I I . B a sic s o f t h e n ew p r o p o s a ls in t h e im p ro v e d s y m m e t r i c in d u c e d p o la r iz a tio n s o u n d in g m e th o d

VNU . JOURNAL OF SCIENCE, M athem atics - Physics. T . XVIII, Nq4 - 2002

T H E A D V A N T A G E S O F T H E N E W P R O P O S A L S I N T H E I M P R O V E D S Y M M E T R I C I N D U C E D

P O L A R I Z A T I O N S O U N D I N G M E T H O D Vu D u e M in h

C o lle g e o f S c ie n c e, V N U

A b s t r a c t .

T h e higher resolution, greater investigating depth, increasing reliability of ge­

ology forecasting results and possibility of expanding the application o f the improved symmetric induced polarization sounding m ethod have been illustrated by theoretical and field medium are th e advantages of the new proposals presented in this article.

I. I n t r o d u c t io n

III th e a rtic le [2], th e ou r n ew p ro p o sa ls, e s p e c ia lly th e P e tr o v sk i in d u c ed p o la r ­ iz a tio n (IP ) p a ra m eter r/p, h a v e b e en in tro d u ced for d a ta p r o c e s s in g in th e in d u ced p o ­ la riza tio n so u n d in g m eth o d ; a s a resu lt, th eir a d v a n ta g e s in c o m p a r iso n to th e p r ev io u s co n v en tio n a l p a ra m e ters h ave b e e n illu str a te d by c a lc u la tin g for th e th e o r e tic a l m ed iu m . H ow ever, th e P etro v sk i tra n sfo rm in g form ula c o n ta in s d e r iv a tio n w h ich is n o t s ta b le , so d esired re su lts are not. a lw a y s o b ta in e d . W ith p u r p o se to o v erc o m e th e s e d isa d v a n ta g e s, w e have p ro p o sed t h e im proved s y m m e tr ic ele c tr o d e array an d th e c o rr esp o n d in g m e a su re ­ m en t p roced u re, th e sim p le a lg eb r a ic tra n sfo r m a tio n s (w ith o u t th e d eriv a tio n ) t o a p p ly to th e r e sistiv e ly so u n d in g m e th o d [ l] . T h o se im p ro v ed s y m m e tr ic e le c tr o d e array an d tra n sfo rm a tio n s are o f scie n tific arid p r a ctic a l sig n ifica n c e. B a s in g o n th o s e research es, w e a lso have p ro p o sed th e im p ro v ed sy m m e tr ic IP s o u n d in g m e th o d (I S I P S ) a n d it h a s b een te s te d e ffe ctiv ely a s th e a rtic le [3].

In th is a r tic le , w e w ill illu s tr a te th e co rr ectn ess a n d a d v a n ta g e s o f th e n ew p r o p o sa ls in th e IS IP S by th eo re tica l a n d p ra ctica l m ed iu m ; p r o p o sin g p o s s ib ility o f e x p a n d in g and ach ieve b e tte r g eo lo g ica l e ffectiv e o f th e n ew p ro p o sa ls t o th e a p p lic a tio n o f th e IS IP S in fact for d a ta p ro cessin g o b ta in e d b y u sin g th e p rev io u s c o n v e n tio n a l IP so u n d in g m e th o d .

I I . B a sic s o f t h e n ew p r o p o s a ls in t h e im p ro v e d s y m m e t r i c in d u c e d p o la r iz a tio n s o u n d in g m e th o d

I I . 1 T h e n e w in d u c e d p o la r iz a tio n p a r a m e te r s

A s know n , t h e apparent p o la r iz a tio n is c a lc u la te d by th e fo llo w in g form ula:

Vk = p*k- Pk/Pkt

( ! )

w here

p ị

a n d

pk

are th e a p p a ren t r e s is tiv itie s o f th e p o la r ized a n d n o n - p o la rized m ed iu m , resp ectiv ely , co rr esp o n d in g t o th e r e s is tiv ity p a ra m eters

p i

a n d

Pi

w h ich are r e la te d by:

p* =

P i / ( I

— r/i) w h ere

i

is th e m e d iu m m o d e l in d ex .

T y p e s e t by

13

14 V u D u c I M i n h

B a sin g o n th e a b o v e d e fin itio n s, w e h a v e a lso d efin ite th e n e w I P p a r a m e te r s [2]

sim ilarly:

- T h e p o la r iz a tio n o f th e sy m m e tr ic In d u ce d P o la riz a tio n s o u n d in g m eth od :

rj9.

