The British Columbia
Geological Survey has completed extensive geological mapping and mineral
deposits studies on northern Vancouver Island over the last several
years. This is an ongoing program of mapping and mineral deposits
studies. Northern Vancouver Island, and particularly the Quatsino Sound
area, is richly endowed in mineral occurrences, has had a successful
mining history, such as the former Island Copper mine (092L
158). The region also has numerous mineral
occurrences, some of which are under-explored but with excellent
potential. The release of these three 1:50 000-scale Geoscience Maps
covers an area extending from Winter Harbour - San Josef Bay on the west
coast to Port Hardy - Port McNeill on the east coast, an area
encompassing NTS sheets 102I/8, 9 and 92L/6, 11, and 12.
Geoscience Map 2006-1 covers the Alice Lake area, 092L/6.
The area is
underlain by a folded and faulted sequence of Upper Triassic
to Middle Jurassic volcanic and sedimentary rocks of the Vancouver
and Bonanza Groups intruded by granitoids of the Island Plutonic
suite. The latter rocks are associated with important calcalkaline
Cu-Mo-Au porphyry, and base and precious-metal skarn and epithermal
mineral occurrences. Cretaceous marine clastic and Tertiary
volcanic-sedimentary strata with lower mineral potential overlie the
Triassic-Jurassic rocks.
These geoscience
maps provide a new stratigraphic framework for the Early Mesozoic
sequences, calibrated by 40Ar/39Ar and U-Pb isotopic dating and
macrofossil and microfossil (conodont and radiolarian) faunas. The
Bonanza group now includes the Upper Triassic Parson Bay Formation,
which contains mapable volcanic/volcaniclastic horizons, overlain by
unnamed volcaniclastic-sedimentary strata of uppermost Triassic to
lowermost Jurassic age, in turn succeeded by Lower to Middle
Jurassic, predominantly volcanic and volcaniclastic sequences of the
informally named LeMare Lake volcanics, formerly "Bonanza volcanics".
The latter term is usefully retained for all volcanic lithologies
within the Bonanza Group, which spans some 40 million years of
magmatic arc evolution from the Late Triassic (Carnian) to the
Middle Jurassic (Bajocian).