196

The accompanying figure shows a belt of magnetite exposures in open-
cuts, strippings, and a shallow shaft for a total length of 920 feet, but these
are separated by intervals of drift varying in width from 25 to 180 feet.
These artificial exposures show no relationship between magnetite and
rock, nor between diorite and limestone. Since many of these are merely
strippings, they afford very little information other than the surface
extent of the magnetite, except in the case of one long trench where an
ore layer may be observed to dip 65 degrees to the southwest. A marked
impression is created that these exposures have little relationship to one
another and that they are entirely unconnected. They seem to be the
exposed parts of a series of irregular-shaped masses of magnetite whose
principal extent is nearly horizontal rather than vertical.

An attempt has been made on Figure 31 to separate exposures of
nearly solid magnetite from other areas characterized by magnetite bunches
and stringers in limestone.

CHARACTER OF THE MAGNETITE

- The magnetite in the bluff at the west end of the property, and within
the tunnel, is a medium-grained, hard, dull black variety containing only
a very small amount of visible sulphides. It is also to a large extent free
from inclusions of silicates, but contains fragments of unreplaced limestone.
Towards the east end of the showings, more pyrite is found in the magnetite,
and there is a greater mixture with bunches of silicates. This may be
due to the fact that in this part of the zone the individual masses of magne-
tite are smaller than towards the west.

ORIGIN OF THE DEPOSIT

The deposit is undoubtedly a partial replacement of a limestone
inclusion or elongated roof pendant in the Beale diorite. The localization
of the magnetite in the tunnel between diorite and limestone, as well as
the development of the typical contact lime-alumina silicates, and the
sporadic nature of the individual showings, prove the replacement to have
taken place under contact metamorphic conditions.

ECONOMIC CONSIDERATIONS
Extent of Deposit

Exposures occur at intervals for a distance of 920 feet, but at no point
except at the portal of the tunnel is a greater width than 40 feet of solid
magnetite exposed. In the bluff at the west end of the deposit there is
a width of about 60 feet of solid ore with an additional 20 or 30 feet of
mixed limestone and magnetite. In all of these cases it is impossible
to determine the direction, and consequently the amount of true width.
Above the portal of the tunnel, there is continuously exposed a vertical
height of 40 feet of magnetite; but with the exception of this and a 10-foot
depth in the shallow shaft at the east end of the property, the greatest
exposed depth is not over 2 or 3 feet.