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Duck Pond, Boundary |
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Labrador & Newfoundland, Canada |
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Cu Zn Ag Au Pb
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Super Porphyry Cu and Au
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The Duck Pond and nearby Boundary volcanic hosted massive sulphide copper-zinc-lead-lead-silver-gold deposits are located ~30 km SE of Buchans and 90 km SW of Grand Falls on the island of Newfoundland in eastern Canada. Boundary is 4.5 km NE of Duck Pond (#Location: 48° 38' 35"N, 56° 29' 16"W).
Regional Setting
See the Northern Appalachian - Overview record (available soon) for detail of the regional tectonic framework and geologic setting of Newfoundland and the Duck Pond and Boundary deposits.
These deposits lie within the Victoria Lake Supergroup, defined as all pre-450 Ma rocks between the Red Indian Line and the Rogerson Lake Conglomerate that defines the base of the Silurian to the SE. As such the supergroup is to the SE of the Red Indian Line and belongs to the Victoria Arc of the peri-Gondwanan Exploits Sub-zone of the Dunnage Terrane, which in turn is part of the Appalachians Central Mobile Belt.
In contrast to the Buchans deposits, which are NW of the Red Indian Line, are within the segment of the Dunnage terrane that belongs to the Notre Dame Subzone. In addition, Duck Pond and Boundary deposits are hosted within volcanic/epiclastic rocks of a primitive arc, largely characterised by arc tholeiites, in contrast to the mature arc that hosts the Buchans deposits (Swinden et al., 1991).
The rocks of the the Victoria Lake Supergroup form an elongate, NE-SW trending belt that is 15 to 35 km wide and ~150 km long, which has also been intruded by rocks that vary from granite to gabbro, but also include fault bounded inliers of 565 to 563 Ma granites. Traditionally the rocks of the Victoria Lake Supergroup have been divided into the Tulks and Tally Pond 'volcanic belts' to the NW and SE respectively. The Victoria Lake Supergroup represents a collage of volcanic rocks and is interpreted to be a composite unit. It has been divided into a number of units, as follows:
• Sandy Brook group - which lies on the SE edge of the supergroup in the Tally Pond area, mostly south of the 563 Ma Crippleback Lake intrusive suite. It comprises Late Neoproterozoic pillowed to massive basalts, mafic tuffs, andesitic flows, siliceous quartz porphyritic rhyolites and sub-volcanic intrusive suites of similar composition, and has been dated at ~563 Ma. The basalts include island arc tholeiitic and continental arc calc-alkaline basalts. The rocks of this group may also host mineralisation in the district, e.g., the Burnt Pond Zn-Pb-Ag-Au VHMS prospect (McNicoll et al., 2010).
• Tally Pond group, ~511 Ma, which has replaced the 'Tally Pond volcanic belt', is a bimodal volcanic assemblage, comprising a lower unit, the Lake Ambrose formation, composed of unmineralised massive to locally pillowed tholeiitic basalt and tuff, pillow breccia, andesites and minor sedimentary rocks. A second unit, the Bindons Pond formation, is made up of aphyric to massive or flow banded dacite, rhyolite, felsic tuff, breccia, volcaniclastic sedimentary rocks and quartz feldspar porphyry. This felsic formation has been subjected to widespread hydrothermal alteration and is host to sulphide mineralisation. The two formations appear to interfinger on all scales, whether representing stratigraphic or structural repetition, although, the Ambrose Formation may be the older.
• Long Lake group, ~511 to 506 Ma, dominated by felsic volcanic rocks, and lesser amounts of mafic volcanic rocks and intercalated volcano-sedimentary rocks. The felsic rocks in the group are more appropriately divided into two main packages: i). a lower stratigraphic package of ~511 Ma, white to grey to pink, aphyric to quartz±feldspar porphyritic, magnetite-bearing, massive rhyolite, and local fine-grained, magnetite-bearing, felsic tuff, which occur in the northern part of the group; and ii). an upper stratigraphic package of ~506 Ma, light-grey to white, blue-quartz±feldspar phyric felsic to intermediate, and medium- to coarse-grained pyroclastic rocks which occur in the southeastern portion of the group. Both packages locally contain fine-grained felsic ash tuff, volcanogenic siltstone and graphitic shale, and both locally host zones of hydrothermal alteration associated with disseminated to massive volcanogenic sulphides, and local iron formation. All of the felsic rocks are assigned to the ~506 Ma Costigan Lake formation, which is ~11 Ma older than the overlying Tulks Volcanic group. The less abundant mafic volcanic rocks in the Long Lake group are dominated by mafic tuff, pillow basalt and breccia. The Long Lake Main deposit is hosted by the lower unit in the SW section of the unit, and contains indicated reserves of 0.407 Mt @ 7.82% Zn, 1.58% Pb, 0.97% Cu, 49 g/t Ag, 0.57 g/t Au (Hinchey, 2014).
