Science, Faculty of
Earth, Ocean and Atmospheric Sciences, Department of
DSpace
UBCV
Jose, Barrie Frederick
Master of Science - MSc
University of British Columbia
The piezoelectric effect of quartz rich rock has been investigated both in the laboratory and a subterranean environment. In the laboratory experiment, rock specimens from the Con Mine, Northwest Territories, were examined for crystal alignment and cut into oriented 3.81 cm (1.5 in) sided cubes. The specimens were clamped, together with the measuring electrodes, between parallel plates of a compression cage designed to apply a consistent and uniform pressure distribution across the samples. A solenoid device applied a stress pulse of highly repeatable amplitude and form to the specimen and an instrumentation amplifier measured the differential piezoelectric voltage between opposite faces of the specimen. The massive samples with random fabrics were expected to yield a net "statistical effect". The measured voltage variations between orthogonal directions were attributed to signal domination by large crystals within the matrix, limited sample volume, microfracturing, and the distribution of non-piezoelectric mineral components within the matrixes of some specimens. The greatest piezoelectric responses were obtained from samples containing large crystals in their matrix. The cubic aggregates which clearly exhibited quartz crystal alignment displayed the theoretically predicted minimum piezoelectric response parallel to the preferred crystal elongation direction. The specimens exhibiting greatest alignment produced the largest piezoelectric responses. The limited experimental evidence indicated that the signal magnitude was also proportional to quartz content and crystal size. Underground trials of two exploration systems were conducted at the Con Mine In the first trial, during periods of low industrial electrical interference, clear piezoelectric signals were observed for source-target distances as large as 55 m and electrode-target distances out to 20 m. Piezoelectric signals were generated by impact of both compressional and shear seismic waves with the exposed quartz vein. While this exploration system operated quite effectively during periods of low electrical noise, a superior filter system was required for the normal conditions. For the second fields test, a more portable, DC powered, instrumentation amplifier with an extensive filter system was designed. Despite the improved filtering, noise levels were significantly higher during this trial and beyond 10 m the initial arrival of the piezoelectric signal was obscured.
FEASIBILITY OF THE PIEZOELECTRIC EXPLORATION TECHNIQUE FOB QUARTZ VEIN DETECTION By BARRIE FREDERICK JOSE Sc. Honours Geophysics, Queen's U n i v e r s i t y , 1977 A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE i n THE FACULTY OF GRADUATE STUDIES (Department of Geophysics and Astronomy) We accept t h i s t h e s i s as conforming t o the r e q u i r e d standard THE UNIVERSITY OF BRITISH COLUMBIA August, 1979 (£) B a r r i e Jose, 1979 I n p r e s e n t i n g t h i s t h e s i s i n p a r t i a l f u l f i l m e n t o f t h e r e q u i r e m e n t s f o r an a d v a n c e d d e g r e e a t t h e U n i v e r s i t y o f B r i t i s h C o l u m b i a , I a g r e e t h a t t h e L i b r a r y s h a l l make i t f r e e l y a v a i l a b l e f o r r e f e r e n c e a n d s t u d y . I f u r t h e r a g r e e t h a t p e r m i s s i o n f o r e x t e n s i v e c o p y i n g o f t h i s t h e s i s f o r s c h o l a r l y p u r p o s e s may be g r a n t e d by t h e Head o f my D e p a r t m e n t o r by h i s r e p r e s e n t a t i v e s . I t i s u n d e r s t o o d t h a t c o p y i n g o r p u b l i c a t i o n o f t h i s t h e s i s f o r f i n a n c i a l g a i n s h a l l n o t be a l l o w e d w i t h o u t my w r i t t e n p e r m i s s i o n . D e p a r t m e n t o f (~~s-e res & r,c/ 1^s&t*& t^iy The U n i v e r s i t y o f B r i t i s h C o l u m b i a 2075 W e s b r o o k P l a c e V a n c o u v e r , C a n a d a V6T 1W5 B P 7 5 - 5 1 1 E i i ABSTRACT The p i e z o e l e c t r i c e f f e c t of quartz r i c h rock has been i n v e s t i g a t e d both i n the l a b o r a t o r y and a subterranean environment. In the l a b o r a t o r y experiment, rock specimens from the Con Mine, Northwest T e r r i t o r i e s , were examined f o r c r y s t a l alignment and cut i n t o o r i e n t e d 3,81 cm (1.5 in) s i d e d cubes. The specimens were clamped, together with the measuring e l e c t r o d e s , between p a r a l l e l p l a t e s of a compression cage designed t o apply a c o n s i s t e n t and uniform pressure d i s t r i b u t i o n a c r o s s the samples. A s o l e n o i d d e v i c e a p p l i e d a s t r e s s pulse o f h i g h l y r e p e a t a b l e amplitude and form t o the specimen and an in s t r u m e n t a t i o n a m p l i f i e r measured the d i f f e r e n t i a l p i e z o e l e c t r i c v o l t a g e between o p p o s i t e f a c e s of the specimen. The massive samples with random f a b r i c s were expected to y i e l d a net " s t a t i s t i c a l e f f e c t " . . The measured vol t a g e v a r i a t i o n s between orthogonal d i r e c t i o n s were a t t r i b u t e d to s i g n a l domination by l a r g e c r y s t a l s w i t h i n the matrix, l i m i t e d sample volume, m i c r o f r a c t u r i n g , and the d i s t r i b u t i o n of non-p i e z o e l e c t r i c mineral components w i t h i n the matrixes of some specimens. The g r e a t e s t p i e z o e l e c t r i c responses were obtained from samples c o n t a i n i n g l a r g e c r y s t a l s i n t h e i r matrix. _ The c u b i c aggregates which c l e a r l y e x h i b i t e d quartz c r y s t a l alignment d i s p l a y e d the t h e o r e t i c a l l y p r e d i c t e d minimum p i e z o e l e c t r i c response p a r a l l e l to the p r e f e r r e d c r y s t a l e l o n g a t i o n d i r e c t i o n , - The specimens e x h i b i t i n g g r e a t e s t a l i g n m e n t produced the l a r g e s t p i e z o e l e c t r i c r e s p o n s e s . , The l i m i t e d e x p e r i m e n t a l e v i d e n c e i n d i c a t e d t h a t the s i g n a l magnitude was a l s o p r o p o r t i o n a l t o q u a r t z c o n t e n t and c r y s t a l s i z e . . Underground t r i a l s o f two e x p l o r a t i o n systems were conducted at t h e Con Mine. . I n t h e f i r s t t r i a l , d u r i n g p e r i o d s of low i n d u s t r i a l e l e c t r i c a l i n t e r f e r e n c e , c l e a r p i e z o e l e c t r i c s i g n a l s were observed f o r s o u r c e - t a r g e t d i s t a n c e s as l a r g e as 55 m and e l e c t r o d e - t a r g e t d i s t a n c e s out t o 20 m. P i e z o e l e c t r i c s i g n a l s were g e n e r a t e d by i m p a ct of b oth c o m p r e s s i o n a l and shear s e i s m i c waves w i t h t h e exposed q u a r t z v e i n . While t h i s e x p l o r a t i o n system o p e r a t e d g u i t e e f f e c t i v e l y d u r i n g p e r i o d s o f low e l e c t r i c a l n o i s e , a s u p e r i o r f i l t e r system was r e q u i r e d f o r the normal c o n d i t i o n s . For t h e second f i e l d s t e s t , a more p o r t a b l e , DC powered, i n s t r u m e n t a t i o n a m p l i f i e r w i t h an e x t e n s i v e f i l t e r system was d e s i g n e d . D e s p i t e the improved f i l t e r i n g , n o i s e l e v e l s were s i g n i f i c a n t l y h i g h e r d u r i n g t h i s t r i a l and beyond 10 m the i n i t i a l a r r i v a l of the p i e z o e l e c t r i c s i g n a l was o b s c u r e d . . TABLE OF CONTENTS iv Page ABSTR ACT ,—. . , . , • \ » • , . v » \ . , • .. • * • * • . ( i i ) Table of Contents - (iv) L i s t of TcLbX^s • * . v « i » v « s * > • * (vi) L i s t of Figures.,,......,,......,.,,......., (vii) Acknowledgements ........................ (ix) PREFACE . (xi) CHAPTER 1:- INTRODUCTION TO PIEZOELECTRIC PHENOMENA 1.1 Polar i z a t i o n Of D i e l e c t r i c s ............... 1 1.2 The Nature Of P i e z o e l e c t r i c Effects ....... 2 1,. 3 Mathematical Representation Of (linear) P i e z o e l e c t r i c E f f e c t s ..................... 5 1;4 C r y s t a l Symmetry Considerations ........... 11 1.5 Physical, Geometrical, And P i e z o e l e c t r i c Properties Of Quartz ...................... 13 1.6 Theoretical Basis For The Pi e z o e l e c t r i c E f f e c t In Quartz Rich Bocks ............... 18 1.6.1 Aggregate Symmetries Which Are Theoretically P i e z o e l e c t r i c ............... 18 1.6,. 2 P r a c t i c a l Considerations Concerning Natural Aggregates . . . . . . . . . . . . . . . . . . 21 CHAPTER 2:- PREVIOUS RESEARCH INTO PIEZOELECTRIC EFFECTS IN ROCKS 2.1 Previous Laboratory Investigations With Rock Specimens ............................ 24 2-1.1 Russian Laboratory Investigations ......... 25 2.1.2 Laboratory Investigations of Starkey and A l l i s o n .............................. 27 2.1.3 Laboratory Investigations by Tuck et ! a l . 29 2.1.4 Laboratory Investigations by Bishop 30 2. 1. 5 Summary ....... .... .... .. .. ........ . 33 2.2 Previous Experiments U t i l i z i n g P i e z o e l e c t r i c Properties For Exploration .. 34 2; 2.1 The Basis Of The P i e z o e l e c t r i c i Exploration Technique , 34 V 2,r2.2 Russian Exploration Investigations ... ..... 36 CHAPTER 3:- LABORATORY MEASOREMENT OF THE PIEZOELECTRIC EFFECT Introduction . ..... -. .. ........ ... ..... 38 3.1 Sample Preparation ........................ 39 3-2 Instrumentation: Development of the 1 Measurement System ........................ . 41 3.3 Experimental Results And Discussion ......., 50 CHAPTER 4:- DEVELOPMENT AND FIELD TRIALS OF A PIEZOELECTRIC EXPLORATION SYSTEM In t ro duct ion ...........-............ ...... 66 4.1 Geology Of The Exploration Target ......... 68 4.2 General Geology ............... . . . . i . . . . . 67 4.1.2 Structural Geology ........................ 69 4^1.3 Origin Of The Gold-bearing Quartz Lenses .. 70 4.2 F i r s t Exploration F i e l d T r i a l ............. . 71 4.2.1 Instrumentation ........................... 71 4.2.2 Test Site.#1: Development Of Operational Procedures 74 4; 2.3 Experiments At Test Site #2 77 4.2.4 Summary Of F i r s t Exploration F i e l d T r i a l ... . 87 4 r3 Second Exploration F i e l d T r i a l ............ 90 4.3.1 Instrumentation ........................... 90 4,. 3.-2 Results Of Second, F i e l d T r i a l ............. 102 CHAPTER 5:- SUMMARY AND SUGGESTIONS 110 Bibliography .............................. 112 Appendix 1 ................................ 120 Appendix 2 ................................ 121 VI LIST OF TABLES Table Page 1,, Defining Eguations For The Direct And Converse Pie z o e l e c t r i c Effect ................. 11 : , i 2. Polymorphs Of Quactz At Atmospheric; Pressure ...................................... 14 3,. Experimental Results Of Massive Con Mine Bocks .......................................... 53 4 . Experimental Results Of Foli a t e d Con Mine BOCkS ..................... mm .. . . . - . - . • ........ . 60 5. F o l i a t e d Specimen Mean Pi e z o e l e c t r i c Signal Amplitudes For Relative Quartz Contents ....... 63 v i i LIST OF FIGURES Figure Page I . , The Belations Between E l e c t r i c a l And Mechanical Properties Of Crystals ............. 4 2. Mechanical Excitation Of E l e c t r i c Charge In .. j The Development Of The P i e z o e l e c t r i c E f f e c t 6 3. Left-handed Quartz Crys t a l .................... 15 4. Eight-handed Quartz Crys t a l ................... 15 5V» Basis Of Subterranean P i e z o e l e c t r i c Exploration ................................... , 35 6. Designation Of The Faces Of The Cubic Bock Specimens ........................ . . . . . . . . . . 40 7. . Prototype System For Laboratory P i e z o e l e c t r i c Measurement ,.,,,........,......;...«»... 43 8. Compression Cage Used In Laboratory Measurements ....................... ..... ...... 45 9,.. F i n a l Version Of The Laboratory Measurement System .......................... ........ ...... 47 10.. Freguency Response Of Amplifier And F i l t e r System . . 49 I I . Demonstration Of The Bepeatability Of The Laboratory Measurement System ........ ,.......,;„... 52 12lf Demonstration Of Beversal Of Signal P o l a r i t y Besulting From Separate Solenoid Core Impacts With Sample #44 In (a) Normal Pos i t i o n , (b) Inverted Position In The Compression Cage ............................... 56 13. Maximum Entropy Power Spectrum Of The Becord In Fig. 12a. ............................. 57 14. P i e z o e l e c t r i c Exploration System Used In F i r s t F i e l d T r i a l 72 15. E l e c t r i c a l Signals Produced By One Hammer Impact 11 m West Of Quartz Vein With Electrodes 11 And 15 m West Of The Vein ...... 78 16. E l e c t r i c a l Signal Produced By One Hammer Impact 15 m West Of Quartz Vein With Electrodes 11 And 15 m West Of The Vein ...... 79 v i i i 17. Example Of Piez o e l e c t r i c Signal Repeatability, Signal Produced Using The Same Parameters As Fig. 16 .................... 80 18. E l e c t r i c a l Signal Produced By One Hammer Impact 46 m East Of Quartz ' Vein With Electrodes 11 And 15 m West Of The Vein ...... 81 19. Maximum Entropy Power Spectrum Of Becord Shown In Fig. 18 .....a..........*......,.....*. 84 20,. P i e z o e l e c t r i c A r r i v a l Times As A Function Of Distance From Shot Point To Quartz Vein .... 85 21., Two Stage Instrumentation Amplifier ,..,..,.»,«.,..,. 92 22.. Schematic Of Complete Amplifier And F i l t e r System- , 94 23. . 60 Hz Active Tunable Notch F i l t e r And Buffer Amplifier 96 24. Frequency Eesponse Of 60 Hz Active Tunable Notch F i l t e r 97 25. Active High Pass F i l t e r And 420 Hz Active Tunable Notch F i l t e r . , 98 26. Frequency Response Of Active High Pass F i l t e r . . 99 27. Gain Of 10 Amplifier And 180 Hz Adjustable High-Q Notch F i l t e r ........................... 100 28. Frequency Response Of 180 Hz Adjustable High-Q Notch F i l t e r 101 29. P i e z o e l e c t r i c Signal Produced By Ten Enhanced Impacts 6.3 m West Of Quartz Vein. One Electrode 10.5 m West Of Vein And Other Situated In Vein. . 104 30. . Subterranean Seismic Survey Considerations! .... . 105 31. P Wave Seismic A r r i v a l Times As A Function Of Distance From Shot Point To Geophone ....... 107 32.. Shear Seismic A r r i v a l Times As A Function Of The Distance Between Shot Point And Geophones ......................... .... ..... ... . . 108 ACKNOWLEDGEMENTS I would l i k e to express my g r a t i t u d e t o my s u p e r v i s o r , P r o f e s s o r Bob E l l i s f o r suggesting the p r o j e c t and h i s h e l p f u l s u ggestions throughout the work..I a l s o thank P r o f e s s o r Garry C l a r k e f o r re a d i n g the manuscript and p r o v i d i n g c o n s t r u c t i v e s u g g e s t i o n s . Bo Chandra provided some i d e a s f o r the prototype compression cages and Bob Meldrum, Don Ru s s e l , Barry Narod, and Peter Michelow discu s s e d t h e i r i d e a s on e l i m i n a t i o n of n o i s e i n the l a b o r a t o r y system. J u l e s L a j o i e of Cominco E x p l o r a t i o n not only acted as l i a s o n with h i s company but provided much welcomed a s s i s t a n c e at t e s t s i t e #1 when the f i r s t f i e l d t r i a l was i n i t s i n f a n c y . Many thanks a l s o to the amiable miners who helped t r a n s p o r t equipment, d r i l l h o l e s , e t c . t h a t could not have .been done alone. A very s p e c i a l debt of g r a t i t u d e i s owed t o Bob Meldrum who shared the f r u s t r a t i o n s , m a l f u n c t i o n s , and burden of the second f i e l d t r i p , . Without h i s capable help i n b u i l d i n g an a l t e r n a t i v e a m p l i f i e r system i n the f i e l d , the t r i a l may have ended much sooner. My dearest f i a n c e , Kathryn I n k s t e r , provided a f o u n t a i n of encouragement as w e l l as t y p i n g the manuscript f. F i n a l l y , the author g r a t e f u l l y acknowledges the funding X provided by Ccminco E x p l o r a t i o n (Vancouver) and the Con Mine (Cominco Ltd,.) which made t h i s work possible,. I would a l s o l i k e to express my a p p r e c i a t i o n to the Government of B r i t i s h Columbia f o r the Graduate Research E n g i n e e r i n g and T e c h n o l o g i c a l (G.R.E.A.T.) s c h o l a r s h i p which supported me d u r i n g the course of t h i s study. x i PREFACE P i e z o e l e c t r i c i t y i s a phenomenon c h a r a c t e r i s t i c a l l y e x h i b i t e d by some, minerals ( p a r t i c u l a r i l y d i e l e c t r i c s , but r a r e l y semiconductors) r e s u l t i n g i n e l e c t r i c a l p o l a r i z a t i o n as the consequence of an a p p l i e d f o r c e . The h i s t o r y of p i e z o e l e c t r i c i t y dates back to 1880 when P i e r r e and Jacques C u r i e f i r s t d i s c o v e r e d the e f f e c t i n v a r i o u s substances i n c l u d i n g R o c h e l l e s a l t , quartz, and tourmaline ( S h i e l d s , 1966). P i e z o e l e c t r i c i t y remained a l a b o r a t o r y c u r i o s i t y u n t i l i n 1916 when Paul Langevin developed an u l t r a s o n i c submarine d e t e c t o r as the f i r s t major a p p l i c a t i o n . About the same time the - mechanical resonance p r o p e r t i e s of quartz were d i s c o v e r e d . A p p l i c a t i o n s of p i e z o e l e c t r i c phenomena are now employed i n many u n r e l a t e d f i e l d s the p r i n c i p a l a p p l i c a t i o n s are. i n s e l e c t i v e wave f i l t e r s , frequency c o n t r o l , and i n t r a n s d u c e r s f o r t r a n s f o r m i n g e l e c t r i c a l energy i n t o mechanical energy and v i c e v e r s a . Ose of the p i e z o e l e c t r i c p r o p e r t i e s of n a t u r a l l y o c c u r r i n g minerals may a l s o one day play a large p a r t i n mineral e x p l o r a t i o n and mine development. Many ore and mineral d e p o s i t s are interwoven with quartz and p e g m a t i t i c v e i n s . Subterranean e l e c t r i c a l , g r a v i m e t r i c , s e i s m i c and r a d i o m e t r i c g e o p h y s i c a l methods have been developed f o r e x p l o r a t i o n w i t h i n mines but are i n e f f e c t i v e f o r d e t e c t i n g these v e i n s . In the Western world, c o s t l y underground d r i l l i n g i s employed at present. However, by 1964, Russian g e o p h y s i c i s t s were r o u t i n e l y u s i n g a method based x i i on the p i e z o e l e c t r i c e f f e c t of rocks c o n t a i n i n g quartz i n at l e a s t two metal mines f o r l o c a t i n g q u a r t z i t i c o r e - b e a r i n g v e i n s and c a v i t i e s f i l l e d with c r y s t a l l i n e . quartz ( V o l a r o v i c h & Sobolev, 1965, 1 968; Parkhomenko, 1971). U n f o r t u n a t e l y , the Eussian papers l a c k e d t h e c l e a r p r e s e n t a t i o n of d e t a i l s r e q u i r e d f o r d i r e c t a p p l i c a t i o n . The g o a l of t h i s t h e s i s was to develop e x p l o r a t i o n i n s t r u m e n t a t i o n and f i e l d procedures, and to determine the l i m i t a t i o n s of the p i e z o e l e c t r i c e x p l o r a t i o n method. Chapter 1 p r o v i d e s background i n t o the nature and mathematical r e p r e s e n t a t i o n of p i e z o e l e c t r i c e f f e c t s . . The p h y s i c a l , geometric, and p i e z o e l e c t r i c p r o p e r t i e s of quartz are d i s c u s s e d i n some d e t a i l along with the b a s i s f o r e x p e c t i n g m u l t i c r y s t a l l i n e aggregates to e x h i b i t " f a b r i c r e l a t e d " p i e z o e l e c t r i c e f f e c t s . , Chapter 2 d i s c u s s e s p r e v i o u s i n v e s t i g a t i o n s i n t o p i e z o e l e c t r i c e f f e c t s i n q u a r t z i t i c r o c k s . . The f i r s t p art of Chapter 2 d e s c r i b e s l a b o r a t o r y measurement of p i e z o e l e c t r i c e f f e c t s o f aggregates by Eussian r e s e a r c h e r s and more r e c e n t l y , t h r e e Western i n v e s t i g a t i o n s (Starkey & A l l i s o n , 1975; Tuck et a l . , 1977; and Bishop, 1978),. The l a t t e r p a r t of the chapter d e s c r i b e s the r e p o r t s of p r e v i o u s Eussian t r i a l s with a p i e z o e l e c t r i c e x p l o r a t i o n system. Chapter 3 d e a l s with development of a l a b o r a t o r y system t o measure the p i e z o e l e c t r i c e f f e c t of rock cubes and the r e s u l t s of measurements on a s u i t e of samples from the Con Mine, Northwest T e r r i t o r i e s are discussed,. , Two f i e l d t r i a l s of p i e z o e l e c t r i c e x p l o r a t i o n systems were x i i i conducted. The i n s t r u m e n t a t i o n , f i e l d procedures, and r e s u l t s are d i s c u s s e d i n Chapter 4.,It i s hoped t h a t t h e i n s i g h t gained i n these f i e l d t r i a l s w i l l be b e n e f i c i a l t o those c o n t i n u i n g development and refinement of t h i s new e x p l o r a t i o n technique. Chapter 5 summarizes the r e s u l t s of l a b o r a t o r y and subterranean e x p l o r a t i o n experiments and provides some sugge s t i o n s t h a t the author hopes f u t u r e i n v e s t i g a t o r s w i l l f i n d h e l p f u l . x i v I t would be i n t e r e s t i n g to know whether t h i s development [of charges by s t r e t c h i n g r u b b e r ] , and t h a t produced by compression, i s p r o g r e s s i v e or sudden, whether the e l e c t r i f i c a t i o n produced by each o f t h e s e o p e r a t i o n s i s t h e same or d i f f e r e n t [ i n s i g n j ] , what pa r t o f the molecules i n the i n t e r i o r of the body and those on the s u r f a c e t a k e i n the t o t a l p r oduction; i t would be e s p e c i a l l y c u r i o u s and perhaps r a t h e r easy to i n v e s t i g a t e i n c r y s t a l l i n e m i n e r a l s , where the: aggregation of the p a r t i c l e s , however r e g u l a r i n i t s assembly, presents i n the d i f f e r e n t d i r e c t i o n s i n the c r y s t a l kncwn d i f f e r e n c e s which can i n f l u e n c e the ease, great or s m a l l , with which the e l e c t r i c i t y i s separated. A.G. Becquerel, 1820. 