DP 480 ERIC LAKE AREA (SAGUENAY COUNTY) - FINAL REPORT EXPLORATION GEOLOGIQUE
NJ INISTERE DES RICHESSES NATURELLES
DIRECTION GENERALE DES MINES
1
ERIC LAKE AREA
SAGUENAY COUNTY
D.S. McPhee
Final report
1977 DP-480 MINISTERE DES RICHESSES NATURELLES EXPLORATION GEOLOGIQUE
ERIC LAKE AREA
SAGUENAY COUNTY
Final report
by
D.S. McPhee
1957
Versé au fichier en avril 1977 DP-480 TABLE OF CONTENTS
Introduction
Location
Access
Previous Work Field Work 2
Acknowledgements
General Description of Area
Topography
Glacial Geology 5
Drainage 6
Climatology 7
n General Geology
General Statement Table of Formations 10
Metamorphosed Sedimentary Rocks 11
Seneral Statement
Quartz -biotite -bligoclase gneiss Quartz-feldspar-hornblende-biotite gneiss 13 Garnet-biotite gneiss 13 Muscovite-biotite gneiss 14 Siliimanite gneiss 14 Amphibolite 15 - IV - Table of Contents (Continued)
Early Intrusive and/or Metasomatic Rocks 16
General Statement 16
Granite gneiss 17
Gaeissic granite 18
Igneous Rocks 19
General Statement 19
Gabbro 19
Olivine gabbro 20
Hornblende gabbro 20
Hyperathene gabbro 20
Normal gabbro 21
Diorite 22
Granite 22
Pegmatite 23
Structural Geology 23
Economic Geology 24
Bibliography 26 LIST OF ILLUSTRATIONS
1- Flat Laurentian peneplain 29
2- Fluted till surface and parallel drainage 29 (missing)
3- Esker complex 30 (missing)
4- Drift in railway cut 31
5- Cross-bedding in stratified drift 31
6- Roche moutonnee-Eric Lake 31
7- Garnet-biotite paragneiss 32
8- Migmatite 32
9- Granite gneiss 33
10-Jointing in massive gabbro 33
PHOTOMICROGRAPHS
11- Granite gneiss 34
12- Amphibolite 34
13- Meta-gabbro 35
14-Gneissic granite 35
15- Garnet-biotite paragneiss 36
16- Olivine gabbro 36
17- Sillimanite gneiss 37
18- Granite gneiss 37
19- Myrmekite 38 MAP. Geology of Eric Lake Area, Saguenay County, P. Q. - 1"= 1 mile THE ERIC LAKE AREA
SAGUENAY COUNTY
P. Q.
INTRODUCTION
LOCATION OF AREA
The Eric Lake Area was mapped for the Quebec Department of
Mines during the summer of 1957. It comprises an area of approximately
320 square miles in Northern Saguenay County, bounded by longitudes 65°35' and 65°50', and latitudes 51°45' and 520101 . Its southern boundary is approximately 122 miles north-northeast of Sept-Iles, a town on the north
shore of the Gulf of St. Lawrence.
ACCESS
The easiest means of access to the area is by the Quebec North
Shore and Labrador railway, which is used to haul iron ore from the Knob
Lake iron deposits to the port of Sept-Iles. The railway bisects the area - the southern and northern boundary being at Mile 122 1/4 and 154 respectively
(distance from Sept-Iles measured along the railway route).
The area may also be reached by aircraft. An excellent airstrip lies near the railway at Mile 134. Float aircraft can land on Eric and
St. Patrick lakes and on several sections of the Magpie River.
Before the development of the railway, Indians used a main portage route through the area along the Magpie River.
PREVIOUS WORK
Since 1951 the Geological Surveys Branch of the Quebec Department of Mines has been conducting a geological reconnaissance programme along the Quebec North Shore and Labrador Railway from Sept-Iles north- - 2 - ward. Doctors Carl Faessler, Paul E. Grenier, Howard R..Hogan,
Roger A. Biais, and Wallace B. Emo have mapped the six areas between the Gulf of St. Lawrence and the Eric Lake area.
The Iron Ore Company of Canada conducted a geological reconnaissance survey throughout the region in 1951 and 1952 at a scale of two miles to one inch in conjunction with an airborne aeromagnetic survey. Part of this unpublished information was made available to the writer.
FIELD WORK
The geological mapping, carried out during the four summer months of 1957, was done on the scale on one mile to one inch on a base map prepared by Canadian Aero Service, Ottawa, Ontario, from aerial photographs. An uncontrolled aerial photograph mosaic was used in conjunction with this base map.
Mapping was done by a system of pace and compass traverses spaced at one-half mile intervals and planned, wherever it was possible to predict, to transect regional structural trends.
Lakeshore geology was done in some detail but with little success.
The heavy overburden, particularly in the southern half of the area, is generally more concentrated in the lake and river valleys.
Railway cuts, in several instances, provided excellent exposures of bedrock.
Royal Canadian Air Force photographs with a scale varying from
2600 feet to 3300 feet to one inch, were used to accurately locate rock exposures.
Base camps were established at Eric Station (Mile 137), Mile 150, - 3 - and St. Patrick Lake (Mile 125.) The corners and eastern parts of the area were covered by fly trips. Base campe were moved within the area by the Cuebec North Shore and Labrador railway. An 18 foot, motor driven canoe was used at the main base camps and on the Magpie
River fly camp. Two 16 foot prospector canoes were used on the fly trips.
