General Geology
Coast Intrusions

Subsequent to the deposition of the Hazelton group, emplacement of
plutonic rocks was widespread throughout the map-area, particularly in the
west half. The period of emplacement persisted at least till the end of the
Cretaceous era, and though no plutonic rocks of Tertiary age were recognized
in the area, post-Upper Cretaceous plutonic rocks occur on Nadina Mountain
(Lang, 1942) just to the north.

Mapping showed that the southwestern one-third of the map-area is
underlain by plutonic rocks of the Coast Intrusions. In addition to this main
mass, and to the east and northeast of it, many stocks, bosses, and cupolas,
commonly possessing no particular characteristic other than a general
similarity to the main mass are present. Several of these plutons are,
however, sufficiently distinctive to be described as separate groups or
individuals. For descriptive purposes the Coast Intrusions have been divided
into the following units.

Maine ASS git een neers Se. 2. oes uh Se ae (8)1
Quanchusnntrusionsy. Pee ce ee ie (7)
DIOMte Rane ease Shek ee shar Rutan ate (4)
GAD Dro ne i ie eee SE tae (3)
IRC oraniterer = ete Vege aS aOR (6)
IRE CES WETILE ei cea tec eee ete ean ere (5)
INMountEBOLOMIIStOC Kae eaten es enna te (10)
SwinosPeakistockr eee te eee soca (9)

Commonly the plutons are separated from one another and only in one
instance were different types found, in contact. However, all are in contact
with the Hazelton group rocks. and two of the plutons were found in contact
with the Lower Cretaceous rocks on Swing Peak and Laventie Mountain.

The term Coast Intrusions was used by Rice (1947, p. 33) to include
those plutonic rocks which occur largely in the Coast Range but may be
present outside that physiographic province. They comprise a distinctive suite
of rocks including granodiorite, granite, quartz diorite, diorite, quartz mon-
zonite, monzonite, and related rocks. In southern British Columbia they
may be separated from an intrusive suite that is less acidic and is characterized
by reddish syenites that locally contain sufficient quartz to be classed as
a granite. This latter suite overlaps the Coast Intrusions in time sequence
and is perhaps a little younger. No general term has been given to these

1 Number in brackets is that of the unit in the map-legend.

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