U-PB EVIDENCE FOR ABITIBI GOLD MINERALIZATION POSTDATING GREENSTONE MAGMATISM AND METAMORPHISM

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 Subprovince4-6, 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. © 1990 Nature Publishing Group.