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63-L-14-E
REPORT No. 31
The Geology
of the
DESCHAMBAULT LAKE AREA
( East Half)
Saskatchewan
by
S. J. T. KIRKLAND
1958
DEPARTMENT OF MINERAL RESOURCES
Geological Sciences Branch
Precambrian Geology Division
J. T. CAWLEY
Deputy Minister
HON. A . C. CAMERON
Minister
PROVINCE
OF
SASKATCHEWAN
REPRINTED 1967
CONTENTS
Page
3
INTRODUCTION
Location and Accessibility
Physiography
3
.................................... .
3
Previous Work ......................................................................................
3
Field Work and Acknowledgments ...
4
References ..........................................
4
GENERAL GEOLOGY
5
General Statement
5
Table of Formations ..... ............................................... .......................... .
5
Volcanic Rocks (1) ..... .................................. .
5
Biotite Gneiss and Schist (2) ...................... ...
.................... .. ..... ......
6
Hornblende and Cale-Silicate Gneisses (3) .... ....... ............
7
Augen Gneiss and Biotite Migmatite (4) ....................................
9
Diorite and Meta-Gabbro (5) ........................
Granodiorite, Quartz Diorite (6) ..............
10
···············
11
···························
12
STRUCTURAL GEOLOGY .. ...... ... ... ..... .................................... ................
14
Pegmatite, Quartz Monzonite (7) ................
Folds
14
Faults
14
ECONOMIC GEOLOGY .
......................................................................... 15
INTRODUCTION
Location and Accessibility
The Deschambault Lake Area, East Half, lies between 54°45' and 55°00' north
latitude and bet,vcen 103°00' and 103°15' west longitude. The centre of the area is
about 85 miles east-southeast of La Ronge and 50 miles west-northwest of Flin Flon.
The closest settlement, Deschambault, is fo ur and three-quarter miles west of the west
boundary of the area at 54 °55' north latitude. The settlement of Pelican Narrows is
12 miles north-northeast of the northeast corner of the area.
During the summer months the area is most readily reached by float-equipped
aircraft which m ay be chartered at La Ronge or Flin Flon. La Ronge and Flin Flon may
be reached by all-weather highways, and both are serviced by regularly scheduled
airline flights. Flin Flon is also serviced by railway.
A well-established canoe route leads from Amisk Lake near Flin Flon, via the
Sturgeon-weir River and Mirond and Pelican Lakes, into the north part of the area.
From La Ronge the area may be reached by canoe via the Churchill River and Wood
and Pelican Lakes. There is also a more difficult canoe route from the southeast part of
Lac La Ronge via Wapawekka Lake and the Deschambault River into the western pare
of Deschambault Lake.
Ready access by canoe to most of the :irea is provided by Deschambault, Pelican,
and Jan Lakes. T he latter two lakes are connected by a narrow channel, and two shore
porcages co1mect Pelican and Deschambault Lakes. The southeastern part of the area is
accessible fro·m Tulabi Lake. This lake if best reached by float-equipped aircraft since
it lies well south of the main canoe route. There is a portage about three miles long,
however, which connects Brock B:iy on Jan Lake w ith the north end ofTulabi Lake.
Physiography
The Deschambault Lake Arca lies within the watershed of the Saskatchewan River.
The west and north parts of the area, including Deschambault, Pelican, and J an Lakes,
drain north via Pelican Lake into Mirond L:ike and the Sturgeon-weir River. The latter
flows southeast from Mirond Lake, through Amisk Lake, to the Saskatchewan River.
The southeast part of the area, around Tulabi Lake, drains directly south via Tulabi
Brook and the Grassberry River into the Saskatchewan River.
The southern part of the area lies only a few miles north of the boundary between
Precambrian rocks and overlapping Paleozoic strata. In this part of the area local relief
averages less than 50 feet and there are numerous swamps and low, drift-covered areas.
In the northern part of the area, between Pelican Lake and the Northeast Arm of Deschambault Lake, and along the fault through Pelican and Jan Lakes, the relief locally
exceeds 100 feet.
Bedrock is well exposed along the shores of the larger lakes and throughout most of
the northern two-thirds of the area. To the south, however, especially west and northwest
of Tulabi Lake, outcrops arc not abundant.
Previous Work
The canoe route from Cumberland Lake on the Saskatchewan River to Pelican
Narrows, via the Grassbcrry River and Deschambault and Pelican Lakes, has been
briefly described by Mcl1mes (1913, pp. 37-38). A reconnaissance geological survey of
the Wapawekka atJd Deschambault Lake area, carried out by DeLury in 1923 and 1924,
included the Deschambault Lake Area, East Half (DeLury, 1926). Areas adjoining on
the east and southeast have been mapped by Wright and Stockwell (1934) andByers(1957).
3
Field Work and Acknowledgments
Geological mapping of the Deschambault Lake Area, East Half, was carried out
during the summer of 1957. Field personnel consisted of H . Squair, senior assistant, and
K. R . Greaves, C. 0 . Mireau, and B. J. Pfeffer, junior assistants.
The examination of rock outcrops along the shores of the major lakes was supplemented by pace and compass traversing of the intervening areas. Traverse spacing
averaged about one-half mile. Vertical aerial photographs, with a scale of approximately
one-half mile to the inch, provided mapping control, and the locations of traverses and
shoreline outcrops examined were plotted in the field on transparent overlays. The
basemap was prepared from vertical aerial photographs having a scale of approximately
one mile to the inch.
Vertical photographic coverage of the area is provided· by aerial photographs on
scales of both one-mile and one-half mile to the inch. These photographs may be obtained
through the National Air Photographic Library, Topographical Surveys, Ottawa,Canada.
References
Budding, A. J., and Kirkland, S. J. T. (1956) : The Geology of the R eindeer River Area;
R ept. N o. 22, D ept. of Mineral Resources, Saskatchewan.
Dyers, A. R. (1957) : Geology and Mineral Deposits of the H anson Lake Area; Rept.
No. 30, D ept. of Mineral Resources, Saskatchewan.
D e Lury, ]. S. (1926):Wapawekka and Deschambault Lakes Area, Saskatchewan; Geol.
