NORTH SHORE of the SAINT-LAWRENCE from AGUANISH to WASHICOUTAI BAY, SAGUENAY COUNTY PROVINCE of QUEBEC, CANADA Department of Mines Honourable C

RG 043(A) NORTH SHORE OF THE SAINT-LAWRENCE FROM AGUANISH TO WASHICOUTAI BAY, SAGUENAY 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 43

NORTH SHORE OF THE SAINT-LAWRENCE FROM AGUANISH TO WASHICOUTAI BAY SAGUENAY COUNTY

by Jacques Claveau

QUEBEC RÉDEMPTI PARADIS PRINTER TO HIS MAJESTY THE KING

1950

Ministère des Richesses naturel:es du Qu{bec 1

:iEIiVICE DOCUMENTATION TE~1i, tcà.3~:

TABLE OF CONTENTS

Page

INTRODUCTION 1 Location of area 1 Means of access 1 Previous work 1 Field work 2 Acknowledgments 3 DESCRIPTION OF THE AREA 4 Topography 4 Vegetation 6 Settlements 6 Industry 7 TABLE OF FORPMATIONS 8 GENERAL GEOLOGY 9 PETROLOGY 13 Sedimentary rocks 13 Gneisses 14 Banded gneisses 14 Granitic gneiss 16 Quartz-dioritic gneiss 17 Basic rocks 19 Granitic intrusives 22 General statement 22 Gneissic granite with occasional augen facies 22 Microperthite granite 23 Small masses and dykes of pegmatite and granite 24 Prehnite rock 25 STRUCTURAL GEOLOGY 25 ORIGIN OF THE BASAL COMPLEX 28 Summary 31 GLACIAL GEOLOGY 32 ECONOMIC GEOLOGY 33 Fluorite 33 Graphite 33 Iron sands 33 Magnetite 35 Pyrite 35 CONCLUSIONS 36

MAP AND ILLUSTRATIONS

Map No. 819.— Geology of the North Shore of the Gulf of St-Lawrence, Aguanish to Vashicoutai Bay...(in pocket) Plates I-A and B.— Terrace of Champlain age near Aguanish.

II-A and B.—Terrace of Champlain age near Natashquan.

III and IV.— Parts of the Natashquan terrace re-worked by the wind into dunes.

V-A. —Aspect of the shore two miles east of Michon Village. B.—View near the entrance to Natashquan harbour.

VI-A.—Western part of the village of Natashquan. B.—.Aspect of the shore near Kegashka.

VII-A. — Mistassini harbour. B.—View near Cap Rouge point.

VIII-A.--Inland topography as seen from near Musouaro. B.—Tidal flat.

IX-A.—Aspect of the shore two miles east of Musquaro. B. — 'Sheeting' of granite, cairn, and triangulation station at Chicoutai point.

X-A.—Entrance to Musquanousse river. B.—Entrance to Washicoutai bay.

XI-A.— Paragneiss injected by pegmatite and quartz nodules. B.—Quartzite.

XII-A.— Paragneiss granitized lit-par-lit. B.—Crumpled granitized paragneiss.

XIII-A.— Thinly interbedded calcareous and quartzitic sedimentary rocks. B.—Crystalline limestone relict beds.

XIV-A.—Crystalline limestone relict beds. B.—Banded gneiss.

XV-A.—Banded gneiss. B.--Banded gneiss in contact with granite.

XVI-A.—Granitic gneiss injected by thin ribbons of pegmatite. B.--Segmented dyke of 'black rock' in gneissic granite.

XVII-A.—Splashy pattern of injection of pegmatite in a dyke of 'black rock'. B.—Nodular structure in dyke of 'black rock' cutting 'microperthite' granite.

-II- XVIII-A. —Gneissic granite displaying 'augen' facies. B.--Pegmatite ribbons injected along foliation of gneissic granite.

XIX-A.— Ptygmatic folding of a pegmatite ribbon in gneissic granite. B.—Cross-joints in granite.

XX-A. --Cross-joints in granite. B. and C.—Feather-joints in gneissic granite.

XXI-A. —Joint planes in granite tending to develop parallel to the foliation. B.— Rectangular jointing in 'microperthite' granite.

XXII-A. —Rock surface well polished and grooved by the ice. B. — 'Crescentic gouges', a type of ice-marking on the rocks.

XVIII --Photomicrographs. A.—Coronas around olivine crystals in olivine gabbro.X 30. B.— Anthophyllite schist. 0)(30.

XXIV --Photomicrographs. -A.—Fluorite in 'microperthite' granite. X80. B.— Microperthite in granite of the same name. )(80.

NORTH SHORE OF THE ST-LANBENCE

AGUANISH TO PASHICOUTAI BAY

SAGUENAY COUNTY

By Jacques Claveau

INTRODUCTION

Location of Area

This report describes the section of the north shore of the gulf of St-Lawrence between the village of Aguanish and Washicoutai bay, which was examined and mapped by the writer during the summer of 1944. Aguanish and Washicoutai bay are both at or near latitute 50°13'N. In a straight line they are some 55 miles apart, Aguanish at longitude 62°05'W. and Washicoutai bay at 60°53'W. Aguanish is about 515 miles below Quebec city and 90 miles nearly due east of Mingan village.

Means of Access

The only regular means of access to the area is the boat service maintained during the navigation season by the Clarke Steam- ship Company, Ltd. The boats have a fairly regular schedule during late spring and summer, but after mid-September the service becomes increasingly uncertain and it is discontinued in late fall or early winter, depending on the severity of the season.

Chartered seaplanes or flying boats could be used, as many deep bays and island-sheltered waters offer excellent landing sites under normal weather conditions.

Throughout the winter, a mail and passenger service to centres along the coast is maintained by Canadian Pacific Airlines.

Previous Work

The present investigation marks the first detailed geological survey of the coast between Aguanish and Washicoutai bay and is an eastward continuation of the detailed investigation of the Precambrian - 2 - rocks of the coast between Mingan and Aguanish carried out by Longleyl in 1943.

Richanison2, prior to 1863, visited the area and on the general map accompanying "Geology of Canada", published in 1863, the rocks along this part of the coast are classed under the very general terms "Laurentian granite and granite gneiss".

De Puyjalon, in 18989 and 19004, described the area as underlain by an assemblage of granitic gneisses, mica schists, and trap and basalt dykes.

In the course of a rapid reconnaissance made in the fall of 1943 between Aguanish and Lobster bay, Longley5 noted a few scattered, small areas of schist and quartzite between Aguanish and Natashquan.

Extensive deposits of magnetic iron sands that occur at the mouth of Natashquan river and that were mentioned in the literature as early as 18696 have been investigated from time to time. A particularly thorough study, to which further reference will be made under the heading of Economic Geology, was carried out during the years 1911, 1912, and 1913 by the Mines Branch of the Federal Department of Mines.

Field Work

The maps used in the course of the work were the marine charts of the Canadian Hydrographic Service and the official survey maps of the coast and rivers,compiled by the Quebec Department of Lands and Forests. i Longley, W.W., North Shore of the St-Lawrence, Mingan to Aguanish, Saguenay County; Que. Dept. Mines, G.R. 42, Pt. I, 1950. 2Logan, (Sir) W.E., Geology of Canada, A Report of Progress Since its Commencement, p. IV and accomp. map; G.S.C., 1863. 3De Puyjalon, Henri, Monograph of the Minerals of the North Shore of the Gulf of St-Lawrence; Report of the Commissioner of Coloniz- ation and Mines of Quebec for 1898, pp. 269-270, 1899. 413e Puyjalon, Henri, Annex to the Report of the Inspector-General of Fisheries; Report of the Commissioner of Lands, Forests, and Fisheries of Quebec for 1900, pp.86-87, 1900. 6Longley, W.f., Aguanish to Lobster Bay, North Shore of the Gulf of St-Lawrence; Que. Dept. Mines, Special Report (unpublished), p.9, 1944. 6Hunt, T. Sterry, Report of Progress from 1866-1869, pp.265-267; G.S.C., 1870. - 3 - The marine charts were found indispensable for navigation and their excellence cannot be too highly praised. They are mercator projections on a scale of 1/69950, or one inch to 1.104 miles,. at latitude 50°05'N. The maps of the Department of Lands and Forests are polyconic projections on a scale of two inches to one mile.

In the initial field work, traverses were made along the shore, using the pace-and-compass method of surveying. This method was soon abandoned, however, when it was found that, owing to the excellence of the available maps, one's position in the field could be very quickly ascertained by inspection of the map. A small draw- ing board, fifteen inches by eighteen inches, on which was tacked a tracing or sketch of the portion of the coast being surveyed, was carried along in the field. Rock outcrops were marked on the tracing or sketch as the observer walked along, and points at which special observations were felt necessary were marked by numbers corresponding to those used in the note-book in which the pertinent data were recorded. Only very seldom was the shoreline so regular that easily recognizable landmarks were lacking. In cases of doubt as to position, the pace-counter and compass were used to re-trace the distance to a known point or to keep record until a conspicuous landmark was reached. The use of aerial photographs, which were secured late in the season, permitted elimination of the pace-and-compass method and also of the tracings mounted on a board. The photographs were carried during the field work and, at each point of observation, a pin-hole was driven through the photograph. Numbers, written on the back of the prints adjacent to the pin-holes, served the same purpose as those used on the sketches.

Four successive base camps were established across the area as the work progressed. A 40-foot motor-driven fishing-boat, owned by Walter Cormier of Havre St-Pierre, was permanently at the disposal of the party and was used for all necessary travelling. It was, however, not well suited for the type of work for which it was required. A boat — which need not be much larger — fitted with living and working quarters for all members of the party would be more satisfac- tory. This would eliminate the necessity for shore camps, which are often very difficult to locate as the site must meet several require- ments. The tents must be protected from heavy coastal winds and be close to fresh water and fire-wood. The camp-site should also be near a proper shelter for the boat, and this must be accessible under all tidal and weather conditions. Thus, the elimination of shore camps would have greatly enhanced the comfort and efficiency of the party.

Acknowledgments

To all the men of his party, the writer extends his thanks and appreciation for discharging their respective duties in a very creditable manner. - 4 - Jean-Charles Bedard, first-year engineering student at the School of Mines, Laval University, acted as junior assistant. Three men from Havre St-Pierre completed the party: W. Cormier and A. Bou- dreault, who manned the boat, and G. Vigneault, who served most effi- ciently as cook.

The writer is grateful to Mr. Gérald Barrette, in charge of the Division of Photogrammetry of the Quebec Department of Lands and Forests, for services rendered in the enlargement of the marine charts of the Canadian Hydrographie Survey.

The photomicrographs accompanying this report were taken in the laboratories of the Faculty of Science of Laval University with the helpful assistance of Dr. P.E. Auger, Professor of Economic Geo- logy in that Faculty.

DESCRIPTION OF THE AREA

Topography

From Aguanish, the shoreline maintains a general course about due eastward for a distance of ten miles and then turns south- easterly to the village of Natashquan. Along this stretch the coast is intricately indented and numerous islands hug the shore. Between Natashquan and Kegashka river, a straight-line distance of about twenty miles, the coast has a southward bulge, the tip of which is at Natashquan point, about eight miles southeast of the village of Na- tashquan. This bulge is formed by Natashquan terrace (described below), and the shore throughout its extent has an extremely even outline. East of Kegashka river, the shoreline follows an average course slightly north of east for a long distance, to well beyond the limits of the present map-area. In its details, however, the coast here is again complexly incised, even more so, as a rule, than west of Natash- quan, and hundreds of islands lie off-shore.

