Geological Investigations of the Courtenay Lake-Cairns Lake Fold Belt and the Hills Lake Embayment, Johnson River Inlier, WoHaston

Domain, Saskatchewan

G.D. Delaney, Z. Jankovic 1 , A. MacNeil 1, J. McGowan 1, and D. Tisdale 2

Delaney, _G.D., Jankovic, Z., MacNeil, _A., McGowan, J., and Tisdale, D. ( 1997): Geological investigations of the Courtenay Lake-Cairns Lake Fold Belt and the Hills Lake Embayment, Johnson River Inlier, Wollaston Domain. northern Saskatchewan; in Summary of lnvest1gattons 1997, Saskatchewan Geological Survey, Sask. Energy Mine5, Misc. Rep. 97-4.

l . Introduction

During the summer of 1997 field work was focused on the Courtenay Lake-Cairns Lake Fold Belt on the southeast side of the Archean Johnson River Inlier (Figure 1) and in the Hills Lake Embayment on its northwest side. This work builds on previous investigations (Delaney, 1993, 1994; Delaney et al., 1995, 1996) designed to develop a better understanding of stratigraphic relationships in Paleoproterozoic supracrustal rocks along the southeastern side of the Wollaston Domain and the context of base metal mineralization in these rocks.

2. Courtenay Lake-Cairns Lake Fold Belt

The Courtenay Lake-Cairns Lake fold belt comprises a unique succession of Paleoproterozoic supracrustal rocks including a basal rift assemblage of coarse siliciclastic rocks and continental tholeiitic mafic volcanics (Fossenier et al., I 995) and an overlying thick rift fill sequence. Exposure throughout the belt is poor. Despite earlier investigations several aspects of the stratigraphy and structure of the belt remain to be resolved. These are key not only to understanding the early evolution of the Wollaston basin but also its metallogenesis.

a) Current Work

Mapping in 1997, as well as during part of the summer of I 996, was carried out around Fordham, Cook, Spence, Brakewell (George)-Wakefield and Causier­Courtenay lakes (Figure 2). In addition core from recent diamond drilling in this region was logged. This infonnation will be compiled as a new I :50 000 geological map for the Courtenay Lake- Cairns Lake fold belt. In conjunction, three B.Sc. theses investigations arc being undertaken at the University of Saskatchewan in collaboration with Dr. K. Ansdell. These projects are: an investigation of the Courtenay Lake Formation in the Cook Lake area by A. MacNeil, a study of felsic volcanics and subvolcanic intrusions in the Courtenay Lake Formation by Z. Jankovic, and a study of the characteristics of the Jansem 2 Cu-Ag showing at Janice Lake by J. McGowan. Preliminary

results are reported elsewhere in this volume, as are the final results of a study of the iron formation member of the Spence Lake Fonnation (Tisdale et al. , this volume).

b) Previous Work

Scientific Work

The study area encompasses the region between Courtenay Lake near the south end of the belt and Fordham Lake, to the southeast of Compulsion Bay, at the northeast end of the belt. It is contained in NTS I :50 000 map sheets 64E-5 (Coombe Lake) and 64 E-12 (Morell Lake). Early geological mapping included that of Weeks (1940) who mapped the northern part of the area at a scale of I :253,440 as part of his Spalding Lake map-sheet. In 1966, the western half of the Morell Lake map area (NTS 64E- l 2) and the northwestern most part of the Coombe Lake map area (NTS 64E-5) was mapped by Chadwick ( 1967) at a scale of I :63,360. A brief overview of the geology was provided in a 1967 report by Pyke and Partridge, which focused on exploration activity. In 1968, Scott ( 1970) mapped the Coombe Lake map area at a scale of I :63,360. The geology of the belt is discussed in a 1970 paper by Karup-Moller based on work for Falconbridge Nickel Mines Ltd. during 1965 and 1966. In a 1970 paper in Economic Geology, Karup-Moller and Brummer described the geology of the George Lake Zn-Pb deposit. Coombe mapped parts of the bel t in 1977 and 1978 (Coombe, 1977, 1978) and subsequently the results of this work were incorporated into a report entitled "Sediment-hosted base metal deposits of the Wollaston Domain, northern Saskatchewan" released in 1994. In 1977, the east half of the Morell Lake map-area was mapped at a scale of I: I 00 000 by Lewry er al. ( 1981 ) as part of a larger mapping project encompa~sing the Compulsion Bay area. During this project Thomas (1978) completed a B.Sc. thesis which described the geology of the Compulsion River area. In 1991, Lemaitre completed a B.Sc. thesis which focused on the stratigraphy, petrology, and genesis of the George Lake deposit and a 1995 B.Sc. thesis by Fossenier ( 1995; Fossenier et al. , 1995) investigated the geochemistry of mafic

~ Department of Geological Sciences. University of Saskatchewan. 114 Science Place, Saskatoon. SK S7N 5£2. Cominco Lid., Suite 2200, 120 Adelaide S1ree1 West. Toronto, ON M5H ITI.

