The eastern Dunnage Zone of the central Newfoundland Appalachians hosts Paleozoic orogenic gold mineralization along a northeast-trending, crustal-scale fault corridor that extends for more than 200 km. This orogenic gold system is characterized by polyphase, structurally controlled, quartz vein systems that cut Neoproterozoic granitoid rocks and unconformably overlying syntectonic, polymict conglomerate and associated transitional to calc-alkaline bimodal igneous rocks.

High-precision chemical abrasion–isotope dilution–thermal ionization mass spectrometry (CA-ID-TIMS) U-Pb geochronology confirms a widespread, latest Silurian magmatic pulse (422–420 Ma) that is attributed to a transient phase of lithospheric extension resulting from asthenospheric and crustal melting related to slab break-off. Syntectonic conglomerate was deposited as a basal unit during extension-related uplift and erosion that lasted until ca. 418 Ma in north-central Newfoundland. Orogenic gold mineralization associated with syntectonic sedimentation and magmatism is hosted within third-order shear vein systems that form offshoots within a triangle zone–like structural corridor between southeast- and northwest-dipping, second-order fault splays and shear zones. The southeast-dipping fault system formed during northwest migration of the Acadian thrust front, whereas the northwest-dipping faults and shear zones are Salinic structures that were reactivated in the Early Devonian.

Primary hydrothermal rutile in the orogenic gold-mineralized quartz veins produced ages of ca. 410 Ma. These ages are consistent with quartz vein emplacement and orogenic gold mineralization as a result of hydrothermal fluid-pressure cycling related to far-field compression and thermal perturbations during the Early Devonian Acadian orogenic cycle. The setting and process evolution of the central Newfoundland gold district are remarkably similar to that of world-class orogenic gold systems of the Canadian Shield.

Some of the most productive orogenic gold deposits are hosted along crustal-scale fault zones in Archean granite-greenstone terranes, such as in the Yilgarn Craton of the Western Australian Shield (e.g., Groves, 1993; Blewett et al., 2010), and Superior Province of the Canadian Shield (e.g., Poulsen et al., 1992; Card and Poulsen, 1998; Poulsen et al., 2000; Percival, 2007; Bleeker, 2015). These Archean fault systems preserve upper-crustal, syntectonic sequences including polymict conglomerate and bimodal calc-alkaline to alkaline igneous rocks (e.g., Hodgson, 1993; Robert, 2001; Bleeker, 2012, 2015), and host gold mineralization in structurally controlled, fault-fill, and extensional quartz vein systems (e.g., Robert and Brown, 1986a, 1986b; Sibson et al., 1988; Groves et al., 1998; Goldfarb et al., 2005; Dubé and Gosselin, 2007). Similar lithologic, structural, and mineralization relationships also characterize younger orogenic gold systems in Proterozoic and Phanerozoic accretionary terranes (e.g., Kerrich and Wyman, 1990; Ansdell and Kyser, 1992; Goldfarb et al., 2007, 2014; Groves et al., 2003; Deng et al., 2019), indicating that orogenic gold-producing tectonic processes have recurred throughout Earth’s history (Goldfarb et al., 2001; Groves et al., 2005; Bleeker, 2015). Detailed studies of systems of different geological ages, therefore, represent key opportunities to construct unifying models for the formation and preservation of orogenic gold deposits.

In the Newfoundland Appalachians, Canada, orogenic gold-mineralized, crustal-scale fault zones (Fig. 1) accommodated Paleozoic orogenesis involving cycles of compression, extension, and strike-slip (e.g., Williams, 1978; Colman-Sadd et al., 1990; O’Brien et al., 1993; van Staal et al., 1998; O’Brien, 2003; van Staal and Barr, 2012). One such fault corridor that extends for more than 200 km southwest to northeast across central Newfoundland is remarkably similar to Archean orogenic gold-bearing fault systems with respect to geology, structure, and distinct geologic processes (Figs. 1 and 2; Tuach et al., 1988; Tuach, 1992; Evans, 1996; Dubé and Lauzière, 1997; Wardle, 2005; Honsberger and Bleeker, 2018; Lincoln et al., 2018; Honsberger et al., 2019a, 2020a). This fault corridor includes the Cape Ray Fault Zone in southwestern Newfoundland (Dubé et al., 1996; van Staal et al., 1996) and the Wood Brook fault and Victoria Lake Shear Zone in central Newfoundland (Figs. 1 and 2; Valverde-Vaquero and van Staal, 2001; Valverde-Vaquero et al., 2006; Sandeman et al., 2014), and is emerging as one of the most prospective orogenic gold domains in Atlantic Canada (Dunsworth and Walford, 2018; Lincoln et al., 2018; Smith, 2021). Resolving the controls on orogenic gold mineralization in central Newfoundland allows for predictive and targeted exploration models to be established in this area of poor outcrop exposure and limited road access.

Multiple phases of Silurian to Devonian deformation, magmatism, and metamorphism are preserved in central Newfoundland (e.g., Dunning et al., 1990; O’Brien et al., 1993; Dubé et al., 1996; van Staal et al., 1998; O’Brien, 2003; van Staal and Barr, 2012; van Staal et al., 2014; Sandeman et al., 2017; Willner et al., 2018); therefore, structural, chemical, and geochronological data are critical for deciphering distinct orogenic and mineralization events. In particular, the assignment of mineralized rocks in central Newfoundland to either the Salinic or Acadian orogenic cycles is problematic because of dynamic transitions between different tectonic environments (e.g., <5 m.y.; van Staal and Barr, 2012). The present study examines the lithologic, structural, geochronological, and lithogeochemical record of latest Silurian syntectonic deposition and magmatism and Early Devonian orogenesis that led to gold mineralization in central Newfoundland.

Williams (1979) divided the island of Newfoundland into four tectonostratigraphic zones (Humber, Dunnage, Gander, and Avalon zones) based on lithologic, paleontological, and lithogeochemical contrasts in pre-Silurian rocks (Fig. 1). The gold-mineralized eastern Dunnage Zone (Exploits Subzone) in central Newfoundland is underlain by peri-Gondwanan Neoproterozoic to Ordovician plutonic, volcanic, and sedimentary rocks that comprise the Penobscot and Popelogan-Victoria arc systems of the Iapetus Ocean (Figs. 1 and 2; Colman-Sadd et al., 1990; Evans et al., 1990; O’Brien et al., 1996, 1997; van Staal et al., 1998, 2005; O’Brien, 2003; Rogers et al., 2005, 2006; Valverde-Vaquero et al., 2006; Zagorevski et al., 2007; van Staal and Barr, 2012). These pre-Silurian rocks of the eastern Dunnage Zone are overlain by Sandbian-Katian black shale and Katian-Llandoverian turbiditic sedimentary rocks of the Badger Group (Fig. 2; Kusky and Kidd, 1996; O’Brien, 2003; Waldron et al., 2012), which are in turn overlain unconformably in north-central Newfoundland by bimodal igneous and associated sedimentary rocks of the Botwood Group (Williams, 1962). The easternmost Dunnage Zone exposes a Late Ordovician sequence of low-grade felsic and mafic volcanic and volcaniclastic rocks (Fig. 2; Red Cross Group, Valverde-Vaquero et al., 2006).

