12

have the persistence of those occupying faults approximately paralleling
the beds, for although the lenses are locally more than 20 feet wide they
pinch out quickly or split up into several veins.

Since any individual vein tends to be confined to a rock type and
does not, as a general rule, strike across several rock types, it is reasonable
to conclude that down the dip the vein will also remain within the same
rock type. The vein will, therefore, pitch along the dip of the strata and
will be found not vertically above or below where it was discovered, but
above or below along the direction of dip of the rock. Any vein of the
diagonal or transverse type if it bottoms on an unfavourable rock member
will ordinarily bottom along the plane marking the junction of the host
rock and the unfavourable rock.

Mining has not yet gone far enough to prove this rule, but if the rule
should be proved it will be obvious that veins may follow a favourable
member down the dip until the structure or rock type becomes unfavour-
able or until a point is reached where fracturing was inadequate. The
best hope for deep mining would appear to depend on the belief that
adequate fractures will occur in the favourable members a considerable
distance down the dip. Because the favourable part of the gold belt
contains numerous veins over such a great length and at considerable
differences of elevation there seems to be little doubt that the vein frac-
tures are very closely related to the general structure and will follow the
favourable rocks down the dip to where, for reasons not yet apparent,
they become inadequate as loci for commercial ore-bodies.

The vein deposits can be divided into four classes, the division being
based on the relationship between the fractures and the structure of the
country rock:

(1) Transverse veins
(2) Diagonal veins
(3) Strike fault veins
(4) Bed veins

The transverse and diagonal veins contain pyrite and arsenopyrite,
and many have small amounts of gold, galena, sphalerite, bismuth-lead
sulphide, marcasite, telluride, and scheelite, in a gangue of quartz, com-
monly with some ankerite, less sericite, and very rarely calcite. In some
veins pyrite approximates 50 per cent of the vein by volume, but in
most veins the quantity of pyrite is smaller. Gold appears to be most
plentiful in the veins containing the most pyrite, but the amounts of the
two minerals are not in direct proportion. Veins with very little pyrite
are In general uncommercial, but those with 50 per cent pyrite are not all
richer than those with 25 per cent pyrite. Arsenopyrite occurs with the
pyrite in most of the veins, but is always a minor constituent. Galena
is rare except in a few veins, mainly in the southern part of the belt.
Scheelite is present in small quantities in many veins throughout the belt
and appears to be most plentiful in the northwestern part. Sphalerite
and marcasite occur locally in a few veins. The lead-bismuth sulphide
occurs in nests in many veins, but is rare. Telluride occurs in very small
quantity associated with the lead-bismuth sulphide.

A characteristic of the transverse and diagonal veins is the coarse-
ness of the pyrite crystals. Typically, the pyrite is in cubes 1 inch or