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UBC Theses and Dissertations

Structural features of coal measures of the Kootenay formation, southeastern Canadian Rocky Mountains Bustin, R. Marc 1980

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STRUCTURAL FEATURES OF COAL MEASURES OF THE KOOTENAY FORMATION, SOUTHEASTERN CANADIAN ROCKY MOUNTAINS A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY IN THE FACULTY OF GRADUATE STUDIES Department of G e o l o g i c a l Sciences We accept t h i s t h e s i s as conforming to the required standards THE UNIVERSITY OF BRITISH COLUMBIA November, 1979 Copyright R.M. B u s t i n BY R.M. BUSTIN In presenting th i s thes is in pa r t i a l fu l f i lment of the requirements for an advanced degree at the Univers i ty of B r i t i s h Columbia, I agree that the L ibrary sha l l make it f ree ly ava i l ab le for reference and study. I fur ther agree that permission for extensive copying of th i s thesis for scholar ly purposes may be granted by the Head of my Department or by his representat ives. It is understood that copying or pub l i ca t ion of this thes is for f inanc ia l gain sha l l not be allowed without my written permission. Department of The Univers i ty of B r i t i s h Columbia 2075 Wesbrook P l a c e Vancouver, Canada V6T 1W5 Date C ~ 2 ^ * ^ i i i F rontispiece: Number 4 p i t . Tent Mountain, Alberta. Coal measures of the Kootenay Formation are folded into a broad but complex syncline. The west limb of the syncline has been faulted out i n part by a west dipping thrust. ABSTRACT Coal measures of the Late Jurassic-Early Cretaceous Kootenay Formation are complexly deformed i n the.southeastern Canadian Rocky Mountains. The s t r u c t u r a l style and associated features of the coal measures are i n part c h a r a c t e r i s t i c of the • F o o t h i l l s Family* of structures. In addition, by virtue of the major contrast i n competency between the coal seams and adjacent stra t a , the s t r u c t u r a l features of the coal measures display considerable variation which, to some extent, can be correlated with the regional and l o c a l s t r u c t u r a l setting., The variation in the s t r u c t u r a l features of the coal measures have a marked influence on the mineability of the coal and both d i r e c t l y and i n d i r e c t l y on coal quality. During deformation the coal seams were the l o c i of i n t e r s t r a t a l s l i p , thrust f a u l t i n g and detachment during f o l d i n g . . The coal seams vary markedly i n thickness; i n some areas coal seams have been thickened as much as an order of magnitude i n response to thrust f a u l t i n g , normal f a u l t i n g and fol d i n g , whereas i n other adjacent areas, the seams may be completely pinched-off or faulted out., Structural thickening of the coal seams has been f a c i l i t a t e d by c a t a c l a s t i c flow of the f i n e l y sheared coal along a myriad of discrete shear surfaces.. The mesoscopic and microscopic f a b r i c of the coal i s c a t a c l a s t i c with the exception of l o c a l areas of apparently high s t r a i n where the v i t r a i n and c l a r a i n components have behaved p l a s t i c a l l y . Shearing of the coal and adjacent strata has resulted i n the introduction and dissemination of formerly discrete rock partings which i n turn have produced abnormally V high ash contents and poor washability c h a r a c t e r i s t i c s and has made the coal more susceptible to oxidation. Measurement of v i t r i n i t e reflectance of coal i n some major shear zones suggests, by comparisipn with samples heated i n the laboratory for short durations, that f r i c t i o n a l heating during shearing may have resulted i n temperatures of up to 450°C. . Adjacent to and within other shear zones there i s no evidence f o r f r i c t i o n a l heating. The presence or absence of f r i c t i o n a l heating may be the result respectively of s t i c k - s l i p and stable s l i d i n g conditions during shear, which i n turn may be a product of variable pore pressures. In underground mines the s t r u c t u r a l features of the roof rock and the coal seams have a pronounced effect on roof s t a b i l i t y . . In the Vicary Creek mine, located i n the hanging wall of the Coleman Fault, the Number 2 seam and some of the roof rock were pervasively sheared as a r e s u l t of i n t e r s t r a t a l s l i p during flexure of the coal measures and possibly as a r e s u l t of drag from overriding thrust f a u l t s . In such areas the coal p i l l a r s have low bearing strength and the cohesion between successive beds in the immediate roof rock has been destroyed, r e s u l t i n g i n poor roof conditions. Slickenside s t r i a e on bedding surfaces, j o i n t s i n the roof s t r a t a and some extension f a u l t s which cut the seam, define a kinematic and dynamic pattern which i s consistent with the regional structure. In the Balmer North, Five Panel and Six Panel mines, located in the northern part of the Fernie synclinorium, the coal measures are only mildly deformed. A cleat system i s present at a l l sample l o c a l i t i e s but no consistent pattern exists which can be related to the o v e r a l l structure or to joi n t s i n the roof and f l o o r . . In the Balmer North mine, young, gently west dipping, shear surfaces are present throughout which, i n conjunction with slickensided bedding surfaces, have promoted roof and coal rib f a i l u r e along north to northwesterly trends. In the Five Panel mine roof and coal r i b f a i l u r e have been f a c i l i t a t e d by steep easterly dipping fractures. The absence of a consistent j o i n t or c l e a t pattern i n the Balmer North, Five Panel or Six Panel mines may be the r e s u l t of mechanical anisotropy of the strata or of multiple episodes of deformation. Striated structures, many of which are conical in form, are common mesoscopic elements on fracture surfaces i n the deformed c o a l . . Such structures, although rarely reported previously i n the l i t e r a t u r e , occur at many l o c a l i t i e s i n the study area. The structures are planar, conical and pyramidal i n form, and are characterized by s t r i a e which radiate from a common apex and 'h o r s e t a i l ' to form subsidiary structures on the master surface. A l l three types of st r i a t e d structures are considered the products of dynamic, b r i t t l e shear fracture.which was possibly f a c i l i t a t e d at f a i l u r e by high i n t e r - and/or i n t r a -p a r t i c l e pore pressure* . v i i TABLE OF CONTENTS PAGE ABSTRACT i v TABLE OF CONTENTS v i i LIST OF FIGURES x i ACKNOWLEDGMENTS x v i i i INTRODUCTION 1 Introductory Statement 1 Geological Setting and General Geology of 2 the Study Area Thesis Format 7 References 10 PART #1. CHARACTERISTICS AND MECHANISMS FOR THE 11 FORMATION OF STRUCTURALLY THICKENED COAL DEPOSITS IN THE SOUTHEASTERN CANADIAN CORDILLERA. . Abstract 12 Introduction " 13 Mechanisms of Structural Thickening 14 Vicary Creek 16 Grassy Mountain 23 Tent Mountain 27 Southern Deposit 28 Northern Deposit 32 .Western Deposit 38 Flow of Coal During Deformation 40 Microfabric of the Coal 45 v i i i E f f e c t of Structural Thickening on Coal Quality 46 and Mining Conclusions 47 Acknowledgments 49 References 50 PART #2. GEOLOGICAL FACTORS AFFECTING ROOF CONDITIONS 53 IN SOME UNDERGROUND COAL MINES IN THE SOUTHEASTERN CANADIAN ROCKY MOUNTAINS Abstract 54 Introduction 57 Vicary Creek Mine 60 Roof Rock Charact e r i s t i c s 60 Lithology and Sedimentology 60 Structural Fabric of the Coal and Roof 63 Rock Kinematic Analysis 66 Dynamics of Deformation 70 Relationship Between Roof Conditions and 72 Geology Balmer North, Six Panel and Five Panel Mines 75 Rocf Rock Characteristics 77 Lithology and Sedimentology 77 Structural Fabric of the Coal and Roof 78 Rock Cleat 80 Kinematic Analysis 82 Dynamics of Deformation 89 ix Relationship Between Geology and Roof 94 Conditions Discussion and Conclusions 97 Acknowledgments 104 References 105 PART #3..EFFECTS OF SHEAR ON COAL QUALITY AND RANK: 108 TEMPERATURES ASSOCIATED WITH SHEAR ZONES AND SOME IMPLICATIONS REGARDING FAULT MECHANICS IN THE SOUTHERN ROCKY MOUNTAINS OF BRITISH COLUMBIA AND ALBERTA Abstract 109 Introduction 111 Experimental Procedure and Analytical 114 Techniques S e n s i t i v i t y of Coal Rank to Heating for Short 116 Durations Mesoscopic and Microscopic Fabric of the 124 Sheared Coal V i t r i n i t e Reflectance of the Sheared Coal 131 Implications of the Anamolous V i t r i n i t e 138 Reflectances E f f e c t of Shearing on Coal Quality 146 Summary and Conclusions 147 Acknowledgments 151 References 152 PART #4. MORPHOLOGY AND ORIGIN OF STRIATED CONICAL 156 STRUCTURES AND RELATED FRACTURES IN BITUMINOUS COAL OF THE SOUTHERN CANADIAN ROCKY MOUNTAINS X Abstract 157 Introduction 158 Occurrence and General Description of the 160 Structures Planar Striated Structures 164 Conical Striated Structures 166 Pyramidal Striated Structures 166 Comparison with Other Structures 170 Origin of the Structures 174 Discussion and Conclusions 180 Acknowledgments 183 References 184 SUMMARY AND CONCLUSIONS 187 x i LIST OF FIGURES FIGURE PAGE 1-1. Index map to the study area showing the major 4 tectonic elements of the Canadian C o r d i l l e r a (modified from Wheeler and Gabrielse, 1972). 1-2. Generalized geological map of part of the 5 southeastern Canadian C o r d i l l e r a , showing location of areas discussed i n the text (modified from Price, 1972).. Abbreviations are the same as those in Figure 1-3 and i n addition: P=Pennsylvanian and Permian, M=Mississippian, D=Devonian, and C=Cambrian. Contours on a l l figures are i n feet.. 1-3. . Summary of Mesozoic-Cenozoic stratigraphy, 6 southeastern Canadian C o r d i l l e r a (modified from (Price, 1972). PABT #1 2-1* Vicary Creek. (A) Geological map of part of the 17 Vicary Creek area. In t h i s and other figures JKk=Kootenay Formation undivided, JKkb=Basal Sandstcne member, and JKkc=Coal Bearing member. (B) Axes of s l i p on slickensided bedding surfaces (•) and extension f a u l t s (•), 'b' i s the b f a b r i c d i r e c t i o n of the seam.. 2-2.. (A) Contraction f a u l t with about 2 m of 20 str a t i g r a p h i c separation i n the roof rock of the Number 2 seam. There i s no o f f set i n the footwall strata in the v i c i n i t y of the outcrop. (£) 'Coal Plow 1 i n hanging wall of the Number 2 seam. Drag f o l d s i n d i c a t i v e of up-dip motion (to the right) of the hanging wall r e l a t i v e to the foot-wall are evident in the coal seam. 2-3. Model showing how extension f a u l t i n g followed by 21 i n t e r s t r a t a l s l i p r e s u l t s i n thinning i n the region of off set and thickening i n advance of the plow. 2-"4. Cross-section of the Grassy Mountain structure 24 showing thickening of the coal and the p r i n c i p a l structures. . Modified from Norris (1971)., 2-5.. (A) Axial region of the major a n t i c l i n a l 25 thickening to the west i n Fig.,2-4., (B) Axial region of the s y n c l i n a l thickening to the east in F i g . 2-4. x i i 2-6. Southern deposit, Tent Mountain. (A) Generalized 29 geological map. , (B) Schematic cross-section through A-B. , (C) Axes of s l i p on slickensided bedding surfaces and contraction f a u l t s (•) ; 'b' i s the b f a h r i c direction of the seam. Legend i s on F i g . 2-12. 2-7. Mosaic of Number 4 seam at present l e v e l of 30 mining. The overlying thrust cuts up-section to the east. In the foofwall of the seam a southeast dipping contraction f a u l t (C) i s v i s i b l e . 2-8. Northern deposit, Tent Mountain. The overlying 33 west dipping thrust has faulted out much of the eastern limb of the syncline. 2-9. Axial region of the syncline in Fig..2-8. The 33 thickened seam i n the hinge at the top of the photo i s Number 7 seam, whereas the underlying seam i s Number 6. 2-10.. Northern deposit, Tent Mountain. (A) Axes of 36 s l i p on contraction f a u l t s (•) , poles to contraction f a u l t s (<*) and s l i p l i n e a r s ( ) . (B) Axes of s l i p on slickensided bedding surfaces (•) -2-11. (A) Idealized r i g h t - s e c t i o n of a f l e x u r a l s l i p 36 (flow) f o l d in which the incompetent bed (shaded) i s thinned on the limbs accompanied by thickening i n the hinge area. The competent bed shows l i t t l e or no variation i n thickness. . Modified from Whitten (1.966) . 2-12. Western deposit. Tent Mountain. (A) Generalized 39 geological map., (B) Schematic, reconstructed cross-section, (C) Axes of s l i p of slickenside s t r i a e on bedding surfaces (•), •B« i s the f o l d axis. 2-13. Boudinage i n interbedded sandstone and coal. The 44 sandstone beds (light toned) are about 0.3 m t h i c k . 2-14. Extension f a u l t with about 4 m of displacement 44 with coal injected into the f a u l t plane. Notice the f o l i a t i o n i n the coal which i s p a r a l l e l to the f a u l t plane. x i i i PART #2 3-1. . Vicary Creek mine. . (A) Structural contour map on 61 the Number 2 seam and p r i n c i p a l s t r u c t u r a l elements in the roof rock. (B) Joint f a b r i c , contours are at 2, 5, 10, 15, and 20% per 1% area. (C) Extension f a u l t f a b r i c , poles (•), axes of s l i p (m) , and s l i p l i n e a r s (-*-), • b' i s the b f a b r i c d i r e c t i o n of the seam. 3-2. Northwest dipping extension f a u l t with about 0.5 64 m of stra t i g r a p h i c separation i n the roof rock i n the.Vicary Creek mine.. Stereo-pair., 3-3. Vicary Creek mine,. Poles (#) , axes of s l i p (•) , 67 and s l i p l i n e a r s (-*-) of slickensided bedding surfaces and trend and plunge of folds (+F) i n the roof rock. 3-4. Poles (o) , axes of s l i p (#) and s l i p l i n e a r s (•*) 67 of slickensided bedding surfaces, and poles (a), axes of s l i p (m) and s l i p l i n e a r s (e-) of extensions f a u l t s and poles (A) to contraction f a u l t s i n the abandoned Race Horse s t r i p mine north of the Vicary Creek mine. 3-5. Poles (•) , axes of s l i p (•) , and s l i p l i n e a r s (—-) 69 of shear surfaces within the Coleman f a u l t plane about 50 m below the portal to the Vicary Creek mine. 3-6. Back-limb reverse f a u l t i n fo l d i n the Number 2 69 seam immediately above the portal at the Vicary Creek mine. Offset across the f a u l t i s about 3 m. 3-7. Thin-bedded carbonaceous roof rock which has 73 parted and caved along slickensided carbonaceous laminae. Roof bolt i n upper most l e f t of the photo for scale.1 3-8. . Thick-bedded, well-jointed and p a r t i a l l y caved 73 roof rock. The cavity i s controlled by joi n t i n g and bedding. . Beds are about 20 cm thick. 3-9. Balmer North, Six Panel and Five Panel mines. uw'SpectoA G\\ Joint and cl e a t f a b r i c ; s t r u c t u r a l contour map (pocket-) on top of the Balmer seam and major s t r u c t u r a l elements. Sterecnet contours are at 2, 5, 10, 15, 20, 25 and 30% per 1% area. . 3-10. Balmer North mine.. Summary diagram of poles (•), 79 axes of s l i p (•) and s l i p l i n e a r s (*)of extension f a u l t s following rotation of bedding to the horizontal. XIV 3-11. Balmer North mine.. Young west dipping shear 79 surface i n coal r i b . . 3-12. Summary of axes of s l i p (•) , s l i p l i n e a r s (-*-) and 83-86 modal poles to cleat sets (•) following rotation of bedding to the horizontal.. Balmer North mine (stations B through L ) , Five Panel mine (station P) and Six Panel mine (stations Q, R, S, U, v, X). 3-13. Balmer North mine. . Summary of axes of s l i p on 87 bedding surfaces and extension f a u l t s (•). 3-14. (A) Baimer North mine. Acute b i s e c t r i c e s (#) of 90 cle a t sets which show some evidence of forming as a re s u l t of shear fracture. (B) Five and Six Panel mines. Acute b i s e c t r i c e s of cl e a t sets which show evidence of forming as a resu l t of shear fracture. 3-15. . Balmer North mine. . Summary of poles to fractures 95 (*) which have f a c i l i t a t e d roof f a i l u r e and control the geometry of caves i n the roof rock and coal p i l l a r s . Pole to bedding (a). 3-16. Balmer North mine.. (A) P a r t i a l l y caved roadway; 96 low angle westerly dipping shear surfaces i n conjunction with steep easterly dipping shear surfaces and slickensided bedding planes have promoted caving and controlled the geometry of the cave. (B) Caved roof rock showing west and east dipping shear surfaces along which the roof rock has separated. 3-17. Balmer North mine. . (A) P a r t i a l l y caved entry; 98 slickensided bedding surfaces have promoted separation of the roof rock along bedding planes. Packsack in the roadway for scale. (B) Unsupporting roof bolt in caved entry. . The steeply dipping shear surfaces have f a c i l i t a t e d f a i l u r e of the roof rock. Conventional roof bo l t s p r o v i d e . l i t t l e support with such steeply dipping fracture surfaces. PART #3 4-1. Maximum v i t r i n i t e reflectance values for coal 117 samples heated in the laboratory for 10 minutes at the indicated temperatures. The d i s t r i b u t i o n , mean and standard deviation of measured values for each sample are shown. X V 4-2. Maximum v i t r i n i t e reflectance values for coal 118 samples heated i n the.laboratory for 1 hour at the indicated temperatures. . The d i s t r i b u t i o n , mean and standard deviation of measured values for each sample are shown. 4-3. Maximum v i t r i n i t e reflectance values for coal 119 samples heated in the laboratory for 4 hours at 1 the indicated temperatures. The d i s t r i b u t i o n , mean and standard deviation of measured values for each sample are shown. 4-4. Maximum v i t r i n i t e reflectance values for coal 120 samples heated i n the laboratory for 7 hours at the indicated temperatures. The d i s t r i b u t i o n , mean and standard deviation of measured values for each sample are shown. 4-<-5. . Summary diagram showing the variation in mean 122 maximum reflectance and standard deviation f o r samples heated at the indicated temperatures and durations. 4-6. Mean maximum v i t r i n i t e reflectances of dispersed 123 organic material and coal from bore holes and from laboratory heated samples (modified from compilations of Bostick, 1973), compared with samples heated in the laboratory i n t h i s study for 10 minutes and 7 hours at the indicated temperatures. , 0=central eastern Oklahoma, Pennsylvanian, 900 m to 3700 m; W= LaSalle County, southwestern Texas, Jurassic, 4000-m to 6100 m; E=Angelina County, eastern Texas, Early Cretaceous, 1200 m to .3400 m; S=Salton geothermal f i e l d , C a l i f o r n i a , Late Pliocene and Pleistocene, 210 m to 2500 m; L=Cameron Parish, Louisiana, Early Miocene, 2500 m to 4600 m; M=Munsterland No. 1 well, northwestern Germany, Carboniferous, 1600 m to 4520 m; V=Volga region, 0SSE, Middle Devonian to Middle Carboniferous, 108 m to 4060 m; 0R=Dpper Rhine graben, Germany, Tertiary and Quaternary; T=Terrebonne Parish, F l o r i d a , Middle Miocene, 5440 m; H=bomb samples, 1.36x10s kPa for 30 to 45 minutes. 4-7. Standard deviation of mean maximum reflectance of 125 laboratory heated samples. 4-8. Mean maximum minus mean minimum reflectance (as 125 measured) of samples heated i n the laboratory. Legend i s the same as that in Fig. 4-7. xvi 4-9. (A) Finely comminuted coal seam i n a shear zone. 126 Notice the more f i n e l y comminuted coal at the base, top, and center of the seam. Pencil f o r scale. (8) Pervasively sheared and polished c o a l . The coarser, folded c l a s t s are more competent, d u l l durain r i c h coal. 4-10. (A) Pervasively sheared and polished c o a l . The 127 thi c k , unsheared and rotated beds are d u l l , durain r i c h c o a l . (B) Pervasively sheared coal with large sandstone i n c l u s i o n . The i n c l u s i o n has apparently been introduced into the seam as a r e s u l t of shearing of the roof rock during i n t e r s t r a t a l s l i p . 4-11,.. Thrust contact between dark brown-gray shales and 129 s i l t s t o n e s of the Fernie Formation (above hammer head) and pervasively sheared and granulated coal of the Kootenay Formation. Stratigraphic separation across the f a u l t i s about 600 m. 4-12. Foliated coal which has been injected into a 129 normal f a u l t plane. The coal 'dike' i s oriented almost perpendicular to bedding., The f o l i a t i o n i s l i k e l y the r e s u l t of rotation of the larger c l a s t s during s l i p . 4-13. S.E.M. photomicrograph of an aggregate of 130 v i t r i t e , c l a r i t e and f u s i t e from a shear zone, x 400. . 4-14. , S.E.M. photomicrograph of a wild f o l d developed 130 in c l a r i t e . , x 40. 4-15. Summary table of mean maximum reflectances and 132-135 standard deviations of sheared coal from f a u l t planes and folds and unsheared coal (where available) from adjacent l o c a l i t i e s . 4-16. Coleman f a u l t plane at Wintering Creek.. At t h i s 137 l o c a l i t y a seam of medium v o l a t i l e bituminous coal occurs i n and has been dragged up the folded f a u l t plane. In addition a s l i c e of Crowsnest Volcanics Formation (Kcr) intervenes between the hanging wall strata of the Kootenay Formation (JKk) and footwall s t r a t a of the Belly River Formation. 4-17,. Relationship between s l i d i n g v e l o c i t y , e f f e c t i v e 143 stress and temperature calculated using Bowden and Tabors (1950) expression and assuming dry s l i d i n g conditions and parameters outlined i n the text. x v i i PART #4 5-1. Conical to oblate s t r i a t e d structure from Tent 161 Mountain. Note the downward p r o j e c t i o n of the cone apices. . 5-2. . Conical to oblate structures showing the d e t a i l 161 of the surfaces. Notice t-he radiating ridges and 'ho r s e t a i l s ' on the structure to the lower r i g h t of the scale. Arrow points to the apex of one such structure. 5-3.. S.E.M. photomicrograph showing the d e t a i l of 163 planar s t r i a t e d structures . x 400. 5-4.. Planar s t r i a t e d structures on cleat surface from 163 the Balmer North coal mine. 5-5,. . Axial orientation of planar s t r i a t e d structures 165 from the Balmer North mine. Lower hemisphere Schmidt net.. Contours are at 2, 5, and 10% per 1% area, 'b' i s the b f a b r i c d i r e c t i o n of the seam and the ac i s the deformational plane. 5-6..S.E.M. photcmicrcgraph of s t r i a t e d semi-conical 167 structures . Stereo-pair, x 20. 5-7. S.E.M. photomicrographs.. (A) Semi-conical 168 st r i a t e d structures.. x 20. (B) Close up of A. x 40. 5-8. . Summary of a x i a l orientation of conical 169 structures at Tent Mountain l o c a l i t y . Lower hemisphere Schmidt net.. 'B' i s the regional fold axis and ac i s the deformation plane of the f o l d . , 5-9. Pyramidal s t r i a t e d structures (A) Interlocking 171 pyramids in a coal lens within a fine-grained sandstone. The slickensided surface . (S) i s terminated at the coal lens. (B) Close up of A. Near v e r t i c a l view of pyramids showing t h e i r r e c t i l i n e a r o u t l i ne. 5-10. Planar s t r i a t e d structures i n coal a r t i f i c i a l l y 175 fractured by high velocity impact. x v i i i ACKNOWLEDGMENTS I am grateful to many people for t h e i r assistance throughout the course of t h i s t h e s i s . Foremost I wish to thank my supervisory committee, Drs. .W.H. Mathews, W.C. Barnes, J.W. Murray and G.E. Rouse for t h e i r encouragement, patience and for t h e i r comments on e a r l i e r drafts of the thesis.. I am indebted to Dr. D.K.. Norris of the Geological Survey of Canada for stimulating discussions i n the f i e l d . The study has also benefited from discussions with Drs. M. Barnes, S.,Mindess and CA. .Brockley of the University of B r i t i s h Columbia. This study would not have been possible.without the co-operation of Coleman C o l l i e r i e s , Kaiser Resources Ltd. and Byron Creek C o l l i e r i e s . These companies provided maps, a n a l y t i c a l data and assistance whenever required. Dr. ,D. Pearson of the B r i t i s h Columbia Department of Mines and Petroleum Resources made available a microscope and polishing equipment for coal analysis f o r which I am most g r a t e f u l . The technical s t a f f at the Department of Geological Sciences were most h e l p f u l . F i n a n c i a l support was received from the Geological Survey of Canada and from Natural Sciences and Engineering Research Council (Canada) Grant A -1107 to Dr. W.H. Mathews. . Most importantly I thank my wife Carol, my daughter Kara and our families for t h e i r moral support, patience.and encouragement throughout the course of my studies. 1 INTRODUCTION Introductory Statement Struc t u r a l l y complex coal deposits i n the eastern Canadian C o r d i l l e r a represent a major proportion of Canada's coal resources. Exploration and exploitation of such coal deposits has, however, been seriously hampered by seemingly unpredictable variation i n coal seam thickness, coal quality and roof and f l o o r rock c h a r a c t e r i s t i c s . , Many of the unforeseen d i f f i c u l t i e s which have been encountered can be attributed to the lack of understanding of the o r i g i n , d i s t r i b u t i o n and s i g n i f i c a n c e or structural features of the coal measures._ Much of our present knowledge of the s t r u c t u r a l c h a r a c t e r i s t i c s of coal measures has been based on research and mining experience with f l a t , undisturbed or only mildly deformed coal deposits. .. As coal reserves i n readily accessible areas diminish, however, there i s becoming an increasing incentive to expand coal mining operations to more s t r u c t u r a l l y complex areas and to greater depths. Mining i n such areas, as pointed out by Norris (1958) over twenty years ago, w i l l require a more intimate knowledge of both the l o c a l and regional geological structure. With the notable exception of the e a r l i e r studies by Norris (1958, 1964, 1966) in the Canadian C o r d i l l e r a , there have been few studies of the s t r u c t u r a l features of complexly deformed coal measures and t h e i r conseguences on mining operations. In the southeastern Canadian Rocky Mountains exceptional exposures of the Late Jurassic-Early Cretaceous Kootenay Formation i n and around mine s i t e s provided an excellent 2 opportunity to observe and document the str u c t u r a l features of the coal measures i n a variety of s t r u c t u r a l settings. The objectives.of t h i s thesis are to describe and interpret the structural features of the coal measures, the behavior of coal during deformation, and to assess those s t r u c t u r a l features which a f f e c t the mineability and quality of coal. The observations of t h i s thesis have bearing on a number of in t e r r e l a t e d problems i n s t r u c t u r a l l y deformed coal measures.„ These are: 1) What are the mechanisms leading to the formation of s t r u c t u r a l l y thickened coal deposits and what are their c h a r a c t e r i s t i c s ? 2) What 'flow' mechanisms are involved i n deformation of the coal? 3) What i n t e r r e l a t i o n s h i p s exist between l o c a l s t r u c t u r a l s t y l e of the coal measures and the regional structure? U) What geological factors have a bearing on roof conditions i n underground mines and what i s the in t e r r e l a t i o n s h i p between the kinematics and dynamics of deformation of the coal measures and the roof conditions of mines i n di f f e r e n t geological settings? 5) What i s the e f f e c t of shearing and resulting comminution of the coal on coal quality and rank? 6) Does f r i c t i o n a l heating occur along major or minor thrust f a u l t s i n the Eocky Mountains and to what extent? and 7) What i s the morphology, genesis and sign i f i c a n c e of s t r i a t e d conical structures and related fractures which occur i n s t r u c t u r a l l y deformed coal seams. Geological Setting and General Geology of the :Study Area The study area l i e s i n the southeastern Canadian Eocky Mountains of Alberta and B r i t i s h Columbia, i n the v i c i n i t y of 3 the Crowsnest Pass (Fig. 1-1)., Within the study area the: Kootenay-Formation ranges i n thickness from 90 m i n the east, south of Blairmore Alberta, to more than 1100 m i n the west, in the Fernie.synclinorium (Fig. 1-2; Gibson, 1977).. The Kootenay Formation conformably overlies interbedded sandstones, shales and s i l t s t o n e s of the Passage Beds of the Fernie Formation and i s unconformably overlain by conglomerates and sandstones of the Blairmore Group (Fig, 1-3). I t i s composed of interbedded dark-grey to black shales, s i l t s t o n e s and raudstones and up to 11 seams of mineable thickness of low- to medium-volatile bituminous coal. l o c a l l y , north of the study area, semi-anthracite c c a l i s present. Jansa (1972) and Gibson (1977) have interpreted the Kootenay Formation as d e l t a i c , i n t e r d e l t a i c and a l l u v i a l sediments deposited as part of a c l a s t i c wedge which prograded to the east and northeast into a Late Jurassic epicontinental sea. The stra t i g r a p h i c nomenclature applied to the Kootenay Formation has recently been summarized and revised by Gibson (1977) who has adopted a three-fold d i v i s i o n consisting of a Basal Sandstone member, a middle Coal Bearing member and an upper Elk member. Gibson's nomenclature i s followed throughout t h i s study. The s t r u c t u r a l setting of the study area i s characterized by the ' F o o t h i l l s Family' of structures, which consists of concentric f o l d s , decollements, low angle thrust f a u l t s and tear f a u l t s of l a t e s t Cretaceous and early T e r t i a r y age and l a t e r normal f a u l t s (Dahlstrcm, 1969, 1970)., The thrust f a u l t s and associated splays are p a r a l l e l to sub-parallel to one another and impart a d i s t i n c t i v e northwest s t r u c t u r a l grain to the 4 Figure 1-1. Index map to the study area showing the major tectonic elements of the Canadian C o r d i l l e r a (modified from Wheeler and Gabrielse, 1972) . Figure 1-2. Generalized geological map of part of the southeastern Canadian C o r d i l l e r a showing the l o c a t i o n of areas discussed i n the text (modified from P r i c e , 1972). Abbreviations are the same as those i n Figure 1-3 and i n ad d i t i o n : P=Pennsylvanian and Permian, M=Mississippian, D=Devonian and C=Cambrian. Contours on a l l figures are i n feet. 6 Cortfititf on or, 6 Louftntidc Drift TTTT .J.J.J.J. | Porcupine MilU "Tph' N I Sf. Mary Ri»*r 'Km' Beorpow *Kbp" Belly River -Kbr' WoptotH 'Ko« Cordivm Koc" Blochitone 'Kob I N ! ! Crowjnejt 'Kcr' Beaver Mints Glodston* _ J Codomin Tf 11 j . ^ , Kootenojr 'jKk' Sulphur Mtn. Pleistocene t c o 8 Poeocene ! Ten Motj'richtion' Sontonian Coiocton Turonion S o C ef^OTVooion u a 0 Alt* Ofi Option NtocorrwOn Upper Middle S Lower Upper Miodie osiic Figure 1-3. Summary of Mesozoic-Cenozoic stratigraphy, southeastern Canadian C o r d i l l e r a (modified from P r i c e , 1972) . 7 southern Canadian Eocky Mountains (Fig. .1-2). Theifolds are concordant with the thrusts and have v e r t i c a l to west-dipping a x i a l surfaces (Price, 1962). Tear f a u l t s l o c a l l y occur i n sets transverse tc the structural grain and usually have large displacements. Total shortening from folding and f a u l t i n g does not vary appreciably along s t r i k e , but rather the displacement i s apparently transferred to adjacent structures such that the cumulative displacement across the whole f a u l t system changes gradually as compared to displacement along i n d i v i d u a l f a u l t s (Price, 1962; Dahlstrom, 1969).. The coal measures of the Kootenay Formation and the underlying incompetent shales of the Fernie Formation have played a fundamental role in determining the s t r u c t u r a l character of the study area (Price, 1962; Norris, 1966; Dahlstom, 1969). Coal seams of the Kootenay Formation were the l o c i of i n t e r s t r a t a l s l i p , thrust f a u l t i n g and detachment during concentric folding and decollement formation. The s t r u c t u r a l style of the coal measures i s thus i n part incongruent with that of the regional structure. Thesis Format The.format of t h i s thesis i s a series of papers, Parts 1 through 4, each of which addresses a particular aspect or aspects of the study as a whole. Each part, although a separate entity, shares a common study area and the common theme of the thesi s as outlined i n the 'Introductory Statement'. In order to avoid r e p e t i t i o n the 'Geological Setting and General Geology of the Study Area' and associated figures appear only once, i n the intr c d u c t i c n to the thesis. 