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7: GEOPHYSICAL METHODS 151

geochemistry, but its extension to geophysics appropriate), the likely duration of the project
has not been notably successful. Displays of and, of course, the availability of personnel. If a
mathematically combined gravity and mag- full-time geophysicist cannot be justified but
netic data have generally succeeded only in some geophysical techniques are to be used,
disguising important features while producing there may be company geophysicists who can
no new insights. Allowing computers to cross- allocate a percentage of their time. Alternat-
correlate geophysics with geology or geochem- ively, consultants can be retained and/or one or
istry is even less likely to give meaningful more of the team geologists can be given re-
results. Correlation is essential but should be sponsibility for day to day geophysical matters,
done in the brain of the interpreter. including supervision of contractors and possi-
Of the various possible correlations, those bly the conduct of some surveys. It is usually
most likely to be useful in the early stages of best if one (and preferably only one) geologist is
an exploration program are between geology, responsible for routine geophysics, but he or
air photographs, and magnetic maps. Struc- she must be able to call on more geophysically
tural dislocations such as faults and shears are experienced help when needed and the freedom
likely to be indicated magnetically and the to seek such help must not be unduly restricted
intersections of magnetic lineaments have by short-term cost considerations. Geophysical
been fruitful exploration targets in many areas. surveys are often among the most expensive
Gravity and radiometric data, along with parts of an exploration program and much
infrared or radar imagery and soils geochem- money can be wasted by a few apparently
istry, may also help in obtaining the best pos- trivial, but wrong, decisions.
sible understanding of the geology. Geophysics Project geologists should not be expected to
provides independent information on the third decide, unaided, on methods, instrument pur-
dimension (depth), and may be especially use- chases, and overall geophysical exploration
ful in preparing regional cross-sections. strategy. In companies with their own geo-
The inherent ambiguity of all geophysical physicists it would be unusual for them to have
solutions makes it essential to use all possible to do so, but where these are not available it is
additional information. For there to be even a all too common for consultants to be called in
chance of a model being correct, it must satisfy only when things have already gone irretriev-
all the known geological and geophysical ably wrong. The instruments purchased, and
constraints. Consequently, it must also be used, the contracts let, and the contractors
continually refined, not only up to but also selected may all have been totally unsuitable
throughout any drilling program. If a worth- for the work required.
while target has been defined but the hole has What, then, can reasonably be expected of
proved unsuccessful, it is not enough to simply a project geologist whose only experience of
blame geophysics. There is a reason for any fail- geophysics may be a few dimly remembered
ure. It may be obvious, as in the case of an IP lectures on a university course several years in
anomaly produced by barren pyrite, but until the past, possibly accompanied by some miser-
the reason has been established, a valid target able days in the field pressing the keys on a pro-
remains to be tested. ton magnetometer or trying to level a gravity
meter? First, and perhaps most important, is a
degree of humility and a willingness to seek
7.17 THE ROLE OF THE GEOLOGIST IN help. Second, a variety of geophysical texts
GEOPHYSICAL EXPLORATION are required and a readiness to read them all
(beware of relying on any single authority).
A mineral exploration program will usually be Third, a realistic attitude is needed. Explora-
the responsibility of a small team, and whether tion programs have limited and usually pre-
this should include a geophysicist is itself a defined budgets, and geophysical instruments
decision that requires geophysical advice. are neither magic wands that reveal everything
Factors to be considered are the types of targets about an area, nor pieces of useless electronic
sought (and therefore the types of methods circuitry inflicted on hard-working geologists