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No. Library of PIoEill Uniuersity
MONTREAL
Received
GEOLOGY
OP AN AKEA IN THE VICINITY OP
GULL AND OLGA LAKES, NORTHWESTERN QUEBEC,
JteOIU. UNIVERSITY. APRIL 1913.
A,O.DUPRESNE.
During the summer of 1912, Dr J.A.Bancroft, Associate Professor of Geology at McGill University ,was instructed by the Quebec Department of Mines to make a geological reconnais- sance of the District ^lorth of Transcontinental Railway in North Western Quebec. Having been fortunate enough to accompany Dr Bancroft as assistant ,1 submit,in this paper,the results of a geological examination of the 80untry surrounding Gull & Olga Lakes,of which I made an independent investigation. LOCATION. The district is situated on the James Bay side of the Height of Land, about mid-way between the Transcontinental and James Bay,one hundred and ten miles east of the Quebec-Ontario boundry. The accompanying key-map shows the relative position of the area. It lies between 76 fi 30' and 77- 30f West Longitude and
49-A50*North Latitude. The district has an area of about five hundred square miles. MEANS OP ACCESS, a) The district is best reached by way of The Grand
JLJ^ Trunk Pacific,starting from Cochrane -Bast and going to the A Natagagan River or the Bell River. The rest of the journey can be made by^ going down either of these rivers to Ma t*a garni A Lake which is situated just west of the district under conside rs ration and is connected with Olga Lake by a River five miles long? This route is certainly very easy and diligent canoemen, leaving the railroad at either point; could reach the discharge of - 2 -
of Bell River in four days. b) Prom James Bay,either up the Nottaway River to
Mattagami Lake or the Rupert or Broadback Rivers/passing through Lake Evans to Gull Lake. People who had travelled through that part of the country claimed the last named river to be preferable. c) Prom Lake St John ,by way of Chibougaman Route going west by the Obatogamafc River. But this is a very long and difficult journey which should not be contemplated except by people travelling for excitement. In 1895 Bell followed an altogether different route the following being a description taken from the Annual Report,
Vol.VIII 1895,ofAGeological Survey of Canada: " In going northward by canoe from Maniwaki,on the Gatineau River,two routes are available ,one by the Gatineau River and its tributory the Gens de Terre and the other by the Desert and its branch the Thomasine. Both are eery difficult for loaded canoes. We left Maniwaki village on the 1st of July and followed the Desert route to Lac des Rapides. This lake has two outlets ,one southward to the Gatineau,and the other northward discharging part of its water into the Upper Ottawa at a pl?ce called " The Barriere"or Dam. From this locality we followed the Ottawa downstream or westward to Grand Lake". Prom this place Bell crossed the Height of Land and went down the Bell River continuing the journey as in(a). Our expedition reached Mattagami Lake by passing down the Harricanaw River and crossing to Aiiard River over a four and half mile portage in Xuskeg. - 3 -
PREVIOUS WORK* In the summers of 1895 and 1896,Bell made a geological reconnaissance of a large tract of country in Northwestern Quebec lying between the Rupert River on the $orth,the Upper part of the Ottawa Hiver on the south ,Jlistassini Lake on the east and the Quebec-Ontario boundary on the >»est« The results of his explorations are contained in the yearly reports of 1895 and 1896 and also in Part K of the Annual Report of 1900,volume XIII. Surveys were conducted by Henry 0*Sullivan on be-half of the Department of Crown Lands of Quebec in the years of 1897 and 1898. GENERAL DESCRIPTION OT THE REGION. Gull and Olga Lakes,owing situated in the center of S what was called by 4uess the n Canadian Shield" are surrounded by typical Laurenti^n country. It is *?. flat or slightly undulating plateau with rounded hills in the south and south-eastern part of the area. These hills do not reach a greater elevation than 500 above the level of Gull Lake . They have received the name of Dalhousie mountains and by the Waswanipi Indirns;are called the Sasegawetchew Mountain During a period of intense glaciation ,which was general in Pleistocene times all over Eastern Canada and the Eastern United States ,the country was profoundly eroded producing a smooth gently rolling surface which is now covered by the debris left by the retreating ice-sheet^ and the accumulation of strati fied sands and clays .containing boulders deposited probably in a glacial lake. - 4 -
The general level of the country is about thirty feet above the surface of the lakes. Mattagami,Olga 8c Gull Lakes are resoectively 616,635,660 feet above the level of James Bay. Gull and Olga lakes form large bodies of water ,the 4 first of which is the larger possessing a roughly elliptical shape with am approximate length of fifteen miles and a width of nine miles . A remarkable feature is the o-^u^^dsaace of boul ders which are strewn on the shores of this lake. One receives the impression of an artificial lake ,the shores of which have been paved with boulders a large percentage of which are granite. At the heads of the bays sandy beaches have developed. Many of the islands in the lake are nothing but accumu~ lations of-boulders ,some being of the Drumlin type. L Eskers were noticed on the northern and pastern shores of the lake, some consisting of gravel and sand,others of large boulders of granite and greenstone. It is most probable that the level of the water in this lake was once much higher than to-day for beaches,in many places extending as far as sixty paces from the actual shore line,may be seen. The upper part of the boulder beach is foundf to be covered with a thick layer of moss "bjcacken^eeds and even in some cases by trees. Gull Lake is the meeting point of two large rivers draining a considerable portion of the country lying to the $ast and north of the area described in this report. Of these the Waswanipi receives the water of Lake Chibougamam ,Qbatagomaia and adjacent lakes ,the other receiving the waters of more or A less unknown area between Waswanipi & Rupert Rivers. - 5 -
