23

The mineral fragments are quartz, orthoclase, and acid plagioclase. One
body of tuff on Evindsen creek is blood red and fine grained. The rock
contains fragments of quartz, feldspar, and felsitic crystalline rocks. The
red colour appears to be due to an abundance of red iron oxide in the
cement around the fragments.

The bodies of feldspar porphyries and augite porphyrites apparently
represent reservoirs, necks, and flows and the corresponding tuffs and
breccias appear to be the products of craters now plugged by necks of
crystalline rock. The slight differences existing between porphyries in
different parts of the area are no greater than what might be expected to
be exhibited by different parts of a magma reservoir. The differences
displayed by the augite porphyrites appear to be in part a matter of
degree of crystallinity and in this respect are no greater than would be
expected in different parts of a single mass. Locally, however, augite
phenocrysts are lacking and the rock then becomes a felsite very little if
at all different in mineral composition from the porphyries, except that
it contains more iron sulphide and is more altered. The augite porphyrite
is not very dissimilar to the feldspar porphyry. Gradations between the two
types, however, are not evident either from field or microscopic study.
The two types appear to differ in age, but it may well be that they had
a common origin in a single large reservoir nowhere now displayed.

In the Theophilus igneous area the main body of augite porphyrite
breccias underlies the felsitic breccias, the upper members of which grade
into conglomerate which in turn grades fairly abruptly into argillite. The
smaller stocks in the district are probably plugs in craters which supplied
the augite porphyrite breccias. The intrusives of McGrath mountain and
their northward extension are probably the upper part of the augite
porphyrite reservoir.

There are points of similarity between the augite porphyrite and
the feldspar porphyry, particularly in the cases of the augite porphyrites
and porphyries of the Copper Belt and Red Bluff types, which are altered
and contain disseminated iron sulphides. South of East creek the Copper
Belt appears to change gradually to a belt containing augite porphyrite
breccia and massive augite porphyrite which though imperfectly traced
may join with the rocks of the Red Bluff type between Washout and Red
Bluff creeks and through them be linked to the augite porphyrites of
McGrath mountain. Assuming that the rocks of the Copper Belt and the
augite porphyrite and indeterminate rocks of the Red Bluff type are
related and are older than the porphyries, it would seem that they represent
a main period of augite porphyrite eruption and that as time went on
the character of the eruptive materials gradually changed until finally
porphyries (felsite) were the product. If the porphyries are younger than
the augite porphyrites there is furnished an explanation of the interruptions
in the Copper Belt which would be due to intrusions of the later eruptions.

The Hazelton group igneous rocks of Anyox district are mainly
a single basic type. The rocks now consist mainly of actinolite but
contain also other products of alteration such as epidote, sericite, and
chlorite. About the only original constituent is plagioclase as basic as
bytownite. Some facies of the rock are very coarse grained. Originally
the rock was probably gabbro.