• Tulks group, ~498 Ma, is an intermediate to felsic dominated sequence with a wide range of compositions, ranging from rhyodacite to rhyolite, with basaltic volcanic rocks. It forms an 80 km long, by 10 to 15 km wide, NE-SW trending belt, just to the SE of the Red Indian Line and in thrust contact with the Long Lake group to the SE. The Tulk Group hosts the Tulks Hill, Tulks East, Daniel's Pond, Bobby Pond and Victoria Mine VHMS deposits, the economically most important of which is the Tulks Hill deposit, with resources of 0.75 Mt @ 6% Zn, 2% Pb, 1.3% Cu, 41 g/t Ag, 0.4 g/t Au (Rogers, et al., 2007). The sequences hosting the main VHMS deposits are composed of (after Hinchey, 2011) quartz-phyric rhyolite and altered felsic to intermediate volcanic rocks, dominated by blue quartz±feldspar-phyric crystal (at Tulks Hill), felsic to intermediate volcanic rocks including ash- and quartz±feldspar crystal tuff, lapilli tuff, coarse-grained volcaniclastic conglomerate and breccia, quartz-phyric rhyolite flows and local basaltic sills (at Tulks East), and intermediate to mafic ash- and crystal- to lapilli tuff (at Daniel's Pond).
• Pats Pond group, ~488 Ma, dominated by intermediate, quartz-phyric and mafic tuffs. The lowest stratigraphic unit is a calc-alkaline pillow basalt, overlain by feldspar±quartz-phyric ash crystal and tuffs. These are stratigraphically overlain by mainly quartz-phyric andesitic tuffs, whilst the stratigraphic top of the group is dominantly basaltic to andesitic tuffs, lapilli tuff and rhyolitic tuffs (Hinchey, 2011). The Boomerang-Domino-Hurricane deposit cluster are hosted by the Pats Pond group. The Boomerang deposit has an indicated resource of 1.36 Mt @ 7.09% Zn, 3.00% Pb, 0.51% Cu, 110.43 g/t Ag, 1.66 g/t Au (Messina Minerals Inc., Press Release, June 21, 2007). An additional 0.7 Mt of inferred resources is estimated for the Boomerang and Domino lenses.
• Other groups, which include the Noel Pauls Brook group (~465 to 455 Ma), Wigwam Brook group (~462 to 455 Ma); Sutherlands Pond group (also ~462 to 455 Ma), Harpoon Gabbro (~465 to 460 Ma) and overlying black shales dated at ~455 Ma.
Local Geology
The Duck Pond and Boundary deposits in Newfoundland are hosted by volcanic rocks of the Cambrian Tally Pond group in the Victoria Lake Supergroup. They are hosted by altered felsic flows, tuffs, and volcaniclastic sedimentary rocks, and the sulphide ores formed in part by pervasive replacement of unconsolidated host rocks. The two deposits appear to be structurally displaced portions of a much larger mineralising system, which developed at 509±3 Ma. Unaltered mafic to felsic volcanic rocks that occur structurally above the orebodies were dated at 514±2 Ma, and hypabyssal intrusive rocks that cut these were dated at 512±2 Ma (McNicoll et al., 2010).
Duck Pond Deposit
In the Duck Pond deposit area, the host Tally Pond group forms three structurally juxtaposed sequences, informally named the Upper Un-mineralised Block, the Mineralised Block and the Lower Sedimentary Block, that form a structural window through an overthrust package of Ordovician sedimentary rocks (Squires et al., 1991). The stratigraphic sequence is complicated by a series of moderately to steeply dipping thrusts and wrench faults, with displacements of from 0.5 to 1 km. The geology of these blocks is as follows (after Evans and Kean, 2002):
• The Upper Unmineralised Block, is >500 m thick and comprises a shallow dipping sequence of cyclic mafic-felsic flows and pyroclastic rocks, locally intercalated with graphitic sedimentary rocks and reworked tuffs (Squires et al., 1990). Gabbroic and porphyritic dykes and sills intrude the sequence along a series of reverse faults. As the block name suggests, alteration and mineralisation within it are rare. The base of the block is defined by the 45°S dipping Duck Pond Thrust, marked by zones of mylonite and fault gouge, juxtaposing the Upper Unmineralised Block over the Mineralised Block.
