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EXPLORATION GEOCHEMISTRY SHORT COURSE MANUAL

Newmont Exploration Limited

NEWMONT EXPLORATION LIMITED

EXPLORATION GEOCHEMISTRY

SHORT COURSE MANUAL

'bibliotec * CFtSO^L. PALACIOS C^ILl-C

Prepared by

J. Alan Coope Owen P. Lavin Erick F. Weiland Newmont Exploration Limited’ Geochemistry Department

and

Lloyd D. James Geochemical Consultant

July 1991 2nd Printing March 1993

'COPYRIGHT ©Newmont Exploration Limited 1991

TABLE OF CONTENTS

TABLE OF CONTENTS........................................................................

j

LIST OF FIGURES........................................................................ LIST OF TABLES........................................................................

v XIV

1.

INTRODUCTION........................................................................

2.

DEFINITIONS................................. t.....................................

2

3.

BRIEF HISTORY........................................................................

4

4.

INFORMATION SOURCES.................................................................

5

5.

BASIC PRINCIPLES...................................................................

7

5.1. 5.2. 5.3.

6. 6.1. 6.2. 6.3. 6.3.1. 6.3.2. 6.3.3.

7. 7.1. 7.2. 7.3. 7.3.1. 7.3.2. 7.3.3. 7.3.4. 7.3.5.

Geochemical Environment..................................................... Characteristic Element Abundancesand Associations......................... Element Associations of MineralDeposits....................................

7 8 14

DISPERSION PROCESSES..............................................................

18

General....................................................................... Primary....................................................................... Surficial Environment....................................................... Chemical Dispersion....................................................... Mechanical Dispersion . . . ,.................... Biological Dispersion.....................................................

13 18

WEATHERING AND SOIL DEVELOPMENT..................................................

General....................................................................... Factors and Processes....................................................... Examples of Surface Environments............................................ Arid and Semi-Arid.......................................................... Humid Tropics.............................................................. Temperate Maritime.......................................................... Continental Middle Latitudes.............................................. Higher Latitudes............................................................

19 25 26

27 27 27 33 33 35 3g 38 40

ii

8.

PRIMARY GEOCHEMICAL HALOES AND PATTERNS ASSOCIATED WITH MINERAL DEPOSITS.................................................................... 41

8.1. 8.2. 8.3.

General......................................................................... Plutonic Association.......................................................... Volcanogenic MassiveSulfide Deposits.......................................

41 42 45

8.4. 8.5.

Sedimentary Exhalitive Deposits............................................. Gold Deposits..................................................................

48 50

9.

SECONDARY GEOCHEMICAL PATTERNS ASSOCIATED WITH MINERAL DEPOSITS............................................................................. 54

10.

ROLE OF GEOCHEMISTRY IN THE MINERAL EXPLORATION SEQUENCE.............................................................................

10.1 10.2 10.3 11.

11.1. 11.2. 11.2.1. 11.2.2. 11.2.3. 11.2.4. 11.3. 11.3.1. 11.3.2. 11.3.3. 11.3.4.

12. 12.1. 12.2. 12.2.1. 12.2.2. 12.2.3. 12.2.4. 12.2.5.

Mineral Exploration Sequence................................................. Role of Geochemistry.......................................................... Integrated Exploration .....................................................

60 60 60 64

PROGRAM DESIGN AND PLANNING OF GEOCHEMICAL EXPLORATION PROGRAMS............................................................................. 66 General........................................................................ Conceptual Models............................................................ Principles................................................................... Objectives................................................................... Procedures................................................................... Examples..................................................................... Orientation..................................................................... Principles............................ •..................................... Objectives................................................................... Procedures................................................................... Examples.................. FIELD SURVEY PROCEDURES............................................................

General........................................................................ Sample Media................................................................... Rocks........................................................................ Soils........................................................................ Stream Sediments........................................................ Lake Sediments.......................................................... Glacial Sediments........................................................

66 68 68 69 69 69 75 75 75 76 82 89

89 90 ‘90 98 106 117 119

iii Vegetation.................................................................. Water...................................................................... Gases...................................................................... Particulates............................................................... Microorganisms............................................................. Animal Tissues...............................................................

129 146 151 159 160 161

13.

FIELD/LABORATORY LIAISON........................................................

162

14.

LABORATORY PROCEDURES.............................................................

163

12.2.6. 12.2.7. 12.2.8. 12.2.9. 12.2.10. 12.2.11.

14.1. 14.1.1. 14.1.2. 14.1.3. 14.1.4. 14.2. 14.2.1. 14.2.1.1. 14.2.1.2. 14.2.2. 14.2.3. 14.2.3.1. 14.2.3.2. 14.2.3.3. 14.2.3.4.

14.2.3.5. 14.2.3.6. 14.2.3.7. 14.3. 14.4.

15. 15.1. 15.2. 15.3. 15.3.1. 15.3.2. 15.3.3. 15.4.

Sample Preparation.......................................................... Drying...................................................................... Crushing and Grinding......... '........................................ Sieving................................................. ;................ Mineral Separation........................................................ Sample Analysis............................................................. Decomposition............................................................. Strong Acid Decomposition.......................................... Phase Selective Leaches (Partial and Sequential Extraction). . . Separation................................................................. Measurement............................................................... Colorimetry............................................................ Fluorimetry............................................................ Atomic Absorption Spectrophotometry.............................. Emission Spectroscopy - DC Arc (DC-ES) and Inductively Coupled Plasma (ICP-ES)................................ X-Ray Fluorescence Spectrometry (XRF).............................. Instrumental Neutron Activation Analysis.......................... Electroanalytical Methods (pH, Eh, and Specific Ion Electrodes,and Jerome Hg Analyser).................................. Data Reporting............................................................... General Conclusions........................................................

QUALITY CONTROL..........;.......................................................

General..................................................................... Principles................................................................... Procedures................................................................... Systematic Duplicate Analysis......................................... Standard Reference Samples.............................................. Duplicate Field Sample Analysis....................................... Recommended Procedure.....................................................

