Latest Silurian syntectonic sedimentation and magmatism and Early Devonian orogenic gold mineralization, central Newfoundland Appalachians, Canada: Setting, structure, lithogeochemistry, and high-precision U-Pb geochronology

Abstract

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.

U–Pb geochronology of Late Silurian (Wenlock to Pridoli) volcanic and sedimentary rocks, central Newfoundland Appalachians: targeting the timing of transient extension as a prelude to Devonian orogenic gold mineralization

“…The processes of polyphase fault reactivation that control orogenic gold mineralization, for example, are only beginning to be constrained (Figs. 1 and 2; Willner et al 2018Willner et al , 2022Honsberger et al 2022). Additionally, the occurrence of extension-related Silurian basins in central and western Newfoundland with strongly bimodal magmatic suites and clastic sedimentary rock sequences (Fig.…”

“…Absolute minimum ages of deposition for clastic sedimentary rocks in central Newfoundland have been estimated from U-Pb rutile and 40 Ar/ 39 Ar white mica ages of ca. 410 Ma (Honsberger et al 2022) and ca. 390 Ma (Willner et al 2018), respectively, in quartz veins that cut polymict conglomerate (Rogerson Lake Conglomerate).…”

“…Instead, gold mineralization is hosted along younger fault/shear zones that overprint, reactivate, and crosscut older stratigraphy and tectonostratigraphic zone boundaries (Figs. 1 and 2; e.g., Honsberger et al 2022). In the Exploits Subzone (Fig.…”

“…In the Exploits Subzone (Fig. 2), for example, gold mineralization occurs along a Devonian crustal-scale thrust fault system that imbricates Gander Zone basement of the Meelpaeg Subzone and Ordovician Exploits Subzone rocks (Kean and Jayasinghe 1980;Colman-Sadd et al 1990;Honsberger et al 2022). This fault system corresponds to the Acadian deformation front and includes the regionally extensive, southeast-dipping Victoria Lake Shear Zone (Valverde-Vaquero et al 2006), which correlates with Noel Paul's Line (Williams et al 1988 Devonian deformation and include the Valentine Lake Shear Zone, which hosts an approximately five-millionounce orogenic gold deposit at Valentine Lake (Dunsworth and Walford 2018;Lincoln et al 2018;Figs.…”

“…422 Ma felsic volcanic and volcaniclastic rocks, granitoid and gabbro bodies, and is locally cut by lower greenschist facies mafic dykes (Honsberger et al 2019(Honsberger et al , 2020. The Neoproterozoic to Late Silurian rocks in central Newfoundland are cut by orogenic gold-bearing quartz vein systems that define the main mineral resource of the central Newfoundland gold belt (Evans 1996;Honsberger et al 2022).…”