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Ontario Department of Mines Geological Branch
Open File Report 5013
Geology of the Fort Frances Area, District of Rainy River
1967
ONTARIO DEPARTMENT OF MINES
GEOLOGICAL BRANCH
OPEN FILE REPORT
No.5013
GEOLOGY OF THE
FORT FRANCES AREA
DISTRICT OF RAINY RIVER
DEC. 4, 1967
Open-file reports are made available to the public subject to certain conditions. Anyone using them shall be deemed to have agreed to these conditions which are as follows:
This report is unedited. Discrepancies may occur for which the Department does not assume liability.
Open-file copies may be read at the following p laces: The Library (Room 1433, Whitney Block), Department of Mines, Parliament Buildings, Toronto.
The office of the Resident Geologist in whose district the area covered by this report is located. A report cannot be taken out of these offices. Handwritten notes and sketches may be made from it. This particular report is on file in the Resident Geologist’s office located at:
20 3 Main St. South, Kenora
Open-file reports cannot be handed out for office reading until a card, giving the name and address of the applicant, is filed with the Resident Geologist or Librarian.
A copy of this report is available for inter- library loan. The Department cannot supply photocopies. Arrangements may be made for photocopying by an outside firm at the user’s expense. The Librarian or Resident Geologist will supply information about these arrangements.
The right to reproduce this report is reserved by the Ontario Department of Mines. Perm is sion for other reproduction must be obtained in 'writing from the Director, Geological Branch. J. E. Thomson, Director, Geological Branch.
ONTARIO DEPARTMENT OF MINES
GEOLOGICAL REPORT
Geology of the Fort Frances Area
by
J.C. Davies
TABLE OF CONTENTS
INTRODUCTION 1
Acknowledgements 2
Previous Geological Work 3
Topography 4
Natural Resources 4
Agriculture 4
F o re s ts 5
Fish and Game 6
Inhabitants 6
GENERAL GEOLOGY 7
Table of Formations 8
Description of Rock Units 9
Basic Metavolcanic Rocks 9
Metasedimentary Rocks 10
Basic and Intermediate Metavolcanic Rocks 11
Early Basic Intrusive Rocks 12
Devlin-Burriss Intrusion 12
Woodchuck Island Homblendite 13
Amphibolite and Metagabbro 13
Porphyritic Acid Intrusive Rocks 14
Frog Creek Quartz Monzonite 14
Sand Bay Hornblende-Biotite Monzonite 15
Miscampbell Porphyritic Granodiorite 16
Halfway Inlet Porphyritic Quartz Monzonite 17
Eguigranular Acid Intrusive Rocks 17
Massive to Foliated Granodiorite and Quartz Monzonite 17
Massive Pink Quartz Monzonite 18
Fault Zone Gneiss 18
Late Basic Intrusive Rocks
D iabase 20
Lim estone 21
Magnetic Properties of the Rocks 22
STRUCTURAL GEOLOGÏ 24
F olding 24
F a u ltin g 24
PLEISTOCENE 28
ECONOMIC GEOLOGÏ 30
Mathieu Property 30
Topham and Norris Property 32
Iro n 35
Great River Mining and Development Syndicate 35
Sand, Gravel and Crushed Stone 36
Peat 37
Arctic Peat Moss Corporation Ltd. 38
RECOMMENDATIONS FOR PROSPECTORS 39
SELECTED REFERENCES 39
- iii -
F ig u res
1 Location of the Fort Frances Area 1
2 Aeroraagnetic Map, Part of the Rainy River District 23
3 Geological Interpretation, Part of the Rainy River District 25
4 Pleistocene Deposits of the Area 29
5 Topham and Norris Property 34
6 Production of Peat Moss, Arctic Peat Moss Corp. Ltd. 38
Preliminary Map* (Back pocket)
P.286 Fort Frances Area,Scale 1 inch to 1 mile.
* Preliminary maps may be purchased at Publications Office,Ontario Department of Mines,Whitney Block,Parliament Buildings,Toronto.
ABSTRACT
The report describes geological features of a 350 square mile area of Precambrian Shield lying north of the Rainy River and west of Rainy Lake.
Narrow folded belts of predominantly metasedimentary rocks, concordantly intruded by granodiorite, are truncated by a major east
-west fault in the north part of the area. Interlayered metasedimentary and metavolcanic rocks, underlying most of the heavily drift-covered south part of the area, are interpreted to have been similarly faulted. Relative ages of the metasedimentary and metavolcanic rocks have not been established.
Axes of major folds and cross folds are considered to trend east
and north-northeast respectively. Basic to acid intrusions appear to
occur at the intersection of two anticlines or two synclines.
Examined sulphide occurrences contain only traces of base metals,
and examined iron formations are narrow. Deposits of gravel and peat
have been commercially exploited.
GEOLOGY OF THE FORT FRANCES AREA
INTRODUCTION
The map-area lies to the west of Rainy Lake and to the north of the Rainy River (Figure 1). It includes the townships of Dance, Griesinger, Burriss, Miscampbell, Devlin, Crozier,
Woodyatt and Roddick, the town of Fort Frances (Mclrvine township), and Indian Reserves 16A, 16D, 18B and 18C. Most parts of the 350 square mile area are readily accessible from existing roads or from the shore of Rainy Lake.
F ig u r e 1 Prior to the publication of aeromagnetic maps in 1962 the
rocks underlying the area were assumed to be mostly granitic
(G.S.C. Map 266a ). Prospecting had been undertaken in a few
places by farmers, trappers and other residents, but mining
companies had not been deeply involved in any exploration
activities. In the Emo area to the west and the Rainy Lake area
to the east, however, mineralized zones had been found in 2. non-granitic rocks, and the aeroraagnetic maps (Figure 2)
indicated that some rock units extended from these areas through the Fort Frances area.
Geological mapping of the Fort Frances area took place during the 1964 field season, except along Rainy River where high water levels prevented mapping of outcrops until 1966. Traverses in areas of abundant outcrop were spaced about 1500 feet apart and were run by pace and compass methods using vertical air photographs at a scale of approximately one inch to 1320 feet for control»
Mapping was largely confined to photo-interpreted outcrops in areas of heavy overburden. Examined outcrops were plotted on acetate sheets taped to the air photographs, and on base maps where geological information was recorded. Outcrop areas and essential geological data were traced onto cronaflex base maps.
The base maps, at a scale of one inch to 1320 feet, were prepared by the Cartography Unit of the Ontario Department of Mines from base maps of the Forest Resources Inventory, Ontario Department of
Lands and Forests.
AC KNOWLBDGEMENTS
Capable assistance in the field was provided ty H. L. King,
6. E. Stutsky, L. A. Jackson and A. G. Zink. Mr. King was
responsible for about one half of the mapping, and Mr. Stutsky for
about one quarter of the mapping.
