RP 555(A) PRELIMINARY REPORT, GEOLOGY OF THE LANTAGNAC - LA TOUCHE AREA, ABITIBI TERRITORY AND ABITIBI-EAST COUNTY

P.R. NO. 555

DEPARTMENT OF NATURAL RESOURCES

Honorable DANIEL JOHNSON PAUL-EMILE AUGER Minister Deputy Minister

Geology of

LANTAGNAC - LA TOUCHE AREA ABITIBI TERRITORY AND ABITIBI-EAST COUNTY

PRELIMINARY REPORT

by

J.A. Maclntosh

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QUEBEC 1966 P.R. NO. 555

P.R. NO. 555

QUEBEC DEPARTMENT OF NATURAL RESOURCES

Honorable DANIEL JOHNSON PAUL-EMILE AUGER

Minister Deputy Minister

GEOLOGICAL EXPLORATION SERVICE

ROBERT BERGERON, Director

Geology of

LANTAGNAC - LA TOUCHE AREA ABITIBI TERRITORY AND ABITIBI-EAST COUNTY

PRELIMINARY REPORT

by

J.A. Macintosh

QUEBEC 1966 P.R. NO. 555 I Preliminary Report.

on

LANTAGNAC - LA TOUCHE AREA

Abitibi Territorÿ and Abitibi-East County

by

J. A. Macintosh

INTRODUCTION

The Lantagnac - La Touche area, covering 380 square miles, was mapped during the summers of 1964 and 1965. It is within latitudes 50°00' and 50°15' and longitudes 75°00' and 75°301 . Included are the northern parts of Guettard, Lamark, and Opémisca townships in Abitibi-East county, and the whole of Julien and parts of Lantagnac, La Touche, Lucière, Turgis, and Livillier townships in Abitibi territory. The area is most easily reached by floatplane, and numerous lakes and several places on and Brock rivers are suitable for floatplane operation. There is a good portage between Brock river and the east end of Eau-Noire lake, and between a tributary of Brock-Ouest river and Opataca lake. Julien creek is navigable by canoe between Julien and Thomelet. (Icon) lakes. The two east-west mid-township lines within the area are easily followed as are the north-south lines between Turgis and Livillier, between Guettard and Lamarck, between Lamarck and Opémisca, and the northern boundary of Lantagnac, Julien, and La Touche townships. The southern boundary of Lantagnac township is difficult to follow, and the southern boundaries of Julien and La Touche townships were not. seen. - 2 -

The area has generally a low relief, and the. topography is marked by northeasterly-trending, broad, drum- linoid hills crossed at right angles by lower, narrow ridges of washboard moraine. The northeast and southwest quarters are particularly flat. Near and over the Moraine Lake stock several hills have a local relief of 300-500 feet, and rocky slopes are common. This more rugged terrain continues t.o the northwest to Quatre-Coins and Turgis lakes. Elsewhere, particularly in the extreme southwest corner and north of Thomele.t lake, isolated hills stand out. In the area bedrock exposure forms less than 5% of the surface. drains a quarter of the area, mainly through Brock river. Half the area drains into La Trêve river through Ruth lake and Mildred creek. A small part at the northwest corner drains into . All these systems empty into the Nottaway. Waposite and Dumas lakes drain the remaining quarter and empty into the Broadback. Thus, all the drainage eventually goes to James bay.

Previous Work

Shaw (1942) mapped the geology of this area as part of a larger area extending to the west and north. A simi- larly large block, including the territory immediately to the east, was mapped by Kindle (1942). Beach (1941) mapped to the south in 1937 and 1938. Gillett (1957) mapped an area to the east of, but not immediately adjoining, the present area. An aeromagnetic map (549G) published by the Department of Mines and Technical Services, Ottawa, covers this area except the northern quarter and along part of the western boundary.

GENERAL GEOLOGY

All the consolidated rocks of the area are Precam- brian. Nearly all the northern half of the area consists- of felsic rocks, including feldspar-quartz-biotite gneisses, granitic and injection gneisses, and a syenodiorite-metasyenite complex as principal members. The syenodiorite appears to intrude the gneisses. The southern half of the area is dominantly an 3

association of volcanic and sedimentary rocks, th.e. larger (pre— Opémisca) part of which carries sills of metagabbro., These rocks, as well as some mafic and ultramaf is bodies, are apparently cut. in the east by granitic stocks varying from granite t.o meta- syenite. In the west, quartz-feldspar porphyries and one small plug of granite were the only felsic intrusions seen. The syeno- diorite complex of the northern half of the area swings southwest and appears to form the western boundary of the southern half of the area.

The structure is marked by generally steep dips of both bedding and schistosity in the sedimentary and volcanic rocks. Dips in the gneisses are commonly moderate and, in a few places, low. The strikes of the sedimentary and volcanic rocks are generally consistent within a band, whereas the gneisses show much variation.

The relations of the volcanic and sedimentary rocks are uncertain, although on a regional scale Opémisca sedimentary and volcanic rocks are said (Gillett, 1957) to overlie the dominantly volcanic, pre-Opémisca sequence of this report. Pre- Opémisca rocks are 'scarce in the eastern third of the area and may be absent to the east (Kindle, 1942). In the southeastern part of the area Opémisca rocks, mainly sedimentary, are exposed in zones that trend north-northeast to east. The Opémisca volca- nics are best developed south of the sedimentary zones toward the southeast corner of the area. The lack of pillow lava, the presence of amphibole porphyry, and their relative pale color and softness distinguish these volcanics from the pre-Opémisca volcanics. About 12 miles to the west, a band of rocks, placed in the Opémisca series by Beach (1941), has an altered, silicic, volcanic rock as its principal member in this area, and associated porphyries that may be rhyolite flows.

The relation of the "central gneiss" to the Opé- misca rocks is not known. There is some interfingering of rock types to the east, but the exposures are too poor for the observer to be certain that the gneisses result from metamorphism of Opémisca rocks. Metagabbroic sills of pre-Opémisca type occur in the "central gneiss" and were not seen in contact. with Opé- misca rocks.

