Re-investigation in the Pickerel River and Limestone ......Xenoliths of diorite-granodiorite (unmapped 11nit) were observed rarely in the area. These contain numerous mafic schlieren
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Re-investigation in the Pickerel River and Limestone-Tulabi Lake Areas
by R. Macdonald and G. A. Posehn
These two areas were re-investigated as part of the project to compile the
geology of the Pelican Narrows (63M) and Amisk Lake (631) areas (see this publi
cation pp. 53-57.
Part I: Pickerel River Area (63M-5-E)
The area under investigation is located where the Pickerel River enters the
Churchill River at Trade Lake, approximately 110 km northeast of La Range,
Saskatchewan. The Trade Lake area was mapped previously by the DMR (Chakrabarti,
1969) at a scale of 1:63,360.
The Trade Lake area in general is situated in a gregarious batholithic domain
(the Glennie Lake Domain; Lewry in press). The Pickerel River vicinity is composed
essentially of volcanic and pelitic metasedimentary rocks which lie in septa
between composite batholiths. The area has lithological and tectonic features in
common with the Archean granite-greenstone belts of the Superior Province, with
the exception of a lack of late-tectonic elastic sedimentation.
The main objectives of this investigation were to test the feasibility of
establishing a stratigraphic sequence in the metamorphosed volcanic rocks and to
see if there is any basis for distinguishing phases and tectonic sequence in the
granites. Approximately 18 geologist-observation days (Posehn 13, Macdonald 5)
were spent in the field.
General Geology
Several supracrustal septa ranging between 0.25 and 2.5 km in outcrop width,
converge at the Pickerel River confluence. In the supracrustals, primary volcanic
features such as tuffaceous bedding, flow layers and pillow structures have been
identified. Tectonic cleavage, foliation and minor folds are also common. Most
of these planar structures strike east-west and dip sub-vertically or steeply to
the north. Mapping has shown the existence in the lithological layers of a broad
symmetry in pattern across the septa (fig. 1). Using limited way up criteria
obtained from pillow lavas, the mapped pattern suggests (1) the eyistence of a
rudimentary stratigraphic succession and (2) the greenstone septum is a fairly
simple tighi-ly folded syncline, slightly overturned to the south.
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LEGEND
METASEDIMENTARY ROCKS (·:::;:;'.~:~ Bf Garnet-bearing biotite metasedimen
tary rocks
~ ,,,:, ',,:'~]
1--·:-~>i',>J
lt!fflffl
---··· ..........
MET AVOLCAN IC ROCKS Vb Metabasaltic flow rocks Vf Felsic to intermediate volcanic Vl Laminated mafic vo l ca nogen i c rocks
Ve Hornblende granulites
GRANITOID ROCKS
Ga Biotite leucogranodiorite
Gg Biotite hornblende granodiorite
Ggs Refoliated biotite hornblende diorite
GM Metagabbroic rocks
Geological boundary (defined, approxima te, assumed) Limit of field mapping
Fault trace
grano-
Schistosity, gneissosity, foliation
Bedding; tops from pillows
Axial plane of minor fold
Mineral lineations
Minor fold axes plunge Trace of major synclinal
-
Fig. 1. - Geology, Pickerel River area
KILOMETERS 0 0
MILES
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The postulated general stratigraphic sequence is:
(4) Garnet-biotite metased imentary rocks (Bf) (3) Basaltic flow rocks (Vb) (2) Laminated volcanic rocks (Vl), with felsic volcanic laye r (Vf)
near the top (1) Hornblend e granulites (Ve), with subordinate felsic volcanic
laye rs (Vf)
INTRUSIVE CONTACT, generally with contaminated margin
Granites
A major synformal axis appears to pass through the upper massive basaltic
flow unit (Vb) in the middle of the greenstone septa . Tops from pillows agree with
the lineations and foliations fnr inference of the synclinal axis and stratigraphic
top.
Supracrustal Rocks
Fine grained hornblend e granulites (Ve), containing minor amounts of biotite,
epidote and diopside , occur at the lowest part of the postulated succession, in
places along the granite contact . The rocks are massive to finely laminated or
flaggy. Felsic volcanic layers occur locally.
