The formation and preservation of precious-metal bearing epithermal and intrusion-related systems are integral aspects of the Late Neoproterozoic tectonic history of the volcano-plutonic arc complexes that characterize the periGondwanan accreted terranes of the eastern Appalachian Orogen. Neoproterozoic high-sulphidation, low-sulphidation and intrusion-related gold systems in peri-Gondwanan terranes in the Newfoundland segment of the orogen were generated during several precisely dated, metallogenically significant, regional magmatic-hydrothermal pulses. These Avalonian gold systems formed in a once-contiguous, Pan-African-cycle orogenic belt, composed of complex assemblages of 760 to 540 Ma calc-alkaline to alkaline arcs and intervening marine and terrestrial siliciclastic sedimentary basins. Accretion of the mineralized arcs to the inboard Paleozoic elements of the Appalachians ocurred primarily in the Silurian and Devonian, during closure of the Cambro-Ordovician Iapetus Ocean. Gold in the Neoproterozoic high-sulphidation systems occurs with copper in vuggy silica and in breccias and/or network fracture systems, within zones of polyphase silica alteration, enveloped by regionally developed zones of quartz–pyrophyllite–andalusite–alunite-bearing metamorphosed advanced argillic alteration. In other instances, regionally developed (and apparently barren) pyrophyllite–diaspore-bearing advanced argillic alteration zones, related to either weakly developed or deeply eroded high-sulphidation systems, are juxtaposed with younger Neoproterozoic low-sulphidation colloformcrustiform banded, silica–adularia vein and breccia systems that contain significant gold grades. Several of the epithermal belts are spatially associated with breccia-hosted Cu-Au and AuCu-Zn mineralization, however, most of this intrusion-related gold formed during demonstrably earlier magmatic events. Large tracts of the mineralized Avalonian belt became submerged by the end of the Proterozoic and remained so, through the early Paleozoic, until Appalachian-cycle collision. Where the Avalonian rocks are far removed from the Appalachian hinterland, Neoproterozoic low-sulphidation mineralization is exceptionally well preserved. Deeper and more extensively tectonized high-sulphidation systems are preserved proximal to and within the Appalachian mobile belt on the Burin Peninsula and Hermitage Flexure regions of southern Newfoundland, respectively. Early tilting of the mineralized succesions and subsequent arc-rifting, collapse and marine incursions, during Late Neoproterozoic through Early Paleozoic break-up and dispersal of the Avalonian belt, helped significantly reduce the rate of erosion, allowing their preservation through time. The recognition of the geochemical, mineralogical and textural signatures of modern highand low-sulphidation epithermal systems in these deformed rocks allows the distinction from mainly younger, shear-zone related (e.g. orogenic) gold systems formed at deeper crustal levels, within the Paleozoic orogenic hinterland.
The Horse Cove Complex (HCC) is a recently recognized late Ediacaran swarm of mafic-to-felsic dykes that occurs in the Newfoundland Avalon Zone. It is focused along the extrapolated trace of the To...
