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Geology of the Ironmask batholith Mathews, William Henry 1941

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GEOLOGY OF THE IRONMASK BATHOLITH by W i l l i a m Henry Mathews A t h e s i s submitted 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 the degree of Master of Applied Science i n the Department of Geology The U n i v e r s i t y of B r i t i s h Columbia A p r i l 1941 TABLE OF CONTENTS page Introd u c t i o n 1 General.. Description. Location 2 A c c e s s i b i l i t y . 2 Exposures 3 Previous Reports 4 General Geology 6 Table of Formations 6 De t a i l e d Geology 7 Cache Creek Series 7 N i c o l a Formation 7 P e r i d o t i t e *• 9 Ironmask Batfeolith 1 2 General D e s c r i p t i o n 1 2 I n t e r n a l R e l a t i o n s 13 E x t e r n a l R e l a t i o n s 13 Petrology 15 Intermediate Type 1 6 Basic Type 1 8 A l k a l i n e Type 19 Hydrothermally A l t e r e d Type 20 Red-Feldspar Type 2 2 Mineralogy P l a g i o c l a s e Feldspar 23 page ' : Orthoclase 24 Quartz 24 Augite 2 5 Hornblende 26 B i o t i t e 27 C h l o r i t e 2 7 Magnetite 28 Apatite 3 1 Epidote 3 2 Carbonates 33 P y r i t e 33 Garnet 34 Titanium Minerals 34 Age and C o r r e l a t i o n 34 G r a n i t i c B a t h o l i t h 35 Quartz-Feldspar Porphyry 36 F r e d e r i c k Formation 36 Kamloops Volcanics 37 Pleistocene and Recent Deposits 39 Economic Geology Magnetite Deposits 39 Copper Deposits 40 ILLUSTRATIONS Figure page 1. Heavily d r i f t covered area west of Sugarloaf H i l l 3 2. Photomicrograph of p e r i d o t i t e , ..X 10 10 3 . Photomicrograph of p e r i d o t i t e , X 3 0 11 4. S t r u c t u r a l s e c t i o n across the Ironmask b a t h o l i t h 14 5. Graph of augite-hornblende r e l a t i o n s 18 6 - Graph of pl a g i o c l a s e f e l d s p a r r e l a t i o n s 23 7 . Graph of orthoclase r e l a t i o n s 24 8. Photomicrograph - zoning i n augite 25 9. Graph of augite r e l a t i o n s 26 10, Graph of hornblende r e l a t i o n s 26 11. Graph of b l o t i t e r e l a t i o n s 2 7 1 2 . Graph of c h l o r i t e r e l a t i o n s 27 13. Photomicrograph - S c h i l l e r structure i n augite 2 8 14. Photomicrograph - Magnetite, c h l o r i t e and epidote secondary a f t e r pyroxene( ?•) . 29 15. Photomicrograph - Magnetite f o l l o w i n g c r y s t a l boundaries and r e p l a c i n g e a r l i e r augite 3 0 16. Graph of magnetite r e l a t i o n s 31 1 7 . ' S p i r a l ' c r y s t a l of a p a t i t e 3 1 18. A p a t i t e occurring along margins and p a r t l y enclosed by c r y s t a l s of primary magnetite 32 19. Graph of a p a t i t e r e l a t i o n s 3 2 20. Graph of epidote (and c l i n o z o i s i t e ) r e l a t i o n s 33 Rosiwal analyses of Ironmask rocks i n rear Map of Ironmask b a t h o l i t h i n rear 1 GEOLOGY OF THE IRONMASK BATHOLITH Introduction The f o l l o w i n g report comprises the r e s u l t s of both the f i e l d I n v e s t i g a t i o n s of a rat h e r basic deep seated i n t r u s i v e body, the s o - c a l l e d Ironmask b a t h o l i t h , s i t u a t e d a few miles t o the south and west of Kamloops B.C., and labrqjbary studies •* fa . of a representative s u i t e of rocks from t h i s i n t r u s i v e . This b a t h o l i t h i s of i n t e r e s t to the geolog i s t not only because of i t s rather unusual composition but al s o because of i t s a f f i l i a t i o n s w i t h commercial and near-commercial deposits of copper and i r o n . The f i e l d i n v e s t i g a t i o n s were ,carried on by a party under Dr.W.E.Cockfield, sent out by the Geological Survey of Canada to continue the g e o l o g i c a l mapping on a scale of fo u r miles to the in c h of the East Half of the Ashcroft Area. In the f i e l d , Dr C o c k f i e l d was a s s i s t e d by the w r i t e r and Mr.;S..A.Kerr. Laboratory studies of the rocks c o l l e c t e d i n the f i e l d were made by the w r i t e r during the winter of 1940-41 at the U n i v e r s i t y of B.C. under the guidance of Dr. C O . Swans on, and i n c l u d i e d the examination of hand specimens, some twenty f i v e t h i n s e c t i o n s , and one polished s e c t i o n of magnetite ore. The w r i t e r here wishes to express h i s a p p r e c i a t i o n of the assistance extended him by Dr. C o c k f i e l d , Dr.H.C.Gunning and Dr. Swanson during the course of the work. General D e s c r i p t i o n Location The Ironmask "batholith extends i n a northwest d i r e c t i o n from Separation Lake, seven miles south of Kamioops, f o r eighteen miles to the v i c i n i t y of Frederick on the north shore of Kamloops Lake, and has a rather uniform width throughout of three miles. Towards it-s- northwestern end, the b a t h o l i t h i s o v e r l a i n by l a t e r v o l c a n i c rocks and the e x i s t i n g exposures represent only a part of i t s t o t a l extent. The b a t h o l i t h , throughout i t s length, l i e s w i t h i n the broad v a l l e y of the Thompson R i v e r and Kamloops Lake and i t s exposures are r e s t r i c t e d i n e l e v a t i o n between 1100/feet above sea l e v e l at the surface of the lake and 3692 feet at the summit of Sugarloaf H i l l . As a consequence of i t s r e l a t i v e l y low e l e v a t i o n , the greater part of the area c o n s i s t s of open grass lands, and except i n creek bottoms and swamps, the remainder i s covered by a l i g h t f o r e s t of Yellov; Pine (Plnus poriderosa) w i t h l i t t l e or no underbrush. S c G e s s i b i l i t y n Roads are numerous throughout the area and there i s no p o i n t on the Ironmask b a t h o l i t h that cannot be approached to w i t h i n two miles by means of automobile. In a d d i t i o n , both shores of Kamloops Lake and the Thompson Riv e r are traversed by the t r a n s c o n t i n e n t a l l i n e s of the Canadian P a c i f i c and Canadian National railways r e s p e c t i v e l y . 3 Exposures Exposures are not, on the whole, e s p e c i a l l y good. Much of the area i s covered by g l a c i a l deposits often of considerable depth. These areas, however, cons i s t l a r g e l y of open grass Figure 1. Heavily d r i f t covered area west of Sugarloaf H i l l , showing drumlinsy shallow a l k a l i n e lakes e t c . where i t i s possible to locate r e a d i l y any outcrops that may be present. On the other hand, the rocks of Ironmask H i l l are t o l e r a b l y w e l l exposed, while several of the h i l l s i n the area, B a t t l e B l u f f , Roper H i l l (Cherry B l u f f ) and Sugarloaf H i l l present on nearly a l l faces almost complete exposures, though at a number of points t h e i r slopes are so p r e c i p i t o u s that they are a c c e s s i b l e only to the most foolhardy rock climber. I n c i d e n t a l l y , reports of r a t t l e s n a k e s on the rocky areas north of Kamloops Lake d i d not encourage the examination of some of the slabby outcrops at too close quarters. However, no snakes were encountered. 