Whitesail Lake Map-Area

is sharp and well defined. The Hazelton group rocks near the contact are
metamorphosed but still easily recognizable as volcanic and sedimentary
types whose attitudes conform approximately to that of the granitic contact.
At several localities on Mount Wells and Michel Peak granitic dykes were
observed extending from the main pluton into the older rocks. Similar
relations were observed associated with the stock on Swing Peak.

Faulted contacts are probably more common than indicated on the map.
They were observed, particularly, associated with the main mass of the Coast
Intrusions south of Tesla Lake and at several localities on Whitesail Lake
and Whitesail Range. At the head of Tahtsa Lake swarms of red granite
dykes cut the metamorphosed rocks. The contacts on these dykes are com-
monly filled with gouge, indicating faulted conditions.

Fractures and joint systems are common in the intrusions of the map-area.
The main joint or fracture pattern of the main mass of the Coast Intrusions
is exemplified by the longitudinal and transverse valleys of the Coast
Mountains. Locally there are joint and fracture patterns that differ from
the major system but the common direction is south 60 degrees east, which
is close to that of the longitudinal valleys of the main mass.

The plutonic rocks included under the heading Coast Intrusions are
not all of the same age but are composed of rocks of several periods of
emplacement. Relations between the plutonic rocks and the volcanic and
sedimentary rocks indicate to some extent the limits in which the period of
emplacement must fall.

Evidence of granitic emplacement early in the Mesozoic era is indicated
by the fragments composing a volcanic breccia on Chikamin Range. This
breccia immediately overlies Middle Jurassic sedimentary beds and contains
fragments and boulders of granitic material up to a foot in diameter. As it is
probable that this breccia, like the underlying beds, is of Middle Jurassic age,
the granitic plutons from which the fragments originated must have been
emplaced in pre-Middle Jurassic time. Stuart (1955) indicated that granitic
dykes and cupolas, included with the greenstone complex at the head of
Tahtsa Lake, are overlain unconformably by rocks equivalent to the Hazelton
group. The evidence, therefore, strongly indicates that some plutonic rocks
were emplaced prior to the deposition of the Hazelton group. As the Hazelton
group is itself cut by many types of plutonic rocks there is no doubt that
much of the plutonic suite was emplaced after the deposition of the Hazelton
group.

The upper limit of the period of emplacement, as indicated by the
available evidence, is in early Tertiary time prior to the deposition of the
Miocene basalts. Within the map-area all of the main plutons are younger

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