- T h e p o la r iz a tio n o f th e (lip o le-a x is In d u ce d P o la riza tio n so u n d in g m eth od :

r)r .

- T h e P e tr o v sk i p o la riza tio n :

Tjp

I I . 2 T h e n e w t r a n s f o r m a t io n s

A c co rd in g t o [3], th e im p ro v ed sy m m e tr ic In d u ce d P o la riza tio n so u n d in g e le c tr o d e array is a llo c a te d a s th e fo llo w in g :

m

2

m

,

a b n

,

n

,

— --- • --- • --- ♦ ---♦ --- • ---• --- w h ere, w ith o n e c u r r e n t-e le c tr o d e se p a r a tio n A B , from th e m e a su re m en t w e m ay o b ta in

Psi(r i)> Vsi(r \)

a n d

Ps

2

(r

2

)> Vs

2

(r

2

),

co rr e sp o n d in g to rj an d r 2. In su ch a w ay 4 curve

P i

\ ,

Pi2

a n d

TỊS\ , ri

„ 2 a re o b ta in e d . T h en :

^ LS (

/0\

a M S - f r J ' (2)

where psr - the dipole-axis resistively sounding curve obtained by transform ing from th(!

s y m m e tric re s istiv e ly s o u n d in g c u rv e p a.

T h e v a lu e s o f P e tr o v sk i r e s is tiv e ly so u n d in g cu rv e

ppar

are c a lc u la te d by th e fo llo w ­ in g form ula:

Ppsr

=

p j ( 2 p sr/ p a -

1). (3)

T h e n a ll th e n ecessa ry in fo r m a tio n w ill b e c a lc u la te d acco rd in g to th e s c h e m a show n o n figure 1.

Figure 1.

S ch em a c a lcu la tin g ..p a ra m eter s by u sin g IS IP S array

T h e a d v a n t a g e s o f t h e n e w p r o p o s a l s i n t h e i m p r o v e d s y m m e t r i c. 15

I I I . C h e c k in g t h e m u tu a l p r in c ip le

W e have m ea su red a n d c a lc u la te d ex p e r im e n ta lly th e m u tu a l p r in c ip le o n th e field m ed iïiu n . B elow w e p resen t o n ly th e e x a m p le r esu lt in T an D a n - H o a n h B o - Q u a n g N in h .

F ig u re 2 sh o w s the a p p a ren t r e sistiv e ly cu rv es

prstr

(ro rstr) p r a c tic a lly m ea su red by t h e im p r o v e d sy m m etric so u n d in g array M A B N ,

Prsng

(ro rsn g ) p r a c tic a lly m ea su red by th e im p r o v e d s y m m e tr ic so u n d in g array A M N B an d th e co r r e sp o n d in g P etr o v sk i re sistiv e ly s o u n d in g curves.

F ig u re 3 sh o w s th e P etro v sk i re sistiv e ly cu rv es

ỌyrstT

(ro p rstr) for array M A B N an d

Pprsng

(rop rsn g) for array A M N B ; th e P etr o v sk i r e sistiv e ly cu rv es

Pprsxd

(ro p rsx d ) d erived fr o m th e tra n sfo rm a tio n o f th e v a lu es

Pr

p ra c tic a lly m e a su re d by th e ID A I P S array an d ơ n e v a lu e Prjxd(r max) m easu red by th e eq u a to ria l d ip o le array a t fin a l siz e p max o f th e I D A I P S array.

ị: ; i .

— r o r s *

— ro rs rç j

; ; . Î . i . — ro p r s tr

. . . . ; - i - . i . . — f c p r e n g

10*1--- — *--- — - *•--- — -— --- ~.-iU

10° to’ 1Ơ*

Figure 2. C u rv es p rstr (rorstr), p rsng (rorsng) a n d co rresp o n d in g Petrovski curves

W e r ea lize th a t curves are fitte d . T h is p roves t h a t th e m u tu a l p r in c ip le is righ t for a ll th e a rra y s, th e ele c tr o d e sp a cin g , th e m e a su r em en ts a s w ell a s th e tr a n sfo r m a tio n s th a t h a v e b e e n u sed to con firm th e m e th o d .

