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The stratigraphy, structure, and ore-deposits of the southern Yukon Armstrong, John Edward 1935

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p. ia Is  f.  if  I 8  AT; no:  The Stratigraphy, Structure, Deposits of the South e r f " Yukon by John- Edward  Armstrong  A Thesis submitted for the Degree of HASTSR 01 APPLIED SOI3I02 in the Department of GEOLOGY  The University of British Columbia APRIL 1935  k^lifs*}'..*?  &7J//  TAB La Off G OUTSETS Page 1 r i i i i i 5  IHTRODTJOTIOST CHAPTER 1 PHYSIOGRAPHY General Topography Gene ral The Coastal System Hie Interior. System Rocky Mountain System Arctic Plateaus . Arctic. Goastal Plain Drainage Pacific Drainage Bering Drainage Arctic Drainage Glaciation . CHAPTER. 11 . STRATIGRAPHY General Statement Correlation of Yukon and Eastern Alaska  J9  10  11 IS  12  12 17 18  22 22 22  Pre-Cambrian  Yukon Group Gene ral Distribution litliology Age ana Correlation Tindir Group Distribution Li thol ogy Age and Correlation Palaezoic General Statement Boundary District Silurian-Cambrian Limestone-Dolomite Group Distribution Li thol ogy Age and Correlation Devonian-Ordovician SMle-Chert Group 1 Distribution Litliology Age and  Correlation  Deyonain Limestones Distribution Li thol ogy Age and Correlation Carboniferous  and  Pexmo'-Garboniferous  Distribution Lithology  •  The limestone-chert group 2 1 ® shale-limestone group The shale-group  25 26 26 26 26 27  33 56 36  36 4o 42 42 44 44 44 44 45 51 51 51 52 52 52 52 ' 53  Sediments  56 56 56 57 58  56  J  P a  Haiti on River formation and S U perad jacent beds §8 Distribution ' 58 Lithology 58 Age and Correlation (Carboniferous and PermoGarboniferous Sediments plus nation River formation) 59 final Correlation of the Carboniferous seSsiments in the Boundary district 68 Southwestern Yukon 59 Gold Series 69 . Distribution 69 M thology 69 Age and Correlation 71 Taku Group 72 Distribution 71 Lithology 71 Age and Correlation 7§ Carboniferous and "Triassic Limestones and associated j. rocks Distribution Lithology Age and Correlation The Upper Beaver River Area "Volcanic Agglomerate, Shale, and Sandstone Distribution _ Lithology A e „ „ S Ord ovici an-Devonian Limestone Distribution Lithology Age and Correlation . Eastern Yukon Distribution Lithology Age Mesozoio Saberge Series Gene ral Distribution Lithology Age and Correlation The Older Yolcanics Distribution Lithology ' Age and Correlation Coast Range Intrusives • Distribution Lithology „ . A S e and Correlation Tertiary Sediments Tertiary Sediments (Kenai*?) Distribution Lithology Age and Correlation  72 72 75 7a 76 ' 76 75 75 76 76 76 77 77 78 78 78 79 79 7g Q1  qi qj 87 92 9g g2  9* qJ 97 g7 98  gg qo 11 It 1G0  Hewer Volcanics Distribution Litliology Age anfl Correlation Acia Volcanics Distribution -Lithology Age ana Correlation Superficial Deposits CHAPTER GEOLOGICAL HISTORY CHAPTER STHUGT0BM) GEOLOGY CHAPTER BHE-DEPOSITS General Statement Windy Arm District Wheaton District Gold-silver quartz veins , Antimony-Silver veins . Silver-Lead veins Gafi.es is Y£hitehorse Copper Belt Aishihik Lake^Dis trict lordenskiold River Area Little Salmon River Apea Eluane District Upper White River District 0 a macks District . Williams and Herritt Creeks Area Rude Creek District Indian River District Sixtymile and Ladue Rivers Area Klondike District l!ift©enmile Greek Area Mayo District Keno hill Galena hill . Other Occurrences Duncan Creek Area Upper Beaver River Area BIBLIOGRAPHY .  111 IT  Y  ..  101) 100 101 102 103 105 104 106 107 110 110 118 118 125 125 125 126 lg7 128 150 151 133 133 135 135 136 136 136 137 140 1AQ 141 141 142 IA3 143 144 145 146 146 147 w  LIST Off ILLUSTRATIOlIS Facing Page Plate 1 [Physiographic provinces of Yukon) 1 Pla£e 2 ("Valley of the Big Greek) 5 Plate 3 (Forth. Work of Big Salmon) 5 Plate 4 (Terraces along the Pelly river) 20 Plate 5 (Looking north across Big Greek) 117 Plate 6 (Looking south across Big Greek) 117 Geological Sec ti ons 118 A-A 118 B-B 118 Q-C 118 Plate 7 (Garmacks 1 ode-gold strike on Mt. Freegold) 137 Map in envelope in back of this report.  JZ  THE STRATIGRAPHY, STRUCTURE, AID ORE-DEPOSITS OF THE SOUTHERN YTJKOIT IITRODUOTIOlf The Yukon Territory forms the northwestern extremity of Canada®  In its greatest extent i t is included between the o o meridians of 124 and 141 west longitude, and between the -naro o allels of 50 and 70 north latitude®  It is bounded on the  north by the Arctic ocean, on the west by Alaska, on the south by British Columbia, and on the east by the lorthwest Territories*  The area of this larfee district is about 1 0 0 , 0 0 0  square miles 0 The entire portion of the area dealt with in this report o lies south of latitude 65 north, except for a section along the International boundary between the Porcupine and Yukon riverso  ~  This report deals with, the .stratigraphy, structure, and ore-deposits 9 with minor sections on physiography and geological history of that portion of the Yukon Territory outlined above.  Most of the information contained herein is tak-  en from the reports as acknowledged in the bibliography and in the footnotes.  As I spent the summer of 1934 as a geolo-  gical assistant on a field party of the Geological Survey of Canada in the Yukon Territory, I am acquainted with most of the salient features of the geology.  Since only a small port-  ion of the area described has been surveyed, and as most of this surveying has been of a reconnaissance or exploratory nature the knowledge of the geology of the area is still very  JL  incomplete and liable to many minor corrections.  For some of  the conclusions drawn I am alone responsible* Under the section on stratigraphy I have attempted' to interpret all the existing knowledge in regard to the latest information, and to correlate the geology of the various portions of the area.  The conclusions are embodied in a correlation  table and shown on a map accompanying this report. As little regarding the structure of the Yukon has been published, the structure as discussed in this report deals primarily with the interpretation of three geological sections across various portions of the Yukon.  These sections were  drawn by myself and are only accurate in so iter as the information is available. The section on ore-deposits consists of summary of the various reports on the lode-deposits of the Yukon, as the only one I have visiited is the lode-gold deposit near Oarmacks. Under physiography, topography, drainage, and glaciation are discussed® The chapter on geological histofy is an interpretation of the various papers on such, with several minor changes, which I thought were justifiable in regard to the existing knowledge. I  am submitting thie report to the D e p a r t m e n t  of  Geology,  University of British Columbia, as a thesis towards the degree of Master of Applied Science in Geological Engineering. Acknowledgements I wish to express my sincere thanks to Dr.S.J.Schofield of the University of British Columbia, who advised and aided  -TEC  me in the compilation of this report,  I also wish to thank  Dr.H.S.Bostock of the Geological Surrey of Canada with whom I worked last summer in the Yukon Territory 0  Some of the  photographs were supplied by Dr. B ostock and some suggestions regarding structure were made by him,  Many of the ideas con-  tained in this thesis are the outcome of many discussions <J.n the geology of the Yukon Territory which we had last summer„  Plate  1  Physiographic provi -j.^ . yI Yukon  •CHAPTER X PHYSIOGRAPHY Generals This section on physiography deals primarily with topography, drainage, ana glaoiatlon; firstly, in general for the northwestern portion of North America, and secondly, in detail for the southern portion of the Yukon territory. •Topography HoaMniMaiiiBiaABaBaB general: The Cordillera of the northwestern portion of North America may be divided into three main physiographic provinces.  Named in order from west to east, these provinces are:  the Coastal system, the Interior system, and the Rocky Mountain system.  In a general way they follow the Pacific coast-  line; that is their trend is northwest in British Columbia, west in Alaska, and intermediate in the Yukon.  Lying to the  north, northeast, and east of the Rocky Mountain system are various plains and 1 owland tracts.  Named in order from north  to east, they are; the Arctic slopes, the Mackenzie lowlands, and the Great Plains. The Coastal System; The Coastal system embraces a broad zone of ranges, and stretches parallel to the Pacific coastline from the forty ninth parallel to the southwest limit of Alaska peninsula, ana makes the same concave curve as the coast line otf Alaska. Besides numerous inferior ranges this system embraces  2..  four important ranges, whose areas are approximately parallel to each other and to the general trend of the coastline.  Of  thea®- the' Coast range. St*Slias range, and Aleutian range lie adjacent to the coast, while the Alaska range is inland and forms the northern border of the system.  The northern limits  of the Coast range, and the eastern limits of the St.Elias and Alaska ranges are found in the southwest corner of the Yukon territory. •In British Columbia the Coastal system consists only of the Coast range.  Shis simplicity of structure is continued  northward as far as Lynn canal, but north, and northwest of this the Coastal system becomes more complex, consisting of the ranges named above. "Eke Coast range extends from near the 49th parallel through British Columbia into southern Alaska and Yukon.  Follow-  ing the coastline 900 miles it passes inland behind the St. Elias range near the head of Lynn canal, and it merges into o the Yukon plateau near lake KLuane in latitude 61 U. and lon^0"' itude 138 30®W. This range consists of an irregular complex of peaks and ridges, possessing l i t t l e symmetry more, than an irregular alignement tt the northwest trending axis.  The peaks have  ragged or needle-like summits, and the ridges precipitous, jagged, or knife-like crests. ed.  The valleys are sharply incis-  The average elevation is from 8000 to 9000 feet in south-  ern B . C . , but gradually decreases northward until it is only 5000 to 6 0 0 0 ' i n the Yukon. The St.Slais range includes the ^hugack, Xenai, and  3.  Skolai mountains which are orographically a western extension of the St. Elias range. "Thus defined"^ the St. Elias range extends northwesterly from Gross sound, bends westerly near the mouth of the Copper river, and near the head of Prince ^ilileaa o  s0Und,  in longitude  147 Y7., turns sharply southwest and merges into the highlands of the Kenai peninsula. w The St. Elias range varies in width from 50 miles at Gross sound to 100 miles at Mt. St. & l i a s , and narrowing to 20 miles in the Kenai peninsula, "This range is a rugged mountain mass parallel with and close to the Pacific coast from Gross sound as far as the entrance to Gook inlet with one spur, the Skolai mountains, stretching to the northwest. vV  On the seaward side the range  presents eh abrupt escarpment, often rising directly from the water, whil§ its northern slopes almost everywhere fall  off  abruptly to the °entral Plateau". The highest peaks in the St. Elias range proper are Mount St. E l i a s , 18,024 , and Mount Logan 1 9 , 5 0 o ' . To the west of St. Elias the southamlcfiled  the Ghugach  mountains stretches parallel to the coast, skirting the northe m slope of Prince W i i i i a m  S0Und  and bending south into the  lesser heights of the Kenai mountains.  The Ghugach mountains  vary in width from 40 to 50 miles and in altitude from 800010,000 feet.—The Kenai mountains vary in width from 50 to 60 1.Brookes, A . E . ,  "The Geography and Geology of Alaska",  U . S . G . S . Prof. Pap. No. 45, P . 2 9 ,  1906.  4-.  miles and in altitude from 6000 to 8000 feet, st Near the 141—parallel  the St.Elias range is split by the  valley of the Qhitina river into the St» Elias range proper and the Skolai mountains.  These latter mountains are rugged  with altitudes from 7,000 to 10,000 feet. To the southwest of the Skolai mountains between merid0 0 0 . 0 ians 142 W. and 145 W. and latitudes 61 30 f and 62 SO8 north, are the Wrangell mountains which are dominantly of volcanic origin.  The highest peaks are Mount Sanford, 16,200 , Mount i i Blackburn, 16,140 , and Mount w rangell, 1 4 , 0 0 0 , and active '  volcano. The Alaska , range the northemost of the Pacific system,  ;.,  is a rugged mountains mass, which extends northeast from the vicinity of lake @lark and, sweeping around the Sushitna and Gopper river basins, forms the watershed between the Pacific drainage on the south and east and the Kuskokwim and Yukon waters on the north and west. miles in width.  The range averages 50 to 60  The culminating peaks are Mount Mo.Kinley,  2 0 , 3 0 0 . , t h e highest on the continent, and Mount Fcraker 17,0001 The eastern end of the Alaska range is split into the Nutzotin, and Skolai mountains.  The latter, which forms a  link between the St. Elais and Alaska ranges, has already been described.  The Nutzotin mountains varyin elevation from 6000 r  • •  to 9000 feet, the highest peak being Mount Allen 1 0 , 2 0 0 . . They are less rugged and contain fewer glaciers than the Skolai mountains.  The Nutzotin mountains occupy, the marginal portion  of the upwarped tract of the Interior plateau.  Plate 2  Valley cf 3 i g Greek Plate  3  r  ilorth Fork cf Big Salmon INTERIOR PLATEAU  s  The transition between the Interior plateau and St.Slias range is very abrupt, but that between the Interior plateau and Hut zo tin mountains is gradual. The Interior System: The Interior system of mountains and plateaus stretches from the western edge of the Rocky Mountain system, and to the eastern edge of the Pacific Mountain system, and extends through British Columbia, Yukon, and Alaska to the Bering Sea, foil owing in a general way the contour of the Pacific coastline. The Yukon plateau, the northern member of the Interior system, is from 250 to 300 miles wide and follows the Yukon river to the sea.  I t is considered to be an uplifted and  dissected peneplain produced by a period of long continued subaerial erosion during a period of crustal stability in Miocene, Pliocene, and Pleistocene time.  This conclusion is  based on the fact that the surface bears no relation to the rock structure being highly discordant to the metamorphic rocks which make up much of the plateau. The plateau is best viewed from a summit that stands back from the major valleys and about the general level of the upland surface.  Then one can see an apparently even and un-  broken skyline off to the horizon. Some minor mountain ranges rise above this general upland level.  They are called the plateau ranges and vafy from  5,000 to 7,000 feet in elevation; whereas, the plateau proper ranges from 3,500 to 4,500 feet in elevation.  The following  6  ranges have been distinguished from the general level  offthe  plateaui(l)fche Pelly and Glenlyon ranges bordering the Pelly river,  and separated from the Mackenzie Mountains by a belt  of plateau country—- rather higher in elevation than the Yukon plateau —  which extends southward from the Pelly  river, embracing the upper Liard and Frances rivers; (2) the northwest extension of the Gassiars; of Quiet lake;  (S) the high group west  (4) the high group between Aishihik lake and th  the lisling river; (5) the Dawson range west of the Lewes Q 0 river, extending from latitude 62 to latitude 63 I . ,  (6) the  Macmillan, Mc.Arthur, and Kalzas ranges north of the Macmillan river; (7) and the Miners range west of lake Laberge. Most of these ranges stand above the general level of the Yukon plateau because of their greater resistance to erosion. A good example is the Dawson range, in which case the peaks consist of roof pendants of volcanics intruded by granitic rocks. When the Yukon plateau was uplifted at the commencement of the present erosion cycle, the land-surface was given the form of a broad, shallow trough sloping downwards from the east and west to a northwesterly trending axial l i n e , approximately coinciding with the present position of the Yukon riv -er system.  This decrease in elevation from the east and  west towards the Yukon river is quite noticeable throughout the Yukon territory. In the southern porticn of the Yukon the uplands were only slightly affected by glaciation, because the bulk of the  7  ice accumulated in the valleys, "However, during Pleistocene and Recent times, the plateau surface, although but slightly modified by moving ice, has been considerably affected by accumulations of snow." "The effect of neve snow is to convert shallow V—shaped valleys into flat U—shaped ones, to efface their drainage lines withoutamaterial change of grade, and to in this manner produce general smoothness of surface.  Since the snowdrifts  have no sliding motion, there is consequently no transportation of material by them; however, because of excessive frostaction, and continued alternations of freezing and thawing, the rocks at the peripheries of the. quiescent snow are finely comminuted and removed by innumerable rills to fill neighbouring depressions." The effects of neve' snow as described above have resulted in the grading of the Yukon plateau, and in the accumulation of much fine material in the minor depressions cf the upland surface.  The presence of snow also tended to preserve the  smooth outlines of the topography, by protecting the surfaces from stream action. The high, steeply-inclined valleys of the Yukon plateau, present topqWphic unconfomities at their contact with the unpland surface. The last great uplift, which affected  1. Caimes, D.D.,  the Yukon plateau,  " Whea(ton District, Yukon Territory," Geol.  Surv.,-Pan.-, Mem. 31,  1912, p.  is.  s brought about rejuvenation of the streams, such that they began to cut valleys in the uplifted surface®  -In the south-  ern portion of the Yukon these valleys were invaded by glaciers during Pleistocene time. When a broad ice-sheet- covers a district it has a moderating effect on the topographic features, but when the ice occupies the valleys only^ a different type of topography is produced.  The V-shaped valleys are transformed into U—  shaped valleys, and, hanging valleys, cirques, and roches y  moulionnees are produced; whereas, the interstream areas remain unaffected.  All of these glacial foims have been observ-  ed in the southern Yukon. The smaller tributary streams in the glaciated area have hanging-valleys.  These streams flow over the upland in wide,  flaring depressions with gentle gradients, but on coming to the- edge of this elevated area they plunge suddenly, through gorge-shaped incisions, to join the master-streams below. Girques occur plentifully along the edges of the master depressions of the glaciated areas.  They occur chiefly at.  the heads of insignificant streams, as those at the heads of larger streams have been reclaimed.  They are so numerous in  places they give a frayed appearance to the valley walls. In the northern portion of the Yukon territory the valleys are practically everywhere V—shaped and characterised by interlocking spurs and other features common to nonglaciated areas. Terraces occur along the main river valleys of the  9  Yukon plateau.  They often occur up to 700 or 800 feet above  the valley-botoms, and generally several are seen hanging to the valley-walls.  Owing to the fragmentary character of  these terraces their origin is somewhat in d oubt.  They must  have been formed since the glacial period, otherwise the valley glaciers would have obliterated them.  Many theories  regarding their origin have been advanced but owing to lack of conclusive evidence it is still in doubt and will not be discussed here. Rocky Mountain Systems The Rocky mountain system extends north through Canada to near the Arctic, and south of Mackenzie bay turns almost at right angles, crosses the international boundary and contines in a direction slightly south cf west across Alaska to the Bering sea.  South of the Yukon territory this system  consists of several ranges; in the Yukon territory only one range is found; and in the system.  A  laska several ranges again make up  The traas-Alaskan mountains are called the  3Sndicott range. In the Yukon the Rocky Mountain system is represented by the Mackenzie mountains.  They are high, (6000 to 8000  f e e t ) , rugged, and unbroken by important lowlands. line is uneven in course and profile.  The cresi  Included are mount*  ains of a more subdued type, with wide branching valleys which are trenched back well into the main divide.  The  structure is characterized by folding, generally on a broad scale, which has thrown the strata into a series of anti-  /o  clines and synclines; but the folding is at times close, the folds being overturned and overthrust. The topographic features are to some extent governed by the geology, although many drainage channels are cut across hard and soft strata alike.are granitic.  The highest and most rugged peaks  The topography of the western portion bears  evidence of long-continued differential erosion, while the eastern portion has the appearance of being in a more youthful topographic stage.  Glacial action has smoothed cut many of  the inequalities of the bedrock and floored the main valleys with drift.The Qgilvie and Selwyn ranges are the western limits of the Mackenzie mountains. Arctic 3?1 ateaus: The Arctic plateaus occur north of the Brookes range and Arctic mountains.  They are made up cf a succession of gently  rolling hills with moderately flaring valleys.  " I n general  the uplands of the Arctic plateaus may be regarded as sloping, down from an elevation of 5000 to 5500 feet at the south to 400 to 600 feet at the north.  This slope, however, is not  believed to mark a plane that has been given an even tilt of this amount but is regarded rather as a surface that has,resulted through long-continued erosion interrupted at times by periods of warping and u p l i f t , so that different parts of the present surface were formed at different times by different processed-  The sum total of these different events,  however, has been to give a general slope downward to the  7/  norths and this has controlled the dominant distribution of She main stream l i n e s , whereby many of the rivers have their courses parallel to this slope from the mountains to the northern margin of the plateau province— for instance, the ' ' ' ' 1• Kukpowruk, Zokolik, Utukok, and Ikpikpuk." Arctic Coastal Plain; A plain rarely more than one half a mile, wide occurs in places along the Arctic coast.  Practically everywhere its  surface is formed of unconsolidated deposits that have been layed down under marine conditions.  The deposits have been  uplifted and partly reworked by other agencies.  The plain  is very youngand has developed no thorough drainage yet, but has numerous ponds and lakes.  1 . Smith, P . S . and Mertie, J . B . , J r . ,  "The Geology and Miner-  al Resources of Northwestern Alaska," ( / . S . G . S . , B u l l . 815, .. p.48 1930,  12  The drainage of the Yukon territory can be divided into 3 divisions, namely. (1) drainage to the Pacific; age to the Bering;  (2)  drain-  (5) and drainage to the Arctic,  Pacific Drainage: The only important river traversing Canadian territory and draining into the Pacific ocean is the Aisek.  This river  and its tributaries rise in the central plateau and traverse the St. Elias range to the sea at Dry bay. the west fork has lake.  its  The A i s h i h i k  source n e a r l a t .  river,  the n o r t h  Dezadeash river  60 S O , N .  fork  of  the  in  Dezadeash  Dezadeash,  has its source in Aishihik lake.  The east fork of the Aisek  river,  its large  the Kaskawulsh  river,  with  tributary  the  Jarvis river, rises in the Kluanehills and flows southeast o to join the Aisek near long. 138 Iff. Another large tributary the  Tatshenshini  and  flows  rises near  southwest  to  join  the B r i t i s h the A i a e k  Columbia  boundary  n e a r the A l a s k a  bound-  ary.  The topography is varied, as the Aisek rises in and flow -s for a short distanoe through the Yukon plateau, and then cuts entirely through the St. Elias range to the sea. Bering  Drainage:  The Yukon river flowing into the B e r i n g sea i s the master stream of northwestern North America.  This mighty river, the  fifth in size on the North American continent, rises in British Columbia, flows northwest as far. as the  Circl<  then sweeps around to the southwest and finally pours its  .e,  great volume of muddy water into the Bering sea, 2300 miles from the source of its longest tributary.  Its basin is out-  lined by the boundaries of the Yukon plateau,  of which its  valley occupies nearly the medial l i n e , and makes with it the same great bend to the southwest, parallel to a similar swing of the mountain systems® The Yukon with the Lewes and Teslin rivers has a catchment area of 330,000 square miles,  of which is in Canada.  The flow at the mouth is 450,000 cubic feet per. second.  The  ourrent is 1 to 2 miles per. hour near the mouth, and 4 to 5 miles per. hour near the source. The chief tributaries of the Yukon river are the Eoyukuk, Tanana, Poreiapine, White, Pelly, and J&ewes.  The first  two do not flow through Canadian territory so are not described in detail here. adian territory.  The last two are completely in Can-  The main river starts at the junction of  the Pelly. The Lewes river rises in a small lake on the northern flank of the Coast range, only 25 miles inland from the head of Lynn canal.  Its upper course is through a chain of lakes,  the more important from south to north being Bennett, Marsh, and Laberge.  Tagish,  Below Tagish lake the valley is from  1 to 3 miles wide, and the river flows through terraces. The only obstructions to travel on the Lewes river are Miles canyon, % i t e h o r s e and Five-Fingers rapids.  The first two  were caused by lava flows, and the third by a partially dissected rook barrier.  14-.  The Lewes river has many tributaries. o  The Takfcini is  confluent from the west in l a t . 61 IT., ana rises in Kusawa lake.  ®ie Teslin is the largest tributary, and is longer  than the Lewes above the junction.  I t rises in Teslin lake,  which is 75 miles long, and flows northwest through a remark -ably straight valley, 2. to 10 miles wide, and deeply incise -fl in the Yukon plateau.  The main tributary of the T^slin,  and Nisutlin, rises near Quiet lake and flows south to about the center of Teslin lake.  The Big Salmon river, which  enters the Lewes river from the southeast near l a t . 62 V , r i s e s . i n Quiet lake. mouth.  The Big falmon forks 30 miles from its  50 miles north of the Big Salmon the Little Salmon  river enters the Lewes from the northeast.  The lordenskiold  river, which has its source in several lakes near l a t . flows north to join the Lewes river at Oaimaoks.  61V,  Big creek,  important because of a lode-gold strike on one of its tributaries, rises in the Dawson range and flows east to join the '' o . • " " Lewes river near long. 137 W. +  Above the Teslin river, the Lewes has one channel only and the water is clear, but below the Teslin it contains numerous islands and sioughs and the water is muddy. The second all-Canadian tributary of the Yukon river, the Pelly, has its source in 2 small lakes, in l a t . near the headwaters of the Liard river.  61V,  I t flows northwest  and west through a broad valley characterized by sand and gravel3  terraces to join the Lewes river at Selkirk.  From  here to the Bering sea the main river is called the Yukon.  IS-  The largest tributary of the Pelly the Maemillan rises in the Selwyn range and flows due west to joizmthe Pelly about 50 miles above the Yukon river. The. Maemillan forks about long. o o 133 W. and l a t e 63 IT*• The Moose and Kalzas rivers rise in the MacArthur and Kalzas ranges and flow southwest to join the Maemillan,  The  R  oss river rises in the Itsi group of  the Selwyn range and flows southwest to join the Pelly at ? o o long. 138 , 3 0 W. and l a t . 62 IJ. • The  s  elwyn river, a small tributary of the Yukon joins  i t from the south about 40 miles above the junction of the Pelly and the Lewes. £he White river is confluent with the Yukon from the west about 60 miles below the Selwyn.  It is a very swift  and muddy stream, and has a wider valley than the Yukon. Its source is in the northern lobe of the Russell glacier, which occupies Skolai pass; a break in the St. Elias range. Hear the international boundary its valley narrows from 8 to 1 to 2 miles in width.  