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HON. G. C. WARDROPE, Minister D. P. DOUGLASS, Deputy Minister M. E. HURST, Director of Geological Branch

Geology of the Big Trout Lake Area

District of Kenora (Patricia Portion)

By P. P. HUDEC

Geological Report No. 23

TORONTO Printed and Published by Frank Fogg, Printer to the Queen©s Most Excellent Majesty 1964

Publications of the Ontario Department of Mines

are obtainable through

Publications Office, Department of Mines Parliament Buildings, Queen©s Park Toronto 5, Ontario, Canada

Geological Report No. 23, paper-bound only: ftl.OO

Orders for publications should be accompanied by cheque, money order, or postal note payable in Canadian funds to Provincial Treasurer, Ontario. Stamps are not acceptable.

in TABLE OF CONTENTS

Geological Report No. 23

PAGE Abstract ------vi Introduction ------l Method of Mapping - . - - . - . . - 2 Acknowledgments ------. 2 Access ------3 Previous Work ------. 3 Topography ------.3 Amount and Distribution of Outcrop - 4 Natural Resources . - ...... 5 Agriculture ------5 Forests and Lumbering ------5 Water Power . - ...... 5 Fish and Game . - ...... 5 Inhabitants ...... 6 General Geology ------7 Table of Formations ------7 Volcanic Group ------8 Sedimentary Group ------9 Greywacke ------9 Quartz-Biotite-Amphibole Schist ------11 Anorthosite Complex ------11 Porphyry Dikes ------14 Granitic Rocks ------14 Basic Dikes ------16 Pleistocene Geology ------16 Recent Deposits ------18 Descriptions of the Volcanic-Sedimentary Belts - - - -19 Big Trout Lake Belt 19 Kino Lake Belt - 21 Fat Lake Belts 22 Severn River Belts ------23 Northern Belt 24 Nemeigusabins Belt ------24 Garrett Lake Belt 24 Structural Geology ------24 Historical Geology ------28 Economic Geology ------29 Copper 29 Zinc ------31 Iron 32 Magnetite-Ilmenite in Anorthosite - 32 Gold 32 Bibliography ------32 Index ------33

IV PHOTOGRAPHS PAGE Aerial view of settlement of Trout Lake on Big Trout Lake 6 Banded greywacke or washed tuffs, Fat Lake south belt 10 Close-up of euhedral crystals in "leopard rock" - - - - -13 Banded "leopard rock" on south shore of Big Trout Lake - - 13 Peat deposit on Big Island, exposed by low water-level - - -18 Chill border between two massive volcanic flows 20 Sheared bedded conglomerate on island in Big Trout Lake - - -20 Banded dragfolded metasedimentary rocks, Severn Lake 22 Faulting of a sedimentary band, Severn Lake - - - - -25

FIGURES PAGE 1 Key map showing location of the Big Trout Lake area - - -vi 2 Sketch map of the major structural features of the area 26 3 Cross-sections along lines indicated on Figure 2 - - - -27 4 Properties in the Fat-Derniere lakes area as of January 30, 1962 - 30

COLOURED GEOLOGICAL MAP (back pocket) Map No. 2045 Big Trout Lake area, Kenora District, Patricia Portion. Scale, l inch to 2 miles. ABSTRACT

The geology of the area was mapped during the field seasons of 1960 and 1961. The mapping was mostly reconnaissance in nature, on the scale of l inch to l mile. All the bedrock is Precambrian in age. Interbedded sedimentary and volcanic belts trend in a northwesterly direction. Volcanic rocks predominate in and around the basin of Big Trout Lake. Pillowed and massive andesite is the principal rock type, but basalt and gabbro flows are also found. Sedimentary rocks predominate in the western part of the area and are of two general types: finely banded tuffs and greywackes; and the more highly metamorphosed quartz-biotite-amphibole-feldspar schists. Gabbroic anorthosite forms a large sill-like body along the north and south shores of the eastern part of Big Trout Lake.

Figure l — Key map showing the location of the Big Trout Lake area. Scale, l inch to 200 miles.

The above rocks are cut by feldspar porphyry dikes. Two granite types enclose and intrude the other rocks: grey granodiorite; and, pink granite and granodiorite. The latter appears to be the younger rock. The area was glaciated by at least two distinct ice-advances, and the deposits of the last advance cover most of the bedrock. The two most conspicuous structures are a regional anticline at the east end of Big Trout Lake, plunging in an easterly direction, and a large granite batholith in the southwest part of the area. Sporadic copper mineralization is found in the volcanic rocks. Minor zinc mineralization, as sphalerite, is present in sedimentary rocks of the Kino Lake belt. Magnetite and ilmenite are associated with the anorthosite body. Essentially barren massive pyrrhotite and pyrite are found at Derniere Lake in the Fat Lake belt.

VI BIG TROUT LAKE AREA By

P. P. Hudec1

INTRODUCTION

Big Trout Lake, one of the largest lakes in northwestern Ontario, occupies about 240 square miles. The lake has long been a trading centre for the Cree Indians. The Northwest Company, in 1793, had a trading post at the east end of Big Trout Lake near its outlet into the Fawn River. In 1830, the Hudson©s Bay Company built a post on what is now Post Island, and has operated it since then. A certain confusion exists about the name of the main lake. This body of water was known formerly as Fawn Lake, and it is so identified in some of the modern atlases. Later, the name Trout Lake was applied to it; still later, it was named Big Trout Lake, the name it bears today. In this report, the name Trout Lake refers only to the settlement and trading post on Post Island in Big Trout Lake. On present maps, and in local usage, Fawn Lake is a small lake west of Big Trout Lake. The Fawn River drains Fawn Lake into the west end of Big Trout Lake, and flows northward from the east end of Big Trout Lake. Bearskin Lake, in this report, refers only to the Indian settlement and trading post on Michikan Lake on the west edge of the map-area. (There is a body of water called Bearskin Lake, but it is well outside the present map-area, and lies about 32 miles south-southwest of Michikan Lake.)2 The presence of basic intrusive rocks, volcanic rocks, and metasedimentary rocks in the Big Trout Lake area has been known since 1886, but no attempt at systematic mapping of these rocks was made until the present survey. The prime reason for the lack of interest would seem to have been the remoteness of the area, but the fact that no mineral prospects have been reported was also a contributing factor. Another deterrent to geological mapping and exploration was the lack of basemaps. The topographic maps of the Canada Department of Mines and Technical Surveys, Ottawa, are the only maps available. These have been compiled from oblique air photographs, and lack detail and accuracy. The basemaps for this survey were compiled by the Cartographic Unit of the Ontario Department of

1 Graduate student, McGill University, Montreal, Que. 2Geographic names used in this report and on the accompanying map (No. 2045, back pocket) are those officially recognized by the Canadian Board on Geographic Names. On the map, official names are accompanied, where necessary, by the local name in parentheses. Fat Lake (see p. 22) was formerly known as Winnin Lake; Jackfish Lake (see p. 28) was formerly known as Mandanne Lake. 1 Big Trout Lake Area

Mines. Information was taken from maps and surveys of the Canada Department of National Defence, the Canada Department of Mines and Technical Surveys, and the Ontario Department of Lands and Forests; much additional information was obtained from air photographs (scale, approx. l inch to l mile) from the Canada National Air Photo Library. The location of Indian Reserve No. 84 is not shown on the final map, owing to the fact that the boundary had not been settled at time of publication. The final coloured geological map, No. 2045 (back pocket), is on the scale of l inch to 2 miles. Method of Mapping The present survey was conducted during the field seasons of 1960 and 1961 under the direction of the author. Slightly less than 7 months was spent in actual mapping. The size of the area mapped is about 4,500 square miles, roughly 80 miles east-west and 58 miles north-south. The area is bounded by north latitudes 53030© and 54030© and west longitudes 890 and 910. The map-area lies in the Patricia Mining Division. Air distance from the settlement of Trout Lake, on Big Trout Lake, to Sioux Lookout is 270 miles, and to Pickle Lake 160 miles. Consideration of the size of the area and the time available necessitated that mapping be of a reconnaissance nature only. Most of the mapping was done along the shores of lakes and rivers. The major rivers of the area were followed for considerable distances; the Fawn River was covered for more than 60 miles downstream, and the Severn River for about 70 miles both upstream and down stream from the settlement of Bearskin Lake. Other navigable rivers were followed either to the boundary of the map-area or as far as they were passable within the map-area. All the larger lakes were visited and their shorelines mapped. Air photographs were used to determine inland areas of outcrop and, where possible, these were mapped by traversing. All mapping in the field was carried out on these air photographs, which were obtained from the Royal Canadian Air Force. An attempt was made to traverse all contacts. The smaller out-of-the-way lakes were visited by means of light aircraft. The vicinities of these lakes had rarely more than two or three outcrops, and the majority had no outcrop at all. Travel by aircraft was found to be very satis factory because it enabled mapping of most of the available outcrops in inaccessible and heavily drift-covered areas, thereby providing a more complete over-all picture. On one of these small lakes, visited by aircraft for half a day, a mineralized area containing massive sulphides was found. It is apparent that not all parts of the area were covered in equal detail, but the degree of detail was principally a function of the availability of outcrops. Acknowledgments The author was ably assisted in the field by W. Cruickshanks, R. R. Keyes, and J. C. Byrne during the summer of 1960, and by F. Charlton, H. A. Frost, L. Farr, and E. G. Bright during the summer of 1961. Mr. Cruickshanks and Mr. Charlton, as senior assistants, were engaged in independent mapping during most of the season. Geological Report No. 23

