ISERHOFF RIVER AREA, ABITIBI-COUNTY PROVINCE of QUEBEC, CANADA Department of Mines Honourable C

RG 049(A) ISERHOFF RIVER AREA, ABITIBI-COUNTY PROVINCE OF QUEBEC, CANADA Department of Mines Honourable C. D. FRENCH, Minister A.-O. DUFRESNE, Deputy Minister

GEOLOGICAL SURVEYS BRANCH I. W. JONES, Chief

GEOLOGICAL REPORT 49

ISERHOFF RIVER AREA

ABITIBI-EAST COUNTY

Jacques Claveau

QUEBEC RÉDEMPTI PARADIS PRINTER TO HIS MAJESTY THE KING

1951

Ministère des Richesses naturelles du Ou'bec

@.JE SERVICE DOCUMENTATION TEC 4 .► IL.

TABLE OF CONTENTS

Page INTRODUCTION 1 Location and access 1 Field work - 2 Acknowledgments 3 Previous work 3 GENERAL DESCRIPTION OF THE AREA 4 Physiography 4 Topography 4 Drainage 5 Climate 8 Timber 8 Game 9 GENERAL GEOLOGY 10 Table of formations 10 General statement 10 Volcanic-sedimentary series 11 Volcanic rocks 12 Hornblende gneiss 15 Sedimentary rocks 16 Structural interpretation of the series in the southern belt 20 Basic intrusive rocks 23 General statement 23 Basic rocks in the volcanic-sedimentary series 24 Anorthosite-gabbro complex 26 Tamprophyre and porphyrite dykes 29 Acidic intrusive rocks 30 General statement 30 Quartz diorite 31 Quartz syenite 32 Quartz leueodiorite 33 Pink granite 34 Pleistocene and Recent 3~ STRUCTURAL GEOLOGY 36 Folding and faulting 36 Shearing 40 ECONOMIC GEOLOGY 42 Recommendations 43 BIBLIOGRAPHY 44 AIXBABETICAL INDEX 46 MAP AND ILLUSTRATIONS

Map No.853.— Iserhoff River area (in pocket)

Plates

Plate I-A.— Two young Indians, Senneterre. B.- Indian winter house, Waswaniiii lake.

Plate II Iserhoff river in the middle part of its course.

Plate III Iserhoff river in the lower part of its course.

Plate IV — Imbault creek.

Plate V — Looking up the Iserhoff River valley.

Plate - VI-A. — Panoramic view looking north from a vantage point east of Imbault lake. B.— View of Baptiste lake.

Plate VII-A.— View of Dalhousie mountains. B.— View 'of a typical hill in the Dalhousie mountains.

Plate VIII-A.— View along the top of a syenitic hill.

B.— Layeredanorthosite-gabbro complex, Dalhousie mountains.

-II-- ISERHOFF RIVER AREA

ABITIBI EAST COUNTY

by Jacques Claveau

INTRODUCTION

Iodation and Access

The Iserhoff River area, mapped by the writer during the summer of 1946, is in Abitibi East county, some 80 miles north of Sen- neterre, a town on the Quebec-Cochrane branch of the Canadian National railway. It is bounded on the east and west by longitudes 76°45'.and 77°00' West, respectively, on the north by latitude 49°45' North, and on the south by the southern boundary of Berthiaume:and Bergères townships, that is, an east-west line about four miles south of latitude 49°30'. This gives an area of some 235 square miles, with a length of about twenty-one miles in a north-south direction and width of eleven miles. The north-south centre-line coincides with the boundary between the following pairs of townships, from south to north, the first named in each case being to the west: Berthiaume and Bergères, Bourbaux and Vignal, and Dussieux and Meulande. The area mapped thus includes a little more than half the width of each of these townships, and from south to north it extends the full length of the four first named and takes in the southernmost mile of Dussieux and Meulande.

The most direct canoe route from Senneterre to the area is by way of Bell river, Wedding river, Duplessis stream, the lower part of O'Sullivan river, the southwestern bay of Waswanipi lake, and Iserhoff river. The last-named flows eastward across the southern part of the map-area and empties into Waswanipi lake at a point four miles east of the eastern border of the sheet.

.An alternative, though somewhat longer, canoe route is by way of Bell river, Mattagami lake, Waswanipi river, and Olga lake to Goéland lake. This gives access to the northern part of the area, whereas the route first described leads to the southern part.

Travel by air affords a much simpler and very easy means of access to the area. Hydroplane service is available from Senneterre, and all suitable landing surfaces in the area, such as Ramsay bay and Baptiste lake, and those within a short distance of the area,. such as Waswanipi lake, are. well within one hour's flying time from Senneterre. - 2 - Most points within the southern half of the map-area, except the district centred about Baptiste lake and the chain of small lakes to the north, can be reached by way of Iserhoff river and one of its main tributaries, Imbault creek. During the earlier part of the summer, when waters are still fairly high, Iserhoff river is easily navigable up to a point two miles and a quarter due east of the western boundary of the area. The river has about ten short rapids within this navigable stretch. Its tributary, Imbault creek, is a small, narrow stream (Plate IV), very difficult to navigate owing to heavy growths of alders which partially choke it. It is navigable, nevertheless, for a mile and a quarter above its confluence with the Iserhoff, whence a portage, three and a quarter miles long, leads to another short navigable stretch through which Imbault lake can be reached.

Baptiste lake, near the western boundary of'the area, is accessible only on foot or by air — the latter means was used by the writer's party. Trails were cut to allow travelling, partly by land and partly by water, from Baptiste lake through the chain of four lakes lying to the north, which route gives access to that part of the northern half of.the area not within easy reach of Ramsay bay.

Most other points in the remainder of the northern half of the area may be reached conveniently either from the southwestern part of extensive Goéland lake, in the northeastern corner of the map- area, or from Ramsay bay, a long, narrow arm extending for some six miles westward from the south end of the lake. Of the many streams that flow into Goéland lake, and principally into Ramsay bay, four are major streams, and two of these are navigable over a considerable distance. That flowing north into the deep, narrow, south-trending arm along the south shore of Ramsay bay is navigable for two and a half miles above its mouth, whence a trail, a mile and a quarter long, leads southeastward to the east-west surveyed line along latitude 49835'30". North of Ramsay bay, the large stream flowing eastward into Goéland • lake was ascended by motor-driven canoe as far as its first small rapid, five miles from its mouth. It was not explored above this point, but it is believed to be navigable by small canoe for some additional distance upstream. Of the other two major streams, the one that flows northward into the eastern end of Ramsay bay is navigable for one mile from its mouth, and the other, which empties.into the head of Ramsay bay, is navigable for a little more than half a mile.

Field Work

For purposes of mapping, the area was covered systematic- ally by pace-and-compass land traverses run at intervals of approximately half a mile and across the trend of the general structure. - 3 - Acknowledgments

The base-map used for plotting the geology was a copy on a scale of half a mile to one inch of a part of the original plans used in the compilation of the Waswanipi sheet (32F) of the National .Topographic Series of the Department of Mines and Resources, Ottawa.

Oblique aerial photographs, taken by the Royal Canadian Air Force, were used in the field and were of some help. Vertical aerial photographs became available later, during the preparation of the report.

The Department of Lands and Forests, Quebec, provided maps and plans of the surveyed lines and major lakes in the area.

The writer was very ably assisted in the field by Paul- Emile Imbault of McGill University, Frank Bussell of the same university, and Paul Emile Grenier of Laval University. The two canoemen, Philippe and Aimé Lebrun, and the cook, Georges Vigneault, discharged their respective duties in a very satisfactory manner.

The efficient and courteous service of Canu9ian Pacific Air Lines and, in particular, of Pilot W.J. Davis, in charge of the Senneterre base, and Pilot Wally Smith, is gratefully acknowledged.

Previous Work

The earliest recorded geological work in the region is that of Robert Bell (1, 2g who surveyed the basin of Nottaway river in 1895 and 1896. J.A. Bancroft (3), in 1912, mapped certain portions . of the basins of the Aarricana and Nottaway, including Goéland lake. More recent geological surveys that embrace the area itself include' those of Cooke (4), Lang (5) in 1931, Norman (7) in 1935, Freeman (11, 12), and'Sproule (9, 10) in 1936. Geological work in adjoining areas includes that of Mackenzie (6) in 1935 in the region to the south, Douglas (8) in 1935 in the region to the southwest, and Freeman and Black (14) in 1940 in the adjacent area to the west.

XNumbers in parenthesis refer to corresponding numbers in the bibliography, page 44. - 4 - GENERAL DESCRIPTION OF TILE AREA

Physiography

Topography

The southern two-thirds of the map-area, with the exception of the lower reaches of Iserhoff river, lie in the northeastern central part of a well-defined topographical unit, characterized by its relatively high elevation and marked relief, and extending over some 650 square miles of Abitibi East county. This unit, elongated along a northwest-southeast axis, is bounded in the northwest by Olga lake, in the northeast by Goéland, 1aswanipi, and Puskitamika lakes, in the south by Wedding river, and in the southwest by a portion of Bell river. Within it are several lakes, none of which are very large. The better known include Wedding, Cameron, Esther, Madeleine, Desjar- dins, Tolman, and Baptiste lakes, all of which, with the exception of the last-named, lie outside, and south of, the present map-area.

The part of the area that belongs to this topographical unit consists generally of gently-rolling hills connected by broad, shallow valleys (Plate VI-A). It is, broadly speaking, an elevated region of low relief, and thus of the nature of a plateau. In the south, however, Iserhoff river has markedly incised this plateau, owing mainly to the presence of an east-west zone of weak sedimentary rocks, along which the river has cut its course.

The highest hills south of the Iserhoff lie roughly along the southern boundary of the area and form the divide between the tri- . butaries of that river and those of Desjardins, Tolman, and Madeleine lakes to the south. The altitude of these hills is estimated at 1,200 to 1,300 feet above sea-level.

In the southern part of the area, which is occupied by an east-west trending belt of volcanic and sedimentary rocks, the topography reflects the structural trend of the bed-rock. The hills are elongated east and west, and in many places they form narrow ridges, a few miles in length, the backbones of which are dykes of gabbro or diorite intruded parallel to the structure of the country rocks. Two prominent isolated hills, which rise about 1,400 feet above sea- level, strajiale the western border of the map-area, one just south of Baptiste lake and the other half a mile north of Iserhoff river (Plate V). Ridges spined by gabbro or diorite are best developed in

xSee Sheet 32SW (Noranda-Waswanipi), scale 8 miles to 1 inch, 1942, National Topographic Series of the Department of Mines and Resources, Ottawa. - 5 - the south-central part of the belt, a short distance away from the northern edge of the Iserhoff River valley.

In the east-central part of the map-area, the plateau region is underlain by granite, which forms characteristic, flat-topped hills with gentle slopes, the upper parts of which are commonly sparsely forested (Plate VIII-A).

In contrast, the plateau region is rather deeply dissect ed and rugged (Plate VII-A) in the west-central part of the area, where the underlying rock, a massif of anorthosite-gabbro, has been carved into high, mostly, bare, hills (Plate VIII B), known as the Dalhousie mountains. The massif extends westward. for some twelve miles beyond the boundary of the map-area as the somewhat lower Opaoka hills (14). The highest summits are found in the central part of the Dalhousie mountains (Plate VII-A), north of Baptiste lake, where the hills stand about 1,600 feet above sea-level.

In the remaining part of the map-area, that lying north of the central plateau region, the features are those of a plain with many swamps and muskegs, where the monotony is broken only by the presence of occasional low, rounded hills of unconsolidated sediments or emerging bed-rock.

The shore of Goéland (Gull) lake is, for the most part, low and formed of coarse gravel, although around Ramsay bay the loose sediments are pierced at several points by rock spurs which, in some places, rise abruptly for a few tens of feet. Sand beaches are few in number and limited in extent.

Drainage

With few exceptions, the streams and rivers of the map- area drain to either Waswanipi or Goéland lake. The former, which lies a few miles east of the area, empties through Waswanipi river into the latter, whose waters, in turn, pass to James bay by way of Olga and Mattagami lakes and Nottaway river. One large stream in the northwestern corner of the area drains directly into Olga lake. Baptiste lake and its tributaries, as well as a few small streams in the southeastern corner of the area, belong to the Bell River drainage system, which is itself directed northward into Mattagami lake.

