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University of Nevada Reno Metamorphic Geology of a Portion

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University of Nevada Reno Metamorphic Geology of a Portion University of Nevada Reno Metamorphic Geology of a Portion of the Bagdad Mining District Yavapai County, Arizona A thesis submitted in partial fulfillment of the requirements for the degree of Master of Science by Daniel E. Collins III May 1977 WiNEs U3RARY m © 1 9 7 8 DANIEL EDWARD COLLINS ALL RIGHTS RESERVED The thesis of Daniel E. Collins is approved: Thesis advisor University of Nevada Reno May .1977 PLEASE NOTE: This dissertation contains color photographs which will not reproduce well. UNIVERSITY MICROFILMS INTERNATIONAL. 1 ACKNOWLEDGEMENT The author is sincerely indebted to the Cyprus Mines Corporation for its interest and generous financial support without which this thesis would not have been possible. I wish to thank in particular Bob Clayton and Joe Sierakowsky for their advice and help while in the field. The guidance of Malcolm Hibbard and Don Noble at the University of Nevada was very much appreciated. I also wish to thank Arthur Baker III who first suggested the thesis area and provided many useful suggestions during the writing. The Nevada Bureau of Mines and Jack Quade of NASA are thanked for access and instruction in the use of the x- ray analysis equipment. I am deeply grateful to John and Constantine Zanarras and to my wife, Merilyn, for their constant companionship. I ABSTRACT An estimated 2,150 meters of eugeosynclinal porphyritic andesites, basalts and volcanic sediments belonging to the Bridle formation were metamorphosed during the Mazatzal Revolution (?) to produce greenschist facies minerology, regional folding, and penetrative fabric elements. Prior to regional metamorphism, the Bridle formation was shallowly intruded by concordant masses of porphyritic trondjhemite and a differentiated Dick Rhyolite. The Dick Rhyolite may have vented onto the marine floor. Cooling of the volcanic-intrusive pile and deep water circulation brought mineralized solutions through the Bridle formation. These produced transecting chlorite alterative pipes with lenses of massive pyrite-sphalerite-chalcopyrite deposited along the stratigraphic bottom of the Dick Rhyolite. High temperature hornfels and intrusive granites occurred toward the end of the metamorphic cycle. Bulk rock chemistry was considerably altered during regional metamorphism or by widespread iron-sodium-magnesium metasomatism prior to regional metamorphism. iv TABLE OF CONTENTS Page ACKNOWLEDGEMENTS i ABSTRACT ii TABLE OF CONTENTS iv LIST OF FIGURES vi INTRODUCTION 1 Location and Accessibility 1 Physiography 2 Purpose 2 METHOD OF INVESTIGATION 5 PREVIOUS WORK 8 GEOLOGIC SETTING 11 LITHOLOGY 16 Yavapai Series 16 Mafic Metavolcanic Rocks 16 Cordierite-Anthophyllite Hornfels 19 Intermediate Metavolcanic Rocks 20 Mica Schist 23 Felsic Metavolcanic Rocks 23 Tuffaceous Metasediments 25 Igneous Rocks 26 Metatrondjhemite 26 Contaminated Metatrondjhemite 27 Quartz-Biotite-Cordierite Hornfels 28 Dick Rhyolite 29 Quartz-Biotite-Andalusite Hornfels 32 Intrusive Metarhyolite 33 Metagabbro 34 Metadiabase 35 Granodiorite Gneiss 36 Pegmatite 37 Alteration 38 Chlorite Schist 38 Quartz-Sericite Schist 40 Covered Areas 41 V TABLE OF CONTENTS Page STRUCTURAL GEOLOGY 42 Metamorphic Structures 42 Mountain Springs Fault 47 Other Faults 49 METAMORPHIC PETROLOGY 51 Mineralogy 51 Regionally Metamorphosed Rocks 51 Plagioclase 52 Chlorite 53 Muscovite 56 Amphiboles 58 Thermally Metamorphosed Rocks 61 Cordierite 61 Andalusite-Sillimanite 62 Anthophyllite 63 Biotite 64 Magnetite 64 Staurolite 65 Chlorite and Sericite 65 Tourmaline and Apatite 66 Metamorphic Facies 68 CHEMISTRY 71 Basic to Intermediate Metavolcanic Rocks 72 Granitic Rocks 74 Contaminated Metatrondjhemite 83 SUMMARY OF METAMORPHIC HISTORY 86 THE MASSIVE SULPHIDE MINERALIZATION 91 BIBLIOGRAPHY 96 PHOTOGRAPHS AND PHOTOMICROGRAPHS 99 V i TABLE OF CONTENTS Page APPENDICES A - Average Mineralogy of Mapped Rock Units 109 B - Chemical Analyses of Mafic to Intermediate 110 Metavolcanic Rocks C - Chemical Analyses of Metatrondjhemite 111 D - Chemical Analyses of Contaminated Metatrondjhemite 112 E - Chemical Analyses of the Dick Rhyolite 113 LIST OF FIGURES 1 - Location Map 4 2 - Geologic Map of a Portion of the Bagdad Mining Area, Yavapai County, Arizona (in pocket) 3 - Stratigraphic Column 15 4 - Contoured S-Pole Diagram of Metamorphic Foliation 46 5 - Plot of Barth's Sodium and Potassium Cations 78 6 - AFK Diagram of Metamorphosed Bridle Volcanics versus Unmetamorphosed Basalts and Andesites 79 1 INTRODUCTION The Bagdad area is part of the Eureka mining district and is located in west-central Arizona approximately seventy kilometers west of Prescott. The mining community of Bagdad is the nearest town. The Bagdad porphyry copper deposit and Precambrian massive sulphide deposits are current producers of copper, zinc, silver, and molybdenum in the area. Past production dates back to the 1880's and also included the recovery of gold, tungsten and lead metals. In the thesis area are exposed Precambrian metamorphosed volcanic and sedimentary rock that play host to massive sulphide ore bodies. Location and Accessibility The thesis covers an area of approximately twenty-nine square kilometers located southwest of the town of Bagdad. This area includes the Old Dick and Bruce mines operated by the Cyprus Mines Corporation (see Figure 1). The area is accessible by dirt roads leading from U. S. Highway 93 or State Highway 97. The dirt road connecting the Old Dick mine and the town of Bagdad is well maintained and traveled. Within the thesis area are numerous jeep and dozer trails that reflect the high level of mineral exploration activity in the area. Bagdad is at the end of State Highway 97 which connects Bagdad with the town of Hillside, forty-two kilometers southeast. 