Note: Descriptions are shown in the official language in which they were submitted.
OD FOR OEOPHYSICA~ E~PLOR~TIOlJ O~ POL~ RAL
i~RE i3
The invention relates -to the geophysics and it deal~
wi-th methods ~or discovering mineral deposit~, involving
seismic exploration and explora-tion usin~ electro~agnetic
oscillations, and mo~e spec~ ically it deals with a method
~or geoph~sical exploration o~ polymineral ore bodies.
A method for geophysical exploration Q~ pol~minsral
o~e bodies is used at the stage o~ prospecting and explora-
tion o~ ore bodies con-taining tin, gold, lead, zinc, merclry;
molybdenum, tungsten9 antimony, rare-earth metals and it
is especially e~fective in explorin~r ore bodies at the stage
o~ working o~ ~nown depositsO
~ istribu-tion of polymineral ore bodies in space in
the county rock is rather complicated. Thickness o~ ore
bodies which are worthy of commercial working depends on
the vallle o~ a mi~eral, a~d in certain application~ it may
be e~pedient to work ore bodies several tens ~ n-timeter
thick.
'~he eæplora-tion o~ polymineral ore bodies is generally
conducted by using geological methods comprising driving
explora~ion working~S drilli~g a system o~ exploration bore-
holes and, a~ter studying the composition o~ cores, deter-
minin~ the presence o~ an ore body. The boreholes are general-
ly spaced apart at about 20 m. This method is rather labour-
-consuming and requires much time a~d money, yet it is not
adequately ef~ec-tive~
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There are also geophysical methods ~or explor3tion
of polymineral ore bodies -~hich ma1~e it pos_ible ~o ac-
celerate the ~rospecting opera-tio~ at lower cost. Poly-
mineral ore bodies ~re known to be prone to an electros-
-ta~ic polarizatio-n under -the action of an external elec-tric
field, and this is -the basi~ o~ a me-thod lor e~ploration
of polymîneral ore bodies by the in~uced polarization
technique (c~. V.A. ~omarov, Electrical Exploration by
the Induced Polarization Technique, 198~, Leningrad,
Nedra Publishing House, p. 391). ~he me~hods comprises
causing alternatin~ or direct current to flow -through a
mass o~ rocks enclosin~ ore bodies under study and measurin~
the tra-nsition characteristic of the induced polarization
of the medium, the presence o~ ore bodies in the polariza-
tion zone bein~ assessed by anomalies in this characteristic.
~ his me-thod canno-t, however, be used to determine -the
number o~ contiguous ore bodies bg the revealed anomaly.
In addition9 under the condi~ions o~ a deposit bein~ wo~ked t
especially in case there are hi~hl~ conduc-tive country rocks,
it is necessarJ -to have a strong curren-t (o~ the order
o~ hundreds Amperes) which is practically impossible. The
use of such method in mines i9 limited by the presence of
elo~gated conductive objects such as pipelines, rails and
cable 9 .
Enown in the art is a method ~or geophysical explora-
tion o~ polymineral ore bodies (c~ USSR Inventor's Cer-
ti~icate No. 972453, filed March 43 1981, publ. Nov. 7,
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~:3~
1982, Of~, Bull. No. 41, Cl~ G 01 V 11/00) ,7hich ~a~es
it possible to ~etermine the number of ore oodies in a
mass o~ county rocks under study in a more accura~e mannsr,
~he method comprises exciting elastic waves in t~e mass
of rocks enclosing ore bodies and recording an electroma,--
ne-tic pulse radiation genexated by the ore bodies under
the action o~ -these elastic waves, the number o~ pol~mi-
neral ore bodies in the roc~ mass under study 'oeing deter-
mined by the number o~ pulse packe~s.
~ he accurac~ o~ determination o~ the number o~ pol~-
mineral ore bodies in ~he rock mass under study by t is
method is rather inadequate since it is not possible bO
define ore bodies of a small thickness as ~he intensi-t~
of electroma~netic radiation depends on the ore bod~
thickness. In addi-tion, the i~tensity of an electroma~netic
pulse radia-tion ~enerated by the ore body also depends
on mineral composi-tion and structure of the ore body~
It is an object of ~he invention to iulprove the ac-
curacy o~ determination o~ the number o~ ore bodies occurring
in a rock mass bein~ studied,
Thi~ object is accomplished by that in a method ~or
geophysical exploration o~ pol~mineral ore bodies compri-
5ing excitin~ elastic waves in the roc~ enclosing ore bodies
~and recordi~g an elec~romagnetic pulse radia-tio~ ge-nerated
by the ore bodies under the ac-tion o~ ~he elastic waves,
the number o~ polymineral ore bodies being determined b~-
the number o~ pulse packets of the radia~ion, acoording
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to the invention, the elastic waves inducing a~ el~o~ro~-
tatic polarization are first excited in ths ~ass ol ~ocks
with a second excitation of ~he elastic ~.~aves bein~ eTfecve.
