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A petrographic study of porphyry intrusives of Hedley, B.C. Lee, James William 1949

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APETROGRAPHIC STUDY-OF PORPHYRY INTRUSIVES AT HEDLEYi'.B?. C. JAMES WILLIAM LEE A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR"THE DEGREE OF MASTER- OF APPLIED" SCIENCE IN. THE DEPARTMENT GF GEOLOGY AND GEOGRAPHY THE UNIVERSITY-OF BRITISH:COLUMBIA APRIL 1 9 4 9 ABSTRACT The Flange-Midway types were found to be petrographically indistinguishable from ordinary sillfe. The cause of the bluish colour of Flange specimens could not be defini tely established. The porphyries may have been altered both by deuteric and by hydro-thermal action. Studies of zoned plagioclases indicate a magmatic or ig in for at least one of the s i l l s . SUMMARY ( i i ) The re la t ive ly small number of th in sections studied does not permit the writer to expound with confidence any new idea concerning the or ig in or the al terat ion of the dikes and s i l l s as a whole or of any one of them i n par t icular . After a c r i t i c a l exam-ination of Dolmage and Brown's paper and a comparison of a l l available petrographic results , including his own, the writer i s incl ined to disagree with the view that the porphyries were altered mainly by deuteric rather than by hydrothermal processes. Augitization of the hornblendes, however, may be partly deuteric because augite i s developed, if/only to a l imited extent, i n rocks unaffected by other al terat ion such as se r l c i t i za t ion and kaol in izat ion. The writer found no mineral that resembled pargasite as described by Schmitt. Dolmage and Brown apparently found no pargasite but instead they recog-nized tremolite occuring i n a manner similar to the pargasite of-Schmitt. Further investigations should be made to determine whether or not tremolite and pargasite are both present. No cause was found for the bluish colour of the Flange dike. Except that tremolite i s lacking i n the mine s i l l s , no c r i t i c a l difference was noted between them and the Flange-Midway types of porphyries. ( i i i ) Scapolite was found to occur e r ra t i ca l ly and not to be always abundant near high grade ore. Regarding the Origin of the porphyries, th© writer believes that the data supplied by Dr. Mantuani on zoned plagioclase crystals are almost conclusive proof of c rys ta l l i za t ion from a magma. / TABLE OF CONTENTS Page ACKNOWLEDGEMENTS i SUMMARY i i INTRODUCTION 1 Location , 1 History . 2 Local and Regional Geology . 3 Purpose of the Investigation 5 Review of the Literature 6 Camsell 6 Bostock 7 Bi l l ings ley and Hume 7 Dolmage and Brown 9 PETROLOGIC DESCRIPTIONS 13 General Description of Material Studied . . 13 The Flange Dike 15 The Midway " S i l l " 18 The Sunny side No. 3 Dike 19 The Mine S i l l s 20 TABLE SHOWING MINERALS PRESENT IN EACH SECTION . 24 BIBLIOGRAPHY . . . " 26 APPENDIX A (PETROGRAPHIC DESCRIPTIONS) . . . . A l ( i) 'ACKNOWLEDGEMENTS• The writer i s indebted to A. E. Eul ler for suggesting the problem and for offering many helpful ideas on how best to solve i t . The geological staff at the Nickel Plate mine are to be thanked for col lect ing the specimens and for supplying the map of locations. Dr. H. C. Gunning and Dr. K. DeP. Watson of the Depart-ment of Geology and Geography at the University of B. C. gave advice and help unstintingly. Dr. L . D. Mantuani's precise' determinations of plagioclases also deserve many thanks. F ina l ly , the writer wishes to thank the Kelowna Exploration Co. Ltd. for permission to carry out the investigation and for their generosity i n supplying the writer with thin sections,•maps, and specimens. C A N A D A D E P A R T M E N T O F M I N E S A N D R E S O U R C E S M I N E S A N D G E O L O G Y B R A N C H B U R E A U O F G E O L O G Y A N D T O P O G R A P H Y L E G E N D 120° 15' 4 9 ° 3 0 T ~ M O D E R N y o r u U T E R T I A R Y Alluvium Chiefly basalt and andesite,- breccia and tuff 1 2 Conglomerate, sandstone J U R A S S I C AND (OR) Y O U N G E R 1 1 | Granite 1 0 Granodiorite I Diorite, gabbro T R I A S S I C (?) I20°OO' 49°30' T R I A S S I C y o o< (/) UJ 2 WOLFE CREEK FORMATION: andesite and basalt; breccia and tuff,- minor sediments HENRY FORMATION: black argillite, tuff, impure limestone HEDLEY FORMAT/ON: limestone, quartzite, cherty quartzite, argillite, conglomerate; breccia, tuff SUNNYSIDE FORM ATI ON: limestone REDTOP FORMATION: limestone, cherty quartzite, siliceous argillite, tuff, some breccia T R I A S S I C AND (OR) O L D E R INDEPENDENCE FORMAT/ON: chert, chert breccia, cherty quartzite, cherty argillite; basalt and andesite flows and breccias BRADSHAW FORMATION: black argillite, tuff, quartzite, breccia; some andesite and limestone Area of continuous overburden '::'.•.•:•.'•.:•:.•'.•::::: Geological boundary (defined, approximate, assumed) ~~ • ••" Fault (defined, approximate) WWWVN Glacial striae Fossil locality © Mine tunnel ~"' Road well travelled Road not well travelled Trail Power transmission line ——•—•—— Power transmission line along road • »—*— Land District boundary Indian Reserve boundary Stream (position approximate) -Intermittent stream Sand bar ^•saaiBBv-Marsh C££?-4& Contours (interval IOO feet) ^ - s o o o - g Contours (position approximate) Height in feet above Mean sea-level S 7 6 4 ' 8 Undivided Geology by H S. Bostock, 1926-1930; and by D.A.McNaughton, 1937. Base-map prepared by the Topographical Survey, 1937, from maps supplied by the British Columbia Department of Lands. Cartography by the Drafting and Reproducing Division, 1940. so" 49i5 120 15' P U B L I S H E D i t s ^ o 49 15' l20°oo' M A P 5 6 8 A H E D L E Y ^ ^ ^ ^ W ^ ^ ^ i * S I M I L K A M E E N A N D K A M L O O P S D I S T R I C T S L £ 3 , 0 2 B R I T I S H C O L U M B I A S c a l e , 6 3 , 3 6 o o r I Inch to I M i l e M i l e s Approximate magnetic declination, 24°East. DESCRIPTIVE NOTES The gold deposits of Nickel Plate mountain commenced production in 1904. For several years thereafter they included, in the Nickel Plate mine, the single largest gold producer in Canada. Total gold production to 1927 was valued at over $11,500,000. Silver and arsenic were also recovered. In recent years the Nickel Plate and Hedley Mascot mines have each produced between 20,000 and 30,000 ounces of gold. The Nickel Plate mountain deposits have been generally described as of the contact-metamorphic type. The ore occurs mainly in sediments near the contacts of gabbro and diorite. Gold values are associated chiefly with abundant arsenopyrite and to a lesser extent with other sulphides of which chalco-pyrite and pyrrhotite are most conspicuous. The gangue con-sists mainly of metamorphic, lime-silicate minerals including garnet, pyroxene, amphibole and a little axinite. The position, shape, and size of the ore bodies are controlled partly by structural features. Partly too, calcareous argillite and quartzite have proved more susceptible to mineralization than other strata. The producing ore bodies and most of the prospects are associated with bodies of diorite and gabbro strongly suggest-ing that they owe their origin to them but similar deposits are associated with granodiorite and veins carrying similar minerals cut granodiorite dykes. Areas containing diorite and gabbro bodies are believed to offer most promise but the areas adjacent to the granodiorite should not be ignored. Gold prospects having the same minerals have been found in Mesozoic strata along the borders of Similkameen valley. Mineral deposits were also noted in the vicinity of the mouth of Whistle creek; near the diorite stock on the east fork of Whistle creek; in the sediments on both sides of the granodiorite south of Johns creek; and in areas of Mesozoic strata north of Winters creek. The areas of undivided Mesozoic formations southwest of Hedley, between Henry creek and the granodiorite, and the area on the west side of the upper part of Hedley creek contain strata similar to those of the Hedley formation which have proved receptive to min-eralization. An area of Mesozoic and earlier stratified rocks extends from east of Okanagan valley west to Princeton. It is cut by intrusives and partly covered by Tertiary rocks but as a whole forms a nearly continuous belt. It is divisible into four irregular segments each composed of a group of rocks that on the whole is younger than that forming the adjoining segment to the east of it. Gneissic rocks of Palaeozoic age lie along Okanagan valley and form the easternmost segment. To the west of this, between the Okanagan and Similkameen valleys near the International Boundary is a segment occupied by a group of rocks of late Palaeozoic age. To the west of this and extending northwesterly along Similkameen valley to Winters creek in the present map-area, is a third segment underlain by a group of several closely folded formations forming a complex synclinal structure. A fossiliferous Permian limestone near Blind creek is believed to be the lowest member of this group on the east side of the structure; on the west side the lowest members are the Brad-shaw and Independence formations. Some fossils of doubtfully Mesozoic age were found in the Independence formation. The strata of this third segment are thus believed to be either of Permian age or Permian and younger. To the westward of these rocks is the fourth segment occupied by another group of for-mations including the Redtop, Sunnyside, Hedley, Henry and Wolfe Creek formations. The rocks of this, the fourth segment are separated from those of the third segment by faults and bodies of intrusive rocks lying along a northeast line passing through Winters creek. Triassic fossils have been found in the Hedley and Henry formations of this group and all the strata are presumably Triassic or younger. They are closely folded but dip mainly west while the Bradshaw and Independence formations and those directly east of them dip mainly east so that the line through Winters creek seemingly follows the axis of a large broken anticline the eastern limb of which has been lifted up relatively to the western limb. The formations of the third segment, with the exception of the Bradshaw and Barslow formations which may be the same, contain a great deal of chert and cherty quartzite. This is true of even those members mainly composed of greenstones. Most of the chert beds are bounded by irregular, undulating surfaces and are separated by thin beds of argillite. There is relatively little fine-grained tuffaceous material among them and most of the volcanic rocks of this group of formations are greenstones consisting of flows and of flow breccias in which the matrix shows flow structures and the fragments are conspicuous. A few massive limestone lenses or patches of limestone breccia are among them. The Bradshaw formation contains much argillite and fine tuff and little chert. Its beds are bounded by even surfaces and in general it resembles the formations to the west but it definitely underlies the Independence formation. To the west of the anticline in the fourth segment, fine tuffaceous and argillaceous material is present in all the formations and all except the Wolfe Creek formation contain calcareous beds. The sediments characteristically are evenly and thinly bedded. The volcanic rocks as a whole appear to be slightly more