General Geology

distinct, in others the rocks are only slightly gneissic. Most of the foliation has
a northwest trend.

The diorite commonly is grey or greyish green and consists of abundant
hornblende and andesine. In a few places it grades into quartz diorite. They are
coarse-grained rocks and, in Nechako River map-area at least, are weathered to
a known depth of 3 feet; in the Nulki hills it was difficult to obtain an unweathered
specimen.

Structural Relations and Age

Whether all the lithological phases of this group were intruded at the same
time or not is a question as yet unresolved. The granites and granodiorites may
have had at one time a mode of emplacement but whether the diorites are similar
in age and origin is not known. No contact was exposed between these two
distinct units and near Finger and Tatuk Lakes they are separated by a band of
metamorphosed Takla volcanic rocks.

As mentioned previously, evidence from Nechako River map-area indicated
an age of emplacement of the Topley Intrusions different from that stated by
Armstrong (1949, pp. 96-97). In discussing the group, he outlined eight reasons
for dating the intrusions as pre-Upper Triassic post-Middle Permian, and evidence
from the Fort St. James area supported this conclusion. One reason given was that
the Topley Intrusions, which were confined to Cache Creek Group rocks, were
not known to intrude Upper Triassic Takla rocks and thus were thought to be
pre-Upper Triassic. This reason was found to be invalid in Nechako River area
(Tipper, 1959a, p. 32). In reviewing the Hazelton and Takla Groups the writer
discussed the age of Topley Intrusions and briefly the pertinent evidence is as
follows:

(1) Boulders and pebbles of Topley granites occur in the chert-pebble
conglomerate unit of the Hazelton Group which is of Middle Jurassic (early
Bajocian) age. Arkoses believed to have been derived from Topley granites are
dated as Middle Jurassic. Topley granites must therefore have been intruded
before Middle Jurassic time.

(2) On the north shore of Frangois Lake, Topley granites intrude the
marine part of the Red Bed Unit but are not in contact with the upper part of
the red beds. Possibly the Topley granites were emplaced while part of this unit
was being laid down; it would then be of latest Triassic age or more probably
Lower Jurassic.

(3) Topley granites intrude fresh andesites and breccias southeast of
Frangois Lake. These volcanic rocks are believed to belong to the Takla Group
because they are not as highly metamorphosed as the normal Cache Creek Group
rocks. The possibility does exist that they may be of Middle or Lower Triassic
age, although such rocks have never been recognized in central British Columbia.

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