Regional geologyRegionalgeology Gem Assemblage - map units ... · and geoscientific investigations...
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Rice Lake 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 kilometres Lake Winnipeg Manitoba Ontario Bissett Gold deposit Geological contact Shear zone, fault Wanipigow Shear Zone Manigotagan Shear Zone Study area .1 1 10 100 .01 .1 1 10 Th/Yb Nb/Yb N-MORB E-MORB OIB DM (Pearce and Peate, 1995) Subduction enrichment Within-plate enrichment .01 .1 1 10 .01 .1 1 Zr/TiO 2 Nb/Y Basalt Andesite/Basalt Rhyolite/Dacite Alkali Basalt 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/PrimitiveMantle Unit 21 Unit 15 1 10 100 Rock/PrimitiveMantle Unit 14 1 10 100 1000 Rock/PrimitiveMantle Unit 9 .001 .01 .1 1 10 40 45 50 55 60 65 70 75 80 SiO 2 Zr/TiO 2 Subalkaline basalt Andesite Rhyodacite/Dacite Rhyolite (Winchester and Floyd, 1977) .1 1 10 1 10 100 Eu/Eu* [La/Yb] CN FI FII FIII (after Lesher et al., 1986) 0 20 40 60 80 100 120 140 160 1 10 100 Zr/Y Y (ppm) FI FII FIII (after Lesher et al., 1986) 1 10 100 1000 1 10 100 1000 Nb (ppm) 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 Rock/Chondrites Unit 13 Unit 12 1 10 100 Rock/Chondrites Unit 11 Unit 11 1 10 100 Rock/Chondrites Unit 11 Unit 10 1 10 100 Rock/Chondrites Unit 9 Chlorite alteration in dacite breccia (9a), east shoreline of Gem Lake Chlorite alteration in dacite breccia (9a), east shoreline of Gem Lake Sericite-altered rhyolite sandstone (11b), central Gem Lake Sericite-altered rhyolite sandstone (11b), central Gem Lake Gossanous rhyolite flow (11a), south shoreline of Gem Lake Gossanous rhyolite flow (11a), south shoreline of Gem Lake Sulphidic clast in conglomerate (16b), Manigotagan River NW of Gem Lake Sulphidic 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), south shoreline 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 with sulphidic clasts (16b) Massive rhyolite conglomerate with sulphidic 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 aphyric rhyolite fragments in pink leucogranite matrix (11d) Intrusion breccia composed of aphyric rhyolite fragments in pink leucogranite matrix (11d) QFP leucogranite (10b) QFP leucogranite (10b) Lapilli tuff (12a), with lapilli composed exclusively of flow-banded rhyolite Lapilli tuff (12a), with lapilli composed exclusively of flow-banded rhyolite Dacite crystal tuff (17a) Dacite lapilli tuff (17a) Massive rhyolite conglomerate with sulphidic 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 aphyric rhyolite fragments in pink leucogranite matrix (11d) QFP leucogranite (10b) Lapilli tuff (12a), with lapilli composed exclusively of flow-banded rhyolite Stormy Lake Garner River Manigotagan River 314 314 Manitoba Ontario 314 N G DL TL SL U G DL TL SL U Long Lake Garner Lake Beresford Lake Gem Lake Beresford Lake Shear Zone Beresford Lake Shear Zone Beresford Lake Shear Zone West Garner Shear Zone West Garner Shear Zone West Garner Shear Zone East Garner Shear Zone East Garner Shear Zone East Garner Shear Zone Long Lake Shear Zone Long Lake Shear Zone Long Lake Shear Zone Beresford Lake anticline Beresford Lake anticline Beresford Lake anticline Stormy Lake Shear Zone Stormy Lake Shear Zone Stormy Lake Shear Zone Ross River Pluton Ross River Pluton Ross River Pluton 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 Road 314 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 G RIFT-INFILL ca a . 2.87 G PLUME- MAGMATISM 2731 +/-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) Beresford Lake Shear Zone - West Garner Shear Zone Disconformity (?) ? ? ca a . 2.87-2.90 G CONTINENTAL-ARC >2.73 G BACK-ARC a (?) ca a . 2.73 G ARC ca a . 2.71-2.72 G ARC-RIFT Unnamed basalt Stovel Lake Fm. Tinney Lake Fm. Dove Lake Fm. Gunnar Fm. Stormy Lake Fm. The Narrows Fm. Disconformity * * * *Geochronology sample (LA-ICPMS; this study) * 500 m * Erosional unconformity 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 and volcaniclastic 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 13 15 15 16 17 18 19 20 20 21 18 11 9 9 11 Subvolcanic intrusion Cryptodome SE NW Bidou Gem Edmunds ca. 5km 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 of the WGSZ, north of Gem Lake Quartz breccia vein in the footwall of the WGSZ, north of Gem Lake En-echelon, quartz and ankerite-filled tension gashes in gabbro dike cutting dacitic volcaniclastic rocks, Gem Lake En-echelon, quartz and ankerite-filled tension gashes in gabbro dike cutting dacitic volcaniclastic rocks, Gem Lake Quartz-ankerite veins in altered dacitic volcaniclastic rocks, Gem Lake Quartz-ankerite veins in altered dacitic volcaniclastic rocks, Gem