A prominent feature of the landscape are flat, monotonous sand terraces which occupy a large part of the area. The first of these terraces is in the vicinity of the mouth of Aguanus river. That part of it west of the river was not examined by the writer but it appears to be of much lesser e_rtent than the part that extends eastward from the river for about eight miles. This consists of sand underlain by clay (Plate I-A) and undoubtedly at one time it extended southward over the numerous long headlands that project from the shore and over the adjacent islands. These are now swept clean, however, and the southern limit of the terrace reaches the sea only at the head of deep, sheltered bays. One exception to this is seen in the beach west of Nichon island. Here it is obvious that the terrace is protected by the strong currents issuing from Aguanus river, which break the - 5 - impact of the waves generated by the prevailing southwesterly summer winds. In addition, it is likely that a good deal of the river's present-day load of sediment is carried by long-shore currents and deposited on that beach. The terrace appears to slope gently toward the west or north*est, its height being fifteen feet at Aguanish and over twenty-five feet near its eastern limit (Plate I-B).

A second terrace, at the mouth of Natashquan river, occupies the huge bulge in the coast — referred to above — and covers an area of some sixty square miles. Its surface is flat to gently undulating. Along its southeastern edge it rises to a mean elevation of 45 feet (Plate II-B) with a local high point of 100 feet at Mont-Joli. The sediments forming this terrace are predominantly sand (Plate IV), but underlying clay appears at a point about four miles up Natashquan river.

A third terrace lies behind the village of Kegashka. It is considerably smaller than the Natashquan and Aguanish terraces and assumes prominence only along the stretch of the shore within lots 4, 5, and 6, range I, of Musquaro township.

Rock outcrops are entirely lacking along that part of the coast occupied by the Natashquan terrace. Along the Aguanish and Kegashka terraces, numerous exposures occur on the points and islands, most of which, as already noted, have been swept clean of sand, although on some of the larger islands this has occurred only over wide marginal zones. Elsewhere along the shore, rock outcrops are almost continuous except for a thin cover of sand, mud, or gravel at the head of some of the bays.

The coast between Aguanish and Washicoutai bay is fairly uniform in elevation and relatively low. If the topography of the rocky basement alone is considered, however, it is found that the relief is greater, and the mean elevation higher, in the eastern part of the map-area, especially the section east of Mistassini harbour, than in the western part. West of this harbour no elevation exceeds 50 feet (Plates V and VI) and the mean elevation is a considerably lower figure. To the east, on the other hand, the elevation exceeds 100 feet at three localities. These are Cap Rouge point, 110 feet; a hill a mile and a half north of Musquaro point, 110 feet; and Chi- coutai point, 102 feet. Although the mean elevation for this part of the area (Plates VII to X) exceeds that for the western part, it is nevertheless much below the 100-foot mark, and probably is not more than 50 feet.

Two very striking features of the rocky shore are its deeply incised character and its fringe of numerous islands and reefs, features indicative of a youthful shore along a recently submerged coast. The sea has had scarcely any erosive effect on the massive Precambrian - 6 - rocks of the headlands and islands. The terraces of young, unconsolidated sediments are proof, on the other hand, of a recent emergence of the coastline which may be still progressing.

The topography of the area is therefore that of a recently submerged coast which has been, and possibly is still being, re- elevated, but which at present stands much below its pre-submergence level. The amount of re-elevation that the coast has undergone is at least 45 feet, this being the mean elevation of the Natashquan terrace. Although Mont-Joli rises 100 feet above the present sea-level, it is an unreliable feature to use as marking the amount of re-elevation, since it is probably a dune formed during the stage of early emergence, before the fixation of plants and trees.

A number of rivers and streams flow southward through the area and empty into the sea. Swamps and small lakes, many of the latter gradually being Invaded by vegetation and transformed into swamps, occupy depressions on the rocky islands and along the coast.

Vegetation

The greater part of the coast is bare of forests.

Large stretches of the Natashquan terrace are capped by a layer of peaty soil on which grow compact stands of black spruce and balsam, but few trees exceed twenty feet in height. Along the imme- diate shore, however, the peaty top-soi) and coniferous trees are largely absent and grassy dunes prevail (Plate III).

Elsewhere, the bed-rock is generally blanketed by thin, peaty soil on which grows brush of the Labrador tea variety.

Settlements

Within the area there are five settlements, all established on the seashore. In order of importance, these are: Natashquan, Aguanish, Michon Village, Kegashka, and Musquaro. The inhabitants of these villages are of French or Acadian descent, except at Kegashka, where they are all of British origin.

Natashquan (plate VI-A) has a population of 380 (this includes Le Poste, a smaller settlement at the mouth of Natashquan river four miles south of the main village). Situated 530 miles below Quebec city, it has a good wharf and a weekly boat service. Its principal buildings are a refrigerating plant, three general stores, a church and presbytery, two schools, a dispensary with nuse in attandance, and a telegraph office. Some 70 Montagnais Indians live on a reserve near - 7 - Le Poste during the summer season. They leave around the middle of August and spend the winter months hunting in the region of the head- waters of Natashquan river.

Aguanish, with a population of 235, is a smaller village at the mouth of Aguanus river, twelve miles west of Natashquan. Michon Village, population 91, is three miles east of Aguanish. These settlements have no wharf facilities and are supplied through Natash- quan. A telegraph office is maintained at Aguanish.

Kegashka, a village of 50 people, is 24 miles due east of Natashquan, but the distance by boat is 34 miles. It is serviced by boats only once a month, and has a telegraph office.

Musquaro, ten miles farther east, has only three families. These is a telegraph office here and a chapel where the Indians from the Natashquan and Romaine reserves, the latter ten miles east of Musquaro, attend their annual mission in August.

Industry

The principal means of livelihood for the inhabitants of the area is cod fishing. Throughout most of the summer the fishing is good on the Natashquan banks, which extend south from Natashquan point. The banks are frequented by fishermen from Natashquan, Michon Village, Aguanish, and even from villages as far west as Havre St-Pierre. The inhabitants of Kegashka fish in deep water several miles out at sea south of their village, where the codfish are less abundant but considerably larger than on the Natashquan banks.

Halibut fishing is not practised on a large scale and only a few are caught during the season.

Salmon fishing is carried on successfully during the early summer at Aguanish by the few families that own the fishing rights at the mouth of Aguanus river.

The villagers of Natashquan supplement their livelihood by the sale of blueberries and rock cranberries which grow in great abundance on the extensive burned and marshy plains stretching behind the village. The berries are picked in September and shipped to Quebec and Montreal.

Agriculture is almost non-existent. A few of the common vegetables such as potatoes, cabbage, lettuce, radishes, beets, and onions are grown on a small scale for local consumption, but not in sufficient quantity to supply the needs of the villagers. The soil is sandy and poorly suited for agriculture, although Michon Village is

- 8 - reputed to have an exceptionally fertile soil for this part of the coast and the residents grow sufficient vegetables for their own needs. The rigorous climate is largely responsible for the poor agri- cultural conditions. The growing season is very short due to the lateness of spring and the early appearance of frosts in the fall.

Very little livestock is raised along this part of the coast, and then only cows and chicken. The cows manage a meagre sub- sistence on scattered patches of miserable grass or on wild hay that grows on the shores of some deep, muddy bays.

Table of Formations

Recent: Unconsolidated sediments re- CENOZOIC QUATERNARY worked by water and wind Pleistocene: Sand and underlying clay (Champlain stage) Glacial débris

Great unconformity

Pegmatite and granite in dykes and small irregular bodies 'Microperthite' granite Olivine gabbro, amphibolite, hornblende-biotite schists, chlorite schists, anthophyllite schists Gneissic granite and augen gneiss Early Quartz-dioritic gneiss (possibly an PRECAMBRIAN orthogneiss ) (basal complex) Granitic gneiss (probably of mixed origin) Banded. gneiss (of igneous and sedimentary origin) Predominantly impure quartzites, with minor amounts of mica- and hornblende- bearing quartz-plagioclase gneisses, and remnants of coarsely crystalline limestone - 9 -

GENERAL GEOLOGY

The consolidated rocks of the map-area are all of Precam- brian age. They are mainly highly metamorphosed and complexly folded types which can be defined as forming a basal complex.

Excluding the large portion of the area covered by the Natashquan sands, where the nature of the rocky basement is unknown, the predominant underlying rocks of the map-area are granitic and of igneous character.

Sedimentary rocks, that is, rocks unequivocally identifiable as such, constitute a comparatively small proportion of the exposures of the area. They include mainly quartzites of moderate to pronounced impurity, subordinate amounts of quartz-biotite gneisses and schists carrying varying proportions of feldspar and hornblende, and occasional remnants of beds of coarsely crystalline limestone and silicate- bearing metamorphic derivatives. A broad belt in which the sedimentary rocks are widely exposed extends from Washtawouka bay to the village of Natashquan. But the rocks of this belt as a whole are far from being sedimentary. In its eastern half lie three bodies of granite of two ages and, throughout the belt in general, the sedimentary rocks have been intimately granitized, or else they carry a very large proportion of igneous material of varied nature in the form of, either concordant or discordant, dykes, sheets, ribbons, lenses, and irregular bodies. Two additional belts of sedimentary rocks occur east of Natashquan. One, which is very small, appears along the east side of Musquaro point and includes thick units of well preserved quartzites. The other, somewhat larger, lies near 'tashicoutai bay and has only poorly preserved sedimentary units. An attempt has been made on the map accompanying this report to show the portions of these sedimentary belts in which sedimentary rocks relatively free from igneous material predominate. It will be seen that such portions are few and that most parts of the belts are shown on the map under symbol '3', which is defined in the map-legend as an 'undifferentiated complex', that is, an inextricable mixture of intrusive and metamorphosed sedimentary rocks.

Outside of these belts, sedimentary rocks are found as incidental inclusions in igneous bodies and also associated with a banded gneiss appearing between Kegashka harbour and Cap Rouge point and at a few other points farther east. Part of the banded gneiss is the result of injection of granitic material along the stratification or other parallel subsidiary planes of sedimentary rocks - schists and quartzites. In many places, the sediments have their original character partially preserved.

A gneiss of granitic composition and showing a faint banding occurs sparingly in the vicinity of the village of Aguanish. This - 10 - gneiss is possibly of mixed origin. Gneisses having the composition of quartz diorite are seen mainly near Kegashka river, at the village of Kegashka and at Tashicoutai bay. There is evidence that the dioritic gneiss is older than the gneissic granite with augen facies to be discussed below. However, its composition is not uniform and it tends locally toward a granitic facies. Its origin is not known but it is obviously complex.

Granitic rocks of indisputable igneous origin are profusely distributed along the coast, and are placed in three groups:

(1)Medium-grained, strongly gneissic, pink granites with no microperthite but with an occasional augen facies developed;

(2)Coarse-grained, moderately gneissic, red, commonly fluorite-bearing, granites with an unusual abundance of microperthite;

(3)Small masses and dykes of granite and pegmatite.