Thanks are extended to the Ontario Department of Lands and Forests for their radio and aircraft service. The help provided by the residents at the Trout Lake and Bearskin Lake posts was much appreciated. Access Owing to the remoteness of the area, air transportation is the only logical method of reaching the area. Aircraft may be chartered either at Sioux Lookout or at Pickle Lake, or advantage may be taken of the scheduled flights originating at either of these localities. Sioux Lookout, although more distant than Pickle Lake from Big Trout Lake, is on the main CNR line; on the other hand, Pickle Lake must first be reached by an unpaved road from the Savant Lake railroad point. A winter tractor-road connects the settlements of Trout Lake and Bearskin Lake with Pickle Lake to the south, and with Ilford, Manitoba, to the west. The road to Pickle Lake was cut within the past few years, and is now used for freight ing all bulk supplies in preference to the Ilford road. Canoe routes into the area are still in use, and the Indians travel for long distances in all directions. The Severn River and the Fawn River are the main routes to Fort Severn on Hudson Bay; from the settlement of Bearskin Lake on Michikan Lake, the upper Severn River provides ready access to Sandy Lake and points south. The south-bound route from Big Trout Lake entails lengthy overland portage from the south shore of Big Trout Lake to the Asheweig River. The route involves 6 miles of portage and 4 miles of water. Up the Asheweig River and by a series of portages, Wunnummin Lake and the Pipestone River may be reached. The Pipestone River arrives at Wunnummin Lake from a southwesterly direction and may be used to reach points south. East of Big Trout Lake, a canoe route crosses a series of small lakes and eventually joins the Asheweig River and Kasabonika Lake on which there is a settlement. The canoe routes and portages within the map-area are indicated on the map. Previous Work One of the first geologists to visit the area was A. P. Low, who travelled down the Severn River to Fort Severn in 1886. His account (Low 1886) is of historical interest only, because little geological mapping was done. The informa tion concerning the geology of Big Trout Lake that at present appears on all maps came from the report of J. B. Tyrrell (1913a); his report contains brief descriptions of the main rock types and many interesting accounts and pictures of the area. Some other information on the area, submitted by prospectors between 1935 and 1940, can be found in the files of the Ontario Department of Mines. A minor gold rush during that period resulted in reconnaissance prospecting, and in the discovery of several narrow isolated sedimentary and volcanic belts crossing the Severn River, as well as the western portion of the Fat Lake belt. Topography The country in and around Big Trout Lake and the Severn River is rather flat. The relief does not exceed 75 feet and can be attributed mostly to eskers and other surficial deposits. Big Trout Lake Area

The topography of the map-area is not uniform. The eastern parts south of the Fawn River vicinity are characterized by long narrow drumlinoid ridges of low relief, all aligned in a northeasterly direction. These are areas of very little or no outcrop, in which drainage is controlled exclusively by these glacial grooves, as exemplified by Otter Lake and the Otter River. Similar topography is found in the region of the Blackbear River, which lies immediately northwest of the mapped area. The topography along the northeast edge of the map-area is very flat and characterized by many miles of swamp and string bogs. The number of lakes diminishes markedly in this area. The major rivers, being deeply incised in clay, have steep banks. The clays form a more or less continuous blanket north of the map-area and form part of the marine clay overlap. The topography of the central part of the area is controlled in part by bedrock and in part by the superficial deposits and is characterized by a large number of lakes. Most of the smaller lakes probably have clay or sand bottoms, but the larger lakes (Big Trout, Severn, and parts of Dinwiddie1 and Misikeyask) are excavated in rock. The bottom relief of the main part of Big Trout Lake is of some interest. The contours of the lake bottom are shown on the coloured geological map (No. 2045). The information was obtained from depth soundings by the Fish and Wildlife Branch of the Ontario Department of Lands and Forests, which surveyed the lake during the summer of 1960. The relief found in the lake is surprising in view of the flatness of the land around it. Troughs 120 feet deep with relatively steep walls are common and, in general, reflect the geological structure. The troughs, where present, follow approximately the contact of the anorthosite and the volcanic rocks. The southwestern part of the area has relatively little drift-cover, and is the only part of the map-area in which bedrock exercises a definite control on the topography. The radial and concentric arrangement of the drainage is quite apparent. The report-area is drained by two major river systems, the Severn and the Fawn. Other rivers of importance are the Blackbear River just northwest of the mapped area, the Witegoo River with headwaters in the north-central part, the Otter River in the east, and the Mishwamakan River with headwaters near Makoop Lake. All waters, including the Fawn River, eventually run into the Severn River and thus into Hudson Bay. The slope of land within the map-area is to the northeast. That the gradient of slope is rather steep, is indicated by a number of rapids encountered on the rivers. Where a river flows across bedrock, the rapids are steep, often in the form of falls. One set of rapids on the Severn River, Akem Falls, has a vertical drop of about 40 feet in a distance of about 100 feet, the water cascading over a series of resistant rock ledges. AMOUNT AND DISTRIBUTION OF OUTCROP The area has been glaciated by at least two distinct ice-advances. As a result, much drift covers the rather flat topography of the region. Outcrops are low and few in number. The northwestern and the northeastern parts of the map-area are virtually devoid of outcrop.

©Formerly known as Mopabrow Lake. Geological Report No. 23

Some parts of the volcanic belts are well exposed, especially along lakeshores. Generally, the volcanic rocks are better exposed than either the sedimentary or the granitic rocks. Natural Resources AGRICULTURE Small-scale farming, sufficient to supply part of the local needs, is carried out by the Cree Indians and by other people permanently stationed in the area. Almost all the vegetables grown in the southern parts of Ontario can be suc cessfully grown in this northern area during the short summer season. FORESTS AND LUMBERING The area is forested principally by black and white spruce. The trees are dispersed and relatively small throughout most of the district. Excellent stands of timber, however, may be found on eskers and sandy ridges. Lack of drainage appears to be the principal deterrent to growth of good timber. White birch, aspen poplar, and balsam poplar are found in large patches among the spruce. They commonly grow on boulder ridges, and on low points and promontories jutting into the lakes. The Canada Department of Indian Affairs has two portable lumber mills that are being used to dress logs into rough lumber, which is used in local con struction ; both Trout Lake and Bearskin Lake are self-sufficient in this respect. Forest fires were rampant in this part of the country in 1961, which was a particularly dry year. The region that includes the present map-area is classed as hinterland by the Ontario Department of Lands and Forests, and no fire-fighting is carried out. WATER POWER Numerous rapids on the Fawn and Severn Rivers could be harnessed, if necessary, to produce hydro-electric power. In particular, Ashaway Falls on the Fawn River and Akem Falls on the Severn River have sufficient drop and water volume to warrant serious consideration. FISH AND GAME Big Trout Lake is a major commercial fishing centre, and abounds in lake trout, whitefish, and northern pike. Pickerel is also found, but is relatively insignificant. Lake trout and whitefish are the principal exports of the area. Sturgeon is caught in the Fawn and Severn rivers and adjacent lakes. Sturgeon fishing, although a lucrative venture, is insignificant when compared to the total weight of fish caught at Big Trout Lake. All fishing is done by the local Indians under the direction of personnel of the Canada Department of Indian Affairs. The fish are flown out daily by chartered aircraft during the fishing season. Waterfowl, including a wide variety of ducks and some Canada geese, are abundant, especially on the smaller lakes and rivers. Heavier game is not plentiful in the bush. No moose was seen by the members of the survey party during the two summers in the area. Fur-bearing animals, although present, are not as plentiful as in other areas west and east. A recent epidemic has decimated the beaver population; as a result, many of the streams that might have been made navigable by beaver dams are now impassable. The Ontario Department of Lands and Forests is at present engaged in restocking the area with beaver. Big Trout Lake Area Inhabitants The settlements of Trout Lake and Bearskin Lake are the permanent homes of about 400 Cree Indians who belong to a single tribe that is governed by an elected Chief and his Councillors. The Chief resides at Trout Lake, the main settlement. Each of the smaller settlements, at Bearskin Lake, and on Kasa bonika, Sachigo, and Wunnumin lakes, has a Councillor who is responsible to the Chief.

Looking east, an aerial view of the settlement of Trout Lake on Big Trout Lake, showing the buildings of the Canada Department of Transport, the post of the Hudson's Bay Company, and part of the village.

Recently, a Reserve has been planned at Big Trout Lake. The Canada Department of Transport maintains a weather station at the settlement of Trout Lake. The station is equipped to make surface and upper- atmosphere observations, and a seismographic station is about to be established. Five families and three or four single men constitute the personnel of the station. A year-round Anglican mission and a government nursing station are maintained at the settlement. A regular grade-school and a summer-school are conducted by four teachers stationed at Trout Lake; the school is run principally for the benefit of the Cree Indian children, but the children of the other permanent residents also attend. Two general stores are operated at Trout Lake and two at Bearskin Lake; in each case, one is a Hudson©s Bay Company Trading Post, the other a "free" trader. The principal source of livelihood for the Indians is the fishing industry. Trapping in recent years was restricted, owing to the beaver-restocking program. The Canada Department of Indian Affairs provides most of the jobs, either in fishing or in local construction projects. The staff of the weather station and other persons with permanent employment locally provide employment for the Indians. Geological Report No. 23

GENERAL GEOLOGY TABLE OF FORMATIONS CENOZOIC Recent: Beach sand and flood plain deposits; fine or ganic lake bottom sediments; peat, sphag num moss. Pleistocene: Boulders; raised beach deposits; esker sands, gravels; non-stratified pebbly till. Unconformity PRECAMBRIAN BASIC DIKES Gabbro, gabbro porphyry; basalt, basalt por phyry; diabase. Intrusive Contact GRANITIC ROCKS Granodiorite gneiss, quartz diorite gneiss; grey quartz diorite; pink granodiorite; granite; pegmatite. Intrusive Contact PORPHYRY DIKES Feldspar porphyry; quartz-feldspar porphyry. Intrusive Contact ANORTHOSITE Amphibolite; gabbro; anorthositic gabbro; gab- COMPLEX broic anorthosite; anorthosite; diorite; quartz diorite. Intrusive Contact SEDIMENTARY GROUP Conglomerate; amphibole - chlorite schist; quartz - biotite - amphibole schist; banded greywacke, waterlaid tuff; greywacke, sub- grey wacke; quartzite. VOLCANIC GROUP Fine-grained extrusive rocks: Amygdaloidal basalt, agglomerate, tuff; pil lowed basalt; massive basalt; pillowed ande site; massive andesite; massive dacite. Coarse-grained volcanic or basic intrusive rocks: Diorite; gabbro.

