Geoscience Map 2006-4: Geology of the Mahatta Creek Area, 092L/5
Northern Vancouver Island
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The British Columbia Geological Survey has completed extensive geological mapping (1:50 000-scale) and mineral deposits studies on northern Vancouver Island over the recent past. Northern Vancouver Island, and particularly the Quatsino Sound area, is richly endowed in mineral occurrences and has had a successful mining history, highlighted by the former Island Copper mine (MINFILE 092L 158). To date, most mining exploration has focussed on the numerous mineral occurrences in the Jurassic Bonanza Group and comagmatic Island Plutonic Suite. The Late Triassic flood basalt province (Karmutsen Formation) and newly discovered Tertiary plutons are under-explored, but have excellent potential. The Mahatta Creek Geoscience Map complements previously released maps (2006-1 to 2006-3) which together cover an area extending from the Brooks Peninsula - San Josef Bay on the west coast to Port Hardy - Port McNeill on the east coast (NTS sheets 102I/8,9 and 92L/5, 6, 11 and 12).
Geoscience Map 2006-4 covers the Mahatta Creek area (NTS 092L/5). The region is underlain by a folded and faulted sequence of Late Triassic to Middle Jurassic 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 epithermal mineral occurrences. The folded Triassic-Jurassic succession is overlain unconformably by Cretaceous marine clastics equivalent to rocks of the Kyuquot, Queen Charlotte and Nanaimo groups which are exposed elsewhere on Vancouver Island and in the Queen Charlotte Islands. These strata are succeeded by Tertiary (Neogene) volcanic and-sedimentary rocks of the Alert Bay volcanic belt. Recently recognized granitoid plutons of Miocene-Pliocene age, the Klaskish Plutonic Suite, appear to be confined to the Brooks Peninsula fault zone and represent intrusive equivalents of the Alert Bay volcanic rocks. The Mahatta Creek and previously published geoscience maps provide a new stratigraphic framework for the Early Mesozoic strata, calibrated by 40Ar/39Ar and U-Pb isotopic dating and macrofossil and microfossil (conodont and radiolarian) faunas. The Bonanza Group now includes the Late Triassic Parson Bay Formation, which contains mappable volcanic-volcaniclastic horizons and is overlain by unnamed volcaniclastic-sedimentary strata of latest Triassic (Rhaetian) to lowermost Jurassic (Hettangian) age. These strata are succeeded by Early (Hettangian) to Middle (Bajocian) Jurassic, predominantly volcanic and volcaniclastic sequences of the informally named LeMare Lake volcanic unit, formerly known as the "Bonanza volcanics". The latter term may be usefully retained to informally refer to all the volcanic rocks within the Bonanza Group, as presently defined.
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