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Geology of the Deer Horn prospect, Omineca M.D., British Columbia Papezik, Vladimir Stephen 1957

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GEOLOGY OF THE DEER HORN PROSPECT, OMINECA M.D. , BRITISH COLUMBIA by VLADIMIR STEPHEN PAPEZIK B.A., University of B r i t i s h Columbia, 1954 A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE i n the Department of GEOLOGY We accept this thesis as conforming to the required standard THE UNIVERSITY OF BRITISH COLUMBIA A p r i l 1957 ABSTRACT The Deer Horn property l i e s astride the contact of the Coast Range ba t h o l i t h and a group of s i l i c e o u s and shaly sediments of Jurassic or Lower Cretaceous age. The contact s t r i k e s westerly and dips about 50° to the South. The southern three f i f t h s of the property are underlain by gran-i t i c rocks, the remaining northern part consists of s l i g h t l y metamorphosed sediments s t r i k i n g approximately west, dipping about 70° south and believed to form an overturned syncline. The rocks are cut by two a l b i t i t e dykes and several minor trap dykes. The g r a n i t i c rocks are divided into two main types, "po r p h y r i t i c " granodiorite and hornblende granodiorite. The l a t t e r contains the main part of the mineral deposit, and i s further subdivided into several v a r i e t i e s produced by t e c t -onic movements and hydrothermal a l t e r a t i o n . A l k a l i metasomat-ism has affected both the g r a n i t i c rocks and - to a lesser extent - the sediments. Some metasomatic features are discussed i n d e t a i l . Two veins or vein systems, the Main and the Contact, l i e i n the hornblende granodiorite and i n the contact zone. They s t r i k e westerly, converge towards the west and dip towards each other, forming a shallow troughlike structure. Both carry sulphides and minor t e l l u r i d e s with gold and s i l v e r . Scheelite occurs sparsely i n the veins and i n bands of epidote-garnet skarn i n the sediments, being somewhat more concentrated i n two areas of f i n e talus i n the western part of the property. The Main vein i s shown to be a replacement vein formed i n a thrust f a u l t . The shearing angle of the f a u l t flattened i n the more b r i t t l e contact zone, and the f a u l t t e r -minated i n a series of complementary shears. The combination of these two factors produced the curving trough-like shape of the vein. The narrow Contact vein was formed i n a l a t e r gravity f a u l t . The zone of in t e r s e c t i o n of the two veins was highly sheared and thus rendered more permeable to the mineralizing f l u i d s . This accounts for the numerous high-grade stringers present near the int e r s e c t i o n . In view of the known and infer r e d l i m i t s of the two veins i t i s not expected that the ore w i l l continue either l a t e r a l l y or i n depth. In presenting t h i s thesis i n p a r t i a l fulfilment of the requirements fo r an advanced degree at the University of B r i t i s h Columbia, I agree that the Library s h a l l make i t f r e e l y available for reference and study. I further agree that permission for extensive copying of t h i s thesis for scholarly purposes may be granted by the Head of my Department or by his representative. It i s understood that copying or publication of t h i s thesis f o r f i n a n c i a l gain s h a l l not be allowed without my written permission. Department The University of B r i t i s h Columbia, Vancouver 8, Canada. Date ACKNOWLEDGMENTS The writer i s greatly indebted to Dr. D.R.Derry, president of Rio Canadian Exploration, for a f i n a n c i a l grant enabling him to c o l l e c t the specimens on the property; to Mr. H.R.Buckles, managing director of Technical Mine Con-sultants , who placed a l l company maps and reports at the writer's disposal; to Drs. K.C. McTaggart, R.M. Thompson, W.H. White and J.V. Ross for t h e i r help and f r u i t f u l suggest-ions during the investigation, and to Mr. J.A. Donnan for his expertly made thin-sections. TABLE OF CONTENTS Page PART I. GENERAL CHAPTER I. Introduction 1 1. Location and access 1 2 . Physical features 2 3 . Climate, water, timber 3 4. Claims and camp f a c i l i t i e s 4 5. History and development of the property . . . . 4 6. Previous geological work 5 7. Basis of this investigation 6 CHAPTER I I . Regional Geology 1. Table of formations 7 2 . Regional setting 7 PART I I . GEOLOGY OF THE PROPERTY CHAPTER I I I . Petrology 1. Granitic rocks 10 (a) Coarse "porphyritic" granodiorite . . . . 10 (b) Hornblende granodiorite 13 (c) A l t e r a t i o n phases of hornblende granodiorite 15 (1) "Mine" granodiorite 15 (2) Sheared s i l i c i f i e d granodiorite . . 17 (3) Gneissic b i o t i t e - g r a n o d i o r i t e . . . 18 (4) Other altered types 20 (d) Mutual relations 21 2. Sedimentary and metamorphic rocks 24 (a) Table of rock units 26 (b) Carbonaceous greywacke 26 (c) Coarse arkose 27 (d) Feldspathic quartzite 28 (e) Black a r g i l l i t e 30 (f) Brown a r g i l l i t e 30 C h i a s t o l i t e schist 32 Feldspathic greywacke 33 Page 3. Dyke Rocks 34 (a) A l b i t i t e 34 (b) Hornblende l a t i t e ( " trap") 35 4 . Rocks a f f e c t e d by metasomatism 36 (a) E p i d o t e - g a r n e t s k a r n . . 36 (b) Q u a r t z - w o l l a s t o n i t e - g a r n e t s k a r n 38 (c) P e r t h i t e - q u a r t z c a t a c l a s i t e 40 (d) A l k a l i metasomatism 44 CHAPTER IV S t r u c t u r e 1. G r a n i t i c r o c k s 49 2. C o n t a c t between g r a n i t i c and s e d i m e n t a r y r o c k s . 50 3. S e d i m e n t a r y r o c k s 51 4. The v e i n s 53 (a) The Main v e i n 53 (b) The C o n t a c t v e i n 55 ( c ) J u n c t i o n o f the v e i n s 56 Cd) O r i g i n o f the v e i n s 57 (e) Summary 61 5. P o s t - m i n e r a l f a u l t s 62 CHAPTER V. M i n e r a l o g y o f the v e i n s 1. P r e v i o u s work 69 2. The Main v e i n 69 3. The C o n t a c t v e i n 71 4. O r i g i n o f the v e i n m i n e r a l s 74 CHAPTER V I . Tungsten m i n e r a l i z a t i o n 1. I n t r o d u c t i o n 76 2. S c h e e l i t e i n the v e i n s 76 3. S c h e e l i t e i n s k a r n 77 4 . The " s c h e e l i t e s l i d e s " 78 B i b l i o g r a p h y 80 ILLUSTRATIONS Key map a f t e r p. 1 Surface geology, Deer Horn Property . i n pookot^ i ^ & p . ~ Geological Plan, 4260 l e v e l -i-n~-p©-ek-et I ^bmeiy Sect i Figure 1. Reaction curves f o r wollastonite . . . a f t e r p. 40 " 2. Composition diagrams f o r wollastonite a f t e r p. 40 " 3. Vandeveer paragenetic diagrams . . . . after p. 75 Main and Contact veins " 4. Vein pattern, 4260 adit -in- poe-k-e-tr-l map " 5. Fault pattern, 4260 adit . -i-n-px^eke^ j ^ . n e t Plate 1. Mt. Lindquist with mine camp and a d i t . . . . p. &1 " 2. View from the adit towards the East . . . . p. 81 " 3. Coarse porphyritic granodiorite p. 82 " 4« C h i a s t o l i t e schist p. 82 " 5. Orthoclase porphyroblast i n c a t a c l a s i t e . . . p . 83 " 6. Orthoclase porphyroblast i n granodiorite . . p. 83 " 7. Contact vein, low grade p. 84 " 8. Contact vein, high grade p. 84 " 9. Hessite in Contact vein, microphotograph . . p. 85 " 10. Hessite i n Main vein, microphotograph. . . . p. 85 The writer i s indebted to Mr. L y a l l Armstrong f o r Plates No. 3 to 8. GEOLOGY OF THE DEER HORN PROSPECT OMINECA M.D., BRITISH COLUMBIA PART I CHAPTER I INTRODUCTION 1. Location and Access The Deer Horn property, a gold-silver-tungsten prospect, l i e s i n a rugged part of the Coast Mountains of B r i t i s h Columbia, at 53 deg. 22« North l a t . , 127 deg. 18 1 West long., i n the Omineca Mining D i v i s i o n . The nearest major settlement and railway s t a t i o n i s Burns Lake, a small town on the main Canadian National Railway l i n e from Edmonton to Prince Rupert; i t l i e s about 85 miles northeast of the property. From Burns Lake, the prospect i s accessible i n two ways: either by a chartered plane landing on Lindquist Lake, connected by a four mile tractor road to the mine camp, or 25 miles by road to Wistaria on the north shore of Ootsa Lake and then 55 miles by boat to the western end of Whitesail Lake. A two mile road leads from this landing to Lake Lindquist. showing position of the Deer Horn property 2 2. Physical Features The area i n which the property i s situated l i e s on the eastern slope of the P a c i f i c Ranges of the Coast Mountains. Near the property and to the West the country has a rugged topography and a high r e l i e f ; towards the East, the r e l i e f be-comes lower and the sharp peaks give way to more rounded summits, u n t i l they f i n a l l y merge with the r o l l i n g Nechako Plateau. Long narrow lakes, such as Tahtsa, Morice, Whitesail and Eutsuk are t y p i c a l for the region. Both shores of these lakes are flanked by northeasterly trending ranges which represent a t r a n s i t i o n between the Coast Mountains proper and the plateau. The entire area was covered by i c e during Pleistocene time, and g l a c i a l e r r a t i c s and s t r i a e are common on some mountain ridges. The usual d i r e c t i o n of these s t r i a e i s about N 60-70 deg. E. A few nailhead s t r i a e observed by the writer on Mount Chikamin, south of Whitesail Lake, trend N 65 E. The western part of the area, p a r t i c u l a r l y west of Deer Horn, i s even today characterized by alpine g l a c i a t i o n , and small snowfields and cirque glaciers are common. The Deer Horn property l i e s on the southern slope of Lindquist Peak, extending from the north shore of Lake Lind-quist at 2900' to the summit more than 5800' high. The greater part of the property and most of the mineral showings l i e above timberline. Outcrops are numerous near the top of the ridge and i n the short intermittent creeks draining the mount-3 ain side, but a large portion of the area, including some c r i t i c a l sections, i s covered by f i n e t a l u s , p a r t i c u l a r l y i n zones of strong shearing. Short grass covers most of the ground farther below the mountain ridge, and large outcrops become rare below timberline. 3. Climate, Water, Timber The area has a t y p i c a l coastal climate with frequent t r a i n and high snowfall. Both lakes are frozen during the winter months and are suitable for ski-equipped a i r c r a f t . Whitesail Lake begins to break up early i n May and f l o a t planes can usually land at Deer Horn Bay i n the second half of the month, while Lindquist Lake usually remains frozen u n t i l l a t e June. The lower parts of the property are free of snow by early July, the upper parts remain covered u n t i l l a t e August. Small patches of snow i n sheltered valleys do not disappear throughout the year. Summers are often hot, but with frequent fog and r a i n . Night frosts appear by the middle of September and new snow may be expected i n the f i r s t half of October. Both lakes freeze again early i n December. Water supply for camp and mine purposes i s good up to 4300 feet, i n several small but permanent creeks. Above this elevation there are only short creeks fed by melting snow; the i r flow varies with the rate of melting and decreases considerably toward the end of September. S u f f i c i e n t timber i s available at lower elevations, p a r t i c u l a r l y i n the t h i c k l y wooded v a l l e y between Whitesail 4 and Lindquist Lakes. The chief species are spruce and hemlock. 4. Claims and Camp F a c i l i t i e s The Deer Horn property consists of 26 f u l l s i z e d claims and 4 f r a c t i o n s , a l l of them Crown granted. Several buildings have been erected i n d i f f e r e n t parts of the area by the owners and exploration companies. The main camp, near the entrance to the a d i t , l i e s at an elevation of about 4200 feet at the end of the mine road. It has two pre-fabricated huts which were used as bunkhouse, cookhouse, o f f i c e and assay laboratory, a core shack and a mechanic's shop. Two smaller huts are situated i n the eastern part of the property, one hut at Lindquist Lake and one near the landing at Whitesail Lake. 5. History and Development of the Property The o r i g i n a l claims were staked i n September 194-3 by the Harrison brothers of Wistaria, to cover the scheelite show-ings i n the western part of the property. During the examin-ation of the showings i n 194-4, F.R.Joubin noticed the gold and s i l v e r r b e a r i n g veins to the East and add i t i o n a l claims were staked. In the summer of 194-4 the group was optioned by the Pioneer Gold Mines Ltd., and an extensive program of trenching and diamond d r i l l i n g was carried out i n the years 194-4, 1945 and 1946. After three years and 13,000 feet of d r i l l i n g the option was allowed to lapse. 5 The group was then bought i n 1950 by the Deer Horn Mines and after more detailed examinations i t was decided to develop the property. In 1953 a road was constructed from Whitesail to Lindquist Lake, and about 1000 feet of d r i l l i n g were done to check the westerly extension of the veins and the scheelite showings, without much success. In 1954- the road was extended to the present camp s i t e , the main camp was b u i l t and i n August 1954- an adit was collared on a vein outcrop at an elevation of 4260 feet. Work i n the adit continued t i l l the end of October 1955> when a t o t a l of 1568 feet of underground workings was completed. In addition, 6700 feet of diamond d r i l l i n g , both surface and underground, were done during the year. At the end of October 1955 the camp was closed down pending further decision by the company. The property i s now i d l e . 6 . Previous Geological Work The property was examined sho r t l y after i t s discovery i n 1944 by S.S. Holland for the B.C. Department of Mines (Holland, 194-4). The Whitesail Lake area, including the property, was mapped i n 1952 by S. D u f f e l l for the GSC ( D u f f e l l , 1952), and the prospect was re-examined i n 1955 by W.R.Bacon of the B.C. Department of Mines (Bacon, 1955). Several company geologists worked on the property, including F.R.Joubin (1944), A.E. Pike (1945) , E.G.Langille (1945) , Charles Ney, (1947)", Paul Young (1953) , D. Ross (1954) R. MacRae (1953) , S.L.Learning (1954-55) and V.S.Papezik (1955) . 6 Surface mapping was done c h i e f l y by F.R.Joubin. Parts of the property were mapped i n some d e t a i l by Pike, Ross and Papezik, and possibly by other geologists whose maps were not available for this investigation. The underground workings were mapped i n part by S.L.Learning and p a r t l y by 7.S.Papezik. A.C.Taplin ( 1 9 5 0 ) studied the mineralogy of the veins at the University of B r i t i s h Columbia. 7. Basis of this Investigation The work was greatly f a c i l i t a t e d by personal knowledge of the property gained by the writer i n the s i x months spent at Deer Horn as mine geologist. During that time he was engaged mainly i n underground mapping and d i r e c t i o n of diamond d r i l l i n g ; he mapped only a small part of the surface i n the v i c i n i t y of the scheelite showings. Deductions i n -volving surface exposures are made mostly on the basis of F.R.Joubin 1s surface map. In September 1 9 5 6 the writer returned to the property for four days to c o l l e c t the specimens on which the main part of this work i s based. Beside a great number of hand specimens, 22 t h i n -sections and a number of polished sections were studied, and several minerals were i d e n t i f i e d by X-rays. CHAPTER II REGIONAL GEOLOGY 1. Table of Formations Formations occurring i n the v i c i n i t y of the Deer Horn Property (After D u f f e l l , 1952) Age Unknown A l b i t i t e dyke, basalt dykes Intrusive contact Jurassic and l a t e r Coast intrusions Granodiorite, d i o r i t e , granite etc. Intrusive contact with Hazelton Group, i n part i n t r u s i v e into Lower Cretaceous beds Lower Cretaceous A r g i l l i t e , arkose, breccia, t u f f , andesite, basalt. Probable unconformity Jurassic Hazelton Group Breccia, t u f f , andesite, basalt; a r g i l l i t e , greywacke, chert, conglomerate, minor limestone. 