• The Mineralised Block, is also >500 m thick, composed of highly altered and deformed, but overall flat-lying felsic flows and pyroclastic rocks, lesser mafic flows and mafic and felsic dykes (Squires et al., 1990). It is interpreted to be wedge-shaped determined by the convergence of the bounding faults above and below. The overprinting alteration is variable represented by an assemblage that includes chlorite, sericite, silicification, carbonates and pervasive pyrite. Deformation is pervasive, and is dominated by moderately south-dipping, subparallel thrusts, disrupting both the stratigraphy and mineralisation.
• The The Lower Sedimentary Block, is >200 m thick, and structural underlies the Mineralised Block. It is composed of turbiditic interbedded graphitic and argillaceous sedimentary rocks (Squires et al., 1990), which are strongly folded and the deformation, interpreted to be the result of a compressive regime related to the thrusting.
These three juxtaposed blocks were subsequently disrupted by an episode of SW-directed thrusting along the north-dipping Terminator Thrust. The thrust is interpreted to offsets the Duck Pond Deposit splitting it into the (upper) Duck Pond and Lower Duck zones. A series of NW-SE trending wrench faults, the Cove, Garage, Old Camp and Loop Road faults offset the stratigraphy of all three blocks, both vertically and laterally, by as much as 500 m.
Both the Duck Pond and Boundary deposits locally exhibit classic textures (Kean, 1985; Squires et al., 1990) that include rhythmically banded sulphides, polylithic sulphide conglomerate debris flows and hydrothermally altered felsic volcanic rocks, although subsequent deformation has often obliterated much of the primary sulphide textures.
The Duck Pond Deposit collectively includes three massive sulphide lenses, which are found at depths of from 250 to 800 m (Squires et al., 1990). These are the:
Duck Pond, the upper of the three lenses, which averages ~18 m in thickness, and lies at depths of approximately 250 and 450 m below the surface. It is estimated to contain in excess of 15 Mt of massive sulphides of which only ~3.88 Mt is considered to be ore, with an average grade of 3.8% Cu, 1.1% Pb, 6.7% Zn, 71.0 g/t Ag and 1.1 g/t Au (Thundermin Resources, 1999). The ore zone is surrounded by coarse- grained massive pyrite, comprising ~65% of the sulphide deposit. The eastern and southern margins of this lens of the deposit are the most strongly deformed, and the sulphide mineralisation has ductile deformation textures and locally mylonitic fabrics related to the juxtaposition of the structural blocks. These features tend to be absent from the pyrite-rich zones where the pyrite has instead been coarsely recrystallised. Hydrothermal alteration related to the massive sulphide mineralisation takes the form of distal, widespread silicification and sericitisation, which passes into pervasive chlorite and ubiquitous disseminated, stringer and locally massive pyrite within ~100 m of the massive sulphides (Squires et al., 1990). The upper Duck Pond deposit is surrounded by a carbonate halo, known as the “chaotic carbonate” zone, consisting of contorted calcite and minor fluorite veins, which replace the strongly chloritised mafic volcanic rocks. This alteration occurs immediately above, below, locally within, and up to 200 m laterally around the deposit and is thought to have formed during the waning stages of hydrothermal activity. The structural complexities have prevented the delineation of any chloritic feeder pipe (Evans and Kean, 2002).
Sleeper Zone, which comprises four 4 to 20 m thick, zinc-rich lenses occurring 50 to 100 m below the Duck Pond deposit (Squires et al., 1990). It is estimated to contain ~1.0 Mt of massive sulphides, of which ~0.68 million tonnes @ 1.7% Cu, 1.2% Pb, 8.7% Zn, 62.5 g/t Ag and 0.5 g/t Au is potential ore (Thundermin Resources, 1999).