IV . C o n f ir m in g t h e c o r r e c tn e s s a n d a d v a n ta g e s o f t h e n e w p r o p o s a ls I V . 1 Calculating values o f the polarization sound ing curves

★

The threc-laycred g CO-electrical model

B y s im u la tio n m e th o d in P C , w e h ave b u ilt th e p ro g ra m s o f calfcu latin g th e p o la r ­ iz a tio n s o u n d in g cu rv es o n layered g e o e le c t r ic a l m o d e ls for d ifferen t e le c tr o d e array by M a tla b la n g u a g e. W o o n ly g ive a sp e cific ex a m p le o f th e th r e e -la y e r e d g e o -e le c tr ic a l m o d e l as fo llo w in g :

pi

= [14.51];

TỊi

= [241);

h x

= [15]; w ith

i

= 1 , 2 , 3

F ig u r e 4 sh o w s th e th e o r e tic a l ID A IP S curve

Tịr

(e ta r ) a n d th e cu r v e co rresp o n d in g to th e I D A I P S cu rv es 7

]sr

(eta sr) o b ta in e d by tra n sfo rm a tio n .

F ig u re 5 sh ow s th e th e o retic a l P etro v sk i cu rve

T)p

(eta p ) a n d th e Petrovski c u r v e

vpsr

(eta p sr) o b ta in e d by tra n sfo rm a tio n .

16

V u DĩẦc M i r t h

F igure 4.

T h e th e o r e tic a l c u r v e

rjr

(eta r) a n d

Figure 5.

T he th eoretical curve

7]p

(etap) c u r v e

ĨỊsr

(e ta s r ) o b ta in e d by t r a n s fo r m a tio n and (etapsr) obtained by transformation

★

The field m edium

T h e te s tin g c a lc u la tio n s h a v e b een p erfo rm ed in T an D a n - H o a n h B o - Q uang N in h an d D a k so n g - G ia Lai. B elow w e o n ly p resen t th e ex a m p le cu rv es m e a su r ed a t p oin t 22 o f th e profile S l l in D ak so n g - G ia L ai.

F ig u re 6 show s c u rv e 7]r (e ta r) p ra c tic a lly m e asu re d by th e ID A IP S array ; th e ID A IP S cu rves 7

]sr

(eta sr) an d

r]p3r

(eta p sr ) o b ta in ed by tra n sfo rm a tio n o f carves

p8) TỊa

p ra ctica lly m ea su red by th e IS IP S array a n d

par.

F igure

6

.

T h e p r a c tic a l c u r v e 7

]r

(e ta r ) a n d

c u r v e 7/irx(e ta s r ),

7J

(e ta p s r ) o b ta in e d by tr a n s fo r m a tio n

In co m p a rin g , p r a c tic a l m ea su red cu rv es an d corresp on d in g cu rv es o b ta in ed by tra n sfo rm a tio n are n early fitte d , o n ly th e v a lu es a t so m e final sizes is n o t th e sam e. T h is proves th e co rrectn ess o f th e a lg eb ra ic tra n sfo rm a tio n s m en tio n ed a b o v e. B esid es, P etro- vski curve a lso h a s reflected clea rly reso lu tio n a b ility - th a t is it s a d v a n ta g es.

I V . 2 P r o c e ss in g d a ta o n th e p ro file

T h e n ew p ro p o sa ls h a v e b e e n a p p lied in tw o directions:

1. P ro c essin g and a n a ly z in g d a ta o b ta in e d p rev io u sly b y th e n o rm a l IP sou nd in g

T h e a d v a n t a g e s o f t h e n e w p r o p o s a l s i n t h e i m p r o v e d s y m m e t r i c... 17

m e th o d in order t o e x p lo it and ad d o th er u sefu l in fo rm a tio n in tw o w ays:

4- In te r p o la tin g values o f cu rv es

TỊk

an d

pk

o b ta in e d p rev io u sly by the n orm al IP so u n d in g m e th o d to v a lu es o f th e im p ro v ed IP cu rves w ith th e co rresp o n d in g sizes o f electro d e sp a cin g a n d co efficien ts.

-f Prom th e s iz e s o f n o rm a l ele c tr o d e array, c a lc u la tin g co rresp o n d in g coefficien ts o f th e im proved e le c tr o d e array.

2. P r o c e ssin g a n d a n a ly z in g d a ta o b ta in e d by th e IS IP S m eth o d .

B elow w e p r e se n t o n ly th e resu lts o f a p p ly in g th e new p ro p o sa ls to ex p lo it d a ta ob ta in ed p rev io u sly b y th e n o rm a l S IP S m e th o d on profile 20 in S o n g G ia n g - Q u a n g N am , w hich w ere m ea su red by U n io n o f P h y sic -G e o lo g y in 1999.