All the bedrock in the area is Precambrian in age. Sedimentary and volcanic rocks appear to be the oldest. Volcanic rocks predominate in and around the basin of Big Trout Lake, but the proportion of sedimentary rocks increases westward toward Severn Lake. The profuse interbedding and gradation of volcanic rocks to tuff and to sedimentary rocks would suggest that they were deposited at about the same time. Andesitic volcanic rocks predominate, the massive and pillowed varieties being about equally abundant. Basalts and coarse- grained flows of gabbro are abundant. Acid volcanic rocks (dacite) are also present, but are rather uncommon. On the whole, the volcanic rocks are inter mediate to basic in composition. The sedimentary rocks may be divided into two general units: those as sociated with the volcanic rocks, and those forming a sedimentary unit. The former association includes waterlaid tuffs, fine-grained greywackes and slates, Big Trout Lake Area and impure quartzites. The sedimentary rocks reflect the composition of the volcanic rocks and, where sheared, are indistinguishable from them. The second unit of sedimentary rocks forms thick sedimentary sequences in the western part of the area around Severn Lake and is composed of quartz-biotite-amphibole- feldspar assemblages of minerals. Inclusions of this rock are commonly found in granitic rocks in various stages of assimilation. Gabbroic anorthosite forms a large sill-like body along the northern and southern shores of the eastern part of Big Trout Lake. The rock is primarily an anorthositic gabbro and gabbro. Pure anorthosite is relatively insignificant, being found as occasional bands and dike-like bodies. Porphyry dikes cut all the above rocks and are especially common in the areas of anorthosite. Feldspar porphyry and quartz-feldspar porphyry with an aphanitic groundmass are the main varieties. Two principal types of granitic rocks were observed: grey granodiorite and quartz diorite; and, pink to red granite and granodiorite. The latter appear to be the younger rocks. Pegmatitic phases of the younger granite may also be found, but those of the grey granodiorite are rare. Gabbroic, basaltic, and diabasic dikes cut all rocks previously mentioned. They are more prevalent in the basin of Big Trout Lake. Pleistocene deposits of till, sand, and gravel form a thick mantle over much of the area. Eskers, drumlins, and drumlinoid ridges are common. Marine clays form a flat featureless plain in the northern part of the map-area and overlie the glacial deposits. Numerous sporadic areas of muskeg and string bogs cover the northern and northeastern parts of the area. The various belts that are referred to throughout the report are shown in a generalized sketch (see Figure 2, p. 26). Volcanic Group The volcanic rocks of the area underlie most of Big Trout Lake and extend in narrow belts, 1-2 miles wide, west and northwest of the lake. Other volcanic belts not connected to the main (Big Trout Lake) belt lie north, northwest, south- west, and south of the lake. The volcanic rocks of the Big Trout Lake belt and other belts are mostly intermediate to basic in composition. Andesite and basalt are the common types. Dacitic rocks are present locally, but are relatively unimportant. The two common modes of occurrence are pillowed and massive flows. The pillows are, on the average, well-preserved; they show chill structure, concentration of vesicles at the top of pillows, and typical form, all of which contribute to top determinations. The massive volcanic rocks range in texture from aphanitic to medium-grained gabbros. The colour of pillowed and massive flows is a shade of green on the weathered surface, but green to black on the fresh surface. Some fine-grained brittle basalts are jet-black on both weathered and fresh surfaces. The mineralogy of the volcanic rocks varies, depending upon the degree of shearing and alteration. The basalts contain pyroxene, or remnants of pyroxene, generally in grains slightly larger than those of the groundmass. The feldspar is plagioclase of andesine-oligoclase composition, occurring as long, small, single- twinned laths in the fine-grained groundmass, and as multiple-twinned broad laths in the coarse-grained rock. Chlorite is present in both altered pyroxene and 8 Geological Report No. 23 altered amphibole. Pyroxene is also seen altering to amphibole. The rocks are highly calcic, as indicated in thin sections by considerable free calcite and zoisite. All volcanic rocks contain some magnetite and sulphides, mainly pyrite. Volcanic rocks that are slightly more acid are found near the northern edge of the Big Trout Lake belt, as well as along the southern boundary of the Northern belt. The rocks are best classified as dacite, and may contain up to 30 percent quartz. The colour is light green, derived from the disseminated fine chlorite. Volcanic breccia is found in many parts of the main (Big Trout Lake) belt, but is limited in extent, being found at the boundaries of flows. Vesicular andesite is present on the south shore of Ernie Island, and can be traced for almost a mile along-strike. In the same area, a massive lava flow exhibits polygonal fractures not unlike mudcracks, and these probably represent fracturing of a solid crust of lava soon after solidification. The fractures are epidotized. A rather peculiar orbicular volcanic rock has been observed in two widely separated localities on Big Trout Lake: on the northeast shore of Bear Island; and, in a bay west of Leopard Point. The rock consists of very fine-grained siliceous and chloritic concentric features, with fine quartz in the centre, a ring of fine chlorite around it, surrounded by a ring of chlorite of different composition. The large rings (^ to l inch in diam.) have small orbicular features within them. The rock is dark, hard, and brittle. Epidotization is a common alteration of all volcanic rocks, especially pillowed lavas. Epidote replaces the centres of some pillows, grows in euhedral crystals along with quartz and calcite at junction of pillows, or forms pods in the massive flows. The effect of the anorthosite on the volcanic rocks is not known, as the two do not have a well-defined contact. The visible contact can best be described as a zone trending through the islands south of Minko Bay. The contact effect here is partial recrystallization of the volcanic rocks into gabbro, and introduction of silica in the form of blue opalescent quartz. The lake-bottom topography indicates a trench more than 100 feet deep in the vicinity of the contact, suggesting that the minerals at the contact are rather soft.

Sedimentary Group The sedimentary rocks in the area can be divided into two major units: a banded greywacke type, and a quartz-biotite-amphibole schist type. The first unit is associated with the volcanic rocks, and the second is more commonly found as narrow belts in granitic areas. Compositionally, the two units are very much alike, but the difference lies in the degree and type of thermal and dynamic metamorphism. GREYWACKE The rocks of greywacke type are light to dark grey and green, fine- to medium-grained, coarsely and finely banded, as well as massive. Conglomerate beds of limited extent are also found. The most common rock type is greywacke, but subgreywacke and impure feldspathic quartzites are locally abundant. The greywacke is frequently interlayered with the volcanic rocks. Volcanic tuff is found associated with both the sedimentary and the volcanic rocks, and it is indistinguishable from the finely banded greywacke. The area in which there is particular difficulty in differentiating between the two rock types is the sheared Big Trout Lake Area belt between the granite masses of Jackfish Bay-Misikeyask Lake and the volcanic-sedimentary belt trending through Kino Lake. Because these rocks are associated with pillowed volcanic rocks and because the volcanic rocks pre dominate, the areas of interlayering are represented on map No. 2045 by the colour assigned to the volcanic rocks.

Banded greywacke or washed tuffs in the Fat Lake south belt; northwest of the Severn River.

The greywackes are characterized by the uniform and persistent banding on weathered surfaces. For the most part, the material making up the greywacke is fine-grained, and banding is generally not evident on the fresh surface of the rock; however, weathering of the exposures brings out the banding well. The total thickness of the banding may range between a few millimetres and several centimetres, but the thickness of any individual band is remarkably constant along-strike. Certain bands may be crumpled and folded without apparently affecting the overlying or underlying layers. An unusual occurrence of banded fine-grained greywackes containing variously-sized boulders and cobbles of granite scattered throughout the formation was found in the Severn River south belt. The pebbles and boulders appear to be rotated and sheared. The banding in the greywackes curves around the boulders without a break. Explanations of the origin and the method of emplacement of the banded greywackes present problems. The rocks are clearly sedimentary and are remark- 10 Geological Report No. 23 ably similar in appearance to the varved clays of Pleistocene. They are in many cases associated with the volcanic rocks, especially pillowed basalts and andesites, and in some cases are mineralogically similar. They are especially prominent in the narrow volcanic-sedimentary belts and more abundant on the periphery of these belts. Petti john (1943) noted the above-mentioned association of grey- wackes and suggested that they represent rapid sedimentation in a tectonically active belt. Banding is explained as a result of periodicity of supply, possibly due to climatic changes. Kuenen (1950) and others explain the banding as having been due to turbidity currents. This explanation would also account for folding of some of the layers and not others. Graded bedding, lack of crossbedding, and the occurrence of boulders and pebbles of granite, can thus be explained. Lean, narrow, but persistent bands of iron formation are found associated with banded greywacke, generally in the vicinity of volcanic rocks. The iron formation consists of bands of quartz-magnetite and grey wacke, about l centimetre in width; the total width of bands of iron formation is about two feet. The iron formation is commonly mineralized with disseminated sulphides, principally pyrite and pyrrhotite, with specks that are possibly chalcopyrite. The sedimentary rocks in the western part of the area are darker in ap pearance, coarser, and contain a greater proportion of biotite and amphibole. They have suffered a higher grade of both thermal and dynamic metamorphism. The original banding, still visible, is reflected in the relative concentration of biotite-amphibole assemblage. The minerals are oriented parallel to the banding. Parallel shearing and dragfolding is common.

QUARTZ-BIOTITE-AMPHIBOLE SCHIST The quartz-biotite-amphibole schist rocks resemble those mentioned in the previous paragraph, except that no banding is evident. The division in this sense is artificial; however, the association of the schist as very narrow belts in granitic rocks without accompanying volcanic rocks serves to distinguish the two groups. The composition of the rock indicates it is a typical Precambrian metasediment, the inclusions of which can be found in granites throughout the area. The age of the sedimentary rocks relative to the volcanic rocks is problemati cal. The common interbedding of the two rocks would suggest that they are roughly equivalent in age. The structural evidence in the east end of Big Trout Lake indicates that the sedimentary rocks overlie the volcanic rocks; on the other hand, if the narrow belts in the western part of the map-area are assumed to be synclinal, then the majority of sedimentary rocks in this area would be strati- graphically below the volcanic rocks. The difficulty is resolved if we assume that the sedimentation and volcanism were contemporaneous, that Big Trout Lake basin was the locale of the volcanism, and that Severn Lake and the Severn River were areas of initial sedimentation that was followed by volcanism.

Anorthosite Complex The term anorthosite is not applicable in the strictest sense, because almost all the rocks of the complex contain more than 10 percent mafic minerals. Gab broic anorthosite (10-22^ percent), and anorthositic gabbro (22^-35 percent mafic constituent), are the principal rock types. The above proportions are based on work by Buddington (1939) and are now in general use. 11 Big Trout Lake Area

