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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.