Transcriber’s Note
When italics were used in the original book, the corresponding text has
been surrounded by _underscores_.
Some corrections have been made to the printed text. These are listed in
a second transcriber’s note at the end of the text.
CANADA
DEPARTMENT OF MINES
GEOLOGICAL SURVEY BRANCH
HON. W. TEMPLEMAN, MINISTER; A. P. LOW, LL.D., DEPUTY MINISTER;
R. W. BROCK, DIRECTOR.
PRELIMINARY REPORT
ON
GOWGANDA MINING DIVISION
DISTRICT OF NIPISSING
ONTARIO
BY
W. H. COLLINS
[Illustration: Colophon]
OTTAWA
PRINTED BY C. H. PARMELEE, PRINTER TO THE KING’S MOST
EXCELLENT MAJESTY
1909
No. 1075
13739-1
CONTENTS
PAGE.
I. Introduction.
1. Location and area 5
2. Statement of work 5
3. History of development 6
II. Summary and Conclusions 8
III. General Character of District 10
1. Means of access 10
2. Topography 11
3. Drainage 14
4. Flora and fauna 15
IV. General Geology 16
1. Outline of Geological history 16
2. Table of formations 18
3. Keewatin 18
General features 18
Obushkong area 18
Duncan Lake area 20
Pigeon lake area 21
Unfinished areas 22
4. Laurentian 23
General features 23
Relations to other formations 24
5. Huronian 25
General features 25
Basal conglomerate 26
Greywacke slate and quartzite 27
Upper conglomerate 27
Arkose 28
Structural features and disturbances 28
Relations to other formations 29
Origin and correlation 31
6. Post-Huronian eruptives 32
Quartz diabase 32
Character of intrusion and distribution
relative to older systems 32
Macroscopic character 33
Microscopic character 34
Local description 36
Age 37
Olivine diabase 38
7. Pleistocene 38
V. Economic Geology 40
1. Silver 40
Distribution 40
Surface indications 40
Structure of veins 41
Composition of veins 41
Local description 42
Future possibilities 44
2. Copper 45
3. Iron ores 45
Hematite 45
Magnetite 46
4. Asbestos 46
Distribution 46
Origin 47
ILLUSTRATIONS.
1. Frontispiece—View at Foot of Duncan Lake 5
2. Diagram illustrating the structure of large hills 12
3. Diagram illustrating geological relationships 16
4. View looking north from middle of Duncan Lake, 550 ft.
hill in distance 20
5. West Branch Montreal River, near Mosher Lake 22
6. Fifth portage on West Branch of Montreal River, showing
Huronian slate 30
7. Inclined Huronian Beds, Duncan Lake 32
R. W. BROCK, Esq.,
Director Geological Survey Branch,
Department of Mines.
SIR,—I beg to submit the following preliminary report upon work done in
the Gowganda Mining Division during the field season of 1908.
I have the honour to be, sir,
Your obedient servant,
W. H. COLLINS.
CHICAGO, March 8, 1909.
[Illustration: Fig. 1. View at foot of Duncan Lake.]
PRELIMINARY REPORT
ON
GOWGANDA MINING DIVISION
DISTRICT OF NIPISSING, ONTARIO
BY
W. H. COLLINS.
--------------
INTRODUCTION.
LOCATION AND AREA.
The portion of the Montreal River region with which the present report
deals lies in the extreme western part of the District of Nipissing, in
the neighbourhood of N. Lat. 47·45, and about 85 miles north of the town
of Sudbury. It includes an area of 350 square miles, most of which lies
between the two large branches of the Montreal river, which empties into
Lake Timiskaming on the west side.
STATEMENT OF WORK.
The Algoma-Nipissing boundary line was run in 1897 by Alexander Niven,
O.L.S. These surveys, with representations of some of the larger lakes,
had been compiled by the Geological Survey of Canada on a scale of 16
miles to one inch;[1] and on a scale of eight miles by the Crown Lands
Department of Ontario. With these as a guide and summary of the existing
geographical knowledge it was decided to make a micrometer and prismatic
compass survey of both branches.
During the past season a prismatic compass and micrometer survey was
made of both branches of the Montreal river and all navigable waters
adjoining them. This work was done by Messrs. T. Firth, J. R. Marshall
and A. B. Moffatt. Most of the small ponds lying some distance from a
canoe route were located by rapid chain and compass methods, and in a
few instances west of Duncan lake by a compass triangulation from
hilltops; the larger ones have been measured by pacing or chaining, the
smaller ones sketched. Some of the more prominent hills were located by
triangulation, and their heights ascertained by aneroid determinations.
The water levels were obtained in the same way, but cannot as yet be
referred to sea-level.
The geological work was performed by the writer, assisted by Mr. Firth.
Besides a thorough examination of all the surveyed routes, a systematic
examination of the intervening country was carried out as closely as the
time and varied requirements of the area would permit. As this was the
first season spent in the district and a continuation of the work is
anticipated, the present results are offered as incomplete and subject
to revision.
HISTORY OF DEVELOPMENT.