ACKNOWLEDGEMENTS
The field assistants during the summer of 1957 were: Magloire Berube, fourth-year engineering geology student of Laval University, Marcel Lizotte of University of Montreal, and David MacNaughton of McGill University.
Moise Bond and Horace Bouchard of Sheidrake acted as canoemer:. To all men of the party the writer extends his thanks and appreciation for carrying out their duties in a satisfactory manner.
The writer is also grateful to the staff of the Quebec North Shore and Labrador railway for their assistance throughout the summer.
GENERAL DESCRIPTION OF AREA
TOPOGRAPHY
The Eric Lake area liew within a low-lying part of the Laurentian
Uplands at a general elevation of 2,000 feet to 2,100 feet. Two distinct topographic divisions are represented in the area.
The southern half of the area is typified by flat to gently rolling topography with extensive sand plains and large areas of fluted surfaces grading into drumlin topography. Several small, rounded monadnocks occur in this section but do not exceed 300 feet in local relief. This part of the area is covered by a thick mantle of glacial drift which has modified - 4 - what pre-glacial relief there once existed.
The area south of Eric Lake is an extensive sand plain. Several
fluted till areas occur in this division. They are characterized by
straight, parallel grooves with intervening ridges. These features
range up to one mile in length and up to 500 feet in width. As their
relief is generally less than 10 feet they are rarely distinguished on the
ground, but are easily identified on aereal photographs by contrasting
vegetation colours. They occur in fields and are essentially elongated
drumlins formed parallel to the direction of ice flow. Such streamlined
forms establish the existence of an actively flowing glacier at the time of
their formation and their long axes form a more reliable indicator of
the direction of glacier movement than striations (Flirrt,1957). Usually
the topography does not reflect the underlying rock structure.
The topography of the northern section differs strikingly from
that to the south, where the uplands are deeply dissected by river
valleys and stand at an elevation of 3,000 feet .
The northern half of the area, through which the height of land for
this region passes, is slightly more rugged than that to the south. Rock
exposures are more numerous and depositional features of glaciation are
considerably less . The highest point on the Quebec North Shore and
Labrador railway occurs at Mile 149 (Elevation 2066 feet above sealevel).
The headwaters of rivers flowing to the north and south occur in this
section. Thus, little downcutting has occurred. Two, irregular,
medium-sized gabbro bodies form reiistant hills in the northern half
of the area and provide a local relief of 400 feet to 500 feet.
The concordance of uplands and hill summits indicate the former
Laurentian peneplain surface (Dresser, 1916). For the Moise River
and its tributaries, which drain the southern part of the area, to maintain - 5 - their courses during uplift of the Laurentian peneplain, Cooke believes that this uplift was initiated during Late Pliocene time (Cooke 1931).
Metamorphosed sedimentary rocks, which have eroded more easily than the more granitic types, form the low-lying areas. Gabbros form the highland areas.
GLACIAL GEOLOGY
Pleistocene glaciation, possibly of more than one age, has considerably modified the topography. Erosional features are not numerous within the area, being largely covered by extensive depositional features.
A roche moutonne was observed near the northwest shore of Eric
Lake. It had a well-polished and striated north or stoss side and plucked southern or lee side. Striae and general form of the roche moutonne indicate a southeast direction of ice movement.
Several glacial striae were observed in the northwest corner of the area with strikes of 150° to 160°.
Depositional features within the area are numerous. A mantle of undifferentiated sand, gravels, and boulders, a hundred or more feet in thickness, covers the valleys. Most of this material is =stratified.
On several river banks striking stratified drift was observed which in
some cases had well-developed cross-bedding. Chemical freshness characterizes the drift deposits indicating that decomposed mantle did not contribute importantly to the drift.
Fluted till and drumlin topography form extensive fields in the area. The long axes of these streamlined forms indicate a southeast direction of ice movement. Where fluted till surfaces were recongnized on the ground they are characterized by white moss covered ridges and swampy or brush covered grooves. - 6 -
Two prominent eskers occur in broad valleys in the central and northwestern part of the area. They are up to five miles in length,
10 to 35 feet high, and ZO to 50 feet wide. They are slightly sinuous and assume a general trend in a southeasterly direction.
Many erratic boulders occur in the region. Most are of the under- lying gneisses indicating a local provenance. Frequently the erratics are concentrated into piles and ridges up to 300 feet in length. These boulder ridges lie parallel to the ice movement.
Kame terraces occur on the sides of broad valleys. They generally have a down-valley profile with a terrace face that assumes an ice-contact form which bas been destroyed in part by undercutting of postglacial streams. The terrace surface is frequently pitted by kettles. Kettles are also numerous in the extensive sand plains. As kettles are characteristic of the terminal zone of a glacier, the extensive sand plains are believed to represent extensive outwash deposits formed during a period of ice stagnation. Kettles observed were 10 to 35 feet deep and 30 to 90 feet in diameter.
DRAINAGE
The drainage of the Eric Lake area is deranged, typical of glaciated regions. There is a complete lack of control on drainage pattern by bedrock or structure. The preglacial drainage has largely been effaced, and the new drainage has not had time to develop to any significant degree of integration. It 1e m Irked by irregular stream courses which flow into and out of Lakes and have only a few short tributaries. Large sections of the interstream areas are swampy and frequently the streams are mere threads of water through the swampy arras. A poorly developed parallel drainage pattern has been formed in certain areas of fluted till and drumlin topography. - 7 -
The headwaters of the West Magpie River are in the central part of the area. Another tributary of this river system drains Eric Lake.