Lake Quartz veins cutting silicified, crackle- textured dacite on the margins of the quartz breccia vein north of Gem Lake Quartz veins cutting silicified, crackle- textured dacite on the margins of the quartz breccia vein north of Gem Lake Quartz-arsenopyrite vein in dacitic volcaniclastic rocks of the Gem assemblage, Manigotagan River Quartz-arsenopyrite vein in dacitic volcaniclastic rocks of the Gem assemblage, Manigotagan River Intense silica-ankerite-arsenopyrite alteration in Edmunds assemblage greywacke (Lily Lake occurrence) Intense silica-ankerite-arsenopyrite alteration in Edmunds assemblage greywacke (Lily Lake occurrence) Quartz breccia vein in the footwall of the WGSZ, north of Gem Lake En-echelon, quartz and ankerite-filled tension gashes in gabbro dike cutting dacitic volcaniclastic rocks, Gem Lake Quartz-ankerite veins in altered dacitic volcaniclastic rocks, Gem Lake Quartz veins cutting silicified, crackle- textured dacite on the margins of the quartz breccia vein north of Gem Lake Quartz-arsenopyrite vein in dacitic volcaniclastic rocks of the Gem assemblage, Manigotagan River Intense silica-ankerite-arsenopyrite alteration in Edmunds assemblage greywacke (Lily Lake occurrence) Mafic geochemistry Mafic geochemistry Felsic geochemistry Felsic geochemistry Introduction SE Rice Lake belt geology SE Rice Lake belt geology Stratigraphy Unit 17 Unit 17 Unit 16 Unit 16 Unit 15 Unit 15 Unit 14 Unit 14 Unit 13 Unit 13 Unit 12 Unit 12 Unit 11 Unit 11 Unit 10 Unit 10 Geology and geochemistry of the Gem assemblage, Rice Lake greenstone belt Geology and geochemistry of the Gem assemblage, Rice Lake greenstone belt Scott D. Anderson Manitoba Geological Survey Scott D. Anderson Manitoba Geological Survey Regional geology Regional geology Gem Assemblage - map units and representative rock types Gem Assemblage - map units and representative rock types Schematic section Schematic section VHMS potential VHMS potential Orogenic gold potential Orogenic gold potential Thanks to: P. Kremer,A. Carlson and C. Chamale, University of Manitoba K. Reid, Brandon University Cactus Cactus Lichen Lichen Poison Ivy Poison Ivy Poison Ivy Clean exposure Clean exposure Clean exposure Geologist-deterrence, Slate Lake Geologist-deterrence, Slate Lake Geologist-deterrence, Slate Lake MGS MGS m a n i t o b a g e o l o g i c a l s u r v e y 1 9 2 8 1 10 Rock/primitive mantle Th Nb La Ce Nd Zr Sm Eu Ti Dy Y Yb Lu 0.1 100 BIDOU THOL; MORB (BABB) GARNER THOL; PLUME GEM CA/THOL; ARC / E-MORB 1 10 Rock/primitive mantle Th Nb La Ce Nd Zr Sm Eu Ti Dy Y Yb Lu 0.1 100 GEM CA/THOL; ARC-EXT. GARNER CA; 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-Pb geochronology in the geologically complex and poorly understood Garner Lake - Gem Lake area, which is located 45 km southeast of Bissett, Manitoba, in the southeastern extremity of the Archean Rice Lake greenstone belt. This area contains several significant gold occurrences, as well as key exposures of the principal supracrustal assemblages in the eastern portion of the Rice Lake belt, and thus represents an important area for understanding the tectonostratigraphy, tectonic evolution and metallogeny of the belt as a whole. This poster summarizes some of the results of 1:20 000 scale bedrock mapping and geoscientific investigations completed since 2002 in the Garner Lake - Gem Lake area, with emphasis on the rock-types, stratigraphy, geochemistry and economic potential of the Neoarchean Gem assemblage, which is interpreted to represent 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 the Archean Superior Province, and is flanked to the north by the ca. 3.0 Ga North Caribou continental terrane and to the south by ca. 2.69 Ga paragneiss and granitoid plutons of the English River Subprovince (see map above). The Rice Lake belt consists mainly of Meso- and Neoarchean, mafic to intermediate volcanic and volcaniclastic rocks, constituting several distinct lithotectonic assemblages. In the eastern Rice Lake belt, these assemblages include the Mesoarchean Wallace (ca. 2.92-2.99 Ga) and Garner (ca. 2.87-2.90 Ga) assemblages, and the Neoarchean Bidou (ca. 2.73 Ga) and Gem (ca. 2.72 Ga) assemblages (see map and stratigraphic columns to lower left). The Bidou assemblage includes synvolcanic quartz diorite and granodiorite plutons, including the ca. 2.73 Ga Ross River pluton in the central portion of the belt. As indicated by the multi- element diagrams below, volcanic rocks in the Garner, Bidou and Gem assemblages can be distinguished on the basis of geochemical attributes. Fluvial and alluvial rocks of the ca. 2.70 Ga San Antonio assemblage unconformably overlie the