Since the discovery of silver cobalt ores at Cobalt in 1903, exploration
has shown the adjacent country to be locally enriched by mineral veins
of the same character and genesis. At the close of 1907 an area 65 miles
long in a north and south direction, and about 45 miles wide, extending
from Lake Timiskaming and the Ontario-Quebec boundary westward, was
known to include at least ten mineralized districts besides the
principal one at Cobalt, of which the most recently found lie near the
Montreal river. It has also become known gradually that these deposits
are closely connected with the post-Huronian quartz diabase of the
region. This diabase was known to extend for a very considerable
distance farther west, leading to the inference that more discoveries
were to be expected in that direction. The spring of 1908 saw interest
centred upon the Montreal River finds, and early in the season active
exploration had commenced. The Montreal river, up to that time, had not
been regarded with special favour, the diabase being considered of no
economic importance, but with the new conceptions gained by exploitation
of the silver-cobalt district, this formation in the west began to
attract attention. At the beginning of the field work, early in July, a
considerable number of prospecting parties were on the ground, as far
west as Duncan and Pigeon lakes. During July and August this movement,
encouraged by the succession of mineral discoveries that were being made
near Bloom and Everett lakes, increased steadily, in spite of the
scarcity of available topographical and geological information dealing
with the region.
Early in August discoveries of native silver were made almost
simultaneously by Messrs. Mann and associates, and by Messrs. Crawford
and Dobie on the west side of Gowganda lake, but were not made public
until the first week in September when the claims were recorded at Elk
Lake and specimens were exhibited. Twenty-four hours later the leading
canoes of an inrushing body of prospectors had reached the new field,
and within two weeks most of the promising country between Gowganda and
Elkhorn lakes and northward had been staked, regardless of the mineral
discoveries necessary to validate the claims. Since then numerous
discoveries have been made, and the news of a new silver field, until
recently confined to the Montreal River and Cobalt districts, has spread
widely. As a consequence, a mid-winter rush is now in progress, and
hundreds of prospectors, regardless of deep snow and severe cold, are
entering the country. Much inadvisable staking will be done, no doubt,
before spring, but the disappearance of the snow and reopening of river
navigation will certainly be followed by an increased rush of
prospectors.
SUMMARY AND CONCLUSIONS.
The results obtained from the field work indicate that the Montreal
River district does not differ essentially from the Cobalt or other
neighbouring districts. The surface has the same rugged monotony of the
pre-Cambrian peneplain, relieved somewhat by ridges of Huronian, which
stand from 300 to 550 feet above the general level. The country is well
watered, and offers exceptional facilities for canoe travel. Pleistocene
deposits are thin, and nearly everywhere the rock formations are well
exposed.
A basement complex underlies the entire region, either appearing at the
surface or hidden beneath areas of Huronian sediments. This basement
consists largely of Laurentian biotite and hornblende gneisses, with
patches of vertically foliated, Keewatin schists caught up in the
former; the intervening contacts forming indefinite zones, in which
intrusive action is manifested. In this report, for convenience, this
complex will be referred to as the Archæan. The Archæan possessed a
peneplanated surface, not greatly different from the present one, which
is well preserved where overlain by erosion remnants of Huronian
sedimentary rocks, but which at other points has been further denuded.
The Lower Huronian rocks are of clastic nature, consisting in ascending
order, of conglomerate, greywacke, slate and quartzite, which pass
conformably into an upper conglomerate; while a granite-like, arkose
member is believed from its similarity to rocks of the same character in
the Cobalt area, to be possibly of later, Middle Huronian age. They are
remarkably well preserved, and show only slight indication of
disturbance. A later intrusion of quartz diabase has developed a system
of dikes in the Archæan and large tongue-shaped areas in the Huronian
believed to represent sills of several hundred feet thickness, lying in
the bedding planes of the Huronian sediments. The diabase magma has been
notably differentiated, giving rise to forms ranging from gabbroid to
syenitic in composition, and to younger aplite dikes. With the diabase
is associated a group of veins containing an association of cobalt and
silver ore identical with that of Cobalt and vicinity. The veins cut
both diabase and aplite as well as the Huronian, and are therefore
younger, but probably not much younger than the aplite, since it
contains some of the minerals found in them. The distribution of the
veins so far as known is confined to the larger diabase areas, the dikes
and smaller bodies being undifferentiated and unmineralized; but the
Huronian adjacent to the diabase also contains veins, somewhat more
siliceous, yet evidently of the same age as the others. Alteration and
impregnation of the country rock has taken place to an unknown, but,
presumably, limited extent. Some of the veins are remarkably rich, and
many of them occupy persistent, well defined fissures. The cause of
these fissures is not yet known, but they appear to be too large and
continuous to have resulted from contraction alone.
GENERAL CHARACTER OF DISTRICT.
MEANS OF ACCESS.
In 1908 the most used route to the Montreal River district started from
Latchford, a station on the Timiskaming and Northern Ontario railway, 93
miles north of North Bay. From this village, situated on the Montreal
river, a line of small steamers made daily trips up the river for 56
miles to Elk lake. This up-river terminus was then a rapidly growing
village. In the spring of 1907 it consisted of a single shack and a
cluster of prospectors’ tents; when seen in October, 1908, it had a
population of over 200 people and all the conveniences of a village of
that size, including a post office with regular mail service, a mining
recorder’s office, lately removed from Latchford, general stores,
hotels, etc.
