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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 d e f i n i t e l y established. The porphyries may have been altered both by deuteric and by hydrothermal action. Studies of zoned plagioclases indicate a magmatic o r i g i n for at least one of the sills.  SUMMARY  (ii)  The r e l a t i v e l y small number of t h i n sections studied does not permit the writer to expound with confidence any new idea concerning the o r i g i n or the a l t e r a t i o n of the dikes and s i l l s as a whole or of any one of them i n p a r t i c u l a r . After a c r i t i c a l examination of Dolmage and Brown's paper and a comparison of a l l available petrographic r e s u l t s , including his own, the writer i s i n c l i n e d 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 limited extent, i n rocks unaffected by other a l t e r a t i o n such as s e r l c i t i z a t i o n and k a o l i n i z a t i o n . The writer found no mineral that resembled pargasite as described by Schmitt. Dolmage and Brown apparently found no pargasite but instead they recognized 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 b l u i s h 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.  (iii) Scapolite was found to occur e r r a t i c a l l y 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 r y s t a l l i z a t i o n from a magma.  /  TABLE OF CONTENTS  Page  ACKNOWLEDGEMENTS  i  SUMMARY  ii 1  INTRODUCTION Location  1  ,  History  .  2  Local and Regional Geology  .  3  Purpose of the Investigation  5  Review of the Literature  6  Camsell  6  Bostock  7  B i l l i n g s l e y and Hume  7  Dolmage and Brown  9 13  PETROLOGIC DESCRIPTIONS 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 BIBLIOGRAPHY  .  . . . "  APPENDIX A (PETROGRAPHIC DESCRIPTIONS) .  24 26  .  .  .  Al  (i) 'ACKNOWLEDGEMENTS•  The writer i s indebted to A. E. E u l l e r 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 c o l l e c t i n g the specimens and for supplying the map of locations. Dr. H. C. Gunning and Dr. K. DeP. Watson of the Department 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 i n a l l y , the writer wishes to thank the Kelowna  Exploration Co. L t d . for permission to carry out the investigation and for t h e i r 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  MINES  O F  M I N E S  A  N  AND GEOLOGY  D  R E S O U R C E S  BRANCH  BUREAU OF GEOLOGY AND TOPOGRAPHY  120° 15'  LEGEND  I20°OO'  49°30T~  49°30'  MODERN Alluvium  y o  TERTIARY  r  Chiefly  basalt  and  andesite,-  breccia  and  tuff  u U  Conglomerate,  1 2  JURASSIC  sandstone  DESCRIPTIVE NOTES  A N D (OR) Y O U N G E R  11  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.  Granite  |  Granodiorite  1 0  I  TRIASSIC  Diorite,  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 chalcopyrite and pyrrhotite are most conspicuous. The gangue c o n 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 suggesting 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 mineralization. A n 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 maparea, 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 Bradshaw 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 formations 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.  gabbro  (?) WOLFE  CREEK  breccia  and  FORMATION:  HENRY impure  FORMATION: limestone  tuff,-  minor  andesite  and  basalt;  sediments  TRIASSIC  y o  o< (/)  black  argillite,  tuff,  UJ 2  HEDLEY quartzite,  FORMAT/ON: limestone, argillite, conglomerate;  SUNNYSIDE  REDTOP siliceous  TRIASSIC  FORM  FORMATION: argillite, tuff,  FORMAT/ON: cherty  quartzite, and  (defined,  Glacial  striae  Fossil  locality  Mine  tunnel well not  cherty breccia  quartzite,  chert,  chert  argillite;  basalt  black andesite  argillite, and  breccia,  and  andesite  breccias  FORMATION: breccia; some  tuff, limestone  overburden  boundary  Road  limestone, some  cherty  of continuous  Geological  Road  Undivided  limestone  INDEPENDENCE  BRADSHAW quartzite,  Fault  8  cherty tuff  A N D (OR) O L D E R  flows  Area  ATI ON:  quartzite, breccia,  (defined,  '::'.•.•:•.'•.:•:.•'.•::::: approximate,  assumed)  approximate)  ~~  •  ••"  WWWVN  © ~"'  travelled well  travelled  Trail Power  transmission  line  Power  transmission  line  Land  District  Indian  •  »—*—  boundary  (position  Intermittent Sand  road  boundary  Reserve  Stream  ——•—•—— along  approximate)  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.  -  stream  bar  ^•saaiBBv-  C££?-4&  Marsh Contours  (interval  Contours Height  (position in feet  Geology  above  IOO feet)  ^-sooo-g  approximate) Mean  by H S. Bostock,  sea-level  1926-1930;  Base-map prepared by the maps supplied by the British Cartography by the Drafting  S 7 6 4  and by D.A.McNaughton,  Topographical Survey, 1937, Columbia Department of and Reproducing Division,  '  1937. from Lands. 1940.  so"  49i5 120  15'  P  U  B  L  I  S  H  E  D  i  49 15' l20°oo'  ts^o  M A P  5 6 8 A  H E D L E Y S I M I L K A M E E N  A N D K A M L O O P S  B R I T I S H  Scale, Approximate  ^ ^ ^ ^ W ^ ^ ^ i *  63,36o  DISTRICTS  C O L U M B I A  o r I Inch t o I M i l e M i l e s  magnetic  declination,  24°East.  L £ 3, 0 2  Old  i  OF  M A P  N I C K E L S  H  O  W  I  N  G  P L A T E  &  M A S C O T OF  L O C A T I O N  M I N E S  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 N i c k e l P l a t e mine i s on the east side o f N i c k e l P l a t e Mountain about 6 0 0 f e e t below the summit. The main p o r t a l and mine camp are a t an e l e v a t i o n of f e e t above sea l e v e l .  An a l l - y e a r road connects t h e mine  with the town of Hedley, kameen V a l l e y .  56OO  4000  f e e t below i n the S i m i l -  V i a the Southern T r a n s - P r o v i n c i a l Highway,  Hedley i s 2 3 m i l e s from Princeton and 5 0 from P e n t i c t o n , both of which a r e on the K e t t l e V a l l e y l i n e o f the Canadian P a c i f i c Railway. Hedley i s a l s o 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 R i v e r near Hedley f l o w s i n a deep U-shaped v a l l e y with dry grassy benches along t h e v a l l e y f l o o r , sparsely wooded lower slopes, and upland  r e g i o n s covered with dense j a c k p i n e f o r e s t s . is  s t r i k i n g , as much as 6000 f e e t over d i s t a n c e s o f a few  miles. of  The r e l i e f  The c l i m a t e i s t y p i c a l of the southern i n t e r i o r  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 u s u a l l y c o l d i n w i n t e r .  History The mining h i s t o r y o f t h e Hedley camp dates from the l a t e 1860 s when p l a c e r g o l d was f i r s t T  from Hedley Creek.  panned  Not u n t i l 1894 were the f i r s t  c l a i m s staked on N i c k e l P l a t e Mountain  lode  and o f the c l a i m s  h e l d a t p r e s e n t , the o l d e s t were r e c o r d e d i n 1 8 9 7 .  The  Y a l e M i n i n g Company operated t h e mine from 1904 t o 1909, the Hedley Gold M i n i n g Company from 1909 t o 1930, and from 1934» t h e Kelowna E x p l o r a t i o n Company.  I n 1936 the  Hedley Mascot Gold Mine began e x t r a c t i n g o r e from the Mascot F r a c t i o n and s i n c e then the Hedley camp has had two a c t i v e mines.  The t o t a l v a l u e o f g o l d produced t o  the end of 1948 amounts t o approximately $37,500,000 o f which t h e Mascot s u p p l i e d $8,000,000.  L o c a l and R e g i o n a l Geology The N i c k e l P l a t e f o r m a t i o n ( a l s o known as t h e Hedley formation) i s p a r t o f a b l o c k o f T r i a s s i c 1930, for  p20AA) sedimentary  about f i v e  r o c k s t h a t extend n o r t h and e a s t  m i l e s from the town o f Hedley.  panel o f sediments,  (Bostock,  In this  the s t r u c t u r e t r e n d s n o r t h - n o r t h e a s t  i n c o n t r a s t t o t h e p r e v a i l i n g northwest  structure of the  o l d e r P a l a e o z o i c r o c k s t o the s o u t h e a s t .  The s t r a t a on  N i c k e l P l a t e Mountain d i p roughly west a t about 3 0 degrees The  c o n t a c t w i t h an u n d e r l y i n g body o f younger g r a n o d i o r i t  a l s o d i p s west but a t a f l a t t e r angle t h a n the beds. A l l the c h i e f ore d e p o s i t s l i e i n t h e N i c k e l Plate formation.  The p r o d u c t i v e s t r a t a a r e i n t e r b e d d e d  l i m e y a r g i l l i t e s and l i m e s t o n e s t h a t a r e l a r g e l y  recrys-  t a l l i z e d t o a g a r n e t - d i o p s i d e - e p i d o t e - c a l c i t e skarn i n the v i c i n i t y  o f the mine.  The term, S k a r n Bowl", has n  been used t o d e s c r i b e t h e bowl shaped trough o f s i l i c a t e a l t e r a t i o n t h a t t r a n s e c t s the bedding and  s t e e p l y a t the n o r t h  south s i d e s and whose bottom d i p s west a t a p p r o x i -  mately the same angle as the sediments.  F o l l o w i n g any  i n d i v i d u a l bed out o f t h e Skarn Bowl, one n o t i c e s a more or  l e s s sudden disappearance  o f s i l i c a t e m i n e r a l s and a  corresponding i n c r e a s e o f c a l c a r e o u s m a t e r i a l .  This  t r a n s i t i o n zone from skarn t o u n a l t e r e d limestone i s u s u a l l y r e f e r r e d t o as the "Marble L i n e " .  