ABSTRACT

The Western Canada foreland basin and overlying post-Eocene succession preserve a nearly continuous succession of sediment derived from the rising Canadian Cordillera from the Jurassic to now. Initially, sediment was derived from the middle of the uplifting Omineca Belt (central Cordillera), exposing progressively deeper rocks including plutono-metamorphic complexes. With continued uplift, the drainage divide stepped eastward and only shallower-level eastern Omineca material was shed to the foreland basin. Laramide uplift, beginning in the Late Cretaceous, exposed more igneous material to be shed into the foreland basin, but an eastward shift of the drainage divide to the Rocky Mountain Belt in the early Tertiary cut off the supply of Omineca debris. Gold is present in four intervals f the foreland-basin succession: gravels of modern rivers draining the Rocky Mountain Belt; middle to upper Tertiary conglomerates derived from the Rocky Mountains; Upper Cretaceous to lower Tertiary sandstones and conglomerates; and a distinctive Lower Cretaceous igneous-clast conglomerate in the Blairmore Group. The latter two occurrences contain up to 90% igneous clasts derived from the gold-bearing Omineca Belt. Gold in the former two occurrences was derived from quartz veins in upper Proterozoic to Lower Cambrian low-grade (greenschist-subgreenschist) metasediments. These quartz veins were formed and exposed during Cretaceous-Tertiary uplift of the Rocky Mountains.

Windows of gold deposition exist in a foreland-basin succession between exposure of primary gold deposits due to uplift and cutoff of source by lateral stepping of the drainage divide. The Western Canada foreland basin contains three such gold deposition windows, the last of which is still open.