It has this narrow valley for  about 80 miles, and then opens into a broad gnetly floored valley, which it follows till it joins the Yukon. ll terraced to the mouth of the Klotassin.  It is we-  The White is  shoal throughout its course, there being many channels„ bars, and islands.  The current varies from 3 to 9 miles per  hour. About 60 miles below its mouth the White forks, the east fork, the Koltassin, leaving the main valley nearly at right angles.  About 80 or 30 miles from the mouth of the  /6  KLotassin it forks, the west fork, the Donjek, joining it from the south.  About 20 miles from its mouth the Donjek is  joined by the M s l i n g from the east. o  The Nisling, which  forks about long, 139 W.,rises in the Dawson range. north fork is called the KLaza river.  The  The Kluane river, whi-  oh rises in Hluane lake, flows north to join the Donjek near lat,  62 ST., The. Ladue river is confluent with the White from  the west about 30 miles from the Yukon river. The Stewart river joins the Yukon from the east about 15 miles below the mouth of the White, source in the Ogilvie range.  The Stewart has its  I t flows through a high plat-  eau region, and is navigable as far as Fraser f a l l s , which are near the head and over 200 miles from the Yukon river. The largest tributary of the Stewart, the Mc'.Questen river, rises in the Davidson group of the Ogilvie range, and i 0 f flows southwest to join the main river at long. 137 30 W. and l a t . 63 30 IT,. The Beaver river and its tributary the Rackla rise in the Ogilvie range and flow southeast to join . 0 :S4o the Stewart at long. 134 W. and l a t . 6 4 H . . Another large tributary of the Stewart, the Hess river, has not been properly located to date, but is believed to have its source near the Northwest Territories boundary, and to flow west, 0' joining the Stewart at long. 134 W . . Sixtymile creek heads in Alaska, flows south and east, and empties in the Yukon near l a t . 63 30-N.. Indian river, important because of its placer deposits, is confluent with the Yukon from the east, about 25 miles  17  below the mouth of the Sixtymile.  It is only a small river,  about 60 miles in length. The Klondike river, also famous, enters the Yukon from the east near l a t . 64 H,  It is a comparatively small stream,  but important because of such famous gold-producing creeks as Dominion, Hunke? Bonanza, and Sldorado.  These are all small  creeks, the maximum width being about 15 to 20 feet. The Fortymile river rises in Alaska, flows east, and joins  the Yukon about 4 0 m i l e s  ary.  I t forks 75  miles  from the I n t e r n a t i o n a l  bound-  from its mouth.  The Tatonduk river rises near the headwaters of the Porcupine, flows west, and enters the Yukon river in Alaska o ® about l a t . 65 I . L The Po roup one river, one of the larger tributaries of the Yukon, is confluent at the great bend,,3 miles north of the Arctic Gircle.  This river has its source at l a t .  65°30 r  Jff.f only 60 miles from the Yukon, but it first flows northeast 100  miles  11211311  hits the Hookies, and then it turns west  and finally southwest.  At the International boundary it pass-  es through a rock canyon called the Ramparts. Arotic.Drainager All the drainage from the eastern slope of the Mackenzie mountains falls into the Mackenzie river y and henoe north to Beaufort sea.  A portion of the drainage of the western slope  of the Mackenzie mountains falls into the Frances river, and thence by the Liard to the Mackenzie river.  The Frances river  has its source near the headwaters of the Pelly, and it flows  '  /8  : ••...•.•.  o  south to join the Liard near l a t , 60 N * ^ The only other tributary of the Mackenzie that drains Yukon territory, Peel.  This river and its tributaries,  is the  the Ogilvie, the Black-  stone, and the Wind, drain most of the northern portion of the Yukon. Glaciation The northern limit of glaciation in the Yukon territory extends in an irregular line from the White river basin northeast to the Mackenzie mountains.  The ice extended down the  valleys of the larger rivers far beyond the general front of glaciation; evidences of the vaileys having been occupied by ice are found down the White as far as the Donjek, down the Lewes to the Five-Fingers rapids, down the Pelly nearly to the Yukon, and down the Stewart to the mouth of the Mo Quest en. The great cordiileran ice-sheet of North America, accord ing to Dawson , swept northwest from its source into the south - * a s t Portion of the Yukon,  Tyrell  estimated this extension  of the ice-sheet to be from 2000 to 3000 feet thiok. a north-  1.  Dawson, G . M . ,  "The Later Physiographical G e o l o g y of the  Rocky Mountain Region in. Canada, with Special Reference to Changes in Elevation and the History of thti Glacial Period", Trans. Roy. Soc., Can., Vol. I l l ,  2,  Seot. IT.  1890.  Tyrell, J . B . " Glacial phenomena in the Canadian Yukon  district  Geol. Soc., Am., B . , 10: 193:198,map, 1 8 9 9 .  19  e m extension of the great Gordilleran glacier was formed on the west slope of the Mackenzie mountains, and the ice moved westward down to, and out across the Yukon piateau.  The move  -ment roughly followed the main drainage channels, that is 9 • ' •• 1 the Pelly and Stewart river3« Xeele estimated the thickness of this ice to have been at least 3000 feet.  Only large vall-  ey glaciers moved northeast from the Mackenzie mountains, but in places they were sufficiently thick to over-ride the platthe  eaus, as alongAPeel river e  A third gathering ground for ice  in the Yukon territory was the St.Elias range, and to this day ice is found about the 7500 foot contour.  The ice extended  from this field down the White as far as the Donjek, and Oaimes estimated the maximum thickness to be 3200 feet. In places in the Yukon the ice moved over the whole country, smoothing and rounding the outline of the h i l l s , and widening the valleys.  A typical example of the topography  formed by this type of glaciation occurs along the river®  u  pper Stewart  In the higher h i l l s the ice was of insufficient thick-  ness to cover the peaks, so it followed the main valleys, and a quite different, type of topography was produced.  A good  example of this is to be found in the Wheaton  1 . Keel, Joseph, "Explorations on the Pelly, Ross and Gravel rivers, in the Yukon and lorthwest territories", Geol. Surv. Gan., Pub. 1097,p« 46, 1910® 2 . Oairnes, D . D . , Surv., Gan.,  "Upper White River district Yukon,"Geol e  Mem. 50, 1 9 1 5 , p .  105.  Plate  20  river district,  S  ands, gravels, and silts are found through-  out most of the unglaciated portions of the Yukon, and they indicate flooded valley conditions at the time of glaciation. These deposits were the materials the glaciers scooped up and carried forward® • In the higher mountains glacial activity continued and sent new ice down through the side valleys after the main valley glaciers had retreated.  These local glaciers extend-  ing across main valleys acted as an obstruction to drainage, and extensive lakes were formed into which glacial streams washed their burden of debris.  Many of these lakes still re-  main; whereas, others have been filled in, and are undoubtedl y the origin of some cf the terraces in the Yukon. The following evidences of glaciation have been noted in the area described above; t i l l , striations, erratics, boulder -clay, pot-holes, glacial lakes, moraines, and terraces. The till is made up of unassorted, part local and part distant, rounded pebbles and boulders.  Some are striated but  the majority are smooth and unglaciated, Striations are usually rare, and when found they more often than not indicate the passage of the glaciers along the main valleys rather than the general direction of the movememt. Erratics are scarce, but a few have been found, the high -est being at 5600 feet. Boulder-clay has been noted on the Lewes, Pelly, Stewart, Peel, and White rivers.  At places it is found interstratified  zt  with grey or brownish,water-lain gravel beds. ' The boulderclay consists of fine sand and stones of all sizes in a paste of hard sandy clay.  Most of the stones are rounded and water-  worn,and many are striated. Pot-holes and glacial lakes of all si^es and descriptions are extremely abundant in some portions of the southern Yukon, I n some areas I have seen hundreds of pot-holes, ranging in size from 10 to 2000 ySs®in width, and from 2 to 50 yds, in depth.  Most of the lakes of definite glacial origin are small  and shallow, but some of the larger lakes might owe their origin to glacial damming. In places, lateral moraines are seen along the sides of the valleys.. ::t  They occur in long narrow lines of transported  material swaying up and down with the irregularities of the surface.  A good example of a lateral moraine is found on the  west side of the valley of Aishihik lake. Lake terraces are found in the glaciated areas, but as mentioned elsewhere in this report there is no suitable explanation for the majority of the terraces found in the Yukon plateau.  2 2  CHAPTER 11 STRATIGRAPHY. General  Statement  A great variety of rooks ranging in age from pre-Cambrian to Recent outcrop in the Yukon territory,,  They include sedi-  mentary, igneous, and metamorphic types, the origin of some of the last being uncertain at times© The oldest rocks of the Yukon belong to the Yukon group, and are believed to be pre-Cambrian in age0  They are all meta-  morphosed to a great extent, and they include quartzites, micaeous and graphitic schists, and crystalline limestones probably of sedimentary origin; and sericite, chlorite, and greenstone schists, amphibolites, and granite gneisses, at least in part of igneous origin c  The igneous schists cut the sedimentary  schists and are therefore the younger®  'Wherever a contact is  found, a group of rocks composed, mainly of dolomites,  shales,  .slates,, quartzites, and argillites overlie the Yukon group unconformable^  This group of rocks, which is pre-Cambrian in  age, is the oldest sedimentary formation in the Yukon and is called  the Tindir group®  Die lower Palaeozoic record is incomplete in most of the Yukon, and except for limestone-dolomite and shaletchert groups along the International boundary, and a series.of Ordovician argillites,  slates, cherts and quartzites along the Ross and  Maemillan rivers lower Palaeozoic rocks are absent in the Yukon. The limestone -dolomite group, which ranges in age from middle Cambrian to Silurian inclusive, overlies unconformable/ the  2. 3  Tindir group®  The shale-chert group ranges in age from Dev-  onian to Ordovician inclusive, and replaces the upper portion of the limestone-dolomite group in places,  The Devonian period  is represented by a series of cherts, cherty quartzites,  slates,  and argillitesfTaku group) in the southern and eastern parts of the Yukone  A group of pyroxenites and periSStites, known as the.  Gold series, are found in the southern Yukon.  They are appar-  ently of Devonian age but as no contact have been found their age is rather uncertain.  Throughout the Yukon,limes tones and  associated elastics were deposited during the Devonian ana Carboniferous periods.  In the southern and eastern portions of  the Yukon the deposition of these limestones and associated elastics continued during Triassic time.  Along the International  boundary these limestones are conformably overlain by freshwater sandstones, shales, and conglomerates of the Nation river series of Permian age®  Overlying unconfoimably these Carbonifer-  ous beds is a series of shales, greywacltes, argillites, conglomerates, and associated tuffs®  arkoses,  This series of sediments,  which includes the Laberge series ana Tantalus Conglomerate, ranges in age from Jurassic into the Cretaceous.  Some of these Pal-  aeozoic and Mesozoic beds are extensively invaded and intimately associated with a group of volcanic rocks (Older Volcanics) oonsisting mainly of andesites, diabases, basalts, and related pyroclastics.  These volcanics appear to be the result of intermitt-  ent vulcanism extending from Carboniferous to at least Cretaceous time.  I n late Jurassic or Cretaceous time the older rocks wes?e  invaded by a group of plutonic igneous rocks (Coast Range Intr-  2-4-  usivSs)  of granitic habit, which range in character from granite  to gafcbro. 'Upper Oretaceous rocks are found inaaxfew scattered localities.  Overlying unconfonnably all these rocks, there occur  in a few places, some loosely consolidated lignite-bearing conglomerates, shales, sandstones, are cf Eocene age*  anl clays (Kenai group), which  Commencing about Eocene  time vulcanism  became active throughout most of the southern Yukon and has per• sisted to the present time.  This vulcanism is represented by  the Fewer Vclcanics, a series of andesites, basalts, and related dyke rocks, with associated tuffs and breccias, and a younger group called the Acid Yolcanics, consisting of rhyolites, granite porphyries, and related volcanics, with associated tuffs and breccias.  Overlying all these foimaticns are the unconsolidated  Pleistocene and Recent formations.^Meh constitute a mantle of great thickness in many places*  They consist of gravel g a s ^ a ;  s i l t , boulder-clay, muok, peat, morainal materials, volcanic aslis -ground-ice, and soil®  25~  I  C O R R E L A T I O N  OF~  E A S T £ I & M  Y U K O N /\LA*SK/\  A N D  zc>  Pre-Gambrian Yukon  Group  General; Under the name "Yukon &roupn arejincluded all the older metamorphic, schistose, and gneissoid rocks, regardless of origin, which is often difficult to determine.  Occasional  beds of crystalline limestone are also found in the Yukon group.  The. Yukon group has been subdivided by Gockfield^n-  to a Hasina and Klondike (?) series, a series of amphibolites, and granite gneisses (Pelly gneisses?)  I will endeavour to  use these names in the following description as much as possible, but on the map accompanying this report the Yukon group will be represented only by one colour, because in many place -3 i t has not been subdivided. Distribution; Bocks of the Yukon group are found throughout the southe m Yukon.  They are the most important and widely distribut-  ed rooks in the Territory.  The principal occurrences are as  follows; fl) between the Stewart and Klondike rivers; tween the Stewart and Beaver rivers;  (2) be-  (3) between the Sixty-  mile and White rivers; (4) along the Maemillan and Pelly rivers-, (5) along the Little and Big Salmon rivers') (6) in the Wheaton river and Atlin districts; (7) in the area between Kluane and Aishlhik lakes* f8)^and^at the headwaters of the Klaza and Hisling rivers. T7 Uookfieid, W.-S. "Sixtymlle and Saflue Kivers Area, Yukon," Geol. Surv., (Jan., Mem. 123, 1921, pp. 12-26.  27  Si thology; The oldest member of the Yukon group is the Hasina series*  These rooks are altered sediments and are represented  by the following types: quartgites, including gneissoid and schltose varieties; mica, quartz-mica, and graphitic schists; green chlorite and actimolite schsts; sheared conglomerates! and crystalline limestones. In the least altered portions the constituents of these various rocks have a parallel arrangement giving to the rocks a laminated appearance; in the most altered portions the rocks are completely recrystallized into fine-grained gneisses and schists distinguished only with great difficulty from the altered igneous rocks,  •  Some typical examples of the quartzites are the schistose quartzites found in the Upper White river areas, and those found in the Sixtymile and ladue rivers area.  The former are  dense, siliceous, light to dark green rocks,consisting mainly of quartz-S-  They cleave imperfectly along the planes of schist  -osity and break prevailingly into rough platy or prismatic fragments.  The latter ^ t h i n l y laminated rooks, consisting  principally of alternating bands of blue-black and white quartzites.  Upon the addition of mica these rooks give way  to serioitio quartzites,  /Which......  are dark green,fine-  grained, closely foliated,and schistose.  They contain much  argillaceous material, and in places grade into slates.  They  have obtained their schistose structure with much mashing and shearing.  In some cases they are banded.  This is apparently  due to bedding since they are of sedimentary origin,  A  2S  gneissoid quartzite represents a more metamorphosed stage of the original sediments than the sericite quartz i t e .  I t is a  white to light grey, banded, gneissoid rock,characterized by the presence of felspar.  The sheared conglomerate represents  ta coarser facies of the quartzite.  It contains elongated  quartz pebbles up to 1 embedded in a matrix of mica schist. With increasing quantities of mica the quartzites pass gradually into quartz-mica schists, and finally mica schists.  Al-  so with increasing quantities of graphite the quartzites pass gradually into graphitic quartzites and finally graphitic schists.  The mica schists are dark and the graphitic schists  are blue black rocks.  • I... '  '  ' '  ' '  Oockfield describes the above types azn seen under the microscope.  "Under the microscope the minerals present are seen to fe© the same in all classes, but to vary in abundance according to the type of rock.  Quartz, the most abundant constituent appear  ~s as a fine mosaic of small compact grains, usually angular to subangular in shape, and divided into bands by parallel lines of blotite and sericite.  In many cases the quartz shows  an unduious or wavy extinction as a result of strain unrelieved by cracking.  A subordinate amount of felspar is sometimes  associated with the quarts*  The micas usually biotite and ser-  icite, are arranged in parallel bands, or sweep in a series, of waves through the granulated mass of quartz and felspar. 1 . uoojmeld, W.JA. '^ixtymile and Sadue Klvers, Area Yukon", Geol, Surv., Canl, Mem. 123, 1921, p. 1 5 .  '  29  B i o t i t e is abundant, ana occurs in small leaves parallel to the planes of schistosity,  Sericite, also abundant, oocurs in  a manner very similar to that of biotite.  Chlorite,  calcite,  kaolin and magnetite are present, and more rarely garnet. Graphite is seen particularly I n the laminated quartzites where the dark bands are due to this mineral.  The graphite is most  abundant along the planes of schistosity, but i t also,  occurs  surrounding the individuals of quartz and penetrating them". McOonnell reports green chlorite and actinolite schists in the Hasina series on the Stewart river. Som© lenses of crystalline to sub-crystalline,  grey, green  -ish-blue to white, sheard and disturbed limestone is found in the Hasina series.  I t contains secondary minerals such as  tremolite and sericite, and it is argillaceous in places. Hext to be considered is the Klondike series of  £ McCTonn-  The schists of this series d i f f e r from the Hasina schists in being mainly i f not wholly of igneous origin.  The original  rocks varied widely in character, surface and deep-seated,acid and basic types having been present.  The principal types are  sericite, chlorite, and greenstone schists.  They resemble in  appearance the most sheared of the granite gneisses on one hand and the most completely reorystallized  rocks of the Hasina  series on the other  1, M c D o n n e l l , " R e p o r t  on the ^ondike tioid i'ieldsf; BeoliT  Surv. Can., An.Rp. 1901,new series, vol.XIV,part B . , P . £. McDonnell, E . G .  op. c i t . , pp. 15-18B.  15B,  3 O  The sericite and ohlorite schists are rfehe most abundant. Sericite and ohlorite are usually present in variable quantities and the predominance of one or the other usually gives the character of the rock.  The sericite schists are light  grey, soft, fissile rocks, with a bright glistening surface due to the abundance of mica.  They cleave readily along fol-  iation planes yielding plates 1 / 8 " to l / 4 " thick.  In pieces  they contain considerable iron ore which oxidizes and gives them a reddish colour.  The chlorite schists are pale to dark  green, soft, friable, rocks, with a smooth soapy feel and a bright glistening appearance.  They also break readily along  the foliation planes into thin plates.  The sericite schists  are more compact than the chlorite schists® Oockfield describes the rocks as seen under the microscope as foil ows: "These rocks are seen to be of simple mineralogical composition, the bulk of the specimens being composed of quartz, felspar, sericite, and chlorite.  Of the felspars both ortho-  clases and plagioclases are present, the plagioclases being usually albite or oligoclose, . numerous minerals of secondary importance occur. zoisite &  These are magnetite, pyrite, hematite,  epidote, zircon, kaolin, and caloite.  The quartz shows  progressive granulation and recrystallization, passing through a stage in which the quartz grains interlock with sutured texture, into varieties in which the quartz has been largely rec r y s t a l l i c a ! i n t o large, clear areas entirely > " S ^ y m i l e and ladue rivers area "SenV a ° a n . , Mem. 123, 1921, p # 18. . ® breci*  Surv  *>  3!  free from strain shadows and containing inclusions of the gran . -ulated material.  Sericite is abundant and occurs in para-  l l e l bands sweeping through the rock.  The chlorite occurs i n  small leaves or aggregates." The greenstone schists are fine-grained, firm, compact, green, laminated rocks.  They include schistose rocks with the  appearance of mashed diabases, andesites, and related Under the microscope several types are distinguished mashed andesites consisting chiefly of plagioclase, able chlorite,with some calcite,  rocks. First  consider-  quartz,, an a iron ores.  Rem-  mants of porphyritio texture preserved with large plagioclase phenoerysts. A Second type contains phenocr^ts  of plagioclase  and augite, also chlorite, zoisite,and iron ores. The amphiboli tes of the Yukon group are dark green rocks of basic composition.  They are fine-textured, dense,  schist-'  ose rocks, which cleave imperfectly along the planes ofasehistosity, and break into rough prismatic pieces.  Quarts is usual-  l y absent in these rooks and when it is found i t is often secondary. ' Gairnes  as follows:  . . 1 describes  the a m p h i b o l i t e s u n d e r the m i c r o s c o p e  "These rocks are found to be composed mainly of  green hornblende, diopside, and carbonates, but contain also varying amounts of quartz, felspar, sericite, sphene.  y  and  iron ore," The hornblende gneiss found in many parts of the Yukon is 1 . Gairnes, D.i).,  ''Upper W h i t i ^ i F l ? r i ^ c t ,  Surv.Gan., Mem® 50, 1 9 1 5 , p .  70.  Yukon, » Geol.  3Z  p r o b a b l y contemporaneous w i t h these amphiboli t e s . corarse-textured  gneissic  and f e l s p a r ,  .  It is a  r o c k , c o n s i s t i n g m a i n l y of hornblende  The youngest rocks of the Yukon group are the granite gneisses or the Pelly gneisses of McGonnell.  These rocks range  from fine-grained schists to coarse-grained granite gneisses. The predominating rocks are grey, and medium-textured, but por -phyries are hot uncommon.  Areas and bands of augen gneiss,  light brown to reddish, and usually consisting of porphyritic individuals of quartz and felspar in a fine-grained groundmass of mica schist, are found frequently alternating with the gran -ular i i r a a ^ j ^ l t ^ x ^ B ^ ^ j g ^ i m ^  varieties  are  coarse with well define a foliati on, but some of the massive varieties have only one direction of cleavage.  Gockfield  gives the following microscopic description of the granite gneisses, "The most abundant minerals are seen to be quartz,  alkali  feldspar, lime-alkali feldspar (oligoclase to andesihe),and b i o t i t ? , muscovite, and more rarely hornblende.  The more com-  mon accessory minerals are epidote, zircon, magnetite, pyrite, apatite, and tourmaline, and the secondary minerals are quartz, s e r i c i t e , chlorite, calcite, hematite, and z o i s i t e . "  ! • Gockfield, W.E. "Sixtymile and Ladue Rivers Geol. Surve. Oan.,.Mem. 1£3 $ 1921, p. 2 3 ,  Area, Yukon  33  Age ana Correlation* The name Yukon group was employed by Oairnes' L to include all the older metamorphosed, schistose and gneissoid rocks® These rocks have been classified as pre-Devonian,  pre-Silurian,  and pre-Ordovician according to the determined age of the lowest fossiliferous strata, and according to the evidence obtain ~ed from igneous intrusions.  G a i m e s was able to demonstrate  that these metamoiphic rocks found along the International boundary were pre-Midaie-Cambrian, and i n all probability preCambrian in age.. facts.  He based his conclusion® on the following  The rocks considered by Gaimes along the International  boundary are a portion of a much larger area of the same rocks along the upper Yukon, Alaska, and classified as pre-Ord ovrician by Brookes and Kindle , as the oldest fossil iferous remains in the overlying limestone-dolomite series were Ordovioian. G a i m e s found Middle-Cambrian fossils in the corresponding limestone along the 141st meridian.  He found these fossils  some distance from the bottom cf the limestone-dolomite series overlying the Tindir group, so he concluded that the latter group was either Lower Cambrian or pre-Oambrian. 1. u a i r a e s , ! ^ . ,  He also con-  "geology of a portion of the rukon-AlasSa  boundary, between the porcupine and Yukon rivers", Geol. Can., Sum. Rept. for 1912, p . 2. Gaimes, D.D.,  Surv.,  11.  "Yukon-Alaska International Boundary",  Geol.,  Surv. C a . , Mem. 6 7 , p p . 40-44(1914) l i J t r ^ l l AAH-» a n d ^ n d l e , E . M . , "Palaeozoic and associated I i x f 19°0 8 ! p . i o f Y U k ° n 9 B ^ l . ' e e o l . Soc. Am. vol  34-  cludes that there is no place for the extensive, thick Yukon group in the complete Palaeozoic sediments found in this district, and that the Yukon group is not l i k e l y a metamorphosed phase of the Tindir group as the two are very dissimilar lithologically.  Further he found in one place just north of t M  Yukon river on the 141st parallel,  the Tindir group overlying  the Yukon group, so he concluded that the latter was undoubtedly older, and in all probability pre-Cambrian. Of. the four divisions of the Yukon group given earlier in this discussion, the Masiina series of altered sediments is the oldest. The igneous schists are intrusive into the rocks of the Uasina series,  the contacts between the' two being extremely  irregular, with areas of sericite schist penetrating into the quartzites and numerous inclusions of the quartzites  occuring  in the sericite schists. There is also evidence that the igneous schists are earl i e r than the granite gneisses,  for small patches of granitic  material are folded and sheared with the schist.  These pat-  ches probably represent injections, of granitic material from the pre-Gambrian batholith. Some of the amphibolites are younger than the lasina s@rS ies and others are probably metamorphosed rocks of this series,. Many have been interjected by the granite gneissesand are there -fore probably differentiates of the same magma, that produced the gneisses,  Ooofcttelfl believes the granite gneisses are  Surv!! O a n l " s S :  l£sf  I  f  r  i  V  e  i  B  3dT  reasons. "As to the relative ages of the igneous schists and granite gneisses, it is probable that dykes, s i l l s , and pegmatites from the granitic magma have penetrated the. igneous schists, showing that the granite gneisses are later than the deformed quartz porphyries (igneous schists).  The dips and strikes of  the two are not always conformable, and in many places the igneous schists, i f followed along the strike are found to pass into granite gneiss.  This would point to a transgressive  batholithib contact." In the Yukon Territory rocks of the Yukon group have been given various names by different writers.  This group includes  McDonnell's Hasina series , Klondike series , Pelly gneisses , 4 " ana probably his Moosehide diabase. The teim Mt.Stevens group has been employed in the south. • •: '5 • .. 6 ' e m Yukon and northern British Columbia to include all the older schistose and gneissoid rocks.  1.McDonnell, E.G.,"Report on the Klondike Gold Fields",  Geol,,  Surv. , 0 a . , Ann. Rept., vol XIV, pt.B, 1901,pp 12B-15B. 2 . Idem, 15B-22B. 3 . McDonnell,E.G. "Hote on the sO»called basal granite of the Yukon valley", The American Geologist, vol XXX, July, 1902 -pv. 1 GO-=6*5. "" ' s-T-f 4 . Same as 1 pp. 22-23B. 5. Dairnes, D.3)."Wheaton district, Yukon Territory" Geol .Surv Can., Memoir.Ho.31, 1912, pp. 40-51. ' Cockfield, W . 