2. The Deer Horn Claim Group i n the Regional Setting The property l i e s on the eastern contact of the Coast Range bath o l i t h and a thick series of sedimentary and possibly 8 some volcanic rocks, which i n this area form an embayment about 6 miles long and 4 miles wide, projecting southwesterly into the batholith. The sediments north of Lindquist Lake have been mapped by S. D u f f e l l (1952) as part of the Hazelton Group of Jurassic age. However, several facts found during the underground work and l a t e r i n v e s t i g a t i o n do not f u l l y support t h i s c l a s s i f i c a t i o n . D u f f e l l (1952, p. 5) says of the Hazelton Group: The most common and c h a r a c t e r i s t i c rocks of the group are volcanic tuffs and breccias. Fragments consist l a r g e l y of volcanic rocks, but include minor amounts of sedimentary and plutonic materials. The fragments range from fine ash to blocks a foot or more i n length, but most are \ to \ inch long ... (Porphyritic) lava flows of andesitic and b a s a l t i c composition form a large part of the Hazelton Group ... The sedimentary rocks include fine-grained black a r g i l l i t e , minor impure limestone, thin-bedded, grey-green chert, and others best described as "tuffaceous greywackes"... Some of the beds contain a high percentage of carbonate. On p. 6 he describes a group of Lower Cretaceous rocks occurring on Swing Peak and Laventie Mountain, about 20 miles North of Lindquist Lake: ... a series of interbedded black a r g i l l i t e s , fawn to grey arkoses and minor volcanic rocks, with an aggregate thickness of about 5000 feet. A r g i l l i t e predominates near the base of the section, and the arkoses are t h i n -bedded near the base but become thicker higher i n the se r i e s . These ... are succeeded by a volcanic series of t u f f s , breccias and flows, very si m i l a r to those of Jurassic age. The relationship of Cretaceous rocks to Jurassic s t r a t a i s uncertain, but i s probably represented by an unconformity. No actual contacts were observed, but the Cretaceous rocks s t r i k e nearly west and dip southerly, while the Jurassic rocks s t r i k e a l i t t l e east of North with dips both east and west. 9 As w i l l be shown l a t e r , the sediments on the Deer Horn property are a series of a r g i l l i t e s , quartzites and ar-koses, s t r i k i n g westerly and dipping to the South. The writer has not seen any rocks on or near the property that could be d e f i n i t e l y described as volcanic t u f f s or breccias, although he has examined volcanic rocks c l o s e l y corresponding to the above description on Mount Chikamin, 10 miles to the East. No chert was found on the property. Occasional pebbles of purplish porphyritic lava occur i n f l o a t , but since they may belong to either group, they are not diagnostic. On the other hand, the Deer Horn sediments are i n part limy, which agrees more with the description of the Hazelton Group. The writer has not seen the type rocks for the Lower Cretaceous Swing Peak Group, and i n the absence of f o s s i l s i t i s impossible to prove to which of the two groups the sediments on the Deer Horn property belong. But on the basis of structure and l i t h o l o g y alone, t h e i r c o r r e l a t i o n with the Hazel-ton Group i s open to some doubt. It i s conceivable that at least part of the sedimentary embayment at Lindquist Peak correlates with the Swing Peak Group. This p o s s i b i l i t y i s admitted by D u f f e l l , who on his map (1952) under the symbol for the Hazelton Group remarks: "May include some undifferentiated 3." ( i . e . Lower Cretaceous beds). 10 PART II GEOLOGY OF THE DEER HORN PROPERTY CHAPTER III PETROLOGY 1. G r a n i t i c Rocks Grani t i c rocks underlie the greater part of the property. On the basis of their mineral composition they can a l l be c l a s s i f i e d as granodiorite, but several types have been recognized. The differences between them l i e mainly i n v a r i a -tions of mineral proportions, i n the anorthite content of the plagioclase, and i n texture. (a) Coarse "po r p h y r i t i c " granodiorite The " p o r p h y r i t i c " granodiorite i s a fresh-looking medium to coarse-grained pinkish g r a n i t i c rock containing con-spicuous euhedral crystals of orthoclase up to 1 inch across. Quartz, orthoclase and plagioclase are essential minerals, accessories are brown b i o t i t e , apatite and sphene. The l a t t e r occurs commonly i n euhedral wedge-shaped crystals up to 1 mm long and mm wide. Small amounts of c h l o r i t e and sulphides were found i n the thin-section. Fine flakes of ob i o t i t e form narrow rims around some of the prominent orthoclase c r y s t a l s and are also enclosed i n them. 11 Quartz forms about 20$ of the rock. It occurs i n clear glassy anhedral grains 3-10 mm across. In thin-section, i t i s s l i g h t l y fractured and shows weak strain-shadows. It i s i n t e r s t i t i a l to euhedral plagioclase c r y s t a l s . The plagioclase shows euhedral to subhedral forms, only s l i g h t l y corroded, with well developed normal o s c i l l a t o r y zoning. This i s a distinguishing feature, not found i n any of the other g r a n i t i c rock types examined. The composition of the plagioclase, determined i n f i v e grains, ranges from An 33 i n the core to An 22 i n the outer zone, averaging about An 27 . The plagioclase i s only s l i g h t l y altered to s e r i c i t e , and many grains are quite clear. Orthoclase occurs i n two d i f f e r e n t ways: as small anhedral grains i n t e r s t i t i a l to plagioclase, and as large oval-shaped grains about 1 inch square. Some of the l a t t e r have i n d e f i n i t e boundaries, enclosing many strongly corroded r e l i c s of quartz, plagioclase, b i o t i t e and sphene; others, much less common, are euhedral orthoclase crystals without the b i o t i t e rim which characterizes the f i r s t mentioned type. The large grains are somewhat cloudy because of a l t e r -ation to clay minerals. Their o p t i c a l orientation i s uniform, but undulating and minutely i r r e g u l a r i n d e t a i l . They contain wavy, branching but generally sub-parallel lamellae of plagio-clase, o p t i c a l l y continuous, probably replacement lamellae. In places, the orthoclase grains show extremely f i n e , s t r a i g h t p a r a l l e l lamination having s l i g h t l y d i f f e r e n t r e l i e f . The 12 lamellae are arranged i n one d i r e c t i o n throughout the grain; this d i r e c t i o n i s not p a r a l l e l to that of the twin-lamellae of the enclosed plagioclase grains, and forms an angle of about 30 degrees with the d i r e c t i o n of the coarser i r r e g u l a r plagioclase lamellae. This feature i s perhaps due to an almost submicro-scopic exsolution of a l b i t e , forming .a micro- to cryptoperthite. The corroded remnants of enclosed minerals become more abundant towards the boundaries of the orthoclase grain, u n t i l the grain "peters out" i r r e g u l a r l y i n a normal g r a n i t i c texture. From the more uniform parts of the sections and the hand-specimens i t appears that the oligoclase forms about 40% of the rock, the i n t e r s t i t i a l ( o r i g i n a l ) orthoclase about 20%, and the large crystals about 10%. B i o t i t e occurs i n dark brown flakes up to 4 mm across but mostly smaller, forming perhaps 7% of the rock. The section shows that i t i s partly altered to c h l o r i t e . About 2% of euhedral sphene, and traces of apatite, magnetite and epidote complete the mineral assemblage. This rock, well exposed along the tractor road near Lindquist Lake, shows a coarse blocky fracture and a few narrow shears. Some of the fractures are coated with epidote, some with a pinkish crust of the calcium z e o l i t e - s t i l b i t e . One 1-inch shear zone i n the granodiorite i s completely impregnated with massive pinkish s t i l b i t e , i n which crushed fragments of the rock are embedded. 13 (b) Hornblende granodiorite The hornblende granodiorite which forms the bulk of the northwesterly part of the int r u s i v e rocks on the property i s a medium-grained l i g h t greenish grey rock of g r a n i t i c tex-ture. It outcrops to the south and west of the mine camp, and the thick Main vein l i e s i n i t . The rock consists mainly of plagioclase, quartz, hornblende and c h l o r i t e , and i s cut by many veinlets of epidote from 1 mm to about 10 mm wide. The ferromagnesian minerals occur i n two ways: as l i g h t greenish grey, i r r e g u l a r , rather i n d i s t i n c t spots about 3 - 4- mm across, which were probably b i o t i t e , nowreplaced by c h l o r i t e , and as dark greenish black sharply defined aggregates consisting main-l y of hornblende. Both are i n places segregated to form clots 5 mm and more across. Some chlorite-epidote veinlets show bleached borders. A few fractures are slickensided, with traces of s t i l b i t e . Orthoclase, sphene, pyrrhotite and p y r i t e are v i s i b l e with a hand-lens. About 40% of the rock, as seen under a microscope, consists of plagioclase. This forms large (2-3 mm) c r y s t a l s , subhedral, now lar g e l y altered to a fine-grained mixture of "water-clear" a l b i t e , quartz, s e r i c i t e , green b i o t i t e , c h l o r i t e , and epidote. Only narrow rims are comparatively free of a l t e r -ation. These show twinning lamellae o p t i c a l l y continuousvith those i n the altered parts and are considered part of the o r i g i n a l plagioclase crystals rather than l a t e r accretions. The plagioclase composition, determined from the less altered rims, i s An 23 . Many grains are s l i g h t l y sheared, showing narrow bands of c a t a c l a s t i c or r e - c r y s t a l l i z e d a l b i t e (?). Quartz occurs as irr e g u l a r anhedral grains i n the in t e r s t i c e s of the plagioclase c r y s t a l s , forming about 20% of the rock. Almost a l l grains show undulating extinction due to s t r a i n . An unusual feature i s the presence of f i n e i n t e r -growths of quartz with orthoclase, not seen i n the other rocks, but very common i n the specimen examined. S l i g h t l y cloudy orthoclase i s present as anhedral grains between plagioclase c r y s t a l s . Some grains show traces of p e r t h i t i c texture (sub-parallel i r r e g u l a r lamellae of plagio-clase arranged at about 20 degrees to cleavage), but this i s much less conspicuous than i n the other rocks, and the t o t a l amount of orthoclase i s smaller, only about 20%. The grain boundaries are highly i r r e g u l a r . B i o t i t e and hornblende are the chief ferromagnesian minerals, c h l o r i t e i s the main a l t e r -ation mineral. The b i o t i t e i s dark brownish green, strongly pleochroic, indicating an i r o n - r i c h v a r i e t y . It occurs as minute s e r i c i t e - l i k e shreds and flakes i n altered plagioclase c r y s t a l s , and as larger aggregates of f i n e flakes associated with and surrounding hornblende. It forms perhaps % of the rock. Hornblende i s present i n clusters of long prismatic c r y s t a l s , commonly corroded by quartz and plagioclase, i n -dicating an early o r i g i n . I t i s dark b l u i s h green, strongly pleochroic (bluish green to greenish yellow) the extincti o n angle Z*e ranges from 15 to 18 degrees. This probably a c t i n -o l i t i c hornblende accounts for another % of the rock. C h l o r i t e , greenish and s l i g h t l y pleochroic, occurs sparsely as small shreds i n altered plagioclase, and as some-what larger masses associated with hornblende. Epidote i s found mainly i n small i r r e g u l a r grains and fine aggregates i n plagioclase, i n hornblende clusters and i n narrow fractures. Small but well-developed crystals of apatite occur i n the clusters of ferromagnesian minerals, and shapeless grains of a carbonate are present i n small amounts. Some fin e magnetite i s scattered i n the c h l o r i t e . (c) A l t e r a t i o n phases of hornblende granodiorite The two g r a n i t i c rocks described above are the main types present on the property. The hornblende granodiorite shows several a l t e r a t i o n phases: 1. "Mine" granodiorite: The "mine" granodiorite occurs mainly on the footwall of a 10 foot wide mineralized quartz vein. The rock is l i g h t grey, medium-grained, with a g r a n i t i c texture and a "bleached" appearance. It consists of quartz, plagioclase, orthoclase and spots of fine-grained greenish c h l o r i t e , which i s a l l that remains of the f e r r o -magnesian minerals. A few small aggregates of sphene are v i s i b l under a hand lens. Fine grains of chalcopyrite and p y r i t e are sparsely disseminated i n the rock, and fracture surfaces are coated with films of a white z e o l i t e (laumontite). About one t h i r d of the rock i s formed of quartz, which occurs i n anhedral grains up to 3 mm across, commonly-fractured and showing undulating extinction due to s t r a i n . Some grains contain a small flake of muscovite i n the center. In several places, small rounded grains of quartz surrounded by orthoclase show o p t i c a l continuity with an adjacent quartz grain, suggesting a l a t e r introduction of the orthoclase. Plagioclase comprises about 20% of the rock. It shows subhedral c r y s t a l s , now strongly altered to s e r i c i t e and clay minerals. It i s not zoned, and i t s composition i s close to An 15. Isolated embayed shreds of plagioclase occur i n orthoclase grains, showing a rough p a r a l l e l arrangement s i m i l a r to that described previously. Orthoclase occurs i n many anhedral grains l-l<jr mm across, only s l i g h t l y altered to clay minerals. It contains numerous minutely i r r e g u l a r but generally p a r a l l e l lamellae of plagioclase (about An 10-13) which give i t a p e r t h i t i c texture. These lamellae have d i f f e r e n t orientation i n d i f f e r e n t ortho-clase grains, but within any one grain they are o p t i c a l l y continuous. They occur throughout the orthoclase, even between and around is o l a t e d remnants of quartz grouped i n an a t o l l - l i k e fashion i n the orthoclase. The plagioclase lamellae are a l -most unaltered, which distinguishes them sharply from the euhed-r a l plagioclase with i t s s e r i c i t i c a l t e r a t i o n . The orthoclase comprises now about A-% of the rock, but i t s o r i g i n a l pro-portion was probably much smaller. 17 Narrow rims of s e r i c i t e occur on the boundaries of orthoclase and quartz grains. A small part of the rock, about 2%, consists of c h l o r i t e . This i s present as frayed shapeless masses, apparently a l t e r a t i o n products of ferromagnesian miner-a l s . It i s commonly associated with f i n e l y disseminated magnetite "dust", suggesting a breakdown of b i o t i t e . Small masses of very fine-grained greenish a n t i g o r i t e (?) occur i n the c h l o r i t e . A few t i n y grains of epidote and several patches and narrow veinlets of a carbonate, which i s probably supergene, are present i n the rock. It also contains sparse disseminated p y r i t e , chalcopyrite and sphalerite. 