The Wacouno River drains the southern part of the area. Ethel Lake is drained by both the Magpie River and the Wacouno River through St. Patrick
Lake. The northern part of the area is drained by the Embarasse River
system which connects with the Ashuanipi River system to the north.
At Mile 149 an abandoned stream channel was observed. This channel
was blocked at its northern end so that lakes formerly draining to the
south are now flowing to the north.
The area, as a whole is poorly drained, with large swampy areas persisting throughout, particularly in the southern half of the area.
The surface is low and streams and swamps remain swollen for a considerable period after a heavy rain.
CLIMATOLOGY
The area lies on the southern boundary of the Taiga Climatic province which is characterized by one to four months during the summa r in which the mean temperature is above 50°F. and a mean winter
temperature of below 32°F. for five months or more.
Summer temperatures in this climatic zone are higher than is normal
for this latitude. Within the limits of the Taiga province the climate is essentially the same and is typically continental. Although high temperatures
do occur in mid summer, the region is subject to invasion of cold air from
the arctic and is not free from the danger of frosts even in July and August.
Rainfall in this area averages forty or more inches annually with the heaviest precipitation occuring between June and October .
Water levels in the lakes and rivers are high in early June and are down six or more feet by the end of July. Runoff is generally rapid in the sandy areas near the West Magpie River so that the river level frequently
rises several inches after a heavy rainfall. - 8 -
GENERAL GEOLOGY
GENERAL STATEMENT
The Eri... Lake area lies within the Grenville Province of the
Canadian Precambrian Shield. Structural trends within the area are dorninatit1y northeast. The high degree of metamorphism of the rocks indicatesthat the region has been subjected to large scale tectonic disturbances.
The gneissic rocks have been highly contorted, as is common in ancient rocks such as these, but it is possible to distinguish regional trends within them and,where rocks are well exposed,to define structure.
Because of the widespread mantle of drift the bedrock is not well exposed in this area. Outcrops are usually small and isolated. The diversity of rock types encountered with poor exposures makes lithologic correlation within the area most difficult particularly on this scale of mapping.
All of the consolidated rocks of the area are Precambrian in age. They are typical of the rocks of the North Shore Region which stretches in a zone north of the Calf of St. La Saguenay River area to east of Havre St. Pierre. The oldest rocks recognized in the area are a highly metamorphosed assemblage. The belts of sediments are poorly defined and few have escaped pervasion or injection of a later granitic material and/or granitizing processes. Hybrid gneisses or migmatites formed by varying amounts of granitic and sedimentary material form indistinct bands. In some places granitic material is clearly intrusive into the older rocks along foliation planes resulting in a lit-par-lit injection gneiss. In many cases the foliation of the granitic material follows that of the adjacent sedimentary rocks resulting in extensive development of migmatites in which the contacts between the granitic component and the metamorphic component are indistinct. 9 Such relationships have been interpreted as due to the intrusion of a granitic magma, to partial refusion of metamorphic rocks in place, or to metasomatism of rocks in place. In crossing a zone of hybrid gneisses the varying lithology suggests that they have been formed mainly by granitizing processes. Highly meta- morphosed sedimentary rocks are followed by migmatites, and with increasing granitic material into granite gneisses, augen granite gneisses, and gneissic granite. The granitic gneisses are possibly, in part, the result of true magmatic origin, but definite field or laboratory evidence is lacking for this distinction . Gabbros and diorites are found as sills, dykes, and medium-sized, irregular stocks which cut the older metamorphosed sediments and granitic gneisses. A pink, medium-grained, massive granite was observed in two exposures cutting the paragneisses and in two exposures cutting gabbro. Large bodies of massive granite are abundant in the region to the south of this map area. Pegmatite dykes are found cutting all the other rocks and are the youngest rocks of the area. In an area such as this, where rock exposures are not abundant, contact features defining the age relationships of the various litholo- gies were not numerous. Where contact features were not aviable, the age relationships established by workers in areas to the south have been followed. Listed, in order of abundance, the consolidated rocks are: metasedimentary gneisses and schists, granitic gneisses, gneissic granite, gabbro, diorite, and various minor dykes. - 10 - The metasedimentary rocks of the North Shore Region have been assigned to the Grenville Series by several of the workers. These rocks form the oldest recognizable group within the region and with their associated granitic gneisses form a characteristic sequence of rocks which is similar to the Grenville Series of southwestern Quebec, southeastern Ontario, and the Adirondack Region. TABLE OF FORMATIONS Sand, gravel, and erratic Cenozoic Recent and Pleistocene boulder s Great Unconformity pegmatite, dykes (not shown on map) Intrusive massive granite Rocks (not shown on map) gabbro, diorite, and related rocks. gneissic granite Early Intrusive and/or Metasomatic