic maps. 

GRANITE AND QUARTZ MONZONITE 

The Squaw Gulch Granite (fig. 15) typically underlies 

a gently rolling terrain in which outcrops are fairly small, 

widely scattered, and deeply weathered. However, granite 

along the west flank of the mountains, particularly along 

the middle reaches of Josephine Canyon, forms prominent 

bosses and ledges and some small clusters of boulderlike 

residual masses. The granite of the type area, along Squaw 

Gulch, and that near Josephine Canyon is characteristically "salmon" colored, or moderate orange pink; the rock 

farther north is grayish orange pink. The granite along 

Squaw Gulch is generally more closely fractured than that 

near Josephine Canyon to the northwest, perhaps, thereby 

weathering to form the prominent bosses and massive 

outcrops. In all areas the least weathered granite is in 

outcrops along the deepest and narrowest canyons. A slab 

of typical granite is shown in figure 16. The rock has a 

hypidiomorphic-granular texture (fig. 17) and a grain size 

of 3 to 8 mm. Myrmekitic and granophyric textures occur 

throughout the batholith and are particularly abundant 

and coarse grained in the southern part of it. In some 

specimens the quartz intergrowths form conspicuous 

rosette patterns and alternate zones of differing grain size 

(fig. 18). 

The modal compositions of 21 specimens of granite are 

shown in table 7. Two specimens (60, 61) are not from the 

batholith in the Santa Rita Mountains; specimen 60 is from 

a boulder in the Cretaceous Salero Formation where that 

formation lies directly on the granite, and specimen 61 is 

from the northern part of the Patagonia Mountains. The 

modes of specimen 58 and, to a lesser extent, specimen 59 

resemble those of the Elephant Head Quartz Monzonite 

more closely than they do the average Squaw Gulch 

Granite. This observation will be referred to again in 

connection with the section on the age and origin of the 

Elephant Head Quartz Monzonite. The correlation of the 

granitic body represented by specimens 58 and 59 with the 

Squaw Gulch Granite is based on geologic relations that 

show the body to be older than the Elephant Head stock, 

for the stock intrudes the Salero Formation, which in turn, 

unconformably overlies the granitic body and its contactmetamorphosed host rocks. These field relations are 

illustrated on the geologic map (Drewes, 1971c) and are 

discussed in greater detail in the report on the structural 

geology of the area (Drewes, 1972b). 

FIGURE 16.-Specimen 45. Squaw Gulch Granite. 

The three main mineral constituents-quartz, orthoclase, and plagioclase-make up more than 93 percent of 

the Squaw Gulch Granite, and accessory biotite, 

magnetite, apatite, and zircon make up the remainder; 

some specimens also contain trace amounts of sphene and 

tourmaline. The quartz forms anhedral grains that have a 

moderately strong undulatory extinction. Orthoclase is 

also anhedral and is slightly kaolinitized to give the finetextured light-gray appearance of the crystals in figure 17. 

Lace and patch perthite are common in the orthoclase; 

they produce the white blotches seen in figure 17 and the 

fine lacy patterns in the orthoclase of figure 18. The 

amount of albite in the perthitic orthoclase averages nearly 

8 percent, and in specimen 43 it exceeds 24 percent. The 

plagioclase has the composition of albite, but its alteration 

to clay minerals and sericite obscures any evidence of 

albitization. Biotite is largely altered to chlorite and in 

some specimens to penninitic chlorite; only specimen 54 

has enough unaltered biotite to be concentrated for 

radiometric dating. The magnetite is ilmenitic. Zircon is 
TRIASSIC AND JURASSIC ROCKS 27 

A B 

FIGURE 17.- Specimen 45. Squaw Gulch Granite, showing typical texture and mineral assemblage. Crystals: perthitic orthoclase (Q), quartz (Q), 

plagioclase ( P), partly chloritized biotite ( 8), ilmenitic magnetite ( im), and apatite (a p). x 20. A, Plain light; B, crossed nicols. 

sufficiently abundant in many specimens to make it 

possible to date the rock by the lead-alpha or fission-track 

method. 

APLITE AND LAMPROPHYRE 

Aplite associated with the Squaw Gulch Granite is pale 

red to pinkish gray in fresh and weathered rock alike. The 

aplite has a grain size of 0.03- 0.3 mm; it typically has a 

sugary appearance in hand specimens and an idiomorphicgranular texture in thin sections. The texture is commonly 

granophyric and rarely finely porphyritic. 

The mineralogic similarity of the aplite to the Squaw 

Gulch Granite is indicated by the following estimated 

mode. Major mineral constituents and their range of 

abundance, in percent, are quartz (25 -35), orthoclase 

(30- 45), and albite plagioclase (15- 25). Accessory 

minerals, in trace amounts, are biotite, ilmenitic 

magnetite, apatite, and sphene. Kaolinite, sericite, 

chlorite, epidote, leucoxene, and iron oxide are the 

alteration minerals which are abundant in some specimens. 

Lamprophyre dikes are mostly only 1 to 3 feet thick and 

are made up of greenish-gra,y to dark-greenish-gray 

andesitic or dioritic rock. The dikes form small clusters of 

parallel bodies in two places along the middle reaches of 

Josephine Canyon. The dikes of both clusters dip 

vertically; one group strikes west and the other northwest. 

Lamprophyre is less resistant to weathering than the 

adjacent granite and so the dikes rarely crop out. 

Under the microscope the lamprophyre is seen to have a 

felty or ophitic texture. Grain size ranges from 0.1 to 1.0 

mm. 

The lamprophyre's strong alteration and the fine grain 

size make it difficult to calculate a mode. Plagioclase is a 

major constituent and is albitized and strongly sericitized. 

A pyroxene, which may be augite, and an amphibole are 

generally represented by pseudomorphs of uralite, chlorite, 

and epidote. A little quartz is present in one specimen and 

magnetite, apatite, and sphene are commonly the accessory 

minerals. Leucoxene, iron oxide, and penninite occur, 

along with the alteration minerals already mentioned. 
28 PLUTONIC ROCKS, SANTA RITA MOUNTAINS, SOUTHEAST OF TUCSON, ARIZONA 

FIGURE 18.-Specimen 48. Squaw Gulch Granite, showing strongly developed granophyric texture and preponderance of orthoclase over 

plagioclase . Crystals: orthocl ase (0), quart z (Q), plagioclase ( p), 

ilmenitic mangetite (im), chloritized biotite (Cb). Crossed nicols; 

X 20. 

MODAL AND CHEMICAL SUMMARY 

The modified triangular diagram of figure 19 graphically 

summarizes the modes of the specimens of Squaw Gulch 

Granite. The solid figure circumscribed around the plotted 

modes has a discoid shape, centered at a point near the 

boundary between the granite and quartz monzonite field 

and 2- 3 percent of the distance from the leucocratic face 

of the composition tetrahedron toward the fernie apex. The 

anomalous mode of specimen 58 is clearly illustrated by its 

position outside the circumscribed figure, although its 

composition is included in the calculation of a mean of the 

modes (table 7). The anomalous composition of specimen 

60 from the boulder, also shown, suggests that further 

study of the composition of the clasts in the conglomerate 

unit in the Salero Formation might add significantly to the 

knowledge of the Mesozoic rocks of the area. 

Chemical and spectrographic analyses and CIPW norms 

of four of the moded specimens of Squaw Gulch Granite 

are listed in table 8 and the chemistry is compared with that 

of other plutonic rocks of the area in figure 10. The 

chemical composition of the granite is very similar to that 

of the Corona stock and of the Elephant Head Quartz 

Monzonite (figs. 10/ -10L). Chemically the granite also 

resembles somewhat the granitoid rocks of the Helvetia 

stocks anti the quartz latite porphyry of the Greaterville 

plugs. The mean chemical composition of the Squaw 

Gulch Granite is most like that of an alkali granite, such 

as the muscovite granite, ofNockolds (1954, p. 1012), with 

a tendency toward the composition of his calc-alkali biotite 

granite. 

AGE AND CORRELATION 

The Squaw Gulch Granite is dated as early Mesozoic 

through its geologic field relations, and it, is more precisely 

dated as Jurassic by radiometric means. With respect to 

formations dated by their fossil content, the granite postdates some Permian rocks and predates the Lower 

Cretaceous Bisbee Group. The age of the granite is further 

restricted as younger than the Piper Gulch Monzonite, 

which is radiometrically dated as Triassic and is judged to 

be of possible Late Triassic age. The granite is also known 

to be older than the Temporal and Bathtub Formations, 

both of which underlie the Bisbee Group, and which are 

assigned to the earliest part of the Early Cretaceous. A 

Jurassic age is therefore indicated by the combined 

evidence from the field relations of the granite to other 

formations whose ages are reasonably well established. 

Two specimens (54 and 45 of table 4) are dated by the 

lead-alpha method of zircon, and one of these is also dated 

by the potassium-argon method on biotite. The two 

lead-alpha ages are in excellent agreement at about 160 

m.y., and the agreement of these ages with the potassiumargon age determination-145 m.y. from specimen 54-is 

reasonably good. The biotite concentrate may have given 

an age that is slightly too young because of chlorite 

contamination of the biotite. Nevertheless, the combined 

results of the three radiometric age determinations indicate 

that the granite is Jurassic or is possibly even restricted to 

Middle Jurassic. 

Granite and quartz monzonite stocks of Jurassic age 

occur in several other ranges in southeastern Arizona. The 

Juniper Flat Granite of the Mule Mountains (fig. 1), 50 

miles southeast of the Santa Rita Mountains, is dated as 

Triassic or Jurassic by Ransome (1904, p. 84) and by 

Gilluly (1956, p. 55) through its geological relations to 

fossiliferous rocks. Creasey and Kistler (1962, p. 01) dated 

this granite, using the potassium-argon method, as 163 

m.y., or Jurassic. In the Sierrita Mountains the Sierrita 

Granite of Lacy (1959) was dated by Damon (1966), using 

the rubidium-strontium method, as 140 m.y. old, and by 

T. W. Stern (in Marvin and others, 1973), using the 

lead-alpha method, as 150 m.y. 

In the Patagonia Mountains granite and quartz 
CRETACEOUS ROCKS 29 

monzonite stocks mapped by F. S. Simons (1974) are dated 

by T. W. Stern (in Marvin and others, 1973), using the 

lead-alpha method, as 160 and 150 m.y., respectively. 

Biotite and hornblende from another granitic stock 

mapped by Simons in the hills a few miles north of Nogales 

is dated as 160 m.y. by the potassium-argon method. The 

similarity in age and composition of all these rocks is 

impressive; apparently a distinctive magmatic event 

affected much of southeastern Arizona at that time. 

CRETACEOUS ROCKS 

Plutonic rocks of Cretaceous age form a series of stocks 

and related small masses of aphanitic rocks that were 

emplaced during the Piman phase of the Laramide 

orogeny. The Piman phase, lasting from about 90 to 63 

m.y. ago (Drewes, 1972b), is the first and more active of 

two phases of that orogeny. In the Santa Rita Mountains 

tectonic activity probably peaked shortly before 72 m.y. 

ago. The Cretaceous plutonic rocks of the area include (1) 

the granitoid rocks of the Corona stock, which is nearly 

synchronous with the peak of tectonic activity, (2) the 

Josephine Canyon Diorite, (3) Madera Canyon 

Granodiorite, and (4) Elephant Head Quartz Monzonite, 

all of which slightly postdate the peak of tectonic activity, 

and (5) a few small intrusive masses of quartz latite 

porphyry, of somewhat equivocal age and association. 

GRANITOID ROCKS OF THE CORONA STOCK 

The Corona stock (fig. 20) underlies an area of several 

square miles at the northern end of the Santa Rita 

Mountains (Drewes, 1971b). On the basis of recently 

obtained radiometric dates, the stock is here assigned to 

the older group of stocks of Late Cretaceous age of the 

region, rather than to the Helvetia stocks, of Paleocene 

age, as previously mapped. Only about 1 square mile of 

stock is exposed within the Sahuarita quadrangle; most of 

the exposed part underlies the adjacent part of the Empire 

Mountains quadrangle, where it was mapped by T. L. 

Finnell (1971), and an unknown amount of the stock 

underlies gravel deposits on the pediment along the north 

flank of the mountains. About half the outcrop area of the 

granitoid rocks shown in figure 20 is on the pediment 

southeast of the community of Corona de Tucson. 

The Corona stock is made up of a variety of granitoid 

rocks whose mutual relations are not fully known. Most of 

the rocks in the part of the stock that lies within the 

Sahuarita quadrangle are quartz monzonite; some of the 

rocks are granodiorite and others are aplite. According to 

T. L. Finnell (oral commun., 1971), the rocks of the 

eastern part of the stock are mainly quartz monzonite and 

include some quartz diorite phases (not shown in fig. 20). 

Granodiorite masses found near the collection site of 

specimen 66 (fig. 20) are enclosed by quartz monzonite and 

so may be inclusions, but unequivocal contact data 

supporting this interpretation have not been found. The 

relation of other granodiorite from near the collection site 

of specimen 65 to the quartz monzonite is unknown. The 

granitoid rocks are intruded by the aplite, as well as by 

small dikes of lamprophyre and veinlets of quartz. 

The outcrop area of the Corona stock is irregular 

shaped, and the stock contains many inclusions or roof 

pendants of the host rocks which are comprised of arkosic 

sandstone and siltstone and of some intercalated thin beds 

of limestone of the Apache Canyon Formation and the 

Shellenberger Canyon Formation of the Bisbee Group. 

The main body of aplite lies within the stock, but many of 

the small bodies of aplite intrude the host rocks near the 

stock. The host rocks near the stock, and particularly in 

the area of aplite intrusives, are contact metamorphosed to 

hornfels and calc-silicate rocks. Where exposed, the 

contact is sharp, and the granitoid rocks near the contact 

seem to lack a chill-zone texture, but they may have a more 

felsic composition, as described in the third following 

paragraph. 

The quartz monzonite of the pediment ·area is mostly 

deeply weathered and that of the hilly terrain forms 

pinkish-gray to grayish-orange-pink, high, rounded bosses 

and piles of boulderlike residual blocks that are 

intermittently veneered by grus. Weathered granodiorite 

masses are brownish gray and are darker than the quartz 

monzonite terrain. Aplite commonly weathers to form very 

pale orange irregular-shaped outcrops, blocky detritus, 

and some grus. The randomly scattered lamprophyre dikes 

are dark gray to greenish gray, typical of porphyritic dacite 

and andesite. 

The quartz monzonite is typically hypidiomorphicgranular in texture; some specimens also have a little 

mosaic, porphyritic or porphyroblastic, and granophyric 

texture. Grains range in size from 1 to 10 mm and in some 

specimens, their size distribution is bimodal. The clustering 

of small grains of some specimens, such as shown in figure 

21, may indicate recrystallization. Aplite has an 

idiomorphic-granular and porphyritic texture. Its 

groundmass grains are about 0.1 mm across, and its 

phenocrysts are 0.15 to 2.0 mm across. 

Five modes of granitoid rock of the Corona stock are 

shown in table 9. Specimen 65 is granodiorite; the others 

are quartz monzonite. Specimens 62 and 63 are from near 

the margin of the stock, which may be the cause of the 

abnormally large content of potassium feldspar of 

specimen 63 and the more felsic composition of specimen 

62. Specimens 64 and 66 are, thus, most typical of the main 

rock type at the western end of the stock, yet their 

composition deviates but little from the mean of all the 

modes. The shape and position of the figure circumscribed 

around the modes plotted on the diagram of figure 22 is 

probably of slight significance because so few, modes are 
30 PLUTONIC ROCKS, SANTA RITA MOUNTAINS, SOUTHEAST OF TUCSON, ARIZONA 

TABLE 7 .-Modes of Squaw Gulch Granite 

[Field numbers are abbreviated: year of collection and collector's initial omitted. Full field number of specimen 41 thus is 650915. Symbols: 

Ro<.:k type .... Granite (includes quartz monzonite) 

Specimen No .. 41 42 43 44 145 46 47 48 49 50 51 252 53 54 55 

Field No ...... 915 229 984 906 249 209 237 190 184 167 166 174 446 605 450 

Quartz ................ 21.5 12.0 11.9 30.0 23.2 31.2 24.0 35.2 37.4 29.4 26.6 22.4 39.6 16.4 38.5 

Plagioclase, total ....... 9.0 35.2 33.9 16.1 36.1 9.7 24.8 14.6 14.9 22.8 11.9 19.6 27.3 37.6 19.7 

(plagioclase in 

perthite) .......... (9.0) (12.9) (24.1) (6.1) (11.3) (2.1) (5.9) (6.6) (10.4) 0 (11.9) (17.6) (3.S) (S.3) (2.6) 

Orthoclase ............ 63.0 46.2 Sl.7 S2.S 37.6 51.2 48.8 47.9 45.0 46.6 59.0 56.5 30.8 41.3 40.4 

Microcline ............ 0 0 0 0 0 0 0 0 0 0 0 0 .7 0 0 

Biotite ................ .I 2.4 .9 .9 1.9 1.1 1.9 1.4 1.3 .6 1.6 .5 1.2 2.3 1.1 

Magnetite ............. .4 .7 1.4 .5 .9 .7 .3 .8 1.0 .6 .9 .5 .4 .9 .3 

Apatite ............... 0 .6 0 .05 .OS .OS . I .I .I Tr. Tr. Tr. 0 .4 Tr . 

Zircon ................ 0 .05 .I Tr. .05 .05 .05 .OS . 3 Tr . Tr. .05 Tr. .I .05 

Sphene ............... 0 1.7 .I 0 Tr. 0 .OS 0 0 0 .OS .5 Tr. 1.0 0 

Tourmaline ........... 0 0 0 0 .2 0 0 0 .05 0 0 0 0 0 0 

Amphibole ............ 0 1.1 0 0 0 0 0 0 0 0 0 0 0 Tr. 0 

Rutile ................ 0 0 0 0 0 Tr. Tr. 0 0 Tr. 0 0 0 0 0 

Total ........... 100.0 99.95 100.0 100.05 100.0 100.0 100.0 100.05 IOO.OS 100.0 100.05 100.05 100.0 100.0 100.05 

Fernie .......... .5 6.6 2.S 1.4 3.1 1.9 2.4 2.3 2.7 1.2 2.5 1.5 1.6 4.7 1.4 

Percent anorthite 

in plagioclase ........ 0 0 0-5 0 0 0 0-5 0 0 0 0? 0? 0-5 0-5 0-5 

Quartz mixing 

index (see text) ....... .92 .85 .86 .74 .61 .87 .39 .92 .86 .73 .97 .69 .9S .92 .88 

I Specimen 4S collected almost at same place as chemically analyzed specimen 63D282 (table 8). 

2 Specimen 52 collected from a small wedge of granite, between two small masses of altered 

rhyolite, that is erroneously shown as Josephine Canyon Diorite (Drews, 1971c). 

3specimen 59 dynamically metamorphosed. 

QUARTZ QUARTZ 

FEMIC 

MINERALS 

POTASSIUM 

FELDSPAR EXPLANATION 

<~"':' 

Granite and quartz 

mom;,onite 

® 

Quartz monzonite·of 

Glove mine area 

1!1 

Jurassic granite from 

Patagonia Mountains 

&. 

Granitoid boulder in 

Salero Formation 

FIGURE 19.-Modified triangular diagram showing modal quartz, potassium feldspar, plagioclase, and fernie minerals of Squaw Gulch Granite. 

available, but the large size of the figure probably reflects 

the diverse rock types that are characteristic of the stock. 

The internal uniformity of the rock, over· a span of 

several centimetres, seems greater than that of the equally 

coarse grained Squaw Gulch Granite (compare quartz 

mixing indexes, tables 5 and 9). 
CRETACEOUS ROCKS 31 

and related rocks 

s, standard deviation; Tr, trace; .. . , not determined] 

Granite im:!udes quartz monzonite- Continued Boulder Granite, 

Quartz monzonite of in Salero Patagonia 

Glove Mine area Formation Mountains 

56 57 58 359 41 - 59 60 61 

353 920 644 919 Mean s 395 460 

32.9 33 .0 14.6 26.0 26.9 8.6 20.6 31.2 

13.9 34.3 50.7 35.9 24.6 11.7 48.0 25.2 

(8 .8) (5.4) (2 .7) (2.7) (7.8) (5.9) (1.3) (24.7) 

52 .3 30.5 27 .6 35.1 45.8 10.2 22 .3 41.6 

0 0 0 0 Tr. 0 0 

.2 2.0 5 3 2.4 1.5 1.2 5.8 .8 

.6 .2 1.4 .5 .7 .3 1.3 .9 

Tr. 0 3 .05 .I .2 . 4 Tr . 

Tr. Tr. .I .05 .06 .07 .I 0 

.I 0 0 Tr. .2 .4 .5 .3 

Tr. 0 0 0 Tr. 0 Tr. 

0 0 0 0 .06 .3 1.0 0 

0 0 0 0 Tr. 0 0 

100.0 100.0 100.0 100.0 99.92 100.0 100.0 

.9 2.2 7. 1 3.0 2.6 1.8 9.1 2.0 

O' 0 0 0 0- 5 0-10 0 

.81 .88 .67 .85 .81 . I .86 .91 

The mineral components of granitoid rocks consist of 

the usual abundant quartz, plagioclase, and potassium 

feldspar, less abundant biotite, and scarce accessory 

minerals. The quartz typically is anhedral, has slightly 

interlocking grain boundaries, and has a moderately strong 

undulatory extinction. The quartz of some specimens, 

however, has straight boundaries and no undulatory 

extinction, and that of others is strongly sutured. 

Plagioclase forms subhedral grains having a strong normal 

compositional zoning. The plagioclase is commonly albite, 

but that of specimen 66 is calcic oligoclase to sadie 

andesine, and the cores of some crystals of other specimens 

are sericitized oligoclase. The potassium feldspars are 

microcline and orthoclase in nearly equal amounts. The 

grid twinning of the microcline is fairly sharp in the small 

crystals (fig. 21) and along the edge of some large ones but 

is indistinct or blurred in the cores of the large grains. 

Perthitic textures are ubiquitous and range from finely lacy 

(fig. 21) to moderately coarse lacy types. Biotite is 

unaltered to partly chloritized and is pleochroic in very 

pale brown to dark brown. Magnetite is ilmenitic, and 

zircon grains are fairly abundant but particularly sma1l. 

Sphene and amphibole occur only in the ·granodiorite 

specimen, and allanite occurs in two specimens: 

A single chemical and spectrographic analysis and 

CIPW norm are given in table 10 ~ The chemical analysis 

closely resembles the analyses of Squaw Gulch Granite and 

Elephant Head Quartz Monzonite (figs. 101-lOL). 

An age of 73.8 m.y. was obtained by the 

potassium-argon method (Marvin and others, 1973) from 

quartz monzonite collected by T. L. Finnell about a, mile 

east of the collection site of specimen 66, and another 

specimen, of a diorite stock that does not extend into the 

TABLE . B.-Chemical and spectrographic analyses and CIPW norms of 

Squaw Gulch Granite 

(Chemical analyses by rapid rock method (Shapiro and Brannock, 1962), with analyses of 

specimen 46, 48, and 55 supplemented by x.ray fluorescence method. Chemical analysts: 

Lowell Artis, S. D. Botts, G. W. Chloe, P. L. D. Elmore, John Glenn, and H. Smith. Spectrographic analyses by semiquantitative method. Spectrographic analysts: W. B. Crandell, J. C. 

Hami lton. a nd Barbara Tobin. Elements looked for but not found: Ag, As, Au, B. Bi, Cd. Eu, 

Ge, Hf, Hg,ln, Li, Nd, Pd, Pr, Pt, Re, Sb, Sm, Sn, Ta, Te, Th, Tl, U, W, and Zn. Symbols: s, standard deviation;<. less than; N, not detected; ... , not determined] 

Rock type . Granite and quartz monzonite 

Specimen No .. 45 46 48 55 45-55 

Field No 282 209 190 450 Mean . .... .. 

Chemical analyses (weight percent) 

Si02 .... 69.1 75.1 75.1 75.5 73.7 3.1 

Al203 .. 15 .2 13.3 13 .0 12.6 13.5 1.2 

Fe203 ... 1.9 1.0 1.3 1.0 1.3 .4 

FeO . . ... 1.0 .08 . 18 .24 .38 .42 

MgO .... .55 .55 .05 .23 .35 .25 

CaO ..... 1.1 .25 .19 .35 .47 .42 

Na20 .. . 4.0 3.0 3.6 3.5 3.5 .4 

K20 ..... 5.2 5.9 5.5 4.7 5.3 .5 

H20- ... .34 .37 .09 .17 .24 .13 

H20+ .. .93 .63 .64 .87 .77 .16 

Ti02 . ... .42 . 17 .18 .21 .25 .12 

P205 .... .16 0 .01 .02 .05 .08 

MnO . . .. .03 .03 .02 .02 .03 .01 

C02 .... .19 <.05 .05 .15 .09 .10 

Total. 100 100 100 100 100 

Spectrographic analyses (weight percent) 

Ba . ... . . 0.07 0.02 0.01 o .. o3 0.03 0.03 

Be .... .. .0003 .0003 .0007 .0002 .0004 .0002 

Ce .. . ... 0 0 .015 0 .004 .008 

Co ...... 0 0 0 .0003 .000 I .0002 

Cr . ..... .00015 0 .00015 0 .00008 .00009 

Cu .....• .0007 .0015 .0015 . 0007 .001 .0005 

Ga . .... • .002 .002 .003 .001 .002 .0001 

La ...... .005 .003 .007 .007 .006 .002 

Mo . .... . .001 0 0 0 .0003 .0005 

Nb ...... .0015 .002 .0015 .001 .0015 .0004 

Pb .....• .002 .0015 .003 .002 .002 .001 

Sc ..... . . .0007 0 .0005 0 .0003 .0004 

Sr ..... . . .02 .005 .003 .007 .009 .008 

v . .... . . .002 .001 0 0 .001 .001 

y ... . .. . .003 .002 .007 .003 .004 .002 

Yb .... . • .0003 N .0007 .0003 .0004 .0002 

Zn .... . . .015 .01 .007 .015 .01 .004 

CIPWnorms 

Q ... : . . . 23 .7 33.7 32.7 36.5 . .... .. .. . .. ... ... 

c ... .... 1.8 1.5 .81 1.5 ....... ... ...... .. or . ...... 30.7 34.9 32.5 27.8 . ... ..... . . . ... . .. 

ab . . . .. . 33.8 25.4 30.4 29.6 ..... .... ... .... .. an . . . . . . 3.2 1.2 .88 .66 . .. . ... . ... . .. .. . . 

ro . . 0 0 0 0 . .. ...... ... .... .. di en ... 0 0 0 0 .. .. . . . .. . ... . ... . 

fs .... 0 0 0 0 ... .. .. ... .. .... .. 

· hyt"· .. 1.4 1.4 .12 .57 . .... . .. . . .. . .... . 

fs . . . . 0 0 0 0 .... ..... ..... .. .. mt ... ... 2.1 0 .12 .23 . ... .. ..... ....... hm . .. . • . .45 1.0 1.2 .84 ... .. .. ....... .. .. il .. ..... .80 .23 .34 .40 . ........ ····· · ... ap . ... . . . 38 0 .02 .05 . . ... .... . ..... . .. cc .... . .. .43 . 0 0 .34 . ...... ..... ...... 

Total. 98.8 99.3 99.1 98.5 ...... .... ... ..... Fernie ) 5.6 2.6 1.8 2.4 ... .... ...... ... .. 
32 PLUTONIC ROCKS, SANTA RITA MOUNTAINS, SOUTHEAST OF TUCSON, ARIZONA 

0 2 3 MILES 

0 2 3 KILOMETRES 

EXPLANATION 

Younger rocks 

Igneous and sedimentary rocks 

Cretaceous gra nitoid rocks of the Corona stock 

a , aplite 

Older rocks 

Igneous and ,·edimentary rocks 

Contact 

Dotted where concealed 

----·-··--·-·-- Fault 

Dotted where concealed 

Q 64 

Chemically 

ana ly zed 

Specimen collection sites and numbers 

o63 

Moded 

FIGURE 20.-Distribution of granitoid rocks of the Corona 

stock and specimen collection sites. Geology east of longitude II0°45'mainly adapted from Finnell (1971). 

Sahuarita quadrangle, is dated at 73 .6 m.y. A nearly 

identical potassium-argon age of 74.1 m.y. was obtained 

by S.C. Creasey (1967; and Marvin and others, 1973) from 

a granodiorite stock in the Whetstone Mountains, 18 miles 

southeast of the Corona stock. A slightly younger age of 

70.3 m.y. was reported by Marvin for the quartz 

monzonite stock in the Empire Mountains (Marvin and 

others, 1973). Similar potassium-argon ages-71.4, 72.9, 

and 75.1 m.y.-were obtained by Bikerman and Damon 

(1966, p. 1232, 1233) from their Amole Granite and the 

FIGURE 21 .-Specimen 64. Quartz monzonite of the Corona stock. 

Zones of small crystals, including subhedral quartz and microcline with 

fairly sharp grid twinning, may indicate recrystallization. Crystals: 

perthitic microcline (M), quartz (Q), plagioclase ( P), ilmenitic 

magnetite (im), and biotite (B). Crossed nicols; X 25. 

Arnole Quartz Monzonite in the northwestern part of the 

Tucson Mountains. 

These three stocks may be genetically related to three 

fields of rhyodacite volcanics. The eastern part of the 

Corona stock is shown by Finnell (1971) to cut the exotic 

block member low in the Salero Formation; an overlying 

rhyodacite member of this formation is dated at 72.5 m.y. 

(Drewes, 1971a). Rhyodacite welded tuff dated at 71.9 

m.y. (Drewes, 1971a, p. C75) occurs along the San Pedro 

River, 15 miles southeast of of the Whetstone stock, and 

other rhyodacite welded tuff 3 miles south of Courtland is 

dated at 72.8 m.y. (Marvin and others. 1973). Similar 

volcanics about 72 m.y. old occur in the Tucson Mountains 

(Bikerman and Damon, 1966, p. 1232). The six centers of 

nearly contemporaneous magmatic activity lie along a 

northwest-trending line, possibly a fracture in the 

basement rocks. A similar, possibly genetic, relation 

between plutonic and volcanic rocks is mentioned in the 

sections in the present report on the San Cayetano stock. 
CRETACEOUS ROCKS 33 

TABLE 9.-Modes of granitoid rocks of the Corona stock 

[Field numbers are abbreviated; year of collection and collector's initial omitted. Full field number 

of specimen 62 thus is 67DI412. Symbols: s, standard deviation; Tr. trace; ... , not determined) 

Specimen No ... .. ...... . .. 62 63 64 65 66 62-66 

Field No. 1412 1411 1415 1422 1420 Mean s ... ........... . .... 

