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CURRENT RESEARCH 2002-E5 Occurrence of bleached mafic flows and their association with stockwork sulphides and banded iron-formation in the Crestaurum Formation of the late Archean Yellowknife Greenstone Belt, Northwest Territories L. Ootes and D.R. Lentz
2002
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©Her Majesty the Queen in Right of Canada 2002 ISSN 1701-4387
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Authors’ address L. Ootes (
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[email protected]) Department of Geology University of New Brunswick Box 4400 Fredericton, New Brunswick E3B 5A3
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Occurrence of bleached mafic flows and their association with stockwork sulphides and banded iron-formation in the Crestaurum Formation of the late Archean Yellowknife 1,2 Greenstone Belt, Northwest Territories L. Ootes and D.R. Lentz Ootes, L. and Lentz, D.R., 2002: Occurrence of bleached mafic flows and their association with stockwork sulphides and banded iron-formation in the Crestaurum Formation of the late Archean Yellowknife Greenstone Belt, Northwest Territories; Geological Survey of Canada, Current Research 2002-E5, 12 p.
Abstract: In the northern part of the late Archean Yellowknife Greenstone Belt, tholeiitic basalt of the Crestaurum Formation is bleached along a 7 km strike length. Unbleached late volcanic gabbro dykes and sills transect the bleached mafic flows and constrain the alteration to synvolcanic processes. Bleaching is likely a result of silicification and Fe leaching with later chloritization of pillow selvages. These altered flows are intercalated with thinly layered, silica-rich, metavolcaniclastic rocks, which have been referred to as ‘cherty tuff’. Petrographic and oxygen isotopic constraints indicate that the chert component is minor. An occurrence of discontinuous chert-magnetite iron-formation and discordant sulphide stockwork are indicative of synvolcanic hydrothermal activity. This hydrothermal activity is likely responsible for local alteration of the mafic flows, but does not explain the large-scale alteration. Stratigraphic considerations suggest that a hydrothermal alteration system existed within the Crestaurum Formation and preceded eruption of the overlying felsic metavolcanic rocks. Résumé : Dans la partie septentrionale de la ceinture de roches vertes de Yellowknife de l’Archéen tardif, on trouve du basalte tholéiitique de la Formation de Crestaurum qui a été blanchi sur une distance de 7 km parallèlement à la direction. Des dykes et des filons-couches de gabbro tardivolcaniques non blanchis recoupent les coulées mafiques blanchies et permettent d’attribuer l’altération à des processus synvolcaniques. Le blanchiment résulte vraisemblablement de la silicification, du lessivage de Fe et de la chloritisation ultérieure des bordures de coussins. Ces coulées altérées sont intercalées de minces couches de roches métavolcanoclastiques riches en silice, que l’on a appelées «tuf cherteux». Les données sur la pétrographie et les isotopes de l’oxygène indiquent que le chert est une composante mineure. La présence de formation de fer à chert-magnétite discontinue et d’un stockwork de sulfures discordant témoigne d’activité hydrothermale synvolcanique. Bien que cette activité hydrothermale ait probablement altéré les coulées mafiques à l’échelle locale, elle n’explique toutefois pas l’altération à grande échelle. Des facteurs stratigraphiques laissent supposer qu’un réseau d’altération hydrothermale existait dans la Formation de Crestaurum avant l’éruption des roches métavolcaniques felsiques sus-jacentes.
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Contribution to EXTECH III Contribution to Targeted Geoscience Initiative
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inductively coupled plasma mass spectrometry (ICP-MS). Analyses for Au, As, Cr, Sb, and Sc were done by instrumental neutron activation analysis (INAA). In-house rock standard (GB-1; Lentz, 1995) was submitted to selectively assess the data quality. Major elements are quoted with less than 4% error, except for K2O, which has a 14% error. Trace elements tend to have a higher degree of variance, particularly those of low abundance, but most trace elements have errors less than 25%. Part of the variance may be attributed to the analytical techniques used. Whole-rock δ18O values have a precision of 0.2‰.
INTRODUCTION The study area is located 15 km north of Yellowknife, Northwest Territories, and is underlain by metavolcanic rocks of the late Archean Yellowknife Greenstone Belt (Fig. 1). This sequence is host to the Crestaurum shear-zone-hosted gold deposit, the principal focus of this EXTECH III study. To define controls and timing constraints on gold deposition, it is necessary to understand the host-rock lithology. An extensive zone of bleached (whitish) metavolcanic rocks of the Crestaurum Formation occurs southeast of the Crestaurum mine area (Fig. 1, 2, 3). It extends laterally along strike for approximately 7 km from the West Bay Fault to the east, to the Yellowknife River Fault Zone to the west, and across the stratigraphy to the southeast. Regional mapping by Henderson and Brown (1966) correctly identified these rocks (in the opinion of the authors) as having a basaltic to andesitic basalt protolith.
GEOLOGY OF THE YELLOWKNIFE GREENSTONE BELT The late Archean Yellowknife Greenstone Belt is a 12 km thick, northeast-trending, southeast-dipping and younging, homoclinal belt of tholeiitic to calc-alkaline metavolcanic rocks in the southwestern Archean Slave Structural Province (Henderson and Brown, 1966; Helmstaedt and Padgham, 1986; Cousens, 2000). It is considered to be a parautochthonous cover sequence that disconformably overlies the >2830 Ma Central Slave Cover Group and the >2900 Ma Central Slave Basement Complex (Isachsen and Bowring, 1997; Bleeker et al., 1999). It is overlain by ca. 2660 Ma Duncan Group metagreywacke-mudstone turbidite (Bleeker, 1996) and unconformably by ca. 2605 Ma Jackson Lake Formation polymictic conglomerate and sandstone (Fig. 1; Isachsen, 1992). Helmstaedt and Padgham (1986) subdivided it into the ca. 2722 to 2701 Ma Kam Group and the 2680 to 2660 Ma Banting Group (Isachsen, 1992).
The Yellowknife Greenstone Belt is best known for shear-zone-hosted gold deposits in metavolcanic and metaturbiditic rocks that collectively have produced over 400 t of gold (Poulsen et al., 2000). Significant volcanogenic massive sulphide deposits do occur in the Slave Province, but because they are located in remote areas, they have not been exploited (Padgham, 1992). It has been suggested that the Yellowknife Greenstone Belt is not an ideal candidate for volcanogenic massive sulphide exploration (Goodwin, 1988) as the felsic metavolcanic rocks have light rare-earth-element-enriched patterns and insignificant Eu anomalies (Goodwin, 1988; Cousens, 2000) compared to the relatively flat rare-earth-element patterns and large Eu anomalies of felsic metavolcanic rocks associated with volcanogenic massive sulphide deposits in the Superior Province (e.g. Lesher et al., 1985). Small volcanogenic massive sulphide-like deposits have been identified near Homer Lake in the northern part of the Yellowknife Greenstone Belt (Padgham, 1992), but are uneconomic. The minor occurrence of banded iron-formation and stockwork sulphides in proximity to mixed felsic and mafic metavolcaniclastic and bleached mafic metavolcanic rocks in the Crestaurum area is evidence of extensive seafloor hydrothermal activity possibly related to volcanogenic massive sulphide genesis. Therefore, the host rocks of the Crestaurum shear-zone-hosted gold deposit may have been enriched in base metals during seafloor alteration prior to gold deposit formation.
