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The geology of Vulcan Ridge : Dewar Creek Area, British Columbia Zajac, Ihor Stephan 1960

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THE GEOLOGY OF VULCAN RIDGE DEWAR CREEK AREA BRITISH COLUMBIA by IHOR STEPHAN ZAJAC B.A., Un i v e r s i t y of B r i t i s h Columbia, 1957 A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE (M.Sc.) i n the Department of GEOLOGY We accept t h i s thesis as conforming to the required standard THE UNIVERSITY OF BRITISH COLUMBIA September, 1960 In presenting t h i s t h e s i s i n p a r t i a l f u l f i l m e n t of the requirements f o r an advanced degree at the U n i v e r s i t y of B r i t i s h Columbia, I agree that the L i b r a r y s h a l l make i t f r e e l y a v a i l a b l e f o r reference and study. I f u r t h e r agree that permission f o r extensive copying of t h i s t h e s i s f o r s c h o l a r l y purposes may be granted by the Head of my Department or by h i s r e p r e s e n t a t i v e s . I t i s understood that copying or p u b l i c a t i o n of t h i s t h e s i s f o r f i n a n c i a l g a i n s h a l l not be allowed without my w r i t t e n permission. Department of The U n i v e r s i t y of B r i t i s h Columbia, Vancouver 3,, Canada. Date v i i ABSTRACT The rocks underlying Vulcan Ridge are mainly Proterozoic metasediments of the Lower and Middle D i v i s i o n of the Aldridge formation, and Proterozoic (or l a t e r ) Moyie i n t r u s i v e s . Most of the metasediments are fine-grained quartzites, p h y l l i t e s , s c h i s t s and hormfelses composed mainly of quartz, b i o t i t e , muscovite and l i t t l e feldspar. Tourmaline i s a minor constituent of most metasediments but i n the upper part of the Lower Aldridge i t commonly forms up to 30 percent of the rocks. I t i s believed to have formed metasomatically by solutions derived from the White Creek b a t h o l i t h . A l e n s - l i k e deposit of breccia-conglomerates makes up the upper most part of the Lower Aldridge. Most of the deposit i s composed of unsorted material - angular to subangular fragments of Aldridge type metasediments imbedded i n abundant fine-grained matrix of s i m i l a r composition. This deposit i s believed to have formed by subaqueous s l i d e s or mudflows. The Moyie i n t r u s i v e s are s i l l - l i k e bodies of d i o r i t i c and gabbroic rocks composed e s s e n t i a l l y of hornblende, plagioclase and v a r i a b l e amounts of quartz. Most of the v a r i a t i o n s i n texture and composition apparent i n some of the in t r u s i v e s are probably due to a l t e r a t i o n but some may also be due to magmatic d i f f e r e n t i a t i o n and to a s s i m i l a t i o n of country-rocks. The metasediments i n the southern part of the area have been subjected to regional metamorphism and are of low metamorphic grade. In the northern part of the area the rocks have been contact metamorphosed. v i i i Within approximately 1% mile of the White Creek b a t h o l i t h they have been metamorphosed to p h y l l i t e s , s c h i s t s and hornfelses which attained or c l o s e l y approached a medium grade of metamorphism c h a r a c t e r i s t i c of the hornblende hornfels f a c i e s . Retrogressive metamorphism i s extensive i n the rocks near the contact of the b a t h o l i t h and i s a t t r i b u t e d to hydro-thermal solutions derived from that i n t r u s i v e . Structure of the rocks south of the White Creek b a t h o l i t h i s dominated by northeasterly trending folds which have been refolded into a large a n t i c l i n e near the b a t h o l i t h , and by northeasterly s t r i k i n g , steep dipping f a u l t s . i i CONTENTS Page Acknowledgements v i Abstract v i i CHAPTER I Introduction 1 Location and a c c e s s i b i l i t y 1 Climate and vegetation 1 Topography and drainage 3 Geological investigations 3 G l a c i a t i o n 4 CHAPTER II Petrology 6 Metasediments 6 Lower Aldridge D i v i s i o n 6 Bedded rocks 6 Tourmaline 14 Ori g i n of tourmaline 17 Breccia-conglomerates 22 Ori g i n of breccia-conglomerates 27 Middle Aldridge D i v i s i o n 29 Igneous Rocks 32 Moyie i n t r u s i v e s 32 Structure 32 Texture and composition 33 C l a s s i f i c a t i o n of rocks 39 i i i CONTENTS - Continued Page V a r i a t i o n i n texture and composition 39 Or i g i n 42 White Creek b a t h o l i t h 45 CHAPTER III Metamorphism 47 Regional metamorphism 47 Contact metamorphism 49 Outer contact metamorphic zone • 49 Inner contact metamorphic zone 56 Grade of metamorphism 61 Retrogressive metamorphism 61 CHAPTER IV Str u c t u r a l geology 64 Folds 64 Faults ' 66 Joints and f o l i a t i o n 67 CHAPTER V Bibliography 68 TABLES Table I. Table of formations 5 II . Optical properties of tourmaline 12 I I I . Composition of tourmaline according to i t s properties 13 i v CONTENTS - Continued Page Table IV. Q u a l i t a t i v e spectrographic analyses of tourmaline 13 V. Modal analyses of Moyie i n t r u s i v e rocks.... 40 VI. Modal analyses of metamorphosed boulders, concretion and of associated rocks 53 ILLUSTRATIONS Figure 1. Location and a c c e s s i b i l i t y of Vulcan Ridge 2 2. Photograph: Tourmaline bearing meta-sediments 9 3. Photomicrograph: I n t e r s t i t i a l feldspar.... 11 4. Photomicrograph: Texture of tourmaline i n Aldridge metasediments 11 5. Sketch map: D i s t r i b u t i o n of tourmaline i n Lower Aldridge metasediments 15 6. Sketch: Lens-like body of sorted breccia-conglomerate 26 7. Sketch: I r r e g u l a r l y shaped body of sorted breccia-conglomerate 26 8. Photomicrograph: Haphazardly intergrown c r y s t a l s of hornblende 35 9. Photomicrograph: Inclusions of hornblende i n plagioclase 35 10. Photomicrograph: Corroded grain of plagio-clase 37 11. Photomicrograph: Myrmekitic intergrowth of quartz and plagioclase 37 12. Sketch map: Location of specimens for modal analyses 41 13. Sketch map: Areas of regional and contact metamorphism 48 V CONTENTS - Concluded Page Figure 14. Sketch: Zoning of a b i o t i t e r i c h fragment.. 50 15. Photograph: Zoned quartz-plagioclase boulder 52 16. Photograph: Polished specimen of zoned boulder 52 17. Photomicrograph: Alt e r e d porphyroblasts of andalusite 57 18. Alte r e d porphyroblast of c o r d i e r i t e or s t a u r o l i t e 57 19. Mineral assemblages of contact metamorphic rocks 62 Maps i n Folder on Back Cover Geological map of Vulcan Ridge V e r t i c a l cross-sections of Vulcan Ridge ACKNOWLEDGEMENTS The author i s indebted to the Consolidated Mining and Smelting Company of Canada for permission to use the information acquired during the mapping of Vulcan Ridge. Dr. O.E. Owens supervised the f i e l d work and kindly a s s i s t e d i n c o l l e c t i n g some of the material for study. The author i s further indebted to Dr. R.M. Thompson and Dr. K.C. McTaggart for t h e i r help with laboratory work and with preparation of t h i s paper. The assistance of Dr. A.M. Crooker with i n t e r p r e t a t i o n of spectrographs plates i s g r e a t f u l l y acknowledged. -1-CHAPTER I INTRODUCTION This thesis i s based on the f i e l d work done by the author for the Consolidated Mining and Smelting Company of Canada during the summer of 1958, and on laboratory study completed during the 1958-1959 winter session of the Un i v e r s i t y of B r i t i s h Columbia. I t deals mainly with petrology, structure, and metamorphism of the rocks underlying an area of about 12 square miles immediately south of the White Creek b a t h o l i t h . LOCATION AND ACCESSIBILITY Dewar Creek area i n the P u r c e l l Mountains of southeastern B r i t i s h Columbia, may be reached by a good gravel road along St. Mary River from Kimberley which l i e s about 25 miles southeast of the area. Vulcan Ridge i t s e l f i s accessible by three pack t r a i l s (figure 1). The t r a i l from the road east of White Creek, leads to D i o r i t e Lake and the West Basin. Another t r a i l from an old timber road at the southern extremity of the ridge r i s e s to an elevation of 4,500 feet along i t s eastern slope. The t r a i l along Dewar Creek provides the only access to the western slope of Vulcan Ridge. CLIMATE AND VEGETATION The average p r e c i p i t a t i o n near Kimberley and Crambrook i s 15 to 20 inches per year (Reesor, 1952).''" P r e c i p i t a t i o n i n the Dewar Creek area, however, i s much heavier with frequent wet summer months. Exceptionally dry summer months are also known i n t h i s area. Dates i n parentheses r e f e r to bibliography on page 68. Figure 1. Location and a c c e s s i b i l i t y of Vulcan Ridge. - 3 -Most of the timber on Vulcan Ridge has been burned o f f so that the ridge i s sparsely forested, but heavy d e a d f a l l , and i n places thick underbrush p e r s i s t s to an elevation of about 5,000 feet. No trees are present about 7,500 feet, but a few open stands of coniferous trees are present j u s t below that elevation. TOPOGRAPHY AND DRAINAGE Vulcan Ridge i s i n the deeply dissected eastern part of the P u r c e l l Range, which r i s e s to 9,500 feet above sea l e v e l . The ridge i s t y p i c a l of the mountains i n t h i s area. I t has steep, but somewhat rounded lower parts, i n places cut deeply by V-shaped v a l l e y s of the t r i b u t a r i e s of White and Dewar Greeks. Its upper reaches have been deeply carved by g l a c i e r s that cut cirques with steep head-walls, sharp ridges and mountain peaks. Small lakes s t i l l occupy some of the cirques at or above 7,000 feet. The area i s drained by numerous creeks which flow into White and Dewar Creeks - the t r i b u t a r i e s of St. Mary River. GEOLOGICAL INVESTIGATIONS The work of H.M.A. Rice (1941) i n the Nelson Map area, east h a l f , covers the part of the Dewar Creek area mapped by the author. Detailed work was done by J.E. Reesor (1958) who mapped the Dewar Creek area i n 1950, 1951 and 1952 on a scale of 1 inch to 1/2 mile. O.E. Owens, geologist of the Consolidated Mining and Smelting Company of Canada, mapped the area on a scale of 1 inch to 1,000 feet i n 1956. Mapping of the area by the author was done on the same scale. -4-GLACIATION The large and numerous cirques are the most prominent g l a c i a l features i n the area. They represent the l a t e s t stage of alpine g l a c i a t i o n which was so strong that above 6,500 feet i t almost completely o b l i t e r a t e d a l l signs of the pre-existing C o r d i l l e r a n i c e sheet which, i n Wisconsin time, covered most of the P u r c e l l Range to i t s present elevation of about 8,000 feet. (Daly 1915, Part I I ) . The somewhat rounded slopes below 5,000 feet s t i l l bear the sign of the C o r d i l l e r a n g l a c i e r and the scattered g l a c i a l e r r a t i c s i n d i c a t e that i t reached an elevation of at l e a s t 6,300 feet. Its former presence above that elevation i s suggested only i n places by f l a t or rounded ridges below 7,500 feet. Southerly movement of the g l a c i e r i n the v a l l e y s i s c l e a r l y indicated by the presence of g l a c i a l e r r a t i c s of p o r p h y r i t i c granodiorite south of the White Creek b a t h o l i t h from which they were derived. A notable feature i n the v i c i n i t y of Vulcan Ridge i s the s c a r c i t y of g l a c i a l deposits. G l a c i a l e r r a t i c s and small amounts of poorly sorted gravels and s i l t s (possibly derived from re-worked g l a c i a l d r i f t ) are the only remnants of g l a c i a l deposits on Vulcan Ridge. The v a l l e y s of Dewar and White Creeks contain some g l a c i a l d r i f t , most of which has been re-worked by the streams. -5-TABLE I . T A i L E OF FORMATIONS (Modi L i e d n H c r R c ' s o r , 1CJ5>0 Era Per i o d Rock U n i t L i t h o l o g \ C e n o z o i c Recent and P l u i b eocene Stream and / l a c i e r d e p o s i t s M e s o z o i c and/or C e n o z o i c J u r .i s s i c or l a t e r White Creel; r a t h o l i t h Q u a r t z m o n z o n i t e , Hornblende-b i u t i t e .;:anod i o r i te , b i o t i t e ^ . r a n o d i o r i t e . INTRUSIVE CONTACT P r o t e r o z o i c or 1 a c e r Mo\ i e I n t r u s i v e s M e t a - J i o r i t i , m e t r - q u a r t z d i o i i l e , m e t a - L,uartz i^.ihbro. INTRUSIVE CONTACT Pr o t e r o z o i c Lower P u r c e l 1 C res ton form . L i o n Green-.^rey w e a t h e r i n g q u a r t z i t e s , a r g i l l a c e o u s q u a r t z i t e s and a r g i l l i t e s . A l d r i d g e f o r m a t i o n Upper D i v i s i o n Rust.