augen granite gneiss Rocks migmatite amphibolite (ortho?) Precambrian quartz-biotite, oligoclase schist, gneiss Metamorphosed biotite-hornblende gneiss Sedimentary rocks ("Grenville type") quartz-feldspar gneiss garnetiferous gneiss sillimanite gneiss amphibolite (para?) METAMORPHOSED SEDIMENTARY ROCKS GENERAL STATEMENT Highly metamorphosed sedimentary rocks outcrop in the southwest corner of the area and extend in a broad band, almost continuously, for over thirty miles. They form the most abundant rock type, under- lying about one-third of the area. The most common types are: quartz-biotite-oligoclase schist and gneiss quartz-feldspar-hornblende-biotite gneiss garnet-biotite gneiss muscovite-biotite gneiss sillimanite schist and gneiss amphibolite of sedimentary origin? Most of the foliation in the rocks of sedimentary origin is believed to be due to a gneissosity superimposed on an original sedimentary layering. Bedding, the most characteristic structure of these rocks, commonly persists in metamorphism as a relict banding which is frequently accentuated through metamorphic differentiation. In spite of the high degree of metamorphism, relict banding exists due to alternating quartz and or feldspar-rich layers and biotite and/or hornblende-rich layers. The writer believes that much of the foliation in the sedimentary gneisses and schiste is mainly due to original variation in chemical composition rather than to metamorphic differentiation. Banding, due to metamorphic differentiation into quartzo- feldspathic and micaceous layers, that develop parallel to the schistosity and therefore to the original bedding, may in part be responsible for these structures and may be more common than is generally suspected. - 12 - Ripple marks, cross bedding, or graded bedding were not observed in the sedimentary rocks. The metamorphosed sedimentary rocks have been intimately penetrated by granitic material and granitized making their distinction from migmatites and granitic gneisses difficult. If the outcrop contained 60 per cent or more of the sedimentary material (paleosome component) it was mapped inthe field as a paragneiss. The boundaries of the paragneiss bands are transitional from a purely sedimentary rock into migmatites or hybrid gneisses, granitic gneisses, and finally into augen granite gneiss and gneissic granite. Such a transition affor ds strong evidence of a metasomatic origin for the mixed gneisses and gneissic granite. QUARTZ-BIOTITE-OLIGOCLASE GNEISS This is a light to dark grey rock depending upon the amount of mafic minerals present. It is fine to medium grained, equigranular and has a distinct layering due to alternating quartz-feldspar-rich and biotite-rich layers . It has a composition of plagioclase 40% to 60%, quartz 15% to 18%, dark brown, strongly pleochroic biotite 12% to 20%. The common accessory minerals are zircon, apatite, hornblende, orthopyroxene, and opaque ores. Some of the gneisses contain small amounts of epidote, clinozoisite, and sphene. The predominant feldspar is plagioclase-oligoclase with an anorthite content of An 25 to An 45 with an average of An 30. Several of the thin sections studied contained potassic feldspars in amounts up to 18%. The plagioclase is frequently highly saussuritized and sericitized makMing its determination dif- ficult. Myrmekitic intergrowths were observed at the plagioclase-potassic feldspar boundaries. - 13 - The writer has used the term "gneiss" throughout the field and petrographic study to refer to an alternation of schistose and granulose bands rather than to restrict the term to a foliated rock of felsic quartz-feldspathic composition. Some of the rocks, however, have formed pronounced foliation of mafic inineral5 and therefore should be termed schists. Foliation, some of the specimens, has also been produced by a parallel or sub-parallel orientation of.feldspar and quartz grains. In places the foliation is poor or lacking making the rock massive over widths of several feet. QUART Z -FELDSPAR-HORNBLENDE-BIOTITE GNEISS This rock is closely associated with the quartz-biotite-oligoclase gneiss. It is medium to coarse grained, has a pronounced gneissic structure and is medium to dark greenish-grey. The rock consists of dark green pleochroic hornblende 10% to 25%, dark brown, parallel orientated biotite 8%, fine grained bands of quartz 5% to 15%, and feldspar 55% to 63%. The feldspar is mainly oligoclase An 30 to An 38, which has been partly saussuritized. Zircon, apatite , small prismatic crystals of sillimanite, and opaque ores are the common accessory minerals. Several bands with a pronounced porphyroblastic structure were observed. The porphyroblasts are eye-shaped, average 1/4 inch in their long dimension which is parallel to the foliation planes and are composed of white plagioclase. The quartz-feldspar-hornblende-biotite paragneiss has essentially the same composition as the dominant paragneiss described above but contains more hornblende. It is usually difficult to distinguish between the two gneisses in the field. GARNET-BIOTITE GNEISS This is a coarse grained, dark grey rock with a pronounced gneissosity. Large, rounded, pink porphyroblasts of garnet up to 3/4 inch in diameter, which may be slightly elongated parallel to the foliation planes, - 14 - are concentrated in the biotite-rich bands. The rock varies in composition. One section contained oligoclase An 30 - 60 per cent, orthopyroxene (enstatite) 5 per cent, biotite 20 per cent, chlorite 5 per cent, garnet 8 per cent, with a deep ; green spinel and zircon as accessory minerals. In another section 1/3 of the feldspar was orthoclase; plagioclase had an anorthite content of An 39 and the rest of the section