3 . "Whitehorse district, Yukon",:Geol. Surv. Can Memoir 150, 1926, pp 8-10. . ' 6 . Dairnes, D . D . , " A t l i n Mining district, British Columbia" Geol,Sthev, ,Can,, Memoir, 37, 1913,pp. 48-51. .*  3<S  There i s some doubt as t i o n as the areas  to the a c c u r a c y o f t h i s  are so w i d e l y  correla-  separated.  1 The term Razor Mountain group was also used by Cairnes. * Tindir  Group  Distributions  Only a few scattered occurrences of the Tindir group, that have been classified as such, have been mapped up to the present.  These are along the international boundary between  the Porcupine and Yukon rivers, and in the Ogllvie range near the headwaters of the Beaver £iver. I n this report I have temporarily classified  several  other occurrences of similar rocks as Tindir group.  These  areas are as follows: fl) along the Maemillan river between .o ' •o . longitudes 133 and 134 west, ( 2 ) and along the upper portion o f the Ross  river.  Lithology;  The Tindir group is composed dominantly of sedimentary rocks, but includes also i n m o s t pi aces some basic volcanics (greenstones).  The sedimentary rocks include, mainly^  quartf  -ites, dolomites, shales, slates, argillites usually altered to phyllites, and occasional beds of conglomerate and-magnesite.  Considerable chert is found with some of these rocks.  As one can see the geological section will be diversified according to the predominance of the various rock types found in this group.  Since these rocks are unfossiliferous and  1 . uairnes JJ.u. "Lewes and Jlordenskiolrivers U o a i district Yukon Territory , - Geol. Surv., G a . , Memoir 1TO.59 1 9 1 0 , p . 2 6 .  37  the. grouping, mapping, ana correlations are entirely dependent on lithological characters, which are sometimes obscure, small areas of newer, formations may have been included in this group, or small areas of less altered rocks of this grout> may have been excluded. The quartzites are usually white to light grey in colour, but occasional beds of brownish, reddish, and greenish quartz -ites are found.  They are finely bedded and thinly textured,  the strata ranging from 1™ to 4 ' in thickness. They disinter grate readily to powders, which, correspond in colour to the parent rock.^ The hardness varies with the composition. Gaim.es describes these rocks under the microscope as foilows%  "These rocks are seen to consist dominantly of inter  -locking and intergrown quartz and felspar grains, with which is always associated a certain amount of sericite that occurs as a binder or matrix filling the comparatively slight amount of interstitial space throughout the rock mass.  Some speci-  mens also contain a certain amount of carbonate, either calcite or dolomite, which with the sericite constitutes a cement for the quartz and felspar grains, and occassionally this carbonate so. increases in amount as to comprise a considerable percentage of the entire rock, in places, there thus appears to be a transition from quartzites to dolomites". The dolomites, which are light grey to buff in colour, resemble very closely the fine-grained greyish quartzites in  38  appearance, so it is often difficult to distinguish hand specimens, especially when the quartzites contain felspar and sericite®  They are thinly bedded, the strata ranging from less  than 1* to 4 * ,  Seams of chert and quartzite less than 1"thick  are intercalated with the dolomites.  The dolcmites usually  weather with a rough surface, and on exposed faces have prevail -ingly a reddish col our due to oxidation of the considerable amount of iron they contain.  Some of the dolomites are cry-  stalline, coarsely textured, and extremely brecciated in addition to being folded and contorted, . They are often intercalated with shale, slate, and limestone. They shales are usually grey to black, but are occasi onall y red to yellow.  They contain thinly bedded, flaky, non-  calcareous members, less thinly beaded black soft shales, and blaok shales intercalated with limestone.  These shales being  softer and less competent tcjresist the stresses and strains to which they have been subjected, have become more crumpled, broken mashed, ana distorted than the dolomites and quartzites. and within a few feet in places folds may be observed in all attitudes ranging from upright to completely reversed, with numerous faults of varying displacements intersecting the beds in different directions.  The rocks are only very slight-  l y metamorphosed, and nowheres have a schistose or gneiss old strucutre, and rarely a slaty structure, they are considerably indurated.  ^owever, in places  Many of the shales contain  a large percentage of hemati te. The slates are generally black or varicus shades of red,  39  grey*  green  or brown.  ernate bands v a r y i n g most p e r s i s t e n t .  Banded  red and g r e e n s l a t e s ,  in thickness  from  to 2 " ,  breaking l/l6"  into plates  or less  are  The c o l o u r s a r e a p p a r e n t l y due to  The s l a t e s h a v e s a d e c i d e d l y s e c o n a r i l y induced onS to s e v e r a l  the  alt-  the oxidation.  cleavage,  feet i n diameter,  and  thick.  The argillites and phyllites vary considerably in colour, but are generally some shade of grey, although occasional greenish, brownish or black members are found. are distinguished  These rocks  from the shales and slates by containing  more mica, and are in general somewhat coarser textured. However, some fine-grained, fiim phyllites with pronounced secondary cleavage have been found.  The phyllites break into  slabs similar to those obtained from the slates.  These rocks  are much folded, crumbled and distorted. O a i r n e s ^ i v e s following microscopic description of the phyllites.  the  "Under  the microscope they are seen to be decidedly of sedimentary origin and prove to be composed dominantly of quartz, and mica.  felspar,  The mica occurs in the form of occasional large  irregular shreds and also as finely disseminated  sericite  peppered plentifully throughout the entire mass". Some indurated conglomerates are found interbeddea with the phyllites. A few sandstones, representing a less metamorphosed stage of the quartzites, are found.  They are medium-textured  ^ukon-AlaikFl^temati onal 6 0 { ^ d a r v  be-'"  .-40  greyish, greenish, reddish, brownish rocks.  Some well defin-  ed ripple marks have been observed in the brownish sandstones, showing that they are shallow water deposits, The greenstones are dominantly diabases, and are represented by dykes, s i l l s , and irregular intrusive masses, intersecting the quartzites, dolomites, shales, slates, and phyllites.  Sills up to 100 feet thick and dykes up to 200 feet  thick are found* Age and Correlation; Kindle and Maddren :pre-Ordivician.  classed the Tindir group rocks as  They classified  these rocks as pre-Ordivician  as the oldest palaeontologically determined beds of the section were Ordivician and the Tindir beds were older. i Kindle's and Maddren*s work Oairnes  Since  3  has found middle Cambrian  fossils in beds supposed foxmerly to be no older than Ordivician in age.  Thus Gaimes classed the Tindtrrrocks as pre-  •Middle Cambrian, • 4: Gaimes  bases his conclusion on the following. "Along  the northernside of Jones ridge, just north cf Harrington creek, the members of the Tindir group distinctly underlie unconfoimably a limestone-dolomite series in which Middle l.KindleS.M.,"Geological reconnaissance of the Porcupine vail'? 7 *v i* : Bull. Geol.Soc.Amer., Vol.Xl X ,1908,pp.320„322. d. Maddren,A.G,, "Geologic investigations along the Canadian Alaska Boundary", U.S.Geol. Surv.,Bull. 520,1912, pp.6-11. 3 . G a i m e s , 3).D., "The Yukon-Alaska International B o u n d a r y between Porcupine.and Yukon rivers", Geol. Surv., Can., Memoir o /.» p. 55, (1914) 4. Gaimes, D.D., Idem pp. 55-56.  7/  Gambri an fossils were founds  Bsiow, the horizon from which,  these Middle Cambrian remains were obtained there occur in places several hundred feet of lithologically similar, but unfossili ferous,limestones, and dolomites, which in all probability represent the lower Cambrian; and underlying these beds unconformably occur the Tindir rocks.  The members of the  Tindir group are thus either of Lower Cambrian or Pre-Cambrian . age.  Considering, however, the great thiokness of these rocks;  the fact that they differ so great lithologically,  from the  overlying beds of Middle and Upper Cambrian age; and that the Lower Cambrian is probably represented by the lowest beds of the overlying limestone-dolomite formation, from which lowest beds no fossils have as yet been obtained, it would seem to the Writer very probable either that the Tindir rocks are entirely of pre-Oambrian age, or that this group includes both Lower Cambrian and Pre-Cambri an members." Btie Tindir group, it may be noted appears to correspond to the Belt Terrane  of British Columbia and the Western States,  officially considered by the United States Geological Survey to represent the latest Algonkian.  Although these rocks are  lithologically and stratigraphically similar, owing to their widely separated occurrences, it was deemed advisable to adopt the new name, "Tindir group". An unconformity is thought to exist between the highly metamorphosed Yukon group and the slightly metamorphosed l«gehofield,3. J . , "Relati onship'ofTEi ErS-Ciam'Erlali Belt! an " Terrane to the Lower Gambri an strata of Southeastern British Columbia," Geol.Surv., Gan., Bulletin No.35, Geol. Series. No, 42, pp. 1-15 (1922) '  metamorphosed Yukon group and the slightly metamorphosed Tindir group,  No direct contacts have, up to date, been  observed in the Yukon Territory. I f the Tindir group corresponds to the Tatalina  group, and as seems quite probable  this unconfonnity also becomes a certaintty, as the Tatalina beds rest unconformable" on the underlying Birch Greek schists. Palaeozoic General  Statement  As most of the geological surveying of the south and central Yukon has been of a reconnaissance or exploratory nature, the classifications are usually indefinite, one group often covering a great range and a wide variety of rocks.  Because of the above reason and the widely separated  occurrences of Palaeozoic rocks in the s cuth and central Yukon, the correlation of such rocks is a rather difficult problem.  And since the mapping of this area is far from  complete I will not endeavour to group all the Palaeozoic rocks into definite sections, but rather to correlate where possible and to treat each group according to the nature of the work done on i t . A fairly complete Palaeozoic section is to be found along the 141st meridian, the Yukon Alaska boundary.• The upper Palaeozoic rocks are represented in the southwestern Yukon.  Other important occurrences of Palaeozoio rocks are  in the Upper Beaver River Area, and in the eastern portion of the Yukon Territory along the Ross and MacMillan rivers. TTPrindl eT&.M., "A ge ol ogi c reconnasssan.ee of"the Fairbanks: quadrangle, Alaska": U.S.Geol.Surv., Bull. 525,1912, pp.37-59  <4-3  Only a few other scattered occurrences have been found up to the present®  4-4-  •  Boun(  3ary District  Silurian-Cambrian Limestone-Dolomi te Grout Distribution: A great thickness of beds including, dominantly, limestones and dolomites,ranging in age from Cambrian to Silurian,a? developed along the Boundary belt, between the Porcupine and Yukon rivers.  They are in a general way restricted to the more  mountainous tracts, being mainly developed in the Xeele and Ogilvie mountains®  The beds are dominantly white to light grey, with occasional dark grey to black, and pink to red beds.  All the beds  on the weathered surfaces are the greyish-blue characterisitc of limestones.  The beds are dominantly crystalline, and in  places white, grey, or red marble beds are to be found.  The  rocks vary from film dense dolomites to coarsely crystalline limestones.  The rocks are characteristically massive, but  where bedding planes are discernable the beds are from 1-6* "• thick, locally 1-6".  Most of the rocks are transitional., few  true dlolmites or limestones occurring, but on the average the rocks are more dolomitic than limy.  They are usually harder,  finer-textured, and lighter-coloured than true limestones. The more dolomitic phases contain cavities, varying in size from microscopic to several inches in diameter and lined with ealGite and quartz, proving the dolomite to be of secondary origin and derived from the limestone, the pore space represent -ing decrease in volume during the process.  4-3-  The entire series is prevailingly siliceous,and in places contains a great amount of chalcedonic quartz and chert. In places intercalated beds of greyish, yellowish or black shales have been noted. appearance.  These often give the rooks a banded  The entire series is conformable throughout and  is found impractable i f not impossible to differentiate, because of intense folding and faulting and lack of fossils. The beds range, in thickness from 4000 1 in the north to 3000? in.the south. Age and Correlations These limestone and dolomite beds are overlain,by the middle Devonian Salmontrout limestone in the north part of the Boundary district, but southward they are gradually replaced by members of the Devonian-Ordovician shale-chert group until the southermost exposures include only Cambrian and Lower Ord ovician members, and are overlain by middle Ord ovi clan members of the shale-chert group.. Wherever the 1cwest beds of the limestone-dSlomite group are found they overlie the members of the Tindir group. .1 : • . . . Cairnes makes the following correlati ons. " These 1 imestone-dolomi te rocks in the northern portion of the beat, appear to correspond, somewhat closely to th<3 V"/' ' ' ' ' -2 • • ••'' ' '• • • *ort Clarence limestone according to Dr. E.M.Kindle who  1.Cairnes, D . D . , " T h e Yukon-Alaska International Boundary, between Porcupine and Yukon Rivers", Geol .Survv, Can. Mem. 67, 1914. pp. 61-62. . . . 2. Collier, A . J . "A reconnaissance of the north-western portion of Seward Peninsula, Alaska," U.S.Geol.Surv. ,Prof. Paper, ITo. 2, 1902, pp. 18-21  examined the fossils from both these districts.  The Port  Clarence limestone is typically developed in the western part of Seward peninsula, Alaska, and the faunas of this terrane represent the nearest geographic approach of American fossil faunas to those of Asia.  These Silurian-Cambrian limestones  and dolomites also correspond lithologically very closely with the Palaeozoic limestone section described by Prindle  as  occurring in the Fairbanks quadrangle, Alaska, except that there no Cambrian beds were identified." The fossils collected are important on account of the Qambrian remains found. The following Cambrian fossils were collected by D . D . Cairnes  and identified by L.D.Burling.  Obelus 2sp, Mngulella  2 sp.  Acrothele cf. croiacea linnarsson Acrotreta Agnostus  4sp. 2 sp®  Ptychoparia sp® Anomocare  sp®  Mostraous Levisia ©bolus  sp. sp.  (Westonia)  Schizambon c f ,  cf.  s t o n e anus  typicalis.  (Y/hitfield).  Waleott  1.Prindle, js.m,, "A geologio reconnasissance of the Fairbanks"" quadrangle, .Alaska": U.S.Geol. Surv., B u l l . 525, 1913.t>t>. 335-339. 2 , D . D . C a i m e s , "The Yukon-Alaska International Boundary, between Porcupine and Yukon Rivers", Geol.Surv., Can. Mem. 67, 1914, pp, 63-75.  4-7  Dicellomus?  sp.  Ourtioia?  sp®  Eurycare?  sp,  Mipromitra (Iphidella) p annul a (White)? Asaphus?sp. Agraulos sp® Anomocare  sp.  Solenopleura  3 sp.  DioelToeephalus Hyolithellus ? Stenotheoa  2 sp.  Oonularla  sp.  Dorgpyge? Heolenus  spe  sp. ?  sp.  The following Ordovieian genera' ana species have been identified By Rtuledemanns Dicranograptus of.ramosusfHall) Retiograptus geinitzianus  Hall  Diplograptus folicaeus ^apworth By Burling!,® •• Obolus  sp.  Ptychoparia  sp®  Isotelus? . Barpes? Atrypa? . Other Trilobites A Later Ordoviclan horizon is represented by the  following fossils as reported by Ruedemann and Burling® Columnar!a alveolata Goldf. Calapoecia canadensis Bill® Favosites aspera?d-Orbingy Halysites catenulatus var, gracilis Ha!}.! ^ndooeras c f , prcteiforme Hall The following Silurian fauna have been identified by 33r. Kindle Favosites of niagarensis Hall Gamarotoechia c f , negleeta Hall Oonchidium c f , greenei Hall and Olarke S;'treptelasma  sp,  Gladopora  sp,  Halyflites catenulatus L i n n . Trematospira of. eamura Hall Bronteus  sp.  Diphyphyllum Labechia 1  Striatopora  sp. sp, sp»  Professor Parks of Toronto University has identified the following Silurian Stromatoporoids as collected by Gairnes. Olathrodictyon vesiculosum ^ich. and Murift Olathrodictyon striatellum Gliathrodictyon monte sp. nov. Mr. lambe reports the following collected by Gairnes. Pavosites gothlandica Lamarck. .  3  ilurian fossils as  49  Boreaster Lambe. .  Dr. Kindle reports the following Silurian fossils as  collecteftsy Gaimes* Gonchidium knighti (Sowerby) • Camarotoechia cf. indianensis Hall Ph olid ops cf, squamiformis Hall Atrypa sp. Atrypa c f . marginalus (Dalman); ©rthis flabellites Foerste Dalmanella c f , elegantula (Dalman) Whi tfieldella c f . nitida Hall Anoplotheoa sp. Illaenus cf. aimatus Hall Stropheodonto sp. ihij^idomella I . s p . Olorinda cf. form!cata Hall Sphaerexoehus sp. Illaenus c f . Imperator Hall Meristina Spirifer Ratiatus;Sowerby Spirifer ni agarensis Sphaerexoehus romingeri Hall Brontiopsis sp.  ••  Gladopora sp. Favosites sp. Oamarotoechiaf?) cf. acinus H a n 6 ' ;  Atrypina sp.  •  .  <5~0  Hucleospira cf ? pisifoimis ^ a l l . Trematospira of, camura H a l l , Sieberella I ,  sp,  Mytilarca (?) of, sigella Hall Platyceras  sp®  Orthoceras  sp.  Dalmanites sp. Reticular! a e f , proxima Kindle® Pterinea • small sp, Proetus sp, Favosites gothlandicus Lamarck® Heliolites interstincta Linn. Halysites catenulatus Linn (Tar) Gyathophyllum  sp®  The above fossils collected by D.D.Cairnes  along the  141st meridian and reported on by 'Dr.Edward W. Kindle, Mr® Lawrence Lamb, and Mr® L.D.Burling of the Canadian Geological Survey, by Dr. Rudolf Ruedemann, Assistant State Palaeontologist of New York, and by Professor W.A.Parks of the University of Toronto show that the 1imestone-dolomite series is represented in the geological timetable from Middle Cambrian to Upper Silurian inclusive. •  1,Cairnes, D.D.  "The Yukon-Alaska International Boundary,  between Porcupine and Yukon Rivers," Geol, Surv., Can., Mem. 67, 1914, pp. 63-75.  :-SV  Devonian-Ordovician Shale-Chert Group ->'-mi. ,  ^  •  ^ ;;;  .'..'.".  yy.;  Distribution: Up to the present this particular group has only been identified along the 141st meridian on Jones ridge north of Harrington creek, but most probably when more geological work has been completed I n /the Yukon Territory, outcrops of this or similar formations may be found. Li thol ogy: • This series consists of closely and finely interbeddea shales and cherts.  The cherts in places are really cherty  shales or shaly cherts,and occur in bed l" to 6" thick, locally often much thinner; or even thicker, in places up to 12".  These cherts are usually coloured dark grey to black.  The shales are grey to black or bluish-grey,with occasional red beds.  The darker beds are in places decidedly calcareous.  These shales are on the average thinly bedded, soft, rocks.  friable  Hard grey quartzitic shales are developed in places.  They contain locally sufficient iron to produce on oxidation a bright red to yellow colouration on weathered surfaces, but only rarely are these rocks red on fresh fracture.  The red  beds decompose readily to a red sand or mud, which often coloun^bare hillsides.  Due to the various coloured sediments and  unequal weathering, this shale-chert series has a banded appearance in pi aces. In places these shale-chert beds have fairly regular dips and strikes, but being soft and Readily pliable^and distorted they are locally very much deformed.  easily  52  Age and Correlation: In the vicinity of Harrington creek these shale-chert beds contain Devonian fossils and airectly overlie middle or lower  Devonian limestone beds.  by Carboniferous shales.  These are in turn, overlain  A few miles farther south these  same beds overlie Ordovieian limestone-dolomite beds and contain Ordovician fossils themselves.  L.D.Burling(1913)  found this shale-chert group to contain both Ordovician and Devonian fossils.  Thus towards the south, these shale-chert  beds rapidly replace the limestone~dolcmite beds in age sense, and range from Ordovician to Devonian inclusive. Devonian Limestones Distributions The Devonian limestones occur mainly in the Eeele and Ogilvie mountains where they are intimately associated with the Silurian-Cambrian limestone-dolomite beds. Lithologys The Devonian limestones closely resemble the S i i u r i a n _ Cambrian limestones and except where fossils occur are almost impossible to separate.  They are usually more homogen-  eous and a darker bluish-grey, also coarsely crystalline. When broken they generally emit a strong oily odour which was not noted in connection with the Silurian-Cambrian limestones* In places beds of white, sugar-grained quartzite appear at the base of the limestone.  These Devonian limestone, beds,  have an aggregate thickness of from 300' to 5 0 0 1 , and wherever contacts were found they were lying unconformably on the Silurian beds.  Age and Correlation: Along the 141st meriaian the Devonian limestones a?est on the Silurian limestone-dolomites series, ana are overlain by Carboniferous limestones and cherts in one locality,and by middle and upper Devonian shales and cherts in another loc -ality.  Therefore they appear to represent almost the entire  Devonian period.  Going southwards along the 141st from the  Porcupine to the Yukon river the limestones are gradually replaced by shales and cherts. Some of these Devonian limestones correspond to the Salmontrout limestone on the Porcupine river as described by 1 vvh,ch Kindle , but does not include all the Devonian limestones of the 141st.meridian. The following fossils were collected by D.D.Gairnes and described by Kindle, who says,  that they are referrable to a  middle Devonian or early upper Devonian horizon, and that some of them are identical with the fauna found by himself in the Salmons rout, limestone. follows:  He divides them into 3 groups as  .  Groupi: Those referrable to the horizon of the Salmontrout limestone on the Porcupine River.  pp ^ g l ^ l l g 2 , 1 1 4 , '  Geol  <  s  o c . Am., Vol X1Z, Oct. 1908,  2.Cairnes, D . D . , " T h e Yukon-Alaska International Boundary 19141 p ^ y f e i  Sn5  YU3C  °n  Rivers  °"  Geo1  -  S u r v  "  be-  4 m . 67,  Singula  sp.  Gamarotoecliia sp® Stropheod onta Gypidula  sp.  sp.  Atrypa reticularis  (Linn)  Atrypa spinosa Hall Schizophoria striatula  (Schlot)  Reticularia? c f . subundifera Retioularia  (M&W,)  sp.  Athyris n . sp. Zaphrentis Favosites  sp. sp,  Reticularia c f , laevia Uucleospira  (Hall)  sp,  Oyathophyllum . sp. Oamdrotoeohia contracta ^all? Stropheodonta arcuata Hall Proetus  sp.  Favcsites of. basaltica Goldf. Alveolites sp. Qhonetes sp. Martinia c f . maia Billings Meri Stella? sp. Me ri st ell a c f . laevis (Vanusem). Pugnops pugnus (Martin) var. Productella c f . spinulicosta Hall Leptaena rhomboidalis (Wilck) '  •J  Spirifer sp®  .  Fenestella sp® .Atrypa c f . flab el lata Goldf. Gonocardium cf® cuneua Oonrad • Cryphaeus? sp. Gyathophyllum c f . Platychisma? Group  qua#drigeminum Goldf.  sp.  11 ; Those which appear to belong to a middle Devonian h or-  ison but which may represent a formation distinct from the Salmontrout limestone* Gladopora c f . dichotoma H a l l . Phillipsastrea verneiulli M. JSdwaras. ,  Proetus c f . macrocephalus Hall® Productella? sp. Atrypa  sp. nov?  Martina c f . m a ia B i n . Stropheodonto sp® Group; 111.; : 'Biose provisionally referred to the Devonian because of fragmentary nature. Favosites sp®  . .  Gamarotoechia sp. Hercinella?  sp.  Oyathophyllum c f .  quafi-rigeminum Goldf.  Favosites c f . hemisphericus Yandell and Shumard Gladopora c f . crystodens B i l l i n g s .  Atrypa reticularis Stropheodonta  sp.  Proetue sp.  •  (Linn).  Dalmani tes? Section of a gasteropod shell® Carboniferous and Peimo-Garboni ferous Sediments Distributions  .  OSiese Carboniferous and Peimo-Oait oni ferous sediments have.been divided into several groups, namely: the limestone ehert group, the shale-limestone group, and the shale group, with almost every gradation between these 3 groups®  The  limestone-chert group has been found extensively along the 11-lst parallel, the largest areas being north cf Jones Ridg and in the U p p e r Canyon of the White river.  The shale*lime-  stone group outcrops extensively in the Eutzotin mountains, and the shale group is to be found at a number of points between Jones Ridge and the Yukon river along the 141st para11 el ® Lithology: II I ii 111 T *1 u ' The limestone-chert group; This group is dominantly of limestone and chert, but includes also occasional beds of dark shale, calcareous sandstone and cherty conglomerate.  The limestone varies in colour  from nearly white to grey to almost black, and on fresh fracture is usually a dark bluish-grey. crystalline®  It is massive, and quite  In places the limestone contains enough?; ehert  pebbles to designate it as a cherty conglomerate®  These  •5/  These pebbles, which are grey to black, are well rounded and vary in size from -p to 2" in diameter.  Throughout the lime-  stone intercalated thin beds cf g r e y chert are found.  In the  Upper Vfh.ite river area a zone of irregular, much altered, mashed and distorted dark c h e r t s and shales 100 1 underlies the limestone.  These  thick directly  rocks break into irregular  particles and are much weathered on the surface. The shale-limestone group;,, This series consists dominatnly of shales, but contains some limestones, sandstones, conglomerates, and related rocks. The shales are usually dark grey, reddish-brown, or black. The limestones and dolomites are nearly white to dark grey and decidedly crystalline.  At ajnumber of points the dark  shales occur interbedded with the limestones, and occasionally the two rocks are finely interlayered, bers being not more than 1 '  the al te mating mem-  or 2' thick.  In other places the  limestone is found intercalacted every 10* to 20®, the strata ranging up to 4 ' .  Occasional B&ftgstlodf limestone up to 50 1  thick are found, and one persistent band 100*-400 1  thick has  been noted. A few reddish beds, which range in composition from a siliceous limestone to a calcareous sandstone,  outcrop.  Near igneous intrusions members of this series are donsiderably indurated, the shales becoming hard, cherty, and bleached, with a banded appearance, due to alternating green, brown, or red strata.  These shales break into iirregular,  sharply angular fragments.  <58  As this series is much folded and distorted, and the lowermost beds have not been seen, the total thickness remains uncertain, but must be at least 1500' and probably double this amount. The shale-groups This group is very similar to the shale-limestone group, and in all probability it represents a more shaly portion of the same series.  The shales are prevailingly soft and fria-  ble, and from light grey to black, with bluish-black being the usual col cur.  The limestone beds are usually not more  than 12" thick, and do not occur to the same extent as thev do in the shale-limestone series.  One of the primary diff-  erences of the shale group from the shale-limestone group is, the prevalence of chert in the former, and the lack of it in the latter.  The ohert, which makes up only a minor portion  of the group, occurs in beds from less than 1 " to 3*  thick.  Grey and brown calcareous sandstones and areanceous clays occur in a few places, but only in small quantities. STati on River formation and Superaddacent beds. •Distribution!  '  The Nation River beds are extensively developed along the International Boundary between the Yukon and Porcupine rivers. The members of the Nation River formation resemble closely in places the overlying Meso z oio sediments, and in numerous localities where fossils cannot be found it is uncertain to which of these formations the different beds belong. Lithologyl  -  The Nation River formation and superajacent beds consist deminently of conglomerates, sandstones, and shales, but includes also occasional beds of limestone.  The pebbles of the  conglomerate are mainly chert, ranging from about 1 / 3 2 " to 1 " in diameter.  The sandstones are greyish  to brownish, me-  dium textured, hard, film rocks,which weather prevailingly to a brownish colour. sandstone occur.  