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A petrographic study of rocks from the Box mine, Athabaska Lake Killin, Alan Ferguson 1939

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illlllllllllllllllllllllllllllllllll^ I A PETROGRAPHIC STUDY 1 1 OF ROCKS FROM | | THE BOX MINE, ATHABASKH LAKE | I BY 1 1 A. F. KTLLIII = A FETROGRAPHIG STUDY OF ROCKS FROM THE BOX MINE, A'l'HABASKA LAKE by Alan Ferguson K i l l i n A Thesis submitted for the Degree of MASTER OF APPLIED SCIENCE in the Department of GEOLOGY The University of Br i t i s h Columbia Ap r i l , 1939 CONTENTS Page PART I Introduction 1 Location and Topography 2 (a) Location 2 (b) Topography 2 Geology 2 (a) General 2 (b) Detailed 4 (1) The Sediments 4 (2) The Mine Granite 4 (3) The Basic Intrusives 6 Bibliography 8 Acknowledgement 9 PART I I Petrography 10 (a) Introduction 10 (b) Megascopic Examination of Specimens 10 (c) Microscopic Examination of Specimens 11 (1) The Abundance of Free S i l i c a 12 (2) Rock Fragments 14 (3) Textural Features 17 (4) Inclusions 18 (5) The Feldspars 19 Page-Conclusion 20 Explanation of Saps . 22 ILLUSTRATIONS Plat© I 15 Plate II 16 Map I In Folder Map II In Folder Map III In Folder PART I -1-A. PETROGRAPHIC STUDY OF ROCKS FROM  THE BOX MIME, ATHABASKA LAKE INTRODUCIIOH The following paper i s a discussion of the rocks i n the v i c i n i t y of the Box Mine near Goldfields, Saskatchewan. A br i e f description of the Box Mine i s given by F. J> Alc o c k \ who made an examination of the property during his reconnaissance survey of the Athaba3ka Region i n 1935* A more detailed survey and report of the Goldfields v i c i n i t y and the Box Mine was made by H. C. Cooke i n 1936. In 1938 Dr. C. 0* Swanson made a careful examination of the property. He noted several features which did not jibe with the descriptions of Alcock and Cooke. In order to make a detailed study, specimens were collected from a l l parts of the mine. (See Maps #1 and 2). Th«Vr« sections were made from several of these rocks and examined by the writer and the results set forth here. 'F. J . Alcock: The Geology of Lake Can. Mem. 196 H. C. Cook: Preliminary Report of Geol. Sur. Can. Paper Athabaska Region - Geol. Sur. Goldfields Area* Saskatchewan -37-3 LOCATION AND TOPOGRAPHY (a) LOCATION The Goldfields area l i e s on the north shore of Lake Athabaska near the extreme northwest corner of Saskatchewan, (See Map 4), The area can be reached by way of the Peace River from the end of the railway or by means of the railway from Edmonton to Waterways and thence down the Athabaska River to Lake Athabaska where regular steamship service i a maintained during the summer. Plane service i s maintained to the mining camps from Prince Albert, Alberta, and also from Edmonton, Alberta. (b) TOPOGRAPHY Goldfields i s situated within the Canadian Shield and the topography i s t y p i c a l of t h i s region. I t is a hummocky country of ridges and h i l l s separated by depressions that are commonly occupied by lakes or swamps. The whole area is characterized by low r e l i e f and disorganized drainage. GEOLOGY (a.) GENERAL In order to give a general idea of the time relations and the general lithol.ogy of the region Alcock's* table of formations i s reproduced below. 1 F. J . Alcock: The Geology of Lake Athabaska Region - Geol. Sur. Can. Mem. I96 -3-TABLE OF FORMATIONS? Athabaska aeries Proterozoic Conglomerate, arkose, sandstone, shale. Basalt flows and dykes UNCONFORMITY Granite INTRUSIVE CONTACT Gabbro, n o r i t e , p e r i d o t i t e , amphibolite INTRUSIVE CONTACT Beaverlodge series Quartzite, conglomerate, iron 1,? formation -:s.-: UNCONFORMITY Archaean Tazin group Granite, granodiorite, quartz-syenite, pegmatite -INTRUSIVE CONTACT Dolomite, limestone, quartzite, a r g i l l i t e , conglomerate, mica schist and gneiss; volcanic flow and fragmental rocks -4 (b) DETAILED GEOLOGY 1 2 Cooke and Alcock have divided the rocks on the property into three main groups: sediments, granite and basic intrusives. Dr. C. 0. Swanson states that there are only two series: sediments and basic rocks intrusive into these sediments* (1) Sediments The sedimentary rocks on the property have been extensively metamorphosed. Originally these rocks consisted of pure quartzites and felspathic sands that could be classed as arkose, greywacke, or pebble conglomerate, and are associated with occasional layers of s i l t and chert. During metamorphism these rocks have been altered, the pure sands becoming massive quartzites and the impure beds are now schists such as mica schist, sericitie quartzite, sheared arkose, etc., or else have become massive and more or less granitic in appearance. (2) The Mine Granite The term "mine granite" is used throughout this paper to designate the ore body which is described by Cooke and Alcock as granite and by Dr. Swanson as granitized sediments. 