4 The N i c k e l P l a t e formation i s intruded by numerous dikes and s i l l s that are u s u a l l y p o o p h y r i t i c 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, C e n t r a l dike and Hot  "sill").  The Flange i s a v e r t i c a l dike that c o i n c i d e s w i t h the main a x i s of the p r i n c i p a l ore bodies; the Midway, a s l i g h t l y c r o s s c u t t i n g " 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 c l o s e l y i n the lower part as w e l l . The ores are bedded replacements of medium t o coarse-grained skarn by a u r i f e r o u s a r s e n o p y r i t e .  Ore  d e p o s i t i o n has been c o n t r o l l e d by (a) p r o x i m i t y to the Marble L i n e , (b) crotches at the i n t e r s e c t i o n s of d i k e s and s i l l s , and (c) axes of northwesterly t r e n d i n g crumples. Dolmage and Brown c l a i m the ores t o 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 t r u s i v e about a mile long and h a l f a mile wide on the west slope of N i c k e l P l a t e Mountain.  U s u a l l y , n e i t h e r lime-  stone nor porphyry i s s u f f i c i e n t l y m i n e r a l i z e d t o make ore. P y r r h o t i t e i s an extremely widespread mineral on N i c k e l P l a t e 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 o f the I n v e s t i g a t i o n Geologists a t the N i c k e l P l a t e mine b e l i e v e they can d i s t i n g u i s h c e r t a i n porphyries by megascopic examination.  B u l l e r (1949) says:  "There i s a decided and mappable d i f f e r e n c e i n appearance between the Flange and adjacent s i l l s i n most p l a c e s .  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, o r be unbleached, but they are always shades of grey i n c o l o r and p o r p h y r i t i c . the  difference?  Why  I s i t due t o o r i g i n a l t e x t u r e and/or  compositional d i f f e r e n c e s or t o a l a t e r a l t e r a t i o n which has a f f e c t e d the two d i f f e r e n t l y , o r t o a greater degree i n one case than the other? the  I n e i t h e r case what may be  s i g n i f i c a n c e o f the d i f f e r e n c e i n terms o f s t r u c t u r e  and/or ore c o n t r o l ? " This describes a problem o f e s s e n t i a l l y the paragenesis of the porphyry c o n s t i t u e n t s i n r e l a t i o n t o ore. ber  The w r i t e r , t h e r e f o r e , undertook t o examine a numo f t h i n s e c t i o n s o f Flange and s i l l porphyries i n  an attempt t o discover any f e a t u r e s o r q u a l i t i e s p e c u l i a r to e i t h e r type o f porphyry that would throw some l i g h t on t h e u l t i m a t e o r i g i n of the ore and i t s  controls.  In an i n v e s t i g a t i o n o f t h i s nature i t i s important to r e a l i z e that the value o f the conclusions must depend on t h e completeness o f coverage as w e 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 a l t e r a t i o n 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 res t r i c t e d by the limited time a v a i l a b l e .  Furthermore,  the unusual mineralogy and high degree of a l t e r a t i o n necessitated a considerable period of i n i t i a t i o n , reducing 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 t h i n sections i s necessary before hypotheses concerning o r i g i n and a l t e r a t i o n can be advanced.  Consequently, the writer  must confine his treatment of the problem mainly to a discussion of published reports and a comparison of h i s petrographic results with those of others.  Review of the Literature Camsell;Camsell, after studying t h i n sections of ore, came to the conclusion that the sulphide and skarn minerals c r y s t a l l i z e d 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 i n idiomorphic arsenopyrite c r y s t a l s as evidence of p r i o r formation of those minerals but decided, on the basis of the intimate intergrowth of skarn and sulphides, that a simultaneous o r i g i n 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.  Billing-  sley, however, questions the concept of "deep-seated sources" and claims that no great depth of cover i s demonstrated f o r t h i s or any other of several g r a n i t i c plutons i n the region (1941, P547). Bostock;Convincing evidence that the sulphides are l a t e r than the s i l i c a t e s of the skarn was presented by Bostock (1930, p234A) who went on to say (p240A) that the l a t e , untwinned, potash (?) feldspar described by Camsell (pl54) would be more e a s i l y explained i f one assumed the granodiorite to be the source of the mineralization. In spite of t h i s and other factors favouring a g r a n i t i c 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. B i l l i n g s l e y and Hume;B i l l i n g s l e y and Hume (1941, p558) l i s t several l i n e s of evidence that favour the growth of the porphyries  8  i n s i t u by r e c r y s t a l l i z a t i o n . Their studies of certain . low angle breccia sheets led them to believe that such zones could have offered ingress to hot f l u i d s capable of r e c r y s t a l l i z i n g the adjacent rocks.  They suggest also  that the granodiorite may have formed by g r a n i t i z a t i o n and that a l l these thermal effects may be as recent as post-Oligocene.  Various writers have postulated several  periods of a l t e r a t i o n i n efforts to explain the complex metamorphism.  B i l l i n g s l e y 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 i n the porphyries were demonstrated by Schmitt ( B i l l i n g s l e y and Hume,  1941, p 5 6 l ) .  "In stage 1, leuc-augite grows at the expense of o r i g i n a l hornblende and augite, i f any.  In stage 2,  the secondary leuc-augite i s replaced by epidote, dipyrdte, pargasite, and sulphides; while o r i g i n a l labradorite or other plagioclase goes to s e r i c i t e , d i p y r i t e , and carbonates. In stage 3, cracks are f i l l e d with leuc-augite, d i p y r i t e , carbonates, c h l o r i t e , quartz (very l i t t l e ) , and arsenopyrite." According to Schmitt, the most noticeable result 'of t h i s alteration i s the decrease of iron i n the a l t e r a t i o n products.  B i l l i n g s l e y infers from t h i s that  the iron removed from the porphyries during the processes of r e c r y s t a l l i a a t i o n 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 i n 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 i n t r o duced during an early stage of a l t e r a t i o n . Dolmage and Brown:Eblmage and Brown (1945) prefer to ascribe the changes i n the porphyries partly to deuteric processes and partly to post-magmatic a l t e r a t i o n rather than to either contact metamorphism or hydrothermal action.  In regard to t h i s they say (p5d): "The f i r s t i s ruled out by the fact that  similar changes i n the femic minerals have been d i s covered i n the unaltered limestones well below the Marble Line:  therefore, the same agency which caused the  skarn a l t e r a t i o n 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 t e r a t i o n .  Further, they noted l i t t l e alteration  of feldspars and state- (p5d) that c h l o r i t e and s e r i c i t e , t y p i c a l hydrothermal minerals, are conspicuously absent.  10  Schmitt, however, described s e r i c i t e and c h l o r i t e as products of the intermediate to late stages of a l t e r a t i o n so that t h e i r "absence" i s l e f t i n considerable doubt. To the writer, i t seems l o g i c a 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 r e c t l y 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, s c a p o l i t i z a t i o n was the most conspicuous result of postmagmatic a l t e r a t i o n . The development of the scapolite mineral, dipyre (Ma Me ), 73  seems to have, been guided by similar controls to those of the ore bodies, the Marble Line probably the most important.  Dipyre occurs p r i n c i p a l l y i n the porphyries and  usually as a replacement of feldspars. In support of t h e i r b e l i e f that the gabbrod i o r i t e complex originated as a true magma rather than by g r a n i t i z a t i o n , Dolmage and Brown c i t e 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  z?  11 contains a cap of gabbro and augite-diorite that gradually grades into the main quartz d i o r i t e mass below.  Though  i t i s apparently a differentiated stock, the explanation of i t s o r i g i n 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 i n t r u s i o n . This assimilation, they say, might produce a more basic capping.  An. alternative, or possibly a supplementary,  mode of o r i g i n 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 c r y s t a l mush. Bowen (1923, p201) states that since the composition of sedimentary rocks i s determined independently of igneous action, they do not correspond to any stage of the magma s s o l i d i f i c a t i o n and thus cannot be placed 1  i n any reaction series.  In view of t h i s i t would be very  unlikely for a rock mass that owed i t s d i f f e r e n t i a t i o n primarily to the assimilation of sedimentary material to have a genuine systematic v a r i a t i o n of composition, i . e . to exhibit l i q u i d l i n e s 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 r u t h .  