Olga Lake which extends in a ^orth Easterly direction, having a length ofl some twelve miles and average width of four miles . Deep bays are seen ortfcsits Eastern side following *^ approximatfcyely the direction of strike of the Keewatin Schist. Thw lake is separated in two parts by a narrow sand bar ,the result of the washing of a gravel and sand hill on the north west side of the narrows ; The southern half of Olga Lake is very shallow and muddy,its water assuming a light brown colour on a windy day. Anywhere in Elizabeth Bay the bottom can be reached with the paddle. Very little rock is exposed along the shore of Gull Lake,while around Olga Lake long stretches of shore are rocky. It is quite remarkable that the southern shores of these lakes show much more numerous outcrops of rock than elsewhere. This agrees with conditions found in other areas of northwestern Quebec. ( Rapport on the Geology and Mineral Resour- ces of LakesKewagama$AKeekeek Re ;ion,Quebec^Bureau of Liines,I9II.) ESKERS. On the north shore of Gull Lake, at the narrows between Lower and Iliddle Gull Lakes,below the little islands marked on Dr Bell's map, a. long narrow ridge formed by glacial detritus was examined , This esker extending towards 20- E is about fifty feet above the level of the lake . Under every upturned tree growing on the esker,boulders,pebbles and sand could be seen Along the ijast shore on the prolongation of the line of the previous esker, long rid-res, probably of the same type oiff deposit were hot iced . Many of the islands and different parts of the )*j*6*»
shore especially on the west side of Gull Lakes,are of the same nature. On the north shore of Gull Lake west of the first esker described,an elliptical accumulation of boulders and sand of a height of 70 feet, covered with Jack Pines , is probably a " Kame M as is also the high bank of gravel and sand at the •sera?* narrows in the center of Olga Lake ,which is responsible for the sand barreltting the lake in two, DRUMLINS. In the center of Gull Lake, a small island is formed on its north side by the bold face of a granite exposure while the south side consists of large angular blocks of granite, weighing many tons ,which have been piled up and form a very typical drumlin such as has been described by Dr Barlow in his report of the Chibougaman district: n The irregular accumula tions of boulders with very little of the finer interstitial matter ( gravel and sand ) have a rather definite elongated outline ,with their longer axis in the direction of the ice ( ) movement,A The origin of these drumlins is still a matter of doubt and dispute and opinion seems divided as to whether a) they were accumulated beneath the ice under special condi tions without the agency of water or (b) that they were deve loped by erosion of pre-existing drift material ", ( Dr Barlow and others t-Rwport on the Geology and Mineral Resources of the Chibougaman Region, P.P.130;) The three rivers discharging Waswanipi,Gull and Olga la kes are swift. The rapids along the^re rivers are not dangerous they are caused chiefly by the accumulation of large boulders -7-
carried by the river where it has had sufficiently high velocity, and deposited when the current slackened on reaching quiter part of the river. Just as the long sand bar in Matagami Lake at the mouth of Olga River was deposited by the slackening of the currett when it comes, to the vast body of water which form the lake. At the discharge of Gull Lake the rapid is caused by hard bands of Keewatin greenstones including a fine grained basic diorite.The barrier at the outlet of Olga Lake is formed by the contact of a Keewatin greenstone and hornblende granite. SOIL, FLORA, FAUNA. The soil around these lakes is probably not suitable for all agricultural purposes on account of its sandy nature,and the large amount of boulders which it'contains. Loam containing boulders covered with a very heavy coating of moss forms the soil on which dack Bine,spruce,balsam,birch,cedar ,poplar^grow to a large size especially on the east side of (iull Lake where the NU ok forest, has not been swept by^ fires which have devastAed the ^nor thern and western parts of the district and a few patiies to the south .On the Dalhousie mountains and adjacent areas.Spruce trees of a diameter of 20 inches have been seen,but the average size is about seven to eight inches. The bear is surely the master of the wild animals inha biting the adjacent country; not less than six were seen in one week and every where on the sand of the beaches fresh tracks were observed . The moose is rather scarce,a few tracks only have been noticed.^ Rabbits are numerous and bald-headed eagles have tee White Pisk,Sturgeon,Pickerel, Pike, are the most common fishes. No trout are present in these lakes. -9- GBNERAL GEOLOGY: *H——PXW^^IIIW immmmm* mm mMMitw> pui As previously stated,the district under consideration shield is situated in the Canadian*"atract of land underlain by ancient largely crystalline rock" which surrounds Hudson's Bay. The two extremes of the Table of Formations of the Earth's crust are represented ,\the Pre-Cambrian and the Quaternaay. The Quaternary comprises morainie deposits,lacustrine and stratified, G\ays ,and sands',peat. The Laurentian Granite,Gneisses and Biorite,underlay more than three-fourths of the region .The Keewatin Rocks occupy the northern part. TABLE OP FORMATIONS mmmmt»mmmwmmmm\ m m turn mm* »»iP"^-»«*tM»tww»Jg QUATERNARY. Boulder citay,Lacustrine stratified,Clays and Sands.Peal; Very great unconformity, POST MIDDLE-HURONIAN. ——^wxw»ww«»— tmtm m m * i .^ mm mmw—• (Keweenawam) ? Newer Diabase (Igneous Contact). LAURENTIAN. Pegmatite,Aplite, Granite^,1 (Biotite /Hornblende Diorites and Hornblendite Gneisses ( igneous Contact) MATTAGAMI SERIES; mmummmmmwmmmmmmmmm '•• I • mmmmuummmmmmm*^— Conglomerate, Anthophyllite schist. ( Unconformity) .? -10- KEEWATIN, Sasega Diorite,( Pre-Laurentian ) Lava-flows ^--Quartz Porphyries, Angite porphyrite, Diorite porphyrites, Homblende7-tmica7C&lori-er & sericite-shists, etc, PLEISTOCENE. A very remarkable feature of the Pleistocene time was what has been called the " Ice Age" ,a period of profound glacia- tion during which the weathered zone of the surface rocks has been removed by the scouring action of the blocs of rock imprisoned in the mass of ice which is supposed to h^ve dome ffom the center of Labrador,distant a,bout five hundred miles in a north-easterly cJ rection. In previous explorations in different parts of Quebec and Ungava, the rocks have been found, striated and grooved; the general direction of these striaes leading to a common point. Eminent geologists have said that a rock to crystallize should cooled very slowly . To explain the coarse crystalline texture of the aranites and diorites found