Lower Duck deposit, located several hundred metres to the east and 300 m below the (upper) Duck Pond deposit, is interpreted to be a faulted portion of the (upper) Duck Pond deposit (Squires et al., 1990) (Figure 22). It averages 13 m in thickness and contains an estimated 3.0 Mt of massive sulphides, that includes 1.0 Mt of ore @ 2.8% Cu, 1.4% Pb, 5.0% Zn, 32.5 g/t Ag and 0.6 g/t Au (Thundermin Resources, 1999). The sulphides are strongly deformed and exhibit ductile deformation features. Both the ore body and the enclosing felsic volcanic rocks are attenuated and much thinner than the Duck Pond lens (Evans and Kean, 2002).
The massive sulphide zones at Duck Pond locally have spectacular banding that superficially resembles bedding. Squires et al. (1991, 2001) suggest that sulphides replaced pre-existing, unconsolidated material in a sub-sea-floor environment, and, in places, faithfully mimic primary features. The venting of mineralising fluids onto the sea-floor is suggested by debris-flow mineralisation in rocks stratigraphically above the main ore lenses. The argillaceous sedimentary rocks may have formed a less permeable 'seal' that trapped much of the fluid and promoted replacement of more permeable units at depth (Squires et al., 2001).
Boundary Deposit
The deposit, comprises three main zones: the North, South and Southeast zones, all of which subcrops beneath a veneer of glacial till that is only a few metres thick, particularly in areas where the deposit is not covered by hanging-wall rhyolitic rocks (Piercey et al., 2014). The North Zone generally dips gently northward and the South Zone dips gently southeastward, although the eastern part of the South Zone locally appears to be dipping north (Kean, 1985). The deposit, which comprises two sulphide lenses, referred to as the North and South zones, contains ~0.5 million tonnes of massive sulphide of which ~0.45 million tonnes grading 3.5% Cu, 3.5% Zn, 0.5% Pb and 22.8 g/t Ag (Thundermin Resources, 1999) is considered to be ore.
These three zones occur at and below the contact between a hanging-wall quartz-phyric assemblage of flow-banded rhyolite flows and breccias (lobe and breccia facies rhyolites) with lesser tuff, and a footwall of aphyric rhyolitic lapilli tuff and tuff. The contacts of the massive sulphides with the hanging wall and the footwall are generally sharp, but the footwall below the massive sulphide exhibits a pervasive alteration. The massive sulphide mineralisation proximal to the footwall alteration exhibits breccia textures, whilst distal parts of sulphide body have well developed banding and laminations and, locally, apparent graded bedding is observed (Kean, 1985). There is generally very little alteration in the footwall in these latter areas. Below the immediate footwall, the lapilli tuffs are interlayered with aphyric rhyolite flows, rhyolite breccias, and distinctive, jigsaw-fit, aphyric rhyolite breccias that are similar to those in the footwall of the Duck Pond and Lemarchant deposits (Squires et al., 2001; Moore, 2003; Squires and Moore, 2004; Copeland et al., 2009). The stratigraphy, facies relationships, alteration and mineralisation are consistent in all three zones of the deposits (Piercey et al., 2014).
The following lithofacies are recognised at the Boundary deposit (after Piercey et al., 2014):
• Lobe and breccia-facies rhyolite - which is brown to grey and dominated by quartz-phyric, flow-banded rhyolite lobes with marginal breccias. Most of the lobes are massive and grade stratigraphically upward into more brecciated to tuffaceous units with flow-banded clasts containing quartz and spherulites that are mostly strongly altered and completely replaced by chlorite and/or quartz. This unit is locally cut by stockworks of pyrite and chalcopyrite, and regionally (i.e., Boundary West prospect) overlain by Zn-rich pyritic mudstone and mineralised mafic flows. In the North zone, thicknesses of the hanging-wall lobe and breccia facies rhyolites increase toward the southeast, broadly coinciding with the thickest accumulations of massive sulphide, thus potentially reflecting eruption into a depression, possibly bounded by a synvolcanic fault.
• Lapilli tuff to tuff - is the dominant footwall host to the Boundary deposit, composed of aphyric rhyolitic lapilli tuff. This tuff includes clast-supported varieties with rounded to subrounded, often spherulitic clasts of aphyric rhyolite, intraclast ash, some dark black to grey rhyolitic fragments, flow-banded rhyolite clasts, and minor argillite, which grades into less abundant matrix supported lapilli tuff with rounded rhyolitic clasts within a grey ash matrix.