8 In Part 1 , the c h a r a c t e r i s t i c s of, and mechanisms leading to the formation of, s t r u c t u r a l l y thickened coal deposits are described.. The rapid variation in coal seam thickness i n the southern Canadian Eocky Mountains has seriously hampered mining in some areas, whereas i n ether areas, s t r u c t u r a l thickening has f a c i l i t a t e d mining of otherwise uneconomic deposits. In thi s paper examples cf st r u c t u r a l l y thickened and thinned coal seams are described from three d i f f e r e n t areas; Grassy Mountain, north of Blairmore, Alberta; Vicary Creek, north of Coleman, Alberta; and at Tent Mountain, north of Corbin, B r i t i s h Columbia. Part 2 considers those geological factors affecting roof conditions i n some underground mines i n the study area. This study examines the o r i g i n and si g n i f i c a n c e of str u c t u r a l features i n coal and roof strata i n two areas of contrasting structural s t y l e : 1) the Vicary Creek mine, located north of Coleman, Alberta, i n the immediate hanging wall of a major thrust, the Coleman Fault; and 2) the Balmer North, Five Panel and Six Panel mines, located near Michel, B r i t i s h Columbia, near the northern end of the Fernie synclinorium., In the.Vicary Creek mine, the coal and roof rock are sheared pervasivel, whereas i n the Balmer North, Six Panel and Five Panel mines the coal measures are only mildly disturbed. Part 3 considers the effects of shear and associated comminution of the coa l cn coal quality and rank and discusses possible temperatures associated with shearing and their implications with regards to f a u l t mechanics. Extensively sheared coal comprises a large proportion of the coal reserves in the study area. In t h i s study the mesoscopic and microscopic 9 f a b r i c s of the sheared coal are described and defined and the effect of shearing on coal quality i s discussed. . In addition, t h i s paper addresses the problem of whether or not f r i c t i o n a l heating occurs alcng major f a u l t s . , Part 4 describes the morphology, o r i g i n and significance of s t r i a t e d conical structures and related fractures which occur i n s t r u c t u r a l l y deformed coal seams. Such structures have only rarely been reported previously i n the l i t e r a t u r e and the i r occurance apparently i s r e s t r i c t e d to coal. In s t r u c t u r a l l y deformed coal seams of the Kootenay Formation, these structures are apparently more abundant and morphologically more diverse than previously described. 10 BEFEBENCES Dahlstrom, CD.A., 1969, The upper detachment i n concentric f o l d i n g : B u l l e t i n of Canadian Petroleum Geology, vol . 17, pp. 326-346,. Dahlstrom, CD.A., 1970, Structural geology in the eastern margin of the Canadian Eocky Mountains: B u l l e t i n of Canadian Petroleum Geology, vol. 18, pp. .332-406. Gibson, D.W., 1977, Sedimentary f a c i e s i n the Jura-Creataceous Kootenay Formation, Crowsnest Pass area, soutwestern Alberta and southeastern B r i t i s h Columbia: B u l l e t i n of Canadian Petroleum Geology, vol. 25, pp. 767-791. Jansa, L. , 1972, Depositional history of the coal bearing Upper Jurassic-Lower Cretaceous Kootenay Formation, southern Eocky Mountains, Canada: Geological Society of America B u l l e t i n , vol. 83, pp. 3199-3222. i Norris, D.K., 1958, Structural conditions i n Canadian coal mines: Geological Survey of Canada, B u l l e t i n no. .44, 54 FP-Norris, D.K., 1964, Microtectonics of the Kootenay Formation near Fernie, B r i t i s h Columbia: B u l l e t i n Canadian Petroleum Geology, vol. 12, pp. 383-398.. Norris, D.K., 1966, The mesoscopic f a b r i c of rock masses about some Canadian coal mines: Proceedings of F i r s t Congress, Internation Society cf Bock Mechanics, Lisbon, Portugal, vol. 1, pp. . 191-198. Price, E.A., 1962, Geological structure of the ce n t r a l part of the Eocky Mountains i n the v i c i n i t y of Crowsnest Pass: Journal Alberta Society of Petroleum Geologists, v o l . 10, pp. .341-351. Price, R.A., 1972, The Canadian Eockies and tectonic evolution of the southeastern Canadian C o r d i l l e r a : i n International Geological Congress Guidebook AC-15, pp. 102-112. Wheeler, J,0. and Gabrielse, H., 1972, The Canadian C o r d i l l e r a : i n Price, E.A. and Douglas, E.J.A. eds., Variation i n tectonic styles i n Canada: Geological Association of Canada Special Paper no. 11, pp. 1-82. PART 1 CHARACTERISTICS AND MECHANISMS FOR THE FORMATION OF STRUCTURALLY THICKENED COAL DEPOSITS IN THE SOUTHEASTERN CANADIAN CORDILLERA 12 ABSTRACT Structural thickening of coal seams of the Late J u r a s s i c -Early Cretaceous Kootenay Formation i n the southeastern Canadian C o r d i l l e r a enables open p i t mining of otherwise marginally economic deposits. In some areas coal seams are s t r u c t u r a l l y thickened by as much as an order of magnitude i n response to thrust f a u l t i n g , normal f a u l t i n g and folding. Structural thickening of the coal seams has been f a c i l i t a t e d by c a t a c l a s t i c flow along a myriad of discrete shear surfaces. In s i t e s of high st r a i n the v i t r a i n and cla r a i n components of the coal show minor p l a s t i c flow.. The fusain- and durain-rich coal behaved as a b r i t t l e material throughout deformation. Along seme major shear zones the rank of the coal, as measured by v i t r i n i t e reflectance, has been increased l o c a l l y by f r i c t i o n a l heating. Other seemingly major f a u l t s evidently had no e f f e c t on coal rank. Shearing of the coal and adjacent strata has l o c a l l y resulted i n the introduction and dissemination of formally discrete rock partings and has markedly increased the ash content of the coal and i t s s u s c e p t i b i l i t y to oxidation. Predicting the d i s t r i b u t i o n of s t r u c t u r a l l y thickened coal requires a closely spaced d r i l l i n g program, a weir planned trenching program and an understanding of the str u c t u r a l s t y l e of the coal measures. 13 INTRODUCTION In the southern Eocky Mountains of alberta and B r i t i s h Columbia s t r u c t u r a l l y thickened coal seams of the Late Jurassic-Early Cretaceous Kootenay Formation occur i n a variety of settings. Structural thickening and associated thinning of coal seams has occurred through a variety of mechanisms and has imparted d i s t i n c t i v e c h a r a c t e r i s t i c s to the coal deposits. In several areas s t r u c t u r a l l y thickened coal deposits have f a c i l i t a t e d open p i t mining cf otherwise marginally economic or uneconomic coal seams. . Because of the complex structures associated with these deposits an understanding of t h e i r c h a r a c t e r i s t i c s and mechanism of formation i s important i n both exploration and evaluation. In the southern Eocky Mountains of Alberta and B r i t i s h Columbia open-pit mines and, to a lesser extent, underground mines provide an exceptional opportunity to study the mechanisms of formation of s t r u c t u r a l l y thickened deposits i n a variety of s t r u c t u r a l settings. In t h i s study deposits at three l o c a l i t i e s are discussed (Fig. 1-2): (1) Vicary Creek north of Coleman, Alberta, i n the hanging wall of the Coleman Fault; (2) Grassy Mountain, north of Blairmore, Alberta, in the footwall of the Turtle Mountain Fault; and (3) Tent Mountain on the B r i t i s h Columbia-Alberta border north of Corbin, B r i t i s h Columbia, on the Lewis Thrust plate. The only previously published accounts of the s t r u c t u r a l l y thickened coal deposits i n the southern Canadian Eocky Mountains are the studies of Norris (1955, 1956, 1958, 14 1959, 1964, 1S66 and 1971) and Johnson (1977). From regional mapping and detailed studies of mine s i t e s Norris documented many of the s t r u c t u r a l attributes of the coal and coal measures and was able to correlate many of the observed features with the regional structure. Subsequent mining operations i n the southern Rocky Mountains have exposed additional features which re-confirm many of Norris' e a r l i e r findings and reveal additional structures not previously apparent. Studies in other coal f i e l d s , including the excellent early compilations by Sax (1946) and Deenen (1942) i n the South Limburg coal basin, the studies of Darton (1940) i n the Northern Anthracite coal basin of Pennsylvania, and the studies by Teichmuller and Teichmuller (1954) and others i n the Ruhr Basin have also done much to further our understanding of the deformation of coal measures. MECHANISMS OF STRUCTURAL THICKENING Excellent exposures of s t r u c t u r a l l y thickened coal seams of the Kootenay Formation occur at several l o c a l i t i e s i n the study area. The scale of the thickened deposits ranges from that of a hand specimen to 130 m and even thicker deposits have been reported frem the subsurface by Johnson (1977). . In the following discussion examples of s t r u c t u r a l l y thickened deposits are described from a variety of s t r u c t u r a l settings to demonstrate some of the d i f f e r e n t mechanisms leading to the formation of s t r u c t u r a l l y thickened coal deposits and to i l l u s t r a t e the behavior of coal during deformation. In a l a t e r section of the paper the general concept of 'flow' of coal during deformation i s discussed and the microfabric and q u a l i t y 15 of the coal axe described. In order to establish the kinematic picture.leading to the formation of the s t r u c t u r a l l y thickened deposits, slickenside s t r i a e ( s l i p linears) were measured on bedding surfaces and f a u l t planes. Although the coal i s commonly extensively polished, s l i p l i n e a r s are r a r e l y present and those which are display a random f a b r i c as a r e s u l t of successive stages of deformation and rotation of the coal and were thus found of l i t t l e use for kinematic analysis. In t h i s study the slickenside s t r i a e are represented i n stereographic projection as the pole tc the plane which i s perpendicular to the shear surface and includes the slickenside s t r i a e on the shear surface. The poles so plotted represent the kinematic-b axis during s l i p (Hoeppener, 1955).. Some slickenside s t r i a e are also represented by the portion of the plane which i s perpendicular to the shear surface and includes the slickenside s t r i a e and an arrow denotes the direction of r e l a t i v e displacement of the hanging wall. The l o c a l f a b r i c axes of the coal seam are defined such that a and b are i n the plane of the interface between the coal and roof rock and the b axis p a r a l l e l s the s t r i k e of the seam; c . i s perpendicular to a and b. The terminology used here with respect to small scale f a u l t s which have been rotated follows Norris (1958), who refers to contraction f a u l t s as those f a u l t s along which displacement has resulted in shortening i n the plane of layering, and extension f a u l t s which r e s u l t i n elongation i n the plane of layering. 16 Vicary Creek At Vicary Creek the Kootenay Formation occurs in the immediate hanging wall of the Coleman Fault, a west dipping thrust f a u l t with a s t r a t i g r a p h i c separation of about 2200 m (Fig. 2-1). A seam of medium-volatile bituminous coal, l o c a l l y referred to as the Number 2 Seam, occurs about 100 m s t r a t i g r a p h i c a l l y above the f a u l t and has been extensively mined at Vicary Creek and adjoining areas. The seam s t r i k e s 175 degrees, p a r a l l e l to the trace of the Coleman Fault and dips between 35 and 45 degrees to the west. I t i s nearly planar but pinches and swells, ranging in thickness from 0.5 m to 10 m, with an average st r a t i g r a p h i c thickness of about 5 m. Although some of the variation i n thickness of the seam may be depositional, the associated structures and character of the coal indicate that i t i s primarily s t r u c t u r a l . . The p r i n c i p a l s t r u c t u r a l features associated with the seam are slickenside s t r i a e on the hanging wall and footwall s t r a t a , contraction and extension f a u l t s which o f f s e t the seam, and small folds and flexures within the hanging wall. Contraction f a u l t s l i e in h01 l, r i s e out of surfaces of i n t e r s t r a t a l s l i p along the hanging wall or within the seam, cut up section at angles of 10 to 35 degrees and pass into other surfaces of i n t e r s t r a t a l s l i p . The extension f a u l t s l i e i n hkl, * The symbols hkl, OkO, hOl, and hkO refer to the orientation of the defined f a b r i c axes where hkl are respectively the a, b, and c f a b r i c axis; '0' indicates parallelism with a f a b r i c axis.. ' F i g u r e 2 - 1 . V i c a r y C r e e k . (A) G e o l o g i c a l map o f p a r t o f t h e V i c a r y C r e e k a r e a . I n t h i s and o t h e r f i g u r e s : JKk=Kootenay F o r m a t i o n u n d i v i d e d , JKkb=Basal S a n d s t o n e member, and J K k c = C o a l B e a r i n g member. (B) Axes o f s l i p on s l i c k e n s i d e d b e d d i n g s u r f a c e s (©) and e x t e n s i o n f a u l t s ( v ) , ' b ' i s the b f a b r i c d i r e c t i o n o f the seam. 18 have displacements between several centimetres and two metres and cut bedding at preferred angles of 40 to 60 degrees. Number 2 Seam i s highly fractured and l o c a l l y pervasively sheared and polished. Systematic c l e a t , i f i t was ever present, has been destroyed by subsequent deformation. , Along major shear planes the coal i s f i n e l y granulated. At some locations drag f o l d s i n d i c a t i v e of up-dip motion of the hanging wall are present in the coal seam. The axis of rotation of slickenside s t r i a e on bedding surfaces and contraction f a u l t s (Fig. 2-1B) defines a mean kinematic-b axis during s l i p which i s nearly horizontal and close to p a r a l l e l to the Jb f a b r i c d i r e c t i o n of the seam. The dir e c t i o n of motion during s l i p i nferred from the slickenside s t r i a e , dip of contraction f a u l t s and drag folds i n the coal seam implies movement of successively high strata towards the east. The axis of rotation of slickenside s t r i a e of the extension f a u l t s does not define a preferred axis of s l i p . , In outcrop, as well as i n underground workings south of the study area (Norris, 1 958), extension f a u l t s cutting the hanging wall strata are commonly o f f s e t i n an up-dip direction, which indicates that seme extension f a u l t s pre-date i n t e r s t r a t a l s l i p . A l a t e stage cf normal fa u l t i n g i s recognized on a regional scale but i s not considered here. The mechanisms leading to st r u c t u r a l thickening and thinning of the Number 2 Seam are clos e l y related to the o v e r a l l kinematic pattern of the coal measures. Contraction f a u l t s , which arise cut cf surfaces of i n t e r s t r a t a l s l i p within the coal seam, r e s u l t in l o c a l duplication and thickening of the seam up 19 to several metres. Because such f a u l t s arise out of surfaces of i n t e r s t r a t a l s l i p , thinning of the seam which must accompany thickening need not be, and rarely i s , localized adjacent the region of thickening (Fig. 2-2A). In several areas, the seam shows marked pinching and swelling which i s not r e f l e c t e d i n f a u l t i n g . In these areas i n t e r s t r a t a l s l i p surfaces, contraction f a u l t s and drag folds within the seam attest to d i f f e r e n t i a l transport of coal up-dip, thinning some areas of the seam and thickening others. Such a mechanism of structual thickening i s augmented i n some areas by early extension f a u l t s and heterogeneities i n the hanging wall of the seam. I n t e r s t r a t a l s l i p has occurred p r e f e r e n t i a l l y along the hanging wall-coal interface i n almost a l l areas. Early extension f a u l t s which cut the seam form d i s c o n t i n u i t i e s i n the plane of s l i p . During d i f f e r e n t i a l displacement of the hanging wall r e l a t i v e to the footwall of the seam, the extension f a u l t s and d i s c o n t i n u i t i e s i n the hanging wall strata are either peeled o f f and dislodged from the hanging wall, f a c i l i t a t i n g s l i p along the hanging wall-coal seam inte r f a c e , or the f a u l t block moves as part of the hanging wall. In the l a t t e r case the f a u l t serves as a 'coal plow' resulting i n thinning of the seam i n the area of o f f s e t and thickening i n advance of the fault (Figs. 2-2B, and 2-3). . Isolated blocks of sandstone and shale which occur i n some highly deformed seams are probably portions of roof strata that formed d i s c o n t i n u i t i e s i n the hanging wall and were subsequently dislodged from the hanging wall during i n t e r s t r a t a l s l i p . The significance of i n t e r s t r a t a l s l i p as a mechanism of 20 F i g u r e 2-2A. C o n t r a c t i o n f a u l t w i t h 2 m o f s t r a t i g r a p h i c s e p a r a t i o n i n the r o o f rock of the Number 2 seam. There i s no o f f - s e t i n the f o o t -w a l l s t r a t a i n the v i c i n i t y o f the ou t c r o p . F i g u r e 2-2B. 'Coal plow' i n hanging-wall of the Number 2 seam. Drag f o l d s i n d i c a t i v e o f up-dip motion (to the r i g h t ) o f the hanging-wall r e l a t i v e to the f o o t - w a l l are e v i d e n t i n the c o a l seam on the l e e s i d e o f the plow. Model showing how e x t e n s i o n f a u l t i n g f o l l o w e d by i n t e r s t r a t a l s l i p r e s u l t s in., t h i n n i n g i n the r e g i o n o f o f f - s e t and t h i c k e n i n g i n advance o f the p l o w . 22 structural thickening i n the Vicary Creek and other areas i s a function of the t o t a l amount of i n t e r s t r a t a l s l i p , the character of the roof rock and, l i k e l y the ambient stress f i e l d . The amount of i n t e r s t r a t a l s l i p i s among other factors, a function of the amount of flexure of the strata and the thickness of the beds (Ramsay1967). Also, a component of i n t e r s t r a t a l s l i p may be related to drag from overriding thrusts, as documented by Norris (1958) i n other areas. In the Vicary Creek area, the footwall of the seam i s rarely exposed and the t o t a l amount of i n t e r s t r a t a l s l i p i s unknown.. At one l o c a l i t y , however, extension f a u l t s on the footwall of the seam have been dislodged from the footwall and transported with the coal in an up-dip dir e c t i o n as much as 0.5 m, i n d i c a t i n g the whole seam has l o c a l l y moved up-dip by at l e a s t t h i s amount. In the now abandoned McGillivray mine south of the study area, Norris (1958) observed a dike in the hanging wall which was offset about 10 m i n an up-dip d i r e c t i o n from i t s continuation in the footwall. The influence of the character of the hanging wall strata on i n t e r s t r a t a l s l i p i s p a r t i c u l a r l y evident i n the Vicary Creek underground mine. Here there i s a good c o r r e l a t i o n between t h i n l y bedded carbonaceous hanging wall strata and l e s s extensively sheared coal, and between t h i c k l y bedded sandstone hanging wall,strata and pervasively sheared c o a l . Apparently the t h i n l y bedded strata f a c i l i t a t e d i n t e r s t r a t a l s l i p along the coal-hanging wall interface whereas the thick bedded sandstones did not, and i n t e r s t r a t a l s l i p occurred within the seam., The affect of the ambient stress f i e l d cannot be evaluated; however, by analogy with simple shear, high normal stress during 23 i n t e r s t r a t a l s l i p would f a c i l i t a t e drag of underlying s t r a t a and thus promote s t r u c t u r a l thickening and associated thinning and shearing of the coal. . Grassy Mountain At Grassy Mountain, coal measures of the Kootenay Formation occur in the immediate footwall of the Turtle Mountain Fault, a west dipping thrust f a u l t with about 150 m of st r a t i g r a p h i c separation i n the area of study (Norris, 1955; 1971)... One exceptional exposure of a s t r u c t u r a l l y thickened coal seam occurs i n an abandoned open-pit mine (Figs. 2-4, 2-5A and 2-5B). The seam i s medium-volatile bituminous coal and occurs in the upper part of the Coal Bearing member which i s thin at t h i s l o c a l i t y and i s disconformably overlain by the Cadomin Formation of the Blairmore Group. The structure, which had been described by Norris (1971), consists of an a n t i c l i n e and two synclines above the coal and two synclines and an a n t i c l i n e below the coal (Fig. 2-4, 2-5A and 2-5B).. The average stratigraphic thickness of the seam i s about 10 m, whereas i t i s about 27 m thick i n the most easterly syncline and about 1.5 m thick i n the hinge of the collapsed a n t i c l i n e (Norris, 1971).. The s t r u c t u r a l f a b r i c of the coal measures at the Grassy Mountain l o c a l i t y has been described by Price (1967). The folds are concentric and c y l i n d r i c a l , although disharmonic i n t o t a l aspect. The o v e r a l l kinematic pattern i s one.of shortening .of hanging wall and footwall strata about a north-trending axis as a result of f o l d i n g and, to a lesser extent, contraction f a u l t i n g . . Extension f a u l t s with displacements of 10 cm to 30 cm —I 30 metres F i g u r e 2 - 4 . C r o s s - s e c t i o n o f the G r a s s y M o u n t a i n s t r u c t u r e s h o w i n g t h i c k e n i n g o f t h e c o a l and t h e p r i n c i p a l s t r u c t u r e s . M o d i f i e d from N o r r i s (1971) F i g u r e 2-5B. A x i a l r e g i o n o f the s y n c l i n a l t h i c k e n i n g t o the e a s t i n F i g . 2-4 . 26 occur l o c a l l y i n the hanging wall strata* The major a n t i c l i n a l structure to the west i n Fig. 2-4 i s developed over a decollement within the coal seam. The basal portion of the seam i s nearly f l a t l y i n g and primary s t r a t i f i c a t i o n i s s t i l l evident. Overlying the.detachment surface and within the seam are numerous d i s t i n c t east and west dipping shear surfaces symmetrically arranged about the a x i a l surface.. Most of the coal within the a n t i c l i n e i s , however, highly brecciated and d i s t i n c t shear surfaces are not evident. .. The s y n c l i n a l thickening of coal to the east i s no longer well exposed. The coal appears to be l a r g e l y pervasively sheared and granulated and d i s t i n c t mappable shear surfaces are not evident. Although transport of the coal into the hinge of the a n t i c l i n e by contraction f a u l t s i s evident i n outcrop, calculations by Norris (1971), made when the exposures were fresh, showed that the t o t a l amount of shortening i n the ac deformational plane of the structure could not account for the area of coal exposed. Norris showed that the cross-sectional area of the seam was. too large by 48% and concluded that coal must have been transported obliquely into the ac deformational plane. The exceptional l o c a l thickening of coal in the Grassy Mountain structure was probably lar g e l y f a c i l i t a t e d by decollement in the c o a l seam or at the l e v e l of the coal seam during folding. , Burns et al.,, (1977), using a t h e o r e t i c a l model of fiamberg (1964), have demonstrated that during folding of interbedded competent and incompetent strata constrained above by the overlying f o l d and below by basement (detachment 27 surface), p l a s t i c layers may be squeezed from the synclinal areas towards the dome. The competent stata which are constrained can accomodate folding only by bending and stretching and i n the late stages of fo l d i n g the central region of the dome i s a region of extension rather than compression (Burns et a l , , 1S77; Eamberg, 1964).. The o v e r a l l structure associated with the:thickened coal seam at Grassy Mountain i s i n close agreement with that predicted by Burns et a l . , (1977). The c o a l , however, has flowed at least i n part c a t a c l a s t i c a l l y , rather than p l a s t i c a l l y , towards the hinge of the a n t i c l i n e . above the decollement and towards the hinge of the syncline below the decollement. i n addition, l a t e extension f a u l t s on the hanging wall of the seam provide evidence for a la t e stage of extension, as predicted by Hamburg (1964), which probably f a c i l i t a t e d transport of coal obligue .to the ac deformation plane of the structure towards the culmination. Tent Mountain At Tent Mountain i n the Lewis Thrust sheet (Fig. 1-2), complexly folded and faulted coal measures of the Kootenay Formation have been exposed by mining operations. Coal seams of anomalous thickness occur at three l o c a l i t i e s where they have been ac t i v e l y mined.. Although the o v e r a l l structure of Tent Mountain i s interwoven, each of the deposits has unique features and they are, therefore, considered separately i n the following discussion. 28 Southern Deposit: On the southern side of Tent Mountain a seam of medium-v o l a t i l e bituminous coal, l o c a l l y referred to as Number 4 Seam, occurs i n the immediate footwall of a westerly dipping thrust f a u l t (Figs. 2-6 and 2-7). The f a u l t has a stratigraphic separation of about 100 m and.a displacement which i s approximately 1 km. The f a u l t dips about 45 degrees to the west at the present l e v e l of mining, f l a t t e n s rapidly with depth and cuts down-section to the north and south. In the footwall of Number 4 Seam occur contraction f a u l t s which are cozonal with the overlying thrust and which have stratigraphic separations up to 2.5 m. In addition, there are several south dipping contraction f a u l t s with s t r a t i g r a p h i c separations up to 2.5 m and low amplitude, west plunging folds and flexures which attest to shortening more or less perpendicular to the s t r i k e of the overlying thrust,. Number 4 Seam has a normal str a t i g r a p h i c thickness of about 4 m immediately to the south of the mine, whereas at the present l e v e l of mining i t i s thickened to 33 m. Down dip the seam f l a t t e n s and thins; i t also,apparently thins to the north and south before being cut off by the overlying f a u l t . . In the region of thickening, the seam i s pervasively sheared and brecciatedj primary s t r a t i f i c a t i o n of the coal has largely been destroyed and i t i s extensively polished. The coal consists of r e l a t i v e l y large blocks (up to 20 cm ) of more coherent fusain-and durain-rich ' d u l l ' coal and rock partings and more f i n e l y brecciated and granulated c l a r a i n - and v i t r a i n - r i c h coal. Many large competent blocks of ' d u l l 1 coal have c l e a r l y been rotated 29 r e 2 - 6 . S o u t h e r n d e p o s i t , T e n t M o u n t a i n . (A) G e n e r a l i z e d g e o l o g i c a l map. (B) S c h e m a t i c c r o s s - s e c t i o n t h r o u g h A - B . (C) Axes o f s l i p on s l i c k e n s i d e d b e d d i n g s u r f a c e s and c o n t r a c t i o n f a u l t s (©), ' b ' i s t h e b f a b r i c d i r e c t i o n o f the. c o a l seam. L e g e n d i s o n F i g . 2-12. 30 F i g u r e 2-7. M o s a i c o f Number 4 seam a t p r e s e n t l e v e l o f m i n i n g . The o v e r l y i n g t h r u s t c u t s u p - s e c t i o n t o the e a s t . I n t h e f o o t w a l l o f t h e c o a l seam a s o u t h e a s t d i p p i n g c o n t r a c t i o n f a u l t (C) i s v i s i b l e . 31 during deformation. Few discrete shear surfaces are evident in the.coal; those which do occur are marked by f i n e l y granulated coal and can be traced only f o r a few metres. Measurements of slickenside s t r i a e on bedding surfaces and contraction f a u l t s and flexures i n the footwall of the seam were made at a l o c a l i t y near the present l e v e l of mining. The axes of rotation during s l i p , when considered i n aggregate, show a f a i r l y well defined kinematic^b axis which was horizontal, northerly trending and closely p a r a l l e l e d the s t r i k e of the overlying thrust f a u l t (Fig, 2 - 6 ). Additional axes of s l i p show considerable scatter, but many are in d i c a t i v e of s l i p about axes of rotation which are more or l e s s perpendicular to the overlying f a u l t . The dir e c t i o n of motion inferred from the slickenside s t r i a e and dip of contraction f a u l t s a t t e s t s to motion of the hanging wall (of the shear planes) both i n an easterly up-dip di r e c t i o n and i n a northerly d i r e c t i o n . The r e l a t i v e timing of the two movements i s not apparent. Structural thickening of Number 4 Seam was the re s u l t of transport of coal both in an easterly up-dip d i r e c t i o n as well as i n a northerly d i r e c t i o n about both axes of rotation during s l i p . . Shortening and thickening of the seam about a horizontal, northerly trending kinematic-b axis of s l i p probably was the res u l t of drag of the coal up-dip along the base of the overlying thrust f a u l t as i t cut progressively up section. Much of the s t r u c t u r a l l y thickened coal i s l i k e l y f a u l t breccia formed during c a t a c l a s i s and flow of the coal as a result of simple shear of the overlying f a u l t . Such an interpretation i s suggested by the paucity of discrete shear surfaces i n the coal 32 and t i e presence of pervasively sheared and polished coal throughout much cf the seam. Southerly dipping contraction f a u l t s , which occur l o c a l l y in the footwall of the seam, r e s u l t i n shortening and thickening of the seam in a northerly d i r e c t i o n . Because the contraction f a u l t s do not cut the hanging wall s t r a t a , displacement of the f a u l t s must be compensated for by thickening and thinning within the coal seam. S i m i l a r l y , flexures and folds i n the footwall of the seam, not evident i n the hanging wall, must re s u l t i n variation i n thickness of the seam. Even i f the f o l d s or f a u l t s preceded the overlying reverse f a u l t they would s t i l l r e s u l t in a variation i n thickness since the overlying thrust i s e s s e n t i a l l y planar. Transport of coal i n front of advancing contraction f a u l t s or away from a n t i c l i n a l flexures and folds was probably also along diffuse shear surfaces, notwithstanding that l a t e r movements may have destroyed the e a r l i e r s t r u c t u r a l f a b r i c of the seam. Northern Deposit: On north-central Tent Mountain, four seams of medium-v o l a t i l e bituminous coal are exposed i n a broad, south-trending syncline (Fig. 2-8). . The syncline i s the immediate footwall of a west dipping thrust f a u l t with a stratigraphic separation of about 600 m and a displacement probably i n the order of several kilometres. The f a u l t cuts abruptly down section to the south where cnly the eastern limb of the syncline i s present. The syncline has been faulted out i n part and flattened by the overriding thrust. The structure of the syncline i s complex and Figure 2-8. Northern deposit, Tent Mountain. The overlying west dipping thrust has faulted out much of the eastern limb of the syncline. Figure 2-9. A x i a l region of the syncline i n F i g . 8. The much thickened seam i n the hinge at the top of the photograph i s Number 7 seam whereas the underlying seam i s Number 6. 34 only those features which relate to the variation i n thickness of the coal seams are discussed here. Contraction f a u l t s and extension f a u l t s are common on both limbs of the syncline. The fa u l t s arise out of surfaces of i n t e r s t r a t a l s l i p , cut across several beds, either up or down section, and then pass into ether surfaces of i n t e r s t r a t a l s l i p . North-trending, east-dipping extension f a u l t s with displacements of 0.5 m to 5 m cut obliguely across the syncline.. ftn additional set of fa u l t s s t r i k e obliguely to perpendicularly to the fo l d axis and are arranged mere or les s symmetrically about the a x i a l surface. These f a u l t s r e s u l t i n contraction or extension in the plane of bedding. . Of the four major seams exposed i n the syncline, the three s t r a t i g r a p h i c a l l y highest seams in the succession show notable variation in thickness around the syncline (Fig. .2-9), whereas the lowest seam i s exposed only on the eastern limb. The uppermost seam, referred to as Number 7, ranges i n thickness around the syncline frcm about 6m on the eastern limb to 17 m i n the hinge area and 12 m i n a flexure on the western limb where i t i s largely faulted out.. Below Number 7 Seam the hinge of the syncline i s p a r t i a l l y collapsed, whereas above the seam the hinge i s of f s e t to the east and the beds are more gently folded. . Number 6 seam ranges i n thickness from about 6 m on the eastern limb to 9 m i n the hinge area and i s faulted out on the western limb. Number 5 Seam ranges i n thickness from 8 m at a point high on the eastern limb to about 30 m at the hinge of the syncline, 2 m at the i n f l e c t i o n point on the western limb and about 25 m in the t i g h t a n t i c l i n a l hinge to the f a r west 3 5 (Fig. 2-8) . Number 4 Seam shows no consistent variation i n thickness. In addition to the variations described above, a l l the seams l o c a l l y vary i n thickness as a result of extension and contraction f a u l t i n g . The coal seams are pervasively sheared and polished in areas of s t r u c t u r a l thickening or thinning, whereas they are only mildly brecciated i n areas of normal stratigraphic thickness. In a l l areas, however, systematic c l e a t , i f i t was ever present, has been destroyed by subsequent deformation., D i s t i n c t shear surfaces s i m i l a r to those evident at Grassy Mountain are present i n most areas; however, Number 7 Seam i s f i n e l y granulated and polished i n the hinge area of the syncline. The axis of rotation of slickenside s t r i a e during s l i p on bedding surfaces (Fig. 2 - 1 0 B ) shows a stongly preferred orientation which i s e s s e n t i a l l y horizontal and p a r a l l e l to the f o l d axis. Many of the contraction f a u l t s are cozonal with, and r i s e out of, surfaces of i n t e r s t r a t a l s l i p . The d i r e c t i o n of preferred motion inferred from slickenside s t r i a e and dip d i r e c t i o n cf contraction f a u l t s (Fig. 2 - 1 0 A ) indicates movement of the hanging wall s t r a t a out of the hinge zone.of the syncline, consistent with f l e x u r a l s l i p folding. In addition to a well defined kinematic-b axis of s l i p there i s a large scatter of s l i p axes on both bedding planes and contraction f a u l t s which have no readily apparent geometric s i g n i f i c a n c e . , Included in t h i s l a t t e r group are f a u l t s which are oriented obliquely and perpendicular to the f o l d axis. The d i r e c t i o n of motion inferred from the slickenside s t r i a e on these f a u l t s indicates F i g u r e 2 - 1 0 . N o r t h e r n d e p o s i t , T e n t M o u n t a i n . (A) Axes o f s l i p on c o n t r a c t i o n f a u l t s ( • ) , p o l e s t o c o n t r a c t i o n f a u l t s (•<) and s l i p l i n e a r s {-*) . (B) Axes o f s l i p on s l i c k e n s i d e d b e d d i n g s u r f a c e s . F i g u r e 2 - 1 1 . I d e a l i z e d r i g h t - s e c t i o n o f a f l e x u r a l - s l i p ( f low) f o l d i n w h i c h t h e i n c o m p e t e n t beds (shaded) a r e t h i n n e d on t h e l i m b s and t h i c k e n e d i n t h e h i n g e a r e a s . The c o m p e t e n t beds show l i t t l e o r no v a r i a t i o n i n t h i c k n e s s . M o d i f i e d from W h i t t e n (1966) . 