acid and feldspathic than those to the east and much tuff and coarse fragmental material is present. In the breccias flow structure is not a common feature and the fragments are often difficult to distinguish. The formations of the fourth segment are not so closely folded as the strata to the east. O l d i M A P O F N I C K E L P L A T E & M A S C O T M I N E S S H O W I N G L O C A T I O N OF S P E C I M E N S 5ct>le I "-= 6 O O ' teW. A*? To accompany then't by J.W-Lcc ^ 3 i ^3 April , A PETROORAPHIC STUDY,OF PORPHYRY INTRUSIVES AT HEDLEY, B.C. INTRODUCTION  Location The Nickel Plate mine i s on the east side of Nickel Plate Mountain about 6 0 0 feet below the summit. The main p o r t a l and mine camp are at an elevation of 5 6 O O feet above sea l e v e l . An a l l - y e a r road connects the mine with the town of Hedley, 4 0 0 0 feet below i n the S i m i l -kameen Valley. Via the Southern Trans-Provincial Highway, Hedley i s 2 3 miles from Princeton and 5 0 from Penticton, both of which are on the Kettle Valley l i n e of the Canadian P a c i f i c Railway. Hedley i s also the northern terminus of a Great Northern Railway spur l i n e coming from O r o v i l l e , Washington, v i a Keremeos. The Similkameen River near Hedley flows i n a deep U-shaped v a l l e y with dry grassy benches along the va l l e y f l o o r , sparsely wooded lower slopes, and upland regions covered with dense jack pine f o r e s t s . The r e l i e f i s s t r i k i n g , as much as 6000 feet over distances of a few miles. The climate i s t y p i c a l of the southern i n t e r i o r of B r i t i s h Columbia, l i g h t t o moderate p r e c i p i t a t i o n , f a i r l y hot i n summer, and usually cold i n winter. History The mining h i s t o r y of the Hedley camp dates from the l a t e 1860 Ts when placer gold was f i r s t panned from Hedley Creek. Not u n t i l 1894 were the f i r s t lode claims staked on Nickel Plate Mountain and of the claims held at present, the oldest were recorded i n 1897 . The Yale Mining Company operated the mine from 1904 to 1909, the Hedley Gold Mining Company from 1909 to 1930, and from 1934» the Kelowna Exploration Company. In 1936 the Hedley Mascot Gold Mine began extracting ore from the Mascot Fraction and since then the Hedley camp has had two active mines. The t o t a l value of gold produced to the end of 1948 amounts to approximately $37,500,000 of which the Mascot supplied $8,000,000. Local and Regional Geology The Nickel Plate formation (also known as the Hedley formation) i s part of a block of T r i a s s i c (Bostock, 1 9 3 0 , p20AA) sedimentary rocks that extend north and east f o r about f i v e miles from the town of Hedley. In t h i s panel of sediments, the structure trends north-northeast i n contrast to the p r e v a i l i n g northwest structure of the older Palaeozoic rocks to the southeast. The s t r a t a on Nickel Plate Mountain dip roughly west at about 3 0 degrees The contact with an underlying body of younger granodiorit also dips west but at a f l a t t e r angle than the beds. A l l the chief ore deposits l i e i n the Nickel Plate formation. The productive s t r a t a are interbedded limey a r g i l l i t e s and limestones that are l a r g e l y recrys-t a l l i z e d to a garnet-diopside-epidote-calcite skarn i n the v i c i n i t y of the mine. The term, nSkarn Bowl", has been used to describe the bowl shaped trough of s i l i c a t e a l t e r a t i o n that transects the bedding steeply at the north and south sides and whose bottom dips west at approxi-mately the same angle as the sediments. Following any in d i v i d u a l bed out of the Skarn Bowl, one notices a more or l e s s sudden disappearance of s i l i c a t e minerals and a corresponding increase of calcareous material. This t r a n s i t i o n zone from skarn to unaltered limestone i s usually referred to as the "Marble Line". 4 The Nickel Plate formation i s intruded by numerous dikes and s i l l s that are usually poophyritic and range i n composition from d i o r i t e to gabbro. Two of these have been named the Flange dike and the Midway " s i l l " (or, at the Hedley Mascot mine, Central dike and Hot " s i l l " ) . The Flange i s a v e r t i c a l dike that coincides with the main axis of the p r i n c i p a l ore bodies; the Midway, a s l i g h t l y crosscutting " s i l l " that l i e s j u s t below the ore bodies i n the upper part of the mine and p a r a l l e l s the ore closely i n the lower part as w e l l . The ores are bedded replacements of medium to coarse-grained skarn by auriferous arsenopyrite. Ore deposition has been controlled by (a) proximity to the Marble Line, (b) crotches at the intersections of dikes and s i l l s , and (c) axes of northwesterly trending crumples. Dolmage and Brown claim the ores to be g e n e t i c a l l y associated with the Toronto stock, a d i f f e r e n t i a t e d i n -trus i v e about a mile long and h a l f a mile wide on the west slope of Nickel Plate Mountain. Usually, neither lime-stone nor porphyry i s s u f f i c i e n t l y mineralized to make ore. Pyrrhotite i s an extremely widespread mineral on Nickel Plate Mountain; one might say i t i s as ubiquitous as i t i s worthless f o r i t never c a r r i e s commercial values. 5 Purpose of the Investigation Geologists at the Nickel Plate mine believe they can di s t i n g u i s h certain porphyries by megascopic examination. B u l l e r (1949) says: "There i s a decided and mappable difference i n appearance between the Flange and adjacent s i l l s i n most places. The former appears b l u i s h , mottled and r e l a t i v e l y h o l o c r y s t a l l i n e whereas the s i l l s may be bleached almost white, or be unbleached, but they are always shades of grey i n color and po r p h y r i t i c . Why the difference? I s i t due to o r i g i n a l texture and/or compositional differences or to a l a t e r a l t e r a t i o n which has affected the two d i f f e r e n t l y , or to a greater degree i n one case than the other? In either case what may be the significance of the difference i n terms of structure and/or ore control?" This describes a problem of e s s e n t i a l l y the paragenesis of the porphyry constituents i n r e l a t i o n to ore. The wr i t e r , therefore, undertook to examine a num-ber of t h i n sections of Flange and s i l l porphyries i n an attempt to discover any features or q u a l i t i e s peculiar to e ither type of porphyry that would throw some l i g h t on the ultimate o r i g i n of the ore and i t s controls. In an in v e s t i g a t i o n of t h i s nature i t i s important to r e a l i z e that the value of the conclusions must depend on the completeness of coverage as we l l as 6 the accuracy of the work. The samples to be studied must be carefully chosen with a view to the elimination of as many complicating factors as possible. Even so, normal variations i n texture, composition, and al terat ion of one s i l l or dike may not be distinguishable from abnormalities i f too few specimens are taken. The number of thio sections studied was re-str icted by the l imited time available. Furthermore, the unusual mineralogy and high degree of al terat ion necessitated a considerable period of i n i t i a t i o n , re-ducing the time spent effectively almost more than the complexity of the problem permits. Dolmage and Brown have shown that a s t a t i s t i c a l study of hundreds of thin sections i s necessary before hypotheses concerning or ig in and al terat ion can be advanced. Consequently, the writer must confine his treatment of the problem mainly to a discussion of published reports and a comparison of his petrographic results with those of others. Review of the Literature Camsell;-Camsell, after studying th in sections of ore, came to the conclusion that the sulphide and skarn minerals c rys ta l l ized together at some time shortly after the intrusion of the dikes and s i l l s (1910, p l 5 4 ) . He 7 recognized small inclusions of epidote, garnet, and diopside in idiomorphic arsenopyrite crystals as evidence of prior formation of those minerals but decided, on the basis of the intimate intergrowth of skarn and sulphides, that a simultaneous origin was the best answer to the problem. Camsell (pl76) believed that the garnet-epidote-diopside assemblage indicated formation under great pressure and consequently at considerable depth. B i l l i n g -sley, however, questions the concept of "deep-seated sources" and claims that no great depth of cover i s demon-strated for this or any other of several granitic plutons in the region (1941, P547). Bostock;-Convincing evidence that the sulphides are later than the silicates of the skarn was presented by Bostock (1930, p234A) who went on to say (p240A) that the late, untwinned, potash (?) feldspar described by Camsell (pl54) would be more easily explained i f one assumed the granodiorite to be the source of the mineralization. In spite of this and other factors favouring a granitic source, Bostock agrees with Camsell that the bulk of the available evidence points to a genetic association of the ores with the diorite-gabbro complex. Billingsley and Hume;-Billingsley and Hume (1941, p558) l i s t several lines of evidence that favour the growth of the porphyries 8 i n s i tu by rec rys ta l l i za t ion . Their studies of certain . low angle breccia sheets led them to believe that such zones could have offered ingress to hot f lu ids capable of rec rys ta l l i z ing the adjacent rocks. They suggest also that the granodiorite may have formed by granit izat ion and that a l l these thermal effects may be as recent as post-Oligocene. Various writers have postulated several periods of al terat ion i n efforts to explain the complex metamorphism. B i l l i ngs l ey believes that both the s i l i c a t i o n of the impure limey sediments and the alteration of the porphyries were effected at some time after the formation of the l a t t e r . Three stages of progressive replacement in the porphyries were demonstrated by Schmitt (Bi l l ings ley and Hume, 1941, p56l). "In stage 1, leuc-augite grows at the expense of o r ig ina l hornblende and augite, i f any. In stage 2, the secondary leuc-augite i s replaced by epidote, dipyrdte, pargasite, and sulphides; while or ig ina l labradorite or other plagioclase goes to s e r i c i t e , d ipyr i te , and carbonates. In stage 3, cracks are f i l l e d with leuc-augite, d ipyr i te , carbonates, ch lor i te , quartz (very l i t t l e ) , and arseno-pyr i te ." According to Schmitt, the most noticeable result 'of th is al teration i s the decrease of iron in the al terat ion products. B i l l i n g s l e y infers from th i s that the iron removed from the porphyries during the processes of recrys ta l l iaa t ion might have provided substance for the ore bodies and the abundant pyrrhotite. Since the auriferous arsenopyrite i s intimately associated with the dipyre and since both of these minerals always come early in any paragenetic sequence, i t i s apparent, according to B i l l i n g s l e y , that the gold was also in t ro-duced during an early stage of a l tera t ion . Dolmage and Brown:-Eblmage and Brown (1945) prefer to ascribe the changes in the porphyries part ly to deuteric pro-cesses and partly to post-magmatic al terat ion rather than to either contact metamorphism or hydrothermal action. In regard to th is they say (p5d): "The f i r s t i s ruled out by the fact that similar changes in the femic minerals have been d is -covered i n the unaltered limestones well below the Mar-ble Line: therefore, the same agency which caused the skarn al terat ion could not have been responsible for the changes i n the hornblendes and augites i n the s i l l s , unless there was another period of contact or thermal metamorphism of which no record i s elsewhere apparent." I f i t were a question of hydrothermal action, they claim, the phenocrysts and groundmass should be equally altered rather than the groundmass bearing the brunt of a l terat ion. Further, they noted l i t t l e alteration of feldspars and state- (p5d) that chlori te and se r ic i te , typ ica l hydrothermal minerals, are conspicuously absent. 