TY  - BOOK
AU  - Dentith,M.C.
AU  - Mudge,Stephen T.
TI  - Geophysics for the mineral exploration geoscientist
SN  - 9780521809511 (hardback)
AV  - QC807 .D46 2014
U1  - 550 23
PY  - 2014///
CY  - Cambridge, United Kingdom
PB  - Cambridge University Press
KW  - Geophysics
KW  - Earth scientists
N1  - Includes bibliographical references and index; CONTENTS
List of online appendices ix
List of figure credits xi
Preface xv
Acknowledgements xvi
1
Introduction
1
1.1
Physical versus chemical characterisation of the
geological environment
2
1.2
Geophysical methods in exploration and mining
3
1.2.1
Airborne, ground and in-ground surveys
3
1.2.2
Geophysical methods and mineral deposits
4
1.2.3
The cost of geophysics
5
1.3
About this book
6
Further reading 11
2
Geophysical data acquisition, processing
and interpretation
13
2.1
Introduction
13
2.2
Types of geophysical measurement
14
2.2.1
Absolute and relative measurements
14
2.2.2
Scalars and vectors
15
2.2.3
Gradients
15
2.3
The nature of geophysical responses
16
2.4
Signal and noise
17
2.4.1
Environmental noise
18
2.4.2
Methodological noise
22
2.5
Survey objectives
23
2.5.1
Geological mapping
23
2.5.2
Anomaly detection
24
2.5.3
Anomaly de
fi
nition
25
2.6
Data acquisition
25
2.6.1
Sampling and aliasing
25
2.6.2
System footprint
27
2.6.3
Survey design
27
2.6.4
Feature detection
31
2.7
Data processing
32
2.7.1
Reduction of data
32
2.7.2
Interpolation of data
34
2.7.3
Merging of datasets
38
2.7.4
Enhancement of data
38
2.8
Data display
48
2.8.1
Types of data presentation
48
2.8.2
Image processing
51
2.9
Data interpretation
?
general
58
2.9.1
Interpretation fundamentals
59
2.9.2
Removing the regional response
60
2.10
Data interpretation
?
qualitative analysis
63
2.10.1
Spatial analysis of 2D data
63
2.10.2
Geophysical image to geological map
67
2.11
Data interpretation
?
quantitative analysis
70
2.11.1
Geophysical models of the subsurface
70
2.11.2
Forward and inverse modelling
74
2.11.3
Modelling strategy
78
2.11.4
Non-uniqueness
79
Summary 81
Review questions 82
Further reading 82
3
Gravity and magnetic methods
85
3.1
Introduction
85
3.2
Gravity and magnetic
fi
elds
86
3.2.1
Mass and gravity
87
3.2.2
Gravity anomalies
88
3.2.3
Magnetism and magnetic
fi
elds
89
3.2.4
Magnetic anomalies
93
3.3
Measurement of the Earth
?
s gravity
fi
eld
94
3.3.1
Measuring relative gravity
96
3.3.2
Measuring gravity gradients
98
3.3.3
Gravity survey practice
98
3.4
Reduction of gravity data
99
3.4.1
Velocity effect
99
3.4.2
Tidal effect
99
3.4.3
Instrument drift
100
3.4.4
Variations in gravity due to the Earth
?
