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The Relationships of Metallogenic Zones and Local Geological Features to Lode Gold Orebodies, Central Sierra Nevada Foothills, California

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The Relationships of Metallogenic Zones and Local Geological Features to Lode Gold Orebodies, Central Sierra Nevada Foothills, California The relationships of metallogenic zones and local geological features to lode gold orebodies, central Sierra Nevada foothills, California Item Type text; Thesis-Reproduction (electronic); maps Authors Sullivan, Jeffery Alan Publisher The University of Arizona. Rights Copyright © is held by the author. Digital access to this material is made possible by the University Libraries, University of Arizona. Further transmission, reproduction or presentation (such as public display or performance) of protected items is prohibited except with permission of the author. Download date 26/09/2021 20:59:16 Link to Item http://hdl.handle.net/10150/557587 THE RELATIONSHIPS OF METALLOGENIC ZONES AND LOCAL GEOLOGICAL FEATURES TO LODE GOLD OREBODIES, CENTRAL. SIERRA NEVADA FOOTHILLS, CALIFORNIA by Jeffery Alan Sullivan A Thesis Submitted to the Faculty of the DEPARTMENT OF MINING AND GEOLOGICAL ENGINEERING In Partial Fulfillment of the 'Requirements For the Degree of MASTER OF SCIENCE WITH A MAJOR IN GEOLOGICAL ENGINEERING In the Graduate College THE UNIVERSITY OF ARIZONA 19 8 0 STATEMENT BY AUTHOR This thesis has been submitted in partial ful­ fillment 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 per­ mission 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: r . ( u z z z : ? ~ / s . / W. C. PETERS Hate Professor of Mining and Geological Engineering TABLE OF CONTENTS Page LIST OF ILLUSTRATIONS......... ........... .. v LIST OF TABLES . .. vi ABSTRACT ........... .... vii 1. INTRODUCTION . .... 1 Geographical and GeologicalSetting ..... 1 H i s t o r y ........... 5 Previous Work . 8 2. REGIONAL GEOLOGIC SETTING . .. 10 Nature and.Distribution of the. Principal Rock T y p e s ................................. 10 Metamorphic Rocks . .. 11 Western Belt ............. 12 > Eastern Belt . .... .. ..... 16 Intrusive Rocks . .... ... ... ., . 17 Serpentinite and Associated Rocks . 17 Granitic Rocks ........... 18 Structural Geology ............... 18 Summary of Geologic H i s t o r y . 21 3. ROCK UNITS . .. 23 Western B e l p ............................ 23 Unit A ...... ............ 23 Unit C ............ 24 Unit B ................... 27 Smartville Block . ........... 28 Rocks of the Melones and Bear Mountains Fault Zones ...... .............. 29 Eastern B e l t . 29 Intrusive Rocks ........... 32 Ultramafic Rocks ......... 32 Granodiorite . ..... .... .34 iii iv TABLE. OF CONTENTS--Continued Page 4. GOLD 0REBODIES . .... ... 35 Introduction . ... 35 Quartz Veins ................ 37 General F e a t u r e s ........... .............. 37 Vein Filling . .............. - . 40 Gouge . '. ... .■ . .. ... 42 Ore Shoots ............... 43 Mineralized Greenstone ..... ............ 44 Mineralized Schists . 45 Alteration ................. 46 Origin of the Gold Orebodies ... 47 5. METALLOGENIC STUDY ............... 49 - The West Belt ..............• . 49 Southern Area . ....... .:. 51 Northern Area . .. 52 Characterization of West Belt Deposits . 54 The East Belt . .... 56 Southern Area . ......... .. 57 Central Area . .... 58 . Northern Area . .......... 60 Characterization of East Belt Deposits . 60 The Mother Lode B e l t ........... 62 Northern A r e a .............. 63 Jacks on-Plymouth . ................... 66 San Andreas . ..... ■............... .. 67 Angels Camp . -. .... 68 Characterization of the Mother Lode . Deposits .............. 69 Comparison of Belts . ... 74 Comparison Between the Mother Lode and Other Mesozoic Lode Gold Belts . 81 Nature.and Distribution of Mesozoic Lode Gold Deposits . 81 Canadian Deposits .... ... 83 Deposits of Eastern Asia .............. 84 Summary of Relationships .............. 84 REFERENCES . ........ ... 86 LIST OF ILLUSTRATIONS Figure Page 1. Index Map Showing Location of the , . Thesis Area . ... ... Y. .. 3 ■ 2. Map of California Showing Gold Bearing Areas and the Thesis Area . 4 3. Geologic Map of the Central Sierra Foothills Showing the Location Of the Three .Gold Belts .... .... 6 4., Simplified Geologic Map of the Central Sierra Nevada Foothills . .... ... 13 5. Stratigraphic Nomenclature Used in Amador County . ............ 14 6. Geologic Map Sacramento A.M.S. Sheet, California (in pocket) . 7. Attitude of the Quartz Veins and Mine Locations Sacramento A.M.S. Sheet, California (in pocket) • . ........... 8. Vein Systems and Approximate District Locations . ........... 50 9. Location and Trend of Veins in the Ophir District . .... ......... 77 10. Location and Trend of Veins in the Central A r e a .................. 78 11. Distribution of Mesozoic Gold Deposits . .• . 82 v LIST OF TABLES Table Page 1. Structural and Lithologic Controls in the Mother Lode R e g i o n .............. 