3 7 most of the movement of the hanging wall was toward the north or northeast (Fig. 2-10A),. These f a u l t s c o l l e c t i v e l y o f f s e t , and in turn are offset by, planes of i n t e r s t r a t a l s l i p , which indicates that s l i p about the f o l d axis ( f l e x u r a l s l i p ) was coeval with s l i p obligue to the fo l d axis. Variation i n thickness of the coal seams from the limbs to the hinge cf the syncline i s not accompanied by a sim i l a r variation i n thickness of competent sandstone units. The o v e r a l l s y n c l i n a l form i s thus analagous to the f l e x u r a l flow folds cf Donath and Parker (1964) which are common i n rocks of moderate d u c t i l i t y and i n sequences with beds of moderate to high d u c t i l i t y contrast. In f l e x u r a l flow fo l d s , as described by Donath and Parker (1964), flow occurs within l e s s competent layers, r e s u l t i n g in layer boundaries that are no longer p a r a l l e l ; r e d i s t r i b u t i o n of material in the layers i s most commcnly r e f l e c t e d by thickening i n the hinges and thinning i n the limbs. In the Tent Mountain syncline the flow of coal into the hinge area, p a r t i c u l a r l y i n the case of Number 7 Seam, was probably i n part the r e s u l t of the sgueezinq together of the competent rock units on the limbs during folding and f l a t t e n i n g r e s u l t i n g i n c a t a c l a s t i c flow of the less competent coal towards the hinge, such as described by Hamsay (1974) during chevron fold i n g . . During formation of chevron f o l d s , and apparently some f l e x u r a l . s l i p f o l d s (Whitten, 1966), d i l a t a t i o n spaces are created in the hinge areas between successive competent layers, which i n conjunction with squeezing in the limbs would f a c i l i t a t e flow cf the coal to the hinge area (Figs 2-11).. In addition to transport of coal i n the ac fabri c (deformational) 3 8 plane of the syncline, extension and contraction f a u l t s may have transported coal to the north obliquely into the hinge area. Local variation in thickness of the seams i s related to both contraction and extension f a u l t s . Faults which r i s e out of surfaces of i n t e r s t r a t a l s l i p cut both up and down section, respectively r e s u l t i n g in thickening and thinning of the coal seams. Faults which transect the coal seams or which l i e within them commonly change markedly i n orientation over short distances, r e s u l t i n g i n a rapid variations i n coal thickness.. Western Deposit: On west-central Tent Mountain a seam of medium-volatile bituminous coal occurs in the core of a syncline which trends 165 degrees (Fig. 2-12). . The western limb of the syncline i s nearly v e r t i c a l or overturned to the west, whereas the eastern limb dips 50 to 60 degrees to the west. On both the east and west limbs numerous northerly trending flexures and folds with amplitudes up to 5 m and wavelengths of 20 m are present. The syncline occurs in the immediate footwall of a west dipping thrust f a u l t with a stratigraphic separation of about 300 m and a displacement which i s on.the order of several hundred metres. The syncline has been accentuated and overturned i n part by the overriding thrust f a u l t . To the north, the syncline has been faulted out, whereas i t opens to the south. Open-pit mining has lar g e l y removed the coal from the core of the syncline, but i t appears that prior to mining the coal deposit was about 130 m wide and 80 m thick i n the hinge area.. The normal str a t i g r a p h i c thickness of the seam i n areas to the east i s about 7 m. The 39 F i g u r e 2-12. W e s t e r n d e p o s i t , T e n t M o u n t a i n . CA) G e n e r a l i z e d g e o l o g i c a l map. (B) S c h e m a t i c r e c o n s t r u c t e d c r o s s - s e c t i o n . (C) Axes o f s l i p o f s l i c k e n s i d e s t r i a e on b e d d i n g s u r f a c e s (.•), ' 3 ' i s t h e f o l d a x i s . 40 coal i s presently exposed i n i s o l a t e d areas on the.footwall, where i t i s extensively fractured and, i n part, f i n e l y granulated. In general, the coal i s not as extensively polished as i t i s i n the northern deposit. The axes of s l i p determined from slickenside striae on strata in the footwall of the seam at accessible areas (Fig. 2-12C) show a well defined kinematic-b axis which i s sub-horizontal and closely p a r a l l e l s the s y n c l i n a l axis. The kinematic-b axis for s l i p on bedding and the d i r e c t i o n of s l i p inferred from the s l i p l i n e a r s are consistent with f l e x u r a l s l i p folding about the f o l d axis of the syncline. Because almost a l l the coal has been mined from the core of the syncline the mechanisms leading to the formation of the much thickened deposit can only be in f e r r e d . The t o t a l aggregate shortening of the seam within the syncline i s not adequate to account f o r the volume of coal in the core of the syncline; coal must therefore have been transported into the hinge area from the limbs of the syncline. The ov e r a l l mechanisms of thickening of the coal were probably analogous to those previously described for the Northern Deposit. The t o t a l thickening of the seam i s , however, much greater, l i k e l y as a result of the ti g h t e r folding and possibly greater degree of fl a t t e n i n g of the syncline. "FLOW" OF COAL DURING DEFORMATION In addition to considering the mechanisms of s t r u c t u r a l thickening i n terms of the kinematics of the coal measures, thickening can be envisaged simply as a re s u l t of flow (mass 4 1 transport) of coal from areas of high stress to areas of low stress. The flow of coal at a l l the examined l o c a l i t i e s has been c a t a c l a s t i c . There i s no evidence on a mesoscopic scale for t r u l y d u c t i l e behavior of the coal i n the usual sense. Cataclasis and p l a s t i c flow represent completely d i f f e r e n t material behavior, respectively b r i t t l e and d u c t i l e , and the laws of p l a s t i c flow cannot be applied to b r i t t l e materials (Sture, 1976). Flow i s generally considered a "...process whereby a rock i s deformed continuously i n space without loss of cohesion...'! (Turner and Weiss, 1963, p. ,37). Loss of cohesion, however, must be considered r e l a t i v e to the scale of the structure and, i f the loss of cohesion i s smaller than the scale of the structure, i t i s a mechanism of flow (Stearns, 1968; Price, 1974). . Cataclasis as a mechanism of flow i n rocks has been studied experimentally (Handin and Hager, 1957; Borg et a l . , 1960; Donath and Fruth, 1971; Kerrich and A l l i s o n , 1978). When a rock loses cohesion as a r e s u l t of b r i t t l e fracture i t may flow by displacement of i t s constituent parts r e l a t i v e to one another, accompanied by d i l a t a t i o n , mechanical abrasion and granulation. The fragments of the rock thus may behave and flow in a macroscopically d u c t i l e - l i k e manner (Stearns, 1968). As indicated by Stearns (1S68), the extent of fracturing can be considered a measure of the r e l a t i v e d u c t i l i t y of the rocks and the degree of dependence on c a t a c l a s i s as.a mechanism of flow. Furthermore, the t o t a l s t r a i n , s t r a i n rate, temperature, and geometry and thickness of the beds w i l l influence the mode of deformation and extent of fracturing (Stearns, 1968; Donath and 42 Fruth, 1971). Because of extensive f r a c t u r i n g , much of the coal i n t h i s study can be considered to have r e l a t i v e l y high d u c t i l i t y as compared to adjacent l i t h o l o g i e s . The fr a c t u r i n g of the coal probably included an i n i t i a l c l e a t system; however, the extensive fr a c t u r i n g which f a c i l i t a t e d c a t a c l a s t i c flow i s probably r e l a t e d to the s t r a i n softening c h a r a c t e r i s t i c s of the c o a l . Strain softening can be considered as the progressive loss of shear resistance with s t r a i n a f t e r peak shear strength.. k common feature of st r a i n softening of materials i n progressive f a i l u r e of rock structures i s that excess stress, when relieved i n one area, i s redistributed fo adjacent areas which may thus be brought to f a i l u r e (Sture, 1976). Sture has experimentally studied the s t r a i n softening behavior of Pittsburg coal and has detailed t-he sequence of progressive f a i l u r e and c a t a c l a s i s . . He found that, at peak strength, shear zones progressed throughout the sample and the 'weakest l i n k ' was the shear zone where the cohesion was smaller than that of the unfractured rock, but where the i n t r i n s i c f r i c t i o n angle may s t i l l be.high.. Dilatation occurs as a resu l t of fracture as i n t a c t coal pieces undergo r i g i d body rotation and tra n s l a t i o n along the shear zone,. Movement further results i n a large d i l a t a t i o n , tearing loose of more fractured pieces and abrasion which changes the angularity and grain-size d i s t r i b u t i o n of the fractured mass (Sture, 1976). During s l i d i n g , the shear zone may 'lock up' and fracture may i n i t i a t e i n another fracture zone, the end r e s u l t being a multitude of diffuse shear surfaces and a c a t a c l a s t i c f a b r i c . 4 3 The high r e l a t i v e d u c t i l i t y of the fractured coal, and i t s a b i l i t y to flow, i s p a r t i c u l a r l y apparent i n small scale structures where the geometry of the enclosing rocks i s completely exposed. , Pig. 2-13 shows boudinage i n interbedded sandstone and coal; the sandstone beds have f a i l e d b r i t t l y i n extension, forming boudins, whereas the more highly fractured coal flowed c a t a c l a s t i c a l l y into the neck regions, indicating that the more highly fractured coal has a very low apparent v i s c o s i t y as compared to that of the sandstone interbeds. F i g . 2-14 shows the occurrence of coal within the plane of an extension f a u l t with about 4 m of o f f s e t ; d i l a t a t i o n i n the f a u l t plane has accommodated flow of coal into the.fault plane, where the coal i s about the same thickness as i n the 'feeder* coal seam.. Based on volumetric considerations, the coal must have been 'injected' rather than simply dragged along the f a u l t plane. Also of i n t e r e s t i n t h i s example i s the development of a crude f o l i a t i o n i n the coal seam p a r a l l e l to the f a u l t plane, probably as a r e s u l t of s l i p p a r a l l e l to the f a u l t and rotation of the larger coal c l a s t s , perhaps s i m i l a r to the development of bedding f o l i a t i o n i n incompetent strata during f l e x u r a l s l i p (Whitten, 1966) . Although s t r u c t u r a l thickening and thinning i s more apparent i n small scale examples which are well exposed, the larger scale examples, previously discussed, also attest to the a b i l i t y of coal to flow to areas of low stress. In other coal f i e l d s s i m i l a r s t r u c t u r a l variations i n thicknesses are probably also a r e s u l t of c a t a c l a s t i c flow of coal. Nickelsen (1963) has described thickening i n the hinge areas of some folds r e s u l t i n g 44 F i g u r e 2-13. B o u d i n a g e i n i n t e r b e d d e d s a n d s t o n e and c o a l . The s a n d s t o n e beds ( l i g h t toned) a r e a b o u t 0.3 m t h i c k . F i g u r e 2-14. E x t e n s i o n f a u l t w i t h a b o u t 4 m o f d i s p l a c e m e n t and c o a l i n j e c t e d i n t o t h e f a u l t p l a n e . N o t i c e the f o l i a t i o n i n t h e c o a l w h i c h i s more o r l e s s p a r a l l e l t o the f a u l t p l a n e . 45 i n a sim i l a r f o l d s t y l e i n central Pennsylvania.. Petraschecfc (1937) described thickening of coal in the hinge areas of some folds and both Petrascheck (1937) and Bessiar (1948) have documented the complex structures and thickening of coal associated with f a u l t s . MICBOFABBIC OF THE COAL Coal from some of the s t r u c t u r a l l y thickened deposits was examined with a reflected l i g h t microscope, with a photometer for v i t r i n i t e reflectance .measurements, and with a scanning electron micrcsccpe. . The r e s u l t s of t h i s study w i l l be reported elsewhere and are only summarized here. The microfabric of the coal from s t r u c t u r a l l y thickened areas i s s i m i l a r to that of the coal from areas of normal stra t i g r a p h i c thickness with the exception of adjacent to major shear zones and i n areas of intense deformation.. The f i n e l y granulated coal along shear zones generally consists simply of fragments of the larger coal c l a s t s with no evidence of i n t e r n a l deformation.. L o c a l l y , however, aggregates consisting of angular fragments of i n e r t i t e - r i c h coal i n a groundmass of v i t r i t e or c l a r i t e occur. In these aggregates the i n e r t i t e components have undergone b r i t t l e fracture whereas the c l a r i t e or v i t r i t e groundmass apparently behaved d u c t i l e l y . Ductile behavior of the c l a r i t e and v i t r i t e i s also apparent from the occurrence of microfolds of si m i l a r style and 'wild' f o l d s . Somewhat si m i l a r structures have also been described from t e c t o n i c a l l y deformed parts of the Buhr Basin by Teichmuller and Teichmuller (1954). The occurrence of coal i n the study area showing evidence of 46 d u c t i l e behavior even on a microscopic scale i s r e s t r i c t e d and may represent areas of 'locking' during c a t a c l a s t i c flow.. Measurements of v i t r i n i t e reflectances were made on the highly pclished and sheared coal to ascertain the e f f e c t of deformation on coal rank. The r e s u l t s of the analysis indicate that adjacent to some shear zones the rank of the coal has been raised to semi-anthracite.. The increase in rank i s not predictable, however; adjacent to some major f a u l t s there i s no evident change whereas in adjacent, seemingly minor, shear zones there may bs a notable increase i n rank. EFFECT OF STBOCTUBAL THICKENING ON MINING AND COAL QUALITY Structural thickening of some coal seams i n the study area has enabled open-pit mining of seams which are otherwise too t h i n . However, in underground mines such as i n the Vicary Creek area the rapid variation in thickness of the coal seam and accompanying i r r e g u l a r i t i i e s i n the hanging wall and footwall strata r e s u l t i n unpredictable and unfavourable mining conditions. Moreover, the pervasively sheared coal forms p i l l a r s of low bearing strength and i t i s not possible to hold the sheared coal i n the roof. Additional problems are also encountered i n predicting coal reserves and d i s t r i b u t i o n of the coal deposits. Even with a densely spaced d r i l l i n g program i t i s d i f f i c u l t to predict the variation in seam thickness or to unravel the structure. The quality of the coal i s also commonly poor. The coal has a disproportionately large amount of ash, poor washability c h a r a c t e r i s t i c s and i s commonly partly oxidized. The high ash 4 7 content and the poor washability of the coal are related at least i n part to shearing and to the dissemination throughout the coal of formerly discrete rock partings. The high ash content of some deposits as mined may be a r t i f i c i a l , r e s u l t i n g from d i f f i c u l t i e s in mechanical mining and the incorporation of protrusions of roof and f l o o r s t r a t a . Oxidation of the coal i s largel y related to the fine grain-size of the sheared coal which markedly increases the s u s c e p t i b i l i t y of coal to oxidation.. In addition, the highly fractured and faulted coal and associated s t r a t a f a c i l i t a t e s exposure even at depth to atmospheric oxygen or c i r c u l a t i o n of oxygenated waters. CONCLUSIONS The mechanisms leading to the formation of s t r u c t u r a l l y thickened coal deposits i n the southern Eocky Mountains of B r i t i s h Columbia and Alberta are closely correlatable with the kinematic pattern of t i e coal measures.. At Vicary Creek, the variation i n thickness cf Number 2 Seam i s a re s u l t of contraction f a u l t i n g , i n t e r s t r a t a l s l i p and extension f a u l t i n g . At Grassy Mountain thickening i s related to folding of the coal measures and decollement at the l e v e l of the coal seam which f a c i l i t a t e d transport of the coal both obliguely to and i n the ac f a b r i c plane of the folds._ At the Southern Deposit at Tent Mountain Number 4 Seam has been thickened as a r e s u l t of drag of portions of the seam up-dip along the base of a thrust f a u l t and, to a lesser extent, as a r e s u l t of contraction f a u l t i n g i n the footwall of the seam. In the Western and Northern Deposits at Tent Mountain thickening of the coal seams i s primarily the 48 r e s u l t of squeezing of coal from the limb regions of the synclines to the hinge areas, s i m i l a r i n gross aspect to that of f l e x u r a l flow and chevron f o l d i n g . In a l l of the examples, structural thickening of the coal resulted at l e a s t in part from c a t a c l a s t i c flow of coal from areas of high stress to areas of lower stress. The apparent d u c t i l i t y cf the coal and i t s a b i l i t y to flow i s a res u l t of intense f r a c t u r i n g and granulation of the coal which re s u l t s in a l o w apparent v i s c o s i t y as compared to that of adjacent l i t h c l c g i e s . There i s ng evidence on a macroscopic scale for t r u l y d u c t i l e behavior and microscopic studies indicate that d u c t i l e behavior of the v i t r i t e and c l a r i t e components of the coal i s r e s t r i c t e d to areas of intense deformation.. V i t r i n i t e reflectance studies show that only rarely i s there;any increase in rank associated with polishing and shearing of the coal. Structural thickening of coal seams in some areas f a c i l i t a t e d open-pit mining of otherwise too th i n seams. However, i n areas of underground mining the rapid variation i n thickness of the seams and the highly sheared character of the coal r e s u l t i n unfavourable mining conditions. I t i s furthermore d i f f i c u l t to predict the coal reserves or extent of the coal deposits and the quality of the coal i s generally poor, with disproportionately high amounts of ash, poor washability c h a r a c t e r i s t i c s and common oxidation. 49 ACKNOWLEDGMENTS I wish to thank Coleman C o l l i e r i e s Ltd.. and p a r t i c u l a r l y t h e i r surveying s t a f f for the i r co-operation and f o r providing subsurface information. D.K. Norris of the Geological Survey of Canada gave many helpful suggestions during the f i e l d work. W.H. , Mathews and W.C. , Barnes kindly reviewed the manuscript and th e i r comments were most appreciated. Financial support was provided by the Geological Survey of Canada and Natural Sciences and Engineering Eesearch Council (Canada) operating Grant A-1107 to W.H. Mathews, Department of Geological Sciences, University of B r i t i s h Columbia. 5 0 BEFEBENCES Bersier, A., 1948, Phenomenes de p l a s t i c i t e dans l e s charbons mollassigues: Eclogae Geologicia Helvetiae, vol. 41, pp. . 101- 112. Borg, I, Freidman, M ., Handin, J. and Higgs, D.V., 1960, Experimental deformation of St. Peter Sand: a study of c a t a c l a s t i c flow: i n Bock Deformation, Geological Society of America Memoir no. 79, pp. 363-384. Burns, K.L., Stephansscn, 0., and White, A. J.E. , 1977, The Flinders Eanges breccias of South A u s t r a l i a - d i a p i r s or decollement: Journal of the Geological Society of London, vol..134, pp. 363-384. Darton, N.H., 1940, Some st r u c t u r a l features of the Northern Anthracite coal basin, Pennsylvania: United States Geological Survey Professional Paper 193-D, 82 pp. Deenen, J.M., 1942, Breuken in kool en gesteente: Mededeelingen van Gedogische S t i c h t i n g . # Serie C-I-2-No.l, 100 pp. Donath, F.A. and Fruth J r , L.S., 1971, Dependence of strain-rate e f f e c t s on deformation mechanisms and rock type: Journal of Geology, vol. 79, pp. 347-371. Donath, F.A and Parker, E.B., 1964, Folds and f o l d i n g : Geological Society of America B u l l e t i n , vol. 75., pp..45^62. Gibson, D.W., 1977, Sedimentary f a c i e s i n the Jura-Cretaceous Kootenay Formation, Crowsnest Pass area, southwestern Alberta and southeastern B r i t i s h Columbia: B u l l e t i n of Canadian Petroleum Geology, vol..25, pp. 767-791. Handin, J.W- and Hager, E.V., 1957, Experimental deformation of sedimentary rocks under confining pressure: tests at rocm temperature on dry samples: B u l l e t i n American Association of Petroleum Geologists, vol. 41, pp.. 1-50. Hoeppener, B., 1955, Tektonik im Schiefergebirge: Geologische Bundschau, vol. 44, pp. 26-55. , Jansa, L, 1972, Depositional history of the coal bearing Upper Jurassic-Lower Cretaceous Kootenay Formation, southern Eocky Mountains, Canada: Geological Society of America B u l l e t i n , v o l . 83, pp. .3199-3222. . Johnson, L.V., 1977, Unusual coal deposits i n the Crowsnest Pass region i n Alberta and B r i t i s h Columbia: Geological Society of America Abstracts with Programs, v o l . 9, pp. 1040-1041. 51 Kerrich, fi and A l l i s o n , I, 1978, Flow mechanisms in rocks: Geoscience Canada, vol. 5, pp. .109-118,. Nickelsen, B.P., 1963, Fold patterns and continuous deformation mechanisms of the c e n t r a l Pennsylvanian folded Appalachians: i n Tectonics and Cambrian-Ordovician stratigraphy, central Appalachians of Pennsylvania: Guidebook, Pittsburgh Geological Society, pp.,13-29. Norris, D.K., 1955, Blairmore, Alberta: Geological Survey of Canada, Map 55-18, with marginal notes. Norris, D.K., 1956, Coal Mountain, B r i t i s h Columbia, Geological Survey of Canada, Map 4-1956, with marginal notes.. Norris, D.K., 1958, Structural conditions of Canadian coal mines: Geological Survey of Canada, B u l l e t i n no.,44, 44 pp. Norris, D.K., 1959, Carbondale Eiver, A l b e r t a - B r i t i s h Columbia: Geological Survey of Canada, Map 5-1959, with marginal notes. Norris, D. K. , 1964, Microtectonics of the Kootenay Formation near Fernie, B r i t i s h Columbia: B u l l e t i n of Canadian Petroleum Geology, vol..12, pp. 383-398., Norris, D.. K., 1966, The mesoscopic f a b r i c of rock masses about some Canadian coal mines: Proceedings of F i r s t Congress, International Society of Eock Mechanics, Lisbon, Portugal, vol. .1, pp. 191-198. Norris, D.K., 1971, Comparative study of Castle Eiver and other f o l d s i n the eastern C o r d i l l e r a of Canada: Geological Survey of Canada, B u l l e t i n no. 205, 58 pp. Fetrascheck, V.W.E., 1937, Verdickunden und Verdruckungen von Kohlenflozen und die Gesetzmassigkeit i h r e r hage: Z e i t s c h r i f t f u r prakitsche Geologie, v o l . 45, pp. 172-176. Price, E.A., 1962, Geological structure of the c e n t r a l part of the Eccky Mountains, in the v i c i n i t y cf Crowsnest Pass: Journal Alberta Society of Petroleum Geologists, vol. 10, pp. 341-351. Price, E.A.# 1967, The tectonic s i g n i f i c a n c e of mesoscopic subfabrics i n the southern Bpcky Mountains i n the v i c i n i t y of Alberta and B r i t i s h Columbia: Canadian Journal of Earth Sciences, vol. 4, pp. .39-70. Price, E.A., 1974, Large-scale g r a v i t a t i o n a l flow of supracrustal rocks.of the southern Bockies: i n De Jong, K.A., and Scholten, S., eds., Gravity and tectonics, John Wiley and Sons., New York, pp. ,441-502. 52 Bamberg. H., 1964, Strain d i s t r i b u t i o n and geometry of fo l d s : B u l l e t i n Geological I n s t i t u t e of Uppsala, vol., 42, pp. . 1-20. Bamsay, J.G.# 1967, Folding and fracturing of rocks: McGraw-H i l l , Inc. New York, 568 pp. Bamsay, J.G., 1974, Development of chevron fo l d s : Geological Society cf America B u l l e t i n , vol. 85, pp. 1741-1754.. Sax, H.G.J., 1946, De Tectoniek van het Carbon i n het Zuid-Liraburgsche Mijngeiied: Mededeelinger van de Geolgische Stichting. , Serie C-1-1-NO. 3, 77 pp.. Stearns, D.W., 1968, Fracture as a mechanism of flow i n naturally deformed rocks: i n Baer, A.J. And Norris, D.K. Eds., Proceedings Conference on Besearch in Tectonics: Geological Survey of Canada, Paper 68-52, pp..79-90. Sture, S., 1976, Strain-softening behavior of geological materials and i t s e f f e c t on st r u c t u r a l response: Unpubl. Ph.D.. Thesis, University of Colorado, 342 pp. Teichmuller, M. and Teichmuller, B., 1954, Zur mikrotektonischen verformung der Kohle: Geologisches Jahrbuch, Band 69, S. 263-286. Turner, F.J. and Weiss, L.F., 1963, Structural analysis of metamorphic tectonites: McGraw-Hill, Inc. New York, 545 PP-Whitten, E.H.T., 1966, Structural geology of folded rocks: Band McNally arid Co., New York, 678 pp. 53 PAET 2 GEOLOGICAL FACTORS AFFECTING ROOF CONDITIONS IN SOME UNDERGROUND COAL MINES IN THE SOUTHEASTERN CANADIAN ROCKY MOUNTAINS 54 ABSTRACT V a r i a b i l i t y i n roof conditions in some underground coal mines in the southeastern Canadian C o r d i l l e r a i s i n part attributed to sedimentary and s t r u c t u r a l features of the roof strata and the coal. Examination and measurements of mesoscopic f a b r i c elements i n accessible parts of the mines at Vicary Creek, located i n the hanging wall of the Coleman Fault, arid the Balmer North, Six Panel and and Five Panel mines, located i n the northern part of the Fernie synclinorium, indicate that a cor r e l a t i o n exists between the s t r u c t r u a l conditions i n the mines and the regional s t r u c t u r a l s e t t i n g . In the Vicary Creek mine, the roof rock ranges from t h i n -bedded, very fine-grained, carbonaceous sandstones and si l t s t o n e s to thick-bedded sandstones which are respectively interpreted as d i s t a l and proximal crevasse splay deposits. The thin-bedded strata include carbonaceous laminae that were preferred horizons for i n t e r s t r a t a l s l i p and which form major st r u c t u r a l d i s c o n t i n u i t i e s along which separation of the roof strata may occur. The thick-bedded sandstones are well jointed res u l t i n g i n a blocky rcof rock which did not f a c i l i t a t e i n t e r s t r a t a l s l i p . Rather, i n t e r s t r a t a l s l i p was accommodated by s l i p within the coal seam i t s e l f r e s u l t i n g i n extensive shearing and comminution of the coal, which has reduced the bearing capacity of coal p i l l a r s . Slickenside s t r i a e on bedding surfaces and some extension f a u l t s define a kinematic pattern which i s consistent with that of the Coleman Fault, the major stru c t u r a l element i n the area of the mine. . Joints l i e in hkl and hkO and appear to be dynamically related to i n t e r s t r a t a l 5 5 s l i p . . Some extension f a u l t s l i e i n hkl and hOk and cannot be related to the ove r a l l structure. At least some.extension f a u l t s pre-date i n t e r s t r a t a l s l i p . They have displacements up to 2 m and, i n conjunction with low amplitude f o l d s and flexures in the roof s t r a t a , l o c a l l y r e s u l t i n poor roof conditions. In the Balmer North, Six Panel and Five Panel mines, the immediate roof rock i s composed of carbonaceous s i l t s t o n e s and very-fine grained sandstones. There i s no marked variation i n roof rock lithology throughout the mines. The lack of l i t h o l o g i c variations, in conjunction with the t r a n s i t i o n a l contact between the roof strata and the coal seam, suggests that the coal and roof rock were deposited on a broad, low energy delta p l a i n , and that alandonment of swamp conditions was gradual. As a re s u l t of f l e x u r a l s l i p during f o l d i n g , bedding surfaces are slickensided which has i n part destroyed the cohesion between successive beds i n the roof rock., Although a cleat system i s evident at almost a l l sampling l o c a l i t i e s , no consistent pattern i s evident that conforms to the regional structure. L o c a l l y i n the Five Panel and Six Panel mines, the cleat appears to be dynamically related to l o c a l flexing of the seam. Joint sets in the roof and f l o o r strata l i e i n hkl and hkO and only at a few l o c a l i t i e s do they conform to the cleat system. Few major extension f a u l t s are present i n the mines. Those which do occur l i e i n hOl. In the Balmer North mine, young, gently west dipping shear fractures (cleat) which l i e in hOl are present throughout the mine. This c l e a t system, i n conjunction with cozonal extension f a u l t s and slickensided bedding surfaces, results i n f a i l u r e of both roof s t r a t a and 56 coal ribs along northerly to northwesterly trends. Slip linears on extension faults and shear surfaces in the coal are antithetic to those expected during flexural s l i p and probably post-date folding. In the Five Panel mine both roof and coal rib failure occur along steep, easterly dipping shear surfaces in conjunction with slickensided bedding surfaces. 57 INTRODUCTION Considerable resources of high quality coking coal occur at depth within the s t r a t i g r a p h i c a l l y and s t r u c t u r a l l y complex southern Rocky Mountains of B r i t i s h Columbia and Alberta. Underground coal mining i n t h i s area has been seriously hampered by seemingly unpredictable variation i n structural conditions and roof rock c h a r a c t e r i s t i c s which are not evident from either the sparse outcrops or exploratory d r i l l holes.. The.purpose of thi s study was to ide n t i f y and assess those geological factors that are associated with and promote roof problems i n underground coal mines i n the Crowsnest Pass area of the southern Canadian C o r d i l l e r a . An objective of the study was to rel a t e the observed roof conditions to the sedimentology and the kinematics and dynamics of deformation of the coal measures i n order to develop geological c r i t e r i a for predicting roof conditions. Presently, underground coal mines i n the.southeastern Canadian C o r d i l l e r a are operating i n a variety of s t r u c t u r a l settings and st r a t i g r a p h i c l e v e l s , thereby providing an opportunity to assess and compare roof conditions and the structural f a b r i c of the mines i n d i f f e r e n t geologic settings.