Canada - Newfoundland and Labrador...This poster is a contribution to the Geological Survey of...
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Ressources naturelles Canada Natural Resources Canada Canada L'Initiative G oscientifique Ciblée 3 é Targeted Geoscience Initiative 3 G Buchans C TG Buchans 1* 2 G.W.H van Hees , A. Zagorevski , M. Hannington 1 2 ; *corresponding author email: [email protected] 1 Department of Earth Sciences, University of Ottawa, 140 Louis Pasteur, Ottawa, Ontario, Canada K1N 6N5 Geological Survey of Canada, 601 Booth St., Ottawa, Ontario, Canada Volcanology and geochemistry of the Lundberg volcanogenic massive sulphide zone, Buchans, Newfoundland Lundberg Facies Figure 5: H3386-Sample G077. Characterized by rhyolitic red groundmass with 15- 30% white, euhedral, feldspar pheno- to glomerophenocrysts. B. Chloritized Brecciated rhyolite, H3378. Characterized by 4cm angular to subrounded rhyolitic clasts with 15-30% feldspar phenocrysts. C. Diabase, H3406. Characterized by black to dark grey, phaneritic to porphyritic texture wtih 0- 15% chloritized pyroxene phenocrysts and amygdule- rich upper and lower contacts. D. Volcaniclastic breccia, H3388. Characterized by sandy to silty, pyritic matrix and dacitic, sandstone, siltstone, chert, basalt, and sulphide clasts ranging from <1 to 60cm. E. Monomictic brecciated dacite with quartz-sericite altered clast margins and up to 15% sericitized feldspar phenocrysts, H3341. F: Quartz-chlorite- carbonate scoreacous, hyaloclastic, basaltic breccia, H3386. A. Rhyolite, D B A C E Lithogeochemistry Figure 6: A. 3 distinct volcanic units are recognized: Basalt/Andesite (green triangle), dacite (orange octagon), and rhyolite (red circle). B. Spider Plot of Basalt/Andesite unit distinguishes a calc- alkaline,mature arc affinity for the basaltic unit. C. La/Y over La separates the rhyodacite and dacite units on the basis of HREE enrichment/depletion. Basalts have similar La/Yb ratios as the dacite, but lower La. D. Spider plot further distinguishes the two felsic calc-alkaline arc units. E. Basalt discrimination diagram of immobile elements Ti and Zr indicates a volcanic arc origin for Lundberg basalts. F. Winchester and Floyd (1977) diagram displaying silica mobility in the three volcanic units. 1 10 100 1000 Th Nb La Ce Nd Zr Sm Eu Gd Ti Dy Y Er Yb Lu Rock/Primitive Mantle Sun & McDonough 1989 Rock/Primitive Mantle D 1 10 100 1000 Th Nb La Ce Nd Zr Sm Eu Gd Ti Dy Y Er Yb Lu Sun & McDonough 1989 B Rock/Primitive Mantle .001 .01 .1 1 10 40 45 50 55 60 65 70 75 80 SiO 2 Zr/TiO 2 Sub-AB Andesite Rhyodacite/Dacite Rhyolite Alk-Bas Com/Pan Phonolite Trachyte Bas/Trach/Neph F Winchester and Floyd 1977 0 10 20 30 40 50 0 5 10 15 20 La/Yb La HREE depleted HREE enriched C 0 100 200 0 5000 10000 Ti Zr IAT B Calc-alkali basalt MORB B=MORB+C-A bas+IAT E Pearce and Cann 1973 .01 .1 1 10 .001 .01 .1 1 Zr/TiO 2 Nb/Y SubAlkaline Basalt Andesite/Basalt Andesite Rhyodacite/Dacite Rhyolite Alk-Bas TrachyAnd Com/Pant Phonolite Trachyte Bsn/Nph A Winchester and Floyd 1977 Implications for Buchans VMS genesis Mineralization within the Lundberg zone is associated with only one felsic volcanic unit (dacite) based on stratigraphic and geochemical constraints. This implies that stockwork mineralization, as well as formation of massive sulphide mounds, was restricted to one stratigraphic horizon. Intense bladed calcite observed within the polymetallic veins of the Lundberg Zone indicates that precipitation of the sulphides was induced by phase separation of hydrothermal fluids by sub-seafloor boiling. Boiling of hydrothermal fluids occurs over a wide range of pressure and temperature conditions, but, as pressure decreases (i.e. shallowing water column) boiling is inevitable. Boiling of the hydrothermal fluid can account for the low grade (1.83% Zn, 0.67% Pb, 0.38% Cu, 5.5g/t Ag) of the Lundberg zone. The rising hydrothermal fluid is depleted in metals upon reaching the seafloor due to precipitation over a large boiling area, and deposition of massive sulphide mounds is limited. The Lundberg Zone exhibits some characteristics of epithermal deposits, suggesting deposition in a low hydrostatic pressure environment; however, it is also associated with typical Kuroko-style VMS mineralization (e.g. Lucky Strike). These contrasting characteristics suggest that the Buchans area represents the transition between typical VMS and epithermal