39

The source of the deposits is not known, but is assumed to be under-
lying parts of the Coast Range intrusives.

The quartz vein deposits can provide only small tonnages. They are
in general too narrow to be attractive as sources of flux and can be mined
only in a small way as silver ore. .

COPPER-BEARING DEPOSITS

The copper-bearing deposits are of two types: (1) vein-like replace-
ments and veins; and (2) disseminations. Very few deposits of the dis-
seminated type occur, but they as ‘well as the vein or vein-like type occur
sn a well-defined belt known locally as the “Copper Belt”. In_upper
Kitsault valley fifteen or more copper-bearing deposits le in the Copper
Belt and one lies in adjacent sedimentary rock. The Copper Belt is
between 5 and 10 miles east of the edge of the Coast Range intrusives
and is nearly but not exactly parallel to the contact. The belt is 15
miles long and about 1 mile wide.

Copper mineralization occurs also in the northeastern part of Alice
Arm district, in the vicinity of Kinskuch lake, but no deposits have yet
been outlined there. A few copper-bearing deposits occur in the southern
part of the district in rock that appears to be a southern continuation
of the Copper Belt.

The rocks of the Copper Belt proper compared with the other igneous
rocks of the area are highly sheared and much altered to, or replaced by,
such minerals as sericite, chlorite, calcite, and pyrite. The belt consists
chiefly of fine-grained, fragmental volcanic rocks and of crystalline rocks
that are probably mainly intrusive. In places the rocks could not be
identified as certainly either massive or fragmental. Inclusions of sedi-
mentary rocks in the intrusives are fairly common. Some inclusions con-
tain considerable disseminated pyrite and chalcopyrite. The rocks are
not different in mineral composition from the other rocks of the area, but
the belt is distinguished by the presence of copper deposits, by the sheared
nature of the rock, and by the universal presence of pyrite. The belt may
continue south and the rocks may change from felsites and feldspar por-
phyries to augite porphyrites.

The disseminated copper deposits appear to be very low grade and
have not been developed to any great extent. No definite ore-bodies have
been found. If any exist they will probably be in areas where copper is
more than ordinarily plentiful. The deposits were formed by the thorough
soaking of the fractured rock with mineral solutions. The deposits of this
type are well exemplified by those on the Red Bluff group. On this prop-
erty a rock of felsite or augite porphyrite type has been sheared, shattered,
altered to sericite, chlorite, and calcite, and into it disseminated pyrite,
chalcopyrite, and pyrrhotite have been introduced.

The veins and vein-like replacements have received some attention
and a few have been developed by adits and by diamond drilling. No
considerable tonnage of copper ore has been indicated at any place, but
a few, vein-like deposits several feet thick, a few hundred feet long, and
containing 2 to 10 per cent copper have been encountered. The deposits