Preliminary Report on Tadoussac Map-Area, Charlevoix, Chicoutimi and Saguenay Counties Province of Quebec, Canada
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RP 266(A) PRELIMINARY REPORT ON TADOUSSAC MAP-AREA, CHARLEVOIX, CHICOUTIMI AND SAGUENAY COUNTIES PROVINCE OF QUEBEC, CANADA DEPARTMENT OF MINES GEOLOGICAL SURVEYS BRANCH PRELIMINARY REPORT ON TADOUSSAC MAP-AREA CHARLEVOIX, CHICOUTIMI AND SAGUENAY COUNTIES BY M. L. MILLER QUEBEC 1952 P. R. No. 266 PRELIMINARY REPORT ON TADOUSSAC MAP-AREA CHARLEVOIX, CHICOUTIMI, AND SAGUENAY COUNTIES by M.L. Miller I N T R O D U C T I'O N Location and Access The Tadoussac map-area is on the north shore of St. Lawrence river about 120 miles northeast of the city of Quebec. The area, which was examined in 1951, is largely in the fifteen-minute quadrangle bounded by latitudes 48°00' and 48°15', and by longitudes 69°45' and 70°00'. About three-quarters of the area lies southwest of Saguenay river, and the remainder, northeast of it. Access to the area is provided by Provincial highway 15 from Quebec city, which follows St. Lawrence river more or less closely, and highway 16, a few miles west of the western boundary, which links St. Simeon and Chicoutimi. Highway 15 is interrupted at Saguenay river, but a car ferry crosses between Baie Ste. Catherine and Tadoussac several times a day. Tadoussac is a port of call for summer cruise ships of the Canada Steamship Lines and during the summer months is also served by a.car ferry from Riviére du Loup on the south shore of St. Lawrence river. Several secondary roads and bush roads suitable for auto- mobile travel extend into the area from the 'two Provincial highways; of these, the most useful are from highway 16 to lake dos Côtes,.Baribeau lake, and David lake, and from highway 15 to Buteux lake, Chicane lake and lake du Basque. A network of roads along the alluvial valleys in the vicinity of Sacré Coeur pro- vides ready access to most parts of the area northeast of Saguenay river. In addition to these roads, numerous bush trails are useful once their location has been determined..... ;The most useful of these trails; now somewhat overgrown, follows an old telephone line from the road end at lake des Côtes to the bush road north of Malbaie lake. Examination of the map suggests that Saguenay river itself should be useful for travel within the area, but precipitous cliffs, which.flank the river in most places, make but little of the area accessible from it.. The only waterway providing reasonably easy travel within the area is the chain of eight lakes, from lake Lyonne to lake Druillettes. A good, short portage connects lake Buteux and lake Druillettes; Fleury, Honorat, Caron, and Buteux lakes, differ in elevation by only a. few feet, and are connected by short rapids down which empty canoes can be lined. A. portage.betWeen Jamay lake and Fleury lake apparently is seldom used and is rather obscure.. Portages between lakes Lyonne, Guay, and Jamay were not seen, but may well exist. '.1-2887 2 The most satisfactory supply centres in, or close to, the area include Sacré Coeur and Tadoussac northeast of Saguenay river. Southwest of that river they include Baie Ste. Catherine, St. Siméon, and Petit Saguenay. General Description of the Area Precipitous slopes bordering most of St. Lawrence and Saguenay rivers bound the upland portions of the area, which is a part of the Laurentian up- lands. Although the upland in general. is. classed as a pene.plain, local relief in this map-area is moderate to high, averaging about 400 feet. Relief is lower in sections underlain by granite, except in areas close to Saguenay river. A ridge-and-valley topography is prominent in areas underlain by a complex of Grenville rocks and granite. Because dips are high in most places, hogback ridges are the most prominent landscape feature, but low cuesta-like ridges oc- cur in the few places where. dips are low, notably in the area underlain by gran- ite gneiss between lakes Honorat and Buteux. Previous Geological Work Faessler (1) examined parts of this and adjoining areas along the St. Lawrence during reconnaissance surveys in 1928 and 1929. .Greig (2) mapped the Bergeronnes-Pontgravé area, northeast of the present area, in 1941. In 1943, Ross (3) examined parts of Callières, Chauveau, Dumas, Sagard, and Saguenay townships. Miller (4) mapped the,St. Siméon area, immediately south of the pres-- ent sheet, during the summer of 1950. p é and the (1) FAESSLER, Carl, Notes on the Geological Traverses between Beau 4 FIL 1 Saguenay River, in the Counties of Montmorency and Ghar~`ovoic; Que. Bur. Mines, Rept. Min. Oper. in the Prov. of Que. during the year 1928 (1929). Geological Exploration on the North Shore, Tadoussac to Escou- mains; Que. Bur. Mines, Ann. Rept. for 1929, Pt. D (1930). (2).. GREIG, E.W., Preliminary Report on Bergeronnes-Pontgravé Map-area, Charle- voix-Saguenay County; Que. Bur. Mines, P.R. No. 166 (1942); Final