2 Physiography The Bagdad area is situated in the Mountain Region physiographic province of Ransome (1919). Rainfall averages fourteen inches annually with higher rainfalls occurring from December to March and from July to September. Flash flooding has been known to accompany heavy summer cloudbursts. Elevation ranges from a low of 950 meters in the south to a high of 1,200 meters in the northern part of the thesis area. The topography consists mainly of low relief, frequently steep, rounded hills carved by intermittent streams. Bridle Creek and Mountain Spring Creek flow south from this area to form broad alluvial aprons. Vegetation is sparse yet defines a zone of transition between arid desert and high mountainous regions. Vegetation consists of a variety of cacti, grasses and mesquite at lower elevations, with juniper and ocotillo occurring at higher elevations. Purpose The purpose of this thesis was to determine the geologic relationships and metamorphic history of a limited area. It was intended also that a more clear model for ore genesis would be evolved and that the collected data would provide 3 useful information for future mineral exploration in the area. The study area was chosen in part for the several occurrences of sulphide ore bodies and mineralized areas in an area where the geologic relationships are poorly understood. The study focused on the country rock rather than mineralization. No attempt was made to do a detailed study of the mineralization in the area except to note the occurrences and stratigraphic relationships. FIGURE 1 1 Las Vegas ARIZONA Locati on M a p 5 METHOD OF INVESTIGATION A geologic map was made of the area using aerial photograph enlargements, then transferring the information onto a compiled base map. Nearly twenty-nine square kilometers were mapped at a scale of approximately 1:6,200 (1"=516'). The base map was compiled from available published and unpublished topographic maps that were enlarged to the same approximate scale as the aerial photographs used in the mapping. The compiled map was reduced by over half to the final scale of 1:13,340 (Figure 2, in pocket). Stream drainage lines were added to the base map to provide reference in those areas where no topographic information was available. The area is bounded on the east and southwest by granitic intrusive batholiths, and on the west by Late Tertiary colluvium deposits. The region north of the Old Dick and Bruce mines was mapped previously by Anderson, Schultz and Strobell (1955). Field work was conducted from September to November, 1971 and in March 1972. Geologic units were differentiated on the basis of type of parent material or by mineralogy. Bedding and foliation attitudes were noted and measured wherever possible. The prefix "meta", used during the geologic mapping, is used in referring to a type of parent material which has been metamorphosed. Since all the rocks are metamorphosed, the "meta" is frequently omitted in the writing in order to avoid its repetitious use. All the mapped geologic units show some degree of regional dynamothermal metamorphism or thermal metamorphism. Thus, a rhyolite is implied to be a metarhyolite unless otherwise stated. Stereo-pair aerial photographs were examined to help locate possible faults that might be exposed in outcrop. These inferred faults are distinguished from mapped faults on the geologic map (Figure 2, in pocket). Rock samples were collected for petrographic analysis and X- ray spectrographic analysis. A total of 235 thin sections were examined in order to determine mineral and fabric relationships. Twenty-five samples were analyzed for bulk chemical composition using a Siemens SR5-1 X-ray spectrometer. X-ray samples were crushed first, using steel gyratory crushers, then pulverized using rotary steel plates. Volborth (1962) estimates that as much as 1% iron may be added to powder samples prepared in this manner. The 7 powdered samples were pressed into pellets about 2 millimeters thick and mounted in bakelite plastic. The contamination was considered to be relatively Low and constant for all the samples analyzed. No analytical corrections were made to eliminate the possible effects from iron contamination. Unfortunately, X-ray spectrometry does not distinguish between elements in different valence states, therefore the total iron is reported as Fe202. The sum of the oxides is often less than 100% because no analyses were made for the minor amounts of C02, H20, MnO, and P20^ usually present.
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