90 Summary of lnvestigation.1· /997

WOLLASTON DOMAIN Proterozoic

PETER LAKE DOMAIN Reworked Archean I L. Proterozoic

D Granfte/gronodlorlte l22J Mofle/ fels/c gnel~sse · :_ ~ and gron/tolds H,..oo __ :-~ Mylonfte . :-

Lower Proterozoic - Courtenay/Co/ms Fold Baff _ :- \ ~ VO/conics, conglomerates, sandstones, pelftes, co/c rocks _ _::-- \

Lower Proterozoic - Wollaston Group

D Arkose/ co/coreous or~

ff?o],j Fonglomerate/ conglomerate

---------- ? Unconformity ?---------

Quartz muscC1,1/te schist

Pe/Itel psommlte

---------- Unconformity ----- --­

Archean

B Fe/sic gronltold

ROTTENSTONE DOMAIN Lower Proterozoic

F5'.,,~ Granite {WB)

:/; fl #) I I 0 10 20

102" ~~~~~~~~--~~~~6(J'

sroo ..

MINERAL OCCURRENCES

• Marina (Pb/Zn)

• Htns Lake (Pb/Zn)

• Simon (Pb/Zn)

e Joannie (Pb/Zn)

• George Lake (Pb/Zn)

" Janice Lake (CU/Ag)

30

""""'" ·= rLINrlo.' .,.._...

Figure 1 - Geological sketch map of the east-central part of the Wollaston Domain (from Delaney et al., 1996) showing the location of the Courtenay I Ake-Cairns Lake Fold Belt and the Hills Lake embayme11t (HLE). The inset map shows the lncation of this area with respect to the major lithostructural domains of the Precambrian Shield of northern Saskatchewan.

Saskatchewan Geo foRica/ Survey 91

Legend

Megacr:yspc granite -granod1onte Souter Lake Fm

[~J Flasered granite "1················-·······························-·-····

Paleoproterozoic

LJ Undi vided

Courtenay Lake Fm

D Quartz arenite . .. .... ... .. ....

D 10'~ L":.:ZJ

Causier Creek Fm

Paleoproterozoic\Archean Peter Lake Domain

/."';';';71 88 Granitoids\paragnciss

Archean Spence Lake Fonnation

• Iron Formation Member

George Lake Fm

0 2 4 6 B 10 L I---.J . ..1..._ L....J -L . . .1.._ '--l. -1

Km

~ l.'.8:.;J Granile

Figure 2 • Geological sketch map of the Courtenay l.ake-Caims I.Ake Fold Belt (includes i11/ormationfrom Coombe, 1994 and 1.,ewry et al., 1981). SI..S, Spence I.Ake Sync/foe.

volcanics of the Courtenay Lake Formation at Courtenay Lake. A 1997 B.Sc. thesis by Tisdale (1997; Tisdale et al., 1996; this volume) described the iron formation member of the Spence Lake Formation. Macdonald and Thomas (1983) and MacDougall (1984) compiled 1:250 000 scale geological and metallogenic maps respectively for the Reindeer Lake north map area (NTS 64E).

Exploration Work

Since the discovery of the George Lake deposit in 1965, the fold belt has been subjected to several exploration programs. Work prior to 1981 is summarized in Coombe (1994). Full details of that and subsequent work are contained in the Mineral Assessment Files of Saskatchewan Energy and Mines.

c) Local Geology

Paleoproterozoic supracrustal rocks of the Courtenay Lake-Cairns Lake Fold Belt occupy the core of the

92

Spence Lake Syncline, a tight upright syncline that trends and plunges shallowly to the southwest (Figure 2; Scott, 1970; Coombe, 1977. 1978, 1994; Lewry et al. , 1981). These rocks arc bound to the northwest by leucocratic granite of the Archean Johnson Ri ver Inlier. On the southeast side is a heterogeneous assemblage of granitoids and paragneiss included in the Peter Lake Domain (Figure I). Contact relationships between rocks of the Peter Domain and supracrustals of the Courtenay Lake-Cairns Lake Fold Belt are variable and discussed in the following sections.

The succession on the southeast limb of the syncline is essentially hornodinal, as much as 4200 m thick and is characterized by significant facies changes and variations in thickness along strike (Figure 2; Coombe, 1994 ). IL has been subjected to upper greenschist to lower amphiboli te facies metamorphism. A number of stratigraphic classifications have been proposed for these rocks (i.e. Karup-Miiller, 1970; Scott, 1970; Lewry et a!. , 1981); that of Coombe ( 1994), which distinguishes five formations, is used in a slightly

Summary of Investigations 1997

modified form in this paper (Figure 3; Coombe, 1994). The northwest limb of the syncline, where exposure is extremely sparse, is underlain by an up to 1900 m thick succession o f predominantly pelitic rocks with lesser arkosic and quartzitic intervals. Tight folding is common and these rocks have been metamorphosed at middle to upper amphibolite facies. This succession, named the Marginal Petites by Coombe ( 1994 ), was considered by him and others (i.e. ScoLt, 1970) to be the facics equivalents of some of the formations on the southeast limb of the synform . This interpretation is supported by remapping and examination of diamond drill core, which suggests that this succession comprises the uppermost four formations recognized on the southeast side of the syn form. Consequently, we advocate that the name Marginal Pelitcs be abandoned and the same formation names as used on the southeast side of the syncline be applied to the more deformed, higher metamorph ic grade units underlying the northwest limb.

