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Petrological study of the dyke rocks of the Whitewater Creek and Lyle Creek area, Slocan district, British.. 1940

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L er? by % / W o r\ ~L- P$ PETROLOGICAL STUDY OF THE DYKE ROCKS OF THE WHITEWATER CREEK AND LYLE CREEK AREA. SLOCAN DISTRICT B r i t i s h Columbia A THESIS SUBMITTED AS PARTIAL REQUIREMENT FOE • THE DEGREE OF MASTER OF APPLIED SCIENCE. rby Roy J . -Maconachie A P R I L 1940 A C K N O W L E D G M E N T S' The w r i t e r wishes to acknowledge s i n - cerely the help givenhim i n the preparation of t h i s C thesis by C. 0. Swanson and H^V. Gunning. CONTENTS P A R T I Page. Location and Access of the Area 1 Topography 1 Climate 3 Timber.... 3 Water Supply... • 4 General Geology 4 Greenstone (includes original flows, pyroclasts and sediments) • • 5 Serpent ine. 6 Dioritic Intrusives 7 Feldspar Porphyry Dykes 9 Veins 9 Relative Ages of Veins and Feldspar Porphyry Dykes........ 12 St ruct ure 13 Alteration 15 Highland Surprise Property: General Geology... 16 Gold Quartz Property. 18 P A R T II Introduction.... 20 Petrography of Thin Sections: Section 13 20 Section 14 22 Section 31 23 Section 35 24 Section 48 25 Section 53 , 26 Section 57.... , 27 Section 60 28 Section 101 28 Section 9A 29 Section 4 30 Section 10.... 31 Section 24...... 32 Discussion: Variations in dykes 33 Wall Hock Alteration 35 Late Magmatic Effects....... 36 CONTENTS' (continued) Page. Summary 37 Conclusions 38 i I N T R O D U C T I O N Treatment of t h i s subject has been divided into two parts. Part I includes d e t a i l regarding the area under consideration with especial reference to general geo- l o g i c a l conditions. Part II includes the p a r t i c u l a r f i n d - ings of pet r o l o g i c a l study of the dyke rocks exposed i n the area. P A R T I Location and Access of the Area. The Lyle Greek—Whitewater Creek area i s situated 2-|- to 3 miles s l i g h t l y eastward of north from the town of Retal- lack, s t a t i o n on the Kaslo-Sandon and Nakusp branch l i n e of the Canadian P a c i f i c Railroad and on the Kaslo-New Denver highway, 18 miles from Kaslo and 13 miles from New Denver. Access to Lyle Creek Basin i s by 3 miles of road from Retallack. White- water Basin l i e s north-westerly from Lyle Creek Basin, separa- ted from i t lay a steep ridge which rises 1200 feet above the f l o o r of the former and 1800 feet above the f l o o r of the l a t - t e r . Access to Whitewater Basin i s by 1 mile of road and 1 sub- sequent mile of t r a i l , from the Lyle Creek road at 1 mile from Retallack. The Highland Surprise camp i s on the north-wester- l y w a l l of Lyle Creek Basin. T o p o g r a p h y . The area i s one of strong r e l i e f . Elevations r i s e to 9000 feet at the summits of sharply pointed mountains and serrated ridges which are aligned to form ranges of general- l y north-westward trend. The valleys between the ranges are 2. deeply incis e d , primarily as a result of g l a c i a l action and l a t t e r l y by rapid erosion of s w i f t l y running water. The an- nual spring runoff i s heavy and reduced flow i s maintained throughout the summer from melting ice which s t i l l l i e s i n g l a c i a l c i r c e s at the heads of the higher basins. The pre- cipitous slopes of the higher walls of the valleys are re- duced at lower elevations by concentrations of talus and moraine material. Surface erosion i s so active that develop- ment of upland meadows i s rare. Evidences of g l a c i a t i o n are common i n the area. Many of the softer rocks have rounded outlines on the surface, from which g l a c i a l grooving has been removed by l a t e r surface erosion; on more resistant rocks, however, str i a e are f r e - quently w e l l preserved. One very interesting exposure was observed on the high south-westward rim of the Whitewater Basin where wel l defined s t r i a e trend southward. At t h i s l o c a t i o n the wal l of the basin i s almost v e r t i c a l f o r 900 feet and the st r i a e occur at the top, on the very edge of the rim on rock i n place which dips at 25 degrees to the southward, that i s , away from the rim and Whitewater Basin. The suggestion i s that, comparatively recently, movement of ice was from higher ground above the present basin. It i s c l e a r l y recognized that the serpentine underlying the basin i s considerably more subject to erosion than the v o l - canic members which flank i t to the south-westward but t h i s 3 i l l u s t r a t i o n of the r a t i o between the two rates of erosion i s s t a r t l i n g and indicates that l o c a l topographic features can be given l i t t l e weight i n consideration of any but very recent events. Climate. A combination of topographic and clima t i c conditions render year-round operation d i f f i c u l t . Heavy snowfall during the winter months produces many slides which frequently make i t impossible to t r a v e l or work on the surface w i t h safety. Snow l i e s at higher elevations u n t i l July and i s seldom gone even from the basins, at a mean a l t i t u d e of from 5000 to 5500 f e e t , u n t i l late i n June. Although i n the ordinary year at least three months of clear weather may be expected, r a i n hampered f i e l d work u n t i l the end of June during the past season and snow storms prevented work e n t i r e l y during one week i n July. Timber. Timber-line i s close to 6000 feet and below t h i s elevation there i s available adequate timber f o r a l l domestic and mining needs, constructional and underground. F i r , pine and cedar are abundant below 5500 feet at loca- tions sheltered from snow-slides and not subject to the effects of active erosion. 