Quartz. ......... .... . ..... 41.7 25.9 28.1 24.4 25.2 29.1 7.2 

Plagioclase, total . ........ .. 32.2 25.0 34.8 38.3 52.8 36.6 10.3 

(plagioclase in perthite). .. 0 0 (3.1) (1.5) (1.8) (1.3) (1.3) 

K-feldspar, total .... .. 20.9 45.8 34.3 35.1 12.0 29.6 13.2 

(orthoclase) .. ... (20.9) (45.8) Tr.? 0 (12.0) (15.7) (19.0) 

(microcline?) . ... ...... 0? Tr.? (34.3) (35.1) 0 (13.9) (19.0) 

Biotite. .... ... . ..... 4.0 2.4 2.4 1.1 5.5 3.1 1.7 

Amphibole. ....... ... 0 0 0 0 2.8 .6 .3 

Magnetite. 1.1 .8 .2 .7 1.0 .8 .4 

Apatite .. .05 .05 .2 Tr. .3 .I .I 

Sphene ......... 0 0 0 .2 .3 .I .I 

Zircon. .......... .05 .05 .05 .I .05 .05 .02 

Allanite. 0 0 0 .I .05 Tr. ... 

Total ... ...... .... 100.0 100.0 100.05 100.0 100.0 100.05 . .. Fernie .. ..... 5.2 3.3 2.8 2.2 10.0 4.8 . .. 

Percent anorthite 

in plagioclase . ... 5? 15? . .. 37 37? . .. (plagioclase rims). (15) (15) (15) (15) (20) (15-20) ... Quartz mixing 

index (see text)·. .94 .98 .98 .96 .98 .97 ... 

JOSEPHINE CANYON DIORITE 

The Josephine Canyon Diorite is a fine- to 

medium-grained plutonic rock that ranges in composition 

from diorite, through quartz diorite and syenodiorite, to 

granodiorite; a subordinate late phase consists of 

fine-grained quartz monzonite. The lithologic term 

"diorite," as applied to the Josephine Canyon Diorite, is 

used to include syenodiorite and quartz diorite as well as 

diorite, in order to emphasize the general compositional 

feature that distinguishes this formation from the 

granodiorites of the area. 

POTASSIUM 

FELDSPAR 

QUARTZ 

TABLE 10.-Chemical and spectrographic analysis and CTPW norms of 

the Corona stock, specimen number 64 I 

[Chemical analysis by rapid rock method (Shapiro and Brannock, 1962), supplemented by atomic 

absorption method. Chemical analysts: Lowell Artis, S. D. Botts, G. W. Chloe, P. L. D. 

Elmore, John Glenn, J. Kelsey, and H. Smith. Spectrographic analysis by semiquantitative 

method. Spectrographic analyst: J. L. Morris. Elements looked for but not found: As, Au, 8, 

Bi, Cd, Eu, Ge, Hf, Hg, In, Li, Mo, Nd, Ni, Pd, Pr, Pt, Re, Sb, Sm, Sn, Ta, Te, Th, Tl, U, W, 

and Zn. Symbol: <, less than) 

Chemical analysis (weight percent) 2 

Si02 ...........•. 

Al203 .......... . 

Fe203 .......... . 

FeO ............ . 

MgO ........... . 

CaO ............ . 

Na20 ........... . 

K20 ............ . 

73.9 

13.3 

.58 

.56 

.33 

1.0 

3.9 

4.5 

H2 {}- ............ 0.07 

H20+............ .24 

TiOz ............. 1.1 

P20s . . . . . . . . . . . . . .04 

MnO............. .04 

COz ............. <.05 

Total ...... I 00 

Spectrographic analysis (weight percent)3 

Ag .............. <0.0001 

Ba . . . . . . . . . . . . . . .07 

Be............... .0002 

Ce . . . . . . . . . . . . . . .015 

Cu . . . . . . . . . . . . . . .0005 

Ga.............. .001 

La . . . . . . . . . . . . . . .01 

Nb.............. .001 

Pb .............. . 

Sc ............... . 

Sr ............... . 

v ················ y ............... . 

Yb .............. . 

Zr ............... . 

0.001 

.0003 

.02 

.0015 

.005 

.0005 

.007 

CIPWNorms 

Q .............. . 

c .............. . or .............. . 

ab ............. . 

an ............. . 

hy Jen ......... . lfs .......... . 

I Field number 1415. 

31.7 

.41 

26.7 

33.1 

4.4 

.83 

0 

hm ................ 58 

il ................. 1.3 

u................. .43 

ap................ .10 

cc . . . . . . . . . . . . . . . . .II 

Total ....... 99.7 

Fernie ....... 3.4 

2 A replicate analysis shows AI2o3, 14.5; H2o-, 0.13; H20 +, 0.47; Ti02, 0.14; P205, 0.08; 

and other minor differences. 

3 A replicate analysis differed only slightly. 

QUARTZ 

FEMIC 

MINERALS 

EXPLANATION 

;-:-.. 

Granodiorite and 

quartz monzonite 

FIGURE 22.-Modified triangular diagram showing modal quartz, potassium feldspar, plagioclase, and fernie minerals of granitoid rocks of the 

Corona stock. 
34 PLUTONIC ROCKS, SANTA RITA MOUNTAINS, SOUTHEAST OF TUCSON, ARIZONA 

The Josephine Canyon Diorite forms two stocks and 

several smaller intrusive masses north and west of the 

stocks (fig. 23). The larger stock is about 15 miles long and 

consists of two cupolas, each about 2 miles wide, 

connected by a narrow septum. The direction of elongation 

of the larger of the stocks is north-northwest, subparallel 

to the structural grain of the area and diverging 15° to 20° 

from the trend of the main outcrop area of the Squaw 

Gulch Granite. The smaller stock of diorite, in the San 

Cayetano Mountains, also trends north-northwest. Many 

of the masses of quartz monzonite also trend 

north-northwest; the larger ones, in the southern cupola of 

the large stock, cap hills suggesting that they may be 

remnants of a once fairly extensive sheet of quartz 

monzonite. The area- underlain by the Josephine Canyon 

Diorite is about 25 square miles; at shallow depths the 

stocks probably extend over a slightly larger area beneath a 

cover of roof rocks and younger deposits. 

The·diorite intrudes rocks as young as the volcanic and 

arkosic rocks of the Salero Formation of Late Cretaceous 

age, and it is unconformably overlain by rocks as old as the 

Gringo Gulch Volcanics of Paleocene (?) age. The grain 

size of rocks near the contacts of the stocks are as coarse as 

that farther from the contacts. To the north, the intrusive 

contacts are fairly sinuous and steep. The host rocks are 

not demonstrably metamorphosed by the diorite, although 

some of them were metamorphosed by the Squaw Gulch 

Granite and so may have been at equilibrium with the 

thermal conditions accompanying emplacement of the 

Josephine Canyon Diorite. To the south, the intrusive 

contacts are less sinuous and dip only moderately steeply 

outward, or away from the stocks. Locally, as in the 

southern part of the San Cayetano Mountains, the host 

rocks are thermally metamorphosed to hornfels, as shown 

on the geologic map (Drewes, 1971c). Roof pendants and 

inclusions of metavolcanic rocks and meta-arkose occur in 

many places and are particularly abundant on the hilltops 

in the southern part of the southern cupola. 

The altered rocks near the Josephine Canyon Diorite are 

locally mineralized. For example, the base-metal deposits 

at and near the Hosey mine of the Mansfield Canyon area 

(Dre~es, 1973, pl. 1) are probably a hydrothermal deposit 

that is, in part, related to the emplacement of the diorite, 

stock. Similarly, the pyrite enrichment of the intensely 

altered inclusions of volcanic rocks in the upper reaches of 

Josephine Canyon may be related to the diorite stock. 

Many of the mineralized quartz veins that cut the diorite 

(Drewes, 1971c, 1973) are spatially unrelated to the 

scattered pyrite and stains of secondary copper minerals 

within the diorite, and for this reason, among others, they 

are taken to be younger than the scattered pyrite and 

copper mineralization~ 

The observations on the distribution of late-phase quartz 

monzonite, the dips of the contacts of the stock, and the 

distribution of inclusions or roof pendants suggest that the 

present level of exposure of the southern cupola of the 

large stock is very nearly the top of the stock. 

PETROGRAPHY 

The diorite rocks that constitute most of the Josephine 

Canyon Diorite are mapped separately from the late-phase 

quartz monzonite (Drewes, 1971c). In most places these 

rocks differ strongly from each other in color and 

mineralogy; the quartz monzonite resembles the aplite 

masses of many of the other plutons of the Santa Rita 

Mountains. But in the northern part of the southern cupola 

the dioritic rocks are a composite of several rock types that 

range from typical dark-gray diorite to a light-pinkish-gray 

granodiorite that resembles the rocks of the late-phase 

quartz monzonite. The granodiorite was mapped 

separately on field sheets but is not shown here; where 

exposures are fairly abundant the map pattern suggests 

that the granodiorite represents an intermediate phase. 

DIORITIC ROCKS 

Terrane underlain by the dioritic rocks is typically 

somber-colored and is commonly more gentle than that 

underlain by other granitoid rocks in situations of similar 

local relief. Small light-brownish-gray knobs and other 

outcrops are irregularly scattered in this terrane and are 

separated by areas containing dark soil and grus. A 

discontinuous veneer or lag concentrate of 6- to 10-inch 

subrounded residual blocks of diorite makes even fairly 

flat diorite areas deceptively tedious to traverse, a feature 

that is almost diagnostic of this formation. The more 

granodioritic rock types of the northern part of the 

southern cupola, between specimen sites 79 and 97 (fig. 

23), form somewhat higher and lighter colored hills than 

those underlain by the typical diorite. 

Specimens of Josephine Canyon Diorite are mostly 

medium dark gray, but those of granodioritic composition 

are pinkish gray to light brownish gray. They are typically 

fine grained and have a speckled appearance (fig. 24) of 

dark or fernie minerals in a background of lighter colored 

minerals. The lighter color of the granodiorite is due to a 

smaller amount of fernie minerals as well as to a whiter or 

pinker shade of the background. Tiny flakes of biotite are 

recognizable in the more granodioritic rocks. Weathered 

diorite is dark brownish gray, much like the color of the 

colluvial deposits formed on it. 

The dioritic rocks have a subophitic texture that is 

unique among the plutonic rocks of the area (fig. 25). A 

few specimens are slightly porphyritic and even fewer have 

a very fine grained granophyric texture. The grain size of 

_the diorite is commonly 1-3 mm; very few of the grains 

are outside the range of 0.1-4.0 mm. The phenocrysts of 
40' 

CRETA CEO US ROCKS 

0 2 3 4 KILOMETRES 

110" 50' 

X Mount Wrightson 

or 

or 

YHOSEY 

MINE 

\ _ Mansfield 

~Y~n 

or 

EXPLANATION 

Younger rocks 

Igneous and sedimentary rocks 

Ki j; :J 

35 

Cretaceous Josephine Canyon Diorite 

Kj , dioritic rocks; includes quartz diorite, 

syenodiorire, and granodiorite 

Kjq , fine-grained quarTz monzonite 

G 

Older rocks 

Igneous and sedimentary rocks 

Contact 

---··········· Fault 

Dotted where concealed 

0 82 

Radiometrically Chemically 

dated ana lyzed 

• 81 

Mod ed 

• <a--Ki 

e u 

FIGURE 23.-Distribution of Josephine Canyon Diorite and specimen collection sites. 

the porphyritic rocks are mostly 1-3 mm long, and the I Typical diorite contains (in approximate order of 

groundmass grains are about 0.1 mm across. decreasing abundance): plagioclase, amphibole, biotite, 
36 PLUTONIC ROCKS, SANTA RITA MOUNTAINS, SOUTHEAST OF TUCSON, ARIZONA 

FIGURE 24.-Specimen 80. Josephine Canyon Diorite, showing fine grain 

size and speckled appearance. 

orthoclase, pyroxene, and quartz; all specimens have 

accessory magnetite, apatite, and zircon, and some also 

have one or more of such accessory minerals as sphene, 

hypersthene, tourmaline, alianite, and pyrite. Most 

plagioclase forms subhedral to nearly euhedral grains, but 

some nearly anhedral grains lie between the laths and are 

poikilitic. Plagioclase is only slightly altered to clay 

minerals and sericite. The anorthite content of most 

plagioclase is 30 to 50 percent, in the range of andesine, but 

that of some specimens, particularly specimens containing 

abundant fernie minerals, is 50 to 65 percent, indicative of 

labradorite. Normal composition zones of calcic oligocalse 

sheathe some grains. Albitized plagioclase appears in only 

a few specimens. Most of the amphibole is probably a 

hornblende with mostly very pale yellowish green to 

pale-green or to pale-bluish-green pleochroism; the 

pleochroism of some amphibole is pale yellowish green to 

moderate green. Some amphibole grains are surrounded by 

biotite grains, Biotite forms anhedral to subhedral grains 

pleochroic in pale yellow brown to moderate brown. They 

are only slightly chloritized, or in some specimens altered 

to penninite and with inclusions of leucoxene. The orthoclase is anhedral, slightly kaolinitized and contains sparce 

and fine bands of perthitic albite. A specimen from one of 

the small intrusive bodies contains sanidine instead of 

orthoclase. The quartz grains are anhedral and have little 

or no undulatory extinction. The pyroxene is probably 

augite, which occurs either as subhedral to euhedral grains 

encased by amphibole or biotite or as grains intricately 

intergrown with amphibole. 

Accessory minerals are more varied and abundant than 

in other plutonic rocks of the area. Ilmenitic magnetite 

occurs as subhedral to euhedral grains in amounts ranging 

from 1 to 5 percent. Euhedral apatite crystals are also 

fairly abundant, in one specimen exceeding 1 percent, and 

euhedral to anhedral zircon crystals occur in amounts of as 

much as about 0.5 percent. Sphene, present in about half 

the specimens, occurs either as overgrowths around 

magnetite or as subhedral to euhedral grains. Schorlite 

tourmaline and pyrite are probably primary minerals but 

occur in only a few specimens as do hypersthene and 

allanite. 

The Josephine Canyon Diorite contains the same 

alteration minerals as the pre-Cretaceous plutonic rocks of 

the area but in less abundance. They include chlorite, 

penninite, sericite, kaolinite, uralite(?), hydromica (?), 

epidote, leucoxene, and iron oxide. Veinlets of quartz and 

calcite and of some of the alteration minerals cut a few of 

the diorite specimens. 

FINE-GRAINED QUARTZ MONZONITE 

The quartz monzonite of the late phase of the Josephine 

Canyon Diorite underlies a terrane slightly more rugged 

and lighter-colored than that underlain by the dioritic 

rocks. The rock typically forms small pale-yellowish-gray 

knobs and ledges which weather to blocky rather than 

subrounded detritus. Surfaces of fairly fresh quartz 

monzonite range from pale red to pale reddish brown to 

light brownish gray; the color varies with the relative 

abundance of orthoclase and fernie minerals. 

The correlation of a large mass of fine-grained 

leucocratic rock in the area of collection sites of specimens 

92 to 95, a mile west of Mount Wrightson, with the quartz 

monzonite member of the Josephine Canyon Diorite rather 

than with aplite of the Elephant Head Quartz Monzonite is 

a tenuous one, based more on geographic proximity than 

on petrographic data. 

The texture of the quartz monzonite ranges from faintly 

porphyritic and subophitic to hypidiomorphic or 

idiomorphic. Nearly half the specimens contain some 

granophyric or myrmekitic texture. Argillic alteration is 

more intense in the quartz monzonite than in the dioritic 

rocks; as a result, finer features are commonly obscured 

and staining is invariably needed in preparing specimens 

for modal analysis. 

Major mineral constituents of the quartz monzonite 

member of the Josephine Canyon Diorite are plagioclase, 

orthoclase, and quartz. Plagioclase forms lath-shaped 

crystals, which are less conspicuous than those in the 

dioritic rocks. Plagioclase of the least altered specimens is 

andesine, and rarely labradorite, some of the plagioclase is 

surrounded by a zone of oligoclase. Plagioclase of most of 

the specimens, however, is albite, presumably as a result of 

deuteric albitization. This plagioclase is much altered to 
CRETACEOUS ROCKS 37 

B 

FIGURE 25 .-Specimen 81 . Josephine Canyon Diorite. Crystals: plagioclase ( p ), orthoclase ( 0 ), quartz ( Q ), biotite ( B), amphibole ( A), 

ilmenitic magnetite ( im ), pyroxene ( p x), and apatite (a p ). X 25 . A, Plain light; B, crossed nicols. 

clay minerals and sericite. The orthoclase forms anhedral 

crystals that are strongly kaolinitized and are perthitic, and 

the quartz forms interstitial anhedral crystals that have 

little or no undulatory extinction. 

Of the less abundant and accessory minerals, biotite 

forms partly chloritized subhedral crystals pleochroic in 

pale greens. Clinopyroxene crystals are colorless and have 

a Z 1\ C of 40° to 45°, suitable for a magnesium-rich 

augite. The magnetite is ilmenitic. Schorlite tourmaline 

forms inclusions in some quartz and biotite, and acicular 

rutile is sparsely present in some biotite. 

MODAL AND CHEMICAL SUMMARY 

Modal analyses of 25 specimens of dioritic rocks and of 

11 of the quartz monzonite (table 11) illustrate the 

mineralogical composition of the Josephine Canyon 

Diorite. The modes of specimens 90 and 91 are excluded 

from the tabulated mean because they are from small 

intrusive bodies so rich in fernie minerals that their 

correlation with the other dioritic rocks remains 

provisional. The modal analyses are summarized on the 

modified triangular diagram of figure 26, which shows a 

good correspondence between the field determination of 

the two members of the Josephine Canyon Diorite and the 

rock classification scheme of the diagram. 

The figure circumscribed around the plotted modes is an 

elongated discoid-shaped body that is tilted toward a point 

lying about a third of the distance from the leucocratic face 

toward the fernie apex of the composition tetrahedron. 

With the field observation that the more dioritic rocks are 

intruded by the more quartz monzonitic ones, it seems 

probable that the magma evolved from one magma 

approximately represented by the lower edge of the 

circumscribed or "modal body" to another represented by 

the upper edge. This trend may be continued with the 

development of the magmas forming the Madera Canyon 

Granodiorite and Elephant Head Quartz Monzonite, 

discussed in some of the following sections of this report. 

The mineralogical data (table 11) reflect compositional 

variations in both geographical distribution and successive 
38 PLUTONIC ROCKS, SANTA RITA MOUNTAINS, SOUTHEAST OF TUCSON, ARIZONA 

TABLE !I.-Modes of 

[Field numbers are abbreviated; year of collection and collector's initial omitted. full field number 

Rock type. Dioritic rocks (includes quartz diorite, syenodiorite, and granodiorite) 

Specimen No .. 167 268 69 70 71 72 73 74 75 76 77 78 79 80 

field No. 731 741 780 1579 1580 407 455 351 300 173 271 2)8 254 361 

Quartz . 9.7 3.7 6.8 3.2 4.9 3.9 13 .2 10.9 8.6 10.2 4.2 7.9 12.2 10.2 

Plagioclase, total. 59.1 60.9 63 .6 65 .1 59.6 62.8 50.1 55.8 59.1 56.6 63.7 63.1 50.0 47.2 

(plagioclase in perthite) . 0 0 0 0 0 0 0 (6.4) 0 0 0 0 (1.7) 0 

Orthoclase . 7.6 4.9 6.0 3.6 6.3 6.4 23.1 15.7 15.8 14.9 10.9 11.5 21.9 22.5 

Hornblende . 11.2 18.5 7.4 13.4 14.0 18.9 0 10.'1 6.1 0 10.6 0 0 0 

Pyroxene (augite?) 0 0 4.3 4.8 6.3 1.7 6.5 .05 1.6 6.7 3.5 9.7 6.5 8.7 

Biotite. 9.2 6.1 8.0 5.8 5.0 2.1 4.3 3.2 4.8 7.4 3.3 3.7 5.7 6.6 

Magnetite. 2.4 3.7 3.5 3.3 3.5 3.7 2.4 3.2 3.0 3.0 3.5 3.4 3.3 2.9 

Apatite . .I .5 .3 .8 .3 .4 .4 .4 .6 .4 .05 .6 .3 .7 

Sphene . .6 1.7 0 0 0 Tr. 0 .4 .I 0 .2 0 Tr. .I Zircon . . . . . . . . . . . . . . . . . .05 Tr. .I .05 .05 .05 .05 .2 .2 .I .05 .I .05 .I Allanite . . . . . . . . . . . . . . . . . Tr. Tr. 0 0 0 0 0 0 0 0 0 0 0 0 

Rutile 0 0 0 0 0 0 0 0 0 0 0 0 0 0 

Tourmali ne . 0 0 0 0 0 0 0 0 .I 0 0 0 .I 0 

Hypersthene . 0 0 0 0 0 0 0 0 0 .7 0 0 0 0 

Total . 99.95 100.0 100.0 100.05 99.95 99.95 100.05 99.95 100.0 100.0 100.0 100.0 100.05 99.0 

Fernie . ........ .. .. 23.6 30.5 23.6 28.1 29.2 26.9 13.6 17.6 16.5 18.3 21.2 17.5 15 .9 19.1 

Percent anorthite 

in plagioclase . 49-60 28 37-45 35-40 38-50 40-46 38-49 35-47 33 43 33-36 40-50 43-49 33-39 33-50 

(plagioclase rims). (28) (25) (28) 

Quart z mixing 

index (see text) .89 .83 .94 .68 1.0 .89 .92 .96 .93 .81 .87 .78 .95 

1 Specimen 67 collected from dioritic component of a mixed rock, dominantly of the quartz 2specimens 68 an\! 90 contain a little modal calcite. 

·monzonite phase. 

QUARTZ QUARTZ 

EXPLANATION 

~";"'\ 

DioritiC rocks; includes 

granodiorite, quartz 

diorite , syenodiorite, 

and diorite 

I@\ 

Fine-grained quartz monzonite ; 

includes some granodiorite and 

syen ite 

111 

Josephine Canyon(?) Diorite 

HI 82 83 84 

274 273 292 263 

12.1 7.8 11.1 9.3 

53.1 53 .4 51.7 54.3 

0 0 0 0 

14.5 20.6 15.1 22.8 

2.4 3.2 1.6 4.9 

4.1 5.5 5.9 3.9 

10.7 4.3 10.7 1.4 

2.5 4.0 2.6 3.2 

.5 1.1 .9 .I 

0 .I .3 0 

.I .05 .05 .05 

0 0 0 0 

0 0 0 0 

0 0 .05 0 

0 0 0 0 

100.0 100.05 100.0 99.95 

20.3 18.2 22 .1 13.6 

37- 47 32- 49 35-40 47-65 

.87 .86 .75 .99 

FEMIC 

MINERA LS 

<%> 

FIGURE 26.-Modified triangular diagram showing modal quartz, potassium feldspar, plagioclase, and fernie minerals of Josephine Canyon Diorite. 

phases developed in the Josephine Canyon Diorite. 

Because the sequential order in which the modes are 

tabulated follows their distribution (fig. 23) from 

northwest to southeast, geographical variations of modes 

are readily seen on scanning table 11 from left to right. 

Toward the southeast, in the large pluton, the abundance 
CRETACEOUS ROCKS 39 

Josephine Canyon Diorite of specimen 67 thus is 650731. Symbols: s, standard deviation; Tr., trace; ... , not determined] 

Dioritic rocks (includes quartz diorite, Josephine 

Canyon(?) Fine-grained quartz monzonite syenodiorite, and granodiorite)-Continued Diorite 

385 86 87 88 89 67-89 290 91 92 93 94 95 96 97 98 99 410o 101 102 92-102 

Mean s Mean s 332 571 575 560 545 631 621 830 835 404 405 348 234 239 235 330 276 262 

6.9 15.6 15.1 8.0 0.9 8.5 3.9 6.2 4.3 22.4 16.2 26.5 16.4 19.5 18.7 24.5 22.3 8.6 24.1 11.8 19.2 5.6 

47.7 49.9 46.1 50.3 66.6 56.1 6.3 50.4 55.4 43.3 44.7 28.7 43.4 37.7 31.9 32.9 27.1 17.1 25.0 34.9 33.3 8.6 

0 (0.6) 0 0 0 (0.4)- (1.4) 0 0 (1.8) 0 0 0 (4.3) 0 0 0 0 0 0 (0.6) (1.4) 

25.2 9.1 23.1 20.5 0 14.0 7.5 4.1 .5 22.8 28.1 34.9 31.8 32.4 43.0 38.4 40.5 66.0 43.4 35.4 37.9 11.2 

11.5? 12.9 5.2 0 0 6.6 6.3 16.8 29.2 0 4.7 .05 1.7 3.4 .4 Tr. .3 .I 0 6.8 1.6 2.4 

6.7 2.2 3.8 7.6 22.2 5.3 4.6 0 0 0 0 0 1.6 1.6 0 0 2.1 5.0 4.4 2.4 1.6 1.8 

.2 8.6 4.0 10.5 3.8 5.6 3.0 J8.0 5.6 10.0 4.0 6.2 3.1 2.4 2.7 2.3 4.4 .6 .7 5.3 3.8 2.7 

1.8 .9 2.2 2.6 5.3 3.0 .9 2.0 2.5 1.2 1.6 2.0 1.6 1.8 3.0 1.5 2.4 2.5 1.9 3.2 2.1 .6 

Tr. .4 .5 .3 1.2 .5 .3 .8 .7 .3 .3 .4 .2 .2 .3 .4 .3 Tr. .3 .2 .3 .I 

Tr. .3 0 .05 0 .2 .4 1.6 1.8 0 .2 1.2 .I .5 0 0 .5 Tr. Tr. 0 .2 .4 

0 .I .05 .I 0 .07 .05 .I 0 Tr. .I .05 . 05 Tr. Tr . Tr. .I . I .2 Tr . .06 .06 

0 Tr. 0 0 0 Tr. .... 0 0 0 .I 0 .05 .3 0 0 0 0 0 0 .04 .09 

0 0 0 0 0 0 ..... 0 0 0 0 .OS Tr. 0 0 0 0 0 0 0 Tr. ..... 0 Tr. 0 Tr. 0 Tr. 0 0 0 0 0 Tr. .2 0 0 0 Tr. 0 0 Tr. ····· 0 0 0 0 0 Tr. ..... 0 0 0 0 0 0 0 0 0 0 0 0 0 0 ..... 

100.0 100.0 100.05 99.95 100.0 99.9 ... 100.0 100.0 100.0 100.05 100.05 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.1 ..... 20.2 25.4 15.7 21.2 32.5 21.3 5.3 39.3 39.8 11.5 11.0 9.9 8.4 10.4 6.4 4.2 10.1 8.3 7.5 17.9 9.7 3.5 

50 45-61 35 41-50 50-65 33-65 ..... 0-28 28-31 25-35 37-35 32-40 38-47 30-33 32-38 0 39-49 0? 28-35 50-57 28-55 ..... 

..... .... .... .. ......... ....... (27) ..... ........ ..... ······································· (26) ........ (25) ················ (35) (0-28) ..... 

.97 .95 .92 .83 ....... .89 .08 .71 .58 .89 .90 

3specimen 85 was collected by F.S. Simons about I mile south of the Mount Wrightson 

quadrangle. 

of orthoclase, and perhaps also of quartz, increases; 

correspondingly, hornblende and possibly also sphene 

decrease in abundance. This mineralogical evidence 

supports field observations of an increasing abundance of 

more granodioritic rock types in the southern cupola. 

Chemical and spectrographic analyses and CIPW norms 

of nine specimens of Josephine Canyon Diorite are given in 

table 12, and the chemical data are summarized in the 

histogram of figure 1 OC. The compositional range of the 

analyzed specimens is small (note the low value of the 

standard deviation of the mean value in table 12). Most 

analyzed specimens are modal granodiorites (fig. 26), but 

one, specimen 69, is a modal diorite whose chemical 

analysis approximates the analytical mean of the five 

dioritic rocks. Thus, analyses of a suite more 

representative of the modal varieties included with the 

dioritic rocks may not significantly alter the mean of the 

chemical analyses of those rocks. The mean chemical 

analysis of the dioritic rocks (table 12) compares poorly 

with the analyses presented by Nockolds (1954, p. 1018, 

1019); for a rock of its high alkali content, the Josephine 

Canyon Diorite is silica poor. 

AGE AND CORRELATION 

The Josephine Canyon Diorite is dated as Late 

Cretaceous or early Paleocene (?) on geologic evidence and 

is dated even more precisely as late Late Cretaceous on 

radiometric evidence. Field relations show the diorite to 

intrude rocks as young as the Salero Formation, a middle 

member of which is dated as 72 m.y. old. The diorite is 

.94 .92 ........................ .95 ........ .92 .83 .91 .04 

4Analyses of specimen 100 is omitted from average inasmuch as the specimen is more intensely 

altered than other rock of this phase. 

unconformably overlain by the Gringo Gulch Volcanics, 

which are dated as Paleocene (?) and which are probably 

older than the rocks of the Gringo Gulch pluton (Drewes, 

1971c and 1972a), dated as about 60 m.y. old. 

Three specimens of Josephine Canyon Diorite are 

radiometrically dated, one of them by both the 

potassium-argon method and the lead-alpha method, and 

the other two only by the lead-alpha method (table 4). The 

potassium-argon age determination of 67.1 m.y. dates the 

relatively young part of the southern cupola. Diorite from 

a deeper part of the stock, in the northern cupola, may well 

be estimated to be about 69 m.y. old. Should the 69-m.y. 

estimate prove to be correct, the discrepancy between the 

ages and the field relations of the Josephine Canyon 

Diorite with the Madera Canyon Granodiorite and the 

Elephant Head Quartz Monzonite is clarified. The three 

lead-alpha ages are consistent with each other at about 62 

m.y. despite the fact that this radiometric dating method is 

usually less reliable than the potassium-argon method. In 

an age range of about 60 m.y. lead-alpha determinations 

are generally several milion years younger than potassiumargon determinations of the same rock. The true age of 

emplacement of the quartz monzonite member may thus be 

about 65 m.y., and it almost certainly is not younger than 

about 63 m.y. The similarity in the lead-alpha ages of the 

dioritic rocks with that of the quartz monzonite member, 

however weak the dating method, lends some support to 

the interpretation that these rocks are genetically closely 

related. 