The granitic gneisses are shown separately as the "northern gneiss", but no definite boundary can be drawn to the north (near Quatre-Coins lake) from the "central gneiss" to outcrops characterized by increasing amounts of injection and granitic gneisses. Diabasi'c and gabbroic dikes trending east-north- east to north-northwest. are probably the. youngest intrusive rocks.

PRECAMBRIAN

Pre-Opémisca

The pre-Opémisca volcanic rocks are characteris- tically dark green to black and fine to aphanit.ic, and are marked by pillows, flow lines and surfaces. They are moder- ately hard to hard. Included with the pre-Opémisca are metagabbros, metadiorites, and fine-grained, dark schists and finely banded rocks, either associated, or on strike, with the pillow lava. Well developed pillow lava was noted in four localities: between Julien and Deux-Granites lakes, where it outcrops sparsely over an area at least 8,000 feet wide and 4 miles long; west and southwest of Julien lake, where the pillows are usually poorly formed; south of Anomalie (Anomaly) lake, where it is 1,000 feet wide and a mile long; and in scattered occurrences west, north and east of Keller lake. Many of the pillows are well formed with chilled edges and massive, fine-grained centers. Some are underlain by a zone of amygdules 1-2 cm. wide. Between individual pillows calcite and quartz stringers are common. Reliable top determinations are rare in the pillows near Julien lake. The most common rock occurring with the pillow lava is aphanitic to fine grained, massive to finely banded to schistose, and dark green to black. There the rocks are aphanitic and hard and show vague flow structures, they are taken to be flows. The finely banded rocks are probably tuffs. Some schistose varieties grade into metagabbroic rocks and pillow lava, but most are. of uncertain origin. In hand specimen they appear to consist of amphibole and chlorite. Rare cherty bands less than 2 inches wide, and lenses of white quartz a few inches wide and a few feet long occur. Pyrite occurs in disseminated fine grains as a very minor constituent. Metagabbroic rocks are common. They are dark green, massive and fine- to medium-grained, and are made up of white to green feldspar and dark hornblende. Perhaps the most. common Table of Formations

ic Pleistocene Ground moraine., washboard moraine, and eskers, sand dunes, stream deposit.s

nozo Recent Ce Diabase dikes Later Diabase Olivine gabbro dike Post-Opémisca Felsic Intrusive Granite Intrusive Rocks Stocks Relative ages Relative ages Porphyry granite. not known not. known Syenit.e Syenodiorit.e Mafic Intrusive Gabbros Rocks Relative ages Ultramafics not known

Northern Feldspar-quartz-biot.it.e gneiss, Gneiss granitic gneiss, injected • gneiss, amphibolite, feld- spar-quartz pegmatite 4 Relative ages not known û Central Feldspar-quartz-biotite gneiss, w Gneiss feldspathic quartzite, Ç-1 feldspathic gneiss, amphi- bole-feldspar gneiss, amphibolite, graphitic gneiss

Sedimentary Rocks - conglom- erate, graywacke, black schist, some undifferentiated Relative volcanic rocks Opémisca ages Volcanic Rocks - altered ande- Group not sitic porphyry, altered . known andesitic massive lava; agglomerate; altered silicic volcanic rock, rhyolitic porphyry

Pre-Opémisca Pillow lava, basic schists, Group sills of metagabbro and quartz metadiorite - 6 .- type consists of _about equal proportions of hornblende in a matrix of finer-grained. feldspar. Commonly these rocks appear to be sills about 100 feet thick. However, they are rarely exposed across their full width, and some, especially among. the finer-grained types, may be massive flows. West of the Moraine Lake stock a metagabbroic sill 500 feet thick forms the core of a rocky hill of pre-Opémisca rocks, and south and southwest of Julien lake half of the outcrops are metagabbros. The western half of the northerly-trending, high ridge immedi- ately west of Petit Eau-Noire lake (Petit Noir) is mainly metagabbro. Elsewhere the pre-Opémisca volcanics lack pillows and apparently have.been'altered to some extent. On the south shore of the western part of Thomelet lake, the pre-Opémisca rocks are epidotized, garnetiferous, probable flows cut by aplite and quartz stringers. Near Bluets lake two rock types are common. One (probably volcanic) is aphanitic to very fine grained, dark green, generally schistose, in part finely banded and commonly garnetiferous. In places it shows textural and color variations arranged in an irregular, meandering manner that suggest flowage effects. Minor amounts of pyrite and pyrrhotite cause a rusty- weathering surface in many places. The second rock (probably a sill) is a fine- to.medium-grained, gray quartz metadiorite. These rocks are well exposed for 24 miles on the hill immediately west of Bluets lake. The few outcrops found are mainly quartz metadiorite and quartz metagabbro; also present is fine-grained, commonly foliated amphibolite carrying minor pyrite and pyrrho- tite. A quarter mile east. of May Bank lake an isolated exposure of metagabbro forms a ridge striking N.,70°E. with a north-facing scarp. This may be an extension of the metagabbros east or west of Eau-Noire lake, or of those near Bluets lake. The western end of the band mapped as pre-Opémisca contains numerous small outcrops of quartz-feldspar porphyry, an aphanitic to medium-grained,, leuco- to mesocratic, gray rock with many phenocrysts of bluish quartz and white feldspar. These outcrops fall roughly into a, band extending southwest from Thomelet lake to near the southern limit of the area. Several of these quartz porphyries were dikes cutting metagabbroic and volcanic rocks. Several on the shore of Thomelet lake are inclu- ded in a granite stock; the remainder are not distinguished on the map from the pre-Opémisca rocks. Opémisca Group

The. Opémisca forms a distinctive group in the southeast corner of the area. To the north exposure. is poor. The most northern band, which surrounds Poudingue lake, consists of black schist and, on the north shore of the lake, an outcrop of conglomerate.

