Exploration Geochemistry Design and Interpretation of Soil Surveys

187 Pages·2016·32.7 MB·English

by  [Rev. in Econ Geol]

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EXPLORATION
GEOCHEMISTRY: DESIGN
AND INTERPRETATION
OF SOIL SURVEYS

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REVIEWS IN
ECONOMIC GEOLOGY

Volume 3

W. K. Fletcher, S. J. Hoffman, M. B. Mehrtens
* A. J. Sinclair & I. Thomson

CONTENTS

GETTING It RIGHT 1. Thomson
THE SOIL SURVEY—DESIGNING AN EXPLORATION PROGRAM S.J. Hoffman
Soll. SAMPLING S.J. Hoffman
ANALYSIS OF SOIL SAMPLES W. K. Fletcher
STATISTICAL INTERPRETATION OF SOIL GEOCHEMICAL DATA A. J. Sinclair
MODELS, INTERPRETATION, AND FOLLOWUP S.J. Hoffman & L. Thomson
CASE HISTORY AND PROBLEM. I

THE TONKIN SPRINGS GOLD MINING DISTRICT, NEVADA, USA M. B. Mehrtens
CASE HISTORY AND PROBLEM 2:

CokD-Y-BRENIN PORPHYRY COPPER, NORTH WALES, GREAT BRITAIN M. B. Mehrtens
CASE HISTORY AND PROBLEM 3:

THE VOLCANOGENIC MASSIVE-SULFIDE TARGET S.J. Hoffman
CASE HISTORY AND PROBLEM 4

THE VOLCANOGENIC MASSIVE SULFIDE, A SECOND EXAMPLE S.J. Hoffman
CASE HISTORY AND PROBLEM 5:

A COPPER PROPERTY S.J. Hoffman

Series Editor: James M. Robertson
REVIEWS IN ECONOMIC GEOLOGY

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FOREWORD

Volume 3 of Reviews in. Economic Geology—Exploration
Geochemistry: Design and Interpretation of Soil Surveys
represents a major effort by ‘and contribution from the Asso-
Gation of Exploration Geochemists (AEG) and especially its
Vancouver connection. The volume draws extensively on
the cumulative teaching, research, and industry experience
fits five authors, and it contains numerous ‘real-life’ exam-
ples of exploration failures as well as successes, A prelim:
Prcry version of this volume served as the text for a jointly
Spansared Society of Economic Geologists (SEG)-AEG Short
Course that was given in F , prior to the com
bined winter meeting of the SEG and annual meetings of
the Society of Mining Engineers and A.J.M.E. in Denver,
Colorado.

thas been a special pleasure to work with W. K. Fletcher
(Department of Geological Sciences, U.B.C.) whose patience
And sense of humor survived the herculean task of initial
text and figure assembly, He met his deadlines despite the

vagaries of changing figure specifications, colleagues’
schedules, and the Canadian Postal System.

Volume 3 has benefited greatly from the professional
attentions of Carol Hjeliming (New Mexico Bureau of Mines
and Mineral Resources editing staff) who now serves 2 the
part-time official assistant to the Series Editor. In addition’
to performing more traditional editorial chores, Carol has
been instrumental in setting up the procedures and print
codes that allowed us to utilize the computer-driven type=
setting equipment of the University of New Mexico Printing
Plant.

Finally, I wish to acknowledge the continuing support,
both moval and economic, of the New Mexico Bureau of
Mines and Mineral Resources and its Director, Frank Kott=
lowski.