Rocks that resemble the Josephine Canyon Diorite in 
40 PLUTONIC ROCKS, SANTA RITA MOUNTAINS, SOUTHEAST OF TUCSON, ARIZONA 

TABLE 12-Chemica/ and spectrographic analyses and CIPW norms of Josephine Canyon Diorite 

[Chemical analyses by rapid rock method (Shapiro and Brannock, 1%2), with analyses of specimens 69, 74, 80, 82, 84, 88, and 94 supplemented by X-ray fluorescence method. Chemical anaiysts: 

Lowell Artis, S. D. Botts, G. W. Chloe, P. L. D. Elmore, John Glenn, and H. Smith. Spectrographic analyses by semiquantitative method. Spectrographic analysts: W. B. Crandell, 

J. L. Finley, J. C. Hamilton, J. L. Harris, A. L. Sutton, and Barbara Tobin. Symbols: s, standard deviation;<, less than; ... , not determined; N, not detected) 

Rock type .... Dioritic rocks (includes quartz diorite, syenodiorite and granodiorite) Quartz monzonite phase 

Specimen 

No.. 69 

Fidd No. . . . 780 

74 

351 

80 

316 

82 

273 

84 

263 

88 

560 

69- 88 

Mean 

94 

404 

99 

235 

100 

330 I 94-100 

Mean s 

Chemical analyses (weight percent) 

Si02 ....... 59.7 61.1 60.2 60.7 58.7 58.8 59.9 1.0 69.9 67.3 67.1 68.1 1.6 

AI203 ..... l7.8 15.5 16.0 15.7 16.6 17.0 16.4 .9 15.0 14.4 15.6 15.0 .6 

Fe203 ...... 2.8 4.0 3.3 3.2 4.3 2.4 3.3 .7 3.1 3.1 2.3 2.8 .5 

FeO ........ 3.1 2.7 3.6 3.2 2.7 3.7 3.2 .4 1.5 1.4 .76 1.2 .4 

MgO ....... 2.9 3.2 3.0 2.4 3.3 2.6 2.9 .3 .60 .65 .10 .45 .3 

CaO ........ 5.2 4.4 5.2 4.8 4.9 5.9 5.1 .5 1.4 2.4 1.7 1.8 .5 

Na2o ...... 3.8 3.4 3.4 3.8 3.8 3.4 3.6 .2 3.3 3.1 3.6 3.3 .3 

K20 ........ 2.5 3.3 2.7 3.3 3.3 2.8 3.0 .4 2.6 4.8 6.6 4.7 2.0 

H20- ..... .18 .15 .26 .28 .27 .19 .22 .05 .18 .38 .29 .28 .10 

H20+ ..... .68 .95 1.0 1.1 .71 1.1 .92 .19 .92 .72 .41 .68 .26 

Ti02 ....... .85 .10 .87 .90 .% .90 .76 .33 .45 .64 .60 .56 .10 

P205 ....... .28 .27 .29 .27 .26 .25 .27 .01 .15 .13 .45 .24 .18 

MnO ....... .08 .90 .08 .II .21 .II .25 .32 .05 ;08 .08 .07 .02 

C02········ .08 <.OS .05 .05 .05 .55 .II .22 <.05 <.05 .05 <.05 .03 

Total. 100 100 100 100 100 100 100 ······ 99 99 100 99 ...... 

Spectrographic analyses (weight percent) 

Ag .... ..... 0 *o *o to to 0 0 0 0 ....... fit<O.OOOI ttiO 0 0 I< 0.0001 ....... Ba .... ..... .I .I .015 .I .15 .15 .I .15 .I 0.05 .07 .15 .I .15 .I 0.4 

Be. ······· 0 .0002 .0001 0 0 0 .0002 .0002 .0001 .0001 .0001 .0003 .0003 .0002 .0002 .0001 

Ce .... ..... 0 0 N 0 N 0 0 0 0 . ...... .01 .02 .015 .05 .02 .02 

Co .... ..... .002 .003 .003 .002 .007 .002 .002 .003 .003 .002 .002 .0007 .0015 0 .001 .001 

Cr .... ..... .0007 .003 .0015 .005 .003 .0015 .003 .015 .004 ;005 .0015 .001 .0015 .0005 .001 .0005 

Cu .... ..... .03 .015 .07 .015 .02 .02 .015 .01 .02 .02 : .01 .007 .015 .007 .01 .004 

Ga .... ····· .001 .005 N .002 N .003 .005 .002 .003 .002 .001 .005 .003 .0015 .003 .002 

La .... .... .005 .005 .07 .007 .003 .005 .007 .005 .01 .02 I 

.007 .01 .007 .015 .01 .004 

Mo .... ..... .0003 0 0 .0007 0 .007 0 .0007 .001 .002 

I 

0 0 0 0 0 . ...... Nb .... ..... 0 0 .002 0 .002 .002 0 0 .0008 .001 . 0007 0 .002 .001 .0009 .0008 Nd .... ..... 0 0 N 0 N .007 0 .005 .002 .003 

I 

0 .007 .007 0 .004 .004 

Ni ... ······ <.003 .002 .002 .005 .015 .0015 .003 .007 .005 .005 .003 .0015 .0015 0 .0015 .001 

Pb .... ..... .001 .0015 .003 .002 .001 .002 .002 .002 .002 .001 .001 .003 .002 .003 .002 .001 

Sc ..... ..... .001 .002 .007 .0015 .002 .001 .0015 .002 .002 .002 .001 .001 .001 .01 .003 .005 

Sr ..... ..... .I .15 .015 .I .015 .05 .15 .I .09 .05 .05 .I .05 .03 .06 .03 

v .... ...... .015 .03 .02 .02 .03 .01 .02 .02 .02 .007 .01 .01 .01 .005 .009 .003 

Y. ......... .002 .003 .007 .003 .001 .002 .003 .003 .003 .002 .003 .005 .002 .005 .004 .002 

Yb ... .... .0002 .0003 . ..... .0003 . ..... .0005 .0003 N .0003 .0001 .0003 .0005 .0005 .0003 .0004 .0001 

Zi. ... .02 .015 .01 .01 .02 .03 .015 .01 .02 .007 .02 .02 .03 .03 .03 .006 

CIPW norms 

Q 12.6 14.4 14.9 13.3 10.1 

c .25 0 0 0 0 

or ...... 14.8 19.5 16.0 19.5 19.5 

ab ...... 32.1 28.8 28.8 32.1 32.1 

an 

{~~ 23.5 17.3 20.4 16.0 "t8.5 

0 1.2 1.4 2.5 1.7 

di en 0 .77 .99 1.7 1.5 fs 0 .30 .34 .57 .04 

h\" 1en ...... 7.2 7.2 6.5 4.2 6.8 

· fs ...... 2.1 2.9 2.3 1.4 .17 

mt 4.1 5.8 4.8 4.6 6.2 

hm. 0 0 0 0 0 

il 1.6 .19 1.7 1.7 1.8 

ap .66 . 64 .69 .64 .62 cc .. .18 0 0 0 0 

Total. 99.1 99.0 98.8 98.2 99.0 Fernie 15.8 19.0 18.7 17.3 18.8 

*t'iT Pairs of replicate analyses. 

both composition and age have not been reported in 

mountain ranges immediately adjacent to the Santa Rita 

Mountains. Somewhat similar rocks, which have been little 

studied and are poorly dated, occur in the Ruby area, 17 

miles southwest of the small stock of Josephine Canyon 

Diorite, and other such rocks occur in Sonora near Nogales 

about 15 miles south of that stock (fig. 1). 

12.7 .................. 37.3 25.2 18.6 ................... (') ·················· 4.6 .06 .64 ................... 16.5 .................. 15.4 28.4 39.1 ................... 28.8 .................. 27.9 26.2 30.6 . .................. 22.9 .................. 6.0 II. I 5.2 ................... .54 .................. 0 0 0 ................... .33 .................. 0 0 0 ................... .18 .................. 0 ·0 0 ................... 6.1 .................. 1.5 1.6 .25 ................... 3.4 .................. 0 0 0 ................... 3.5 .................. 3.7 2.9 .98 ................... 0 .................. .55 1.1 1.6 ................... l.7 .................. .86 1.2 1.1 ................... .59 .................. .36 .31 I. I ................... 1.3 

98.5 

17.6 

.................. 0 0 ll ................ · ... 

................... 98.2 98.1 99.3 . .................. ··················· 7.0 7.1 5.1 ................... 

MADERA CANYON GRANODIORITE 

The Madera Canyon Granodiorite is a coarse-grained, 

light-gray to medium-gray speckled rock in which dark 

minerals are moderately to very abundant. The 

granodiorite is in a stock in the Madera Canyon area (fig. 

27) that trends northwest and is wedge shaped, tapering to 
CRETACEOUS ROCKS 41 

or 

or 103.0 5 

~ 0 2 3M I LES 

~---.------'---r__j_--,-L----' 

0 2 3 KI LOMETRES 

EXPLANATION 

Younger rocks 

Igneous and sedimentary rocks 

Cretaceous Mad era Canyon Granodiorite 

K m, Hranodiorite 

Kmp , porphyritic granodiorite 

K m m, melanocratic granodiorite 

Older rocks 

Igneous and sedimentary rocks 

- --- ---- -------

Contact 

Dotted where concealed 

------ ------··- Fault 

Dotted where concealed 

.1o9 0 110 

*? 

Moded Chemically Radi ome trically 

an al yzed dated 

Specimen collection sites and numbers 

FIGURE 27 .-Distribution of Madera Canyon Granodiorite ; 

and specimen collection sites. 

the southeast. The stock underlies an area of about 10 

square miles; about 6 square miles of this area is directly 

underlain by granodiorite; the remainder is projected 

beneath a thin gravel cover on the pediment off the mouth 

of Madera Canyon. 

The granodiorite intrudes mainly the Mount Wrightson 

Formation and the Piper Gulch Monzonite, both of 

Triassic age, and the southeastern end of the stock intrudes 

the Josephine Canyon Diorite. Sedimentary rocks· 

intercalated in the Mount Wrightson Formation are 

strongly contact metamorphosed along the eastern margin 

of the stock, as shown on the geologic map (Drewes, 

1971c), but the volcanic rocks of the formation are no 

more altered near the stock than they are away from it. The 

contact zone, as observed at collection site 103 (fig. 27), is 

narrow and chilled. Inclusions of epidotized and 

chloritized quartz diorite, probably derived from a nearby 

Triassic intrusive mass, form inclusions in the granodiorite 

near the eastern margin of the stock, midway between 

collection sites 126 and 127. The rocks on both sides of the 

contact in this area are also slightly pyritized. In general 

the contact is sharply defined, steeply inclined, and regular 

in trend; but near the southeastern end of the stock it is 

steeply to gently inclined and, consequently, irregular in 

trend. Apparently the southeastern outcrops lie near the 

top of that part of the stock, whereas the northwestern 

outcrops lie a considerable distance beneath the original 

top of the stock. 

PETROGRAPHY 

The Madera Canyon Granodiorite consists of three rock 

types each distinctive in texture or in composition. A 

nonporphyritic granodiorite is the most widespread type; it 

crops out from the narrow end of the stock almost to the 

mouth of Madera Canyon, where it appears to grade into a 

porphyritic granodiorite. The porphyritic granodiorite 

underlies the northwestern part of the stock, largely in the 

pediment area. Melanocratic granodiorite underlies an 

elongate area along the northeastern side of the stock, 

where it is separated from the other two types of 

granodiorite by younger intrusive rocks of the Elephant 

Head Quartz Monzonite and by a prong of the host rocks. 

The term "melanocratic" will be used hereafter for a rock 

with an unspecified but relatively large amount of dark 

minerals. 

GRANODIORITE 

The nonporphyritic granodiorite, to be referred to 

hereafter simply as "granodiorite," is much less resistant 

to weathering than the adjacent rocks, and so it underlies 

low areas, such as the bottom of Madera Canyon. This 

weathering characteristic is largely the result of the 

friability of the rock, which disaggregates readily to form 

extensive slopes of grus and a few small outcrops. 

Outcrops of granodiorite are most accessible in the 
42 PLUTONIC ROCKS, SANTA RITA M~.-UNTAINS, SOUTHEAST OF TUCSON, ARIZONA 

roadcuts a few hundred feet south of the Santa Rita Lodge 

(area of specimen 113, fig. 27), as well as along trail cuts 

and in the bottoms of the narrowest canyons. Rocks from 

these relatively unweathered outcrops are illustrated by 

figure 28. The granodiorite typically has a hypidiomorphic-granular texture and a 2- to 5-mm grain size (fig. 29). 

Near the southeast end of the stock the grain size is slightly 

smaller and some specimens have a bimodal size 

distribution of grains, with the smaller ones only 0.1 to 0.5 

mm long. Specimens from the northwest end of the 

granodiorite area, on the other hand, contain some crystals 

6 to 7 mm long that resemble underdeveloped phenocrysts. 

Some granophyric texture is commonly evident in all 

specimens. 

Common minerals of the granodiorite are quartz, 

orthoclase, plagioclase, biotite, and hornblende (fig. 26). 

The quartz is anhedral and has little or no undulatory 

extinction; in rocks whose grains have a bimodal 

distribution, quartz is commonly among the smaller group 

of crystals. The orthoclase is anhedral or subhedral and 

contains a fine lacy perthitic intergrowth of albite. One 

specimen taken about 2 em from the contact of the 

granodiorite with the Josephine Canyon Diorite contains 

sanidine instead of orthoclase. Plagioclase is subhedral; it 

generally has a composition of calcic oligoclase to sadie 

andesine, but in a few specimens it is albitized. The biotite 

is subhedral and is pleochroic in pale yellowish brown to 

moderate brown. Hornblende forms euhedral to subhedral 

crystals pleochroic in pale yellowish green to pale grayish 

green. In the northern part of the granodiorite body some 

of the biotite and hornblende are clustered, as they 

typically are in the nearby melanocratic granodiorite. 

Accessory minerals invariably include ilmenitic 

magnetite, apatite, and zircon, and some specimens also 

contain a trace of sphene, rutile, and beryl(?). Some 

magnetite grains are surrounded by sphene. The zircon is 

moderately abundant and fairly coarse for zircon, reaching 

a grain size of about 0.4 mm. 

Secondary minerals are moderately scarce and consist of 

kaolinite, sericite, chlorite, leucoxene, and epidote. 

PORPHYRITIC GRANODIORITE 

Aside from its phenocrysts, the porphyritic granodiorite 

closely resembles the nonporphyritic type. Indeed, the two 

units may be gradational, with the porphyritic rock 

characteristic of the core of the stock and the 

non porphyritic rock present along an unrecognized narrow 

border zone and more extensively present in the narrow 

southeastern shoulder of the stock. Unweathered, 

nonfriable outcrops of the porphyritic granodiorite are 

scarce; some of the freshest material is available in a rock 

dump along the edge of Madera Canyon nearest to the 

collection site of specimen 120 (fig. 27). 

The texture of the rock is noteworthy for its scattered 

phenocrysts which are 3 to S em long. Despite the 

FIGURE 28.-Specimen 113. Nonporphyritic type of Madera Canyon 

Granodiorite. 

occurrence of phenocrysts and the coarse-grained 

groundmass, the rock differs from the Continental 

Granodiorite by having fewer phenocrysts and 

ferromagnesian minerals and being much less altered. Very 

locally, Yz to 1 mile northwest of collection site 120, the 

porphyritic granodiorite contains some schlieren of more 

leucocratic quartz monzonite and some of more 

porphyritic rocks. 

In thin section, the porphyritic granodiorite is seen to 

differ from the nonporphyritic type in that the potassium 

feldspar commonly has indistinct or blurred grid twins 

typical of microcline. One specimen also contains 

accessory allanite. 

MELANOCRATIC GRANODIORITE 

The melanocratic granodiorite is a nonporphyritic 

dark-gray rock that contains abundant hornblende and 

biotite and a gray plagioclase (fig. 30). Clustered 

ferromagnesian minerals give the rock a faintly mottled 
CRETACEOUS ROCKS 43 

A B 

FIGURE 29.- Specimen 113. Nonporphyritic type of Madera Canyon Granodiorite. Crystals: plagioclase ( p ), quartz ( Q ), orthoclase ( 0 ), biotite 

( B), hornblende ( H), ilmenitic magnetite ( im), and sphene ( S ). x 20. A, Plain light; B, crossed nicols. 

appearance. It is most easily accessible near collection site 

127 (fig. 27) in the northern part of the outcrop area. 

The clustering of small crystals of biotite and the 

bimodal distribution of grain size in many specimens of 

melanocratic granodiorite suggest mild recrystallization. 

Strongly sutured grain boundaries and a peculiar 

wormy-looking granophyric intergrowth also suggest 

recrystallization. 

The minerals in the melanocratic granodiorite are mostly 

the same as those in the other types of granodiorite. Most 

of the plagioclase has the composition of andesine and that 

of two specimens is calcic andesine, but some of the 

plagioclase is albitized. The biotite of one specimen is 

pleochroic in pale olive green to medium olive green, rather 

than in brown. Schorlite tourmaline is a common accessory 

mineral, and allanite is a rare one. 

MODAL AND CHEMICAL SUMMARY 

Modal analyses of 25 specimens of Madera Canyon 

Granodiorite are shown in table 13. The abundance of 

fernie minerals in the nonporphyritic and in the porphyritic 

granodiorite is about 5 percent less than that in the 

melanocratic granodiorite. Two of the hybridized 

specimens, 116 and 122, that are excluded from the modal 

means in table 13 have probably been altered by the nearby 

intrusive body of Elephant Head Quartz Monzonite. The 

other hybridized rock, specimen 103, is from a contact 

chill zone along which there may have been some 

assimilation. The modes are plotted in a modified 

triangular diagram, figure 31. Hornblende and biotite 

together make up about 10 percent of the rock, with 

substantial amounts of both minerals present in most 

specimens. However, specimen 104 contains biotite and no 

hornblende, and specimen 105 contains hornblende and a 

very minor amount of biotite, suggesting that these 

minerals may proxy for each other. 

An enclosing shell drawn around the plotted modes in 

figure 31 is subspherical and is centered along the 

boundary between the granodiorite and quartz monzonite 

fields and about 15 percent of the way from the leucocratic 

face of the composition tetrahedron toward the fernie 

apex. The modes for each of the three types of granodiorite 
44 PLUTONIC ROCKS, SANTA RITA MOUNTAINS, SOUTHEAST OF TUCSON, ARIZONA 

TABLE 13.-Modesof 

[Field numbers are abbreviated; year of collection and collector's initial omitted . Full field number of specimen 

Rock type .. . .... Granodiorite 

Specimen No · · ... •. . Ito3 104 105 106 107 108 109 110 Ill 112 113 114 115 104- 115 

Field No. 2403 Mean s ... . ... ... 363 765 1581 833 836 828 769 837 843 .826 810 847 

Quartz . . . . .... . . 24.8 24.1 19.1 23.1 21.4 23 .7 17.5 21.9 16.0 18.3 22.5 17.9 24.2 20.8 2.9 

Plagioclase, total . 52.7 47.9 40.3 45.2 36.2 39.0 44.6 41.8 42.8 47.5 47.1 48.7 43.4 43.7 3.9 

(plagioclase in 

perthite) . . . . . 0 (I. 7) (1.6) (2 .0) (1 .3) (2.0) (0.2) 0 (1.6) (2.9) (1.2) 0 (1.9) (1.4) (0.9) 

Orthoclase ...... . 0 16.1 28.0 19.3 31.8 27.0 25.5 26.2 23.3 21.5 17.8 12.9 21.6 22.6 (5.5) 

Sanidine . ..... ... 10.6 0 0 0 0 0 0 0 0 0 0 0 0 0 .... .. Hornblende ..... . 0 0 9.3 3.5 1.8 3 6.3 4.9 9.7 3.9 5.7 10.9 2.4 5.1 3.4 

Biotite . .. . . . . ... 10.7 11.4 .5 5.4 6.4 5.7 3.7 3.7 5.6 6.5 4.3 6.2 6.4 5.5 2.5 

Pyroxene .. ..... . 0 0 0 1.3 0 0 0 0 0 0 0 0 0 .I .4 

Magnetite .... ... .7 .5 1.9 1.5 1.6 1.5 1.2 1.1 1.4 1.2 1.7 2.2 1.4 1.4 .4 

Apatite . .. . ... . .. .3 Tr. .3 .4 .2 .2 .5 .I .3 .4 .2 .I .I .2 .2 

Sphene ... . .. . ... 0 0 .6 .3 .5 .6 .6 .3 .9 .7 .7 1.1 .2 .5 .3 

Zircon .. ..... ... .2 Tr. Tr. .05 .I Tr. .I Tr. Tr. .05 .05 0 Tr. .03 .04 

Allanite ..... .. .. 0 0 0 0 Tr. 0 0 0 0 0 0 0 0 Tr. .. ... . Rutile .... .. . ... . 0 Tr. 0 0 0 0 0 0 0 0 0 0 0 Tr. . ... . . Tourmaline .. . . . . 0 0 0 0 0 0 0 0 0 0 0 0 0 0 • •• • 0 

Total . . . . . 100.0 100.0 100.0 100.05 100.0 100.0 100.0 100.0 100.0 100.05 100.05 100.0 99.7 99.93 0 • • •• • 

Fernie ... .. 11.9 11.9 12.6 12.4 10.6 10.3 12.4 10.1 17.9 12.7 12.6 20.5 10.5 12.8 3.2 

Percent anorthite 

in plagioclase ... 28 32-42 5-37 35 - 42 133-37 28-37 32-34 29-35 33-40 33 32-37 32-37 28-31 28-37 .. .... (plagioclase 

rims) ... ..... .. . .. . .. . .. . .. . ... . . . . . . . . • • • • • • • •• 0 • • 0 •••••••• • • • • • • • • 0 • •• •• (23) (20) . ..... . (20) (21) • 0 ••• • 

Quartz mixing 

index (see text) . . ...... .89 .88 .85 .85 .70 

1 Specimen is hybridized. 2 Actual sample collection site is at dump V. mile southwest of source site shown on map, 

figure 27. 

3 Modal orthoclase includes a microcline (?). 

4omits hybridized specimens 103, 116, and 122. 

fall within smaller subspherical circumscribed figures. The 

modal ranges of the nonporphyritic and the porphyritic 

granodiorite overlap, bearing out the field evidence that 

these rocks are gradational. No sucb overlap occurs for the 

melanocratic figure and those of the granodiorite and 

the porphyritic granodiorite figures. 

The low value of the quartz mixing index of the 

melanocratic granodiorite relative to the other types may 

be the result of minor redistribution of quartz; this is 

compatible with the other evidence suggesting mild thermal 

metamorphism of the rock. 

Chemical and spectrographic analyses and CIPW norms 

of specimens of Madera Canyon Granodiorite are shown 

in table 14. The chemical data are summarized in the 

histogram of figure 10D, which shows the rock to be 

unique among the several granodiorites of the Santa Rita 

Mountains in having nearly equal amounts of CaO, Na20, 

and K20. The mean of the chemical analyses is fairly close 

to that of the average of hornblende-biotite granodiorite 

tabulated by Nockolds (1954, p. 1014). 

AGE AND CORRELATION 

The Madera Canyon Granodiorite is, on geologic 

evidence, considered to be younger than the Josephine 

Canyon Diorite and older than the Elephant Head Quartz 

.96 .90 .97 .93 .97 .91 .94 .90 .07 

FIGURE 30.-Specimen 127. The melanocratic type of Madera Canyon 

Granodiorite. 
CRETACEOUS ROCKS 

Madera Canyon Granodiorite 

103 thus is 6305103. Symbols: s, standard deviation; Tr., trace; ... , not determined] 

Porphyritic granodiorite 

1116 117 118 119 

873 874 872 865 

37.5 26.0 21.8 28.5 

28.9 37.8 47.6 46.0 

0 (1.9) (1.4) (0.2) 

29.9 21.3 18.2 15.3 

0 0 0 0 

.7 4.0 5.5 .05 

2.5 9.2 4.7 9.2 

0 0 0 0 

.3 .9 .9 .8 

.1 .4 .2 .1 

.1 .3 1.1 .05 

Tr. .1 .05 .05 

0 0 0 0 

0 0 0 0 

0 0 0 0 

100.0 100.0 100.05 100.05 

3.7 14.9 12.4 10.2 

0? 30-35 30 27-30 

....... • • • • • 0. 0 0 0 •••• (20) 

.97 .86 1.0 .63 

Melanocratic granodiorite 

120 121 117- 121 1122 123 124 12S 126 127 

877 889 Mean s 825 908 824 867 869 902 

27.3 20.7 24.9 3.4 16.3 12.2 12.1 8.2 11.0 9.3 

42.0 43.2 43.3 3.R 34.1 37.3 50.1 47.6 45.5 49.0 

(I. I) (0.2) (1.0) (0.8) (3.0) (5.6) (4.8) (2.4) (3.3) (3.0) 

2 23.7 14.8 18.7 3.8 23.7 34.7 16.9 42.1 23.6 28.6 

0 0 0 ...... 0 0 0 0 0 0 

1.3 8.0 3.8 3.2 11.0 6.5 10.5 11.2 9.2 5.4 

4.6 9.9 7.5 2.6 11.2 4.4 7.3 6.1 7.0 5.4 

0 0 0 ...... 0 0 0 0 0 0 

.7 1.7 1.0 .4 1.6 2.3 1.2 2.9 1.7 1.6 

.3 .3 .3 .1 .8 .6 .6 .5 .6 .3 

.1 1.3 .6 .6 1.1 1.9 1.0 1.4 1.3 .4 

Tr. .1 .06 .04 .15 .1 .15 Tr. .05 .05 

Tr. 0 Tr. ...... Tr. 0 .1 Tr. Tr. 0 

0 0 0 ...... 0 0 0 0 0 0 

0 0 0 • • 00 •• 0 0 0 0 0 Tr. 

100.0 100.0 100.16 ······ 99.95 100.0 99.95 100.0 99.95 100.05 

7.0 21.3 13.1 5.4 25.9 15.8 20.9 22.1 19.9 13.1 

35 28-33 28-35 .. ... . 0? 37 38-49 36 40 27 

(21) . . . . . . . (20) .. ... . I" o ooo o o . ...... • 0 ••••• ••• • • • 0 ..... (20) 

.78 .92 .84 .I .60 .80 .81 .82 .80 .68 

EXPLANATION PLAGIOCLASE 

"'®' 

Granodiorite; includes some 

quartz monzonite 

® 

Granodiorite; includes somt> quartz 

monzonite; hybridized 

'&"" 

Porphyritic granodiorite 

& 

Porphyritic granodiorite; hybridized 

~ 

Melanocratic granodiorite; includes 

some quartz monzonite 

G 

Melanocratic granodiorite; includes some 

quartz monzonite; hybridized 

,........ 

Total Madera Canyon Granodiorite 

45 

! 122- 127 4104 -127 

Mean s Mean s 

10.6 1.8 19.4 5.8 

45.9 5.1 43.8 5.3 

(3.8) (1.3) (1.7) (1.5) 

25.2 6.8 21.7 7.3 

0 ...... . . .. . . ..... 

8.6 2.5 5.1 3.7 

6.0 1.2 6.1 2.6 

0 ...... .. .. . . . .. . . 

1.9 .7 1.4 .6 

.5 .1 .3 .2 

1.2 .6 .6 .5 

.09 .05 .05 .05 

Tr. ...... Tr. • ••• 0 • 

0 ...... Tr. . ..... 

Tr. . . . . . . Tr. •• 0 ••• 

99.99 ...... 98.45 ...... 

18.3 3.8 13.6 4.4 

28-49 ..... 28-49 ..... 

(20) ..... (20-23) ..... 

.78 .06 .86 .1 

FIGURE 31.-Modified triangular diagram showing modal quartz, potassium feldspar, plagioclase, and fernie minerals of Madera Canyon 

Granodiorite. 
46 PLUTONIC ROCKS, SANTA RITA MOUNTAINS, SOUTHEAST OF TUCSON, ARIZONA 

TABLE 14.-Chemica/ and spectrographic analyses and CIPW norms of Madera Canyon Granodiorite 

[Chemical analyses by rapid rock method (Shapiro and Brannock, 1962), with specimen 113 supplemented by X-ray fluorescence method and specimens 118, 124, and 127 supplemented by atomic 

absorption method. Chemical analysts: Lowell Artis, S. D. Botts, G. W. Chloe, P. L. D. Elmore, John Glenn, H. Smith, and Dwight Taylor. Spectrographic analyses by semiquantitative 

method. Spectrographic analysts: W. B. Crandell, J. L. Finley, and J. L. Harris. Elements looked for but not found: Ag, As, Au, Bi, Cd, Eu, Ge, Hf, Hg, In, Li, Nd, Pd, 

Pr, Pt, Sb, Sm, Sn, Ta, Te, Th, Tl, U, W, and Zn. Symbols: s, standard deviations;<, less than; ... , not determined; N, not detected] 

Rock type .......... 

Specimen No ................. 110 

Field No ....... -........... 769 

s i02 

A 

F 

F 

M 

c 

N 

K 

H 

H 

T 

p 

................ 1203 ............... 

e203 ............... 

eO ................. 

gO ................ 

aO ................. 

a20 •••••••••••• 0 •• 

20 ................. 

20- ••• 0. ••••• •• 0. 

20+ ..... ····· .... i02 ................ 

'205 ................ 

M nO ................ 

c 02 ................. 

67.9 

15.6 

1.7 

1.4 

1.4 

3.1 

3.6 

3.8 

.11 

.81 

.42 

.13 

.06 

< .05 

Total .......... 100 

••••••• 0 ••••••••••• 

a .................. 

B 

B 

B 

c 

c 

c 

c 

G 

L 

M 

N 

N 

p 

e .................. 

e .................. 

0 .................. 

r •••••••• 0 •••••• 0 •• 

u .................. 

a .................. 

a .................. 

0 .................. 

b ................ ·-· 

jl .................. 

b .................. 

s c ................... 

s 

s 

v 

y 

y 

n .................. 

r ................... 