These three types are arranged above in order of age, the first group being the oldest. This order, however, does not strictly apply in the case of the pegmatites which, although they are all included in the third group, may be of at least two different ages since, at a few places, pegmatite is seen cutting pegmatite. Pegma- tites are also more commonly abundant in the granite of the first group than of the second group, which would tend to indicate that the granite of the first group was accompanied by its own pegmatites and later was cut again by pegmatites associated with the granite of the second group. However, as cutting relationships between pegmatites are very scanty, the question of two possible ages of pegmatites must remain open.

Granites of the first and second groups, outcropping in large masses, form the greater part of the rock exposures of the map- area. In addition, representatives of the first group and pegmatites of the third group occur abundantly in, and saturate so to speak, large portions of the sedimentary belts and the three gneiss members.

Six masses are classed with the first group. They are: (1) the granite extending from Aguanish to east of the village of Michon; (2) the granite around the large bay about three miles northwest of Natashquan; (3) the granite of Kegashka harbour, presumably extending eastward as a narrow, pinching-out sheet as far as Kegashka bay; (4) the small granite body on the east side of Mistassini harbour; (5) the granite of Musquaro point; and (6) the granite one mile east of Mus- quaro. There is serious doubt regarding the age of the last mass. It is not strongly gneissic, as a rule, and closely resembles a small - 11 - body of granite that cuts the 'microperthite' granite near Musqua- nousse river. Thus it may belong to the third group.

Although the granite of the first group is described as occurring in masses, it must be made clear that, in the general pic- ture acquired during the field work, this granite is conceived as forming the general basement in which sedimentary remnants, and possibly old intrusives as well, are embedded and into which are intruded the granitic rocks of the second and third groups and the 'black rocks' to be described shortly. This conception is consistent with the occurrence of this granite not only in large, ill-definea masses but as the predominant igneous member of the 'undifferentiated complex' shown on the map, and it also serves the purpose of clarifying, in its broad outlines, the otherwise inextricably complex geology.

The granite of the second group, the so-called 'microperthite' granite, is found in five large masses: (1) the granite one mile west of Thériault island; (2) the granite at Natashquan; (3) the granite of Curlew point; (4) the granite of the large bay and of some of the islands west of Musquaro point; and (5) the large granite mass stretching east and west of Musquanousse river. In addition, two small masses, probable offshoots of the 'microperthite' body west of Thériault island, outcrop in the vicinity of Washtawouka bay, and a third small mass occurs just east of the village of Musauaro.

Evidence that the granite masses belonging to the first group are older than those of the second is to be seen in several localities. Inclusions of the gneissic granite of Aguanish and Michon Village are found in the offshoot of 'microperthite' granite on the eastern limit of the village of Michon. Inclusions of a granite similar to the gneissic granites of Kegashka harbour and of the east shore of Mistassini harbour occur in the Curlew point 'microperthite' granite. 'Microperthite' granite is in contact with gneissic granite at one place along the west side of Musquaro point. Here the 'microperthite' granite is only faintly gneissic whereas the gneissic granite has a very pronounced banding and is obviously the older of the two.

The granites of the first and second groups are cut by dykes and small irregular bodies of fine-grained granite and also of pegmatite. These, constituting the granites of the third group, vary in facies and may differ in age as well. The pegmatites are generally pale pink in colour, more rarely salmon-red. They appear to be younger than the granites of this group, since in some places they cut the latter. However, a composite dyke, consisting of pegmatite with borders of fine-grained granite, was seen near Michon island cutting the Aguanish-Michon gneissic granite. This may indicate that certain granites and pegmatites of the third group are closely related in age. - 12 - With the exception of a small body of pegmatite on the island opposite the village of Michon, none of the rocks of the third group form masses that are large enough to be shown on the map.

A persistent member of the basal complex of the map-area is a very dark-coloured to black rock which occurs in narrow dykes, or numerous small, irregular bodies, generally intruded in concordance with the trend of the enclosing rocks. The largest of these bodies (and the Only one shown on the map) outcrops on the east side of the mouth of Musquaro river and on nearby islands. Although the greater part of this body is highly altered, especially along its borders, a very fresh facies, having the composition of olivine gabbro, is occasionally found in its central zone.

No fresh facies was observed- among any of the other 'black rocks' of the map-area. The common metamorphic representative is a plagioclase-biotite amphibolite, although pure amphibolite, chlorite schist, and in one place anthophyllite schist, were encountered. Some of these concordant bodies may represent schists of sedimentary origin, especially where they are found along the bedding of quartzites and bear no apparent proof of an intrusive nature. But where they occur within granite masses and show persistent width and homogeneity, lack associated quartzites, or exhibit chilled borders preserved in spite of the metamorphism, the evidence is in favour of igneous rather than sedimentary origin.

The 'black rocks' occur abundantly in all rocks older than the 'microperthite' granite. They are Çound in the latter only rarely, which suggests that the most active period of intrusion of basic rocks was after the intrusion of the gneissic granite that has occasional augen facies and before the intrusion of the 'microperthite' granite. But there must have been a second period of intrusion of basic dykes to account for those in the 'microperthite' granite. That there were in fact two periods is demonstrated by the occurrence in quartz-dioritic gneiss, on one of the small islands one mile west of the mouth of Kegashka river, of a black dyke of chloritic composition intruded along the foliation of the gneiss and cut at right angles by a second black dyke having the composition of an anthophyllite schist.

The dykes of the second generation are altered almost as highly as those of the first, and certainly cannot be classed with the late Precambrian diabase which occurs in other parts of the coast and is seldom altered.

The 'black rocks' are older than the pegmatites, which cut and frequently intrude them in very intimate fashion. However, in the case of the anthophyllite and chlorite dykes referred to above, - 13 - both are found cutting pegmatite, a fact which strengthens the sug- gestion, already expressed in the discussion of the pegmatites, that there are two ages of pegmatite.

PETROLOGY

Sedimentary Rocks

Quartzites, which range in composition from moderately pure to impure feldspathic and micaceous types, constitute practically all the sedimentary rocks of the map-area. The impure types are better termed quartz-feldspar-biotite gneisses, for they approach an average granite in composition and resemble a granite gneiss owing to their high degree of metamorphism.

The metamorphism of the sedimentary rocks has been very drastic. They have been profusely intruded by granitic rocks which cut them erratically in irregular bodies or penetrate them intimately along their bedding and other parallel auxiliary planes. In the latter mode of intrusion, known as migmatization, the granitic rocks are injected in innumerable sheet-like bodies (Plates XI-A, XII-A, XII-B), ranging in width from over a foot to mere films. In schistose, highly impure beds, the lit-par-lit injection along the planes of schistosity has been so intimate as to produce gneisses which cannot be differentiated from orthogneisses. In more massive beds, there has been a pervasion of granitic fluids along sub-microscopic channels. The net result of the intense granitization is that all the sedimentary rocks tend to look like granites and it is only by the presence of bedding that their sedimentary origin may be diagnosed. There are rare portions of the sedimentary belts, usually fairly pure massive quartzites (Plate XI-B),which have escaped granitization, and there must be, on the other hand, some portions of migmatized paragneiss unrecogniz- able as sedimentary rock because the bedding has been obliterated by intense metamorphism.

The mineralogy of the quartzites and quartz-feldspar- biotite gneisses is simple. Common minerals are quartz, microcline, plagioclase, and biotite, while accessories include hornblende, zircon, apatite, sphene, muscovite, calcite, magnetite, and pyrite. Most of these minerals are very fresh with the exception of the plagioclase, which has the composition of oligoclase and is generally considerably altered to sericite.

Certain beds of paragneiss have a composition which denotes a special original character. They consist almost entirely of oligoclase and deep green hornblende. The plagioclase is granular, while the hornblende may assume a similar habit or else occur in long, feathery crystals. Some biotite may be present as well as other accessories such as magnetite, apatite, sphene, and, in one of the - 14 - thin sections examined, hypersthene. Quartz is usually very subordinate if not entirely lacking. Such metamorphic rocks are indicative of original beds having a high chloritic content and probably some calcareous impurities as well.

Small amounts of coarsely crystalline limestone are found associated with quartzitic sedimentary rocks at a point three and a quarter miles east of Michon Village and at a few other localities. These occurrences are merely of mineralogical interest. In some instances, the limestone appears as lenticular bands in quartzite (Plates XIII-B, XIV-A). These lenticles are distributed in rows along the bedding of the quartzite. They show strong flow lines and are clearly the remnants of originally continuous beds which have been squeezed and drawn out under pressure between thick quartzite beds to the point of having been severed into discontinuous lenticular segments. In other instances, the limestone forms thin units interbedded with the quartzite (Plate XIII-A). It is interesting to note that, in this case, the limestone beds have not been segmented, because of the incompetence of the thin quartzite beds to cause rupture. Instead, the limestone and quartzite have yielded by crumpling.

Secondary silicates are found in the limestone in crystals thinly scattered between calcite grains or closely packed in layers along certain horizons. The common silicate is a pale green diopside which in places is partly replaced by serpentine. Other minerals include scapolite, sphene, phlogopite, bluish-green hornblende, pyrite, and occasionally graphite. Quartz, in round grains which were obviously present in the original sediment, is found recrystallized side by side with calcite in some parts of the limestone, indicating that the conditions of metamorphism did not always allow the combination of quartz and lime, a reaction which requires the dissociation of the carbonate and the escape of carbon dioxide.

Gneisses

Banded Gneiss

The main occurrence of banded gneiss is in a broad belt extending from west of Kegashka to Cap Rouge point. Other very narrow belts are encountered at six localities between Musquaro point and Chicoutai point.

The banded gneiss is a peculiar type of composite rock which has the appearance of an assemblage of parallel, alternating light- and dark-coloured bands (Plates XIV-B, XV). In width the bands vary from a very small fraction of an inch to several feet, but - 15 - common widths are less than six inches. The principal minerals in the gneiss are quartz, feldspar, biotite, and hornblende. Each band is a combination in certain proportions of the first two or more of these four minerals, and thus may have any composition from that of an aplite or a pegmatite to that of a quartz-feldspar rock in which biotite or hornblende, or both, predominate. Any individual band has a uniform composition throughout and its colour is largely dependent on the amount of dark minerals present.

In the commonest type of banded gneiss, bands of aplitic granite alternate with bands of granitic gneiss of moderate to high biotite or hornblende content, and the banding is sharply defined (Plates XIV-B, XV). There are some exposures of banded gneiss in which the banding is apparent only on close examination, due to the fact that aplitic bands alternate with bands that are poor in dark minerals and thus offer little contrast in colour and composition. A thin section of the typical gneiss shows that the light bands consist almost entirely of orthoclase, intermediate ohigoclase, and quartz, with rare flakes of biotite aligned parallel to the banding, and practically no other accessories. The dark bands contain about 30 per cent of biotite and hornblende, the former predominating, not more than 10 per cent of quartz, and over 50 per cent of orthoclase and plagioclase. Accessories include relatively abundant apatite, as well as pyrite, sphene, and some tiny zircons enclosed in biotite. The texture is fine in both types of band and tends to be saccharoidal, being markedly so in the dark bands.

