The Iron Formation Member of the Spence Lake Formation, Lower Proterozoic Courtenay Lake-Cairns Lake Fold Belt, Wollaston

Domain, Saskatchewan

D. Tisdale 1, G. Delaney, and K. Ansde/1 1

Tisdale , D., Delaney, G. , and Ansdell , K. (1996): The Iron Formation member of the Spence La~e F.ormation , Lower Proterozoic Courtenay Lake-Cairns Lake fold belt, Wollaston Domain , Saskatchewan; in Summary of lnvest1gat1ons 1996, Saskatchewan Geological Survey, Sask. Energy Mines, Misc. Rep. 96-4 .

The Courtenay Lake-Cairns Lake fold belt (Money, 1968; Scott, 1970), also referred to as the Courtenay­Cairns Lake belt (Coombe, 1977, 1978a, 1994; Lewry et al., 1981 ), the Compulsion River Belt (Pyke and Partridge, 1967), or the Compulsion River Fold Belt (Karup-M0ller, 1970; Karup-M0ller and Brummer, 1970), along the southeast side of the Wollaston Domain (Figure 1), comprises a unique asse~blage Lower Proterozoic supracrustal rocks. These include conglomerates and continental thol~iitic volca.nics at the base (Fossenier et al., 1995) overlain by a .thick succes­sion of quartzites, graphitic mudstones, variably calcare­ous fine-grained siliciclastic rocks, arkoses, and rare carbonates. They host the George Lake deposit of about 5 million tonnes grading 2.65 percent Zn and 0.35 percent Pb (Coombe, 1994) in quartzite as well as other occurrences of Pb-Zn mineralization. Near the top of the succession, in the Spence Lake area, is an oxide and silicate facies iron formation member whose charac­ter and geological setting are poorly understood. Some workers have suggested this iron formation is similar to ones associated with Pb-Zn mineralization in the Broken Hill area of Australia. The purpose of this project is to investigate the characteristics of the !ron formation and its bounding units and to evaluate its metallogenic significance with respect to Pb-Zn minerali­zation in the belt.

The study area lies around Spence Lake in the eastern part of Morell Lake map area (NTS 64E-12). Spence Lake is located approximately 20 km east of Highway 905 and about 15 km south of Compulsion Bay, on Wollaston Lake. Mapping at 1 :10 000 scale, and locally more detailed was undertaken on all known outcrop of iron formation' and enclosing rocks. Outcrop is typically poor, limiting the scope of mapping and ?PPOrtunit~ f.~r detailed geological observations. Magnetic suscept1b1hty data were measured for different rock types and samples collected for petrographic and geochemical studies. This work was performed as part of an honors dissertation by D. Tisdale at the University of . Saskatchewan, and is part of a larger study of the strati­graphy and base metal mineralization of the Wollaston Domain by Delaney (Delaney, 1993, 1994; Delaney et al. , 1995, this volume; Fossenier et al., 1995; Purser and Delaney, 1994).

1 . Previous Work

a) Scientific Work

The first geological mapping done by Weeks {1941) con­sisted of a 1 inch to 4 mile scale map of the northern portion of the area; the southern part was mapped at the same scale in 1968 by Baer {1969). In 1966, the western half of the Morell Lake map area (NTS 64E-12), was mapped at a scale of 1 :63,360 by Chadwick (1967). In 1967, Pyke and Partridge d!scussed the ~arly exploration activity, including prospecting, and provided a brief geological overview of the area. In 1968, Scott {1970) mapped the Combe Lake map area (64E-5), located to the south of the Morell Lake map area, at a scale of 1 :63,360. In 1970, Karup-M0ller described the geology of the Compulsi.on Riv~r fold .b~lt, bas~d on work for Falconbridge Nickel Mmes L1m1ted during 1965 and 1966. Also in 1970, Karup-M0ller and Brummer described the geology of the George Lake deposit, located about 10 km southwest of Spence Lake . In 1978, Coombe (1978a) mapped the Spence Lak~ a~ea as part of an ongoing study of base metal potential in the Wollaston Domain (Coombe, 1977, 1978a and b, 1994). Coombe {1978a, 1994) i~cluded brief de.scrip­tions and ,provided the only published geochemical data for the iron formation member of the Spence Lake Formation. In 1977, the east half of Morell Lake map area was mapped at a scale of 1:100 000 scale by Lewry et al. {1981) as part of a larger mapping project encompassing the Compulsion Bay area. Th~mas . {1978) described the geology of the Compulsion River area including the Spence Lake area based on map- . ping completed under this project. A study of the strati­graphy, petrology, ·and genesis of the G~org~ Lake. deposit by Lemaitre {1991) included a brief d1scuss1on of regional stratigraphic relationships in the CourteAay .. ,. Lake-Cairns Lake Fold Belt, and of the origin of the iron formation and its metallogenic significance. Macdonald and Thomas (1983) and MacDougall {1984) compiled 1 :250 000 scale bedrock geological and metal­logenic maps respectively for the Reindeer Lake north map area (NTS 64E) .