„ In t h i s study, the Vicary Creek mine located i n the immediate hanging wall of the Coleman Fault, north of Coleman Alberta, and the Balmer North, Five Panel and Six Panel mines at the northern end of the Fernie Synclinorium, near Michel, B r i t i s h Columbia were studied (Figs. 1-1 and 1-2). Examination of the mines entailed mapping of roof strata and mesoscopic f a b r i c elements of both the roof s t r a t a and the coal i n accessible.parts of the 58 mines. although some areas with poor roof conditions were not accessible, a s p e c i a l e f f o r t was made to examine and sample the roof strata around and i n areas presently experiencing roof support problems. Roof conditions i n underground mines are not only a product of the inherent geological factors, but also r e f l e c t the mining methods which are determined not only by the geology, but by economics, engineering and other considerations. In t h i s study only the inherent geological factors are considered; i t i s not the purpose of the study to assess or pass judgement on mining methods. I t i s hoped, however, that t h i s study might prove useful, i f not i n presently operating mines, i n mines which may be developed i n the future in similar geological settings. Previous studies of the s t r u c t u r a l conditions of coal mines in the southeastern C o r d i l l e r a have been made by Norris (1958, 1963, 1965, 1966),. The present study i s i n part an extension of the e a r l i e r work of Norris to some presently operating coal mines. Other pertinent studies of geological factors a f f e c t i n g roof and s t r u c t u r a l fa b r i c i n coal mines include those of Diessel and Moelle (1965) and Shepherd and Fisher (1978) i n Australian coal f i e l d s , the studies of Benedict and Thompson (1973) and Moebs (1977) i n Pennsylvania, Krauss et a l , , (1979) in I l l i n o i s , and Deenen (1942) and Sax (1946) i n the Dutch coal f i e l d s . In t h i s study, mesoscopic f a b r i c elements are plotted on the lower hemisphere of Schmidt equal area stereonets, The terminology of Sanders (1942) i s followed with respect to the 59 f a b r i c d i r e c t i o n s . Three mutually perpendicular f a b r i c axes are referred to as a, b and c where a and b are i n the:plane of bedding and c i s perpendicular to a and b . The b axis i s p a r a l l e l or subparallel to the f o l d axis (B) or, i n the case of homoclinal seguences, i t i s defined as p a r a l l e l to the s t r i k e of the seam. In order to deduce the kinematic picture and dynamic history, slickenside s t r i a e are represented i n stereographic projection by a portion of the great c i r c l e which passes through the pole to the shear surface and the slickenside s t r i a e . . The plotted segments are thus centered about the axis of rotation during s l i p on t h e i r respective surfaces (Hoeppener, 1955).. The sense of r e l a t i v e motion on the slickensided surface has been inferred from either the roughness or accretion methods (Norris and Barron, 1968) and where the d i r e c t i o n of motion i s deduced an arrowhead i s used to show the r e l a t i v e motion of the hanging wall. The orientation of the intermediate p r i n c i p a l stress at f a i l u r e (^ 2) i s uniquely defined by the axis of rotation of the s l i p l i n e a r s . . The orientation of the maximum p r i n c i p a l stress (61) and l e a s t p r i n c i p a l stress (63), however, can be inferred only from the character and symmetry of the. j o i n t and cleat systems. According to theories of b r i t t l e fracture and laboratory t e s t s , tension (extension) fractures occur between complementary sets of shear fractures and the acute angle between the shear fractures i s bisected by <£l (Stearns, 1968, Friedman, 1975). Without representatives from a l l three sets i t may not be possible to resolve the stress geometry during deformation (Norris, 1S67). Also, i t i s not always possible to 60 d i f f e r e n t i a t e regional fractures from those associated with a p a r t i c u l a r structure (Currieand Reik, 1977), In t h i s study the geometry of fractures and th e i r interpretation are discussed in terms of the sub-patterns recognized and described by.Stearns (1964, 1968) VICARY CREEK MINE At the Vicary Creek mine the Kootenay Formation consists of 150 m of interbedded dark-grey to black shales, s i l t s t o n e s , dark-grey sandstones and three seams of medium-volatile bituminous c o a l . The formation occurs i n the immediate hanging wall of the Coleman Fault, a major west dipping thrust f a u l t with an estimated 2200 m of stratigraphic separation (Fig. .1-2). . A steep west-dipping splay of the Coleman Fault repeats the upper part of the Kootenay Formation i n the region of the mine s i t e . The Vicary Creek mine i s developed i n the uppermost coal seam which l o c a l l y i s named the Number 2 seam. The mine workings at the portal are located 50 m s t r a t i g r a p h i c a l l y above the Coleman Fault and 40 m below the overlying splay-fault., Within the mine workings, the Number 2 Seam strikes 170° and dips between 35° and 45° to the west (Fig. .3-1). The seam i s being mined by following the roof; nowhere i n the mine are f l o o r s t r a t a exposed. , Roof Rock C h a r a c t e r i s t i c s Lithology and Sedimentology: The immediate reef rock of the Number 2 Seam was mapped 3-1. Vicary Creek mine. (A) S t r u c t u r a l contour map on top of the Number 2 seam and p r i n c i p a l s t r u c t u r a l elements i n the roof rock. (B) J o i n t f a b r i c , contours are at 2, 5, 10, 15, and 20% per 1% area. (C) Extension f a u l t f a b r i c , poles (•) , axes of s l i p (">) , and s l i p l i n e a r s (—) , 'b' i s the b f a b r i c d i r e c t i o n of the seam. 62 throughout the accessible part of the mine.. Two l i t h o f a c i e s are recognized (Fig. 3-1); a thick-bedded sandstone l i t h o f a c i e s which occurs i n the southern portion of the mine workings and a thin-bedded sandstone and s i l t s t o n e l i t h o f a c i e s present i n the northern part of the mine. The t r a n s i t i o n between the two l i t h o f a c i e s i s gradational and i s not well exposed. The thick-bedded sandstone l i t h o f a c i e s consists predominantly of f i n e -grained, p a r a l l e l to ir r e g u l a r bedded, quartzose sandstone. The thin-bedded sandstone and s i l t s t o n e l i t h o f a c i e s i s composed of fine-grained, wavy to irre g u l a r bedded, carbonaceous sandstones and s i l t s t o n e s , discrete coaly laminae, very t h i n seams of coal and carbonaceous shale. , Strata overlying the immediate roof rock are v i s i b l e only i n areas of caving. In caved areas the immediate roof rock appears to p e r s i s t s t r a t i g r a p h i c a l l y f o r at least 0.5 m. Loc a l l y , thin seams of coal or thin beds of carbonaceous shale are present 1 m to 3 m above.the immediate roof. Very l i t t l e sedimentological evidence i s provided by the immediate reef rock .. Generally, however, the f a c i e s change from the thick-bedded sandstone l i t h o f a c i e s in the south, to the thin-bedded sandstone and s i l t s t o n e l i t h o f a c i e s to the north i s sim i l a r to f a c i e s change from proximal to d i s t a l crevasse splay deposits documented from recent and extensively studied ancient d e l t a i c environments (Eeineck and Singh, 1973; Home et a l . , 1978). The t r a n s i t i o n from swamp conditions responsible f o r formation and accumulation of the coal (peat) i s abrupt in the southern part of the mine, attesting to rapid i n f l u x of c l a s t i c d etritus during flooding and inundation of the swamp. In the 63 northern part of the mine, however, contemporaneous lower energy conditions prevailed, resulting i n the deposition of f i n e r grained sediment and possibly periodic re-establishment of the swamp prior to complete destruction of the peat forming environment. Structural Fabric of the Coal and Eoof Rock: In the Vicary Creek mine the main mesoscopic s t r u c t u r a l f a b r i c elements are extension f a u l t s , small folds, j o i n t s and slickenside s t r i a e on bedding planes. Figure 3-1 summarizes the d i s t r i b u t i o n and orientation of some of the s t r u c t u r a l elements. The d i s t r i b u t i o n of folds and f a u l t s shown on the accompanying st r u c t u r a l contour map (Fig. ,3-1) r e f l e c t s in part the a c c e s s i b i l i t y to various parts of the mine, but also i s representative of the clustering of the structures. From the modal attitude of the coal seam the ac f a b r i c plane and the b d i r e c t i o n are defined and are plotted together, with poles to joi n t s and f a u l t s on the stereonets shown i n Figs.. 3-1B and 3-1C. Extension f a u l t s occur throughout the mine (Figs. 3-1A and 3-2) and have str a t i g r a p h i c separations varying from a few millimetres to two metres. They cut bedding at angles close to 60°, i n agreement with the mean dip of extension f a u l t s reported i n other coal mines in the southeastern C o r d i l l e r a by Norris (1958). Although the orientation of the f a u l t s shows considerable scatter there i s a f a i r l y d i s t i n c t maximum which l i e s i n Okl (Fig. 3-1A). Only one contraction f a u l t was observed in the underground workings; i t l i e s i n Okl and has a F i g u r e 3-2. Northwest d i p p i n g e x t e n s i o n f a u l t w i t h about 0.5 m o f s t r a t i g r a p h i c s e p a r a t i o n i n the r o o f rock i n the V i c a r y Creek mine. S t e r e o - p a i r . <7l 65 stratigraphic separation of 1 m. The paucity of contraction f a u l t s in underground coal mines i n the southeastern Canadian C o r d i l l e r a was previously noted by Norris (1958), who has reported that extension f a u l t s out number contraction f a u l t s by 10:1. In open p i t mines adjacent to the underground workings at Vicary Creek, several contraction f a u l t s were mapped which l i e in hOl and cut the roof s t r a t a at angles between 10° and 35°. , Such contraction f a u l t s , i f present, would be d i f f i c u l t to recognize i n the underground mine. Concentric, north to northwest plunging f o l d s with amplitudes ranging from 1 m to 2 m and with wavelengths up to 6 m occur at several l o c a l i t i e s (Fig..3-1). Although the folds are not numerous they result i n exceedingly poor roof conditions and are described in a l a t e r section. Jointing i n the roof rock i s r e s t r i c t e d to the thick-bedded sandstone l i t h o f a c i e s . Tie j o i n t system i s summarized i n F i g . 3-1B and i s d i v i s i b l e into three d i s t i n c t sets. One set l i e s in the ac f a b r i c plane (OkO), whereas the other two sets l i e in hkl. The acute angle between them i s about 30° and i s bisected by the ac f a b r i c plane of the roof rock. No c h a r a c t e r i s t i c surface markings were noted on any of the j o i n t s . Slickenside s t r i a e on bedding elements are present throughout the mine and are p a r t i c u l a r l y prevalent i n the t h i n l y bedded sandstone and s i l t s t o n e l i t h o f a c i e s . In these str a t a , i n t e r s t r a t a l s l i p was f a c i l i t a t e d by carbonaceous laminae and i t now imparts a slabby to platy s p l i t to the roof rock and destroyed the interbed cohesion. •Kinematic Analysis S l i p l i n e a r s are rarely present on polished surfaces i n the coal even though shear surfaces pervade the coal seam i t s e l f , and those present define a random f a b r i c attesting to subsequent deformation and rotation. Consequently, the following discussion i s based l a r g e l y on the kinematic pattern determined from the roof and f l o o r rock and adjacent strata rather than the coal seam.. S l i p l i n e a r s and the axis of rotation during s l i p measured on bedding surfaces of the immediate roof rock are presented i n F i g . 3-3. In aggregate the axis of rotation defines a nodal kinematic-t axis for s l i p which i s nearly ho r i z o n t a l , trends 170°, and i s almost p a r a l l e l to the defined b fa b r i c axis of the seam. In addition to t h i s well defined axis of s l i p , there i s a second population of s l i p axes which i s also sub-horizontal, but trends 195°,.. Cross-cutting relationships between the two populations of s l i p l i n e a r s observed at two l o c a l i t i e s indicate that motion about the b-fabric axis of the seam preceded the oblique motion. Measurement of well-defined slickenside s t r i a e on extension f a u l t s was rarely possible i n the underqround workings. The few measurements made (Fig. 3-1C) show a broad scatter of axes of s l i p that are more or less p a r a l l e l to the a fa b r i c d i r e c t i o n of the seam. The r e l a t i v e timing of extension f a u l t i n g and i n t e r s t r a t a l s l i p i s not evident in the underground workings.. Consequently, measurements were made of slickenside st r i a e on bedding surfaces and extension f a u l t s in the roof and fl o o r 67 N W f / v \ • \ • 1 — • * / • / \ *  / ' * / X. \ . • • F i g u r e 3 - 3 . V i c a r y C r e e k mine.. P o l e s (©) , axes o f s l i p ( B ) , and s l i p l i n e a r s (-*-)' o f s l i c k e n s i d e d b e d d i n g s u r f a c e s and t r e n d and p l u n g e o f f o l d s i n t h e r o o f r o c k (*F) . N / a • / ° 1 * D \ °a O p \ 0 ° _D ° 0, nrn o D O r * n D O -e- o ° "° ° \ ° ^ ' O o a * „ o °° * / • j s F i g u r e 3 - 4 . P o l e s ( o ) , axes o f s l i p (©) and s l i p l i n e a r s {-&•) o f s l i c k e n s i d e d b e d d i n g s u r f a c e s , and p o l e s ( • ) , axes o f s l i p (a) and s l i p l i n e a r s (•&) o f e x t e n s i o n f a u l t s and p o l e s (A) t o c o n t r a c t i o n f a u l t s i n the now abandoned Race H o r s e s t r i p mine n o r t h o f t h e V i c a r y C r e e k m i n e . 68 strata of an abandoned open pit mine developed i n the Number 2 seam to the north of the underground mine. . The.axes of s l i p of extension f a u l t s and on bedding surfaces are cozonal, horizontal to sub-horizontal, and closely approximate the defined b f a b r i c d i r e c t i o n of the seam (Fig. 3 - 4 ) . At t h i s l o c a l i t y many extension f a u l t s i n the f l o o r of the seam are o f f s e t up to 50 cm i n an up dip di r e c t i o n indicating that f a u l t i n g , at least i n part, has preceded i n t e r s t r a t a l s l i p . . Other extension f a u l t s that are not o f f s e t may post-date i n t e r s t r a t a l s l i p . Unlike the extension f a u l t s in the underground mine that l i e i n Okl or hkl, the f a u l t s i n the open p i t mine l i e i n hOl. Hence, extension f a u l t s i n the underground mine may not be related to the same deformational event, or may not have the same deformational history as those i n outcrop. , The reason why the orientations of the f a u l t s are so di f f e r e n t i s not evident. . In order to relate the l o c a l kinematic pattern evident i n both the mine and adjacent outcrops to the regional structural pattern slickenside striae.on shear surfaces within the Coleman Fault plane were measured. . The measurements were made d i r e c t l y below the mine portal, in a wedge of highly sheared green mudstone and s i l t s t o n e cf the Crowsnest Volcanics Formation which l i e s within the Coleman Fault., Figure 3-5 summarizes the orientation of the s l i p l i n e a r s and associated axes of s l i p . Although the shear planes are curved, a d i s t i n c t preferred orientation of the s l i p axes i s evident which defines a modal kinematic b-axis that i s nearly horizontal, and closely p a r a l l e l s the defined t - f a b r i c d i r e c t i o n of the coal seam and the modal kinematic-b axis during s l i p . In addition to t h i s / • / • • / • / * v • • \ ••• - I ~-—* • j. • • • X s Figure 3-5. Poles (•), axes of s l i p (•) and s l i p l i n e a r s {-+•) of shear surf aces . w i t h i n the Coleman F a u l t plane, about "50"m below the p o r t a l of the V i c a r y Creek mine. F i g u r e 3-6. B a c k - l i m b r e v e r s e f a u l t i n a f o l d i n the Number 2 seam above the p o r t a l a t t h e V i c a r y C r e e k m i n e . O f f s e t a c r o s s t h e f a u l t i s a b o u t 3 m. 70 well defined axis of s l i p , there i s a scatter of s l i p axes which are generally subhorizontal and trend east-northeast. This group i s generally of similar orientation to the second, younger set of kinematic-b axes observed i n roof strata of the mine (Fig. 3-3); hence they may be.products of the same.period of movement. Dynamics of Deformation The mesoscopic f a b r i c of the roof rock and associated outcrops provides evidence f o r at least three periods of deformation each which may represent a d i f f e r e n t deformational phase i n which the orientation of 1 was d i f f e r e n t . These are: 1) extension f a u l t i n g , i n which the kinematic-b axis paralleled the b f a b r i c d i r e c t i o n (open p i t mine); 2) i n t e r s t r a t a l s l i p , i n which the kinematic-b axis c l o s e l y p a r a l l e l e d the b fabric d i r e c t i o n ; and 3) a l a t e r stage of i n t e r s t r a t a l s l i p , i n which the kinematic-b axis was sub-horizontal and trended to the southwest-northeast. Based on the symmetry of the jo i n t system i n the roof rock, jointing i s considered contemporaneous with the f i r s t phase of i n t e r s t r a t a l s l i p as discussed l a t e r . There i s no evidence for the chronology of the extension f a u l t s i n the underground mine. On a regional scale a late stage of normal f a u l t i n g i s evident but i t does not appear to be geometrically or g e n e t i c a l l y related to the measured f a u l t s i n the mine, and i s therefore not considered here. The kinematic-b axis of mesoscopic f a b r i c elements uniquely defines the l o c a l orientation of 62 at f a i l u r e . The near parallelism of the modal kinematic-b axis of some extension 71 f a u l t s , i n t e r s t r a t a l s l i p surfaces, and shear surfaces i n the Coleman Fault plane indicates that c?2 maintained a nearly horizontal, northerly trend throughout deformation.. I t further suggests that a genetic rel a t i o n s h i p exists between the structures. Extension f a u l t s cozonal with i n t e r s t r a t a l s l i p surfaces, although they i n part c l e a r l y precede some i n t e r s t r a t a l s l i p , also probably followed at least some rotation of the coal measures. . Otherwise, i t would be completely fortuitous that the structures are cozonal. Independent indicators of the orientation of <^1 during extension f a u l t i n g are absent. However, 6\ can be considered to have been oriented approximatly normal to bedding at f a i l u r e , i n keeping with experimental observations (Griggs and Handin, 1960), and as documented i n other coal mines by Norris (1967)., The close agreement between the kinematic-b axis during i n t e r s t r a t a l s l i p of the rcof rock and the defined b-fabric d i r e c t i o n of the coal seam i s s i m i l i a r to that expected during f l e x u r a l s l i p folding of eequences i n which a planar anisotropy ex i s t s (Donath and Parker, 1964). I n t e r s t r a t a l s l i p probably occurred, at least i n part,, during.buckling of the coal measures i n response to rotation on the.Coleman Fault, as suggested by the congruence of t h e i r respective kinematic-b axis. A component of i n t e r s t r a t a l s l i p may also be related to shortening within the Coleman Fault plane as a r e s u l t of overriding thrust sheets as has been suggested i n some other areas by Norris (1958) and evident from the l o c a l structure adjacent the mine (Fig. 3-6). The orientation of (>1 during i n t e r s t r a t a l s l i p can show considerable angular variation with respect to bedding 72 (Donath and Parker, 1964). The symmetry of the j o i n t system in the roof rock, however, provides an independent estimate of the stress geometry at f a i l u r e . By analogy with the symmetry of extension and shear fractures produced i n laboratory studies and documented in the f i e l d (Donath, 1963; Stearns, 1968; and others), the conjugate j o i n t sets i n the roof rock are considered to be shear fractures whereas the set p a r a l l e l to the ac f a b r i c d i r e c t i o n are extension fractures. The stress geometry at f a i l u r e thus indicates that the maximum pri n c i p a l stress was p a r a l l e l with the a f a b r i c d i r e c t i o n of the seam and in close agreement with that predicted from the regional di r e c t i o n of tectonic shortening. The l a t e r stage of i n t e r s t r a t a l s l i p evident from s l i p l i n e a r s i n the roof strata suggests that some re-oriexitation of the stress f i e l d occurred during the l a t e r stages of deformation. Relationship Between Roof Conditions and Geology In the Vicary Creek mine, a close c o r r e l a t i o n exists between the two recognized l i t h o f a c i e s i n the roof rock and the roof conditions. The thin-bedded carbonaceous sandstone and s i l t s t o n e l i t h o f a c i e s forms a roof rock with a platy s p l i t . The s p l i t i s p a r a l l e l to bedding and occurs along carbonaceous laminae where i n t e r s t r a t a l s l i p has destroyed the cohesion between beds (Fig. 3-7). The thick-bedded sandstone l i t h o f a c i e s , on the other hand, i s commonly well jointed, r e s u l t i n g i n a blocky roof rock i n which roof f a i l u r e i s f a c i l i t a t e d along joint planes (Fig..3-8). In addition to the above association, a good cor r e l a t i o n exists between the type of F i g u r e 3 - 7 . T h i n - b e d d e d c a r b o n a c e o u s r o o f r o c k w h i c h has p a r t e d and caved a l o n g s l i c k e n s i d e d c a r b o n a c e o u s l a m i n a e . Roof b o l t i n u p p e r -most l e f t o f t h e p h o t o g r a p h f o r s c a l e . F i g u r e 3 - 8 . T h i c k - b e d d e d , w e l l j o i n t e d and p a r t i a l l y c a v e d r o o f r o c k . The c a v i t y i s c o n t r o l l e d by j o i n t i n g and b e d d i n g . Beds a r e a b o u t 20 cm t h i c k . 74 roof rock and the extent of f r a c t u r i n g of the coal seam. The thin-bedded sandstone and s i l t s t o n e l i t h o f a c i e s i s associated with less extensively sheared coal than either the thick-bedded sandstone l i t h o f a c i e s or areas i n which the upper portion of the seam i s composed of d u l l coal.. Such an association suggests that the thin-bedded sandstone and s i l t s t o n e l i t h o f a c i e s f a c i l i t a t e d i n t e r s t r a t a l s l i p along the roof of the seam during deformation, or within the immediate roof rock. On the other hand, where the upper portion of the seam contains either d u l l c o al, which i s more competent, or thick-bedded sandstone-, i n t e r s t r a t a l s l i p apparently occurred to a.greater extent within the seam. . Shearing and comminution of the coal as a result of i n t e r s t r a t a l s l i p has markedly reduced the bearing capacity of the coal p i l l a r s . Failure of the coal r i b s r esults from 'flow' of the coal out of the r i b s rather than by f a i l u r e along discrete surfaces. Calculations of the bearing capacity of p i l l a r s developed i n such highly sheared coal would require considering the coal as a pre-failed aggregate already past peak strength, and within the region of s t r a i n softening. Local variations i n the roof-rock c h a r a c t e r i s t i c s are associated with f a u l t s and folds. Extension f a u l t s disrupt the adjacent roof rock, and f a c i l i t a t e f a i l u r e along sheared bedding planes. . None of the observed extension f a u l t s completely o f f s e t the seam. It i s impossible, however to predict the orientation cr l o cation of the minor f a u l t s even to adjacent roadways.. Small folds in the roof rock are associated with p a r t i c u l a r l y bad roof conditions. The bedding surfaces of the folds are extensively slickensided as a r e s u l t of f l e x u r a l s l i p , which has 7 5 destroyed the cohesion between successive bedding planes. An associated problem i s the l o c a l s t r u c t u r a l thickening and thinning of the seam associated with folding.. Because of the highly sheared character of the coal i t i s not possible to hold coal i n the roof. . Consequently, i n areas of s t r u c t u r a l thickening, the coal must be either completely removed or s p e c i a l supports emplaced.. As i n the case of f a u l t s , the occurrence of f o l d s i s unpredictable.. Once located, however, the folds can be projected to adjacent roadways with confidence. In several areas roof f a i l u r e i s associated with the occurrence of coal i n the strata overlying the immediate roof rock. The coal seams provide poor anchorage for roof bolts and form major d i s c o n t i n u i t i e s . The coal i s not evident i n outcrop adjacent the. mine s i t e and may either represent a f a u l t repeat of part of the Number 2 Seam or a separate seam of r e s t r i c t e d l a t e r a l continuity, BALMEB NOETH, SIX PANEL AND FIVE PANEL MINES The Balmer North, Six Panel and Five Panel mines are located at the ncrth end of the Fernie synclinorium, a major stru c t u r a l element on the Lewis thrust plate (Fig..1-2). The Fernie synclinorium i s s t r u c t u r a l l y discordant with the underlying Paleozoic strata (Dahlstrom, 1969) and i s characterized by northerly trending, broad, open, doubly plunging f o l d s with curved a x i a l surfaces. . The Balmer North mine i s located cn the nest dipping flank of the gently south-plunging Natal syncline, whereas the Six Panel and Five Panel mines are located on the east dipping flank of the Michel 76 syncline (Fig. 3-9).. Between the Michel and Natal synclines i s a r e l a t i v e l y low amplitude, faulted a n t i c l i n e . . The eastern flank of the a n t i c l i n e i s upthrown, with a stratigraphic separation on the order of 100 m, along two p a r a l l e l high angle reverse f a u l t s which have been referred to as the Mackay f a u l t (s) by Crabb (1962). The Kootenay Formation i n the region of the mine s i t e i s about 600 m thick and contains 11 coal seams ranging from 1 m to more than 12 m thick. . The Balmer North, Six Panel and Five Panel mines are developed i n the thickest and lowest seam of mineable thickness, referred to as the Balmer seam. Within the Balmer North mine the Balmer seam str i k e s 1700 and dips between 15° and 40o to the west. In the northeastern part of the mine the seam dips gently to the east. In the Six Panel and Five Panel mines, the Balmer seam str i k e s approximately 178° and dips between 35° and 47° to the east. In a l l of the mines, henceforth referred to c o l l e c t i v e l y as the Michel mines, the seam i s being mined following the roof. The Balmer North mine and Six Panel mines are presently being mined using continuous miners, whereas i n the Five Panel mine, hydraulic methods are used. Because of the mining method i n the Five Panel mine and because the Six Panel mine i s s t i l l i n the development stage, observations were limited primarily to v e n t i l a t i o n raises. The data collected in these mines are thus largely r e s t r i c t e d to cleat measurements i n the coal and j o i n t measurements i n the rock tunnels. In the Balmer North mine access to d i f f e r e n t areas was excellent and i t was possible to obtain data from a number of p a r t i a l l y caved areas. In the following discussion 77 the Balmer North, Six Panel and Five Panel mines are considered c o l l e c t i v e l y because of t h e i r s i m i l i a r s t r u c t u r a l s t y l e and roof rock c h a r a c t e r i s t i c s . . More emphasis i s placed, however, on observations i n the, Balmer North mine because of i t s greater a c c e s s i b i l i t y . , " Roof Rock Cha r a c t e r i s t i c s Lithology and Sedimentclogy: The immediate roof rock of the Balmer seam consists of highly carbonaceous shales, s i l t s t o n e s and mudstones. The contact between the Balmer seam and the roof rock i s gradational over 0.5 m to 1.0 m i n the Balmer North mine, whereas i n the Six Panel and Five Panel mines the contact i s more abrupt. Generally, however, there i s no notable l a t e r a l variation i n lit h o l o g y of the roof rock at the scale of the mine. In the Balmer North mine, the immediate roof rock consists of carbonaceous s i l t s t o n e s , shales and mudstones which pass upwards to t h i n - to thick-bedded, f i n e - to medium-grained sandstones with rare carbonaceous laminae.. The sandstones are p a r a l l e l to wavy bedded, whereas the mudstones and s i l t s t o n e s are primarily homogeneous. Locally, well preserved plant remains are present on thfe bedding planes of the mudstones. In the Five Panel and Six Panel mines the roof rock consists of carbonaceous s i l t s t o n e s and shales that grade upward into t h i n - to medium-^bedded, f i n e - to medium-grained sandstone. The shales, s i l t s t o n e s and sandstone are p a r a l l e l to wavy bedded. Similar to the Vicary Creek mine, l i t t l e diagnostic 7 8 sedimentological evidence i s provided by the roof rock i n the Michel mines. The gradational contact between the Balmer seam and roof rock does, however, indicate gradual abandonment of the swamp areas and slower rates of c l a s t i c sediment i n f l u x compared to the more abrupt transitions, i n the Vicary Creek mine area. . Structural Fabric of the Coal and Roof Rock: In the Michel mines the major mesoscopic structural f a b r i c elements are extension f a u l t s , j o i n t s and c l e a t . Slickenside s t r i a e on bedding elements i n the roof rock could be measured only at a few l o c a l i t i e s because of the height of the roof and the presence of thick rock dust. Extension f a u l t s , although present throughout the mines, rarely have displacements exceeding 20 cm. The only major extension f a u l t observed occurs i n the northern part of the Balmer North mine. This f a u l t dips steeply to the west and has a displacement of 1.5 m to 3 m. Figure 3-10 summarizes the s l i p l i n e a r s , axes of s l i p and poles to extension f a u l t s with displacements greater than 5 cm. Although the orientation of f a u l t s show considerable scatter, the majority are p a r a l l e l or sub-parallel to the fold.axis ( l i e i n hOl).. Most extension f a u l t s cut bedding at angles between 10° and 35° and have an angular rotation component of between 5° and 30°. Jointing i s pervasive i n medium- to thick-bedded sandstones above the immediate roof rock and in the footwall strata of the Balmer seam throughout the Michel mines. The orientation of the j o i n t s measured at l o c a l i t i e s within the access rock tunnels to the mines are summarized in Fig..3-9. 79 N / • • / •* ••»" , / _ \ • ~* mK. .+ "1 . • S \ f \ • ' " \ % g - - ' \ * •J<f\-• • / • • . / • / • • / • s F i g u r e 3-10. Balmer n o r t h mine. Summary diagram o f po l e s (•), axes of s l i p ('•) and s l i p l i n e a r s (—) of e x t e n s i o n f a u l t s f o l l o w i n g r o t a t i o n o f bedding to the h o r i z o n t a l . F i g u r e 3-11. Balmer North mine. Young, west d i p p i n g shear s u r f a c e i n c o a l r i b . 80 The joints are planar, have no surface markings and impart a flaggy to blccky s p l i t to the rocks. In the Five Panel rock tunnel a well developed steep westerly dipping j o i n t set which i s p a r a l l e l to the f o l d axis (hOl) i s present at a l l three sample l o c a l i t i e s . In addition, at sample stations N and 0, there i s a prcminent, nearly v e r t i c a l joint set which l i e s in OkO. At stations M and 0 j o i n t sets l i e i n hkO. In the Balmer North mine (station A), only one prominent joint set which l i e s in hkO, i s present. In the Six Panel mine (station T) the j o i n t system i s poorly developed. Cleat: Cleat, the naturally occurring fractures (joints) i n coal, was measured at sample l o c a l i t i e s throughout the underground mines in order to determine i f a consistent or predictable orientation exists and to interpret t h e i r o r i g i n . The importance of c l e a t orientation in mining practice i s well documented. Coal has been mined p a r a l l e l to the d i r e c t i o n of the major c l e a t to take advantage of the preferred parting since the advent of coal mining. The orientation of the cleat system also r e s u l t s i n a strong permeability anisotropy which i s important i n degassing the coal seam prior to mining (McCullock, et a l . , 1974; hcCullock et a l . , 1976) and both the orientation and spacing of the c l e a t influence the bearing strength of coal p i l l a r s and the s i z e - c c n s i s t of run-of-the-mine coal (Touseull, 1977). In most coal seams two major cleat sets are recognized, which are referred to as face and butt c l e a t . The face cleat i s the major fracture set within the coal seam whereas the butt 81 cleat i s short, generally poorly defined, and commonly truncated at angles cf about 90° by the face c l e a t . Invariably, the face and butt cleat have been reported to be perpendicular to bedding. Many of the previous studies on the o r i g i n and orientation of cleat have been summarized by McCullock et a l . , (1974). The o r i g i n of cleat has been considered either endogenetic, related to compaction and c o a l i f i c a t i o n , or exogenetic, related to tectonic forces. In the Michel mines the d i s t i n c t i o n and c l a s s i f i c a t i o n of cleat as face or butt i s not possible. Cleat measurements, summarized in F i g . 3-9, show that at some l o c a l i t i e s up to f i v e d i s t i n c t sets of cleat i s present, none of which are necessarily perpendicular to bedding, whereas at other l o c a l i t i e s , no d i s t i n c t cleat sets are present. In the Balmer North mine, both systematic and nonsystematic c l e a t sets occur at most sample l o c a l i t i e s (Fig. 3-9). The most prominent systematic c l e a t set (following rotation of bedding to the horizontal) dips between 5° and 15° to the west and l i e s i n hOl. This c l e a t set i s p a r a l l e l to the major set of extension f a u l t s , has polished and commonly slickensided surfaces and truncates, and in some areas o f f s e t s , other cleat sets (Fig. 3-11). Other systematic c l e a t sets present at some l o c a l i t i e s include northeasterly and northwesterly trending sets which l i e in hkO. The surface of these cleat sets are commonly polished, and l o c a l l y there are radiating, s t r i a t e d structures somewhat resembling chevron marks occurring. Other well defined cleat sets occur at p a r t i c u l a r stations but are not represented at adjacent s i t e s . 82 In the Five and Six Panel mines, a systematic cleat set i s present at a l l sample l o c a l i t i e s . This c l e a t s t r i k e s north to northwesterly, and i s perpendicular to sub-perpendicular to bedding (hkO to h k l ) . It i s planar, commonly polished and spaced at between 10 cm and 40 cm, imparting a blocky s p l i t to the coa l . At l e a s t one additional systematic c l e a t set i s present at most l o c a l i t i e s which st r i k e s in a north to northeasterly d i r e c t i o n , and i s sub-perpendicular to bedding (hkl to hkO). The c l e a t sets are planar, but not always well developed, and t h e i r surfaces are commonly d u l l . C o l l e c t i v e l y , the c l e a t sets i n the Five and Six Panel mines show l i t t l e or no preferred orientation with respect to the f a b r i c axis of the syncline. At many i n d i v i d u a l sample l o c a l i t i e s , however, the north and northeasterly s t r i k i n g c l e a t sets are symmetrically disposed such that the acute angle between them i s bisected by the l o c a l ac f a b r i c plane of the seam. The north to northwest s t r i k i n g c l e a t sets at most l o c a l i t i e s are close to p a r a l l e l with the l o c a l Jb f a b r i c d i r e c t i o n of the seam as determined by the orientation of the roof rock. Kinematic Analysis S l i p l i n e a r s and axes of s l i p on c l e a t surfaces, together with the medal poles to systematic c l e a t sets following rotation of bedding to the horizontal, measured i n the Balmer North mine, are shown in Fig. 3-12B through 3-12L; a composite of a l l s l i p axes on c l e a t surfaces and extension f a u l t s are shown i n F i g . 