Surv., Canada, Sum. R ept. 1924, Pt. B, pp. 23-50.
Kirkland, S. J. T. (1957): The Geology of the Manawan Lake Area, North Half; Rept.
No. 27, Dept. of Mineral R esources, Saskatchewan.
Mcinnes,W. (1913): The Basins of Nelson and Churchill Rivers; Geo!. Surv., Canada,
Mem. No. 30.
Wright, J. F. and Stockwell, C.H. (1934): West Half of Amisk Lake Area, Saskatchewan;
Geol. Surv., Canada, Sum. R ept. 1933, Pt. C, pp. 12-22.
4
GENERAL GEOLOGY
General Statement
The consolidated rocks in the D eschambault Lake Area, East Half, are of Precambrian
age. Unconsolidated Pleistocene glacial deposits and R ecent alluvium form a thin,
discontinuous mantle which masks much of the bedrock in the south eastern part of
the area.
Table of Formations
Cenozoic
R ecent and Pleistocene
Till, gravel, sand, peat.
Great Unconformity
Precambrian
Granitic R ocks
Pegmatite, quartz monzonite
Intrusive Contact
Granodiorite, quartz diorite,
hybrid and gneissic granodiorites.
Basic R ocks
Diorite, meta-gabbro.
Intrusive Contact
Migmatite
Metamorphosed sedimentary
and volcanic rocks
Augen gneiss, biotite migm:1tite.
Hornblende and calc-silicate
gneisses.
Biotite gneiss and schist, locally
garnetiferous; nodular meta-sedimentary gneiss containing one or
more of muscovite, sillim:mite,
cordierite, and andalusite ; hornblende-biotite gneiss, slaty metasediment.
Basic volcanic flow rocks.
The oldest rocks recognized are metamorphosed sediments, represented chiefly by
quartzo-feldspathic, biotite gneisses. Small amomm of interlayered calc-silicate and
hornblende gneisses represent impure calcareous sediments. On the Northeast Arm of
Deschambault Lake very minor amounts of basic volcanic flow rocks are interlayered
with meta-sedimentary gneisses. In the eastern part of the area and north ofDeschambault
Lake, biotite migmatite and augen gneiss represent a gradation between meta-sedimentary
gneisses and granitic rocks.
Three types of igneous rocks are intrusive imo the meta-sedimentary gneisses.
Basic rocks, ranging in composition from olivine gabbro to dark, biotite-hornblende
diorite, outcrop mainly on islands in Deschambault Lake. They are gradational into quartz
diorite and granodiorite which form large intrusive masses in the western half of the area.
In the eastern part of the area and west of the Northeast Arm of Deschambault Lake
gneissic granodiorite and quartz diorite are the most abm1dant intrusive rocks. Small
masses of quartz m onzonite and pegmatite are intrusive into the other rock types and
appear to be the youngest consolidated rocks in the area.
Volcanic Rocks (1)
Basic volcanic flow rocks (1) outcrop near the north boundary of the area on two
small islands and in a narrow unit along the east side of the Northeast Arm ofDescham-
5
bault Lake. They are very fine-grained and have medium to dark blackish green fresh
surfaces and lighter greenish grey weathered surfaces. The~· are massive to weakly
foliated and locally exhibit poorl r developed pillow structures. J ust north of the north
boundary of the area the volcanic rocks arc intcrlayered with very fine-grained, black
to greyish green, fmel y laminated, slaty met:1-scdimcnts. T heir age relative to the bulk
of the meta-sedimentary gneisses is unknown.
Microscopically the volcanic rocks show a poorly foliated to frlty mass of very
fine-grained, medium green actinolite in blades up to 0.4 millimeter long and 0.06
millimeter wide. Vcry fine-grained fclsic constituents occupy the interstices between
actinolite blades. Indistinct layers up to several millimeters wide contain yellowish brown
biotite which partially replaces actinolitc. The rock consists of about 80 per cent actinolite
and 20 per cent fclsic constituents. Biotitc and fine, irregular grains of an opaque mineral
are minor constituents. In the thin biotite-bcaring layers about 10 per cent of the actinolite
is replaced by biotite.
Biotite Gneiss and Schist (2)
Biotite gneiss and schist (2) of sedimentary origin occupy a zone one and one-half
to three miles wide which trends north-south through the centre of the area. In the
southwest part of the area this zone curves to the west and northwest around a large
mass of granodiorite. Similar rocks lie along the Northeast Arm of D eschambault Lake.
Smaller units of meta-sedimentary biotite gneiss occur throughout the area.
These meta-sedimentary rocks arc fine to locally medium grained, with medium
to dark grey fresh and lighter grey weathered surfaces. Q uartz, plagioclase, and biotite
arc the major constituents. Fine garnet occurs locally as a prominent accessory. Fine
gneissic layering, with individual layers ranging from a fraction of an inch to several
inches thick, is due to slight variations in grain size and relative abundance of biotite
in adjacent layers. Granulitic and schistose layers up to several feet wide, and beds of
nodular meta-sediment (2a) up to two feet thick, occur with the gneissic rock. In places,
thin, lens-like stringers of quartz or quartz and feldspar accentuate the gneissosity, and
in the southwest part of the area and north of Deschambault Lake abtmdant stringers of
granitic to fine pegmatitic material give the rock a migmatic appearance. Quartzsericite schist, derived from meta-sediments, outcrops in several localities along the east
side of the Northeast Arm of Deschambault Lake.
Microscopically the texture of the biotite gneiss and schist (2) is granoblastic, with
quartz and plagioclase forming a simple mosaic and biotite flakes showing parallel
orientation. Some specimens relatively rich in biotite have a texture approaching
lepidoblastic. The average grain size in six thin sections examined ranges from 0.2 to
0.4 millimeter. T he compositional range shown in the six thin sections is 33 to 38 per cent
quartz, 26 to 46 per cent plagioclase, and 21 to 38 per cent biotite. Garnet occurs in five
of the thin sections, ranging in amount from a trace to three per cent. Zircon, apatite,
magnetite, and graphite are minor constituents. The plagioclase in six thin sections
ranges in composition from intermediate oligoclase to intermediate andesine.