Therefore, one should not  12  r e l y too strongly on t h e i r c r i t e r i o n of systematic variation as proof of magmatic o r i g i n . Furthermore, Bowen believes that only i n 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 o r i g i n as long as assimilation of sedimentary material i a accepted as the cause of these v a r i a t i o n s . 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 s m i s directed only against cert a i n c r i t e r i a used by them to support t h e i r views. The writer would possibly have emphasized the zoning of f e l d 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 d e t a 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 s t r a t a .  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 d e f i n i t e l y crosscutting bodies are s t r u c t u r a l l y related to ore inasmuch as no important ore has yet been found without the association of a crosscutting dike and the marble-skarn t r a n s i t i o n zone.  The data concerning  location, geological r e l a t i o n s , and significance of each sample, as l i s t e d i n Appendix A were supplied by A. E . Buller (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 i g h t 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 i s t i n c t i o n of colour as fine as one can observe. Four specimens were spectrographed by R. G. McCrossan and only a b r i e f inspection sufficed to show that there were no strong indications of rare elements. This ruled out the p o s s i b i l i t y that some of the sphene might actually be monazite.  15  The Flange Dike A l l Flange specimens were o r i g i n a l l y either hornblende andesite porphyries or hornblende d i o r i t e porphyries.  The phenocrysts of plagioclase are generally  zoned.and are composed of intermediate to basic andesine, A b - Ab • 5 o  Hornblende was by far the most abundant mafic  fe0  mineral i n the o r i g i n a l rock, i n fact only one section contains evidence for primary augite.  The hornblende  occured as euhedral, prismatic phenocrysts. an accessory common to a l l sections.  Apatite i s  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 a l t e r a t i o n to k a o l i n , s e r i c i t e ,  sphene, and, i n some places, c a l c i t e gives the sections a clouded, confused appearance.  In many grains the chief  a l t e r a t i o n i s i n t e r n a l , i n other peripheral.  The andesine  phenocrysts i n several sections are partly replaced by quartz and, i n one section, by late a l b i t e . Tremolite porphyroblasts have developed as pseudomorphs after the euhedral hornblende phenocrysts. The new mineral has approximately a p a r a 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 p a r t i a l replacement of the tremolite by b i o t i t e  16  or by pyrrhotite i s shown.  In only one section i s there Section 3 contains  even a suggestion of primary augite.  a few phenocrysts of colourless augite that d i f f e r from the usual, narrow hornblende crystals and yet do not have t y p i c a l l y pyroxene outlines.  In shape, these grains  resemble the andesine phenocrysts but no feldspar elsewhere 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 phenocrysts.  These may have been caused by stress i n the rock  prior to complete s o l i d i f i c a t i o n or by the hornblende grains j o s t l i n g one another i n a moving c r y s t a l mush. No uniformity of the groundmass minerals i s indicated by the refractive index t e s t s .  These show i n  a l l sections at least some groundmass with n<-bals though i n 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 groundmass.  Scapolite i s r e l a t i v e l y 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 , 1 1 , and 15, both i n o r i g i n a l composition and i n response to a l t e r a t i o n . The chief difference between 15 (possibly a s i l l ) and 1 4 , a very near s i l l , i s i n the composition of the plagioclase  17  phenocrysts.  In 15, these are A b , i n 14, Ab . Both , 5 5  40  rocks o r i g i n a l l y had hornblende either as the p r i n c i p a l or only mafic mineral.  The hornblende i n 15 i s e n t i r e l y  altered to tremolite whereas i n 14 i t i s only partly altered and the a l t e r a t i o n product i s colourless augite. Both sections are s l i g h t l y a l b i t i z e d and both contain minor b i o t i t e .  Scapolite, c l i n o z o i s i t e , and c a l c i t e , which  are present i n 14, are either not present i n 15 or obscured by the intense k a o l i n i z a t i o n 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 k e 14. No cause was found that would account s a t i s f a c t o r i l y 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 part 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 unlikely 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 e c c e n t r i c i t y of the feldspar or of the tremolite, or by some f i n e l y divided mineral simil a r to the dendritic blue aggregates  occurring  in  1.  18  • The Midway " S i l l " . The composition of plagioclase phenocrysts i n Midway specimens varies within five per cent of A b A n ^ , 60  intermediate andesine.  0  Zoned c r y s t a l s are common and  a l t e r a t i o n to kaolin and s e r i c i t e 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 i n 17 may help explain the sieve texture of the tremolite and augite grains.  The sections with  much colourless augite also contain secondary a l b i t e ( ? ) . Sphene and apatite occur i n a l l specimens and i n 8 (1) sphene i s p a r t i c u l a r l y 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 t h i s conception.  Compared to t y p i c a l Mid-  way material, 16 contains a more basic, plagioclase, A b  5o  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 a l b i t e as i n 8" (1) and 8 (2).  The Sunnyside No. 3 Dike Samples 6 and 7 are very s i m i l a r .  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 p a r t i c u l a r l y abundant i n 7 .  Zoning  cannot be seen i n the feldspars of either section but i n 6 i t could e a s i l y have been obscured by a l t e r a t i o n .  The  feldspars i n 6 are d e f i n i t e l y more altered than those i n 7 and c l i n o z o i s i t e i s lacking i n 7« The labradorite (?) i n 6 i s possibly a much more c a l c i c feldspar than that i n 7 but i t s determination i s somewhat doubtful owing to the strong a l t e r a t i o n . On the whole, 6 and 7 appear to be similar enough, p a r t i c u l a r l y with regard to mafic a l t e r a t i o n , 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 e v e l .  Dealing f i r s t with 14, 16, and 18 (b); one  notices that the plagioclase phenocrysts are mostly subhedral 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, c a l c i t e and b i o t i t e occur i n minor amounts.  Scapolite and c l i n o z o i s i t e 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^ to Ab . Except 18 (b), which i s without s e r i c i t e , 0  65  the feldspars are altered to k a o l i n , s e r i c i t e , c a l c i t e , and sphene.  In 18 (b), augite p a 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 partly replaced by secondary albite that also veins the groundmass.  Only minor  amounts of albite occur i n 14. Primary hornblende, p a r t l y altered to colourless  21 augite and to brown b i o t i t e , occurs i n 14.  Several stages  from p a r t i a l to complete replacement or r e c r y s t a l l i z a t i o n are found i n t h i s section (Appendix A, pA36)•  However,  i n 16 and 18 (b), a l l hornblende has been augltized completely. The fresh d i o r i t e porphyry from the Mascot 3700 l e v e l i s b a s i c a l l y about the same as the other s i l l s but i t lacks most of the a l t e r a t i o n that has affected them. The greenish brown hornblende phenocrysts, however, are s l i g h t l y altered to b i o t i t e and to colourless augite. The b i o t i t e 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.  Alteration of either  groundmp.ss or phenocrysts i s n e g l i g i b l e .  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 t h i s 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 c r y s t a l ; border, the main part around  22 the core; and periphery, the outermost t h i n s h e 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 i n (A) reached A n , others were as low as Q 7  An . 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 r y s t a l l i z e 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 r y s t a l l i z e soon after (B).  At that time, the phase  separating from the melt was basic labradorite. The largest phenocryst possesses a very t h i n shell 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 c r y s t a l  (C) have about the same composition as the phase i n e q u i l i b rium with the melt when the periphery was formed.  The  2 3  oligoclase-andesine groundmass i s the f i n a l product of crystallization.  Thus we have, a complete sequence of  c r y s t a l l i z a t i o n beginning with basic bytownite i n the core of the largest phenocryst and ranging through i n t e r mediate and basic labradorite i n the smaller phenocrysts to acidic andesine i n the groundmass and late veinlets of the large grains.  ••  Minerals Plagioclase  Sections  3*  1  2  40  30  20  -  -  15  15  Hornblende Tremolite  15  11  15' 8(1)  45  30  25  -  -  5  15  Augite  -  Sfiapolite  ?  -  Sphene  1  1  -  -  Apatite  2  1  1  1  Quartz  2  2  -  2  Calcite  -  ?  