3-13. Throughout the Balmer North mine s l i p l i n e a r s on bedding and cleat surfaces define one major preferred orientation, more 83 Figure 3-12. Summary of axes of s l i p (a), s l i p l i n e a r s (-*-) , and modal poles to cl e a t sets (.©) following r o t a t i o n of bedding to the h o r i z o n t a l . Balmer North mine (stations B through L ) , Five Panel mine (station P) and Six Panel mine (stations Q, R, S, U, V, W, and X). 86 Q,R,S. B u,v,w,x. u * . / X / w • \ »u \ *w \ w,x \ • \ » V w / -r B 87 N F i g u r e 3 - 1 3 . B a l m e r N o r t h m i n e . Summary o f axes o f s l i p on b e d d i n g s u r f a c e s and e x t e n s i o n f a u l t s ( • ) . 88 or l e s s within the ac f a b r i c plane (deformational plane) of the f o l d ; thus, the modal kinematic-b axis during s l i p closely approximates the f o l d axis. Other s l i p l i n e a r s show considerable scatter and do not define a preferred orientation. Also, they do not appear to be geometrically related either to the l o c a l or regional f a b r i c axis of the seam.. S l i p l i n e a r s and associated axes of s l i p of extension f a u l t s (Fig 3-10) i n the Balmer North mine, considered i n aggregate, indicate the presence of two poorly defined kinematic patterns. The f i r s t i s defined by s l i p l i n e a r s which are sub-parallel to the ac plane of the f o l d , with axes cf s l i p which diverge from the fold axis by up to 159. The second pattern i s also poorly defined and i s characterized by s l i p l i n e a r s which l i e i n hkl, trend i n a more or less northerly d i r e c t i o n and have axes of s l i p which plunge gently to the east. In the Five Panel and Six Panel mines, the s l i p l i n e a r s and axes of s l i p (Fig. 3-12P through 3-12X) show one major preferred orientation of s l i p that c l o s e l y p a r a l l e l s the ac f a b r i c plane, and has a modal kinematic-b axis of s l i p which approximates the f o l d axis. Additional s l i p l i n e a r s which l i e in hkl show a wide dispersion and are not r e a d i l y related to either the geometry of the f o l d nor the l o c a l f a b r i c axis of the seam. The preferred orientation of s l i p l i n e a r s and axes of s l i p i n the Balmer North mine and in the Five and Six Panel mines are congruent with the geometry of the synclines, which suggests that a genetic r e l a t i o n s h i p e x i s t s . A l l s l i p l i n e a r s which are cozonal with the ac deformation plane of the f o l d i n the Balmer North mine, l i e on the pervasive and best developed 89 c l e a t set, which dips gently to the southwest and cuts bedding at angles between 10° and 150. The d i r e c t i o n of motion can rarely be inferred from the s l i p l i n e a r s but, where possible, they invariably suggest southwest transport of the hanging wall, p a r a l l e l to that of some extension f a u l t s . Although the congruence of the axis of s l i p with the f o l d axis suggests a genetic r e l a t i o n s h i p , the d i r e c t i o n of motion and the parall e l i s m with some extension f a u l t s i n the roof strata suggests that they are i n c i p i e n t extension f a u l t s . . Furthermore, the direction of motion i s a n t i t h e t i c to that which would be predicted during f l e x u r a l s l i p . In the Five and Six Panel mines s l i p l i n e a r s sub-parallel to the ac deformation plane of the . seam l i e mainly on c l e a t surfaces which dip steeply to the east following rotation of bedding to the horizontal.. I f the cleat set formed l a t e , however, the s l i p l i n e a r s could have formed as westerly dipping shear surfaces. The direction of the motion of the hanging wall on these surfaces i s unknown. Dynamics of Deformation The orientation of the major f o l d s , including the Michel and Natal synclines and adjacent reverse and thrust f a u l t s i n the region of the Michel mines indicates a consistent d i r e c t i o n of shortening i n a northeasterly d i r e c t i o n . The geometric rel a t i o n s h i p between j o i n t and cleat sets at the sample l o c a l i t i e s does not, however, suggest a consistent stress geometry during deformation.. In Fig . 3-14A and 3-14B the acute b i s e c f r i c e s between a l l cleat sets showing some evidence of shear at l o c a l i t i e s in a l l the mines are plotted. I f the shear 90 F i g u r e 3 -14B. F i v e and S i x P a n e l m i n e s . A c u t e b i s e c t r i c e s o f c l e a t s e t s w h i c h show some e v i d e n c e o f f o r m i n g as a r e s u l t o f s h e a r f r a c t u r e . 91 surfaces are conjugate sets and related to the same stress geometry then t h e i r acute b i s e c t r i c e s should approximate <->1 (Stearns, 1968) and have a more or l e s s consistent orientation, which i s not the case. Furthermore, no simple rotation about any axis w i l l decrease the observed dispersion., The observed dispersion of the acute b i s e c t r i c e s at the d i f f e r e n t sample l o c a l i t i e s may r e f l e c t inhomogeneities of the strata and th e i r anisotropy (Price, 1967; Curry and Eeik, 1977), superimposed stress geometries r e s u l t i n g i n a chaotic f a b r i c or highly divergent stress f i e l d s . at most l o c a l i t i e s i n the Five Panel and Six Panel mines conjugate cleat and j o i n t sets are bisected by the l o c a l l y defined ac f a b r i c plane of the seam determined from the l o c a l orientation of the.roof rock. . The cl e a t sets have polished surfaces which, i n conjunction with t h e i r symmetry, suggests that they are conjugate shear fractures formed during b r i t t l e fracture with <^1 p a r a l l e l to the l o c a l a f a b r i c d i r e c t i o n s i m i l i a r to the type 1 fractures of Stearns (1968). The coincidence of the acute b i s e c t r i x of the conjugate cleat and joint sets further suggests that the fracture patterns are related to the l o c a l stress f i e l d of varying geometry rather than one o v e r a l l stress f i e l d related to the general f o l d pattern.. The north trending, nearly v e r t i c a l c l e a t set present at most sample l o c a l i t i e s show considerable variation i n orientation. These fracture surfaces rarely show evidence of displacement, suggesting an extensional o r i g i n . However, they are not si n g u l a r l y diagnostic of any p a r t i c u l a r stress geometry. In the Balmer North mine, with the exception of the well defined west dipping c l e a t set that p a r a l l e l s extension f a u l t s , 92 there i s no consistent cleat or j o i n t system among the sample l o c a l i t i e s . Furthermore, only at sample station L (Fig. 3-9L) i s there any apparent geometric relationship between conjugate cl e a t sets and l o c a l f a b r i c d i r e c t i o n s of the seam. a t t h i s l o c a l i t y the acute b i s e c t r i x between conjugate cleat sets i s close to p a r a l l e l to the l o c a l a f a b r i c d i r e c t i o n , which suggests that these sets are probably conjugate shear fractures. The orientation of &\ for formation of the fractures i s thus coincident with, and thus probably related to the stress geometry during l o c a l flexure of the seam. ftt other sample stations i n the Balmer North mine there are no apparent geometric relationships between cl e a t and l o c a l f a b r i c d i r e c t i o n of the seam. , Because of the d i v e r s i t y of c l e a t orientations at different l o c a l i t i e s , i t i s not possible to resolve the stress geometry at f a i l u r e . Moreover, i t cannot be established whether the present c l e a t pattern r e f l e c t s multiple stress geometries and f a i l u r e , or the ef f e c t of anisotropy of the.coal res u l t i n g from more than one episode of frac t u r e . The slickensided major west-dipping cleat set present in the Balmer North mine and the steep east-dipping set i n the Five and Six Panel mines both l o c a l l y o f f s e t other c l e a t sets and, therefore are probably younger., &s previously discussed, the coincidence of the axes of s l i p of the fracture.surfaces, the f o l d axis and seme extension f a u l t s suggests a genetic relationship e x i s t s . If these late-formed fractures are genetically related to folding and developed as a r e s u l t of extension due to bending or buckling, these fractures should p a r a l l e l the s t r i k e of the beds around the fold and their 93 orientation should change with the dip of the beds (Stearns, 1968). I f , however, they are related to a late stage of extension and normal f a u l t i n g , the fractures may have a si m i l a r orientation regardless of bedding orientation and dip. The orientation of bedding within the mines does not vary appreciably and thus neither of the above p o s s i b i l i t e s can be dismissed s o l e l y on the basis of the geometry. Most extension f a u l t s observed in t h i s study and i n studies by Norris (1958) and Sax (1946) cut bedding at preferred angles of 60". The shear fractures and many extension f a u l t s i n the Balmer North mine, however, occur at angles of 10° to 30° to bedding. Either such fractures and f a u l t s formed with ^1 orientated oblique to the v e r t i c a l and the f a b r i c d i r e c t i o n of the seam or the mechanical anisotropy of the coal measures f a c i l i t a t e d formation of shear at a highly acute angal to bedding.. Similar west dipping shear surfaces in the coal and westerly dipping extension f a u l t s have also been described by Norris (1964) from the now abandoned.A-North mine developed in the A seam and, l i k e the Balmer North mine, located i n the Natal syncline. The A seam i s s t r a t i g r a p h i c a l l y much higher in the Kootenay Formation than the Balmer seam but, s i g n i f i c a n t l y , both the axes of s l i p and direction of motion of the extension f a u l t s i n the A-North mine are nearly i d e n t i c a l to those reported here from the Balmer North mine. The A-North mine was located i n the hinge of the Natal syncline and the seam and the strata s t r i k e about 100°. The s i m i l a r orientation of extension f a u l t s and orientation of shear surfaces in the c c a l between the A-North and Balmer North mines, even though the s t r i k e of coal measures i s markedly 94 d i f f e r e n t , strongly suggests that the extension f a u l t s and west dipping shear surfaces are not genetically related to folding but rather, that they are la t e formed structures related to regional extension,. Geological Factors Affecting goof Conditions The a c c e s s i b i l i t y of p a r t i a l l y caved areas i n the Balmer North mine afforded an excellent opportunity to assess those geological factors a f f e c t i n g roof s t a b l i t y . , In the Six Panel mine, which i s under development, no observations of poor roof conditions were made and i n the Five Panel mine observations of poor roof conditions could only be made at a distance. In the Balmer North mine areas of poor roof conditions and p a r t i a l l y caved areas c h a r a c t e r i s t i c a l l y occur as narrow, northeasterly trending zones, . In the caved areas roof rock fractures which were kinematically active and control the geometry of roof f a i l u r e , are summarized i n Fig,,3-15. Roof f a i l u r e i s controlled by three d i s t i n c t s t r u ctural d i s c o n t i n u i t i e s i n the roof rock: 1) an easterly dipping set of slickensided fractures which i n t e r s e c t bedding at angles between 5° and 30°; 2) a westerly dipping set of slickensided fractures which cut bedding at preferred angles of 10° to 40°; and 3) slickensided bedding surfaces.. Most roof f a i l u r e s or partings of roof rock have occurred along the intersection of these s t r u c t u r a l d i s c o n t i n u i t i e s . , P a r t i c u l a r l y important i s the int e r s e c t i o n of bedding and the westerly dipping fracture set. The caved areas are invariably p a r a l l e l to the s t r i k e of the westerly dipping set (Fig. 3-16) and the dip of the fractures, N B a l m e r N o r t h m i n e . Summary o f p o l e s t o f r a c t u r e s (•) w h i c h h a v e f a c i l i t a t e d r o o f f a i l u r e and c o n t r o l t h e geometry o f c a v e s i n t h e r o o f r o c k and f a i l u r e o f c o a l . p i l l a P o l e t o b e d d i n g (H). F i g u r e 3-16A. B a l m e r N o r t h m i n e . P a r t i a l l y c a v e d roadway; low a n g l e , w e s t e r l y d i p p i n g s h e a r s u r f a c e s i n c o n j u n t i o n w i t h s t e e p , e a s t e r l y d i p p i n g s h e a r s u r f a c e s and s l i c k e n s i d e d b e d d i n g p l a n e s have promoted c a v i n g and c o n t r o l the- geometry o f c a v e s . F i g u r e 3-16B Caved r o o f r o c k showing west and e a s t d i p p i n g s h e a r s u r f a c e s a l o n g w h i c h t h e r o o f r o c k has s e p a r a t e d . 97 i n conjunction with the width of the roadways and raises, control the size of many of the caved areas. . Other areas of major roof problems i n the Balmer North mine are s o l e l y related to the absence of cohesion between successive bedding planes r e s u l t i n g from i n t e r s t r a t a l s l i p and the presence of incompetent strata i n the immediate roof rock of the seam. In these areas the lack of cohesion between successive beds has resulted i n poor anchorage of roof bolts which, i n conjunction with j o i n t planes and steeply dipping fractures, has f a c i l i t a t e d en masse f a i l u r e . c f roof rock (Fig. 3-17). F a i l u r e of coal ribs i s also closely related to c l e a t orientation in the Balmer North mine.. In roadways p a r a l l e l to the s t r i k e of the pervasive west dipping cleat set, the r i b s have sloughed or f a i l e d along these fracture surfaces (Fig, 3-11). Failure of the coal ribs i s less common along roadways or raises obligue to the major c l e a t sets; where f a i l u r e has occurred i t i s generally along induced 'rupture' fractures which are rough, curviplanar surfaces s i m i l i a r to the ruptured fracture surfaces of Deenen (1942).. In the Five Panel mine observations made at a considerable distance from p a r t i a l l y caved areas suggest that roof f a i l u r e i s la r g e l y contolled by steep east dipping shear surfaces and t h e i r intersection with slickensided bedding surfaces. Because the shear surfaces dip at high angles, the caves appear to be a r e a l l y smaller and r e s t r i c t e d more l a t e r a l l y than those examined i n the Balmer North mine. DISCUSSION AND CONCLUSIONS Norris (1958, 1964, 1966) documented notable differeces 98 F i g u r e 3-17A. B a l m e r N o r t h m i n e . P a r t i a l l y c a v e d e n t r y ; s l i c k e n s i d e d b e d d i n g s u r f a c e s have promoted s e p a r a t i o n o f t h e r o o f r o c k a l o n g b e d d i n g p l a n e s . P a c k s a c k i n the roadway f o r s c a l e . F i g u r e 3-17B. U n s u p p o r t i n g r o o f b o l t i n c a v e d e n t r y . The s t e e p l y d i p p i n g s h e a r s u r f a c e s have f a c i l i t a t e d f a i l u r e o f the r o o f r o c k . C o n v e n t i o n a l r o o f b o l t s p r o v i d e l i t t l e s u p p o r t w i t h s u c h s t e e p l y d i p p i n g f r a c t u r e s . 99 in t i e s t r u c t u r a l conditions of Canadian coal mines. He was able to demonstrate that where the coal measures were only, mildly deformed such as i n the Drumheller coal area (central Alberta) and the S p r i n g h i l l , Joggins and Sydney coal areas (Nova Scotia), the c l e a t system and primary sedimentary structures, were i n t a c t and there was no appreciable i n t e r s t r a t a l s l i p r elated to deformation. . In mines of the southern Canadian C o r d i l l e r a (new abandoned) Norris demonstrated that the coal seams were highly deformed as a r e s u l t of d i f f e r e n t i a l movement between roof and f l o o r strata and that extension f a u l t s were common, much more so than contraction f a u l t s . Norris further concluded that deformation of coal seams in d i f f e r e n t areas of the southeastern C o r d i l l e r a are nearly i d e n t i c a l despite differences i n regional setting (Norris, 1958). . The r e s u l t s of t h i s study generally concur with the findings of Norris (1958, 1964, 1966). The Vicary Creek mine and the Michel mines have dif f e r e n t s t r u c t u r a l settings, yet they are a l l characterized by the prominence of extension f a u l t s and by major s t r u c t u r a l d i s c o n t i n u i t i e s i n the roof rock i n the form of slickensided bedding surfaces. Fundamental differences do e x i s t however, between the mines.. In the Vicary Creek mine the coal has been highly sheared and comminuted; a number of folds cccur i n the roof s t r a t a and the roof rock throughout most of the mine has been extensively sheared as a r e s u l t of i n t e r s t r a t a l s l i p . In the Michel mines, on the other hand, the cleat system i s i n t a c t , the roof rock i s less extensively sheared and the roof conditions are a product largely of l a t e formed shear fractures and extension f a u l t s . . Such differences 100 are the re s u l t of not only the s t r u c t u r a l settings of the mines, but also more p a r t i c u l a r l y , the extent of shortening and i n t e r s t r a t a l s l i p of the coal measures. In the.Michel mines i n t e r s t r a t a l s l i p i s probably completely the r e s u l t of f l e x u r a l s l i p folding of the broad, open Michel and Natal synclines, whereas i n the Vicary Creek mine, i n addition to f l e x u r a l s l i p , a component of s l i p i s probably related to drag (simple shear) from overriding thrust f a u l t s , as described e a r l i e r . Furthermore, in the Vicary Creek area, the Kootenay Formation i s thin and the Number 2 Seam i s e s s e n t i a l l y the only major incompetent bed in the stratigraphic succession and may, therefore, represent the locus of s l i p as compared to the Kootenay Formation i n the region of the Michel mines which i s much thicker and contains 11 major seams of coal. The greater thickness of the Balmer seam i n the Michel mines compared with the Number 2 Seam in the Vicary Creek mine cannot solely account for the observed contrast i n conditions. The thicker seam should t h e o r e t i c a l l y experience a greater degree of f l e x u r a l s l i p between roof and.floor strata during folding or buckling (Ramsay, 1967) which i s the opposite of that observed. Marked l i t h o l o g i c variations and sedimentary d i s c o n t i n u i t i e s such as documented i n the roof s t r a t a of many mines (Diessel and Woelle, 1965; Donaldson, 1977; Home et a l . , 1978; Krausse et a l . , 1979) are not evident i n the:Vicary Creek or Michel mines. The subtle variations in lithology that are present, however, stongly influence the response of.the roof strata and the seam to deformation.. The i n t e r r e l a t i o n s h i p between lit h o l o g y and extent of deformation i s p a r t i c u l a r l y 101 evident i n the Vicary Creek mine where contrasting roof conditions are related.to the response of the d i f f e r e n t roof rock l i t h o l o g i e s to the same stress system, v i z . the development of platy roof rock i n thin-bedded carbonaceous sediments which f a c i l i t a t e d i n t e r s t r a t a l s l i p , and the formation of a jointed, blocky roof rock i n thick-bedded, coarse-grained sediments which were more amenable to j o i n t i n g . . The absence of marked variations in roof rock l i t h o l o g i e s i n the Vicary Creek mine i s probably l a r g e l y a r e s u l t of the scale of the mining operations. In outcrop and i n abandoned s t r i p mines, marked variations in l i t h o l o g y , a t t r i b u t a b l e to channeling, are evident. In the roof rock of the Balmer seam the absence of major l i t h o l o g i c variations l i k e l y r e f l e c t deposition on a wide, sediment starved, delta plain which f a c i l i t a t e d continuous deposition of peat for long periods of time.. The gradational contact between seam and roof rock also attests to slow abandonment of the swamp as compared to rapid flooding and channeling conditions conducive to formation of heterogeneous roof rock (Home et a l . , 1978) .. Such a depositional environment for the Balmer seam i s supported by the great l a t e r a l continuity and homogeneity of the underlying sandstone unit, which i s more than 384 km i n length and at l e a s t 160 km i n width (Gibson, 1977). In the studied mines, many of the structural fa b r i c elements of the roof rock can be readily related to the kinematics and dynamics of deformation of the coal measures. However, the geological factors a f f e c t i n g roof conditions and mineability of the coal seam can be predicted only i n a general sense. In the Vicary Creek Mine, even though deformation of the 102 roof rock and coal seam i s l a r g e l y congruent with the regional structural environment i t i s not possible to predict the subtle variations in l i t h o l o g y of the roof rock or occurrences and location of folds and extension f a u l t s , a l l of which markedly affect roof conditions. It i s , however, reasonable to predict both from the Vicary Creek Mine and other, now abandoned mines, (Norris, 1958) that mines developed in similar s t r u c t u r a l settings w i l l be characterized by: 1) pervasively sheared coal of low bearing strength; 2) profusion of extension f a u l t s of varied orientations and displacements; 3) highly sheared and , incoherent roof rock which w i l l provide poor anchorage for normal roof bolts; and 4) variations in roof rock l i t h o l o g i e s which, i f present, w i l l markedly influence roof conditions. Once major roadways are developed i t should further be possible to map the location of folds and predict t h e i r trends, map l i t h o l o g i c variations i n the raof rock and designate areas i n which swarms of extension f a u l t s may occur. . In, the Michel mines i t i s not possible to predict the orientation of cleat or j o i n t systems in the adjacent sandstones from regional or l o c a l structure. The cleat pattern, p a r t i c u l a r l y i n the Balmer North mine, appears to r e f l e c t a much more complicated stress pattern tlian would be predicted from the broad, open folding of the area. Pervasive shear fractures in the coal and roof rock, which are apparently late structures, i n conjunction with slickensided bedding surfaces, control the geometry of caves and roof i n s t a b i l i t y in the mines. These structures show l i t t l e variation in orientation throughout the mines. Orientation of roadways and v e n t i l a t i o n raises oblique 103 rather than p a r a l l e l to the s t r i k e of such structures would markedly increase the roof s t a b i l i t y and bearing strength of coal p i l l a r s . Similar to the Vicary Creek mine, i t i s not possible to predict the location of extension f a u l t s . Comparable roof conditions i n mines of s i m i l a r s t r u c t u r a l setting as the Michel mines would be d i f f i c u l t to predict; the dynamics of the deformation r e s u l t i n g i n formation of late shear fractures and extension f a u l t s which aff e c t the roof conditions i s unknown. . Flexural s l i p accompanying folding and resulting i n loss of cohesion between successive beds of roof strata can be predicted to occur i n almost a l l coal mines i n the eastern Canadian C o r d i l l e r a . The intensity of i n t e r s t r a t a l s l i p i s paramount i n determining roof conditions and character of the coal in a l l of the mines studied. 104 ACKNOWLEDGEMENTS I thank Coleman C o l l i e r i e s and Kaiser Eesourses Ltd. for providing access and plans to t h e i r respective mines. . Kaiser Eesourses kindly drafted F i g . .3-9. This study has benefited from discussions with Dr. D.K, .Norris of the Geological Survey of Canada and the enginerring s t a f f s of Coleman C o l l i e r i e s and Kaiser Resources Ltd. Early drafts of t h i s paper were read by Drs. W.H. . Mathews, W.C. Barnes, J.W,. Murray and G, E. Eouse. and I thank them f o r their comments., Finan c i a l support for t h i s study was received from the Geological Survey cf Canada and a Natural Sciences and Engineering Council (Canada) Grant A-1107 to Dr. W.H. Mathews. 105 References Benedict, L.G., and Thompson, R.S., 1973, The use of .geological information to describe coal-mine roof conditions: Paper presented at the Annual Meeting of the American Chemical Society, Chicago, I l l i n o i s , August, 1976. Crabb, J . J . , 1962, Coal mining i s southeastern B r i t i s h Columbia, an h i s t o r i c a l outline: Journal of the Alberta Society of Petroleum Geologists, v o l . 10, pp. 767-791. Currie, J.B. and Reik, G.A., 1977, A method of distinguishing regional d i r e c t i o n of j o i n t i n g and of i d e n t i f y i n g joint sets associated with i n d i v i d u a l geological structures: Canadian Journal of Earth Sciences, v o l . 14, pp. 1211-1228. . Dahlstrom, CD.A., 1969, The upper detachment i n concentric fol d i n g : B u l l e t i n Canadian Society of Petroleum Geologists, v o l . .17, pp. 326-340,. Deenen, J.M., 1942, Breuken i n kool en gesteente: Mededeelingen van de Geologische S t i c h t i n g , Serie C-1-2-No..1, 100 p. Diessel, C.F.K, and Moelle, K.H.R., 1965, The application of • analysis of the sedimentary and st r u c t u r a l features of a coal seam and i t s surrounding strata to the operations of mining: Eighth Commonwealth Mining and Metallurgical Congress, Melbourne, Aus t r a l i a , vol. 6, 19 p. Donaldson, A.C, 1 977, Origin of coal seam d i s c o n t i n u i t i e s : in Voelker, R.M., ed. , Proceedings coal seam d i s c o n t i n u i t i e s symposium: D*Appolonia, Pittsburgh, Pa. Donath, F.A., 1963, Fundamental problems i n dynamic st r u c t u r a l geology: i n Donnelly, T.W., ed., The earth sciences, problems and progress i n current research: University of Chicago Press, Chicago, pp..83. Donath, F.A. .and Parker, R.B., 1964, Folds and f o l d i n g : Geological Society! of America B u l l e t i n , v o l . 75, pp. 45-62. Friedman, M. , 1975, Fracture in rocks: Review of Geophysics and Space Physics, vol. 13, pp. 352-358. Gibson, D.W. , 1977, Sedimentary f a c i e s of the Jura-Cretaceous Kootenay Formation, Crowsnest Pass area, southwestern Alberta and southeastern B r i t i s h Columbia: B u l l e t i n Canadian Society of Petroleum Geologists, vol. 25, pp. 767-791. Griggs, D. and Handin, J . , 1960, Observations on fracture and a hypothesis of earthquakes: i n Rock Deformation a symposium: Geological Society of America Memoir 79, pp. .347-365. 106 Hoeppener, B., 1955, Tektonik im Schiefergebirge: Geologische Eundschau, vol.,44, pp. 26-58. Horne, J.C. Ferm, J.C., Carvccio, F.T. .and Eaganz, B.P. 1978, Depositional models in coal exploration and mine planning i n Appalachian region: Americn Association of Petroleum Geologists B u l l e t i n , v o l . 16, pp. 2379-2411.. Krausse, H..-F., Damberger, H.H., Nelson, W.J,., Hunt, S. E., Ledvine, C.T. , Trewargy, C G . and White, W.A., 1979, Eoof strata of the Herrin (No. 6) coal member i n mines in I l l i n o i s : Their geology and s t a b i l i t y : I l l i n o i s Minerals Note 72, 54 p. McCulloch, CM., Deul, M. and Jeran, P. W. , 1974, Cleat i n bituminous c o a l : United States Bureau of Mines, Beport of Investigations 7910, 24 p. McCulloch, CM., Lambert, S.W. and White, J. B-, 1976, Determining cleat orientation of deeper coal beds from overlying coals: United States Bureau of Mines, Beport of Investigations 8116, 19 p. Moebs, N.N., 1977, Eoof rock structures and related roof support problems i n the Pittsburgh coal bed of southwestern Pennsylvania: United States Bureau of Mines, Beport of Investigations 8230, 30 p. Norris, D.K., 1958, Structural conditions i n Canadian coal mines: Geological Survey of Canada B u l l e t i n no. ,44, 54 P' Norris, D.K., 1963, Microtectonics of the Kootenay Formation near Fernie, B r i t i s h Columbia, B u l l e t i n Canadian Society of Petroleum Geologists, vol. 12, pp. 383-398. Norris, D.K., 1965, Structural analysis of part of the A-North coal mine, Michel, B r i t i s h Columbia: Geological Survey of Canada Paper 64-24, 13 p. Norris, D . K - » 1966, The mesoscopic f a b r i c of rock masses about some Canadian coal mines: Proceedings of the F i r s t Congress, International Society of Bock Mechanics, Lisbon Portugal, vol..1, pp. 299-321. Norris, D.K., 1967, Structural analysis of the Queensway f o l d s , Ottawa, Canada: Canadian Journal of Earth Sciences, vo l . 4, pp. 299-321. 1 Norris, D.K. and Barron, K., 1968, Structural analysis of features of natural and a r t i f i c i a l f a u l t s : i n Baer, A.J. and Norris, D.K. eds., Proceedings, conference on research i n tectonics: Geological Survey of Canada Paper 68-52, pp. ,136-174. , 107 Popp, J,T. and Mcculloch, CM., 1976, Geological f a c t o r s a f f e c t i n g methane in the Beckley coal bed: United States Bureau of Mines, Report of Investigations 8137, 35 p. Price, R.A., 1967, The tectonic significance of mesoscopic subfabrics i n the southern Rocky Mountains i n the v i c i n i t y of the Crowsnest Pass of Alberta and B r i t i s h Columbia: Canadian Journal of Earth Sciences, vol. 4, pp. 37-70. Ramsay, J.G., 1967, Folding and f r a c t u r i n g of rocks: McGraw H i l l Inc. New York, . 568 p. Reinech, H.-E. and Singh, I.B., 1973, Depositional sedimentary Environments: Springer-Verlag, New York, 439 p. Sander, B., 1942, Uber Flachen- und Achsengefuge (Westende der Hohen Tauern, I I I Bericht) (Geologie des Tauern-Westendes): Mitteliungen der Reichsstelle fur Bodenforschungler 2weigstelle Wein, vol. 4, pp. 1-94. . Sax, H.G.J., 1946, De.Tectoniek van het Carbon i n j e t Zuid-Limburgsche Mijngebied: Mededeelingen van de Geologische Stichting Serie C-1-1-No. 3, pp. 1-77.. Shepherd and Fisher, 1978, Extended figures and tables f o r the inter-ccmparison of f a u l t s , roof f a i l u r e and mining rate in a New South Wales C o l l i e r y : CSIRO Investigation Report 125, 6 p. Stearns, D.W., 1964, Macrofracture patterns on the Teton a n t i c l i n e , northwestern Montana: Transactions American Geophysical Union, vol.. 45, pp. 107-108. Stearns, D.W., 1968, Certain aspects of fracture i n naturally deformed rocks: i n Riecker, R.E., ed., National Science Foundation Advanced Science Seminar i n Rock Mechanics, Boston College: Air Force Cambridge Research Laboratories, Bedford, Massachusetts, vol. 1, pp. 97-110. Touseull, J.A., 1977, Stereographic method of determinig whether planes of weakness transect p i l l a r s : United States Bureau of Mines, Report of Investigations 8230, 30 p. . 