The w riter wishes to thank the Fort Frances Agency of the Indian
Affairs Branch for arranging permission to map in the Indian Reserves,
and for providing information relative to the Reserves. The Ontario Department of Lands and Forests in Fort Frances supplied information on forests, fish and game. Agricultural statistics were provided by the Ontario Department of Agriculture and data on gravel deposits were supplied by the Ontario Department of
Highways and George Armstrong Co. Ltd.
The cooperation of the many residents of the area is gratefully acknowledged.
PREVIOUS GEOLOGICAL WORK
The earliest geological observations of the Rainy Lake area were made by Dr. J. J. Bigsby (1851, 1854).
Systematic mapping of the Rainy Lake area was undertaken by
A. C. Lawson of the Geological Survey of Canada (Lawson, 1888).
His conclusions regarding the relative ages of sedimentary and volcanic rocks resulted in much controversy, a summary of which has been given by Goldich et al (1961, p.36-40)• Or. Lawson
remapped part of the Rainy Lake area in order to review his earlier conclusions (Lawson, 1913) and the western boundary of this map coincides with the eastern boundary of the present map-area.
The Emo area to the west was mapped by the Ontario Department of Mines (Fletcher and Irvine, 1954)® The part of Koochiching
County in Minnesota which lies adjacent to the present map-area has not been systematically mapped geologically, though a description of some outcrops and a tentative geological map have been published (Thiel, 1947). TOPOGRAPHY
The area is divided into two topographically distinct units along a line extending approximately from Dance P.0, to Fort Frances.
To the southwest the overburden is heavy, muskegs are extensive, outcrops are mostly small and relief is very low. To the northeast bedrock exposures are abundant and maximum relief is about 100 feet.
Natural drainage is poorly developed in the area of low relief, but many of the muskegs have been partially drained by ditching. Large muskegs also occur in the northeastern part of the area but the drainage pattern, which approximately parallels geological structure, is better developed than to the southwest.
NATURAL RESOURCES
Agriculture
The area adjacent to the Rainy River was early recognized to be suitable for farming. T. 0. Bolger (1886) on the basis of limited observations, considered that the soil "cannot be excelled
in any part of the Dominion".
The 1961 Census states that in the municipalities of Lavallee
and Alberton, which includes all the townships in the map-area except Miscampbell and G riesinger\ there were 177 farms and a farm
population of 795» The farm population has since been decreasing.
Of 43,400 acres of farm land, one third was "improved land" and
over one fifth was "woodland". Hay and oats accounted for 77 percent
and 20 percent respectively of the 11,000 acres of crops, the
remainder being wheat, barley and mixed grains.
Gross annual income from agriculture in the whole of the
1. Miscampbell township, which is nnoi*ganized, had twelve farmers in 1961. There are no farms in Griesinger township. D istrict of Rainy River was just over two million dollars from
1958 to 1964. In 1964 the sale of forest products from deeded lands made up almost 37 percent of this income, dairy products and livestock each accounted for about 29 percent, and the remainder was from the local sale of farm produce and from the sale of hay, seed, grain and woolo
F o re s ts
An early demand for timber was established during construction of the Canadian Pacific Railway. Material for ties and poles was cut from both sides of the Rainy River and water driven to the present site of Kenora.
The first sawmill was established at Fort Frances in 1873»
Reconstruction has since taken place a number of times, the most continuous lumber operation being that of J. A. Mathieu Ltd. from
1922 to 1954.
First production of paper from the mill of Fort Frances
Pulp and Paper Company to o k p lace in 1914, f iv e y e a rs a f t e r completion of a dam and powerhouse. The company amalgamated with others in 1941 to form the Ontario-Minnesota Pulp and Paper
Company.
Logs supplied to the mills are jack pine, spruce, balsam and p o p la r, in order of importance. In addition to timber from deeded lands, 7676 cords of pulpwood and a small amount of fuelwood and sawlogs were harvested from Crown Lands in the map-area during the
1964-65 season. It is estimated that 40 percent of the forest in the area has been cut over.
Two major forest fires have occurred since the area was
settled. The first, in 1910, destroyed much of the timber on farm lands. The second, in 1938, spread over most of Dance and
Griesinger townships and Indian Reserve 16D and took the lives of
20 persons in Dance township.
Fish and Game
Rainy Lake, a summer vacation area, contains an ample supply of pickerel and northern pike for angling, ^little commercial
fishing is still undertaken in the area, the value in 1964 being about 5000 dollars.
Within the northeast half of the area deer are abundant. Moose and grouse also are present. Fur-bearing animals in order of abundance
are beaver, otter, muskrat, mink, fox, squirrel and wolf. The value of raw fur from the eight traplines in the map-area was about 3300 dollars in the 1964-65 season.
Inhabitants
Fort Frances, which in 1965 had a population of 9420, is the
principal centre of population. The Couchiching Band, which owns
Indian Reserves 16A, 16D and 18B, and the Strangecoming Band, which owns Reserve 18C, had populations of approximately 520 and
25 respectively. The total number of residents in the map-area in
1965 was estimated to be 10,800. The pulp and paper m ill is the
principal industry and the main employer. GENERAL GEOLOGY
The consolidated rocks of the Rainy River D istrict are all of Precambrian age. Two major fault zones which join about 60 miles east of Fort Frances (O.D.M. Map 2115) divide the D istrict into three distinct geological areas.
Belts of predominantly metavolcanic rocks draped between granitic batholiths characterize the north area. Metasedimentary
schists and gneisses intruded by small oval stocks of granite
are characteristic of the south area. In the central area or
fault wedge metasedimentary and metavolcanic rocks are present
in about equal amounts and basic intrusive rocks are more abundant than to the north or south.
Most of the map-area lies within the fault wedge (Figure 3)•
The relative ages of the metasedimentary and metavolcanic rocks
are not known. Interlayering of the two rock types is indicated,
and in the map-area it is suggested that the oldest rocks are of volcanic origin and that these are exposed in northern Miscampbell township. The dominant structural features appear to be doubly
plunging folds, the cores of which have been invaded by basic to
acid intrusions. Diabase dikes cut all other rocks.