1 CHAPTER U INTRODUCTION TO - PIEZOELECTRIC PHENOMENON -1.1 POLARIZATION OF DIELECTRICS -A number of forms of e l e c t r i c a l p o l a r i z a t i o n have been observed i n d i e l e c t r i c s . In metals the e l e c t r o n s are f r e e to move,.,In d i e l e c t r i c s , the charged p a r t i c l e s under the i n f l u e n c e of an a p p l i e d e l e c t r i c f i e l d , may undergo only l i m i t e d s h i f t s or i n the case of p o l a r molecules a r e o r i e n t a t i o n may take p l a c e . . Some recognized forms of p o l a r i z a t i o n i n d i e l e c t r i c s are e l e c t r o n or i o n displacement, d i p o l e , i o n or e l e c t r o n r e l a x a t i o n , and i n t e r f a c i a l p o l a r i z a t i o n . P o l a r i z a t i o n by e l e c t r o n displacement takes pla c e as the r e s u l t of the s h i f t of e l e c t r o n r e l a t i v e to the nucleus of an atom or ion when an e l e c t r i c f i e l d i s applied,. In the case of i o n i c p o l a r i z a t i o n (or atomic p o l a r i z a t i o n ) , i o n s of one s i g n s h i f t with r e s p e c t to i o n s o f the opposite s i g n when an e l e c t r i c f i e l d i s a p p l i e d . R e l a x a t i o n p o l a r i z a t i o n takes p l a c e when p o l a r molecules or molecules c o n t a i n i n g p o l a r r a d i c a l s are present, as well as t h e r m a l l y e x c i t e d d e f e c t s or " h o l e s " . I n t e r f a c i a l p o l a r i z a t i o n occurs i n m a t e r i a l s which are inhomogeneous i n t e x t u r e and have l a y e r s w-ith d i f f e r i n g e l e c t r i c a l p r o p e r t i e s . (Parkhomenko, 1S71) . An e l e c t r i c f i e l d i s nQt %h.e only f a c t o r which may l e a d to p o l a r i z a t i o n o f a d i e l e c t r i c . P o l a r i z a t i o n may a r i s e as a r e s u l t of other f a c t o r s i n some types of d i e l e c t r i c m a t e r i a l s because of t h e i r s t r u c t u r a l p e c u l i a r i t i e s . . F o r example, the p a r t i c u l a r s t r u c t u r e of some d i e l e c t r i c s termed " p y r o e l e c t r i c " r e s u l t s i n 2 charge pol a r i z a t i o n on some c r y s t a l boundaries when heat i s applied. . Secondly, some d i e l e c t r i c s termed " e l e c t r e t s " can maintain a polarization charge for long periods of time following removal from the f i e l d . T hirdly, there i s a r e l a t i v e l y limited c l a s s of materials i n which polarization takes place under the ef f e c t of mechanical force or deformation, even i n the absence of an external e l e c t r i c f i e l d . This polarization phenomenon of d i e l e c t r i c s (and rarely semiconductors) i s known as " p i e z o e l e c t r i c i t y " , and i t s measurement in rocks w i l l be the p r i n c i p a l focus of t h i s thesis. 1.2 THE N&TORE OF PIEZOELECTRIC EFFECTS I f a pie z o e l e c t r i c c r y s t a l i s subjected to stress or mechanical pressure i n certain directions r e l a t i v e to the cr y s t a l faces, the c r y s t a l becomes e l e c t r i c a l l y polarized with an e l e c t r i c moment of magnitude proportional to the applied stress. Depending on the pressure applied and the nature and size of the p i e z o e l e c t r i c material, e l e c t r i c potentials ranging from a f r a c t i o n of a volt to many thousands of volts can be obtained (Shields, 1966), This generation of an e l e c t r i c charge upon application of stress i s known as the " d i r e c t p i e z o e l e c t r i c e f f e c t " . The derivation of the name p i e z o e l e c t r i c i t y from the greek word "piezo" meaning "pressure" obviously translates as "pressure e l e c t r i c i t y " . . Conversely, i f a p i e z o e l e c t r i c c r y s t a l i s polarized by application of an e l e c t r i c f i e l d , i . e . by application of a voltage across the c r y s t a l by electrodes, mechanical stresses 3 are produced w i t h i n the c r y s t a l and i t changes i t s shape. The e x i s t e n c e of t h i s "converse p i e z o l e l e c t r i c e f f e c t " i s a thermodynamic consequence of the d i r e c t p i e z o e l e c t r i c phenomenon. I f the converse e f f e c t i s taken a stage f u r t h e r by a p p l y i n g an a l t e r n a t i n g voltage t o the e l e c t r o d e s , the c r y s t a l i s set i n t o mechanical v i b r a t i o n . I f the frequency i s adjusted u n t i l i t becomes equal to the n a t u r a l frequency of v i b r a t i o n of the c r y s t a l , the phenomenon of resonance o c c u r s : the amplitude of v i b r a t i o n of the c r y s t a l becomes very l a r g e , and c o r r e s p o n d i n g l y l a r g e p i e z o e l e c t r i c charges are.developed on i t s s u r f a c e s (Vigoureux, 1939). The c r y s t a l behaves l i k e an o s c i l l a t i n g c i r c u i t with an e f f i c i e n c y and s t a b i l i t y f a r s u p e r i o r to those o b t a i n a b l e by i n d u c t o r s and c a p a c i t o r s . P i e z o e l e c t r i c c r y s t a l s thus are e l e c t r o m e c h a n i c a l t r a n s d u c e r s c o u p l i n g e l a s t i c and d i e l e c t r i c phenomena ( F i g . 1 ) . A p o r t i o n of the mechanical energy of e l a s t i c s t r a i n i n c i d e n t upon a c r y s t a l i s transformed i n t o e l e c t r o m a g n e t i c energy. The r a t i o of these e n e r g i e s , o f t e n r e f e r r e d to as the p i e z o e l e c t r i c c o u p l i n g f a c t o r k i s a measure of the energy c o n v e r s i o n e f f i c i e n c y of the c r y s t a l and i s dependent on the e l a s t i c and d i e l e c t r i c p r o p e r t i e s o f the c r y s t a l . A f u r t h e r property of p i e z o e l e c t r i c m a t e r i a l s i s t h e i r dependence upon temperature. , I f heated beyond the C u r i e temperature of the m a t e r i a l , l o s s of p i e z o e l e c t r i c p r o p e r t i e s r e s u l t s because the charged p a r t i c l e s l o s e t h e i r o r d e r l y arrangement and assume a random p a t t e r n due to the g r e a t e r m o b i l i t y of the atoms. The l o s s of p i e z o e l e c t r i c p r o p e r t i e s i s permanent and w i l l not be r e g a i n e d a f t e r c o o l i n g below the Curie . DISPLACEMENT STRAIN ELECTRIC FIELD STRESS FIGURE 1 :- THE RELATIONS BETWEEN ELECTRICAL AND MECHANICAL PROPERTIES OF CRYSTALS (modified after Nye, 1962) 5 p o i n t u n l e s s the m a t e r i a l c o o l s i n the presence of an e l e c t r i c f i e l d . 1.3 MATHEMATICAL REPRESENTATION OF (LINEAR) PIEZOELECTRIC EFFECTS. Development of the fundamental p i e z o e l e c t r i c c o n s t i t u e n t equations f o r s i n g l e c r y s t a l i n t e r a c t i o n s through thermodynamical arguments i s q u i t e lengthy and w i l l not be d e s c r i b e d here. The reader i s i n s t e a d r e f e r r e d t o Cady (1946), Born & Huang (1966), Mason (1966), T i e r s t e n (1969) or Juretschke (1974),. A g u a l i t a t i v e d e s c r i p t i o n of the mechanical e x c i t a t i o n of a p i e z o e l e c t r i c charge i n quartz has been gi v e n by Meissner (1927). As a f i r s t approximation, the s i l i c o n and oxygen atoms i n a q u a r t z c r y s t a l S i 0 2 are s i t u a t e d i n a s i x - s i d e d s t r u c t u r e such t h a t they have o v e r a l l e l e c t r i c a l n e u t r a l i t y ( F i g . 2a). I f a s t r e s s i s a p p l i e d to the p i e z o e l e c t r i c c r y s t a l i n c e r t a i n d i r e c t i o n s , the displacement of i o n s r e s u l t s i n a charge p o l a r i z a t i o n as shown i n F i g s . 2b and c. Conventions have been e s t a b l i s h e d f o r the mathematical r e p r e s e n t a t i o n of p i e z o e l e c t r i c phenomenon with r e s p e c t to the v a r i o u s c r y s t a l symmetry c l a s s e s and are now o u t l i n e d f o l l o w i n g Nye (1972). I t i s found t h a t when a gen e r a l s t r e s s o~7j (second-rank tensor) a c t s on a p i e z o e l e c t r i c c r y s t a l , each of the t h r e e components o f the p o l a r i z a t i o n v e c t o r Pi are l i n e a r l y r e l a t e d to a l l n i n e components of c ; . Thus the g e n e r a l r e l a t i o n between P,-FIGURE 2 :- MECHANICAL EXCITATION'OF ELECTRIC CHARGE IN THE DEVELOPMENT OF THE PIEZOELECTRIC EFFECT. (after Meissner, 1927) as 7 and crij f o r the " d i r e c t p i e z o e l e c t r i c effect'? i s Pj =&ijk &jk ... (1) where the d .jk are the " p i e z o e l e c t r i c moduli" --'components of a t h i r d -rank tensor with 27 c o e f f i c i e n t s . I f one co n s i d e r s a p p l i c a t i o n of pure shear s t r e s s e s , a p h y s i c a l l y r e a l i z a b l e s o l u t i o n r e q u i r e s t h a t d;jk =d;kj >.<••<• (2) thus r e d u c i n g the number of independent c o e f f i c i e n t s t o 18. In p r i n c i p l e , i f u n i a x i a l t e n s i l e s t r e s s e s cr,, , Q-2Z , and a~ss could be a p p l i e d and the r e s u l t i n g p o l a r i z a t i o n components measured, values o f the p i e z o e l e c t r i c moduli f o r which j=k might be found. The p i e z o e l e c t r i c moduli t e n s o r may be thought of as a cubic a r r a y as f o l l o w s : 1st layer 2nd layer 3rd layer i = 1 i = 2 i = 3 ^111 ^112 ^113 ^211 ^212 ^213 ^311 ^312 ^313 (d121) d122 d123 (d221) d222 d223 [d321) d322 d323 . . . (3) (d13l) d133 (d23l) (^232) ^233 (^33l) ( ^ 3 3 2 ) d , 333 The non-independent c o e f f i c i e n t s are shown i n bra c k e t s i n the above e g u a t i o n . The t r a n s f o r m a t i o n from f u l l t e n s o r n o t a t i o n t o the more advantageous matrix n o t a t i o n i s accomplished by maintaining the same f i r s t s u f f i x but r e p l a c i n g the second and t h i r d s u f f i x e s of te n s o r n o t a t i o n by a s i n g l e s u f f i x as i n (4),.. 8 Tensor n o t a t i o n 11 22 33 23,32 31,13 12,21 m a t r i x n o t a t i o n 1 2 3 4 5 6 (4) F a c t o r s o f 1/2 are a l s o i n t r o d u c e d such t h a t (3) i n terms o f the new symbols appears as: d 11 i ^ l 8 1^15 ^12 £ ^ 1 4 d2i ^d2i \di& • ^22 ^*^24 i ^23 . ^31 i ^ 3 0 1^35 ^32 £ ^ 3 4 dm .. (5) t h u s . ' l l "12 T 1 2 a 2 2 L " 3 1 ° 2 3 J 3 1 T 2 3 J 3 3 J J 3 J (6) and e q u a t i o n (1) becomes, P; =dijOj (1=9,2,3; .j=1,2, 6) ... (7) where 1 a„ d,* d „ d „ d * d,< a* d 2 2 d 2 ? d 2^ \ d „ d J 2 d w d* dw-(8) The rows of t h i s m a t r i x c o r r e s p o n d t o the l a y e r s i n the arrangement (3) and have t h e advantage of g r e a t e r compactness than t h e t e n s o r n o t a t i o n . 9 The e x i s t e n c e : o f the.converse p i e z o e l e c t r i c e f f e c t i s a thermodynamical consequence of the d i r e c t e f f e c t (see Nye,1972, Chapter X). A p i e z o e l e c t r i c c r y s t a l changes shape when an e l e c t r i c f i e l d i s a p p l i e d . I t i s found t h a t there i s a l i n e a r r e l a t i o n between the components of the vector E; g i v i n g the e l e c t r i c f i e l d i n t e n s i t y w i t h i n the c r y s t a l and the components of the s t r a i n t e n s o r €jk which d e s c r i b e the . change of shape. Moreover, the c o e f f i c i e n t s connecting the f i e l d and the - s t r a i n i n the converse e f f e c t are the same as t h o s e r connecting - the s t r e s s and the p o l a r i z a t i o n i n the d i r e c t e f f e c t . E x p l i c i t l y , when the d i r e c t e f f e c t i s w r i t t e n as P/ =&;jk<Tjk . . . (1) the converse e f f e c t i s w r i t t e n €jk = d ^ E/ ... (9) Equation (9) may a l s o be w r i t t e n i n matrix n o t a t i o n by making the f o l l o w i n g s u b s t i t u t i o n f o r the s t r a i n components: i €12 e31 -> he e22 c23 ha - e3! €23 €33. i e 5 «3. ... (10) i n matrix n o t a t i o n , the converse e f f e c t i n g e n e r a l i s w r i t t e n : €j -4,y B , (i=1,2,3; j=1,2,...,6) . (11) 10 The f o l l o w i n g scheme.summarized the p i e z o e l e c t r i c equations i n the matrix n o t a t i o n . Read h o r i z o n t a l l y by rows i t g i v e s the d i r e c t e f f e c t , and read v e r t i c a l l y by columns i t g i v e s the converse e f f e c t . €2 e3 «5 e6 • 1 a2 °a a6 °6 I Pi dn di2 d13 du d16 d16 E2 P. d2i d 2 2 d23 d2i d25 d2Z E3 P3 d3i d32 d33 d3i d3S d36 ... (12) Table 1 compares the eq u a t i o n s converse p i e z o e l e c t r i c e f f e c t s i n n o t a t i o n . d e f i n i n g the d i r e c t and the t e n s o r and the matrix 11 TABLE J Defining Equations For The Direct And Converse P i e z o e l e c t r i c Effect I *• 1 T 1 | | Tensor notation| matrix notation I | | ( i , j,k=1,2r3) I (i=1,2,3;j=1,2,...,6) | I d i r e c t e f f e c t | P/ =&/j*ojk | P; =d,yc/ I I converse e f f e c t | €jk =&,yk E/ | €j =&// E/ I after Nye, (1972) CRYSTAL SYMMETRY CONSIDERATIONS -The 18 matrix notation c o e f f i c i e n t s of the p i e z o e l e c t r i c moduli are general enough to represent the p i e z o e l e c t r i c properties of any c r y s t a l (equations 14),. The symmetry inherent in the various c r y s t a l structures eliminates some of the pi e z o e l e c t r i c moduli and causes others to have numerical relationships. Hence, i n order to understand the relationships e x i s t i n g f o r c r y s t a l s i t i s necessary to consider the c r y s t a l systems and the symmetries e x i s t i n g i n c r y s t a l s . The i d e a l c r y s t a l i s referred to i d e n t i c a l unit c e l l s which are usually chosen to be the smallest parallelepiped from which the c r y s t a l can be constructed. Bravais showed that the number of types of polyhedra that w i l l completely f i l l space i s seven. The seven c r y s t a l systems evolved from the Bravais l a t t i c e s are, in order of increasing symmetry, the t r i c l i n i c , monoclinic, orthorhombic, tetragonal, t r i g o n a l , hexagonal, and cubic 12 (isometric). These 1 c r y s t a l systems are further divided into 32 point groups or c r y s t a l classes.. Now suppose a c r y s t a l with a centre of symmetry were subjected to a general stress and became polarized. Then imagine the whole system, c r y s t a l plus stress, i s inverted through the centre of symmetry. The stress being centrosymmetrical, w i l l be unchanged; so also w i l l the c r y s t a l ; but the p o l a r i z a t i o n w i l l be reversed in direction..We are l e f t with the same c r y s t a l as before under the same stress with the reverse p o l a r i z a t i o n . This s i t u a t i o n i s only possible i f the p o l a r i z a t i o n i s zero. Hence, a c r y s t a l with a centre of symmetry cannot be p i e z o e l e c t r i c . The equality cf some of the p i e z o e l e c t r i c moduli or their elimination may be deduced by similar symmetry arguments. Many rel a t i o n s must be found by a more a n a l y t i c a l approach. The qeneral approach (Mason,1966) makes use of the transformation properties of tensors by introducinq an element of symmetry and specifying that the c r y s t a l properties s h a l l remain unchanged after such a rotation. Application of group theory i s preferred by some authors. Of the 32 recognized classes of symmetry, 11 have a centre of symmetry and may not be p i e z o e l e c t r i c (Parkhomenko, 1 9 7 1 ) F o r the remaining c r y s t a l symmetries, charts of the non-vanishing c o e f f i c i e n t s in the p i e z o e l e c t r i c moduli matrixes may be found i n Nye (1972). Of the minerals with these symmetries, the p i e z o e l e c t r i c effect has been established quantitatively or q u a l i t a t i v e l y i n about 30% (Parkhomenko,1971). ,The orthorhombic, cubic, and monoclinic c r y s t a l systems possess 60, 43, and 42 p i e z o e l e c t r i c minerals respectively. Tetragonal, rhombohedral, 13 and hexagonal systems each have 29-35 pi e z o e l e c t r i c minerals and the t r i c l i n i c system has only 12. 1.5 PHYSICAL, GEOMETRICAL & PIEZOELECTRIC - PROPERTIES OF QUARTZ. Having gained some insight into the nature of p i e z o e l e c t r i c phenomenon, the i r causes, and the mathematical representation of the phenomenon, we now focus on the p a r t i c u l a r p i e z o e l e c t r i c mineral of i n t e r e s t to us - guartz. Quartz i s a good d i e l e c t r i c with a d i e l e c t r i c constant of about 4,.5. The conductivity i s much greater along the p r i n c i p a l axis than across i t , but both are small (Vigoureux, 1939) . The p i e z o e l e c t r i c coupling c o e f f i c i e n t described e a r l i e r i s about 0.1 for guartz. Quartz also exhibits pyroelectric behavior, becoming e l e c t r i f i e d when heated. With respect to abundance in the earth*s crust, i t i s second only to the alumino-^silicates, and i s a primary rock-forming mineral. Such rocks as quartzite and sandstone consist almost e n t i r e l y of quartz. Quartz i s found i n s i q n i f i c a n t quantities in igneous rocks, including quartz porphyry, qranite, granite porphyry, d i o r i t e , and others. Both j large and small veins are commonly f i l l e d with guartz. Other than guartz, the only common rock-forming minerals with s i g n i f i c a n t p i e z o e l e c t r i c moduli are tourmaline, nepheline, and sphalerite. Quartz i s a polymorphic mineral having four forms. The temperature range of s t a b i l i t y , c l a s s of symmetry and a representation of the non-vanishing c o e f f i c i e n t s of their p i e z o e l e c t r i c moduli matrix are shown i n Table 2. By far the L E A F 14 OMITTED IN PAGE N U M B E R I N G , 15 most common form i s -guartz and a p e r f e c t c r y s t a l ( F i g . 3 or Fig..4) c o n s i s t s of a hexagonal prism terminated at e i t h e r end by a hexagonal pyramid., This d e s c r i p t i o n however i g n o r e s the f a c e s marked " s " and "X". Both r i g h t and l e f t - h a n d e d forms (enantiomorphs) occur i n nature and should be an important f a c t o r when c o n s i d e r i n g the p i e z o e l e l e c t r i c e f f e c t of a quartz aggregate. Fig.3 Left-handed quartz ' Fig,4 Eight-handed quartz c r y s t a l c r y s t a l ( a f t e r Vigoureux, 1939) The l i n e j o i n i n g the v e r t i c e s of the two pyramids i s an 16 a x i s of symmetry (denoted by Z ) , but the symmetry i s not hexagonal but only t r i g o n a l (Vigoureux, 1939). In the b a s a l plane p e r p e n d i c u l a r to t h i s t r i g o n a l ( t r i a d , p r i n c i p a l or o p t i c ) a x i s , t h e r e are t h r e e d i a g o n a l (diad, or a-axes) axes p a r a l l e l t o the f a c e s m of the hexagonal prism. The three d i r e c t i o n s c o p l a n a r with and p e r p e n d i c u l a r to the d i a d axes are denoted Y. These are not axes of symmetry. For right-handed °< -quartz ( t e t r a g o n a l system) the d,y moduli i n matix n o t a t i o n have the form (Nye,1972): P2 *3 C7 0 0~2 •d// 0 d* 0 0 0 0 o "d* -2d 0 0 0 0 0 ... (13) The x, , x 2 , and x3, d i r e c t i o n s correspond to X, Y, and Z i n f i g u r e s 3 and 4,. To a p p r e c i a t e the p h y s i c a l s i g n i f i c a n c e of equation 13 and understand the p i e z o e l e c t r i c response of guartz to s t r e s s , i t i s u s e f u l to c o n s i d e r a few examples. R e c a l l that ^ i o~2 i G~3 t are pure s t r e s s e s while cr4 , a's , and o~i r e p r e s e n t shear s t r e s s e s . I f a t e n s i l e s t r e s s cr, or crz i s a p p l i e d p a r a l l e l t o x, or xt r e s p e c t i v e l y , the only p o l a r i z a t i o n which develops i s p a r a l l e l to x, (the diad axis) with a magnitude of P, =d,/C; i n the f i r s t case and P, ^d^cn, i n the l a t t e r c a s e . Furthermore, a shear s t r e s s about x, again r e s u l t s i n only a p o l a r i z a t i o n P, =d / 40} about the diad a x i s (xy ). A p o l a r i z a t i o n along xz may be produced o n l y by a shear crs about x 2 g i v i n g P 2 = -d / 4o> or by a shear csi about x 5 1 7 g i v i n g P 2=-2d / / &l . From eg u a t i o n 13 i t may a l s o be seen t h a t , no matter how the c r y s t a l i s s t r e s s e d , the p o l a r i z a t i o n - p a r a l l e l to the t r i g o n a l ( t r i a d , p r i n c i p a l , c, or opt i c ) a x i s should be zero. The diad axes of quartz are g e n e r a l l y r e f e r r e d t o as the " e l e c t r i c a l axes". The measured values of the p i e z o e l e c t r i c moduli, d,y , f o r r i g h t handed °< - quartz i n r a t i o n a l i z e d m-k-s, a r e : j - 2 . 3 2.3 0 -0.67 0 0 ^ 0 0 0 0 0.67 4.6 \ 0 0 0 0 0 0 X 10-12 (14) Coulombs/Newton (frcm Cady,1946 and Nye, 1972),- For l e f t - h a n d e d oi-guartz the d„ and d./4 values are of opposite: s i g n . 