163 164 164 170 171 175 175 179 183 186 187 189 191 193

201 206 211 212 214 214 217

217 218 219 219 219 219 222

iv 16.

INTERPRETATION....................................................................

224

16.1. Definition and General Procedure.......................................... 16.2. Data Compilation.......................................................... 16.3 Geochemical Pattern Delineation........................................... 16.3.1. Data Display Maps........................................................ 16.3.1.1. Posting Geochemical Values.......................................... 16.3.1.2. Symbol Maps............................................................. 16.3.1.3. Contour Maps.......................................................... 16.1.1.4. Image Analysis........................................................ 16.3.1.5. Catchment Basin Maps.................................................. 16.3.2. Class Selection........................................................... 16.3.2.1. Data Specific..................... f.................................. 16.3.2.2. Serial................................. *.............................. 16.4. Geochemical Anomalies..................................................... 16.5. Statistical Analysis........................................................ 16.5.1. Univariate................................................................. 16.5.2. Multivariate............................................................. 16.6. Data Management............................................................. 16.7. Data Assessment and Integration..........................................

224 226 226 228 230 231 241 250 258 258 260 260 262 264 266 276 277 282

17.

FOLLOW-UP..........................................................................

283

18.

REPORT WRITING...................................................................

285

19.

LONG TERM STORAGE OF DATA ANDSAMPLES.............................

286

20.

CONCLUSIONS AND RECOMMENDATIONS.....................................

287

21.

LIST OF REFERENCES..............................................................

289

V

LIST OF FIGURES FIG 2.1

FIG FIG FIG FIG

5.1 5.2a 5.2b 5.3

FIG 5.4 FIG 5.4 FIG 6.1

FIG 6.2 FIG 6.3 FIG 6.4 FIG FIG FIG FIG

6.5 6.6 6.7 6.8

FIG 7.1 FIG FIG FIG FIG FIG FIG FIG FIG FIG

7.2 7.3 7.4 7.5 7.6 7.7 7.8 7.9 8.1

FIG 8.2

FIG 8.3 FIG 8.4 FIG 8.5

FIG 8.6 FIG 8.7

The stages of exploration geochemistry related to a "House of Cards"....................................................................................................... Geochemical Cycle.................................................................................... Location map............................................................................... . ... . Nickel content............................................................................................ Relationship between geology and the pattern of nickel in residual soil, Nguge region, Tanzania..................................... Element associations of some mineral deposits..................................... continued ................................................................................................ Approximate position of some natural environments as characterized by Eh and pH....................... t.................................................................. Eh and pH values of mine waters, (x) oxidized ore zone; (•) primary ore zone........................................................................... 21 Eh-pH for the system Zn-O-H-S-C....................................................... Fields of stability of solids and dissolved zinc species ........................................................................... 22 Eh-pH for system Au-CI-O-H ................................................................ Eh-pH for system Au-CI-O-H ............................................................... Fractional adsorption of metals............................................................. Absorption-desorption results with changing pH for Mn-oxide exposed to solutions of 10'3M Co.......................................... Distribution and extent of main types of weathering of silicate rocks.................................................................................. 29 Hypothetical soil profile showing the principal horizons........................ Map of the main zonal and intrazonal soils................... Fersiallitic profile (see general key) ...................................................... Profiles of ferruginous and ferrallitic soils (see general key)............... Profile of brown soil (see general key)................................................. Isohumic profiles (see general key)...................................................... Podzolic soil profile (see general key) ................................................. Ranker profile (see general key)............................................................. Some typical examples of general geologic settings of ore deposits..................... Diffusion aureoles around an orebody and a small vein, WisconsinIllinois Zn district............................................................... 42 Variation of K and Rb in barren and mineralized granitoids................. Variation of Rb:Sr and K:Rb in granitoids............................................ Relation between Sn content of granites and tin mineralization, eastern Australia............................................................... 44 Schematic diagram illustrating form of geochemical anomalies in rocks around massive sulfide deposits in New Brunswick, Canada. . Range and average of Cu, Hg, Zn, and Mn .......................................

3 7 11 12 13 16 17

21

22

23 23 24

25

31 34

36 36 38 39 40 40

41

43 43

47 48

vi

FIG FIG FIG FIG

8.8 8.9 8.10 8.11

FIG 8.12

FIG 9.1 FIG FIG FIG FIG

9.2 9.3 9.4 9.5

FIG 9.6 FIG 10.1. FIG 10.2

FIG 11.1

FIG 11.2 FIG 11.3 FIG 11.4

FIG 11.5

FIG 11.6

FIG 11.7

FIG 11.8 FIG 11.9 FIG 11.10

FIG 11.11

Distribution of O and Mn in limestone ............................................... Distribution of total Mn in limestone................................... 49 Geochemistry of the Jason Deposit................................... .. Alteration patterns, distribution of Au, Ag, Tl, W, Sb, As, and Hg in bedrock at Round Mountain, Nevada, U.S.A........................................ Distribution of Au, As, and Sb in rock chips and fracture coatings around the Pinson Mine, Nevada, U.S.A.................... 53 Classification and general characteristics of the principal types of surficial dispersion patterns............................................ 54 Syngenetic (clastic) patterns in residual overburden. .... . . . . Syngenetic (clastic) patterns in transported overburden.............. .. Principal types of dispersion patterns in surface drainage. ...... . . Syngenetic (clastic) pattern in, outwash fan and piedmont sheetwash alluvium................................................................. 57 Epigenetic patterns in transported overburden. Similar dispersion may also contribute to patterns in residual overburden. 59 Decision and activity stages from commodity selection to finding an ore deposit.................................................................... 61 Optimum relationships between geology and some associated disciplines, including exploration geochemistry, in an integrated mineral exploration program................................... 55 The stages of exploration geochemistry related to a "House of Cards"................................................................ 67 Simplified conceptual geochemical dispersion model showing formation of geochemical anomalies................................ 68 Idealized model for rock type change ................................ Model B1 (Cordillera). Idealized models for geochemical dispersion of mobile elements in well-drained and poorly drained ground residual soils (see Fig 11.3. for legend).......................... 71 Model E2 (Cordillera). Idealized models of the effect of chemical mobility of elements on th'eir dispersion pattern in till-covered areas (see Fig 11.3 for legend).................................................. 72 Idealized models for geochemical dispersion of mobile elements in areas of stratified drift............................................ Landform situation B. Complete deep weathered profile, moderate relief........................................................................ 74 Hypothetical frequency distributions .......................................... Profile distribution of Pb, Zn, and Sb ................................... Graphical representation of lead, zinc, and antimony over mineralized vein at 18 to 24-in. depth, Trench A................................ 83 Horizontal distribution of perchloric acid-extractable zinc as a function of size fraction in soils over lead-zinc mineralization, Ar Ridaniyak, Kingdom of Saudi Arabia.............................................. ’ 84