Volcanic Rocks

In the southeast corner of the area, volcanic rocks are porphyritic to even-grained, soft and green. Commonly they carry equant, dark green amphibole, or pale green to white plagioclase phenocrysts in a fine to aphanitic matrix. A faint schistosity may be seen on the weathered surface. The northern border of the main body of these rocks is characterized by a schistose, coarse-grained feldspar porphyry with phenocrysts up to 1 cm. long. At the contact with the gabbro to the south the volcanics are hard and massive, resembling the fine-grained, chilled gabbro. Several outcrops of agglomerate with porphyritic andesite as pebbles and matrix appear to define a narrow band. cut by the above-mentioned gabbro. This agglomerate is indicated as conglomerate by Beach (1941). About 11 miles to the west volcanics form a north- east-trending band about 3 miles long and 1/4 to 1 mile wide. Altered, chert-like silicic volcanics are the main component of this band. These rocks are aphanitic, black to dark gray and hard where fresh, but pale gray and soft weathering. In many places they are very finely veined by anastomosing, thin lines of paler chert-like material, which appears to fill minute, closely-spaced fractures. The fracture surfaces are not conchoi- dal, and in this the rock differs from chert. Along the south- east shore of Pichamobi bay (arm), and for the most part just south of the map-area, a similar rock is associated with a conglomerate carrying pebbles of fine-grained feldspar porphyry. Also associated are beds or sills of a bright green, aphanitic, rusty-weathering, in part calcareous rock, and a biotite lampro- phyre-like rock up to 20 feet thick. The main exposure of the chert-like rock is separ- ated from the similar rock to the north by gray, aphanitic quartz- feldspar porphyry, which appears t.o extend north to Julien creek. 8

The porphyry is believed to .be. volcanic because the matrix is similar to the silïcic rocks of the band. However, it also resembles the rocks of the dike zone extending south from Thomelet lake in the pre-Opémisca group.

Sedimentary Rocks

Conglomerate and black schist are the most wide- spread sedimentary rocks, but they form few outcrops. The best. exposed are the graywackes, or tuffs, and associated black schists near Crinkle creek and the lower part. of Brock river. Along Chibougamau river at and below the last rapids similar rocks occur, but the shearing here makes it difficult to separate sedimentary from volcanic rocks. The graywacke resembles fine-grained feldspar porphyry. It is medium gray and faintly schistose, and has scattered, angular quartz grains, as well as irregular frag- ments of dark rocks generally less than 1 cm. across. The latter are apparently black slate and fine-grained feldspar porphyry. The best exposure of black schist is a few hundred feet south of, and parallel to, Crinkle creek. It is gray to black weathering and aphanitic, and has a marked schistosity and, locally, slaty cleavage. Pyrite grains are common, as are pyrite lenses up to 5 mm. long. Also common are short stringers of dark quartz, small drag-folds along the planes of schistosity, and minute cross faults. On an island in Brock river, at the portage to Chibougamau river, graywacke with numerous inclusions 1-2 feet across of black schist appears to cut across the black schist; this is possibly an effect of slumping in unconsolidated sediments. Farther north along Brock river the few outcrops appear to be argillites. Conglomerate outcrops were found at five widely separated localities, and conglomerate bedrock is suggested elsewhere by two bands of float. The conglomerate consists of 25-50% cobbles, generally 2-4 inches but up to 8 inches in diameter. The cobbles are of felsic and mafic intrusive rocks in equal proportions. Some pebbles of chert and aphanitic, dark rocks are also present. The felsic cobbles are commonly medium- grained, massive to porphyritic granite; the mafic cobbles are fine- to medium-grained metagabbros. The matrix is in thin, light and dark gray, fine-grained, feldspathic to amphibolitic bands, with quartz, chlorite, and biotite. Central Gneiss

The Central Gneiss forms a band across the mid- latitude of the area but is much wider westward. It includes paragneiss principally, but dark schists and gneisses that probably are metamorphosed basalts are also present.. The princi- pal rock is a gray medium-grained, garnetiferous, feldspar- quartz-biotite schist to gneiss. White and clear quartz stringers are locally abundant. Pyrite is widely disseminated and rusty- weathering outcrops form a prominent horizon from south of Dumas lake to north of Petites-Plages lakes. Massive to faintly schis- tose feldspathic rocks and quartzitic rocks form large outcrops. In the latter, bands up to 2 inch thick of fine- to medium- grained quartz alternate with bands of gray feldspar and an acicular mineral, apparently sillimanite. Amphibole and foliated amphibole-feldspar rocks are prominent at the western border of the Central Gneiss from Boucle lake southward. Along the north- ern border between Quatre-Coins and Dumas lakes similar dark gneisses occur with dark, amphibole-quartz(25%)-feldspar-garnet gneiss. Black schists rich in pyrite were seen at several points towards the east. South of Quatre-Coins lake narrow bands of fine-grained graphite occur in an outcrop of feldspar-quartz- muscovite gneiss. Between Dumas and Deux-Granites lakes the structure of the Central Gneiss is conformable with the pre-Opémisca rocks to the south. Farther west, the gneisses are contorted. The gneisses may be metamorphic equivalents of the Opémisca rocks. The contact is arbitrarily drawn north of the conglomerate at Poudingue lake. In this connection it may be noted that associated with the conglomerate west of Eau-Noire lake is a foliated, garnetiferous quartz-amphibole gneiss. The Deux-Granites Lake stock intrudes the Central Gneiss.

Northern Gneiss

In the northeast corner of the area a few outcrops of feldspathic gneisses consist of white to pale green feldspar, quartz, and biotite or hornblende or fine chlorite. The gneissic structure varies and generally is ill defined. West and northwest of Quatre-Coins lake, granitic injection(?) gneiss is predominant, and granite and feldspar- quartz pegmatite stringers cut biotite-feldspar-quartz and - 10 - amphibole gneisses. This granitic material: is not. common in the Central Gneiss and appears to become more. abundant. towards the northwest corner of the area.