Occasional bands of yellowish or reddish The shales are greyish to yellowish in col-  our and range in character from friable to hard and somewhat slaty, and from quite fine to corarse and arenaceous.  The  limestones, which occur as thin intercalated beds with the more arenaceous ,and argillaceous sediments, are light grey, • semi ^crystalline to crys talline, and have a typical limestone appearance. As set forth in the discussion to follow,  the fossils  collected by Gairnes from the intercalated limestones were determined by ^ r . G-irty, who stated that they were of Artinskian or Upper Geschelian age.  In piaoes the Nation River  beds are overlain by members of the shale-limestone group. For convenience the age and correlation of these beds .will' b e discussed along with the other Carboniferous sediments previously described® Age and 0 or relation:  (Garboni ferous_ and_ Pe_imo-Oarb onife_rous  ISeajiments plus Nation River J?ormation). Gairnes  considers the members of the limestone-chert  series to be older than members of the shale-limestonG series for several reasrons« ' • i.<Jairnes"l).!D.,|lUpper White «iver D i s t r i c t Yukon," Ueol.Surv"; ° a n . , Mem.,50. 1915,nr.,74-75.  go  " I n the first place, the upper limestone member of the limestone-chert series i s , wherever noted, considerably thicker than any of the limestone members of the shale-limestone series, and furthermore, these limestone-chert rocks are overlain by a great thickness of older volcanic rocks, and in their occurrence thus differ from members of the shale-limestone beds as observed throughout the district®  The lime-  stone-chert beds are furthermore not more recent than the shale-limestone beds, as these are overlain by Mesozoio beds, •and the limestone-chert beds oontain Carboniferous  fossils.  The limestone-chert beds are thus contemporaneous with or older than the Shale-limestone series, and the evidence obtainable would point to their being slightly older." H o n g the International Boundary (141st meridian) three fairly definite Carboniferous horizons have been identified. The lowest is represented by the Mississippian fossils obtained  from  ^ p P f  the; limes tone-chert group,  «ffie ,  Mfxi; niore recent h o M z m . . r e p r e s e n t e d by.tht Geschelian  •••  fossils obtained from the shale group, shale-limestone group, and from the upper portion of the limestone-chert group.  The  most recent horizon is represented by fossils from the Nation River formation and shale-limestone group, which are Artinskian or Upper Geschelian age, and thus belong to the Upper Pennslyvanian or possibly Peimian age. The members of the limestone-chert group overlie the Devonian limestone, underlie the Nation River beds, and contain both Mississippian and Pennslyvanian (Geschelian)  fossils.  73/5  Hie general section of the shale beds very closely resembles lithologically the Carboniferous portion of the Calico Bluff section on the Yukon river a few miles west of the International Boundary.  The Calico Bluff beds contain  Mississippian fossils and none have been found in the shale group up to the present.  Since, however, these shale beds  rest on Devonian shales and cherts, it would seem quite possible that Mississippian members are also included in the shale group. Since most of the fossils collected by Gairnes from the shale-limestone series were obtained from the included limestone members, and since these fossils have been by Dr. Girty identified with those from the limestones that occur at the mouth of the Nation river, it would seem evident that these limestones at the mouth of the Nation river, correspond with certain of the limestones of the shale-limestone series. Also as these limestones at the mouth of the Nation river are thought to overlie the members of the Nation River formation, and as some of the members of the shale-limestone series, lithol ogically resemble the members of the Nation River formation, it is probable that these members of the shale-limestone series correspond to beds of the nation River formation, whereas various other members of the shale-limestone series are probably more recent and more ancient than the Nation River beds. ' ••••• 1 ' ' .' _ — B r o o k e s includes these Garboniferous beds in M a 'llutzotin 1 .Brookes,A.a. , iSA reconnaissance from Pyramid harbor to teazlG City, Alaska". TJ.S.Geol.Surv. , 21st, Ann. Rept., pt. 11 1899 9 -1900, pp. 559-360. ' P ™  '62.  series,  Moffit and Knopf have also described similar rocks  in the Nabesna-White Rivers district.  Limestones, cherts  and. related rocks that lithologically resemble members of the 1imestone-chert group are extensively developed on the MacMi 11 an river .  The members of this group are also included  in the Braeburn limestones which are extensively developed in the Yukon , and northern British Columbia  9  and are dominant-  l y of Carboniferous age, but may also include Devonian members. • • ' The following fossils were collected  Cairnes  5  ' from the  lower portions limestone-chert group and tenatively identified by Dr. George M. Girty as Mississippian. Spirifer striatus  (Martin)?  Lithostrotion? sp® Anisotrypa sp® Rhipidomelia?  sp®  Produotus semireticulatus w  (Martin)  a f f . pileiformis Mc.Chesney.  1 .Moffit,I 1 .H. and Knopf, Adolph, "Mineral resources of the Uabesna-White Rivers district, A l a s k a " : U . S . Geol. Surv. .Bull. 4 1 7 , 1 9 1 0 t p p . £0-25. • .V-;" 2 . Mc.Oonnell,R.G., Ann® Rep®, Geol. Surv.Can., Vol.XT.1902. pp 31A-34A. * 3® Cairnes, D . D . , "Preliminary Memoir on the Lewes and lord enski old Rivers coal district".Geol, Surv®,Can.,Mem. ITo.5.1910 pp. 2 8 , 2 9 . > •<5ockfield , 'Whitehorse district, Yukon "Geol .Su^v. Can. Mem. 150, 1926,-pp. 11-14. _ ' 4® Cairnes,D.D. /'Portion of Atlin district, British C o l u m b i a , with special reference to lode-mining". Geol. Surv..Can Mem . 37, 1912, pp. 53-54. . 5.Cairnes, D . D . , " T h e Yukon-Alaska International Boundary, between Porcupine and Yukon Rivers," Geol. Surv., Can., Mem® 6?» 1914, pp. 93-95.  63  productus Aff, inflatus Mc.Chesney. "  Arkansanus.  Oamarotoechia? sp. Moorefieldella Eurekensis (Walcott)? Spir-iferella? Bellerophon  sp®  sp.  ~ . 1 The following fossils were oolleoted by C a irnes from the shale-group, shale-1imestone group, and the upper portions of the limestone-chert group and iaentified by Girty as Penn~ s i yvani an {Geschel i an)«, Zaphrentis  sp.  Syringopora  sp»  . Favosites sp. Fenestella  2 sp®  Gystodictya  sp.  Dichotrypa?  sp»  Batostomella  sp.  Schizophoria sp. a f f . Troductus .  aff.  aagardi  resupinoiaes. Toula®  semireticulatus.  "  aff®  f a s c i a tus  "  a f f . humboldti d' Orb.  "  m  • sohrenki.  "  lf  wallacianus Derby.  ; ' j'^-p••'. •,. -..;.. v. .... l.Gairnes,D.D.Op. c i t . , pp. 94-101. Gairnes, •W 1 '. "Upper White River district, Yukon", Geol, Surv., Can.; Mem. 50, pp. 75-79, (1915)  Spirifer cameratus Tach. non Norton? "  sp®  Spiriferlna a f f . ornata. "  sp.  Glelotliyridina? sp. Plagioglypta? sp. S tenop ora  sp.  Polypora sp. leioclema sp. Mthostroti on sp. Orthocerae sp» Qhonetes a f f . geinitzianus. Rhynchopora a f f . niki tini. Marginigera a f f ,  typicalis.  Gamarotoechia? sp® Gamarophoria? sp. Squamularia a f f . perpl exa? Snchostoma sp® Thamniscus? sp. Aviculrpecten sp® Gampophyllum sp,• Derfeya? sp. Girtyella? sp. Reticularla? . sp.'Gompcsi ta? sp. Mstulipora? sp. Oystoaietya? sp.  G5-  Productus a f f . "  Gruenewaldti.  " .  inflatus McOhesney.  "  TJ  Arkansanus?  "  "  tenuistriatus Tern,  Syringoe leans • sp, Pugnax mutata Hall. Eumetria Terneuiliana Hall, samondia sp. Hemitrypa? sp, Spirifer a f f . aiarcoui ^aagen. Martini a? sp. Oliothyridina a f f . pec tini fera Sow. Marginifera. sp, a f f , involuta ^seher. Pinnatopyra sp. Haistedia a f f . indue a Waagen. Myalina a f f . Keokuk Hall. Reticular!a a f f , lineata Martin. Spirifer a f f . M k i t i n i  Tscher.  Produotus a f f . ounrirostria Sehell. Morcliynus sp. Paraparchites sp. Ghaetetes? sp. Produotus a f f . pustulatus Keys. n  "  oancrini formi s Tscher.  "  "  Juresacransis Tsoher.  "  "  pcrrectus Kut.  Gomposita aff. trinuclea Hall.  £6  Platyceras sp. Ghonetos a f f . ostiolatus Girty. "  .  "  vartolatus d ? Orb„  Spirifer cameratus•Martin. Michelinia sp. Produotus semireticulatus ^artin® Spirifer a f f . fasciger Keys. " .  f!  Tastubensis Tscher.  "  "  Condor d<Orb.  Squamularia a f f . perplexa McOh.es. Hustedia a f f . Indica Waagen. Pleurotomaria sp* ".. Lingula a f f . albapinensis Walcott. Rhrpidomella© Schuchertella a f f . Ghemugensis C 0 nrad. Ghonetes a f f . Geinitsianus Waagen. The following fossils were collected by G a i m e s 1 from the Nation River formation and shale-limestone group and identified by Girty as Artinskian or Upper Geschelian, thus UpperPennslyvanian or possibly Permain. lenestella 3 sp. Lingulidiscina sp. Derbya sp. Ghonetes a f f . variolatus D*Orb. 1.Cairnes, ^ . . " T h e Yukon/Alaska International Boundary, hetween Porcupine and Yukon Rivers," Geol.Surv., Gaa., Mem.67, 1914,pp. 93-95. G a i m e s , D.D.,"Upper White River district, Yukon," Geol .Surv. Can., Mem. 50, 1915, pp. 75-79.  67  Ghonetes a f f . Geinitzianus "  "  w  aagen.  ostiolatus Girty.  Produc tus a f f . Mamma tus Keys. "  "  Humboiati D'Orb. ,  "  "  Gruenewaldti Stuck,  n  "  Koninekianus V e m ,  •y".;;.  Wall so i anus Dqrby,  "  "  tenuistriatus Vern.  "  "  aagardi Toula.  Tegulifera? a f f , Uralioa Tscher. Pygnax Rockyrnontanus Marc ou? Rhynchopora a f f . variabilis Stuck. n  "  Mkitini  Tscher,  Spirifer a f f , reetangulus Kut, "  "  Nikitini  Aviculipecten 4 sp. Griffith!des sp. Spiriferina sp. Polypora sp® Pro due tus a f f . schrenki. Gleiothyridina sp. Bucanopsis a f f . meekana. Haticopsis sp®  Tscher.  6 S  Final Correlation of the Oarbonl ferous sediments in the Boundary district  - ;\^3pper: fhi  'Rvi .Boundary -Di s.t®  vshal s-I lines tone? Artinsltian  ;shale-|,im©s tone \ Nation River.•'•••V; ;vO:£:XJpper. Tffii'ite  v  ;; ;pendslyv-aniian  beds®  v river  eg® sh, ss®  :: ' :"ihal^-l;iine&'tone  shale-group  v group: JJeseheMan. wlimestone—che rt group • v. Uppex.' Mississippian.  :  limestone-che rt group®  i  I  ;  'it  6P  Southwestern Yukon • .  Gold  Series  Pistributi on; Pyroxenite and Periodoti te occur at numerous localities throughout the southwestern Yukon, the largest known areas being in the Wheaton River district.  Smaller areas have been  found throughout the Whitehorse district, and in the mountains at the head of the Big Salmon river.  An area of serpentine  was found on the shore of Drury lake.  The Gold Series consists of pyroxeni tes, perid otites, and amphib elites.  The pyroxeni tes and periodoti tes are massive,  and medium to dark grey with a greenish tinge.  They sometimes  have a coarse granular texture, and at other times no traces of such a texture can be found.  Iothing is usually megascopic  cally visible except pyroxene, olivene, and their alteration products.  The weathered surface is coarsely pitted, and has  a bright redd ish-brown appearance due to a c oating cf iron oxide.  Because of this characteristic weathering,  outcrops  of these rocks may be seen miles away, especially when the rays of the sun are shining directly on them.  Associated with these  basic rocks are numerous veins filled with serpentine and, in some cases corasely crystalline amphibole. have a width not exceeding four inches®  The largest veins  In other eases out-  crops consisting d ominantly of serpentine or amphibole have been found.  The serpentine is dark olive-green with a waxy  lustre and has a pale brown coating of weathered products.  7o  I t is traversed in many places by chyrsoli te asbestos.  The  amphiboli tes are also dark greenish rocks, and in appearance are very similar to the pyroxenites and periodotites,  but'are  prevailingly finer textured® •• 1 • •  ..  •  •  Oockfield describes the pyroxeni tes and periodotites under the microscope as follows: "Under the microscope the texture of the basic rocks was seen to be hypidiomorphic granular and rather coarse grained. In one section the rock contains about 80% olivene, in another over'95%.  Ghromite is prominent as an accessory, probably  making up 2% of the rock.  The rock lower in olivene contains  about 20% of a brownish mineral with a high index of refraction (but less than that of olivene) and a good oleavage in one direct!cn e  It was so much altered that its extinction  angle could not be determined, but it is probably an altered orthorhombic pyroxene. product.  Serpentine is an important alteration  Magnetite occurs in fine grains.  There are also  aggregates of talc and serpentine with interfingering fibres* Oairnes as follows:  describes the amphibolites under the microscope "Under the microscope,they are found to be ©qui-  granular rocks composed chiefly of hornblende cf which two varieties occur! one variety consists of large allotriomorphie grains of a brown hornblende, which occur distributed 1 . Oockfield, w.jtf.t"Wiii tehorse District, ^ ^ ^ ^ " S ^ T r ^ n F r1" Oan., Mem. 150,1926,p. 1 1 . 2 , Oairnes, D . D . , "Wheaton District, Yukon Territory." Geol. Surv., Can*, 1912, Mem.31,p.49.  7 /  throughout the rook, and have every appearance of being primary; the other variety composes most of the rock masses, is a green, fibrous actinolite.  Occurs to some extent in the  foiw of small veinlets cutting the brown amphiboles and also may be primary.  Considerable magnetite is also present as  well as sec ondary c ale ite chl ori te, serpentine," Age and Correlations Part of Cairnes Perkins group corresponds to the Gold Series.  Cairnes states that these rocks cut members of the  Mount Stevens (Yukon) group*  "No other definite information  was obtained in the district concerning the age of these rocks, but from their lithologic similarity to rocks, but other parts of the Yukon and in northern British Columbia, they are thought to be probably of about Devonian age". Taku  Group  Distributions The largest known area is between Tagish and Bennett lakes.  A small outcrop occurs in the valley of the Norden-  ski bid river.  A belt cf argillites extends from Dezadeash to  KLuane lake, and although these argillites have not been definitely correlated with those of the Taku group I will describe them here, because of their lithological  similarity.  Li thol Qfiys 13ie Taku group consists of a series of cherts, cherty quartzites, slates„ and argillites.  The cherts are light and  dark grey to bl6ck. but in piaoes are reddish on weathered T T C a i r n e s " W h e a t o n Kiver, Yukon Territory!*, Geol.Surv., Can., 1912, Mem. 31, p . 4 9 . ,  72  surfaces*  They are hard, massive, brittle, and break into  sharp irregular fragments.  The cherty quartzites are thinly  bedded,, grey or light coloured rocks, except where iron-stained, when they have a red, weathered surface.  The slates, which  grade into finely bedded and massive quartzites, are finely bedded,possess the typical slaty structure, cleaving quite readily along the foliation planes, and are in places much folded and disturbed® The argilli tes of Dezadeash lake, are dark, coarsely bedded rocks, usually massive, and seldom cleaved.  'They contain  a number of greyish quartzitic bands and occasional conglomeratic phases. Age and Q orrel a ti onf The rocks of the Taku group underlie the Carboniferous limestones.  They have been referred to the Lower Cache Creek  series on a lithological basis and are therefore probably Devonian in age.  This correlation is open to question and  therefore the name Taku group was proposed by Gairnes. Garb oniferous and Triasslc Limestones and associated rocks« Distributions  :  Through the southern Yukon the limestones and minor quantities of associated clastic rocks are extensively developed,  the more important areas being as follows:(1)  Triassie:  (a) in the hills on the eastern side of Lake Laberge;fb)  in  the hills on both sides of the Lewes river from lake Laberge to twelve miles north; (o) east of lake Laberge and west of the Teslin river and extending into the Little Salmon area;  73 fd) in the vicinity of Coghlan lake, ELusha ana Hand anna creeks., ana extending to Eagle's nest on the lewes river, (2) Carboniferous or Triassic, or both:  fa) in the hills east of  the Lewes river and extending from Lake Laberge to Whitehorse; fb) in the vicinity of Windy arm, Taku arm, Tagish lake, and Ibex river.  Although the majority of these rocks are probably  Triassic, the second classification has been made because the rocks in this group have been classified in part as Oarboniferous on the basis of fragmentary fossil remains, and until further work has been done on them it would not be justifiable to classify them entirely as Triassic on a lithological and very iincomplete palaeontological  basis,  Lithol ogyi The bulk of the rooks are limestones, but a few clastics are also to be found•  The limes tones are whi te to medium grey  and bluish on fresh fracture.  The pure carbonate rocks are  coarsely crystalline, but the more argillaceous types are finegrained and crypto-crystalline,  These rooks are some times  massive, but at other times bedded, in which case the strike and dip usually change rapidly.  These limestones are usually  metamorphosed?being prevailingly in the state of marble with veins of caloite throughout.  Specimens are often curiously  and handsomely marked with black bands and spots.  S0me beds  contain considerable silica in the foim cf chert and these weather rough.  The limestones are sometimes found in bands  and patches in other rocks, such as in the andesites along the Little Salmon river.  The associated clastics are ar^illites  7<f and greywackes similar to those of the Laberge series. Age and Correlations (and Plasties) These 1imestones^have been classified is Carboniferous, Devonian-Carboniferous , Carboniferous-Triassic, and Triassic the last being definitely established, and the Carbonifercus reasonably certain, so in all probability they range from Carboniferous to Triassic inclusive.  This confusion as to  the range is undoubtedly due to the fact that; in some places the limestones are devoid cf fossils, in others only fragmentary remains are to be found, and no-where has a really good collection been obtained.  Also possibly more than one  •fpaanation is represented. The foil owing fossiliferous evidence as to the age has been obtained: In one locality Cockfield  1'  :  • •  collected some brachiopods,  which were thought by Kindle to be Devonian. On the basis of "Fusilina" from the limestones of Windy Arm Gr.M, Dawson classified these rocks as Carboniferous and correlated them with the Upper Cache creek beds of southern British. Columbia. . "' '. \ 3 -  Kindle places one collection made by Cockfield in the Triassic, several fossils of this age being represented, the most definite being the compound coral Isastrea. 1® Cockfield ,W.jS. , "Whi tehorse district, Yukon Terri tory "Geol . Surv., Can., Mem..150, 1926, p c 1 3 . 2. Daws on, G.M., "Report on an exploration in the Yukon district, Northwest Territories, and adjacent parts of British Columbia", Geol. Surv., Can., Ann. ,Rp. ,3:B .1888 ,-o.l73B . 3. Cockfield,W S E„ t "Whitehorse district, Yukon Territory", -Geol, Surv., Can,, Mem.150. 1926,p.13*  7<5~  Gockfield established an arsa of Triaasio clastic rocks along the lower portions of the little Salmon river.  Again  the evidence is fragmentary, the most important fossils being flattened Pseudomontis subcileularis? From fossils collected in the liaberge area Lees makes the following classification ana proposes the name Braeburn series for these Triassic rocks®  3 .  This name Braeburn was first  . .  used by Gairnes to designate the limestones in the same area which he thought to be of Carboniferous age. Lower Liassic Noric Pseudomonotis zone,  Laberge beds Pseud dmohotis subcirculari s, Gabb  0oral zone.  :*:Isas;trea; o 0 f vane ouverehs'i s ( Gl app and Shinier) and other fragmentary corals -ew species of Variamusituii and a sponge c-vf • Steinmania utricuius Regny.  K a m i a Juvavites zone  Juvavite s sub in te rruptus -Meg's*., ' Hal oltea orahtissma Sml th. ?  Trias°sfc f i ?i a t^ E ; ' & 3 5? e S f V ; occurrence of the marine the.southern Yukon", Proc. and Trans., Roy. Sec. 5 ' ><Tl • s 1 2 0 1 ^ ' PP- 101-104,1931. ° " m e m c l r on t h e L e w e a and Herder— s-c-old rivers coax district, Geol. Surv., Can., Mem^.igio.ppg'e.  re  ThgJJpper Beaver River Area Volcanic Agglomerate. Shale, ana Sandstone Distribution: "These rocks are fauna outcropping on the upper reaches of the Beaver .'.river* Lithology: The major part of this series is volcanic in origin. The balk of the agglomerates are comppsed of a aark purt>le, aogite-mica andesite, in which are pebbes and boulders of many rocks of the Tindir group and other formations.  Among  the pebbles which have been examined were quartzites,  slates,  limestones, calcareous sandstones, and greenstones.  Under  the microscope the secondary minerals, calcite and chlorite, were found to predominate, but occasional crystals of biotite. augite, brown volcanic glass, ana turbid felspar were also noted.  The groundmass, where unaltered to ealCite, is micro-  crystalline.  Associated with these agglomerates are beds cf  dark coloured shales and sandstones.  The principal exposures of these rocks are near the base of the Ordovician-Devonian limestone.  Outcrops at other  localities suggest however they may occur at higher horizon, so they are tenatively grouped with - the limestone as Ordovician to Devonian in range® Ord ovician-Dayon1an Limestone distributions The limestone occurs in the two bands, one north and west _Pf Carpenter creek, the other north of the Beaver river and  77  east of Carpenter creak. .Lithologyi The limestone is almost invariably white or slate coloured, and as a whole is somewhat massive bedded over the greater part of the area, though shaly and sandy members occur. Age and Correlation: The limestone overlies unccnformably the TinSir group, which is at least pre-Ordovician.  Prom the fossils collected  by Cockfield and identified by E.M. Kindle, it seems that the limestone is represented in the Devonian to a slight extent and predominantly in the Ordovician and Silurian eras. The following fossils were collected and identified: "lot lc.7662: Horizon, Devonian, Favosites c£, " Cyrtina  digitatus.  "  radiatus.  "  umbonata.  Lot No. 7956: Horizon, Favosites cf.  Silurian.  favosus.  Stromatopora cf. antiquua. Lot No. 7960: Horizon,  Silurian.  Bryozoa (undeterminable) Megalomus cf. canadensis, Lot No. 7961: Horizon, Qladopora cf.  Silurian.  cervicomis,  Orthis flab ell i tes. Whitfieldella nitida. Lot No. 7964: Horizon, S i i u r i a n  or  Ordovician.  Actinoceras pp. allied to A. ri chard son!«  73  I  Lot Ho. 7963: Horizon, Silurian or Ordivician. Strcmbodes sp® Zaphrentis vel. Strephteasma sp. ^ridophyllum sp. Lot Ho. 7958: Horizon, Silurian and Ordivician, Favosites ef. Favosus. Columnaria alveolata. Bryozoa? not determinable® Gornulites n. s p . Lophosphira sp. Lot No. 7959: Horizon,  Ordivician.  Oolumnaria alveolata e Saphrentis?, sp. Sridophyllum of. rugosum, Halysites n. sp, Eastern Yukon Distri but!on Owing to the exploratory nature cf the work done in the eastern portion cf Yukon I will not attempt to describe and classify the rocks in detail but deal with them as a ggroup. Ordovician sediments are found at the following localities: (1) from Slate rapids to Woods!de mountains along the Pelly river; (2) along the Ross river for fifty miles commencing at False Canyon, and from Lewes lake to the Divide; head of the % c M i l l a n river.' in the Ogilvie range.  (3) at the  Devonian sediments predominate  Calcareous sediments probably of Carbon-  iferous age are found in the following areas: :(«), forming a large portion of the mountain group north of the Besvozv and  79  west of the Rackla rivers;  (2) in the MacMillan mountains.  Ucn-calcarecus Carboniferous sediments occur in the Zalzas range in the vicinity cf the Moose river, Lithology HI a 11  II frifihf.j  The Ordovieian rocks consist of a series of dark grey argillites and slates, black cherts and chert breccias, -ites, and bands of dark crystalline limestones.  quartz  'These rocks  are usually thin bedded, often occurring as alternating bands of Gatek argillites and dark compact quartzites. The Devonian rocks consist of a series of limestones, quartzites, and ferruginous slates. heavly bedded, and crystalline. a characteristic yellow®  The limestones are dark,  The ferruginous slates weather  -  The limestones cf Beaver river area and the MacMillan mountains are white, coarsely crystalline rocks. The non-calcareous Carboniferous sediments are composed of hard dark argillites, passing in places into quartzite bands and inclosing occasional beds of limestone.  Underlying  the argillites are a band of breccias or agglomerates consisting mostly of angular fragments of dark and occasionally green and red cherts, imbedded in a siliceous matrix.  The chert  breccias are followed in descending order by slates,  alternat-  ing in places with dark cherts. Agej The Ordovieian rocks were determined as such by indentifi~ cation, of Ord ovieian graptolites ftft) in the argillites at various localities.  j  S o  TM  j  limestones, ferruginous slates, and quartzites of  |  the Ogilvie mountains were concluded to b e D e v o n i a n i n age  |  on account of some fossils found in.these rocks by Mr.Camsell  J j . | •  i  on the .'Wind and Peel rivers® ' - .  =  > . o,  .  "  The limestones are classified as Carboniferous because crinoid stems of Carboniferous age were found in them in the MacMilian mountains, and also because they overlie the Devonian rocks of the Ogilvie range.  Possibly they are cf Triassic  age as are similar limestones in the southern portion of the Yukon Territory®. The cherts, chert breccias, and quartzites found on the MacMilian are tenatively classed as Carboniferous on their lithological similarity to the rocks cf the Taku group, which are Carboniferous, also because they lie conformably under the limestones®  This last reason would lead to the belief  that they extend down through the Devonian, and until more detailed work is done thSy cannot be more definitely correlated  •a/  Mesozoic LaBerge  Series  Generals: Included Tantalus ically found  under  Conglomerate, - which  is  ations,  often  I have  also  the Upper White to  These  rocks  north  of  lying  between  litholog.  fossils  the  two  are  form-  sediments  of  are l i t h o l o g i c a l l y  appear  extensively  expecially river  at  in  the  to r e p r e s e n t  a  during Mesozoic  sim~  later time.  Range  developed  throughout  following  localities:(1)  Tantalus B u t t e ;  the U o r d e n s k i old  of Lake l a b e r g e ;  rict  which  of sedimentation  are  the L e w e s  the Coast  the M e s o z o i c  the  and  and w h e n no  to s e p a r a t e  here  but  is  •  southern Yukon,  of  series,  period  Distributions  Impossible  grouped  Series"  confoimable with  series,  river district,  the L a b e r g e  or prolonged  west  quite  "Laberge  is  s i m i l a r to the L a b e r g e it  liar  this heading  and i e w e s  (4^and/in  intrusives.  t h e y f o r m the g r e a t e r p a r t  (2)  in  rivers;  the W h i t e h o r s e  the  the  (3$  area  east  and  district  In  the U P P e r W h i t e  cf  the l u t z o t i n  river  east dist-  range.  Lithology: Shales, arkoses, The  and  Tantalus  conglomerate, seams. trict  argillites,  t u f f s make u p t h e b u l k Conglomerate but  also  The M e s o z o i c are deminently  erates,  sandstones"  consists  contains  sediments shales,  and g r e y w a c k e s .  conglomerates, of  the L a b e r g e  chiefly  sandstone,  series.  cf massive  beds  shale,  coal  o f the U p p e r W h i t e  argillites,  greywackes  and  river  sandstones,  of  dis-  conglom-  Minor quantities of limestone are  QZ  found in these fomiations.  Sufficient work has not been a one  in order to establish a stratigraphic sequence® The shales of the Saberge series proper are often light grey to black and occur in successive zones 20' to 30'  thick*  Some of these shales are iron stainea and thus are red.  The  barker, and denser shales occur with the arkoses and sandstones in layers  to 1 " thick.  The shales of the Tantalus O o n ..  glomerate are usually fine-textured, black rocks, which exhibit slaty cleavage.  They are often- found in fine or coarse  beds next to the coal seams.  The lighter shales are dominant-  ly interbedded with sandstones, the beds varying from coarse to fine.  