• 0 ••••••••• 0 •••••• 0 

0. ••••••• 0 ••••••••• 

b .................. 

z r 0 0 •• 0 ••••••••••••• 

A 

c 

or. 

ab 

an 

{wo. di en .. 

fs .. 

hy·{en. fs. 

mt 

hm 

il 

ap 

cc 

Total 

Fernie 

0 

.07 

.0001 

.01 

.0007 

.001 

.002 

.001 

.007 

0 

0 

0 

.0007 

.0007 

0 

.05 

.007 

.002 

.0002 

.01 

23.9 

.36 

22.4 

30.4 

14.2 

0 

0 

0 

3.5 

.58 

2.5 

0 

.80 

.31 

.11 

99.1 

7.8 

Granodiorite 

113 I 110,113 

Mean 826 

65.7 66.8 

16.3 16.0 

2.1 1.9 

1.7 1.6 

1.7 1.6 

3.8 3.5 

3.9 3.8 

3.0 3.4 

.12 .12 

.62 .72 

.55 .49 

.23 .18 

.05 .06 

.11 .06 

100 100 

0 0 

.1 .09 

0 .00005 

0 .005 

.001 .0009 

.001 .001 

.02 .01 

.001 .001 

.005 .006 

.0003 .00015 

0 0 

<.003 <.003 

.0005 .0006 

.0007 .0007 

0 0 

.07 .06 

.007 .007 

.0015 .002 

.0015 .0002 

.01 .01 

21.6 

.54 

17.7 

33.0 

16.7 

0 

0 

0 

4.2 

.57 

3.0 

0 

1.0 

.55 

.25 

99.1 

9.6 

Porphyritic granodiorite Melanocratic granodiorite 

117 118 I 117,118 124 125 127 I 124-127 110- 127 

Mean 867 802 Mean Mean s 874 872 824 

Chemical analyses (weight percent) 

68.6 67.5 68.1 60.5 . ........ 60.4 60.5 65.1 3.7 

15.2 15.1 15.2 16.5 ......... 16.1 16.3 15.8 .6 

2.1 2.2 2.2 2.5 ......... 2.8 2.7 2.2 .4 

1.2 1.4 1.3 3.3 ......... 3.2 3.3 2.0 1.0 

1.0 1.2 1.1 2.3 ......... 2.6 2.5 1.7 .6 

3.5 3.6 3.6 4.5 ......... 4.0 4.3 3.8 .5 

3.6 4.0 3.8 3.7 . ........ 3.8 3.8 3.8 .2 

3.2 3.3 3.3 4.1 ......... 4.6 4.4 3.6 .6 

.12 .14 .13 .09 . ........ .07 .08 .11 .02 

.51 .52 .52 .78 . ........ .65 .72 .65 .13 

.58 .66 .62 .98 ......... .99 .99 .72 .24 

.17 .19 .18 .44 ......... .49 .47 .28 .15 

.05 .07 .06 .17 ......... .19 .18 .10 .06 

<.05 <.05 < .05 < .05 ......... < .05 <.05 .06 .05 

100 100 101 100 ......... 100 100 100 ····· .... 

Spectrographic analyses (weight percent) 

0 0 0 0 0.007 0 0.002 0.001 0.003 

.1 .1 .1 .015 .015 .015 .015 .06 .04 

0 .0001.5 .0001 .0002 .0003 .0003 .0003 .00015 .0001 

.015 .01 .01 N N .05 .05 .01 .02 

.0005 .0007 .0006 .007 .005 .0015 .005 .002 .003 

.0007 .001 .0009 .0015 .003 .0015 .002 .001 .0007 

.0005 .007 .004 .015 .03 .005 .002 .01 .01 

.0015 .0015 .0015 N N .0015 .0015 .0009 .0007 

.01 .007 .009 .015 .015 .01 .015 .01 .004 

0 0 0 0 0 0 0 .0004 .Oool 

.0003 0 .00015 .003 .007 .0015 .004 .002 .003 

0 0 0 .015 .003 0 .006 .003 .006 

.03 .0007 .015 .002 .001 .002 .002 .005 .01 

.0007 .0007 .0007 .007 .015 .0015 .008 .004 .005 

.003 0 .0015 0 .0015 0 .0005 .0006 .001 

.07 .05 .06 .015 .01 .05 .03 .05 .02 

.005 .005 .005 .015 .03 .007 .02 .01 .009 

.0015 .001 .001 .015 .003 .005 .008 .004 .005 

.00015 .0001 .0001 N N .0003 .0003 .0003 .0005 

.015 .02 .02 .007 .01 .05 .02 .02 .01 

CIPWnorms 

27.1 23.4 11.0 9.4 

0 0 0 0 

18.9 19.5 24.2 27.2 

30.5 33.9 31.3 32.2 

15.9 13.5 16.3 13.3 

.03 1.2 1.2 1.3 

.03 1.0 .75 .87 

0 0 .35 .37 

2.5 2.0 5.0 5.6 

0 0 2.3 2.0 

2.6 2.8 3.6 4.1 

.48 .25 .... 0 0 

1.1 1.3 1.9 1.9 

.40 .45 1.0 1.2 

.11 .11 .11 .11 

99.6 99.4 99.0 99.6 '"' 

7.2 9.1 16.2 17.5 
CRETACEOUS ROCKS 47 

31 ° 

40' 

y r 

0 

0 

110" 55' 

2 

2 3 

yr .......... "" ' .. ·:- .... . 

X M ou nt Ho p kins 

or 

3 4 MILES 

4 Kl LOMETA ES 

EXPLANATION 

You nger rocks 

Igneous and sedimentary rocks 

Cretaceous Elephan t Hea d Quartz Mon zonite 

Key , quartz monzonite of the Yoas stock 

K eqc, quartz monzonite of the Quantrell stock, 

coarse-grained phase 

K eqf. quartz monzonite of the Quantrell stock, 

fine-r;rained phase 

Older rocks 

Igneous and sedimentary rocks 

Contact 

Dotted where concealed 

---------··--- Fault 

Dotted where concealed 

o l 2 8 Q 1 3 0 *1 32 

Mod ed Chemically Rad iometricall y 

analyzed dated 

Specimen collection sues and numbers 

FIGURE 32.-Distribution of Elephant Head Quartz Monzonite and specimen collection sites. 

Monzonite, which are radiometrically dated as 67 to 69 

m.y. old (table 4). In addition, the nonporphyritic type of 

Madera Canyon Granodiorite was dated by the 

potassium-argon method by P. E. Damon (written 

commun., 1964) as 67.9 ±2.1 m.y. Because the precise site 

at which his specimen was collected is uncertain, the rock 

was not resampled for further dating. 

Granodiorite similar in both age and composition to the 

Madera Canyon Granodiorite has not been reported in 

ranges adjacent to the Santa Rita Mountains. Other 

granodiorite stocks of similar appearance-occur in both the 

Sierrita Mountains (Cooper, 1974) and the Patagonia 

Mountains (Simons, 1973), but they are about 10 m.y. 

younger. 

ELEPHANT HEAD QUARTZ MONZONITE 

The Elephant Head Quartz Monzonite is a composite of 

the Quantrell and Yoas stocks and consists of 

coarse-grained pinkish-gray leucocratic rock that underlies 

much of the rugged terrain around Elephant Head and the 

mouth of Madera Canyon (fig. 32). It underlies several 

areas that total about 18 square miles, and it may also 

underlie a considerable area beneath the piedmont gravel 

northwest of Elephant Head. 

The main mass of quartz monzonite lies west of the 

upper reaches of Madera Canyon; it is slightly elongate to 

the northwest, a trend followed by most of the intrusive 

tongues and inclusions of host rocks in the quartz 

monzonite. Another mass of quartz monzonite lies 

northeast of the upper reaches of Madera Canyon and 

trends north, and small masses crop out between the larger 

ones. 

The attitude of the sides of the present plutonic masses 

suggests that in most places the original tops of the masses 

were a considerable distance above the present level of 

exposure. The trace of the eastern contact of the mass 

northeast of Madera Canyon is straight and the contact 

dips steeply outward; the quartz monzonite contact at the 

southern end of the mass probably also dips steeply 

outward. The other contacts are concealed by gravel. The 
48 PLUTONIC ROCKS, SANTA RITA MOUNTAINS, SOUTHEAST OF TUCSON, ARIZONA 

eastern contact of the larger mass of quartz monzonite is 

irregular but generally is steep. To the north the mass is 

faulted, and to the northwest it intrudes quartz diorite 

along a very irregular but mostly steep contact. However, 

to the south the contact dips gently outward and in places 

trends irregularly, and several large flat-bottomed roof 

pendants cap the highest hills. These features suggest that 

the upper contact of the stock plunges gently southward; to 

the south the top is exposed near the present surface, and 

to the north it has been removed by erosion. Small 

outcrops of quartz monzonite between the two larger 

masses of identical rock indicates that the septum of 

granodiorite along Madera Canyon probably does not 

extend far beneath the surface. Very likely then, the two 

masses are cupolas of a single stock. 

Generally the contacts of the quartz monzonite are fairly 

sharp and without noticeable chill zones or contactmetamorphosed aureoles, but the exceptions at several 

places are instructive. At one locality the contact of the 

smaller cupola, northeast of specimen collection site 141 

(fig. 32), forms a gradational zone at least 400 feet wide. 

The rock toward the quartz monzonite is fine grained and 

light pinkish gray, and it contains only a few small clots of 

dark minerals. Toward the granodioritic host the rock 

gradually is grayer and the clots are progressively larger 

and more abundant, until they resemble the clusters of 

felty-textured biotite aggregates of the granodiorite, except 

that the hybrid rock has a sprinkling of small white 

feldspar crystals more typical of the quartz monzonite. The 

biotite in the nearby host rock is recrystallized, probably 

as a result of contact metamorphism produced by the 

emplacement of the small cupola of quartz monzonite. At 

a second locality, between the collection site of specimens 

147 and 148 along Agua Caliente Canyon (fig. 32), the 

quartz monzonite intrudes a quartz diorite that is assigned 

to the Josephine Canyon Diorite. Not only is the contact 

very irregular, but also the quartz monzonite contains 

many small inclusions, and some larger ones of the quartz 

diorite. Some of these inclusions appear to be 

incompletely digested granodioritelike rocks. In both of 

these places, some of the host rocks seem to be assimilated, 

and in the Agua Caliente Canyon area some stoping may 

also have occurred along the sides of the stock. At a third 

locality, near the southern tip of the large cupola along 

Montosa Canyon, the wallrocks and roof pendants are 

increasingly intensely altered toward the quartz monzonite. 

These host rocks are arkose, dacitic volcanic tuff, and 

breccia of the Salero Formation, which are so widely 

argillitized and locally are so strongly pyritized that the 

primary minerals of the rock are almost entirely replaced. 

This alteration appears to be a hydrothermal rather than a 

thermal contact effect, but even so the alteration probably 

is genetically related to the stock, which is the youngest 

intrusive rock of significant size in the area. Perhaps the 

alteration was particularly strong in this area of the fairly 

flat shoulder on the southern tip of the stock because 

.upward-streaming fluids were more abundant than 

outward-moving fluids. Finally, a body of fine-grained 

Elephant Head Quartz Monzonite, erroneously shown as 

Josephine Canyon Diorite on the geologic map and section 

A-A· of the Mount Wrightson quadrangle (Drewes, 

1971c), intrudes a small unmapped inclusion of tuff 

breccia north of Montosa Canyon (specimen collection site 

144, fig. 32). 

PETROGRAPHY 

The large cupola is a composite mass of two stocks; the 

larger and older Quantrell stock underlies a gentler terrain 

than the smaller and younger Y oas stock. The Quantrell 

stock includes the rocks of the small cupola, and it 

contains some fine-grained quartz monzonite,.as well as the 

common coarse-grained kind. Along the east side of the 

Y oas stock, which is named for Y oas Mountain near the 

center of the stock (fig. 32), the contrast in weathering 

characteristics is very striking, as shown in figure 33. 

Rocks of the Yoas stock underlie some of the most rugged 

country in the area, including the 2,000-foot-high rock 

dome of Elephant Head, for which the formation is 

named, but the eastern part of the stock near the edge of 

the pediment underlies more gentle terrain. Rocks of part 

of the Quantrell stock adjacent to the Yoas stock (see 

geologic map, Drewes, 1971c) also underlie gentle terrain, 

but some of the Quantrell stock in the high ridges east of 

the Quantrell mine underlies bold knobs. In most places 

the contact between the stocks is concealed, but east of 

Elephant Head it is exposed and the quartz monzonite of 

the Yoas stock forms a chill zone 5 to 10 feet wide against 

the Quantrell stock. The trend of this contact is straight 

and its dip is moderately steep to the east. Biotite in the 

rocks of the Quantrell stock is recrystallized or contact 

border of the Y oas stock is recrystallized or contact 

metamorphosed to felty aggregates of small crystals. The 

contact southwest of Yoas Mountain is irregular and in 

places is concealed by small intrusive bodies of 

lamprophyre and aplite, mostly too s~ll to show on the 

scale of the geologic map of the Mount Wrightson 

quadrangle. At this locality the geologic map of the 

quadrangle erroneously shows two lamporphyre dikes as 

Josephine Canyon Diorite. 

The Quantrell stock is made up mostly of a 

coarse-grained quartz monzonite, but it also includes 

masses of fine-grained quartz monzonite or aplite, most of 

which are intrusive into the coarse-grained rock and are 

small and tabular. Larger masses of fine-grained rock lie 

along the edge of the stock on the west side of Madera 

Canyon and southwest of Y oas Mountain, where a few 

small bodies of aplite associated with the Yoas stock may 

have been mapped with the slightly older and 

petrographically identical aplite of the Quantrell stock. 
CRETA CEO US ROCKS 49 

QUANTREll 

STOCK 

FIGURE 33.-View, toward northeast, of Elephant Head and the east-dipping contact between the Yoas stock, underlying the rugged terrain, and the 

Quantrell stock, underlying the gentle terrain. 

QUANTRELL STOCK, 

COARSE-GRAINED QUARTZ MONZONITE 

The coarse-grained quartz monzonite of the Quantrell 

stock underlies a varied terrain of gentle slopes partly 

veneered by grus and interspersed blocky debris, and of 

fairly rugged ridges and some chasmlike canyons. The rock 

is massive and contains at least three prominent sets of 

widely spaced joints. It is a light brownish gray to light 

pinkish gray and weathers to brownish gray. Specimens 

typically are coarsely granular and contain only a sparse 

scattering of ferromagnesian minerals (fig. 34). 

The quartz monzonite has a hypidiomorphic-granular 

texture and a grain size commonly 4 to 8 mm (fig. 35). 

Some specimens have poikilitic grains and fine-grained 

myrmekitic, granophyric, and perthitic textures, but the 

granophyric intergrowths of one specimen are coarse. 

Specimen 135 has a weak metamorphic texture 

superimposed upon the hypidiomorphic-granular one: 

small crystals of quartz are scattered between the more 

abundant coarse crystals, crystal boundaries are strongly 

sutured, and biotite occurs in clusters of small felty 

crystals. The strong undulatory extinction of quartz 

crystals in rocks of the Quantrell stock collected near the 

contact with the Y oas stock may reflect minor intrusive 

pressure during emplacement of the Yoas stock. 

The rock is made up mainly of quartz, plagioclase, 

orthoclase or microcline and contains small amounts of 

biotite, magnetite, apatite, sphene, and zircon. Some 

specimens also have a trace of amphibole, allanite, 

monazite, pyrite, and tourmaline. The quartz is anhedral 

and generally has a slight to moderate undulatory 

extinction. The plagioclase is subhedral, is strongly altered 

to clay minerals and sericite, and has a composition of 

albite. About 20 percent of the moded plagioclase occurs 

as perthitic intergrowths. Potassium feldspar is anhedral to 

subhedral and is moderately kaolinitized. Patch perthite is 

more common than lace perthite and is very coarse in some 

specimens. Biotite is pleochroic in pale yellow brown to 

moderate brown and is partly altered to penninitic chlorite, 

sericite, leucoxene, and iron oxide. Magnetite is probably 

ilmenitic, and zircon is euhedral, fairly large, and 

abundant when compared to that in most other plutonic 

rocks of the area. Amphibole is pleochroic in 'bluish green. 

Alteration minerals include a trace of epidote, in addition 

to those already mentioned. 

QUANTRELL STOCK, 

FINE-GRAINED QUARTZ MONZONITE 

The fine-grained quartz monzonite of the Quantrell 

stock is generally a little more resistant to weathering than 

the adjacent coarse-grained rock. The rock is closely 
50 PLUTONIC ROCKS, SANTA RITA MOUNTAINS, SOUTHEAST OF TUCSON, ARIZONA 

FlGURE 34.-Specimen 134. Elephant Head Quartz Monzonite, a coarsegrained rock of the Quantrell stock. 

fractured, and the large mass on the west flank of Madera 

Canyon also has a weakly developed, steeply eastward 

dipping flow foliation and is pervasively silicified and 

pyritized. (See geologic map, Drewes, 197lc.) 

Specimens of fine-grained quartz monzonite are very 

pale grayish orange pink to light pinkish gray. Grain size is 

mostly 0.2 to 2 mm throughout the suite of specimens, 

although the range is much less in individual specimens. 

An idiomorphic- to hypidiomorphic-granular texture is 

dominant and parts of many specimens have a fine-grained 

granophyric texture. 

The fine-grained rock type contains the same principal 

minerals as the coarse, but somewhat fewer kinds of 

accessory minerals are present. The characteristics of the 

minerals are substantially like those in the coarse-grained 

quartz monzonite. The alteration minerals are also the 

same but are more abundant in the fine-grained rock than 

in the coarse-grained. 

FIGURE 35- Specimen 132. Coarse-grained Elephant Head Quartz Monzonite from the Quantrell stock . Crystals: orthoclase ( Q), plagioclase 

( p ), quartz (Q), chloritized biotite (c b), magnetite (mt), apatite (a p), 

and allanite ( a I), Plain light; X 20. 

YOAS STOCK, 

COARSE-GRAINED QUARTZ MONZONITE 

The quartz monzonite of the Yoas stock is almost 

entirely coarse grained, and it underlies some extremely 

rugged terrain. The rock is massive and is cut by several 

sets of joints, which are strikingly prominent on the many 

bold outcrops between Elephant Head and the southern 

end of the stock (fig. 33). Away from the sharp contact on 

the east side of the stock, the joints are fairly widely 

spaced, but in a zone 400 to 700 feet wide along this 

contact the joints are commonly 1 to 3 feet apart, with 

additional microfractures spaced at intervals of less than 

an inch. Viewed from a distance, the rock looks slightly 

pinker than the adjacent quartz monzonite of the Quantrell 

stock, perhaps because bold outcrops of the Yoas stock are 

less weathered than the gentler terrain of the Quantrell 

stock. The quartz monzonite of the Yoas stock is generally 

free of inclusions, but that in the canyon south of Elephant 
CRETACEOUS ROCKS 51 

Head contains partly assimilated gray andesitic to dioritic 

inclusions mostly 2 to 12 inches across and rarely many feet 

across. Quartz veinlets, lamprophyre dikes, and a few 

aplitic bodies cut the quartz monzonite, apparently at 

random orientation. 

Grain size in quartz monzonite of the Y oas stock is 

typically 4 to 7 mm and in some specimens is as much as 

10 mm. Hypidiographic-granular texture is ubiquitous and 

a few specimens also have some intergranular texture and 

some poorly developed granophyric texture. Lace type and 

patch type of perthitic intergrowths are equally common, 

and they vary widely in size. 

Mineralogically the quartz monzonite of the Y oas stock 

is indistinguishable from that of the Quantrell stock. 

MODAL AND CHEMICAL SUMMARY 

Modal analyses of 29 specimens of Elephant Head 

Quartz Monzonite are listed in table 15. The mean of these 

modes is much like that of the Squaw Gulch Granite (table 

7), except that it has 36 percent (instead of 25 percent) 

plagioclase, slightly more biotite, and a greater variety of 

accessory minerals. 

The modified triangular diagram of figure 36 graphically 

summarizes the modal data. A figure drawn around the 

plotted modes has an hemielliptical shape, flattened 

against the leucocratic face of the composition tetrahedron 

and centered in the quartz monzonite field. The ranges of 

the modes of the coarse-grained rocks of the two stocks are 

coextensive, and the modes of the fine-grained rock are 

centered slightly closer to the quartz-plagioclase edge of 

the composition tetrahedron than those of the 

coarse-grained rocks. 

A comparison of the modal ranges for the three large 

plutons of late Late Cretaceous age shows systematic 

changes. Only the figures circumscribed around the three 

groups of modes-for the Josephine Canyon Diorite, 

Madera Canyon Granodiorite, and Elephant Head Quartz 

Monzonite-are shown together in figure 37, along with 

the estimated positions of the centers of the figures. In the 

order from the oldest to the youngest pluton, as 

determined from field relations, the composition of the 

magma shifted from a fernie-plagioclase-rich point to an 

alkali-quartz-rich point. In direction and amount the shift 

is similar to that which occurred between the phases of the 

Josephine Canyon Diorite. The circumscribed figures have 

also changed from a tilted discoidal body with a 

near-vertical short axis, to a stibspherical body, to a 

hemielliptical body with a near-horizontal short axis. 

The trend of compositional change of the rocks is 

compatible with the typical model of fractionating magma 

in which the more "basic" fractions are emplaced before 

the more "acidic" fractions. However, some of the data 

on the age of these plutons, discussed in the next section, 

indicate that such a model may at least be oversimplified, if 

it is at all tenable. The change in the configuration of the 

figures drawn around the plotted modes is intriguing, but 

no speculation on its possible significance is offered here. 

Chemical and spectrographic analyses and CIPW norms 

of four coarse-grained specimens of Elephant Head Quartz 

Monzonite are shown in table 16 and are summarized in, 

the histogram of figures 10K -10£. Chemically this rock is 

very similar to the Squaw Gulch Granite and the quartz 

monzonite of the Corona stock. The Elephant Head 

Quartz Monzonite has slightly more K2<) and less CaO and 

Na20 than the granite, as reflected by the difference in the 

abundances of orthoclase or microcline and of plagioclase 

of rocks (tables 7, 15). Chemically, the rock resembles 

Nockolds' (1954, p. 1012 -1016) biotite adamellite and 

possibly some of the granite types. 

AGE AND CORRELATION 

The Elephant Head Quartz Monzonite is given a late 

Late Cretaceous age on the basis of interpretation of 

evidence from field relations and radiometric dating, some 

of which is conflicting. The field relations consistently 

show that the quartz monzonite is (1) younger than the 

Salero Formation, which is altered along the contact of the 

Quantrell stock, (2) younger than the inclusions of quartz 

diorite, which are correlated with the Josephine Canyon 

Diorite, and (3) younger than the Madera Canyon 

Granodiorite, which is metamorphosed near the contact 

with the small cupola. Because a low grade of 

metamorphism is a widespread feature in the Santa Rita 

Mountains, and because contact metamorphic zones are 

generally indistinct or erratic around stocks of all ages, 

determining age relations from this evidence requires 

caution. The evidence of the relationship to the quartz 

diorite inclusions is weak because it is based on a second 

interpretation of the identity of the rock. The combined 

field evidence is thus seen as consistent but not strong. 

Radiometric dates of two specimens of Elephant Head 

Quartz Monzonite, obtained from the coarse-grained rock 

of the Quantrell stock, are listed in table 4. Separate dates 

by the potassium-argon method on biotite and by the 

lead-alpha method on zircon are given for each specimen. 

The two ages obtained by each method are nearly 

identical, but the potassium-argon ages are about 68 m.y. 

and the lead-alpha ages about 180 m.y. The close 

agreement of the dual results by each method is probably 

not fortuitous, although further dating information is 

certainly desirable, particularly in view of the uncertainties 

besetting the lead-alpha method. Because evidence of 

recrystallization in the quartz monzonite is lacking, except 

for the immediate vicinity of the Yoas stock, an 

explanation involving a late Late Cretaceous thermal 
52 PLUTONIC ROCKS, SANTA RITA MOUNTAINS, SOUTHEAST OF TUCSON, ARIZONA 

Intrusive mas~ .. . . . . . . . . . . . . . 

Rock type ...... ·················· 

Specimen No ...................... 128 IJ29 130 131 132 133 

Field No. ························· S19 669 701 734 7S4 74Q 

Quartz ........................... 32.1 22.9 23.7 27.2 27.4 32.2 

Plagioclase, total .................. 24.9 37.0 33.4 29.0 40.4 37.8 

(in perthite) ·················· (14.7) (6.1) (7.S) (3.0) (3.9) (9.2) 

K-feldspar, total .................. 40.7 38.1 39.0 41.9 29.S 26.6 

(orthoclase) .................. (40.7) 0 (39.0) (41.9) (9.9) (26.6) 

(microcline?) ................. 0 (38.1) 0 0 (19.7) 0 

Biotite ........................... .8 1.1 3.3 1.1 1.4 2.2 

Amphibole ....................... 0 0 0 0 0 .3 

Magnetite ........................ 1.4 .8 .3 .s .8 .6 

Apatite .......................... Tr. .I .2 .OS .I . I 

Sphene .......................... Tr. Tr. Tr. .2 .3 .I 

Zircon ........................... .I .05 .05 .I .I . I 

Allanite .......................... 0 0 0 0 Tr. 0 

Monazite(?) ...................... Tr. 0 0 0 0 .05 

Pyrite ........................... 0 Tr. 0 0 0 0 

Tourmaline ······················ 0 0 0 0 Tr. 0 

Total ......................... 100.0 IOO.OS 99.95 IOO.OS 100.0 IOO.OS 

Fernie ........................ 2.3 2.0 3.9 1.9 2.7 3.4 

Percent anorthite 

in plagioclase .......... . . . . . . . . . . . 0 0-5 U-5 0 0-S 0-5 

TABLE 15.-Modes of Elephant 

[Field numbers are abbreviated; year of collection and collector's initial omitted. Full field number 

Quantrell stock 

Coarse·grained quartz monzonite 

134 13S 136 137 138 139 140 "141 142 128-142 

846 7S3 888 sao 879 876 844 866 901 Mean 

33.3 26.4 24.0 29.4 27.0 18.7 34.8 29.S 27.7 27.8 4.3 

36.1 32.S 43.3 4S.8 20.S 37.7 31.7 3S.3 38.1 34.9 6.6 

(IS. I) (2.3) (13.1) (6.9) (2.2) (S.O) (7.6) (10.3) (8.2) (7.7) (4.2) 

29.7 37.3 26.8 22.S 49.0 41.8 30.9 32.1 30.3 34.4 7.3 

(29.7) (26.1) (26.8) (22.S) (49.0) 0 0 0 0 (20.8) (17.8) 

0 (11.2) 0 0 0 (41.8) (30.9) (32.1) (30.3) (13.6) (16.6) 

.8 2.6 4.6 1.3 2.4 1.0 1.4 2.1 2.7 1.9 I.l 

0 0 0 0 .6 0 0 0 0 .06 .2 

.I 1.1 1.0 .6 .3 .8 .9 .6 .7 .7 .I 

Tr. Tr . .2 . OS .OS Tr . . I Tr . Tr. .07 .07 

0 .I .I . 4 Tr . 0 .2 .2 .4 .I .I 

Tr. Tr . . OS Tr . . I Tr . Tr. 0 .OS .05 .04 

0 0 0 0 0 Tr. 0 . 2 .OS Tr . 

0 0 0 0 0 0 0 0 0 Tr. 

0 0 0 0 0 0 0 0 0 Tr. 

0 0 0 0 0 0 0 0 0 Tr. 

100.0 100.0 IOO.OS IOO.OS 99.9S 100.0 100.0 100.0 100.0 100.0 

.9 3.8 S.9 2.3 3.4 1.8 2.6 3.1 3.9 2.9 1.4 

S-10 0-10 5-10 5-10 5-10 10 5-10 5-10 5± ...... (plagioclase rims) .. ·············· ············································································· (6) ................ . ............ Quartz mixing 

index (see text) .... . . . . . . . . . . . . . . . . . . . . . . .93 .61 .74 .88 .73 .79 .57 .78 .67 .90 .65 .93 .90 .94 .79 .13 

I Specimen 129 obtained from mine dump near shaft that bottoms in quartz monzonite. 

QUARTZ QUARTZ 

POTASSIUM 

FELDSPAR EXPLANATION 

(!) 

Coarse- Finegrained grained 

Quartz monzonite of 

1!1 

Coarse-grained quartz 

monzonite of the Y oas stock 

,...... the Quantrell stock Total Elephant Head Quartz Monzonite 

FIGURE 36.-Modified triangular diagram showing modal quartz, potassium feldspar, plagioclase, and fernie minerals of the Elephant Head 

Quartz Monzonite. 

alteration of a Jurassic stock is as unsatisfying as an 

explanation based on a loss of lead from the zircon. 

Nevertheless, these conflicting ages may indicate a more 

complex history of emplacement and subsequent 

development of the stock than seems apparent from field 

evidence alone. This matter deserves further study. 
CRETACEOUS ROCKS 

Head Quartz Monzonite 

of specimen 128 thus is 640579. Symbols: s, standard deviation; Tr., trace; ... , not determined) 

Quantrell stock-Continued Yoas stock 

Fine-grained quartz monzonite Coarse-grained quartz monzonite 

143 144 145 146 147 2148 149 ISO 143-150 lSI 152 153 154 155 156 

842 670 698 703 742 740 736 7fi7 Mean s 747 781 783 785 787 885 

35.4 29.3 31.6 25.2 26.1 26.9 25.3 32.7 29.1 3.8 21.6 28.0 20.6 35.5 19.4 27.0 

25.2 41.1 39.6 46.7 39.3 33.7 43.5 33.8 37.9 6.8 43.5 30.4 35.0 21.6 39.2 44.6 

(2.5) (1.4) (2.1) 0 (3.6) (5.0) (0.4) (3.9) (2.4) (1.7) (18.S) (5.7) (5.4) (9.0) (11.4) (8.6) 

38.5 25.2 26.0 20.3 31.4 35.8 24.1 32.3 29.2 6.3 27.7 39.8 41.9 42.2 38.8 26.7 

(38.5) (21.4) (26.0) (20.1) (31.4) (3S.8) (24.9) (32.3) (28.8) (6.7) (6.4) (37.7) (41.9) (41.2) (38.8) (26.7) 

0 (3.8) 0 (0.2) 0 0 (0.1) 0 (.5) (1.3) (21.3) (2.1) 0 0 0 0 

Tr. 2.5 1.2 5.5 1.7 1.9 S.2 .9 2.4 2.Q 2.4 .3 1.2 .6 1.1 1.0 

0 0 Tr. 0 0 .2 0 0 .03 .I 2.9 0 0 0 Tr . 0 

. 8 1.8 .9 1.3 .9 .6 1.3 .I 1.0 .5 1.1 .6 1.1 Tr. .8 .7 

.I .I .I .2 .2 .3 .2 .I .2 . I .2 .05 .I Tr. Tr . .OS 

0 Tr. .4 .8 .3 .5 .3 .05 .3 .3 . 6 .3 Tr. .I .6 Tr . 

Tr. Tr. Tr. Tr. .I .I .05 .05 .04 .04 Tr. .05 .OS Tr. . I Tr . 