in different areas of the Laurentian continent one must suppose a heavy cover inn; of reck which by its weight would produce pressure,and also act as a none conductive covering. The different bands of schists which are found as curtains in the granite seem to confirm this theory, What became of these overlaying rocks ? A large portion of them have certainly been eroded and carried away during the long period of time which has elapsed since Pre-cambrian times. Then came the glaciers which have removed all the weathered portion of the rock leaving a fresh sttiated surface. - II- As the ice-sheet retreated under the thawing action of a milder climate , a narrow strip of water was first formed between the Height of Land and the front of the glacier.lt was probably a bay, having its outlet near Lake Temiskaming, of another glacial laite to the south , Lake Algonxin. As time elapsed the southern margin of the ice moved northward increa sing the width of the glacial licke ,and conjointly lowering its level till it became too low to outflow into tthe Lake Algon- as trv OL -qiiiir, and by this time the recess of the glacial front give^ access to James I3ay ,Lake Obiway ,having found another outlet, was drained. During the period of existence of this ^reat Lake, the dirty and silty waters produced by the melting of the ice have deposited in layers, at the bottom of the lake, and the particles 6f clay^and sand, etc,which it had in suspension t while a few drifting and wandering icebergs droppedjhere and there ,the load of boulders and other materials they carried. The great amount of boulders found in the district examined,may be explained by assuming that we are dealing here with the eastern shore of Lake Ojibway described by A.P.Coleman in the I8th Report of the Ontario bureau of Mines 1909. Among other bouldersfsome of a light yellow - 12 - colour containfing fossils of the Niagara limestone can be seen along the sandy beaches of the lakes. Also a boulder of yellow arenaceous limestone was found on the east shore of Gull Lake near the narrows to Middle Gull Lake. But no rocks of these types have been f&und in place: and their origin is still a problem to be solved. Another interesting boulder was found on a £and beach about one mile from Red Chute,on the north shore pf ^lga Lake , It is a large angular block oJf rock about three feet high containing pebbles of biotite granite and of Quartz Porphyry, the' biggest of which must have a length of about twelve inches . All the pebbles are- elongated in one direction. the result of pressure, the pebbles of Quartz-Porphyryp ;Having oeen more deformed than those .of granite, have a larger ratio between their length and their width and have developed a sericitic schist in which the eyes of quartz have been^ well preserved . Prom the size and the angular edges of this boul der one is led to suspect that the bed rock from which it was plucked cannot be far away, presumably somewhere north of Olga Lake. Around Gull and Olga Lates the surface outcrops are well striated and grooved*fand roches moutonnees are common. The rocksc ofrfche Keewatin preserve these glacial marks much better than the coarsely crystalline granite and diorite of the Laurentian. This is probably due to the more - 13 - pronounced weathering of the latter. The process of degradation was accompanied by that of aggradation. The eskers of the east side of Gull Lake, the kames and drurnlins which have been previously mentioned and also- the sandy stratified clays and boulder clays are the products of this aggradation. After the complete recession of the glaciers there was a rearrangement of the material left by the Ice,, Sb that to-day we have Post-Glacial or Recent deposits ;; sand beaches, clays,silts deposited on the floSvs of certain bays. The arrangement of boulders in rapids is going on at the present time. Their is a deposit of four to five feet of peat in Elizabeth Bay. ( Olga Lake ). At the foot of Dalhousie Mountains is a terrace of about twenty feet above the level of the water consisting of sandy boulder clay not stratified ,cut by deep gulches , probably due to the accumulation of wash from the mountains in the post-glacial times. POST MIDDLE-HURONIAN : KS^^h^TANv? The only rock of this age is a very hard dark coloured rock cutting granite. This rock is classed as Post Middle-Huronian ,not b# its field relation in this district, but by its unmistakable petrographic resemblance to thewNewer Diabase M of prpbable Keweenawan age found in the vicinity - 14 - of Lake Temiskaming. Near its contacts the " Newer Diabase" of this district is a very fine grained dark coloured rock,but as we move from the contact towards the center of the dike, the rock becomes coarser and coarser till,at\the center of the a. dike,the rock resemblesAgabbro. The n Newer Diabase M consists of plaglioclase feldspar which has crystallized in the form of laths showing and beautiful twins of the Albite*?ericline laws . It has crystal- to the rock lized prior to augite imparting remarkable typical Ophitic m °" Structure of diabases, ihe afcgite is of a light colour, slightly pleochroic,has a high index of refraction a^d high bi-refringence and an extinction angle of about 38° , A few crystals have the close cleavage of diallage. Some of the augite crystals show good pyroxene twin and in others Herring bone structure is displayed, A part of the augite has been uralitized,but primary hornblende is also present. The rock also contains a little amoant of quartz,which has crys- tallized after the piagiocl^se but before the augite. a little iron ore, probably magnetite a,nd some chlorite ^he dikes of M Newel? Diabase M were found at four different places in the area examined. First on one of the sharp points of boulders of Index Point,on Gull Lake, a ^ The other constituents are - 15 - small flat outcrop was found. The three other exposures of Newer Diabase w were found in contact wmth biotite-granite on the west side of the southern portion of Olga Lake. One dike,a liitle over one mile south of the narrows,stands out from the granite with a contact running in a direction N 59° E and dipping at an angle of W£52<2 About three and a half miles south of the same narrows ,always on the west side, a small island owes its existence to a dike of " Newer Diabase M cutting granite. The contact wall having a direction S IP E . On the south shore of Olga Lake, a fourth exposure of the same type of rock,probably a dike,was also noticed of with the smooth rounded