49 50

53

55 53 57

70

73

76 83

vii FIG 11.12 FIG 11.13 FIG 11.14

FIG FIG FIG FIG

12.1 12.2 12.3 12.4

FIG 12.5 FIG 12.5c FIG 12.6

FIG 12.7 FIG 12.8 FIG 12.9 FIG 12.11 FIG 12.10

FIG 12.12 FIG 12.13 FIG 12.14

FIG 12.15 FIG 12.16

FIG 12.17

FIG 12.18 FIG 12.19 FIG 12.20a FIG 12.20b

Summary of maximum gold dispersion trend obtained in the minus 80 m fraction of wadi sediments for 8 gold prospects. 86 Grain-size distribution of some eolian materials from the Central pediplain (Kingdom of Saudi Arabia)............................... 87 Stream sediment survey of River Sende, Sierra Leone. Data on -80 mesh fraction............................. 88 Cretaceous granitoids in the Canadian Cordillera ................................ Distribution of mean Zn content in granitoids ...................................... Simplified geology in the Goosley-Owen lake area ............................. Distribution of As and Cu around the Bradina and Goosley deposits ................................................................................ Carlin District, Nevada. Locations of samples collected for analysis. See Figure 12.5c for explanation of geologic symbols......................... Carlin District. Geological Legend........................................................ Example of ridge-and-spur soil-sampling pattern, Cebu Project, Republic of Philippines. Data on -80-mesh fraction............................. Example of base-of-slope sampling pattern, Lemieux District, Quebec. Data on -1cm fraction....................................... 99 Spatial variation of anomalous soil samples ..................................... Outlines of areas that contain anomalous values.............................. Detailed geochemistry (Zn) in the vicinity of the Perkoa Deposit, Burkino Faso. Values in ppm.............................................................. Regional soil geochemistry (Zn) in the area around the Perkoa Deposit, Burkino Faso. Values in ppm................................................. Reconnaissance laterite geochemistry over the Saddleback Greenstone Belt........................... Diagrammatic cross-section in lateritic duricrust. Comparison of Au anomalies in -6 + 2 mm lags and -6 mm soils, Eastern Goldfields Province, Western Australia................................................................................... Zinc anomalies in soils, Buchans District............................................. Empire Mining District, Colorado. Gold distribution in mull ash. Light stipple, ash contains 0.2-0.59 ppm gold; heavy stipple, ash contains at least 0.6 ppm gold. Heavy lines are veins.............. 107 Empire Mining District, Colorado. Gold distribution in soil (6-to 12inch depth). Light stipple, soil contains 0.2-0.59 ppm gold; heavy stipple, soil contains at least 0.6 ppm gold. Heavy lines are veins. Hemlo Gold District, Ontario. Williams Option - gold in humus. ... Hemlo Gold District, Ontario. Williams Option - gold in basal till, -250 mesh fraction........................ Water discharge of a river under ordinary conditions with normal amounts of water............................................................ 110 Water discharge of a river during a major flood. Overbank sedimentation takes place on the river plain................. 110

93 93 . 94

94 96 97 99

100 101 102 102 104 104

105 105

107 108 108

viii FIG 12.21

FIG 12.22

FIG 12.23

FIG 12.24a FIG 12.24b

FIG 12.25 FIG 12.26 FIG 12.27 FIG 12.28

FIG 12.29 FIG FIG FIG FIG FIG FIG

12.30 12.31 12.32 12.33 12.34 12.35a

FIG 12.35b FIG 12.36

FIG 12.37 FIG 12.38

FIG 12.39 FIG 12.40

A diagrammatic depiction of how geochemical dispersal patterns for active stream sediment and overbank sediment may be influenced by mineralization and sediment sources... 111 Hot nitric acid soluble Mo in overbank sediment, Norway. An anomalous sample down stream from the Nordli deposit is indicated with an arrow................................................................... 112 Geochemical results for the 1970-71 stream sediment survey. Que River Prospect, Tasmania............................................... 114 Sample location map for Magruder Mine area, Georgia............................................................................. 115 Downstream dispersion from zinc, copper, and lead in minus 80-mesh stream sediments and oxide coatings, Magruder Mine area....................................................... 115 Copper content of organic stream sediments in the Vehkavaara area, Pajala district.................................................................... 116 Cut-away section of sample bailer for lake-sediment sampling. ... Distribution of U in lake sediments in the vicinity of the Key Lake U-Ni deposit, Saskatchewan................................................. 118 Uranium (ppm) in lake sediments near the Rabbit Lake uranium deposit, Saskatchewan. Location of deposit shown by solid triangle............................................................................. 118 Distribution of Zn (ppm) in nearshore lake bottom materials, Agricola Lake area, N.W.T............................................................ 119 Gold in lake sediment, Cape Ray Fault area, Newfoundland............. Gold in lake sediment, White Bay area, Newfoundland...................... Simplified sketch of the reverse circulation drilling system............... Idealized geochemical dispersion model for lodgement till................ Diagrammatic overburden profiles in the Abitibi clay belt, Ontario. . Results of reverse circulation drilling from Golden Pond, Quebec.. 125 Results of the initial and follow up phases of reverse circulation drilling at Golden Pond East, Quebec......... 125 Owl Creek Gold Mine, Timmins, Ontario. Gold values for "Older" ti».......... 126 Owl Creek Gold Mine, Timmins, Ontario. Gold values for Matheson till...................................................................................... 126 Murphy-Hoyle J. V., Timmins area, Ontario, Canada. Gold in till anomaly plotted in relation to induced polarization/resistivity and horizontal loop electromagnetic survey results............ 127 Gold distribution in the -63 m and nonmagnetic heavy-mineral fraction of till associated with mineralization at Hemlo, Ontario. ... Comparison of the Au distribution in the heavy-mineral concentrate and the -63 m fraction of tills from Owl Creek, Ontario. 128