4. Water-Supply. Available water is subject to seasonal fluc- tuation and practically a l l the small creeks which may be of good flow up until July are completely dry by the end of August. The exceptions are Lyle Greek and Whitewater Creek, but even these are greatly reduced by the time seasonal run- off is complete. General Geology. The rocks of the area under consideration be- long to the Kaslo Series of Triassic age. In Memoir 173, Geological Survey of Canada, C. E. Cairnes divides this ser- ies into volcanic rocks, intrusives, serpentine and sediments and sub-divides the volcanic rocks into pyroclastics and flows. The region has been subjected to metamorphism, dynamic and hydrothermal, which has obscured many of the ori- ginal characteristics of the rocks and the contacts between the individual members. While i t is not possible to be cer- tain, i t is probable that much of the volcanic material was originally andesitic in composition. As most of the volcanic rocks are chloritized it has been found convenient to classify the pyroclastic, flow and sedimentary members as greenstones. Strictly, the sediments should probably not be included in this classification but in the area they are not abundant 5. and scarcely distinguishable from the volcanics. D i o r i t i c intrusives and serpentine are e a s i l y i d e n t i f i e d by the charac- t e r i s t i c s given below. The remaining rock type i n the area i s represented by the feldspar porphyry dykes of current i n - terest i n t h i s thesis and petrological description of them i s deferred to Part II. Greenstone (includes o r i g i n a l flows, •pyroclasts and sediments.) Of the three o r i g i n a l constituent members the flows are the only ones which may be i d e n t i f i e d with any de- gree of ease. Typically pale-green or light-green on the weathered surface, s l i g h t l y darker-green or grey on fresh fracture, fine to medium-grained i n texture, the diagnostic feature i s flow structure which i s apparent occasionally on a broad scale. V i s i b l e when seen i n place, i n i t s e n t i r e t y , but seldom authoritative i n fragmentary hand samples, t h i s structure i s generally represented by f i n e l i n e s or e l l i p t i - c a l outlines of colour either l i g h t e r or darker than the re- mainder of the rock. Such flow structure i s best seen on the south-westward side of the serpentine. Where flow struc- ture i s not available as a guide and the ground mass i s f i n e - grained and homogeneous, as i n large areas on the north-east- ward side of the serpentine, i t i s sometimes possible to d i s - tinguish the flows by means of isolated fragments of unabsorbed early crust. However, these c r i t e r i a are unreliable as such i s o l a t i o n s may often represent coarse fragmental material 6 in finely divided pyroelastics. Of the pyroclasts a few examples were seen, notably underground at the Highland Surprise, where it was possible to define at least small areas with some assurance. Under a hand lens, or occasionally in the hand specimen, these rocks may be seen to be fragmental in origin. Sediments are apparently rare in this sec- tion; none were seen with characteristics as defined by Cairnes. This however is not surprising, as they are pro- minent nowhere in the Kaslo Series. There may be some sediments exposed underground at the Highland Surprise but the writer saw no rock which could be classified de- finitely as such although there are several exposures in which bedding appears obvious at first sight. Closer ex- amination of these exposures shows, however, that the i l - lusion is created by a near parallel arrangement of quartz and albite stringers which follow lines of shearing in high- ly metamorphosed rock which was probably originally pyro- olastic. Serpentine. The serpentine is the most extensive and best defined member of the Kaslo Series. Of a north-west strike, with a dip steeply to the south-westward i t has ex- 7. posed widths up to 2500 feet. On weathered surfaces the serpentine is typically black, green of shades from dull to bright, pink or light-brown; the last two colours grade fre- quently almost to white. The extreme softness and de- cided greasy feel are easily recognizable characteristics. The greasiness is due to the abundant production of talc as the result of alteration. Fibrous appearance along shear planes is due to the production of serpentine wool. The whole member probably represents an original ultra-basic injection which has reached its pre- sent composition by simple hydration or other more invol- ved metamorphic processes. That i t was originally intru- sive is emphasized by inclusions of greenstone within it and by the narrow but well defined branches which lead off the main mass. On the accompanying map several of these fingers are indicated to the south-westward of the main body. Moritic Intrusives. With the exception of the feldspar por- phyry dykes a l l the minor intrusives seen in the area are approximately dioritic in composition. Typically dark- green in colour, these rocks are composed essentially of 8 oligoolase-andesine plagioclase and shreddy amphibole. There is practically no visible quartz. Fine to medium- grained, they may sometimes be distinguished from the vol- canics by slightly coarser texture but frequently the ex- act margin between the two rocks is indeterminate by a gra- dational relationship and numerous small inclusions of vol- canic rock. However, with the fine-grained, homogeneous and massive facies of the diorite it is usually possible to make distinction from the volcanics only on freshly broken, wetted surfaces where the amphibole and plagioclase are apparent. Structurally this member is probably best described as a series of irregular plugs, of no definite form. Younger than the serpentine, the intrusions took particular advan- tage of structural weaknesses in the greenstone marginal to i t , as suggested by a vague line of concentration along the north-eastward contact of the serpentine and some elongation of the individual exposures parallel to its length. On the accompanying map only two areas of diorite are indicated, one on the Gold Quartz property and one above the Highland Surprise workings, and in neither case are the exact bound- aries defined. While i t is unlikely that there is any gene- tic relation between the diorite and the mineral deposits in the district, it does appear that mineralized veins may be localized in fractures marginal to the individual bodies and, in one case, a vein was seen within the diorite itself. 