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RP 552(A) PRELIMINARY REPORT, GEOLOGY OF SAINT-MICHEL-DES-SAINTS (WEST) AREA, JOLIETTE, BERTHIER AND MASKINONGE COUNTIES P.R. NO. 552 DEPARTMENT OF NATURAL RESOURCES Honorable GASTON BINETTE PAUL-EMILE AUGER Minister Deputy Minister Geology of SAINT-MICHELDES•$AINTS (WEST) AREA JOLIETTE, BERTH! ER AND MASKINONGÉ COUNTIES PRELIMINARY REPORT by Kees Schryver 76° 79° 72' 70° 6(1' ,P 1. v -~ lyo ~ I t `~ t ' '`. v I ~.`„ Dnbea y f4' L.duOale rv ~ .Foreiri '*, . 4.- Pam , . 51-Féliia.i. ^L ~ ~ ~ ~~\ ~ rn ._._Chaioi \. ►r y\ RobervalwlJa R Rinouâi . 3EAY01 ,Atvida GOUN , : . &rôrilk• ~- - Tsarina < ` U. E> B,- E ï ~ +a°- . piQ_ _ y ~\ —r : I - s - . t ~ 4iriire-do-Loup I — t âi ~ /// i \ L. N n„u~~. ' -@JV MJiere ~ t 1\ ` /;„,;o1, I. Kemp, t i La Tirol / L ~~ ~ ,~ iÎ .@ { . W - J , ~ ~r ~ , / µo.. P ? ( ( , Monk _ i, R -Pierre I / • 4 ' ~ 1 ., ~M1{„_ ,.: ~ . ~~ / . / L. lindn R ~, fleY k. ~ //~ l Lac Frontière ,r~- ~1 V f \ 18 1 I ' / Grena" Mire ~ . ~~ , n. ~ 11MAIN" T Mire ( `~ . 2/ ll. S.:\ 46°a --_ TMt.rd nee ih' >✓ . ` Joliette, e1 \'atr . ~ . ,. _ t l .... , 1 ~ ~ ~ Dru~drRN Mesae6eRe; / Ladruls • ~ /. / ~ f~ R` ; Lae 'gigantic -~A . Al,,,, ~~ \ 11i ONTARIO ~ il„yhfnnpe _1 ` 7 d‘<_~ `41} ~„eaN. ..J 76° 74° 72' QUEBEC 1966 P.R. NO. 552 P.R. NO. 552 QUEBEC DEPARTMENT OF NATURAL RESOURCES Honorable GASTON BINETTE PAUL-EMILE AUGER Minister Deputy Minister GEOLOGICAL EXPLORATION SERVICE ROBERT BERGERON, Director Geology of SAINT-MICHEL-DES-SAINTS (WEST) AREA JOLIETTE, BERTHIER AND MASKINONGÉ COUNTIES PRELIMINARY REPORT by Kees Schryver QUEBEC 1966 P.R. NO. 552 Preliminary Report on SAINT-MICHEL-DES-SAINTS (WEST) AREA Joliette, Berthier and Maskinongé Counties. by Kees Schryver INTRODUCTION The Saint-Michel-des-Saints (West) area was mapped geologically during the summer of 1965. It corresponds to the National Topographic Series map (31-1/12-West), and comprises about 210 square miles bounded by latitudes 46°30' and 46°45', and by longitudes 73°45' and 74°00'. It includes parts of Gamelin and Gouin townships in Joliette county, parts of Brassard, Courcelles and Provost townships in Berthier county, and a part of Masson township in Maskinongé county. The center of the area is about 80 miles north- northwest of Montreal. Highway 43 crosses the area from the southeastern corner to Saint-Michel-des-Saints in the north- eastern quarter. Other villages in the area are Saint-Zénon and Saint-Ignace-du-Lac. Saint-Zénon is on Highway 43; Saint-Ignace- du-Lac can be reached from Saint-Michel-des-Saints by gravel road. Numerous gravel roads branching from Highway 43 make most of the area readily accessible. The area is part of the Laurentian Uplands and is marked by gentle hills and a local relief rarely exceeding 500 feet. The highest point is 5 miles west of Saint-Zénon and is 2,450 feet above sealevel. The lowest part of the area is the - 2 - depression of Taureau reservoir and Kaiagamac lake, a little less than 1,200 feet above sealevel. Drainage of the area is mainly northward to Matawin river and the Taureau reservoir, and eventually east- ward from the reservoir by way of Matawin river to the Saint- Maurice. Many streams and lakes lie in linear depressions of marked preferred orientations. They are parallel to the trend of lithological units where underlain by norite, augen gneiss and feldspar-quartz granulite. Elsewhere the general southeast- northwest orientation dominates, as noted in the areas to the east and to the southeast (Schryver 1963, 1966). The major part of the area is heavily wooded — cultivated land being confined to some of the broader valleys. Small outcrops are abundant in most of the hilly country; outcrops larger than 2,500 square feet are rare. GENERAL GEOLOGY The area forms part of the Grenville province of the Canadian Shield, and all the consolidated rocks are Pre- cambrian in age. The rocks can be classified as of sedimentary, of unknown, and of igneous origin. Unit 1 consists mainly of biotite-garnet gneisses, which are commonly interlayered with rocks of undoubted sedi- mentary origin such as quartzites, garnet-sillimanite gneisses, crystalline limestones and talc-silicate rocks. Contacts are gradational or sharp across the strike and gradational along the strike. Only the crystalline limestones and talc-silicate rocks form bodies that are large enough to be shown separately on map No. 1611. Unit 2 consists mainly of feldspar-quartz gneisses, which are commonly interlayered with darker rocks on all scales from laminae a few millimeters thick to layers 1 meter thick. Only a few mafic-rich bodies ("pyroxene-amphibolites") could be mapped separately. The distinction between the "paragneisses" (Unit 1) and the "common gneisses" (Unit 2) is equivocal in many places. Rock types assigned to one or the other category may be inter- layered within the same outcrop. In such cases the dominant - 3 rock type determined the unit to which the outcrop was assigned. Other ambiguous features are the occurrence of biotite-rich gneisses without garnet, and quartzo-feldspathic