\ w e a t h e r i n g a r g i l l i t e s and a r g i l l a c e o u s q u n r t z i t e . s . A l d r i d g e format i o n M i d d l e D i v i s i o n Grey w e a t h e r i n g q u a r t z i t e s , a r g i l l a c e o u s q u a r t z i t e s and minor a r g i l l i t e s . A l d r i d g e forma t i o n Lower D i v i s i o n G i e y - r u s t y w e a t h e r i n g b r e c c i a -c o n g l o m e r a t e s . Girey w e a t h e r i n g q u a r t z i t e s . Grey and r u s t y w e a t h e r i n g a r g i l l i t e s and a r g i l l a c e o u s q u a r t z i t e s . - 6 -CHAPTER II PETROLOGY METASEDIMENTS The metasediments outcropping on Vulcan Ridge are largely-composed on quartzites, p h y l l i t e s , s c hists and hornfelses. They belong to the Lower and Middle d i v i s i o n s of the Aldridge formation, and are the metamorphic equivalents of quartzites, a r g i l l i t e s and argillaceous quartzites present i n other less metamorphosed parts of the formation. Although of higher metamorphic grade, they w i l l be described as quartzites, a r g i l l i t e s and argillaceous quartzites to indicate t h e i r r e l a t i o n to equivalent but less metamorphosed Aldridge rocks i n other areas. To sim p l i f y d e s c r i p t i o n , a r g i l l i t e w i l l r e f e r to micaceous rocks with less than 50 percent of quartz, and argillaceous quartzite to s i m i l a r rocks with 50 to 75 percent of quartz. Quartzite w i l l denote rocks predominantly made up of quartz with less than 25 percent of micaceous material. This c l a s s i f i c a t i o n i s adhered to throughout t h i s report. In Dewar Creek area, the Aldridge formation i s divided into Lower, Middle and Upper d i v i s i o n s mainly on the basis of colour of weathered rocks and on the dominance of a r g i l l i t e s or quartzites i n each d i v i s i o n . LOWER ALDRIDGE DIVISION The Lower Aldridge rocks i n t h i s area may be e a s i l y sub-divided into two types: Bedded rocks and breccia-conglomerates. Bedded Rocks The bedded rocks which make up most of the Lower Aldridge represent a ser i e s of thin-bedded a r g i l l i t e s , thick and thin-bedded argillaceous - 7-quartzites and thick-bedded quartzites. The a r g i l l i t e s are l i g h t grey, brownish grey, i n places dark grey and t y p i c a l l y rusty weathered rocks made up predominantly of b i o t i t e , muscovite and lesser amounts of quartz. They are generally fine-grained, massive or s l i g h t l y f o l i a t e d (hornfelses and p h y l l i t e s ) but become medium-grained and schistose where highly deformed. A l l of them are thin-bedded (beds less than 1 foot t h i c k ) . The i n d i v i d u a l beds, which are commonly from 1/4 to 4 inches thick, are inter-bedded s i n g l y or i n groups, with quartzites and argillaceous quartzites. The groups of thin-bedded a r g i l l i t e s are commonly made up of beds of s i m i l a r thickness, texture and composition and may be from 1 to 20 feet thick. Graded and current bedding are not uncommon i n many of the thin-bedded a r g i l l i t e s . The former i s recognized i n the f i e l d by an increase of quartz towards the bottom, and mica, p a r t i c u l a r l y b i o t i t e , towards the top of the beds. Some of the argillaceous beds also have a c r i n k l e d upper surface which may represent r i p p l e marks. Argillaceous quartzites are s i m i l a r to the a r g i l l i t e s but are generally thicker bedded and show fewer changes i n composition within the beds. Quartzites, unlike a r g i l l i t e s and some of the argillaceous quartz-i t e s , are thick-bedded (beds commonly 2 to 3 feet thick) and i n v a r i a b l y massive. Individual beds show l i t t l e change i n composition along s t r i k e or from the top to bottom of a bed. No graded bedding, r i p p l e marks, or cross-bedding was ever observed i n any of the quartzites i n the f i e l d . A notable d i s t i n c t i o n of some of the quartzites i s t h e i r very l i g h t grey -'8-colour, coarser grain and the presence of b i o t i t e c l u s t e r s (a f r a c t i o n of an inch i n diameter) which give these rocks a d i s t i n c t "spotty" appearance. A few c o n c e n t r i c a l l y zoned quartz-mica concretions, 2 to 3 inches in diameter are also present i n these beds. In t h i n - s e c t i o n , the quartzites, a r g i l l i t e s and argillaceous quartzites are seen to be composed mainly of b i o t i t e , muscovite and quartz, which appear i n various proportions i n the d i f f e r e n t rock types. The argillaceous quartzites consist of small (.03 - .2 mm.) angular, commonly i r r e g u l a r l y shaped, p a r t i a l l y interlocked quartz grains and varying amounts of i n t e r s t i t i a l b i o t i t e and (or) muscovite. A r g i l l i t e s , under the microscope, are s i m i l a r to argillaceous quartzites except that they contain more mica. Most of the mica i s fin e grained but a few large, stubby, commonly p o i k i l o b l a s t i c c r y s t a l s of b i o t i t e and muscovite are also present, i n places oriented at r i g h t angles to the f o l i a t i o n . In f o l i a t e d a r g i l l i t e s ( p h y l l i t e s and s c h i s t s ) the micas are coarser grained than quartz or other minerals and well oriented. Quartzites resemble a r g i l l i t e s and argillaceous quartzites i n t h i n - s e c t i o n but contain d i s t i n c t l y more quartz and are somewhat coarser grained (grains i n a few places up to .5 mm.). Feldspars-*- can be seen i n thin-sections of various rock-types, but i n most of them they do not form more than -5 percent of a l l the minerals. ^ A l b i t e , microcline and orthoclase appear to be the most common feldspar. Oligoclase-andesine was i d e n t i f i e d i n several t h i n sections but i t was d i f f i c u l t to estimate the amount of t h i s plagioclase as most of i t i s very f i n e grained and poorly twinned so that i t could have been mistaken for quartz. Figure 2. Tourmaline bearing metasediments of the Lower Aldridge. Note the d i s t r i b u t i o n of tourmaline p a r a l l e l to the bedding and concentration of the mineral near the top of beds (upper l e f t ) . The specimen on the lower r i g h t , i n addition to tourmaline and quartz contains about 50 percent of feldspar. (Specimens are natural s i z e ) . -10-Exceptions are the rocks near contacts of the Moyie i n t r u s i v e s where the feldspars ( e s s e n t i a l l y a l b i t e ) increase appreciably i n amount and commonly form up to 20 percent of the rock. A few feldspathic quartzites and a r g i l l a c e o u s quartzites are also present i n the upper part of the Lower Aldridge, where some of these rocks contain 10 to 20 percent or more (figure 2) of a l b i t e and K-feldspar. The feldspars ( e s p e c i a l l y a l b i t e and orthoclase) are i n places very f i n e grained, highly intergrown (figure 3) and appear to form an i n t e r s t i t i a l matrix of the quartz grains. The increase of a l b i t e i n the metasediments near the contacts of Moyie i n t r u s i v e s , i s r e l a t e d to the i n t r u s i v e s rather, than to any p a r t i c u l a r bed or rock-type. This suggests that at l e a s t some of the a l b i t e i n these metasediments was introduced from the i n t r u s i v e s . Con-s i d e r i n g that the i n t r u s i v e s have been at l e a s t p a r t i a l l y a l b i t i z e d ( p . 36 ) i t i s l i k e l y that the metasediments at t h e i r contacts were s i m i l a r l y affected. The abundance of feldspar i n the quartzites and a r g i l l a c e o u s quartzites, i n the upper part of the Lower Aldridge, cannot be r e l a t e d i n the f i e l d to any intrusives,veins or pegmatites but, the i n t e r s t i t i a l texture of feldspar i n these rocks i s s i m i l a r to that formed by some of the a l b i t e i n the a l b i t i z e d quartzites near Moyie i n t r u s i v e s , and i s almost i d e n t i c a l to that formed by felds par i n the " g r a n i t i z e d " quartzites at Bingham, Utah, (Stringham, 1952). Since the feldspar i n both of these places has apparently been introduced from nearby i n t r u s i v e s i t i s possible that the i n t e r s t i t i a l feldspar i n the upper part of the Lower Aldridge was also introduced from outside sources. Introduction of feldspar from outside sources would explain the high concentration of feldspar i n these rocks, which has not been reported from any other parts -11-Figure 3. I n t e r s t i t i a l feldspar i n feldspathic quartzite. The rounded grains are quartz, x 150 Figure 4. Typical texture of tourmaline i n the Aldridge metasediments. x 50 TABLE I I OPTICAL PROPERTIES OF TOURMALINE No. O c c u r r a n c e Co l our i n handspec imen Indeces o£ r e t r a c t i o n P l e o c h r o i s m B i r e f -r i n g e n c e no n f n 0 Tie 1 P e g m a t i t e B l a c k 1.662 1. 634 Dark b l u e c o l o u r l e s s .028 2 Ve i n B l a c k 1. 655 1.628 B l u e - g r e e n c o l o u r l e s s .027 3 V e i n Br own 1. 661 1.634 Brown b l u i s h greer c o l o u r l e s s .027 4 Metasediments B l a c k 1.654 1.628 Green-browr Very l i g h t y e l l o w to c o l o u r l e s s .026 5 Metasediments Dark brown 1. 666 1.638 Brown Very l i g h t y e l l o w to c o l o u r l e s s . .028 •13-TABLE I I I COMPOSITION OF TOURMALINE ACCORDING TO ITS OPTICAL PROPERTIES lLjC a 2 M g 8 K 6 A l i Q S i i 2 0 6 2 do ¥ O O -*0 I l 8 C a ? ( F e , M n ) h B 6 A l l Q S i l 7.062 10 . 60 2. i-o U8Na2Mg6B6All2Sil2062 oZ '<=> HyNa2 (Fe ,Mn) 6 B 6 A l l 2 S i l 2 0 6 2 ( A f t e r W i n c h e l l , 1951) TABLE IV QUALITATIVE SPECTROGRAPillC ANALYSES OF TOURMALINE Major Elements M i n o r Elements T r a c e Elements 1 Si,Al,B,Fe,Mg,Na - Ca, L i (?) 2 Si,Al,B,Fe,Mg,Na - Ca, L i (?) 3 S i,Al,B,Fe,Mg,Na - Ca, L i (?) 4 Si,Al,B,Fe,Mg,Na - Ca, L i (?) 5 Si,Al,B,Fe,Mg,Na - Ca, L i (?) ? Q u e s t i o n a b l e as o n l y 1 l i n e was i d e n t i f i e d on s p e c t r o g r a p h i c p l a t e -14 -of the Aldridge formation, except those near i n t r u s i v e s and centres of hydrothermal a c t i v i t y . Minor constituents of the a r g i l l i t e s , quarzites and argillaceous quartzites are i r o n oxides, p y r i t e , graphite, apatite, sphene, leucoxene and zircon. Garnet was only found i n two thin-sections, i n which i t formed less than 1 percent of a l l the minerals. C h l o r i t e i s only common i n the southern part of the map area where some a r g i l l i t e s contain up to 15 percent of the mineral. Tourmaline Tourmaline i s a common constituent of Aldridge rocks and deserves s p e c i a l comment. The mineral i s most abundant i n the upper part of the Lower Aldridge, but i s also present i n some pegmatites, veins and other rocks i n the area. In pegmatites i t appears as plumose aggregates or sin g l e j e t -black c r y s t a l s up to 3 inches long, imbedded i n a coarse-grained quartz feldspar matrix. The c r y s t a l s are i n v a r i a b l y shattered and commonly transgressed by small quartz-feldspar v e i n l e t s . Tourmaline bearing veins are found i n various parts of the area. Most of them are less than one inch thick, but a few quartz-tourmaline veins up to 1 foot thick are also present. The veins are commonly vuggy, have sharp contacts with unaltered wall-rocks, and frequently contain no other minerals besides tourmaline and quartz. Most of the tourmaline i s confined to the veins and r a r e l y extends for more than a few inches into the adjacent rocks. Two types of tourmaline are found i n the ve i n s : black and brown ( T a b l e l l ) . The black tourmaline occurs i n most veins as i r r e g u l a r l y stacked, vuggy aggregates of slender c r y s t a l s (up to \ inch -15-L E G E N s c a l e ; I i n - 10 0 0 f t . M i d d l e A l d r i d g e L o w e r A l d r l d g e ; q u a r t z i t e s a r g i l l a c e o u s q u a r t z i t e s c r g i n i t e s Lower A l d r i d g e b r e c c i a - c o n g l o m e r a t e s Moyie I n t r u s i v e s T o u r m a l i n e g r e u t e r t h a n 2 % F a u l t s G e o l o g i c a l c -ontdc ts 1 A n t i c l i n e -16-long) and less commonly as r a d i a t i n g c l u s t e r s . The brown needle-like tourmaline, on the other hand, i s more commonly found i n t i g h t l y stacked columnar groups which project at r i g h t angle to the vein contacts. The two tourmalines are r a r e l y found together. In a few places where both of them were present i n the same vein, the black tourmaline appeared to be the l a t e s t mineral to have developed as i t formed coatings and encrustations on the brown tourmaline and the other minerals present. Although tourmaline i s found i n most metasediments i n the area i t r a r e l y forms more than 1 or 2 percent of these rocks.' Notable exceptions are the a r g i l l i t e s and argillaceous quartzites i n the Upper Lower Aldridge (figure 5), many of which contain 20 to 30 percent ( i n beds less than 6 inches thick) and, i n a few places, as much as 60 percent (in beds less than 1 inch thick) of the mineral. Tourmaline i n these rocks i s of the two types which are distinguished by t h e i r black and dark brown colour, ( i n t h i n - s e c t i o n by pleochroism, see Table I I ) . Both tourmalines, of which the dark brown v a r i e t y i s the most common, are haphazardly intermingled i n the same bed or occur i n separate beds e n t i r e l y unassociated with one another. Both occur as dominantly euhedral, needle-l i k e c r y s t a l s (average c r y s t a l 5 mm. i n diameter, 3 mm. long), commonly with abundant inclusions of quartz and feldspar (figure 4). Many of the c r y s t a l s are fractured and separated along the base, and commonly well oriented p a r a l l e l to the bedding and f o l i a t i o n . They are either uniformly d i s t r i b u t e d throughout a bed or concentrated into bands p a r a l l e l to the bedding, i n places d u p l i c a t i n g such sedimentary features as r i p p l e marks, current and graded bedding (figure 2). In some beds tourmaline also appears i n streaks, lenses and i r r e g u l a r patches which were never seen to extend across contacts of adjacent beds. Such i r r e g u l a r concentrations are not very common. In most beds, l a t e r a l changes i n tourmaline content are gradational and i n most places i n s i g n i f i c a n t . A group of beds (approximately 4 feet thick) i n Orange Tent Basin, s i m i l a r to those i n figure 2,for instance, were followed i n continuous outcrop for about 150 feet without apparent change i n content and d i s t r i b u t i o n of tourmaline. Variations of tourmaline content from bed to bed, however, are abrupt and commonly great, so that a bed containing over 25 percent of tourmaline may be adjacent to one with less than 1 or 2 percent of the mineral. Such a l t e r n a t i n g tourmaline-rich and tourmaline-deficient beds are common throughout the "tourmaline zone" i n the upper part of the Lower Aldridge. O r i g i n of Tourmaline The d i s t r i b u t i o n and abundance of pegmatites are d i r e c t l y r e l a t e d to the White Creek b a t h o l i t h and there can be l i t t l e doubt that these pegmatites and the tourmaline within them were derived from that source. The tourmaline i n veins was probably also derived from the b a t h o l i t h . The alternate p o s s i b i l i t y that tourmaline was "sweated out" of tourmaline bearing metasediments during metamorphisms seems improbable. Not only i s most of the tourmaline i n the metasediments d i f f e r e n t from that i n the veins, but the veins themselves are not r e s t r i c t e d to, or e s p e c i a l l y concentrated i n tourmaline r i c h rocks. Some of them occur hundreds of feet away from any rocks r i c h i n that mineral. The o r i g i n of tourmaline i n Aldridge metasediments i s not as c l e a r . Four possible o r i g i n s could be suggested: d e t r i t a l , authigenic, metamorphic and metasomatic. -18-Tourmaline i s a f a i r l y common d e t r i t a l mineral, and some grains l i k e those described by Reesor (1958, p. 8) could be of th i s o r i g i n . Most tourmaline, however, i s d e f i n i t e l y not d e t r i t a l . If the tourmaline was d e t r i t a l one would expect i t to concentrate along the bottom of graded beds of a r g i l l i t e and argillaceous quartzite, but the converse i s true (;.f'igure '2.). In addition, the c r y s t a l s of tourmaline are euhedral, much larger than any grains i n the surrounding rock and much too abundant to be of d e t r i t a l o r i g i n . Small amounts of authigenic tourmaline are known to occur i n some sediments, (Alty 1933, Krynine 1946), but were never i d e n t i f i e d i n any of the rocks i n this area. Even i f authigenic tourmaline was o r i g i n a l l y present and then r e c r y s t a l l i z e d during metamorphism to i t s present form, the small quantities i n which i t occurs i n sediments (PettiJohn 1957, p. 670) could not account for the