Pleistocene and Recent deposits cover a large part of the
area and the only '’mineral” production from the area has been
from these deposits. TABLE OF FORMATIONS
CENOZOIC R ecent: Stream, lake, bog and swamp deposits Pleistocene: Sand, gravel, boulders, silt and varved clay
Unconformity
PRECAMBRIAN Late Basic Intrusive Rocks: D iabase
Intrusive Contact
Fault Zone Gneiss: Banded recrystallized mylonite
Gradational Contact
Equigranular Acid Intrusive Rocks: Pegmatite, aplite Massive pink quartz monzonite Massive grey granodiorite and quartz monzonite, foliated grey granodiorite and migmatite
Gràdational Contact
Porphyritic Acid Intrusive Rocks: Porphyritic monzonite and quartz monzonite Porphyritic granodiorite Hornblende-biotite monzonite
Intrusive Contact
Early Basic Intrusive Rocks: Amphibolite (in part may be recrystallized volcanic rock), metagabbro Metadiorite, metagabbro, hornblendite
Intrusive Contact
Basic and Intermediate Metavolcanic Rocks: Agglomerate, flows and tuff Hornblende-biotite schist (in part may be metasedimentary)
Metasedimentary Rocks: Iron formation Greywacke, biotite schist, paragneiss Arkose, sandstone, siliceous schist Conglomerate, pebbly greywacke
Basic Metavolcanic Rocks: Hornblende schist, recrystallized basalt Lapilli tuff BASIC METAVOLCANIC ROCKS
The rocks which are considered to be the oldest in the map-area are probably of metavolcanic origin» They are best exposed in northeastern Miscampbell township in a northwest plunging remnant of an anticlinal fold.
Two rock types are distinguishable. Dark biotite hornblende schist containing white lenses has been called lap illi tuff.
The white la p illi average about 2 mm wide and 25 mm long and constitute from 25 to 40 percent of the rock. A fragmental origin is supported by the presence of a number of darker
"bombs" up to 25 cm. long. Closely associated with this lensy rock is massive medium grained amphibolite believed to be an altered basaltic flow.
Near the anticlinal axis extending from northern Crozier township to the south shore of Stanjikoming Bay a number of remnants of presumed volcanic origin occur. The largest of these, in northeastern Crozier township, is considered to be altered basaltic tuffs and flows. Hornblende and plagioclase
(andesine) in grains 0.1 to 0.3 mm long are present in about equal amounts, and sphene and epidote are abundant.
An outcrop of coarse hornblendite in southern Miscampbell township is seen in thin section to consist in part of fine grained clinopyroxene and plagioclase, enclosed and partially replaced by large hornblende grains. The rock may have been a highly metamorphosed basalt.
The basic rocks described above are equated with those outcropping on Reef Point and Gash Point of Rainy Lake, immediately east of Stanjikoming Bay. Metasedimentary Rocks
The mica schists of the eastern part of Rainy Lake have been studied in some detail (Lawson, 1913, p.6-35). Essentially they are quartz-feldspar-biotite rocks. Zoisite, megnetite, muscovite, garnet and cordierite are present in some rocks.
Chemically the schists are sim ilar to shales (Lawson, 1913,
p .3 L ).
Similar schists occur in parts of the Fort Frances area,
especially along the Rainy River. Close to the river, near
the west outskirts of the town of Fort Frances, the highly
dragfolded schists include siliceous siltstones, slate, iron
rich slate, greywacke, fine felsic tuff and pebbly conglomerate.
A complex metamorphic history is indicated by garnet which has
been partly replaced by chlorite (penninite) which in turn has
been partly replaced by red-brown biobite in a nodular schistose
greyw acke.
The oldest metasediments in the area are considered to be
greywacke and rusty quartz pebble conglomerate which occur in
a zone extending from northwestern Crozier township to the
peninsula between Stanjikoming and Haymarsh Bays. These are in
turn overlain by the rocks described above.
The youngest metasediments are considered to be those in
which iron formation is abundant. These rocks are biotite
rich greywackes, typically composed of about $0 percent
plagioclase (An3O),25 to 30 percent quartz, 20 to 25 percent
biotite and traces of epidote, magnetite, sphene, hematite,
pyrite and apatite. Igneous looking textures of paragneiss, presumably of greywacke origin, indicate the possibility of melting having taken place. The iron formation consists of thin magnetite rich layers interbanded with the greywacke.
The magnetite is coarse in most places and unaccompanied by h e m a tite .
The relationship of the metasedimentary and metavolcanic rocks is assumed to be complex so that the above indicated sequence of metasedimentary rocks very likely contains interlayered pyroclastic and flow material.
BASIC AND INTERMEDIATE METAVOLCANIC ROCKS
Metavolcanic rocks which are interpreted as lying above the main body of sedimentary rocks outcrop in two parts of the m ap-area.
East and west of the strong magnetic anomaly in western
Crozier township the rocks are mostly of pyroclastic origin.
Basaltic and andesitic tuff with minor agglomerate and thin flows occurs in southeastern Devlin township. In western
Crozier township agglomerates predominate, with some tuff and pillow lavas. Garnet is present in the basic rocks of both these areas. The metavolcanics of northwestern Crozier township are andesitic, and in part possibly dacitic.
The hornblende schists of western and southwestern Dance township were considered by Fletcher and Irvine to be of metasedimentary origin (Map 1954-2). These rocks reveal no primary banding and consist of 50 to 60 percent hornblende,
30 to 35 percent plagioclase (about An50), 5 percent quartz and minor magnetite, sphene and epidote. The w riter believes that they are compositionally similar to a basalt, and that along strike in Burriss township they lie above the^sediments.
EARLY BASIC INTRUSIVE ROCKS
Rocks classified as basic intrusions are those with a coarse grained texture and a mafic mineral content in excess
of 25 percent. Two types occur in the area; in one the outline of the intrusion is irregular and original textures are preserved and in the other an elongate, concordant shape is characteristic
and original textures are largely obliterated by amphibolitization.
Devlin-Burriss Intrusion
A large part of Devlin and Burriss townships is apparently underlain by basic intrusive rocks,. Granitic rocks have
intimately invaded these basic rocks in places. Outcrops are
few in the two townships.
Fletcher and Irvine (1954, p.17) have described hypersthene
gabbro from adjacent Lash and Carpenter townships but encountered
difficulty in defining its lim its because of lack of outcrop.
The fresh rock contains 50 to 60 percent labradorite feldspar and
the remainder consists of two pyroxenes. The Devlin-Burriss
and Lash-Carpenter intrusions may originally have been connected.
The acid intrusions which occur between the above mentioned
basic bodies have modified the mineralogy of the Devlin-Burriss
portion. The original rock is considered to have been a two
pyroxene gabbro containing 60 to 65 percent plagioclase. Some quartz was introduced into the gabbro, the plagioclase was partly altered and partly replaced by microperthite, and the pyroxenes were largely altered to amphibole which in turn was partly replaced by biotite. Apatite is an accessory mineral.,
On the basis of the present composition the rock would be called a diorite or, where microperthite is more abundant, a syenodiorite.
Woodchuck Island Hornblendite
A number of outcrops of coarse hornblendite occur at the southwest corner of Woodchuck Island and small islands in
Rainy Lake lying to the west and southwest. The hornblendite contains angular blocks of gneissic biotite granodiorite and is cut by aplite and pegmatite.
Black amphibole grains, up to 12 mm long and almost equidimensional, constitute about 80 to 90 percent of the rock. The remainder is mostly carbonate and feldspar.
Additional work is required to determine the origin of this ro c k .