• Jigsaw-fit tuff breccia - which is virtually identical to those in the footwall of the Duck Pond deposit (Squires et al., 1991; Squires et al., 2001). They comprise white to grey, aphyric rhyolite clasts with minor interfragment felsic ash. Fragments are polygonally jointed to subangular, and the breccias are mostly clast supported. The jigsaw-fit breccias are more abundant in deeper parts of the deposit and are associated with massive rhyolite flows and flow-top angular rhyolite fragment breccias.
• Rhyolite flows and flow breccias - occurring as aphyric rhyolite flows in a series of relatively densely packed, grey to white, massive to flow-banded, aphyric rhyolite flows that grade upward into breccias containing flow-banded rhyolite clasts, black relict glass to pumiceous clasts, and ash.
• Quartz-feldspar porphyry dykes - are relatively rare, but locally intrude both the lapilli tuff and lower footwall felsic volcanic and volcaniclastic units. They locally they display peperite textures, and are grey to white with sharp margins, exhibiting minor sericite-quartz alteration, similar to those at the Duck Pond deposit.
• Pillow lavas - which are relatively uncommon in the Boundary deposit stratigraphy, and only found at depth, where they are intercalated with predominant felsic volcanic rocks. They are grey-green to brown, amygdaloidal, and exhibit variable bleaching (silicification) and Fe-carbonate alteration, while some of the pillows have quartz patches and chlorite- and quartz-filled amygdules. In regional holes, footwall strata pass stratigraphically downward from volcaniclastic to more coherent flows and intrusions, and to associated coarse, jigsaw-fit breccias and volcaniclastic rocks, particularly below the South and Southeast zones, where the footwall to mineralisation contains more flows and intrusive rocks (Piercey et al., 2014).
Mineralisation in the North, South Southeast zones and is dominated by Cu-Zn-rich massive sulphide, with variable amounts of base-metal-poor pyritic sulphide, although the latter is less abundant compared to the Duck Pond deposit, and occurs primarily in the basal portions of the various zones, and rarely, it is also found distal to the Cu-Zn mineralisation.
Most of the sulphides occur at the contact between the hanging-wall, quartz-phyric lobe and breccia facies rhyolite and footwall lapilli tuff. It is not a single continuous lens at this contact, but instead, a series of lenses with hanging wall- and footwall contacts that are conformable to semi-conformable to stratigraphy, and occur within 10 m vertically below this contact, typically hosted by porous footwall lapilli tuff and coarser fragmental units. The multiple horizons typically comprise a core of massive sulphide that, together with the bedding-parallel sheets, have a broad tree branch-like morphology.
The mineralisation occurs as a series of forms (after Piercey et al., 2014), including:
• Stringer sulphides occurring within abundant clasts and in the matrix to clasts, comprising of fine-grained to granular pyrite and lesser chalcopyrite and sphalerite occupying ~10 to 20 vol.% of the rock, forming the matrix to rhyolite lapilli, or surrounding the jigsaw-fit fragments in rhyolite flows.
• clast-rich massive sulphides - the stringer sulphides grade into clast-rich massive sulphide that consists predominantly of pyrite, sphalerite and chalcopyrite, with abundant, variably altered clasts of rhyolite. The clasts range from aphyric rhyolite lapilli, angular rhyolite fragments, to larger rounded rhyolitic fragments.
• massive pyritic sulphides with chalcopyrite stringers, massive sulphide in this and the following group contain up to 90 to 95 vol.% sulphide with varying proportions of pyrite, sphalerite, and chalcopyrite, and includes pyrite with stringers of sphalerite and chalcopyrite, and chalcopyrite with sphalerite and minor pyrite. There are abundant fragments of altered rhyolite within the massive sulphides.
• chalcopyrite- and sphalerite-rich massive sulphides, see above, and
• bedded sulphides consisting of laminated pyrite with lesser sphalerite and chalcopyrite that have mm- to cm-scale bands of sulphide.