18 1-6 THEORETICAL BASIS FOE THE PIEZOELECTRIC EFFECT IN QUARTZ-RICH ROCKS 1.6,1 AGGREGATE SYMMETRIES WHICH ARE THEORETICALLY PIEZOELECTRIC I f a quartz aggregate has a " f a b r i c " , t h a t i s , i f the c r y s t a l s or more s p e c i f i c a l l y t h e i r e l e c t r i c a l axes are o r i e n t e d i n p r e f e r r e d d i r e c t i o n s , the aggregate may e x h i b i t p i e z o e l e c t r i c p r o p e r t i e s . Shubnikov et a l . , (1946*; from V o l a r o v i c h and Sobolev,1968) extended the concepts of c r y s t a l l o g r a p h i c symmetry to p r e d i c t p i e z o e l e c t r i c e f f e c t s i n v a r i o u s aggregate symmetries and determined t h e i r p i e z o e l e c t r i c moduli. T h i s work has been extended by Parkhomenko (1971)., I f an aggregate c o n t a i n s an a x i s of symmetry about which an i n f i n i t e s i m a l r o t a t i o n can be made without a n o t i c e a b l e change i n o r i e n t a t i o n of the f a b r i c , such an a x i s i s r e f e r r e d t o as the a x i s . Parkhomenko (1971) s t a t e s t h a t n a t u r a l guartz aggregates c o n t a i n s t a t i s t i c a l l y equal numbers of both enantiomorphs and under t h i s h y p o t h e s i s shows that the aggregate may only be p i e z o e l e c t r i c i f i t i s of the f o l l o w i n g 2 symmetries: (1) symmetry <*> m ( I n t e r n a t i o n a l Symbols) the d i a d ( e l e c t r i c a l ) axes are p o l a r p a r a l l e l t o the ^ - a x i s and the c (optic) a x i s are d i s t r i b u t e d randomly i n the plane p e r p e n d i c u l a r to the °°-axis. t 19 P i e z o e l e c t r i c moduli = (2) symmetry 6m2 the d i a d axes are p o l a r p a r a l l e l and the c-axes are p a r a l l e l . P i e z o e l e c t r i c moduli = a,/ 0 0 0 0 0 0 0 p 0 -2d 0 0 0 0 0 0 Wellmer (1970a*, 1970b*; from Bishop, 1978) suggested the p o s s i b i l i t y of an unequal p r o p o r t i o n of the two enantimorphs. The a d d i t i o n a l p i e z o e l e c t r i c symmetries which Bishop (1978) d e s c r i b e d f o r s i n g l e enantimorph aggregates are: (3) symmetry <*> 2 (a) c-axes p a r a l l e l t o ^ - a x i s with the d i a d axes randomly d i s t r i b u t e d i n the plane p e r p e n d i c u l a r t o the °° - a x i s . (b) +/- Y-axes p a r a l l e l to 0 0 - a x i s with diad and c-axes random i n the plane p e r p e n d i c u l a r to the°* -axis,. (c) d i a d a x i s p a r a l l e l t o ^ - a x i s with Y and c 1 In German axes random i n the plane p e r p e n d i c u l a r t o the °*>-axis. 0 0 d / 4 0 0 0 0 0 - d ^ 0 0 0 0 0 0 (4) symmetry <^£> d i a d axes p o l a r p a r a l l e l to - a x i s with c-axes random i n the plane p e r p e n d i c u l a r to the °°-axis. P i e z o e l e c t r i c moduli = (5) symmetry 32 c-axes p a r a l l e l p a r a l l e l . . P i e z o e l e c t r i c moduli = P i e z o e l e c t r i c moduli = with d i a d axes p o l a r 0 &/4 0 0 0 0 0 0 0 0 0 0 (6) symmetry 622 c-axes p a r a l l e l with diad axes p a r a l l e l but net p o l a r p a r a l l e l . 21 P i e z o e l e c t r i c moduli = Bishop d i d not propose t h a t the symmetries (3)-(6) a c t u a l l y e x i s t i n nature but r a t h e r t h a t i f an imbalance i n the number of g r a i n s of each enantimorph occurred then the " l e f t - o v e r " g r a i n s might possess one o f the single-handed aggregate forms. 1.6.2 PRACTICAL CONSIDERATIONS CONCERNING NATDBAL AGGREGATES In a r e a l t e x t u r e , other m i n e r a l components which do not e x h i b i t p i e z o e l e c t r i c e f f e c t s are a l s o u s u a l l y p r e s e n t . The e f f e c t s of p i e z o e l e c t r i c a l l y n e u t r a l components on the s i z e s of the p i e z o e l e c t r i c moduli depends not only on the amount o f such m a t e r i a l which i s present, but a l s o on the nature of i t s d i s t r i b u t i o n r e l a t i v e t o the other components (Parkhomenko, 1971) . To determine i f the aggregate symmetries d i s c u s s e d above are present i n a p a r t i c u l a r rock sample i s d i f f i c u l t . When a rock undergoes deformation, guartz along with c a l c i t e . and the micas are known to e x h i b i t some degree of c r y s t a l l o g r a p h i c alignment. F o r t h i s reason, these common rock-forming minerals are o f t e n used i n p e t r o f a b r i c i n v e s t i g a t i o n s i n t o rock deform-a t i o n . I n the case of g u a r t z , "pole f i g u r e s " of the o p t i c or c-a x i s are u s u a l l y p l o t t e d from u n i v e r s a l stage measurements..The 2 2 o r i e n t a t i o n of these o p t i c axes may a l s o be s t u d i e d i n t h i n s e c t i o n using a p o l a r i z i n g microscope. Since the o p t i c axes tend to p a r a l l e l the l o n g e s t dimensions of needle shaped g r a i n s (Sander, 1930; Griggs and B e l l , 1938) and l i e i n the planes of disc-shaped g r a i n s (Parkhomenko, 1956) t h e i r alignment under s t r e s s i s not s u r p r i s i n g . . However, an understanding of the deformation mechanisms r e s p o n s i b l e f o r t h i s alignment i s f a r from complete. The q u e s t i o n of g r e a t e r concern to us, i . e . , whether alignment cf the d i a d ( e l e c t r i c a l ) axes i s o c c u r r i n g i s d i f f i c u l t to determine e x p e r i m e n t a l l y and even l e s s understood i n terms of deformation mechanisms.„Since the e l e c t r i c a l axes w i l l not respond d i f f e r e n t l y t o a s t r e s s (a non-polar f i e l d ) , Tuck e t al,. (1 977) have hypothesized t h a t alignment of the e l e c t r i c a l axes would r e g u i r e a p o l a r f i e l d , i , e . . an e l e c t r i c f i e l d t o operate d u r i n g c r y s t a l alignment or r e c r y s t a l l i z a t i o n . Thus a p i e z o e l e c t r i c rock would r e c o r d the p a l e o e l e c t r i c f i e l d a c t i n g on i t d u r i n g formation or r e c r y s t a l l i z a t i o n . . T h e y noted t h a t i d e n t i f i c a t i o n of p a l e o e l e c t r i c f i e l d s would not only be of c o n s i d e r a b l e i n t r i n s i c i n t e r e s t but a l s o of great commercial s i g n i f i c a n c e i f r e l a t e d to e l e c t r o c h e m i c a l l y a c t i v e ore d e p o s i t s . U n f o r t u n a t e l y , the o r i e n t a t i o n of the e l e c t r i c a l axes cannot be found i n t h i n s e c t i o n s i n the manner the o p t i c axes can. Under f a v o u r a b l e c i r c u m s t a n c e s , evidence of the geometric o r i e n t a t i o n of quartz g r a i n s may be obtained f o r a few c l a s s e s of rocks by X-ray d i f f r a c t i o n methods. However, Parkhomenko (1971) a s s e r t s t h a t the presence of o r i e n t e d e l e c t r i c a l axes i n quartz aggregates i s best e s t a b l i s h e d e x p e r i m e n t a l l y by 23 o b s e r v a t i o n of the p i e z o e l e c t r i c e f f e c t i t s e l f . . Whatever mechanisms are r e s p o n s i b l e , some n a t u r a l l y deformed rocks are known t o e x h i b i t c o n c e n t r a t i o n s of diad ( e l e c t r i c a l ) axes. Examples are the Poughquag q u a r t z i t e analysed by Higgs et a l . (1960) and g u a r t z i t e S c i 293 analysed by Bunge and Wenk (1977) . 24 CHAPTER 2:- PREVIOUS RESEARCH INTO PIEZOELECTRIC EFFECTS IN ROCKS.. 2.1 PREVIOUS LABORATORY INVESTIGATIONS WITH ROCK SPECIMENS When d e a l i n g w i t h s i n g l e g u a r t z c r y s t a l s , b o t h the " d i r e c t " and " c o n v e r s e " p i e z o e l e c t r i c e f f e c t s d e s c r i b e d i n s e c t i o n 1.2 are commonly measured. Use o f t h e w e l l known r e s o n a n t a n t i r e s o n a n t method f o r s t u d y i n g c o n v e r s e e f f e c t s i s not f e a s i b l y employed when d e a l i n g w i t h aggregates,. The sharp maximum of the the resonance c u r v e i s observed o n l y when t h e p i e z o e l e c t r i c element has a s i n g l e degree of freedom. Rocks, w i t h many degrees of freedom r e q u i r e d t o e x p r e s s t h e i r f a b r i c , e x h i b i t f l a t resonance c u r v e s which l i m i t r e s o l u t i o n o f t h e c o n v e r s e e f f e c t . I n a d d i t i o n , the s m a l l magnitude o f the c o n v e r s e e f f e c t would n e c e s s i t a t e the use of a g e n e r a t o r w i t h e x t r e m e l y h i g h power c a p a c i t y (Parkhomenko, 1971). The measurement methods used t h u s f a r have , t h e r e f o r e been based on t h e " d i r e c t p i e z o e l e c t r i c e f f e c t " and have been s u b d i v i d e d i n t o " s t a t i c " o r "dynamic" methods, depending on t h e manner i n which the m e c h a n i c a l f o r c e s are a p p l i e d . T h i s a u t h o r f i n d s i t l e s s ambiguous t o r e f e r t o t h e s e methods as the " i m p a c t " and " o s c i l l a t i n g s t r e s s " methods r e s p e c t i v e l y . In t h e f i r s t c a s e an impact or d e l o a d i n g t a k e s p l a c e a b r u p t l y , w h i l e i n t h e second c a s e , the sample i s s u b j e c t e d t o a s i n u s o i d a l s t r e s s o f h i g h f r e q u e n c y ( u s u a l l y u l t r a s o n i c ) . Of t h e few a u t h o r s who have p u b l i s h e d on t h e phenomenon of 25 p i e z o e l e c t r i c i t y i n rocks, the m a t e r i a l has o f t e n been s p e c u l a t i v e and sometimes c o n t r a d i c t o r y . . Both l a b o r a t o r y and f i e l d o b s e r v a t i o n s of the p i e z o e l e c t r i c e f f e c t i n a v a r i e t y of g u a r t z - b e a r i n g r o c k s had been r e p o r t e d i n the U,,S,S.R. , f o r more than twenty years ( V o l a r o v i c h and Parkhomenko, 1954; Parkhomenko, 1957, 1959,1971) but were not f o l l o w e d by c o n f i r m a t i o n s i n Western l i t e r a t u r e . , M o r e r e c e n t l y r e s u l t s have been p u b l i s h e d by A u s t r a l i a n workers i n a paper by Tuck e t a l . (1977) and the Ph.D. theses of Tuck (1977) and Bishop (1978).. In a d d i t i o n to the above, the unpublished i n v e s t i g a t i o n s of Starkey and A l l i s o n (1975) on rock samples from the Con Mine, Northwest T e r r i t o r i e s , are a l s o d i s c u s s e d , 2,. 1. 1 RUSSIAN LABORATORY INVESTIGATIONS, A f t e r Sobolev (1947) t h e o r e t i c a l l y p r e d i c t e d the e x i s t e n c e of p i e z o e l e c t r i c aggregate symmetries, the. f i r s t r eported experimental evidence was p u b l i s h e d by V o l a r o v i c h and Parkhomenko (1954). Much of the Russian work s i n c e has been done by Parkhomenko and has been summarized i n her book " E l e c t r i f i c a t i o n Phenomena i n Rocks" (1971),. I n these f i r s t experiments l o n g i t u d i n a l measurements (on the f a c e s being s t r e s s e d ) were made on rock cubes employing the "impact" method. An i n i t i a l " c o n t a c t e l e c t r i f i c a t i o n " was observed on l o a d i n g which was apparently due to the p l e x i g l a s s i n s u l a t i o n . A f t e r n e u t r a l i z i n g the p l e x i g l a s s by h e a t i n g , the specimen was s t r a i n e d to 30% of i t s b r e a k i n g s t r e n g t h using the s p e c i a l l y c o n s t r u c t e d TsNII TMASh h y d r a u l i c p r e s s with a c a p a c i t y of 30 26 tons. The r e s u l t a n t l o n g i t u d i n a l p o l a r i z a t i o n was measureable by e l e c t r o m e t e r s , vacuum-tube v o l t m e t e r s , and ammeters with DC p r e a m p l i f i e r s . The v o l t a g e r e v e r s e d p o l a r i t y i f the sample was i n v e r t e d i n the press and " r o c k s with l i t t l e or no g u a r t z gave l i t t l e or no response" (Parkhomenko, 1971),. , Experiments with o s c i l l a t i n g s t r e s s sources employing resonant e l e c t r o m a g n e t i c presses and l a t e r p i e z o e l e c t r i c t r a n s d u c e r s were a l s o undertaken. To record the p i e z o e l e c t r i c e f f e c t s , V o l a r o v i c h and Parkhomenko (1954,1955) made use of an u l t r a - s o n i c seismoscope designed by E i z n i c h e n k o et a l . (1953). Measurements on a l a r g e number of f i n e - , medium-, and c o a r s e - g r a i n e d c u b i c samples which l e d Parkhomenko (1971, pg. 17) t o conclude t h a t "the p i e z o e l e c t r i c e f f e c t i n s m a l l samples of c o a r s e - g r a i n e d rocks, having volumes of 8 t o 10 cm 3 i s determined not by a p i e z o e l e c t r i c t e x t u r e but r a t h e r by the presence of unigue guartz g r a i n s . " a c c o r d i n g t o Parkhomenko (1971, pg.29), the optimum cube s i z e f o r p i e z o e l e c t r i c measurement i s 4X4X4 cm i f the quartz g r a i n s are of 2 t o 3 mm diameter.. She a l s o experimented with e l e c t r o d e c o n t a c t area and found t h a t the standard d e v i a t i o n of the observed data was decreased s i g n i f i c a n t l y by i n c r e a s i n g the c o n t a c t area from 60 to 90% of the f a c e s being measured. Parkhomenko (1971, pg,114) a l s o found t h a t e i t h e r the "pulse" or " o s c i l l a t i n g s t r e s s " methods were s u i t a b l e f o r q u a n t i t a t i v e measurements of the p i e z o e l e c t r i c moduli f o r h i g h l y r e s i s t a n t guartzose rock i n c l u d i n g vein guartz, q u a r t z i t e , g r a n i t e , g n e i s s , some sandstones, and others. I n rock types such as b a s a l t , d i a b a s e , gabbro, s y e n i t e , skarn, and others which do 27 not contain quartz grains, no p i e z o e l e c t r i c e f f e c t was observed (Parkhomenko,1971,pg. 115). Some ambiguity e x i s t s in that she further stated, " i t proved to be quite important that the po l a r i t y of the e l e c t r i c a l e f f e c t be established i n order to confirm that the e f f e c t i s pi e z o e l e c t r i c i n nature." Presumably, e l e c t r i f i c a t i o n e f f e c t s were seen i n non-quartz bearing rocks but these signals were not attributed to pi e z o e l e c t r i c phenomenon. 1•2 LABORATORY INVESTIGATIONS BY STARKEY AND ALLISON At the request of Cominco Ltd., Starkey and A l l i s o n (1975) undertook measurements on a series of cubic samples from the Con Mine, Northwest-Territories, The specimens were cut int o 1-inch cubes with the three pairs of faces i d e n t i f i e d as: A. P a r a l l e l to f o l i a t i o n , s h i s t o s i t y , or vein wall.. B. Perpendicular to A and p a r a l l e l to the l i n e a t i o n present. C. Perpendicular to A and B. A sample holder was constructed to confine the rock cube between a f l a t , brass anvil plate and the hemispherical point of a brass screw. After applying confining pressure to the screw by hand, an 8.4 gm s t e e l b a l l was dropped from a height of 15 cm onto the screw. The resultant s i g n a l was recorded on a storage oscilloscope and photographed. In a l l , 26 samples were measured in directions A,B, and C as denoted above. The experimental r e s u l t s are given in Appendix 1. It should be noted that maximum signals f o r d i f f e r e n t samples 28 were obtained i n each of the three orthogonal d i r e c t i o n s . . Starkey and A l l i s o n (1975) o p t i m i s t i c a l l y concluded: "as a p r o s p e c t i n g t o o l p i e z o e l e c t r i c e f f e c t s appear to o f f e r a method f o r the l o c a t i o n of g u a r t z - v e i n s i n the Con Mine ar e a , e s p e c i a l l y i f the experiments are c a r r i e d out i n d r i l l holes where c o n f i n i n g pressures are high and where shock waves can be produced by e x p l o s i o n . Furthermore, the r e s u l t s obtained i n t h i s p r e l i m i n a r y study, suggest t h a t with more d e t a i l e d work one might be able t o d i f f e r e n t i a t e between d i f f e r e n t types of quartz v e i n s , " In l i g h t of problems encountered by t h i s author during development of sample h o l d e r s and s t r e s s apparatus, there are a number of areas of concern i n v o l v i n g the design of t h e i r measuring eguipment. In order to o b t a i n an accurate and meaningful impression of the p i e z o e l e c t r i c response of an aggregate i t i s of fundamental importance t h a t the p o l a r i z a t i o n charge be averaged over the measured p a i r of f a c e s by e l e c t r o d e s which cover a l l or as much of the s u r f a c e area as p o s s i b l e . The measurements of Starkey and A l l i s o n would be dominated by the c r y s t a l s i n the l o c a l i t y of the screwpoint (about 1 mmz c o n t a c t a r e a ) . A l s o , with t h e i r e l e c t r o d e arrangement, d i f f e r e n c e s i n c o n t a c t r e s i s t a n c e at the screwpoint due t o v a r i a t i o n s i n contact p r e s s u r e , s u r f a c e roughness, and inhomogenieties i n the rock m a t e r i a l c o u l d cause l a r g e v a r i a t i o n s i n the magnitude of the s i g n a l . Poor screwpoint c o n t a c t o f t e n r e s u l t s i n an extremely high impedance between the e l e c t r o d e s . Nearly i d e n t i c a l s i g n a l s i n a l l three o r t h o g o n a l d i r e c t i o n s f o r t h e i r samples may suggest v i b r a t i o n s r a t h e r than p i e z o e l e c t r i c e f f e c t s dominated t h e i r r e c o r d s . 29 . 3. LABORATORY INVESTIGATIONS BY TJJCK ET AL, Tuck e t a l , (1977) and Tuck (1977) conducted t e s t s on a p p r o x i m a t e l y 1"-sided cubes o f q u a r t z - b e a r i n g g r a n i t e and g u a r t z i t e . These workers hoped t o determine whether the p i e z o e l e c t r i c e f f e c t i n t h e s e r o c k t y p e s was due t o a p i e z o e l e c t r i c f a b r i c o r merely a " s t a t i s t i c a l e f f e c t " due t o a f i n i t e number o f g u a r t z g r a i n s p r e s e n t i n the f a b r i c . Tuck's f i r s t e x p e r i m e n t s i n v o l v e d g r a n i t e s f o l l o w i n g Parkhomenko's r e p o r t e d s u c c e s s w i t h these r o c k s , . The f i r s t e x periment employed the "impact method" by d r o p p i n g a weight onto a compressed specimen and r e c o r d i n g t h e a m p l i f i e d l o n g i t u d i n a l component f o r the 3 o r i e n t a t i o n s on a s t o r a g e o s c i l l o s c o p e . No s i g n a l s were r e c o r d e d which were a t t r i b u t e d to p i e z o e l e c t r i c i t y . The second e x p e r i m e n t s i n v o l v e d s u b j e c t i n g t h e specimens to a one t o n s t r e s s i n a h y d r a u l i c p r e s s and measuring t h e l o n g i t u d i n a l p o t e n t i a l d i f f e r e n c e developed on an e l e c t r o m e t e r when the s t r e s s was suddenly r e l e a s e d . A c c o r d i n g t o Tuck (1977, pg. 101), " r e p e a t e d measurements on specimen f a c e s d i d not i n d i c a t e any r e l i a b l e p i e z o e l e c t r i c v o l t a g e s . The upper l i m i t of any e f f e c t was about 100mv, c o r r e s p o n d i n g t o 1,3 X 10-* o f t h e s i n g l e c r y s t a l e f f e c t . " Tuck's l a s t experiment i n v o l v e d a 1,3 cm-sided cube of the Poughquag q u a r t z i t e which has been e x t e n s i v e l y s t u d i e d g e o l o g i c a l l y . The o p t i c and e l e c t r i c a l axes o f t h e q u a r t z g r a i n s i n t h e s e r o c k s are both h i g h l y a l i g n e d ; the o p t i c a x i s a l i g n m e n t b e i n g one o f t h e . s t r o n g e s t known. The g u a r t z i t e sample and a 30 r e f e r e n c e X-cut quartz c r y s t a l were clamped together with t h e i r e l e c t r o d e s i n a G-clamp. E l a s t i c o s c i l l a t i o n s were e x c i t e d by a hammer blow and the l o n g i t u d i n a l v o l t a g e s from both specimens were r e l a y e d t o a dual beam storage o s c i l l o s c o p e . The l i n e a r i t y of the s i g n a l with s t r e s s and r e v e r s a l of i t s p o l a r i t y with i n v e r s i o n of the q u a r t z i t e specimen convinced Tuck t h a t s i g n a l s were t r u l y p i e z o e l e c t r i c but he found no c o n c r e t e evidence of a p i e z o e l e c t r i c f a b r i c . Tuck (1977, pg. 111) summarized his f i n d i n g s : "In c o n c l u s i o n , i n g u a r t z - b e a r i n g r o c k s such as sandstone, g n e i s s , and g r a n i t e the p i e z o e l e c t r i c e f f e c t i s a s t a t i s t i c a l e f f e c t -due to the f i n i t e number of guartz g r a i n s i n the sample. A l s o , f o r most vein q u a r t z and q u a r t z - b e a r i n g rocks showing l a r g e r p i e z o e l e c t r i c e f f e c t s than i n g r a n i t e , the e f f e c t may be due p r i m a r i l y to the presence of l a r g e r g r a i n s or groups of l a r g e r g r a i n s i n the sample." Tuck and h i s a s s o c i a t e s d i s p u t e d the r e s u l t s of Parkhomenko and the other E u s s i a n workers and doubted the e x i s t e n c e of p i e z o e l e c t i c f a b r i c s . 