The Botwood Group is a Late Silurian syntectonic sequence that includes gray, green, and red siltstone and sandstone in north-central Newfoundland (i.e., Botwood basin) and polymict conglomerate (Rogerson Lake Conglomerate, Kean and Jayasinghe, 1980) in central Newfoundland (Williams, 1962; Williams et al., 1972; Colman-Sadd et al., 1990; Williams, 1993; Williams et al., 1995; O’Brien, 2003; Pollock et al., 2007). The magmatic rocks of the Botwood Group consist of: volcanic rocks of the bimodal Laurenceton Formation (Williams et al., 1972); latest Silurian igneous rocks of the composite Fogo Island Intrusive Suite (Elliott et al., 1991; Aydin, 1995; Sandeman and Malpas, 1995; Hamilton and Kerr, 2016; Graham et al., 2020); Late Silurian–Early Devonian plutonic rocks of the Mount Peyton Intrusive Suite (Strong, 1979; Blackwood, 1982; Dickson, 1993; Sandeman et al., 2017), and latest Silurian monzonite intrusions in the southern part of the Botwood basin (Fig. 2; Colman-Sadd et al., 1990; Rogers et al., 2005; Honsberger et al., 2020a). A critical unit of the Botwood Group is an ~28 × 15 km felsic volcanic rock sequence (Stony Lake volcanic rocks) constrained by two independent U-Pb ages at ca. 422 Ma (Fig. 2; Dunning et al., 1990; McNicoll et al., 2008). Based on a lack of structural fabric in the volcanic rocks and an absence of exposed contact relationships, the Stony Lake volcanic rocks were inferred to lie unconformably on sandstones of the Botwood Group (e.g., Dunning et al., 1990; Williams et al., 1993; Pollock et al., 2007); however, observations presented in van Staal et al. (2014) suggests that these volcanic rocks may be interstratified with, or underlie, sedimentary rocks of the Botwood Group.

The Botwood basin narrows considerably toward the southwest and to the northeast (Colman-Sadd et al., 1990; O’Brien, 2003; Rogers et al., 2005). In the southwest, it is composed of the gold-mineralized Rogerson Lake Conglomerate, which is an unmetamorphosed to lower greenschist facies, purplish-gray to gray polymict conglomerate (±intercalated gray to pinkish sandstone). The Rogerson Lake Conglomerate is typically poorly sorted and clast supported and contains locally sourced, deformed to undeformed, pebble- to cobble-sized clasts of felsic igneous rocks, mafic volcanic rocks, sandstone, siltstone, shale, and jasper, within a matrix of sand, silt, and clay (Figs. 3A and 3B; Kean and Jayasinghe, 1980; Rogers et al., 2005; Pollock et al., 2007; this study). The Rogerson Lake Conglomerate is associated with gold-mineralized felsic volcanic (Fig. 3C) and volcaniclastic rocks, granitoid and gabbro bodies, and locally cut by chloritoid-bearing mafic dikes; hence, peak metamorphism of these rocks locally reached lower greenschist facies (Yardley, 1989; Figs. 3D and 3E). Deformed structural panels of the Rogerson Lake Conglomerate are preserved along a southwest-northeast structural corridor that parallels, and occurs in the overall structural footwall of, the crustal-scale Victoria Lake Shear Zone in central Newfoundland (Fig. 2; Rogers et al., 2005; van Staal et al., 2005). The Rogerson Lake Conglomerate structural corridor hosts a highly prospective orogenic gold system, which includes an approximately four to five million ounce gold deposit in Neoproterozoic rocks at Valentine Lake (Lincoln et al., 2018) and numerous gold showings and prospects hosted within the conglomerate (e.g., Wilding Lake prospect; Figs. 1 and 2; Evans, 1996; Honsberger et al., 2019a, 2019b, 2020b). The gold-mineralized Neoproterozoic rocks at Valentine Lake include trondhjemite, tonalite, gabbro, and mafic dikes of the Valentine Lake Intrusive Suite (Fig. 3F; Evans et al., 1990; van Staal et al., 2005; Rogers et al., 2006; Lincoln et al., 2018).

Southeast of the gold-mineralized Rogerson Lake Conglomerate corridor, Silurian to Devonian granitoid rocks (e.g., a large volume of the North Bay Granite Suite, ca. 417–400 Ma; Dickson, 1990; Dunning et al., 1990; Kerr, 1997) intrude metasedimentary and associated rocks of the southeasternmost Dunnage Zone where they are structurally imbricated with Gander Zone assemblages along the Victoria Lake Shear Zone (Fig. 2). In central Newfoundland, the Gander Zone assemblages are subdivided into the Meelpaeg Subzone in the southwest and the Mount Cormack Subzone in the northeast (Fig. 2; Williams et al., 1988). The southwestern continuation of the Victoria Lake Shear Zone is the highly strained, southeast-dipping Cape Ray Fault Zone (Fig. 1; Wilton, 1983; Dubé et al., 1996; Dubé and Lauzière, 1997). The Cape Ray Fault Zone is delineated by a panel of Ordovician bimodal volcanic and clastic sedimentary rocks, including mylonitized polymict conglomerate, greywackes, and siltstones (Dubé et al., 1996; van Staal et al., 1996). Structurally controlled gold mineralization along the Cape Ray Fault Zone represents another prospective orogenic gold deposit in Newfoundland (Dubé and Lauzière, 1997; Wardle, 2005; Matador Mining Ltd., 2020).

Three structural cross-sections presented in Figures 46 are based on fieldwork in the present study and existing geological maps (see Fig. 2 caption for references). Northeast-southwest–striking bedding and foliation, as well as fold axes, in the unmetamorphosed to lower greenschist facies Rogerson Lake Conglomerate are generally subparallel to the crustal-scale fault planes that control orogenic gold mineralization. In the present interpretation, the Rogerson Lake Conglomerate and associated orogenic gold mineralization are confined to a geometrical triangle zone–like structural domain (e.g., Couzens and Wiltschko, 1996; Jones, 1996) that is defined by a change in vergence of fault systems from southeast-dipping to northwest-dipping across central Newfoundland (Figs. 46). The southeast-dipping fault system includes the Wood Brook fault and Victoria Lake Shear Zone, which are Devonian structures in central Newfoundland that overrode the Gander-Dunnage Zone boundary and emplaced metamorphic rocks of the Meelpaeg nappe during the Acadian orogenic cycle (Van der Velden et al., 2004; Valverde-Vaquero et al., 2006; van Staal and Barr, 2012). The northwest-dipping fault system, which includes the Red Indian Line, was formed during latest Ordovician to Middle Silurian collision of the Penobscot-Victoria arc system with composite Laurentia (Figs. 46; van Staal et al., 1998; Zagorevski et al., 2007).

At Valentine Lake, a truncated synformal panel of the Rogerson Lake Conglomerate occurs structurally between the Valentine Lake Intrusive Suite to the northwest and felsic volcanic rocks of probable Late Silurian age to the southeast (Fig. 4, A–A′). The panel of the Rogerson Lake Conglomerate is juxtaposed against the Valentine Lake Intrusive Suite along a steeply northwest-dipping, sheared unconformity with a reverse sinistral shear sense, referred to as the Valentine Lake Shear Zone (Figs. 2, 3F, and 4; Lincoln et al., 2018). The coarse-grained, locally derived granitoid clasts in the Rogerson Lake Conglomerate along the Valentine Lake Shear Zone (Fig. 3B), combined with regional measurements of bedding in the conglomerate, suggest an overall stratigraphic younging-direction toward the southeast (Figs. 46). The fault splay that bounds the southeastern margin of the Rogerson Lake Conglomerate near Valentine Lake, the Wood Brook fault (Valverde-Vaquero et al., 2006), is correlative sensu lato with the Dog Bay Line in north-central Newfoundland (Fig. 1; Williams, 1993; Williams et al., 1993), which is a zone of strong deformation and faulting in the northeastern Botwood basin (Dickson, 2006; Dickson et al., 2007; Pollock et al., 2007).