9 Feldspar Porphyry Dykes* These dykes are apparently the youngest rocks i n the area. They are intrusive into fractures i n the green- stone marginal and approximately p a r a l l e l to the serpentine contact. In width they vary from 1 to 10 feet, often with marked v a r i a t i o n i n width along the str i k e which tends to produce c h a r a c t e r i s t i c a l l y l e n t i c u l a r outline. Like that of the serpentine, t h e i r s t r i k e i s generally north-west; the dip i s usually north-eastward but i t varies r a d i c a l l y , . even between the two w a l l s . As an example, underground at the Highland Surprise one w a l l of a dyke dips at 10 degrees to the north-eastward and the other stands v e r t i c a l l y . In colour these rocks are grey on fresh sur- faces and shades of pale-pink, light-brown or white on weathered surfaces. Veins. Two types of vein occurrence have been ex- posed at the Highland Surprise. Both are i n the fractures of north-west s t r i k e i n the greenstone marginal to the ser- pentine. For purposes of i d e n t i f i c a t i o n one type w i l l here be referred to as "vein", the other as "vein-zone". The veins are composed of quartz and c a l c i t e gangue which contains gold- bearing sulphides. The sulphides are p r i n c i p a l l y p yrite and 10 chalcopyrite. Ho free gold was seen i n hand specimens but microscopic examination shows i t to occur as blebs i n the p y r i t e . Samples from the Highland Surprise yielded a con- siderable amount of free gold on the Haultain Super-Panner. The veins on the north-eastward margin of the serpentine have proved upon development to be s u f f i c i e n t l y mineralized by gold-bearing sulphides to warrant serious con- sideration; those on the south-westward margin, by evidence of surface exposures alone, are almost barren of sulphides. Those on the south-westward contact appear to have been de- posited at comparatively low temperatures; drusy structure i s common, wall-rock a l t e r a t i o n i s almost absent i n many places and several angular and unaffected inclusions of w a l l - rock were noted w i t h i n the vein-quartz. To date development indicates considerable weakness and i r r e g u l a r i t y both along the s t r i k e and on the dip of the veins. The veins have naturally assumed the habit of the fractures and, l i k e the feldspar porphyry dykes, are variable i n width along the s t r i k e . However, the veins are even more ir r e g u l a r than the dykes, p a r t i c u l a r l y when the wall-rock i s highly sheared, f o r , while the general occur- rence of vein-quartz may continue on s t r i k e , i n d i v i d u a l strands are often highly contorted and i r r e g u l a r i n dip as a result of having followed minor l o c a l folds and frac- tures i n the greenstone. In other places the width of 11. vein-quartz may pinch abruptly to a single narrow stringer. Vein widths vary up to 5§ feet; t h i s may be of s o l i d quartz or may be comprised of several strands or l e n t i c u l a r bunches of quartz and included low-grade rock. Where vein and f e l d - spar porphyry dyke occur together i n the same fracture the vein gains strength from the competency of the dyke. The vein-zones may be representative of the veins at locations where vein solutions were not abundant and where fracture of the greenstone was represented by t i g h t shearing rather than by w e l l maintained openings. In at least one case there i s apparently a t r a n s i t i o n on s t r i k e from vein-zone to vein. The width of the vein-zones i s comprised of very narrow stringers of a l b i t e and quartz which strikes north-west. P y r i t e i s disseminated sparsely i n the quartz, i n the a l b i t e and i n the included and margin- a l greenstone. Highly altered, the marginal greenstone i s often dark i n colour, homogeneous and compact. To date the gold content i n the vein-zones has been found to be small but i f there i s proved to be t r a n s i t i o n from them to the veins the zones may be followed as a guide i n development. The veins may prove to be simple shoots with- i n the vein-zones but there i s some suggestion that there may be cross-fracturing of the vein-zone shearing and that the i n - tersections of the two sets of fractures permit concentra- 12 tions of mineralization along the cross-fractures. Nowhere was it possible to see two fracture-systems which actually crossed but at two locations veins which contain commercial values strike north to north-east as against the general vein- zone strike to the north-west. In the course of further ex- ploration particular attention should be given to the possi- bility that there is such a secondary and less conspicuous fracture-system. Relative Ages of Veins and Feldspar Porphyry Dykes. The close areal association of veins and dykes ••MiHHMHMaqMpnMMiriMMaiMlriHariiiMa naturally suggests that there may be some genetic relation between them. Structural relations at the Highland Surprise indicate that there the dykes are generally younger than the veins. However, at the Gold Quartz property there is at least one very good exposure in which quartz stringers lead off from a strong vein and f i l l fractures in a dyke which lies on the vein wall. Thus it appears>Athat there may be local precedence of either veins or dykes in certain sections of the area but it is probable that on a broad scale vein deposition and dyke intrusion were probably nearly contemporaneous. (Pbrthur def- erence to this subject ««N Sfcirf IE.) \ Structure. As described, by Cairnes, ''the Kaslo rocks form an almost structureless mass". However, i n his report he give such data as are available concerning the thickness of the Kaslo Series and the nature of the contacts with underlying M i l f o r d Series and the younger Slocan Series. On the map ac- companying t h i s report the contact of the Kaslo and Slocan Series i s indicated and, as described by Cairnes i n the area farther south-eastward, there i s l i t t l e apparent discordance between the two series. The Kaslo-Milford contact does not occur i n the area under consideration but i t s extension from the location as mapped on Cairnes' sheet i s exposed approxi- mately 1-jr miles north-eastward from the north-westward l i m i t of t h i s area. At that point the contact crosses the south fork of Cooper Creek and there i t s general l i n e may be d i s - tinguished e a s i l y by the marked difference i n the weathering of the two formations. The s l a t e s , a r g i l l i t e s and limestone of the M i l f o r d Group weather with c h a r a c t e r i s t i c a l l y rounded outline i n strong contrast to the ruggedness of the Kaslo Series. On the basis of Cairnes' areal work the s t r i k e of the Kaslo Series i s taken as north-west, the dip steeply to the south-westward. Heavy shearing coincident with and subsequent to folding has resulted i n marked sehistosity 14 parallel to the bedding-planes. Much of this shearing pro- bably occurred just prior to the intrusion of the Nelson Batholith. In unsheared and comparatively unsheared green- stone at least three sets of joints have been developed; one of these strikes north-west, dips steeply