Appendix 1 – U-Pb geochronology
U-Pb analytical techniques
Heavy mineral concentrates were prepared from the samples using standard mineral separation techniques, including: crushing, grinding, hydrogravimetric Wilfley™ table, and heavy liquid separation. This was followed by final separation of the zircon grains by magnetic susceptibility using a Frantz™ isodynamic separator and hand-picking. 
SHRIMP II (Sensitive High Resolution Ion MicroProbe) analyses were conducted at the Geological Survey of Canada using analytical procedures described by Stern (1997), with standards and U-Pb calibration methods following Stern and Amelin (2003).  Zircons from the samples and fragments of the GSC laboratory zircon standard (z6266 zircon, with 206Pb/238U age = 559 Ma) and a secondary zircon standard (Temora 2) were cast in an epoxy grain mount (see Table 1 for GSC mount#), polished with diamond compound to reveal the grain centers, and photographed in transmitted light. Internal features of the zircons (such as zoning, structures, alteration, etc.) were characterized in back-scattered electron (BSE) and cathodoluminescence (CL) modes utilizing a Zeiss Evo 50 scanning electron microscrope (SEM). Mount surfaces were evaporatively coated with 10 nm of high purity Au.  Analyses were conducted using an O- primary beam, projected onto the zircons with an elliptical spot (ranging in size from 13μm x 16μm (K100) to 17μm x 23μm (K120); see Table 1 for the spot size used for each sample). The count rates of ten masses including background were sequentially measured over 6 scans with a single electron multiplier and a pulse counting system with deadtime of 23 ns.  Off-line data processing was accomplished using customized in-house software.  The SHRIMP analytical data is presented in Table 1, where the 1 external errors of 206Pb/238U ratios reported in the data table incorporate a 1.0% - 1.1% error in calibrating the standard zircon (Stern and Amelin, 2003).  No fractionation correction was applied to the Pb-isotope data; common Pb correction utilized the Pb composition of the surface blank (Stern, 1997).  The data are plotted in concordia diagrams with errors at the 2 level (Fig. 11), using Isoplot v. 3.0 (Ludwig, 2003) to generate the plots.  
U-Pb isotope dilution thermal ionization mass spectrometry (ID-TIMS) techniques utilized in this study are modified after Parrish et al. (1987), with treatment of analytical errors after Roddick (1987). U-Pb ID-TIMS analytical results are presented in Table 2 and displayed in concordia plots (Figure 5).  All ages uncertainties are presented at the 2s level.
Sample description and interpretation
Mary March Brook group
Seal Pond rhyolite
Seal Pond rhyolite (Fig. 2) is exposed along the Hungry Mountain Thrust northeast of Seal Pond. This rhyolite has been previously assigned to the Sandy Lake Formation (Davenport et al. 1996); however, has been recently reassigned to the Mary March Brook group (Zagorevski and Rogers 2008, 2009). The sampled locality (RAX06A012; z9556) comprises sericitic, well-foliated rhyolite with large (up to 2 cm) quartz glomeroporhyrocrysts (Fig. 3d). The sample yielded abundant euhedral stubby prismatic to prismatic zircon crystals, most ranging in size from 50 mm to 200 mm and many with fractures and numerous inclusions. BSE-SEM images reveal grains with no zoning to moderately well-developed growth zoning. Many zircon grains are somewhat altered, but there is no evidence of inherited cores. SHRIMP II analyses define a single age population (Fig. 5a) and a concordia age is calculated to be 461.5 ± 1.9 (MSWD of concordance and equivalence = 1.12; probability = 0.22; n=37). Taking into account the error associated with the zircon standards analyzed on the SHRIMP grain mount, the crystallization age of the Seal Pond rhyolite is interpreted to be 461.5 ± 4 Ma.
Repeater tower rhyolite
The Repeater tower rhyolite (Fig. 2) was previously included in the Upper Buchans Subgroup or the Lundberg Hill Formation (Davenport et al. 1996); however, it has been reinterpreted to form part of the Mary March Brook group (Zagorevski and Rogers 2008, 2009). It comprises grey-weathering, dark grey fresh, quartz-phyric finely flow-banded rhyolite. The sample (RAX05911; z8975) yielded zircon crystals ranging in size from 50 mm to 200 mm and include equant, multifaceted grains, prismatic crystals, and subhedral grains. Euhedral zircon grains that are interpreted to magmatic in origin exhibit strong growth zoning. The sample also contains abundant grains with evidence of inheritance, including grains with core-rim relationships (Fig. 5b) and entirely inherited grains. One inherited grain was analyzed using SHRIMP II at c. 623 Ma (grain 2, Table A1). The remainder of the analyses define a single age population (Fig. 5b) and a concordia age is calculated to be 461.5 ± 2.7 (MSWD of concordance and equivalence = 0.77; probability = 0.86; n=21). Taking into account the error associated with the zircon standards analyzed on the SHRIMP grain mount, the crystallization age of the Repeater tower rhyolite is interpreted to be 461.5 ± 4 Ma.