108 PART 3 EFFECT OF SHEAR ON COAL QUALITY AND RANK: TEMPERATURES ASSOCIATED WITH SHEAR ZONES AND SOME IMPLICATIONS REGARDING FAULT MECHANICS IN THE SOUTHERN ROCKY MOUNTAINS OF BRITISH COLUMBIA AND ALBERTA 109 ABSTRACT Coal seams of the Late Jurassic-Early Cretaceous Kootenay Formation are extensively sheared in parts of the southern Rocky Mountains of B r i t i s h CclumJbia and Alberta. The.coal seams were the l o c i of i n t e r s t r a t a l s l i p during f l e x u r a l s l i p folding, and major-thrust f a u l t s , reverse and normal f a u l t s are l o c a l i z e d in the coal seams or transect the seams at low angles. The mesoscopic f a b r i c of the seams i s c a t a c l a s t i c . Microscopically, there i s evidence for l o c a l ductile behavior of the c l a r i t e component of the c o a l . Measurements of v i t r i n i t e reflectance of coal i n some shear zones suggest, by comparision with samples of coal heated i n the laboratory for short durations, that f r i c t i o n a l heating may have resulted l o c a l l y in temperatures of up to 450°C. Adjacent to and within other shear zones, however, there i s no evidence of f r i c t i o n a l heating. The presence or absence of f r i c t i o n a l heating i s considered the r e s u l t , respectively, of s t i c k - s l i p and stable s l i d i n g conditions during f a u l t i n g . . The r e s u l t s imply that regions of s i g n i f i c a n t and less s i g n i f i c a n t e f f e c t i v e stress may.exist along some thrust and reverse f a u l t s . This supports the Hubbert and Rubey hypothesis of high pore f l u i d pressure f a c i l i t a t i n g overthrust f a u l t i n g . , In addition, however, to areas of low e f f e c t i v e stress, areas of higher e f f e c t i v e stress e x i s t which may r e f l e c t loss of high f l u i d pressures. High temperatures calculated along the Coleman Fault occur i n a region in which the f a u l t i s folded and a s l i c e of Crowsnest Volcanics has been dragged up along the f a u l t plane.. Such areas where f a u l t s rapidly cut up section are probably 110 regions of stress concentration and adjacent fractured and faulted rocks may f a c i l i t a t e dissipation of high f l u i d pressure. The thermal effects of shearing on coal quality are insignificant. Mechanical granulation as a result of shear of the coal and associated rock partings and interbeds of sandstone and shale result in disproportionately high ash contents, poor washability characteristics and rapid oxidation of the coal. 111 INTEODUCTION Complex folding and f a u l t i n g of the Late Jurassic-Early Cretaceous Kootenay Formation i n the southern Canadian Eocky Mountains was f a c i l i t a t e d ty the presence of thick seams of incompetent c o a l . The coal seams were the l o c i for i n t e r s t r a t a l s l i p during f l e x u r a l s l i p .folding, and major thrust, reverse and normal f a u l t s are l o c a l i z e d within the coal seams or transect the seams at low angles. To accommodate deformation, the coal, on a mesoscopic scale, either flowed c a t a c l a s t i c a l l y along a myriad of diffuse shear surfaces or was transported en mass along a few discrete shear planes. Tectonic transport of the coal i n some areas has produced subs t a n t i a l l y thickened coal deposits, some of which are presently being mined.. Extensively sheared coal, p a r t i c u l a r l y where t e c t o n i c a l l y thickened, comprises a large proportion of the coal reserves in the southern Canadian Eocky Moutains.. The primary purposes of t h i s study were to describe and define the mesoscopic and microscopic f a b r i c of the highly sheared coal and to evaluate the effect of shear on coal guality. The multitude of shear zones within the coal seams and the occurrence of coal i n the immediate footwall or hanging wall of, as well as within, major f a u l t planes also provided an excellent opportunity to assess, by measurement of coal rank, whether or not any thermal a f f e c t s are associated with f a u l t i n g . Previous studies by Teichmuller and Teichmuller (1966) demonstrated that a l o c a l r i s e in coal rank was associated with the Sutan overthrust f a u l t i n the Euhr Basin. , Ghosh (1970) described a s i g n i f i c a n t increase i n rank in t e c t o n i c a l l y 112 disturbed parts of coal seams i n Lower Gondwana coal of the Darjeeling-Himalaya. Both of these studies attributed the l o c a l increase i n rank to f r i c t i o n a l heating during deformation and both documented an associated increase in the o p t i c a l anisotropy of the v i t r i n i t e component of coal adjacent to shear zones. F r i c t i o n a l heating along f a u l t zones has been considered t h e o r e t i c a l l y by McKenzie and Brune (1972), Cardwell et a l . , (1978), Moore and Sibson (1978) and others.. Cardwell et a l . , (1978) calculated temperature d i s t r i b u t i o n s during and after f a u l t i n g f o r f a u l t s of f i n i t e width and McKenzie and Brune (1972) obtained solutions f o r planar f a u l t s . F r i c t i o n a l heating along subduction zones has been considered t h e o r e t i c a l l y by Toksoz and Bird (1 977), Bird (1978) and many others." On some f a u l t planes in metamorphic t e r r a i n s , the presence of pseudotachylite or hyalcmylonite, which show some evidence for flow indicate that, at least l o c a l l y , melting has occurred (Scott and Drever, 1954; Philpots, 1964; Ermanovics et a l . , 1972; Masch, 1973; Wallace, 1976). In some f r i c t i o n a l s l i d i n g experiments of sandstone on limestone (Friedman et a l . , 1974; Tu e l f e l and Logan, 1976), melting has apparently occurred and high temperatures have been documented (Bowden and Tabor, 1950). Most f a u l t s , however, show no evidence of melting or of high temperatures. Because t h e . s e n s i t i v i t y of coal to temperature change.is much greater than that of common minerals i t i s an ideal rock with which to assess what thermal a f f e c t s , i f any, are associated with f a u l t i n g . The use of coal rank measurements as an index to thermal metamorphism i s well documented (Dutcher, et 113 a l . , 1974; Bostick, 1979).. Although some differences of opinion exist, i t i s generally accepted that the c o a l i f i c a t i o n process i s governed primarily by r i s e i n temperature and the time during which th i s occurs., The affect of time and temperature on c o a l i f i c a t i o n has been demonstrated experimentally (Karweil, 1956; Huck and Patteisky, 1964; Chandra, 1965a) by examination of deep bore-holes of known temperature (Castano and Sparks, 1974; Bostick et a l . , 1979) and metamorphic and intrusive aureoles (Bostick, 1973).. Pressure, although responsible for compaction and reduction of moisture i n low rank coals and anisotropy in higher rank coals, i s not considered an important factor i n c o a l i f i c a t i o n . Huck and Patteisky (1964) and others have suggested that pressure may actually retard c o a l i f i c a t i o n . Bostick (1973) found i n hydrothermal experiments that there was no change in the degree of c o a l i f i c a t i o n when pressures were varied between 2.05x10* kPa and 1.105x10s kp a a t constant temperatures,. The e f f e c t of shear stress on coal rank has received l i t t l e study. , Teichmuller (1968) and Taylor (1971) have postulated that shear stress may f a c i l i t a t e formation of graphite at lower temperatures then generally considered necessary for i t s formation. In t h i s study samples of coal were collected s p e c i f i c a l l y to evaluate the e f f e c t s of shear on coal rank and quality and to evaluate the temperatures associated with shearing. Samples of pervasively sheared coal were co l l e c t e d within coal seams, from adjacent major thrust and reverse f a u l t s and from i s o c l i n a l l y folded seams i n the Kootenay Formation at Tent Mountain and Vicary Creek (Fig. .1-2). Wherever possible, samples were 114 col l e c t e d incrementally away from the f a u l t planes. Because part of the purpose of t h i s study was to evaluate temperatures associated with shearing, i t was also necessary to establish the s e n s i t i v i t y of changes i n coal rank to di f f e r e n t temperatures and durations of heating. Previous studies by Chandra and Bond (1956), Bostick (1973) and others established change i n coal rank with temperature for periods of heating of a few hours to several months. Preliminary measurements and t h e o r e t i c a l considerations suggest, however, that i f heating was taking place, i t was of very short duration. I t was therefore necessary to heat coal samples experimentally f o r very short durations and for a variety of temperatures.. I t was also advantageous to obtain experimental data f o r coal within the study area since change i n rank i s not l i n e a r with temperature for coal of d i f f e r e n t ranks.. EXPERIMENTAL PROCEDURE AND ANALYTICAL TECHNIQUES In order to assess the change i n coal rank with temperature and duration of heating a large sample of v i t r a i n -r i c h medium-volatile bituminous coal was collected from an adit within the study area. , The sample was crushed to -20 mesh U.S. Standard sieve s i z e and s p l i t into sub-samples.. Each sub-sample was placed in a 25 ml ampoule which was then thoroughly flushed with nitrogen, p a r t i a l l y evacuated and sealed. The sub-samples were then heated i n a furnace f o r times ranging from 10 minutes to several days and at temperatures ranging from 100°C to 600°C. Seme f i e l d samples were also crushed to -20 mesh whereas other samples were impregnated with epoxy for examination of the 115 fabric,. Inorganic material in some samples was removed prior to sample preparation by l i q u i d separation techniques using a zi n c -chloride solution or tetrachloroethylene with a density of 1.60 gm cm - 3. The crushed and treated samples were then formed into p e l l e t s using Trans-optic powder as described by Bustin et a l . , (1977). A l l the samples were polished to a f i n a l g r i t size of 0.0 2 urn. Measurements of coal rank were made using the v i t r i n i t e reflectance method following the procedures outlined by Bustin et a l . , (1977). A L e i t z MPV 1 microscope equipped with a photcmultiplier, stable voltage supply and d i g i t a l readout were used. The microscope was equipped with a polarized halogen l i g h t , a narrow band f i l t e r at 546 nm wavelength and a 50x o i l immersion objective with an 8 um e f f e c t i v e aperture. Standardization of the photomultiplier was with a glass standard of 1.01% Ro. Whenever possible, at least 50 measurements were made per sample and both the maximum and minimum reflectance were recorded i n order to establish the degree of anisotropy of the v i t r i n i t e . Measurement of v i t r i n i t e reflectance to esta b l i s h the degree of c o a l i f i c a t i o n (rank) i s well documented (see McCartney and Teichmuller, 1S72). In t h i s study the use of v i t r i n i t e reflectance to determine rank had a number of advantages over other methods: (1) because the method was performed microscopically i t was possible to analyze samples with abundant inorganic material which otherwise would have had to be completely separated; (2) i t was possible to make multiple measurements on blocks of sheared coal; and (3) i t was possible 116 to analyze very small amounts of coal such as are present i n some f a u l t planes. S e n s i t i v i t y cf c o a l rank to heating for short duration The maximum reflectances of samples heated f o r 10 minutes, 1 hour, 4 hours, and 7 hours for d i f f e r e n t temperatures are summarized i n Figs,. 4-1, 4-2, 4-3 and 4-4.. A l l the samples heated to temperatures of 200°C and greater show a s t a t i s t i c a l l y s i g n i f i c a n t 1 increase i n mean reflectance regardless of heating duration. A sample heated at 160°C for 7 hours showed no s t a t i s t i c a l l y s i g n i f i c a n t increase i n mean reflectance. An excellent c o r r e l a t i o n exists between increasing temperature and mean reflectance for each of the heating durations. The only notable exception i s the sample heated to 280°C for 7 hours (Fig. 4-4) which has the same reflectance as a sample heated to 200°C for the same duration. The lower v i t r i n i t e reflectance of the sample heated to the higher temperatures cannot be explained. The rate of change of v i t r i n i t e reflectance with increasing temperature i s nearly l i n e a r for a l l heating durations up to about 400°C. Between 400°C and 6 0 0 O C there i s an exponential increase i n reflectance with increasing temperature. This jump i n reflectance corresponds to the onset 1 A l l reported s t a t i s t i c s are at the 99% confidence l e v e l using Students • t* t e s t i 117 ioo H 40 I 20-~ T 0.8 A unheated 0.6 1.0 i 1.2 — 1— 1.4 1.6 ~ l — 1.8 — i — 2.2 2.0 Reflectance, % — i — 2.4 —I— 2.6 2.8 —I— 3.0 3.2 F i g u r e 4 - 1 . M a x i m u m . v i t r i n i t e r e f l e c t a n c e v a l u e s f o r c o a l samples h e a t e d i n the l a b o r a t o r y f o r 10 m i n u t e s a t t h e i n d i c a t e d t e m p e r a t u r e s . The d i s t r i b u t i o n , mean and s t a n d a r d d e v i a t i o n o f measured v a l u e s f o r each sample a r e shown. 600 500 C 500-400 H O CO 0) 0) k . cn a> Q 300 H 200-100-m e a n • x s t anda rd dev iat ion * unheated 1 /fV___ 2.2 —1 1 1 1 3.0 3.2 3.4 3.5 0.6 " a s 1.0 1.2 1.4 ~ 1 — 1.6 1.8 — 1 — 2.0 2.4 2.6 2.8 Reflectance, % r e 4 - 2 . Max imum v i t r i n i t e r e f l e c t a n c e v a l u e s f o r c o a l s a m p l e s h e a t e d i n t h e l a b o r a t o r y f o r 1 h o u r a t t h e i n d i c a t e d t e m p e r a t u r e s . T h e d i s t r i b u t i o n , mean a n d s t a n d a r d d e v i a t i o n o f m e a s u r e d v a l u e s f o r e a c h s a m p l e a r e M CO s h o w n . 119 500-i 100-1 40 %20-X unheated 0.8 1.2 1.6 Ref lectance, 1 2.0 F i g u r e 4 - 3 . Max imum v i t r i n i t e r e f l e c t a n c e v a l u e s f o r c o a l s a m p l e s h e a t e d i n t h e l a b o r a t o r y f o r 4 h o u r s a t t h e i n d i c a t e d t e m p e r a t u r e s . T h e d i s t r i b u t i o n , mean a n d s t a n d a r d d e v i a t i o n o f m e a s u r e d v a l u e s f o r e a c h s a m p l e a r e s h o w n . 600-, 500H 400 O <n a> o CO Q) Q 300 200 100H 40, X20. -_0J unheated 0.8 1.6 2.4 Ref lectance, yo 3.2 4.0 F i g u r e 4 - 4 . Maximum v i t r i n i t e r e f l e c t a n c e values f o r c o a l samples heated i n the l a b o r a t o r y f o r 7 hours a t the i n d i c a t e d temperatures. The d i s t r i b u t i o n , mean and standard d e v i a t i o n of measured values f o r each sample are show, O 121 of melting of the coal (420-450°C). Figure 4-5 which summarizes the data presented i n Figs. 4-1, 2, 3 and 4, shows the ef f e c t s of heating durations at constant temperature on v i t r i n i t e " reflectance of the coal. Below 500<>C the duration of heating has l i t t l e e f f e c t on the mean maximum reflectance of the coal. At 500°C there i s a marked increase i n reflectance with heating duration; and the sample heated to 600<>C f o r 10 minutes has lower mean reflectance than the sample heated at 500°C for 1 hour. In Fig.,4-6 some of the data from t h i s study are.compared with reflectance and temperature data from bore-hole samples and laboratory analysis compiled by Bostick (1973),. , This figure demonstrates the importance of heating duration on v i t r i n i t e reflectance for any given temperature. Other laboratory studies show sim i l a r results (Chandra and Bond, 1956; Taylor, 1961; Ghosh, 1967). In general i t can be concluded that very short heating durations, such as those i n t h i s study, re s u l t i n lower reflectances for a given heating temperature than longer heating durations. However, with d i f f e r e n t very short heating durations, as used i n this study, the reflectances for a constant temperature are only notably d i f f e r e n t at high temperatures. I t i s also evident that with medium-volatile bituminous coal heating below 200°C for short durations has no detectable e f f e c t cn coal rank as measured by v i t r i n i t e reflectance. One of the most notable features of the experimentally heated coals of t h i s study i s the large increase i n variance of the reflectance measurements with increased temperature and the associated increase i n mean anisotropy of the v i t r i n i t e 600-500 H 400 H (/} 3 <D 300 o LU LU CC ( I J 200 111 Q 100 -H 7hrs. 10 min H 4 h r s . 1 h r . -4 hrs. -1 hr. 4 hrs. 10 min. ^-7 hrs. *~1 hrs. y 7 hrs. , . ,^-"10 min. ^ j S ^ - —4 hrs. "*^1 hr. 7 hrs. 7 days unheated 10 min. 1hr. 1 hr. 10 min. 1 hr. 7 hrs. ~i i i — i — i — i — r ~ 0.8 1.0 1.5 ~ ~ \ — i — i — i — i — i — i — i — i — r 2.0 2.5 1 — I — r — 3.0 ~\ r 3.5 MEAN MAXIMUM REFLECTANCE (Ro %) F i g u r e 4 - 5 . Sumniary d i a g r a m s h o w i n g t h e v a r i a t i o n i n mean r e f l e c t a n c e a n d s t a n d a r d d e v i a t i o n f o r s a m p l e s h e a t e d a t i n d i c a t e d t e m p e r a t u r e s and d u r a t i o n s . to ro Long burial 0 100 2 0 0 3 0 0 4 0 0 5 0 0 6 0 0 PRESENT ROCK TEMPERATURE ( ° C ) Figure 4-6. Mean maximum v i t r i n i t e r e f l e c t a n c e of dispersed organic material and c o a l from bore holes and laboratory heated samples (modified from compilation of Bostick, 1973) compared with samples heated i n the laboratory for 10 minutes and 7 hours i n t h i s study at the indicated temperatures. 0=central eastern Oklahoma, Pennsylvanian, 900 to 3700 m; W=LaSalle County, southwestern Texas, J u r a s s i c , 4000 to 6100 m; E=Angelina County, eastern Texas, Ea r l y Cretaceous, 1200 to 34 00 m; S=Salton geothermal f i e l d , C a l i f o r n i a , Late Pliocene and Pleistocene, 210 2500 m; L=Cameron P a r i s h , Louisiana, E a r l y Miocene, 2500 to 4600 m; M=Munsterland No. 1 w e l l , northwestern Germany, Carboniferous, 1600 to 4520 m; V=Volga region, USSR, .Middle Devonian to Middle Carboniferous, 108 to 4060 m; 0R=Upper Rhine graben, Germany, T e r t i a r y and Quaternary; T=Terresbonne P a r i s h . F l o r i d a , Middle Miocene. 5440 m; H=bomb samples, 1.36xl0 5 kPa, 30 to 4 5 minutes. 124 (Figs. 4-7 and 4 - 8 ) . . The increase i n variance and anisotropy are not independent, as suggested by the co r r e l a t i o n between Fig s . 4-7 and 4 - 8 . Such a large variance and anisotropy i s not ch a r a c t e r i s t i c of normal coal with the same mean maximum reflectance and probably i s the r e s u l t of di f f e r e n t reaction rates of the v i t r i n i t e . / Such large variances and anisotropies are not evident with longer heating durations. The large variance and anisotropy are not considered to i e the resu l t of non-uniform heating because the samples heated f o r 7 hours have si m i l a r variances as samples heated for 10 minutes. MESOSCOPIC AND MICBOSCOPIC FABEIC OF THE SHEAEED COAL Deformation and shearing of coa l seams i n the study area has been i n response to f o l d i n g , f a u l t i n g , and i n t e r s t r a t a l s l i p . . Almost a l l the examined coal seams show some evidence of shear and i n some areas the primary s t r a t i f i c a t i o n and systematic c l e a t , i f ever present, have been largely destroyed. On a mesoscopic scale, the coal seams have a c a t a c l a s t i c -brecciated f a b r i c consisting of highly fragmented and rotated blocks.of coal. , Adjacent to some major f a u l t s and i n areas of intense deformation the coal i s f i n e l y comminuted (Fig. 4-9) . Both the larger blocks and the f i n e l y granulated coal are extensively polished. , More competent beds of d u l l coal and interbeds and partings of sandstone and shale are commonly l e s s fragmented (Fig. 4-10) , although i n highly deformed seams they too are f i n e l y granulated. , Shear planes cross-cutting or within the coal seams are most commonly represented by either polished surfaces on blocks F i g u r e 4 - 7 600 - i 500 to 4 0 0 -3 W CD O 300-C0 UU LU 9£ 200-o HI a 100-125 A O O o C»A 0 °0 L E G E N D A-10 min. 0-1 hr. • -4 hrs. 0 - 7 hrs. 0.3 I 0.4 0.5 0.1 0.2 STANDARD DEVIATION of MEAN MAXIMUM REFLECTANCE (Ro%) S t a n d a r d d e v i a t i o n o f mean max imum r e f l e c t a n c e o f l a b o r a t o r y h e a t e d s a m p l e s . 600 -i 500: 0) 4 0 0 ^ 3 • O 300-CO LU £ 200 H o LU Q 100-0 o 0 A 0 0.5 1.0 MEAN MAXIMUM- MEAN MINIMUM REFLECTANCE (Ro%) F i g u r e 4 - 8 . Mean max imum m i n u s mean m i n i m u m r e f l e c t a n c e ( a s m e a s u r e d ) o f s a m p l e s h e a t e d i n t h e l a b o r a t o r y . L e g e n d i s t h e same a s t h a t i n F i g . 4 - 7 . F i g u r e 4 - 9 A . F i n e l y comminuted c o a l seam i n a s h e a r z o n e . N o t i c e t h e more f i n e l y comminuted c o a l a t t h e b a s e , top and c e n t e r o f t h e seam. P e n c i l f o r s c a l e . F i g u r e 4-9B. P e r v a s i v e l y s h e a r e d and p o l i s h e d c o a l . The c o a r s e r , f o l d e d c l a s t s a r e more c o m p e t e n t , d u l l , d u r a i n r i c h c o a l . 127 Figure 4-10B, P e r v a s i v e l y sheared c o a l w i t h a l a r g e sandstone i n c l u s i o n . The i n c l u s i o n Las apparently been introduced i n t o the seam as a r e s u l t of shearing of the roof rock d u r i n g i n t e r s t r a t a ! s 1 ip. 128 of coal or by planar or curvi-planar bands of f i n e l y granulated coal i n a coarser-grained groundmass (Fig. 4-9A). In many areas, such as shown i n F i g . 4-9B, d i s t i n c t shear surfaces are not evident, yet the coal i s intensely polished and brecciated and markedly varies i n thickness over short distances. In such areas the coal has apparently f a i l e d as a b r i t t l e material and flowed c a t a c l a s t i c a l l y along a multitude of diffuse shear planes. At some . l o c a l i t i e s continued deformation or successive stages of deformation have further complicated the f a b r i c of the coal. Highly fragmented c o a l , adjacent to and within major shear planes, i s commonly f o l i a t e d p a r a l l e l to the shear plane. In some areas such as shown in Figs. 4-11 and 12, the coal present within the f a u l t plane (fault gouge) has been dragged up the f a u l t for distances which l o c a l l y must exceed tens of metres. . The f o l i a t i o n of the coal i s probably a r e s u l t of granulation and rotation of the coarser coal c l a s t s during s l i p . The microfabric of the sheared coal i s generally similar to the mesoscopic f a b r i c , consisting of angular, brecciated fragments cf coal without evidence of ductile behavior. Locally, i n areas of apparently high shear s t r a i n , the c l a r i t e component of the coal has behaved d u c t i l y , flowing and engulfing adjacent fragments of i n e r t i t e and ash which underwent b r i t t l e f a i l u r e (Fig. ,4-13). Ductile behavior of the c l a r i t e component of the coal i s also evident i n microfolds of s i m i l a r style and 'wild' f o l d s (Fig. 4-14). The optic axes of the.brecciated fragments do not define a common orientation as was found by Smyth (1968) in brecciated coals of the Tomago coal measures, 129 F i g u r e 4-11. T h r u s t c o n t a c t between d a r k - b r o w n - g r a y s h a l e s and s i l t s t o n e s o f the F e r n i e F o r m a t i o n (above hammer head) and p e r v a s i v e l y s h e a r e d and g r a n u l a t e d c o a l c o a l o f t h e Kootenay F o r m a t i o n ( b e l o w ) . S t r a t i g r a p h i c s e p a r a t i o n a c r o s s f a u l t i s a b o u t 600 m. F i g u r e 4-12. F o l i a t e d c o a l w h i c h has been i n j e c t e d i n t o t h e p l a n e o f a n o r m a l f a u l t . The ' d i k e 1 i s o r i e n t a t e d a l m o s t p e r p e n d i c u l a r t o b e d d i n g . 130 F i g u r e 4 - 1 3 . S . E . M . p h o t o m i c r o g r a p h o f an a g g r e g a t e o f v i t r i t e , c l a r i t e and f u s i t e from a s h e a r zone, x 4 0 0 . F i g u r e 4 - 1 4 . S . E . M . p h o t o m i c r o g r a p h o f a ' w i l d 1 f o l d d e v e l o p e d i n c l a r i t e , x 4 0 . 131 which suggests that the maximum obtained degree of c o a l i f i c a t i o n was preceeded by at least some rotation of the c l a s t s . Ribbon-l i k e and vesicula r structures, such as described by Ghosh (1970) from highly deformed coals from the Darjeeling-Himalaya, are not evident. , However, i f such structures had formed they would undoubtly have been destroyed as a r e s u l t of repeated shearing and comminution of the coal., VITBINITE REFLECTANCE OF THE SHEARED COAL The v i t r i n i t e reflectances of sheared co a l and adjacent unsheared coal from 28 d i f f e r e n t l o c a l i t i e s are tabulated and b r i e f l y described i n Fig..4-15.. S i g n i f i c a n t anomalously high v i t r i n i t e reflectance cf the sheared coal as compared with unsheared coal occurs at l o c a l i t i e s 2, 5, 8, 24, 25, 27 and 28 (Fig,. .4-15). . At some locations (such as l o c a l i t i e s 6 and 10) the sheared coal has a s l i g h t l y lower mean reflectance than the unsheared coal. such coal has evidently not been exposed to high temperatures and the lower than normal reflectance may be a product of inseam v a r i a b i l i t y pr, more l i k e l y , the result of oxidation, which tends to s l i g h t l y lower the reflectance and has occurred p r e f e r e n t i a l l y i n the f i n e l y comminuted sheared coal. High mean maximum reflectance values were obtained from samples collected immediately adjacent to f a u l t s as well as samples coll e c t e d at some distance from the actual hanging wall but within the coal f a u l t gouge., At l o c a l i t y 24 anomalously high values are separated by intervening lower values. The sheared coal samples with anomalously high v i t r i n i t e reflectances are not macroscopically distinguishable from those LOCALITY LOCALITY DESCRIPTION 1. A d j a c e n t t h r u s t i n upper p a r t o f Kootenay Fm. w i t h a s t r a t i g r a p h i c s e p a r a t i o n o f about 1500 m. T e n t M t n . 2. A d j a c e n t t h r u s t i n lower Kootenay Fm. w i t h s t r a t i g r a p h i c s e p a r a t i o n o f about 200 m. T e n t Mtn. 3. Hinge a r e a t i g h t l y f o l d e d seam i n upper Kootenay Fm. T e n t M t n . 4. H i n g e a r e a t i g h t l y f o l d e d seam i n upper Kootenay Fm. T e n t Mtn. 5. S h e a r e d c o a l seam, lower Kootenay Fm. D i s p l a c e m e n t unknown, T e n t M t n . 6. S h e a r e d c o a l seam, m i d d l e p o r t i o n o f Kootenay Fm. T e n t M t n . D i s p l a c e m e n t unknown. 7. S h e a r e d c o a l seam, lower Kootenay F m . , T e n t Mtn. D i s p l a c e m e n t unknown. 8. S h e a r e d c o a l w i t h i n f a u l t p l a n e w i f h about 10s o f meters o f d i s p l a c e m e n t , l o w e r - m i d d l e Kootenay Fm. T e n t M t n . 9. S h e a r e d c o a l w i t h i n c o a l seam as a r e s u l t o f i n t e r s t r a t a l s l i p , upper Kootenay Fm. T e n t M t n . NORMAL REFLECTANCE SHEARED COAL REFLECTANCE 0.86 ± 0. 06 a d j a c e n t f a u l t 0. 85 + 0.065 10 cm below 0.86 + 0.066 30 cm below 0.92 + 0.07 4 m below 0.89 + 0.55 1.03 ± 0. 08 a d j a c e n t f a u l t 1. 35 + 0.28 a d j a c e n t f a u l t 1. 32 + 0.25 1 m below 1.04 + 0.06 unknown h i n g e a r e a 1.02 + 0.60 h i n g e a r e a 0.93 + 0.60 l i m b 0. 89 + 0.04 unknown h i n g e 0.92 + 0.06 0.93 ± 0. 03 from s h e a r e d 1.18 + 0. 30 p o r t i o n o f seam 1.04 ± 0. 07 from s h e a r e d 1. 01 + 0.10 p o r t i o n o f seam 1 . 0 8 . ± 0. 08 from s h e a r e d 1.0 2 + 0.05 p o r t i o n o f seam 0.97 ± 0. 06 a d j a c e n t f a u l t 1. 10 + 0.06 a d j a c e n t f a u l t 1. 10 + 0.07 0.97 ± 0. 06 a d j a c e n t r o o f 1 .03 ± 0 .08 r o c k o f c o a l seam F i g u r e 4-15. Summary t a b l e o f mean maximum r e f l e c t a n c e and s t a n d a r d d e v i a t i o n o f s h e a r e d c o a l from f a u l t p l a n e s and f o l d s and u n s h e a r e d c o a l (where a v a i l a b l e ) from a d j a c e n t l o c a l i t i e s . CO LOCALITY LOCALITY DESCRIPTION NO 10-.. T i g h t l y f o l d e d c o a l seam l a r g e l y s h e a r e d , upper Kootenay Fm. T e n t M t n . 11. A d j a c e n t t h r u s t i n upper p a r t Kootenay Fm. T e n t M t n . S t r a t i g r a p h i c s e p a r a t i o n i s about 600 m. R e f e r t o F i g . 4-11. 12. T i g h t l y f o l d e d and s h e a r e d c o a l , upper Kootenay Fm. T e n t M t n . L o c a l i t y shown i n F i g . 4 - 9 B . 13. A d j a c e n t t h r u s t i n lower Kootenay Fm. T e n t Mtn. S t r a t i g r a p h i c s e p a r a t i o n i s about 30 m. . 14. S h e a r e d c o a l from w i t h i n a c o a l seam, lower Kootenay Fm. T e n t M t n . D i s p l a c e m e n t ( i n t e r s t r a t a l s l i p ) unknown. 15. S h e a r e d c o a l a d j a c e n t r e v e r s e f a u l t w i t h 2 m d i s p l a c e m e n t , l o w e r Kootenay F m . , T e n t M t n . 16. S h e a r e d c o a l w i t h i n a c o a l seam l o w e r Kootenay F m . , T e n t M t n . D i s p l a c e m e n t ( i n t e r s t r a t a l s l i p ) unknown. 17. A d j a c e n t r e v e r s e f a u l t upper Kootenay F m . , T e n t Mtn. D i s p l a c e m e n t l e s s than s e v e r a l m e t r e s . F i g u r e 4-15 c o n t i n u e d AL REFLECTANCE 0.9 7 ± 0.06 SHEARED COAL REFLECTANCE h i n g e a r e a 0.94 ± 0.05 0.97 ± 0. 06 a d j a c e n t f a u l t 0.95 + 0.06 15 cm below 0.95 + 0.09 2 5 cm below 1.00 + 0.07 35 cm below 1.00 + 0.06 0.97 ± 0. 06 s y n c l i n a l 0.98 + 0.0 5 h i n g e unknown a d j a c e n t f a u l t 1.08 + 0.06 unknown w i t h i n seam 1.00 + 0.05. unknown a d j a c e n t f a u l t 1.03 ± 0.06 unknown w i t h i n seam 1.01 ± 0.70 w i t h i n seam 0.92 ± 0.09 unknown a d j a c e n t f a u l t 0.92 + 0.11 LO 00 LOCALITY LOCALITY DESCRIPTION 18. A d j a c e n t . r e v e r s e f a u l t , lower Kootenay F m . , T e n t Mtn. D i s p l a c e m e n t unknown 19. A d j a c e n t r e v e r s e f a u l t , upper Kootenay F m . , T e n t M t n . D i s p l a c e m e n t 10s o f m e t r e s . 20. A d j a c e n t t h r u s t i n upper Kootenay F m . , T e n t M t n . S t r a t i g r a p h i c s e p a r a t i o n 600 t o 700 m. 21. A d j a c e n t r e v e r s e f a u l t upper Kootenay F m . , T e n t M t n . D i s p l a c e m e n t unknown. 22. A d j a c e n t t h r u s t i n lower Kootenay F m . , T e n t M t n . s t r a t i g r a p h i c s e p a r a t i o n about 20 m. 23. A d j a c e n t t h r u s t i n lower Kootenay F m . , V i c a r y C r e e k . D i s p l a c e m e n t unknown. S t r a t i g r a p h i c s e p a r a t i o n 10s o f m e t r e s . 2 4-. A d j a c e n t and w i t h i n Coleman F a u l t p l a n e , W i n t e r i n g Creek n o r t h o f V i c a r y C r e e k . S t r a t i g r a p h i c ' s e p a r a t i o n about 2500 m. F i g u r e 4-15 c o n t i n u e d NORMAL REFLECTANCE unknown SHEARED COAL REFLECTANCE a d j a c e n t f a u l t 1.10 ± 0.0 4 unknown a d j a c e n t f a u l t 0. . 82 0, .05 unknown a d j a c e n t f a u l t 0. ;94 + 0. .04 a d j a c e n t f a u l t 0. . 85 + 0. , 10 unknown a d j a c e n t f a u l t 1. 0 4 + 0. ; i i a d j a c e n t f a u l t 0. 34 + 0. 11 a d j a c e n t f a u l t 0. 88 + 0. 07 1.0 0 i 0.0 6 . a d j a c e n t f a u l t 1. 01 + 0. 06 1.09 ± 0.12 a d j a c e n t f a u l t 1. 25 + 0. 26 1. 20 ± 0.10 1.21 + 0.12 a d j a c e n t f a u l t 1.. 25 + 0. 26 1.08 ± 0.16 3 m above 1. 42 + 0. 09 ( o x i d i z e d ? ) 1 . 5 m above 1. 42 + 0. 09 20 cm above 1. 22 + 0. 09 20 cm above 1. 21 + 0. 09 10 cm above 1. 3.6 + 0. 11 a d j a c e n t f a u l t 1. 78 + 0. 30 I—1 ,6. LOCALITY LOCALITY DESCRIPTION 25. Sheared c o a l w i t h i n seam, lower Kootenay Fm. V i c a r y Creek, Displacement ( i n t e r s t r a t a l s l i p ) unknown. 26. T i g h t l y f o l d e d c o a l seam, lower Kootenay Fm., V i c a r y Creek. 27. Adjacent normal f a u l t i n lower Kootenay Fm. at V i c a r y Creek. Displacement l e s s than 4 m. 28. Sheared c o a l w i t h i n c o a l seam, upper Kootenay Fm. Tent Mtn. Displacement ( i n t e r s t r a t a l s l i p ) unknown NORMAL REFLECTANCE SHEARED COAL REFLECTANCE 1.05 ± 0.11 adjacent shear 1.24 ± 0.10 adjacent shear 1.13 ± 0.12 unknown sheared c o a l 1.04 ± 0.10 i n hinge 1.21 ± 0.07 adjacent f a u l t 1.27 ± 0.07 1.08 ± 0.03 adjacent f a u l t 1.21 ± 0.07 adjacent f a u l t 1.09 ± 0.09 136 with normal v i r i n i t e reflectance values. Furthermore, the associated structure and f a b r i c of the coal are.not notably d i f f e r e n t between areas of high and normal values. The only exception i s along the Coleman Fault (Fig. 4-15; Loc. 24), which has the largest stratigraphic separation of any f a u l t studied as well as the highest mean reflectance (1.78%) and the thickest associated coal f a u l t gcuge. The variance and anisotropy of reflectance measurements of sheared coal with anomalous v i t r i n i t e reflectance i s compararable with that cf laboratory heated coal of similar reflectance. . A l l the samples have s i m i l a r large variances and anisotropies.. As found i n t h i s study, Marshall and Murchinson (1971) observed an increase in anisotropy with coal samples which were heated in the laboratory to progressively higher temperatures and they further documented an increase i n anisotropy from low to higher rank coal. The variances of v i t r i n i t e reflectance measurements of coal heated i n the laboratory i n t h i s study and those of f i e l d samples with high values are also s i m i l a r to those reported from shear zones by Teichmuller (1975) . Prior to discussing the implications of the reflectance values i t i s necessary to consider the o v e r a l l l i m i t a t i o n s of the data. The mean of the anomalously high v i t r i n i t e reflectance values of the samples, i f considered separately, would correlate with an increase i n rank from medium-volatile bituminous coal to low-volatile bituminous coal and semi-anthracite. . Because of the large variance of the v i t r i n i t e reflectance values, i t i s unlikely that these samples would have 137 F i g u r e 4 - 1 6 . Coleman F a u l t p l a n e a t W i n t e r i n g C r e e k , j u s t n o r t h o f V i c a r y C r e e k . A t t h i s l o c a l i t y a seam o f m e d i u m - v o l a t i l e b i t u m i n o u s c o a l o c c u r s i n and has b e e n d r a g g e d up the f a u l t p l a n e . I n a d d i t i o n a s l i c e o f Crowsnest V o l c a n i c s F o r m a t i o n (Kcr) i n t e r v e n e s between t h e h a n g i n g - w a l l s t r a t a o f the Kootenay F o r m a t i o n (JKk) and f o o t w a l l s t r a t a o f the B e l l y R i v e r F o r m a t i o n . 138 the same chemical composition as normal coal with the same mean reflectance (also refer to Chandra, 1965a). Furthermore, because distinguishing the d i f f e r e n t macerals, p a r t i c u l a r l y v i t r i n i t e from semi-fusinite and macrinite, i s based i n part on t h e i r reflectance, i t i s possible that highly r e f l e c t i n g v i t r i n i t e , in highly fragmented coal which has been successively sheared, may have been misidentified and thus not included in the analysis, which would result i n values which are too low. Nevertheless with the large number of p a r t i c l e s measured and samples examined, i t i s unlikely that the l a t t e r problem has seriously affected the r e s u l t s or the conclusions subsequently drawn. IMPLICATIONS OF THE ANOMALOUS VITRINITE REFLECTANCES The occurrence of natural samples with anomalously high v i t r i n i t e reflectance . values i n conjunction with t h e i r large variance suggests that these samples have l o c a l l y been exposed to high temperatures. „ Furthermore, the high temperatures must have existed f o r short durations; otherwise, considering any reasonable thermal conductivity of coal or coal plus f l u i d , the zone of thermally affected coal would be much more extensive than the narrow zones observed. The high temperatures are therefore considered the res u l t of f r i c t i o n a l heating during s t i c k - s l i p f a u l t i n g . . High temperatures could not have been generated by f a u l t creep because of the very slow rates of slippage during creep (McKenzie and Brune, 1972). Moreover, had high temperatures been generated as a r e s u l t of f a u l t creep, the thermal halo i n the region of the shear zone would have been 139 much wider. Even along the Coleman Fault plane (Fig. 16; l o c . . 