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The geology of Steele, Bonis, and Scapa townships, District of Cochrane, Ontario Lumbers, Sydney Blake 1960

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THE GEOLOGY OF STEELE, BONIS, AND SCAPA TOWNSHIPS, DISTRICT OF COCHRANE, ONTARIO by SYDNEY BLAKE LUMBERS B.Sc, McMaster University, 1958 A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE i n the Department of GEOLOGY We accept this thesis as conforming to the required standard THE UNIVERSITY OF BRITISH COLUMBIA A p r i l , 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 th a t 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 tha t 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 (jieo U The U n i v e r s i t y of B r i t i s h Columbia, Vancouver 8, Canada. ABSTRACT Steele, Bonis, and Scapa townships, i n the D i s t r i c t of Cochrane, Ontario, are underlain by a steeply i n c l i n e d Precambrian metavolcanic-metasediment assemblage that i s i n  truded by s i l l s , dikes, stocks, and batholiths. The metamorphosed Bonis volcanics and Steele Lake volcanics are c h i e f l y intermediate to basic lavas. The Scapa and Steele metasediments are composed mainly of meta morphosed greywacke, c a l c - s i l i c a t e rocks, and iron-formation. Metamorphosed ultrabasic and basic intrusions occur i n the Bonis volcanics and Scapa metasediments. The metasediments and Steele Lake volcanics show a regional metamorphic zoning r e l a t i v e to the Case bat h o l i t h on the north margin of the area. C h l o r i t e , b i o t i t e , garnet, and s t a u r o l i t e zones are distinguished over an area up to eight miles wide south of the bath o l i t h . The regional metamorphic zoning i s attributed to intrusion of the Case bat h o l i t h . The Bonis volcanics have been metamorphosed at thei r contact with the Sargeant b a t h o l i t h that underlies the southeast part of the area. The Bonis volcanics have acted as a " r e s i s t o r " i n protecting the metasediments from meta- morphism by the Sargeant batholith. A narrow contact aureole occurs i n the Scapa metasediments adjacent to the Scapa stock. Potash metasomatism and high water pressures have prevented the formation of alumina-rich minerals within the aureole. Diabase dikes of two ages cut a l l other rocks i n the area. The easterly trending rocks of the metavolcanic- metasediment assemblage are l o c a l l y deflected' around the western end of the concordant Sargeant batholith. A spodumene-bearing pegmatite dike found i n the Case bat h o l i t h i s of economic i n t e r e s t . TABLE OF CONTENTS Page CHAPTER I Introduction . . . 1 Means of Access 2 F i e l d Methods 3 Topography and Drainage 4 Rock Exposures 5 G l a c i o f l u v i a l Deposits 7 Drainage 8 Natural Resources 9 CHAPTER II General Geology 11 Previous Geological Work 11 General Geology . . . 12 CHAPTER III Metavolcanic-Metasediment Assemblage 17 Introduction 17 Metasediments 20 Scapa Metasediments , . 2 0 Greywacke 21 (1) B i o t i t e Zone 23 (2) Garnet Zone 27 (3) S t a u r o l i t e Zone 29 Scapa Stock Aureole 33 Iron-formation 37 C a l c - S i l i c a t e Rocks 42 Prehnite Veins 43 Steele Metasediments 44 Greywacke 46 (1) C h l o r i t e Zone 46 (2) B i o t i t e Zone 52 C a l c - S i l i c a t e Rocks . . . . 54 Amphibole and Plagioclase-Rich Schists . . 57 Miscellaneous Metasediment 58 Metavolcanics . 59 Steele Lake Volcanics 59 Amphibolite 59 (1) B i o t i t e Zone 61 (2) Garnet and S t a u r o l i t e Zones . . . 63 Interbedded Metasediment . . . . 66 Miscellaneous Rocks 67 Bonis Volcanics 68 Basic to Intermediate Volcanics 71 Acid Volcanics 78 Rocks of Indefinite O r i g i n 79 Page Summary of the Metamorphism 81 Metamorphism of the Greywackes 83 Metamorphism of the Steele Lake Amphibolites. 87 Metamorphism of the Bonis Volcanics 88 Cause of the Metamorphism 90 CHAPTER IV Intrusions . 94 Ultrabasic and Basic Intrusions 94 Serpentinite 94 Amphibolite 95 D i o r i t e . 98 Acid Intrusions . 98 Sargeant Bath o l i t h 98 Western Contact of the Batho l i t h . . . . 107 Northern Contact of the Ba t h o l i t h . . . . 112 Summary of the Sargeant Bath o l i t h . . . . 113 Case Batholith 115 Scapa Stock 124 Lamprophyre 126 Late Basic Intrusions 127 CHAPTER V St r u c t u r a l Geology 132 General Features 132 Faults 133 Structures Related to the Acid Intrusions . . . . 138 Jointing 139 CHAPTER VI Cenozoic 140 Pleistocene . . 140 G l a c i a l Deposits 142 G l a c i o f l u v i a l Deposits 144 Barlow-0jibway Varved Clay 144 Barlow-0jibway Sand and Gravel 145 Recent 146 CHAPTER VII Economic Geology 14? Sulphide Mineralization , 147 Iron 149 Lithium . . . 149 Bibliography 151 ILLUSTRATIONS Figure Page 1. Key map showing the location of Steele, Bonis, and Scapa townships. Scale ; 1 inch to 50 miles . . 1 2 . Sketch map showing the d i s t r i b u t i o n of meta morphic zones developed within the metavolcanic- metasediment assemblage. Scale, 1 inch to 2 miles 18 3. Sketch map showing the s t r u c t u r a l geology of Steele, Bonis, and Scapa townships. Scale, 1 inch to 2 miles 134 4. Sketch map of the Pleistocene geology of the map-area, Scale, 1 inch to 2 miles 141 5. Geological map of Steele, Bonis, and Scapa townships, Scale, 1 inch to 1/2 mile . . . . . i n pocket Plate IA View of Steele ridge, looking north from Peat's Point 6 IB View looking north towards L i t t l e Joe and Case Lakes from the f i r e tower 6 IIA Photomicrograph of graded bedding i n greywacke . . 26 IIB Photomicrograph showing a porphyroblast of twinned c h l o r i t o i d 26 IIIA Photomicrograph of a "spongy" s t a u r o l i t e porphyroblast . 30 IIIB Photomicrograph of an altered s t a u r o l i t e metacryst 30 IV Photomicrograph of hornfels, 20 feet south of the Scapa stock contact 36 VA Intraformational breccia layer i n Steele meta sediments 45 VB Massive greywacke overlying greywacke with graded beds 45 VI Contorted bedding i n the Steele metasediments . . 48 Plate page V i l a Photomicrograph of massive greywacke 50 VIIB Photomicrograph of massive greywacke showing d e t r i t a l o l igoclase grains . 50 VIIIA Sheared metasediments i n the railway cut . . . . $1 VIIIB Cross-bedding i n graded beds overl a i n by massive greywacke 51 IXA Graded bedding truncated by massive greywacke . 53 IXB Amphibole-plagioclase schist 53 XA Photomicrograph of sheared massive greywacke . . 55 XB Photomicrograph of a quartz v e i n l e t i n sheared greywacke 55 XIA Photomicrograph of garnet amphibolite 65 XIB Photomicrograph of diabasic amphibolite . . . . 65 XIIA Pillowed, porphyrjtic, intermediate to basic lava 70 XIIB Pillowed non-porphyr^rtic lava 70 XIIIA Photomicrograph of porphyrytic intermediate to basic lava (andesite?) 73 XIIIB Photomicrograph of schistose amphibolite . . . . 73 XIVA Photomicrograph of t u f f interbedded with the basic to intermediate volcanics 77 XIVB Photomicrograph of schistose amphibolite . . . . 77 XVA Porphyrttic intermediate to basic lava 80 XVB Contorted tuffaceous sediment (?) folded around a porphyry dike 80 XVIA Photomicrograph of serpentinite, l o t 4, concession C, Steele township 96 XVIB Photomicrograph of amphibolite showing r e l i c t o p h i t i c texture 96 Plate Page XVIIA Photomicrograph of pyroxene d i o r i t e 101 XVIIB Photomicrograph of quartz d i o r i t e 101 XVIIIA Photomicrograph of quartz monzonite, Bonis township 106 XVIIIB Photomicrograph of granodiorite 106 XIXA Intrusion breccia, l o t 2, concession D, Steele township 108 XIXB Intrusion breccia, l o t 1, concession D, Steele township 108 XX Photomicrograph of feldspar porphyry 110 XXI Photomicrograph of quartz monzonite showing myrmekite 118 XXII Spodumene-bearing pegmatite dike, l o t 5, concession V, Steele township 122 XXIII Photomicrograph of Scapa Stock leucogranite . . 125 XXIVA Photomicrograph of o l i v i n e diabase 130 XXIVB Photomicrograph of quartz diabase showing micrographic intergrowths of quartz and plagioclase 130 XXV Northeast- and northwest-trending f a u l t s i n an outcrop i n eastern Scapa township 135 XXVIA Gravel p i t i n the prominent esker s t r i k i n g south through the centre of the map-area . . . 143 XXVIB S t r a t i f i e d gravel as seen i n a gravel p i t on the southern slope of Steele ridge 143 TABLES Table 1 Table of formations 15 2 Mineral assemblages of the greywackes and amphibolites i n the metamorphic zones of the metasediments and Steele Lake volcanics . . ACKNOWLEDGMENTS The writer i s indebted to Dr. M.E. Hurst, P r o v i n c i a l Geologist, Ontario Department of Mines, for permission to use f i e l d work carried out for the Department of Mines as a basis for th i s thesis. Many helpful suggestions and c r i t  icisms during the preparation of the thesis by Dr. K.C. McTaggart and Dr. J.V. Ross are g r a t e f u l l y acknowledged. Assistance i n the f i e l d was given by Mr. W. Leszezyszyn, Mr. J . J . Cavarzan, and Mr. L. Carlson. Mr. Leszezyszyn, as senior assistant, was responsible for part of the f i e l d mapping. Assays were made by the s t a f f of the P r o v i n c i a l Assay o f f i c e , Ontario Department of Mines. CHAPTER I INTRODUCTION S t e e l e , Bonis and Scapa townships are l o c a t e d i n the D i s t r i c t o f Cochrane about 50 m i l e s due east o f the town o f Cochrane, w h i c h i s l o c a t e d at the j u n c t i o n o f the O n t a r i o N o r t h l a n d r a i l w a y and the n o r t h e r n branch o f the Canadian N a t i o n a l R a i l w a y s . The southern p a r t o f S t e e l e township and the southwest corner o f Bonis township together comprise a major p o r t i o n of the n o r t h shore o f Lower Lake A b i t i b i . F i g u r e 1 . Key map showing the l o c a t i o n o f S t e e l e , B o n i s and Scapa t o w n s h i p s . 2 Recorded intere s t i n the map-area dates back to 1906, when, according to Baker, 1 many prospectors t r a v e l l e d to Lake A b i t i b i i n search of gold, following the staking rush at Cobalt. Copper was discovered i n the metavolcanic rocks occurring i n northern Steele township In the l a t e 1920's. Since t h i s time prospecting a c t i v i t y has been more or less continuous and a v a r i e t y of exploration work performed. No mineral production has been reported from the three town ships. MEANS OF ACCESS The A b i t i b i Power and Paper Company's Trans-Limit road and main haulage road together give direct access from Iroquois F a l l s to northern Steele township, the southern part of Scapa township, the northwestern corner of Bonis township and Eades, a f l a g stop on the Canadian National Railway. The roads are gravel surfaced and passable i n a l l seasons. The northern branch of the Canadian National railways traverses the southern part of Steele and the eentral part of Bonis townships. Daily, except Sunday, t r a i n service l i n k s Eades with Cochrane, 54.5* miles to the west, and var ious points within the province of Quebec, 17 miles to the east. There are numerous old logging haulage roads within the three townships and except where they cross muskegs, 1 Baker, M.B., Lake A b i t i b i Area, Ont. Bur. Mines. V o l . XVIII, pt. 1, 1909, p. 268. most of them are overgrown. They s t i l l provide easy access by foot to many parts of the map-area, as they have now be come major game t r a i l s . A good t r a i l , once along a telephone l i n e , runs due north from Mace on the C.N.R. to the f i r e tower i n northern Steele township. An old portage extends from 50 feet east of milage 58 on the Trans-Limit road to the northern boundary of Scapa at Kabika Lake. FIELD METHODS The present survey was conducted by the writer for the Ontario Department of Mines during the summer of 1959. The manuscript map used for the compilation was provided by the Ontario Department of Lands and Forests and compiled from a i r photographs taken i n 1946 and 1947 for the Forest Resources Inventory. Further topographic d e t a i l s have been added from information collected during the course of the f i e l d work. The f i e l d mapping of the townships was carried out on a scale of 1 inch to 1320 feet. Geological i n f o r  mation, obtained by shoreline geology and pace-and-compass traverses tied to the C.N.R., roads, and surveyed l i n e s , was plotted on a i r photographs. This information, i n turn, was plotted on the manuscript map. As the f i n a l map was pro duced on a scale of 1/2 mile to the inch, many of the out crops had to be generalized and s l i g h t l y enlarged. That portion of the Trans-Limit road i n Steele township was surveyed by chain and compass, and t i e d to 4 a v a i l a b l e i r o n bars and wooden survey p o s t s . Chained and p i c k e t e d l i n e s run i n S t e e l e and Scapa townships by the A b i t i b i Power and Paper Company d u r i n g the w i n t e r o f 1959 were a l s o used i n the f i e l d work. P l a n s o f prospects and diamond d r i l l l o g s , o b t a i n e d from p r o p e r t y owners, and assessment work d a t a f i l e d at Timmins w i t h the r e s i d e n t g e o l o g i s t , O n t a r i o Department o f M i n e s , were a l s o used i n p l o t t i n g g e o l o g i c a l d a t a . TOPOGRAPHY AND DRAINAGE The area l i e s w i t h i n the l a r g e u n d u l a t i n g B a r l o w - Ojibway c l a y p l a i n and i s f l a t to g e n t l y r o l l i n g . A prom i n e n t rock r i d g e ( S t e e l e Ridge) w i t h i n t e r m i x e d P l e i s t o c e n e d e p o s i t s extends across the n o r t h e r n p a r t o f the a r e a , from the western boundary o f S t e e l e township eastward i n t o Hep burn t o w n s h i p . To the n o r t h o f the r i d g e the area i s low and swampy, i n t e r r u p t e d at i n t e r v a l s by rocky k n o l l s and d e p o s i t s o f g l a c i a l o r i g i n . To the s o u t h , the l a n d s lopes g e n t l y towards Lake A b i t i b i . A l t i t u d e s i n the three townships range from 1395 feet3 a t the t r i a n g u l a t i o n s t a t i o n under the S t e e l e f i r e tower to 868 f e e t , the e l e v a t i o n o f Lake A b i t i b i . Mace on the C . N . R . has an e l e v a t i o n o f 880 f e e t . A bench mark on 2 A l t i t u d e s are from sheet No . 32 D/NW, N a t i o n a l t o p o g r a p h i c s e r i e s , un less o therwise s t a t e d . 3 J . E . L i l l y , Dominion G e o d e s i s t , r e p o r t s t h i s e l e v a t i o n to be accura te to w i t h i n 15-20 f e e t and to r e f e r to the t a b l e t under the f i r e tower . 5 the c u l v e r t where the C . N . R . c rosses Forks Creek has an e l e v a t i o n o f 886.2 f e e t . Bench marks a long the C . N . R . i n B o n i s township i n d i c a t e the g e n e r a l e l e v a t i o n r i s e s s l i g h t l y to about 908 f ee t j u s t east o f the e a s t e r n boundary o f Bonis t o w n s h i p . A l t h o u g h the h i g h e s t p o i n t a long S t e e l e r i d g e i s under the f i r e tower , another prominent h i g h i s l o c a t e d i n the southern p a r t o f l o t 2, concess ion I I I , S t e e l e township . T h i s i s r e p o r t e d to be about 150 f e e t lower i n e l e v a t i o n i 4 than the h i l l on w h i c h the f i r e tower i s l o c a t e d . The r i d g e i s composed o f l e s s r e s i s t a n t rocks i n Scapa township than i n S t e e l e township and, as a r e s u l t , the e l e v a t i o n s here are l o w e r . ROCK EXPOSURES Rock exposures are c o n f i n e d almost e n t i r e l y to the h i l l y a r e a s . The main h i l l s i n c l u d e S t e e l e r i d g e , a rocky k n o l l i n the n o r t h e a s t e r n corner o f S t e e l e t o w n s h i p , a low r i d g e i n the w e s t - c e n t r a l p a r t o f S t e e l e t o w n s h i p , and rocky k n o l l s i n the nor thwestern and n o r t h e a s t e r n p a r t s o f Bonis t o w n s h i p . E l s e w h e r e , rock outcrops are w i d e l y s c a t t e r e d and few. The v o l c a n i c and b a s i c i n t r u s i v e rocks are best ex posed and most r e s i s t a n t to e r o s i o n . N e a r l y a l l o f S t e e l e r i d g e i n S t e e l e toxmship i s composed o f v o l c a n i c s and on Lake A b i t i b i the v o l c a n i c and b a s i c rocks are b e t t e r exposed 4 Herbert J . B e a t t y ( O . L . S . ) , from township surveys f i l e d w i t h the O n t a r i o Department o f Lands and F o r e s t s . 6 Plate I A—View of Steele ridge, looking north from Peat's Point. The prominent h i l l just to the l e f t of the centre of the photographhas an elevation of 1395 feet. B—View looking north towards L i t t l e Joe and Case Lakes from the f i r e tower on Steele ridge. Note the low muskeg area surrounding Case Lake. 7 a long the shore than the o ther rock t y p e s . A g lance at the g e o l o g i c a l map w i l l show the s t r o n g i n f l u e n c e that the d i a  base d i k e s have had i n p r e s e r v i n g outcrops o f the meta- sedimentary r o c k s . A t most exposures the metasedimentary rock i s cut by diabase d i k e s . Diabase d i k e s a l s o form c o n  spicuous e l e v a t i o n s a long S t e e l e r i d g e and i n southern Bonis township . Outcrops o f a c i d i n t r u s i v e s are almost e n t i r e l y c o n f i n e d to n o r t h e a s t e r n Bonis township where they form a prominent s e r i e s o f r o c k y k n o l l s , and to the area n o r t h o f S t e e l e r i d g e i n S t e e l e township . The g r a n i t e s tock i n Scapa township forms a l o w , rounded k n o l l and probably he lped p r e s e r v e the metasedimentary exposures i n t h i s p a r t o f the a r e a . GLACIOFLUVIAL DEPOSITS A prominent t r i a n g u l a r a p r o n , composed o f sand, pebble g r a v e l , and boulder g r a v e l , s t r a t i f i e d i n p l a c e s , and t h i n n i n g to the s o u t h , extends from the southern s l o p e o f S t e e l e r i d g e i n S t e e l e township to about the southern bound a r y o f concess ion I . S e v e r a l s m a l l h i l l s and r i d g e s occur w i t h i n the apron and i n p l a c e s i t i s i n t e r r u p t e d by low muskeg a r e a s . The apron i s wides t d i r e c t l y south o f the f i r e tower on S t e e l e r i d g e , the h ighes t e l e v a t i o n i n the a r e a . Where e l e v a t i o n s are l e s s a long S t e e l e r i d g e the apron i s p r o p o r t i o n a t e l y n a r r o w e r . 8 An esker w i t h a s s o c i a t e d outwash d e p o s i t s t rends southward from K a b i k a Lake i n the northwest corner o f Scapa township to a p o i n t on the C . N . R . , due south o f Bonis Lake i n Bonis township . Numerous k e t t l e l a k e s are s c a t t e r e d a long the t r e n d o f the esker and t r i b u t a r i e s o f Forks Creek have cut through i t i n many p l a c e s . A t r i b u t a r y o f Forks Creek occupies a h o l l o w found at the i n t e r s e c t i o n o f the esker and S t e e l e r i d g e . Another e s k e r , somewhat lower than the one mentioned above, crosses the main haulage road at the g r a v e l p i t s i n Scapa t o w n s h i p . T h i s r i d g e d i e s out about h a l f a m i l e to the south o f the r o a d . To the n o r t h i t appears to b lend i n t o the P l e i s t o c e n e d e p o s i t s occupying the southern s l o p e o f S t e e l e r i d g e i n Scapa t o w n s h i p . DRAINAGE P i n n a t e dra inage predominates i n the a r e a , a l t h o u g h p o o r l y developed r a d i a l dra inage occurs about the g r a n i t e s t o c k i n n o r t h e r n Scapa township . I n t e r f l u v i a l areas are p o o r l y d r a i n e d . Most o f the streams are consequent on the Bar low-0 j ibway c l a y p l a i n and are i n a y o u t h f u l stage o f development, c h a r a c t e r i z e d by V-shaped v a l l e y s and r a p i d s . In the low a r e a s , p a r t i c u l a r l y i n Bonis township many o f the l a r g e r streams appear to have a t t a i n e d e a r l y m a t u r i t y . The water o f many streams and Lake A b i t i b i has a t u r b i d appear ance due to f i n e l y suspended c l a y e y p a r t i c l e s d e r i v e d from the c l a y s u n d e r l y i n g much o f the a r e a . 9 S t e e l e r i d g e i s an e f f e c t i v e water d i v i d e . A l l streams d r a i n i n g the southern s lopes o f the r i d g e f l o w i n t o Lake A b i t i b i , whereas a l l those on the n o r t h s l o p e f l o w northward or westward. Mace Creek and West Mace C r e e k , t o  gether w i t h t h e i r t r i b u t a r i e s d r a i n most o f southern S t e e l e t o w n s h i p . The w e s t - c e n t r a l p a r t o f S t e e l e i s d r a i n e d by the Kaminis inakwa R i v e r w h i c h f lows southwest through P l i n y and P u r v i s townships to Lake A b i t i b i . L i t t l e Joe Creek d r a i n s the a r e a about L i t t l e Joe L a k e . I t f l o w s around the western end of S t e e l e r i d g e and cont inues southwestward where i t j o i n s the C i r c l e R i v e r i n P l i n y township . The drainage In the remainder o f S t e e l e township i s to the n o r t h v i a Case Lake and the Case R i v e r , w h i c h u l t i m a t e l y f l o w s i n t o the Burhtbush R i v e r , 25 m i l e s to the n o r t h o f S t e e l e township . The area n o r t h o f S t e e l e r i d g e i n Scapa township i s d r a i n e d by the K a b i k a R i v e r , a t r i b u t a r y o f the Burntbush R i v e r . Forks Creek and Departure Creek , a long w i t h i t s t r i b u t a r i e s West Departure Creek and Balkam Creek , d r a i n the remainder o f Scapa township and much o f Bonis t o w n s h i p . The southeas tern corner o f Bonis township i s d r a i n e d by the A y l e n R i v e r . NATURAL RESOURCES The map-area i s s i t u a t e d w i t h i n the t imber l i m i t s o f the A b i t i b i Power and Paper Company. Most o f the t r e e s i n 10 B o n i s and the southern p a r t s o f S t e e l e and Scapa townships have been cut f o r p u l p . As a r e s u l t , these areas are now covered c h i e f l y by p o p l a r , b i r c h and a l d e r . In p l a c e s , enough t ime has e lapsed s i n c e the end o f l o g g i n g o p e r a t i o n s to a l l o w the growth of young spruce and balsam. The remainder o f the a r e a , except f o r muskegs, i s covered by a mature growth o f s p r u c e , balsam and j a c k p i n e . I n the muskegs b l a c k s p r u c e , tamarack and a l d e r are commonly f o u n d . Gedar was seen o n l y i n muskeg and wet areas i n l a n d from the e a s t e r n shore o f Northeas t B a y . Moose, b l a c k b e a r , r a b b i t , f o x , beaver and skunk are common i n the a r e a . Deer , bush c a r i b o u , mink and m a r t i n are r a r e l y seen. Numerous beaver dams occur i n the streams and i n p l a c e s f l o o d i n g makes t r a v e l d i f f i c u l t . W h i t e f i s h , p i c k e r e l , p i k e and suckers can be caught i n Lake A b i t i b i and many of the streams c o n t a i n brook t r o u t . Commercial f i shermen have operated from Mace but d u r i n g the 1959 f i e l d season no commercial f i s h i n g was done. Trapping i n the area has f a l l e n o f f c o n s i d e r a b l y i n recent years because o f poor f u r p r i c e s . CHAPTER I I GENERAL GEOLOGY PREVIOUS GEOLOGICAL WORK Except f o r B o n i s township and that p a r t o f the map- a r e a b o r d e r i n g on Lake A b i t i b i , no p r e v i o u s g e o l o g i c a l map or r e p o r t has been p u b l i s h e d on the three townships . Almost the e n t i r e r e g i o n to the e a s t , west and n o r t h i s unmapped g e o l o g i c a l l y . A few e a r l y r e p o r t s by the G e o l o g i c a l Survey o f Canada and the O n t a r i o Bureau o f Mines c o n t a i n b r i e f r e f e r e n c e s to the geology o f the a r e a a long the shore o f Lake A b i t i b i . M . B . Baker and N . L . Bowen made a reconnaissance g e o l o g i c a l survey o f the Lake A b i t i b i a rea i n 1908 and they produced a g e n e r a l i z e d g e o l o g i c a l map o f the southern par t o f S t e e l e and a l l o f B o n i s t o w n s h i p . I t i s u n l i k e l y , however, t h a t they a c t u a l l y t r a v e r s e d much o f Bonis t o w n s h i p . Most o f the i n t e r p r e t a t i o n was probably based upon outcrops found a long the shore o f Lake A b i t i b i and the Canadian N a t i o n a l r a i l w a y . C.W. K n i g h t et a l , have g i v e n a complete b i b l i o  graphy of the A b i t i b i r e g i o n up to 1918 and numerous r e f e r  ences to the map-area are made i n t h e i r r e p o r t . M r . W.H. Thompson o f Kennco E x p l o r a t i o n (Canada) L i m i t e d , k i n d l y made a v a i l a b l e to the w r i t e r a p r i v a t e r e p o r t and map on the geology o f p a r t s o f S t e e l e , Bonis and B e r r y t o w n s h i p s . 12 Other government r e p o r t s and p u b l i c a t i o n s d e a l i n g w i t h the geology o f the map-area are i n c l u d e d i n the f o l l o w  i n g b i b l i o g r a p h y : McOuat, W a l t e r , G e o l o g i c a l Survey o f Canada, 1872 -3 . O g i l v i e , Wm., Report o f E x p l o r a t i o n Survey to Hudson B a y , 1891. B a k e r , M . B . , Lake A b i t i b i A r e a , Ont . B u r . M i n e s . V o l . X V I I I , p t . 1 , 1909, p p . 263-283. K n i g h t , C . W . , Burrows , A . G . , H o p k i n s , P . E . , and P a r s o n s , A . L . , A b i t i b i - N i g h t Hawk Gold A r e a , Ont . B u r . M i n e s . V o l . X X V I I I , p t . 2 , 1919, p p . 1 - 7 0 . G l e d h i l l , T . L . , Ben N e v i s , Munro, K a m i s h k o t i a , and Other Base M e t a l A r e a s , D i s t r i c t s o f Cochrane and T i m i s k a m i n g , Ont . Dept . M i n e s % V o l . X X X V I I , p t . 3 , 1928, p . 49 . K i n d l e , E . D . , Gold Occurrences o f O n t a r i o East o f Lake S u p e r i o r , G e o l . S u r v . C a n . , Memoir 192, 1936, p p . 1 -4 . Map 48G. Geophysics Paper 48 , G e o l . S u r v . C a n . . 