Dunn Colin E. Biogeochemistry in Mineral Exploration
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Handbook of Exploration and Environmental Geochemistry
VOLUME 9
Biogeochemistry in Mineral Exploration
HANDBOOK OF EXPLORATION AND ENVIRONMENTAL GEOCHEMISTRY
M. Hale (Series Editor)
1. ANALYTICAL METHODS IN GEOCHEMICAL PROSPECTING
2. STATISTICS AND DATA ANALYSIS IN GEOCHEMICAL PROSPECTING
3. ROCK GEOCHEMISTRY IN MINERAL EXPLORATION
4. REGOLITH EXPLORATION GEOCHEMISTRY IN TROPICAL AND
SUB-TROPICAL TERRAINS
5. REGOLITH EXPLORATION GEOCHEMISTRY IN ARCTIC AND
TEMPERATE TERRAINS
6. DRAINAGE GEOCHEMISTRY
7. GEOCHEMICAL REMOTE SENSING OF THE SUB-SURFACE
8. LIFE CYCLE OF THE PHOSPHORIA FORMATION
9. BIOGEOCHEMISTRY IN MINERAL EXPLORATION
Handbook of Exploration and Environmental Geochemistry
VOLUME 9
Biogeochemistry in Mineral
Exploration
COLIN E. DUNN
Consulting Geochemist
Sidney, BC, Canada
Amsterdam Boston Heidelberg London New York Oxford
Paris
San Diego San Francisco Singapore Sydney Tokyo
Elsevier
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First edition 2007
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CONTENTS
Editor’s Foreword .......................................... XIII
Preface .................................................. XV
Chapter 1. Introduction ...................................... 1
Setting the scene. .................................. 1
Biogeochemistry and geobotany. . ...................... 1
General considerations and distinctions. . . .............. 1
History of geobotany.............................. 4
History of biogeochemistry . . . ...................... 5
Plant evolution and chemistry . . . ...................... 10
Barrier mechanisms . . .............................. 17
Chapter 2. Plant Function, Chemistry and Mineralogy . . .............. 21
Plant requirements . . . .............................. 21
Element uptake and function.......................... 24
Root form and controls on element uptake. . .............. 27
Summary comments on chemical requirements of plants . . . . . . 28
Mineralogy of plants . .............................. 30
Chapter 3. Field Guide 1: Climatic and Geographic Zones .............. 37
Selection of plant species. . . .......................... 37
Orientation . . . .................................. 38
Boreal (northern) forest . . .......................... 42
Black spruce .................................. 44
Balsam fir . . .................................. 47
Alder . ...................................... 48
Temperate coniferous forest . . . ...................... 49
Temperate deciduous forest . . . ...................... 50
Tundra. . ...................................... 51
Arid and semi-arid environments – general comments . . . . . . 52
North America – arid and semi-arid . .................. 52
Northern basin and range. . . ...................... 52
Southern basin and range, and desert of the southwestern
USA and Mexico. .............................. 52
Central America . . . .............................. 53
North Africa-arid – southern Morocco into the Sahara Desert 53
Mediterranean coast .............................. 53
Middle East – from Turkey and Armenia, through Saudi Arabia
to Pakistan, and Africa east of the Sahara. .............. 54
Central, West and South Africa ...................... 54
India . . . ...................................... 55
China, Mongolia and Japan . . . ...................... 56
Australia ...................................... 57
South America (excluding the Amazon) . . .............. 58
Humid tropics – Amazon, West Africa, Indonesia . . . . . . . . . 59
Summary notes . .................................. 60
Chapter 4. Field Guide 2: Sample Selection and Collection . . . .......... 63
General considerations .............................. 63
Seasonal variations . .............................. 66
Summary considerations of seasonal variations – a practical
approach ...................................... 72
Selection of tissue type .............................. 73
Element differences among plant species . . .............. 74
The inhomogeneity of trees . . . ...................... 77
Bark . . . ...................................... 81
Twigs . . . ...................................... 85
Foliage. . ...................................... 86
Trunk wood . . .................................. 89
Treetops . ...................................... 90
Cones. . . ...................................... 96
Stunted trees of the Tundra . . . ...................... 97
LFH/forest litter/humus. . .......................... 99
Flowers, seeds, spores and pollen . . . .................. 100
Summary . . ...................................... 102
Sample collection .................................. 106
Precautions. . . .................................. 106
Field accessories . . . .............................. 109
Sample bags . . .................................. 111
Sample size. . . .................................. 113
Samples required for quality control . .................. 113
Checklist for vegetation sample collection and site observations 114
Field drying and shipping .......................... 116
Alternative samples. . . .............................. 116
Saps.......................................... 116
VI
Contents
Fungi . . . ...................................... 119
Moss . . . ...................................... 120
Seaweed . ...................................... 122
Geozoology ...................................... 124
Chapter 5. Survey Design and Comparisons with Other Sample Media . . . . . 127
Introduction...................................... 127
Survey design . . . .................................. 129
Scale of survey . . .................................. 130
Low density (1 site per 10 km
2
or greater) – Reconnaissance level 130
Moderate density (1 site per 1–10 km
2
)................. 134
Semi-detailed surveys (1 site per 0.25–1 km
2
)............. 136
Detailed surveys (25–200 m spacing) . .................. 139
Comparisons with other types of geochemical survey. . . . . . . . . 143
Vegetation versus Soils . . .......................... 144
Vegetation versus Glacial Tills . ...................... 146