2.1 r 4 LABOBATOBY INVESTIGATIONS BY BISHOP Recently the r e s u l t s of a Ph.D. t h e s i s by Bishop (1978) have become a v a i l a b l e . H i s system may employ th e most e l a b o r a t e " o s c i l l a t i n g s t r e s s " device yet d e v i s e d and, u n l i k e the Eussian papers, h i s s t u d i e s have been e x p l a i n e d i n d e t a i l . Bishop mentions having v i b r a t i o n a l problems with the sample-holder apparatus. He attempted to i n c r e a s e the resonant 31 f r e q u e n c i e s of the v i b r a t i o n s above the range of o p e r a t i o n (approximately 5-1000 Hz) by use of p r o g r e s s i v e l y more massive sample holders,. He e v e n t u a l l y overcame the v i b r a t i o n a l problem by s t r e s s i n g the specimen h y d r a u l i c a l l y with a p i s t o n and c y l i n d e r arrangement coupled to a cam d r i v e n by an e l e c t r i c motor. He a l s o g i v e s accounts of problems i n a p p l y i n g uniform s t r e s s a c r o s s the sample f a c e and of v a r i o u s p l a s t i c i n s u l a t o r s developing charges when s t r e s s e d . The d i f f e r e n c e between two simple charge a m p l i f i e r s , one attached to each e l e c t r o d e across the specimen was measured. One shortcoming of Bishop's set-up was the i n a b i l i t y of h i s specimen holder t o accept samples of d i f f e r e n t dimensions. The specimens were a r b i t r a r i l y c u t i n t o cubes of 2,-93 cm edge l e n g t h (volume=25» 15 cm 3) without regard to rock f a b r i c ( l i n e a t i o n e t c . ) . , a c c o r d i n g t o the sample volumes suggested by Parkhomenko (1971), Bishop»s samples should have been.much too s m a l l to e x h i b i t t r u e " f a b r i c r e l a t e d " e f f e c t s . Bishop t e s t e d rocks which were both f i n e and coarse g r a i n e d , weakly and s t r o n g l y deformed, and with simple and complex f a b r i c s . The r e s u l t s of most specimens i n c l u d i n g q u a r t z i t e s , g n e i s s e s and g r a n i t e s were found t o be c o n s i s t e n t with t h e e f f e c t expected from an aggregate with non-polar o r i e n t a t i o n (the s t a t i s t i c a l e f f e e t ) H o w e v e r , c o n t r a r y to Tuck and h i s a s s o c i a t e s . Bishop r e p o r t e d t h a t a few specimens -mylonites - showed a c l o s e . agreement between the o p t i c a l l y observed c - a x i s p a t t e r n and the p i e z o e l e c t r i c a l l y p r e d i c t e d pattern... .He argued t h a t three specimens of mylonites he s t u d i e d (Poughguag, R i s f j a l l e t , and Snake Range) e x h i b i t e d a p i e z o e l e c t r i c e f f e c t r e l a t e d t o the f a b r i c but t h a t l a r g e r 32 samples than were . a v a i l a b l e were necessary f o r d e f i n i t e proof, B e c a l l t h a t Tuck et a l (1977) concluded from t h e i r experiments with t h e Poughguag q u a r t z i t e t h a t although being an e x c e l l e n t candidate t o d i s p l a y f a b r i c r e l a t e d p i e z o e l e c t r i c e f f e c t s , only a " s t a t i s t i c a l e f f e c t " was observed. Bishop's evidence was based on three c r i t e r i a : the magnitude of the experimental values compared with the expected values of a sample with no p r e f e r r e d o r i e n t a t i o n , the c o r r e l a t i o n between specimens with the same o r i e n t a t i o n c u t from the one sample, and the c o r r e l a t i o n between the o p t i c a l l y and p i e z o e l e c t r i c a l l y determined c - a x i s p r e f e r r e d o r i e n t a t i o n s . Why some rocks showed a t r u e p i e z o e l e c t r i c e f f e c t and not others Bishop could not e x p l a i n . For example only 1 of the 3 B i s f j o l l i t m ylonites he t e s t e d showed an e f f e c t r e l a t e d t o f a b r i c , .The Mt. I s a mylonite samples i n d i c a t e d a s t a t i s t i c a l e f f e c t o n l y . Bishop a l s o noted the n e c e s s i t y of checking f o r the r e v e r s a l i n p o l a r i t y when the sample i s i n v e r t e d i n the ho l d e r . He observed t h a t specimens of b a s a l t or marble do not show a r e v e r s a l of s i g n , w h i l s t e f f e c t s from guartz bearing rocks, though not n e c e s s a r i l y of l a r g e r magnitude, w i l l do so. Thus i t seems t h a t Bishop a l s o n o t i c e d extraneous e l e c t r i c a l s i g n a l s from rocks not bearing quartz as Parkhomenko (1971) apparently had. 33 1 - 5 SUMMARY Of t h e few a u t h o r s who have p u b l i s h e d on l a b o r a t o r y measurement of the p i e z o e l e c t i c e f f e c t , t h e m a t e r i a l has o f t e n been s p e c u l a t i v e and c o n t r a d i c t o r y . The R u s s i a n w o rkers have s t u d i e d t h e s e e f f e c t s f o r more than twenty years and have c l a i m e d a g r e a t d e a l o f s u c c e s s . B i s h o p , Tuck and a s s o c i a t e s , and m y s e l f have found i n a d e g u a c i e s i n the R u s s i a n l i t e r a t u r e . The c o n c l u s i o n s which have been made a r e o f t e n u n j u s t i f i e d on t h e b a s i s of the e v i d e n c e p r e s e n t e d . F o r t h e r e a s o n s d i s c u s s e d , t h e r e s u l t s of S t a r k e y and A l l i s o n a r e t h o u g h t i n c o n c l u s i v e . More r e c e n t work p r e s e n t e d by Tuck ( 1 9 7 7 ) and B i s h o p ( 1 9 7 8 ) i s c o n t r a d i c t o r y . Tuck i s s k e p t i c a l o f any f a b r i c , r e l a t e d p i e z o e l e c t r i c e f f e c t s w h i l e B i s h o p c l a i m s t h a t t h r e e samples he t e s t e d d i s p l a y such an e f f e c t . In view o f the d i f f i c u l t i e s e n c o untered by p r e v i o u s i n v e s t i g a t o r s and t h e i r c o n t r a d i c t o r y r e s u l t s , i t was d e c i d e d t h a t a new l a b o r a t o r y measurement system s h o u l d be d e v i s e d and a sample s u i t e of Con Mine r o c k s t e s t e d p r i o r t o t h e e x p l o r a t i o n t r i a l s t c v e r i f y t h a t the p i e z o e l e c t r i c e f f e c t c o u l d be measured i n t h e s e samples. I n c h a p t e r 3 t h e l a b o r a t o r y e x p e r i m e n t s and r e s u l t s are d i s c u s s e d . 34 2.2 PREVIOUS EXPERIMENTS UTILIZING PIEZOELECTRIC PROPERTIES -FOR EXPLORATION 2.2.1 THE BASIS OF THE PIEZOELECTRIC EXPLORATION TECHNIQUE The p i e z o e l e c t r i c underground e x p l o r a t i o n technique was o u t l i n e d by V o l a r o v i c h and Sobolev (1968),. The b a s i s of the method i s the c o n v e r s i o n of mechanical energy to el e c t r o m a g n e t i c energy when n a t u r a l l y p i e z o e l e c t r i c bodies such as quartz veins are p r e s e n t . The mechanical energy i s provided i n the form of s e i s m i c waves generated by an e x p l o s i o n or impact ( f i g . . 5 , ( 1 ) ) . When the s e i s m i c waves (2) pass through a quartz v e i n or pegmatite (3), an ele c t r o m a g n e t i c f i e l d (4) i s generated i n a l l d i r e c t i o n s and a r r i v e s e s s e n t i a l l y i n s t a n t a n e o u s l y at a l l r e c e i v i n g s t a t i o n s (5). The el e c t r o m a g n e t i c f i e l d can then be detected with grounded e l e c t r o d e s (rod or plate) or magnetic antenna and be a m p l i f i e d and recorded. According to Parkhomenko (1971), the o s c i l l o g r a p h record may i n c l u d e the e l e c t r o m a g n e t i c p r e c u r s o r from the d e t o n a t i o n , the s e i s m o e l e c t r i c E - e f f e c t , the p i e z o e l e c t r i c s i g n a l from the t a r g e t , the p i e z o e l e c t r i c e f f e c t of the surrounding r o c k s , s p h e r i c s , and i n d u s t r i a l n o i s e , The E - e f f e c t i s a second order e l e c t r o s e i s m i c phenomenon o c c a s i o n a l l y observed i n s o i l s and rocks c o n t a i n i n g the i o n s of d i s s o l v e d s a l t s . . E l e c t r i c a l p o l a r i z a t i o n of the s o l u t i o n w i t h i n the pores may l e a d to e l e c t r i f i c a t i o n of the rock when i t i s s e i s m i c a l l y e x c i t e d . , She a l s o p o i n t s out t h a t s e p a r a t i o n of v a r i o u s p a r t s o f the FIGURE 5 :- BASIS OF SUBTERRANEAN PIEZOELECTRIC EXPLORATION 1 EXPLOSION OR IMPACT 2 SEISMIC WAVE 3 QUARTZ OR PEGMATITE VEIN 4 ELECTROMEAGNETIC WAVE GENERATED 5 GEOPHONE AND ELECTRODE ARRAY 36 e l e c t r i c a l s i g n a l provides some d i f f i c u l t y which i s not always surmountable when the E - e f f e c t and the e l e c t r o m a g n e t i c emission from the e x p l o s i o n precursor o v e r l a p . To overcome t h i s problem, t i e measuring e l e c t r o d e s must be f a r enough away from the d e t o n a t i o n p o i n t (approx. 5-10 metres) so t h a t the p r e c u r s o r e l e c t r o m a g n e t i c event i s weak, and the e l e c t r i c a l s i g n a l from the p i e z o e l e c t r i c response may be recognized, 2.2. 2 RUSSIAN EXPLORATION INVESTIGATIONS The f i r s t r e p o r t e d f i e l d t e s t s (1957-1958) took plac e i n the U r a l s and Kazakhstan ( V o l a r o v i c h e t a l . , 1959). A hammer was used as the s e i s m i c source and the e l e c t r o d e s were i n the form of br a s s rods and p l a t e s . The a m p l i f i e r had a maximum gain of 100 dB with a bandpass of 40-1000 Hz, Transverse and l o n g i t u d i n a l p r o f i l e s ( e l e c t r o d e s moved, impact p o i n t fixed) were made acro s s outcropping quartz and pegmatite v e i n s and over a sediment covered quartz v e i n . D e t e c t i o n p o i n t s were l o c a t e d not c l o s e r than 5 metres and not f a r t h e r than 40 metres from the impact poin t and " a t these d i s t a n c e s the p i e z o e l e c t r i c e f f e c t was r e q i s t e r e d very d i s t i n c t i v e l y while the i n t e r f e r e n c e o r i g i n a t i n g at the impact was almost i m p e r c e p t i b l e " ( V o l a r o v i c h et a l . , 1962). In underground e x p l o r a t i o n t r i a l s which f o l l o w e d V o l a r o v i c h & Sobolev (1965) designed a system known as the PEEF - 2 with a 300-800 Hz bandpass and a small charge (100 to 200 grams) o f e x p l o s i v e as the source. Although very few d e t a i l s of the system or r e s u l t s were gi v e n , these authors concluded: 37 "much experimental i n f o r m a t i o n has now been amassed on the p r o s p e c t i n g and e x p l o r a t i o n p o t e n t i a l o f the p i e z o e l e c t r i c method. I t appears t h a t the. e f f e c t i v e range of the method i s 80 metres, with a v e i n l o c a t i o n d i s t a n c e e r r o r o f 10 to 20% The experiments made over a number of years show t h a t both i n o p e r a t i n g mines and at the s u r f a c e the g e o p h y s i c a l p i e z o e l e c t r i c p r o s p e c t i n g method i n c r e a s e s the e f f i c i e n c y o f g e o l o g i c e x p l o r a t i o n . The method i s now being employed at two d e p o s i t s , " Model experiments of p i e z o e l e c t r i c phenomenon o c c u r r i n g i n gua r t z v e i n s when s t r u c k by. e l a s t i c waves have a l s o been simulated i n the l a b o r a t o r y ( V o l a r o v i c h and Parkhomenko, 1959; Parkhomenko, 1961; Sobolev e t a l . , 1966) but w i l l not be d i s c u s s e d here. A f t e r p r e s e n t i n g -the r e s u l t s of the l a b o r a t o r y measurements on a s u i t e of Con Mine rocks (Chapter 3), the r e s u l t s of two e x p l o r a t i o n t r i a l s are discu s s e d i n Chapter 4, 38 CHAPTER - 3: LABORATORY MEASUREMENT OF THE PIEZOELECTRIC EFFECT. At the commencement of the l a b o r a t o r y i n v e s t i g a t i o n , the only l a b o r a t o r y experiments known were those of the Russian r e s e a r c h e r s and those of Starkey & A l l i s o n . As d e s c r i b e d e a r l i e r , the Russians had measured p i e z o e l e c t r i c e f f e c t s i n a v a r i e t y of rock types and r e l a t e d the measurements to the rock f a b r i c . Starkey & A l l i s o n d i d not d i s c u s s t h e i r r e s u l t s i n terms of f a b r i c but noted s i g n i f i c a n t d i f f e r e n c e s i n s i g n a l magnitude between g u a r t z - r i c h & q u a r t z - d e f i c i e n t Con Mine r o c k s . In the Russian r e p o r t s o f s u c c e s s f u l and r o u t i n e use of p i e z o e l e c t r i c e x p l o r a t i o n systems, few d e t a i l s were given of i n s t r u m e n t a t i o n or survey procedures. The o b j e c t i v e s of t h i s program was to develop an e x p l o r a t i o n system and an understanding of the f i e l d parameters i n v o l v e d . The l a b o r a t o r y measurements were thus o r i g i n a l l y intended only as a guick v e r i f i c a t i o n of the r e p o r t e d l a b o r a t o r y work, p a r t i c u l a r l y Starkey & A l l i s o n ' s s i n c e t h i s t h e s i s i n v o l v e s the same rock s u i t e . The aim of t h i s experiment was t o examine the r e l a t i v e magnitude of p i e z o e l e c t r i c response f o r v a r i o u s Con Mine rocks and h o p e f u l l y t o detect i n those samples which showed p r e f e r e n t i a l alignment of the quartz c r y s t a l s , a minimum s i g n a l on the p a i r of cube faces which were p e r p e n d i c u l a r t o the c r y s t a l e x t e n s i o n s . In a s i n g l e quartz c r y s t a l , the charge p o l a r i z a t i o n p a r a l l e l t o the c or o p t i c a x i s i s zero r e g a r d l e s s of the s t r e s s a p p l i e d ( s e c t i o n 1.5). Thus, f o r a c r y s t a l aggregate e x h i b i t i n g c axes alignment, minimum charge p o l a r i z a t i o n should r e s u l t p a r a l l e l t o the alignment. 39 3.1 SAMPLE PREPARATION. Twenty-nine rock samples from the Con Mine l o c a t e d i n Y e l l o w k n i f e , N o r t h w e s t - T e r r i t o r i e s were c o l l e c t e d and provided by mine g e o l o g i s t Del Myers. At Cominco's Research Laboratory i n Vancouver, a l a r g e 16" diameter diamond saw was used t o hew the samples i n t o roughly e g u i d i m e n s i o n a l bodies. The cut f a c e s of the hand specimens were then s t u d i e d f o r c r y s t a l alignment or other f a b r i c f e a t u r e s . A f t e r n o t i n g any f a b r i c p r e sent, the samples were c u t i n t o o r i e n t e d cubes with s i d e lengths of about 11 cm. For samples with d i s c e r n i b l e rock f a b r i c o r where l o n g i t u d i n a l alignment of the guartz g r a i n s was e v i d e n t , one cut was made p a r a l l e l t o the f o l i a t i o n plane and two p e r p e n d i c u l a r , one being p a r a l l e l t o the l i n e a t i o n and one p e r p e n d i c u l a r to the l i n e a t i o n . The d e s i g n a t i o n of these d i r e c t i o n s i s i l l u s t r a t e d i n f i g u r e 6. Each f a c e of the sample underwent s e v e r a l stages of g r i n d i n g and p o l i s h i n g on a p o l i s h i n g wheel. T h i s served to remove any saw marks and l e a v e the s u r f a c e s as smooth and f l a w l e s s as p o s s i b l e and to b r i n g the samples to the standard s i z e of 3.81 cm (1.5 in),.Slow g r i n d i n g and p o l i s h i n g procedures were used to prevent "burning" of the s u r f a c e and t o ensure that o p p o s i t e f a c e s were p a r a l l e l . The sample volume of the standard s i z e cube used was 55,3 cm 3 and hence was s i g n i f i c a n t l y l a r g e r than the sample volumes of 2,08 cm 3, 16.4 cm 3, and 25.1 cm 3 used by Tuck (1977), Starkey and A l l i s o n (1975), and Bishop (1 978) r e s p e c t i v e l y . R e c a l l t h a t the s m a l l e r the sample volume, the more l i k e l y i n d i v i d u a l c r y s t a l s w i l l dominate the measurements. - DESIGNATION OF THE AXES OF THE CUBIC ROCK SPECIMENS P a r a l l e l to the f o l i a t i o n plane or s c h i s t o s i t y but perpendicular to the li n e a t i o n s or c r y s t a l alignment Peappendicular to the f o l i a t i o n plane or s c h i s t o s i t y P a r a l l e l to the c r y s t a l alignment or l i n e a t i o n s and to the f o l i a t i o n plane or s c h i s t o s i t y ( a f t e r Jose et al., 1978) 41 masking f a b r i c e f f e c t s and leading to false i n t e r p r e t a t i o n . A few of the samples were o r i g i n a l l y too small to be cut to t h i s standard s i z e and several others were incompetent and fractured during the cutting operations. These were cut into as large a parallelepiped as possible. Dimension of non-standard s i z e are guoted i n tables 3 and 4. To remove any traces of cutting o i l , the samples were washed thoroughly with alcohol and dried. , 3.2. INSTRUMENTATION: DEVELOPMENT OF-THE MEASUREMENT SYSTEM, . Since the guartz c r y s t a l s present i n the specimen act as electromechanical transducers the laboratory system may be subdivided into two categories: the.sample holder and stress producing apparatus, and the po l a r i z a t i o n charge measuring, amplifying and recording system. A l l parts of the system underwent many prototypes. To measure the " d i r e c t " p i e z o e l e c t r i c e f f e c t by the "impact" method, various sample holders and stressing apparatus were designed and tested. The f i r s t experiments were sim i l a r to those of Starkey and A l l i s o n (1977) and Tuck (1 977). These involved dropping a st e e l b a l l from a fixed height onto an open face of the specimen which was clamped together with the measuring electrodes i n a vice. The variations of t h i s system which were t r i e d were a l l found unsatisfactory f o r a number of reasons. Triggering the recording system from the si g n a l produced by the impact clipped 42 the s t a r t o f the signal,. Great c a r e had to be taken to ensure a r e p e a t a b l e " c l e a n " h i t by the f a l l i n g weight and many v i b r a t i o n a l e f f e c t s not a t t r i b u t a b l e t o p i e z o e l e c t r i c phenomenon were seen. I t was a l s o thought p r e f e r a b l e t o s t r e s s the specimen i n the d i r e c t i o n of compression r a t h e r than p o s s i b l y producing e l e c t r o d e - r o c k s l i p p a g e by s t r e s s i n g the specimen t r a n s v e r s e l y to the compression. E v e n t u a l l y a sample h o l d e r and s t r e s s i n g apparatus r e f e r r e d to as a "compression cage" was designed. The prototype was f a i r l y s i m i l a r to the f i n a l s t r e s s i n g device except f o r the i n s u l a t i n g m a t e r i a l and t h a t one of the e l e c t r o d e s was only a bras s screw. The a m p l i f y i n g and r e c o r d i n g p a r t of the system was chosen t o be compatible with the requirements of the f i e l d program (see Chapter 4), This prototype system i s shown i n f i g u r e 7. Leads from the e l e c t r o d e s were fed i n t o a T e k t r o n i x model AH-502 d i f f e r e n t i a l a m p l i f i e r and from t h e r e to one channel of a Nimbus ES-1200 enhancement seismograph f o r r e c o r d i n g . The p r i n c i p a l f u n c t i o n of the a m p l i f i e r was impedance matching between the high impedance rock samples and low input impedance seismograph. A r e f e r e n c e s i n u s o i d a l s i g n a l of known amplitude was fed i n t o a second channel of t h e seismograph u n i t . Further experimentation l e d to the c o n c l u s i o n t h a t use of the screw f o r an e l e c t r o d e was improper. S e v e r a l forms of e l e c t r o d e s were then t e s t e d . Conductive neoprene (commonly used f o r i n t e g r a t e d c i r c u i t storage) was t e s t e d both dry and sa t u r a t e d with copper sulphate s o l u t i o n (CuSO^ . 