2 . Sheared s i l i c i f i e d granodiorite: The s i l i c i f i e d granodiorite forms a band about 100 feet wide near the northern contact of the i n t r u s i v e . It i s a very l i g h t pinkish grey, medium - to coarse-grained rock with g r a n i t i c texture, con-s i s t i n g mainly of quartz and feldspar, and cut by numerous quartz veinlets from 1 mm to a few centimeters wide. Dark minerals are almost completely absent. The rock i s strongly fractured and sheared, and films of s e r i c i t e have developed on the fracture planes. Crystals of p y r i t e up to 3 mm across are disseminated i n the rock, and brown limonite s t a i n i s common on fractures. Under the microscope, the rock i s seen to consist of about 30% quartz, 50% plagioclase, 20% orthoclase and very minor amount of s e r i c i t e . Its brecciated nature and mortar structure are evidence of strong mechanical crushing. The unzoned plagio-clase i s highly ©trained, sheared and fractured. Bending and displacement of the twin-lamellae are common. The composit-ion of thi s plagioclase, averaged from 6 determinations, i s about An 13 . Several large grains show a peculiar kind of mottled twinning, i n which short discontinuous sub-parallel twin lamellae are thickened and joined l a t e r a l l y to produce a "hatching" e f f e c t . The twin lamellae show o p t i c a l continuity and wavy extinction. This i s possibly secondary twinning due o to s t r e s s . Quartz occurs i n anhedral i n t e r l o c k i n g grains, i s fractured and shows undulating extinction. In part of the section the grains are coarse, probably part of the o r i g i n a l rock, but generally they are small, in t e r l o c k i n g and concen-trated i n narrow bands traversing the rock i n a l l d i r e c t i o n s . These are hydrothermal v e i n l e t s . Quartz i s here associated with some orthoclase and muscovite. Orthoclase, p a r t l y a l t e r -ed to clay minerals, i s also found i n large anhedral grains that are part of the o r i g i n a l rock. The d i s t i n c t i v e grains of perthite with plagioclase lamellae, common i n the previous types, are absent. No ferromagnesian minerals are present i n the section examined. 3 . Gneissic b i o t i t e - g r a n o d i o r i t e : Gneissic b i o t i t e -granodiorite occurs i n a wide band on the hanging wall of "the Main vein. The rock i s medium-grained, dark greenish grey, with a gneissic texture. It consists mainly of quartz, f e l d -spar and b i o t i t e . B i o t i t e i s present i n an unusual amount, 19 about 25%, segregated i n i r r e g u l a r bands % - 3 mm wide. Many-small lenses ("augen") of quartz i n fine-grained matrix suggest that the texture was produced by shearing. Some spec-imens show disseminated epidote and orthoclase veinlets with epidote c r y s t a l s . In thin-section, the rock shows fin e - to medium-grain-ed gneissic texture. Bands of f i n e l y crushed quartz and f e l d -spar alternate with small lenses of somewhat coarser i n t e r -locking quartz grains and with i r r e g u l a r bands of large flakes of b i o t i t e . The b i o t i t e i s brownish green, strongly pleo-chroie. The flakes are mostly s t r a i g h t , but i n several places they are seen to curve around plagioclase and quartz grains included -in the bands. The mineral also occurs i n very f i n e flakes of s e r i c i t i c habit, disseminated between the main b i o t i t e layers. Quartz forms about 30% of the rock. Feldspar i s strongly altered to s e r i c i t e and clay minerals, plagioclase more so than orthoclase. Only traces of twinning remain i n the plagioclase, the rest being l a r g e l y obliterated by shear-ing. Determination of composition by the Michel-Levy method on four badly preserved grains indicated An 25. Some ortho-clase grains contain the usual i r r e g u l a r lamellae of plagio-clase; others are almost c l e a r , only s l i g h t l y altered. The l a t t e r occur with quartz i n the crushed bands. Orthoclase and oligoclase each account for about 20% of the rock. Small euhedral to subhedral crystals of apatite are 20 f a i r l y common i n the b i o t i t e bands, cutting sharply across b i o t i t e flakes. Anhedral bands of epidote are also concen-trated i n and near the b i o t i t e layers, while f i n e flakes of greenish c h l o r i t e are disseminated i n the quartz-feldspar bands. 4. Other altered types: The two remaining types are c l e a r l y the result of hydrothermal a l t e r a t i o n connected with the formation of the veins. They were not examined micro-s c o p i c a l l y . One of these occurs i n the immediate v i c i n i t y of the Main vein and i n small g r a n i t i c inclusions i n the vein. This rock is l i g h t greenish white, crumbly, has a rough s c h i s t o s i t y and consists of quartz, crushed feldspar and s e r i c i t e . There i s no trace of the usual mafic minerals. Quartz veinlets a f r a c t i o n of an inch wide cut the rock. They have f a i r l y sharp but i r r e g u l a r boundaries and are believed to have formed pa r t l y by replacement. Small grains of sulphides occur i n the veins, and specks of c h l o r i t e were seen about 1 inch from the veinl e t s i n some specimens. The other hydrothermally altered type was found i n a road cut about 1 mile east of the a d i t . There the rock i s cut by several westerly s t r i k i n g , steeply dipping quartz veins up to 10 inches wide, containing masses of fine-grained magnetite, minor pyrite and some chalcopyrite. The rock between these veins is intensely altered. It consists of quartz and some feldspar grains, crushed and sheared, embedded i n a very f i n e -grained soft greenish matrix which consists probably of c h l o r i t e . 21 In parts adjacent to the v e i n l e t s , and p a r t i c u l a r l y where the rock i s invaded by offshoots of the quartz s t r i n g e r s , limonite mixes with the c h l o r i t i c matrix coloring i t brown. The bound-ary between the green c h l o r i t i c and the brown l i m o n i t i c part i s very i r r e g u l a r , but sharply defined, i n places by a narrow rim of concentrated limonite. The m e t a l l i c minerals are con-fined to the quartz s t r i n g e r s . (d) Mutual relations Unfortunately, the d i f f e r e n t rock types described above have not been mapped i n d e t a i l , so that t h e i r mutual relations are not well known; but from the specimens av a i l a b l e for i n v e s t i g a t i o n i t appears that only two main types are distinguished. One d i s t i n c t i v e type i s the "po r p h y r i t i c " granodior-i t e . Its fresh appearance and the abundance of large euhedral crystals of orthoclase are so c h a r a c t e r i s t i c of the rock i n the southeastern part of the property that the rock was mapped as a separate unit on the early maps. The other main type i s the hornblende granodiorite which forms the northwestern part of the Deer Horn i n t r u s i v e s . Its dark, greenish, fine-grained appearance contrasts so sharply with the coarse pinkish rock to the southwest that the probab-i l i t y of two separate intrusions almost forces i t s e l f on the observer. It i s regrettable that their contact was not studied i n d e t a i l ; under the circumstances th e i r age relations cannot be established. The other types of i n t r u s i v e rocks l i e within 22 the body of the hornblende granodiorite, and may have been de-rived from i t by various tectonic and hydrothermal processes. The "mine granodiorite" i n texture resembles the hornblende granodiorite, but d i f f e r s from i t by i t s s c a r c i t y of mafic minerals and by i t s much more conspicuous replacement of quartz and plagioclase by orthoclase. This rock l i e s close to a thick quartz vein (the Main vein), which c e r t a i n l y required a great amount of hydrothermal a c t i v i t y for i t s formation. These hydrothermal solutions were probably responsible for the removal of the mafic constituents; an extreme example of this bleaching are the crumbly s e r i c i t i z e d remnants of granodiorite i n the vein. A s i m i l a r o r i g i n seems l i k e l y for the " s i l i c i f i e d granodiorite" on the northern contact of the i n t r u s i v e . This crushed bleached rock, cut by innumerable small quartz s t r i n g e r s , l i e s up-dip from a narrow but persistent quartz vein which marks a prominent and well defined shear zone underground. It may then represent the upward continuation of the shear, which became less sharply defined as i t passed from the steeply dipping (70 deg.S) s i l i c e o u s sediments through the f l a t t e r con-tact (55 deg. South) into the overlying i n t r u s i v e rock. This may explain the f a i r l y wide shattered zone, the numerous i r r -egular stringers instead of one persistent vein, and the re-moval of mafic constituents by the percolating hydrothermal solutions. However, both the "mine" and the " s i l i c i f i e d " granodiorite have a more sodic oligo&lase than the normal horn-blende granodiorite, which i s d i f f i c u l t to explain without invoking complicated metasomatic processes requiring much more and better evidence than that available at present. While these two types are characterized by t h e i r lack of mafic minerals, the gneissic b i o t i t e granodiorite i s con-spicuous by their abundance. It l i e s on the hanging-wall of the westerly s t r i k i n g , northerly dipping Main vein at a d i s t -ance of about 20 feet from the vein; the intervening band i s strongly hydrothermally altered. To the north, this" rock grades into non-gneissic greenish g r a n i t i c rock which was not c l o s e l y studied but which i n the f i e l d resembles the hornblende grano-d i o r i t e outcropping farther south. The f o l i a t i o n i n the gneissic rock i s roughly p a r a l l e l to the Main vein, following i t s r o l l s and changes of s t r i k e . The gneissic texture of the rock i s considered to be the result of the shearing which pre-ceded the formation of the Main vein and l o c a l i z e d i t ; the b i o t i t e appears r e - c r y s t a l l i z e d under d i r e c t i v e s t r e s s , and the crushed nature of the quartz and feldspar also suggest that the rock was formed under c a t a c l a s t i c metamorphism. The reason for the increase of mafic constituents i s uncertain. The "bleached" zone -around the Main vein dips gently to the North, the band of sheared s i l i c i f i e d granodiorite described above dips steeply to the South. These two zones intersect i n the area that has been investigated at a depth of about 100 - 500 feet below surface, thus i s o l a t i n g between them a wedge-like block of non-bleached granodiorite. An increase of mafic minerals here may be due to redeposition of the mafics pre-viously removed from the Wo bleached zones, and the enriched band may perhaps be described as a "mafic front". One of the most conspicuous features of both main in t r u s i v e types i s the introduction of p e r t h i t e , replacing e a r l i e r quartz and feldspar. But since this potash metasom-atism affects also some sedimentary rocks, i t w i l l be discussed i n d e t a i l l a t e r . In several previous company and government reports (S.S.Holland, Dept. of Mines, 1945; L a n g i l l e , 1945; Ney, 1947; and others), the intrusive rocks have been variously described as granite, granodiorite, quartz d i o r i t e and d i o r i t e . On Joubin's surface map they are marked as granite (the coarse "porphyritic" type) and quartz d i o r i t e (the hornblende grano-d i o r i t e ) , and i n the l a t e r d r i l l - l o g s they were divided by the writer into granodiorite (pinkish, leucocratic) and quartz d i o r i t e (greenish, mesocratic). However, examination of t h i n -sections, not available to the previous workers, shows that most of these names are incorrect. As some d i f f e r e n t i a t i o n i s desirable i n any eventual detailed work on the property, i n i t i a l s or numbers may be used to d i s t i n g u i s h the main types. 2 . Sedimentary Rocks The sedimentary rocks on the property are f i n e - to medium-grained rocks of s i l i c e o u s , feldspathic and carbonaceous composition. They form units from about 1 foot to several tens of feet t h i c k , but usually not uniform i n composition. In nearly every unit there are variations i n the proportions of quartz and carbonaceous material, which are unfortunately not s u f f i c i e n t l y d i s t i n c t i v e to enable the tracing of any such bed for a greater distance. The following table of rock units shows only the pre-dominant types. It i s to be understood that they are i n t e r -bedded with, and grade i n t o , thinner beds of s l i g h t l y d i f f e r e n t composition. The rocks are l i s t e d i n t h e i r s t r a t i g r a p h i c order. The s t r a t i g r a p h i c a l l y lowest known rock i s the carbon-aceous greywacke which i s i n contact with the hornblende d i o r i t e on the d r i f t l e v e l ; the s t r a t i g r a p h i c a l l y highest and youngest rock i s the feldspathic greywacke outcropping on the surface. The structure of the sedimentary rocks w i l l be considered i n a l a t e r chapter. The hornblende granodiorite overlies part of the sedimentary assemblage, so that some of the rocks do not outcrop, and are known only from the adit and d r i l l - h o l e s . The table i l l u s t r a t e s the thickest section of s e d i -ments seen on the property, and i s based on two d r i l l - h o l e s near the western end of the adit and on the i r l i n e a r contin-uation on the surface. 26 (a) SEDIMENTARY AND METAMORPHIC ROCK UNITS Rock Thickness Remarks Feldspathic greywacke over 500' Upper contact not mapped Interformational breccia l 1 C h i a s t o l i t e s c h i s t 330' Restricted i n l a t e r a l extent Brown a r g i l l i t e Black a r g i l l i t e 370' 75' On contact with the i n -trusion on the surface Feldspathic quartzite 155' Carbonaceous greywacke over 65 ' Contains beds of skarn, black a r g i l l i t e and coarse arkose On contact with the i n -trusion i n the adit elevation LOWER SEDIMENTARY CONTACT UNKNOWN (b) Carbonaceous greywacke This rock, adjacent to the intru s i v e contact i n the adit elevation, was logged as "black t u f f " . It i s a dark grey to black carbonaceous greywacke consisting of fragments of quartz, orthoclase and some rock fragments. They are commonly very small, only".rarely reaching 4- mm i n diameter, subangular to angular and s l i g h t l y elongated; they are embedded i n a very fine-grained mixture of carbonaceous matter and s e r i c i t e . The 27 proportions of fragments and matrix, and of the s e r i c i t i c and carbonaceous components of the matrix vary widely giving the rock a l t e r n a t i v e l y a rather coarse fragmental and a f i n e r a r g i l l i t i c appearance. Fine grains of pyrrhotite are abundantly disseminated i n the rock; l o c a l l y , lenses of massive pyrrhotite several inches across and a few feet long are found. Pyrite i s somewhat less common. Towards the north, the greywacke loses most of i t s carbonaceous material and grades into coarse arkose and f e l d -spathic quartzite. It does not outcrop. Although the rock is intruded by the granodiorite, i t does not show any s t r i k i n g effects of contact metamorphism, beyond the formation of s e r i c i t e and conversion of the carbon-aceous matter into graphite. It was not examined microscop-i c a l l y . (c) Coarse arkose As the carbon content of the matrix almost disappears and the proportion of quartz and feldspar grains increases considerably, the rock grades into a coarse arkose. The gran-ules of quartz and feldspar are subangular, from 1-3 mm across, are present i n about equal amounts, and embedded i n a f i n e -grained s e r i c i t i c matrix. The rock i s l i g h t greenish grey and has a peculiar granular appearance resembling the bleached granodiorite near the veins. Locally i t contains lenses and streaks of pyrrhotite s i m i l a r to those i n the carbonaceous greywacke. It was seen only i n the adit where i t occurs rarely as narrow bands. In thin-section, some of the orthoclase grains are fractured and veined by s e r i c i t e , but f a i r l y free from i n -clusions. These are c l e a r l y allochthonous and part of the o r i g i n a l sediment. But many others contain irr e g u l a r fragments of quartz i n o p t i c a l continuity with adjacent quartz grains, and are possibly autochthonous, metasomatic. A l l quartz and most of the orthoclase grains show wavy extinction due to s t r a i n . The rock i s strongly sheared, with a mortar structure. (d) Feldspathic quartzite For a greater part of i t s length the adit runs approx-imately p a r a l l e l to a thick bed of feldspathic quartzite which was mapped underground and logged as "greywacke". Except for i t s smaller grain-size, this rock appears very si m i l a r to the coarse arkose. It i s d u l l grey i n color and consists of rounded grains of quartz