10 Schmitt, however, described ser ic i te and chlori te as pro-ducts of the intermediate to late stages of al terat ion so that their "absence" i s l e f t i n considerable doubt. To the writer, i t seems log ica l that the groundmass should be affected more by hydrotherraal action than the phenocrysts. The exchange of substance between crystals and the permeating f l u i d depends d i rec t ly on the area available for reaction. Therefore, since the groundmass possesses a much greater surface per unit volume than the phenocrysts, i t i s reasonable to assume that i t should be correspondingly more altered, other things being equal. According to Dolmage and Brown, scapoli t izat ion was the most conspicuous result of postmagmatic a l terat ion. The development of the scapolite mineral, dipyre (Ma73 Me z ? ), seems to have, been guided by similar controls to those of the ore bodies, the Marble Line probably the most impor-tant. Dipyre occurs pr inc ipa l ly i n the porphyries and usually as a replacement of feldspars. In support of their bel ief that the gabbro-dior i te complex originated as a true magma rather than by grani t izat ion, Dolmage and Brown c i te a number of petrographic and petrologic c r i t e r i a such as porphyritic texture, zoned feldspars, resorbed phenocrysts, and systematic variations i n composition. They would make the source of the Toronto stock also the source of the magma that formed the porphyry s i l l s . The Toronto stock 11 contains a cap of gabbro and augite-diorite that gradually grades into the main quartz d ior i te mass below. Though i t i s apparently a differentiated stock, the explanation of i t s or igin i s made d i f f i c u l t by the fact that the more basic phases are above the more sodic ones. Dolmage and Brown picture the upper magma layer as having assimilated considerable lime and magnesia from the sedimentary strata arched up and possibly brecciated by the force of in t rusion. This assimilation, they say, might produce a more basic capping. An. alternative, or possibly a supplementary, mode of or igin was postulated i n which the gabbroic capping would represent an enrichment of augite and labradorite brought about by f i l t e r pressing the late magmatic f l u i d out of a crysta l mush. Bowen (1923, p201) states that since the com-position of sedimentary rocks i s determined independently of igneous action, they do not correspond to any stage of the magma1s so l id i f i ca t ion and thus cannot be placed i n any reaction series. In view of this i t would be very unlikely for a rock mass that owed i t s differentiat ion primarily to the assimilation of sedimentary material to have a genuine systematic variat ion of composition, i . e . to exhibit l i q u i d l ines of descent that f a l l on smooth curves. Dolmage and Brown, unfortunately, had no suitable chemical analyses to guide them, and without analyses, studies of variations i n composition give at best only an approximation to the t ruth. Therefore, one should not 12 re ly too strongly on their c r i te r ion of systematic variation as proof of magmatic o r ig in . Furthermore, Bowen believes that only in rare instances i s a magma charged with enough.superheat to assimilate the quantity of foreign matter necessary to effect a signigicant change i n i t s composition. I t i s the writer*s opinion, therefore, that the evidence of systematic variations i n composition should not be.used to uphold a magmatic or igin as long as assimilation of sedimentary material i a accepted as the cause of these variat ions. The writer does not intend the foregoing statements to convey the impression that he disagrees with the magmatic hypothesis of Dolmage and Brown. On the contrary, his c r i t i c i sm i s directed only against cer-ta in c r i t e r i a used by them to support their views. The writer would possibly have emphasized the zoning of f e ld -spars more than Dolmage and Brown. 13 PETROLOGIC DESCRIPTIONS General Description of Material Studied Samples of several types of porphyry intrusives from the Nickel Plate mine were carefully chosen to give a broad coverage. Five specimens of Flange dike, three of Midway " s i l l " , two of Sunnyside No. 3 dike, and four of mine s i l l s were examined i n de ta i l both megascopically and microscopically. In addition, several other samples were studied i n a general way. A l l the samples are from bodies of rock that show definite intrusive relationships to the enclosing strata. Even though most of the s i l l s are con-cordant they are a l l found to cut the bedding i n d e t a i l . The defini te ly crosscutting bodies are structural ly re-lated to ore inasmuch as no important ore has yet been found without the association of a crosscutting dike and the marble-skarn t ransi t ion zone. The data concerning location, geological relat ions, and significance of each sample, as l i s t ed i n Appendix A were supplied by A. E. Bul ler (1949), chief geologist at the Nickel Plate mine. The colour of each hand specimen was compared to the Rock Colour Chart of the National Research Council, Washington, D.C.. The very s l ight differences i n hue, 14 chroma, and value make i t impossible to describe the colours appropriately with ordinary terms. The notations used, however, enable one to describe accurately a d is t inc t ion of colour as fine as one can observe. Four specimens were spectrographed by R. G. McCrossan and only a br ief inspection sufficed to show that there were no strong indications of rare elements. This ruled out the poss ib i l i t y that some of the sphene might actually be monazite. The Flange Dike 15 A l l Flange specimens were o r ig ina l ly either hornblende andesite porphyries or hornblende d ior i te por-phyries. The phenocrysts of plagioclase are generally zoned.and are composed of intermediate to basic andesine, A b 5 o - Ab f e 0 • Hornblende was by far the most abundant mafic mineral in the or ig ina l rock, i n fact only one section contains evidence for primary augite. The hornblende occured as euhedral, prismatic phenocrysts. Apatite i s an accessory common to a l l sections. Euhedral, hexagonal grains and stubby prisms of i t remain fresh even i n the most altered sections. The feldspar phenocrysts vary i n shape from subhedral to euhedral and constitute about 30 per cent of each rock. Widespread al terat ion to kaol in , se r i c i t e , sphene, and, i n some places, ca lc i te gives the sections a clouded, confused appearance. In many grains the chief al terat ion i s internal , i n other peripheral. The andesine phenocrysts i n several sections are partly replaced by quartz and, in one section, by late a lb i t e . Tremolite porphyroblasts have developed as pseudomorphs after the euhedral hornblende phenocrysts. The new mineral has approximately a pa ra l l e l orientation to the old but i s colourless and usually contains abundant inclusions that produce a sieve texture. In several grains a pa r t i a l replacement of the tremolite by b io t i t e 16 or by pyrrhotite i s shown. In only one section i s there even a suggestion of primary augite. Section 3 contains a few phenocrysts of colourless augite that d i f fer from the usual, narrow hornblende crystals and yet do not have typ ica l ly pyroxene outl ines. In shape, these grains resemble the andesine phenocrysts but no feldspar else-where i n the section i s replaced by augite. Cataclastic structure i s not shown by any of the groundmass or the feldspars but several grains of tremolite are apparently pseudomorphous after broken and bent hornblende pheno-crysts. These may have been caused by stress i n the rock prior to complete so l id i f i ca t ion or by the hornblende grains jos t l ing one another i n a moving crysta l mush. No uniformity of the groundmass minerals i s indicated by the refractive index tests . These show in a l l sections at least some groundmass with n<-bals though in three, the greater part of the groundmass has n ^ b a l s . A certain amount of a l k a l i feldspar, therefore, i s probably present i n each specimen as a constituent of the ground-mass. Scapolite i s re la t ive ly abundant i n 3 and also occurs sparsely i n 1. Sections 2, 3 , and 11 are- normal Flange types. From underground mapping, 1 may be s i l l rather than Flange but microscopically i t i s very similar to 2, 11, and 15, both i n or ig ina l composition and in response to a l terat ion. The chief difference between 15 (possibly a s i l l ) and 14, a very near s i l l , i s i n the composition of the plagioclase 17 phenocrysts. In 15, these are A b 5 5 , i n 14, Ab 4 0 . Both , rocks o r ig ina l ly had hornblende either as the pr inc ipa l or only mafic mineral. The hornblende in 15 i s ent irely altered to tremolite whereas i n 14 i t i s only partly altered and the al terat ion product i s colourless augite. Both sections are s l i gh t ly a lb i t ized and both contain minor b i o t i t e . Scapolite, c l inozo i s i t e , and ca l c i t e , which are present i n 14, are either not present in 15 or obscured by the intense kaolinizat ion and s e r i c i t i z a t i o n . The writer, i f given a choice for 15 of either Flange or s i l l , would favour Flange, especially i f the comparison was with a s i l l l i ke 14. No cause was found that would account sa t i s -fac to r i ly for the persistent bluish colour of Flange specimens. The unknown blue mineral i n 1 may have some effect but i t occurs i n such minute amounts that unless very much more of i t i s present i n sub-microscopic par-t i c l e s i t could not impart even a weak colour to the rock. Quartz i s the only mineral found exclusively i n Flange specimens but i t i s extremely unl ikely to be the colouring agent, the more so because i t i s absent from one bluish specimen. The colour, therefore, must be caused either by some eccentrici ty of the feldspar or of the tremolite, or by some f inely divided mineral s imi-l a r to the dendritic blue aggregates occurring i n 1. 