Nodular biotite meta-sedin1cnts (2a), although occurring commonly as thin beds
in the more uniform biotite gneiss, also form the bulk of the meta-sediments in some
localities around the southeast part of Deschambault Lake. They are characterized by
nodules, usually flattened parallel to the foliation, which consist most commonly of a
mixture of quartz and sillimanite. In places feldspar and muscovite also occur in the
nodules. The nodules range up to one-half inch in diameter and one-quarter inch thick,
but most commonly they are in the order of one-quarter inch in diameter. They are
slightly more resistant to weathering than the enclosing rock and consequently they
stand out slightly in relief on weathered surfaces. In places distinct beds, one inch to
two feet wide, are apparent due to variation in the size and abundance of nodules.
Beds of non-nodular biotite meta-sediment of similar width occur with the nodular beds.
6
Three thin sections of rocks comaining sillimanite nodules show an average grain
size of about 0.3 millimeter. Lens-like knots of fine quartz and fibrous sillimanite occur
in a matrix of quartz, plagioclase and biotite. Muscovite in one thin section occurs
mainly as a th.in, discontinuous border around the sillimanitc-quartz nodules. The main
constituents, as shown in the thin sections, arc 29 to 44 per cent quartz, nine to 34 per cenc
plagioclase, 20 to 43 per cent biotite, and three to 15 per cent sillimanite. Microcline and
muscovite each occur in one section , and zircon, apatite, and opaque minerals arc minor
constituents. The plagioclase in one th.in section was identified as calcic oligoclase.
Nodules of pale bluish cordicritc up to one-quarter inch in diameter occur in the
biotite meta-sediments in places. In thin section the rock is similar to the biotite gneiss (2)
and nodular meta-sediment (2a) previously described, except that 15 to 25 per cent or
the rock consis_ts of cordierite nodules. The cordierite is altered along fractures to very
fine micaceous and isotropic minerals and is partially replaced by fibrous sillimanitc.
The plagioclase was identified in one thin section as calcic oligoclase.
Very fine-grained to aphan.itic meta-sediments (2b), in part finely layered and
slaty in appearance, outcrop mainly in a narrow zone along the river co1mccting
Deschambault and Pelican Lakes. These rocks :ire dark steel-grey to brownish coloured
on fresh surfaces and weather greyish brown. Very small garnets are abundant in places
and metacrysts of pale pinkish andalusite occur locally.
The meta-sediment (2b) microscopically shows a grain size of0.05 to 0.1 millimeter.
There is a pronounced parallel alignment of micaccous minerals and a notable elongation
of quartz and plagioclase grains parallel to the foliation. Two thin sections show 36 to
47 per cent plagioclase, 16 to 27 per cent quartz, and 32 to 37 per cent biotite. Garnet
porphyroblasts up to 1.25 millimeters in diameter form five per cent of one section.
Apatite, zircon, and opaque minerals are minor constituents, and a small amount of
chlorite occurs as an alteration product of biotitc.
Hornblende-biotite gneiss (2c) forms part of a meta-sedimentary unit in the eastcentral part of the area, about one and one-half miles west of Brock Bay. The rock is
very similar to the biotite gneiss (2) but approximately one third of a total mafic content
of 30 per cent is hornblende.
Hornblende and Cale-Silicate Gneisses (3)
Hornblende and calc-silicate gneisses outcrop in a northerly trending zone in the
eastern part of the area, and form narrO\V units west of the Northeast Arm and along
the Southeast Arm of Deschambault Lake.
In the eastern part of the area the homblendic rocks are fine-grained and very dark
grey to greenish black in colour. The main constituents are hornblende and plagioclase,
with hornblende usually forming 60 per cent or more of the rock. Structurally the
hornblendic rocks range from granulitic to finely gneissic, with the latter type most
abundant.
East of Pelican Lake, in the northeastern part of the irea, hornblende gneiss, biotite
gneiss, and hybrid hornblende granodiorite are intimately interlayered (3a). The hornblendic rock in this tmit is strongly gneissic, with individual gneissic layers ranging from
a fraction of an inch to one inch wide. Hornblende is the main mafic constituent but
biotite is usually also present. A thin. section of typical rock shows interlocking grains
of plagioclase, quartz, and hornblende, and strongly aligned, ragged flakes of biotite.
The average grain size is about 0.5 millimeter. The rock consists of about 55 per cent
intermediate andesine, 30 per cent quartz, and 15 per cent biotite and hornblende.
Apatite and opaque minerals are minor constituents, and a small amow1t of ch.lorite
occurs as an alteration product of biotitc.
The most abundant hornblendic rock type in the area is a hornblende gneiss with
thin. diopsidic layers and streaks (3b). Individual gneissic layers are mainly one-eighth
7
to one-half inch in width. Fine-grained, dark, hornblendic layers alternate with slightly
coarser, light grey, feldspathic layers and pale greenish streaks rich in diopside. In places
diopside is abtmdant and the rock is essentially a pale greenish diopsidic gneiss with thin
hornblendic layers (3c).
A thin section of typical hornblende gneiss witl1 diopsidic layers (3b) shows a mineralogical layering, with hornblendic, diopsidic, and felsic layers ranging from 1.5 to
10 millimeters thick. The average grain size is about 0.2 millimeter, but some plagioclase
grains in the slightly coarser, felsic layers are 1.25 millinieters long. The felsic and
diopsidic layers have a granulitic texture and the hornblende grains in the hornblendic
layers show alignment parallel to the layering. The rock consists of about 41 per cent
plagioclase, 30 per cent hornblende, 17 per cent diopside, and 12 per cent quartz. Sphene,
epidote-zoisite, apatite, garnet, and opaque minerals are minor constituents. The plagioclase is intermediate andesine.
Two thin sections of diopsidic gneiss (3c) show fine layering due to variations in
felsic and mafic constituents. Thin streaks of very fine-grained sphene parallel the
layering. The grain size of the main constituents is about 0.4 millimeter. The sections
show 64 to 68 per cent intermediate andesine, 14 to 18 per cent diopside, one to seven
per cent hornblende, three to six per cent sphene, a trace to three per cent biotite, and
two to 14 per cent quartz. Apatite, carbonate, and opaque minerals are minor constituents.