Intrusive Rocks

Ultramafics

Ultramafic rocks occur in three widely separated parts of the area: one towards the northeast corner, the second in the southeast, and the third in the southwest. The northeastern mass extends northwest 11,000 feet from the eastern boundary of the area and averages about 4,000 feet wide.. It is well exposed on Brock-.Ouest.river. Strong compass deflections were noted just east of the Brock- Ouest.. Most of the rock is dark brown to black, coarse-grained pyroxenite that carries 1-2% of reddish black biotite and less than 10% olivine. The most easterly_ outcrops are of amphibolite and very fine-grained metagabbro. The southeastern mass includes part of Anomalie lake and is roughly square (7,000 feet north-south and 9,000 feet east-west). Here mafic and ultramafic amphibole-pyroxene rocks are brecciated and intruded by diorite, the whole causing a magnetic anamaly and forming ,a broad ridge. The most common rock is dark, massive, medium grained and amphibole-rich. The breccia is best exposed on the floor and eastern wall of a steep valley running north-northeast from the northwest corner of Anomalie lake, where the intruding diorite consists of white feldspar, hornblende, and minor quartz. East of the main breccia zone for 12 miles similar diorite is common as small stringers. In the main breccia zone the fragments are up to 2 feet across, and some may be pre-Opémisca volcanic rocks. The limits of the complex as mapped are largely based on the magnetic anomaly. An extension of the anomaly to the northwest of the above-mentioned valley lies over what appears to be a sill of pre-Opémisca-type metagabbro that is intruded and brecciated by biotite garnite. This is mapped with the north-south band of pre-Opémisca rocks. Lying south of this brecciated metagabbro, and forming the west side of the valley, is a ridge of what appears to be pre-Opémisca volcanic flows cut by a stockwork of dioritic dikes a few inches wide. Large blocks of a similar amphibole-pyroxene rock occur to the north. on the northeast shore of Eau-Noire. lake and suggest that the magnetic anomaly northeast of the lake may be caused by a similar ultramafic body.

The southwestern ultramafic mass underlies a hill and magnetic anomaly at the west end of Thomelet lake. It trends northwest for 7,000 feet and is up to 3,500 feet wide. The rock is black, dark gray weathering (with rusty spots and pits 1-2 mm. across), and medium-grained pyroxenite. Pyroxene altering to amphibole is the major mineral; olivine and black metallic minerals are minor. Except for a few small patches of coarse- grained gabbro the rock is uniform. The only contact seen was with a diabase dike that, farther north, also cuts metagabbro. A northerly extension of the ultramafics, not shown on the map, may account for the continuation of the magnetic anomaly over the low ground here.

Gabbros

A complex mapped by Beach (1941) is represented near the southeastern corner of the present area by a very coarse-grained, pale gabbro that appears to be partly chloritized. The feldspar is white and is in tablets up to 2 inch long. A few plates of pale green mica occur. A contact with the Opémisca volcanic rocks was seen at one point, and here fine- and coarse- grained, narrow gabbro dikes cut an indurated, very fine-grained, dark rock. Some of the gabbro near the contact has coarse pyrox- ene phenocrysts in a fine-grained matrix. An elliptical mass of metagabbro 9,000 feet long and up to 3,000 feet wide trends east-northeast through Julien lake. Poorly defined layers a•few inches wide strike east-north- east and dip northerly at Julien lake. Here also the rock is light colored and medium grained, but most is dark green to black, fine- to medium-grained, quartz metagabbro. Dikes and irregular bodies of coarse-grained to pegmatitic quartz gabbro are common on the western slope of the ridge east of the lake. Near the Moraine Lake stock the rock is a garnetiferous amphi- bole-quartz gneiss cut by numerous aplitic dikes. This gneiss may be an altered pre-Opémisca rock. On the point on the eastern shore of Julien lake there is a carbonatized zone 25 feet wide. - 12 -

Syenodiorite

Syenodiorite underlies at least. 100 square miles in the northern half of the area and extends beyond the area to the north, east and perhaps also to the west. The main part of the mass is gray, medium-grained diorite made up of pyroxene (40%), amphibole, biotite, andesine, potassium feldspar (10%), and less than 5% quartz. In many exposures the dark minerals are aligned. Pink, dark syenite, poor in biotite, is present locally. Northeast from Ruth lake a narrow band of "Northern Gneiss" may be syenodiorite. Near this band are outcrops of feldspar-quartz pegmatites up to 100 feet across.

Syenite

An elliptical syenite mass about 4 miles long and 2 miles wide is outlined around Eau-Noire lake in the south- eastern part of the area. Two types of syenite within this mass are approximately defined by the 1,900 gamma isomagnetic line (Map 549G). The syenite within this limit is medium- to fine- grained, whereas that outside is coarser (up to 5 mm.). The finer-grained syenite is pale pink to gray, and carries horn- blende (10%), biotite (10%), and quartz (up to 5%). The coarser syenite lacks quartz and carries up to 40% of amphibole, pyrox- ene, or biotite. In the southern part of the mass outcrops of dark syenite and of olivine gabbro are associated. On a small island at the east end of the lake metagabbro (epidotized ?) is cut by narrow dikes of dark syenite. Between Eau-Noire and Petit Eau-Noire lakes diabase cuts dark, locally porphyritic syenite. Inclusions of feldspar-amphibole rock are common in the syenite.

Granite

Feldspar porphyry granite forms a stock-like body, 5 by 3 miles in extent, around Moraine lake. Pink to gray feld- spar phenocrysts up to 1 cm. long make up 20% of the rock. The groundmass consists of fine- to medium-grained quartz (to 25%), white to pink feldspar. (55%), and biotite (20%). Subhorizontal joints give scarp faces a stonewall appearance. No change in the character of the granite was noted at the few contacts seen with pre-Opémisca rocks. Sills and dikes of aplite, fine-grained granite, porphyry granite, and some pegmatite occur to within 50 feet of the contact. A sill of porphyry granite, 12 feet wide, - 13 - in pre-Opémisca. banded schist: showed no change in grain size. at either contact. .

Rounded and subrounded, fine-grained, me.socrat.ic, gray, feldspar-amphibole inclusions, 1-24 inches across, are common. Many carry pinkish feldspar crystals up to 1 cm. long.

The granite to the east of Deux-Granites lake is of two types (see map). The contact between the two types could be placed within 200 feet at one locality. One (the larger part) is porphyritic and very similar to that of Moraine lake. It is in contact with the Central Gneiss to the north and east, and with pre-Opémiscâ rocks to the south. The northern contact is generally conformable but here and there the granite cuts the gneiss and becomes finer-grained; quartz stringers and aplite, granite, and granite porphyry dikes are common near the contact. To the east, this contact is more complex owing to shearing and lit par lit injection. Inclusions were seen in this phase but not in the more even-grained phase.