Iserhoff river follows an easterly course, clearly con- trolled in part by a zone of weak sedimentary rocks, and in part by the northern border of a mass of quartz syenité in contact with the former. The portion of its course between points five and a half miles and - 6 - three miles from the eastern boundary of the map-area — where the river flows along the border of the syenite (Plate II) — is commonly marked by the close proximity along'the south bank of steep, rocky slopes. Throughout most of its course, the river meanders across its relatively broad and flat valley-bottom (Plate III) as a sluggish stream, broken here and thereby short rapids. However, as the upper limit of its navigable length, is approached, the river becomes less meandering and the current stronger, until, some two miles from the western border of the area, it finally breaks into continuous rapids near its headwaters.

Imbault creek, the main tributary of Iserhoff river within the boundaries of'the map-area, leaves Imbault lake through a tract of low, marshy ground that extends for a mile.eastward from the south end of the lake. This marshy tract; which at one time was an extension of the lake itself, is dammed at its eastern end by a low barrier of bed- rock. The creek, after crossing the marsh with a winding course in which the meanders are numerous and nearly, closed, spills through a small gap in the rocky barrier and begins a swift descent eastward from the plateau region. After three miles, the creek has reached approximately the same level as the Iserhoff. At this point, where also it is joined by a large stream from the north, the creek turns sharply south and,in a sluggish,meandering course, broken in two places by very small rapids, proceeds toward its confluence with the Iserhoff, a mile and a quarter downstream.

The small river flowing into the deep and narrow, south- . trending arm of Ramsay bay takes its source west of Imbault lake. It runs swiftly northward at the bottom of a steep, V-shaped.trench eroded in unconsolidated sediments, until, some three miles from its mouth and near its junction with a large tributary coming from the southeast, it enters a broad and prominent valley. From this point on it gradually assumes, and thence follows, a sluggish and meandering course to Ramsay bay. A feature of interest on the west wide of this broad valley, some two miles above the mouth of the river, is the presence of a hanging valley occupied by a large stream flowing from the west. This stream, after a long, meandering course across the plateau region to the west and southwest, reaches the main valley at a level well above that of the main stream, and thus has to make a steep, impetuous descent down the valley slope before joining it.

At one time, the main valley must have extended southward toward the region of the headwaters of the river, since, from the point where it narrows to be replaced by the V-shaped trench as far as Imbault lake, no bed-rock is exposed along, or in the immediate neighbourhood of, the river. The latter cuts deeply into a thick cover of glacial debris which apparently buried the valley during Pléistocène time. The - 7 - river is now engaged in the process of slowly re-opening the upper part of the ancient, broad valley, which likely extends from the south ann of Ramsay bay to the west side of Imbault lake.

Similar conditions apply to the neighbouring river to the east. A well-defined original valley was largely buried, and a large stream is now at work re-opening it. Here, however, the restora- tion is somewhat more advanced, either because the work of degradation has been more intensive or because the thickness of the cover of loose sediments is less.

As only small parts of these ancient valleys are exposed, one can but speculate on the features that exerted control on their formation. In the case of the western river, the presence of the deep, narrow arm of water, the occurrence of a zone of shearing along the eastern shore of this arm, and the existence of a prominent hanging valley entering the main valley, tend to indicate that the valley lies . along a regional zone of weakness due to faulting or shearing. In the case of the eastern river, a zone of weakness parallel to that of the western river is conceivable, but, apart from a few aligned scarp fades along the east side of the lower stretch of the valley, there is little substantial evidence available.

The small river entering the head of Ramsay bay has a steep gradient, and its course within the map-area is mainly a turbu- lent descent from the high anorthositic plateau to Ramsay bay. As to the northeastward-flowing river north of Ramsay bay, it is known to the writer only over its lower course, where it flows sluggishly across a monotonous plain to empty into Goéland lake through a low gap in the volcanic rocks of the west shore of the lake.

The map-area includes within its plateau section a few small lakes, and, in its northeastern corner, the southwestern part of extensive Goéland lake. The latter is rudely circular in shape and is about ten miles in diameter. It appears to be rather shallow, and extensive accumulations of boulders lying at, or close to, the water- level are of common occurrence. Its prominent southwestward extension, Ramsay bay, constitutes a puzzling feature. It is deeper than the remainder of the lake as indicated by steep-sided, high-standing islands and frequently abrupt shores. It coincides, also, with an area of extreme geological complexity, especially in its eastern part. It may, therefore, lie along a zone of structural deformation in the bed-rock. - 8 - Climate

The study of the climate of the region was limited to daily readings, whenever possible, of maximum and minimum temperatures, and to rudimentary observations of the direction of the wind and the quantity of rainfall.

During the latter half of June (1946), the average maximum temperature was 80°F., and the average minimum 41°F. The prevailing winds blew from the southwest and rainfall was abundant. A twelve- hour rain during the night of June 23-24 swelled the Iserhoff, within the following twenty-four hours, to a height of six feet above its pre-rain level.

In July, the average maximum temperature was 75.5°F. and the average minimum 46.5°F. The records indicate a low rainfall and prevailing winds from the west and southwest.

In August, the average maximum and minimum temperatures were 67.5°F. and 44°F., respectively. Although rain was frequent, the total rainfall was low. The prevailing winds blew from the west.

Frost was recorded on six occasions, twice in June, thrice in July, and once in early September. The observations were dis- continued after September 6th.

Except on the days of heavy rain, complete overcast was rare. On approximately two-thirds of the summer days, the skies had moderate overcast, generally below 50 per cent, or, more rarely, were cloudless.

Timber

Forest fires which, prior to 1912 (3), devastated this area and the surrounding region, have left profound scars. The only prominent remaining stretch of tall forest — mainly spruce trees — which could be utilized by the lumber industry covers the area south of Iserhoff river and extends as far as Madeleine lake, some two miles beyond the southern boundary of the map-area.

Additional recoverable timber is present in lesser quantity in an irregular belt of somewhat disconnected patches of dense forest that extends across the area, passing immediately south of the southwestern extension of the prominent belt of unconsolidated sediments and south of Imbault lake. Still another stand of tall spruce forms a band, about a mile in width, along the southeastern border of - 9 - the anorthosite-gabbro mass, between Baptiste lake and the western shore of the deep, south-trending arm of Ramsay bay.

Elsewhere in the area, spruce and balsam that have grown since the fires are small and commonly superseded by a contemporaneous growth of jack-pine, aspen, and birch. Jack-pine is particularly prevalent along the valley of the Iserhoff, in the belt of unconsolidated sediments, and north of Bamsay bay. Aspen thrives, and in places grows to trees of appreciable size, throughout the entire area drained by the two main streams entering eastern Ramsay bay. Birch reaches its greatest development on the hillsides of the Dalhousie mountains.

Alders are encountered along many small streams and in a few restricted areas of muskeg, and also, somewhat erratically, among the thick growths of jack-pine north of Ramsay bay.

Game

Numerous tracks of moose and bear were observed but the animals themselves were seen on two or three occasions only.

Beaver, muskrat, otter, fox, and rabbit are present in small numbers. Partridge and other game-birds are scarce.

- 10 - GENERAL GEOLOGY Table of Formations

GIId07AIC Quaternary Sand, gravel, clay.

Great unconformity

Pink granite, pegmatitic granite, pegmatite

Acidic Quartz leucodiorite Intrusives Quartz syenite

Quartz diorite

Lamprophyre dykes

Anorthosite-gabbro layered complex yitrJC A1 tRRTAN Basic Intrusives Gabbro associated with the volcanic- sedimentary series

Intrusive contact

Greywacke and feldspathic quartzite Volcanic- sedimentary Conglomerate Series Hornblende gneiss Altered lavas, mostly andesitic; locally, associated bedded tuffs

General Statement

The consolidated rocks of the Iserhoff River area consist of acidic igneous rocks intruded into a complexly-folded assemblage of volcanic, sedimentary, and basic igneous rocks.

Volcanic and sedimentary rocks, occurring together, under- lie about one-third of the map-area. Two belts of these rocks cross the area from west to east, one in the north, the other in the south. Both are parts of extensive, generally east-trending, bands of these - 11 - rocks which lie as roof pendants in the large intrusive masses of acidic rocks of the Waswanipi-Mattagami region.

Intruding the rocks of these belts concordantly are numerous, and generally small, long and narrow bodies of basic igneous rocks (gabbro). The main occurrence of basic igneous rock, however; is a layered complex of anorthosite and gabbro that underlies a well- defined, semi-elliptical area of some 40 square miles in the western half of the area, north of the southern belt of volcanic and sedimentary rocks.

One period, at least, of regional folding is clearly recorded in the attitude of the volcanic-sedimentary series, and possibly in that of the layered complex of anorthosite-gabbro as well. The latter represents the western end of the Bell River complex, which Freeman (12) described as a folded lopolith. If Freeman's interpretation is correct, the intrusion of the mass antedates the period of major folding. The gabbro found within the volcanic-sedimentary rocks may or may not be older than the layered complex, although it is believed to be possibly pre-folding in age, or at least coeval with the major folding.

The acidic igneous rocks of the area belong, as mentioned above, to the large masses of acidic rocks of the Waswanipi-Mattagami region, and they include, in order of decreasing age, quartz diorite, quartz syenite, and pink granite. Each of these three types underlies a separate, well-defined section of the map-area. These rocks exhibit clear consanguinity and their differences in age are thought to be of a small order. They are all deformed to some degree and very likely the oldest members, if not all, were intruded during the final stages of the period of regional folding that involved, primarily, the volcanic, sedimentary, and basic igneous rocks.

Volcanic-Sedimentary Series

A complex assemblage of volcanic and sedimentary rocks, with which are associated many small bodies of gabbro,.underlies a considerable portion of the map-area in the south and a smaller portion in the north.

The southern belt, bordering but lying mostly north of Iserhoff river, extends, with east-west trend, across the entire width of the map-area. Some eight miles wide at the western boundary, it becomes gradually narrower until it is only about two and a half miles wide near the eastern boundary, where it disappears beneath the unconsolidated sediments blanketing the lower reaches of Iserhoff river and local tributaries. - 12 - The northern belt underlies an area that is approximately centred about Goéland lake and the.eastern part of Ramsay bay. Its southwestern margin is clearly defined west of Goéland lake by a line entering the map-area at its northwest corner and running southeast to' Ramsay bay. From there, however, it is impossible to draw a satisfactory boundary between the rocks of the belt and the surrounding granite which penetrates them in a very intricate fashion. The boundary may be described approximately as crossing Ramsay bay about two and a half miles from its mouth, and extending southward to include a long, narrow, finger-like body of sedimentary and volcanic rocks in the granite. Thence it continues with easterly trend, fairly close to the southern shores of Ramsay bay and Goéland lake.

Volcanic Rocks

The lavas of the area are andesitic but they usually lack clearly-diagnostic characters such as pillow and brecciated structures, amygdaloidal and porphyritic textures, and others. They may be identi- fied in the field only by their close resemblance to the rock of outcrops that do possess features indicative of lavas. The identification is thus based mainly on the criteria of grain size and colour. The application of these already limited criteria is much complicated by the fact that the lavas are strongly metamorphosed and commonly schistose, and that, associated with them, are interbedded sedimentaries and many small concordant intrusive bodies, these also being generally as altered as the volcanics. The microscopic criteria of composition and texture, although they provide aanitional information, are well known to be somewhat limited, in themselves, in rocks that have been strongly metamorphosed. It follows, therefore, that in many instances it is not possible to distinguish with certainty between the volcanic, sedimentary and intrusive rocks of the belt.

There occurs, for example, south and west of the upper and lower part, respectively, of Imbault creek, a persistent hornblende gneiss, the origin of which is still in doubt. It is not unlike certain rocks of the area that are definitely metamorphosed sedimentaries, but its microscopic characters do not preclude the possibility of a volcanic origin. This gneiss is discussed separately, following the description of the typical volcanics.

Distribution - Throughout the northern belt of volcanic and sedimentary rocks, lavas predominate. They are andesitic, strongly schistose, and metamorphosed.

In the southern belt, where sedimentaries seem to be preponderant, lavas occur mainly in an area extending for some ten square •- 13 - miles south and southeast of. Baptiste lake. They are again found in a somewhat narrow band parallel to, and from half a mile to a mile and a half north of, Iserhoff river. This band, marked by several prominent hills and interrupted ridges which commonly have steep sides facing south, traverses the entire map-area in an east-west direction, and its eastern end crosses the Iserhoff where the river takes a sharp turn and flows northward for more than one mile. Typical volcanics also form most of the exposures within a restricted area between half a mile and a mile and a half south of Imbault lake.

If the hornblende gneiss referred to above is regarded as a metamorphosed lava, the ratio of volcanics to sedimentary rocks in the southern belt would be considerably increased, since the area underlain by the gneiss merges westward into the volcanics south of Imbault lake and southward into the eastern half of the band of volcanics paralleling Iserhoff river.