4 Previous Reports The f i r s t g e o l o g i c a l examination of the Ironmask b a t h o l i t h was made i n 1877 by G.M.Dawson who studied the-Geqlogical Survey of Canada - Report of Progress 1877-78 exposures on e i t h e r shore of Kamloops Lake. At that time,' he concluded that the great thickness of surrounding T e r t i a r y v o l c a n i c rocks, dipping outwards from the b a t h o l i t h and composed of a considerable quantity of agglomeratic m a t e r i a l represented the f l a n k s of a great volcano of which the d i o r i t e of Cherry and B a t t l e B l u f f s was the core. In a second report Geological Survey of Canada - Annual Report 1894 - The Kamloops Map-sheet - by G.M.Dawson i n 1894, Dawson r e i t e r a t e d h i s b e l i e f that Cherry and B a t t l e B l u f f s represented a "focus of v o l c a n i c a c t i v i t y of the T e r t i a r y period" though admitted that a great part of the d i o r i t e mass "must be regarded as the f l o o r upon which the T e r t i a r y formations r e s t " . R.A.Daly i n 1911-12 a f t e r examining exposures of the Ironmask b a t h o l i t h along the south shore of Kamloops Lake Geological Survey of Canada - Memoir 68 - Golden to Kamloops by R.A.Daly a l s o the same report abbreviated i n -Geological Survey of Canada - Guide Book No.8 - Part I I pages 232-233 - by R.A.Daly 5 concluded -" . . . th a t the Cherry B l u f f body i s an i n j e c t i o n ( l a c c o l i t h i c ; ? ) of pr e - T e r t i a r y and l a t e T r i a s n i c or p o s t - T r i a s s i c date. A f t e r i t s i n t r u s i o n i t was unroofed by erosion and, during the Oligocene, was covered with the lavas and freshwater sediments of the Kamioops group. The l a t t e r were afterwards buckled i n t o a roughly domical s h e l l about the e x t r a o r d i n a r i l y strong and tough mass beneath them. This deformation was presumably contemporaneous with that which has deformed the Oligocene formations elsewhere i n the plateau region. "However mistaken t h i s explanation may be i n d e t a i l s , i t i s c l e a r l y more In accord w i t h the f a c t s than Dawson's suggestion that the Cherry B l u f f mass represents a p r i n c i p a l vent of the T e r t i a r y lavas." D e s c r i p t i o n s of the i n d i v i d u a l / mineral deposits associated with the Ironmask b a t h o l i t h are to be found i n the Reports of the B.C.Minister of Mines from 1889 to 1928, and a d e t a i l e d account of the i r o n deposits has been published i n Volume I , Economic S e r i e s No.3 of the Geological Survey of Canada ( I r o n Ores of B r i t i s h Columbia and the Yukon). General Geology The Ironmask b a t h o l i t h Is i n t r u s i v e i n t o v o l c a n i c and sedimentary rocks of T r i a s s l c age, and occurs i n close proximity to s t i l l o lder sedimentary rocks of Permo-Carboniferous age'. I t i s unconformably o v e r l a i n by po s s i b l y two se r i e s of v o l c a n i c rocks, the younger containing interbedded freshwater sediments of Oligocene age. A l l the formations of the area are o v e r l a i n by a mantle of g l a c i a l d r i f t from zero to many fe e t i n thickness, and l o c a l l y by f l u v j a t i l e and l a c u s t r i n e deposits of L a t e - G l a c i a l and Recent age. Table of Formations Age Name Character Recent L a t e - G l a c i a l P leistocene Alluvium 0 -Raised de l t a s 0 -" W h i t e s l l t s " 0 -G l a c i a l d r i f t 0 -400 1 200' 50' 200' unconformity Oligocene Up. Kamloops Voles. B a s a l t , t u f f , aggl.2000'+ T r a n q u i l l e Seds. Lacustrine deposits, shale, sandstone, conglomerate, coal 100' - 500' Lower Kamloops R h y o l i t e , dacite etc V o l c a n i c s 1000'+ unconformity(?) (?) F r e d e r i c k form. Agglomerates, flows etc. unconformity Upper Mesozoic Quartz porphyry dikes and and(?) Lower stocks T e r t i a r y G r a n i t i c b a t h o l i t h (to south of Ironmask area) Ironmask b a t h o l i t h Pyroxenite, gabbro, d i o r i t e , monzonite, a l b i t l t e P e r i d o t i t e i n t r u s i v e contact 7 i n t r u s i v e contact Up.Triassic N i c o l a formation Flows, t u f f , agglomerate, limestone, conglomerate I (§000 * + disconformity(?) Pennsylvanian Cache Creek A r g i l l i t e , amphibolite or Permian Ser i e s D e t a i l e d Geology Cache Creek Series The oldest rocks occurring i n the v i c i n i t y of the Ironmask b a t h o l i t h are the a r g i l l i t e s and amphibolites exposed south of Separation Lake and i n occasional bands near Kamloops. F o s s i l evidence has proved t h i s s e r i e s to be of Pennsylvanian or Permian age, and,therefore, part of Dawson's Cache Creek S e r i e s . At a number of po i n t s , t h i s Series i s apparently cut by s t r i k e f a u l t s , some of which have s u f f i c i e n t displacement to b r i n g i t s s t r a t a i n t o contact with beds of the N i c o l a formation at l e a s t s e v e r a l hundred f e e t s t r a t i g r a p h i c a l l y higher. Exposures at the contact of the Ironmask b a t h o l i t h and these sediments, near Separation Lake, were extremely-poor and the r e l a t i o n s could not be s a t i s f a c t o r i l y determined. I t i s quite possible that another of the s t r i k e f a u l t s marks the contact, but the Ironmask b a t h o l i t h which intrudes the T r i a s s i c N i c o l a formation, i s c l e a r l y younger than the Cache Creek s e r i e s . N i c o l a Formation Overlying the Cache Creek s e r i e s w i t h no apparent angular 8 unconformity i s the N i c o l a formation. At the base i s several hundred feet of conglomerate containing fragments of a r g i l l i t e and q u a r t z i t e derived from the Gache Greek s e r i e s . Overlying the conglomerate i s a great thickness, probably of.the order of 5000 f e e t , of v o l c a n i c m a t e r i a l , flows, agglomerates and o c c a s i o n a l l y w e l l bedded t u f f s , a l l of which may now be classed under the general term 'greenstones'. At one horizon only, a rather t h i c k bed of limestone was observed, but i t could be traced f o r only a l i m i t e d distance along i t s s t r i k e . The N i c o l a formation i s exposed over a greater part of the area mapped (see.map at endrof['report -), except towards the centre where i t has been intruded by the Ironmask b a t h o l i t h or buried under the Kamloops v o l c a n i c s . No f o s s i l s were obtained i n the N i c o l a i n t h i s area, but i t i s l i t h o l o g i c a l l y s i m i l a r to rocks ten to twenty miles to the south and west, i n which T r i a s s i c f o s s i l s have been found, and to the rocks of the type s e c t i o n on N i c o l a Lake, t h i r t y miles south. The N i c o l a formation has been folded, i n t h i s area, i n t o at l e a s t one major northwesterly trending syncline whose a x i s passes close to E d i t h Lake at the south end of the Ironmask b a t h o l i t h . Elsewhere i n the area, the rocks are too massive to permit I n t e r p r e t a t i o n of the general s t r u c t u r e , but whatever bedding has been observed s t r i k e s from N30°W to N60°W and c l o s e l y p a r a l l e l s the contact of the b a t h o l i t h . In d e t a i l , the a c t u a l contact of the N i c o l a formation w i t h the Ironmask b a t h o l i t h i s very d i f f i c u l t to l o c a t e . The s i m i l a r i t y of many of the phases of the i n t r u s i o n (e.g. specimens 3535, 3534§ etc.) to the much metamorphosed intruded greenstones was frequently "baf f l i n g . Numerous tongues of the i n t r u s i v e rocks penetrating the adjacent greenstones haveaiproduced a zone of v a r i a b l e width i n which rocks of both types may be found. Widespread a l t e r a t i o n by l a t e r hydrothermal s o l u t i o n s throughout the length of t h i s zone has, i n a d d i t i o n , e f f e c t i v e l y o b l i t e r a t e d any d i s t i n c t contacts between the i n t r u s i v e tongues and the greenstones. Many times • the contact of the Ironmask b a t h o l i t h was mapped as the middle of t h i s indeterminate zone between the r e l a t i v e l y unaltered greenstone and the unaltered and uncontaminated d i o r i t e and gabbro. P e r i d o t i t e One and a h a l f miles southeast, of Jacko Lake i s an area a few miles i n extent of p e r i d o t i t e . The exposures are on a small i s o l a t e d h i l l completely surrounded by an area of d r i f t beneath which are i t s contacts w i t h the N i c o l a formation. At one point, however, the p e r i d o t i t e i s cut by a d i o r i t e dike which has been re f e r r e d to the Ironmask b a t h o l i t h whose main mass i s exposed about three quarters of a mile to the northward. I t may conceivably be a part of the N i c o l a formation, although s i m i l a r rocks have not yet been found elsewhere i n t h i s v o l c a n i c s e r i e s . On the other hand, i t may represent a phase of