A Review of Iron Oxide Copper-Gold Deposits, with Focus on the Wernecke Breccias, Yukon, Canada, as an Example of a Non-Magmatic End Member and Implications for IOCG Genesis and Classification

Abstract

New data indicate Wernecke Breccia-associated iron oxide copper-gold (IOCG) deposits likely formed from moderate-temperature, high-salinity, non-magmatic brines. The breccias formed in an area underlain by a sedimentary sequence that locally contained evaporites (potential source of chloride and possibly sulfur) and was thick enough to produce elevated fluid temperatures. Metals (Fe, Cu, Co, U) were probably derived from host strata, transported as chloride complexes, and precipitated due to changes in fluid temperature and pressure during brecciation. These new data suggest that the spectrum of genetic models for IOCG deposits that typically invoke formation from magmatic or hybrid magmatic–non-magmatic fluids should be expanded to include those systems that formed in a non-magmatic environment. Modifications to the definition of IOCG systems are proposed that reflect the degree of involvement of magmatic and/or non-magmatic fluids and the nature of the mineralizing environment. A division into magmatic, non-magmatic, and hybrid magmatic–non-magmatic IOCG types is suggested. Typical magmatic end-member IOCG deposits include Lightning Creek and Eloise, Australia. Hybrid magmatic–non-magmatic IOCG examples include Ernest Henry and Olympic Dam, Australia. The Wernecke Breccia and Redbank deposits are suggested as possible representatives of non-magmatic IOCG end members. End-member magmatic IOCG deposits have similarities to some porphyry deposits, whereas non-magmatic IOCG end members share characteristic with some sediment-hosted Cu deposits, suggesting that the range of IOCG deposits may form a link between intrusive- and sediment-related deposits.