1948. GENERAL GEOLOGY Rocks o f the S t e e l e , Bonis and Scapa map-area are e n t i r e l y Precambrian i n age. They comprise a complex o f m e t a v o l c a n i c and metasedimentary r o c k s , i n t r u d e d by s i l l s , d i k e s , s tocks and b a t h o l i t h s that v a r y w i d e l y i n compos i t ion and age. The metavolcanic-metasediment assemblage u n d e r l i e s about t w o - t h i r d s o f the a r e a and c o n s i s t s o f an unknown t h i c k n e s s o f s t e e p l y i n c l i n e d metamorphosed greywacke, i r o n f o r m a t i o n , b a s i c to i n t e r m e d i a t e v o l c a n i c s and a c i d v o l c a n i c s . The base o f t h i s assemblage has not ye t been f o u n d . The m e t a v o l c a n i c s and metasediments are i n p a r t conformable and i n p a r t e i t h e r nonconformable , o r i n f a u l t e d c o n t a c t . The assemblage has been d i v i d e d i n t o f o u r rock u n i t s by the w r i t e r , f o r w h i c h the names Scapa metasediments, S t e e l e Lake v o l c a n i c s , S t e e l e metasediments and B o n i s v o l c a n i c s are proposed . A v a r i e t y o f i n t r u s i v e rocks ranging from u l t r a b a s i c to b a s i c i n c o m p o s i t i o n occur i n the Bonis v o l c a n i c s and Scapa metasediments. These rocks form narrow s i l l s , d i k e s and i r r e g u l a r masses. Some o f the s i l l s appear to be d i f f e r  e n t i a t e d i n t o b a s i c and u l t r a b a s i c p o r t i o n s , o t h e r s are complex i n o r i g i n . Some o f the b a s i c i n t r u s i o n s o c c u r r i n g i n the Bonis v o l c a n i c s are sheared and the t rend o f the s c h i s t o s i t y d i f f e r s r a d i c a l l y from t h a t o f the surrounding v o l c a n i c f l o w s . Two b a t h o l i t h l c i n t r u s i o n s have invaded and meta morphosed the rocks o f bo th the p r e c e d i n g groups . The Case b a t h o l i t h to the n o r t h d i f f e r s markedly i n compos i t ion and t e x t u r e from the Sargeant b a t h o l i t h to the s o u t h . The Case b a t h o l i t h i s g r a n o d i o r i t i c to g r a n i t i c i n compos i t ion and i n p a r t p e g m a t i t i c whereas the Sargeant b a t h o l i t h i s d i o r i t i c i n c o m p o s i t i o n and i n p l a c e s g n e i s s i c . The S t e e l e and Scapa metasediments together d i s p l a y a w e l l - d e v e l o p e d metamorphic z o n i n g r e l a t i v e to the Case b a t h o l i t h . A s s o c i a t e d w i t h the two b a t h o l i t h s are a number o f porphyry d i k e s and a g r a n i t e s tock (Scapa s t o c k ) . Most o f the porphyry d i k e s w h i c h occur i n the S t e e l e metasediments 14 a l o n g the shore o f Nor theas t Bay are metamorphosed and sheared and are t h e r e f o r e cons idered as e a r l y m a n i f e s t a t i o n s o f the Sargeant b a t h o l i t h . The r e l a t i v e ages o f the two b a t h o l i t h s i s unknown but both are younger than the meta- volcanic -metasediment assemblage and the u l t r a b a s i c and b a s i c i n t r u s i v e s . Two se ts o f diabase d i k e s i n t r u d e a l l o t h e r rocks i n the a r e a . One set composed o f q u a r t z diabase t rends n o r t h and the o t h e r , composed o f diabase and o l i v i n e d i a b a s e , n o r t h - e a s t w a r d . Outcrops o f t h e i r i n t e r s e c t i o n were not found but evidence from other areas to the s o u t h , where the same t r e n d i n l a t e b a s i c d i k e s has been n o t e d , i n d i c a t e s the n o r t h - s o u t h set to be the o l d e r . Most o f the Precambrian rocks are b u r i e d by e x t e n s i v e d e p o s i t s o f c l a y , boulder c l a y , s a n d , and g r a v e l . Much o f the c l a y , as shown i n s e c t i o n s a long Lake A b i t i b i and i n road c u t s , i s varved i n d i c a t i n g the d e p o s i t i o n o f m a t e r i a l i n a p o s t - g l a c i a l l a k e . In land from Lake A b i t i b i boulder t r a i n s , e s k e r s , and outwash d e p o s i t s are common. These d e p o s i t s are a l l P l e i s t o c e n e i n age and owe t h e i r o r i g i n to the e x t e n s i v e W i s c o n s i n i c e - s h e e t . Recent d e p o s i t s c o n s i s t c h i e f l y o f peat formed In the swamps, r i v e r , and beach d e p o s i t s . I n the f o l l o w i n g summary o f the g e o l o g i c a l s u c c e s s i o n the terms K e e w a t i n , T i m i s k a m i n g , Algoman, Matachewan and Keweenawan have been avoided and o ther names, d e s c r i p t i v e o f the r o c k u n i t s , have been used i n s t e a d . As p o i n t e d out by Gunning and Ambrose and more recently by G i l l the terms Keewatin, Timiskaming, etc., have l i t t l e s t r a t i g r a p h i c s i g  n i f i c a n c e , and indeed they tend to confuse the issues i n  volved. No attempt has been made to separate the rocks into Late Precambrian (Proterozoic) and Early Precambrian (Archean) as these terms imply absolute age, the evidence for which i s lacking at the present time. Correlation with other areas must await further mapping. TABLE OF FORMATIONS CENOZOIC Recent: Peat, beach deposits, r i v e r deposits. Pleistocene: Varved clay, boulder clay, s i l t , sand, pebble gravel, boulder gravel. UNCONFORMITY PRECAMBRIAN Late Basic Intrusions Late Diabase: O l i v i n e diabase and diabase dikes Early Diabase: Quartz diabase dikes. Intrusive Contact Acid Intrusions Scapa Stock: pink medium-grained granite 1 Gunning, H.C., and Ambrose, J.W., The Timiskaming- Keewatin Problem i n the Rouyn-Harricanaw Region, North western Quebec, Trans. Roy. Soc. Can., Sec. 4, Vol . XXXIII 1939, pp. 19-49. 2 G i l l , J.E., Precambrian Nomenclature i n Canada, Trans.Roy.Soc. Can., y 0 l . XLIX, Sec.4, 1955, pp. 25-29. 16 Case B a t h o l i t h : H y b r i d r o c k s , l e u c o g r a n o d i o r i t e , l e u c o c r a t i c quar tz monzoni te , pegmat i t e , a p l i t e , Q u a r t z - f e l d s p a r porphyry and f e l d s p a r porphyry d i k e s . (Age r e l a t i o n s h i p between Case b a t h o l i t h and Scapa s t o c k , and Sargeant b a t h o l i t h i s unknown) Sargeant B a t h o l i t h : Hornblende and pyroxene d i o r i t e quar tz d i o r i t e , g n e i s s i c quartz d i o r i t e , quar tz monzoni te , g r a n o d i o r i t e , h y b r i d r o c k s . F e l d s p a r porphyry and q u a r t z - f e l d s p a r porphyry d i k e s , r a r e p e g m a t i t e . I n t r u s i v e Contact U l t r a b a s i c and B a s i c I n t r u s i o n s : S e r p e n t i n i t e , u r a l i t - i z e d p y r o x e n i t e , a m p h i b o l i t e , d i o r i t e . I n t r u s i v e Contact M e t a v o l c a n i e - Metasediment Assemblage Bonis v o l c a n i c s : In termedia te to b a s i c l a v a s ; p i l l o w lavas 5 a m p h i b o l i t e ; p o r p h y r i t i c b a s a l t ; a c i d l a v a and agglomerate; some t u f f and f l o w b r e c c i a ; rocks o f i n d e f i n i t e o r i g i n . F a u l t (?) (Age r e l a t i o n s h i p between the Bonis v o l - - c a n l c s and the d i v i s i o n s l i s t e d below i s not known.) S t e e l e metasediments: S t e e l e Lake v o l c a n i c s : Metamorphosed greywacke; in terbedded c a l c - s i l i c a t e r o c k s ; h o r n b l e n d e - p l a g i o c l a s e s c h i s t . A m p h i b o l i t i z e d i n t e r m e d i a t e to b a s i c l a v a , p i l l o w l a v a , p o r p h y r y t i c b a s a l t ; amphi- bo le s c h i s t ; rocks o f i n  d e f i n i t e o r i g i n ; some i n t e r  bedded metasediment. Scapa metasediments: Metamorphosed greywacke, garnet and s t a u r o l i t e s c h i s t s ; I n t e r  bedded c a l c - s i l i c a t e r o c k s , i r o n f o r m a t i o n ; r a r e a r k o s e . CHAPTER I I I METAVOLCANIC-METASEDIMENT ASSEMBLAGE i in Li I n i n i a u . a i a r a e a ram TI •» m g r a n n i g i - j , J U I j j a - a j i - a l T INTRODUCTION N e a r l y a l l o f Scapa township , about t h r e e - f o u r t h s o f S t e e l e township and the extreme n o r t h e r n and nor thwestern p a r t s o f B o n i s township are u n d e r l a i n by rocks be longing to the meta- volcanic -metasediment assemblage. The s t r u c t u r a l t r e n d and g e n e r a l c h a r a c t e r i s t i c s o f the assemblage c l o s e l y resemble those o f Archean rocks w h i c h occur w i t h i n the S u p e r i o r P r o v  i n c e 1 o f the Canadian S h i e l d . The s t r a t i g r a p h y o f the i n d i v i d u a l u n i t s i s o n l y i m p e r f e c t l y known. For reasons to be d i s c u s s e d l a t e r under " S t r u c t u r a l G e o l o g y " , the S t e e l e metasediments are cons idered to l i e conformably on top o f the S t e e l e Lake v o l c a n i c s w h i c h , i n t u r n , appear to be conformable upon the Scapa metasediments. A f a u l t zone may separate the Bonis v o l c a n i c s from the r e s t o f the u n i t s i n the assemblage. Metamorphic z o n i n g developed i n the metasediments 2 resembles the B a r r o v i a n type o f z o n i n g developed i n the 1 The map-area l i e s w i t h i n the S u p e r i o r P r o v i n c e as d e f i n e d by G i l l (Trans . Roy. Soc . Can. ) v o l . 43 , Sec . I V , 1949, p p . 61-69. 2 Read, H . H . , The G r a n i t e Controversy ( I n t e r s c i e n c e P u b l i s h e r s , I n c . , 1957) p . 203. Gives an e x c e l l e n t rev iew o f the z o n a l concept and m o d i f i c a t i o n s a p p l i e d to i t . (Numerous a d d i t i o n a l re ferences may be obta ined from Read's d i s c u s s i o n ) . 18 „ . . .»«, . . STAUROLITE ISOGRAD »«<xx«» GARNET ISOGRAD _ I N F E R R E D BIOTITE ISOGRAD . . . . . . LIMIT OF CONTACT ZONE - BONIS VOLCANICS 1 CHLORITE ZONE 2 BIOTITE ZONE 3 GARNET ZONE 4 STAUROLITE ZONE F i g u r e 2 . S k e t c h map showing the d i s t r i b u t i o n o f metamorphic zones developed w i t h i n the m e t a v o l c a n i c - m e t a  sediment assemblage. S c a l e : 1 i n c h to 2 m i l e s . Grampian Highlands o f S c o t l a n d . Four o f the s i x zones d e f i n e d i n the Grampian Highlands are represented i n the zones r e c o g  n i z e d w i t h i n the map-area. The most s o u t h e r l y exposures o f the S t e e l e metasediments l i e w i t h i n the c h l o r i t e zone and these are assumed to grade i n t o the b i o t i t e zone developed i n both the S t e e l e and Scapa metasediments to the n o r t h and nor theas t o f the c h l o r i t e zone . Garnet and s t a u r o l i t e zones occur i n the Scapa metasediments adjacent to the Case b a t h o l i t h i n S t e e l e t o w n s h i p . The d i s t r i b u t i o n o f the v a r i o u s zones are i n d i c a t e d i n F i g u r e 2, together w i t h the approximate p o s i t i o n o f the garnet and s t a u r o l i t e i s o g r a d s . Accura te d e l i m i t a t i o n o f the i s o - grads was not p o s s i b l e owing to the poor q u a l i t y and r a r i t y o f rock exposures . Because the area i s g e n e r a l l y f l a t no i n  f o r m a t i o n c o u l d be o b t a i n e d r e g a r d i n g the probable d i p o f i s o g r a d i c s u r f a c e s . The b i o t i t e i s o g r a d i s e n t i r e l y h y p o t h e t i c a l as no outcrops were found w h i c h showed the f i r s t appearance o f b i o t i t e . The metasediments o c c u r r i n g near the boundary be tween concess ions I and G are i n the lower par t o f the b i o t i t e zone and t h e r e f o r e nearer the b i o t i t e i s o g r a d than o ther rocks w i t h i n t h i s zone i n S t e e l e township . F i g u r e 2 a l s o shows the approximate l i m i t o f a contact zone ad jacent to the Sargeant b a t h o l i t h w i t h i n which the B o n i s v o l c a n i c s have been a m p h i b o l i t i z e d , sheared , r e c r y s t a l l - i z e d , o r h o r n f e l s e d . In a d d i t i o n , a narrow contact a u r e o l e d e v e l  oped i n the Scapa ' 'metasediments b o r d e r i n g the Scapa Stock i n Scapa township i s i n d i c a t e d . I n d e s c r i b i n g the p e t r o l o g y o f the metasediments and the S t e e l e Lake v o l c a n i c s , the p l a n o f treatment w i l l be based on the p r o g r e s s i v e changes which take p l a c e w i t h i n c r e a s i n g metamorphism. Because the l i t h o l o g y and metamorphism o f the metasediments are much the same, these rocks w i l l be d i s  cussed before the m e t a v o l c a n i c s . METASEDIMENTS SCAPA METASEDIMENTS The Scapa metasediments separate the S t e e l e Lake v o l  c a n i c s from the Case b a t h o l i t h i n S t e e l e township and u n d e r l i e much o f the n o r t h e r n h a l f o f Scapa township . A one and a h a l f m i l e area o f d r i f t separates the Scapa metasediments from a few exposures o f s i m i l a r metasediments o c c u r r i n g i n the s o u t h e a s t e r n corner o f Scapa and adjacent p a r t s o f Hepburn t o w n s h i p . These l a t t e r rocks w i l l be d e s c r i b e d w i t h the S t e e l e metasediments , a l t h o u g h t h e i r r e l a t i o n s h i p to the two meta sedimentary u n i t s i s a t present unknown. Metamorphosed, grey to b l a c k greywacke and in terbedded c a l c - s i l i c a t e rocks make up most o f the Scapa metasediments. Layered i r o n - f o r m a t i o n and magnes ium-r ich rocks occur s p o r  a d i c a l l y . Mass ive greywacke and greywacke showing graded bedding are both found i n most o u t c r o p s . Arkose i s r a r e . 21 Greywacke Greywacke w i t h graded beds commonly c o n t a i n s a narrow zone o f s l a t e or p h y l l i t e at the top o f the i n d i v i d u a l c o u p l e t s and such metasediment has f r e q u e n t l y been r e f e r r e d to as " g r e y w a c k e - s l a t e . " 3 The in terbedded s l a t e probably forms l e s s than 15 per cent o f the t o t a l volume of the r o c k . For p u r  poses o f t h i s t h e s i s , the d e f i n i t i o n o f greywacke w i l l be t h a t 4 used by P e t t i j o h n i n h i s d e s c r i p t i o n o f Archean s e d i m e n t a t i o n . Of the v a r i o u s d e f i n i t i o n s put f o r t h t h i s one appears to summarize the greywackes o f the map-area the b e s t . The d e f i n  i t i o n i s reproduced below: "Greywacke connotes a type o f sandstone marked by (1) l a r g e d e t r i t a l quartz and f e l d s p a r ( "phenocrys ts " ) set i n a (2) prominent to dominant " c l a y " m a t r i x (and hence absence o f i n f i l t r a t i o n o r m i n e r a l cement) w h i c h may on low-grade metamorphism(diagenesis) be converted to c h l o r i t e and s e r i c i t e and p a r t i a l l y r e  p l a c e d by carbonate , (3) a dark c o l o r (4) g e n e r a l l y tough and w e l l i n d u r a t e d , (5) extreme a n g u l a r i t y o f the d e t r i t a l components ( m i c r o b r e c c i a ) (6) presence i n s m a l l e r or l a r g e r q u a n t i t i e s o f rock f ragments , m a i n l y c h e r t , q u a r t z i t e , s l a t e , o r p h y l l i t e , and (7) c e r t a i n macroscopic s t r u c t u r e s (graded b e d d i n g , i n t r a f o r m a t i o n conglomerates o f sha le or s l a t e c h i p s , s l i p bedding e t c ) , and (8) c e r t a i n rock a s s o c  i a t i o n s . " The o r i g i n a l c l a y m a t r i x o f a l l the greywackes w i t h i n the map-area has been converted to c h l o r i t e , s e r i c i t e and/or micas by metamorphism. Rock fragments are r a r e and quar tz p r e  dominates over f e l d s p a r i n n e a r l y a l l the r o c k s . The greywackes 3 P e t t i j o h n , F . J . , Archean S e d i m e n t a t i o n , B u l l .  G e o l . Soc . A m . , V o l . 54, 1943, pp . 944-945. 4 I b i d , p . 957 22 are therefore feldspathic according to Pettijohn's c l a s s i  f i c a t i o n of sandstones.^ Individual graded beds are commonly less than one- quarter inch to several inches thick but a few are a foot or two thick. Massive greywacke, without bedding, i s less common than greywacke with graded beds. Within the b i o t i t e zone porphyroblasts of mica up to one-quarter inch i n size occur i n the fine s i l t y and shaley parts of the beds and i n the higher grades of metamorphism the b i o t i t e i s accompanied or displaced by i d i o b l a s t i c garnet and s t a u r o l i t e . The f i n e  grained parts of the i n d i v i d u a l graded bed thus become coarser i n grain than the sandy portions, and the bed as a whole has undergone metamorphic inversion. Sedimentary structures such as cross-bedding, channelling and intraformational conglom erate were not seen i n the Scapa metasediments. Graded bedd ing and c l a s t i c textures are well preserved i n the lower grades of metamorphism but the increased s c h i s t o s i t y i n the upper part of the garnet zone and i n the s t a u r o l i t e zone des troys these features. S i l t y or shaley parts of the graded beds are more susceptible to deformation than the coarser parts. Schistos i t y i s well developed i n a l l the fine-grained rocks occurring i n the Scapa metasediments and i t increases i n i n t e n s i t y with r i s i n g metamorphic grade. In places the incompetent s i l t y or shaley parts of the couplets have been i n t r i c a t e l y drag- folded between the competent sandy parts. % Pettijohn, F.J., Sedimentary Rocks, Second ed. Harper and Bros. New York, 1957, pp. 290-293. 23 Concordant quar tz v e i n l e t s , commonly l e s s than one i n c h w i d e , are u b i q u i t o u s i n the sheared greywackes and they i n c r e a s e i n number and w i d t h w i t h an i n c r e a s e i n the i n t e n s i t y o f s h e a r  i n g . In many p laces where the greywacke i s h i g h l y sheared , boudinage s t r u c t u r e i s found i n the quartz v e i n l e t s . Narrow d i s c o r d a n t quartz v e i n s , which are wider than the concordant t y p e s , and o f a l l o r i e n t a t i o n s , cut the greywackes i n a number o f p l a c e s . These i n c r e a s e i n number and s i z e near the Case b a t h o l i t h , the Scapa s tock and adjacent to porphyry d i k e s . Except f o r f a u l t i n g , the d i s c o r d a n t quar tz v e i n s are undeformed. (1) B i o t i t e Zone The massive greywackes are n o n - f o l i a t e d i n the lower par t o f the b i o t i t e zone and s l i g h t l y s c h i s t o s e i n the upper p a r t o f the zone . The massive greywackes c o n s i s t c h i e f l y o f b i o t i t e , f e l d s p a r and q u a r t z . C h l o r i t e i s r a r e l y an e s s e n t i a l c o n s t i t u e n t and muscovite and s e r i c i t e are not common. M u s c o v i t e occurs o n l y i n the upper p a r t o f the zone . Rock fragments (mainly c h e r t ) are present but i n v a r i a b l y form l e s s than 5 per cent o f the w h o l e . Accessory m i n e r a l s i n c l u d e t o u r m a l i n e , e p i d o t e , sphene, m a g n e t i t e , i l m e n i t e , p y r i t e and a p a t i t e . I n r a r e i n s t a n c e s quartz and f e l d s p a r occur i n about equal amounts and c o n s t i t u t e about 80 per cent of the r o c k . Such r o c k s , r e f e r r e d to as a r k o s e , are p i n k i s h i n c o l o u r and occur i n narrow l a y e r s about two inches t h i c k . Q u a r t z , which forms up to 45 per cent o f the w h o l e , occurs as r e l a t i v e l y l a r g e c l a s t i c g r a i n s (up to 0 .7 mm) w i t h sutured borders and a l s o as f i n e g r a i n s s c a t t e r e d through the groundmass. The l a r g e r quar tz g r a i n s are markedly e longate and are grouped i n l e n t i c u l a r aggregates or narrow v e i n l e t s i n the upper p a r t of the z o n e . The f e l d s p a r i s m a i n l y untwinned, p o r p h y r o b l a s t i c and r e c r y s t a l l i z e d a l b i t e , c o n t a i n i n g many i n c l u s i o n s o f quartz and clouded by s e r i c i t e . In the h igher p a r t o f the zone a l b i t e i s c l e a r and the p o r p h y r o b l a s t s are l a r g e r (up to 0 .4 mm) than i n the lower p a r t o f the zone . Some d e t r i t a l o l i g o c l a s e and r a r e potash f e l d s p a r occur i n the lower part o f the zone but were not seen i n the upper p a r t . Reddish-brown b i o t i t e w i t h X^pa le to y e l l o w i s h and Z and Y=reddish brown forms 15 to 25 per cent o f the r o c k s . I t occurs as evenly d i s t r i b u t e d p o r p h y r o b l a s t s , c h a r a c t e r i z e d by numerous p l e o c h r o i c h a l o e s , and as f i n e - g r a i n e d o r i e n t e d f l a k e s i n t e r g r o w n w i t h c h l o r i t e i n the groundmass. C h l o r i t e i s most abundant i n s l i g h t l y s c h i s t o s e o r i g i n a l l y massive greywackes w h i c h suggests that b i o t i t e becomes u n s t a b l e w i t h i n c r e a s i n g shear ing s t r e s s as p o i n t e d out by T u r n e r . ^ D i s t i n c t g r a i n s o f muscovi te i n t e r g r o w n w i t h b i o t i t e were found i n the massive greywackes from the upper p a r t o f the zone . Rock fragments l o s e t h e i r i d e n t i t y w i t h i n c r e a s i n g s c h i s t o s i t y . T o u r m a l i n e , i n stumpy p r i s m s , i s u b i q u i t o u s i n the greywackes and has a b l u e - g r e e n p l e o c h r o i s m w i t h 0= 6 T u r n e r , F . J . , P r o g r e s s i v e R e g i o n a l Metamorphism i n Southern New Z e a l a n d , G e o l . M a g . . V o l . 75» 1938, pp . 160- 174. b l u e - g r e e n and E=co lour less to p a l e y e l l o w . V a r i a t i o n i n c o l o u r w i t h i n a s i n g l e g r a i n o f tourmal ine was a l s o noted w i t h the d i f f e r e n t c o l o u r s arranged i n zones . E p i d o t e and a p a t i t e are r a r e i n the massive greywackes. M a g n e t i t e , p y r i t e , and i l m e n i t e (rimmed by sphene) occur as anhedra l g r a i n s w i t h the planes o f f o l i a t i o n sweeping around them. The greywackes showing graded bedding have a good s c h i s t o s i t y p a r a l l e l to the bedding and they c o n t a i n the same m i n e r a l s as the massive greywackes,- but the micaceous compon ents and c h l o r i t e p l a y a more important r o l e . The coarser sandy p a r t s o f the graded-beds have a s m a l l e r average g r a i n s i z e (about 0 .1 mm), than t h a t o f the massive greywackes. Quartz and f e l d s p a r are e longate i n h a b i t and u s u a l l y complete ly r e c r y s t a l l i z e d w i t h the former m i n e r a l o f t e n o c c u r r i n g i n l e n t i c u l a r aggregates and narrow v e i n l e t s . Some c l a s t i c quartz occurs i n the lower p a r t o f the zone but the g r a i n s have sutured borders or they are s t r a i n e d and crushed. No c l a s t i c f e l d s p a r or rock fragments were n o t e d . A l b i t e , which i s clouded by s e r i c i t e i n the lower p a r t o f the zone , i n c r e a s e s i n g r a i n s i z e and i s c l e a r i n the upper p a r t o f the zone . A few p o r p h y r o b l a s t s o f c h l o r i t o i d w i t h a very weak p l e o c h r o i s m were seen i n one t h i n s e c t i o n . I n the lowest grade rocks b i o t i t e , i n t e r g r o w n w i t h c h l o r i t e and w h i t e m i c a , i s conf ined to i n c i p i e n t p o r p h y r o  b l a s t s o c c u r r i n g i n the a r g i l l a c e o u s l a y e r s . W i t h i n c r e a s i n g metamorphism the b i o t i t e p o r p h y r o b l a s t s become more homogeneous and d i s p l a y numerous p l e o c h r o i c haloes around minute i n d i s t i n c t PLATE II A. Photomicrograph of graded bedding i n greywacke, Scapa township. Incipient b i o t i t e porphyroblasts (B) are concen trated i n the argillaceous layers con taining quartz, s e r i c i t e , muscovite, and c h l o r i t e . Polarized l i g h t X16. B. Photomicrograph showing a porphyroblast of twinned c h l o r i t o i d (Chd) i n an argillaceous layer of a graded bed, Scapa township. B=biotite, A=albite, Q=quartz. Polarized l i g h t X16. i n c l u s i o n s , w h i l e f l a k e s o f b i o t i t e appear i n the groundmass o f both the a r g i l l a c e o u s and sandy p a r t s o f the graded-beds . As the amount o f b i o t i t e i n c r e a s e s the w h i t e mica content d e  creases but the c h l o r i t e content remains more or l e s s unchanged. In the upper p a r t o f the b i o t i t e z o n e , b i o t i t e p o r p h y r o b l a s t s are l e s s numerous and the rock more homogeneous. The micas and c h l o r i t e are c o a r s e r - g r a i n e d and the a r g i l l a c e o u s l a y e r s become markedly p h y l l i t i c . A l l the m i n e r a l s except quar tz and some opaque m i n e r a l s c r y s t a l l i z e d e i t h e r w h o l l y or i n p a r t a f t e r s h e a r i n g movements ceased. The a l b i t e i s a product o f n e o c r y s t a l l i z a t i o n as i n  d i c a t e d by i t s sutured borders a g a i n s t o ther m i n e r a l s , i t s u n c l e a v e d , untwinned c h a r a c t e r , and the s i e v e t e x t u r e which i t d i s p l a y s . A r a t h e r unusual p h y l l i t i c greywacke was found w i t h i n the b i o t i t e zone i n the eas tern p a r t o f Scapa t o w n s h i p . B l a c k s p e c k l e d a r g i l l a c e o u s l a y e r s predominate i n the r o c k . In t h i n s e c t i o n c o n s i d e r a b l e f i n e , dusty g r a p h i t e can be seen s c a t t e r e d throughout the a r g i l l a c e o u s l a y e r s . B i o t i t e , o c c u r r i n g as p o r p h y r o b l a s t s , c o n s t i t u t e s about 25 per cent o f the r o c k . G r a p h i t e i s r a r e or absent e lsewhere . ( 2 ) Garnet Zone The t y p i c a l rocks o f the garnet zone are g a r n e t i f e r o u s c h l o r i t e - b i o t i t e - f e l d s p a r - q u a r t z s c h i s t s and b i o t i t e - m u s c o v i t e - f e l d s p a r - q u a r t z s c h i s t s . Garnet i s best developed i n the o r i g i n a l l y a r g i l l a c e o u s p a r t s o f graded beds. Except f o r the 28 narrow a u r e o l e about the Scapa s t o c k , garnets were found o n l y i n the Scapa sediments o c c u r r i n g w i t h i n S t e e l e township . The garnet i s the common p i n k i s h v a r i e t y , presumably a lmandine . I t occurs as i d i o b l a s t i c g r a i n s up to 2 m i l l i m e t e r s i n s i z e and i s g e n e r a l l y more abundant and coarser i n g r a i n away from the b i o t i t e zone . H e l i c i t i c s t r u c t u r e occurs i n a few o f the garnets i n the lower p a r t o f the zone but most show no evidence o f r o t a t i o n d u r i n g growth . Some garnet has p a r t l y a l t e r e d to c h l o r i t e but most i s f r e s h . C h l o r i t e i s abundant i n many o f the rocks i n the lower par t o f the zone but i s r a r e i n the upper p a r t . Muscov i te i n c r e a s e s as the amount o f c h l o r i t e decreases . Secondary p e n n i n i t e has grown across b i o t i t e and muscovi te g r a i n s i n some o f the rocks from the upper p a r t o f the zone . Quartz i s comple te ly r e c r y s t a l l i z e d and occurs i n narrow elongate l enses and i n v e i n l e t s , o r as i n d i v i d u a l e l o n  gate gra ins : , commonly w i t h sutured b o r d e r s . A l b i t e i s present i n the lower p a r t o f the zone but o l i g o c l a s e ( A n 2 c j - 3 o ) , showing reversed z o n i n g , i s common i n the upper p a r t o f the zone . B o t h the o l i g o c l a s e and a l b i t e are c l e a r and untwinned and occur as anhedra l g r a i n s more or l e s s e longated p a r a l l e l to the s c h i s t o s i t y . B i o t i t e forms about 20 to 25 per cent o f the whole , and i s the reddish-brown v a r i e t y noted i n the b i o t i t e zone . I t occurs as s m a l l , deformed f l a k e s , o r i e n t e d p a r a l l e l to the s c h i s t o s i t y and as undeformed p o r p h y r o b l a s t s which grow across the s c h i s t o s i t y and u s u a l l y r e l a t e d to the metamorphosed a r g i l l a c e o u s p a r t s o f the o r i g i n a l sediment . 29 Accessory c o n s t i t u e n t s i n c l u d e t o u r m a l i n e , opaque m i n e r a l s (mainly p y r i t e ) , epidote and a p a t i t e . P y r i t e occurs as e longate anhedra l g r a i n s l y i n g p a r a l l e l to the s c h i s t o s i t y . (3) S t a u r o l i t e Zone Most of the rocks w i t h i n the s t a u r o l i t e zone possess a w e l l - d e v e l o p e d s c h i s t o s e and g n e i s s i c s t r u c t u r e . O r i g i n a l sedimentary s t r u c t u r e s are absent and coarse quartz s t r i n g e r s and l e n s e s , up to one i n c h or more i n w i d t h , l y i n g p a r a l l e l to the f o l i a t i o n , are abundant. Some o f the quartz v e i n l e t s c o n  t a i n minor p l a g i o c l a s e (About AH^Q ) * The s t a u r o l i t e i s i d i o - b l a s t i c , o c c u r r i n g as c r y s t a l s up to one i n c h i n diameter which are commonly i n t e r p e n e t r a t i n g twins that s tand out i n r e l i e f on weathered s u r f a c e s o f o u t c r o p s . The garnet occurs as i d i o - b l a s t i c g r a i n s , u s u a l l y about 1/8 i n c h i n s i z e , and i s a more deeply co loured v a r i e t y than that w i t h i n the garnet zone . S e v e r a l i n c l u s i o n s o f metasediment were found w i t h i n the Case b a t h o l i t h , p a r t i c u l a r l y near the contac t w i t h the Scapa meta sediments . G r a n o b l a s t i c t e x t u r e i s common i n the i n c l u s i o n s , as w e l l as i n the metasediment ad jacent to the c o n t a c t . The t y p i c a l rock types developed are q u a r t z - p l a g i o c l a s e , g a r n e t - b i o t i t e - s t a u r o l i t e s c h i s t , g a r n e t - b i o t i t e - p l a g i o c l a s e - quar tz s c h i s t , b i o t i t e - q u a r t z - p l a g i o c l a s e h o r n f e l s and b i o t i t e - m u s c o v i t e - q u a r t z - p l a g i o c l a s e h o r n f e l s . The b i o t i t e forms o r i e n t e d , undeformed f l a k e s up to 1 mm. i n l e n g t h , and conta ins numerous p l e o c h r o i c haloes around d i s c e r n a b l e z i r c o n i n c l u s i o n s . The p l e o c h r o i s m i s l e s s pronounced than i n the lower grades PLATE III 3 0 A Photomicrograph of a "spongy" stauro l i t e porphyroblast i n s t a u r o l i t e - o l i g o - clase-biotite-quartz s c h i s t . Lot 5, concession I?, Steele township. S= s t a u r o l i t e , G=garnet, B=biotite, Q= quartz, P=pyrite. P l a i n l i g h t X16. B Photomicrograph of an altered stauro l i t e metacryst i n garnet-quartz-oligo- c l a s e - b i o t i t e - s t a u r o l i t e schist. Lot 6, concession IV, Steele township. Sr= s e r i c i t e , S=staurolite, G=garnet, B= b i o t i t e , Q=quartz, P=pyrite. Polarized l i g h t X16. 