Ric

eLake

belt

Limestone

Paragneiss

Granite, orthogneiss

San Antonio assemblage (ca. 2.70 Ga)

Edmunds assemblage (ca. 2.70 Ga)

Gem assemblage (ca. 2.72 Ga)

Quartz diorite (ca. 2.73 Ga)

Bidou assemblage (ca. 2.73 Ga)

Garner assemblage (ca. 2.9 Ga)

Wallace assemblage (ca. 2.99 Ga)

Granitoid rocks

Paleozoic

English River Subprovince

Uchi Subprovince

North Caribou Terrane

0 10 20

kilometresLake

Winnipeg

Manito

ba

Onta

rio

Bissett

Gold deposit

Geological contact

Shear zone, faultWanipigow Shear Zone

Manigotagan Shear Zone

Studyarea

.1 1 10 100.01

.1

1

10

Th

/Yb

Nb/Yb

N-MORB

E-MORB

OIB

DM(Pearce and Peate, 1995)

Subduction

enrichm

ent

With

in-plate

enrichm

ent

.01 .1 1 10

.01

.1

1

Zr/

TiO

2

Nb/Y

Basalt

Andesite/Basalt

Rhyolite/Dacite

AlkaliBasalt

Trachy-Andesite

Trachyte

Alkali Rhyolite

Phonolite

Foidite

(Pearce, 1996)

Th Nb La Ce Pr Nd Zr Sm Eu Ti Dy Y Yb Lu

Unit 21

1

10

100

Th Nb La Ce Pr Nd Zr Sm Eu Ti Dy Y Yb Lu

Rock/P

rim

itiv

eM

antle

Unit 21

Unit 15

1

10

100

Rock/P

rim

itiv

eM

antle

Unit 14

1

10

100

1000

Rock/P

rim

itiv

eM

antle

Unit 9

.001 .01 .1 1 1040

45

50

55

60

65

70

75

80

SiO

2

Zr/TiO2

Subalkalinebasalt

Andesite

Rhyodacite/Dacite

Rhyolite

(Winchester and Floyd, 1977)

.1 1 101

10

100

Eu/Eu*

[La/Y

b] C

N

FI

FII

FIII

(after Lesher et al., 1986)

0 20 40 60 80 100 120 140 1601

10

100

Zr/

Y

Y (ppm)

FI

FII

FIII

(after Lesher et al., 1986)

1 10 100 10001

10

100

1000

Nb

(pp

m)

Y (ppm)

syn-collisional

within plate

ocean ridge

(Pearce et al., 1984)

La Ce Pr Nd PmSm Eu Gd Tb Dy Ho Er Tm Yb Lu

Unit 17

1

10

100

La Ce Pr Nd PmSm Eu Gd Tb Dy Ho Er Tm Yb Lu

Ro

ck/C

ho

nd

rite

s

Unit 13

Unit 12

1

10

100

Ro

ck/C

ho

nd

rite

s

Unit 11

Unit 11

1

10

100

Ro

ck/C

ho

nd

rite

s

Unit 11

Unit 10

1

10

100

Ro

ck/C

ho

nd

rite

s

Unit 9

Chlorite alteration in dacite breccia(9a), east shoreline of Gem LakeChlorite alteration in dacite breccia(9a), east shoreline of Gem Lake

Sericite-altered rhyolite sandstone (11b),central Gem LakeSericite-altered rhyolite sandstone (11b),central Gem Lake

Gossanous rhyolite flow (11a), southshoreline of Gem LakeGossanous rhyolite flow (11a), southshoreline of Gem Lake

Sulphidic clast in conglomerate (16b),Manigotagan River NW of Gem LakeSulphidic clast in conglomerate (16b),Manigotagan River NW of Gem Lake

Chlorite alteration in dacite breccia(9a), east shoreline of Gem Lake

Sericite-altered rhyolite sandstone (11b),central Gem Lake

Gossanous rhyolite flow (11a), southshoreline of Gem Lake

Sulphidic clast in conglomerate (16b),Manigotagan River NW of Gem Lake

Dacite crystal tuff (17a)Dacite crystal tuff (17a) Dacite lapilli tuff (17a)Dacite lapilli tuff (17a)

Massive rhyolite conglomerate withsulphidic clasts (16b)Massive rhyolite conglomerate withsulphidic clasts (16b)Bedded pebble conglomerate (16a)Bedded pebble conglomerate (16a)

Pillowed basaltic andesite flow (15a)Pillowed basaltic andesite flow (15a)