Northeast and along-strike of Valentine Lake, orogenic gold mineralization is hosted in the Rogerson Lake Conglomerate and associated felsic volcanic and volcaniclastic rocks that comprise the Wilding Lake prospect (Honsberger et al., 2019a, 2019b). In this area of central Newfoundland (Fig. 5, B–B′), the Rogerson Lake Conglomerate and associated igneous rocks occur within two deformed structural blocks that are juxtaposed along the Wood Brook fault (Fig. 5B; Honsberger et al., 2020a), where the northeastern extension of the Valentine Lake Shear Zone places the Rogerson Lake Conglomerate against Neoproterozoic volcanic rocks. The southeastern boundary of the Rogerson Lake Conglomerate is truncated by a northwest-directed fault splay that uplifts Ordovician rocks of the Red Cross Group, micaceous metasedimentary rocks that are correlative with the Gander Zone, and a latest Silurian monzogranite at Wilding Lake that stitches the Dunnage–Gander Zone boundary (Fig. 5).

Northeast along-strike toward the Botwood basin, the Victoria Lake Shear Zone merges with the northwest-directed Great Burnt Lake Shear Zone (Piasecki, 1995; Figs. 2 and 6, C–C′), which forms the structural base of Ordovician high-grade metamorphic rocks of the Mount Cormack Subzone (Rivers et al., 1990; Owen, 1992) while overriding the Stony Lake felsic volcanic rocks and associated clastic sedimentary rocks of the southern Botwood basin with gold-mineralized monzonite intrusions (Fig. 6; Anderson and Williams, 1970; Barbour and Churchill, 1999; Evans and Vatcher, 2009). The Stony Lake felsic volcanic rocks may be preserved as a dome-like structure that is conformable with the southern portion of the Botwood basin (Figs. 2 and 6). The Rogerson Lake Conglomerate is not well preserved in this area; although, Neoproterozoic rocks correlative with the Valentine Lake Intrusive Suite (Sandy Brook Group and Crippleback Lake Intrusive Suite, Rogers et al., 2006) are cut by a structure that may correlate with the Valentine Lake Shear Zone (Fig. 6; e.g., O’Brien, 2003; Rogers and van Staal, 2005a, 2005b). The fault zone bounding the northwestern margin of the Crippleback Lake Intrusive Suite correlates with the Northern Arm fault to the northeast (Figs. 1, 2, and 6; e.g., O’Brien, 2003; Rogers and van Staal, 2005a, 2005b).

The ~4–5 Moz (million ounce) orogenic gold deposit at Valentine Lake is defined by mineralized, moderately to steeply dipping fault-fill and shallowly dipping extensional quartz vein sets that cut Neoproterozoic tonalite of the Valentine Lake Intrusive Suite along the Valentine Lake Shear Zone (Fig. 4; Lincoln et al., 2018). Gold-mineralized, quartz-tourmaline-pyrite (“QTP”) vein systems and associated geology at Valentine Lake are comparable lithologically and structurally to orogenic gold systems of the Abitibi greenstone belt (e.g., Robert and Poulsen, 2001; Marathon Gold Corp. [Mountain Lake Resources Inc., July 2012 press release]; Honsberger and Bleeker, 2018; Lincoln et al., 2018).

Approximately 30 km northeast of the Valentine Lake deposit, high-grade gold-mineralized, locally tourmaline-bearing quartz veins of the Wilding Lake prospect cut the siderite-, ankerite-, and sericite-altered Rogerson Lake Conglomerate and associated felsic volcanic rocks (Fig. 5; Evans and Vatcher, 2016; Honsberger et al., 2019b, 2020a). Detailed mapping and structural analysis of two gold-bearing vein systems that are ~1 km apart (Elm Zone and Alder Zone) indicate that the gold mineralization is associated with at least four generations of structurally controlled vein sets (Figs. 7 and 8; Honsberger et al., 2019b). In the Elm Zone, a moderately southeast-dipping, semi-continuous, laminated quartz fault-fill shear vein (V1b) that ranges from less than 0.5–2 m thick is exposed for ~230 m along strike, and is associated with 5–10-cm-thick, gently southeast-dipping, extensional quartz veins (V1a) that emanate from the main shear vein (Figs. 79A) and form typical “flat veins.” In the Alder Zone, a network of 2–4-cm-thick, interconnected, anastomosing quartz veins form a main shear vein, which reaches ~1 m in thickness and can be traced for ~35 m (Fig. 7A). An early, generally east-west–striking, foliation (S1) in the Rogerson Lake Conglomerate is rotated counter-clockwise into parallelism with the main shear veins in both locations to form an S2 fabric, which is consistent with sinistral kinematics (Figs. 79A). Furthermore, south-southwest to south-southeast–plunging slickenlines on the main shear veins indicate north-northeast to north-directed reverse sinistral motion (Figs. 7B and 8).

Three sets of younger extensional quartz veins and fractures (V2, V3, and V4) overprint the oblique reverse shear vein systems in the Rogerson Lake Conglomerate (Figs. 79C). Vein sets V2 and V4 are steep, generally east-west–striking, massive quartz veins that range from less than 5 cm to more than 30 cm in thickness, whereas moderately northwest-dipping extension fractures containing vuggy quartz characterize V3 (Figs. 89C). V3 veins are oriented subparallel to a chloritoid-bearing mafic dike adjacent to the Elm Zone (Fig. 8). Subvertical V4 veins display dextral asymmetry with respect to vein tail geometry implying that late-stage strike-slip was operative locally, but also may reflect a regional phase of dextral transpression (e.g., O’Brien, 2003). All quartz vein sets are associated spatially (V1–4) and cut the same deformed fabric (S1-S2) in the Rogerson Lake Conglomerate, thus, likely formed relatively close in time when the hydrothermal system was active. A late, shallowly dipping cleavage defines the axial planes of locally developed, mesoscopic, reclined to recumbent folds that overprint all structures in the study area (Figs. 7B and 9A).

Primary hydrothermal mineral assemblages in structurally controlled veins of the Wilding Lake prospect (Figs. 5 and 7) consist of quartz, pyrite, chalcopyrite, tourmaline, rutile, and gold, whereas secondary alteration assemblages include malachite (Cu2(CO3)(OH)2), goethite (FeO(OH)), bornite (Cu5FeS4), acanthite (Ag2S), fischesserite (Ag3AuS2), lenaite (AgFeS2), hematite, native silver, silver-poor electrum, antimony-bearing siderite, bismuth, gold, and silver-gold and bismuth tellurides and sulfosalts (Figs. 9D9F). Native gold occurs in all vein sets either as free gold in quartz, blebs in goethite-altered pyrite and chalcopyrite, or as wire gold in goethite-altered fractures that cut pyrite and chalcopyrite grains (Figs. 9D and 9E). Furthermore, gold occurs with pyrite and chalcopyrite grains that display alteration mantles consisting of Ag-Fe-Cu-S-bearing minerals such as lenaite and bornite (Fig. 9F). In addition to gold mineralization, felsic volcanic rocks of the Wilding Lake prospect (Figs. 3C and 5B) also locally host galena, sphalerite, pyrite, and arsenopyrite-bearing, quartz-vein-related mineralization (Honsberger et al., 2020b).