durin~ -the -time interval within which the electrosta',ic
polarization charge ,-tlll e~ists,
In case a known ore bodJ is availa~le in the rnass
of rocks, it is advisable also to record variation o~ -the
e~ectros-tatic polarization charOe of such an ore body,
the subsequent excita-tion of the elastic waves being eI'-
fected when ~the charge is at its maximumO
It is kno~Jn ~hat an elec~romag~etic pulse ra~iation
appears in polymineral ore bodies under -the action o~ an
elas-tic wave. The in-tensity o~ the electric ~ield at a
distance of 1 m ~rom -the source o~ the elastic wave is
reater than 107-1~8 ~/m and is higher than the in-tensit~
o~ piezoelectric, contact and seismoelectric field by a
~actor of hundreds and even thousands.
~ he charge rise time of the electrostatic polariza-tion
and the relaxation time depend on mlneral composition o~
an ore body, The charge rlse -time ranges frcm several seconds
to tens o~ seconds. ~he charge relaxation ~ime is s~veral
mlnutes~
~ 11 polymineral bodies in a rock mass being studied
a-re polarized whatever their thickness.
The amplitude of the electroma,~netic radiation pulses
ge~erated u~der -the action o~ the elas-tic waves ~rom the
polarized ore bodies is grea-ter than -the a~plitude o~
pulses o~ the electromagneti~ xadia-tion ge~era-ted by
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no~-polarized ore ~odies. At the moment at ~lhich the Glestro-
sta~ic olariza-tion char~e o~ an ore body reaches its
maximum value -the a,nplitude o~ the electromagnetic radia-
tion induced by -the elastic l~aves excited in ~he rock mass
at this momen-t increases b~ from 2 to 5 times deriendi~g
on mineral composition of the ore body. ~his allo~s ~he
electromagnetic radia~ion ~rom small-thickness ~re
bodies and lrom ore bodies located at a substantial distance
~rom the point of recording o~ the electromagnetic radia~io~
to be recorded thus improving the accuracy o~ determi~ation
o-f the ~umber o~ ore bodies in the rock mass being studied.
~ he invention will now be described ~ith re~erence
to a speci~ic embodimen-t o~ a me-thod lor geophysical e~plora-
tion of pol-Jmineral ore bodies illustrated in the accompan~ing
drawin~s, in which:
Fi,ure 1 is a time char-t showi~g varia-tio~ ol -the
electros-tatic polarization charge of ore bodies having
the Oalenite-sphalerite composition, according to the
invention;
~ igure 2 i9 a time chart showing variation o~ the
electrostatic polarization charge of ore bodies o~ the
~uar-tz-an-timonite~ci~nabar composition;
Figure ~ i5 a time chart ~howing the electxomagne-tic
pulse radia-tion.
A method fox geophysical exploration of polymineral
ore bodies con.sists in the followi~g.
Elastic waves are exci-ted in a rock mass under study
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to induce an electromagnetic radiation and an elsct~os~ic
polarization of ore bodies. For that ?urpose, an e~plo~ e
charge is blown-up, the charge yield dependin~ on ~he -~olw~e
o~ the rock mass bei~g s-tudied.
Exploration by -the method according ~o -the invention
is mos-t ~requently conduc-ted in a mass o~ rocks rangin~ up
to about 10~ m ~rom the p~in-t o~ explosionO ~he charge ~ield
mainly depends on the conditions for the propagation ol ths
elastic waves -through the mass o~ rocks under stud~, the
mass size and mineral composition of ore bodies.
Generally the mass o~ a char~e~ e.g. o~ ammonite ohar~e
does not exceed 6 ~g~ In applications vlhere the mass under
s-tudy is small- irom 10 to 20 m, the elastic-waves can
be excited by using non-explosive sources. An explosive
cbarge is generally placed in the mou-th o~ an available
borehole or in a recess at -the ~loor o~ a working.
The electros-tatic ~ield o~ polymineral ore bodies ma-
ni~ests itsel~ in the ~orm of a posi-tive charge a-t their
sur~ace~ and the time charts 1 (Figure 1) and 2 (~iæure 2)
showing Yaria~ions o~ the charge ~or two deposits that
have been investigated are given in the drawings, wherein
the surface charge densit~ ~ in 10~9c~m2 is plotted on
the ordinates a~d time in seconds is plotted on the abscissae.
By -the -time mome~t to~0 (be~ore the momen~ of explosion)
there is a natural ch~rg~ o~ ore bodies with a sur~ace
~ensit~ ~ O (~ig. 1) and ~ O (Fi~ure 2). A~ter the
explosio~ a charge rise occurs5 ~he time $max in which
the charge attains its maxi~um value ~ max depending on
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mineral composition o~ an ore body and is about tma~=1 s
for the galenite-sphalerite ore bodies (Figure 1) and
about t~g=14 s for the quar~tæ-antimonite-cinnabar ore
bodie~. The charge relaxation time is up to several
minutes.
