Montana oil and mining journal. [volume] (Great Falls, Mont.) 1931-1953, 1939-11-11

table or source Of moisture.
1t was also noted that rocks that
exhibit a marked parallelism OF
their tabular crystals or grains are
electrically anisotropic. in that they
conduct currents more readily in
one plane than in another. The
parallelism may be primary, pro-
dued by deposition or molten flow,
or it may be a secondary structure,
imposed by metamorphism on sedi-
mentary and igneous rocks alike.
| The resistivity of such rocks is
| least in planes parallel to the long
axes OF tabular crystals and grains
and il reaches maximum at right
angles
In numerous instances. magnetic
anomalies were observed in the field
which cannot be explained by the
laws of magnetism as evolved in
the laboratory and which have com
mon acceptance Definite evidence
indicates that the subject OF mag
netism is considerably more com
pick than formerly supposed and
it appears highly probable that the
most important contributions to
knowledge in this field will result
from studies in applied geophysics
rather than from Investigations of
purely academic nature
One real hindrance to the pro-
gress of practical geophysics is the
frequent presence of superficial
anomalies having no bearing upon
ore or oil occurrence Such ano-
males result chiefly from variations
in the physical characteristics of
weathered zones and OF the drift
cover as well as from marked re-
lief in the bedrock surface. These
variations are erratically distributed
and, inasmuch as they are seldom
apparent to the eye their pre-
sence is unpredictable The effects
which they give rise have to be
eliminated, either by suitable tech
nique or instruments. in order to
prevent the masking of deep-seated
and more important. reactions.
The significance of these numer-
Gus factors which have TO be con
sidered in applied geophysics is
more readily apparent to the geo.
logists than to the physicist. 1t is
not strange. therefore, that the
modern trend has been for the
actual application of geophysical
methods. to pass from the hands of
the physicist into those of the geo.
logist The former, of course, will
always occupy an important role,
chiefly in designing new. apparatus
and in evolving new methods, to
much the same extent that he al
ready participates in other fields of
science and engineering.
The geophysical apparatus and !
methods in use today are suffi- |
GENTLY advanced to reveal hidden |
features and structures of funda-
mental Importance; 1t is now up to
the geologist and mining engineer |
to give intelligent direction for the |
use of this new aid in prospecting /
and to provide every possible key
for interpreting the results.
All the instruments employed in
geophysical work are built for
field use 80 most OF them are self
contained and easy to handle The
effects of the inevitable superficial
are either automa-
tically eliminated or else they may
be avoided by controlling the depth
at which the characteristics OF the
formations are deter
mined The results obtained are in
such simple form that they can
be plotted on maps or diagrams and
expressed in quantities from which
The geologist can make his inter-
probation easily, that is, translate
he geophysical data into terms of
geology formations, or structure,
ind thus indicate and outline areas
where the mining man should have Il
he best chances of finding ore
liberalization.
Success in geophysical work re-
Iuires that definite geological in
be used as a starting {
Joint and as a constant check. +;
tests should be made
where the geological formations
nd structural relations are accur-
tely known.
Much new experience and a great
r knowledge of the physical con-
itions surrounding ore deposits as
veil as clues to new methods Of {
ttacking certain structural prob
ems have been obtained from work F:
ng out the problems in the field
Inder natural conditions. Ore de-
,osits can often be detected at
much greater distances than can be
ccounted for theoretically, and {
hese can Ibe confirmed by small
Gale experiments. 1t often be-
ONES evident that the performing
PROCESSES have altered and changed
o a considerable degree, the physi-
al characteristics of the rocks in
which the ore bodies occur. Zones
f shearing. alteration, or secondary
minerals often surround ore bodies.
iometimes the ore naturalization
xtends far into the wall rock in
radually decreasing amounts. Such :
ones of scant naturalization. al Il
Grafton. and shearing. etc. differ
physically from the wall rock and
. is often possible in a geophysical
urvey to trace such zones and. by
ollowing them, indicate the pre-
ence of THE ore body. Some
ines the Undertaking solutions