Zircon alteration in wallrock of Pamour and Hoyle Pond Au deposits, Abitibi granite-greenstone belt: Constraints on timescales of fluid flow from depth-profiling techniques

Quartz-carbonate vein Au deposits in the Timmins-Porcupine gold camp, Abitibi Subprovince, have equivocal protracted parageneses and formed during late to post-Kenoran (2750-2670 Ma) deformation and metamorphism. SIMS U-Pb and delta18O depth-profiling and LA-ICPMS REE depth-profiling techniques were employed on unpolished wallrock zircons to resolve temporal constraints on mineralization and hydrothermal fluid sources at Hoyle Pond and Pamour mines. Depth-profiling techniques successfully uncovered <3 mum alteration domains in zircon rims based on Th/U, REE, and isotopic signatures, and rim 207Pb/206Pb ages are significantly younger than host rock ages. Zircon alteration is from a complex interplay of recrystallization and localized dissolution-reprecipitation of metamict to fully crystalline zircon during hydrothermal fluid flow. Alteration of Hoyle Pond and Pamour zircons at 2660 Ma correlates to intensely mineralized and deformed quartz-carbonate-Au shear veins, and this age represents peak fluid infiltration at the mines coinciding with peak regional metamorphism. Subsequent zircon alteration correlating to thin, shallow-dipping and less altered / mineralized vein networks occurred at 2640 Ma, and this age likely represents a late hydrothermal fluid pulse at the end of regional retrograde metamorphism. Protracted hydrothermal alteration along discrete zones within the camp continued into the Proterozoic. Th/U and 18O values of zircon alteration domains suggest that fluids were most likely derived from lower crustal metamorphic and/or plutonic activity. While the underutilized depth-profiling technique has resolved ∼200 m.y. of continuous crustal evolution and fluid flow in the southern Abitibi, further investigation of the southern Abitibi is required to clarify the genetic relationship between Au mineralization and zircon alteration.