CONTENTS 



Abstract 



Introduction 



Scope of the report 



Location and accessibility 



Topography 



Climate and vegetation 



Previous work 



Present investigation 



Mapping methods 



General geology 



Franciscan group 



Bibliography of the Franciscan group 



Clastic sedimentary rocks 



Gray wa eke 



Siltstone and shale 



Alta 



Conglomerate 



Organic and chemical sedimentary rocks 



Limestone 



Chert 



Volcanic rocks (greenstones) 



Lavas 



Pyroclastic rocks 



Nontachylitic tuffs and breccias 



Tachylitic tuffs and breccias 



Chemical composition of the greenstone 



Metamorphic rocks 



Hornblende rocks 



Glaucophane rocks 



Chlorite-la wsonite rock 



Quartz-muscovite schists 



Quartz-actinolite schist 



Actinolite-chlorite rocks 



Metachert 



Origin of metamorphic rocks 



Age of the Franciscan group 



Thickness of the Franciscan group 



Origin of the Franciscan group 



Serpentine 



Gabbros and related rocks 



Silica-carbonate rock 



Other Upper Cretaceous rocks 



Eocene rocks 



Temblor and Monterey formations 



Santa Clara formation 



Quaternary alluvium 



Landslides -. 



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Geologic structure 77 



Methods used in determining the structures 78 



Preliminary outline of the geologic structure 79 



Major structural blocks 82 



Santa Teresa block 82 



Los Capitancillos block 82 



El Sombroso block 84 



Folds 85 



Folds in rocks of the Franciscan group 85 



Folds in post- Franciscan rocks 88 



Faults 90 



Shear zones 90 



Strike-slip faults 91 



Dip-slip faults 93 



Faults due to intrusion of serpentine 94 



Tension fractures 95 



Ore deposits 95 



Quicksilver ore bodies 96 



Mineralogy 96 



Ore minerals 96 



Accompanying sulfides 97 



Gangue minerals 99 



Character of the ores 102 



Size of the ore bodies 106 



Grade of the ore bodies 107 



Localization of the ore bodies 108 



Lithologic control 108 



Structural control 110 



Examples of ore control 112 



Genesis 122 



Age of the quicksilver ores 122 



Character of the mineral) zing agents 122 



Depth of deposition of the quicksilver ores. 122 



Pressure and temperature of ore deposition. 123 



Relation to intrusive rocks 124 



Relation to mineral springs 125 



Summary of origin of the quicksilver ore 



bodies 125 



Other metallic deposits 125 



Copper 125 



Chromite 126 



Manganese 126 



Nonmetallic mineral resources 126 



Building stone 126 



Limestone 126 



Serpentine 127 



Gravel, sand, and loam 127 



Road metal.. 127 



in 