volcanic rocks and likely represent the proximal equivalents to basinal turbidites of the ca. 2.70 Ga Edmunds assemblage, which overlaps the south margin of the Rice Lake belt. These assemblages provide a punctuated record of magmatism, sedimentation and orogenesis spanning roughly 200 m.y. Broadly comparable assemblages in the Red Lake and Birch-Uchi belts in northwestern Ontario provide a basis for regional-scale tectonostratigraphic correlations. Mesoscopic overprinting relationships indicate at least six generations of ductile deformation structure in the eastern Rice Lake belt. In the Garner Lake - Gem Lake area, a series of generally northwest-trending, relatively low-strain lithostructural domains are separated by a complex network of ductile and ductile-brittle high-strain zones that typically preserve evidence of at least two increments of ductile, noncoaxial deformation. Of these, the Beresford Lake Shear Zone (BLSZ) represents the most significant and apparently long-lived structural discontinuity. East of the BLSZ, generally north-younging rocks of the Garner assemblage are juxtaposed to the south across the West Garner Shear Zone (WGSZ) with generally west-younging rocks of the Bidou and Gem assemblages. The Garner assemblage is juxtaposed to the east, across the East Garner Shear Zone, with an 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 the core of the Rice Lake belt. At Gem Lake, structures associated with late-stage transcurrent shear deformation, including southeast-trending dextral high-strain zones, mesoscopic and macroscopic z-asymmetric folds, and late brittle faults, overprint and reactivate early high-strain fabrics resulting in very complex map patterns. Metamorphic mineral assemblages west of the BLSZ and southwest of the WGSZ indicate peak metamorphism in the low- to middle-greenschist facies. South of Garner Lake, the hornblende and garnet isograds coincide with the WGSZ, and indicate an abrupt increase to peak amphibolite-facies metamorphism northeast of the shear zone, consistent with observed northeast- over-southwest kinematic indicators. Along the south margin of the Rice Lake belt, greenschist-facies supracrustal rocks are tectonically juxtaposed and locally interleaved with ca. 2.69 Ga (Corfu et al., 1995) paragneiss of the English River Subprovince along a series of greenschist-facies high-strain zones, which include the regional-scale Manigotagan Shear Zone and subsidiary structures. The paragneiss records high-temperature, low-pressure regional metamorphism of metasedimentary rocks that are the distal equivalents to the Edmunds assemblage. The geology of the Garner Lake - Gem Lakes area is shown on Preliminary Map PMAP2006-7 (at right). The Neoarchean Gem assemblage overlies the ca. 2.73 Ga Bidou assemblage and consists of a thick succession of primary and variably reworked felsic to mafic volcanic flows and pyroclastic rocks 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 to pink 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 eastern margin of the belt are chemically and texturally similar to the overlying unit 11 rhyolite, and are thus tentatively interpreted to be the subvolcanic equivalent. Davis (1994) obtained a U-Pb zircon age of 2722+/-2 Ma from quartz-phyric rhyolite breccia of unit 11 at Gem Lake, which overlaps a ca. 2.72 Ga age obtained from a leucogranite pluton (unit 10) at Garner Lake. These rocks are overlain by a thick heterogeneous succession of coarse volcaniclastic rocks, with minor 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 are compositionally and texturally similar to pillowed basalt and basaltic andesite flows and associated coarse volcaniclastic rocks of unit 15. These rocks are intimately intermixed and overlain by discontinuous intervals of bedded heterolithic epiclastic rocks (unit 16). The uppermost portion of the Gem assemblage is locally marked by white to buff to light green-grey dacitic volcaniclastic rocks 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 are characterized by enriched and fractionated LREE, with moderate negative Nb anomalies and weakly fractionated and enriched HREE. These rocks plot between E-MORB and typical arc-tholeiite on basalt discrimination diagrams. Basalt flows and sills from the Bidou (unit 9) and Edmunds (unit 21) assemblages are 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 relatively flat, weakly fractionated HREE and moderate negative Eu anomalies (Eu/Eu* 0.4- 2.0). The HFSE signatures indicate an affinity to extension-related, within-plate volcanism. 