Petrology, geochemistry, and geochronology of the root N’ cellar low sulfidation epithermal prospect in Newfoundland, Canada

The Root N’ Cellar Au-Ag-Te epithermal occurrence (RNC), located on the Burin Peninsula of Newfoundland, Canada, is an incredibly well-preserved Neoproterozoic volcanic system. The RNC is hosted within the Avalon Terrane in Newfoundland, which represents the easternmost extent of the Canadian segment of the Appalachian Orogen in Newfoundland. The host rocks of the prospect area consists of dominantly mafic, chemically bimodal sequence (basaltic andesite – rhyodacite) of flows and volcaniclastic rocks with common alteration assemblages including a proximal SiO₂ + K-rich sericite (illite) + adularia, and a more distal propylitic (epidote + carbonate + chlorite) assemblage. The rhyodacites at the RNC have been dated at 578 – 574 Ma, coinciding with the main period of Avalonian arc magmatism, and consistent with the known age of the Marystown Group. Petrology, geochemistry and geochronology indicate that the RNC likely formed in an arc-adjacent, intra-arc, or back arc basin tectonic environment. Analysis of alteration induced geochemical patterns from an assay database details alteration assemblages and mass balance chemistry changes indicative of formation from near-neutral pH reduced fluids, typical of low sulfidation epithermal systems. Furthermore, the preservation of geochemical trends suggest that the Discovery Trench to have seen hydrothermal fluid conditions similar to those associated with central to upper portions of a geothermal upflow zone.