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 80° 78° 76° 74° 72° 52° F.arrmnbi — 52' BAIE JAMES de I l Bale de fl°1.1 Rupert House Hannah R.de Rapert ~Lae Mutasd~ ( y _____ iI u• \ ` ykyr_ i1 / bEvans'~ i ^ ``, ~ f t~L. A(baneÿ t r I I ~~ ~Qii / X. BroaJback , i I ô ~ J/® / ti I ~ ~ ~ ‘.....--"1, j~} ~ %` .An;n;ca ^ (r / 16 v ' a I Q U É• ; 50° L L.Raronirhi _.50' ;ua , ~ ' ~ 7 1,1, Pa, l Grasser ~^1~. i L. ~ L. au Goéland ~ « .. , ~.. ~5',,_ f.h;GuJpamaa I„ I Mampmi t ` ~ ! ; L. ara abn I L. Wasunaipi~ ~~ Z i 'Pa .~ "L. Sieu6~Fnther I ~ O I jI tiL. (h1Erillon ( I °D«I6n I~~~~ Mamie I Beatty villa ré • r^'"?'~ St-FéBcieri ÿ' }' L. Abitibi ; L. Parent h jn' lupaLl uee anrds MberrJ 1IYaranda 1 etui Z. L..Na(arric Rk_tiFRVUiR~ ' , (.Ul'IV ~ Vald'or I L. cufpuea 0~ 25 50 i . i ~~ .y ° ~~ Milles M~.<s ~ .- ~ I 80° 78° 76° 74° 72° 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 Chibougamau 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. Chibougamau river 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 Omo river. 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 .