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 are composed 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 shallow subaqueous volcanism associated with the initiation of a ca. 2.72 Ga arc-rift basin within the Bidou volcanic arc. Type FII and FIII rhyolites host several important VHMS deposits in the Superior Province (Lesher et al., 1986), and the association of extension-related volcanism and VHMS deposits has been well documented in the literature. At Gem Lake, the rhyolitic succession contains semi-concordant zones of sericite-pyrite alteration, with minor intercalations of laminated black chert and sulphidic epiclastic rocks that may represent paleoexhalative horizons. Altered sulphidic clasts (sericite- pyrite) are observed in overlying units of heterolithic volcanic conglomerate, indicating that the sericite-pyrite alteration observed at Gem Lake may be syngenetic. Stringer- style chlorite alteration is also observed, and occurs along the eastern shoreline of Gem Lake in dacitic volcaniclastic rocks of the underlying Bidou assemblage. These attributes indicate that, in addition to the demonstrated potential for orogenic gold deposits, the Gem Lake area is prospective for VHMS deposits. The proposed depositional setting (i.e., subaerial to shallow-subaqueous, arc-rift) is particularly favourable 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 zones in close spatial association with the major southeast-trending, domain-bounding, high-strain zones that dominate the map pattern in the area. Hence, proximity to these zones appears to represent an important, property-scale exploration parameter. Detailed prospecting along these zones, with emphasis on potential chemical or structural traps, will prove useful in identifying exploration targets. As described by numerous authors, lode-gold deposits in greenstone terranes show a distinct spatial association with zones of transition from lower to upper greenschist- facies regional metamorphism, which broadly coincide with the coeval transition from brittle to ductile deformation. In this regard, the West Garner Shear Zone (WGSZ), which coincides with an abrupt, northeastward change from greenschist- to amphibolite-facies metamorphism, may be a particularly attractive exploration target. North of Gem Lake, the footwall of the WGSZ contains several stockwork-breccia quartz-vein systems, one of which is traced along strike for 1.2 km, suggesting that the footwall of the WGSZ was a significant locus for hydrothermal fluid flow. Elsewhere, gold mineralization in hosted by quartz-ankerite-pyrite veins in strongly altered (ankerite-sericite-pyrite) rocks within shear zones cutting the Garner, Bidou and Gem assemblages, or by quartz-ankerite-arsenopyrite veins in zones of intense ankerite-silica-arsenopyrite alteration associated with shear zones and/or iron- formations in the Edmunds assemblage, or shear zones in the adjacent Gem assemblage. A. Galley, GSC
Transcript of Regional geologyRegionalgeology Gem Assemblage - map units ... · and geoscientific investigations...
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
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.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
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Th Nb La Ce Pr Nd Zr Sm Eu Ti Dy Y Yb Lu
Rock/P
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Unit 21
Unit 15
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Rock/P
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Unit 14
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Unit 9
.001 .01 .1 1 1040
45
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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
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Zr/
Y
Y (ppm)
FI
FII
FIII
(after Lesher et al., 1986)
1 10 100 10001
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Nb
(pp
m)
Y (ppm)
syn-collisional
within plate
ocean ridge
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La Ce Pr Nd PmSm Eu Gd Tb Dy Ho Er Tm Yb Lu
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10
100
La Ce Pr Nd PmSm Eu Gd Tb Dy Ho Er Tm Yb Lu
Ro
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Unit 12
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Ro
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ho
nd
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Unit 11
Unit 11
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Ro
ck/C
ho
nd
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Unit 11
Unit 10
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Ro
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ho
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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