1  1  Eiotite  1  1  -  -  1  -  1  1  1  -  Albite Clinozolsite Epidote Actinolite Chlorite Chloropal Kaolin  5 '5  -  y  y y  Sericite  •  y  Sulphides  P  P C,PJA  Grroundmass (n)  >  P" Pyrrfcotite A  Arsenopyrite  ri  C  6halcopyrite  <  >  <  s:(2)  17  10  30  -'  -  -  -  -  15  20  2  ?  1  -  1  2  1  1  1  1  1  -  -  -  1  1  -  -  2  1  -  -  -  1  ?  -  -  -  1  -  -  -  -  2  -  -  •  y  P.. 3  P"  •  •  P  P,A  -  TABLE SHOWING MINERALS PRESENT IN EACH SECTION Minerals  Sections 7! 14 16  l8Cb)  21  10  10  40  20  -  -  15  10  -  -  5  3  2  10  30  3  -  1  5  2  5  -  -  1  1  .1  1  1  2  -  2  1  1  1  1  I  Quartz  -  -  -  -  -  -  Calcite  -  1  -  1  1  1  -  Biotite  -  -  1  1  -  1  Albite  -  -  -  1  -  5  -  Clinozoisite  ?  1  1  1  -  -  Epidote  ?  -  -  -  -  1  -  -  -  -  -  -  -  2  -  y  y  19  6'  Plagioclase  15  20  35  35  Hornblende  -  -  -  Tremolite  10  15  Augite  -  Scapolite Sphene Apatite  Actinolite Chlorite Chloropal Kaolin  y  -  -  y  Sericite  •  y  y  Sulphide s  -  p  P.C  . vGroundma s s cf. n  bftls  (n)  -  -  1  -  y  C  P,0 <  -  P  BIBLIOGRAPHYB I l l i n g s l e y , P . a n d Hume,C.R. C(194l) TJhe ore deposits !  of N i c k e l P l a t e  Mountaln.Hedley,B.C.Can.  Irist. Min.. and Met. Trans.., v o l . 44, p5 24590. Bbatock,Hr,S.. (1930) Geology; and ore. deposits of N i c k e l P l a t e Mountain, Hedley,F.C.. Geol.. Survey* Can.., Summ. Rept .. 1929, pt.A, J  p 198,-25 2A.. :  BowenjN>;L.. (1928) The e v o l u t i o n of the igneous rocks,. P r i n c e t o n U n i v e r s i t y 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. Do Image, V i . andKfown-iC. E.G.  2.  (1945) Contact metamor-  phism at N i c k e l P l a t e Mountain, Hedley, BriC.Can. I n s t . Min. and"..Met. Trans.,vol. 48, p27-67. Mantuani,L.D..(1949) Personal communication. Schmitt,H..(1933) Communication to Kelowna E x p l o r a t i o n Co. L t d .  APPENDIX A L i s t of Abbreviations and Symbols Ab  albite  absorp  absorption  An  anorthite  bals  Canada balsam  biax  -  biaxial  c  -  v e r t i c a l c r y s t a l axis  £  -  epsilon, index of refraction of extraordinary ray  ext  -  extinction  interf  -  Interference  1-fast  -  elongation p a r a l l e l to the vibration d i r e c t i o n of the fast ray  1-slow  -  elongation p a r a l l e l to the vibration d i r e c t i o n of the slow ray  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 for extraordinary ray  -  n for ordinary ray  n  e  n^  dispersion for red l i g h t  r  (thin) section  sect X sect  cross section dispersion for v i o l e t l i g h t  v  angle between optic axes  2V  X  vibration d i r e c t i o n of the fastest ray  Y  -  vibration direction of the intermediate ray  Z  -  vibration direction of the slowest ray  010, 001, etc  -  M i l l e r indices of c r y s t a l faces  A -  angle  JL -  normal to  H - p a r a l l e l to > -  greater than  < -  less than  (+)  -  o p t i c a l l y positive  (-)  -  o p t i c a l l y negative  +_ -  approximately  A. Loc. B. Geol. Rein.  -  Location of specimen  - 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. L o c . ; 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 f a u l t .  Ore occurs  above and below it.. C. S i g n 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 k e , striated f e l d spar with random orientations are uniformly distributed i n the aphanitic groundmass.  Pyrrhotite and lesser amounts of  chalcopyrite and pyrite and f i n e l y disseminated through the specimen but are noticeably more concentrated along fractures and j o i n t s .  No mafic minerals are v i s i b l e .  E. Thin Section Minerals Present Andesine  Est. j> • 40  Characteristics biax (+), max ext/\_L010 23° n>bals (1.55);  Tremolite  15  Ab  66  An  +0  biax (-), 2V 70* ± , 1-slow, n ^ b a l s (1.63), Z A  c  l l " -14* ,  long diagonal of X sect = slow ray> generally colourless but s l i g h t l y greenish  A2 Minerals Present  Characteristics  Eat. %  . i n places  Tremolite Cont'd.  verging towards  actinolite. tan colour, pleochroic, max  Biotite  absorp / / polarizer,  1-slow,  mod b i r e f . n >bals (1.60),  Apatite  euhedral  grains, colourless, low b i r e f . uniax (+), low biref, low re-  Quartz  l i e f , n> bals. apparently uniax (+), high  Sphene  biref, n * 1.7+. Scapolite (?)  1-fast, mod biref, n=1.55t, small platy grains. 1-slow, low r e l i e f , low i n -  Sericite  t e r f colours, fibrous, colourless, small grains, opaque, white, associated with  Kaolin  feldspar. Pyrrhotite  opaque, bronze colour  Blue mineral  s l i g h t l y pleochroic blue to colourless, dendritic  struc-  ture, n y bals (1.57), low i n t e r f colours, 1-fast, +; / / ext. Groundmass  37  some n< bals, may include a l kali  feldspar.  A3 Description The plagioclase v i s i b l e i n the hand specimen proves to be andesine of about Ab A n ^ composition. Most gQ  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 a l t e r a t i o n  clouds even the freshest grains and i s often responsible for an apparent zoning by affecting either internal or peripheral regions more than the r e s t .  Plagioclase feldspar also occurs  i n the groundmass as laths less than 0.04 mm long.  These are  altered too much to be i d e n t i f i e d . Several crystals of andesine have been partly replaced 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 s e r i c i t e , and occasional, irregular blebs of. sulphides. Tremolite occurs as pseudomorphs after hornblende phenocrysts and as irregular patches i n the groundmass.  It  can be distinquished from scapolite by i t s positive elongation and inclined  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 i g h t l y greenish and poss i b l y should more correctly be called t r e m o l i t e - a c t i n o l i t e . One elongate grain i s d i s t i n c t l y fractured but the enclosing groundmass shows no evidence of movement.  Like the feldspar  A4  phenocrysts, tremolite also contains inclusions, some of which when augmented by small patches of a l t e r a t i o n impart a sieve texture to small areas.  A second stage of a l t e r a t i o n  i s indicated by small, anastomosing shreds and streaks of b i o t i t e 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 n i c o l s , appear black and dark grey respectively.  A s t r i k i n g feature of a l l the apatite  i s i t s complete freedom from a l t e r a t i o n .  I t appears most  frequently as inclusions i n phenocrysts of feldspar and r e placed hornblende. Pyrrhotite i s found sparingly over most of the section and i s rather large, Irregular masses close to p a r a l l e l fractures about h a l f an inch apart.  Some tremolite  pseudomorphs near the fractures are p a 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 o r i g i n a l crystal.  Although chalcopyrite and pyrite were v i s i b l e i n the  hand specimen they could not be i d e n t i f i e d i n the t h i n section. 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 f e l d -  spar i s shown by blebs of quartz elongated p a r a 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 t h i s  mineral seems rather low and the acute rhombic sections characteristic of sphene are very rare.  However, the mode of  occurrence i s d e f i n i t e l y 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 p a r a 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 s e r i c i t e can be seen though i t forms, a rather small percentage of the s l i d e .  Similarly 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 i s kaolin. A blue pleochroic mineral was observed i n two small dendritic aggregates consisting of minute, r a d i a l , prismatic crystals.  Except that the index of refraction was too low,  the properties of this mineral agree' quite well with those of crocidolite.  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 comprise 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.  B. Geol. R e i n . :  E l . 5450.  This dike specimen i s taken from the marbleskarn t r a n s i t i o n zone.  Nearby mineralization  i s low grade ore. C. S i g n i f . ;  Normal Flange type.  D. Hand Specimen This rock i s a fractured,  rusty-weathering  made up of plagioclase phenocrysts i n an aphanitic gray (  / ) groundmass.  Pyrrhotite i s evident,  porphyry greenish  particularly  along small fractures, and the presence of chalcopyrite i s suggested by occasional specks of malachite i n weathered jointsi E. Thin Section Minerals Present Andesine  Characteristics  Est, jo 30  biax M max ext A JL 010 26°, Afe 5o  A n  Tremolite  15  5o  Z/\c 12°-13°, same as tremolite i n section 1  Sericite  10  1-slow, fibrous habit, low r e l i e f , mod b i r e f  Quartz  2  normal quartz  Apatite  1  normal apatite  Sphene  1  normal sphene  Biotite  traces  Tan mineral  almost i s o t r o p i c , pale tan, s l i g h t l y pleochroic, n<apatite.  A7  Pyrrhotite  opaque, bronze, pock-marked  5  surface Magnetite (?)  .  opaque, black, small, i r r e g u l a r specks, chiefly i n former hornblende grains  Unidentifiable groundmass -  including some kaolin (probably) and possibly some carbonate.  DescriptionIt 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. kaolin and to s e r i c i t e .  It i s altered i n places to  A l t e r a t i o n most commonly proceeds  from the Interior of crystals outward, leaving a rim of r e l a t i v e l y clear material surrounding a dusty core of s e r i c i t e and k a o l i n .  