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GEOLOGY of the MEADOWBANKIRON FORMATION-HOSTED GOLD DEPOSITS

GEOLOGY of the MEADOWBANKIRON FORMATION-HOSTED GOLD DEPOSITS

GEOLOGY of the MEADOWBANKIRON FORMATION-HOSTED GOLD DEPOSITS

1 2 2 2 3Ross Sherlock , Brian Alexander , Roger March , Jeff Kellner , Bill Barclay1. Canada-Nunavut Geoscience Office, Iqaluit, Nunavut; 2. Cumberland Resources Ltd., Vancouver B.C.; 3. W.A. Barclay Exploration Services Ltd. Toronto Ont.

The geology of northwest Hudson Bay consists of Archean and Proterozoic supracrustal sequences and plutonic rocks. The Archean supracrustal sequences (Woodburn Lake and Prince Albert groups) are intruded by granites which are inturn overlain by pre-Hudsonian basins (Amer and Hurwitz grous). Post-Hudsonian basins (Baker Lake and Thelon basins) unconformably overly both sequences. The Woodburn Lake group is Archean in age but has been overprinted by the Paleoproterozoic Husonian Orogeny (Henderson et al., 1991). The extent of the proterozoic reworking and the implications for gold mineralization in the district is uncertain.

Daly BayComplex

MGb

Rg

Kgb

WLg

KRg

PAg

PAg

Pg

Hg

Hg

Ag

TH

BL

r S.Z.emA

Wager S.Z.

enoZ cinotceT dribwonS

Pyke Fault

Cha

nter

y S.Z

.

62° 62°

68°

92°

CommitteeBay

Hudson Bay

Post-Hudsonian Proterozoic Basins

Pre-Hudsonian Proterozoic Basins

BL - Baker LakeTH - Thelon

Pg - Penrhyn GpAg - Amer GpHg - Hurwitz Gp

Archean Supracrustal RocksPAg - Prince Albert GpWLg - Woodburn GpKRg - Ketyet River GpMGb - MacQuoid-Gibson beltRg - Rankin Inlet GpKgb - Kaminak greenstone belt

Rankin Inlet

Baker Lake

Arctic Circle

Meliadine Area

Meadowbank Area

unconformity

unconformity

0 100 200 km

39

60

33

28

Banded iron formation, magnetite-quartz-amphibole ± pyrrhoitite, pyrite and gold

Ultramafic assemblage, talc-amphibolite, locally spinifex textured

Quartzite, quartz-pebble conglomerate

Intermediate volcaniclastic rocks, dacitic-rhyodacitic in composition,locally showing well defined bedforms and blue quartz phenocrysts

Intermediate-felsic volcanic rock, dacite-rhyodacite in composition, massive unitlikely flow or shallow intrusions, locally abundant blue quartz phenocrysts

Massive plagioclase-amphibolite intrusive, gabbroic in composition

Granite, dated at 2612 Ma Apparent dip of S /S composite fabric, from drill sections1 0

S /S composite fabric, dipping & verticle1 0

F /F fold axis, folding S , and possible earlier foliations1 2 0

S fabric, crenulating and deforming ealier S /S fabrics4 1 0

dipping & verticle, axial planar to F4

F fold axis, that deform earlier S /S composite fabrics4 1 0

45

640000m. E.639000m. E.638000m. E.

7212000m. N.

7213000m. N.

7214000m. N.

7215000m. N.

7212000m. N.

7213000m. N.

7214000m. N.

7215000m. N.

7216000m. N.7216000m. N.

638000m. E. 640000m. E.639000m. E.

