Figure 45. Grit of the Tom succession of the Snowshoe
Group on Island Mountain where it overlies the Island
Mountain amphibolite. (GSC 191040)

Olive and grey micaceous quartzite consists of poorly
sorted clasts of quartz (glassy clear, white and minor blue)
and minor feldspar (Fig. 45). Secondary muscovite, albite
and minor chlorite form the matrix. Zircon and second-
ary tourmaline compose most of the accessories.

Sheared quartzite contains a similar mineralogy as the
micaceous quartzite, except that it has less matrix mica
and contains | to 4% garnet. The quartz grains are pencil
forms with ratios of long to short axes of 4 or 5 to 1.
The garnet forms an interstitial growth with fractured
mylonitic quartz and occurs as fragments of distended
grains separated by sericite. The sheared quartzite is inter-
layered with muscovite schist and is mainly near the con-
tact with the underlying Island Mountain amphibolite.

The thrust sheet containing the Tom succession has
no known root and must now represent a klippe, pos-
sibly of a large overturned fold of Tom succession and
Island Mountain amphibolite. The distended and inter-
stitial garnets together in the sheared quartzite sequence
suggest a history of garnet growth outlasting shearing.
The age and correlation of the Tom succession is
unknown.

Sugar limestone

The Sugar limestone consists entirely of crinoidal lime-
stone. It is unique in the Barkerville Terrane as the only
recognizable crinoidal limestone.

The limestone is exposed in one locality at the head
of Sugar Creek, after which it is informally named. It
was first described by Struik (1980) as part of the Green-
berry limestone of the Guyet Formation. Later (1982a,
b) I distinguished it from the Greenberry limestone which
is restricted to the Mississippian. The thickness is less than
15 m.

The Sugar limestone rests sharply on black siltite and
phyllite of the Hardscrabble succession on the southwest

slope of Hardscrabble Mountain. There is no indication
that the contact is a fault.

The grey limestone consists of some 30% of 0.5 to
2 mm size crinoid stem fragments, less than 6% silt size
quartz and feldspar grains (some of which may be second-
ary), and a finely crystalline dusty calcite matrix. The rock
is disrupted by approximately 5% stylolites. Locally the
limestone is silicified to light grey chert in 2 to 6 cm bands,
possibly defined by bedding.

The disorganized bioclasts suggest reworking prior to
deposition in the limestone. The reworking may be a
result of wave action or sediment flow in a subaqueous
environment. There is no mixing of shallow and deep
water fauna within the limestone to indicate the trans-
port of shallow water debris into deeper water.

Age and correlation. The Sugar limestone is Lower
Permian as determined from extracted conodonts
(Orchard and Struik, 1985; see Appendix A). The exist-
ence of this Lower Permian limestone is critical in the
reconstruction of the geological history of the area. It
implies that within the Barkerville Terrane there may be
an unconformity of Paleozoic age. Because the strati-
graphic sequence below the unconformity is completely
different from that underlying the Permian of the Cari-
boo Terrane it implies that the Paleozoic stratigraphy
and/or structural history of the two terranes is different.
Either of these cases requires that the terranes be suffi-
ciently separated in space to allow for the different
geological histories.

Several units of the Barkerville Terrane are correlated
with units of the Eagle Bay Formation. The Eagle Bay
Formation is part of the Kootenay Terrane, which has
an unconformity between lower Paleozoic clastic rock
and overlying Mississippian to Permian(?) rock. The
unconformity below the Lower Permian Sugar limestone
may be the same.

Island Mountain amphibolite

The Island Mountain amphibolite consists mainly of
amphibolite with minor amounts of tuff(?) and cataclastic
quartzite. This amphibolite is distinguished from that of
the Ramos succession by its lack of associated carbonate
and coarsely crystalline amphibole. The finely crystalline
amphibolite of these units appears much the same in hand
specimen.

The amphibolite forms the peak of Island Mountain
and underlies the drainage area of Tom Creek. It was pre-
viously mapped as a hornblende gneiss of the Snowshoe
Formation by Sutherland Brown (1957), as undifferen-
tiated Snowshoe Formation by Campbell et al. (1973) and
as unit Se by Struik (1982a). Good reference areas include
Island Mountain and Tom Creek. Thickness of the
amphibolite is less than 150 m.

The Island Mountain amphibolite is believed to be
thrust onto grit, pelite and limestone (assigned to the
Downey succession) because of the stratigraphic omis-