)

Strike faults are the commonest type in the belt. These parallel the
strike and dip of the strata and are of the normal type, but in some there
was also some movement along the direction of strike. Faults of this type
do not follow the bedding around sharp curves in strike and dip but cross-
cut such places at a low angle. The throw on these faults is less than 25
feet and on many is less than 6 feet. In general such a fault with a
throw of only 20 feet has much crushed rock in it and the rock where not
crushed is drag-folded. Some have branch faults that may swing to a
widely different strike before they end. The lengths of the strike faults have
not been measured but some are at least 500 feet long. The strike faults
may be related to those striking north but a relationship has not been
proved. A branch of a northerly striking fault may curve to parallel the
beds but the strike faults may not all be branches of the larger northerly
striking ones. The strike faults appear to be late and may be younger
than those striking north.

Uglow has mapped a set of northeasterly striking and northwesterly
dipping normal faults that are younger than the late Paleozoic rocks of
the area, but none of these faults was recognized with certainty in the
gold belt. Faults striking northeast are crossed by the Shamrock tunnel
near Barkerville, but the displacement could not be ascertained.

MINERAL DEPOSITS

The mineral deposits of the belt consist of quartz veins and of pyritic
replacements. Many of the quartz veins contain much pyrite and are of
value because of their gold content. The replacement deposits consist of
pyrite and are also valuable because of their gold content.

Veins. A great many of the pre-mineral fractures are occupied by veins.
The veins and also the unmineralized pre-mineral fractures are strikingly
related to the rocks and to the geological structure. An understanding of
this relationship has a vital bearing on the problems of mine development
and search for ore-bodies.

The different rock types reacted differently under stresses causing frac-
turing. Limestone is cut only by the stronger fractures. The limy clastic
sediments did not fracture readily. The argillites where not severely
sheared fractured well. Quartzites also fractured readily, but argillaceous
quartzites appear to have been the most favourable rock for fractures.
The degree of fissility induced by shearing stresses also influenced fractur-
ing. Some very fissile, fine-grained quartzites have many joint cracks,
some occupied by narrow veins, whereas quartzites only slightly sheared
have fewer but more persistent fractures. Fractures are rare in argillaceous
rocks that have been sheared to graphite schists, but slight shearing appears
te have rendered argillites more amenable to fracturing.

A characteristic of most of the transverse fractures and veins is that
they do not continue across rocks of dissimilar type. If a fracture is
strong in an argillaceous rock it fades out rapidly in adjoining quartzite,
and if another is strong in quartzite it dies out rapidly in adjoining
argillites. But sections consisting of argillites and quartzite interbedded in
thin beds act as a unit and fractures may persist through.