Amphibolite and Metagabbro
Coarse grained black weathering amphibolite and metagabbro outcrops in a number of places in the area, mostly along zones which are elongate parallel to the strike of enclosing metasedimentary and metavolcanic bands. The widest and most persistent of these zones extends from near Boffin Lake to the east edge of the map-area.
Both the amphibolite and metagabbro consist primarily of plagioclase (andesine) and amphibole. The metagabbro retains traces of original igneous textures but grades into the amphibolite which does not. Quartz, epidote, biotite and magnetite occur as minor minerals in most of the rocks.
Chlorite, sericite and sphene normally are present as alteration products. The rocks are probably basaltic in composition, sim ilar to Lawson’s basic facies of syenite
(1913, Analysis II, p.9l). They may be recrystallized flows, coarse flows, sills or dikes.
PORPHYRITIC ACID INTRUSIVE ROCKS
Several elongate bodies of porphyritic acid intrusive rocks were mapped in the area. With one exception these rocks occur within or adjacent to metasedimentary and raetavolcanic
ro c k s.
Frog Creek Quartz Monzonite
Pink weathering porphyritic quartz monzonite, grading
imperceptably into porphyritic granodiorite and porphyritic monzonite, extends from the northwest corner of Crozier township to the outlet of Stanjikoming Bay. Twinned microcline
phenocrysts, 5 to 35 mm long, in most places have a preferred
orientation which is parallel to the flakes of biotite in the
ro c k .
The microcline phenocrysts, which are set in a groundraass
of oligoclase grains 1 to 3 ™ long, contain minute round
inclusions of the oligoclase and of quartz. Evidence for growth of phenocrysts in place is seen in most of the rocks examined. Irregularly shaped small microcline grains make up a small proportion of the feldspar in some rocks. The oligoclase is twinned in part and slightly zoned and commonly is a little altered to sericite
and replaced at the edges by microcline. Quartz, which constitutes up to 27 percent of the rock, tends to occur in elongate clusters and may in part be introduced. Biotite also occurs in clusters with some epidote, magnetite, sphene, and hornblende.
The rock appears to have been a granodiorite into which potash, and possibly silica, have been introduced. Porphyritic monzonite and porphyritic granodiorite represent variations in which introduction of potash and introduction of silica, respectively, have predominated.
One half mile to the south of this quartz monzonite and parallel to it lies a narrow body of similar rock containing
20 to 25 percent quartz. The relationship of these rocks to the metasediments may have a bearing on their origin.
Sand Bay Hornblende-Diotite Monzonite
Similar to the above but less porphyritic and more mafic rich is the body of monzonite to quartz monzonite which extends southwest from Sand Bay through Fort Frances. The north edge of this monzonite lies about 2000 feet northwest of the C.N.R. in eastern Mclrvine township and coincides approximately with the north shore of Rainy River in
southwestern Mclryine township. The south edge is very poorly defined but, on the basis of outcrops in Minnesota, the monzonite
is about 6500 feet wide. It extends to the east of Sand Bay and is continuous with Lawson1s Pukamo Island mica syenite-gneiss
(1913, p.67-89).
The rock consists of microcline grains 5 to 10 mm long
in an aggregate of oligoclase and microcline grains 1 to 3
mm long. The coarser microcline has replaced the finer
grained feldspars. Biotite and hornblende, together with a
little epidote, magnetite and sphene, are concentrated in
clusters. The mafic clusters constitute 1$ to 25 percent of th e ro c k .
Miscampbell Porptyitic Granodiorite
Lying within the nose of the folded metavolcanics in
northeastern Miscampbell township is white weathering granodiorite
with very large (2 to 5 cm.) anhedral microcline crystals
developed sparsely throughout. The rock also contains 25 to 30
percent quartz and about 5 percent biotite, both of which
occur predominantly in lenses averaging 3 mm wide and up
to 5 cm. lo n g .
The granodiorite appears to be similar to other granodiorites
in the area, except for the development of the large microcline
crystals and the quartz lenses. Its distribution, however, is
curious in that it extends along strike of foliation as far as
Stanjikoming Bay where it appears to nose out. This "canoe”
shaped body, lying in the core of the doubly plunging antiform
may be stratigraphically controlled. Halfway Inlet Porphyritic Quartz Monzonite
A body of grey weathering porphyritic quartz monzonite
lies north of the fault zone gneiss in the vicinity of Halfway
Inlet. The twinned euhedral microcline crystals are 2 to 3 cm.
long and diversely oriented in most places. The body appears
to be a phase of the surrounding granodiorite but relationships
are obscure.
EQUIGRAMULAR ACID INTRUSIVE ROCKS
The granitic rocks which underlie much of the northern
half of the map-area are mostly similar compositionally. Two
main rock types have been distinguished.
Massive to Foliated Granodiorite and Quartz Monzonite
Medium grained grey to buff weathering granodiorite is the
most abundant rock type. Unzoned equidimensional plagioclase
grains (An20 - An25) occurs with microcline, quartz and biotite
in typical igneous textures. Total feldspar makes up about 70
percent of the rock, of which less than one-fifth is normally
microcline. The quartz content of the rock is in most places
close to 25 percent, part of which is lensy in some rocks and
may be introduced. The biotite flakes are about 0.5 mm long
and may lie in a preferred orientation.
A variation of the above occurs where the granodiorite
has intimately invaded metasediments. Mineralogically this
results in an increased biotite content, distinct foliation,
and locally, increased magnetite content. The relationships
in these migmatite zones are complex so that it is in many places difficult to distinguish the biotite rich granodiorite from the "granitized" metasedirnent.
Massive Pink Quartz Monzonite
Pink weathering quartz monzonite containing less than
2 percent mafic minerals occurs in a number of places in the area. It forms mappable units in the southeast quarter of
Dance township and the extreme northeast corner of the area.
Contacts with the grey granodiorite are gradational, however, and the two appear to be closely related.
Mineralogically the pink rock contains just over 70 percent feldspar about half of which is plagioclase (An30) and half microcline. Quartz grains are strained and generally evenly distributed throughout the rock. Biotite, epidote, sericite and magnetite together make up about 2 percent of the ro c k .
Some of the microcline appears to have replaced plagioclase.
It is possible that the pink quartz monzonite represents a phase of the grey granodiorite very low in iron and magnesia and richer in potash.
FAULT ZONE GNEISS
In the area east of Standingstone Point, Lawson (1913,p.91-96) has described two intimately related gneissic rock types which he has termed banded biotite granite gneiss and porphyroid gneiss.
The former, he concluded, owes its banding to viscous flow in a heterogeneous magma. The latter is recognized as a cataclastic rock. Both rock types are considered to be marginal facies of batholiths, and the porphyroid gneiss is in part considered to have been intruded as a dike.
Similar rocks occur in the map-area and, as in Lawson's area, the rocks are gradational and occur along a continuous zone. The rocks are here called the fault zone gneiss.
