Preliminary Report, Geology of Saint-Michel-Des-Saints (West) Area, Joliette, Berthier and Maskinonge Counties

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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

Kees Schryver

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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

Kees Schryver

QUEBEC 1966 P.R. NO. 552

Preliminary Report

SAINT-MICHEL-DES-SAINTS (WEST) AREA

Joliette, Berthier and Maskinongé Counties.

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 sedimentary 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 interlayered 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 parallelism 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. - 4 -

TABLE OF FORMATIONS

e un

r ag

Most abundant ic Q in

be rock type(s) ive qi ig Era log t um n Or la ho it Re L

(Quartz-) monzonite, 6 ") (quartz-) monzonitic gneiss " ite ? " on s lex 5 Feldspar-quartz neous Monz granulite isse Comp l Ig ER

ne he

UNG 4 Mangeritic augen gneiss; ic hog t YO neous M Granitic augen gneiss AN "Or "Ig

( "St- s

3 d Leuconorite; Jotunite(?) an neou Ig

CAMBRI Quartzo-feldspathic

gneiss; Biotite- es E 2 pyroxene-amphibole iss mmon gneiss PR known isses Co ne g Un

ne Pyroxene-amphibolite g

ing es OLDER d

n Biotite-garnet gneiss; ro

iss Quartzite; Garnet-

1 sillimanite gneiss; w ne rrou Crystalline limestone; Su

rag b Calc-silicate rock a Pa 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 proportions 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 surfaces of the other rocks, in particular of those rich in sillimanite 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 interlayered 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: orthopyroxene, 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. These bodies consist of some of the minerals mentioned above, particularly diopsidic pyroxene. The color of the relatively pure limestones is white on both weathered and fresh surfaces. The weathered surfaces of less pure limestones, particularly those rich in scapolite, opaque minerals and graphite, are crumbly and rusty brown.

Foliation is poorly developed and is expressed by vague compositional layering; lineation is poorly developed or absent.

Unit 2.

Quartzo-feldspathic Gneiss; Biotite-pyroxene-amphibole Gneiss

The gneisses and amphibolites of Unit 2 are interlayered and grade into each other. The gneisses consist of some or, less commonly, all of the minerals feldspar, quartz, biotite, pyroxene, amphibole and iron(-titanium) oxide in widely varying proportions, but in that order of frequency of occurrence. An average mode cannot be given, as the compositions are extremely heterogeneous. By far the most common rock type is a fine- grained, whitish or light pinkish weathering feldspar-quartz- magnetite-biotite gneiss, with a color index of less than 5, 1% or 2% mafic being about average. The most abundant dark mineral in the mafic-rich gneisses (i.e., those with color index of 10-30) is biotite, but any of the other dark minerals can be dominant. Important in any consideration of metamorphic facies is the fact that orthopyroxene, amphibole, and/or biotite may coexist within an outcrop or even a hand specimen. The only general rule seems to be that orthopyroxene is never the dominant mafic mineral in rocks that contain more than a trace of quartz. Consequently the metamorphic facies throughout the area is the amphibole-granulite facies. - z -

The gneisses are characteristically in laminae 1-5 mm. thick. However, layering on a larger scale is common and all gradations up to layers 1 meter thick have been observed. Foliation and lineation are generally present and are expressed by preferred orientation of individual grains and small aggregates of grains.

Pyroxene-amphibolite

This rock is so named because pyroxene is commonly second in abundance amongst the mafic minerals. Pyroxene-amphibolites are closely interlayered with the other rocks of Unit 2 and, in many places, with the rocks of Unit 1. They are included in Unit 2 for no other reason than that their origin is unknown. Locally they form bodies of mappable size but their most common mode of occurrence is in boudinaged layers 1 cm. to 1 meter thick.

The amphibolites vary widely in mode and fabric, which probably indicates a diversity of genesis. The most common rock type has a color index of about 50, and the minerals are, in order of abundance, plagioclase, amphibole, pyroxene (ortho- and/or clinopyroxene). Biotite is commonly absent, magnetite is markedly less abundant than in any other rock type in the area, and garnet is rare.

Unit 3

Leuconorite and Jotunite(?)

The leuconorites consist of plagioclase, pyroxene, biotite, iron(-titanium) oxide and minor amphibole. The grain size ranges from 1 to 10 mm., the entire range commonly being present in a hand specimen. The rock is grayish green and weathers whitish to light buff or rusty brown. Feldspar is in gray to bluish gray laths and in finer anhedral green or, rarely, pinkish grains. (It is mainly on the basis of the lath-shape of the plagioclase that the leuconorites are thought to be of igneous origin.) Pyroxene, the dominant mafic mineral, makes up 5-30% of the rock. It occurs interstitially between and around the plagioclase laths and may partly enclose them. Biotite is commonly present up to amounts of 5% of the rock. - 8 -

Foliation is moderately developed in the leuconorites and is expressed by form-orientation of plagioclase laths and/or small aggregates of mafic minerals. Lineation is commonly absent, but in a few places where plagioclase laths are absent the mafic minerals are perfectly aligned in small, discontinuous rods.