James M. Robertson
Series Editor
Socorro, N. Me
April, 1987
CONTENTS sar

FOREWORD

THE ULTIMATE bbeala ti DIAMOND DRILL
PREFACE, PROGRAI

BIOGRAPHIES aC
THE EprrHerMAt GoLo Depostr. . 3
Chapter 1—GETTING IT RIGHT, CONCLUDING SUMMARY «0... 33
INTRODUCTION ... .. 1 ANSWERS TO EPITHERMAL GOLD DEPOSIT i
CHOICE OF METHODS 1 QUESTIONS . 33
OPTIMIZING SURVE 2 REFERENCES 38
BASIC OBJECTIVES - 2
Optimum Target Identificatio 2 cn) ter 3—SOIL SAMPLING
Maximum Geochemical Contras 3 INTRODUCTION ..... Aico
5 THE SOIL SURVEY AS PART OF THE EXPLORATION
Cost Effectivenes: 6 PROGRAM. ni cecgn anime
JRVEY PARAMETERS 7 AN EXPLORATION EXAMPLE—THE “QUICK

10 DIRTY” VERSUS THE “SLOW AND

10 PROFESSIONAL” APPROACH .c10.000secsuecesees ML
10 GEOCHEMICAL FACTORS AFFECTING TRACE

10 ELEMENT DISTRIBUTION: SOIL

10 DESCRIPTIONS. ,
u SAMPLE TYPE. +++»
W SAMPLE NUMBER ., .-
DESCRIPTION OF THE A\ iW TOPOGRAPHY, .
ASSUMED . 11 Sire DRAINAGE AND GROUNDWATES SEEPAGE
Quesnions. i Ge OVERBURDEN ORIGIN %

Soit PH .

Su
ORIENTATION STUDIES
The Orientation Si

A Literature Study

A Theoretical Orientation
SURVEY ORGANIZATION AND OPERATION
PROBLEM 1; MOLYBDENUM IN SIERRA LEON!
Owjectivi

Ree
45

z

OBJECTIVE...
DESCRIPTION OF THE AREA,
ASSUMED .....+50 ++ i
QUESTIONS.
EFE!

12 Soi HORIZON
13 Rock Tyre.
CONTAMINATION
COARSE FRAGMENTS.
GAMMA COUNT AT SAMPLE SITE...
Chapter 2—THE SOIL SURVEY—DESIGNING AN OTHER PARAMETERS—COMPOSITION ANDYOR SITE ~
EXPLORATION PROGRAM ee
INTRODUCTION .
PHASE 1—THE OFFICE
THe UNCONFORMITY-1 RELATED Uns
THe EprrHerMat Gop Deposit.
PHA THE FIELD ORIENTATION VIS)
THE UNCONFORMITY-RELATED URANIUM DEPOSIT ..
Introduction
Athabasca Basi
Thelon Basin.
Hornby Bay Basin
The Preliminary Field V
THe EprrirrMAt Got Derostr.
CONTINUED OFFICE PLANNING ....
THe UNc NORM Ret ATED Uranium Deroste
THE
REGIONAL EXPLOR: TION %
THe UNCONFORMITY-RELATED URANIU!
THE ErrHerMAL Goup Depostr .
THE ROUTINE SOIL SURVEY .....
THE UNCONFORMITY-RELATED URAN'
THE EprrtieRMat GOLD Depostr...

APPENDIX I.
21 APPENDIX II
22 APPENDIX Ill

22 Chapter 4—ANALYSIS OF SOIL SAMPLES.
23. INTRODUCTION .
24 DISTRIBUTION OF
24 SAMPLE PREPARATION, .
25 SAMPLE DECOMPOSITION
INTRODUCTION « ..+-5
STRONG DECOMPOSITION
PARTIAL EXTRACTIONS
ANALYTICAL METHOD
QUALITY CONTROL AND RELIABILITY........-.....
RANDOM ERRORS AND PRECISION . x
SysreMAnic ERRORS .
CONTAMINATION

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uM Deposit
REVIEWS IN
ECONOMIC GEOLOGY

(ISSN 0741-0123) Volume 3

EXPLORATION
GEOCHEMISTRY: DESIGN
AND INTERPRETATION

in cooperation with
The Association of Exploration Geochemists

ISBN 0-9613074-2-0

The Authors:
W. K. FLETCHER S. J. HOFFMAN
Department of Geological Sciences Selco Division
6339 Stores Road BP Resources Canada Limited
University of British Columbia 700-890 West Pender Street
Vancouver, BC Canada, V6T 2B4, Vancouver, BC Canada, V6C 1KS.