and orthoclase embedded i n a fine-grained s i l i c e o u s and feldspathic matrix, with some carbonaceous matter. The fragments are mostly less than 1 mm across, although a few are up to 3 mm long. The rock i s very hard, compact and breaks with a jagged or almost conchoidal fracture. It contains very f i n e grains of pyrrhotite, abundantly distributed i n the matrix. The Contact vein i n the adit l i e s i n th i s rock. It i s commonly accompanied by a 1 - 3 foot band of l i g h t grey s i l i c e o u s rock, i n places extending on both sides of the vein, but mostly l y i n g at a short distance to one side. The vein favors the hanging-wall of the band i n the western part of the adit; to the east of a prominent dyke the relations are less clear. The l i g h t colored rock was mapped as " a p l i t e " under-ground, but is merely a purer feldspathic quartzite, with most of the carbonaceous content of the matrix either simply absent or leached out. The p o s s i b i l i t y of leaching i s suggested by the fact that numerous t h i n veinlets of pyrrhotite i n the grey quartzite show d i s t i n c t l y bleached and s i l i c i f i e d boundaries s i m i l a r to the light-colored rock described above. However, as the l i g h t band l i e s at a short distance from the vein and the intervening rock has a normal grey color, the l i g h t colored band i s be-liev e d to be of sedimentary rather than hydrothermal o r i g i n . The grey quartzite i s cut by numerous narrow fractures from 1 mm to about 2 inches wide. These are f i l l e d mainly with quartz, some c a l c i t e and grains of pjirrhotite with minor sphalerite and galena. In one section of the adit the fractures commonly contain a d e l i c a t e l y fibrous pink Mn-bearing var i e t y of z o i s i t e ( t h u l i t e ) , and r a r e l y small crystals of pyrrhotite. Near the western end of the d r i f t the quartzite con-tains bands of massive epidote, brown garnet of the grossular-ite-andradite series and quartz, with gradational boundaries. The lime s i l i c a t e bands l o c a l l y carry disseminated scheelite and fine-grained hessite. This skarn w i l l be considered i n more d e t a i l i n a l a t e r section. Beds of black a r g i l l i t e from 2 to 1 0 feet thick occur commonly i n the feldspathic quartzite. (e) Black a r g i l l i t e As the proportion of quartz and feldspar grains dim-inishes, the grain-size greatly decreases and the carbonaceous content of the matrix increases, the feldspathic quartzite grades into black a r g i l l i t e . The t y p i c a l black a r g i l l i t e i s a uniform, t h i n l y laminated rock with poorly developed s c h i s -t o s i t y and a s i l k y l u s t e r on fractures. Commonly i t contains t h i n lenses and films of pyrrhotite p a r a l l e l to the bedding planes. Although i t l i e s closer to the i n t r u s i v e contact than the band of the c h i a s t o l i t e schist mapped on the surface, i t does not contain any c h i a s t o l i t e c r y s t a l s . The only observable effect of metamorphism i s the conversion of the o r i g i n a l car-bonaceous shale into a r g i l l i t e . The main horizon of black a r g i l l i t e contains several beds of feldspathic quartzite. (f) Brown a r g i l l i t e , (metamorphosed) This rock forms the horizon marker used i n c o r r e l a t i n g the sediments intersected by the d r i l l - h o l e s with those mapped on the surface. On surface i t i s i n contact with the grano-d i o r i t e . It i s greyish brown, brown weathering, compact, with only traces of s c h i s t o s i t y and a d u l l to s i l k y l u ster on fractures. 31 I t i s cut by many narrow v e i n l e t s f i l l e d w i t h q u a r t z , some f e l d s p a r and a c t i n o l i t e . Quartz and f e l d s p a r p e n e t r a t e f o r a s h o r t d i s t a n c e i n t o the w a l l s o f the f r a c t u r e s . L o c a l l y , t h e s e q u a r t z - a c t i n o l i t e bands become abundant and g i v e t h e r o c k a g r e e n i s h appearance; t h i s i s p r o b a b l y t h e o r i g i n a l " g r e e n s t o n e " mapped on t h e s u r f a c e . Narrow v e i n s c u t t i n g a c r o s s t h e q u a r t z - a c t i n o l i t e bands c o n t a i n c r y s t a l s o f a d u l a r i a up t o 1 cm l o n g . I n d r i l l - c o r e s t h i s i s a f i n e - g r a i n e d brown b i o t i t i c r o c k c o n t a i n i n g numerous s m a l l l e n s e s and v e i n l e t s o f q u a r t z , s u r r o u n d e d or bo r d e r e d by narrow zones of g r e e n i s h f i n e - g r a i n e d a c t i n o l i t e and c h l o r i t e . T h i s r o c k i s the "brown t u f f " o f some d r i l l - l o g s . I n t h i n - s e c t i o n , t h e r o c k c o n s i s t s o f a v e r y f i n e -g r a i n e d assemblage o f q u a r t z , an u n d e t e r m i n a b l e f e l d s p a r , brown b i o t i t e , a c t i n o l i t e f o r m i n g minute r o s e t t e s , minor c h l o r i t e and e p i d o t e . One o f t h e many narrow v e i n l e t s common i n t h i s t y p e o f r o c k c o n t a i n s q u a r t z and c r y s t a l s o f a c t i n o l i t e up t o 2 mm l o n g . The b i o t i t e i s l e a c h e d out on b o t h s i d e s o f the v e i n l e t f o r about 1 mm; o n l y q u a r t z and a c t i n o l i t e r o s e t t e s r emain i n p l a c e . The assemblage q u a r t z - f e l d s p a r - a c t i n o l i t e - b i o t i t e -c h l o r i t e - e p i d o t e i s c h a r a c t e r i s t i c o f the " g r e e n s c h i s t " meta-morphic f a c i e s , b i o t i t e - c h l o r i t e s u b f a c i e s . A c c o r d i n g t o Tu r n e r and Verhoogen, (p. 469)> t h i s assemblage, w i t h some m o d i f i c a t i o n s , may be t h e p r o d u c t o f low-grade metamorphism o f a calcareous shale. This idea i s supported by the presence of bands of calc s i l i c a t e skarn interbedded with the brown a r g i l l i t e . (g) C h i a s t o l i t e s c h i s t The brown a r g i l l i t e grades over a short distance into a black, very fine-grained schistose rock with a glossy l u s t e r , the c h i a s t o l i t e s c h i s t . This rock contains about 10$ of conspicuous randomly oriented metacrysts of andalusite, var. c h i a s t o l i t e , 2 - 3 mm long and Jj- - 1 mm wide. The mineral shows the c h a r a c t e r i s t i c black cross of impurities and i s mostly altered to a white c l a y - l i k e substance. In the f i e l d the metacrysts appear about 10 feet from both contacts of the band of the black schist and increase i n size towards the center In thin-section, the rock shows about 10% metacrysts and 90% carbonaceous matrix. The matrix consists of f i n e l y divided quartz, s e r i c i t e and carbonaceous matter, which i s so abundant that i t obscures any less obvious minerals that may be present. The s e r i c i t e flakes show a roughly p a r a l l e l arrange-ment which i s probably responsible for the s c h i s t o s i t y of the rock. The c h i a s t o l i t e metacrysts cut sharply across the s e r i -c i t e f o l i a t i o n ; only a s l i g h t bending of the mica flakes was observed i n places. The c h i a s t o l i t e i t s e l f i s strongly altered to s e r i c i t e , only shreds of the o r i g i n a l mineral remain. The a l t e r a t i o n i s the res u l t of surface weathering. The rock i s a black shale that has undergone a low-grade dynamothermal metamorphism to c h i a s t o l i t e s c h i s t . The gradual disappearance of the c h i a s t o l i t e metacrysts towards the contacts of the black s c h i s t may be due to a more s i l i c e o u s nature of the gradational contacts. A sim i l a r compositional difference may also explain the lack of metamorphic minerals i n the black a r g i l l i t e found underground and described above. This rock possibly did not have enough clay minerals i n the matrix to supply the necessary A l for the formation of andalusite (h) Feldspathic greywacke The s t r a t i g r a p h i c a l l y highest rock mapped on the property i s a feldspathic greywacke. It i s a grey, fine-grained fragmental rock consisting of quartz, feldspar and b i o t i t e , with a very dense appearance, weathering to a f i n e l y p i t t e d buff-colored surface. In thin-section i t shows about 30% quartz, 30% ortho-clase, 20% plagioclase and 20% matrix. The matrix consists mainly of b i o t i t e with minor s e r i c i t e and carbonaceous matter. The quartz i s rounded to subangular and commonly r e c r y s t a l l i z e d to a mosaic of small grains, showing s t r a i n - e f f e c t . Ortho-clase occurs i n subangular grains partly altered to s e r i c i t e . The plagioclase i s a l b i t e , An 7. It occurs i n rounded grains, mostly c l e a r , with well-developed twinning. B i o t i t e forms small flakes i n the matrix, curving around quartz grains. The rock has a very rough p a r a l l e l texture, probably representing the o r i g i n a l bedding. Some carbonaceous matter, very f i n e -grained quartz and some feldspar make up the rest of the matrix. According to PettiJohn's c l a s s i f i c a t i o n of sand-stones (Pettijohn, 1954), this rock i s a feldspathic greywacke. 3. Dyke Rocks There are two types of dykes on the property. One i s a l i g h t colored northerly trending dyke with a steep westerly dip, which cuts both the g r a n i t i c rocks and the sediments. It was mapped as " f e l s i t e " and i s believed to mark the trace of a prominent f a u l t . The other type, logged as "trap", s t r i k e s westerly, i s nearly v e r t i c a l , cuts only the intrusive and i s not considered s t r u c t u r a l l y important. (a) A l b i t i t e ("Felsite") The li g h t - c o l o r e d dyke, found both on the surface and underground, consists of a l b i t i t e . The rock i s l i g h t greenish grey, fine-grained, s l i g h t l y porphyritic i n i t s c h i l l e d border-phase. The groundmass consists mainly of sodic plagioclase and minor quartz and orthoclase. It contains feldspar pheno-crysts up to 2 mm long. One thin-section from a surface outcrop was examined, i t shows that the groundmass plagioclase, forming about 85$ of the rock, i s a l b i t e , An 2-4. It occurs i n euhedral to subhedral c r y s t a l s , i s cloudy and altered to s e r i c i t e and clay minerals. Quartz i s sparse (5$). It forms i r r e g u l a r i n t e r s t i t i a l grains i n the plagioclase groundmass. Muscovite (10%) occurs commonly i n fine-grained aggregates and larger isolated flakes. Carbon-ate, epidote, c h l o r i t e and hematite (?) occur i n small amounts. The mineral composition of this rock resembles strongly that of the a l b i t i t e described by Leedal from the Cluanie region, Inverness, Scotland (Leedal, 1952), and may possibly have a sim i l a r o r i g i n . Leedal describes a series of changes i n the a l b i t i z a t i o n of a rock of grano d i o r i t i c com-position: 1. Quartz was replaced by feldspar; 2. Plagioclase was a l b i t i z e d ; 3. cleavelandite replaced quartz and the feldspars; 4. i n some cases K-feldspar p a r t l y replaced plagio-clase. The f i r s t two changes may have occurred i n the dyke at Deer Horn; there i s no evidence for the l a s t two. (b) Hornblende L a t i t e ("trap") The dark-colored dykes found on the surface and i n some d r i l l - h o l e s consist of a fine-grained dark greenish-grey rock, f i n e l y p orphyritic, showing a f e l t e d mass of needle-like feldspar crystals up to 2 mm long and less than \ mm wide, embedded i n a microcrystalline c h l o r i t i c groundmass. Pyr i t e and magnetite are f i n e l y disseminated i n the rock. A thin-section shows that the plagioclase forms about 40$ of the rock, hornblende and epidote account for about 10$, and the rest i s groundmass consisting mainly of c h l o r i t e and l a t h - l i k e feldspar m i c r o l i t e s . No free quartz was observed. The plagioclase phenocrysts show imperfect twinning, i n part obliterated by a l t e r a t i o n . The feldspar i s sodic o l i g o c l a s e , An 15-20. It i s to some extent replaced by "water-clear" a l b i t e . It i s possible that the plagioclase was o r i g i n a l l y more basic, but was made sodic by a l a t e r metasomatic process. 36 On the basis of the present composition the rock should be c l a s s i f i e d as "hornblende l a t i t e " . But as there i s some doubt as to i t s o r i g i n a l nature, the purely descriptive term "trap" could be retained. 4. Rocks affected by Metasomatism Some rocks found on the property do not f i t r e a d i l y into the above categories, because they have been strongly affected by contact phenomena, i n some cases pyrometasomatism, with the possible introduction of i r o n and alumina, i n others by the introduction of potassium from the g r a n i t i c rocks into the country rocks. As they are rather inte r e s t i n g p e t r o l o g i c a l l y and i n some instances economically, they w i l l be considered separately. (a) Epidote - garnet skarn Numerous bands of epidote-garnet skarn occur i n the feldspathic quartzite, i n the brown a r g i l l i t e and on the con-tact of brown a r g i l l i t e and c h i a s t o l i t e s c h i s t . D r i l l - h o l e s show that i t occurs, although sparsely, throughout the whole section of sedimentary rocks explored by d r i l l i n g . The skarn bands i n the a r g i l l i t e were mapped only on the surface. They are 1 - 3 feet wide and follow the general attitude of the sediments. The rock consists of massive epidote, garnet and quartz with some c h l o r i t e . The garnet and epidote form separate parts of the bands, the garnet being mostly con-centrated i n the center and the epidote on the outside, but not 37 without exceptions. Their mutual boundaries are i r r e g u l a r but f a i r l y sharp; the t r a n s i t i o n a l zone i s less than ^" wide. The epidote i s the yellowish green v a r i e t y " p i s t a c i t e " . The garnet belongs to the grossularite-andradite s e r i e s . On the basis of i t s s p e c i f i c gravity i t l i e s closer to the andradite end, i t s probable composition being Gr 40 Ad 60. Where the rock i s fractured, the fractures contain well-developed crystals of the mineral adjoining the fracture, (either epidote or garnet but not both), with quartz. This may suggest some mobilization and re-deposition of the skarn minerals. But many of the c r y s t a l - l i n e d fractures are vuggy and f a i r l y open, so that the minerals may have c r y s t a l l i z e d i n a c a l c i t e v e i n l e t , from which the carbonate was l a t e r leached out. Other fractures, from -§• to 1" wide, are f i l l e d with quartz. Some of them contain sparse scheelite and even more r a r e l y galena, with small amounts of tetradymite. The skarn i n the feldspathic quartzite i s known only from underground exposures. It was seen i n the western part of the adit as a 2 - 3 foot wide band, and as much narrower bands nearby. The usual thickness varies from a few inches to about 2 feet; somewhat thicker bands were intersected i n some of the d r i l l - h o l e s . . The rock i s fine-grained, compact, and consists mainly of massive epidote with lesser amounts of garnet. The separation of the two minerals i s not so clear cut as i n the skarn i n the brown a r g i l l i t e ; the minerals are often mixed, or the garnet occurs as streaks i n the epidote. A thin-section of one epidote band shows that the rock contains a considerable amount of i n t e r s t i t i a l quartz. Epidote penetrates into the q u a r t z i t i c wall-rocks i n small i r r e g u l a r grains, and disappears within a short distance. In one place i n the d r i f t , a small lens of c a l c i t e i n the skarn band contained well-developed crystals of quartz and euhedral crystals of garnet up to 1 cm across, but this type of occurrence was quite exceptional. The rock i s cut by narrow vein l e t s of quartz and c a l -c i t e , commonly containing sphalerite, galena and minor t e l l u r -ides. Fine-grained sphalerite and hessite were found dissem-inated e r r a t i c a l l y i n the skarn band near the western end of