12

elongated in the direction of movement of glacial ice in the nearby valleys,
and glacial erratics are found close to the summits of the highest cones.
The cones, therefore, must have been in existence during at least a part
of the Pleistocene. The older sedimentary and igneous rocks, in contact
with flows and cinders where they normally would be protected from ice
erosion taking place after the cones were built, are fresh and unweathered,
thus suggesting an earlier glaciated surface. The cones were, therefore,
formed during the Pleistocene. In Dease Lake map-area Johnston found
glacial erratic boulders in the volcanic tuffs and considers the cinder cones
to be of early Pleistocene age.

ECONOMIC GEOLOGY

Prospectors have been at work in Cassiar district since about 1860,
but production was small until placer gold was discovered on Thibert
creek in 1873. Placers were discovered on Dease and McDame creeks
shortly after those on Thibert creek and in 1874 the production of gold
from the district was $1,000,000. This was the best year and despite new
discoveries on creeks in the outlying districts production declined steadily
after 1875. The total value of gold taken from Cassiar district amounts
to about $5,000,000, of which $1,500,000 is reported to have been taken
from McDame creek and $1,200,000 each from Dease and Thibert creeks.

During the past ten years interest in Cassiar district has been revived
by new placer discoveries. These discoveries, although relatively unim-
portant, are interesting because they show that placer deposits are not
confined to McDame, Dease, and Thibert creeks, but do occur in other
localities where geological conditions are somewhat similar.

Despite the large production of placer gold, very little effort had been
made prior to 1933 to locate lode gold deposits. In 1934, a quartz stringer
containing high-grade gold ore was found on Quartz creek, a tributary of
McDame creek. A ton of ore from this vein was shipped out by airplane
and was found to contain 4 ounces of gold. The shipment aroused a good
deal of outside interest, especially when it was reported that other veins
in the district contained free gold. By the end of the 1935 season, several
hundred claims had been staked in the vicinity of Quartz City, near the
junction of Snow and Quartz creeks, and about forty veins containing
free gold had been found.

GOLD PLACERS

According to Johnston,! placer gold deposits occur in three or pos-
sibly four different ways in Dease Lake area. ‘“‘(1) In gravels resting on
bedrock in the old high-level channels of Dease and Thibert creeks. These
gravels are only a few feet thick and are cemented in places. They are
probably pre-Glacial (late Tertiary) in age. They formed the most
important source of placer gold in the district, except the beds of those
streams where the old channel has been cut away. (2) In glacial or (and)
interglacial gravels that partly fill the old stream channels and present
valleys. Some gold was included in the glacial drift by ice-erosion of pre-
existing placers and was reconcentrated to some extent by stream action.

1 Johnston, W. A.: Op. cit.