(1) Department of Geological Sciences, University of Saskatchewan, 114 Science Place, Saskatoon, SK S7N 5E2.

12 Summary of Investigations 1996

b) Exploration Activity

Since the discovery in 1965 by George Flatland of Pb­Zn bearing quartzite boulders at George Lake and the subsequent delineation of the George Lake deposit by Falconbridge during the period 1965-1970 (Coombe, 1994), the Spence Lake area has been included in sev­eral major exploration programs. Results of this activity are contained in the Mineral Assessment files of Saskatchewan Energy and Mines. Most of these pro­grams paid cursory attention to the iron formation member of the Spence Lake Formation, although J.L. Macleod of Esso Minerals Canada drew parallels be­tweM it and the iron formations in the Broken Hill area of ~ustralia which are associated with sulphide minerali­zation (SE~ Assessment File 64E-0011 ). The Spence Lake area 1s currently under disposition to Far West Mining Ltd. who are in the midst of a major multifaceted exploration program.

WOLLASTON DOMAIN Proterozoic

§ Gronite/gronodior1te

~ Mylonite

Lower Proterozoic

D .Arkose/colcareous orkose

~ Fonglomerate/conglomerote

-----? UNCONFORMITY ?-----~ Quartz muscovite schist

§ Pelite and psommite

-----? UNCONFORMITY ?----­Archean m Felsic gran itoid

ROTTENSTONE DOMAIN Lower Proterozo1c

D Granite (Wothomon Botholith)

PETER LAKE DOl.4AIN Reworked Archean and Lower Proterozoic rocks Ll Mofic and felsic gneiss and gronitoids

0 10 20 JO

km

5700'

LEGEND

W Mineral occurence s: 1 Morino (Pb-Zn) 2. Hills Lake (Pb-Zn) J . Simon ( Pb-Zn) 4. Joannie (Pb-Zn) 5 . George Lake (Pb-Zn) 6 . Janice Lake (Cu -Ag)

---- Fau lt

2. Geological Overview of the Woll~ton Domain

The Courtenay Lake-Cairns Lake Fold Belt occurs along the southeast side of the Wollaston Domain adja­c~nt to the Peter Lake Domain (Figure 1; Lewry and Sibbald, 1977). The Wollaston Domain comprises a northeast-trending, generally tightly folded linear belt of siliciclastic metasediments and minor metavolcanics segmented by interfolded remobilized Archean grani­toids (Money, 1968, Money et al., 1970; Ray, 1979; Lewry and Sibbald, 1979, 1980; Ray and Wanless, 1980; Lewry, 1981; Stauffer, 1984). Southeast of Courtenay Lake, the eastern boundary of the Wollaston Domain is marked by the Needle Falls Shear Zone (Munday, 1974; Ray, 1974; Lewry and Sibbald, 1980; Stauffer and Lewry, 1993). Along much of the Courtenay Lak~airns Lake Fold Belt, however,

PETER LAKE • DOMAIN ...,

!ICY

Wr-------------t

Fig~re 1 · Geological sketch map.of the ea~t-central part of the Wollaston Domain showing the location of the Courtena Lake­Cairns Lake Fold Belt and other /Jthotecton,c elements referred to in the text (modified from Macdonald and Thomas (1'83) Ray (1983a and b), and Delaney et al. (1995)). '

Saskatchewan Geological Survey 13

boundary relationships with the adjacent Peter Lake Domain are ambiguous (Coombe, 1994). The western boundary between the Wollaston Domain and the Mudjatik Domain, which forms the high-grade core of the Cree Lake Zone, is marked by a change in struc­tural style from linear to arcuate {Lewry and Sibbald, 1980). Compositionally heterogeneous granitoid rocks predominate and supracrustal rocks are subordinate in the Mudjatik Domain. The relationship between these supracrustal rocks and those in the Wollaston Domain has been suggested to be equivocal (Bickford et al., 1994), although this opinion is not founded on any new data. Earlier workers, who had mapped in these areas, have suggested that the supracrustal rocks of the two domains were in structural and stratigraphic continuity (Munday, 1978; Lewry and Sibbald, 1980). To the west of the Courtenay Lake-Cairns Lake Fold Belt, su­pracrustal and granitoid rocks of the Wollaston Domain are overlain by Athabasca Group sandstones and con­glomerates.