The anorthosite complex forms a broad belt, in places several miles wide, from Minko Bay eastward along the north shore of Big Trout Lake. A similar belt trends along the southern part of Big Trout Lake. The complex is thought to form a thick sill that has been folded into a steeply plunging anticline, of which the north and south belts are the limbs of the fold. Secondary folding is suggested by the local thickening and change in the direction of linear features. The rocks of the complex appear to be massive in most outcrops, but large- scale banding is evident, separating the complex into amphibolitic gabbro, pyroxene gabbro, anorthositic gabbro, gabbroic anorthosite, and relatively small and infrequent pure anorthosite bands. Evidence of repeated local banding and gneissosity can be found in several localities. The colour of the rock varies from light grey to dark green, depending on the mafic content. The contact of the complex with the volcanic rocks is characterized by a gabbroic zone that is high in magnetite and ilmenite. This contact, of the anorthosite with the volcanic rocks, is the stratigraphic bottom of the sill, and the magnetite-ilmenite con centration probably represents fractional settling-out of these minerals from the anorthositic melt. That the magnetite-ilmenite mineralization is indigenous to the complex and not a recrystallization phenomenon of "greenstone" is brought out by two facts: the volcanic rocks as a whole contain almost no ilmenite and little magnetite; secondly, a polished-section examination of the minerals shows exsolution textures of ilmenite in magnetite. The exsolution indicates slow cooling of the melt, a fact also brought out by the coarseness of the rock and the ubiquitous zoning of plagioclase feldspar. According to Ramdohr, the unmix ing temperature is 7000C., but the author believes the unmixing temperature to be lower. An exceptional type of unmixing of pyroxene and ilmenite was observed in several thin sections. The ilmenite is found as thin laths occupying cleavage traces of the pyroxene. Most of the original pyroxene has been altered to chlorite and epidote, and its former existence is implied by the presence of ilmenite-filled cleavage traces. Mineralogically, the anorthosite body is composed of plagioclase feldspar of about Ango composition, augite, and amphibole, in varying proportions to give the earlier-mentioned types of rock. Excessive alteration, in part deuteric, in part hydrothermal, has altered the highly calcic plagioclase into zoisite, epidote, and calcite, and has altered the pyroxene and amphibole into chlorite. The plagioclase is in places partly, in other places completely, replaced. Hydrothermal alteration is evident in the vicinity of two granite stocks, one in the northeastern part of Big Trout Lake, the other in the western extremity of the northern arm, west of Post Island. The description above is of the northern limb of the sill. The southern limb, although similar in many respects, seems to represent only the upper part of the intrusive body. The rocks appear to be less basic, and to contain less associated magnetite and ilmenite, and better-developed feldspar crystals; in general, they resemble the assemblage found along part of the northern boundary of the northern limb. The plagioclase is subhedral to anhedral and, in places, forms what has been called "leopard rock". Leopard rock consists of almost euhedral single crystals of plagioclase up to 6 inches in diameter embedded in a gabbroic matrix. The size of the individual crystals seems to depend on the concentration of the individual crystals in the gabbroic groundmass; the lower the concentration, 12 Geological Report No. 23

A close-up of "leopard rock", showing the euhedral crystals of plagioclase in a gabbroic matrix; on Leopard Point, south shore of Big Trout Lake.

Banding of the anorthosite on Leopard Point, south shore of Big Trout Lake. The dark bands are amphibolitic gabbro, the spotted bands "leopard rock".

13 Big Trout Lake Area

the bigger the crystals. A striking example of leopard rock is found on Leopard Point on the south shore of Big Trout Lake, in which amphibolitic gabbro and gabbroic anorthosite are repeatedly interbanded. Large plagioclase crystals (the leopard spots) are present in the amphibolitic gabbro, and show visible concentric zoning. The sill in the Leopard Point area is folded into a large concentric plunging fold, possibly a syncline. The rocks at the stratigraphic top of the sill contain an abundance of blue quartz. This zone probably represents the acid fraction of the sill; the rock can be called a quartz diorite. Porphyry Dikes Two types of porphyry dikes are found cutting all rocks except the granite in the eastern half of Big Trout Lake. The dikes vary in width from a few feet to about thirty feet, and are especially profuse in the central part of Big Trout Lake in the vicinity of Big Island. The most abundant and widespread of the porphyry dikes is a sanidine and plagioclase porphyry. Both feldspars are euhedral in outline, and plagioclase exhibits pronounced zoning. Random crystals of zoned amphibole are found. The groundmass is green-grey and very fine-grained. Quartz-feldspar porphyry is light grey and consists of phenocrysts of sanidine and plagioclase and large eyes of quartz. The groundmass is aphanitic. A third, rather uncommon, feldspar porphyry is light green to pink. Plagioclase is present as phenocrysts, and a large proportion of its groundmass is made up of fine-grained quartz, with some chlorite, sericite, and calcite. The contacts of the dikes with the country rock are sharp, and there is no visible alteration. The dikes appear to have filled large fractures in the rock, for they seem to have followed any random opening, often angling sharply, without a consistent direction of either strike or dip. Most of the dikes are light-weathering and very easily distinguished from the country rock. The fresh surface, on the other hand, commonly resembles that of the volcanic andesite. One of the main distinguishing features of the porphyry dikes is the well-developed closely-spaced jointing. In places where only poor surface exposures were available, this charac teristic served to distinguish the dikes from the somewhat porphyritic volcanic rocks that were occasionally found. The feldspar porphyry dikes are found as dike-like inclusions in the hybrid granite of the area; these inclusions are found in all stages of assimilation, and appear also as resistant patches of unaltered dike in the granite. This indicates that the age of the dikes is pre-granite and post-anorthosite complex, because they are found cutting both the volcanic rocks and the anorthosite.

Granitic Rocks The granitic rocks of the area are mostly granodioritic and dioritic in com position. In the following discussion the terms "granite", "granodiorite", and "diorite" imply the gneiss of the same composition. In fact, the gneisses are more common than the massive granites. The grey quartz diorite forms the bulk of the granitic rocks. The rock is medium- to coarse-grained, and light to dark grey with pink streaks and patches. The average composition of the rock is as follows: quartz, 20-35 percent; albite- oligoclase, 30-60; and biotite-amphibole, 0-40 percent. Other minerals are 14 Geological Report No. 23 sericite, calcite, and chlorite. Zircon and apatite are locally present as accessory minerals. The amphibole-biotite content is greatly dependent on the amount of assimilated material. The inclusions of metasediments of the quartz-biotite- amphibole-plagioclase schist variety are common, despite the fact that no sedimentary rocks are found in the vicinity. The inclusions are to be found in all stages of incorporation in the quartz diorite. They are mostly recrystallized into amphibolide quartz diorite, diorite, or amphibolite, depending on the original composition of the sedimentary rocks. The amount of incorporated sedimentary material determines the over-all composition of the quartz diorite. The bulk of the grey quartz diorite mass seems to have formed by anatexis (granitization?) of the sedimentary rocks. The Jackfish Bay granite mass is a good example of granitization in the map-area. Various rock types, from diorite to orthodox granite, exist in great profusion, and in greater confusion, throughout the mass. Blocks (several hundred square feet in area) of recrystallized sedimentary and volcanic rocks are suspended in the quartz diorite and are, themselves, quartz dioritic in com position. The enclosing quartz diorite may in turn rest in sharp contact against anothei type of quartz diorite. The boundaries between various rocks are very sharp; the major changes across the boundary are in the biotite-amphibole content. The Jackfish Bay mass seems to represent multiple stoping and anatexis of the overlying rocks that occurred in such a way that each succeeding block was immersed in a melt made more basic by the assimilation of previous xenoliths. Magmatic stoping is illustrated well on Echo Point where huge blocks of volcanic rocks are cleaved and suspended in a granodiorite and granite. This characteristic of the magmatic stoping is to be found all along the volcanics-granite contact. The contact is very sharp, but no chilled borders were observed. The pink microcline granite and granodiorite are younger and intrude the grey quartz diorite. The rock is fine- to medium-grained, and is composed of 25-35 percent quartz, 10-30 percent microcline and 20-50 percent plagioclase (albite-oligoclase). Biotite accounts for 2-10 percent of the rock and is the only ferromagnesian mineral present. The granite is generally found as dikes or small stocks, and the granodiorite as larger bodies associated with the quartz diorite. The granodiorite accounts for about 40 percent of the granitic rocks. Where the rocks are gneissic, the microcline in the rock tends to be segregated into irregular bands. The individual microcline crystals tend to be larger than those of the surrounding minerals and have apparently grown in-place. Complete gradation exists between quartz diorite and granodiorite. There is considerable evidence that much of the granodiorite and granodiorite gneiss is the result of potassium metasomatism. The true pink granites exist (in the granite areas) as irregular bodies of limited size (no greater than half a mile in diameter) and generally have transitional boundaries with the granodiorite. The pink granite areas probably represent centres of potassium metasomatism. That this granite was probably in a nearly molten state is indicated by the presence of numerous granite dikes that cut both the granodiorite and quartz diorite; on the other hand, the granodiorite and quartz diorite, if molten, were not as mobile. No dikes are found that would correspond to quartz diorite. The border phases of granitic rocks in contact with volcanic rocks, sedi mentary rocks, or anorthosite, are ordinarily granodioritic to granitic in com position and relatively poor in ferromagnesian minerals. However, the centres 15 Big Trout Lake Area of such bodies, as well as the general granitic terrain, are more granodioritic to quartz dioritic in composition with a higher proportion of ferromagnesian minerals. The granite porphyry is associated with the granite masses in the western part of the area, and its composition is identical to that of the pink microcline granite from which it probably originated. The feldspars are present as pheno- crysts in a fine- to medium-grained granitic groundmass. The granite porphyry dikes may be younger than the feldspar porphyry dikes. Pegmatites of the younger intrusive are more common, and are generally bi- mineralic, in this case composed of quartz and microcline. They occur as stringers and as small irregular bodies grading into the normal pink granite. A clear-cut age- relationship between the older and younger granites is observed where the pink pegmatites and granite cut the grey granodiorite.

Basic Dikes Basic dikes, of diabase, basalt, basalt porphyry, and coarse gabbro equiva lents, are found cutting all rocks of the area. They are especially prominent in the basin of Big Trout Lake, but are to be found also in the Severn River area. A 100-foot-wide dike is found on the Severn River, 2 miles upstream from the Bearskin Lake post. This rock can best be described as a medium- to coarse- grained gabbro. Most dikes are 1-20 feet wide. The rock is fine-grained, dark green to black, and in some places porphyritic, diabasic, or massive. There is no well-defined trend to the dikes, but the general strike appears to be in northerly and north easterly directions, corresponding with the major joint directions of that par ticular area. As in the case of porphyry dikes, most of the diabase dikes are rather erratic in nature, pinching and swelling, following curved paths, or stopping abruptly. The cross-cutting relationships clearly indicate the diabase dikes to be younger than the granite or the porphyry dikes.