5H20),. Both methods were abandoned, the former because the r e l i a b i l i t y of the co n t a c t seemed a f u n c t i o n of the c o n f i n i n g pressure and the l a t t e r TRIGGERING GND CHANNEL NIMBUS 9 ES-1200 ENHANCEMENT SEISMOGRAPH CHANNEL 6 PIN: 27 17 18 11 12 WAVETEK VOLTAGE CONTROLLED GENERATOR GND + DIGITAL VOLTMETER PREAMP OUTPUT TEKTRONIX ' 21^ STORAGE OSCILLOSCOPE TEKTRONIX AM-502 DIFFERENTIAL AMPLIFIER TEKTRONIX TM-503 POWER MODULE TRIGGER SWITCH 4 - 1 2 V GELL/CELL BATTERIES BRASS PLATE ROCK SAMPLE 6-1" BOLTS PLEXIGLASS PLATE BRASS SCREW (ELECTRODE) STEEL BOX FOR SHIELDING FROM ELECTRICAL NOISE FIGURE 7 :- PROTOTYPE SYSTEM FOR LABORATORY PIEZOELECTRIC MEASUREMENT (after Jose et a l . , 1978) 44 because of the possible galvanic or second order seismoelectric e f f e c t s . The faces of some samples were coated with s i l v e r paint to ensure a perfect contact with the electrode plates. The e f f e c t of the s i l v e r paint could not be f u l l y understood so i t was decided to be s a t i s f i e d with a dry, less-perfect contact rather than adding an additional complication to the measurement, Experiments with " i n s u l a t i n g " materials substituted in place of the sample to measure the noise l e v e l also disclosed that some materials, thought to be adequate in s u l a t o r s , also resulted i n a charge po l a r i z a t i o n when stressed. The r e s i s t i v e and capacitive properties of several p l a s t i c s (polyethylene, a c r y l i c - p l e x i g l a s s , poly-vinyl-chloride (PVC) , lexan, formica) and wood were investigated and i t was found that the i polyethylene did not produce a measurable s i g n a l when stressed.. Henceforth, two 1/ 2 inch thick discs of polyethylene were placed between the plates of the 1/ 8 inch thick copper electrode plates as shown in figure 8 , . The electrode plates were made s l i g h t l y larger than the standard sample size so that polarization charge over the entire face of the sample was recorded. To obtain meaningful and repeatable measurements, i t i s es s e n t i a l that the loading of the sample be normal to and evenly distributed across the. measurement faces and of consistent magnitude for each measurement.,As shown in figure 8 , the f i n a l version of the compression cage was constructed of two 5-inch diameter plates; one of 1/ 5 inch thick brass and the other of 1 inch thick plexiglass. The cubic rock samples were compressed between the plates by means of six 1/4 inch b o l t s . The.spacing 45 SOLENOID CORE' SWITCH h-6 VOLT GELL/CELL RECHARGEABLE BATTERIES ff +-1/5" THICK BRASS PLATE COPPER FOIL CUBIC ROCK SAMPLE COPPER ELECTRODE POLYETHELENE THICK PLEXIGLASS 6- i " BOLTS FIGURE 8 : - COMPRESSION CAGE USED IN LABORATORY MEASUREMENTS 46 between the b o l t s was designed so t h a t standard s i z e d samples c o u l d be s l i p p e d i n and out of the cage by merely l o o s e n i n g the b o l t s . U n l i k e Bishop's system, a l a r g e range of sample s i z e s c o u l d be accommodated. With t h i s arrangement, the specimen was f i r s t c a r e f u l l y c e n tered i n the cage and the 6 b o l t s g r a d u a l l y t i g h t e n e d using a Hazet torque wrench to 5 f t . - l b s . (6.8 N-m) torque. I n t h i s manner, a c o n s i s t e n t and even pressure d i s t r i b u t i o n f o r each measurement was ensured.. The purpose of t h i s f i r s t stage of compression was not only to ensure good e l e c t r o d e c o n t a c t with the rock s u r f a c e but a l s o t o allow s e p a r a t i o n of c o n t a c t e l e c t r i f i c a t i o n phenomena from the p i e z o e l e c t r i c e f f e c t when the second stage of compression (the impact) was a p p l i e d , To reduce 60 Hz r a d i a t i o n from power mains, f l u o r e s c e n t l i g h t s , e t c . , the compression cage was slung w i t h i n a s t e e l box f o r s h i e l d i n g ( F i g , .9). The s t e e l box was placed on a 5 cm t h i c k foam pad on a s t u r d y bench. T h i s procedure e l i m i n a t e d v i b r a t i o n a l pickup i n the frequency range of i n t e r e s t ( v i b r a t i o n s present were of much lower freguency). T h i s proved to be a more f i t t i n g a l t e r n a t i v e t o the use of more massive sample h o l d e r s to dampen v i b r a t i o n s . As an e x t r a p r e c a u t i o n s e v e r a l l a r g e e l a s t i c bands were wrapped about the c o n f i n i n g b o l t s t o dampen any p o s s i b l e v i b r a t i o n s from f l e x u r e of the b o l t s . To apply a r e p e a t a b l e and c o n s i s t e n t s t r e s s pulse t o the sample, a s o l e n o i d was mounted atop the b r a s s p l a t e of the compression cage. The s o l e n o i d was powered by 4 rechargeable 6-,STEEL SHIELDING BOX 47 r f - , COMPRESSION CAGE SOLENOID "HITTER" A DIFFERENTIAL AMPLIFIER FOAM CUSHION y/////////// TEKTRONIX TYPE 5 4 9 ROCKLAND MODEL 0 2 2 F DUAL HI / LO FILTER DUAL STORAGE OSCILLOSCOPE AND \ A 0 KHz -> 3 0 0 Hz CAMERA LOW PASS HIGH PASS I FIGURE 9 :- FINAL VERSION OF LABORATORY MEASUREMENT SYSTEM 48 v o l t g e l / c e l l b a t t e r i e s p l a c e d i n s e r i e s . Upon a c t i v a t i o n o f a s w i t c h , t h e s o l e n o i d c o r e slammed i n t o the b r a s s p l a t e p r o p a g a t i n g the e l a s t i c shock wave t h r o u g h t h e sample. : A s h o r t l e n g t h o f t w i s t e d - p a i r f o i l - s h i e l d e d i n s t r u m e n t a t i o n c a b l e was chosen t o c a r r y t h e p i e z o e l e c t r i c s i g n a l from t h e two e l e c t r o d e s t o t h e i n p u t o f a d i f f e r e n t i a l i n p u t p r e a m p l i f i e r c o n s t r u c t e d a t t h e Department of G e o p h y s i c s and Astronomy, U. B . C . The two c a b l e s i n s i d e the s h i e l d box; the t r i g g e r c a b l e t o t h e . s o l e n o i d and t h e c a b l e from th e e l e c t r o d e s , were b o t h t a p e d s e c u r e l y t o the i n s i d e of the box t o m i n i m i z e any movement upon i m p a c t . The s h i e l d i n g box and a l l metal p a r t s o f the c o m p r e s s i o n cage were grounded. A f t e r p r e a m p l i f i c a t i o n , t h e p i e z o e l e c t r i c s i g n a l s were f e d through a Rockland Model 1022F Dual HI/LO f i l t e r . The h i g h and low pass B u t t e r w o r t h networks i n c o r p o r a t e d i n the Rockland f i l t e r were a d j u s t e d f o r a 300 t o 10 KHz bandpass. The measured f r e q u e n c y response o f the a m p l i f i e r and f i l t e r system i s shown i n f i g u r e 10, A f t e r f i l t e r i n g , the s i g n a l s were d i s p l a y e d on a T e k t r o n i x 549 d u a l -s c r e e n s t o r a g e o s c i l l o s c o p e and photographed.. The h i g h impedance a m p l i f i e r (10 s ohms) ser v e d as an impedance matching i n t e r f a c e between th e h i g h impedance ro c k and t h e f i l t e r s and s t o r a g e o s c i l l o s c o p e . O m i t t i n g t h i s s t a g e as S t a r k e y and A l l i s o n d i d would g i v e f a l s e a m p l i t u d e s f o r very h i g h impedance samples. The p r e a m p l i f i c a t i o n o f t h e . s i g n a l h e l p e d i n c r e a s e the s i g n a l / n o i s e r a t i o by d e c r e a s i n g t h e r e l a t i v e p r o p o r t i o n o f i n d u c t i v e p i c k u p i n t h e l a t e r s t a g e s of t h e system. S i n c e t h e o s c i l l o s c o p e was a l s o t r i g g e r e d v i a the s o l e n o i d s 49 F I G . 1 0 : F R E Q U E N C Y R E S P O N S E O F A M P L I F I E R k F I L T E R S Y S T E M 1 0 2 1 0 3 ' 1 0 4 1 0 5 F R E Q U E N C Y ( H Z ) 50 t r i g g e r s w i t c h , the delay time mechanism i n c o r p o r a t e d i n t o the o s c i l l o s c o p e could be p r e s e t with a delay time s l i g h t l y l e s s than the time i n t e r v a l between a c t i v a t i o n of the switch and impact upon the brass p l a t e . T h i s prevented l o s s of the i n i t i a l p o r t i o n of the s i g n a l , 3.3 EXPERIMENTAL RESULTS AND DISCUSSION A f t e r the c u b i c rock specimens had been prepared, t h e i r t e x t u r e and f a b r i c were once again examined o p t i c a l l y under m a g n i f i c a t i o n . I f some degree of c r y s t a l alignment was observed or i f tJie rock possessed a d e f i n i t e f a b r i c i t was placed i n the " f o l i a t e d " sample group. Note t h a t here c r y s t a l alignment r e f e r s only t o the e l o n g a t i o n of the c r y s t a l and does not n e c e s s a r i l y imply e l e c t r i c a l axes alignment. The t h r e e o r t h o g o n a l d i r e c t i o n s o f the cube were l a b e l l e d A, B, and C where p o s s i b l e a c c o r d i n g to the convention d e s c r i b e d e a r l i e r (see f i g u r e 6)• The remaining samples were placed i n the "massive" group,. Although the quartz content of the specimens was ranked as low, i n t e r m e d i a t e , or high, a l l of the samples contained a s i g n i f i c a n t amount of t h i s m i n e r a l . The t o t a l time r e q u i r e d to l o a d , compress and measure a s i n g l e p a i r of f a c e s of a sample was approximately 30 minutes. Ten measurements were . taken f o r each of the orthogonal d i r e c t i o n s and the mean and standard d e v i a t i o n c a l c u l a t e d . For a l l the measurements, the maximum peak-to-peak amplitude was used. I t was found t h a t the impedance of the sample v a r i e d g r e a t l y between specimens and indeed o f t e n s i g n i f i c a n t l y f o r the 51 three d i r e c t i o n s of a p a r t i c u l a r specimen..Since the r e s i s t a n c e was o f t e n too high to ne measured by c o n v e n t i o n a l ohmeters, the conductance i n nanosiemens was measured using a Fluke model 8020A multimeter and t a b u l a t e d . When the p r e a m p l i f i e r was used i n d i f f e r e n t i a l r a t h e r than common-mode, the common-mode r e j e c t i o n of the d i f f e r e n t i a l c o n f i g u r a t i o n g r e a t l y reduced the magnitude of the background nois e (mostly 60 Hz) while l e a v i n g the p i e z o e l e c t r i c s i g n a l magnitude unchanged. Thus the p i e z o e l e c t r i c s i g n a l was indeed being generated across the rock specimen.. The f a c t t h a t a s i g n a l was not d i s c e r n a b l e w i t h i n the l i m i t a t i o n s of the system when a block of p o l y e t h y l e n e was s u b s t i t u t e d i n place of the rock specimen p r o v i d e d c o n f i r m a t i o n t h a t v i b r a t i o n a l , t r i g g e r p u l s e p r e c u r s o r , and other e l e c t r i c a l n o i s e sources were not i n h e r e n t w i t h i n the measurement system. A t y p i c a l p i e z o e l e c t r i c r e c o r d i s shown i n f i g u r e 11 a S b. The two photographs were taken f o r separate impacts of the s o l e n o i d core upon the sample and demonstrate the high degree of r e p e a t a b i l i t y t h a t the compression cage and s o l e n o i d s t r e s s i n g d e v i ce can achieve. Because of the time delay mechanism i n c o r p o r a t e d i n t o the storage o s c i l l o s c o p e the low l e v e l of background noise may be seen at the s t a r t of the r e c o r d s . I t i s b e l i e v e d t h a t the.complex shape of the s i g n a l i s due to m u l t i p l e r e f l e c t i o n s w i t h i n the sample. The higher f r e q u e n c i e s g e n e r a l l y tend to become p r o g r e s s i v e l y dampened i n l a t e r stages of the r e c o r d s . Of the massive samples (Table 3 ) , the p i e z o e l e c t r i c s i g n a l magnitude v a r i e d from a minimum of 1.36 my (sample #48) to a FIGURE 11:- Demonstration of r e p e a t a b i l i t y of laboratory measurement system. Photographs taken o f p i e z o e l e c t r i c signals r e s u l t i n g from separate solenoid core impacts on sample #41. Vein sample of intermediate to high quartz content. [ 1000 mV/div at gain=100; 0.5 msec/div ] "TABLE 3 EXPERIMENTAL RESULTS MASSIVE CON MINE ROCKS SAMPLE NUMBER PETROGRAPHIC DESCRIPTION RELATIVE QUARTZ CONTENT (low,int,or high) CONDUCTANCE (nanosiemens) Mean of 10 Measured P.E. Signals (mV p-p) STANDARD DEVIATION DIMENSION IF OF NON-STANDARD SIZE 21 Fine to medium grained quartz & carbonate v e i n l e t s i n c h l o r i t e s c h i s t . Brecciated texture. i n t 75 120 / 4 5 . 7 0 2 2 . 6 0 1 5 . 9 5 0 .21 0 .06 0 .06 24 * Very f i n e grained metabasalt cut by f i n e stringers and vei n l e t s of quartz. low-int 250 285 2 7 . 4 5 3 3 . 8 0 0 .08 0 .06 1" 30 Massive aphanitic to coarse grained white to smoky quartz vein sample. Brecciated texture. int-high 135 740 335 23.40 6 6 . 2 0 3 ^ . 8 5 0.10. 0 . 5 0 0 .07 1 - 3 5 " 0 . 9 5 " 38 ** Pyrrhoti t e-b earing very f i n e to coarse grained, white and smoky mottled qtz vein sample. int-high 1200 555 1 3 - ^ 0 3 8 . 7 0 0 . 1 3 0 .07 41 Medium to coarsely grained milky qtz vein sample with f i n e sulphide s t r i n g e r s . high 915 1160 5000 52 .20 4 4 . 3 0 7 7 - 9 0 0.24 0 .08 0 .10 TABLE 4 continued . SAMPLE NUMBER PETROGRAPHIC DESCRIPTION RELATIVE QUARTZ CONTENT (low, i n t , o r high) FACE DESIG-NATION CONDUCTANCE (nanosiemens) MEAN OF 10 MEASUERD P.E. SIGNALS (mV p-p) STANDARD DEVIATION DIMENSION IF OF NON-STANDARD SIZE 40 ## F i n e g r a i n e d t o i n t - h i g h a r b i t 85 14.10 0 . 4 3 a p h a n i t i c white q u a r t z v e i n sample B 170 2 5 . 6 5 0.04 with t h i n s u l p h i d e bands. a r b i t 715 5-36 0 . 0 2 42 ### F i n e l y banded i n t A 335 2 0 . 6 0 0 . 1 5 quart z-carbonat e -c h l o r i t e - s e r i c i t e B 77P 10.82 0 . 1 0 s u l p h i d e s c h i s t . C 400 3^-90 0 . 1 2 REMARKS:- * F r a c t u r i n g a l o n g one of the A fa c e s p r o h i b i t e d measurement i n t h i s d i r e c t i o n . ** Very s l i g h t alignment o f c r y s t a l s i n C d i r e c t i o n observed. A and B d i r e c t i o n s chosen a r b i t r a r i l y ; . *** D e f i n i t e alignment of the s p l i n t e r y quartz c r y s t a l s i n approximate alignment with the C d i r e c t i o n . Other d i r e c t i o n s are a r b i t r a r y though and due to f r a c t u r i n g on the s u r f a c e , one of the d i r e c t i o n s (dimension 0 . 9 " ) was immeasurable. # F r a c t u r i n g along, one of the B fa c e s p r o h i b i t e d measurement i n t h i s d i r e c t i o n . The q uartz c r y s t a l s appear h i g h l y a l i g n e d p a r a l l e l to t h e i r o p t i c axes. ## The B d i r e c t i o n was chosen p e r p e n d i c u l a r to banding. The other d i r e c t i o n s were chosen a r b i t r a r i l y . cn ### T h i s sample was not a p e r f e c t "standard" specimen. One corner o f the 'cube was broken o f f . 55 maximum of 77,9 mV (sample #41), a f a c t o r of about 57 g r e a t e r . Sample #41 had the h i g h e s t quartz content. While some samples co n t a i n e d a l e s s e r amount of q u a r t z , i t i s b e l i e v e d t h a t the s m a l l e f f e c t s e x h i b i t e d by sample #48, ranked at i n t e r m e d i a t e quartz c o n t e n t , were due to the mottled d i s t r i b u t i o n of p i e z o e l e c t r i c a l l y n e u t r a l c h l o r i t e - s e r i c i t e components throughout the specimen together with the s m a l l quartz q r a i n s i z e and m i c r o f r a c t u r i n g . , As expected, massive samples with l a r g e r guartz q r a i n s such as samples #30 and #41 i n q e n e r a l d i s p l a y l a r g e r e f f e c t s than f i n e r grained samples such as #48 and #49, A c r i t e r i o n f o r v e r i f i c a t i o n t h a t a s i g n a l i s p i e z o e l e c t r i c i s r e v e r s a l of s i g n a l p o l a r i t y when the sample i s i n v e r t e d i n the compression cage. The photographs i n f i g u r e s 12 a & b were taken of sample #31 i n the B d i r e c t i o n , normal and i n v e r t e d p o s i t i o n s r e s p e c t i v e l y , . The f i r s t few p u l s e s were r e l i a b l y reproduced upon reassembly i n the compression cage, and the subsequent wavetrains of the two photographs c o n t a i n o n l y s l i g h t v a r i a t i o n s . I t may be concluded t h a t the compression cage used i n c o n j u n c t i o n with the torque wrench, serves q u i t e adequately to apply a pressure of c o n s i s t e n t maqnitude and d i s t r i b u t i o n a c r o s s the sample and t h a t the secondary s t r e s s pulse produced by the s o l e n o i d core i s extremely r e p e a t a b l e . F i g u r e 12a (a r e c o r d of the maximum s i g n a l observed) was d i g i t i z e d and i t s power spectrum p l o t t e d ( F i g . 13) using the.maximum entropy method (MEM) power spectrum r o u t i n e s of T.J,, D l r y c h and C. Walker, U n i v e r s i t y of B.C. The frequency ranqe of i n t e r e s t i s w e l l w i t h i n the passband of the a m p l i f i e r and f i l t e r systems. FIGURE 12:- Demonstration of reversal of signal p o l a r i t y r e s u l t i n g from separate solenoid core impacts on sample #44 (B direction) with the sample i n normal p o s i t i o n (a) and inverted (b) i n the compression cage. Vein sample of very high quartz content. [ 5000 mV/div at gain=100; 0.5 msec/div] > MEM POWER 1 .CL 2000 4000 FREQUENCY 6000 8000 FIGURE 13 :- MAXIMUM ENTROPY POWER SPECTRUM OF PIEZOELECTRIC RECORD SHOWN IN FIGURE 12(a). on 58 The m u l t i - s p i k e d nature o f F i g . 13 may be due t o s i g n a l domination by s e v e r a l of the l a r g e s t c r y s t a l s i n the matrix. The frequency of the p i e z o e l e c t r i c response of the v a r i o u s c r y s t a l s i z e s d i s t r i b u t e d throughout the matrix may a l s o be a f u n c t i o n of t h e i r size,. Two types of p i e z o e l e c t r i c e f f e c t s are r e a l i z a b l e when d e a l i n g with m u l t i c r y s t a l l i n e g uartz aggregates. For a specimen with random g r a i n o r i e n t a t i o n (massive sample group) , one would expect l i t t l e v a r i a t i o n i n the r e s u l t s of the three orthogonal measurements, the v a r i a t i o n s and magnitude de c r e a s i n g with a decrease i n g r a i n s i z e , w h i l s t l a r g e v a r i a t i o n s might be expected from specimens with an a p p r o p r i a t e f a b r i c ( f o l i a t e d sample group). Thus, i f the rock specimen l a c k s " f a b r i c " , that i s , i f there i s no p r e f e r e n t i a l alignment of the p o l a r i z a t i o n v e c t o r s of the i n d i v i d u a l c r y s t a l s , then one would expect the aggregate not to e x h i b i t a p i e z o e l e c t r i c e f f e c t . However, i t i s u s u a l l y observed t h a t the response of the specimen i s not zero, but t h a t due t o l o c a l c r y s t a l domination and non-^finite number of guartz g r a i n s , a net " s t a t i s t i c a l e f f e c t " i s u s u a l l y observed. Measurements of the three p e r p e n d i c u l a r s e t s of f a c e s of the "massive" c u b i c rock specimens were expected to y i e l d s t a t i s t i c a l e f f e c t s of roughly the same magnitude. Three of the e i g h t samples (#24, #30, #49) were of non-standard s i z e so must be excluded from the comparison. Of the remaining samples, #44 appears to best approximate a homogeneous sample of random c r y s t a l d i s t r i b u t i o n d i s p l a y i n g a s t a t i s t i c a l p i e z o e l e c t r i c e f f e c t . I t i s thought t h a t the v a r i a t i o n s i n s i g n a l magnitude 59 between orthogonal d i r e c t i o n s of a sample are due t o p h y s i c a l inhomogeneities r e f l e c t e d i n the measured v a r i a t i o n s i n conductance and t o some e x t e n t s i g n a l domination by the l a r g e r c r y s t a l s i n the matrix. I t appears t h a t the f i n e r grained samples, such as #44, approximate to a much c l o s e r e x t e n t , the i n f i n i t e number of c r y s t a l s r e q u i r e d t o o b t a i n c a n c e l l a t i o n of random c r y s t a l p o l a r i z a t i o n v e c t o r s . I t i s l i k e l y t h a t i f l a r g e r sample volumes co u l d be obtained, those orthogonal measurements of samples with l a r g e r quartz elements present such as #41 would show g r e a t e r p a r i t y . I t should not be r u l e d out t h a t some o f the o r thogonal measurement v a r i a t i o n s may be f a b r i c r e l a t e d . For some specimens there was a suggestion of f a b r i c alignment but i f i t was g u e s t i o n a b l e the sample was placed w i t h i n t h i s massive group. The r e s u l t s of g r e a t e s t importance are those of the " f o l i a t e d " sample group (Table 4 ) . As d e s c r i b e d i n s e c t i o n 1.5, except f o r s t a t i s t i c a l e f f e c t s due to l i m i t e d sample volume or n o n - i n f i n i t e c r y s t a l numbers, the C d i r e c t i o n should i d e a l l y e x h i b i t a zero p i e z o e l e c t r i c response or, at l e a s t , a s m a l l e r s i g n a l than A or B d i r e c t i o n s . The s i g n a l amplitude v a r i e d from 5,. 36 mV (samples #27 & #40) to a maximum of 246 mV (sample #31) , a f a c t o r of 46 g r e a t e r . The mean p i e z o e l e c t r i c s i g n a l magnitudes were computed f o r the r e l a t i v e quartz compositions. As shown i n Table 5 the s i g n a l magnitude i s indeed r e l a t e d t o the amount of quartz present. " F o l i a t e d " samples #33, #34, #35, #39 a l l e x h i b i t e d minimum p i e z o e l e c t r i c responses i n the "C" d i r e c t i o n as t h e o r e t i c a l l y predicted,. Of these samples, #35 and #39 e x h i b i t e d the g r e a t e s t TABLE 4 EXPERIMENTAL RESULTS OF FOLIATED CON MINE ROCKS SAMPLE NUMBER PETROGRAPHIC DESCRIPTION RELATIVE QUARTZ CONTENT ( l o w , i n t , or high) FACE. DESIG-NATION ( CONDUCTANCE (nanosiemens) MEAN O F .10 MEASURED P.E. SIGNALS (mV p-p) STANDARD DEVIATION DIMENSION IF OF NON-STANDARD SIZE 27 Very f i n e l y banded l o w - i n t A 715 5 .36 0 . 2 0 —" s u l p h i d e - b e a r i n g 28 . 65 0 . 0 6 q u a r t z - c h l o r i t e - B 255 s e r i c i t e s c h i s t . Quartz i s v e r y C 1055 3 2 . 0 0 . 1 5 f i n e to a p h a n i t i c . 31 * Very coarse g r a i n - v e r y h i g h A 570 2 4 6 . O o 0 . 5 7 1 . 3 5 " ed t o p e g m a t i t i c 1 1 6 . 0 0 . 4 5 q u a r t z - c a r b o n a t e B 300 v e i n sample. Minor s u l p h i d e - b e a r i n g c h l o r i t e s c h i s t . 33 - F i n e l y banded l o w - i n t A 1000 20.40 0 . 1 0 c h l o r i t e s c h i s t w i t h minor q u a r t z B 360 3 8 . 5 0 0 . 1 2 and carbonate 0.14 v e i n l e t s . C 770 1 5 . 4 5 " O N o TABLE 4 continued . . . SAMPLE NUMBER PETROGRAPHIC DESCRIPTION RELATIVE QUARTZ CONTENT ( l o w , i n t , or high) FACE DESIG-NATION CONDUCTANCE (nanosiemens) MEAN OF 10 MEASURED P.E. SIGNALS (mV p-p) STANDARD DEVIATION DIMENSION IF OF NON-STANDARD SIZE F i n e t o medium -gr a i n e d white qtz: v e i n specimen. Minor a n k e r i t e . - 'high a r b i t a r b i t C 625 690 435 5 6 . 7 0 48 .20 4 3 . 6 0 0 .16 0.14 0 .08 ^ «j *** H i g h l y f r a c t u r e d f i n e t o medium gr a i n e d dark smoky gray q u a r t z v e i n sample which tends to s p l i n t e r when s u b j e c t e d t o p r e s s u r e . v e r y h i g h a r b i t C 590 715 1 1 6 . 9 4 7 2 . 1 0 0 .26 0 . 1 3 39 # Very h i g h l y f r a c t -ured, incompetent, f i n e to c o a r s e l y g r a i n e d smoky q t z v e i n sample. Contains some ; s u l p h i d e s and c h i -o r i t e - a n k e r i t e -s e r i c i t e s c h i s t . S p l i n t e r y t e x t u r e . h i g h A C 100 100 5 5 , 9 0 2 1 . 8 5 0.40 0 - 3 5 1 . 4 " 1 . 6 5 " as TABLE 3 continued . . . SAMPLE NUMBER PETROGRAPHIC DESCRIPTION ^ RELATIVE QUARTZ CONTENT ( l o w , i n t , o r high) CONDUCTANCE (nanosiemens) MEAN OF 10 MEASURED P.E. SIGNALS (mV p-p) STANDARD DEVIATION DIMENSION IF OF NON-STANDARD SIZE 44 Contact o f a very-f i n e g r a i n e d meta-b a s a l t w i t h a f i n e g r a i n e d t o aphan-i t i c q u a r t z v e i n of sugary t e x t u r e . l o w - i n t 1430 6?0 740 11.18 14 . 0 5 1 0 . 6 0 0 . 0 5 0.10 0.04 ^8 *** F i n e t o medium gr a i n e d s u l p h i d e -b e a r i n g q u a r t z v e i n sample m o t t l e d throughout w i t h c h l o r i t e - s e r i c i t e s c h i s t . i n t 833 8 . 3 X ±0* 5 . 6 5 1 . 36 0.02 0.01 49 F i n e g r a i n e d q u a r t z cut by s u l p h i d e & c h l o r i t e bands and s t r i n g e r s . Minor carbonate. i n t 1.1 X 10* 20 3300 4.08 33 . 25 10.87 0.01 0 . 26 0.02 1" 1.2" 1 . 