The southeastern, or smaller, part of this granite mass is cream colored and fine to medium grained, and consists mainly of feldspar, quartz (25%) and biotite (10%). Feldspathic dikes up to a foot wide are common. To the southeast this granite is separated from the porphyritic phase by a steeply-dipping series 700-1,500 feet thick of black schist, garnetiferous and pyrite-rich dark schist, and pillow lava. North of Crinkle creek near its junction with Brock river, massive, fine- to medium-grained, gray granite forms a hill 1,000 feet in diameter. The granite consists of albite (60%), quartz (10%), biotite (10%), muscovite (10%), fine-grained calcite (5%), and pyrite (1%).

South of Thomelet lake two outcrops of granite with, to the north, several outcrops of rhyolitic quartz porphyry are sheared and, locally, pyrite-bearing.

Olivine Gabbro Dike

This dike, shown by Beach (1941) to cross the northern part of the Mechamego Lake area, extends east-north- east discontinuously to a point 4,000 feet southwest of Anomalie lake. In places it is a sill dipping steeply north. The width ranges from 100 to 400 feet. The dike varies in composition, texture, structure, and width. Generally it is greenish gray, medium-grained gabbro with coarse, poikilitic, pyroxene crystals. 14 -

Diabasic texture is common, and a fine-grained, ultramafic phase is local. At one place, where the dike is 100 feet wide, it is cut by an anastomosing system of 50 or more dark fine- grained dikes a few inches wide. Several contacts seen between the dike and pre-Opémisca rocks displayed chilled margins in the former and alteration to hornfels across 10-20 feet in the latter. Two outcrops of olivine gabbro 9,000 feet northeast of Anomalie lake may be the continuation of this dike.

Late Diabase

Good exposures of diabase near Eau-Noire lake suggest two dikes about at right angles to each other. The. more definite one strikes north-northwest for 6 miles. Between Eau-Noire and Petit Eau-Noire lakes circular joints with diameters of 5-10 feet are well developed; the joints are hori- zontal and perpendicular to the walls of the dike. The more indefinite dike, based on two exposures 12 miles apart and on the trend of the eastern (gabbroic) exposure, strikes east- northeast.

Other diabase was seen about 4,000 feet northwest of Petit Eau-Noire lake., and as a narrow dike in the ultramafics northeast of Anamaiie lake, and in the gabbro near the south- eastern corner of the area. The last two dikes strike northerly.

CENOZOIC

Pleistocene and Recent

In the area glacial striae indicate that ice moved to the southwest, corresponding to the predominent direction of the stream and lake pattern. The resulting drumlinoid topography and the ridges of washboard moraine at right angles form a recti- linear stream pattern. Two large eskers parallel the direction of ice advance for 7 miles: one along Brock river and the other along the western shore of Eau-Claire lake. Both have wide mar- gins of sand. Sand dunes up to 10 feet high were noted at two points north of Chibougamau river, and probable dunes were seen northwest of Eau-Claire lake. Cobble beaches occur on the ridge - 15 -

of metagabbro east Of, and 200-300 feet above,' Julien lake.. • Boulder moraine .is found throughout the area .but. is best: devel- oped over the granitic gneiss and the syenodiorit.e.

STRUCTURE

As the pre-Opêmisca pillow lavas face southeasterly where determinations can be made, the group appears to belong to one limb of a major fold. This limb appears to have been cross- folded by the granitic stock and the metagabbro in the south- eastern quarter of Julien township. Shaw (1940) postulates a fault striking north- northeast through the region of poor outcrop. in the eastern part of the present area. The only evidence seen by the writer of such a fault was sheared and contorted conglomerate 12 miles north-northwest from the junction of Brock and Chibougamau rivers. Drag-folds and cross-cleavage indicate left-hand movement. The schistosity here strikes northeasterly. Schistosity and cross-cleavage in the rocks along Chibougamau river above its junction with the Brock suggest a strike fault. On Crinkle creek a drag-fold 15 feet across plunges 50° to N.10°E. and indicates right-hand movement. A well-defined linear on the aeromagnetic map (549G) that is an extension of the Pichamobi Bay topographic linear passes northeasterly through the west end of Porphyry lake. Where the aeromagnetic linear ends to the northeast, west of the Moraine Lake stock, an olivine diabase dike 100 feet wide occurs and continues to the east-northeast for 1,000 feet to the small lake at the end of the aeromagnetic linear. The quartz porphyries and altered silicic tuffs of Pichamobi bay are along the southwest end of this linear. The linear may be a fault line. The attitude and distribution of pillow lava about Pichamobi bay suggest that the Opémisca rocks here are separated from the pre- Opémisca rocks by an angular unconformity or by a fault.

ECONOMIC GEOLOGY

The following review of past work in the area is based on public files in the Mineral Deposits Branch of the Department and on field work by the writer. These sources - 16 - indicate encouraging showings of gold, copper, and nickel, which have been the main objects of exploration in. this area. Cobalt. and molybdenum are also reported, and there ara interesting widths of massive pyrrhotite and pyrite. Most of the exploration has been along a wide band extending northeastward from Pichamobi bay of La Trêve lake to Dumas and May Bank lakes. The area of pre-Opémisca rocks lying south of Thomelet lake and west of Keller lake, in the southwest. corner of the area, appears to have received relatively little attention. It differs in character from the remaining area of pre-Opémisca rocks by the presence of numerous, small silicic intrusions, a factor suggesting that this locality warrants closer prospecting. The higher ground here appears to be covered with only a thin layer of soil. During the traversing, samples of stream sediment. were taken from the banks of streams near the water's edge. A sampling density of one sample per square mile was sought. These samples were assayed for Cu, Pb, Zn, and Mo. In the following summary, the figures in brackets refer to numbered localities on the map.

