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The mineralogy and geology of the Akaitcho area, Yellowknife, Northwest Territories Manifold, Albert Hedley 1947-12-31

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THE MINERALOGY AND GEOLOGY OF THE  AKAITCHO AREA, YELLOWKNIFE," NORTHWEST TERRITORIES BY ALBERT HEDLEY MANIFOLD. A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF APPLIED SCIENCE In The Department of GEOLOGY AND GEOGRAPHY THE UNIVERSITY OF BRITISH COLUMBIA APRIL 1947 CONTENTS PAGE ABSTRACT ACKNOWLEDGMENTS INTRODUCTION General Statement 1 Lo c a t i o n 1 Physiography . .• 2 H i s t o r y of the Akaitcho Property 2 ECONOMIC GEOLOGY General Statement .. . 2 Production and Power 4 Types of Deposits 5 GENERAL GEOLOGY Volcanics .-. 6 Sediments 6 Intrus ive s 6 STRUCTURAL GEOLOGY Fau l t s 7 Shear Zones 9 Formations 9 Akaitcho Ore Body ' 10 DETAILED GEOLOGY OF THE AKAITCHO AREA General Statement 10 Rock Types 11 Flows 11 D i o r i t e - Gabbro I n t r u s i v e s 15 B i r d Porphyry I n t r u s i v e s 16 Diabase Dykes 17 MINERALOGY General Statement 18 M e t a l l i c M inerals 19 P y r i t e 19 Arsenopyrite 19 S t i b n i t e 20 Cha l c o p y r i t e ' 20 S p h a l e r i t e 21 P y r r h o t i t e 21 Sulpho-Salts T e t r a h e d r i t e 21 Bournonite i 22 Gold 23 A l t a i t e 24 Non-metallic Minerals., Quartz 24 C a l c i t e 24 CONTENTS - Continued. PAGE Non-metallic Minerals C h l o r i t e 25 S e r i c i t e 25 Paragenesis 25 M i n e r a l i z i n g S o l u t i o n s 34 WALL ROCK ALTERATION 34 TYPE OF DEPOSIT 36 AGE OF DEPOSIT 37 CONCLUSIONS 37 BIBLIOGRAPHY 39 LIST OF ILLUSTRATIONS Figure 1 L o c a t i o n Map 3 Figure 2 General Geology 8 Figure 3 Block Diagram i n pocket Pla t e s 1 to 12 Photomicrographs of P o l i s h e d Sections 28 to 33 Pl a t e 13 Photomicrograph of Thin S e c t i o n 35 Table 1 Samples of Hole 54 19 Table 2 M i n e r a l sequence 27 Photographs 1 to 4 - Formations i n the Area ABSTRACT The Akaitcho property borders the northern claims of the Giant Y e l l o w k n i f e property. Diamond d r i l l i n g has revealed an ore body l y i n g along a t e r r a c e i n a s t e e p l y - d i p p i n g m i n e r a l i z e d shear zone. The shear i s contained i n Pre- cambrian v o l c a n i c rocks a l l of which have been more or l e s s r e g i o n a l l y metamorphosed. Adjacent to the ore, the rocks c o n t a i n much introduced quartz, c a l c i t e , and p y r i t e . Sulphide m i n e r a l i z a t i o n i s sparse but the ore i s quite com plex w i t h an abundance of p y r i t e , a r s e n o p y r i t e , s t i b n i t e , and s u l p h o - s a l t s present. The gold i s very f i n e - g r a i n e d , the l a r g e s t p a r t i c l e observed m i c r o s c o p i c a l l y being 150 microns i n diameter. I t i s disseminated i n a quartz-carbon ate gangue and i s a l s o c l o s e l y a s s o c i a t e d w i t h sulphides e s p e c i a l l y a r s e n o p y r i t e and v e i n l e t s of s u l p h o - s a l t s . Based upon the mineral assemblage, the a l t e r a t i o n zone, and the general nature of the ore, the deposits would be cl a s s e d as mesothermal. 6 ACKNOWLEDGMENTS The w r i t e r wishes to express h i s a p p r e c i a t i o n to the many persons whose k i n d a s s i s t a n c e and co-operation made t h i s i n v e s t i g a t i o n p o s s i b l e . To Dr. H.G. Gunning of the U n i v e r s i t y s t a f f the w r i t e r i s extremely g r a t e f u l f o r the valuable suggestions and c o n s t r u c t i v e c r i t i c i s m . Acknowledgment i s due to Dr. H.V. Warren and Dr. K. Watson, a l s o of the U n i v e r s i t y s t a f f , f o r t h e i r k i n d a s s i s t a n c e i n determination of various minerals. To Mr. C.E. Anderson and Mr. J . MacLeod of Probisher E x p l o r a t i o n Company the w r i t e r i s indebted f o r t h e i r co-operation i n supplying d r i l l core samples and general i n f o r m a t i o n about the property. A p p r e c i a t i o n i s expressed f o r the work of Dr. R.M. Thompson of the G e o l o g i c a l Sciences at the U n i v e r s i t y of Toronto who d i d the X-ray powder photograph through the k i n d permission of Dr. Peacock. The w r i t e r wishes to thank h i s classmates Mr. L. Gouin who d i d many spectrographic analyses and Mr. J . Lamb who a s s i s t e d g r e a t l y i n the study of p o l i s h e d s e c t i o n s . In the prepar a t i o n of p o l i s h e d and t h i n s e ctions a p p r e c i a t i o n i s expressed f o r the a s s i s t a n c e of Mr. J . Donnan, t e c h n i c i a n of the G e o l o g i c a l Department. 1 THE MINERALOGY AND GEOLOGY OF THE AKAITCHO AREA, YELLOWKNIFE  NORTHWEST TERRITORIES  INTRODUCTION General Statement: A r a p i d l y developing mining area i n Canada to-day i s that of Y e l l o w k n i f e , Northwest T e r r i t o r i e s . While the Negus and Con gold mines have been e s t a b l i s h e d there since 1938 i t was not u n t i l the recent d i s c o v e r y of the ore-bodies of the Giant Y e l l o w k n i f e Gold Mines that the area gave promise of l a r g e tonnage mining. Since that time much e x p l o r a t i o n work has been c a r r i e d on. One of the most i n t e r e s t i n g p r o p e r t i e s being developed now i s that of the Akaitcho Gold Mines, L i m i t e d . Diamond d r i l l i n g since the l a t t e r part of 1944 has i n d i c a t e d an ore-body, which, although not having anything l i k e the dimensions of the Giant ore-bodies, should prove to be p r o f i t a b l e . The main purpose of t h i s i n v e s t i g a t i o n i s to study the. Akaitcho ore i n p o l i s h e d s e c t i o n to determine the various minerals present and t h e i r r e l a t i o n to each other. Along w i t h t h i s i n v e s t i g a t i o n i s a petrographic study of some of the main rock types i n the area and of the a l t e r e d w a l l - rocks of the d e p o s i t . L o c a t i o n and T r a n s p o r t a t i o n ; The Akaitcho property l i e s approximately f o u r miles north of the town of Y e l l o w k n i f e . The southern p o r t i o n borders the Giant property. A s e r v i c e a b l e road constructed 2 i n the summer of 1946, runs through the property to Yellow k n i f e . Physiography: The low r e l i e f and many lakes of the country are t y p i c a l f eatures of Pre-cambrian topography. Great Slave Lake has an e l e v a t i o n of 495 f e e t while the highest h i l l i n the immediate v i c i n i t y of