15

on this point. On the other hand, since some of these A veins join trans-
verse or diagonal veins, it is evident that some at least are of the age of
the B veins.

After the formation of the early bed veins and the silicification of some
beds, the belt was subjected to fracturing and the fractures were mineralized
with quartz to form the transverse and diagonal veins. Some of the A
veins were formed presumably at the same time as they have very similar
mineralization and join transverse or diagonal veins.

The fractures in which the transverse and diagonal veins occur were
formed after the rocks were folded and sheared. This is shown by the
clean way they cross sheared rock, by their lack of deformation, by their
change in strength and behaviour as they penetrate bands sheared in
different degrees, and by details of replacement in the wall-rocks. Their
parallelism and general similarity over distances of 8 miles or more suggest
strongly that all formed as a result of one general system of stress and in
one period.

The shapes and pattern of the fractures suggest that some were formed
by compression, some by tension, and some by torsion. The minor trans-
verse flexures occurring in some of the sheared rocks of the gold belt suggest
compression parallel to the strike of the rocks. Torsional stress is suggested
by sets of small, closely spaced, quartz-filled fractures occuring in
en €chelon arrangement. Many curving fractures filled by branch veins
ane also many straight vein-filled fractures appear to have been formed by

nsion.

While the fractures were being formed, or after they were formed, vein-
forming solutions filled the fractures to form veins. As was previously
stated, some veins have short, wedge-shaped branches projecting into the
convex side of associated flexures. This suggests strongly that the flexures
antedate the veins. If, as is suggested, the flexures are earlier than the
veins, and considering that the flexures are associated with narrow
fractures with no quartz and also with quartz veins of all sizes and that
the width of the flexure is in all cases about the same, it follows that the
veins were formed by filling of open spaces and not to any extent by
replacement. It also follows that inasmuch as large open fractures could
not exist, the fractures opened gradually as they were filled with quartz.
This gradual widening may have been accomplished by pressure exerted by
the vein-forming materials or by tensile stresses in the rocks. The writer
believes that the vein-forming solutions were under pressure but that this
pressure would not be sufficient to force the walls apart and, therefore,
that the openings widened by tension. Veins formed in this way will taper
to the ends, will tend to be widest in the central part of the fracture, and
although they may be lenticular the tendency will be to uniformity in width
with an absence of very wide bulges, and these are the characteristics of
the gold belt veins. If the vein-forming solutions were well distributed or
if the rocks were thoroughly fractured the tendency would be to form
many small veins rather than a few big ones.

The wall-rocks of the veins contain much coarsely crystalline pyrite.
Cubes of pyrite occur many feet from any vein, but a great many examples
serve to show that pyrite is more plentiful near veins than at a distance
of several feet, and there seems little doubt the pyrite was formed from

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