18 • The Midway " S i l l " . The composition of plagioclase phenocrysts i n Midway specimens varies within f ive per cent of A b 6 0 A n ^ 0 , intermediate andesine. Zoned crystals are common and al terat ion to kaolin and ser ic i te i s considerable, especially i n 19. No uniformity of groundmass feldspars can be claimed since refractive indices both above and below that of balsam were found. Nowhere i s there any positive evidence of primary augite but pseudomorphs of secondary augite and of tremolite after hornblende are common. The p o i k i l i t i c texture observed in 17 may help explain the sieve texture of the tremolite and augite grains. The sections with much colourless augite also contain secondary albi te (?) . Sphene and apatite occur i n a l l specimens and i n 8 (1) sphene i s par t icular ly abundant. In spite of the fact that much high grade ore i s found near these specimens, scapolite, i n very minor amount occurs i n only one section, 8 (2). Sample 16, according to one interpretation of the geological sections of the mine, i s Midway " s i l l " . . The petrographic data, though they are not too convincing, disagree with th i s conception. Compared to typ ica l Mid-way material, 16 contains a more basic, plagioclase, A b 5 o An, ; a higher percentage of scapolite (scapolite content 19 probably varies l o c a l l y ) ; and abundant colourless augite but no secondary albi te as i n 8" (1) and 8 (2). The Sunnyside No. 3 Dike Samples 6 and 7 are very s imi lar . The ground-mass of each has n<bals and i n both the hornblende i s altered to augite and tremolite. Both also contain scapolite but i t i s par t icular ly abundant i n 7 . Zoning cannot be seen in the feldspars of either section but i n 6 i t could easi ly have been obscured by a l tera t ion . The feldspars i n 6 are def ini te ly more altered than those i n 7 and c l inozois i te i s lacking in 7« The labradorite (?) i n 6 i s possibly a much more calc ic feldspar than that i n 7 but i t s determination i s somewhat doubtful owing to the strong a l tera t ion. On the whole, 6 and 7 appear to be similar enough, par t icular ly with regard to mafic a l terat ion, to be classed as the same dike. They resemble 3 and 1 7 , Flange and Midway respectively, i n that they contain both tremolite and augite whereas the rest of the specimens have either one or the other. 20 The Mine S i l l s Like the rocks discussed before, a l l the mine s i l l s are either meta-andesite porphyries or meta-diorite porphyries except the very fresh specimen from the Mascot 3700 l eve l . Dealing f i r s t with 14, 16, and 18 (b); one notices that the plagioclase phenocrysts are mostly sub-hedral to euhedral and that zoning i s a common feature. Hornblende, i n euhedral, prismatic phenocrysts, was the primary mafic i n a l l sections. In addition to the .regular accessories, apatite and sphene, calci te and biot i te occur i n minor amounts. Scapolite and c l inozois i te occur i n both "14 and 16 but chloropal i s found only i n 16. The groundmass of each specimen probably contains some,alkali feldspar, since n<bals i n most instances. It i s worthy of note that tremolite i s conspicuously absent from a l l of these mine s i l l s . The plagioclase phenocrysts vary i n composition from Ab^0 to Ab 6 5 . Except 18 (b), which i s without se r ic i te , the feldspars are altered to kaol in , se r ic i t e , ca lc i t e , and sphene. In 18 (b), augite pa r t i a l l y replaces large andesine crystals as well as parts of the groundmass. In the same section, andesine i s part ly replaced by secon-dary albite that also veins the groundmass. Only minor amounts of albite occur i n 14. Primary hornblende, part ly altered to colourless 21 augite and to brown b io t i t e , occurs i n 14. Several stages from par t i a l to complete replacement or recrys ta l l i za t ion are found i n this section (Appendix A, pA36)• However, i n 16 and 18 (b), a l l hornblende has been augltized com-plete ly . The fresh d ior i te porphyry from the Mascot 3700 level i s basical ly about the same as the other s i l l s but i t lacks most of the al terat ion that has affected them. The greenish brown hornblende phenocrysts, however, are s l ight ly altered to b iot i te and to colourless augite. The b io t i te occurs as shreds along cleavage planes, the augite, as narrow reaction rims. The plagioclase crystals vary i n size almost enough to give the rock a seriate rather than a porphyritic texture. Most of the grains are well twinned and many are also zoned. Alterat ion of either groundmp.ss or phenocrysts i s negl igible . The writer i s most fortunate to have obtained from Dr. L. Dolar-Mantuani (1949) a number of very precise determinations.of the plagioclases i n this section. These results were obtained by using the Fedorov universal stage and consequently are of an accuracy far superior to that of ordinary petrographic work. The following table l i s t s the percentage of An of the various parts of (A), the largest phenocryst; (B), a smaller phenocryst; (C), a grain somewhat larger than the groundmass; and (D), the groundmass. Core refers to the innermost part of a crys ta l ; border, the main part around 22 the core; and periphery, the outermost th in she l l . A B C D Core 83 70 64 ' 30 Border 73 Periphery 37 4-6 48 Veinlets inside 35 Each figure i n the above table represents an average of several determinations; for instance some parts of the core in (A) reached A n Q 7 , others were as low as A n e o . These data are i n complete accord with what one would expect of a rock that had formed from a true magma. Basic bytownite, forming the core of the largest phenocryst, was the f i r s t plagioclase to c rys ta l l i ze from the magma. The border part of (A), acidic bytownite, was already well developed when the core of the smaller phenocryst, (B), began to form. Grains of the size represented by (C) began to c rys ta l l ize soon after (B). At that time, the phase separating from the melt was basic labradorite. The largest phenocryst possesses a very thin shel l of composition A n 3 7 . The grains (B) and (C) may also have such rims but i f so, they are too narrow for separate determination. The veinlets inside the crystal (C) have about the same composition as the phase i n equi l ib-rium with the melt when the periphery was formed. The 2 3 oligoclase-andesine groundmass i s the f ina l product of c rys ta l l i za t ion . Thus we have, a complete sequence of c rys ta l l i za t ion beginning with basic bytownite i n the core of the largest phenocryst and ranging through inter-mediate and basic labradorite i n the smaller phenocrysts to acidic andesine i n the groundmass and late veinlets of the large grains. • • Minerals 1 2 Sections 3* 11 15' 8(1) s:(2) 17 Plagioclase 40 30 20 45 30 25 10 30 Hornblende - - - - -' - -Tremolite 15 15 15 5 15 - - -Augite - - 5 - - 15 20 2 Sfiapolite ? - '5 - - ? 1 -Sphene 1 1 - - 1 2 1 1 Apatite 2 1 1 1 1 1 1 -Quartz 2 2 - 2 - - - -Calcite - ? 1 1 - 1 - 2 Eiot i te 1 1 - - - - - -Albite - - - - 1 1 -Clinozolsi te - - 1 - - - - 1 Epidote - - 1 1 - ? - -Actinol i te - - 1 - - - - 2 Chlorite - - - 1 - - - -Chloropal - - - - - - - -Kaolin y y • Serici te • y y y • • Sulphides P P C,PJA P..3 P" P P,A -Grroundmass (n) > < > < P" Pyrrfcotite A Arsenopyrite r i C 6halcopyrite TABLE SHOWING MINERALS PRESENT IN EACH SECTION Minerals Sections l8Cb) 21 19 6' 7! 14 16 Plagioclase 15 20 35 35 10 10 40 Hornblende - - - 20 - - 15 Tremolite 10 15 10 - - -Augite - 5 3 2 10 30 3 Scapolite - 1 5 2 5 - -Sphene 1 1 . 1 1 1 2 -Apatite - 2 1 1 1 1 I Quartz - - - - - - -Calcite - 1 - 1 1 1 -Biot i te - - - 1 1 - 1 Albite - - - 1 - 5 -Clinozoisi te ? 1 - 1 1 - -Epidote ? - - - - 1 -Actinol i te - - - - - - -Chlorite - - - - - - 1 Chloropal - - - - 2 - -Kaolin y y y y Serici te • y y y Sulphide s - p P.C C P,0 - P . vGroundma s s (n) < cf. n bftls BIBLIOGRAPHY-BIllingsley,P.and Hume,C.R.!C(194l) TJhe ore deposits of Nickel Plate Mountaln.Hedley,B.C.Can. Irist. Min.. and Met. Trans.., v o l . 44, p5 24-590. Bbatock,Hr,S.. (1930) Geology; and ore. deposits of Nickel Plate Mountain, Hedley,F.C.. Geol.. Survey* Can.., Summ. ReptJ.. 1929, pt.A, p 198,-25:2A.. BowenjN>;L.. (1928) The evolution of the igneous rocks,. Princeton University Press. Buller,A.E..(1949) Personal communication.. Camsell,.C. , (1910) The geology and ore deposits of the Hedley-Mining; D i s t r i c t , B r i t i s h Columhia, Geol. Survey Can., Mem. 2. Do Image, V i . andKfown-iC. E.G. (1945) Contact metamor-phism at Nickel Plate Mountain, Hedley, BriC.Can. Inst. Min. and"..Met. Trans.,vol. 48, p27-67. Mantuani,L.D..(1949) Personal communication. Schmitt,H..(1933) Communication to Kelowna Explor-ation Co. Ltd. APPENDIX A L i s t of Abbreviations and Symbols Ab albite absorp absorption An anorthite bals Canada balsam biax - b i ax ia l c - ver t i ca l crystal axis £ - epsilon, index of refraction of extraordinary ray ext - extinction in ter f - Interference 1-fast - elongation para l le l to the vibration direct ion of the fast ray 1-slow - elongation para l le l to the vibration direct ion max - maximum mod - moderate u> - omega, index of refraction for ordinary ray n - index of refraction n* - least n n^ - intermediate n - greatest n n e - n for extraordinary ray n^ - n for ordinary ray of the slow ray r dispersion for red l igh t sect (thin) section X sect cross section v dispersion for v io le t l i gh t 2V angle between optic axes X vibrat ion direct ion of the fastest ray Y - vibration direct ion of the intermediate ray Z - vibration direction of the slowest ray 010, 001, etc - M i l l e r indices of crystal faces A - angle JL - normal to H - pa ra l le l to > - greater than < - less than (+) - opt ica l ly positive (-) - opt ica l ly negative +_ - approximately A. Loc. - Location of specimen B. Geol. Rein. - Geological relations i n the v i c i n i t y from which the specimen i s taken. C. Signif. - Significance of the specimen; reasons for choosing i t ; suggested comparisons to other specimens. (5GY4/1) Designation of colour as given i n the Rock Colour Chart of the National Research Council, Wash., D.C. SECTION 1 A. Loc. ; A 07 d r i f t , 6 f t . from N contact. B. Geol. Rein; This specimen i s from a peculiar bulge or stubby thick s i l l extending outward from the Flange but separated from i t by a faul t . Ore occurs above and below it.. C. S ign i f . ; The rock i s probably Flange but may be s i l l . D. Hand Specimen Sample No. 1 i s a dark greenish gray (5G4/1) porphyritic rock with an aphanitic groundmass. Phenocrysts, up to several mm i n length, of l a t h - l i ke , str iated fe ld-spar with random orientations are uniformly distributed i n the aphanitic groundmass. Pyrrhotite and lesser amounts of chalcopyrite and pyrite and f inely disseminated through the specimen but are noticeably more concentrated along fractures and joints . No mafic minerals are v i s i b l e . E. Thin Section Minerals Present Est. j> • Characteristics Andesine 40 biax (+), max ext/\_L010 23° n>bals (1.55); Ab 6 6 A n + 0 Tremolite 15 biax (-), 2V 70* ± , 1-slow, n^bals (1.63), Z A c l l " -14* , long diagonal of X sect = slow ray> generally colour-less but s l igh t ly greenish A2 Minerals Present Tremolite Cont'd. Biot i te E a t . % Apatite Quartz Sphene Scapolite (?) Serici te Kaolin Pyrrhotite Blue mineral Groundmass 37 Characteristics . i n places verging towards ac t ino l i t e . tan colour, pleochroic, max absorp / / polarizer, 1-slow, mod biref . n >bals (1.60), euhedral grains, colourless, low biref . uniax (+), low biref , low re-l i e f , n> bals. apparently uniax (+), high biref , n * 1.7+. 1-fast, mod biref , n=1.55t, small platy grains. 