Over much of their extent, supracrustal rocks of the Wollaston Domain are broadly divisible into a thin , locally graphitic, basal pelitic succession which includes semipelites and quartzites and a thick upper succession of arkoses and calcareous arkoses (Money 1966, 1968; Ray, 1979). Ray (1979) proposed the name Wollaston Group for these rocks. Restricted, unique assemblages (including conglomerates, quartzites, arkoses and minor volcanic rocks) occur in narrow, areally restricted strips along the southeastern margin of the domain (Ray, 1979; Delaney, 1993). The stratigraphic relationship be­tween these rocks and the Wollaston Group is generally unclear; however, locally, such as in the Nelson Lake area, fanglomerates of the Janice Lake Formation over­lie a thin but distinctive quartzofeldspathic gneiss unit which lies above the basal pelitic succession recog­nised throughout much of the domain (Delaney et al., this volume). In the Hidden Bay area of Wollaston Lake, what is believed to be the uppermost part of the supracrustal succession comprises a unique assem­blage of amphibolite, quartzite, and marble (Wallis , 1971; Sibbald, 1979)

The structural history of the Wollaston Domain and the broader Cree Lake Zone has been described by Lewry and Sibbald (1980) whose deformation event terminol­ogy is used in this report. The Cree Lake Zone, on the southern margin of the Hearne Province (Lewry and Collerson, 1987), is a highly reactivated region whose thermotectonic evolution began with the mobilization of underlying basement rock in the Mudjatik Domain, form­ing lobate nappe structures (Lewry and Sibbald, 1980). In the Wollaston Domain, upright basement dome structures developed surrounded by supracrustal rocks. A bedding-parallel foliation developed within the supracrustals and adjacent granitic basement during this doming event, referred to as the D1 period of defor­mation (Lewry and Sibbald, 1980) . This foliation was subsequently refolded by tight, upright to steeply inclined, northeasterly trending, doubly plunging folds during the 0 3 phase of deformation, during which the linear structural style of the Wollaston Domain was created .

14

3. Local Geological Setting

Lower Proterozoic supracrustal rocks of the Courtenay Lake-Cairns Lake Fold Belt are interpreted to occupy the core of the southwest-trending and plunging Spence Lake Synform (Scott, 1970; Coombe, 1977, 1978a, 1994; Lewry et al., 1981). This structure is bound to the northwest by the Archean Johnson River Inlier, and to the southeast by the Peter Lake Domain. The mostly sedimentary succession on the southeast limb of the synform has been subjected to upper greenschist to lower amphibolite facies metamorphism. It is much as 4200 m thick, is characterized by significant lateral vari­ations, and has been subdivided into five formations (Figure 2; Coombe, 1994). In contrast, on the northwest limb of the synform, a predominantly pelitic succession , named the Marginal Pelites, which is metamorphosed to middle to upper amphibolite facies, is estimated to be about 1900 m thick (Coombe, 1994). The following brief account of the supracrustal succession is based on de­scriptions by Coombe (1994), Scott (1970), and Lewry et al. (1981) supplemented the by the authors' observa­tions. Stratigraphic nomenclature is that of Coombe (1994).

a) Southeast Limb Spence Lake Synform

The Courtenay Lake Formation

This formation consists of a basal sequence of conglom­erate and arkose with intercalated mafic volcanics and fine-grained feldspar-porphyroblastic rocks interpreted to be derived from felsic volcanic and volcaniclastic rocks. Recent work by Fossenier et al. (1995).has demonstrated that the mafic volcanics are continental tholeiites likely emplaced in a rift setting. The upper part of the formation is primarily quartzite with some interca­lated aluminous pelitic rocks represented by muscovitic schists that locally contain porphyroblabsts of andalusite and/or staurolite .

The Souter Lake Formation

This formation is divided into two members, a meta­argillite, and an overlying quartzite unit. The dark grey, slaty meta-argillite, which is in places gossanous and weakly layered, is only 60 to 70 m thick. The upper part of the formation is a thick sequence of mostly quartz arenite with intercalated grit , argillite, and conglomerate.

The George Lake Formation

The George Lake Formation comprises a 550 m thick sequence of dark grey, variably slaty, in part iron sul­phide-bearing, laminated meta-argillite with minor inter­calated siltstone and a distinctive variety of wacke characterized by ubiquitous, randomly oriented, white feldspar porphyroblasts. Some of the slaty parts of the meta-argillite contain significant graphite and are electro­magnetic conductors. Airborne geophysical surveys have been used to estimate a strike length of about 60 km for this formation .

Summary of Investigations 1996

The Spence Lake Formation

This formation is lithologically variable with significant lateral facies changes. It comprises calcareous and non­calcareous argillites and siltstones, sandstones,

b) Northwest Limb Spence Lake Synform

The Marginal Pelites

marbles, and locally iron formation . The maximum thick­ness, reached in the Spence Lake area, is 1200 m. The iron formation member, the focus of this research, occurs near the top of the formation only in the vicinity of Spence Lake. The iron formation and the units which bound it, are described in more detail in following sections.