consisted of quartz, biotite and contained large porphyroblasts of garnet in bands which formed 15 per cent of the rock. MUSCOVITE-BIOTITE GNEISS This rock is medium grained, medium grey, Gneissosity is not pronounced in the hand specimen. The rock consists of oligoclase 45% quartz 25%, muscovite 20%, and biotite 10%. Zircon and opaque ore are the common access ory minerals. The muscovite and biotite occur in narrow bands separated by coarse granular bands of feldspar and quartz. SILLIMANITE GNEISS Sillimanite is an important constitubnt of many of the gneisses in the area. The sillimanite gneiss is a fine to medium grained rock, medium to dark grey and shows fine banding less than 1/8 inch wide. The gneiss is frequently associated with garnet-rich paragneisses and garnet is usually an important constituent of this rock. The rock consists of 45% plagioclase An 19 - 20, quartz showing undulating extinction 40%, biotite 2% - 3%, sillimanite 8 - 10%. The rock may also contain up to 5% garnet, with opaque minerals and zircon as common accessory minerals. In one of the hand specimens pink potassic feldspar with quartz and plagioclase form bands up to i inch wide. Potassic feldspars were not recognized in the thin sections but the occurrence of myrmekite at feldspar crystal boundaries indicate that it is present. - 15 - AMPHIBOLITES In the Grenville Province amphibolites frm major rock units of the "Grenville type!' assemblage. Most of the amphibolites have evolved from parent rocks of unknown origin. Unlike the paragneisses , neither the bulk composition nor the present metamorphic mineral constituents suggests a particular origin (Engel, 1956). They are foliated rocks composed essentially of hornblende and plagioclase. They are characteristic rocks of the amphibolite facies and are among the commonest rocks formed by regional metamorphism of moderate to high grade. Segregation layering may not be present and foliation may not be pronounced in varieties poor in mica. Amphibolites may be formed from diverse kinds of rocks. They may be formed from basic igneous rocks, from impure calcareous and dolomitic sediments, or from pure limestones by the introduction of silica, magnesia, and iron through metasomatic processes. Although the textural and mineralalogical character, as well as field relationships/may indicate the parent rock of a given amphibolite a definite distinction of amphibolites of sedimentary origin in the Eric Lake area is problematical. As the exposures of this type of rock were generally sac isolated, contact features were rarely available to suggest their genesis. When the amphibolites occur in conformable relationships to the paragneisses, they have been called 'hornblende gneiss' by workers in the North Shore region (Blain, 1954, Grenier, 1952, Hogan, 1952). The amphibolite consist s of plagioclase, hornblende, quartz, pyroxene, and biotite. They are medium to coarse grained, slightly gneissic to highly foliated, and have a dark brownish-grey weathered surface and a medium to dark grey fresh surface. They contain 45-55% andesine An 30-33 5% quartz, and 25% dark green pleochroic hornblende. The content of the mafic minerals varies from rock to rock. Biotite may be absent or form 8% of the rock; in one thin section, pale green diopside formed 30%. - 16 - Accessory minerals are garnet, apatite, and ephene; opaque ore varies from less than 1% to 7%; sillimanite may be present in amounts up to 2%. Abundant greenish diopside is characteristic of amphibolites derived from mixed calcareous sediments (Williams, Turner, and Gilbert, 1955). There is the possibility, however, that some of these rocks, classified as sediments, are of igneous origin. No occurrences of crystalline limestone, found in other areas of the region, were observed in the Eric Lake area. The nearest reported occurrence of crystalline limestone in the North Shore Region is in the Manitou Lake area, a distance of 65 miles south-southeast of this area (personal observation 1956). EARLY INTRUSIVE AND/OR METASOMATIC ROCKS GENERAL STATEMENT Few of the older sedimentary rocks in the area have escaped varying degrees of migmatization. Associated with the paragneisses, the hybrid gneisses form a complex which is common to many areas of the Grenville Province (Hewitt, 1957)• The paragneisses have been intimately intruded by granitic material which hascblitezated their original characteristics. Associated with the paragneisses, and with increasing granitic material, are migmatites, granitic gneisses, augen granite gneisses, and gneissic granite. The transition from one rock type to another is gradational so that their separation into distinct lithological units is difficult. The granitic com- ponent generally shows a gradational contact with the metamorphosed host rock, but sharp, injection-type gneisses were not uncommon. lgistinctions, made in the field, in the classification of the hybrid gneisses were based on the amount of granitic material present and its mode of occurrence in the host rock. If 75% or more of the exposure - 17 - was paragneiss, it was mapped as such. If the neosome component formed 25 to 50% and occurred as distinct bands, the rock was called a migmatite. With 50 to 75% granitic material and 25% paragneiss, as distinct continuous layers, the rock was called a granite gneiss.. The gneissic granite consisted of 75% or more of granitic material. On the scale of mapping, migmatites have not been separated from the other gneisses. For mapping purposes, 65% or more of paragneiss present in the exposure was used as a boundary. Although much of the gneissic granite is a more highly metasomatised facies of the granite gneiss, some of it possibly, is