the Ironmask b a t h o l i t h intruded somewhat e a r l i e r than the d i o r i t e d i k e , although the abundance of o l i v i n e i s c e r t a i n l y not c h a r a c t e r i s t i c of the o l i v i n e - f r e e 10 Ironmask rocks. The w r i t e r i s , however, i n c l i n e d to consider the p e r i d o t l t e as a minor i n t r u s i v e unrelated to e i t h e r the N i c o l a or Ironmask rocks. In t h i n s e c t i o n , t h i s rock was found to co n s i s t of large grains of o l i v i n e , averaging 4mm i n diameter, embedded i n a groundmass of serpentine, pigeonite, k a o l i n and magnetite. The rock therefore c l o s e l y corresponds to the d e s c r i p t i o n of a w e h r l i t e . In s p i t e of the p a r t i a l s e r p e n t i n i z a t i o n of the o l i v i n e g r a i n s , i t i s s t i l l p ossible to recognise t h e i r Figure 2 . Photomicrograph of p e r i d o t i t e showing mode of occurrance, o r i e n t a t i o n e t c . of o l i v i n e Slide SSI I A Xto o r i g i n a l o u t l i n e as e l l i p t i c a l and tending to be oriented, presumably by flow. The rounding of many of the corners of the o l i v i n e c r y s t a l s i s suggestive of abrasion and i s i n accord w i t h Bowen's hypothesis that u l t r a - b a s i c rocks are intruded as a granular mass w i t h a small amount of b a s a l t i c f l u i d as a l u b r i c a n t . The matrix, composed l a r g e l y of pigeonite w i t h smaller amounts of serpentine, magnetite and a fr^e k a o l i n i z e d feldspar!?) does not, however, resemble a normal 11 b a s a l t , nor does i t occur i n very minor amounts, but forms about 45% of the rock, e f f e c t i v e l y separating nearly a l l of the o l i v i n e g r a i n s . I t i s f a i r l y evident that the o l i v i n e grains had c r y s t a l l i z e d before the i n t r u s i o n of the rock to i t s present p o s i t i o n but there i s no reason to believe that i t was formed as a c r y s t a l accumulation from which the matrix had been squeezed. A Rosiwal a n a l y s i s of the rock i s as follows Figure 3 . Photomicrograph of p e r i d o t i t e showing character of matrix and development of serpentine and secondary magnetite i n o l i v i n e . Phenocrysts Matrix O l i v i n e Serpentine Magnetite 32% 23% Plgeonlte Serpentine Magnetite K a o l i n 25% 17% t o t a l t race 55% t o t a l 2.5% 0.5% 45% Ironmask B a t h o l i t h General D e s c r i p t i o n As has already been mentioned, the Ironmask b a t h o l i t h i s a si n g l e i n t r u s i v e mass,eighteen ih±lesn3>ongyethreeymiles wide, elongated i n a northwesterly d i r e c t i o n p a r a l l e l to the r e g i o n a l s t r i k e of the surrounding folded rocks. The b a t h o l i t h was buried i n ea r l y T e r t i a r y times under a t h i c k cover of v o l c a n i c rocks which have since been s u f f i c i e n t l y eroded to expose i t i n three i s o l a t e d areas. The f i r s t and l a r g e s t of these areas, at the southeast end of the b a t h o l i t h i s eleven miles i n length and f o r the most part i s bounded by the oldei& intruded rocks. To the north and west, however, the i n t r u s i v e disappears under a cover of l a t e r voloanies to reappear again as the Cherry and B a t t l e B l u f f masses on Kamloops Lake. This second area i s roughly e l l i p t i c a l i n plan, four and a h a l f miles from east t o west, two and a h a l f miles from north to south, and i s almost p e r f e c t l y b i s e c t e d by the waters of Kamloops la k e . The t h i r d and smallest exposure of the Ironmask b a t h o l i t h , at the i n t e r s e c t i o n of Cherry and Pendleton creeks, c o n s i s t s of only one or two outcrops i n an area probably not over an acre i n extent. In the f i e l d , the Ironmask rocks are characterized by a gray, greenish gray or l e s s often pink to red c o l o r , a lack of quartz and often an abundance of dark minerals and of magnetite, and an extreme amount of J o i n t i n g making i t d i f f i c u l t to procure a fr e s h hand specimen of any s i z e . The f e l d s p a r s have of t e n l o s t t h e i r glassy l u s t r e both as a 13 r e s u l t of hydrothermal a l t e r a t i o n and of the weathering favored b'y the extreme j o i n t i n g . The texture i s , i n general, f i n e r grained than i n normal g r a n i t i c rocks, thouth frequently showing considerable v a r i a t i o n s w i t h i n a small area. Most of the rocks can, however, be r e a d i l y recognized as d i o r i t e s and gabbros. I n t e r n a l R e l a t i o n s Daly has a p t l y described the b a t h o l i t h as ' s c h l i e r i c and heterogeneous'. Throughout the i n t r u s i v e body are numerous masses or 's c h l i e r e n ' of l i m i t e d extent and d i f f e r i n g markedly both i n texture and composition from the normal rock, though grading i n t o i t across vague contacts. An e x c e l l e n t example of such a v a r i a t i o n was found at s t a t i o n 3 5 1 4 where three phases with great d i f f e r e n c e s i n g r a i n s i z e and some d i f f e r e n c e s i n composition (Specimens 3 5 l 4(A-C), t h i n sections 3 5 1 4 B and 3514-C) appeared on a si n g l e outcrop p o s s i b l y twenty feet i n diameter. Generally, as a r e s u l t of both vague contacts and poor exposures i t was impossible to determine, anything of the form, age r e l a t i o n s or o r i g i n of these abnormal phases. L o c a l l y , as at the Ironmask mine,A of a l b i t i t e and b a s a l t , almost c e r t a i n l y g e n e t i c a l l y r e l a t e d to the b a t h o l i t h could be seen c u t t i n g the country rock. In the case of the a l b i t i t e d i k e s , there i s some i n d i c a t i o n that they o r i g i n a t e d by replacement rather than by the i n t r u s i o n of a soda r i c h magma. Ext e r n a l R e l a t i o n s Mention has already been made of the elongation of the Ironmask "batholith p a r a l l e l to the r e g i o n a l s t r i k e of the intruded rocks and the l o c a l p a r a l l e l i s m of i t s contact to the s t r i k e of the adjacent "beds. At f i r s t s i g h t , these f a c t s , along with the rather uniform width of the i n t r u s i v e would i n d i c a t e a l a c c o l i t h i c or s i l l - l i k e form as,indeed, was suggested "by Daly.- A reference to the s t r u c t u r a l Southwest Northeast Figure 4. S t r u c t u r a l s e c t i o n across the Ironmask b a t h o l i t h and major syncline i n N i c o l a formation along l i n e A •+ A i n map. Scale l" = 2 miles N i c o l a formation Q—r Granite <yy Cache Cr. s e r i e s Ironmask b a t h o l i t h X"7 s e c t i o n ( f i g . 4 . ) accross the b a t h o l i t h and intruded rocks north of E d i t h Lake i n d i c a t e s , however, that t h i s impression i s i n c o r r e c t . There, the b a t h o l i t h occupies the e n t i r e east limb of a syncline between i t s a x i s and the base of the N i c o l a three miles to the east. Not a trace of the i n t r u s i v e i s to be found between the s y n c l i n a l a x i s and the base of the N i c o l a , nearly four miles to the southwest. I t seems evident, therefore, that the Ironmask rocks have not been intruded along any horizon i n the enclosing Nicola, formation and, t h e r e f o r e , belong to a c r o s s - c u t t i n g body of 15 s u f f i c i e n t s i ze (about 45 square miles) to warrant the term b a t h o l i t h . The structure of the rocks close to i t s contacts, moreover, suggests that the i n t r u s i v e rocks have 'replaced' by stoping etc. rather than displaced the beds as would be expected i n a l a c c o l i t h or p h a c o l i t h , nor i s there any apparent zoning w i t h i n the i n t r u s i v e mass. Petrology In the t h i n s e c t i o n s , the rocks of the Ironmask b a t h o l i t h can be shown to have the same heterogeneous character as was evident i n the f i e l d . They range, i n general, from an augite monzonite to a