1 H. C. Cooke - Preliminary Report Goldfields Area, Saskatchewan -Geol. Sur. Can. Paper 37"3 2 F. J. Alcock • Geology of Lake Athabaska Region, Saskatchewan -Geol. Sur. Can. Mem. 196 The term ia one used by Dr. Swanson in his description of the geology of the mine. 1 2 Cooke and Alcock state that the ore body on the property consists of a s i l l - l i k e granite mass of Post-. 3eaverlodge age but do not agree on the definition of its boundaries. The rock is described by them as being highly altered but prior to alteration consisted mainly of albite feldspar containing orthoclase, together with quartz and some ferro-magnesiah minerals now mainly altered to chlorite. Dr. C. 0, Swanson states that this mine granite is a thoroughly granitized portion of the sedimentary series and not, as the name indicates, a true igneous body. The reasons given for this conclusion are set forth in the following quotation from the geological report of Dr. Swanson: "That the mine granite is merely a highly granitized portion of the sedimentary series is shown by the presence of numerous gradations to sedimentary types, not only at the main contacts, but also throughout the granite body. The more the body is studied, the clearer the transitions to sedimentary types appear, and the further they can be traced. It i s , of H. C. Cooke - Preliminary Report Goldfields Area, Saskatchewan Geol. Sur. Can. Paper 37-3 F. J. Alcock - Geology of Lake Athabaska Region, Saskatchewan -Geol. Sur. Can. Mem. I96 -6-course, possible that the granitization is due to reaction with igneous liquids, but, if so, the volume of the reaction products is unusually predominant,- so much so that the writer failed to find any portion of the body that could be definitely called igneous." Some examples of the gradations mentioned in the above paragraph are given in the report and are repeated here. There is a large, rather uniform body in the upper part of the granite body east of $1 shaft which resembles a rhyolite porphyry and in places grades out into a fine grained felspathic quartzite or mica schist. Another coarser porphyry grades into an arkosic schist and is associated with so-called siliceous granite which itself grades into sericitie quartzite. (3) The Basic Intrusives These rocks were originally diabases or related types. Using Dr. Swanson*s classification, these rocks are younger than the sediments which theyintrude but older than the metamorphic action and also the mineralizing action as they have been sheared to chlorite and hornblende schists, also in places they are cut by the quartz- pyrite veins and the marginal parts often show good values. -7-Cooke and Alcock disagreed upon the age of these rocks; Cooke stating that the basic intrusives are younger than the mine granite while Alcock maintained that they are older than the granite body. It might be pointed out that the problem of the age of the basic intrusives has no significance (apart from deciding whether they occurred before or after granitization of the sediments) i f the mine granite boay is considered to be sedimentary in origin. 1 H. C. Cooke - Preliminary Report Goldfields Area, Saskatchewan -Geol. Sur. Can. Paper 37-3 2 F. J. Alcock - Geology of Lake Athabaska Region, Saskatahewan -Geol. Sur. Can. Mem. I96 -8-BIBLIOGRAPHY Cooke, H. C. (1937) "Preliminary Report Goldfields Area, Saskatchewan"; Geological Survey of Canada,Paper 37*3 Alcock, F. J. (1936) "Geology of Lake Athabaska Region, Saskatchewan"; Geological Survey of Canada, Memoir 196 Related Subjects Anderson, G. H. (1937) "Granitization, A l b i t i z a t i o n , and related phenomena i n the Northern Inyo Range of C a l i f o r n i a -Nevada"; B u l l e t i n of the Geological Society of America., volume 48, number 1, page 1-74 ACKNOWLEDGEMENT The writer wishes to acknowledge the assistance and advice given by Dr. C. 0. Swanson i n the work undertaken and also to thank him for his courtesy i n giving the writer access to his private report on the geology of the