A greyish green, diopsidic gneiss (3c) containing disseminated pyrrhotite and fine
graphite, outcrops at the north end of a small lake about three quarters of a mile west
of the Northeast Arm of Deschambault Lake and one and one-half miles south of the
north bom1dary of the area. Microscopically the rock is very similar to the diopsidic
gneiss already described, but it also contains a considerable amount of carbonate and
epidote-zoisite associated with the pyrrhotite and graphite. In addition, some of the
diopside is partially altered to green, actinolitic amphibole. A thin section of the rock
shows about 39 per cent diopside, 23 per cent plagioclase, 13 per cent quartz, 15 per cent
epidote-zoisite, four per cent sphene, two per cent pyrrhotite'1111d graphite, two per cent
carbonate, two per cent amphibole, and a trace amount of apatite.
Intimately mixed hornblendic and calc-silicate gneisses (3d) outcrop on several
islands in the southern part of Deschambault Lake near the west boundary of the area.
Dark, hornblendic, gneiss bands, a few inches to several tens of feet w ide, are interlayered
with fine-grained, light grey to greyish buff, siliceous calc-silicate gneisses. The dark,
hornblendic bands form about 35 per cent of the unit. A thin section of the hornblendic
rock shows a granoblastic mosaic of plagioclase and hornblende, witli an average grain
size of about 0.1 millimeter. It consists of about 65 per cent hornblende and 35 per cent
plagioclase. Sphene, quartz, and opaque minerals are minor constituents. The composition
of the plagioclase is tmk.nown.
A thin section of siliceous calc-silicate rock shows a granoblastic mosaic of untwinned
plagioclase and quartz. The average grain size is about 0.05 millimeter. Parallel streaks
of quartz, up to 0.6 millin1eter wide, contain elongated grains up to one millimeter long.
Patches of epidote-zoisite and carbonate occur adjacent to the quartz stringers. Very
fine-grained sphene, in irregular to rounded grains is abundant throughout the section
but there is also some concentration into thin streaks. Muscovite occurs along some of
the sphene-rich streaks. The section shows about 58 per cent plagioclase, 18 per cent
quartz, 14 per cent epidote-zoisite, six per cent sphene, and four per cent muscovite.
C arbonate forms less than one per cent of the rock. Anotlier thin section of similar
calc-silicate gneiss also shows thin layers rich in diopside and actinolite-tremolite, and
streaks of carbonate with associated epidote-zoisite and muscovite. This latter section
shows about 61 per cent sodic andesine, 13 per cent actinolite-tremolite, ten per cent
quartz, five per cent diopside, six per cent carbonate, and five per cent sphene. Epidotezoisite and muscovite are minor constituents.
8
One thin section of siliceous calc-silicate gneiss shows poikiloblastic grains of
scapolite up to two millimeters long in a matrix having a grain size of about 0.08 millimeter. The rock consists of about 40 per cent intermediate andesine, 25 per cent scapolite,
16 per cent quartz, seven per cent hornblende, seven per cent carbonate, two per cent
diopside, and one per cent each of biotite, sphene, and microcline.
The mineralogical composition, continuous gneissic banding, and intimate interlayering of various calc-silicate rock types, suggests that the hornblendic and calc-silicate
gneisses represent metamorphosed, calcareous sediments. Although some of the darker,
hornblendic gneisses could represent metamorphosed basic volcanic rocks the common
occurrence of thin diopsidic streaks suggests a probable sedimentary origin.
Augen Gneiss and Biotite Migmatite (4)
Augen gneiss and biotite migmatite (4) outcrop m ainly along the eastern margin
of the map area and to a lesser extent north of Deschambault Lake near the western
boundary of the area.
The augen gneiss and biotite migmatite in the eastern part of the area are medium
to coarse-grained and medium to light grey, or locally buff, in colour, Typically the
augen gneiss consists of whitish porphyroblasts of plagioclase, one-eighth inch to one
and one-half inches in diameter, set in a matrix of fine-to- medium-grained plagioclase,
quartz, and biotite. The plagioclase porphyroblasts form 10 to 25 per cent of the rock.
In places the porphyroblasts form beaded stringers parallel to the gneissosity, and the
rock has the appearance of a veined m.igmatite rather than an augen gneiss. The feldspathic vein material constitutes 30 to 35 per cent of some migmatite outcrops. In places,
layers up to several feet wide do not contain feldspar porphyroblasts and in these layers
the rock is essentially the same as the biotite gneiss (2) of sedimentary origin. Garnet is
a common accessory mineral and west of J an Lake pale bluish cordierite also occurs
locally. A small amount of fine, disseminated graphite is usually also present. In several
places along the west shore of J an Lake the rock has a rusty weathered surface and is
schistose over widths of five to ten feet. In these schistose bands the rock carries much
fine, disseminated pyrite and abundant graphite.
A thin section of augen gneiss shows porphyroblasts of plagioclase up to ten millimeters long set in a groundmass of plagioclase, quartz, and biotite having an average
grain size of 0.5 millimeter. The rock consists of about 56 per cent sodic andesine, 29
per cent quartz, and 15 per cent biotite. Potash feldspar, zircon, apatite, graphite, and
carbonate are minor constituents.
A thin section of typical veined biotite m.igmatite from the west shore ofJan Lake
shows porphyroblasts of plagioclase up to 2.5 millimeters long in a schistose m atrix of
plagioclase, quartz, and biotite. Scattered porphyroblasts of garnet range up to 1.25
millimeters in diameter. The rock consists of about 30 per cent plagioclase, 35 per cent
quartz, and 35 per cent biotite. Garnet, zircon, and graphite are minor constituents.
The plagioclase in both the porphyroblasts and groundmass is sodic andesine.
A thin section of rock from a rusty, graph.itic zone in augen gneiss shows porphyroblasts of plagioclase up to 4.5 millimeters long and garnets up to 2.5 millimeters in diameter. The average grain size of the matrix is about 0.6 millimeter. The matrix consists
of plagioclase, quartz, microcline, and biotite. Graphite and pyrite are closely associated
with and appear to partially replace biotite. The rock consists of about 28 per cent sodic
to intermediate andesine, 32 per cent quartz, 10 per cent microcline, 16 per cent biotite,
seven per cent graphite, five per cent garnet, and two per cent pyrite.