map, No. 629 (1947). (3) ROSS, S.H., Preliminary Report on the Geology of the Sagard-Callières Re- gion, Charlevoix, Chicoutimi and Saguenay Counties; Que. Dept. Mines, P.R. No. 244 (1950) (4) MILLER, M.L., Preliminary Report on St. Siméon Map-Area; Que. Dept. Mines, P.R. No. 252 (1951) -3 - GENERAL GEOLOGY General Statement The consolidated rocks of the map-area are igneous and metamorphic rocks of Precambrian age. About one-tenth of the area is underlain by Grenville- type metamorphic rocks, such as hornblende and mica schists and gneisses, and quartzites. The remaining rocks are chiefly granitic and occur as long, rela- tively thin layers with Grenville rocks, or as more or less separated masses. In general, the larger granitic masses are gneissic, especially close to their margins, although the central parts are commonly devoid of readily-apparent gneissosity. Pegmatite dykes are common throughout the map-area and appear to be genetically related to the granites. One large mass of highly quartzose rock termed "silexite" is of undetermined origin. The more extensive and continuous areas of Quaternary sediments occur inland in valleys or on low ground near St. Lawrence and Saguenay rivers. Table of Formations Pleistocene 'and recent gravel, sand, Quaternary CENOZOIC and clay Silexite Pegmatite Intrusive rocks ' Pink leucocratic granite Biotite granite, gneissoid biotite granite, biotite granite gneiss PRECAMBRIAN Hornblende schists and gneisses (in- cluding partly granitized equivalents) Grenville series Mica schists and gnoisses, quartzites (including partly granitized equiva- lents) Grenville Series The Grenville rocks of the area may be assigned to one or other of two units shown on the accompanying map. The mica schists and gnoisses, and quartzites, are derived from sedimentary rocks. Most of the hornblende schists and gneisses probably were also once sedimentary rocks, but some of them may haire formed in part by metamorphism of basic intrusive rocks. - a - Mica Schists and Gneisses, Quartzites (including partly granitized equivalents) These metasedimentary rocks are found mainly as three irregular masses in the southern half of the area. Two of these form parts of a crescent-shaped band, about half a mile wide, in the southwestern corner of the map-area. At the northeastern end of this band, hornblende gneisses and mica gneisses inter- f;inger, but within the band there is no interlayering of these two rock types on a mappable scale. The third metasedimèntary mass, a roughly triangular-shaped area in the vicinity of Lyonne and Malbaie lakes, is about four miles long. It terminates on the west against the mass of hornblende gneiss mentioned above, and on the east separates into two thinning and diverging "fingers" trending northeastward and southeastward, respectively, with granite gneiss between them. The micaceous metasedimentary rocks consist chiefly of rusty-weather- ingr highly-contorted, biotite-muscovite schists and gneisses shot through with irregular white pegmatites. Some layers have distinct oval to lenticular white "eyes", up to one inch long, which appear to be aggregates of sillimanite or muscovite, or both. Garnet is rare. Granitization (i.e., the process by which rock is made more like granite by recrystallization and by introduction of min- erals such as quartz and feldspar) in some places has altered the rock to such an extent that it has come to resemble closely biotite granite gneiss,.from which it is distinguishable only with.difficulty. Micaceous metasedimentary rocks are found mostly in the band mapped near the western boundary of the map- area. The Lyonne lake-Malbaie lake metasedimentary mass consists principal- ly of quartzite, which in most places is so highly granitized as to resemble a fine-grained, quartz-feldspar pegmatite. Mica gneiss occurs toward the western extremity of the mass. The quartzite is a dense-looking, white or light grey weathering rock, usually with a smoothly glaciated surface. Layering is absent or obscure, but locally the quartzites, particularly in the darker units con- taining some biotite, have a laminar parting which may be relict bedding. Feld- spathization is common and is shown by anhedral pink to flesh-coloured feldspar in short branching streaks. Dykes and irregular masses of pegmatite are common in the gneissic rocks such as the mica and hornblende gneisses, but they are rarely seen in the quartzites. The massiveness and competence of the quartzites was not favour- able for the formation of larger bodies of pegmatite. Hornblende Schists and Gneisses (including partly granitized equivalents) Rocks with hornblende (or hornblende and biotite) in excess of 25 per cent and exposures with more than 25 per cent hornblende schist or gneiss have been included with the hornblende schist and gneiss unit on the accompanying map. Thus, many of the units shown on the map as hornblende schist and gneiss are actually largely granitic.