Gold

Fortunata Mines Limited. - Claims held by this company in the northeast corner of Guettard township include a quartz vein discovered and trenched over about 1,500 feet by Prospectors Airways in 1936. A geologic report was made for Central Chibou- gamau Mines Limited in 1952, and a report of further stripping and sampling was made in 1953 to Brunswick Quebec Development Limited. The latter report gives the assays of six samples from quartz veins ($3.46 to $24.25 in gold per ton; widths not stated) both the quartz and the wall-rock carrying the gold. Reference is also made to a wide carbonated shear zone in porphyritic andesite 1,000 feet to the southeast. A visit to a vein in this area (1) revealed that many drill holes were put down along and near the trenched vein, much of the core being on the property. The vein as now exposed is trenched continuously for about 300 feet. It occurs at the northern contact of a thoroughly altered dike, possibly meta- diorite, striking N.35°E. and cutting steeply-dipping pillow lava which strikes N.75°E. The quartz vein averages 2 to 3 feet wide, but is split into several irregularly-parallel parts across -17.- a width of. about 5 feet, the.. parts being separated by. a dike. and possibly: by sheared volcanic rock.. The quartz. is white to gray with irregularly-distributed pyrite. The. 'southern contact of the inetadiorite dike was not exposed. The claims presently held by Fortunata Mines Limited are: Certificate 88734. Claims 2-, 3 , and 4 " 88735 " 2, 3, and 4 88736 2, 3, and 4 These claims were held by the Maxwell-Angus-Kellar group in 1946. Other claims are held by individuals. A geologic compilation map (.1946) outlining pros- pecting in the "Lac La Trêve Mining Area", including the south- western corner of the present map-area (mainly in Guettard township), indicates some zones of sulfides, gossans, and quartz veins.

Copper - Nickel - Cobalt

Tomiska Copper Mines Limited. - This company had two showings on the La Trêve Lake. gabbro dike just south of the Lantagnac-La Touche area in the northwest quarter of Lamarck township on ground now held by individuals. Available is a company report (1956) on an electrical resistivity and magnetometer survey, and a company report (1957) on prospecting, trenching, and six packsack drill holes. Both showings are on the southern contact of the dike. One is mineralized over a width of 12 feet with pyrrhotite, chalcopyrite, pentlandite, and a cobalt mineral in scattered blebs and disseminated grains, a chip sample giving 0.73% Ni, 0.65% Cu, and 0.20% Co. The second, 950 feet to the west, was exposed over a width of 6 feet with similar minerali- zation. The drill holes indicate a width of about 10 feet to a depth of 75 feet down the dip, with values of 0.35-0.75% Ni and 0.20-0.90% Cu; no cobalt was reported. Mention is made of discoveries in 1956 on this dike to the east and west.

Kenmac Chibougamau Mines Limited. - A company geologic report and map (1957) shows the location of this company's claims (now abandoned) staked to cover part of the La Trêve Lake dike in Lamarck township, and the location of other companies' showings along the dike, including those on the Latulippe claims, one of - 18 - which lies within the present area. This last showing may be near location, (2) which lies on the Latulippe claims, and where a few grains of chalcopyrite, pyrite, and pyrrhotit.e were seen in a pyroxenitic phase at the south contact of the. dike.

Sagamore Mines, Limited. - Available are two company reports (1957) on electromagnetic surveys near the east end of Thomelet lake in Julien township. Mention is made of previous drilling along the probable extension of some of the anomalies yielding graphitic slates and minor sulfides. During traversing a diamond- drill hole, probably put down by Canadian Nickel Company, was found (3;16) and roads indicate that several holes were drilled nearby. No claims are now held here.

New York and Honduras Rosario Mining Company. Company reports on prospecting, on a magnetometer and electromagnetic survey (1957), and on the logs of three diamond drill holes (1958) in the northwest corner of Guettard township are available. Two main sulfide showings are described. One, at least 100 feet wide and 500 feet long, contains pyrite, pyrrho- tite, and small amounts of chalcopyrite in sheared, silicified volcanic rock. The second is an exposure 30 by 30 feet of coarse- grained gabbro cut by two shears with small masses and disse- minated grains of pyrrhotite and pyrite, the pyrrhotite being at least partly nickeliferous. Other occurrences of sulfides are mentioned. During a traverse, two drill holes, with the core stacked nearby, were found (4). These are probably holes 1 and 2, indicated as being about 500. feet northwest of the first showing and about 2,000 feet northwest from the third hole. A summary of the drill logs follows: D.D.H. 1: bearing, N.30°E.; inclination, 45°; length, 356 feet; 290 feet of intermediate volcanics with scattered pyrite and pyrrhotite; 62 feet of silicic to intermediate dikes in eleven sections. D.D.H. 2: bearing, S.45°E.; inclination, 45°; length, 357 feet; 4 feet of casing; 262 feet of intermediate volcanics with three sections, 22', 21', 18', carrying 5-10%, 2-3%, and 10% respectively of sulfides, mainly pyrrhotite; 83 feet of silicic to intermediate dikes in four sections. D.D.H. 3: bearing, S.50°E.;, inclination, 45°; length, 312 feet; casing, 4 feet; 226 feet of intermediate volcanics with two sections, 9 and 30 feet, of 10% and 5% sulfides

- 19 -

respectively.;. 26..feet of pyroxenit.e with paleinclusions; 3 feet of pyrbxenite with. 2% pyrrhot.it.e;' 45 feet. of :quartz.-feldspar porphyry.

Cross-Canada Explorations Ltd. - A company report (.1957) gives the location of two claim groups about Boucle lake and Petites- Plages lake, in Julien and Lantagnac townships and mentions a nickel-copper discovery made nearby by Trans Canada Explorers. No claims are now held in these localities.

Burrex Mines Limited. - A company report (1955) is available on a claim group staked on the basis of a gossan zone on the east- west center line in central Julien township. No claims are now held here.

Sporran Mines Limited. - This company holds five claims southeast of May Bank lake in the northwest quarter of La Touche township: Certificate 116695 Claims 1, 3, 5 It 116670 " 1, 2 A pile of core at (5) consists of black schist and altered mafic rocks, in part with pyrite. In the southwest quarter of Julien township this company holds five claims lying north of Julien creek along the possible extension of the Opémisca rocks running northeast from Pichamobi bay. Certificate 116663 Claims 1, 2, 4, 5 116666 " 1 Roads to drill sites were found here (6) and 3 miles to the northeast, but no further data are available.