The linear persistence of the bands in the gneiss is errat- ic. Some are continuous over long distbnces, others taper out or break up into a number of thin filaments within a short distance. More rarely, small portions of the aplitic element are seen in stout lenticles or irregular splashes in the darker element in a fashion which leaves no doubt that the former is intrusive into the latter. In biotite-rich schistose bands, the aplitic injection tends to be very elaborate, assuming the form of numerous thin ribbons (Plates XIV-B, XV-A). In certain bands of schists, the fashion of injection of igneous material is very unusual, and a type of 'spotted' rock is produced in which the 'spots' consist of numerous rectangular phenocrysts of feldspar with intergrown quartz. The presence of feldspar and quartz in coarse crystals indicates that the permeating fluids were of a pegmatitic character. The activity of such fluids is also frequently recognized in aplitic bands which locally pass into, or are cut by, pegmatite. The latter may take the place of aplite in some exposures, but as a rule aplitic bands are the more common.

The original character of the rock intruded by the aplitic element cannot always be ascertained. In some instances it has the appearance of a true igneous rock of granitic composition. In others, - 16 - it is distinctly a sedimentary rock, such as a quartzite, or a paragneiss, such as a biotite- or hornblende-quartz-feldspar gnéiss or schist.

The banded gneiss appears, therefore, to be the result of the injection in a peculiar fashion of a granitic magma (predominantly aplitic) into pre-existing sedimentary rocks and even, perhaps, orthogneiss. Thus, except for its peculiarly regular structure, which persists over a considerable area, the banded gneiss is not much different in nature from the 'undifferentiated complex' of the sedimentary belts, and is indeed similar in many respects to some small portions of those belts which have been granitized lit-par- lit.

Granitic Gneiss

Under this name is included mainly a rock of granitic composition and of somewhat doubtful origin, though it is apparently older than the 'gneissic granite with occasional augen facies'. Four small exposures occur near Aguanish and it continues to outcrop west of the village for a distance of at least six miles into the adjacent map-area, where it has been termed 'banded gneiss' by Longleyl.

In the exposures examined by the present writer, the gneiss is a granitic rock, which may be of mixed or composite origin, intruded along its foliation by thin ribbons of pegmatite (Plate XVI-A). The foliation is generally strongly marked, but the pegmatite ribbons are not always present. It is very different from the banded assemblage described previously, which occurs near Kegashka and is termed by the writer 'banded gneiss'.

Longley classed all the gneisses of his area as either 'augen' or 'banded' gneisses and was inclined to believe they were all recrystallized sedimentary rocks. Along the east side of the mouth of Aguanus river, there is a rocky escarpment which consists at its base of the pegmatite-ribboned granitic gneiss, although here it is in a highly fissile, bedded-like, sheared state. Near the top of the escarpment, the gneiss is in sharp contact with a coarser, compact, gneissic granite which, when followed southward along its exposures, is seen to develop gradually an augen texture. The augen granite and the pegmatite-injected gneiss here may be interpreted as two different masses, and the latter, being more deformed, is probably the older. The writer has no reason to believe the augen mass to

1Longley, W.W., North Shore of the Saint-Lawrence, Mingan to Aguanish, Saguenay County; que. Dept. Mines, G.R. 42, Pt.I, 1950. - 17 - be of sedimentary origin. He is in doubt about the other mass, however, and the term granitic gneiss is used to underline this uncer- tainty and in preference to the term 'banded gneiss', which is reserv- ed for the peculiar banded assemblage at Kegashka.

The granitic gneiss is a reddish, compact, medium-grained rock showing a strong foliation and even a fine banding of its own in addition to that created by the presence of many fine ribbons of injected pegmatite. The pegmatite stringers are generally parallel to the foliation and seldom exceed a fraction of an inch in width; but at times they cut across the foliation, in which case they tend to assume a greater width. The composition of the gneiss is typical of most of the granitic rocks of the region. Microcline accounts for 45 per cent, quartz for 25 per cent, sericitized oligoclase with clear, sodic, partial rims, for 25 per cent or more, and biotite for 5 per cent. Common accessories are zircon and apatite, with occasional magnetite and pyrite.

A small, unimportant mass of fine-grained, dark-coloured, biotite granite gneiss, found at the eastern limit of the village of Michon, as well as small inclusions of granite seen in the 'granite with augen facies' between Aguanish and Michon, may be mentioned in connection with the granitic gneiss. These have not been correlated with any large mass. They are known only to be older than the 'granite with auger fades'.

Quartz-dioritic Gneiss

This gneiss is a medium- to coarse-grained, strongly gneissic, dark grey rock occurring at Washicoutai bay, at Kegashka, west of Kegasnka harbour, and in a very small elongated body two miles west of Thériault island.

At Washicoutai bay, the gneiss outcrops along the western shore of the bay and extends westward for a distance of one mile, beyond which it becomes largely lost in a complex of granite and sedimentary rocks. It resists erosion well and forms several prominent cliffs. The foliation is sometimes faint, but as a rule it is well-marked and occasionally strong enough to produce a distinct banding. In two thin sections examined, the plagioclase content is about 70 per cent, the quartz 20 per cent, and the biotite with subordinate hornblende 10 per cent. In another thin section, the quartz content is higher at the expense of the dark minerals. The plagioclase is acid oligoclase which carries poorly visible, tiny, blade-like intergrowths of a mineral of lower refractive index which is probably orthoclase. The alteration is weak to pronounced in the feldspar and hornblende, the former changing to white mica and more rarely to calcite and some clinozoisite, the latter to a serpentinous product - 18 - which has migrated into fractures in the feldspar. Hematite, also, is found throughout the rock and may be present in appreciable amount. Accessories, which are not very abundant, include apatite, magnetite, and zircon.

The quartz-diorite gneiss forming some of the islands at Kegashka may extend westward under water in a broad arc and link with a mass of similar gneiss found in exposures on the mainland and on some of the islands west of Kegashka harbour. This mass would then be an elongated unit of some eight miles of interrupted length, con- cealed under water at its eastern end and under the eastern border of the Natashquan terrace at its western end. The typical gneiss contains over 55 per cent of acid to intermediate oligoclase, 30 per cent of quartz, and 10 to 15 per cent of hornblende and subordinate biotite. A specimen from Verte island, where granitic intrusives are found abundantly in the gneiss, shows that the gneiss locally tends toward a granitic composition. The plagioclase content is around 40 per cent and that of the ferromagnesian minerals around 5 per cent. On the other hand, quartz accounts for 40 per cent of the constituents and microcline and orthoclase for 15 per cent. It is likely that the potassic feldspar and some quartz have been acquired from the granitic intrusives. Additional evidence of granitization is seen in the fact that certain portions of the mass show development of pegmatitic phenocrysts and that the gneiss in general has an abundance of accessories such as sphene — in large crystals — apatite, and magnetite.

A variety of pegmatitic rock occurs in the gneiss in irregular splashes or in bands concordant with the foliation. It is frequently gradational into the gneiss and carries compact clusters and stout individual crystals of hornblende which give the exposures a 'peppered.'appearance. Thin sections show that the rock is predominantly an aggregate of equidimensional, sub-angular crystals of oligoclase in a matrix of microcline and quartz. Accessories include interstitial hornblende, abundant apatite, and some pyrite and magnetite. This moderately coarse-grained rock is of the nature of a true pegmatite, but it is older than the usual pink to red pegmatite of the area, by which it is cut. From the way in which it gradually merges with the quartz-diorite gneiss, it is obviously related to it. It may be of a late pegmatitic differentiate of the gneiss or perhaps represents certain portions of the gneiss which have undergone a peculiar type of metamorphism attended by pegmatitization.

The quartz-dioritic gneiss, although abundantly intruded by pegmatitic, aplitic, and other granitic rocks and, locally, almost of granitic composition itself, forms fairly well-defined units and it may, for that reason, be regarded as of igneous origin. Its field characters are complex, however, and it is undoubtedly safer to leave the question of its origin open. Plate I

A--Terrace of sand underlain by clay at Aguanish. The terrace, about fifteen feet high here, is of Champlain age.

B—The Aguanish terrace near its eastern limit. It is over twenty-five feet high here. Plate II

A—Natashquan sand terrace of Champlain age. View facing the channel north of foncas island, at the mouth of Natashquan river.

B—Natashquan terrace along its southeastern edge. (Photo by W. W. Longley, 1943). Grass-covered dunes of the Natashquan terrace along the border of the sea. theAspect wind of into the dunes. Natashquan terrace in a view looking toward Vieux Poste point. The upper layers have been re-worked by Plate V

A—Rocky shore and islands two miles east of Michon village, showing the very low relief.

B—View of the shore and islands near the entrance to Natashquan harbour. The cliff on the left — the highest point west of Natashquan — is 48 feet high. Plate VI

A—Western part of village of Natashquan. Low rounded islands and shore. The rock here is "microperthite" granite.

,~. :.~..

. ,F 4,.. •

B—Aspect of the shore near Kegashka. The photo shows a narrow channel between the mainland and an island. Plate VII

harbour as A--The archipelago fringing the eastern shore of Mistassini viewed from the top of the 110-foot headland at Cap Rouge point. Note the striking parallel arrangement of the islands.

B—View looking toward Cap Rouge point from a point inside Mistassini harbour. The 110-foot headland of Cap Rouge point appears at the extreme left. The islands belong to archipelago shown in Plate VII-A. Note the distinctly more accentuated relief. Plate VIII

A—Head of the broad bay between Cap Rouge point and Musquaro point. The view, looking northwest, shows the topography of the interior. Photo taken at high tide.

B—A portion of the same bay as Plate VIII-A, showing the extensive tidal flat at low tide. Plate IX

A—Deeps narrow bay with rugged shores, two miles east of Musquaro. High cliff on the right is the western edge of the easternmost body of 'microperthite' granite.

B—Rugged shoreline on east side of Chicoutai Point. The small cairn on the hill in the foreground indicates that the bay affords shelter for boats. Triangulation station on the far hill. Note jointing and 'sheeting' of the granite. Plate X

A--Entrance to Musquanousse river.

B—Entrance to Washicoutai bay. Plate XI

A--Quartz-biotite-feldspar paragneiss injected by pegmatite ribbons and quartz-rich nodules. Locality : small island one and a quarter miles Pngt of Wnshtawouka bay.

B—Quartzite. The rock here is simply recrystallized. No injection of igneous material along the bedding planes has taken place. Locality : in granite on large island three-quarters of a mile north of Shag islet. Plate XII

A—Paragneiss granitized lit-par-lit (migmatization). Locality : a point on the shore three and a half miles east of Michon village.

B—Crumpled granitized paragneiss. Locality : island one mile east of Gannet rock. Plate XIII

A—Thinly interbedded calcareous and quartzitic sedimentary rocks, closely folded and cut by pegmatite in the upper right corner. Locality : point on the shore three and a quarter miles east of Michon village.

13—Relict beds (the two elongated light grey lenticular bands in the middle of photo) of coarsely crystalline limestone. Locality : same as Plate XIII•A. Plate XIV

A—Remnants of a limestone bed. Locality : same as Plate XIII-B.

B—Banded gneiss. Locality : two miles east of Kegashka. Plate XV

A---Banded gneiss. Locality : two miles east of Kegashka.

B—The upper half of the outcrop is banded gneiss in contact with granite below. Locality : Cap Rouge point. Plate XVI

A—Granitic gneiss injected along its foliation by thin ribbons of pegmatite. Locality : first falls on Aguanus river.

B—Dyke of 'black rock' in gneissic granite, showing segmentation at several points. Locality : island one mile southeast of Michon village. Plate XVII

A—Curious injection pattern of pegmatite in a dyke of 'black rock'. Locality : large island about one mile northwest of Shag islet.