From this point, which forms the headquarters and point of departure for
Montreal River prospecting parties, a variety of routes lead westward.
The Montreal river may be ascended to the Forks, where its two branches
unite, but the stream is rapid, and, especially in high water, difficult
of ascent, besides offering a very indirect route to the most frequented
districts. The Bloom Lake route, a map of which accompanies the Report
of the Bureau of Mines, Ontario, 1907, was, during 1908, very commonly
used. This route, 9 miles in length and consisting of a chain of small
lakes and portages, leads, from a point on the main river 11 miles above
Elk Lake, directly west to the East branch. From the East branch a
multiplicity of courses are open. Both East and West branches are easily
navigable, being for the most part lake-like and sluggish, broken by
occasional swift river-like stretches in which rapids occur. Good
portages exist at all these places so that travel either up or down
stream presents no difficulty. Numerous good canoe routes connect the
two branches and Duncan and Pigeon lakes, and allow of easy access to
the country in the west.
But since the writer left the field the great influx of prospectors has
caused marked improvements in the connexion of the area, especially the
Gowganda district, with outside railway points. A sleigh road has been
opened from Charlton on the Timiskaming and Northern Ontario railway to
Elk Lake, and thence about 32 miles south-westward to the east shore of
Gowganda lake. It is understood that heavy grades make travel somewhat
arduous, but the trip from Elk Lake is made easily in a day.
On February 4, a sleigh road about 65 miles long was completed between
Gowganda and Sellwood, the present terminus of the northern extension
from Sudbury of the Canadian Northern railway. A regular stage route now
connects Sellwood, Phoenix, Burwash lake, Elkhorn lake, and Gowganda.
However, neither the road to Elk Lake nor that to Sellwood are yet
suitable for summer use, so that with the coming of spring, canoe travel
must be again resorted to. It is also reported that preliminary surveys
for the extension of the railway to Gowganda are in progress. Meanwhile
a business centre is springing up on the east side of Gowganda lake. A
sawmill was put in operation on February 3, but has since been stopped
owing to its location within a government timber reservation. A town
plot has been laid out at the foot of the lake and lots are now
purchasable from the Ontario Department of Lands, Forests and Mines.
Buildings are being erected as rapidly as the supply of material
permits. A branch of the Royal Bank of Canada has been opened, and the
Canadian Bank of Commerce and others propose to be on the ground within
a short time. Postal connexions have been established via Sellwood, and
as soon as possible a mining recorder’s office is to be opened. So
swiftly are events transpiring that before the present report takes
printed form, this paragraph will be in need of revision. However, only
the developments of a permanent nature and of essential interest to
prospective visitors to that region have been given. For the 1909 field
season Gowganda will probably be the headquarters for prospecting
parties in the neighbourhood of the East and West branches and Wapus
creek.
TOPOGRAPHY.
Attention is given here rather to the details than the general aspect of
the country. It exhibits the usual monotonous succession of low rocky
hills and lake-containing depressions, the even horizon seen from the
summit of any large hill, being only rarely notched by a prominence of
unusual height. In the spring of 1908 virtually the whole area was
forested, but during September the extreme dryness of the country and
the unusually large number of camping parties combined to cause bush
fires over much of the country between the East and West branches. The
vegetable loam has been removed from extensive tracts leaving the rock
formations exposed, but the charred tree trunks have fallen so as to
cover the burnt districts with a ‘slash,’ which greatly impedes
cross-country travel, so that what has been gained in one respect is
more than counterbalanced in another. Especially is this the case in the
country west of Gowganda and Obushkong lakes, and near the Forks.
The general surface may be characterized as of comparatively low-relief,
the hills not often rising over 200 feet, but here and there over the
country are conspicuous elevations, visible at long distances, which
form useful landmarks and from whose summits comprehensive birds-eye
impressions of the surrounding country are possible. Structurally they
appear to be, in a few cases, resistant knobs of Keewatin, which project
well above the general peneplain level, but more commonly they are
tilted ridges of Huronian. A characteristic representative of the latter
type forms a long ridge beginning a mile and a quarter north-east of
Duncan lake and extending thence for several miles in a north-easterly
direction. The south-east side of this ridge slopes gently at an angle
corresponding with the dip of the beds, but the north-west face is an
abrupt cliff dropping almost perpendicularly for about 400 feet to a
flat sandy plain which extends westward and northward for several miles,
beyond which are other monadnock-like knobs. The accompanying diagram is
intended to represent the structure in vertical cross-section.
[Illustration: Fig. 2.—Vertical section across Huron Ridge, North of
Duncan Lake.]
Another ridge of similar character, standing 550 feet above the level of
Duncan lake, is visible from the ridge just described and from points on
Duncan and Otto lakes, and adjoining country. Its position as indicated
on the map is about four miles north of the large island in the middle
of Duncan lake, a view of it from this point being shown in fig. 4. In
this case the east face is perpendicular. A prominent hill of the same
kind is visible from Obushkong lake, lying a short distance to the
north-west of that body. Just west of Mosher lake as represented in fig.