A. J. SINCLAIR
Department of Geological Sciences
6339 Stores Road
University of British Columbia
Vancouver, BC Canada, V6T 2B4.

M. B. MEHRTENS
U.S. Minerals Exploration Company
141 Union Boulevard, Suite 100
Lakewood, Colorado 80228

I. THOMSON
Placer Development Limited
1055 Dunsmuir Street
Vancouver, BC Canada, V7X IPI.

Series Editor: JAMES M. ROBERTSON
New Mexico Bureau of Mines & Mineral Resources

Campus Station
Socorro, NM 87801

QOCIRTY OR RCONQOMIC GRO! ORICTS
AN
EXPLORATION
REFERENCES ..

Chapter 5—-STATISTICAL. INTERPRETATION OF
SOIL GEOCHEMICAL DATA

Percentiles - 100
HistoGkAM a 100
CONTINUOUS DISTRIBUTION: ; 100
STANDARD NORMAL DISTRIBUTION 101

LOGNORMAL DISTRIBUTIONS - -«
Firtinc A NORMAL Curve TO A HistoGRAM -
CUMULATIVE DISTRIBUTIONS
Connpence Limits
F anv T Tests .
Prosasitry GRAPHS:
CORRELATION .
INTRODUCTION «..-0<05senssenerss
ANALYSIS OF A MATRIX OF CORRELATION
COEFFICIENT Seeds seseees
“CORRELATION” OF POPULATIONS «..-.-++
CorkeLaTions AMONG Prrcentace Dat.
AUTOCORRELATION Reaeeses ret
PosstpLe PROBLEMS IN| CORRELATION STUDIES ..
SIMPLE LINEAR REGRESSION
INTRODUCTION bee
SUNOMARY OF FORMULAE. ..<.+.020200e000 5
SOME APPLICATIONS OF LINEAR REGRESSION
Decree oF Fr « eacatensnee

ERRoS IN Bort VARIABLES ..
(CHI SQUARE DISTRIBUTION
INTRODUCTION +
GOopNess OF F1
Two-way Co
FINAL REMARKS .
REFERENCES:

ENCY TABLES.

‘Chapter 6—MODELS, INTERPRETATION, AND.
FOLLOWUP
MODELS ... 5 rs

Be erie tisos 17
GENERAL BACKGROUND ..... 17
LANDSCAPE GEOCHEMISTRY . 117

IpEAuze Mopeis
EXAMPLES...
APPLICATIONS « -
INTERPRETATION ......--
LANDSCAPETOPOGRAPHY

PH-EW/ELEMES Mositrry-
ANOMALY FOLLOWUP.

REFERENCES ...

Chapter 7—CASE. HISTORY AND. PROBLEM 1: THE
TONKIN SPRINGS GOLD MINING DISTRICT,
NEVADA, U.S.A. «000 0ser4eree 9

Chapter 8—CASE HISTORY AND PROBLEM 2:
COED-Y-BRENIN PORPHYRY COPPER,
NORTH WALES, GREAT BRITAIN «...++++

Chapter 9—CASE HISTORY AND PROBLEM 3: THE
VOLCANOGENIC MASSIVE-SULFIDE TARGET

PRELIMINARY STUDIES 139
FIELD ORIENTATION. 139
CONTINUED OFFIC PLANNING 141
PROPERTY EVALUATION .- 141

‘ANOMALY FOLLOWUP—DRILL TI TING. .