Porphyritic andesite breccia (15b)Porphyritic andesite breccia (15b)

Equigranular gabbro(14a)Equigranular gabbro(14a) Porphyritic gabbro (14b)Porphyritic gabbro (14b)

Flow-banded rhyodacite (13a)Flow-banded rhyodacite (13a) Rhyodacite tuff (13b)Rhyodacite tuff (13b)

Flow-banded rhyolite (12a)Flow-banded rhyolite (12a)

Massive rhyolite flow (11a)Massive rhyolite flow (11a)

Intrusion breccia composed of aphyricrhyolite fragments in pink leucogranitematrix (11d)

Intrusion breccia composed of aphyricrhyolite fragments in pink leucogranitematrix (11d)

QFP leucogranite (10b)QFP leucogranite (10b)

Lapilli tuff (12a), with lapilli composedexclusively of flow-banded rhyoliteLapilli tuff (12a), with lapilli composedexclusively of flow-banded rhyolite

Dacite crystal tuff (17a) Dacite lapilli tuff (17a)

Massive rhyolite conglomerate withsulphidic clasts (16b)Bedded pebble conglomerate (16a)

Pillowed basaltic andesite flow (15a)

Porphyritic andesite breccia (15b)

Equigranular gabbro(14a) Porphyritic gabbro (14b)

Flow-banded rhyodacite (13a) Rhyodacite tuff (13b)

Flow-banded rhyolite (12a)

Massive rhyolite flow (11a)

Intrusion breccia composed of aphyricrhyolite fragments in pink leucogranitematrix (11d)

QFP leucogranite (10b)

Lapilli tuff (12a), with lapilli composedexclusively of flow-banded rhyolite

StormyLake

GarnerRiver

Manigotagan

River

314

314

Ma

nito

ba

Onta

rio

314

N

G

DL

TL

SL

U

G

DL

TL

SL

U

LongLake

GarnerLake

BeresfordLake

GemLake

Bere

sfo

rdL

ake

Sh

ear

Zo

ne

Bere

sfo

rdL

ake

Sh

ear

Zo

ne

Bere

sfo

rdL

ake

Sh

ear

Zo

ne

West G

arner Shear Zone

West G

arner Shear Zone

West G

arner Shear Zone

EastG

arn

er

Shear

Zone

EastG

arn

er

Shear

Zone

EastG

arn

er

Shear

Zone

Long

Lake

Shear

Zone

Long

Lake

Shear

Zone

Long

Lake

Shear

Zone

Beresford Lakeanticline

Beresford Lakeanticline

Beresford Lakeanticline

Sto

rmy

Lake

Sh

ear

Zo

ne

Sto

rmy

Lake

Sh

ear

Zo

ne

Sto

rmy

Lake

Sh

ear

Zo

ne

RossRiverPluton

RossRiverPluton

RossRiverPluton

Upper Bidou assemblage

The Narrows formation

Stormy Lake formation

Gunnar formation

Unnamed formation

Stovel Lake formation

Tinney Lake formation

Dove Lake formation

Lower Bidou assemblage

Garner Narrows unit

Garner Lake intrusive complex

Garner Lake extrusive complex

Tonalite, quartz diorite

Edmunds assemblage

Gem assemblage

Garner assemblage

Granitoid (unseparated)

Gabbro

Leucogranite

Tectonized rocks(uncertain precursor)

Shear zone/fault

Geological contact

Younging direction

Road314

Gold occurrence

Gabbro

U

SL

TL

DL

G

U

SL

TL

DL

G

Past-producing mine

Gabbro

Felsic volcanic rocks

Kilometres

0 1 2

ca a. 2.71-2.70 GRIFT-INFILL

ca a. 2.87 GPLUME-

MAGMATISM2731 +/-3 Ma(Turek et al., 1989)

2731 +/-3 Ma(Turek et al., 1989)

2728 +/-8 Ma(Turek et al., 1989)

2728 +/-8 Ma(Turek et al., 1989)

2870 +/-1 Ma(this study)2870 +/-1 Ma(this study)

ca. 2.88-2.90 Ga(this study)

ca. 2.88-2.90 Ga(this study)

2722 +/-2 Ma(Davis, 1994)2722 +/-2 Ma(Davis, 1994)

2723 +/-3 Ma(this study)2723 +/-3 Ma(this study)

2731 +/-3 Ma(Turek et al., 1989)

2728 +/-8 Ma(Turek et al., 1989)

2870 +/-1 Ma(this study)

ca. 2.88-2.90 Ga(this study)

2722 +/-2 Ma(Davis, 1994)

2723 +/-3 Ma(this study)

Bere

sfo

rdLake

Shear

Zone

-W

estG

arn

er

Shear

Zone

Dis

confo

rmity

(?)