The Marginal Pelite unit comprises predominantly pelitic to semipelitic, locally graphitic schists interlayered with fine-grained psammites and lesser quartzites. Much of this sequence is similar to the basal pelitic unit found throughout the Wollaston Domain. In the Causier Creek area, Coombe (1994) recognised three subdivisions in the Marginal Pelites. From northwest to southeast these are:

The Causier Creek Formation

This unit, which is estimated to be at least 400 m thick, consists of pink to buff, very strongly foliated arkose. Epidote and other calc-silicate minerals, as well as disseminated magnetite, occur at the base of the unit giving this part of the formation a distinctive magnetic signature.

1) northwestern pelites: the same rock types as described for the Marginal Pelite unit,

500

400

~ 300 ai E 00

100

0

E LL

~ _g 0) 0 C 0)

g

E LL

0) -"' _g > 0 C

i ::J 0 0

Legend

D EJ

~ ~ D iii E]

Elli ~ CJ

2) calcareous quartzite: an approximately 100 m thick sequence of thin- to medium-bedded quartzite with minor intercalated pelite, and

3) southeastern pelites: a 600 m sequence of gritty pelites with intercalated banded metasiltstones and calc-silicate-bearing rocks.

Arkose

Calcareous arkose

Mudstones with intercalat­ed turbiditic sandstones

Garnetiferous pelite

Iron formation

Cale-silicate-bearing siltstone/sandstone

Marble

Calcareous argillite/pelite

Argillite with intercalated siltstone

Quartzite

Slatey argillite

Quartz-sericite schist

Mafic volcanics

Conglomerate

Felsic volcanics

4. Description of the Iron Formation and Enclosing Units

The geology of the Spence Lake area is shown in Figure 3a; Figure 4 is a schematic stratigraphic sec­tion showing the context of the iron formation. In detail, from oldest to youngest , the following members are distinguished: calc-silicate­bearing siltstone, mudstone and sandstone, garnetiferous pelite, iron formation, and mudstone with intercalated turbiditic sandstone.

a) Cale-silicate-bearing Siltstone/Sandstone

This unit, which is best exposed at the southern end of Spence Lake, comprises a sequence of alternat­ing laminae to thin beds of calc­silicate-bearing, light greenish grey weathering siltstone and dFab · green weathering mudstone. Thin to medium beds of calc-silicate­bearing sandstone are intercalated in these rocks.

Figure 2 - Composite stratigraphic column for the southeast limb of the Courtenay Lake-Cairns Lake Fold Belt in the Brakewe/1-Spence Jakes area (derived from Coombe, 1994).

b) Garnetiferous Pelite

Outcrops of the garnetiferous pelite occur at the northeastern end of Spence Lake, on the tip of the larger, more southerly penin­sula at the southwest end of the lake and on, and adjacent to, the

Saskatchewan Geological Survey 15

Fi ure 3a

0 2 3 4 5 X

-+··· km ·····t-···

SLF

Figure 3b

\

0 i'.J.e,

·00 .;'"' -~:1 '<) £Jc,O

""0

I • tr,_.

57°30'

Outcrop Antiform Synform Fault Spence Lake Fault

"

103"30'

0 2

km

Lower Proterozoic

CI] Marginal Pelite Unit ?

[TI Causier Creek Fm

Ci] Spence Lake Fm

[JO Iron Formation Member

[I] George Lake Fm

[I] Souter Loke Fm

LJ Courtenay Lake Fm

Archean

LJ Johnson River Inlier

Archean ond Proterozoic

!PLD I Peter Loke Domain

- > 5000 gammas

ll!II 2500 - 5000 gammas

~ 0 - 2500 gammas

3 4 5

Figure 3 - a) Geological sketch map of the Spence Lake area. Outcrop locations for the iron formation and enclosing units are from 1996 field work; geological contacts are derived from field observations, interpretation of an airborne magnetometer survey by Esso Minerals Canada (SEM Assessment File 64E-0011), and Map 213-1 by Coombe (1994) . b) Calculated vertical gradient map, from Esso Minerals Canada (SEM Assessment File 64E-0011), showing the expression of the magnetic high associated with the iron formation member of the Spence Lake Formation.

16 Summary of Investigations 1996

small bay to the southwest of that peninsula. This mem­ber which is approximately 50 m thick, weathers dark grey and locally rusty brown in some 3 to 5 cm thick lay­ers. Alternating recessive weathering, garnet-rich pelite layers and more resistant semipelitic layers, also con­taining garnets, are characteristic. Thickness of individ­ual layers ranges from a few millimetres to as much as 5 cm. Within the thicker semipelitic layers even, parallel laminations are common. In the pelites, garnets com­monly exhibit a gradual decrease in grain size from coarse to medium at the base to fine at the top of indi­vidual beds. Garnets are typically euhedral and range up to 5 mm in diameter.