Other grains, however, consist of a fresh inner  part and an altered s h e l l .  Clear, zoned feldspars with very  d i s t i n c t (under crossed n i c o l s ) 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 i o t i t e 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.  It contains  many small, rounded inclusions which serve to distinguish from the feldspar associated with i t .  it  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.; C. S i g n i f . :  Medium grade ore occurs i n the v i c i n i t y .  Normal Flange type cutting Yellow ore.  D. Hand Specimen Sample 3 i s a dark b l u i s h gray (5B4/1), s l i g h t l y 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 o l d , tight fractures. Pyrrhotite and chalcopyrite are disseminated In minute flecks throughout the specimen and occur i n t h i n , v e i n - l i k e concentrations along some fractures. E. Thin Section Minerals Present Andesine  Est. % 20  Characteristics Ab twinning, max extAX 010 21°, biax (-+), Ab^An^  Tremolite  15  ZAc 15°-20°, 1-slow, n>bals (1.6+)  Colourless Augite  5-10  Z/\c 40°, biax (-+-), 2V 50° direction of smaller ext  is  slower ray, r e l i e f high (n>1.7), b i r e f up to 0.027. C l i n o z o i s i t e (?)  anomalous bright blue i n t e r f colours, r e l i e f low for c l i n ozoisite.  A10 Apatite  1  normal apatite.  A c t i n o l i t e (?)  1  Z A C 16°, n=1.59 , max b i r e f 0.029, many rhombic sections (long diagonal slow) ZV90° , at least 1 good cleavage,  Calcite  1  normal c a l c i t e  Sericite  5  "normal s e r i c i t e  Kaolin  10  Epidote (?)  1  normal k a o l i n high relief;.mod to high, variable b i r e f  Unknown mineral  vermicular habit, also wider blades, biax (-+•), «V60°, colourless to pale green pleochroism, e x t / / i n narrow shreds, 1-slow, XAc and Z A C i n other grains up to. 39°  Pyrrhotite  2  Arsenopyrite  <1  irregular grains sparse euhedral and subhedral grains, opaque, s i l v e r y , high relief.  Chalcopyrite  «  1  bright yellow, opaque, small grains.  G-roundmass  30-55  n<bals, very low r e l i e f , probably contains much a l k a l i feldspar  All 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 o n . Albite twinning i s well developed In most of the phenocrysts and i n some, poor g r i d twinning suggests the p o s s i b i l i t y of microcline but such grains have an index of refraction d i s t i n c t l y higher than the groundmass.  The chief a l t e r a t i o n i s to kaolin but s e r i c i t e and  scapolite have also formed from andesine.  Numerous inclusions  and islands of a l t e r a t i o n 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 i g i n a l l y twinned and the pseudomorphs s t i l l reflect t h i s phenomenon. Other phenocrysts, probably of augite, have been i  altered to colourless augite.  These grains are noticeably  clouded by a l t e r a t i o n 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. C l i n o z o i s i t e , epidote or both occur sparsely as a l t e r a t i o n products of andesine.  The d i s t i n c t i v e anomalous  blue, f i r s t - o r d e r 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 t h i s mineral and, together with the high r e l i e f suggest either epidote or e l i n o z o i s i t e . 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 t h i s instance by randomly oriented tremolite grains.  Arsenopyrite shows a tendency to be associated with  the scapolite and pyrrhotite with the a c t i n o l i t e (?) 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 z e d . Prom this i t could be inferred that the a l t e r a t i o n of plagioclase and, possibly, orthoclase supplied material for the c a l c i t e and s e 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 n i c o l s are not crossed. No plagioclase was seen i n the groundmass and no quartz or sphene could be i d e n t i f i e d .  A13 A porphyritic texture has been inherited from the o r i g i n a l rock.  Locally, sieve texture i s shown by several  minerals, p a r t i c u l a r l y 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  uniax (-), i n t e r f colours  5-10$  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. R e i n . : ffrom Central fault zone with high grade ore nearby. C. S i g n i f . :  Unusually blue Flange dike material.  D. Hand Specimen White plagioclase and somewhat bleached hornblende phenocrysts are. the only non-metallic minerals i d e n t i f i a b l e 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-  t a i n a t h i n f i l m of whitish material that does not effervesce with cold d i l u t e hydrochloric a c i d .  The specimen has a strong  kaolin odour. E. Thin Section Minerals Present  Est. %  Andesine  45-50  Characteristics biax (+), max extA±010 23°, n>bals, Ab An 60  Tremolite  5-10  4o  length slow,, ext A 6°-18°, r e l i e f high, n=1.64+, max i n t e r f colour second, order green, b i r e f of 0.027  Apatite  1  normal apatite  Quartz  2  normal quartz  A15 Epidote (?)  Max, 2V±90°, high r e l i e f  <1  n=1.7+, variable interference colours but most are not as high as they should be. Calcite  normal c a l c i t e .  1  Chlorite (?)  <^ 1  mod r e l i e f , n=1.60, 1-fast, fibrous, wavy extinction, / / or small ext/l, low i n t e r f colours (bluish i n grays), semi-radiating aggregates, normal pyrrhotite  1-2  Pyrrhotite Sericite  normal s e r i c i t e  Kaolin  normal k a o l i n mostly n>bals, but some n<bals  + 40  Groundmass Description  Almost a l l ofthe plagioclase phenocrysts show albite twinning; many are well zoned, and a vew are almost e n t i r e l y altered to s e r i c 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  c r y s t a l with good twinning gave a difference i n extinction angles of five degrees corresponding to a variation i n A6 content of about 4 per cent, with the inner part more c a l c i c 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, c a l c i t e , epidote (or c l i n o z o i s i t e ) , and c h l o r i t e (?).  Semi-  radiating aggregates•of fine, fibrous c h l o r i t e (?) l i e p a r a 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 i d e n t i f i c a t i o n . 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 c a l l e d a meta-diorite porphyry.  A17  SECTION 11 A. L o c :  903 d r i f t .  El.  5165.  B. Geol. Rein.:  I n strong skarn zone with good ore nearby.  C. S i g n i f . :  i s t h i s more bleached than No.  Why  14?  D. Hand Specimen P l a g i o c l a s e i s not n e a r l y as n o t i c e a b l e i n t h i s as i n other specimens of Flange Dike.  A l s o , the mafic  phenocrysts and t h e i r pseudomorphs are so c l o s e t o the dark greenish-gray  colour (5G4/1) of the groundmass t h a t one  must look c a r e f u l l y to see the p o r p h y r i t i c t e x t u r e , P y r r h o t 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 r a t h e r than sulphides.  Proof that the f e l d s p a r s are h i g h l y  a l t e r e d i s amply supplied by a strong a r g i l l a c e o u s odour. E. Thin S e c t i o n M i n e r a l s Present  Characteristics  Est. 30  Andesine  b i a x {+)  H  ZV, max ext/U.010  n> balsam, A b ^ Tremolit e-Actinolite  24?,  An^ .  low i n t e r f e r e n c e c o l o u r s ,  15  n* = 1.64  ±, b i a x (-), ZV  75-6*0, ext A up to 15°,  weakly  t i n t e d green i n some g r a i n s , < 1  Sphene  very high r e l i e f , high b i r e f , o c c a s i o n a l acute rhombic sections,  Apatite  ^  1  normal.  AlS Kaolin Sericite  15  imparts dusty look t o f e l d s p a r ;  5  normal  Pyrrhotite  normal  A l b i t e (?)  b i a x , very low r e l i e f , low biref, clear, 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 s e c t i o n are much more a l t e r e d than those i n other Flange specimens.and the groundmass f e l d s p a r s 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 o f the f e l d s p a r s makes i t s e l f evident i n the clouded, dusty appearance of the e n t i r e s e c t i o n . The l a r g e t r e m o l i t e g r a i n s 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 p y r r h o t i t e . The best example o f t h i s i s a l a r g e phenocryst near the center of the s e c t i o n that appears t o have been completely a l t e r e d t o t r e m o l i t e , which l a t e r became p a r t i a l l y  replaced  by p y r r h o t i t e and by a c l e a r , c o l o u r l e s s , f r e s h l o o k i n g 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 t o be associated with the greenish t r e m o l i t e  (tremolite-actino-  lite). A considerable  amount o f f i n e grained  tremolite.  developed i n the groundmass as w e l l as i n the hornblende  A19 and some o f the andesite phenocrysts gives the specimen a definite 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 o f the f e l d s p a r may have l e d t o an underestimation of the p r o p o r t i o n o f andesine phenocrysts i n the specimen and consequently t o an i n c o r r e c t name f o r the rock b u t , 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 t h a t the combined  phenocrysts o f andesine and t r e m o l i t e - a c t i n o l i t e only 45 per cent o f the s e c t i o n .  make up  A20 SECTIONS g {!]_ & 8 (2) A. Loe.;  From f o o t w a l l o f £.3  B. G e o l . R e i n . ; C. S i g n i f . ;  stope. E l .  High grade ore above and. below t h i s  T y p i c a l Midway s i l l . lar  5215.  