Certain thinly-bedded formations, consisting of alternating light and dark bands, that are found in a few localities in close proximity to lavas, may be tuff beds.

Petrography - In rare exposures of typical lavas, the rock is light green and andesitic, amygdaloidal, and exhibits pillow structure. Weathering has dissolved the filling of many vesicles, rendering the rock vesicular or 'spongy' at the surface. The rock consists essentially of plagioclase (andesine) and hornblende, with grain size ranging.from 0.02 mm. in some flows to much finer in others. It contains occasional phenocrysts of feldspar which, in the thin sections examined, are seen to be invaded by swarms of small hornblende needles and aré partly replaced by a fine mosaic of plagioclase crystals. The phenocrysts have the composition of basic andesine and they show alteration to white mica. The feldspar of the groundmass is slightly more acidic andesine. The amygdules consist of aggregates of acid plagioclase (oligoclase) in somewhat larger crystals than those of the groundmass. Quartz is found in small amount in some of the amygdules. Minor constituents of the rock are magnetite, leucoxene, apatite, and chlorite (after hornblende) .

The average andesitic lava of the area, however, is weak- ly to strongly schistose and altered, and in many places it lacks characteristic structures and textures. The deformation and alteration it has suffered may, to some extent, have caused the obliteration of the original characters. Amygdaloidal and porphyritic features, more . or less well preserved, may be seen in some thin sections of the rock. Thus, certain schistose types still show skeletal plagioclase phenocrysts beclouded with secondary white mica or strongly corroded around their borders. Small round areas, occupied by feldspar crystals larger - 14 - than those of the groundmass, probably represent amygd.ules. In altered types with weak or almost absent schistosity, Original phenocrysts are well preserved as pseudomorphs of white mica, carbonate, or even chlorite. The ferromagnesian minerals of the schistose lava occur in long, thin shreds which usually wrap around amygdules and phenocrysts, where these are still present. In some instances, the hornblende is superimposed over the fine groundmass in large, corroded crystals full of tiny, clear inclusions of feldspar and quartz; this poikiloblastic texture reaches its greatest development in the banded lavas described below. Some specimens carry actinolite in fine, pale green needles, instead of the usual deep green hornblende. Biotite is rare to absent. 'It is seldom easy to detect the presence of quartz in the fine ground.- mass. When recognized, it is, as a rule, in grains somewhat larger than those of the other minerals of the groundmass, or again, it may be in relatively large, shapeless patches or, more rarely, in veinlets traversing the rock. It is suspected that the quartz to form these grains and patches has, like that of the veinlets, been introduced into the rock. Sphene, and in some occurrences quite abundant epidote, are common accessory minerals in the altered andesite. Magnetite and. pyrite and their oxidation products, hematite and limonite, are of sporadic occurrence. Common alteration products, such as white mica, carbonate, and chlorite, are present in varying abundance.

A banded, heavy and compact rock encountered throughout the volcanic-sedimentary belt, and more especially around, and east of, the small lake two miles south of Imbault lake, has all the features of a highly metamorphosed andesite. It consists predominantly of hornblende, but is characterized by an arrangement of alternating hornblende-rich and plagioclase-rich layers. The bands vary widely in width within a range that seldom exceeds a small fraction of an inch, although, in some places, layers of solid hornblende, one-half to one- quarter of an inch wide, were noted. Under the microscope, the hornblende is seen to be porphyroblastic in habit, that is, it assumes a much larger size than the plagioclase crystals. It appears to have grown in the fine groundmass, absorbing plagioclase grains, some of which have remained as inclusions and so impart a sieve texture (poikiloblastic texture) to the rock. The growth of such crystals implies a segregation of ferromagnesian material by diffusion, a process that could lead, under appropriate conditions, to a segregation of hornblende into bands, or to the production of foliation as defined by Harker. The banding, or foliation, results from an elevation of

xHARKER, Alfred, Metamorphism; Methuen and Co., Ltd., London, 1939, p.203. - 15 - temperature in a stratified or schistose rock subjected to metamorphism. Although it is more apt to be produced in a stratified rock, it is obvi- ous that, to some degree at least, a schistose lava would have the re- quisite planar. properties conducive to the formation of banding. The plagioclase varies from basic oligoclase to acid andesine, and its grain size is about the same as that of the typical andesites. This banded rock has the overall composition of an intermediate lava and seems to have been derived from an andesite rendered schistose during the folding of the series and later subjected to high-temperature conditions during the emplacement of the granite.

A medium-grey lava found in restricted occurrences among the andesites of the volcanic band parallel to Iserhoff river has the composition bof rhyolite. The rock weathers white, is moderately schistose, and on fresh fractures is seen to be distinctly porphyritic, although the original phenocrysts of feldspar and quartz are now completely' replaced by dark green chlorite. The grounamass is a granular aggregate of sericitized and kaolinized orthoclase with interstitial clear quartz. In certain parts of the rock, a fine graphic intergrotth of quartz and feldspar is noted. Plagioclase is rare and usually altered. Some clear feldspar may be sanidine. Ferromagnesian minerals are very subordinate and are thoroughly altered, as a rule, to a mass of chlorite and serpentine. Occasionally some bleached biotite is preserved.

A dark, compact, garnet-bearing, amphibolite which is encountered in some abundance south of Baptiste lake in an area where lavas and gabbro are prevalent, is undoubtedly derived from one or other of these igneous rocks. The amphibolite is a solid mass of feathery amphibole in erratic orientation, some of which is partly chloritized. It carries a few metacrysts of garnet containing inclusions of a colourless amphibole, probably tremolite, in fine needles. Present also are a little finely-disseminated magnetite and ilmenite, apatite (rarely), and quartz, in veinlets.

Hornblende Gneiss

Distribution - This gneiss has already been mentioned as occurring mainly north of the eastern half of the band of volcanics that parallels Iserhoff river, that is, south and west of the upper and lower part, respectively, of I.'nbault creek. The line of demarcation between the gneiss and the volcanics ti the south is indefinite, as the latter are of the banded type discussed previously and are not always readily distinguishable from some varieties of the gneiss itself. The gneiss extenes for approximately a mile south from the northern border of the volcanic-sedimentary belt, and it may possibly occur farther south interbedded with the banded andesite. Westward, it gives place rather - 16 - abruptly to typical- volcanics occurring between half a mile and one mile south of Imbault lake.

Petrography - The typical hornblende gneiss is a rock characterized by the presence of hornblende needles, two to one mm. or less in length, in a fine groundmass. The groundmass is whitish-grey, or-occasionally buff-coloured owing to limonitic stain. A rude banding, due to the concentration of the hornblende along certa n planes parallel to the schistosity, is apparent in places. In no instance, however, does the banding become as pronounced as in the typical banded andesite. The essential difference between these rocks is the distinctly lower ferromagnesian content of the latter.

The origin of the hornblende gneiss is doubtful, as the occasional presence elsewhere along the belt, both among certain lavas and unequivocal greywackes, of an almost identical gneiss demonstrates the dual possibility of its derivation from either volcanic or sedimentary members. It may thus be the metamorphic product either of a lava of somewhat less basic character than the average andesite of the series, or of a greywacke.

Even under the microscope, the fine groundmass is difficult to resolve, but it appears to be chiefly basic oligoclase. In grain size, the gneiss is intermediate between the average greywacke and the average andesite of the series. There is, however, a faint suggestion of more rounding of the grains than in the lavas. The plagioclase is clear and has indices of refraction close to those of quartz. The latter, therefore, cannot be recognized readily, and it is not certain whether or not it is present in the fine groundmass. Some obvi- ous quartz, in relatively large grains and in veinlets along the schistosity, clearly has been introduced. Hornblende occurs in large, sieve- like crystals (poikiloblastic texture) and thus is of porphyroblastic habit, as it is in the banded andesite. This is to be expected since the gneiss, except for its lower hornblende content, has much the same composition as the andesite and, since areally the gneiss and anaesite are adjacent, they must have been subjected to the same conditions of of metamorphism.

Accessory minerals in the gneiss include, mainly, biotite, garnet, magnetite and ilmenite, sphene, some zircons in the biotite, and apatite (rarely).

Sedimentary Rocks

Distribution - Sedimentary rocks occur mainly in two bands, each more than a mile in width, trending approximately east-west 17 - and located in the southern belt Of the volcanic-sedimentary. series. The better defined Of the two bands constitutes the southern border of the series and is physiographically expressed as a marked, trough-like valley which, along practically the whole of its course, is occupied by the main stream of the area, Iserhoff river. It is probable that the band persists eastward beneath the cover of unconsolidated sediments in which the lower stretch of the river flows, at least as far as the point where the river makes a sharp bend northward near the eastern boundary of the area and leaves the band. The depression, or valley, that characterizes this sedimentary band throughout the map-area persists eastward beyond the sharp bend in the river and is now occupied by a tributary stream flowing westward. It is likely that at one time the Iserhoff flowed eastward in this tributary valley, instead of making its present sharp loop toward the northwest before resuming its easterly course toward Waswanipi lake. A mile and a half west of the sharp northward turn in the river, the sedimentary rocks are intruded by a small granitic mass, which apparently is elongated with the trend of the formations and is probably an isolated off-shoot from nearby intrusive bodies.

The second band of sedimentary rocks seems to parallel the first. On the west, it enters the map-area from one and a half.to two and a half miles north of Iserhoff river. It is marked topographically by the presence of a flat, elongate plain, commonly covered by muskeg. Outcrops are scarce, poorly exposed as a rule, and commonly they are broken and disturbed at the surface. The band. is known with reasonable certainty to extend eastward for six miles, that is, to the vicinity of the small lake two miles south of Imbault lake. There is no clear evidence that it continues east of this small lake, where banded andesite prevails, and thus it may be cut off west of the lake by a north- south fault that would also traverse and offset the southern band of sedimentaries, a possibility which is discussed later in this report.

Sedimentary rocks are exposed at a point three miles . northeast of Baptiste lake and possibly also just north of that lake, where, however, positive identification of the rocks as of sedimentary origin is not possible. The occurrence within the series of similarly doubtful rocks which may or may not be of sedimentary origin is not un- common. Actually, in the northern belt of the series, sedimentary rocks have been recognized with certainty in only one or two localities. One of these occurrences is on the island at the entrance to Ramsay bay, where sedimentary rocks are found interbedded with lavas, both cut by concordant dykes of porphyrite.

A group of rock exposures south of Baptiste lake illus- trates well-the intimate relationship between sedimentaries and volcan- - 18 - ics. The outcrops are a mile and a auarter south of the lake and half a mile from the west boundary of the map-area. Here, a short distance north of the belt of unconsolidated sediments, there is a low, south- facing escarpment formed of north-dipping, feldspathic quartzite, with intercalates of intensely altered rock, possibly a former gabbro. About 50 feet north of the quartzite, and separated from it by overburden, are several outcrops of pillowed andesite, with the tops of the flows facing north. The northernmost of these outcrops of andesite, although very small, shows andesite in contact with quartzite. The latter is on the north side of the contact, which is unspectacular and obscure but is rectilinear over its short exposed length. The quartzite is very thinly bedded and impure near the andesite but tends to be in thicker and purer beds away from it. One bed of pure, fine-grained; white quartzite, with lines of black sand in it, is up to six inches in thickness. These quartzites have the same strike and the same steep northerly dip as those of the southern exposures, although they are of somewhat different composition and appearance. After some ten feet of overburden, the next outcrop northward is altered lava, and, still farther north, amphibolitic gneiss, likely derived from andesite, is exposed.

In summary, this last occurrence presents within.the short distance of less than 500 feet a succession, in ascending order, of feldspathic quartzite, pillowed andesite, quartzite, and lava. The formations are presumably right-side-up and face north. But. even if they are overturned, it still remains a demonstrated fact.that,here at' least, lavas and sedimentary rocks do occur in the series as closely- repeated intercalates.

Conglomerate was seen at three localities, all within the limits of the two main sedimentary bands. In the southern band, conglomerate is found three and a half miles southeast of Imbault lake. It dips very steeply to the south and is exposed across the strike for a width of 50 feet. It lies practically at the northern limit of the southern band (though an isolated outcrop of greywacke is exposed some 1,300 feet to the north) and is assumed, for the present, to lie at the base of that band. Following this assumption, the conglomerate must be in normal position, since it dips to the south.