d) Descriptions of Formations

The Courtenay Lake Formation

This formatio n consists of conglomerates and arkoses with intercalated amphibolites derived from mafic volcanics and quartz and feldspar-porphyroblastic quartzofe ldspathic rocks interpre ted as felsic volcanic and volcaniclastic rocks. Facies changes are co mmon (Figure 4 ). For example, in the Courtenay Lake area most of the siliciclastic part of the fonnation is arkosc intercalated with thin beds of conglo merate and conglomeratic arkosc, whereas at Cook Lake the formation is predominantly a pebble to cobble conglomerate (McNeil et al. , this volume) containing mostly clasts of a foliated leucocratic quartzofeldspathic rock. Still farther to the northeast at Fordham Lake conglomerates and grits are the most abundant, the conglomerates being characterized by pebble to bo ulder size fragments of a variety of mostly Icucocratic grani toids (Figure 5).

E u..

~ 0 -' (!) u c 2s. (/)

500 ai E

400 g,u:

., 1 g~ i 1- 300 0 .9

~ : 200 I 100 I ~ \ 0 .9 .

- E .Jl1 u.. :::,

~

E u..

~ .9 > 0 c g :::, 0 u

Legend

; - - 1 Arkose

Volcanic rocks occur at two stratigraphic levels. At both Courtenay and Cook Lakes the lower volcanic

member, which is thin and not laterally continuous, includes pillowed to massive mafic volcanics that lie unconformably

··- - _J

j: < ?i Calcareous arkose I.-· c; .,

\:.L--:--__ --. -=_. ~I Mudstones with intercalated _ _ turblditic sandstones

t _ --I Garnetiferous petite . ..,...- ·-· I

r-J L...:.._. Iron Formation

[' ,,.,.. ~J Cole-silic ate-bearing t..: ,:..,,:. ~I siltstone

Marble

Ji-~-_::-7J Calc-orgillite/Pelite " I :_ J

l _. . . l Argillite with intercalated I - · · - , siltstone

\ . . - . · : - ·. 1 Quartzite 1·· . . . I

1---, Slotey orgillite t - .: J

I Quartz-serieite schist I. ·=- J

~<v:>:'.·J Mafic volcanics L'' "_: ";:_ v\

l;?_:;~"j Conglomerate 1:..: .:,;:,. ;

w i:- •1 Felsic volcanics l. _. ! . . J

on quartzofeldspathic paragneiss (Figure 4). In conuast, at Fordham Lake, a thick, laterally continuous amphibolite occurs near the base (Figure 6). In some areas, fe ldspar and quartz.­feldspar porphyries occur at or near the base of the formation. For example at the Wakefield Lakes, southwest of Souter Lake, there is a sheared contact between quartz-feldspar porphyry and granitoids of the adjacent Peter Lake Domain. The upper volcanic member, which includes amphibolites, quartz-feldspar porphyries (Figure 7), and possible volcaniclastic rocks, generally is thicker and more la te rally extensive and porphyries arc more significant.

Rocks of the Courtenay Lake Fonnation apparently don' t occur on the northwest limb of the Spence Lake Syncline.

Figure 3 - Composite stratigraphic column for tire southeast limb of th_e Courtenay Lake-Cairns Lake Fold Belt in the Brakewell·Spence lakes area (modified after Coombe, 1994).

Fossenier et al. ( I 995) demonstrated that the mafic volcanics from the two volcanic members at Courtenay Lake arc tholeiites probably cmplaced in a continental rift setting. New data presented hy MacNeil et al. (this volume) and other data obtained during the current study show that

Saskatchewun Geoloi:ical Survey 93

I 600

• I. 400

~ I t i ::, 1· 200

~

L o

Legend

'.:."."'.} Granite/granodiorite

1 - --; , .. Intrusive contact

Souter Lake

tAAi\0::~1.\W.1

~!!!1 /c. <', ·"'·"' ; ,,, ···· .·,

viJ?N!/v'<f\A~

;f ::J Amphibolite

[ : i Quartz arenite

Cook Lake

Fordham Lake

If! f.{, r: . ' , , · ',,•I\';) ,I

J"''•"•"• " '" ' " " '"'l

Shear zone r{::{:/:/{\:/z} :

E ,' ::'.,~.I Quartz/feldspar porphyry

~ ~==~ Volcaniclastic

j E~B Intermediate vo(canic

f:&! Pillowed mafic volcanic

• Andalusite-magnetite schist

1 1 1 I. ;•;,, ···1-, : • . i'( . ,I Y··r::"·~·il.'.~ ·.,·,.,,, '

\ \/V -!\IVV\/'t,-

Unconformity Grit

(') '51

I· • . . Conglomerate

~:'.:-:.] Granite I paragneiss

~ Diorite I. ----' Arkose

Figure 4 - Schematic stratigraphic sections for the Courtenay I.Ake Formation.

mafic volcanics from the fonnation elsewhere in the bell have similar geochemistry. There are some exceptions, however, such as the amphibolite near the base of this formation at Fordham Lake, and one of the mafic flows southeast of Souter Lake which have an oceanic island arc signature. Further work will be required to explain these variations.

