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1977

centraltonalite

0 5 10 15 20 km

Wlsz

Asz

3 11

9

12

6

4

2

13

8

1

10

5

7

7

7

7

94 9200 00

66 00

67 00

Simplified structural map of the NTS 56K showing the distribution of structural domains. The structural data for selected domains are shown in the accompanying diagrams. Asz = Amer shear zone; Wlsz = Walker Lake shear zone.

Lower-hemisphere, equal-area stereographic projections for structural data from domains 1, 2 and 3 (see accompanying domain map). (a) Linear structural data for domain 1(squares are fold axes, triangles are lineations). Note the shallow to moderate plunges of the linear data. (b) Planar structural elements for domain 1. Note the NNE-trends and variable dips of the foliations. (c) Linear structural for domain 2. (d) Planar structural data for domain 2. (e) Linear structural data for domain 3. (f) Planar structural data for domain 3. Planar elements are plotted as poles, and include all measured foliations (generation was commonly not interpretable in the field). Overall, linear features trend NE and have moderate to shallow plunges whereas foliations are variable but generally NE-trending and moderate to steeply dipping.

Domain 1

n=52

N

a

Domain 2

n=47

N

c

n=39

N

e

Domain 3

Pla

na

r e

lem

en

tsL

ine

ar

ele

me

nts

n=106

b

n=86

d

n=113

f

L o w e r - h e m i s p h e r e , e q u a l - a r e a stereographic projections for structural data from domains 4 (central tonalite), 5 and 7 (see accompanying domain map). (a) Linear and planar data from domain 4. Squares are lineations, dots are foliations. Note the variable orientations of both the linear and planar structures. (b) Linear structural data for domain 5 showing the NNE-WSW trends and shallow, doubly plunging linear features. (c) Planar structural elements for domain 5. Shallowly dipping foliations are typical whereas steeply dipping foliations occur along mylonitic zones. (d) Dominant NE-SW, doubly plunging linear structural data for domain 7. (e) Variably dipping, NE-trending layering (S0?) and S1 foliations; f) Variably dipping, NE-trending S2 (dots) and steeply dipping, NNW-trending S3 (diamonds) foliations.

Domain 7

Both linear and planar

n=173

N

d

n=82

S2-S3?f

S0-S1

n=268

eN

Lin

ear

ele

ments

Domain 5

N

n=173

b

n=266

c

aN

n=63

Domain 4

Pla

nar

ele

ments

GENERAL OVERVIEW

The Committee Bay Belt is underlain by northeast-trending rocks of the Archean Prince Albert Group (Heywood, 1967; Schau, 1982; Sandeman et al., 2001a), flanked to the north and west by paragneisses and associated peraluminous and metaluminous granitoids, and to the south and east by metaluminous granitoids. The Prince Albert Group comprises dominant metasedimentary rocks including semipelite, psammite, iron formation and quartzite with less abundant metavolcanic sequences incorporating predominant, spectacular, spinifex-textured komatiites, and uncommon pillowed to massive basalts and intermediate to felsic volcaniclastic rocks. The metamorphic grade in the main supracrustal belt is upper greenschist facies, but to the west and north the grade increases to amphibolite facies with consequent development of metasedimentary diatexites and paragneisses with accompanying peraluminous melt lenses. Intrusive units, interpreted as cogenetic in the volcanic rocks, range from rare gabbro through common quartz diorite and diorite, abundant tonalite to granodiorite and rare granite and crop-out south, east and northwest of a approximately oval plutonic body of tonalite (central tonalite) interpreted to be younger than the supracrustal belts and dated (U-Pb TIMS: zircon) at ca. 2718 ± 2 Ma (T. Skulski, pers. Comm.).