Copper Prince Mines Limited. - A company report (1958) on an electromagnetic survey just east of the present area, in the northeast quarter of La Touche township, mentions a few outcrops of quartz-biotite schistose slate and graphitic slate with minor pyrite and pyrrhotite. - 20 -

Diamond Drill Logs

The following are brief summaries of drilling. logs available. The lengths given are the totals for all sections of a given rock type, except for sections rich in sulfides and for which individual lengths are given. The locations given by numbers in brackets referring to numbered locations on the map • are based generally on claim maps.

Sevigny Claims

(7) Guettard township; the hole is probably somewhat. south of this location, on claim 4, certificate 45236, since abandoned; the ground now being held by individuals; drilled in 1951; bearing, S.22°E.; inclination, 75°; length, 1,0,05 feet.; 360 feet of conglomerate and silicic sediments with 210 feet. carrying 10-60% sulfides; 15 feet of quartz diorite; 540 feet of graywacke; 20 feet of slate.

Canadian Nickel Company Limited

(8)Lantagnac township; D.D.H. 10276; 1957; bearing, S.80°W.; inclined 45°; length, 533 feet; casing, 15 feet; graphitic tuff, 465 feet; tuff with pyrite and pyrrhotite bands, 42 feet. (9)Lantagnac township; D.D.H. 5979, 1957; bearing, N.48°W.; inclined 450; length, 645 feet; casing, 12 feet; andesite, 540 feet; rhyolite, 60 feet; graphitic tuff with pyrite and pyrrho- tite, 30 feet; massive pyrite and pyrrhotite, 17 feet. (10)Lantagnac township; D.D.H. 10280; 1957; bearing, N.20°E.; inclined '45°; length, 658 feet; casing, 52 feet; ande- site, 200 feet; aplite, 12 feet; graphitic tuff with pyrite bands, 20 feet; graphitic tuff, 380 feet. (11)Lantagnac township; D.D.H. 13300; 1957; bearing, S.10°W.; inclined 50°; length, 312 feet; casing, 36 feet; ande- site, 125 feet; graphitic tuff, 151 feet. (12)Lantagnac township; D.D.H. 10249; 1957; bearing, N.10°E.; inclined 45°; length, 348 feet; casing, 25 feet; ande- site and graphitic tuff, 152 feet.; graphite with stringers of pyrite and pyrrhotite, 19 feet; graphitic tuff, 152 feet. .21 -

(1.3.). Julien .township; D.D.H. 13290;. 1957; bearing, S.45°W.; inclined 45e; length, .470 feet; casing, .29 .feet; graywackei 20 feet; rhyolite, 270 feet; chlorite and mica schist, 140 feet; massive pyrite and pyrrhotite, 1.5 feet. (14)Julien township; D.D.H. 13292; 1957; bearing, S.45°W.; inclined 450; length, 585 feet; casing, 22 feet; garnetiferous sedimentaries, 122 feet; sheared tuff, 441 feet; D.D.H. 13295; 1957; bearing, N.45°E.; inclined 50°; length, 397 feet; casing, 23 feet; rhyolite, 53 feet; tuff, 155 feet; tuff with pyrrhotite stringers, 76 feet; breccia with sulfides, 89 feet.

(15)Julien township; D.D.H. 13293; 1957; bearing, N.52°E. ~ inclined 45°;. length, 475 feet; casing, 79 feet; tuff, 370 feet; breccia, 8 feet; scattered pyrite and pyrrhotite. (16)Julien township; D.D.H. 14801; 1957; bearing, N.10°W. inclined 50°; length, 412 feet; casing, 101 feet; andesite, 150 feet; tuff breccia, 76 feet; tuff breccia with bands of pyrite and pyrrhotite, 14 feet; graphitic tuff, 70 feet. (17)Julien township; D.D.H. 13298; 1957; bearing, N.55°W. inclined 50°; length, 398 feet; casing, 14 feet; quartzite, 368 feet; carbonate, 12 feet; massive pyrrhotite, 4 feet. (18)Julien township; D.D.H. 13283; 1957; bearing, S.25°E. inclined 50e; length, 303 feet; water, 8 feet; casing, 43 feet; quartz with pyrite and pyrrhotite, 12 feet (between gabbro, 90 feet, and greenstone agglomerate, 140 feet). (19)Julien township; D.D.H. 13280, 13280 A, and 13280 B; casings, 89, 67, and 39 feet; abandoned. (20)Julien township; D.D.H. 13285; 1957; bearing, S.47°E.; inclined 50e; length, 335 feet; casing, 34 feet; tuff, 145 feet; graphitic tuff with pyrrhotite and pyrite, 54 feet; peridotite, 10 feet, with occasional chalcopyrite streaks through 5 feet; quartz diorite, 86 feet. (21)Guettard township; D.D.H. 10250; 1957; bearing, N.90°W. inclined 450; length, 370 feet; casing, 8 feet; andesite, 170 feet; graphite, 15 feet, with minor pyrite, pyrrhotite, and chalcopyrite; quartz breccia and carbonate, 5 feet, with minor pyrite, pyrrhotite, and chalcopyrite; tuff 170 feet. - 22

(22)La Touche township; D.D.H. 13296; 1957; bearing, west; inclined 50°; length, .404 feet.; casing, 23. feet; O.D. (?. olivine. diabase), 274 feet, minor pyrite and pyrrhot.it.e; graphitic zone, 5 feet; andesite, 102 f.eet., with siliceous zones and minor pyrite and pyrrhotite. (23)La Touche township; D.D.H. 13.297; 1957; bearing, north; inclined 50°; length, 500 feet; casing, 22 feet; graywacke, 322 feet; tuff, 48 feet; graphitic tuff with bands of pyrite and pyrrhotite, 108 feet. D.D.H. 13299; 1957; bearing, north; inclined 45°; length, 462 feet; casing, 30 feet; graywacke, 345 feet; tuff with pyrite and pyrrhotite, 44 feet; graphitic tuff, 26 feet; tuff, 17 feet.