The term "jotunite" is applied to a heterogeneous assemblage of rocks occurring mainly near the boundaries of leuconorite and mangeritic augen gneiss, although it is not certain that true jotunite is the dominant member of the assemblage. A common rock is fine-grained (1 to 2 mm.), equigranular, and saccharoidal, and has a color index of 20-40. It contains plagioclase, potassium feldspar, (quartz), pyroxene, magnetite, apatite, (amphibole, biotite). This rock carries a few feldspar megacrysts and, especially where the texture of the rock around the megacrysts is slightly sub-ophitic, it is intermediate between leuconorite and augen gneiss in habit as well as in general mineral content.

Like most of the other rocks of the Igneous Complex, the "jotunites" are not laminated and are moderately well foliated and lineated by preferred form-orientation of small aggregates of grains.

Unit 4

Mangeritic Augen Gneiss; Granitic Augen Gneiss

Mangeritic and granitic augen gneisses occur in the Igneous Complex only. They are very similar in fabric, the basis of the subdivision being the dominant type of feldspar and the proportions of quartz and mafic minerals. The contacts of Unit 4 are well defined, but those of the two gneisses within the unit are gradational and, as mapped, are rough approximations only.

Foliation and lineation are well defined in the gneisses by parallel aggregates of fine grains and by the alignment of feldspar metacrysts.

Mangeritic augen gneiss is well exposed in the southern part of the area along the gravel road from Saint- Zénon to Sarrazin lake, north of Juneau lake. It consists mainly of feldspar, quartz, pyroxene, amphibole, and iron (-titanium) oxide; garnet and biotite are rare. The weathered surface is 9 rough and fragments of feldspar megacrysts stand out. The color of the weathered surface is whitish to light buff; the fresh surface is grayish green. Feldspar (plagioclase and orthoclase in approxi- mately equal amounts) occurs in grains ranging in size from a fraction of a millimeter to 5 cm. The larger grains are subhedral crystals; the finer ones are, at least in part, products of granulation and recrystallization of larger crystals and they commonly form lens-shaped aggregates. Well preserved, subhedral, equant to ellipsoidal feldspar megacrysts make up 15-60% of the rock. Thin, white weathering, fine-grained rims and zones can be seen in some megacrysts on glacially polished outcrops. Quartz, in anhedral grains up to 3 mm. in diameter, makes up 5-15% of the rock. The other minerals have a grain size similar to that of quartz. Pyroxene (ortho- and clino-) or, less commonly, amphibole is the dominant mafic mineral (5-20% of the rock). Magnetite (3%) is invariably present. Pyroxene, amphibole, magnetite, and most of the quartz occur together in thin, discontinuous, well-oriented aggregates curving around the feldspar megacrysts. Granitic augen gneiss is best exposed on the shore of Croche lake, near the northern boundary of the Igneous Complex. This gneiss consists of feldspar, quartz, amphibole, biotite, iron(-titanium) oxide and pyroxene, commonly in that order of abundance. As its texture is similar to that of the mangeritic augen gneiss, only the differences with the latter will be mentioned: a) Potassium feldspar (microcline) strongly dominates over plagioclase; b) Quartz makes up 15-35% of the rock; c) The color index ranges from 2 to 8; d) Amphibole or, less commonly, biotite is the dominant mafic mineral.

Unit 5

Feldspar-quartz Granulite

Granulite is well exposed in the southern part of the area along the gravel road from Saint-Zénon to Sarrazin lake, - 10 - north of Sauvage lake. It is pinkish gray and weathers white. In hand specimen, this rock is practically indistinguishable from some of the quartzo-feldspathic gneisses of Unit 2. How- ever, the granulite occurs in homogeneous, mappable bodies, whereas the quartzo-feldspathic gneisses are laminated and are interlayered with other rocks.

The granulites consist of perthite, quartz (25- 35%), magnetite, biotite and amphibole. The color index ranges from 1 to 5, magnetite and minor biotite commonly being the only mafic minerals. As in typical granulites, the quartz occurs in elongate lenticles, giving the rock a very strong lineation. Foliation is poorly developed or is absent. Feldspar occurs in 2-5 mm., generally equant grains. Locally, the rock contains many small ultramafic clots, consisting of a rim of light brown mica and a center of black amphibole. They have the same ellipsoidal shape and orientation as the quartz lenticles.

Unit 6

Monzonitic Rocks

Monzonitic rocks occur in the Igneous Complex in the southeast corner of the area, and in three separate bodies in the northwest quarter. Gneissic lamination and lineation are commonly well developed in the latter bodies (the "St-Michel Monzonite"). In the Igneous Complex, lamination is poorly developed or absent, the texture is hypidiomorphic granular, and lineation is rare.