18

40

30

23

40

20

21

20

18

10

10

40

18

30

30

10

10

18

24

40

18

18

5

10

20

40

36

38

37

32

20

30

26

30

34

20

46

20

20

48

39

44

30

12

18

20

20

3830

20

32

35

39

35

12

34

60

58

55

25

52

22

5820

32

20

57

38

65

38 45

66

10

58

38

69

40

70

48

65

10

18

28

42

72

50

68

78

58

60

58

64

45

38

26

60

60

66

50

62

70

80

60

45

72

60

6048

70

60

20

60

48

38 80

60

62

80

60

51

66

80

50

72

45

66

80

77

76

66

80

30

50

22

36

70

70

82

80

5

15

70

5

15

70

15

70

570

15

65

20

25

10

60

50

10

10

15

55

60

35

60

60

65

35

60

45

20

20

60

60

70

4540

70

80

30

40

2555

75

45

40

4860

35 88

75

18

10

33

4755

4530

3030

3878

60

80

50

50

6042

30 20

2570

2245

22

2575

2520

30

3540

6035

35

50

28

3040

4550

30

25

35

50

35

45

20

45

55 45

15

50

6525

35

45

45

75

40

70

45

30

30

45

Third P

ort

age &

Bay

Zone D

eposi

ts

Nort

h P

ort

age D

eposi

t

Goose

Isl

and D

eposi

t

North Portage Section

Third Portage Section

Goose Island Section

scale 1:10,000

Scale 1:2,500

Goose Island

Scale 1:2,500

Third Portage

Scale 1:2,500

North Portage

Total

Class Tonnes Grade (g/t) OuncesMeasured 1,191,000 6.58 252,100Indicated 6,584,000 5.65 1,196,200Inferred 3,467,000 5.60 623,800

Total 11,242,000 5.73 2,072,100

Third Portage

Class Tonnes Grade (g/t) OuncesMeasured 1,031,000 6.40 212,000Indicated 4,914,000 5.31 839,700Inferred 1,427,000 5.66 2,59,700

Total 7,372,000 5.53 1,311,400

Goose Island

Class Tonnes Grade (g/t) OuncesMeasured 75,000 10.63 25,700Indicated 636,000 9.80 200,400Inferred 456,000 9.50 139,400

Total 1,167,000 9.74 365,500

Bay Zone

Class Tonnes Grade (g/t) OuncesMeasured 51,000 5.38 8,800Indicated 394,000 4.67 49,100Inferred 239,000 4.64 35,500

Total 684,000 4.71 103,400

North Portage

Class Tonnes Grade (g/t) OuncesMeasured 34,000 5.10 5,600Indicated 640,000 4.71 97,000Inferred 1,345,000 4.38 189,200

Total 2,019,000 4.49 291,800

Open Pit Mining Reserve

Tonnes Grade (g/t) Ounces*P/P reserve 5,502,000 5.44 962,400

Resource-Reserve TableCumberland Resource Ltd. press releases

March 29, 2000; April 27, 2000

All deposits except Goose Island are reported at a 2.5 g/t gold cutoff. Goose Island is reported at a 6 g/t gold cutoff. Bay Zone and Third Potage deposits assays were capped at 45 g/t gold; Goose Island assays were capped at 35 g/t gold; no assay capping was applied to North Portage. Resource and reserve classifications are in accordance with the Canadian Institute of Mining, Metallurgy and Petroleum guidelines.

2612 ± 4 Ma2612 ± 4 Ma

00'65° 00'65°

05'96°

05'96°

78

64

35

32

60

38

25

38

40

10

30

80

70

30

75

2020

50

60

44

35

60

65

75

60

5040

68

72

70

80

5460

70

70

70

82

40

26

45

78

71

12

68

60

22

60

75

45

65

65

70

Meadowbank Area

Iron Formation, banded quartzmagnetite-amphibole, local pyrrhotitepyrite

Quartzite, with local quartz pebbleconglomerate

Gabbroic intrusions

Felsic Intrusions 2600-2620 Ma

Ultramafic schists, characterized bytalc-tremolite-serpentinite, probablekomatiitic basalt protolith

Volcanic wacke, slates and phyllites,minor ferruginous sediments

Felsic-intermediate volcanic sedimentsminor massive felsic flows/intrusives, minortalc schists and ferruginous sediments,interbedded with iron formation2710 +3.5/-2.1 Ma

0 0.5 1.0 km

Simplified geological map of the Woodburn Lake group in the Meadowbank area (Zaleski et al., 1997a; 1999a).

Armitage, A.E., James, R.S., and Goff, S.P. 1996: Gold mineralization in Archean banded iron formation, Third Portage Lake area, Northwest Territories, Canada. Exploration and Mining Geology, v. 5, p.1-15.

Henderson, J.R., and Henderson, M.N. 1994: Geology of the Whitehills-Tehek Lakes area, District of Keewatin, Northwest Territories (parts of 56D, 56E, 66A and 66H); Geological Survey of Canada, Open File 2923, scale 1:100 000.

Kerswill, J.A., Goff, S.P., Wilkinson, L., Jenner, G.A., Kjarsgaard, B.A., Bretzlaff, R., and Samaras, C. 1998: An update on the metallogeny of the Woodburn Lake group, western Churchill Province, Northwest Territories; in Current Research 1998-C, Geological Survey of Canada, p. 29-41.

