Geoscience Map 2011-04: Geology, Geochronology, Lithogeochemistry and Metamorphism of the Alice Lake Area, Northern Vancouver Island (NTS 092L/06 and part of 092L/03) 1:50 000 scale
View Geoscience Map 2011-4 (PDF, 5.3 MB)
Geoscience Map 2011-4 (1:50 000-scale) is the fourth in a series of five new geological maps (Geoscience Maps 2011-1 to 2011-5) of northern Vancouver Island which together provide a revised Early Mesozoic stratigraphic framework and Mesozoic-Tertiary plutonic history for southern Wrangellia. Geoscience Map 2011-4 describes the geology, geochronology, lithogeochemistry and metamorphism of the Alice Lake area (NTS 092L/06 and part of 92L/03). The map area is underlain by a folded and faulted sequence of Late Triassic to Early Jurassic volcanic and sedimentary rocks of the Vancouver and Bonanza groups intruded by granitoids of the Early to Middle Jurassic Island Plutonic Suite. The deformed Triassic-Jurassic rocks are unconformably overlain by Cretaceous marine clastics and the eroded remnants of Tertiary (Neogene) volcanic edifices (Alert Bay volcanic unit). Intrusive counterparts of the Tertiary rocks include dikes and a granitoid pluton. The Late Triassic Quatsino limestone attains its maximum thickness (>900 m) and youngest age (Carnian to Early Norian) in the Alice Lake area. The limestone hosts significant base- and precious-metal skarn occurrences (e.g. the former Merry Widow and Old Sport mines) associated with Early Jurassic gabbroic and more leucocratic intrusions of the Island Plutonic Suite (Merry Widow Mountain Pluton). Skarn mineralization is also associated with the Early Pliocene Victoria Lake Pluton, the youngest member of the Late Miocene to Early Pliocene Klaskish Plutonic Suite. This composite pluton comprises an older granodiorite-porphyry phase (5.15 Ma) which has engulfed an enclave of Alert Bay volcanic rocks, and a younger quartz monzodiorite phase (4.6 Ma). Major structures in the area include steeply dipping, northerly and northwesterly-trending faults, and a younger intersecting set of northeasterly-trending structures related to the Brooks Peninsula Fault Zone. One such structure east of Neroutsos Inlet exhibits Early Pliocene or younger motion where it cuts the western margin of the Victoria Lake Pluton. Regional metamorphism is generally characterized by very low-grade mineral assemblages (prehnite-pumpellyite to zeolite facies) except in the vicinity of faults and intrusive contacts where the rocks may reach upper greenschist to amphibolite grade, respectively.
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