A theoretical and experimental study of the electromagnetic method of geophysical prospecting

357 Pages·16.609 MB·English

by  Ward, Stanley H

31362
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Stanley Harry Ward
name of au th or-'nou de i'a iitfiir
A theoretical and experimental study of the electromagnetic
title OF THESIS/77w de la th*v
method of» geophysical prospecting.___________;________
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A TH^OH TTICAL Aft D jLwP.^I;:^TAL STUD1& .
OF
'i’ll; JLiCTROI.'.AGT ^TIC METHOD
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by
H. ’-ard
A Thesis submitted in conformity v.ith
‘the requirements for the decree of Doctor of .Philosophy
in, tho University of Toronto. \H .
'+
'
* * &
• Or
. October 1952 ■ .' • .V .
0 S.H. WARD 1977
*• .,*5*
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. . ' V ' UNIVERSITY OP TORONTO.
, SCHOOL OF GRADUATE STUDIES
'■! - ‘ S' • ••'•'. " : • ‘ - ' " . • '
^ . PRO'GRAMMEOF THE FifcAL ORAL EXAMINATION
FOR THE DEGREE OF DOCTOR’ OF PHILOSOPHY
f
STANLEY HARRY WARD.
2:00 p.m., Wednesday,'October 29th,1952,
Room #1?0, Vallberg Building
A THEORETICAL AND EXPERIMENTAL STUDY OF THE ELECTROMAGNETIC
~ T “ !------- ~ M5TH0IT OP "SEgpjfeSTCSI TftggPECTI fla --------------------
. Cotamit*tee in -Chaise * "
0 ’ \ ’ ‘ “ *
Professor B. Cfaalmerd, Chairman.-
. Professor W.H.' Watsoh '
Professor J.T, Wilsoft
Professor M .A.Preston
• Pro’fessor R.W. fc>cKay .
Professor C/ Barnes ■ •
Professor J.M.\Anderson
t < Professor J.N.P. Hume ‘ ' • ’
Prqfessor. 0* Sinclair
Professor G'.B. Langford.
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
' ' THfcSIS
A' T1 5TICAL AND EXPERIMENTAL STUpY OF THE ELECTROMAGNETIC
METHOD OF GEOPHYSICAL PROSPECTING
(Summary)
The main purpose of this investigation is to
obtain information concerning th ev ariatio n with'frequency
of^the response of geologid conductors. To facilita te th is,
a new electromagnetic Exploration technique employing an-
inductive system with a vertical endrgizing-coil has been
devised. Its advantages, lim itations and future possibilities
are discussed.
1 , This investigation is broader in scope than previous
studies insofar as the frequency of the source field is
completely variable over the audio-frequency range. Further,
a correlation between laboratory and field work has been
attempted in some instances. Knovm sulphide and magnetite
occurrences have been surveyed arid the results of the laboratory
work employed in the analysis of the data collected in tho
field*. ‘ ‘ i
‘ * ■« k
The advantages of the new technique, as compared
with other techniques, are discussed in conjunction with the
results of a survey over a known occurrence of nickeliferons
sulphide m ineralization. Many of the advantages arise from *'
the use of several-frequencies rather than the customary
•single frequency.
• \ .• ' • •
The theoretical response of a ferromagnetic, ..
conducting sphere in a harmonically-varying, uniform, magnetic
fie ld is analysed. This analysis reveals" that it is possible
to.determine uniquely the dimensions, position, conductivity
and permeability of a hidden sphere from study'at. a number of
frequencies,'of the indqced magnetic fields of t^e sphere. • i
It is demonstrated that the response cf a conducting- magnetic
• body of arbitrary shape in a magnetic fiefd of arbitrary
form is a function of a type sim ilar to that for the sphere.
The discussion l-eads .to a fundamentally new application of *
the (electromagnetic method; the determination of the' percentage
of ferric iron in a magnetite deposit. . • ;
t Scale model experiments* have been made to assist in
the interpretation of--the field data. ’ A description is given
of, the. variable frequency model system employed. •>
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'BIOGRAPHY
.
- - . . . . . . . 1
1923 - Born, Vancouver,'.B.C. ^
1949 - B.A'.Sq., University of Toronto.
1949-50 r Demonstrator, Department of Physics,
? University of Toronto.
1950 - M.A., University of Toronto.
1949-52 - School of Graduate .Studies, . .
' University of Toronto.
' ' 4 • . /. * • *. ‘ .............................................
GRADUATE STUDIES
Major Subjects:
^ Gravitational Methods in. Geophysics ) Dr. G.D. Garland
Seminar- in Geophysics. )
Dielectric and< Magnetic S usceptibilities - Prof. R.W.- McKay
•• •>*• . ' •
J Minor Subjects:
Theoretical Seismology. Dr. D.V. Anderson • . .
Dynamics and Quantuxn Dynamics r Professor M.A. Preston
* » ~ •' * %
Mathematical-Theory of - . L
‘ k E lectricity ,and Magnetism - Prof. A.T.C. Stevenson.
. . ' *’ • * * * •
. * ' PUBLICATION .'
S.H; Wdrd, - A Method fo r Measuring and Electrical.
Conductivity of Diamond,Drill.Core Specimens,
submitted.for publication to "Geophysics."
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
The main purpose of th is -investigation is to obtain
/ L--
information, concerning the variation with frequency of the response
* /
.Of geologic conductors, To* fa c ilita te this,, a new electromagnetic
exploration technique employing an inductive system w ith.a vertical
energizing coil has been devised. Its advantages, lim itations apd.
future possibilities are discussed. , v
This investigation'is broader in scope than previous t
0 •' A. • ' . .. . . .
studies insofar as the frequency of.the source field is completely
• * - xi •
variable over the Sud^o-frequency range. Further,.a correlation
-• ■ ' * i. ’ * * ■ / * " . <
between laboratory.and field, work; has been attempted'in some instances,
known esulphide and magnetite occurrences have been surveyed and
P ' . * • * •, « * •
* * • • * >
the results o f. thevla'boratory work, employed in the analysis of *the data
collected in- the field. . *_ . . * V
• • .. . * • * ' • *
) % ■ • 1 • •
The advantages of the new technique, a? compared with othgr * *
•. •' * • # - ♦ • • »
iV « • % *
.
techniques, are discussed ^n conjunction with the results of a *.
survey over a known, occurrence of nickelif erous sulphide mineralizatiop.
•• . . * . • •. ■ ' *• ” * • ■ ' ■ ‘ '■
Many of the advantages arise"from the upe of several frequencies * ^
. • :■ . \
rather than the customary-single frequency. : *
• *■ .. • .. ■ . . . .
' Hie ‘theoretical ^rtfsppnsp. of a ferromagnetic, conducting
sphere in’ a harmonically-varying, uniform, magnetic .fie ld 'is analysed.
This analysis reveals that it is possible to determine uniquely the:
dimensions, position■ ■ ', con’d uctiv« ity* , a•n d p. ermeability of a. hidden' i '
sphere from study, at a number of frequencies, of the induced-magnetic •
fields of the sphere. It is demonstrated that the response of a
conducting magnetic body of arbitrary Shape in a magnetic field of.
arbitrary form is a function of a type sim ilar to that for the sphere.
• • ■/'
.'■■■ 0 ■ ♦
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
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» Acknowledgement a
i ' , *
■* ’ * .
-The w riter wishes to thank various members of the
Department of Physics at .the University of Toronto for the help
,.they have kindly offered him during the course of this study.
Professors W.H.Watrfon, J.T.W ilson, M. A. Preston, and H.W.BcKay . *
• A ■* ■ * . . . . .. . • * * ** , « *
have provided helpful advice and criticism .- The latter has part-
- > ■ •« . .
ioQlarly been a source of counsel and encouragement. t
.=• . i _ *
The^huge mechanical task of . preparing and assembling
\ * *. * ' '>'v *
the manuscript and diagrams mas entrusted to the very capable
■ * •
hands of Angela Burlinson. Assisting her with the typing were
• , • -
Barbara Hardy and Dorothy Perryman. The w riter wishes to
thank thed a ll. • ,
The Rational Research council of Canada provided
, financial assistance for equipment and field expenses. The *
' ♦ » '
kcPhar engineering -Company of Canada Ltd., and McPhar Geophysics
Limfted, constructed the field equipment and donated a sub-
•,v ; ■' * \
stan tial part of it to the University of Toronto. The senior
' - v - ' '
* members of. the McPhar group, (Messrs. C artier, Davidson, Harvey,
- McLaughlin,*'and Rof>inson) kindly.'offered much assistance
. ' • . -F-
w ith-practical-aspecth of . the problem.' .. >
~ . • V N. • ' '
The w riter was. enabled -to continue this research
by receipt of MbRoe-Gllciiriat Scholarships for the ^academic
years 1950-51 and 1951-52.
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.