Structural and metamorphic evolution The Yellowknife Greenstone Belt has undergone at least three stages of Archean deformation, the nomenclature for which has been extrapolated from the Duncan Lake Group turbidite units (Fig. 1) that overlie the greenstone belt to the east (Bleeker and Beaumont-Smith, 1995). First-generation deformation (D1) predates granitoid intrusion and is defined by pillow flattening and local foliations (S1) with local isoclinal folds (F1) in the volcaniclastic rocks. The second stage of deformation (D2) is defined by penetrative fabrics (S2) that are axial planar to belt-scale, asymmetrical Z-folds. Although S2 fabrics are found in the mafic volcanic rocks, they are best observed in the felsic volcaniclastic units. Third-generation fabrics (S3) are well developed in the Jackson Lake Formation and occur as a result of sinistral shear on the Yellowknife Greenstone Belt. The Yellowknife Greenstone Belt was not in the shortening field (i.e. not folded), although local S3 crenulation cleavages were developed in S2 (W. Bleeker, pers. comm., 2002). All rock types in the Yellowknife Greenstone Belt have been offset by Proterozoic faults (e.g. West Bay Fault; Fig. 1).
ANALYTICAL TECHNIQUES Samples for whole-rock geochemical analysis and δ18O were collected during the 2000 field season. All weathered surfaces were cut off and samples were washed and individually wrapped in resealable bags. Geochemical analysis and δ18O were completed at Activation Laboratories Ltd., Ancaster, Ontario. Samples were crushed, mechanically split, and pulverized using a mild steel mill to minus 150 mesh. Major elements, Zr, V, and Y were analyzed by fusion inductively coupled plasma emission spectrometry (ICP-ES). Trace elements and rare-earth elements were analyzed by digestion
Current Research 2002-E5
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Intrusion of Defeat Suite plutonic rocks (2630–2620 Ma; Davis and Bleeker, 1999) into the Yellowknife Greenstone Belt (Fig. 1) created metamorphic aureoles that parallel the intrusive contacts. These aureoles grade outward from
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Proterozoic
62o40″
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Dogrib diabase dykes
114 00″
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N
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Archean Plutonic rocks
Bay
Duckfish Granite
lt Fau
Biotite+magnetite granite
Prosperous Granite Two-mica granite
Zone of bleached Crestaurum Fm. basalt
Defeat plutonic suite
Prosperous Lake
Anton plutonic suite
ake
undifferentiated granite, granodiorite, tonalite, and diorite
Walsh L
CRESTAURUM
undifferentiated granitoid rocks
Gabbro sills m Ka
undifferentiated: intrude the Kam and Banting groups
Fig. 2 lt
r Ma
u Fa
Supracrustal rocks
ti n ult Fa
Jackson Lake Formation undifferentiated sandstone and conglomerate
PTARMIGAN
Duncan Group
Yellowknife
Kamex Formation: mafic volcanic rocks with interlayered intermediate volcaniclastic rocks Yellowknife Bay Formation: mafic volcanic rocks with interlayered sedimentary rocks
lt au nF
Kam Group
ga mi
Mafic and felsic volcanic rocks and mudstone turbidite
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CON
Townsite Formation: felsic volcanic rocks Crestaurum Formation: mafic volcanic rocks with interlayered sedimentary rocks Chan Formation: mafic volcanic rocks with abundant synvolcanic gabbro dykes and sills
Central Slave Cover Group undifferentiated felsic volcanic rocks, banded iron-formation, and quartzite
Great Slave Lake
Basement rocks Central Slave Basement Complex Anton Complex: gneissic tonalite and granodiorite
Proterozoic brittle fault
5 Kilometres
Study area
o
mine location, main headframe only
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114 35″
Symbols
62 15″ o
Figure 1. Geology of the Yellowknife Greenstone Belt and the southern portion of the Yellowknife Domain. Information: zone of bleached Crestaurum Formation mafic flows (vertical hatching) (modified from Helmstaedt and Padgham, 1986); Central Slave Basement Complex and Central Slave Cover Group (Bleeker et al., 1999), and Kamex Formation (Cousens and Falck, 2000).
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amphibolite through transitional (or epidote amphibolite) to greenschist grade (Boyle, 1961; McDonald et al., 1993; Thompson, 2001). This metamorphic event is suggested to overprint a regional greenschist-grade metamorphic event that began before and continued after intrusion of the Defeat Suite plutonic rocks (Thompson, 2001). All rock types considered herein have been metamorphosed so the prefix ‘meta’ has been dropped from this point forward.
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Geology of the Kam Group This study focuses on rock types of the lower Kam Group. Helmstaedt and Padgham (1986) changed the Kam Formation to group status and subdivided it into four formations; from base to top these are the Chan, Crestaurum, Townsite, and Yellowknife Bay formations; a fifth, the Kamex Formation, was added by Cousens and Falck (2000). The Chan Formation comprises basaltic flows that have been extensively intruded by synvolcanic and postvolcanic gabbro dykes (MacLachlan and Helmstaedt, 1995) and lacks
Shear 20
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Lo 78 Lo 79
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Lo 310
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100 200 Metres
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62°34′41″N Lo 78
Ryan Lake Pluton
sample location
quartz-feldspar porphyry dyke stratigraphic younging direction
gabbro dyke or sill (undifferentiated) Crestaurum Formation mafic volcanic rocks
Crestaurum gold mine (abandoned)
Crestaurum Formation felsic volcaniclastic rocks
zone of intensely bleached mafic flows
Chan Formation mafic volcanic rocks A
B
stratigraphic section in Figure 3
Figure 2. Simplified geology of the Crestaurum mine area. Areas of intense altertation, sample locations, and figure locations presented in the paper are shown. Stratigraphic younging directions are defined by pillow textures and flow-top breccia in the mafic volcanic rocks and by graded bedding and flame structures in the volcaniclastic rocks (modified from Ootes, 2002).