In the Upper White river district dark grey and  slate coloured shales and argillites are the most conspicuous, but in places banded or ribbon like beds oocur.  These banded  shales, on the weathered surface, have an alternating light and dark layered appearance.  On fresh fracture they are dark  grey, black, dark green, or red.  In places the banding is due  to the varying texture and not to the colour, such as finegrained, thinely-bedded greywackes interstratified with the shales present a finely banded appearance due to unequal resistance to weathering of the various layers.  In the vicinity  of intrusive igneous rocks, expecially granitic intrusions, the shales and argillites have become bleached and indurated, and transformed into hard cherty rocks with alternating white or greyish and dark grey to black bands.  The argillites  break into sharp angular pieces, and do not as a rule cleave readily along their bedding planes s'o as to produce slab or  S3 ..  plate like fragments® The upper portion of the laberge series contains some massive beds of medium-grained brown sandstones® M  A coerse,  white to yellow, loosely cemented, calcareous sandstone®, eon staining quartz pebbles in a white cement, also occurs near the top of the series.  Lower in the series are some coarse  <2ark green, loosely cemented sandstones, and some reddish calcareous sandstones. aceous sandstones.  Associated with the tuffs are some tufThe sandstones of the Tantalus Conglom-  erate occur in massive beds, and contain quartz, chert, and slate in a siliceous matrix.  The sandstones of the Upper  :  White river district contain grey of green,  fine-textured  i  rocks, and coarse, yellowish or grey, firm, consolidated rocks. In the Laberge series occur thick, massive beds of conglomerate.  The pebbles and boulders of this conglomerate vary  in si?© from sand grains to footballs, and are mainly andesitic fragments derived from the older volcanics, and pebbles ident -leal in composition with the Coast Range granodiorite. coarse basal conglomerate has also been located.  A  It contains  pebbles of granite, of fine-grained greenish volcanics, and of greywackes. |  "  The Tantalus Conglomerate, which occurs in  massive beds, is made up almost entirely of quartz, chert, and slate pebbles in a siliceous matrix.  The pebbles are uni-  form in size, 1" to 2 " in diameter being the average.  Con-  gl omerates were noted only in a few places in the Upper White river district and are prevailingly finely textured, bedded, firmly consolidated rocks. pebbles of dark argil I ite and. chert,,  thinly  They contain abundant  a  Arkoses are well represented in the lower psrtion of the labergecseries.  They are interbedded with tuffs, the total  thickness of the series being about 2000 feet.  They vary in  colour from light to dark grey, reddish grey, or pale green® ish grey, and are dense-textured, compact ffooks, which, occur only in heavy massive beds.  No arkoses have been found in  the Tantalus Conglomerate or the Mesozoic sediments of the 1 Upper White river district.  Gairnes describes these arkoses  as seen under the microscope as follows: "The arkoses were seen to consist chiefly of rounded and angular particles of plagioclase, as well as some, quartz, and a few rock fragments, all cemented by a matrix that consists chiefly of kaolin, and some calcite.  In some cases the ma-  trix contains a great amount of secondary biotite, produced by metamorphic processes," Greywackes have been found in the laberge series and in the Mesozoic sediments cf the Upper White river district. They.are usually grey, green, or brown,and interbedded with dark shales and argillites. The tuffs of the Laberge series are of two main types; fl) fine-grained bedded, and (2) medium-grained, massive. The two varieties occur interbedded or separately.  The bedded  tuffs occur in greater abundance than the non-bedded.  1 . Gairnes, D . D . , "Wheaton* District, Yukon Territory". -Surv., Can., Memoir M. 31, 1912, p . 5 5 ,  Geol.  The bedded tuffs are medium-grey, dense rocks with, conohoidal fractures,  Distinct beading planes are spaced from  1 to £ inches apart.  Parallel to, and between these, are  indistinct narrow bands of colour slightly darker than the rest of the rock.  Roughly parallel joints occur in two places  A reddish brown, oxidized coating follows the bedding and joint-planes, •••'••• M The microscope show these bedded tuffs to be elastics* 9  made up of small, angular ^zagments of felspar and quarts* The felspar is mostly plagioclase, but some of it has an index of refraction less than Canada balsam and is probably orthoclase.  Quartz is present in small quantity.  The inter-  stitial material consists largely of altered products, kaol i n , calcite, biotite, abundant ohloritic material, oxide, and leucoxene.  iron  This was originally the finest grained  material and would naturally be affected most by metamorphic processes,  Pyrrhotite, magnetitle, and titamite are access-  ory, . The non-bedded tuffs are fine to medium-grained and vary in col our from light to dark grey and from grey to green. They are often difficult to distinguish from an igneous rock such as a diabse or basalt.  These rocks have the character-  istics of an impure sandstone, arkose, or greywacke.  On the  fresh surface the rocks are dense, compact, and massive, and the weathered surfaces reveal their elastic nature.- Oock^ield records the following descri-pticn of the microscopic JL»t»ock±ield,vif.J£., "Whi tehorse District, Yukon territory Ge ol» Surv., Can., Mem. 150, 19£6, p. I7 e 2.Cockfield, W.E."Whitehorse D i s t r i c t Y u k o n Territory" Geol. Surv., Can., Mem. 150, 1 9 2 6 , p . l 8 .  characters of these massive tuffs. "The texture in all eases is clearly fragmental, the great bulk of the fragments being more or less broken crystals cf individual minerals with, a few of volcanic rocks, the rock in the class of crystal tuffs c  ^his places  In only one case is  the proportion of rock fragments large enough to approach that of a lithie  tuff. Plagioclase of various compositions is far  the most abundant constituent, and in general makes up 60 to 70 % of the rock.  The plagioclase varies from albite to andesine  and different placioclases occur in the same section.  Quartz  is present as a rule, making up,nab out 1 5 $ of the rock, but in the smaller fragments it is difficult cfefe distinguish from the felspars making an accurate determination of the percentage impossible. embayed.  Some of the large quartz grains are rounded and .  Green hornblende, somewhat altered to chlorite is  commonly present and in some cases makes up 10% of the rock. Potash felspar present to a minor degree 0 "The foil owing accessory minerals were observed,, jfcStami te, apatite, biotite, augite, p'yrite, and probably pyrrhotite. The felspar showed varying degrees of alteration to white.mica and kaolin.  The interstitial material is highly altered, and  is to be expected as it consisted  originally of the finest  volcanic ash. It is typically a dark brownish, cloudy aggregate of various secondary minerals,  o f vfcich the  grains are of s ^ i c r o s c o p i S dimensions.  individual  Ohloritic  material  is as a rule prominent and calcite in some cases is prese nt in an important amount.  Other secondary minerals of less  37  common occurrence are; epidcte, zcisite, and leucoxene.  In  some cases secondary biotite is abundant in the interstitial material and is considered to be the result of igneous metamorphism. "Fragments of rocks were reconized in some sections. "The tuffs show more variation in size of grains than they do in proportions of their constituents." Age and Correlation* Only a few contacts between the Laberge tuffs and the Triassic limestone and associated clastics have been examined, and in such cases an angular unconformity seems to exist, but the evidence is not conclusive as the bedding of the limestone is.usually indistinct.  The contact of the tuff  with the Coast Range granodiorit e is of an extremely undulatory nature, and the fact that large apophyses are connected with the main body of the intrusive prove beyond a doubt that the tuff is intruded by the granodiorite* Fossils were collected by Cookfield from some of the shale beds and reported on as follows by Buckman: "The examples submitted reveal the presence in Yukon Territory of strata of Lower Inferior Oolite dosn to middle Lias.  The accompanying table gives the results;  The evidence  is in some eases very good; in others doubtful.  loCockfield , W . E . , "Whitehorse District, Yukon Territory",Geo! . Surv., Can., Mem. 1 5 0 , p . 2 1 , 1926. *  ss  Laberge Series , EInglish  English.  3tratigraphic ; Age Term  .  Southern Yukon  English  IFature of  Heme ra  ev i d enc e  Term  [Lower Inferio r Lud v/igian aalensis Dolite  Genus  Pleydellia  Absent (?)  3anavarinan  Fair  Bumortierian Dumortieria Dumortieria  Fair  or moorei dispansum  phlysecgrammDceras  Fair  Grammoceratar . (struck man li Pseud ogra- Good  Upper Lias ; Haugian  pedicum)  rimoceras  striatulum  Grammoceras  Good  Variablus .  Haugia  Poor  Harpoceratan faleifuerum 'iarpceeras garatum  Amal the i an £.Igori anum Middle Lias  Poor  Slegant uliaras  Poor  Amaltheus  Good.  sequenzicera, Liparooeratai davoei  Prodactylio3 eras  ""air  99  The fossils indicate strata ranging in age from Middle Lias to Inferior' Oolite, that is strata cf various stages exclusive of the oldest, of the lower Jurassic and earliest Middle Jurassic." In Gairnes collections from the '-^antalus area, the following three fossils were especially identified, v i z , dawsoni, lerinea maudensis, and Rhynchonella  Trigonia  orthidiodes,  which are all regarded as Jurassicofoimso The laberge series of the southern Yukon can be referred to the Jurassic, with the known range from the lower Jurassic to the lower part of the Middle Jurassic, and with the possibility these limits may be further extended•  This range is  for the laberge series proper and is exclusive of the Tantalus Conglomerate and the Mesozoic sediments of the Upper White river district, both of which have been incorporated with the laberge series in this discussion. The Tantalus conglomerate overlies, to all appearance, conformably, the laberge series.  From the coal seams at  Tantalus mine fossils pi ants were collected by Gairnes ,and examined by Dr. Penhallow, who says: "All the material appears to be same as the specimen of Thyrsopteres elliptic®, Fontaine, as figured by Ward in the "Status of the Mesozoic Floras of the United States", vol. X1V111, p l . l Z X l ,  figs 12  and 13, and to this the present specimens are provisionally referred s It is to be observed, however, that there seems to 1."Siirnes:, D . D . , "lewes and Hcrdenskiold Kivers 6oal District" Gecl.Surv.^Can. Mem. 5, ppf33-35),f1910). d* gairnes, D . D . , "lewes and ITordenskiolc! Rivers Goal District" . 0 , Geol. :Surv., ,,Cazu, ••Mem. .6,.. pi38.i.i9;l( '  90  be some question as to the ooirectness of Wards reference, since the specimen cited is quite distinct from the original, type of Thyrs op teres elliptica as described by Fontaine! fin "Potomac Floras",vol .XV",p,133,pl.XXlV, figs. 3 and 3 a ) , and it is quite possible that further and more complete specimens may show this to be an entirely new species®  A somewhat re-  lated flora was described by me in 1898 as. obtained by Mr.J.B . Tyrell from the Uordenskiold.  All the specimens shown, how-  ever, were specimens of Gladopliebis and they indicated Oretaceous age. "The specimens from, the Tantalus mine present a flora with the same facies as those from  the lord enski old river, and  the whole confirm to flora of ^Kootanie age". (Lower 0 ret ace ous) o •• More recent work in 1915 in the Wheaton area, resulted in ' ' 1 ' further specimens being collected, of which Gaimes wrote, "fossil plants from these beds collected during the past summer, which have been determined by Dr.F.H.Enowlton,  of the  United States Geological Survey, to be of Jurassic age.  Dr.  Knowlton al so states that some of the species have been found in the Kootenay or have at least been reported from that formation". From the evidence given above it can be seen the Tantalus Oonglomerate is either lower Cretaceous, upper Jurassic or both in age, and due to the lates evidence the upper Jurassic age is favored.  1.Gaimes,D.D.,"Geol.  Surv., Gan., Sum. Rpt., 1915, page 4 1 .  103/5  ••  1 Fossils collected by Cairnes from the Mesozoic sediments  cf the Upper White river district were reported on by Dr.T.W. Stanton of the United States Geological Survey who states: "These fossils are also Aucella and are believed to represent a variety of Aucella crassicollis and to be of lower Cretaceous age". . . . . 2 Similar rocks have been described by Moffit and Knopf*, in the Habesna-White River district, Alaska, and they have reported fossils of the Jurassic and Triassic periods from them.  Therefore, as these rocks resemble lithologically the  Mesozoic beds in the U p p e r White river district, and in both areas constitute a correspondingly prominent part of the Butzotin mountains, and since in the Upper White river district these beds overlie upper Carboniferous sediments, it would seem altogether probable that in the Upper White river district these Mesozoic beds include not only Cretaceous but also Jurassic and even possibly Triassic members. These Mesozoic beds correspond closely with the Laberge and Tantalus Conglomerate of the southern Yule on. From the above discussion it is quite evident that the Laberge series, inclusive of the Mesozoic sediments of the Upper White river district, and the Tantalus Conglomerate, ranges in age from the lower Jurassic to the Cretaceous in-  1.Cairnes, D.D."Upper White River District Yukon,S Geol.Surv. Can., Mem. 50, 1915, pp. 86-87. . ' 2^Moffit F.H. and E h o p f . A . , " Mineral resources of the labesnaft lcnn  I?rLaiStriGt*  Alaska  »,T  U s  ' - Geol. Surv., Bull. 417,  $>2  elusive, and possibly includes a few Triassic beds. •1 ' • • The Sutbshi series of Gairnes in part correspond to the Iiabergev.seri.es. The Older Volcanics The Older volcanics are a group of semi-basic to basic rocks, and appear to represent a long but intermittent period of vulcanism.  They are in part younger and in part older  than the Laberge series, so will be considered as Carboniferous to Cretaceous inage. Distribution: These rocks are extensively developed throughout the southern Yukon and especially in the foil owing localities: (1) in the Upper White river district north of Beaver creek; (2) on both sides of the Lewes river from Selkirk to Carmacks; (3) in the Semenoff h i l l s ;  (4) in the Boswell mountains;  in the hills east of the Hordenskiold river; ern portion of the Whitehorse area; ( 7 )  (5)  (6) in the east-  between Sekulmun and  Aishihik lakes; and in many other smaller areas*  In many  localities the older sedimentary rocks are everywhere minutely and persistently invaded, intruded, and overlain by these older volcanics. Lithology! The Older volcanics include, mainly, andesites, basalts, diabses, porphyrites, as well as their aocompanying and related tuffs and breccias.  Minor quantities of deep-seated,  basie rocks such as diorite„ gabbis. and amphibolite have 1 . Oairnes, D . D . , " A Preliminary report on the Conrad and Whitehcrse mining districts," geol. Surv., Can., Pub. 1 9 0 8 , p . 3 1 .  93  been included. their wide ogical but  range  rocks v a r y  of colour,  composition.  in places  with  These  texture,  They are  and  quartze  schistose  and  prevail,  but browns,  some d u l l  brown colours  colour,  reds,  are caused  as p y r i t e  by  and b l u e s the  with  pJ^ioxeae^oanfeBiotft©';-  ioclase  felspar. rocks  veined  volcanics  a laminated  less  than i filled  chit)rite,  inch in with  and  a mottled  or  even  diameter.  chalcedonic appearance  dark groundmass,  due  i n appearance  which none  of  the m i n e r a l  with  and  are  is predomin-  horngreen  plagIn  ranging  but u s u a l l y of  in  being  these  cavities  mainly zeolites,  calcite,  many o f these  &<& l a r g e ,  throughout  dark  green  aphanitic.  the a m y g d u l e s  Thus,  or owing to w h i t e  through an otherwise  or pale  one i n c h ,  either  distributed  contrasted  eye»  of g r e y  The m a j o r i t y  quartz«,  of  cf iron which  is usually  than  finely,  The red  of nearly black  secondary minerals,  feldspar phenocrysts  scattered  to more  compact,  occur.  are amygdaloidal,  from m i c r o s c o p i c  naked  these  These v o l c a n i c s  and  The g r o u n d m a s s  size  have  rocks,  and  dark shades  oxidation  phenocrysts  blende,  these  cf wlich  and m a g n e t i t e „  ately prophyritic,  are  given  are c h a r a c t e r i s t i c a l l y  textured,  places  and  appearing  also,  to  and m i n e r a l -  fractured,  At a f e w p o i n t s  due  structure.  . These v o l c a n i c s  present,  fresh  distorted,  h a v e become l o c a l l y metamorphosed  appearance  structure,  dominantly  are c o n s i d e r a b l y  calcite  in general  amygdule rock.  other d u l l ,  constituents  light  rocks,  coloured  a finely  textureds  fillings  being  Such  types  dark dense  are v i s i b l e  to  are rocks the  in  S>4  The associated tuffs and breccias range from dense, finely textured ash. rocks to coarse, massive breccias.  The  breccias are composed chiefly cf igneous material ana the cemented rock fragments are quite angular.  M e r e the tuface-  ous fragments fell on surfaces covered with erosion products the resulting clastic contains boulders and pieces of whatever materials were exposed on the old surface, where they fell on andesitic surfaces they contain no foreign material. Gockfield describes the older volcanics under the microscope as follows:  "Under the microscope the rocks are seen to  possess a variety of compositions and of structures® Plagioclase is always present and generally occurs in two gene rati qns.  It ranges from cligoclase to bytownite in composition,  but by far the more common plagioclases are andesine and labradorite. groundmasso  The acid plagioclase is present chiefly in the The ferromagnesism minerals include hornblende,  biotite, pyroxene, and olivene.  Both the common green horn-  blende and the brown basaltic hornblende occur, but the foime-? is by far the more common*  |ioti6e is also common and in  some cases is the only ferrcmagnesian mineral present.  Bio-  tite and hornblende occur together and exist in both generations,  Pyroxene, usually diopside, is present, but seldom in  phenocrysts of sufficient size to be detected by the nake eye. Olivene has been noted in some  of the augi te andesites, Pyrite  and magnetite' are abundant, in many cases in specks large enough to be detected with the naked eye. --- ^ ^ J ^ ^ l f o f t of these rocks in s one cases is well 1 .OocKfield , W . E . , "Whi tehorse District, Yukon;Terri tory" f TSeoTT SuT>V  - •»  P Tr 0 ca-n in  * t ^emoir 150,p.24,1926  .  9?  advancefl, ana in many instances masks the original character® Calci te, chlorite epidote, and zoisite are abundant as seennd^ ary constituents, "The s true ture of the rocks is usually porphyritic, and the phenocrysts, as described above, consist of plagioclase and the ferromagnesian minerals®  Phenocrysts are as a rule  fairly abundant® rf  The groundmass is either holocrystalline or partly  glassy; in the former case the structure is in most cases pilot axitic , and in the latter hyalopilitic. "The rocks range from aidesites to basalts.  In the form-  er case mica andesites, hornblende andesites, and augite mentioned above are largely andesitic in character." In addition to the above, even quartz has been found in some of the more acidic members, such as the Herdenskiold dacites. .  • • ••  Age and Correlation: The only evidence available concerning the age of these rocks is that obtained by a study of their relation to rocks of known age.  As some of these volcanics cut and overlie the  Cretaceous-Carboniferous sediments of the Upper White river district, it is quite probable that some of them are more recent than the Cretaceous beds. In the labesna-Whi te rivers district, A l a s k a evidence has been obtained indicating that the copper-bearing volcanics there, which appear to be the same as those in the Upper White rivei? district, are of upper 1. Mof?iTt!F7H77—and~^tiopf^ SdolphT^'Mineral resources cf~the Uabesna-White Rivers district, Alaska, " U . S . Geol. Surv., Bull. 417.1910,p-D 17-27.  96  Carboniferous age*  In the southern Yukon, evidence has been  found showing that portions of the Older volcanics are definitel y intrusive into the Saberge beds, and may therefore, be considered younger.  Cairnes believed  this period of vulcanism  represented by the Older volcanics was in some measure contemporaneous with the deposition of the Laberge beds.  The similar-  ity of the tuffs of the Laberge series and these of the older volcanics led him to draw this conclusion,,  The Older volcanics  are probably all older than the Coast Range granodiorite. They probably include members ranging in age from Pennslyvanian to Cretaceous, and thus represent a long intermittent period of: vulcanism. In the Yukon territory portions of this series of rocks have been given various names by the men who have worked in the North.  The "Older Volcanics" include Cairnes Chieftain 1 2 3 Hill group and Perkins group , his Hutshi group , Schwatka 4 5 andesites , and Herdenskiold dacites , and his Windy Aim ser••••.• ••••••6e: ' f 7 ies« The "Older Volcanics-also include, the Augite andesites 8 g of Cockfield, Divisi on4 of Gwillim, and the Porphyrite series of Dawson,, T & 2 - ( J a i r n e s , i > . , ,f$heaton Bi stHc"t757~Geo"lT"SurT», ^an77"Mem7Il, pp. 59-64,46-51, 1912. 3 , 4 , 5 . Cairnes, D.D.,"Preliminary memoir on the Lewes and Nordenski old rivers coal district, Yukon territory", Memoir 5. pp. 39-42,42-43, 29-35. 1910. 6. Cairnes, D.D.,"Conrad and Whitehorse Mining District", Geol. Surv., Can., Pub. 982, p e 29, 1908. 7 Cockfield, W.JS.,"Upper Beaver River area, Mayo district, Yukon territory", Geol. Siorv., Can.., Sum. Rp. 1 9 2 4 , p t . A . p . 7 a . 8 Gwillim, J . C . , "Atlin Mining D i s t r i c t , " Geol.Surv., Can., Ann. Kept., vol. Xll pt. B . p. 28. 9 Dawson, G.M.."Report on an exploration intlbhe Yukon district, Northwest Territory, and adjacent portion of British Columbia, Geol. Surv;, Can*, Ann. Rp., 3. part. b. 1888,-p.  97  Ooast Range latrusives Dig tributi on: Kie rocks discussed here include the Ooast Range intrusives as well as granitic rocks in other parts of the Yukon. These other intrusives have been correlated with the Ooast Range Intrusives on lithological evidence and lack of conflict, ing influence. The Ooast Range batholith coincides with the Ooast Range mountains, which merge with the Yukon plateau near H u a n e lake. Great bodies of granitic rocks are found; between the Lewes; ¥isling,  and White; and in the mountainous tracts of the east-  e m portion of the Yukon territory.  Smaller  gran-  itic intrusives occur throughout the interior plateau. Li thol ogys The typical rocks can be classified grancdiorites.  as monzonites or  They are generally grey in colour, and fresh  and unaltered in appearance, but at times enough pink felspar is present to give them a pinkish tinge. •  'They are medium to  coarse-grained, and usually composed of less than 2 0 $ quartz, alkali and soda-lime feldspars in about equal amounts, and biotite or hornblende or both. With the increase of orthoclase and decrease of plaioclase, typical granites have been noted, and the increase  of  plagioclase and augite with a corresponding decrease of orthoclase has given rise tus diorites. •An earlier phase cf the Ooast Range intrusives is the syenite porphyries.  They are typically very coarse-grained  110  and composed of large pink orthoclase phenocrysts inja  grey,  coarse-grained grcundmaes of orthoclase, plagioclase, and hornblende,  The rocks vary from these to hornblende syenites  rich in hornblende and plagioclase, and on the other hand to granite prophyrites. Throughout the Yukon territory large dykes varying in composition from granite to diori te porphyries are found. They are seen to possess a hoiocrystalline, porphyritic structure, and to consist of a microgram tic or micropegmatitic quarts _ .. .feaa'csa-rs felspar groundmass m which alkali^are plentiful, and in which bioti te and hornblende usually occur.  These dytes are believed  to be connected with the larger intrusive bodies. 4ge and Correlations I t is evident that the granitic intrusions of the Yukon territory embody a number of different phases, which probably represent a considerable range in age©  Boulders of grano-  diorite in the lower and middle Jurassic Laberge series indicate the presence of pre-Jurassic intrusions in the Yukon. In many piaces, however, these granitic intursicns are found cutting both the Older Volcanics and the Laberge series.  This  would indicate at least an upper Jurassic period of intrusion, which probably continued into the 1ower Cretaceous period.  In  the Upper vlhite river district, conglomerates of the Mesozoic sediments contain grani tic pebbles, and the 1 ower Cretaceous sediments are in turn cut by the granitic intrusives.  This  would suggest an intrusion during the Laramide disturbance. This is also upheld by the absence of Cretaceous deposits through-  99  out the Yukon.  In conclusion it may be said that these gran-  itic intrusives represent a period of intermitteBt igneous activity commencing in pre-Jurassic  time and culminating in the  Laramide revolution® Tertiary Tertiary  Sediments  (Kenai?)  Distributions The Kenai sediments have only a minor a real distribution in the Yukon territory, the occurrences being as follows: (1) several small outcrops in the Upper White river district near the international boundary;  (2) some small areas along Matson  creek, a tributary of the Sixtymile river;  (3) at the Junction  of the lorth Pork and the Klondike rivers;  (4) along the Indian  river:  (5) small areas on the Jarvis^l-^-and" at the junction  of the Frances and Liard rivers® Li thol ogy: These sediments consist of alternating beds of loosely consolidated, grey to brown sandstones with conglomerates, and grey to black clays and shales®  All the beds ar6 soft and  decrepitate readily to form sand and clay beds, of lignite are associated with them.  S0me thin seams  As a rule the beds dip  at moderate angles but are very irregular in this respect, often changing suddenly in degree and direction. The sandstones are arkose in character showing angular and sub angular grains of quartz, turbid feldspar, and colour- . less mica in thin sectiens.  •  The shales are dark, dense, compact rocks, and contain fossil wood,  / oo  :n  Some of these rocks are indurated, owing to 'the infiltrat-  ion of the silica from the volcanics, which cut them. Age and Correlation: Thes e Tertiary beds appear to correspond to members of the Kenai series, which includes the oldest know. Tertiary rocks in the Yukon and Alaska, and which is generally referred to the upper Eocene*  The age was determined fey Dr. Enowlton on the  evidence of the fossil leaves collected by Mr. A. JcOollier"1" from the lignite beds. •  2  •  Oaimes  •  •  draws the following conclusions:  P,Since, however, Kenai beds in some districts rest conformably on upper Oretacecus, and form with it a continuous series without any perceptible stratigraphical break, it Is possible that the Kenai Series includes some lower Eocene, Since, also, the Kenai includes seams of lignite,  it is cust-  omary to include in that formation all Tertiary beds containing coal®  Thus possible that pe@§t,. and pre-Eocene lignite  . beds have been included in the Kenai".  ..  Hewgiyplo anic s Distributi on: An important group of volcanics reeks comprised mainly of andesites and basalts occur in the following localities; .(1) in the mountain group which lies to the west and southwest of lake Tschawsahmon valley:  (2) along the Sixtymile river between  Bedrock and Fivemile creeks, and at the junctions of Fitymile ereek:  (3) along Matson creek:  (4) along the Indian river near  gftZQffej^ Lewes river: (5) at the uoilier, A , J . "The coal resources of the Yukor, Alaska." U.S. G.S. Bu.ll» 218, 1903, pp. 17-19. •2. Cairnes, -D.35.., " % p e r White river district, Yukon". G.G.S. item., n 0 . 5 0 , p . 