6 " REMARKS 1-F r a c t u r i n g a l o n g one f a c e made measurements p o s s i b l e f o r o n l y two d i r e c t i o n s Length between unraeasTare'd p a i r of f a c e s was app r o x i m a t e l y 1.7 i n c h e s . ** F r a c t u r i n g a l o n g one f a c e p r o h i b i t e d measurement i n one d i r e c t i o n . Dimension between ^ unmeasured f a c e s was app r o x i m a t e l y s t a n d a r d l e n g t h . F r a c t u r i n g a g a i n p r o h i b i t e d measurement i n one d i r e c t i o n . Dimension between r e m a i n i n g p a i r o f f a c e s was app r o x i m a t e l y 0 . 9 i n c h e s . 6 3 alignment of the elongated c r y s t a l s and c o r r e s p o n d i n g l y l a r g e d i f f e r e n c e s between C and remaining d i r e c t i o n s . The r e s u l t s of samples #27 and #42 do not f i t t h i s pattern,. For these samples however, the c r y s t a l l o g r a p h i c o r i e n t a t i o n c o u l d not be seen and the f a c e s were designated a c c o r d i n g t o l i n e a t i o n s w i t h i n the f i n e banding alone. TABLE - 5 F o l i a t e d Specimen Mean P i e z o e l e c t r i c S i g n a l Magnitude - For B e l a t i v e Quartz Content Quartz Content l e w - i n t high very h i g h Mean I Standard D e v i a t i o n (mV) 2 3 . 4 | 1 2 . 0 6 I 4 5 . 2 5 I 1 4 . 1 7 I 1 3 7 . 8 I 7 5 . 1 3 i n c o n c l u s i o n , the C d i r e c t i o n minimum p i e z o e l e c t r i c responses 64 of the " f o l i a t e d " sample group p r o v i d e some evidence t h a t f o r at l e a s t some of the Con Wine samples, the p i e z o e l e c t r i c response i s not merely " s t a t i s t i c a l " but i s " f a b r i c r e l a t e d " . U n f o r t u n a t e l y , many of the o r i g i n a l samples provided were e i t h e r too s m a l l or incompetent to be c u t to standard size,,What would be necessary to e s t a b l i s h d e f i n i t e proof of " f a b r i c r e l a t e d " e f f e c t s i s a s u f f i c i e n t l y l a r g e number of specimens, a l l with the same o r i e n t a t i o n cut from one rock sample or s e v e r a l p o i n t s w i t h i n the same v e i n . . S i m i l a r i t y between p i e z o e l e c t r i c measurements f o r each p a r t i c u l a r o rthogonal d i r e c t i o n f o r a l l specimens would be the only reguirement. D e s p i t e the f a c t t h a t the "standard s i z e " sample volume was much g r e a t e r than t h a t used by Starkey and A l l i s o n (1975), Tuck e t a l . (1977), or Bishop (1978), the "massive" sample r e s u l t s suggest t h a t s t i l l l a r g e r samples are r e g u i r e d , p a r t i c u l a r i l y i f l a r g e c r y s t a l s are present. I t appears t h a t the : d i s t r i b u t i o n of n o n - p i e z o e l e c t r i c mineral components throughout the rock and presence of m i c r o f r a c t u r i n g may g r e a t l y reduce the p i e z o e l e c t r i c response (sample #48). The conductance measurements taken suggest that even a p p a r e n t l y massive samples are l a c k i n g i n homogeneity. . The l a b o r a t o r y apparatus designed and b u i l t f o r t h i s part of the t h e s i s c o u l d : 1. Apply a c o n s i s t e n t and uniform pressure d i s t r i b u t i o n a c r o s s the f a c e s of a wide range of sample s i z e s 2. Apply a s t r e s s p u l s e of h i g h l y r e p e a t a b l e amplitude and form 65 3. Receive the r e s u l t a n t p i e z o e l e c t r i c charges from the sample f a c e s and provide q u i t e s u f f i c i e n t a m p l i f i c a t i o n and f i l t e r i n g 4. D i s c r i m i n a t e between p i e z o e l e c t r i c responses and v i b r a t i o n a l or other e l e c t r i c a l phenomena. S i g n i f i c a n t p i e z o e l e c t r i c responses may not only be obtained from samples e x h i b i t i n g c r y s t a l alignment but a l s o from massive samples with an apparently random f a b r i c . While the samples showing g r e a t e s t alignment (#31 & #35) e x h i b i t e d e f f e c t s about t h r e e times l a r g e r than any massive samples, i t appears t h a t massive guartz veins i n the mine environment should a l s o e x h i b i t r e c o g n i z a b l e responses. I t i s a l s o l i k e l y t h a t f a b r i c inhomogeneities on the s c a l e . o f the sample s i z e used would be l e s s s i g n i f i c a n t i n the " f u l l s c a l e " f i e l d o p e r a t i o n s and t h a t a guartz v e i n might approach more c l o s e l y a m o n o c r y s t a l l i n e response. In view of the p i e z o e l e c t r i c responses obtained from the Con Mine sample s u i t e i t was f e l t t h a t t r i a l s of an e x p l o r a t i o n system t o d e t e c t quartz veins at the mine should proceed. 66 CHAPTER 4: DEVELOPMENT AND FIELD TRIALS OF A -PIEZOELECTRIC EXPLORATION SYSTEM INTRODUCTION By 1964, Russian g e o p h y s i c i s t s had developed a f i e l d t echnigue based on the p i e z o e l e c t r i c e f f e c t f o r l o c a t i n g g u a r t z i t i c o r e-bearing v e i n s . As d e s c r i b e d i n s e c t i o n 2.2.1 (see fig , . 5) the s e i s m i c waves generated by an e x p l o s i v e or impact source compress the guartz o r pe g m a t i t i c vein which generates an el e c t r o m a g n e t i c f i e l d d e t e c t a b l e by e l e c t r o d e s or a magnetic antenna. The time delay between the e x p l o s i o n and the ele c t r o m a g n e t i c a r r i v a l i s then a measure of the source-quartz v e i n separation,. U n f o r t u n a t e l y the Russian papers l a c k e d the c l e a r p r e s e n t a t i o n r e q u i r e d f o r d i r e c t a p p l i c a t i o n . Development of s u i t a b l e eguipment and f i e l d procedures were t h e r e f o r e r e q u i r e d . Cominco L t d . funded two e x p l o r a t i o n f i e l d t r i a l s . A f t e r a b r i e f g e o l o g i c a l d e s c r i p t i o n of the e x p l o r a t i o n t a r g e t the r e s u l t s of these t r i a l s are d i s c u s s e d . 67 1 GEOLOGY OF THE EXPLORATION TARGET THE GOLD - BEARING QUARTZ LENSES OF THE-CON MINE The Archean (older than 2480 m. y . ) , one of the l a r g e s t and g r e a t e s t p e r i o d s of m i n e r a l i z a t i o n i n the e a r t h ' s h i s t o r y , accounts f o r numerous l a r g e and r i c h d e p o s i t s of i r o n , manganese, g o l d , copper,- molybdenum, z i n c , n i c k e l , and asbestos. Most Archean d e p o s i t s are c l o s e l y a s s o c i a t e d with greenstone b e l t s , t h e i r r e l a t e d sedimentary p i l e s , and t h e i r d e r i v a t i v e g r a n i t i c bodies; i n essence, the basement rocks of the Precambrian s h i e l d s of Canada, A u s t r a l i a , I n d i a , A f r i c a , A r a b i a , U.S.S.R*, and B r a z i l - G u i a n a . The p a r t i c u l a r t a r g e t f o r t h i s e x p l o r a t i o n t r i a l i s one such a u r i f e r o u s d e p o s i t - the Con Mine, l o c a t e d on the west s i d e of Y e l l o w k n i f e Bay on the north shore of the Great Slave Lake i n the Northwest T e r r i t o r i e s . 1,. 1 GENERAL GEOLOGY D e t a i l e d d e s c r i p t i o n s of the g e n e r a l geology and s t r u c t u r e o f the Y e l l o w k n i f e area have been given by Boyle (1961) and Henderson and Brown (1966). The f o l l o w i n g i s a summary o f these r e p o r t s . Four main types of rocks occur w i t h i n the Y e l l o w k n i f e d i s t r i c t - v o l c a n i c s ( Y e l l o w k n i f e group, d i v i s i o n A), sediments (Yellowknife group, d i v i s i o n B), g r a n o d i o r i t e s , g r a n i t e s and 68 a l l i e d r o c k s , and the l a t e diabase dykes and b a s i c s i l l s . , The sequence of meta v o l c a n i c s (Kam Formation) i s at l e a s t t h i r t y thousand f e e t t h i c k and i s c o n f i n e d to the west s i d e of y e l l o w k n i f e Bay (McMurdo, 1975).. T h i s f o r m a t i o n c o n s i s t s of flows, interbedded t u f f s , and p y r o c l a s t i c s , and t h e i r g e o l o q i c a l f e a t u r e s suggest t h a t they were l a i d down i n a sea or ocean. The v o l c a n i c assemblage a l s o c o n t a i n s many conformable s i l l s of gabbroic c o m p o s i t i o n . Both the flows and conformable s i l l s are cut by numerous dykes of gabbroic and d i o r i t i c composition. The sediments of the Yello w k n i f e group c o n s i s t of greywacke, p h y l l i t e , s l a t e , a r g i l l i t e , g u a r t z i t e , arkose, and conglomerates,. Some, l a v a f l o w s , t u f f s , and p y r o c l a s t i c s are interbedded with these sediments. The sediments of the Y e l l o w k n i f e Group apparently l i e conformably on the v o l c a n i c seguence and are l i k e l y of marine o r i g i n . Boyle (1976), b e l i e v e s the g e n e r a l enrichment of the Ye l l o w k n i f e and other greenstone flows i n the v o l c a n i c b e l t s of the Precambrian s h i e l d s r e p r e s e n t periods d u r i n g which r e d u c i n g , s a p r o p e l i c sedimentation c o n d i t i o n s p r e v a i l e d . These rocks are c o n s i d e r a b l y e n r i c h e d i n carbonate, potassium, phosphorous, sulphur and carbon p o i n t i n g to the p r o b a b i l i t y t h a t they were formed under re d u c i n g c o n d i t i o n s where b i o l o g i c a l a c t i v i t y played a l a r g e p a r t i n c o n c e n t r a t i n g the.sulphur and carbon. 69 4. 1, 2 STBUCTUBftL GEOLOGY The greenstones of the d i s t r i c t are f o l d e d i n t o a broad n o r t h e a s t e r l y plunging asymmetric s y n c l i n e . The northwest limb of the greenstone b e l t c o n s i s t s of a simple homoclinal s u c e s s i o n of v o l c a n i c flows t h a t dip and face southeast. Underground mapping at the Con mine (McMurdo, 1975) shows t h a t t h i s simple h o m o c l i n a l concept holds t r u e to depths of f i v e . t h o u s a n d f e e t at l e a s t i n the v i c i n i t y of the Con shear. The southeast limb i s overturned and i s i n part f o l d e d i n t o a s u b s i d i a r y a n t i c l i n e . The sediments of the Y e l l o w k n i f e group are complexly f o l d e d i n t o i s o c l i n a l f o l d s which i n t u r n have been c r o s s f o l d e d . Two ages of shear zones occur i n the greenstone b e l t . A. E a r l y shear zones which p a r a l l e l the l a v a flows i n s t r i k e and dip and c o n t a i n a few s m a l l , high grade quartz l e n s e s , and B. Shear zones which t r a n s e c t the l a v a flows and c o n t a i n the l a r g e economic g o l d - g u a r t z veins and l e n s e s . Boyle(1961), Henderson and Brown (1966), McMurdo (1975) and o thers b e l i e v e t h a t f a i l u r e i n the shear zones took place along zones of weakness r e s u l t i n g i n a f l o w - l i k e t h r u s t movement. In the shear-zone systems i n the v o l c a n i c b e l t , ore shoots are comprised o f s i n g l e or m u l t i p l e p i n c h i n g , s w e l l i n g , and merging v e i n s , l e n s e s , or l e n s swarms of gold bearing quartz (McMurdo, 1975). Here the p r i c i p a l ore c o n t r o l s are shear-zone j u n c t i o n s and f l e x u r e s and drag f o l d e d p a r t s of the l a r g e s c h i s t zones (Boyle,1961). 70 1.3 OBIGIN OF THE GOLD-BEARING QUARTZ LENSES In s p i t e of the d e t a i l e d s t u d i e s conducted over s e v e r a l decades on these d e p o s i t s , t h e i r o r i g i n s t i l l remains an enigma. I n v e s t i g a t i o n s t o date suggest t h a t the ore shoots are " t r u e " shear zones which t r a n s e c t the flows and s i n c e no h i g h l y e n r i c h e d h o r i z o n s have yet been found, an e x h a l a t i v e - s e d i m e n t a r y o r i g i n seems improbable,. Boyle (1961) supports the d i l a t a n t theory f o r form a t i o n of the l e n s e s . While i t appears t h a t much of the quartz has been co n c e n t r a t e d by d i l a t a n t processes, the e x t e n t to which t h i s mechanism i s r e s p o n s i b l e f o r the c o n c e n t r a t i o n of g o l d and s i l v e r i s s t i l l under debate. Although the c o u n t r y r o c k s most c e r t a i n l y c o n t a i n s u f f i c i e n t q u a n t i t i e s of these elements to account f o r the ore d e p o s i t s , i t i s d i f f i c u l t t o prove c o n c l u s i v e l y t h a t these host r o c k s have been depleted i n these elements. Boyle (1961), has brought f o r t h many c o n t e n t i o u s p o i n t s concerning a magmatic-hydrothermal o r i g i n . A s t a t i s f a c t o r y model f o r the area has not yet been proposed. 71 4.2 FIRST EXPLORATION FIELD TRIAL* 4.2,1 INSTRUMENTATION, Although the b a s i c i d e a s of p i e z o e l e c t r i c e x p l o r a t i o n were presented i n the Russian papers, the t e c h n i c a l d e t a i l s of survey procedures or i n s t r u m e n t a t i o n r e c e i v e d only scant mention. Thus the e x p l o r a t i o n system was d e v i s e d from b a s i c p r i n c i p l e s f o r the f i r s t f i e l d t r i a l . A f t e r p r e l i m i n a r y l a b o r a t o r y measurements of a s u i t e of Con Mine rocks, the l a b o r a t o r y system was transformed i n t o the e x p l o r a t i o n system with minor a l t e r a t i o n s . The i n s t r u m e n t a t i o n and deployment chosen f o r the f i r s t underground t e s t s i s shown i n F i g , 14. Into the walls of the t u n n e l (1), f i f t e e n cm long copper e l e c t r o d e s were p l a c e d i n s h o r t , i n c l i n e d , d r i l l h o l e s (2) to r e c e i v e the e l e c t r i c a l component of the p i e z o e l e c t r i c s i g n a l . To ensure proper e l e c t r i c a l c o n t a c t , t h e . h o l e s were f i l l e d with copper sulphate (CuSO^. 5H 20) , a h i g h l y c o n d u c t i v e s o l u t i o n . The p i e z o e l e c t r i c s i g n a l frcm a p a i r of e l e c t r o d e s was fed along the i n n e r core of the c o - a x i a l c a b l e s (3) t o the i n p u t s of a T e k t r o n i x AM-502 D i f f e r e n t i a l A m p l i f i e r and i t s Tekronix TM-515 Power Module (4), The outer conductors of the c o a x i a l c a b l e s were then grounded to provide s h i e l d i n g . . The p a i r of e l e c t r o d e c a b l e s were a l s o braided about one another f o r as much of t h e i r l e n g t h s as p o s s i b l e to reduce i n d u c t i v e pickup and maximize common-mode s i g n a l r e j e c t i o n . The AM-502 a m p l i f i e r was chosen f o r i t s high common-mode-rejection-ratio (100 dB, DC to 50 kHz), s e l e c t a b l e high and low pass f i l t e r s , and a d j u s t a b l e gain and DC o f f s e t . 6 7 8 9 10 l l 12 13 14 WALLS OF UNDERGROUND TUNNEL DIFFERENTIAL ELECTRODE PAIRS SHIELDED CABLE FROM ELECTRODES TO AMP THREE AMPLIFIERS AND POWER MODULE SHIELDED CABLE FROM AMPLIFIERS TO SEISMOGRAPH CABLE 12 CHANNEL .SEISMOGRAPH CABLE GEOPHONES STORAGE OSCILLOSCOPE MONITOR DC TO AC POWER CONVERTER 12 VOLT CAR BATTERY 12 CHANNEL ENHANCEMENT SEISMOGRAPH 12 VOLT GELL/CELL BATTERY BLASTER UNIT TRIGGER CABLE TO EXPLOSIVE OR HAMMER SOURCE FIGURE 14 :- PIEZOELECTRIC EXPLORATION SYSTEM USED IN FIRST FIELD TRIAL (after Jose et a l . , 1978) to 73 The i n p u t impedance was 1 hsi p a r a l l e l e d by approximately 47 pF, The output from t h i s p r e a m p l i f i c a t i o n stage t r a v e l l e d by s h i e l d e d c a ble (5) to connect with the s e i s m i c c a b l e (6) along which the s i g n a l s d e t e c t e d by the WHS model Z-3 geophones (7) were a l s o f e d . A T e k t r o n i x 214 p o r t a b l e storage o s c i l l o s c o p e (8) was used to monitor the p i e z o e l e c t r i c s i g n a l s and background noise l e v e l . The TM-515 power module, being AC d r i v e n , n e c e s s i t a t e d the use of a Heath Model MPW-10 power c o n v e r t e r (9) and 12 v o l t car b a t t e r y (10) to run i t . The power c o n v e r t e r i s r a t e d at 175 Watts continuous or 240 Watts i n t e r m i t t e n t output at 117 VAC and 60 Hz from a 12 - v o l t car b a t t e r y . The Nimbus ES-1200 12-channel seismograph with d i g i t a l memory and enhancement c a p a b i l i t i e s (11) was powered by rechargeable Globe PP 1200 g e l / c e l l b a t t e r i e s (12).. A b l a s t e r u n i t (13) was used t o detonate the e x p l o s i v e s e i s m i c source and simultaneously a c t i v a t e the s e i s m o g r a p h s d i g i t a l memory. A l t e r n a t i v e l y , a hammer attached t o the t r i g g e r c a b l e (14) could be used as the se i s m i c source. The l i g h t from the author's headlamp was capable o f d e v e l o p i n g the Kodak Linagraph d i r e c t p r i n t photographic paper o f the seismograph p e r m i t t i n g viewing while underground. A f t e r some experimentation, the a d j u s t a b l e high and low frequency c u t - o f f f i l t e r s of the a m p l i f i e r were s e t f o r a 100 1000 Hz bandpass f o r the d u r a t i o n of the Con Mine t e s t s . 74 4,2.2 TEST SITE #j: DEVELOPMENT OF OPERATIONAL PROCEDURES The p r e l i m i n a r y t e s t s o f t h e e x p l o r a t i o n system at t h e Con Mine were conducted between June 29th and J u l y 10th, 1978 a t c r o s s - c u t B4506 XCE on the 4500 f o o t depth l e v e l , An exposed 1 t o 2 f o o t t h i c k q u a r t z v e i n which c r o s s c u t s t h e d r i f t a t t h i s s i t e had been examined p r e v i o u s l y by Myers and L a j o i e (1977), Both hammer blows and v a r i a b l e numbers o f s i m u l t a n e o u s l y d e t o n a t e d seismocaps were used as s e i s m i c energy s o u r c e s . The seismocaps were u s u a l l y d e t o n a t e d w i t h i n an unused e l e c t r o d e h o l e and t h e h o l e tamped w i t h water and r u b b l e t o i n c r e a s e e x p l o s i v e c o u p l i n g . As mentioned i n t h e R u s s i a n l i t e r a t u r e , an e l e c t r o m a g n e t i c p r e c u r s o r s p i k e was p i c k e d up on the e l e c t r i c c h a n n e l s due to t r i g g e r i n g of the seismograph d i r e c t l y by t h e b l a s t e r u n i t o r , when, f o r hammer t r i g g e r i n g , the l o n g t r i g g e r c a b l e r e e l was used. T h i s p r e c u r s o r was e l i m i n a t e d by k e e p i n g t h e c a b l e r e e l and b l a s t e r u n i t away from t h e i n s t r u m e n t s and e l e c t r o d e : c a b l e s and by b r a i d i n g t h e e l e c t r o d e c a b l e s about one a n other t o reduce i n d u c t i o n , . Once some o f t h e s e problems had been e l i m i n a t e d i t was found t h a t the n o i s e l e v e l a t t h i s s i t e . w a s s t i l l t o o g r e a t t o p e r m i t d e t e c t i o n o f the p i e z o e l e c t r i c s i g n a l . S e v e r a l t y p e s o f n o i s e i n the 60 Hz band v a r y i n g from almost pure s i n e waves t o i r r e g u l a r s p i k e d forms were d e t e c t e d . When the n o i s e l e v e l was m o n i t o r e d , l a r g e , sometimes a b r u p t , v a r i a t i o n s i n a m p l i t u d e and s i g n a l c h a r a c t e r c o u l d be seen t h r o u g h o u t th e work day. Attempts t o a m p l i f y t h e p i e z o e l e c t r i c s i g n a l t o a 75 r e c o g n i z a b l e l e v e l , r e s u l t e d i n the background n o i s e , . a l s o undergoing a m p l i f i c a t i o n , o v e r d r i v i n g the enhancement seismograph's memory which was used f o r data s t o r a g e . The 60 Hz noise c o u l d be monitored by touching the l e a d s o f the storage o s c i l l o s c o p e d i r e c t l y a g a i n s t the rock s u r f a c e while the p i e z o e l e c t r i c e x p l o r a t i o n equipment was not o p e r a t i n g . Hence i t appeared t h a t at l e a s t a m a j o r i t y of the p r o h i b i t i v e n o i s e at t e s t s i t e #1 was due to mine o p e r a t i o n s such as a s l u s h e r i n a nearby scram, power c a b l e s , and telephone l i n e s . Since the output o f the DC t o AC power c o n v e r t e r used t o supply the a m p l i f i e r package was a square r a t h e r than s i n u s o i d a l wave, a p o r t i o n o f the i r r e g u l a r n o i s e s p i k e s a l s o o r i g i n a t e d from t h i s source.. A s m a l l p o r t a b l e Honda generator brought as an a l t e r n a t i v e power source could not be te s t e d because of s a f e t y r e s t r i c t i o n s so f o r f u t u r e t e s t s i t was decided a DC powered a m p l i f i e r should be used. As Cominco's seismograph u n i t was only a v a i l a b l e f o r a l i m i t e d time, i t was decided t h a t a s o l u t i o n of t h i s n o i s e problem should not be attempted i n t h i s t e s t p e r i o d . Another s u i t a b l e quartz vein exposure i n a l e s s e l e c t r i c a l l y " n o i s y " area of the mine was t h e r e f o r e sought. D e t a i l e d n o i s e surveys were made at s e v e r a l s i t e s u s ing the T e k t r o n i x 214 p o r t a b l e o s c i l l o s c o p e as a noise monitor. The s i t e s examined as p o t e n t i a l c a n d i d a t e s f o r t e s t s i t e #2 i n c l u d e d 3711 AX, 3711 XCE, 3701, 3913N, 41205G, 4111A, and a s i t e on 4500 l e v e l near the B3 Wince. The B3 Wince s i t e was s e l e c t e d . 