I s the a l t e r a t i o n  to that i n other  sill. simi-  sills?  D. Hand Specimen Sample 8 (1) i s a l i g h t g r e e n i s h - g r a y porphyr  i n which one  can d i s c e r n sparse bleached hornblende  phenocrysts up t o seven o r e i g h t mm s m a l l e r phenocrysts  (5GY8/1)  l o n g and more numerous  of f e l d s p a r , some o f which are  S u l p h i d e s are n o t i c e a b l y absent small, i s o l a t e d grains.  The  except f o r a few  striated.  extremely  specimen has a somewhat  monotonous appearance owing t o t h e f a c t t h a t and groundmass blend p a r t i c u l a r l y w e l l .  phenocrysts  The r o c k g i v e s o f f  a s t r o n g a r g i l l a c e o u s odour. E. T h i n S e c t i o n M i n e r a l s Present Andesine  3  (1) Est. % 25  Characteristics b i a x {+) max n ^ b a l s , Ab  Augite  20  Z c 43°, n  e x t A i . 010  ZZj  An b a l s (1.75), i n t e r f  c o l o u r s mostly low but some up  Sphene  2  to  2nd  ZV  60°  o r d e r y e l l o w , b i a x (-+-), +.  r e l i e f h i g h n = 1.8"+, e x t i n c t i o n not complete ( o n l y t o b l u i s h ) , b i a x (+), 2V 25-30°, d i s p e r s i o n r?v  strong.  A21 Calcite  < 1  normal  Apatite  < 1  normal  A l t e r a t i o n mixtures of K a o l i n ,  sericite, low t o mod b i r e f .  epidote ( ? ) , s c a p o l i t e (?) Pyrrhotite  < 1  normal  A l b i t e (?) o r an alk Feldspar  2  colourless (pinkish),  n<bals,  b i a x (•+), ZV l a r g e . Groundmass  50-60  mostly n < b a l s , 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 , // e x t .  Description The f e l d s p a r phenocrysts are h i g h l y a l t e r e d t o f i n e grained cloudy masses of k a o l i n , s e r i c i t e , and poss i b l y some epidote.  Twinning l a m e l l a e 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 o f zoning are present.  Most commonly the outer p a r t s o f c r y s t a l s are  more a l t e r e d than the center.  The groundmass i s too much  a l t e r e d t o a l l o w a p l a g i o c l a s e determination and, i n view of i t s g e n e r a l l y low index probably contains mostly a l k a l i feldspar. Next t o andesine, c o l o u r l e s s a u g i t e i s the most abundant m i n e r a l .  I t occurs as pseudomorphs a f t e r horn-  blende and a l s o as small xenoblasts t h a t may be i s o l a t e d or i n groups.  S i e v e - l i k e t e x t u r e i s produced i n the l a r g e r  augite g r a i n s by patterns of a l t e r a t i o n t o c a l c i t e ,  A22  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 s p a r s e l y d i s t r i b u t e d through the s e c t i o n . U s u a l l y i t s high' b i r e f r i n gence produces high order i n t e r f e r e n c e colours but i n two or three g r a i n s only about f i r s t order yellow i s reached. These g r a i n s , i n s t e a d of e x t i n g u i s h i n g , merely become dark blue.  They g i v e a b i a x i a l p o s i t i v e i n t e r f e r e n c e f i g u r e  with a 2V of l e s s than 30°.  Strong a x i a l d i s p e r s i o n can  be seen with r>v. The c r y s t a l l o b l a s t i c t e x t u r e of the groundmass and the probably o r i g i n a l composition of l e s s than 45 cent phenocrysts  per  of andesine and hornblende make t h i s  specimen an a u g i t i z e d meta-andesite. SECTION 3 (2) M i n e r a l s Present  Est. %  Andesine  10-15  Characteristics max ext/U-010 24°, biax (+), 2V 70°, A b  55  An (originally 4 5  much higher p r o p o r t i o n , poss i b l y 30-40$) Augite  20  biax (+), 2V+60 ( o f f center 0  o p t i c a x i s f i g u r e ) ZAc  42°,  r e l i e f high, v a r i a b l e i n t e r f colours. Sphene Apatite  ^  1  normal  1  normal  A23 uniax (-), 1 - f a s t , // e x t ,  Scapolite  many i n c l u s i o n s , n < b a l s (1.540) b i a x (+), 2V about 70°, very low  Albite  r e l i e f , colourless, clear, n < b a l s (1.53.). Kaolin  ) )  Sericite  )  Arsenopyrite Pyrrhotite  probably considerable but very f i n e grained and w e l l d i s t r i b u t e d , < 1 «  Groundmass  1 60  s i l v e r c o l o u r , opaque, euhedral g r a i n s , high r e l i e f , normal mostly n^-bals but some n-^-bals.  Description Highly a l t e r e d andesine phenocrysts are b a r e l y d i s t i n g u i s h a b l e from the clouded, c r y s t a l l o b l a s t i c groundmass.  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 o t h e r s .  There i s a tendency  f o r stronger a l t e r a t i o n i n t h e centers of some g r a i n s so t h a t r e l a t i v e l y f r e s h rims a r e l e f t e n c l o s i n g clouded cores." Large a u g i t i z e d hornblende phenocrysts are given pronounced sieve t e x t u r e by numerous i n c l u s i o n s 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 f e l d s p a r phenocrysts.  The i n t e r -  ference colours of pyroxene i n the phenocrysts a r e , on the average, much higher than those o f the small xenoblasts, the former being u s u a l l y 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 y e l l o w .  A24 A mineral t h a t i s probably s c a p o l i t e occurs adjacent t o an a r s e n o p y r i t e c r y s t a l and along a nearby f r a c ture.  At f i r s t i n s p e c t i o n the index of r e f r a c t i o n appears  too low f o r s c a p o l i t e .  E p s i l o n 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 s e c t i o n the balsam was found by the use of index o i l s t o have a r e f r a c t i v e index c l o s e t o 1.541* The lowest value of n W i n c h e l l , i s 1.535*  e  f o r (-) s c a p o l i t e , according t o  The (+) s c a p o l i t e , m a r i a l i t e , has a  value o f n„ o f 1.523 but the mineral i n t h i s s e c t i o n i s d e f i n i t e l y (-). Small anhedral g r a i n s of a c l e a r , c o l o u r l e s s mineral w i t h low r e l i e f are found i n v a r i o u s p a r t s o f the section —  i n the groundmass, i n the andesine  phenocrysts  and o c c a s i o n a l l y with the a l t e r a t i o n products i n l a r g e augite g r a i n s . The p r o p e r t i e s suggest t h a t i t i s untwinned, secondary  albite. This rock i s very h i g h l y a l t e r e d and r e c r y s t a l -  lized.  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 e i t h e r porphry o r m e t a - d i o r i t e porphyry.  meta-andesite  I t has w e l l  developed  c r y s t a l l o b l a s t i c , s i e v e , and p r o p h y r o b l a s t i c t e x t u r e s but no d i s t i n c t i v e s t r u c t u r e s .  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. S i g n i f . ;  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 l o c a l disseminations of  pyrrhotite and i n one of these a single euhedral c r y s t a l of arsenopyrite occurs. E. Thin Section Minerals Present  Est.  Andesine  30  Characteristic s biax (+), large 2V, max ext AJ_ 010 23°, n>bals, Ab  Tremolite  30  40  An^ .  biax (-), large 2V, Z A C 10°-19°, 1-slow, polysynthetic twins.  Augite  < 2  Z A C 39°, high r e l i e f , low i n t e r f colours. green, pleochroic, Z A C 10°-13°,  Actinolite  1-slow, r e l i e f same as tremolite, f i n e grains. Sphene  < 1  normal  Apatite  <  1  normal  Clinozoisite  < 1  normal  A26 Calcite  2  Kaolin  normal nprmal  R e c r y s t a l l i z e d Groundmass material  n>bals, b i a x (+), 2V 6 0 ° .  Description Andesine phenocrysts a r e zoned and mostly w e l l twinned though a l t e r a t i o n l o c a l l y obscures such s t r u c t u r e s . Andesine l a t h s i n some t r e m o l i t e grains i m p l i e s a l i m i t e d p o i k i l i t i c texture.  K a o l i n and c a l c i t e form the c h i e f  a l t e r a t i o n products o f the andesine. Several former hornblende phenocrysts contain both t r e m o l i t e and a u g i t e .  I n one, t r e m o l i t e forms an  i r r e g u l a r r i m 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 t o say that e i t h e r i s t h e e a r l i e r . The rock has l o c a l s i e v e , b l a s t o p o i k i l i t i c , and b l a s t o p o r p h y r i t i c t e x t u r e s .  Because o f the r e c r y s t a l -  l i z a t i o n and the f a c t that the andesine and former hornblende 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  of N43 - A l stope, F - f l o o r .  F.W.  B. Geol. Rein.:  Midway " s i l l " c r o s s c u t s crumpled beds here.  C. S i g n i f . :  E l . 4425.  R i c h ore i s found above.  Midway " s i l l " from Morning s e c t i o n of the mine •  D. Hand Specimen Sample 19 i s a dusky o l i v e rock (8Y6/3) t h a t i s f r a c t u r e d , s l i g h t l y sheared, and apparently deeply weathered.  K a o l i n i z e d phenocrysts of f e l d s p a r appear as  l i g h t e r coloured spots on c l e a n s u r f a c e s . Along f r a c t u r e s , c h l o r o p a l - l i k e m a t e r i a l and p y r r h o t i t e are v i s i b l e . The rock has a p e c u l i a r earthy odour. E. Thin S e c t i o n M i n e r a l s Present  Est. %  Characteristics  Andesine  15-20  max extA-1-010 22°,  Tremolite  10-15  ZAC  n>bals,  1 0 ° - 1 4 ° , poor b i a x  (-)  i n t e r f f i g u r e , n=1.65, 1-slow. Sphene  < 1  normal  Clinozoisite  normal  Epidote (?)  n = 1.7+,  Kaolin  40-50  // e x t , 1 - f a s t .  white, opaque, s l i g h t l y s t a i n e d by l i m o n i t e occasionally.  A28 Description The h i g h l y a l t e r e d andesine phenocrysts are barely d i s t i n g u i s h a b l e from the enclosing mass o f k a o l i n , epidote ( ? ) , and c l i n o z o i s i t e . poorly preserved.  