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Ryan Lake Pluton and quartz-feldspar porphyry dykes Gabbro dykes and sills (undifferentiated)
Absolute stratigraphic position unknown
Volcaniclastic rocks with abundant mafic components Banded iron-formation
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Crestaurum Fm. mafic flows: unbleached; bleached Crestaurum Fm. felsic volcaniclastic rocks
Varied amygdaloidal and variolitic pillowed flows
Chan Fm. mafic flows Sh2 0
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Absolute stratigraphic position unknown
Abundant amygdaloidal and variolitic pillowed flows
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~25 metres thick
CS
Tuff and banded iron-formation horizon up to 7 m thick
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amygdaloidal pillows
C
Tuff horizon up to 5 m thick
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Shear 20 (sinistral offset) CSZ Crestaurum shear zone
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Sh20
A
Stratigraphic younging direction Stratigraphic section from Figure 2
Figure 3. Idealized stratigraphic section (not to scale) of the Chan and Crestaurum formations in the Crestaurum mine area. Offset along Shear 20 has transposed bleached mafic flows, banded iron-formation, and related volcaniclastic units to an apparent lower stratigraphic position. Sections compiled from mapping by Henderson and Brown (1966) and Ootes (2002).
felsic volcaniclastic members (Helmstaedt and Padgham, 1986). The Crestaurum Formation is dominated by basaltic flows that locally have a pervasive bleached appearance. A number of felsic volcaniclastic horizons 1 to 20 m thick occur within the Crestaurum Formation, which also has fewer synvolcanic and postvolcanic gabbro dykes than the Chan Formation (Helmstaedt and Padgham, 1986).
intermediate volcaniclastic rocks of the Kamex Formation occur at the top of the Kam Group (Cousens and Falck, 2000; Fig. 1). Seafloor-altered mafic flows have been identified in the Yellowknife Bay Formation in the southern part of the Yellowknife Greenstone Belt (e.g. McDonald et al., 1993). Only minor portions of the Crestaurum Formation and even less Chan Formation are exposed in the southern part of the belt. These Crestaurum and Chan formation rocks include some seafloor-altered mafic flows (e.g. local garnet porphyroblasts within altered pillowed flows), but for the most part do not have the extensive bleached appearance of the Crestaurum Formation pillowed flows in the area of the Crestaurum mine.
Immediately overlying the Crestaurum Formation are the rhyolitic and dacitic rocks of the Townsite Formation that have been dismembered by large postvolcanic gabbro dykes (Henderson and Brown, 1966; Helmstaedt and Padgham, 1986). Yellowknife Bay Formation basaltic andesite and volcaniclastic rocks overlie the Townsite Formation (Helmstaedt and Padgham, 1986). Basaltic andesite and
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Chan Formation basalt is extensively intruded by at least three generations of late- to postvolcanic gabbro dykes and sills (Henderson and Brown, 1966; Ootes, 2002), which include 1) dark brown- to green-weathered, medium- to coarse-grained gabbro with radiating, locally irregularly shaped amphibole phenocrysts up to 1 cm (#7 dykes of Henderson and Brown, 1966), 2) dark brown- to black-weathered, fine- to medium-grained gabbro with plagioclase phenocrysts up to 2 cm (#8a dykes of Henderson and Brown, 1966), and 3) brown- to green-weathered, fine- to medium-grained gabbro (#8 dykes of Henderson and Brown, 1966).
GEOLOGY OF THE CHAN AND CRESTAURUM FORMATIONS IN THE CRESTAURUM MINE AREA The Crestaurum mine area (Fig. 2), located 15 km north of Yellowknife, is underlain by Chan Formation mafic volcanic flows and Crestaurum Formation bleached mafic volcanic flows and volcaniclastic rocks. The stratigraphic exposure and laterally traceable bleached mafic flows (Fig. 1) make this area a superb location to study the cause and effects of seafloor alteration in the Crestaurum Formation (Fig. 1, 2, 3). Previous studies in the area include mapping by Henderson and Brown (1966), a field-trip guide by Padgham (1987), a geochemical transect by Cunningham and Lambert (1989), U-Pb geochronology by Isachsen (1992), and a geochemical and Nd isotope transect by Cousens (2000).
Chan Formation basalt and postvolcanic gabbro dykes and sills are intruded by a multiphase granitic to quartz dioritic pluton 500 m west of the Crestaurum mine site (Fig. 2). This pluton is the likely source of numerous quartz-feldspar porphyry dykes (2658 ± 2 Ma, Isachsen, 1992; 2678 ± 8 Ma, Padgham, 1985) that trend southeast and cut all Kam Group rock types (Henderson, 1985; Ootes, 2002). This constrains the age of the gabbro dykes to older than about 2670 Ma. Some gabbro dykes were likely synchronous with mafic volcanism throughout the Kam Group (>2700 Ma).
Important structures in the area include the Crestaurum shear zone, Shear 20, and the Daigle Fault (Fig. 2). The Crestaurum shear zone trends 035°/55°SE and obliquely transects volcanic rocks and postvolcanic gabbro and quartz-feldspar porphyry dykes of the Chan and Crestaurum formations (Fig. 2). It hosts the Crestaurum gold deposit and field evidence (Ootes, 2002) indicates it is syn- to post-D2 (≤2600 Ma; Davis and Bleeker 1999). Shear 20 is a well exposed shear zone that trends north, dips 85° to 90° east, and transects and displaces rocks of the Chan and Crestaurum formations. It has left laterally offset and juxtaposed younger Crestaurum Formation rocks against older Crestaurum and Chan formation rocks (Fig. 2; Ootes, 2002). This indicates that the felsic volcaniclastic rocks west of Shear 20 and the volcaniclastic rocks east of Shear 20 are not related (Fig. 2, 3, 4). The Daigle Fault is not exposed, but is defined by a 060° linear trend through the Crestaurum mine area (Fig. 2, 3) and is suggested to have minimal offset (Henderson and Brown, 1966).
Crestaurum Formation The Crestaurum Formation is composed of a wider variety of rock types than the underlying Chan Formation. For simplicity, these rock types are described herein as they occur in stratigraphy. An intermixed unit of reworked felsic volcaniclastic rocks occurs at the base of the Crestaurum Formation. It is about 25 m thick with delicately laminated to 30 cm thick beds. Relic depositional structures include local graded bedding, flame structures, and syndepositional folding. Volcaniclastic beds have a plagioclase and quartz groundmass with subangular quartz phenoclasts (Fig. 4). Fine-grained tuffaceous beds are common with a groundmass of microcrystalline quartz and minor to abundant fine-grained muscovite and carbonate. Mafic volcanic clasts or relic volcanic fragments are common, but are now chlorite and epidote. Postdepositional structures include well preserved S1 and S2
Chan Formation Rocks of the Chan Formation in the Crestaurum mine area are composed of dark to light green-weathered, amphibolite- to greenschist-grade (Thompson, 2001), pillowed to massive flow basalt and basaltic andesite. Numerous primary volcanic textures are evident in the basalt, including pillow selvages from 1 to 30 cm thick that locally indicate younging to the southeast, quartz and carbonate amygdales in upper stratigraphic flows, and polygonal cooling cracks in massive flow basalt. Primary minerals in these mafic volcanic flows include rare clinopyroxene (P. Thompson, pers. comm., 2001) and pseudomorphs of fine-grained muscovite after plagioclase phenocrysts. Near the top of the Chan Formation local areas of bleaching become evident (Fig. 4) and indicate that the process that bleached the Crestaurum Formation mafic flows had a minor effect on the upper Chan Formation mafic flows. Sample LO79 (Fig. 2, 4) has a moderately bleached appearance, but is geochemically similar to other Chan Formation pillowed flows (Table 1).