Box Mine. P A R T II -10-PETROGRAPHY (a) INTRODUCTION Dr. Swanson, when co l l e c t i n g the specimens for petrographic study did so with the d e f i n i t e idea of obtaining a representative of each rock-type at the mine. Specimens were collected from a l l parts of the mine and especial attention was given to the contact zones between the g r a n i t i c and sedimentary groups. Where gradations occured i n the rock, two specimens were taken, one of the sedimentary and one of the g r a n i t i c material. These specimens were designated by the same numbers so that, though there are forty-three specimens in a l l , they are numbered from one to thirty-two consecutively (there being two number t h i r t y ' s , two number thirty-one's, e t c . ) . The exact location of each specimen gathered i s shown on maps I and I I which show the surface geology and underground workings respectively of the mine. (b) MEGASCOPIC EXAMINATION OF THE SPECIMENS The specimens when examined megascopically range i n variety from the pure vein quartz (specimen number 3) to a rock resembling a porphyritic granite (specimen 30). When examined closely the rocks, even those most nearly resembling granite, showed an overabundance of quartz. Some of the q u a r t z i t i c specimens show an almost gneissic structure and many of the rock specimens are pinkish i n color, the pink color i s apparently due to pink feldspar. -11-(c) MICROSCOPIC EXAMINATION OF THE SPECIMENS Fourteen thin sections were made from certain of the specimens collected. A l i s t of the specimens from which then sections were made and a brief description of each i s given below: Specimen 1 - S l i d e 1 - Quartzite Specimen 4 - Slide 2 - Granitized quartzite Specimen 5 - Slide 3 - Hanging-wall quartzite Specimen 6 - Slide 4 - Porphyry Spe cimen 9 - Slide 5 - Quartzite Specimen 14 - Slide 6 - Red quartzite Specimen 15 - Slide 7 Granitized quartzite (?) Specimen 16 - Slide 8 - Hanging-wall s e r i t i c i z e d quartzite Specimen 20 - Slide 9 - S e r i t i c i z e d quartzite grading i n t o granite Specimen 25 - Slide 10 - Footwall quartzite Specimen 30s- Slide 11 - Quartzite Specimen 30g- Slide 12 - Granitized quartzite Specimen 31s-Slide 13 - Quartzite Specimen 31g" Slide 14 - Granitized quartzite The above descriptions are f i e l d terms used to designate the hand specimens when they were collected. Under the microscope, a general s i m i l a r i t y i n a l l the sli d e s was noted, especially i n those from specimens taken i n -12-the gradation zones ( i . e . specimens 30s and 30g)• Several features were noted i n these slides which supported the contention of Dr. C. 0. Swanson that the material comprising the mine granite i s a 1 metamorphosed or granitized sediment and not, as stated by Cooke 2 and Alcock , a true igneous rock. The special features noted include: (1) The abundance of free s i l i c a (2) The presence of rock fragments (3) Textural features (4) Inclusions (5) The feldspars (1) THE ABUNDANCE OF FREE SILICA This i s the most conspicuous feature of a l l the s l i d e s . In every s l i d e examined, quartz i s the predominating mineral present. The quartz occurs i n two ways i n the s l i d e s : (1) as the p r i n c i p l e constituent of the fine-grained groundmass which i s t y p i c a l of a l l the slides and (2) as larger grains arid aggregates of grains scattered throughout this groundmass. 1 ' ' ' ' ' ' ' ~ H. C. Cooke: Preliminary Report, Goldfields Area, Saskatchewan -Geol. Sur. Can. Paper 37-3 2 F. J. Alcock: Geology of take Athabaska Region, Saskatchewan -Geol. Sur. Can. Mem. 196 -13-With the aid of an eyepiece containing a grid of four hundred squares, counts were made on several of the slides to determine the approximate percentage of each of the principal minerals. An average count on any of the slides yields over sixty per cent quartz, a percentage much higher than that found in any normal true igneous rock. As an example, the average count for slide twelve, specimen 30g» a rock which, in the hand specimen resembles granite, yields approximately seventy-five per cent quartz, eighteen per'cent feldspar and seven per cent sericite, chlorite and material too find-grained to be accurately determined. The counts were made exclusive of vein quartz which 1 is quite distinct and easily recognized as such. Cooke states that the solutions which introduced the quartz of the quartz veins have permeated the whole