5, two round hills of about equal size rise 300 feet above the water
level. The more southerly of the two is of Keewatin, while that to the
north is composed wholly of diabase, Huronian lying around the base of
each. Bold, but less individualized elevations are common in the
neighbourhood of Kenisheong lake, and other localities. All these hills
are markedly rocky and free from soil.
Less conspicuous than these great masses are certain minor, but
persistent features which are directly referable to geological
conditions. Within Huronian areas there is a distinct tendency toward
the development of a system of parallel ridges similar in structure and
mode of origin to the hill at the north-east of Duncan lake. This
feature is developed with special regularity in the southern part of the
wedge between Duncan lake and the West branch, where a succession of
north and south ridges alternate with strips of swampy ground. The
western faces of the ridge are bare and cliff-like, while the eastern
slopes are gentle, well soil-covered and forested.
The post-Huronian diabase is an equally potent topographical factor. Its
surface is one of marked irregularity, but the peculiarly distinctive
features occur at its contacts with the Huronian. These contacts appear
to be zones of low erosive resistance, and are commonly coincident with
ravines, walled on one side by diabase, on the other by Huronian. Small
lakes may occur at intervals along them as, for example, between Firth
lake and the West branch. This erosion feature is well shown by the
configuration of Gowganda lake, where diabase bodies are unusually
abundant; both of the long arms to the north-west lie in trough-like
depressions marking the edges of the eastern diabase mass. The same
tendency in an incipient condition is observable on the east side of the
large peninsula where a series of three land-locked bays extend along
the contact between the eastern diabase mass and the Huronian. Near the
middle of Duncan lake, a diabase-Huronian contact which crosses the lake
diagonally is marked by two deep bays, one extending to the north, the
other southward. While this tendency is an evident one it is not to be
understood as invariable; the large island in Duncan lake between the
two above-mentioned bays is sufficient to indicate that contacts may lie
in high ground, yet even here there are minor features indicating the
contact zone to be structurally weak.
Another less explicable topographic peculiarity becomes apparent only
upon scrutiny of the drainage system. A brief consideration of the map
shows that both East and West branches follow peculiar zig-zag courses
running north for a short distance, then turning abruptly east, this
feature recurring repeatedly. In some instances the east-west portion of
both branches lies in the same line. In the case of Zigzag lake and
adjacent portions of the West branch this feature is repeated with an
almost conventional regularity, which precludes attributing it to chance
causes. Many of the smaller lakes—Foot lake, for instance—exhibit the
same character on a small scale. This abnormality has been commented
upon by investigators in the country to the east, the courses there,
however, being N.E.-S.W. and N.W.-S.E. Regional faulting is suggested in
explanation. The canyon-like east and west walls of Zigzag lake suggest
such conditions, but a discussion of the matter must be deferred until
further data can be collected.
DRAINAGE.
All the drainage water escapes by way of the Montreal river, whose two
chief tributaries are the East and West branches, the latter being
considerably the larger. The East branch is without feeders of important
size, but the West branch receives a large creek, the Wapus, from the
south, and a considerable volume of water enters through Duncan lake.
In common with most rivers traversing the pre-Cambrian region, this
water system is marked by a volume of dormant water enormously greater
than that being transported at any given moment. With few exceptions the
many small tributary brooks rise in lakes or groups of lakes
surprisingly large in size, compared with the volume of the out-flowing
streams; Otto and Lehmann lakes are drained by a rather sluggish rivulet
8 feet wide and 6ʺ deep, although their combined area is about two
square miles. The larger streams themselves are only successions of
irregular lake expansions which empty from one to another by short,
river-like portions containing rapids and falls. The descent is
therefore accomplished by a succession of abrupt steps rather than an
evenly graded slope. This juvenile condition is directly ascribable to
the geological character of the country; soil deposits are insignificant
in quantity, leaving exposed a resistant and uneven rock floor in which
the streams are unable to carve channels for themselves. Failing to do
so they select the readiest egress by filling up impervious rock basins
and spilling over at the lowest points into lower ones. In consequence
of the scantiness of soils and frequency of natural settling basins, the
waters of the whole system are free from suspended matter, and hence
lack of an effective graving instrument. Exceptions to this general
character occur in the extensive sand plain to the north and west of
Duncan lake, where the several small creeks that traverse it are of
ordinary fluvial form and gradation, and the waters of which transport
large quantities of sand to Duncan lake.
FLORA AND FAUNA.
Where not recently burned the country is fairly well forested, the
density and character of growth being dependent upon soil and drainage.
The best timber is in low ground and near watercourses where conditions
for growth are most favourable and the probability of fire least. Recent
fires have done much damage around Nest, Obushkong and Gowganda lakes.
Probably the best timber lies near Duncan lake. Trees do not grow very
large as a rule and are not especially good for making lumber, but
provide an abundant supply of materials for pulpwood, railway ties, fuel
and for mine use.