Buchans Group
Clementine rhyolite 
The Clementine rhyolite (Fig. 2) is very poorly exposed at surface but was sampled in drill core west of Buchans near the Clementine deposit. In the sampled and adjacent drill core, the rhyolite structurally overlies volcanogenic conglomerate that hosts transported sulphide breccia of the Clementine prospect and amygdaloidal mafic volcanic rocks thought to represent the Ski Hill Formation (Calhoun and Hutchinson, 1981). The relationships observed in the Clementine area are similar to the mine stratigraphy in the Lundberg zone (van Hees et al., 2012). The sampled drill core did not contain sulphides, but rather intersected a Silurian (?) diabase dyke at the level of the orebody. Approximately 15 m of brick red, pink, to green, aphyric to finely quartz-phyric, flow banded rhyolite flow was sampled to constrain the age of the Clementine rhyolite (RAX07A525; GSC lab # z9332; DDH CM-94-01, at approximately 210 m depth). The massive rhyolite is gradational and interlayered with auto-brecciated rhyolite, suggesting that it forms a cryptodome with multiple autobreccia and flow tongue horizons (Fig. 3g). 
The sample yielded abundant zircon crystals ranging in size from 50-200 mm. Zircon morphologies include predominantly euhedral stubby prismatic to prismatic crystals; however, subfaceted grains and resorbed-looking fragments are also present. Most zircon grains contain numerous inclusions and fractures. Backscatter (BSE) and cathodoluminescence (CL) scanning electron microscope (SEM) images revealed many euhedral crystals with well-defined growth zoning (Fig. 5c). Numerous zircon grains with small potential cores are present but were not analyzed. SHRIMP II analyses from the rhyolite comprised a single age population (Fig. 5c). A concordia age of these analyses is calculated to be 465.0 ± 2.2 (MSWD of concordance and equivalence = 1.00; probability = 0.28; n=25).Taking into account the associated error on the standard zircon grains analyzed on the SHRIMP grain mount, the crystallization age of the Clementine rhyolite is interpreted to be 465 ± 4 Ma. 
Oriental rhyolite
The Oriental rhyolite (Fig. 2, 3h) was interpreted to form part of the Buchans River Formation byThurlow and Swanson, 1987. It was sampled from a surface outcrop at the northern limit of a large exposure along Buchans River (RAX05913; z8774). To the south of the sampled locality, the rhyolite has been interpreted to host the Oriental orebody. The sampled locality comprised beige weathering, dark grey fresh, columnar jointed, sparsely quartz and feldspar porphyritic rhyolite. The rhyolite is cut by fine epidote-rich veinlets. The sample yielded zircon grains ranging from 50 mm to >200 mm in size and include euhedral stubby prisms to elongate crystals and subhedral grains with rounded facets. Many grains contain inclusions or fractures and some are quite altered. The sample contains grains with inherited cores and core-rim relationships as well as entirely inherited zircon grains (Fig. 12d, e). BSE-SEM imaging reveals weak growth zoning in some of the zircon grains. SHRIMP II analyses of zircon grains yielded several age populations. The oldest population is comprised of Archean zircons of various ages (c. 2.5 to 3.4 Ga; Table 1, Fig. 5d) which are interpreted to represent inherited components. A single analysis of c. 500 Ma zircon (grain 6, Table A1) suggests a late Cambrian inherited component. A concordia age calculated for the dominant age population is determined to be 465.3 ± 2.6 Ma (MSWD of concordance and equivalence = 1.14, probability = 0.22; n=30). Taking into account the error associated with the zircon standards, the crystallization age of the Oriental rhyolite and the age of VMS mineralization in the Oriental orebody is interpreted to be 465 ± 4 Ma. A younger population of zircons was also analyzed from the sample and is Silurian in age (427± 6 Ma, n=4; grains 15, 77, 86, 91, Table 2, not plotted). This younger population is interpreted as zircon growth during the Silurian, either in small igneous veinlets related to the voluminous adjacent Silurian Topsails Igneous Suite (Whalen, 1989) or as a result of late hydrothermal metamorphism and devitrification of glassy matrix.