the d r i f t . Scheelite occurs commonly - though i n small quantities - i n the skarn, mainly connected with fractures and quartz v e i n l e t s . (b) Quartz-wollastonite-garnet skarn The quartz-wollastonite-garnet skarn i s known only from one d r i l l - h o l e , about 150 feet below the surface, near the contact with the granodiorite. It i s fine-grained, granular, with a sugary texture, and almost white with brown spots. The spots, 2 - 4 mm across, are garnet of the grossularite-andra-dite s e r i e s . Quartz grains up to 2 mm i n diameter are embedded i n the white matrix, which consists of fine-grained fibrous wollastonite. The rock i s cut by a few narrow quartz veinlets w i t h s i l i c i f i e d b o rders, and an i r r e g u l a r zone of a y e l l o w i s h porous m i n e r a l l i e s on the c o n t a c t of the s i l i c i f i e d and the w o l l a s t o n i t i c m a t r i x . In t h i n - s e c t i o n , the bulk o f the m a t r i x i s seen to c o n s i s t of a f e l t e d mass of n e e d l e - l i k e c r y s t a l s of w o l l a s t o n -i t e , some i r r e g u l a r g r a i n s of d i o p s i d e , minor epidote and f i n e -grained q u a r t z . The i l l - d e f i n e d , very f i n e - g r a i n e d y e l l o w i s h m i n e r a l i s probably a l t e r e d s c a p o l i t e . O r t h o c l a s e penetrates the groundmass and r e p l a c e s to some extent many of the quartz g r a i n s . The o r i g i n a l rock before metamorphism c o n s i s t e d probably of quartz g r a i n s embedded i n a m a t r i x of s l i g h t l y magnesian and perhaps somewhat s h a l y l i m e s t o n e , quartz and p o s s i b l y some f e l d s p a r . When i t was i n t r u d e d by the grano-d i o r i t e , the quartz-magnesian limestone assemblage was meta-morphosed t o q u a r t z - w o l l a s t o n i t e - d i o p s i d e . A garnet of the g r o s s u l a r i t e - a n d r a d i t e s e r i e s developed from the c a l c i u m , aluminum and i r o n i n the impure ma t r i x . T h i s was probably a l t e r e d to c h l o r i t e by the l a t e r s i l i c a - b e a r i n g s o l u t i o n s t o produce the g r e e n i s h spots i n the s i l i c i f i e d band. The c a l c i t e , which i s commonly present i n the rock, even i n the w o l l a s t o n -i t e m a t r i x , i s c o n s i d e r e d to be supergene. A f t e r the con-s o l i d a t i o n of the i n t r u s i v e , the potassium metasomatism pr e -v a l e n t i n that a r e a a f f e c t e d the metamorphosed rock t o some extent, and o r t h o c l a s e p a r t l y r e p l a c e d some of the quartz g r a i n s . 40 Since the assemblage quartz-wollastonite-diopside is stable over a very wide range of temperature and pressure conditions, and since the rock, close to a large intrusive body, can hardly be considered as a closed chemical system, the physical conditions during the formation of the skarn can-not be reliably determined. It is only possible to state that the temperature at which the rock was formed was probably higher than 300° C, which is the temperature necessary for the formation of wollastonite at 1 atm. (after Danielsson, quoted in Mason, 1952, p. 221), and lower than 750° C, the maximum temperature of granitic magma (Bowen, 1940). Danielsson's work modified Bowen's earlier reaction curve for the formation of wollastonite, and showed that i t may be actually steeper and shifted towards lower temperature. (See Figure 1). The probable range of composition of the original rock, based on the relative proportions of the metamorphic minerals, is given in Figure 2. (c) Perthite-quartz cataclasite A complex fragmental rock forms a band about 5 feet wide approximately 20 feet north of the intrusive contact in the eastern part of the d r i f t , adjacent and parallel to the Contact vein. The rock is grey to greenish grey, spotty, and consists of rounded to sub-angular grains of quartz and f e l d -spar embedded in a s e r i c i t i c matrix. The proportion of grains to matrix and the size of the fragments varies in different Figure I. A B DC 300 4 S 6 7 8 9 I O O C ' C A reaction curve 3 for the formation of d i o p s i d e ( B o w e n ) B reaction curve f or the formation of wollastonite (Danielsson) C reaction curve 6 for the formation of wollastonite ( Bowen) . D maximum temperature o f granitic magma ( B o w e n ) . Figure 2. Paired composition diagrams for Bowen's reaction equation No. 6 : CaC03 + Si0 2=* C a S i 0 3 * C 0 2 Q quartz, Ca calc i te , Di diopside, Wo wollastonite, Fo forsterite, Pe penclase Shaded - probable original composition of the wollastonite skarn specimens. A common and conspicuous feature of the rock i s the presence of orthoclase porphyroblasts, rounded or r e c t -angular, forming about \ to % of the rock. The largest of them i s 0 . 7 " by 1 .5"» with sharp straight boundaries, others are smaller and less regular. Quartz grains are commonly included i n the porphyroblasts. Narrow bands of epidote occur i n some specimens, and fine-grained pyrrhotite and pyrite are disseminated i n the rock i n a considerable quantity. Schis-t o s i t y i s imperfectly developed. The rock was mapped under-ground as "porphyry", but i n view of i t s apparently c a t a c l a s t i c o r i g i n the name " c a t a c l a s i t e " i s more su i t a b l e . A thin-section shows an inequigranular assemblage of quartz and orthoclase grains i n a fine-grained s e r i c i t i c matrix with some b i o t i t e . The rock i s strongly sheared and i n places has a d i s t i n c t mortar texture. The orthoclase is p e r t h i t i c , cloudy, altered to clay minerals. One large porphyroblast i s broken into several coarse grains; the contacts between them are generally s t r a i g h t , but minutely i r r e g u l a r , suture-like. Some grains show coarse Karlsbad twinning. Exsolution lamellae of a plagioclase with v i s i b l e a l b i t e twinning are present, but not common. However, almost a l l orthoclase grains show traces of extremely f i n e twinning and some p a r a l l e l l i nes which may be very fine micro-p e r t h i t i c exsolution lamellae of a l b i t e . The relations of perthite with quartz are rather complicated. For the most part, quartz occurs i n large grains, subangular, showing some s t r a i n - e f f e c t s . Many grains are broken up on contact with orthoclase, and fragments of quartz appear as rounded "islands" i n the orthoclase. But i n other parts of the section quartz veinlets cut the orthoclase, and several euhedral crystals of quartz occur i n the middle of a feldspar grain. This shows that at least a part of the quartz is l a t e r than the orthoclase. Fine-grained bands of both minerals, probably c a t a c l a s t i c , appear between larger grains. Another section was cut from a rock showing many grains of orthoclase and quartz, but no large porphyroblasts. This rock i s obviously c a t a c l a s t i c . The larger fragments are subangular, show s t r a i n - e f f e c t s and are commonly fractured, quartz more so than orthoclase. The appearance of the ortho-clase i s s i m i l a r to that described above. Quartz f i l l s some narrow fractures i n the feldspar. The fine-grained matrix i n which the grains and porphyroblasts are embedded consists of s e r i c i t e , minor b i o t i t e , very f i n e quartz and some orthoclase. A carbonate i s f a i r l y common i n the rock, p a r t i c u l a r l y i n i t s more crushed parts and near sulphide grains. Some of the euhedral quartz c r y s t a l s • mentioned e a r l i e r are moulded on sulphide c r y s t a l s . The s u l -phides, very common i n the rock, are mostly pyrrhotite with lesser p y r i t e and sparse sphalerite. It i s almost impossible to es t a b l i s h d e f i n i t e l y the o r i g i n a l nature of this rock, but some speculations on i t s mode of formation may be j u s t i f i e d . It forms a band about 5 feet wide, approximately 20 feet north of the intru s i v e con-tact i n the eastern part of the d r i f t , i n the sedimentary s e r i e s , adjacent to and p a r a l l e l to the Contact vein. There-fore i t i s probable that i t was o r i g i n a l l y a sedimentary rock. The high percentage of quartz i n i t suggests that i t was of a si l i c e o u s nature. After the int r u s i o n of the granodiorite the rock was permeated by the potassium-bearing f l u i d s emanating from the in t r u s i v e , and large orthoclase porphyroblasts were formed i n i t . The available material does not allow any p r o f i t a b l e speculations on why this rock was more favorable for the i r f o r -mation than others. The tectonic movements that produced the Contact shear (and thus l o c a l i z e d the l a t e r Contact vein) shattered the metasomatized rock and broke up the large por-phyroblasts , giving the rock i t s present c a t a c l a s t i c texture. The large i d i o b l a s t i c porphyroblast mentioned above either escaped shattering for some unknown reason, or i s l a t e r than the shearing, and shows perhaps the s i z e , i f not the shape, of the porphyroblasts before the shearing. During the formation of the Contact vein, the sheared rock was penetrated by solutions bearing s i l i c a , carbonate and sulphides. These f i l l e d some fractures i n the orthoclase with quartz and deposited the sulphides throughout the rock. The rare euhedral quartz crystals present i n the porphyroblasts seem to have formed on the surface of the sulphide grains, re-placing the orthoclase. Thus, the " c a t a c l a s i t e " i s a complex matasomatic rock hydrothermally altered. (d) A l k a l i metasomatism The writer believes that a l k a l i metasomatism was an important process contributing to the a l t e r a t i o n of the rocks along the igneous contact. The large, biotite-rimmed ortho-clase grains i n the "porphyritic" granodiorite, the i r r e g u l a r p e r t h i t i c grains i n the hornblende granodiorite and i t s de-r i v a t i v e s , and the orthoclase porphyroblasts i n the " c a t a c l a s i t e near the Contact vein are the resu l t of introduction of potassium into s o l i d rocks. The orthoclase porphyroblasts i n a l l types of rocks have many features i n common: (a) they are of a larger size than most other minerals, i n places conspicuously so. (b) they are p e r t h i t i c , containing i r r e g u l a r narrow sub-p a r a l l e l lamellae of sodic plagioclase. (c) most of them show very f i n e straight p a r a l l e l l i n e s showing some difference i n r e l i e f and birefringence. These may be almost sub-microscopic exsolution lamellae of a l b i t e . These fi n e lamellae do not cross the larger i r r e g u l a r plagioclase lamellae, disappearing for a short distance on both sides of them. (d) Some porphyroblasts contain clusters of rounded quartz grains i n o p t i c a l continuity with a larger 4-5 quartz grain outside the orthoclase. This suggests that the quartz i s replaced by feldspar, (e) most porphyroblasts i n the g r a n i t i c rock have very i r r e g u l a r "frayed' 1 boundaries, with a rapidl y i n -creasing number of inclusions towards the borders. The grains f i n a l l y "peter out" i n unaltered rock. The above features may indicate the common o r i g i n of the ortho-clase porphyroblasts. The fact that potassium metasomatism was active along the g r a n i t i c contact i s proved to the writer's s a t i s f a c t i o n by the presence of the orthoclase porphyroblasts i n the now cata-c l a s t i c "porphyry", believed to be a sedimentary rock. It i s d i f f i c u l t to v i s u a l i z e an other than metasomatic o r i g i n for these large feldspar grains and p a r t i c u l a r l y for the i d i o b l a s t i c porphyroblast l-jjs- inch long, mentioned above. However, the o r i g i n of the orthoclase grains and cry s t a l s i n the granodiorite i s less clear-cut. The p o s s i b i l i t y that the whole body of granodiorite i s of metasomatic o r i g i n may be excluded at the s t a r t . The presence of the quartz-wollastonite-garnet rock on the contact proves that the granodiorite arrived i n a hot state and there-fore probably as magma, no matter what i t s ultimate o r i g i n . The problem then i s whether the orthoclase grains i n the grano-d i o r i t e are porphyroblasts or phenocrysts. The writer believes that both types are represented, but the porphyroblasts greatly predominate. Careful examination of specimens from the coarse "porphyritic" granodiorite shows that i t contains two types of prominent orthoclase forms: one i s the subhedral pinkish type with numerous inclusions near i t s margins and commonly surrounded by a narrow ( 1 - 2 mm) zone of b i o t i t e . The other i s euhedral, with pe r f e c t l y straight sharp boundaries, fewer inclusions and no b i o t i t e rim. In thin-section, one of the o l a t t e r type crystals shows a number of small plagioclase i n -clusions i n the form of subhedral to euhedral crystals arranged i n a l i n e p a r a l l e l to the (010) cleavage of the orthoclase. The plagioclase crystals are zoned i n a simple progressive way, the composition varying from An 38 i n the inner cores to An 20 i n the outer zone. These are mantled by clear untwinned a l b i t e . A metasomatic o r i g i n of t h i s orthoclase c r y s t a l would not explain the d i s t i n c t and regular alignment of the plagioclase inclusions. The zoning of the plagioclase c r y s t a l s indicates that they were not formed simply by a l a t e r replace-ment of the orthoclase. An explanation acceptable to the writer i s that this orthoclase. c r y s t a l - along with some others having the distinguishing features described above - i s a true phenocryst. During i t s c r y s t a l l i z a t i o n from a magmatic l i q u i d i t enclosed e a r l i e r formed small crystals of plagioclase and aligned them along one of i t s main crystallographic d i r e c t i o n s . The a l b i t e rims were formed l a t e r during exsolution of the excess soda to form the fine p e r t h i t i c lamellae, or at a s t i l l l a t e r stage, together with the coarser i r r e g u l a r lamellae of a l b i t e . These were possibly formed by la t e replacement of orthoclase by sodic plagioclase. The other type of orthoclase crystals and grains shows some metasomatic features, such as the corroded remnants of partly replaced quartz grains and the b i o t i t e rim. The b i o t i t e , at f i r s t regularly distributed throughout the rock, was dissolved when the orthoclase was prec i p i t a t e d , and removed outwards. It was then re-deposited on the boundaries of the newly formed feldspar grain. It i s perhaps possible to v i s u a l -i z e a continuous process of solution and r e - p r e c i p i t a t i o n of the b i o t i t e as the orthoclase c r y s t a l grew from a nucleus, u n t i l f i n a l l y the growth stopped and the b i o t i t e , displaced from the area now occupied by the orthoclase, was fixed as a narrow " b i o t i t e front" around the feldspar grain. Although no exact measurements were made, thi s hypothesis appears plausible quantitatively. By v i s u a l estimate, the amount of b i o t i t e i n the rim i s approximately equal to that which would have been present i n the area now occupied by orthoclase, assuming uniform d i s t r i b u t i o n of the mica throughout the rock. The apparent absence of an analogous zone of quartz and plagioclase, which had to be removed together with the b i o t i t e , does not pose any problem. A narrow zone of b i o t i t e i s conspicuous and immediately noticeable; a si m i l a r zone of quartz and plagioclase, which may well be present, would be indistinguishable from the normal constituents of the rock. 48 Thus, two processes, magmatic c r y s t a l l i z a t i o n and potassium metasomatism, account for a l l the large orthoclase crystals i n the porphyritic granodiorite. The hornblende granodiorite and i t s derivatives do not contain any phenocrysts, and the large orthoclase grains replacing quartz, as seen i n some of the thin-sections of this type of rock, are considered to be metasomatic. A l k a l i metasomatism