The two other exposures of conglomerate are in the southern part of the northern band of sedimentaries. The outcrops are near the small lake two miles south of Imbault lake where the band is thought to end against a fault, and they are complicated by the presence of small intrusions of gabbro and granite. One group of outcrops lies three-quarters of a mile west-southwest of the small lake and the other groupa auarter of a mile from the lake'in the same direction. The conglomerate has a general east-west strike and a moderate northward - 19 - dip. Complex movements are indicated, however, by abrupt changes in strike, and no accurate estimate of the thickness of the conglomerate is possible, although the scattering of outcrops suggests a rather large width. No information is available as to the top of the beds, but it is presumed that the conglomerate, which occurs at the southern border of the band, lies stratigraphically at the base of the sedimentary band, in which case the beds are not overturned, since they dip to the north.

Petrography - The average sedimentary rock of the area, or rather its present representative, is a light grey rock that contains varying amounts of biotite. It is more or less schistose, depending on the proportion of biotite, and is imperfectly banded. The banding effect is likely an original sedimentary feature, although it may have been emphasized by the metamorphism to which all the rocks of the series have been subjected.

In the rock of the two main sedimentary bands, the mica content is frequently high. The rock is accordingly quite schistose and disintegrates readily into slabs, some of which are of a considerable size. The Iserhoff valley, in particular, is littered at several points along its sides with accumulations of these fragments. They have seldom been transported far, as evidenced by their angular shape and also by the fact that they commonly form a mantle over actual outcrops, or a talus at the foot of small cliffs.

Under the microscope, it is seen that quartz and feldspar occur in grains of uniform size and roundness. The grain size ranges from place to place between 0.05 and 0.25 mm., the average being about 0.15 mm. The groundmass is so fine that the percentages of quartz and feldspar cannot be readily ascertained, unless the rock is markedly altered and the feldspar charged with white mica. In most of the altered specimens, feldspar is more abundant than quartz. Orthoclase may be present, but the preponderant feldspar is oligoclase, in untwinned grains. Thus, the average sedimentary rock seems to have the composition of a greywacke, although the types in which quartz is abundant or in excess of feldspar might be better termed feldspathic quartzite. Typical quartzites, with negligible feldspar content, do not seem to • occur in the bands of predominantly sedimentary rocks. The occurrences known at present are in areas where volcanics are predominant, as, for instance, the pure white quartzites in the previously-described succession of lavas and sedimentary rocks south of Baptiste lake, and the impure quartzite associated with volcanics one mile north of Iserhoff river, near the western boundary of the map-area. -20- Common accessory minerals in the sedimentary rocks include garnet, epidote, and, in some specimens, clinozoisite. Other minerals of erratic occurrence are hornblende, sphene, muscovite, zircon, pyrite, magnetite, and. tremolite (observed in one specimen only).

The matrix of the conglomerate has the composition of a greywacke. It contains abundant pebbles of a grey, often leucocratic, granite; of quartz; of a dark amphibolitic and chloritic schist; of a hornblende rock similar to the light portions of the previously-described banded andesite; and of a fine-grained, light-coloured rock, presumably of sedimentary origin. All the pebbles are deformed to a certain extent and flattened in a direction parallel to the schistosity of the matrix. Granite and quartz pebbles are least deformed,.those of hornblende rock show intermediate deformation, and those of schist and of the light-coloured rock are in long, thin ribbons. The largest pebble of granite observed is about six inches in diameter.

The persistence in length and thinness, and their abundance along certain horizons, of many ribbons of light-coloured rock suggest that, in some cases, they may represent original, thin, argil- laceous or siliceous interbeds in the conglomerate. Such interbeds, subjected to deformation in a heterogeneous medium such as the present conglomerate, may have been broken into thin, tapering lenses of greatly varied length, such as those seen. However, there are also some thin, but short and rounded, pebbles of the same rock that must have had a different origin.

The pebbles of schist are doubtless derived from the lavas. The rock from which the granitic pebbles are derived ras not seen in place in the area.

In the easternmost exposure of conglomerate, three narrow intercalates of a much altered rock were seen, two of which appear to be in a slightly discordant position with respect to the schistosity and oriented pebbles of the conglomerate. These intercalates, which are about eighteen inches in width, are probably dykes of a rock of intermediate composition.

Structural Interpretation of the Series in the Southern Belt

As the information available from the volcanic-sedimentary series is limited and is conjectural in part, any structural interpretation must be regarded as tentative.

The southern band of sedimentaries dips to the south in its eastern part and contains, in one locality along the northern border - 21 - of the band, a conglomerate formation. The conglomerate is assumed to be at the base of the band and thus to lie with the top of the beds facing south. In the eastern half of the band, where the dips are southward, the formations would thus be right-side-up, whereas in the western half where they dip to the north, they would be overturned.

The second sedimentary band is a short distance north of, and parallel to, the southern band. It has been traced with reasonable certainty from the western border of the area to the small lake two miles south of Imbault lake. It dips to the north and contains along its southern border, at distances of less than one mile southwest of the small lake, several exposures of conglomerate. Little is known of the attitude of these beds, but it is assumed at present that the conglomerate lies stratigraphically at the base of the band. With this assumption, it follows that the tops of the beds are to the north and the band is right-side-up, since it dips to the north.

The fact that the northern sedimentary band seems to end at the small lake south of Imbault lake brings to attention the similar fate of the band of hornblende gneiss that lies northeast of the small lake and ends abruptly north of the latter, to be replaced by typical volcanics. Both appear to end against a common north-south line which could constitute a major fault across the series. If the gneiss is interpreted as a metamorphosed greywacke, it could be, on the east side of the fault, the offset segment of the northern sedimentary band occurring west of the fault, in which case the east side of the fault would have apparently moved north with respect to the west side.

The presence of a fault with apparent horizontal displacement as suggested above seems to find pertinent confirmation in the attitude of the southern sedimentary band and adjacent syenite to the south. The southward prolongation of the fault line that explains the two northerly 'breaks' in the series traverses the contact between the southern sedimentary band and adjacent syenite to the south at a point where either a sharp fold or a break must be assumed in the course of the contact. The contact, which is generally parallel to the trend of the series and on the west side of the presumed break line parallels the average course of the Iserhoff at a distance of a quarter of a mile or more to the south, suddenly appears, on the east side of the break, shifted northward several hundred feet, and eastward it follows closely the south bank of the river.

The above facts thus seem to bear out the existence of a major fault trending between north and northeast and passing just west of the small lake two miles south of Imbault lake. The northward extension of the fault into the district east of Imbault lake, as shown -22 - on the accompanying map, is largely conjectural, although it is support- ed to some extent by the highly sheared, crumpled, and altered state of the volcanics in the vicinity of the lake.

It is.important to note that the features of discontinuity and deformation, which the postulated fault readily explains, lie within, and in line with, a major regional north-south zone of shearing. This zone is expressed at Bamsay bay by a strong shear and by several marked scarps, which may be fault scarps, in line with the postulated fault to the south. Sproule (9) pointed out the existence of this zone of fracture within the present area as well as south of it, and even suggested that it possibly extended for several tens of miles southward.

A ready interpretation of the occurrence of two sedimentary bands is that they are possibly the repetition, 'by folding, of one single band. The folding axis would be a roughly east-west line running through the volcanics lying between the two bands. Since the conglomerate in both bands is thought to occur at the base, and since it lies on the margins of the bands closest to the folding axis, the fold would be anticlinal. East of the fault, the location of the anticlinal axis depends on whether or not the hornblende gneiss is regarded as being of sedimentary origin. The question must remain open for the present, although it may be mentioned that the interpretation of the gneiss as a lava does not exclude the possibility of an anticlinal structure. Either large upward displacement or rotation of the east block of the fault, followed by erosion to the level of the. west block, could explain the absence of the eastern segment of the northern sedimentary band within the actually limited extent of the series.

West of the fault, inspection shows that the assumed anticline is overturned to the south as its southern limb dips for the most part to the north.

The relative ages of the sedimentary and volcanic rocks are not definitely known. Certainly, the minor conformable sedimentary intercalates among the volcanics, such, for instance, as the feldspathic quartzites and pure quartzites south of Baptiste lake, must be regarded as contemporaneous with the volcanics. They mark short intervals of quiescence attended by sedimentation during a period of recurrent out- pouring of lavas.

The bulk of the sedimentary rocks, however, such as those of the two main sedimentary bands, are Temiskaming-type and may mark the beginning of a period of sedimentation. The presence of conglomerate at the base of the bands indicates an erosional unconformity and favours the idea of a time break between the bulk of the sedimentary Plate I

A- Two young Indians from the Senneterre summer reserve.

B- Indian house built by the Indians of the Waswanipi reserve for winter quarters, southwest of Waswanipi lake. Iserhoff river in the middle part of its course. Hills on the right are of quartz syenite. ✓.-„ +--'.. ..~.+--s----. ...:~.-~... ...- . «.-.+- r ,r~-..-.^"'' ._.---'..~~, •..%~,.,w"~s^- ~~_...-~^".w~~~~~..:.N~-,-~„ ...-r~e~^`.a-.` .rm.-..: ='~,:~""'~~^~~•~^~~.~---^"',,. ~-~~ V y^` ~~-~„-..~°'^`r ~ ✓ =~-~...--..--..+~::~•~. -~—'='`~='r'..--~^ ..r-~~°`~ ..-^~. ~~'~~~~`~✓"",..-.~~.~,~w~`"~ r ~„~° . •r~• `~~; °~ ✓~..-';~~ •~~~,,, ~~ w- ,•,-. ...~...,`" - ° ~~-~ w~~,,,~.~„~~~,..~^~ q,.+-""'"..~~`"= ,~.;::',„~..~^- °"'~..-.~...- ✓ •T-+.~..~;;:"`~""""~ _r~.-«~::.k:..~,R',~...,....._.:....~^"..~:.:~~.-w^~5:~"'~-r::.~.~..-.z...=t•" ,,,~.a.- ,.,.~+,.~^.»:'"~~,-,:.•t~.~""s ,...~°",:ô .~..~-'w° ...,~_...— _

Iserhoff river in its lower reaches near Waswanipi lake. Note the dense growth of tall aspen trees on the flat extent of clay bordering the river. Travelling along the lower part of narrow, winding tmbault creek. Looking (westward) up the Iserhoff River valley from a hill on the south side of the river midway along its course. High hill on centre horizon lies on the north side of the valley and straddles the western boundary of the map-area. -a

Frr

A - (Above) - View looking north from a vantage point east of Imbault lake. Low flat hill at right is of granite and lies north-northeast of the lake. Rugged hills in the distance at left are the southeastern outliers of the Dalhousie mountains.

B - (Left) - View looking northeast from the high hill south of the west end of Baptiste lake. Hills on the horizon are the southeastern outliers of the Dalhousie mountains. Plate V I I

A- View looking northeast toward the central and most elevated section of the Dalhousie mountains. Taken from a vantage point four miles north of Baptiste lake.

B- View of a typical hill in the Dalhousie mountains. Location is three miles north of Baptiste lake.

Ministère des Richesses naturelle: du Cu(bec

SERVICE DOCUMENTATION T4 H..IQJE Plate VII I

A- Typical view along the top of a high syenitic hill in the southeastern corner of the area. Note the partial denuda- tion and sparse vegetation common to these hills.

B- Anorthosite-gabbro complex, Dalhousie mountains . Heterogeneity of the mass is well illustrated. At left, the dark rock is coarse gabbro; in the centre is anorthosite with mafic bands; at right is anorthosite with irregular segregations of mafic minerals. Location is close to the western boundary of the area, three and three-quarter miles north of Baptiste lake. - 23 - rocks and the volcanics. No clear angular unconformity could be detected between them, and the bands appear to be conformable with the volcanics. It is possible that such an unconformity exists but that it is too small to show in the trends of the formations. A small angular unconformity can hardly be proved or disproved unless the sedimentary rocks and the volcanics are seen in actual contact.

The suggestion that the bulk of the sedimentary rocks may be younger than the volcanics is partly in accordance with the suggested anticlinal structure in the southern part of the series. The sedimentaries, repeated by anticlinal folding, belong to a single band and the volcanics lying along the axial plane of the fold are overlain by the sedimentaries. Difficulties arise, however, owing to the presence on the north side of the northern sedimentary band, west of the north- south fault, of an extensive area of volcanics that apparently overlie 'the sedimentaries of the band, since the indications are that, south of Baptiste lake, the tops of the flows face to the north. Unless some undetected feature has caused the sedimentaries merely to appear to be overlain by the volcanics whereas in reality they may be younger, it is obviously impossible to regard them as marking the beginning of a major period of sedimentation. The sedimentary bands may thus simply mark quiet stages in a period of vulcanism, and resemble in that respect the minor intercalates. It is also possible, on the other hand, that an east-west strike fault limits the northern sedimentary band on its north side and that the series south of this break has been down- faulted, bringing the sedimentaries to rest against, and in appearance stratigraphically below, the northern volcanics.