White pine is the most valuable species, but although individuals attain
thicknesses of 20ʺ to 40ʺ they are too scarce to render this timber
worth the search. Good red pine is more abundant. Jack pine is a very
common tree, especially in sandy districts, _e.g._, north-west of Duncan
lake; but is small and worthless. The common and most widely distributed
species are spruce, balsam, cedar, poplar, white and yellow birch.
Tamarack is not abundant. Clumps of small red maples were seen to the
south-west of Pigeon lake.
The East and West branches are not well suited for carrying logs as
there are extensive lake expansions without current on each and the
rapids are shallow. Excellent water-power is obtainable at the 40 foot
fall on the West branch above Fort Matachewan.
Wild animals are not abundant, and will probably become less so as the
country is occupied by prospecting and mining camps. Moose were
plentiful in 1908 and some black bears were seen. As a source of food
the abundance of pickerel and pike is of much greater importance. Brook
trout do not occur in the Montreal River waters, but are caught farther
to the west and north.
GENERAL GEOLOGY.
OUTLINE OF GEOLOGICAL HISTORY.
Though the geology of the region presents considerable complexity of
detail, the general historical facts are distinct and go to show that
the whole complex of formations and systems is capable of separation
into four major divisions widely different from one another. The mutual
relationships of these divisions, a knowledge of which is essential to a
thorough comprehension of the geology, are succinctly expressed by the
accompanying diagram.
[Illustration: Fig. 3.—Diagram illustrating geological relationships of
Montreal River district.]
The oldest division, the Keewatin, comprises a complex association of
metamorphosed rocks, principally eruptive, characterized by
well-developed, secondary schistosity and prevalently dark colours. They
dip at angles approaching 90° and range in texture from soft, fissile,
chorite schists to fine-grained gneisses or altered diabases. In the
Montreal River district the Keewatin areas are not entirely visible,
being overlain by other rocks, but they are thought to represent the
bottoms of trough-like folds, produced by the upward intrusion of
igneous matter which now constitutes the Laurentian. The latter forms
the second division, its origin being apparent from the foregoing
statement. It is wholly igneous, consisting of granite and allied
coarsely crystalline rocks essentially pale-coloured owing to their
richness in quartz and feldspars. Gneissic structure has been developed
in varying degrees, so that all gradations between granite and gneisses
exist; but it never attains the perfection found in the Keewatin. Near
their contacts with the Keewatin, the gneisses are apt to contain dark
bands and ribbons of the latter so highly crystalline as to conceal
their identity.
Wherever visible the surface of the Keewatin and Laurentian presents an
irregular, deeply worn appearance, the result of extremely protracted
exposure to erosive agencies. To the best of geological knowledge the
same conditions hold where they lie buried under the Huronian,
indicating that a great period of denudation separates the latter from
the Archæan. The combined Keewatin and Laurentian, or Archæan system, is
therefore to be conceived as forming at all points in the district an
ancient denuded foundation or floor upon which rests the much younger
Huronian system.
This third division is, in the Montreal River district, wholly
sedimentary and easily distinguished from the other rocks by its bedded
structure and clastic nature. As it is the only sedimentary system
represented, its members are not easily confused with any other,
especially as their original structure is not obscured by metamorphic
alteration. Locally this is not strictly true; in the vicinity of
diabase intrusions they have been hardened and shattered so as to
simulate the Keewatin, but the zones of alteration are narrow and
readily identified by their gradation into adjacent areas of less
altered types. At present the Huronian forms a discontinuous rock mantle
over the Archæan, formerly more complete, but now worn through in places
so as to expose portions of the crystalline basement.
The fourth division includes all eruptives known to be younger than the
Huronian. Owing to the discontinuity of the latter it is not always easy
to decide what rocks should be included in this group, for in some cases
rather fresh-looking eruptives occur in the Keewatin which probably
would also intrude the Huronian were it present; lacking the necessary
information their chronological position can be only loosely fixed. By
far the most extensive and important of the post-Huronian eruptives is
the diabase with which the silver deposits are associated. This
penetrates both Archæan and Huronian, but is ordinarily distinguishable
by its unusual freshness, dark colour, and crystalline appearance. In
certain cases, to be described subsequently, it may be confused with
certain other diabases. Magmatic differentiative processes have evolved
diabase types of very dissimilar appearance and mineralogical
composition, of which a pink aplite occurring in dike form is the most
extreme. Olivine diabase dikes are also present in the region, but in
far less abundance.
Of little importance are the sands and gravels of glacial origin which
lie thinly in the depressions and lower lands of the present glaciated
surface.
TABLE OF FORMATIONS.
The geological events may be briefly enumerated in ascending order as
follows:—
Deposits of glacial débris and weathering products of present surface.
Erosive period with glaciation.
Diabase intrusions.
Huronian sedimentation.
Erosion period.
Laurentian intrusion.
Keewatin.
KEEWATIN.
_General Features._
This system is considered as a complex assemblage of metamorphosed
igneous rocks whose common and marked characteristics are pronounced
alteration and deformation, accomplished in pre-Huronian times. A
limited amount of sedimentary material, such as the iron ore formation,
is also represented. These old diabases, porphyries and related types
are much altered and have developed a more or less uniform schistosity
through the secondary development of micaceous minerals, but in other
respects the complex shows extreme inconstancy and variety from point to
point. For this reason the various localities are separately described.