Next in succession are distinctive and widespread occurring laminated volcanic
rocks (Vl). These are predominantly mafic with interlayers of felsic volcanic and/
or pelitic material, epidotic in places . Minor clistic zones with felsic volcanic
and ''gabbroic '' clasts, as well as several gossans were seen in this unit which is
interpreted as an interlayered tuffaceous sediment.
Near the top of the laminated volcanic unit is a felsic volcanic layer (Vf).
This rock is slightly porphyritic, acid to intermediate in composition, green to
pink in weathered surface, highly fractured, locally rusty and in places weathered
to sericite-muscovite schist.
The top of the volcanic sequence com?rises very fine grained and massive
basaltic flow rocks (Vb). Primary volcanic features observed include vesicules,
amygdules, minor tuffaceous beds and pillows.
Fine grained garnet-biotite metasediment (Bf) succeeds the volcanic rocks on
Archibald Island. Some of these contain large feldspar blasts; biotite-rich
varieties also occur. Several phases of intrusive white leucopegmatite have been
boudinaged, thrusted and rotated to appear as pseudo-granite clasts.
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Gabbroic Rocks
Coarse grained porphyritic gabbroic rocks (MG) occur north along the Pickerel
River, where layered gabbroic, dioritic and anorthositic rocks have also been
observed. This unit is highly sheared in places and cont~ins moderate amounts of
pyrite, chalcopyrite and pyrrhotite. These mafic rocks appear to have intruded
the volcanic succession.
Granitoid Rocks
A sequence of granitic phases has been established . This sequence is particu
larly well displayed in the migmatites mapped by Chakrabarti (op. cit .) around
Trail Bay, just west of the present area.
Xenoliths of diorite-granodiorit e (unmapped 11nit) were observed rarely in the
area. These contain numerous mafic schlieren and restites, suggesting possible
origin by anatexis of maf ic rocks. Biotite-hornblende granodiorite (Gg) is a major
unit, intrusive into supracrustals along the shores of Trade Lake. This rock has
marginal migmatite zones and is mod erately foliated to gneissic locally. Biotite
leucogranodiorit e (Ga) intrudes supracrustals and unit Gg . The margins of this
granodiorite contain more mafic minerals including hornblende, and are also
xenolithic and highly sheared or faulted. Grey biotite granite (unmapped unit) is
a fine grained rock which occurs in small dykes and irregular masses cross - cutting
most other rock types.
Late Refoliation, Shearing and Faulting
The granodiorites on the southern shore of Trade Lake are strongly refoliated
(see Macdonald, this publication, p.56). Strong shearing, seen in sub-mylonites,
is extensive on the margins of the biotite leucogranodiorite (Ga). The existence
of NNE-trending faults is inferred from offset of units, displacement of aero
magnetic contours, airphoto lineaments and the rare observation of shearing .
Part II Limestone-Tulabi Lakes Area (Parts of 63L-10-NW, -11-NE and 14-SE)
(See map in folder)
This area lies median to~ large splay of the Tabbernor Lake fault zone at
the southern margin of the Precambrian Shield and is generally accessible from the
Hanson Lake Road connecting Flin Flon with Smeaton. The area was mapped previously
at 1:63,360 scale by the DMR and there has been a fair amount of company exploration
and drilling in connection with sulfide mineralization in the volcanic rocks.
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The objectives of this investigation were to fill blanks in Padgham's (1968)
map, to attempt reconciliation of lithological units set up by Padgham with those
of Byers (1957), Kirkland (1958) and Pyke (1966) in adjoining sheets by Tulabi Lake
and to attempt stratigraphic correlation and structural synthesis between the areas.
Padgham's area (part of 63L-ll-NE), which comprises about two-thirds of the
accompanying map, has been remapped in some detail. The northern and eastern
fringes of the new map have been produced by partial remapping or modification of
Byers and Kirkland's maps, which are accordingly acknowledged. The extreme western
part of the map of the Hanson Lake area by Coleman and Gaskarth (1970) has also
been incorporated.
The area is unusually complex, both lithologically and structurally, and a
large number of rock units have been defined. These detailed descriptions will be
described in a subsequent publication or placed on department open file. The 57
geologist-days spent examining the rocks in the field (Posehn 43, Macdonald 14)
have been only partially sufficient to meet the objectives of the investigation.
General Geology
The area is cut by N-S, NNE, NNW and NW tr ending faults, splays of the gene
rally north-south trending Tabbernor Lake fault zone. The more dominant of these
faults have divided the area into a number of more or less distinctive geological
sub-regions or segments (fig. 2; see also the geological map in accompanying
folder) .
