Preliminary Report on Vienne Area, Abitibi Territory and Abitibi-East Electoral District P

RP 337(A) Preliminary report on Vienne area, Abitibi territory and Abitibi-East electoral district P. R. NO. 337 PROVINCE OF QUEBEC. CANADA DEPARTMENT OF MINES HON. W. M. COTTINGHAM. MINISTER A.-O. DUFRESNE. DEPUTY MINISTER GEOLOGICAL SURVEYS BRANCH I. W. JONES, CHIEF PRELIMINARY REPORT ON VIENNE AREA ABITIBI TERRITORY AND ABITIBI-EAST ELECTORAL DISTRICT BY L. B. GILLETT QUEBEC 1957 P. R. NO. 337 M-D-4294 PRELIMINARY REPORT ON VIENNE AREA by L. B. Gillett INTRODUCTION The Vienne area comprises about 245 square miles, bounded by lati- tudes 50000' and 50°15' and longitudes 74°30' and 74049.4'. It includes most of Vienne township and parts of Rageot, Chérisy and La Rochette townships in Abitibi Territory, and parts of Barlow, and Cuvier townships in Abitibi-East electoral district. The southeastern corner of the map-area is 7 miles north- west of Chibougamau. The most practical means of access is by air from Caché lake, a hydroplane base on the Chibougamau - St. Félicien highway, 6 miles from Chi- bougamau, to any one of several lakes or to parts of Brock river. The Vienne area may also be reached by canoe along Chibougamau river, from Gwillim lake to Chevrillon lake, or along Opémisca river from Lake Opémisca. Travel within the area is facilitated by such water routes as Lac du Sauvage, Crinkle creek, Brock and Opémisca rivers, and by cut lines. The area is essentially level except in the northern part, north of Brock river, where low hills prevail. The average elevation is about 1,250 feet above the sea. Glacial drift, muskeg and lake deposits mantle most of the area. Hence, outcrops are generally scarce except north of Brock river, near Crinkle creek, and along the shores of Lake du Sauvage. No outcrops were found in some 15 square miles in the southwestern corner of the area. Brock river and its tributaries, North Brock river and Crinkle creek, drain most of the northern and western parts of the area. Opémisca river drains the southwestern corner toward the southwest into Lake Opémisca. The eastern third of the area drains into du Sauvage and Chevrillon lakes and Blaiklock river. All drainage eventually reaches Chibougamau river and flows to James Bay via the Chibougamau-Nottaway river system. Previous Work The area adjoining the Vienne area to the south was geologically mapped by Norman in 1936, 1937, and 1938, and that to the east by Sabourin in 1955. Sabourin also examined about 45 square miles along the eastern side of the Vienne area. The information he obtained is used in the present report. In 1941, Kindle explored a large region including the Vienne area; his pub- lished map is at a scale of 1 inch to 4 miles. 2 GENERAL GEOLOGY A11 the consolidated rocks of the area are Precambrian in age. Vol- canic rocks (Pre-Opémisca) and rocks of sedimentary origin with some intercalated lavas (Opémisca) trend east-west. Bedding planes and flow surfaces are vertical or nearly so. The metamorphic grade, in general, increases toward the north. Quartzo-feldspathic orthogneiss and paragneiss underlie the northern quarter of the area. The paragneiss is conformable with Opémisca schists to the south and may belong to the Opémisca series. The orthogneiss is thought to be Post-Opémisca. A large mass of gabbro-diorite with minor associated hornblendite and granodiorite intrudes the Opémisca rocks south of Lake du Sauvage. A much smaller gabbro-diorite body occurs 9 miles to the north, also in Opémisca rocks. Stocks of porphyritic granite, syenite porphyry, and a syenite-diorite complex intrude the Opémisca rocks. The acidic intrusive rocks all are less altered than the gabbroic rocks. Diabase dykes, and a feldspar porphyry dyke similar in composition to the diabase, are probably the youngest rocks in the area. The feldspar porphyry intrudes the porphyritic granite. TABLE OF FORMATIONS PLEISTOCENE Sand and boulder ridges, AND RECENT till, silt, and clay Feldspar porphyry, diabase, porphyroblastic diabase Forphyritic granite, monor equigranular granite and granodiorite Syenite porphyry Post-Opémisca Syenite-diorite complex Gabbro with dioritic, hornblendic, and granodioritic facies PRECAMBRIAN Orthogneiss and paragneiss, minor pegmatite Greywacke, boulder and pebble conglomerate, slate, tuff, hornblende schist, Opémisca Series porphyritic andesite; iron formation, chert, arkose, quartzite, and amphibolite Andesite with some rhyolite Pre-Opémisca and tuff PRECAMBRIAN Pre-Opémi sca Keewatin-type lavas occur in southern Vienne and in northern Cuvier and Barlow townships. The rock is light grey-weathering, dark green and aphanitic. Although chloritized and epidotized, it was probably an andesite orig- inally. Fillows, averaging one foot long and eight inches high, are best pre- served in Cuvier township, where they indicate that the tops of the flows are toward the north. Lenses of similar, but more highly deformed, andesite occur