U-Pb analyses of zircon crystals from six igneous rocks were performed at the Jack Satterly Geochronology Laboratory (JSGL) in the Department of Earth Sciences at the University of Toronto following chemical abrasion–isotope dilution–thermal ionization mass spectrometry (CA-ID-TIMS) methods (Supplemental Material 1 and 21). Additionally, U-Pb ID-TIMS analyses of rutile crystals from tourmaline-bearing quartz veins of the Wilding Lake prospect and Valentine Lake deposit were carried out, respectively, at JSGL and Memorial University of Newfoundland (Supplemental Materials 1 and 2). U-Pb data are summarized in Table 1 and plotted graphically in Figure 10.

Sample 1: BNB18-IHNL-008, Monzonite Intrusion, Paradise Lake

Abundant, unaltered, euhedral zircon crystals were recovered from a monzonite intrusion in the Botwood basin at Paradise Lake (Fig. 2). Four concordant U-Pb results, from three single grains and one fraction of two grains, yield 206Pb/238U dates with a weighted mean age of 420.69 ± 0.77 Ma (MSWD = 3.4; Fig. 10A), which is interpreted as the time of emplacement of the intrusion. Slight scatter of one analysis to the left of the concordia curve possibly reflects analytical bias on the 207Pb measurement.

Sample 2: BNB19-IHNL-317, Monzonite Intrusion, Sandy Lake

Abundant, lath-like zircon crystals were recovered from an auriferous monzonite intrusion in the southernmost part of the Botwood basin near Sandy Lake (Fig. 2). U-Pb results for three platy single zircon grains are concordant and overlapping and give a weighted mean 206Pb/238U age of 422.06 ± 0.47 Ma (MSWD = 1.3; Fig. 10B). This is interpreted as the best age estimate for crystallization of the Sandy Lake monzonite and maximum age for the contained gold mineralization.

Sample 3: BNB18-IHNL-197, Felsic Volcanic Rock, Wilding Lake Prospect

Abundant, unaltered, subhedral to euhedral zircon crystals were recovered from a mineralized felsic volcanic unit of the Wilding Lake prospect. The two youngest results of 9 zircon fractions analyzed were concordant and overlapping. These have a weighted mean 206Pb/238U age of 422.42 ± 0.62 Ma (MSWD = 0.29; Fig. 10C), which is interpreted as the best age estimate for deposition of the volcanic rock. Six older concordant results (z2–7), which range in age from 426.6 Ma to 423.8 Ma, are interpreted as either xenocrysts or antecrysts. The oldest (z1) plots discordantly and if anchored at ca. 422 Ma, projects to ca. 2.33 ± 0.4 Ga.

Sample 4: BNB18-IHNL-080b, Feldspar Porphyry, Wilding Lake Prospect

Abundant, variably altered zircon crystals, and translucent euhedral grains, were recovered from a mineralized plagioclase feldspar porphyry of the Wilding Lake prospect. Initial U-Pb analyses of three zircon grains (a clear fragment with undefined original morphology, a zircon tip, and two long prismatic crystals with square cross-sections) produced concordant 206Pb/238U dates of 576 Ma, 558 Ma, and 422.3 ± 0.5 Ma, respectively. The older dates were obtained on inherited grains and a focus was placed on dating only elongate grains with square cross-sections. Concordant results from such grains gave 206Pb/238U dates of 426.58 ± 0.77 Ma and 424.34 ± 0.72 Ma (z3–4), which are considered dates from inherited grains. Data for three additional analyses provide a weighted mean 206Pb/238U age of 422.17 ± 0.38 Ma (z5–7; MSWD = 0.91; Fig. 10D), which is considered the best age estimate for emplacement of the porphyry. Results for one slightly discordant (z8) and one significantly discordant (z9) grain analysis are interpreted as having lost Pb and are therefore not included in the age estimation.

Sample 5: BNB19-IHNL-295, Undeformed Monzogranite, Wilding Lake Pluton

Euhedral, short prismatic and elongate zircon crystals were recovered from an undeformed monzogranite, the Wilding Lake pluton, which intrudes rocks southeast of the Wood Brook fault (Fig. 2). Analysis of five single zircon crystals produced a cluster of concordant results. The weighted mean 206Pb/238U age of all five results gives an age of 421.80 ± 0.77 Ma (MSWD = 2.5). If we assume that the two youngest grains have lost a minor amount of Pb, the weighted mean age is 422.22 ± 0.45 Ma (MSWD = 0.37), which is considered the best age estimate for emplacement of the monzogranite (Fig. 10E).

Sample 6: BNB18-WL-029, Granodiorite Basement, Wilding Lake Prospect

Abundant, variably altered, subhedral zircon crystals were recovered from a drill core sample of granodiorite (Wilding Lake prospect) that underlies the Rogerson Lake Conglomerate. U-Pb analysis of three fresh, pink shards of zircon from this granodiorite produced two concordant and overlapping dates with a weighted mean 206Pb/238U age of 564.0 ± 4.3 Ma (MSWD = 3.1 Ma; Fig. 10F), and a 207Pb/206Pb weighted mean age of 565.0 ± 2.3 Ma (MSWD = 0.31). The third result was discordant toward ca. 400 Ma, which may reflect extensive Pb loss through micro-cracks, despite the generally pristine appearance of the crystal, or, less likely, younger zircon growth. The ca. 565 Ma age is consistent with peri-Gondwanan Neoproterozoic rocks of the Crippleback Lake and Valentine Lake intrusive suites and Sandy Brook Group in central Newfoundland (Evans et al., 1990; Rogers et al., 2006).

Sample 7: BNB18-IHNL-180, Mineralized Quartz Vein, Wilding Lake Prospect

Translucent, orange rutile crystals were recovered from a mineralized hydrothermal quartz vein (V4) in the Elm Zone of the Wilding Lake prospect (Fig. 7). U-Pb analysis of four single rutile crystals yield 206Pb/238U dates of 407 ± 4 Ma, 403 ± 9 Ma, 395 ± 6 Ma, and 393 ± 3 Ma (Fig. 10G). The weighted mean of all 4 results gives an average age that has a mean square of the weighted deviates (MSWD) of 10. An MSWD of 1 or slightly higher is expected in a unimodal age population when analytical errors are correctly chosen; however, our MSWD of 10 for all 4 results indicates that the scatter is likely due to geological reasons. Rutile is not expected to contain inherited components in a hydrothermal environment, which would bias the dates toward an older age. Therefore, the older two overlapping dates are interpreted to most closely represent the time of rutile crystallization, whereas the younger dates probably reflect a minor amount of Pb loss. The mean age of the two older results is 406.7 ± 3.8 Ma (MSWD = 0.67), which is taken as the best but minimum age estimate for the time of rutile crystallization given the possibility of Pb loss.

Sample 8: VL313-245, Mineralized Quartz Vein, Valentine Lake Deposit

High-quality (euhedral, inclusion free), orange rutile crystals were recovered from a hydrothermal quartz-tourmaline-pyrite vein (V1a) of the Valentine Lake deposit and separated into three fractions of three, five, or six crystals for dissolution, chemical separation, and analysis. There is insufficient 207Pb in these samples to trust 207Pb/235U or 207Pb/206Pb ages and this is reflected in the large uncertainties parallel to the X axis of the concordia diagram. The individual 206Pb/238U ages and uncertainties are: R1 = 410.3 ± 8.6 Ma, R2 = 410.7 ± 6.2 Ma, R3 = 411.0 ± 6.2 Ma. The weighted average of these three overlapping 206Pb/238U ages is 411 ± 4 Ma (MSWD = 0.008; Fig. 10H). We note that both of our rutile ages overlap within error.