The foregoing discussion discloses the complexity of the structure of the series and demonstrates clearly that much additional information will have to be secured before a satisfactory interpretation is possible.

Basic Intrusive Bocks

General Statement

Numerous small, generally concordant, bodies of gabbro are found within the volcanic-sedimentary series, and a large mass of banded anorthosite-gabbro crops out in the west-central part of the area, immediately north of the southern belt of volcanic and sedimentary rocks.

The relationship between the large mass of anorthosite- gabbro and the smaller masses of gabbro is not known with certainty. As discussed later, the heterogeneous anorthosite-gabbro mass is believed to have been originally a lopolith, now folded with the volcanic- - 24 - sedimentary series. It is not cut 'by any basic rocks other than a very limited number of lamprophyre dykes. The fact that the gabbro found within the volcanic-sedimentary series does not appear to cut the anorthosite-gabbro mass suggests that perhaps it is older than the latter, or possibly, contemporaneous with it. However, at present, there is no direct evidence to that effect.

Even the evidence for the folding of the large mass is not altogether satisfactory. But if the folding be admitted, as well as the older age of the small, elongated. masses of gabbro within the volcanic-sedimentary series, then it must be accepted that the latter were largely intruded as sills, since they are concordant, as a rule, to the trend of the volcanic and sedimentary rocks.

The layered mass of anorthosite-gabbro is definitely older than all the acidic intrusives, as it.is cut by dykes of the oldest of these, namely, quartz diorite. The gabbro in the volcanic-sedimentary series is not clearly older than all the granitic intrusives, as it is only known to be cut by the youngest acidic intrusive, namely, a pink granite and its pegmatitic facies. However, it is not known to cut any of the older acidic intrusives and it is very probably older than most of the acidic rocks. At Desjardins lake, in the Bruneau area, immediately to the southwest of the present area, Douglas (8) noted the occurrence in the 'greenstones' of small masses of olivine diabase older than the granite of the region.

Basic Rocks in the Volcanic-sedimentary Series

These rocks appear to be in the form of concordant elongated bodies or narrow lenticular masses no more than a few tens of feet in maximum width. They may not everywhere be concordant masses, as in one case at least, in the band of volcanics north of Iserhoff river, the border of one gabbro body was found to cut across the schistosity of the lavas at an angle of about 25 degrees. No accurate information is available regarding the length of the gabbro masses, but some are believed to persist for several miles.

Elongated masses of gabbro form the backbone of several of the ridges and high hills marking the band of volcanics parallel to Iserhoff river, and of a couple of prominent hills immediately south of the west end of Baptiste lake.

Petrography - Fresh olivine gabbro is found between Imbault lake and Iserhoff river, at the south end of the small lake lying in the band of volcanics that parallels the Iserhoff. The outcrop is fairly extensive and partly in the form of a steep cliff facing - 25 - south. At its west end it is cut by a dyke of pink, muscovite-rich pegmatite, 25 feet wide. In the gabbro there are splashes of barren, white and rose quartz. On the top of the scarp, the gabbro rapidly becomes fine-grained northward and gives place to finely-schisted andesite. The contact between the two is ill-defined and partly obscured by overburden. The rock in the south-facing scarp wall is medium grained, fresh, olivine gabbro with a pronounced ophitic texture. Pyroxene, occasional grains of which are altered to uralite, forms over 50 per cent of the rock; it has the small axial angle of pigeonite. The olivine (about 5 per cent) is generally fresh, .with some grains showing incipient serpentinization. The plagioclase is labradorite (Anal)) in zoned crystals, the cores of which are altered to kaolinite and white mica.

A thin section of a specimen collected a mile and a half toward the west-southwest from the chilled northern border of what may be the western continuation of the same body as above shows profound alteration. The texture is again ophitic but the grain is as fine as that of a coarse-grained lava. No olivine is seen and little pyroxene remains. The latter is replaced by minerals of the chlorite-serpentine group. The feldspar, with the exception of a few small laths, has been replaced by white mica.. A few feet south of the chilled border, the rock is medium-grained and indistinguishable, in hand specimen, from the fresh olivine gabbro first described.

Elsewhere in the area, the gabbro is rarely fresh. Most commonly it. is a rather medium- to coarse-grained, often schistose, hornblende-rich rock, some of which, in hand specimen, resembles diorite.

That there are true diorites associated with the gabbro has not been clearly established. As just mentioned, there are altered rocks resembling diorite, but these must be regarded as metagabbros because of their close field association with typical gabbro. To these, the term 'diorite' is applied as a field name only.

It must be ar3mitted, also, that even where diorites occur with no relation to typical gabbro, it is not certain that they are true diorites, and the term must again be considered as a field name. It applies to rocks consisting of hornblende and plagioclase and having somewhat the appearance of diorite. The reason for this restriction is that no typical diorite has yet been found in the area, and rocks thus named in the field have turned out to be, when evamined.under the microscope, highly metamorphosed types having little in common with true diorite. - 26 - The specimen, collected from the band of volcanics paralleling 2serhoff river, half a mile west of the point where the band. ,crosses the river, and which appears to be representative of the isolated field 'diorites', is a rock of apparent medium grain containing a preponderance of dark minerals. As seen in thin section, the light- coloured minerals are rather fine-grained and form an extremely confus- ed assemblage consisting mostly of feldspar with some quartz, and many small needles and flakes of hornblende and biotite. The dark minerals are green hornblende and very subordinate brown biotite, occurring in large, felty crystals and frequently Yn sheaf-like arrangement. The feldspar is plagioclase, as its refractive index is noticeably above that of balsam, but it lacks twinning and is full of minute colourless inclusions which impart to the crystals a mottled appearance. The groundmass is suggestive of a lava, and the rock is more likely a metamorphosed andesite than a diorite. Thus, although the evidence is still somewhat inconclusive and of a negative nature, it nevertheless suggests the absence of intrusive masses of a true dioritic nature associated with the gabbro. Consequently, the term 'diorite' must, for the time being, be understood to be a field name only.

Within the northern belt of the sedimentary-volcanic series are a few porphyrite or porphyry dykes having the composition of quartz leucodiorite or granodiorite. These, however, are totally different from the diorites just described. They are believed to be related genetically and in time of intrusion to the large mass of.quartz diorite exposed in the northwest corner of the area. For that reason, they are discussed later in this report. '

Anorthosite-gabbro Complex

A complex intrusive mass of anorthosite-gabbro with a strongly layered structure occupies a semi-elliptical area of some 40 square miles in the west-central part of the map-area and extends westward into the Opaoka River area. The central part of this hard and resistant mass has been carved into a group of some of the loftiest hills of the Abitibi region, known as the Dalhousie mountains.

The intrusive mass in the present area is believed to constitute the eastern end of a large elongate body, some 40 miles in total length, extending through the central part of Opàoka River area (14) and for a short distance beyond its northwest corner into the Kitchigama lake area (13). This long body has a maximum width of about eleven miles and stretches roughly east ana west in the shape of a fat, slightly-curved lens, convex southward. It is bounded on the south mostly by the older volcanic-sedimentary series and on the north by a younger batholith of quartz diorite, which penetrates it deeply'in -2?- places, and even breaks through it completely over a width of three miles in the vicinity of Opaoka lake, which lies four miles west of the present map-area. Thus, the Dalhousie Mountains intrusive mass is isolated from its much larger parent mass to the west by some three miles of younger quartz diorite.

Freeman (12) believed *that the anorthosite-gabbro was originally intruded in the form of a lopolith into the probably un- disturbed volcanic-sedimentary series, and later was folded with the surrounding formations into a tight syncline. His evidence of folding rests mainly on the fact that, in its western part, the intrusive displays compositional zones parallel to the elongation of the body and symmetrically located on either side of a central longitudinal axis. The synclinal structure was also demonstrated by Black from a study of the structure and textures of the differentiated layers of the complex. Although in both instances the evidence of folding is taken from the western part of the intrusive mass, it is assumed that the folding has affected its whole length. Freeman noted that in the Dalhousie Mount- ains intrusive, which represents the easternmost portion of the lopolith, the zoning was obscured by the profound alteration of the rock. The present writer confirms both the absence of recognizable zoning, and the evidence of alteration, principally in the form of replacement by hornblende of all the pyroxene and of some feldspar. Thus, the synclinal folding can be neither proved nor disproved within the map-area. The syncline, if present, would be overturned to the north, as evidenced by the south-dipping attitude of the layered intrusive mass and the similar attitude of the volcanic-sedimentary series near the southern border of the mass. The. concordant nature of the intrusive with respect to the series is indicated by the parallelism in strike of the layers of the intrusive and the formations of the series.

The anorthosite-gabbro is cut by dykes of quartz diorite, lamprophyre, and pegmatite, and by veins of barren quartz. A notable group of xenoliths of the rock of the complex is seen in the quartz diorite in a restricted area near the western boundary of the map-sheet, some two and a half miles north of the northern border of the anorthosite-gabbro mass. Around the western half of Ramsay bay, and along the northern shore in particular, the anorthosite-gabbro is riddled with small masses of quartz diorite, indicating that a zone of great complexity marks the contact between the two intrusives.

$Black, J.M., The Bell River Igneous Complex; Ph.D. Thesis, McGill Univ., 1942, (unpublished). - 28 - Petrography - The Dalhousie Mountains intrusive may be described as a heterogeneous mass of anorthosite and gabbro, marked by an extreme variability (Plate VIII B) throughout, and averaging a gabbroic anorthosite in overall composition, that is, a rock that could be defined as an anorthosite with about 30 per cent of ferromagnesian minerals. The rock of the mass is banded or layered, the banding being either sharp or, more commonly, gradational. Within a distance of a few feet across the banded rock, all intermediate types, from a pure white anorthosite to a dark gabbro or, locally, even to a pyroxenite, are likely to occur. The grain is generally coarse. The'rock has white to grey feldspar as the light-coloured component, and hornblende as the dark mineral. Pyrite, finely disseminated or in small veinlets, is not rare. Titanifeours magnetite is present in places in the more gabbroic types, and in a few instances is seen in relative abundance, although never in the massive state, in certain bands marked by a rusty appearance. A thin section of a specimen from a band that appears fairly representative of the mass as a whole shows hornblende in poikilitic crystals or sometimes in aggregates of smaller, needle-like individuals. The feldspar is highly calcic, with the composition of 'bytownite (An75), and possibly is more basic than the average plagioclase of the mass, which Freeman estimated to be Anna. It occurs in equidimensional crystals, averaging 2 mm., showing sutured mutual boundaries and pronounced incipient alteration to white mica. The grains contain many small inclusions of both feldspar and quartz, and also of hornblende. All inclusions are obviously replacement products. Granulation around the borders of the feldspar crystals, resulting in mortar structure, is commonly observed. Quartz is seen also in small veinlets crossing the feldspar grains, or in myrmekitic intergrowth with some of the smaller crystals of plagioclase.

Most of the features described by Freeman and by Black in their detailed studies of the complex were encountered by the writer in the Dalhousie Mountains intrusive. To re-describe them.here would serve no useful purpose. Two features that were not observed by those two authors in other parts of the complex may be briefly mentioned, however. One is a blocky structure, consisting of rounded blocks of anorthosite a few inches in diameter enclosed in a dark green, amphibolitic matrix. It was seen on a small outcrop on the southeast shore of the small lake two and a half miles north of Baptiste lake. The second feature is the presence of abundant red garnet in altered amphibolitic bands of the complex near its southern border. The garnet was seen in the southernmost outcrops along the portage linking the first and second lakes north of Baptiste lake, and again at a point about a mile due east of those outcrops. - 29 - The complex likely owes its origin to crystallization differentiation 'in situ', undoubtedly complicated, in Black's (14) words, by "repeated inflows of magma and many other processes". The magma inflows must have been on a small scale and are taken to mean residual magma squeezed out of, and spread between, partly-crystallized neighbouring layers of an already crudely-differentiated magma, in the fashion outlined by Bowen.

Lamprophyre and Porphyrite Dykes

Dykes of lamprophyre having the composition of hornblende kersantite (Johannsen) or malchite (Grout) were noted cutting- the anorthosite-gabbro complex. They were not found among the younger intrusive rocks of the map-area and for that reason it is suspected that they are older than those rocks.

Lamprophyres may, and probably do, occur in the volcanic- sedimentary series, but thus far they have not been detected with certainty owing to their close resemblance to recrystallized andesite. As the dykes have steep dips and appear to fill fracture systems produced during folding, there seems to be little doubt that they were injected at some time appreciably later than the folding of the series and the complex. Since they are generally deformed, however, they must have been affected by late-folding or post-folding movements, presumably by disturbances that attended the emplacement of the granitic masses.

