Volcanic and hydrothermal reconstruction of the Pilley's Island volcanogenic massive sulfide district, central Newfoundland

Abstract

Pilley's Island in the Central Mobile Belt, Newfoundland, Canada, is host to a cluster of bimodal felsic Zn-Pb-Cu-Au-Ag volcanogenic massive sulfide (VMS) deposits. In the Pilley's Island terrane, VMS-bearing felsic volcanic rocks are derived from the remelting of a hydrated, arc basalt substrate; these have been juxtaposed by thrust faulting against barren mafic volcanic rocks derived from partial melting of slab metasomatized mantle wedge within an Ordovician peri-Laurentian subduction zone. -- Sulfide formation likely took place within a peri-Laurentian arc rift based on immobile element signatures. The deposits formed via sub-seafloor replacement of volcanic flows or volcaniclastic strata, with evidence including: large, gradational alteration and mineralization haloes surrounding the deposits and relict host rock fragments with in the sulfide. -- Zones proximal to mineralization exhibit muscovite ± illite alteration and elemental vectors to mineralization include loss of SiO₂, CaO, Na₂O and grains of Fe₂O₃, K₂O, base metals, and volatile elements (As, Sb, Tl).