Lithogeochemical methods are described in Supplemental Material 2, whereas data for bimodal igneous rocks associated with the Rogerson Lake Conglomerate and Botwood Group are presented in Figures 1113 and Supplemental Material 3 (Tables S1 and S2; see footnote 1). Some scatter in alkali and large ion lithophile elements may reflect local mobilization during lower greenschist facies metamorphism or lower grade hydrothermal alteration; however, overall regional consistency in lithogeochemical data implies that alteration processes did not completely obscure igneous chemical signatures (e.g., Pearce et al., 1984; Wilson, 1989).

Mafic dikes that intrude the Rogerson Lake Conglomerate and Botwood basin range from basalt (gabbro) to andesite (leucodiorite) in terms of their total alkali and SiO2 contents, and all are basalt in the immobile trace element classification plot of Pearce (1996) (Figs. 11A and 11B). The dikes are transitional between the calc-alkaline and tholeiitc magma series, whereas basaltic andesite to andesite of the Botwood Group in north-central Newfoundland (Laurenceton Formation, Table S2) is transitional to calc-alkaline in composition (Figs. 11A11C). In contrast, strongly sheared and altered Ordovician basaltic andesite and andesite are tholeiitic (Red Cross Group, Figs. 11A11C). Latest Silurian (U-Pb samples 3–5; Stony Lake volcanic rocks, Table S2), and locally Ordovician (deformed monzogranite), felsic igneous rocks along the Rogerson Lake Conglomerate corridor are rhyolite and granite, whereas latest Silurian monzonite intrusions in the southern portion of the Botwood basin (U-Pb samples 1 and 2) have higher alkali to silica ratios and intermediate silica concentrations similar to drilled Neoproterozoic granodiorite (Figs. 11A and B). On the SiO2 versus Fe* (FeOtot / (FeOtot +MgO)) plot (Frost et al., 2001; Frost and Frost, 2008), Ordovician to latest Silurian felsic igneous rocks are ferroan and distinct from magnesian Neoproterozoic granodiorite (Fig. 11D). Collectively, latest Silurian bimodal igneous rocks associated with the Rogerson Lake Conglomerate and Botwood basin overlap compositionally with mafic and felsic phases of the Mount Peyton Intrusive Suite (Figs. 1, 2, and 1113; Dickson and Kerr, 2007; Sandeman et al., 2017).

The Nb/Y versus Y + Nb plot (Fig. 12A, Whalen and Hildebrand, 2019) discriminates arc, slab failure, and A-type granitic compositions (e.g., Pitcher, 1983, 1993; Barbarin, 1990), which are further subdivided into post-collisional compositions following slab failure (A2) and compositions consistent with emplacement in a continental rift or ocean island (A1; Eby, 1990, 1992). Latest Silurian felsic igneous rocks plot entirely in the A2 field, whereas the single sample of Neoproterozoic granodiorite basement from drill-core plots in the arc field (Fig. 12A). The Th/Yb versus Nb/Yb diagram (Pearce, 2008) is utilized for discriminating magmatic interaction with Th-enriched continental crust or lithospheric mantle because oceanic basalt compositions fall consistently along a diagonal mantle array, whereas rocks formed on continental margins and in volcanic arcs plot above the array (Fig. 12B). All latest Silurian bimodal igneous rocks of central Newfoundland plot above the oceanic basalt array, with mafic dikes retaining lower Th/Yb and Nb/Yb values than felsic igneous rocks and Botwood Group basalt (Fig. 12B).

Mafic dikes that cut the Rogerson Lake Conglomerate and southern portion of the Botwood basin exhibit multi-element patterns generally similar to basalts of the Botwood Group and gabbro of the Mount Peyton Intrusive Suite (Figs. 13A and 13B). Primitive mantle-normalized multi-element patterns for these mafic rocks display minor to moderate enrichment in light rare-earth elements (LREE) relative to heavy rare-earth elements (HREE), as well as modest to prominent negative Nb anomalies with respect to Th and La (Figs. 13A and 13B). Latest Silurian felsic igneous rocks have overlapping multi-element patterns, with moderate to prominent negative Sr, Ba, Nb, P, and Ti anomalies similar to Mount Peyton granite (Figs. 13C and 13D). An altered felsic volcanic rock clast from the Rogerson Lake Conglomerate of the Wilding Lake prospect retains trace element concentrations and a multi-element pattern that are similar to drilled Neoproterozoic granodiorite basement and other igneous rocks of the Valentine Lake and Crippleback Lake intrusive suites (Fig. 13E; Table S2).

Deposition of the Rogerson Lake Conglomerate and Botwood Basin

Regionally, sedimentary and volcanic rocks of the Botwood Group disconformably overlie 433 Ma and older sedimentary rocks of the Badger Group (e.g., O’Brien, 2003; van Staal et al., 2014), which were deformed during the Salinic orogenic cycle (van der Pluijm et al., 1993). Considering that the Badger Group–Botwood Group unconformity may represent a time gap of up to seven million years (ca. 433–426 Ma, van Staal et al., 2014), and that a ca. 420 Ma monzonite intrudes the Botwood basin (Fig. 10A), deposition of sedimentary rocks in the southern portion of the Botwood basin may be bracketed between ca. 426 Ma and ca. 420 Ma. Moreover, the close association of ca. 422 Ma igneous rocks with the Rogerson Lake Conglomerate implies that the Rogerson Lake Conglomerate was deposited in the late Ludlow–Pridoli during lithospheric extension at approximately the same time as syntectonic magmatism. If felsic volcanic rock clasts in the Rogerson Lake Conglomerate (Fig. 3A) were sourced partly from the ca. 422 Ma rocks, unroofing of the syntectonic magmatic rocks during extension may have contributed to the deposition of the Rogerson Lake Conglomerate sequence. Farther northeast where the Botwood basin is widest (Fig. 1), deposition was probably initiated earlier, prior to extensional emplacement of the ca. 425–418 Ma Mount Peyton Intrusive Suite (Sandeman et al., 2017).

As confirmed by drilling (Evans and Vatcher, 2016), the Rogerson Lake Conglomerate is a basal unit in the Wilding Lake area that occurs nonconformably above Neoproterozoic rocks that are correlative with the Crippleback Lake and Valentine Lake intrusive suites (Fig. 10F; Evans et al., 1990; Rogers et al., 2006). Granitoid clasts in the Rogerson Lake Conglomerate at Valentine Lake (Fig. 3B), combined with multi-element signatures for a clast at Wilding Lake (Fig. 13E), suggest that the underlying Neoproterozoic rocks are included as clasts in the Rogerson Lake Conglomerate. This implies syntectonic deposition of the Rogerson Lake Conglomerate during uplift of the underlying Neoproterozoic rocks. If syntectonic extension was diachronous from northeast to southwest across central Newfoundland, the Rogerson Lake Conglomerate may represent a time-transgressive, basal sedimentary unit of the Botwood basin, as opposed to the stratigraphic top of the Botwood Group (Pollock et al., 2007). Relatively undeformed sandstone at the top of the Rogerson Lake Conglomerate stratigraphy in central Newfoundland (e.g., Figs. 3A and 5B) could represent molasse deposition associated with the onset of Early Devonian, Acadian compression and thrusting. The only absolute age constraints on Acadian deformation of the Rogerson Lake Conglomerate are the ca. 410 rutile ages herein from cross-cutting mineralized quartz veins (Fig. 10H). Further high-precision detrital zircon geochronology is required to fully establish lateral correlations in stratigraphy between the Rogerson Lake Conglomerate and Botwood Group farther to the northeast.