in the northern part of the area, a mile or so south of the gneisses. This andesite has a platy cleavage, and the pillows, facing south, interfinger lat- erally due to intense deformation. Some of the coarser-grained andesite shows that the rock is composed of 50 per cent mafic minerals and 50 per cent pla- gioclase. West of Chevrillon lake and south of the gabbroic mass, pale green or pale grey, white-weathering rhyolite predominates. Small, rounded, quartz grains are scattered in the hard siliceous groundmass. Some intercalated thin- bedded rock of similar appearance is probably tuff. Opémisca Series The Opémisca series underlies half the map-area, and includes a large number of rock types. Sedimentary rocks predominate; volcanics are rel- atively scarce. The metamorphic grade tends to rise toward the north, where secondary amphibole may be introduced and where the schistosity is generally more pronounced. ThP most common rock of the Opémisca series is a fine-grained, dark grey greyvacke. The rock usually is in thin beds, although bedding is inconspicuous on many exposures. Amphibole needles, randomly oriented in the plane of schistosity, are best developed in the more schistose greywacke. Boulder conglomerate is also very common. The boulders,in a greywacke matrix, are chiefly granite, with some diorite, hornblendite, greywacke, and lava. They are well-rounded and are elongated parallel to the schistosity. Most are about eight inches long and four inches thick, although boulders up to two feet across are common. The conglomerate is interbedded with greywacke here and there. The best exposures of the conglomerate are on the shores of du Sau- vage lake and near Crinkle creek. At Crinkle creek, both pebble and boulder conglomerate are abundant. Four conglomerate bands, varying in width from 1,000 to 2,000 feet, were seen at du Sauvage lake. Two of these bands merge to form one band about a mile wide. At Crinkle creek, the northernmost of four glomerate bands is about one mile wide. It is probable that some of the conglomerate has been repeated by folding. Black slate, tuff, and minor arkose, quartzite, and chert occur as isolated beds in greywacke and hornblende schist. The slate is characterized by disseminated pyrite, and contorted grey quartz veins are common. The rock believed to be tuff is pale green, fine-grained, thinly bedded, and siliceous. - 4 - A 65-foot band of pale green and grey banded chert is exposed immediately south of a diabase dyke, one mile northeast of Lake Claire. Tuff and chert are exposed on the eastern shore of du Sauvage lake, two miles from the southern end. Arkose and quartzite occur as isolated lenses near the gneiss-schist contact. Iron formation about 300 feet thick is exposed in the southern half of Rageot township. It is characterized by a high magnetite content in some lay- ers, and by lesser amounts of disseminated pyrite and siderite in others. Beds of blue, siliceous slate two inches to two feet thick regularly alternate with arkosic or quartzitic beds two or three times as thick. The blue slate, rich in finely disseminated magnetite, contains 32.3 per cent Fe and 48.5 per cent Si02. Porphyritic andesite is exposed in a few places in Rageot township. The aphanitic, dark green matrix encloses stubby, euhedral, grey, feldspar pheno- crysts, averaging 1/3-inch in length, and oriented by primary flowage. Lenses of pillowed andesite similar to the Pre-Opémisca andesite occur about one mile south of the gneisses; these may belong to the Opémisca series. Lenses of Hornblende schist and amphibolite occur more commonly within l miles of the schist-gneiss contact. Generally, the hornblende needles lie in the plane of schistosity, but in some exposures the hornblende crystals are not oriented and the rock resembles a diorite. Grain size and the feldspar and quartz content of the schists are quite variable, and depend on the composition of the original rock. Post-Opémisca Orthogneiss and Paragneiss Quartzo-feldspathic hornblende or biotite gneisses of sedimentary or igneous origin underlie the northern quarter of the area. The rock in the eastern part of Chérisy township is mainly banded, hornblendic, granitic gneiss (orthogneiss). Farther west, the rock is a finer-grained, grey, biotite gneiss of granitic composition and probably of igneous origin. In La Rochette township most of the rock is believed to be paragneiss. Here a gneissic arkose, containing up to 50 per cent leafy quartz extends 21/2 miles north of the schist-gneiss contact. This rock could be mistaken for gneissic granite. One mile west of the map-area, at the schist-gneiss contact, coarse-grained gneissic arkose is interbedded with fine-grained hornblende schist. Thus, the change northward frcm schist to paragneiss seems to be due to original composition rather than to change in metamorphic grade. A few dykes of pink biotite granite or pegmatite cut the gneisses.

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