1-slow, low re l i e f , low i n -terf colours, fibrous, colour-less, small grains, opaque, white, associated with feldspar. opaque, bronze colour s l igh t ly pleochroic blue to colourless, dendritic struc-ture, n y bals (1.57), low i n -terf colours, 1-fast, +; / / ext. some n< bals, may include a l -k a l i feldspar. A3 Description The plagioclase v i s ib le i n the hand specimen proves to be andesine of about AbgQ An^ composition. Most of the phenocrysts are euhedral and have more or less well preserved twinning lamellae. Some grains show a faint zoning, others contain abundant inclusions. Incipient al terat ion clouds even the freshest grains and i s often responsible for an apparent zoning by affecting either internal or peripheral regions more than the rest . Plagioclase feldspar also occurs i n the groundmass as laths less than 0.04 mm long. These are altered too much to be ident i f ied . Several crystals of andesine have been partly re-placed by quartz that has worked i n along the cleavage to form irregular elongated blebs. Other inclusions common i n the feldspar grains are apatite, sphene, numerous streaks of se r ic i t e , and occasional, irregular blebs of. sulphides. Tremolite occurs as pseudomorphs after hornblende phenocrysts and as irregular patches i n the groundmass. I t can be distinquished from scapolite by i t s positive elongation and incl ined extinction, from hornblende by i t s lack of colour and i t s extinction angle, and from augite by i t s refractive ' index and extinction angle. Though most of the tremolite i n this section i s colourless, some i s s l igh t ly greenish and pos-s ib ly should more correctly be cal led t remoli te-act inol i te . One elongate grain i s d i s t inc t ly fractured but the enclosing groundmass shows no evidence of movement. Like the feldspar A 4 phenocrysts, tremolite also contains inclusions, some of which when augmented by small patches of al terat ion impart a sieve texture to small areas. A second stage of al terat ion i s indicated by small, anastomosing shreds and streaks of biot i te that have been introduced along the cleavage i n a few grains of tremolite. Apatite occurs i n hexagonal sections and i s stubby prisms which, under crossed nicols , appear black and dark grey respectively. A s t r ik ing feature of a l l the apatite i s i t s complete freedom from al terat ion. I t appears most frequently as inclusions i n phenocrysts of feldspar and re-placed hornblende. Pyrrhotite i s found sparingly over most of the section and i s rather large, Irregular masses close to para l l e l fractures about hal f an inch apart. Some tremolite pseudomorphs near the fractures are pa r t i a l l y replaced by irregular areas of pyrrhotite, producing a blotchy appearance but leaving l i t t l e doubt as to the shape of the or ig ina l cry-s t a l . Although chalcopyrite and pyrite were v i s ib le i n the hand specimen they could not be ident i f ied i n the thin sec-t ion . Irregular, somewhat globular areas of f a i r l y clear quartz i n clouded feldspar phenocrysts indicate a certain amount of s i l i c i f i c a t i o n . That the quartz invades the fe ld-spar i s shown by blebs of quartz elongated para l l e l to the feldspar cleavage. • A5 Accessory sphene i s usually enclosed i n the larger feldspar and tremolite grains. The r e l i e f of this mineral seems rather low and the acute rhombic sections characteristic of sphene are very rare. However, the mode of occurrence i s def ini te ly that of sphene. Scapolite may be present but i f so, i t Is a very minor constituent. A few platy grains, too small to give an interference figure, showed para l l e l extinction, negative elongation, and appeared to have the correct birefringence and r e l i e f for scapolite. In much of the feldspar, fine, fibrous shreds of ser ic i te can be seen though i t forms, a rather small percen-tage of the s l ide . Similar ly a part of the feldspar i s kaollnlzed but i t i s d i f f i c u l t to judge exactly how much is kaol in. A blue pleochroic mineral was observed i n two small dendritic aggregates consisting of minute, r ad ia l , prismatic crystals . Except that the index of refraction was too low, the properties of this mineral agree' quite well with those of crocidol i te . However, an interference figure could not be obtained so the name must remain in. doubt. Since i t has blastoporphyritic and sieve textures and since the andesine and former hornblende phenocrysts com-prise more than 50 per cent of i t s volume, the rock should be called meta-diorite porphry. A6 SECTION 2 A. Loo.; 431 d r i f t , 2 f t . from N contact. E l . 5450. B. Geol. Rein. : This dike specimen i s taken from the marble-skarn t ransi t ion zone. Nearby mineralization i s low grade ore. C. S igni f . ; Normal Flange type. D. Hand Specimen This rock i s a fractured, rusty-weathering porphyry made up of plagioclase phenocrysts i n an aphanitic greenish gray ( / ) groundmass. Pyrrhotite i s evident, par t icular ly along small fractures, and the presence of chalcopyrite i s suggested by occasional specks of malachite i n weathered jointsi E. Thin Section Characteristics Minerals Present Est, jo Andesine 30 Tremolite 15 Serici te 10 Quartz 2 Apatite 1 Sphene 1 Biot i te Tan mineral biax M max ext A JL 010 26°, Afe5o-A n 5 o Z/\c 12°-13°, same as tremolite i n section 1 1-slow, fibrous habit, low r e l i e f , mod bi ref normal quartz normal apatite normal sphene traces almost isotropic, pale tan, s l i gh t ly pleochroic, n<apatite. A7 Pyrrhotite 5 opaque, bronze, pock-marked surface Magnetite (?) . opaque, black, small, i rregular specks, chiefly i n former hornblende grains Unidentifiable groundmass - including some kaolin (probably) and possibly some carbonate. Description-It i s suspected that a l l the feldspar i s andesine because, although some of I t i s untwinned none has an index of refraction less than balsam. It i s altered i n places to kaolin and to se r ic i t e . Alterat ion most commonly proceeds from the Interior of crystals outward, leaving a rim of re la t ive ly clear material surrounding a dusty core of ser ic i te and kaol in . Other grains, however, consist of a fresh inner part and an altered she l l . Clear, zoned feldspars with very dis t inct (under crossed nicols) concentric bands also occur. Groundmass feldspar, as near as can be determined, i s of the same composition as the phenocrysts. As i n Section 1, evidence of stress i s shown by a single large tremolite grain that has been bent and then fractured. Other tremolite pseudomorphs after hornblende show the usual amphibole cross-section and blade-like p r i s -matic sections. Sphene i s less abundant than i n the f i r s t section; otherwise i t , apatite, and b io t i te occur i n much the same manner as has already been described. A8 Quartz, some of which replaces andesine, occurs sparingly i n only a few parts of the section. I t contains many small, rounded inclusions which serve to dist inguish i t from the feldspar associated with i t . A9 SECTION 3 A . L o c ; 633 d r i f t , 4 f t . from N contact. E l . 5310. B. G-eol. Rein. ; Medium grade ore occurs i n the v i c i n i t y . C. S ign i f . : Normal Flange type cutting Yellow ore. D. Hand Specimen Sample 3 i s a dark bluish gray (5B4/1), s l i gh t ly mottled porphyry with abundant phenocrysts of plagioclase and a few larger ones of somewhat bleached hornblende. The mottled appearance Is produced by irregular greenish gray (5G-Y6/1), bleached areas associated with old, tight fractures. Pyrrhotite and chalcopyrite are disseminated In minute flecks throughout the specimen and occur i n th in , vein- l ike concen-trations along some fractures. E. Thin Section Minerals Present Est. % Andesine 20 Tremolite 15 Colourless Augite 5-10 Clinozoisi te (?) Characteristics Ab twinning, max extAX 010 21°, biax (-+), Ab^An^ ZAc 15°-20°, 1-slow, n>bals (1.6+) Z/\c 40°, biax (-+-), 2V 50° direction of smaller ext i s slower ray, r e l i e f high (n>1.7), bi ref up to 0.027. anomalous bright blue in ter f colours, r e l i e f low for c l i n -ozois i te . A10 Apatite Act inol i te (?) 1 1 Calcite Serici te Kaolin Epidote (?) Unknown mineral Chalcopyrite G-roundmass 1 5 10 1 Pyrrhotite 2 Arsenopyrite < 1 « 1 30-55 normal apatite. Z A C 16°, n=1.59 , max bi ref 0.029, many rhombic sections (long diagonal slow) ZV90° , at least 1 good cleavage, normal calc i te "normal ser ic i te normal kaolin high relief; .mod to high, variable biref vermicular habit, also wider blades, biax (-+•), «V60°, colour-less to pale green pleochroism, ex t / / i n narrow shreds, 1-slow, XAc and Z A C i n other grains up to. 39° irregular grains sparse euhedral and subhedral grains, opaque, s i lvery , high r e l i e f . bright yellow, opaque, small grains. n<bals, very low r e l i e f , probably contains much a l k a l i feldspar A l l Description The andesine phenocrysts are subhedral to euhedral and vary i n size from 0.3 to 1.5 mm. Some show a pronounced primary zoning and a few convey the impression of zoning owing to internal s e r i c i t i z a t i on . Albite twinning i s wel l developed In most of the phenocrysts and i n some, poor gr id twinning suggests the poss ib i l i t y of microcline but such grains have an index of refraction d i s t i nc t l y higher than the ground-mass. The chief al terat ion i s to kaolin but ser ic i te and scapolite have also formed from andesine. Numerous inclusions and islands of al terat ion i n the phenocrysts commonly produce a texture similar i n appearance to sieve texture. Tremolite, pseudomorphous after euhedral hornblende phenocrysts, consitutes a considerable part of the section. Some of the hornblende was o r ig ina l ly twinned and the pseudomorphs s t i l l reflect this phenomenon. Other phenocrysts, probably of augite, have been i altered to colourless augite. These grains are noticeably clouded by al terat ion and only very small areas of clear mineral are available for interference figure tests. Deter-mination of optic sign therefore was very d i f f i c u l t and unreliable. Cl inozois i te , epidote or both occur sparsely as al terat ion products of andesine. The d is t inc t ive anomalous blue, f i rs t -order interference colours and the v a r i a b i l i t y A12 of birefringence i n grains showing higher colours attract attention to this mineral and, together with the high r e l i e f suggest either epidote or e l inozois i te . Neither cleavage nor elongated grains were observed so the- extinction angle, could not be measured. A few rather large areas of scapolite (3 mm.) and other smaller patches are formed chiefly at the expense of andesine phenocrysts. The usual sieve texture of the scapolite i s effected i n this instance by randomly oriented tremolite grains. Arsenopyrite shows a tendency to be associated with the scapolite and pyrrhotite with the ac t inol i te (?) and unknown vermicular mineral. Accessory apatite consitutes about one per cent of the section and occurs i n the groundmass and phenocrysts indiscriminately. Calcite occurs i n a few highly irregular grains near a part of the section where the feldspars are generally well s e r i c i t i zed . Prom this i t could be inferred that the al terat ion of plagioclase and, possibly, orthoclase supplied material for the calc i te and se r i c i t e . The groundmass probably contains a large proportion of a l k a l i feldspar as i t s index of refraction i s everywhere less than balsam and the r e l i e f i s so low as to make most.of i t almost disappear i f the nicols are not crossed. No plagioclase was seen i n the groundmass and no quartz or sphene could be ident i f ied . A13 A porphyritic texture has been inherited from the or ig ina l rock. Locally, sieve texture i s shown by several minerals, par t icular ly by porphyroblasts of scapolite and the larger tremolite and augite phenocrysts. Meta-andesite porphyry i s probably the best name for the rock since i t i s composed of less than 50 per cent phenocrysts and the remainder consists of aphanitic material. Addenda to Minerals Present Section 3 Scapolite 5-10$ uniax (-), in ter f colours middle f i r s t order, low r e l i e f , / / ext, 1-fast, sieve texture. A14 SECTION 11 A. Loe.t At 800 Station. E l . 