surfaee^a roche moutonnee. The contact with granite was followed for about one hundred feet. - 16 « LAURENTIAN. In a general statement we may say that three*. fourths of the district is underlain by rocks of .Laurentian age. In the southern part of the sheet Keewatin lava-flows and other greenstones have been removed by a profound erosion exposing a large batholith of intrusive igneous acid rocks, of a light colour ,The rock-types developed include Granites Grano-diorites, Diorites and Gneisses. wherever Granite is found in contact with the Keewatin schistsinto which it intrude.it is always seen to in send into the Keewatin country-r6ckAthe form of dikes passing outward in all directions ,sometimes appearing as hands of granitoid or porphyroid Rock within the Keewatin following the schistosity . Elsewhere little stocks can be seen intru- ding the dark greenstones,either a mica or hornblende schist, and sending little off-shoots into theseschists. An example of a section ( represented on Plate 2 ) through a%miniature batholith*can be seen on one of the islands at the mouth of Waswanipi River on the east side of Gull Lake. Sometimes pipe-like intrusions have been formed., as on one of the islands'of the northern part of Olga Lake,ywhere - a few dikes emanating from the plug traverse the Keewatin c greenstones .--.•-•— @*anite also occurs as small lenticular bodies in the Keewatin schists ^ Plate III) . In many places the granite stands out prominently - 17- |in dome-shaped knobs ,which are in part covered by a thick blamket of moss ,Labrador tea, sheep-laurel, wildcherry and a few small black spruces. Granites may be divided according to structure into massive and gneissoid.Between the two types no sharp division exists. The two t^pes blend one into the other and from selected specimens a completely linked gradation could be shown. The massive types include biotite granite, hornblende granite ,mica-hornblende granite, grano-diorite and diorite. The gneisses could be subdivided into two classes: a) being due simply to the parallel arrangement of the constituent minerals especially the ferro-magnesian silicates b) consisting of alternating bands of dark and light coloured rock,which can be called n intrusion gneisses rt. Granites of the massive and gneissoid types are holocrystalline,of a light colour varying from white to pink. As essential minerals it carries quartz,feldspars and one or more Fe-Mg silicates . Qua,rtz can always be detected by the naked eye,.the grains often being as large as peas, and forms nearly one-third of the rock and from examination under .the microscope is found to be the last mineral to crystallize. The felds7^ars include both orthoclase^ mi cro c-line and piagioclase . - 18 - , Orthocla.se may be untwinned , but Baveno and Carlsbad twins are frequent . Plagioclase is recognised by its polysynthetic twinning , its periclime twinning and also the zonary banding which permits altera tion of certain zones more rapidly than other upon weathe ring . Usjipon alteration $he plagioclase feldspar yields mica in little colorless flakes ,epidote and calcite. hviicrochine with its typical crosshatched structure is present in some of the thin sections. According to the predominating ferro-ma.gnesian constituent we have biotit-e or homblende granite. Or,if both minerals are in nearly equal amount as is generally the case , we have a homblende-biotite granite. The ferro-magnesian minerals are ordinarily the first to crystallize following the law which Rosenbush has termed :"Law of decreasing basicity." As accessory minerals there occur little zircons imbedded sometimes in feldspar ,sometime in biotite, Sphene^trongly pleochroi c .^^5?^^ _. can be seen in large quantity in the thin sections of hombleride-biotite granites,ex^nnioninl ly twinned . A little muscovite is present in certain slides. Apatite , Iron pyrite and magnetite also occur, Sericite,epidote, zoisite, calcite and chlorite are secondary minerals, the products of decomposition . - 19 - In one slide of grano-diorite. inclusions in two epidote crystals of a browm slightly pleochroic mineral with a high double refraction was noticed. It is probably allanite. A homblende granite poor in quartz and con taining a large percentage of plagioclase feldspar is termed a grano-diorite, this type was found on an Island in Gull. Lake, Near the contact with Keewatin greenstones the granite was found to be always rich in hornblende and even in some cases it is ^nke only ferro-magnesian constituent, e,g/ below Red Chute, In a general sense one may say that hornblende-granite is a. contact phase of the batholitic in trusion; . On Index Point ,Gull Lake, the homblende granite has crystals of homblende of about one eighth of sn inch in length. Diorite.as a phase of granite intrusion may be found in certain little plugs as on the west side of the northern half of Olga Lake, On the periphery of the intru sions we have homblendic phases ( homblendite ) as we go towards the center of the plug the morecid constituents form a larger percentage of the rock until the maximum acidity is reached at the center , In certain phases the diorites - 20 - contain biotite as on a small island at the inlet of Olga River. PORPHYRITIC STRUCTURE. On the north eqst side of Gull Lake,a mica hornblende granite has a porphyritic appearance due to the large sized crystals of feldspar. Nearby ,dikes of granite with porphyritic structure can also be seen, Aplitic and pegmatitic phases of the intrusions have come through cracks and fissures formed during the contrac tion caused by the cooling of the magma. They represent the last spasms of the dying activity of a period of intense igneous action. - 21 - GNEISSES. Both Granitic and Dioritic types, in a/.