9 5 , 1915, '  /ol:  . junction of the Lewes ana Pelly rivers;  (6) between Wolverine  and Big Greeks; (7) in the vicinity of Oaimacks (8) both sides of the Lewes below Tantalus, and both sides of the Kordenskiold river for 10 or 12 miles up; and along the Ibex river;  (10)  and in the MaeMillan mountains and along the south fork of the MacMillan river® '  •  Li thol ogy; These volcanies are dominantly flow rocks, but often eontain intercalated Tfeuff, breccia, and ash beds, which give them a stratigraphic appearance.  The lavas usually occur as a series  of horizontal superimposed sheets which dip away from the vents and conform to the topographic features to a certain extent.  The lavas often exhibit a columnar structure/  The beds  of tuffs and breccias often weather in the form of hoodooes or irregular pillars* Qf the flow rocks„ augite-andesites, diabases, and basalts predominate, but many types transitional from the acid andesites are found.  They have a bright fresh appearance but on  further examination are found to be deeply weathered®  Black  and various shades of green and red predominate^ but reds ranging from dull brick to bright veimillion, are by no means rare.  or even lavender  These lavas are poiphyritic rocks of  medium coarseness containing phenocrysts of the intermediate feldspars, basaltic hornblende, pyroxene, and^iotite or olivBne  *  In  texture they range from glassy to hoiocrystalline and  from extremely pumicecus to quite dense,  They are in addition  dominantly amygdaloidal, the amygdules usually being empty, but at times containing calcite, zeolites, epidotes, or chlorites.  /oz  In addition to these lavas, dark, greyish-green to nearly black, dense basaltic rocks intrude not only the older rocks, but also the earlier members of the lavas® l"When examined under the microscope these volcanics are seen .to possess mainly a porphyri tic structure, the groundmassc ranging from partly glassy or hypohyaline to hoiocrystalline, but being rarely coarser than microcrystalline e  Pilolaxitic  structures characterize the groundmass of many of the hoiocrystall ine porphyri tic types, but when a certain amount of brownish glass occurs in the groundmass, the structure is designated as hyalcpilitic 0  Some specimens also possess a typical ophitic  structure which is diagnostic of the diabases® "The dominant minerals comprising these volcanics are lime-alkali feldspars, ranging from oligoclase to basic labradorite, some alkali feldspar, augite, hypersthene, basaltic hornblende, biotite, and olivene®  dioxide,  iron ore is also  abundant in.the more basic members; in addition other accessories occur, as well as a number of secondary minerals including, mainly calcite, chlorite, and epidote® Age and 0 orrelatlon; The volcanic activity which produced these newer volcanics is all of very recent date geologically speaking®  That sS. the  latest flows are very recent are borne cut by the freshness of the volcanic products and their very slight modification by • ^L glaciation Mendenhall who studied similar flews in the Cooper Gaimes, D.D®,"Upper White river district. Yukon". Geo'l.— bV 2 u r v . , Can., .Mem. 50, 1915, p.99® Mendenhall9 W® C ®, "The Geology of the Central Conner River Region Alaska, U . S . Geol. Surv., Prof® Paper No® 41, pj? 54-62,(1905)' '  /© 3  River region of Alaska says:"These flows, therefore, instead of preceding the deformation of the early Tertiary plain, are later-than the dissection which followed its uplift, and are to be regarded as very recent indeed® Portions of these lavas cut and overlie the Eocene sediments f Kenai? ) and there is evidence that portions are contemporaneous with Kenai sedimentation for tuffs were found inter-bedded with some of the Kenai sandstones in the Sixtymile and Ladue rivers area.  Therefore it is qui te probable  that this period of vulcanism began during Eocene time* From the above it may be concluded that the period of volcanic- .activity represented by the new<?rVoleanies extended from  Eocene to Recent time.  These rocks may be correlated with the Wrangel lavas of 1 .. 2 Menderihall, and Moffit and Knopf . MacOonnells Andes!tes and 3 Gairnes Caimacks basalt, are also included under the newer volcanics® Acicl Yolc anics Distri bullion: The Acid Yolc anics have a limited distribution,  outcrops  being noted in the following localities : ( 1 ) in the'western portion of the Wheaton river district;  (2) along the inter-  .1 .Moffit F.H.,and Knopf,A., "Mineral- resource of Habesna-White Rivers district, Alaska", U.S.Geol. Surv., B u l l , , 4 1 7 , 1910,pp, 3 ® 2.McOonnell;,A.Gr,, "Preliminary, report on the Klondike gold fields, Yukon", Geol .Surv., Can., Pub.,984,p 0 26B , 1900. 3® Gairnes,D.D.,"Wheaton district Yukon"terrltory", Geol. Surv., Can., Mem. 31, p e 65, 191 £. "Preliminary memoir on the Lev/es and lordenskiold rivers coal district," Geol.Surv., Can. , Mem.5, p . 4 4 , 1910 o  Jo4national Boundary near Deep creek; (3)  north of the White  river and southwest of lake Tshawsahmon valley;  (4) and in the  western half-of the CJ a macks district® lii thol ogy; ' The Acid volcanics, which are light-coloured porphyri tic rocks, are mainly rhyolites, phyries.  tuffs, breccias, and quartz porp-  Often pyrite oxidizing to limoni te gives them a  bright red or yellowish appearance® The rhyoli tes are light-coloured, fine-grained, massive, porphritie rocks with widely spaced joints®  Scattered through-  out them are small brown ana black spots of iron oxide® Quartz, feldspar, hornblende, and bioti te are the chief phenocrysts, the first two being by far the most abundant. quartz phenccrysts are usually rounded and embayed®  The  The feld-  spar crystals usually have well definedeSnsders, but at times are irregular®  The groundmass isanholocrystalline, mediums to  fine-grained aggregate of quartz and feldspar®  The flow  structure is usually emphasized by weathering® The tuffs and breccias are massive, greenish to purplishgrey, rocks with vertical joints®  They contain fragments of  rhyolitic materials, ranging in size from microscopic to several inches in diameter.  These rocks contain considerable for-  eign material where they overlie older rocks.  Occasionally  these tuffs are bedded® and in such cases they have a varicoloured appearance, owing to the fact that different bands contains different quantities of iron. In places pumiceous or amygdaloidal phases occur and are notably rough to touch.  Jos  The above rooks are cut by quartz-porphyry dykes.  These  dyke rocks range in colour from yellow to greenish-grey,  They  are compact rocks, which have a clear ringing sound when struck with a hammer0  Dull smo2q?y quarts3 and., decomposed feldspar are  fhe predominating phenocrysts.  These are set in an aphanitie  groundmass. 1 Oaiines describes these rocks under the microscope as follows: "Microscopically,  the rhyoli tes are seen to always  have a pcrphyritic structure, the phenocrysts being generally megascopic.  Orthoclase is considerably the most abundant min-  eral of the first generation, and occurs in large idimorphic forms which often exhibit Garlsbad twinning, and are frequently considered altered to museovite.  Quartz exists mainly in six-  sided and four-sided crystals, which often show individuals occasionally are seen, and are generally much altered to kao« l i n and quartz„  Accessory iron ores are also commonly present,  and apatite and zircon occur. "The groundmass is generally hoiocrystalline, althbugh in some instances it is hypohyaline, and might then be described as ranging from percrystalline(extremely c r y s t a l l i n e with some glass) to a oc rys tall ine (dominantly crystalline).  A micro-  pegmatitle fabric is the most characteristic of these gpoundmasses, and beautiful intergrowths of quartz and feldspar are seen, representing the crystallization of eutectie mixtures of these minerals.  Microgram tic fabrics also occur, but are  less common than the micropegmatitic.  In such cases, the  groundmass is holocrystalline granular, and consists chiefly l . O a i r n e s , G . 0 . , B e a t o n -uigtrict, Yukon •HrHtoryfT7"~geol. ~ Survo, Can., Mem. 31, pp8 69-70, 1910s  /06  •of quartz ana alkali feldspar. . In the hypohyaline varieties, more or less devitrified .spherulites commonly occur, and are often in bands or layers parallel to the original flow structure.  In other cases, the glass is more or less evenly dist-  ributed throughout the groundmass® "The clastic rocks are seen to consist chiefly of rhyolite fragments which frequently exhibit typical conchoidal fractures, and, at time?, are defini tely the broken or expLodea portions cf vesicular masses of rhyolitic lavas. places these rocks contain fragments of andesite,  In  granitic  rocks, e t c . , which occur associated with other materials.  A  considerable amount of partly devitrified glass also occurs in them, both as a matrix and as fragments." Age and •••.Correlation:--". These volcanics cut the Hewer volcanics wherever members of the two groups come in contact, shewing that the Acid volcanics are at least of late Tertiary and possibly early Pleistocene age.  In places they have flowed over the present land  surface  since it has become uplifted and eroded to nearly its present form, the topographic features having since been modified  only  by glacial action and recent erosion, •1 . • • 2 "••"• ' ' In the southern Yukon and northern B r i t i s h Columbia, they were originally subdivided into the Wheaton River Volcanics and the KLusha Intrusives but this subdivision was without value and consequently abandoned» 1 . Gairnes, D.3)77wWheaton district, , v Geol. Surv., Can., Mem.3i" 1912, pp. 66-72,Sum.Itpt., 1 9 1 5 , p c 4 2 . * 2 . C a i r n e s , D , D . , "Portions of Atline mining d i s t r i c t " Geol.Surv. Can., Mem. 37,1913,pp 67-68. 3 . Cairnes, D . D . ,Geol. Surv., Can. , Sum., Rpt.1915.-D.42.  /07  Superficial Deposits The Pleistocene ana Recent terraneg of the Yukon are lithologically similar and sometimes grade into each, other so that, in most cases they are not differentiated but are regarded as a single stratigraphic unit®  These terrenes floor all the  principal valleys of the Yukon and constitue a thim mantle overlying the consolidated rock formations throughout the greater part of the Yukon, particularly in the less mountainous areas.  On the geological map accompanying this thesis, the  colour representing,  Superficial deposits is employed chiefly  to indicate the occurrence of the main heavy valley accumulations where the nature of the underlying bedrock is very uncertain or totally unknown; but does not include the thin irregular mantle of dominantly recent materials which extend over the uplands and through which bedrock is frequently exposed and thus fairly well Miown, Mueh of the Pleistocene is connected directly or indirectly with the epoch of glaciation.  Two types of deposits can  often be distinguished, englacial and exglacial; the former includes drifts,  tills,  and a little morainal material as well  as other foims of washed gravel deposits, the latter includes gravels, sands, and silts which are spread out as a mantje during the retreat of the ioe|  The fine! si Its of the upper Lewes  river basin were probably deposi ted during floods .accompanying the retreat of the ice, as suggested by contained boulders, and the fact that the silts overlie glacial t i l l s .  In the glaciated  regions the above types of deposits predominate, but usually show reworking and redeposition during the retreat of the ice  /oe  ana in Recent times.  The glacial materials had a great effect  on the. drainage systems of the southern Yukon, and many of the changes in the stream courses are attributed originally to glacial damming." in the'unglaciated regions exglacial deposits and products of rock deoompoasition are found.  '^hese decompesi tion  products were concentrated by gravity and 'water during late  ;  Tertiary, Pleistocene, and Recent times. Also included in the Superficial deposits are muck, soil, ground-ice and surface-ice, and volcanic ash. The muck represents accumulati ons of vegetable material mixed with sand and soil.  It is usually black in colour, and  frequently contains layers and bands of gravel, sand, and s i l t . The muck is a result of the frozen condition of the soil preventing run-off and allowing vegetable matter to accumulate. The soils in the unglaciated regions are mingled rock debris in various stages of decomposition. Ground-ice is practically everywhere present a few inches or. a few feet below the surface.  Surface-ice is only found in  the higher mountainous areas, such as in the Soast Range. A peculiar, feature of the southern Yule on is a layer of volcanic ash or pumiceous sand.  It has been noticed as far  south as Lake Bennett and northward to below Selkirk on the Yule on.  I t varies in thickness from 1 inch at Lake Bennett to  75-100 feet thick at the face of the St.Eli as mountains. This ash lies near the surface, the vegetation being rooted in it.  It is of very recent occurrence.and has fallen since  top  the present waterways cut their courses to approximate their present depths®  ^t would appear to have fallen tranquilly and  all at one time as no intercalated layers of foreign material are found in the original deposits« In general appearamce it resembles a white to light yellow course sand * the grains of which are dominantly pumiceous and light enough to float®  The particles range in size  from loss than 1 mm. to 5 inches in diameter, the average size being 1 to 5 mms. in diameter.  no  •  0HAPT3R '  GEOLOGICAL  HISTORYJEC  •Hie oldest known rocks in the Yukon are the metamcrsbosefl sediments of the Yukon group.  These are caller' the Hasina series in  the Yukon, and the Birch Greek series in Alaska, and -consist of rapidly alteinating bands of quartzite, • quartz-mica, -mice, -an* graphitic schist, shearer] conglomerate, and crystalline limestone, Th.ese rocks represent siliceous, arenaceous, and when local conditions were favourable, calcareous.deposits laid flown at the bottom of an early p re-Cambrian see,,  This sea occupied what is now the  Interior plateau region cf Yukon and Alaska, and overlapped the Coastal system mountains. 'This period of sedimentation was' followed by one of -uplift end igneous intrusion.  These intrusives are now represented by sericite  schists, .chlorite schists,. siophlboli tea, and granite gneisses.  The  sericite schists were probably derived from quarts porphyries and allied types of-rooks, and the chlorite schists and empliibolitss from more basic rocks representing a later period of intrusion.  The gran-  ite gneisses owe their origin to intrusion of bathcliths of granitic material ranging i n composition from an acid granite to a fliorite, Gcokfield: believes that the igneous schists and granite gneisses are not contemporaneous in age, but that the-gneiss.is intrusive into the -schists,  Co ok field,  "Siztymile and la^ue Rivers Area, Yukon", Gaol  Oan.., Mem. 123,  1921, pa*e 85.-'  ///  As a result cf this period were me tamorph. os eel«  cf  unrest, the-earlier sediments  •  '  The uplifted landmass was probably a northern extension of the -ancient landmass of Gascadia« Subsequent to the consolidation of .the Hasina series, and the intrusion of the granitic material, and the ether events of what was undoubtedly a long and complex history, the sediments regarded middle Cambrian were deposited.  as'^re-  These sediments are represented by  the Tatalina group in Alaska, and the Tindir group in the Yukon,  These  rocks overlie unconformably the Yukon group, and the felflspatbic members-are believed to have been derived in part from the granitic gneisses® The typical rocks of the Tindir group are quarts tes, slates } conglomerates, dolomites, and greenstones.  shales,  These rocks rep-  resent siliceous, argillaceous, arenaceous, calcareous, and volcanic materials laid down in the sea during a period of crustal  instability o  ®  The occurrence cf conglomerates among the most southern outcrops' indicate the nearness of the shoreline,  Ibis sea probably occupied a  g e o m c l i n a l area north of that, occupied by the earlier pre-Oambrian sea.  This area is now represented by the northern part of the in-  terior of Alaska, the Ogilivie, and Mackenzie mountains. During early Palaeozoic the eastern and northern shorelines of Oascadia moved westward and southward respectively until they occupied Positions near the present coast of lorth America,  To the east and  north of Gascadia was a shallow sea, '  DUrillg  Csanbria  *  tlffie  continental sea probably ha^ not reach,.  " 8 greatest extent, but occupied a similar area to that cockled ^  sea; that is, .from the Arctic ocean region  southeast to the Ogilivie and H a c k e e i e mountains and south. Ill "CO  b,  /iZ British 0clurabia«  The irop*r sn-i raid-le OsKibrian de-pcsits cf the  Yukon consist entirely cf limestone, which is a typical marine . daposi t» During Ore!ovieian end Silurian times this sea reaeh^i its maximum distribution and covered all ox the Yukon ana Alaska.  Ord ovieian  an-? S i i u r i a n limestones are found as far south as southeastern Alaefca. 'These calcareous deposits are proof that typical marine conditions war* prevalent throughout the Yukon and Alaska at this time, " Middle Devonian rocks overlie unconformably upper Silurian'rocks, .and it is therefore probable that during late Silurian or early Devonian time a great portion of the Yukon and Alaska was involved in.  a  widespread dynamic revolution, which caused extensive, defecation and metamorphism of the older rocks, and was accompanied by considerable volcanic activity,  The pyroxeni tes an*' peridctites of the southern.  Yukon were probably erupted here,  I t the end of this period a consid-  erable area was above the sea, and a long erosion interval ensued.. Some time before middle Devonian a great nart of the Yukon and Alaska sank, below the sea, and m  limestones were deposited  throughout Alaska  the Ogilvie and Mackenzie mountains of the Yukon during the  middle Devonian periods This sea invasion prevailed at least into the Carboniferous and several thousand feet of calcareous, siliceous, and argillaceous sediments, now represented by quartzites, cherts, slates, and limestones v/ere deposited,  This marine sedimentation reached a maximum in Missi-  esippian and Permian times, but shoaling appears to have ocoured during upper-Devonian and Peimslyvanian times,  8S  evidenced by the  occurrence of non-marine sediments, and a more limited distribution of tbe marine sediments of these two periods. thS  YUkC11  Slia  Alasl£a  In the interior regions cf  ^oloanio activity accompanied this shoaling  '  f/3 uc  irn-r ,,e-cicn was croucht to n close by wiSespr-ed  near the close cf Permian time. Yukon and Alaska was uplifted.  formation  The whole area occupied by the The absence cf sediments indicates an  erosion, interval- from the middle Perr^ain to the upper Triassic period. About this time vulcanism became active,  and basic lavas were extruded  in the southern Yukon and Alaska B Upper Triassic  time was a period  iments, limestones, argillites,  cf subsidence, and marine'sed-  and greywackes, were laid down in a  geosynclinal area which embraced all of the Yukon and Alaska*  The  Triassic period terminated in an uplift® The lower Jurassic beds (Xaberge series)  of the Yukon were laid  down on the eroded surface of the upper Triassic beds. contact may be seen along the shore of lake Laberge.  This ercsicn The erosion of  the upper Triassic beds is borne out by''the fact that the upper Limestone, member of this period varies in thickness from place to place. The lower and middle Jurassic sediments of the Yukon territory consist chiefly of sandstones,' shales, arkoses, greywackes, end conglomerates,,  tuffs,  The coarse Character of these sediments shows that  they were deposited, in geosynclinal areas between landmasses, such area which occupied  One  the central portion of the Yukon extended  from the Ogilvie and Mackenzie mountains in the east to the St-llias range in the west, • These Jurassic sediments are associated with volcanic rocks, the chief types being basic and semi-basic laves, rocks«  tuffs, breccias, and  This vulcanism' commenced before, and persisted after sed-  imentation, and undoubtedly  W as  an early phase of the late Jurassic  and early Cretaceous period of cnistal disturbance and mountain building®  In most localities evidence of the local origin of these  volcanics has bsen found,  The intrusion of the g r a n i t e raises of the r £ 3 i f i c Oo^st renge began during'the period of lower Jurassic volcanic activity, ' not culminate however, until upper Jurassic  it did  time, en--, it continued  probably on a rapidly declining scale to an .unsown date ir te.o.e tec ecus. imc  ®  aS  re ~  This period of orustal disturbance and igneous intrnsi  i on i s  the  Jurraslfle  evolution,.  In .northwestern fforth imeriea  ae  ual mountain building occured along- the Pacific coastal region, with ..minor,parallel granitic intrusions in the Interior plateau.  At this  time the Coast ranges were elevated* . The late Jurassic period was also a period of vigorous erosion and most of the -Yukon and Alaska was reduced to an area of low relief before the beginning of a retace 0 us time. During early Cretaceous,, seas probably covered  0f  mcst  the Yukon  and Alaska, except the areas occupied by the mountain ranges elevated during the Jurasside revolution, intense erosion.  These areas were still undergoing  Sower Cretaceous sediments occur on the U ? p e r  ^  ^  Porcupine, and-Peel? rivers, Middle Cretaceous time was a period of orogenic activity,  The  Goast ranges were rejuvenated, and the Brookes range, the area south. of the Alaska range, and th.e western part of the Ogiivie and Mackenzie mountains were elevated.  .  Partial submergence of Alaska, and the northern Yukon occurred in upper Cretaceous time. •  The sep imro^Pri -ku0 bea ,inv-acieci the Yukon valley to near the  international boundary PTrre-irrn-n^ region, ^ r r .the t »Arctic slope, the .ac,_y, the one ir.^rcupme Mackenzie lowlands, and part of the Pacific 111term xuoixio xi Thorax „  The mountainous  areas existing at that time weie not submerged, but supplied the materials to the sea, and by the close of the Cretaceous period they were reduced to a condition approximating peneplanation. v/ith. the exception of the Alaska range and the Mackenzie mountain*  4/5 the ins. jor tee tenia- f 3 *tvr*s -of the Yukon an-i Alaska 17-1-3 well developed in upper Cretaceous • time„  *-  At the dlose of the Mesosoie period the whole of the w^eiit-dav Yukon and Alaska was above sea-level.  This entire region underv/ent  •uplift and mountain, building during the Sararaide revelutior cf Tertiary, probably Eocene time.  '  The Alaska end Mackenzie ranges prc-  par were elevated during this disturbance, and the Coast and Brookes ranges were refolded, thus starting anew their erosion cycles*  The  folding which took place during the La rami-a e revolution was accompanied. by batholi thic intrusions, been exposed, so far by erosion.  only a very small part of which, have The .IQusha ' intrusives • of the southern  Yukon are undoubtedly a phase of these intrusions® Contemporaneous with, the Laramide revolution was the deposition of lignite-bearing,  fresh-water'sediments in local basins in the upper  Yukon .(river) basin® •  :  Yolcanic invasions in the lowland regions of this age preceded,  followed, or occurred during this period of uplift,  A a a result of  what appears to be the oldest of these invasions basalts pierced the older formations and flowed over the land surface.  Typical develop- •  Dient of these lavas may be seen along the Lewes river at Selkirk, Tantalus, Oarmacks, Miles Canyon, and 'iThitehorse Bapid.E0 These more basic lavas are pierced-and overlain by more acid- volcanics.  These latter  vqlcanics flowed over the surface .in thin sheets, and in. places were •accompanied by great amounts of related tuffs and breccias.  Good  exposures are found . throughout the southern Yukon. Tbe close <r£ the Oligocsne was marked by local orogenic movements 1 which folded or tilted the early Terti ary rocks S, J . ,  "The  ^oT^ic^'H^^rof^S^DcrcTm"?  Canada", Trans. R C y. ° C G -. Can,, ^ e c t J Y , ,  1923. vol .XVII,  u^s.101-108  This disturbance' was accompanied" by volcanic activity. of crustal stability f o l l o w s  A long period'  an* what is now the Yukon plateau was  reduced to an almost featureless plain.  Some-writers believe also  that the Coast range and ad-joining tracts were also peneplanatea. I n Pliocene or Pleistocene ion was again uplifted®  time the northwestern 0 ord ill era reg-  This uplift was apparently differential,  being greatest in the regions where the present mountain ranges occur, and-least along the main axis of the Yukon plateau® " '• The result was that the Yukon plateau was given the contour of a broad shallow trough, the approximate axis being marked by the present positions of the Lewes, and Yukon rivers, and the limbs by the Coastal and Rocky Mountain si/stems.  Because of this u p l i f t ,  the rejuvenated  streams cut deep incisions and soon formed separate mountains and ridges® Also because of this uplift and a probable change in climate the higher tracts, including the ranges of the Coastal system, during the Pleistocene, became the gathering grounds for glaciers,  and huge tong-  ues o f ice moved down the sides of the ranges cut across the Yukon plateau,  Glaciation predominated in the valleys, broadening and deep-.,  aning them,, end steepening their walls,'  Yast amounts cf rnorainol and  other materials were carried northward on the way. to the Bering sea, and the floors of the main valley bottoms of the southern Yukon are keenly covered with these deposits.  In conclusion it may be said  that,  there were several advances-of the -ice-sheet, and that the-last great advance probably obliterated most of the results of former glaciation. ?or amore detailed discussion, on glaciation read the earlier section ln  -this thesis on- the•isame.  -'  -  •  After the retreat of the ice the topography was "nearly the same "S it is tor-clay.  The "streams have since been engaged .in removing  Plats  5  ^ ^ t U i g north oaross 'Bij Oreek Plate  6  looking south sorose Big Greek  Differential in-a elation of the valley wall s  / / y  glacial material' from their vallS^s and the majority cf them as yet, especially in the 'glaciated areas, to bedrock.  have not succeeded in trenching  I n some cases <3 rand and silt terraces have been formed  along the streams,  These terraces might be due to entrenchraent by  igfes streams c£'glacial,extra glacial,  or glacial lake deposits, but  as said before in .this thesis, their origin is very much in doubt High level terraces are common in the unglaciated areas, and . / are probably due to solifluction processes. ~ ti> - -K Another feature developed in He cent times is/?aeyrametrical valleys, as a result cf differential .insclaticn acting on the frozen debris cf.their sides®  Valley sides exposed to the sun erode cuick-  ly due tc rapid thawing, and those away from the sun'much more slowly, because they hold their frozen debris.  A good example of this Is the  valley off B i g ©reeE: ' f F i g . ^ g Volcanic activity also, took place during Quaternary  times, as  is evidenced by recent lava flows, cinder cones, and the white ash deposit cf the southern Yukon an* the present activity of Mount .gel, Alaska,  1, Eakin,, H.M.  '  .  . ••  "The Yukon-Xoyukuk Region, Alaska, "  651, 1916,. p-. ,78a '  .• •  U . 3 . G . S . , Bull  •  & SOL.QG/C  S£  S e c t i o n  C  7"/OA/ S  A r / \  J  2.  Quaternary  ~7&rf/ary  S&ds,  3. ASesozo/c  Ir/ass/c  A/orr-Ca/ca *r<s>ous S^c/s.  &  Carboniferous  /-/7T7 €'s.i~or7&  6Upper  fh/aeozoic  Se>c/s.  Und/fferent/atec/  Pa/aco^o/c  ySee/s V J/rrcZ/r Pre-  M / d c / P  T°rt/a  ry  &  Group  •  Yu fc'o/7 Srou/o  Ca/n/i r/ a rj  (pua  Pre- Ca tt7 ibrsa 77 /o.  fer/ra-ry  AJesozo/c  Ifa/carr /c s  //7 //  T~£>077/Parous <§ /Vftpsozo/ \/b/carr/c s  c  frt/s/ves  GEQ/_oG/CAt.  SEC  Mesoxzotc  M>n-Ca /careo us Sea's •s  f FbZaeozD/c vSffcJ^.  //rtc/t r Group Pre-M,< f g " Tert/a-rp &  <paa /^„a ^  <4>/carr/cs  _  1  Carbo-mYe-rous & Mesozoic.  I-^O/co/7/C S  %  Sec i-/oa/ E>  i  C 7~7 O /\/  C-C  HQ  CHAPTER T2T Struetural  Geology  Since most of the surveying that has been done in the Yukon is predominafufely of a reconnaissance or exploratory nature, I shall not attempt to indicate more than the barest outline of the largest structural features.  Part of this  discussion will be devoted to the interpretation of three geological cross sections taken across various parts of the Yukon.  