General Geology

as a whole appears to have suffered alteration by percolating solutions. On
the east side of Sias Mountain the orthoclase phenocrysts of this hornblende
granite are up to 1 inch long. Thin sections of this rock also show the
feldspars to be clouded and the hornblende altered to chlorite and magnetite.

South of Musclow Lake the plutonic rock is a medium-grained, dark grey
granodiorite consisting of 65 per cent andesine Anjo, 20 per cent hornblende
and minor biotite, and 10 to 12 per cent quartz, the remainder accessory
minerals.

Between Tahtsa and Nanika Lakes red granite, grey quartz diorite,
and dark granodiorite are present. Tsah Mountain is composed largely
of a red hornblende granite that shows evidence of alteration by deuteric
action and is similar to the rock between Surel and Lindquist Lakes.

On Redslide Mountain the plutonic rock is a medium-grained horn-
blende-biotite granite, in which the feldspars have a slightly pink colour.
In thin section all minerals but quartz appear to have suffered deuteric
alteration. Near Anzac Lake and Tableland Mountain the stocks are a
medium- to fine-grained pink granite. In thin section, the feldspars and
ferromagnesian minerals are seen to be altered.

The plutonic rock composing the stock on Sibola Peak is a dark grey
hornblende-biotite granodiorite. Diorite and a light coloured granite outcrop
on Chikamin Range but a large part of the pluton is covered by the cirque
glacier on the peak.

The plutons in the vicinity of Tagetochlain Lake and Nadina River
differ from the regular Coast Intrusions in that they are porphyritic. The
feldspar, which is oligoclase, occurs in phenocrysts up to 4 inch by 4 inch
in size in a groundmass of fine-grained quartz, plagioclase, and hornblende.
Hornblende of the common variety may also occur as phenocrysts. These
rocks may be classed as porphyritic diorites.

The granodiorite in the vicinity of Kitlope Lake had suffered less
alteration than the plutonic rocks observed elsewhere in the main mass. In
localities close to the contact with the Hazelton group the plutonic rocks
are commonly red or pink and invariably altered. In some of these cases the
red colour was due to the inclusion of hematite particles in the feldspars.
Commonly the feldspars are altered to zoisite and sericite, and the hornblende
is altered to chlorite and magnetite.

Quanchus Intrusions (7). The Quanchus intrusions underlie a large
part of the high plateau between Eutsuk and Ootsa Lakes. They form the
core of the Quanchus Range, Michel Peak, Chef Ridge, and the southern
slope of Eutsuk Peak. They also outcrop along the shore of Eutsuk Lake

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