* 1. Southeast Arm s egment
This area contains several granites, raft ed and injected migmatites, and
mixed supracrustals, mainly semi-pelites.
Strongly sheared hornblende granodiorites (Gs) are found in the eastern
portion of this segment, adjacent to the west margins of the West Sarginson Lake
fault. This rock unit may be related to the moderately foliated to strongly
gneissic biotite hornblende granitic to granodioritic rocks (Gg, Gf; see map for
distribution); it is affected more by late intense cataclasism along the fault
zone. Late-to-post tectonic, massive to poorly foliated, garnet-bearing muscovite
biotite granitic to monzonitic rocks intrude the mixed supracrustals (Ga, Gm).
Late pink leucopegmatites of extremely variable textural variation, which
contain garnet, muscovite, tourmaline and beryl, locally intrude the supracrustals
* Southeast Arm, Deschambault Lake
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KILOMETERS c:1 ::E3::::E3:0:::==7""""':?'= I O
MltES I AH
Fig. Geological sub -domain s or segments describe d in text, LimestoneTulabi Lakes area
and form a large part of the area at Unser Lake .
2. Unser Lake schist belt
Confined essentially between the Unser Lake, and West and East Sarginson Lake
faults, this is a narrow ENE-trending segment. The southern part of the belt, in
the vicinity of the Hanson Lake Road, is characterized by andalusite, or chiastolite
bearing schists (Bta). The schists are finely interlayered argillaceous to psam
mitic meta --sediments (Bt) which contain~ nd graded beds .
3. -;\
Northern Lights volcanics l-l-6 .
1 lf6 ~
This wedge - shaped segment, well exposed along the Hanson Lake Road, comprises
predominantly mafic volcanics, but intermediate to felsic volcanics are also well
developed, particularly along the southern and eastern margins.
Original volcanic features observed were: pillows (with epidosite as core in
fillings or as material between pilloid forms), agglomeratic , ones (autobreccia t ed
* Provisionally named, after the North•xn Lights Lodge nearby .
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flows), minor interlayered graded tuffaceous sediments with coarse elastic zones,
vesicles and amygdules, and mimetic recrystallized hornblende phenocrysts.
4. Tulabi Lake assemblage
This southward-narrowing wedge comprises mixed supracrustals, with a dominance
of hornblendic rocks. Feldspathoblastic biotite gneisses occur in the north, but
the main mass comprises a thick mafic gneiss layer flanked on each side by f e lsic
(or arkosic) calc-silicate gneisses. To the south and south-east the rocks are
injection migmatites. The metamorphic grade is generally at amphibolite facies.
5. Jackpine - Hanson Lake segment
The core of the Jackpine Lake fold is composed of feldspathoblastic biotite
gneisses (Bx) (in the majority in the cross section along the road) and felspatho
blastic granodiorites (G )with a minority of migmatized mafic rocks. Similar rocks
appear to fold around the Tulabi Lake synform to the northwest. The rock units,
even taking into account their migmatized state,essentially differ from those of
the Tulabi Lake assemblage.
South of the Jackpine Lake fold lie the Hanson Lake volcanics (Byers, Coleman
and Gaskarth, op. cit.), an assemblage very similar lithologically to the Northern
Lights Group.
Structure
Fold structures in the western segments (1 to 3, Fig, 2) dominantly trend
north-south. These folds are generally tight (sub-isoclinal) with sub-vertical
axial planar surfaces. Fold plunges are also generally steep, and dominantly to
the north . Less common southerly, westerly and easterly lineations in the South
east Arm segment suggest possible cross folding. The steep northerly·-plunging folds
in the Northern Lights volcanics appear to be more open in style.
East of the Tulabi Brook fault (in segments 4 to 6), the folds are larger in
scale, even more open and trend northeast. The Tulabi Lake synform plunges gently
to the southwest. The Jackpine fold in the eas t (Coleman and Gaskarth, 1970) is a
broad southerly closing, vertically plunging fold of bathtub form with very steep
plunge.
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Late Shearing and Faulting
Shear fabrics are prominent in several areas:
(a) Southeast Arm of Deschambault Lake: Here mafic (? gabbroic or mafic volcano
genic sedimentary) rocks, semi-pelitic gneisses and late granites and/or grano
diorites have been sheared into flaggy gneisses, phyllonites or sub-mylonites.