The location of these sections has of necessity been  determined by the districts which have been investigated rath er than by those- which might be expected to illustrate dynamic history.  As some of the information used in the construction  of these sections is of a very fragmentary nature, many changes and corrections will undoubtedly be made once more detailed work has been completed. The general trend of the structural lines parallel to the coast and to the mountain systems is the most striking feature of the structure of the northwestern portion of lorth America. The structure 3?£s0lYes itself into three sections; the Coastal mountain system, the Yukon plateau, and the Rocky mountain system. The axes of the mountain ranges of the Coastal system show a marked parallelism, but their history is by no means •uniform.  The St.Elias range seems to be composed of a complex  of folded Mesozoic sediments along with many intrusions.  The  Wrangell mountains consist of Recent and Tertiary volcanics resting on the bevelled edges of folded Mesozoic rocks.  The  Hutzotin mountains are composed of closely folded sediments  1/9  (Mesozoic and Palaeozoic) •  _  The rocks of the Ooast range are  igneous9 being intruded as a great batholi th.  Owing to the  lack of information regarding the St. E l i a s , Wrangell, and Uutzotin mountains I shall not endeavour to enlarge upon their structure, but as a greater amount of work has been done on the Ooast range I shall attempt a morejdetailed interpretation of the structure of this range. The Ooast range batholith. underlies the entire Ooast range, and outcrops over the greater part of it®  The southwestern  portion of the Yukon territory is a favourable district in which to observe the relations of the granitic materials to the invaded materials, as in spite of considerable erosion a portion of these still remain.  Remnants of the roof and inelusions are  to be found in this area, especially in the eastern portion* Farther west the older rocks do not occur, as the intrusives have risen considerably higher along the central portions of the batholi th than at its margin, and in such places erosion has bein sufficiently great to have removed all portions, of the older materials which may have existed• The manner in which the batholith attacked the overlying formations is illustrated in geological section A—A a  The O eastern contact dips, steeply, to the east, from 55-70 E . 1 Oockfield also presumed the western contact to be steep. contacts are highly irregular.  The  Shattering of the wall rock by  the intrusive, and the irregularity of contact are well exhibited along the eastern margin of the .ba thaiith. In piaces lo Cockfield,W.S., "Aishihik lake district, Yukon", tfum. Rp.19^5 5,Geol e Surv., Oan., part A. P . 7A.  /ZO  blocks and fragments of the older rocks, too small to be shown by the scale used in the construction of the geological cross sections, are included in the granite.  These blocks  vary from a few inches to many yards in width*  In many cases  the smaller blocks have a rounded and indefinite outline pointing to a partial absorption by the intrusive®  Tongues  and stringers of granitic material pierce the inclusions, but nowhere is a minute interfingering of .the magma and the older rocks to be found.  In the Wheaton district several long, re-  latively marrow curtains of pre-Jurassic rocks occur in the batholith.  They are cut by valleys to over 5000 feet and are  just as wide at the bottom.  Oairnes , from his work in the  Wheaton district, drew the following conclusi on: " I t would ap-oear thus that the invading magma intruded the overlying rocks in the form of great tongues, dykes, e t c . ;  from which were given  off smaller branching portions which penetrated the older materials to a considerable degree in some places," The only apparent effeet that the granitic magma has had on its walls is to cause recrystallizati on to some extent, and thus give them a denser texture.  Even this metamorphism extends  Gnly a few feet from the intrusive border.  A certain amount of  marginal assimilation seems to have taken place also,, as the granite in contact with a darker rock is darker near the contacts This effect does not extend for more than 20 or 30 feet. The method of mechanical invasion appears to be that of overhead storing—the batholith advancing by breaking away fr lo Oairnes, D.IJTT^Wheaton District, Yukon Territory^ Seo:  • Suit.y-Oan., .Mem.-31,• 1912, u , 75®  ,/sv  the roof of fragments or blocks which sank in the magma that • 1 rose to replace them* Daley has shown that blocks of an avercoypos^fon  age^sink in a magma of an average composition owing to its temperature and consequent less density,,  Therefore in this district  the blocks would'readily sink, as the intrusive has about the same average composition throughout, and the walls are usually more basic,, It is almost certain that a cover was maintained over the magma until it cooled,*  In the southern -Yukon quite distinct  roof fragments still exist (see section A T A . ) , which are apparently portions of a cover that originally completely roofed the intrusivesc  It would also appear that the roof of the  batholith was highly irregular (see section A T A , ) .  Peaks of the  fe3?&Mti<Shboay are found to the east of the main batholith.  The Yukon plateau, which is in reality a broad gecsyncline, has an axis trending northwest in the Yukon territory and marked approximately by the position of the Lewes and Yukon rivers 0  The broad general features are only an expression  of the rock structure, the major streams occupying valleys trending northwests  Throughout the plateau the northwest trend  is well marked, but the general structure is often complicated by minor folding and faulting*. ... From a study of section B-B and from field  observations  there appears to be a large syncline in the rocks of the Yukon group found in the Interior plateau.  East of the junction of  the Macmillan and Pelly rivers all such rocks clip to the south ^-f-.'.'^^anics or igneous Intrusion, "Amer. Jour. Vol. Zv, April, 1903, pp. 269-299.  Sc.—  /2Z  -west 9 van3 west of the junctions to the northeast.  Therefore  it would appear that the axis of the syneline isrsomewheres near the junction of the Pelly and the Macmillan: rivers * axis has the general northwest trend.  The  That this syneline is  of great size is quite evident, but just where its boundaries are is still a problem to be solved.  It is undoubtedly com-  plicated by minor structural features, and it may give way to anticlinal structures to. the east and west,  From the  apparent persistences of this syneline in the Garmacks region, it would seem most probable that here lies the clue to the general structure of the plateau region. The younger beds all have the, same general northwest trend, and probably conform to the same broad structural features .of the Yukon group, but locally show a more complicate ed system of foldingo  In places the folds are broad and gentle  (see sectionO-G) and in other places quite close and steep (see section A-A)  ,  numerous faults of considerable displacement may occur in the Yukon territory, but where they intersect massive igneous rocks at the surface they are difficult tcr deteet0  Thus  only one prominent break has been detected.  This fault, which I occurs m the Wheaton river, district, was traced by Gaim.ee -v. V • ' • • • • . • . . . - • ,-... J fl'  for over 10 miles, and it has a displacement of 5,000-6,000I e The general structural features are obliterated  in many  parts of the Yukon plateau by immense quantities of volcanic materials.  These include the Older, Hewer, and Acid volcanics.  The.Older volcanics are dominantly of a local origin, and are prevailingly intrusive into the surrounding reeks and occur still included in them in the foim of dykes and irregular masses in the position in which they originally cooled below the land surface (see section O-O).  In certain localities these  volcanics occur as flows, having come to the surface along fract. ures in the older rocks, and poured cut over these from long ineision-like vents„ The tiewer  volcanics are believed to be local in origin,  welling up through fissures which are now found thriugh -^ich :.n nor  as dykes cutting the underlying' formations  and even piercing the older members of the flows0 The Acid volcanics are also 1 i>c'al in origin.  They were  extruded through, fissures at or near the localities where they are now found, and as the magma from which they were formed was highly fluid, small dykes extend for great distances. Eeele describes the strueture cf the Rocky Mountain System as follows:  "The structure of these mountains differs from  that of the ranges to the west, being apparently due to fracturing, buckling, and faulting of the strata, and the residual masses present the appearance c f a series of faul ted and tilted blocks.  The principal lines of fracture are ina northwest-  southeast direction, and the beds have a prevailingly southwesterly dip 0 "Escarpments produced by tilted strata, overlooking fault 1 . Kelle, Joseph, "A Reconnaissance across the Mackenzie Mountains on the Pelly,.Ross, and Gravel Rivers, Yukon and North-~ west Teritories", Geol. Sunr., Oan., Pub. 1097, 1910, p 0 17 e  JZ4-  valleys, are the most prominent features, but they So not appear to presist in alignment for any great distance. Hie ranges to the west that Ke'ele mentions are the Plateau ranges, and they usually have granitic cores (see sections VA-A and B-B. )» ' ! " 1  ' '  ' '  McG-onnell describes the structure of the Rocky Mountain system, where crossed by himself along the Rat river, as foilows:  "The geological section obtained is somewhat imperfect,,  as our scanty supplies allowed of no delay, but sufficient was leassit to show that the range has on the whole an anticlinal strasitUire, although the general anticline is obscured in places by subordinate folds, and is probably broken by faults„  In  the eastern plateau the beds are nearly horizontal, but approaching the mountains they incline greatly eastwards, and in '•••••.• o •o the center of the eastern range have dips from SO to 70 in the same direction.  In the western range the same dip prev~  ails, but the inclination is much l e s s , and the beds flatten out when the mountains are replaced by the elevated western plateau©  The horizontal attitude is retained for some miles,  but before reaching the western edge of the plateau the beds bend down and dip gently to the west".  1. McDonnell, R.G.,"Report on an JSxpl oration in the Yukon and Mackenzie basins, N . W . T . , " , Geol. Surv., Can., Ann. R p . , new series, vol. XV, 1888-89, p» 120 D.  IZS  CHAPTER  V  ORE——DEPOSITS General  Statement  Lode deposits are widely distributed  throughout the ex«  piored portions of the Yukon, and embrace a considerable variety of types including gold quartz Veins, antimony-silver veins, silver-lead veins, silver-copper veins, copper veins, tungsten quartz veins, gold conglomerate deposits, and contact metamor« phic deposits which are mainly of importance for the copper ores and of the gold magnetite deposits they contain* The principal areas in whioh lode deposits occur,  include  the following, which are mentioned in order commencing at the south and proceeding northward: Windy arm district, Wheaton district, Whitehorse copper belt, Aishihik lake district, Hordenskiold river area. Little Salmon river area, Kluane district, Upper Whi te river district, Carmaeks district,  w  illiams and .  Merritt creeks area, Rude creek district, Indian river district, Sixtymile and Ladue river area, Elondike district, Fif tee smile creek area, Mayo district, Dunean creek area, and Upper Beaver river area®  Of these, the Windy aim district, Wheaton distriet,  Whitehorse copper belt, Aishihik lake district, Hordenskiold river area, Kluane district, and Upper White river district are situated along the eastern edge of the mountains of the Coastal system, and constit&te a portion of the well mineralized belt, extending through the Yukon and British Columbia, and genetically connected with the Coast range batholith* Of these numerous districts in which lode deposits are known to occur, only the Klondike district, Whitehorse copper  belt,Mayo district and -Windy arm district have been or are producersc  Ore has been shipped from the T7hi tehcrse copper  belt and the Windy arm district, and a limited amount of quartz has been mined in the Klondike,,  At present the only locality  from which concentrates and ore are being shipped is the Mayo districts  Various reasons may be assigned to the fact that so  few properties have been developed, but the most important is the lack of cheap transportation,.  Another reason retarding  further development of some of the properties, is the fact that many of the properties, were once worked on a small scale, all the higher grade ore being extracted,  thus making them less  attractive for future development,, Windy Aim District The strip of country lying between lake Bennett and Windy arm of Tagish lake is called the. Windy arm district.  It is  important because of the gold«silver deposits found therein. These deposits.occur chiefly in fissure veins, either in the Mesozoic vclcanics and associated tuffs (Older volcanics)  or  in the granitic rocks of this area, which are related to the Coast range batholith. The vein fillings consist chiefly of quartz with stifc^' ordinate, amounts of caleite and barite. characteristic metalliferous mineral„  Galena is the most Other common minerals  are arsenopyrite chalcopyrite stibnite, sphalerite pyrite, and tetrahedrite.  Rare minerals occasionally found are; arg-  entite, pyrargyrite.  stephanite, jamesonite chaleocite real-  gar,, orpiment, malachite, azuri te, yukonite (hydrous arsenate ^ iron anl_calcium(native gold, native silver, native copper 1.Tyre 11, J.B.&Braham,R.P. D . , "Yukon!te, a Few Hydrous Arsenate of f ora T a i s h L a k e rn » Yukon Territory", Trans, Roy, cl LJ. ^ < uifo^ /WJL JL ?» O © e  '27.  ana tellurides.  Oxidation products of copper and lead are  also found®  r  The veins occur in clean cut fissures c regular, slickensided, and grooved«  The walls are  These fissures are usually  narrow and have persistent strikes® The genesis of these veins is the same as that of similar veins in the Wheaton river district and will be discussed under the section dealing with that district. The most important properties are the Big Thing, Montana, M & M, and Venus«  At the Big Thing the vein cuts granitic o o rocks and strikes IT.55 and dips H.W. £5 • It is 2~8S thick and contains chiefly quartz, arsenopyrite, and pyrite, with sub ordinate amounts of galena, chalcopyri te and s tibni te. The veins at the Montana, M & Mo, and Venus occur in andesites and strike nearly north ana dip about 15 W.  The vein at the  Montana is 2' to 5 s thick, 1500' long, and contains in a gangue of quartz , gal ena, arsencpyri te, pyri te, pyrargyri te, argent! te and native silver.  The vein at the M & M • is 6" to 12" thick  and contains pyrargyri te, stephani te, friebergite, and tetrahedrite in a gangue of quarts* in a fissure zone 9'  At the  Venus the ore occurs  thick and 400' long*  The chief metalli-  ferous minerals are . galena, pyri te, arsenopyrite, yukoni te, chalcopyri te and chalccci te.  jamesonite,  Th.e assay values run  up to. $15'..per ton at the Big Tiling, | 80 per ton at •the M & M. and $50 ton at the Venus« n  Wheaton I)istrict;  The Wheat on district is situated in the. souths most part of • the Yukon,:Most of the ore-deposits occur in a belt 16 miles  long and 9 miles wide extending from Hodnett mountain past mt. Stevens» . Other deposits occur on mt® Anderson and CJarb on and Ohieftain h i l l s , Four distinct types of ore-deposits are found in the district, namely: 1.  Gold-silver quartz veins®  2*  Antimony-silver veins®  3®  Silver-lead veins.  4®  0ontact-metamorph 1 c ^ore-deposits®  •Only one representative of the contact metemorpMe oredeposits is found in this district and as it is similar in all 7  respects to some of the Wh.iteh.orse copper deposits it is more suitably described with, them® Gold-silver quarts veins: /  These deposits are similar to those found in the Windy  arm district*  They occur chiefly in granitic rocks of the Ocast  range intrusives. and also in the schistose members of the Yukon group®  The veins found in the granitic rocks are fairly  straight and quite persistent for considerable distances- whereas the veins-.in the schists occur in lense-shaped masses or irregular fissures, which may connect the lenses®  One vein in  the granite has been traced for more than 3 0 0 0 , , but.:most' of them are only 200r to 30,0s long 6  'They range in thickness from a few  inches ot Y'^the average being 4<*  Most of the lenses are 6*  to 8 5 thick and 2& to 4 0 ' long, but one has been found that is 30 s wide and 100' longV -  •  •  .The fissures are fault fissures the .walls being s.llckensidefcfc and-gouge and brecciated materials are found with some of the veins,  /Z9  ;  The veins fillings consist of quartz .with subordinate  amounts of calcite* mine ral o  Galena, is the characteristic metalliferous  Pyrite, chalcopyri te, native gold, sylvani te, hessite,  petzite, and telluric ochre also occur.  Oxidation is only  slight and near the surface. Most of the properties are undeveloped and the values rarely exceed more than #10 per ton,  Some of the properties  with good showings are the Tally-Ho gulch group and the Mascot group®  The former is situated on a brecciated fault zone. 4* to  IB' wide and 200* long, and contains values in gold and silver averaging $20 per ton. ,The vein on the latter is over 2000' long and 2 9 5 ' t o 6' wide, and assays from $15 to §30 per ton in gold and silver®  Other properties worthy of note are the Mount  Anderson,, Whirl wind y and Sheep Mountain groups. Oockfield summarizes-the genesis,of these deposits as given by .Gairnes as JSl-i.owss  "  "Gairnes shows that if* these gold-silver quartz -feeing of Windy arm andWheaton districts are connected with the intrusion of .igneous rocks, they must belong to the period, of intrusion, of the Ooast range'granites; for they cut these granites, and are older than all the igneous rocks of the district, which are themselves newer than the granitic intrusives/  Ih the field the  veins are everywhere ass-GOiated with these granitic rocks... The solutions depositing the. eres traversed the fractures in the.' outer, c ooler part of these granitic rocks, while the interior of the j P ^ f a ^ ^ Mem® 150, 1926, pps. 44.  condition." ' , vtboj.. ourv., .oan.,  fis-fll?ll:i2?-:-:D- * * * * * * * ^ s t r i c t ' ! , Gteol. Susy.  Can.', Mem, 51, , p p .  /30A  Antlmony-gllYerv¥eiaas : These are found on Oar.bon and Okieftain h i l l s .  The ae«.  . posits are of a very u n g u a l type and are found in only a few other localities in the world, eeg8. Frieberg, Germany, and east of Broken hilly, lew South Wales. ,  These antimony-silver deposits occur in fissure veins in  the Coast range intrusives, and in the andesites and breccias of the Older volcanics.  Due to superficial deposits most of the  veins have been traced not over 2 0 0 ' , but two have been traces over; 20001®  They vary in wid th from 5lf to . 6f , the average  of the more valuable being from 1'  to 3'®  -  The fissures are  simple in form® Stibnite is the chief metalliferous mineral found in the veins.  It is most commonly assodaSted wi th sphalerite and  jamescnite.  'The chief gangue minerals are quartz, calcite,  and barite„  The ores rich in silver usually contain galena  and grey copper and only a minor amount of stibnite c Assays running over 500 ounces of silver per ton have been obtained,but are exceptional.  Most of the ores containing  galena and; tetrahedrite carry loo to 2co ounces.  Better grade  stibnite ores contain 50^to 65 fo antimony. Oxidation is shallow ana rarely extends more than 2' except where the fissures are open. On Ghieftain hill one vein 5* thick has been found.  The  vein consists chiefly of quartz and stibnite with a little sphalerite.  The vein is irregular narrowing rapidly to 6 " .  On Garb on hill the Fleming property and Godells CIains are the most Important. On the foimer the vein is about 2* thick and  /3/  contains 20$ antimony, 15 to 30 ounces of silver and less than §1 in gold®  On the latter £ claims, 21 to 6' thick, have been  traced more than 2000'®  The veins consist of quartz impreg«  nated with jjamesonite and arsenopyrite« ' 1 Gockfield gives the following genesi s«  "She minerals  present and the textures of the orecall indicate that the ores belong to the upper vein zone,  Oairnes portulates a connexion  between these veins ana the igneous rocks that occur in the vicinity and argues that the materials composing the veins were deposited in the granitic rocks and already cooled andesites and breccias, while the underlying magma from which were derived was still hot and molten.  He points to the probability that  the Older volcanics and Coast range granitic intrusives were derived from a common magmas * As it has since been proved that the Older volcanics are earlier than the Coast range intrusives } the view that these deposits owe their origin to the magma of the Goast range intrusives may be accepted, and it would appear that the underlying parts of this magma remained in a highly heated condition for a considerable period," Silver-Lead veins; They occur in a northerly trending belt, 3000' 1ong„ and 1000 s wide 8 on the eastern side of Idaho h i l l .  These veins  possess many points in common with the silver-gold quartz ireins* They occur in tabular deposits in the arkoses of the Laberge series. In a general way the veins follow the strike and dip ' - • o ' o . o Q h e elastic rocks, stc~ 1.12 W., dip- 70 Wa In many places 1 . Gockfield, W.E.,"Whitehorse district, Yukon," Geol. SurvTT" Gan9>. Mem..' 150 s 1926 s pf 46®  /32A  the veins are very irregular and indefinitely defined e  They  vary in thickness often changing rapidly from 8" to 10" to 3' to 4.'  ®  The vein fillings consist of quartz, calcite, galena, arsenopyrite, sphalerite, pgtrite and ehalcopyrite B pyrite and galena are the chief minerals.  Quartz, arseno-  The ores generally  contain only a few cents to the ton in gold, and rarely have more than #2«  Assays of better-grade ore yielded approximately  50 ounces of silver and 40$ lead. The only important properties are the Nevada and Union mines.  On the former IS veins have been found, ranging, in thick-  ness from 4" to 12" ( 1 is 2^-* thick), but in a few places masses of ore ranging, with included rock, from 2J-f'o 4 ' , SO1 1ong were found.  thick and 5 to  On the latter only 2 veins have been ex-  posed , and these are similar to those at the Nevada mines except that they contain much less galena, and so consist mostly of quartz, calcite, arsenopyrite, pyrite chalcopyrite and sphalerite, Gockfieia gives the following genesis for these deposits,. '•IfGai m e s cites evidence to show that the detiosits of Union mine^ and Nevada mines are metasomatic replacements of arkoses of the Laberge series, and the solutions travelled along the bedding planes of the clastic rock, fillea with ore minerals any small spaces that may have existed, and replace d the rock material on either side,," of the ore-bearing solutions is unknown, but i "The source they are believed to be connected with the intrusive rocks cf 1.Oockfield S W.E.,"Whitehorse district, Yukon," Geol„ Surv., Can.. Mem. 150, 1926 s p e 47® 2 , Oairnes, D . D . , "Wheaton District, Yukon Territory", Geoi.Snrv®, Oan., Mem. 31, 1912 S p . 129-140.  /33A  the locality®  As the age of the deposits is not known except  that they are later than the Jurassic Laberge series which contains them, i t is difficult to state to which period of vulcanism they belongs  I t is known, however, that the Ooast range in-  trusives are responsible for the greater part of the mineraligation of the Wh'itehorse district, and it is possible that the formation of these silver-lead deposits is also due to the intrusion cf the °oast range batholith 8  More detailed mapping of  the Wheaton district has shown the probability of these rocks n extending below the mineralized area at no great depth. Genesis! .  . ',1 • '  .  .  . .  Cairnes comes to the following conclusion for all three types of deposits.  They have been deposited by hydrothernal  solutions, emanating from below, in the upper vein zone 9 under conditions of low temperature and pressure.  He bases his cor."  elusion on mineral associations and wall~rock alterations e Whitehorse Copper Belt The Whitehorse copper belt is situated along the valley of the Lewes river 4 to 5 miles from Whitehorse.  It is a belt 12  miles long and 1 mile wide extending from a point east of Dugdale northwest to the base of Mt.Haeckel. The deposits are of the contact metamorphic type and usually occur in irregular bunches or lenses quite independent of one another.  The rocks of economic importance are the granites of  the Coast range intrusives and the Carboniferous 1imestones® ore-deposits usually occur in the limestones at or near the contacts w&th the granites, but a few deposits have been found 1.Cairnes, D*D'. 5 Op*"cTt77~PPs» 87-140.  ~~~  ?he  in the granites®  The deposits in the granites contain more  of the non-metallic minerals than those in the limestones© The chief copper bearing minerals are eh£lcopyrite and bcurnite, along with minor amounts of tetrahedrite and chalocite®  Magnetite and hematite are abundant and pyrite and  pyrrhotite are to be found in smaller quantities©  Other met-  allic minerals that occur are; arsenopyri te, stibni te, sphalerite, molybdenite^ and small quantities of native gold and silver.  The principal non-metallic minerals ares garnet, augite,  tremolite (wollastonite) , actinoli te, epidote, calcite,. clinochlore, serpentine, and quarts. Oxidation has prevailed only to;a slight extent, the iron ' sulphides not being appreciably changed„ and the copper sulphides osidized to no greater depth than 100'®  The chief minerals  resulting from the oxidation of the copper sulfides are : malachite, azurite, chrysocolla, and malaconite0 Eiere are two main types of ore-bodies: hematite masses, and (2) silicate ore-bodies.  (l) magnetite and The magnetite  ore-bodies are important and occur in the limestone, granite, at the contact©  The more important ore-bodies of this type and  their size are: Best Chance 360'^Arctic Chief 2 3 0 s , and Chief 1 2 0 ' .  Pueblo.  Little  Magnetite is always plentifull and it is impreg-  nated with boumite and chalcopyrite. is about 4 $ .  The average copper content  Only one large hematite ore-body occurs, the  In this deposit the original sulphides have been largely  converted by ground-waters into carbonates, oxides and silic»» ates.  or  A large number of the  silicate ore-bodies have been  found in both the granites and the limestones, but the only  /34A  important deposits were in the limestones®  Worthy cf note are  the Grafter, Copper King, War Eagle, and Valerie,  They occur in  tabular masses about 100T in length, and contain bournite and chalcopyrite with small quantities of gold and silver,.  The copper  c on tent averages about Qfo* These deposits display the following properties of contact metamorphic deposits: (3$  the limestones are close to or in dir-  ect contact with the granites that altered them; (£) veins, except thin secondary seams, are unknown;  (3) ore-bodies are very irreg~  ular and vary in s i z e from a few inches to several hundred feet: (4)  the minerals are those of contact metamorphic deposits;  (5)  the minerals, metallic and non-metallic, were deposited met-  asomatically in the limestones and granites, and with few exceptions are products of one period of mineralization; sive itself has been mineralized;  (6) the intru-  (7) marmorization and silicifie-  ation of the limestones.  .  The extensive and simultaneous mineralization of the intrude ing and intruded rocks was explained by Oockfield by assuming that it was effected by hot solutions moving upward, ana that it took place after the magma had solidified to some depth. The peri od of mineralization represented by these contact • metamorphic deposits foil owed closely the intrusion of the Coast range batholith in late Jurassic or early Cretaceous time,  These  types cf deposits represent a period cf high temperature and pressure. Besides the properties mentioned in the above description. a similar t y p g o f contact metamorphic deposit occurs in the 1. Oockfield, W7ET7, Whitehorse district, Yukon Territory," Geol» .Surv,, Can., Mem. 150. 