Implications of Latest Silurian Magmatism

Enrichment of Fetotal in the 422–420 Ma felsic igneous rocks, coupled with elevated Y and Nb concentrations, is consistent with post-collisional, A-type granite compositions (Figs. 11C11D and 12; Pitcher, 1983; Frost et al., 2001; Whalen and Hildebrand, 2019). The occurrence of transitional to calc-alkaline mafic rocks and ferroan felsic igneous rocks with clastic sedimentary rocks of the Rogerson Lake Conglomerate and Botwood basin is consistent with bimodal magmatism in a within-plate, extensional environment (Figs. 2, 3, 11, and 12). Multi-element patterns for all rocks display prominent negative Nb anomalies with respect to Th and La (Fig. 13), indicating an origin through partial melting of crust and/or mantle that have been modified by subduction zone processes (e.g., Green, 1995; Tiepolo et al., 2001; Larocque and Canil, 2010).

In collision zones, slab break-off may cause asthenospheric and lithospheric decompression melting, which in turn may cause ascending mantle-derived magmas to interact with the lower to middle crust as extension occurs during uplift and collapse of the lithosphere (Pitcher, 1983, 1993; Barbarin, 1990, 1999). The mafic rocks generated through such a process are transitional, tholeiitic to calc-alkaline rocks that closely resemble continental tholeiites of large igneous provinces (e.g., Parana-Etendeka traps, South America; Peate and Hawkesworth, 1996). In this context, the 422–420 Ma ferroan felsic magmas are likely anatectic products of the lower to middle crust associated with higher heat flow accompanying emplacement of mantle-derived basaltic magmas (Strong and Dupuy, 1982). The contemporaneous mafic and felsic magmas may undergo mixing during ascent and storage in the crust. Accordingly, 422–420 Ma magmatism is interpreted to have occurred during a transient phase of lithospheric extension immediately following the terminal compressional phase of the Salinic orogenic cycle, and immediately prior to Early Devonian compression that marks the onset of the Acadian orogenic cycle in southern Newfoundland (ca. 420 Ma; Dunning et al., 1990; van Staal and Barr, 2012; van Staal et al., 2014). Continental extension-related bimodal magmatism associated with the transition from the late Salinic to the early Acadian orogenic cycle is also documented along-strike in gold-mineralized terranes of the New Brunswick Appalachians (Van Wagoner et al., 2002; Wilson et al., 2017).

The 422–420 Ma ages for felsic magmatism in central Newfoundland are comparable with latest Silurian crystallization ages for the Stony Lake felsic volcanic rocks (423 +3/−2 Ma, Dunning et al., 1990; 422 ± 2 Ma, McNicoll et al., 2008), as well as latest Silurian to Early Devonian ages for the bimodal Mount Peyton Intrusive Suite (ca. 425–418 Ma, Sandeman et al., 2017). Furthermore, a 422 ± 2 Ma age is documented for a composite dike adjacent to, and immediately west of the Dog Bay Line along the north-central Newfoundland coast (Elliott et al., 1991). The 420 Ma age for the monzonite intrusion in the southwest portion of the Botwood basin (U-Pb sample 1) is comparable to a lower intercept zircon age of 420 ± 2 Ma for a granite from the bimodal Fogo Island Intrusive Suite (Aydin, 1995; Kerr, 2013; Donaldson et al., 2015), as well as a 421.2 ± 0.6 Ma age for the associated basal rhyolite of the Brimstone Head Formation, a correlative of the Botwood Group on Fogo Island (Hamilton and Kerr, 2016). Crystallization ages of 421 ± 4 Ma for felsic volcanic breccia of the Laurenceton Formation (Botwood Group) in north-central Newfoundland, and 418.5 ± 4 Ma for felsic tuff of the Botwood Group along the north-central coast (van Staal et al., 2014), overlap within error the 422–420 Ma phase of magmatism in central Newfoundland. In southwestern Newfoundland, latest Silurian crystallization ages are recorded in gabbro (424 +4/−3 Ma) and granite (424 ± 2 Ma) that intrude Ordovician volcanic and sedimentary rocks of the Windsor Point Group (Brown, 1972) along the Cape Ray Fault Zone (Wilton, 1985; Dubé et al., 1996; van Staal et al., 1996). Ultimately, consistency in regional geochronological data for latest Silurian igneous rocks suggests that ca. 422 Ma magmatism was widespread along the length of the northeast-trending, gold-mineralized corridor of the eastern Dunnage Zone from Cape Ray to Fogo Island (Fig. 1).

Structural Controls on Gold Mineralization

Orogenic gold mineralization in central Newfoundland is hosted by Neoproterozoic granitoid rocks and overlying latest Silurian, syntectonic sedimentary and volcanic rocks that occupy a triangle zone–like structural domain (e.g., Couzens and Wiltschko, 1996; Jones, 1996; Figs. 46) between the northwest-dipping Valentine Lake Shear Zone and the southeast-dipping Wood Brook fault, both of which are interpreted to be second order structures associated with a first-order detachment fault at depth (Figs. 46). The triangle zone–like setting is interpreted to have formed in the Early Devonian based on ca. 410 Ma rutile in hydrothermal extensional veins along the Valentine Lake Shear Zone (Valentine Lake deposit) and Wood Brook fault (Wilding Lake prospect). Assuming that northwest migration of the Acadian thrust front formed the northwest-directed Wood Brook fault (e.g., Valverde-Vaquero et al., 2006; Willner et al., 2018), the Valentine Lake Shear Zone is interpreted to be a product of southeast-directed, Early Devonian backthrusting. In this model, northwest-dipping, latest Ordovician to mid-Silurian (e.g., van Staal et al., 1998; Zagorevski et al., 2007) thrust faults southeast of the Red Indian Line were reactivated as backthrusts during Early Devonian compression (Figs. 46).

The structural geology and mineralogy of the mineralized quartz vein systems in central Newfoundland (Figs. 4, 5, and 7) are characteristic of the tectonic processes that form orogenic gold deposits (e.g., Robert and Brown, 1983, 1986a, 1986b; Roberts, 1987; Sibson et al., 1988; Robert and Poulsen, 2001; Goldfarb et al., 2005; Dubé and Gosselin, 2007; Bleeker, 2015). Orogenic gold mineralization is hosted within third-order reverse shear zones that form quartz vein offshoots from the second-order Valentine Lake Shear Zone and Wood Brook fault (Figs. 4, 5, and 7). In this context, metalliferous (Au-Ag-Cu-Fe + Sb + Te + Bi), silica-rich fluids charged with sulfur and gold were channeled at depth along a first-order detachment fault, brought to the surface by second-order thrusts, and then injected into the surrounding rocks in response to changing fluid-pressure dynamics (e.g., Sibson et al., 1988). Such fault systems that form as a result of transient pore fluid overpressure in the crust are referred to as arterial faults because they channel hydrothermal fluids along interconnected fault networks (Sibson, 2019). Laminations in the main quartz veins (V1) that cut the deformed Rogerson Lake Conglomerate of the Wilding Lake prospect (Fig. 9C) are consistent with cyclic fluid injection along the reverse shear planes as a result of fluid pressure fluctuations across the brittle-ductile transition (e.g., Ramsay, 1980; Sibson et al., 1988; Cox, 1995; Robert et al., 1995; Wilkinson and Johnston, 1996; Sibson, 2004). Subsequent to initial deformation of the Rogerson Lake Conglomerate (Fig. 14A), shallowly dipping extensional veins (V1a) formed when fluid pressure first exceeded lithostatic pressure and reverse shearing was initiated, whereas moderately dipping, laminated, reverse shear veins (V1b) formed slightly later to accommodate cyclic fluid injection (Figs. 14B and 14C; e.g., Robert and Brown, 1986a, 1986b; Cox, 1995).