MacLean dacite
The MacLean dacite (Fig. 2, 3i) forms part of the Buchans River Formation (Thurlow and Swanson, 1987), where multiple (crypto)-domes and related tuffaceous rocks have been documented associated with the Buchans ore. The MacLean dacite was sampled from a subsurface drill core on Level 18 of the MacLean orebody (RAX07A526, z93331; DDH H2192 from 51.2 to 66.75m). The dacite comprises predominantly brecciated bluish-grey aphyric dacite flow that is gradational with polymictic breccia containing high grade sulphide clasts stratigraphically above and below the dacite. Examination of adjacent drill core revealed similar relationships, although the flow was significantly thinner. The sample yielded zircon crystals ranging in morphology from stubby prisms, prisms to fragments. Many of the zircon grains are quite small (<100 mm; the majority are 50-70 mm in size). Some of the very small stubby prismatic crystals are quite clear, without inclusions or fractures, but many of the zircon grains contain fractures and numerous fluid, melt and mineral inclusions of galena (Fig. 5e). BSE- and CL-SEM images reveal faint growth or sector zoning in many of the grains. Grains with potential inherited cores are also present. SHRIMP II analyses from zircon grains interpreted to be magmatic in origin comprised a single age population. A concordia age of these analyses is calculated to be 463.1 ± 1.9 (MSWD of concordance and equivalence = 0.87; probability = 0.78; n=37). Taking into account the error associated with the zircon standards analyzed on the SHRIMP grain mount, the crystallization age of the MacLean dacite and the age of VMS mineralization in the MacLean orebody is interpreted to be 463 ± 4 Ma.
Crystal tuff, Buchans River
Crystal tuff along Buchans River (Fig. 2) forms part of the Sandy Lake Formation of Thurlow and Swanson (1987).  A sample of crystal tuff (RAX05912; z8770) yielded abundant zircons ranging in size from 50 mm to 200 mm. Morphologies include well faceted, equant, stubby and elongate prismatic crystals, some of which display growth zoning and rare sector zoning. BSE-SEM imaging also revealed that small potential cores are present in some of the zircon grains; however, these were not analyzed. ID-TIMS analysis of three multigrain zircon fractions revealed a significant inherited component. A chord constructed using just the two most concordant of the analyses has a lower intercept of 463 ± 2 Ma (inset of Fig. 5f). SHRIMP II analyses of zircon grains from the tuff comprise a single population (Fig. 5g) with a concordia age calculated to be 462.2 ± 2.6 (MSWD of concordance and equivalence = 0.94; probability = 0.58; n=23). Taking into account the associated error on the standard zircon grains, an age of 462 ± 4 Ma is taken to be the eruption age of the Buchans River crystal tuff. The alternate interpretation of this unit as sedimentary rock requires that the age of 462 ± 4 Ma is the maximum age of deposition.
Red Indian Lake Group
Red Indian Lake rhyolite
Red Indian Lake rhyolite, which is exposed in outcrop north of Red Indian Lake (Fig. 2, 3n), has been previously assigned to the Lundberg Hill Formation (Davenport et al., 1996) and the Red Indian Lake Group (Rogers et al., 2005). The sampled locality (RAX07A009; z9371) comprises rhyolitic tuff with quartz phenocrysts. The sample yielded abundant euhedral zircon crystals predominantly ranging from 100 mm to 200 mm and including stubby prismatic to elongate grains, many with abundant fractures and inclusions. BSE- and CL-SEM imaging also reveal the presence of zircon grains with probable inherited cores. SHRIMP II analyses define a single age population (Fig. 5h) and a concordia age is calculated to be 465.3 ± 2.3 (MSWD of concordance and equivalence = 1.13; probability = 0.22; n=32). Taking into account the error associated with the zircon standards analyzed on the SHRIMP grain mount, the crystallization age of the Red Indian Lake rhyolite is 465 ± 4 Ma.
Mary March wilderness park rhyolite
Mary March wilderness park rhyolite is exposed north of Red Indian Lake (Fig. 2) and has been previously re-assigned to the Red Indian Lake Group (Rogers et al., 2005; Zagorevski and Rogers, 2008; Zagorevski and Rogers, 2009). The sampled locality (RAX06A142A; z9555) comprises a grey-green glassy massive felsic volcanic rock with abundant 1-2 mm pink feldspar phenocrysts. The sample yielded abundant euhedral zircons with equant to stubby prismatic morphologies and ranging from 70 mm to 200 mm in size. BSE- and CL-SEM images of many of the zircon grains display sector and/or growth zoning. Several grains with possible small cores were also observed but not analyzed. SHRIMP II analyses define a single age population (Fig. 5i) with a concordia age of 464.1 ± 2.3 Ma (MSWD of concordance and equivalence = 0.97; probability = 0.54; n=29).  Taking into account the error associated with the zircon standards analyzed on the SHRIMP grain mount, the crystallization age of the Mary March wilderness park rhyolite is 464 ± 4 Ma.

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