Trough cross-laminated quartz arenite (Figure 8) occurs near the base of the formation both southwest of Souter Lake and at Fordham Lake (Figures 4 and 6). Although contacts between the quartz arenitc and adjacent units are either sheared or covered, in both areas it is apparently underlain by quanz feldspar porphyry.

Figure 5 • Boulder conglomerate of the Courtenay I.Ake Formation, Fordham I.Ake.

94

Contact relationships with rocks of the Peter Lake Domain are variable. At Cook Lake, there is an unconformity between the Counenay Lake Formation and variably granitized quartzofeldspathic paragneiss and leucocratic granitoids of the Peter Lake Domain (MacNeil et al., this volume). Locally lenses of andalusite porphyroblastic magnctite-sericite schist interpreted to be derived from laterites occur along th is unconfonnity. Similarly, nonheast of Courtenay Lake, al though relationships arc more obscure, there is also apparently an unconfonn ity between the formation and fine-grained quartzofeldspathic paragneiss of !he Peter Lake Domai n (Coombe, 1994; Karup-Moller, 1970). Jn contrast, southeast of Souter Lake a shear wne marks the contact between quartz feldspar porphyries of the Courtenay Lake Formation and granitic rocks of the Peter Lake Domain. At Fordham Lake, granites intrude the Courtenay Lake Formation both nonheast and southwest of the lake as well as along the base (Figure 6).

The Souter Lake Formation

The Souter Lake Formation comprises quartz arenite to sub-arkose that locally contains intercalated gri t, mudstone, and conglomerate (Coombe, 1994). Thickness varies from about 200 m near Courtenay Lake to about 1200 mat Souter Lake. Our defini tion of the formation follows that of Scott's ( 1970) Souter Lake Group in that we include in the basal part, from the Souter Lake area, quartzite with intercalated aluminous pclitic rocks represented by graphitic slate

Summary of Investigations /997

i:--:--:-:-:- -.~ --~ I I· r I·

I I I I I

I

103"15'

lJ <: : i·' ·' ·.·.· . . . .. .. .. . . . r· .. : . . l' I· r . .. . . . .. . . . . r \· r·. . . ... ·:.·:: .- .. .. L·: . .. . .. . . . .

f .. . r. \·

I L : . • ... • . . . • • • . •.. 1· · . . . . . . ... . .. . I· I I ,· I.' l ". \· \ . . r. r I· I.'

I ..... ·.1 . . . . . 1 ·.....::....·~ Overburden

Legend

Megacrystic leucocratic granite ~

Porphyroblastic mesocratic granodiorite 1 -..j

·· intrusive contact ··

Paleoproterozoic

CJ . . . Quartz - feldspar porphyry

Mafic volcanic I volcaniclastic

0 1

Grit

Plagioclase porphyritic mafic volcanic

Conglomerate

Mudstone - siltstone

Amphibolite

Quartzite

Figure 6 • Geological sketch map of the Courtenay Lake Formation, Fordham !Ake area.

Saskatchewan Ceolo11ica/ Survey

2

95

and muscovitic schists that contain porphyroblasts of andalusite, biotite, garnet, and/or staurolite. Although Coombe ( 1994) included these rocks in the Courtenay Lake Formation, it is argued that there is a distinct break between them and the arkoscs, conglomerates, and volcanics. Although there arc no known exposures of the formation on the northwest limb of the Spence Lake Syncline, thick intersections of quartz. arenite and sub-arkose encountered there in recent diamond drilling by Far West Mining Ltd. indicates its continuity.

The George Lake Formation

The George Lake Formation comprises a 550 m thick sequence of dark grey, variably slaty, in part iron­sulphide-bcaring, laminated mudstone with minor intercalated siltstone and a distinctive variety of wacke characterized by ubiquitous, randomly oriented, white feldspar. Some of the slaty parts of the mudstonc contain significant graphite. Both magnetic anomalies and electro-magnetic conductors are a~sociated with the formation. Airborne geophysical surveys have been used to estimate a strike length of about 60 km for this formation and allow it to be traced around the closure of the Spence Lake Syncline and along a part of the northwestern limb (Figure 2).

Figure 8 • Lenticular bedded quartz arenite, Courtenay lake Formation, Fordham [Ake.

96

The Spence Lake Formation

The Spence Lake Formation differs from the other argi llaceous formations of the Courtenay Lake-Cairns Lake Fold Belt in containing signili<.:ant amounts of calcite and/or calc-silicate minerals. It has a highly variable nature, and ranges in thickness from 500 m in the southwest to 1200 m in the Spence Lake area (Coombe, 1994). Within the formation. many sedimenlary facies arc recognized, although some arc quite thin and have limited lateral extent.

