374 V. DOLMAGE.

numerous small veins in the pyrite. These veins become so large
and numerous in some of the pyrite as to leave only small skel-
etons of the original grains. Associated with the chalcopyrite,
and intergrown with it in a manner strikingly similar to the
graphic structure, is a large amount of zinc blende. It replaces
the gangue and pyrite, and appears in every way to have been de-
posited with the chalcopyrite. The common rule for the sequence
of ihese two minerals is for the blende to slightly precede the
chalcopyrite, but no evidence could be found to prove that rule:
in this ore.

The bornite-chalcopyrite ore of the central part of the vein
is by far the richest, specimens collected by W. F. Robertson
assayed 63 per cent. copper, 81 oz. silver, and 0.04 oz. gold per
ton. The transition from the chalcopyrite-pyrite ore to the bor-
nite ore cannot be traced owing to the lack of outcrops, but in
the main shaft it was noted that there was more chalcopyrite at
the ends than in the center of the shaft. ‘The structures seen
under the microscope showed mutual contacts between the chal-
copyrite and bornite in most of the cases but towards the south
of the tunnel there was some chalcopyrite which forms narrow
rims around the bornite with many spikes pointing into it, and
giving it a distinctly later appearance. This ore contains also a
large amount of silver-bearing tetrahedrite which was seen as
rounded or elongated masses with smooth even contacts in the
bornite and chalcopyrite, but with a preference for the chalco-
pyrite, or the contacts of the bornite and chalcopyrite. It was
never seen in veins and is undoubtedly primary, having come in
with the copper sulphides or in places slightly later than them.
Magnetite grains become common in the eastern part of the
main trench. They contain small veinlets of hematite which
never go beyond the edges of the magnetite, and many of them
are sprinkled over with numerous specks of chalcopyrite which
- grade down in size to submicroscopic. A few of these grains
were composed of bornite, and some of the larger ones were
slightly altered to covellite. Tetrahedrite was also found. No
hematite outside of the magnetite grains was seen in this ore ex-
cepting a very few scattered blades and rounded grains in the