Y e l l o w k n i f e i s 865 f e e t . Maximum r e l i e f i s a fforded mainly by f a u l t - l i n e scarps and bodies of i n t r u s i v e rocks. Much of the drainage i s conformable to the major f a u l t systems and general trend of the formations. One of the c h i e f c h a r a c t e r i s t i c s of the area i s the l a r g e amount of bare outcrop. Between the outcrbppings are d r i f t - covered areas of muskeg. H i s t o r y of the Akaitcho Property: The property was o r i g i n a l l y known as the A.E.S. group and c o n s i s t e d of twenty-four claims staked i n 1936 f o r the A e r i a l E x p l o r a t i o n Syndicate, L i m i t e d . P r o b i s h e r E x p l o r a t i o n Company optioned the property i n 1944 and l a t e r i n that year i organized the Akaitcho Gold Mines, L i m i t e d , to c a r r y on development work. To the present date diamond d r i l l i n g has been c a r r i e d on and has r e v e a l e d a promising gold-bearing zone. ECONOMIC GEOLOGY General Statement: T o t a l production of gold from the Y e l l o w k n i f e d i s t r i c t has amounted to over f i f t e e n m i l l i o n d o l l a r s . This has been p r i n c i p a l l y from the Con mine of the Consolidated Mining and Smelting Company of Canada and the Negus mine of Negus Gold Mines, L i m i t e d . These two mines began producing i n 1938 and 1939 r e s p e c t i v e l y . Several other mines such as the Thompson- Lundmark, Gamlaren, and Ptarmigan have produced f o r short periods. The l a s t mentioned mines have been i d l e f o r some time but i n the l a t t e r p a r t of 1946 the Thompson-Lundmark was being dewatered i n p r e p a r a t i o n f o r f u r t h e r development and production. Production and Power: The two main producers each t r e a t about one hundred tons of ore per day, although the production has been increased l a t e l y . Operating costs vary from fourteen to nineteen d o l l a r s per ton w i t h the grade of ore being approximately 0.8 ounces of gold per ton. The Giant Y e l l o w k n i f e property intends to m i l l 2000 tons per day and w i t h such a tonnage should reduce operating costs c o n s i d e r a b l y . Both d i e s e l and h y d r o - e l e c t r i c power are used by the mines. D i e s e l o i l i s obtained by barge from Fort Norman and • e l e c t r i c i t y i s obtained from a h y d r o - e l e c t r i c plant owned by the Consolidated Mining and Smelting Company of Canada and l o c a t e d about f i f t e e n miles north of Y e l l o w k n i f e at the head of Prosperous Lake. A new h y d r o - e l e c t r i c p l a n t i s now being constructed on the Snare R i v e r about 120 miles from Yellow k n i f e . The f i r s t part should be completed i n 1948 and w i l l supply 8000 horse-power. Further development i s planned and the p r o j e c t w i l l e v e n t u a l l y r e s u l t i n the production of an estimated 25,000 horse-power. 5 Types of Deposits: Gold deposits i n the d i s t r i c t can be c l a s s i f i e d as two general types. (a) Deposits i n v o l c a n i c rocks Examples: Con Mine, Negus Mine, Giant Y e l l o w k n i f e Gold Mines, Limited.,'Akaitcho Gold Mines, Limited,-and Crestaurum Gold Mines, L i m i t e d . (b) Deposits i n sedimentary rocks Examples: Camlaren Mines, L i m i t e d , Thompson-Lundmark Gold Mines, L i m i t e d , and Ptarmigan Mines, L i m i t e d . The g o l d of the deposits i n v o l c a n i c rocks i s contained i n quartz-carbonate veins or masses of v e i n l e t s w i t h i n s t e e p l y dipping shear zones. Ore-bodies of the Negus and Con mines have mining widths up to twenty f e e t but some of those of the Giant mine are up to f o r t y f e e t or more. M e t a l l i c content of the ore zones i s small but a wide v a r i e t y of minerals i s represented. Most of the g o l d of the deposits i n sedimentary rocks occurs i n veins or lenses of f a i r l y pure quartz. Some veins are found p a r a l l e l to the bedding and some c r o s s i n g the bedding. One v e i n of the Camlaren Mines forms a saddle-reef at the c r e s t of a f o l d . Other veins and lenses are found associated w i t h drag f o l d s and a x i a l planes of f o l d s . The gold deposits i n the v o l c a n i c s have proven up to the present to be more extensive and by f a r the most important. I t i s probable the v o l c a n i c s f r a c t u r e and shear more so than 6 t h e s e d i m e n t s a n d t h u s a r e m o r e f a v o r a b l e h o s t r o c k s . GENERAL GEOLOGY V o l c a n i c s ; T h e Y e l l o w k n i f e a r e a i s u n d e r l a i n c o m p l e t e l y b y P r e c a m b r i a n r o c k s . V o l c a n i c a n d s e d i m e n t a r y f o r m a t i o n s o f t h e Y e l l o w k n i f e G r o u p , c l a s s i f i e d a s A r c h e a n i n a g e , a r e t h e o l d e s t e x p o s e d r o c k s . T h e v o l c a n i c s c o n s i s t m a i n l y o f a n d e s i t i c f l o w s m a n y o f w h i c h e x h i b i t p i l l o w s t r u c t u r e . Some o f t h e f l o w s a r e m a s s i v e a n d f a i r l y c o a r s e - g r a i n e d w h i l e o t h e r s show v e s i c u l a r o r a m y g d u l a r s t r u c t u r e s . A f e w f l o w s a r e o f a s p h e r u l i t i c o r v a r i o l i t i c n a t u r e . S e d i m e n t s : T h e r e a r e t w o g e n e r a l t y p e s o f s e d i m e n t s t e r m e d l o c a l l y " h o t " a n d " c o l d " . T h e " h o t " s e d i m e n t s c o n s i s t o f q u a r t z - m i c a s c h i s t , k n o t t e d s c h i s t , s l a t e a n d p h y l l i t e b o r d e r i n g i n t r u s i v e g r a n i t i c b o d i e s . T h e y g r a d e o u t w a r d t o c o m p a r a t i v e  l y u n a l t e r e d a r e a s o f a r k o s e , s l a t e , a n d g r e y w a c k e , t h e s o - c a l l e d " c o l d " s e d i m e n t s . I n t r u s i v e s ; P r e s e n t i n t h e a r e a a r e n u m e r o u s g r a n i t i c i n t r u s i o n s t w o o f w h i c h now a r e d e f i n i t e l y k n o w n t o b e d i f f e r e n t i n a g e . T h e o l d e r t y p e i s a u n i f o r m , f a i r l y c o a r s e - g r a i n e d g r a n o d i o r - i t e c o n t a i n i n g c o n s i d e r a b l e a m o u n t s o f b i o t i t e a n d h o r n b l e n d e w h i l e t h e y o u n g e r t y p e i s a m u s c o v i t e - b i o t i t e g r a n i t e a c c o m p a n i e d b y many t o u r m a l i n e - b e a r i n g p e g m a t i t e d y k e s . T h e r e a r e a l s o many m i n o