Boudin-like lenses of dark hornblendic rock form five to ten per cent of some
augen gneiss outcrops near Jan Lake. These hornblendic lenses range from typical
boudins about six inches wide and 12 inches long to streaks about one foot wide and
five to six feet long. Many of the boudins are surrounded by a layer, one-quarter to
three-eighths inch wide, of fine-grained feldspar and quartz. Inside this layer is another
9
layer of similar width which is rich in fini:-grained biotitc and garnet. The central part
of the boudins is typicall y a massive, fine-to-mediulll-graincd, hornblendic rock ranging
from dioritic to amphibolitic in appearance. Some of the larger hornblendic blocks arc
fmely gneissic and closel y resemble the hornblende gneiss of probable sedim.cntary
origin (3).
In the eastern part of the area small bodies of pegmatite and granodiorite (6), and
thin unmappablc units ofbiotitc meta-sedimentary gneiss (2) and hornblende gneiss (3) ,
arc intimately nlL'Ccd with the augcn gneiss and };,iotitc migmatite.
The biotitc migmatite (4) in the northwestern part of the area varies from a veined,
m igmatic, meta-sedimentary gneiss to a m iglllatic, granodioritc-likc rock. The veined
type of migmatitc consists of a fine-grained, meta-sedimentary, biotite gneiss with
stringers and lenses of medium-to-co:mc-graincd, fcldspathic, pegmatitic, or biotitc-rich
rock. The coarser-grained stringers and lenses, ranging from one inch to eight inches
wide, form 10 to 35 per cent of the migmatite.
Microscopically the fine-grained portion of the veined migmatic gneiss closely
resembles the biotite meta-sedimentary gneiss (2). It consists essentially of a granoblastic
mosaic of plagioclase and quartz with parallel aligned flakes of biotite. The average
grain size is about 0.5 millimeter. The rock consists of about 49 per cent calcic oligoclase,
26 per cent quartz, 24 per cent biotite, and one per cent graphite and pyrite. Zircon and
apatite arc accessory constituents.
The coarser-grained portion of the m igmatitc shows plagioclase grains two to eight
millimeters long and elongated quartz grains up to four millimeters long. Strongly
aligned flakes of biotite curve around the larger plagioclase grains. Muscovite and needles
of sillimanite occur with the biotitc. This part of the migmatite consists of about 41
per cent calcic oligoclase, 36 per cent quartz, 20 per cent biotitc, and three per cent
muscovite. Zircon, sillimanitc, and graphite arc minor constituents.
Diorite and Meta-Gabbro (5)
Intrusive rocks, ranging in composition from diorite to m eta-gabbro, outcrop on
islands in Deschambault Lake and in small bodies on the north and soutlnhores of the
lake near the west boundary of the area. These rocks are medium grained, massive, and
dark greyish black to black and grey mottled in colour.
Diorite rocks w1derly most of Ellis Island in east-central D eschambault Lake and
also form small bodies at the north end of Carey Island and on a small peninsula on the
south shore of the lake. Three thin sections show massive mosaics of plagioclase and
hornblende and scattered aggregates of biotite flakes. The plagioclase grains, ranging
from 0.5 millimeter to four millimeters in size, are blocky to prismatic in form and
show Carlsbad, albite, and pericline twinning. Many of the grains exhibit undulose
or "bullseye" extinction under crossed nicols, and low to medium, patchy saussuritization
is typical. The hornblende, in anhedral to subhedral grains, is moderately pleochroic
from pale yellowish green to medium green. Many grains contain abundant fine opaque
inclusions, and some show schiller structure. Biotite, strongly pleochroic from pale
straw yellow to rusty brown, occurs for the most part in small aggregates. A small
amount of quartz occurs in fine, interstitial grains. The three sections show 49 to 55
per cent plagioclase, 38 to 45 per cent hornblende, a trace to eight per cent biotite, a trace
to four per cent quartz, and traces of apatite and opaque minerals. The plagioclase was
identified in one section as sodic labradorite.
On the north shore of Deschambault Lake, at the west boundary of the area, a
more gabbroic-looking rock outcrops. A thin section shows a massive mosaic of plagioclase and hornblende, with an average grain size of about 0.75 millimeter. T he plagioclase exhibits the same features as that in the diorite. The hornblende is also similar to
that in the diorite, but it has a more patchy greenish colouration and most grains are
riddled with opaque schiller inclusions. A small amount of biotite is closely associated
10
with the hornblende, and a minor amount of pale greenish chloritc occurs in small
patches which have radiating structures. The section shows about 62 per cent plagioclase,
34 per cent hornblende, three per cent biotitc, and one per cent fine opaque minerals.
Chlorite and apatite arc m inor constituents.
A more basic rock outcrops on small isbnds one and one-half miles southeast of the
south end of Ellis Isb nd. T his rock is medium-grained, massive, and dark greenish
black in colour. In thin section it shows grains of olivine up to 1.2 millimeters in diameter
and prismatic grains of pbgioclasc ranging from one millimeter to two millimeters.
V cry well developed n:Ktion rims between the olivine and plagioclasc consist chief! y
of colourless to weakly plcochroic, pale bro wn amphibolc. T he olivine grains arc also
altered along cleavage and fracture planes to greenish and greenish brown, scrpcntinclike minerals. Although much altered this rock appears to represent an olivine gabbro.
Granodiorite, Quartz Diorite (6)
Granodiorite and quartz dioritc are the m ost abundant granitic rock types in the
area. Well foliated, biotitc to hornblcnde-biotitc granodiorite and quartz diorite (6)
form a long intrusive bod r between Pelican Lake and the Northeast Arm of Deschambault
Lake. Similar rocks also form a large intrusive m ass just south of D eschambault Lake, as
well as several smaller bodies along the south shore and on islands in the lake. A strongly
foliated, relatively biotite rich type (6a) and sheared portions of the quartz diorite (6c)
arc distinguished on the accompanying map. T hese rocks arc gradational into one
another and also into some of the diorite and meta-gabbro (5).
