Geoscience Map 2009-2: Geology of the Nimpkish-Telegraph Cove Area, Northern Vancouver Island092L/7, 10
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Geoscience Map 2009-2 (1:50 000) describes the bedrock geology of the Nimpkish-Telegraph Cove area of northern Vancouver Island (NTS 092L/7, 10). The map complements Geoscience Maps 2006-1 to -4 showing the geology of the Quatsino Sound area to the northwest and supercedes Open File Map 2006-5. The map area is underlain by a folded and faulted sequence of Triassic volcanic and sedimentary rocks of the Vancouver and Bonanza groups intruded by granitoids of the Early to Middle Jurassic Island Plutonic Suite. The latter intrusions are associated with important calc-alkaline Cu-Mo-Au porphyry, base- and precious-metal skarn and rare, manto-type massive sulphide occurrences. The deformed Triassic-Jurassic rocks are unconformably overlain by Late Cretaceous marine clastics equivalent in part to the Nanaimo Group. Minor intrusions include subvolcanic dikes and sills comagmatic with volcanic strata of the Karmutsen Formation and Bonanza Group, granitoids of the Island Plutonic Suite and a Tertiary dike possibly related to the Neogene Alert Bay volcanic unit to the north.
The oldest rocks in the map area belong to the thick (~6 km) flood basalt succession of the Triassic (Carnian to possibly Ladinian) Karmutsen Formation (Vancouver Group) which comprises three distinct members: a lower pillow basalt unit; a middle hyaloclastite unit; and an upper subaerial flow unit. This emergent succession represents the evolution of an oceanic plateau and is well exposed in coastal outcrops between Telegraph Cove and Robson Bight. The Quatsino limestone at the top of the Vancouver Group rests disconformably on Karmutsen basalt and marks subsidence of the plateau prior to deposition of predominantly carbonate-siliciclastic strata of the Late Triassic (latest Carnian/Norian to Rhaetian) Parson Bay Formation at the base of the Bonanza Group. The youngest volcanic strata form basaltic to rhyolitic volcaniclastic deposits and minor flows, and are mainly preserved in the core of a north-northwesterly-trending syncline in the Hankin Range just east of Nimpkish Lake. Early Jurassic strata of the LeMare Lake volcanic succession, the main phase of Bonanza volcanism, are entirely absent due to erosion or non-deposition.
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