Figure 55. Serpentinite of the Crooked amphibolite,
where it is A) foliated near Sovereign Mountain (Canadian

nickel for scale; GSC 191045) and B) evenly shear banded
near Etheridge Creek. (GSC 191046)

The serpentinite has not been examined microscopi-
cally. It varies from massive to brecciated, and local folia-
tion does not parallel the regional trend (Fig. 55). Talc
locally is associated with the serpentinite as discontinuous
lenses parallel to the regional foliation. Ultramafic rock
strongly foliated in the regional trend occurs locally with
the serpentinite. It consists of serpentine and remnant
pyroxene and plagioclase. Asbestiform serpentine rarely
fills uncommon thin fractures. The resistant serpentinite
forms irregular and steep topography.

Age and correlation

The Crooked Amphibolite may be the sheared and meta-
morphic equivalent of the Antler Formation and there-
fore part of the Slide Mountain Group, but no direct link
between the units has been made. If they are equivalent
the Crooked Amphibolite would be composed of Missis-
sippian to Permian rocks.

76

Economic geology

Minor amounts of copper staining in basalt and diabase
on Twin Sisters Mountain is the limit of recognized eco-
nomic minerals in the Antler Formation.

Structure and metamorphism

Discussion of the structure and metamorphism of the
Slide Mountain Terrane is divided into two sections; the
first dealing with the Antler Formation and the second
with the Crooked Amphibolite. Deformation within these
rocks may have occurred during and after emplacement
against adjacent terranes.

Antler Formation

Structures within the Antler Formation are divided into
3 categories. From oldest to youngest they are 1) soft sedi-
ment, 2) semiductile, and 3) brittle. The soft sediment
deformation may have formed in a completely different
structural regime than the other two categories.

Soft sediment deformation

The thin-bedded chert commonly hosts open to isoclinal
folds which predate the cleavage, and are restricted to
discrete horizons separated from undeformed chert by
bedding-parallel detachment surfaces. Their form varies
from recumbent long-limbed isoclines to box and irreg-
ular folds. The shear sense of the folds indicates mainly
northeastward transport.

The paleoslope along which these rocks moved may
have resulted from the same topography differential,
causing thrusting of the Antler Formation over Barker-
ville and Cariboo terranes.

Semiductile shortening

Included within this category are thrusts, and folds and
cleavage. The metamorphic minerals grow both parallel
to and across the cleavage.

Thrusts. The thrust faults duplicate stratigraphy within
the Antler Formation alone. They are determined from
repetition of conodont-bearing chert horizons. Because
the thrust faults are unseen, it is not known what their
intersection angles with bedding are, and in what direc-
tion they cut downsection. The thrust sheets determined
are on the order of 500 m thick, and contain the entire
age range known for the Antler Formation. The faulting
postdates Lower Permian rocks included in the thrust
sheets. It signifies shortening possibly caused by flow of
the Antler Formation down the paleoslope (recorded by
the soft sediment folds) and/or represent duplication
during the emplacement of the terrane.

Folds and cleavage. Folds involve all rocks of the Antler
Formation but are more obvious or prevalent in the sedi-
mentary rocks. They are of all scales, generally open to