melagabbro, and include a small f r a c t i o n of s t i l l more a c i d types, a l b i t i t e , and more basic types, j a c u p i r a n g i t e . V a r i a t i o n s from the normal types, le a d i n g to concentrations of hornblende or to more c a l c i c or sodic feldspars are not uncommon, and attempts to e x p l a i n these v a r i a t i o n s by simple magmatic processes, such as c r y s t a l s e t t l i n g , were completely unsuccessful. While, i n general, the rock types f a l l i n a more, or l e s s complete s e r i e s between the most basic and the most a c i d v a r i e t i e s , such as would be expected i n normal d i f f e r e n t i a t i o n , the e f f e c t s of other processes, f o r example hydrothermal a l t e r a t i o n , are superimposed on the f i r s t to Introduce some of the complexities noted. Apart from these v a r i a t i o n s , however, the rocks show a number of c h a r a c t e r i s t i c features throughout. Quartz i s almost completely absent, having been found i n only one ( s l i d e 4017) of the twenty two rocks examined i n t h i n s e c t i o n . No feldspathoids were found i n any s l i d e . Augite i s present, often i n abundance, i n eighteen of the twenty two rocks examined, and i n three of the remaining four i t i s believed to have been o r i g i n a l l y present but since replaced by c h l o r i t e . No orthorhombic pyroxene was found. Magnetite i s commonly present i n amounts from 3% to 6% and i n only two rocks (245 dike and 245 wall) i s i t absent. A p a t i t e i s present i n a l l but three of the rocks, though u s u a l l y i n very minor amounts. The f e l d s p a r s show considerable v a r i a t i o n i n composition but are almost u n i v e r s a l l y badly a l t e r e d to s e r i c i t e or k a o l i n or both. Orthoclase was found i n only four of the rocks, though i t may have been undetected amid some of the badly a l t e r e d p l a g i o c l a s e i n others. The rocks examined could be roughly grouped i n t o four main c l a s s e s , the f i r s t , an intermediate type making up the greater part of the i n t r u s i v e body, the second a basic d i f f e r e n t i a t e , the t h i r d an a l k a l i n e d i f f e r e n t i a t e , and the f o u r t h hydrothermally a l t e r e d rocks of e i t h e r the intermediate or a l k a l i n e types. A f i f t y ^ type, characterized by a dark red c o l o r , which has been studied i n the hand specimens alone, may be included with the former types. Intermediate Type Probably ninety percent of the area of the Ironmask b a t h o l i t h i s occupied by rocks of the intermediate type, which c o n s i s t e s e n t i a l l y of an intermediate p l a g i o c l a s e f e l d s p a r v a r y i n g from kb-j^n^ t o AbcjyAn^, and e i t h e r augite or hornblende or both. The proportion of the 17 p l a g i o c l a s e to the ferromagnesian minerals shows wide v a r i a t i o n s from 90:7.5 ( s l i d e 3 6 6 3 ) to 2 5 : 6 2 ( s l i d e 3535i-A) . Other than being confined to the range of compositions already mentioned, the feld s p a r shows no systematic v a r i a t i o n s w i t h e i t h e r the percentage of dark minerals or the r a t i o of augite to hornblende. The most mafic rock of the intermediate type (specimen 2525|A) with 62% of dark minerals contains one of the most sodic feldspars (Ab^An^g) , while another specimen' (3514C) w i t h only 3 7 $ of dark minerals has one of the most c a l c i c f e l d s p a r s {Ahj)'jAri^) . Specimen 3514-B wit h a remarkably high concentration of hornblende has the most c a l c i c f e l d s p a r found (Ab^Ang^) but specimen 3535iB with almost as much hornblende has one of the most sodic feldspars (Abc^Ani^) of the intermediate type. One character i n t h i s type i s ..quite outstanding and suggests a twofold s u b d i v i s i o n ; nearly a l l the rocks, e s p e c i a l l y i n the darker phases, show a strong predominance of augite over hornblende o r , a l t e r n a t i v e l y , of hornblende over augite. Both v a r i e t i e s may occur w i t h i n a few feet of eachother (specimens 3 5 3 5 s A , 3535§B) with n e i t h e r showing any i n d i c a t i o n s of hydrothermal a c t i v i t y . A graph of the hornblende-augite r e l a t i o n s ( f i g u r e 5 . a l s o f i g s . 9 , 10) i n d i c a t e s that there i s present the e f f e c t s of some process, not yet understood, leading to a concentration of e i t h e r hornblende or augite, but not both, i n what was probably o r i g i n a l l y a more f e l s i c rock. During t h i s concentration of dark minerals, the f e l d s p a r remained apparently unchanged. A f i n a l product of t h i s process 6 f 18 augite -hornblende! % hornblendel - augite 10 •SSSS£A ^ 3 U'STA , / / ' 9 hoi V % dark minerals 13sssie fj0r-s\t>l <rsi e/i/~r-Figure 5. Graph of augite-hornblende r e l a t i o n s concentration i s the nearly pure pyroxenites of the basic type. No s i m i l a r nearly pure hornblende r i c h rock (hornblendite) was discovered i n the b a t h o l i t h but such might be expected. In the intermediate type neither quartz nor feld s p a t h o i d minerals were found. Except i n specimens 3702 and 3512 on which hydrothermal s o l u t i o n s probably have been a c t i v e , a p a t i t e i s present i n only very small amounts, 0.5% or l e s s . Magnetite i s present i n amounts varying from 3% t o 13% and showed l i t t l e or no preference f o r e i t h e r the a u g i t e - r i e h or the hornblende-rich rocks. B i o t i t e was l i k e w i s e present i n small amounts i n both the a u g i t e - r l c h and the hornblende-rich v a r i e t i e s . Basic Type Two rocks were found to be representative of the ba s i c type, both from more or l e s s l i m i t e d areas, a mile and a h a l f apart and a auarter of a mile or l e s s from the southwestern edge of the b a t h o l i t h near Peterson. There i s , then, an apparent concentration of t h i s type to one margin of the b a t h o l i t h , but i n view of the absence of s i m i l a r concentrations of other types to various parts or margins of the b a t h o l i t h and of the l i m i t e d number of outcrops of the basic type, great no ^ s i g n i f i c a n c e i s attached to t h i s l o c a l i z a t i o n , ctThe two*. roekseeohsisttof about 8 0 $ to 8 5 $ augite and 6% t o 13% magnetite, w i t h minor amounts of indeterminate f e l d s p a r , hornblende, c h l o r i t e etc. B i o t i t e was recognised i n both hand specimens but d i d not appear i n the plane of the sections. The augite occurs as large i n t e r l o c k i n g grains which do not i n any way i n d i c a t e that the rock i s a c r y s t a l accumuaJL^ion as Bowen suggests, rather i t appears t o have c r y s t a l l i z e d from an o r i g i n a l l y completely f l u i d a u g i t e - r i c h magma. Magnetite occurs i n the augite c r y s t a l s as replacements i n i t i a t e d along the g r a i n boundaries. Exposures of these two u l t r a b a s i c bodies, were, unfortunately too poor to permit determination of t h e i r age r e l a t i o n s with the adjacent rocks of the intermediate of /fcet>«.r/iar-fh type but t h e i r p o s i t i o n close to a contacts would suggest t h a t they are part of an e a r l y c h i l l e d ( ? ) border. A l k a l i n e Type Rocks of an a l k a l i n e type form probably several percent of the Ironmask b a t h o l i t h , and have been recognized i n three of the t h i n sections. They are d i s t i n g u i s h e d from the intermediate type i n containing a considerable amount of orthoclase ( 3 0 $ to 50$) and, i n general, a smaller amount of dark minerals. They can be c l a s s i f i e d as syenites and syenodiorites or as monzonites. The p l a g i o c l a s e ranges from Kb^Y^n43 'fco about AbgQAn2o a n d makes up about 40$ to 5 0 $ of the rock. The dark minerals are normally augite, more or l e s s a l t e r e d to c h l o r i t e , and l e s s often hornblende. B i o t i t e i s absent. Magnetite makes up from 3$ to 4$ of the rock, s l i g h t l y l e s s than i n the intermediate type and a p a t i t e from 0 . 