Alternate pink and grey layers, one to two inches wide, are typical of the banded rocks. The pink layers contain more potash feldspar and less biotite than the slightly coarser grey layers. On well exposed outcrops many of the layers may be seen to pinch out over a length of ten to twenty feet. Larger feldspar crystals have developed along certain of the layers and a re up t o 15 mm long in some ro c k s.
Typically the rock consists of grains of plagioclase and potash feldspar about 0.5 to 1.5 mm long, set in a matrix of finer grained plagioclase, quartz and potash feldspar. The coarser plagioclase grains are mostly twinned, cracked and strained and exhibit incipient alteration to albite and sericite.
The matrix plagioclase grains average 0.1 mm long, are untwinned, and are intergrown with quartz. Potash feldspar is mostly untwinned orthoclase, the larger grains of which contain minute inclusions of quartz. Biotite grains are mostly less than 1 mm long and only slightly oriented parallel to schistosity. Epidote is a common accessory mineral and magnetite, apatite and sphene are also present.
The fault zone gneiss is not a typical mylonite in that there has been much recrystallization. Lawson (1913, p.92) describes the minerals of his banded gneiss as being "perfectly fresh" and textures as being "hypidiomorphic granular". Within the present map area all examined rocks from the fault zone gneiss show evidence of strain or crushing, and the large potash feldspar grains show evidence of growth in place. It is concluded that the fault zone gneiss developed under conditions of extreme stress, while the rocks were at elevated temperatures. Local rem eltin g may have o ccu rred .
LATO BASIC INTRUSIVE ROCKS
D iabase
A number of northwest trending brownish weathering diabase dikes occur in the area. The dikes, which are up to 200 feet wide, cut all other consolidated rocks of the area.
Lawson (1888, p.147-163) has described in detail the characteristics of diabase dikes of the area. The following points are some of those which he listed in summary:
1. Sharp contact 2. Passage from coarse texture at centre to aphanitic at sides. 3. Granular character towards centre, porphyritic at sides. 4. Prevalence of quartz and garnets towards centre and absence near contact. 5. Presence of enstatite at sides, absent towards centre. 6. Augite plates which are made up of an interlocking mosaic of irregularly shaped grains. 7. Uralitization of augite. Examination of diabase from the map-area has confirmed most of the above points.
LIMESTONE
Lawson (1913, p.110-111) has described "a small outcrop of cream coloured fossiliferous limestone, emerging from beneath the glacial drift1' in Section 1? of Crozier township.
He admitted that it may have been a huge erratic, but was of the opinion that it was not. Fossils in the rock were of upper Ordovician (Richmond) age.
During the present survey efforts to locate the limestone were unsuccessful. The writer spoke to local residents who had similarly searched in vain.
It is possible that outliers of Paleozoic rocks occur in the heavily drift covered area. Large erratics were not observed, but their absence at the surface may have resulted from their use as a source of lime. The writer considers that the limestone described by Lawson was an erratic which was subsequently removed. MAGNETIC PROPERTIES OF THE ftOCKS
Results of aeromagnetic surveys of the area, compiled, at a scale of one inch to four miles on Map 7O91G> are presented greatly simplified in Figure 2.
The most prominent magnetic anomalies occur over bands of raetasediments which contain iron formation (compare Figures 2 and 3)• Metasediments with low magnetic intensity near the west and east edges of Figure 2 are those which Fletcher and
Irvine (1954) and Lawson (1913) consider to be the oldest rocks of their respective areas» Metasediments with low magnetic intensity occur in the south central part of the area, and these are considered to be lower in the sequence than the magnetite bearing metasediments.
Metavolcanic rocks within the map-area are mostly of low magnetic intensity. East of Rainy Lake, however, a band of magnetite bearing basic metatuff has a high magnetic
in te n s ity .
Granitic rocks across the north half of the area have
low magnetic intensities. In the central part of the map-area the higher magnetic intensity of the granodiorite is undoubtedly
due to the greater number of inclusions of metasediments and matavolcanics. The large basic intrusion in the west central
part of the area is a magnetic low. F IG U R E 2 STRUCTURAL GEOLOGY
The interpreted structural geology of part of the Rainy Lake area is shown in figure 3. It must be emphasized that very few localities have been observed in Which top directions could be determined, and that the interpretation has been made almost wholly on the basis of the geometry of the geological plan.
The writer considers that most intrusions have occurred close to fold axes and have not seriously distorted the fold pattern in the older rocks.
F olding
Axial traces of major fold axes in the Rainy Lake area are oriented approximately east-west. The anticline which passes through the stratigraphically critical area of Rice Bay
(Lawson, 1913) is considered to split to the west and thus, in the map-area,three anticlines are indicated, their axes diverging to the west. Foliation and bedding plane attitudes are consistent with steeply north dipping axial planes.
Drag fold axes on the other hand do not conform to any simple pattern, and a series of cross folds is assumed to be present. The location of axial traces of these cross folds as determined by oppositely plunging drag folds would conform closely with the location as determined by the distribution of rock types (figure 3).
F a u ltin g
Small scale movement along slip planes and shear zones is apparent in many outcrops throughout the map-area. Most of this F IG U R E 3 movement has been parallel to foliation or bedding, and air photo lineaments which parallel foliation may be surface
expressions of strike-slip faults.
A major east-west fault zone extends through Dance and
Griesinger townships. The cataclastic nature of rocks from
this zone was first recognized by Lawson (1913, p.93-96) in the area east of Rainy Lake. Fifty miles east of Lawson’s map-area Hawley (1929, p.16-21) provided evidence for a major fault between sediments to the south and volcanics to the north, and both Irvine (1963, p.20) and Kaye (1967, p.24-25)
considered that the fault extended east through their map areas in the vicinity of Lac des Mille Lacs.
West of Hawley’s area Moore (1939, p.2l) suggested that the fault died out, and in the Bennett-Tanner area Young (i960, p.14) did not recognize any east-west faulting. Nonetheless it appears, from aeroraagnetic data and air photograph interpretation, that the fault zone is continuous from Dance township to
Lac des Mille Lacs. West of Dance township the fault may be traced an additional 10 miles along a quartz monzonite zone
(O.D.M. Map 1954-2) so that the fault has a total length of at least 175 miles. Within the map-area, and as far east as
L ittle Turtle Lake (Lawson, 1913# p.94) the fault zone has a width of from 1500 to 3æ0 feet and a dip from vertical to
steep north. The aeromagnetic pattern, the rock type distributon
and small scale structural data all indicate right-handed movement
(north side moved east relative to south side). Slickensides in central Dance township plunge five to ten degrees west. Hawley
(1929, p.17-21) recorded dips close to vertical and plunges thirty degrees east, and suggested that the movement had been right-handed.
A linear topographic depression, which from Shoal Lake to Rainy Lake is occupied by the Seine River, marks the contact between metasediments to the south and metavolcanics to the north. Adjacent to this depression many of the rocks are highly sheared, and the zone is considered to be a fault zone (O.D.M.