31 w i t h X= l i g h t y e l l o w , Z and Y= l i g h t r e d d i s h brown. C h l o r i t e i s a b s e n t , except where the rocks have undergone r e t r o g r a d e metamorphism. Muscovi te i s c o n f i n e d to the rocks c o n t a i n i n g no s t a u r o l i t e and l i t t l e or no g a r n e t . The m a t r i x o f most o f the rocks c o n s i s t s o f a grano- b l a s t i c aggregate o f quartz and p l a g i o c l a s e . The p l a g i o c l a s e (about An2g) i s zoned w i t h a s o d i c core and a c a l c i c r i m . In the h o r n f e l s e s and the s c h i s t s ad jacent to the contact w i t h the Case b a t h o l i t h , zoned p l a g i o c l a s e g i v e s way to c l e a r unzoned and f r e q u e n t l y twinned p l a g i o c l a s e w h i c h v a r i e s i n compos i t ion from about Ang8 "to A n ^ g . The p l a g i o c l a s e o f the sedimentary i n c l u s i o n s o c c u r r i n g w e l l w i t h i n the Case b a t h o l i t h i s more c a l c i c , having a compos i t ion o f about A n ^ . S t a u r o l i t e appears f i r s t as s m a l l spongy p o r p h y r o b l a s t s but i t forms l a r g e i d i o b l a s t i c c r y s t a l s near the contact w i t h the Case b a t h o l i t h . I n some rocks the s t a u r o l i t e has a l t e r e d i n p a r t to s e r i c i t e w h i c h forms a wide r i m around a c e n t r a l core o f r e l a t i v e l y f r e s h s t a u r o l i t e . (See P l a t e . I l l B ) . Garnet forms i d i o b l a s t i c c r y s t a l s , some o f which are s i e v e - t e x t u r e d , and c o n t a i n numerous i n c l u s i o n s o f q u a r t z . B o t h s t a u r o l i t e and garnet have o n l y r a r e l y t h r u s t a s i d e o ther m i n e r a l s d u r i n g growth. The i n c l u s i o n s i n d i c a t e tha t no r o t a t  i o n o f garnet and s t a u r o l i t e c r y s t a l s has o c c u r r e d . Accessory c o n s t i t u e n t s i n c l u d e a p a t i t e , t o u r m a l i n e , opaque m i n e r a l s , and r a r e e p i d o t e . Coarse euhedral a p a t i t e and t o u r m a l i n e are p a r t i c u l a r l y common and perhaps more abundant than i n the metasediments w i t h i n the lower metamorphic zones . Because o f the bu lk c o m p o s i t i o n a l requirements f o r the f o r m a t i o n o f s t a u r o l i t e , t h i s m i n e r a l i s not w i d e l y d i s t r i b u t e d i n the s t a u r o l i t e zone . I t i s abundant, however, i n the o r i g i n a l l y a r g i l l a c e o u s p a r t s o f graded beds. O l i g o  c l a s e and s o d i c andesine are w i d e l y d i s t r i b u t e d and appear to be the t y p i c a l index m i n e r a l s o f t h i s zone . Vogt^ has a l s o noted o l i g o c l a s e or more c a l c i c p l a g i o c l a s e to be the t y p i c a l index m i n e r a l i n the h ighes t grades o f metamorphism i n the S u l i t e l m a r e g i o n o f Norway. As noted e a r l i e r , c a l c - s i l i c a t e rocks are commonly found interbedded w i t h the Scapa meta sediments and the greywackes are always f e l d s p a t h i c . I t i s t h e r e f o r e p o s s i b l e t h a t the poor development o f s t a u r o l i t e i n many o f the rocks i s due to an o r i g i n a l c a l c i c and f e l d  s p a t h i c na ture o f the metasediments. Q James has i n d i c a t e d that the s i m i l a r i t y i n compos i t ion between s t a u r o l i t e and c h l o r i t o i d would suggest that c h l o r i - t o i d would be e q u a l l y common i n a lower zone o f metamorphism and that s t a u r o l i t e might be expected to develop from c h l o r i  t o i d . C h l o r i t o i d i s extremely r a r e i n the Scapa metasediments so that no paragenet i c r e l a t i o n s h i p c o u l d be e s t a b l i s h e d . Absence o f k y a n i t e and a n d a l u s i t e i n the meta sediments suggests tha t the bu lk compos i t ion o f the rocks was not a p p r o p r i a t e f o r the development o f these m i n e r a l s . T h i s 7 V o g t , T . , S u l i t e l m a f e l t e t s G e o l o g i og P e t r o g r a f i ( w i t h E n g l i s h summary), N o r s e s . G e o l . u n d e r s a k e l s e . 121, 1927. 8 James, H . L . , Zones o f R e g i o n a l Metamorphism i n the Precambrian o f N o r t h e r n M i c h i g a n , B u l l . G e o l . Soc . Am. V o l . 66, 1955, P . 1^65. absence together w i t h the s c a r c i t y o f potash f e l d s p a r and the abundance o f c h l o r i t e i n lower grades o f metamorphism, s t r o n g  l y suggests tha t the rocks as a whole are d e f i c i e n t i n potash and do not c o n t a i n excess a l u m i n a . Scapa Stock A u r e o l e A narrow contact a u r e o l e , rang ing between 300 and 65t) f ee t i n w i d t h occurs w i t h i n the Scapa metasediments b o r d e r i n g the Scapa g r a n i t e s t o c k . The contact i s exposed o n l y at i n t e r v a l s a long the southern margin o f the s t o c k . Two zones can be d i s t i n g u i s h e d w i t h i n the a u r e o l e - an outer garnet zone , w h i c h grades away from the s tock over a d i s t a n c e o f up to 600 f e e t i n t o the metasediments o f the b i o t i t e zone i n Scapa t o w n s h i p , and an i n n e r zone o f h o r n f e l s about 100 fee t w i d e , w h i c h grades i n t o f i n e - g r a i n e d g r a n i t e and the t y p i c a l medium-grained g r a n i t e o f the s t o c k . In approaching the aureo le from the south o r west the f i r s t obvious contact e f f e c t s o f the s tock on the meta sediments are (1) an i n c r e a s e i n the number o f both concor dant and d i s c o r d a n t quar tz s t r i n g e r s , (2) an i n c r e a s e i n the i n t e n s i t y o f shear ing o f the f i n e - g r a i n e d greywackes, and (3) a coarsening o f the b i o t i t e p o r p h y r o b l a s t s o c c u r r i n g i n the a r g i l l a c e o u s p a r t s o f graded beds . W i t h i n the outer p a r t o f the aureo le the s t r i k e and d i p o f the bedding and s c h i s  t o s i t y show s i g n i f i c a n t v a r i a t i o n s from the normal and i n many p l a c e s the f i n e - g r a i n e d metasediments are h i g h l y f o l d e d and c r e n u l a t e d . Garnet occurs as i d i o b l a s t i c c r y s t a l s i n the a r g i l l a c e o u s l a y e r s up to 600 fee t from the s t o c k , and the metasediments appear to be l a r g e l y r e c r y s t a l l i z e d w i t h o r i g i n a l sedimentary s t r u c t u r e s becoming vague or e n t i r e l y o b l i t e r a t e d w i t h i n the a u r e o l e . Numerous m i c r o s c o p i c f r a c t u r e s cut a l l the rocks i n both the garnet and h o r n f e l s zones . C h l o r i t e and s e r i c i t e a l t e r a t i o n occurs i n the garnet zone metasediments up to 2 mm. from the f r a c t u r e s which are f i l l e d w i t h a v e r y f i n e  g r a i n e d f i b r o u s m a t e r i a l w i t h low b i r e f r i n g e n c e and r e l i e f ( z e o l i t e ? ) . Cubes o f p y r i t e are a l s o a s s o c i a t e d w i t h the a l t e r e d p o r t i o n s o f the r o c k s . A c o l o u r l e s s amphibole w i t h a p o s i t i v e o p t i c s i g n and i n c l i n e d e x t i n c t i o n , t e n t a t i v e l y i d e n t i f i e d as cummingtonite , was found s c a t t e r e d through a massive greywacke c o n t a i n i n g o l i g o c l a s e near the h o r n f e l s zone . A few s l i g h t l y twinned and s i e v e - t e x t u r e d g r a i n s resembl ing a l t e r e d f e l d s p a r were noted i n one r o c k . The g r a i n s c o u l d not be i d e n t i f i e d w i t h c e r t a i n t y , but they may represent c o r d i e r i t e . The s t r i k e o f r e l i c t bedding at the o u t e r margin o f the h o r n f e l s zone i s q u i t e v a r i a b l e , rang ing between N50°E and N70°W. G r a n i t e porphyry d i k e l e t s and g r a n i t i c s t r i n g e r s , u s u a l l y l e s s than 4 inches w i d e , i n t r u d e the h o r n f e l s e s up to 50 f e e t or so from the c o n t a c t . At the outer margin o f the h o r n f e l s zone the r o c k , which resembles massive greywacke, i s n o n - f o l i a t e d , g r e y i s h - brown i n c o l o u r , and i s spot ted w i t h many f l a k e s o f b i o t i t e . I n t h i n s e c t i o n the groundmass o f the rock i s complete ly r e -c r y s t a l l i z e d and has a g r a n o b l a s t i c t e x t u r e . O r i g i n a l c l a s t  i c quar tz g r a i n s are grouped together i n e longate aggregates , and p o i c i l o b l a s t s o f o l i g o c l a s e , p o o r l y o r i e n t e d f l a k e s o f reddish-brown b i o t i t e , and i d i o b l a s t i c p a l e green amphibole are a l s o p r e s e n t . About 50 f ee t from the g r a n i t e contact the rock i s l i g h t green i n c o l o u r , s l i g h t l y f o l i a t e d , even- g r a i n e d , and i s h i g h l y a l t e r e d , c o n t a i n i n g abundant c h l o r i t e and s e r i c i t i z e d p l a g i o c l a s e . A l l v e s t i g e o f bedding i s l o s t about 20 f e e t from the f i n e - g r a i n e d g r a n i t e , and the rock i s p i n k i s h i n c o l o u r , and g r a n i t i c . In t h i n s e c t i o n , numerous i d i o b l a s t i c o l i g o c l a s e and m i c r o c l i n e g r a i n s , w i t h i n c l u s i o n s o f q u a r t z , b i o t i t e and t o u r m a l i n e , l i e i n a f i n e g r a n o b l a s t i c aggregate o f quar tz and f e l d s p a r . G r e e n i s h to dark brown b i o t i t e w i t h X= l i g h t y e l l o w , Z and Y= dark brown to green , and p i s t a c i t e are evenly d i s t r i b u t e d throughout the r o c k . Adjacent to the f i n e - g r a i n e d g r a n i t e the h o r n f e l s d i f f e r s from the preceding d e s c r i p t i o n o n l y i n be ing coarser and e v e n - g r a i n e d , and f r e s h e r , and i t conta ins muscovi te as w e l l as b i o t i t e . E p i d o t e i s not present and accessory sphene and a p a t i t e are abundant. The occurrence o f p o r p h y r o b l a s t i c m i c r o c l i n e up to 20 f e e t from the g r a n i t e suggests t h a t potash has been added to the sediment from the g r a n i t e . The a l t e r a t i o n o f the rocks w i t h i n the a u r e o l e i s i n d i c a t i v e o f the a c t i o n o f l a t e - stage v o l a t i l e s and s o l u t i o n s eminat ing from the s tock i n t o the metasediments and f a c i l i t a t e d by the development o f Plate IV Photomicrograph of hornfels, 2 0 feet south of the Scapa stock contact. The rock i s composed of a l b i t e and altered plagioclase, microcline (M), b i o t i t e (B), quartz (Q), and accessory muscovite, sphene and apatite. Polarized l i g h t X16. s m a l l f r a c t u r e s . Of p a r t i c u l a r i n t e r e s t i s the apparent absence o f q o r d i e r i t e a m i n e r a l t y p i c a l o f contact a u r e o l e s . I r o n - F o r m a t i o n Gross^ has r e c e n t l y d e f i n e d i r o n - f o r m a t i o n as f o l l o w s : " I r o n - f o r m a t i o n i s cons idered to i n c l u d e s t r a t i - g r a p h i c u n i t s o f bedded or laminated rocks w h i c h c o n t a i n 15 per cent or more i r o n i n w h i c h the i r o n m i n e r a l s are commonly in terbedded w i t h q u a r t z , cher t or carbonate , and where the banded s t r u c t u r e o f the ferrugenous rocks conforms i n p a t t e r n and a t t i t u d e w i t h the bedded s t r u c t u r e o f the adjacent sedimentary , v o l c a n i c , or meta- sedimentary r o c k s . " T h i s d e f i n i t i o n i s used i n d e s i g n a t i n g the f o l l o w i n g rocks as i r o n - f o r m a t i o n . A l s o , a l l the i r o n i n the i r o n - f o r m a t i o n o f the map-area has combined w i t h s i l i c a to form amphiboles , g a r n e t , s t i l p n o m e l a n e and o ther s i l i c a t e m i n e r a l s o f meta morphic o r i g i n . L i t t l e or no magnet i te or o ther i r o n - o r e m i n e r a l s occur i n the i r o n - f o r m a t i o n rocks o f t h i s a r e a . The best exposures o f i r o n - f o r m a t i o n are cut by the prominent n o r t h - s o u t h diabase d i k e near i t s southern end i n Scapa township . At t h i s l o c a l i t y the i r o n - f o r m a t i o n has been s t r i p p e d at i n t e r v a l s a long s t r i k e . The i r o n - f o r m a t i o n s t r i k e s p a r a l l e l to the metasediments and d i p s 20°to 90° s o u t h . I t was t r a c e d a long s t r i k e f o r 870 f e e t and i t s w i d t h averages about 10 f e e t . The rock compr is ing the i r o n - f o r m a t i o n i s e s s e n t i a l l y 9 G r o s s , G . A . , A C l a s s i f i c a t i o n f o r I r o n D e p o s i t s i n Canada, Can. M i n . J o u r n . V o l . 80 , 1959, p p . 88. a l a y e r e d g r u n e r i t e - q u a r t z r o c k . In p l a c e s massive rocks composed o f g r u n e r i t e , hornblende and q u a r t z , and c h l o r i t e , b i o t i t e , muscovite and epidote are abundant. M u s c o v i t e - a l b i t e - b i o t i t e - c h l o r i t e - q u a r t z s c h i s t a l s o occurs i n t e r  bedded w i t h the above rock t y p e s . P y r i t e and p y r r h o t i t e are found d isseminated throughout the i r o n - f o r m a t i o n and are commonly found up to 120 f e e t away from the i r o n - f o r m a t i o n i n the metasediments. The l a y e r e d g r u n e r i t e - q u a r t z rock c o n s i s t s o f narrow bands o f r u s t y quartz up to 2 inches i n w i d t h a l t e r n a t i n g w i t h bands c o n s i s t i n g m a i n l y o f g r u n e r i t e and b l u e - g r e e n hornblende . The i r o n - f o r m a t i o n i s h i g h l y c o n t o r t e d i n p l a c e s and the quar tz l a y e r s accentuate drag f o l d i n g . In t h i n s e c t i o n the q u a r t z l a y e r s are composed almost e n t i r e l y o f i n t e r l o c k i n g quar tz g r a i n s , averaging about 0 . 7 m i l l i m e t e r s i n d i a m e t e r , w h i c h c o n t a i n a l i m o n i t i c s t a i n around t h e i r b o u n d a r i e s . G r u n e r i t e , o c c u r r i n g as l a t h s commonly arranged i n r o s e t t e s , i s concentra ted next to the quartz l a y e r s . B l u e - g r e e n h o r n  blende i s a l s o abundant i n the amphibole l a y e r s and commonly predominates over g r u n e r i t e . T r a i n s o f f i n e - g r a i n e d magne t i t e , bounded by f i n e h a i r - l i k e f r a c t u r e s c o n t a i n i n g a brown i s h s t a i n are common. S t i l p n o m e l a n e , a s s o c i a t e d w i t h the g r u n e r i t e and hornblende i s an a l t e r a t i o n p r o d u c t . The g r u n e r i t e i s o p t i c a l l y n e g a t i v e w i t h X= c o l o u r l e s s , Z and Y= p a l e y e l l o w to c o l o u r l e s s . Z o c c a s i o n a l l y has a g r e e n i s h t i n g e . N e a r l y a l l the g r u n e r i t e shows p o l y s n y t h e t i c t w i n n i n g a long the p lane ( 1 0 0 ) . B l u e - g r e e n hornblende i s found i n p a r a l l e l o r i e n t a t i o n w i t h g r u n e r i t e and i n the massive g r u n e r i t e - h o r n b l e n d e - q u a r t z r o c k , g r u n e r i t e pr isms appear to have terminated i n t h e i r o r i g i n a l growth i n the b l u e - g r e e n hornblende . The b l u e - g r e e n hornblende a l s o occurs i n independent i n d i v i d u a l s and i s o p t i c a l l y n e g a t i v e w i t h X= y e l l o w i s h , Y= green and Z= b l u e - g r e e n . The hornblende c o n t a i n s many i n c l u s i o n s o f a p a t i t e and other u n i d e n t i f i a b l e m i n e r a l s , around some o f which p l e o c h r o i c haloes have been d e v e l o p e d . The i d e n t i f i c a t i o n o f bo th amphiboles was checked by X - r a y d i f f r a c t i o n . R i c h a r d z , 1 G > > 1 0 a has d e s c r i b e d a s i m i l a r r e l a t i o n s h i p between g r u n e r i t e and b l u e - g r e e n hornblende from the Lake S u p e r i o r r e g i o n i r o n o r e s . I n both the Lake S u p e r i o r and Scapa township l o c a l i t i e s the g r u n e r i t e and hornblende are f r e s h and the t r a n s i t i o n from one to another i s very s h a r p . I t i s u n l i k e l y t h a t the b l u e - g r e e n hornblende i s due to a l t e r  a t i o n of the g r u n e r i t e . James"'"'1" has shown that l a y e r e d g r u n e r i t e - q u a r t z rocks i n N o r t h e r n M i c h i g a n have been d e r i v e d from pr imary s e d i  mentary s i l i c a t e and carbonate i r o n - f o r m a t i o n . James f u r t h e r c o r r e l a t e s the g r u n e r i t e - r i c h rocks w i t h h i s carbonate and 10 R i c h a r d z , S . , G r u n e r i t e Rocks o f the Lake S u p e r i o r Region and t h e i r O r i g i n , J o u r n . G e o l . V o l . 35 , 1 9 2 7 , p p . 690-707. 10a R i c h a r d z , S . , The Amphibole G r u n e r i t e o f the Lake S u p e r i o r R e g i o n , Am. J o u r n . S c i . V o l . 14, 1927, p p . 150-154. 11 James, H . L . , Zones o f R e g i o n a l Metamorphism i n the Precambrian o f N o r t h e r n M i c h i g a n , B u l l . G e o l . Soc . Am. V o l . 6 6 , 1955, P P . 1 4 5 5 - 1 4 8 8 . s i l i c a t e f a c i e s o f pr imary i r o n - f o r m a t i o n . The i r o n - f o r m a t i o n o f Scapa township l i e s w i t h i n the b i o t i t e zone and i t s metamorphism d i f f e r s markedly from the n o r t h e r n M i c h i g a n i r o n format ions d e s c r i b e d by James. G r u n e r i t e , epidote and garnet are not found w i t h i n the b i o t i t e zone i n n o r t h e r n M i c h i g a n and the quar tz o f l a y e r e d i r o n - f o r m  a t i o n i s markedly f i n e r i n g r a i n than that o c c u r r i n g i n Scapa. Other rocks p o s s i b l y d e r i v e d from an o r i g i n a l f e r r u  ginous sediment occur w i t h i n the garnet zone i n l o t s 1 and 2, c o n c e s s i o n IV o f S t e e l e township . These are in terbedded w i t h the metasediments and are l a y e r e d w i t h narrow l a y e r s r i c h i n garnet a l t e r n a t i n g w i t h q u a r t z - r i c h and a m p h i b o l e - r i c h l a y e r s . Disseminated p y r i t e and p y r r h o t i t e are common. The rock i n l o t 1, concess ion IV i s composed l a r g e l y o f g a r n e t , b i o t i t e and q u a r t z , w i t h c h l o r i t e and minor g r u n e r i t e , cummingtonite , and b l u e - g r e e n hornblende . G r u n e r i t e and cummingtonite are commonly found as i n c l u s i o n s i n l a r g e garnet p o r p h y r o b l a s t s . The c h l o r i t e i s a secondary a l t e r a t i o n product o f garnet and amphibole . A m p h i b o l e - r i c h l a y e r s o f the rock o c c u r r i n g i n l o t 2, concess ion IV are composed o f 15 per cent garnet and b i o t i t e , 65 per cent b l u e - g r e e n amphibole , c o n t a i n i n g numerous p l e o - c h r o i c haloes and i n c l u s i o n s o f a p a t i t e , and accessory quartz and m u s c o v i t e . The garnet i s p a r t i a l l y a l t e r e d to c h l o r i t e and p i s t a c i t e . 12 James, H . L . , Sedimentary F a c i e s o f I r o n - F o r m a t i o n , E c o n . G e o l . V o l . 49, 1954, p p . 235-293. An unusual massive rock was found near the Case b a t h o l i t h i n l o t 3, concess ion IV o f S t e e l e . T h i s rock i s p e t r o g r a p h i c a l l y s i m i l a r to manganiferous s c h i s t s d e s c r i b e d by T i l l e y 1 ^ from the L e w i s i a n o f S c o t l a n d . The rock occurs as a narrow l a y e r about 5 f e e t wide interbedded w i t h the metasediments and i s composed of 40 per cent g a r n e t , 17 per cent cummingtonite ( r a r e l y w i t h i n t e r g r o w n b l u e - g r e e n h o r n  blende) , 30 per cent quartz and accessory p y r i t e and sphene. The garnet i s i n d i s t i n c t l y a n i s o t r o p i c and p a l e p i n k under uncrossed n i c o l s , p r o p e r t i e s s u g g e s t i v e of s p e s s a r t i t e . H e l e c i t i c s t r u c t u r e i s common i n the g a r n e t , which c o n t a i n s numerous quartz and g r e e n i s h amphibole i n c l u s i o n s . Some o f the garnet i s a l t e r e d p a r t i a l l y to c h l o r i t e and e p i d o t e . Quartz forms l a r g e i n t e r l o c k i n g g r a i n s up to 1.5 m i l l i m e t e r s i n s i z e w h i c h are h i g h l y f r a c t u r e d i n p l a c e s . To summarize, the i r o n - f o r m a t i o n resembles the Huron- i a n type r a t h e r than the Keewatin type as d e s c r i b e d by 14 Bruce and i n many p a r t i c u l a r s , except metamorphism, i t i s s i m i l a r to the N o r t h e r n M i c h i g a n i r o n - f o r m a t i o n s . The Scapa i r o n - f o r m a t i o n was d e r i v e d from a f e r r u g i n o u s sediment , p r o  bably interbedded s i d e r i t i c chert and f e r r u g i n o u s s h a l e , which upon metamorphism, was changed to the l a y e r e d and massive s i l i  c a t e - r o c k s now found interbedded w i t h the metamorphosed greywackes. 13 T i l l e y , C . E . , Cummingtoni te-bear ing Rocks from the L e w i s i a n , G e o l . M a g . , V o l . 75, 1938m p p . 76-81. 14 B r u c e , E . L . , Precambrian I r o n F o r m a t i o n s , B u l l . G e o l . Soc . Am., V o l . 56, 1945, pp . 589-602. 42 C a l c - S i l i c a t e Rocks C a l c - s i l i c a t e rocks occur as narrow l a y e r s i n t e r  c a l a t e d w i t h the metamorphosed greywackes. The l a y e r s range i n t h i c k n e s s from l e s s than 1 i n c h to 6 inches and are t r a c e  a b l e f o r c o n s i d e r a b l e d i s t a n c e s i n the o u t c r o p . A few l a y e r s p i n c h and s w e l l a long s t r i k e , but u n i f o r m i t y o f t h i c k n e s s i s the r u l e r a t h e r than the e x c e p t i o n . The c a l c - s i l i c a t e l a y e r s are s i m i l a r to those d e - 15 s c r i b e d by P e t t i j o h n y from the Thunder Lake area o f O n t a r i o and c a l l e d hornblende g r a n u l i t e by h i m . In handspecimen the rock resembles d i o r i t e w i t h numerous needles o f g r e e n i s h amphibole s c a t t e r e d i n a f i n e - g r a i n e d l i g h t co loured m a t r i x . The rock weathers a b u f f c o l o u r but i s l i g h t grey on a f r e s h s u r f a c e . In t h i n s e c t i o n the l a y e r s are composed o f a grano b l a s t i c m a t r i x o f q u a r t z , c a l c i c p l a g i o c l a s e and epidote i n w h i c h are randomly o r i e n t e d r o s e t t e s and sheaves o f b l u e - g r e e n amphibole . The p l a g i o c l a s e i s u s u a l l y c louded by s e r i c i t e , making i t s d e t e r m i n a t i o n d i f f i c u l t , but i t appears to be near andesine i n c o m p o s i t i o n . Sphene, p y r r h o t i t e , and carbonate are f requent a c c e s s o r i e s . Some specimens c o n t a i n s m a l l amounts o f g a r n e t . P i t t i j o h n found b i o t i t e i n some o f the l a y e r s o c c u r r  i n g at Thunder Lake . Zoned ca lcareous nodules a l s o occur i n 15 P e t t i j o h n , F . J . , Archean Metaconcre t ions o f Thunder L a k e , O n t a r i o , B u l l . G e o l . Soc . A m . , V o l . 51 > 1940, p p . 1846-1847. Thunder Lake area and a l t h o u g h no nodules were found i n the Scapa metasediments , they do occur i n the S t e e l e m e t a s e d i  ments. B u f f - c o l o u r e d , a m p h i b o l e - b e a r i n g , massive greywackes, c o n t a i n i n g c o n s p i c u o u s , randomly o r i e n t e d , g r e e n i s h amphi bole g r a i n s are e i t h e r a s s o c i a t e d w i t h the c a l c - s i l i c a t e l a y e r o r in terbedded w i t h the metasediments. In t h i n s e c t i o n the amphibo le -bear ing greywackes are s i m i l a r to the " n o r m a l " massive greywacke d e s c r i b e d above o c c u r r i n g i n the b i o t i t e zone except f o r the occurrence o f 10 - 20 per cent b l u e - green amphibole , found as p o i k i l o b l a s t i c c r y s t a l s and r o s e t t e s and o l i g o c l a s e . Accessory c l i n o z o i s i t e and carbonate are a l s o common. A rock composed almost e n t i r e l y o f t r e m o l i t i c h o r n  blende was found about 1/2 m i l e due south of the western boundary o f the Scapa s t o c k . C l i n o z o i s i t e and p y r i t e are a c c e s s o r i e s and much o f the amphibole i s p a r t i a l l y a l t e r e d to t a l c . The amphibole has a n e g a t i v e o p t i c s i g n and i s m a i n l y c o l o u r l e s s under uncrossed n i c o l s , a l t h o u g h a few g r e e n i s h patches do o c c u r . No c a l c - s i l i c a t e rocks were seen w i t h i n the s t a u r o - l i k e - z o n e . P r e h n i t e V e i n s P r e h n i t e v e i n s were noted c u t t i n g a number o f the metasediments i n Scapa township . The v e i n s appear to be most 44 abundant near b a s i c i n t r u s i v e s and diabase d i k e s , a l t h o u g h i n some p l a c e s no c o r r e l a t i o n between b a s i c igneous rock and the occurrence o f p r e h n i t e i n the metasediments c o u l d be made. The metasediment adjacent to the v e i n s i s moderately to h i g h l y a l t e r e d . Where the v e i n s are numerous and bunched together i n the r o c k , the a l t e r a t i o n i s q u i t e i n t e n s e and p y r i t e and garnet are f o u n d . STEELE METASEDIMENTS The S t e e l e metasediments are exposed o n l y w i t h i n S t e e l e t o w n s h i p , where they occur as w i d e l y s c a t t e r e d low outcrops i n the h i g h e r areas and a long the n o r t h shore of Northeas t Bay. In t h i s l a t t e r l o c a l i t y the metasediments are separated from the remainder o f the S t e e l e metasediments by an area o f varved c l a y and muskeg, about 1.5 to 2 m i l e s w i d e . However, the metasediments a long the l a k e shore have the same s t r i k e and face i n the same d i r e c t i o n as those to the n o r t h . I t i s p o s s i b l e t h a t a l l these rocks do not form a cont inuous u n i t and t h e r e f o r e the metamorphic z o n i n g i n t h i s p a r t o f the map-area should be cons idered t e n t a t i v e . B o t h concordant and d i s c o r d a n t quartz v e i n s , having i d e n t i c a l c h a r a c t e r i s t i c s to those o c c u r r i n g i n the Scapa metasediments are u b i q u i t o u s . Near the assumed contact w i t h the B o n i s v o l c a n i c s the d i s c o r d a n t quar tz v e i n s are commonly . f a u l t e d . No i r o n - f o r m a t i o n or manganese-r ich rocks were found w i t h i n the S t e e l e metasediments. Hornblende-and p l a g i o - c l a s e - r i e h s c h i s t s o f u n c e r t a i n o r i g i n occur in terbedded 45 Plate V A Intraformatiorial breccia layer i n Steele metasediments. Lot 8 , concession D, Steele township. The fi n e l i n e s cutting across the outcrop are g l a c i a l s t r i a e . B Massive greywacke overlying greywacke with graded beds, indicating the top of the succession faces south (away from the observer). Lot 7, concession D, Steele township. 