184

deposit is not enclosed on both sides by the intrusive. It is an alteration
and a replacement of limestone by contributions of iron-bearing compounds
from the crystallizing intrusive; and fragments of unreplaced limestone
may be observed in the tunnel to be completely surrounded by magnetite.
The magnetite may also be observed to occur to some extent within shat-
tered parts of the quartz diorite, and in some places this rock is altered,
as well as the limestone, to a group of typical contact silicates.

An attempt has been made to separate a mass of relatively solid
magnetite from an encircling zone of mixed magnetite and highly metam-
orphosed rock. The aureole of mixed material contains less than 50 per
cent of magnetite by volume. Within this are isolated patches of highly
metamorphosed rock, either quartz diorite or limestone. They occur
irregularly and presumably are the same as the zones of sheared and
altered rock encountered by the tunnel.

The cross-section on line A-B through No. 2 tunnel illustrates the
structure of the deposit insofar as it can be deciphered. The section is
constructed from the field data obtained from the exposures and from
No. 2 tunnel, combined with data taken from Lindeman’s published report
on his investigations of 1907. The course of the lower tunnel is not accur-
ately known, since its portal is caved; and consequently its location on
the map is approximate. The dump from the lower tunnel was examined
carefully and was found to consist partly of magnetite, so there is every
reason to credit its passing through a zone of that mineral. Regarding
the geology of this tunnel Lindeman (16) states that it ‘Shad been run in
the same direction (as No. 2 tunnel) for 114 feet into the hill, going through
limestone and diorite. The last few feet, however, show magnetite,
dipping in towards the hill.”

CHARACTER OF THE MAGNETITE

Much of the magnetite in this deposit is impure, mixed with metam-
orphosed rock and impregnated with pyrite. A large part of the outcrop
is rusty from the oxidation and hydration of the pyrite. The central
part of the deposit, however, as outlined in the figure, contains only
small quantities of pyrite and rock. The colour of this part of the exposure
is dull black, with an absence of rusty stain, and the magnetite is coarser
in grain. Broken, angular pieces of this magnetite show slickensided
surfaces, and there is a bluish tone to their black colour.- The detailed
character of this body of magnetite may best be illustrated by quoting
from the field notes the log of the upper (No. 2) tunnel, distances reading
from zero at the portal:

Feet
0— 10: Decomposed rocky magnetite.
10— 14: Sand of garnet with little magnetite.
14— 28: Sheared magnetite with some sulphides.
28— Good grade magnetite with small amount of sulphides.
39— 47: Band of altered silicates.
47— 58: Solid magnetite with considerable disseminated pyrite.
58— 68: Good grade magnetite.
68— 82: Solid lenses of magnetite with considerable sulphides. Some lenses are almost
pure magnetite but are short, appearing only in one wall.
82—100: Fairly solid magnetite.
100—108: Sheared and mineralized contact silicates with veins and irregular bunches of
magnetite.

There is no information available giving corresponding data for the
lower (No. 1) tunnel.