5215. B. Geol. Rein . : ffrom Central fault zone with high grade ore nearby. C. S ign i f . : Unusually blue Flange dike material. D. Hand Specimen White plagioclase and somewhat bleached hornblende phenocrysts are. the only non-metallic minerals ident if iable i n the rock sample. The bluish-gray. (5BG6/1), mottled (5B7/1-5G5/1), aphanitic groundmass dominates the general appearance, the phenocrysts blending rather inconspicuously with i t . Very fine, irregular pyrrhotite grains are. dissem-inated widely throughout the specimen but are not noticeably concentrated along fractures. Instead, the fractures con-ta in a thin f i lm of whitish material that does not effervesce with cold di lute hydrochloric acid. The specimen has a strong kaolin odour. E. Thin Section Minerals Present Andesine Tremolite Apatite Quartz Est. % Characteristics 45-50 biax (+), max extA±010 23°, n>bals, Ab 6 0An 4 o 5-10 length slow,, ext A 6°-18°, r e l i e f high, n=1.64+, max in ter f colour second, order green, b i ref of 0.027 1 normal apatite 2 normal quartz A15 Epidote (?) <1 Calcite Chlorite (?) 1 <^  1 1-2 + 40 Max, 2V±90°, high r e l i e f n=1.7+, variable interference colours but most are not as high as they should be. normal ca lc i t e . mod r e l i e f , n=1.60, 1-fast, fibrous, wavy extinction, / / or small ext/l, low in ter f colours (bluish i n grays), semi-radiating aggregates, normal pyrrhotite normal ser ic i te normal kaolin mostly n>bals, but some n<bals Pyrrhotite Serici te Kaolin Groundmass Description Almost a l l ofthe plagioclase phenocrysts show albite twinning; many are well zoned, and a vew are almost ent irely altered to se r ic i t e . Strain twinning i n a few crystals may be an indication of deformation but this i s not reflected by any other structure i n the section. One zoned crystal with good twinning gave a difference i n extinction angles of five degrees corresponding to a variat ion i n A6 content of about 4 per cent, with the inner part more calcic than the outer. Sieve texture i s common to the larger tremolite phenocrysts and i n the smaller ones polysynthetic twinning i s poorly developed. The largest grain of tremolite i n the A16 section i s about 3 mm. long but the hand specimen contains several over 10 mm. A- narrow fracture has been f i l l e d with quartz, ca lc i te , epidote (or c l inozo i s i t e ) , and chlori te (?). Semi-radiating aggregates•of fine, fibrous chlori te (?) l i e pa ra l l e l to the fracture. Quartz also occurs elsewhere i n the section as anhedral grains up to 0.5 mm. i n diameter. I t can be distinguished by i t s c l a r i t y , i n contrast to the clouded feldspars, and by the presence i n i t of minute, round inclusions. The groundmass contains a few plagioclase laths that are altered too much to allow positive ident i f ica t ion . Most of the groundmass has an index of refraction higher than balsam but at least some has a lower index. The rock has a blasto-porphyritic texture produced by the altered phenocrysts of andesine and hornblende i n an aphanitic groundmass. Sieve texture i n the tremolite porphyroblasts i s common. Since the phenocrysts constitute 50 to 60 per cent of the section, and since the groundmass grains are mostly below 0.5 mm. In diameter, and since the rock has been altered to a marked degree, i t should be cal led a meta-diorite porphyry. A17 SECTION 11 A. L o c : 903 d r i f t . E l . 5165. B. Geol. Rein.: In strong skarn zone with good ore nearby. C. S i g n i f . : Why i s t h i s more bleached than No. 14? D. Hand Specimen Plagioclase i s not nearly as noticeable i n t h i s as i n other specimens of Flange Dike. Also, the mafic phenocrysts and t h e i r pseudomorphs are so close to the dark greenish-gray colour (5G4/1) of the groundmass that one must look c a r e f u l l y to see the porphyritic texture, Pyrr-hot i t e i s f i n e l y disseminated throughout the specimen but the few small shears are l i n e d with a s o f t , greenish mineral rather than sulphides. Proof that the feldspars are highly altered i s amply supplied by a strong argillaceous odour. E. Thin Section  Minerals Present Est. Andesine 30 Tremolit e-Actino-l i t e 15 Sphene < 1 Apatite ^ 1 C h a r a c t e r i s t i c s biax {+) H ZV, max ext/U.010 24?, n> balsam, A b ^ An^ . low interference colours, n* = 1.64 ±, biax (-), ZV 75-6*0, ext A up to 1 5 ° , weakly t i n t e d green i n some grains, very high r e l i e f , high b i r e f , occasional acute rhombic sections, normal. AlS Kaolin 15 imparts dusty look to feldspar; S e r i c i t e 5 normal Pyrrhotite normal A l b i t e (?) biax, very low r e l i e f , low b i r e f , c l e a r , colourless. Groundmass 50 some has an i n d e x ^ b a l s some > bals. Description The andesine phenocrysts i n t h i s section are much more altered than those i n other Flange specimens.and the groundmass feldspars are completely r e c r y s t a l l i z e d . K a o l i n i z a t i o n of the feldspars makes i t s e l f evident i n the clouded, dusty appearance of the ent i r e section. The large tremolite grains possess the usual sieve texture and twinning* Some, moreover, show c l e a r l y that they have been replaced i n t e r n a l l y by py r r h o t i t e . The best example of t h i s i s a large phenocryst near the center of the section that appears to have been completely altered to tremolite, which l a t e r became p a r t i a l l y replaced by pyrrhotite and by a cl e a r , colourless, fresh looking mineral that may be a l b i t e . P y r r h o t i t e , though i t i s disseminated i n i r r e g u l a r patches through the specimen, has a s l i g h t tendency to be associated with the greenish tremolite (tremolite-actino-l i t e ) . A considerable amount of f i n e grained tremolite. developed i n the groundmass as w e l l as i n the hornblende A19 and some of the andesite phenocrysts gives the specimen a d e f i n i t e c r y s t a l l b b l a s t i c texture. The extensive a l t e r a -t i o n of the feldspar may have l e d to an underestimation of the proportion of andesine phenocrysts i n the specimen and consequently to an incorrect name f o r the rock but, from the observed data, such as they are, t h i s rock i s a meta-andesite porphyry. I t w i l l be noted that the combined phenocrysts of andesine and t r e m o l i t e - a c t i n o l i t e make up only 45 per cent of the section. A20 SECTIONS g {!]_ & 8 (2) A. Loe.; From footwall of £.3 stope. E l . 5215. B. Geol. Rein.; High grade ore above and. below t h i s s i l l . C. S i g n i f . ; Typical Midway s i l l . Is the a l t e r a t i o n simi-l a r to that i n other s i l l s ? D. Hand Specimen Sample 8 (1) i s a l i g h t greenish-gray (5GY8/1) porphyr i n which one can discern sparse bleached hornblende phenocrysts up to seven or eight mm long and more numerous smaller phenocrysts of feldspar, some of which are s t r i a t e d . Sulphides are noticeably absent except f o r a few extremely small, i s o l a t e d grains. The specimen has a somewhat monotonous appearance owing to the f a c t that phenocrysts and groundmass blend p a r t i c u l a r l y well. The rock gives o f f a strong argillaceous odour. E. Thin Section 3 (1) Minerals Present Est. % C h a r a c t e r i s t i c s Andesine 25 biax {+) max extAi. 010 ZZj Augite 20 n ^ b a l s , Ab An Z c 43°, n bals (1.75), i n t e r f colours mostly low but some up to 2nd order yellow, biax (-+-), ZV 6 0 ° + . Sphene 2 r e l i e f high n = 1.8"+, extinction not complete (only to b l u i s h ) , biax (+), 2V 25-30°, dispersion r ? v strong. A21 Ca l c i t e < 1 normal Apatite < 1 normal A l t e r a t i o n mixtures of Kaolin, s e r i c i t e , low to mod b i r e f . epidote ( ? ) , scapolite (?) Pyrrhotite < 1 normal A l b i t e (?) or an alk Feldspar 2 colourless (pinkish), n<bals, biax (•+), ZV large. Groundmass 50-60 mostly n<bals, probably much a l k a l i feldspar, including trace of a n t i g o r i t e (?) 1-slow, pale green, low r e l i e f , // ext. Description The feldspar phenocrysts are highly altered to f i n e grained cloudy masses of k a o l i n , s e r i c i t e , and pos-s i b l y some epidote. Twinning lamellae are s t i l l preserved i n a number of c r y s t a l s and a few poor examples of zoning are present. Most commonly the outer parts of c r y s t a l s are more altered than the center. The groundmass i s too much altered to allow a plagioclase determination and, i n view of i t s generally low index probably contains mostly a l k a l i feldspar. Next to andesine, colourless augite i s the most abundant mineral. I t occurs as pseudomorphs a f t e r horn-blende and also as small xenoblasts that may be i s o l a t e d or i n groups. Sieve-like texture i s produced i n the larger A22 augite grains by patterns of a l t e r a t i o n to c a l c i t e , k a o l i n , and sphene and r a r e l y , replacement by a l k a l i f e l d -spar. Large anhedral masses of sphene are sparsely dis-t r i b u t e d through the section. Usually i t s high' b i r e f r i n -gence produces high order interference colours but i n two or three grains only about f i r s t order yellow i s reached. These grains, instead of extinguishing, merely become dark blue. They give a b i a x i a l p o s i t i v e interference f i g u r e with a 2V of l e s s than 30°. Strong a x i a l dispersion can be seen with r>v. The c r y s t a l l o b l a s t i c texture of the groundmass and the probably o r i g i n a l composition of l e s s than 45 per cent phenocrysts of andesine and hornblende make t h i s specimen an augitized meta-andesite. SECTION 3 (2)  Minerals Present Est. % Characteristics Andesine Augite Sphene Apatite 10-15 20 ^ 1 1 max ext/U-010 24°, biax (+), 2V 70°, Ab 5 5 A n 4 5 ( o r i g i n a l l y much higher proportion, pos-s i b l y 30-40$) biax (+), 2V+600 (off center optic axis figure) ZAc 42°, r e l i e f high, variable i n t e r f colours. normal normal A23 Scapolite A l b i t e Kaolin ) ) S e r i c i t e ) Arsenopyrite < 1 Pyrrhotite « 1 Groundmass 60 uniax (-), 1-fast, // ext, many inclusions, n<bals (1.540) biax (+), 2V about 70°, very low r e l i e f , colourless, c l e a r , n < bals (1 .53.). probably considerable but very f i n e grained and well d i s t r i b u t e d , s i l v e r colour, opaque, euhedral grains, high r e l i e f , normal mostly n^-bals but some n-^-bals. Description Highly altered andesine phenocrysts are barely distinguishable from the clouded, c r y s t a l l o b l a s t i c ground-mass. Twinning i s s t i l l preserved on a few c r y s t a l s and zoning i s poorly developed i n others. There i s a tendency f o r stronger a l t e r a t i o n i n the centers of some grains so that r e l a t i v e l y fresh rims are l e f t enclosing clouded cores." Large augitized hornblende