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Figure 4. a) Moderately bleached pillowed flows with thick, chloritized pillow selvages near the top of the Chan Formation; b) Felsic volcaniclastic rocks at the base of the Crestaurum Formation; c) unbleached pillowed flow lower in the Crestaurum Formation; d) typical bleached pillowed flow with chloritic pillow selvages higher in the Crestaurum Formation; e) banded iron-formation; f) felsic and mafic volcaniclastic rocks that lie 50 m along strike and stratigraphically above the banded iron-formation; g) coarse-grained stockwork with pyrite, pyrrhotite, and magnetite in a chloritic groundmass; h) unbleached postvolcanic gabbro dykes transecting bleached pillow flows of the Crestaurum Formation. This figure is not shown on Figure 2, but represents a site about 2 km southwest of the location of Figure 2 along strike of the bleached pillow flows.
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b
a
00LO1030
Lapilli Tuff
c
d
e
f
Mafic beds
Mafic beds
h
g
Contact
Gabbro
5 cm
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Table 1. Whole-rock geochemical data for mafic volcanic rocks of the Chan and Crestaurum formations. Sample locations are shown on Figure 2. Chan Formation Sample no. wt.%
SiO2 Al 2O 3 Fe 2 O 3 MnO MgO CaO Na 2 O K 2O TiO2 P2 O5 LOI TOTAL ppm V Co Ni Cr Sc Cu Zn Ga Ge Rb Sr Y Zr Hf Nb Ta Th U Cs Ba La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb Lu W Tl Pb Bi As Sb Au (ppb) Zr/TiO 2 La n /Ybn Eu/Eu* 18
δ O(SMOW)
Crestaurum Formation
00L071
00L076
00L077
00L078
00L083 00L079 porph. bleached flow
45.2 13.18 14.86 0.30 8.94 11.79 1.24 0.78 0.90 0.07 2.40 99.7
52.7 15.64 11.71 0.21 4.59 10.18 2.24 0.41 1.18 0.14 1.42 100.4
51.6 15.26 9.79 0.24 5.20 11.83 1.01 0.93 1.17 0.10 1.45 98.6
47.2 14.72 16.16 0.35 7.23 7.93 2.33 0.23 0.86 0.07 2.39 99.4
51.3 51.2 15.25 12.67 11.57 18.11 0.21 0.32 4.40 3.33 12.85 9.92 0.74 1.65 0.14 0.47 0.86 2.01 0.08 0.20 2.75 0.19 100 100.1
228 63 79 180 40 230 159 17 1.0 27 110 19 56 1.8 0.2 0.15 1.7 0.3 3.9 120 4.8 9.7 1.25 6.7 2.1 0.86 2.5 0.53 3.5 0.74 2.3 0.34 2.35 0.36 29 0.1 39 3.5 17 17 <2
270 48 74 266 34 46 106 19 1.3 22 150 24 96 2.8 0.4 0.36 4.4 0.9 2.4 109 12.9 26.5 2.94 13.9 3.5 1.25 3.7 0.70 4.5 0.93 2.9 0.43 2.77 0.42 1 0.1 32 2.7 33 25 26
252 34 89 270 34 27 51 15 0.8 40 127 24 95 2.7 0.2 0.35 3.9 0.8 2.1 275 12.6 26.2 2.96 13.8 3.4 1.17 3.7 0.70 4.5 0.96 3.0 0.45 2.89 0.44 1 0.1 5 1.1 11 30 77
279 65 133 268 42 205 147 18 1.1 2 63 21 63 1.8 0.2 0.14 1.2 0.2 0.2 33 3.7 9.2 1.24 6.8 2.3 1.00 2.7 0.59 3.8 0.81 2.7 0.40 2.55 0.40 <0.5 <0.05 22 0.9 3 8 <2
0.006 1.46 1.14
0.008 3.33 1.05
0.008 3.12 1.00
0.007 1.04 1.24
6.1
7.6
6.8
7.3
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270 52 122 269 41 87 98 17 1.4 6 166 19 57 1.7 0.2 0.14 1.4 0.2 0.4 41 3.6 9.0 1.24 6.8 2.3 0.89 2.7 0.56 3.6 0.77 2.5 0.38 2.44 0.37 2 0.1 14 11.5 31 22 <2 0.007 1.05 1.10 8.3
405 38 20 42 44 73 75 22 1.3 10 78 38 140 4.3 1.4 0.37 1.8 0.4 1.4 62 7.8 20.2 2.82 14.9 5.0 1.81 5.7 1.12 7.6 1.61 5.0 0.77 5.18 0.82 2 0.1 6 4.2 3 10 <2 0.007 1.08 1.04 7.1
Crestaurum Fm.- variolitic pillows
00L0230 00L0231 00L0280 00L0307 00L0310 00L0150 00L0150 bleached bleached bleached bleached bleached 'A' 'B'
00L0228 altered
00L01029 altered
61.6 13.78 6.16 0.14 2.75 5.44 3.36 0.65 0.73 0.06 4.87 99.5
56.2 19.50 8.91 0.11 3.65 4.35 1.59 0.90 1.01 0.11 3.01 99.4
54.9 16.60 8.04 0.19 5.24 9.32 2.33 0.76 0.87 0.09 1.28 99.6
51.7 13.39 8.70 0.20 7.23 9.97 2.16 0.04 0.50 0.06 5.72 99.7
50.5 13.53 8.65 0.19 7.08 11.26 1.51 0.02 0.50 0.06 6.86 100.1
50.4 11.44 13.92 0.29 9.30 9.70 0.80 0.18 0.56 0.05 2.41 99.1
51.6 10.61 14.66 0.30 9.07 10.49 0.69 0.31 0.56 0.05 1.93 100.3
47.8 13.37 9.60 0.26 5.50 11.93 1.10 0.11 0.49 0.05 9.06 99.3
59.1 11.67 7.89 0.19 4.29 6.05 3.53 0.10 0.55 0.06 5.66 99.1
191 62 157 409 31 116 69 14 0.9 16 78 14 50 1.5 0.2 0.12 1.6 0.3 0.9 79 3.4 7.9 1.00 5.2 1.6 0.60 1.7 0.35 2.4 0.51 1.5 0.23 1.47 0.22 <0.5 0.1 8 0.3 13 5 9
291 60 245 569 50 99 80 20 1.6 18 64 20 65 2.0 0.2 0.18 1.7 0.3 1.3 134 4.5 10.7 1.40 7.3 2.2 0.81 2.4 0.54 3.6 0.75 2.4 0.34 2.09 0.30 1 0.1 <5 0.3 10 5 15
257 64 197 521 46 33 74 19 0.9 30 149 16 53 1.8 0.2 0.17 1.4 0.4 3.6 136 4.6 8.9 1.22 5.6 1.6 0.62 1.9 0.40 2.4 0.56 1.6 0.24 1.51 0.23 1 0.2 8 1.0 5 10 12
206 45 192 437 46 54 87 15 1.0 <1 111 13 44 1.1 0.2 0.10 1.6 0.3 0.1 18 3.4 7.5 0.90 4.7 1.4 0.53 1.6 0.33 2.2 0.48 1.5 0.22 1.50 0.23 <0.5 <0.05 10 0.1 2 4 <2
207 43 71 438 46 89 69 15 0.9 <1 94 14 40 1.2 0.2 0.09 1.7 0.3 0.1 17 3.5 7.8 0.93 4.8 1.5 0.57 1.7 0.37 2.4 0.54 1.7 0.26 1.70 0.28 <0.5 <0.05 6 0.2 1 4 <2
223 63 111 727 46 <10 96 12 1.5 5 99 13 44 1.2 0.2 0.10 1.4 0.2 0.7 35 3.1 7.3 0.93 5.1 1.5 0.61 1.8 0.36 2.4 0.52 1.5 0.24 1.55 0.25 1 <0.05 14 1.4 3 8 332
216 59 190 735 45 87 99 12 2.0 11 89 12 36 1.2 0.2 0.10 1.0 0.2 2.0 56 2.7 6.3 0.84 4.6 1.3 0.64 1.6 0.35 2.3 0.49 1.6 0.23 1.58 0.24 <0.5 0.1 8 5.6 4 8 3