117

120 120 121 122 123

128

ix

FIG 12.41a FIG 12.41b FIG 12.42

FIG 12.43 FIG 12.44

FIG 12.45 FIG 12.46 FIG 12.47 FIG 12.48

FIG 12.49 FIG 12.50 FIG 12.51 FIG 12.52

FIG 12.53

FIG 12.54 FIG 12.55 FIG FIG FIG FIG FIG FIG

12.56 12.57 12.58 12.59 12.60 12.61

FIG 12.62

FIG FIG FIG FIG

12.63 12.64 14.1 14.2

FIG 14.3

Species distribution, geology along a transect across several zones of Helichrysum leptolepis (DC) occurrences in Witvlei area, Namibia. 133 Species distribution, geology along a transect across several zones of Helichrysum leptolepis (DC) occurrences in Witvlei area, Namibia. 132 Vegetation associations and Helicbrysum leptolepis (DC) occurrences over one area near Witvlei, Namibia....... 131 Copper values in surface soil in area shown in Fig. 12.42........ 134 Sample sites and contoured Au values for the Standard Hillarea, California. Gold in plants determined by INAA................................... 138 Base map showing site locations............................................... 139 Gold levels along traverse A .............................................................. 139 Variations in the gold content of a variety of organs in a balsam fir growing over mineralization, sampled at varying heights................... 140 Comparison for poorly drained ground for spruce, fir and B horizon soils.................................................... 141 Comparison for birch, alder, and B horizon soils ............................ 141 Comparison for freely drained ground for spruce, fir, and B horizon soils................................................... 142 Comparison for alder and B horizon soils.......... 142 Elements in ash of outer scales of spruce bark, Nova Scotia: (a) (above) gold, (b) (above) arsenic, (c) (next page) antimony, (d) (next page) selenium ........................................................................... 144/145 Regional uranium concentration levels in lake waters -(a) with and (b) without contaminated samples...................................... 149 (a) Radon and (b) uranium concentration levels in stream water without contaminated samples .......................................................... 150 Map showing distribution of molybdenum in ground water, Pima Mining District, Arizona................................................... 152 Correlation plots for groundwaters in Arizona. . . 153 The Track Etch Process. ;.................................................................. 155 Track Etch Sample Cup. .................................................................. 155 Radon contour map of the Lone Gull U discovery.............................. 156 Components of the Aurex Hg-vapor integrative detector.................... 157 Schematic representation of Hg-vapor measurement utilizing the Aurex detector...................................................................................... 157 Plan of simplified geology and COS dispersion pattern in surface microlayer at Johnson Camp, Arizona.......................... 158 CO2 content of soil air over mineralized breccia pipe, Arizona........... 159 Plot of log B. cereus................................ 160 Sample preparation safety curves for gold bearing materials............. 166 Size of sample required to contain an expected 20 particles of Au................................................................................. 167 Relation of Au grain size and grade for analysis............................... 168

X

FIG 14.4

FIG 14.5 FIG 14.6 FIG 14.7a FIG 14.7b FIG 14.8 FIG 14.9 FIG 14.10 FIG 14.11 FIG 14.12 FIG 14.13 FIG 14.14 FIG FIG FIG FIG FIG FIG FIG FIG

14.15 14.16 14.17a 14.17b 14.17c 14.17d 14.18 14.19

FIG 14.20a FIG 14.20b FIG 14.20c FIG FIG FIG FIG FIG FIG FIG FIG FIG

14.21 14.22 14.23 14.24 14.25 15.1 15.2 15.3 15.4

A Heavy-mineral concentration procedure using a shaking table followed-up by heavy liquid separation.......................... 173 Flow sheet from separation of sediment samples into magnetic (M) and nonmagnetic (NM) fractions.................................... 174 Schematic representation of the ability to release metals .............. Distribution of copper, molybdenum, and cold-extractable heavy metals in soils, Sheslay area, British Columbia............ 178 Distribution of copper, molybdenum, and cold-extractable heavy metals in soils, Sheslay area.......................................... 178 Schematic diagram of the classic Pb fire assay procedure......................................................................... 184 Linear working range........................................................................... Determination of As by generation of arsine...................................... Schematic diagram of atomic absorption spectrophotometers............................................................................. Errors in uncorrected and background corrected measurements of Pb............................................................................. Apparatus for AAS determination of elements................................. Cold vapor generation and determination of Hg by AAS.................................................................................................. A double beam mercury vapor meter................................................ Analysis by AAS. Sensitivities with respect tocrustal abundances Direct reading spectrograph with grating andD.C. arc source. . . . Photographic spectrograph with prism............................................... Inductively coupled plasma.................................................................. Direct current plasma........................................................................... Analysis of samples by DC-ES............................................................ Analysis by ICP-AES. Sensitivities withrespect to crustal abundances ........................................................................................ X-ray spectrometer. Wavelength dispersive........................................ X-ray spectrometer. Energy dispersive................................................ X-ray spectrometer. Portable unit with isotope source............................ Analysis by XRF. Sensitivities with respect to crustal abundances Detection limits by XRF at 95% confidence level. . Analysis by INAA. Sensitivities with respect to crustal abundances. A pH electrode and silver/silver chloride reference electrode............ Some of the pathways for preparation, dissolution and analysis of exploration samples.............................................................................. Random and systematic errors............................................................. Precision and accuracy.......................................................................... Graphical plot of duplicate analytical data............................................ Graphical plot of SRS analytical data....................................................