24) no large scale thermal effects were observed that would provide evidence for sustained high heat flows as a result of f a u l t creep or the emplacement of a 'hot 1 thrust sheet such as documented elsewhere by Beech and Fyfe (1972) and Bustin et a l . . (1977) . Accepting a very short heating duration, the c a l i b r a t i o n curves established i n t h i s study (Figs. 4-2, 4-3, 4-4, and 4-5) can be used to approximate the temperatures reached during s l i p . The highest mean v i t r i n i t e reflectance obtained along the Coleman Fault would correspond to temperatures of 450°C as long as the e f f e c t i v e heating time was l e s s than 7 hours. I f the eff e c t i v e heating time was one month, Bosticks' (1973) curve (Fig. 4-6) would suggest the temperature was i n the.order of 380°C. Other anomalously high values, i n the range of 1.45% Ro,, along the Coleman Fault correspond to temperatures of about 435°C. At location 2 a value of 1.35% Ro. equates with a temperature of 410°C whereas values of 1.20% at locations 5 and 25 correspond to temperatures of about 400°C. I f the values at locations 8, 18, 27 and 28 are s i g n i f i c a n t they could correspond to temperatures of 200<>c to 380°C for short durations. The anomalous v i t r i n i t e reflectances thus represent temperatures which are probably between 100°C and 350°C greater than the ambient temperature, based on an estimated geothermal gradient of 25 °C km-i and a depth of b u r i a l of 4 km (100 °C). The absence of measurable heating effects along some shear zones as ccmpared to others may be the r e s u l t of: 1) aseismic creep (stable sliding) rather than s t i c k - s l i p during 140 shear; 2) low e f f e c t i v e stress across the shear zone; or 3) slow rates of s t i c k - s l i p s l i d i n g . Stable s l i d i n g and s t i c k - s l i p s l i d i n g have been studied experimentally by Byerlee (1970), Stesk et a l . , (1974), Summers and Byerlee (1977) and others who have shown that the f r i c t i o n a l properties and f a u l t s t a b l i t y are dependent on e f f e c t i v e stress, temperature, surface roughness and thickness and composition of f a u l t gouge. Summers and Byerlee (1977) found i n experiments that, with f a u l t gouge of uniform thickness, dry samples of widely d i f f e r e n t rock materials exhibited s t i c k - s l i p behavior when the confining pressure was i n the order of 1.5X105 kPa to 3.0X10S kPa. Such pressures were considered to be the point where.sufficient force was applied to close cracks and lock grains together, forcing deformation to take place by f r a c t u r i n g through grains, as compared to lower pressures where grains apparently l i f t over each other. They further found that i f water was present i t had a s t a b i l i z i n g influence by reducing the e f f e c t i v e stress when either trapped between rocks of low permeability or loosely bounded in a mineral structure, such as i n hydrated clays. The thickness of the f a u l t gouge i s probably important i n determining whether or not s t i c k - s l i p or stable s l i d i n g w i l l occur, and there i s a correlation between f a u l t displacement and thickness of f a u l t gouge (Otsuki, 1978); however, during s t i c k -s l i p f a u l t i n g the f a u l t plane can be considered to be planar.. Engelder et a l . , (1975) have shown that zones of s l i p are t h i n , even in the presence of f a u l t gouge, i n laboratory experiments but, as discussed by Cardwell et a l , , (1978), i t i s not clear whether t h i s i s actually t i e case with f a u l t s . . 141 Heating as a r e s u l t of f r i c t i o n a l s l i d i n g has been investigated by Bowden and Tabor (1950) who have demonstrated that, when two bodies s l i d e past each other, the f r i c t i o n between them i s proportional to the normal force and not to the surface area because the bodies are only in contact at asperi t i e s and the normal force i s transmitted through the as p e r i t i e s . . The area of contact i s thus determined by the y i e l d pressure of the a s p e r i t i e s . The law of f r i c t i o n F=0N (1) where F i s the f r i c t i o n a l force, 0 i s the c o e f f i c i e n t of f r i c t i o n and N i s the normal force, i s thus related to the yie l d pressure of the a s p e r i t i e s . , McKenzie and Brune (1972), however, have argued that (1) w i l l not apply when the normal force exceeds some function of the stress since the contact area w i l l then be independent of the normal force. They further suggest that at depths at which most earthquakes occur (1) w i l l not apply because at depths below 3 km both surfaces must be contact everywhere.. McKenzie and Brune (1972) and Cardwell et a l . , (1978) have t h e o r e t i c a l l y calculated temperatures r e s u l t i n g from f a u l t i n g based on these assumptions. Although such calculations may be applicable to deep seated earthquakes, as they suggest, along f a u l t s i n t h i s study the e f f e c t i v e normal stress was probably not cf the magnitude envisaged by these authors. Low e f f e c t i v e stress during thrust f a u l t i n g has been argued on mechanical grounds by numerous authors (Hubbert and Eubey, 1959; C a r l i s l e , 1S63). Furthermore the presence of a s p e r i t i e s , on 142 some scale, i s probably l a r g e l y responsible for the 'locking' of f a u l t s , the ensuing accumulation of e l a s t i c s t r a i n energy and the eventual f a i l u r e which i s reguired for s t i c k - s l i p i n the f i r s t place (Byerlee, 1970). Nor does i t seem possible for high temperatures such as inferred from t h i s study and assumed by McKenzie and Erune (1972) to occur during stable s l i d i n g . . accepting that the usual law of f r i c t i o n (1) applies, the temperature change occurring during f r i c t i o n a l s l i d i n g between two bodies of s i m i l a r composition along the plane of s l i d i n g i s given by (Bowden and Tabor, 1950): T-To=uvg (HPm^8JK) where T-To i s the change i n temperature, u i s the k i n e t i c c o e f f i c i e n t cf f r i c t i o n , v i s the s l i d i n g v elocity, g i s the g r a v i t a t i o n a l constant, W i s the load on the contact area, Pm i s the y i e l d point of the material, J i s the mechanical equivalent of heat and K i s the thermal conductivity. In Fig.,4-17, di f f e r e n t potential temperatures are given as a function of load and s l i d i n g velocity using 0=0.2 (modified from Chappie, 1975), Pm=1.789 dynes cm-* (modified from Hobbs, 1964) and K=5 x10-3 cal cm-* s e c - 2 °C (modified from Hendrickson, 1972). a number of assumptions were necessary to construct Fig. 4-17, the most important of which i s the assumption of dry conditions. Under lubricated conditions i n laboratory experiments of Bowden and Tabor (1950), high temperatures were reached during s l i d i n g f r i c t i o n at moderate v e l o c i t i e s and loads, but the temperatures were as much as several hundred degrees Celsius lower than under 10 2 10 3 10 4 10 5 10 Effective S t ress , kPa Figure 4-17. Relationship between s l i d i n g v e l o c i t y , e f f e c t i v e • s t r e s s and temperature c a l c u l a t e d using Bowden and Tabors (19 50) expression and assuming dry s l i d i n g conditions and parameters o u t l i n e d i n text. I-1 144 dry conditions. During f a u l t i n g some lu b r i c a t i o n probably exists ( C a r l i s l e , 1963) but i t cannot be quantitatively evaluated. Assuming that Pm, K and u remain constant with r i s i n g temperature and velocity also introduces error i n the calculations but t h i s error i s considered i n s i g n i f i c a n t as compared to the uncertainity i n assuming dry f r i c t i o n . C l e a r l y only the broadest conclusions can be drawn from F i g . 4-17. Even i f the assumptions outlined above are correct a temperature change of 350°C could correspond to pressures as low as 2.0X103 kPa with s l i d i n g v e l o c i t i e s of 1 m s~* or pressures as high as 2.0X105 kPa i f the s l i d i n g velocity was i n the order of 1 cm s _ l (Fig. 18). Calculations of McKenzie and Brune (1972) and Cardwell et a l . , (1978), although based on d i f f e r e n t assumptions, have similar l i m i t a t i o n s . High temperatures are t h e o r e t i c a l l y predicted during f r i c t i o n a l s l i d i n g over a wide range of e f f e c t i v e stresses and s l i p v e l o c i t i e s . Nevertheless, i t i s possible tc draw some general implications and to speculate further about f a u l t mechanics from the obtained values. F i r s t , along shear zones where high temperatures were measured there had to be a r e l a t i v e l y high e f f e c t i v e stress considering reasonable rates of s t i c k - s l i p (10 to 100 cm s- 1) and based on the fact that s t i c k - s l i p must have occurred; second, the e f f e c t i v e stress and/or s l i p velocity were probably different during successive episodes of s l i p along the same f a u l t zone, in as much as markedly d i f f e r e n t anomalous temperatures are calculated from the same f a u l t zone (e.g., loc. 24). Because i t i s not known whether s t i c k - s l i p f a u l t i n g as compared to stable s l i d i n g occurred along shear zones where 145 no high temperatures were measured, i t i s not possible to evaluate the e f f e c t i v e stress. However, that no detectable change i n rank was observed i n many f a u l t zones indicates, by comparison with the experimentally heated coal samples, that shearing did not re s u l t i n temperatures i n excess of 200°C. . The absence of such temperatures during f a u l t i n g implies, by analogy with experimental studies (Logan, 1975; Summers and Byerlee, 1977), that the ef f e c t i v e stress was lower in these areas. The most important general implication of the results i s that along reverse and thrust f a u l t s there are areas of s i g n i f i c a n t and less s i g n i f i c a n t e f f e c t i v e stress.. Such does not detract from but rather supports the contention of Hubbert and Eubey (1959) that high f l u i d pressure could r e l i e v e the e f f e c t i v e normal stress to the degree that large thrust sheets could be pushed down slope under gravity without i n t e r n a l shear f r i c t i o n . As an alternative to low e f f e c t i v e stress and high pore pressure, i t would be necessary to invoke a f a u l t mechanism involving viscous deformation, such as suggested by Smoluchowski (1909) and Kehle (1970). In terms of pore pressure areas of high e f f e c t i v e stress may represent areas of drainage. For example, the high temperatures calulated along the Coleman Fault were obtained from samples collected at a l o c a l i t y where the f a u l t steps rapidly up section and a s l i c e of Crowsnest Volcanics Formation has been dragged into the f a u l t plane along with the c o a l . Areas where f a u l t s rapidly,step up.section are undoubtedly areas of stress concentration; and furthermore, such areas are probably better drained because of associated extensive fracturing and f a u l t i n g of the surrounding rocks. 146 EFFECT ON COAL QUALITY The e f f e c t of shear on quality i s p r i n c i p a l l y mechanical rather than thermal.. Only along the Coleman Fault can the thermal a f f e c t s associated with shearing be considered s i g n i f i c a n t and even at t h i s l o c a l i t y a bulk sample analysis would probably reveal only a minor increase in rank. Even such pervasively sheared and polished coal as shown i n Fig. 4-10 shows no notable increase i n rank. More important, however, are the mechanical effects of shearing which have greatly comminuted the coal and associated rock partings.. Sheared coal in areas of tectonic thickening has been extensively mined i n the study area; these coal deposits have disproportionately high amounts of ash, poor washability c h a r a c t e r i s t i c s and are commonly partly oxidized. The degree of oxidation of the coal i s d i r e c t l y proportional to the extent of comminution. The large surface area the comminuted coal has f a c i l i t a t e d rapid and extensive oxidation of the c o a l . Moreover, the presence of numerous f a u l t planes and fractures i n adjacent rocks and the coal seams has enabled deep penetration of atmospheric oxygen and c i r c u l a t i o n of oxygenated waters., Such i s the case on a large scale in the v i c i n i t y of Vicary Creek, where extensively granulated coal i n areas of normal f a u l t i n g i s more highly oxidized and has a lower free-swelling index than coal either up- or down-dip from the region of f a u l t i n g . An a d d i t i o n a l example i s the highly faulted and tectonic a l l y thickened and comminuted coal deposits at Coal Mountain, B r i t i s h Columbia, which are also oxidized i n part (B r i t i s h Columbia Task Force on Coal, 1976). 147 The disproportionately high ash content of deposits of highly sheared coal i s largely the r e s u l t of comminution during shearing of otherwise discrete rock partings and interbeds of sandstone and shale (Fig. 11b). The poor washability of the coal i s probably s i m i l a r l y the re s u l t of comminution of the ash during shearing. In addition, p l a s t i c flowage of the c l a r i t e and associated engulfment cf formerly discrete ash p a r t i c l e s r e s u l t s in the formation of aggregates* . Within the aggregates the ash i s f i n e l y disseminated and thus not readily separated. SUMMARY AND CONCLUSIONS Pervasively sheared coal comprises a large proportion of some coal deposits i n parts of the southern Rocky Mountains of B r i t i s h Columbia and Alberta. On a mesoscopic scale the coal has a brecciated f a b r i c and adjacent to some f a u l t s the coal i s f i n e l y granulated and extensively polished. The microfabric of the sheared coal i s generally s i m i l a r to the mesoscopic f a b r i c consisting of angular fragments of coal with no evidence of duct i l e behavior. In areas of apparently high s t r a i n the c l a r i t e component of the coal flowed p l a s t i c a l l y , forming aggregates consisting of brecciated fragments of i n e r t i t e and v i t r i t e in a c l a r i t e groundmass. Microfolds of similar s t y l e and 'wild' folds are also present. Samples of medium-volatile bituminous coal heated i n the laboratory at temperatures up to 600°C and durations up to several days resulted i n v i t r i n i t e reflectances lower than those previously reported for lcnger durations of heating. There i s 148 very l i t t l e difference however, between the reflectances of v i t r i n i t e i n samples heated for 10 minutes or 7 hours. The lowest temperature of heating which resulted i n a detectable change i n v i t r i n i t e reflectance was 200°C. The change i n reflectance with heating i s almost l i n e a r up to the melting point of the coal where there i s an exponential r i s e i n reflectance. Samples heated for short durations have large anisotropies and a greater variance than normal coals, probably as a re s u l t of d i f f e r e n t reaction rates of the v i t r i n i t e rather than the e f f e c t of pressure or shear as previously suggested. Measurement of v i t r i n i t e reflectance of samples c o l l e c t e d from 28 d i f f e r e n t l o c a l i t i e s , adjacent to major and minor shear zones a n d , i s o c l i n a l folds, revealed a s i g n i f i c a n t change i n rank adjacent to some shear zones and no detectable change i n others. There i s no macroscopic d i s t i n c t i o n , however, between areas of high and normal v i t r i n i t e reflectance. Using the correlation curves established from the experimentally heated samples, the highest measured mean reflectance (1.78% Bo.), measured in coal within the Coleman Fault plane, may correspond to a temperature of up to 450°C. , Such a temperature i s i n the order of 350°C greater than that calculated considering a normal geothermal gradient and an estimated maximum depth of b u r i a l . , Other anomalously high v i t r i n i t e reflectances correspond to temperatures between 200 and 430°C. The anomalously high v i t r i n i t e reflectances are r e s t r i c t e d to very narrow zones adjacent to and within the shear zones which, considering any reasonable thermal conductivity, required a very short heating duration. The high temperatures 149 are therefore considered to be the r e s u l t of f r i c t i o n a l heating during s t i c k - s l i p f a u l t i n g . The absence of measurable temperatures i n some areas may be the r e s u l t of stable s l i d i n g as ccmpared to s t i c k - s l i p f a u l t i n g . , The obtained temperatures, when considered i n conjunction with t h e o r e t i c a l relationships, have major implications with regard to reverse and thrust f a u l t mechanics.. These are: (1) high temperatures are l o c a l l y reached during f a u l t i n g as a resul t of f r i c t i o n a l heating; (2) s t i c k - s l i p f a u l t i n g occurs at least i n part along such f a u l t s ; and (3) areas of s i g n i f i c a n t e f f e c t i v e stress e x i s t along the f a u l t s but also areas of lower and less s i g n i f i c a n t e f f e c t i v e stress e x i s t . In general the implications of the re s u l t s support Hubbert and Eubey's (1959) hypothesis that high pore f l u i d pressure may ex i s t along major f a u l t s but the res u l t s also suggest that areas of lower pore pressure may e x i s t . High temperatures measured along the Coleman Fault were obtained from an area where the f a u l t i s folded and a s l i c e of Crowsnest Volcanics i s present i n the f a u l t plane.. In such areas stress concentration probably existed and drainage of high pore pressure may have been f a c i l i t a t e d by the extensive f r a c t u r i n g of the footwall and hanging wall str a t a . , The effect of shear on coal qu a l i t y i s primarily related to mechanical comminution of the coal. Thermal e f f e c t s due to f r i c t i o n a l s l i d i n g are not s i g n i f i c a n t on the scale of the coal deposits. The highly sheared coal has disproportionately high amounts of ash and poor washability c h a r a c t e r i s t i c s and i s oxidized i n part. The high ash content and poor washability of 150 the coal are principally related to the comminution of former discrete rock partings and interbeds of sandstone and shale. The extent of oxidation of the coal i s directly proportional to the fine grain size and greater surface area of the coal, which facilitated rapid rates of oxidation. In addition faulting and fracturing of the associated strata during shearing promoted deep penetration of atmospheric oxygen and circulating oxygenated waters. 15 ACKNOWLEDGEMENTS I thank Coleman C o l l i e r i e s for access to t h e i r property and for providing a n a l y t i c a l data and subsurface information. This study has benefited from discussions with Drs. ,C-A. Brockley, W.C. Barnes and W.H. Mathews of the University of B r i t i s h Columbia. E a r l i e r drafts of t h i s paper were read by W.H. Mathews, W.C._Barnes, J.W. Murray and G,.E. Rouse. I am endebted to Dr. D. Pearson of the B r i t i s h Columbia Department of Mines and Petroleum Resources for providing access to a microscope and sample preparatory eguipment for coal analysis. F i n a n c i a l support was provided by the Geological Survey of Canada and by Natural Sciences and Engineering Research Council (Canada) Grants to Drs. W.H. Mathews (A-1107) and to W.C. 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Wallace, R.C., 1976, P a r t i a l fusion along the Alpine f a u l t zone, New Zealand: Geological Society of America B u l l e t i n , v o l . 87, pp. 1225-1228. 156 P A R T 4 M O R P H O L O G Y A N D O R I G I N O F S T R I A T E D C O N I C A L S T R U C T U R E S A N D R E L A T E D F R A C T U R E S I N B I T U M I N O U S C O A L O F T H E S O U T H E R N C A N A D I A N R O C K Y M O U N T A I N S 157 ABSTRACT Striated structures, many of which are con i c a l i n form, are common mesoscopic features i n bituminous coal of the southern Canadian Eocky Mountains. The structures are planar, conical to pyramidal i n outline and are characterized by s t r i a e which radiate from a common apex and bifurcate or 'horsetail* to form secondary structures on the master surface. They are up to 20 cm in length, 4 cm i n width and have apical angles varying from 10o to 50°. The s t r i a t e d structures occur at numerous l o c a l i t i e s i n both highly sheared coal and only gently folded seams. The conical s t r i a t e d structures c l o s e l y resemble some shatter cones developed i n fine-grained rocks whereas the planar s t r i a t e d structures are somewhat similar to chevron-structured, hackle-marked j o i n t s . The pyramidal structures are apparently unique to coal. A l l three types of structures are considered to be the r e s u l t of b r i t t l e shear fracture based on t h e i r occurrence, o r i e n t a t i o n , and morphology and on experimentally produced fractu r e s . The apparently r e s t r i c t e d occurrence of the structures to coal i s l i k e l y a r e s u l t of the low t e n s i l e and compressive strength of bituminous c o a l , possibly augmented by high i n t e r - and/or i n f r a - p a r t i c l e gas pressure r e s u l t i n g from devolatization of the coal during progressive c o a l i f i c a t i o n . . 158 INTRODUCTION Conical structures which occur in rocks have generally been referred to as either shatter cones or cone--in-cone structures. , Shatter cones are c o n i c a l fracture surfaces which have been attributed to the passage of intense shock waves associated with a cryptoexplosion (Bucher, 1963; Manton, 1965; Dietz, 1968), whereas cone-in-cone structures are considered diagenetic, c r y s t a l l i z a t i o n features (Woodland, 1964a; Pettijohn, 1975). In addition to shatter cones and diagenetic cone-in-cone structures, tliere are a few descriptions of conical structures which occur primarily i n bituminous c o a l . This l a t t e r group of structures somewhat resembles shatter cones (cf. Dietz, 1968) but are neither associated with cryptoexplosion structures nor evidence for the.passage of intense shock waves. Conical structures i n coal were documented by Garwood (1892) from the coal f i e l d s of Durham and South Wales and by Gresely (1892) who referred to 'cone-in-cone* structures i n coal from L e i c e s t e r s h i r e , Belgium and western Pennsylvania. More recently, conical structures have been described i n coal from Wales (Tarr, 1932) , New Zealand (Fyfe and Wellman, 1937; Bartram, 1941), the Netherlands (Deenen, 1942), Poland (Kwiecinska, 1963; Gorezyea and Kwiecinska, 1963) and West V i r g i n i a and Idaho (Price and Shaub, 1963).. Conical structures somewhat resembling shatter cones have also been described from Cambrian shales at l o c a l i t i e s i n C a l i f o r n i a and Newfoundland (Kay and Hansman, 1971) and from carbonaceous. Cretaceous shales i n Colorado (Woodland, 1964b).. 159 The o r i g i n of the conical structures has been attributed to a variety of processes. Gresely (1892) suggested that they originated 'as a kind of c r y s t a l l i z a t i o n ' and Tarr (1932) and Woodland (1964b) have proposed that they form by some diagenetic process.. Price and Shaub (1963) and Kwiecinska (1963) considered a tectonic o r i g i n , whereas, Bucher (1963) suggested that shrinkage of the.coal i n conjunction with overburden pressure may have been important. A l l of the above interpretations have been hampered by the paucity of the structures and because the specimens described and interpreted by Bartram (1941), Bucher (1963), Price and Shaub (1963) and Woodland (1964b) were not collected i n place by these authors. In bituminous coal i n the southern Canadian Bocky Mountains s t r i a t e d structures, many of which are conical i n form, are a conspicuous mesoscopic f a b r i c element.. These structures are c l e a r l y of the same type as the c o n i c a l structures previously described from coal; however, i n western Canadian bituminous coal, the conical structures are apparently much more abundant and morphologically more diverse than previously described, . The structures occur at numerous l o c a l i t i e s in both pervasively sheared coal and i n gently folded seams, which provide.an excellent opportunity to assess the o r i g i n of the structures. The purpose of t h i s paper i s to document the occurrence and c h a r a c t e r i s t i c s of these i n t e r e s t i n g structures and to discuss their possible o r i g i n and s i g n i f i c a n c e . Striated structures occur i n coal of the Kootenay Formation at numerous l o c a l i t i e s within the Crowsnest Pass area. . 160 A detailed examination of the structures was made at three l o c a l i t i e s : 1) north of Coleman, Alberta i n the Coleman thrust S-heet; 2) at Tent Mountain on the B r i t i s h Columbia-Alberta boundary i n the Lewis thrust sheet; and 3) i n the Balmer North coal mine near Michel, B r i t i s h Columbia near the north end of the Fernie synclinorium (Fig.,1-2). In the Balmer North mine the coal seams are gently folded, whereas at the Coleman and Tent Mountain l o c a l i t i e s they are, for the most part, pervasively sheared. OCCUBEENCE AND GENEBAL DESCEIPTION OF THE STBUCTUEES The s t r i a t e d structures display a great variation i n morphology, size and orientation. Their unifying c h a r a c t e r i s t i c i s the presence of s t r i a t i o n s which radiate from a common apex and which commonly bifurcate or ' h o r s e t a i l ' to form subsidary s t r i a t e d structures on the master surface (Fig. 5-1 and 5-2).. The radiating pattern of the s t r i a e d i f f e r e n t i a t e s these structures from slickenside s t r i a e . Also, the absence of well developed transverse r i b s , the absence of i n t e r n a l structure and gross morphology serve to distinguish them from diagenetic coneT in-ccne structures or c r y s t a l l i z a t i o n structures such as those described by Woodland (1964a), P e t t i John (1975) and others. The planar s t r i a t e d structures, as described l a t e r , are somewhat si m i l a r to chevron-structured, hackle-marks common on some j o i n t surfaces i n recks. At a l l l o c a l i t i e s , the c o n i c a l structures are r e s t r i c t e d to the coal seams and to lenses of coal within sandstones or shales. , They occur i n both c l a r a i n - and v i t r a i n - r i c h coal and 161 F i g u r e 5-1. C o n i c a l to o b l a t e s t r i a t e d s t r u c t u r e s from Tent Mountain. Note the downward p r o j e c t i o n of the cone a p i c e s . F i g u r e 5 - 2 . C o n i c a l to o b l a t e s t r u c t u r e s showing the d e t a i l of the s u r f a c e s . N o t i c e the r a d i a t i n g r i d g e s and ' h o r s e t a i l s ' on the s t r u c t u r e s to the lower r i g h t of the s c a l e . Arrow p o i n t s to the apex of one such s t r u c t u r e . 162 commonly cross-cut s t r a t i f i c a t i o n in the coal,. The structures occur on, or define, d i s t i n c t fracture sets i n the coal. Their surface has a s i l k y to d u l l l u s t r e , i n marked contrast to the glossy l u s t r e of major shear surfaces which occur i n the coal. The s t r i a e are i n t r i c a t e l y developed on the surface.. The s t r i a e commonly terminate against adjacent s t r i a e or secondary s t r i a e (Fig. 5-2) and do not cross-cut or overprint each other._ In cross-section the conical structures display no inter n a l morphology with the exception of the outline of the regularly spaced s t r i a e along the edges. V i t r i n i t e reflectance measurements made from the centre to the edge of the structures show no measurable variation i n rank of the co a l . Radial l i n e s oriented perpendicular to the s t r i a e on the surface of the st r i a t e d structures are commonly present p a r t i c u l a r l y i n the v i t r a i n - r i c h samples.. Observations of the st r i a t e d structures at high magnification revealed a heterogenous, •rough 1 surface (Fig. 5-3) sim i l a r to that shown on hackle-marked j o i n t surfaces by Syme Gash (1971) and Dov (1979). Graphite plates, such as those found on surfaces of conical structures i n coal by Gorezyea and Kwiecinska (1963) were not observed. Based on variation i n morpholoy three types of s t r i a t e d structures are recognized: 1) planar s t r i a t e d structures, which are e s s e n t i a l l y two dimensional; 2) con i c a l s t r i a t e d structures, in which at least one side of the 'cone' i s well-developed; and 3) pyramidal structures. Although gradations e x i s t between the three type of s t r i a t e d structures, they are considered to represent natural end members and are discussed separately below. F i g u r e 5-3. S.E.M. photomicrograph showing the d e t a i l of a planar s t r i a t e d s t r u c t u r e , x 400. F i g u r e 5-4. Planar s t r i a t e d s t r u c t u r e on c l e a t s u r f a c e from the Balmer North c o a l mine. 164 Planar Striated Structures Planar s t r i a t e d structures, similar to t h e i r three-dimensional counter parts, have well-developed s t r i a e which radiate from a commcn apex and subsidiary radiating structures formed by •horsetailing' of the s t r i a e (Fig. 5-4).. The structures range from 5 cm i n length and 1 cm in width to 15 cm i n length and 3 cm i n width and have length to width r a t i o s i n the.order of 5:1 to 10:1., Apical angles vary between 10° and 35° and average 15°. , These structures everywhere occur i n p a r a l l e l oriented sets on well developed fracture surfaces. On p a r a l l e l fractures, the axes of the structures have a strongly preferred o r i e n t a t i o n , whereas on conjugate sets of fractures they are commonly oriented with th e i r apices i n opposite.directions on opposed fractures such that the bases of the structures meet at an obtuse angle. Planar s t r i a t e d structures were observed at most l o c a l i t i e s and are p a r t i c u l a r l y abundant in the Balmer North coal mine. Figure 5-5 summarizes the a x i a l orientation of the structures and the b f a b r i c d irection of the seam which i s sub-p a r a l l e l with the regional f o l d axis (B). Although the structures show considerable variation i n azimuth, two d i s t i n c t maxima are present which are more or less symmetrically disposed about the ac f a b r i c plane of the seam. The structures l i e p a r a l l e l to the plane of bedding and on conjugate fractures. The orientation of the s t r i a t e d structures i n the Balmer North coal mine are p a r a l l e l to bedding, i r r e s p e c t i v e of l o c a l structure, which suggests that the structures were formed early in the deformational history of the seam. 165 N n=65 F i g u r e 5 - 5 . A x i a l o r i e n t a t i o n o f p l a n a r s t r i a t e d s t r u c t u r e s from t h e B a l m e r N o r t h m i n e . Lower h e m i s p h e r e S c h m i d t n e t . C o n t o u r s • a r e a t 2, 5, and 101 p e r 1% a r e a ; 'b' i s t h e b f a b r i c d i r e c t i o n o f t h e seam and ac i s t h e d e f o r m a t i o n a l p l a n e . 166 Conical Striated Structures This type of s t r i a t e d structure has at least one side which i s conical i n form (figs, 5-6 and 5-7). The.cones ra r e l y exceed 5 cm in length and have a basal width ranging from 5 mm to 5 cm. The length to width r a t i o varies between 2:1 and 5:1 and the apical angle between 5° and 35°.. The apex i s rounded to sharp and p a r a s i t i c secondary cones are invariably developed on the master cone surface. Individual cones are r a r e l y separable from adjacent ones. One conical surface i s generally very well developed, and parting of the coal along the cone.surface i s f a c i l i t a t e d , whereas the other side of the cone i s poorly developed and displays l i t t l e tendency to part from the surrounding c o a l . The c o n i c a l structures are known to occur i n sheared coal only at the Coleman and Tent Mountain l o c a l i t i e s . A plot of the apical orientation of the cones at two adjacent l o c a l i t i e s on Tent Mountain (Fig. .5-8) depict two d i s t i n c t maxima. . Other plots, not shown, show d i s t i n c t maxima at p a r t i c u l a r l o c a l i t i e s . However, there i s no apparent r e l a t i o n s h i p between the orientation maximia and the f a b r i c d irections of the seam at these l o c a l i t i e s . Extensive shearing of the seams and accompanying c a t a c l a s t i c flow of the coal (Bustin, 1979) has probably preceded, at least in part, the formation of the structures, resulting i n the lack of consistent orientation.. Pyramidal Striated Structures These structures are characterized by t h e i r sharp apex gure 5 - 6 . S.E.M. photomicrograph o f s t r i a t e d s e m i - c o n i c a l s t r u c t u r e s . S t e r e o - p a i r , x 2 0 . F i g u r e 5-7A. S . E . M . p h o t o m i c r o g r a p h ; s e m i -s t r i a t e d s t r u c t u r e s , x 20. c o n i c a l 169 N F i g u r e 5 - 8 . Summary o f a x i a l o r i e n t a t i o n o f c o n i c a l s t r u c t u r e s a t T e n t M o u n t a i n . L o w e r h e m i s p h e r e S c h m i d t n e t . ' B ' i s t h e r e g i o n a l f o l d a x i s a n d a c i s t h e d e f o r m a t i o n p l a n e o f t h e f o l d . 