The Mining Corporation of Canada Limited

(24)Julien township; D.D.H. JU-1-1; .1959; bearing, N.25°E.; inclined 510; length, 464 feet; casing, 29 feet; sili- ceous and chloritized andesite and tuff, garnetiferous, with minor pyrite and pyrrhotite and with three sections of 77, 3, and 17 feet with, respectively, 10-65%, 50%, and to 65% pyrite and pyrrhotite. Assay values for Au, Cu, and Ni were nil. (25)Julien township; D.D.H. JU-1-2; 1959; bearing, N.41°E.; inclined 51°; length, 400 feet; casing, 35 feet; andesite and tuff, chloritized and in part silicified and carbonitized, with scattered pyrite and pyrrhotite, 181 feet; andesite tuff, to 60% pyrite and pyrrhotite, 46 feet; graphitic tuff, minor sulfides, 11 feet; rhyolite, quartz eyes, 120 feet. Assay values for Au, Cu and Ni were nil.

McIntyre Porcupine Mines Limited

(26)Julien township; 1961; D.D.H. 158-S-1; bearing, north; inclined 45e; length, 252 feet.; casing,. 9 feet; andesite, minor quartz, calcite, pyrite, and pyrrhotite, minor chalco- pyrite; graphitic schist, 29 feet., with sulfides to 40%, and two sections of massive sulfides of 4 and 5 feet; quartz-sericite schist, 2 feet; chlorite schist, 51 feet, with pyrite and pyrrho- tite to 20%, minor chalcopyrite at one point; tuff, 28 feet, pyrite and pyrrhotite, scattered chalcopyrite; fine-grained diorite, 29 feet, at end of hole. - 23 -

D.D.H.. 158-S-2;. 990 feet west of the. above.;, bearing, north, inclined 45°, length', .296 feet; casing, 8 feet; ande.sit.e.- basalt, .249 feet:, with quartz and carbonate stringers, minor pyrite and pyrrhotite; brecciated basalt, 40 feet, with sulfides to 50%, including minor chalcopyrite, in a quartz-chlorite- sulfide matrix; felsite, dark gray to dark brown, in ten sections, 37 feet; quartz-talc, 7 feet, with sulfides, 50%; the hole ending in massive andesite or possibly fine-grained diorite. The core for these holds is stacked nearby.

Additional Indications of Mineralization

The following were noted during the traverses of this area. (27)a rusty-weathering outcrop, 10 by 30 feet, of mafic gneiss; bands of hornblende with 10% garnet.; amphibolite with 15% pyrite. An assay gave a trace of gold. (28)a small outcrop of black schist rich in narrow streaks of pyrite. (29)a small outcrop of black, silicified schist rich in narrow streaks of pyrite. (30)pyritiferous black schist with numerous pyrite spheres up to 4-inch diameter. (31)a few grains of chalcopyrite in chloritized and sili- cified metagabbroic rocks, associated with aplite. (32)a few grains of chalcopyrite and of molybdenite in sheared, siliceous, fine-grained, dark rocks cut by aplite; previously trenched. (33)a boulder of epidotized melasyenite carrying stringers of chalcopyrite apparently as fracture fillings. (34)a few grains of chalcopyrite in a carbonatized chlo- rite schist. (35)a few grains of chalcopyrite in white quartz stringers in a sheared, andesit.ic, hornblende porphyry. (36)massive pyrrhotite with disseminated, very fine-grained chalcopyrite in a trenched showing 5-10 feet wide in siliceous, dark, fine-grained rock. - 24 -

(37)drill core, on the drill site, with massive pyrite and pyrrhotite and black schist. The 500 feet of hole ended in 25 feet of dark, feldspar porphyry with coarse phenocrysts and some pyrite; apparently a dike. (38)float beside a trench in overburden. Several quartzose boulders one foot across with massive pyrrhotite and streaks of chalcopyrite. Two samples assayed traces of gold, copper, and nickel. (39)a small pond and lake the bottoms of which are covered by 4-inch of limonite. (40)a small stream draining muskeg with similar limonite deposits. (41)a few grains of chalcopyrite in pale, coarse-grained gabbro: (42)a few grains of chalcopyrite in a coarse-grained gabbro stringer, trenched and drilled; near a contact between a diabase dike and the Thomelet Lake ultramafic. (43)silicified, pyrite-bearing, sheared, fine-grained pre-Opémisca lava cut by white quartz veins and some brown carbonate stringers. Trenched and blasted. A sample assayed a trace of gold. (44)a few grains of chalcopyrite associated with a small stringer of bluish quartz in a fine-grained metagabbro. (45)a stream sediment sample with high values in molyb- denum, lead, and zinc. (46)a thin gossan over a band of massive, pyritiferous gray quartz, partly brecciated, with lesser amounts of siliceous black schist, this is apparently conformable with the Central Gneiss and is exposed over a width of 50 feet and a length of 100 to 200 feet.

Geochemistry

Stream sediment samples were taken when a stream was crossed in the course of'a traverse and the samples were sent to the.Department's Laboratory in Quebec to determine their tenor of copper, zinc, lead and molybdenum. These values are shown on the accompanying geological map. 25 -

BIBLIOGRAPHY

Bartley,.C.M. (.1946) Lac-La Trêve. Mining Area; compilation. MSS'. in files of .Quebec Dept.. Nat. Res.

Beach, H.H. (1941) Michwacho Lake, Abitibi Territory, Quebec; Geol. Surv. Canada, Map 623A.

Mechamego Lake., Abitibi Territory, Quebec; Geol. Surv. Canada, Map 608A.

Shaw, G. (1942) , Abitibi and Mistassini Territories, Quebec, Map 712A Geo. Surv. Canada.

Kindle, E.D. (1942) Brock River Map-area, Abitibi and Mistas- sini Territories, Quebec; Geol. Surv. Canada, Summ. Account, Paper 42-4.

Gilbert, J.E. (1955) Branssat-Daine. Area, Abitibi-East County,. Quebec; Quebec Dept. Mines, Geol. Rept. 64.

Gillett, L.B. (1957) Vienne Area, Abitibi Territory and Abi- tibi-East Electoral District; Quebec Dept. Mines, Prelim. Rept.. 337.

Low, A.P. (1906) Map 918, Chibougamau Region;-Geol. Surv. Canada.

Map 549G; Geophysics Paper 549; Lac .Dumas-, Abitibi Territory and Abitibi County, Geol. Surv. Canada (1957).