46 w i t h the metasediments adjacent to the S t e e l e Lake v o l c a n i c s . M a s s i v e , and amphibole -bear ing greywackes are more abundant than greywacke w i t h graded beds , i n c o n t r a s t to the Scapa metasediments , a l t h o u g h greywacke w i t h graded beds occurs i n n e a r l y a l l the o u t c r o p s . I n d i v i d u a l sha le or p h y l l i t e beds, except f o r those o c c u r r i n g i n the graded- bedded greywackes and a r k o s e , were not seen. Greywacke (1) C h l o r i t e Zone In the outcrop the greywackes are m a i n l y unsheared and g r e e n i s h - g r e y to dark grey i n c o l o u r . I n p laces the f i n e - g r a i n e d s l a t y p o r t i o n s o f graded beds are s c h i s t o s e and the s c h i s t o s i t y i n c r e a s e s i n degree and frequency towards the B o n i s v o l c a n i c s c o n t a c t . At the r a i l w a y cut i n l o t 3 , concess ion F , the f i n e r - g r a i n e d greywackes are p h y l l i t i c . In p l a c e s the greywackes have been p y r i t i z e d and on a weathered s u r f a c e such rocks are speck led w i t h s m a l l r u s t y s p o t s . Con t o r t e d bedding and drag f o l d i n g are common adjacent to shear zones , porphyry d i k e s and near the Bonis v o l c a n i c s c o n t a c t . The i n d i v i d u a l graded-beds range from l e s s than 1/8 i n c h to 2 f ee t or more t h i c k . C r o s s - b e d d i n g occurs i n graded- beds n o r t h of the r a i l w a y t r a c k i n l o t 8 , concess ion E . S t r u c t u r e s sugges t ive o f c r o s s - b e d d i n g were a l s o noted i n numerous o ther l o c a l i t i e s but most o f t h e s e , when examined i n d e t a i l , proved to be minor c r e n u l a t i o n s or v a r i a t i o n s i n the s t r i k e o f the b e d d i n g . (See P l a t e V B ) . 47 C h a n n e l l i n g , l o c a l u n c o n f o r m i t i e s between massive greywacke and greywacke w i t h graded beds , and i n t r a f o r m a t i o n a l b r e c c i a s are common. A l l these s t r u c t u r e s are compatable w i t h the t u r b i d i t y c u r r e n t theory f o r the f o r m a t i o n o f graded beds. Some o f the i n t r a f o r m a t i o n a l b r e c c i a s resemble t a i l 16 and u n d e r p l i g h t d e s c r i b e d by Shrock . They c o n s i s t o f t a b u l a r and angular p ieces o f f i n e - g r a i n e d greywacke and s i l t - stone i n a sandy m a t r i x , which are found at the base o f the sandy p a r t s o f graded beds. The fragments range from l e s s than 1/8 i n c h to over 2 inches i n s i z e . The b r e c c i a zones r a r e l y exceed s i x inches i n w i d t h and are l e n t i c u l a r a long t h e i r s t r i k e . A l a y e r o f i n t r a f o r m a t i o n a l b r e c c i a up to 40 f ee t wide occurs i n an outcrop a long the shore i n l o t 8 , con c e s s i o n D. The fragments have an i d e n t i c a l compos i t ion to the adjacent greywacke and the l a y e r as a whole has been sheared and p y r i t i z e d w i t h p y r i t e cubes up to 3/4 o f an i n c h o c c u r r i n g a long the boundaries of the f ragments . I n t h i n s e c t i o n the greywackes are composed m a i n l y o f q u a r t z , c l a s t i c f e l d s p a r , a l b i t e , c h l o r i t e , s e r i c i t e , rock fragments and carbonate . P y r i t e and t o u r m a l i n e are common accessory m i n e r a l s , and z i r c o n , m a g n e t i t e - i l m e n i t e , sphene, ep idote and a p a t i t e are r a r e l y f o u n d . B i o t i t e occurs i n some greywackes adjacent to porphyry d i k e s . Muscovi te i s 16 Shrock , R . R . , Sequence i n Layered Rocks , ( M c G r a w - H i l l Book C o . ) , New Y o r k , 1948, p p . 161-162. Plate VI Contorted bedding i n the Steele meta sediments near a porphyry dike (to the r i g h t ) . Lot 6 , concession E, Steele township. r a r e and occurs o n l y i n the more h i g h l y sheared rocks near the Bonis v o l c a n i c s . O r i g i n a l c l a s t i c t e x t u r e i s w e l l preserved i n a l l but the f i n e - g r a i n e d greywackes. In n e a r l y a l l the specimens examined, c h l o r i t e and s e r i c i t e envelope and embay the c l a s t i c g r a i n s . In some r o c k s , p a r t i c u l a r l y near the Bonis v o l c a n i c s , p r e f e r r e d o r i e n t a t i o n of c h l o r i t e and s e r i c i t e i s pronounced and appears to be o f metamorphic o r i g i n . Q u a r t z , r a n g i n g from 20 to 40 per cent o f the whole , i s the most abundant m i n e r a l i n a l l the rocks examined. I t occurs m a i n l y as subangular , i n e q u i d i m e n s i o n a l , s l i g h t l y to markedly s t r a i n e d g r a i n s up to 0 .9 mm. i n s i z e . F e l d s p a r w h i c h c o n s i s t s o f c l a s t i c o l i g o c l a s e , r a r e K - f e l d s p a r , and r e c r y s t a l l i z e d a l b i t e forms 15 to 20 per cent o f the greywackes. A l b i t e , c louded by s e r i c i t e , i s l e s s abundant than c l a s t i c f e l d s p a r , except near porphyry d i k e s . I t i s uncleaved and untwinned, and c o n t a i n s i n c l u s i o n s of q u a r t z . White m i c a , r a n g i n g from 20 to 35 per cent predom i n a t e s over c h l o r i t e i n a l l the r o c k s . C h l o r i t e , forming 6 to 20 per cent o f the whole , occurs i n two o p t i c a l l y d i s t  i n c t v a r i e t i e s . The most common v a r i e t y has a l i g h t green to l i g h t y e l l o w p l e o c h r o i s m and a h i g h e r b i r e f r i n g e n c e than the o ther v a r i e t y , which has a deeper green p leochro i sm and e x h i b i t s the anomalous u l t r a - b l u e i n t e r f e r e n c e c o l o r t y p i c a l o f p e n n i n i t e . Both c h l o r i t e s are o p t i c a l l y p o s i t i v e . The more h i g h l y p l e o c h r o i c v a r i e t y , p o s s i b l y r i c h i n i r o n and Plate VII A Photomicrograph of massive greywacke, lo t 10, concession D, Steele township. Subangular, strained quartz (Q) and feldspar (F) fragments l i e i n a f i n e  grained matrix of c h l o r i t e (Ch), s e r i  c i t e and quartz. Polarized l i g h t X16. Cb = carbonate. B Photomicrograph of massive greywacke, showing d e t r i t a l oligoclase grains (Og). Lot 9> concession D, Steele township. Q= quartz. Polarized l i g h t X 4 7 . P l a t e V I I I 51 A Sheared metasediments i n the r a i l  way c u t , l o t 3 , concession F, S t e e l e township. The metasediments l i e d i r e c t l y west of the assumed contact w i t h the Bonis v o l c a n i c s . B Cross-bedding i n graded beds over l a i n by massive greywacke. The top of the succession i s to the south ( D i r e c t i o n of the arrow). Lot 8 , concession E, Steele township. magnesium, i s common i n rocks o c c u r r i n g i n the western p a r t o f the outcrop a r e a . W i t h an i n c r e a s e i n s c h i s t o s i t y and degree o f r e c r y s t a l l i z a t i o n the l i g h t e r - c o l o u r e d v a r i e t y (aluminum c h l o r i t e ? ) predominates . C h l o r i t e a l s o has a deeper p l e o c h r o i s m adjacent to p y r i t e and magnet i te g r a i n s . Carbonate which occurs i n c l o t s or v e i n l e t s i n the greywackes i n amounts ranging from 2 to 20 per c e n t , i s commonly i r o n - s t a i n e d and more abundant i n the coarser greywackes and i n the greywackes near the Bonis v o l c a n i c s than e lsewhere . I t i s e s p e c i a l l y common i n and adjacent to a l t e r e d porphyry d i k e s , where i t r e p l a c e s many o f the o ther m i n e r a l s . Most o f the carbonate was probably i n t r o d u c e d i n t o the metasediments . A narrow v e i n o f p r e h n i t e was found i n one specimen o f greywacke adjacent to an a l t e r e d lamprophyre (?) d i k e i n l o t 9» concess ion D. (2) B i o t i t e Zone Many o f the sedimentary s t r u c t u r e s noted i n c o n n e c t i o n w i t h the greywackes o f the c h l o r i t e zone are present i n the lower p a r t o f the b i o t i t e zone . No i n t r a f o r m a t i o n a l b r e c c i a or c r o s s - b e d d i n g were seen , however. F r e s h and u n u s u a l l y c l e a n exposures o f the greywackes occur on an o l d l o g g i n g road t h a t crosses the outcrops i n l o t 10, concess ion I . H e r e , the f i n e , graded bedding s t r u c t u r e o f the greywackes i s e x c e l l e n t l y p r e s e r v e d . In a few p laces massive greywacke cuts across the graded- beds forming l o c a l u n c o n f o r m i t i e s , a f e a t u r e p o s s i b l y Plate IX A Graded bedding truncated by massive greywacke. The light-coloured band i n the graded beds near the bottom of the photograph i s a c a l c - s i l i c a t e layer. Lot 10, concession I, Steele township. B Amphibole-plagioclase schist inter bedded with metamorphosed grey wacke near the southern contact with the Steele Lake volcanics. Lot 9, concession IV, Steele town ship. 54 due to s c o u r i n g brought about by the a c t i o n o f t u r b i d i t y c u r r e n t s (See P l a t e IX A ) . In outcrops to the n o r t h many of the d e t a i l e d s e d i  mentary s t r u c t u r e s have been des t royed by shear ing but graded- bedding i s v i s i b l e and d i s t i n c t . Near the contact w i t h the S t e e l e Lake v o l c a n i c s the metasediments are h i g h l y sheared and c o n t o r t e d , and t r a v e r s e d by numerous patchy quar tz v e i n s up to 4 fee t w i d e . In t h i n s e c t i o n , q u a r t z , a l b i t e , c h l o r i t e and b i o  t i t e predominate . S e r i c i t e i s uncommon and muscovi te was seen o n l y i n a few rocks near the S t e e l e Lake v o l c a n i c s . Some c l a s t i c o l i g o c l a s e was noted i n the massive greywackes o c c u r r  i n g i n the extreme southern par t o f the outcrop a r e a . P y r i t e , magnet i te (and i l m i n i t e ) , sphene, t o u r m a l i n e , ep idote and r a r e l y a p a t i t e are accesory m i n e r a l s . A few shear z o n e s , w h i c h t r e n d p a r a l l e l to the s t r i k e o f the metasediments were found south o f the S t e e l e Lake v o l c a n i c s . The rocks w i t h i n the shear zones are m a i n l y q u a r t z - c h l o r i t e - a l b i t e s c h i s t s and some c o n t a i n f i n e dusty g r a p h i t e . B i o t i t e i s a minor c o n s t i t u e n t . C a l c - S i l i c a t e Rocks Amphibo le -bear ing greywacke and t h i n c a l c - s i l i c a t e l a y e r s in terbedded w i t h greywacke are common i n the b i o t i t e zone . I n a d d i t i o n , c a l c - s i l i c a t e n o d u l e s , s i m i l a r to those d e s c r i b e d by P e t t i j o h n from Thunder Lake occur i n massive greywacke i n outcrops o c c u r r i n g i n l o t 10, concess ion I . 55 Plate X A Photomicrograph of sheared massive greywacke. Lot 6 , concession I, Steele township. A= a l b i t e , Q= quartz, B= b i o t i t e . Polarized l i g h t X16. B Photomicrograph of a quartz veinlet (Q.V.) i n sheared greywacke. Lot 5» concession I I , Steele township. The rock consists of quartz, a l b i t e , musco- v i t e , and b i o t i t e . P o l a r i z e d l i g h t Xl6. A m p h i b o l e - b e a r i n g greywacke i s e s p e c i a l l y abundant i n the outcrops o c c u r r i n g east o f Mace Creek. These rocks r e  semble the amphibole -bear ing greywacke i n the Scapa meta sediments i n most r e s p e c t s , a l t h o u g h epidote ( c l i n o z o i s i t e ) and carbonate are more abundant, and the coarse, sandy p a r t s o f g r a d e d ' b e d s , as w e l l as massive greywacke are amphibole- b e a r i n g i n the S t e e l e metasediments. Some o f the amphibole -bear ing greywackes are l a y e r e d c o n t a i n i n g q u a r t z - a n d p l a g i o c l a s e - r i c h l a y e r s up to 1/4 i n c h t h i c k , w h i c h a l t e r n a t e w i t h s l i g h t l y t h i c k e r amphibole- and b i o t i t e - r i c h l a y e r s . Carbonate i s most abundant (up to 5 per cent ) i n the l a y e r e d v a r i e t i e s which may have o r i g i n a l l y c o n t a i n e d c h e r t y beds. Examinat ion i n t h i n s e c t i o n o f the amphibole -bear ing greywackes o c c u r r i n g i n graded-beds shows a sharp t r a n s i t i o n from amphibole to non-amphibole -bear ing r o c k . The coarse : p a r t s o f the i n d i v i d u a l graded beds c o n t a i n abundant b l u e - green hornblende , p l a g i o c l a s e (about An^ o ) and e p i d o t e , where as the f i n e r - g r a i n e d p a r t s are composed e s s e n t i a l l y o f b i o t i t e , c h l o r i t e , quartz and a l b i t e . T h i s suggests t h a t the sandy p a r t s were o r i g i n a l l y ca lcareous and more permeable to ground water f l o w . The nodules are etched i n t o r e l i e f by weather ing o f the o u t c r o p s . No i n t e r n a l s t r u c t u r e was noted i n the n o d u l e s , except f o r the f a i n t sugges t ion of z o n i n g . In g e n e r a l the nodules are c o a r s e r - g r a i n e d than the e n c l o s i n g rock and the abundance of l a r g e unor ien ted hornblende c r y s t a l s g ives the m a t e r i a l a d i o r i t e - l i k e appearance. No d e t a i l e d t h i n s e c t i o n study was made of the nodules or m a t r i x . 17 P e t t i j o h n and o t h e r s c o n s i d e r n o d u l e s , such as d e  s c r i b e d h e r e , to be the product o f metamorphism of ca lcareous c o n c r e t i o n s . Amphibole-and P l a g i o c l a s e - R i c h S c h i s t s A m p h i b o l i t i c s c h i s t s c o n t a i n abundant b l u e - g r e e n hornblende , c a l c i c p l a g i o c l a s e , e p i d o t e , and carbonate . Some o f the rocks resemble the a m p h i b o l i t e s o f the S t e e l e Lake v o l c a n i c s w h i l e o t h e r s resemble the c a l c - s i l i c a t e r o c k s . The ca lcareous types form a narrow zone about 6 f e e t wide at the contact between the S t e e l e Lake v o l c a n i c s and the S t e e l e metasediments. These are t y p i c a l l y e p i d o t e - p l a g i o - c l a s e - q u a r t z - h o r n b l e n d e s c h i s t s c o n t a i n i n g s c a t t e r e d g r a i n s o f accessory carbonate and sphene. The rocks resembl ing the m e t a v o l c a n i c s occur as narrow l a y e r s , l e s s than a foot t h i c k and are t y p i c a l l y q u a r t z - c h l o r i t e - p l a g i o c l a s e - h o r n b l e n d e s c h i s t s . In both v a r i e t i e s amphibole c o n s t i t u t e s 30 per cent or more o f the r o c k , w h i l e p l a g i o c l a s e ranges from 17 to 25 per cent and quartz from 20 to 25 per c e n t . The o r i g i n o f these rocks i s u n c e r t a i n . They may represent metamorphosed ca lcareous beds , b a s i c to i n t e r m e d  i a t e l a v a s , o r i n t r u s i v e r o c k s . The ca lcareous nature o f 17 O j D i c i t . , p . 1849 these rocks b o r d e r i n g the S t e e l e Lake v o l c a n i c s may be due to the m o b i l i z a t i o n o f carbonate from the v o l c a n i c s i n t o o r i g i n a l sedimentary rocks d u r i n g metamorphism. M i s c e l l a n e o u s Metasediment A few outcrops o f metasedimentary rocks occur i n the extreme southeast corner o f Scapa township and adjacent p a r t s o f Hepburn township . These rocks are e s s e n t i a l l y b i o t i t e - a l b i t e - c h l o r i t e - m u s c o v i t e - q u a r t z s c h i s t s and metamorphosed greywackes, i d e n t i c a l to those o c c u r r i n g i n the lower p a r t o f the b i o t i t e zone o f the S t e e l e and Scapa metasediments. The rock o c c u r r i n g adjacent to the assumed contact w i t h the Bonis v o l c a n i c s i n Scapa township i s h i g h l y sheared , and c o n t a i n s s c a t t e r e d cubes o f p y r i t e . The p l a t e y m i n e r a l s are c o n t o r t e d but some b i o t i t e l i e s across the f o l i a t i o n p l a n e s , i n d i c a t i n g i t developed a f t e r the shear ing movements i n the rock had ceased. I t i s not p o s s i b l e , as y e t , to c o r r e l a t e these rocks w i t h e i t h e r the S t e e l e or Scapa metasediments. Because they occur near the Bonis v o l c a n i c s c o n t a c t , these rocks have been grouped w i t h the S t e e l e metasediments. 59 METAVP LOAN ICS STEELE LAKE VOLCANICS The S t e e l e Lake v o l c a n i c s , w h i c h l i e w i t h i n the b i o  t i t e , g a r n e t , and s t a u r o l i t e zones as d e f i n e d by the meta sediments , form a narrow l e n t i c u l a r band composed o f amphi b o l i t e w i t h some in terbedded metasediment and metamorphosed rocks o f i n d e f i n i t e o r i g i n . The band i s s l i g h t l y l e s s than one m i l e wide i n l o t 4 , concess ion I I I , S t e e l e township . From t h i s p o i n t i t t h i n s to l e s s than 1/2 m i l e at the wes tern boundary o f S t e e l e township . The band a l s o t h i n s to the east but j u s t across the boundary between S t e e l e and Scapa townships i t i s covered by g l a c i a l d e b r i s and does not o u t c r o p a g a i n w i t h i n the map-area. A m p h i b o l i t e Some of the a m p h i b o l i t e s are s c h i s t o s e and c o n t a i n g a r n e t , but most are p o o r l y f o l i a t e d and e x h i b i t r e l i c t v o l c a n i c s t r u c t u r e s . A m y g d a l o i d a l , p i l l o w e d , m a s s i v e , d i a - b a s i c , and p o r p h y r i t i c types were d i s t i n g u i s h e d . A l l o f the a m p h i b o l i t e s are b e l i e v e d to have been d e r i v e d from b a s i c to i n t e r m e d i a t e l a v a f l o w s . A l t h o u g h the d i a b a s i c types were mapped as f l o w s , some may be i n t r u s i v e . The v o l c a n i c s t r u c t u r e s are best preserved w i t h i n the b i o t i t e zone , but they do occur i n the h i g h e r grades o f metamorphism. P o r p h y r i t i c l a v a was found o n l y a long the southern margin o f the v o l c a n i c s a d  jacent to the S t e e l e metasediments. The p i l l o w s t r u c t u r e i s s i m i l a r to tha t d e s c r i b e d from other areas w i t h i n the Canadian S h i e l d . Most p i l l o w s are h i g h l y deformed, r e n d e r i n g them o f l i t t l e v a l u e i n de termining tops i n f l o w s . Some p i l l o w s have a bleached core surrounded by a dark-green r i m adjacent to t h e i r s e l - vege. E x c e l l e n t exposures o f t h i s type o f p i l l o w occur a long the T r a n s - L i m i t road i n l o t 9, concess ion IV of S t e e l e town s h i p . The o r i g i n o f p i l l o w s has been the sub jec t o f much 18 19 20 debate . Cooke, James and Mawdsley , Henderson , Moore , 21 and more r e c e n t l y W i l s o n have reviewed the problem ade q u a t e l y . The evidence now appears to favour a subaquous o r i g i n f o r p i l l o w s t r u c t u r e . There i s s t i l l some q u e s t i o n as to the mechanism whereby p i l l o w l a v a i s formed at the top o f n o n - p i l l o w e d f l o w s showing g r a i n g r a d a t i o n . A l i m i t e d search o f the l i t e r a t u r e f a i l e d to uncover a s a t i s f a c t o r y e x p l a n a t i o n o f t h i s sequence which i s commonly encountered i n Precambrian v o l c a n i c t e r r a i n s . 18 Cooke, H . C . , James, W . F . , and Mawdsley, J . B . , Geology and Ore D e p o s i t s of Rouyn-Harricanaw R e g i o n , Quebec, G e o l . S u r v . Canada. Memoir 166, 1931. 19 Henderson, J . F . , On the Format ion o f P i l l o w Lavas and B r e c c i a s , T r a n s . Roy. Soc . Canada, V o l . X L V I I , S e c . 4 , 1953, PP . 23-32. 20 Moore, E . S . , Notes on the O r i g i n o f P i l l o w Lavas T r a n s . Roy. Soc . Canada, V o l . X X I V , Sec . 4 , 1930, pp.137-139. 21 W i l s o n , M . E . , O r i g i n o f P i l l o w S t r u c t u r e i n the E a r l y Precambrian Lavas o f Western Quebec, J o u r . G e o l . V o l . 68, I960, p p . 97-102. 61 S c h i s t o s e a m p h i b o l i t e s are c o n f i n e d to the garnet and s t a u r o l i t e zones o f metamorphism. The occurrence o f garnet i n metamorphic d e r i v a t i v e s o f b a s i c igneous rocks has been d e s c r i b e d from a number o f a r e a s , but perhaps the c l a s s i c a l work i n t h i s r e g a r d , and indeed on the metamorphism 22 o f b a s i c igneous rocks i n g e n e r a l , i s that by Wiseman. The p r o g r e s s i v e metamorphism o f the S t e e l e Lake v o l c a n i c s d i f f e r s from that o f Wiseman's S c o t t i s h e p i d i o r i t e s i n the almost complete absence of c h l o r i t e and the abundance o f hornblende i n the b i o t i t e zone . (1) B i o t i t e Zone W i t h i n the b i o t i t e zone the a m p h i b o l i t e s are f i n e - to medium-grained and l i g h t - g r e y or p a l e - to d a r k - g r e e n i s h b l a c k i n c o l o u r . S l i g h t f o l i a t i o n , accentuated by hornblende g r a i n s i s v i s i b l e i n many o f the r o c k s . Microscope study i n d i c a t e s the l i g h t c o l o u r s are due to the abundant d e v e l o p  ment o f e p i d o t e , a l b i t e , and quar tz which was probab ly i n p a r t i n t r o d u c e d . The dark c o l o u r s are due to abundant hornblende and some b i o t i t e . Except where i t has formed from the a l t e r a t i o n o f hornblende , no c h l o r i t e was found i n the t h i n s e c t i o n s examined. Accessory sphene, i r o n - o r e and c a r  bonate are common. The hornblende i s o p t i c a l l y n e g a t i v e and d i s t i n c t l y 22 Wiseman, J . D . H . , The C e n t r a l and Southwest H i g h  l a n d E p i d i o r i t e s . A Study i n P r o g r e s s i v e Metamorphism, G e o l . S o c . London Quart . J o u r n . . V o l . 90, 1934, p p . 355- 417. 62 pleochroic with X= l i g h t yellowish-green, Y= green and Z= l i g h t b l u i s h green. The pleochroism varies markedly within a single grain, some areas being colourless or only f a i n t l y pleochroic. Hornblende ranges from 30 to 60 per cent i n the amphibolite studied and i t forms the largest grains i n these rocks. The feldspar i s fine-grained and contains many i n  clusions of c l i n o z o i s i t e , quartz and carbonate. R e l i c t , polysynthetically twinned, c a l c i c plagioclase occurs rarely i n the diabasic amphibolites, with the twin lamellae i n  variably bent. The feldspar i s usually a l b i t i c but accur ate determinations of the composition were remdered d i f f i c u l t owing to the fine-grained character, numerous in c l u s i o n s , s e r i e i t i e a l t e r a t i o n , and lack of twinning i n the feldspar, tmphibolite i s highly r e c r y s t a l l i z e d adjacent to the diabase dike i n l o t s 1 , 2 and 3 j concession I I I , Steele township, and contains zoned plagioclase with a composition of about A n 3 0 . Epidote, ranging from 2 to 25 per cent, occurs as granular aggregates i n the groundmass of most of the amphi bo l i t e s and as coarse grains f i l l i n g amygdules. Most of the epidote i s p i s t a c i t e showing very s l i g h t or no pleochroism. C l i n o z o i s i t e i s confined to inclusions i n feldspar. B i o t i t e i s the reddish-brown variety noted i n the metasediments. It i s found i n association with hornblende and may therefore be an a l t e r a t i o n product of that mineral. The amount of b i o t i t e i n the amphibolites ranges from 0 to 15 per cent. Sphene commonly rims magnetite-ilmenite-grains. In a few rocks "leucoxene" occurs intergrown with magnetite and has presumably replaced o r i g i n a l ilmenite intergrown with magnetite. ( 2 ) Garnet and St a u r o l i t e Zones In handspecimen many of the amphibolites i n the garnet and s t a u r o l i t e zones d i f f e r from those i n the bio t i t e zone only i n having a coarser grain. Pillow structure and grain gradation within i n d i v i d u a l flows can be seen i n many places, p a r t i c u l a r l y i n lo t s 8 and 9, concession IV, Steele township. Deformation of the pillows render them of l i t t l e use i n determining the tops of flows. Garnet, occurring i n d e f i n i t e layers, i s well de veloped i n the amphibolites i n l o t s 1 0 , 11 and 1 2 , con cessions IV and V, Steele township. The garnet-bearing amphibolites possess a good s c h i s t o s i t y and are frequently associated with highly schistose amphibolites which display feathery hornblende grains and contain no garnet. Where the amphibolites are markedly schistose the only r e l i c t volcanic structure noted was highly deformed pillow lava. Garnet was found only within shear zones i n other l o c a l  i t i e s within the Steele Lake volcanics. In t h i n section, the amphibolites are similar to those i n the b i o t i t e zone. B i o t i t e and epidote are less abundant and the former mineral i s absent from most of the 64 specimens examined. The p r i n c i p a l constituents are blue- green hornblende, plagioclase, quartz and l o c a l l y , garnet. Accessory carbonate, sphene and iro n ore are common. With i n the s t a u r o l i t e zone apatite, probably introduced, be comes an important accessory constituent. Hornblende displays the patchy pleochroism noted i n the b i o t i t e zone but the pleochroism i s more intense with X= yellowish green, Y- green and Z= deep blue-green. The l i g h t e r areas within the i n d i v i d u a l hornblende grains have a less intense pleochroism but no colourless patches were seen. Hornblende has a uniform pleochroism and forms porphyroblasts displaying h e l i c i t i c structure or feathery grains i n the schistose amphibolites. In both the garnet and s t a u r o l i t e zones quartz appears to be less abundant than i n the b i o t i t e zone. A l - bit e i s not common i n the garnet zone but zoned and twinned plagioclase with an average composition of An^tj i s abundant. In the s t a u r o l i t e zone the plagioclase averages about An^Q* The plagioclase i s usually clear, r e l a t i v e l y free from i n  clusions, and coarser i n grain size than the a l b i t e of the biotite-zone. Feldspar was not found i n garnet amphibolite. Epidote, which i s rare or lacking i n the s t a u r o l i t e zone, i s commonly found i n abundance i n the garnet zone where i t forms up to 25 per cent of the garnet amphibolites. The garnet of the garnet amphibolites i s anhedral, sieve- textured, and forms large porphyroblasts up to one inch i n Plate XI 65 A—Photomicrograph of garnet amphibolite showing a large porphyroblast of gar net. Lot 11 , concession IV, Steele township. G=garnet, E=epidote, Q= quartz, H=hornblende, Mt=Magnetite. P l a i n l i g h t X16. B—Photomicrograph of diabasic amphibo l i t e . Lot 7» concession IV, Steele township. Note sphene (Sp) rimming illme n i t e (I) grains. Hb=hornblende, Q=quartz, AF=altered feldspar. P l a i n l i g h t X l 6 . s i z e (see P l a t e X I A ) . I n c l u s i o n s o f p i s t a c i t e , carbonate and quar tz are common and h e l i c i t i c s t r u c t u r e , i n d i c a t i n g the garnets r o t a t e d d u r i n g growth i s p r e s e n t . Only a s m a l l p r o p o r t i o n o f the a m p h i b o l i t e s l i e w i t h i n the s t a u r o l i t e zone . The rocks examined from t h i s zone are g r a n o b l a s t i c w i t h r e l a t i v e l y l a r g e randomly o r i e n  ted hornblende prisms l y i n g i n a f i n e - g r a i n e d groundmass o f r e c r y s t a l l i z e d quar tz and p l a g i o c l a s e . Accessory a p a t i t e i s evenly d i s t r i b u t e d i n the groundmass. Inter.bedded Metasediment Two narrow l a y e r s o f metasedimentary rocks i n t e r  bedded w i t h the a m p h i b o l i t e s