Ribbon chert of the Antler Formation on

Figure 54.
Sliding Mountain. (GSC 191044)

The white mica and chlorite, both primary and sec-
ondary, form concentrations defining fine and coarse
layering. Detrital grains of quartz are rimmed by mica
and locally deflect foliation where it exists. Pressure solu-
tion of detrital quartz grains has produced sutured and
cuspate boundaries. Stylolites were found in all cherty
sediments examined except the pure chert. Two genera-
tions of stylolites were noted in one sample. The promi-
nent direction of stylolites is parallel to the bedding and
this is offset by vertical stylolites: the two generations may
have been penecontemporaneous. Veining generally at
high angles to bedding existed prior to the stylolites along
which they are offset. Veinlets are filled with various
forms of silica. Cherts with no stylolites are suspected
to have also undergone pressure solution, but did so
without formation of stylolites because of their purity.
Sutherland Brown (1957) reported that detrital mineral
trains crossed veinlets showing their nondilational mode
of formation.

A thin bed of tan siltstone interbedded with clean grey
cherts on the ridge northwest of Mount Murray was seen
nowhere else.

Age and correlation

Unsuccessful attempts were made to extract radiolarians
from the cherty sediments following the procedure out-
lined by Pessagno and Newport (1972). Certain cherty
pelites, however, yielded conodonts, which, although
slightly etched, were sufficiently recognizable to be iden-
tified to species level in several cases. The faunal descrip-
tion provided by M.J. Orchard is given in Appendix A.

The described conodonts are the only datable fossils
known from the Antler Formation and identify at least
part of it as Early Mississippian to Early Permian.

The Antler Formation correlates with other volcanic
assemblages of the Slide Mountain Terrane (Struik and
Orchard, 1985), the Carboniferous or Permian Anvil
Range Group and allochthonous coeval ophiolitic rocks
of the Anvil Allochthon (Tempelman-Kluit, 1979), the
Sylvester Group in Cassiar Mountains, the Nina Creek
succession of Omineca Mountains and the Fennell For-
mation and Kaslo Group of southern British Columbia.
Age relationships between the Antler Formation and
underlying units indicate a thrust contact between them.
Presently the age data and stratigraphic-structural rela-
tionships between the Antler and older formations require
a minimum displacement for the Antler Formation of
50 km eastwards.

Crooked Amphibolite

This unit consists of amphibolite, serpentinite, sheared
mafic and ultramafic rocks and talc. It is distinguished
from the Antler Formation by its shear fabric and amphi-
bolite, but is indistinguishable from the Island Mountain
amphibolite of the Snowshoe Group.

The unit is exposed in a thin northwest-trending zone
from Wingdam to Cariboo Mountain. It extends beyond
the map area northward to near Prince George and south-
ward to Clearwater. There is no type area; the name was
derived from Crooked Lake where the unit is involved
in a regional antiform-synform pair and was described
by Campbell (1971). It varies in rock type along its length,
being mostly serpentinite northwest of Cariboo River and
amphibolite to the southeast. The Crooked Amphibolite
may be up to 300 m thick, but is locally missing.

The contact to the east with Barkerville Terrane is a
fault, marked by shear within adjacent rocks. To the west
the contact with Triassic and younger rocks of Quesnel
Terrane is thought to be stratigraphic because of region-
al continuity but locally displays shearing.

The amphibolite is dark green and weathers dark olive
green. It consists primarily of amphibole, chlorite, plagio-
clase and epidote. Crystal size ranges from 0.01 to 1 cm
on average with epidote being the smallest. The amphi-
bole is mostly actinolite, which is locally mixed with horn-
blende, and defines the foliation. The plagioclase is oli-
goclase and the chlorite generally forms mats as part of
the matrix. Accessory minerals include sphene and calcite.

4D