?

?

ca a. 2.87-2.90 GCONTINENTAL-ARC

>2.73 GBACK-ARC

a (?)

ca a. 2.73 GARC

ca a. 2.71-2.72 GARC-RIFT

Unnamedbasalt

Stovel LakeFm.

Tinney LakeFm.

Dove LakeFm.

GunnarFm.

Stormy LakeFm.

The NarrowsFm.

Dis

confo

rmity

*

*

*

*Geochronology sample

(LA-ICPMS; this study)

*

500 m

*

Erosionalunconformity

Garner Narrows unit

Garner Lake intrusive complex

Garner Lake extrusive complex

Lower Bidou assemblage

Upper Bidou assemblage

Gem assemblage

Edmunds assemblage

Garner assemblage

Fe-/Mg-tholeiitic basalt flows,gabbro, chert

Gabbro

Feldspathic greywacke, siltstone, chert

Feldspathic greywacke, chert, conglomerate,basalt, felsic tuff, iron formation

Gabbro

Quartz diorite/granodiorite(Ross River pluton)

Dacitic volcaniclastic rocks,pillowed andesite flows

Intermediate to felsic flows andvolcaniclastic rocks

Gabbro

Greywacke-mudstone turbidites,conglomerate, basalt

Leucogranite

Komatiitic basalt, Mg-tholeiitic basalt,calcalkalic basalt, iron formation

Peridotite, pyroxenite, gabbro

Intermediate to felsic volcaniclastic rocks,conglomerate, iron formation

Bidou assemblage

10

9

11

12

1315

1516

17

18

19

20

20

21

18

11

9

9

11

Subvolcanic intrusion

Cryptodome

SE NW

Bidou

Gem

Edmunds

ca

.5

km

ca. 6 km

14 11

chlorite alteration

sericite-pyrite alteration

FI

FI

FII-FIII

FII-FIII

FI

FI QFP granite

Dacitic volcaniclastic rocks

Pillowed flows; related volcaniclastic rocks

Rhyolite flows, domes, breccias

Rhyolitic volcaniclastic rocks; monolithic

Gabbro

Greywacke-mudstone turbidites

Quartz greywacke

Conglomerate Rhyolitic volcaniclastic rocks; heterolithic

Dacitic crystal tuff, tuff breccia

Bedded epiclastic rocks

Quartz breccia vein in the footwall ofthe WGSZ, north of Gem LakeQuartz breccia vein in the footwall ofthe WGSZ, north of Gem Lake

En-echelon, quartz and ankerite-filledtension gashes in gabbro dike cuttingdacitic volcaniclastic rocks, Gem Lake

En-echelon, quartz and ankerite-filledtension gashes in gabbro dike cuttingdacitic volcaniclastic rocks, Gem Lake

Quartz-ankerite veins in altereddacitic volcaniclastic rocks, Gem LakeQuartz-ankerite veins in altereddacitic volcaniclastic rocks, Gem Lake

Quartz veins cutting silicified, crackle-textured dacite on the margins of thequartz breccia vein north of Gem Lake

Quartz veins cutting silicified, crackle-textured dacite on the margins of thequartz breccia vein north of Gem Lake

Quartz-arsenopyrite vein in daciticvolcaniclastic rocks of the Gemassemblage, Manigotagan River

Quartz-arsenopyrite vein in daciticvolcaniclastic rocks of the Gemassemblage, Manigotagan River

Intense silica-ankerite-arsenopyritealteration in Edmunds assemblagegreywacke (Lily Lake occurrence)

Intense silica-ankerite-arsenopyritealteration in Edmunds assemblagegreywacke (Lily Lake occurrence)

Quartz breccia vein in the footwall ofthe WGSZ, north of Gem Lake

En-echelon, quartz and ankerite-filledtension gashes in gabbro dike cuttingdacitic volcaniclastic rocks, Gem Lake

Quartz-ankerite veins in altereddacitic volcaniclastic rocks, Gem Lake

Quartz veins cutting silicified, crackle-textured dacite on the margins of thequartz breccia vein north of Gem Lake

Quartz-arsenopyrite vein in daciticvolcaniclastic rocks of the Gemassemblage, Manigotagan River

Intense silica-ankerite-arsenopyritealteration in Edmunds assemblagegreywacke (Lily Lake occurrence)

