Hybrid Granitoid Rocks of the Southern Snake Range, Nevada GEOLOGICAL SURVEY PROFESSIONAL PAPER 668 Hybrid Granitoid Rocks of the Southern Snake Range, Nevada By DONALD E. LEE and RICHARD E, VAN LOENEN GEOLOGICAL SURVEY PROFESSIONAL PAPER 668 A study of assimilation and the resulting systematic and interrelated differences in chemistry and mineralogy within a well-exposed granitoid outcrop area of 2O square miles UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1971 UNITED STATES DEPARTMENT OF THE INTERIOR ROGERS C. B. MORTON, Secretary GEOLOGICAL SURVEY William T. Pecora, Director Library of Congress catalog-card No. 72-811324 For sale by the Superintendent of Documents, U.S. Government Printing Office Washington, D.C. 20402 CONTENTS Fage Chemistry and mineralogy of the granitoid rocks Con. Abstract.._-___--___--__-_-___-_-_-_._____--_______ 1 Mineralogy. _________________________________ 21 Location and geologic setting-___-__----_-_________-__ 1 Petrography and petrology of the granitoid rocks-___- 29 Previous work and purpose of this paper.______________ 2 Snake Creek-Williams Canyon area.____________ 29 Intrusive structures, form, and contact effects...------- 3 Petrography. ____________________________ 29 Snake Creek-Williams Canyon area_______________ 4 Petrology. _______________________________ 31 Pole Canyon-Can Young Canyon area__-------___- 5 Petrogenesis.. _ ___________________________ 33 Young Canyon-Kious Basin area.________________ 6 Pole Canyon-Can Young Canyon area_________ 38 Summary of intrusive rocks._____________________ 7 Young Canyon-Kious Basin area.______________ 40 Chemistry of the sedimentary rocks.___.____-_---_____ 7 Aplites______--__-__-_-__------____-_-_____-__ 40 Chemistry and mineralogy of the granitoid rocks- ______ 10 Age relations of the intrusive types________________ 43 Techniques of this study__-_--_________-_-_____ 10 Chemistry-____________________________________ 20 Source of beryllium mineralization__________________ 43 Major elements..,__________________________ 20 Summary and conclusions_______________________ 44 Minor elements.____________________________ 20 References cited._________________________________ 45 Conclusions on chemistry of granitoid rocks___- 21 Index_________________________________________ 47 ILLUSTRATIONS PLATE 1. Generalized geologic map and sections of the area north and northeast of the Mount Wheeler mine, White Pine County, Nevada-_-___--____________________________________-_----__-_-___----____ In pocket FIGUKE 1. Index map showing location of report area._________________________________-__________---------_-- 2 2. Columnar section showing stratigraphic position of analyzed sedimentary rock samples._________________ 10 3. Diagrams showing relation between CaO content and contents of eight major-element oxides in granitoid rocks-________________________________...________________-_-.________---___- 22 4. Variation diagram comparing Daly's average andesite-dacite-rhyolite with granitoid rocks of the Snake Creek-Williams Canyon area.______________________________----__-_-____-_-_____-_--____-_--- 24 5. Diagram showing relation between CaO content and powder density in granitoid rocks of the Snake Creek- Williams Canyon area__---__-___--______________-__-_-_____-_--_------_----___----_----_--_- 24 6. Diagrams showing relation between CaO content and La, Y, Zr, Ba, and Sr contents in granitoid rocks of the Snake Creek-Williams Canyon area______________________________________________________ 25 7. Diagram showing relation between contents of CaO and F for selected granitoid rocks___________________ 27 8. Diagrams showing relation between CaO content and contents of modal quartz, microcline, biotite, and plagioclase in granitoid rocks of the Snake Creek-Williams Canyon area.__________________________ 27 9. Diagram showing relation between CaO content of rock and angular difference between 20(iiii) and 20asi) X-ray reflections of constituent plagioclase, Snake Creek-Williams Canyon area.____________--_-__- 27 10. Diagram showing general relations between CaO content and accessory mineral contents for granitoid rocks of the Snake Creek-Williams Canyon area._____________-____________-_-_---_-___--______------ 28 11. Diagram showing general relations between CaO content and mineralogy for granitoid rocks of the Snake Creek-Williams Canyon area.