of igneous origin. No means of distinguishing the Z types was found, although where sharp contacts were observed between the paleosome and neosome component resulting in a lit-par-lit , injection type gneiss, a magmatic origin for the granite is indicated. GRANITE GNEISS This hybrid gneiss, including migmatite, contains 25%to about 75% granitic material with at least 25% continuous bands of the paleosome component. The neosome component frequently shows a coarse augen structure, with eye-shaped porphyroblasts which form discontinuous, irregular streaks. Some of the banded granite gneisses show that the neosome component occurs as lens-like forms 1/8 to 1/4 inch wide and up to 4 inches long, suggesting that they represent a further development of the augen granite gneiss facies. The granitic material of these gneisses consists of orange- pink potassic feldspars which may occur as coarse porphyroblasts 1 inch wide and 1 4 inches long or as bands and lenses 4 inch or less thick. Where the gneiss is porphyroblastic the paleosome component wraps around the - 18 - augens resulting in a fluxion structure. The paleosome component is fine to medium grained and may occur in bands up to several feet thick but is usually inch or less. The gneissosity is produced by the bands of the host rock. The composition of the granite gneisses is: plagioclase- An 30, 20%; orthoclase 40%, quartz 18%, biotite 10%; in several of the thin sections sillimanite in amounts up to 1Z% occurs: apatite, chlorite, zircons, garnet, opaque ore (rutile), sphene, epidote, and clinozoisite may be present in varying amounts as accessory minerals. Myrmekite has been formed at plagioclase-orthoclase crystal boundaries. GNEISSIC GRANITE The origin of the gneissic granite is difficult to determine. Three possibilities exist. I) The rock was a massive, igneous granite which was later foliated. Z) Foliation is a primary feature producing an orthogneiss. 3) The rock is an advanced phase of metasomatic processes which have granitized the sedimentary rocks. The writer favours the third possibility. No clearly defined boundaries mark the transition from paragneiss to granite gneiss to gneissic granite. The lineation of the granite gneisses and gneissic granite is predcsninantl_y concordant with that of the paragneisses which indicates that they have behaved as a structural unit during deformation. The mineral assemblage of both the granite gneisses and gneissic granite is similar. The degree of gneissosity varies in the gneissic granite depending upon the continuity of the mafic minerals which may occur as thin (less than 1/8 inch), indistinct. continuous bands, or due to parallel-orientated short, discontinuous streaks. - 19 - The rock is coarse grained, granular, and orange-pink in colour. The composition is similar to that of the augen granite gneiss. It consists of 45% to 65% feldspar which is orth oclase and micpoline- micreperthite, and may contain 10% or less of altered plagioclase. Quartz forms 20 to 25% of the rock. The mafic minerals vary considerably in their presence and amount. Biotite may form from less than 1% to 10% of the rock; orthopyroxene in one of the sections forms 8%; sillimanite may be absent or form 8%; chlorite, garnet, hornblende, apatite, zircon, and opaque ore form the accessory minerals. Myrmekite is commonly obsverved. IGNEOUS ROCKS GABBRO GENERAL STATEMENT Several small bodies of gabbro occur as cliffs and rounded hills in the area. Four larger bodies occur in the northern part of the area. The mass in the northwest has a rounded outline and forms the highest section of the area. The large, irregular mass in the northeast is elongated in a north-northeast direction. The mass in the north central part of the area is elongated in a north-south direction. Exposures in the vicinity of the gabbro bodies were not abundant so that the contact features were not observed. Gabbro was observed in other exposures as small sills and discordant bodies cutting the older gneisses. The composition of the gabbros varies both within individual masses and from mass to mass. Examples of the following types were studied in thin section: Olivine gabbro Hypersthene gabbro Hornblende gabbro Normal gabbro - 20 - OLIVINE GABBRO The olivine gabbros occur in the northwest mass as coarse to very coarse grained, dense , massive, and have a medium greenish-grey to dark bluish-grey fresh surface and a dark rusty weathered surface. In thin section secondary coronas are observed. The olivine crystals are enveloped by hypersthene, augite, Spinel, and hornblende formed as an alteration of the pyroxenes. Labradorite- An 50-53, forms 60% of the rock, olivine 10% , hornblende 5%, augite 10%, hypersthene 10%, and biotite 2%. In one section a small vein of quartz has been introduced. Iddingsite and serpentine (antigorite) are alteration products of the olivine. Accessory minerals are apatite, and opaque ores including rutile. HORNBLENDE GABBRO Hornblende gabbro occurs in the large northwest body and in small isolateu masses. It is a medium to coarse grained rock with a buff- grey weathered surface and a dark grey fresh surface. The rock may be massive or slightly foliated (ortho-amphibolite). It consists of 35% andesine An 33-38, dark green hornblende 30%, pale green diopside 15%, dark green biotite 15% and opaque ore 5%. Chlorite may be present as an alteration of hornblencie; secondary quartz is present in one section; apatite is the typical accessory mineral. HYPER; THEME GABBRO Hypersthene gabbro occurs in the large northeast mass. It is a massive, coarse grained rock with a buff-grey weathered surface and a medium-grey fresh surface. It consists of 63% labradorite An 54, strongly