during the waning stages of metamorphism the tempera-
ture would drop and the precipitation could proceed at
greater depths than previously.

Galena, sphalerite and barite are hosted by carbon-
ates and clastic rocks ascribed to the Downey succession
and black siliceous slate, phyllite and argillite ascribed
to the Hardscrabble Mountain succession along Cunning-
ham Creek and near Roundtop Mountain (Longe and
Hodgson, 1978; 52°55’N, 121°22’W). The barite appears
to be stratiform and the galena contains impurities of
silver. Some quartz veins in the units contain gold and
scheelite. Gossans with anomalous concentrations of zinc,
silver and cadmium overlie black fine grained clastic rocks
of the Harveys Ridge succession on Harvey’s Ridge
(Fraser, 1978; 52°51.2’2N, 121°22’W).

Scheelite is found in quartz veins (Mulligan, 1983) in
host rocks of Hardscrabble Mountain and Downey
succession.

Structure and metamorphism

The Barkerville Terrane consists of essentially one struc-
tural package; defined as a deformed sequence of rock
separated from others by an angular unconformity. The
Snowshoe Group, as the main structural package, may
be overlain unconformably by a younger one, the
Permian Sugar limestone. Within the Snowshoe Group
there may be two structural packages divided by a pro-
posed unconformity beneath the Downey succession. In
spite of this possibility the Snowshoe Group is treated
as one structural package.

Structures of the Snowshoe Group are divided into
3 categories; from oldest to youngest they are 1) shear,
2) ductile shortening, and 3) brittle shortening and exten-
sion. The categories highlight aspects of a spectrum of
strain conditions. The spectrum began with shear in the
latest Triassic(?) and ended with brittle extension due to
uplift in the Eocene. The metamorphism is included in
the discussion of the structures because it controls to a
large degree the strain parameters. The strain environ-
ment is emphasized over the superposition of structural
elements. As a consequence there will be little importance
attached to designating structures as S, or S) etc.,
although for comparison purposes this is done in its
simplest form in Table 16.

Shear

This category of structures, formed by shear, consists of
mylonitization (as defined by Wise et al., 1984), bedding-
cleavage, and isoclinal recumbent, commonly rootless
folds. It includes the oldest structures.

Mylonitization

Mylonite of the Snowshoe Group is concentrated in two
areas; along the western margin of the Barkerville
Terrane, and near the Island Mountain amphibolite.

Table 16. The structures of the Barkerville
Terrane organized into a deformation series (D)
of surfaces (S), and folds (F).

Event Structure Metamorphic mineral |

D. Extension faults which trend Quartz, pyrite, gold, |
NNE and N, commonly vein ankerite, scheelite, |
filled, generally with oblique dis- galena (some evidence |
placement (some of these faults for earlier formation), |
may be D,). silver |

| D, Open folds, warps, kinks, and _—Chlorite (retrograde),
Crenulations (F,) of variable tourmaline (could also
Orientation; reverse strike faults, have grown post

| (F,) steeply dipping. chlorite). Period of

quartz, pyrite, gold,

| ankerite, scheelite,

galena and silver

mineralization may

have started at this

time

D; Spaced crenulation axial surface Quartz, muscovite,
cleavage (S;); asymmetric flow biotite? chloritoid

(S;, to concentric folds (F,) plunge

Fz) to NW but may have variable

Orientation where they are E

directed

| D, Ductile shear
Pervasive axial surface cleavage Muscovite, biotite,
(S,) asymmetric flow folds (F,) garnet, quartz
| (S,, plunge to the NW, but may have
| F,) variable orientation where they
are E directed

D, Ductile shear, bedding cleavage Muscovite, quartz,
(S;); isoclinal recumbent root- albite?
(S,, less folds (F,) that plunge NW

Sutherland Brown (1957) described flaser quartzite from
the Snowshoe Formation where it is presently mapped
as the Downey succession.

The most intensely mylonitic rocks, including some
ultramylonite, are at the contact of the Crooked and
Island Mountain amphibolites. This proximity is assumed
to imply that the amphibolites are thrust onto the Snow-
shoe Group. The sense of shear has not been determined
for these rocks, however, Rees and Ferri (1983) suggested
that the Crooked Amphibolite is thrust to the east over
the Snowshoe Group, as determined from features within
the Quesnel Lake orthogneiss near Seller Creek. The
study is restricted to one outcrop of gneiss and relies
heavily on features of the rock which may be younger
than the initial shear fabric of the Snowshoe Group rocks.

The mylonitic fabric is defined by elongated quartz
grains supported in a matrix of fine grained recrystallized
quartz, sericite, muscovite and variable amounts of
sphene and opaques. Where primary feldspar is present
the crystals are strained, but elongation of the grains takes
place by fracturing. Because of this the feldspar occurs
commonly as augen. Foliation of the mylonite is defined

67