Pleistocene Geology The area has suffered at least two distinct and recognizable periods of glaciation. Most of the evidence of the earlier glaciation has been obliterated by the later Labrador glacier. J. B. Tyrrell (1913b) postulated an earlier glaciation called "Patrician" with a centre located several miles southeast. He based his conclusions on a number of observations of glacial striae and stoss-and-lee relationship of glacial erosion on outcrops. Though the concept of Patrician glaciation has fallen into disfavour in recent years, there is, nevertheless, considerable evidence to support it. The movement of the ice from the southeast to the northwest resulted in deep scouring and grooving of the rock. The scourings may be found on the protected southern exposures of outcrops, and on very low outcrops that may have been protected by till. That this glacial movement from the southeast was more than a merely local phenomenon is indicated by a persistent strike of striae of about N.400W. found over a wide area. No surficial deposits were found that could be attributed to this glaciation. The Labrador glacier is responsible for most of the surface topography and drainage pattern now found in the area. The general direction of flow of ice was S.300W. in the eastern and S.450W. in the western part of the map-area. The 16 Geological Report No. 23 eastern part of the area is covered by thick glacial drift grooved into a series of low, parallel drumlinoid ridges. The ridges are, on the average, l mile long and about 1,000 feet wide. Similar features may be found in southern and north eastern parts of the map-area. Two distinct till layers have been observed in a pit at the Trout Lake post. The lower till is pale yellow (Munsell chart hue 2.5Y, 7/4) and about 8 feet thick, and rests on a thin layer of gravel that directly overlies the bedrock. The upper till, light yellow-brown (Munsell chart hue 10YR, 6/4), and 5-10 feet thick, rests with a sharp contact on the yellow till. At another pit exposure, squeezing of the yellow till in the form of a lens into the brown till was observed. All colour comparisons were made on dry samples. Another till, grey to green in colour, is found exposed along the banks of the Fawn River. Relationship of this till to the two at the Trout Lake post is unknown. The study of the two tills at the Trout Lake post shows them to be different in this respect. The lower yellow till contains a greater proportion of dark igneous pebbles; the upper brown till contains a greater proportion of pebbles of Paleozoic rocks, as well as a few fossils. STUDY OF Two TILLS AT TROUT LAKE

Number Mafic Sedimentary of Pebbles Granite Igneous percent percent percent 297 20.9 10.1 69.0 Yellow lower till 544 21.5 24.3 54.0

PARTIAL CHEMICAL ANALYSIS OF Two TILLS AT TROUT LAKE

Total Iron Fe2O3 CaO MgO percent percent percent 1.81 14.53 3.80 2.75 16.53 4.22

The genetic relationship of the two tills is not clear. The only source of the Paleozoic sedimentary rocks lies northeast of the map-area, indicating that the two tills were derived from essentially the same area. The somewhat greater fissility of the lower till and the similar chemical composition of the two tills would indicate that the lower till could be a lodgement till, the upper an ablation till, both deposited by the Labradoi glacier. Bedded, cross-bedded, and ripple-marked deposits of sand can be found as ridges along the south shore of Weir Lake, the north shore of Sandybank Lake, the north shore of Big Trout Lake, and the Minko Bay shores of Big Trout Lake. A cross-sectional exposure of a 50-foot ridge on the north shore of Big Trout Lake shows gradation toward the east from very fine grained (minus-200-mesh) silty sand with ripple marks to a very coarse crossbedded beach sand and gravel along the eastern flank of the ridge. The ridges probably represent an old beach of a proglacial lake, the predecessor of Big Trout Lake. Eskers are numerous and more or less continuous. They generally follow the direction of the last glacial movement, except in the vicinity of the Makoop River and Severn Lake, where they trend in an east-west direction. The material 17 Big Trout Lake Area of the eskers is the normal bedded sand and gravel. The pebbles and cobbles are principally granitic, but diabase and volcanic pebbles are also present. There is also a minor amount of chert and limestone pebbles. Recent Deposits River gravels, and clays, swamp accumulations and beach sands and gravels comprise the recent deposits. The Severn River is silt-laden, and wherever the current slackens, either by debouching into a lake or by widening of the river, deposits of silt and clay braid the river into several channels. The deposits in a lake form broad flat plains through which the river has cut deep channels. Under normal conditions, the mud flats are submerged about 1-2 feet under water.

Peat deposit on the west shore of Big Island; exposure of the peat was due to the unusually low water-level in Big Trout lake in the summer of 1961. This picture serves to illustrate the drop in the water-level throughout the area as a result of two excessively dry years.

Peat deposits were found in two localities, one in the extreme northeast corner of the area, the other on the west shore of Big Island. The latter deposit was exposed by an unusually low water-level. The shores of Big Trout Lake, especially the eastern and southern parts, are characterized by extensive sandy and pebbly beaches. The sand along the south shore forms several parallel offshore bars. An interesting feature along the south shore beaches is a single sand ridge that rises as high as 15 feet. The ridge was probably formed by storm waves at a time when the water-level of the lake was slightly higher; it is now stabilized and undergoing erosion. Inland from the ridge, the land is generally swampy. Pebbles were examined on the pebble beaches in the vicinity of Post Island. The pebble counts were prompted by the presence of iron-bearing pebbles that seem to be in greater concentration in the vicinity of Post Island than anywhere 18 Geological Report No. 23 else. A number of pebbles of similar type were found for a distance of 50 miles in an up-glacial-flow direction. The pebbles were principally siliceous siltstones and quartzite containing hematite. Two of the largest pebbles were analyzed by the Laboratory Branch of the Ontario Department of Mines; the analyses showed, respectively: 8.6 percent iron, 48.8 percent silica; and, 8.2 percent iron, 74.2 percent silica. Strips 2 feet wide and 12 feet long, the long direction perpendicular to the beach, were selected at various localities, the two end sites being separated by about 4 miles; the locations (not shown on map No. 2045) are on the mainland shoreline beaches of Big Trout Lake northeast of Post Island. Samples for examination wore taken from the first layer of pebbles and cobbles; the sand fractions were estimated. The results were as follows: PEBBLE COUNT, BIG TROUT LAKE

Fine Coarse- Iron- grained grained bearing Location Granite Igneous Igneous Limestone Chert Pebbles Rock Rock percent percent percent percent percent percent 1...... 26 60 8.6 4.0 0 1.4 2...... 35 55 3 4 1.6 3...... 27 57 5 8 1 1.4 4...... 23 66 4 2 4 1.2 5...... 21 66 0 1 8 4.0 26 61 3 4 4 1.9

SAND FRACTION, BIG TROUT LAKE

Granite Dark (mafic) Light (sedimentary) 20 60 20

The marked difference between till and beach pebble concentrations is in the volcanic and basic intrusive pebbles. This reflects the fact that the pebbles picked were, on the average, much larger than the till pebbles and obviously of local derivation. The rock particles in till range from sand- to pebble-size, the small pebbles predominating.

DESCRIPTIONS OF THE VOLCANIC-SEDIMENTARY BELTS The volcanic rocks and the associated sedimentary rocks that have been generally described in the previous section are shown in the accompanying figures. A detailed description of each belt is given below.

Big Trout Lake Belt Much of the general discussion concerning the volcanic rocks (pp. 8, 9) is directly applicable to the Big Trout Lake belt because the bulk of these rocks is found in the basin of this lake. The main body of volcanic rocks is composed of alternating layers of varying thicknesses of massive volcanic rocks and pillowed lavas. The several occurrences 19 Big Trout Lake Area

Chill border between two massive volcanic flows; south shore of Ernie Island, Big Trout Lake.

Sheared bedded conglomerate on a small island 2 miles south of Big Island in Big Trout Lake. The relationship between bedding and shearing indicates the exposure to be on a north limb of a syncline.

20 Geological Report No. 23 of chilled borders between massive flows would indicate that the rocks were built up by several outpourings of lava. Why pillowed lavas alternate with massive volcanic rocks is not clear; the explanation undoubtedly depends on the method of formation of pillowed lavas, which at present is not well understood. The Big Trout Lake belt is an excellent locality for the study of pillowed lavas and their formation; the pillows are well-preserved, generally unaltered, and associated with various other volcanic rocks. The more altered and sheared volcanic rocks are found along the axes of the main folds and in the vicinity of the granite and anorthosite intrusives. Around the periphery of the anorthosite body and in some of the thicker flows, the rock becomes gabbroic in texture. The notable feature of the Big Trout Lake belt is the almost total absence of sedimentary rocks in direct association with the lava flows. The only occurrence of note is a jasper-pebble conglomerate found in two shoals in the middle of Big Trout Lake. The shoals were found exposed only during the second summer in the area, at which time the water-level was very low. A sheared conglomerate and agglomerate are found on a rocky island in the same area. These sedimentary rocks are very unlike any seen in other parts of the area and may represent a much younger deposit. They appear to occupy the trough of a syncline, another factor in favour of their younger age.

Kino Lake Belt The Big Trout Lake belt, which is the main volcanic belt that occupies the basin of Big Trout Lake, splits into the Kino Lake and Fat Lake belts at the west end of Big Trout Lake; here, the Kino Lake belt trends northwesterly. The belt curves in a gentle arc and at Severn Lake the general strike is southwest. The belt apparently pinches out southwest of Severn Lake. At Big Trout Lake the rocks are mainly pillowed and massive volcanic rocks with occasional tuff and sedimentary beds. The sedimentary beds increase in number to the west and are interbedded with the lava flows at Kino Lake. The lava flows are intermediate to basic in composition, massive, and fine- and coarse-grained in texture. Thin tuffaceous bands occur within the volcanic rock sequence. The sedimentary rocks are siliceous greywackes and sericitized impure quartzites. They are only a few hundred feet wide; most of the rocks are of volcanic origin. A small body of peridotite is exposed for about 150 feet on the west shore of the narrows between Misikeyask Lake and Miku Lake. The rock is composed principally of serpentine and chlorite, is highly sheared, and occurs next to the contact with the granite. At the west end of Kino Lake, the belt narrows abruptly. West of Kino Lake, an outcrop was observed at Severn Lake where metasediments and tuffs constitute most of the rock. The tuff bands are narrow, 10-20 feet, and often contain a few l-inch-wide magnetite bands. The total width of the magnetite- rich zone is about l foot. The sedimentary rocks are highly metamorphosed and recrystallized to amphibolite and quartz-feldspar-amphibole schist. The belt thins and pinches-out west of Severn Lake. The rocks are strongly sheared and dragfolded. The B-lineation of the sheared rocks plunges in a northeasterly direction at the east end of Severn Lake, is nearly horizontal in the west half of 21 Big Trout Lake Area the lake, and plunges in a southwesterly direction at the west end of the lake. Bedding-plane(?) faults have been observed within the sedimentary rocks. North of and parallel to the Kino Lake belt is a short belt of metasedimentary rock, now composed of quartz-feldspar-biotite schist. Magnetite bands similar to those of the Kino Lake belt are found. The belt is cut by numerous dikes of granite and pegmatite and probably represents a remnant of infolded sedimentary rocks related to the Severn Lake belt.

Banded dragfolded metasedimentary rocks; east shore of Severn Lake.