ANSWERS.
SUMMAI = 146
REFERENCES ..- 146
Chapter 10—CASE HISTORY AND PROBLEM 4:

THE VOLCANOGENIC MASSIVE SULFIDE,

A SECOND EXAMPLE
PRELIMINARY STUDIES... 147

FIELD OBSERVATIONS ... ¥
CONTINUED OFFICE PLANNING -
PROPERTY EVALUATION ...
ANOMALY FOLLOWUP-—DRIL!
ANSWERS...
SUMMARY...

Chapter 11—CASE HISTORY AND PROBLEM 5:
A COPPER PROPERTY

PRELIMINARY STUDIES

FIELD ORIENTATION.
NortH Cirque -
Nori CREEK. .
Norm Tir. =
TABLETOP HIGHLANDS
Souti CIRQUE.
Main VALLEY

LORATION
OFFICE PLANNING
JALUATION ..
GEOLOGY .. 2 5
(GEOPHYSICAL SURVEYS
Son, GEOCHEMISTRY PSOE
ANOMALY FOLLOWUP—DRIL
ANSWERS. ...-05000005 .
SUMMAR'
Ri z

TABLES OF CONVERSION FACTORS . Inside back cover
PREFACE

The principles and practical considerations underlying
utilization of soils as a medium for exploration geochem-
istry are well described in several textbooks, Moreover, not
only are soil surveys routinely undertaken in such diverse
environments as tropical Tntereae and arctic permafrost,
soils are probably the most frequently collected and ana-
lyzed medium in exploration geochemistry. What, then, is
the justification for devoting the third volume in the Society
of Economic Geologists Reviews in Economic Geology to this
apparently routine, well established prospecting method?

Unfortunately, it is the experience of the contributors to
this volume that effectiveness of soil surveys is often com-
promised when the conceptual simplicity of the method
leads to its unthinking application, For example, failure to
appreciate the characteristics of the geochemical environ-
ments of a landscape can lead to collection of the wrong
sample material or choice of unsuitable methods of sample
preparation and analy imilarly, emphasis on speed rather
than quality of sampling, rigid adherence to standard lab-
oratory methods, and simplistic interpretations of high yal-
ues can result in exploration dollars being wasted on false
anomalies while genuine, but more subtle, anomalies go
unrecognized or are assigned low priorities. In contrast to
the foregoing, rational application of soil surveys depends
on the successful selection and linkage of appropriate meth-
ods of sample collection, analysis, and interpretation—often
on the basis of an initial orientation survey. Decisions must
be made at each step and an error at any single step may
jeopardize the entire exploration effort,

Chapters in this volume discuss each step in the soil
survey from sample collection through analysis and statis-
tical interpretation of the data to selection of targets for
followup. Factors to be considered and the decisions that
must be made are illustrated by numerous examples and
case histories. However, rather than presenting the case
histories in a simple narrative fashion, we have attempted
to challenge the reader, by asking questions as each case

history unfolds, to become a participant in the
process. In some—but not al we have:
answers (or our opinions as to what reasonable ans\
might be). The case histories are largely from our ownt
rience and many reflect our geographical ;
northern glaciated A We do not believe this to |
deficiency insofar as this volume is intended not as pai
prehensive guidebook to interpretation of soil. but
as an troduction to undertaking surveys in a 1

and logical fashion, Indeed this volume will be a success if
its omissions provoke you into asking similar (though not
necessarily the same) questions of your own geochemical,
landscapes and soil pede
ACKNOWLEDGEMENTS—In Heepare this volume the
authors were assisted by many individuals and organiza-
tions who ey contributed ie time, technical facil-
ities, experience, and comments. We are especiail eful
to carteapedlve enpiee for their Suppartand fre
to use company oe ay tories: kite when Choe ‘were not
entirely flattering. many who encouraged and assisted,
the following deserve oe mention: Riofinex and CARGO |
Partners for giving M. B. Mehrtens use of the Coed
Brenin and Tonkin Springs case histories, respectivel
Selco, D. K. Mustard, C, M. H, Jennings and G. G.
for their assistance to Stan Hoffman; and Placer
‘ment Limited for their support of lan Thomson's contri-
butions, Donna M. Baylis greatly assisted K. Fletcher in
Chi and preparing the text, Finally, we must acknowl
edge the patience of Jamie Robertson, Series Editor, Reoiews
int Economic Geology, and the support of both the Association.
of Exploration Geochemists and the Society of Economic
Geologists. .

