10

In the southern part of the area serpentine is believed to be intrusive
into the Dease series and in the northern part of the area it is associated
with bodies of augite porphyrite which occur in the lower part of the
McLeod series and also to some extent throughout the series. A granite
dyke intrudes the serpentine 3 miles northwest of the large bend in Muddy
river. The serpentine is, therefore, of McLeod age believed to be Jurassic.
Similar occurrences of serpentine in southern British Columbia and in
southern Yukon are considered to be Jurassic in age.

Batholithic Rocks

Batholithic rocks occupy approximately 50 per cent of the map-area.
The Cassiar batholith crosses the central and northern parts of the area
in a northwest direction and is from 20 to 25 miles wide. Several large
bodies of older rocks occur as roof pendants or inclusions within the batho-
lith. The granitic body of Hotailuh mountains is exposed for 20 miles
along its northern contact and is known to be at least 10 miles wide.
Several outlying stocks of granite occur on both sides of the Cassiar
batholith.

The batholithic rocks are usually massive, medium to coarsely crys-
talline, and dark to light grey in colour. They range in composition from
diorite to granite. Gneissic and schistose phases are found close to the
inclusions and roof pendants of the older rocks. Aplitic and pegmatitic
varieties occur locally in both the Hotailuh and Cassiar intrusive masses.

The contact between the batholithic rocks and the McLeod formation
is fairly flat in Hotailuh mountains. On the north side of the Cassiar
batholith the contact is steep and east of Dease river is believed to be a
fault contact.

The age of the batholithic rocks is not definitely known. They are
intrusive into volcanic and sedimentary rocks of the McLeod series. The
McLeod series is correlated on the basis of lithological character with
Jurassic sediments and volcanics of central British Columbia and southern
Yukon, so the indicated age of the batholithic rocks is not older than
Jurassic.

Dykes

Dykes are of very infrequent occurrence in the area, but there are at
least three types. Dykes so highly altered that the rock type could not
be ascertained are abundant near Quartz City. They are roughly parallel
to one another and strike north 30 degrees to 60 degrees east, crossing the
intruded rocks at right angles to their strike. Though observed only in the
voleanics it is not known whether they are restricted to these rocks or
extend along the strike into adjoining sediments. On the mountain at
Snow creek the dykes are 1 foot to 10 feet wide and are so closely spaced
that they constitute 10 to 20 per cent of the total rock in a belt 2 to 3
miles wide. Some of the rock in the canyon on Quartz creek near its
junction with Trout creek appears to be the same as that of the dykes,
but in this place it occurs in widths up to 300 feet. A striking feature of
the dykes is that they contain many narrow quartz veins parallel to their
strike and also commonly have quartz veins along one or both walls.