By inspection of the map three fairly well defined areas are
distinguishable, in addition to which are portions of several others.
_Obushkong area._
Much of the country between Obushkong and Firth lakes is underlain by
Keewatin. On the east, south and west sides, these rocks disappear
beneath the Huronian or are interrupted by masses of diabase, but on the
north they merge into Laurentian gneiss, the contact with which is
ill-defined. Although some of them retain much of their original massive
character, well defined schistosity is the dominant feature. The schists
stand vertically or at angles little less than 90° and trend in a
general east and west direction. A series of compass observations made
at points over the whole area show the strike to vary from N. 65° E. to
S. 75° E.
One of the most abundant rock types is a stratiform, finely speckled
hornblende gneiss or schist, the black hornblende cleavage faces giving
it a glistening appearance on newly broken surfaces. It is quite fresh,
perfectly crystalline and usually eminently fissile, but sometimes
grades into a nearly massive dioritic form of undoubted igneous nature.
Extensive exposures occur around Gould lake where the gneiss is
traversed by numerous stringers of quartz, rusty in colour from the
oxidation of pyrite. It is also well exposed near McLaughlin and
McIntosh lakes and to the east and south-east of Foot lake. A fine
grained chlorite schist of dull greenish black colour is common in this
and all the other areas in the district. To the north-east of Serpentine
lake it appears as a sheared phase of a weathered diabase, but it has
also been derived from porphyry, exposures being seen between Foot and
Obushkong lakes, where feldspar phenocrysts appear on weathered surfaces
of the schist as pale, oblong spots. What is probably iron formation was
observed at points 25 chains south of Gould lake, and 10 chains south of
a little pond just east of Serpentine lake. Both outcrops consist of
banded, grey quartzite interlaminated with chlorite schist, but
magnetite-bearing bands were not found. Occasionally, narrow bands of
pale grey, felsitic schists may be seen among the more common darker
rocks. From evidence obtained at various points, these appear to have
resulted from the decomposition and shearing of granite porphyry dikes
probably connected with the Laurentian, and which penetrated the
Keewatin during the time of Laurentian intrusion. Serpentine was
observed between Foot lake and Obushkong at 20 chains from the latter.
The surface is covered by a loose network of fine seams of asbestos
which weather white and render the rock somewhat conspicuous. Its
recognition is further simplified by the dull green, amorphous
appearance of fresh surfaces, the slight translucence of thin edges and
the glistening green seams of asbestos which traverse it abundantly. The
same rock is more extensively exposed on the south-west of Serpentine
lake and on Firth lake half a mile north of the portage leading to the
former, also at less than a quarter of a mile south of this portage. It
is associated with and derived from a dark green massive rock to which
the name wehrlite is applicable, and a more detailed description of
which appears later.
_Duncan Lake Area._
A Keewatin area of considerable extent lies between Duncan lake and the
West branch in the vicinity of L’Africain and Beaverhouse lakes. Unlike
the Obushkong area, the prevalent strike of the schists is nearly north
and south, the greatest divergence noted being 25° W. In the former case
Laurentian lies to the north, while in the present one it occurs on the
east; in both cases the schistosity coincides approximately with the
direction of the line of contact. On account of the swampy character of
the country just west of the river and the scarcity of outcrops, this
area was not completely explored, but wherever examined the Keewatin, as
in the Obushkong area, consists predominantly of hornblende and chlorite
schists, greenstone and decomposed diabase; but serpentine was not
found. A nearly black diabase containing small grains of pyrite was
observed 20 chains south-east of the southerly extending bay on Duncan
lake, and outcrops of the same material were traced for about half a
mile northward. Probably the same type was encountered just north of
Beaverhouse lake and at some other points. Its unfoliated condition and
fresher appearance than the adjacent rocks lead to the opinion that it
is really post-Keewatin and intrusive, but the absence of younger rocks
with which to correlate it, renders its exact age indeterminable. This
rock exhibits enough resemblance to fractured contact edges of the
post-Huronian diabase to make their distinction in the field rather
difficult. At half a mile east of the south end of L’Africain lake is
diabase which from lack of sufficient data has been mapped as Keewatin,
although it may be identical with the post-Huronian variety. L’Africain
lake lies in glistening hornblende gneiss with which are associated
ribbons of a coarser hornblende gneiss belonging to the Laurentian of
the area farther east. Greenstone and chlorite schists are the principal
rocks around Beaverhouse lake. Associated with them and to the
northward, are dikes of light coloured, granite porphyry, usually only a
few feet wide, in some of which the original massive structure remains,
while others show various gradations toward a felsitic, sericite-bearing
schist. The isolated patch of Keewatin indicated on the map as occurring
about half a mile east of the wide portion of Duncan lake, is a well
foliated green schist in which oval white spots represent squeezed
feldspar phenocrysts.
[Illustration: Fig. 4. View looking north from middle of Duncan Lake,
550ʹ hill in distance.]