The lower part of the formation comprises a monotonous dark grey to grey weathering sequence of thin-bedded variably calcareous pclite. The pclite is very fine- to medium-grained, slaty to phyllitic and composed of quart,. amphibole, diopsidc, plagioclasc, and calcite. Some beds contain fine-grained garnet and/or pyrite. One kilometre northeast of Courtenay Lake, on the west side of Causier Creek, near the base of the formation, is a SO m thick interval of mudstones and siltstoncs containing from I to 5 m th ick weakly calcareous quartzite layers. This important marker also occurs on the northwest side of the Spence Lake Syncline in the vicinity of Causier Creek. Coombe (1994) named the quartzite there "calcareous quartzite'' and the adjacent rocks the Northwestern and Southeastern Pclites.

Overlying the lower part of the formati on is a thick sequence of mudstonc with intercalated wackc and siltstone. Siltstone forms laminated huff to light grey weathering beds. Iron sulphides are common throughout much of this sequence and parts contai n abundant calc-si licate minerals. In the Courtenay Lake area, near the top of the Spence Lake formation is a I lo 2 m wide, light grey, foliated layer of calcareous marble that contains boudinaged quartz laminae and some trace diopside (Coombe, 1994 ). This marhle unit is overlain by a narrow interval of calcareous mudstone and siltstone, which has a gradational contact with calcareous arkosc of the overlying Causicr Creek Formation.

In the northeast. around Spence Lake, the uppermost part of the Spence Lake Formation comprises a sequence of calc-silicate-bcaring siltstone and sandstone, garnetifcrous pelite, iron formation, and mudstonc with intercalated turbidit ic sandstone. These rocks arc described in a paper by Tisdale et al. (this volume).

The Causier Creek Formation

This format ion, which is estimated to he ahout 4()(J m thick, occupies the core of the Spence Lake Synforrn. It consists of pink, buff or light grey arkosc locally with maroon and light grey colour hands. A strong mineral lineation generally mash primary structures although locally cross beds arc sti ll preserved. Parts of the arkosic sequence contain epidote, hornblende. and other calc-sil icatc minerals. Disseminated magnetite oc.:curs in the basal part of the format ion and gives it a distinctive magneti c.: signature.

S1111111wry of IIIVl!Sli[(lllio n .1· 1997

e) Structure

Bedding is preserved throughout much of the sequence underlying the southeast limh of the Spence Lake Syncline. Cross bedding, in the Courtenay Lake Formation in the Courtenay and Cook lakes areas, and graded bedding in the Souter Lake Formation , consistently indicate younging to the northwest to the core of the syncline. Rare crosshedding was also observed in the Causicr Creek Formation on both sides o f the axis of the Spence Lake Syncline. On the northwest side of the syncline, bedding is generally obscured as most of these rocks have been converted to schists and phyllites.

At least four epi sodes of deformation have affected rocks in the Courtenay Lake-Cairns Lake fold belt. As the first two correlate with the DI and 03 events described by Lewry and Sibbald (1980) in the adjacent Mudjatik Domain, that event te rminology is used here. Structures attributed to the D2 event in the Mudjatik Domain are not recognized. DI formed a prominent foliation sub-parallel to bedding. Rare intrafolial isoclinal folds observed in diamond drill core were also formed during this event. D3 formed the Spence Lake Syncline (Lewry et al., 1981 ), a large-scale tight upright syncline that plunges moderately to the southwest (Figure 2; Coombe, 1977, 1978, 1994; Thomas, 1978; Lewry et al., 1981 ). Tight to isoclinal (F3) minor folds plunge moderately to the southwest and have a vertical axial surface. An axial plane parallel crenulation cleavage (S3) is developed at a low angle to SI . A horizontal to shallowly plunging mineral stretching Iineation parallels the fold axes. Because of sparse exposure , much of the information about the morphology o f the Spence Lake Syncline has been derived from ground and airborne geophysical surveys completed during various exploratio n programs. Particularly revealing is an airborne magnetic survey by Esso Minerals Canada in 1986 (SEM Assessment File 64E-OO 11 ). The form and closure of the Spence Lake Syncline (Figure 2) and tight folding on its northwest limb arc defined by the highly magnetic iron formauon member of the Spence Lake Formation and hy the weaker magnetic anomaly associated with the George Lake Formation.

04 formed steeply northeast-plunging Z symmetry minor folds with vertical axial surfaces and an associated strain slip cleavage. These struc tures are particu larly abundant in the Causier-Cour_tenay lakes area. North-trending bnttle to bnttle-ductrle generally sinistral faults, such as the Spence Lake Fault (Figure 2), developed as a result of D5 , the final episode of deformation.

f) Discussion of the Early Origin of the Courtenay Lake-Cairns Lake Fold Belt

From our work we propose a preliminary model for the early evolution of the Courtenay Lake-Cairns Lake fold hclt and present some thoughts o n the base metal potential of these rocks. Basement to the Courtenay Lake Formation was a heterogeneous terrain of quartzofcldspathic paragneiss and leucocratic