A very small narrow metasedimentary belt crosses Fawn Lake just south of Kino Lake. The rocks are quartz-feldspar-biotite schist, similar to the ones described above. All three of the above belts have a regional schistosity paralleling the long axis of the belts. Dragfolds that have an easterly plunge are numerous. The sense of movement indicated by the dragfolds suggests that the north side moved east relative to the south side. Fat Lake Belts The northern branch of the Big Trout Lake belt swings in a north-north westerly direction east of Misikeyask Lake, and is joined at Arguing Lake by the westerly-trend ing Northern belt. The combined belts continue in a northwesterly direction to Fat Lake,1 and beyond. At the middle of Fat Lake, the belt is split by granite into two narrow extensions that are best exposed on the Severn River; these two extensions are named the Fat Lake north belt and the Fat Lake south belt. ©Fat Lake is the name recognized officially by the Canadian Board on Geographic Names. The name Winnin Lake is incorrect, although it appears on Preliminary Maps Nos. 89 and 121, and in Preliminary Reports Nos. 1960-4 and 1961-9. (There is a lake officially named Weenin, but this lies north of the present map-area at approx. Lat. 54038©N., Long. 89055©W.) 22 Geological Report No. 23

The southern boundary of the belt is composed principally of sedimentary rocks and volcanic tuffs. The rock types range from impure quartzites to quartz-chlorite schist. The principal rock, however, is a banded greywacke that is dark grey and mostly fine-grained. Most of the belt, especially the northern part, is composed of volcanic rock that is intermediate to basic in composition, and medium to dark grey and green. The volcanic rocks are found principally as massive flows, but pillowed lava and agglomerate are also found. The rocks of the Fat Lake south belt crossing the Severn River change progressively across-strike from greywacke on the southwest to strongly sheared talc-chlorite schist, then to banded tuff and conglomerate, and finally to basic volcanic rocks on the northeast. Some parts of the volcanic rocks strongly affect the compass needle. Because close field examination failed to reveal the presence or exposure of magnetic minerals, it is assumed that the magnetic rock must lie some distance below the surface. Similar magnetic disturbance was observed roughly along-strike at Fat Lake where some pieces of float were found to contain magnetite in sericite schist. The Fat Lake north belt crosses the Severn River about 8 miles downstream from the Fat Lake south belt. The rocks in the northern extension are all siliceous tuffs cut by numerous pink granite and pegmatite dikes. The rocks are dragfolded and the folds have an easterly plunge of 400. Pyrite mineralization is common in the more siliceous parts of the tuffs. Severn River Belts Three narrow belts cross the Severn River northeast of the above occurrence. The most northeasterly lies just south of the junction of the two branches of the Severn River. The Severn River south belt is very narrow (about 24 mile) and strikes a little north of west. It is composed of completely indurated silicified volcanic tuff. The rock is very hard and forms rapids and falls on both branches of the river; the falls on the northern branch, Akem Falls, have a vertical drop of 40 feet in a distance of about 100 feet. The southern edge of the belt presents a perfect example of granitization. A complete transition can be traced, across the strike, from banded granite gneiss to silicified volcanic tuffs. The Severn River middle belt is a remnant of a sedimentary belt that has been thoroughly granitized. It is no more than Y^ mile wide, and for the most part it is composed of very coarse, porphyritic biotite-rich, crumbly pink granite, with abundant large inclusions and long bands of biotite-amphibole rock repre senting the original sedimentary rock. On the north branch of the river these inclusions are mineralized with pyrite, pyrrhotite, and chalcopyrite. The Severn River north belt is estimated to be about l mile wide, and is composed principally of metasediments. Most of the rock is in some stage or other of transformation to granite gneiss. The northern part of the Severn River north belt is made up of a band, about 2,000 feet wide, of tuff and pillowed volcanic rocks. The rock between the middle belt and the north belt is a grano diorite and quartz diorite gneiss derived by granitization of the sedimentary rocks of these belts. The two most northeasterly belts probably converge somewhere east, because rocks of similar type have been found in two different areas along the strike, in lakes just south of Witegoo Lake. 23 Big Trout Lake Area

Northern Belt The Northern belt, an east-west belt lying north of Big Trout Lake, joins the Fat Lake belt at Arguing Lake, and extends east to, and crosses, the Fawn River and the Otter River. Exact boundaries cannot be definitely established owing to lack of outcrops, but contacts have been found within Y^ mile in several places. The rocks appear to be principally pillowed and massive volcanic rocks, with some quartz-talc schists and chlorite schists near the southern contact with granite. At Fawn River, the belt is less than 2 miles wide, but continues with approximately the same width southeastward and crosses the Otter River. A very coarse-grained rock, grading from gabbro to diorite in composition, was found on a small lake about 6 miles northeast of Minko Bay. The rock was included under the anorthosite unit in the map legend for lack of better cor relation. Nemeigusabins Lake Belt Most of the rocks of the Nemeigusabins Lake belt (see Figure 2) are altered volcanic rocks that are more altered than those of other belts. The volcanic rocks are pillowed, fine-grained, and chloritic. Some of the thicker flows are medium- to coarse-grained gabbroic rocks. The colour is dark to light green. Some beds of sedimentary rocks are present east of Nemeigusabins Lake. The belt is at least 5 miles wide at Nemeigusabins Lake, but seems to end or curve abruptly to the east and west; no exposures of the volcanic rocks were observed outside the map-area on the Asheweig River or on Long Dog Lake to the east. The possible western extension of the belt is masked by thick over burden. Reconnaissance flights to the small lakes west failed to reveal any outcrops of volcanic rocks.

Garrett Lake Belt A presumably small sharply curving sedimentary and volcanic belt exists on the river between Garrett Lake and Makoop Lake (see Figure 2). Owing to the difficulty of travel on the river, it was impossible to obtain more than a sketchy idea of the extent of this belt. Its shape, as presented in Figure 2, is also somewhat conjectural. The metasediments are of the quartz-biotite schist variety. Indistinct pillows were observed in the volcanic rocks.

STRUCTURAL GEOLOGY Some aspects of structure have already been discussed in dealing with the individual volcanic-sedimentary belts. However, because all rocks in the map- area are a part of a general regional picture, structure as a whole must be taken into account. In gathering structural information in the field, particular attention was paid to small shears, prominent joints, and lineations in the rocks. Interpretation of air photographs was carried out, and all linears and trends (except north easterly) were plotted; those with a general northeasterly direction were not 24 Geological Report No. 23 plotted because in these it was impossible to distinguish between a bedrock linear and a glacial linear feature. A higher degree of correlation was found to exist between air-photo linears and ground measurements.

Faulting of a competent sedimentary band, without apparent effect on the surrounding rock, indicates plastic or mobile state of the rocks; east shore of Severn^Avorn Lake.In Ir A

The first observation on the structure of the area is the over-all east-west and northwest trends of rocks, corresponding to the general trend in the Keewatin Province. The variations imposed on this regional trend are the result of great batholithic intrusions. The primary structure of the Big Trout Lake belt is a large, easterly-plunging anticlinorium. The easterly plunge of lineation is characteristic of the rocks of the area. The vertical sections, a, b, c, d, in Figure 3 serve to illustrate the general aspects of the structure. These vertical sections, highly idealized, are drawn along the lines indicated on Figure 2. Evidence of secondary flexure folding related to batholithic intrusions is found in the configuration of the belts, in the trends of the linears, and in the persistent jointing and shearing that cannot be assigned to the primary folding of the belts. The controlling feature for the secondary structures appears to be a large circular batholith with its centre about 20 miles east of Makoop Lake and extending to the Severn Lake Big Trout Lake volcanic belts. A radial and concentric pattern is evident in the arrangement of the drainage. The radial 25 Big Trout Lake Area

j——— Synclinal axis.

Anorthosite intrusive. l ——j Anticlinal axis.

Volcanic and sedimentary rocks. Drag-folds.

Geological boundary. Lineament.

H A Line of section. See opposite page.

Scale of Miles 10 20

O.D.M.1188

Figure 2 (above) — Sketch map of the major structural features of the Big Trout Lake area.

Figure 3 (opposite) — Cross-sections along lines indicated on Figure 2.

26 Geological Report No. 23

: :"i©: Anorthosite intrusive. * Volcanic and sedimentary rocks.

Horizontal Scale, l inch to 10 miles O.D.M.1189

27 Big Trout Lake Area linears, trending northeasterly to northwesterly are reflected in the jointing and shearing patterns on the ground. The axes of flexures probably parallel the joint directions and shear directions. Chalcopyrite and quartz mineralization is found filling some of the radial fractures in the eastern part of Big Trout Lake and concentric fractures in the western part of the map-area. The displacement of the rocks, as shown by dragfolds, indicates that the northern parts moved eastward relative to south. In the Severn Lake Kino Lake belt, this movement parallels the concentric pattern of the linears, and is found both inside and outside the belt. Local but intense folding is evident in the rocks of Jackfish1 Lake in the Fat Lake belt. The drainage pattern strongly indicates that the Fat Lake belt and the Severn River belts continue northwestward and join with the Schmitt and Stables lakes belts which were described by Meen (1938).

HISTORICAL GEOLOGY To better understand the distribution of the rocks and structure in the area, a chronological sequence of geological events might be helpful. The sedimentary rocks are presumed to be of a similar, or perhaps a slightly younger, age than the volcanic rocks. They are commonly interbedded. The sedimentary rocks are apparently more abundant in the lower beds of the vol canic-sedimentary belts in the western part of Big Trout Lake, and more abundant in the stratigraphically higher position in the eastern part of the map-area. To explain this relationship, it is necessary to assume that volcanism was initiated in the basin of Big Trout Lake, spreading westward the erosional products as sediments. Volcanic activity then gradually spread westward. After the cessation of volcanism, a sedimentary blanket was laid over the volcanic rocks. The remnants of this blanket are found around the nose of the anticline and in the syncline of Big Trout Lake. After the deposition of volcanic and sedimentary rocks, anorthosite intruded in the form of a sill. The sill intruded approximately along the contact between the volcanic rocks and the sedimentary rocks. The initial thickness of the sill is probably shown by the thickness of the southern arm in the southeast part of Big Trout Lake. The intrusion must have occurred at considerable depth, because no chill phenomena are evident, and the coarseness of the rock coupled with differentiation banding of the sill indicates very slow cooling. There is some evidence that part of the sedimentary rock overlying the sill was incorporated or recrystallized into the anorthosite body; this is indicated by inclusions of sedi mentary rocks with gradational contacts into anorthosite, and the high quartz content of the anorthosite near the sedimentary rock contact. The rocks were then folded into a series of anticlines and synclines. In the eastern part, the net result of folding was a large anticlinorium. Concurrent with or closely following the folding was the intrusion of large granitic batholiths. The shears, granite dikes, and quartz veins, all of which are found cutting the folded rocks, would suggest that the batholithic intrusions were the final orogenic phase. The batholiths have refolded what once probably were east-west trending folds into their present arcuate trends. The large batholiths in the southwestern and

1Jackfish Lake is the name recognized officially by the Canadian Board on Geographic Names; the lake was formerly known as Mandanne. 28 Geological Report No. 23 western parts of the map-area lifted the folded rocks into their present easterly- plunging position. The batholiths have also incorporated, by syntexis, most of the former sedimentary rock cover. The evidence of this is the ubiquitous presence of inclusions of the sedimentary rock in all stages of assimilation deep within the granitic batholiths. Erosion and peneplanation, followed by glaciation, have resulted in the present morphology of the region.