B—Dyke of 'black rock' in 'microperthite' granite. Note development of nodular structure in dyke. Locality : small island two miles southeast of Musquaro. Plate XVIII

A--Gneissic granite displaying striking 'augen' fades. Note concordant pegmatite. Locality : eastern edge of village of Aguanish.

B--Pegmatite ribbons injected along foliation of gneissic granite. Locality : half a mile east of Michon island. Plate XIX

A—Ptygmatic.folding of a pegmatite ribbon in gneissic granite. Locality : same as Plate XVIII-B.

B—Large, open fractures (cross-joints) in the granite. Locality : east side of Chicoutai point. Plate XX

..'.~~- , i~ ...... - 4.30.-.-,., -,. , ~---"-:.,a~.. ' . _ ï:;--- - -N.....Qa., __

A—Cross-joints. Some of the fractures are open and displacement of the walls is shown. Numerous other fractures have healed and appear as streaks of darker shade parallel to the open joints. Locality : half a mile east of Michon island.

B—Feather joints, arranged en échelon along C—Feather joints. Locality: one and a half cross-joint. Locality : same as Plate XX-A. miles east of Gannet rock. Plate XXI

A—Joint planes in granite tending to develop parallel to the foliation. Local- ity : one mile west of Thériault island.

B—Rectangular jointing in 'microperthite' granite. Locality : Cap Rouge point. Plate XXII

A—Rock surface well polished and grooved by the ice. Locality : point on the shore three miles east of Michon village.

_ ~-- ~ ~:~

• - riftlar

•

B—'Crescentic gouges; a type of ice-marking on the rocks. Locality : Ke- gashka bay. Plate XXIII

A—Fresh olivine gabbro from the Musquaro mass, showing beautiful coronas around the olivine. Natural light. X30.

B—Anthophyllite schist. The minerals are anthophyllite (dark grey), plagioclase, magnetite blebs. Natural light. X30. Plate XXIV

A—Crystals of fluorite (F) in 'microperthite' granite. Natural light. X80.

B—'Microperthite' in granite of the same name. Crossed Nicols. X80. - 19 - A band of quartz-dioritic gneiss about 250 feet wide and of unknown length is found two miles west of Thériault island, along the western edge of a sedimentary inclusion in 'microperthite' granite. The contact between the gneiss and the granite is largely gradational, but on an island, where the gneiss is better exposed, the contact is sharper and it is clear that the gneiss is the older rock. The contact between the gneiss and the sedimentary inclusion is not exposed. A thin section of the gneiss reveals over 50 per cent of shattered microcline and oligoclase crystals, 35 per cent of fresh to corroded green hornblende, some biotite and fresh quartz, relatively abundant apatite, and zircon and magnetite-ilmenite. The gneiss may be a true intrusive older than the granite or the result of metamorphism of a chloritic type of sedimentary rock. In either case, it is certain that it has been considerably contaminated by the 'microperthite' granite.

Basic Rocks

The largest exposures of basic rock in the map-area are encountered on the east side of the mouth of Musquaro river and on nearby islands. They seem to constitute a narrow, elongated mass — the greater part of which is under water — half a mile wide and with a known length of two miles but open at both ends.

The westernmost of the three small islands lying close to shore on the east side of the mouth of the river is about in the centre of the mass. The rock of this island is a fresh, dark green gabbro with a purplish tinge. In thin section it is seen to consist of plagioclase, olivine, _)yroxene, amphibole, biotite, magnetite, apatite, and serpentine. There are two pyroxenes, an orthorhombic variety displaying very faint pink pleochroism and approaching enstatite, and a monoclinic variety, augite. Coronas (Plate XXIIFA) around the olivine crystals are very common. They are formed by swarms of minute crystals of the two pyroxenes, greenish amphibole needles, and biotite, disposed radially in concentric rings about large olivine crystals. Within the coronas, the common arrangement is to find, progressing outward from the olivine, enstatite, augite, amphibole, and biotite, although one or more of these four minerals may be wanting. Augite, and to a lesser extent biotite, also occur individually in large crystals throughout the rock. The olivine exhibits the characteristic cracks filled with serpentine and blebs of magnetite. The plagioclase, which is calcic labradorite and constitutes over 60 per cent of the rock, is fresh and frequently in well-zoned crystals.

Elsewhere throughout the Musquaro mass, the rock is deeply altered to a plagioclase amphibolite carrying varying amounts of chlorite, biotite, and other common minerals. - 20 - Many smaller masses of dark-coloured rocks, previously referred to as 'black rocks'(p. 12), which are found persistently in dykes, sheets, or irregular bodies throughout older rocks of the region, also have the average composition of a plagioclase amphibolite and, like the amphibolite of the Musquaro body, may have been derived from an original gabbro.

The average 'black rock' contains over 50 per cent of hornblende, between 30 and 40 per cent of plagioclase (oligoclase to andesine), from 5 to 10 per cent of biotite, variable amounts of accessories such as apatite, sphene, epidote, and magnetite-ilmenite, as well as occasional minute crystals of zircon, secondary hypersthene or diopside, quartz, and chlorite. The chlorite is generally the alteration product of hornblende and is frequently accompanied by minute amounts of carbonate. The texture is at times granoblastic, at times schistose, but, with a decrease in plagioclase, the hornblende crystals tend to grow larger and longer, until an extreme development is reached in the case of certain pure amphibolites which are a compact, felty mass of long, feathery crystals.

Although departure of the 'black rocks' from the above average composition is widespread, it seems that most types can be explained by assuming that the rocks were metamorphosed under various conditions and to different degrees, without having recourse to the hypothesis that different types are derived from rocks of different original composition, such as diorite, lamprophyre, and certain sedimentary rocks, although this may have been the case in some instances.

The degree of deformation (Plates XVI-B, XVII-B) and the amount of igneous injection (Plate XVII-A) suffered by the 'black rocks' indicate plainly that they have undergone severe and varied metamorphism and thus it is to be expected that many diverse and some unusual types of rock would result.

In some types chlorite is abundant, and even pure chloritic rocks, which were probably derived from pure amphibolites, are encountered. Opposing the pure amphibolites, there are 'black rocks' in which biotite and plagioclase exceed the hornblende. Such types could obviously have been derived from a large variety of original rocks, but, in the absence of reliable criteria, their origin must remain problematical.

Among especially unusual types of 'black rocks' are an anthophyllite schist, and amphibolitic dykes containing very large crystals of plagioclase.

The anthophyllite rock was encountered at one place only, on an island one mile west of the mouth of Kegashka river. The rock is fine-grained and, as the anthophyllite is recognizable only under - 21 - the microscope, the anthophyllite-bearing dyke is not easily identifiable in the field and it is possible that there is more than one such dyke in the region. On close examination of the hand specimen, a somewhat fibrous texture is apparent and a few porphyroblasts of biotite are recognized. Seen in thin section, the rock is very fresh, with long, slender, rrismatic crystals of anthophyllite, disposed in parallel orientation (.Plate XXIII-B), forming 80 per cent of the constituents. Acid oligoclase., usually in equidimensional grains, comprises most of the remainder. There are also some biotite, many blebs of magnetite, and, rarely, zircon. Anthophyllite schists may be the result of the metamorphism of basic or ultrabasic rocks'. Since, at Kegashka river, the schist occurs°in the form of a dyke cutting across the structure of older rocks, it is perfectly plausible to regard it as the metamorphic facies of a basic rock, Possibly gabbro.

A few dykes of 'black rock' that contain large crystals or pockets of crystals of plagioclase were encountered within the area. One of the most striking of these dykes outs the 'microperthite' granite near Cap Rouge point. It is much sheared and exhibits a nodular structure (Plate XVII-B) which is rather an effect produced by the wrapping of schistose layers around massive portions of the dyke than a true structure. The 'nodules' are formed of massive plagioclase amphibolite, in which crystals of calcic andesine up to several inches in length are embedded. Some of the 'nodules' are single plagioclase crystals, either rounded or euhedral in outline, wrapped in sheared chloritic or micaceous material. Under the microscope, the amphibolite is seen to consist of abundant hornblende and minor biotite which tend to lie in parallel planes in a mosaic of small crystals of oligoclase-andesine.

In four or five occurrences, small accumulations of calcite, in the form of short and narrow lenticular wrappings, were seen on parts of the periphery of some large crystals of andesine. This feature suggests the possibility that the 'dyke' is the result of metamorphism of a calcareous bed. All field evidence, however, is opposed to this conclusion, and the amphibolite clearly seems to be a dyke cutting the granite. It is persistent in width for at least 300 feet, being lost under water at both ends, and shows clean-cut contacts against the granite. The granite itself is a fluorite- bearing, true intrusive type, homogeneous, and free from any sedimentary inclusions.

'Harker, A., Metamorphism, p. 276; Methuen and Co., Ltd., London, 1932.

Minls r..ioses natureL'eF c1i, bec

SERViC .,,L)':;.IM tiVTATIO:;+ ...... - 22 -

Granitic Intrusives

General Statement

Granites which to the writer seem to be of indisputable igneous origin appear to belong to three general stages of igneous activity. The oldest stage was marked by the birth of great masses of medium-grained pink granite which is now strongly gneissic - and, in many instances, could even be called a gneiss — and occasionally exhibits an augen facies.

The term 'birth' is used with the expressed purpose of underlining the fact that this granite may not have been 'intruded' in the ordinary sense of the word, as will be outlined later.

The granite of the second stage is a somewhat pegmatitic type, coarse-grained, fluorite-bearing, and extremely rich in microperthite. It occurs less abundantly than the granite of the first stage, into which it is intruded in clear-cut masses of moderate size.

The third stage of igneous activity was marked by the injection into all the older rocks of very small, but abundant, masses of pegmatite and fine-grained granite.

Gneissic Granite with Occasional Augen Facies

Seventeen thin sections of specimens of this granite from all parts of the map-area disclose an extremely uniform composition. Microcline with subordinate amounts of orthoclase, intermediate oligoclase, and quartz are present in about equal amounts and account for 90 per cent of the total constituents. Eiotite and minor amounts of hornblende make up the remainder. Accessories include apatite, sphene, zircon, magnetite, ilmenite, and pyrite. In the augen facies at Aguanish, biotite and hornblende in equal amounts account for 20 per cent of the constituents. Epidote was seen in one or two sections only. Accessories arc usually sparse, but in a few of the sections remarkable quantities of sphene in large crystals, zircon, apatite, and epidote were noted.

The rock is exceptionally fresh, the commonest alterations being the incipient change of plagioclase to white mica and the chio- ritization of hornblende. The microcline and quartz are perfectly fresh, although the latter invariably shows undulatory extinction. Two outstanding features of this granite are the omnipresence of abundant microcline and the very frequent partial rimming of both the sericitized and fresh crystals of oligoclase by clear sodic feldspar. The rims are apparently a secondary growth as they generally are - 23- defined sharply enough against the oligoclase to allow comparative measurements of the indices of refraction to be made by means of the Becke line. These rims are not found in the 'microperthite' granite but are encountered again in the late granite dykes. Intergrowths of feldspar and feldspar, or of feldspar and quartz, are of very rare occurrence.