5 $ to 1.0$, s l i g h t l y more than i n the intermediate type. Quartz, forming 5 . 5 $ of the rock, was found i n one s e c t i o n . A t y p i c a l monzonitic texture i s developed i n two of the three specimens examined, large orthoclase c r y s t a l s enclosing numerous unoriented p l a g i o c l a s e c r y s t a l s . Hydrothermally A l t e r e d Type Not only because of the great v a r i a t i o n showed by the rocks of t h i s type but also beeause. of t h e i r economic i n t e r e s t i n r e l a t i o n to the mineral deposits, a considerable number of sections were examined. I t should not be assumed from t h i s , however, that they are extremely abundant, though they form a more important c l a s s and are considerably more widespread than i n most large i n t r u s i v e s . A f a i r l y complete s u i t e of these rocks was obtained from the v i c i n i t y of the Ironmask mine, i n c l u d i n g not only a l t e r e d country rock but a l s o l a t e r minor i n t r u s i v e s which were found to have preceeded or accompanied the hydrothermal a l t e r a t i o n . During the course of the f i e l d work around t h i s mine, the great extent of the a l t e r a t i o n had not been f u l l y r e a l i z e d and no attempt was made to r e l a t e the specimenss e i t h e r t o the ore body or to recognisable s o l u t i o n channels. I t iB- not p o s s i b l e , therefore, to trace the stages i n a l t e r a t i o n from the f r e s h country rock to the material close to the veins and d i k e s . One or perhaps two other specimens (3512 and(?) 36f&A) from other parts of the b a t h o l i t h were recognized to have suffered some a l t e r a t i o n and have been included i n t h i s c l a s s . One of the l e a s t a l t e r e d rocks i n the v i c i n i t y of the Ironmask mine, specimen 3702, was found to be a gabbro (bordering on d i o r i t e ) which d i f f e r s from the normal intermediate type of Ironmask rocks only i n having a considerably greater amount o f - a p a t i t e ( 3 % ) 5 s e r i c i t i z e d f e l d s p a r s and some epidote. I t seems probable, therefore t h a t the appearance of these three minerals i s the forerunner of the a l t e r a t i o n . The remainder of the a l t e r e d rocks are characterized e s p e c i a l l y by the complete a l b i t i z a t i o n of the p l a g i o c l a s e f e l d s p a r s , often w i t h no great amount of s e r i c i t e ( o r i g i n a l compositional d i f f e r e n c e s from 3702?). This a l b i t i z a t i o n may be associated w i t h the 1 i n t r u s i o n ' o f the small a l b i t i t e dikes (specimens 245, 246) found at a number of points near the mine. These d i k e s , probably an a p l i t i c phase of the b a t h o l i t h , show no w e l l defined contacts w i t h t h e i r w a l l s from which they can be d i s t i n g u i s h e d only by t h e i r almost complete l a c k of dark minerals. Indeed the s i m i l a r i t y i s so great as to suggest that the a l b i t i t e has been formed l a r g e l y by replacement of the w a l l s w i t h some leaching of dark minerals and of magnetite. These same dikes also 22 contain about 5% of c a l c i t e and may be r e l a t e d to the source of carbonate/ a l t e r a t i o n observed i n most of these rocks. Besides the a l b i t e and carbonate, the c h a r a c t e r i s t i c minerals i n the hydrothermal a l t e r a t i o n include c h l o r i t e , p a r t i a l l y or completely r e p l a c i n g augite and hornblende* epidote, a l s o sometimes r e p l a c i n g augite and hornblende but u s u a l l y i r r e g u l a r l y d i s t r i b u t e d with no apparent r e l a t i o n to e a r l i e r minerals, and forming up to 25% of the rock. .Apatite occurs i n somewhat smaller amounts than i n the p a r t i a l l y a l t e r e d type (specimen 3702), S i d e r l t e i s present i n small amounts, o c c a s i o n a l l y i n close proximity to c a l c i t e . The absence of ankerite i n the carbonates i n d i c a t e s that there was l i t t l e or no excess of magnesia during the a l t e r a t i o n of the rocks. I t i s worth no t i n g that t h i s development of the minerals a l b i t e , epidote, c h l o r i t e and c a l c i t e as w e l l as t h e i r wide d i s t r i b u t i o n around the v e i n zone, i s c h a r a c t e r i s t i c of p r o p y l i t l z a t i o n , as developed at the type l o c a l i t y , V i r g i n i a C i t y , Nevada, and Indicates moderately high P r o p y l i t l z a t i o n and Related Types of A l t e r a t i o n of the Comstock Lode - R o b t . Coats - Economic Geology Vol 35 pages 1 - 16, January-February 1940 temperatures of the m i n e r a l i z i n g s o l u t i o n s . Red-feldspar type The f i f t h type, characterized by a red c o l o r , p a r t i c u l a r l y i n the f e l d s p a r s , has not been studied i n t h i n s e c t i o n and may conceivably be a s u b d i v i s i o n of one of the 23 preceeding types. The co l o r of the rock i s a uniform or mottled b r i c k red depending on the abundance of the strongly colored twinned f e l d s p a r . Dark minerals may be present i n abundance or almost completely absent. Orthoclase may be present i n some specimens but no quartz was observed i n any. Thisrtype apparently has a more l i m i t e d d i s t r i b u t i o n than the a l k a l i n e type, but i s s t i l l not uncommon. Mineralogy P l a g i o c l a s e Feldspar P l a g i o c l a s e f e l d s p a r s o c c a s i o n a l l y oceur as more or l e s s well-formed c r y s t a l s , not in f r e q u e n t l y oriented (specimen 3703 w a l l ) , but are normally ragged or subhedral i n t e r s t i t i a l c r y s t a l s . A few (e.g. specimen 4017) show zoning but the majority are of uniform composition throughout the c r y s t a l . The p l a g i o c l a s e s are generally, though not always, badly a l t e r e d to s e r i c i t e or k a o l i n or both. A g r a p h i c a l representation of t h e i r composition with respect to the percentage of ferromagnesian minerals i s given i n f i g u r e 6. A b 1 0 0 A n 0 A b 5 Q A n 5 0 •35'*= „ • ii'tO 0 60 A b D An / o a % ferromagnesian minerals 24 Orthoclase Orthoclase i s found i n only four of the twenty two sections, and i n one of these i t forms probably only 0.5$ of the rock. I t normally occurs i n rocks having a mqnzonitic texture, that i s w i t h large orthoclase c r y s t a l s e nclosing numerous smaller unoriented p l a g i o c l a s e c r y s t a l s . In' specimen 4017, however, t h i s texture i s not developed and at one point at l e a s t , orthoclase occurs at the terminations of a p l a g i o c l a s e c r y s t a l , sharing common cleavage planes. I t seems possible i n t h i s case that the orthoclase has a c t u a l l y replaced some of the p l a g i o c l a s e . Where they occur together orthoclase a l t e r s to k a o l i n more r e a d i l y than does p l a g i o c l a s e . I t i s found i n quantity i n rocks of the Ironmask batholitfcr only i n the a l k a l i n e type. 5Q 7° orthoclase 0 50 $ ferromagneslan minerals Figure 7. Orthoclase r e l a t i o n s Q.uartz Quartz was found In only one of the twenty two t h i n sections of.Ironmask rocks examined. In t h i s s e c t i o n (4017) i t forms 5.5$ of the rock and occurs as small subhedral to anhedral grains d i s t r i b u t e d throughout the rock and apparently of magmatic o r i g i n though l a t e r than most of the minerals 25 present. I t i s quite e a s i l y recognized by i t s lack of a l t e r a t i o n and there can be very l i t t l e doubt as to i t s absence i n other se c t i o n s . Augite Augite occurs as euhedral or subhedral c r y s t a l s from l e s s than 0.1 to several m i l l i m e t e r s i n length. In a number of cases these c r y s t a l s showed a d i s t i n c t o r i e n t a t i o n , probably a r e s u l t of flow. In a few sections, notably 3642A, zoning i s present, but normally the c r y s t a l s are quite uniform. Frequently they contain small i n c l u s i o n s of secondary c h l o r i t e and secondary magnetite and i n a number of cases are appreciably u r a l i t i z e d . In a d d i t i o n to the u r a l i t i z a t i o n , they are also sometimes p a r t i a l l y replaced by large though ragged c r y s t a l s of 'primary' hornblende. The augite shows a decided tendency to pluck during the gr i n d i n g of the sections and though i t was attempted to cor r e c t f o r t h i s i n the Rosiwal analyses, i t i s probable that Figure 8 . Zoning i n augite , specimen 3642A Grossed Tlicols X 30 26 i t i s almost u n i v e r s a l l y underestimated. 