ECONOMIC GEOLOGY Very little prospecting activity has been reported from the area. The only signs of mineral exploration are several pits, and two shallow drillholes on the southeast tip of Big Island in Big Trout Lake. The work was done some 25 years ago with the hope of discovering gold. No gold was found, and only low copper assay values were reported, by Consolidated Mining and Smelting Company of Canada Limited. 1 Early in 1960, a group of claims was staked on a reported copper showing on the east shore of Minko Bay in Big Trout Lake. As a result of a preliminary report by the writer (Hudec 1960) on the first summer©s mapping, 36 claims were staked on a zinc showing in the vicinity of Kino Lake. Trenching and prospecting, as well as routine geologic mapping of the claim group, was carried out during the summer of 1961. Some 240 claims were staked in the vicinity of Derniere Lake following the publication of the second preliminary report (Hudec 1961) in which an occurrence of massive and disseminated sulphides was described. Prospecting, ground and airborne surveys were carried out by exploration companies.

Copper Copper mineralization, although minor, is persistent throughout the area. The most common occurrence of copper is in quartz veins cutting volcanic rocks. The width of the veins is from a few inches to two feet. Generally only one or two veins have chalcopyrite, although the volcanic rocks are cut by a number of quartz veins in the immediate vicinity. The veins seem to represent late-stage hydrothermal deposits, mainly fracture-fillings, and are probably related to the granite intrusions. They are generally found in prominent shear zones. Following are the four locations of quartz-chalcopyrite mineralization noted by the writer: east shore of Minko Bay, south shore of Ernie Island, north shore of Bibby Bay, south part of Nemeigusabins Lake. Hydrothermal replacement of volcanic rocks by sulphides containing minor copper was observed on the southeast tip of Big Island in Big Trout Lake. Pits and two diamond-drillholes were put down years ago over the showing, but returned only scattered chalcopyrite mineralization with low copper assay values. The sulphides are principally pyrite and pyrrhotite, and are present as massive and disseminated replacement of the volcanic rocks. Two more chalcopyrite occurrences were found within ^ mile of the above showing: a 1-inch-wide seam of chalcopyrite in the volcanic rocks, found on the south shore of Big Island; and,

J Letter from D. C. McKechnie to J. Satterly, dated 9 March 1940. Drillhole No. l, 466 feet; No. 2, 504 feet in length. 29 Big Trout Lake Area

30 Geological Report No. 23 a pyrite-pyrrhotite-chalcopyrite replacement of the chill border of pillows, found on one of the small islands just off Big Island. An interesting prospecting area is the Fat Lake belt of volcanic rock, espe cially near its northern boundary. The belt is split by a granite body that has caused folding, shearing, and faulting. Strongly contorted tuffs on Jackfish Lake, 2 miles northeast of Fat Lake, indicate considerable disturbance in this area. The volcanic rocks and tuffs have been mineralized, chiefly by pyrite. On a portage between Fat Lake and a small lake to the east, a sequence of mineralized tuff bands is encountered. Mineralization is disseminated, consisting of pyrite and pyrrhotite. Similar mineralized float has been found on the north shore of Jackfish Lake. On the south shore of Derniere Lake, a highly mineralized zone, at least 30 feet wide, was discovered. The zone is impregnated with pyrite and pyrrhotite, but seams of chalcopyrite were also observed. A body, 3 feet wide, of massive pyrrhotite and pyrite occurs within the zone. It is visible only at low water and probably forms a discontinuous lens within the mineralized zone. The visible lateral extent of the zone is about 1,000 feet. The preliminary exploration by mining companies in the area indicates that the zone extends for at least a mile both northwest and southeast of the Derniere Lake showing. A hole drilled in 1962, immediately northwest of Derniere Lake, has cut a mineralized zone very similar to that in the showing. The massive sulphides are found in a brecciated volcanic rock, and the disseminated mineralization is found in banded tuffs or sedimentary rocks. A granite contact is indicated within 500 feet north of the Derniere Lake showing and parallels the mineralized zone. Samples taken by the writer from different localities along the zone and from the massive sulphides were assayed by the Laboratory Branch, Ontario Department of Mines, Toronto, and were found to contain only traces of copper, nickel, zinc, and gold. Similar results were obtained when the drill core mentioned above was assayed. The inclusions and remnants of the metasediments in granite of the Severn River middle belt are mineralized with chalcopyrite, pyrite, pyrrhotite, and magnetite. A grab sample taken by the author assayed 0.12 percent copper. The fact that every inclusion examined on the northern branch of the Severn River was consistently mineralized might warrant some prospecting. The mineralized rock is composed principally of biotite and amphibole, and about 10 percent apatite and 10 percent combined sulphides and magnetite. Similar inclusions that were less amphibolitic, found in the Severn River middle belt but on the southern branch of the Severn River, were not conspicuously mineralized.

Zinc A gossan was observed in the sedimentary rocks along the south shore of a small lake north of Kino Lake. The mineralization, in the form of sphalerite, is present within a band of highly silicified and sericitized impure quartzite found within the volcanic rocks. The mineralization is not continuous and fades out east of the showing. However, a similar but rather small occurrence has been found along-strike at two other points on Kino Lake. An assay of 1.88 percent zinc was obtained from a selected sample taken here by the author. Extensive and complicated faulting in the vicinity of Kino Lake indicates that further prospecting is warranted. 31 Big Trout Lake Area

Iron MAGNETITE-ILMENITE IN ANORTHOSITE As mentioned in the description of the anorthosite intrusive, magnetite and ilmenite are found concentrated along the stratigraphic bottom of the sill. Magnetic anomalies, of the magnitude of 500-700 deflection of a dip needle, were observed over the contact of anorthosite and the volcanic rocks. Normal readings of a dip needle were from 00-100 north. The anomalies were observed in Big Trout Lake, in which the average depth of water is greater than 50 feet, and are greater in magnitude than any found on land directly over magnetite-ilmenite con centrations. The location of the anomalies is shown on map No. 2045. The magnetite-ilmenite mineralization found on land exists along the southwest shore of a peninsula south of the post at Trout Lake, and on Camp Island in the eastern part of Big Trout Lake. In these localities, the magnetite-ilmenite mineralization constitutes up to 40 percent of the rock. A maximum dip needle anomaly of 900 was observed near the south shore of Big Trout Lake in the vicinity of Leopard Point. The anomaly was recorded for a distance of 300 feet in an open part of the lake in an area indicated on map No. 2045. The cause of this anomaly is thought to be a high concentration of magnetite, although the anorthosite rock in this area is relatively free of this mineral. Gold Gold mineralization was reported from the area, in 1946 by C. H. Riordon of Conwest Exploration Company, principally in the northwestern part of the map-area at Fat Lake and in the narrow belts crossing the Severn River. These belts probably extend into and join with the volcanic belts in the Sachigo River area, which lies about 50 miles west of the present map-area. Gold has been mined at Sherman Lake, by Sachigo River Exploration Company Limited, during the period 1938-1942. Total production was then valued at 31,951,084, but operations have long since been suspended. None of the samples submitted by the author for assay returned more than a trace of gold.

BIBLIOGRAPHY Buddington, A. F. 1939: Adirondack igneous rocks and their metamorphism; Geol. Soc. America, Mem. 7. Hudec, P. P. 1960: Preliminary report on the geology of Big Trout Lake area, District of Kenora; Ontario Dept. Mines, P.R. 1960-4. 1961: Preliminary report on the geology of Big Trout Lake-Severn River area, District of Kenora (Patricia Portion); Ontario Dept. Mines, P.R. 1961-9. Kuenen, P. H., and Migliorini, C. I. 1950: Turbidity currents as a cause of graded bedding; in Journal Geol., Vol. 58, pp. 99-126. Low, A. P. 1886: An exploration of country between Lake Winnipeg and Hudson Bay (via Berens and Severn rivers); Geol. Surv. Canada, Vol. II, pt. F. Meen, V. B. 1938: Geology of the Sachigo River area; Ontario Dept. Mines, Vol. 46, 1937, pt. 4, pp. 43-46. Pettijohn, F. J. 1943: Archean sedimentation; Geol. Soc. America Bull., in Vol. 54, pp. 925-72. Tyrrell, J. B. 1913a: Hudson Bay exploring expedition; Ontario Bureau of Mines (nowOnt. Dept. Mines), Vol. XXII, pt. 1. 1913b: The Patrician glacier south of Hudson Bay; 12th International Geol. Congress, pp. 523-34. 32 INDEX

A PAGE PAGE Access...... 3 Dikes...... 7, 8, 14-16 Acknowledgments...... 2, 3 Dinwiddie Lake...... 4 Agriculture...... 5 Dragfolding, photo...... 22 Air transport...... 2,3 Drainage...... 4 Akem Falls...... 4, 5, 23 Amphibolite...... 21 Andesite...... 8, 9, 11 Eastgate Syndicate...... 30 Anomalies, magnetic...... 32 Echo Point...... 15 Anorthosite complex...... 7-9, 28 Economic geology...... 29-32 Iron in...... 12, 32 Epidotization...... 9 Lithology and photos...... 11-14 Ernie Island...... 9 Arguing Lake...... 22, 24 Mineralized veins...... 28 Ashaway Falls...... 5 Rocks, photo...... 20 Asheweig River...... 3 Eskers...... 17, 18 B Banding, notes and photos...... 10-13, 22 Farquharson, S...... 30 Basalt...... 8. 11, 16 Farr, L...... 2 Basic intrusive rocks...... 7, 16 Fat Lake...... 10, 22, 23 Batholithic intrusions...... 25, 28, 29 Gold...... 32 Beaches, pebble...... 18, 19 Mining claims on...... 30 Bearskin Lake post...... l, 6, 16 Sulphides...... 31 Bibby Bay...... 29 Faulting, notes and photo...... 25 Bibliography...... 32 Fawn Lake...... 1,22 Big Island...... 14 See also Big Trout Lake. Peat, photo...... 18 Fawn River...... l, 3-5 Sulphides...... 29, 31 Glacial deposits...... 17 Big Trout Lake...... l Rocks...... 24 Beaches, pebble...... 18, 19 Feldspar porphyry ...... 14 Bottom topography...... 4,9 Fish and game...... 5 Glacial deposits...... 17 Flowage, rock...... 25 Magnetic anomalies...... 32 Flows, lava...... 8, 9, 21 Rocks...... 8, 9, 12, 14 Photo...... 20 "leopard rock", photos...... 13 Folding...... 12, 14, 25, 28 volcanic-sediments belt...... 19-21 Formations, table of...... 7 Settlement, photo...... 6 Frost, H. A...... 2 Sulphides...... 29, 31 Volcanism...... 11, 28 Breccia, volcanic...... 9 Gabbro...... -..?, 8, 16 Mineralized...... 31 Amphibolide...... 12-14 Bright, E. G...... 2 Anorthositic...... 11, 12 Byrne, J. C...... 2 Garrett Lake...... 24 Geographic names...... l, 22, 28 Geology, economic...... 29-32 Camp Island, magnetite...... 32 Geology, general...... 7-24 Cenozoic...... 7, 16-19 Geology, historical...... 28 Chalcopyrite...... 23, 28, 29, 31 Geology, structural...... 24-28 Charlton, F...... 2 See also Folding. Conglomerate...... 20, 21 Glacial deposits...... 17, 18 Consolidated Mining and Smelting Co. Glaciation...... 16 of Canada Ltd...... 29 Gneisses...... 14 Conwest Exploration Co...... 32 Gold...... 32 Copper...... 29, 31 Gossan, zinc in...... 31 Cruickshanks, W...... 2 Granitic rocks...... 7,8 Inclusions in, mineralized...... 23, 31 Lithology...... 14-16 D Porphyritic...... 23 Dacite...... 9 Granitization...... 15, 23 Derniere Lake...... 29 Granodiorite...... 15 Mineralized zone...... 31 Greywacke...... 9-11, 21 Mining properties...... 30 Banded, photo...... 10 33 Big Trout Lake Area