The augen texture is not common and is best displayed in the rock exposed near Aguanish (Plate xVIII-A) and to a lesser degree in that at Michon islaru7. It appears to be a purely local feature developed in parts of the masses where special conditions of stress prevailed. A thin section of the typical augen granite at Aguanish discloses that the 'eyes' are usually single crystals, or aggregates of several large crystals, of microcline and quartz which show com- plete recrystallization. The rock is strongly gneissic and the quartz tends to form elongated patches lying in the plane of the foliation. Quartz has also penetrated the feldspars and ferromagnesian minerals along cracks and cleavage planes. The plagioclase is much altered and intensely fractured and thus has not recrystallized as have the microcline and quartz.

'Microperthite' Granite

Typically, this *is a coarse-grained, reddish rock containing over 50 per cent of microcline-microperthite, 30 per cent of quartz, 15 per cent free plagioclase of acid to intermediate oligoclase composition, and approximately 5 per cent of biotite and hornblende. Accessories include fluorite in moderately large crystals (Plate XXIV-A) interstitial to other minerals or occasionally lying along the cleavage of ferromagnesians or feldspars, as well as apatite, magnetite, a few zircons, and some sphene. When fluorite is present, apatite is usually wanting, but when the former is absent the latter is very abundant. Of eleven thin sections examined from the several masses of this granite in the area, five contain fluorite.

The abundance of microperthite is the prominent characteristic of this granite. The potassic feldspar is generally microcline, but orthoclase was noted in some of the sections. The composition of the intergrown plagioclase was not ascertained, but it is likely albitic and of the exsoluted type. It is most frequently in the form of narrow, elongated lenticles, but occasionally is in tear- shaped globules or short, thick lenses. The amount of exsoluted feldspar may be very large and the narrow blade-like lenticles closely packed together (Plate XXIV-B). It appears that the more abundant the intergrown plagioclase, the fewer are the grains of free plagioclase in the rock.

The 'microperthite' granite is very fresh, as a rule, although it is invariably foliated and in places very strongly gneissic. - 24 - A somewhat brownish-grey or yellowish facies is encountered in the Musquanousse River mass. It is prominent along the western edge of the mass, on the west side of the mouth of Musquanousse river, and at Chicoutai point. It also occurs less conspicuously in some parts of the Curlew Point and Natashquan masses. In the Musqua- nousse mass, this facies is found in the granite at or near its contact with banded gneiss. It may thus be a contact facies, but it is by no means encountered at every contact of the granite with other rocks. The composition of the greyish facies was found to be the same as that of the normal reddish facies, except in the case of one section where the quartz content is unusually low.

Small Masses and Dykes of Pegmatite and Granite

The average granite dyke cutting the granite of the first and second groups is barely distinguishable under the microscope from the average granite of the first group. Most of the dykes, however, exhibit only a weak foliation or even lack it entirely, and tend toward a finer grain than the granite they cut. Otherwise, they have similar proportions of the same constituents and even display around their plagioclase the clear sodic rims typical of the granites of the first group.

There are a few small plugs of fine-grained granite which cut the 'microperthite' granite and are likely of the same period of intrusion as the dykes. They are 50 feet or less in diameter and are very similar in appearance to the dykes. An unusual small stock of coarse porphyritic granite, fifteen feet by twenty feet, was observed cutting gneissic granite on an island a mile and a half northwest of Shag islet. The granite consists mainly of microcline with subordinate quartz and plagioclase, small amounts of biotite, and very minor sphene and zircon. An interesting peculiarity of this small stock is its incipient greisenization, that is, the replacement of its minerals by large veinlets and patches of sericite and quartz. Some large microcline crystals carry a network of sericite veinlets, and most of the biotite, when not chloritized, is largely replaced by quartz and sericite.

Pegmatites are very abundant in the area but they seldom form large bodies. Most commonly they appear as dykes or ribbons concordant with the general structure. The pegmatite is uniform in composition and colour. It is pale pink and contains predominant potassic feldspar with lesser amounts of quartz, either free or graph- ically intergrown, and subordinate pale green or brownish-grey, well- striated plagioclase. In the quartz-dioritic gneiss of Kegashka, a slightly different type of pegmatite is found in long, lenticular bands, apparently filling tension fractures. It is a beautiful salmon-red colour due to the predominance of orthoclase of the same - 25 - shade. Against the walls of the fracture, the rock consists of orthoclase with rare crystals of brownish plagioclase but no quartz. Progressing inward, quartz appears and gradually increases in amount, while the feldspars decrease and finally disappear, the central part of the fractures being filled entirely by quartz.

Aplites have already been mentioned in the description of the banded gneiss, of which they constitute a prominent part. They are also encountered elsewhere in the area and are particularly widespread in splashes and ramified veinlets in the quartz-dioritic gneiss underlying the islands near the mouth of Kegashka river.

Prehnite Rock

At a point half a mile east of Michon island, where sedimentary inclusions in gneissic granite, and the granite itself, have been locally complexly folded and sheared, zones of fracture have been filled by abundant pegmatite, quartz, prehnite, and some calcite, the last named occupying quartz-lined vugs. The prehnite forms a dense, hard, creamy-white rock which closely resembles rhyo- lite. A thin section of the rock shows solid prehnite with a drusy texture. The druses contain coarsely crystalline quartz, and epidote is sparsely disseminated throughout the prehnite.

STRUCTURAI, GEOLOGY

All the important rock masses of igneous character in the area are foliated to some degree. The foliation may be strong enough to produce a banded effect where segregation of the dark minerals has occurred or it may be mild and expressed only by a Com- mon orientation of the platy constituents.

The most remarkable characteristic of the rock assemblages is their concordance of structure. It is the nearly universal case to find the foliation of the granitic masses, the banding of the gneisses, and the bedding of the sedimentary rocks, all parallel to one another. This parallelism was observed in the field wherever these various rocks are in contact, but it is perhaps most strikingly illustrated on the map by the strike and dip symbols.

The 'black rocks' and the granitic rocks younger than the 'gneissic granite with augen facies' occur in sharp contact with the enclosing rocks. Contacts between the gneissic granite and the older rocks, however, are commonly gradational and marked by a zone of highly variable width and regularity in which is found an inextricable mixture of igneous-like and sedimentary-like material. -26 - The diversity in character of the contacts is perfectly consistent with the writer's view that the area consists of a floor of granite in which older rocks are included and into which younger igneous rocks have been intruded. As will be discussed in the following chapter, the floor is regarded as a product of fusion at the base of a geosyncline sinking under loading at the top. Consequent- ly, the rocks older than the floor and embedded in it, such as sedimentary rocks and possibly old intrusives in them, would not, as a rule, be expected to display sharp contacts, as they literally soaked in the melted base and possibly contributed, through assimilation, considerable material to the nascent magma. The rocks younger than the floor were intruded when the latter was at least partly solid- ified and were accordingly apt to form clear-cut bodies with sharp contacts. Such is, indeed, the case, with the added peculiarity, however, that they always tend to lie conformably with the old structures.

The 'microperthite' granite seems to be present in restricted bodies which are conformable with the structure of the older rocks and appear to tend toward a lenticular shape. The lenticular or somewhat phacolithic shape is presumably attained in the case of the Cap Rouge Point granite, as is suggested on the map where the shape is interpreted from an examination of aerial photographs showing the trend of the enclosing gneisses. From what is exposed of the Curlew Point mass, to the southwest, it is strongly suspected that it also assumes the shape of a lens, very thick in the centre and very thin at the ends.

The lenticular forms and the conformity of the later granites with the earlier structures indicate intrusion under heavy load or at great depth, that is, before any of the overlying load on the floor of granite had been removed.

The conformity of structures in the area is further empha- sized by the dykes of 'black rock', pegmatite, and granite, which are, for the most part, concordant with the trend of the enclosing rock. The black rocks and many of the granite dykes possess, in addition, a schistosity or a foliation which also agrees with the neighbouring structures. The area between Michon island and Michon Village is one of the outstanding localities showing a profuse injection of pegmatite dykes along the foliation (Plate XVIII-B) of the 'gneissic granite with augen facies'.

The 'black rocks', being older than the pegmatites, have themselves been subjected to the intrusion of pegmatites in concordant dykes and thin ribbons, as well as in an irregular, 'splashy' pattern (Plate XVII-A).

The trend of the bedding, banding, and foliation varies widely across the area. In certain zones, as between Chicoutai point - 27 - and Washiooutai bay for instance, the strike and dip may change abruptly and erratically, indicating localities of profound disturbance and complex geology. More commonly, however, the change of trend is gradual. The average direction of strike oscillates between northwest and northeast and the average dip is to the east at a moderate to steep angle.

An interesting reversal of dip is noted in the Musquanous- se River granite, however. The western part of the mass dips to the east, but, at a point one mile west of the river, the dip passes through vertical and reverses to the west. As the foliation of the granites of the area generally follows the walls of the enclosing rocks, the reversal of dip would suggest that the Musquanousse mass assumes a wedge shape at depth.

No general pattern of folding can be outlined. There are many minor local folds but these cannot be linked to any pattern of major folds. Striking ptygmatic folds are displayed by some pegmatite ribbons (Plate XIX-A) in the gneissic granite near Michon island. These highly crumpled ribbons can hardly be explained otherwise than as injections of pegmatite into a plastic rock which was undergoing, under high pressure, slow differential movement along its planes of foliation.

The rocks of the area are traversed by a great number of fractures. Most of them are irregular and do not follow any definite pattern. The most prominent regular fractures are of the nature of joints which are to be found throughout the area. These joints, because they tend to be transverse to the trend of the bedding, banding, and foliation, may be termed cross-joints. They trend between N.40°E. and E.-W. and dip about vertically. Some are only narrow cracks in the rock but others are wide, open fractures (Plate XIX-B), along some of which slickensiding and a small displacement may be observed (Plate XX-A). A deep-red coloration of the walls is commonly noted and some of the narrow joints are filled with quartz and epidote. Feathers or tension joints were found in four or five places arranged en échelon in zones along the cross-joints (Plate XX-B) or in zones parallel to them (Plate XX-C).

In gneisses or strongly gneissic granites, there is, in places, a tendency for joint planes to develop parallel to.the planes of foliation (Plate XXI-A).

1Gault, H.R., Petrography, Structures, and Petrofabrics of the Pinck- neyville Quartz Diorite, Alabama; G.S.A., Bull., Vol. 56, p. 219, 1945. -28 - Rectangular jointing is encountered in some parts of the granite masses (Plate XXED). As the three directions of jointing do not differ greatly in the various localities, they may be the result of regional forces. One set of planes is horizontal. The other two sets are close to vertical and trend between E.-W. and N.75°E., and N.-S. and S.15°E., respectively.

'Sheeting' of the granite is beautifully illustrated (Plate IX B) on the east side of Chicoutai point. The sheeting planes are horizontal and cut joint planes which are parallel to the foliation of the granite and dip at an angle of less than 40 degrees. The 'sheeting' is very pronounced at the top of the cliff and distinctly decreases in intensity toward the base, that is, at depth. The sheet structure may be the result of the release of pressure following withdrawal of the ice-sheet, an explanation which has been offered' for a similar structure in granites of other glaciated areas.

On Verte and Kegashka islands, several narrow dykes of salmon-red pegmatite which exhibit a banded structure, that is quartz in the centre and feldspar at the walls, fill elongated lenticular fractures in the quartz-dioritic gneiss. The fractures appear to be of the tension type. They dip nearly vertically and all have the same trend, S.35°BFI.