s
rotation and shape
100
3.4.5
Variations in gravity due to height and
topography
102
3.4.6
Summary of gravity data reduction
106
3.4.7
Example of the reduction of ground gravity data
106

3.5 Measurement of the Earth?s magnetic
fi
eld
106
3.5.1
The geomagnetic
fi
eld
109
3.5.2
Measuring magnetic
fi
eld strength
112
3.5.3
Magnetic survey practice
114
3.6
Reduction of magnetic data
116
3.6.1
Temporal variations in
fi
eld strength
116
3.6.2
Regional variations in
fi
eld strength
117
3.6.3
Terrain clearance effects
117
3.6.4
Levelling
117
3.6.5
Example of the reduction of
aeromagnetic data
117
3.7
Enhancement and display of gravity and
magnetic data
118
3.7.1
Choice of enhancements
122
3.7.2
Reduction-to-pole and pseudogravity
transforms
123
3.7.3
Wavelength
fi
lters
124
3.7.4
Gradients/derivatives
125
3.8
Density in the geological environment
127
3.8.1
Densities of low-porosity rocks
127
3.8.2
Densities of porous rocks
129
3.8.3
Density and lithology
130
3.8.4
Changes in density due to metamorphism
and alteration
131
3.8.5
Density of the near-surface
133
3.8.6
Density of mineralised environments
133
3.8.7
Measuring density
134
3.8.8
Analysis of density data
134
3.9
Magnetism in the geological environment
135
3.9.1
Magnetic properties of minerals
136
3.9.2
Magnetic properties of rocks
138
3.9.3
Magnetism of igneous rocks
140
3.9.4
Magnetism of sedimentary rocks
144
3.9.5
Magnetism of metamorphosed and
altered rocks
145
3.9.6
Magnetism of the near-surface
151
3.9.7
Magnetism of mineralised environments
151
3.9.8
Magnetic property measurements and their
analysis
155
3.9.9
Correlations between density and magnetism
159
3.10
Interpretation of gravity and magnetic data
160
3.10.1
Gravity and magnetic anomalies and their
sources
160
3.10.2
Analysis of gravity and magnetic maps
163
3.10.3
Interpretation pitfalls
164
3.10.4
Estimating depth-to-source
165
3.10.5
Modelling source geometry
167
3.10.6
Modelling pitfalls
167
3.11
Examples of gravity and magnetic data from
mineralised terrains
169
3.11.1
Regional removal and gravity mapping of
palaeochannels hosting placer gold
169
3.11.2
Modelling the magnetic response associated
with the Wallaby gold deposit
172
3.11.3
Magnetic responses from an Archaean granitoid
?
greenstone terrain: Kirkland Lake area
173
3.11.4
Magnetic responses in a Phanerozoic Orogenic
terrain: Lachlan Foldbelt
179
3.11.5
Magnetic and gravity responses from
mineralised environments
186
Summary 188
Review questions 190
Further reading 190
4
Radiometric method
193
4.1
Introduction
193
4.2
Radioactivity
194
4.2.1
Radioactive decay
194
4.2.2
Half-life and equilibrium
195
4.2.3
Interaction of radiation and matter
196
4.2.4
Measurement units
197
4.2.5
Sources of radioactivity in the natural
environment
198
4.3
Measurement of radioactivity in the
fi
eld
199
4.3.1
Statistical noise
199
4.3.2
Radiation detectors
201
4.3.3
Survey practice
204
4.4
Reduction of radiometric data
205
4.4.1
Instrument effects
205
4.4.2
Random noise
206
4.4.3
Background radiation
207
4.4.4
Atmospheric radon
207
4.4.5
Channel interaction
208
4.4.6
Height attenuation
208
4.4.7
Analytical calibration
208
4.5
Enhancement and display of radiometric data
209
4.5.1
Single-channel displays
209
4.5.2
Multichannel ternary displays
209
4.5.3
Channel ratios
210
4.5.4
Multivariant methods
210
4.6
Radioelements in the geological environment
210
4.6.1
Disequilibrium in the geological environment
212
4.6.2
Potassium, uranium and thorium in
igneous rocks
216
4.6.3
Potassium, uranium and thorium in altered
and metamorphosed rocks
216
4.6.4
Potassium, uranium and thorium in
sedimentary rocks
217
4.6.5
Sur
fi
cial processes and K, U and Th in the
overburden
217
4.6.6
Potassium, uranium and thorium in
mineralised environments
219
4.7
Interpretation of radiometric data
220
4.7.1
Interpretation procedure
222
4.7.2
Interpretation pitfalls
222
4.7.3
Responses of mineralised environments
223
4.7.4
Example of geological mapping in a fold and
thrust belt: Flinders Ranges
227
4.7.5
Interpretation of
γ
-logs
229

Summary 232
Review questions 232
Further reading 233
5
Electrical and electromagnetic methods
235
5.1
Introduction
235
5.2
Electricity and magnetism
237
5.2.1
Fundamentals of electricity
237
5.2.2
Fundamentals of electromagnetism
243
5.2.3
Electromagnetic waves
246
5.3
Electrical properties of the natural environment