Mafic geochemistryMafic geochemistry

Felsic geochemistryFelsic geochemistry

Introduction

SE Rice Lake belt geologySE Rice Lake belt geology

Stratigraphy

Unit 17Unit 17

Unit 16Unit 16

Unit 15Unit 15

Unit 14Unit 14

Unit 13Unit 13

Unit 12Unit 12

Unit 11Unit 11

Unit 10Unit 10

Geology and geochemistry of the Gemassemblage, Rice Lake greenstone beltGeology and geochemistry of the Gemassemblage, Rice Lake greenstone belt

Scott D. AndersonManitoba Geological Survey

Scott D. AndersonManitoba Geological Survey

Regional geologyRegional geology Gem Assemblage - map units andrepresentative rock typesGem Assemblage - map units andrepresentative rock types

Schematic sectionSchematic section

VHMS potentialVHMS potential

Orogenic gold potentialOrogenic gold potential

Thanks to:P. Kremer, A. Carlson and C. Chamale, University of ManitobaK. Reid, Brandon University

CactusCactus

LichenLichen

Poison IvyPoison IvyPoison Ivy

Clean exposureClean exposureClean exposure

Geologist-deterrence, Slate LakeGeologist-deterrence, Slate LakeGeologist-deterrence, Slate Lake

MGSMGSman

itob

ageologica

l

survey

1928

1

10

Ro

ck/p

rim

itiv

em

an

tle

Th Nb La Ce Nd Zr Sm Eu Ti Dy Y Yb Lu0.1

100

BIDOUTHOL; MORB

(BABB)GARNERTHOL; PLUME

GEMCA/THOL;

ARC / E-MORB

1

10

Ro

ck/p

rim

itiv

em

an

tle

Th Nb La Ce Nd Zr Sm Eu Ti Dy Y Yb Lu0.1

100

GEMCA/THOL;ARC-EXT.

GARNERCA; ARC(adakite) BIDOU

CA; ARC(adakite)

Basalt and basaltic andesite

Dacite and rhyolite

In 2002, the Manitoba Geological Survey initiated a program of bedrock mapping,structural analysis, lithogeochemistry, Sm-Nd isotope studies and U-Pbgeochronology in the geologically complex and poorly understood Garner Lake -Gem Lake area, which is located 45 km southeast of Bissett, Manitoba, in thesoutheastern extremity of the Archean Rice Lake greenstone belt.

This area contains several significant gold occurrences, as well as keyexposures of the principal supracrustal assemblages in the eastern portion of theRice Lake belt, and thus represents an important area for understanding thetectonostratigraphy, tectonic evolution and metallogeny of the belt as a whole.

This poster summarizes some of the results of 1:20 000 scale bedrock mappingand geoscientific investigations completed since 2002 in the Garner Lake - GemLake area, with emphasis on the rock-types, stratigraphy, geochemistry andeconomic potential of the Neoarchean Gem assemblage, which is interpreted torepresent a ca. 2.72 Ga arc-rift succession with significant potential for volcanic-hosted massive sulphide (VHMS) and orogenic gold deposits.

The Rice Lake greenstone belt is situated in the western Uchi Subprovince of theArchean Superior Province, and is flanked to the north by the ca. 3.0 Ga NorthCaribou continental terrane and to the south by ca. 2.69 Ga paragneiss andgranitoid plutons of the English River Subprovince (see map above). The RiceLake belt consists mainly of Meso- and Neoarchean, mafic to intermediatevolcanic and volcaniclastic rocks, constituting several distinct lithotectonicassemblages.

In the eastern Rice Lake belt, these assemblages include the MesoarcheanWallace (ca. 2.92-2.99 Ga) and Garner (ca. 2.87-2.90 Ga) assemblages, and theNeoarchean Bidou (ca. 2.73 Ga) and Gem (ca. 2.72 Ga) assemblages (see mapand stratigraphic columns to lower left). The Bidou assemblage includessynvolcanic quartz diorite and granodiorite plutons, including the ca. 2.73 GaRoss River pluton in the central portion of the belt. As indicated by the multi-element diagrams below, volcanic rocks in the Garner, Bidou and Gemassemblages can be distinguished on the basis of geochemical attributes.

Fluvial and alluvial rocks of the ca. 2.70 Ga San Antonio assemblageunconformably overlie the volcanic rocks and likely represent the proximalequivalents to basinal turbidites of the ca. 2.70 Ga Edmunds assemblage, whichoverlaps the south margin of the Rice Lake belt.