177

190 191 193 195 197

200 200 201 202 202 203 203 204 205 208 208 208 210 210 211 213 215 217 218 220 221

xi

FIG 15.5 FIG 16.1

FIG 16.2 FIG 16.3

FIG 16.4 FIG 16.5 FIG 16.6 FIG FIG FIG FIG FIG

16.7 16.8 16.9 16.10 16.11

FIG 16.12 FIG 16.13 FIG 16.14 FIG 16.15 FIG 16.16 FIG 16.17

FIG 16.18 FIG 16.19

FIG 16.20 FIG 16.21

Model for insertion of control samples to determine analytical accuracy and precision ............................................... 222 The stages of exploration geochemistry related to a "House of Cards"........................................................... 225 Diagrammatic representation of the data integration process in geochemical interpretation ..................................... 227 Map showing relation of Cu in dambos and outlet-stream sediments to location of ore horizon, Baluba area, Zambia. Data on -80-mesh fraction............................................................................. 229 Cu data obtained from the organic soil horizon samples at the end of the second field season (25 x 100 m grid).............. 230 Examples of sets of symbols used in point symbol geochemical maps........................................................ 231 Examples of point system and worm diagram representations ............................................................. 232 Sn content of -28 + 65 mesh soils.................................................... 234 Sn content of -80 mesh drainage sediments................................. 235 Nordkallott Project. Ni content of heavy mineralfraction of Tills . . 236 Distributions of Nb in stream sediments....................................... 238 Distribution of Be in stream sediment, Ishashaarea, south-western Uganda. (A) Indicates position of undisturbed pegmatite discovered by sediment sampling........................................................................... 238 Variation in nickel content of stream sediments derived from different areas of basic rocks...................................................... 239 Example of point symbol usage in a regional map.............................. 240 Gold in Till (-63 fraction) Geochemical Atlas of Finland.................... 242 Multivariate point-symbol maps: (a) pie diagram; (b) pseudo­ histogram; and (c) windrose representation................ 243 Stream sediment data displayed spatially in the form of KleinerHartigan trees................................................................. 243 Molybdenum distribution in soils as shown by sampling at a constant depth (mainly A horizon) and uniformly from the B horizon.......................................................... 244 Rectilinear soil sampling grid, Petolahti, Finland .............................. 244 Contour map for zinc (ppm) in 2156 B-horizon soil samples, Key Anacon, New Brunswick, Canada. Sample stations at 100 ft (30 m) along lines 400 ft (122 m) apart........................................................... 245 Example of moving window in two successive patterns ........................................................................ 246 Contour map for zinc (ppm) in B-horizon soil samples, Key Anacon, New Brunswick, Canada, averaged over 602 non-overlapping 400 x 400 ft (122 x 122 m) blocks........................................... 247

xii

FIG 16.22

FIG 16.23

FIG 16.24

FIG 16.25 FIG 16.26 FIG 16.27

FIG 16.28 FIG 16.29

FIG 16.30 FIG 16.31 FIG 16.32

FIG 16.33 FIG 16.34 FIG 16.35 FIG 16.36 FIG 16.37 FIG 16.38 FIG 16.39 FIG 16.40

FIG 16.41 FIG 16.42 FIG 16.43 FIG 16.44

FIG 16.45

Contour map for zinc (ppm) in B-horizon soil samples, Key Anacon, New Brunswick, Canada averaged over 300 non-overlapping 600 x 600 ft (183 x 183m) blocks............................................ 248 Contour map for zinc (ppm) in B-horizon soil samples, Key Anacon, New Brunswick, Canada, averaged over 186 non-overlapping 800 x 800 ft (244 x 244m) blocks............................................ 248 Examples of 8 nearest neighbors to a central grid node................................................................................ 249 920 lake sediment samples in a portion of NTS sheet 64N, Kasmere Lake Sheet.................................................................... 249 Contours of uranium in lake sediments............................................... 250 Distribution of cell averaged Zn in stream sediments........................................................................ 251 Distribution of gap filled unsmoothed Zn in stream sediments........................................................................ 251 Geochemical Atlas of Finland Ba contents in -62 m fraction of till................................................................................ 254 Geochemical Atlas of Finland Ni and Cu in -62 m fraction of till. . . . 254 Geochemical Atlas of Finland Alignment of geochemical patterns and significant mineral deposits........................................................... 255 Distribution of gold and pathfinder elements in southwest Scotland: (a) gold in pan concentrates; (b) arsenic; (c) antimony; (d) bismuth................................................................................................... 256 Plate 2. Image analysis of geochemical data for south west Scotland............................................................................................... 257 Samples localities, streams and catchment basins for a study area. 258 Maps showing (a) observed and (b) residual zinc values................... 259 Maps showing (a) Location of sample sites and (b) Spatial distribution of radon in lake bottom waters of "Dop" Lake............... 261 Hypothetical soil profile across a mineralized zone............................ 264 Hypothetical soil profile illustrating spurious anomalies related to geological and geomorphological complexities........... 265 Development of a break of slope anomaly, etc. in mountainous areas. Anomaly may have hydromorphic and clastic components. 265 Overlap of values in background and ore populations (derived as random samples from two log-normally distributed populations). . . 267 Definition of box-plot as a graphical display ..................................... 268 Empiracial distribution of Al and Mn displayed by EDA techniques . 268 Log probability plot of (a) a single background population and (b) of two combined populations .......................................... 269 Probability graphs (cumulative curves) for Zn and Cu in B horizon soil samples over the Daisy Creek strata-bound copper prospect, western Montana. Cumulated from high to low values . 270 Probability graph of Cu in soils......................................................... 271

xiii

FIG 16.46 FIG 16.47 FIG 16.48 FIG 16.49

FIG 16.50 FIG 16.51 FIG 16.51 FIG 16.52

Frequency curves for (a) normal, (b) lognormal, (c) normal with outliers and (d) multipopulation distributions................ Distribution of (x ± 1s)(x ± 2s), (x ± 3s) data for a normal population......................................................................... Relationship of mean, median and mode as determined by direction of skewness................................................................ • • Kurtosis nomenclature for peaked, normal and flat (bell-shaped) data distribution............................................................................................... Log10 transformed (a) vs untransformed (b) Mo data from a granite body .................................................................................................... Northern Fennoscandia Mineral Resource Assessment Map .......... Legend (continued) .................................................................. A diagrammatic representation of some typical factors which influence the selection and rating of significant geochemical patterns...................................................................................................