^ition to their development ; as massive rocks are capable of taking on a gneissoid structure. This consists of a more or less parallel arrangement of its minerals, principally of its ferrp-magnesian silicates but also of orthoclase and quartz . As defined ? this structure has probably an igneous origin. When the rock was still in a fluid or semi-filiuid state, flowing movements produced the orientation of the already crystallized minerals, Nearly everywhere in the granite area the rock has a more or less pronounced gneissoid structure,except on the drumiin island and a. f-w other places. On the nofcth shore of Sasega Bay ~-^- ,a coarse typical gnessoid mica granite may be seen cutting a fine grained biotite granite. On the east side of Gun Lake occur gneisses of the second variety consisting of alternating dark and light coloured bands. The dark bands are similar to the mica schists of Keewatin age ,the light bands being of a granitoid rock having itself a gneisnsic structure of the first type. In the field one has the impression that this structure was produced by the introduction of the granite magma along the planes of schistosity of the Keewatin Rocks as if it had spread out along the leaves of a book„the intruding fluid metamorphosing the rock mineralogically,changing it to a mica schist ,which upon weathering becomes rusty. Elsewhere a structure resembling much a marble - 22 — cake was produced by dynamic action while the schist was in a semi-flmid state. Still another type of intrusion-gneiss can be produced as a contact phase of the granite intrusion. A number of angular blocks of schist have been caught in the magma, and having retained their metamorphosed identity, form a braccia which does hot answer the definition of a gneiss but which by its relations can be placed with this ©lass of r o ck. - 25 - MATAGAMI SERIES. In the bottom of a large bay formed by Index Point, on Gull Lake, is a smoothly glaciated outcrop of a dark schistose rock, which contains pebbles of a light colou red crystalline rock. Two of the pebbles are of white milky quartz, the others are probably of acid diorite, some being rich in mica. The pebbles which have been elongated by the action of pressure have a length of about five inches equal to about three times their width. This exposure is similar in direction to a band of Keewatin rocks having a direction of about S. 20° E, ANTHOPHYLLITE SCHIST. Near the granite contact on the north shore of sasega Bay occurs a light grey coloured schist in the band of Matagarni series. In hand specimen crystals of mica and homblende may be distinguished which an^orientated in the same direction, giving a gneissoid appearance to the rock. Little red garnets may also be seen. Under the microscope the rock was found to consist of quartz,feldspar,hornblende, biotite, zircon, a little spheiae and iron ore. Quartz and feldspar ,some of it being plagio clase showing characteristic twinning,form toe largest part - 24 - of the rock. Hoitiblende has a strong oleochroism from light yellow to 6eer> blue and parallel extinction , Therefore it is an orthorornbic amphibole,* and since this mineral pro>ved to be optically positive it must be anthoohyllite. A similar rock from the Haliburton and Bancroft area aas been described by Br s Adams & Barlow. "--•---*. ( Memoir No 6 i Geology of the Haliburton and Bancroft area. Province of Ontario,1910, by Prank.D.Adams and Alfred.E,Barlow,). There the Orthorhom- bic amphibole was found upon analysis to be gedrite. The rock beside numerous garnets contains a large amount of cordierite crystals giving typical pleochroic halos. But one crystal of garnet was seen and no cordierite could be found in the specimen from Gull Lake. A similar band of sedimentary rocks has been found by Dr Bancroft on Matagami Lake,to which he has given the name of Matagami sezties , Though it contains pebbles of granite,on lake Matagami.this series is traversed by dikes of granite implying &he existence of the conglomerate bands before the last intrusion of granite. PRE-LAURSNTIAN. Keewatin ? Studying the rocks in the order in which they were intruded we first have a massive coarsely crystallized light coloured rock, with a greenish tinge occurring mostly south of Olga Lake and forming the hammocks of the south-west - 25 - portion of Gull Lake . The Sasega diorite,the name given to the rock which was first observed on Sasegawetchew or Dalhou sie Mountains consists of crystals of palegreen hornblende , showing good lozenge shaped basal sections ,sometimes much altered to chlorite. Large plagioclase crystals of a very basic variety ( Labrad*rite 8c Bytownite) are fresh and comprise consi- 5erable percentage of the rock; they are always twinned according to the albite law and less frequently according to pericline A Law, The Plagioclases of two specimens of the Sasega Diorite,one representing the general phase of the rock and a seconfl representing a lighter coloured phase poor in hornblende, but ric& in muscovite,were determined by their specific gravity, using Thoulet's solution,and also by the indices of refraction, losing heavy oils. For analysis the hand specimens were crushed to pass through a 80 mesh sieve and the fine dust removed by rising a 1 sieve of 100 meshes , All the feldspar of the first 3ample sank in a solution of a specific gravity of 2,692, Cheir indices of refraction ranging from 1,563 to 1,572, Comparing these results with the tables given in Iddings book >n""'Ock rineralsHit was found to correspond to A b_ ,A n or 1 * k jabradorite . The plagioclase of the second specimen has ..; a higher specific gravity, equal to 2,738 with indices of refraction varying form 1,572 t6 1,582 which can be approximately ' y represented by the formula A b-j_ An^ ,cor- - 26 - responding to Bytownite. Epidote is present in very large quantity and though it shows good cleavage it is not probable that any of it is primary. Some is undoubtedly of secondary origin ( filling cracks ) . Sometimes the center of the epidote polarizes with the indigo blue colours of zodsite,but the margin of the crystal is of a strong orange yellow and red colours, A little biotite^is imbedded in the hornblende loften altered to chlorite and iron orei Muscovite is present, Sphe:ne stained with hema tite can be seen. The hornblende appears to be secondary ^possibly having been derived from the alteration of pyroxenef but so fresh is the plagioclase that one must be cautious before dsjUrt* £a£*+4* t*af/&* S/z****. /&L& Chibougamau, The origin of the rock is described in the following words : It is regarded as the most reasonable expla nation X that this very advanced decomposition has been occa sioned by the magmatic waters which accompanied and to a very large extent immediately followed the granite intrusion .It would seem essential moreover to the accomplishment of such profound alteration that these superheated waters and vapours must have traversed the ano^thosite batholith in every direction permeating the whole mass,breaking down the unsta ble products and converting these to the conditions of sta bility at present witnessedJJ( 2 ) An exposure of rock found in Elizabeth Bay shows a dioritie phase of the same batholith containing very little hornblende ,its place