C 0 += 0 E 0

LL

C

~

LJ . .

~ Ed

• - . '_: .

Legend

Mudstone with intercalated turbiditic sandstones

Mudstone with intercalated layers of oxide facies iron formation

Oxide facies iron formation

Silicate facies iron formation

Garnetiferous pelite

Cale-silicate-bearing siltstone

-. -

A

B

Near the top of this member is a distinctive 4 m wide marker band that contains discrete elliptical fine-grained quartz clots and thin quartz layers (inset D on Figure 4) . In cross section, the quartz clots have a lenticular habit and are commonly 3 to 6 cm long and 0.5 to 1.0 cm thick; in plan view they have an amoeboid shape (Figures 5 and 6). Quartz layers are typically 1 to 2 cm thick, discontinuous and commonly have been boudinaged.

Thin, dark green weathering beds, rich in fine-grained calc-silicate minerals, which are rare throughout much of the garnetiferous pelite unit, are common in the gra­dational contact zone with the overlying silicate facies of the iron formation. Rare lenses of calc-silicate miner-

als contain minor iron sulphides and chalcopyrite.

This member exhibits a strong bedding-parallel foliation and in pelitic layers a prominent crenula­tion cleavage inclined at a low angle to the main foliation .

c) Iron Formation

. . .... . .. .

This member is exposed at the northeast end of Spence Lake, at the northeast end of the drumlin located 1 km northwest of the lake and near the southwest end of the lake. The iron formation is divisible into oxide and silicate facies occur­ring both independently and as mixtures. An airborne magnetic survey by Esso Minerals Canada identified a strong magnetic anom­aly which corresponds to the posi­tion of the iron formation and indicates a potential strike length of 30 to 35 km (Figure 3b) .

50

40 al t 30 E

20

10

0

EF40

EE0

.. __ D_t,o -. . E

·-.. u 5 ·------... 0

Figure 4 - Schematic stratigraphic section of the iron formation member of the Spence Lake Formation and its bounding members. Sketches labeled A to D on the right illus­trate detailed relationships within this sequence: A, dotted pattem=turbiditic sandstone, gray=mudstone; B, dotted pattem=magnetite-bearing mudstone, black=magnetite banded oxide facies iron formation ; C, black=magnetite-rich bands, white=silica-rich bands containing various amounts of fine-grained garnet and calc-silicate minerals; and D, dashed pattem=gamet-rich pelitic bed, black ellipses in dotted pattem=quartz lenses in calc-si/icate-bearing siltstone.

Saskatchewan Geological Survey

Silicate Facies

There is a gradational contact between the gametiferous pelite and the silicate facies of the iron formation. The contact, however, is defined as the base of the first bed of buff weathering fine-grained garnet-cummingtonite-grunerite rock.

Above the gradational base, the silicate facies is well layered and characterized by predominant fine­grained, buff-pink weathering garnet-calc-silicate layers, and more green grey weathering thin­ner layers richer in calc-silicate minerals (Figure 7). Siliceous layers occur in some outcrops. Internal lamination, common in the thicker beds, is defined by garnet concentrations. Locally, layers

17

appear truncated by those adjacent, suggesting scour­ing. Magnetite, where present, is generally dissemi­nated, although thin, magnetite-rich laminae occur near the top of the silicate facies. Also within the silicate facies are thin layers of medium-grained calc-silicate minerals lacking garnets, and almost monomineralic layers of medium-grained euhedral garnets, which can be traced laterally for tens of metres. In rare localities there are elliptical quartz lenticles similar to those near the top of the gametiferous pelite. Towards the top of the silicate facies iron formation, there is an increase in the proportion of calc-silicate-rich layers associated with the gradual transition into the oxide facies above.

Oxide Facies

The oxide facies of the iron formation includes some or all of following parts: a gradational base, a middle which is banded, and an upper part which is sediment contaminated. Although generally the oxide facies has a gradational contact with underlying silicate facies rocks, in some places it apparently overlies the gametiferous pelite member with a fairly sharp contact where the

Figure 5 - Quartz lenses in the gametiferous pelite member.

Figure 6 - Plan view of quartz lenses in the gametiferous pelite showing their amoeboid shape.

18

silicate facies is absent. The two facies grade laterally into each other, in some cases rather abruptly.