south-west- ward; the second strikes north-west, dips flatly south- westward; the third strikes north-east, dips steeply south- eastward. By the evidence available to date the veins and feldspar porphyry dykes strike north-west and dip north- eastward or south-westward. One possible explanation of the origin of the fractures through which their solutions passed is that the fractures were formed by the intrusive action of the serpentinized s i l l . If so, there may be a set of conju- gate fractures as suggested earlier in discussion of the vein- structure. A second possible explanation of the origin of the fractures is that the serpentine behaved as a structural unit during the folding of the older rocks, with the production of fractures against and nearly paralleling the serpentine con- tact. A third possible explanation is that the fractures were caused by strains produced in the marginal rocks during change in volume within the s i l l attendant upon composition changes from the original rock to serpentine. It should be understood that a generalization 15. is intended when reference is made to vein and dyke fractures of north-west strike which approximately parallel the serpen- tine contact. Underground at the Highland Surprise there is variation in strike of as much as 30 degrees between the veins and dykes and the serpentine contact and a definite tendency for the veins to strike slightly farther to the west than the serpentine contact. Alteration. The most marked alteration is that of the ser- pentine to talc and carbonate in the vicinity of the veins on the Highland Surprise property. This effect is so far advan- ced that where intersected by underground workings walls and back of adits may be held only by considerable effort. eration adjacent to the veins is generally confined to widths which may be as much as 6 feet but which are often considerably less. In the vein-zones alteration has taken place in the greenstone which remains within the limits of the zone as well as in the marginal rock. Typical of this alteration is the darkened colour of the 16 rock and the presence of scattered p y r i t e . At the Highland Surprise i t has been found that where marginal to veins such wall-rock, u n s i l i c i f i e d , dark i n colour and mineralized spar- ingly by p y r i t e , w i l l often contain s u f f i c i e n t value i n gold to be of milling-grade; marginal to the low-grade vein-zones i t has not found to be of value. There has apparently been l i t t l e or no active emanation from the feldspar porphyry dykes. The only effect they have had has been to bake the greenstone f o r a very nar- row width at the contact. IS aU/CC\. »<"\ RaC I' 3E~ HIGHLAND SURPRISE PROPERTY General Geology. Considerable d e t a i l applicable to t h i s p a r t i - cular property has been given already i n the general state- ment . The rocks exposed underground are greenstones, as de- fined previously, of the Kaslo Series, intruded by irregular masses of d i o r i t e and by feldspar porphyry dykes. The under- ground workings follow the margin of the basic i n t r u s i v e , now converted to serpentine, and the veins and the dykes both p a r a l l e l approximately the contact between the serpentine and the greenstone. The greenstone i s schistose and largely c h l o r i - t i z e d ; i n proximity to the veins i t i s commonly darkened by hydrothermal a l t e r a t i o n , 17. As detailed in the general statement, dis- tinction is made between two types of vein-structure which are designated as "vein" and "vein-zones" respectively. Further development is required to show whether the veins are merely shoots within the vein-zones or whether the veins are concentrations at the intersections of cross-fractures with the fractures of the vein-zones. The vein-zones strike north-west, dip north-eastward or south-westward; indications are that any cross-fractures strike north or north-east. Sul- phide mineralization within the veins consists of pyrite, chalcopyrite and small amounts of galena and sphalerite. Py- rite is usually the only sulphide present in the vein-zones and in the wall-rock. It is necessary to emphasize the extreme irregularity of the structure of the veins. Due to the in- competency of the wall-rock, widths will pinch from mineable widths to a stringer within a few feet and the dip will change as much as 90 degrees. At the same time, however, the occur- rence of quartz will be maintained on the same general line of strike. Geologic detail and detail of underground development is given on the plan which accompanies this thesis. By the small amount of information available cor- relation is dangerous between exposures of rock members or 18 of vein-structure. GOLD QUARTZ PROPERTY As at the Highland Surprise, the veins ex- posed here are i n greenstone, on the north-eastward side of the serpentine but here the veins are farther from the serpentine contact than are those at the Highland Surprise. Probably as a result of the greater distance from the ser- pentine contact the greenstone i n which the Gold Quartz veins occur i s generally more massive and compact than that exposed underground at the Highland Surprise. A l - though the greenstone-serpentine contact i s covered by overburden toward the eastward end of Whitewater Basin, i t may be placed approximately as on the accompanying map. Hear the vein-exposures the greenstone i s intruded by i r - regular masses of d i o r i t e and by feldspar porphyry dykes. The veins upon which development has been concentrated s t r i k e north-west. Thus rock types and st r i k e of the veins at the Gold Quartz duplicate conditions at the Highland Sur- p r i s e . There are however, two marked points of difference between the two deposits. One i s that there are noticeable amounts of galena and sphalerite with the p y r i t e and chalco- p y r i t e i n the Gold Quartz veins. The second difference i s that at the Gold Quartz there are exposed at least three narrow quartz veins which s t r i k e north-east or east. 19. Practically no work has been done on these veins but they may be of importance as indicators of fractures which inter- sect the principal fracture-system of north-west strike. At an elevation of 6300 feet, surface-stripping has exposed a vein which strikes north 20 to 25 degrees west, dips 60 to 70 degrees eastward. The vein is exposed over a length of 200 feet. There are usually one or two well maintained bands of quartz which vary in width from 6 to 24 inches. Between these bands, and outside them, quartz stringers occur irre- gularly in the greenstone. Sulphides are disseminated in the quartz and in the greenstone and the total width of the lode varies from 24 to 84 inches. Within some of the wider bands of quartz there are longitudinal openings which are coated on the walls by milky, crystalline quartz. This evidence, with the presence of noticeable amounts of galena and sphalerite in the vein, suggests there may be some cor- relation between the present surface and temperature condi- tions which pertained at the time of vein deposition. No such open structure and l i t t l e or no galena or sphalerite is present in the veins exposed at the Highland Surprise where the upper adit is 600 to 1300 feet lower than the Gold Quartz exposures. 