r i n t r u s i v e s o f a d i o r i t i c o r g a b b r o i c n a t u r e a p p e a r i n g i n some c a s e s t o b e i n t h e f o r m o f 7 s i l l s . C u t t i n g the v o l c a n i c s are larg e numbers of b a s i c dykes r a r e l y over twenty-five f e e t i n width. They have a composit i o n s i m i l a r to the flows and are d i s t i n g u i s h e d i n the f i e l d only by c a r e f u l examination. The w r i t e r has n o t i c e d them only In areas of v o l c a n i c r o c k s . Presumably they were formed during the p e r i o d of vulcanism and may represent feeders f o r some of the l a t e r f l o w s . Another type of dyke i s one t h a t has been l o c a l l y termed " b i r d porphyry". I t i s a f a i r l y l a t e dyke c u t t i n g the type mentioned i n the previous paragraph and a l s o c u t t i n g the di o r i t e - g a b b r o i n t r u s i v e s . However, i n a l l cases observed the " b i r d porphyry" has been cut by diabase dykes. Considered to be the youngest c o n s o l i d a t e d rocks of the area are the l a t e quartz-diabase and o l i v i n e - d i a b a s e dykes which cut a l l other formations. The C4 shear zone of the Con mine i s cut by an u n a l t e r e d and unsheared diabase dyke. (7, p. 108) STRUCTURAL GEOLOGY F a u l t s : The most s t r i k i n g s t r u c t u r a l f e a t u r e of the area near Y e l l o w k n i f e i s the system of n o r t h - s t r i k i n g , s t e e p l y - d i p p i n g f a u l t s . A l a r g e v e r t i c a l diabase dyke shows a t o t a l d i s  placement of approximately eleven miles across the zone'with the r e l a t i v e displacement along the i n d i v i d u a l f a u l t s being g e n e r a l l y the east side to the no r t h . P l a i n l y v i s i b l e from the a i r i s the West Bay F a u l t w i t h a h o r i z o n t a l displacement 0 FIGURE Z - MAP SHOWING GENERAL GEOLOGY OF YELLOWKNIFE DISTRICT 9 • of f i v e m i l e s . The v e r t i c a l displacement, though not proven, i s b e l i e v e d to be q u i t e s m a l l . Crossing the Akaitcho property and running i n t o the West Bay F a u l t from the east i s the Akaitcho F a u l t w i t h a l e f t - h a n d h o r i z o n t a l displacement of about 5000 f e e t . Shear zones along the f a u l t s are quite narrow c o n s i d e r i n g the amount of displacement. A l l the evidence of the West Bay F a u l t as seen i n d r i l l cores from the Giant property i s s e v e r a l inches of gouge. The age of major f a u l t i n g cannot be placed any more d e f i n i t e l y than post- diabase and p r e - P l e i s t o c e n e . Shear Zones: The main known ore-bodies l i e i n shear zones adjacent to the West Bay F a u l t . These zones have a general north-south s t r i k e and v a r y i n g d i p s . The general b e l i e f of competent g e o l o g i s t s who have st u d i e d the area i s that the ore-bodies are o f f s e t by the f a u l t . I t i s p o s s i b l e the s t r e s s e s that f i n a l l y r e s u l t e d i n the f a u l t f i r s t produced the shear zones. The en echelon arrangement of the shears and t h e i r p r o x i m i t y to the f a u l t support t h i s s u p p o s i t i o n . Formations; Within the area u n d e r l a i n by v o l c a n i c s , the f l o w s , interbedded t u f f s and chert bands have n o r t h - e a s t e r l y s t r i k e s and steep dips w i t h the tops, where determined, to the south east. On the Akaitcho property d r i l l core s e c t i o n s show t h a t the flows d i p from f o r t y - f i v e t o s i x t y degrees at the surface but tend to f l a t t e n s e v e r a l hundred f e e t underground. 10 Akaitcho Ore Body: The general structure of the mineralized shear zone on the Akaitcho property may be seen in the accompanying block diagram. The shear as closely as can be interpreted from diamond d r i l l cores more or less parallels the dip of the flows. In i t s southern part the shear dips steeply to the east at the surface and then at a depth of 400 feet i t flattens to a terrace. It then continues at a shallow dip. The approximate outline of the ore body i t s e l f is shown on the block diagram. It can be seen to occur where the shear zone flattens. Where the terrace is most pronounced the ore body attains i t s maximum thickness and value. This feature seems to be the main structural control. If at greater depth the shear zone flattens again ore may be encountered there. DETAILED GEOLOGY General Statement: The rocks examined represent a f a i r l y low grade type of regional metamorphism in which the minerals albite, epidote, sericite, chlorite, and calcite are produced. Occasionally minor amounts of quartz and calcite have been introduced i n the form of small veinlets. These with veinlets of epidote could be attributed to late volcanic effects. Some of the main rock types have been chosen for examination and a f i e l d and microscopic description of each is given. 11 Rock Types: (a) Flows: (1) L i g h t Colored P i l l o w Lava: This l a v a as seen i n the f i e l d weathers a l i g h t grey c o l o r . P i l l o w s t r u c t u r e while almost o b l i t e r a t e d i s d i s t i n g u i s h a b l e i n s e v e r a l p l a c e s . W i t h i n the p i l l o w s but near the borders are numerous amygdules c o n s i s t i n g of quartz wi t h v a r y i n g amounts of c h a l c o p y r i t e and p y r r h o t i t e . M i c r o s c o p i c a l l y the rock i s seen to c o n s i s t of amygdules up to s e v e r a l mm. i n diameter i n a f i n e - g r a i n e d matrix of epidote, s e r i c i t e , carbonate, a l b i t e , and a l i t t l e c h l o r i t e . There are 'some la r g e grains up to 1.5 mm. i n l e n g t h that . appear to have been f e l d s p a r but are now completely a l t e r e d to carbonate and s e r i c i t e . The amygdules c o n s i s t of coarse grains of quartz, c a l c i t e , epidote, and s e r i c i t e w i t h p y r r h o t i t e and c h a l c o p y r i t e being present i n a few of them. Some of the amygdules show co n c e n t r i c bands towards the outer edges. The w r i t e r had considered t h i s type as more a c i d i c than an andesite but there i s very l i t t l e quartz i n i t and a sodium cob a l t n i t r a t e s t a i n i n g t e s t proved no potassium compounds present. The o r i g i n a l l a v a was l i k e l y a n d e s i t i c but the presence of minor c h l o r i t e i n d i c a t e s an i n i t i a l small percentage of ferromagnesian