272 274 275

275 276 278 279

281

xiv LIST OF TABLES

Geochemical characteristics of selected elements. • • • • ................... 9 Average abundances (ppm - except where otherwise indicated) of selected elements in some common rock types..... 10 TABLE 5.3 Associated elements (pathfinders) useful in ore-typing.................................................................................................. TABLE 6.1 Relative mobilities of elements in the surficial environment.................. 20 TABLE 7.1 Types of climatic weathering................................................................... 30 TABLE 7.2 Plant associations.............................. 32 TABLE 8.1 Characteristic zoning patterns around some copper and molybdenum porphyry deposits. Zoning given is from the deposit outward. ..... 44 TABLE 8.2 Summary of change to lower case Local-scale geochemical responses in bedrock around some volcanic-and sediment-hosted massive sulfide deposits from recent literature.............. 46 TABLE 8.3 Summary of local and mine scale geochemical response from some elements in host rocks around massive sulfide deposits in Australasia, Europe and North America.................................. 47 TABLE 8.4 Characteristic geochemical responses for some gold deposits. .... 51 TABLE 10.1 Possible roles of some common geochemical survey sample media at various stages of mineral exploration......... 62 TABLE 11.1 Parameters to be derived from a properly planned orientation survey............................• • • •................ : ' ' ’;............. ' 78 TABLE 11.2 Major factors to be evaluated by an orientation survey in residual soil of transported overburden................... • • • •................... 79 TABLE 11.3 Check list of factors to be optimized by an orientation survey preparatory to rock sampling.......................... 80 TABLE 11.4 Check list of factors to be optimized and evaluated by an orientation survey preparatory to drainage sampling...... 81 TABLE 11.5 Check list of factors to be optimized and evaluated by an orientation survey preparatory to biogeochemical sampling............ 82 TABLE 12.1 Summary of elements................................. .••••;.............................. 92 TABLE 12.2 Checklist for the organization of a geochemical soil survey.............. 109 TABLE 12.3 Seasonal changes in the gold content of ashed alder twigs and leaves.......................... ••••••........................... :'' 135 TABLE 12.4 Basic rules to be applied at each sampling station when conducting a biogeochemical survey................. 137 TABLE 12.5 A summary for the application of hydrogeochemical prospecting in different environments............ .............. 147 TABLE 14.1 Potential contaminants from laboratory materials............................... 170 TABLE 14.2 Comparison table of U.S.A., Tyler, Canadian, British, French, and German standard sieve series............. ........................ 172 TABLE 14.3 Classification of some dissolution techniques useful in exploration geochemistry............................................... 176

TABLE 5.1 TABLE 5.2

XV

TABLE 14.4 Variation of Cr from different lithologies with five digestion procedures....................................................................... 180 TABLE 14.5 Accuracy of acid digestions ............................................................... TABLE 14.6 Comparison of six stream-sediment analyses for Ni........................... TABLE 14.7 Decomposition techniques for some resistantminerals.................. TABLE 14.8 Hypothetical examples of metal extracted (ppm) by "Total" and "Partial" methods from background and anomalous samples........... TABLE 14.9 Preferred analytical methods and analytical detection limits (ppm) for solid state geological materials at a typical major commercial geochemical laboratory (Chemex)................................. 188 TABLE 14.10 Some colorimetric reagents used in analysis of geochemical samples..................................................... 192 TABLE 14.11 Correction for background absorption in lead analysis of a synthetic rock solution............................................ 195 TABLE 14.12 Some interferences in the determination of trace elements in geological matrices by flame atomic absorption spectrophotometry. TABLE 14.13 Application of hydride generation to analysis of geochemical samples by atomic absorption spectrophotometry...... 198 TABLE 14.14 Characteristics of some specific ion electrodes (based on Orion Research literature) ..................................................... 213 TABLE 14.15 Evaluation of performance of analytical methods commonly used in exploration geochemistry........................................... 216 TABLE 17.1 Common failings encountered in follow-up of geochemical soil surveys............................................................................ 284

181 182 182 185

196

BIBI IOTEO CELSQ L. PALACIOS CAPft/LLQ

1.

INTRODUCTION

Although geochemistry is being used appropriately within many company exploration projects, more efficient and cost effective application could probably be often achieved if closer attention were given to certain critical fundamental principles. To assist attainment of this objective, the Geochemical Department will be organizing periodic geochemical workshops. It is intended that these will enable review of the fundamentals of exploration geochemistry as well as provide forums within which Newmont’s current geochemical practices can be objectively assessed, and possible improvements suggested and discussed.

This manual is designed to provide background material for the workshops and will be distributed to all participants. Obviously it is neither possible nor even desirable to cover the entire field of exploration geochemistry in this context, but basic principles and potential problem areas are briefly reviewed. The more rarely used methods, such as stable and radioisotope analysis, fluid inclusion analysis, laser induced luminescence, etc., are not discussed. Details of these, together with additional information on the more common methods can be found in specialist publications. This manual begins with a brief discussion of the history, basic principles and role of geochemical exploration. Subsequent sections provide more detailed discussions of the primary components of successful programs, including conceptual models, program design, technique selection, quality control, field and laboratory procedures, interpretation, follow-up, and last, but by no means least, report writing. A fairly extensive list of up-todate and useful references is provided in the final chapter.