The base of the oxides facies is marked by the first appearance of magnetite-rich laminae which increase in number upward, passing into 'classic' banded magnet­ite-bearing oxide facies iron formation (Figure 8) which is about 6 m thick. Rhythmically alternating, millimeter­thick, dark grey weathering, magnetite-rich laminae and grey to light grey laminae composed mostly of quartz, and variable but typically minor amounts of magnetite, garnet, and amphibole are characteristic. For example in the large outcrop area 1 km northwest of Spence Lake, fine-grained garnet is common in the light grey bands, whereas at the southwest end of the lake, these contain both garnet and amphibole and at the northeast end of the lake, mostly quartz. At the northeast end of the lake, the banded interval is overlain by a 20 to 30 m thick, mixed sequence of grey weathering magnetite­bearing mudstones in beds up to 1 O cm thick and inter­calated with 2 to 3 cm thick beds of banded magnetite oxide facies iron formation. A narrow interval of the gametiferous pelite is overlying.

Figure 7 - Silicate facies of the iron formation member of the Spence Lake Formation.

Figure 8 - Magnetite-banded oxide facies iron formation, Spence Lake Formation.

Summary of Investigations 1996

d) Mudstone with Intercalated Turbiditic Sandstone

Above the iron formation, at the northeast end of Spence Lake, is dark grey weathering, massive to lami­nated argillite, with thick beds of light grey weathering sandstone containing some granule-size quartz grains and large, tabular, wispy terminated fragments of the argillite. The sandstone beds, some of which are graded, are interpreted to be turbidites.

5. Structure

The Spence Lake area has undergone at least three deformation events. The D, event generated a tectonic foliation sub-parallel to bedding. A second event resulted in (F3) folding of this structure on moderately southwest-plunging axes. This second event correlates with the regional 03 event of Lewry and Sibbald (1980). A northeast-striking crenulation cleavage, S3, inclined at a low angle to S, and parallel to the axial plane of minor F3 folds formed in the pelitic beds. The last defor­mation event resulted in north-trending brittle to brittle­ductile faults that commonly display sinistral offset. The Spence Lake Fault, at the southwest end of Spence Lake, is an example of these regional fractures.

Previous workers (Coombe, 1977, 1978a, 1994; Thomas, 1978; Lewry et al., 1981) have suggested that the Courtenay Lake-Cairns Lake Fold Belt comprises a large-scale tight to isoclinal F3 synform, named the Spence Lake Synform by Lewry et al. (1981 ), that plunges moderately to the southwest. Structural data from sparse outcrop, coupled with magnetic and EM data acquired during exploration programs, suggest the synform closes to the northeast of Spence Lake. Lewry et al. (1981) noted an apparent contradiction to this simple structural picture because northeasterly plunging fold closures occur elsewhere, such as at Fordham Lake and along the Compulsion River. A subsequent air­borne magnetic survey by Esso Minerals Canada in 1986 (SEM Assessment File 64E-0011 ), also revealed that the structural pattern in the Spence Lake area is probably more complex than a simple synform. Vertical gradient data from this survey (Figure 3b) integrated with ground magnetic susceptibility data and outcrop data suggest that the iron formation has been deformed into three tight folds, the most southeasterly of which corresponds to the previously recognised Spence Lake Synform. The vertical gradient data also clearly defines the late north-trending Spence Lake Fault and its sinis­tral offset.

6. Discussion

Some workers, such as Macleod of Esso Minerals Canada (SEM Assessment File 64E-0011), have sug­gested that the iron formation member of the Spence Lake Formation is not a banded iron formation in the strict sense . The term "iron formation" was defined by James (1954, p239) to mean: "a chemical sediment, typically thin bedded or laminated, containing 15 percent or more iron of sedimentary origin, commonly but not necessarily containing layers of chert". James

Saskatchewan Geological Survey

(1954) recognised four different facies of iron formation: sulphide facies, carbonate facies, oxide facies, and silicate facies. The sulphide facies typically consists of black slates with as much as 40 percent pyrite content. Carbonate facies iron formations comprise interbedded iron-rich carbonate and chert. Two principle types of oxide facies iron formation are recognised: hematite­banded iron formation marked by interbedded finely crystalline hematite and jasper or chert, and magnetite­banded iron formation marked by magnetite interbed­ded with chert, carbonate or iron silicate. Silicate facies iron formation contains hydrous ferrous silicates as the main component. James (1954) also noted that magnet­ite-banded iron formation, as in the case with the Spence Lake iron formation, is intimately associated with and subtly grades into silicate facies. Analyses of a group of grab samples of the iron formation by Coombe (1994) revealed that most contained in excess of 15 percent iron. On the basis of the preceding review, which underlines the similarity between the iron forma­tion member of the Spence Lake Formation and the definition of iron formation and its facies as presented by James (1954), we argue that it is a true iron forma­tion .