20. P A R T II DCTRODUOTION,. Following are detailed reports of microscopic study of t h i n sections of the feldspar porphyry dykes. The sections represent various surface exposures and under- ground exposures at the Highland Surprise property. Exact locations at which the specimens were obtained are ind i c a - ted on the accompanying map and plan of the Highland Sur- prise workings. In c l a s s i f y i n g the rocks represented by the t h i n sections, unstriated a l b i t e has been included with orthoclase and microcline as a l k a l i feldspar. By t h i s usage most of the igneous rocks may be termed microgranites. Those i n which the feldspar i s predominantly sodic plagio- clase are indicated by the addition of " a b l i t e " or " a l b i t e - oligoclase" to the rock name. PETROGRAPHY OF THIN: SEOTIONS Section 15 Uicrogranite (Albite) The section consists of subhedral to euhedral feldspar i n a microcrystalline ground-mass. The feldspar 21 i s about half albite (Ab. 93, An. 7) and half orthoclase. A very few quartz grains of subhedfal to anhedral outline are present; these are of smaller size than the feldspars but are definitely larger than the average grains size in the ground-mass. The ground-mass is essentially subhedral to quartz. Alteration of the feldspars has proceeded gen- erally with the production of sericite, muscovite and kao- l i n . Chlorite i s scattered throughout the ground- mass, usually in small specks which have vague orientation as though drawn out into lines. Some of i t i s i n t e r s t i t i a l between the feldspars. It i s suggested that the chlorite i s due principally to alteration of original bi o t i t e , some of which is s t i l l present although bleached. Carbonates are general in the ground-mass and seaming the feldspars. These are probably of supergene origin. Subhedral to euhedfal pyrite i s scattered through the ground-mass. The section illustrates Bowen's reaction series w e l l — e a r l y crystallization of feldspars, later biotite, f i n - a l ground-mass of residual biotite and quartz. 22 Section 14 Contact of microgranite with greenstone In the microgranite feldspars, 25% * a b l i t e — oligoclase (Ah. 84, An. 16) and 75% - orthoclase, occur i n microcrystalline ground-mass of feldspar and quartz. There are a few r e l a t i v e l y large anhedral grains of quartz. The feldspars are altered markedly with the production of s e r i c i t e , muscovite and k a o l i n . The ground-mass shows d e f i n i t e l i n e s of flow- age around the feldspar growths, indicating the l a t e r f l u i d i t y of the f i n a l s i l i c e o u s extracts. The greenstone i n contact with the micro- granite has been reduced to a mass of c h l o r i t e , kaolin and residual quartz. By f i e l d observation and from t h i s section i t appears u n l i k e l y that there has been much hydro- thermal a l t e r a t i o n of the o r i g i n a l rock (now greenstone) by the i n t r u s i v e . On the other hand, a considerable amount of c h l o r i t e i n the microgranite i s probably derived from the greenstone although some of i t results from the a l t e r a t i o n of b i o t i t e which occurs as a minor o r i g i n a l constituent of the igneous rock. Carbonates are general. Obviously l a t e , as evidenced by the unbroken passage of carbonate veinlets 23. from ground-mass to greenstone, t h i s mineralization i s pro- bably supergene i n o r i g i n . Subhedral to euhedral pyrite i s scattered through the ground-mass. Section 31 Microgranite The p r i n c i p a l feldspar i s orthoclase. Several large plates are present but most of the section i s com- posed of granophyric intergrowths of smaller fragments of orthoclase and a l b i t e (Ab. 89, An. 11) with quartz. There i s no defined ground-mass as i n sections 13 and 14. Sub- hedral to euhedral inclusions of plagioclase w i t h i n the larger plates of orthoclase are common. One hexagaial out- l i n e •, which appeared to be of quartz, was observed w i t h i n orthoclase but the occurrence was too small to permit posi- t i v e i d e n t i f i c a t i o n . A l t e r a t i o n i s advanced, with the production of c h l o r i t e from b i o t i t e ; kaolin and s e r i c i t e from the f e l d - spars. Magnetite grains, subhedral to euhedral, are scattered through the section. 24 Section 55 Microgranite The feldspars i n the section consist of large subhedral to anhedral growths of microcline, 80% + and smaller grains of albite-oligoclase (Ab. 86, An. 14) 20% -. These, and a few anhedral grains of quartz l i e i n a mioro- c r y s t a l l i n e ground-mass of which quartz i s ; the p r i n c i p a l constituent. The texture i s thus microporphyritic. Air though there are inclusions of plagioclase c r y s t a l s w i t h i n the microcline they are not numerous enough or of s u f f i - c i e n t l y d i s t i n c t i v e pattern to permit the use of the term p o i k i l i t i c . There i s also d e f i n i t e replacement of a l b i t e by microcline. Rotting of the feldspars, with the produc- t i o n of s e r i c i t e and k a o l i n , i s f a r advanced i n many i n - stances; frequently t h i s process has proceeded outward from the centre of the c r y s t a l . B i o t i t e , anhedral, i s scattered through the ground-mass; a small amount of c h l o r i t e i s probably se- condary a f t e r the b i o t i t e . Two large shreds of b i o t i t e , which appears to be ly i n g on top of the section, are ap- parently secondary. There i s very l i t t l e carbonate i n t h i s section. Scattered subhedral to euhedral pyrite grains show a l t e r a t i o n to hematite. 