H PAGE O PAGE Historical geology...... 28 Orbicular rock. Hudson©s Bay Co...... 1,6 Otter River 24 I Ilmenite...... 12, 32 Inclusions...... 11, 14, 15, 28 "Patrician" glaciation ...... 16 Mineralized...... 23, 31 Peat, notes and photo...... 18 Inhabitants...... 6 Pebbles, iron-bearing...... 18, 19 Iron...... 32 Pegmatites...... 16 In pebbles...... 18, 19 Peridotite...... 21 See also Magnetite. Phelps Dodge Corp. of Canada Ltd.. . . 30 Iron formation...... 11 Pillowed lava...... 8-11, 21, 23 Pleistocene deposits...... 7, 8 Geology...... 16-18 J Porphyries...... 8, 14, 16 Jackfish Bay...... 15 Porphyritic granite...... 23 Jackfish Lake...... 28 Post Island...... 18 Mining claims...... 30 Precambrian rocks...... 7-16 Sulphide deposits...... 31 Prospecting...... 29, 31, 32 Jointing...... 25, 28 Pukatawagon Lake...... 30 In porphyry dikes...... 14 Pyrite and pyrrhotite ...... 11, 23, 29 K Kasabonika Lake...... 3, 6 Q Keyes, R. R...... 2 Quartz-biotite schist...... 11, 22 Kino Lake...... 10 Inclusions in granite...... 15, 23 Volcanic-sedimentary belt...... 21, 22 Quartz diorite...... 14, 15 Zinc prospects near...... 29, 31 Quartz-feldspar porphyry ...... 14 Quartz veins...... 28, 29 Quartzite...... 21, 23 Mineralized...... 31 Lavas. See Volcanic rocks. Leopard Point...... 13, 14 Magnetic anomaly...... 32 "Leopard rock", notes and photos... . .12-14 Lumbering...... 5 Recent deposits...... 7, 18, 19 Riordon, C. H...... 32 M Magnetite...... 11, 12, 32 In float...... 23 Mandanne Lake...... 28 Sachigo River Exploration Co. Ltd... . . 32 Map, geological, coloured...... back pocket Sand deposits...... 17, 18 Mapping method...... 2 Sandybank Lake...... 17 Maps, sketch. Schists...... 11, 21-24 Mining properties, locations...... 30 Magnetite in...... 23 Structural features...... 26 Sections, geological...... 27 Mcintyre Porcupine Mines Ltd...... 30 Sedimentary rocks...... 7, 8, 28 McKechnie, D. C...... 29 Associated with volcanics...... 10, 11 Metasedimentary rocks...... 11, 21-23 belts, descriptions...... 19-24 Banded, photo...... 22 Faulting in, photo...... 25 Mineralized...... 23, 31 Granitization...... 15, 23 Michikan Lake...... l Lithology and photo...... 9-11 Mineralization...... 28, 29, 30-32 Sulphides in...... 31 Inclusions...... 23, 31 Severn Lake...... 17, 21 Mining properties...... 30 Rocks, photos...... 22, 25 Minko Bay...... 12, 17 Severn River...... 3, 4, 18 Copper...... 29 Rocks...... 16, 22, 23 Misikeyask Lake...... 4, 21 mineralized...... 23, 31 Mopabrow Lake ...... 4 Water power...... 5 Sherman Lake ...... 32 Sill, anorthosite...... 12, 14, 28 N Sphalerite...... 31 Natural resources...... 5 Structural geology...... 24-28 Nemeigusabins Lake...... 24, 29 See also Folding. Newconex Ltd...... 30 Sulphides...... 11, 23, 29, 31 Newmont Mining Corp. of Canada Ltd. 30 Surveys, geological...... 2, 3 34 Geological Report No. 23

T PAGE PAGE Talc schists...... 23, 24 Volcanic rocks...... 7-9, 28 Tills, notes and analyses...... 17 Belts, descriptions...... 19-24 Topography ...... 3-5 Contact, anorthosite...... 12, 21 Lake bottom...... 4, 9 granite...... 15 Trout Lake post...... l, 3 Flows, photo...... 20 Glacial deposits...... 17 Sediments associated with...... 10, 11 Iron near...... 32 Sulphides in ...... 29, 31 Notes and photo...... 6 Volcanism...... 28 Tuffs...... 9, 10, 21 Mineralized...... 23, 31 W Silicified...... 23 Water power...... 5 Tyrrell, J. B...... 3, 16, 32 Weir Lake...... 17 Winnin Lake. See Fat Lake. Witegoo Lake...... 23 V Z Veins, mineralized...... 28, 29 Zinc...... 29, 31

S.OOO-S16S mh-196S 35

Map 2045 Big Trout Lake Area.

Glacial striae.

Sand and gravel. Strike and dip of schistosity.

Esker, Strike of vertical schistosity.

Small rock outcrop. Strike of schistosity, dip unknown.

Boundary of rock outcrop. Strike and dip of gneissosity. Sulphide mineralization

Geological boundary, defined. Strike of vertical gneissosity.

Scale, l inch to 200 miles Geological boundary, approximate. Stratiform foliation, inclined. N. T. S. reference 53 G, 53 H, 53 l, 53 J

Geological boundary, assumed.

Strike and dip; direction of top unknown.

^, O o0 Strike and vertical dip; direction of top Lineation (plunge known, plunge un F. River,creek, stream, R = rapids; F falls unknown. known).

Direction (arrow) in which inclined beds face as indicated by cross bedding. Jointing, inclined. Trail, portage, winter road.

Direction (arrow) in which overturned beds face as indicated by cross bedding; Lake bottom contours in feet. dip in direction of loop. Datum lake level.

Direction in which lava flows face as Drag-folds. (Arrow indicates direction of indicated by shape of pillows. plunge).

LEGEND

CENOZOIC*

RECENT Beach sand and flood plain deposits. Fine organic lake bottom sediments. Peat, sphagnum moss.

PLEISTOCENE Boulders. Raised beach deposits. Esker sands, gravels. Non-stratified pebbly till. 54W UNCONFORMITY

PRECAMBRIAN** BASIC DIKES Ga Gabbro, gabbro porphyry. 6b Basalt, basalt porphyry. Gc Diabase. INTRUSIVE CONTACT GRANITIC ROCKS 5a Granodiorite gneiss, quartz diorite gneiss. 5b Grey quartz diorite. 5c Pink granodiorite, 5d Granite. 5e Pegmatite. INTRUSIVE CONTACT PORPHYRY DIKES***

4a Feldspar porphyry. 4b Quartz-feldspar porphyry.

INTRUSIVE CONTACT ANORTHOSITE COMPLEX 3a Amphibolite. 3b Gabbro. 3c Anorthosite gabbro. Rocks down the Otter River an t ran i tlc. A narrow uolcinlc- 3d Gabbroic anorthosite. ntery belt crosses the Otfei River at 53*56' latitude, Stilks of the belt li H551V, See Prilimfnary Guloifcal Mep 3e Anorthosite. No. P. 121. 3f Diorite. ___ O 3g Quartz diorite. INTRUSIVE CONTACT SEDIMENTARY GROUP**** 2a Conglomerate. 2b Amphibole-chlorite schist. 2c Quartz-biotite-amphibole schist, 2d Banded greywacke, waterlaid tuff. 2e Greywacke, subgreywacke. 2f Quartzite.

Tht rocks for fifteen miles up tht Severn River vt (ranHie, df VOLCANIC GROUP**** Si, b, e, d,* vlfiety. Fine-grained extrusive rocks. la Amygdaloidal basalt, agglomerate, tuff. J 1 b Pi l lowed basalt. 1c Massive basalt, id Pillowed andesite. 1e Massive andesite. If Massive dacite.

Coarse-grained volcanic or basic intrusive rocks. 53050' 1g Diorite. 1h Gabbro.

*Unconsolidated deposits. Cenozoic deposits coincide with the lighter coloured or other areas in which out crops are absent or have not been mapped. For the most part these areas are covered with muskeg or swamp. -~ fLJ~\ **Bedrock geology. Outcrops and inferred extensions of each rock map unit are shown, respectively, in deep and light tones of the same colour,

***Not mapped in separate colour. ****Sedimentary and volcanic groups are interbedded and probably equivalent in age.

ONTARIO DEPARTMENT OF MINES HON. G. C. WARDROPE, Minister of Mines D. P. Douglass, Deputy Minister M. E. Hurst. Director, Geological Branch

Map 2045 BIG TROUT LAKE AREA KENORA DISTRICT, PATRICIA PORTION

53"40' - 53"40' Scale l: 126,720 or l Inch to 2 Miles SOURCES OF INFORMATION 234567 Geology by P. P. Hudec and assistants, 1960, 1961.

Cartography by ft. B. Robinson and D. W. Robeson, Ontario Department of Mines, 1963.

Base map compiled by the Cartographic Unit of the Ontario Department of Mines from maps and surveys by the Department of National Defense, Department of Mines and Technical Surveys, Ontario Department of Lands and Forests, with much additional information from air photographs of the National Air Photo Library. The boundary of Indian Reserve 84 is not shown pending final settlement. The magnetic declination in this area was approxi mately r W., 1961. Published 1964