356 V. DOLMAGE.

chalcopyrite, chalcocite, hematite and tetrahedrite, associated with
epidote and quartz.

There are two types of deposits, those consisting of small re-
placement bodies disseminated through a porous and _ highly
epidotized bed of tuff, usually more highly concentrated along
joint fissures which cut the bed vertically; and those which are
clearly open fissure fillings, with well-defined walls, and a gangue
of banded quartz.
The Replacement Type.

The best example of the replacement ore bodies is the Excelsior
claim in Dominion basin, one of the most promising deposits in
the district. The mineralized bed of tuff outcrops on the nearly
vertical wall of the basin at an elevation of 5,750 and 300 feet
above the bottom of the basin. This bed, which is highly altered
and carries a large amount of bornite, chalcopyrite and chal-
cocite, is interbedded with the typical unaltered tuffs of the
Hazelton formation. The strata dip about 18 degrees to the
south, away from the contact. Near the south end of the outcrop
the tuffs are cut at nearly right angles by a 20-foot diabase dyke
which carries a small amount of chalcopyrite and a large amount
of magnetite.

The tuffs adjoining the mineralized bed are purplish, dense,
fine-grained rocks with conspicuous crystal fragments of feldspar
up to a centimeter in length, and are typical of most of the tuffs
of the Hazelton formation. Close to the ore-bearing bed they
are highly impregnated with epidote, and near the ore shoots
contain a considerable amount of bornite and chalcopyrite.

Lhe Mineralized Bed—The bed which carries the copper is
an unusual rock both in appearance and composition, due to its
nearly complete alteration to hornblende and epidote. The most
normal phase, or that which is encountered at a distance from the
ore shoots, is a yellowish-green rock, containing in a dense, fine-
grained groundmass, phenocrysts of green, fibrous hornblende
up to 3 or 4 millimeters in diameter. Under the microscope it
was found to consists entirely of epidote and hornblende in about
equal amounts, with a very few grains of hematite, and a great