Map 2115).
To the west, the proposed fault is covered by thick glacial deposits, but can be traced on aeromagnetic maps through Woodyatt and Roddick townships. Air photographs show at least two parallel lineaments, one coinciding with the aeromagnetic anomaly, another lying to the south along the Rainy River. The presence of a fault beneath the north lineament would satisfactorily explain the truncation of the southwest trending magnetic area in Crozier and Devlin townships. Movement would probably be right-handed. Dips of sheared rocks along the Seine River are vertical.
It is proposed that the fault zone crossing the north part of the map-area be called the Little Turtle-Ouetico fault, and that the fault zone crossing the south part of the map-area be
called the Seine River fault. Cross-folding within the fault wedge and movement along the faults may be genetically related. PLEISTOCENE
The first systematic study of the unconsolidated surface deposits of the Rainy River area was by Johnston (1915).
Additional studies were made by Zoltai (1961) while undertaking a regional compilation of Pleistocene geology. Their findings are summarized below.
Four glacial movements are recorded in the area. The oldest, from the north-northwest, deposited about 6 feet of calcareous till. This till was highly oxidized, indicating that a prolonged interglacial period followed. The next glacial advance was from the northeast, extending beyond the area and depositing sandy till with an abundance of boulders but little clay. Most of the glacial striae recorded in figure 4 refer to this glacial movement.
Following a short interglacial period, a glacier advanced from the west spreading thin calcareous till as far east as
Fort Frances. A marginal lake was formed as this glacier retreated. Gritty clays were deposited and then exposed as the lake drained.
The final ice advance was from the northeast, but its terminus was near the north edge of the map-area where a moraine was built up. A second lake was formed during the retreat of this glacier. Lake action denuded many outcrop areas and more varved clays were deposited in topographic lows.
Figure 4 indicates the types of surficial deposits which occur in the map-area. FIGURE 4 PLEISTOCENE FEATURES, FORT FRANCES AREA l p ro d u ctio n o f th e a re a t o d a te . S ig n ig ic a n t o ccu rren ces
o f precious metals and base metals are not known in the area although abundant sulphides have been encountered at one location. A number of bands of iron formation occur in the area but exposures indicate that the iron content is low.
Mathieu Property
From 1953 to 1955 an attempt was made to evaluate the mineral potential of 13,120 acres in the townships of Devlin,
Crozier, Woodyatt and Roddick. The land, most of which was owned by Mr. J. A. Mathieu and the remainder of which was optioned to him, is heavily drift covered. Only two outcrop areas, both in Section 2 of Devlin township, are known to occur on the property.
An outcrop of coarse diorite containing inclusions of andesite occurs near the western boundary of Section 2, Devlin township. At the east edge of the outcrop are veins of quartz containing tourmaline, ankerite and pyrite, which fill north- northwest trending gash fractures. Two small pits have been blasted, but a grab sample of mineralized vein material taken by the writer assayed only a trace of gold.
In the eastern part of Section 2, Devlin township andesitic to basaltic tuff, agglomerate and flows outcrop over a strike
length of 1700 feet. Along the southeast side of the outcrop,
quartz-tourmaline veins carrying a little pyrite occur in
places, and some work has been done on them. An assay of a grab sample of this vein material revealed only a trace of gold.
Following dip needle traverses in 1954> ten holes were drilled on the property. Three of the holes were drilled southeast and east of the large outcrop, intersecting andesitic to basaltic meta volcanic rocks. Minor pyrite was observed in the core of one hole. Along the north line of Section 1, Devlin township, approximately one mile northeast of the large outcrop, four more holes were drilled. Minor chalcopyrite was cut in mixed meta sediments and meta volcanics of the easterm ost of these holes.
Three holes in Section 7 of Crozier township all intersected grey granite, two of the holes passing through vertical depths of 214 and 263 feet of overburden respectively before hitting bedrock. Topham and Morris Properties
Rock outcrop on the property of W. Topham in the southeast corner of Lot 11, Concession IV, Burriss Township, is in part capped with gossan. In 1906 a syndicate formed by 13 local residents undertook to develop the property for its iron
content. The following year a twelve foot long trench was
sunk and, according to Mr. Topham, an offer of $30,000 for the mining rights was rejected. Ko further work was done until
1958 when a second trench forty feet long was blasted by
Stratmat Ltd., about ten feet west of the original trench.
Property to the west was staked by Noranda Mines Ltd. in 1953, but work was confined to Carpenter township.
An airborne geophysical survey by Texas Gulf Sulphur
Company in 1965 in d ic a te d th a t th e main anomalous a re a la y to the south of the trenched zone. Mr. Topham’s property and the
adjacent property of R. Norris were optioned by Texas Gulf and
ground geophysical and geological surveys were followed by the
drilling of four holes.
The surface geology of the property is shown in figure 5.
Foliated grey rocks, probably a mixture of basic tu ff and meta
sediments lie to the north and a complex of paragneiss and
granodiorite lie to the south. The contact may be a fault
zone. Small gossan-covered intrusions of altered gabbro
containing some pyrite occur in places near the contact.
All d rill holes intersected metasediments, altered gabbro
and granodiorite. The altered gabbro contains some pyrrhotite
and pyrite, but the heaviest sulphide concentrations occur in
the metasedimentary rocks, particularly where these are most siliceous. Pyrrhotite in excess of ten percent occurs in all the holes, over widths of from 35 feet to 156 feet. Specks of chalcopyrite were seen in places but all of the sulphide zones were devoid of base metals except in trace quantities. F IG U R E 5 IRON Iron formation occurs in a number of metasedimentary bands
in the map-area. The strongest magnetic anomaly is in the western
part of Crozier township but, lying under an estimated 200 feet of
overburden, the iron formation here has not been intersected by
drilling. Development of heavily drift covered iron deposits
near Emo is being considered by Great West Mining and Smelting
Corp. Ltd., and should this development take place the
Crozier iron formation should be examined.
Great River Mining and Development Syndicate
Fifteen claims were staked in 1965 by Great River Mining
and Development Syndicate along the magnetite bearing metasediments
west of Boffin Lake. Ground magnetometer work was followed by
the drilling of one hole in September 1965.
The metasediments are mostly greywacke but in a number of
places thin magnetite-rich bands constitute from one quarter
to one half of the total volume. The maximum observed width
was about 25 feet, in which the iron content was estimated to
be about 25 percent.
Magnetic anomalies occur, however, over widths of up to
one quarter mile so that greater concentrations of magnetite
may be present. The magnetite is sufficiently coarse grained
to be readily separated from the host rock.