W. K. Fletcher

Chairman

Short Course Committee

Association of Exploration Geochemists
BIOGRAPHIES

W. K. FLETCHER received both his B.Sc. in Geology and
Ph.D. in Applied Geochemistry at the Imperial College of
Science and Technology, University of London. He joined
the tment of Geological Sciences, University of British

rolumbia in 1968 and is now an Associate Professor. During
Jeaves of absence he has been Chief seochemist to MIN-
DECO (Zambia) and Geochemist and Team Leader to the
United Nations Project at the Southeast Asia Tin Research
‘and Development Centre in Malaysia. He is an author of
more than fifty scientific papers on applied geochemistry
fand of a textbook Analytical Methods in Geochemistry Pros-
pecting. He is a former council member of the Association
‘of Exploration Geochemists and is the current Chairman of
the association's Short Course Committee.

STAN J. HOFFMAN received his B.Sc. in Geology and
Chemistry from McGill University and his M.Sc. and Ph.D.
in exploration geochemistry at the University of British
Columbia. He has more than twenty y’ of field-related
experience working for a number of mineral exploration
companies including INCO, Amax, Rio Tinto and BP Min-
erals. He is currently Senior Geochemist for the Selco Divi-
sion of BP Resources Canada Limited and is based in
Vancouver. He has actively advanced use of geochemistry
‘by the mineral exploration community through short courses,
organization of symposia (GOLD-81 and GEOEXPO/86) and
compilation of a manual on “Writing Geochemical Repo
{Association of Exploration Geochemists, Special Volume
12). He is a Member of Council of the Association of Explo-
ration Geochemists and President of the AEG for 1987-1988.

MIKE B. MEHRTENS has a B.Sc. in Geology and received
his Ph.D. in Applied Geochemistry (1966) from the Imperial
College of Science and ‘Technology, University of London.
He has been employed in mining and exploration for base
and precious metals in Zambia, South Africa, the United
Kingdom, Saudi Arabia, and Panama. He is currently Pres-
ident of U.S. Minerals Exploration Company (USMX) based.
in Denyer, Colorado

ALASTAIR J. SINCLAIR, P. Eng., has had 24 years of
teaching, research, and consultancies in the mineral indus-
try. He has taught economic geology, geological data anal-
ais, and geostatistics during a 22-year career in the
partment of Geological Sciences, The University of Brit-
ish Columbia, where he is now Professor and Head of
Department. During that period he has been involved in a
broad range of local and international consulting for numer-
ous mining companies as well as the Provincial government
and the United Nations, particularly in the fields of mineral
property evaluation, mineral exploration data analysis, and
geostatistical ore reserve estimation. His research and field
work since the late 1950's has led to more than 100 scientific
and technical publications, many of which have direct appli-
cation to exploration for and evaluation of mineral deposits,
Dr. Sinclair has served in executive capacities for a variety
of professional organizations including The Canadian Insti-
tute of Mining and Metallurgy, The Mineral Deposits Divi-
sion of the Geological Association of Canada, and the Society
of Economic Geologists and is active in the Association of
Professional Engineers of British Columbia.