being partly taken by muscovite visible in a hand specimen. The rock has a slight gneissoid structure. In places the rock shows segregations of large crystals of dark green hornblende,resembling very much ttu> a horn.Iendite,,the result of magmatic differentiation. The rock is massive and heavy, consisting principally of altered hornblende crystals bleached and chloritized ,cut by veinlets pp 158. Report on the Geology and Mineral Resources of the Chibougamau Region, Quebec, I9II. - 23 - filed with epidote . A few crystals of diallage showing good typical pyroxene twinning are seen. The feldspar is altered to sericite, calcite and epidote. Zircon crystals with pleochroic A halos are embedded in the horribJande^ Small amount of biotite and a few small needle like crystals of apatite are present. The Dalhousie Mountains which have been com pletely swept by a very recent fire offer a good field for investigation . They were found to be a vast body of intru- 3ion-braccia. Large angular pieces of Diorite of very irregu- Lar shape are imbedded in a fi*e grained biotite granite. That this Sasega Diorite is older than the Lau rentian Granite is evident from the fact that dikes of granite jut it , and also the fact that fragments of it form a braccia with '$. biotite granite as matrix. From its relation to the granites,the rock may be classed as Pre-Laurentian if the term'Laurentian is restricted to granites pnd dioritesand their gneissoid equivalents. - 29 - KEEWATIN. The Keev/atin formation rests upon the gra nites and gneisses of the district and is- traversed by dikes of granite, granite porphyry and aplite. This defi nitely shows that the rocks of this formation have been formed prior to the intrusion of the batholith of granite. The term Keewatin has been applied in other parts of the country to the oldest known formation of this easter part of North America, In general,,rocks of the Keewatin formation » ate of a-dark greenish colour,though light greenish rocks are also seen. The subsequent igneous intrusions of basic and acid rocks have produced a schistose structure due to accompanying dynamic action, and hew minerals have been and formed, e. g* tourmaline garnet some due to dynamic and others to thermal l metamorphism. The Keewatin formation consists of a large number of lava-floww which include rhyolites, quartzr-por- phyries augite porphyrites and accompanying ;- c VoLeainic ashes and tuffs and other rocks the original cha- By reason of the racter of which is undiscernibleAthe secondary changes of intense metamor- phism. rocks of the type of sericite,rcalcareousxepido- tecalc- ,ChloriteTBiotitej» G©#a-iferous Luca-and Hornblende- schists have been produced. - 30 - &t the close of the period prior to the ad vance of the granite batholith ,'diorite and plutonic rocks rich in hornblende have been injected,occurring in the form of lenses,through the Keewatin schist. The Keewatin rocks belong to the oldest known formation in this area as well as in other areas. All over the central portion of the Laurentian continent ,resting on the granite batholith but,cut by dikes originating from r .... J it*are series of much metamorphosed schists which have been termed Keewatin first b# La.wson, in the Lake of the Woods &nd R^iny -*-- lake region, Dr Robert Bell, in his report on the Keology of the Basin of Nottaway River in 1900; described the rocks of the northern parts of Gull and Olga lakes as forming " part of the Great Huronian Belt which was supposed to extend from Lake Superior to Lake Mistassina a distance following its axis ,of more than 700 miles, (2) In places greenstones of this period show remarkable pillow - structure as on an island in Olga Lake near the mouth og Gull River,This structure ,as it has been observed -.- in other parts of the world,was pro duced by the pouring out of lavaflows under the sea. Many bands of greenstones at el impregnated ( I ) pp 377, Pre-Cambrian Geology of N.A.Lull, 360 U.S.G.S. (2) pp 8k, Report on the Geology of the Basin of Nottaway River, 1900 C,G,S. 31 - to a variable degree with iron pyrite,which upon weathering imparts to the rock a rusty appearance .Chlorite schists 6* seem to be specially favoured in this pyritisation.Such schists -when in contact with band&of granite or granite- porphyry ,becoming very rust^r upon weathering. Sometimes iron pyrite with a little .e»jLaoo-pyrite is segregated in pockets of smaitl size as can be seen on the east side of Gull Lake. Keewatin schists are often cut by wuar"tz veins forming lenses containing some p:,rite and chalco pyrite ,but assays of a few specimens failed to show any gold. Quartz veins are especially numerous along No the contact with the granite batholith wide veins were seen. Lenses of calcite,- . .- ---..., contaiining perfect little hexagons of quartz,also occur in theschis The scliistosity of the Keewatin rocks which is everfcw;"iere much pronounced is very constant running about N,75°E- • The East and V/est side of Gull Lake are formed by two bands of highly metamorphosed Keewatin schists,, the one on the west side being much more prominent. It contains a band of the Metagami Series, Minute faults and shearing planes ,cutting Keewatin, can be seen through out the area. QUARTZ PORPHYRY. The Quartz porphyries are fine-grained rocks - 32 - of a very light colour with a/reddish or a greyish tinge , even sometimes as white as pare marble. Dissirninated through the are fine grained ground.rrass little phenocrysts , varying in size A from the diameter of a pin's head to that of a pea, "'" ' of colorless or light blue quartz. This rock wherever found had been squeezed and had developed a more or less pronounced schistose structure, at times even the pressure has been so great as to develop a slaty structure! as on the north bank at the mouth of Gull Kiver. Gull River runs along a band of Quartz Por phyry, In places a preponderance of feldspar phenocrysts has been noticed. The eyes of quartz: are not evenly distri buted in the rock as s iown on the o&tcrop at the bottom of Bay West of Endex Point on Gull Lake, In a" band twelve feet wide of Quartz Porphyry, eyes of quartz,of the size of a oin, were seen on the east side of the band but none could be seen on the west side , The rock ^presumably a rhyolite, gradually changing to the a m-.ydoloidaj. rhyolite . The original gas cavities being subsequently filled with quartz . Bands of Quartz .Porphyry were also seen at different points in 1st,2nd,3rd bays of Olga Lake. (See page 32A.) Under the microscope a large number of phe nocrysts of quartz can be seen having irregular outlines , - 32A ~ The study of outcrops of 2ns* Bay,Olga Lake, gave,from North to South/the following sequence • First a band of squeezed Quartz Porphyry passing to a sericite schist is followed by bands of Calc-schist and chloriteschist. 