78 43 180 396 44 94 77 11 0.6 1 93 15 167 1.3 0.2 0.08 1.2 0.3 0.2 12 3.5 6.9 0.95 4.4 1.3 0.47 1.7 0.36 2.3 0.50 1.6 0.22 1.42 0.24 <0.5 <0.05 <5 0.1 1 3 14
158 69 167 849 31 51 33 9 0.7 4 110 8 35 0.7 0.2 0.07 0.6 0.1 0.3 14 1.6 3.9 0.54 2.8 0.9 0.37 1.0 0.19 1.2 0.25 0.8 0.11 0.71 0.11 >0.5 <0.05 <5 0.7 21 6 7
0.007 1.64 1.12 10.5
8
0.006 1.54 1.08
0.006 2.18 1.07
0.009 1.63 1.09
0.008 1.47 1.07
0.008 1.42 1.13
9.7
8.4
8.8
8.3
7.8
0.006 1.23 1.33
0.034 1.77 0.96
0.006 1.59 1.25
8.8
9.9
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fabrics and F1 and F2 folds. Isachsen and Bowring (1997) termed these felsic volcaniclastic rocks the ‘Crestaurum Chert’ (chert has been dropped herein as no true chert has been identified) and defined a maximum age of 2827 Ma using U-Pb zircon geochronology. This is significantly older than the overall age of 2722 Ma suggested for this unit (Isachsen and Bowring, 1997) and is attributed to inheritance from the underlying Central Slave Cover Group (Isachsen and Bowring, 1997; Bleeker et al., 1999).
Abundant base-metal-bearing pyrite, pyrrhotite, and magnetite in quartz and carbonate veins were identified in drillhole DDH-NB-94-4, completed by Nebex in 1994 (Fig. 2). They are interpreted as a stockwork sulphide feeder zone formed by low-temperature hydrothermal venting on the seafloor. These stockworks have been identified only in this drillhole and do not outcrop. They contain coarse-grained pyrite with grains up to 2 cm, medium-grained pyrrhotite, and fine- to medium-grained, disseminated magnetite within quartz and calcite stringers and veins; they are hosted within highly altered mafic volcanic rocks (Fig. 4g).
Immediately overlying the felsic volcaniclastic rocks are dark green-weathered variolitic pillowed flows of the Crestaurum Formation with preserved pillow selvages and varioles up to 0.5 cm. These pillows are terminated and not correlative across the Daigle Fault (Fig. 2, 3). On the southeast side of the Daigle Fault and on the west side of Shear 20 (Fig. 2), the Crestaurum Formation consists of massive flows, variolitic pillowed flows, pillowed flows with quartz and minor carbonate amygdales, and pillowed flows with neither varioles nor amygdales. In most cases the pillowed flows have well preserved pillow selvages and where there is evidence of tops, they consistently young to the southeast. Some massive flows occur lower in the section; they are distinguished from the fine- to medium-grained gabbro by local bleached patches and rare flow breccia. The pillowed flows become increasingly bleached to the southeast (up the stratigraphy; Fig. 3, 4). Figures 4c and d show the difference between unbleached pillowed flows (Fig. 4c) lower in the stratigraphy and extensively bleached flows (Fig. 4d) higher up. Primary minerals have not been identified in the bleached pillowed flows and the groundmass has abundant fine-grained quartz, phyllosilicates, chlorite, and pyrite. Locally, the bleached pillowed flows contain a green-weathered phyllosilicate mineral that looks like fuchsite, but does not contain chromium or vanadium (H. Falck, pers. comm., 2000, regarding unpub. data of F. Santaguida). Local interflow sedimentary rocks are felsic volcaniclastic dominated with intermixed siltstone and sandstone.
The gabbro dykes and sills that cut the Chan Formation also transect the Crestaurum Formation. They are unbleached and stand out not only relative to the Crestaurum Formation bleached flows at outcrop scale (Fig. 4h), but also on a 1:20 000 colour airphoto. As previously mentioned, they must be older than about 2670 Ma and the oldest dykes are likely synchronous with mafic volcanism in upper formations of the Kam Group (>2700 Ma; Isachsen and Bowring, 1997). This constrains the alteration of the Crestaurum Formation mafic flows to older than 2700 Ma, suggesting a synvolcanic origin.
GEOCHEMICAL AND OXYGEN ISOTOPE CONSIDERATIONS Lithogeochemical and oxygen isotope (δ18OSMOW) data for a variety of Chan and Crestaurum formation pillowed flows are presented in Table 1. The geochemical analyses of the Chan Formation mafic flows are consistent with their unbleached physical appearance. Their δ18O values, which fall within the range of typical subaqueous basaltic flows (Muehlenbachs, 1998), attest to their unbleached nature. Sample LO83 has different physical and chemical attributes compared to other mafic flows. It has a fine-grained groundmass with plagioclase phenocrysts up to 1 cm, similar to a #8a dyke (Henderson and Brown, 1966), but is transected by a #7 gabbro dyke and has been interpreted as a porphyritic massive flow (Henderson and Brown, 1966; Ootes, 2002). Crestaurum Formation pillowed flows have higher SiO2 values and lower Fe2O3T values than Chan Formation pillowed flows, consistent with their bleached appearance. This, and a corresponding increase of δ18O(SMOW) with SiO2 content, is evidence that the bleaching resulted from Fe leaching and/or silica dumping during pervasive hydrothermal alteration.