high concentration of tourmaline i n the l o c a l metamorphic rocks. Formation of tourmaline by metamorphism of boron r i c h sediments i s another p o s s i b i l i t y . Goldschmidt and Peters (Turner, 1948), found that some marine clays contain up to .1 percent of B2O3 and suggested that tourmaline i n metamorphic equivalents of such rocks could be derived from th e i r o r i g i n a l boron content and would not ne c e s s a r i l y indicate metasomatism. This view i s upheld by Helmquist and Elligtsgaard-Ramussen (Frondel 1957) who at t r i b u t e d tourmaline i n some metamorphic rocks i n Sweden and Greenland to metamorphism rather than to metasomatism. Frondel (1957) also admits that tourmaline i n some metamorphic rocks could be of thi s o r i g i n . -19-A s i m i l a r o r i g i n of tourmaline i n Aldridge metasediments might be suggested by the following: (a) The highest concentration of tourmaline i s i n the upper part of the Lower Aldridge, where i t s d i s t r i b u t i o n i s s t r a t i g r a p h i -c a l l y c o n t r o l l e d . (b) The abundance of tourmaline i n t h i s area i s not v i s i b l y r e l a t e d to any one of i t s possible sources - veins, pegmatites or the White Creek b a t h o l i t h . (c) The tourmaline i n metasediments shows various signs of deformation (commonly well aligned, fractured and separated along the base), as well as do the rocks i n which i t occurs. Tourmaline veins and v e i n l e t s present i n the same rocks, however, bear no sign of deformation. Even the smallest, vuggy v e i n l e t s are not fractured or displaced and neither are most of the f r a g i l e , needle-like c r y s t a l s within them. Obviously, most of the tourmaline veins formed a f t e r deformation of the adjacent rocks and therefore, could not have been the source of tourmaline i n metasediments. Although the above evidence might favour metamorphic o r i g i n of the tourmaline i n metasediments, such o r i g i n cannot very well explain the abundance of the mineral i n these rocks. The tourmaline commonly makes up to 30 percent of the rocks i n the upper part of the Lower Aldridge, which would have had to contain o r i g i n a l l y about 3 percent of B2O3. This amount i s about t h i r t y times greater than the highest concentration of B2O3 i n sediments reported by Goldschmidt and Peters (.1 percent B2O3 i n marine cl a y s ) . The diff e r e n c e becomes even greater for a r g i l l i t e s and argillaceous quartzites which contain up to 60 percent of tourmaline e s p e c i a l l y i f one considers -20-that these rocks were not clays o r i g i n a l l y . One could s t i l l argue and suggest that even i f a small amount of boron was present i n the o r i g i n a l sediments i t could have been "mobilized" and concentrated i n c e r t a i n rocks during metamorphism. Such method of concentration seems possible considering the high m o b i l i t y of boron, but magmatic concentration of the element i s more l i k e l y . Evidently, the magma of the white creek b a t h o l i t h was able to concentrate baron. This i s indicated by the presence of tourmaline i n m i a r o l i t i c cavities^-within the b a t h o l i t h and by the presence of tourmaline i n veins and pegmatites undoubtedly derived from.' i t . I t seems unnecessary, therefore, to assume a metamorphic o r i g i n of tourmaline, e s p e c i a l l y when the o r i g i n a l boron content of the metasediments cannot be proved. C e r t a i n l y large quantities of boron i n the o r i g i n a l sediments cannot be assumed as most of them were not marine cl a y s , i n which boron i s known to be high, but sandstones and sandy s i l t s t o n e s i n which boron, i f present at a l l , would have been only i n very small quantities (Rankama and Sahama, 1950). I t i s true of course, that the tourmalines i n veins and pegmatites derived from the b a t h o l i t h , are not i d e n t i c a l to those i n the metasediments. They are, however, s i m i l a r in composition (Table IV). This s i m i l a r i t y suggests that the tourmalines were formed by somewhat s i m i l a r solutions which were probably derived from a common source - the White Creek b a t h o l i t h . It i s not c l e a r why tourmaline i s highly concentrated i n the upper part of the Lower Aldridge. The abundance of a r g i l l i t e s i n t h i s part of the Aldridge may be part of the answer as the f i e l d evidence Personal communication. J.V. Ross, Assistant Professor, U n i v e r s i t y of B r i t i s h Columbia. -21-c l e a r l y shows that tourmaline has p r e f e r e n t i a l l y replaced argillaceous rocks. The a v a i l a b i l i t y of rocks favorable for replacement, however, cannot alone explain the abundance of tourmaline i n the upper part of the Lower Aldridge. This part of the Aldridge, i s more argillaceous than some other parts of the formation (Middle Aldridge, c e n t r a l part of the Lower Ald r i d g e ) , but argillaceous rocks, even though not as abundant, are present i n many other parts of the formation where tourmaline is present only i n small amounts. This, and the fact that tourmaline replacement proceeds p a r a l l e l to bedding rather than across i t , would make i t necessary for the feeder or feeders of tourmaline bearing solutions to be d i r e c t l y connected to the now tourmalinized beds. No such connections could be found i n the f i e l d , but they could be present at depth, down-dip from the present l o c a t i o n of tourmaline r i c h meta-sediments. This p o s s i b i l i t y i s not u n l i k e l y , considering that the tourmaline zone i n the upper part of the Lower Aldridge i s not far away from a large a n t i c l i n a l structure which plunges towards the b a t h o l i t h and i s i n a favourable p o s i t i o n to be intercepted by veins, pegmatites or off-shoots from the b a t h o l i t h . The differences i n temperatures and pressures of the solutions which deposited tourmaline can probably explain why the black and''brown tourmaline was deposited i n veins and why the dark brown tourmaline was formed i n metasediments. The vuggy and c r u s t i f i e d nature of the veins suggests that the solutions which deposited the black and brown tourmaline were at low temperature and pressure. Therefore these solutions were probably not able to extensively penetrate and replace country-rocks so that most of the tourmalines that formed were deposited i n veins. The -22-dark brown tourmaline, on the other hand, was the e a r l i e s t tourmaline to form (pp.16,19). Therefore, i t seems l i k e l y that the solutions from which i t was formed were at higher temperature and pressure than the l a t e r solutions and were, therefore., more capable of penetrating and replacing s o l i d rock. Breccia-Conglomerates Breccia-conglomerates occur only on or just below the Lower Aldridge-Middle Aldridge contact. They appear i n the form of a l e n s - l i k e deposit which can be traced i n outcrop from east of D i o r i t e Lake Basin for approximately 2\ miles to the Orange Tent Basin. Small outcrops of breccia-conglomerates which appear i n the same s t r a t i g r a p h i c horizon south of Orange Tent Basin, suggest that t h i s deposit extends to the southern extremity of Vulcan Ridge and has a t o t a l length of approximately 5 miles. The thickest part of the deposit i s i n D i o r i t e Lake Basin where the t o t a l thickness of breccia-conglomerates i s from 500 to 1000 feet. To the south and to the east of this basin, the deposit continuously decreases i n thickness and f i n a l l y disappears. The deposit as a whole appears to be conlormable with the surrounding metasediments. wherever the lower contact appears i n outcrop i t i s p a r a l l e l to the adjoining s t r a t a . Where i t cannot be observed d i r e c t l y , i t s p o s i t i o n i n most places can be in t e r r e d within a few feet. In these places i t also appears to be p a r a l l e l to the bedding of the adjacent rocks. If small i r r e g u l a r i t i e s are present on i t s surface they cannot be detected. The upper contact of the deposit i s not very well exposed but where i t does appear i n outcrop, i t i s seen to be conformable to the overlying rocks. -23-The deposit within the boundaries just described consists almost e n t i r e l y (95 percent or more) of breccia-conglomerates i n which the fragments of various sizes and shapes are haphazardly d i s t r i b u t e d throughout an abundant, f i n e grained matrix. These breccia-conglomerates w i l l be referred to as "unsorted breccia-conglomerates". The re s t of the deposit i s made up ot several thin beds of a r g i l l i t e s and argillaceous quartzites, and ot a few small but d i s t i n c t bodies composed of well sorted fragments. The l a t t e r w i l l be ref e r r e d to as "sorted breccia-conglomerates". The fragments which make up about 30 percent of the unsorted breccia-conglomerates, are angular, subangular, i n places highly contorted and r a r e l y well rounded. They vary i n length from a f r a c t i o n of an inch to 3% feet. Those less than 2. inches long constitute over 80 percent of a l l the fragments. Composition of most of thefragments as well as t h e i r texture and colour, are very s i m i l a r to the massive a r g i l l i t e s and argillaceous quartzites of the Lower Aldridge. Fragments of Aldridge type quartzites and a few fragments of b i o t i t e s c h i s t s are also present. The most unusual "fragments" are the large boulders exposed i n D i o r i t e Lake Basin which consist mainly of quartz and c a l c i c plogioclase. Most of them are rounded and commonly very i r r e g u l a r i n outline. Some of them are spindle-shaped and resemble volcanic bombs. The matrix which surrounds the fragments i n the unsorted breccia-conglomerates i s grey, commonly rusty on weathered surface, fine-grained and t y p i c a l l y massive. Its average composition, based on the modal analyses of f i v e specimens from various parts ot the breccia-conglomerates i s given below: -24-Quartz 51% Feldspar 5% B i o t i t e 23% Muscovite 18% Tourmaline 1% Sphene j Zircon I P y r i t e Iron Oxides Apatite _> 2% This composition i s very s i m i l a r to the composition or many fragments i n the breccia-conglomerates and to the composition of many a r g i l l i t e s and arg i l l a c e o u s quartzites i n the Lower Aldridge. The composition, colour and fine-grained texture of the matrix and of the fragments are so s i m i l a r i n many places that the two can barely be distinguished from one another on a fresh, unweathered surface of the rock. The d i s t r i b u t i o n of fragments i n the matrix or any one part of the deposit of breccia-conglomerates, appears to be e n t i r e l y haphazard. Considering the deposit as a whole, however, i t i s apparent that the d i s t r i b u t i o n of fragments has a d e f i n i t e pattern. It i s evident that the largest fragments are generally most abundant i n the thickest part of the deposit. The fragments larger than 2 inches are most abundant i n D i o r i t e Lake Basin where the deposit i s the thick e s t . This part of the deposit also contains the largest fragments which are up to 3% feet long. East of t h i s basin where the deposit diminishes i n thickness to less than 200 feet and f i n a l l y disappears, the largest fragments are 3 inches long. S i m i l a r l y , the largest fragments immediately south of the basin are up to -25-1 foot long, and i n Orange Tent Basin where the deposit i s about 200 feet thick the largest fragments are only up to 6 inches long. South of Orange Tent Basin where the breccia-conglomerates are only 2 to 70 feet thick, the largest fragment i s not longer than 1 inch. The sorted breccia-conglomerates which form less than 5 percent of the whole deposit are present only i n a few places. These breccia-conglomerates have the shape of throughs or lenses or of very i r r e g u l a r l y shaped masses (figure 6,7). They are composed of well sorted, angular, subangular and rounded fragments, with various amounts of well to moderately well sorted sandy-argillaceous material. A c h a r a c t e r i s t i c feature of a l l sorted breccia-conglomerates i s the s t r i k i n g s i m i l a r i t y of the fragments and t h e i r matrix to the fragments and matrix of the surrounding unsorted breccia-conglomerates. An unusual type of "fragmental" material appears within the unsorted breccia-conglomerates i n D i o r i t e Lake Basin. In outcrop t h i s material occupies an oval-shaped area, approximately 100 feet long and 20 feet wide, elongated roughly at r i g h t angle to the s t r i k e of the bedding above and below the breccia-conglomerates i n which i t occurs. This "fragmental" material consists of 1/2 to 4 inch fragments surrounded by a fine-grained matrix. The fragments which make up approximately 50 percent of t h i s deposit are rounded, subangular and very commonly highly contorted. Many of the fragments have very i n d i s t i n c t or gradational boundaries with the surrounding matrix. Both fragments and the matrix are made up almost e n t i r e l y of three minerals: medium-grained, fibrous and r a d i a t i n g a c t i n o l i t e , f i n e to -26-F i g u r e G. S k e t c h oc an o u t c r o p i n Orange Teat R a s i n showing a l e n s - i i . . c bod) o i s o L ' t c i b i ' i i c c i a - c o n ^ l o m e r j l e s u r r o u n d e d by u n s o r t e d b r e c c i a - c o n g l o m e r a t e . La'.