~ hen, during the time :Lnterval within which the
electrostatic polarization of ore bodies still obtains,
elastic waves are re-excited in the rock mass under s~ud7,
e.O~. b~ blowing-up an explosive charge~ The seco,nd explosion
i9 generally made adaacent -to -the point o~ the ~irst explo-
sion~ at a distance precluding detonation o~ the explosive.
~he weiOh~ o~ the second explosive charge may be lo~er
than that o~ the firs~ onec The second explosion can, e.g.
be made with an ammonite charge of 1 kgo
The optimum time for the re-excitation o~ the elastic
waves i9 the mome~t at which the value of the el~ctrostatic
polarization charge achieves its maximum. In order to de-
termine this time momen-t, an instrument for recording
~Jariation o~ -the electrostatic polarization charge, e.g.
an electro~eter with preriodical screeni~g o~ the measuring
electrode i9 ins-talled in a known ore body undercut by a
worki~g. By watchi~g 0~ the sereen of an electronic oscillo-
soope or a like instrument varia~ion o~ the electrostatic
polarizatio~ pote~tial, the maxi~um value of charge is
visually determin~d and the re-e~citation o~ the elastic
waves and recording o~ the electromagnetic pulse radiatio~
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of -the ore bodies are e~ected at that moment, the nlmber
o~ packe-ts o~ the radia-tion pulses determini~g the num'oer
of polymineral ore bodies.
Figure 3 shows a time chart illustrati~, the diagram
o~ the electroma~netic ~ulse radiation. The vol-tags U
in Volts at the output of' a recorder is plotted on the
ordinates and time t in ms is plotted on the abscissae7
~he ore body radia-tion is in the ~orm ol packets 3,4,5 o~
noise-like signals consisting o~ short pulses of different
amplitude and polarity. ~hree packets 3, 4, 5 oY ~ulses
can be seen on -the dia~ram ~rom which it follo~Js that in
-the rock mass under study -three ore bodies worthy of co~mer-
cial worki~g are discovered by t'ne method according to the
invention.
For better understandinO o~ the in~-ention; the ~ol-
lowing speci~ic example o~ its prac-tical realization is
given belowq
~ he method ~or geophJsical exploration o~ polymineral
ore bodies was tested on a deposit for prospecting ore
bodies o~ the quar~tz-atimonite-cinnabar composi-tion. An
electrometer ~or recording variation o~ the electrostatic
polariza~ion charge o~ -the ore bod~ was installed on an
ore body stripped by driving a worki~g. ~hen an ammonite
charge o~ 4 kg was blown-up a-t one point o~ the working.
Under the aotion of an elastic wave caused by the
explosion an electromagnetic radiation was genera-ted by
ore bodies available in the rock mass under stud~, and
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variation o~ the electrostatic polarizatio~ charOe was
recorded and visuall~ observed. At the mo~ent wnen ~he
density of the electrostatic polarization charOe achis-Jed
the maximum value of 6 _~.10 ~C/m2, a second explosion
of an ammoni-te charOe o~ as made 14 s after the lrs.
explosion a-t a distance of about 1~ m from the poi~t of
e~citation of the elastic waves by the ~irst charge. The
ampli~ude of the electromagnetlc radiation pulses was
0.5; 1.3; 2.0 and 0.8 V ~or various objec-ts. ~herefore, four
ore bodies were recorded in-the rock mass under study.
To determi~e the distance to a respec-tive ore body,
t~ pulse arri~al time was also recorded. ~his -time was
for -the above amplitudes ~.25; o.1; 1~.15; 14.1 ms, res-
pec~ivel~.
Given the velocity of propaga-tion o~ the elastic wave
through the county rock enclosing the ore body 7 -this
distance could be easil~ found ~hus, with a velocity in
solid limestones of 5.5 m/ms, ~he dis-tance -to the most
remo-te ore body is 14 1 ms05.5 m/ms=78 m from the point
of explosion In -the process of verification, these ~our
ore bodies were actually undarcu-t by exploration boreholes.
For comparing the me~hod according ~o the inven-tion
with the prior art method, the amplitude o~ pulses o~ -the
elec-tromagne-tic radiation of ore bodies induced by the
firs-t explosion was recorded. Three ore bodies were dis-
coveredO ~he amplitudes o~ pulses were 0~1, 004; and
1 0 V, respectively, with their arrival -times 3~2; 6.1
and 1~.2 ms, respectively~ There~ore, the amplitude o~ the
si~n31s emitted by the polarized oodies increased bJ a
fac-tor ~ro~ 2 -to 5 so that an ore body could be discoverea
tha-t had not been discovered after the ~irst explosion
~hen the ore bodies had no-t been polarized.