These assemblages provide a punctuated record of magmatism, sedimentationand orogenesis spanning roughly 200 m.y. Broadly comparable assemblages inthe Red Lake and Birch-Uchi belts in northwestern Ontario provide a basis forregional-scale tectonostratigraphic correlations.

Mesoscopic overprinting relationships indicate at least six generations of ductiledeformation structure in the eastern Rice Lake belt. In the Garner Lake - GemLake area, a series of generally northwest-trending, relatively low-strainlithostructural domains are separated by a complex network of ductile andductile-brittle high-strain zones that typically preserve evidence of at least twoincrements of ductile, noncoaxial deformation. Of these, the Beresford LakeShear Zone (BLSZ) represents the most significant and apparently long-livedstructural discontinuity.

East of the BLSZ, generally north-younging rocks of the Garner assemblage arejuxtaposed to the south across the West Garner Shear Zone (WGSZ) withgenerally west-younging rocks of the Bidou and Gem assemblages. The Garnerassemblage is juxtaposed to the east, across the East Garner Shear Zone, withan extensive granitoid domain of uncertain age and affinity. West of the BLSZ,macroscopic map patterns and younging criteria in the Neoarchean succession,comprising the Bidou, Gem and Edmunds assemblages, define the regional-scale Beresford Lake anticline, which is the dominant structural feature in thecore of the Rice Lake belt.

At Gem Lake, structures associated with late-stage transcurrent sheardeformation, including southeast-trending dextral high-strain zones, mesoscopicand macroscopic z-asymmetric folds, and late brittle faults, overprint andreactivate early high-strain fabrics resulting in very complex map patterns.

Metamorphic mineral assemblages west of the BLSZ and southwest of theWGSZ indicate peak metamorphism in the low- to middle-greenschist facies.South of Garner Lake, the hornblende and garnet isograds coincide with theWGSZ, and indicate an abrupt increase to peak amphibolite-faciesmetamorphism northeast of the shear zone, consistent with observed northeast-over-southwest kinematic indicators.

Along the south margin of the Rice Lake belt, greenschist-facies supracrustalrocks are tectonically juxtaposed and locally interleaved with ca. 2.69 Ga (Corfuet al., 1995) paragneiss of the English River Subprovince along a series ofgreenschist-facies high-strain zones, which include the regional-scaleManigotagan Shear Zone and subsidiary structures. The paragneiss recordshigh-temperature, low-pressure regional metamorphism of metasedimentaryrocks that are the distal equivalents to the Edmunds assemblage.

The geology of the Garner Lake - Gem Lakes area is shown on Preliminary MapPMAP2006-7 (at right).

The Neoarchean Gem assemblage overlies the ca. 2.73 Ga Bidou assemblage and consists of athick succession of primary and variably reworked felsic to mafic volcanic flows and pyroclasticrocks that ranges up to at least 2.0 km thick.

At Gem Lake, the lower portion of the assemblage consists mainly of rhyolitic volcanic,volcaniclastic and intrusive rocks composed of high-silica, FII- and FIIIa-type (Lesher et al., 1986)tholeiitic rhyolite. On the basis of texture and colour, two units are distinguished: buff to white topink quartz-phyric to aphyric rhyolite (unit 11) and overlying grey to black aphyric rhyolite (unit 12).Leucogranite plutons (unit 10) that intrude the Bidou and Garner assemblages along the easternmargin of the belt are chemically and texturally similar to the overlying unit 11 rhyolite, and are thustentatively interpreted to be the subvolcanic equivalent. Davis (1994) obtained a U-Pb zircon age of2722+/-2 Ma from quartz-phyric rhyolite breccia of unit 11 at Gem Lake, which overlaps a ca. 2.72Ga age obtained from a leucogranite pluton (unit 10) at Garner Lake.

These rocks are overlain by a thick heterogeneous succession of coarse volcaniclastic rocks, withminor occurrences of flow-banded to massive flows composed of buff to grey, sparsely porphyritic,tholeiitic dacite and rhyolite (unit 13). Unit 14 consists of gabbro sills and dikes, which arecompositionally and texturally similar to pillowed basalt and basaltic andesite flows and associatedcoarse volcaniclastic rocks of unit 15. These rocks are intimately intermixed and overlain bydiscontinuous intervals of bedded heterolithic epiclastic rocks (unit 16). The uppermost portion ofthe Gem assemblage is locally marked by white to buff to light green-grey dacitic volcaniclasticrocks of calcalkalic affinity (unit 17).