were found i n l o t 9 , c o n  c e s s i o n IV and i n l o t s 1 and 2, c o n c e s s i o n I I I o f S t e e l e t o w n s h i p . The metasediment l a y e r i n l o t 9 i s one to three f e e t t h i c k . The l a y e r i n l o t s 1 and 2 i s t h r e e to t en fee t t h i c k and was t r a c e d f o r a d i s t a n c e of 3/4 o f a m i l e . I t i s p o s s i b l e tha t bo th occurrences are p a r t o f one continuous l a y e r w h i c h marks an i n t e r r u p t i o n i n the v o l c a n i c a c t i v i t y . The rocks are e s s e n t i a l l y b i o t i t e - q u a r t z - f e l d s p a r s c h i s t s . Garnet i s an accessory i n the metasediments o c c u r r i n g i n l o t 9 and a l s o i n l o t s 1 and 2 near the wide p o r  phyry s i l l . A specimen from l o t 2, concess ion I I I was ex amined i n t h i n s e c t i o n and found to c o n t a i n c o n s i d e r a b l e m i c r o c l i n e and sphene i n a d d i t i o n to b i o t i t e , q u a r t z , a l b i t e and accessory e p i d o t e . The metasediment i n l o t 1 , con c e s s i o n I I I i s composed of about 25 per cent b i o t i t e , 52 67 per cent quartz and a l b i t e , 10 per cent c h l o r i t e and a c c e s s  ory a p a t i t e , t o u r m a l i n e , sphene, opaque m i n e r a l s , and m u s c o v i t e . M i s c e l l a n e o u s Rocks Inc luded under m i s c e l l a n e o u s rocks are a number o f rocks o f u n c e r t a i n o r i g i n . A rock c o n t a i n i n g numerous c o a r s e , randomly o r i e n t e d hornblende l a t h e s embedded i n a f i n e  g r a i n e d b l u i s h - g r e y m a t r i x i s w i d e l y spread throughout the a m p h i b o l i t e s . The rock conta ins l a r g e i r r e g u l a r patches o f carbonate which upon weather ing l e a v e behind conspicuous c a v i t i e s up to 1/2 i n c h i n s i z e . In t h i n s e c t i o n the rock i s t y p i c a l l y composed of about 15 per cent i d i o b l a s t i c b l u e - g r e e n hornblende , 30 per cent red-brown b i o t i t e , 10 to 15 per cent e p i d o t e , 15 to 20 per cent quartz and about 15 to 20 per cent f e l d s p a r . I d i o  b l a s t i c garnet and opaques are common a c c e s s o r i e s . I r r e g u l a r v e i n l e t s and lenses o f quartz are present i n the g r a n o b l a s t i c groundmass. The rock may o r i g i n a l l y have been a t u f f . Other rocks o f i n d e f i n i t e o r i g i n occur near the southern edge o f the v o l c a n i c s i n l o t s 7 and 8, concess ion I I I , S t e e l e township . These rocks are prominent ly l a y e r e d and form a zone about three fee t w i d e . Dark green to b l a c k l a y e r s , composed of about 30 per cent b l u e - g r e e n hornblende , 15 per cent b i o t i t e , 35 per cent quartz and a l b i t e , and 18 per cent e p i d o t e , a l t e r n a t e w i t h l i g h t - g r e y to w h i t e l a y e r s composed of a g r a n o e l a s t i c aggregate o f q u a r t z , f e l d s p a r , b i o t i t e and e p i d o t e . The dark l a y e r s resemble the normal m e t a v o l c a n i c s . Quartz predominates i n the l i g h t e r co loured l a y e r s w i t h most o f the fe ldspar" , ep idote and some carbonate c o n f i n e d to a narrow zone adjacent to the b l a c k l a y e r s . The m a t e r i a l o f the l i g h t l a y e r s appears to p a r t i a l l y r e  p l a c e adjacent p a r t s o f the dark l a y e r s . In a d d i t i o n to the m i n e r a l s a l r e a d y ment ioned, a few p i n k i s h , i n d i s t i n c t l y a n i s o  t r o p i c g r a i n s o f garnet are found s c a t t e r e d through the l i g h t e r l a y e r s . The l i g h t l a y e r s may represent o r i g i n a l c h e r t y h o r i z o n s i n the v o l c a n i c s . Pegmati te d i k e s , f e l d s p a r porphyry d i k e s and s i l l s , and quar tz v e i n s a l s o occur i n the a m p h i b o l i t e s . The pegma t i t e d i k e s are e s p e c i a l l y common i n the western par t o f the m e t a v o l c a n i c s which l i e c l o s e s t to the Case b a t h o l i t h . BONIS VOLCANICS Good exposures o f the Bonis v o l c a n i c s occur on the i s l a n d s l y i n g o f f the mouth o f Forks Creek and a long the e a s t e r n s h o r e l i n e o f Northeast Bay . A few s c a t t e r e d ex posures a l s o occur i n l a n d n o r t h o f the r a i l w a y t r a c k i n S t e e l e t o w n s h i p , i n the n o r t h e r n p a r t o f Bonis township and i n the s o u t h e a s t e r n corner o f Scapa township . The assumed contact between the Bonis v o l c a n i c s and the Sargeant b a t h o l i t h i s based m a i n l y on meager g e o p h y s i c a l data and should be c o n  s i d e r e d t e n t a t i v e . The same i s t r u e f o r the n o r t h e r n con-69 t a c t which has o n l y been p a r t l y d e f i n e d due to the s c a r  c i t y o f o u t c r o p s . The o r i g i n a l m i n e r a l assemblages o f the l a v a s have been destroyed and i t i s u s u a l l y not p o s s i b l e to determine p e t r o g r a p h i c a l l y whether a g i v e n specimen i s b a s a l t i c or a n d e s i t i c . For t h i s reason the d a r k e r , more b a s i c v o l c a n i c s w i l l be r e f e r r e d to as b a s i c to i n t e r m e d i a t e l a v a s . B a s i c to i n t e r m e d i a t e l a v a s can r e a d i l y be d i s t i n g u i s h e d from a c i d l a v a s , however, because o f g r e a t e r d i f f e r e n c e s i n the o r i g i n a l m i n e r a l compos i t ion between these two groups . Attempts have been made to f i n d c r i t e r i a to d i s t  i n g u i s h between h i g h l y metamorphosed b a s a l t s and a n d e s i t e s . 23 (See f o r example S a t t e r l y ) . I t appears t h a t the o n l y s o l  u t i o n to the problem i s d e t a i l e d m i c r o s c o p i c work accompanied 24 by numerous a n a l y s e s . Bienvenu has made a s tudy of the m e t a v o l c a n i c rocks o f the A b i t i b i r e g i o n i n Quebec and con c l u d e s that many o f the v o l c a n i c s were normal p l a t e a u t y p e s . S a t t e r l y 2 ^ and o t h e r s have expressed the o p i n i o n t h a t many m e t a v o l c a n i c rocks mapped as a n d e s i t e s are a c t u a l l y b a s a l t s . 23 S a t t e r l y , J . , P i l l o w Lavas from the Dryden- Wabigoon A r e a , Kenora D i s t r i c t , O n t a r i o , Univ . o f Toronto  S t u d i e s , G e o l . S e r . Wo. 46 , 1941, p p . 119-136. 24 B i e n v e n u , R . , The Chemical Composi t ion o f some M e t a v o l c a n i c Archean Rocks , U n i v . o f L a v a l . M . S c . T h e s i s . 1955, PP . 1-59. 25 I b i d . , p . 132. Plate XII A— P i l l o w e d , porphyritic, intermediate to basic lava (andesite?) i n an island o f f the mouth of Forks Creek. I B — P i l l o w e d non-porphyritic lava i n an island o f f the mouth of Forks Creek. Tops face northwest (towards the observer). B a s i c to Intermediate V o l c a n i c s B a s i c to i n t e r m e d i a t e v o l c a n i c s range i n c o l o u r from dark g r e y i s h - g r e e n to pa le green . Non-porphyr±tic and ^ p o r p h y r j r t i c v a r i e t i e s are r e c o g n i z e d . B o t h occur as i n t e r  bedded f lows ranging from 12 to 35 f e e t t h i c k . The f lows are o c c a s i o n a l l y amygdalo ida l and f r e q u e n t l y p i l l o w e d , and a few show f l o w b r e c c i a t o p s , thus making p o s s i b l e d e f i n i t e top d e t e r m i n a t i o n s . A l a v a f l o w exposed i n a lumber road i n l o t 9 , c o n  c e s s i o n V , Bonis t o w n s h i p , was s t u d i e d i n d e t a i l as the v a r  i a t i o n w i t h i n i t i s t y p i c a l of a l l the f lows found w i t h i n the Bonis v o l c a n i c s . The sequence, from top to bottom i s as f o l l o w s : 1.5 f e e t f l o w b r e c c i a 2 " p i l l o w l a v a 17 " massive l a v a 12 " d i a b a s i c l a v a 1 " massive l a v a The contact between each p a r t i s g r a d a t i o n a l . The t h i c k n e s s o f the v a r i o u s u n i t s v a r i e s c o n s i d e r a b l y from f l o w to f l o w . Unless d e f i n i t e evidence o f i n t r u s i o n was f o u n d , the d i a b a s i c or gabbroic rocks seen were mapped as f l o w s . In t h i n s e c t i o n , the non-porphyr^ ' t i c v a r i e t y i s seen to be composed of 25 to 45 per cent b l u e - g r e e n h o r n  b l e n d e , 0 to 20 per cent c h l o r i t e , 1 to 40 per cent epidote and 15 to 35 per cent f i n e - g r a i n e d quartz and f e l d s p a r . B i o t i t e i s r a r e l y present and sphene, found as r ims about m a g n e t i t e - i l m e n i t e - g r a i n s , and p y r i t e are common accessory m i n e r a l s . In some c a r b o n a t i z e d r o c k s , carbonate forms as much as 35 per cent of the whole. Epidote i s mainly the i r o n - r i c h variety p i s t a c i t e , although c l i n o z o i s i t e i s not uncommon. Cores of p i s t a c i t e grains found i n veinlets or amygdules contain dusty i n  clusions. The hornblende i s commonly fibrous, but i n coarse parts of flows i t i s prismatic or i n laths with X= yellowish green, Y= green and Z= blue-green. Feldspar and quartz are f i n e l y divided throughout the groundmass. Some rocks, which appear to have no feldspar, contain abundant c h l o r i t e . R e l i c t microscopic laths of feldspar, ranging i n composition from An 2^ to An^g and d i s  playing polysnthetic twinning, and corroded borders, are abundant i n a few rocks. Rec r y s t a l l l z e d feldspar i s a l b i t i c . The amygdules of the amygdaloidal types are f i l l e d with quartz, epidote, a l b i t e , c h l o r i t e and r a r e l y t a l c . They are commonly e l l i p s o i d a l , and r a r e l y spherical. R e l i c t textures other than amygdules are rare. One specimen showed a f a i n t o p h i t i c texture. The minerals form a f e l t e d aggre gate i n most of the non-porphyritic rocks, with hornblende generally being the coarsest mineral and c h l o r i t e , epidote, quartz, feldspar and the accessory minerals scattered through the groundmass. F o l i a t i o n i s present but not well developed. The porphyritic variety i s composed e s s e n t i a l l y of the same minerals as the non-porphyrytic variety but f e l d  spar and quartz are more abundant, forming 35 to 50 per cent of the rock. Epidote and hornblende are proportionately le s s abundant and c h l o r i t e i s inva r i a b l y present constituting 73 P l a t e X I I I A—Photomicrograph of p o r p h y r i t i c i n t e r  mediate to basic l a v a (andesite ? ) . Fractured and o s c i l l a t o r y zoned p l a g i o  c l a s e ( P I ) , and quartz (Q) l i e i n a f i n e - g r a i n e d groundmass of hornblende, quartz, c h l o r i t e , epidote, and b i o t i t e . P o l a r i z e d l i g h t X16. B—Photomicrograph of s c h i s t o s e amphibolite, l o t 12, concession V, Bonis township. Sieve-textured hornblende (H), containing i n c l u s i o n s of quartz and carbonate (Cb) l i e i n a groundmass of quartz, p l a g i o c l a s e and epidote. P o l a r i z e d l i g h t X16. 5 to 15 per cent o f the whole . The f e l d s p a r i s c a l c i c ( A n ^ ) and occurs as r e l a t i v e l y f r e s h to h i g h l y a l t e r e d phenocrysts up to 3 mm. i n s i z e . One rock shows p a r t i c u l a r l y f r e s h , twinned pheno c r y s t s o f p l a g i o c l a s e (See P l a t e X I I I A ) . A d e t a i l e d study of the p l a g i o c l a s e phenocrysts showed that they are o r i g i n a l phenocrysts and not developed d u r i n g metamorphism. T h i s i s i n d i c a t e d by the f o l l o w i n g ? (1) Some of the phenocrysts d i s p l a y i n t r i c a t e o s c i l l a t o r y e u h e d r a l z o n i n g . (2) Many o f the phenocrysts are p a r t l y to w h o l l y a l t e r e d to s e r i c i t e and e p i d o t e . (3) Most phenocrysts have corroded borders and are f r a c t u r e d or c r u s h e d . (4) R e l a t i v e l y u n a l t e r e d phenocrysts are complete l y f r e e from i n c l u s i o n s . (5) The phenocrysts are a l i g n e d p a r a l l e l to the f o l i a t i o n o f the r o c k . (6) C a r l s b a d and 26 a l b i t e - C a r l s b a d t w i n s , w h i c h a c c o r d i n g to G o r a i are c h a r a c t e r i s t i c o f the v o l c a n i c and p l u t o n i c r o c k s , are common 27 and (7) Zoned c r y s t a l s , s i m i l a r to those d e s c r i b e d by Ross ' from the G a r i b a l d i v o l c a n i c s are f o u n d . The o r i g i n a l p o r p h y r i t i c charac ter and a quartz and f e l d s p a r content o f up to 50 per cent suggests tha t the p o r p h y r i t i c v a r i e t y was o r i g i n a l l y a n d e s i t i c . Chemical ana lyses coupled w i t h the p e t r o g r a p h i c evidence o b t a i n e d 26 G o r a i , Masao, P e t r o l o g i c a l S t u d i e s on P l a g i o c l a s e T w i n s , Am. M i n . , V o l . 36, 1951, pp. 884-901. 27 Ross , J . V . , Combinat ion t w i n n i n g i n P l a g i o c l a s e F e l d s p a r s , Am. J o u r n . S c i . V o l . 255, 1957, pp . 650-655. 75 would go f a r to s t rengthen t h i s c o n c l u s i o n . The r e l a t i v e l y low quartz and f e l d s p a r content o f the non-porphyr;±tic v a r i e t y i s i n d i c a t i v e o f o r i g i n a l b a s a l t . Other rocks grouped w i t h the b a s i c to i n t e r m e d i a t e v o l c a n i c s are exposed a long the shore near the r a i l w a y i n l o t 3» concess ion F , S t e e l e t o w n s h i p , and i n the Mace Crab I s l a n d s . The rocks are c h l o r i t e - f e l d s p a r s c h i s t s , composed predominant ly o f c h l o r i t e , q u a r t z , p l a g i o c l a s e ( a l b i t e and o l i g o c l a s e ) , carbonate and b i o t i t e . In t h i n s e c t i o n , o r i e n t e d , e longate masses, up to 3 m i l l i m e t e r s i n s i z e , composed of f i n e p l a g i o c l a s e l a t h s , or c h l o r i t e , epidote and g r e e n i s h b i o t i t e , l i e i n a f i n e - g r a i n e d m a t r i x o f angular q u a r t z , f e l d s p a r and c h l o r i t e . The c h l o r i t i c masses are l a r g e r than those o f p l a g i o c l a s e and g i v e the rock a spot ted appearance. The rock o c c u r r i n g near the r a i l w a y t r a c k i s l e s s deformed and i s composed of e longate c h l o r i t e - b i o t i t e - e p i d o t e masses l y i n g i n a groundmass o f f i n e p l a g i o c l a s e l a t h s and q u a r t z . Much o f the carbonate appears to have been i n t r o d u c e d i n a l l the rocks examined. W i t h i n the contact zone , w i t h the Sargeant b a t h o l i t h the b a s i c to i n t e r m e d i a t e v o l c a n i c s are complete ly r e c r y - s t a l l i z e d , w e l l - f o l i a t e d and coarse i n g r a i n , resembl ing the a m p h i b o l i t e s developed i n the S t e e l e Lake v o l c a n i c s . At the contac t w i t h the Sargeant b a t h o l i t h the rocks are h o r n f e l s e d . A few of the rocks have a g n e i s s i c banding that i s due p o s s i b l y to metamorphic d i f f e r e n t i a t i o n . V o l c a n i c s t r u c t u r e s are r a r e w i t h i n the contact zone and a l l o r i g i n a l t e x t u r e s are d e s t r o y e d . The hornblende becomes i n t e n s e l y p l e o c h r o i c i n approaching the Sargeant b a t h o l i t h , c h l o r i t e i s r a r e or ab sent and the p l a g i o c l a s e i s c a l c i c and complete ly r e c r y s t a l l - i z e d . In the o u t e r p a r t o f the contact zone , p o r p h y r o b l a s t s o f s o d i c p l a g i o c l a s e and hornblende are not uncommon The contact between the Sargeant b a t h o l i t h and the Bonis v o l c a n i c s i s w e l l exposed i n an outcrop o c c u r r i n g i n l o t 1 , concess ion V I , Bonis township . Here a g r a n o b l a s t i c q u a r t z - p l a g i o c l a s e - h o r n b l e n d e rock i s cut by a few m i n e r a l  i z e d f r a c t u r e s c o n t a i n i n g p y r r h o t i t e and c h a l c o p y r i t e . The p l a g i o c l a s e i s commonly twinned and has a compos i t ion o f about A n - ^ . A fexir t u f f a c e o u s l a y e r s are interbedded w i t h the b a s i c to i n t e r m e d i a t e l a v a s . One o f these i s p a r t i c u l a r l y w e l l exposed a long the shore of Northeast Bay i n l o t 2, con c e s s i o n D , S t e e l e township . The t u f f and adjacent l a v a s are cut by numerous b a s i c s i l l s and d i k e s , near which the t u f f has been metamorphosed to v a r y i n g degrees . The l e a s t meta morphosed t u f f i s sheared and composed of b i o t i t e , c h l o r i t e , q u a r t z , f e l d s p a r and minor muscovite w i t h accessory opaques and carbonate . I t i s f i n e - g r a i n e d and d i s p l a y s graded--bedding w h i c h i n d i c a t e s tops to the n o r t h , i n agreement w i t h the d e t e r m i n a t i o n s made from the p i l l o w l a v a s . A few rounded v o l c a n i c rock fragments a l s o occur i n the r o c k . Near the b a s i c i n t r u s i v e s l a r g e , s i e v e d p o r p h y r o b l a s t s o f hornblende Plate XIV 77 A—Photomicrograph of t u f f interbedded with the basic to intermediate volcanics, l o t 2 , concession D, Steele township. The rounded rock fragment (R) l i e s i n a fine-grained matrix of quartz, feldspar, mica, c h l o r i t e , and carbonate. P l a i n l i g h t X16. B—Photomicrograph of schistose amphibo l i t e , l ot 8, concession VI, Bonis town ship. Hornblende (H), magnetite (Mt), and minor b i o t i t e l i e i n a fine matrix of epidote, quartz, and feldspar (MX). P l a i n l i g h t X16. up to 3 mm. long are developed. Interbedded w i t h the p o r - p h y r o b l a s t i c h o r n b l e n d e - r i c h rock i s a g a r n e t i f e r o u s q u a r t z - c h l o r i t e - h o r n b l e n d e rock w i t h a w e l l developed h e l i c i t i c s t r u c t u r e . A c i d V o l c a n i c s N e a r l y a l l the exposures o f a c i d v o l c a n i c s occur w i t h i n the contact zone w i t h the Sargeant b a t h o l i t h and as a r e s u l t they are g e n e r a l l y h i g h l y a l t e r e d , making i t i m  p o s s i b l e to t e l l the o r i g i n a l na ture of the r o c k . The more h i g h l y a l t e r e d types are d i s c u s s e d below under a separate h e a d i n g . The a c i d v o l c a n i c s are best exposed i n l o t 4 , c o n  c e s s i o n A , S t e e l e township . The rocks are m a i n l y f i n e  g r a i n e d , massive to p o r p h y r i t i c , and l i g h t green to l i g h t grey i n c o l o u r , w i t h a red or p i n k i s h t i n g e . B a n d i n g , sugges t ive o f f l o w l i n e s , i s commonly present i n the massive r o c k s . In places an agglomerate , c o n t a i n i n g l i g h t c o l o u r e d drawn-out fragments up to 3 inches long set i n a g r e e n i s h - grey m a t r i x , i s in terbedded w i t h the massive and p o r p h y r i t i c v a r i e t i e s . A specimen o f a r e d d i s h banded rock ( r h y o l i t e ? ) from l o t 4 , concess ion A was examined i n t h i n s e c t i o n and found to c o n t a i n numerous crushed and a l t e r e d phenocrysts of o l i g o  c l a s e and r a r e potash f e l d s p a r , set i n a f i n e - g r a i n e d , f e l t y m a t r i x of q u a r t z , f e l d s p a r , muscovi te and c h l o r i t e . B i o t i t e and s m a l l cubes o f p y r i t e are not uncommon. The groundmass 79 has a streaked appearance, brought about by trains of epidote and c h l o r i t e which probably represent poorly preserved flow l i n e s . A pale f e l s i t i c rock displaying prominent banding, accentuated by fine garnet grains occurs i n l o t 1, concession D , Steele township. In thin section the rock i s w e l l - f o l i a t e d and composed of elongate quartz and feldspar grains with aligned b i o t i t e , muscovite and c h l o r i t e scattered through the groundmass. The garnet i s associated with quartz i n layers which are s l i g h t l y coarser i n grain than the rest of the rock. Rocks of Indefinite O r i g i n Most of the rocks described below occur adjacent to the Sargeant batholith i n l o t 1, concession D , Steele town ship. The rocks range from p y r i t i z e d p h y l l i t i c types to garnetiferous quartz-feldspar-mica schists and highly con torted gneissic amphibolites. A garnet-magnetite-hornblende rock was found at the contact with the batholith. The rock has a pronounced granoblastic texture and contains about 15 per cent f i n e l y disseminated magnetite. This was the only i r o n - r i c h rock found within the Bonis volcanics, although Knight et a l 2 8 refer to "much iron-formation" i n the v i c i n i t y of l o t 1, concession D . 28 C.W.Knight, et a l . , Abitibi-Night Hawk Gold Area, Ont. Bur. Mines. Vol. XXVIII, pt. 2, 1919, p. 25. 80 Plate XV A — P o r p h y r i t i c intermediate to basic lava i n an island o f f the mouth of Forks Creek. B—Contorted tuffaceous sediment (?) folded around a porphyry dike (to the l e f t ) and containing q u a r t z - f i l l e d gash fractures. Lot 4 , concession C, Steele township. Highly sheared and contorted rocks occur i n l o t s 3 and 4 , concession C, Steele township, interbedded with basic to intermediate lavas and cut by porphyry dikes and basic i n - 29 t r u s i v e s . M.B. Baker has called the rocks "rusty-weather ing dolomite". Where they are cut by porphyry dikes, tension cracks f i l l e d with quartz have formed from which low gold values have been reported. A th i n section study of four t y p i c a l specimens shows the rock to be a carbonatized q u a r t z - f e l d s p a r - s e r i c i t e - c h l o r i t e schist containing abundant epidote and cubes of py r i t e . One of the specimens studied contained numerous elongate, highly altered fragments up to one inch i n si z e . The interbedded lavas are only s l i g h t l y deformed and the rock i n question i s dragged against the lavas, suggesting i t was less resistant to deformation than the lavas. The rock may have o r i g i n a l l y been a tuffaceous sediment. SUMMARY OF THE METAMORPHISM The mineral assemblages of the greywackes and amphi bo l i t e s i n the metamorphic zones of the metasediments and Steele Lake volcanics are summarized i n Table 2. Unfortunate l y the lack of both bulk analyses of the various rock types and chemical analyses of the various metamorphic minerals 29 Baker, M.B., Lake A b i t i b i Area, Ont. Bur. Mines. Vol . XVIII, pt. 1, 1909, p. 270. 30 Baker, M.B., Ibid., p. 270. 82 Table 2 T A B L E I Miner at As semblaaes o f ihe Greywackes one/ Amphibolites in the. Mttamorphic Z.one.s o-f the. Met-Lse.dime.nts and Stee.Ce. Lake. ]/o Lcanics CHLORITE ZONE . BIOTITE ZONE GARNET ZONE STAUROLITE ZONE Clastic quartz. tie.crysta.llii.ed qvari-g. Clastic feldspar Albite O/igoc last GREYWACKE Sz-rici-te. Chlori-ke. Musco vi he. | Ga-met | AMPHIBOLITE Quartz. Albite. Reiict PLa.9i0cla.se. Epidote. Calcic P/agioclasi pleo c hro ism • Biotiit Ahiphibole 27ncrease in Garntt precludes a thorough discussion of the mineral assemblages. The c a l c - s i l i c a t e rocks, iron-formation, and amphi bole and p l a g i o c l a s e - r i c h schists occurring i n the Scapa and Steele metasediments, and rocks of i n d e f i n i t e o r i g i n occurring in; the Steele Lake volcanics are excluded from the table. These rocks w i l l not be discussed further. METAMORPHISM OF THE GREYWACKES Quartz forms strained, and s l i g h t l y elongate de- t r i t a l grains up to 0.9 mm i n diameter i n the c h l o r i t e zone which are mechanically crushed and drawn out and s l i g h t l y r e c r y s t a l l i z e d i n the b i o t i t e zone; at the garnet isograd the quartz i s completely r e c r y s t a l l i z e d with remnant d e t r i t a l quartz v i s i b l e only i n the massive greywackes. In the upper part of the garnet zone and i n the s t a u r o l i t e zone no recog nizable d e t r i t a l grains are l e f t . In the finer-grained v a r i e t i e s d e t r i t a l quartz i s destroyed i n the b i o t i t e zone and i t occurs either i n elongate spindle-shaped aggregates and i n d i v i d u a l grains that l i e with th e i r long axes p a r a l l e l to the s c h i s t o s i t y , or as narrow v e i n l e t s . This habit i s maintained and i n t e n s i f i e d i n the upper part of the b i o t i t e zone and i n the garnet and s t a u r o l i t e zones. R e c r y s t a l l i z - ation i s therefore a much more active process than mechanical processes i n the higher grades of metamorphism. C l a s t i c feldspar i s common i n the c h l o r i t e zone but occurs only i n the massive greywackes i n the lower part of 84 the b i o t i t e zone. It i s apparently absent i n the higher grades of metamorphism. A l b i t e i s clouded by s e r i c i t e and contains numerous inclusions i n the c h l o r i t e zone. In the upper part of the b i o t i t e zone the s e r i c i t e i s resorbed and alumina expelled, the a l b i t e forming clear, untwinned porphyro blasts which are s l i g h t l y larger i n size than those occurring i n lower grades. Oligoclase, showing reversed zoning,, i s common i n the garnet zone. In the upper part of the garnet zone and i n the s t a u r o l i t e zone, plagioclase i s commonly unzoned and twinned, p a r t i c u l a r l y near the Case bat h o l i t h contact. Concomitant with an increase i n c a l c i c plagioclase and the occurrence of abundant garnet and s t a u r o l i t e , epidote and c h l o r i t e show a decided decrease and are appar ently absent i n the s t a u r o l i t e zone. Epidote, however, i s only an accessory i n the greywackes and i n many rocks occurring i n the lower grades of metamorphism i t i s e n t i r e l y lacking. The occurrence of plagioclase i n the garnet and s t a u r o l i t e zones poses a problem. The mineral assemblage present i n the greywackes i n the lower grades of metamorphism appears quite adequate to supply a l l the constituents except calcium for the formation of c a l c i c plagioclase. (Epidote i s apparently not present i n s u f f i c i e n t quantities to supply a l l the calcium needed). If c a l c - s i l i c a t e rocks were o r i g i n a l l y present i n the upper part of the garnet zone and i n the s t a u r o l i t e zone, then these rocks, upon metamorphism, could have supplied calcium for the formation of c a l c i c plagioclase. Cordierite was not found i n the metasediments border ing the Case batholith and i t appears to be rare or lacking i n the narrow contact aureole developed i n the Scapa metasedi ments adjacent to the Scapa stock. In the l a t t e r l o c a l i t y the absence of c o r d i e r i t e may be due i n part to a l t e r a t i o n . The evidence cited i n connection with the contact aureole shows that the rocks have been fractured and altered, pre sumably by hydrothermal solutions from the granite forming the stock. Water pressures were therefore probably high. 31 W.S.Fyfe and F.J. Turner indicate that at tempera tures below 490°C, c o r d i e r i t e i s stable at low water press ures, but i f water pressures are high i t i s unstable. There fore, within the cooler outer portions of the Scapa stock aureole high water pressures could account for the absence of c o r d i e r i t e . Petrographic study of the hornfelses within the inner part of the aureole shows that microcline (and there fore potash) has been introduced into the metasediments. Yoder's theory that c o r d i e r i t e i s unstable i n the presence of an excess of potash^ 2 would thus explain the lack of cordier i t e within the hornfels zone of the aureole. 31 Fyfe, W.S., and.Turner, F.J., Correlation of Metamorphic Facies with Experimental Data, i n Metamorphic  Reactions and Metamorphic Facies, Memoir 73> Geol. Soc. Am. 1958, p. 165. 