★

The results o f processing and analyzing data obtained previously by the norm al S IP S m ethod on profile 20

(se e figu res 7, 8)

• L ine 20 w a s form ed in th e N o r th e a st - S o u th w est d ir e ctio n p erp en d icu la rly to the folding stru ctu re w ith N o rth w e st - S o u th e a st d irectio n in th e S o u th e a st o f G ia n g R iver.

Figure 7. C ontour section Tị on th e profile 20 (%) (S o u rc e : U n io n o f P h y s ic -G e o lo g y )

• A lo n g th e p rofile, th e fo llo w in g m a in g eo lo g ica l fo rm a tio n s are identified:

-f B en g ia n g - Q u e so n m a g m a co m p lex :

G E O L O G I C A L S E C T I O N IN GIANG RIVEK QUANG NAM

0 2 0 0 4 0 0 6 0 0 8 0 0 1 0 0 0 1 2 0 0

Figure 8 : Geological section of th e profile 20

( S o u r c e : U n io n o f P h y s ic -G e o lo g y )

18 V u D u c M i n h

M ain co m p o n en ts: g ra n o d io rite, b io tite h orn b len d e, a n d to r a n ite b io t.te h o r n ­ b lende. S p ecific p h y sica l fea tu res are r e sistiv ity w ith

p

= 2, 000 — 3 ,0 0 0 oh m s.m p o ­ la riza tio n 7/fc = 3 — 5%

D irectio n s:

1. G ra n o d io rite o f B e n G ia n g - Q u e so n co m p lex , p h a se 2;

2. S ch ist o f K h am d u e fo rm a tio n , layer 3;

3. S ch ist o f K h a m D u e fo rm ation , layer 2;

4- A ltered zones;

5. Faults;

6. V en ts o f gold -su lfu ric q uartz.

+ T h e m etarn orp h ic sed im en ta ry rock s o f K h am D u e fo rm a tio n co n sist of:

- U p p er layer: b io tite - g ra n ite q u artz sh ale, m ic a q u artz, a n d p la g io ela se - bi-

otite quartz. Specific physical features are resistivity w ith p = 1,000 — 2,000 ohm s.m ,

p o la riza tio n w ith

T]k

= 2 — 4%.

- Lower layer: B im ica g n eis, b im ica q u artz, b io tite g n eis, sc h is t, a n d b io tite q u a rtz.

S p ecific p h y sica l fea tu res are r e sistiv ity w ith

p

= 500 - 1 ,0 0 0 o h m s.m , stim u la te d p o la r ­ iz a tio n w ith

7]k

= 2 — 4%.

M eta m o rp h ic sed im en ta ry fo rm a tio n s w ere str o n g ly fo ld ed a n d d ivid ed by d eep fa u lts p erp en d icu la r ly w ith th e su rv ey ed profile. A lo n g th e fa u lts, rock s are stro n g ly d e stro y ed a n d in filtra te d by su lfu ric ores. D estro y ed zone h a s sm all re s is tiv ity p = 2 0 0 —500 o h m s.m an d high p o la riz a tio n

T]k

= 3 — 5%.

G old b ea rin g p o ly m e ta l su rp h id e - q uartz z o n e s h a v e th e r e s is tiv ity relev a n t to altered zo n es an d high p o la r iza tio n

rjk

= 5 — 10%.

• T h e aim o f th e IP so m id in g m e th o d is to so lv e th e fo llo w in g tasks:

+ T o s tu d y folded str u c tu r e s alon g th e su rveyed profile;

4- T o d efin e gold b ea rin g su rp h id e - q u artz zon es.

★

The results o f applying the new proposals to exploit data

W ith a p p ly in g th e n ew p ro p o sa ls to e x p lo it d a ta o b ta in e d p r ev io u sly by th e norm al S IP S m e th o d o n profile 20 in S o n g G ia n g - Q u a n g N a m th en co n to u r se c tio n s o f p o la r­

iz a tio n h ave b een c a lcu la ted and rep orted . B elow w e o n ly present, th e ex a m p le c o n to iư s e c tio n s

T)sr

an d

Tjpsr

o n figures 9, 10.

F igure 9.

C o n to u r s e c tio n 7

]sr

(%)

T h e a d v a n t a g e s o f t h e n e w p r o p o s a l s i n t h e i m p r o v e d s y m m e t r i c . 19

Figure 10. C ontour section 77 pnxd (%)

The results of applying the new proposals in the ISIPS to exploit d a ta obtained on

p rofile 20 in S o n g G ia n g - Q u a n g N a m can b e seen th a t:

-f Detail division of geological com ponents in the section;

- M a g m a tic g ra n o d io r ite fo rm a tio n is ch a racterized by r e s is tiv ity 2,0 0 0 - 3,000 o h m s.m , p o la r iz a tio n 4 - 5%;

- M e ta m o rp h ic se d im en ta ry rock s o f K h a m D u e fo rm a tio n s are ch aracterized by r e sistiv ity 1,000 - '2,000 o h m s.m , p o la r iza tio n 3 - 5%.