rock, even the pore spaces, and deposited quartz. In this way, he explains the abundance of free quartz in the rocks. A close examination of the slides reveals features that disprove this theory. Where quartz veins or the edges of quartz veins were visible in the thin sections, the boundaries are clean-cut and definite and the veins show no diffusion or grading out into the surrounding rocks. If Cooke's hypothesis were true, i t would seem reasonable that some part of the granite body w ould have escaped the silicifying action and H. C. Cooke - Preliminary Report Goldfields Area - Geoli Sur. can. Paper 37"3 14-would show a true granite composition. Although the specimens were gathered from a l l parts of the body of the mine granite, no rock of true granite composition was found among these specimens. The abundance of quartz i n the slides can be seen f a i r l y w e l l i n Plate I , pagel5» and Plate I I , pagel6. (2) . ROCK FRAGMENTS In many of the slid e s occur aggregations of quartz grains which strongly resemble rock fragments. These can c l e a r l y be seem i n Plate I , pagel5 » taken from slide 9» specimen 20, and i n Plate I I , page 16, taken from specimen 31g« These rocks i n the hand specimen resemble a true granite and were collected from the body of the mine granite. Similar aggregations of quartz grains were found i n the slides from the quartzite specimens and the fact that these fragments were noted i n the sections from the quartzite as wel l as i n those from the mind granite would preclude the p o s s i b i l i t y that the fragments occur as inclusions or xenoliths i n a granite body. Aggregates of feldspar grained alone and some of both quartz and feldspar grains were noted but these are not common and not as large as the aggregates of pure quartz grains';,. I t was noted that these fragments often give the rocks a pseudo-porphyritic appearance. What appears to be a phenocryst i n the hand specimen i s often seen to be an aggregation of quartz grains when examined -under the microscope. -15-PLATE I Rock Fragment: the form and size of this fragment can be clearly seen in this picture. Several smaller fragments can be seen but not so clearly. An idea of the fairly fine grained groundmass and the abundance of quartz typical of a l l specimens can be obtained from this picture. Slide 9» Specimen 20 X nicols -16 PLATE II i , _ Rook fragments and feldspar phenocrysts can be plainly seen here. The feldspar consists of perthite. The fine grained groundmass and abundance of quartz are visible here as in Plate I. Slide 14, Specimen 31g X nicols -17-The presence of these rock fragments in the specimens collected from the mine granite strongly suggests a sedimentary origin for this rock. (3) TEXTURAL FE&TURES The textures of the rocks examined vary greatly. Some specimens are medium grained with no large crystals while others exhibit a strong porphyritic texture. In order to distinguish between the mine granite and the hybrid rocks pooke^ relies on texture, classing a l l the rocks of medium to coarse grain as granite and those with uneven grain as hybrid rocks. This basis of classification of the rocks did not seem valid to the writer. Examination of the hand specimens and the thin sections revealed some quartzites containing large grains or phenocrysts of feldspar and large grains of quartz and others having a uniformly medium-grained appearance while the mine-granite specimens, although a l l have a porphyritic appearance, show a great variation in the number and size of the phenocrysts of quartz and feldspar. When slides taken from specimens gathered in the gradation or contact zones were examined, a marked similarity in 1 H. C. Cooke - Preliminary Report Goldfields Area, Saskatchewan -Geol. Sur. Can. Paper 37-3 -18-texture and mineral composition was noted. The slide taken from the sedimentary rock contained more sericite and showed a slightly more schistose texture than that taken from the granitized material No quartz grains were noted in the slides having even faint crystal outline, many of the smaller quartz grains having rounded and most of the larger grains ragged borders. The ragged borders may have been formed during recrystallization and growth of the quartz grains. The feldspar grains exhibit a stronger tendency to appear as euhedral or subhedral crystals. An example can be seen in the large crystal of perthite in Plate II, page 16. Feldspar grains were