-e h a s i n s i i o w i n ^ i r r e g u l a r ! ) shaped bouy of s o r t e d b r e c c i a - c o n g l o m e r a t e . -27-medium-grained quartz, and c a l c i c plagioclase (labradorite to anothite). Smaller amounts of b i o t i t e and c l i n o z o i s i t e are also present. Small disseminated grains which appear i n some fragments and the surrounding matrix are apatite, z i r c o n , sphene, p y r i t e , p y r r h o t i t e , galena and sc h e e l i t e . The composition of th i s rock, with the exception of a c t i n o l i t e , s c h e e l i t e and some of the sulphides, i s s i m i l a r only to the large, i r r e g u l a r boulders i n the unsorted breccia-conglomerates and to a few of the concretions near the White Creek b a t h o l i t h . No other rocks of s i m i l a r composition could be found i n the map area. Of some i n t e r e s t are the 2 inch to 3 feet thick groups of t h i n -bedded and laminated a r g i l l i t e s and argillaceous quartzites, which occur i n a few places within the unsorted breccia-conglomerates. Although widely separated from one another, these beds have very s i m i l a r texture, composition and structure. They are fine-grained, t h i n l y bedded and roughly p a r a l l e l to the contacts of the breccia-conglomerates with the underlying or the overlying bedded rocks. They are rather uniform i n thickness and have sharp contacts with the surrounding unsorted material. Most of these beds could not be traced i n outcrop for more than a few tens of feet and t h e i r terminations were seen only i n two places (both i n D i o r i t e Lake Basin) where the beds ended abruptly along the s t r i k e i n unsorted breccia-conglomerates. Composition and texture of these beds i s almost i d e n t i c a l to s i m i l a r beds underlying the deposit of breccia-conglomerates. O r i g i n of the Breccia-conglomerates The lack of sor t i n g , abundance of fine-grained matrix and the lack of s t r a t i f i c a t i o n within most of the breccia-conglomerates i n t h i s area might suggest an o r i g i n s i m i l a r to that of g l a c i a l t i l l . However, -28-the p o s s i b i l i t y that these rocks are g l a c i a l deposits i s very s l i g h t . G l a c i a l t i l l i t e s are characterized by some, i t not a l l ot the following: underlying s t r i a t e d surface, s t r i a t e d and otten faceted fragments, varied s i z e and l i t h o l o g y ot the fragments, stru c t u r e l e s s matrix and ass o c i a t i o n with varied clays and other bedded sediments which contain raf t e d pebbles or debris. The lack, of these features i n the breccia-conglomerates and i n the bedded rocks with which they are associated, precludes g l a c i a l o r i g i n . Furthermore, i t a g l a c i e r did e x i s t i n the area occupied by these breccia-conglomerates, one would expect to f i n d some evidence of g l a c i a t i o n along the same s t r a t i g r a p h i c horizon i n other areas. Such evidence, however, has not been found i n t h i s or any other part or the Aldridge formation. The only other deposits which would c l o s e l y resemble the breccia-conglomerates i n t h i s area would be those formed by mudtlows or sub-aqueous s l i d e s . The l a t t e r would seem more probable as there i s no evidence which would suggest that the surface on which the breccia-conglomerates were deposited, was ever exposed above water. If the deposits were formed by mudriows - the mudflows must have been sub-' aqueous. S l i d e s and mudtlows are not uncommon in subaqueous environment (PettiJohn 195/, Kuenen 1957) and would best explain the lack of s o r t i n g and s t r a t i t i c a t i o n i n most of the breccia-conglomerates, the s t r i k i n g s i m i l a r i t y o l i t s iragments and matrix to the underlying Aldridge metasediments, and the presence ot contorted fragments. A series of such s l i d e s or flows, superimposed on one another with occasional i n t e r v a l s of normal sedimentation, could explain the thickness and shape of the . deposit, and the presence of thin-bedded a r g i l l i t e s and a r g i l l a c e o u s quartzites within i t . The bedded a r g i l l i t e s and argillaceous quartzites -29-wouid represent the periods of normal deposition (evidently the same as the conditions under which s i m i l a r rocks immediately below the breccia-conglomerates were deposited), and the shape of the deposit would correspond to a section roughly at r i g h t angle to the d i r e c t i o n or How ot the s l i d e s . The thickest part of the deposit probably represents areas where the tiows had the greatest v e l o c i t y and were able to carry the largest amount ot material and the coarsest fragments. The l e n t i c u l a r or channel-like deposits or sorted breccia-conglomerates were probably tormed either by small streams which flowed over parts of the deposit b r i e r l y exposed above water, or by subaqueous t u r b i d i t y currents. To torm such deposits, the subaerial or subaqueous currents needed only to remove some ot the tine grained matrix of the unsorted breccia-conglomerates and p a r t i a l l y r e d i s t r i b u t e the remaining fragments. This method ot lormation i s suggested by the s i m i l a r i t y of the fragments and the matrix or the sorted breccia-conglomerates to thcs e of the adjacent unsorted breccia-conglomerates. The i r r e g u l a r l y shaped masses ot sorted breccia-conglomerates were probably formed by slumping of l e n t i c u l a r or channel-like deposits or sorted material previously formed by the currents. The o r i g i n or trie a c t i n o l i t e - p l a g i o c l a s e rock (described on page 25) i s uncertain but the presence or highly contorted fragments suggests soft sediment detormation. This deposit, therefore, might represent a slumped, possibly muddy calcareous sediment, l a t e r metamorphosed and moditied by hydrothermal solutions to a rock of the present composition. MIDDLE ALDRIDGE DIVISION This part ot the Aldridge rormation consists ot a series ot thick and thin-bedded a r g i l l i t e s , quartzites and argillaceous quartzites -30-which are s i m i l a r i n most respects to the equivalent rocks of the Lower Aldridge. The d i v i s i o n as a whole d i f f e r s from the Lower Aldridge i n that i t contains more quartzites and fewer thin-bedded a r g i l l i t e s and argillaceous quartzites. Its grey, rather than rusty weathering also serves to d i s t i n g u i s h i t from the Lower Aldridge D i v i s i o n . Another d i s t i n c t c h a r a c t e r i s t i c of the Middle Aldridge, e s p e c i a l l y of i t s lower part, i s the abundance of concretions and "spotted" quartzites. The concretions are most abundant i n massive quartzites, commonly near the centre of the beds. They were not seen i n any thin-bedded arg i l l a c e o u s beds or i n any beds of quartzite less than 4 inches thick. These concretions are e l l i p s o i d a l bodies, h a l f an inch to 1% feet long and elongated p a r a l l e l to the bedding, composed of one to several a l t e r n a t i n g zones. The zones are from 1/10 to 1 inch wide, black, white, dark to l i g h t grey, concentric, i n most places sharply defined and r a r e l y • discontinuous. In most of the concretions the zones appear to be outside of the core of the concretion but i n many of them the contacts of the core with the surrounding rock are not d i s t i n c t , so that the p o s i t i o n of the zones i n r e l a t i o n to the cores cannot be d e f i n i t e l y determined. Differences between various parts of the concretions are mainly due to the content and d i s t r i b u t i o n of b i o t i t e , muscovite and quartz - the three main minerals of the rocks i n which these concretions occur. Feldspar, sphene, p y r i t e , i r o n oxides, a p a t i t e , tourmaline and carbonate also appear i n these concretions but only i n small amounts. Sphene i s more common i n b i o t i t e r i c h parts of the concretions, and carbonate i s i n v a r i a b l y confined to the core. In one concretion a l b i t e -31-appeared to be more common i n the quartz r i c h (white) zones than i n any other parts of the concretion or the surrounding qua r t z i t e . O r i g i n of the concretions i s probably epigenetic as indicated by t h e i r r e s t r i c t e d occurrence within quartzites (the best sorted and o r i g i n a l l y the most porous rocks) and by the s i m i l a r i t y of t h e i r com-po s i t i o n to the surrounding quartzites. They were probably formed by c i r c u l a t i n g ground waters which r e d i s t r i b u t e d the cement of quartz grains i n the o r i g i n a l sandstones. Spotted quartzites are l i g h t grey, massive, equigranular rocks with scattered rounded " c l u s t e r s " of b i o t i t e . In thi n - s e c t i o n , most of the b i o t i t e " c l u s t e r s " are seen to be composed of a b i o t i t e - r i c h core which i s surrounded by a quartz or quartz-muscovite zone. Some of the c l u s t e r s have a c e n t r a l part made up e s s e n t i a l l y of quartz, and surrounded by a rim of b i o t i t e . In two thin-sections, the b i o t i t e c l u s t e r s are seen to be surrounded by three a l t e r n a t i n g b i o t i t e r i c h and b i o t i t e d e f i c i e n t zones. A b i o t i t e c l u s t e r i n another thin-section i s seen to consist of b i o t i t e r i c h core which also contains carbonate and small amount of sphene. This core i s surrounded by a quartz r i c h , b i o t i t e d e f i c i e n t zone i n which apatite i s more abundant than i n any other part of the same rock. This zone, i n turn, i s surrounded by a narrow b i o t i t e rim. A l l of the above described zones are concentric and well defined. The shape of these c l u s t e r s i s spheroidal or e l l i p s o i d a l . Most of the e l l i p s o i d a l c l u s t e r s are elongated p a r a l l e l to the bedding and some are two to three times as long as they are wide. A l l of the b i o t i t e c l u s t e r s observed by the wr i t e r , measured less than 1/2 inch i n t h e i r longest dimension. -32-Spotted quartzites have been reported i n other parts of the Aldridge formation by Rice (1937) and Hoadley (1947), both of whom at t r i b u t e d the o r i g i n of the b i o t i t e c l u s t e r s to contact e f f e c t s of the Moyie i n t r u s i v e s . Some of the spotted quartzites i n th i s area are also present near Moyie i n t r u s i v e s , but i d e n t i c a l rocks are also found hundreds of feet away from these i n t r u s i v e s and as far as 5 miles south of the White Creek b a t h o l i t h . C l e a r l y , the development of spotted quartzites i s not only a contact metamorphic phenomena. On the contrary, the concentric zoning, composition, shape and occurrence of some of the clu s t e r s are s i m i l a r to those of the large concretions i n quartzites. This s i m i l a r i t y of b i o t i t e c l u s t e r s and concretions suggests a common o r i g i n of both of these concretionary forms. Although metamorphism and possibly hydrothermal solutions have, at least p a r t i a l l y , modified the composition of the small b i o t i t e " c l u s t e r s " and large concretions, and accentuated some differences i n t h e i r structure, i t i s doubtful whether any of these agents were the p r i n c i p a l cause of th e i r formation. IGNEOUS ROCKS MOYIE INTRUSIVES The i n t r u s i v e s r e f e r r e d to as Moyie s i l l s (Daly, 1912), P u r c e l l s i l l s (Schofield 1915), P u r c e l l i n t r u s i v e s (Rice 1935, 1937, 1941) and Moyie intrusions (Reesor 1952) have been described by these authors from various parts of the Purc e l l s i n south-western B r i t i s h Columbia. Similar i n t r u s i v e s i n the area of Vulcan Ridge w i l l be re f e r r e d to by the author as Moyie Intrusives. Structure Most of the i n t r u s i v e s , exposed i n good outcrop on both slopes of Vulcan Ridge, are s i l l - l i k e bodies, i n general concordant to the -33-intruded country-rocks. In d e t a i l , however, t h e i r concordance i s not perfect. Even the most s i l l - l i k e bodies commonly cut across a few feet of bedding. The upper contact of one s i l l cuts about 30 feet of the adjacent metasediments at an angle of about 60 degrees to t h e i r s t r i k e . In places where the s i l l s branch out they cross-cut even greater thickness of rock and become dyke-like. Such discordant i n t r u s i v e s are most common in highly deformed parts of the area, but not a l l of t h e i r discordant contacts are i n t r u s i v e . Some, undoubtedly, were formed by post i n t r u s i v e f o l d i n g and f a u l t i n g of the surrounding rocks rather than by emplacement of the i n t r u s i v e s . A l l of the i n t r u s i v e s i n the area have well defined contacts and are e a s i l y distinguished from the adjacent metasediments. Most of them are i r r e g u l a r l y jointed and massive i n appearance. F o l i a t i o n i s well developed only near f a u l t s , i n some highly folded parts of the i n t r u s i v e s and near some of t h e i r contacts. Inclusions of country rocks are found near some of the contacts of the i n t r u s i v e s , e s p e c i a l l y where the i n t r u s i v e s cut sharply across the bedding of the adjacent metasediments. Most of these in c l u s i o n s have well defined contacts and do not appear to have moved very far from the parent rock. In other parts of the i n t r u s i v e s , inclusions are few and appear to be at least p a r t l y "digested" by the i n t r u s i v e s as indicated by t h e i r d i f f u s e and gradational contacts with the surrounding rocks. Texture and Composition In outcrop the i n t r u s i v e s are dark green to l i g h t greyish green and massive i n appearance. Their weathered surface i s generally smooth -34-but becomes p i t t e d where feldspars have weathered out of the rock. On fresh surface the rocks are grey to l i g h t greenish grey and are seen to be composed of dark green hornblende set i n a l i g h t grey to white matrix i n which feldspar and a few grains of quartz may be distinguished with a hand lens. Most of these rocks are medium-grained and roughly equi-granular, but fine-grained, f o l i a t e d , p o r p h y r i t i c and coarse-grained v a r i e t i e s are also present. Thin-sections show the rocks to be composed e s s e n t i a l l y of hornblende, plagioclase and the always present but v a r i a b l e amounts of quartz and epidote. B i o t i t e and c h l o r i t e appear i n most of the sections but are only abundant i n those of highly al t e r e d rocks. Sphene, leucoxene, ilmenite, magnetite, p y r i t e , z i r c o n and apatite are also present but only i n small q u a n t i t i e s . Hornblende i s the most abundant and c h a r a c t e r i s t i c constituent of the i n t r u s i v e s . I t commonly makes up 40 to 60 percent of the rocks but l o c a l concentrations of up to 80 percent are not uncommon. In a few parts of the i n t r u s i v e s i t forms less than 10 percent of the rock and i s absent from some of the highly al t e r e d rocks and most i n c l u s i o n s . The strong to moderate pleochroism (x = pale green, y = green, z = b l u i s h green) i s c h a r a c t e r i s t i c of a l l hornblende i n the i n t r u s i v e s of t h i s area. Te x t u r a l l y , hornblende shows greater v a r i a t i o n than any other constituent of the i n t r u s i v e s . I t i s fin e to very coarse-grained, euhedral to anhedral, stubby or a c i c u l a r , uniformly d i s t r i b u t e d throughout the rock or concentrated into patches of haphazardly intergrown c r y s t a l s (figure 8 ), r a d i a t i n g c l u s t e r s or f a n - l i k e aggregates. Needle-like inclusions i n other minerals p a r t i c u l a r l y p l a gioclase are common (figure 9 ) . Sieve textures, -35-Figure 9. Inclusions of hornblende (dark, prismatic c r y s t a l s ) i n plagioclase. xlOO -36-formed by numerous inclusions of quartz are also abundant. Plagioclase i s the next most abundant constituent a f t e r hornblende and commonly forms 10 to 20 percent of the rocks. I t occurs as subhedral to anhedral, dominantly l a t h - l i k e c r y s t a l s , .5 to 3 mm long. Inclusions of quartz and epidote are common and i n places almost completely replace the mineral. Plagioclase varies from a l b i t e (approximately An5) to labr a d o r i t e (An6s). Such v a r i a t i o n i n composition may occur within one i n t r u s i v e (table V ). Zoning i s best developed i n c a l c i c plagioclase and i s of the normal type. I t consists of 1 or at the most 3 sharply defined zones which become progressively more sodic away from the cores of the c r y s t a l s . Zoning i n sodic plagioclase i s very i r r e g u l a r . I t appears as wide, d i f f u s e sodic rim which grades into a more c a l c i c , commonly mottled andlhighly corroded core (f i g u r e l O ) . Most of the a l b i t e c r y s t a l s are not zoned. The corroded r e l i c t s of c a l c i c plagioclase i n a l b i t e - o l i g o c l a s e c r y s t a l s , indicate that at least some plagioclase i n the i n t r u s i v e s was a l b i t i z e d (Turner and Verhoogen, 1951, p. 202). Most of the unzoned a l b i t e was probably also produced by a l b i t i z a t i o n of c a l c i c plagioclase. Quartz commonly forms 5 to 20 percent of the i n t r u s i v e rocks but i n places up to 60 percent or more of the mineral may be present. I t i s most abundant immediately on the contact of some i n t r u s i v e s , near p a r t i a l l y "digested" quartzite i n c l u s i o n s , and i n the upper parts of some of the s i l l s . T e x t u r a l l y , quartz shows less v a r i a t i o n than any other mineral. It i s i n v a r i a b l y fine grained and roughly equigranular. I t occurs most commonly as i r r e g u l a r c l u s t e r s of roughly equidimensional grains Figure 11. Myrmekitic intergrowth of quartz and plagioclase (crossed n i c o l s ) . x 120 -38-(commonly associated with plagioclase) and as inclusions i n other minerals. A few myrmekitic intergrowths of quartz and plagioclase are also present. Quartz i n these intergrowths i s not o p t i c a l l y oontinuous and forms i r r e g u l a r patterns (figure 11), suggesting replacement rather than eutectic c r y s t a l -l i z a t i o n of the two minerals. B i o t i t e and c h l o r i t e appear to be formed by a l t e r a t i o n of hornblende. In some of the highly a l t e r e d rocks near some f a u l t s and hydrothermal veins, b i o t i t e and c h l o r i t e have e n t i r e l y replaced t h i s mineral. Epidote was seen i n a l l specimens of the i n t r u s i v e s . I t i s in v a r i a b l y associated with plagioclase, i n places almost completely replacing i t and forming imperfect pseudomorphs with quartz. A small amount of a c t i n o l i t e i s present i n two i n t r u s i v e s . I t is probably an a l t e r a t i o n product of hornblende. Sphene and ilmenite are the most common accessory minerals of the i n t r u s i v e s . Sphene occurs as small disseminated grains, as cl u s t e r s of grains and as rims around ilmenite. Two v e i n l e t s of the mineral were also seen i n thin - s e c t i o n . Ilmenite occurs as scattered i r r e g u l a r grains commonly associated with sphene. Apatite which i s the le a s t common constituent of the rocks appears as small fractured prismatic c r y s t a l s , commonly separated and replaced by quartz along the fractures p a r a l l e l to the base. Zircon was not d e f i n i t e l y i d e n t i f i e d but i t s presence i s suggested by strong pleochroic halos around minute grains i n b i o t i t e and hornblende. C l a s s i f i c a t i o n of Rocks Depending on the amount of quartz and the composition of pla g i o c l a s e , the rocks may be c l a s s i f i e d as quartz gabbros, d i o r i t e s and quartz d i o r i t e s . Since most of these rocks have undergone considerable a l t e r a t i o n , the names meta-diorite, meta-quartz gabbro and meta-quartz d i o r i t e would be appropriate. For convenience of d e s c r i p t i o n however, the shorter names w i l l be used i n further discussion of these rocks. Variations i n Texture and Composition The most apparent changes i n composition and texture of the i n t r u s i v e s are due to hornblende which shows great v a r i a t i o n i n texture and d i s t r i b u t i o n (p. 34 ). Many of these changes can be seen on close examination of most outcrops of the i n t r u s i v e s . The greatest changes i n texture and d i s t r i b u t i o n of hornblende are i n the upper part of s i l l I (figure 12) where p o r p h y r i t i c rocks are present. These rocks are i n the form of i r r e g u l a r and discontinuous lenses which are roughly p a r a l l e l to the upper contact of the s i l l . They are composed of various amounts of fin e to very coarse, f a n - l i k e aggregates of hornblende, set i n a medium-grained, roughly equigranular quartz-plagioclase matrix. Similar p o r p h y r i t i c rocks occur near some of the quartz veins i n other i n t r u s i v e s i n the area and i n the upper parts of some of the i n t r u s i v e s described by Rice (1941, p. 25). In a ddition to the l o c a l v a r i a t i o n s i n texture and d i s t r i b u t i o n of hornblende, s i l l s I, II and I l a (figure 12) show changes i n composition which have a d e f i n i t e trend. Some of these changes are evident from the modal analyses tabulated on page 40 , which show that i n general, the TAELE-V. MODAL ANALYSES OF MOYIE INTRUSIVE ROCKS Intrus ive S i l l I S i l l II S i l l I l a Sample No. 1 2 3 4 5 6 1 2 3 4 1 2 3 4 Hornblende 51 54 10 42 32 38 " 68 49 43 44 66 65 49 59 Plagioclase 12 14 20 10 30 22 14 12 18 21 20 13 21 18 1 Quartz 17 15 31 13 27 8 8 15 24 19 4 5 12 1 B i o t i t e 7 6 23 8 5 4 2 6 8 8 3 2 4 8 Epidote 3 2 14 24 4 24 1 8 4 4 4 7 8 3 Sphene 3 3 1 1 2 3 2 X 2 X 5 4 1 Ilmenite 4 5 X 1 X 3 5 2 X 2 2 2 1 Ch l o r i t e 1 1 X 1 1 1 X 2 Apat i t e 1 X X X X 2 X 1 X X X Carbonate X Approximate average anorthite content 20 22 5 52 12 68 10 22 25 20 23 15 8 30 " a c t i n o l i t e and hornblende x less than 1 percent -41-Moy ie I n t r u s i v e * L E G E N D s c a l e : I in . - I O O O f t . 5 0 0 0 -C on t o u r ( i n t e r v a l : IOOO ft.) M e t a s e d i m e n t s G e o l o g i c a l C o n t a c t s Figure 12. Sketch map showinj location of specimens for nodal analyses of Moyie in t r u s i v e rocks. -42-content of quartz and plagioclase increases and the content of hornblende decreases i n the upper parts of these s i l l s . These changes are also evident i n the f i e l d except that they are not as gradational or progressive as some of these analyses might suggest. Textural changes i n s i l l s I, II and I l a are commonly very e r r a t i c and cannot be re l a t e d to any p a r t i c u l a r part of the s i l l s . However, i n general these s i l l s are coarser grained i n t h e i r c e n t r a l and upper parts than they are at t h e i r contacts with metasediments. The thick s i l l immediately west of H a l l Lake f a u l t , was examined i n several places, but did not show any great changes i n texture or composition except i n places along i t s upper contact, where i t was d i r e c t l y adjacent to a quartz-feldspar pegmatite. Near the pegmatite, the hornblende i n the s i l l i s almost e n t i r e l y replaced by b i o t i t e , and the content of quartz and plagioclase i s considerably higher than i n most other parts of th i s s i l l . Small amounts of orthoclase and a c t i n o l i t e also appear near theipegmatite. Away from the pegmatite t h i s rock grades sharply into "normal" d i o r i t e and quartz d i o r i t e of the s i l l . Textural and compositional changes i n other in t r u s i v e s i n the area are minor. They appear as l o c a l concentrations of hornblende or quartz and plagioclase, as quartz-rich p a r t l y "digested" inclusions of country rock or as b i o t i t e - c h l o r i t e a l t e r a t i o n s near some veins and f a u l t s . These v a r i a t i o n s appear to have no r e l a t i o n to the shape or contacts of the i n t r u s i v e s and may appear i n any parts of the s i l l s or dykes. Or i g i n The o r i g i n of Moyie in t r u s i v e s has been discussed i n d e t a i l by Daly (1912), S c h o f i e l d (1915) and Rice (1934, 1937). They a l l believed -43-these rocks to be derived from a common parental magma, but d i f f e r e d i n th e i r i n t e r p r e t a t i o n s of the changes i n composition within the i n t r u s i v e s . Daly proposed a s s i m i l a t i o n of inclusions of the surrounding sedimentary rocks and d i f f e r e n t i a t i o n of the magma by gravity as the mechanism by which the various gabbroic to g r a n i t i c rocks of the in t r u s i v e s originated. In Schofield's opinion a s s i m i l a t i o n of country rocks contributed l i t t l e to the composition of the i n t r u s i v e s , but d i f f e r e n t i a t i o n was important. He assumed a p a r t i a l l y d i f f e r e n t i a t e d r e s e r v o i r from which basic and a c i d i c magmas were intruded i n the forms of s i l l s and dykes. A f t e r emplacement, the basic i n t r u s i v e s d i f f e r e n t i a t e d further into basic and a c i d i c phases while the basic i n t r u s i v e s consolidated without much further change. Rice agreed that d i f f e r e n t i a t i o n could produce some of the basic and a c i d i c portions of the s i l l s , but also proposed the d i f f u s i o n of v o l a t i l e s , due to thermal gradients within the i n t r u s i v e s , as a method by which some of the d i f f e r e n t i a t e s may have originated. Some of the theories concerning the o r i g i n of the i n t r u s i v e s , proposed by these authors, could explain some of the differences i n composition within the i n t r u s i v e s i n this area. D i f f e r e n t i a t i o n by gravity could explain the increase of hornblende towards the lower contacts and the corresponding increase i n plagioclase and quartz content i n the upper parts of s i l l s I, II and I l a . A s s i m i l a t i o n of quartz r i c h sediments might also account for the abundance of quartz i n the upper portions of some -44-of the s i l l s . Most of the v a r i a t i o n s i n texture and composition of the s i l l s i n t h i s area, however, are probably due to a l t e r a t i o n rather than to any of the primary processes proposed by Daly, S c h o f i e l d and Rice. Hornblende, which i s the most abundant mineral i n the Moyie i n t r u s i v e s , has been c l e a r l y shown by S c h o f i e l d to be the a l t e r a t i o n product of pyroxenes. Similar hornblende i n the B e l t i a n i n t r u s i v e s of Idaho has been shown by Gibson, Russel and Jenks (1938) to have formed by hydrothermal a l t e r a t i o n of pyroxenes. Rice (1941) agrees with t h e i r conclusions. No d i r e c t evidence has been found i n the i n t r u s i v e s of t h i s area to prove this type of a l t e r a t i o n , but the plumose r a d i a t i n g and fan-l i k e textures of hornblende do suggest, secondary-hydrothermal rather than primary mode of i t s o r i g i n . The great and commonly rapid v a r i a t i o n i n grain s i z e , needle-like protrusions and disseminations of hornblende i n other minerals and i n some of the sediments near contacts of the i n t r u s i v e s also favour hydrothermal o r i g i n . The occurrence of p o r p h y r i t i c rocks with f a n - l i k e aggregates of hornblende near some of the hydrothermal veins which cut across i n t r u s i v e s of uniform texture, c l e a r l y shows that at le a s t some hydrothermal solutions were capable of r e c r y s t a l l i z i n g and r e d i s t r i b u t i n g some of the constituents i n the i n t r u s i v e s . The presence of gabbros, d i o r i t e s and quartz d i o r i t e s within the same i n t r u s i v e and gradation of one rock-type into another, does not n e c e s s a r i l y prove magmatic d i f f e r e n t i a t i o n . The main di f f e r e n c e between some of these d i o r i t e s and gabbros i s the composition ( a l b i t e content) of the plagioclase. Since most of the plagioclase i n these rocks has been at l e a s t p a r t i a l l y a l b i t i z e d , some of the d i o r i t e s probably formed by -45-a l b i t i z a t i o n of the pr e - e x i s t i n g gabbros and not by magmatic d i f f e r e n t i a t i o n . Some of the quartz i n the quartz d i o r i t e might have been introduced by hydrothermal solutions, as suggested by the rep'lacement-l i k e myrmekitic intergrowths of quartz and plagioclase and by some of the embayed and "corroded" minerals i n contact with the quartz. Orthoclase and some of the quartz i n the b i o t i t e quartz d i o r i t e at the upper contact of the s i l l described on page 42, c e r t a i n l y appears to have been derived from the adjacent pegmatite. The foregoing evidence shows that most of the differences i n composition of the s i l l s are due to secondary a l t e r a t i o n and indicates that most of these a l t e r a t i o n s were hydrothermal. A s s o c i a t i o n of the a l t e r a t i o n s with some of the veins and pegmatites, which were probably derived from the White Creek b a t h o l i t h , suggests t h i s b a t h o l i t h as t h e i r source. The a l t e r a t i o n s of the i n t r u s i v e s , however, are not l o c a l but are known to extend into other areas far removed from any i n t r u s i v e s or other centres of hydrothermal a c t i v i t y . This, as pointed out by Scott (1954) would suggest deuteric o r i g i n of these solutions. WHITE CREEK BATHOLITH The White Creek b a t h o l i t h occupies an oval-shaped area of approximately 140 square miles i n the ce n t r a l part of the Dewar Creek map-area (Reesor, 1958). According to Reesor, the b a t h o l i t h consists mainly of gradational, roughly concentric zones of b i o t i t e granodiorite, hornblende-biotite granodiorite, p o r p h y r i t i c quartz monzonite and leuco-quartz monzonite, arranged i n that order from the outer to the inner part -46-of the b a t h o l i t h . Reesor believes the b a t h o l i t h to have ori g i n a t e d by in t r u s i o n of a highly mobile quartz monzonite magma which forced aside and p a r t i a l l y assimilated the surrounding country rocks. The differences i n composition within the b a t h o l i t h are interpreted "as being due s o l e l y to d i f f e r e n t amounts of wall-rock assimilated during emplacement and subsequent re a c t i o n of th i s material with the o r i g i n a l quartz monzonite magma