pleochroic hypersthene 18%, dark green hornblende 15%, and biotite 4%. - 21 - NORMAL GABBRO Thin sections of this gabbro were studied from isolated outcrops and within the northwest body. The rock is medium to coarse grained, has a medium to dark grey fresh surface and a dark grey to rusty weathered surface. It has the following composition: 1 2 3 4 plagioclase An 30 - 57% An 37 - 48% An 42 - 67% An 45 - 48% hornblende 18 1 2 13 hypersthene 10 7 5 5 diopside -augite 10 11 15 15 quartz - 13 3 7 biotite 5 3 8 10 opaque ore tr. 7 tr. Z apatite tr. tr. tr. tr. zircon - tr. tr. - No. 1 - within the northwest mass. No. 2 - foliated (ortho-amphibolite) isolated outcrop near the northwest mass. No. 3 , 4 - isolated occurrences from gneissic granite and paragneiss areas, respectively. The gabbros have been slifhtly altered but not in a uniform manner. Both fresh, massive and slightly uralitized varieties occur within the same mass. The pyroxenes which occur in most of the sections, have been largely unaltered. Olivine has reacted with the adjacext calcic plagioclase forming kelphytic rims after crystallization. Foliated gabbros of the amphibolite facies (Specimen No. 2, above) occurs along gabbro contacts. - 22 - DIORITE Two gneissic rocks found as isolated exposures near the smaller gabbro body in the northeast appear massive in the hand specimen but with microscopic examination show a gneissic or fluxion structure produced by parallel flakes of biotite. They are medium to dark pinkish-buff-grey. They are classified as quartz diorites or granodiorites. Near the northwest gabbro body a massive gabbro was traced into a coarse grained, buff coloured rock which was cut by granite. These hybrid rocks consist of 50% to 60% oligoclase or andesine, 20% potassic feldspar, 10% to 30% quartz and 8 to 10% biotite. In two of the speciments the biotite has largely been altered to sillimantte. Myrmekite is present at the feldspar grain boundaries. Augite and orthopyroxene altering to hornblende were observed in the specimen from the northeast. Opaque ore, spine', zircon, epidote, and clinozoisite are the accessory minerals in this specimen. The low colour index, and the presence of potassic feldspars and quartz distinguishes the dioritic facies from the gabbros, with which they are closely associated. These hybrid rocks are believed to have been formed from the gabbros by the intrusion of granite. In two occurrences they were traced transitionally into massive gabbro. In both instances the exposure was cut by granite. It is likely that the potassic feldspar and quartz have been introduced from the granitic intrusions. GRANIT E Massive granite is rare in the Eric Lake area. It was observed in the southern part cutting paragneisses and in the north cutting gabbro. Massive granite is abundant in the adjacent area to the south. The rock is pink, medium to coarse grained, and equigranular. Both milky and clear quartz was seen in one of the hand specimens. The composition is: well-twinned microcline 55%, plagioclase (oligoclase-An 28) 25% - 23 - quartz 15 to 20%; biotite is common to all the specimens and may form up tog% of the rock. Common accessory minerals are muscovite (up to 1%), opaque ores (ilmenite and rutile), apatite, hornblende, and chlorite (as an alteration of biotite). Myrmekite is common to all the specimens. PEGMATITE Pegmatites are abundant in the area but do not form large bodies. Most commonly they occur as dykes that are concordant with the general structure. They vary from inch to 4 feet in thickness and are a white or pink in colour. They consist of plagioclase, orthoclase, quartz, biotite, and magnetite. STRUCTURAL GEOLOGY The structure within the Eric Lake area is quite complex, similar to that throughout the Canadian Shield. The abundance of gneissic rocks in this area indicates that the region has undergone large-scale tectonic activity. The gneisses have been complexly folded and cross folded but a regional trend within the area is quite evident. The pa- ragneisses and mixed granitic gneisses have been plastically de- formed and/ with the lack of exposure, details of structure wi- thin any one section of the area cannot be worked out. Strikes of genissosity are reasonably consistent throughout the area and are usually north-northeast. Dips are steep to vertical, with the exception of the southwest corner where two exposures indicate an area of flat-lying sedi- ments, possibly a broad demi*cal structure. Strikes within the north-half of the area are consistent, whereas considerable variation exists in the south. - 24 - The structure within the gneissic granite and granitic gneisses is consistent with that of the older metasedimentary gneisses, indicating that they have acted as a structural unit during deformation. With increasing content of mafic minerals in the metamorphic gneisses the degree of gneissosity becomes more pronounced. The sties within the granitic gneisses are consistent but a wide variation in direction and amount of dip indicates that these gneisses were produced in zones of plastic deformation. Within the sedimentary gneisses the foliation has been produced by lithologie variation resulting in a "quasi-bedding foliation", (Buddington, 1956). The intrusive rocks have both conformable and cross-cutting relationships to the older gneisses. The northwest gabbro body has deformed the surrounding gneisses to conform to the outline of the gabbro. The larger northeast body is conformable to a certain degree with the surrounding gneisses. The smaller bodies of gabbro occur as sills which conform to the surrounding structures. Massive granite occurs as dykes cutting both the older gneisses and gabbro. Jointing which