170 and pyramidal form. They are up to 3 cm i n length and 3 cm in width and have length to width r a t i o varying from 3:1 to 1:1. The apical angle of most structures are close to 45°, The base of the pyramids i s rectangular to square. The structures nearly everywhere.occur i n alternating sets such that every other cone apex points i n the opposite d i r e c t i o n to i t s adjacent neighbor (Fig. 5-9) . — The.pyramidal structures are most commonly oriented perpendicular to and abut slickensided surfaces.. In some cases, such as shown i n Fig, . 5-9A, a slickensided surface.in a sandstone or shale disappears upon passing into a coal lens and pyramidal structures are developed with apices oriented approximately 90° to the projected trace of the slickensided surface. In the observed samples, there appears to be no consistent r e l a t i o n s h i p beteen the rectangular form of the base of the pyramids and the d i r e c t i o n of motion i n f e r r e d from the orientation of the slickenside s t r i a e . The pyramidal structures were observed only at the Tent Mountain l o c a l i t y , . With the exception of observed relationships between slickensided surfaces and the pyramids discussed above there i s no apparent co r r e l a t i o n between the s t r u c t u r a l f a b r i c d i r e c t i o n of the coal measures and the pyramids. Comparison with Other Structures The s t r i a t e d structures of t h i s study resemble some previously described •cone-in-cone' structures i n coal and also have seme features i n common with shatter cones and chevron-r structured hackle-marked j o i n t s . 171 F i g u r e 5-9A. F i g u r e 5 - 9 B P y r a m i d a l s t r i a t e d s t r u c u t u r e s . I n t e r l o c k i n g p y r a m i d s i n a c o a l l e n s w i t h i n a f i n e - g r a i n e d s a n d s t o n e . The s l i c k e n s i d e d s u r f a c e (S) t e r m i n a t e s a t the c o a l l e n s . C l o s e up o f F i g . 5-9A. A n e a r l y v e r t i c a l v i e w o f the p y r a m i d s showing t h e i r r e c i l i n e a r o u t l i n e . 172 Previously described conical structures i n coal are s i m i l a r to the conical st r i a t e d structures of t h i s study i n the following respects: 1) they consist of s t r i a e which radiate from a common apex and which commonly ' h o r s e t a i l ' to form subsidiary cones; 2) they have apical angles which vary between 15° and 50°; 3) they are of s i m i l a r dimensions; and 4) one side of the cone i s invariably better developed than the other side. The only previous description of pyramidal structures i n coal i s that of Kwiecinska (1963), who has described 'pyramidal cones' frcm coal cf the Lower Sil e s i a n coal basin. As with the pyramidal structures of t h i s study the cones described by Kwiecinska . occur i n inverted sets and are bounded by a planar surface.,. 'Cockscomb c c a l ' and 'double cone-in-cone' coal, referred to by Gresley (1892), also may be similar to the pyramidal structures of t h i s study. Planar s t r i a t e d structures have not previously been described from coal, with the exception of the study of Deenen (1942); however, i t i s possible that these structures would not have been grouped with the conical forms.. Bucher (1963) and Dietz (1968) have alluded to the s i m i l a r i t i e s between the conical structures i n coal and shatter cones. Bucher (1963) has argued that because of the s i m i l a r i t y of the structures, the shatter coning mechanism may not require the impact speed of meteorites, whereas Dietz (1968) has stated that the conical structures in coal, although s u p e r f i c i a l l y resembling shatter cones, are not shatter cones. The conical structures i n coal closely resemble shatter cones developed i n fine-grained rocks such as dolomites, limestones and shales 173 shown by Dietz (1968) and Manton (1965), which have small a p i c a l angles (compare Fig. 5-1 with Plate V of Dietz, 1968 and with F i g . .5-3 of Manton, 1965). The a p i c a l angle of most shatter cones i s i n the crder of 90°, which i s the . most notable morphological difference from the conical structures i n coal. Shatter cones are also invariably considered to be associated with cryptoexplosion features and require intense shock pressures for t h e i r formation. Theoretical considerations by Johnson and Talbot (1964) led them to suggest that shatter cones are shock features formed as a r e s u l t of the interaction of an e l a s t i c precursor in the shock front with an inhomogeneity i n the rock. For shatter cones to form they have, therefore, argued that the strength of the shock wave must exceed the Hugoniot e l a s t i c l i m i t of the material. This t h e o r e t i c a l argument cannot be r e a d i l y applied to conical structures i n coa l . There i s no evidence for the passage of intense shock waves in associated l i t h o l o g i e s and the experimentally determined Hugoniot for coal shows " p r a c t i c a l l y no evidence for an e l a s t i c y i e l d point"- (Butcher and Stevens, 1975, p. .151). The planar s t r i a t e d structures of t h i s study closely resemble chevron-structured hackle-marked joints such as those described by Syme Gash (1971) and Dov (1979). The only s i g n i f i c a n t difference i s that the chevron structures are always bounded by two sub-parallel i n t e r f a c i e s (Syme Gash, 1971), whereas the s t r i a t e d structures i n coal commonly occur i n p a r a l l e l sets on the same fracture surface. 174 ORIGIN OF THE STRUCTURES Early theories concerned with the or i g i n of the conical structures i n coal alluded to t h e i r s i m i l a r i t i e s with •cone-in-cone ' structures of diagenetic o r i g i n . . The morphology of 'cone-in-cone 1 structures i s , however, markedly d i f f e r e n t from that of the conical structures i n coal. As to t h e i r formation in coal, a diagenetic c r y s t a l l i z a t i o n or pressure-solution o r i g i n of the structures i s not feasible because of the i n s o l u b i l i t y of coal i n most natural solutions (Price and Shaub, 1963).. An organic o r i g i n can also be dismissed because of the absence of i n t e r n a l structure and because s t r a t i f i c a t i o n passes through the structures. A l l of the features of the structures described i n t h i s study suggest that they are b r i t t l e fracture surfaces. In an attempt to produce the structures experimentally, a number of macroscopically unfractured blocks of bituminous and sub-bituminous coal were impacted at v e l o c i t i e s ranging from 1 m s - 1 to 1250 ms - 1. In a l l of the high v e l o c i t y experiments the coal f a i l e d along a multitude of surfaces at various orientations. No conical structures were formed i n any of the.experiments. However, planar s t r i a t e d structures, s i m i l a r to those previously described here, were v i s i b l y developed i n blocks of bituminous coal impacted at speeds of about 350 m s~ l (Fig. 5-10).,, Low v e l o c i t i e s did not r e s u l t i n formation of the structures whereas in experiments at higher v e l o c i t i e s the coal was so in t e n s i v e l y fractured that i t was impossible to reconstruct the i n d i v i d u a l surfaces. The planar s t r i a t e d structures a r t i f i c i a l l y created in 175 F i g u r e 5-10. P l a n a r s t r i a t e d s t r u c t u r e s i n c o a l a r t i f i c i a l l y f r a c t u r e d by h i g h v e l o c i t y i m p a c t . 176 the bituminous coal formed on fractures oriented between 0° and 50° from the d i r e c t i o n cf impact. Such re s u l t s c l e a r l y support neither a shear nor an extension o r i g i n of the structures. Shear fractures can form at various orientations with respect to the maximum p r i n c i p a l stress (61), depending on the difference between <=1 and the minimum p r i n c i p a l stress (<^ 3) and the magnitude of 61. There i s a range of shear fractures that can, therefore, develop at orientations close to those of t e n s i l e fractures (Syme Gash 1971). Shear fractures are generally expected t c shew some shear displacement (Conrad and Friedman, 1976), however there i s l i t t l e agreement on whether other s t r i a t e d hackle-marked structures such as found in rocks, metals, glass (Murgatroyd, 1942; Syme Gash, 1971, Dov, 1979; and others) and plexiglas (Correscio and Soperstein, 1977), which show no evidence of shear displacement, are t e n s i l e or shear fractures. Eased on t h e o r e t i c a l considerations, Syme Gash (1971) has suggested that hackle-marked surfaces are diagnostic of shear j o i n t s on dynamic fracture surfaces (see also Dov, 1979) and r e s u l t from the i n t e r a c t i o n of compressional and t e n s i l e stress waves. The planar s t r i a t e d structures of t h i s study are considered shear fracture surfaces. The orientation of the structures on conjugate fracture sets bisected by the l o c a l ac fa b r i c d i r e c t i o n of the seam in the Balmer North mine suggests, by analogy with the geometry of shear fractures described by Stearns (1964, 1968) and others, that the st r i a t e d structures develop on shear fractures i n which no f i n i t e displacement has occurred.. Futhermore, i t i s unlikely that such closely spaced 177 p a r a l l e l , or conjugate sets of fractures could form i n extension because formation of one fracture surface would disrupt the l o c a l t e n s i l e f i e l d such as described by Adams and Sines (1978). Formation of the s t r i a e however, probably does require t e n s i l e and compressicnal wave interactions such as argued by Syme Gash (1971), The low angle many of the experimentally produced fractures made with d i r e c t i o n of impact as was found i n t h i s study i s not e a s i l y explained. I t i s possible that the fractues are a product of stress wave interactions at the free surface of the coal samples, perhaps si m i l a r to some of the complex stress wave interactions predicted on t h e o r e t i c a l grounds by Syme Gash (1971). A l t e r n a t i v e l y , the experimental r e s u l t s may r e f l e c t the presence of oriented flaws which would markedly affect fracture orientations (Adams and Sines, 1978), but which were not present during natural fracturing of the coal. The conical and pyramidal s t r i a t e d structures are also considered to be shear fractures. For formation of perfectly conical structures, a r a d i a l l y disposed stress system would be necessary such that c>1 i s p a r a l l e l to the cone axis (Price and Shaub, 1963; Bucher, 1963), Such conditions are probably no more ccmmon in coal than i n other rocks, however, coal has a much lower strength than most other rocks (Hobbs, 1964) and a much f i n e r grain size (Butcher and Stevens, 1975)., In addition, simultaneous.(dynamic) r a d i a l b r i t t l e shear fracture of the coal may have been augmented by high i n t e r - and i n t r a - p a r t i c l e gas pressure r e s u l t i n g from devolatization of the coal during c o a l i f i c a t i o n , which would further increase the b r i t t l e n e s s of the coal. High gas pressure associated with coal i s well 178 documented i n underground mines where explosive release of carbon dioxide and methane r e s u l t in outbursts or blowouts (Norris, 1958; Popp and McCulloch, 1976). Variation in gas pressure and i n the orientation of the greatest p r i n c i p a l stress plus heterogenities of the coal probably account f o r the observed v a r i a t i o n i n apical angle of the cones.. As discussed by Price and Shaub (1963), perfectly symmetrical cones would require perfectly uniform l a t e r a l stresses which would be r a r e l y encountered, and thus incomplete cones would be developed more commonly. However, i t i s unlikely that formation of the cones in coal i s completely analogous to those produced i n materials under uniaxial compression, as suggested by Price and Shaub (1963). Formation of conical structures i n heterogeneous materials such as concrete i s generally considered to be product of l a t e r a l confinement of the specimen i n contact with the platens of the testing instrument (Neville, 1959). The close association between the pyramidal s t r i a t e d structures and slickensided surfaces observed i n t h i s study suggests that a genetic r e l a t i o n s h i p exists between the structures. , Similar pyramidal structures bounded by planar structures i n coal described by Kwiecinska (1963) furthermore indicate that t h i s association i s not unique to coal of t h i s study. I f the pyramidal structures are shear fractures analagous to the conical structures, as t h e i r general morphology suggests, the orientation of c»1 required for t h e i r formation would make an angle of between 45° and 90° with that required for the formation of adjacent slickensided surfaces. A s i m i l a r stress re-orientation i s also required i f the pyramidal 179 structures are considered to form in a t e n s i l e stress f i e l d . Two equally probable (or improbable) mechanisms for the formation and association of these structures e x i s t . F i r s t , i t can be argued t h e o r e t i c a l l y (Lajtai, 1968, 1969; Jaeger and Ccok, 1971) that f a i l u r e i n one d i r e c t i o n along the axis of the pyramids or the slickensided surface r e s u l t i n a l o c a l reorientation of the stress f i e l d . Second, i t i s possible that the structures formed simultaneously i n response.to the same stress system.. Compressive or t e n s i l e stress waves (primary or secondary), propagating from a fracture in one medium, upon reaching an interface i n a d i s s i m i l a r medium (the coal) w i l l be proportionally transmitted or r e f l e c t e d depending on the angle of incidence of the wave, the r e l a t i v e densities (and c h a r a c t e r i s t i c wave velocities) of the two media (Syme Gash, 1971). The energy of the o r i g i n a l wave i s proportioned and redistributed among a new set of waves. In the second medium, fracturing can occur at various geometries i n response to t e n s i l e or compressive pulses, or a combination of the two, i f the t e n s i l e or compressive strength of the material i s exceeded (Syme Gash 1971). Of interest i n t h i s study i s the r e f l e c t i o n of transmitted waves. The pyramidal structures,in coal invariably are i n lenses bounded above and below by d i s s i m i l a r l i t h c l c g i e s (Fig. 5-9), which would r e s u l t in r e f l e c t i o n of the transmitted waves. Fracture by reflected stress waves has been discussed by Syme Gash (1971) however, i t i s unknown whether the r e f l e c t e d stress waves would be capable of fracturing the coal, nor i s i t possible to predict from present theory why the structures have a pyramidal outline. Both re-orientation of the 180 ambient stress f i e l d and the r e f l e c t i o n of incident stress waves could account for the observed structures, yet t h e i r i s no clear evidence or t h e o r e t i c a l argument for accepting one or either of these p o s s i b i l i t i e s over the other. DISCUSSION AND CONCLUSIONS The s t r i a t e d structures described i n t h i s study are more abundant and morphologically more diverse.than previously described conical structures i n coal. Nevertheless, the s i m i l a r i t y in gross aspect, det a i l s of the s t r i a e and the ubiquitous occurrence of secondary structures indicate that the structures have a common o r i g i n . A l l previously described conical structures i n c c a l s i m i l a r to those of t h i s study have been from bituminous c c a l . It i s l i k e l y that such a r e s t r i c t e d occurrence r e f l e c t s the low strength of bituminous coal compared to either higher or lower rank coal (Brown and Hjorns, 1963), possibly augmented by i n t e r - and/or i n t r a - p a r t i c l e gas pressure r e s u l t i n g from progressive devolatization of the coal during the c o a l i f i c a t i o n process. The apparently greater abundance of the s t r i a t e d structures in coal of the Kootenay Formation i n t h i s study area as compared to other coal deposits msy be related to the chronology of deformation of the coal measures r e l a t i v e to the degree of c o a l i f i c a t i o n . The Kootenay Formation was rapidly deposited and buried to depths probably exceeding 3000 m during Late Jurassic and Early Cretaceous time and was probably u p l i f t e d from the Late Cretaceous through the Eocene. Compared to most Carboniferous coals, the rates of b u r i a l and u p l i f t were 181 rapid, perhaps sc rapid that the i n t e r - or i n t r a - p a r t i c l e pore pressure could not be dissipated to the extent possible with slower rates of b u r i a l and u p l i f t . Alternatively, the paucity of s t r i a t e d structures i n other coal deposits may simply r e f l e c t the lack of systematic investigation of fracture morphology of the coal. This l a t t e r suggestion i s , i n part, supported by the large percentage of descriptions of conical structures i n coal by i n d i v i d u a l s who did not c o l l e c t the samples i n place, but who appreciated t h e i r significance. The r e s t r i c t e d occurrence of the conical structures to coal as compared to adjacent l i t h o l o g i e s i s probably a product of the r e l a t i v e l y low compressive and t e n s i l e strength of coal, perhaps i n conjunction with a further loss of strength and increased b r i t t l e n e s s resulting from i n t e r - and/or i n t r a -p a r t i c l e pore pressure. The s i m i l a r i t i e s between conical structures in coal and shatter cones, as discussed by Bucher (1963), does suggest that they are the same type of structure. Conical structures of t h i s study are considered to be three-dimensional planar s t r i a t e d structures, but formed from a nearly r a d i a l stress system. Based on the s i m i l a r i t y between the planar s t r i a t e d structures of t h i s study and chevron-structured, hackle-marked j o i n t s , i t i s suggested that three-dimensional, conical structures should form i n other rocks given a r a d i a l l y disposed stress system. Thus, the lack or r a r i t y of such structures with the exception of those associated with, or considered to be associated with cryptoexplosion structures, indicates that intense stress waves are necessary f o r t h e i r formation i n most rocks (Dietz, 1968). As pointed out by Bucher 182 (1963), however, high f l u i d pressure or gas pressure may augment the formation of conical structures in rocks by increasing their brittleness in much the same way as high inter- or intraparticle gas pressure may have facilitated the formation of the conical structures in coal of this study. 183 ACKNOWLEDGMENTS * I thank Coleman C o l l i e r i e s and Kaiser Resources Ltd. for the i r co-operation during the course of th i s study. Dr. D.K. Norris of the Geological Survey of Canada f i r s t pointed out the unusual structures and suggested that the structures warrented further study. This paper was improved as a re s u l t of discussions with Dr. S Mindess on fracture morphologies. This paper has benefited from reviews by Drs.„W.H. Mathews, W.C. Barnes, J.W. Murray and G.E. Rouse of the University of B r i t i s h Columbia. F i n a n c i a l support for t h i s study was provided by Natural Sciences and Engineering Research Council (Canada) Grant A-1107 to W.H. Mathews, and by the Geological Survey of Canada. 184 EEFEEENCES Adams, M. and Sines, G., 1978, Crack extension from flaws i n a b r i t t l e material subjected to compression: Tectonophysics, vol. 49, pp. 97-118. Bartrum, J.A., 1941, Cone-in-cone and other structures i n New Zealand coals: New Zealand Journal of Science and Technology, v o l . 32, pp. 209b-215b. Brown, R.L. and Hiorns, F.J., 1963, Mechanical Properties: i n Lowry H.H., ed., Chemistry of coal u t i l i z a t i o n ; John Wiley and Sons Inc., New York, pp. 119-149. 1 Bucher, W.H, 1963, Cryptoexplosion structures caused from without cr from within the Earth ? ("Astroblemes" or "Geoblemes"): American Journal of Science, vol. 261, pp. 597-649. Bustin, R.M., 1979, Charac t e r i s t i c s and mechanisms for the formation of s t r u c t u r a l l y thickened coal deposits i n the southeastern Canadian C o r d i l l e r a : Ninth International Congress of Carboniferous Stratigraphy and Geology, Abstracts of Papers, pp. 27-28. Butcher, B.M., and Stevens, A. L., 1975, Shock wave response of Window Eock coal: International Journal of Eock Mechanics and Mining Sciences, and Geomechanical Abstracts, v o l . 12, pp. 147-155. Conrad, E.F.,II. and Friedman, M., 1976, Microscopic feather fractures in the f a u l t i n g process: Tectonophysics, vol. . 33, pp. .187-198. Corrasco, L.G. and Saperstein, L,W. , 1977, Surface morphology of p r e - s p l i t fractures i n plexiglas models: International Journal of Rock Mechanics and Mining Sciences,and Geomechanical Abstracts, v o l . 14, pp. .261-275. Deenen, J.M., 1942, Breuken i n Koel en Gesteente: Medeelingen van de Geologiche Stichting, Serie C-1-2-NO. 1, 101 p.. Dietz, E.S., 1968, Shatter cones i n cryptoexplosion structures, in French, B.M. and Short, N.M., eds., Shock metamorphism of natural materials. Mono Book Corp., Baltimore, pp. 267-284. Dov, B, 1979, Theoretical considerations on mechanical parameters of j o i n t surfaces based on studies on ceramics: Geological Magazine, v o l . 116, pp. .81-92.. Fyfe, H.E. and Wellman, H., 1937, Blackburn C o a l f i e l d : New Zealand Geological Survey Annual Beport, v o l . 31, pp. , 32-33, 185 Garwood, E.J., 1892, Cone-in-cone structure: Geological Magazine, vol. 29, pp. 334-335, Gorezyca, S. and Kwiecinska, B.; 1963, Microstructure of cone-in-cone coals from the Lower S i l e s i a n Coal Basin: Academie Polonaise des Sciences, Warsaw. B u l l e t i n Serie des Sciences Chemiques, Geologiques et Geographiques, vol. 11, no. 4, pp. 207-215, Gresley, W.S, 1892, "Cone-in-cone" structure: Geological Magazine, vol. .29, pp. 432. Hobbs, D,.W., 1964, The strength and s t r e s s - s t r a i n c h a r a c t e r i s t i c of Oakdale coal under t r i a x i a l compression: Geological Magazine, vo l . .47, pp. .423-435. Jaeger, J.C. and Cook, N.G.W., 1.971, Fundamentals of rock mechanics: John Wiley and Sons Inc., New York, 583 p.. Johnson, G.P. and Talbot, E.J., 1964, A t h e o r e t i c a l study of the Shockwave o r i g i n of shatter cones: M.S. Thesis, Air Force I n s t i t u t e of Technology Wright-Patterson Air Force Base, Ohio, 90 p. Kwiecinska, B., 1963, Cone-in-cone coals i n the Lower S i l e s i a n Coal Basin: Academie Polonaise Des Sciences, Warsaw. B u l l e t i n , Series des Sciences et Chemiques, Geologiques et Geographiques, vol. 11, no..4, pp. 201-210. L a j t a i , E.Z., 1968, B r i t t l e fracture in dir e c t shear and the development of second order f a u l t s and tension gashes: in Baer, A.J., and Norris, D.K., eds., Conference on research i n tectonics, Ottawa, Canada, Geological Survey of Canada, paper 68-52, pp..96-112. L a j t a i , E,Z., 1969, Mechanisms of second order f a u l t s and tension gashes: Geological Society of America B u l l e t i n , v o l . 80, pp. . 2253-2272. Manton, W.L., 1965, The orientation and o r i g i n of shatter cones in the Vredefort Eing: Annals, New York Academy of Science, vol. 123, pp. 1 019-1049,. Murgatroyd, J.B., 1942, The significance of surface marks on fractured glass: Journal of the Society of Glass Technology, S h e f f i e l d , v o l . 26, pp. .155-171. Ne v i l l e , A.M, 1959, Some aspects of the strength of concrete (Part 3): C i v i l Engineer, London, vol. 54, pp. 1435-1439. Norris D.K., 1958, Structural conditions i n Canadian coal mines: Geological Survey of Canada B u l l e t i n no.,44, 54 p.. 186 Pettijbhn, F.J., 1975, Sedimentary Rocks: Harper and Row, New York, 628 p. , Popp, J.T. and McCulloch, CM., 1976, Geological factors a f f e c t i n g methane in the Beckley Coalbed: United States Department of the I n t e r i o r , Bureau of Mines Report,of Investigations, no. .8137, 35 p. Price, P.H. and Shaul), B.M. , 1963, Cone-in-cone i n coal: V i r g i n i a Geological Survey, Report of Investigations, vol. 22, pp. 1-9. Roy, D.W. and Hansman, R.H, 1971, Two occurrences of shatter cone l i k e fractures: Geological Society of America B u l l e t i n , vol. 82, pp. 3183-3188,. Stearns, D.W., 1964, Macrofracture patterns on Teton Ant i c l i n e , northwestern Montana: Transactions of the American Geophysics Union, vol..45, no..1, pp. 107-108. Stearns, D.W., 1968, Certain aspects of fracture i n naturally deformed rocks: i n Riecker, R.E., ed., National Science Foundation advanced science seminar i n rock mechanics, Boston College; A i r Force Cambridge Research Laboratories, Bedford, Massachusettes, v o l . 1, pp. 97-116. Syme Gash, P.J., 1971, A study of surface features related to b r i t t l e and sensi-brittle f r a c t u r e : Tectonophysics, vol. 12, pp. ; 349-391,. . Tarr, W.A., 1932, Cone-in-cone: i n Twenhofel, W.H., ed., Treatise on Sedimentology 2nd. . Ed., Williams and Wilkiiis Co., Baltimore, pp. 719-721. Woodland, B.G., 1964a, The nature and o r i g i n of cone-in-cone structures: Fieldiana: Geology, vol. 13, no. 4, pp. .187-305. Woodland, B.G., 1964b, A note on a new type of c o n i c a l structure in shale: Journal of Sedimentary Petrology, vol. 34, pp. .680-683. 187 SUMMARY AND CONCLUSIONS The s t r u c t u r a l style and associated features of coal measures of the Kootenay Formation i n the southeastern Canadian Rocky Mountains i s i n part t y p i f i e d by the " F oo t h i l l s Family" of structures. In addition, by virtue of the major contrast i n competency between the coal seams and adjacent sandstone units, the s t r u c t u r a l style of the coal measures displays considerable variation which, to some extent, can be correlated with the regional and l o c a l s t r u c t u r a l settings and l i t h o l o g i c variations of the s t r a t a . During deformation the coal seams were the l o c i of i n t e r s t r a t a l s l i p , and high angle reverse.faults, normal f a u l t s and thrust f a u l t s commonly o f f s e t the seams. In many areas the coal i s pervasively sheared and the o r i g i n a l depositional f a b r i c has been destroyed. The mechanisms leading to the formation of s t r u c t u r a l l y thickened coal deposits varies considerably.in the study area. In a l l areas, however, structural thickening has been f a c i l i t a t e d by c a t a c l a s t i c 'flow* of the coal from areas of high stress to areas of lower stress. At Vicary Creek the variation i n thickness of the. Number 2 Seam i s a r e s u l t of contraction f a u l t i n g , extension f a u l t i n g and i n t e r s t r a t a l s l i p . At Grassy Mountain, thickening i s related to folding of the coal measures and decollement at the l e v e l of the coal seam, which f a c i l i t a t e d transport of the coal both p a r a l l e l and obliguely to the ac f a b r i c plane of the f o l d . At the Southern deposit of Tent Mountain, Number 4 Seam has been thickened as a r e s u l t of drag and plowing of portions of the seam up-dip along the base of a major thrust f a u l t and, to a lesser extent, as a r e s u l t of 188 contraction f a u l t i n g i n the footwall of the seam. In the Western and Northern deposits on Tent Mountain thickening of the coal seams i s p r i n c i p a l l y the r e s u l t of squeezing of coal from the limbs of folds into the hinges, s i m i l a r i n gross aspect to that documented for f l e x u r a l flow and chevron f o l d i n g . In underground mines the s t r u c t u r a l features of the coal measures have a pronounced a f f e c t on roof conditions. In the Vicary Creek mine the Number 2 Seam has been pervasively sheared by i n t e r s t r a t a l s l i p r e s u l t i n g from f l e x u r a l s l i p and possibly from drag from overriding thrust f a u l t s . The coal p i l l a r s , which largely consist.of highly sheared c o a l , have a correspondingly low bearing strength and f a i l by flowage of coal out of the r i b areas rather than along discrete shear planes., Minor variations i n roof rock l i t h o l o g y have notably influenced the response of the strata to deformation. Thin-bedded s t r a t a , interpreted as d i s t a l crevasse splay deposits, contain discrete laminae of carbonaceous material which were preferred horizons for i n t e r s t r a t a l s l i p and which now comprise major st r u c t u r a l d i s c o n t i n u i t i e s along which roof f a i l u r e may occur. Thick-bedded s t r a t a , interpreted as proximal crevasse splay deposits, did net f a c i l i t a t e i n t e r s t r a t a l s l i p , but rather are well jointed, r e s u l t i n g i n a blocky roof rock which requires completely d i f f e r e n t support devices than thinner-bedded strata. Slickenside s t r i a e on bedding surfaces and some extension f a u l t s define a kinematic pattern which i s consistent with the regional structure. Joints i n the roof rock l i e i n hkl and hkO and are dynamically related to i n t e r s t r a t a l s l i p . Some extension f a u l t s pre-date i n t e r s t r a t a l s l i p . . Faults, low amplitude f o l d s and 189 slickensided bedding surfaces i n the roof strata r e s u l t l o c a l l y i n poor roof conditions. In the Balmer North, Six Panel and Five Panel mines, located in the northern end of the Fernie synclinorium, the coal measures are only mildly deformed. A c l e a t system i s evident at almost a l l sanple l o c a l i t i e s , but no o v e r a l l consistent pattern e x i s t s . J o i n t sets in roof and f l o o r s trata l i e i n hkl and hkO and only at a few l o c a l i t i e s do they conform to adjacent cleat systems in the coal. Only a few major extension f a u l t s , which l i e i n hOl, are present i n the mines. In the Balmer North mine young, gently west dipping shear surfaces are present throughout which, i n conjunction with cozonal extension f a u l t s and slickensided bedding surfaces, have promoted f a i l u r e of both roof rock and coal p i l l a r s along north to northwesterly trends. In the Five Panel mine both coal p i l l a r s and roof rock f a i l u r e have been f a c i l i t a t e d by steep, easterly dipping shear surfaces i n conjunction with slickensided bedding surfaces.. The absence cf a consistent c l e a t or j o i n t system i n the mines may be the res u l t of the mechanical anisotropy of the coal measures or multiple episodes of deformation. Intensely sheared and comminuted coal i s common throughout much.of the study area. On a mesoscopic scale the coal has a brecciated ,fabric. Adjacent to and within major shear zones the coal i s very f i n e l y granulated and polished. The microfabric of the coal i s generally s i m i l a r to the mesoscopic f a b r i c , consisting of angular fragments of coal with no evidence cf t r u l y d u c t i l e behavior with the exception of areas of apparently high s t r a i n where the c l a r i t e component of 190 the coal l o c a l l y has flowed p l a s t i c a l l y . Measurements of v i t r i n i t e reflectance of coal i n some shear zones suggest, by comparison with samples heated i n the laboratory for short durations, that f r i c t i o n a l heating may have resulted i n temperatures of up to 450°C along the shear planes. Adjacent to and within.ether shear zones, however, there i s no evidence of f r i c t i o n a l heating.. The presence or absence of f r i c t i o n a l heating may be the r e s u l t respectively of s t i c k - s l i p as ccmpared to stable s l i d i n g conditions during f a u l t i n g . The results also imply that regions of s i g n i f i c a n t and i n s i g n i f i c a n t stress may exist during thrust and reverse f a u l t i n g , which may have been the result of variable pore pressures. The thermal e f f e c t s of shearing on coal quality are i n s i g n i f i c a n t . However, mechanical comminution as a r e s u l t of shearing of the coal and associated rock partings has resulted i n a disproportionately high ash content and poor washability c h a r a c t e r i s t i c s , and have . promoted pervasive oxidation of the coal even at considerable depths below the weathering horizon. Striated structures, many of which are conical i n form, are a common mesoscopic feature on fracture surfaces i n the coa l . The structures are c o n i c a l , planar and pyramidal in form and are characterized by s t r i a e which radiate from a common apex and "horsetail* to form secondary structures on the master surface., Although such structures have been reported previously from coal, the structures are much more abundant and morphologically more diverse i n deformed coal seams of the study area. The abundance of the structures i n the study area may be related to the deformational history of the seam. A l l three 191 types of s t r i a t e d structures recognized are considered to have formed during b r i t t l e shear frac t u r e . The apparently r e s t r i c t e d occurrence of the structures to coal i s l i k e l y the result of the low t e n s i l e and compressive strength of c o a l , possibly augmented by high i n t e r - and/or i n t r a - p a r t i c l e pore pressure.resulting from d e v o l a t i l i z a t i o n of the .coal during c o a l i f i c a t i o n . 

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