minerals. (2) Dark Green P i l l o w Lava: The lava,has a dense f i n e - g r a i n e d appearance and weathers a dark green p u r p l i s h c o l o r . P i l l o w s t r u c t u r e i s present but 12 i s n o t s o p r o m i n e n t a s i n o t h e r t y p e s . T h e r o c k i s v e r y f i n e - g r a i n e d w i t h t h e l a r g e s t g r a i n o b s e r v e d , a f e l d s p a r l a t h , b e i n g o.35 mm. i n l e n g t h . Some s m a l l e r g r a i n s o f h o r n b l e n d e a r e p r e s e n t b u t t h e y a r e l a r g e l y a l t e r e d t o c h l o r i t e . T h e r e i s c o n s i d e r a b l e f e l d s p a r i n t h e f o r m o f a l b i t e . C a l c i t e i s p r e s e n t i n a b o u t t h e same q u a n t i  t y a s f e l d s p a r . T h e r e a r e m i n o r a m o u n t s o f s e r i c i t e . M a g n e t i t e i s s e e n a s m a s s e s o f s m a l l grains a n d a few l a r g e r e u h e d r a l g r a i n s . P y r i t e a l s o o c c u r s a s l a r g e e u h e d r a l g r a i n s . M u c h o f t h e m a g n e t i t e i s i n i t s o r i g i n a l f o r m b u t some i s p r o b a b l y f r o m a l t e r a t i o n o f h o r n b l e n d e . T h e d a r k c o l o r o f t h e l a v a i s due t o t h e l a r g e a m o u n t s o f c h l o r i t e , m a g n e t i t e , a n d p y r i t e . T h i s l a v a l i k e l y r e p r e s e n t s a n o r i g i n a l l y b a s i c t y p e . (3) L i g h t G r e e n P i l l o w L a v a : T h i s t y p e i s b y f a r t h e m o s t w i d e s p r e a d . The p i l l o w s v a r y i n s i z e f r o m o n e f o o t i n d i a m e t e r u p t o s i x f e e t i n c e r t a i n i n s t a n c e s . C e n t r e s o f t h e p i l l o w s h a v e a h a r d g l a s s y a p p e a r a n c e . T h e b o r d e r s a r e q u i t e t h i c k a n d w e a t h e r a b r o w n c o l o r . No a m y g d u l e s w e r e o b s e r v e d i n t h i s t y p e . 13 r Elongated p i l l o w s i n l i g h t - g r e e n l a v a The main c o n s t i t u e n t s of the lava are c n l o r i t e and b a s i c anaesine f e l a s p a r each being present i n about equal amounts. Some of the f e l d s p a r has been a l t e r e d to c l i n o z o i s i t e . Present i n minor amounts are small i r r e g u l a r grains of carbonate and a few euhedral grains of magnetite. Quartz has been introduced i n the form of v e i n l e t s up to 0.1 mm. i n width ana a l s o as masses of f i n e g r a i n s . Several horizons of t h i s type of l a v a occur i n the area. As seen i n the f i e l d the v s r i o l i t e s , i n d i v i d u a l l y measuring up to an i n c h or more, are founa i n groups up to s e v e r a l f e e t i n diameter. U ) V a r i o l i t i c Lava: 14 Photograph showing a c l u s t e r of v a r i o l i t e s The matrix i s mainly a mass of f i n e - g r a i n e d andesine f e l d s p a r , a few small grains of hornblende, considerable amounts of c h l o r i t e , c a l c i t e , end some epidote. The v a r i o l i t e s have a s i m i l a r composition but are f i n e r - g r a i n e d . Masses of extremely f i n e - g r a i n e d epidote cloud the outer parts of the v a r i o l i t e s . Numerous euhedral grains of magnetite up to 0.15 mm. i n diameter are seen i n the matrix but only o c c a s i o n a l l y i n tne v a r i o l i t e s . Crossing one s e c t i o n i s a small v e i n l e t of epidote 1.5 mm wide wi t h grains elongateu perpendicular to the v e i n w a l l s . The grains have been bent ana f r a c t u r e d p a r a l l e l to the v e i n w a l l s showing some movement has taken place. A l s o c u t t i n g across the s e c t i o n are small v e i n l e t s of quartz and c a l c i t e up to 0.5 mm. i n width. I t may be noted tnat i n the " l i g h t - c o l o r e d " and " b a s i c " flows the f e l d s p a r i s predominantly a l b i t e while i n the " v a r i o l i t i c " and " l i g h t - g r e e n " flows the f e l d s p a r i s andesine 15 The f i r s t two types r e p r e s e n t a h i g h e r grade of metamorphism. T h i s i s borne out by the f a c t t n a t b o t h are near m i n e r a l i z e d s h e a r zones. (b) D i o r i t e - Gabbro I n t r u s i v e s : These are b o d i e s up t o s e v e r a l hundred f e e t i n w i d t h and s e v e r e l thousand f e e t i n l e n g t h . While s i l l - l i k e I n appearance t n e y can be seen to c u t a c r o s s the f l o w s i n numerous p l a c e s . The r o c k i s f a i r l y c o a r s e - g r a i n e d and p r e s e n t s a m o t t l e d weathered s u r f a c e . C o n t a c t o f d i o r i t e (D) c u t t i n g a c r o s s a f l o w (F) Two o f these i n t r u s i v e s were examined m i c r o s c o p i c a l l y . Hornblende i s the most abunaant c o n s t i t u e n t w i t h andesine f e l d s p a r i n almost the same amount, iviuch o f the hornblende has been a l t e r e d to c n l o r i t e w h i l e tne f e l d s p a r has been p a r t l y a l t e r e d to s e r i c i t e , c a l c i t e , and e p i d o t e . In one of the r o c k s t h e r e are a few g r a i n s of q u a r t z . In b o t h s e c t i o n s s m a l l amounts o f an opaque m i n e r a l are p r e s e n t showing a 16 leucoxene-type of alteration. One of the rocks has a few small cross-fibre veinlets .of actinolite up to 0.1 mm. in width, (c) Bird Porphyry Intrusives: These are dark green rocks generally in the form of dykes with numerous clusters of white phenoerysts. Individual phenoerysts vary in size up to an inch or two in diameter and generally lack good crystal boundaries-. The main constituent of the groundmass is hornblende. Its short blocky appearance indicates i t has been derived from pyroxene. It is partly altered to a few small flakes of biotite and chlorite. Labradorite feldspar is the next mineral in abundance. Much of i t is clouded with sericite and epidote. Apart from the phenoerysts the dykes have a typical gabbroic texture. The white phenoerysts were probably a l l feldspar but they have been completely altered to zoisite, epidote, a l i t t l e sericite and carbonate. L i t t l e shreds of chlorite projecting into the edges of the phenoerysts indicate the reaction of the groundmass with the earlier crystallized phenoerysts either before or after consolidation. A l i t t l e magnetite and hematite are present in the matrix. Barlows', in the Ottawa Naturalist, 1895, has given an excellent description of an almost identical type of dyke occurring near Algoma in the Lake Huron Dist r