Along the eastern boundary and in the southwestern and northwestern parts of
the area a gneissic gr:modiorite (6b) is the m ost common type. Much pegmatite and
quartz monzonite is intermixed w ith this granodiorite.
H ybrid granodiorite and quartz diorite (6d) outcrop along a zone extending from
the northeast comer of the area to a point midway between Tulabi and D eschambault
Lakes. A crushed and altered, hybrid granodiorite to diorite-like rock (6e) outcrops in
the southern part of the zone.
The granodiorite and quartz dioritc (6) are medium-grained, light to dark grey
in colour, and well foliated. They cannot be distinguished from one another in the field
but they do show slight differences in thin section. The granodiorite consists of anhedral,
interlocking grains of plagioclase, quartz, and microcline, and strongly aligned flakes
of biotite. The average grain size is about one millimeter. Three thin sections show 23 to
25 per cent quartz, 50 to 53 per cent plagioclase, 15 to 23 per cent biotite, and one to
nine per cent microclinc. Zircon and apatite arc accessory constituents. The plagi_oclase
is calcic oligoclase to sodic andesinc.
Four thin sections of quartz diorite show 14 to 27 per cent quartz, 39 to 59 per cent
plagioclase, 13 to 29 per cent biotite, and a trace to 17 per cent hornblende. Apatite,
zircon, and sphenc are minor constituents. A small amount of microcline occurs in two
sections. The plagioclase, slight! y 1nore anorthite-rich than in the granodiorite, ranges
from sodic to intermediate andesine.
The biotite-rich granodiorite and quartz diorite (6a) show a much more pronounced
foliation than the rocks just described, and have a slightly higher biotite content. The
plagioclase, as determined in two thin sections, is sodic andesine.
Sheared quartz diorite (6c) occurs in places along the margins of the granodioritequartz d.iorite mass between Pelican and D eschambault Lakes. This rock is medium to
dark grey in colour and has a pronounced foliation due to very closely spaced shear planes.
In thin section it shows augen-like, renmant grains of plagioclase up to two millimeters
long set in a matrix of plagioclasc and quartz having an average grain size of about 0.1
millimeter. The lai;ger plagioclase grains show curved and broken albite twin lamellae
and exhibit undulose extinction. The biotite is much more fine-grained than in the
11
normal quartz diorite and occurs in ragged flakes mainly along the closely spaced shear
planes. Biotitc flakes along the shear planes curve around the large plagioclase remnants.
The mineral composition is essentially the same as tlut of the normal quartz diorite, but
small amounts of carbonate, epidotc, and pcnninite occur as alteration products of the
plagioclase and biotite.
The gneissic granodioritc (6b) is mainly medium-grained and varies from light grey
to pink in colour. Gneissic layering, with individual layers ranging from a fraction of
an inch to about one inch in thickness, is due to variations in grain size and mineralogical
composition. In the eastern part of the area thin stringers of pegmatitic and granitic
m aterial are common, and abundant small dykes and irregular bodies of pegmatite and
quartz monzonite cut the gneissic granodiorite. Thin layers and bondin-like blocks of
hornblendic rock, similar to those occurring in the augcn gneiss and biotite migmatite,
are common in the granodiorite near J:m Lake. In places augen gneiss and gneissic
granodiorite arc intimately mixed. In the souchwcstcrn and northwestern parts of the
area the gneissic granodiorite is more uniform in appearance and hornblendic inclusions
and pegmatitic stringers are less common.
In thin section the gneissic granodiorite (Gb) shows anhcdral, interlocking grains of
plagioclase, quartz, and microclinc. The average grain size is about one millimeter.
Biotite, and hornblende where present, tend to be concentr2ted in definite thin layers.
Layers relatively rich in quartz or microcline are usually also apparent. The plagioclase,
which commonly shows albite or combined albite and pericline twins, is intermediate
oligoclase.
Three thin sections of t ypical gncissic granodiorite show 20 to 30 per cent qua1tz,
54 to 66 per cent plagioclase, five to ten per cent microcline, and four to nine per cent
biotite. Zircon, apatite, and opaque minerals are minor constituents. A thin section of
darker grey granodioritc shows 24 per cent quartz, 39 per cent plagioclase, 24 per cent
hornblende, 12 per cent biotite, one per cent microcline, and traces of zircon, apatite,
and sphene.
The hybrid hornblende granodiorite and quartz diorite (6d) arc, for the most part,
strongly gneissic rocks. Thin gncissic layers rich in hornblende or hornblende and biotite
are abundant, and small, unmappable units of hornblende gneiss and augen gneiss are
common. The gneissosity is much more pronounced and the mafic content generally
higher than in the gneissic granodioritc (6b ). In places the gneissic layering is very uniform
and continuous along strike and is suggestive of sedimentary bedding. Locally the hybrid
granodiorite and quartz diorite are more massive in appearance and are characterized by
a highly variable, patchy hornblende content.
About midway between Tulabi Lake and the outlet of Deschambault Lake the
hybrid granodiorite is highly crushed and altered in some outcrops. The rock here is
cut by numerous, narrow, m ylonitic zones, and tiny veinlets and stringers of epidote.
The feldspars are altered to a deep pink or reddish colour and the mafic minerals are
largely altered to chlorite. Microscopically the rock shows highly crushed plagioclase,
some hornblende, and much epidote-zoisite, penninite, and carbonate. Quartz was not
observed in the two thin sections examined.
Pegmatite, Quartz Monzonite (7)
P egmatite and quartz monzonite (7) form numerous small intrusive bodies, mainly
in a broad zone trending north-south through the centre of the area. The largest bodies
occur as long, narrow, conformable intrusions in the m eta-sedimentary biotite gneisses.
Only the larger bodies are shown on the accompanying map, since there are innumerable
dykes and small bodies of pegmatite that are too small to be indicated. In the vicinity
of Pelican Lake these small unmappable bodies constitute up to 30 per cent of some outcrops of meta-sedimentary gneiss.