Zaleski, E., Corrigan, D., Kjarsgaard, B.A., Kerwill, J.A., Jenner, G.A., and Henderson, J.R. 1997b: Preliminary results of mapping and structural interpretation from the Woodburn project, western Churchill Province, Northwest Territories; in Current Research 1997-C; Geological Survey of Canada, p. 91-100.

Zaleski, E., Duke, N.L., L'Heureux, R., and Wilkinson, L. 1999a: Geology, Woodburn Lake group, Amarulik Lake to Tehek Lake, Kivalliq Region, Nunavut; Geological Survey of Canada Open File 3743, scale 1:50 000.

Zaleski, E., L'Heureux, R., Duke, N., Wilkinson, L., and Davis, W.J. 1999: Komatiitic and felsic volcanic rocks overlain by quartzite, Woodburn Lake group, Meadowbank River Area, Western Churchill Province, Northwest Territories (Nunavut); in Current Research 1999-C; Geological Survey of Canada.

Kerswill, J.A., Goff, S.P., Kjarsgaard, B.A., Jenner, G.A. and Wilkinson, L. 2000: Highlights of recent metallogenic investigations in western Churchill Province, Nunavut, Canada: implications for mineral exploration in Archean greenstone belts; [extended abstract] in GeoCanada 2000- The Millennium Geoscience Summit CD-ROM, Calgary, Abstract 736.

Pehrsson, S., Wilkinson, L., Zaleski, E., Kerswill, J., and Alexander, B. 2000: Structural geometry of the Meadowbank deposit area, Woodburn Lake group implications for a major gold deposit in the Western Churchill Province; [extended abstract] in GeoCanada 2000, Calgary Alberta.

Zaleski, E., Corrigan, D., Kjarsgaard, B.A., Kerswill, J.A., Jenner, G.A. and Henderson, J.R. 1997a: Geology, Woodburn Lake group, Meadowbank River to Tehek lake (66H/1, 56E/4), District of Keewatin (Nunavut), Northwest Territories; Geological Survey of Canada, Open File 3461, scale 1:50 000.

NEqual Area(Schmidt)

Axial N = 99

Poles to S1/Socomposite fabric

NEqual Area(Schmidt)

Axial N = 19

F1 fold axes

A B

C

D

Stereonet plot of poles to the composite S /S fabric (A) and measured F and F axes (B). For both plots 0 1 1 2

circles represent data from the North Portage area and diamonds are from the Third Portage area. (C) Photograph of F folds and axial planar cleavage from Trench D at the Third Portage deposit. (D) 2

Photograph of F fold in drill core with a strong axial planar S cleavage from the Third Portage deposit 2 2

(sample TP98 291, 38.5 m).

NEqual Area(Schmidt)

Axial N = 14

Poles to S4 fabric

NEqual Area(Schmidt)

Axial N = 52

F4 fold axes

A B

CStereonet plot of poles to S fabric (A) 4

and measured F axes (B). For both plots 4

circles represent data from the North Portage deposit and diamonds from the Third Portage deposit. (C) Photograph of F folds from the North Portage area.4

The stratigraphy, that hosts the deposits, consists of felsic to intermediate volcaniclastic rocks and interbedded iron formation. The stratigraphic sequence is polydeformed with four phases of deformation recognized regionally; two of which have substantially modified the geometry of the strata. The initial phase of deformation was a progressive transposition of the stratigraphy with tight to isoclinal folding which culminated in low angle high strain zones. This progressive deformation event appears to have controlled the distribution of gold mineralization. Overprinting, NE-SW shallow plunging folds further modified the geometry of the mineralized body.

Structural Geology

Sulphide bearing iron formation. Sulphides are dominately pyrrhotite and lesser pyrite. Arsenopyrite is rare to absent Auriferous narrow blue quartz veins, in D /D fabric and cut by D , hosted by felsic 1 2 4

volcaniclastic rocks Coarse grained ampbiboles in iron formation, often where mineralized these are overprinted and deformed by strong D fabrics2

The distribution of gold in the Third Portage deposit is well defined by closely spaced drilling (~25 m) and surface trenching, and is similar in style and geologic setting to the adjacent North Portage, Bay Zone and Goose Island deposits. Mineralization, at the Third Portage deposit, is best developed at the lithologic contact between an ultramafic body and the volcanosedimentary package. The ultramafic body may represent the core to an east verging antiform or alternatively may be a boudin within the transposed/flattened stratigraphy. Mineralization is almost entirely restricted to the structural footwall or the hinge area of the ultramafic body; occurring only sporadically and weakly in the structural hanging wall of the ultramafic unit. The hanging wall is low-strain with planar lithologic contacts and S /S fabrics, whereas the footwall is generally higher strain with contorted F folds and strong S 0 1 2 2

fabrics.