The monzonites are green (color index of 10-20) and weather white to light buff. They consist of feldspar, quartz, pyroxene, amphibole, magnetite and rare biotite, in grain sizes ranging from 2 to 5 mm. Amongst the feldspars either plagioclase or perthite dominates; they occur commonly in equant grains, but in some varieties plagioclase is lath-shaped. In some types of monzonite,feldspar megacrysts are present, but these are very rarely ellipsoidal in shape or well aligned, as they are in the augen gneisses. Quartz may be present in amounts up to 15%; in the monzonites of the Igneous Complex quartz is commonly absent. Amphibole or pyroxene or both are the dominant mafic minerals. STRUCTURAL GEOLOGY

During the field work the orientations of about 1,000 foliation planes and 300 lineation lines were measured. These fabric elements could not be related to any specific type or phase of folding, as minor folds are very rare in the area (in marked contrast with the Courcelles-Gautier and Houde-Masson areas: Schryver, 1963, 1966). Furthermore, it can be seen from the geological map, that the shapes of the geological contacts can hardly be interpreted as intersections of simple folded planes with the surface. In fact, key-horizons, suitable for tracing out larger structural features are absent in the major part of the area underlain by the rocks of Units 1 and 2. It is only in the Igneous Complex that well-defined contacts can be traced through significant curves, without giving undue weight to the orientations of foliation planes. However, which parts of which contacts are igneous and in their original position, which are igneous and in a "secondary" position, and which are simply tectonic contacts, are questions that must remain unan- swered. In any case, all the rocks in the area have been deformed together, at least once, as indicated by the parallelism of lineation lines throughout the area.

The most remarkable feature of the foliation planes is the parallelism between those measured within and those outside the Igneous Complex, in a zone of about 1 mile around the Complex. Furthermore, wherever a lithological contact could be drawn accurately, it was found that the foliation is parallel to the contact at least in strike, and probably also in dip. This rule seems to hold even for major curves in the contacts, and has been used to determine contacts where outcrops are not abundant.

ECONOMIC GEOLOGY

Les Mines de Silice Supérieure Ltée has (1965) two groups of claims in the area: one in Brassard and one in Provost township, with the main interest centering on the former.

The Brassard township claims are 4i miles north of Saint-Michel-des-Saints in Range I, lots 12-14 (C-183906, - 12 - claims 1, 2 and 3), and Range II, lots 13-16 (C-183913, claims 1 to 4) and lots 11-12 (C-199894, claims 1 and 2). The main showing is in Range I on lot-line 12-13, about 800 feet south of Range II. It consists of massive white to light pinkish quartz in a prism 180 feet long, averaging 70 feet wide (30 feet wide in the western part to 110 feet wide in the eastern part), and tapering to zero at an average depth of 56 feet (drilling evidence). It is flanked by zones up to 2 feet wide rich in coarse-grained orthoclase. It is in the center of a pegmatite body in quartz-monzonitic gneiss. The lens has been estimated (Maurice, 1965) to contain about 28,000 tons. Development work has included the building of an access road 3.8 miles long, stripping, and 12 diamond drill holes. A showing of less impor- tance occurs about 500 feet south on the same (12-13) lot-line on the west shore of des Pins bay in Taureau reservoir. Some stripping has been done here (Maurice 1965).

The Provost Township deposit is 9 miles southeast of Saint-Michel, or 2 miles east-northeast of Saint-Zénon. It is a band of quartz between garnetiferous quartzite and biotite gneiss. Some trenching and 15 diamond drill holes indicated a thickness of 15 feet of good-quality material, as well as a parallel zone also about 15 feet thick of lesser-quality, over a length of 1,650 feet.

Claims here include (1965):

Range XIII, lots 5 and 6(205831, claims 1 and 2) lots 7 and 8(204090, claims 3 and 4) Range XIV, lot 1(219293, claim 1) Range XV, lot 1(219293, claim 2)

Ilmenite

An ilmenite-magnetite showing about 3 miles south of Saint-Zénon, in lot 17 of Range A, Provost township, was examined by Hogg in 1956. The showing consisted of "diorite" with bands and rich disseminations of ilmenite-magnetite. A magnetometer survey of the surroundings suggested the presence of "small disconnected mineralized zones".

Feldspar

A pegmatite vein near the ilmenite showing de- scribed above, and close to the lot 17-18 line of Range A, - 13 -

Provost township, was examined by Maurice in 1952. This vein is in biotite schist and probably parallel to the schistosity, which has an easterly strike and nearly vertical dip. The vein is 30 feet wide but of undetermined length. The amount of quartz mixed with the feldspar would demand some method of concentra- tion of the feldspar to make it economic.

REFERENCES

Hogg, W.A. (1956) Magnetite-Ilmenite Deposit on Lot 17, Range A, Provost Township. MSS. in Files of Quebec Dept. of Nat. Resources. Maurice, O.D. (1952) Gisement de Feldspath de Saint-Zénon; MSS. in Files of Quebec Dept. of Nat. Resources.

Maurice, O.D. (1965) Les Mines de Silice Supérieure Ltée; MSS. in Files of Quebec Dept. of Nat. Resources.

Schryver, K. (1963) Courcelles-Gautier Area; Preliminary Report, MSS. in Files of Quebec Dept. of Nat. Resources. Schryver, K. (1966) Geology of Houde-Masson Area, Berthier and Maskinongé Counties (Preliminary Report); Quebec Dept. of Nat. Resources, P.R. No. 531.