12
The quartz monzonitc is typically lcucocratic, pink to greyish buff in colour,
111cdium to coarse grained, and massive to locally strongly foliated. Just west of Pelican
Lake the m ost common type is a moderate!y foliated, pink coloured, biotitc-muscovite
quartz monzonite (7b). In the long, linear body wl1ich extends from about a mile east
of the outlet of Deschambault Lake to the south boundary of the area, the quartz
monzonite is very strongly foliated to finely sheared and has an augen-likc, porphyritic
texture (7c). In the southwestern part of the area porphyritic quartz monzonite (7c)
outcrops locally j ust cast of the Sourhwcst Arm of Deschambault Lake. Gncissic quartz
monzonite (7d), mixed with granodioritc and pegmatitc, outcrops mainly in the southwestern part of the area and around the north part ofJan Lake. Along the southwestern
part of Pelican Lake, and at the southeast corner and along the Northwest Ann of
Deschamabulc Lake, large bodies of pcgmatite (7a) cut the meta-sedimentary gneisses.
Thin sections of quartz 111onzonite (7) show anhcdral, interlocking grains of plagioclase, microcline microperthitc, and quartz. The average grain size is slightly greater
than one millimeter. Microclinc and quartz arc interstitial with respect to the plagioclasc
and the microclinc partially replaces it. The p lagioclase, intermediate oligoclase, occurs
in untwinned grains and grains showing Carlsbad, albite, and pcriclinc twins. Biotite,
strongly pleochroic from pale straw yellow to rusty brown , occurs in small, ragged
flakes partially altered to pcnninitc. Two thin sections show 33 to 34 per cent quartz,
34 to 44 per cent plagioclasc, 21 to 31 per cent microclinc, and a trace to two per cent
biotite. Zircon and apatite arc accessory minerals and one section contains about one
per cent hornblende.
Microscopicall y the biotitc-muscovitc quartz monzonitc (7b) shows a si1nilar
texture and mineralogy, but it has a m ore prominent foliation due to a greater mica
content. Four thin sections show 33 to 36 per cent quartz, 23 to 37 per cent plagioclase,
22 to 32 per cent microcline, one to six per cent biotite, and three to four per cent
muscovite. Zircon occurs as a minor accessory 111.incral. The plagioclase, as in the other
quartz monzonite, is intcr111cdiatc oligoclasc.
In thin section the porphyritic quartz 111onzonitc (7c) shows anhcdral grains of
microcline and microcline microperthitc, three to five millimeters in diameter, set in a
matrix of plagioclasc, quartz, and microclinc having a grain size of 0.1 to 0.6 millimeter.
Biotitc flakes, pleochroic from straw yellow to 111cdiu111 brown, show good parallel
alignment, and arc partially altered to pcnninitc. The plagioclase, intermediate oligoclase, shows medium saussuritization. Three thin sections show 28 to 42 per cent quartz,
29 to 45 per cent plagioclase, 19 to 23 per cent m icroclinc, and six to seven per cent
biotitc. Zircon and apatite arc minor constituents. A trace amount of muscovite occurs
in two sections and one section contains about one per cent garnet.
The gneissic quartz monzonitc (7d) shows microscopic features similar to quartz
monzonites already described. The overall mineral composition is approximately the
same, but there is segregation of the various minerals into indistinct gncissic layers.
North ofJan Lake thin layers of granodiorite occur with the quartz 111onzonitc and thin
lenses and streaks of hornblcndic rock arc common. T he gncissic quartz monzonite in
the southwestern part of the area is intimately mixed with granodioritc, pcgmatite, and
remnants of meta-sedimentary biotite gneiss.
Bodies of pegmatite (7a) are abundant throughout the area. In the meta-sedimentary
gneisses they are mainly in the form of si.lls a few feet to about 20 feet wide. The larger
bodies, shown on the map, are also roughly conformable. They consist of about 80
per cent pink to locally whitish pcgmatite and 20 per cent gradational quartz monzonitc
and remnants of m eta-sedimentary gneiss. T he pcgmatitcs arc m ineralogically very
simple, consisting essentially of feldspar and quartz. T he grain size is usually two to four
inches, but graphic intcrgrowths of quartz and feldspar up to ten inches across occur in
places. The feldspar is chiefly microclinc or microcline micropcrthite, but some oligoclase
is practically always present. Biotite and muscovite, in books up to three inches across,
are the main accessory minerals, but they rarely form more than five per cent of the rock.
13
Bbck tourmaline, apatite, m agnetite, garnet, a11d sillimanite occur locall y in very small
amounts.
R emnant streaks and layers of meta-sedimentary bioticc gneiss arc abundant in the
larger pcgmatite bodies. In places these remnants are sufficiently abundant to give the
rock a coarsely gneissic structure which parallels the gncissosity in the surrounding
meta-sediments.
STRUCTURAL GEOLOGY
Folds
The main structural feature in the eastern part of the area is che Jan Lake anticline,
a north-northeast trending, doubly-plunging fold . The eastern limb of this structure
lies east of the map area, except for a small portion between Brock Bay and Tulabi Lake.
Around the north end of Dunsmore Bay on Jan Lake, about one and one-half miles
cast of the narrows between Pelican and Jan Lakes, the fold plunges about 45 degrees
north. Around the north end of H arper Island minor folds and crenulations indicate
a plunge of 25 to 30 degrees north. Between Harper Island and Tula bi Lake g ncissosity
attitudes and minor folds suggest a southerly plunge, and at Tulabi Lake the nose of the
fold, as outlined by a hornblende gneiss unit, plunges south at 30 to 40 degrees. The limited
structural data available suggest that the axial plane of the fold dips steeply cast.
In the meta-sedimentary gneiss zone which trends through the centre of the area
there is a general lack of marker units or primary sedimentary features. The general dip
throughout m ost of the zone is steeply west. Along the South Arm of Pelican Lake,
however, gneissosity and bedding attitudes suggest an anticlinal structure plunging
steeply southwest. Crenulations and minor folds in this locality have a general southwest
plunge of 55 to 60 degrees. The intervening syncline between the Jan Lake and Pelican
Lake anticlines probably lies along the zone of hornblende gneiss and h ybrid granodiorite
that trends south-southwest fro:n the narrows between Pelican and J an Lakes.
N ear' the southeast comer of D eschambault Lake the meta-sedin1entary g neisses
curve around a boss of granodiorite and quartz diorite. On the north, west, and south
sides of the boss the gneisses dip steeply away from the contact. The relationship along
the cast side of the boss is obscured by an intrusion of pegmatitc and quartz monzonite.