phenocrysts are given pronounced sieve texture by numerous inclusions and rounded a l t e r a t i o n patches. Augite xenoblasts have developed abundantly i n the groundmass and i n some feldspar phenocrysts. The i n t e r -ference colours of pyroxene i n the phenocrysts are, on the average, much higher than those of the small xenoblasts, the former being usually second order blues and greens, the l a t t e r r a r e l y above f i r s t order yellow. A24 A mineral that i s probably scapolite occurs adjacent to an arsenopyrite c r y s t a l and along a nearby f r a c -ture. At f i r s t inspection the index of r e f r a c t i o n appears too low f o r scapolite. Epsilon i s d e f i n i t e l y l e s s than balsam but i n t h i s section the balsam was found by the use of index o i l s to have a r e f r a c t i v e index close to 1.541* The lowest value of n e f o r (-) scapolite, according to Winchell, i s 1.535* The (+) sca p o l i t e , m a r i a l i t e , has a value of n„ of 1.523 but the mineral i n t h i s section i s d e f i n i t e l y (-). Small anhedral grains of a clear, colourless mineral with low r e l i e f are found i n various parts of the section — i n the groundmass, i n the andesine phenocrysts and occasionally with the a l t e r a t i o n products i n large augite grains. The properties suggest that i t i s untwinned, secondary a l b i t e . This rock i s very highly altered and r e c r y s t a l -l i z e d . I t s o r i g i n a l composition has been s u f f i c i e n t l y obscured that i t might now be c a l l e d either meta-andesite porphry or meta-diorite porphyry. I t has w e l l developed c r y s t a l l o b l a s t i c , sieve, and prophyroblastic textures but no d i s t i n c t i v e structures. A25 SECTION 12 A. Loc.: F.W. of 4.1 stope on 4 Level. B. Geol. Rein.: Footwall s i l l of Orange ore bed. Good ore above and below. C. Signif.; Midway s i l l from 4 Level. Compare to No. 16. D. Hand Specimen Pale feldspar and bleached hornblende phenocrysts are almost the same colour as the greenish-gray (5GY6/1) groundmass. The rock contains local disseminations of pyrrhotite and in one of these a single euhedral crystal of arsenopyrite occurs. E. Thin Section  Minerals Present Est. Andesine 30 Tremolite Augite Actinolite Sphene Apatite Clinozoisite 30 < 2 < 1 < 1 < 1 Characteristic s biax (+), large 2V, max ext AJ_ 010 23°, n>bals, Ab40 An^ . biax (-), large 2V, Z A C 10°-19°, 1-slow, polysynthetic twins. Z A C 39°, high r e l i e f , low interf colours. green, pleochroic, Z A C 10°-13°, 1-slow, r e l i e f same as tremolite, fine grains. normal normal normal A26 Ca l c i t e 2 normal Kaolin nprmal Re c r y s t a l l i z e d Groundmass material n>bals, biax (+), 2V 60°. Description Andesine phenocrysts are zoned and mostly well twinned though a l t e r a t i o n l o c a l l y obscures such structures. Andesine l a t h s i n some tremolite grains implies a l i m i t e d p o i k i l i t i c texture. Kaolin and c a l c i t e form the chief a l t e r a t i o n products of the andesine. Several former hornblende phenocrysts contain both tremolite and augite. In one, tremolite forms an i r r e g u l a r rim aroundaugite and i n another, augite rims tremolite. Since the two minerals are so c l o s e l y i n t e r -grown, i t i s d i f f i c u l t to say that either i s the e a r l i e r . The rock has l o c a l sieve, b l a s t o p o i k i l i t i c , and blastoporphyritic textures. Because of the r e c r y s t a l -l i z a t i o n and the fact that the andesine and former horn-blende phenocrysts account f o r more than 50 per cent of the rock, i t i s a meta-diorite porphyry. A27 SECTION 12 A. Loc.t F.W. of N43 - A l stope, F-floor. E l . 4425. B. Geol. Rein.: Midway " s i l l " crosscuts crumpled beds here. Rich ore i s found above. C. S i g n i f . : Midway " s i l l " from Morning section of the mine • D. Hand Specimen Sample 19 i s a dusky o l i v e rock (8Y6/3) that i s fractured, s l i g h t l y sheared, and apparently deeply weathered. Kaolinized phenocrysts of feldspar appear as l i g h t e r coloured spots on clean surfaces. Along f r a c -tures, chloropal-lik e material and pyrrhotite are v i s i b l e . The rock has a peculiar earthy odour. E. Thin Section Minerals Present Est. % Ch a r a c t e r i s t i c s Andesine 15-20 max extA-1-010 22°, n>bals, Tremolite 10-15 Z A C 10°-14°, poor biax (-) i n t e r f f i g u r e , n=1.65, 1-slow. Sphene < 1 normal C l i n o z o i s i t e normal Epidote (?) n = 1.7+, // ext, 1-fast. Kaolin 40-50 white, opaque, s l i g h t l y stained by limonite occasion-a l l y . A28 Description The highly altered andesine phenocrysts are barely distinguishable from the enclosing mass of k a o l i n , epidote ( ? ) , and c l i n o z o i s i t e . A l b i t e twinning i s only poorly preserved. Tremolite, with good sieve texture, i s mostly pseudomorphous a f t e r euhedral hornblende phenocrysts. On account of the strong weathering, the rock ' can not be named accurately but i t may be either meta-andesite porphyry or meta-diorite porphyry. A29 SECTION 6 A, L o c : N end of stope on 1 l e v e l (S.S. No. 3) E l . 5590. B. Geol. Rein.: This i s a narrow dike that crosscuts Line, apparently c o n t r o l l i n g ore. C. S i g n i f . : S.S. No. 3 dike specimen f o r comparison with Flange, Midway, and sample 7. D. Hand Specimen This rock i s a medium greenish gray (5gy5/1) porphyry comprised of an aphanitic groundmass and pheno-crysts of plagioclase and altered hornblende, those of the l a t t e r a t t a i n i n g a length of nine or ten mm. Fine grained pyrrhotite that i s disseminated through the specimen and also somewhat concentrated along occasional fractures causes the fracture surfaces to weather a grayish brown ( 5 Y R 3/2). The larger tremolite-hornblende phenocrysts appear to be' i n t e r n a l l y replaced by p y r r h o t i t e . The rock has a d i s t i n c t , but not strong, argillaceous odour. E. Thin Section Minerals Present Est. % Characteristics Plagioclase 20-25 n^bals, doubtful e x tA J . 010 beds i n a t i g h t f o l d near the Marble 30°. Tremolite 15 normal Augite 5-10 Z A C 43°, n = 1.7+, pale yellow i n t e r f colours, some euhedral grains, at l e a s t one good cleavage. A30 Apatite C l i n o z o i s i t e 2 1 Sphene Ca l c i t e '< 1 ^ 1 S e r i c i t e Kaolin Scapolite Pyrrhotite Groundmass Description 5 15 <Z<L 1 45 normal biax (+) ( ? ) , 2V about 80°, n = 1.74, e x tA with cleavage 15°, blue i n t e r f colours i n f i r s t order gray zone, normal uniax (-), high b i r e f , variable r e l i e f , l a t h shaped and i r r e g u l a r grains. normal normal normal normal mostly n< bals. The plagioclase i s too much altered to be p o s i t i v e l y i d e n t i f i e d but very hazy a l b i t e twinning on two grains indicated an ex t i n c t i o n angle of about 30°• This would place i t i n the labradorite d i v i s i o n (Ab^ A n ^ ) . Kaolin i s the chief a l t e r a t i o n product followed i n impor-tance by s e r i c i t e and c a l c i t e . Feldspar phenocrysts are distinguished from the groundmass only with d i f f i c u l t y but phenocrysts of other minerals are usually sharply euhedral. Small tremolite prisms and aggregates are developed almost a l l through the section, p a r t i c u l a r l y i n altered feldspar phenocrysts. In addition, some augitized A31 hornblende phenocrysts are now peripherally replaced by pseudomorphic tremolite. The augite i s r e s t r i c t e d to narrow, i r r e g u l a r streaks p a r a l l e l to the cleavage. Both the augite and tremolite have the same interference colours and, on account of the cloudiness i n the section, barely noticeable difference i n r e l i e f but the ext i n c t i o n angle of the outer t r e m o l i t i c part i s only 10° to 17° whereas the inner part, extinguishes at about 43° • One of these tremolite-augite grains that has been both bent and f r a c -tured and another deformed grain of augite give evidence of stress i n the rock. Proof that some of the augitized phenocrysts were o r i g i n a l l y hornblende i s supplied by the narrow, truncated rhombic sections- t y p i c a l of amphiboles. C l i n o z o i s i t e occurs i n grains up to 0.6 mm i n diameter i n several parts of the section. Pyrrhotite however i s much scarcer than i n previously described sec-t i o n s . The rock possesses c r y s t a l l o b l a s t i c and blasto-porphyritic texture and minor c a t a c l a s t i c structure. The o r i g i n a l composition has been somewhat obscured but, as close as can be determined, i t leads to the choice of * meta-andesite porphyry f o r the rock name. A 3 2 SECTION 2 A. L o c : From S.S. No. 4 Shaft. E l . 5590. B. Geol. Rein.; Probably the continuation of S.S. No. 3 dike but in the footwall limestone. Carries only minor mineralization l o c a l l y . C. Signif.: Compare i t s alteration to that of No. 6. D. Hand Specimen This sample i s a dark greenish gray ( 5 G Y 4 / 1 ) porphyritic rock. It i s traversed by occasional frac-tures containing pyrrhotite, calcite, and chalcopyrite along which the rock breaks, exposing rusty weathered sur-faces. The sulphides are also disseminated in small par-t i c l e s through the rock. Numerous striated feldspar phenocrysts, a l l less than two or three mm long, and a very few altered, euhedral hornblende phenocrysts up to 1 0 mm long comprise the v i s i b l y crystalline part of the rock, the rest being a mottled, aphanitic groundmass. The rock has a strong argillaceous odour. E. Thin Section Minerals Present Est. % Andesine Tremolite 3 5 - 4 0 10-15 Scapolite 5-10 Characteristics max ext /tx 0 1 0 2 0 ° , n>bals, biax (4-), 2 V 7 0 ° , Ab 6 o An 4 0 . biax (-), 2 V large, Z/vc 1 1 ° - 1 4 ° , colourless, 1-slow, mod r e l i e f , n S . . 1 . 6 5 + . normal A33 Augite 2-5 Apatite Sphene S e r i c i t e Kaolin Pyrrhotite Chalcopyrite Groundmass Description 1 > 1 < 1 <: 1 biax ( + ) (?) , r e l i e f high, n >bals.(1.73) , Z A C 43°, colour-l e s s , normal normal normal normal normal normal n<bals and some n ^ b a l s . The section contains abundant euhedral andesine phenocrysts that vary i n size from 0.2 mm to one mm. They show rather poor a l b i t e twinning and are not zoned. Ka o l i h i z a t i o n and s e r i c i t i z a t i o n have proceeded quite independently of c r y s t a l boundaries so that s h e l l s of a l t e r a t i o n of varying i n t e n s i t y do not occur. Scapolite, i n l a r ger grains though l e s s i n t o t a l volume than s e r i c i t e or k a o l i n , has also developed from feldspar. Apatite inclusions i n the feldspar are common. Most of the tremolite i s apparently pseudomor-phous a f t e r hornblende and, i n addition to the euhedral outlines, has inherited a rough polysynthetic twinning i n some instances. Some grains of tremolite contain r e l i c s of either colourless hornblende or augite. In such c r y s t a l s the outer part has an extin c t i o n angle of the order of 15°, the inner part, 43°. The r e l i e f i s A34 d e f i n i t e l y lower f o r the outer material but the i n t e r -ference colours are exactly the same. Chalcopyrite and pyrrhotite occur as opaque, dendritic threads following cracks and cleavage i n a few c r y s t a l s of feldspar and scapolite. A few i n d i s t i n c t l a t hs of plagioclase can be seen i n the groundmass but most of the Becke l i n e t e s t s proved an index of r e f r a c -t i o n l e s s than balsam. This could indicate a l b i t e . The section has blastoporphyritic texture and minor sieve and porphyroblastic textures as w e l l as rather poor c a t a c l a s t i c structure i n the form of occasional bent tremolite grains. The preponderance of phenocrysts over groundmass and the aphanitic grain size of the l a t t e r j u s t i f y the name, meta-diorite porphyry. A35 SECTION 1^ A. L o c : F.W. of b l i s t e r at 9 . 