a f t e r emplacement" (Reesor, 1958, p. 61). A part of the outer zone of t h i s b a t h o l i t h i s exposed on the northern extremity of Vulcan Ridge. It i s composed of a grey, p o r p h y r i t i c b i o t i t e granodiorite, which consists of 5 to 15 percent of microclene phenocrysts (up to 1 inch long) set i n a medium-grained, equigranular matrix of plagioclase and smaller amounts of microclene, quartz and b i o t i t e . Minor constituents, distinguished i n t h i n section, are hornblende, epidote, a l b i t e and sphene. Numerous b i o t i t e r i c h inclusions are present throughout the b i o t i t e granodiorite near the contact of the b a t h o l i t h with the Aldridge metasediments. The inclusions are elongated i n v e r t i c a l or steeply southward dipping planes which roughly p a r a l l e l the contact of the b a t h o l i t h . -47-CHAPTER I I I METAMORPHISM REGIONAL METAMORPHISM "The rocks of the Lower P u r c e l l series i n Dewar Creek map-area have been affected mainly by dynamic and dynamo-thermal metamorphism. I t i s notable that the grade of metamorphism reached has been u n i v e r s a l l y low...mineral assemblages are c h a r a c t e r i s t i c of the lowest grade of metamorphism, and belong to the b i o t i t e - c h l o r i t e or muscovite-chlorite subfacies of the green s c h i s t f a c i e s " (Reesor, 1958, p. 21). The only rocks of the Vulcan Ridge map-area which may f a l l into t h i s lowest grade category are the Aldridge metasediments i n the southern part of th i s area (figure 13). The metasediments are fine-grained massive quartzites, and a r g i l l i t e s and argillaceous quartzites most of which have been metamorphosed to fine grained quartz-biotite-muscovite p h y l l i t e s and sc h i s t s . A notable s i m i l a r i t y of these rocks i s the presence of c h l o r i t e which i n some of them forms up to 15 percent of a l l the minerals. The presence of c h l o r i t e and the evidence of deformation i n these metasediments corresponds well with s i m i l a r r e g i o n a l l y metamorphosed rocks i n other parts of the Dewar Creek map-area described by Reesor. The metamorphic grade of metasediments i n the cent r a l part of the Vulcan Ridge area i s uncertain. Quartz-biotite-muscovite i s the t y p i c a l mineral assemblage of metasediments i n this area but plagioclase and small amounts of c h l o r i t e are also present. A l b i t e i s the most common plagioclase i n these rocks but i n a few of them i t i s o l i g o c l a s e or andesine. Mineral assemblages such as these are not c h a r a c t e r i s t i c of any one metamorphic facies but the dominance of biotite-muscovite assemblage, small amount of c h l o r i t e and the presence of oligoclase-andesine i n these rocks suggests that they are of somewhat higher metamorphic grade than the rocks i n the southern part of the Vulcan Ridge area. -48-Figure 13. Sketch map showing areas of regional and contact metamorphism. -49-The i n t e n s i t y of metamorphism i n this area may be due to strong deformation, c l e a r l y evident i n the Lower Aldridge metasediments on the eastern slope of the ridge, or to contact metamorphic e f f e c t s of the White Creek b a t h o l i t h . CONTACT METAMORPHISM The area of contact metamorphism near the White Creek b a t h o l i t h extends along Vulcan Ridge for at le a s t 1% to possibly 2% miles south of the b a t h o l i t h . This area can be divided into an inner and an outer contact metamorphic zone (figure 13). The inner zone i s composed e s s e n t i a l l y of fi n e to medium-grained, commonly "knotty" s c h i s t s and hornfelses and the outer zone of mainly fine-grained p h y l l i t e s , hornfelses and s c h i s t s . The t r a n s i t i o n of the inner into the outer zone i s sharp but the t r a n s i t i o n s of the outer zone into r e g i o n a l l y metamorphosed areas i s very gradational. OUTER CONTACT METAMORPHIC ZONE In outcrop, the p h y l l i t e s s c h i s t s and hornfelses of this zone, with exception of some concretions and of some zoned fragments and boulders i n the breccia-conglomerates, are t e x t u r a l l y very s i m i l a r to the r e g i o n a l l y metamorphosed sediments of the area. The only t e x t u r a l change i n the metasediments of th i s zone seen i n th i n - s e c t i o n , i s the appearance of granoblastic texture i n some of these rocks and the presence of mica porphyroblasts, which i n some p h y l l i t e s and sc h i s t s are oriented at r i g h t angle to f o l i a t i o n . The most c h a r a c t e r i s t i c feature of the;metasediments i n the outer contact zone i s the almost complete absence of c h l o r i t e . Of the 22 thin-sections of various metasediments from this zone, only two contain c h l o r i t e , and i n both of them i t s presence can be at t r i b u t e d to retrog r e s s i v e metamorphism induced by hydrothermal solutions. Also c h a r a c t e r i s t i c of -50-the rocks i n t h i s zone i s the f i r s t appearance of highly c a l c i c p l a g i o c l a s e , garnet, a c t i n o l i t e , hornblende, diopside and possibly c o r d i e r i t e . The most unusual rocks of t h i s contact zone are some of the boulders and zoned fragments i n the breccia-conglomerates and some of the concretions i n quartzites. The zoned fragments are of various s i z e s , shapes and composition. They consist of a cent r a l fragment of a r g i l l i t e , a r gillaceous quartzite or less commonly quart z i t e , surrounded by one or several (commonly 1 to 3) b i o t i t e r i c h zones (1/8 to 1/4 inch wide), roughly p a r a l l e l to the outl i n e of the fragment (figure 1 4 ) . Figure 14. Zoning of a b i o t i t e r i c h fragment within unsorted breccia-conglomerate. The main differ e n c e between the l i g h t and dark zones i s i n t h e i r b i o t i t e content. Some fragments are also surrounded by a l i g h t grey ( b i o t i t e d e f i c i e n t ) zone which may be up to several inches wide. Zoning in s i d e of the fragments consists of a b i o t i t e r i c h zone, along the periphery of the fragments, which grades inward into a b i o t i t e d e f i c i e n t zone and then again into a b i o t i t e r i c h core of the fragment. Some fragments have only one b i o t i t e zone along the contact of the fragments with the surrounding rocks. -51-The zones around the fragments are s i m i l a r to the zones of some of the concretions, whose primary o r i g i n i s a t t r i b u t e d to percolating ground waters (p. 31). Ground waters may have also r e d i s t r i b u t e d the cement of the material surrounding the fragments to produce concentric zones which were further accentuated and developed by metamorphic d i f f e r e n t i a t i o n . The zones within the fragments may have been produced by metamorphic d i f f e r e n t i a t i o n alone. They may have formed by d i f f u s i o n of b i o t i t e towards the boundaries of the fragments, and by secretion of the mineral into the fractures which might have existed on the contacts of the fragments with the surrounding rocks (Barth 1952, p. 317). The zones on the inside and on the outside of the fragments may have also originated by d i f f u s i o n s i m i l a r to the manner i n which "Liesegang r i n g s " are produced i n some gels (Carl and Amstutz, 1958). The most conspicuous zoned rocks within the breccia-conglomerates are some of the boulders exposed i n D i o r i t e Lake Basin (figure 15). The boulders have a c h a r a c t e r i s t i c l i g h t grey to white-weathered surface which makes them stand out from the grey or rusty-weathered breccia-conglomerates. Unweathered parts of the boulders are l i g h t grey to brownish-grey, f i n e -grained, dense, massive and d i f f i c u l t to scratch or break with a hammer. B i o t i t e i s the only mineral which can be recognized i n hand specimen. I t i s i r r e g u l a r l y d i s t r i b u t e d throughout the boulders or concentrated near the cores and (or) near the boundaries of the boulders. Thin-sections show that the boulders are made up almost e n t i r e l y of quartz, c a l c i c plagioclase and b i o t i t e . Other minerals are minor (tableVI ). The quartz and plagioclase (average grains . 1 mm i n diameter) form an even-grained mosaic throughout which are scattered randomly oriented grains -52-Figure 15. Zoned quartz-plagioclase boulder (a). Note the sharp t r a n s i t i o n of the reaction zone (b) into the surrounding unsorted breccia-conglomerate (c). Figure 16. Polished specimen of a zoned boulder. (a = boulder, b = reaction zone; see analyses 3a and 3b on page 53 ). Note the d i s t r i b u t i o n of b i o t i t e (black). The wide b i o t i t e band defines the contact between the boulder and the rea c t i o n zone. -53-TAl'LE V I . MODAL ANALYSES OF METAMORPHOSED BOULDERS, CONCRETION AND OF ASSOCIATED ROCKS B o u l d e r s C o n c r e t i o n l a l b ] c 2a 2b 2c 3 a 3 b 4k 4n Quart 7. 69 41 65 54 40 55 41 29 55 e0 P l a g i o c l a s e 13 4 3 6 13 36 1 18 47 23 8 * B i o t i t e 7 8 24 25 12 35 32 14 10 C I i n o z o i s iv.e 2 6 X X 5 1 4 5 Garnet 3 X 3 3 H o r n b l e n d e 10 D i o p s i d e 3 Sphene X 2 1 1 2 2 2 X X Z i r c o n X X X X X X X Apat i t e X X X X 1 X X T o u r m a l i n e X X P > r i t e X x 1 2 1 X P y r r h o t i te 4 X 2 2 3 X G a l e n a X U n i d e n t i i.'ied opaque m a t e r i a l 2 5 2 X X A n o r t h i t e c o n t e n t 75 ? ?'? 62 7 11 92 77 85 a = b o u l d e r b - r e a c t i o n /.one c - b r e c c i a - c o n g l o m e r a t e s s u r r o u n d i n g r e a c t i o n zone k = c o n c r e t i o n n = q u a r t z i t e s u r r o u n d i n g c o n c r e t i o n x = l e s s than 1 p e r c e n t I --- p r o b a b l y l a b r a d o r i t e - a n o r t h i t e II = p r o b a b l s o l i y o c L a s e - a n u e s i n e a l b i t e or K - f e l d s p a r -54-of b i o t i t e (.2 to 1.0 mm i n diameter). C l i n o z o i s i t e i s commonly associated with plagioclase, and sphene and zircon, i f present, are most abundant i n b i o t i t e r i c h parts of the rocks. The remaining minerals are randomly d i s t r i b u t e d throughout the quartz-plagioclase matrix. A few rhombic to roughly equidlmensibnal, p o l y s y n t h e t i c a l l y twinned grains, i n one of the boulders, resemble c o r d i e r i t e but cannot be d e f i n i t e l y i d e n t i f i e d . X-ray powder photographs of portions of the rock where the mineral i s most abundant give only patterns of plagioclase (closest to anorthite) or of plagioclase and quartz. A l l of the above described boulders are surrounded by sing l e zones which extend a f r a c t i o n of an inch to several inches away from the boulders and i n most places grade abruptly into the surrounding unsorted breccia-conglomerates. These zones are commonly of uniform thickness and c l o s e l y follow the outline of the boulders. In outcrop, the zones are almost i d e n t i c a l to the boulders they surround. Thin-sections of the zones show that the zones are s i m i l a r i n composition to the adjacent boulders (table VI ) . They consist of quartz-plagioclase and q u a r t z - p l a g i o c l a s e - b i o t i t e fragments surrounded by an unequigranular matrix composed mainly of quartz, plagioclase and various amounts of b i o t i t e . The quartz grains are of various sizes and randomly d i s t r i b u t e d . The plagioclase i s t y p i c a l l y very fine-grained (average grains are .01mm i n diameter), roughly equigranular and i s commonly associated with euhedral to subhedral, randomly oriented prismatic c r y s t a l s of c l i n o z o i s i t e . The plagioclase i s commonly i n t e r s t i t i a l . B i o t i t e (up to 1.2 mm i n diameter) i s haphazardly d i s t r i b u t e d throughout the zones, -55-but i n places i t i s concentrated into discontinuous and poorly defined bands p a r a l l e l to the outlines of the boulders. The textures of these zones, i n general, resemble the textures of the surrounding breccia-conglomerates. Composition i s the main differ e n c e between the two rocks (table VI). The fragments and the unequigranular matrix of the breccia-conglomerates are e s s e n t i a l l y made up of quartz and b i o t i t e whereas s i m i l a r fragments and matrix of the zones are mainly composed of quartz and plagioclase. A few metamorphosed concretions i n same of the Middle Aldridge qu a r t z i t e s , approximately 3000 feet south of White Creek b a t h o l i t h , are s i m i l a r i n texture and composition to the previously described boulders. These metamorphosed concretions, s i m i l a r i n shape and d i s t r i b u t i o n to those described on page 30, are composed of one to two green to grey, d i s j o i n t e d , concentric zones, enveloped i n a white to l i g h t grey, f i n e -grained matrix. Composition of one of these concretions i s given i n table VI. Hornblende, diopside, garnet and c l i n o z o i s i t e occur mainly i n the concentric zones of the concretions. They are commonly anhedral and intergrown with quartz and pl a g i o c l a s e . These intergrowths are very s i m i l a r to the "amoeboid" textures i n metamorphosed calcareous concretions described by Conybeare (1951). The fine-grained matrix which envelopes the concentric zones and constitutes most of the concretions i s composed mainly of fine-grained, roughly equi-granular quartz and pl a c i o g l a s e . The texture and composition of t h i s matrix i s almost i d e n t i c a l to the quartz-plagioclase matrix of the zoned boulders. This s i m i l a r i t y of boulders and concretions suggests that both of them were formed by s i m i l a r processes from rocks of s i m i l a r composition. The -56-concretions were probably formed by thermal metamorphism of calcareous qua r t z i t e concretions, and the boulders by thermal metamorphism of boulders of calcareous quartzite. The quartz-plagioclase zones which surround the boulders were probably formed during metamorphism by reac t i o n of the calcareous boulders with the surrounding argillaceous breccia-conglomerates. i I N N E R CONTACT METAMORPHIC ZONE The metasediments i n th i s zone are sch i s t s and hornfelses which are the metamorphic equivalents of Middle Aldridge quartzites, a r g i l l i t e s and argillaceous quartzites. In hand specimen, the s c h i s t s and hornfelses are grey to l i g h t grey rocks composed mainly of quartz, b i o t i t e and muscovite. The sc h i s t s are fine to medium-grained and commonly strongly f o l i a t e d . The hornfelses are t y p i c a l l y fine-grained and massive. Many of the s c h i s t s , and a few of the hornfelses, have a c h a r a c t e r i s t i c "knotted" appearance due to elongate, commonly cigar-shaped or i