i c t . At that time the phenoerysts were known as "Huronite". In memoir 166 ( 3, p. 143) reference was made to a 17 s i m i l a r type of dyke at Matachewan, Ontario. The dykes have the same p o r p h y r i t i c character but a l t e r a t i o n of the phenoerysts i s from l a b r a d o r i t e f e l d s p a r to k a o l i n and s e r i c i t e . At Matachewan the dykes were c l a s s i f i e d as pre- Cobalt i n age. (d) Diabase Dykes: The diabase dykes as seen i n the f i e l d weather to a c h a r a c t e r i s t i c reddish-brown c o l o r . The specimen used i n t h i s study i s from tne l a r g e dyke showing the h o r i z o n t a l o f f s e t of the West Bay F s u l t . This dyke i s about 400 f e e t i n width being very coarse-graineu i n the centre. A small lake along a diabase dyke. The depression was probably caused by p l u c k i n g of the ice i n Pleistocene times. Observed i n t h i n s e c t i o n trie rock i s seen to have t y p i c a l o p h i t i c t e x t u r e . The two main c o n s t i t u e n t s are la r g e c r y s t a l s of pigeonite up to 3 mm. i n diameter moulded around l a t n s of l a b r a d o r i t e f e l d s p a r . Considerable magnetite i s present p a r t l y as l a r g e euhedral grains up to three mm. i n diameter and as small grains and snreds w i t h i n a l t e r e d 18 crystals of hornblende and pigeonite. Some of the feldspar is altered to epidote and sericite while the hornblende is partly altered to chlorite and biotite. A few small grains of hematite are present within the rock. The feldspars and ferromagnesian minerals in'the diorite- gabbro, bird porphyry, and diabase intrusives just considered do not exhibit the same grade of metamorphism seen in the flows. Being much later than the flows, the intrusives were not affected by the regional metamorphism. MINERALOGY General Statement; In the study of the Akaitcho ore two factors are soon noted. These are: f i r s t , the sparse mineralization and second the fine texture of the ore minerals. The total metallic content of the ore zone does not average more than five per cent. Figure one Is representative of the type of mineral ization. Many different minerals are present in the ore but due to the fine texture their exact identification is very d i f f i c u l t . No doubt further examination of the ore w i l l reveal numerous minerals not mentioned in this report. Samples of ore for this investigation were obtained from core sections of diamond d r i l l holes 54 and 72.' The ^ location of the d r i l l holes, which are a l l vertical may be seen in figure three. The actual sampling of hole 54 was as follows: 19 Table 1. Samples of H 0 l e 54. Sample No. Footage Assay - oz / ton 1 368.6 - 370.6 trace 2 371.6 - 373.3 0.01 3 373.3 - 375.2 0.60 4 375.2 - 3.77.2 0.43 5 377.2 - 379.4 0.80 6 379.4 - 380.4 0.10 7 380.4 - 381.4 0.01 Five samples were taken from hole 72 along a core-length of 4.2 f e e t averaging 0.5 ounces of gold per ton, the highest i n d i v i d u a l assay being 0.9 ounces. I d e n t i f i c a t i o n of the various minerals was based upon o p t i c a l and p h y s i c a l p r o p e r t i e s , etch r e a c t i o n s , microchemical analyses, and i n some cases spectrographic analyses. To e s t a b l i s h the i d e n t i t y of bournonite an X-ray powder photo graph was taken by Dr. R.M. Thompson of the U n i v e r s i t y of Toronto. M e t a l l i c M i n e r a l s ; P y r i t e i s one of the most abundant minerals i n the ore. I t i s very euhedral o c c u r r i n g i n the form of cubes and pyritohedrons. O c c a s i o n a l l y i t i s i n t i m a t e l y a s s o c i a t e d w i t h arsenopyrite and as such i t loses i t s euhedral c h a r a c t e r . The p y r i t e grains are found i s o l a t e d i n the quartz-carbonate gangue and a l s o as c l u s t e r s forming small v e i n l e t s . Figure one shows a few grains of p y r i t e w i t h a r s e n o p y r i t e along small v e i n l e t s p a r a l l e l to shearing i n the ore zone. Many f r a c t u r e s i n p y r i t e are f i l l e d w i t h gangue minerals. Arsenopyrite i s present i n the ore i n almost the same qu a n t i t y as p y r i t e and occurs i n much the same manner. I t i s 20 very euhedral being generally in the form of diamond-shaped crystals or elongated needle-like crystals. Arsenopyrite and pyrite where occurring together are irregular in outline. However, in one case a diamond-shaped crystal of arsenopyrite was found completely surrounded by massive pyrite. The crystal grains of arsenopyrite are scattered with random orientation throughout the quartz-carbonate gangue. Occasionally the grains are fractured and veined by quartz and carbonate but this feature i s less frequent than in pyrite. Stibnite is a f a i r l y common mineral being present in most of the sections examined. It occurs as irregularly shaped grains in the gangue minerals. These grains consist of numerous differently oriented crystals. Where occurring as isolated particles i t occasionally has minute inclusions of a whiter mineral. These particles are much too small to test adequately so the identity of the mineral is s t i l l unknown. Figure two represents the type of occurrence. Some stibnite forms very fine veinlets in fractured quartz. It is most abundant, however, in veinlets of massive grey sulphides where i t is intimately associated with jamesonite and other sulpho- salts. Where i t occurs as last described i t contains minute inclusions of gold. A more complete description w i l l be given later when the veinlets of grey sulphides are considered. Chalcopyrite is not very abundant but is present in the sections from both diamond d r i l l holes. In the samples from hole 5 4 i t occurs as small irregularly shaped particles closely associated w i t h s t i b n i t e . The c h a l c o p y r i t e grains border the outside boundaries of much l a r g e r s t i b n i t e g r a i n s . 