Pyrite Re-Os Geochronology of Carbonate-Hosted Zn-Pb Deposits of the Canadian Cordillera

Abstract The Cambrian-Devonian platform carbonate rocks found throughout the eastern Canadian Cordillera are important hosts of Zn-Pb sulfide mineralization. Models for mineralization commonly invoke either Laramide compression, or hydrothermal circulation associated with an active tectonic margin that was present during the Paleozoic. To distinguish between these possibilities, we have dated two Zn-Pb deposits from the northeastern Canadian Cordillera (Robb Lake and Prairie Creek) using pyrite Re-Os geochronology. The age of Robb Lake (348 ± 26 Ma) overlaps with that of the clastic-dominated deposits in the Kechika trough, located directly to the west, and is consistent with both sets of deposit types being related to a common metallogenic system. Pyrite collected from stratabound sulfides and quartz-carbonate-sulfide veins from the main orebody at Prairie Creek was dated to 315.7 ± 8.3 Ma and is statistically indistinguishable from the age of 322 ± 10 Ma calculated from Mississippi Valley-type mineralization distal to the main orebody. Our Re-Os dates require that mineralization at Prairie Creek and Robb Lake occurred during the Paleozoic, in stark contrast to previous age estimates made by paleomagnetism (<150 Ma). Consequently, Zn-Pb mineralization in the northern cordillera formed in response to an active margin that existed along the western margin of North America during the Paleozoic, and it is not related to the Laramide compression.