1 0 0 50 augite 0 •i*3* . J 7 = I ye ^ s y $ ferromagnesian minerals Figure 9. Graph of augite r e l a t i o n s 1 0 0 Hornblende Hornblende occurs as subhedral to anhedral c r y s t a l s from 6 . 2 mm to sever a l m i l l i m e t e r s i n length, normally almost double that of the augite i n the same s l i d e . I t s pleochroism i s as f o l l o w s -X Y Z Brownish yellow y e l l o w i s h green green Pale greenish brown brownish green dark brownish green I t i s o c c a s i o n a l l y p a r t l y or completely a l t e r e d t o c h l o r i t e and some epidote. Inclus i o n s of f e l d s p a r s , augite and magnetite are not uncommon. 50 hornblende 0 r<*>~ .?S3<'« 0 % ferromagnesian minerals Figure 1 0 . Graph of hornblende r e l a t i o n s 1 0 0 B i o t i t e B i o t i t e occurs as p a r t i c u l a r l y ragged grains, generally, though not i n v a r i a b l y , i n a s s o c i a t i o n w i t h the other ferromagnesian minerals. I t i s never more than a minor component, forming u s u a l l y l e s s then 3%, probably nowhere more than 10% of the rock. Oddly enough, though i t i s present i n the b a s i c type and, to a l i m i t e d extent, i n both the hornblende-rich and a u g i t e - r i c h v a r i e t i e s of the Intermediate type, i t i s not found i n the a l k a l i n e type. 10 Jo b i o t i t e 0 I 0 % ferromagnesian minerals 100 Figure 11. Graph of b i o t i t e r e l a t i o n s C h l o r i t e C h l o r i t e occurs as a secondary mineral i n any one of the other ferromagnesian minerals. Though i t i s present i n nearly a l l the rocks, i t i s more abundant i n the f e l s i c than i n the mafic phases, and i s best developed i n the hydr©thermally a l t e r e d type where i t forms up to 20% of the rock. 20 | *• J c h l o r i t e / ><£«>•. , _,„ Q J^T"' -ten. , ( 7 M ,3S3fiA 0 Jo ferromagnesian minerals 100 Figure 12. Graph of c h l o r i t e r e l a t i o n s 28 Magnetite //ft** Magnetite has f i v e main types of occurrences i n the Ironmask b a t h o l i t h , as primary c r y s t a l s , exsolved i n c l u s i o n s , secondary i n c l u s i o n s , replacements and l a t e r veins. Primary magnetite occurs as euhedral or subhedral c r y s t a l s of various s i z e s , u s u a l l y somewhat l e s s than the average g r a i n s i z e of the enclosing rock, and scattered throughout the rock. I t may be e n t i r e l y enclosed i n f e l d s p a r , or, l e s s often, i n hornblende, and not infrequently i s concentrated i n the neighborhood of the 1'emic minerals. I t i s r a r e l y found completely enclosed i n augite and probably was formed subsequent to t h i s mineral, and presumably e a r l i e r than the enclosing f e l d s p a r or hornblende. The d i f f i c u l t y i n d i s t i n g u i s h i n g t h i s type from some of the b e t t e r formed replacement c r y s t a l s makes i t d i f f i c u l t , however, to estimate the importance of t h i s type of occurrance. E x s o l u t l o n or S c h i l l e r s t r u c t u r e , c o n s i s t i n g of minute Figure 13. S c h i l l e r s tructure i n augite, several swarms of the exsolved rods occurring near the centre of the photo. X 30 rods of an opaque black mineral, was found i n only one s e c t i o n 29 (s e c t i o n 3535§A). Since the coarse magnetite i n t h i s rock was found by chemical t e s t s to contain no detectable amounts of titanium, and since there i s l i k e w i s e no evidence 1 i n the c o l o r of the enclosing augite of the presence of t h i s element, i t was assumed that these rods were not composed of ilmenite or r u t i l e . While i t must be admitted that no d e f i n i t e determination of the composition of these rods can be r e a d i l y made, i t i s almost c e r t a i n that they are magnetite. They occur i n swarms or clouds, generally towards the centre of augite c r y s t a l s , and are oriented i n two (or three) d i r e c t i o n s u s u a l l y but apparently not always p a r a l l e l to the cleavage. The augite o c c a s i o n a l l y shows a s l i g h t zoning which appears to be r e l a t e d to the o u t l i n e s of the clouds of i n c l u s i o n s . S i m i l a r rods are a l s o found i n hornblende, both i n swarms and i r r e g u l a r l i n e s , and are probably derived from augite which has been replaced by the hornblende. Secondary magnetite Is found as f i n e i r r e g u l a r grains scattered through augite which has been a l s o p a r t l y a l t e r e d to c h l o r i t e . A r a t h e r s t r i k i n g though hardly t y p i c a l 3 0 occurrance i s i n a w e l l defined rectangular pattern ( f i g . 14) i n what appears to be an a l t e r e d pyroxene c r y s t a l , now c h i e f l y c h l o r i t e and epidote (Specimen 200). Perhaps the most common occurrance of magnetite i s as i r r e g u l a r grains r e p l a c i n g the e a r l i e r minerals. Magnetite of t h i s type i s developed almost u n i v e r s a l l y at c r y s t a l boundaries and has evidently made room f o r i t s e l f by corroding the adjacent minerals ( f i g u r e 15.). The wide-spread and rather uniform d i s t r i b u t i o n of t h i s replacement magnetite i n d i c a t e s , however, that i t was not subsequently introduced along f i s s u r e s e t c . but was probably p r e c i p i t a t e d from the i n t e r s t i t i a l f l u i d s at the c l o s i n g stages of the c r y s t a l l i z a t i o n of the magma. The f i f t h occurrance of magnetite i s i n ve i n s , apparently p r e c i p i t a t e d from hydrothermal s o l u t i o n s , i s discussed i n more d e t a i l under Economic Geology (page-??) Figure 15. Magnetite f o l l o w i n g c r y s t a l boundaries and rep l a c i n g e a r l i e r augite. ( s l i d e 4020B) Crossed TJicols X 3 0 31 20 % ' magnetite 0 ft QeloA • if '4' 0 % ferromagnesian minerals Figure 16. Graph of magnetite r e l a t i o n s 100 A p a t i t e A p a t i t e occurs i n the t y p i c a l c l e a r and c o l o r l e s s hexagonal rods scattered, apparently at random, through the f e l d s p a r s . One r a t h e r unusually shaped c r y s t a l , a hollow Figure 17. " s p i r a l " c r y s t a l of a p a t i t e i n a l t e r e d f e l d s p a r X 135 s p i r a l , i n and p a r t l y enclosing a l t e r e d feldspar ( s l i d e i s i l l u s t r a t e d i n f i g u r e 17. An a s s o c i a t i o n strongly developed i n specimen \ i s a p a t i t e along the outer edge and p a r t l y enclosed by primary!?) magnetite ( f i g u r e 18). The l a t t e r a s s o c i a t i o n i s not, however, common i n other specimens. A p a t i t e i s present i n a l l but three of the rocks 32 Figure 18. Ap a t i t e occurring along margins and p a r t l y enclosed by c^ysu/s of primary magnetite. Groundmass of rock augite and f e l d s p a r . X 30 examined i n t h i n sections. I t i s found i n greater q u a n t i t i e s i n the a l k a l i n e type than i n the intermediate type and i s absent In both specimens of the basic type. I t i s present i n greatest amount, however, i n those rocks which have been subjected to hydrothermal a l t e r a t i o n . I t s presence has a l s o been reported i n magnetite v e i n s . Iron Ores of B.C. and the Yukon - pages 114, 126 3 % a p a t i t e 0 I W . . . . » W T ,}iis 0 % ferromagnesian minerals 100 Figure 19. Graph of a p a t i t e r e l a t i o n s Epidote Epidote and, l e s s often, c l i n o z o i s i t e are found i n very minor amounts i n a number of apparently unaltered rocks, They are widely developed, however, only i n the rocks 33 appreciably a l t e r e d by hydrothermal a c t i o n , where Iheyamay form up to 25% of the rock. Epidote l i k e a p a t i t e i s also found i n magnetite veins (polished section) 25$ enidote . . . ' . :.