Whitesail Lake Map-Area

Coast Intrusions include many varieties of granitic and dioritic rocks.
Commonly these intrusions have metamorphosed the volcanic and sedimen-
tary rocks in contact with them, particularly in the region of the main mass
which occupies a large part of the southwest corner of the area. As the
dominant rock group of the area is of Middle Jurassic age and all except
two small stocks cut only Middle Jurassic rocks there is little evidence
indicating the relative ages of the various granitic types. Rarely were two
types found in contact. The late Lower Cretaceous rocks mentioned above
are cut by two small stocks included with the Coast Intrusions indicating
that at least some of the intrusive bodies were emplaced in post-Jurassic time.

A series of flows, mainly acidic, but including some andesite, basalt,
tuff, and minor sedimentary rocks of continental character outcrops along
Whitesail River and Ootsa Lake. Freshwater shells and poorly preserved
plant remains suggest this series to be Upper Cretaceous or later in age and,
though it has been considerably deformed, it was not found to be invaded
by the Coast Intrusions. Beds of this series are in unconformable contact
with the Hazelton group and in places have a coarse conglomerate at the
base. The localities where these features were observed are now flooded by
the Aluminum Company of Canada’s project.

Lying unconformably above these acidic rocks and in places directly
on old granitic surfaces are undisturbed (Oligocene) or later basaltic lavas,
which have their greatest extent in the vicinity of Chef Ridge. These rocks
are fresh looking and easily recognized by their undisturbed condition.

Thick accumulations of till, fluvioglacial material and alluvium occur
along the main valleys and in the plateau region along the eastern boundary.

Mineral deposits occur mainly along the eastern boundary of the main
mass of Coast Intrusions, with gold, silver, lead, zinc, copper, and tungsten
minerals having been found. The showings, though persistent in length, have
been too narrow to work, but it is possible, now that the area has become
more accessible, that some will become economic.

Structurally the area is one of gentle folding which locally becomes
intense, the structure of each range appears to be controlled by the granitic
intrusion that forms the core of the highest peak and rarely do structures
continue from one range to another.

Faults are particularly common along the contact of the main mass
of Coast Intrusions and may be found to a lesser extent near more or less
isolated cupolas. In the vicinity of Tesla Lake the pattern appears to have
been block faulting. No major faults were mapped but faulting on a major
scale may have been responsible for the valleys of the large lakes, possibly
in early Cretaceous time.

28