25 Section 48 Micromonzonite The section i s heavily altered. Euhedral to anhedral"crystals of albite-oligoclase (Ah. 83, An. 17) and of anhedral quartz are isolated as individuals and in groups by a microscrystalline ground-mass. Potash feld- spar was not identified. The quartz and feldspar grains are interlocked characteristically and/or the quartz occurs as i n t e r s t i t i a l f i l l i n g between the feldspar. There i s more quartz than in the previous sections and i t s percentage of total f e l s i c content much more nearly approaches the upper limit (66%) permissable i n a granite. The ground-mass, in the form of veinlets, is now mainly chlorite, sericite and kaolin with some quartz and a l i t t l e feldspar. Much, or perhaps a l l , of the chlorite has been derived from biotite, the latter present through- out the section in bleached form. - Alteration of the feldspars has proceeded so far that in some cases the original outline i s indicated only by the secondary minerals, of which sericite is the most common. There is l i t t l e or no development of carbonates. There are one or two specks of magnetite but no. pyrite in the ground-mass. 26. Section 53 Microgranite Large sub to anhedral .plates and smaller sub to euhedral crystals of microcline {80% 4^) and sub to euhedral crystals of albite- oligoclase (20%, -) (Ab. 83, An. 17) lie in a microcrystalline ground-mass to'produce a microporphyritic texture. In places the ground-mass is almost cryptocrystalline but it appears to be composed prin- cipally of quartz with minor amounts of feldspar. There are definite evidences of replacement between microcline and the plagioclase. While there are examples which might be taken as indicative of a late mag- matic concentration of albite, the weight of evidence is in favor of the normal action—replacement of plagioclase by microcline. Kaolin and sericite are present, as alteration products of the feldspars. Biotite occurs throughout the ground-mass as interstitial f i l l i n g between the feldspars and at the con- tacts of ground-mass and feldspars. Chlorite results from the alteration of the biotite. Lines of flowage in the ground-mass are indicated by the arrangement of the biotite and chlorite. 27. A few larger quartz grains concentrated i n the ground-mass or marginally to the feldspar crystals suggest f i n a l c r y s t a l - l i z a t i o n of quartz, even a f t e r consolidation of the ground- mass proper. A considerable amount of magnetite but no py- r i t e occurs i n the section. Section 57 Microsyenite (Albite) A l b i t e (Ab. 89, An. 11), common horneblende, (20 to 25$) a l i t t l e quartz, (less than 5%), and probably some orthoclase, constitute most of the section. The tex- ture i s almost h o l o c r y s t a l l i n e . A late fracture-system traverses the section, the present f i l l i n g of which i s p r i n c i p a l l y k a o l i n , s e r i c i t e and carbonate. Kaolin and s e r i c i t e are general, p r i n c i p a l l y as the result of a l t e r a t i o n of the feldspars. B i o t i t e i s closely associated with the horne- blende. Chlorite results from a l t e r a t i o n of the b i o t i t e . There i s present a small amount of magnetite and hematite; no p y r i t e . 28. Section 60 Microsyenite This section represents intensely altered rock. Albite-oligoclase (Ah. 85, An. 15), orthoclase and a l i t t l e quartz are probably the only o r i g i n a l minerals. The quartz represents less than 5% of the o r i g i n a l f e l s i c constituents. .A considerable amount of b i o t i t e occurs i n streaks, probably as an a l t e r a t i o n product of amphibole—of which there are a few residual and badly decomposed plates. Chlorite has resulted from the a l t e r a t i o n of b i o t i t e . The arrangement of the b i o t i t e suggests shearing of the rock subsequent to con- s o l i d a t i o n , a conclusion borne out by the f i e l d evidence. A l - ter a t i o n of the feldspars has produced considerable s e r i c i t e and kao l i n . Carbonates are p l e n t i f u l and general, probably supergene i n o r i g i n . An iron mineral, which i s ei t h e r pyrrhotite or tarnished p y r i t e , occurs i n streaky.concentrations p a r a l l e l - ing the b i o t i t e . Section 101 Contact. Microgranite (Albite-Oligoclase) and greenstone In the microgranite albite-oligoclase (Ab. 85, An. 15), a very small amount of quartz and probably some 29. orthoclase occur as phenocrysts i n a microcey stalline. ground- mass which i s p r i n c i p a l l y quartz. S e r i c i t e and kaolin are secondary from the a l t e r a - t i o n of the feldspars. Chlorite i s present as a l t e r a t i o n pro- duct of b i o t i t e some of which, bleached, remains i n the sec- t i o n . The c h l o r i t e defines l i n e s of flowage i n the ground- mass. Carbonates, of supergene o r i g i n , are p l e n t i f u l . In the ground-mass there are two large euhedral crystals of p y r i t e , some smaller grains and some specks of magnetite. The greenstone i s p r i n c i p a l l y c h l o r i t e , with kaol i n and carbonates. Some quartz and feldspar was pro- bably derived from the microgranite. Section 9A Microgranite (Albite) Phenocrysts of al b i t e (Ab. 93, An. 7) and ortho- clase occur i n a microcrystalline ground-mass which i s essen- t i a l l y quartz. The orthoclase i s subhedral to; the plagioclase subhedral to euhedral. Bleached b i o t i t e , i n the process of a l t e r a t i o n to c h l o r i t e , i s disseminated through the ground-mass and defines l i n e s of flowage i n i t . 30 A small amount of quartz, c r y s t a l l i z e d i n larger grains than that i n the ground-mass, i s apparently the re- sult of very late concentration. The form of t h i s quartz i s v e i n - l i k e . Carbonates are common, generally of close as- sociation with the feldspars; i n some cases they occur as fracture f i l l i n g i n the feldspars. Muscovite and s e r i c i t e are the usual products of a l t e r a t i o n of the feldspars. Anhedral magnetite and sub to euhedral p y r i t e are disseminated i n the ground-mass. Section 4 Greenstone This section represents wall-rock 4 feet from the dyke of section 101. Ch l o r i t e , k a o l i n and carbonates are the p r i n c i p a l constituents, with minor quantities of residual quartz and feldspar. B i o t i t e occurs i n close re- lationship to the c h l o r i t e and i s apparently the source of much of i t . P y r i t e i s scattered through the section. There i s a d e f i n i t e tendency f o r the constituent minerals to be arranged approximately i n p a r a l l e l bands i n - dicative of shearing. 