Basic Geological Mapping

Preface to the Fourth Edition ix

Preface to the Fifth Edition xi

1 Introduction 1

1.1 Outline and Approach 1

1.2 Safety 2

1.3 Field Behaviour 4

1.4 A Few Words of Comfort 5

2 Field Equipment 6

2.1 Hammers and Chisels 6

2.2 Compasses and Clinometers 8

2.3 Hand Lenses 13

2.4 Tapes 14

2.5 Map Cases 14

2.6 Field Notebooks 15

2.7 Scales 16

2.8 Protractors 16

2.9 Pencils, Erasers and Mapping Pens 17

2.10 Acid Bottles 18

2.11 Global Positioning System (GPS) and Mobile Phones 19

2.12 Other Instruments 23

2.13 Field Clothing 26

3 Topographic Base Maps 27

3.1 Types of Geological Map 27

3.2 Topographic Base Maps 29

3.3 Geographic Coordinates and Metric Grids 30

3.4 Grid Magnetic Angle 33

3.5 Position Finding on Maps 34

3.6 Use of Air Photography as a Mapping Tool 43

3.7 Suitability of Images for Geological Mapping 48

4 Methods of Geological Mapping 50

4.1 Strategy for the Mapping Programme 50

4.2 Mapping by Following Contacts 51

4.3 Traversing 52

4.4 Exposure Mapping 55

4.5 Mapping in Poorly Exposed Regions 57

4.6 Superficial Deposits 62

4.7 Drilling 66

4.8 Geophysical Aids to Mapping 67

4.9 Large-Scale Maps of Limited Areas 71

4.10 Underground Mapping 74

4.11 Photogeology 76

5 Technological Aids to Mapping 80

5.1 Digital Terrain Models 80

5.2 Topographic Surveying Techniques 86

6 Field Measurements and Techniques 95

6.1 Measuring Strike and Dip of Planar Structures 95

6.2 Plotting Strike and Dip 101

6.3 Recording Strike and Dip 101

6.4 Measuring Linear Features 102

6.5 Folds 105

6.6 Faults 110

6.7 Thrusts 112

6.8 Joints 112

6.9 Unconformities 114

6.10 Map Symbols 114

6.11 Specimen Collecting 116

6.12 Field Photography 118

6.13 Panning 124

7 Mappable Rock Units and Lithology 126

7.1 Lithostratigraphy and Sedimentary Rocks 126

7.2 Sedimentary Formations 127

7.3 Rock Descriptions 128

7.4 Identifying and Naming Rocks in the Field 129

7.5 Fossils 133

7.6 Phaneritic Igneous Rocks 134

7.7 Aphanitic Igneous Rocks 135

7.8 Veins and Pegmatites 135

7.9 Igneous Rocks in General 136

7.10 Pyroclastic Rocks 138

7.11 Metamorphic Rocks 138

7.12 Economic Geology 140

8 Field Maps and Field Notebooks 146

8.1 Field Maps 146

8.2 Field Notebooks 154

9 Fair Copy Maps and Other Illustrations 162

9.1 Fair Copy Maps 162

9.2 Transferring Topography 163

9.3 Transferring Geology 163

9.4 Lettering and Symbols 164

9.5 Formation Letters 165

9.6 Layout 165

9.7 Colouring 167

9.8 Stratigraphic Column 167

9.9 Overlays 168

9.10 Computer Drafting of the Fair Copy Map 169

10 Cross-Sections and 3D Illustrations 171

10.1 Cross-Sections 171

10.2 Method of Apparent Dips 175

10.3 Down-Plunge Projection Method 177

10.4 Balanced Cross-Sections 179

10.5 Columnar Sections 179

10.6 Block Diagrams 180

10.7 Models 183

11 Geological Reports 185

11.1 Preparation 186

11.2 Revising and Editing 186

11.3 Layout 186

11.4 The ‘Introduction’ 188

11.5 Main Body of the Report 188

11.6 The ‘Conclusions’ Section 191

11.7 Text Illustrations 191

11.8 References 192

11.9 Appendices 193

11.10 Some Final Thoughts 193

Appendix A: Adjustment of a Closed Compass Traverse 195

Appendix B: Field Equipment Checklist 197

Appendix C: Indicators of Stratigraphical Way-Up 202

Appendix D: Useful Chart and Tables 203

References 205

Index 209