Saskatclu'Wan Geolu~ical Survey

granitoids. Zircons from one of these granitoids, near the Courtenay Lake area have yielded a U-Pb age of 2086 +52/-8 Ma (Anneslcy et al. , 1992). Rifting took place in a humid tropical climate which locally formed latcrites. These arc preserved as lenticular bodies of andalusite porphyroblastic magnetite-sericite schist at the unconformity and on top of a basal pillowed mafic volcanic flow at Cook Lake (MacNeil et al., this volume). Rifting created a basin margin charact~rized by along-strike changes in basement structures s1m1lar to alternating depressed and raised piano keys. Early in che rifting there was an episode of bimodal volcanism that, at least locally, was subaqueous forming the pillows at Cook and Courtenay lakes. The increase in relief associated with rifting formed a braidplain or braided fluvial regime. During the waning stages of sedimentation there was a second more extensive episode of bimodal volcanism. Hot humid tropical conditions prevailed during a hiatus afte r deposition of the Courtenay Lake Formation and formed soils subsequently eroded and deposited as the highly aluminous schists found intercalated in hematitic quartz arcnites in the basal part of the overlying Souter Lake Formation at Courtenay Lake. This formation comprises fluvial to shallow water sediments al the base and overlying proximal turbidites that record the initiation of flexural subsidence in the rift basin and mark the heginning o f rift cover sedimentation. Continued subsidence and a reduction in sediment size and quantity led to deposition of the fine-grained . argillaceous sediments of the George La.~e Form~uon in an cuxinic trough that paralleled the ntt sag axis. As the basin became further starved to tine-grained siliciclastic detritus, carbonates precipitated and mixed with the argillaceous sediments forming the basal part of Spence Lake Formation (cf. Coomhe, 1994) . . Reactivation of some basement structures associated with initial rifting created a complex basin architec t_ure recorded hy the many contrasting facies that comprise the upper part of the Spence Lake Formation. These ranged from an approx imately 30 km long restricted suh-basin in which deep-seated hydrothermal fluids vented and precipitated as iron formation (Tisdale et al .. this volume) to emergent lagoonal tlats on which carbonate breccias formed. A major regression and uplift of adjacent granitoid tcrranes l~d to deposition _of arkoses of the Causicr Creek Formation concluding rift cover sedimentation

Since the discovery in 1965, of the quartzite-hosted George Lake deposit of about 5 million tonnes grading 2.65 percent Zn and 0.35 percent Pb (Karup-Mollcr and Brummer, 1970; Coombe, 1994), the Courtenay Lake-Cairns Lake fold belt has been the focus of numerous exploration programs for base metal mineralization . This work has resulted in the discovery of other occurrences o f base metals such as the quartzite-hosted Joannie showing, the base metal­bearing quartz veins of the George NW zone (Coombe, J 994) and argillitcs of the Spence Lake Formation, near Highway 905, that contain 1347 ppm Ph and 7782 ppm Z n (SEM Assessment File 64E-OO 11 ).

Sedex deposits, a major source of Zn , Pb, and Ag, most commonly form in rift-cover sequences, similar to that

97

in the Courtenay Lake-Cairns Lake Fold Bell, by the venting of hydrothermal fluids at or just below the sediment-water interface (Lydon, 1996). The Spence Lake Formation is probably the most favorable target unit for a major scdex deposit in the belt. Iron formation near the top of the formation, in the Spence Lake area, is evidence of hydrothermal fluid activity (Tisdale et al., th is volume). Lead- and Zn-rich argillites, in the Courtenay Lake area, al about the same stratigraphic level as the iron formation, may be the distal expression of base metal-bearing hydrothermal fluids. Another important parameter was the presence of sediment-starved sub-basins such as that in which the iron formation accumulated.

An important constraint on this type of mineralization is that it is apparently restricted to sedimentary sequences younger than 1800 Ma (ibid.). Kirkham and Roscoe ( 1993) have hypothesized that early ocean waters were devoid of H2S due to the significant reservoir of Fe2

• in anoxic Archean and Paleoproterozoic seas. Conditions favorable for the deposition of sedex-typc deposits would only have existed with the completion of oxyatmoversion ca. 1800 Ma and the accompanying extraction of the significant build up of reduced iron in ocean waters. These constrainL~. if valid, could have significant implications on the potential of the sedimentary rocks of Courtenay Lake-Cairns Lake fold belt to host sedex­style mineralization in spite of some key indicators. Near Courtenay Lake, basement to the fold belt has been dated at 2086 +52/-8 Ma (Annesley er al., 1992). Timing of deposi tion of the Courtenay Lake Formation has not yet been determined, however, work currently in progress to date zircons from quartz feldspar porphyries should help constrain this event. Further modeling is also required on the key parameters active during deposition of the rift cover sequence.

3. Hills Lake Embayment

The Johnson River Inlier, along the southeast side of the Wollaston Domain, is a northeast-trending Archean granitoid body flanked by Paleoproterozoic supracrustal rocks (Figure I). The inl ier, which is up to 12 km wide and has a strike length of 240 km in the Saskatchewan part of the domain, is generally straight sided with only local infol<ling of the adjacent supracrustal rocks into its margins (Delaney et al .. 1996). Some of these infolds may be original depositional features modified by subsequent deformation which served as the loci for Pb-Zn mineralization. An exceptional example of this general style is the area to the east of Hills Lake where a large subcircular-shaped body of sedimentary rocks protrudes into the inlier. This feature will he referred to as the Hills Lake embayment.