+ T h e b rok en zone, d e s t n ic t e d a lo n g th e fa u lts is d e a r ly d efin ed . T h is zo n e is ch a ra cterized by low r e sistiv ity ‘200 - 800 o h m s.m , p o la riz a tio n 6 - 8%; d efin in g in m ore d e ta il th e g o ld b e a rin g sur phi d e - q u artz zo n es w ith th e p o la r iz a tio n from 8 to 10%.

T h e contour s e c tio n

TỊpsr

, sev era lly , d efin ed clearly and in d e ta il th e v e n t b o d ie s w ith the

polarization from 8 to 10%.

We see clearly th at applying the new proposals in the ISIPS to calculate the ap­

parent resistivity and polarization values perm its defining research objects in more detail and locating m ore clearly.

V . C o n c l u s i o n s

1. For th e first tim e, th e P etr o v sk i IP p a ra m eters (e sp e c ia lly r/p) h a v e b een p r o ­ p o sed and th e ir scien tifica lly th e o r e tic a l b a se b u ilt an d a d v a n ta g es th a t th e y e x h ib it higher re so lu tio n a n d g r e a te r in v e s tig a tin g d e p th th a n th e c o n v en tio n al p a ra m e te rs pk i Vk have

been confirmed by us.

ã

2.

T h e n ew p ro p o sa ls in th e IS IP S h a v e h ig h scien tific relia n ce , rea lly u sefuln ess,

and scientific and practical significance. T hey elim inated the fundam ental disadvantage

th a t the transform ation betw een curves through the unstable derivation existed for a

long time. One of the advantages of our proposal is only using the simple and reliable

algebraic form ulas to transform curves. C reating algorithm s of processing and analyzing

the d ata using the new proposals in the ISIPS basing on selecting reliable information

w ith comprehensiveness. T hey also have m ade the geology forecasting results clearer and

20 V u D u c M i n h

m ore reliable, reflected th e n early real IP effect o f s tu d y o b je c ts, in cr e a se d reso lu tio n o f w eak a n o m a lies. A ll o f th o se h a v e illu str a te d th e d istin g u ish ed a d v a n ta g e s o f th e n e w p rop osals.

3. E x p a n d in g and in crea sin g p o ssib ility o f th e a p p lica tio n o f IP so u n d in g m e th o d , n o t o n ly for n ew m ea su rem en t p ro ject, b u t also for e x p lo itin g an d a d d in g oth er u sefu l

in form ation to su p p o r t th e p ro c essin g an d a n a ly zin g o ld o b ta in ed p r e v io u s IP d a ta . T h is is q u ite a new p rob lem a n d v ery n ecessa ry for th e IP so u n d in g m e th o d .

W e co n tin u e t o d ev elo p a n d c o m p le te th is d ire c tio n o f p ro ce ssin g a n d a n a ly zin g th e IP so u n d in g d a ta b a sin g o n e x p lo itin g th e a b o v e n ew p ro p o sa ls have m a d e by th e a u th o r, as w ell a s co n tin u e to d ev elo p th is n ew d ire ctio n for 2 D - 3 D a lg o r ith m s.

R e fe re n c e s

1. L ê V iếl D ư K hương, V ũ Đ ức M in h , C ác phương pháp m ới ư o n g đ o sâu điỏn ư ở dùng tổ hợp hê cực đo hợp lý , T ạ p c h í C á c

Khoa

h ọ c v ề

Trái

đ ấ t, 23 3 (2 0 0 1 ), tr. 2 1 7 -2 2 4 . 2. Vu D uc M inh, Le V ie t D u K h u o n g , Som e Induced-P olarization so u n d in g m eth o d s and

th eừ ab ility in in v estig a tin g g e o lo g ic a l m edium ,

VNU. Journal o f Science, N atural

S c ie n c e s , t X V II 4 ( 2 0 0 1 ) , pp. 2 8 -3 4 .

3. Vu D uc M inh , Induced-P olarization Sounding m ethods in a n ew m anner,

Jo urnal o f

G eology

, S eri B, N o. 17, 18(2 0 0 1 ), pp. 94-101.