The emerging Paleozoic gold district of central Newfoundland: new insights on structural controls and tectonic drivers of gold mineralization and preservation

Abstract

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.