- •... . IfilM-. 0 % ferromagnesian minerals 100 Figure 20. Graph of epidote (and c l i n o z o i s i t e ) r e l a t i o n s . Carbonates C a l c i t e i s found only i n rocks of the a l k a l i n e type and i n rocks that have been a l t e r e d by hydrothermal s o l u t i o n s . I t i s u s u a l l y present only i n minor amounts and was never found forming more than 5% of the, rock (spec 245 d i k e ) . I t i s , however, the commonest gangue mineral i n most of the copper deposits associated w i t h the b a t h o l i t h and i s also found i n the magnetite veins. S i d e r i t e was recognized i n only three sections (3703 w a l l and 3703 di k e , 245 wall) where i t formed from 0.5 to 1.0% of the rock. I t was r e a d i l y d i s t i n g u i s h a b l e from c a l c i t e by i t s extremely high r e l i e f ( indes 1.63 to 1.87) P y r i t e P y r l t e , occurring as occasional comparatively large g r a i n s , was found i n only two sections (3512 and 200) where i t made up from a tracfe to 0.5$ of the rock. I t does not appear to be a common product of the hydrothermal processes. I t i s abundant, though not ex c e p t i o n a l l y so, i n the mineral deposits associated w i t h the b a t h o l i t h . Garnet Small c r y s t a l s of garnet were discovered i n the c a l c i t e gangue i n one of the magnetite veins of the Moose claim. They were ev i d e n t l y deposited along with the c a l c i t e and magnetite and i n d i c a t e that the v e i n i n which they were found had been formed by high temperature hydrothermal s o l u t i o n s . Titanium Minerals In specimens from the Ironmask b a t h o l i t h described i n appendix I of the report on the Kamloops Map-sheet (1894) ( s l i d e s 96 - 99) i l m e n i t e and i t s decomposition product leucoxene were reported. In the sections examined by the w r i t e r , no evidence of the presence of e i t h e r of these two minerals was found. In a d d i t i o n , a number of the rock specimens were crushed and ahmagnetic product tested chemically f o r tit a n i u m , but the t e s t s were i n a l l cases negative. Age and C o r r e l a t i o n L i t t l e can be s a i d d e f i n i t e l y as to the age of t h i s b a t h o l i t h . I t cuts s t r a t a of Upper T r i a s s i c age and had been intruded and unroofed at l e a s t once before the Oligocene. I t i s p r o v i s i o n a l l y r e f e r r e d to the Upper Mesozoie .'. One small stock, almost d i r e c t l y across the Thompson R i v e r from Walhachin, seventeen miles west of the Ironmask "batholith, shows a strong resemblance to the l a t t e r i n t r u s i v e i n the hand specimens but has not yet been examined i n t h i n sections. The Copper Mountain stock, ninety miles south of the Ironmask b a t h o l i t h , a l s o shows considerable resemblance to the l a t t e r i n t r u s i v e , not only i n the composition of i t s rocks but a l s o i n being associated with copper deposits. In the Copper Mountain stock, however, orthoclase i s not • r e s t r i c t e d to the f e l s i c rocks but may a l s o appear i n the gabbroic types. Moreover, the^ structure of t h i s stock bears no resemblance to the Ironmask b a t h o l i t h , nor does the hydrothermal a l t e r a t i o n associated w i t h the copper deposits. Geological Survey of Canada - Memoir 1 7 1 - Geology and Ore Deposits of Copper Mountain B.C. - by V.Dolmage Apart from these two igneous bodies, mentioned above, the w r i t e r knows of no others i n B r i t i s h Columbia that show any marked resemblance to the Ironmask b a t h o l i t h . G r a n i t i c B a t h o l i t h The northern t i p of a large g r a n i t i c b a t h o l i t h appears at the southern border of the area mapped around the Ironmask b a t h o l i t h . This g r a n i t i c mass, however, i s quite d i s s i m i l a r i n composition, i n associated metamorphism and i n external r e l a t i o n s to the Ironmask b a t h o l i t h , and w i l l not be discussed f u r t h e r . 3 6 Quartz-Feldspar Porphyry A number of small stocks, dikes and (?) s i l l s of quartz and feldspar porphyry have been found i n the v i c i n i t y of the Ironmask b a t h o l i t h (see specimens 3 5 5 4 , 3642B). The phenocrysts are p l a g i o c l a s e , varying from a l b i t e to andesine, and, i n smaller amounts quartz. The matrix c o n s i s t s of a f i n e grained mass of orthoclase, quartz and some p l a g i o c l a s e . Ferromagnesian minerals, augite, hornblende, b i o t i t e and c h l o r i t e , occur as badly a l t e r e d phenocrysts scattered throughout the rock. Magnetite i s notably d e f i c i e n t . Both s e r i c i t e and carbonate are present often i n small amounts, and„sufficient l i m o n i t e to give the rock a reddish c o l o r . At f i r s t i t was considered that these porphyries were s a t t e l l t e s of the Ironmask b a t h o l i t h but petrographic studies have brought f o r t h no evidence f o r such a supposition. The abundance of quartz and the absence of magnetite are features not at a l l c h a r a c t e r i s t i c of Ironmask rocks. Moreover, the presence of such a c i d i n t r u s i v e s even at some distance from the Ironmask b a t h o l i t h would i n d i c a t e that they have no genetic r e l a t i o n to t h i s P l u t o n i c body. Some, at l e a s t , more c l o s e l y resemble the extr u s i v e s of the Kamloops s e r i e s (lower part) and may a c t u a l l y be feeders to these v o l c a n i c s . F r e d e r i c k Formation Evidence brought f o r t h during the c l o s i n g days of the f i e l d season Indicates that there may e x i s t along the north side of Kamloops Lake a few miles west of B a t t l e B l u f f a group of v o l c a n i c rocks younger than the Ironmask b a t h o l i t h and older than the Kamloops Volcanics, c a l l e d here the Frederick formation, a f t e r a s t a t i o n by that name on the Canadian National Railway. In t h i s area are both flows and agglomerates, both apparently much more Indurated and metamorphosed than the adjacent Kamloops v o l c a n i c s , and containing at several points fragments c l o s e l y resembling Ironmask monzonites. Time was not a v a i l a b l e to o u t l i n e the areas of t h i s formation nor to determine I t s s t r u c t u r a l r e l a t i o n s w i t h the N i c o l a formation and wit h the Kamloops v o l c a n i c s . The areas shown i n the accompanying map as part of t h i s formation can,, as yet, be considered as only d o u b t f u l l y e s t a b l i s h e d . Kamloops Volcanics The Kamloops v o l c a n i c s e r i e s c o n s i s t s of a rather t h i c k group of l a v a s , ranging from o l i v i n e b a s a l t to r h y o l i t e or d a c i t e , agglomerates, t u f f s , dikes and s i l l s , together with an important sedimentary horizon, the T r a n q u l l l e beds. The most important part of t h i s s e r i e s was l a i d down i n what was ev i d e n t l y an early T e r t i a r y v a l l e y trending Nj50°W across the area but the upper parts of the ser i e s was probably l a i d down on upland areas on the flanks of t h i s v a l l e y . Subsequent erosion has l e f t the greater part of the v a l l e y f i l l i n g as an i r r e g u l a r but nearly continuous area of v o l c a n i c s and sediments at the centre and north of the map-area sand i s o l a t e d areas of the upper part of the s e r i e s , generally on the present h i l l - t o p s . 