paleoenvironments. Acknowledgements This poster is a contribution to the Geological Survey of Canada Targeted Geoscience Initiative 3: Appalachians. We would like to acknowledge both Alvin Harris and Stewart Cochrane of the Newfoundland Geological Survey for access and assistance at the Buchans core storage facility. Royal Roads Corp. for supporting this research. Lastly, we acknowledge the SEG for their interest and financial contribution to the above research. Legend Diabase Rhyodacite Exhalative Barite Volcaniclastic breccia Dacite Basalt Geochemistry sample location Alteration and mineralization Alteration throughout the Lundberg zone varies from weak to intense, varying within, and between stratigraphic units. Alteration of the groundmass of the rhyolite to chlorite (green- to black), sericite (white to beige), hematite or specularite is common. Alteration of the volcaniclastic breccia is limited to rare strong sericite and weak chlorite, whereas mineralization is common with 1-2% massive sphalerite, galena, chalcopyrite, and pyrite clasts averaging 1 cm, but up to 20 cm in length. Not only does mineralization occur as clasts, but also as brecciated exhalitive barite deposits along similar horizons. The brecciated exhalative deposits are metal-rich, consisting of up to 4.52 % combined Zn-Pb-Cu, 102.77 g/t Ag, and nearly 1g/t Au over 3.92m. The dacite unit typically has a quartz-sericite-pyrite altered groundmass with feldspar phenocrysts reflecting the same alteration. The dacite is typically unmineralized, but rare massive chalcopyrite veins are observed having average grades up to 5.3g/t over 1 m. The basalt unit is typically altered to chlorite and quartz- sericite assemblages, and hosts the majority of the Lundberg zone, a polymetallic, sphalerite- galena-chalcopyrite stockwork. Along these mineralized quartz-carbonate-rich veins, alteration haloes of chlorite and sericite-fuchsite are rare, but observed. Bladed calcite and quartz pseudomorphs of bladed calcite are common within mineralized veins, with individual blades ranging from <1 to 3 cm in length. Alteration and Mineralization of Major Volcanic Units Figure 7: A. Chloritized rhyolite, H3396-Sample G013. B. Hematized rhyolite, H3408. C. Silicified Dacite with chalcopyrite veining, H3386. D. Silicified basalt, H3406-Sample G199. E. Quartz-sericite-fuchsite alteration within the basalt, H3393. F. Bladed calcite with disseminated pyrite and sphalerite, H3398. G. Disseminated sphalerite-galena-pyrite veins, as well as in-situ brecciation of basalt, H3369A, H. Bladed calcite, as well as an alteration halo of sericite-fuchsite around a quartz-carbonate vein, H3365. I. Exhalative barite, H3378. A 1cm 2cm G B E 1cm H C F 1cm 3cm I Geochemistry 80 samples were analysed at ActLabs, Ontario. Major oxides were determined by Fusion ICP, whereas trace elements were determined by Fusion-MS. Preliminary geochemical analysis of the first 40 samples has distinguished two separate felsic volcanic units, and a basalt/andesite (Figure 5). All units have distinct Nb anomalies, and a negative REE slope indicating a calc- alkaline arc affinity. The two different varieties of felsic volcanic rocks are differentiated based on REE’s: The dacite is HREE-enriched, whereas the rhyolite is HREE-depleted. The HREE- enriched dacite is uniquely associated with mineralization as it is observed to lie stratigraphically in-between the volcaniclastic breccia and stockwork mineralized basalt. Stratigraphy Facies 1, a Basalt, is up to 360m thick constrained by drill hole depth. Facies 2, a dacite, ranges 5-40m thick, averaging 20m thick. Facies 3, a volcaniclastic breccia, ranges from 2-60m thick, averaging 5m thick. Facies 4, a rhyolite, ranges from 5-130m thick, locally thickening to 195m. All units except the dacite are intruded by diabase ranging from <1 to 130m thick. All 4 facies are correlative across much of the study area with some units pinching and swelling along across strike (i.e volcano-sedimentary and dacite). All facies gently dip to the northwest exposing more of the rhyolite in westward drill holes. Facies 1 is part of the Ski Hill formation, and the rest of the facies are grouped into the Buchans River Formation which hosts the ore. F 1cm Architecture of the Lundberg Zone H-08-3369A H-08-3365 H-08-3372 H-08-3376 H-08-3396 H-08-3388 H-08-3395 H-08-3393 H3341 100 200 H-08-3378 300 100 200 H3344 300 400 Thickness (m) 