33 - and sometimes much corroded margins . A large percentage of the quartz crystals have been fractured ,most probably by pressuretwhilst some of them pulled apart and the cracks filled with secondary calcite. The groundmass consists of calcite,sericitic mica, a little chlorite and a fine grained mosaic of quartz and feldspar. In certain slides tourmaline crystals have been found .most probably the result of boron vapors exhalated during the intrusion of the granite batholith . Sometimes little crystal of Zircon are also, seen, pyrite and pyrrhotite have been recognised in certain slides. A similar occurrence was foundf by E.S.Moore near Lake Superior in Onamau Area. (i). RHYOLLTBS & SERICITIC SCHISTS; Accompanying the Quartz Porphyry are bands of rock of a light greenish colour, very fine--rained and f resembling the Quartz*Porphyry except in one feature. The^# are no phenocrysts of quartz which are to be seen . On account of its fine grained mass the rock has a felsitic character. Rhyolites,like the other Kwewatin rockSjhave suffered from metamorphism and a soft silver micaceous Rock was developed producing,as a result,a sericite schist. (I) pp225 18th Annual Report, Bureau of Mines, Ontario 1909. - 34 AUGITE PORPHYRITS. At the foot of the rapid, on Gull River,an exposure of a schistose rock,of a dark greenish colour, containing phenocrysts of a stumpy dark green mineral over _pns; ei_gth.^of an inch in length,with a square basal section was examined^ The rock strikes N.650 E. and dips vertically as do all the other schists. Under the microscope these phenocrysts , which are ab_jundant, were found to be augite .with an extinc tion angle of about 40°* ^he crystals are of a light greenish brown colour slightly pleochroic and haw a very high double refraction. Hornblende is also present probably a.product of uralitization,sometimes it is altered to chlorite. Many Crystals of augite have a corona of chlorite due to their peripheral alteration. The groundmass consists of chlorite and sericite with iron,pyrite,black iron ore, a little epidote,quartz,feldspar and calcite, CHLORITE SCHISTS. Chlorite schists are the most abundant of Keewatin greenstones , They have always a, pronounced schis tose structure with sometimes a tendancy to become slaty. They are found often alternating with bands of porphyrias and porphyrites. It is very difficult wven under the micros cope to discover og what rock they are the alteration product* Quartz is sometimes a very common mineral of these rocks, - 35 - Feldspar of alkaline and soda-calcic varieties are present recognisable by characteristic twinnings. In one slide a structure resembling rn ch that of a trachyte , the laths of feldspar are roughly elongated in one direction ,the grains of quartz having a rough elliptical contour and the space between the different grains is filled with chlorite, sometimes of a b3iue color. Many chlorite schists are altered porphyritic rocks,since altered phenocryst can be distinc tly seen in some slides. Calcite is present in large amount in some instances ,as a product of decomposition, Epidote and aoisite are not uncommon. Some rocks can be classed as intermediate between sericitic and chloritic schists. Chlorite schists always contain a varying amount of iron ore ,often as iron pyrite ,which can be seen in hand specimen, Tourma&ine is sometimes present and was always formed before the rock became schistose, for crystals cauld be seen whieh had been fractured and the pieces pulled apart. Eyes of quartz with a morter structure have been seen under the microscope, A band of a dark grey schist was found on Olga Lake, near the inlet of Gull River ,with an undulating surface caused by a number of minute shearing planes distinctly seen; they are minute craaaullations. CALCAREOUS SCHISTS, On the North bank of Gull River,near its mouth - 36 - are exposures of Greenschists forming a light coloured band with a distinctly gneissoid structure which is due to parallel arrangement of a greenish mine. It runs from East to West and upon weathering becomes very rusty. Under the microscope the rock is seen to be composed chiefly of granular* calcite, some of the granules being typically termi^ed. Irregular bands of a, pleochroic greenish mineral with put cleayage make up , in scaty aggre gates ( the remainder of the rock. It is evidently chlorite. Grains of quartz and feldspar are present forming lenticular mosaics , Iron pyrite isalso seen. On the south shofce, near the point of the 2nd Bay on the east side of Olga Lake, an exposure of greenschist can be seen containing large eyes of calcite, This was previously an amygdoloidal lava ,the amygdales of which have been filled with calcite. On the south:side of Gull River ,about two miles below the rapids,can be seen 'fcy an exposure of an epidote rich calc-schist. The rock is of an olive green colour and very schistose ,containing alongits planes of schistosity a large number of black needles of tourmaline. - 37 - Under the microscope this rock is seen to con* tain a large amount of calcite,chlorite,epidote,zoisite, some quartz, deep blue crystals of tourmalinertrahsversaly fractured and some iron ore in the form of hematite, BIOTITE SCHISTS, The Biotite schist is a contact rock,it is nearly ?=lwajrs found along the contact of the granite batho lith. It is the result of thermal metamorphism of greenstones, Inclusion of greenstones in granite have been changed to a biotite-rich rock. The aureole of altered greenstones around! a batholith of granite is nearly always a biotite rich schist. On the east side of Gull Lake a purple gray slaty schist very micaceous having a cranulated surface was found ,t#ese undulations in the schist were undoubtedly caused by dynamic metamorphism . Under the microscppe the rock was found to and consist of biotite .muscoviee,chlorite ^arranged in parallel to the rock a schistose disposition giving *A structure , on a gmalllscale ,--„-.-- .„..