Gold is contained within sulphide-bearing iron formation (Armitage et al., 1996; Kerswill et al., 1998), characterized by disseminated to semimassive pyrrhotite-pyrite which preferentially replaces magnetite (Armitage et al., 1996). Mineralization is also developed in the felsic-intermediate volcanic package as disseminated pyrrhotite and pyrite along with narrow grey quartz veins also containing pyrrhotite and pyrite.

Sulphides show a variety of relationships with deformation fabrics. Pyrrhotite, pyrite and sulphide-bearing quartz veins can be aligned along S /S fabrics as well as within S foliations overprinting S /S fabrics (Kerswill et al., 0 1 2 0 1

2000; Pehrsson et al. 2000). Spatially, at the Third Portage deposit, the bulk of the mineralization is concentrated at the structural footwall or hinge area of ultramafic units within, and adjacent to, high strain zones defined by penetrative S fabrics. Suggesting either different generations of sulphides or that the sulphides are related to the progressive D -D deformation event and concentrated in areas of higher strain.2 1 2

Mineralization

The degree of transposition of the host stratigraphy makes it difficult to trace individual units within the felsic volcaniclastic and iron formation package. Even in the Third Portage area, where trenching and close spaced diamond drilling provides exceptional data density, the surface trace of the individual units is uncertain. The gold mineralization however is very continuous along strike and down dip. Mineralized envelopes, of greater than 1.0 g/t Au show good continuity and can be traced for 100's of meters. It is this feature of the mineralization which has enabled Cumberland to produce a proven-probable mining reserve. Mineralization occurs in iron formation and volcaniclastic rocks and is more continuous than any individual stratigraphic interval.

Armitage et al. (1996), based on whole rock and mineral chemistry, has shown that auriferous iron formations are characterized by a mineral assemblage of cummingtonite and biotite with pyrrhotite-pyrite-magnetite and quartz. Barren, but sulphidic, iron formations are characterized by an assemblage of grunerite ± hornblende + stilpnomelane with pyrrhotite, pyrite, quartz and magnetite. Whereas barren, non sulfide-bearing, iron formations are characterized by quartz and magnetite. Based on these mineral assemblages and their relationship to gold mineralization, Armitage et al. (1996) have suggested that mineralization is related to metasomatic fluids that have altered the iron formation with the introduction of Mg-K-Ca-S-As-Cu and Au during D -D deformation.1 2

Although speculative; it is possible that metasomatic fluids, introduced into dilational sites during D -D deformation, altered the iron formation and locally the volcaniclastic rocks. The mechanical 1 2

contrast between the ultramafic and volcaniclastic rocks partitioned strain into the volcaniclastics and iron formation, which preferentially localized dilational settings. This allowed fluid influx and the resulting alteration assemblages, described by Armitage et al. (1996), to be concentrated in the higher strain corridor adjacent to the ultramafic rocks. The progressive nature of D -D formed the 1 2

various relationships of sulphide minerals and deformation fabrics.

Summary

Geochemistry

0.0

2.0

4.0

6.0

8.0

10.0

12.0

14.0

16.0

18.0

20.0

0.0 50.0 100.0 150.0 200.0

Y (

ppm

)

Zr (ppm)

Zr/Y

= 5

Zr/Y = 10

Zr/Y ratios for the felsic volcanic rocks range between 7 and 12, suggesting acalc-alkaline geochemical affinity

<d/l

2.00

4.00

6.00

8.00

10.00

12.00

14.00

16.00

18.00

<d/l 0.200 0.400 0.600 0.800

Series1

Series2

Iron Formation

Intermediate Volcanics

AlO

(%

)2

3

TiO (%)2

Immobile element ratios for the iron formations, form a straight line, consistent withthe ratios from the felsic volcanic rocks. This suggests that a detrital felsic volcaniccomponent was added to the iron formations during deposition.

sedi

men

tary

inpu

t of f

elsic

volcan

ic d

etrit

us

into

iron

form

atio

n

.01 .1 1 10.001

.01

.1

1

Zr/TiO2

Nb/Y

SubAlkaline Basalt

Andesite/Basalt

Andesite

Rhyodacite/Dacite

Rhyolite

Alk-Bas

TrachyAnd

Trace element data for the flesic volcanic rocks, showing that they are rhyodacitic to daciticin composition