The southern margin of the map sheet corresponds to the northeast trace of the Amer shear zone, represented by moderately northward-dipping, highly flattened and lineated metasedimentary rocks that structurally overlie a range of granitoid rocks of the Walker Lake intrusive complex. Therein the Amer shear zone is characterized by a number of protomylonitic strands developed in both the granitoid and supracrustal rocks. The northern edge of the central tonalite incorporates, in the northwest, moderately southward dipping, L>S tectonized peraluminous and metaluminous granites containing supracrustal remnants. In the northeast, a series of east-west trending, south-dipping panels of interspersed granodiorite and metre-scale layered metasedimentary rocks are cut by steeply-dipping, mylonite zones, termed the Walker Lake shear zone (Dufresne and Williamson, 1996). The latter is characterized by shallowly plunging linear features indicative of late horizontal movement. The far north and northwest is underlain by an intrusive complex of foliated biotite+potassium feldspar augen granodiorites with rare metasedimentary xenoliths, all cut by an array of equigranular, biotite+magnetite monzogranite. To the immediate east and northeast of the central tonalite, a narrow north-trending supracrustal belt is cut by numerous north-trending shear zones exposed as talc-chlorite schists. In 100 m scale boudins exposed therein, komatiitic flows and internal stratigraphic sequences are well preserved, and are at low metamorphic grade (sub-green schist). Intruding the eastern side of the north-trending belt is a series of granitic rocks exhibiting widespread northeast-southwest trending gneissic texture arising from transposition of a net-vein complex. The granitoids and the adjacent supracrustal belt are cut by an anorthosite body and all are cut by foliated and massive metaluminous monzogranite. The map area is interpreted to represent a crustal scale shear zone: a central block bounded by dextral C planes, between which the northeast -trending supracrustal rocks have been shortened and dextrally rotated along S-planes. This deformation occurred late D2 (or D3?) much of which we consider is Proterozoic (Sandeman et al., 2001b).

Numerous favorable targets for mineral exploration have been identified in the Laughland Lake map area. Because of lithostratigraphic similarities with the Woodburn Lake group exposed to the southwest, the most favorable setting is auriferous sulphide mineralization in iron formation. Sulphides in the iron formations predominantly occur in association with secondary quartz veins, but disseminated, presumably primary sulphides are, however, locally abundant. Pyrrhotite and pyrite are the main sulphide minerals, but minor arsenopyrite and chalcopyrite were observed locally. Other noteworthy mineral occurrences include (see Sandeman et al., 2001a): (1) sulphide bearing quartz-carbonate veins that occur in intensely lineated mafic volcanic rocks and in fine grained gabbro; (2) meter-scale rusty quartz veins in tonalite contain up to ca. 50 % pyrite; (3) a previously drilled (Aquitane Company of Canada) showing of densely disseminated pyrite-pyrrhotite hosted in a gabbroic body near the intrusive contact of the Laughland Lake anorthosite complex may provide favorable targets for platinum group elements and; (3) thick komatiite flows (> 10-15 metres) and their associated cumulate-dominated sequences within the east-central supracrustal belt and their close association with Fe-rich, sulphidic metasedimentary rocks highlights their potential for primary Ni-Cu and PGE mineralization and possibly subsequent structurally controlled Au mineralization.

REFERENCES

Dufresne, M. and Williamson, J. 1997. Gold exploration in the Committee Bay greenstone belt, Northwest Territories. In Exploration Overview (Compiled by Igboji, I.E., Goff, S.P. and Beales, P.), DIAND, Yellowknife, Northwest Territories.

Heywood, W.W., 1967. Geological notes northeastern District of Keewatin and southern Melville Peninsula, District of Franklin, Northwest Territories (parts of 46, 47, 56, 57). Geological Survey of Canada Paper 66-40, 20p.

Sandeman, H.A., Brown, J., Studnicki-Gizbert, C., MacHattie, T., Hyde, D., Johnstone, S., Greiner, E. and Plaza, D. 2001a. Bedrock mapping in the Committee Bay Belt, Laughland Lake area (NTS 56K) central mainland, Nunavut. In Current Research, Geological Survey of Canada Paper 2001-C (available at http://www.nrcan.gc.ca/gsc/bookstore/index_e.html).

Sandeman, H.A., Studnicki-Gizbert, C., Brown, J., and Johnstone, S., 2001b. Regional structural and metamorphic geology of the Committee Bay Belt, Laughland Lake area (NTS 56K) central mainland Nunavut. In Current Research, Geological Survey of Canada Paper 2001-C (available at http://www.nrcan.gc.ca/gsc/bookstore/index_e.html).

Schau, M., 1982. Geology of the Prince Albert Group in parts of Walker Lake and Laughland Lake map areas, District of Keewatin. Geological Survey of Canada, Bulletin 337, 62p.

FUTURE INVESTIGATIONS:

The joint Canada-Nunavut Geoscience Office - Geological Survey of Canada Committee Bay Integrated Geoscience Project will continue with bedrock and surficial mapping of the northern half of NTS 56J and the southern half of NTS 56O in the upcoming 2001 field season. Supporting geoscientific research includes:

1) a belt-wide, airborne magnetic program with 400 m line spacing

2) an extensive program of U-Pb TIMS geochronology

3) integrated lithogeochemical and radiogenic tracer isotopic investigations of the Archean volcanic assemblages

4) integrated lithogeochemical and radiogenic tracer isotopic investigations of Archean and Proterozoic plutonic rocks

5) regional, integrated structural-metamorphic studies in conjunction with U-Pb SHRIMP geochronology

6) belt-wide prospecting coverage and assay sampling

7) belt-wide drift prospecting and till geochemistry

8) four thematic, Ph.D and M.Sc projects

?