0 0 .2 0 Tr. 0 .05 0 Tr. ... .... .05 Tr. 0 0 Tr. 0 

0 0 0 0 0 0 0 0 0 . . . . . . . . 0 0 0 0 0 0 

0 0 0 0 0 0 0 0 0 ........ 0 0 0 0 0 0 

0 0 0 0 0 0 0 0 0 ........ 0 0 0 0 0 0 

100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.2 ........ IOO.OS 99.5 99.95 100.0 100.0 100.05 

.9 4.4 2.8 7.8 3.2 3.6 7.1 1.2 4.0 2.5 7.2 1.3 2.5 .7 2.6 1.7 

0-5 0-5 5-10 0-5 5-10 0-5 0-5 0-5? s± ........ 0-25? 5-10 0 0 0-S 0-5 

... ..... ··············· ··········· ...... ·········· ············· ............... ··············································· ........ .. ....... . ..... .. ...... . .. . ..... . .. ······· ....... ...... . . . . . . . . . . . . . . ··············································· .... .. .84 .99 .95 .99 .69 .95 .93 .91 .II .% .62 .38 .90 .92 .64 

2 Specimen 148 obtained from a coarse-grained inclusion in a body of quartz diorite that 

intrudes a large mass of fine grained quartz monzonite. 

POTASSIUM 

FELDSPAR 

QUARTZ QUARTZ 

EXPLANATION 

----- Elephant Head Quartz Monzonite 

Madera Canyon Granodiorite 

Josephine Canyon Diorite, 

dioritic rocks 

Josephine Canyon Diorite, finegrained quartz monzonite 

6<e-6-.6. 

Estimated centers of circumscribed 

figures to modes. Arrow shows shift 

from oldest, .6., to youngest, 6 

53 

151-156 128-156 

Mean s Mean s 

25.4 6.1 27.6 4.6 

3S.8 8.7 35.9 7.0 

(9.8) (4.9) (6.6) (4.7) 

36.2 7.1 33.3 7.3 

(32.3) (13.9) (25.4) (15.1) 

(3.9) (8.6) (8.0) (13.7) 

1.1 .7 1.9 1.4 

.5 1.2 .I .5 

.7 .4 .8 .4 

.07 .07 .09 .08 

.3 .3 .2 .3 

.04 .04 .05 .04 

Tr. ······· Tr. ······· 0 ······· Tr. . . . . . . . . 

0 ······· Tr. ········ 0 . . . . . . . Tr. . . . . . . . . 

100.1 . ....... 99.9 ········ 2.7 2.3 3.2 1.9 

0-28 ······· 5± ........ 

.............. ················· ·············· ················· .74 .23 .81 .16 

FIGURE 37 .-Modified triangular diagram comparing the range of distribution of the modes of the Josephine Canyon Diorite, Madera Canyon 

Granodiorite, and Elephant Head Quartz Monzonite. 

Quartz monzonite stocks around 68 m.y. old are not 

present in the Sierrita, Patagonia, Empire, and Rincon 

Mountains, or in the Canelo Hills, adjacent to the Santa 

Rita Mountains. Most of the plutonic rocks in these ranges 

have a granodiorite composition and are either older or 

younger by 10 m.y. 
54 PLUTONIC ROCKS, SANTA RITA MOUNTAINS, SOUTHEAST OF TUCSON, ARIZONA 

TABLE 16.-Chemical and spectrographic analyses and CIPW norms of Elephant Head Quartz 

Monzonite, coarse-grained rocks 

[Chemical analyses by rapid rock method (Shapiro and Brannock, 1962), with analyses of specimens 139 and 155 supplemented by atomic 

absorption. Chemical analysts: Lowell Artis, S.D. Botts, G. W. Chloe, P. L. D. Elmore, John Glenn, H. Smith and Dwight Taylor. 

Spectrographic analyses by semiquantitative method. Spectrographic analysts: W. B. Crandell and J. L. Harris. Elements looked for 

but not found: Ag, As, Bu, B, Bi, Cd, Eu, Ge, Hf, Hg, In, Li, Mo, Ni, Pd, Pr, Pt, Re, Sb, Sm, Sn, Ta, Te, Th, Tl, U, W, and Zn. 

Symbols: s, standard deviation;< , less than; and ... , not determined) 

Intrusive mass ··························· Quantrell stock Yoasstock 

Specimen No ............................. 130 139 I 130,139 151 ISS 

Mean Field No. ............................... 701 876 747 787 

Chemical analyses (weight pen:ent) 

SiOz ··································· 72.2 73.7 73.0 67.2 74.7 

Al2o 3 .................................. 14.4 13.7 14.1 15.5 13.6 

Fe2o 3 .................................. 1.1 1.5 1.3 1.9 .90 

FeO .................................... .74 .56 .65 1.2 .36 

MgO ··································· .40 .13 .27 1.4 .10 

CaO .................................... .75 .70 .73 2.9 .63 

Na2o ·································· 4.4 2.9 3.7 4.4 4.0 

KzO .................................... 4.7 5.7 5.2 3.8 4.7 

HzO- ································· .09 .09 .09 .22 .10 

HzO+ ................................. .82 .34 .58 .52 .47 

TiOz ··································· .24 .43 .34 .49 .38 

PzOs··· ................. ·········· ··.· .. 0 .06 .03 .16 .02 

Mno2 .................................. .13 .05 .09 .10 .OS 

C02 .................................... < .05 < .05 <.OS <.OS <.OS 

Total ............................. 100 100 100 100 100 

Spectrographic analyses (weight percent) 

Ba ..................................... 

Be ..................................... Ce ····································· Co ..................................... 

Cr ····································· Cu ····································· Ga ..................................... 

La ····································· Nb ..................................... 

Nd ..................................... 

Pb ····································· Sc ...................................... 

Sr ...................................... 

v ······································ y ······································ Yb ..................................... 

Zr ..................................... 

Q .................................... . 

c ..................................... . 

0.05 

.0005 

.01 

0 

0 

.0002 

.001 

.007 

.0015 

0 

.0005 

.0003 

.01 

.0007 

.003 

.0003 

.03 

26.4 

.84 

27.8 

37.2 

3.4 

0 

0 

0 

1.0 

.30 

1.6 

0 

.46 

0 

.II 

Total ............................. 99.1 

Fernie . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.5 

TERTIARY ROCKS 

O.o7 

.0015 

.02 

0 

0 

.00007 

.0015 

.015 

.0003 

.01 

.003 

0 

.01 

0 

.002 

.0002 

.003 

33.7 

1.7 

33.7 

24.6 

2.8 

0 

0 

0 

.32 

.32 

.72 

1.0 

.82 

.14 

.II 

99.9 

3.4 

0.06 O.o7 0.05 

.0001 .0003 .0003 

.015 .01 0 

0 .0007 0 

0 .001 0 

.0005 .01 .00003 

.001 .0015 .0015 

.001 .007 .003 

.0009 .001 .001 

.005 0 0 

.002 .001 .. 001 .0002 .0007 0 .01 .OS .005 .0004 .005 0 .003 .002 .002 .0003 .0002 .0002 .03 .03 .01 

CIPWDOI'IIII 

19.7 32.1 

0 .95 

22.5 27.8 

37.3 33.8 

11.3 2.7 

.71 0 

.62 0 

.002 0 

2.9 .25 

.01 0 

2.8 .22 

0 .75 

.93 .72 

.38 .OS 

.II .II 

99.3 99.5 

8.5 2.1 

1151, 155 130-ISS 

Mean Mean 

71.0 71.6 3.3 

14.6 14.3 .9 

1.4 1.4 .4 

.78 .72 .36 

.75 .51 .61 

1.8 1.2 1.1 

4.2 3.9 .7 

4.3 4.7 .8 

.16 .13 .06 

.so .54 .20 

.44 .39 .II 

.09 .06 .07 

.08 .08 .04 

<.05 <.OS 

100 100 

0.06 0.06 0.01 

.0003 .0003 .0001 

.005 .01 .01 

.0004 .0002 .0004 

.0005 .0003 .0005 

.005 .003 .005 

.0015 .002 .0003 

.005 .008 .005 

.001 .001 .0005 

0 .003 .005 

.001 .001 .001 

.0004 .0003 .0003 

.o3 .02 .02 

.003 001 .002 

.002 .002 .0005 

.0002 .0002 .0005 

.02 .o3 .01 

The youngest plutonic rocks and related intrusive rocks 

in the Santa Rita Mountains are mainly of Tertiary age. 

They form small intrusive masses, such as small stocks, 

plugs, and dikes, and some of the rocks have an aphanitic 

and porphyritic texture, rather than a granitoid one. All 

these intrusive bodies were probably emplaced fairly close 

to the surface. Some of them appear to spread downward 

and so may well be the tops of larger stocks. Others are 

probably genetically related to contemporaneous volcanic 

rocks of nearby areas. 

These youngest plutonic rocks consist of four groups; 

the three oldest were emplaced late during the Laramide 

orogeny, and the youngest is postorogenic. Rocks of the 

Gringo Gulch pluton and of some other unrelated masses 

of quartz latite porphyry, latest Cretaceous or early 

Paleocene in age, are the oldest group. Granodiorite of the 
TERTIARY ROCKS 55 

Heivetia stocks was emplaced next, followed shortly 

thereafter by quartz latite porphyry of the Greaterville 

plugs. Granodiorite of the San Cayetano stock, which was 

emplaced during the late Oliocene, is the youngest rock. 

ROCKS OF THE GRINGO GULCH PLUTON 

AND OTHER ROCKS 

Small stocks, plugs, and dikes of microgranodiorite, 

hornblende dacite porphyry, and quartz latite porphyry 

crop out at several places in the southern quarter of the 

Santa Rita Mountains (fig. 38). Many of these rocks are 

strongly altered; as a result, their original composition is 

uncertain and their radiometric age is unobtainable. 

Discussing these rocks together is done for convenience 

and is not meant to imply a demonstrable genetic 

association. Indeed, some of the rocks may even be of 

latest Cretaceous age, as shown on the geologic map of the 

Mount Wrightson quadrangle (Drewes, 1971c), and other 

rocks may be as much as 10 m.y. younger. 

The least altered and, hence, the most thoroughly 

studied of these intrusive masses is the Gringo Gulch 

pluton. In plan it is an elliptical body covering almost half 

a square mile in the low hills 1 mile north of the junction of 

Gringo and Temporal Gulches. A smaller plug, cropping 

out near the Patagonia village garbage dump 2 miles south 

of that junction, is related to the pluton. The pluton is a 

composite body; two small areas in the core of the pluton 

contain light-brownish-gray microgranodiorite, and 

light-gray to medium-gray hornblende dacite porphyry 

forms most of the pluton, as well as all of the related plug. 

The large size, unaltered condition, and abundance of 

hornblende phenocrysts are the most striking features of 

this rock, and their uniqueness in the area suggest the 

correlation of the plug with the rock of the outer part of 

the pluton. 

The rocks of the Gringo Gulch pluton underlie a small 

basin and form only a few small outcrops as compared to 

the surrounding host rocks, which are mainly pyroclastic 

rocks of the Gringo Gulch Volcanics of probable 

Paleocene age. The plug, however, underlies a small knoll 

and forms outcrops slightly more resistant to weathering 

than its host rocks, pyroclastic and epiclastic rocks also of 

the Gringo Gulch Volcanics. In most places the host rocks 

next to the pluton and plug are not particularly strongly 

altered, but those west of the pluton are silicified and 

intensely argillitized, perhaps owing to the action of fluids 

from the pluton. The contact of the northern, 

topographically higher part of the pluton dips gently 

outward, but that along the southern, lower end of the 

pluton dips steeply. The southern part of the pluton 

contains inclusions of altered volcanic rocks. No chilled 

contact zones have been found along the borders of the 

hornblende dacite porphyry against the host rocks or on 

either side of the contact between the porphyry and the 

microgranodiorite. 

Several large intrusive masses that underlie areas of l4 to 

1 square mile and many smaller masses consist of quartz 

latite porphyry or latite porphyry. A swarm of short dikes 

and pipes is associated with one large mass near Mansfield 

Canyon, 2 miles northwest of the Gringo Gulch pluton 

(fig. 38). Two other large masses of quartz latite porphyry 

lie between the Salero mine and Josephine Canyon, and a 

sill-like mass occurs in the northern end of the San 

Cayetano Mountains. In general, the rocks of these 

intrusive masses are about as resistant to weathering as the 

adjacent rocks. They form some small outcrops and a few 

cliffs, and they disintegrate to a blocky detritus. Both fresh 

and weathered rocks are mostly pale red to grayish orange 

pjnk. They are all finely porphyritic, and phenocrysts are 

mostly of a pink altered plagioclase and altered mica and, 

in comparison to other rocks in the area, relatively free of 

quartz. The edges of these intrusive bodies lack chilled 

margins, and the host rocks are not contact 

metamorphosed. 

In certain details, however, these intrusive masses differ 

from each other. The quartz latite porphyry, which 

intrudes the Mount Wrightson Formation near Mansfield 

Canyon, is ameboid shaped, is surrounded by the swarm of 

small dikes, and contains some bodies of brecciated latite 

porphyry. This intrusive mass may be a large breccia pipe 

formed from a highly fluid magma, and it could be of 

Mesozoic age. The intrusive masses between Salero mine 

and Josephine Canyon have a subelliptical shape, and they 

intrude rocks at least as young as the Salero Formation and 

possibly as young as the Josephine Canyon Diorite. These 

rocks are flow laminated and in many places the dips of the 

foliation are steep and the strike seems to be irregular. The 

contact along the west side of the northernmost of these 

masses dips moderately eastward and that on the east side 

is about vertical, so apparently the size of that mass 

diminishes downward. These intrusive masses were 

probably formed from a fairly viscous magma, and they 

may be plugs or laccoliths. The intrusive mass in the 

northern part of the San Cayetano Mountains forms a 

thick southward-dipping sheet of gray latite porphyry that 

intrudes the Salero Formation. Its geologic relations with 

an adjacent stock of Josephine Canyon Diorite are 

concealed. 

Under the microscope, the microgranodiorite of the 

Gringo Gulch pluton is seen to be made up of about 

equally abundant crystals of a larger size (1- 4 mm) and a 

smaller size (0.03 - 0.1 mm}, arranged in a hypidiomorphic-granular texture. The rock contains mostly 

plagioclase, quartz, orthoclase, biotite, and hornblende, 

and trace amounts of ilmenitic magnetite, apatite, zircon, 

and allanite(?}, as shown by the modes in table 17. The 

larger crystals of plagioclase have the composition of calcic 
56 PLUTONIC ROCKS, SANTA RITA MOUNTAINS, SOUTHEAST OF TUCSON, ARIZONA 

0 2 3 4 KILOMETRES 

Younger rocks 

Surficial depnsils 

Grosvel)or Hills Volcan ics 

EXPLANATION 

<1: 

Granod iori te i= 

Mainly rhyodacile and rhyolite S10ck of !he San ~ wf[. agglomerate, and flows 

~ ~ 

Cayetano Mountains 1--

1 (fl >-

::Ja: 

o::!: 

WfJntrusive rocks :i ~ 

Includes hornblende daci1e of !he Grinxo Gulch pllllan J t.J fand quartz latite porphyry of a/her plutons a: a: 

m, microgranodiorite of the Gringo Gulch pluton U 0 

Older rocks 

l:meous and sedimentary rocks 

.159 

Moded 

-~----------- --

Contact 

Doued where concealed 

----------------- Fault 

Dotted where concealed 

Q1 96 

Chemically 

analyzed 

* 160 

Radiometrically 

dated 

Specimen collection siles and numbers 

FIGURE 38.-Distribution of rocks of Gringo Gulch pluton and .>ther rocks and specimen collection sites. 

andesine and the smaller ones are calcic oligoclase. Biotite 

is pleochroic in pale yellow brown to moderate yellow 

brown and is slightly altered to penninite. Hornblende 

forms fairly long subhedral crystals largely altered to 

actinolite and to a rim of iron oxide. Quartz and orthoclase 

are typically smaller grains. 

Hornblende dacite porphyry of the Gringo Gulch pluton 

and of the associated plug has a felty and granular 
TERTIARY ROCKS 57 

groundmass and phenocrysts as much as_ 1 em long. 

Phenocrysts make up 15 to 40 percent of the rock and are 

chiefly of hornblende and plagioclase, but some are augite 

and magnetite. The plagioclase phenocrysts have an 

andesine or labradorite composition, and in some 

specimens they are partly albitized. The hornblende 

phenocrysts are mostly euhedral, and in one specimen they 

form a sheathe around a xenocryst of quartz. They are 

pleochroic in light olive brown to dark olive brown or olive 

green and are slightly altered to chlorite, epidote, and iron 

oxide. The groundmass biotite forms small crystals 

pleochroic in yellowish brown that are largely chloritized, 

and the pyroxene is probably augite. 

The quartz latite porphyry of the other intrusive masses 

is a strongly altered rock that has an idiomorphic-granular 

groundmass. Phenocrysts are4 to 7 mmlpng and make up 

15 to 25 percent of the rock. They are much-albitized 

plagioclase and some chloritized and sericitized biotite; a 

few specimens contain a perthitic potassium feldspar. 

Trace amounts of magnetite, apatite, quartz, sphene, 

zircon, amphibole(?), and pyroxene(?) are present in 

various combinations. Alteration minerals are very 

abundant and include clay minerals, chlorite, sericite, 

leucoxene, epidote, actinolite(?), calcite, chalcedony, and 

iron oxide. 

The few available modes are plotted on the modified 

triangular diagram of figure 39. The hornblende dacite 

porphyry is a modal syenodiorite that is similar to the 

rocks of the Josephine Canyon Diorite. 

The chemical and spectrographic analyses and CIPW 

norms of two specimens of the Gringo Gulch pluton, 

which are shown in table 18 and are plotted in figure 10£, 

suggest the microgranodiorite to be compositionally 

similar to the granodiorite of the San Cayetano stock (table 

23). The chemical analyses show that hornblende dacite 

porphyry is not simply a fine-grained variety of the 

microgranodiorite, as in a chilled-border phase. For 

example, the microgranodiorite contains at least 10 percent 

more Si02 than does the porphyry. Even assuming that 

this difference is due to a secondary enrichment, and so 

removing the excess and recalculating the analytical results 

to 100 percent, the microgranodiorite has much more K2P 

and less total iron, MgO, and CaO than the daCite 

porphyry. The rocks must have been crystallized from 

separate, but perhaps genetically related, magmas, even 

though they were contemporaneously emplaced in the 

same pluton, as is shown by their radiometric ages. 

The age of the rocks of the Gringo Gulch pluton is more 

accurately determined by radiometric methods than by 

geologic relations. The pluton is known to antedate the 

Gringo Gulch Volcanics, which are younger than the 

Josephine Canyon Diorite. Most of the other rocks of the 

group are found to antedate the Salero Formation, and one 

of the intrusive masses may antedate the Josephine Canyon 

Diorite. An upper age limit cannot be determined from the 

geologic relations. 

Nearly identical radiometric potassium-argon ages of 60 

m.y. (Marvin and others, 1973) are obtained from biotite 

of the microgranodiorite and from hornblende of the 

hornblende dacite porphyry. No ages were determined on 

the other rocks of the group. 

The Gringo Gulch pluton and the related plug, and 

possibly also most of the other rocks, are considered to be 

emplaced penecontemporaneously with the deposition of 

the Gringo Gulch Volcanics, during the tectonically 

quiescent interval between the Piman and Helvetian phases 

of the Laramide orogenv. 

GRANITOID ROCKS OF THE 

HELVETIA STOCKS 

During the late Paleocene seven small elliptical stocks, 

mainly of granodiorite and quartz monzonite, intruded the 

complexly deformed rocks of the northern part of the 

Santa Rita Mountains (fig. 40). They underlie areas of 

about JA to 2 square miles, and most of them are elongate 

in a northwest direction. Collectively I refer to the stocks 

as the Helvetia stocks; individually they include the 

Helvetia, Shamrod, South Johnson Ranch, and Johnson 

Ranch stocks of quartz monzonite and granodiorite, the 

Southeast stock entirely of quartz monzonite, the 

Huerfano stock wholly of granodiorite, and the Sycamore 

stock of quartz diorite. Compositionally, most of the rocks 

are nearly the same despite the different rock names that 

are applicable, but the quartz diorite is sufficiently 

different that the Sycamore stock may be a genetically 

distinct intrusive mass. The stocks were emplaced, 

approximately contemporaneously, during faulting of the 

Helvetian phase of the Laramide orogeny (Drewes, 1972b) 

and before the mineralization of the Helvetia mining 

district (Drewes, 1973). 

The stocks intrude a wide assortment of rocks of 

Precambrian and Paleozoic ages, and they are covered by 

much younger gravel deposits. They are also cut by faults, 

which are intruded by quartz latite porphyry of the 

Greaterville plugs. The host rocks are metamorphosed, 

and the zone of metamorphism is wider to the south than 

to the east, where unaltered Mesozoic rocks have been 

faulted against the older rocks. Although the intensity of 

metamorphism does not seem to increase immediately 

adjacent to the stocks, it does gradually decrease southward about 3 miles away from the stocks. This thermal 

event may have begun as early as the time of intrusion of 

the stocks of Helvetia but it probably extended through the 

time of injection of the plugs of Greaterville as well, and so 

it is not, strictly speaking, a contact metamorphic effect of 

one stock. 

The intrusive contacts of the Helvetia stocks are mostly 

straight and are vertical or dip steeply outward. In a few 

places apophyses of the stocks extend a short distance mto 
58 PLUTONIC ROCKS, SANTA RITA MOUNTAINS, SOUTHEAST OF TUCSON, ARIZONA 

POTASSIUM 

FELDSPAR 

,&196 

(!] 160 

Syenodiorite 

(dacite) 

158° 

EXPLANATION 

0 

Hornblende dacite porphyry of 

the Gringo Gulch plugs 

(!] 

Microgranodiorite of the 

Gringo Gulch plugs 

~ 

Granodiorite of the 

San Cayetano stock 

FIGURE 39.-Modified triangular diagram showing modal quartz, potassium feldspar, plagioclase, and fernie minerals of rocks of the Gringo Gulch 

pluton and of the San Cayetano stock. 

the host rocks, and, along the ~ast side of the Shamrod 

stock, a large block of Cambrian Bolsa Quartzite is 

engulfed in the stock. Chill zones were not found along the 

margins of the stocks. 

PETROGRAPHY 

The granitoid rocks of the Helvetia stocks are generally 

light gray to yellowish gray or light brownish gray, coarse 

grained, massive, and slightly altered. The quartz 

monzonite and aplitic rocks of the Southeast stock (fig. 40) 

are slightly more orange or pink than are the rocks of the 

other stocks, and the rocks of the Sycamore stock are 

medium gray to medium greenish gray. Several of the 

stocks underlie, in part, the pediment at the foot of the 

mountains where they are deeply weathered. They also 

underlie some gentle slopes and low hills beneath the more 

rugged outcrops of Paleozoic rocks. Only the rocks of the 

Southeast stock and aplitic masses in the Huerfano stock 

form bold outcrops. The granitoid rocks are cut by widely 

spaced joints, and, locally, they weather to low rounded 

bosses or extensive fairly flat surfaces that are separated by 

abundant grus and overlain by scattered rounded residual 

blocks. The rocks of most of these stocks are nearly free of 

inclusions; exceptions are the Shamrod stock, which 

contains a large engulfed block on the east side, and the 

Sycamore stock, which contains large masses of Paleozoic 

rocks and granodiorite. The granitoid rocks are cut by a 

few widely scattered and mostly small dikes of 

lamprophyre and aplite (Drewes, 1972b, pl. 5). Huerfano 

Butte is underlain by the largest of the aplite masses and 

the nearby granodiorite is silicified. Other smaller aplite 

and lamprophyre dikes extend across the contacts of stocks 

or are entirely within the host rocks near the stocks. 

Most of the rocks have a hypidiomorphic-granular 

texture, a 3 to 7 mm grain size, and slight or no alteration 

(figs. 41, 42). A trace of microgranophyric texture is 

present in most specimens, and some of the finer grained 

rocks are idiomorphic granular or have a mosaic texture. A 

bimodal distribution of grain size occurs in the specimens 

of the Southeast stock, in the nearby end of the Helvetia 

stock, and in the southeast end of the South Johnson 

Ranch stock. Large irregular intergrowths of quartz in 

feldspar also are common in specimens from the east end 

of the Southeast stock. The texture of the Sycamore stock 

is subophitic and the grain size of the rock is only 0.5 to 3 

mm. In a few specimens from the other stocks crystals are 

as much as 9 mm long, and one specimen has phenocrysts 

as much as 18 mm long. 

The dominant minerals in the granitoid rocks are quartz, 

plagioclase, potassium feldspar, biotite, and, in the 

Sycamore stock, hornblende. The quartz is generally 

anhedral and rarely subhedral, and that of most stocks has 

little or no undulatory extinction. However, quartz of the 

South Johnson Ranch stock has moderate to strong 

undulatory extinction, possibly suggesting that stresses 

along the faults where the highly elongated stock was 

emplaced had not been fully relieved at the time of 

emplacement. The Sycamore stock contains relatively 

minor amounts of quartz that has a moderate undulatory 

extinction. 
TERTIARY ROCKS 59 

TABLE 17 .-Modes of Gringo Gulch pluton and related plug TABLE 18 .-Chemical and spectrographic analyses and CIPW norms of 

(Field numbe rs are abbreviated; year of collection and collecto r's initial omitted. Full field number the Gringo Gulch pluton of specimen 157 thus is 630199. Symbols: Tr., trace; . . , not determined] 

Rock type Hornblende dacite porphyry Micrograna· 

diorite 

Intrusive mass Pluton Plug P luton 

Specimen No 1.17 158 159 160 

Field No. 199 661 257 281 

Quartz . . 1.3 lo 4.2 1o.8 lo 19.8 Plagioclase . 73.5 5.0 58 .6 21.8 10.8 52.1 

Orthoclase . 9.9 0 18.9 0 0 14.9 Pyroxene (augite?) 5.0 .5 .7 .3 .5 0 Hornblende . 3.3 3.3 9.0 5.3 5.8 5.4 Biotite . .9 0 2.4 1.0 0 4.7 Magnetite . 5.5 1.2 5.9 2.6 1.4 2.5 Apatite .. . ... ..... .. .6 0 .3 0 0 .4 Sphene . Tr. 0 0 0 0 0 Ziron . 0 0 Tr. 0 0 .2 Allanite . . 0 0 0 0 0 Tr. 

Total 100.0 10.0 100.0 31.8 18.5 100.0 

Fernie . 15.3 5.0 18.3 9.2 7.7 13.2 

Percent anorthite 

in plagioclase . 60-68 0 - 37 38 - 55 35 - 47 

(plagioclase rims) .. (37) (24) 

1 Phenocrysts. 

The plagioclase varies slightly in habit and composition 

from stock to stock. It typically forms subhedral grains. 

Plagioclase of the southern four stocks is slightly and 

finely perthitic, but that of the other stocks is rarely 

perthitic. The composition of the plagioclase of the 

Sycamore stock is andesine, except for the outer zones of 

some crystals, which are oligoclase. The composition of 

the plagioclase in the other stocks is oligoclase or albite. 

Several stocks have only albite or only oligoclase except for 

the rims of some crystals, but the Helvetia stock has 

oligoclase in some specimens and albite in others, perhaps 

suggesting an incompleted diagenetic alteration. Sericite 

and clay-minerals alteration products are generally sparse. 

The potassium feldspar also has variable features in tne 

stocks of Helvetia. It generally forms anhedral to 

subhedral crystals. The Southeast stock has only 

orthoclase, the Huerfano and Helvetia stocks have both 

orthoclase and microcline(?), and the Shamrod, South 

Johnson Ranch, and Johnson Ranch stocks have only 

microcline(?). The identity of the microcline is in doubt 

because the grid twinning is very blurred, perhaps because 

it is partly obliterated. Both kinds of potassium feldspar 

occur in accessory amounts in the Sycamore stock. Lace 

and patch types of perthite are about equally abundant, 

and kaolinite alteration is typically slight. 

The biotite generally occurs in subhedral and partly 

chloritized crystals that are pleochroic in yellow brown to 

dark brown. Several specimens from the South Johnson 

Ranch stock that have a bimodal grain size contain small 

biotite crystals in aggregates, suggesting that they were 

probably recrystallized. The biotite of one specimen of the 

Sycamore stock is pleochroic in yellow brown to dark olive 

(Chemical analyses by rapid rock method (Shapiro and Brannock, 1962), with specimen 157 supplemented by X-ray method. Chemical analysts: Lowell Artis, S. D. Botts, G. W. Chloe, 

P. L. D. Elmore, and H. Smith. Spectrographic analyses by semiquantitative method. Spectrographic analyst, J. C. Hamilton. Elements looked for but not found : Ag, As, Au, B, Bi, Cd, 

Ce, Eu, Ge, Hf, Hg, In, Li, Mo, Nd, Pd, Pr, Pt, Re, Sb, Sm, Sn, Ta, Te, Th, Tl, U, W, and Zn( 

Rock Hornblende dacite type . . porphyry 

Specimen No .... . . .. . . ... . . 

Field No. 

157 

199 

Chemlcalana1yses (welghl percent) 

Microgranodiorite 

160 

281 

Si02 . . . . . . . . . . . . . . . . . . . 59.0 66.9 

Alz03 00 00 00 00 00 .. .. 

