U-Pb evidence for Abitibi gold mineralization postdating greenstone magmatism and metamorphism

Abstract

Two widely held theories for the origin of Archaean lode gold deposits, the magmatic¹ and metamorphic replacement² models, predict that gold emplacement should have occurred near the end of late, syn-kinematic greenstone magmatism. Here we report that at the Camflo mine in the Abitibi subprovince of Canada, U–Pb ages for rutile and titanite in auriferous alteration (2,625 ± 7 Myr) are much younger than the age of the host quartz syenite (2,680 ± 4 Myr) and ages for regional magmatism (>2,670 Myr)³ and metamorphism (˜2,680 Myr)⁴. Mineral associations and Pb–Pb systematics indicate that the hydrothermal minerals record crystallization ages that are probably coeval with the gold mineralization. These ages, and others from the Abitibi Subprovince^4–6, rule out a direct connection between gold and magmatism or metamorphism associated with regional folding of the greenstone belt. They are broadly contemporaneous with metamorphism at deep crustal levels⁷, and may record late devolatilization of the lower crust.