on the borders of a g r a n i t i c i n t r u s i v e , r e s u l t i n g i n the formation of feldspar porphyro-blasts i n the intrusive and i n the adjoining country rocks, i s a very common phenomenon. Turner and Verhoogen's hypothesis (T&V, 1951 > P. 289) that the potash metasomatism i s brought about by f l u i d s expelled from s t i l l - c r y s t a l l i z i n g g r a n i t i c magma i n the i n t e r i o r of the i n t r u s i o n , appears reasonable to the writer. CHAPTER IV. STRUCTURE 1. Gr a n i t i c Rocks As mentioned above, the Deer Horn property l i e s on the contact of g r a n i t i c rocks of the Coast Range ba t h o l i t h and sedimentary rocks of Jurassic or Lower Cretaceous age. The g r a n i t i c rocks have been divided into two main types, the "porphyritic" granodiorite and the hornblende granodiorite. Unfortunately, t h e i r contact i s rather distant from the mine workings and does not appear to have any d i r e c t influence on the mineralization. For t h i s reason i t was not studied i n d e t a i l during the work on the property, and the pre-cise relations of the two g r a n i t i c types are unknown. But the opinions of a company geologist who had b r i e f l y examined the area may be quoted. E.G.Langille i n his report of October 194-5 divides the intrusives into three classes: 1. Fine-grained d i o r i t i c dykes cutting both g r a n i t i c rocks and sediments; 2. Coarse fresh-appearing granites, and 3. Diorites and quartz d i o r i t e s . (These correspond respectively to the a l b i t i t e , " p o r p h y r i t i c " granodiorite and hornblende granodiorite as used i n this study.) "The l a t t e r rock is the oldest and appears to be a s i l l ; i t s dip i s only s l i g h t l y steeper than the h i l l - s i d e , i t s hanging wall has been partly removed by erosion." (Langille i s not quite c e r t a i n whether this i s a s i l l or a dyke, but he c a l l s i t a s i l l since i t conforms i n s t r i k e with the Hazelton beds.) "The 'quartz d i o r i t e ' i s intruded by the coarse ' g r a n i t e 1 , which forms the large mass south of Lindquist Lake" (across the lake from Deer Horn.) The underground work on the property completed 10 years after Langille's i n v e s t i g a t i o n shows that his quartz d i o r i t e i s not a s i l l , because i t cuts across and overlies several s i l i c e o u s and carbonaceous beds, preventing them from outcropping on the surface. However, his idea of a tabular structure for this type of int r u s i v e rock may be correct. The two rock types have probably int r u s i v e r e l a t i o n s to each other. They have been found to alternate i n deeper d r i l l - h o l e s i n sections ranging from 20 to 200 feet i n width, with f a i r l y sharp contacts. But since they have not been closely studied during the f i e l d work, t h e i r r e l a t i v e age cannot be determined. 2. Contact between Gran i t i c and Sedimentary Rocks The contact between the i n t r u s i v e rocks and the sediments i s f a i r l y sharp, except for a band about 5 - 10 feet wide which usually has a hybrid appearance. The contact st r i k e s generally East, but with l o c a l i r r e g u l a r i t i e s and f a u l t o f f s e t s . It dips i n general to the South at 50 - 55 degrees, but this attitude i s far from regular, as was established by d r i l l i n g along the contact. It has probably many l o c a l r e -versals of dip, offshoots and f a u l t offsets of various mag-nitude. For example, a v e r t i c a l diamond d r i l l - h o l e c o l l a r e d i n the in t r u s i v e penetrated 210 feet of g r a n i t i c rocks, cut through the contact and entered altered sediments. Afte r 100 feet i t again intersected granodiorite and continued i n i t for 170 feet before i t was stopped. The second i n t e r s e c t i o n here represents a thick offshoot or a bulge. A probable l a t e r a l o f f s e t was encountered i n another d r i l l hole, i l l u s t r a t i n g the i r r e g u l a r nature of the contact. 3. Sedimentary Rocks The investigation of the structure of the sediments is rather complicated by the lack of good horizon markers. The s i l i c e o u s and carbonaceous sediments encountered i n the adit are interbedded, alternate rapidly and usually have grad-a t i o n a l contacts, presenting a picture which - though complex i n small d e t a i l - i s rather monotonous i n general. Only one good horizon marker was found, which can be used for c o r r e l a t i n g the beds intersected underground with those found on the sur-face. This i s the greenish brown a r g i l l i t e mapped as "green-stone'' on surface and logged as "brown t u f f " i n d r i l l - h o l e s . This bed was reached underground by two holes which may give an i n d i c a t i o n of i t s trend but w i l l not y i e l d i t s exact a t t i -tude, because the two intersections are separated by the a l -b i t i t e dyke. The dyke marks an important f a u l t along which a movement i s believed to have occurred. The strike of the sediments on the surface varies locally from N65W to S80W, but in general it is almost due West. The dip, as determined on surface, ranges from 40° South to 70° South. Underground, the strike is again westerly, but the dip becomes predominantly 60 - 70 degrees. If the horizon marker is reasonably continuous in the 500 feet between the drift elevation and its outcrop on the surface, without any major faulting, the generalized dip of the sediments would be about 60 - 70 degrees. In some rocks, such as the chiastolite schist, bedding is obscure and schistosity becomes prominent; but most of the rocks are not highly schistose. The schis-tosity is usually parallel or subparallel to the bedding. As mentioned, the above contacts are mostly gradat-ional over distances varying from a. few inches to several feet. But one outcrop along the surface contact of the chiastolite schist and feldspathic greywacke was found to contain a narrow band (about 1 foot) of fragments of black argil l i te from a fraction of an inch to 1 inch across, embedded in a matrix of a lighter grey siltstone. A thin-section shows that some of the argil l i te fragments are "drawn out" by later shearing, but generally are angular, elongated, with sharp boundaries. The siltstone grades northward into the only slightly coarser-grained feldspathic greywacke. The rock is then clearly an interformatiorrbreccia, showing that the feldspathic greywacke overlies the andalusite schist. As both rocks dip to the South and the greywacke lies to the North of the schist, their s trat i -graphic position is apparently reversed and the beds are over-turned. Although this conclusion was reached independently, a l a t e r study of the company reports showed that the idea was not new. It was f i r s t expressed i n 194-7 by Chas. Ney, who writes: "In hole 22, many good examples of bedding indicated that the top of the succession faced downward. This evidence from d r i l l - c o r e s requires v e r i f i c a t i o n . I f correct, i t means that the whole area i s part of an overturned f o l d . " (Ney 1947) This mutually supporting evidence shows that the sedimentary rocks at the Deer Horn property are part of a southern limb of an overturned syncline, whose a x i a l plane strikes westerly and dips to the South. 4. The Veins The main ore-bearing structures on the property are two persistent quartz veins, the "Main" and the "Contact", d i f f e r i n g i n attitude, thickness, structure and to some extent i n t h e i r mineral content. There are many other minor veins and stringers on the property, but they have not been traced over any great distances. They are narrow and only sparsely di s t r i b u t e d i n the country rocks and are not considered econ-omically important. (a) The Main Vein The Main vein, from 5 to 1 5 feet thick, outcrops in t e r m i t t e n t l y for a t o t a l distance of about 2000 feet. This was the vein discovered and staked by Joubin i n 1944. A great part of i t s length i s covered by talus and t h i n s o i l , and a considerable amount of trenching was necessary to e s t a b l i s h i t s trend. From the surface exposures and underground develop-ment i t appears that the general trend of the vein near the surface i s about N60W/30 NE. A greater p r e c i s i o n i s hardly possible due to the fact that the vein i s far from s t r a i g h t ; i t shows frequent r o l l s , changes of s t r i k e , pinching and swell-ing, and i s cut by a set of northerly s t r i k i n g faults which displace i t for distances ranging from 50 to possibly 250 feet. From a consideration of the contour map i t appears that the s t r i k e of the vein changes from westerly i n the eastern part to northwesterly near i t s western end, possibly with several minor r o l l s i n between. Its dip near the surface i s about 30 to 35 degrees NE. However, diamond d r i l l i n g indicates, and the a d i t confirms, that the vein changes dip underground. It flattens as i t approaches the contact of the granodiorite and the sediments, and f i n a l l y curves upward, forming a trough-like structure which ends against the Contact vein. The northeasterly limb of this "trough", the upward extension of the vein, i s not a single continuous structure, but rather a series of i r r e g u l a r branch-ing stringers about 1 to 2 feet thick, which often carry high values. The greater part of the Main vein, excepting only this series of s t r i n g e r s , l i e s i n the granodiorite. It w i l l be shown that this stringer zone, although usually considered an i n t e g r a l part of the Main vein structure, may have a more complicated s t r u c t u r a l o r i g i n . The vein has i n d e f i n i t e , highly ir r e g u l a r boundaries, strongly bleached and p a r t l y s i l i c i f i e d walls, and contains numerous inclusions of wall-rock near i t s contacts. It i s believed to be a replacement vein. (b) The Contact Vein on Although the Contact vein does not outcrop vthe sur-face, i t s attitude i s better known, because i t was followed by the adit. In the eastern part of the a d i t i t strikes N 87 W with minor l o c a l v a r i a t i o n s , and dips 60 to 73 degrees South. After crossing the a l b i t i t e dyke, i t s general s t r i k e changes to S 81 W and the dip varies between 60 and 65 degrees. The Contact vein i s much narrower than the Main vein, being usually 6 to 12 inches wide i n the d r i f t . In some places, such as the No. 2. Raise, i t narrows s t i l l more, forms 2" to 3" lenses, and for short distances disappears altogether, leaving only a strong shear. For a greater part of i t s known length the vein i s well-defined, has sharp sheared walls and ribbon structure; the m e t a l l i c minerals are commonly deposited on shear planes i n the quartz. Near the western end of the adit the vein s p l i t s i n two and f i n a l l y i n several minor stringers which fuse to-gether, forming a quartz lens about 3 feet thick and 25 feet long, with i n d e f i n i t e boundaries and almost barren* This lens narrows again towards the West and f i n a l l y disappears i n the w a l l , 200 feet from the end of the d r i f t . The shear probably continues beyond that point; a d r i l l - h o l e near the west end of the d r i f t intersected a quartz stringer 3 inches thick 9 feet to the North of the d r i f t . (c) The Junction of the Veins The junction of the veins i s marked by a zone of quartz s t r i n g e r s , that plunges about 14 degrees easterly. This r e l a t i o n was observed underground, where the zone was intersected i n the adit and also i n a r a i s e 320 feet west of the f i r s t i n t e r s e c t i o n and 75 feet above the d r i f t elevation. Both zones of stringers are so s i m i l a r i n their shape, a t t i -tude, thickness, mineralization and wallrocks that i t i s most l i k e l y that they are connected. The observed attitude of the stringer Zone corresponds almost exactly to the d i r e c t i o n of i n t e r s e c t i o n obtained by p l o t t i n g the two veins on a stereonet, assuming N 60 W/25 NE for the Main vein and N 8? W/70 S for the Contact vein. However, i f , as was commonly assumed, the southerly dipping stringers are simply a continuation of the Main vein with a reversed dip, t h e i r junction with the Contact vein would necessarily have to plunge i n the opposite d i r e c t i o n . (Taking the stringers as N 60 W/30 8W, the Contact vein as N 87 W/70 S, the plunge of t h e i r i n t e r s e c t i o n i s 18 degrees i n the d i r e c t i o n S 83 W.) The westerly plunge has not been observed. Besides, some of the s t r i n g e r s , formerly considered to be the "frayed" s p l i t northeastern limb of the Main vein trough, are now shown to l i e i n the footwall of the vein, s t r u c t u r a l l y below the trough, so that a new i n t e r p r e t a t i o n of t h e i r s i g n i f i c a n c e i s necessary. (See Figure 4). (d) The Origin of the Veins The hornblende granodiorite, host rock of the Main vein, i s strongly sheared. This i s p a r t i c u l a r l y conspicuous on the hanging wall of the vein, where the rock has acquired a prominent gneissic structure. This structure becomes less d i s t i n c t with increasing distance from the vein. The f o l i a t i o n i s generally p a r a l l e l to the attitude of the vein, following f a i r l y c l o s e l y i t s i r r e g u l a r i t i e s . This suggests that the vein originated i n a shear zone. The low angle of dip of the Main vein suggests that the shear was probably a thrust f a u l t . Such a f a u l t may also explain the change of dip with depth, a fact established by d r i l l i n g . The dip flattens and f i n a l l y reverses as the vein, and the o r i g i n a l f a u l t containing i t , approaches the contact of the granodiorite and s i l i c e o u s sediments. It i s probable that the competency of the g r a n i t i c border zone and the s i l i c -eous sediments was d i f f e r e n t from that of the main mass of the granodiorite. I f the border zone i s considered more b r i t t l e , as seems l i k e l y , the shearing angle i n i t would decrease and the dip of the f a u l t would thus become f l a t t e r . Fractures p a r a l l e l to the complementary shearing plane, dipping f l a t l y i n the opposite d i r e c t i o n , would develop at the same time; this may possibly be the way i n which the f a u l t terminates. The curved trough-like shape of the Main vein may therefore be due to a combination of the o r i g i n a l t h r u s t - f a u l t , f l a t t e n i n g i n the more b r i t t l e border zone of the i n t r u s i v e , and i t s complementary shear-planes. The Contact vein also marks the plane of a strong f a u l t . A movement along this f a u l t continued even afte r the formation of the vein, as i s evident from the sheared nature of the walls and the ribbon structure. This shear had developed approximately p a r a l l e l to the dip of the bedding of the s e d i -ments near the contact. Since the dip of the sediments and of the contact with the int r u s i v e diverge with depth, the shear should increase i t s distance from the i n t r u s i v e i n the down-dip d i r e c t i o n . Up-dip, the shear must approach the contact, intersect i t and pass into the overlying granodiorite. This was found to be true. The sheared bleached granodiorite near the contact, which contains numerous quartz veinlets and was mapped as " a p l i t e " on the surface, i s considered to mark the upward extension of the Contact f a u l t . The steep dip of the f a u l t suggests that i t was a gravity f a u l t . A supporting evidence may be found i n the f l a t southerly dip of the quartz stringers i n the contact zone, some of which cross the Main vein and appear i n the footwall of the Main vein i n the d r i f t . These stringers are considered to mark the d i r e c t i o n of the fracture cleavage related to the Contact shear. I f this theory i s correct, t h e i r attitude i n -dicates that the f a u l t responsible for th e i r formation was a gravity f a u l t . A