The dykes, which do not exceed eighteen inches in width, fill two intersecting sets of fractures in the anorthosite, with trends respectively N.40°L. and N.80°-85°. The fractures of the first set are well reflected in the drainage pattern of the Dalhousie mountains. Occasionally they (and the dykes filling them) parallel the layering of the mass but more commonly they cut across it at a small angle. The more easterly trending fractures have little topographic expression, but dykes having this trend are of more frequent occurrence than those filling the northeast fractures. The dykes dip to the south or southeast at 60 to 80 degrees.

The lamprophyres are known to be older at least than the pegmatites of the area (which mark the final stage of the granitic intrusions), since one dyke cut by pegmatite was seen five and a half miles north-northeast of Baptiste lake.

Bowen, N.L., Crystallization-Differentiation in Magma; Jour. Geol., Vol. 27, pp.393-430, 1919. - 30 - In all these dykes, the rock is very similar. It is dark greenish and heavy, and in some of the dykes it tends to be slightly schistose. Hornblende is the predominant mineral and not infrequently it displays a schiller structure under the microscope. The plagioclase has the composition of basic andesine (An45); in some dykes it is in part altered to kaolinite, white mica, and epidote. Magnetite is ubi- quitous, occurring as 'schiller' in the hornblende and as blebs throughout the rock. Biotite is a very minor constituent of some of the dykes.

A few narrow dykes of porphyrite or porphyry were encountered as concordant intercalates in the rocks of the northern belt of the volcanic-sedimentary series. Somewhat similar dykes, but with a less- pronounced porphyritic texture, cut the anorthosite-gabbro complex. Most of these dykes differ little in composition from the quartz diorite that forms a large mass in the northwest corner of the area, and all of them occur within a short distance of'it. Furthermore, some are almost identical with a porphyritic facies of the quartz diorite encountered in the border of the mass on the north shore of Ramsay bay. It seems fairly certain, therefore, that all these porphyritic dykes are closely related to,the intrusion of the neighbouring quartz diorite.

The porphyrites consist of phenocrysts of oligoclase (Anyo) in a granular groundmass of plagioclase of much the same composition, with variable amounts of hornblende and biotite, quartz in large patches, and occasional grains of epidote and apatite.

Acidic Intrusive Rocks

General Statement

A little more than half of the exposed bed-rock in the map- area consists of igneous rocks of acidic character which intrude the volcanic-sedimentary series and the anorthosite-gabbro complex.

In composition, as well as in areal distribution, the acidic rocks fall into three types, namely:

(a)Quartz diorite (b)Quartz syenite (c)Pink granite

On Ramsay bay, the ouartz diorite is cut by the pink granite, and inclusions that correspond closely in composition and facies to the quartz diorite are found in the pink granite east and northeast of Im- bault lake. These facts show that the quartz diorite is older than the granite. The quartz diorite and the quartz syenite are not found in association, but the quartz diorite is assumed to be the older of the - 31 - two. No clear contact relationships between the quartz syenite and the granite were observed, but the local tendencies of the granite toward a pegmatitic facies suggest that it is the youngest of the three intrusives.

Megascopically, the three types of acidic intrusives resemble one another fairly closely and none is a clearly typical rock type. In composition, the diorite and syenite incline toward a granite, and the pink granite itself is, on the whole, deficient in dark minerals. It is believed that the three intrusives are closely related genetically to the same general granitic magma.

Quartz Diorite

Distribution - The quartz diorite forms a mass, some fifteen square miles in extent, in the northwest corner of the area, wedged between the volcanics to the northeast and the anorthosite-gabbro complex to the south. It is known (14) to extend for a considerable distance westward beyond the limits of the present map-area. Small bodies of the `rock are seen cutting the volcanic-sedimentary servies in the vicinity of Goeland lake and also the anorthosite-gabbro complex. The diorite is itself cut repeatedly by, and occurs as inclusions in, the granite on the south side of the eastern part of Ramsay bay.

Petrography - The quartz diorite is a grey to, in places, slightly pinkish, medium-grained rock which possesses a distinct foliation and consists essentially of plagioclase, quartz, and biotite. It is not a typical diorite due to its relatively low ferromagnesian and high quartz content, and it could well be termed a quartz monzonite, or an oligoclase or soda granite. However, these names would still not describe the rock adequately, and since Freeman and Plack (14), in the adjoining Opaoka River area to the west, have given the name Olga ouartz diorite to the main mass of the same intrusive body; the term quartz diorite is retained here for uniformity.

The plagioclase is sodic to intermediate oligoclase (An17_20), and occurs in relatively large, zoned crystals with approximately rec- tangular outlines. Alteration to white mica is not infrequent and, when present, is more intensive in the calcic cores than elsewhere.

Some of the information on the petrography of the acidic intrusives was supplied by P.E. Imbault, the writer's senior assistant in the field, who wrote a thesis entitled "The Acidic Plutonic Rocks of the Iserhoff River Area" in partial fulfillment of the requirements for the degree of Master of Science, McGill University, 1947 (unpublished). - 32 - Quartz is present in large enhedral grains with strong undulatory extinction, and biotite in small flakes, straw-yellow in colour and f resh in appearance.. Much epidote, often in large well- formed crystals, is associated with the biotite. In one thin section, the biotite flakes, accompanied by stringers of epidote, are moulded around large crystals of plagioclase and quartz. Subordinate amounts of microcline are present in some parts of the rock, usually in small crystals along the borders of plagioclase grains..

The rock of the border portion of the mass exhibits diverse facies but is characterized, in general, by marked granulation and a greater content of microcline and biotite than the average rock. North of Ramsay bay, near its contact with the anorthosite-gabbro, the quartz diorite is, in places, fine-grained and massive, in others, coarse- to medium-grained and very strongly gneissic. Near its contact with the volcanic rocks, it is suite coarse and porphyritic and unusually rich in dark minerals. Generally ,at these contacts, the plagioclase phenocrysts are traversed by parallel fractures, but no extensive granulation of. the rock is evident. On the other hand, along the contact close to the northwest corner of the map-area, the rock is strongly ' granulated and characterized by the presence of green hornblende accompanying chloritized biotite. ouartz Syenite

Distribution - Most of the map-area south of Iserhoff river is underlain by acidic intrusive rocks of the.composition of quartz syenite. These rocks belong to an extensive intrusive mass, some twenty- five miles long and seven miles wide; elongated along an east-west axis, and lying, for the most part, south of the map-area (6). Within the area, the syenite forms a relatively-elevated region of massive, flat- topped hills with gentle slopes. Its northern border stands in marked relief against soft, easily-eroded sedimentary rocks of the southern volcanic-sedimentary belt, and has exerted a clear control on most of the course of the Iserhoff, which flows easterly along, or close to, the northern edge of the syenite.

Petrography - The rock is medium-grained, pink in colour, and generally shows a distinct alignment of the dark minerals. It consists of plagioclase, microcline, hornblende, and variable amounts of quartz.

Throughout most of the mass, within the limits of the present area, little or no quartz is apparent in hand specimens and, as a rule, only a small amount is found under the microscope. Thus, the rock can be termed a quartz syenite. A true granite rock occurs, however, in the western part of the mass, where the intrusive crosses the - 33 - southern boundary of the map-area. The rock there is well foliated and the quartz is clearly visible in large grains flattened along an axis parallel to the alignment of the dark minerals. It carries biotite and muscovite instead of hornblende. A muscovite-bearing pegmatite is frequently found in association with it.

The granitic and syenitic rocks may be facies of the same mass and mutually gradational, as both show the same degree of deformation. On the other hand, the fact that in the granite the ferromagnesian mineral is biotite, and the fact that the rock has pegmatitic tendencies, suggest that it may be somewhat later than the syenite. In composition and character, the granitic facies is similar to the pink granite occurring in a large body north of the main volcanic-sedimentary belt. It may be a small offshoot from that body and thus probably intrusive into the syenite.

Occasionally, the hornblende-bearing rock contains enough quartz to be classed as granite, but such facies are of limited occurrence and are undoubtedly gradational into the normal quartz syenite.

In the part of the mass lying south of the map-area, Mac- kenzie (6) found the rocks to be granitic (or granodioritic) and syenitic, and termed them 'gneisses'. As he makes no mention of their dark mineral content or relationship, it is to be assumed that they are mutually gradational and possibly of the hornblende type.

In the typical quartz syenite, the plagioclase is calcic oligoclase and is markedly predominant over the microcline. In all but one of the thin sections examined, the ferromagnesian mineral is deep green hornblende; in the exception referred to it is pale green, uralit- ic hornblende associated with a pyroxene, probably diopside. Quartz, in variable but usually very minor amount, is present in small, interstitial grains. Epidote, sphene, and apatite are abundant.

Quartz Leucodiorite - A fine-grained, light grey rock was seen in contact with the quartz syenite on a small exposure about hai-e a mile south of the Iserhoff and two and three-quarter miles west of the east border of the area. The contact between the two rocks is fairly sharp but gives no indication of their relative ages.

This rock consists chiefly of plagioclase (An25-30) with some 10 per cent of quartz, 15 per cent of biotite, and minor hornblende. It carries abundant epidote, some sphene, and some apatite. Many of the plagioclase crystals show partial to complete alteration to white mica and saussurite, and even the fresh-looking grains are full of innumerable, very tiny inclusions. Chlorite is present in small amount as a product of alteration of either biotite or hornblende, or of both. - 34 - This rock is almost unquestionably of igneous origin, but it is not known at present whether it is older or younger than the Quartz syenite. Its Plagioclase is distinctly more calcic than that of the quartz diorite of the northern part of the area. Also, the rock is more typically dioritic and could be termed, adequately, auartz leucodiorite.

Pink Granite

Distribution - The pink granite occurs throughout the whole east-central half of the map-area, between the southeastern shore of Goeland lake and the northern limit of the southern belt of volcanic- sedimentary rocks. It forms much the same type of topography as the syenite of the south, namely, a plateau region with flat-topped, gently- sloping, massive hills.

Petrography - The rock is pink, medium-grained, and poor in dark minerals. It has the composition of a biotite granite with sodic tendencies:

Plagioclase (An14_17) 15-20% Potassic feldspar 30-40% Quartz 25-40 Biotite 4-8â

Common accessory minerals include muscovite, epidote and allante, apatite, and magnetite.

The potassic feldspar is chiefly microcline, although orthoclase was observed in some of the thin sections. It is fresher than the plagioclase, which frequently shows alteration to white mica. This rock, however, is definitely the least altered of the three types of ac'_iic intrusives occurring in the area.

Biotite is the characteristic dark mineral and the predominant mica, but muscovite is fairly common and, in some facies, prevails over the biotite, especially where the mass tends to be pegmatitic.

In most of the thin sections examined, the rock shows signs of mild granulation around the borders of the larger mineral grains. Another constant feature is the occurrence of some quartz in vermicular intergrowth with, and as globule within, the microcline, and, less commonly, around the borders of the plagioclase. Microperthitic inter- growths are less frequent. - 35 - The granite bordering the west side of the shear and fault zone on the south shore of Ramsay bay has been transformed into a strongly gneissic rock that may be termed a 'leaf-gneiss'. The leaf- gneiss structure is best developed immediately along the shear zone. Under the microscope, the rock shows a mosaic of equant grains of feldspar, which is obviously the result of granulation, and long, narrow patches of quartz, flattened parallel to the alignment of the biotite.. The deformation of the granite here is strictly local and is due to movement along the fault zone. Away from the fault, the leaf structure disappears progressively.

Pleistocene and Recent

The Pleistocene ice-sheet moved over the region in a direction slightly west of south, as indicated by the attitude of the glacial striae. Following the retreat of the glaciers, most of the area was submerged under the eaters of glacial lake Barlow-Ojibmay. . It is estimated, however, that at least one-fifth of the area — chiefly the elevated parts of the anorthositic and granitic massifs and probably some prominent morainic hills as well — escaped flooding by the waters of the lake. These unsubmerged areas included the following: the central part of the anorthosite-gabbro mass, which formed an 'island'•with a diameter of some.six miles; most of the area of granitic rocks south of the Iserhoff; two large granite 'islands' lying along the eastern border of the map-area, immediately north and south, respectively, of the small lake six miles northeast of Imbault lake; two or more 'islands' of similar rock close to, and a short distance north-northeast of, Imbault lake; and several prominent isolated hills, one south of the middle part of Ramsay bay and the others at various points within the southern belt of the volcanic-sedimentary series, but mostly between Baptiste lake and Iserhoff river.