76 4.2.3 EXPERIMENTS AT TEST SITE #2 The q u a r t z v e i n exposure i n the main d r i f t of 4500 l e v e l near the B3 Wince was v o i d of power c a b l e s and the average e l e c t r i c a l n o i s e l e v e l from work i n t h i s s e c t i o n of the mine was lower than at the p r e v i o u s s i t e . The exposed quartz vein which t r a n s e c t s the t u n n e l i s h i g h l y c o n t o r t e d and i r r e g u l a r i n shape. The v e i n averages about 0.5 m i n width and the c o n t a c t with the host rock i s g u i t e sharp. The t e s t s a t t h i s s i t e were conducted between J u l y 14th and 19th by the author. A diamond d r i l l was used to make the i n c l i n e d h o l e s f o r e l e c t r o d e emplacement. The p r e c a u t i o n s taken to reduce n o i s e a t t e s t s i t e #1 were again implemented. In a d d i t i o n i t was found t h a t grounding the a m p l i f i e r console and i n v e r t e r t o g e t h e r t o a s c r e w d r i v e r d r i v e n i n t o the ground next to a r a i l of the t r a i n t r a c k s helped f u r t h e r to reduce the n o i s e l e v e l . As an added p r e c a u t i o n , f o i l was wrapped about the i n v e r t e r and l o n g t r i g g e r c a b l e r e e l t o reduce any r a d i a t i o n emitted by these. The e l e c t r o d e c a b l e s were a l s o b r a i d e d about each other to reduce i n d u c t i o n i n the l e a d s . Measurements with ohmmeters and voltmeters between e l e c t r o d e h o l e s i n d i c a t e d t h a t c u r r e n t s flowing w i t h i n the rock walls were sometimes s u b s t a n t i a l . These c u r r e n t s were l i k e l y of i n d u s t r i a l r a t h e r than t e l l u r i c o r i g i n , _ U n d e r most circumstances an o f f s e t at the commencement of the record c o u l d be prevented by n u l l i n g these c u r r e n t s with the DC o f f s e t c o n t r o l of the a m p l i f i e r . The only r e s t r i c t i o n s t o surveying were when 77 communication and the h o i s t buzzer system l o c a t e d at the nearby B3 Wince was being used. E l e c t r i c a l s i g n a l s , c l e a r l y from these sources, were then recorded by the e x p l o r a t i o n system. At t h i s new t e s t s i t e , d u r i n g a period when the e l e c t r i c a l i n t e r f e r e n c e s i g n i f i c a n t l y abated, h i g h l y r e p e a t a b l e p i e z o e l e c t r i c s i g n a l s with e x c e l l e n t s i g n a l n o i s e r a t i o s were recorded. Some t y p i c a l p i e z o e l e c t r i c r e c o r d s which e x h i b i t most of the i n t e r e s t i n g f e a t u r e s of these s i g n a l s are shown i n f i g u r e s 15, 16, 17, and 18,. F i g u r e 15 shows a t y p i c a l r ecord from an e l e c t r i c a l channel. I t was produced by one hammer impact approximately 11 meters west of the guartz v e i n . The p a i r of e l e c t r o d e s which r e c e i v e d the s i g n a l was l o c a t e d 11 and 15 meters west of the v e i n . .Note t h a t there appears to be two main phases of a r r i v a l s and t h a t t h e r e i s a delay b e f o r e the f i r s t a r r i v a l c orresponding to the time taken f o r the s e i s m i c wave to t r a v e l from the shot p o i n t to the quartz v e i n . .. F i g u r e 16 shows the e l e c t r i c a l s i q n a l produced by one hammer impact approximately 15 metres west of the quartz v e i n . Once a q a i n , two main phases o f a r r i v a l s can be seen and, as would be expected, an a r r i v a l time delay with r e s p e c t to f i q u r e 15 can a l s c be n o t i c e d . The h i g h l y r e p e a t a b l e . nature of the s i g n a l s i s e x e m p l i f i e d i n record 17 produced by a d i f f e r e n t hammer impact at the same l o c a t i o n and same instrument s e t t i n g s as f o r record 16. F i g u r e 18 shows the e l e c t r i c a l response produced by one hammer impact approximately 46 metres east of the q u a r t z vein exposure. A delay o f 8 msec was present on the seismograph. The. weaker f i r s t a r r i v a l and stronger second t=0 : . WAIN (M) ARRIVAL (S AND.RAYLEIGH GENERATED) • INITIAL (I) ARRIVAL (P WAVE GENERATED) -. FIGURE 15 :- ELECTRICAL SIGNAL PRODUCED BY ONE HAMMER IMPACT 11 m .WEST OF THE QUARTZ VEIN AND . : •." ELCTRODES.il AND 15 m WEST OF THE VEIN. ,\'/ I 2 n d PHASE FIGURE 16 :- ELECTRICAL.SIGNAL.PRODUCED BY ONE HAMMER IMPACT 15 m WEST OF' THE QUARTZ VEIN AND ELECTRODES 11 AND 15 m WEST OF THE VEIN. INITIAL; 5 ^ I N (I^f):/.-TYPE ARRIVAL (S AND RAYLEIQ-I WAVE GENERATED). INITIAL (I) ARRIVAL (P WAVE 'GENERATED) - •. 'FIGURE 17 :- EXAMPLE OF PIEZOELECTRIC SIGNAL REPEATABILITY. • . • - • ELECTRICAL SIGNAL PRODUCED USING THE. SAME ' ' PARAMETERS AS FIGURE 16. NOTE THE HIGH DEGREE.. OF REPEATABILITY BETWEEN THESE FIGURES.- . t=8 msec '—INITIAL AND.MAIN'(I^M) ARRIVAL. (S AND RAYLEIGH WAVE GENERATED) "-^-INITIAL (I) ARRIVAL... (P WAVE: GENERATED) •' .FIGURE 18 :- PIEZOELECTRIC SIGNAL PRODUCED BY ONE.HAMMER • '. • : IMPACT 46 m EAST OF THE QUARTZ VEIN AND - .." ' '• •• ' ELECTRODES . 11 AND 15 m'- WEST OF VEIN. A TIME : DELAY OF 8 msec WAS PRESET ON THE SEISMOGRAPH. 2 82 a r r i v a l b o t h c o r r e s p o n d t o the f i r s t a r r i v a l phase seen on the p r e v i o u s r e c o r d s . T h i s p a r t i c u l a r r e c o r d t e r m i n a t e s b e f o r e i n i t i a t i o n o f t h e second phase. I n t h i s r e c o r d , the i n i t i a l and main s i g n a l s c f t h e f i r s t phase o f a r r i v a l s have now become c l e a r l y s e p a r a t e . I t i s b e l i e v e d t h a t t h e s e s i g n a l s have been g e n e r a t e d by the a r r i v a l s o f the c o m p r e s s i o n a l (P) ' and shear (S) s e i s m i c waves a t the q u a r t z v e i n . As the s h o t p o i n t i s moved s u c c e s s i v e l y f u r t h e r from t h e . q u a r t z v e i n , d i f f e r e n c e i n t r a v e l t i me of the P and S waves becomes i n c r e a s i n g l y e v i d e n t through t h e t i m e s e p a r a t i o n o f the p i e z o e l e c t r i c r e s p o n s e s produced by t h e s e waves. T h i s o b s e r v a t i o n i s not s u r p r i s i n g s i n c e i t was shown i n s e c t i o n 1*5 t h a t shear as w e l l as c o m p r e s s i o n a l s t r e s s e s may produce p i e z o e l e c t r i c r e s p o n s e s . For t h e p r o p a g a t i o n of a d i s t u r b a n c e i n a h a l f s p ace, sometimes c a l l e d Lamb's problem, t h e shear and fiayleigh wave v e l o c i t i e s a r e about 0.58 and 0.53 r e s p e c t i v e l y o f t h e P wave v e l o c i t y (Ewing e t a l . , 1957). The R a y l e i g h wave t h e r e f o r e has a v e l o c i t y of about 0.92 of t h e shear wave v e l o c i t y . The a r r i v a l o f t h i s wave s h o r t l y a f t e r t h e s h e a r wave i s l i k e l y r e s p o n s i b l e f o r the l a r g e a m p l i t u d e of the second a r r i v a l . I n t h e few R u s s i a n p i e z o e l e c t r i c e x p l o r a t i o n p u b l i c a t i o n s , no mention has been made o f t h e a b i l i t y t o d i s t i n g u i s h between "P" and "S or R a y l e i g h " wave r e l a t e d p i e z o e l e c t r i c r e s p o n s e s , The p o o r e r q u a l i t y and many t i m e s l o w e r s i g n a l t o n o i s e r a t i o o f t h e i r r e c o r d i n g s may have p r o h i b i t e d t h i s d i s c r i m i n a t i o n . F i g u r e 18 was d i g i t i z e d a t 0,4 msec i n t e r v a l s . The maximum en t r o p y s p e c t r a l d e c o m p o s i t i o n r o u t i n e s o f T . J , , U l r y c h and C. Walker ( U n i v e r s i t y o f B r i t i s h Columbia) were used t o p l o t the 83 power spectrum (Figure 19) of the s i g n a l . Host of the energy i s l o c a t e d i n the 400-700 Hz band with two peaks c l o s e to 500 and 600 Hz. The a r r i v a l s on the " p i e z o e l e c t r i c " r e c o r d s were c l a s s i f i e d as i n i t i a l (I) type i n d i c a t i n g a weak a r r i v a l d i s t i n g u i s h a b l e from the low background n o i s e ( f o r example f i r s t a r r i v a l , F i g , 15); main (W) type i n d i c a t i n g a s t r o n g a r r i v a l i n the midst of the p i e z o e l e c t r i c s i g n a l t r a i n ; and i n i t i a l - m a i n (I-W) type, i n d i c a t i n g a strong sudden a r r i v a l e a s i l y d i s t i n g u i s h e d over the low examples of these three a r r i v a l types are best seen on F i g s . . 16 and 18, F i g . 20 shows a p l o t of these a r r i v a l times as a f u n c t i o n of the measured d i s t a n c e from the shot p o i n t t o the exposed q u a r t z v e i n . Apparently there are 4 sources f o r the e l e c t r i c a l s i g n a l s . As mentioned p r e v i o u s l y , i t i s b e l i e v e d that both the P and S s e i s m i c waves are producing p i e z o e l e c t r i c responses c o r r e s p o n d i n g to l i n e s (a) and (b) r e s p e c t i v e l y of F i g . 20. The apparent v e l o c i t i e s of l i n e s (a) and (b) , 4666 m/sec (15,311 f t / s e c ) and 2777 m/sec (9114 f t / s e c ) r e s p e c t i v e l y , are i n ge n e r a l agreement with l a b o r a t o r y v e l o c i t y a n a l y s e s of Con Wine samples conducted by King (1975) (Appendix 2 ) . The sources of the e l e c t r i c a l responses which p l o t on l i n e s (c) and (d) are not c l e a r . . These "second phase" a r r i v a l s are a l s o o f h i g h l y r e p e a t a b l e form and often of g r e a t e r amplitude than the " f i r s t phase" a r r i v a l s c o n t a i n i n g the "P and S generated" p i e z o e l e c t r i c s i g n a l s . The i n f o r m a t i o n which we seek - the d i s t a n c e to the quartz v e i n - i s a l s o apparently given by l i n e (c) which has an apparent v e l o c i t y of about 390 metres/sec. I t i s p o s s i b l e these MEM POWER 0 500 : 1000 1500 FREQUENCY FIGURE 19 :- MAXIMUM ENTROPY POWER SPECTRUM OF RECORD SHOWN IN FIGURE 18. oo FIGURE 20 85 P I E Z O E L E C T R I C A R R I V R L T I M E S FOR V A R I O U S D I S T A N C E S FROM SHOT P O I N T TO QUARTZ V E I N 0 20 4 0 SO S . P . - Q . V . D I S T R N C E ( M ) 86 a r r i v a l s c o r r e s p o n d t o the sound waves ( v e l o c i t y approx,. 345 metres/sec) of t h e impact t r a v e l l i n g down t h e t u n n e l . L i n e ( d ) , c o r r e s p o n d i n g t o v e r y l a t e a r r i v a l s w i t h an approximate v e l o c i t y o f 250 m e t r e s / s e c , has a t i m e d e l a y a s s o c i a t e d w i t h i t . A p o s s i b l e s o u r c e f o r these s i g n a l s has n o t yet been found. The n a t u r e o f t h e problem makes i t d i f f i c u l t t o prove t h a t s i g n a l s such as t h o s e of l i n e s (a) and ( b ) , F i g , 20, are of p i e z o e l e c t r i c o r i g i n . N e v e r t h e l e s s , a number o f " a u t h e n t i c i t y " t e s t s v e r i f i e d t h a t t h e s e s i g n a l s a r e t r u e p i e z o e l e c t r i c r e s p o n s e s from the exposed g u a r t z v e i n . These t e s t s a r e now o u t l i n e d below. When the seismograph was t r i g g e r e d by s t r i k i n g the hammer a g a i n s t a hand h e l d r o c k r a t h e r than t h e w a l l o f t h e d r i f t , t h e o u t p u t on t h e p i e z o e l e c t r i c c h a n n e l was n e g l i g i b l e , . T h i s t e s t ensured t h a t t h e t r i g g e r p u l s e t r a v e l l i n g a l o n g the t r i g g e r c a b l e ( F i g . 14, (14)) o r any o t h e r p a r t o f t h e e x p l o r a t i o n system was not r e s p o n s i b l e f o r any p o r t i o n of t h e s i g n a l s such as t h o s e shown above. I f t h e e l e c t r o d e s were suspended i n the a i r r a t h e r t h a n p l a c e d i n t h e CuSGy.5H 20 f i l l e d d r i l l h o l e s , a g a i n a s i g n a l was net observed. F i g u r e s 15 t o 18 and o t h e r r e c o r d s c o m p r i s i n g l i n e s (a) and (b) o f F i g . 20 not o n l y d i s p l a y t h e expected l i n e a r i n c r e a s e i n d e l a y time p r o p o r t i o n a l to t h e s h o t p o i n t - q u a r t z v e i n d i s t a n c e , but are a l s o i n agreement w i t h l a b o r a t o r y v e l o c i t y measurements o f Con Mine r o c k s conducted by K i n g (1975), To ensure t h a t t h e s i g n a l s were not due t o changes i n c o n t a c t p o t e n t i a l as a r e s u l t of movement of the e l e c t r o d e s as 87 the s e i s m i c wave passed by, the f o l l o w i n g t e s t was designed..The shot p o i n t - g u a r t z vein d i s t a n c e was kept f i x e d and f o r d i f f e r e n t s h o t s , the r e c e i v i n g e l e c t r o d e s were moved to v a r i o u s l o c a t i o n s up to 20 metres on e i t h e r s i d e of the v e i n . As p r e d i c t e d i n the theory of the e x p l o r a t i o n technique the a r r i v a l time remained constant p r o v i d i n g f u r t h e r evidence t h a t the observed s i g n a l s are indeed p i e z o e l e c t r i c . . T h i s t e s t a l s o showed t h a t second order s e i s m o e l e c t r i c e f f e c t s of e l e c t r o k i n e t i c o r i g i n were not a concern. The p i e z o e l e c t r i c s i g n a l s showed an expected decrease i n amplitude i n v e r s e l y p r o p o r t i o n a l to the Shot P o i n t - Q u a r t z Vein distance,. The Russian p i e z o e l e c t r i c e x p l o r a t i o n system PEEF-2 designed by V o l a r o v i c h and Sobolev (1965) has a bandpass of 300-800 Hz. The p i e z o e l e c t r i c energy of the s i g n a l s recorded by the author were a l s o w i t h i n t h i s range ( F i g . 19). Due to the l o o s e rock r u b b l e about the f l o o r of the t u n n e l d i f f i c u l t i e s were encountered with geophone emplacements. T h i s r e s u l t e d i n u n s a t i s f a c t o r y s e i s m i c r e s u l t s . A more c a r e f u l experiment employing h o r i z o n t a l geophones was planned f o r the next f i e l d t r i a l . 4.2.3 SUMMARY OF FIRST EXPLORATION FIELD TRIAL. Tests of the p i e z o e l e c t r i c f i e l d system a t the Con Mine y i e l d e d very encouraging r e s u l t s . E x c e l l e n t p i e z o e l e c t r i c responses were observed under a v a r i e t y of i n s t r u m e n t a l c o n f i g u r a t i o n s . 88 By the use of s h i e l d e d and braided c a b l e s and c a r e f u l deployment, noise c o u l d be reduced and the t r i g g e r i n g p r e c u r s o r e l i m i n a t e d . However, development of a bet t e r f i l t e r i n g system was r e q u i r e d to d i s c r i m i n a t e a g a i n s t e l e c t r i c noise sources w i t h i n the mine. In order to e l i m i n a t e the noisy power co n v e r t e r stage, a DC powered a m p l i f i e r was recommended..During p e r i o d s of low e l e c t r i c a l i n t e r f e r e n c e , p i e z o e l e c t r i c s i g n a l s were observed out t o s o u r c e - t a r g e t d i s t a n c e s of 55 metres (the l i m i t of the t r i g g e r c a b l e a v a i l a b l e ) and e l e c t r o d e - t a r g e t d i s t a n c e s of 20 metres (the f u r t h e s t d r i l l h ole from the guartz v e i n f o r e l e c t r o d e emplacement). At these d i s t a n c e s c l e a r p i e z o e l e c t r i c a r r i v a l s were observed without use of the enhancement c a p a b i l i t i e s of the system. I f the s i g n a l enhancement c a p a b i l i t i e s were used the e f f e c t i v e e x p l o r a t i o n range should be even g r e a t e r . P i e z o e l e c t r i c s i g n a l s were observed when both shear and compressional s e i s m i c waves str u c k the quartz v e i n . Osing the compressional and shear s e i s m i c v e l o c i t i e s from f i e l d experiments or the l a b o r a t o r y v e l o c i t y a n a l y s e s of Con Mine rocks conducted by King (1975), the p o s i t i o n of the quartz v e i n i s e a s i l y found from the p i e z o e l e c t r i c a r r i v a l times o f l i n e s (a) and (b) of F i g . .20. The s i g n a l / n o i s e r a t i o of t h i s system appears many times g r e a t e r than the systems d e s c r i b e d i n the fiussian p u b l i c a t i o n s which have not re p o r t e d p i e z o e l e c t r i c s i g n a l s due t o shear waves.,Electrode spacing does not appear to be a c r i t i c a l parameter and as expected, the more e n e r g e t i c seismic sources produced l a r g e r e l e c t r i c a l responses. The m o b i l i t y of the presen t system i s adequate and i t can be operated with d i f f i c u l t y by one person as i t was a t t e s t s i t e 89 #2, although a two-man op e r a t i n g team would g r e a t l y improve e f f i c i e n c y . The system operated in, the harsh mine environment without s i g n i f i c a n t problems but a d d i t i o n a l environmental packaging w i l l be r e g u i r e d f o r an e x p l o r a t i o n system, 90 4. 3 SECOND EXPLORATION FIELD TRIAL 4,3.1 INSTRUMENTATION To e l i m i n a t e DC t o AC power c o n v e r s i o n n o i s e encountered on t h e p r e v i o u s f i e l d t r i p , t h e d e c i s i o n was made t o use a DC powered a m p l i f i e r , A s u i t a b l e one was not c o m m e r c i a l l y a v a i l a b l e . The d e c i s i o n t o d e s i g n and b u i l d such an a m p l i f i e r p e r m i t t e d t h e i n c o r p o r a t i o n o f s p e c i a l i z e d f i l t e r i n g i n t o a much more compact, rugged system s u i t e d t o the wet, h a r s h , underground environment. As i n the f i r s t f i e l d t e s t , i t was d e c i d e d t o employ a d i f f e r e n t i a l i n s t r u m e n t a t i o n a m p l i f i e r , t h a t i s , one which a m p l i f i e s t h e d i f f e r e n c e between two s i g n a l s and has d i r e c t -c o u p l e d i n p u t s . These a m p l i f i e r s , a l s o known as t r a n s d u c e r a m p l i f i e r s r e l y on l i n e a r feedback p r i n c i p l e s and a r e g e n e r a l l y used i n a p p l i c a t i o n s where e x t r a c t i n g and a m p l i f y i n g low l e v e l d i f f e r e n t i a l s i g n a l s r i d i n g on h i g h common-mode v o l t a g e s i s very i m p o r t a n t (Burr-Brown, 1979). S i n c e the i n p u t s a r e t y p i c a l l y from t r a n s d u c e r s o r g u a r t z o s c i l l a t o r s , t h e s e a m p l i f i e r s are w e l l s u i t e d f o r the f i r s t s t a g e o f t h e e x p l o r a t i o n i n s t r u m e n t a t i o n , The i d e a l c h a r a c t e r i s t i c s o f t h e s e a m p l i f i e r s a re i n f i n i t e i n p u t impedance, z e r o o u t p u t impedance, no DC o f f s e t s o r d r i f t , z e r o a m p l i f i e r n o i s e , a c o n s t a n t g a i n f a c t o r w i t h no g a i n e r r o r ( i m p l y i n g l i n e a r i t y ) , and complete r e j e c t i o n o f s i g n a l s ccmmon t o both i n p u t s (common-mode r e j e c t i o n ) , The o u t p u t v o l t a g e i s developed s i n g l e - e n d e d w i t h r e s p e c t t o ground 91 and i s equal t o the product of the a m p l i f i e r gain and the d i f f e r e n c e of the two i n p u t v o l t a g e s . The a m p l i f i e r system which was o r i g i n a l l y designed and intended f o r use durin g the second f i e l d t r i a l was i r r e p a r a b l y damaged at the mine s i t e due to s t a t i c d i s c harge i n the extremely dry A r c t i c winter environment p r i o r t o commencement of the t e s t s . T h i s n e c e s s i t a t e d use of a s i m p l e r a l t e r n a t i v e a m p l i f i e r which underwent many m o d i f i c a t i o n s i n the f i e l d , r e s u l t i n g i n the system d e s c r i b e d below. The a u x i l i a r y i n s t r u m e n t a t i o n a m p l i f i e r , was a l s o a two stage device i n c o r p o r a t i n g three a m p l i f i e r s ( F i g . 21).. The f i r s t stage u t i l i z e d a PMI OP-10 i n t e g r a t e d c i r c u i t ] c h i p c o n t a i n i n g two independent m o n o l i t h i c high- performance o p e r a t i o n a l a m p l i f i e r s i n a d u a l - i n - l i n e package. Extremely t i g h t matching between channels i s provided on a l l c r i t i c a l parameters i n c l u d i n g o f f s e t v o l t a g e , t r a c k i n g o f o f f s e t v o l t a g e vs.. temperature, non-i n v e r t i n g b i a s c u r r e n t s , a n d common mode power supply r e j e c t i o n r a t i o s . The common mode r e j e c t i o n r a t i o and i n p u t impedance are t y p i c a l l y 123 dB and 160 G i l r e s p e c t i v e l y . . The 3 - a m p l i f i e r design, while more complex than a 2 - a m p l i f i e r i n s t r u m e n t a t i o n amp, has the advantages of convenient o v e r a l l g a i n adjustment by trimming a s i n g l e r e s i s t o r (Eg, F i g . 22) and of wide common-mode volta g e handling c a p a b i l i t y at any o v e r a l l g a i n , p l u s improved ga i n l i n e a r i t y . F or the t h i r d a m p l i f i e r i n c o r p o r a t i n g the second stage o f the ins t r u m e n t a t i o n a m p l i f i e r , a PMI OP-01 was chosen. The OP-01 combines high slew r a t e , f a s t s e t t l i n g time output performance with e x c e l l e n t D.C. i n p u t c h a r a c t e r i s t i c s , A 100 pF c a p a c i t o r was added to each of the OP-10 i n p u t s f o r DC +12 1/ DC OFFSET ADJ~UST "INPUT +INPUT o COMMON 1SOK MODE ADJUST GUARD D7?