CHAPTER II
GENERAL GEOLOGY
GENERAL STATEMENT

Stewart-Bear River area is at the eastern margin of the Coast Range
batholith which forms the Coast mountains from Vancouver to the north-
western boundary of Yukon. It is generally conceded that intrusive rocks
have been the source of most of the metalliferous deposits in British Col-
umbia, and with this idea in view much geological work has been concen-
trated along the borders of the Coast Range batholith. The formations
bordering the batholith in the area being described are of volcanic and
sedimentary rocks, chiefly Mesozoic, but in part possibly older. They are
part of a long belt of similar rocks fringing the batholith for most of its
length in British Columbia. In some places in this belt the ages of the
Mesozoic rocks have been determined within narrow limits, but in most
places this is not so.

The oldest rocks of the Stewart-Bear River area are the Bitter Creek
argillites. These are overlain conformably by a series of volcanic rocks
composing the Bear River formation. Both these formations contain metal-
liferous deposits. Locally overlying the voleanic rocks is the Nass forma-
tion, a series of argillites and other sediments in general void of mineral
deposits. Intrtsive into the Bear River and Nass formations are stocks
of augite porphyrite, most of which contain metalliferous veins. The east-
ern contact of the Coast Range batholith passes through the area and the
batholith and its many related intrusives are later than the rocks previously
mentioned. Pleistocene drift and Recent clays are present locally.

The Nass formation, in general barren of mineral deposits, is more
largely developed northeast of the area where it occupies a large, elongated
district lying east of and roughly paralleling the Coast Range batholith.
The width of the mineralized country is, therefore, the distance between
the western edge of the area occupied by the Nass formation and the east-
ern edge of the batholith. This distance in the vicinity of Portland canal
is approximately 18 miles. In other words the mineral belt is, in general.
coextensive with the area underlain by rocks that border the batholith and
are older than the Nass formation.