At the entrance to the Southeast Arm of D eschambault Lake, at the west boundary
of the area, calc-silicate and hornblende gneisses o utline a synclinal structure plunging
steeply southeast. Mineral lincations and axes of minor fo lds in this locality have a
general plunge of 50 to 60 degrees southeast.
At the w est boundary of the area, just north of Deschambault Lake, hornblende
gneiss units outline an anticlinal structure plunging 40 to 50 degrees north. Most of the
west limb of this fold lies west of thc' map area.
Just west of the Northeast Arm of Deschambault Lake the trend of hornblende
g neiss units and gneissosity attitudes suggest a northerly plunging synclinal structure.
Gneissic granodioritc occupies most of the axial portion of this fold. To the northwest,
about two and one-half miles east-southeast of the northwest comer of the area, a
migmatite unit outlines a probable anticlinal structure plunging steeply north.
Faults
A major fault trends northwest through the narrows between Pelican and Jan Lakes
in the northeastern part of the area. This fault is part of a regional fault structure which
extends from the H anson Lake area on the south at least as far north as· Numabin Bay
at the south end of Reindeer Lake, a distance of over 100 miles. Parts of this m ajor fault
zone have been described previously (Budding and Kirkland, 1956, pp. 33-34; Kirkland,
1957, p. 18 ; Byers, 1957, p. 30). In the D eschambault Lake area the fault lies along a
14
marked topographic depression occupied by lakes or swamp. The meta-sedimentary
biotite gneiss which outcrops on either side of the depression west of Pelican Lake is
highly j ointed and cut by numerous irregular shears. At the narrows between Pelican
and Jan Lakes the rocks are also highly fracrnred and there is much red iron-staining of
the feldspars and some chloritization of mafic minerals. Southeasterly trending, epidotefilmed shears are common, some of them showing slight, left hand strike separation.
One southeasterly trending breccia zone, about one foot wide, shows slight dragging
along the w alls which also indicates left hand movement.
Along the cast sh.ore of the narrow part of Pelican Lake, near the north boundary
of the area, th.in brecciated zones up to several inches wide occur in hornblende gneiss
and hybrid granodioritc. These zones lie p.irallcl to the gneissosity and the relative
direction of movement along them wa~ not established. Some reddening of feldspars
and slight chloritization of mafic mincr,1ls is apparent in several places. It is inferred that
a fault lies along th.is part of the lake close to the east shore. This fault, if present, is
probably a branch of the m aj or fault previously described.
A marked topographic linear depression, occupied largely by swamp, extends in
a north-northeasterly direction from near the centre of the south boundary of the area
to a point about three miles west of the south end of Harper Island. Along this depression
meta-sedimentary biotitc gneisses arc locally highly sheared and in places there is much
red iron-staining of feldspars and chloritization of ma.fies. Slickensidcd shear surfaces
and zones of fine breccia up to six inches wide trend parallel to the depression. Some of
these show left hand strike separation. This linear depression is probably the expression
of a fault zone and an inferred fault is indicated on the accompanying map. The fault
m ay extend north to Pelican Lake but its location north of that indicated is uncertain.
ECONOMIC GEOLOGY
Only a few traces of mineralization were observed in the area. The m ineralization
appears to be of two types; disseminated graphite-pyrite zones in au gen gneiss and biotite
m.igmatitc, and pyrrhotite-pyrite disseminations in calc-silicate and hornblendic rocks.
In the augen gneiss and biotite migmatite along the west shore of Jan Lake rusty
zones, a few inches to ten feet wide, contain considerable graphite and fine, disseminated
pyrite. A th.in section of typical rock from one zone shows about seven per cent graphite
and two per cent pyrite. No other sulphide minerals were observed. T he graphitepyrite zones are strictly conformable and arc probably of sedimentary origin. Disseminated flakes of graphite occur in many places in the meta-sedimentary biotite gneiss.
On the west shore ofJ an Lake, .one-half mile due west of the north tip of Harper
Island, a lens of diopsidic to hornblcndic calc-silicate gneiss occurs in veined biotitc
migmatite. This lens, two and one-half to three feet wide and about 25 feet long, has a
rusty weathered surface and in places contains a very small amotmt of fine, disseminated
pyrrhotite and pyrite and a few, very small, scattered grains of chalcopyritc.
In much altered hybrid granod.ioritc, three miles west-southwest of the south tip
of H arper Island, a thin hornblcndic zone contains a small amotmt of fine, disseminated
pyrite. No other sulphide minerals were observed.
At the north end of the small island in the south bay of Pelican Lake, two and onchalf miles southwest of the narrows between Pelican and Jan Lakes, a small amount of
patchy malachite staining occurs along foliation planes in meta-sedimentary biotitc
gneiss. No sulphide minerals were observed.
At the north end of a small lake, two miles south and two and one-quarter miks
cast of the northwest corner of the area, diopsidic calc-silicate gneiss contains a small
amount of fine, disseminated pyrrhotite and flakes of graphite. The rock is cut by
veins, about one-half inch wide, of quartz and minor greenish coloured feldspar
Small blcbs of pyrite and a trace of clukopyritc ocrnr in the veins.
15
In the Hanson Lake Area, which. lies just southeast of the Deschambault Lake Area,
four base metal sulphide deposits of possible economic importance have been discovered
(Byers, 1957). In his study of the area B yers found that the sulphide deposits lie within
or close to north-trending faults or shear zones. The most important host rocks
appear to be tuffaceous sediments and calc-silicate rocks. From the minor amount of
mineralization noted in the Deschambaulc Lake Area, the homblendic and calc-silicate
rocks also appear to be the most favourable host rocks for sulphide mineralization.
The most favourable localities for prospecting appear to be the zone ofhornblendic and
calc-silicate rocks in the eastern part of the area, especially near the inferred fault southeast
of D eschambault Lake, and the areas underlain by hornblendic and calc-silicate rocks
in the northwestern part of the area.
Printed by
LAWRENCE AMON, Printer to the Queen's
REGINA, SASKATCHEWAN
1967
16
Most Excellent Majesty.