The mantle of loose sediments is thick and widespread in the low areas but rapidly becomes thin and patchy toward the higher ground. Clay is particularly abundant along the lower reaches of Iser- hoff river and Imbault creek and along the large stream that forms the north branch of the latter. There are noteworthy deposits also along the lower part of all the main streams of the area except for the large stream entering the head of Ramsay bay. The best exposures of verved clay, with flat concretions, were seen about half way up the Iserhoff or four miles south of Imbault lake.

An extensive accumulation of unconsolidated sediments, seemingly in. part of morainic and in part of lacustrine origin, forms a band from one to two miles wide extending diagonally across the map- area from south of Baptiste lake to the eastern part of Ramsay bay. The - 36 - material of the band varies greatly from place to place. South and east of Baptiste lake, it consists of yellow, clayey sand, which forms particularly extensive plains. North of Imbault lake, dlay is more abundant and the band is deeply dissected into an intricate network of ravines and steep-sided hillocks by a large stream and its tributaries which traverse it. Farther north, toward Ramsay bay, the material of the band is largely coarse gravel. This large accumulation of loose sediments obviously contains, in some of its parts, abundant material that could be utilized for road-building or other similar purposes.

STRUCTURAL GEOLOGY

Folding and Faulting

The rocks of the volcanic-sedimentary series are characterized by a persistent bedding schistosity which indicates that they have been subjected to tight or isoclinal folding. In the southern belt, the folding has been along east-west axes; in the northern belt, judging from the rather limited information available within the confines of the present area, the folding would appear to have taken place along northwest-southeast axes.

The general strike of the schistosity in the southern belt varies between east and east-northeast, the latter trend prevailing, as a rule, in its southern half. Some notable local departures from the general trend are discussed below. The dip is overwhelmingly to the north, and generally steep, except in the eastern half of the belt, where the sedimentary rocks and some adjacent volcanics dip to the south. South of Imbault lake and Imbault creek, the dip is commonly vertical or very steep to the north or,in places, to the south.

In the northern belt, of which relatively little is exposed, the trend of the schistosity is parallel to the line of contact between the rocks of the series and the bordering intrusive rocks. Thus it is to the northwest, west of Goéland lake; to the north in the narrow inclusion south of Ramsay bay; and approximately due east along the southeastern shore of the lake and on the island lying at the entrance to Ramsay bay. In the broadest part of the belt, that is, west of Goéland lake, the rocks of the series dip very steeply to the northeast. Elsewhere, the dip of the schistosity is subject to rapid change, as the series is somewhat fragmentary and disturbed,owing to intimate penetration by the granite.

The layering in the anorthosite-gabbro complex trends fairly uniformly in a N.60°E. direction and dips south at an average angle of 65 degrees. A schistosity present in some gabbroic layers parallels the layering in strike and dip. There is some indication, as shown by - 37 - the attitude of the strike in the eastern part of the mass, that the layering tends to parallel the border of the intrusive. The evidence for this is rather scanty, however, and, moreover, some of the strike observations in the area of the magnetic 'anomaly', south of the west end of Ramsay bay, may be erroneous due to local magnetic attraction. Minor folding or crumpling and small-scale faulting were observed at several points throughout the mass. Somewhat larger disturbances are recorded on the map and are evident from the sharp departure of the strike from the average trend. One such conspicuous irregularity, due to either folding or faulting within the mass, appears near the border of the map-area, five miles north of Baptiste lake.

A mild to strong gneissic character is found in the syenite south of Iserhoff river and in the quartz diorite in the northwest corner of the area. In both cases, the dark constituents of the rock tend to be aligned along planes parallel to the border of the intrusive mass. In the syenite, the gneissic trend is predominantly east-west, but the dip can seldom be reliably ascertained. In the quartz'diorite, the trend is west to northwest and the dip is steeply to the north or northeast.

In the central granite mass, there is generally no marked gneissic trend. This is possibly due in part to its leucocratic nature.

The structural interpretation of the volcanic-sedimentary series has been discussed previously in this report. Anticlinal folding along an east-west axis passing between the two sedimentary belts has been postulated, as also has a major transverse north-south fault, dis- rupting the series midway in its east-west length, south of Imbault lake. Presuming that the bulk of the sedimentary rocks are younger than the volcanics, the possibility of an east west fault along the northern border of the northern sedimentary belt, west of the north-south fault, has also been mentioned, which could explain, through down-faulting of the southern block, why the volcanics south of Baptiste lake apparently overlie the sedimentary rocks of the belt.

According to Freeman and Black (14), the lopolithic sheet of anorthosite-gabbro is folded into a tight syncline. Judging from the trend of the layering in the banded anorthosite within the present map-area, the synclinal axis would trend approximately N.60°E., some- where through the central portion of the Dalhousie Mountains intrusive.

The anticline of the volcanic-sedimentary series is largely overturned to the south-so that its axial plane dips north, whereas the syncline is overturned to the north so that its axial plane dips south. The axial planes of these two folds are thus mutually convergent downward. - 38 - The folding is clearly not limited to a simple anticlinal- synclinal structure. As mentioned previously, minor folding occurs throughout the anorthosite-gabbro mass. Similar folding was also observed throughout the volcanic-sedimentary series, as shown by sudden deviations of the strike of the schistosity from the average local trend and by reversals of dip. In several instances, such changes are of suffi- ciently large areal extent to appear on the map, anrï some of these are discussed below; in numerous other cases, however, the folding is of the nature of small-scale, obscure crumpling, complicated by shearing and minor faulting, and is too limited to be shown on the map.

The sedimentary-volcanic series in the area lying north and northeast of Baptiste lake shows some remarkable deviations from the regional trend. At the south end of Mad lake, the series has its average easterly trend, but westwardly and northwestwardly from there the trend swings rapidly to the north, and the series thus appears to wrap around the southwestern part of the lake. East of the.lake is an exposureless tract extending for some two miles eastward and bounded on the north by anorthosite with easterly-striking structures, on the east by'north-striking formations of the volcanic-sedimentary series, and on the south by east-striking formations of this series.

The attitude of the rocks of the volcanic-sedimentary series west, south, and east of Mad lake suggests that the lake and the exposureless area east of it are underlain by an.east-trending igneous mass that was emplaced by pushing a large portion of the sedimentary-volcanic series southward. This could produce the northward-striking, and in part wrapping, attitudes of the formations at the west and east ends of this postulated intrusive body.

The finding, by .the writer's party, of exposures of anorthosite at the south end of Mad lake led to the belief that the presumed intrusive body was a southward bulge of the large anorthosite-gabbro massif of the Dalhousie mountains or a large faulted block of that massif that had been driven southward into the series. However, the subsequent discovery, during more detailed work in this area by the Dominion Gulf Company, in 1948, of several exposures of granite on the west side of the lake indicated the possibility that the intrusive body is granite. The ,flatness of the exposureless tract favours an underlying granite rather than anorthosite, for it is well recognized that, within the region, the latter forms a rugged topography whereas the granite gives rise to fairly flat or gently-rolling surfaces. The intrusive body is most likely a phacolith, and it is not improbable that its southeast part connects under the band of unconsolidated sediments passing east of Baptiste lake with the very large granite mass to the east. This would - 39 - leave the sedimentary-volcanic rocks on the eastern side of the phacolith in the form of a large, crescent-shaped inclusion in the granite.

Additional evidence of complexity in the vicinity of Bap- tiste lake is the general reversal of dip noted in the volcanic-sedimentary series north of the lake with respect to the formations south of the lake. The latter are known to be right-side-up and to dip north. In the hills north of the lake, the formations dip consistently south and southwest, but their true attitude could not be determined. However, since the layered anorthosite is thought to form a syncline with south limb overturned to the north, and since the series north of the lake, where found in close proximity to the anorthosite, is closely concordant with it, it follows that the tops of the beds would be to the north; in other words, the volcanic-sedimentary series north of the lake would be, overturned along with the layered. anorthosite. On the other hand, if the tops of the beds north of the lake were shown to face to the south, the dip reversal would intricate the presence of a small synclinal fold with axis following the elongation of Baptiste lake.

The vicinity of Baptiste lake lies between two distinct major structures, namely, the Dalhousie Mountains syncline and the anticline oP the volcanic-sedimentary series. Since the axial planes, of - these two folds converge downward. — a condition which may be taken to mean tight and complex folding — secondary folding or faulting, or likely both, must be present in the region between them, probably in the vicinity of Baptiste lake. The lake itself, which forms a marked topographic depression, is possibly the locus of a fault. There can be little doubt that the folding that occurred, as suggested by the con- verging axial planes, was of a type susceptible to produce marked strike faulting.

Several hills and interrupted ridges of relatively-marked relief, oriented along axes with east to east-northeast trend, constitute a conspicuous feature in the band of volcanics parallel to Iserhoff river. Some of these that are of short extent, have steep slopes on the north and south, and consist mainly of gabbro, are possibly monadnocks. Others, with steep scarp faces on the south side and low, gentle, in places almost imperceptible, slopes on the north side, may well be due to faulting. They are usually characterized by greater length, and the gabbro member in them is not always conspicuous., A careful inspection of. vertical aerial photographs shows an almost uninterrupted south- facing scarp extending for a length of four miles from the south end of the small lake two miles south of Imbault lake eastward to Iserhoff river. A prominent scarp face also bounds the south side of the high hill lying across the western boundary of the area just north of the Iserhoff, and continues east-northeast beyond that hill for two miles. - 40 - In the region south of Imbault lake, the aerial photographs show also a few parallel east-west lines, several miles in extent, which are seldom marked by distinctive topographic features, but rather by a delicate variation or change in the vegetation. These may be either narrow gabbro bodies or faults.

The rectilinear character of the scarps, ridges, and lines, and their parallelism with the local trend of the formations, show that the faults, if any, are strike faults, and that both the gabbro bodies and the faults, as the case may be, are steeply dipping and closely concordant in attitude with the volcanic and sedimentary rocks.

The comparatively deep, trench-like depression of the valley of the Iserhoff marks, it is thought, a major zone of weakness through the southern part of the area. The valley trench lies in the southern part of the southern sedimentary belt and follows a general east- northeasterly direction parallel to the bedding and bedding schistosity of the sedimentary rocks. No rock exposures were seen along the valley floor, but the sedimentary. formations outcropping occasionally on the lower part of the valley sides are of a highly-fissile nature. It is thus reasonable to assume that the exposureless valley bottom is underlain by a zone of highly-sheared and readily-eroded sedimentary rocks which constitutes a major shear-zone fault or strike fault through the area. _

Shearing

One well-defined shear zone was observed in the area. It is localized at the contact between granite and volcanics along the east shore of the deep, narrow bay projecting south from the middle part of Ramsay bay. The direction of shear is close to north-south and parallel to the trend. of the volcanics, as well as to that of the contact between them and the granite. It dips steeply to the east, in the vicinity of 80 degrees. The shear zone has been recognized along its strike from the shore of Ramsay bay to a point a little less than one mile to the south, beyond which exposures are lacking. Ât the contact, where the shearing has been most intense, the volcanics have been converted to a crumbly, chlorite schist,_and the granite to a leaf- gneiss. Exposures of the chlorite schist were found as far as 200 feet east of the contact, and, to the west, a gneissic character still persists in the granite on the opposite shore of the narrow bay, for a distance of almost half a mile. Disseminated pyrite occurs in the schisted granite near its contact with the volc'anics.

Several prominent scarp faces, which parallel in orientation the above shear and may represent faults, wall the lower stretch of the - 41 - valley at the mouth of which the shear occurs. The most conspicuous parts of these scarps have been indicated on the map. As shown, they occur on both.sides of the valley, and the shear, if projected southward, would lie between them and at the bottom of the valley. The most persistent scarp is on the west side of the valley and is characterized by the presence in its middle part of , a prominent hanging valley in which a large stream flows eastward from the tableland to the west.

It will be recalled that the postulated fault in the south between Imbault lake and Iserhoff river trends toward the above shear and scarps, thus indicating the presence throughout the entire area, from Ramsay bay to south of the Iserhoff, of a major zone of shearing and faulting which may be of considerable importance in respect to the economic possibilities of the area.

An exposure of granite on the south shore of Ramsay bay, one Mile east of the main shear, shows. a set of closely-spaced fractures striking N.15°W. which probably represent minor shearing related to the main shear.

local shearing of erratic orientation is apparent at many places in the volcanics around Ramsay bay and Goéland lake, where the rocks have been intimately invaded and crumpled by the granite. The rocks of the volcanic-sedimentary series exposed along Imbault creek, ,, three-quarters of a mile east of Imbault lake, are also sheared and deformed, probably due to the fact that they lie in the vicinity of the major zone of deformation of, the area or, more specifically, along the northward projection of the north-south fault through the series.