Iron formations have been further divided into three main types based on their geological setting; Superior Type, Algoma type, and Rapitan type (Gross, 1983, 1993). The Superior type are formed in shelf and plat­form basins along the margins of continental shelves and contain dolomites, quartzites, black shales, and minor associated volcanic rocks. Algoma-type iron for­mations are found close to volcanic centres, and are associated with shales, greywackes, turbidite sedi­ments, and volcanic rocks. Rapitan-type iron formations are thought to form in grabens and fault-scarp basins near continental margins. As cautioned by Gross (1983), however, these types merely represent refer­ence points in a continuum as iron formations form in a broad spectrum of environments. A detailed model for the environment of the Spence Lake iron formation awaits petrographic and geochemical analysis as well as a careful analysis of the local and regional strati­graphic context of this member.

.7. Acknowledgments

Wayne Darch (Noranda Exploration Co. Ltd.), Bob Hindson (Far West Mining Ltd.), and Tom Carpenter (Discovery Consultants) are thanked for their f[?nk ex­change of ideas and for providing access to confidential data collected during their companies' exploration pro­grams.

8. References Baer, A.J . (1969): Precambrian geology of the Geike River

map area (74H), Saskatchewan; Geol. Surv. Can., Pap . 68-41 , 11p.

Bickford, M.E., Collerson, K.D., and Lewry, J.F. (1994): Crustal history of the Rae and Hearne provinces, southwestern Canadian Shield, Saskatchewan: Constraints from geochro­nologic and isotopic data; Precamb. Resear. v68, p1 -21.

19

Chadwick, B. (1967): The geology of the Morell Lake area (west half), Saskatchewan; Sask. Dep . Miner. Resour., Rep. 116, 24p.

Coombe, W. (1977): La Ronge-Wollaston belts base metals project: George, Hills, Johnson, and Kaz lakes and Geike River areas; in Summary of Investigations 1977, Saskatchewan Geological Survey, Sask. Dep. Miner. Resour., p85-1 04.

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

_____ (1978b): Wollaston base metals project, Duddridge Lake to Meyers Lake; in Summary of Investigations 1978, Saskatchewan Geological Survey, Sask. Dep. Miner. Resour., Misc. Rep. 78-10, p98-108.

_____ (1994): Sediment-hosted base metal deposits of the Wollaston Domain, northern Saskatchewan; Sask. Energy Mines, Rep. 213, 108p.

Delaney, G.D. (1993): A re-examination of the context of U­Cu, Cu, and U mineralization, Duddridge Lake, Wollaston Domain; in Summary of Investigations 1993, Saskatchewan Geological Survey, Sask. Energy Mines, Misc. Rep. 93-4, p73-85.

_____ (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, p53-61.

Delaney, G.D., Maxeiner, A.O., Rawsthome, M.L., Reid , J., Hartlaub, R., and Schwann, P. (1995): Geological setting of sediment-hosted copper mineralization in the Janice Lake area, Wollaston Domain; in Summary of Investigations 1995, Saskatchewan Geological Survey, Sask. Energy Mines, Misc. Rep. 95-4, p30-48.

Fossenier, K., Delaney, G.D., and Watters, B.R. (1995): Litho­geochemistry of volcanic rocks from the Lower Proterozoic Courtenay Lake Formation, Wollaston Domain; in Summary of Investigations 1995, Saskatchewan Geological Survey, Sask. Energy Mines, Misc. Rep. 95-4, p49-60.

Gross, G.A. (1983): Tectonic systems and the deposition of iron-formation; Precamb. Resear., v20, p171-187.

_____ (1993): Industrial and genetic models for iron ore in iron-formations; in Kirkham, R.V., Sinclair, W.D., and Duke, J.M. (eds.), Mineral Deposit Modeling, Geol. Assoc. Can., Spec. Pap. 40, p151-170.

James, H.L. (1954): Sedimentary facies of iron-formation; Econ. Geol., v49, no3, p235-285.

Karup-M0ller, S. (1970): Geology of the Compulsion River Fold Belt; Western Miner, v43, no2, p35-51.

Karup-M0ller, S. and Brummer, J.J. (1970): The George Lake zinc deposit, Wollaston Lake area, northeastern Saskatchewan; Econ. Geol., v65, p862-874.

Lemaitre, R. (1991): The stratigraphy, petrology, and genesis of the George Lake sandstone-hosted zinc deposit; unpubl. B.Sc. thesis, Queen's Univ., 69p.

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Lewry, J.F. (1981): The age and geological history of the Wollaston, Peter Lake, and Rottenstone domains in northern Saskatchewan: Discussion; Can. J. Earth Sci., v18 , p178-180.

Lewry, J.F. and Sibbald, T.1.1. (1977): Variation in lithology and tectonometamorphic relationships in the Precambrian base­ment of northern Saskatchewan; Can. J. Earth Sci., v14, p1453-1467.

_____ (1979): A review of pre-Athabasca basement geology in northern Saskatchewan; in Parslow, G.R. (ed.), Uranium Exploration Techniques, Sask. Geol. Soc., Spec. Publ. 4, p19-58.