100 200 100 200 100 200 100 200 100 100 100 100 100 200 300 400 A A’ Buchans Group The Buchans mining camp is characterized by a number of unusually high grade low-tonnage volcanogenic massive sulphide deposits (VMS) hosted by a bimodal calc-alkaline continental arc sequence. The mining camp produced a total of 16.2 Mt of ore at an average grade of 14.5% zinc, 7.6% lead, 1.3% copper, 126g/t Ag, and 1.37g/t Au rivalling most other VMS districts. The Buchans Group has been separated into the Lundberg Hill, Ski Hill, Buchans River, and Sandy Lake Formations. The Lundberg Hill Formation is characterized by felsic pyroclastic rocks, rhyolite, tuffaceous wacke, siltstone, minor basalt, chert and iron formation. The Ski Hill Formation is characterized by basaltic to andesitic pyroclastic rocks with minor felsic tuff. The Buchans River Formation is characterized by rhyolite, felsic tuff, pyritic siltstone, polylithic conglomerate, and high grade in situ and transported sulphide ore bodies. The Sandy Lake Formation is characterized by basaltic pillow lava, epiclastic and polylithic pyroclastic volcanics, tuff, and tuffaceous sedimentary rocks. .Figure 3: Compilation map of geology by Davenport (1996), structure and deposit data by Thurlow (1987), and drill hole distribution by Royal Roads Corp. just west of the town of Buchans. ! ( ! ( H-3396 H-3394 H-3393 H-3395 H-3388 H-3378 H-3376 H-3365 H-3344 56°52'0"W 56°52'0"W H-3341 H-3369A H-3372 A A’ Rothermere orebodies Lucky Strike orebody 0 375 750 1,125 1,500 187.5 Meters Legend Top Sails Granitic Intrusive Suite Sandy Lake Formation Buchans River Formation Ski Hill Formation Lundberg Hill Formation Buchans Geological Setting The Buchans Group (465 Ma) lies within the Annieopsquotch accretionary tract (AAT), a section of accreted peri-Laurentian continenal arcs and backarcs formed during the Early to Middle Ordovician (Figure 1). The AAT is bound to the west by the Lloyds River fault, found adjacent to the Notre Dame and Dashwoods Arc, and to the west by the Red Indian Line, a major suture zone separating rocks of peri- Laurentian and peri-Gonwanan affinity. The formation of the AAT is characterized by the formation of two arcs: The Robert’s Arm and Red Indian Lake/Buchans Arcs (Figure 2). Sub-greenschist to amphibolite facies metamorphism is syn- to post accretion, and associated with either burial (prehnite-pumpellyite) or contact metamorphism. Accretion of terranes to Laurentia was progressive. The Buchans Group was accreted and imbricated along west-dipping, oblique-reverse faults. Although major structures have been recognized, multiple generations of folding and faulting occurs with common reactivation of faults making structural interpretations extremely difficult. Lloyd’s River backarc Robert’s Arm arc Composite Laurentian margin 475 Ma 468 - 465 Ma Skidder backarc Lloyds River Fault Future Red Indian Line Humber Zone Gander Zone Avalon Zone Gondwanan Margin Laurentian Margin Dunnage Zone Dunnage Zone Notre Dame Subzone Carboniferous Basins Ophiolitic Rocks Avalonian rocks in the Hermitage Flexure Exploits Subzone Notre Dame Bay Gulf of St. Lawrence N RIL RIL RIL HMT HMT Gullbridge Notre Dame Arc Exploits Subzone Annieopsquotch accretionary tract Gander Zone 57° 49° 57° 49° 0 50 100 km Buchans Figure 2: Tectonic setting and development of the AAT. First, formation of the Roberts Arm arc associated with west-dipping subduction outboard of the composite Laurentian margin. Next, accretion of the , formation of the Buchans group within the Red Indian Lake arc, local extension forming the Skidder basalt and continued closing of the Iapetus Ocean and further deformation. Roberts Arm arc Figure 1: Distribution of the 4 main geological zones of Newfoundland and the location of the Annieopsquotch accretionary tract. Figure 4: Stratigraphy and geochemistry of the Lundberg Zone. The basaltic unit is commonly silicified and sericitized at upper contacts within the mineralized polymetallic stockwork often mimicking dacititic textures. The volcanicalstic breccia is much thicker to the far west of the study area, and typically grades down-hole into normally graded sandstone, and siltstone with dispersed felsic clasts . The dacite unit is exclusively associated with the volcaniclastic breccia which hosts massive sphalerite-galena-pyrite clasts, however, the other felsic unit (rhyolite) observed at the top of the section is barren.