-;..;------. Quartz and feldspar make* the groundmass, The rocks also contains tourmaline,zircon,granular sphene. and calcite . A thin section of a light grey coloured biotite schist was found to contain corroded crystals of garnets, epidote and zoisite ,grains of iron ore surrounded by color- - 38 - less leucoxene and zircon crystals. The granular >?roundma3s of the rock with its rounded grains of quartz and feldspar gives the rock the appearance of an arkose. GURNITIPEROUS MICA SCHIST; On the east side of, Olga Lake ,along the contact with the granite , near Large island is a 1 and of garnitiferous mica schist . Perfect little crystals of garnet can be seen in hand specimens. Under the microscope the garnetahave a pink colour and an idiomorphic outline. Biotite and colorless mica ( muscovite ) are present in large amount. Epidote is present, polarizing in beautiful yellows. A little quartz and feldspar form the graundmass. HORNBLENDE SCHISTS. Hornblende schists like the biotite schists are most common around the intrusions of igneous rocks. in They also constitute the dark bands* some of the intrusion gneisses .. Inclusions of Keewatin rocks,in granite,have been altered to hornblende schist. On the south shore of Gull Lake,7near the discharge of Waswanipi River,an inclusion of Keewatin rock - 39 - is altered to dark greyish hornblende schist. The rock con sists essentially of pleochroic hornblende crystals in paral lel orientation giving a pronounced schistose structure to y the rock . The rock^contains feldspar,quartz,sericite, epidote and wedge-shaped crystals of sphene. Po i nt In the bottom of Bay west of IndeKfon the west shore of Gull Lake ne«r the outcrop of conglomerate , a large exposure of a distinctly banded rock was found to be an epidote rich hornblende schist. The rock consists of al ternating bands,about one-fourth of an inch wide,of epidote and hornblende „ This banding is so regular that the rock may be taken for sediment,but under the microscope it is found to contain phenocryts <©f untwinned feldspar. A rock displaying the same physical charac teristic but distinctly porphyritic was found on the north shore of Sasega Bay. A very fine grained dark bluish grey rock with a slightly schistose structure was found on Large Island in Olga Lake intruding the Keewatin rocks. The intrusion is elliptical in shape and about 500 feet in length. Under #he microscope,green pleoc iroic hornblende with subordinate green chlorite forms the great bulk of the rock,,Some quartz is present and a large percentage of fine - 40 - granules of iron ore are dissirninated through the whole rock. Some colorless mica, probably sericite^nd a little calcite fa?om the remainder of the rock. It is an altered basic intrusive rock most probably related to the granite batholith on the contact of which it was found. - 41 - DYKE ROCKS. At two different points on the east siore of Gull Lace, near the inlet of Waswanipi ri^er, granite containing inclusions of Keewatin schists,and south of the narrows between Gull and Middle Gull Lakes,Keewatin .%Quartz^* Porphyry are cut by dikes consisting of a very dark massive crystalline rock containing biotite and other phenocrysts , Under the microscope the rock is seen to consist of large idiomorphic crystals of augite showing typlaal twinning and biotite,Augite being first to crystallize- The Biotite is often altered to green chlorite and is also surrounded by an " Opacite rim " ,The rock is rich in magnetite crystallizing in aubes and derived forms . Pheno- cryts of plagioclase feldspar are completely altered to calcite and muscovite. Granular sphene is present also Leu- coxene and a few garnets have been seen embedded in biotite. The chlorite sometimes assumes a blue color . Large crystals of Apatite are seen. Iron pyrire is also present . The rock is ^n augite porphyrite,probably an augite Kersantite. The direction~of the principal dike is N 48° E. and its width is about 80 inches. The rock is younger than, granite since it cuts it. Though not possessisag any definite facts as to the age of sucft a dike one can probably associate it with the - 42 - Keewanawan period since it was the next great period of activity and the fact that dikes the Newer Diabase of thejbO/wv*. A period exist in the area. On the morth shore of the 3rdt Bay on Olga Lake occurs a dyke of squeezed Diorite porphyrite cutting dark Keewatin greenstone. In hand specimen the rock shows a distinctly porphyritic appearance ,light coloured phenocrysts of feldspar are distinctly seen. Under the microscope the rock is seen to consist of phenocrysts of plagioclase decomposed to epidote. quartzjcalcite and zoisite, the dark constituents being actinolitic hornblende with magnetite dust along certain bands and enveloping |he decomposed phenocrysts of plagio clase , This dike is probably associated with the granite intrusion. On the morth side of Gull River near its mouth a small dike of dark grey porphyry showing beautiful eyes of blue quartz and other phenocrysts is seen cutting Keewatin Quartz Porphyry . The dike strikes N 48° S,has a width of two inches and was traced for more than fifteen feet. This dike is of a special class consisting of pheno crysts of quartz,plagioclase ,orthoclase, some being much altered, embedded in a dark nearly isotropic groundnaass. - 43 - l-hi-v* %*ZcX*oYJ Pieces of foreing rocks can be seen,in thio olidhe, to con sist of quartz,plagioclase and a few crystals of biotite. This dike may be classed with those sand stones dikes, elaborately described by J.S.Diller In an article published in 1890 in the Bulletin of the Geological Society of America.These sandstonesdikes are of a grey colour, t#e iron oxide contained in the rock imparting to it,upon vmmg weathering4a yellowish tinge. A hand specimen of this rock will show much biotite imbedded in a fine grained groundmass con- sisting of quartz,plagioclase,composite grains of metamorphic rocks and a few accessory minerals inclosed in a cement of calcite. - 44 - After a review of the characteristics of crystals formed in an igneous rock as compared to those of sedimentary rock,Diller concludes to the filliigof fissures,supposed to have been formed by earth-quakes,by solid particles subsequently cemented. Rejecting the hypo thesis of a. filling from the surface on the bases of stra tification and orientation of flfekes of biotite,he ascer tains that the sand was forced into the fissures. By the shearing strains which have distorted the grains and the fact that a number of dikes do not reached the surface he states that the movement , in the fissure,was from below upwards,caused by violent pressure. In 1783 during the great alabrian earthquake craterlets were formed just in the same way. ~F*LATEL 7T