The pillowed and massive flows of the Crestaurum Formation east of Shear 20 and north of the Daigle Fault are pervasively bleached below and above the volcaniclastic horizon. The bleached pillowed flows continue on the southeast side of the Daigle Fault, but the relationship to units on the north side is undefined (Fig. 2, 3). This extensively bleached zone of pillowed flows extends southeastward to the top of the Crestaurum Formation (Fig. 1). The volcaniclastic horizon east of Shear 20 consists of two units from 1 m to 7 m thick with finely laminated to 30 cm thick beds. The beds of the first unit are commonly fine to very fine grained, contain varied amounts of mudstone, siltstone, and mafic tuffaceous and felsic tuffaceous material, and are devoid of magnetite. Banded iron-formation characterizes the second unit and occurs within the volcaniclastic rocks (Fig. 3, 4), but is only traceable for 3 m. Its discontinuity can be explained by the intrusion of numerous gabbro and quartz-feldspar porphyry dykes that have inhibited correlation of the volcaniclastic units (Fig. 2). Fine-grained magnetite and Fe-rich chlorite compose the groundmass of the banded iron-formation.
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Variolitic pillowed flows of the Crestaurum Formation are also included in Table 1. Three of the samples have geochemical and δ18OSMOW values that are consistent with the bleached and moderately bleached samples of the Chan and Crestaurum formations. Sample 1029 was collected about 1 m above the felsic volcaniclastic horizon (Fig. 2) and is moderately sheared and altered. This accounts for the variation of the chemical constituents of this sample compared to other variolitic pillowed flows. Lithogeochemistry and δ18OSMOW of the felsic volcaniclastic rocks west of Shear 20 and the banded iron-formation and stockwork sulphides (Fig. 2) are presented in Table 2.
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Table 2. Whole-rock geochemical data for Crestaurum Formation felsic volcaniclastic rocks, banded iron-formation, and stockworks from drillhole DDH-NB-94-4. Sample locations are shown on Figure 2. Felsic volcaniclastic rocks and banded iron-formation Sample no. LO1025 LO1026 wt.% 81.3 69.6 SiO 2 14.34 9.58 Al 2O 3 2.77 1.43 Fe 2O 3 0.06 0.03 MnO 1.79 0.80 MgO 3.97 1.87 CaO 0.88 0.31 Na 2 O 2.97 2.75 K 2O 0.21 0.14 TiO 2 0.06 0.06 P 2 O5 3.83 2.14 LOI 100.5 100.4 TOTAL ppm V Co Ni Cr Sc Cu Zn Ga Ge Rb Sr Y Zr Hf Nb Ta Th U Cs Ba La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb Lu Tl Pb Bi As Sb Au (ppb)
26 1 <20 28 3 <10 36 19 <0.5 60 74 4 73 2.3 0.2 0.11 2.0 0.4 3.2 116 7.3 15.0 1.56 6.3 1.1 0.40 0.9 0.12 0.6 0.12 0.3 0.05 0.31 0.04 0.2 5 0.4 1 5 7
6 1 53 13 2 <10 <30 8 <0.5 36 27 2 70 1.5 0.2 0.07 1.1 0.3 1.4 90 3.4 7.4 0.84 3.3 0.6 0.19 0.5 0.07 0.4 0.08 0.2 0.03 0.22 0.03 0.1 <5 <0.1 1 3 <2
Zr/TiO 2 Lan /Yb n Eu/Eu
0.035 16.80 1.27
0.051 11.19 1.04
δ18O*(smow)
10.5
11.1
Drillhole DDH-NB-94-4
LO1027 LO1028 LO1030 75.7 71.5 78.5 13.43 14.98 11.07 1.71 2.06 1.62 0.02 0.04 0.05 0.82 1.17 0.68 1.66 2.63 1.88 0.56 0.71 4.13 3.60 3.76 0.87 0.18 0.21 0.17 0.06 0.06 0.07 2.37 3.03 1.25 100.3 100.1 100.2
LO203 73.8 14.09 1.85 0.03 0.54 1.05 3.98 2.29 0.21 0.07 1.12 99.0
BIF 56.4 8.34 24.06 0.63 5.50 0.99 0.01 0.06 0.24 0.07 4.18 100.5
NB-94-4 NB-94-4 NB-94-4 *NB-94-4 925′ 902′ 945′ 830′–832′ 18.1 5.7 45.4 3.93 0.42 1.98 12.23 37.67 54.06 52.12 15.96 1.00 0.30 0.26 0.52 2.61 2.13 1.86 5.65 18.76 3.92 9.31 9.84 (0.01) 0.04 0.03 (0.01) 0.06 0.02 (0.01) 0.02 0.15 0.08 0.02 1.87 0.02 0.02 (0.01) 0.23 8.85 20.71 7.12 91.2 90.4 98.8
13 5 699 23 3 21 <30 11 0.6 61 43 3 78 1.8 0.2 0.10 1.5 0.3 2.5 124 4.1 8.3 0.92 3.5 0.6 0.20 0.5 0.08 0.4 0.08 0.2 0.04 0.21 0.03 0.1 6 0.2 3 3 2
21 3 <20 70 3 <10 <30 17 0.6 81 84 4 89 2.5 0.2 0.18 2.3 0.6 4.3 344 6.1 12.1 1.25 5.1 0.8 0.31 0.8 0.12 0.7 0.14 0.5 0.07 0.47 0.07 0.3 6 0.8 6 7 <2
62 10 47 13 23 28 78 13 0.5 <1 4 35 167 5.1 5.4 0.72 14.3 3.5 <0.1 <3 51.4 81.8 8.03 34.3 6.8 1.19 6.3 0.99 6.2 1.31 4.3 0.66 4.27 0.70 <0.05 10 1.7 1 5 <2
13 54 31 10 5 47 805 1 <0.5 5 61 4 12 <0.1 <0.2 0.02 5.4 0.7 <0.1 <3 1.3 2.1 0.27 1.2 0.3 0.07 0.5 0.09 0.6 0.14 0.5 0.08 0.50 0.07 <0.05 206 <0.1 64 7 85
0.044 14.25 1.09
14 2 <20 30 3 16 <30 14 <0.5 70 54 3 73 1.5 0.2 0.07 1.3 0.3 3.5 143 4.7 9.7 1.07 4.1 0.7 0.24 0.6 0.08 0.5 0.09 0.3 0.03 0.22 0.03 0.2 <5 0.2 3 3 <2 0.035 15.52 1.16 10.4
9 4 <20 58 2 16 <30 8 0.6 18 49 3 67 1.5 0.2 0.10 1.4 0.4 0.6 98 3.4 7.3 0.88 3.7 0.7 0.25 0.6 0.09 0.5 0.10 0.3 0.04 0.26 0.04 <0.05 <5 0.1 3 3 <2 0.040 9.65 1.17 10.5
0.042 9.36 1.17
0.070 8.64 0.55
0.049
281 53 32 162 32 <10 125 21 0.8 <1 260 31 97 2.9 2.7 0.37 1.3 0.2 0.2 <3 8.3 23.5 3.31 17.3 5.0 1.76 5.0 0.95 5.5 1.10 3.3 0.45 2.93 0.41 <0.05 11 1.0 5 4 <2 0.005
44 9 44 21 8 25 309 8 <0.5 <1 64 18 55 0.6 <0.2 0.16 4.0 1.0 0.2 <3 8.9 15.8 1.87 7.6 1.7 0.39 2.2 0.36 2.2 0.47 1.4 0.20 1.35 0.23 <0.05 <5 <0.1 5 2 <2
47 101 <40 26 12 113 142
45 29 10 1.0 <0.5 2.3 <0.5 <0.1 <50 6.7 12.0 9.0 1.0 <0.2 <0.5
1.00 0.18 10 11.0 93 11 51
0.036
10.1
NOTE: Sample *NB-94-4 (830′–832′) analyzed by INAA only.