Transcript of Canada - Newfoundland and Labrador...This poster is a contribution to the Geological Survey of...
Ressources naturellesCanada
Natural ResourcesCanada Canada
L'Initiative G oscientifique Ciblée 3é
Targeted Geoscience Initiative 3G
Buchans
CTGBuchans
1* 2G.W.H van Hees , A. Zagorevski , M. Hannington
1 2; *corresponding author email: [email protected]
1
Department of Earth Sciences, University of Ottawa, 140 Louis Pasteur, Ottawa, Ontario, Canada K1N 6N5 Geological Survey of Canada, 601 Booth St., Ottawa, Ontario, Canada
Volcanology and geochemistry of the Lundberg volcanogenic massive sulphide zone, Buchans, Newfoundland
Lundberg FaciesFigure 5: H3386-Sample G077. Characterized by rhyolitic red groundmass with 15-30% white, euhedral, feldspar pheno- to glomerophenocrysts. B. Chloritized Brecciated rhyolite, H3378. Characterized by 4cm angular to subrounded rhyolitic clasts with 15-30% feldspar phenocrysts. C. Diabase, H3406. Characterized by black to dark grey, phaneritic to porphyritic texture wtih 0-15% chloritized pyroxene phenocrysts and amygdule-rich upper and lower contacts.D. Volcaniclastic breccia, H3388. Characterized by sandy to silty, pyritic matrix and dacitic, sandstone, siltstone, chert, basalt, and sulphide clasts ranging from <1 to 60cm. E. Monomictic brecciated dacite with quartz-sericite altered clast margins and up to 15% sericitized feldspar phenocrysts, H3341. F: Quartz-chlorite-carbonate scoreacous, hyaloclastic, basaltic breccia, H3386.
A. Rhyolite,
D
BA
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LithogeochemistryFigure 6: A. 3 distinct volcanic units are recognized: Basalt/Andesite (green triangle), dacite (orange octagon), and rhyolite (red circle). B. Spider Plot of Basalt/Andesite unit distinguishes a calc-alkaline,mature arc affinity for the basaltic unit. C. La/Y over La separates the rhyodacite and dacite units on the basis of HREE enrichment/depletion. Basalts have similar La/Yb ratios as the dacite, but lower La. D. Spider plot further distinguishes the two felsic calc-alkaline arc units. E. Basalt discrimination diagram of immobile elements Ti and Zr indicates a volcanic arc origin for Lundberg basalts.F. Winchester and Floyd (1977) diagram displaying silica mobility in the three volcanic units.
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Implications for Buchans VMS genesis
Mineralization within the Lundberg zone is associated with only one felsic volcanic unit (dacite) based on stratigraphic and geochemical constraints. This implies that stockwork mineralization, as well as formation of massive sulphide mounds, was restricted to one stratigraphic horizon. Intense bladed calcite observed within the polymetallic veins of the Lundberg Zone indicates that precipitation of the sulphides was induced by phase separation of hydrothermal fluids by sub-seafloor boiling. Boiling of hydrothermal fluids occurs over a wide range of pressure and temperature conditions, but, as pressure decreases (i.e. shallowing water column) boiling is inevitable. Boiling of the hydrothermal fluid can account for the low grade (1.83% Zn, 0.67% Pb, 0.38% Cu, 5.5g/t Ag) of the Lundberg zone. The rising hydrothermal fluid is depleted in metals upon reaching the seafloor due to precipitation over a large boiling area, and deposition of massive sulphide mounds is limited. The Lundberg Zone exhibits some characteristics of epithermal deposits, suggesting deposition in a low hydrostatic pressure environment; however, it is also associated with typical Kuroko-style VMS mineralization (e.g. Lucky Strike). These contrasting characteristics suggest that the Buchans area represents the transition between typical VMS and epithermal paleoenvironments.