00 • 16.3 15.9 

Fe20J.... . ... . .... .. . .. 3.4 2.7 

FeO. . .. . .... . . .. . ..... 2.8 1.4 

MgO . . . . . . . . . . . . . . . . . . 2.6 1.4 

CaO.. . .. .. . ..... . .... . 4.7 2.8 

Na20 . . . . . . . . . . . . . . . . . 4.4 4.0 

K 2 0oo 00 00 00 00 00 00 00 00. 2.4 3.2 

H20-. ... . . . . . . . . ... . . . 1.1 .36 

H 20+ . . . . . . . . . . . . . . . . 1.4 .90 

Ti02 . . . . . . . . . . . . . . . . . . .98 .56 

P 20 5 .. . .. . .. . .. . .• ... . .21 .18 

MnO.... ... . ... . . . . . . . .14 .06 

co2 .. .. .... ...... ..... __ .1_2 _________ ._1o __ 

Total . . .. . . .. . . .. 100 

Spectrographic analyses (weight percent) 

Ba ... . . ..... . . ..... ... . 

Be . ..... .. . .... . . . .... . 

Co . . ..... . .. . . . . .... .. . 

Cr .. ... . . . . . ....... ... . 

Cu ..... ...... . . . . ... . . . 

Ga .. . . .. .. ... . . . .... . . . 

La 00.00 00 00 00 00 00 ... 000 

Nb oooo·· ··· oo ooo ooooooo 

Ni ..... ...... ..... . . .. . 

Pb ....... . .. .... .. . ... . 

Sc .. .. .. . . . . . . ....... . . . 

Sr .... .. . ... . .... . . . .. . . 

v ooo ooOOoooo oo oo o ooOoOo 

Y oooo .. .. oo oooooooooo oo 

Yb . . .. .. . .. . .. ... ..... . 

Zr ... . . . .. . .... . .. . . . . . 

0.05 

.0002 

0 

0 

.001 

.002 

0 

.003 

0 

.002 

0 

.003 

0 

.0015 

.0003 

.007 

CIPW norms 

100 

0. 15 

0 

.0007 

.001 

.01 

.003 

.005 

0 

.0007 

.007 

.0007 

.07 

.01 

.002 

.0002 

.007 

Q .... . . .. ..... . .... .. oo 11.5 24.1 

c 00.00 .. 0 •• 00 .. 00 • • 00 00 0 1.0 

or .. . . . . . . . . . . . . . . . . . . . . 14.2 18.9 

ab .. 00 00. 00 ..... 00..... 37.2 33.8 

an . . . . . . . . . . . . . . . . . . . . . 17.6 12.1 

{

wo.. . . . ... .. ... .. .. 1.5 0 

di en . . . . . . . . . . . . . . . . . . 1.1 0 

fs. .. .. . ... .. ..... . . .17 0 

hy Jen oo . . 00 00 .. 00 00 .. 00 5.3 3.5 

1 fs ............ .. .. . . .80 0 

mt .. . ..... . .. ... . .. .... 4.9 3.1 

hm .. . .. . .. . . . . ..... .... 0 .57 

il 00 00 00 .. 00 .. .. 00 00 .. 00 1.9 1.1 

aP. . . . . . . . . . . . . . . . . . . . . . .50 .43 

cc 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 _ _..:..:.2::..;7 __________ .2_3 _ ___, 

Total ...... ... . .. . 

Fernie . .......... . 

96.9 

16.4 

98.8 

8.9 
60 PLUTONIC ROCKS, SANTA RITA MOUNTAINS, SOUTHEAST OF TUCSON, ARIZONA 

31 ° 

55' 

50' 

110° 50' 

or 

0 

0 

110° 45' 

or 

2 3 MILES 

2 3 KILOMETRES 

EXPLANATION 

Younger rocks 

Igneous rocks and surficial deposits 

Quartz latite porphyry 

Rocks of the Greaterville pl11gs 

jfjj Tgc J 

Granitoid rocks 

Tg , granodiorite, quartz monzonite, and 

quartz diorite 

T gc , grani10id rocks; concealed beneath 

pediment gravel 

Older rocks 

t ex: 

<! 

lex: 

w 

IIgneous, sedimentary, and medamorphic rocks 

• 191 

Moded 

-----------------

Cont act 

Dotted where concealed 

----------------- Fault 

Dolled where concealed 

0 190 

Chemica ll y 

ana lyzed 

-X-163 

Radiometrically 

dated 

Specimen collection sites and numbers 

FIGURE 40.-Distribution of granitoid rocks of the Helvetia stocks and Greaterville plugs and specimen 

collection sites. 

brown. Penninitic chlorite alteration seems to be slightly 

more common in the northern part of the stock than in the 

southern part. 

The hornblende of the Sycamore stock and that of one 

specimen of the South Johnson Ranch stock is euhedral to 

subhedral, and it is pleochroic in blue green or moderate 

green to olive green or olive brown. 

Accessory minerals of the Helvetia stocks commonly 

include magnetite, apatite, sphene, and zircon. These 

minerals are more abundant in the rocks of the Sycamore 

stock than in the other rocks. A few specimens from the 

Southeast stock and Shamrod stock contain trace amounts 

of allanite and tourmaline. 

MODAL AND CHEMICAL SUMMARY 

The modal composition of 23 specimens of the Helvetia 

stocks are shown in table 19 and are summarized on the 

modified triangular diagram of figure 43. The figure 

drawn around the entire suite of modes forms an 

irregular-shaped flattened body superficially similar to that 

representing the modes of the Josephine Canyon Diorite 
TERTIARY ROCKS 61 

FIGURE 41.-SpecJmen 174. Quartz monzomte of the Helvetia stocks. 

(fig. 26). However, viewed in more detail, the modes of the 

Helvetia rocks form two clusters, one representing quartz 

diorite of the Sycamore stock and a second representing 

the other stocks. The modes of the Josephine Canyon 

Diorite, in contrast, spread uniformly throughout the. 

circumscribed figure, and so they are believed to be of 

rocks derived from rather closely associated magmas or 

perhaps differentiates of a single magma. The Helvetia 

rocks seem to require a derivation from two magmas that 

are either unrelated or only distantly related. 

A figure drawn around the modes of all the rocks except 

those of the Sycamore stock forms a nearly hemispherical 

body flattened against the leucocratic face of the 

composition tetrahedron and centered along the boundary 

between the quartz monzonite and granodiorite fields. In 

shape and position this figure is about midway between 

those of the Elephant Head Quartz Monzonite (fig. 36) and 

the Madera Canyon Granodiorite (fig. 31). 

Chemical and spectrographic analyses and CIPW norms 

of 11 of the moded specimens of the Helvetia stocks are 

assembled in table 20 and are summarized in the histogram 

of figure lOG. The chemical similarity of these rocks and 

the quartz latite porphyry of the Greaterville plugs (fig. 

FIGURE 42.-Specimen 174. Quartz monzonite of the Helvetia stocks. 

Crystals: quartz (Q), plagioclase ( P), microcline (M), biotite (B), 

ilmenitic magnetite (im), and sphene ( S ). Plain light; X 20. 

lOll) is discussed in the description of that porphyry. ln 

content of total iron and MgO. the rocks of the Helvetia 

stocks are approximately the same as the granite and 

quartz monzonites of the Santa Rita Mountains (figs. 

101-lOK); the content of Na20 and K20 resembles that 

of some granodiorite (fig. lOD), and the content of CaO is 

intermediate between that of the two rock groups. The 

chemistry of these granitoid rocks, exclusive of the quartz 

diorite of the Sycamore stock, is somewhat similar to 

Nockolds' (1954, p. 1014) average adamellite and 

muscovite-biotite granodiorite, but the silica and the 

calc-alkali components do not closely match. 

AGE AND CORRELATION 

Through geologic relations with other rocks, the 

Helvetia stocks are dated as Cretaceous or Paleocene. The 

stocks postdate the Willow Canyon Formation of the 

Bisbee Group, for an apophysis of the Johnson Ranch 

stock intrudes this formation, and it also intrudes some old 

faults of the Helvetian phase of the Laramide orogeny, 

one-third mile northeast of the Johnson Ranch (Drewes, 
62 PLUTONIC ROCKS, SANTA RITA MOUNTAINS, SOUTHEAST OF TUCSON, ARIZONA 

TABLE 19.- Mode of granitoid rocks 

[Field numbers are abbreviated;· year of collection and collector's initial omitted. Full field number of 

Rock type .. ····· · Aplitic quart z monzonite Dominantly granodiorite Granodiorite Dominantly 

quartz ~onzonite 

Intrusive mass . Southeast stock Helvetia stock Huerfano stock Shamrodstock 

Specimen No . .. 161 162 161,162 163 164 16S 166 167 I 163-167 168 169 170 168-170 171 172 

Mean Mean Mean field No. 1143 IISS lOS I 1107 IOS4 1190 1163. 1426 1109 1403 1168 1313 

Quartz ····· ········· 3S.2 31.7 33.S 27.7 23.6 31.9 29.S 34.9 29.S 26.1 2S.7 34.0 28.6 19.1 23.0 Plagioclase, total .. 31.8 4S.8 38.8 S0.9 49.7 43.7 47.7 46.8 47.8 48.8 48.9 47.7 48.S S4.1 42.6 (plagioclase in 

perthite) . (1.9) (0.2) (1.1) (0.4) (0.9) (0.6) 0 (1.8) (0.7) 0 (0.8) 0 (0.3) (4.4) (4.S) 

K-feldspar, total . . 30.8 18.4 24.6 19.7 2S.2 21.6 20.2 IS.4 20.4 21.2 20.8 IS.3 19.1 24.6 32.1 (orthoclase) . (30.8) (18.4) (24.6) (18.9) (2S.2) (21.6) 0 0 (13.1) (21.2) 1(20.8) 0 (14.0) 0 0 (microcline?) . 0 Tr. Tr. (0.8) Tr. 0 (20.2) (IS.4) (7.3) 0 Tr. (IS.3) (S.I) (24.6) (32.1) Biotite .. 1.7 2.9 2.3 1.3 1.3 1.8 2.4 2.3 1.8 3.2 3.6 2.0 2.9 1.6 1.3 Amphibole .... ... .... 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 Magnetite ..... . . .... .3 1.0 .7 .2 .2 .7 .I .s .3 .s .6 .7 .6 .4 .8 

Apatite. Tr. .2 .I .OS .05 .3 Tr. .I .I .OS .2 .2 .2 .I .2 

Sphene ........ .... . . .I Tr. .OS .2 0 .OS .OS Tr. .OS .OS .I .I .I .OS .OS 

Zircon .. ....... .I Tr. . OS Tr. 0 Tr. .OS Tr . Tr. .I Tr. Tr . .OS .OS 0 

Allanite .. 0 Tr. Tr. 0 0 0 0 0 0 0 .I 0 .OS 0 0 

Tourmaline{?) ........ 0 Tr . Tr. 0 0 0 0 0 0 0 0 0 0 0 0 

Total. .. . . 100.0 100.0 100.1 IOO.OS 100.05 IOO.OS 100.0 100.0 99.9S 100.0 100.0 100.0 100.1 100.0 IOO.OS 

Fernie. 2.2 4.1 3.2 1.7 1.5 2.8 2.6 2.9 2.3 3.9 4.6 3.0 3.9 2.2 2.3 

Percent anorthite 

in plagioclase ........ 0 - S? 30 13-30 S-10 (S-10) 2S-31 2S 2S -30 S-10 27 29 27-29 12 

(plagioclase rims) .. .... . . (10) 

Quartz mixing 

index (see text) . .87 .77 .99 

I Modal orthoclase, ? spec1men 169, mcludes some samdme (.). 

1972b, pl. 5). In one place, a half a mile east of Helvetia, 

and in another place, extending from about a mile 

southeast to about a mile northeast of the ranch, faults 

that cut the Helvetia stocks are intruded by plugs of quartz 

latite porphyry of late Paleocene age. 

A more definite age of the stocks is provided by 

radiometric dating (table 4). Replicate potassium-argon 

ages of biotite from specimen 163 date the Helvetia stock 

as 53.5 m.y., or late Paleocene. A single age determination 

of biotite from specimen 170 dates the Shamrod stock as 

53.9 m.y. (Marvin and others, 1973), an age nearly 

identical to those of the Helvetia stock and well within the 

limitations of the analytical method. 

Plutonic rocks of the same age as the Helvetia stocks 

have not been identified in the ranges next to the northern 

part of the Santa Rita Mountains. The batholith-sized 

body of Ruby Star Granodiorite of the Sierrita Mountains 

(fig. 1) is somewhat similar to the rocks of the Helvetia 

stocks but is at least 5 m.y. older (Cooper, 1974). The 

rocks of the Helvetia stocks, other than the Sycamore 

stock, are similar to the quartz Iatite porphyry of the 

Greaterville plugs in the content of major elements and in 

age but differ in the content of some trace elements and in 

texture. These differences apparently have economic 

significance, for, although these two groups of intrusives 

are largely coextensive, the Helvetia stocks are not 

genetically associated with mineralization, whereas the 

Greaterville plugs are. 

The Helvetia stocks were probably emplaced passively 

from a viscous magma during late Laramide orogenic 

times. Stoping accompanied the emplacement of the 

Shamrod and Sycamore stocks, but indications of stoping 

.82 

(10) (10) (10) (S) (S-10) (S) 

.69 .83 .82 .70 .79 .77 .7S .44 

are lacking in the others. The viscous or dry aspect of the 

magma is indicated by the straight-trending contacts and 

elliptical shape of the stocks, as well as by the absence of 

signs of mineralizing fluids, The host rocks were probably 

metamorphosed beginning at the time of emplacement of 

the Helvetia stocks, and the cooling may have taken place 

after the the intrusion of the Greaterville plugs. This timing 

is suggested by the coextensive distribution of much of the 

metamorphic terrane with the stocks and with most of the 

plugs, as well as by the widespread occurrence of 

radiometric dates of 55 m.y. in the stocks, plugs, and 

recrystallized biotite of the metagranodiorite host rock 

(table 4, specimen 19). The area may also have been 

strongly uplifted and deeply eroded concurrently with the 

Helvetian phase of faulting, for, whereas the Helvetia 

stocks are coarse grained, only slightly younger rocks of 

the Greaterville plugs are fine grained. 

QUARTZ LATITE PORPHYRY OF THE 

GREATERVILLE PLUGS 

In the northern part of the Santa Rita Mountains, eight 

plugs and many smaller masses of quartz latite porphyry 

were intruded during late Paleocene time (fig. 40). This 

rock is locally known as the "ore porphyry" for its close 

association with mineralization in the Greaterville and 

Helvetia mining districts of the Santa Rita Mountains and 

in the mining districts of other mountain ranges of this part 

of Arizona. The quartz latite porphyry forms 

ameboid-.shaped masses and is distinctive in its habit and 

appearance. It is finely granular and porphyritic and 

contains fairly abundant small biotite (or chlorite) crystals 

and bi'pyramidal quartz phenocrysts. The plugs and 
TERTIARY ROCKS 

of the Helvetia stocks 

specimen 161 thus is 6601143. Symbols: s, standard deviation; Tr., trace; ... , not determined] 

Dominantly quartz monzoniteContinued 

Shamrod stock-Continued 

173 174 171-174 

Mean 1337 1612 

23.0 24.5 22.4 

44.0 41.6 45.6 

(2.9) (7.5) (4.8) 

30.0 30.0 29.2 

0 0 0 

(30.0) (30.0) (29.2) 

2.6 3.3 2.2 

0 0 0 

.2 .3 .4 .2 .2 .2 

.05 .05 .05 

0 . 05 Tr. 

0 0 0 

Tr. 0 Tr. 

1100.05 100.0 100.05 

3.0 3.9 2.9 

15 ........ 12-15 

..... .. (5-10) (5-10) 

.85 .98 .76 

Granodiorite and quartz monzonite 

South Johnson Ranch stock 

175 176 177 

1225 1286 1375 

27.5 33.0 29.8 

52.9 38.4 45.7 

(1.8) 0 0 

15.1 23.2 .3.0 

0 0 0 

(15.1) (23.2) (13.0) 

4.2 5.0 10.1 

0 0 0 

.2 .3 1.1 

.05 .05 .2 

.05 Tr. 0 

Tr. .05 .I 

0 0 0 

0 0 0 

100.0 100.0 100.0 

4.5 5.4 11.5 

24-27 24-29 27 

.............................. 

.80 .49 .65 

Southeast stock 

(!] 

Helvetia stock 

0 

Huerfano stock 

178 

1392a . 

30.8 

35.9 

0 

24.9 

0 

(24.9) 

8.0 

0 

.2 

.2 

0 

Tr . 

0 

0 

100.0 

8.4 

14-17 

• • • • • • 0 

.% 

Johnson Kane~ 

175-H8 179 180 

Mean 1390 1406a 

30.3 37.9 24.2 

43.2 33.3 44.7 

(0.5) 0 0 19.1 26.4 19.7 

0 0 0 

(19.1) (26.4) (19.7) 

6.8 2.1 8.9 

0 0 1.0 

.5 .2 .5 

.I .05 .3 

Tr. .05 .7 

Tr. .05 .05 

0 0 0 

0 0 0 

100.0 100.05 100.05 

7.4 2.4 11.4 

14-29 13 27-30 

........ ................. 

.73 .95 .61 

EXPLANATION 

£ 

Shamrod stock 

0 

South Johnson Ranch stock 

'-/ /' Johnson Ranch stock 

stock 

179,180 181 

Mean l4()6b 

31.1 10.3 

39.0 50.2 

0 0 

23.1 1.4 

0 0 

(23.1) (1.4) 

5.5 16.0 

.5 19.0 

.4 1.2 

.2 .7 

.4 1.2 

.05 .05 

0 0 

0 0 

100.2 100.05 

7.1 38.1 

27-30 50 

......... (25) 

.78 .% 

Quartz diorite 

:sycamon: stocil 

182 183 

1402 1404 

9.1 15.0 

52.1 57.2 

0 0 

.8 4.0 

0 (4.0) 

(0.8) 0 

0 14.9 

34.3 6.7 

1.8 1.3 

.5 .2 

1.4 .6 

.05 .05 

0 0 

0 0 

100.05 99.95 

38.0 23.8 

32? 33-37 

.......... (24) 

.92 .89 

PLAGIOCLASE 

Sycamore * stock 

181-183 

Mean 

11.5 

53.2 

0 

2.1 

(1.3) 

(0.7) 

10.3 

20.0 

1.4 

.5 

1.1 

.05 

0 

0 

100.2 

33.4 

32-50 

(25) 

.92 

Granodiorite and quartz monzonite 

Quartz diorite 

63 

161- 180 

Mean s 

28.1 5.0 

45.4 5.6 

(1.4) (2.1) 

22.1 5.5 

(6.0) (10.0) 

(16.2) (11.6) 

3.6 2.7 

Tr. ........ .4 . 3 

.I .1 

.I .2 

.03 .03 

Tr. ........ 

Tr. ········ 

99.83 

4.2 3.0 

5-30 ........ (5-10) ........ 

.77 .16 

F.IGURE 43.-Modified triangular diagram showing modal quartz. potassium feldspar. phlgioclase. and fernie minerals of the granitoid rocks of 

the Helvetia stocks 

related smaller intrusive masses are collectively herein 

referred to as the Greaterville plugs. 

A cluster of plugs, small pipes, and dikes intrude the 

W 1llow Canyon and Apache Canyon Formations of the 

Bisbee Group in the Greaterville area. The cluster is 

elongated with its long axis oriented northwest along the 

Boston syncline, which is interpreted to be a disharmonic 

structure within the upper plate of a thrust fault that 

extends northward beyond the Helvetia area. This cluster 

of intrusive bodies is surrounded by a zone of contact:-
64 PLUTONIC ROCKS, SANTA RITA MOUNTAINS, SOUTHEAST OF TUCSON, ARIZONA 

TABLE 20.-Chemica/ and spectrographic analyses and CIPW norms of granitoid rocks of the Helvetia stocks 

[Chemical analyses of specimens 167, 173, 178, and 181 by rapid rock method (Shapiro and Brannock, 1962), supplemented by atomic absorption method; other specimens analyzed by single solution 

method (Shapiro and· Massoni, 1968). Chemical analysts: Lowell Artis, S. D. Botts, G. W. Chloe, P. L. D. Elmore, John Glenn, J. Kelsey, and H. Smith. Spectrographic 

analyses by semiquantitative method. Spectrographic analysts: W. B. Crandell and J. L. Harris. Elements looked for but not found: As, Au, B, Bi, Cd, Eu, Ge, Hf, Hg, In, Li, 

Nd, Pd, Pr, Pt, Rb, Sb, Sm, Sn, Ta, Te, Th, Tl, U, W, and Zn. Symbols: s, standard deviation; <• Jess than; ... , not determined; Tr., trace] 

Rock type ......... Granodiorite and quartz monzonite Quartz diorite Granodiorite and 

quartz monzonite 

Intrusive mass .... Helvetia stock Huerfano Shamrod stock South Johnson Rancl:), stock Johnson Sycamore stock 

stock Ranch 

stock 

Specimen No ...... 165 167 lt6S,167 170 172 1'73 J 172,173 176 177 178 . r76-178 179 181 183 \181,1831 165-179 

Mean Mean Mean Mean Mean s Field No ......... 1054 1163 1403 1313 1337 1286 1375 1392a 1390 l 1406b 1404 

Chemical analyses (weight percent) 

Si02 ............ 71.1 72.8 72.0 71.9 il.9 71.8 71.9 72:5 71.2 72.3 72.0 73.1 55.4 56.4 55.4 72.9 0.7 

Al203 ...... , .... 15.1 14.6 14.9 15.2 15.0 15.9 15.5 14.2 14.3 14.7 14.4 14.8 16.9 16.0 16.5 14.9 .5 

Fe2o3 ........... .94 .96 .95 .50 .68 .78 .73 .54 1.0 .53 .69 .30 2.9 3.5 3.2 .69 .2 

FeO ............. .60 .40 .50 .64 .56 .56 .56 .% 1.5 .% 1.1 .64 5.7 4.6 5.2 .76 .3 

MgO ............ .43 .33 .38 .35 .25 .36 .31 .58 1.0 .46 .68 .36 4.3 3.3 3.8 .46 .2 

CaO ............. 1.6 1.4 1.5 2.3 2.0 1.7 1.9 2.3 3.1 1.9 2.4 1.9 6.2 6.3 6.3 2.0 .5 

Na2o ........... 4.5 4.1 4.3 4.3 4.3 4.6 4.5 3.4 3.0 3.6 3.3 3.9 3.4 2.8 3.1 4.0 .5 

K20 ............. 4.0 4.0 4.0 3.7 4.1 3.4 3.8 4.0 3.2 4.0 3.7 3.7 2.2 2.8 2.5 3.8 .3 

H20- ........... .12 .14 .13 .20 .ll .13 .12 .21 2.0 .10 .77 .36 .18 .33 .26 .37 .6 

H20+ ·········· 1.0 .37 .69 .51 .58 .46 .52 .79 .78 .44 .67 .74 .75 1.5 1.1 .63 .2 

Ti02 ............ .23 .12 .18 .20 .20 .14 .17 .23 .35 .16 .25 .17 1.1 1.1 1.1 .20 .07 

P205·· .......... 0 .06 .03 .10 .08 .06 .07 .II .18 .08 .12 .05 .23 .36 .30 .08 .05 

MnO ............ .II .05 .08 0 .07 .06 .07 .07 .12 .06 .08 .02 .17 .08 .13 .06 .04 

C02············· .08 <.OS <.05 <.05 <.OS <".05 <.OS .10 < .05 < .05 <.05 <.OS <.OS .94 .47 <.05 <.05 

Total ...... 100 99 100 100 100 100 100 100 100 99 100 100 99 100 ., 100 ....... 

Spectrographic analyses (weight percent) 

Ag ............... 0 0 0 <o.ooo1 <O.OOOI 0 <:0.0001 <O.OOOI <O.OOOI 0 <O.OOOI <O.OOOI 0 <o.OOOI <O.OOOI <0.0001 ...... Ba ............... .15 .07 .I .07 .07 .07 .07 .07 .07 .I .08 .07 .07 .07 .07 .08 . 03 

Be ............... .0003 .0002 .0003 .0003 .0002 .0003 .003 .0002 .0002 .0003 .0002, .0003 .0001 .0001 .0001 .0003 .0001 

Ce ............... .01 0 .005 .01 .01 .05 .03 0 0 .02 .01 .01 .01 .01 .01 .01 .02 

Co ............... .0003 0 .00015 0 0 0 0 0 0 0 0 0 .003 .002 .003 Tr. ...... Cr ............... <.0003 0 0 0 0 0 0 0 0 .0003 .0001 0 .0015 .0015 .0015 Tr. ...... Cu ............... .001 .0002 .0006 .0007 .0003 .0002 .0003 .003 .001 .0001 .001 .0005 .02 .01 .015 .0008 . 0009 

Ga ............... .0015 .0015 .0015 .001 .001 .0015 .001 .001 .001 .0015 .001 .001 .002 .001 .0015 .001 .0003 

La ............... .007 0 .004 .007 .007 .02 .015 0 .007 .007 .005 .007 .005 .007 .006 .007 .006 

Mo ............... 0 0 0 0 0 0 0 0 0 0 0 0 .0003 0 .0002 0 ...... Nb ............... .0007 .001 .0009 .002 .001 .001 .001 .001 .001 .001 .001 .001 0 .0007 .0004 .001 . 0004 

Ni ............... 0 0 0 0 0 0 0 0 0 0 0 0 .005 .003 .004 0 ...... 

Pb ............... .0015 . 0007 .001 .0005 .001 .0007 .0009 .001 .001 .002 .001 .003 .0003 .001 .0007 0 ...... 

Sc ................ .0005 . 0003 .0004 0 0 .0003 .0002 .0003 .0003 .001 .0005 0 .002 .001 .0015 .0003 .0003 

Sr ................ .007 .05 .06 .03 .02 .05 .04 .015 .02 .03 .02 .03 .I .05 .08 .03 .01 

v ................ .0015 .0015 .0015 .0007 .001 .0015 .001 .0015 .002 .002 .002 .0007 .02 .01 .015 .001 .0005 

y ................ .0015 .002 .002 .003 .002 .002 .002 .003 .003 .003 .003 .003 .005 .003 .004 .003 .0008 

Yb ............... .00015 .0002 .0002 .0003 .0002 .0002 .0002 .0003 .0003 .0003 .0003 .0003 .0005 .0003 .0004 .0003 .00006 

Zr ··············· .01 .007 .009 .015 .01 .007 .009 .005 .01 .007 .007 .01 .007 .02 .01 .009 .003 

CIPWnorms 

Q ................ 26.0 30.6 2T.5 26.8 28.0 31.7 33.3 31.3 31.6 6.3 12.8 ................ c ················ .41 1.2 . 30 .16 1.8 .59 .81 1.3 1.2 0 0 ................ or ................ 23.9 23.8 21.9 24.3 20.1 23.6 18.9 23.8 21.8 13.1 16.5 ················ ab ··············· 38.8 34.9 36.4 36.4 38.9 "28.8 25.4 30.7 33.0 28.9 23.7 ················ an 

r······· 8.1 6.3 10.4 9.1 7.7 10.1 13.9 8.6 8.8 24.5 22.8 ················ 0 0 0 0 0 0 0 0 0 1.9 .06 ················ di en ............ 0 0 0 0 0 0 0 0 0 1.1 .04 ················ fs ............ 0 0 0 0 0 0 0 0 0 .70 .02 ................ 

hy ~~:::::::::::. 1.1 .83 . 87 .62 .90 1.4 2.5 1.2 .90 9.6 8.2 ··············· 0 0 .43 .27 .26 1.1 1.6 1.2 .68 5.9 3.9 ............... mt ....... 1.4 1.1; . 73 .99 1.1 .78 1.5 .77 .44 4.2 5.1 ··············· hm ..... 0 .20 0 0 0 0 0 0 0 0 0 ················ il ················ .46 .23 .38 .38 .27 .44 .67 .31 .32 2.1 2.1 ················ ru ................ 0 0 0 0 0 0 0 0 0 0 0 ················ ap ··············· 0 .14 .24 .19 .14 .26 .43 .19 .12 .55 .85 ················ cc . ............... 0 .II .II .II .11 .23 .II .II .II .11 2.1 ················ 

Total ...... 100.2 99.4 99.3 99.3 99.3 99.0 99.1 99.5 99.0 99.0 98.2 ················ Fernie .... 3.0 2.6 2.8 2.6 2.8 4.2 6.8 3.8 2.6 26.2 22.4 . ...... . ~ ............... 

metamorphosed rocks about 1 mile wide and 2 miles long. 

The shale and siltstone of the Cretaceous formations are 

hornfelsed, the intercalated calcareous beds are altered to 

calc-silicate rock, and the arkose and conglomerate beds 

are also altered. 

Other plugs and dikes of quartz latite porphyry intrude 

complexly faulted Paleozoic and Cretaceous rocks in the 

Helvetia mining district (Drewes, 1972b, pl. 5). The plugs 

of this group are fairly widely scattered and are not 

controlled by a single structural feature as they are in the 

Greaterville area, but some of the plugs intrude 

northwest-trending faults. In plan, the plugs have an 

irregular shape, and many of their apophyses intrude 

faults. The host rocks of the intrusives in the Helvetia area 
TERTIARY ROCKS 65 

are also metamorphosed, except for the rocks east of the 

plugs near the Johnson Ranch, near collection sites 183 

and 195. Metamorphosed Paleozoic rocks are typically 

altered to marble or tactite, and the Cretaceous rocks, 

mostly arkosic siltstone and sandstone of the Willow 

Canyon Formation, are locally hornfelsed and are widely 

and strongly argillitized and weakly mineralized. 

The larger of the two plugs in the Rosemont area (fig. 

40) underlies a basin in which the traces of many faults 

converge. The many apophyses of this plug and the 

surrounding dikes suggest that the magma was fairly fluid 

and that it readily spread along the available planes of 

weakness. It may also have spread laterally along the thrust 

fault beneath the Cretaceous rocks, as was suggested in the 

Greaterville district (Drewes, 1970, p. A10). Both the 

abundance of tactite and the intensity of mineralization 

and argillitization increase near the plug, and tactite and 

mineral deposits occur along the faults in the Paleozoic 

rocks near the plugs (Drewes, 1973a, figs. 3- 13). The 

rocks in the Rosemont area of the Helvetia mining district 

have over the years been extensively explored for economic 

deposits of copper, lead, zinc, and silver. 