thrust f a u l t i s u n l i k e l y for two reasons: the steep dip, and the absence of northerly dipping fracture cleavage which would be the necessary r e s u l t of a reverse type of movement. Accepting the p o s s i b i l i t y that some of the southerly-dipping high-grade quartz stringers i n the contact zone occupy cleavage fractures of the Contact f a u l t , i t remains to be explained why, i f the junction of each i n d i v i d u a l cleavage plane (with the given attitude) with the Contact vein must plunge westerly, the whole zone of stringers plunges easterly. It i s conceivable that the cleavage fractures de-veloped mostly along the i n t e r s e c t i o n of the two f a u l t s i n the previously sheared and possibly p a r t l y s i l i c i f i e d b e l t . Recalling that the quartz stringers were formed by replacement, i t i s possible that the zone along the i n t e r s e c t i o n of the two fault s was sheared twice, once i n connection with the f l a t reverse f a u l t of the Main v e i n , for the second time i n conn-ection with the Contact f a u l t . This rendered i t much more permeable for the l a t e r s i l i c a - b e a r i n g solutions, which deposit-ed their load i n the numerous int e r s e c t i n g fractures, p a r t l y replacing the wall-rock and thus forming the i n t r i c a t e network of quartz strin g e r s . The veinlets terminate gradually a short distance from the i n t e r s e c t i o n , as they pass from the highly sheared contact zone into the less affected granodiorite. The easternmost d e f i n i t e i n t e r s e c t i o n of the Contact vein was found i n a d r i l l - h o l e d r i l l e d almost due north of the entrance to the a d i t . A surface d r i l l - h o l e 2000 feet east of the adit intersected the contact of the i n t r u s i v e and 4-0 feet of altered sediments ending i n the brown a r g i l l i t e , but did not f i n d the Contact vein. However, a short section of the quartz-wollastonite skarn near the contact carries dissemin-ated p y r i t e , and gave some gold and s i l v e r values on assay. It i s possible therefore that the contact vein pinches out somewhere between the adit and this d r i l l - h o l e , but the miner-a l i z i n g solutions diffused through the crushed rock for some distance beyond the termination of the actual vein. A s i m i l a r s i t u a t i o n was observed i n the western part of the property, where small grains of galena were found i n an epidote-garnet skarn, i n the scheelite s l i d e , not connected with any d e f i n i t e vein. The distance between the scheelite s l i d e and the d r i l l - h o l e which f a i l e d to f i n d a vein i n the contact zone i s about 4000 feet. The ground to the west of the scheelite s l i d e (which covers a strong northerly-trending shear zone) has never been tested by d r i l l i n g , so that no information on a possible extension of the Contact vein or Contact f a u l t to the West i s available. But the s p l i t t i n g of the vein and the d i f f u s e nature of i t s western part i n the d r i f t , where i t gets farther from the g r a n i t i c contact, may indicate that this vein pinches out somewhere i n the v i c i n i t y of the scheelite s l i d e s . It i s of course e n t i r e l y possible that another f a u l t , with or without a vein, takes over and continues i n the same d i r e c t i o n . The available information i s not s u f f i c i e n t for any speculations on the t o t a l extent and manner of termination of the reverse f a u l t containing the Main vein. (e) Summary In the writer's opinion, the two veins occupy two prominent f a u l t s . A f l a t reverse f a u l t i n the granodiorite was formed f i r s t , f l a t t e n i n g i n the more b r i t t l e border zone of the i n t r u s i v e and petering out i n a series of complementary shears. This was followed by a steep tight normal f a u l t passing from the intru s i v e through the contact zone into the sediments. The two faults converge towards the West. The zone of t h e i r i n t e r s e c t i o n was very highly sheared. Both were l a t e r invaded by s i l i c a - b e a r i n g solutions which formed the two quartz veins, replacing the wallrock i n the now s t a t i c reverse f a u l t and near the western end of the normal f a u l t , where the move-ment was at a minimum, but penetrating only s l i g h t l y into the central parts of the normal f a u l t where the movement continued during and after mineralization. Many i r r e g u l a r quartz s t r i n g -ers, well mineralized, were formed i n the badly sheared and thus highly permeable zone of i n t e r s e c t i o n of the two f a u l t s . The south-dipping veins found i n the footwall of the Main vein are either q u a r t z - f i l l e d complementary shear fractures related to the reverse f a u l t , or cleavage fractures of the normal f a u l t . The Contact f a u l t pinches out on both ends within a distance of about 4000 feet. Downdip, i t may pinch out as i t s distance from the f l a t t e r dipping i n t r u s i v e contact increases. This would be analogous to i t s approaching termination near the western end of the d r i f t . A l t e r n a t i v e l y i t may pass into underlying i n t r u s i v e such as was mentioned i n paragraph two of this chapter, and become merely an unmineralized shear s i m i l a r to that i n the bleached crushed granodiorite on the surface. In either case there i s no reason to expect that i t w i l l con-tinue for a long distance downwards. The high-grade st r i n g e r zone i s apparently limited to the in t e r s e c t i o n of the two veins, one of which i s known to terminate i n one d i r e c t i o n while the other i s neither known nor expected to continue beyond the end of the f i r s t . Therefore, i t i s reasonable to assume that this zone w i l l be limited both h o r i z o n t a l l y and v e r t i c a l l y . It should be emphasized that the above speculations are only hypotheses based on limited evidence. They agree with given data, correlate many of them and are not contradicted by any known fa c t . To prove these hypotheses i t would be necessary to re-examine the available core, to unify the nomenclature of the rocks found i n d i f f e r e n t d r i l l - l o g s , to r e - c l a s s i f y a l l quartz intersections into the four p r i n c i p a l categories (Main vein, Intersection zone, Contact vein and Other fractures) to plot the d r i l l - h o l e s on this basis and thus to determine the actual p o s i t i o n and extent of the ore-bearing structures. 5. Post-mineral Faults Post-mineral f a u l t i n g i s widespread on the property. Only major faults showing s i g n i f i c a n t displacements have been mapped on the surface. Faults of lesser importance, though probably common, are usually d i f f i c u l t to recognize due to the talus and s o i l cover. The underground workings show much better both the great number of f a u l t s and the r e l a t i v e i n s i g n i f i c -ance of most of them. The surface f a u l t s were mapped by F.R.Joubin, mainly i n a belt along the int r u s i v e contact which contains the Main vein. Most of the faul t s i n the western and central part of the property s t r i k e northwesterly and northerly. Northeasterly s t r i k e i s more common i n the eastern part though not without exceptions. Almost a l l the faults dip westerly, i n the order of 50 to 60 degrees. But i n the absence of a more detailed map and a good c o r r e l a t i o n of the f a u l t system with a topo-graphic map, s t r u c t u r a l deductions from the f a u l t pattern do not appear j u s t i f i e d . In the a d i t , numerous faults cut the Contact v e i n and most of them displace i t , but generally only for a short distance. A great majority of the displacements are i n the order of a few inches to one foot, the maximum displacement of the Contact vein being 5 feet. One major exception i s the probable f a u l t marked by the a l b i t i t e dyke, which w i l l be considered l a t e r . The f a u l t s usually s t r i k e between N30W and N30E, but on the hanging-wall of the a l b i t i t e dyke faults s t r i k i n g N30E to N45E are common. The dips are usually steep, the majority i n the 60 to 90 degree range and i n the westerly d i r e c t i o n . (See Figure 5 ) . The adit traverses only a small part of the property and i s affected only by three of the major fault s mapped on the surface. One i s a northerly s t r i k i n g f a u l t dipping 50W and displacing the Main vein i n the hanging-wall block 4-0 feet to the North r e l a t i v e to the footwall. Two closely-spaced faul t s of similar attitude were found underground i n the area indicated by projecting the surface f a u l t to the elevation of the adit; they displace the Contact vein 1 foot to the South and 2 feet to the North respectively. Assuming that one of them i s the continuation of the surface f a u l t , the r e l a t i v e movement can be reconstructed. Both f a u l t s indicate a move-ment i n the same d i r e c t i o n and of the same order of magnitude, about 15 to 20 feet, the hanging-wall block moving up and to the North r e l a t i v e to the footwall block. The proportion of the s t r i k e - s l i p to the d i p - s l i p component i s about 2 :3 . Although this i s not to be regarded as an exact determination, i t may give a f a i r i n d i c a t i o n of the order of magnitude of the movement on those faults a f f e c t i n g both veins i n the adit area. Obviously, i t w i l l not hold true for the fau l t s with markedly greater displacement i n the eastern part of the property. As mentioned before, the Contact vein under-ground i s cut by numerous faults displacing i t for a short distance. It is suggested that very few of them reach the Main vein; most of them are only l o c a l fractures and the move-ment on them is much smaller than that on the major f a u l t s . A second type of f a u l t i n g was also indicated by the underground workings. A prominent f a u l t was mapped on the sur-face i n the area of the scheelite s l i d e s , s t r i k i n g N20W, with an undetermined dip. I t i s marked by a low gully and was be-lieved to have a considerable displacement. But when the adit approached the area below the surface trace of the f a u l t , i t intersected instead an 80 foot zone of cl o s e l y spaced minor f a u l t s , displacing the Contact vein from 3" to 12" i n a step-l i k e horst-and-graben fashion, without changing i t s general trend. The d r i f t did not even have to deviate from a straight l i n e . If this fault-zone correlates with the f a u l t mapped on the surface, as i s almost c e r t a i n l y the case, the zone st r i k e s N17W and dips 84 degrees easterly. The t h i r d of the major fractures reaching from the surface to the adit elevation i s a northerly trending f a u l t containing the a l b i t i t e dyke. This fracture interrupts the regular trend of the Contact vein and displaces i t about 40 to 50 feet to the South on the hanging-wall of the dyke r e l a t i v e to the footwall. The dyke, which can be well correlated with i t s surface exposure, s t r i k e s N26W and dips 70 SW. It i s about 20 feet thick on the surface and 12 feet in the adit. Its foot-wall is straight and cuts sharply across the Contact vein, on its hanging-wall i t shows a few short apophyses and a sharp contact with the wall rocks. The wall-rocks are the usual assemblage of thin-bedded impure feldspathic quartzite and black argi l l i te found in the drift . But while the rocks on the footwall of the dyke are fairly free from fractures, the hanging-wall rocks show a great number of faults and joints. These are concentrated in a zone which is 80 feet wide in the drift , and strike predominantly easterly and northeasterly. Some of the fractures contain one-inch wide bands of gouge and some vugs with calcite and small crystals of laumontite, var. leonhardite (calcium zeolite). Most show no apparent displace ment; this of course may be difficult to determine in the monotonous assemblage of sediments present in that part of the drift . The Contact vein was encountered again 70 feet west and 27 feet south of the point where it was cut off by the dyke. It appears first in the south wall as a narrow mineral-ized quartz stringer striking N 75 W, but within 15 feet i t widens to 4 inches and changes its strike to S 81 W, which it maintains with only slight variations for the next 700 feet. This is a definite change from the strike to the east of the dyke, which is N 87 W. The position of the vein between the dyke and its re-appearance in the adit is not known; a hole was drilled to the South close to the hanging-wall of the dyke but had to be stopped due to a heavy flow of water before i t reached the c r i t i c a l section. But the curving of the vei n and of some more d i s t i n c t beds of sediments suggests a drag on a f a u l t . The fracture containing the dyke marks also an im-portant change i n the attitude of the in t r u s i v e contact, from almost westerly on the footwall of the dyke to S75W on the hanging wall. The l a t t e r attitude i s maintained for 800 feet to the end of the explored section. Whereas to the east of the dyke the contact i s never more than 20 - 30 feet distant from the Contact vein, i t increases i t s distance from about 40 feet on the hanging wall of the dyke to 130 feet near the end of the d r i f t 780 feet to the west. Thus both the Contact vein and the igneous contact change s t r i k e on crossing the dyke, rotating 12 and 15 degrees respectively, counter-clockwise. Unfortunately the available data are not s u f f i c i e n t to solve the movement on the f a u l t . But several suggestions can be made. (a) Since the Contact vein and the igneous contact d i -verge with depth, their increasing distance west of the dyke may mean that the western block has moved up, r e l a t i v e to the eastern block. (b) Some r o t a t i o n a l movement has to be postulated to account for the change of s t r i k e and the suspected drag of the vein. (c) Since the walls of the dyke are not sheared, the dyke was emplaced after the movement on the f a u l t had ceased. With the exception of the "dyke" f a u l t , the post-mineral f a u l t i n g on the property i s only of small importance i n the s t r u c t u r a l s e t t i n g . The major fa u l t s displacing the Main vein would present some mining d i f f i c u l t i e s , but t h i s problem i s not l i k e l y to ari s e for a considerable time. CHAPTER V MINERALOGY OF THE VEINS 1. Previous Work The ore minerals of the Deer Horn property were studied previously at the University of B r i t i s h Columbia by J.W. Young (1946) and i n more d e t a i l by A.C. T a p l i n (1950) . Both worked on selected specimens from the surface exposures of the Main vein, but the exact locations of t h e i r specimens are not known. In addition, the writer b r i e f l y examined ad d i t i o n a l sections from the Contact vein, obtained underground. 2. The Main Vein The minerals i d e n t i f i e d by T a p l i n i n the Main vein are: p y r i t e , arsenopyrite, chalcopyrite, s p h a l e r i t e , galena, c o s a l i t e (Pb2Bi2S5), Tetradymite (Bi2Te 2S ), tellurbismuth (Bi2Te3), a l t a i t e (PbTe), hessite (Ag2Te) and gold. Argentite was i d e n t i f i e d t e n t a t i v e l y . To this excellent l i s t the writer can only add s c h e e l i t e , pyrrhotite and magnetite. The l a t t e r mineral i s common i n parts of the Main vein but almost absent i n the Contact vein. On the other hand, pyrrhotite i s more common or perhaps more conspicuous, i n the Contact vein. Scheelite was seen i n small amounts underground and w i l l be considered l a t e r , i n connection with the "scheelite s l i d e s " . 