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The felsic volcaniclastic samples have similar major, trace, and rare-earth elements and Zr/TiO2 ratios, consistent with a volcaniclastic origin. The narrow range of δ18OSMOW values, with the highest value coincident with the highest SiO2 values, further supports a predominant volcaniclastic rather than a chemical origin (Knauth and Epstein, 1976). However, some chemically precipitated rocks (i.e. chert) are likely to occur in the package. The banded iron-formation is composed of 24.1 weight per cent Fe2O3T with no anomalous precious or base-metal values. Four samples of stockwork sulphides, collected at 252 m, 273 m, 280 m, and 286 m respectively, indicate locally anomalous contents of Zn (805 ppm), Pb (206 ppm), Cu (113 ppm), and Au (85 ppb).
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may account for localized bleaching; however, bleached flows occur stratigraphically above this horizon, indicating that the main bleaching event was most likely linked to an episode of volcanism that postdated banded iron-formation deposition, but preceded the eruption of the overlying Townsite Formation. The aerial extent and similarity of these bleached mafic flows to altered flows associated with volcanogenic massive sulphide deposits, in particular those of Noranda (Gibson et al., 1983) and Matagami (MacGeehan, 1977), highlight the possibility of undiscovered volcanogenic massive sulphide deposits in the Yellowknife Greenstone Belt.
CONCLUSIONS DISCUSSION
Crestaurum Formation metavolcanic rocks in the Yellowknife Greenstone Belt are bleached for about 7 km along strike and almost entirely across strike. Unbleached gabbro dykes and sills transect the bleached volcanic rocks of the Crestaurum Formation and the unbleached volcanic rocks of the Chan Formation. Some gabbro sills and dykes are likely synchronous with mafic volcanism within the Kam Group, suggesting they are older than about 2700 Ma. This constrains the alteration in the Crestaurum volcanic rocks to older than 2700 Ma, during building of the volcanic pile on the seafloor. The occurrence of banded iron-formation, stockwork sulphides, and silicified Crestaurum mafic flows in close proximity is strong evidence of hydrothermal activity and venting on the seafloor. This is only a local phenomenon, however, and the pervasive silicification of Crestaurum Formation mafic flows can only be explained by a large-scale hydrothermal event beneath and probably near the base of the overlying Townsite Formation. Although it has been suggested the Yellowknife Greenstone Belt is an unlikely candidate for volcanogenic massive sulphide deposits, the similarity between the bleached mafic flows and those of Noranda and Matagami, Quebec, leaves open the possibility of a yet undiscovered volcanogenic massive sulphide deposits in the Yellowknife Greenstone Belt.
The spatial association between banded iron-formation and the stockwork sulphides (Fig. 2) suggests that exhalative components are proximally related to the development of the synvolcanic stockwork feeder zone. Liaghat and MacLean (1992) used mass balance calculations and a tuff-exhalative mixing model to show the igneous and exhalative proportions in the Key Tuffite at Matagami, Quebec. In our study, a precursor tuffaceous component was not identified so mass balance calculations were not undertaken. The banded iron-formation unit was likely a product of exhalative activity during which Fe and Si were chemically precipitated after seafloor hydrothermal venting. The bleached mafic flows could be related to hydrothermal activity linked to the development of the stockwork feeder systems in the sequence. As the stockwork system developed and hydrothermal fluids circulated through the volcanic pile, Fe may have been leached from the pillows leaving abundant silica and alkali elements (Table 1), leading to the bleached appearance. The bleaching may also be a result of silica dumping, possibly coupled with the dissolution of Fe. The selvages of the bleached pillows are chloritized (Fig. 4) and may be explained by the development of a large hydrothermal circulation system in the volcanic package, evident by the extensive area of bleached flows (Fig. 1). As the volcanic pile thickened, the previously bleached pillowed flows were buried deeper into a zone where chloritization dominated (e.g. Franklin, 1996). Fluids working through the volcanic pile at this depth would likely follow the easiest flow path, in this case the pillow selvages. This generated bleached or ‘silicified’ mafic volcanic rocks with chloritized selvages. The best way to quantify the extent of alteration is to perform mass-balance calculations to define ‘real’ gains and losses of elements. Mass-balance calculations were not performed here as most samples were derived from different flows, some with distinct geochemical signatures. As well, a ‘least altered’ sample from the Crestaurum Formation was not found as unbleached and pillowed flows generally contained abundant carbonate and quartz stringers throughout.
ACKNOWLEGMENTS This is a contribution to the EXTECH III project. We thank the EXTECH III advisory committee, Hendrik Falck (Government of the Northwest Territories), Peter Thompson (P. Thompson Consulting), Wouter Bleeker (Geological Survey of Canada), and Valerie Jackson (Indian and Northern Affairs Canada) for help, support, and advice. Invaluable field assistance was provided by Erica Nyssonnen (2000) and Sara Richard (2001). A thorough review by J. Kerswill significantly improved the manuscript. Funding and transportation were provided by the EXTECH III project, by an Indian and Northern Affairs Canada–Northern Student Training Program grant to L. Ootes, and by a NSERC grant to D. Lentz.