Another plug in the Helvetia area, the Summit plug, 

underlies a knoll along the crest of the range near the 

intersection of many faults. Unmapped roads cross the 

crest of the range north and south of the plug. Although 

the Summit plug underlies steep slopes and cliffs, the 

terrain is less rugged than that underlain by the 

Precambrian and Cambrian rocks to the south. A breccia 

pipe lies along a fault on the south side of the plug and an 

apophysis of the plug extends a:long part of the fault. 

Tactite occurs in favorable rock around the plug, and some 

of the tactite and other rocks along faults near the plug are 

mineralized. Creasey and Quick (1955) described a small 

copper deposit in the breccia pipe. 

The Helvetia plug intrudes altered Paleozoic and 

Cretaceous rocks of a large klippe and also Precambrian 

rocks beneath the klippe near Helvetia townsite. The plug 

underlies moderately low areas containing small outcrops. 

The plug is inferred to have intruded a major 

northwest-trending fault overlain by the klippe, and it 

probably spread along the thrust fault beneath the klippe. 

The field relations, described in detail elsewhere (Drewes, 

1972b), show that the plug antedates the klippe, although 

Heyman (1958) and Michel (1959) each interpreted the plug 

to be part of the klippe and to be rooted 1 Y2 miles to the 

southeast at the Summit plug. Copper ore has been mined 

from tactite and from highly mineralized faults at several 

localities near the Helvetia plug. 

The Sycamore plug, not to be confused with the 

Sycamore stock (fig. 40), differs slightly from the other 

plugs, but it is categorized with them because the 

differences could be explained by a local variation in the 

environment of emplacement. The plug underlies 

moderately low hills, where it primarily intrudes a major 

northwest-trending fault (Drewes, 1972b, pl. 5). Some 

apophyses of the plug intrude this fault for several miles, 

and a small pipe of quartz latite porphyry lies along the 

northern extension of this fault. Some rocks of the dike 

northwest of the plug are brecciated, indicating minor fault 

movement after the emplacement of the dike. A few 

outcrops of tactite lie west of the plug and the rocks of this 

area contain few visible copper minerals, but analyses 

show that the content of gold and silver of these rocks is 

greater than it is in rocks near the other plugs (Drewes, 

1973, p. 5). 

PETROGRAPHY 

The quartz latite porphyry of the Greaterville plugs is a 

rather distinctive rock, and the local term "ore porphyry" 

is applied even where the rocks are unmineralized. 

Indicators of the ore porphyry include fairJy abundant, 

moderately large, doubly terminated or bipyramidal quartz 

phenocrysts and small biotite or chlorite crystals. The rock 

is typically pale yellowish brown to light gray, and is 

closely fractured, and IS considerably altered. Because of 

the rapid weathering favored by this fracture habit, the 

rock mostly underlies gentle hills or basins in which 

outcrops are small and the slopes are covered with small 

blocky detritus. Iron oxides stain many of the fracture 

surfaces, and scattered grains of pyrite, chalcopyrite(?), 

and some copper oxides are disseminated in the rock. 

Although most of the fractured and weakly mineralized 

rocks are deeply weathered, some are tresh and contain 

unaltered primary biotite and feldspar crystals with 

lustrous cleavage surfaces. 

The rocks of the Sycamore plug (fig. 40) differ slightly in 

appearance from the others in that some are pale pink or 

pale purple and in that they contain fewer phenocrysts and 

little or no biotite. Furthermore, rocks from the core of the 

plug are moderately coarse grained rather than aphanitic. 

The relations between the coarse core rock and the 

surrounding aphanitic rock are uncertain; as mapped and 

described herein, they are considered to be gradational, but 

it is also possible that the plug is a composite body having a 

core of quartz monzonite related to the Helvetia stocks and 

a rim of quartz latite porphyry. 

Under the microscope the quartz latite porphyry is seen 

to consist of about 30 percent (common range 20 to 40 

percent) phenocrysts 2 to 5 mm, rarely as much as 8 mm, 

long (fig. 44) and of about 70 percent groundmass, mostly 

of a 0.02-mm size. The groundmass has an idiomorphicgranular texture and is considerably altered to clay 

minerals. The texture of the core rocks of the Sycamore 

plug is hypidiomorphic granular, and its grain size is 2 to 9 

mm. The dikes near this plug have a cryptocrystalline 

texture, and some specimens have a cataclastic texture. 

The dominant minerals of the quartz latite porphyry are 
66 PLUTONIC ROCKS, SANTA RITA MOUNTAINS, SOUTHEAST OF TUCSON, ARIZONA 

FIGURE 44.-Specimen 185. Quartz latite porphyry of the Greaterville 

plugs showing porphyritic texture and fine-grained groundmass. Crystals: quartz ( Q), biotite (B), chloritized biotite (cb), plagioclase 

( P ), potassium feldspar ( p f), apatite tap), and magnetite (mt). Plain 

light; X 25 . 

quartz, plagioclase, potassium feldspar, and biotite. The 

quartz phenocrysts are mostly equant and euhedral, but 

some specimens also have a few partly resorbed, embayed, 

and rounded crystals; all are nearly without undulatory 

extinction. Groundmass quartz is anhedral and also free of 

undulatory extinction, except in the specimens having 

cataclastic texture. These specimens also have some quartz 

in pods along shear or flow bands. Plagioclase occurs as 

subhedral to euhedral phenocrysts and anhedral 

groundmass crystals that are much altered to sericite and 

clay minerals. Compositional zoning is emphasized by 

variations in the intensity of alteration. The composition 

of the plagioclase in the plugs in the Helvetia area is mostly 

andesine with rims of oligoclase. The composition of the 

plagioclase in the plugs in the Greaterville area is 

labradorite with rims of andesine; a few specimens are 

albitized. Plagioclase from the moderately coarse-grained 

rock of the core of the Sycamore plug is oligoclase; 

plagioclase from the surrounding rock cannot be 

determined petrographically, because of the fine grain size 

and the intensity of the alteration. Potassium feldspar is 

mostly in the groundmass as kaolinitized anhedral crystals, 

but in some specimens it occurs as larger subhedral grains 

with poikilitic rims. The potassium feldspar in specimens 

from the Greaterville area and the Rosemont plug is 

orthoclase, whereas that in specimens from the other plugs 

is, at least in part, sanidine. About half the specimens 

contain trace amounts of perthitic intergrowths that 

commonly form a fine lacy texture; in one specimen such 

intergrowths form a reticulate texture. Biotite is pleochroic 

in pale yellow brown to dark brown, and in most 

specimens it is largely chloritized. Oxybiotite, pleochroic in 

reddish brown, occurs in two specimens from widely 

separated plugs. 

The accessory minerals are magnetite, apatite, sphene, 

and zircon, and, in some specimens, pyrite, allanite, and 

rutile. The pyrite, like magnetite, occurs in scattered 

crystals, and may be primary, even though in the more 

mineralized rock it includes secondary grains and veinlets. 

Secondary minerals are mainly clay minerals, sericite, 

and chlorite, and, in lesser amounts, iron oxide, leucoxene, 

epidote, and, in one specimen possibly tremolite. The more 

intensely mineralized porphyry contains traces of copper 

oxides, chalcopyrite, pyrite, galena, cerussite, and possibly 

sphalerite. 

MODAL AND CHEMICAL SUMMARY 

Modes of 12 specimens of quartz latite porphyry are 

listed in table 21 and are summarized on the modified 

triangular diagram of figure 45. The figure drawn around 

the tightly clustered plots of the modes of the porphyry 

resembles an ellipsoid which is centered about a point in 

the right half of the quartz monzonite field and almost 5 

percent of the way from the leucocratic face of the 

composition tetrahedron toward the fernie apex. Specimen 

186 seems to be anomalous in plagioclase for this group of 

modes, but more analyses are needed to properly assess its 

position on the diagram. The modes of this formation 

about 5 percent higher in potassium feldspar than those of 

the Helvetia stocks. 

Chemical analyses of six specimens are listed in table 22 

and are summarized in the histogram of figure lOH. The 

slightly greater abundance of CaO and Na20 and lesser 

amounts of Si02 in specimen 184, from a plug in the 

Greaterville area, than in the specimens from the plugs in 

the Helvetia area is reflected in the slight difference in the 

modes of these rocks. The quartz latite porphyry of these 

plugs is chemically similar to the granitoid rocks of the 

Helvetia stocks, aside from the quartz diorite stock. The 

mean of the analysis of the ore porphyry resembles 

somewhat the biotite adamellite of Nockolds' (1954, p. 

1014) except that it contains more NazO and less K20, 

total Fe, and MgO. 
TERTIARY ROCKS 67 

The modal data, combined with some petrographic 

descriptions, suggest that the plugs were emplaced from a 

fairly hot, fluid magma. The abundant sanidine and rare 

oxybiotite in the ore porphyry and the concentration of 

tactite in chemically suitable rocks near some plugs are 

indicative of a high magma temperature. Magma fluidity is 

suggested by the ameboid shape of some plugs, by theabundance of dikes, and by the association with abundant 

hydrothermal mineralization. 

AGE AND CORRELATION 

The age of the quartz latite porphyry of the Greaterville 

plugs obtained through radiometric dating methods is 

more definitive than that obtained through the 

observations of geologic relations to dated rocks. The 

porphyry intrudes rocks as young as the Apache Canyon 

Formation of the Bisbee Group, and it is unconformably 

overlain by gravel no older than Pleistocene age. It does 

not come into contact with the granitoid rocks of the 

Helvetia stocks, although there are some similarities 

between the rock in the core of the Sycamore plug and the 

rocks of the Helvetia stocks. 

The porphyry does, however, intrude faults, some of 

which truncate the Helvetia stocks. For example, the 

Sycamore plug and nearby dikes and pipes are intruded 

along faults that cut the Johnson Ranch and Sycamore 

stocks a half a mile northeast of Johnson Ranch (Drewes, 

1972b, pl. 5). Similarly, the Helvetia plug is seen to 

truncate the east edge of the klippe at Helvetia, which is 

faulted across the Shamrod and Helvetia stocks. The 

postulated age relation between the coarse-grained (older) 

stocks and the fine-grained (younger) plugs L8 compatible 

with an environment of emplacement that changed during 

the brief interval between two times of intrusive activity. 

The earlier intrusives may have been relatively deep-seated 

and the later ones relatively shallow, as a result of local 

tectonic action, uplift, and consequent erosion. 

Three potassium-argon ages were obtained from biotite 

concentrates derived from separate plugs; they are 

specimens 189, 192, and the unnumbered specimen 

following 192 in table 4 (field number 68D1472, fig. 40), 

which has not been modally or chemically analyzed. The 

ages range from 55.7 to 56.3 m.y., a range sufficiently 

small to provide considerable confidence in their accuracy. 

The confidence is only justified, however, if the plugs are 

known to be emplaced simultaneously. This evaluation of 

three nearly identical ages is similar to that of the 

radiometric ages of the Helvetia stocks; the ages support 

each other only if independent evidence shows that the 

intrusive events were coeval. There is, indeed~ some cause 

to doubt that either the faulting or the intrusive activity of 

the Helvetian phase of the Laramide orogeny, or both 

events, were geologically instantaneous events (Drewes, 

1972b, p. 32-33). 

One dating problem is obvious: the radiometrically 

determined ages indicate that the Greaterville plugs are 

about 2 m.y. older than the Helvetia stocks, whereas their 

geologic relations suggest that the stocks are older than the 

plugs. The resolution of this problem may require 

additional dating of minerals other than biotite and 

perhaps the dating of more of the stocks and plugs. 

Additional fieldwork may yet lead to direct evidence of the 

relationship between these intrusive bodies. Furthermore, 

controls are needed to measure the range of time that may 

elapse between the emplacement of an intrusive body and 

its cooling to a temperature at which the radiometric 

"clock" is set. 

Intrusive rocks resembling the quartz latite porphyry, or 

ore porphyry, of the Greaterville plugs occur in at least two 

nearby ranges. The ore porphyry of the Sierrita Mountains 

(fig. 1) is described by Cooper (1974) as a quartz 

monzonite porphyry, but its groundmass is clearly 

aphanitic and of the same size as that of the Greaterville 

plugs. His quartz monzonite porphyry has the same 

distinctive bipyramidal quartz phenocrysts and small 

biotite crystals, and it is spatially and probably also 

genetically related to the ore deposits at the Sierrita, 

Esperanza, Twin Buttes, and Pima mines. It is dated as 

53.5 m.y. by Damon and Mauger (1966) and as 56.9 m.y. 

by S.C. Creasey (1964, written commun.), ages suggestive 

of those of the Helvetia stocks and Greaterville plugs. 

Other intrusive rocks resembling the ore porphyry are 

found in the Empire Mountains and in the hills between 

them and the Santa Rita Mountains (Finnell, 1971). Some 

of these intrusive rocks are also associated with copper 

mineralization, but they are not radiometrically dated and 

cannot be closely dated by geologic means. 

GRANODIORITE OF THE SAN CAYETANO 

STOCK 

A small stock of granodiorite, of late(?) Oligocene age, 

is the youngest plutonic rock of the Santa Rita area. The 

stock crops out over an area of about a half a· square mile, 

and it probably extends beneath the piedmont gravel for 

another half a square mile or more. It appears to have 

steep contacts and no apophyses or chilled-contact zone. 

The host rocks are mainly Josephine Canyon Diorite but 

also include some rhyodacite porphyry dikes; none of the 

host rocks are contact metamorphosed near the stock. 

Other rhyodacite porphyry dikes of the same swarm 

intrude the stock, so dikes and stock may be 

penecontemporaneous. 

The granodiorite is a massive, moderately coarsegrained light-gray rock that weathers to form low knolls, 

boulderlike residual blocks, and extensive deposits of g~s. 

The rock has a hypidiomorphic-granular texture and a 

small amount of myrmekitic and lacy perthitic texture and 

a maximum grain size of 4 mm. As listed in the modal 
68 PLUTONIC ROCKS, SANTA RITA MOUNTAINS, SOUTHEAST OF TUCSON, ARIZONA 

TABLE 21.-Modes of quartz latite porphyry of the Greaterville plugs 

[Field numbers are abbreviated; year of collection and collector's initial omitted. Full field number of specimen 184 thus is 650894. Symbols: s, standard deviation; Tr., trace; ... , not determined; 

a{?) following number indicates uncertainty in the reported value; a{?) preceding number indicates uncertainty in identification of core or rim position within crystal) 

Intrusive mass ............... Plugs at Greaterville Rosemont plug Summit plug Helvetia plug Sycamore 

plug 

Specimen No ................. 184 185 186 184-186 1187 It88 187,188 189 190 191 189-191 192 193 194 192-194 195 184- 195 

Field No. 894 893 Mean Mean Mean Mean Mean s ··················· 921 1098 1129 118S 1183 1209 124S 1244 1236 1224 

Quartz ...................... 20.9 22.9 24.4 22.7 22.8 29.6 26.2 27.9 26.1 21.0 2S.O 24.1 30.6 21.8 25.S 2S.2 24.8 3.2 Plagioclase, total .... . . . . . . . . . 47.1 4S.2 S6.1 49.S 4l.S 43.S 42.5 41.9 37.0 47.0 42.0 44.9 43.4 42.0 43.4 4S.3 44.{i 4.6 (plagioclase in perthite) .... (0.3) {Tr.) (Tr.) (0.1) 0 0 0 (Tr.) (Tr.) 0 (Tr.) (Tr.) 0 (1.6) (O.S) (3.1) (0.4) (1.0) 

K-feldspar, total .. ··········· 26.6 26.3 13.6 22.2 33.0 23.2 28.1 26.3 31.8 27.6 28.6 27.4 22.4 33.0 27.6 26.2 26.5 S.3 (sanidine) .. ············· 0 0 0 0 0 0 0 (26.3)? (31.8) (27.0) (28.6) (27.4)? (22.4)? (33.0) (27.6) (26.2) 16.2) (4.5) 

(orthoclase) ... . . . . . . . . . . (26.6) (26.3) (13.6) (22.2) (33.0) (23.2) (28.1) 0 0 0 0 0? 0? 0? 0 0 11.6) (13.7) 

(microcline) ..... .. ...... 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 (Tr.) (Tr.) . ..... Biotite ........ ..... .... ..... 4.2 3.9 4.2 4.1 2.1 2.7 2.4 3.0 3.3 3.S 3.3 2.7 2.2 1.8 1.9 2.9 3.0 .8 Magnetite ... ........ .... . ... .3 1.1 .2 .5 .6 .8 .7 .7 1.3 .8 .9 .3 1.0 1.1 .8 .I .7 .4 Pyrite ......... ... ....... . .. 0 0 1.2 .4 0 Tr. Tr. 0 0 0 0 Tr. 0 Tr. Tr. Tr. .I .I Apatite .. . . . . . . . . . . ...... ... Tr. .3 .2 .2 Tr. .I .05 .2 .2 .I .2 .4 .I .05 .2 .2 .2 .1 Sphene ......... ... ... .... . . .8 .2 .I .4 Tr. .05 Tr. Tr . .2 Tr. .07 .I .3 .3 .2 .I .2 .2 Zircon ..... ..... ....... . .... .I .05 Tr. .OS Tr. Tr. Tr. Tr. .I Tr. Tr. .05 Tr. Tr. Tr. 0 Tr . . ..... Allanite ..... ..... ... .... .... 0 .05 0 Tr. 0 0 0 0 0 0 0 .OS 0 Tr. Tr. 0 Tr . . ..... Rutile ... ... ............ .... 0 0 0 0 Tr. .1 .OS 0 0 0 0 0 0 Tr. Tr. 0 Tr. . ..... 

Total .... ········ ..... 100.0 100.0 100.0 100.05 100.0 100.05 100.0 100.0 100.0 100.0 100.07 100.0 100.0 IOO.OS 99.6 100.0 00.1 . ..... Fernie .... ········ .... 5.4 5.6 5.9 5.7 2.7 3.7 3.2 3.9 5.1 4.4 4.5 3.6 3.6 3.2 3.1 3.3 4.3 1.1 

Percent anorthite 

in plagioclase .... ... ....... ?0-10 29-37 32-34 29-37 27 . . .. ... 27 20-28 23 ?12 20-28 25? 12 23-24 23-25 ?10 20-37 ...... (plagioclase rims) ..... .... ...... (23) (24) (?5 -24) ....... .. ..... . ...... ····················· (?12) ··············· (10) (?10) ········ (5-24) . ..... Quartz mixing 

index (see text) . ......... .75 .84 .87 .82 . ...... ....... ....... ..... 86 . ..... .81 .84 .94 .98 .92 .95 .77 .86 .08 

I Modes of specimens 187 and 188 are less reliable than the other modes because these specimens are finer gramed and more strongly altered. Quartz: K-feldspar ratio of spectmen 183 adJusted 

15 percent as based on ratios typical of this group of rocks. 

POTASSIUM 

FELDSPAR 

QUARTZ QUARTZ 

50 EXPLANATION 

Plugs at Greaterville 

[!] 

Rosemont plug 

.&.. 

Summit plug 

0 

Helvetia plug 

0 Sycamore plug 

Total Greaterville plugs 

PLAGIOCLASE 

FIGURE 45.-Modified triangular diagram showing modal quartz, potassium feldspar, plagioclase, and fernie menerals of quartz latite porphyry of the 

Greaterville plugs. 
TERTIARY ROCKS 69 

TABLE 22.-Chemica/ and spectrographic analyses and CIPW norms of quartz latite porphyry of the Greaterville plugs 

[Chemical analysis of specimen 195 by single solution method (Shapiro and Massoni, 1968); other specimens analyzed by rapid rock method (Shapiro and Brannock, 1962), supplemented by atomic 

absorption method. Chemical analysts: Lowell Artis, S. D. Botts, G. W. Chloe, P. L. D. Elmore, John Glenn, J. Kelsey, and H. Smith. Spectrographic analyses by semiquantitative method. Spectrographic analyst: J. l. Harris. Elements looked for but not found: As, Au, B, Bi, Cd, Co, Eu, Ge, Hf, Hg, In, Li, Nd, Ni, Pd, Pr, Pt, Re, Sb, 

Sm, Sn, Ta, Te, Th, Tl, U, W, and Zn. Symbol: s standard deviation;<, less than; ... , not determined] 

Intrusive mass .. .... . .............. Plug at Summit plug Helvetia plug Sycamore Greaterville plug 

Specimen No .. 185 189 190 ~ 192 194 192,194 195 185-195 

Mean Mean Mean 

Field No. 893 1185 1183 1245 1236 1224 

Chemical analyses (weight percent) 

Si02 •••••• 0 0 •••••••• 0 •••••••••••••• 0 •• 69.4 72.5 72.2 72.4 272.9 72.6 72.8 70.9 71.8 1.3 

Ab03 ••• 0 •••••••••••••••••••••••••••• 16.0 14.4 14.7 14.6 14.2 14.4 14.3 15.0 14.8 .7 

Fe203 • 0 •••••••••• 0 •••••••••••••••••••• 1.8 1.2 1.2 1.2 .86 .94 .90 .78 1.1 .4 

FeO ................................... .82 .36 .52 .44 .76 .60 .68 .84 .65 .2 

MgO 0 •••••••••••• 0 •••••••••••••••••••• .51 .46 .46 .46 .49 .47 .48 .58 .50 .05 

CaO ................................... 2.3 1.7 1.2 1.5 1.4 1.6 1.5 2.3 1.8 .5 

Na 20 ••• 0 •••••••••••••••••••••••••• 0 •• 4.2 3.8 3.5 3.7 4.2 4.2 4.2 3.7 3.9 .3 

K20 ................................... 3.5 4.4 4.6 4.5 4.0 3.9 4.0 3.8 4.0 .4 

H20- ................................. .21 .17 .08 .13 .04 .05 .05 .22 .13 .1 

H20+ 0 ••••••• 0 ••••••••••••••••••••••• .89 .67 .74 .71 .51 .51 .51 .98 .72 .2 

Ti02 .................................. .39 .14 .17 .16 .15 .15 .15 .16 .19 .1 

P203 .................................. .14 .07 .08 .08 .08 .06 .07 .11 .09 .03 

MnO •••••••••••••••• 0 •••• 0 •••••••••••• .06 .02 .07 .05 .03 .04 .04 .16 .06 .05 

C02 ................................... .05 <.05 <.05 <.05 <.05 <.05 <.05 .28 .05 .01 

Total .......................... 100 100 100 100 100 100 100 100 100 ......... 

Spectrographic analyses (weight percent) 

Ag • • • ••• • • • • • •• • •••••••••••• 0 0 ......... 0 0 <0.0001 <o.ooo1 40 <0.0001 <0.0001 <0.0001 <0.0001 ......... Ba • 0 •••••••••••••••••••••••••••••••••• .1 .07 .1 .09 .07 .07 .07 .07 .08 0.02 

Be .................................... .0001 .003 .0003 .0003 .0003 .0002 .0003 .0002 .0002 .00008 

Ce .................................... .01 .03 0 .015 .02 .03 .03 .01 .02 .01 

Cr .................................... 0 .0003 0 .00015 .002 0 .001 0 .0004 .0008 

Cu .................................... .0003 .05 .15 .1 .015 .07 .04 .0003 .05 .06 

Ga .................................... .0015 .0015 .0015 .0015 .0015 .0015 .0015 .001 .0015 .0002 

La .................................... .005 .01 0 .005 .007 .01 .009 .007 .007 .004 

Mo .................................... .0003 .0003 0 .00015 0 0 0 .0003 .00015 .00015 

Nb .................................... .001 .001 .001 .001 .001 .001 .001 0 .0008 .0004 

Pb .................................... .0003 .0007 .0007 .0007 .0005 .0003 .0004 .001 .0006 .0003 

Sc ..................................... .0005 .001 .0003 .0007 .0007 .0003 .0005 .0003 .0005 .0003 

Sr ..................................... .05 .03 .03 .03 .03 .03 .03 .015 .03 .01 

v ..................................... .003 .0015 .0015 .0015 .0015 .0015 .0015 .0015 .002 .0006 

y 0000000 0 0 0000000 0 0 0 0 00 0 000 0 0 0 I 000 0000 .002 .002 .0015 .0002 .0015 .002 .0002 .002 .002 .0003 

Yb .................................... .0002 .0002 .00015 .0002 .00015 .0002 .0002 .0002 .0002 .00003 

Zr .................................... .015 .007 .01 .009 .01 .007 .009 .01 .01 .003 

CIPWnonns 

Q . . . . ........ .. . .......... ......... ... 26.3 29.6 31.5 . ........ 29.7 29.5 ......... 29.8 .................. c .. .. ....... ... . .......... ..... .... ... 1.6 .58 2.1 ..... .... .73 .62 ....... .. 1.5 .................. or ..................................... 20.6 26.0 27.3 ... ... ... 23.7 23.1 . ........ 22.5 . ................. ab . . ........ ... . .......... ........ .... 35.4 32.2 29.7 . ........ 35.7 35.7 ......... 31.4 .................. an . .......... .. . ......... ........ .. ... 10.2 7.7 5.1 . ........ 6.1 7.3 ......... 8.9 .................. {WO ................................ 0 0 0 ......... 0 0 . ........ 0 . ................. di 

;sn ... ·.:::::::::::::::::::::::::::::: 

0 0 0 ... ... ... 0 0 ......... 0 .................. 0 0 0 .... ..... 0 0 ......... 0 .................. 

hy {;;_. ........ :::::::::::::::::::::::::::: 1.3 1.1 1.2 .... ..... 1.2 1.2 . ........ 1.4 .................... 0 0 0 ... ...... . 50 .15 .. ....... .93 ................... mt . . ......... .. . ........ ......... .. ... 1.7 .82 1.4 .. .. ....... 1.3 1.4 . ........ 1.1 .................. hm .................................... .62 .64 .23 ......... 0 0 .. ....... 0 .................. i1 . . . ......... .. . ..... .. .. ........ .. ... .74 .27 .32 .. .. ...... .29 .29 . ........ .30 .................. ap . .. ..... .. . . . . ......... ....... ... ... .33 .17 .19 . ........ .19 .14 ......... .26 . ................. cc ..................................... .II .11 .11 .. .. ····· .11 .11 . ........ .64 . ................. 

Total ............................ 98.9 99.2 99.2 .. ....... 99.5 99.5 ......... 98.7 ................... Fernie . ... .. ...... .......... .. ... 4.8 3.1 3.5 ......... 3.6 3.3 . ........ 4.6 .................. 

I Average of two replicate analyses. 3 A replicate analysis shows Cu, 0.03; Ni, 0.0005; Pb, 0.002; Sc, 0.003; Mo and Be, not 

2A replicate analysis shows Fe203, 0.28; FeO, 1.2; MgO, 0.34; CaO, 2.1; P205, 0.15; detected; and other minor differences. 

and other rninor differences. 4 A replicate analysis shows As< 0.0001; La, 0.003; Pb, 0.005; Sc,O; and other minor 

differences. 
70 PLUTONIC ROCKS, SANTA RITA MOUNTAINS, SOUTHEAST OF TUCSON, ARIZONA 

analyses of table 23, the dominant minerals are quartz, 

plagioclase, orthoclase, biotite, and amphibole. The modes 

are plotted on the modified triangular diagram of figure 

39. The quartz is anhedral and has a slight undulatory 

extinction, and the orthoclase is subhedral to anhedral. 

The plagioclase, also subhedral, has a composition of sodic 

andesine. Biotite is pleochroic in pale yellowish brown to 

dark brown and is only slightly chloritized. Amphibole, 

probably a hornblende, is pleochroic in pale yellowish 

green to pale olive green. Accessory minerals are ilmenitic 

magnetite, apatite, sphene, and zircon. Secondary minerals 

are sericite, epidote, kaolinite, iron oxides, and leucoxene, 

all in small amounts. 

Chemical and spectrographic analyses and a CIPW 

norm are listed in table 24, and the chemical analysis is 

summarized on the histogram of figure lOP. 

The granodiorite of the San Cayetano stock is dated as 

27.6 m.y., or late(?) Oligocene, by the potassium-argon 

radiometric method using a biotite concentrate. The 

radiometric age is compatible with the age range available 

through the geologic relations to other rocks. 

Granitoid rocks of Oligocene age are not known in 

nearby ranges, but granodiorite stocks of Oligocene age 

were found in the Rincon Mountains (Drewes, 1974), 

which is the next range northeast of the Santa Rita 

Mountains (fig. 1) and more than 50 miles from the San 

Cayetano stock. 

The granodiorite of the San Cayetano stock is, however, 

genetically related to a pile of rhyodacite vitrophyre 

volcanics in the Grosvenor Hills, immediately east of the 

TABLE 23.-Modes of granodiorite of the San Cayetano stock 

[Field numbers are abbreviated; year of collection and collector's initial omitted. Full field number 

of specimen 196 thus is 640570. Tr ., trace] 

Specimen No ................... 196 197 1%,197 

Field No. Mean 

····················· 570 687 

Quartz .................. 23.2 22.4 22.8 

Plagioclase, total ......... 50.6 47.7 49.2 

(in perthite) .......... (Tr.) 0 (Tr.) 

Orthoclase ............... 15.4 20.7 18.1 

Hornblende .............. 4.5 3.2 3.9 

Biotite .................. 5.2 5.3 5.3 

Magnetite ............... .8 .4 .6 

Apatite .................. .2 .2 .2 

Sphene .................. .1 .1 .1 

Zircon .................. .05 Tr. Tr. 

Total ............ 100.05 100.0 100.2 

Fernie ............ 10.8 9.2 10.1 

Percent anorthite 

in plagioclase .......... 32-35 29-32 29-35 

Quartz mixing 

index (see text) ........ 0.99 0.94 0.97 

San Cayetano Mountains. The volcanic rocks were 

intruded at shallow depths by several rhyodacite vitrophyre 

laccoliths, whose feeder dikes extend westward toward a 

major normal fault at the eastern foot of the San Cayetano 

Mountains, along which the San Cayetano block was 

raised a few thousand feet (Drewes, 1971c). The swarm of 

rhyodacite porphyry dikes of the San Cayetano Mountains 

which are penecontemporaneous with the stock occupy the 

same fracture system intruded by the rhyodacite vitrophyre 

feeder dikes of the laccoliths. The dikes, laccoliths, and 

volcanic rocks are petrographically and chemically very 

similar, and these rocks also are chemically somewhat like 

the granodiorite. Furthermore, the radiometric ages of the 

stock, the laccoliths, and the lava flows are almost 

identical. Because of these similarities, the stock is believed 

to be the remains of a magma chamber, which was the 

source of a western extension of the volcanic pile, now 

eroded away. If this interpretation is correct, a similar 

stock may underlie the volcanic pile at a depth of several 

thousand feet. Details of this complex magma system are 

described by Drewes (1972a). 

