A GEOLOGIC STUDY OF THE PONTATOC MINE GEOLOGIC STUDY OF THE PONTATOC MINE AREA, PIMA COUNTY, ARIZONA…

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  • A geologic study of the Pontatocmine area, Pima County, Arizona

    Item Type text; Thesis-Reproduction (electronic)

    Authors Medhi, Purnendu Kumar, 1936-

    Publisher The University of Arizona.

    Rights Copyright is held by the author. Digital access to this materialis made possible by the University Libraries, University of Arizona.Further transmission, reproduction or presentation (such aspublic display or performance) of protected items is prohibitedexcept with permission of the author.

    Download date 17/07/2018 03:20:38

    Link to Item http://hdl.handle.net/10150/553996

    http://hdl.handle.net/10150/553996

  • A GEOLOGIC STUDY OF THE PONTATOC MINE AREA,

    PIMA COUNTY, ARIZONA

    by

    Purnendu K, Medhi

    A Thesis Submitted to the Faculty of the

    DEPARTMENT OF GEOLOGY

    In Partial Fulfillment of the Requirements For the Degree of

    MASTER OF SCIENCE

    In the Graduate College

    THE UNIVERSITY OF ARIZONA

    1964

  • STATEMENT BY AUTHOR

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

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

    SIGNED:

    APPROVAL BY THESIS DIRECTOR

    This thesis has been approved on the date shown below:

    W. C. LACY Professor of Geology

    C. LACY Date

  • ACKNOWLEDGMENTS

    The author acknowledges his gratitude to Dr. Willard C.

    Lacy, for his encouragement and constant help throughout his graduate

    study, for the suggestion of this problem, and for his constructive crit

    icism s during the preparation of this thesis.

    The Alumni Association of the University of Arizona aided in

    this project with a special research grant for which the author is very

    grateful.

    The author extends thanks to Mr. Fred Pashley of the U. S,

    Geological Survey, D r .. Eldred D. Wilson and Mr. Wesley Peirce of

    the Arizona Bureau of Mines, and Dr. S. P. Bag of the Chemistry

    Department of the University of Arizona for helpful discussions regard

    ing different problems encountered in preparation of this thesis.

    Finally, the author wishes to express his thanks to his wife,

    Mrs. Sarah Jane Medhi, for her constant help and encouragement dur

    ing the writing of this thesis.

  • TABLE OF CONTENTS

    Page

    LIST OF ILLUSTRATIONS ........................ ..................................... .. vi

    LIST OF TABLES ................................................................................... vii

    ABSTRACT........... ............................ ............ .......................................... viii

    CHAPTER I INTRODUCTION............................................................. 1

    Location .................................................................... 1Previous Studies .................................................................. 3Purpose of Study .................................................................................. 3Method of Study .................................................................................... 4Geography........................................................ "............................... 4

    CHAPTER H GEOLOGIC SETTING......................................... 6

    CHAPTER HI METAMORPHIC ROCKS THE CATALINA GNEISS ......................................................................................................... 8

    Distribution............................................................................................. 8Field D escription.................................................................................. 8Petrography .......................................................................................... 9

    Quartz ........................................................................................ 10Oligoclase (A n g t^ s ) ................... 10Microcline ....................................................... 11Muscovite and B io t it e ....................................................... 11Garnet and Z ir c o n ..................................................... 11Chemical A n a ly sis ................................ : ................................ 11

    D iscu ssion .................................................................................... 12Age and Correlation ........................................................................... 13

    CHAPTER IV SEDIMENTARY ROCKS ..................................... 14

    iv

  • V

    TABLE OF CONTENTS Continued

    Page

    Cenozoic D ep osits............................. 14Distribution ....................................................................................... 14

    General Character and Petrography........................................... 16Age and C orrelation .................................... 17

    CHAPTER V STRUCTURAL GEOLOGY ......................................... 19

    Santa Catalina Foothill Fault ................ 19Cross F aults................................................... 26F o ld s .................................................................................................... 27Joints ............................................................................................. 27Foliation and Lineation .......... 29

    CHAPTER VIECONOMIC GEOLOGY ........................... 31

    Mining History ........................... 31M ineralization.......................................................................... 33A lteration ............... .*....................... .................................................. 35Ore Control ... . .......................................................................... 37Par a g e n e s is ........................................................................ 38

    CHAPTER VH CONCLUSION .......................................... 41

    CHAPTER VHI LITERATURE C IT E D ............... .................. ; ____ 43

  • LIST OF ILLUSTRATIONS

    Figure . Page *

    1. Location m a p ................................................................ ............ .. 2

    2. Composition of the Cenozoic deposits .................................... 15

    3. Deformation of the Catalina Gneiss at the north endof Campbell Avenue ............................................. .. 21

    4. Structure and deformation of the lower .Pantano Beds . . . . 22* - $

    5. Diagram showing foliation in the Catalina G n e is s ............... 23

    60 Paragenetic sequence of the ore minerals ............................ 39

    Plate Page

    1. Geologic map of the Pontatoc mine a r e a ................................ in pocket

    20 Structural map of the Catalina Gneiss, Pontatocmine area ................................................................................... 20

    vi

  • LIST OF TABLES

    Table Page

    1. Spectrographic analyses, of the ore of the Pontatoc .m in e .............* .............................................................................. 34

    vii

  • ABSTRACT

    The Pontatoc mine area is located at the southern base of the

    Santa Catalina Mountains 9-1 /2 m iles northeast of Tucson, Arizona.

    Catalina Gneiss of Cretaceous(?) age and Pantano Beds of

    Tertiary age are the dominant rock types in the area. The Catalina

    Gneiss has undergone at least two periods of metamorphism one as

    early as Precambrian time, and the later one during post-Cretaceous

    time. Metamorphism during the post-Cretaceous period was cataclastic,

    and it is responsible for the present-day appearance of the Catalina

    Gneiss. The Pantano Beds consist of conglomerates composed of frag

    ments of granite, quartzite, limestone, volcanic rocks, and Catalina

    Gneiss. These beds are subdivided into three members upper, mid

    dle, and lower on the basis of their rock composition. The lower and

    the middle members contain more exotic materials than the upper

    member; the upper member is composed mainly of gneissic material

    and is very sim ilar in composition to the alluvial-fan deposits of Recent

    age.

    The two rock units are separated by an old east-trending fault

    the Santa Catalina foothill fault. This fault probably existed before the

    deposition of the Pantano Beds and probably underwent more than one

    viii

  • ix

    period of movement. Field evidence suggests that the final movement

    was reverse movement. The Pantano Beds were deposited against this

    fault at or near their present position. There is no evidence in the

    Pontatoc mine area to assume the Pantano Beds as a thrust block.

    Copper metallization of the Pontatoc mine area is of m eso-

    thermal intensity, and the paragenetic sequence of minerals is quartz,

    pyrite, chalcopyrite, molybdenite(?), bornite, chalcocite, and covellite;

    the latter two minerals are of super gene origin. Wall-rock alteration

    in the Pontatoc mine is very well defined but restricted to a small zone.

    It is cl