ed

220

succeeded by a series of altered volcanic rocks (interstratified tuffs, breccias,
flows, or sills). East of these is a marked longitudinal depression with no
rock exposures, beyond which is the steep side hill on which the magnetite
occurs, underlain by an easterly dipping series of highly altered rocks,
partly rosette porphyrite and partly tuff and breccia. Continuous expos-
ures of massive rosette porphyrite extend easterly from the hanging-wall
of the magnetite zone at least to the cliffs east of the railway grade. It is
also found beneath the foot-wall of the magnetite and is believed to be in
the form of sills. It is intensely altered to garnet and epidote on both
sides of the magnetite zone. The porphyrite was the only igneous rock
observed in the area mapped.

OCCURRENCE OF THE MAGNETITE

Magnetite occurs in two parallel belts, conformable to the structure
of the rock series, and, therefore, dips easterly 40 degrees to 55 degrees
into the hill. It is found throughout a longitudinal distance of 310 feet,
but is separated by drift into four principal exposures, varying in length
from 34 to 104 feet, and in width up to 11 feet. The continuation of the
zones is broken by a dip fault near the middle of the area and their
depth has only been proved for 15 feet, as far as can be ascertained. Both
foot-wall and hanging-wall are fractured and metamorphosed almost beyond
recognition. There is no evidence of limestone along the side hill.

CHARACTER,OF THE MAGNETITE

Only very small amounts of solid magnetite occur in this deposit.
It is essentially a mixture of magnetite and garnet, and the garnet is either
irregularly disseminated through the magnetite or occurs in a number of
thin, elongated, lenticular, closely-spaced streaks that produce a marked
banding in the deposit. This banding dips into the hill parallel to the
walls of the lode, and is believed to be a relic of original tuffaceous bedding
in the host rock (Compare Crown Prince, and Copper Island deposits).

ORIGIN OF THE DEPOSIT

The deposit is believed to have originated by the replacement of tuff
or tuff-breccia beds between walls of rosette porphyrite, since the banded
structure characteristic of tuff replacements is strongly evident here.
The association and character of the magnetite suggest strongly a contact
metamorphic origin, but sufficient areal field work was not done to enable
the writer to point to the magmatic source of the replacing solutions.
The porphyrite itself may have been the contributing agent, but, if so,
it was at the same time rather intensely endomorphosed.

ECONOMIC CONSIDERATIONS

The following analyses, taken from the available literature, are quoted
to make the description more complete.

A. Carmichael, H.: Bibliography, No. 6, ‘Average sample of the ore on the dump.”
B. Lindeman, E.: Bibliography No. 16, ‘‘Average sample of the ore dump.”