_____ (1980) : Thermotectonic evolution of the Churchill Province in northern Saskatchewan; Tectonophysics, v68, p45-82 .

Lewry, J.F., Thomas, D.J., Rees, C.J., and Roberts, K. (1981): Geology of an area around Compulsion Bay, Wollaston Lake; Sask. Miner. Resour., Rep. 205, 27p.

Lewry, J.F. and Collerson, K.D. (1987): The Trans-Hudson Orogen: Extent, subdivision, and problems; in Lewry, J.F. and Stauffer, M.A. (eds.), The Early Proterozoic Trans­Hudson Orogen of North America , Geol. Assoc. Can., Spec. Pap. 37, p1-14.

Macdonald, R. and Thomas, M.W. (1983): Compilation bed­rock geology, Reindeer Lake north , NTS area 64E; Sask. Energy Mines, Rep. 232, 1:250 000 scale map with mar­ginal notes.

MacDougall, D.G. (1984): Metallogenic map series, Reindeer Lake north, NTS area 64E; Sask. Energy Mines, Rep. 239, 1 :250 000 map with marginal notes.

Money, P.L. (1966) : The geology of the Daly Lake are-a (east half), Saskatchewan ; Sask. Dep. Miner. Resour., Rep. 108, 48p.

_____ (1968): The Wollaston Lake fold-belt system, Saskatchewan-Manitoba; Can. J. Earth Sci., v5, p1489-1504.

Money, P.L., Baer, A.J., Scott, B.P., and Wallis, R.H. (1970): The Wollaston Lake Belt, Saskatchewan, Manitoba, North­west Territories; in Baer, A.J. (ed.), Symposium on Basins and Geosynclines of the Canadian Shield, Geol. Surv. Can., Pap. 70-40, p170-200.

Munday, R.J. (1974): lie-a-la-Crosse (east) area: Reconnais­sance geological survey of 730-NE and 730-SE; in Summary Report of Field Investigations by the Saskatchewan Geological Survey 197 4, Sask. Dep. Miner. Resour., p20-24.

_____ (1978): The shield geology of the lie-a-la-Crosse (east) area, Saskatchewan (part of NTS area 73-0); Sask Dep. Miner. Resour., Rep. 189, 27p.

Purser, J. and Delaney, G.D. (1994): Geological setting of the Fannon Lake area (NTS 74A-6W), Wollaston Domain, Saskatchewan; in Summary of Investigations 1994, Saskatchewan Geological Survey, Sask. Energy Mines, Misc. Rep. 94-4, p70-74.

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

Summary of Investigations 1996

Ray, G.E. (1974): Foster Lake (south)-La Ronge (NW) area: Reconnaissance geological survey of 73P-13(E), 73P-14, 74A-2; in Summary Report of Field Investigations by the Saskatchewan Geological Survey, Sask. Dep. Miner. Resour., p14-19.

_____ (1979): Reconnaissance bedrock geology, Wollaston Lake east (part of NTS area 64L) ; in Summary of Investigations 1979, Saskatchewan Geological Survey, Sask. Miner. Resour., Misc. Rep 79-10, p19-28.

_____ (1983a) : Compilation bedrock geology, Geike River, NTS area 74H; Sask. Energy Mines, Rep. 229, 1 :250 000 scale map with marginal notes.

_____ (1983b): Compilation bedrock geology, Foster Lakes, NTS area 74A; Sask. Energy Mines, Rep. 228, 1 :250 000 scale map with marginal notes.

Ray, G.E. and Wanless, R.K. (1980) : The age and geological history of the Wollaston , Peter Lake, and Rottenstone domains in northern Saskatchewan; Can. J. Earth Sci., v17 , p333-347.

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

Saskatchewan Geological Survey

Sibbald, T.1.1. (1979): NEA/IAEA test-area: Basement geology; in Summary of Investigations 1979, Saskatchewan Geological Survey, Sask. Dep. Miner. Resour., Misc. Rep. 79-10, p77-85.

Stauffer, M.R. (1984) : Manikewan: An early Proterozoic ocean in central Canada, its igneous history and orogenic closure; Precamb. Resear., v25, p257-281 .

Stauffer, M. R. and Lewry, J.F. (1993): The Needle Falls shear zone: Its movement history and geodynamic significance in the Trans-Hudson Orogen; Can . J. Earth Sci., v30 , p1338-1354.

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

Wallis, R.H. (1971): The geology of the Hidden Bay area, Saskatchewan; Sask. Dep. Miner. Resour., Rep. 137, 75p.

Weeks, L.J . (1941 ): Spalding Lake, northern Saskatchewan; Geol. Surv. Can ., Map 596A, 1 inch to 4 mile scale map with marginal notes.

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