(b) The granodiorites (Gs) along the western margin of the Unser Lake schist belt
are extensively and heterogeneously sheared over a width of one kilometre or more .
The shears, which are represented by a pervasive shear foliation, numerous thin
mylonitic bands, pseudo-tachylite and black quartz, commonly trend NE or NNE, some
what obliquely to the late brittle fault pattern. This obliquely-trend ing shear
foliation is persistant throughout the body of gneissic granodiorite and gneisses
in the northern apex of the Northern Lights segment.
(c) Intense shearing and brecciation have been observed along the Tulabi Brook
fault, where it has affected intermediate to felsic volcanic rocks, granites, migma
tite and pegmatite.
(d) Intense shearing and mylonitizationare also present generally along the western
margin of the Hanson Lake volcanics. In places, particularly in the felsic flows
it is difficult to distinguish shear from primary flow textures.
The discrete faults indicated on the map represent loci of brittle-type
rupture, presumably late in the tectonic sequence . The fault lines are largely
obscured by muskeg and/or lake, and have been inferred by (1) discontinuity or off
set of lithological units, (2) marked topographic lineaments (for example the fault
bounded Unser schist belt is marked by a prominent topographic scarp to the north
west) and (3) fracture patterns apparent from air photos or from the air.
The West and East Sarginson Lake faults form a parallel pair about one kilo
metre apart which traces south from the Shield through outcrop of the Ordovician
limestone as extremely strong fractures joints or topographic lineaments.
Synthesis
1. The Northern Lights volcanics appear to be lithologically and structurally
similar to the Hanson Lake volcanics (Byers, 1957, Coleman and Gaskarth, 1970),
occupying an outcrop area of similar dimension (Fig. 2), Semi-pelitic to pelitic
fine grained meta-sediments :1nd mineralization are associated with each group.
2. The faults along the western margin of the Unser Lake schist belt mark a
major junction between two distinct geological domains, batholithic to the west
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and supracrustal to the east. Gneissic granodiorites east of the belt are inter
preted to be of supracrustal origin (see Macdonald, this volume, p,55). There
is also a change in structural style and metamorphic grade across the faults.
3. The Tulabi Lake assemblage (segment 4), although at a relatively higher
metamorphic grade than the Northern Lights and Hanson Lake volcanics, nevertheless
clearly contains rocks of volcanic origin. These include massive amphibolites,
laminated calcareous hornblende gneisses and distinctive garnetiferous dacites
which have compositional equivalents in the two volc~nic groups. A conspicuous
pink quartzofeldspathic rock forms a traceable layer around the Tulabi Lake synform
and may be equivalent to the granites (Gl) in the Northern Lights volcanics and the
granite of the Hanson Lake area. The last-mentioned granite has been dated by
Coleman (1970) using the Rb/Sr isochron method at late Ar chean. We suggest that
the lithological assemblages of the Hanson Lake, Tulabi Lake and Northern Lights
areas may comprise largely volcanic rocks of one general stratigraphic unit, late
Archean in age.
References
Byers, A.R. (1957): Geology and Mineral Deposits of the Hanson Lake Area, Saskatchewan, Sask. Dept. Mineral Resources, Rept. No. 30.
Charkrabarti, A.K. (1969): The Geology of the Trade Lake Area (East Half), Saskatchewan, Sask. Dept. Mineral Resources, Rept. No. 134.
Coleman, L.C. and Gaskarth, J.W. (1970): Geology and Geochemistry of the Hanson Lake Area, Saskatchewan, Sask. Research Council, Geol. Div., Rept. No. 10.
Kirkland, S.J.T. (1958): The Geology of the Deschambault Lake Area (East ~alf),
Saskatchewan, Sask. Dept. Mineral Resources, Rept. No. 31.
Lewry, J.F. (in press): The Geology of the Glennie Lake area, Saskatchewan, Sask. Dept. Mineral Resources, Rept. No. 143.
Padgham, W.A. (1968): The Geology of the Deschambault Lake District, Saskatchewan, Sask. Dept. Mineral Resource, Rept. No. 114.
Pyke, M.W. (1966): The Geology of the Pelican Narrows and Birch Portage Areas, Saskatchewan, Sask. Dept. Mineral Resources, Rept. No. 93.
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