98

a) Present and Previous Work

Mapping during the summer of 1997 focused on the area between Hills and Zentner lakes and added to work completed in the summer of 1996 where the area. to the west of Hills Lake was mapped. The study area 1s included in the west half of the Morell Lake map-area (NTS 64E- l 2) which was mapped at a scale of I :63,360 by Chadwick ( 1967). Since the 1963 discovery of Pb-Zn mineralization at Hills Lake, there have been several exploration programs conducted in that area. Work prior to 1978 is summarized in Coombe ( 1994); details of that, and subsequent work, is contained in the Mineral Assessment Files of Saskatchewan Energy and Mines.

b) Local Geology

Outcrop exposure is generally poor. particularly for supracrustal rocks in the embayment.

The Hills Lake embayment is interpreted to be a Type I interference basin structure. On hoth the northeast and southwest sides of the embayment, granite of the Johnson River Inlier occupies a series of shallowly plunging anti formal ridges and synformal keels (Figure 9). The granite is overlain by medium-grained to coarse-grained biotite gneiss and fine-grained melanocratic garnet-biotite granulite, rocks similar to those forming the basal pelitic assemblage that unconformably overlies the inlier along its northwest side (Delaney et al .. I 996). Fine-grained quartzofeldspathic rocks that locally contain biotitic-, hornblendic-, or diopsidic-bcaring intervals overlie the pelit ic rocks. The core of the embayment is underlain by conglomerate characterized hy a generally intact framework of poorly sorted angular clasts composed mostly of arkose (Figure I 0). This unit is similar to fanglomerates of the Janice Lake Formation in the vicinity of Janice Lake (Delancy et al .. I 995: Figure I ). In most exposures, the supracrustal rocks exhibit a very strong mineral stretching lineation; in the conglomerate, the clasts have commonly been very strongly elongated (Figure l 1 ). These linear elements generally plunge shallowly to the west (Figure .12). This is interpreted to be parallel to the fold axis, which defines the embayment, which is at a high angle to northeast-trending F3 folds typical of the Johnson Ri ver J nlier.

Fanglomerates in the embayment indicate that the major episode of uplift that formed this unit is much more extensive than previously recognized (Delaney er al. , 1996). Furthermore, this increases the prospective area that may be favorable for sediment-hosted copper mineralization similar to that at Janice Lake.

Summary of fllves1i,:t1tions /997

103•55·

Legend

Granite - paragneiss intrusive contact······-·-·--.... ·----­

Paleoproterozoic

F:'3 Undi~ided p~a~eiss i?c~udes ~ arkos1c and b1ot1t1c vaneties ~ ~ Fanglomerate

0 1 2 3 4

km

~ Highly strained ~ _ quartzofeld~athic paragneiss _

[] Arkose

Q Biotitic gneiss, quartzite unconformity ...................................... .

Archean

Granite

Figure 9 - Geological sketch map of the Hills Lake Embayment.

Smka1chewan GeoloKical Survey

5

West of Hills Lake Fault

99

f'igure 10 - Conglomerate (fanglomerate) in tl,e Hills ]Ake Embayment. Note the large angular clast of arkose just above the scale

Figure 11 • Strongly rodded clasts in conglomerate unit in the Hills lake embayment.

N

u

c

. a

...... ___ ./

·-----.--------Figure 12 - Equal area stereo11et plot of mineral lineations and rodded clasts, Hills Lake embayment. Zentner Lake area lineations; number of sample points=46, mean lineation azimuth is 255.5°, and mean lineatio11 plunge is 4.2°.

JOO

4. Acknowledgments

Wayne Darch (Noranda Exploration Co. Ltd .), Bob Hindson (Far West Mining Ltd.), Ken Daughtry (Discovery Consultants), and Just in Reid (Cominco Ltd.) are thanked for their frank exchange of ideas and for access to confidential information and drill core.

5. References Anneslcy. l.R .. Madore. C., and Krough, T.E. ( 1992): U-Pb

geochronology of some granitoids from the Peter Lake Domain: A summary; in Summary of Investigations 1992, Saskatchewan Geological Survey , Sask. Energy Mines. Misc. Rep. 92-4, p 168-171.

Chadwick. R. ( 1967): The geology of the Morell Lake area {west half) Saskatchewan: Sa.~k. Dep. Miner. Resour., Rep. 116, 24p.

Coombe, W. ( 1977): La Runge-Wollaston helts base metals project; ;,, Summary of Investigations 1977, Saskatchewan Geological Survey. Sask. Dep. Miner. Resour .. p85-104.

____ ( 1978): Wollaston base metals project. Spence Lake area; in Summary of Investigations 1978, Saskatchewan Geological Survey. Sask. Dep. Miner. Resour., Mi ,c. Rep. 78- 10, p92-97.

____ ( 1994): Sediment-hosted base metal deposits of the Wollaston Domain. northern Saskatchewan; Sask. Energy Mines. Rep. 21 3. IO!!p.

Delancy. G.D. ( 1993): A re-examination of the context of U­Cu, Cu. and U mineralization, Duddridge Lake, Wollaston Domain; in Summary of Investigations 1994. Saskatchewan Geological Survey, Sask. Energy Mine~. Misc. Rep. 93-4, p53-6 I.