32 Yoder, H.S., The MgO-Al2C>3-Si02-H20 System and the Related Metamorphic Facies, Am. Jour. S c i . , Bowen Vol., 1952, pp. 569-627. 86 The absence of c o r d i e r i t e i n the Scapa metasediments near the Case bat h o l i t h may be due to the nature of the rock comprising the Case batholith. In t h i s connection the 33 following statements by Yoder are s i g n i f i c a n t . "It i s probable that i n those cases where the micas are stable, as i n muscovite - b i o t i t e granite, c o r d i e r i t e w i l l not form i n the aureole i n the presence of an excess of K 20. The micas i n the metamorphosed rock w i l l persist up to the contact. In those cases i n which the micas are not stable even i n the presence of an excess of K2O, as i n a pyroxene - or amphibole - bearing granite, c o r d i e r i t e would be stable." As w i l l be shown l a t e r , the rocks comprising the Case batho l i t h i n Steele township do not contain amphibole or pyroxene but a l l contain b i o t i t e and muscovite. I f the Scapa meta sediments adjacent to the Case bat h o l i t h contain an excess of potash, Yoder's explanation accounts for the lack of c o r d i e r i t e . Sedimentary structures, are well preserved i n the c h l o r i t e zone and the lower part of the b i o t i t e zone. In the upper part of the b i o t i t e zone and i n the garnet and stauro l i t e zones, they are gradually o b l i t e r a t e d by shearing and r e c r y s t a l l i z a t i o n . S c h i s t o s i t y commonly p a r a l l e l s bedding i n the grey wackes, which suggests that bedding provided the surfaces of minimum strength along which s l i p was i n i t i a t e d . B i o t i t e and muscovite are undeformed i n many of the greywackes but 33 Yoder, H.S. 0p_. C i t . , p. 624. c h l o r i t e i s usually bent. Garnet and s t a u r o l i t e rarely show indications of movement during growth and both minerals are commonly i d i o b l a s t i c . METAMORPHISM OF THE STEELE LAKE AMPHIBOLITES The most important changes which take place i n the amphibolites from the b i o t i t e through to the s t a u r o l i t e zones are: 1. A s l i g h t decrease i n the amount of quartz. 2 . An increase i n the anorthite content of plagio clase, together with a decrease i n the amount of inclusions i n the plagioclase. 3. The appearance of zoning and twinning i n the plagioclase. 4. A decrease i n the amount of epidote, p a r t i c u l a r l y near the s t a u r o l i t e zone, together with a sl i g h t increase i n the anorthite content of the plagio clase i n the s t a u r o l i t e zone. 5. A marked increase i n the pleochroism of amphibole. 6. Local occurrence of garnet independent of shear zones i n the garnet zone. 7 . An increase i n o v e r a l l grain size of the amphi b o l i t e s . 8 . The development of s c h i s t o s i t y i n the garnet zone. Re l i c t micro-textures derived from the o r i g i n a l volcanic rocks are rar e l y seen i n the b i o t i t e zone and they are absent i n a l l the higher grades. Volcanic structures, as seen i n the outcrop, are more or less preserved i n a l l three zones, although they appear to be more abundant i n the b i o t i t e zone. Pillow lava i s moderately to highly deformed, but i t s degree of deformation does not appear to be related to the grade of metamorphism. The occurrence of garnet i n the amphibolites i s not r e s t r i c t e d to the garnet zone. It was found near and i n shear zones which are ubiquitous i n the Steele Lake volcanics. However within the garnet zone, garnet i s l o c a l l y developed 34 i n apparent independence of shear zones. Poldervaart has given a b r i e f summary of the role of garnet i n metamorphosed basalts and i t appears that the formation of garnet depends upon many factors, which for the most part are only im pe r f e c t l y known. It i s not confined to a pa r t i c u l a r grade of metamorphism within b a s a l t i c rocks and i t s value as an index mineral i s open to question. METAMORPHISM OF THE BONIS VOLCANICS The basic to intermediate volcanics occurring near the outer margin of the contact zone with the Sargeant b a t h o l i t h l i e within the albite-epidote hornfels facies as 34 Poldervaart, A r i e , Metamorphism of B a s a l t i c Rocks: A Review, B u l l . Geol. Soc. Am.. Vol. 6 5 , 1953, pp. 259-274. defined by Turner-^. The volcanics i n the inner part of the contact zone l i e within Turner's hornblende hornfels f a c i e s , and contain r e c r y s t a l l i z e d c a l c i c plagioclase and less r e l i c t plagioclase than the rocks within the albite-epidote hornfels f a c i e s . No pyroxene was found i n the basic to intermediate volcanics. Water pressures were therefore high enough to allow hydrated s i l i c a t e s to c r y s t a l l i z e , even at the contact with the Sargeant batholith. The occurrence of tourmaline i n the basic intrusives cutting the lavas (see page 97) indicates that boron has been introduced into the rocks. Increase i n the pleochroism of amphibole with an increase i n metamorphic grade as observed i n the metavolcanic rocks of the map-area, has also been reported by Turner and Compton^?. The more deeply coloured amphiboles are commonly high i n alumina. The fa b r i c of many of the pillow lavas occurring i n the Bonis volcanics shows a li n e a r orientation but i n places the pillows themselves are not noticeably deformed. In addition, the f a b r i c of some highly deformed pillows displays 35 Turner, F.J., Mineral Assemblages of Individual Metamorphic Facies i n Metamorphic Reactions and Metamorphic  Facies. Memoir 73, Geol. Soc. Am. 1958, PP. 199-239. 36 Williams, H. Turner, F.J., and G i l b e r t , CM., Petrography (W.H. Freeman and Co. 1955), p. 242 37 Compton, R.R., Significance of Amphibole Para- genesis i n the Bidwell Bar Region, C a l i f o r n i a , Am. Min., V o l . 43, 1958, pp. 890-907. 90 the same degree of l i n e a r orientation as that of the non- deformed pillows. E l l i p s o i d a l amygdules are also w e l l - preserved i n some f o l i a t e d lavas. These features suggest that the li n e a r o r i e n t a t i o n i s not due to para-metamorphic deformation. It i s also possible that some pillows were de formed shortly after t h e i r formation, while s t i l l i n a p l a s t i c state. CAUSE OF THE METAMORPHISM The metasediment-metavoleanic assemblage has been subjected to raised temperatures and probably strong com pressive forces, as suggested by the metamorphic zoning and the regional deformation which the assemblage displays. It would seem there are two possible causes of metamorphism. F i r s t , the assemblage has been metamorphosed by the batho- l i t h s , and second, the assemblage has been subjected to region a l metamorphism during deep b u r i a l and deep-seated magmatic a c t i v i t y . The evidence i n support of both p o s s i b i l i t i e s i s meagre. I f the second mechanism i s envoked, then i t i s reason able to assume that the Case bat h o l i t h has destroyed some of the regional zonation within the metasediments which i t i n  trudes. This would account for the absence of kyanite and s i l l i m a n i t e zones within the metasediments near the contact with the Case batholith. However, as suggested on pages 32 and 33, the bulk composition of the metasediments may be such as to preclude the formation of kyanite and s i l l i m a n i t e . The occurrence of hornfelses i n places along the con tact between the bath o l i t h and the Scapa metasediments could be interpreted as a contact effect of the ba t h o l i t h on previously metamorphosed metasediments. The writer favours the int r u s i o n of the Case batho l i t h to account for the metamorphic zonation i n the meta sediments and Steele Lake volcanics. The best evidence i n favour of thi s hypothesis follows: (1) S t a t i c c r y s t a l l i z a t i o n of most of the garnet, s t a u r o l i t e , and micas within the metasediments. If the metamorphism i s syntectonic as implied i n the second mechanism, then these minerals could be expected to show evidence of movement or deformation. ( 2 ) The garnet and s t a u r o l i t e isograds are arranged p a r a l l e l to the contact of the Case ba t h o l i t h i n Steele township and they cut across l i t h o l o g i c a l boundaries. The metamorphic zones can be correlated with meta morphic facies as follows: Chlo r i t e zone B i o t i t e zone Garnet zone St a u r o l i t e zone Greenschist facies Almandine Amphibolite facies Few of the rocks within the metamorphic zones display "stable" assemblages, except i n the c h l o r i t e zone and i n the upper parts of the b i o t i t e , garnet and s t a u r o l i t e zones. Rarity 92 of stable assemblages i s what one would expect i n the pro gressive metamorphism of the metavolcanic-metasediment assemblage as the re s u l t of heat and pressure effects exerted by the Case batholith. The close spacing between the contact of the batho l i t h and the s t a u r o l i t e isograd, and between the s t a u r o l i t e and garnet isograds (see Figure 2) suggest that both i s o - gradic surfaces have a very steep gradient and the contact of the b a t h o l i t h i n Steele township also probably dips steeply. The garnet and s t a u r o l i t e isograds intersect the regional trend of the Scapa metasediments at a low angle but tend to follow the regional trend of the Steele Lake volcanics at t h e i r western end. The isograds are i n effect s l i g h t l y refracted where they enter the Steele Lake volcanics. This r e f r a c t i o n i s probably due to the greater resistance which the volcanics show to changes i n metamorphism. The Sargeant batholith has profoundly metamorphosed the Bonis volcanics at their contact. The metamorphic grade, however, drops o f f sharply from the contact zone and the Sargeant batholith has apparently had l i t t l e or no effect on the Steele and Scapa metasediments. This effect again, i s possibly due to the resistance of the basic to intermediate lavas to metamorphic change. The volcanic rocks occurring within the map-area are probably examples of Read's " r e s i s t e r s " . The narrow aureole superimposed upon the rocks occurring i n the b i o t i t e zone i n Scapa township i s the re sult of the intrusion of the Scapa stock. The width of the aureole suggests that the contacts of the stock dip steeply. The superimposition of the Scapa stock aureole upon the regionally zoned Scapa metasediments suggests that the stock was intruded af t e r the Case batholith. 35 Read, H.H., Metamorphism and Gra n i t i z a t i o n , i n The Granite Controversy, Interscience Publishers, Inc., New York, 1957, p. 347. CHAPTER IV INTRUSIONS ULTRABASIC AND BASIC INTRUSIONS Small i r r e g u l a r masses, narrow s i l l s and dikes of ultrabasic and basic intrusions cut both the Bonis volcanics and the Scapa metasediments and are themselves cut, i n turn, by the acid intrusives and late basic i n t r u s i v e s . They con s i s t of serpentinite, amphibolitized gabbro and diabase, and possibly d i o r i t e . Some of the rocks of this group may represent the f i l l i n g s of conduits for the e a r l i e r extrusive a c t i v i t y . SERPENTINITE The serpentinites are greenish-black on a fresh surface and a bright bluish-green on a weathered surface. With the aid of a hand lens, numerous specks of magnetite and chromite can be distinguished. Most of the serpentinites are hard and massive but a few are highly sheared. Microscopic study shows these rocks to be composed lar g e l y of fibrous a n t i g o r i t e , pseudomorphous after o l i v i n e , cut by c h r y s o t i l e and serpophite v e i n l e t s and containing scattered subhedral to anhedral chromite grains. The antigor i t e pseudomorphs are commonly altered about t h e i r borders to t a l c and magnesite. Magnetite occurs both as d i s t i n c t c r y s t a l s and i n i r r e g u l a r grains, and i n bands ou t l i n i n g the o r i g i n a l o l i v i n e c r y s t a l s . Tremolite and magnetite are associated with carbonate veins and occur together i n masses i n t e r s t i t i a l to a n t i g o r i t e pseudomorphs (altered pyroxene?). Chromdte i s commonly opaque but i n some specimens a translucent, red-brown core can be seen. Clusters of three or more grains of chromite occur i n t e r s t i t i a l l y to altered o l i v i n e grains. An unusual c h l o r i t e was found i n one rock associated with f i n e l y disseminated opaque material and streaks of a reddish-brown i s o t r o p i c substance (Maghemite?). The c h l o r i t e has a very pale lavender to pinkish pleochroism that i s p o s s i b l y due to chromium1. Serpentinite occurs at Peat's Point and on the islands and adjacent mainland near the mouth of Forks Creek. At the l a t t e r l o c a l i t y the serpentinite i s i n contact with u r a l i t - ized pyroxenite (or peridotite) and metagabbro i n one of the islands, and appears to be part of a d i f f e r e n t i a t e d s i l l about 650 feet thick. Baker 2 obtained an analysis of the serpen t i n i t e at Peat's Point and found i t to conform to a t y p i c a l dunite* AMPHIBOLITE Amphibolite, derived by metamorphism from gabbro and 1 Winchell, A.N., Winchell, H., Elements of Optical  Mineralogy Part I I , Descriptions of Minerals, (John Wiley and Sons IncV, 195D, p. 386. 2 Baker, M.B., Lake A b i t i b i Area, Ont. Bur. Mines, V o l . XVIII, pt. 1, 1909, p. 274. 96 P l a t e XVI A—Photomicrograph of s e r p e n t i n i t e , l o t 4, concession C, S t e e l e township. Pseudo- morphs of a n t i g o r i t e a f t e r o l i v i n e are rimmed by t a l c and magnesite. P o l a r i z e d l i g h t X16. B—Photomicrograph of amphibolite showing r e l i c t o p h i t i c t e x t u r e . Lot 3 5 concess ion B, St e e l e township. H= hornblende, Pl= p l a g i o c l a s e . Also present are c h l o r i t e , epidote, quartz and opaque minerals, P o l a r i z e d l i g h t X16. diabase, i s the most abundant rock type of the basic i n t r u - sives. The amphibolites are composed of 40 to 65 per cent blue-green hornblende, ranging i n size from less than one millimeter to one centimeter, set i n a fine-grained ground- mass of epidote, quartz and feldspar. R e l i c t laths of plagio clase up to one millimeter long are present and where these are abundant, the rock shows ophitic texture. B i o t i t e and carbonate are common and altered magnetite-ilmenite i s an accessory. Tourmaline i s rare. The hornblende and r e l i c t plagioclase laths are de formed and broken. In many of the amphibolites hornblende forms large rounded aggregates, giving the rock a porphyro- b l a s t i c appearance, or i t i s fibrous and pseudomorphous after pyroxene. F o l i a t i o n i s not well-developed, although many of the amphibolites are sheared near the contact zone with the Sargeant batholith. Evidence of multiple intrusion of the s i l l - o r dike l i k e bodies i s present i n many l o c a l i t i e s . The best example of multiple i n t r u s i o n occurs in a well-exposed outcrop at the eastern boundary of Scapa. Here, a metagabbroic s i l l , about 10 feet wide, showing c h i l l e d contacts against the meta sediments, i s intruded by irre g u l a r dikes of a second meta gabbroic rock, ranging from 1/2 inch to 4 feet i n width, which display c h i l l e d margins against the f i r s t . Dissemin- ' ated p y r i t e , pyrrhotite and chalcopyrite are abundant at the contact between the two rocks. Altered quartz diabase i s exposed i n a few rock reefs l y i n g o f f Peat's Point and to the southwest of the prominent point to the south of Peat's Point. In th i n section the rock has a well-preserved o p h i t i c texture but a l l the o r i g i n a l pyroxene has been u r a l i t i z e d and the plagioclase alte r e d . Micropegmatitic intergrowths of quartz and plagio clase can s t i l l be seen. DIORITE Possibly d i o r i t i c rocks occur i n the Mace Crab Islands and cutting the. d i f f e r e n t i a t e d s i l l i n the islands o f f the mouth of Forks Creek. At the l a t t e r l o c a l i t y the rock i s s l i g h t l y altered and porphyrytic. The phenocrysts are o s c i l l a t o r y zoned oligoclase set i n a fine-grained f e l t y aggregate of quartz and feldspar. Pale blue-green hornblende prisms up to 2 mm. long are also abundant. ACID INTRUSIONS SARGEANT BATHOLITH The name Sargeant batholith i s proposed for a grano- d i o r i t i c to d i o r i t i c mass centered i n Sargeant township and covering an area of about 400 square miles. The bat h o l i t h extends to the eastern shore of Lower Lake A b i t i b i , the northern shore of Upper Lake A b i t i b i and across the Inter- p r o v i n c i a l boundary into Desmeloizes township. Its northern and eastern extent into Sargeant and Desmeloizes township i s only approximately known. M.B. Baker made a reconnaissance of that portion of the ba t h o l i t h bordering on Lower and Upper Lake A b i t i b i i n 19083. He described the rock comprising t h i s part of the b a t h o l i t h as hornblende granite, which i n places becomes a hornblende syenite. U n t i l the present survey, no other work has been published on the batholith. In Bonis township the rocks vary considerably i n 4 composition. Pyroxene and hornblende d i o r i t e , gneissic quartz d i o r i t e , quartz d i o r i t e , quartz monzonite and grano- d i o r i t e are the p r i n c i p a l rock types. In general, the more acid rocks occur near or at the western margin of the batho l i t h . Numerous quartz-feldspar porphyry and feldspar por phyry dikes, granite dikes and pegmatitic dikes extend from the b a t h o l i t h into the enclosing Bonis volcanics. Intrusion breccia and a variety of hybrid rocks occur at the contact with the Bonis volcanics i n Steele township. The b a t h o l i t h i s poorly exposed within the map-area making i t d i f f i c u l t to correlate the various rock types. Many of the ba t h o l i t h rocks contain amphibolite i n  clusions, possibly derived from the Bonis volcanics. Peg matite and a p l i t e are rare. The hornblende d i o r i t e s and quartz d i o r i t e s are 3 0p_. c i t . , p. 238 4 The acid intrusives of both the Sargeant batholith and Case ba t h o l i t h are c l a s s i f i e d according to Brown (Trans, Can. Inst. Min.and Met., Vol. LV, 1953, pp. 53-56) . 100 similar i n handspecimen. They are both coarse to medium- grained, grey to pinkish, mesocratic rocks with a pronounced f o l i a t i o n , due to a sub-parallel alignment of i n d i v i d u a l hornblende c r y s t a l s , b i o t i t e and c h l o r i t e flakes, and i n  clusions of amphibolite. Pyroxene d i o r i t e i s poorly f o l i a t e d , medium-grained, leucocratic and pinkish with a d i s t i n c t blue-grey tinge. Pyroxene quartz d i o r i t e also has a blue- grey tinge. D i o r i t e and pyroxene-bearing quartz d i o r i t e were found only i n l o t s 1 and 2, concession V, Bonis township. The pyroxene-bearing rocks form i r r e g u l a r patches i n the pinkish quartz d i o r i t e s and may represent assimilated i n  clusions. Although f o l i a t i o n i s pronounced i n nearly a l l the rocks examined, i t was d i f f i c u l t to measure i n the outcrop owing to the thick vegetation cover. The composition of the d i o r i t e s and quartz d i o r i t e s i s approximately 35 to 60 per cent plagioclase, 3 to 25 per cent hornblende, 0 to 20 per cent b i o t i t e , 5 to 15 per cent quartz with accessory epidote, c h l o r i t e , apatite, muscovite, sphene, tourmaline and opaques. Where pyroxene i s present i t varies from 7 to 15 per cent. A l l specimens examined i n thin section were stained i n order to detect the presence of potash feldspar, but thi s mineral was found i n only one quartz-diorite and i n very small percentages. Zoned and twinned plagioclase, forming subhedral grains up to 4 mm., i s most abundant i n the pyroxene d i o r i t e s . P l a t e XVII 101 A—Photomicrograph of pyroxene d i o r i t e showing hypersthene (hy) surrounded by diopside (D). Lot 2, concession V, Bonis township. Pl= p l a g i o c l a s e , H= hornblende, B= b i o t i t e . P l a i n l i g h t X16. B—Photomicrograph of quartz d i o r i t e , l o t 1 , concession V, Bonis township. Pl= p l a g i o c l a s e , Q= quartz, Py= pyroxene, B= b i o t i t e . Other c o n s t i  tuents include hornblende, epidote, a p a t i t e and rare K-feldspar. P o l a r  iz e d l i g h t X l 6 . Poorly zoned grains exhibit carlsbad-albite twins. In composition the plagioclase varies from An^Q to A n ^ and i n a l l but the pyroxene-bearing types i t i s moderately to highly s e r i c i t i z e d . In the more highly altered rocks the plagio clase i s partly replaced by a l b i t e . Quartz and muscovite occur as anhedral grains i n t e r  s t i t i a l to the plagioclase. Dark green hornblende occurs i n large euhedral to subhedral c r y s t a l s , most of which contain numerous inclusions. Euhedral pyroxene i s rimmed by horn- blend and/or b i o t i t e , and i n the more highly altered rocks the pyroxene i s completely replaced by hornblende. The pyroxene i s diopsidic and some grains contain a pinkish pleo- chroic core of hypersthene. B i o t i t e i s most abundant i n the pyroxene-bearing types. Hypidiomorphic-granular texture i s common but one of the quartz d i o r i t e s i s markedly unequigranular and s l i g h t l y p o r p h y r i t i c . Quartz and feldspar are fractured or crushed. Gneissic quartz d i o r i t e i s common i n l o t s 1 and 2, concession IV, Bonis township. In handspecimen, the rocks are medium-grained, greyish i n colour, and possess a promin ent gneissic banding. Some appear to have rounded porphyro blasts of feldspar while others have narrow pinkish bands up to 1/4 inch wide composed largely of feldspar and trending p a r a l l e l to the f o l i a t i o n . The gneissic d i o r i t e s appear to be large inclusions i n quartz monzonite. In t h i n section the composition i s not unlike that 103 of the quartz d i o r i t e s . Epidote and b i o t i t e are generally- more abundant and pyroxene was not seen. Cataclastic tex ture i s well-developed. Plagioclase i s twinned and zoned and has a composition i d e n t i c a l to that of the d i o r i t e s and quartz d i o r i t e s . The quartz monzonites are medium-grained, massive to w e l l - f o l i a t e d , pinkish, leucocratic to mesocratic rocks. The mesocratic v a r i e t i e s occur i n the eastern part of Bonis township, whereas the leucocratic v a r i e t i e s are confined to the outer margins of the batholith. In thin section the quartz monzonites are composed of approximately 30 to 40 per cent plagioclase, 2 to 20 per cent blue-green hornblende, 10 to 20 per cent quartz, 15 to 25 per cent K-feldspar, and accessory epidote, c h l o r i t e , b i o t i t e , sphene, apatite, and opaques. Euhedral pyroxene, rimmed by hornblende was found i n one quartz monzonite, occurring i n l o t 1, concession IV, Bonis township. K-feld spar comprises about 1/3 of the t o t a l feldspar of t h i s rock so that i t is, close to quartz d i o r i t e i n composition. In a l l the other rocks examined K-feldspar formed more than 1/3 but less than 2/3 of the t o t a l feldspar. Zoned and twinned plagioclase, varying i n composition from An 2 8 to A n ^ forms large euhedral to subhedral grains up to 3 mm. Where twinning i s well-developed, zoning i s only f a i n i l y present or absent. Nearly a l l the plagioclase i s moderately to highly s e r i c i t i z e d , the s e r i c i t i z a t i o n being most intense i n the cores of zoned c r y s t a l s . 104 Twinned microcline forms small subhedral grains, more or less i n t e r s t i t i a l to plagioclase. The microcline :.; : i s : p a r t l y replaced by a l b i t i c feldspar and where t h i s pro cess i s almost complete small blebs of microcline, a l l i n o p t i c a l continuity, are l e f t i n an a n t i p e r t h i t i c intergrowth with a l b i t e (See Plate XVTIIA). Many of the microcline grains contain small inclusions of plagioclase which have commonly: developed myrmekitic intergrowths with the micro c l i n e . Myrmekite was also seen at the contact between i n d i v  idual plagioclase and microcline grains. Quartz i s i n t e r  s t i t i a l to the feldspars and commonly replaces other minerals. Hornblende i s o p t i c a l l y i d e n t i c a l to that of the d i o r i t e s and quartz d i o r i t e s . It i s p o i k i l i t i c with i n  clusions of quartz and feldspar, and partly altered to c h l o r i t e , epidote and b i o t i t e . Most of the quartz monzonites have a hypidiormorphic- granular texture, although a few are s l i g h t l y p o r p h y r i t i c . P r e h n i t e - f i l l e d fractures were found i n one specimen near the eastera margin of the batholith. Plagioclase and horn blende appear to have c r y s t a l l i z e d early. Much of the potash feldspar and quartz c r y s t a l l i z e d a f t e r the major c r y s t a l l i z  ation period of plagioclase. Granulation of the quartz and feldspar i s rare or absent and this rock type i s generally more highly altered than the d i o r i t e s , quartz d i o r i t e s and gneissic d i o r i t e s . Rocks of granodioritic composition were found only at 105 the contact with the Bonis volcanics. They are pink, leu c o c r a t i c medium to coarse-grained, massive to porphyritic rocks, which contain abundant quartz. The granodiorites form the matrix to intrusion breccia i n Steele township and they occur as irre g u l a r dikes and masses extending into the Bonis volcanics i n both Steele and Bonis townships. Much of the bat h o l i t h outcropping along the shore of Lake A b i t i b i i n concession A, Steele township i s granodiorite, which grades into hybrid rocks at the contact with the amphibolite. Microscopic study shows the granodiorites to be com posed of approximately 45 to 50 per cent oligoclase (An28"3o) 20 per cent K-feldspar, 20 to 25 per cent quartz and access ory b i o t i t e , muscovite, epidote, hornblende, sphene, apatite, z i r c o n c h l o r i t e and opaques. The plagioclase occurs as zoned and twinned subhedral to anhedral grains which i n the massive v a r i e t i e s i s moderate l y altered to s e r i c i t e and i n the porphyritic v a r i e t i e s r e l a t i v e l y fresh. O s c i l l a t o r y zoning i s common i n the porphyritic granodiorite plagioclase. The K-feldspar i s commonly a l b i t i z e d , p a r t i c u l a r l y i n the non-porphyritic rocks. Myrmekite i s present and one specimen showed the r e c t i l i n e a r 5 type described by Spencer and attributed to dire c t c r y s t a l l  i z a t i o n . As i n the quartz monzonites, much of the K-feldspar 5 Spencer, E., Myrmekite i n Graphic Granite and i n Vein Perthite, Min. Mag., Vol. XXVII, 1945, pp. 79-98. 