At various other. points throughout the volcanic-sedimentary series, intense schistosity, parallel to the regional trend of the formations and accompanied by marked alteration, affords evidence of shearing movements parallel to the elongation of the belts of the series.

The rocks south of Baptiste lake are traversed by a regular system of shear fractures which trend N.30°W., across the bedding schistosity, and are spaced a fraction of an inch or more apart. quartz stringers following the bedding schistosity have been broken up and dis- placed into an 'en échelon' pattern by these fractures. Along any in- dividual fracture, the slippage amounts to less than one inch and the . east side has moved south with respect to the west side. -42 -

ECONOMIC GEOLOGY

Mineralization, chiefly pyrite with some chalcopyrite, is seen frequently in the rocks of the volcanic-sedimentary series. At one place at least, along the Ramsay Bay shear, the sulphides occur in the granite itself.

In the southern part of the area, sulphide mineralization is relatively widespread in the rocks of the series, and more especially in the volcanic members between Inbault lake and the small lake two miles south. Sporadic mineralization occurs, also, eastward of the small lake, all along the band of volcanics that parallels Iserhoff river. In the north, mineralization is found at several points along the Ramsay Bay shear; in an inclusion of volcanics in thé anorthosite- gabbro complex, two and a half miles southwest. of the shear; and on most of the islands and around the shore of Goéland lake inhere volcanics are encountered, particularly on the three islands north of the shear, in the volcanics of the northwestern shore at the mouth of Ramsay bay, and in most of the exposures within a radius of about a mile from the mouth of the large river flowing into Goéland lake from the west.

It is possible to see, in the localization of all the above occurrences, a distribution along a north-south axis coinciding with the major zone of shearing and faulting in the area. As mentioned before, this zone extends, in a direction slightly east of north, between the southern boundary of the map-area and the south shore of Ramsay bay, and passes close to the east side of Imbault lake. Evidence is lacking, owing to the absence of outcrops, to show that the zone persists north of the Ramsay Bay shear. Assuming that it does continue, it would traverse the eastern part of the peninsula separating Goéland lake and Ramsay bay. The fact, that aerial photographs of this locality show linear features in line with the Ramsay Bay shear and passing about half a mile west of the eastern shore of the peninsula supports this assumption. In the northern half of the map-area, sulphide mineralization is found along the regional break and west of it, within a distance of three miles, and notably in the vicinity of the mouth of the large river flowing into Goéland-lake, that is, tw6 and a half miles west of the 'break'. In the south, mineralization occurs along the break and east of it, up to a distance of four miles or more, the best concentrations seen being south of Imbault lake and at a point some threè and a half miles east of the break, in the band of volcanics parallel to Iserhoff.river. There exists, therefore, a distinct con- nection between the regional zone of faulting and shearing and the known mineral occurrences of the map-area. - 43 - The sulphides occur, either disseminated or in small stringers, in silicified volcanics and associated intrusive intercalates, but seldom in the sedimentary rocks. None of the occurrences seen by the writer are of economic importance in themselves. They. indicate, however, that mineralizing activity has occurred in the rocks of the region, and thus the possibility of finding deposits of economic interest exists.

Numerous veins of quartz, some up to 30 inches in width, were encountered throughout the area; they occur in rocks of all types. Those in, the rocks of the volcanic-sedimentary series almost invariably parallel the schistosity, although occasionally they cut across it at _a very small angle. Some veins south of Imbault lake, in the vicinity of the regional north-south 'break', trend in a north-south direction. host of the veins are barren; some are sparsely mineralized with 'write or other sulphides or have a slight rustiness due to the oxidization of these minerals. Of five assays, made in the laboratories of the Quebec Department of Mines, of grab samples from the best-looking occur- rendes of mineralization in various parts of the map-area, none showed the presence of gold.

Recommendations

It has been shown that a prominent zone of faulting and shearing', trending approximately north-south, extends through the central part of the Iserhoff River area, and, furthermore, that the mineral occurrences of the area appear to be closely associated with this zone. The zone traverses, among other rocks, those of a volcanic-sedimentary series present in the southern and northern parts of the map-area. In the south, the series trends east-west and is sheared in the same direction. In the north, the series trends, and is sheared, in a northwest- southeast direction. There are thus in the area two,major directions of shear cut by a later north-south zone.of fracture. The two main shear directions are parallel, respectively, to the elongation of the belts of the volcanic-sedimentary series in which they occur: one is east-west or possibly a little toward the east-northeast; the other is northwest-southeast.

Although sulphide mineralization does occur within the north-south zone of fracture itself, as in the Ramsay Bay shear and locally south of Imbault lake, it is more common near, or a short distance away from, the zone, and tends to be localized along the shears that parallel the elongation of the belts of the series. In aridition to being confined, in almost all cases, to the rocks of the volcanic- sedimentary series, the sulphide mineralization seems to show, even r

-44 - among the rocks of the series, a preference for the volcanics and small intercalated intrusive bodies.

The fact that no gold mineralization was observed, and' that assays of the few specimens collected for that purpose yielded negative results, need not deter further prospecting.

In the region to the south — at Rose (Madeleine) lake, Cameron lake, in the Florence River area, and elsewhere — many notable discoveries of gold mineralization have been made along the safde north- south zone of shearing and faulting whose northward projection extends across the present map-area. This encourages the hope that similar discoveries will be made along the zone in the Iserhoff River area.

BTT3TTOGRAPHY

(1)BELL, Robert, Geol. Surv. Can., Ann. Rept., Vol.VIII, Part A, 1895, pp.75-85; Vol.IX, Part A, 1896, pp.64-74. (2)BELL, Robert, Report on the Geology of the Basin of Nottaway River; Geol. Surv. Can., Ann. Rept., Vo1.XIII, Part'K, pp.1-11, 1900, Map No.702. (3)BANCROFT, J.A., Report on the Geology and Natural Resources of Certain Portions of the Drainage Basins of the Harricanaw and Nottaway Rivers; Que. Dept. of Mines, Fish., Rept. on Mining Operations in the Prov. of Que. for the year 1912, pp.131-198. (4)COOKE, H.C., Some Stratigraphie and Structural Features of the Pre- cambrian of Northern Quebec; Jour. Geol. Vol. 27, 1919, pp.65-78, 180-203, 263-275, 367-382. (5)LANG, A.H., Waswanipi Lake Area; Geol. Surv. .Can., Summ. Rept., 1932, Part D, pp.36-43. (6)MACKENZIE, G.S., Currie Township Map-Area, Abitibi District; Que. Bur. Mines, Ann. Rept., 1935, Part B, pp.81-108, Map No. 353. (7)NORMAN, G.W.H., Preliminary Report, Waswanipi Map-Area, Northern Quebec; Geol. Surv. Can., Paper 36-3, 1936. (8)DOUGLAS, G.Y., Bruneau Township and Surrounding Area, Abitibi District; Que. Bur. Mines, Ann. Rept., 1936, Part B, pp.37-60, Map No 402. - 45 - (9)SPROULE, J.C., Preliminary Report, East Half, Waswanipi Map-Area, Quebec; Geol. Surv. Can., Paper 37-5, 1937. (10)bER0U1E, J.C., Puskitamika Lake Sheet; Geol. Surv. Can., Map No. 570A, 1940. (11)FREMAN, B.C., Replacement Shells Around Batholiths in the Waswa- nipi District, Quebec; Jour. Geol. Vol. 46, 1938, pp.681-699. (12)FREEMAN, B.C., The Bell River Complex, Northwestern Quebec; Jour. Geol., Vol. 47, 1939, pp.27-46. (13)LONGEEY, W.V., Kitchigama Lake Area, Abitibi Territory; Que. Dept. • Mines, G.E. 12, 1943, Map No. 509. (14) .ftiEhMAN, B.C., and BLACK, J.M., The Opaoka River Area, Abitibi Territory; Que. Dept. Mines, G.R. 16, 1944, Map No. 581. r

- 46 - AT—PHABETICAL INDEX

Page Page Acidic igneous rocks 11 Dalhousie mountains 5,26,27 Actinolite ... 14 Intrusive 28,37 Allanite 34 Syncline 39 Altitude of hills 4 Dept. Lands and Forests Amphibolite 15 Services of 3 Andesite 18,20,25 Diabase, olivine 24 Anorthosite 38 Diorite , 25,26,31 Anorthosite-gabbro 23,24,26 Diorite, quartz 24,26,27 27,36,42 Dominion Gulf Company Anticlinal structure 22,23 Discovery by 38 Apatite 13,15,16,33,34 Douglas, G.V. - Ref. to work by 3,24 Bancroft, J.A. - Dykes 20,24,26 Ref. to work by 3,8 Lamprophyre 29 Banding 14,16,19 Pegmatite 25 Baptiste lake 2,19,22,24 Porphyrite •30 Base-map 3 Basic igneous rocks 11 Epidote 14,20,30,32,33,34 Bell River complex 11 Bell, Robert - Faulting 18,21,22,23,39,41,42 Ref. to work by 3 Feldspar 13,19,25,26,28,34 Biotite 14,16,19,26,30,31,32,33,34 Ferromagnesian minerals .. 14,15,33 Black, J.M. - Folding 21,36,37,38 Ref. to work by 3,27,28,29,31,37 Formations 10,13,39 Bowen, N.L. - Freeman, B.C. - Ref. to work by 29 Ref. to work by 3,11,27,28,31,37 'Breaks' 21 Bruneau area 24 Gabbro 11,18,23,24,25 Russell, Frank - Olivine 24,25 Acknowledgment to 3 Garnet 16,20,28 Gneiss 22,33 Canadian Pacific Air Lines - Amnhibolitic 18 Services of 3 Hornblende. 21,22 Canoe routes 1 Granite ... 11,18,20,24,30,31,32,34 Carbonate 14 35,38,41 Chalcopyrite 42 Granodiorite 26 Chlorite 13,14,33 Gravel 36 Clay 35,36 "Greenstones" 24 Clinozoisite 20 Grenier, Paul Emile - Conglomerate 18,19,20,21,22 Acknowledgment to 3 Consolidated rocks 10 Greywacke 18,19,20 Cooke, H.C. - Ref. to work by 3 Harker, Alfred - - 47 - Page Page Ref. to work by 14 Pegmatite 25,33 Hematite 14 Photographs 3,42 Hornblende .. 14,15,20,26,30,32,33 Pigeonite 25 Gneiss 12,13,16 Plagioclase . 15,25,30,31,32,33,34 Kersantite 29 Porphyrite 17,25,30 Pyrite 14,20,28,40,42,43 Ice sheet 35 Pyroxene 25 Igneous rocks 10,11 Ilmenite 15,16 Quartz ... 13,16,19,20,25,26,28,32 Imbault, Paul Emile - 33,34,43 Acknowledgment to 3 Diorite 11,30,31,32 Ref. to work by 31 Leucodiorite 33,34 Stringers 41 Kaolinite 25,30 Syenite 11,30,32 Kitchigama Lake area 26 Quartzite 22 Feldspathic 18,19,22 Labradorite 25 Takes of area 4 Rhyolite 15 Lamprophyre 24,29 Rivers of area 5 Lang, A.H. - Royal Canadian Air Force Ref. to work by 3 Services of 3 Lavas 12,15,18,20,22 Leucodiorite, quartz 26 Schist - Leucoxene 13 Amphibolitic 20 Limonite 14 Chloritic 20 Longley, W.W. - Sedimentary rocks . 10,11,16,17,18 Ref. to work by 26 19,21,22,23,36,37 Shear zones 22,40,42 Mackenzie, G.S. - Sills '24 Ref. to work by 3,32,33 Sphene 14,16,20,33 Magnetite ... 14,15,16,20,28,30,34 Sproule, J.C. - Malchite 29 Ref. to work by 3,22 Metagabbro 25 Sulphides 42,43 Mica 14,19,25,30 Syenite 21,31 Microcline 32 Temperature of area 8 Mineralization 42,43,44 Temiscaming type rocks 22 Muscovite 20,34 Tremolite 20 Uralite 25 Norman, G.W.H. - Volcanic rocks .... 10,11,12,13,19 Ref. to work by 3 21,22,23,26,42 Volcanic-sedimentary series .23,24 Olga quartz diorite 31 26,36,37,38,39,41,43 Olivine 25 Xenoliths 27 Opaoka River area 26 Zircons 16,20 Orthoclase 15,19 Zoning 27 r-