The single hole, drilled to a depth of 545 feet, intersected
the iron formation at a point between lines of the ground
magnetometer survey. The rock encountered consisted of
metagreywacke and paragneiss, with a few thin bands of iron
formation. The maximum width of iron formation in the d rill
hole was eight feet, and this was estimated to contain about
30 percent iron. SAND, GRAVEL and CRUSHED STONE
The sand and gravel industry is important to the economy of the Fort Frances area. A number of pits have been developed, most of which lie along the southwest side of bare bedrock areas (figure 4)•
Rural road construction and maintenance requirements in the map-area have, since 1962, averaged about 50,000 yards per year. Much of this has come from the Department of Highways’ "Labelle1’ pit in Lot 8, Concession IV of Dance township, where a crusher is located. A second crushing plant is located in the pit of George Armstrong Co. Ltd., in
Section 18 of Mclrvine township. This company, which in
1967 commenced crushing quarried bedrock, supplies most of the sand and gravel required by the town of Fort Frances,
About 25 percent of the material in the Armstrong pit is waste, 45 percent is sand and 30 percent is gravel (G. Armstrong, personal communication). The Labelle pit is estimated to contain less waste but to have a similar sand to gravel ratio. Analyses of coarse aggregate by the Department of Highways shows that in both pits about 75 percent of the material is granitic and 25
percent is coarse to fine basic rocks and greywacke. The
Armstrong pit gravel was overlain by clay and capped by about
6 inches of limestone-bearing gravel.
Crushed rock for construction of the Rainy Lake causeway
has been obtained from a quarry in Indian Reserve 18B, about
one-half mile west of the approach to the causeway. All of the pits are privately owned except the Labelle pit which is owned by the Department of Highways. There are, therefore, no figures available on yards removed or gross value. It has been estimated, on the basis of pit dimensions, that about 1.2 million cubic yards of sand, gravel and crushed
stone has been removed from tho pits, of which close to one
half would have come from the Armstrong pit and one quarter
from the Labelle pit.
PEAT
The demand for peat moss for horticultural purposes in
the United States and Canada has, from 1953 to 1963, resulted
in a three-fold increase in production for the Canadian peat
moss industry. A critical factor in the development of peat
bogs is accessibility to transportation and markets and,
therefore, many of the bogs north of the Rainy River may
warrant examination.
A preliminary evaluation of some bogs in the area has
been presented by Graham and Tibbetts (1965)» They have
suggested that bogs in east central Burriss township and
sections 11 to 14 of Devlin township "merit further
investigation". They have also suggested small scale
production of peat moss from sections 17, 20, 22 and 23 of
Crozier township might be possible, and.that sections 21 and
22 of Woodyatt township and section 26 of Mclrvine township
might be developed as market gardens.
Research into the possibilities of using humified peat
as a binder in the pelletizing of iron orc is being undertaken FIGURE 6 PRODUCTION OF PEAT MOSS, ARCTIC PEAT MOSS CORP. LTD.
The results may have important implications for the iron ore industry of the Rainy River D istrict.
ARCTIC PEAT MOSS CORPORATION LTD.
The Arctic Peat Moss Corporation Ltd. commenced operations in
1941 on property located in Sections 7 and 8 of Crozier township.
According to Leverin (1946) the slightly humified peat moss has a depth of about four feet. The peat was cut by hand and dried in the field prior to processing and baling in a plant located on the p ro p e rty .
A total of 17,168 tons of peat moss valued at $596,090 was produced up to cessation of operations in 1952. Yearly production is shown graphically in figure 6. REC0I1MBNDATI0N3 FOR PROSPECTORS
The well exposed part of the map-area is largely granitic and contains very little sulphides» The fault zone gneiss may be the most favourable area for prospecting. Traces of molybdenite have been found in the gneiss, and in adjacent
Kingsford township a molybdenite showing has been uncovered in the gneiss.
The potential of the poorly exposed part of the map-area is not readily assessed. Both metasedimentary and metavolcanic areas contain minor amounts of pyrite, and traces of chalcopyrite and gold occur in places.
During the 1964 field season some geochemical work was done on stream sediments over the large basic intrusion in Devlin and
Burriss townships. Results were negative, possibly because of very high water levels throughout the summer. Depth of overburden may make geochem ical work im p ra c tic a l.
Further assessment of the peat bogs of the area should be undertaken as these are large and well located with respect to
transportation.
SELECTED REFERENCES.
T exts
Bigsby, J.J. (1851), Erratics of Canada; Quart. Jour. Geol. Soc. London. Vol. 7, Part I, p. 215-238 (1854), The Geology of Rainy Lake, South Hudson Bay; Quart. Jour. Geol. Soc. London, Vol. 10, Part I, p. 215-222. Bolger, T.O. (1886), D istrict of Rainy River; Rept. Commissioner Crown Lands Prov. Ont., p. 48-51.
Fletcher, G.L. and Irvine, T.IJ. (1954), Geology of the Emo Area; O.D.M. V ol. 63, P art 5.
Goldich, S.S. et al. (1961), The Precambrian Geology and Geochronology of Minnesota; Minn. Geol. Surv. Bulletin 41.
Graham, R.B. and Tibbetts, T.E. (1965), Evaluation of Peat Moss in Some Bogs of the Rainy River D istrict, Ontario; Dept. Mines Tech. Surveys Bulletin T.B. 65.
Hawley, J.E. (1929), Geology of the Sapawe Lake Area; O.D.M. Vol. 38, Part 6, p.1-58.
Irvine, T.N. (1963), Western Lac des Mille Lacs Area; O.D.M. Ceol. Rept. No. 12.
Johnston, W.A. (1915), Rainy River D istrict Ontario, Surficial Geology and Soils; G.S.C. Mem. 82.
Kaye, L. (1967), Eastern Lac des Mille Lacs Area; O.D.M. Geol. Rept. No. 48.
Lawson, A.C. (1888), Report on the Geology of the Rainy Lake Region; G.S.C. Ann. Rept. Vol. VIII.
(1913), The Archean Geology of Rainy Lake Re-Studied; G.S.C. Memoir No. 40»
Leverin, H.A. (1946), Peat Moss Deposits in Canada; Can. Dept, Mines and Resources Rept. No. 817.
Thiel, G.A. (1947), The Geology and Underground Waters of Northeastern Minnesota; Minn. Geol. Surv. Bulletin 32.
Young, W.L. (I960), Geology of the Bennett-Tanner Area; O.D.M. Vol. 69, Part 4»
Zoltai, S.C. (1961), Glacial History of Part of Northwestern Ontario; Proc. Geol. Assoc. Can. Vol. 13, p.61-83. Maps
Geol. Surv. Canada. Map, 266 a. The Kenora Sheet, 1938.
Ont. Dept. Mines. Map 1954-2. The Emo Area. Map P286. Fort Frances Area.
O.D.M.-G.S.C. Aeromagnetic maps No. 1158G, 1159G, 1166G, 11676, 7O91G
Ont. Dept. Lands Forests. Map S.165. Kenora-Rainy River Surficial Geology, 1965.