Relating the bleached pillowed flows to the stockwork sulphides can only be done on a local scale. The hydrothermal event that formed the banded iron-formation and stockwork
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Isachsen, C.E. and Bowring, S.A. 1997: The Bell Lake Group and Anton Complex: a basement-cover sequence below the Archean Yellowknife greenstone belt revealed and implicated in greenstone belt formation; Canadian Journal of Earth Sciences, v. 34, p. 169–189. Knauth, P.L. and Epstein, S. 1976: Hydrogen and oxygen isotope ratios in nodular and bedded cherts; Geochimica et Cosmochimica Acta, v. 40, p. 1095–1108. Lentz, D.R. 1995: Preliminary evaluation of six in-house rock geochemical standards from the Bathurst Camp, New Brunswick; New Brunswick Department of Natural Resources and Energy, Minerals and Energy Division, Miscellaneous Report 18, p. 81–89. Lesher, C.M., Goodwin, A.M., Campbell, I.H., and Gorton, M.P. 1985: Trace-element geochemistry of ore-associated and barren felsic metavolcanic rocks in the Superior Province, Canada; Canadian Journal of Earth Sciences, v. 23, p. 222–237. Liaghat, S. and MacLean, W.H. 1992: The Key Tuffite, Matagami mining district: origin of the tuff components and mass changes; Exploration and Mining Geology, v. 1, no. 2, p. 197–207. McDonald, D.W., Duke, N.A., and Hauser, R.L. 1993: Geological setting of the NERCO Con Mine and the relationship of gold mineralization to metamorphism, Yellowknife, N.W.T.; Exploration and Mining Geology, v. 2, no. 2, p. 139–154. MacGeehan, P.J. 1977: The geochemistry of altered volcanic rocks at Matagami, Quebec: a geothermal model for massive sulphide genesis; Canadian Journal of Earth Sciences, v. 15, p. 551–570. MacLachlan, K. and Helmstaedt, H. 1995: Geology and geochemistry of an Archean mafic dike complex in the Chan Formation: basis for a revised plate-tectonic model of the Yellowknife greenstone belt; Canadian Journal of Earth Sciences, v. 32, p. 614–630. Muehlenbachs, K. 1998: The oxygen isotope composition of the oceans, sediments, and the seafloor; Chemical Geology, v. 145, p. 263–273. Ootes, L. 2002: Geology of the Crestaurum Mine Area, Yellowknife Greenstone Belt, N.W.T.; Northwest Territories Geology Division, Yellowknife, Northwest Territories; Northwest Territories Open File 2002-01, scale 1:2500. Padgham, W.A. 1985: Observations and speculations on supracrustal successions in the Slave Structural Province; in Evolution of Archean Supracrustal Sequences, (ed.) L.D. Ayres, P.C. Thurston, K.D. Card, and W. Weber; Geological Association of Canada, Special Paper 28, p. 133–151. 1987: Guide to parts of the Crestaurum, Townsite, and Yellowknife Bay Formations and the Banting Group; in Yellowknife Guide Book: A Guide to the Geology of the Yellowknife Volcanic Belt and its Bordering Rocks, (ed.) W.A. Padgham; Geological Association of Canada, p. 55–79. 1992: Mineral deposits in the Archean Slave Structural Province; lithological and tectonic setting; Precambrian Research, v. 58, p. 1–24. Poulsen, K.H., Robert, F., and Dubé, B. 2000: Geological classification of Canadian gold deposits; Geological Survey of Canada, Bulletin 540, 106 p. Thompson, P.H. 2001: Metamorphism and the origin of gold deposits in the Yellowknife Greenstone Belt, Phase 3 — from belt-scale metamorphic zones and thin sections to exploration targets; 29th Yellowknife Geoscience Forum, Yellowknife, Northwest Territories; Program and Abstracts of Talks and Posters, p. 83–84.
REFERENCES Bleeker, W. 1996: Thematic structural studies in the Slave Province, Northwest, Territories: the Sleepy Dragon Complex; Geological Survey of Canada, Current Research 1996-C, p. 37–48. Bleeker, W. and Beaumont-Smith, C. 1995: Thematic structural studies in the Slave Province: preliminary results and implications for the Yellowknife Domain, Northwest Territories; Geological Survey of Canada, Current Research 1995-C, p. 87–96. Bleeker, W., Ketchum, J.W., Jackson, V.A., and Villeneuve, M.E. 1999: The Central Slave Basement Complex, Part 1: its structural topology and autochthonous cover; Canadian Journal of Earth Sciences, v. 36, p. 1083–1109. Boyle, R.W. 1961: The geology, geochemistry, and origin of the gold deposits of the Yellowknife District; Geological Survey of Canada, Memoir 310, 193 p. Cousens, B.L. 2000: Geochemistry of the Archean Kam Group, Yellowknife Greenstone Belt, Slave Province, Canada; Journal of Geology, v. 108, p. 181–197. Cousens, B.L. and Falck, H. 2000: Peeking under Yellowknife Bay: bedrock geochemistry from drill core, southern Yellowknife Belt; 28th Yellowknife Geoscience Forum, Yellowknife, Northwest Territories; Program and Abstracts of Talks and Posters, p. 17–18. Cunningham, M.P. and Lambert, R.StJ. 1989: Petrochemistry of the Yellowknife volcanic suite at Yellowknife, N.W.T.; Canadian Journal of Earth Sciences, v. 26, p. 1630–1646. Davis, W.J. and Bleeker, W. 1999: Timing of plutonism, deformation, and metamorphism in the Yellowknife Domain, Slave Province, Canada; Canadian Journal of Earth Sciences, v. 34, p. 1169–1187. Franklin, J.M. 1996: Volcanic-associated massive sulphide base metals; Chapter 6.3 in Geology of Canadian Mineral Deposit Types, (ed.) O.R. Eckstrand, W.D. Sinclair, and R.I. Thorpe; Geological Survey of Canada, Geology of Canada, no. 8, p. 158–183 (also Geological Society of America, The Geology of North America, v. P-1, p. 158–183). Gibson, H.L., Watkinson, D.H., and Comba, C.D.A. 1983: Silicification: hydrothermal alteration in an Archean geothermal system within the Amulet Rhyolite Formation, Noranda, Quebec; Economic Geology, v. 78, p. 954–971. Goodwin, A.M. 1988: Geochemistry of Slave Province volcanic rocks. Yellowknife Belt; Contributions to the Geology of the Northwest Territories, Northwest Territories Geology Division, Department of Indian and Northern Affairs, Yellowknife, v. 3, p. 13–25. Helmstaedt, H. and Padgham, W.A. 1986: A new look at the stratigraphy of the Yellowknife Supergroup at Yellowknife, NWT — implications for the age of gold-bearing shear zones and Archean basin evolution; Canadian Journal of Earth Sciences, v. 23, p. 454–475. Henderson, J.B. 1985: Geology of the Yellowknife–Hearne Lake area, District of Mackenzie: a segment across an Archean basin; Geological Survey of Canada, Memoir 414, 135 p. Henderson, J.F and Brown, I.C. 1966: Geology and structure of the Yellowknife greenstone belt, District of Mackenzie; Geological Survey of Canada, Bulletin 141, 87 p. Isachsen, C.E. 1992: U-Pb zircon geochronology of the Yellowknife volcanic belt and subjacent rocks, N.W.T., Canada: constraints on the timing, duration, and mechanics of greenstone belt formation; Ph.D. thesis, Washington University, St. Louis, Missouri, 164 p.
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