GEOLOGICAL AND AR-40/AR-39 GEOCHRONOLOGICAL CONSTRAINTS ON THE TIMING OF QUARTZ VEIN FORMATION IN MEGUMA GROUP LODE-GOLD DEPOSITS, NOVA-SCOTIA

The results of geological and Ar-40/39 Ar geochronological investigations of several gold districts hosted by the Meguma Group are presented. Observations at both the macro- (deposit to ore zone) and micro- (hand sample to thin section) scale indicate that quartz vein formation followed major Acadian folding and metamorphism (ca. 400 +/- 10 Ma) and was broadly coincident with mafic-felsic magnatism at ca. 370 Ma. Ar-40/39 Ar analyses of vein-fill mica and amphibole from the Beaver Dam, Moose River, Fifteen Mile Stream, Upper Seal Harbour and Caribou deposits indicate ages of ca. 380 Ma to ca. 362 Ma. The age data are interpreted to reflect discrete hydrothermal events with rapid cooling following crystallization of vein constituents. The age data do not reflect either variable amounts of resetting by later granitic intrusions or diachronous cooling. Genetic models that interpret the generation of the auriferous quartz veins as either before or during major Acadian folding are considered to be inconsistent with the present results. Instead, a model is favored that interprets quartz vein formation in the context of continued transpression of the Meguma Terrane following regional folding and metamorphism.