31. Farther consideration i s given to t h i s section under the heading "Wall-Rock Al t e r a t i o n " . Section 10 (2 sections! Vein-zone Section 10-39 RJM i s one made f o r the w r i t e r ; section 10-39S was made for the B. C. Department of Mines. The l a t t e r consists of a feldspathic ground-^mass traversed by veinlets of anhedral quartz and sub to anhedral a l b i t e (Ab. 91, An. 9). Beside the laths of feldspar the ground- mass contains some anhedral quartz and some b i o t i t e i n the process of a l t e r a t i o n to c h l o r i t e . Carbonatization, ap- parently of supergene o r i g i n i s general i n both the ground- mass and the v e i n l e t s . Pyrite and magnetite are scattered through the ground-mass but are not present i n the v e i n l e t s ; i n one or two instances magnetite occurs in. close r e l a t i o n - ship to concentrations of b i o t i t e - c h l o r i t e . Section 10-39 RJM represents almost the same location as 10-39S but i n i t the ground-mass and veinlets are predominantly of anhedral quartz. There i s some of feldspar present i n the ground-mass, but any o r i g i n a l l y i n the veinlets has been replaced to such an extent that exact i d e n t i f i c a t i o n i s impossible. 32 Section 24 This section represents a location where isola- tions of dyke rock and vein mineralization lie closely to- gether in greenstone. The isolations have resulted from the simultaneous weakening and dispersion of a narrow dyke and a narrow vein which occur closely together and parallel. The feldspathic ground-mass in the section re- presents the greenstone wall-rock. Traversing the ground- mass are veinlets of quartz and albite (Ab. 91, An. 9). Both quartz and albite crystals are anhedral; both are comparatively fresh. The greenstone ground-mass is similar to that in Section 10 and alteration has proceeded similarly. There is a considerable amount of sub to eu- hedral pyrite in the ground-mass, apparently earlier than the quartz-albite veinlets. 33. DISCUSSION Or i g i n a l l y t h i s t h esis was to be concerned only with the dyke rocks of the area, to provide simple descrip- t i o n s of them and to record any variations between the i n - divi d u a l intrusions. However, i n the course of that record- ing a l i t t l e information has been obtained which i s other than s t a t i s t i c a l . This information suggests some points of i n t e r e s t , the chief of which i s that there may be a genetic relationship between the dykes and the gold quartz veins. The ensuing discussion i s based on these suggestive f i n d - ings but i t s value i s necessarily l i m i t e d by the small num- ber of sections studied. Variations i n the dykes The sections studied are representative of a l l the dykes i n the area and the sections show closely related mineralogical composition. By these facts and from the generally s i m i l a r physical characteristics of a l l the dykes, i t may be assumed reasonably that a l l of them belong to one family and a l l represent one limited period of intrusion. The variations noted are i n pre- sence or absence of pyrite and magnetite, i n a l b i t e con- tent of the plagioclases, i n presence or absence of po- tash feldspar, i n amount of quartz, i n ground-mass and coarsely c r y s t a l l i n e , and i n femiea present. These data may be summarized thus: 34. Section P y r i t e Magnetite FELDSPAR QUARTZ Plagio- Potash clase Fsp. Ground- Coarse- mass l y Cry- s t a l l i n e Femic 13 Present Absent Ab. 93 Ortho- clase P r i n c i - p a l l y quartz Slight amount B i o t i t e - c h l o r i t e 14 Present Absent Ab. 84 Ortho- clase Felds- par & quartz Slight amount B i o t i t e - c h l o r i t e 31 Absent Present Ab. 89 Ortho- clase None as in Sects. 13 & 14 Consid- erable amount Biot i t e - c h l o r i t e 35 Present Absent Ab. 86 Micro- c l i n e P r i n c i - p a l l y quartz Slight amount B i o t i t e - c h l o r i t e 48 Absent Absent Ab. 83 None i d - e n t i f i e d A l i t t l e quartz & feldspar Consid- erable amount B i o t i t e - c h l o r i t e 53 Absent Consid- erable amount Ab. 83 Micro- c l i n e P r i n c i - p a l l y quartz Slight amount B i o t i t e - c h l o r i t e 57 Absent Present Ab. 89 Ortho- clase (?) None Slight amount B i o t i t e - c h l o r i t e ; horn^blende 60 Present (?) or (Pyrrho- t i t e ?) Absent Ab. 85 Ortho- clase S l i g h t - ly over half qu- a r t z , re- Slight amount Considerable b i o t i t e . A very l i t t l e amphibole mainder p r i n c i p a l l y altered fsp. 101 Present Present Ab. 85 9A Present Present Ab. 93 Ortho- . P r i n c i p a l l y Very B i o t i t e - clase quartz Slight c h l o r i t e (?) amount Ortho- P r i n c i p a l l y Slight B i o t i t e - clase quartz amount c h l o r i t e (vein ?) 35. From such a compilation i t was hoped some i n - formation might he forthcoming as to the ages of the dykes, re- l a t i v e to the parental magmatic stage. However, due to repeated contradictions w i t h i n i t , the table i s of l i t t l e use i n t h i s connection except i n the cases of sections 57 and 60. In these two cases the presence of araphibole as a femic c o n s t i t - uent suggests that the two dykes thus represented may be more closely related to the o r i g i n a l magma and hence s l i g h t l y older than the others which were studied. The absence of a ground- mass r i c h i n quartz i n section 57, also lends to t h i s assump- t i o n . Wall Rock Alt e r a t i o n It has been mentioned i n Part I and under Section 14 that i t i s the writer's opinion that there has been l i t t l e hydrothermal a l t e r a t i o n of the wall rock by the dykes. There i s commonly an inch or two of purely thermal a l t e r a t i o n but t h i s appears to be the only effect on the w a l l rock d i r e c t l y attributable to the i n t r u s i v e s . Casual examination of the area would not support t h i s view as there i s frequently a marked darkening of the greenstone marginal to the dykes, as mentioned i n Part I and represented by section 4. However, bands of t h i s dark- ened rock, up to 10 feet wide, may be found where there i s no 36 dyke marginal to them. Further, as exposed to date at the High- land Surprise, wherever t h i s c h l o r i t i z e d phase of the greenstone does occur, there i s always vein or vein zone wit h i n i t s margins and s t r i k i n g with i t . Thus the relationship appears to he between the a l t e r a t i o n and the vein