2 Stope chute. E l . 5165. B. Geol. Rein.: Good ore above and below i n strong skarn. C. S i g n i f . : A mine s i l l that i s unbleached. Compare to Midway. D. Hand Specimen This medium greenish gray (5GY5/I) porphyry consists of an aphanitic groundmass and phenocrysts, r a r e l y exceeding two or three mm i n length, of dark, ac i c u l a r hornblende and l e s s noticeable s t r i a t e d f e l d -spar. Small euhedral arsenopyrite c r y s t a l s are very sparsely disseminated i n the groundmass. The rocii i s traversed by a few t i g h t fractures that are sealed by either c h l o r i t i c material or very fine-grained, brown, p y r r h o t i t e - r i c h bands. Only a weak argillaceous odour i s given o f f . E. Thin Section Minerals Present Est. % Characteristics  Labradorite 35 biax (+•), 2V large, max extA-i-010 32°, low r e l i e f , low b i r e f , n>bals, Ab^ p An( Hornblende 20 long prismatic c r y s t a l s , biax (-), large 2V, n>bals 1.68, Z A C 11°, 21°, 26°, pleochroic yellowish green-brownish green. Augite 5 rims around and replacement of hornblende, biax (-), mod-large 2V, Z A C 42°, n>bals (1.72). A36 B i o t i t e Apatite Scapolite C a l c i t e C l i n o z o i s i t e < 1 1 2 1 A l b i t e Kaolin S e r i c i t e Sphene Chalcopyrite Groundmass Description 5 (?) 5 (?) 1 _45 normal normal normal variable r e l i e f , high b i r e f , i n clust e r s of small round grains, anomalous blue i n t e r f colours, biax (+j, 2V>70, ext/llO°, 1-slow. biax (-+-), large 2V, low b i r e f , low r e l i e f , n-^bals. normal normal normal normal n>and<bals. Some of the feldspars are well zoned and the majority s t i l l show f a i r a l b i t e twinning but a few are almost completely ka o l i n i z e d . Late a l b i t e has apparently been introduced along i r r e g u l a r , discontinuous v e i n l e t s and l o c a l l y has replaced the groundmass. i A u g i t i z a t i o n of hornblende phenocrysts i s w e l l i l l u s t r a t e d by many cr y s t a l s i n t h i s section. The a l t e r a t i o n i n a l l cases proceeds inwards from the periphery, working along cleavage planes and small fractures so that a narrow s h e l l of the colourless augite develops around a hornblende c r y s t a l . Later stages are presented by islands A37 of unaltered hornblende i n augite and f i n a l l y by completely augitized phenocrysts. B i o t i t e shreds also occur i n the hornblende, p a r t i c u l a r l y along cleavage planes. C l i n o -s o i s i t e , s c apolite, and c a l c i t e are a l t e r a t i o n products of the groundmass. Kaolin and s e r i c i t e , though also i n the groundmass, are confined p r i n c i p a l l y to the labradorite phenocrysts. Sieve texture i s shown by the few scapolite c r y s t a l s and some c l i n o z o i s i t e . On the bases of i t s aphanitic groundmass, i t s large proportion of phenocrysts, and the r e c r y s t a l l i z a t i o n of a considerable part of the rock, i t i s best named a meta-diorite porphyry. A3'8 SECTION 16 A. L o c : F.W. of Red Ore on 4 Level. E l . 5450. B. Geol. Rein.: Contains a parting of skarn and r i c h ore. C. S i g n i f . : Mine s i l l ( ? ) . Compare to Midway. D. Hand Specimen The colour of t h i s rock grades from a brownish gray (5YR4/1) almost to a greenish gray (5G6/1). Occasional small phenocrysts of feldspar are barely d i s c e r n i b l e i n the aphanitic groundmass. Pyrrhotite and chalcopyrite impart a rusty weathering q u a l i t y to the specimen and kaolin i s attested to by a strong argillaceous odour. A few com-pact areas of about two mm i n diameter are composed of a black, amorphous-looking material c l o s e l y associated with py r r h o t i t e . This i s shown to be chloropal by microscopic work. E. Thin Section Minerals Present E s t . % Andesine-Labradorite 10-15 Augite Scapolite 10 5-10 Chloropal (Nontronite) 2 Cha r a c t e r i s t i c s biax (•+-), 2V = 70°, max ext A j -010 26°, n>bals, Absoknso, ( o r i g i n a l l y probably 25-30%) biax (+), 2V « 60°, Z A C 43°, n = 1.70, colourless, sieve texture. uniax (-), 1-fast, // ext, n>bals, sieve texture, uniax (-), n = 1.60, blue-Chloropal (Nontronite) Cont. B i o t i t e Apatite Sphene 1-2 < 1 < 1 C l i n o z o i s i t e <1 « : 1 A 3 9 green colour, pleochroic from b l u i s h green to brownish green, vague twin-ning, normal normal normal anomalous blue i n t e r f colours, ext A 21°, biax (+-) ( ? ) , high r e l i e f , normal normal normal normal normal most of groundmass n<bals. C a l c i t e Kaolin S e r i c i t e 10 (?) Pyrrhotite 5 Chalcopyrite < 1 Groundmass 50-55 Description The feldspar phenocrysts are very highly altered and the goundmass i s l a r g e l y r e c r y s t a l l i z e d . Twin-ning i s almost completely obscured but zonal structure i s s t i l l preserved i n several c r y s t a l s . S e r i c i t e i s the most widespread a l t e r a t i o n product of feldspar but k a o l i n , c a l -c i t e , scapolite, c l i n o z o i s i t e , and sphene have also developed at i t s expense. Augite, often with good sieve texture, i s par t l y pseudomorphous a f t e r hornblende and i s i t s e l f re-placed to a minor degree by b i o t i t e . Irregular masses of A40 b i o t i t e are also found i n areas containing abundant pyrrhotite. Sieve texture i s w e l l shown by most of the large scapolite xenoblasts. The inclusions consist of sphene, pyrrhotite, c a l c i t e , and unreplaced fragments of feldspar. Chloropal, i n two compact masses, occurs cl o s e l y associated with pyrrhotite. A l l parts of each mass have a p a r a l l e l orientation and therefore give exactly the same off-center, almost u n i a x i a l interference f i g u r e . The mineral e x t i n -guishes p a r a l l e l to a set of i n d i s t i n c t , discontinuous twinning lamellae at an angle of 80° to a second even le s s d i s t i n c t banding. Meta-andesite porphyry i s the most suitable name fo r the rock because plagioclase and former horn-blende phenocrysts constitute l e s s than 50 per cent of i t , the groundmass i s aphanitic, and a l t e r a t i o n has i n t r o -duced new minerals and r e c r y s t a l l i z e d the o l d . A41 SECTION 18 A. L o c : F.W. of Yellow Ore at 4 Station. B. Geol. Rein.: Contains streaks of arsenopyrite; high grade ore l i e s above i t . Ct. S i g n i f . : Mine s i l l f o r comparison with 16 and 17; any o r i g i n a l difference? D. Hand Specimen This rock consists of sparse, minute grains of mafics and pale plagioclase phenocrysts i n a l i g h t greenish gray (5G8/1) groundmass. A few small specks of pyrrhotite and one c r y s t a l ,of arsenopyrite are v i s i b l e . The rock emits only a f a i n t argillaceous odour. E. Thin Section 18 (b) Minerals Present E s t . % C h a r a c t e r i s t i c s Andesine 10 biax (+), large 2V, max extAX Augite 30 010 16°, n>bals, k\5 An 3 5 . Z A C 36°-40°, biax (+), 2V 65°> high r e l i e f , i n large grains and small laths i n groundmass. A l b i t e (?) 5 biax (+), 2V 75°, n-^bals, low r e l i e f , low b i r e f , c l e a r , colourless. Kaolin general cloudiness caused by Epidote 1 white, semi-opaque material. // ext, 1-slow, biax (-) large 2V, high r e l i e f . A42 Sphene 2 normal Ca l c i t e -<• 1 normal Apatite < 1 normal Groundmass 11-= bals and some n:>bals. Description The andesine phenocrysts are so highly altered that t h e i r a l b i t e twinning i s mostly obscured. Short la t h s of colourless augite have developed at the expense of feldspar and the groundmass as a whole. A few f a i r l y large grains of augite (up to 0.8 mm) gave e x t i n c t i o n angles up to 40° and good b i a x i a l p o s i t i v e interference figures. two grains and several subhedral areas, possibly former andesine phenocrysts, consist of mosaics of equidimensional, anhedral a l b i t e grains. Camsell (1910, p87) believed such aggregates of secondary feldspar to be pseudomorphs a f t e r pyroxene. Similar grains occur i n a minute, discontinuous v e i n l e t about 0.1 mm wide that also contains several euhedral c r y s t a l s of sphene. and i t s o r i g i n a l l y porphyritic texture, t h i s rock i s now a meta-andesite porphyry. A l b i t e p a r t i a l l y replaces andesine i n one or By v i r t u e of i t s extensive r e c r y s t a l l i z a t i o n A43 SECTION 21 A. L o c : Mascot Low Level Tunnel. E l . 3750. B. Geol. Rein.: Occurs i n a strong skarn zone with abundant pyrrhotite but no gold. C. S i g n i f . : Unusually fresh-looking s i l l . Could i t be fundamentally the same as the other s i l l s ? D. Hand Specimen Prominent, dark hornblende phenocrysts up t o f i v e or s i x mm long form about 15 per cent of the rock. Smaller, le s s noticeable phenocrysts of feldspar blend with the medium gray ( / ) aphanitic groundmass i n which a l i t t l e fine-grained pyrrhotite i s disseminated. No fractures, j o i n t s , or shear planes interrupt the massive character. A f u r t h e r contrast to the other por-phyries studied f o r t h i s report i s i t s fresh appearance. E. Thin Section Minerals Present Est. % Ch a r a c t e r i s t i c s Andesine 40-45 phenocrysts; max extA_L010 23°, n>bals, biax (-+•), 2V 75° , (groundmass extA 20°) Hornblende 10-15 brown, strongly pleochroic yellow-brown to green-brown, cross sections show 2 cleavages at 56° (measured) long diagonal s slow ray. biax (-), 2V 75-80°, n = 1.68, A44 Augite Hornblende Cont. Clinochlore 2-5 1 ZAc 15° + . Z A C 40°, n> hornblende (1.7+). uniax (+), e x t A 8O, 1-fast, i n t e r f colours i n low grays, n = 1.58, pale green. B i o t i t e 1 normal Apatite < 1 normal Pyrrhotite 1 normal Groundma ss a l l has n> bals. Description The subhedral to euhedral andesine phenocrysts are well twinned and may show d i s t i n c t zoning. There i s almost enough va r i a t i o n i n size among them to produce a seriate texture. Some groundmass feldspar i s also twinned and none i s altered to any extent. Euhedral phenocrysts of greenish brown horn-blende, often complexly twinned, range i n size from 0.5 mm to 4 mm. Although t h e i r o v e r a l l shape i s euhedral, they give evidence of p a r t i a l resorption because the contacts with the groundmass are highly i r r e g u l a r i n d e t a i l . L o c ally the outer s h e l l of a phenocryst seems to have been granulated, p a r t i c u l a r l y at the ends of elongate c r y s t a l s . Augite has developed i n the peripheral zone of each grain to a more or less marked degree. I t can be distinguished from the hornblende by i t s lack of colour, much greater extinction angle, and higher r e l i e f . B i o t i t e occurs both as a primary constituent and as a minor a l t e r a t i o n product of hornblende. On account of the aphanitic groundmass and the abundance of andesine and horblende phenocrysts, t h i s rock i s a d i o r i t e porphyry. 

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