70 According to Ta p l i n , pyrite was the e a r l i e s t s u l -phide deposited, perhaps simultaneously with arsenopyrite. Both are fractured, pyrite more than arsenopyrite, and chalco-pyrite f i l l s some of the fractures. Both sphalerite and chalco-pyrite are l a t e r than the iron minerals, and probably simul-taneous. Minute exsolution globules of chalcopyrite i n sphaler-i t e were noticed. Cosalite and tetradymite are considered by Taplin to be the next minerals i n the paragenetic sequence. Cosalite was l a t e r p a r t l y replaced by galena. Tetradymite i s believed to be e a r l i e r than the lead sulphide, because i t had some d i r e c t i o n a l influence on the replacement of c o s a l i t e by galena and because i t contains sparse crenulated v e i n l e t s of galena. But as i t also contains, i n other places, i s o l a t e d remnants of galena and hessite, i t may be i n part l a t e r . The "remnants" of hessite i n tetradymite would indicate that the s i l v e r mineral i s e a r l i e r than the tetradymite, though i t s relations to the sulphides are not known. The early t e l l u r i d e s were followed by tellurbismuth and a l t a i t e . Native gold, a rare constituent of the ore, was the l a s t mineral deposited. Pyrrhotite, found by the writer i n the Main vein material, f i l l s fractures i n magnetite and i s thus the l a t e r of the two; i t i s p a r t l y replaced by chalcopyrite, which shows that i t i s e a r l i e r than the copper mineral. No good paragenetic c r i t e r i o n for the age of the magnetite was found i n the sect-ions studied by the wr i t e r , but on l o g i c a l grounds magnetite i s considered to be one of the e a r l i e s t minerals, i f not the e a r l i e s t . 71 Native gold, as determined by Taplin, occurs i n hessite, tetradymite, tellurbismuth and galena. Taplin be-lieves that much of the gold value comes from gold present i n the chemical composition of the hessite. However, the highest gold content, reported i n analyses of hessite, does not exceed 5% (4.73%, reported i n Dana, p. 185, 1944; 2.29%, reported by Thompson, 1949} p. 356) . Considering the low percentage of hessite i n the ore, i t i s doubtful whether this a d d i t i o n a l source of gold values i s s i g n i f i c a n t . The writer i s i n c l i n e d to believe that native gold, very f i n e l y disseminated and per-haps commonly associated with hessite, is responsible for the gold assays. The higher values, e r r a t i c a l l y d i stributed i n parts of the quartz stringers i n the i n t e r s e c t i o n zone, could then be l o g i c a l l y explained by the presence of somewhat coarser, though s t i l l microscopic, grains of gold. 3. The Contact Vein As the specimens from the Contact vein which does not outcrop were not available to Tapli n , seven sections cut from this vein were examined by the writer. The minerals found i n the vein are pyrrhotite, p y r i t e , s p h a l e r i t e , chalcopyrite, galena, a l t a i t e and hessite. Mag-n e t i t e , arsenopyrite, bismuth t e l l u r i d e s , c o s a l i t e and gold, present i n Taplin's sections, were not seen i n the material from the Contact vein. The writer does not wish to draw any far-reaching conclusions from this difference i n mineralogy. While T a p l i n worked with specimens selected for t h e i r content of megascopic t e l l u r i d e s , the writer's specimens were intended to represent an average sample of the vein material, and a discrepancy due to d i f f e r e n t methods of c o l l e c t i n g i s e n t i r e l y possible. But a few facts may perhaps be s i g n i f i c a n t . Magnetite, which is common i n the Main vein, i s rare i n the Contact vein. This difference, together with the pre-dominance of pyrrhotite i n the Contact vein, i s so conspicuous that i t was used as a c r i t e r i o n for distinguishing material from the two veins i n d r i l l - c o r e s . I f magnetite was the f i r s t mineral deposited, as i s commonly the case, then i t s absence i n the Contact vein may mean that the deposition of minerals there began l a t e r than i n the Main vein. An a l t e r n a t i v e poss-i b i l i t y i s that more sulphur was available i n the sedimentary environment of the Contact vein. The absence of c o s a l i t e , tetradymite and tellurbismuth a l l bismuth minerals - from the Contact vein sections may also be s i g n i f i c a n t . Although the bismuth t e l l u r i d e s are abundant and conspicuous i n the sections from the Main vein, no mega-scopic bismuth t e l l u r i d e s were found i n the Contact vein by the writer, nor by other geologists who have seen the under-ground workings. S.L.Learning, the writer's predecessor at Deer Horn, wrote i n one of his reports, describing the mineralogy of the eastern part of the a d i t : "Tellurides are undoubtedly present, as they have been noted i n the surface showings of the Main vein. However, none have been seen i n quantity large enough for positive i d e n t i f i c a t i o n . Hessite and tetradymite have been reported by others." It may, of course, be argued that bismuth t e l l u r i d e s have simply been missed underground and that they are not present i n the polished sections studied by the writer while occurring elsewhere i n the Contact vein. But i f they do occur there, the writer believes that they are present i n much smaller quantities than those shown i n Taplin*s work on the Main vein. S i m i l a r l y , c o s a l i t e was not found i n the Contact vein, either underground or i n the writer's polished sections. I f the three bismuth minerals are t r u l y absent from the Contact vein, this may be due to some unknown chemical factor which prevented the p r e c i p i t a t i o n of bismuth compounds while per-mitting the deposition of others, formed simultaneously with the bismuth minerals elsewhere. The amount of a l t a i t e i s small, but the mineral i s commonly present i n the galena, as rounded grains from 5 to 40 microns across, and as straight laths about 5 - 1 0 microns wide and up to 70 microns long. Although no regular arrangement was noticed (the grains are too widely separated to show any con-spicuous alignment), the l a t h - l i k e and rounded shapes suggest the p o s s i b i l i t y of exsolution. Hessite i s very rare i n the sections from the Contact vein seen by the writer. It i s nearly always associated with some of the larger grains of a l t a i t e , as ir r e g u l a r and l a t h -l i k e forms. The usual arrangement shows a rounded grain of a l t a i t e surrounded by galena and cut by a less regular and somewhat elongated grain of hessite, or containing a l a t h of hessite on or near i t s boundary. The hessite does not extend into the galena, and there i s a strong p o s s i b i l i t y that i t was here exsolved from the galena, either d i r e c t l y and simultan-eously with a l t a i t e , or i n d i r e c t l y , from previously exsolved a l t a i t e . In any case, the amount of hessite i n the ore i s very small, but may be s u f f i c i e n t to account for the usual low s i l v e r assays i n this type of ore. A detailed mineralographic study of a great number of representative specimens from both veins would be necessary to determine whether the differences i n mineralogy between the two veins are r e a l or apparent, and what i s their cause. 4. Origin of the Vein Minerals As both veins occur i n or near a large body of in t r u s i v e g r a n i t i c rock, i t i s perhaps unnecessary to look be-yond the i n t r u s i v e i t s e l f for a source of the mineralizing f l u i d s . The veins were probably formed by hydrothermal s o l -utions expelled from a c r y s t a l l i z i n g body of granodiorite. However, i t has been shown above that the Main vein was formed by replacement i n a shear zone i n the hornblende granodiorite, which means that this part of the i n t r u s i v e must have been s o l i d before the a r r i v a l of the s i l i c a - b e a r i n g f l u i d s . Recalling that the two main g r a n i t i c types - horn-75 blende granodiorite and "porphyritic" granodiorite - show mutual int r u s i v e r e l a t i o n s , i t may be suggested that the mineralizing f l u i d s came from the porphyritic granodiorite, which had been intruded into the already s o l i d hornblende granodiorite. Although no dire c t evidence of the l a t e r age of the "porp h y r i t i c " rock i s available, the above explanation appears more l o g i c a l than an appeal to the "hot i n t e r i o r " of the i n t r u s i v e , which would be necessary i f i t is postulated that the hornblende granodiorite, containing the Main vein, was the l a t e r of the two g r a n i t i c types. V A N D E V E E R P A R A G E N E T I C D I A G R A M S CHAPTER VI. TUNGSTEN MINERALIZATION 1. Introduction Scheelite was the mineral that f i r s t attracted a t t -ention to the property and led to i t s staking i n 194-3. The mineral occurs i n both major veins and i n the bands of c a l c -s i l i c a t e s interbedded with the sediments. The two prominent "scheelite s l i d e s " belong to the second category. The Deer Horn scheelite i s pure white to honey yellow i n color; the yellow type i s most common i n the Contact vein, the white type i n the skarn. However, both types fluoresce i n the same b l u i s h white color, without a trace of the yellowish fluorescence c h a r a c t e r i s t i c for the molybdenum-rich members of the scheelite-powellite s e r i e s , so that the molybdenum content of the scheelite i s c e r t a i n l y very low. 2. Scheelite i n the Veins Scheelite occurs sparsely i n both veins, though i t was not found i n the quartz outcrops on the surface. It was seen i n the Main vein i n the adit as small grains aligned i n zones roughly p a r a l l e l to the dip. It can be recognized only with the aid of an u l t r a v i o l e t lamp and i t s quantity here i s n e g l i g i b l e . It i s s l i g h t l y more abundant i n the Contact vein. In i t s eastern part, the Contact vein contains only sparse and widely scattered grains of scheelite from about mm to 3 mm i n s i z e . The quantity of scheelite increases somewhat towards the western end of the ad i t , but even the best sections were not considered to be commercial. Here i t usually occurs i n narrow streaks concentrated i n those parts of the vein that are comparatively free of me t a l l i c sulphides. As the scheelite i s thus almost iso l a t e d from the other minerals i n the vein, i t s p o s i t i o n i n the paragenetic sequence i s not known. 3. Scheelite i n Skarn Scheelite was observed i n the fine-grained garnet-epidote rock, here described as "skarn", both on the surface and underground. On the surface i t appears concentrated mainly i n the area of the two "scheelite s l i d e s " i n the west-ern part of the property, but sparse scheelite was found i n specimens collected by the writer 1000 feet east of the a d i t , over 2500 feet east of the s l i d e s . It occurs as small grains and narrow ( 1 - 2 mm) stringers located mostly i n quartz v e i n -l e t s and on fractures. The occurrence of scheelite so far east of the previously known surface l o c a l i t i e s may mean that the tungsten mineral i s sparsely, and probably e r r a t i c a l l y , d i s t r i b u t e d throughout the skarn bands, p a r t i c u l a r l y where they are fractured and intersected by quartz s t r i n g e r s . But as the bands themselves are quite narrow (from a few inches to about 2 feet) 78 and widely separated, this new f a c t probably has no great economic s i g n i f i c a n c e . 4. The "scheelite s l i d e s " The r e l a t i v e l y most conspicuous occurrence of scheelite on the surface - and the one that led to the staking of the property - is i n two separate areas of talus i n the western part of the claim-group. The two talus zones are referred to as the "Eastern" and the "Western" scheelite s l i d e s . Both consist of fragments of brown a r g i l l i t e and epidote-garnet skarn from •*j>-" to about 3" across, covering the steep mountain-side to a depth of about 1 foot. The Western s l i d e has an average width of 180 feet and i s 1600 feet long, extending from the top of the ridge at 5740 feet down to 4700 feet„elevation. Buried i n the talus are several small outcrops of brown a r g i l l i t e with narrow quartz s t r i n g e r s , l o c a l l y carrying sch e e l i t e . Small scheelite grains are f a i r l y common i n the talus fragments, p a r t i c u l a r l y those derived from bands of lime s i l i c a t e s , but most fragments are barren. The Eastern s l i d e is of lower grade and considerably smaller, extending for about 500 feet downslope from a large outcrop of brown a r g i l l i t e with several narrow skarn zones and a few quartz stringers up to 4" wide. Both slides are separated by 300 - 400 feet of barren black, s c h i s t . The area of the scheelite s l i d e s l i e s astride a major f a u l t found by detailed surface mapping and by d r i l l i n g . As the tungsten mineralization appears r e s t r i c t e d to quartz ve i n l e t s and fractures, the writer believes that the scheelite was introduced into the rocks by the s i l i c a - b e a r i n g solutions that have elsewhere formed the two major veins. The solutions penetrated along fractures produced by pre-mineral f a u l t i n g . The c a l c - s i l i c a t e rocks were perhaps more favorable to the v deposition of scheelite than the aluminous a r g i l l i t e , and l o c a l i z e d most of the tungsten. Later tectonic movements strongly fractured the rocks and enabled the scheelite bearing fragments to accumulate under the influence of gravity i n the present "scheelite s l i d e s . " The greater concentration of scheelite i n this area may then be the result of (a) pre-existing fracture zone which increased the permeability of the rocks to the mineral-i z i n g solutions, and (b) post-mineral f a u l t i n g and crushing which i s responsible for the formation of the conspicuous talus zones. 80 BIBLIOGRAPHY Bowen, N.L., Progressive metamorphism of s i l i c e o u s limestone and dolomite. Jour. Geol., V o l . 48 , No. 3 j 194-0. Bacon, W.R., Harrison Gold (Deer Horn Mines Ltd.) Minister of Mines, B.C., Ann. Rept. 1955 9 p. 25. D u f f e l l , S., Whitesail Map Area, B r i t i s h Columbia, G.S.C. Paper 52 -21 , 1952. Holland, S.S., Harrison Gold, Whitesail Lake. Minister of Mines, B.C., Ann. Rept. 1944, p. 176. Harrison Gold, Whitesail Lake, Minister of Mines, B.C. Ann. Rept. 1945, p. 71 . L a n g i l l e , E.G., Harrison Gold Property, Unpublished report, Pioneer Gold Mines. Learning, S.L. Underground geology, 4260 ad i t , Deer Horn Mines Ltd., Unpublished Report, May 1955. Leedal, G.P. , The Cluanie igneous i n t r u s i o n , Inverness and Ross. Quart. Jour. Geol. Soc. London, Dec. 1952, pp. 33-63 . Mason, B., "Principles of Geochemistry". Wiley, 1952. Ney, C , Geological observations, Harrison Gold Property, Unpublished report, Jan. 1947. Palache-Berman-Frondel, "Dana's System of Mineralogy", V o l . 1 . , 7 th ed., Wiley, 1944. Papezik, V.S. Summary Report on the Deer Horn Mine, Un-published Report, November 1955. Pettijohn, F.J., C l a s s i f i c a t i o n " o f sandstones. Jour. Geol., V o l . 62 , 1954, No. 4 , pp. 360-365. Robertson, F.,~and Vandeveer, P.L., A new diagrammatic scheme for paragenetic relations of the ore minerals. Econ. Geol. Vol. 47 , No. 1 . , pp. 101-105. T a p l i n , A.C., Mineralogy of the Harrison Group, Lindquist Lake, B.C. Unpublished report, U.B.C., 1950. Thompson, R.M., The t e l l u r i d e minerals and the i r occurrence i n Canada. Am. Min., Vol. 3 4 . , 1949, pp. 342-382. Turner, F.J., and Verhoogen, J . , "Igneous and Metamorphic Petrology". McGraw-Hill, 1951. P l a t e 2. View from the a d i t towards the East. 3. Coarse porphyritic granodiorite. Plate 4. C h i a s t o l i t e s c h i s t . Plate 5 . Orthoclase porphyroblast i n perthite-quartz c a t a c l a s i t e . Plate 6. Orthoclase porphyroblast i n porphyritic granodiorite. Note the b i o t i t e rim. Plate 7 . Contact vein, low grade. Ribbon texture. Plate 8. Contact vein, high grade. 85-, Plate 9. Contact vein, x 204. He hessite, A l a l t a i t e , Ga galena, Py pyrrhotite. Plate 10. Main vein, x 65. He hessite, Te tellurbismuth, Al a l t a i t e . 

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