mineralization rather than between the a l t e r a t i o n and the dykes. It i s possible to explain t h i s metamorphic effect independently of the dykes i f i t i s assumed to be dynamic i n o r i - g i n , contingent upon fo l d i n g p r i o r t o the intrusion of the dykes and f a c i l i t a t e d by water as a constituent of the o r i g i n a l rock and also perhaps by water of supergene o r i g i n carried downward by the f o l d i n g ; There i s nothing i s section 4 to indicate that the rock could not have reached i t s present condition from, say, an o r i g i n a l andesite, by dynamic metamorphism alone. Late Magmatic Effects Section 10 and section 24 indicate that a l b i t e and some of the quartz of the vein zones were of simultaneous c r y s t a l l i z a t i o n . This suggests a t r a n s i t i o n from magmatic to hydrothermal conditions and possible genetic correlation between the dykes, i n which a l b i t e i s a common constituent, and the vein mineralization. 37 /SUMMARY Part I 1. F i e l d relations show the dyke of section 60 to be older than the quartz vein which l i e s on i t s w a l l . 2. Several of the dykes exposed underground at the Highland Surprise cut through the vein zones and i n two cases concentrations of vein mineralization l i e on both walls of dykes. 3. The recurrent proximity of dykes and vein structure, p a r t i c u l a r l y on the north-east side of the serpentine, suggests the p o s s i b i l i t y of genetic relationship.between dykes and veins. Part I I 1. Sections 57 and 60 may represent dykes i n - truded e a r l i e r than the others of which t h i n sections were stud- ied but the relationship between the plagioclases i n a l l the sec- tions i s s u f f i c i e n t l y close to permit assumption that the t o t a l time i n t e r v a l was short during which intrusion took place. 2. Typical darkening of the greenstone i n which veins and vein-zones occur i s believed to be an effect of dynamic metamorphism, completed p r i o r to the intrusion of the dykes. 3. The presence of a l b i t e i n the vein zones and the prominence of a l b i t e i n the dykes further suggest-s possible genetic relationship between vein mineralization and dykes. .38. COHOLUSIOKS 'While f i e l d relations indicate general s i m i l a r i - t i e s between the dykes and leads to the assumption that they are of close genetic r e l a t i o n s h i p , microscopic study was necessary to show that the relationship i s very close indeed. This statement i s based on the small compositional range of the plagioclases. The. dyke of section 60 i s known d e f i n i t e l y to be e a r l i e r than the vein on i t s w a l l and hence i t i s assumed that the greater part of the intrusive action was complete before vein and vein zone mineralization took place. This must be only an assumption because there i s l i t t l e d e f i n i t e evidence of a general t r a n s i t i o n from magmatic to hydrothermal conditions; the pre- sence of a l b i t e and quartz stringers i n the vein zones may not be taken as proof; nor can the common presence of pyrite i n the dyke rocks. However, based on t h i s assumption, explanation i s possible of the r e l a t i o n between veins, vein-zones and dykes, as exposed at the Highland Surprise. At t h i s property, because the dykes intersect the veins and vein zones, they have been con- sidered to be l a t e r than the quartz-sulphide mineralization. The alternative explanation, based on the fore- going assumption, i s that, following stoping intrusion of the dykes into the normal, sheared greenstones, fractures were set up i n the r e l a t i v e l y competent, regionally metamorphosed bands 39 of greenstone. These fractures would result from minor crustal adjustments, probably chiefly tensional.' The tendency would be for them to remain in the competent bands and to parallel the length of the dykes. While the metamorphic bands and the dykes are parallel in general, there are cases in which the dykes intersect the bands at flat angles. At these in- tersections the fracturing would not be of sufficient strength to penetrate the dykes and would tend to be dispersed or change direction toward, that of the dyke contact. Upon the entry in- to the fractures of the mineralizing solutions responsible for vein deposition, the areas.which offered the maximum space for f i l l i n g would be at and near the dyke contacts; by the time of deposition from the final, richest solutions those centres would offer the only remaining openings to permit the present concentrations of high grade ore. 8J30 Mtn. £/. SO30 M i n . • £/. 0O4O :'t::y.i^'/'n<K Mild tn - & SS3o r £/. #32 O >s-ffMk Mt. 3^'ennon L E G E N D SLOCAN SZQIES 5 l j t w , a r^ i l t i , quo»-+Jtit« , J i r n ^ s f o n e ( m p a r t f o J b i l i f c r o u s ) , canq\omerafc , and t u f f a c e o u s &ed\menis. K A 5 L 0 5 E I 7 I E 5 r i .. r \ | ~ | D l O p l T E - M a r k e d an j y w h e r e i t ou t c r ops i n l \ i ' i \ c o n s i d e r a b l e masses, margins i r r e g u l a r omi N 1 ' ' ' no* d e f i n e d . S E f ? P E N T l N E • O a r k q r e e n o n freshest sur- faces ; p tn t c , b l a c k . , w h i t e , f r i g h t g r e e n , I'Cjht g r e y on . v e a t h e r e d s u r f a c e s . / , ^ y . GPE*E/v5TON£ - M a i i i i / e o n d s c h i s t o s e . R o w s . ' . \ j P y r o c l a S t i c S , and no i n o r O c c u r r e n c e s of" Sed- m«n+s , o i l m e t a m o r p h o s e d t o r n o « d i f f e r e n t l o t i o n d i f f i c u l t . P r e d o m i n a n t l y dark Qreen i n colour and fine i n grain. Scale IOOO IOOO L E G E N D Q u a r t z V e i n s Feldspar Povphry O^kes / A d i t s C a m p s G e o l o q i c a l B o u n d a r i e s , Defined G e o l o q i c a l b o u n d a r i e s . Appro*imate Geo l o g i c a l bovndaries, A s s u m e d T r a i l s P o o d s Colours Con fours , A p p r o x i r n a t e Glac< e r s Lokt f s 2 0 0 0 3 OOO sea feet 3 & o l o q y of the LYLC O c c k - WHIT&W*TER Cr««Vc Affca.. Prajr.'n^ by J,S. r \ c l * l o s \ . 120 Porta! El. 5456 G E N D Sheared Green s t o n e S e r p e n t i n e D i o r i t e Feldspar Porphurcj V e i n V e i n Z o n e - and h i g h l y a l t e r e d G r e e n - s t o n e , w h i c h is dork in color, p y r i t i z e d , a n d s e a m e d b y Quariz sfrinqers. P a i s e , t o p l ? a i s e , bottom Sample Uocaiion EZD 110 P o r t a l E l . 5 6 0 0 N0<?TM DETAIL OF 100 L E V E L Scale 20 O Z0 40 60 feet 7


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