Structural relationships documented in detail within the third-order, reverse shear vein systems of the Wilding Lake prospect indicate that the main fault-fill and extensional vein sets (V1) are overprinted by at least three generations of quartz veins (V2–4; Figs. 7, 8, and 14D14F). Overprinting quartz vein relationships are explained by progressive changes in the directions of the principal stresses at ca. 410 Ma during ductile to brittle deformation related to the Early Devonian Acadian orogenic cycle (Fig. 14). Overlapping U-Pb rutile ages of V1b and V4 veins indicate that all generations of vein sets are close in age (ca. 410 Ma, Figs. 10 and 14). Comparable mineralogy and trace-element geochemistry of the reverse shear veins and overprinting vein sets suggest that the various vein sets formed from a common fluid source. Rotation of the principal stresses controlled the development of brittle pathways for gold-bearing, silica-rich fluids to be mobilized and deposited as younger vein sets (Figs. 14D14F). Abundant, vuggy quartz-filled fractures (V3) that cut the reverse shear veins of the Wilding Lake prospect, as well as the Rogerson Lake Conglomerate host rock, provide evidence for brittle deformation and accompanying fracture-induced fluid transport (Fig. 9C). The association of gold with secondary malachite (Cu2(CO3)(OH)2) and iron oxyhydroxide (goethite), combined with dissolution-related alteration textures, is consistent with late-stage supergene alteration of gold-mineralized rocks in central Newfoundland (Figs. 9D9F; e.g., Reich and Vasconcelos, 2015).

Timing of Orogenic Gold Mineralization

The ca. 410 Ma ages for primary hydrothermal rutile in mineralized quartz veins in central Newfoundland (Figs. 10G and 10H) are interpreted as the best estimates for the timing of Early Devonian quartz vein emplacement and orogenic gold mineralization. These ages post-date Salinic metamorphism in the Dunnage Zone (443–421 Ma, Willner et al., 2018) and are compatible with Acadian thrusting after ca. 418 Ma in central Newfoundland (Dunning et al., 1990; Valverde-Vaquero et al., 2000, 2006; Van der Velden et al., 2004) and ca. 415–410 Ma Acadian ductile deformation in north-central Newfoundland (McNicoll et al.., 2006). Along the Cape Ray Fault Zone in southwestern Newfoundland, metamorphic monazite and titanite record Acadian reverse sinistral shearing between ca. 415 Ma and 412 Ma (Dunning et al., 1990; Dubé et al., 1996). The ca. 410 Ma ages also correspond with two identical 406 ± 2 Ma 40Ar/39Ar plateau ages for sericite from the Mosquito Hill gold prospect along the southeastern margin of the Mount Cormack Subzone in central Newfoundland (Fig. 1; Sandeman et al., 2013), as well as with latest Silurian to Early Devonian oblique sinistral transpression documented throughout southwestern and north-central Newfoundland (e.g., Currie and Piasecki, 1989; O’Brien et al., 1993; Hibbard, 1994; Dubé et al., 1996; O’Brien, 2003; Sandeman et al., 2018).

Pyrite Re-Os geochronology from orogenic gold-bearing veins along splays of the Baie Verte–Brompton Line fault system in northwest-central Newfoundland yielded ages of 420 ± 7 Ma and 411 ± 7 Ma for the Stog’er Tight and Pine Cove deposits, respectively (Kerr and Selby, 2012), whereas hydrothermal zircon from the Stog’er Tight deposit was dated at 420 ± 5 Ma (Fig. 1; Ramezani et al., 2000). Farther west in the Humber Zone along White Bay (Fig. 1), 40Ar/39Ar geochronology along splays of the Doucers Valley Fault Zone brackets orogenic gold mineralization between 419 Ma and 408 Ma (Kerr and van Breemen, 2007; Minnett et al., 2012). These geochronological data suggest that orogenic gold mineralization along the Baie Verte–Brompton Line and Doucers Valley fault systems may have occurred prior to ca. 410 Ma. Regardless, north- and northwest-dipping thrust faults that host mineralization along the Baie Verte–Brompton Line (Poulsen et al., 2000) are incompatible with Early Devonian westward migration of southeast-dipping Acadian thrusts across the Dunnage Zone (Willner et al., 2018). The gold-mineralized, north- and northwest-dipping fault splays of the Baie Verte–Brompton Line system may instead represent latest Ordovician to Middle Silurian, or older, thrust splays that were reactivated as backthrusts in the latest Silurian to Early Devonian, potentially as a result of far-field compression associated with collision of Avalonia and composite Laurentia.

Hydrothermal xenotime from a gold-mineralized vein of the Nugget Pond deposit near the Baie Verte–Brompton Line records a Late Devonian age of 374 ± 8 Ma (Sangster et al., 2008), similar to an 40Ar/39Ar plateau age of 374 ± 1 Ma (Sandeman and Dunning, 2016) for secondary muscovite associated with late-stage gold mineralization along White Bay in the Humber Zone of western Newfoundland (Fig. 1). These ages are consistent with Late Devonian gold mineralization along the Baie Verte–Brompton Line and Doucers Valley fault systems (Kerr and Selby, 2012), which begs the question as to whether the central Newfoundland fault system also hosts an as yet unrecognized phase of Late Devonian gold mineralization.

Tectonic Evolution

In the Humber Zone and western Dunnage Zone of Newfoundland, bimodal magmatism related to the Salinic orogenic cycle ranges in age from ca. 450 Ma to ca. 423 Ma, with voluminous felsic magmatism at ca. 427 Ma (Dunning et al., 1990; Kerr, 1997; Whalen et al., 2006; van Staal et al., 2014; Sandeman and Dunning, 2016). In the eastern Dunnage Zone, immediately to the west of the Salinic suture zone, post-Salinic bimodal igneous rocks range in age from ca. 425 Ma to 418 Ma, with a widespread pulse of felsic magmatism at ca. 422 Ma (Fig. 10). A transition from arc to non-arc magmatism at ca. 434 Ma (Sandeman and Dunning, 2016) in the Humber Zone during Early Silurian (Telychian) Salinic collision of Ganderia with composite Laurentia is interpreted to correspond to the initiation of slab rollback-related magmatism, which gets progressively younger west to east across central Newfoundland toward the Salinic suture zone (Whalen et al., 2006; van Staal et al., 2014). In this model, ca. 425 Ma to 418 Ma bimodal magmatism resulted from slab steepening, tear, and break-off during rollback (Fig. 15A). A-type (A2) geochemical signatures for ca. 422 Ma felsic igneous rocks (Fig. 12A) are consistent with late syn- to post-collisional uplift and lithospheric extension (e.g., Pitcher, 1983, 1993; Barbarin, 1990); therefore, it is reasonable that deposition of the rocks of the southern portion of the Botwood basin and Rogerson Lake Conglomerate corridor accompanied crustal uplift and extension produced by rising, return flow asthenosphere initiated by slab break-off just prior to ca. 425 Ma (Fig. 15A; e.g., Whalen et al., 2006). Comparable tectonic models involving latest Silurian syn-extensional magmatism and sedimentation have also been proposed in the New Brunswick, Quebec, and New England Appalachians (e.g., Malo and Kirkwood, 1995; Van Wagoner et al., 2002; Malo, 2004; Rankin et al., 2007; Tremblay and Pinet, 2016; Dorais et al., 2017; Wilson et al., 2017; Perrot and Tremblay, 2021).