gneisses with garnet. In such cases, the associated rocks determined the assignment of outcrops to Unit 1 or Unit 2. Consequently, virtually all geological boundaries between these units are rough approximations. Most of the boundaries are probably gradational. A complex of presumably igneous, but strongly deformed and at least partly recrystallized, rocks was outlined in the southern part of the area (the "orthogneisses" of Units 3 to 6). In marked contrast to Units 1 and 2, each of these units consists of virtually one rock type only, and each of the rock types forms bodies sufficiently large to be mapped separately. Also, the contacts of the Igneous Complex with the surrounding gneisses are definite in many places, and most of the contacts between the various units within the Igneous Complex are also definite, although relatively thin transition zones are common. No small offshoots of orthogneisses into the surrounding gneisses were seen, but inclusions of paragneisses and common gneisses are abundant locally in the Igneous Complex, and some of the larger ones are shown on the accompanying map. Thus, apparently the paragneisses and common gneisses are older than, and are intruded by, the Igneous Complex. The possibility that the inclusions are relicts of a sedimentary cover co-folded with a basement of igneous origin seems remote because the boundary of the Complex with the surrounding gneisses conforms with the trend of the units within the Complex. Also, the paral- lelism of lineations in the inclusions, the Igneous Complex, and the surrounding gneisses indicates that all these rocks were deformed together. The foliation in the Igneous Complex and that in the surrounding gneisses is also remarkably parallel. The mineral species and associations and the fabric of most rock types indicate regional metamorphism of the amphibole-granulite facies. PR E CAMBRI AN Era OLDER YOUNGER Relative age 2 4 3 5 6 L 1 ithologic unit number Surrounding gne isses "Orthogneisses" TABLE OFFORMATIONS ("Ig qi neous Complex" Q Common and"St- MichelMonz onite") Paragneisses gneisses - 4 b a w ro Unknown Igneous Igneous? Origin (Quartz-) monzonite, Pyroxene-amphibolite Calc-silicate rock Crystalline limestone; Quartzite; Garnet- Quartzo-feldspathic Granitic augengneiss Leuconorite; Jotunite(?) Biotite-garnet gneiss; Mangeritic augengneiss; Feldspar-quartz Most abundant (quartz-) monzonitic sillimanite gneiss; gneiss gneiss; pyroxene-amphibole granulite rock type(s) gneiss Biotite- DESCRIPTION OF ROCK TYPES Unit 1. Biotite-garnet Gneiss, Quartzite, Carnet-sillimanite Gneiss These rocks are well exposed in the southwestern corner of the area along the gravel road from Sarrazin lake to Bois-Franc lake, in the southeastern part of the area along the gravel road from Saint-Zénon: northeastward, and in the northern part of the area north of Saint-Michel along the shore of Taureau reservoir. The gneisses consist of some or all of the minerals feldspar, quartz, biotite, garnet, sillimanite, graphite, iron (-titanium) oxide, pyrite and rutile in widely varying propor- tions but commonly in that order of abundance. Cordierite has been identified in some biotite-rich gneisses south of Saint- Zgnon. An average mode cannot be given, as the gneisses are extremely heterogeneous in mineralogical composition; it can only be said that rocks consisting of feldspar, quartz, biotite and garnet are by far the most abundant. The relatively pure quartzites are light gray or white on both weathered and fresh surfaces. The weathered sur- faces of the other rocks, in particular of those rich in silli- manite or graphite or both, are rusty brown to bluish black. Fresh surfaces are rarely seen, owing to the deep weathering, but where seen they are mostly gray or green. Foliation and lineation are well developed. Folia- tion is expressed by compositional layering and by orientation of most minerals. Lineation is formed mainly by preferred orientation of the long axes of quartz lenticles and sillimanite c-axes. Crystalline Limestone, Calc-silicate Rock These rocks are well exposed north of Saint-Michel along the shore of Taureau reservoir. They are closely inter- layered with the other rocks of Unit 1 but locally form bodies of mappable size. The essential minerals are one or more of calcite, scapolite and diopsidic pyroxene. The accessory minerals are, in order of abundance, sphene, an opaque mineral (unidentified), plagioclase (generally in the absence of scapolite), quartz, dark brown to colorless mica, pyrrhotite, amphibole, reddish garnet, forsterite (in the absence of quartz), and graphite. Each of the following minerals was identified only once: ortho- pyroxene, chondrodite, serpentine, wollastonite, epidote and grossularite. The essential minerals give the rock its medium- grained, equigranular texture. The accessory minerals are markedly smaller and commonly perfectly idioblastic. In some places, angular and rounded bodies up to 6 feet long and 2 feet across are surrounded by a matrix of crystalline limestone.

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