n places roughly equidimensional mica c l u s t e r s . Most of the cl u s t e r s are less than 1/4 inch i n length, although a few of the cigar-shaped c l u s t e r s are up to 2 inches long. In t h i n - s e c t i o n (figurel7) most of the elongate c l u s t e r s are.seen to consist almost e n t i r e l y of f e l t y masses of s e r i c i t e . These c l u s t e r s probably represent al t e r e d porphyroblasts of andalusite. A few of the elongate c l u s t e r s made up of biotite-muscovite or bi o t i t e - m u s c o v i t e - c h l o r i t e may be al t e r e d porphyroblasts of s t a u r o l i t e . The roughly equidimensional c l u s t e r s composed of b i o t i t e and muscovite or of b i o t i t e , muscovite and c h l o r i t e may possibly be alte r e d porphyroblasts of c o r d i e r i t e . -57-Figure 17. Clusters of haphazardly i n t e r -grown s e r i c i t e (A) i n q u a r t z - b i o t i t e -muscovite s c h i s t . These c l u s t e r s are probably altered porphyroblasts of andalusite (crossed n i c o l s ) . x 50 Figure 18. Cluster of haphazardly i n t e r -grown b i o t i t e and muscovite (B) i n quartz-biotite-muscovite s c h i s t . This c l u s t e r could possibly be alt e r e d porphyroblast of c o r d i e r i t e or s t a u r o l i t e . x 50 -58-None of the above porphyroblasts i s sheared or otherwise deformed, i n d i c a t i n g that most of the contact metamorphic rocks i n the area have undergone l i t t l e or no s t r u c t u r a l deformation a f t e r contact metamorphism. Quartz i s the most common constituent of most hornfelses and s c h i s t s i n the inner contact zone. I t i s fine-grained and commonly forms a roughly equidimensional mosaic of p a r t l y interlocked grains. Fine, dust-l i k e inclusions are common i n the ce n t r a l parts of some of the grains. The i n c l u s i o n free borders of these grains probably represent the quartz which was added to the o r i g i n a l quartz grains during metamorphism. A c h a r a c t e r i s t i c feature of many schists and hornfelses i n the inner metamorphic zone, i s the appearance of myrmekitic intergrowths of quartz and plag i o c l a s e , e s p e c i a l l y along the grain boundaries of the feldspar. The intergrowths are widely d i s t r i b u t e d but generally do not form more than 1 or 2 per cent of any one rock. B i o t i t e and muscovite are the next most common constituents a f t e r quartz. In hornfelses, b i o t i t e and muscovite are fine-grained and randomly oriented. In s c h i s t , the diameter of an average grain of b i o t i t e or muscovite i s about .15 mm but i n a few sc h i s t s i t i s up to ten times that s i z e . B i o t i t e i n a l l s c h i s t s , with exception of the b i o t i t e i n alte r e d porphyroblasts of s t a u r o l i t e and c o r d i e r i t e , i s commonly well oriented p a r a l l e l to the planes of f o l i a t i o n . Muscovite, on the whole, shows less preferred o r i e n t a t i o n than b i o t i t e . In some s c h i s t s , both randomly and p r e f e r e n t i a l l y oriented muscovite plates are present. The discordant o r i e n t a t i o n of muscovite indicates that at l e a s t some of the muscovite i n s c h i s t s has c r y s t a l l i z e d a f t e r the rocks have been deformed. Late c r y s t a l l i z a t i o n i s c e r t a i n l y true of s e r i c i t e which -59-shows no preferred o r i e n t a t i o n whatsoever. Late formation of these minerals i s further indicated by the presence of small v e i n l e t s of muscovite and s e r i c i t e i n some of the highly deformed rocks. These v e i n l e t s are not sheared or displaced, c l e a r l y i n d i c a t i n g that the v e i n l e t s and the minerals within them formed a f t e r the deformation of the surrounding rocks. Plagioclase i s present i n a l l t h i n sections of the rocks from the inner contact zone and commonly forms 5 to 20 percent of a l l the minerals. Two specimens of quartz-plagioclase-mica s c h i s t contain approximately 40 and 55 percent of the mineral. Most plagioclase, i n specimens from various parts of t h i s zone, i s of a remarkably uniform composition. I t i s o l i g o c l a s e , varying from An20 t o An27 i n d i f f e r e n t specimens. Andesine and a l b i t e are rare. In several specimens, the o l i g o c l a s e grains have a narrow zone of a more sodic or a more c a l c i c p l a gioclase along the grain boundaries. The zone i s commonly less than .05 mm wide and c l o s e l y follows the o u t l i n e of the plagioclase grain. Its o r i g i n i s probably metamorphic, representing the adjustment of the plagioclase composition to the composition of the surrounding rock. The above described zoning i s apparent only in rocks of the inner contact metamorphic zone. C h l o r i t e i s present i n many sch i s t s and hornfelses but i n most of them i t does not make up more than 5 percent of a l l the minerals. I t occurs commonly as subhedral, randomly oriented plates, disseminated throughout the rock or concentrated into p a r t l y r a d i a t i n g c l u s t e r s . In a few rocks i t i s present as i n c i p i e n t a l t e r a t i o n of b i o t i t e . In one t h i n - s e c t i o n i t was seen as extensive replacement of garnet. -60-The presence of c h l o r i t e i n the inner contact zone can probably be a t t r i b u t e d to hydrothermal solutions derived from the White Creek b a t h o l i t h . Microclene and orthoclase are absent from most of the hornfelses and s c h i s t s but form 1 to 5 percent of the minerals i n some of the rocks near the contact of the b a t h o l i t h . Garnet appears i n one th i n - s e c t i o n . It occurs as anhedral grains which are strongly al t e r e d to c h l o r i t e . Accessory constituents of the s c h i s t s and hornfelses are sphene, zircon , a p a t i t e , tourmaline, epidote, p y r i t e , p y r r h o t i t e and s p e c u l a r i t e . An u n i d e n t i f i e d radioactive mineral i s a minor (commonly less than 1 percent) but widespread constituent of the s c h i s t s and hornfelses i n the inner contact metamorphic zone. I t occurs as euhedral to subhedral, short prismatic or possibly tabular c r y s t a l s , on the average about .1 mm long, commonly associated with c h l o r i t e and i n places with a l t e r e d porphyroblasts of andalusite. I t has a high p o s i t i v e r e l i e f and i s commonly surrounded by strong pleochroic halos i n c h l o r i t e and b i o t i t e . I t i s b i a x i a l and s l i g h t l y pleochroic (pale yellow to almost c o l o u r l e s s ) . In polarized l i g h t i t i s yellow to grey, apparently i s o t r o p i c i n places. This mineral was probably introduced by hydrothermal solutions derived from the White Creek b a t h o l i t h . A rock d i f f e r e n t from the above described s c h i s t s and hornfelses, appears at the contact of the b a t h o l i t h i n the northwestern part of the map-area. The rock occupies about 20 to 50 feet wide, 100 to 200 feet long area, elongated p a r a l l e l to the contact of the b a t h o l i t h . In hand specimen the rock i s a greenish-grey, fine- to coarse-grained migmatite composed -61-of a highly contorted mixture of thin-bedded metasediments (bedding commonly d i s j o i n t e d and barely perceptible i n places) and of feld s p a t h i c bands and v e i n l e t s . In thin- s e c t i o n , the migmatite i s seen to consist mainly of quartz, plagioclase, potassium feldspar, b i o t i t e and c h l o r i t e . C h l o r i t e forms up to 20 percent of the rock i n a few places. GRADE OF METAMORPHISM The present, complete mineralogical assemblages of the contact metamorphic rocks, are not i n equilibrium as these rocks have undergone various stages of retrogressive metamorphism. Subsequently, they cannot be c l a s s i f i e d according to a s p e c i f i c metamorphic facies of a d e f i n i t e metamorphic grade. Disregarding the retrograde changes i n these rocks, however, the following metamorphic changes and metamorphic grade can be deduced. The Aldridge rocks within approximately \\ miles of the b a t h o l i t h , depending on t h e i r composition at the time of metamorphism, were metamorphosed to p h y l l i t e s , s c h i s t s and hornfelses most of which attained or c l o s e l y approached the following assemblages: quartz-biotite-muscovite, quartz-plagioclase-biotite-muscovite and quartz-plagioclase-biotite-muscovite-andalusite (with c o r d i e r i t e i n a few places). In the calcareous concretions and boulders the assemblages probably were: quartz-plagioclase, quartz-p l a g i o c l a s e - b i o t i t e and quartz-plagioclase-diopside (with garnet or hornblende i n places). These assemblages would belong to the hornblende hornfels facies (figure 19) and indicate a medium grade of metamorphism. RETROGRESSIVE METAMORPHISM Retrogressive metamorphism i s extensive i n the rocks of the inner H o r n b l e n 1 c H o n i ' d s F a c i c s . ACF Diagram Hornblende H o r n f e l s F a c i e s . AKF Diagram f o r Rocks w i t h Excess S i 0 2 and K20 l o r Rocks w i t h Excess S i 0 2 and AI2O F i 0 u r e 19. M i n o r a ] assembla ,es oC c o n t a c t metamorphic r o c k s d i.sre^ar i i n , ; the changes pro hr".ed by r e t r o g r e s s i v e metamorphism. C i r c l e s r e p r e s e n t v a r i o u s I'Oii s from the i n n e r and o u t e r c o n t a c t metamorphic zones. (Diagrams ; I t e r F;. l o , T urner and V e r h o o ^ e i i , L95o) . -63-contact metamorphic zone. I t i s indicated by the abundance of completely a l t e r e d porphyroblasts of andalusite, c o r d i e r i t e and s t o u r o l i t e , and by the widespread occurrance of c h l o r i t e . The retrograde changes i n the rocks of the outer contact zone are suggested only i n a few places by the presence of unstable mineral assemblages such as c l i n o z o i s i t e - c a l c i c p l a g i o c l a s e , c l i n o z o i s i t e - c a l c i c plagioclase-diopside-hornblende or b i o t i t e -m u s c r i t e - c h l o r i t e . Most of the retrograde changes i n both of the contact metamorphic zones are undoubtedly due to hydrothermal solutions derived from the White Creek b a t h o l i t h . L i t t l e retrogressive metamorphism can be a t t r i b u t e d to deformation, as most of the contact rocks i n the area have not undergone much s t r u c t u r a l deformation a f t e r contact metamorphism (p.58 ). -64-GHAPTER IV STRUCTURAL GEOLOGY FOLDS The Lower Aldridge rocks i n the Vulcan Ridge area have been folded into large and small northeasterly trending folds and then refolded into a large a n t i c l i n i c a l structure near the White Creek b a t h o l i t h . Two large open folds - an a n t i c l i n e and a syncline (cross-sections I- I I , III-IV) form the main structure of the Lower Aldridge. In the c e n t r a l parts of the area, the a x i a l planes of these folds are nearly v e r t i c a l and t h e i r axes which s t r i k e approximately north 25 degrees east are h o r i z o n t a l or plunge gently northward. In the northern part of the area the axis of the syncline swings around to the east as the f o l d becomes refolded with the r e s t of the Aldridge rocks near the White Creek b a t h o l i t h . The a n t i c l i n e i s probably refolded i n a s i m i l a r manner. Small folds (see geological map of the area) with amplitudes of 5 to 30 feet (two such folds had amplitudes of 50 to 60 feet) are numerous i n the Lower Aldridge, e s p e c i a l l y near the folded parts of the Moyie i n t r u s i v e s and near the crest and the trough of the two large folds described above. The a x i a l planes of most of these folds are v e r t i c a l or dip steeply northeast or southwest, and t h e i r axes s t r i k e north to north 45 degrees east. The plunge of t h e i r axes varies from 12 degrees southwest to 25 degrees northeast. On the whole, these folds are roughly p a r a l l e l to the two main folds i n the Lower Aldridge. The s i z e , shape and abundance of many of the small folds i s c l e a r l y r e l a t e d to the Moyie i n t r u s i v e s . This i s evident i n many, places i n the -65-f i e l d where r e l a t i v e l y undisturbed metasediments within the two main folds i n the area become progressively more and more folded as they approach the in t r u s i v e s so at t h e i r contacts the metasediments become t i g h t l y folded. In places t h i s change from unfolded to folded rocks i s very abrupt. These folds probably formed at the same time as the two main folds i n the area when the less competent metasediments were compressed against the more competent Moyie i n t r u s i v e s . Folds, comparable i n s i z e to those described above, but not as t i g h t l y folded, are also abundant at the head of D i o r i t e Lake Basin and West Basin. Here the a t t i t u d e of the folds varies considerably from place to place, but on the whole these folds form an i r r e g u l a r " a n t i c l i n o r i u m " within the large a n t i c l i n a l structure near the White Creek b a t h o l i t h . The Middle Aldridge rocks i n the map area are dominated by a large a n t i c l i n a l structure formed by the i n t r u s i o n of the White Creek b a t h o l i t h which changed the s t r i k e of the Aldridge s t r a t a from northeast to southwest. With the exception of t h i s f o l d and a few minor folds near some of the i n t r u s i v e s , the Middle Aldridge appears to be l i t t l e folded. In the southern part of the area i t s beds s t r i k e north 20 degrees east and dip 50 to 70 degrees northwest. In the northern part of the area, i n general, they s t r i k e north 60 degrees west and are v e r t i c a l or dip steeply northeast or southwest. -66-FAULTS Northeasterly s t r i k i n g f a u l t s are the most common f a u l t s i n the area. Most of them s t r i k e north 10 to 25 degrees east and are v e r t i c a l or dip steeply northwest. These f a u l t s are most abundant i n the highly folded parts of the Lower Aldridge where they commonly p a r a l l e l the a x i a l planes of f o l d s . H a l l Lake f a u l t i s the largest northeasterly s t r i k i n g f a u l t i n the area. According to Reesor (1958) t h i s f a u l t extends northward along the west side of White Creek, swings eastward i n the northern part of the area and terminates against the White Creek b a t h o l i t h . He estimates the displacement along t h i s f a u l t of at le a s t 1500 feet. Two steeply dipping f a u l t s with an apparent displacement of 100 to 150 feet, are roughly p a r a l l e l to the a x i a l plane of the large, northwesterly trending a n t i c l i n a l structure near the White Creek b a t h o l i t h . Very small shears, with a t t