_Pigeon Lake Area._
West of Pigeon lake and the Montreal river, much of the country examined
is underlain by Keewatin. Schistosity is less developed than in either
of the preceding areas. The rocks are chiefly diabases and porphyry much
decomposed and locally squeezed. Diabase occurs on both sides of Pigeon
lake near its central islanded part and along the bay which extends
south to Brush lake. An original diabase structure is sufficiently well
preserved to show lath-like feldspars in hand specimens, but frequently
the rock is altered to a chloritic mass. Around the bay extending toward
Brush lake, this old diabase forms a rude wall intersected by a
reticulating system of fractures filled with calcite, the resultant
structure simulating that of a breccia. Shear zones seen on the east
shore exhibit a pseudo-conglomeratic structure, the more resistant
pieces of diabase having been partially rounded by the shearing movement
and embedded in a matrix of finely pulverized rock matter. The same
diabase apparently occurs all along the Montreal river where it follows
the Algoma-Nipissing line. About half a mile above Pigeon lake it forms
a 90 foot cliff on the west side of the river, near the top of which is
a fresher looking, unfoliated eruptive. The form of this body was not
ascertained, but microscopic examination of the specimen taken,
determines it to be a hornblende lamprophyre, so probably it is a dike
or thin sheet. The rock is fine-grained, dark green in colour and
characterized by stout prisms of hornblende about one-quarter of an inch
long, embedded in a finer, microcrystalline ground mass. Under the
microscope it appears much decomposed. This rock was also observed near
mile post 67 of the Algoma-Nipissing boundary, near the east end of the
63 chain portage leading to Breese lake and at other points, in all
cases the exposures being of small extent.
In the last mentioned locality the predominant rock is an altered
porphyry of ash grey colour. Around Porphyry lake it occurs in a fairly
massive, easily recognizable condition, the feldspars showing as square
white spots one-quarter of an inch in diameter in a grey, ground mass.
On Breese lake it has been squeezed to a felsite schist, striking N. 20°
W. In small amounts it is associated with post-Huronian diabase on the
hills lying near the Montreal river and just south of the 63 chain
portage.
The 300 foot hill south-west of Mosher lake is composed of a fine
Keewatin greenstone whose surface is curiously weathered so as to
suggest a spheroidal structure. It is marked off into round areas a foot
or more in diameter by a sinuous network of weathered-out grooves. The
main body of the rock is ordinary fine-grained greenstone, but the
enclosing grooves have been formed in porphyritic zones about an inch in
width. Among other types of less abundant distribution is an actinolite
rock seen by the unassisted eye to consist of a felty mass of acicular
crystals of actinolite, sometimes half an inch long. This rock was
observed 12 chains east of the islanded part of Pigeon lake; also at
points west of Montreal river below Pigeon lake.
_Unfinished Areas._
The Keewatin formation occupies the space between Near lake and the West
branch, only part of which has been mapped. The rocks of this area are
well foliated, standing as usual, vertically, and striking about N. 60°
E. The exposures on the east shore of Near lake are entirely of fissile,
chlorite schist, abundantly traversed by small barren quartz veins.
Farther east the chlorite schist gives place to glistening, stratiform
(laminated) hornblende gneiss with which are associated bands of a
coarser hornblende gneiss, evidently the equivalent of granite. In one
locality the stratiform rock contains subangular fragments of the
coarser variety, quartz and a greyish eruptive rock, the resultant
structure resembling that of a metamorphosed conglomerate or breccia. As
some of the brecciated fragments occur near by in continuous bands
within the stratiform gneiss, the clastic structure is to be ascribed to
deformative movement instead of original sedimentation. A number of
fine-grained quartz diabase dikes occur in the immediate vicinity.
A considerable portion of the east shore of Kenisheong lake consists of
high, bare Keewatin hills, composed largely of chloritic schists,
vertically inclined and striking east and west. Secondary calcite is
richly disseminated, causing free effervescence when the rock is treated
with acid. Pyrite is also abundant, sometimes segregated to form a lean
ore, and at several points weathered superficially to limonite,
colouring the cliffs dull red. Much-altered diabase like that on Pigeon
lake is also present in subordinate amount.
[Illustration: Fig. 5. West Branch Montreal River, near Mosher Lake.]
Keewatin rocks also occur just east of Gowganda lake. A single brief
visit was paid for the purpose of observing the iron formation which
appears at this place, and further mention of which is made on a
subsequent page.
LAURENTIAN.
_General Features._
Practically all the Laurentian lies in a continuous area, east of the
West branch and extending beyond the limits of the map sheet. A smaller
body occurs just west of Pigeon lake. The foliation in the Laurentian is
less distinct than in the Keewatin and much less perfect. Its component
rocks are mainly granite and allied plutonic types which pass by easy
gradations into well-defined gneisses. Two principal granites are
distinguishable; one containing black mica as its chief coloured
constituent, the other hornblende. Both exhibit local variations in
composition and crystalline texture, but are always pale grey rocks of
ordinary granitic appearance.
