IOCG Environments in Canada: Characteristics and Vectors to Ore

Prospective geological environments for polymetallic iron-oxide copper-gold (IOCG) deposits in Canada are currently most common in Proterozoic settings but Phanerozoic examples occur within the Appalachian Orogen and the Cordillera, and Archean examples may be present. Among the Proterozoic settings, the superb glacially-polished cross-sectional exposures of magnetite- and hematite-group IOCG systems in the Great Bear Magmatic Zone record many of the processes required to form giant IOCG deposits, including: 1) regional- to deposit-scale element mobility driven by magmatic-hydrothermal systems; 2) superimposition of extensive prograde and retrograde alteration assemblages including late-stage hematite after earlier magnetite; and 3) repeated and focussed trapping and precipitation of metals within structural and lithological traps. The evolving hydrothermal fluids gave rise to an extraordinary range of IOCG deposits that form a continuum with porphyry and epithermal systems. Among the other known Canadian settings, we review the Cobequid-Chedabucto Fault Zone and the Central Mineral Belt districts as case examples of crustal-scale fault control and polyphase build-up of IOCG systems during orogenesis and the Wernecke Breccias.