1926, p* 50* '  /3ST  Wheaton districts creeks,  This is at the Fleming claim near Becker .  On it is a magnetite mass which averages about  and $2 gold®  1%  copper  .  The chief shippers of the Whitehorse copper belt were the Puebl;©9 Copper King, Grafter, and Valerie. 140,000 tons.  The Pueblo shipped  The War Eagle ana the Carlisle also shipped a  few thousand tons.  They all suffered heavy operation losses  due to the type of deposit, and high cost, of transportation. Aishihik "Lake District The Aishihik lake deposits are in reali ty at Gil tana lake, which is a small lake 15 miles northwest of Hucfcchi lake®  They  are contact metamorphic deposits of the same type as the copperbearing magnetite deposits of the Whitehorse copper belt,  The  ore-bodies in limestones occur interbanded with mica schists and quartzites of the Yukon groupe and 100' to 200' long.  The bands are 6( to 10* wide  The copper content ranges from ljtc 9% s  Only a slight amount cf development work has been d one on the properties. '  lord ens ki old River AreaAnother contact metamorphic copper deposit known as Mack's  copper occurs 5 miles southwest of Montague.  The ore oc curs in  a fine-grained greenish porphyrite at or near its contact with a limestone, and consists chiefly of magnetite with hematite in minor quantities, both being more or less impregnated with copper minerals, chiefly chalcopyrite, malachite, and szurite* The main mass which is in the form of a knoll 200' by 400' contains only a low percentage of copper.  J3&-  .  .  Little Salmon River Area A silver-leaa vein or lense of minor importance occurs 7 miles from the head of Little Salmon lake near the head of the first large creek entering the Hagundy river from the north. The deposit occurs in a schist near the border of the Glenlyon batholith, and consists of galena, sphalerite, siderite, chalcopyrite and pyrite in a quarts gangue®  The ore-body averages  about 20 ounces of silver per: ton and 50$ lead» Zluane District In the extreme northwest corner of the Kluane district near Quill, Burwash, and Tetamagouche creeks are a series of greenstones, mainly andesites, basalts, and diabases with reddish amygdules.  Th^volcanics are probably contemporaneous  with the Older volcanics of the Upper White river district. Patches of sediments, such as shale, limestone, and chert of Mesozcic age, occur in the volcanics®.  'STheoamyaulgs, ofe&he? in  glreeiistone.seeontain malachite, azurite, and|boumite with calcite, quartz, and epidote*  As the deposits ars small9  irregular,  and non-persistent they show little promisee Upper White River District Gold quartz veins and copper deposits occur in this district, but as the deposits are low-grade, and as the district is at present almost Unattainable no deposits of economic . importance have been developed. Although many gold quartz and so-called gold quarts claims have been located very few have been developed, and consequently most of the claims have lapsed•  The only deposit that has  been developed, to any extent is one along Rabbit creek.  Here  Plata 7  r  k  ^  Cannuoka lode-gcld strike on Mt, ^Teegcld at  right  79 7 „  a fault zone, containing • (Older volcanics) ®  to 5* quartz,, occurs in greenstones  The mineralization is very slight, only a  little disseminated pyrite and chalcopyri te occurring. Copper deposits, similar, to those in the H u a n e  district,  have-been found and many claims have been located, but only one property has been developed©  This is the Discovery Copper  Grant on the southeast side cf the White river,  miles up-  stream from Canyon city® . "Hie copper occurs for the most part in finely textured, reddish, amygdaloidal amdesites of the Older volcanics®  Many of tM  amygdules are filled with chlorite.  |  These volcanics are traversed by numerous irregular fractures", which in places contain slabs of native copper®  Most of these  slabs are small9 but a few weigh several, hundred pounds, and one weighed 6000 pounds.  Harrow calcite veins containing chal-  cocite as well as stringers of cuprite and disseminated native copper traverse the volcanics in places®  The native copper,  which is an oxidation' pro due t of chaleocite, does not extend more than a few feet below the , surface Although as yet no valuable ore-deposits have been found in the Upper White river district it should be a good area to prospect, as it lies in the well mineralized zone parallel to the eastern contact of the Coast range batholith. Garmaeks  District  A lode gold strike was made in the .east end of the Dawson range in 1930.  The properties that have been staked are sit-  uated on Mount Free gold and Mc'Dade h i l l ,  Mount Freegold, wMSti  has. an elevation of 4 , 7 7 2 ' , is a. ridge lying between Seymour and  x  /3 6  Stoddard creeks, northward flowing tributaries of Big creek. Mc1 Dade hill lies to the east of Stoddard creek.  Mount Free-  gold is approximately BO miles west of the Lewes river and approximately 30 miles northwest of Oarmacks.  Mc'Dade hill is  about 5 miles east of Mount Freegcld. Quartzites, schists, and gneisses of the Yukon group, and syenite porphyries, granodiorites, and granites of the Mesosoic intrusives outcrop on Freegold ridge ana grani tes and granodiorites on McDade hill® cherty in appearance. quartz and mica.  The quartzites are finely crystalline and The schists are composed chiefly of  The genisses are composed cf felspar,  mica ; and hornblende.  quartz,  These gneisses, schists, and quartzites  are usually thinly bedded.  The metamorphic rocks have been in-  truded by the syenites, granodiorites, and granites. ite porphyries are very coarsegrained,and  The syen-  are composed of large  .pink orthoclase phenocrysts in a grey, coarse-grained groundmass of orthoclase, plagioclase, and hornblende. syenites are typical of these ro<2ks„  Hornblende  The granodi ori tes and gran-  ites vary from a grey granodi ori te to a pink grani te, the former containing more hornblende than the latter.  The granod-  iorites and granites are younger than the syenite poiphyri tes, for I: dykes of the former are found cutting the latter.  Rhyolite,  . quartz porphyries, Tamprophyre, afid andesitic dykes, aplites, and pegmatites cut the granodi ori tes and granites. Bostock divides the mineral deposits into three groups:  fl)  the magnetite deposits of contact metamorphic type in the rocks cf  H b os t ock ,H. ATi s Geol. Surv., Can., 1933, p , .13 A 1 1 .  '  y  *.  .  >  J3S>  the metam orphic series on the northwest side of the summit of Mount Ere eg old ® ( 2 )  the pyritiferous vein deposits in the  granitic rocks on the south side of the mountain; and (3) the mixed sulphide vein deposit in the granitic rocks of MaSBaae hill. The contact metamorphic magnetite deposits have been developed on the Augusta, Margaret, Badger, and Morning claims. The minerals present are magnetite, limonite, specularite, free gold, quartz, actinolite, garnet, and visible to the naked eye. quartzites and schists.  epidote.  The gold is  The wall-rock consists of altered ' 1 Bostock says the mineralization poss-  ibly owes its origin to the syenite porphyry,, A considerable number of pyritiferous veins have been found on the Rambler, ITabol?, and adjoining claims.  These veins are  composed of chiefly of quartz7j3obtaining crystals of pyrite, and they vary in width from a few inches to 5-g-1 , the average being about l 1 .  The quartz is very finely crystalline and has a  pale ; bluish grey colour.  This colour is due to minute cubes of  pyri te and some crystals of arsenopyri te disseminates through the -quartz.  Some very favourable assays have been obtained  from these veins. On Mc"Dade hill a mixed sulphide vein«, varying in width from 3* to 6 ' ,  is found cutting the granite.  The vein is Com-  posed of white, crystalline quartz, pyrite, galena, sphalerite, and tetrahedrite.  The vein and the wall-rocks bme  been subject to intense weathering.  everywhere  The assays made have not  been encouraging0 l* B 0 3 t n e k ' H : S * ' " 1 , i i e Industry of Yukon,1931," Geol. Surv -> 0 a n - . Sum.Rp., 1931, part A, p. 12A, 1932c .  At. present the. 33VA. Timmins Corporation of Montreal lias an option on Mr. Langhams group of claims on Mount Freegold9and they/ have a crew of men at the property nowe Williams ana Merritt Breeks Area Merritt creek flows east and empties in the Lewes river 5 miles below Yukon Crossing®  Williams creek is one mile farther  downstream® The predominating rock formations are a series of amphibolj tes and granites®  The amphibolites, which are schistose and  much altered, consist of .plagioclase. and green hornblende, and are invaded by the granites, which are greyish to pinkish crystalline rocks®  The ore^deposits occur at or near the contacts  of these two formations, and consist of veins of quartz impregnated. with bournite, chalcopyrite 9 malachite, and a little free gold*  Caimeg concludes that the ores are genetically comected  with the granites, the ore-bearing solutions being an after effect of the intrusion of the granite mass. The more important properties are the Bonanza Eing, Dawson', Monte Crist? and Homes take.  The veins on these properties vary  in thickness from a few inches to six feet, and in values from less than ifo copper to over 4 $ . generally less than $ 1 ,  The gold and silver values are  ;  '  Rude Creek District Rude creek is 15 miles west of the Lewes river.  I t is only  a small creek 5 miles long, a tributary of Dip creek, which in turn flows into the Elotassin river. . l . uairnes, D.STT^mCiams and Merritt Creeks", Geol. Surv.. (Tan. 8 Sum. Rpe 1909,.p e -58. . *  A*/  The chief rocks of the district are the schists cf the Yukon group,  the Older volcanics,  the Hewer volcanics.  The ore-deposit occurs in the granite of the  Coast Range intrusives. the granite.  the Coast Range intrusives, and  I t is a small fissure vein which replaces  The contact between the granite and fissure is  irregular, and minerals are found depcsi ted in the granite for 1 varying distances up to 4 0 " from the. contact.  Cockfield  says;"the  fissure has the appearance of a short and irregular contraction crack, formed at the time of cooling of the granitic mass"®  The  chief minerals are galena and sphalerite wi th minor amounts of pyrite and carbonates of lead and z i n c . The importance of the deposit is mainly as indication of mineralization, showing that the area is worthy cf further prospecting,, Indian River District A gold conglomerate deposit has been staked along Indian •river and a tributary of i t .  The congl omerate is composed of  well-rolled, oval-shaped, white ? quartz pebbles, and a smaller quantity of schist pebbles.  These pebbles vary in size from a fract-  ion of an inch to several inches in diameter, and they are cemented together with a whi te to light grey siliceous cement,schist and quartz„  The gold is detrital, occurring in the matrix, and the  deposit may be considered  to be an. ancient placer.  ues are low, being about $2 per,  The assay val-  ton,  Sixtymile and Ladue Rivers.Area A small ore-deposi t of minor importance occurs at the head of Miller ea?eek.  In this vicinity the chief rocks are quartz-mica  sgbists of the Yukon group. They contain bands of limestones uy 1 . Cockfield,W.E.,"Silver-lead Deposits of Rude Creek, Yukon", Gecl. Surv., Can., Sum. Rp. 1927, n . 11A-13A.  /4-Z  to 500T in length ana 501 in width,  Small quarts veins cut one  of these limestone kands9 but So not penetrate far into the schists. Klondike District This area embraces such famous gold producing creeks as Bpnanza, Hunker, Eldorado, Dominion, Suiphur, Gold Bottom, and Soda®  The typical rocks of this area are those of the Yukon  group, especially the chloritic and sericitic schists of the Hasina series 0 Quartz veins are widely distributed  throughout these older  schistose rocks, and although most of these depositsQjare small and non-persistent the total amount of quartz is great®  Typical  fissure veins are uncommon, ana on account of the schistose nature of the rocks they pass into lenses, bunches, stringer and sheetlike veins._  These vary in size from a fraction of an inch wide  and 6 inches long to a few feet wide and several hundred feet long 0 They are sometimes interbeaded with the schists and at other times cut them in all directions© The quarts is free milling and only slightly mineralized, the chief metallic consti tuents being small quantities of pyri te, and rarely magnetite, chalcopyrite, galena, and native gold,,  The  quartz is white to grey, and often rusty on fracture faces. Many claims have been staked, but more development work will have to be done on most of them in order to obtain a fair approximation of the average values®  Most of the properties that have  been developed to any extent are of a low-grade type*  Veins and  mineralized zones that could be worked cojointly look the most favourable®  •/43  The more important properties are: the lone Star property on Bonanza creek; the Gorden mineral claim on Bear creek;, the lloyd, Green Gulch, ana Gold Run groups on Zing Dome; the Bos §ar group on the divide between Soda and Bonanza creeks; the Mitchell group between Gold Bottom and Hunker creeks; and the Portland group on Dominion creek.  Of these the Lone Star property  is the only one from which ore has been shipped, 294-5 tons of ore from this property averaged $ 3 . 9 0 per. ton in gold* Pifteenmile Greek Area Fifteenmile creek enters the Yukon river from the west 25 miles below Dawson city. ities:  The ore-deposits occur in three Ideal-  fl) a mile below the mouth of Fifteenmile creek: ( 2 )  6 miles  below the mouth of Mfteenmile creek opposite the mouth of Roal creek: and f3) 5 miles, further down the river opposite the month, of Oassiar creek. The chief rooks of the district are quartz-mica schists of the Hasina series and mashed diabases similar to the Moosehide diabases. schists©  Lenses of limestone and dolomite are found within the Porphyrite dykes intrude the schists 0  Silver-lead veins and bunches are found in the limestone and dolomite lenses.  The chief gangue mineral is quarts, and the most  abundant metalliferous minerals are galena and sphalerite^  Minor  quantities of c hale opyri te, malachite, and azuri te are also found. The mineralization is meagre and the deposits are small, so it is very doubtful whether mining could be made to pay* Mayo -District The ore-deposits of this district may be divided into,(l) Keno hill deposits, (2) the Galena hill deposits, and (5)  other  the  occurrences.  Eeno hill is 40 miles northeast of May p, and.Galena  hill 13 miles-southwest of Eeno h i l l .  Mayo is situated 180 miles  above the mouth of the Stewart, and this river joins the Yukon 72 miles above Dawson.  These hills are situated in the Yukon plateau  at elevations of about 5 , 5 0 0 ' , 3 , 0 0 0 ' above the valley bottoms. The whole district is underlain by quartzites,  quartz-mica  schists, mica schists, and graphitic schists of the Yukon group, probably the Hasina series.  These schists are intruded by dykes,  s i l l s , and laccoliths' of greenstone.  These greens tones J Older  volcanics?) represent andesites or related rook types.  The contain  hornblende, altered feldspar, and a small amount of the original quartz and titanite.  Both the Yukon group schists and the green-  stones are cut by dykes of quarts-porphyry and granite-porphyry* On Galena hill these dykes are represented by rhyolitic phases. Eeno h i l l : The ore-deposits are important because of their lead and silver content. ure veins.  The prinicpal ore-shoots occur in fault fissures or fissTherseare two main sets of fissures.  a general trend of jr. s o - 4 0 a n d  The earlier have  at the time of formation were  mineralized with quartz and' arsenopyrite,  When the second set of  fissures were fozmed the earlier ones served as tbhe main circulation channels, and consequently were re-mineralised, so that they now contain many valuable deposits.  The second set of fissures  make angles of 70 to 80°with the first.  During this second stagdi  of fissurlng the following minerals were deposited: galena, sphalerite, friebergite, siderite, pyrite, barlte, and calcite.  A third  set of fractures, formed subsequent to the deposition of the ore-  J4-5-  bodies, out the ore-deposits into a series of blocks.  The ore-  deposits are primary, only a slight amount of secondary enrichment having taken place.  The following secondary, enriched minerals  are found: native silver, pyrargyrite (ruby silver) , and plbly» basite*  Oxidation is slight, manganite, limonite and cerussite  being found• 40'  The veins range in size from mere gash veins to zones  to 50' in width, and 2 miles long.  The ore-shoots have not  great depth,400* to 600' usually being the maximum.  The silver is  found in the galena as an isamorphous sulphide, and in the tetrahedrite where it replaces the copper up to S O ^ f r i e b e r g i t e ) . ores that have been shipped averaged 200 oz/a per. ton in silver and 59%  lead.  The best deposits run about 90 pss per, ton in silver.  The most important vein, that has been worked, is the SadieFriend ship-Treadwell  vein.  This v e i n -  or r a t h e r z o n e ,  i s  on  western side of Eeno h i l l , and varies in thickness from 10'  t h s  to 4 0 ' ,  110,000 tons cf ore has been taken from the Sadie mine, which is situated on this vein* Galena H i l l ;  !i  A corresponding set of fractures to those of Keno hill occur here,  Stockwell classified the veins under four groups. (1) Sid-  erite-galena-friebergite veins with a manganiferous gangue.  They  contain small quantities of quartz, pyrite, chalcopyrite, azurite, malachite, limonite, and cerussite.  The silver values are usually  high 0 (2) Veins in which the gangue is quartz or ankerite. ese oxide is not so conspicuous.  Mangan-  Galena, sphalerite, and pyrite  are usually abundant, and limoni te, cerussite, chalcopyrite, and r l ^ x l r ^ ^ ^ f ^ - ^ ^ ^ ^ i ^  ^ i W o i ! - ! ^  1  "  ^ l u e s are fairly high.  The Silver King mine was located on a similar type of vein, but the gangue was sideritic, and friebergite and pyrargyrite were plentiful.  The vein v,was 8' wide and 150' long.  (3) Quartz-arsenopyrite veins in which ankerite, calcite, white mica, pyrite,galena, and sphalerite occur in minor quantities. The values in silver are low. (4) An unimportant quartz-3tibnite vein carrying low silver values. At present none of the properties are being worked. Other Occurrences?  •  Similar silver-lead deposits are found on Buntker, Rambler, and Sourdough hills, and on Mount Cameron. foot of McQuesten lake, hill.  Rambler hill is at the  Sourdough hill lies just suuth of Galena  Mount Cameron is 65 miles northeast of Mayo®  All the prop-  erties in these localities are still in the prospect state,, Duncan Creek Area Quartz veins have been staked along Dublin gulch, which enters Haggart creek, a tributary of the M C Quest en river.  The mineral-  ised belt strikes northerast-3outhwest, and is 8 to 9 miles long. Light grey, greenish, and reddish banded quartzites, micaeous and schistose; and quartz-mica and chlorite schists of the Yukon group are the chief rocks of the mineralized area. truded by a grey biotite granite, by dykes M  They are in-  a decomposed and  •  altered grani te ; and by dykes of diabase. The quartz veins, occur near the granite o ozrtae'fctin a fissured belt cf schists and quartzites*  The veins usually follow approx-  imately, the strike of the country rock, that is northeast-southwest, but occasional cross veins are found.  A typical feature of  this area is the association of gold with green scorodite ( a  hydrous arsenate of ferrous, iron) .  The quartz ana scorodite  ooeus in the nature of a pay-streak, 4 " to 20" wide, striking with ,and in the veins.  The walls of the original fissures have  suffered metasomatic alteraticns.  The green scorodite pay-streak  lias an irregular outline. The veins are heavily mineralized t the chief minerals being quartz, arsenopyrite, scorodite, pyri te, and free gold,  '  teaching  and oxidation of the sulphide ores has taken place throughout the zone for a depth, of 40 to 50 feet. The assay values range from nil to $10  per. ton.  The chief  properties ares -tlafe. Stewart, Oatto, Olive, Shamrock, Blue Lead, Eagle, and Independence groups®  The Stewart, O a tto, Olive, and  Eagle groups show the most promise, and are worthy of further development once transportation difficulties are rsmediSd, Also in the % b l i n gulch area a few ramifying quarts veinlets, containing crystals of scheelite, have been found®  These  veins intersect the pegmatite -zone of the granite, and they are probably the source of the scheelite in the stream. Upper Beaver River Area This area is the part of the watershed of the Beaver river ' lying west of Braine creek.  Discoveries of silver-lead veins  have been made on several M l l s f namely; Carpenter, Silver, Grey . Copper, and McKay®  These hills l i e in the Ogilvie range and have  elevations- of about 6,500'  to 7 , 0 0 0 ' ,  This belt is apparently  a northeast extension of the fceno-Galena hills mineralized area. , The most important rocks of the area are a series of pre- ' Cambrian quartsites, slates, limestones, and conglomerates, a series  /4-e,  of pr@-©M'<§vi®.ian volcanic agglcan©rates, shales, and sandstones, a series of Ordovician to Devonian limestones, and a series of intrusive and extrusive augite-andesites and augite-diorites 0 The prs-Cambrian series may be correlated with the Tindir group, and the augite-di orites and andesites with the Older volcanics. The ore-deposits consist of silver-lead and silver-copper ores, the former being more plentiful.  The silver-lead veins•  consist of galena with subordinate tetrahedrite and sphalerite in a gangue of quartz or calcite®  there te trahedrite asd pre sent  the silver content increases, but even relatively pure samples of tetrahedrite run only 70 ozs per e ton® On Silver hill the ore-deposits occur as short transverse fissure veins in a series cf  intercalated cale areous or dolomitic  sandstones and impure sandy limestones. ies are several bodies-of greenstone.  Intrusive into this serMineralization apparently  took place by replacement of the wall-rock along the fissures. The impure limestones were the most favourable for this replacement process.  The ores are not confined to the fissures and min-  erals have often been disseminated through the country rock.  The  C M S f minerals are galena and sphalerite, with minor quantities of pyri te in a gangue of calcite and sideri te, with a little quartz.  The veins range in width from 6" to 6»,  traced from 100'  to 2 0 0 ' .  and have been  The assay values show about 4 to 9 oun-  ces of silver per. ton and 65 to 70 percent lead. Only one vein has been found on Grey Copper h i l l ,  it con-  sists of te trahedrite, pyrite, and sideri te wi th some quartz, azurite, and malachite.  It is 24 to 30  inches wide and assayed  52 ounces of silve r to the ton©  Float cf "tetr ahed ri t e carrying  up to 1,100 ounces of silver to the ton have been found„ I  On McKay hill quartz-galena-te trailed rite deposits occu^ in , ~ and at the borders cf small masses of largely amygdaloidal and. e si tes and andesitic breccias ; i n which calcite fills the amygdules and replaces the original constituents of the rock® are known in the Tindir slates occurring here.  -  ITo deposits  The positions of  the exposed bodies and the distribution of float indicate that one mineralized zones crosses the southern face of McKay hill^n A . o with a general strike of U.SO magnetic. This zone appears to be a number-of distinct lenses arranged along a single line® The assays run. approximately from 4 to 40 ounces of silver and 20 to 80io lead® lone of the • ores which to date have been located in place in the Beaver river district are rich, enough to permit a mining at a profit under existing conditions of transportation®  IV  BIBLIOGRAPHY B a r r e n , J. Oology of the Marysville mining district, Montana: a study of igneous intrusion and contact metamorphism. U . S . G . S . , Professional .Paper Ho. 57, 178pp. map,  (1907)  Bostock, H . S . The  mining industry of Yukon® 1951, Canadian Geol. Surv„s  • Sum® Rp®, 1931, part A, 2e  (1932)  The mining industry of Yukon. 1932, Canadian Geol.Surv., Sum. Rp 0 , 1932, part A 11,  3  *  T:he  (1933)  mining industry cf Yukon* 1935, Canadian Geol e Surv 09  Sum. Rp., 1933, part A, (1934). Brock, R.Wi 1® The directors report of the Canadian Geol. Surv. Sum, Rp. t 1909, pps, 9-46,(1910) Brookes, A.H. 1 . 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S® ,Bull c 630, 130 pps.  (1916)  Ooekfi eld ,WeEe 1* Mayo area, Yukon, Can. Geol. Surv., Sum. Rp., 1918,  pt.B,  pps. 1-15, (1919) 2 e Silver-lead deposits of Twelve mile area, Surv®, Sum. Rp., 1918, pt. B . , pps. 15-17,  Yukon.Oan.Geol. (1919)  3 . Explorations in the Ogilvie range, Yukon.Oan.  Geol.Surv.,  Sum. Rp., 1919, p t . B . pps. 1-3, (1920) 4 e Mayo area, Yukon. O a n . Geol. Surv-. Sum. Rp. 1919, 3-7,  pt.B.,pps,  (1920)  5. Sixtymile and ladue rivers area, Yukon. Can.Geol.Surv., Mem.123, 6opps., 6  (1921)  * Silver-lead deposits of the Eeno Hill area, Mayo district. Yukon.Oan. Geol. Sunr. ,Sum.Rp. ,1920,pt.A.,pps.1-6.  7  * ^  silver-lead deposits of Mayo district,  Jour®, vol.42, no,3, pps,44-45, Jan.81,  (1921)  Yukon.Oan.Min.  (1921)  8 . Silver-lead deposits of Davidson mountains, Mayo district, Yule on. Oan. Geol, Surv., Sum. Rp., 1 9 2 1 , pt.A,pps.  1-6,(1922)  8 . Recent mining developments in the Mayo district, Yukon Oan. Min. 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A partial bibliography of publications referring to the geology ana mineral industry of Alberta, B . C . , and Yukon. Oan, Min. Inst. J , 1 1 , pps, 433-444,  (1908)  Heydon,A.T, 1 . Geology of the Whitepass. Min. & Sc. P r e s s . , 77, 133 p.  (1898)  2 , Headwaters cf the Lewes river. Min. Sc. Press., 78, 65,  (1099)  Johns ton,J.R.  ^  1 . Geology of the Yukon Territory with special reference to Alaska. A thesis presented for the degree of master of  j  i  applied science, Universi ty of British Oolumbia, Vancouver, B . C . , April, (1934)  ' ;  Keele.J. '  !  I  1 . A reconnaissance survey on the Stewart river. Oan. Geolc Surv., Sum. R p . , 1905, pps, 32-36,  !'•  (1906)  2 . Report on the upper Stewart river region, Yukon,Oan. Geol. Surv., Ann. Rp. 1 6 , 0 . , 23 p p s . ,  (1906)  3® Explorations on the Pelly, Ross, Gravel rivers, in the Yukon and Northwest Territories. Oan. Geol.Surv., Sum. Rp., 1908, pps. 33-37, (1909)  H  4© A reconnaissance across the Mackenzie mountains on the Pelly,- Ross, and Gravel rivers, Yukon and northwest Territories.Can. Geol. Surv. , Pub. 1097,  (1910)  Kindle, E.M. 1® Porcupine valley region. Geol.Soc. Am.,Bull,vo, 19, pps® 315-318,  (1908)  t  XI  Iis-es,E. J . and Cockfield ,W.S e Occurrence of marine Triassic in southern Yu3con.Rcy.Scc. Cans Trans., 5 rd series, v o l . 2 5 , sect,  4 , pps, 101-104,  (1931) Maclean, T.A. 1®Lode mining in the Yukon, and investigation of the quartz deposits in the Klondike division. Oan. Mines B r # ,  205pps.(1914) ^  Maddren, A . G . 1« Hie Koyukuk-Chandalar region, Alaska, U . S . G . S . , B u l l . 5 3 2 ,  (1913)  i  2  ® Geologic investigations along the Oanada-Alaska boundary . U.S.G.S.,Bull.  520  (1914)  Martin,G.C. 1 . The mesozoic stratigraphy cf Alaska*.  U.S.G.S..Bullc776,(1926)  Mo Connell,R.G.  i  1 . Glacial features of part of the Yukon and Mackenzie basins, SsolVSoeJ. 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Rp., 14, B , 71, pps a (1905) 11® The ICLuane mining district, southwestern portion of the Yukon district® Can.Geol. Surv,, Sum. Rp., 1904, A,pps. 1-18,  (1905)  1 2 . Recent mineral discoveries on Windy Arm, Tagish lake, Yukon. Oan. Geol. Surv. t 12 pps.,  (1905)  13® Report on the headwaters of the White river. Can. Geol® Surv., Sum. Rp.,1905, pps. 19-26,  (1906)  1 4 . Klondike district. Oan. Geol.Surv., Sum.Rp., 1906, pps.20. 21, (1906) . 15* The Whitehorse copper belt s Yukon Territory. Oan, Geol, Surv., 63 pps.,  (1909)  Mendenh all ,17.0. 1  '  ^ort Hamlin to Kotzebue sound. U.S.G.S..Professional Paper, Ho.10,  2  *  111(3  (1902)  geology of the central Oopper river region, Alaska.  U.S.G.S..Professional Paper, Ho.41, Mertie,J.B.  (1905)  jr 0  ls  1,10  Qhandalar-Kogukuk region, A1 aslsa. U. S. G. S.,Bui 1,773,(1925)  2#  The  geology and mineral resources cf northwestern Alaska.  .  X///  U . S . G . S . ,B ul 1,815 , (1930) So The Eagle-01 role district, Alaska, U . S . 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