38 D e t a i l e d mapping of the main sedimentary horizon i n t h i s s e r i e s shows that the beds have been t i l t e d , subsequent to d e p o s i t i o n , about 3 ° to 1 5 ° to the north or northeast. V a r i a t i o n s from t h i s a t t i t u d e have been observed, but they are never on a large scale. Since the t i l t i n g has a component along the a x i s of the T e r t i a r y v a l l e y mentioned above, the lower part of the s e r i e s i s exposed at one end, the southern, and the upper part at the other. The moderately •strong r e l i e f of the present topography, however, introduces some i r r e g u l a r i t y i n t h i s d i s t r i b u t i o n . Gn the f l a n k s of the T e r t i a r y v a l l e y , p a r t i c u l a r l y near Cherry and B a t t l e B l u f f s , flows have been observed to dip towards the centre of the basin, but i n nearly a l l cases these dips have been i n t e r p r e t e d as o r i g i n a l rather than the r e s u l t s of subsequent f o l d i n g . Dawson's and Daly's i n t e r p r e t a t i o n s of the doming of the Kamloops v o l c a n i c s e r i e s about the Ironmask b a t h o l i t h by orogenic movements i s , therefore, unsubstantiated. D e f i n i t e evidence was obtained, northwest of B a t t l e B l u f f , o f the unconformity between the Kamloops v o l c a n i c s e r i e s and the Ironmask b a t h o l i t h . In t h i s v i c i n i t y i s an area of f o s s i l i f e r o u s T r a n q u i l l e beds, containing at the base a conglomerate or b r e c c i a with angular fragments of the u n d e r l y i n Ironmask rocks. The sedimentary rocks are, here, evide n t l y lapping against a steep sided b l u f f or peninsula of the older igneous rocks. F o s s i l s obtained from t h i s s e r i e s , a l l from the l a c u s t r i n e T r a n q u i l l e beds, i n d i c a t e ah e a r l y T e r t i a r y , probably upper Oligocene age. Pleistocene and Recent Deposits Pleistocene and Recent deposits, g l a c i a l t i l l , varved c l a y s , r a i s e d d e l t a s , alluvium etc., are d i s t r i b u t e d throughout the area. Some of the ma t e r i a l i n these deposits has been derived from formations as much as t h i r t y miles d i s t a n t and the d r i f t chnot, therefore, be considered as a r e l a i b l e i n d i c a t i o n of the underlying rock. Economic G-eology Magnetite Deposits Iron Ores of B r i t i s h Columbia and Yukon - Economic G-eology S e r i e s No.35 Volume I - Geological Survey of Canada -pages 109 - 128 - G.A.Young As e a r l y as 1877 Dawson remarked on the presence of magnetite veins i n the v i c i n i t y of Cherry B l u f f , but i t was not t i l l 1889 that any attempt was made to work them commerically. From that date t i l l 1902, a deposit at the west end of Cherry B l u f f , the Glen Iron mine, was worked i n t e r m i t t e n t l y . The ore was shipped both to the Tacoma and T r a i l smelters, where i t was u t i l i z e d as a f l u x i n g agent rather than a source of merchantable i r o n . A t o t a l of about 15,000 tons of ore was shipped from t h i s deposit. A second group of magnetite deposits occurs some eight miles southeast of the Glen Iron mine or about a mile west of Ironmask l a k e , on the Moose, Magnet, Si g n a l and A n v i l 40 claims. - Though the reserves have been estimated as possibly 250,000+ tons, there has been no production and very l i t t l e e x p l o r a t i o n on these claims. The magnetite occurs i n veins as much as f o r t y feet i n width but very l e n t i c u l a r and averaging not over ten or twenty feet i n width and i n many cases much l e s s even than t h i s . Associated w i t h the magnetite i s a moderate to small amount of included country rock which may or may not have been a l t e r e d to epidote e t c . , a p a t i t e , c a l c i t e and i n at l e a s t one v e i n some garnet A. With the exception of the garnet, a l l the minerals are found, often i n considerable amounts, i n the rocks of the Ironmask b a t h o l i t h . Though i t i s true that the country rock at these deposits, gabbro to monzonite, has s u i t a b l e mechanical properties f o r the development of f i s s u r e veins, the s i m i l a r i t y i n the mineralogy of these deposits to the Ironmask b a t h o l i t h , together with t h e i r r e s t r i c t i o n i n d i s t r i b u t i o n to the Ironmask b a t h o l i t h , makes i t evident that t h e i r source was i n t h i s i n t r u s i v e . They are regarded by the w r i t e r as the products of the e a r l y high temperature hydrothermal s o l u t i o n s given o f f by the b a t h o l i t h not long a f t e r i t s c r y s t a l l i z a t i o n Copper Deposits In 1 8 9 5 the discovery of copper m i n e r a l i z a t i o n near the summit of Coal H i l l i n i t i a t e d a rush i n which a large number of low grade deposits were located. The great majority of these deposits l i e i n the Ironmask b a t h o l i t h w i t h i n a few hundred feet of i t s periphery, a few l i e towards the centre of the b a t h o l i t h , and a very l i m i t e d number are i n the intruded N i c o l a formation close to the b a t h o l i t h . Of a l l these deposits, however, only one, the Ironmask (and i t s continuation, the E r i n ) ever progressed beyond the prospect stage. This mine had a rather v a r i e d caree>ry commencing production i n 1904 and continuing i n t e r m i t t e n t l y t i l l 1928, with a t o t a l production of between 25,000 and 50,000 tons of ore. The Copper King mine, s i t u a t e d not f a r from the G-len Iron mine on Cherry B l u f f , has had a small production, some of i t during- the past year, but a f i r e i n October which destroyed the m i l l has apparently brought the operation to a c l o s e . Mention has already been made of the remarkable d i s t r i b u t i o n of the copper deposits along the periphery of the b a t h o l i t h . Indeed, i t was onee suggested that the contact of the b a t h o l i t h might w e l l be p l o t t e d along the nearly continuous b e l t of mineral claims which extends from E d i t h Lake to beyond Sugarloaf H i l l and from Ironmask Lake to the v i c i n i t y of Separation Lake. This d i s t r i b u t i o n i n i t s e l f i s e x c e l l e n t evidence of the genetic r e l a t i o n s of the copper deposits to the b a t h o l i t h . i t s e l f The deposits c o n s i s t of veins or stockwefks i n w e l l defined f i s s u r e and brecciated zones or as i l l defined Impregnations which may or may not be associated w i t h obvious s o l u t i o n channels. In the case of the Ironmask mine, thes m i n e r a l i z a t i o n i s as l a t e as,or l a t e r than the a l b i t i t e dikes c u t t i n g the p l u t o n i c rocks. The t y p i c a l copper minerals are c h a l c o p y r i t e , b o r n i t e and c h a l c o c i t e , together w i t h t h e i r 42 oxidation products, malachite, a z u r i t e and c u p r i t e . Associated .primary gahgue minerals are magnetite, often i n large amounts, p y r i t e , c a l c i t e and, r a r e l y , quartz. Hematite, lead minerals and chrysoeolla have "been reported from i s o l a t e d deposits but are e v i d e n t l y scarce. Gold values are generally low (approximately 0.05 oz per ton at the Ironmask mine), s i l v e r values almost ne g l i g a b l e . As i n the case of the magnetite deposits, the minerals found in^the copper deposits, magnetite, and c a l c i t e are a l s o c h a r a c t e r i s t i c of the rocks of the Ironmask b a t h o l i t h as i s the d e f i c i e n c y of quartz. The a s s o c i a t i o n of chalcopyrite with magnetite i s a l s o noted i n the magnetite deposits (see page 4 0 ) . The w a l l rock a l t e r a t i o n , as at the Ironmask mine, may be the r e s u l t s of moderately high temperature so l u t i o n s but the ore m i n e r a l i z a t i o n i s probably mesothermal. 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