The hornblende granite is a medium grained, fresh looking rock of
speckled appearance, owing to the black hornblende crystals which lie
scattered through the main mass of light grey feldspar and quartz. It is
of uniform aspect, local variations of colour and texture being
insignificant. As revealed under the microscope by a single thin
section, it is an ordinary hornblende granite verging towards a syenite.
Common green hornblende of idiomorphic prismatic habit, and usually
twinned parallel to 100, is the principal ferromagnesian mineral. It is
quite fresh, hence a few flakes of chlorite in the section were taken to
represent an original small content of biotite; an acid oligoclase and
orthoclase are the most abundant constituents; quartz is subordinate.
Apatite, zircon and iron ore, probably magnetite, are accessory.
Hornblende granite is the commonest Laurentian rock in the neighbourhood
of L’Africain and Sedge lakes, where it is in contact with the Keewatin.
It also occurs on the East branch just below Obushkong lake. The area
west of Pigeon lake seems to be composed wholly of this rock, outliers
of which extend to Brush lake, and the islands and east shore of Pigeon
lake. Here, however, it is distinctly syenitic, quartz being subordinate
or absent. A distinctly porphyritic structure is apparent on Pigeon
lake; the feldspars being well crystallized and lying in a finer
grained, holocrystalline ground mass.
Biotite granite and gneiss are most prevalent in the northern and
eastern portions of the area. No microscopic examination of these rocks
has been made by the writer, consequently, little can be said regarding
their composition. They are of much the same texture as the hornblende
type, but show a somewhat higher degree of gneissification. Biotite is a
fairly abundant constituent, but is more or less altered to chlorite.
Sometimes, as may be seen on the East branch, two miles below Obushkong
lake, chloritized mica forms enclosing films about the large feldspar
grains, developing a slight ‘augen’ structure. Stockwork-like quartz
veins are frequent, particularly on the West branch between Near and
Sedge lakes and at the south end of Kenisheong lake. At the latter point
the biotite gneiss is well foliated and steeply tilted. A body of deep
red, biotite granite of undetermined extent and relationship was
observed on the east side of Kenisheong lake. Pegmatite dikes almost
certainly occur in this region, although not actually observed. Near
Crotch lake the granite is locally of unusually coarse texture, although
not truly pegmatitic.
Although the two granites described appear to be the essential
constituents of the Laurentian they usually contain a variable
proportion of other material, some of which at least is not really
Laurentian. Over the entire area, but more noticeably in the vicinity of
contacts with the Keewatin, they include narrow ribbons or lenses of a
glistening stratiform hornblende gneiss, closely resembling the gneiss
of this sort described under the Keewatin system. In some cases these
bands are portions of the Keewatin caught up by the Laurentian material
at the time of its intrusion and highly metamorphosed by it. Excellent
examples of this may be seen on the East branch at the foot of the
marshy stretch two miles below Obushkong lake. These inclusions are
mapped as Laurentian, being an almost constant feature, and for map
purposes inseparable from it. They are to be distinguished—a difficult
matter—from other dark inclusions believed to be drawn out, basic
segregations of Laurentian magmas; the latter are commonly less sharply
defined.
Like the other formations of the region, the Laurentian is cut by
diabase dikes of post-Huronian age which, owing to their dark colour,
are conspicuous among the lighter granite rocks. In the neighbourhood of
Zigzag lake they are abundant, and are usually from twenty to sixty feet
or more in width, the smaller of which are not large enough to map.
The relationships of the Laurentian to the other systems of the region
are expressed by the contacts with them. Between Obushkong and Firth
lakes and toward L’Africain lake it is largely in contact with Keewatin.
This contact is a vaguely defined zone rather than a line, the
formations being separated by the intermediate strip containing mingled
portions of both. Proceeding across this strip from the Laurentian to
the Keewatin, the gneisses of the former become charged with ribbons of
highly crystalline schist, already described. Near the Keewatin edge
these increase in quantity and sometimes appear as tongue-like
protrusions of that system. This condition exists along the east of
L’Africain lake; on the shores of the lake the formation is dominantly
Keewatin, but the stratiform hornblende gneiss is traversed along the
strike by thin bands of Laurentian hornblende gneiss. A few chains
eastward the gneiss bands are wider, and, at a distance of 10 chains,
hornblende granite is continuous.
Where terminated by diabase the contact is definite and not marked by
notable alteration on either side. Contacts with the Huronian are
equally sharp and unconformable, in every case the Laurentian
disappearing beneath the sedimentary formation; at the south end of
Kenisheong lake the Huronian has been trenched to a depth sufficient to
expose the underlying gneissic floor near the water’s edge.
HURONIAN.
_General Features._
Much of the area mapped, especially the north-western portion, is
composed of Huronian rocks. Originally they must have been much more
extensive, probably continuous, but erosion has removed them partially
or entirely, leaving irregular remnants distributed over the Archæan.
The top of the series is gone; consequently complete vertical sections
cannot be found. In other respects they are little changed and preserve
almost perfectly their bedding and clastic structure. Even their
positions assumed at the time of deposition have changed little for the
present strata seldom dip more steeply than 30°. They are overlain only
by unconsolidated Pleistocene materials.
_Basal Conglomerate._