ORIGIN OF THE BASAL COMPLEX

The profound disturbance and complex relationships of all the rocks of the coast indicate that they were involved in mountain- building phenomena.

Considering mountain-building in its very broad aspects, it may be stated that the process begins with deposition of sediments in a geosynclinal basin or trough which is undergoing gradual sinking as it is being filled. The continually increasing load of sediments causes a progressive building-up within the geosynclinal area of powerful stresses which lead ultimately to large-scale and complicat- ed folding of the accumulated strata. Evidence shows that large masses of igneous rocks are associated with major mountain folds and, indeed, where erosion has proceeded deeply enough, such as 'in the very old mountain systems, granitic cores are found at the 'roots' of the vanished mountain ranges. One view holds that magma generation results from the sinking of the crustal block underlying the floor of the geosynclinal basin to a depth where the temperature becomes suf- ficiently high to allow melting to take place in the depressed granitic

2Jahns, R.H., Sheet Structure in Granites; Jour. Geol., Vol.51, p.71, 1943. - 29 - crustal block. An igneous cycle is thus started, following which magmatic activity rises to a peak of intensity, then declines gradually,and finally dies out.

Viewing the present area in the light of this over- simplified outline of the processes of orogeny, one may begin by considering it as a small portion of a vast geosyncline of deposition' that existed in the earth's crust in Archaean time. Little is known of the geosynclinal history or even of the folding (at least as far as the general region of the north shore of the lower St-Lawrence is concerned) except that the sediments that were deposited and later folded were predominantly quartzitic, judging from what remains of them at present. That the stage was eventually reached at which conditions of temperature and pressure allowed melting to take place below, and possibly in, the floor itself of the geosyncline — as postulated in the theory of mountain building outlined above — is conceivable and, in fact, this hypothesis provides one possible explanation of the complex geology of the area. The generated magma would naturally tend to stope its way upward through the floor and into the base of the accumulated sedimentary rocks. Portions of these would be granitized by intimate diffusion of granitic fluids, or migmatized by injection of tenuous magma between the foliae of the rocks. Other portions would resist or escape the pervasive actidn of the granitic fluids and, except for metamorphic recrystallization and deformation, would retain their original character. The magma would likely not progress very far upward before reaching conditions under which it would begin to congeal. Differentiation would likely come into play in the magma chamber below the congealing roof and, as the igneous activity gradually waned, small differentiated masses would be injected into the overlying complex assemblage.

It is believed that erosion along the coast in general has proceeded to about the level of the former floor of the original geosyncline of deposition and that the 'gneissic granite with occasional augen facies' represents the generated granitic magma that stoped its way up through the floor of the geosyncline. This granite or a similar rock is a common member of the known parts of the coast and pre- vails in the present area. It occurs in undefined masses and rather like a 'basement' in which all the other rock types, some older, some younger, than the gneissic granite, form bodies of determinable dimension and shape.

The rocks older than this granite include (1) those of sedimentary character which occur in skeletal patches and are granit-

'Since the present area lies within what is believed to be the eastern extension of the Laurentian fold system, the geosyncline impli- ed would be the Laurentian geosyncline from which the Laurentian mountains arose in Archaean time. - 30 - ized in various fashions, (2) the banded gneisses which, as mentioned earlier in this report, are for a large part sedimentary rocks injected lit-par-lit, and (3) various types of gneisses, some Of which, such as the granitic gneiss of Aguanish, are thought to be para- gneisses, while others, such as the quartz-diorite gneiss found throughout the area, may be orthogneisses.

Though the presence in the gneissic granite of various types of gneisses derived from sedimentary rocks is readily under- stood, the possible occurrence of orthogneisses is more involved as it raises the question of their origin. The possibility that such probable orthogneisses as the quartz-diorite gneiss represent portions of the original crust or floor is rejected because of the fact that in some occurrences at least they occur in structural concordance with sedimentary rocks and thus are either metamorphosed sediments or injected concordant igneous masses. If true igneous rocks, these gneisses are likely to represent an early generation and injection of magma that preceded the main stoping-up process of the large granite masses.

Another of the many problens of complex relationship found along the coast is the occasional occurrence in the 'gneissic granite with augen facies' of included blocks of a very similar gneissic granite. SuCh is the case, for instance, on Michon island where a block of granite, ten feet by fifteen feet, is included in the'gneissic granite with augen facies'. The included granite possesses a gneissic structure parallel to that of the enclosing granite, a fact suggesting that both rocks acquired their gneissic character simul- taneously. They appear very much alike at first glance, but close inspection reveals that their contact is sharp and that on fresh fractures the enclosed granite is finer-grained, and thus appears slightly darker, than the other. The included granite carries hornblende instead of biotite and it lacks the augen structure which is apparent — though not highly developed in this particular locality - in the enclosing granite. Under the microscope, both granites show the same proportions of the same light-coloured minerals: microcline, quartz, and plagioclase (An26), and the same accessories: apatite, sphene, zircon, epidote, and magnetite. Biotite is the exclusive dark constituent in the enclosing granite. Hornblende is the predominant dark mineral in the enclosed granite but small amounts of biotite are also present.

The writer is inclined to interpret the included blocks of granite as being derived from magma that had already congealed in the roof of the magma chamber but that was later broken through during a renewed impulse of upward migration of the underlying liquid mass. - 31 - The younger rocks found in the 'basement' of gneissic granite with augen facies include the 'black rocks' (altered basic intrusives), the microperthite granite, and various small masses of fine-grained granite and pegmatite. All of these form bodies of easily determinable tabular or lenticular shape indicative of structurally controlled injection under heavy load.

It is believed that the first major igneous phase (represented by the 'gneissic granite with augen facies') subsided suffi- ciently for the granite to reach at least a plastic stage and develop a strong gneissic character under the action of the folding stresses and yet be rigid enough to direct any further magmatic invasion along its strongly developed foliation. Some basic dykes were intruded at this time along the planes of foliation. Proof that, following the solidification of these basic dykes, the granite continued to behave plastically, in some parts of its mass at least, under the action of the deforming stresses is seen in the deformation and segmentation of some of these dykes of 'black rocks' (Plate XVI-B).

The intrusion of masses of microperthite granite followed closely, and this granite probably acquired its gneissic character during its slow, structurally controlled, injection into the pre- existing, partly plastic, complex. More basic dykes and finally small masses of fine-grained granite and of pegmatite were intruded, again largely in concordant fashion, indicating that the basement was still under a tremendous load.

Pegmatites, like the 'black rocks', are of more than one age and it is presumed that a pegmatitic phase accompanied the birth of the floor or 'basement'.

Summary

By considering the present area as a small and deeply-eroded part of a very large region that was involved in a mountain-building cycle and attendant igneous activity, some reasonable explanations of the very complex geology can be offered.

The history of the igneous activity alone is considered, as little is known in the present area of the history of original deposition and of folding. The igneous cycle is assumed to have been caused by magma generation taking place in the granitic crust underlying the base of the geosyncline of deposition at some critical stage of the mountain-building cycle. The igneous history as recorded in the rocks of the area is as follows:

(1) Igneous injection on a limited scale (represented by the possible orthogneisses of the area) in the overlying sedimentary rocks. - 32 - (2) Emplacement of the main granitic magma, accompanied by granitization and pegmatitization of earlier rocks (main magma of this stage is now represented by the 'gneissic granite with augen facies').

Injection of small, basic masses ('black rocks').

Invasion of limited masses of 'microperthite' granite.

Second injection of basic dykes ('black rocks').

Injection of small masses of fine-grained granite and of pegmatite.

The abundance of granite in the area shows that the section, as now exposed, is that of the complex near the base of the original geosyncline. Thus the assemblage may be termed most ade- quately a basal complex.

GLACIAL GEOLOGY

Glaciation has left its mark on the exposures along the shore. Although striae are not everywhere conspicuous on the rock surfaces, they are eminently displayed in many places (Plate XXIFA). Outcrops are often well rounded and, where the ice has moved parallel to the structures, 'fluting', due to erosion of softer streaks, bands, or dykes in the rock, has often been produced.

Morainic accumulations and erratics, although not abundant, are occasionally encountered. Small erratics near sea-level are not to be considered as being of true glacial deposition, since a certain amount of 'ice-rafting' takes place every year. This yearly trans- portation probably explains the presence of blocks of Palaeozoic limestone among sea-level accumulations of boulders. The closest known outcrops of Palaeozoic limestone are some 45 miles west of Aguanish, and throughout the region the Pleistocene ice-sheet is known to have moved almost due south.

A special type of markings (Plate XXII-B) in the rock, observed near Kegashka, appears to be a peculiar effect of ice-plucking, resulting in what are known as 'crescentic gouges'1.

Unconsolidated sediments, deposited during the Champlain sub-stage, form the extensive terraces described earlier in this report. They consist of bedded and cross-bedded sands underlain by laminated clay (Plate I-A). No preserved shells were found in any of the deposits.

1Lahee, F.H., Field Geology, p.25; McGraw-Hill Book Co., Inc., New York, 1923. - 33 - Along Natashquan river, near its mouth, tree trunks were observed on the south bank, emerging through the well-bedded sands near the foot of the escarpment. As there is no evidence here that the bedded sands are not of Champlain time, the trees are considered to be of pre-Champlain age.

ECONOMIC GEOLOGY

Fluorite

Fluorite occurs as microscopic scattered crystals and in veinlets in some of the 'microperthite' granite. This is of interest in so far as it points to the possibility of more important occurrences of this mineral in the 'microperthite' granite and perhaps in the surrounding rocks as well.

Fluorite was observed in thin sections from the following masses of 'microperthite' granite: the small body on the eastern border of Nichon Village; the large masses one mile west of Thériault island; at Curlew point; immediately east of Cap Rouge point; and at Chicoutai point.

Graphite (No. 3)X

Occasional flakes of graphite were observed in a lens of coarsely crystalline limestone included in crumpled quartzites along the eastern border of the most westerly band of sedimentary rocks, about three miles east of the village of Michon. This limestone lens and a few other similar ones are displaced and squeezed segments of thin limestone layers that originally were interbedded with the quartzitic sedimentary rocks. The possibility of finding commercial deposits of graphite in the area is very small, as the mineral is restricted to the limestone which, in turn, is very rare along the stretch of coast examined.

Iron Sands (No. 5)

Large deposits of iron sands occur near the mouth of Natash- quan river. They extend along a six-mile stretch of the shore between the mouth of the river and Mont-Joli, a small hill two and a quarter miles east of the lighthouse at Natashquan point. The black iron sand forms elongated lenticular patches in buff-coloured sand and is best seen on the beach or nearby along a low escarpment cut by the surf. The lenses extend for several hundred feet inland under a cover

The numbers within brackets refer to localities indicated on the map. - 34 - of grassy dimes in the western part of the deposits and of heavily wooded, peaty top-soil in the eastern part.

The Natashquan iron sands have been known since the early days of mining in Canada, but it was not until 1911 that serious attention was focused on them and a thorough study, which continued for three consecutive years, was undertaken by the Mines Branch of the Federal Department of Mines.