U.S. Geol. Survey. Map G.P.-472. Aeromagnetic Map and Geologic Map of Northeastern Minnesota, 1965.
ONTARIO DEPARTMENT OF MINES
PRELIMINARY GEOLOGICAL MAP NO. P. 286 FORT FRANCES AREA FORT FRANCES AREA DISTRICT OF RAINY RIVER
District of Rainy River Scale: 1 inch to 1 mile
Location: The town of Fort Frances is situated in the southeast corner of the N.T.S. Reference 52 C/ll, 52 C/l4, 52 C/l2, 52 C/l3 map-area. Previously mapped areas adjoin to the east (Lawson, 1913) and to O.D.M. - G.S.C. Aeromagnetic Maps: the west (Fletcher and Irvine, 1954)- 1158C, 1159^, Hh6G, 116 7 G Mineral Exploration: Pits have been sunk by prospectors on a number of small sulphide zones and iron formation bands. Systematic ground geophysical, geochemical or geological surveys had not been undertaken in any part of the area up to the summer of 1964. General Geology: The oldest rocks of the area are of volcanic and sedimentary origin. The actual sequence of the volcanic and sedimentary units has not been determined, but part of the sediments are continuous with the Coutchiching sediments described by Lawson (1913)- Most of the volcanic and sedimentary rocks occur in the southern heavily drift-covered part of the area. Banded hornblende and hornblende-biotite schist occupies a position which structurally appears to be the. oldest in the map-area. These rocks may be of sedimentary or tuffaceous origin, and probably include basic flows. Lapilli tuff is associated with hornblende schist in northeastern Miscampbell township. Conglomerate containing small elongate quartz pebbles appears to form a marker horizon across northern Crozier township and eastward to Rainy Lake. The conglomerate is about 25 to 180 feet wide where exposed, and is interbanded with greywacke, siliceous schist and possibly volcanic flows or tuff. Minor conglomerate occurs with siliceous schist, greywacke and acid tuff near the west end of Fort Frances. Thin iron-rich bands occur with the conglomerate in the southern part of the area and with well banded greywacke in the vicini ty of Boffin and Wasaw lakes. Most of the volcanic rocks appear to lie structurally above the dominant ly sedimentary section. Basic and intermediate flows, agglomerate, and tuff occur, and aeromagnetic data indicate that iron formation may be interbanded. Garnets have formed in some of the basic volcanic rocks. The older basic intrusive rocks underlie much of Devlin and Burriss town ships and contain small inclusions of finer grained volcanic rocks. The ba sic igneous rocks were originally diorite and gabbro but some of the plagio- clase has been replaced by microcline. Coarse-grained pyroxenite occurs in southwestern Miscampbell township, and about one mile southeast of Hanging- stone Point on Rainy Lake. The pyroxene has been partly altered to amphibole in these rocks. Medium- to coarse-grained amphibolite is associated with the sedimentary rocks and contacts appear to be concordant with the sedimentary rocks. These rocks may be sills, coarse flows, or possibly recrystallized limy sediments. The terms monzonite and quartz monzonite have been used for the coarse grained grey-weathering rocks which in places contain large pink phenocrysts of microcline. The rocks are mostly foliated and contain less than 15 percent quartz. Inclusions of fine-grained sedimentary and volcanic rocks and coarse amphibolite occur in the monzonite and quartz monzonite. Acid intrusive rocks underlie much of the well exposed northeastern part of the area. Most of the rocks are well foliated and in places grade into paragneiss or contain numerous dark inclusions. Pink massive granite occurs in parts of Dance township and in the northeastern part of the map area. Granodiorite containing a few very large pink feldspar grains forms a distinct unit adjacent to the hornblende schists in northeastern Miscampbell township. All of the acid intrusive rocks are cut by thin aplitic and pegmatitic veins. Mylonite occurs in an east-west zone which cuts across the area near its northern edge. The rock is so well banded in places that it appears to be sedimentary, but contacts are gradational with the surrounding acid intrusive rocks. Porphyroblasts of feldspar have developed in places. Diabase dikes cut all of the other rocks and are up to about 200 feet wide in places. Small diabase dikes commonly occur close to the larger dikes. Trends of most dikes are similar but offsets are numerous and do not appear to be related to faulting. Upper Ordovician limestone, reported to occur in section 17 of Crozier township (Lawson 1913, p. 110) was not found during the present survey. Pleistocene sand, gravel and clay deposits are very thick in parts of the southern portion of the area. Over 100 feet of such overburden has been reported in the adjacent area to the west. Limestone pebbles are common in gravels as far north as the line which approximately divides the well exposed part of the area from the poorly exposed part. Structural Geology: Graded bedding has not been recognized in the sedimentary rocks. Only one outcrop of pillow lava was seen and it is small and poorly exposed. Structural interpretation has been made on the basis of rock d istri bution and on structural data obtained from the area to the west. The approximate positions of east-west fold axes are shown on the map. North-south cross folding is probable and the assumed position of a north-south anticline in Crozier township is shown. The east-west mylonite band occupies a zone of major faulting and shearing, and terminates the structures which occur to the south. Other recognized zones of shearing are small. Economic Geology: Most of the small sulphide occurrences in the area have been sampled by the writer. The maximum gold content found was 0.01 ounces per ton. Chalcopyrite occurs with pyrite in a few places. Geochemical tests of stream sediments were undertaken on the LaVallee River. Results were neg ative, possibly because of high water levels in 1964. Small specks of molybdenite were seen at a number of places in the mylo nite. Other sulphides were not noted in this zone. The outcrops of iron formation which were examined contained a large pro portion of greywacke interbands. The magnetite is coarse and would be easily concentrated, however, and it is possible that areas occur west of Boffin Lake SOURCES OF INFORMATION in which the amount of greywacke is small compared to the amount of magnetic iron formation. Geology by J. C. Davies and assistants, 1964.
Recommendations: Geochemical testing of the area underlain by basic intrusive Basemap derived from aeromagnetic maps II58G, 1159G, 1166G and H 67G rocks at a time of normal water levels may produce positive results. Copper with corrections in detail by J. C. Davies. and nickel occur in the basic rocks of the Emo area to the west. Ontario Department of Mines: Map No. 1954-2. Ontario Department of Investigations of the iron formation west of Boffin Lake may uncover Mines and Geological Survey of Canada: Aeromagnetic Series Maps Nos. magnetite-rich zones sufficiently wide and free from greywacke to permit mining. 1158G,' H 59G, 1166G, 1167G.
Bibliography: Lawson A.C.: The Archean Geology of Rainy Lake Re-studied, Geological Survey of Canada Map No. 98A. G.S.C. Memoir 40, 1913. Magnetic declination approximately 4° East, i960. Fletcher G.L. and Irvine T.N.: Geology of the Emo Area, C.D.M. Vol. LXIII, pt. 5, 1954. Issued 1965*