106 Plate XVIII Ax-Photomicrograph of quartz monzonite showing K-feldspar (Kf) replaced by a l b i t e (Ab). Lot 3j concession IV, Bonis township. Quartz (Q) hornblende, b i o t i t e , epidote, sphene and apatite are also present. Polarized l i g h t X 4 7 . B—Photomicrograph of granodiorite show ing an altered zoned plagioclase c r y s t a l . Lot 1, concession D, Steele township. Pl= plagioclase, Q= quartz, M= muscovite, Kf= K-feldspar. Epidote, c h l o r i t e , apa t i t e and sphene are also present. Polar ized l i g h t X16. appears to have c r y s t a l l i z e d after the main c r y s t a l l i z a t i o n period of the plagioclase. Hornblende, muscovite and bio t i t e are the most abundant accessories. The hornblende ~ i s partly altered to c h l o r i t e and epidote. Western Contact of the Bath o l i t h Granodioritic dikes cutting amphibolite are abundant along the shore and i n the adjacent islands of concession A, Steele township. Numerous inclusions of amphibolite are found within the granodiorite along the shore and i n places the amphibolites have been p a r t i a l l y assimilated by the granodiorite forming hybrid rocks, with a gneissic banding and containing large porphyroblasts of feldspar. No thi n section study has been made of the various hybrids developed but they are indicated on the geological map by the symbol " 4 h " . Intrusion breccia i s well-exposed i n granodiorite outcrops bordering on Northeast Bay i n lots 1 and 2 , con cession D, Steele township. Angular blocks of amphibolite up to 3 feet i n size display varying degrees of assimilation. Some of the amphibolite blocks show a mineralogical zoning with a pinkish rim, presumably containing a high proportion of feldspar, enclosing a dark green to black amphibolitic core. Other blocks contain abundant epidote, while s t i l l others show randomly oriented gneissic banding. Many of the blocks have been broken and rotated and a few are cut by irr e g u l a r granodiorite d i k e l e t s . P l a t e XIX 108 the v a r i a b l e degree of a s s i m i l a t i o n of the amphibolite blocks and the complex nature of the block i n the foreground. B — I n t r u s i o n b r e c c i a , l o t 1, con cession D, St e e l e township. Note the g r a n o d i o r i t e dikes c u t t i n g through the amphibolite gneiss i n  c l u s i o n and the apparent higher degree of a s s i m i l a t i o n of the lower part of the i n c l u s i o n . Numerous feldspar porphyry dikes, many of which have a general east-northeast trend, occur i n the Steele meta sediments along the northern shore of Northeast Bay up to four miles from the western contact of the batholith. Nearly a l l the dikes are moderately- to highly altered and some are sheared and may be off s e t by cr o s s - f a u l t s . The dikes range i n width from a few feet to about 100 feet and i n general they conform to the bedding of the metasediments, although l o c a l cross-cutting relationships e x i s t . Some of the dikes show a s l i g h t grain gradation from f i n e - to medium-grained at the margins to coarse-grained i n the centre of the dike. A few porphyry dikes, less than two feet wide cut across the bedding of the metasediments at low angles. Where the feldspar porphyry dikes are highly altered and sheared, they resemble the greywacke which they intrude and could be mistaken for conglomerate bands interbedded with 6 the greywacke. Indeed Knight et a l refer to a "conglomerate s c h i s t " occurring i n l o t 6 , concession E, Steele township. No conglomerate was found at this l o c a l i t y but sheared porphyry dikes do occur. In t h i n section the porphyry dikes are composed of about 25 to 40 per cent iron-stained carbonate, 5 to 15 per cent c h l o r i t e and accessory amounts of b i o t i t e , muscovite, apatite and p y r i t e . 6 Knight, et a l . , Abitibi-Night Hawk Gold Area, Ont. Bur. Mines, Vol. XXVIII, pt. 2 , 1919, p. 2 3 . 110 Plate XX Photomicrograph of feldspar porphyry, l o t 6, concession E, Steele township. Twinned, altered plagioclase pheno crysts (PI) l i e i n a fine-grained matrix of quartz, feldspar, s e r i c i t e , c h l o r i t e , and carbonate (Cb). Polarized l i g h t X 1 6 . I l l The plagioclase occurs as zoned and twinned euhedral phenocrysts up to 3 mm i n s i z e . It i s moderately to highly s e r i c i t i z e d and partly replaced by a l b i t e . The fresher grains appear to be about An 2^ i n composition. In the sheared porphyries the plagioclase phenocrysts are crushed, and fractured, and zoning i n the phenocrysts i s rare. Fractured phenocrysts are healed by carbonate. The remaining constituents commonly form a f i n e  grained matrix to the plagioclase phenocrysts but i n some specimens c h l o r i t e occurs i n coarse patches up to 2 mm i n size which may represent altered ferro-magnesian minerals. The r a t i o of plagioclase phenocrysts to matrix i s commonly low but i n a few specimens t h i s r a t i o i s quite high and the porphyrytic character of the rock i s not apparent i n hand- specimen. The carbonate occurring i n the feldspar porphyry dikes has been introduced as i t occurs i n veins and lenses or i t replaces other minerals. A feldspar porphyry dike cutting the metasediments at the western end of the railway cut i n l o t 3» concession E, Steele township i s only s l i g h t l y carbonatized, although i t has been sheared. It consists of euhedral plagioclase ( a l b i t i c ) phenocrysts up to 1 mm i n size set i n a f i n e  grained schistose groundmass composed mainly of quartz, c h l o r i t e and muscovite. The plagioclase phenocrysts are oriented p a r a l l e l to the s c h i s t o s i t y and they display a well-developed discontinuous patchy twinning which, according 1 1 2 to Emmons and Mann/ i s due to s t r a i n and c a t a c l a s i s . The phenocrystw are free from inclusions and some are broken. Mineralized quartz veins containing p y r i t e , pyrrhotite and chalcopyrite cut the dike i n a few places but they also appear to be deformed. Other porphyry dikes cut the Bonis volcanics along the eastern shore of Northeast Bay. Some resemble the feldspar porphyry dikes cutting the Steele metasediments i n that they are sheared and carbonatized and s t r i k e roughly east-northeast. A few quartz-feldspar porphyry dikes trend north- south and are l i t t l e a ltered, coarse i n grain and unsheared. They contain phenocrysts of quartz as well as plagioclase. Granular epidote, a mineral absent i n the feldspar por phyries, i s common. Northern Contact of the Batho l i t h The northern contact i s exposed i n only two l o c a l  i t i e s within the map-area, i n l o t 9» concession V and i n lo t 1 , concession VI, Bonis township. The northern contact of the batholith appears more regular than the western con tact with only a few porphyry dikes present and no intrusion breccia. 7 Emmons, R.C., and Mann, V., A Twin-Zone Relation ship i n Plagioclase Feldspar, i n Selected Petrogenic  Relationships of Plagioclase, Memoir 5 2 , Geol. Soc. Am., 1 9 3 3 , pp. 41-54. 113 In l o t 1, concession VI, the contact between the bat h o l i t h and the Bonis volcanics i s exposed on the side of a small rock k n o l l . The contact i s sharp and appears to dip v e r t i c a l l y . The rrock i n contact with the Bonis volcanics i s syenodioritic i n composition and grades abruptly into horn blende plagioclase hornfels developed i n the Bonis volcanics. In handspecimen the syenodioritic rock contains numerous porphyroblasts of plagioclase up to 4 mm i n size set i n a matrix predominantly composed of hornblende crystals up to 3.5 mm i n s i z e . The rock i s composed of 35 per cent zoned and twinned plagioclase porphyroblasts, 30 per cent blue-green i d i o b l a s t i c hornblende, 8 per cent quartz, 15 per cent epidote and accessory sphene, apatite and opaques. Epidote ( p i s t a c i t e ) and quartz envelope hornblende and plagioclase grains and occur as inclusions i n hornblende and plagioclase. The composition of the plagioclase i s about An 2 3 but the cores of zoned porphyroblasts appear to be more sodic. The texture i s granoblastic. Summary of the Sargeant Bat h o l i t h The p r i n c i p a l rock types of the Sargeant batholith, as exposed within the map-area, are f o l i a t e d quartz d i o r i t e and quartz monzonite. Hornblende and pyroxene d i o r i t e s possibly developed by the assimilation of amphibolite, occur l o c a l l y i n association with the quartz d i o r i t e s . At the western contact of the batholith i n Steele township the rocks 114 are more acid.O, consisting mainly of granodiorite. The occurrence of intrusion breccia at the western contact of the batholith, together with numerous amphi- b o l i t i c inclusions, within the body of the batholith, the zone of hornfels developed along an apparently sharp northern contact, the many granodiorite and porphyry dikes extending into the Bonis volcanics from the batholith, and the lack of migmatites i n the associated country rock, p a r t i c u l a r l y i n the metasediments, are a l l features strongly suggestive of an intrusive o r i g i n for the Sargeant batholith. Altered and sheared feldspar porphyry dikes occurr ing i n the Steele metasediments were probably an early manifestation of the b a t h o l i t h and they were sheared and altered as a result of the main intrusion of the batholith. The north-south quartz-feldspar porphyry dikes appear to have been emplaeed after the main period of intrusion of the Sargeant batholith. The concordant nature of the altered feldspar porphyry dikes with the Steele metasediments and the apparent o v e r a l l e l l i p t i c a l shape of the intrusion, with i t s long axis trending p a r a l l e l to the regional s t r u c t  ure of the metasediments and metavolcanics, suggests that the b a t h o l i t h i s a concordant intr u s i o n . The writer i s of the opinion that the b a t h o l i t h is s i m i l a r to the circumscribed g r a n i t i c plutons described by Read 8 and other European geologists. These plutons are 8 Read, H.H., The Granite Controversy, Inter- science Publishers, Inc., 1957. 115 supposedly formed from a semi-crystallized viscous magma moving past mostly stationary walls and make their way into the country rocks, by "plain pushing and shoving." Such an o r i g i n for the Sargeant batholith would account for many of the features noted within the map-area. The more acid character of the batholith near i t s western margin may be due to post-intrusion a l t e r a t i o n or to d i f f e r e n t i a t i o n of the magma. Not enough data are available to decide between the two alternatives but the a l b i t i z a t i o n of the K-feldspar and rarely of the plagioclase feldspar, plus the general o v e r a l l altered nature of the rocks suggests comparison with the Bourlamaque-Granodiorite 9 b a t h o l i t h i n Quebec, described by Gussow. The o r i g i n a l quartz-gabbro of the Bourlamaque bat h o l i t h was altered to a l b i t e - t o n a l i t e by sodic hydrothermal solutions, guided by shear and breccia zones. CASE BATHOLITH The g r a n i t i c rocks occurring i n the northern part of Steele township are considered to be part of a large batho l i t h centred i n Case township to the north of Steele. The name Case batholith i s proposed for t h i s mass. The f u l l extent of the bath o l i t h i s unknown, but from reconnaissance surveys made by the writer during the 1959 f i e l d season, i t 9 Gussow, W.C., Petrogeny of the Major Acid In trusives of the Rouyn-Bell River Area of North Western Quebec. Trans. Roy. Soc. Canada, 1937, Sec. 4, pp. 129-161. 116 i s known to extend at least 10 miles to the northwest of the northern boundary of Steele township and to underlie much of Case township. Within Steele township the rocks comprising the bat h o l i t h range i n composition from leucogranodiorite near the contact with the Scapa metasediments, to leucocratic quartz monzonite away from the Scapa metasediments. The rocks are pink i n colour, massive and coarse-grained. Numerous pegmatite dikes and ir r e g u l a r pegmatitic patches occur i n the granodiorites and quartz monzonites. A pegmatite dike occurring i n quartz monzonite i n lo t 5} concession V contains spodumene, columbite-tantalite and molybdenite. Pegmatites occurring i n the metasediments and metavolcanics near the contact with the Case ba t h o l i t h i n l o t s 8 to 12, concession IV, Steele, commonly contain scattered plates of molybdenite but no spodumene or colum b i t e - t a n t a l i t e was found i n them. A l b i t i z e d quartz-feldspar porphyry dikes and f e l d  spar porphyry dikes are abundant i n the Scapa metasediments both i n Steele and Scapa townships. A few also occur i n the Steele Lake volcanics. The porphyry dikes s t r i k e p a r a l l e l to the regional structure. They d i f f e r from the porphyry dikes associated with the Sargeant batholith i n containing abundant K-feldspar and rare accessory r u t i l e . The composition of the granodiorite i s approximately 50 to 55 per cent plagioclase (An28) 5 15 to 25 per cent 117 quartz, 7 to 15 per cent K-feldspar and accessory epidote, muscovite, b i o t i t e , c h l o r i t e , sphene, zi r c o n , apatite, tourmaline and rare opaques. The percentages of K-feldspar were estimated from stained specimens. Some of the granodiorites are porph y r i t i c , con taining large phenocrysts of plagioclase. In a l l the grano d i o r i t e s the plagioclase occurs as euhedral to subhedral, twinned and zoned grains up to 3 mm. i n siz e . In twinned grains alternate twin lamellae are s e r i c i t i z e d , suggesting a difference i n composition between adjacent twin lamellae. Some of the plagioplase i s replaced by a l b i t e . The K-feldspar i s both twinned and untwinned and p e r t h i t i c . Film, s t r i n g , rod, patch and vein perthite occur i n both twinned and untwinned K-feldspar. Where a l b i t e has almost e n t i r e l y replaced K-feldspar grains ant i p e r t h i t e i s formed. The K-feldspar i s finer-grained than the plagio clase and myrmekite i s found developed at grain contacts between these minerals. Quartz occurs as anhedral grains, many of which are strained and fractured with the fractures commonly abutting against adjacent plagioclase and K-feldspar grains. Un- fractured and unstrained quartz heals the fractures commonly. Both quartz and K-feldspar are i n t e r s t i t i a l to plagioclase, indicating they c r y s t a l l i z e d after the main c r y s t a l l i z a t i o n period of the plagioclase. Adjacent to a p l i t i c and pegmatitic dikelets and veins cutting the P l a t e XXI Photomicrograph of quartz monzonite showing myrniekite developed i n a small i n c l u s i o n of p l a g i o c l a s e i n K- f e l d s p a r . Lot 9, concession V I , S t e e l e township. Q= quartz. P o l a r i z e d l i g h t X16. 119 granodiorites the plagioclase, K-feldspar and quartz are a l l markedly fractured and crushed. The a l b i t e occurring i n these rocks i s large l y due to replacement. The f i l m and str i n g perthites are probably due to exsolution. The composition of the quartz monzonites i s approx imately 25 to 35 per cent plagioclase (An 2^_ 2g), 3° t o 4 0 per cent K-feldspar, 25 to 35 per cent quartz and accessory muscovite, b i o t i t e , c h l o r i t e , apatite, zircon and opaques. As i n the case of granodiorite the percentage of K-feldspar was estimated from stained specimens. The character of the plagioclase, quartz and K- feldspar i s e s s e n t i a l l y the same i n the quartz monzonites as in the granodiorites. Inclusions of K-feldspar i n plagio clase are common, however, and i n places quartz and plagio- clase inclusions were seen i n K-feldspar. Thin rims of sodic plagioclase were noted on some borders of plagioclase grains. The thin rims are both twinned and untwinned with the rest of the in d i v i d u a l plagioclase grains. Sodic plagio clase borders are especially common around plagioclase inclusions i n K-feldspar. Most of the perthite seen i s of the exsolution variety ( f i l m s t r i n g and rod perthite) and i n general, a l b i t i z a t i o n i s less pronounced i n the quartz monzonites than i n the granodiorites. The rocks are fresh but a l l the quartz and feldspar i s fractured adjacent to pegmatitic d i k e l e t s . 120 B i o t i t e and muscovite form large conspicuous grains i n the quartz monzonites and together they form as much as 10 per cent of the rock. Some rocks contain l i t t l e or no b i o t i t e , but abundant muscovite, and i n others, the reverse rela t i o n s h i p holds. Although accessory epidote i s common i n the grano d i o r i t e s , none was found i n the quartz monzonites examined i n t h i n section. Homogeneous hybrid rocks occur i n a number of places within the batholith, p a r t i c u l a r l y at or near the contact with the Scapa metasediments. A l l these rocks are porphyro- b l a s t i c and they contain no K-feldspar. They are es s e n t i a l l y quartz-plagioclase rocks but a l l contain minor blue-green hornblende and greenish brown b i o t i t e . The composition of the hybrid rocks i s approximately 55 to 70 per cent plagioclase (An^..-^)» 15 to 20 per cent quartz, 10 to 12 per cent b i o t i t e , 2 to 8 per cent hornblende, and accessory c h l o r i t e , sphene, apatite and epidote ( p i s t a c i t e with cores of a l l a n i t e ) . The plagioclase occurs as twinned and zoned anhedral porphyroblasts and i d i o b l a s t s , up to 3 mm. i n size i n a f i n e  grained matrix of quartz, plagioclase, b i o t i t e , hornblende and the accessories. B i o t i t e frequently envelopes plagio clase porphyroblasts. Inclusions of p a r t i a l l y assimilated metasediments are commonly associated with the hybrid rocks and i t would appear that the hybrids owe the i r o r i g i n to the mixing of 1 2 1 sedimentary material with the "magma" of the batholith. No detailed study was made of the pegmatites, a l  though sp e c i a l attention was given to those containing minerals of economic signi f i c a n c e . The pegmatites vary widely i n size and shape. Some are tabular or di k e - l i k e i n form, others are quite i r r e g u l a r . The pegmatite-dikes occurring within the batholith range i n width from less than one inch to about 100 feet. Sharp contacts of many of the dikes suggests intrusion into the host rocks (granodiorite and quartz monzonite). In thin section the rock adjacent to the dikes i s invariably fractured and embayed by a p l i t i c material which commonly forms a border phase to the peg matites. The o r i g i n of the irregular pegmatitic bodies i s unknown. Both the irr e g u l a r masses and dikes of pegmatite are more or less evenly d i s t r i b u t e d throughout the Case ba t h o l i t h i n Steele township. The largest dikes were found near the contact with the Scapa metasediments. The contact between the pegmatite and a p l i t e i s gradational. The border phase i s commonly scalloped and contains trains of garnet. Hexagonal quartz grains, and plates of muscovite up to two inches i n size are conspicuous constituents of the pegmatites i n handspecimen. The spodumene-hearing pegmatite dike occurring i n lo t 5j concession V i s complex 1 0 and zoned. This i s the 10 Complex i n the sense of Landes (Am. Min., v o l . 1 8 , 1933, P P . 95-103). 122 Plate XXII Spodumene-bearing pegmatite dike, l o t 5, concession V, Steele township. only complex pegmatite noted within the batholith. The peg matite displays a narrow a p l i t i c border phase i n places and contains numerous quartz-rich patches which appear to form the core of the pegmatite. Spodumene crystals up to 3 feet long and 6 inches across are most abundant i n the quartz- r i c h patches. Columbite-tantalite, muscovite and tourmaline are found with the spodumene. Molybdenite i s rare. Pegmatites occurring i n the Steele Lake volcanics and Steele metasediments i n the v i c i n i t y of lots 7 to 11 , concession IV, Steele township, are composed larg e l y of coarse quartz with only minor amounts of feldspar and mica. Molybdenite i s sparsely distributed i n these pegmatites, usually i n association with a p l i t i c and feldspathic portions of the pegmatite. In summary, the Case b a t h o l i t h as exposed i n Steele township i s decidedly more acid than the Sargeant batholith. The porphyry dikes associated with the Case bat h o l i t h d i f f e r s i g n i f i c a n t l y from those associated with the Sargeant batho l i t h i n containing appreciable K-feldspar. The pegmatitic character of the Case batholith i s also i n marked contrast to that of the Sargeant batholith. The development of a contact metamorphic aureole, an apparent concordance with the intruded rocks, and lack of associated migmatites suggest that the Case bat h o l i t h may also be a circumscribed pluton. It may therefore belong to the same orogenic cycle as the Sargeant batholith. 124 The apparent differences i n composition between the Case and Sargeant batholiths may be due to o r i g i n a l d i f f e r  ences i n the i n i t i a l magmas giving r i s e to the batholiths. However both batholiths could conceivably have been derived from a common magma i n which case the compositional d i f f e r  ences could be brought about by the diff e r e n t contamination effects of sediment as opposed to basic to intermediate lava. SCAPA STOCK The Scapa stock i s composed of a medium-grained, massive, uniform, pink, leucogranite. The composition of the granite i s approximately 40 to 45 per cent K-feldspar (mainly twinned microcline) 25 per cent plagioclase, 20 to 25 per cent quartz, 6 to 10 per cent b i o t i t e , and accessory muscovite, c h l o r i t e , epidote, sphene, zircon and opaques. The percentages of K-feldspar vwsere estimated from stained handspecimens. The K-feldspar i s p e r t h i t i c . String and rod per- thi t e s are common, as well as patch and vein v a r i e t i e s . The former two types are thought to be formed by exsolution, whereas the l a t t e r two types by replacement. The anhedral K-feldspar i s intergrown with, and i n t e r s t i t i a l to, plagio clase. Myrmekite has been developed at the junction of some plagioclase and microcline grains, as well as i n inclusions of twinned plagioclase i n K-feldspar. The plagioclase i s subhedral to anhedral, occurring 125 Plate XXIII Photomicrograph of the Scapa stock leuco- granite. Q= quartz, B= biotite-, Kf= K-feldspar, Pl= plagioclase. Polarized l i g h t X16. i n well-twinned and zoned grains up to 1.5 mm. i n s i z e . Most of the plagioclase i s s e r i c i t i z e d and i n many places i t i s partly replaced by a l b i t e . The composition i s about Ah 2^. Quartz, which occurs as anhedral grains, i s i n t e r  s t i t i a l to both the feldspars. The b i o t i t e has a reddish-brown to brownish-green pleochroism and appears to be partly altered to c h l o r i t e . It commonly contains inclusions of zircon and epidote ( p i s t a  c i t e with a l l a n i t e cores). The granite has a hypidiomorphic-granular texture. Plagioclase probably began to c r y s t a l l i z e early, followed by concomittant c r y s t a l l i z a t i o n of plagioclase and K-feld spar. The a l t e r a t i o n i n the rock may have been deuteric i n part. The acid character of the Scapa stock suggests i t may be a s a t e l l i t i c off-shoot of the Case batholith. IAMPROPHYRE A few highly altered, rusty-weathering, greenish- grey rocks, which occur as dikes intruding the Steele meta sediments along the northern shore of Northeast Bay are grouped together under the general heading lamprophyre. The o r i g i n of these rocks and the i r o r i g i n a l character are unknown. The dikes are commonly less than 2 feet wide, a l  though one dike measured about 3.5 feet. 127 In thin section a sample collected from l o t 7, concession E, Steele township, was found to consist of approximately 30 per cent carbonate, 30 per cent quartz, 25 per cent c h l o r i t e , 15 per cent muscovite, and rare b i o t i t e and opaques. A l l the minerals occur as a medium-grained massive aggregate and a l l but carbonate and muscovite, are anhedral. The muscovite occurs as randomly oriented laths, while the carbonate i s found as small rhombs. A few i r r e g u l a r quartz ve i n l e t s also cut the rock. The relationship between the lamprophyre(?) and the i n t r u s i v e rocks i s not known. The dike rocks could be re lated to either the ultrabasic and basic intrusives or to the acid i n t r u s i v e s . In one l o c a l i t y a lamprophyric dike was noted to be o f f s e t by a shear zone i n the Steele meta sediments. No lamprophyric rocks were found i n the Steele metasedi ments north of Lake A b i t i b i , i n the Scapa sediments, or i n the metavolcanic rocks. LATE BASIC INTRUSIONS Diabase dikes trending north and northeast and ranging i n width from a few feet to 460 feet intrude a l l other rocks within the map-area. The dikes cut cleanly across the various rock units and have sharp c h i l l e d con tac t s , with fine-grained, glassy margins and medium to coarse-grained centres. No evidence of stoping or re placement was found and each i n d i v i d u a l dike has a uniform composition. Where the dikes cut the bedding of metasedi- mentary rocks at oblique angles the metasediments have been displaced at right angles to the walls of the dike. The dikes are sinuous along s t r i k e and t h e i r dip i s v e r t i c a l or nearly so. There appears to be no relationship between the regional structure developed i n the e a r l i e r rocks and the o r i e n t a t i o n of the diabase dikes. Numerous workers i n mapping areas to the south and southwest of Lake A b i t i b i have noted the same trend i n late diabase dikes as noted above. Invariably the north-trending group i s cut by the northeast-trending group and i s there fore older. No exposed intersections of the dikes were found within the map-area but i t i s inferred from the areas to the south and southwest that the north-trending group i s the older. Accordingly, t h i s group i s calle d early diabase and the other late diabase. Within northeastern Ontario the e a r l i e r diabase i s commonly referred to as Matachewan i n age and the l a t e diabase as Keweenawan i n age. In handspecimen the early and late diabase are much a l i k e . They a l l weather a c h a r a c t e r i s t i c "foxy"-brown colour, which i s s l i g h t l y more pronounced i n o l i v i n e diabase. In addition purplish augite and coarse magnetite grains are read i l y seen only i n the o l i v i n e diabase. Diabasic texture i s well-developed i n a l l but the fine-grained v a r i e t i e s found at the margins of the dikes. 129 The early diabase dikes are a l l quartz diabase, containing andesitic labradorite (An^ Q) i n micrographic intergrowths with quartz and o p h i t i c a l l y intergrown with euhedral to subhedral augite. P y r i t e and magnetite are also present, the former mineral f i l l i n g fractures i n plagio clase laths. Most of these rocks are more or less altered, the augite i s u r a l i t i z e d and c h l o r i t i z e d , plagioclase i s saussuritized and b i o t i t e i s found i n association with the opaques.minerals. The l a t e diabase dikes are diabase and o l i v i n e diabase. The dike s t r i k i n g through Steele and Scapa town ship i s diabase, whereas the one i n Bonis township i s o l i v i n e diabase. In thin section the diabase i s moderately to highly altered and secondary quartz i s present. The plagioclase i s more c a l c i c than i n the quartz diabases, about An^g^Q. The amount of quartz present varies with the degree of a l t e r a t i o n . Where the plagioclase i s intensely saussurit ized up to 4 per cent quartz occurring i n i r r e g u l a r blebs, but never i n micrographic intergrowths, i s found. Augite i s commonly altered to serpentine and c h l o r i t e and the opaque constituents are rimmed by sphene, indicating the presence of t i t a n i f e r o u s magnetite or ilmenite. P y r i t e i s also found. P l a t e XXIV A—Photomicrograph of o l i v i n e diabase, l o t 7, concession I I , Bonis township. A= a u g i t e , 0= o l i v i n e , Pl= p l a g i o c l a s e . P o l a r i z e d l i g h t X16. B—Photomicrograph of quartz diabase showing micrographic intergrowths of quartz and p l a g i o c l a s e . P o l a r i z e d l i g h t X47. 