AcknowledgementsThis poster is a contribution to the Geological Survey of Canada Targeted Geoscience Initiative 3: Appalachians. We would like to acknowledge both Alvin Harris and Stewart Cochrane of the Newfoundland Geological Survey for access and assistance at the Buchans core storage facility. Royal Roads Corp. for supporting this research. Lastly, we acknowledge the SEG for their interest and financial contribution to the above research.
LegendDiabaseRhyodaciteExhalative BariteVolcaniclastic brecciaDaciteBasaltGeochemistry samplelocation
Alteration and mineralization
Alteration throughout the Lundberg zone varies from weak to intense, varying within, and between stratigraphic units. Alteration of the groundmass of the rhyolite to chlorite (green- to black), sericite (white to beige), hematite or specularite is common. Alteration of the volcaniclastic breccia is limited to rare strong sericite and weak chlorite, whereas mineralization is common with 1-2% massive sphalerite, galena, chalcopyrite, and pyrite clasts averaging 1 cm, but up to 20 cm in length. Not only does mineralization occur as clasts, but also as brecciated exhalitive barite deposits along similar horizons. The brecciated exhalative deposits are metal-rich, consisting of up to 4.52 % combined Zn-Pb-Cu, 102.77 g/t Ag, and nearly 1g/t Au over 3.92m. The dacite unit typically has a quartz-sericite-pyrite altered groundmass with feldspar phenocrysts reflecting the same alteration. The dacite is typically unmineralized, but rare massive chalcopyrite veins are observed having average grades up to 5.3g/t over 1 m. The basalt unit is typically altered to chlorite and quartz-sericite assemblages, and hosts the majority of the Lundberg zone, a polymetallic, sphalerite-galena-chalcopyrite stockwork. Along these mineralized quartz-carbonate-rich veins, alteration haloes of chlorite and sericite-fuchsite are rare, but observed. Bladed calcite and quartz pseudomorphs of bladed calcite are common within mineralized veins, with individual blades ranging from <1 to 3 cm in length.
Alteration and Mineralization of Major Volcanic Units
Figure 7: A. Chloritized rhyolite, H3396-Sample G013. B. Hematized rhyolite, H3408. C. Silicified Dacite with chalcopyrite veining, H3386. D. Silicified basalt, H3406-Sample G199. E. Quartz-sericite-fuchsite alteration within the basalt, H3393. F. Bladed calcite with disseminated pyrite and sphalerite, H3398. G. Disseminated sphalerite-galena-pyrite veins, as well as in-situ brecciation of basalt, H3369A, H. Bladed calcite, as well as an alteration halo of sericite-fuchsite around a quartz-carbonate vein, H3365. I. Exhalative barite, H3378.
A
1cm2cm G
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E1cm
H
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Geochemistry
80 samples were analysed at ActLabs, Ontario. Major oxides were determined by Fusion ICP, whereas trace elements were determined by Fusion-MS. Preliminary geochemical analysis of the first 40 samples has distinguished two separate felsic volcanic units, and a basalt/andesite (Figure 5). All units have distinct Nb anomalies, and a negative REE slope indicating a calc-alkaline arc affinity. The two different varieties of felsic volcanic rocks are differentiated based on REE’s: The dacite is HREE-enriched, whereas the rhyolite is HREE-depleted. The HREE-enriched dacite is uniquely associated with mineralization as it is observed to lie stratigraphically in-between the volcaniclastic breccia and stockwork mineralized basalt.