'In the ore from hole 72 c h a l c o p y r i t e has quite a d i f f e r e n t manner of occurrence. In sample f o u r i t i s c l o s e l y a s s o c i a t e d w i t h p y r r h o t i t e and p y r i t e . I t i s a l s o present as e x s o l u t i o n blebs i n s p h a l e r i t e . Figure three shows t h i s type of occurrence and a l s o grains of c h a l c o p y r i t e and p y r r h o t i t e w i t h smooth boundaries. S p h a l e r i t e i s a comparatively rare m i n e r a l . In sample f o u r of hole 54 a few small i s o l a t e d grains are found s c a t t e r e d throughout the quartz-carbonate gangue. More of the mineral i s present i n samples four and f i v e of hole 72. Here i t i s c l o s e l y a s s o c i a t e d w i t h p y r i t e and c h a l c o p y r i t e . In sample f i v e i t occurs as separate grains and a l s o as blebs i n c h a l c o p y r i t e . P y r r h o t i t e i s only i n f o o t w a l l samples from hole 72. I t occurs as massive grains i n a quartz gangue. P a r t l y , how ever, i t i s found as l o o s e l y - k n i t grains i n masses of smali opaque non-metallic p a r t i c l e s that appear to be an a l t e r a t i o n product of some o r i g i n a l c o n s t i t u e n t of the rock. I n both cases i t i s ofte n a s s o c i a t e d w i t h c h a l c o p y r i t e . Figures three and four represent the two types of occurrence. S u l p h o - s a l t s ; T e t r a h e d r i t e i s present i n samples two and three of hole 54. In sample two i t occurs w i t h bournonite and p y r i t e i n a matrix of quartz surrounded by a l t e r e d w a l l rock. Around the borders of the t e t r a h e d r i t e are a few p a r t i c l e s of gold. In 22 sample three t e t r a h e d r i t e borders a g r a i n of a r s e n o p y r i t e . W i t h i n t h i s g r a i n are c l u s t e r s of f i n e p a r t i c l e s of go l d . This i s seen i n f i g u r e f i v e . While the mineral has been r e f e r r e d to as t e t r a h e d r i t e microchemical analyses prove the presence of small amounts of a r s e n i c . The mineral probably represents an isomorphous mixture of t e t r a h e d r i t e and t e n n a n t i t e although t e t r a h e d r i t e i s by f a r the major c o n s t i t u e n t . Bournonite i s around the borders of t e t r a h e d r i t e appar e n t l y r e p l a c i n g i t . The i d e n t i f i c a t i o n of the mineral was confirmed by Dr. R.M. Thompson. He states t h a t , although only very small amounts of mineral were obtained f o r an X-ray powder photograph, three d i s t i n c t l i n e s f o r bournonite were observed. Twinning can be n o t i c e d i n the bournonite. Figure s i x shows the e f f e c t of etching by potassium-cyanide. Bournonite i s negative while t e t r a h e d r i t e s t a i n s a l i g h t brown w i t h the p o l i s h i n g scratches becoming pronounced. O c c a s i o n a l l y found i n the ore are pockets and small v e i n l e t s of grey sulphides. The c o n s t i t u e n t minerals are mainly a mixture of jamesonite, other s u l p h o - s a l t s , and s t i b n i t e . Several spectrographic analyses showed the presence * "of s i l v e r , g o l d , l e a d , i r o n , and antimony. The minerals seem to be antimonides e n t i r e l y f o r i n no spectrographic or micro chemical a n a l y s i s was any a r s e n i c present. Gold i s present as small p a r t i c l e s at the boundaries of the various minerals i n tne v e i n l e t s and a l s o as blebs w i t h i n the minerals. The source of the s i l v e r i s not d e f i n i t e l y known but i n the 23 jamesonite are small i n c l u s i o n s of. a d i f f e r e n t mineral. This mineral i s negative to potassium-hydroxide, d i s t i n g u i s h i n g i t from jamesonite, and gives strong r e a c t i o n s w i t h potassium- cyanide and m e r c u r i c - c h l o r i d e . These t e s t s along w i t h others i n d i c a t e the presence of a s i l v e r mineral but the i n c l u s i o n s are too s m a l l to i s o l a t e and t e s t c o n c l u s i v e l y . Gold i s c h a r a c t e r i z e d by: f i r s t the smallness of the p a r t i c l e s and second, i t s wide v a r i e t y of occurrences. A f a i r l y l a r g e p a r t i c l e of v i s i b l e gold was noted i n sample three hole 54. G e n e r a l l y the g o l d can only be detected by microscopic examination. The l a r g e s t p a r t i c l e observed m i c r o s c o p i c a l l y i s 150 microns i n diameter. Figure seven shows a g r a i n measuring t h i r t y microns i n diameter. A l l the gold i s a deep yellow c o l o r so i t contains very l i t t l e s i l v e r . I t s general manners of occurrence are as i s o l a t e d g r a i n s , and a s s o c i a t e d w i t h various s u l p h i d e s . When occ u r r i n g alone i t i s found as very small p a r t i c l e s w i t h i n quartz grains and s c a t t e r e d throughout a matrix of quartz and carbonate. Commonly i t i s at the borders of carbonate and quartz grains but never wholly w i t h i n the carbonate. Sample f i v e , hole 54, i s from a two-foot s e c t i o n of core assaying 0,8 ounces of gold per ton but the only g o l d noted i n the s e c t i o n i s f i n e grains disseminated i n a quartz carbonate gangue. The sulphide content of t h i s part of the core s e c t i o n i s very low compared to other parts that d i d not have as hig h assays. 24 P y r i t e and a r s e n o p y r i t e commonly have gold i n or close to them. Figure eight shows a p a r t i c l e of gold w i t h i n a g r a i n of p y r i t e . Figure nine shows gold and a r s e n o p y r i t e while f i g u r e ten shows gold at a boundary of carbonate and quartz close to both arseno p y r i t e and p y r i t e . The a s s o c i a t i o n of gold w i t h the s u l p h o - s a l t s and s t i b n i t e i s much more intimate than i t s a s s o c i a t i o n w i t h p y r i t e and a r s e n o p y r i t e . As p r e v i o u s l y mentioned, gold occurs as c l u s t e r s of small p a r t i c l e s and blebs w i t h i n t e t r a h e d r i t e , as small g r a i n s w i t h i n and at the borders of d i f f e r e n t minerals i n the v e i n l e t s of grey s u l p h i d e s . In examining d r i l l core i n the f i e l d , s e c tions c o n t a i n i n g these grey sulphide minerals are thought to be i n d i c a t i v e of good assays. The reason f o r t h i s i s r e a d i l y seen when the ore i s examined m i c r o s c o p i c a l l y . A l t a i t e (?) occurs w i t h s t i b n i t e i n sample f o u r , hole 72. The mineral cannot be s t a t e d d e f i n i t e l y to be a l t a i t e but i t has the c h a r a c t e r i s t i c p r o p e r t i e s and etch r e a c t i o n s . Micro chemical analyses and a spectrographic a n a l y s i s show the presence of t e l l u r i u m and l e a d so i t i s presumed to be a l t a i t e . Figure eleven shows t h i s mineral i n contact w i t h s t i b n i t e . Non-metallic Minerals.; Quartz and c a l c i t e are the two main gangue minerals