A l b i t e twinning i s only  Tremolite, with good sieve t e x t u r e , 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 metaandesite porphyry or meta-diorite porphyry.  A29 6  SECTION  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 t h a t crosscuts beds i n a t i g h t f o l d near the Marble  L i n e , 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 w i t h Flange, Midway, and sample 7.  D. Hand Specimen This rock i s a medium greenish gray (5gy5/1) porphyry comprised of an a p h a n i t i c groundmass and phenoc r y s t s of p l a g i o c l a s e and a l t e r e d hornblende, those of the l a t t e r a t t a i n i n g a l e n g t h of nine or t e n mm.  Fine  grained p y r r h o t i t e t h a t i s disseminated through the specimen and a l s o somewhat concentrated along o c c a s i o n a l f r a c t u r e s causes the f r a c t u r e surfaces to weather a g r a y i s h brown (5YR3/2).  The l a r g e r tremolite-hornblende  phenocrysts  appear t o 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, a r g i l l a c e o u s odour. E. Thin S e c t i o n M i n e r a l s Present  Est. %  Characteristics  Plagioclase  20-25  n^bals, d o u b t f u l e x t A J .  010  30°.  Tremolite  15  normal  Augite  5-10  Z A C 43°, n  =  1.7+,  pale  y e l l o w i n t e r f c o l o u r s , some euhedral g r a i n s , at l e a s t one good cleavage.  A30 Apatite  2  normal  Clinozoisite  1  biax (+) ( ? ) , 2V about 80°, n = 1.74, e x t A with cleavage 15°, blue i n t e r f colours i n f i r s t order gray zone,  Sphene  '< 1  normal  Calcite  ^ 1  uniax (-), high b i r e f , v a r i a b l e r e l i e f , l a t h shaped and i r r e g u l a r g r a i n s .  Sericite Kaolin  5  normal  15  normal  Scapolite  normal  Pyrrhotite  <Z<L 1  Groundmass  45  normal mostly n< b a l s .  Description The p l a g i o c l a s e i s too much a l t e r e d t o 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 g r a i n s i n d i c a t e d an e x t i n c t i o n angle of about 30°• This would place i t i n the l a b r a d o r i t e d i v i s i o n (Ab^ A n ^ ) . K a o l i n i s the c h i e f a l t e r a t i o n product f o l l o w e d i n importance by s e r i c i t e and c a l c i t e .  Feldspar phenocrysts are  d i s t i n g u i s h e d from the groundmass only with d i f f i c u l t y but phenocrysts of other minerals are u s u a l l y sharply euhedral. Small t r e m o l i t e prisms and aggregates are developed almost a l l through the s e c t i o n , p a r t i c u l a r l y i n a l t e r e d f e l d s p a r phenocrysts.  I n a d d i t i o n , some a u g i t i z e d  A31 hornblende phenocrysts are now p e r i p h e r a l l y replaced by pseudomorphic t r e m o l i t e . The augite i s r e s t r i c t e d t o narrow, i r r e g u l a r streaks p a r a l l e l t o the cleavage.  Both  the augite and t r e m o l i t e have the same i n t e r f e r e n c e c o l o u r s and, on account of the cloudiness i n t h e s e c t i o n , b a r e l y n o t i c e a b l e d i f f e r e n c e i n r e l i e f but the e x t 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° t o 17° whereas the inner part, extinguishes at about 43° • One o f these t r e m o l i t e - a u g i t e g r a i n s that has been both bent and f r a c tured and another deformed g r a i n o f augite give evidence of s t r e s s i n the rock.  Proof that some of the a u g i t i z e d  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 t o 0.6 mm i n diameter i n s e v e r a l p a r t s of the s e c t i o n . P y r r h o t i t e however i s much scarcer than i n p r e v i o u s l y described sections. The rock possesses c r y s t a l l o b l a s t i c and b l a s t o p o r p h y r i t i c t e x t u r e and minor c a t a c l a s t i c s t r u c t u r e . The o r i g i n a l composition has been somewhat obscured but, as close as can be determined, i t leads t o the choice o f * meta-andesite porphyry f o r the rock name.  A32  SECTION 2 A. L o c :  From S.S. No. 4 Shaft.  B. Geol. Rein.;  E l . 5590.  Probably the continuation of S.S. No. 3 dike but i n the footwall limestone.  Carries only minor mineralization l o c a l l y . C. S i g n i f . :  Compare i t s a l t e r a t i o n to that of No.  6.  D. Hand Specimen This sample i s a dark greenish gray porphyritic rock.  (5GY4/1)  I t i s traversed by occasional f r a c -  tures containing p y r r h o t i t e , c a l c i t e , and chalcopyrite along which the rock breaks, exposing rusty weathered surfaces.  The sulphides are also disseminated  t i c l e s through the rock.  i n small par-  Numerous s t r i a t e d feldspar  phenocrysts, a l l l e s s 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 c r y s t a l l i n e part of the  rock, the rest being a mottled, aphanitic groundmass. The rock has a strong a r g i l l a c e o u s odour. E. Thin Section Minerals Present  Est. %  Andesine  3 5 - 4 0  Characteristics max  ext /tx 0 1 0 2 0 ° , n > b a l s ,  biax (4-), 2 V 7 0 ° , Ab Tremolite  10-15  mod 5-10  An  40  .  biax (-), 2 V large, Z/vc 1 1 ° - 1 4 ° ,  Scapolite  6o  colourless, 1-slow,  relief, n  normal  S  ..1.65+.  A33 Augite  2-5  biax ( + ) ( ? ) , r e l i e f high, n > b a l s . ( 1 . 7 3 ) , Z A C 43°, colourless,  Apatite Sphene  1  normal  > 1  normal  Sericite  normal  Kaolin  normal  Pyrrhotite  < 1  normal  Chalcopyrite  <: 1  normal n < b a l s and some n ^ b a l s .  Groundmass Description  The s e c t i o n contains abundant euhedral andesine phenocrysts t h a t vary i n s i z e from 0.2 mm t o one mm. They show r a t h e r poor a l b i t e twinning and are not zoned. K a 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 t h a t s h e l l s o f 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 g e r g r a i n s 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 f e l d s p a r .  Apatite  i n c l u s i o n s i n the f e l d s p a r are common. Most o f the t r e m o l i t e i s apparently  pseudomor-  phous a f t e r hornblende and, i n a d d i t i o n t o the euhedral o u t l i n e s , has i n h e r i t e d a rough p o l y s y n t h e t i c twinning i n some instances.  Some grains of t r e m o l i t e contain r e l i c s  of e i t h e r c o l o u r l e s s hornblende o r a u g i t e .  I n such  c r y s t a l s t h e outer part has an e x t i n c t i o n angle of the order of 15°, the inner p a r t , 4 3 ° . 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 m a t e r i a l but the i n t e r ference colours are e x a c t l y the same. C h a l c o p y r i t e and p y r r h o t i t e occur as opaque, d e n d r i t i c threads f o l l o w i n g cracks and cleavage i n a few c r y s t a l s of f e l d s p a r and s c a p o l i t e . A few i n d i s t i n c t l a t h s of p l a g i o c l a s e 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 i n d i c a t e a l b i t e .  The s e c t i o n has b l a s t o p o r p h y r i t i c texture and minor sieve and p o r p h y r o b l a s t i c textures as w e l l as r a t h e r poor c a t a c l a s t i c s t r u c t u r e i n the form of o c c a s i o n a l bent tremolite grains.  The preponderance of phenocrysts over  groundmass and the a p h a n i t i c g r a i n s i z e of the l a t t e r j u s t i f y the name, m e t a - d i o r i t e porphyry.  A35 SECTION 1^ A. L o c :  of b l i s t e r at 9 . 2 Stope chute. E l . 5165.  F.W.  B. Geol. Rein.: C. S i g n i f . :  Good ore above and below i n strong skarn.  A mine s i l l t h a t i s unbleached.  Compare to  Midway. D. Hand Specimen This medium greenish gray (5GY5/I) porphyry c o n s i s t s of an a p h a n i t i c groundmass and  phenocrysts,  r a r e l y exceeding two or three mm i n l e n g t h , of dark, a c i c u l a r hornblende and l e s s n o t i c e a b l e 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 f r a c t u r e s t h a t are sealed by e i t h e r c h l o r i t i c m a t e r i a l or very f i n e - g r a i n e d , brown, p y r r h o t i t e - r i c h bands.  Only a weak a r g i l l a c e o u s odour i s given o f f .  E. Thin Section M i n e r a l s Present Labradorite  Est. % 35  Characteristics b i a x (+•), 2V l a r g e , max extA-i010 32°, low r e l i e f , low b i r e f , n > b a l s , Ab^p An  (  Hornblende  20  long p r i s m a t i c c r y s t a l s , b i a x (-), l a r g e 2V, n > b a l s Z A C 11°, 21°, 26°,  1.68,  pleochroic  y e l l o w i s h green-brownish green. Augite  5  rims around and replacement of hornblende, b i a x (-), mod-large 2V, Z A C 42°, n > b a l s (1.72).  A36 Biotite  < 1  normal  Apatite  1  normal  Scapolite  2  normal  Calcite  1  v a r i a b l e r e l i e f , high b i r e f , i n c l u s t e r s o f small round g r a i n s , anomalous blue i n t e r f c o l o u r s ,  Clinozoisite  b i a x (+j, 2V>70, ext/llO°, 1-slow. b i a x (-+-), l a r g e 2V, low b i r e f ,  Albite  low r e l i e f , n-^bals. Kaolin  5 (?)  normal  Sericite  5 (?)  normal  Sphene  normal  Chalcopyrite Groundmass  1 _45  normal n>and<bals.  Description Some o f the f e l d s p a r s are w e l l zoned and the m a j o r i t y s t i l l show f a i r a l b i t e twinning but a few are almost completely k a 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 o f hornblende phenocrysts i s w e l l i l l u s t r a t e d by many c r y s t a l s i n t h i s s e c t i o n .  