i t u d e s i m i l a r to that of the above described f a u l t s , are common near the cr e s t of the same a n t i c l i n a l structure. These northwesterly s t r i k i n g shears and f a u l t s probably formed during the emplacement of the White Creek b a t h o l i t h as the metasediments were pushed southward and folded into the large a n t i c l i n a l structure. JOINTS AND FOLIATION There are two prominent sets of j o i n t s i n the area. One i s roughly p a r a l l e l to the a x i a l planes of the northeasterly trending folds i n the area, and the other to the a x i a l plane of the large f o l d near the White Creek b a t h o l i t h . The former, i s the most prominent and the most intense of the two. I t i s so intense on the lower, southeastern slope of Vulcan Ridge and near the crest of the main- northeasterly trending -67-a n t i c l i n e i n the Lower Aldridge, that i t obscures the bedding of the thin-bedded a r g i l l i t e s and ar g i l l a c e o u s quartzites. The j o i n t s which roughly p a r a l l e l the plane of the f o l d near the White Creek b a t h o l i t h are most common near the crest of that f o l d . There are other numerous j o i n t s i n the area p a r t i c u l a r l y i n the Moyie i n t r u s i v e s , which cannot be r e l a t e d to any of the major folds i n the area. The most prominent f o l i a t i o n i n the metasediments of the area i s developed p a r a l l e l to the bedding. I t i s best developed i n highly folded, a r g i l l a c e o u s (micaceous) rocks. The most intense f o l i a t i o n p a r a l l e l to the bedding, i s found i n the metasediments within approximately 2000 to 3000 feet of the White Creek b a t h o l i t h . The i n t e n s i t y of f o l i a t i o n i n the rocks of t h i s area i s probably due to the aligment of b i o t i t e and muscovite caused by the shearing and compression of the rocks during the emplacement of the White Creek b a t h o l i t h , and also to the continued growth of b i o t i t e and muscovite, i n the already established planes of f o l i a t i o n , during contact metamorphism a f t e r emplacement. Cross f o l i a t i o n i s developed only l o c a l l y near f a u l t s and near the crests and throughs of folds. On the whole i t i s much less prominent than the f o l i a t i o n p a r a l l e l to the bedding. -68-CHAPTER V BIBLIOGRAPHY A l t y , S.W. , 1933, Some properties of authigenic tourmaline from Lower Devonian Sediments: Am. Mineral, v o l . 18, pp. 351-355. Ba r r e l , J . , 1925, Marine and t e r r e s t r i a l congromerates: Geol. Soc. America B u l l . 36, pp. 291-341. Barth, Tom. F.W., 1952, Theoretical petrology: New York, Willey & Sons. B i l l i n g s , M.P., 1942, S t r u c t u r a l geology: New York, Pr e n t i c e - H a l l . Blackwelder, E., 1932, An ancient g l a c i a l formation i n Utah: Jour. Geol. v o l . 40, pp. 289-304. Brown, C.B., 1938, On theory of g r a v i t a t i o n a l s l i d i n g applied to T e r t i a r y of Ancon, Equador: Geol. Soc. London Quart. Jour. v o l . 94, pp. 359-370. Carol, J.D., and Amstutz, G.C., 1958, Three-dimensional Liesegang rings by d i f f u s i o n i n a c o l l o i d a l matrix and t h e i r s i g n i f i c a n c e for the i n t e r p r e t a t i o n of geological phenomena: Geol. Soc. America B u l l . , v o l . 69, pp. 1467-1468. Conybeare, C.E.B., 1951, An occurrance of orb i c u l a r structure of metasomatic o r i g i n i n the Gold Coast: Geol. Mag., v o l . 88, pp. 145-147. 1951, On s i g n i f i c a n c e of metamorphosed calcareous concretions i n Lower Birrimian schists of the Gold Coast: Geol. Mag., v o l . 88, pp. 267-272. Crowell, J.C., 1955, Dir e c t i o n a l - c u r r e n t structures from the pre-Alpine f l y s h , Switzerland: Geol. Soc. America B u l l . v o l . 66, pp. 1351-1384. 1957, Or i g i n of pebbly mudstones: Geol. Soc. America B u l l . , v o l . 68, pp. 993-1010. Daly, R.A., 1912, Geology of the 49th p a r a l l e l : Geol. Surv. Canada, Mem. 76, Part I, I I . De S i t t e r , L.V., 1959, S t r u c t u r a l geology: New York, McGraw-Hill. Dixon, E.E.L., and Hudson, R.G.S., 1931, A mid-Carboniferous boulder bed near S e t t l e : Geol. Mag., v o l . 68, pp. 81-92. -69-Emmons, W.H., and Lancy, F.B., 1926, Geology and ore deposits of the Ducktown mining d i s t r i c t : U.S. Geol. Survey, Prof. Paper 139, pp. 19-21, plates VIII to XIV. Escola, P., 1938, On e s b o i t i c c r y s t a l l i z a t i o n of o r b i c u l a r rocks: Journ. Geol., No. 3, pp. 448-486. Frondel, C., and C o l l e t t e , R.L., 1957, Synthesis of tourmaline by reaction of mineral grains with NaCl-H3B03 solutions, and i t s implications i n rock metamorphism: Am. Mineral., v o l . 42, pp. 754-758. Fyfe, W.S., Turner, F.J., and Verhoogen, J . , 1958, Metamorphic reactions and metamorphic f a c i e s : Geol. Soc. America, Mem. 73. Gibson, Russel and Jenks, W.F., 1938, Amphibolitization of s i l l s and dykes i n the Libby quadrangle, Montana: Am. Mineral., v o l . 23, pp. 302-313. Goodspeed, G.E., 1942, Orbicular rock from Buffalo Hump, Idaho: Am. MineraL, v o l . 27, pp. 37-47. Hoadley, J.W., 1947, The metamorphism of the rocks of the Aldridge formation Kimberley, B.C.: M.A. Sc. thesis (unpublished), U n i v e r s i t y of B r i t i s h Columbia. Hutton, CO., 1939, The s i g n i f i c a n c e of tourmaline i n the Otago s c h i s t s : Roy. Soc. New Zealand, Trans., v o l . 68, pt. 4, pp. 405-406. Jones, O.T., 1937, On the s l i d i n g and slumping of submarine sediments i n Denbighshire, North Wales, during Ludlow period: Geol. S o c , London, Quart. Jour. v o l . 93, pp. 241-283. Kindle, CH. and Whittington, H.B. , 1958, Stratigraphy of the Cow Head Region, Western Newfoundland: Geol. Soc. America B u l l . , v o l . 69, pp. 315-342. Krumbein, W.C, 1933, Textural and l i t h o l o g i c v a r i a t i o n s i n g l a c i a l t i l l : Jour. Geol., v o l . 41, pp. 382-408. 1940, Flood gravel of San Gabriel Canyon, C a l i f o r n i a : Geol. Soc. America B u l l , v o l . 51, pp. 639-676. Krynine, P.D., 1946, The tourmaline group i n sediments: Jour. Geol., v o l . 54, pp. 65-87. Kuenen, Ph. H., 1950, Marine geology: New York, John Wiley & Sons. 1952, T u r b i d i t y currents and submarine slumps: Am. Jour. S c i . , v o l . 250, pp. 849-873. -70-Kuenen, Ph. H., and M a g l i o r i n i , C.I., 1950, T u r b i d i t y currents as cause of graded bedding: Jour. Geol., v o l . 35, pp. 91-127. Mansfield, G.R., 1906, The c h a r a c t e r i s t i c s of various types of conglomerates: Jour. Geol., v o l . 14, pp. 550-555. McWhae, J.R.H., 1950, Carboniferous breccia of B i l l e f j o r g e n , Vestspitzbergen: Geol. Mag., v o l . 87, pp. 287-298. Norton, W.H., 1917, A c l a s s i f i c a t i o n of b r e c c i a s : Jour. Geol., v o l . 25, pp. 160-194. Pettijohn, F.J., 1949, Sedimentary rocks: New York, Harper. Rankama, K. , and Sahama, Th. G., 1950, Geochemistry: U n i v e r s i t y of Chicago Press. Reesor, J.E., 1952, Dewar Creek, map-area: Geol. Surv. Canada, Paper 52-14. 1958, Dewar Creek map-area with sp e c i a l emphasis on the White Creek b a t h o l i t h , B r i t i s h Columbia: Geol. Surv. Canada, Mem. 292. Reny, 0., Lakeman, R., and Van der Meulen, E., 1955, Submarine s l i d i n g i n western Venezuela: Am. Assoc. Pet. Geol. B u l l . , v o l . 39, pp. 2053-2067. Reynolds, S.H., 1928, Breccias: Geol. Mag., v o l . 65, pp. 97-106. Rice, H.M.A., 1934, The geology and economic geology of the Cranbrook d i s t r i c t , B r i t i s h Columbia: Ph. D. thesis (unpublished) C a l i f o r n i a I n s t i t u t e of Technology. 1935, Emphibole from the P u r c e l l s i l l s , B r i t i s h Columbia: Am. Mineral., v o l . 20, pp. 507-509. 1937, Geology of Cranbrook area: Geol. Surv. Canada, Mem. 207. 1941, Geology of Nelson map-area, east h a l f : Geol. Surv. Canada, Mem. 228. Sch o f i e l d , S.J., 1915, Geology of Cranbrook map-area: Geol. Surv. Canada, Mem. 76. Scott, B., 1954, The D i o r i t e Complex beneath the S u l l i v a n Orebody with i t s associated a l t e r a t i o n s : M. Sc. thesis (unpublished), Queen's University. Snyder, F.G., and Odell, J.W., 1958, Sedimentary breccias i n the southeast Missouri lead d i s t r i c t : Geol. Soc. America B u l l . , v o l . 69, pp. 899-926. -71-Stringham, B., 1953, G r a n i t i z a t i o n and hydrothermal a l t e r a t i o n at Bingham, Utah: Geol. Soc. America B u l l . , v o l . 64, pp. 945-992. Swanson, CO., and Gunning, H.C, 1945, The geology of S u l l i v a n mine: Canadian Inst. Min. Met., v o l . 48, pp. 645-667. Turner, F.J., 1948, Mineralogical and s t r u c t u r a l evolution of the Metamorphic rocks: Geol. Soc. America, Mem. 30. Turner, F.J., and Veerhoogen, 1951, Igneous and metamorphic petrology: New York, McGraw-Hill. Twenhofel, W.H., 1950, P r i n c i p l e s of sedimentation: New York, McGraw-H i l l . Winchell, N.W. , and Winchell, H., 1951, Elements of o p t i c a l mineralogy: Part I I , New York, McGraw-Hill. Woodford, A.O., 1925, The san Onofre b r e c c i a : U n i v e r s i t y of C a l i f o r n i a P u b l i c a t i o n , Geology, v o l . 15, pp. 195-280. TABLE I. TABLE OF FORMATIONS (Modified a f t e r Reesor, 1958) Era Period Rock Unit Lithology Cenozoic Recent and Pleistocene Stream and g l a c i e r deposits . Mesozoic and/or Cenozoic Jurassic or l a t e r White Creek Batholith Quartz monzonite, Hornblende-b i o t i t e granodiorite, b i o t i t e granodiorite. INTRUSIVE CONTACT Proterozoic or l a t e r Moyie Intrusives Meta-diorite, meta-quartz d i o r i t e , meta-quartz gabbro. INTRUSIVE CONTACT Proterozoic Lower Pu r c e l l Creston formation Green-grey weathering quartzites, argillaceous quartzites and a r g i l l i t e s . Aldridge formation Upper D i v i s i o n Rusty weathering a r g i l l i t e s and argillaceous quartzites. Aldridge formation Middle D i v i s i o n Grey weathering quartzites, argillaceous quartzites and minor a r g i l l i t e s . Aldridge formation Lower D i v i s i o n Grey-rusty weathering breccia-conglomerates. Grey weathering quartzites.. Grey and rusty weathering a r g i l l i t e s and argillaceous quartzites. TABLE II OPTICAL PROPERTIES OF TOURMALINE No. Occurrance Colour i n tiandspecimen Indeces of r e f r a c t i o n Pleochroism B i r e f -ringence n o Vie n 0 n f 1 Pegmatite Black 1.662 1.634 Dark blue colourless .028 2 Vein Black 1.655 1.628 Blue-green col o u r l e s s .027 3 Vein Brown 1.661 1.634 Brown bl u i s h greeri c o l o u r l e s s .027 4 Metasediments Black 1.654 1.628 Green-brown Very l i g h t yellow to colourless .026 5 Metasediments Dark brown 1.666 1.638 Brown Very l i g h t yellow to colou r l e s s . .028 TABLE III COMPOSITION OF TOURMALINE ACCORDING TO ITS OPTICAL PROPERTIES H8Ca2Mg8B6AliQSil2067. 60 Ao 3 0 HftCa?(Fe,Mn)sBfiAllf)Sil ?0fi? 40 , to *• 'o So H8Na2Mg6B6All2Sil2062 QZ 'O H8Na2(Fe,Mn)6B6AI12Sil2062 (After Winchell, 1951) TABLE IV QUALITATIVE SPECTROGRAPHIC ANALYSES OF TOURMALINE Major Elements Minor Elements Trace Elements 1 S i,Al,B,Fe,Mg,Na - Ca, L i (?) 2 Si,Al,B,Fe,Mg,Na - Ca, L i (?) 3 S i,Al,B,Fe,Mg,Na - Ca, L i (?) 4 Si,Al,B,Fe,Mg,Na - Ca, L i (?) 5 Si,Al,B,Fe,Mg,Na - Ca, L i (?) ? Questionable as only 1 l i n e was i d e n t i f i e d on spectrographic plate TABLE V. MODAL ANALYSES OF MOYIE INTRUSIVE ROCKS Intrusive S i l l I S i l l II S i l l H a Sample No. 1 2 3 4 5 6 1 2 3 4 1 2 3 4 Hornblende 51 54 10 42 32 38 " 68 49 43 44 66 65 49 59 Plagioclase 12 14 20 10 30 22 14 12 18 21 20 13 21 18 Quartz 17 15 31 13 27 8 8 15 24 19 4 5 12 7 B i o t i t e 7 6 23 8 5 4 2 6 8 8 3 2 4 8 Epidote 3 2 14 24 4 24 1 8 4 4 4 7 8 3 Sphene 3 3 1 1 2 3 2 X 2 X 5 4 1 Ilmenite 4 5 X 1 . X 3 5 2 X 2 • 2 2 1 C h l o r i t e 1 1 X 1 1 1 X 2 Apatit e 1 X X X X 2 X 1 X X X Carbonate X Approximate average anorthite content 1 2 0 22 5 52 12 68 10 22 25 20 23 15 8 30 * a c t i n o l i t e and hornblende x less than 1 percent TABLE VI. MODAL ANALYSES OF METAMORPHOSED BOULDERS, CONCRETION AND OF ASSOCIATED ROCKS Boulders Concretion l a lb l c 2a 2b 2c 3a 3b 4k 4n Quartz 69 41 65 54 40 55 41 29 55 80 Plagioclase 13 43 6 13 36 1 18 47 23 8* B i o t i t e 7 8 24 25 12 35 32 14 10 C l i n o z o i s i t e 2 6 X X 5 1_ 4 5 Garnet 3 X 3 X 3 Hornblende 10 Diopside 3 Sphene X 2 1 1 2 2 2 X X Zircon X X X X X X X Apatite X X X X 1 X X Tourmaline X X Pyrite X X 1 2 1 X Pyrrhotite 4 X 2 2 3 X Galena X Unidentified opaque material 2 5 2 X X Anorthite content 75 ? 11 62 ? 11 92 11 85 a = boulder b = reaction zone c = breccia-conglomerates surrounding reaction zone k = concretion n = quartzite surrounding concretion x - less than 1 percent ? probably labradorite-anorthite 11 = probably oligoclase-andesine * = a l b i t e or K-feldspar Figure 1. Location and a c c e s s i b i l i t y of Vulcan Ridge. L E G E N D scale -I in.= 1000 ft. Middle Aldridge Lower Aldridge1 quartzites argillaceous quartzites argillites Lower Aldridge breccia-conglomerates Moyie Intrusives Tourmaline greater than 2 % Faults Geological oont6cts •| Anticline 1 ( 1 1 \ / 1 — 1 / Figure 5. Sketch map showing d i s t r i b u t i o n of tourmaline m the Lower Aldridge metasediments. Figure 6. Sketch of an outcrop i n Orange Tent Basin showing a l e n s - l i k e body of sorted breccia-conglomerate surrounded by unsorted breccia-conglomerate;., Figure 7. Sketch of an outcrop i n D i o r i t e Lake Basin showing i r r e g u l a r l y shaped body of sorted breccia-conglomerate. Moyie Intrusives L E G E N D scale -.1 in.- IOOO ft. 5 ooo' Con tour (interval: IOOO ft.) Metasediments Geological Contacts Figure 12. Sketch map showing l o c a t i o n of specimens for modal analyses of Moyie i n t r u s i v e rocks. Figure 13. Sketch'map showing areas of regional and contact metamorphism. Hornblende Hornfels Facies. ACF Diagram Hornblende Hornfels Facies. AKF Diagram for Rocks with Excess Si02 and K20 for Rocks with Excess Si02 and AI2O Figure 19. Mineral assemblages of contact metamorphic rocks disregarding the changes produced by retrogressive metamorphism. C i r c l e s represent various rocks from the inner and outer contact metamorphic zones. (Diagrams af t e r Fyfe, Turner and Verhoogen,1958). 8 0 0 0 — I N E 7 0 0 0 6 0 0 0 10 \ \ V \ \ *V\'\ v V \ '< 1 1 A - /t A \ \ \ v \ . \ \ \, i 1 ! V I V E R T I C A L C R O S S - S E C T I O N S of V U L C A N RIDGE W h i t e C r e e k b a t h o l i t h M o y i e I n t r u s i v e s C r e s t o n F o r m a t i o n M i d d l e A l d r i d g e la L o w e r A l d r i d g e I a : b r e c c i a - c o n g l o m e r a t e s I. a r g i l l i t e s , q u a r t z i t e s , and a r g i l l a c e o u s q u a r t z i t e s b e d d i n g f a u l t g e o l o g i c a l c o n t a c t s s c a l e . - I i n = I O O O f t . W 

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