80 vi ABSTRACT The gold quartz veins of the Mother Lode region, central Sierra Nevada foothills, California, are distrib­ uted among three north-trending belts, the West belt, the East belt and the Central, or Mother Lode, belt. The structural.and lithologic controls of the gold deposits along each belt are examined and analyzed. Two of the belts, the West belt and the Mother Lode belt, have strong, spatial associations with regional structures, while a third belt, the East belt, is associated only with local structures. Because of the lack of a regional structure, the use of the term East belt should be discontinued. In the West and Mother Lode belts, there is little relation­ ship between productivity and specific locations along a belt, therefore location cannot be used to predict productivity. The productivity of the gold deposits in a particular area is dependent on local structure and lithologic features rather than on regional features. CHAPTER 1 INTRODUCTION This thesis concerns a major portion of one of the more important lode gold districts in the history and development of the western United States, the Mother Lode. The district has been unproductive for several years but takes on a renewed importance because of the present high price of gold. Primarily the structural and metallogenic features of the northern Mother Lode region are studied. These features are characterized and compared to features both within and outside of the Mother Lode region. Information has been obtained from a variety of sources including publications of the California Division of Mines and the United States Geological Survey. Field work was limited to a two-week geological reconnaissance of the region. The ideas presented are meant to help exploration geologists identify targets for detailed field study in this and other similar lode gold districts. Geographical and Geological Setting The area studied covers approximately 7,500 square miles in central California. It is bounded to the west and east by 122°00' and 120°00' west longitude and to the south and north by 38°00' and 39°00' north latitude (figure 1). The fraction of the area actually involved in gold mineralization is small. Gold quartz veins are con­ fined to a 20-mile-wide belt of north- to northwest- trending metamorphic rocks' and of small plutons, having varying composition, that intrude these rocks. This mineralized belt occurs west of the Sierra Nevada batholith in a region commonly referred to as the Sierran foothills. The topography of the. foothills is rolling, with an average elevation of 1,500 feet. Vegetation normally in­ cludes grass and small types of brush along with various types of pine and fir trees. West of the foothills the metamorphic rocks are covered by younger sediments o f Xthe Great Valley sequence. ' / - . The thesis area includes only a portion of one of the gold-bearing regions of California. The two most extensive gold areas in the state are found in Mesozoic rocks within the Klamath Mountains and Sierra Nevada geo- morphic provinces (figure 2). The deposits, both placer and vein type, in the Sierra Nevada province occur in a zone that stretches from Butte.County in the north to Mariposa County in the south. The southern and central sections of this mineralized zone contain a series of structurally related quartz veins which are termed the 3 X.trjy t ^ O o i- ^ e to'-.Ti AREA L t'J D O R A D O ' I . y S A C R A M E N T O ' ^ T" M^Hymouth— "q 9 '---- - ^ S A C R A M E N T O i Vv 3 hr‘^ r L / j '''^-<>> JACKSON ^ k v % . i rX '. , -VvVi^fl e C &mp ! (//-- ^STOCKTOW j ^ ^ ’^-vCONTRA COSTA ) SAN^"JOAOUI' \) X'—_ I .-, PAN FRANCISCO ,— ^ A M E D A i /_ v I I i T > ^ - V L MARIPOSA —A Figure 1. Index Map Showing Location of the Thesis Area. After Knopf (1929). 4 MAP OF CALIFORNIA SHOWING GOLD-BEARING AREAS AND GEOMORPHIC PROVINCES SCALE 40____80 120 Miles TH E S IS AREA EXPLANATION I KLAMATH MOUNTAINS H CASCADE RANGE MODOC PLATEAU COAST RANGES GREAT VALLEY SIERRA NEVADA BASIN RANGES MOJAVE DESERT TRANSVERSE RANGES PENINSULAR RANGES COLORADO DESERT GOLD-BEARING AREA Figure 2. Map of California Showing Gold Bearing Areas and the Thesis Area. After Clark (1969). Mother Lode vein system. This thesis examines the northern part of the Mother Lode system where three north- to northwest-trending belts of gold-bearing quartz veins have been defined. The central belt is by far the most productive and is known as the Mother Lode belt. The belts flanking the Mother Lode belt are known as the West and East belts (figure 3). : ' History Gold mining in the Mother Lode region has a long and colorful history. Some of the color and vitality of the region during its boom period is recorded in. stories Such as "Roughing It" and "The Jumping Frog of Calaveras County" by Mark Twain and in several short stories by Bret Harte. Placer gold was discovered in the Mother Lode region at Sutter s Mill on the American River near Coloma by James Marshall.
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