The structurally controlled central Newfoundland gold belt is emerging as one of the next significant mining jurisdictions in Canada. Gold mineralization is associated with crustal-scale faults that preserve synorogenic conglomerates, similar to the setting of orogenic gold in the Archean Abitibi greenstone belt. Recent exploration in the Wilding Lake region exposed a system of auriferous quartz veins hosted within sedimentary and volcanic rocks. Detailed lithological and structural documentation of these newly exposed zones was conducted to examine controls on gold mineralization and place the vein system into a regional context. Field data demonstrate that the main 'Elm' quartz vein extends for approximately 230 m along strike, is up to 2 m wide and cuts the conglomerate host within an oblique sinistral shear zone that accommodated north-northeast-directed thrusting. An early set of moderately dipping extensional quartz veins, consistent with oblique sinistral shear, emanate from the main vein. A later, more steeply dipping set of extensional quartz veins crosscut the main vein and the earlier vein set, and are consistent with a component of horizontal extension. Chalcopyrite and malachite occur locally in the early vein set, but are more abundant overall within the younger vein set. A nearly conjugate set of steeply dipping extension fractures crosscut the main vein and the two vein sets. These fractures are filled typically with vuggy quartz and unaltered and altered sulphides. Field data are consistent with progressive deformation characterized by early oblique compressional sinistral shear and subsequent components of subhorizontal extension and minor dextral strike-slip.
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.
The formation and preservation of orogenic gold deposits are associated with a predictable set of magmatic, structural, and tectonic processes that have recurred throughout Earth's history. In world-class Archean gold districts, such as in the Superior Province of the Canadian Shield and the Yilgarn Craton of the West Australian Shield, the main gold-mineralized fault zones are characterized by early imbrication, lithospheric extension, synorogenic magmatism and sedimentation, thick-skinned re-imbrication, and late-stage strike-slip. Such an evolution results in the occurrence of gold-mineralized, upper crustal sequences of synorogenic magmatic and sedimentary rocks above terranes of granitoid rocks and/or older poly-deformed volcanic rocks. Targeted exploration for orogenic gold mineralization relies on remnant panels of synorogenic rocks (e.g. polymict conglomerate and bimodal magmatic rocks) as first-order field indicators of structurally controlled gold preservation along prospective crustal-scale fault zones. Paleozoic crustal-scale fault zones in central Newfoundland have been known to host significant gold mineralization and recent major discoveries (e.g. Valentine Lake gold deposit) and associated exploration suggest the emergence of a new district centred on the footwall rocks of the Victoria Lake shear zone. Fieldwork, combined with structural analysis and high-precision U-Pb geochronology throughout central Newfoundland, demonstrates that the structurally controlled Paleozoic gold district is remarkably similar to the much older Archean Abitibi gold district in scale, geological setting, structural architecture, synorogenic magmatism and sedimentation, style of mineralization, tectonic evolution, and process rates. In central Newfoundland, orogenic gold occurs within footwall blocks of an overall northwest-directed fault system that juxtaposed and deformed Neoproterozoic basement granitoid rocks and Late Silurian to Early Devonian synorogenic rocks during the Acadian Orogeny. Preliminary high-precision U-Pb zircon and rutile geochronology demonstrates that the key tectonic interval driving gold mineralization and synorogenic sedimentation and magmatism, including syenogranite and monzonite intrusions, occurred between 424 and 407 Ma, approximately the same relative time interval (15-20 million years) as the Abitibi greenstone belt. The similarities between the gold systems of central Newfoundland and the Abitibi imply that a common predictable set of structural and tectonic processes throughout Earth's history, and thus independent of time, have led to the deposition and preservation of orogenic gold mineralization.
Crustal-scale fault zones in central Newfoundland are being recognized as significant gold-mineralized structures. In particular, a northeast-trending structural corridor in the eastern Dunnage Zone (Exploits subzone), delineated by the Rogerson Lake Conglomerate, contains highly prospective vein-hosted gold deposits. Such mineralized vein systems, exposed near Valentine Lake (Marathon Gold Corp.) and Wilding Lake (Antler Gold Inc.), are products of progressive Paleozoic deformation and fluid-pressure cycling along crustal-scale faults that cut the Late Silurian to Early Devonian Rogerson Lake Conglomerate and underlying Neoproterozoic basement rocks. Well exposed, gold-bearing quartz-vein systems in the Wilding Lake area reveal a kinematic history that involved a main phase of reverse sinistral shearing and subsequent transient phases of horizontal extension, oblique compression, and, at least locally, components of late dextral strike-slip. High-grade gold mineralization is associated with siderite-ankerite-sericite alteration of the host rocks, structurally controlled quartz-vein emplacement, and supergene alteration of pyrite and chalcopyrite. Gold-bearing vein sets contain quartz, pyrite, chalcopyrite, tourmaline, native gold, Ag-poor electrum, bismuth-silver-gold tellurides, rutile, and secondary goethite, malachite, and acanthite. Prospective gold exploration targets in the Wilding Lake area are Late Silurian feldspar porphyry and felsic volcanic rocks overlying the Rogerson Lake Conglomerate, as well as, rheologically favourable Neoproterozoic basement granitoids that may provide a setting similar to that at Valentine Lake.
An occurrence of blueschist-facies metamorphism in the Appalachian orogen is newly recognized in northwestern New England, United States. Inclusions of glaucophane and omphacite occur in a relict garnet core from a retrogressed garnet-barroisite amphibolite of the Belvidere Mountain Complex in Vermont. Pressure-temperature pseudosection and mineral composition isopleth calculations demonstrate that the Belvidere Mountain Complex blueschist-facies mineral assemblage of glaucophane–magnesio-hornblende–omphacite–chlorite–rutile–quartz–clinozoisite–garnet was stable at ~1.65–2.0 GPa and ~450–480 °C. Garnet-absent amphibolite with barroisite and chlorite inclusions in clinozoisite records high-pressure epidote-amphibolite–facies metamorphism at ~1.0–1.4 GPa and ~515–550 °C. These new findings quantify deep subduction of the Belvidere Mountain Complex during the Cambrian to Ordovician Taconic orogenic cycle and suggest that more blueschist-facies mineral assemblages could be revealed in the Appalachians with detailed analysis of retrogressed rocks.
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