Geochemical Department personnel are always available to assist in the planning and budgeting of exploration programs, and the selection and/or development of appropriate geochemical techniques. Consultation at an early stage could sometimes help prevent crises developing down the foad.

2 2.

DEFINITIONS

The objective of exploration geochemistry, or geochemical prospecting, is to apply the principles governing the distribution and migration of elements in the natural environment to the search for mineral deposits. Success is based on a fundamental premise, which is substantiated by extensive empirical data, that the chemical composition of certain constituents of the natural environment in the vicinity of a mineral deposit differ from those of similar constituents where there is no mineral deposit. Detection of these differences requires systematic measurement of one or more chemical or chemically influenced properties of a naturally occurring material. The property measured is most commonly the trace concentration of some chemical element or group of elements; however, it may sometimes also include molecular and isotopic compositions and bacterial counts. The naturally occurring material may be rock, soil, stream sediment, glacial sediment, surface water, groundwater, vegetation, microorganisms, animal tissues, particulates, or gases including air.

Although exploration geochemistry involves many of the basic principles of the science of geochemistry, it encompasses a far wider range of practical concerns. A geochemical exploration program comprises a number of critical phases (including design and planning, sampling, sample preparation, analysis, and interpretation), the relative importance and interdependence of which are clearly illustrated by the "house of cards" (Fig. 2.1). Each successive independent function is wholely dependent on those preceding so that errors or inadequacies in one will negatively effect all those that follow. For example, no matter how accurate and precise the techniques used for analysis or how advanced the statistical treatments and computer programs used for data handling and interpretation, problems resulting from inadequate or improper sampling and/or sample processing cannot be overcome.

Exploration geochemistry is of course only one of a cost effective number of techniques available to the exploration geologist which can assist in the location of concealed ore deposits, and also provide efficient coverage of large areas. It does, however, possess certain potential advantages over many others in that it generally depends on direct measurement of target or closely associated elements, rather than indirectly related phenomena. It must be emphasized that geochemical prospecting, like other mineral exploration techniques, is primarily a geological activity and must always be applied and interpreted within a sound geological framework. To do otherwise is to invite failure!

3

FIG 2.1

The stages of exploration geochemistry related to a 'House of Cards'. (Modified after Lavin. Grant, and Nichol, 1987)

4 3.

BRIEF HISTORY

It is clear from historical records that the principles of geochemical exploration have been applied in prospecting over several thousands of years. The prospector who panned for gold and traced the colors upstream to a bedrock source used mineralogical observations in a similar way to the modern geochemist, who utilizes careful sampling and sensitive chemical analyses to outline patterns of dispersion in the surficial environment. Geobotanical indicators were recognized as early as the eighth and ninth centuries (Boyle, 1967). The mid-sixteenth century writings of Biringuccio and Agricola describe the analysis of natural waters, springs, and their residues (Hawkes, 1957; Boyle, 1967).

Levinson (1974) records that modern methods of exploration geochemistry were first used in the early 1930's in the Soviet Union. Shortly thereafter the methods were applied in the Scandinavian countries, particularly Sweden. In North America, the earliest geochemical surveys were carried out between 1938 and 1940 by Lundberg in Newfoundland and in 1944 by Warren in British Columbia (Brummer et al., 1987). The first comprehensive geochemical exploration studies commenced at the US Geological Survey under the leadership of H. E. Hawkes in 1947 and at the Geological Survey of Canada with R. W. Boyle in the early 1950's. The Geochemical Prospecting Research Center was established at the Imperial College of Science and Technology in London in 1954 under the direction of J. S. Webb. In France, research related to exploration geochemistry began in 1955. The successful application and adaptation of geochemical exploration techniques in all parts of the world, the rapid development of analytical and computer technology, and improvements in field transportation have made geochemistry one of the more cost effective and widely applied exploration disciplines. Analytical capability is such that relatively rapid, sensitive analysis can be achieved for virtually all metals of economic interest. Continuing research is expanding our established capability to cost-effectively detect and interpret dispersion patterns related to mineral deposits in a wide variety of often complex environments.

Through multi-element analysis, geochemical data can reveal multi-parameter signatures related to distinct geological units and processes. This capability, when applied to rock samples, permits geological correlation as well as the more precise delineation of otherwise invisible alteration features related to mineralization. When applied to soil and other types of samples, multi-element data can help outline major geological units and, in some cases, identify the presence of mineralization buried under extensive cover (Hoffman, 1987).

5 4.

INFORMATION SOURCES

The body of technical literature in the English language dealing with exploration geochemistry has grown dramatically over the years, particularly since the founding in 1970 of the Association of Exploration Geochemists (AEG). This Association’s official technical publication (the Journal of Geochemical Exploration - JGE), and newsletter (EXPLORE), are excellent sources of useful information, especially when used in conjunction with the AEG Bibliography volumes (Hawkes, 1982, 1985, and 1988). The proceedings of various international (generally biennial) and regional symposia organized since 1970 by the AEG, are also useful references. Initially these were published as individual volumes by the local sponsoring organizations, but more recently have been presented in special volumes of the JGE: 1966 - Ottawa, Canada 1968 - Golden, U.S.A. 1970 - Toronto, Canada 1972 - London, England 1974 - Vancouver, Canada 1975 - Fredericton, Canada 1976 - Sydney, Australia 1978 - Denver, U.S.A. 1980 - Hannover, Germany 1982 - Saskatoon, Canada 1983 - Espoo, Finland 1985 - Toronto, Canada 1987 - Orleans, France 1989 - Rio de Janeiro, Brazil

(Cameron, 1967) (Canney, Bloom, and Hansuld, 1969) (Boyle, 1971) (Jones, 1973a) (Elliot and Fletcher, 1975) (Govett, 1976) (Butt and Wilding, 1977) (Watterson and Theobald, 1979) (Rose and Gundlach, 1981) (Parslow, 1983) (Bjorklund, 1984) (Garrett, 1987) (Jenness, 1989) (Rose and Taufen, 1991)