The ca. 425–418 Ma extensional phase was probably accommodated by the development of listric normal faults that controlled syntectonic magmatism and sedimentation, but these faults were overprinted entirely (inverted) during subsequent thick-skinned thrust reactivation (Fig. 15). The association of ca. 422 Ma igneous rocks with the Rogerson Lake Conglomerate may indicate that the syntectonic extensional phase was shorter-lived, and probably started later, along the orogenic gold-mineralized trend than in the main Botwood basin (Figs. 1 and 2). This interpretation is compatible with ca. 420–417 Ma inversion of the La Poile basin (Fig. 1; Dunning et al., 1990; O’Brien et al., 1991), which marks the onset of northwest-younging, Early Devonian Acadian ductile deformation in southwestern Newfoundland (van Staal and Barr, 2012; van Staal et al., 2014). Near the Victoria Lake Shear Zone in south-central Newfoundland, deformation and metamorphism in the Meelpaeg nappe were active by ca. 418 Ma (Fig. 15B; Valverde-Vaquero et al., 2000, 2006; van Staal et al., 2014).

The ca. 410 Ma ages for hydrothermal rutile from structurally controlled quartz veins in central Newfoundland provide constraints on the absolute timing of reverse sinistral shearing associated with Early Devonian Acadian orogenic gold mineralization (Fig. 15B). The Early Devonian rutile ages fall within the age range for the North Bay Granite Suite (ca. 417–400 Ma, Dunning et al., 1990; Kerr, 1997), which intrudes rocks of the Gander Zone southeast of the Victoria Lake Shear Zone (Fig. 5). Additionally, comparable Early Devonian ages were obtained for plutonic rocks of the Loon Bay pluton (ca. 408 Ma, Elliott et al., 1991) and some rocks of the composite Fogo Island Intrusive Suite (410–407 Ma, Graham et al., 2020; Fig. 1). These Early Devonian igneous rocks were emplaced during a voluminous phase of syn-convergence Acadian magmatism (ca. 415–395 Ma) in the Gander Zone and Exploits Subzone that may have resulted from delamination and/or flat-slab subduction of Avalonia beneath the trailing margin of composite Laurentia (Fig. 15B; Kerr, 1997;van Staal et al., 2009). The temporal correspondence of Early Devonian orogenic gold mineralization in the eastern Dunnage Zone with voluminous Acadian magmatism in the Gander Zone warrants further research on fluid sources and fluid mixing within the orogenic gold-bearing hydrothermal system of central Newfoundland.

New high-precision CA-ID-TIMS U-Pb zircon geochronology constrains the timing of felsic magmatism along the length of the orogenic gold-mineralized corridor in central Newfoundland to 422–420 Ma, which may predate, or was approximately coeval with, the deposition of the Rogerson Lake Conglomerate. The association of clastic sedimentary rocks with latest Silurian bimodal igneous rocks throughout central Newfoundland is consistent with syntectonic formation in an extensional basin (e.g., O’Brien, 2003) immediately prior to the Early Devonian, Acadian orogenic cycle. Lithogeochemistry of latest Silurian bimodal igneous rocks is compatible with emplacement in a supra-subduction zone setting as a result of slab break-off (e.g., Whalen et al., 1997; van Staal et al., 2014; Dostal et al., 2020). Based on regional geochronological constraints in the southern and eastern portions of the Botwood basin (this study; Sandeman et al., 2017), this transient phase of extension that preceded orogenic gold mineralization occurred between ca. 425 and 418 Ma in central Newfoundland, but was probably time-transgressive across the Dunnage Zone. In the tectonic model presented herein (Fig. 15), inferred listric normal faults that formed during late syn- to post-Salinic extension were inverted and reactivated as thrust faults and mineralized during the Early Devonian.

Orogenic gold mineralization appears to be focused in a triangle zone–like structural domain defined by southeast- and northwest-dipping, crustal-scale fault systems in central Newfoundland (Figs. 15B). In this interpretation, some latest Ordovician to Middle Silurian, northwest-dipping thrust faults were reactivated to produce southeast-directed backthrusts and shear zones (e.g., Valentine Lake Shear Zone), and were important for localizing gold-bearing fluids (Figs. 46 and 15B). Early Devonian (ca. 410 Ma), gold-mineralized, ductile-brittle quartz vein systems formed progressively as third-order, structurally controlled offshoots of second-order fault splays and shear zones controlled by a major detachment fault at depth (Figs. 47), which is consistent with fluid-pressure cycling along steepening reverse fault zones across the brittle-ductile transition (~10 km, Gleason and Tullis, 1995; Sibson et al., 1988; Sibson, 2004). Such a setting and process evolution for the orogenic gold-bearing vein systems in central Newfoundland are remarkably similar to that of economically significant orogenic gold systems of the Abitibi greenstone belt of the Canadian Shield (Bleeker, 2015; Honsberger and Bleeker, 2018).

The timing of orogenic gold mineralization in central Newfoundland is best constrained by ca. 410 Ma ages for hydrothermal rutile in mineralized quartz veins. The progressive development of Early Devonian, gold-mineralized vein sets is compatible with regional compression and metamorphism during the Acadian orogenic cycle (e.g., O’Brien, 2003; Valverde-Vaquero et al., 2006; van Staal et al., 2009, 2014; Willner et al., 2018). The temporal correspondence of orogenic gold mineralization with Early Devonian, Acadian magmatism (e.g., van Staal et al., 2009; Fig. 2) warrants further research on fluid sources and mixing in central Newfoundland. For example, poly-metallic and poly-metalloid associations with gold (Ag, Cu, Sb, Bi, W, Te) in the altered Rogerson Lake Conglomerate and associated quartz vein sets may support a magmatic volatile contribution (e.g., Sillitoe and Thompson, 1998; Thompson et al., 1999; Hart, 2007; Pokrovski et al., 2013). On the other hand, metal and metalloid associations with gold may be an inherited signal due to gold-bearing metamorphic fluid flow through bedrock that was enriched previously in magmatic volatiles. More research on the age, composition, and tectonic setting of Early Devonian magmatism in central Newfoundland is important for investigating a potential link with orogenic gold mineralization.

This work represents a product of Natural Resources Canada’s Targeted Geoscience Initiative 5. Thanks to Antler Gold Inc., John Hinchey, Marathon Gold Corp., Sherry Dunsworth, Nic Capps, Graham Layne, Tim Froude, and Tyler Nickson for useful discussions and assistance. This manuscript benefitted from internal review by Alex Zagorevski and external reviews by the associate editor and anonymous reviewers. NRCan contribution number 20210306.

1Supplemental Material. Supplemental Material 1: Zircon and Rutile Populations: Figure S1. Reflected light microphotographs of zircon (A–F) and rutile (G) crystal populations from rocks analyzed for U-Pb geochronology. (A) BNB18-IHNL-008. (B) BNB19-IHNL-317. (C) BNB18-IHNL-197. (D) BNB18-IHNL-080b. (E) BNB19-IHNL-295. (F) BNB18-WL-029. (G) BNB18-IHNL-180. Supplemental Material 2: Analytical Chemistry Methods. Supplemental Material 3: Lithogeochemical Data: Table S1: Lithogeochemical data obtained at ALS Geochemistry Laboratories for igneous rocks in central Newfoundland; Table S2: Lithogeochemical data obtained at the Geological Survey of Newfoundland and Labrador for igneous rocks in central Newfoundland. Please visit https://doi.org/10.1130/GSAB.S.18858221 to access the supplemental material, and contact editing@geosociety.org with any questions.
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