IAN THOMSON received his Ph.D. in Applied Geochem-
istry for research at Imperial College of Science and Tech-
nology, University of London. On graduation he joined
Barringer Research Limited where, over an eight-year period,
he was involved in the development of field and analytical
techniques in geochemistry, and consulting and project work
in Canada, the U.S.A., Central and South America, the
southwest Pacific islands and the Middle East. In 1978 he
joined the Ontario Geological Survey where, for three years,
he was involved in a number of studies including deep-
overburden-till sampling in the Abitibi Clay Belt and an
examination of the impact of acid rain on the geochemistry
of lakes. He joined Placer Development Limited in 1981 as
Senior Geochemist and later became Manager Western Can-
ada Exploration based in Vancouver. In 1987 he joined Pan
Orvana Resources as Chief Geologist. He is a former Pres-
ident of the Association of Exploration Geochemists and
the Canadian Geoscience Council and is author of numer-
ous publications on applied geochemistry.
Chapter 1

GerTinG It RIGHT

I. Thomson

INTRODUCTION

Asmineral exploration becomes increasingly difficult, costly
and competitive, success is essential; there is no room for
waste or inefficiency. Exploration must be truly cost effec
tive. The present book is concerned ultimately with the
interpretation of geochemical surveys. However the data to
be interpreted are the product of the field survey and thus
only as good as the work that went into these earlier phases.
The truism “garbage in—garbage out” is as relevant here as
anywhere.

Every exploration geochemical survey has three com:
ponent parts

(1) Sampling
(2) Analysis
(3) Interpretation

These are independent yet interdependent functions.
Failure to execute one step correctly will negate all efforts
in the succeeding steps. By and large the function that is
most costly, and ‘certainly most difficult to repeat, is the
field survey. Any deficiences at this stage will have fatal
effects on the remainder of the project. Analysis of the sam-
ples is, indeed, costly and an area of necessary concem.
However, if samples have been collected properly it is not
unreasonable to suppose that they can be reanalyzed should
this be deemed necessary or useful. Ultimately interpre-
tation, provided that sampling and analysis are reliable, is
an exercise that can be repeated many times using a variety
of techniques or models depending on supplementary
information available and the skills and prejudices of var-
ious geologists or geochemists.

The design and execution of a geochemical survey is thus
crucial to its success. Surveys can be, and are, optimized
to find specific targets in particular environments. Such fine
tuning requires an understanding of applied geochemistry,
knowledge of the environment in which the survey will be
carried out and an appreciation of the target being sought

Before considering these points in more detail, itis worth
defining the nature of a geochemical survey in more general
terms and establishing clearly the role of the survey in an
exploration program

The basic premise of exploration geochemistry is that the
systematic sampling and analysis of naturally occurring
materials will reveal features indicative of the presence of

potentially economic mineralization. This is a
simple statement for it begs the questions—what mal
should be sampled?; how and for what entities should these
samples be analyzed?; and what features will be revealed?
We will consider these points in more detail in later Sections.
The key wording here is “systematic sampling and anal-
ysis.” Regular and consistent application of a technique across
‘a property should produce a common database, a synoptic
picture of the distribution of elements or compounds, that
‘will meet the twin objectives of any exploration survey:

(1) Identification of targets likely to represent
dain! significant mineralization.
(2) Confident elimination of barren ground.

Itis thus important to know both the advantages and the
limitations of any survey or survey Lat A good geo-
chemist should be able to interpret every feature on a geo-
chemical map: the lows as well as the highs. This is not
always the case. A frightening number of dollars have been
Spent on conventional soil surveys over areas of deep trans-
ported overburden. The resulting geochemical patterns are
Spiel, flat and uninteresting. Many interpretations have
concluded, wrongly, that the absence of a geochemical
response proves that these areas haye no economic poten-
tial. This is a false assumption since such a survey technique
is inappropriate for these conditions.

It is the experience of the writers of this manual that,
today, the majority of geochemical surveys are carried out
mechanically with litte thought of the suitability of the
techniques employed. Frequently a stock “recipe” is used—
“B" horizon soils, sieve to minus 80 mesh, anah for so
many elements, look for the high numbers. Relatively little
effort is required to significantly increase the effectiveness
of your surveys.