also noted with ragged or sutured borders against the finer grained quartz groundmass. Again this may be due to recrystallization and growth of the feldspar grains during metamorphism of the rock. (4) INCLUSIONS Although there appears to be some evidence of recrystallization and growth of quartz grains during metamorphism, no inclusions of foreign material were noted in the grains. The explanation for this may lie in the superabundance of quartz in the rocks. -19-In the more granitized specimens some feldspars were found containing inclusions of quartz and sometimes of other feldspars. These occuurrences are not numerous but wlhere they occur they indicate a building up or growth of the feldspars rather than t h e i r breaking down i n a true igneous rock. I t may be that inclusions are found i n the feldspars and not i n the quartz, because the feldspar has greater r e c r y s t a l l i z i n g power and the crystals grow fast enough to include foreign material rather than push i t aside. (5) THE FELDSPARS Many of the feldspars i n the s l i d e s examined show extensive a l t e r a t i o n , possibly by the mineralizing solutions. Perthite i s abundant i n the s l i d e s , also a l b i t e , a l b i t e -oligoclase, oligoclase and orthoclase. I t was noted that there was a marked difference i n the amount of s e r i c i t e i n the quartzite and g r a n i t i c specimens, the quartzite containing more s e r i c i t e than the more g r a n i t i c rock. I t i s possible that a chemical action took place between the s e r i c i t e and quartz to form orthoclase during the process of g r a n i t i z a t i o n . Apart from the inclusions and ragged borders mentioned under the heading Inclusions, the feldspars offer no -20-definite evidence as to the original character of the rock. No incongruous feldspars were found in any of the slides examined. CONCLUSION In Part I of this paper the writer has attempted to give a clear picture of the problem involved* — Is the ore body of the Box Mine a true igneous body, or is i t a granitized sediment! — and at this point would again like to quote Dr. Swanson: "At first thought, the difference between a true granite, and a body of sediments that look like granite, might not seem very significant. But the resemblance is really only superficial. The internal structures in the two cases follow separate principles, and for this reason the setting of the ore deposits takes on quite different aspects, depending on whether the country rock is considered igneous or sedimentary," In Part II have been set forth the criteria which, to the writer, point conclusively to the sedimentary origin of the granitic body. A brief summary of these criteria follows: In the field, gradations occur from rocks of granitic appearance directly into rocks of sedimentary type, such as mica and arkosic schists. -21-Uhder the microscope, the two most conclusive features are: (1) The abundance of quartz in a l l the slides examined; the amount far exceeding that found in any normal granite of igneous origin* (2) The presence of rock fragments which strongly suggest a sedimentary origin. Less indicative features are: texture, rounded borders of some quartz grains, ragged borders of other quartz grains and some feldspar grains and inclusions of foreign material in some of the feldspar grains. In the mind of the writer, these rocks should be classed as granitized sediments and not as a true igneous body* EXPLANATION OF MAPS Maps 1 and 2 are taken from Dr. Swans on's report of the mine. They are reproduced here to show the locations of the different samples taken. The position of each sample i s marked by the number of that sample within a c i r c l e . Map 1 shows the surface geology of the mine and an idea of the different l i t h o l o g i c a l units can be obtained. The red marks the general contacts of the mine granite and the others are the different sedimentary and metamorphosed ser i e s . Map 2 covers the underground workings of the mine up to the date of examination. Map 3 i s taken from the report of H. G. Cooke^" and shows the surface geology of the mine as mapped by him. The map i s self explanatory. H. .C. Cooke - Preliminary Report Goldfields Area, Saskatchewan -Geol. Sur. Can. Paper 37-3 MINE PL FIN BOX MINE GEOLOGY OF BOX PROPERTY GOLDFIELDS, SASKATCHEWAN Qu&r/z/fe Geo/o<^iC6>/ boundary, position apprax/mjite 


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