NEW CONSTRAINTS ON THE TIMING OF MOLYBDENITE MINERALIZATION IN THE DEVONIAN ACKLEY GRANITE SUITE, SOUTHEASTERN NEWFOUNDLAND: PRELIMINARY RESULTS OF Re-Os GEOCHRONOLOGY

New Re–Os molybdenite ages are presented from three prospects (Motu, Ackley City and Wylie Hill) located along the southern margin of the Ackley Granite suite, southeastern Newfoundland. These dates provide new constraints on the timing of high-level granite emplacement and contemporaneous granophile mineralization, and also provide a comparison with previous estimates for the age of the granite and associated mineral deposition. The ages indicate a single episode of spatially related, late-stage, syngenetic mineralization at Motu (378.1 ± 1.7 Ma, n = 1), Ackley City (379.7 ± 1.7 Ma, n = 5) and Wylie Hill (380.2 ± 1.6 Ma, n = 2). The results suggest that all three prospects formed synchronously at 379.6 ± 1.7 Ma (weighted average, n = 8). The Re–Os dates are similar to, but slightly older than previous Ar–Ar magmatic and hydrothermal mica (biotite/muscovite) ages. The preliminary Re–Os dates yield a precise timing for roof-zone crystallization and syngenetic mineral deposition in the Ackley Granite suite and also support temporal correlation of the Ackley Granite with other Late Devonian (Frasnian) granitoid plutons such as the Francois and St. Lawrence granites. The presented Re–Os molybdenite geochronology has great potential in constraining the precise timing of late magmatism and associated mineralization in Newfoundland, and facilitating correlations with analogous regions in Europe and North America.