/V£ OUTPUT TO SHtELDiA/G-10 FIGURE 21 :- TWO STAGE INSTRUMENTATION AMPLIFIER 93 i s o l a t i o n . Diodes were also added to the inputs of the matched f i r s t stage amplifiers to protect against recurrence of s t a t i c discharge damage. A. variable resistance Bj was a further modification so that common-mode-rejection could be tuned maximally. , k further addition which proved e s s e n t i a l i n f i e l d operations was a DC offset control..When operating i n the f i e l d from a "remote" source (not connected to amplifier ground) the s i g n a l source must be returned to power supply common.. If t h i s i s not done, the input bias currents which are the currents that flow i n t o (cr out of) either of the two OP-10 inputs, that i s , the JFET leakage currents f o r the FET input stage, w i l l r e s u l t i n saturation of the amplifier. For the underground operations, i t was thus found necessary to insert the two 10 Mil r e s i s t o r s (Eg). By having one of these resistances variable, source impedance imbalance due to differences i n the two electrodes and t h e i r cables could also be nulled. The degeneration of common-mode r e j e c t i o n caused by the capacitance of the s h i e l d cable can be reduced with an active guard drive (Burr-Brown, 1979). k guard drive employing and buffer amplifier was also added and could be switched i n when desired. The buffer amplifier ensured that l i t t l e current was drawn from the gain r e s i s t o r across the instrumentation amplifier. During the course of the exploration t r i a l s i t was found necessary to add several f i l t e r s to the o r i g i n a l system,. The p r i n c i p a l e l e c t r i c a l noise sources within the mine were 60 Hz, i t s harmonics, and higher freguency pulses from buzzers and communication equipment..The complete schematic of the amplifier together with i t s b u i l t - i n f i l t e r s i s shown i n Fig, 22. The J INPUTS COAXIAL ELECTRODE CABLES GUARD DRIVE ~=r INSTRUMENTATION AMPLIFIER AMPLIFIER HAMMOND"! 148-Q TRANSFORMER T e l e c t r o n i c s F l 6 l 60 Hz P a s s i v e Notch F i l t e r s 60 Hz A c t i v e Tunable Notch F i l t e r A c t i v e H i g h - P a s s F i l t e r 420 Hz A c t i v e Tunable Notch F i l t e r 180 Hz A d j u s t a b l e High-Q Notch F i l t e r BUFFER AMPLIFIER OUTPUT TO SEISMOGRAPH FIGURE 22 :- SCHEMATIC OF COMPLETE AMPLIFIER AND FILTER SYSTEM U 3 95 s i g n a l s frcm the two d i f f e r e n t i a l e l e c t r o d e s were each f e d along the i n n e r conducting core of a c o a x i a l c a b l e . The outer conductor could e i t h e r be grounded or d r i v e n by the guard d r i v e d e s c r i b e d e a r l i e r . As w e l l as having c l o s e l y matched c h a r a c t e r i s t i c s , the two e l e c t r o d e c a b l e s were a l s o braided about one another f o r as much of t h e i r l e n g t h s as p o s s i b l e t o reduce i n d u c t i v e pickup and have as high commons-mode s i g n a l r e j e c t i o n as p o s s i b l e . Since the magnitude of the i n d u s t r i a l n o i s e would r e s u l t i n s a t u r a t i o n of the a m p l i f i e r f o r s i g n i f i c a n t gain s e t t i n g s , i t was e s s e n t i a l t h a t a l a r g e p o r t i o n of the 60 Hz n o i s e be e l i m i n a t e d p r i o r t o a m p l i f i c a t o n . For t h i s purpose a T e l e c t r o n i c s F161 60 Hz p a s s i v e band-reject f i l t e r was i n s t a l l e d at each of the e l e c t r o d e i n p u t s to the a m p l i f i e r . , To allow g r e a t e r f l e x i b i l i t y i n deployment, s o l i d f o i l s h i e l d e d t w i s t e d - p a i r i n s t r u m e n t a t i o n c a b l e was used f o r the t r i g g e r i n g and d e t o n a t i o n c a b l e . . T h i s g r e a t l y reduced e l e c t r o m a g n e t i c d e t o n a t i o n p r e c u r s o r pickup. As shown i n Fig u r e 22, a number of forms of post-a m p l i f i c a t i o n f i l t e r i n g were s e l e c t a b l e , The output from the i n s t r u m e n t a t i o n a m p l i f i e r c o u l d be passed through a u n i t y gain p r o t e c t i v e b u f f e r a m p l i f i e r , a 60 Hz tunable a c t i v e notch f i l t e r or an a c t i v e high pass f i l t e r . When the high pass f i l t e r was o p e r a t i o n a l the p r i n c i p l e r e s i d u a l n o i s e observed was 420 Hz, A 420 Hz tunable a c t i v e notch f i l t e r which c o u l d be used congruently with the a c t i v e high pass f i l t e r was t h e r e f o r e added. The u n f i l t e r e d b u f f e r p r o t e c t e d output and 60 Hz a c t i v e tunable notch f i l t e r i s shown i n f i g u r e 23. , The freguency response of the l a t t e r i s shown i n f i g u r e . 24, The a c t i v e high 96 + 12 V INPUT FROM INSTRUMENTATION AMPLIFIER FREQUENCY ADJUST UNFILTERED BUFFER PROTECTED OUTPUT 60 Hz NOTCH FILTER OUTPUT FIGURE 23 :- 60 HZ ACTIVE TUNABLE NOTCH FILTER AND BUFFERED AMPLIFIER 97 F I G U R E 2 4 : F R E Q U E N C Y R E S P O N S E O F 6 0 H Z A C T I V E T U N R B L E N O T C H F I L T E R c r cr o 1 0 ] 1 0 2 1 0 3 F R E Q U E N C Y ( H Z ) INPUT PROM 2200pF INSTRUMENT- o—1| ATION AMPLIFIER C, 22K -s/VsAAA-330K 2200pF — I r — R, | 68K 2 V R / R 2 C , C HIGH PASS FILTER FREQUENCY ADJUST OUTPUT FROM o HIGH PASS FILTER OUTPUT FROM HIGH PASS AND 420 HZ NOTCH FILTER 420 HZ NOTCH FILTER FIGURE 25 :- ACTIVE HIGH PASS FILTER AND 420 HZ ACTIVE TUNABLE NOTCH FILTER oo 99 F I G U R E 2 6 : F R E Q U E N C Y R E S P O N S E OF 6 0 HZ A C T I V E H I G H P A S S F I L T E R F R E Q U E N C Y - ( H Z ) INPUT FROM FIRST STAGE FILTERS X 10 AMPLIFIER 022 ^ uF .022 pF 12 V OUTPUT o FROM X10 AMPLIFIER OUTPUT FROM XI0 * AMPLIFIER AND 180 HZ NOTCH FILTER ^ Q CONTROL 100 K 180 HZ NOTCH FILTER FIGURE 27:- GAIN OF 10 AMPLIFIER AND 180 HZ ADJUSTABLE HIGH-Q NOTCH FILTER o o 101 F I G . 28:FREQUENCY RESPONSE OF 180 HZ RDJUSTRBLE HIGH-Q NOTCH FILTER 1 0 1 1 0 2 1 0 F R E Q U E N C Y ( H Z ) 102 pass f i l t e r t o g e t h e r with the 420 Hz a c t i v e tunable notch f i l t e r i s shown i n f i g u r e 25. The freguency response of the high pass f i l t e r i s shown i n f i g u r e 26. A f t e r s e l e c t i o n of t h i s f i r s t stage o f f i l t e r i n g the output was fed through an a m p l i f i e r with a gain of 10, Having two stages o f a m p l i f i c a t i o n such as t h i s i s p r e f e r r a b l e t o having the f u l l a m p l i f i c a t i o n on the i n s t r u m e n t a t i o n a m p l i f i e r . A f t e r t h i s secondary a m p l i f i c a t i o n , the s i g n a l could be f e d d i r e c t l y to a Hammond 148-Q tr a n s f o r m e r output o r be f i r s t f e d through a 180 Hz a d j u s t a b l e high Q notch f i l t e r ( F i g . 27). The freguency response of the 180 Hz f i l t e r i s shown i n f i g u r e 28. 4.3.2 SECOND FIELD TBIAL EESOLTS For the f i r s t t e s t s of the r e v i s e d e x p l o r a t i o n system, i t was decided t c r e t u r n to the s i t e of previous sucesses - the quartz vein exposure on the 4500 f o t depth l e v e l near the B3 Wince. The t e s t s were conducted between March 14th and 27th, 1979. In a d d i t i o n t o the n e c e s s i t y o f d e v i s i n g a secondary replacement a m p l i f i e r system i n the f i e l d , a number of other instrument malfunctions o c c u r r e d . The a c i d i c water vapour i n the mine caused a malfunction of the seismograph p r e v e n t i n g r e c o r d i n g d u r i n g p a r t o f the f i e l d t r i a l . As w e l l , the b l a s t e r u n i t a l s o was i n o p e r a t i v e _ f o r p a r t of the experiment. Of g r e a t e r concern was the i n c r e a s e d n o i s e l e v e l encountered at t h i s s i t e i n comparison with the previous t r i a l . 103 The noi s e l e v e l was monitored on the storage o s c i l l o s c o p e and co u l d be seen t o vary i n magnitude and c h a r a c t e r throughout the day. Not only was the nominal 60 Hz n o i s e g r e a t e r than encountered p r e v i o u s l y but the DC c u r r e n t s w i t h i n the rock w a l l were o f t e n l a r g e enough t o s e r i o u s l y l i m i t a m p l i f i c a t i o n . Buzzer p u l s e s from the h o i s t equipment at the nearby B3 Wince were again r e g i s t e r e d c l e a r l y on the e x p l o r a t i o n system. Despite the much improved f i l t e r i n g system, s i g n a l s could only be c o n f i d e n t l y r e c o g n i z e d f o r l i m i t e d shot point - quartz v e i n d i s t a n c e s ( l e s s than 10 m)..Figure 29 shows a p i e z o e l e c t r i c r e c o r d taken under moderate noi s e l e v e l s . One e l e c t r o d e of the d i f f e r e n t i a l p a i r was l o c a t e d w i t h i n the v e i n while the other was 10.5 metres west of the vein. The p i e z o e l e c t r i c s i g n a l was produced by 10 hammer impacts, 6.3 m west of the v e i n , enhanced upon one another.,A s i g n a l was not d i s c e r n i b l e beyond background n o i s e l e v e l i f the e l e c t r o d e s were removed from t h e i r CuS0^.5H 20 f i l l e d h o l e s and suspended i n the a i r . The poor q u a l i t y of the s e i s m i c r e c o r d s from the f i r s t f i e l d t r i p was not only due to d i f f i c u l t i e s from emplacement of the qeophone s p i k e s i n t o the l o o s e rock r u b b l e but a l s o because they measured the v e r t i c a l component of qround motion..As shown i n F i g , 30, most of the compressional energy a t the geophone l o c a t i o n s i s t r a v e l l i n g p a r a l l e l t o the t u n n e l . The p a r t i c l e motion i s h o r i z o n t a l and thus w i l l not be detected by the geophones. . Geophones measuring the h o r i z o n t a l component of ground motion and s e t on l e v e l l e d p l a t f o r m s proved more s u c e s s f u l i n the second f i e l d t r i a l . An array of ten of these geophones o r i e n t e d to measure the component of ground motion t=0" \l . ,. •; ; 10 m s e c — — — — • . — * -1 . i r v - : , . . .-• |i--:--r • • • • f , ,' • ^ ' • • • 1 i . - , . , , , . . — • , . i ' • • , _ _ _ _ _ _ _ — ^ — : 1 ~ . - - ; — i — • j — • • r - ^ - i - j - : — i - p + ~ * — < - - • - - — : . • - -1 : — ' "I" t f l 1-;-!" * l ' , •': ' ' i i .. ! 1 • ' i ' I * j , .; _ | j " — ! — : — ; — 1— U — — . - • . ' [ - - ' - - - — - • = | ; , ^ u . . - . . . . . - - ; - - r - " i - • ) . - ; — ~ [ ' - • • ; , j ; , i > F W f r : r V : ' r ~ - i j L - ^ i i . : . . : - •- • •• r;r! • ! . • ' . ! : i r j - J - t i r t i : . j . : . ; - \ — " j ^ j ^ l — i — \ — i — • — : — | — i ^:~ZZ.IZZZ''Z1Z^J..ZZ.'• ZZZZZ..Z" >L'i •'• ; ! " ~ \ ~ : ' ' • — — - — : — ' • ' . v . . . ——" • - — - j ' ' ; , — - v ,' • ' I i •!•••. -i i—:—. " PIEZOELECTRIC SIGN !. . « . ; '. J BACKGROUND NOISE ' AL ' FIGURE 29 PIEZOELECTRIC SIGNAL PRODUCED BY 10 ENHANCED IMPACTS 6.3 METRES WEST-OF QUARTZ VEIN, ONE ELECTRODE SITUATED WITHIN VEIN AND -•OTHER ELECTRODE LOCATED 10.5 METRES WEST- OF VEIN. o 4-105 GROUND MOTION COMPONENT' MAXIMIZED BY:-1 V e r t i c a l Geophone 2 Horizontal Geophone Oriented P a r a l l e l to Tunnel 3 Horizontal Geophone Oriented Perpendicular to Tunnel Wall FIGURE 30 :- SUBTERRANEAN SEISMIC SURVEY CONSIDERATIONS 106 p a r a l l e l to the t u n n e l were used. The compressional s e i s m i c a r r i v a l times f o r two enhanced hammer blows beyond one end of the array are shown i n F i g . 31. The recorded shear s e i s m i c a r r i v a l s c o u l d be maximized by o r i e n t i n g the geophones p e r p e n d i c u l a r t o the w a l l s of the t u n n e l . The g r e a t e s t amount of s e i s m i c energy was s t i l l c o n t ained i n the shear and E a y l e i g h waves and the shear a r r i v a l times f o r 3 sepa r a t e r e c o r d s are shown i n F i g . 32. The f i e l d measured shear and compressional v e l o c i t i e s Sooo m/sec {3843 f t / s e c ) and i"/25" m/sec {i4,8'4 f t / s e c ) r e s p e c t i v e l y , are i n g e n e r a l agreement with not only the l a b o r a t o r y v e l o c i t y analyses o f Con Mine samples conducted by King (1975, Appendix 2) which averaged 5993 m/sec (19,663 f t / s e c ) and 3331 m/sec (10,927 f t / s e c ) r e s p e c t i v e l y , but a l s o the M p s e u d o " - v e l o c i t i e s of the P and S generated p i e z o e l e c t r i c s i g n a l s (Fig>" 20, l i n e s (a) and (b)). Thus, the h y p o t h e s i s of p i e z o e l e c t r i c s i g n a l s being generated by both P and S sei s m i c waves i s c o n s i s t e n t with the s e i s m i c f i e l d measurements. Since f u r t h e r progress i n improving p i e z o e l e c t r i c s i g n a l r e s o l u t i o n under the e l e c t r i c a l noise l e v e l would l i k e l y have been minimal and t h i s e l e c t r i c a l i n t e r f e r e n c e showed no i n d i c a t i o n o f abatement, i t was decided to abandon the second f i e l d t r i a l a f t e r completion of the s e i s m i c measurements. A R R I V A L T I M E ( M S E C ) o ro 4 ^ co ZOT FIG 32: . 'SHEAR SEISMIC FiRRIVRL TIMES AS R FUNCTION OF SHOT POINT-GEOPHONE DISTRNCE 109 CHAPTER 5:- SUMMARY AND SUGGESTIONS The compression cage and s o l e n o i d " h i t t e r " designed f o r the l a b o r a t o r y measurements was capable of appl y i n g a c o n s i s t e n t and uniform pressure d i s t r i b u t i o n a c r o s s the c u b i c samples and a s t r e s s pulse of h i g h l y r e p e a t a b l e amplitude. and form. The s t r e s s i n g , measuring, and a m p l i f i c a t i o n systems were f r e e of v i b r a t i o n a l and e l e c t r i c a l noise w i t h i n experimental l i m i t a t i o n s . . The method of suspending the compression cage i n a s h i e l d i n g box proved to be an agreeable a l t e r n a t i v e to the use of massive sample h o l d e r s used by o t h e r s . Although the standard sample s i z e used was l a r g e r than those o f Starkey and A l l i s o n (1975), Tuck (1977), or Bishop (1978), l a b o r a t o r y measurements on the massive samples i n d i c a t e d t h a t s t i l l l a r g e r samples were r e q u i r e d t o reduce the e f f e c t s of inhomogeneities. The l i m i t e d number of quartz specimens which e x h i b i t e d good alignment suggest t h a t such guartz v e i n s or samples may d i s p l a y p i e z o e l e c t r i c responses up to 3 times g r e a t e r than t h e i r massive c o u n t e r p a r t s . Samples with g r e a t e r guartz content g e n e r a l l y d i s p l a y e d l a r g e r responses and the l i m i t e d experimental evidence a l s o suggested t h a t s i g n a l amplitude was p r o p o r t i o n a l t o c r y s t a l s i z e . For f u t u r e l a b o r a t o r y experiments a gu a r t z vein e x h i b i t i n g a high degree o f alignment should be sought. I f a s u f f i c i e n t l y l a r g e number of samples with s i g n i f i c a n t volumes (100- 200 cm3) cou l d be cut with the same o r i e n t a t i o n , s i m i l a r i t y between 110 p i e z o e l e c t r i c measurements f o r each p a r t i c u l a r orthogonal d i r e c t i o n would provide a s t a t i s t i c a l b a s i s f o r more d e f i n i t e c o n c l u s i o n s than permitted by the sample s u i t e used here,. During a p e r i o d of reduced e l e c t r i c a l i n t e r f e r e n c e i n the f i r s t f i e l d t r i a l , c l e a r p i e z o e l e c t r i c a r r i v a l s were recorded and a s s o c i a t e d with the impact of compressional and shear s e i s m i c waves with the guartz v e i n . These p i e z o e l e c t r i c a r r i v a l s were l i n e a r l y r e l a t e d to the d i s t a n c e from shot point to the t a r g e t guartz v e i n with " p s e u d o " - v e l o c i t i e s compatible with both seismic records taken during the second f i e l d t e s t s and l a b o r a t o r y v e l o c i t y measurements. Based on the observed d i s t a n c e - t i m e r e l a t i o n s h i p ( F i g . 20) and the known sei s m i c v e l o c i t i e s , the p i e z o e l e c t r i c technique of l o c a t i n g guartz veins i s f e a s i b l e . H o r i z o n t a l geophones ( p r e f e r a b l y cemented t o the rock w a l l by p l a s t e r of p a r i s or other adhesives) should be o r i e n t e d to measure the ground motion p a r a l l e l to the l e n g t h of the tunnel and p e r p e n d i c u l a r t o the tunnel w a l l f o r maximum P and S s e i s m i c wave r e s o l u t i o n r e s p e c t i v e l y . The method of d r i l l i n g i n c l i n e d holes and using copper sulphate e l e c t r o l y t e f o r e l e c t r o d e emplacement worked w e l l and i s recommended f o r f u t u r e i n v e s t i g a t o r s . S u c c e s s f u l r e c o r d s were obtained f o r e l e c t r o d e s e p a r a t i o n s from 2 to 20 m and e l e c t r o d e -t a r g e t d i s t a n c e s of 15 m. The l e n g t h of the e l e c t r o d e of the c a b l e s matched f o r maximum common-mode r e j e c t i o n . I f o p e r a t i n g i n a very noisy environment such as the Con Mine, placement of s m a l l s e l f - c o n t a i n e d a m p l i f i e r s between the a c t u a l e l e c t r o d e s and e l e c t r o d e c a b l e s may reduce the i n d u c t i v e pickup p o r t i o n of 111 the n o i s e . However, the a c t u a l common-mode no i s e r e c e i v e d by the e l e c t r o d e s from the rock w a l l may only be reduced by f i l t e r i n g . L i m i t a t i o n s i n f i l t e r i n g w i l l l i k e l y p r o h i b i t p i e z o e l e c t r i c e x p l o r a t i o n i n mine environments when i n d u s t r i a l noise such as a t the Con Mine i s present. The r e s u l t s of the f i r s t f i e l d t r i a l suggest t h a t i n e l e c t r i c a l l y g u i e t environments or during periods when mining op e r a t i o n s are t e m p o r a r i l y suspended, the p i e z o e l e c t r i c e x p l o r a t i o n technique may be used to s u c e s s f u l l y l o c a t e quartz v e i n s . Although the geometry of the mine provides an i d e a l s e t t i n g f o r development of the p i e z o e l e c t r i c e x p l o r a t i o n technique, u n l e s s noise l e v e l s are f i r s t t e s t e d and found a c c e p t a b l e , i t i s recommended t h a t f u t u r e i n v e s t i g a t o r s conduct t h e i r t r i a l s on e l e c t r i c a l l y g u i e t s u r f a c e vein exposures. Future i n v e s t i g a t o r s should develop c a l i b r a t i o n c o n t r o l s f o r more p r e c i s e measurement of the p i e z o e l e c t r i c v o l t a g e s . T h i s would be h e l p f u l i n a t t e n u a t i o n s t u d i e s t o determine the l i m i t a t i o n s of the t e c h n i g u e . The d i g i t a l sampling r a t e of the seismographs memory should be i n c r e a s e d or tape. r e c o r d i n g used so t h a t the time s c a l e of the i n i t i a l p o r t i o n of the r e c o r d may be expanded. The p i e z o e l e c t r i c response of v e i n s of d i f f e r e n t s i z e , geometry ( t a b u l a r , i s o m e t r i c , etc.) and c r y s t a l c h a r a c t e r may be g u i t e d i f f e r e n t and should be i n v e s t i g a t e d . The use of antennae may one day prove.a v i a b l e r e c e i v e r a l t e r n a t i v e to the e l e c t r o d e arrangement used here. 112 BIBLIOGRAPHY • "The o r i g i n of the gol d - g u a r t z d e p o s i t s , Y e l l o w k n i f e , N.W.T-'s", Econ. Geol. V. . 57. " A c o u s t i c f i e l d s and waves i n s o l i d s " , V o l . 1, John Wiley & Sons, New York. 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H e f t e 10 (Computer-Einstag i n der G e o l o g i e ) , 267-292. 120 APPENDIX 1:-- EXPERIMENTAL RESULTS OF STARKEY AND ALLISON Peak—to-Peak P i e z o e l e c t r i c S i g n a l s (mV) Sample rock Type o r i e n t a t i o n A B C 1 C h l o r i t e S c h i s t 60 60 2 C h l o r i t e S c h i s t — . 20 — -3R C h l o r i t e S c h i s t 30 60 100 3Q Quartz 120 150 750 4 Metagabbro 40 40 5 Quartz 600 200 150 22A Meta-andesite 15 13 20 22C Meta-andesite — - 15 12 22E T h i n Q u a r t z / c a l c i t e 32 36 16 Vein I n S e r i c i t e S c h i s t 22F Quartz V e i n 40 44 160 23B S i l i c e o u s C h l o r i t e S c h i s t 18 40 23C Q u a r t z / c a l c i t e Vein 86 600 230 23E Quartz & Minor C a l c i t e Vein 110 800 200 23F Q u a r t z / c a l c i t e Vein 48 38 130 25A S i l i c e o u s C h l o r i t e S c h i s t 30 35 25B Meta-andesite 14 22 25C Meta-andesite . 25D Meta-andesite - r - — P -25E Quartz C h l o r i t e S c h i s t — . _ — 30 25F Quartz Vein In 280 32 26 S e r i c i t e / c h l o r i t e S c h i s t 25G S i l i c e o u s C h l o r i t e S c h i s t — - 14 25H S i l i c e o u s C h l o r i t e S c h i s t — 251 Meta-andesite - r -I m p l i e s No Response 1=0, 636 DR=0 $4,31, $4,44T $SIGN0FF 121 APPENDIX 2 . •VELOCITY ANALYSES. OF, CON MINE ROCKS . CONDUCTED: BY KING (1975) V e l o c i t i e s , f t / s e c j S a m p l e No. D e s c r i p t i o n C o m p r e s s i o n a l S h e a r | D22A D i a b a s e 2 1 , 0 8 0 - 1 2 , 1 5 0 D22B M e t a g a b b r o 2 1 , 0 0 0 1 2 , 0 7 0 D22C M e t a b a s a l t 1 9 , 4 3 0 1 1 , 8 8 0 D22D C h l o r i t e s c h i s t 1 8 , 4 0 0 1 0 , 5 0 0 D 2 2 E Q t z . - c a r b o n a t e - s e r i c i t e - c h l o r . s c h . 1 8 , 5 0 0 1 0 , 2 2 0 '. D 2 2 F Q u a r t z • 1 9 , 1 4 0 1 1 , 8 5 0 D22G C h l o r i t e s c h i s t 1 8 , 8 8 0 9 , 3 0 0 D 2 3 A C h l o r i t e s c h i s t . 2 0 , 0 1 0 . 9 , 9 2 0 D 2 3 B C h l o r i t e - s e r i c i t e - q t z - c a r b . s c h . 1 8 , 0 3 0 1 0 , 4 3 0 D23D Q u a r t z 1 9 , 0 8 0 1 2 , 0 6 0 D23E Q u a r t z 1 8 , 3 6 0 1 1 , 8 2 0 D 2 3 F C h i o r i t e - q u a r t z - c a r b . s c h i s t 2 0 , 0 0 0 1 0 , 5 6 0 D 2 5 A C h l o r i t e s c h i s t 1 9 , 3 0 0 8 , 0 7 0 D25B M e t a b a s a l t 2 0 , 3 0 0 1 1 , 2 8 0 D25C M e t a g a b b r o 2 2 , 2 1 0 1 2 , 4 3 0 D25D M e t a d i a b a s e ' 2 0 , 6 2 0 1 1 , 6 2 0 D 2 5 E C h l o r i t e s c h i s t 1 9 , 1 5 0 9 , 3 8 0 D 2 5 F S e r i c i t e s c h i s t 1 8 , 7 8 0 9 , 1 5 0 D25G Q u a r t z 1 9 , 1 7 0 1 2 , 4 4 0 D25H S e r i c i t e s c h i s t 1 9 , 5 3 0 9 , 7 1 0 D 2 5 I M e t a b a s a l t 2 1 , 9 1 0 1 2 , 6 3 0
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Geophysics
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Feasibility of the piezoelectric exploration technique for quartz vein detection
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