Nechako River Map-Area
Structural Relations and Age

All rocks included in this group are younger than the Takla Group. In Fawnie
Range at the west end of Johnny Lake and on Tatelkuz and Kuyakuz Mountains
the granite batholiths intrude Hazelton Group rocks. At the southwest end of Euchu
Lake gneissic granodiorites are in fault contact with Hazelton Group sediments.
Boulders and pebbles of these granitic rocks occur in early Tertiary conglomerates.
With the reservation that all these rocks may not have been emplaced at the same
time, the age of this group can be stated as younger than Middle Jurassic (Bajo-
cian) and older than early Tertiary.

The mode of emplacement of this group is uncertain. The granitic batholiths
of Fawnie and Nechako Ranges have very sharp contacts with the intruded rocks.
The composition and texture is uniform to the contact and in the intruded rocks
there is a narrow zone of hornfels, although the contact effect is not pronounced
nor does it extend more than a few feet from the contact. Dykes or pegmatites
were seldom observed. Around Tetachuck Lake, although some of the granitic
rocks were emplaced with a very sharp contact, the diorites and granodiorites
more commonly have a gradational contact, particularly where basic volcanic
rocks are intruded. In such examples, position of the contact must be arbitrarily
selected—a difficult matter where the gradation is over distances of a mile or
more. Inclusions and dykes further complicated the decision.

Correlation

This group cannot be readily correlated with any well-known group. The
Topley Intrusions are older and lithologically different. The Omineca Intrusions
bear some lithological resemblance but differ in form, topography, and outcrop
patterns and may not be the same age. Also, the Topley Intrusions separate the
Omineca Intrusions from these in Nechako River area. The Coast plutonic rocks
of the Coast Mountains are lithologically similar, but these rocks are not within
the Coast Mountains, topographically or physiographically. Duffell (1959) in-
cluded adjacent rocks of Whitesail area with the Coast plutonic rocks and the
bodies discussed here too may be satellites of the main mass of the Coast
Mountains. Granodiorites of Bulkley and Babine Mountains (Armstrong, 1944a,
b) have a similar position in space and time, and they are considered to be satel-
lites of the Coast plutonic rocks.

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