TABLE 24.-Chemical and spectrographic analyses and CIPW norms of 

granodiorite of the San Cayetano stock, specimen number 196 1 

[Chemical analysis by rapid rock method (Shapiro and Brannock, 1962) supplemented by X-ray 

fluorescence method. Chemical analysts: Lowell Artis, S.D. Botts, and P. L. D. Elmore. Spectrographic analysis by A. L. Sutton, Jr. Elements looked for but not found: Ag, As, Au, B, Bi, 

Cd, Ce, Eu, Ge, Hf, Hg, In, Li, Mo, Nb, Nd, Pd, Pr, Pt, Re, Sb, Sm, Sn, Ta, Te, Th, Tl, U, 

W, and Zn. Symbol:<· less than] 

Chemical analysis (weight percent) 

SiOz ............. 69.5 

A1 2 0 3 ........... 15.2 

Fe 203 . . . . . . . . . . . 1.0 

FeO............. 1.1 

MgO . . . . . . . . . . . . 1.4 

CaO............. 3.2 

Naz 0 .. .. .. . .. . 4.4 

K20 . . . . . . . . . . . . 2.8 

H20- ............ 0.27 

HzO+ ............. 58 

Ti02 . . . . . . . . . . . . . .31 

P20s . . . . . . . . . . . . . .14 

MoO............. .04 

C02 .............. <.05 

Total ...... 100 

Spectrographic analysis (weight percent) 

Ba ............. . 

Be .............. . 

Co ............. . 

Cr .............. . 

Cu ............. . 

Ga ............. . 

La ............. . 

Ni .............. . 

Q .............. . 

or .............. . 

ab .............. . 

an .............. . 

{

wo ......... . 

di en .......... . 

fs .......... . 

I Field number 570. 

0.1 

.0002 

.001 

.007 

.0005 

.002 

.003 

.005 

Pb ............... 0.0015 

Sc................ .001 

Sr................ .07 

v................ .007 

y ................. 002 

Yb............... .00015 

Zr................ .01 

CIPWnorms 

24.6 

16.5 

37.2 

13.5 

.62 

.46 

.10 

hy j en ........... 3.0 

l fs............ .66 

mt ............... 1.5 

il................. .59 

ap................ .33 

Total ...... 99.1 

Fernie...... 7.3 
PLUTONIC ROCKS, SANTA RITA MOUNTAINS, SOUT}JEAST OF TUCSON, ARIZONA 71 

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Geologic Map. 

A 

Abstract ............................. . 

Age. See Radiometric dates. 

Page 

1 

Agua Caliente Canyon. . . . . . . . . . . . . . . . . . . 47 

Alaskite, Continental Granodiorite . . . . . . . . U 

Amole Granite . . . . . . . . . . . . . . . . . . . . . . . . . 82 

Amole Quartz Monzonite . . . . . . . . . . . . . . . . 82 

Apache Canyon Formation. . . . . . . . . . . . . . . 29, 63 

Apache Group. . . . . . . . . . . . . . . . . . . . . . . . . . 5 

Aplitie rocks, Continental Granodiorite . . . . 9, 10, 11 

Corona stock . . . . . . . . . . . . . . . . . . . . . . . 29 

Elephant Head Quartz Monzonite . . . . . 48 

Helvetia stocks . . . . . . . . . . . . . . . . . . . . . 58 

Huerfano stock . . . . . . . . . . . . . . . . . . . . . 58 

Pinal Schist . . . . . . . . . . . . . . . . . . . . . . . . 7 

Squaw Gulch Granite. . . . . . . . . . . . . . . . 25, 27 

Y oas stock . . . . . . . . . . . . . . . . . . . . . . . . . 51 

Artis, Lowell, analyst ... 16, 23, 31, 33, 40, 46, 54, 59, 

64, 69, 70 

B 

Batholith, Squaw Gulch Granite . . . . . . . . . . 24 

Bathtub Formation . . . . . . . . . . . . . . . . . . . . . 6 

BisbeeGroup ......................... 6, 29,61,63 

Bolsa Quartzite. . . . . . . . . . . . . . . . . . . . . . . . . 5, 9, 15 

engulfed block. . . . . . . . . . . . . . . . . . . . . . 58 

Boston syncline. . . . . . . . . . . . . . . . . . . . . . . . . 63 

Botts, S.D., analyst ... 16, 23, 31, 33, 40, 46, 54, 59, 64, 

Box Canyon ........................... . 

xenoliths ......................... . 

Breeeia pipe, Mansfield Canyon .......... . 

Summit plug ...................... . 

c 

69,70 

7,9 

10 

55 

65 

Cambrian rocks, Bolsa Quartzite .......... 5, 9, 15, 58 

Canelo Hills Volcanics . . . . . . . . . . . . . . . . . . . 17 

Cave Creek, quartz diorite . . . . . . . . . . . . . . . 23 

Chloe, G. W ., analyst ..... 16, 23, 31, 33, 40, 46, 54, 59, 

64,69 

Continental Granite..................... 5, 7, 9 

aplitie rocks . . . . . . . . . . . . . . . . . . . . . . . . 11 

correlation . . . . . . . . . . . . . . . . . . . . . . . . . 15 

granodiorite . . . . . . . . . . . . . . . . . . . . . . . 9 

modal analysis . . . . . . . . . . . . . . . . . . . . . 11, 13 

recrystallized . . . . . . . . . . . . . . . . . . . . . . 24 

Copper Belle Monzonite Porphyry . . . . . . . . 23 

Copper deposit, Summit plug. . . . . . . . . . . . . 65 

Corona de Tucson. . . . . . . . . . . . . . . . . . . . . . . 29 

Corona stock................. . . . . . . . . . . 6, 29,31 

Correlations, Continental Granodiorite . . . . 15 

Copper Belle Monzonite Porphyry . . . . 23 

Corona stock . . . . . . . . . . . . . . . . . . . . . . . 31 

Courtland area . . . . . . . . . . . . . . . . . . . . . 23,82 

Elephant Head Quartz Monzonite . . . . . 51, 53 

Empire Mountains . . . .. . . . . . . . . . . . . . . 16, 82, 67 

Greaterville plugs . . . . . . . . . . . . . . . . . . 67 

Harris Ranch Monzonite . . . . . . . . . . . . . 23 

Helvetia stocks . . . . . . . . . . . . . . . . . . . . . 15 

Josephine Canyon Diorite. . . . . . . . . . . . 39 

Juniper Flat Granite . . . . . . . . . . . . . . . . 28 

Madera Canyon Granodiorite. . . . . . . . . 44 

Mule Mountains . . . . . . . . . . . . . . . . . . . . 28 

Nogales........................... 40 

Patagonia Mountains ............. 16, 24, 28, 47 

Piper Gulch Monzonite . . . . . . . . . . . . . . 23 

Rincon Mountains . . . . . . . . . . . . . . . . . . 15, 70 

Ruby area . . . . . . . . . . . . . . . . . . . . . . . . . 40 

INDEX 

Correlations-Continued Page 

Sierrita Granite . . . . . . . . . . . . . . . . . . . . 28 

Sierrita Mountains ......... 15, 23, 28, 47, 62, 67 

Squaw Gulch Granite. . . . . . . . . . . . . . . . 28 

Tucson Mountains . . . . . . . . . . . . . . . . . . 82 

Whetstone Mountains . . . . . . . . . . . . . . . 17, 82 

Cottonwood Canyon. . . . . . . . . . . . . . . . . . . . . 7 

Crandell, W.B., analyst ..... 16, 23, 31, 40, 46, 54, 64 

Cretaceous rocks . . . . . . . . . . . . . . . . . . . . . . . 29 

Bathtub Formation . . . . . . . . . . . . . . . . . 6 

Bisbee Group ..................... 6, 29, 61,63 

Corona stock....... . . . . . . . . . . . . . . . . 6, 29, 31 

Elephant Head Quartz Monzonite ... 6, 43, 47, 49 

Fort Crittenden Formation . . . . . . . . . . 6 

Josephine Canyon Diorite ....... 6, 33, 34, 39, 41 

Madera Canyon Granodiorite. . . . . . . . . 6, 40 

Salero Formation ........... 6, 24, 26, 32, 47, 55 

Temporal Formation . . . . . . . . . . . . . . . . 6, 24 

D 

Dikes, Greaterville area . . . . . . . . . . . . . . . . . 64 

Helvetia mining district . . . . . . . . . . . . . 64 

Helvetia stocks. .. . . . . .. .. .. . . .. .. .. 58 

lamprophyre, Continental 

Granodiorite .. . .. .. .. .. .. .. 13 

map error, Y oas Mountain . . . . . . . 48 

Mansfield Canyon. . . . . . . . . . . . . . . . . . . 55 

rhyodacite porphyry . . . . . . . . . . . . . . . . 67 

San Cayetano Mountains . . . . . . . . . . . . 70 

Squaw Gulch Granite, lamporphyre . . . 27 

Diorites, Josephine Canyon Diorite . . . . . . . 33,34 

San Cayetano Mountains . . . . . . . . . . . . 34 

See also Quartz diorites. 

See also Syenodiorites. 

E 

Elephant Head . . . . . . . .. .. .. .. .. .. .. .. .. 47, 48 

Elephant Head Quartz Monzonite . . . . . . . . . 6, 47 

age............................... 51 

correlation......................... 51, 53 

intrusion . . . . . . . . . . . . . . . . . . . . . . . . . . 43· 

modal analysis .. .. .. .. .. .. .. .. .. .. . 51 

Quantrell stock . . . . . . . . . . . . . . . . . . . . . 49 

Y oas stock . . . . . . . . . . . . . . . . . . . . . . . . . 50 

Elmore, P.L.D., analyst .. 16, 23, 31, 33, 40, 46, 54, 59, 

Empire Mountains, quartz monzonite stock 

Enzenberg Canyon, xenoliths ........... . 

Esperanza mine ....................... . 

F 

Faults, Continental Granodiorite ........ . 

fracture, Corona stock .............. . 

Greaterville area .................. . 

Greaterville plugs, quartz 

latite porphyry ............ . 

Helvetia stock ..................... . 

Johnson Ranch stock ............... . 

Laramide orogeny, Helvetian phase .. . 

northwest-trending, Helvetia 

mining district ............ . 

Pinal Schist ....................... . 

quartz diorite ..................... . 

Santa Rita fault sear ............... . 

Shamrod stock .................... . 

shear zone, Continental Granodiorite .. 

South Johnson Ranch stock ......... . 

64, 69,70 

82 

10 

67 

9,15 

82 

64 

57 

67 

67 

7, 57.61 

64 

7 

23 

6 

67 

10 

58 

Faults-Continued Page 

Sycamore plug . . . .. .. .. .. .. . . .. . . .. 65 

Sycamore stock .. .. .. .. .. .. .. .. .. .. 67 

thrust, Helvetia area . . . . . . . . . . . . . . . . 63 

Finley, J.L., analyst .................. 16, 23, 40, 46 

Florida Canyon, quartz diorite. . . . . . . . . . . . 23 

Fort Crittenden Formation . . . . . . . . . . . . . . 6 

G 

Garner Canyon Formation . . . . . . . . . . . . . . . 5 

Geologie history .. .. .. .. .. .. .. .. .. .. .. .. 3 

Glenn, John, analyst .. 16, 23, 31, 33, 40, 46, 54, 64, 69 

Glove mine . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24 

Gneisses, granite gneiss . . . . . . . . . . . . . . . . . 7 

Pinal Schist . . . . . . . . . . . . . . . . . . . . . . . . 6 

Granite gneiss . . . . . . . . . . . . . . . . . . . . . . . . . . 7 

Granites, Amole Granite. . . . . . . . . . . . . . . . . 82 

Juniper Flat Granite . . . . . . . . . . . . . . . . 28 

Sierrita Granite . . . . . . . . . . . . . . . . . . . . 28 

Squaw Gulch Granite. . . . . . . . . . . . . . . . 24, 26 

Granitiod rocks, Corona stock . . . . . . . . . . . . 29 

Granodiorites, Continental Granodiorite . . . 9 

Corona stock . . . . . . . . . . . . . . . . .. . . . . . . 29 

Gringo Gulch pluton. .. .. .. .. .. .. .. .. 55 

Helvetia stock.. . . . . . . . . . . . . . . . . .. .. 57 

Helvetia stocks . . . . . . . . . . . .. . . . . .. .. 57 

Huerfano stock . . . . . . . . . . . . . . . . . . . . . 57 

Johnson Ranch stock . . . . . . . . . . . . . . . . 57 

Josephine Canyon Diorite............ 33,34 

Madera Canyon Granodiorite. . . . . . . . . 40 

mierogranodiorite .. .. .. .. .. .. .. .. .. 55 

San Cayetano stock ...... , . . . . . . . . . . 67 

Shamrod stock .. .. .. .. .. .. .. .. .. .. . 57 

South Johnson Ranch stock . . . . . . . . . . 57 

Whetstone Mountains . . . . . . . . . . . . . . . 82 

Greaterville, Continental Granodiorite . . . . 15 

Greaterville mining district . . . . . . . . . . . . . . 62 

Greaterville plugs . . . . . . . . .. . . . . . . . . .. .. 62 

age .............................. . 

correlation ........................ . 

modal analysis .................... . 

petrography ...................... . 

Gringo Gulch .......................... . 

Gringo Gulch pluton ................... .. 

age .............................. . 

modal analysis .................... . 

Gringo Gulch Volcanics ................ .. 

Grosvenor Hills, rhyodacite 

vitrophyre volcanics ....... . 

Grosvenor Hills Volcanics ............... . 

H 

67 

67 

66 

65 

55 

6,55 

57 

57 

6,55 

70 

6 

Hamilton, J.C., analyst ............... 23, 31, 40,59 

Harris, J .L., analyst ........... 16, 40, 46, 54, 64, 69 

Harris Ranch Monzonite . . . . . . . . . . . . . . . . . 23 

Helvetia, Continental Granodiorite. . . . . . . . 15 

Helvetia mining district . . . . . . . . . . . . . . . . . 62 

Helvetia plug, copper ore . . . . . . . . . . . . . . . . 65 

Helvetia stock. . . . . . . . . . . . . . . . . . . . . . . . . . 58, 67 

Helvetia stocks . . . . . . . . . . . . . . . . . . . . . . . . . 6 

age............................... 61 

granitoid rocks . .. .. . . . . . . .. . . . . . . .. 57 

granodiorite .. .. .. .. .. .. .. .. .. .. .. . 57 

modal analysis .. .. .. .. .. .. .. .. .. .. . 60 

plugs of quartz latite porphyry . . . . . . . 62 

quartz monzonite . . . . . . . . . . . . . . . . . . . 57 

Helvetia townsite, klippe . . . . . . . . . . . . . . . . 65 

Hornblende dacite porphyry . . . . . . . . . . . . . 55 

Hosey mine . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34 

73 
74 

Page 

Huerfano Butte. . . . . . . . . . . . . . . . . . . . . . . . . 58 

Huerfano stock . . . . . . . . . . . . . . . . . . . . . . . . . 57 

aplitic masses . . . . . . . . . . . . . . . . . . . . . . 58 

Hydrothermal deposit, 

J osevhine Canyon Diorite. , . . 34 

J 

Johnson Ranch, plugs . . . . . . . . . . . . . . . . . . . 65 

Johnson Ranch stock . . . . . . . . . . . . . . . . . . . . 57, 67 

Josephine Canyon . . . . . . . . . . . . . . . . . . . . . . 55 

lamprophyre dikes . . . . . . . . . . . . . . . . . . 'l:1 

Squaw Gulch Granite. . . . . . . . . . . . . . . . 26 

Josephine Canyon Diorite. . . . . . . . . . . . . . . . 33 

age............................... 39 

correlation . . . . . . . . . . . . . . . . . . . . . . . . . 39 

dioritic rocks . . . . . . . . . . . . . . . . . . . . . . . 34 

intrusion .. .. .. .. .. .. .. .. .. .. .. .. .. 41 

map error . . . . . . . . . . . . . . . . . . . . . . . . . 48 

petrography . . . . . . . . . . . . . . . . . . . . . . . 34 

Juniper Flat Granite, correlation . . . . . . . . . 28 

Jurassic rocks . . .. .. . . . . .. .. .. .. .. . . . . .. 17 

Squaw Gulch Granite ............. 10, 17, 18,24 

K,L 

Kelsey, J., analyst ...................... 33, 64,69 

Klippe, Helvetia townsite. . . . . . . . . . . . . . . . 60 

Laccoliths, San Cayetano Mountains ..... . 

Lamporphyre dikes, Yoas Mountain, 

map error ................ . 

Lamprophyre rocks, Squaw Gulch Granite . 

Lamprophyres, Continental Granodiorite .. 

Corona stock ...................... . 

Elephant Head Quartz Monzonite .... . 

Helvetia stocks .................... . 

Pinal Schist ...................... .. 

Squaw Gulch Granite .............. .. 

Yoasstock ........................ . 

Laramide orogeny ..................... . 

Helvetian phase ................... . 

Piman phase ...................... . 

M 

70 

48 

'l:1 

9,13 

29 

48 

58 

7 

25,'l:T 

51 

5,17,57 

6, 61,67 

6,9,29 

Madera Canyon . . . . . . . . . . . . . . . . . . . . . . . . 50 

mouth............................. 47 

Piper Gulch Monzonite . . . . . . . . . . . . . . 18 

rock dump . . . . . . . . . . . . . . . . . . . . . . . . . 42 

quartz diorite .. .. .. .. .. .. .. .. .. .. .. 23 

Madera Canyon Granodiorite. . . . . . . . . . . . . 40 

age............................... 44 

correlation. . . . . . . . . . . . . . . . . . . . . . . . . 44 

granodiorite .. .. .. .. .. .. .. .. .. .. .. . 41 

inclusions . . . . . . . . . . . . . . . . . . . . . . . . . . 41 

melanocratic granodiorite. . . . . . . . . . . . 42 

modal analysis .. . .. .. .. .. .. .. .. .. .. 43 

petrography . . . . . . . . . . . . . . . . . . . . . . . 41 

porphyritic granodiorite . . . . . . . . . . . . . 42 

quartz diorite recrystallized . . . . . . . . . . 24 

Magma development, Elephant 

Head Quartz Monzonite . . . . . 51 

Gringo Gulch pluton. . . . . . . . . . . . . . . . . 57 

Josephine Canyon Diorite. . . . . . . . . . . . 37 

Mansfield Canyon. . . . . . . . . .. .. .. .. .. .. .. 34 

dikes.............................. 55 

Piper Gulch Monzonite . . . . . . . . . . . . . . 19 

Map errors discussed.. .. . . . . . . . . . . . . . . . . 48 

Mavis Wash, Continental Granodiorite . . . . 15 

Mazatzal Revolution . . . . . . .. . . . . . . . . . . . . 7 

Microgranodiorite .. .. .. .. .. .. .. .. .. .. .. 55 

Mineralization, Elephant Head 

Quartz Monzonite. . . . . . . . . . . 48 

Helvetia plug .. .. .. . . .. . . . . . . . . . . . . 65 

Josephine Canyon Diorite. . . . . . . . . . . . 34 

Piper Gulch Monzonite . . . . . . . . . . . . . . 19 

Rosemont area . . . . . . . . . . . . . . . . . . . . . 65 

Summit plug . . . . . . . .. .. .. .. .. .. .. .. 65 

Sycamore plug . . . .. .. .. .. .. .. . . .. .. 65 

INDEX 

Mines, Esperanza ...................... . 

Glove ............................ . 

Hosey ............................ . 

Pima ................ : ............ . 

Salero ............................ . 

Sierrita ......................... .. 

Twin Buttes ...................... . 

Modal analysis ....................... .. 

Modal tetrahedron ..................... . 

Modes, Continental Granodiorite ........ . 

Corona stock ...................... . 

Elephant Head Quartz Monzonite .... . 

Greaterville plugs ................. . 

Gringo Gulch pluton ............... .. 

Helvetia stocks .................... . 

Madera Canyon Granodiorite ........ . 

Piper Gulch Monzonite ............. . 

quartz diorite .................... .. 

Squaw Gulch Granite .............. .. 

Sycamore stock ................... . 

Montosa Canyon ....................... . 

map error, Josephine Canyon Diorite .. 

Piper Gulch Monzonite ............. . 

Monzonites, Piper Gulch Monzonite ...... . 

See also Quartz monzonites. 

Morris, J .L., analyst .................. .. 

Mount Hopkins, Piper Gulch Monzonite ... . 

Mount Wrightson Formation ............ . 

Continental Granodiorite cobbles .... . 

Madera Canyon Granodiorite intrusion 

Mansfield Canyon, intrusion ........ . 

Mount Wrightson pile .................. . 

Mount Wrightson quadrangle map error, 

Josephine Canyon Diorite ... . 

lamporphyre dikes ......... ; ....... . 

O,P 

Ore porphyry ......................... . 

defined ........................... . 

Patagonia Mountains, Squaw Gulch Granite 

Permian rocks, Rainvalley Formation .... . 

Petrography, Continental Granodiorite ... . 

Corona stock ...................... . 

Elephant Head Quartz Monzonite, 

Quantrell stock ............ . 

Yoasstock .................... . 

granite gneiss ..................... . 

Greaterville plugs ................. . 

Gringo Gulch pluton, hornblende 

dacite porphyry ........... . 

microgranodiorite ............ .. 

quartz latite porphyry .......... . 

Helvetia stock ..................... . 

Huerfano stock .................... . 

Josephine Canyon Diorite ........... . 

Madera Canyon Granodiorite ........ . 

Pinal Schist ...................... .. 

Piper Gulch Monzonite ............. . 

Shamrod stock ................... .. 

Southeast stock ................... . 

South Johnson Ranch stock ......... . 

Squaw Gulch Granite ............... . 

Sycamore plug .................... . 

Sycamore stock ................... . 

Pima mine ............................ . 

Pinal Schist ........................... . 

petrography ...................... . 

Pipe, Sycamore plug ................... . 

Piper Gulch Monzonite ................. . 

age ..................... ·········· 

intrusion ......................... . 

modal analysis .................... . 

petrography ...................... .. 

Plugs, Greaterville area ................ . 

Helvetia .......................... . 

Helvetia stocks .................... . 

Johnson Ranch .................... . 

Page 

67 

24 

34 

67 

55 

67 

67 

11 

13 

12,13 

29 

51 

66 

57 

60 

4& 

19,21 

24 

28 

61 

47 

48 

19 

17 

33 

19 

5,18 

15 

41 

55 

17 

48 

48 

6,62 

65 

24 

5 

9,10,12 

29 

49,50 

50 

9 

65 

56 

55 

57 

58 

58 

34 

41 

7 

19 

58 

58 

58 

25 

66 

58 

67 

3,6 

7 

65 

6,17 

23 

41 

19,21 

19 

64 

65 

62 

65 

Plugs-Continued 

Rosemont ........................ . 

Summit .......................... . 

Porphyries, Gringo Gulch pluton ......... . 

hornblende dacite porphvry ......... . 

ore porphyry, Greaterville plugs ..... . 

quartz latite porphyry .............. . 

rhyodacite porphyry dikes .......... . 

Precambrian rocks ..................... . 

Apache Group ..................... . 

Continental Granite ................ . 

granite gneiss ..................... . 

Pinal Schist ....................... . 

Q 

Quantrell mine ........................ . 

Quantrell stock ........................ . 

Quartz diorite ......................... . 

age .............................. . 

modal analysis .................... . 

Quartz diorites, Helvetia stocks ......... . 

Josephine Canyon Diorite ........... . 

Sycamore stock ................... . 

Triassic quartz diorite .............. . 

Quartz latite porphyry ................ .. 

Quartz latite porphyry of the 

Greaterville plugs ......... . 

Quartz monzonites, Amole 

Quartz Monzonite .......... . 

Continental Granodiorite ........... . 

Corona stock ...................... . 

Elephant Head Quartz Monzonite .... . 

Empire Mountains ................. . 

granite gneiss .................... .. 

Helvetia stock ..................... . 

Helvetia stocks .................... . 

Johnson Ranch stock ............... . 

Josephine Canyon Diorite ........... . 

Patagonia Mountains ............... . 

Quantrell stock .................... . 

Shamrod stock ................... .. 

South Johnson Ranch stock ......... . 

Squaw Gulch Granite .............. .. 

Yoasstock ........................ . 

R 

Radiometric dates, 

Continental Granodiorite ... . 

Elephant Head Quartz Monzonite .... . 

Greaterville plugs ................. . 

Gringo Gulch pluton ............... .. 

Helvetia stocks .................... . 

Josephine Canyon Diorite ........... . 

Madera Canyon Granodiorite ........ . 

Piper Gulch Monzonite ............. . 

quartz diorite .................... .. 

San Cayetano stock ................ . 

Shamrod stock ................... .. 

Squaw Gulch Granite ............... . 

Rain valley Formation .................. . 

References cited ....................... . 

Rhyodacite welded tuff, San Pedro River .. 

Rosemont plug ........................ . 

Ruby Star Granodiorite ............... .. 

s 

Salero Formation ...................... . 

argillitized ........................ . 

boulder ........................... . 

exotic block ....................... . 

intrusion ........................ .. 

Salero mine ........................... . 

San Cayetano Mountains, rhyodacite 

porphyry dikes ........... .. 

sill-like mass ...................... . 

San Pedro River, rhyodacite welded 

tuff, age .................. . 

Page 

66 

65 

55 

55,57 

62 

55,57 

67 

6 

5 

5,7,9,24 

7 

3,6 

48 

48 

23 

24 

24 

61 

33 

57 

23 

55 

62 

32 

9,11 

29 

47 

32 

7 

57 

57 

57 

33,36 

28 

49 

57 

57 

25,26 

50 

15 

51 

67 

57 

62 

39 

47 

23 

24 

70 

62 

28 

5 

71 

32 

65 

62 

6,24 

47 

26 

32 

26,55 

55 

70 

55 

32 
Page 

Santa Rita fault scar . . . . . . . . . . . . . . . . .. .. 6 

Santa Rita Lodge . .. .. .. .. .. .. .. .. . .. .. . 42 

San Cayetano stock . . . . . . . . . .. .. . . .. .. .. 67 

age............................... 70 

Sawmill Canyon . . . . . . . . . . . . . . . . . . . . . . . . 7 

Shamrod stock ......................... 57, 58,67 

age............................... 62 

engulfed Bolsa Quartzite. . . . . . . . . . . . . 58 

Shellenberger Canyon Formation . . . . . . . . . 29 

Sierrita Granite, correlation . . . . . . . . . . . . . 28 

Sierrita mine. . . .. . . . . . . . . . . . . . . . . . . .. .. 67 

Sierrita Mountains, ore porphyry . . . . . . . . . 67 

Sill-like mass, San Cayetano Mountains. . . . 55 

Smith, H., analyst .16, 23, 31, 33, 40, 46, 54, 59, 64, 69 

South Johnson Ranch stock . . .. .. .. . . .. . . 57, 58 

Southeast stock .. .. .. .. .. . . . . . . . . . . . . . . 57, 58 

Squaw Gulch . . . . . . . . . . . . . . . . . . . . . . . . . . . 26 

Squaw Gulch Granite ................. 10, 17, 18, 24 

age............................... 28 

aplite . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27 

Continental Granodiorite, 

metamorphosed . . . . . . . . . . . . 15 

correlation . . . . . . . . . . . . . . . . . . . . . . . . . 28 

granite............................ 26 

lamprophyre . . . . . . . . . . . . . . . . . . . . . . . 27 

INDEX 

Squaw Gulch Granite-Continued 

modal analyses .................... . 

petrography ...................... . 

quartz monzonite .................. . 

Summit plug .......................... . 

Sutton, A.L., analyst .................. . 

Page 

26,28 

25 

26 

65 

40,70 

Sycamore plug . .. .. . . . . . . .. .. . . . . . . . . . . 65, 67 

Sycamore stock ........................ 57, 58,67 

engulfed block. . .. . . . . .. .. . . . . . . . .... . 58 

modal analysis .. . .. .. .. .. .. .. .. .. .. 61 

Syenodiorites, Gringo Gulch pluton . . . . . . . 57 

Josephine Canyon Diorite. . . . . . . . . . . . 33 

Piper Gulch Monzonite . . . . . . . . . . . . . . 17 

quartz diorite .. . . .. .. .. .. .. .. . . . . . . 24 

T 

Taylor, Dwight, analyst .............. 16, 23, 46, 54 

Temporal Formation . . . . . . . . . . . . . . . . . . . . 6, 24 

Temporal Gulch . . . . . . . . . . . . . . . . . . . . . . . . 55 

Piper Gulch Monzonite . . . . . . . . . . . . . . 18 

Tertiary rocks . . . . . . . . . . . . . . . . . . . . . . . . . . 54 

Gringo Gulch pluton. .. .. .. .. .. .. . . . . 57 

Gringo Gulch Volcanics . . . . . . . . . . . . . . 6, 55 

Grosvenor Hills Volcanics . . . . . . . . . . . . 6, 70 

75 

Page 

Tobin, Barbara, analyst . .. .. .. .. .. . . . . . . 31, 40 

Triassic rocks . . . . . . . . . . . . . . . . . . . . . . . . . . 17 

Canelo Hills Volcanics . . . . . . . . . . . . . . . 17 

Gardner Canyon Formation . . . . . . . . . . 5 

Mount Wrightson Formation .... 5, 15, 18, 41, 55 

Mount Wrightson pile . . . . . . . . . . . . . . . 17 

Piper Gulch Monzonite . . . . . . . . . . . . . . 6, 17, 41 

quartz diorite .. . .. .. .. .. .. .. .. .. .. . 23 

Twin Buttes mine. .. .. . . . . .. .. . . . . .. .. .. 67 

V-Y 

Volcanics, Gringo Gulch Volcanics ....... . 

Grosvenor Hills Volcanics ........... . 

rhyodacite vitrophyre, Grosvenor Hills 

volcanics of Red Mountain .......... . 

Whetstone Mountains, granodiorite stock .. 

Whetstone stock ....................... . 

Willow Canyon Formation .............. . 

Xenoliths, Box Canyon ................. . 

Enzenberg Canyon ................ _ .. 

Y oas Mountain, map error .............. . 

Yoasstock ............................ . 

6 

6 

70 

6 

32 

32 

61,63 

10 

10 

48 

48,50 

tr U.S. GOVERNMENT PRINTING OFFICE, 1976--677-340/94