General Geology

in British Columbia are many groups of rocks that are at least in part
correlative with the Takla group, such as the Vancouver group of Vancouver
Island and the Nicola group of southern British Columbia. Armstrong (1949,
pp. 58-62) gives a complete list of these groups west of the Rocky Mountains.
Commonly they are unfossiliferous and because of this character some Takla
group rocks may have been included with the Hazelton group.

Hazelton Group

The name Hazelton group was applied in 1909 to a series of interbedded
marine and continental sedimentary and volcanic rocks that underlie a large
part of west-central British Columbia, east of the Coast Mountains. These
rocks are mainly of Jurassic age but appear in places to grade upwards into
Lower Cretaceous strata, particularly where the beds are of continental
origin. Many workers have investigated these rocks in various parts of
central British Columbia, but to date it has not been possible to define their
upper and lower limits, or the proportion of volcanic and sedimentary strata.
These strata vary from place to place and a section at one locality will be
greatly different from that at another. The Lower Middle Jurassic (Bajocian)
succession of sedimentary strata provides a widespread horizon marker that
is easily identified by its abundant fossil content. This unit is commonly
underlain and overlain conformably by volcanic rocks. Volcanic rocks of
the group are characterized by a high proportion of tuff and breccia. Flows
are mainly andesitic or basaltic but more acid varieties do occur. Overall
the volcanic rocks are dominantly andesitic in character. Greywackes form
a large proportion of the Bajocian sedimentary rocks, commonly formed of
tuffaceous material derived either from the erosion of earlier tuff beds or
by original deposition of tuffaceous material in water. Less common than the
greywackes are dark argillites and light grey-green chert. No limestone beds
were observed but some of the sedimentary strata are high in calcium.

As the rocks of the group are mainly of Jurassic age they are intruded
by the Coast Intrusions, which has caused some dislocation and a general
metamorphism that has given rise to the formation of epidote. This pistachio-
green mineral is very common in all rocks of the group and is particularly
abundant in contact zones.

History

The term ‘Hazelton Group’ was first used by W. W. Leach (1910) to
include the sedimentary rocks found near the town of Hazelton and the
porphyritic tuff, breccia, and flows that occur in the Telkwa River valley. The

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