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 f r a c t u r e s so t h a t a narrow s h e l l o f the c o l o u r l e s s augite develops around a hornblende c r y s t a l .  L a t e r stages are presented by i s l a n d s  A37 of unaltered hornblende i n augite and f i n a l l y by completely a u g i t i z e d phenocrysts. hornblende,  B i o t i t e shreds a l s o occur i n the  p a r t i c u l a r l y along cleavage planes.  Clino-  s o i s i t e , s c a p o l i t e , and c a l c i t e are a l t e r a t i o n products of the groundmass.  K a o l i n and s e r i c i t e , though a l s o i n  the groundmass, are confined p r i n c i p a l l y to the l a b r a d o r i t e phenocrysts. Sieve t e x t u r e i s shown by the few s c a p o l i t e 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  a p h a n i t i c groundmass, i t s l a r g e 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 o f the rock, i t i s best named a m e t a - d i o r i t e porphyry.  A3'8 SECTION 16 A. L o c :  F.W.  o f Red Ore on 4 L e v e l .  B. G e o l . R e i n . : C. S i g n i f . :  E l . 5450.  C o n t a i n s a p a r t i n g o f skarn and r i c h o r e .  Mine s i l l  (?).  Compare t o Midway.  D. Hand Specimen The  c o l o u r o f t h i s r o c k grades from a brownish  gray (5YR4/1) almost t o a g r e e n i s h g r a y (5G6/1).  Occasional  s m a l l phenocrysts o f f e l d s p a r are b a r e l y d i s c e r n i b l e i n t h e a p h a n i t i c groundmass.  P y r r h o t i t e and c h a l c o p y r i t e impart  a r u s t y weathering q u a l i t y t o the specimen and k a o l i n i s a t t e s t e d t o by a s t r o n g a r g i l l a c e o u s odour.  A few com-  pact a r e a s o f about two mm i n diameter are composed o f a b l a c k , amorphous-looking m a t e r i a l c l o s e l y a s s o c i a t e d pyrrhotite.  T h i s i s shown t o be c h l o r o p a l by  with  microscopic  work. E. T h i n  Section  M i n e r a l s Present  Est. %  Andesine-Labradorite  Augite  10-15  Characteristics b i a x (•+-), 2V = 7 0 ° , max ext A j 010 26°, n > b a l s ,  Ab kn ,  ( o r i g i n a l l y probably  25-30%)  so  so  b i a x (+), 2V « 6 0 ° , Z A C 4 3 ° ,  10  n  =  1.70, c o l o u r l e s s , s i e v e  texture. Scapolite  5-10  uniax (-), 1 - f a s t , // e x t , n > b a l s , sieve texture,  Chloropal  (Nontronite)  2  uniax (-), n = 1.60, b l u e -  A39  Chloropal (Nontronite) Cont.  green c o l o u r , p l e o c h r o i c from b l u i s h green t o brownish green, vague t w i n ning,  Biotite  1-2  normal  Apatite  < 1  normal  Sphene  < 1  normal  Clinozoisite  <1  anomalous blue i n t e r f c o l o u r s , ext A 21°, b i a x (+-) ( ? ) , high relief,  «: 1  Calcite Kaolin  normal  Sericite  10 (?)  Pyrrhotite Chalcopyrite Groundmass  normal  normal  5  normal  < 1  normal  50-55  most o f groundmass n < b a l s .  Description The f e l d s p a r phenocrysts are very h i g h l y a l t e r e d 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 . Twinning i s almost completely  obscured but zonal s t r u c t u r e i s  s t i l l preserved i n s e v e r a l 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 f e l d s p a r but k a o l i n , c a l c i t e , s c a p o l i t e , c l i n o z o i s i t e , and sphene have a l s o developed a t i t s expense. Augite, o f t e n w i t h good sieve t e x t u r e , i s p a r t l y pseudomorphous a f t e r hornblende and i s i t s e l f r e placed t o a minor degree by b i o t i t e .  I r r e g u l a r masses of  A40 b i o t i t e are a l s o found i n areas containing abundant pyrrhotite. Sieve t e x t u r e i s w e l l shown by most of the l a r g e s c a p o l i t e xenoblasts.  The i n c l u s i o n s c o n s i s t of sphene,  p y r r h o t i t e , c a l c i t e , and unreplaced fragments of f e l d s p a r . Chloropal, i n two compact masses, occurs c l o s e l y associated with p y r r h o t i t e .  A l l parts of each mass have a p a r a l l e l  o r i e n t a t i o n and therefore g i v e e x a c t l y the same o f f - c e n t e r , almost u n i a x i a l i n t e r f e r e n c e 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 l e s s d i s t i n c t banding. Meta-andesite porphyry i s the most s u i t a b l e name f o r the rock because p l a g i o c l a s e and former hornblende phenocrysts c o n s t i t u t e l e s s than 50 per cent of i t , the groundmass i s a p h a n i t i c , and a l t e r a t i o n has duced new minerals and r e c r y s t a l l i z e d the o l d .  intro-  A41 SECTION 18 A. L o c :  F.W.  o f Yellow Ore a t 4 S t a t i o n .  B. G e o l . R e i n . :  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 d i f f e r e n c e ? D. Hand Specimen T h i s rock c o n s i s t s o f s p a r s e , minute g r a i n s of m a f i c s and p a l e p l a g i o c l a s e phenocrysts gray  (5G8/1) groundmass.  and one  in a light  greenish  A few s m a l l specks o f p y r r h o t i t e  c r y s t a l ,of a r s e n o p y r i t e are v i s i b l e .  The  rock  emits o n l y a f a i n t a r g i l l a c e o u s odour. E . T h i n S e c t i o n 18 M i n e r a l s Present Andesine  (b) Est. % 10  Characteristics b i a x (+), l a r g e 2V, max 010  Augite  30  16°, n > b a l s , k\  An  5  extAX 3 5  .  Z A C 36°-40°, b i a x (+), 2V 65°> high r e l i e f , i n large grains and  Albite  (?)  5  small l a t h s i n groundmass.  b i a x (+), 2V 75°, n - ^ b a l s , r e l i e f , low b i r e f ,  low  clear,  colourless. g e n e r a l c l o u d i n e s s caused by  Kaolin  white, Epidote  1  semi-opaque m a t e r i a l .  / / ext, 1-slow, b i a x l a r g e 2V, h i g h  (-)  relief.  A42 Sphene  2  normal  Calcite  -<• 1  normal  Apatite  <  normal  1  11-= b a l s and  Groundmass  some n:>bals.  Description The andesine phenocrysts are so h i g h l y a l t e r e d that t h e i r a l b i t e twinning i s mostly obscured.  Short  l a t h s of c o l o u r l e s s augite have developed at the expense of f e l d s p a r and the groundmass as a whole. l a r g e grains of augite (up t o 0.8 mm)  A few  fairly  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 i n t e r f e r e n c e figures. A l b i t e p a r t i a l l y replaces andesine i n one  or  two g r a i n s and s e v e r a l subhedral areas, p o s s i b l y former andesine phenocrysts, c o n s i s t of mosaics of anhedral a l b i t e g r a i n s .  equidimensional,  Camsell (1910, p87) b e l i e v e d such  aggregates of secondary f e l d s p a r t o be pseudomorphs a f t e r pyroxene.  S i m i l a r g r a i n s occur i n a minute,  v e i n l e t about 0.1 mm wide that a l s o contains  discontinuous several  euhedral c r y s t a l s of sphene. By v i r t u e of i t s extensive  recrystallization  and i t s o r i g i n a l l y p o r p h y r i t i c t e x t u r e , t h i s rock i s a meta-andesite porphyry.  now  A43 SECTION 21 A. L o c : Mascot Low L e v e l Tunnel. B. Geol. Rein.:  E l . 3750.  Occurs i n a strong skarn zone with abundant p y r r h o t i t e but no g o l d .  C. S i g n i f . :  Unusually f r e s h - l o o k i n g 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 o r s i x mm long form about 15 per cent of the rock. Smaller, l e s s n o t i c e a b l e phenocrysts of f e l d s p a r blend with the medium gray (  / ) a p h a n i t i c groundmass i n  which a l i t t l e f i n e - g r a i n e d p y r r h o t i t e i s disseminated. No f r a c t u r e s , j o i n t s , o r shear planes i n t e r r u p t t h e massive c h a r a c t e r . A f u r t h e r c o n t r a s t t o the other porp h y r i e s studied f o r t h i s report i s i t s f r e s h appearance. E. Thin S e c t i o n M i n e r a l s Present  Est. %  Andesine  40-45  Characteristics phenocrysts; max extA_L010 23°, n > b a l s , b i a x (-+•), 2V 7 5 ° , (groundmass extA 20°)  Hornblende  10-15  brown, s t r o n g l y p l e o c h r o i c yellow-brown  t o green-brown,  cross s e c t i o n s show 2 cleavages at 56° (measured) long diagonal s slow r a y . b i a x (-), 2V 75-80°, n = 1.68,  A44  Hornblende  ZAc 15° + .  Cont.  Augite  2-5  Clinochlore  1  ZAC  40°,  n> hornblende (1.7+).  uniax (+), e x t A 8O, 1 - f a s t , i n t e r f c o l o u r s i n low grays, n = 1.58, pale green.  Biotite  1  normal  Apatite  < 1  normal  1  normal  Pyrrhotite  a l l has n> b a l s .  Groundma ss Description  The subhedral t o euhedral andesine phenocrysts are w e l l twinned and may show d i s t i n c t zoning.  There i s  almost enough v a r i a t i o n i n s i z e among them t o produce a seriate texture.  Some groundmass f e l d s p a r i s a l s o twinned  and none i s a l t e r e d t o any e x t e n t . Euhedral phenocrysts of greenish brown hornblende, often complexly twinned, range i n s i z e from 0.5 t o 4 mm.  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 r e s o r p t i o n because the contacts with the groundmass are h i g h l y i r r e g u l a r i n d e t a i l . L o c a l l y the outer s h e l l o f a phenocryst seems t o 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 p e r i p h e r a l zone of each g r a i n to a more or l e s s marked degree.  I t can be d i s t i n g u i s h e d  from the hornblende by i t s l a c k of c o l o u r , much g r e a t e r e x t i n c t i o n 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 o f hornblende. On account o f the a p h a n i t i c 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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