247
5.3.1
Conductivity/resistivity
247
5.3.2
Polarisation
253
5.3.3
Dielectric properties
255
5.3.4
Properties of the near-surface
255
5.4
Measurement of electrical and electromagnetic
phenomena
257
5.4.1
Electrodes
258
5.4.2
Electrical and electromagnetic noise
258
5.5
Self-potential method
260
5.5.1
Sources of natural electrical potentials
260
5.5.2
Measurement of self-potential
262
5.5.3
Display and interpretation of SP data
263
5.5.4
Examples of SP data from mineral deposits
265
5.6
Resistivity and induced polarisation methods
266
5.6.1
Electric
fi
elds and currents in the subsurface
268
5.6.2
Resistivity
269
5.6.3
Induced polarisation
271
5.6.4
Measurement of resistivity/IP
273
5.6.5
Resistivity/IP survey practice
275
5.6.6
Display, interpretation and examples of
resistivity/IP data
278
5.6.7
Interpretation pitfalls
289
5.6.8
Resistivity/IP logging
293
5.6.9
Applied potential/mise-à-la-masse method
294
5.7
Electromagnetic methods
299
5.7.1
Principles of electromagnetic surveying
299
5.7.2
Subsurface conductivity and EM responses
306
5.7.3
Acquisition of EM data
312
5.7.4
Processing and display of EM data
316
5.7.5
Interpretation of EM data
318
5.7.6
Interpretation pitfalls
326
5.7.7
Examples of EM data from mineral deposits
328
5.8
Downhole electromagnetic surveying
330
5.8.1
Acquisition of DHEM data
330
5.8.2
Display and interpretation of DHEM data
333
5.8.3
Examples of DHEM responses from mineral
deposits
337
5.8.4
Induction logging
339
5.9
Airborne electromagnetic surveying
339
5.9.1
Acquisition of AEM data
340
5.9.2
AEM systems
342
5.9.3
AEM survey practice
344
5.9.4
Display and interpretation of AEM data
345
5.9.5
Examples of AEM data from mineralised terrains
345
Summary 347
Review questions 348
Further reading 349
6
Seismic method
351
6.1
Introduction
351
6.2
Seismic waves
352
6.2.1
Elasticity and seismic velocity
353
6.2.2
Body waves
353
6.2.3
Surface waves
354
6.3
Propagation of body waves through the subsurface
354
6.3.1
Wavefronts and rays
354
6.3.2
Fresnel volume
355
6.3.3
Seismic attenuation
356
6.3.4
Effects of elastic property discontinuities
357
6.4
Acquisition and display of seismic data
363
6.4.1
Seismic sources
363
6.4.2
Seismic detectors
364
6.4.3
Displaying seismic data
364
6.5
Seismic re
fl
ection method
366
6.5.1
Data acquisition
367
6.5.2
Data processing
369
6.6
Variations in seismic properties in the geological
environment
383
6.6.1
Seismic properties of common rock types
384
6.6.2
Effects of temperature and pressure
387
6.6.3
Effects of metamorphism, alteration and
deformation
388
6.6.4
Seismic properties of mineralisation
389
6.6.5
Seismic properties of near-surface environments
390
6.6.6
Anisotropy
391
6.6.7
Absorption
391
6.6.8
Summary of geological controls on seismic
properties
392
6.6.9
Measuring seismic properties
392
6.7
Interpretation of seismic re
fl
ection data
393
6.7.1
Resolution
393
6.7.2
Quantitative interpretation
396
6.7.3
Interpretation pitfalls
397
6.7.4
Examples of seismic re
fl
ection data from
mineralised terrains
398
6.8
In-seam and downhole seismic surveys
401
6.8.1
In-seam surveys
402
6.8.2
Tomographic surveys
403
Summary 405
Review questions 406
Further reading 406
References 408
Index 426
N2  - "Providing a balance between principles and practice, this state-of-the-art overview of geophysical methods takes readers from the basic physical phenomena, through the acquisition and processing of data, to the creation of geological models of the subsurface and data interpretation to find hidden mineral deposits. Detailed descriptions of all the commonly used geophysical methods are given, including gravity, magnetic, radiometric, electrical, electromagnetic and seismic methods. Each technique is described in a consistent way and without complex mathematics. Emphasising extraction of maximum geological information from geophysical data, the book also explains petrophysics, data modelling and common interpretation pitfalls. Packed with full-colour figures, also available online, the text is supported by selected examples from around the world, including all the major deposit types. Designed for advanced undergraduate and graduate courses in minerals geoscience, this is also a valuable reference for professionals in the mining industry wishing to make greater use of geophysical methods." --Publisher's description
ER  -