Stratigraphy
Facies 1, a Basalt, is up to 360m thick constrained by drill hole depth. Facies 2, a dacite, ranges 5-40m thick, averaging 20m thick. Facies 3, a volcaniclastic breccia, ranges from 2-60m thick, averaging 5m thick. Facies 4, a rhyolite, ranges from 5-130m thick, locally thickening to 195m. All units except the dacite are intruded by diabase ranging from <1 to 130m thick. All 4 facies are correlative across much of the study area with some units pinching and swelling along across strike (i.e volcano-sedimentary and dacite). All facies gently dip to the northwest exposing more of the rhyolite in westward drill holes. Facies 1 is part of the Ski Hill formation, and the rest of the facies are grouped into the Buchans River Formation which hosts the ore.
F
1cm
Architecture of the Lundberg Zone
H-08-3369A H-08-3365H-08-3372H-08-3376H-08-3396H-08-3388 H-08-3395 H-08-3393H3341
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The Buchans mining camp is characterized by a number of unusually high grade low-tonnage volcanogenic massive sulphide deposits (VMS) hosted by a bimodal calc-alkaline continental arc sequence. The mining camp produced a total of 16.2 Mt of ore at an average grade of 14.5% zinc, 7.6% lead, 1.3% copper, 126g/t Ag, and 1.37g/t Au rivalling most other VMS districts. The Buchans Group has been separated into the Lundberg Hill, Ski Hill, Buchans River, and Sandy Lake Formations. The Lundberg Hill Formation is characterized by felsic pyroclastic rocks, rhyolite, tuffaceous wacke, siltstone, minor basalt, chert and iron formation. The Ski Hill Formation is characterized by basaltic to andesitic pyroclastic rocks with minor felsic tuff. The Buchans River Formation is characterized by rhyolite, felsic tuff, pyritic siltstone, polylithic conglomerate, and high grade in situ and transported sulphide ore bodies. The Sandy Lake Formation is characterized by basaltic pillow lava, epiclastic and polylithic pyroclastic volcanics, tuff, and tuffaceous sedimentary rocks.
.Figure 3: Compilation map of geology by Davenport (1996), structure and deposit data by Thurlow (1987), and drill hole distribution by Royal Roads Corp. just west of the town of Buchans.
!(
!( H-3396
H-3394
H-3393
H-3395
H-3388
H-3378
H-3376 H-3365H-3344
56°52'0"W
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Rothermere orebodies
Lucky Strikeorebody
0 375 750 1,125 1,500187.5
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Legend
Top Sails Granitic Intrusive Suite
Sandy Lake Formation
Buchans River Formation
Ski Hill Formation
Lundberg Hill Formation
Buchans
Geological Setting
The Buchans Group (465 Ma) lies within the Annieopsquotch accretionary tract (AAT), a section of accreted peri-Laurentian continenal arcs and backarcs formed during the Early to Middle Ordovician (Figure 1). The AAT is bound to the west by the Lloyds River fault, found adjacent to the Notre Dame and Dashwoods Arc, and to the west by the Red Indian Line, a major suture zone separating rocks of peri-Laurentian and peri-Gonwanan affinity. The formation of the AAT is characterized by the formation of two arcs: The Robert’s Arm and Red Indian Lake/Buchans Arcs (Figure 2). Sub-greenschist to amphibolite facies metamorphism is syn- to post accretion, and associated with either burial (prehnite-pumpellyite) or contact metamorphism. Accretion of terranes to Laurentia was progressive. The Buchans Group was accreted and imbricated along west-dipping, oblique-reverse faults. Although major structures have been recognized, multiple generations of folding and faulting occurs with common reactivation of faults making structural interpretations extremely difficult.
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Figure 2: Tectonic setting and development of the AAT. First, formation of the Roberts Arm arc associated with west-dipping subduction outboard of the composite Laurentian margin. Next, accretion of the , formation of the Buchans group within the Red Indian Lake arc, local extension forming the Skidder basalt and continued closing of the Iapetus Ocean and further deformation.
Roberts Arm arc
Figure 1: Distribution of the 4 main geological zones of Newfoundland and the location of the Annieopsquotch accretionary tract.
Figure 4: Stratigraphy and geochemistry of the Lundberg Zone. The basaltic unit is commonly silicified and sericitized at upper contacts within the mineralized polymetallic stockwork often mimicking dacititic textures. The volcanicalstic breccia is much thicker to the far west of the study area, and typically grades down-hole into normally graded sandstone, and siltstone with dispersed felsic clasts . The dacite unit is exclusively associated with the volcaniclastic breccia which hosts massive sphalerite-galena-pyrite clasts, however, the other felsic unit (rhyolite) observed at the top of the section is barren.