both being g e n e r a l l y f i n e - g r a i n e d though some coarse c r y s t a l s are present. On the whole they are present i n the zone i n about equal proportions but the c e n t r a l part of the ore zone has a 25 l i t t l e greater proportion of quartz.. Even here the rock appears as a mass of intermixed fine quartz and calcite crystals. There are various ages of both quartz and calcite as small veinlets may be seen cutting across other areas of these same minerals. Chlorite is i n varying proportions in every sample. It is only present as a few widely scattered shreds in the centre of the ore zone but these shreds become coarser and more numerous as either wall is approached. Sericite.is found mainly as narrow veinlets and clusters of small crystals closely associated with the metallics. Paragenesis: The following table shows the proposed sequence of deposition of the various minerals. It is d i f f i c u l t to place several mineral's because of their limited occurrence. Also there may be several ages of mineralization. Pyrrhotite may form a separate stage of mineralization as i t is unusual to find i t and stibnite so closely associated. Pyrite and arsenopyrite appear to bev the earliest crystallized minerals. Intermixed masses of the two minerals indicate a simultaneous deposition. Grains of massive pyrite can be seen formed around euhedral grains of arsenopyrite but the reverse is also true. Quartz was deposited early with pyrite and arsenopyrite but its deposition much later. After much of the pyrite and arsenopyrite were deposited there was a period of fracturing followed by further 26 deposition of quartz and carbonate. Pyrrhotite is an early mineral but i t is later than some quartz as irregular grains of i t are seen formed around euhedral edges of quartz crystals. There is no evidence to show that pyrrhotite was deposited in a different period of mineralization. Some chalcopyrite was formed at approximately the same time as pyrrhotite. Some of i t was much later being more closely related to the f i r s t deposition of stibnite. Exsolution blebs of chalcopyrite are seen in sphalerite and exsolution blebs of sphalerite are seen in chalcopyrite so the two minerals were deposited at approximately the same period. No chalcopyrite bordering stibnite has any associated sphalerite. It is d i f f i c u l t to place tetrahedrite in the sequence for i t has few associations. However^ i t is seen to be later than pyrite, quartz, and some calcite. Bournonite replaces tetrahedrite so is later. Stibnite appears to have two periods of deposition. Its f i r s t was as isolated grains and veinlets in a quartz-carbonate gangue. The later deposition was simultaneous with that of jamesonite and other sulpho-salts within the veinlets of grey sulphides previously described. Altaite (?) appears to be later than stibnite but due to it s rare occurrence and the small size of the particles i t is d i f f i c u l t to place accurately. Gold appears to have several deposition periods or at least a very long single period. It is found with early quartz 27 and i n p y r i t e and arsenopy r i t e g r a i n s . These f a c t s i n them selves do not.prove e a r l y g o l d , but i n t h i s r espect, the problem i s s i m i l a r t o tha t of many other p r o p e r t i e s such as Hedley B.C. (9, p.5) In such occurrences gold i s considered to be an e a r l y mineral. Gold i s deposited l a t e r at approximately the same time as t e t r a h e d r i t e . S t i l l l a t e r was i t s d e p o s i t i o n w i t h sulpho- s a l t s i n v e i n l e t s of grey s u l p h i d e s . TABLE 2. MINERAL SEQUENCE P y r i t e Arsenopyrite Quartz Gold P y r r h o t i t e C h a l c o p y r i t e S p h a l e r i t e T e t r a h e d r i t e Bournonite Jamesonite S t i b n i t e A l t a i t e C a l c i t e o 28 X 50 P l a t e 1. P h o t o m i c r o g r a p h showing the g e n e r a l c h a r a c t e r o f the m i n e r a l i z a t i o n . P y r i t e ( P ) , A r s e n o p y r i t e ( A ) , Q u a r t z (Q), and Carbonate (C) X 350 P l a t e 2. S t i b n i t e ( S t ) w i t h unknown i n c l u s i o n s (U) 29 X 4 0 0 P l a t e 3. C h a l c o p y r i t e b l e b s (Ch) i n s p h a l e r i t e (Sph) and C n a l c o p y r i t e b o r d e r i n g p y r r h o t i t e (Py) P y r i t e (p) X 1-50 P l a t e 4. Heterogeneous mass o f p y r r h o t i t e and s m a l l g r a i n s of an unknown opaque m i n e r a l (0) i n q u a r t z (Q) and carbonate (C) 30 X 450 P l a t e 6. B o u r n o n i t e (B) r e p l a c i n g t e t r a h e d r i t e (T). The t e t r a h e d r i t e has been e t c h e d w i t h ECU 3 1 X 475 P l a t e 8. A p a r t i c l e of gold (Au) i n p y r i t e (P) 3 2 X 500 Plat e 10. T y p i c a l occurrence of f i n e p a r t i c l e s of gold (Au) w i t h p y r i t e (P) and arsenopyrite (As) 33 X 450 P l a t e 11. A l t a i t e ( A l ) i n a m a t r i x of s t i b n i t e ( S t ) and a l t e r e d s t i b n i t e ( A.St) X 450 P l a t e 12. Jamesonite ( J ) and s t i b n i t e ( S t ) w i t h smooth b o u n d a r i e s i n the v e i n l e t s o f g r e y s u l p h i d e s . The s t i b n i t e has been e t c h e d w i t h KCN. 34 Mineralizing Solutions: The medium of the ore and gangue minerals may be con sidered to be hot aqueous solutions containing the elements Fe, As, Au, S i , Cu, Zn, Pb, Sb, Ca, S, and Te. When precipitated from solution the elements combined to form the various minerals deposited in the sheared zones of the host rocks. Although there is l i t t l e evidence of replacement by the precipitating minerals much of the sheared material in the ore zone must have been dissolved. I n i t i a l l y much arsenic, s i l i c a , and iron were precipitated. Later the precipitating minerals showed an increase of antimony but a sharp decrease in the content of arsenic. WALL ROCK ALTERATION "The wall rocks have been l i t t l e altered by the ore solutions. Previous to ore deposition, as borne out in chapter five,-the rocks were probably altered largely to albite, chlorite, epidote, and calcite. Calcite and quartz have been introduced hydrothermally in large quantities and near the sulphides there has been much sericitization. Chlorite, shreds may be seen in the ore i t s e l f gradually increasing in quantity away from the ore until they become a major constituent of the rock. One core sample was taken nine feet away from the edge of the ore on the hanging wall side and another was taken four feet away from the ore on the footwall side. Both specimens show much calcite and quartz in fine-grained masses and some coarse grains. In some cases these have been cut by later veinlets of quartz and calcite. 