77.

rocks at or close to the granodiorite contact. This body of magnetite
seems to be quite separate from the main occurrence, which lies to the
east and 100 or more feet above it.

At the southwest end of the ridge, 3,500 feet away from the main.

tunnel and across an intervening area of greenstones, are other exposures
of magnetite. These for the most part occur in a stretch of 300 feet
ending at the side of a small stream. Five groups of outcrops are visible.
Each is small and consists of a few inches or several feet of comparatively
pure, fine-grained magnetite with bordering zones of greenstone impreg-
nated with magnetite. A short distance downstream, a body of magnetite
a few feet wide is visible for a short distance. ;

MODE OF ORIGIN

The main ore occurrence at the northeast end of the ridge presents
many of the essential characters of the type of deposit known as contact-
metamorphic which is exemplified by the magnetite deposits of Texada
island and elsewhere. In this case the replacement has taken place along
the contact of a body of limestone with underlying, fine-grained, igneous
rocks presumably belonging to a voleanic series. The plane of contact
in spite of irregularities has a general low dip. The magnetite-garnetite
zone seems to be sharply defined, both against the underlying igneous
rocks and the overlying limestone. Any gradation that exists must be
confined to thicknesses of not more than 5 feet. In a few places exposures
are sufficient to indicate that in these places there is no gradation at all.
The magnetite-garnetite mass appears to replace only the limestone, but
there is no available direct evidence indicating that replacement of the
igneous rocks has not also taken place. The lower boundary of the mag-
netite-garnetite body seems to be a gently warped plane. The upper
boundary, against limestone, seems less regular. For instance, the long
projection into the limestone from the southeast seems to indicate a
marked rise in the “roof” of the ore zone. The magnetite-garnetite
body presumably was produced by agents accompanying the granodiorite
of the lower western slopes of the ridge, though the two rocks are not now
in contact. The body of magnetite lying west of the tunnel entrance, and
the occurrences of magnetite at the southwest end of the ridge, both le
in the voleanic rocks at or close to the edge of a mass of granodiorite.
These deposits also appear to be replacement bodies, but replacing volcanic
rocks and not limestone.

ECONOMIC CONSIDERATIONS

The group of small outcrops of magnetite and magnetite-impregnated
rock at the southwest end of Iron hill do not appear to indicate the presence
of a deposit, or deposits, of magnetite of economic value. The limited expos-
ures at the best show only 2 or 3 feet of ore, the rest is low grade.
The area partly impregnated with magnetite is closely limited on the
south and east by exposures of barren greenstone. In the opposite direct-
ions it may be that more important deposits exist, but if so they are drift-
covered.

The 50-foot long outcrop of magnetite situated 400 feet west of the
main tunnel may belong to an important body of ore, but the present

17135—6}