131 The o l i v i n e diabase d i f f e r s l i t t l e from the ordinary- diabase, except for the presence of up to 15 per cent o l i v i n e , occurring i n fresh to highly altered granular grains. The plagioclase has a composition of about A n ^ j s l i g h t l y more c a l c i c than that of the ordinary diabase. Magnetite, common ly rimmed by b i o t i t e i n altered v a r i e t i e s comprises up to 10 per cent of the whole. Pyrite i s rar e l y seen. Augite has a reddish to s l i g h t l y v i o l e t pleochroism (titanaugite?), and frequently forms reaction rims about o l i v i n e , indicating the o l i v i n e began to c r y s t a l l i z e before augite. Both o l i v i n e and augite are o p h i t i c a l l y intergrown with plagioclase. The plagioclase i n a l l the diabases is. well twinned and zoning i s not uncommon. 11 J . E . G i l l and R.L 1Esperance i n a review of diabase dikes of the Canadian Shield have summarized the various suggestions put f o r t h to account for the o r i g i n of quartz and o l i v i n e diabase. The best hypothesis appears to be one involving d i f f e r e n t i a t i o n of a uniform b a s a l t i c magma during c r y s t a l l i z a t i o n . The dikes formed from magmas injected along fractures brought about either by pressure transmitted through the magma or by external tensional forces acting across the fractures or both together. 11 G i l l , J.E., and L 1Esperance, R., Diabase Dikes i n the Canadian Shield, Trans. Roy. Soc. Canada, Vo l . XLVI, Sec. 4 , 1952, pp. 25-36. CHAPTER V STRUCTURAL GEOLOGY  GENERAL FEATURES Much of the data used i n the interpretation of the st r u c t u r a l geology came from outcrops exposed along the lake, i n roads, and at the bases of overturned trees. The general s t r u c t u r a l relations are summarized i n Figure 3» which shows the po s i t i o n of s t r u c t u r a l trend l i n e s based upon measured attitudes of bedding and/or s c h i s t o s i t y , the s t r i k e of secondary cleavage possibly developed as the result of the intr u s i o n of the batholiths, and a l l top determinations made. The metavolcanic-metasediment assemblage can be divided s t r u c t u r a l l y into two main units. The Bonis v o l  canics which face to the north, comprise one unit, and the Steele metasediments, Steele Lake volcanics and Scapa meta sediments face south and together comprise the second unit. Both units are steeply inclined and have undergone folding and compression caused by the intrusion of the batholiths and the Scapa stock. The s t r i k e of s c h i s t o s i t y and bedding i n the assem blage ranges from S.70°E. i n northern Steele township to east i n Scapa township. The Steele metasediments along the shore of Northeast Bay have a general N.70°E trend. The Bonis volcanics are markedly deformed around the western margin of the Sargeant batholith. 133 No conclusive evidence could be obtained to i n d i  cate i n which d i r e c t i o n the Steele Lake volcanics face. Because they appear to be interbedded with the metasediments which i n turn appear to face south, i t i s tenta t i v e l y con cluded that the Steele Lake volcanics overly the Scapa metasediments and are themselves overlain by the Steele metasediments. From the above i t would appear that the second unit forms a monoclinal structure facing south. However, the evidence i s too incomplete to form such a conclusion. It. i s a good p o s s i b i l i t y that major folds do exist within this unit which would complicate the stratigraphy and make the general relationship between the rock units considerably more complex than indicated. No closures are apparent within the metavolcanic- metasediment assemblage which suggest that the assemblage as a whole, does not plunge steeply. Drag folds and line a t i o n s plunge steeply to the east. FAULTS Numerous small faul t s were noted i n many of the meta sediment outcrops examined. In general two main sets appear to be present, a northeast and a northwest-trending set. The northeast set i s better developed than the northwest and i n a few outcrops the northeast set was noted to cut across and displace the northwest set. Left-handed movement i s 134 LEGEND SYMBOLS + + + 1 + + + ACID INTRUSIVES i TOP DETERMINATION IN SEDIMENTS SECONDARY CLEAVAGE METASEDIMENTS ^ TOP DETERMINATION IN VOLCANICS •gf | DRAG FOLDS (ARROW INDICATES DIRECTION OF PLUNGE) i l l 11 I • ' I I " I i . II METAVOLCANICS GEOLOGICAL BOUNDARY -*J0- PLUNGE OF LINEATION STRUCTURAL TREND LINES Figure 3 . Sketch map showing the structural geology of Steele, Bonis and Scapa townships. Scale: 1 inch to 2 miles. Plate XXV Northeast-arid northwest-trending faults i n an outcrop i n eastern Scapa township. The dark layer i s a narrow basic s i l l . Note that the north-east set ( o f f s e t t i n g the basic s i l l ) i s better developed than the northwest set. 136 common i n the northeast set, and right-handed movement pre dominates i n the northwest set. Plate XXV shows the t y p i c a l development of these f a u l t s as seen i n the outcrop. Other f a u l t i n g , indicated by mylonite zones, occurs i n l o t 1, concession E, and l o t 9 5 concession D, Steele township and at the northern boundary i n the northeast corner of Scapa township. In the l a t t e r l o c a l i t y the mylon i t e zone i s about 1/2 inch wide while i n the other two l o c a l  i t i e s i t i s 1/2 to 3 feet i n width. In each case the mylon i t e zones s t r i k e p a r a l l e l to the trend of the enclosing rock. Other small f a u l t s were seen near some of the contacts be tween the ultrabasic and basic intrusives and the Bonis volcanics, along the eastern shore of Northeast Bay. Numerous shear zones p a r a l l e l l i n g the regional trend of the metavolcanic-metasediment assemblage were found i n the Steele Lake volcanics and the Steele and Scapa metasediments. These range greatly i n width from a few inches to many feet. The largest and most consistent were found i n the Steele Lake volcanics where they appear to be related to incompetent zones within the volcanics and probably formed as a result of stress exerted on the volcanics during folding and the intr u s i o n of the batholiths. The largest shear zone (up to 700 feet wide) occurs near the southern contact with the Steele metasediments. A l l the shear zones within the Steele Lake volcanics are mineralized and can readily be seen i n 137 the outcrop owing to the development of rusty gossans. The shear zones dip steeply and many are v e r t i c a l . The reversal of attitudes found i n the Steele meta sediments and Bonis volcanics near th e i r contact i s suggest ive of a f a u l t , possibly a thrust f a u l t . The Bonis volcanics are highly deformed and possess a poorly developed cata- c l a s t i c texture near the assumed contact. The Steele meta sediments are markedly sheared i n the railway cut immediately west of the assumed contact and both the Bonis volcanics and Steele metasediments are moderately to strongly carbon- atized there. A l l these features are suggestive of a f a u l t but they may also be explained i n part by the intrusion of the porphyry dikes into the Steele metasediments, and to contact effects i n the outer part of the contact zone with the Sargeant batholith. However i f a f a u l t was formed at the contact between the Bonis volcanics and the Steele meta sediments as a result of the intrusion of the Sargeant batho l i t h i t would be d i f f i c u l t to explain the reversal i n a t t i t u d e . It i s more l i k e l y that this reversal i s the result of thrust f a u l t i n g coupled possibly with folding prior to the i n t r u s i o n of the batholith. It i s improbable that s t r i k e f a u l t i n g would bring the two units together with t h e i r present attitudes. The northeast-trending diabase dike occurring i n 138 Scapa township i s apparently cut by a northeast f a u l t near the eastern boundary of the township. The evidence for the fa u l t was obtained mainly from a i r photographs. The fa u l t occupies a narrow gully to the east of which the dike i s sharply dragged to the south. To the west of the f a u l t the dike l i e s about 200 feet north of i t s position on the east ern side. The o f f s e t of la t e diabase dikes by northeast-trend ing f a u l t s has been noted i n Quebec"1" and f a u l t i n g of the diabase dikes occurring to the south of Lake A b i t i b i appears to be common. STRUCTURES RELATED TO THE ACID INTRUSIONS The.regional structure of the metavolcanic-meta sediment assemblage has been sharply deflected around the western end of the Sargeant batholith. Both the Sargeant and Case batholiths appear to be concordant with the meta- volcanics and metasediments. The shape of the Case batholith i s not known but the Sargeant bat h o l i t h i s roughly e l l i p t i c a l i n plan with i t s long axis trending p a r a l l e l to the regional structure. P l o t t i n g the planes of s c h i s t o s i t y , occurring i n the. Bonis volcanics, on a stereogram shows that these rocks 1 G i l l , J.E., The Canadian Precambrian S h i e l d , Jubilee Volume. Can. Inst., Min. Met., 1948, p. 29. 139 plunge steeply around the western margin of the Sargeant bath o l i t h . The steep plunge i s probably due to the intrusion of the batholith. ' The Scapa stock has highly crumpled and folded the metasediments at i t s contact but does not appear to have had any marked effects on the general trend of the metasediments• away from the contact. The metasediments display e r r a t i c dips i n the contact zone, although near the western end of the in t r u s i o n the bedding appears to dip about 40° towards the contact. This body i s probably a concordant intrusion. Numerous smaller structures have been formed i n the metasediments and metavolcanics possibly as a result of the int r u s i o n of the batholiths. A regional or secondary cleav age occurs i n the metasediments and ultrabasic and basic i n t r u s i v e s , p a r t i c u l a r l y i n the v i c i n i t y of the Sargeant bath o l i t h and the borders of the Steele Lake volcanics. The s t r i k e of the cleavage trends east-northeast. JOINTING Jointing was noted i n a few places. From the few readings made i t appears that there are two major sets, one s t r i k i n g to the north and dipping nearly v e r t i c a l l y and the second l y i n g h o r i z o n t a l l y and. approximately at right angles to the f i r s t . 140 CHAPTER VI CEN0Z0IC  PLEISTOCENE During the Pleistocene Epoch four g l a c i a l stages occurred south of the Great Lakes. Within the map-area record of only the l a s t stage, the Wisconsin ice-sheet i s found. When the ice-margin of this ice-sheet had retreated from south of the Great Lakes to a point beyond the contin ental divide, north of the Upper Great Lakes, g l a c i a l Lake Barlow-0jibway was impounded between the height of land and the retreating ice-margin. This lake expanded northward be yond the map-area and attained a maximum width of 150 miles and a length of about 600 miles."1" Lake A b i t i b i i s one of the larger remnants to be found i n the clay belt of Northern Ontario of g l a c i a l Lake Barlow-0jibway. Before the g l a c i a l lake drained completely, a re- advance of the ice-sheet (Cochrane advance) occurred from a point at least 35 miles north of the town of Cochrane. The southern l i m i t of the advance has not been completely mapped. No in d i c a t i o n of the Cochrane advance was found i n the map- area. 1 Geology and Economic Minerals of Canada, Economic  Geology S e r i e s . No. 1 (4th ed), Geol. Surv. Canada, 1957, p. 480. 141 Figure 4. Sketch map of the Pleistocene geology of the map- area showing the latest movement of the Wisconsin ice-sheet and the d i s t r i b u t i o n of g l a c i a l , g l a c i o - f l u v i a l , and Barlow-0jibway deposits. 142 p O.L. Hughes, i n mapping the s u r f i c i a l geology to the west of Steele township, has divided the Pleistocene de posits into several categories, most of which were recognized within the map-area. These deposits are described below and t h e i r d i s t r i b u t i o n i s shown i n Figure 4. The average of some 70 readings of g l a c i a l s t r i a e obtained from storm-washed outcrops along the shores of Northeast Bay indicate that the l a t e s t d i r e c t i o n of movement of the Wisconsin ice-sheet was S.9°E. Glaeiali.striae were noted on inland outcrops only i n l o t 5 5 concession I I I , Steele township and the d i r e c t i o n measured agrees with that determined from the s t r i a e on outcrops along the lake shore. In addition, the orientation of modified g l a c i a l deposits and eskers also indicate that the l a t e s t movement of the i c e - sheet was south-southeast. The l a t e s t d i r e c t i o n of movement of the ice-sheet, as determined within the map-area, agrees favourably with that determined by Hughes. GLACIAL DEPOSITS G l a c i a l deposits were seen on the flanks of many of the bedrock exposures and they are p a r t i c u l a r l y well scattered about Steele ridge, both i n Steele and Scapa townships. Most of the g l a c i a l deposits have been modified by wave- action of g l a c i a l Lake Barlow-0jibway to large concentrates of boulders and i n places to beach deposits of boulders and 2 Hughes, O.L. S u r f i c i a l Geology, Iroquois F a l l s , Cochrane D i s t r i c t , Ontario, Map 46-1959. Geol.Sur.Canada,1959. P l a t e XXVI A — G r a v e l p i t i n the prominent esker s t r i k i n g south through the centre of the map-area. Lot 11, concession V, Bonis township. B — S t r a t i f i e d g r a v e l as seen i n a g r a v e l p i t on the southern slope of Steele r i d g e . Lot 2 , concession I I , S t e e l e township. 144 gravel. Examples of the l a t t e r type of deposit occur i n lot s 2 and 3 , concession VI, Steele township. GLACIOFLUVIAL DEPOSITS The main g l a c i o f l u v i a l deposits are the prominent esker i n the centre of the map-area, l y i n g immediately to the east of the eastern boundary of Steele township and the small esker i n the south-central part of Scapa township. Both eskers have been more or less modified, presumably by the waters of g l a c i a l Lake Barlow-0 jibway.. Numerous Karnes were seen i n the northwestern corner of Steele township and scattered through the apron extending south from Steele ridge i n Steele township. Some of the sand and gravel deposits adjacent to the southern slope of Steele ridge i n Steele township are s t r a t i  f i e d and may be i n part of g l a c i o f l u v i a l o r i g i n . BARLOW-OJIBWAY VARVED CLAY Varved clay, deposited i n g l a c i a l Lake Barlow- Ojibway by subglacial streams, underlies most of the area. Varved clay i s p a r t i c u l a r l y abundant i n southern Steele town ship and i n Bonis and the southern part of Scapa townships. Varved clay lapped up onto the flanks of the eskers was noted i n road cuts along the main haulage road i n l o t 11, concession V, Bonis township, and i n Scapa township. Fine sand and s i l t were seen interbedded with the varved clays 145 where they lap the flanks of the eskers. Thin beds of s i l t also occur intercalated with the varved clays i n the north- central portion of Bonis township. BARLOW-0JIBWAY SAND AND GRAVEL The triangular apron extending south from the south ern slope of Steele ridge appears to o v e r l i e the varved clay i n many places. The apron probably originated from sand and f i n e gravel washed from the g l a c i a l and g l a c i o f l u v i a l deposits bordering Steele ridge by the waters of g l a c i a l Lake Barlow-0jibway. Sand deposits overlying clay on the flanks of the eskers probably have, a similar o r i g i n . Other sand and gravel deposits north of Steele ridge i n Steele township may also have originated from the wave-action of Lake Barlow-0jibway but owing to t h e i r poor exposure i t could not be confirmed that these deposits o v e r l i e the clay. The sparse d i s t r i b u t i o n of sand and gravel along higher elevations i n Steele ridge and a few of the other rock knobs occurring i n the map-area suggests that these were at one time islands i n g l a c i a l Lake Barlow-0jibway. The beach deposits noted i n l o t s 2 and 3> concession VI, Steele town ship are at a lower elevation than the bare rock knobs along Steele ridge. This indicates that the g l a c i a l lake probably shallowed considerably as the resu l t of i s o s t a t i c adjustments following the retreat of the ice-sheet and was broken up into several smaller lakes. Case Lake could be a remnant of such a lake. 146 RECENT Recent deposits consist mainly of woody sphagnum peat and other organic material now c o l l e c t i n g i n the swamps and muskegs. Boulder gravel, sand, and pebble gravel beaches are being formed along the shores of Northeast Bay and some d e t r i t a l material i s also being deposited along stream v a l l e y s . CHAPTER VII ECONOMIC GEOLOGY Prospectors and exploration companies have been active i n the map-area for more than 50 years. Stripping, surface trenching, diamond d r i l l i n g , air-borne and ground geophysical surveys, and geochemical surveys have been carried out but no deposits of economic value have, as yet, been proved. Most of the exploration work has been confined to the areas underlain by the metavolcanic rocks. SULPHIDE MINERALIZATION Sulphide mineralization occurs mainly as replacement deposits i n shear zones and i n association with quartz veins i n the metavolcanics. Minor amounts of p y r i t e , pyrrhotite, and chalcopyrite are found i n quartz v e i n l e t s cutting por phyry dikes. The majority of mineralized quartz veins were seen within the contact zone between the Bonis volcanics and the Sargeant batholith. The veins are commonly less than 3 inches wide and i r r e g u l a r , with scattered p y r i t e , and rare chalcopyrite and pyrrhotite mineralization occurring near the i r walls. Molybdenite i s rare i n quartz veins cutting the Steele Lake volcanics. F i f t y mineralized and concordant shear zones, ranging from less than one foot to 350 feet wide, were mapped i n the Steele Lake volcanics. The shear zones are most abundant 148 near the northern and southern contacts with the metasediments and the widest shear zones occur near the contact with the Steele metasediments i n l o t s 2 and 3, concessions II and I I I , Steele township. ..Shear zones are also well-developed near the metasediment interbedded with the volcanics. Here and there, the shear zones appear to have formed i n the v i c i n i t y of flow contacts. The longest shear zone mapped measured about 1900 feet along s t r i k e but most are considerably shorter than t h i s . Although some shear zones may be continuous with one another, most appear to be unrelated and to grade abruptly into non-sheared volcanics. Mineralization within the shear zones consists mainly of massive and disseminated p y r i t e and pyrrho t i t e , occurring as layers up to 8 inches ,wide and con cordant with the s t r i k e and dip of the shear zones. Chalco- p y r i t e i s rare and sphalerite very rare. S i l i c i f i e d massive rocks, alternating with amphibole, c h l o r i t e , and mica-rich s c h i s t s , and quartz stringers occur i n the shear zones. Narrow trains of garnet are common i n the s i l i c i f i e d rocks but rare i n the sch i s t s . The meta- - volcanics adjacent to the shear zones are s i l i c i f i e d and markedly amphibolitized. Twenty-four grab samples taken from shear zones showed only traces of copper, lead, z i n c , n i c k e l , gold and cobalt, upon assay. The low assays appear to confirm the apparent s c a r c i t y of. copper, lead, and zinc mineralization 149 noted i n the outcrop and they further indicate that n i c k e l and gold are not present i n economic proportions. IRON The iron-formation occurring i n the Scapa meta sediments i s of very low grade and limited i n extent, with most of the iron occurring i n the form of s i l i c a t e s . It i s not at present of economic i n t e r e s t . LITHIUM The most interesting rock i n the map-area from an economic standpoint, appears to be the complex pegmatite occurring i n the Case bat h o l i t h i n l o t 5» concession V, Steele townhip. The pegmatite has been described i n connect ion with the discussion of the Case batholith. The dike was traced i n an east-west d i r e c t i o n for a distance of 825 feet along s t r i k e and i t attains a maximum width of 100 feet. The dike " h o r s e - t a i l s " into several stringers at i t s western end and i s covered by vegetation and g l a c i a l debris at the eastern end of i t s outcrop area. The only mineral of economic significance i n the dike appears to be the spodumene which occurs as well-formed c r y s t a l s up to 3 feet long and 6 inches i n cross-section. The spodumene content of the dike i s estimated at 10 to 15 per cent. It i s best developed i n the quartz-rich core of the dike, although a few crystals were noted i n pegmatitic 150 stringers extending from the dike into the surrounding quartz monzonite. A grab sample taken from the dike assayed 0.65 per cent lithium and showed a trace of beryllium. Care f u l l y selected spodumene gave 7.63 per cent L i 2 0 upon analysis. The presence of spodumene pegmatite i n the Case batho l i t h suggests comparison with the Lacorne batholith some 110 miles to the southeast of the map-area i n the province of Quebec. Recent studies of the Preissac-Lamotte-Lacorne region by Siroonian, Shaw and Jones3" shows i t to constitute a L i - r i c h geochemical province. The occurrence of spodumene pegmatite i n the Case b a t h o l i t h deserves the attention of prospectors and exploration companies and further work may reveal a similar L i - r i c h geochemical province within the region underlain by the b a t h o l i t h i c intrusives p a r t l y mapped during the 1959 f i e l d season. 1 Siroonian, H. A., Shaw, D.M., and Jones, R.E., Lithium Geochemistry and the Source of the Spodumene Peg matites of the Preissac-Lamotte-Lacorne Region of Western Quebec, Can. Min., Vol. 6, pt. 3, 1959, pp. 320-338. BIBLIOGRAPHY 151 Ambrose, J.W., Progressive Ki n e t i c Metamorphism i n the Missi Series Near F l i n f l o n , Manitoba, Amer. Journ. S c i . , Vol. 32, 1936, pp. 257-286. Baker, M.B., Lake A b i t i b i Area, Ont. Bur. Mines, Vol. XVIII, pt. 1, 1909, pp. 263-283. Barth, T.F.W., Theoretical Petrology, John Wiley and Sons Inc., New York, 1952. Bienvenu, R., The Chemical Composition of Some Meta-volcanic Archean Rocks, Univ. of Laval, M.Sc. Thesis, 1955 s PP. 1-59. B i l l i n g s , M.P., S t r u c t u r a l Geology, Second ed i t i o n , Prentice- H a l l Inc., New York, 1954. Brown, I., Nomenclature of Igneous Rocks, Trans. Can. Inst. Min. and Met., Vol. LV, 1953, pp. 53-56. Bruce, E.L., Precambrian Iron Formations, B u l l . Geol. Soc. Amer., Vol. 56, 1945, pp. 589-602. Cooke, H.C., James, W.F., and Mawdsley, J.B., Geology and Ore Deposits of Rouyn-Harricanaw Region, Quebec, Geol. Surv. Canada, Memoir 166, 1931. Crompton, R.R., Significance of Amphibole Paragenesis i n the Bidwell Bar Region, C a l i f o r n i a , Amer. Mineral, Vol. 4 3 , 1958, pp. 890-907. Emmons, R.C., and Mann, V., A Twin-Zone Relationship i n Plagio clase Feldspar, i n Selected Petrogenic Relationships of Plagioclase, Memoir 52, Geol. Soc. Amer., 1953, pp. 41-54. Fyfe, W.S., Turner, F.J., and Verhoogen, J . , Metamorphic Reactions and Metamorphic Facies, Memoir 73 , Geol. Soc. Amer. 1958. Geology and Economic Minerals of Canada, Economic Geology Series, No. 1 ( 4 t h e d i t i o n ) , Geological Surv. Canada, 1957. G i l l , J.E., The Canadian Precambrian Shield, Jubilee Volume, Can. Inst., Min. and Met., 1948, pp. 20-48. — j and L !Esperance, R., Diabase Dikes i n the Canadian Shield, Trans. Roy. Soc. Canada, Vol. XLVI, Sec. 4 , 1952, pp. 25-36. G l e d h i l l , T.L., Ben Nevis, Munro, Kamishkotia, and other Base Metal Areas, D i s t r i c t s of Cochrane and Timis- kaming, Ont. Dept. Mines, Vol. XXXVII, pt. 3, 1928, p. 49. Gorai, Masao, P e t r o l o g i c a l Studies on Plagioclase Twins, Amer. Mineral., Vol. 36, 1951, pp. 884-901. Gross, G.A., A C l a s s i f i c a t i o n for Iron Deposits i n Canada, Canadian Min. Journ., Vol. 80, 1959, pp. 87-89. Gunning, H.C., and Ambrose, J.W., The Timiskaming-Keewatin Problem i n the Rouyn-Harricanaw Region, North western Quebec, Trans. Roy. Soc. Canada, sec. 4, Vol. XXXIII, 1939, pp. 19-49. Gussow, W.C., Petrogeny of the Major Acid Intrusives of the Rouyn-Bell River Area of North Western Quebec, Trans. Roy. Soc. Canada, 1937, Sec. 4, pp. 129-161. Henderson, J.F., On the Formation of Pillow Lavas and Breccias, Trans. Roy. Soc. Canada, Vol. XLVII, Sec. 4, 1953, pp. 23-32. Hughes, O.L., S u r f i c i a l Geology, Iroquois F a l l s , Cochrane D i s t r i c t , Ontario, Map 46 - 1959, Geol. Surv. Canada, 1959. James, H.L., Sedimentary Facies of Iron-Formation, Econ. Geol., Vol. 49, 1954, pp. 235-293. } Zones of Regional Metamorphism i n the Precambrian of Northern Michigan, B u l l . Geol. Soc. Amer., Vol. 66, 1955, p. 1455-1488. Kindle, E.D., Gold Occurrences of Ontario East of Lake Superior, Memoir 192, Geol. Surv. Canada, 1936. Knight, C.W., Burrows, A.G., Hopkins, P.E., and Parsons, A.L., Abitibi-Night Hawk Gold Area, Ont. Bur. Mines, Vol. XXVIII, pt. 2, 1919, pp. 1-70. Landes, K.K., Origin and C l a s s i f i c a t i o n of Pegmatites, Amer. Mineral., Vol. 18, pp. 33-56, 95-103. Moore, E.S., Notes on the Origin of Pillow Lavas, Trans. Roy. Soc. Canada, Vol. XXIV, Sec. 4, 1930, pp. 137-139. Pettijohn, F.J., Archean Metaconcretions of.Thunder Lake, Ontario, B u l l . Geol. Soc. Amer., Vol. 51, 1940, pp. 1841-1850. 153 Pettijohn, F.J., Archean Sedimentation, B u l l . Geol. Soc. Amer., Vol. 54, 1943, pp. 925-972. , Sedimentary Rocks, second edition, Harper and Bros., New York, 1957. Poldervaart, A r i e , Metamorphism of B a s a l t i c Rocks : A Review, B u l l . Geol. Soc. Amer., Vol. 65, 1953, pp. 259-274. Read, H.H., The Granite Controversy, Interscience Publishers, Inc., New York, 1957. Richardz, S., Grunerite. Rocks of the Lake Superior Region and t h e i r O r i g i n , Journ. Geol., Vol. 35, 1927, pp. 690-707. — 9 The Amphibole Grunerite of the Lake Superior Region, Amer. Journ. S c i . , Vol. 14, 1927, pp. 150- 154. Ross, J.V., Combination Twinning i n Plagioclase Feldspar, Amer. Journ. S c i . , Vol. 255, 1957, pp. 650-655. S a t t e r l y , J . , Pillow Lavas from the Dryden-Wabigoon Area, Kenora D i s t r i c t , Ontario, Univ. of Toronto, Studies, Geol. Ser. No. 46, pp. 119-136. Shrock, R.R., Sequence i n Layered Rocks, McGraw-Hill Book Co., New York, 1948, pp. 161-162. Siroonian, H.A., Shaw, D.M., and Jones, R.E., Lithium Geochemistry and the Source of the Spodumene Peg matites of the Preissac-Lamotte-Lacorne Region of Western Quebec, Canad. Mineral., Vol. 6, pt. 3, 1959, pp. 320-338. Spencer, E., Myrmekite i n Graphic Granite and i n Vein Perthite, Mineral. Mag., Vol. XXVII, 1945, pp. 79-98. Turner, F.J., Progressive Regional Metamorphism i n Southern New Zealand, Geol. Mag., Vol. 75, 1938, pp. 160-174. , and Verhoogen, J . , Igneous and Metamorphic Petrology, McGraw-Hill Book Co., New York, 1951. T i l l e y , C.E., Cummingtonite-bearing Rocks from the Lewisian, Geol. Mag., Vol. 75, 1938, pp. 76-81. 154 Vogt, T., S u l i t e l m a f e l t e t s , Geologi og P.etrografi (with English Summary), Norges. geol. Undersakelse, No. 121, 1927. Williams, H., Turner, F.J., and G i l b e r t , CM., Petrography, W.H. Freeman and Co., New York, 1955. Wilson, M.E., Origin of Pillow Structure i n the Early Pre cambrian Lavas of Western Quebec, Journ. Geol., Vol. 6 8 , I 9 6 0 , pp. 97-102. Winchell, A.N., and Winchell, H., Elements of Optical Mineralogy, pt. I I , Descriptions of Minerals, John Wiley and Sons, Inc., New York, 1951. Wiseman, J.D.H., The central and Southwest Highland Epidior- i t e s . A Study i n Progressive Metamorphism, Geol. Soc. London, Quart. Journ., Vol. 90, 1934, pp. 335T417 Yoder, H.S., The MgO-AlpOo-S^-HpO System and the Related Metamorphic Facies, Amer. Journ. S c i . , Bowen Vol., 1952, pp. 569-627. 

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