________________________________________________________________ 28 12. Graph showing distribution of CaO in granitoid rocks of the Snake Creek-Williams Canyon area._________ 28 13. Silica variation diagram for CaO and Na_O+K2O in granitoid rocks of the Snake Creek-Williams Canyon area_______________________________________________________________________________________ 32 14. Diagram showing relation between Rittmann index and SiO2 content for granitoid rocks of the Snake Creek- Williams Canyon area____________-_____________________________-__________-__----___-___--_- 32 15-17. Diagrams showing normative albite, orthoclase, and quartz in granitoid rocks: 15. Snake Creek-Williams Canyon area____________________-___-_______-_-_--_-______-_----_- 33 16. Pole Canyon-Can Young Canyon area_________________---_____-_-_--------___-----_------- 34 17. Young Canyon-Kious Basin area___________________________________________-_______-_-____ 34 18. Diagram showing modal plagioclase, microcline, and quartz in granitoid rocks iof the Snake Creek-Williams Canyon area_______________________________________________________________________________ 34 19. Sketches of stained rocks from the Snake Creek-Williams Canyon and the Pole Canyon-Can Young Canyon areas. _____________________________________________________________________________________ 35 in IV CONTENTS Page FIGURE 20. Diagram showing relation between CaO content and H2O(+) content for granitoid rocks of the Snake Creek- Williams Canyon area and the Pole Canyon-Can Young Canyon area___________________________ 38 21. Diagram showing relation between CaO content of rock and angular difference between 20dii) and 29(m) X-ray reflections of constituent plagioclase, Pole Canyon-Can Young Canyon and Young Canyon- Kious Basin areas-_______-___-___-------_---_-__--------_-__--------_-___-__________________ 39 TABLES Page TABLE 1. Analytical data for Osceola Argillite (of Misch and Hazzard, 1962), Prospect Mountain Quartzite, and Pioche Shale_ 8 2. Analytical data for Wheeler limestone (of local usage) and Pole Canyon Limestone____________________ 9 3. Field numbers of analyzed granitoid rock samples keyed to sample numbers on plate l_-_-__------_--__- 11 4. Limits of detection, by emission spectrography, for minor elements in sedimentary and granitoid rocks considered in this report_----_---_--__-__-_-__-___---___-_--__-------_---_----------_-------- 11 5-7. Analytical and other data for granitoid rocks: 5. Snake Creek-Williams Canyon area__---_-_-._---_---_---_--------------------------_-------- 12 6. Pole Canyon-Can Young Canyon area________-__-_____-__-__-_--__-_--___-_----_-----_----_ 18 7. Young Canyon-Kious Basin area--__-_-__--_--__-___---_--------_--------------_----------- 19 8. Correlation coefficients for 87 granitoid rocks of the Snake Creek-Williams Canyon area.___._--__--_____ 26 9. Average compositions of sedimentary rocks studied-________________________________________________ 36 10. Analytical and other data for aplites.__--_.-____--_--__-_-_-_-_--__-____-__---___-_-_-_--_----__-- 42 HYBRID GRANITOID ROCKS OF THE SOUTHERN SNAKE RANGE, NEVADA By DONAU> E. LEE and EIOHABD E. VAN LOENEN ABSTRACT basic rare earths; and whole-rock concentrations of rare con­ A detailed field and laboratory study of igeneous rocks exposed stituents such as total cerium earths, Zr, P, Ti, Ba, Sr, an-I F a few miles north of the Mount Wheeler mine in the southern increase sympathetically with whole-rock calcium. Snake Range of Nevada showed many well-defined and inter­ The granitoid rocks described are exposed just beneath the related differences in the chemistry and mineralogy of the surface of a thrust fault, and the eastern part of the intrusive granitoid rocks within an outcrop area of about 20 square outcrop has been cataclastically deformed by movement on the miles. Chemical controls were established by major- and minor- thrust. The main intrusive phase and some associated aplite element analyses of 133 granitoid rocks; mineralogical con­ crystallized during Middle Jurassic time (about 160 million trols were established by modal analyses of all the analyzed years ago), but the nonpegmatite beryllium mineralization at rocks and by mineral separation work on 30 of them. the Mount Wheeler mine probably resulted from hydrothermal The well-exposed granitoid rocks range in composition from activity related to a middle Tertiary (28-33 million years f go) granodiorite with 4.5 percent CaO (63 percent SiO2) to quartz aplite phase. monzonite with 0.5 percent CaO (76 percent SiO2). For various reasons, we relate mineralogical and other chemical trends to LOCATION AND GEOLOGIC SETTING CaO instead of to SiO2, but the major-element chemistry of these rocks is that expected in a series of magmatic differentiates. The area studied is about 50 miles southeast of Ely, Amounts of essential minerals (quartz, feldspars, micas) in Nev., in the southern part of the Snake Range of these rocks also fit the idea of differentiation. Nevada, a prominent north-south range just west of In a field setting less ideal for a detailed study, it would the Utah boundary, in the eastern part of the Bssin indeed seem best