Mafic and intermediate flows and sills of the Gem assemblage (units 14 and 15)are composed of basalt and basaltic andesite that exhibit transitional calcalkalic-tholeiitic affinities. Primitive-mantle normalized extended-element profiles arecharacterized by enriched and fractionated LREE, with moderate negative Nbanomalies and weakly fractionated and enriched HREE. These rocks plotbetween E-MORB and typical arc-tholeiite on basalt discrimination diagrams.

Basalt flows and sills from the Bidou (unit 9) and Edmunds (unit 21) assemblagesare shown for comparison.

Felsic volcanic rocks of the Gem assemblage consist mainly of rhyolite and high-silica rhyolite (68-81 wt.% SiO , anhydrous), with minor dacite, that exhibit

transitional calcalkalic-tholeiitic affinities (Zr/Y 4-30). Chondrite-normalized multi-element profiles exhibit strongly enriched and fractionated LREE, with relativelyflat, weakly fractionated HREE and moderate negative Eu anomalies (Eu/Eu* 0.4-2.0). The HFSE signatures indicate an affinity to extension-related, within-platevolcanism. Elevated Y and Yb contents, with correspondingly low Zr/Y and[La/Yb] ratios, classify these rocks as FII- and FIIIa-type rhyolites in the scheme

of Lesher et al. (1986).

2

N

Felsic flows and vent-proximal fragmental volcanic rocks of the Gem assemblage arecomposed of FII- and FIIIa-type (Lesher et al., 1986) tholeiitic dacite, rhyolite and high-silica rhyolite, which exhibit HFSE signatures indicative of extension-related, within-plate volcanism. These rocks are provisionally interpreted to record subaerial to shallowsubaqueous volcanism associated with the initiation of a ca. 2.72 Ga arc-rift basinwithin the Bidou volcanic arc. Type FII and FIII rhyolites host several important VHMSdeposits in the Superior Province (Lesher et al., 1986), and the association ofextension-related volcanism and VHMS deposits has been well documented in theliterature.

At Gem Lake, the rhyolitic succession contains semi-concordant zones of sericite-pyritealteration, with minor intercalations of laminated black chert and sulphidic epiclasticrocks that may represent paleoexhalative horizons. Altered sulphidic clasts (sericite-pyrite) are observed in overlying units of heterolithic volcanic conglomerate, indicatingthat the sericite-pyrite alteration observed at Gem Lake may be syngenetic. Stringer-style chlorite alteration is also observed, and occurs along the eastern shoreline ofGem Lake in dacitic volcaniclastic rocks of the underlying Bidou assemblage.

These attributes indicate that, in addition to the demonstrated potential for orogenicgold deposits, the Gem Lake area is prospective for VHMS deposits. The proposeddepositional setting (i.e., subaerial to shallow-subaqueous, arc-rift) is particularlyfavourable for the development of Au-rich VHMS systems (e.g., Eskay Creek).

The Garner Lake -Gem Lake area contains several occurrences of auriferous quartz-carbonate veins, which are hosted by discrete, ductile and brittle-ductile shear zonesin close spatial association with the major southeast-trending, domain-bounding,high-strain zones that dominate the map pattern in the area. Hence, proximity tothese zones appears to represent an important, property-scale explorationparameter. Detailed prospecting along these zones, with emphasis on potentialchemical or structural traps, will prove useful in identifying exploration targets.

As described by numerous authors, lode-gold deposits in greenstone terranes showa distinct spatial association with zones of transition from lower to upper greenschist-facies regional metamorphism, which broadly coincide with the coeval transition frombrittle to ductile deformation. In this regard, the West Garner Shear Zone (WGSZ),which coincides with an abrupt, northeastward change from greenschist- toamphibolite-facies metamorphism, may be a particularly attractive exploration target.North of Gem Lake, the footwall of the WGSZ contains several stockwork-brecciaquartz-vein systems, one of which is traced along strike for 1.2 km, suggesting thatthe footwall of the WGSZ was a significant locus for hydrothermal fluid flow.

Elsewhere, gold mineralization in hosted by quartz-ankerite-pyrite veins in stronglyaltered (ankerite-sericite-pyrite) rocks within shear zones cutting the Garner, Bidouand Gem assemblages, or by quartz-ankerite-arsenopyrite veins in zones of intenseankerite-silica-arsenopyrite alteration associated with shear zones and/or iron-formations in the Edmunds assemblage, or shear zones in the adjacent Gemassemblage.

A. Galley, GSC