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COPPER SILVER VEINS OF TELKWA DISTRICT. 359

into the bornite. The former relation is shown in Plate XXIIL.,
A. The contact between the two minerals in many places is not
sharp but the one color fades out very gradually into the other,
forming a mixed zone. Besides this chalcocite there is some
of a distinctly secondary nature which follows minute fractures
cutting through the bornite-chalcocite intergrowths. Where the
fracture traverses bornite areas it is lined with this secondary
chalcocite, and where it crosses the chalcocite, covellite is de-
posited. These veinlets frequently have chalcocite centers and
chalcopyrite margins, as shown in Plate XXIIL., B.

Chalcopyrite occurs sparingly in all the specimens and like the
chalcocite is of two generations. It occurs as a primary mineral
in the gangue sometimes occupying spaces which were originally
phenocrysts, and also in the bornite where the smooth rounded
contacts, and mutual intergrowths indicate a contemporaneous
deposition with that mineral. :

It also commonly occurs in a distinctly later generation, and
frequently forms extremely narrow but persistent borders be-
tween the bornite and the gangue, or between the bornite and the
hematite, in places penetrating the bornite along minute fissures.
These fissures often contain chalcocite in their centers and cut
independently both chalcocite and bornite. The replacement has
not gone far but numerous small spikes of chalcopyrite can be
seen shooting out into the bornite along crystallographic lines as
if an early stage of the lattice structure were being developed.
This is shown in Plate XXIII., B; the white mineral is the chal-
copyrite. Plate XXIV., A, shows one of these veinlets cutting
across a bornite area into an area of chalcocite.

Galena is sparingly present and is found only in the bornite
and bornite-chalcocite graphic structures, where it forms small
blebs or more often fine films appearing as almost submicroscopic
lines in the polished sections. These films are usually arranged
in one definite direction, and are probably controlled by the
cleavage of the bornite. Their arrangement is, however, only
approximately maintained and the thickness is also quite variable.
They have no connection with any fractures and are undoubt-

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