For many years the Institution of Mining and Metallurgy (London), and also occasionally the Canadian Institute of Mining and Metallurgy, have organized symposia on prospecting techniques. The main emphasis has generally been on geochemical exploration in glaciated terrain: 1973 1975 1977 1979 1982 1984 1986 1988

- Trondheim, Norway - Edinburgh, Scotland - Helsinki, Finland - Dublin, Ireland - St. John’s, Newfoundland - Glasgow, Scotland - Kupio, Finland - Halifax, Nova Scotia

(Jones, 1973b) (Jones, 1975) (IMM, 1977) (IMM, 1980) (Davenport, 1982a) (IMM, 1984) (IMM, 1986). (MacDonald, 1988)

6 Some attention has recently also been given to arid terrain: 1984 - Rabat, Morocco 1988 - Perth, Australia

(IMM, 1985) (AIMM, 1988).

Over the years the Journal of Exploration Geochemistry has included a number of extremely useful volumes dealing with conceptual geochemical exploration models for a variety of weathering environments. These discuss: (i) (ii) (iii)

(iv)

The Canadian Cordillera and Canadian Shield - (Bradshaw, 1975); Norden (Scandinavia and Greenland) - (Kauranne, 1976a); The Basin and Range Province of the Western United States and Northern Mexico - (Lovering and MacCarthy, 1978); Australia - (Butt and Smith, 1980).

The JGE has also produced a number of other useful special volumes, including: (i) (ii)

Exploration Geochemistry in the Appalachians (Govett, 1976); Geochemical Exploration in Arid and Deeply Weathered Terrain - (Davy and Mazzucchelli, 1984).

Thorough English language treatments of the basic principles of exploration geochemistry have been produced, amongst others, by Rose, Hawkes and Webb (1979) and Levinson, McCammon and Hitchon, (1980). Anyone involved in exploration geochemistry would be well advised to consider becoming a member of the Association of Exploration Geochemists. The annual dues are low and the publications received are of a generally high standard. They contain numerous useful case histories, review articles, descriptions of new techniques, etc., and should, in any case, be a prominent component of any mineral exploration library.

7

5.

BASIC PRINCIPLES

5.1.

Geochemical Environment

Geologically and geochemically the earth constitutes a dynamic system in which matter is moved from one place to another, and changed in form and composition by a variety of processes, including melting, crystallization, erosion, dissolution, precipitation, vaporization and radioactive decay. The geochemical cvde (Fig. 5.1) diagrammatically illustrates these complex physicochemical changes and the variety of pathways that earth material and their contained elements follow in response to these processes. It conven­ iently defines the major deepseated and surficial geo­ chemical environments which are distinguished by gross differences in pressure, temperature and chemistry.

The deep-seated environ­ ment extends downward from the lowest levels reached by circulating surface waters to the deepest levels at which normal rocks can be formed. It is characterized by high tempera­ ture and pressures, restricted circulation of fluids, and relatively low free-oxygen content (Rose, Hawkes and Webb, 1979). Magmatic and metamorphic processes pre­ dominate. In contrast, the surficial environment o f weathering, erosion and sedimentation at (or near) the surface of the earth is generally characterized by low tempera­ tures, nearly constant low pressure, free movement of aqueous solutions, and abundant free oxygen, water and carbon dioxide.

FIG 5.1

Geochemical Cycle. (Rose, Hawkes, and Webb, 1979)

8

The great majority of geochemical prospecting programs have been concerned with the surficial environment as this is the most readily accessible. However, improved exploration technology and the exhaustion of near surface exploration potential, particularly in some of the more developed mineral districts, is now resulting in greater attention being given to the deep-seated environment. Geochemists have long recognized systematic behavior amongst certain element groups and established classification schemes based on observed natural groupings (Goldschmidt, 1923 and 1954, and Table 5.1). These are:

(i) (ii) (iii) (iv) (v)

siderophile, affinity for iron, concentrated in the Earth’s core; chalcophile, affinity for sulfur, concentrated in sulfides; lithophile, affinity for silicates, concentrated in the Earth’s crust; atmophile, present as gas in the atmosphere; biophile, occurring as biological material.

In the recent past, modified versions of Goldschmidt’s classification have been developed which cover more of the observed complexities (e.g. Table 5.1). In practice these can assist the recognition of geochemical environments with which specific mineral deposit types might be associated. 5.2.

Characteristic Element Abundances and Associations

Individual rock types display characteristic average element abundance levels and associations (Table 5.2). For example ultrabasic rocks generally contain relatively high Co, Cr and Ni and low Ba, F, Ga, Pb, Ti, TI compared to other common rock types. On the other hand basic rocks are characterized by relatively high Ag, Cu, Ti, V. The contrast between the element abundance levels in adjacent major rock units is sometimes so pronounced that regional geochemical concentration patterns related to bedrock, or even derived surficial material (e.g. soils, and stream sediments), closely reflect local and regional geology (Figs. 5.2a, 5.2b, and 5.3). The fact that some rock types contain relatively high concentrations of certain elements which are significant in geologic, but not economic terms, obviously needs to be taken into account when interpreting data from geochemical exploration programs. In exploration geochemistry the normal element abundance level in an unmineralized earth material is commonly referred to as the geochemical background for that particular material. However, as element distribution in specific earth material (e.g. rock, soil, stream sediment, etc.) is rarely uniform, even when it is derived from an apparently homogeneous source, it is more realistic to visualize background as a range rather than an absolute value. Any departures from normal ranges, be they positive or, more rarely, negative, are viewed as anomalous. The upper and lower limits, above or below which, respectively, values are considered to be anomalous, are defined as thresholds.

9

GEOCHEMICAL CHARACTERISTICS OF THE ELEMENTS Goldschmidt's clasS'f'Cahon

Siderophile

Chalcophile

Lithophile

Atmophile

Biophile

TABLE 5.1

Au Ge C Mo Re Fe Ru Os

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