Comparison of multi-media reconnaissance-level surveys using
plants, soils, and sediments from lakes and streams . . . . . . . . 148
Summary . . ...................................... 149
Chapter 6. Sample Preparation and Decomposition. .................. 151
Introduction...................................... 151
Washing . . ...................................... 151
Thorough washing using solvents or dispersants .......... 151
Washing in water . . .............................. 154
Particle and sample size . . . .......................... 159
Sample decomposition .............................. 163
Dry ashing. ...................................... 165
Element volatilization . . . .......................... 165
Dry ashing – the realities . .......................... 169
A special case: Vegetation from sites near smelters or other sites of
point-source metal emissions .......................... 174
Wet decomposition . . . .............................. 178
Microwave digestion . . .............................. 179
Selective leaching .................................. 180
Fusions . . . ...................................... 185
Standard reference materials and analytical controls . . . . . . . . . 186
Summary . . ...................................... 189
Chapter 7. Plant Analysis . . .................................. 191
‘Fit for purpose’ . .................................. 192
Analytical techniques . .............................. 194
Analytical instrumentation . .......................... 196
VII
Contents
Atomic absorption spectrometry...................... 196
Inductively coupled plasma emission spectrometry (ICP-ES) . . 197
Inductively coupled plasma mass spectrometry (ICP-MS) . . . . 200
Instrumental neutron activation analysis (INAA) .......... 204
X-ray fluorescence (XRF) .......................... 208
Summary . . ...................................... 209
Chapter 8. The Eden Project – Source of a Biogeochemical Database. . . . . . 213
Introduction...................................... 213
Samples in the collection . . . .......................... 213
Soil in the biomes.................................. 214
Foliage collection from the biomes...................... 215
Chapter 9. Biogeochemical Behaviour of the Elements . . . .............. 229
Introduction...................................... 229
The importance of data quality . . ...................... 229
Elements in plants and their relevance to mineral exploration. . . 231
Aluminium (Al) . . . .............................. 232
Antimony (Sb) .................................. 233
Arsenic (As) . . .................................. 234
Barium (Ba) . . .................................. 236
Beryllium (Be). .................................. 237
Bismuth (Bi) . . .................................. 239
Boron (B)...................................... 240
Bromine (Br) . .................................. 241
Cadmium (Cd) .................................. 242
Calcium (Ca) . .................................. 243
Cerium (Ce) . . .................................. 244
Cesium (Cs) . . .................................. 245
Chromium (Cr) .................................. 246
Chlorine (Cl) . .................................. 248
Cobalt (Co) . . .................................. 248
Copper (Cu) . . .................................. 249
Dysprosium (Dy) . . .............................. 250
Erbium (Er) . . .................................. 250
Europium (Eu) .................................. 251
Fluorine (F) . . .................................. 251
Gadolinium (Gd) . . .............................. 251
Gallium (Ga) . .................................. 251
Germanium (Ge). . . .............................. 252
Gold (Au) . . . .................................. 253
Hafnium (Hf) . .................................. 257
Halogens (F, Br, Cl and I) .......................... 258
VIII
Contents
Holmium (Ho) .................................. 259
Indium (In). . . .................................. 259
Iodine (I) ...................................... 259
Iridium (Ir). . . .................................. 259
Iron (Fe) ...................................... 259
Lanthanum (La), the rare earth elements (REE) and yttrium (Y) 260
Lead (Pb) ...................................... 264
Lithium (Li) . . .................................. 266
Lutetium (Lu). .................................. 267
Magnesium (Mg) . . .............................. 267
Manganese (Mn). . . .............................. 268
Mercury (Hg) . .................................. 269
Molybdenum (Mo) . .............................. 275
Neodymium (Nd) . . .............................. 278
Nickel (Ni) . . . .................................. 279
Niobium (Nb). .................................. 282
Osmium (Os) . .................................. 283
Palladium (Pd) .................................. 283
Phosphorus (P) .................................. 283
Platinum (Pt) and the platinum group elements (PGEs) –
palladium (Pd), iridium (Ir), osmium (Os), rhodium (Rh) and
ruthenium (Ru) .................................. 285
Praseodymium (Pr) . .............................. 290
Promethium (Pm) . . .............................. 290
Potassium (K). .................................. 291
Radium (Ra) . .................................. 291
Rhenium (Re) . .................................. 292
Rhodium (Rh) .................................. 295
Rubidium (Rb) .................................. 295
Ruthenium (Ru) . . . .............................. 296
Samarium (Sm) .................................. 296
Scandium (Sc). .................................. 297
Selenium (Se) . .................................. 298
Silver (Ag) . . . .................................. 299
Sodium (Na). . .................................. 302
Strontium (Sr) .................................. 303
Sulphur (S). . . .................................. 304
Tantalum (Ta) .................................. 306
Tellurium (Te) .................................. 308
Terbium (Tb) . .................................. 310
Thallium (Tl) . .................................. 310
Thorium (Th) . .................................. 312
Thulium (Tm). .................................. 314
IX
Contents