____ ( 1994 ): Geological setting of sediment-hosted copper mineralization in the area southwest of Janice Lake, Wollaston Domain; in Summary of investigations 1994. Saskatchewan Geological Survey. Sask. Energy Mines, Misc. Rep. 94-4. p53-6 I.

Delaney. G.D .• Maxeiner, R.O., Rawsthorne, M.L.. Reid. J. , Hartlauh. R .. and Schwann, P. (1995): Geological setting of sediment-hosted copper mineralization in Janii:e Lake area, WollaMon Domain: in Summary of Investigations 1995. Sa~katchcwan Geological Survey. Sask. Energy Mines, Misc. Rep. 95-4. p30-48 .

Delaney, G.D., Tisdale, D .. and Davies, H. {! 996): Stratigraphic relationships and base metal mineralization in the lower Proterozoic supracrustal assemblage along the Archean Johnson River Inl ier, Wollaston Domain, Sa~katchewan; i11 Summary of investigations 1996. Saskatchewan Geological Survey, Sask. Energy Mines, Misc. Rep. 96-4, p3- J I.

Fossenier, K. ( 1995): Lithogeochemistry of meta volcanic rocks from the Courtenay Lake Formation. Courtenay Lake, Saskatchewan; unpubl. B.Sc. (honours) thesis . Uni v. Regina, SOp.

Fossenier. K .. Delaney. G.D., and Watters, R.R. (1995): Lithogeochemistry of volcanic rocks from the Lower Proterowic Courtenay Lake Formation, Wollaston Domain: i11 Summary of Investigations 1995.

Summary of ifl vl'Stigations / 997

Saskatc hewan Geological Survey. Sask. Energy Mines. Misc. Rep. 95-4. p49-60.

Karup-Moller, S. ( 1970): Geology of the Compulsion Ri ver Fold Belt; Western Miner. v4 3. no2. p35-5 I .

Karnp-M<illcr. S. and Brummer. J.J. ( 1970): The George Lake 7.inc deposit , Wollaston Lake area. northeastern Saskatchewan; Econ. Geol. , v65. p862-874 .

Kirkham. R.V. and Roscoe. S.M .. ( 1993): Atmospheric evolu tion and ore deposit fo rmation; Re~ource Geology Special Issue . No. 15. pl-1 7.

Lemaitre. R. ( 199 ! }: The stratigrnphy. petrology amJ genesis o f the Georgc Lake sandstone-hosted zinc deposit; unpuhl. B.Sc. thcsis. Queen's Univ .. 69p.

Lewry, J.F. and Sibhald T.1 .1. ( 1980): Thcrmotcctonic evolut ion of the C hurchi ll Province in northern Saskatchewan: Tecwnophysics. v68. p45-82.

Lewry, J.F., T homas. D.J., Recs. C .J .. and Roherts, K. ( 198 I ): Geology of an area around Compulsion Bay. Wollaston Lake : Sask. Miner. Resour .. Rep. 205, 27p.

Lydon. J .W . ( 1996}: Sedimentary exha!ative sulphides (Sedex): in Eckstrand. O .R., Sinclair, W .D .. and Thorpe. R.I. (eds.) . Geology of Canadian Mineral Deposit Types, Geo I. Surv. Can .. Geology of Canada, no8. p I 30- 152.

Macdonald. R. and Thomas. M.W. ( 1983): Compilation bedrock geology. Reindeer Lake North. NTS area 64E; Sask. Energy Mines. Rep. 232 ( I :250 000 scale map with marg inal notes).

MacDougall . D.G. ( I 984 ): Metallogenic map series. Reindeer Lake north. NTS area 64E; Sask. Energy Mines. Rep. 239 ( I :250 000 scale map with marginal notes).

Pyke. M.W. and Partridge, E.F. (1967): Occurrence of base metal mineralization along the Wollaston-Sandlly lakes trend; Saskatchewan Industrial Exposition and Mineral symposium (INDEX) 1967. Regina Proc., p322-330.

Scott, R.P. ( 1970): The Geology of the Combe Lake area. Saskatchewan; Sask. Dep. Miner. Rcsour., Rep. 135, 32p.

Tisdale. D.T. ( 1997): Name, o rigin. and economic s ignificance of the iron formation member of the Spence Lake Formation. Woll aston Domain, Saskatchewan; unpubl. B.Sc. thesi s. Uni v. Saskatchewan, 54p.

Thomas, D. ( 1978): The geology of the Compulsion River area, Saskatchewan; unpuhl. B.Sc. thesis. Univ. Regina, 20p.

Tisdale , D .T., Delaney. G .D .. and Ansdel l. K. ( 1996): The iron formation me mber o f the Spence Lake Formation. Lower Proterozoic Councnay Lake- Cairns Lake Fold Belt, Wollaston Domain. Saskatchewan; in Summary of lnvcsligations I 996. Saskatchewan Geological Survey. Sask. Energy Mines. Misc. Rep. 96-4, p 12-2 1.

Weeks. L.J. ( 1940): Spalding Lake, no rthe rn Saskatchewan: Geol. Surv. Can., Map 596A.

SaskarchC'wan Geological Survey IOI