In 1911, MacKenzie' investigated, by means of bore-holes cut with a seven-inch sand auger, a narrow east-west trending area of 169 acres extending from the mouth of the river to Natashquan point, an approximate distance of three and a half miles, and extending about 500 feet inland. As a result of this work he estimated that, within this area to an average depth of sixteen feet, there were available 5,800,000 tons of crude sand which would yield 500,000 tons of magnetic concentrates containing 67 per cent of iron.

In the following year2 he returned with a four-inch drill, using a steel pipe casing which permitted boring below ground-water level, and investigated in detail the sands at the tip of the peninsula. The area covered extended for two miles east of the mouth of the river and about 1,500 feet inland, and totalled some 184 acres. In 1913, Parsons9 examined an area of 340 acres, stretching from Natashquan point to Mont-Joli and extending 2,000 feet inland.

This three-year investigation showed that, between the mouth of the river and Mont-Joli, there was available a total of more than 27,000,000 tons of dry, crude sand, from which might be recovered an average of 6.54 per cent of magnetic concentrates4.

During six days spent at the mouth of Natashquan river the present writer collected fourteen samples between the tip of the peninsula and Natashquan point. The samples were obtained at inter- vals of 1,000 feet among the grassy dunes of the seashore. The sampling method used was extremely crude. It consisted of digging a test pit, one foot in diameter and three feet deep, and of taking a representative sample of the sand extracted from the hole.

1MacKenzie, G.C., The Magnetic Iron Sands of Natashkwan; Mines Branch, Dept. of Mines, Ottawa, Pub. No. 145, 1912. 2MacKenzie, G.C., Summary Report for 1912; Mines Branch, Dept. of Mines, Ottawa, pp. 69-71, 1913. 3Parsons, C.S., Summary Report for 1913; Mines Branch, Dept. of Mines, Ottawa, pp.90-96, 1914. 4From a blue-print issued by the Dept. of Mines, Ottawa. - 35 - Assays of the fourteen samples gave an average of 19 per cent iron and 4.85 per cent titanium dioxide.

The phosphorus, sulphur, and vanadium contents of the sands were investigated in a natural wave concentrate collected from the beach. The sample assayed:

Phosphorus 0.04 per. cent Vanadium 0.10 per cent Sulphur Nil

Tests made in the laboratories of the Quebec Department of Mines on the possibility of concentrating the magnetite by magnetic separation gave encouraging results. Using a Dings magnetic tube tester, a product was obtained which contained 84.7 per cent magnetite and 4.38 per cent titanium dioxide.

Zircon is present in the sands, but only in very minute amount. It averaged 0.02 per cent by weight in the fourteen samples taken by the writer. Being a heavy mineral, it follows the magnetite and ilmenite. In the natural wave concentrate, for instance, its percentage is 0.80.

-Magnetite (No. 1)

Magnetite occurs in pegmatite as nodules up to the size of an egg, though generally much smaller, at a point half a mile southwest of Michon Village. It is also present in lesser amount in other pegmatite dykes of the area. All such occurrences are of mineralogical interest only.

Pyrite (Nos. 2, 4, and 6)

Fine whitish pyrite (No. 2), disseminated in impure quartzite, occurs at a point about two and a quarter miles east of the village of Nichon. The shoreline here trends slightly east of north, coinciding closely in orientation with the sedimentary beds, which strike about north-northeast and dip steeply east. The mineralization is distributed in a zone from ten to twenty feet wide which parallels the trend of the quartzite beds, following a course close to the water-line. The mineralized zone, as indicated by its rusty- weathering surface, can be followed for a total distance of 2,200 feet, although interrupted here and there by water or overburden. In one place, there are, in addition to the disseminated pyrite, splashes and lenticular veinlets of this mineral up to two feet long and half an inch wide. An assay of a sample carrying the disseminated mineralization gave 0.002 oz. gold and 0.054 oz. silver per ton, and 0.07 per cent copper. -36- Disseminated pyrite (No. 4) and chalcopyrite were seen in gabbro at a point on the shore a mile and a half due east of Gannet rock. The gabbro is in the form of a dyke, 40 feet wide, intruded concordantly along beds of quartzite. The dyke strikes roughly north- south and dips 35 degrees to the east. The mineralization, which is very scattered, was observed in the chilled eastern border of the dyke.

An occurrence of pyrite (No. 6) was also noted in Mistas- sini harbour, at a point on the shore four and a quarter miles west of the village of Musquaro. The mineralization occurs at the contact between gneissic granite and pink pegmatite, along a zone twenty feet long and ten inches in maximum width, trending N.55°W. and dipping 40 degrees to the northeast. The zone has a strong schistosity parallel to its strike and consists of pyrite veinlets, half an inch or less in width, in a rust-laden host-rock composed of mica, quartz, and a soft, greenish mineral, which is probably serpentine. The pegmatite wall of the vein contains considerable magnetite which persists, although in gradually decreasing amount, for a distance of six to seven feet from the mineralized zone. Assay of a sample taken from the richest portions of the veins gave 0.02 oz. gold and 0.046 oz. silver per ton, and 0.12 per cent copper.

CONCLUSIONS

The area between Aguanish and Washicoutai bay is underlain by a complex assemblage of very old rocks. The geology is very similar to that of many well-known areas of the Grenville sub-province of Ontario and southern Quebec, and it is probable that the oldest rocks are of Grenville age.

With the exception of the Natashquan iron sands, which are secondary deposits of the transported type, no appreciable mineral occurrences have been encountered anywhere in the area. Judging from the results of the present investigation, the coastal region between Aguanish and Washicoutai bay seems to hold little promise for the prospector.

This statement must not be taken as condemnation of the coastal region as a whole, since, as has been found along other sections of the coast, there may be rather abrupt changes in the rock assemblages from place to place. Therefore, the unexplored areas cannot be written off as unfavourable for prospecting until they have at least been geologically mapped.

However, the presence of fluorite in the 'microperthite' granite is of interest. In some places, the fluorite occurs in veinlets along fractures in earlier minerals, indicating that it was in- -37- traduced at a late stage in, or even subsequent to, the crystalliz- ation of the granite. The possibility remains, therefore, that care- ful search might reveal interesting concentrations of fluorite in the 'microperthite' granite or even in the surrounding rocks.

It is recommended that the masses of this granite and the older rocks in their vicinity be investigated. For this reason, and as a guide to the prospector, the probable inland extension of one of the masses of 'microperthite' granite — that east of Cap Rouge point — has been outlined on the map from a study of the local structure. - 38 - ArPHAxETICAL TIMEX

Page Page Access into area 1 Contacts 25,26 Acknowledgments 3 Copper 35,36 Agriculture in area 7 Cormier, Malter - Aguanish 7 Fishing boat of 3,4 Aguanish terraces 5 Amphibole 19 De Puyjalon, Henri - Amphibolite 12,21 Ref. to work by 2 Amphibolitic dykes 20 Description of area 4 Anthophyllite - Diopside 14 Rock 20 Dioritic gneiss 10 Schist 12,20,21 Dykes - Apatite - Amphibolitic 20 Accessory mineral 13,15,17,18,19 Basic 31 20,22,23 Black rock 26 Aplites 25 Chlorite 12 Assay results 35 Gabbro 36 Augen granite 16 Granite 10,23,24,26 Auger, Dr. P.E. - Pegmatite 10,24,26 Acknowledgment to 4 Epidote - Basal complex 9,28 Accessory mineral .. 20,22,25,30 Basic dykes 31 Exposures 19 Basic rocks 19 Bédard, Jean-Charles Feldspar 15,28 Junior assistant 4 Potassic 23 Biotite 13,15,19,21,22,30 Field work 2,3 Granite gneiss 17 Fishing in area 7 'Black rocks' 12,20,21,25,31 Fluorite 33,36 Boudreault, A. - Accessory mineral 23 Boatman with party 4 Foliation 17,25,27 Formations, Table of 8 Calcite - Fractures 25,28 Accessory mineral 13,21,25 Canadian Hydrographie service .. 2 Gabbro 36 Canadian Pacific Gault, H.R. - Airlines service 1 Ref. to work by 27 Chalcopyrite 36 Geology - Chicoutai Point 5 Economic 33 Chlorite 19,20 General 9 Dykes 12 Glacial 32 Schists 12 Structural 25 Clarke Steamship Co. Ltd. Glaciation 32 Services of 1 Gneiss 9,10,14,18,30 Climate of area 8 Gneissic granite 10,22,30 Consolidated rocks 9 Gold 35,36 -39- Page Page Granite 10,11,22,23,29 Magnetic iron sands 2 Granite dykes 10,23,24,26 Magnetite - Granitic gneiss 16,17 Accessory mineral 13,17,18,19 Granitic intrusives 22 22,23,30,35 Granitic rocks 10 Magnetite-ilmenite 20,35 Graphite 14,33 Marine charts 2,3 Metamorphic rocks 13,14 Harker, A. - Michon village 7 Ref. to work by 21 Microcline 13,17,19,22,30 Hematite 18 Microperthite 10,22,23 Hornblende 14,20,30 Granite 11,21,26,31,33 Accessory mineral 13,18,22 Mineralized zone 35,36 Hunt, T. Starry - Mineralogy of rocks in area ... 13 Ref. to work by 2 Mont-Joli 6 Muscovite - Igneous cycle 29,31 Accessory mineral 13 Igneous rocks 28 Musquaro 7 Ilmenite - Musquaro point 5 Accessory mineral 22 Industry within area 7 Natashquan 6 Inhabitants of area 6 Natashquan iron sands 34 Intrusive s, granitic 22 Natashquan terraces 4,6 Iron 35 Iron sands 33,34 Oligoclase 21 Olivine 19 Jahns, R.H. - Orthoclase 15 Ref. to work by 28 Outcrops 5 Jointing 28 Paragneiss 13 Kegashka 7 Parsons, C.S. Kegashka terraces 5 Ref. to work by 34 Pegmatite 10,18,24,31 Lahee, F.H. - Dykes 10,24,28 Ref. to work by 32 Stringers 17 Laurentian granite and Pegmatite-injected gneiss 16 granite gneiss 2 Petrology 13 Le Poste 6,7 Phlogopite 14 Limestone 9,33 Phosphorus 35 Crystalline 14 Photographs, use of aerial 3 Location of area 1 Photomicrographs 4 Logan, (Sir) W.E. - Plagioclase 13,17,19,23,30 Ref. to work by 2 Amphibolite 20,21 Longley, W.W. - Plagioclase-biotite Work done by 2,16 Amphibolite 12 Prehnite rock 25 MacKenzie, G.C. - Pyrite 14,15,35,36 Ref. to work by 34 Accessory mineral 13,17,22

-40 - Page Page Pyroxenes 19 Sphene 14,15 Accessory mineral 13,20,22 Quartz 13,14,15,23,25,30 23,30 Quartz-biotite gneiss 9 Streams of area 6 Quartz-dioritic gneiss .. 17,18,19 Sulphur 35 24,30 Quartzites 9,13 Table of formations 8 Tension joints 27 Rivers of area 6 Terraces ... 5,6 Titanium dioxide 35 Sands - Topography 4,6 Magnetic iron 2 Natashquan 9 Vanadium 35 Scapolite 14 Vegetation 6 SChists 9 Vigneault, G. - Sedimentary rocks 9,13 Cook for party 4 Serpentine 19,36 Settlements 6 Work in area 1 Sheeting of granite 28 Shoreline of area 4 Zircon - Silicates 14 Accessory mineral 13,15,17,18 Silver 35,36 22,23,30