MINERALOGY OF THE PERALUMINOUS SPRUCE PINE PLUTONIC SUITE, MITCHELL, AVERY, AND YANCEY COUNTIES, NORTH CAROLINA by William Brian Veal (Under the Direction of Samuel E. Swanson) ABSTRACT The Spruce Pine plutonic suite consists of numerous Devonian (390-410 ma) peraluminous granitic plutons, dikes, sills, and associated pegmatites. The mineralogy of pegmatites and host granodiorites from seven locations was studied to determine the extent of fractionation of the pegmatites relative to the granodiorite. Garnets in the plutons are almandine- spessartine and some display epitaxial overgrowths of grossular garnet. Similar garnets are found in the pegmatites. Pegmatitic muscovite contains several percent iron and is compositionally similar to muscovite from the host granodiorite. Feldspars in the granodiorites and pegmatites are compositionally similar (plagioclase Ab69-98; k-feldspar Or95-98). The lack of compositional variation between minerals in pegmatites and host granodiorites indicates the pegmatites were not the result of extreme fractionation and indicates that pegmatite mineralogy can be used to characterize the mineralogy of an entire granodiorite body. INDEX WORDS: Spruce Pine, Pegmatites, Granodiorite, Garnet, Muscovite, Feldspar MINERALOGY OF THE PERALUMINOUS SPRUCE PINE PLUTONIC SUITE, MITCHELL, AVERY, AND YANCEY COUNTIES, NORTH CAROLINA by WILLIAM BRIAN VEAL B.S., Georgia Southwestern State University, 2002 A Thesis Submitted to the Graduate Faculty of The University of Georgia in Partial Fulfillment of the Requirements for the Degree MASTER OF SCIENCE ATHENS, GEORGIA 2004 © 2004 William Brian Veal All Rights Reserved MINERALOGY OF THE PERALUMINOUS SPRUCE PINE PLUTONIC SUITE, MITCHELL, AVERY, AND YANCEY COUNTIES, NORTH CAROLINA by WILLIAM BRIAN VEAL Major Professor: Samual E. Swanson Committee: Michael F. Roden Paul A. Schroeder Electronic Version Approved: Maureen Grasso Dean of the Graduate School The University of Georgia August 2004 ACKNOWLEGEMENTS Many people have helped me along my educational path. I thank my parents for giving me a sense of right and wrong and for their never-ending support in everything I do. I thank my brother for the fun in the mudpits and drives to the mountains. I thank my wife for understanding the long hours and tolerating the incessant geology references I make in everyday speech. At the University of Georgia, I would like to thank my major advisor, Dr. Samuel E. Swanson, and my committee members, Dr. Michael Roden and Dr. Paul Schroeder, for generous help and guidance needed to complete this project. I thank all of my committee members for their patience with me as I strove to complete this project. Many thanks to Chris Fleischer for assistance with the many microprobe riddles that came my way. I thank the UGA Department of Geology for financial support through the Wheeler-Watts and Allard Funds. Through the department’s generous help, I was able to complete my field work and present my data at the Northeastern/Southeastern joint meeting of the Geological Society of America. In Spruce Pine, Mr. Alex Glover proved to be a valuable contact and provided me with much information on the Spruce Pine mining district that helped to guide my research. Mr. Bob Schabilion was gracious enough to give me access and allow me to sample Hootowl Mine and Bon Ami Mine. Mr. Alex Glover allowed access and permission to sample from the Pete Lawson Mine. Many thanks to all of them, without which this project would be much smaller in scale. Most of all, thanks to God for standing beside me when I face the challenges of my life, for carrying me when I cannot stand, and for Allison. iv TABLE OF CONTENTS Page ACKNOWLEDGEMENTS........................................................................................................... iv LIST OF TABLES....................................................................................................................... viii LIST OF FIGURES ....................................................................................................................... ix CHAPTER 1 INTRODUCTION ..........................................................................................................1 History of Mining in the Spruce Pine District .............................................................1 Purpose of Project........................................................................................................4 2 PEGMATITE PETROGENESIS....................................................................................5 Types of Pegmatites.....................................................................................................5 Crystallization of Pegmatites .......................................................................................7 3 GEOLOGIC BACKGROUND.....................................................................................16 Tectonic Setting .........................................................................................................16 Ages of Spruce Pine Granitoid Rocks .......................................................................20 Geology of Spruce Pine Granites and Pegmatites .....................................................20 Intrusions....................................................................................................................20 Petrology of the Spruce Pine Intrusions.....................................................................24 Geochemistry of Granitoid Rocks and Pegmatites ....................................................24 Bulk Elemental Analysis............................................................................................24 Mineralogy of Spruce Pine Granitoid Rocks.............................................................25 v Crystallization History of Spruce Pine Pegmatites....................................................33 4 METHODS ...................................................................................................................37 Field Mapping and Sampling.....................................................................................37 Microprobe Procedures..............................................................................................40 5 BODIES STUDIED......................................................................................................41 Crabtree Creek Exposure ...........................................................................................41 Field Mine..................................................................................................................45 Bon Ami Mine ...........................................................................................................45 Hootowl Mine ............................................................................................................54 Exposure on Roan Road.............................................................................................59 6 RESULTS .....................................................................................................................65 Mineralogy of the Pegmatites ....................................................................................65 7 DISCUSSION.............................................................................................................115 Pegmatite Zones.......................................................................................................115 Granodiorite Mineralogy .........................................................................................115 Pegmatite Mineralogy..............................................................................................117 Post-Magmatic Recrystallization.............................................................................125 8 CONCLUSIONS.........................................................................................................129 Recommendations for Future Work.........................................................................130 REFERENCES CITED................................................................................................................131 APPENDICES .............................................................................................................................134 A ELECTRON MICROPROBE ANALYSIS ROUTINES FOR GARNET, MUSCOVITE, AND FELDSPAR.............................................................................134 vi B MINERAL ASSEMBLAGES IN GRANODIORITE AND PEGMATITE SAMPLES FROM SPRUCE PINE, NORTH CAROLINA......................................138 C ELECTRON MUCROPROBE ANALYSES OF GARNETS FROM SPRUCE PINE GRANODIORITES AND PEGMATITES......................................144 D ELECTRON MICROPROBE ANALYSES OF MUSCOVITE AND BIOTITE FROM SPRUCE PINE GRANODIORITES AND PEGMATITES .........................160 E ELECTRON MICROPROBE ANALYSES OF PLAGIOCLASE AND ALKALI FELDSPAR FROM SPRUCE PINE GRANODIORITES AND PEGMATITES............................................................................................................189 F ELECTRON MICROPROBE ANALYSES OF EPIDOTE FROM SPRUCE PINE GRANODIORITES AND PEGMATITES.......................................209 vii LIST OF TABLES Page Table 1: Estimated metamorphic conditions of Spruce Pine Thrust Sheet...................................18 Table 2: Radiometric dates of selected Spruce Pine materials. ....................................................21 Table 3: Chemical compositions of Spruce Pine granitoid rocks and pegmatites........................26