Hudson Bay

CommitteeBay

RAE

HEARNE

RAE

STZ

Paleozoic cover

Proterozoic supracrustal rocks

Archean supracrustal belts

Archean & Proterozoic granitesand Archean gneiss belts

KB

MB

RBYB

WB

CB

CB 2000 Study-area

20012002

ar zoneehs remA

Wager eshear zon

Map showing the location of the study-area relative to the main lithotectonic features of the Western Churchill Province. Key: CB - Committee Bay belt; WB - Woodburn Lake belt; MB - Macquoid belt; RB - Rankin Inlet belt; YB - Yathkyed belt; KB - Kaminak belt; STZ - Snowbird Tectonic zone.

Plate 5: Mm- to cm-scale bedding in biotite psammite and semipelite. Note the light coloured (coarse-grained) base and darker coloured (fine-grained) tops of these beds. Note also the pebble-rich channel in the centre of the photograph. Two dollar coin for scale.

5

Plate 13: Well-foliated, biotite-rich granodioritic gneiss of the Kuagnat Complex characterized by abundant lenses and bands of coarse-grained to pegmatitic syenogranite. Small rock pick for scale.

13

Plate 7: Metasedimentary diatexite or paragneiss of the Prince Albert Group comprising pinch and swell bands of muscovite+biotite syenogranite (leucosome) with biotite + plagioclase ± garnet ± sillimanite melanosome. Two dollar coin for scale.

7

Plate 15: Coarse-grained plagioclase megacrystic gabbroic anorthosite of the Laughland Lake anorthosite complex. Pencil magnet is 10 cm long.

15

Plate 4: Finely laminated, interlayered magnetite-quartz (chert?: oxide facies) and garnetite-grunerite (silicate facies) iron formation of the Prince Albert Group. Two dollar coin for scale.

4

Plate 8: Moderately foliated, medium-grained biotite+hornblende quartz diorite cut by a foliation parallel vein of foliated biotite tonalite. Both are cross-cut by a foliated and openly folded vein of biotite monzogranite. Two dollar coin for scale.

8

Plate 16: Massive, medium-grained, salmon-pink biotite+magnetite±fluorite monzogranite. This unit is correlated with the ca. 1830 Ma Hudson monzogranites exposed in the region. Two dollar coin for scale.

16

Plate 3: Well preserved komatiite exposed on a resistant ridge due west of the central tonalite. Note the banding separating spinifex (grey-green) from cumulate zones (orange) . Penci l for scale is 14 cm long.

3

Plate 14: Medium-grained, biotite+magnetite, potassium-feldspar augen granite of the Walker Lake Intrusive Complex. Two dollar coin for scale.

14

Plate 6: Matrix supported polymictic conglomerate with subangular clasts of quartzite and felsic to intermediate volcanic in an intermediate composition matrix. Two dollar coin for scale.

6

Plate 2: A felsic lithic tuff containing moderately flattened felsic and intermediate volcanic fragments. Two dollar coin for scale.

2

Plate 1: Poorly exposed, upper greenschist facies pillowed basalt with ca. 60 cm diameter pillows. Brunton compass for scale.

1

Plate 12: Gneissic potassium feldspar augen monzogranite of the Kuagnat complex containing abundant, diffuse metasedimentary schlieren. Small rock pick for scale.

12

Plate 11: Millimetre to decimetre-scale bedding in annealed quartz arenite. The thin, mm-scale bedding is defined by pale-pink, hematite stained heavy mineral bands. Pencil magnet is 10 cm long.

11

Plate 10: Medium-grained, weakly foliated biotite+hornblende+titanite+allanite tonalite of the central tonalite. One dollar coin for scale.

10

Plate 9: Foliated, grey, biotite+epidote tonalite occurs as flattened enclaves in a pink biotite+magnetite monzogranite. Two dollar coin for scale.

9

16

15

14

13

12

1110

3

7

8

6

5

4

1

9

2

2718+- 2 Ma

#

Sandeman, H.A.I., Canada-Nunavut Geoscience Office, 626 Tumiit Plaza, P.O. Box 2319, Iqaluit, Nunavut, X0A 0H0 (hsandema@nrcan.gc.ca)

Geology of the Archean Prince Albert Group, Committee Bay supracrustal belt, Rae Province, Central Mainland, Nunavut

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