35 Feldspar i s present i n the form of a l b i t e some c r y s t a l s a l s o being f r a c t u r e d and veined by c a l c i t e . Much of the c h l o r i t e i s i n s h r e d - l i k e form. This has l i k e l y been formed by shear ing a c t i o n r a t h e r than nydrothermal s o l u t i o n s . A very i n t e r e s t i n g feature may be noted i n the w a l l rock At the property the appearance of numerous greyish-brown f l e c k s i n the d r i l l core i s taken as i n d i c a t i o n of p r o x i m i t y to the ore zone. A s i m i l a r type of occurrence has been noted at the Giant property. There i t i s r e f e r r e d to as "snowflake a l t e r a t i o n " . The close-spaced f l e c k s ere g e n e r a l l y l e s s than one-eighth of an in c h i n lengt h . They have an i r r e g u l a r o u t l i n e and random o r i e n t a t i o n . X 35 Plat e 13. Photomicrograph of a t h i n s e c t i o n from sample 7, hole 54, showing "snowflake a l t e r a t i o n " . Note the mesh of i n t e r s e c t i n g shreds (black) w i t h i n a matrix of quartz, c a l c i t e , snd c h l o r i t e . 36 Observed microscopically the flecks are seen to consist of small shred-like particles that suggest an original crystal outline. Plate thirteen shows a network of shreds within a single fleck. The general form is rhombic but i t is d i f f i c u l t to surmise just what the original mineral was. Under the high power objective lens the shreds exhibit a fine crystalline form possessing a high birefringence. In polished sections the flecks look much like small grains of sphalerite. Some of them contain numerous small crystals of a metallic mineral possibly magnetite. A spectrographic analysis proved no titanium to be present, thus eliminating the possibility of leucoxene. However, the proximity of these grain masses to the ore zone suggests hydrothermal alteration of some original constituent of the rock to a type of clay mineral. • TYPE OF DEPOSIT The following points seen in this examination would tend to classify the deposit as mesothermal: 1. The general mineral assemblage such as pyrite, arseno pyrite, chalcopyrite, sulpho-salts, and their paragenesis are characteristic of mesothermal deposits. 2. No vugs or comb structure were noticed in the sections examined. 3. There is no abundance of high temperature minerals and no characteristic low temperature minerals. 4. The alteration zone seems to be typical of mesothermal deposits. Pyrrhotite, considered to be a high- temperature mineral 37 i s present only i n one place and i n small amounts. The presence of s t i b n i t e and a l t a i t e could be explained as a p r e c i p i t a t i o n at a l a t e stage when the s o l u t i o n s were c o o l e r . AGE OF DEPOSIT There i s l i t t l e evidence upon which to base the age of m i n e r a l i z a t i o n . G e n e t i c a l l y r e l a t e d to the Akaitcho ore body are those of the Con, Negus, and Giant mines. In the Con mine, the shearing i n which Vein 17 i s formed i s younger than a l a t e diabase dyke. (5 (b) :p.39). A l s o i n the Con mine the C4 shear zone i s cut by an u n a l t e r e d l a t e diabase dyke (7, p. 108) These dykes are considered t o be l a t e Proterogoic i n age. I t appears as though the m i n e r a l i z i n g s o l u t i o n s were introduced towards the end of diabase i n t r u s i o n . J o l i f f e (5 ( b ) , p. 41) proposed that channelways f o r the ascent of ore s o l u t i o n s were provided by the major f a u l t s . I n many places , e s p e c i a l l y near the Giant mine, the f a u l t zones are very narrow to permit the passage of s o l u t i o n s . A l s o , the same type of m i n e r a l i z a t i o n i n the ores would be expected t o occur i n the f a u l t s but t h i s i s not the case. There i s a p o s s i b i l i t y , then, of some other channelways f o r the ore- forming s o l u t i o n s . CONCLUSIONS In w r i t i n g conclusions to t h i s r e p o r t a comparison i s made w i t h neighboring d e p o s i t s . The mineral assemblage of the Akaitcho ore i s very s i m i l a r to that of the Giant, Negus, and Con mines. The f i n e texture of the m i n e r a l s , the quartz- c a r b o n a t e - c h l o r i t e - s e r i c i t e gangue, and the v e i n l e t s of grey 38 sulphides are common to each ore. A l l the deposits are in shear zones close to the West Bay Fault. The Giant property with i t s numerous ore bodies is just to the south of the Akaitcho property. In the opinion of the writer i t seems reasonable to expect that, providing favorable structure is present, other ore bodies w i l l be found on the Akaitcho property. The Giant ore-bodies have been proven to a depth of over 500 feet while those of the Con mine have been proven e- to approximately 2000 feet. It is not improbably that those of the Akaitcho w i l l also continue to similar depths. The fine texture of the gold, generally - 200 mesh, and the presence of arsenic and antimony are factors to be con sidered in milling the ore. 39 BIBLIOGRAPHY. 1. Barlow/, A.E. 'Ottawa N a t u r a l i s t , 1895 2. Bateman, A.M. Economic Min e r a l Deposits 3. Cooke, H.C, James, W.F., and Mawdsley, J.B. Memoir 166. Geology and Ore Deposits of Rouyn- Harricanaw Region, Quebec. 1931 4. Harker, A. Metamorphism 5. J o l l i f f e , A.W. (a) P r e l i m i n a r y Report. Y e l l o w k n i f e R i v e r Area, Northwest T e r r i t o r i e s , Paper 3 6 - 5 , 1936. (b) P r e l i m i n a r y Report, Y e l l o w k n i f e Bay - Prosperous Lake Area, Northwest T e r r i t o r i e s . Paper 38 - 21, 1938. (c) Rare Element Minerals i n Pegmatites, Y e l l o w k n i f e , Beaulieu Area, Northwest T e r r i t o r i e s . Paper 44 - 12, 1944. 6. Lindgren, W. M i n e r a l Deposits. 7. Lord, C.S. Memoir 230. M i n e r a l Industry of the Northwest T e r r i t o r i e s . 1941 8. T y r r e l l , G.W. The P r i n c i p l e s of Petrology. 9. Warren, H.V. and Cummings, J.M. T e x t u r a l R e l a t i o n s i n Gold Ores of B r i t i s h Columbia. SCALE FROBISHER EXPLORATION CO. LTD. AKAITCHO Y E L L O W K N I F E GOLD MINES LTD. BLOCK DIAGRAM OF MINERALIZED SHEAR ORE SHOOT ' SHE AR ZONE : A M A N I F O L D C O L / R T E S Y O F J " MacLLOD 

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