Alteration within the deposit predominantly consists of chlorite and quartz-sericite of varying intensity, with locally abundant dolomite (i.e., the 'chaotic carbonate') and Fe-carbonate (ferromagnesite). The alteration assemblage and extent varies between the footwall and hanging-wall lithofacies. In the footwall, all alteration types are present, from unaltered to weakly altered when ~100 m from mineralisation to intensely altered proximal (i.e., within 10 m) to mineralisation. The footwall lapilli tuff becomes increasingly altered proximal to mineralisation, changing from rocks that are relatively fresh, to quartz-sericite, to quartz-sericite-chlorite, to intense chlorite, locally with chaotic carbonate near mineralisation. In moderately altered lapilli tuff, clasts have concentric alteration patterns with fresh cores surrounded by rims of quartz and sericite, whilst the matrix of ash between the clasts is commonly replaced by chlorite. As the alteration intensity increases, the clasts have chlorite-altered rims and quartz-sericite- altered cores within a matrix completely replaced by chlorite. As the alteration intensity increases further, the clasts and ash are entirely replaced by black chlorite with stringer sulphides, and local 'chaotic carbonate' consisting of spheres and dendrites of dolomite that overprint, but are cogenetic with, chlorite (Piercey et al., 2014).
The hanging wall rocks have also undergone considerable alteration, dominated by patchy to pervasive quartz-sericite, with only minor patchy chlorite. Typically, the rhyolite flows are white with flow-banded and massive zones that have been moderately to strongly quartz-sericite altered, whilst the ash-rich zones have been chloritised. Disseminated pyrite-(chalcopyrite-sphalerite) grains occur within the rhyolite flows, and fine-grained iron oxides are sometimes distributed parallel to the flow banding. Iron-rich carbonate alteration is also present throughout the deposit and the entire Tally Pond Group, occurring as mm-scale spots that overprint all other alteration types (Piercey et al., 2014).
Total pre-mining proved + probable ore reserves at Duck Pond and Boundary were:
- 5.5 Mt @ 3.3% Cu, 5.8% Zn, 0.9% Pb, 59 g/t Ag, 0.8 g/t Au, (Aur Resources Inc., press release, December, 2001).
Remaining ore reserve and mineral resource estimates, as at December, 31, 2013 were (Teck website, 2014):
Proved + probable reserve - 0.90 Mt @ 3.16% Cu, 3.91% Zn,
Measured + indicated resource - 0.80 Mt @ 3.19% Cu, 4.8% Zn.
The most recent source geological information used to prepare this decription was dated: 2012.
This description is a summary from published sources, the chief of which are listed below.
© Copyright Porter GeoConsultancy Pty Ltd. Unauthorised copying, reproduction, storage or dissemination prohibited.
Duck Pond
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Selected References:
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Evans, D.T.W. and Kean, B.F., 2002 - The Victoria Lake Supergroup, central Newfoundland - its definition, setting and volcanogenic massive sulphide mineralization.: in Newfoundland Department of Mines and Energy, Geological Survey, Open File NFLD/2790, 68p.
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McNicoll V, Squires G, Kerr A and Moore P, 2010 - The Duck Pond and Boundary Cu-Zn deposits, Newfoundland: new insights into the ages of host rocks and the timing of VHMS mineralization: in Can. J. Earth Sci. v. 47, pp. 1481-1506.
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McNicoll, V., Squires, G., Kerr, A. and Moore, P., 2008 - Geological and metallogenic implications of U-Pb zircon geochronological data from the Tally Pond area, Central Newfoundland: in Current Research, 2008, Newfoundland and Labrador Department of Natural Reesources, Geological Survey, Report 08-1, pp. 173-192.
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Piercey, S.J., Squires, G. and Brace, T., 2018 - Geology and lithogeochemistry of hydrothermal mudstones from the upper block near the Duck Pond volcanogenic massive sulfide (VMS) deposit, Newfoundland, Canada: evidence for low-temperature venting into oxygenated mid-Cambrian seawater: in Mineralium Deposita v.53, pp. 1167-1191.
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Piercey, S.J., Squires, G.C. and Brace, T.D., 2014 - Lithostratigraphic, Hydrothermal, and Tectonic Setting of the Boundary Volcanogenic Massive Sulfide Deposit, Newfoundland Appalachians, Canada: Formation by Subseafloor Replacement in a Cambrian Rifted Arc: in Econ. Geol. v.109, pp. 661-687.
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Porter GeoConsultancy Pty Ltd (PorterGeo) provides access to this database at no charge. It is largely based on scientific papers and reports in the public domain, and was current when the sources consulted were published. While PorterGeo endeavour to ensure the information was accurate at the time of compilation and subsequent updating, PorterGeo, its employees and servants: i). do not warrant, or make any representation regarding the use, or results of the use of the information contained herein as to its correctness, accuracy, currency, or otherwise; and ii). expressly disclaim all liability or responsibility to any person using the information or conclusions contained herein.
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