has been controlled by linear structures is evident in both the meta sedimentary and granitic rocks. Strike joints, paralleling the foliation of the gneisses are common. Joints, perpendicular to the foliation direction, are frequently produced. They gel erally trend in the direction in which the foliation dips. ECONOMIC GEOLOGY No concentrations of economic minerals were found within the map area, although magnetite and ilmenite were observed as fine disseminations within the gabbro bodies and older gneisses. - 25 - Gravel deposits along the W eat Magpie River have been used extensively for railway fill and in the building of the airstrip at Mile 134. - 26 - BIBLIOGRAPHY Adams, F.D., 1896, Report on the Geology of a portion of the Laurentian Area Lying to the north of the Island of Montreal, Que., Geol. Surv. Can. Ann. Rep. Barth, T.F.W., 1951, Theoretical Petrology, Wiley. Blair, T.A. , 1942, Climatology, Prentice-Hall. Slats, R.A. , 1953, Wacouno River Area, Saguenay County, P.Q. , Que. Dept. Mines, Prelim. Rep. No. 290. 1954, Waco Lake Area, Saguenay County, P.O., Que. Dep. Mines, Prelim Rep. No. 304. Buddington, A.F., 1939, Adirondack Igneous Rocks and Their Metamorphism, G.S.A. Mem No. 7. 1956, The Correlation of Rigid Units, Types of Folds and Lineation in a Grenville Belt, The Grenville Problem, Roy. Soc. Can. Spec. Pub. No. 1. Claveau, J. , 1950, North Shore of the St. Lawrence from Aguanish to Washicoutai Bay, Saguenay County, P.O., Que. Dept. Mines Geol. Rep. No. 43. Cooke, H.C. , 1929, Physiography of the Canadian Shield, Roy;. Soc. Can. Trans. Vol. 23. 1931, Pre-Pliocene Physiography, Roy. Soc. Can. Trans. Vol. 25. Cooper, G.E., 1957, Johan Beets Area, Saguenay County, P.O., Que. Dep. Mines, Geol. Rep. 74. Erno, W . B., 1955, Mule Lake Area, Saguenay County, P.Q. , Que. Dep. Mines, Prelim Rep. No. 324. - 27 - Emo, W.B.. 1955, Basic Intrusives of the Waco Lake Area, Unpublished Thesis, McGill University. Engel, A.E.J. , and Engel, C.. 1953, Grenville Series in the Northwest Adirondack Mountains, N.Y., G.S.A. Bull. Vol. 64. Engel, A.E.J. , 1956, Apropos the Grenville, The Grenville Problem, Roy. Soc. Can. Spec. Pub. No.1. Flint, R.F., 1957, Glacial and Pleistocene Geology, Wiley. Faessler, C.. 1945, Moisie Aga: , Saguenay County, P.O., Que. Dip. Mines, Geol. Rep. No. 21. Gill, J.E. , 1948, The Canadian Shield, Structural Geology of Canadian Ore Deposits, C.1.M. M. Grenier, P .E. , 1952, Nipissis River Area, Saguenay County, P.Q. . Que. Dep. Mines Prelim. Rep. No. 272. 1957, Beets Area, Saguenay County, P.Q., Que. Dep. Mines Geol. Rep. No. 73. Harker. A.H. , 1932, Metamorphism, Methuen. Hewitt, D.F. , 1957, The Grenville Province. Tie Proterozoic in Can.. Roy. Soc. Can. Spec. Pub. No. 2. Hogan, H.R. , 1952. Nipisso Lake Area, Saguenay County, P.Q., Que. Dep. Mines, Prelim. Rep. No. 280. Holmes, A. , 1920, The Nomenclature of Petrology, Murby. Jenkins. J.T. , 1956, Manitou River Area, Saguenay County, P.O., Que. Dep. Mines, Prelim. Rep. No. 326. Longley, W.W. , 1948, Forget Lake Area. Saguenay County, P.O., Que. Dep. Mines, Geol. Rep. No. 36. Ramberg, H., 1953, The Origin of Metamorphic and Mitasomatic Rocks, Chicago Press. -28 - Read, H.H., 1956, The Granite Controversy, Methuen. Rogers, A .F. , and Kerr, P.F. , 1942, Optical Mineralogy, McGraw-Hill. Thorubury, W.D., 1956, Principles of Geomorphology, Wiley. Tsuboi, S., 1923, A Dispersion Method of Determining Plagioclases in Mineral Flakes, Min. Meg. Vol. 20. Turner, F . J.. and Verhoogen, J., 1951, Igneous and Metamorphic Petrology, McGraw-Hill. Tyre11, G.W. , 1952, Principles of Petrology, Methuen. Waddington, G.W. , 1950, North Shore of the St. Lawrence fiQm Mingan to Aguanish, Saguenay County, P.O., Que. Dep. Mines, Geol. Rep. 42. Williams, H., Turner, F.J. , and Gilbert, C.M., 1955, Petrology. Freeman Co. W inchell , AN., 1947. Elements of Optical Mineralogy, Wiley. 1. Flat Laurentian Peneplain Surface -k12- p\rkA 0 Q_5\ MaNuc-n Z. Fluted Till Surface with parallel drainage pattern r - 30 - La Oeh e~s~ mculq~o.nf~ 3. Esker complex in the northern part of the area - 31 - 4. Drift in railway cut-Mile 137.5; thickness approximately 70 feet• 5. Cross-bedding in Stratified Drift 6. Roche Moutonne - Eric Lake; plucked, lee (south) side to left - 32 - 7. Garnet-biotite paragneiss 8. Migmatite; pink granite with conformable and cross-cutting relationships to biotite paragneiss - 33 - 9. Granite Gneiss Istoor41 ,1' silSj 10. Jointing in Massive Gabbro - 34 11. Granite gneiss; alternating granulose, quartz-feldspar and schistose biotite (Bi) - sillimanite (Si) bands; plane light; field = 4. 5 mm. 12. Amphibolite; plagioclase (plag) - diopside (Di) - and magnetite (Mag ); plane light; field - 4.5 mm. - 35 - 13. Meta-gabbro; parallel orientated biotite (Bi)-hypersthene (hyp)-diopside (Di) - magnetite (Mag) with plagioclase (plag); plane light; field - 4.5 mm. 14. Gneissic granite; fluxion structure; sillimanite (Si) Altering from biotite (Bi) and muscovite (Musc) with quartz (qtz); plane light; field - 4.5 mm. - 36 - 15. Garnet-biotite paragneiss; parallel orientation of biotite(Bi) with garnet(g) and plagioclase(plag); plane light; field - 4.5 mm. #4 1• yrs. ~ 1 st p4 r i• - , - ~Ÿ 4.R 16. Corona in olivine gabbro; olivine (ol) altering to hypersthene (hyp) and serpentine (S) with plagioclase (plag); plane light field - 4. 5 mm. - 37 - 17. Sillirnanite gneiss; typical cross section of sillim.anite (Si) with garnet (g), magnetite (}4) and plagioclase (plag); plane light, field - 1.45 nun. 18. Granite; microcline twinning; x-nicols; field - 1.45 mm. - 38 - 19. Gneissic granite; myrrnekite; quartz-plagioclase intergrowths producing vermicular forms; x-nicols; field - 1.45 mm.