CHOICE OF METHODS

From the outset, the selection of any technique is depend-
enton the mineralogy and geochemistry of the ta
sought. The composition of a mineral body will determine
the elements that can be used, Copper is clearly ideal for a
copper deposit, but for arsenic to be useful in a gold search:
it must be present in the gold mineralization. Newey is
only useful for mercury-bearing bodies of mineralization,
etc, ete. Further, the mineralogy of the target, in combi-
> Cuarrer 1

ion with the secondary environment, will determine the
ae ‘of dispersion. For camp copper dispersion is both
Thydromorphic and ‘mechanical while tin, typically, is almost
entirely mechanical as grains of cassiterite, with a further
contribution from tin in biotite and other accessory min:
erals.
The second
‘of the target

int to consider is the relative disposition
jis may be characterized (Figure By as io)

wutcropping ore, (2) partially outcropping ore, (3) burie
paged a vba cover, and (4) blind ore bodies
completely concealed within their host rocks. Clearly, dif-
ferent techniques are required for these various conditions,
Direct surficial sampling will be effective in cases (1) and
(2) although rather different geochemical responses should
be anticipated. Cases (3) and (4) demand optimized tech-
niques that will see through cover, search beneath cover,
sniff gases seeping from mineralization, detect leakage or
identify halos in the surrounding, rocks.

SAPONTION OF ORE OFFONITS

FIGURE 1.1—The variable disposition of mineral deposits with
respect to the present day daylight surface, For explanation see
text,

Then there is the scale of application. Geochemical sur-
veys are used at various stages in mineral exploration with
four levels of intensity readily appreciated:

(1) Regional—recognition of mineral belts or min-
ing camps.
2) Local-—identification of targets for evaluation.
(3) Property—defining the limits of mineralized
und
(4) Deposit—location of individual ore bodies.

As shown in Figure 1.2 these also represent increasing
levels of effort, complexity of problem, sophistication of
technology, expenditure per unit area and, frequently, the
Sequence of an exploration program. Techniques applicable
at the regional scale, with broadly spaced samples, are
incapable of providing the definition necessary at the prop-
erty and deposit scale. Conversely, the very detailed sam-
pling and sophistication of technology used to locate
individual ore bodies are far too tedious and costly to apply
at the local and regional scale. y i

oe MSITY
OST PER UNIT AREA
HEGIONAL LOCAL _PROPERTY__OEFOSUT

318 ourctor

as

Ele arian

ale ‘OUTCROP.

ae ASTSy

zz

Re

Si wuRED

5

ak Ke

bd [9

nino

= ———
INCREASING LEVELS

FIGURE 1.2—Some factors influencing the choice of mineral ex-
ploration survey techniques.

Ultimately there is the need to integrate geochemistry
with the overall exploration strategy. Depending on the
character of the target, level of application, surficial envi-
ronment and availability of personnel, geochemistry may
take a lead or supporting role in an exploration program.
Occasionally it may have no place at all, Frequently. it is
misapplied with surveys run to see what happens, to satisly
contractual or assessment work commitments or simply
because they are always run. Such surveys are very rarely
truly successful

Howy, then, are geochemical surveys optimized within a
particular exploration program?

OPTIMIZING SURVEY TECHNIQUES

To optimize a geochemical survey a variety of techniques
are available to the geochemist. The collective experience
of some 50 years of exploration geochemistry can be brought
to bear on the problem at hand. It is, however, necessary
to be quite clear about what is wanted in an individual
survey. The key feature is identified by Hawkes and Webb
(1962) as RELIABILITY, which refers to the probability of
obtaining and recognizing indications that an orebody is/is
not present within a survey area. In constructing a reliable
survey method, four characteristics are deemed desirable
and represent the Basic Survey Objectives

Basic Objectives

Optimum target identification

A target, if present, should be clearly visible in the geo-
chemical data. It may be characterized by an increase or
decrease in abundance of certain elements or a diagnostic
association of elements, Regardless of the details, it should
be easily distinguishable from the remainder of the survey
data, a feature achieved by - i