170

Below the falls (See Figure 28) the country rock for some distance
is finely crystalline, bedded, grey limestone, dipping from 50 degrees
to 60 degrees upstream, and cut by at least two diorite porphyrite dykes or
sills. Above the falls, the exposures are inadequate, but the creek seems
to flow on a basement of fine-grained, altered, and pyritized diorite, which
is believed to be intrusive into the limestone e. The contact between the
two rocks is nearly flat-lying above the falls, changing to a very steeply
dipping position underneath the falls (See Figure 28, section C-D). A
6-foot dyke of diorite porphyrite cuts in a northwesterly direction across
the fine-grained diorite and the magnetite. This dyke is characterized by an
abundance of lath-shaped plagioclase phenocrysts lying in parallel orien-
tation with their direction of elongation nearly at right angles to the
walls of the dyke, and producing a kind of fluxion structure dipping to
the southeast. The dyke dips 80 degrees to 85 degrees to the southwest,
and on both sides of it the fine-grained diorite and the magnetite are
impregnated with considerable very fine-grained pyrite.

The contact zone of the diorite and the limestone in its limited exposure
of about 75 feet trends about north 70 degrees west, which corresponds
aprox mated? with the general trend of formations in the district.

OCCURRENCE OF THE MAGNETITE

At least three separate bodies of magnetite occur in the small stretch
of Bugaboo creek embraced within the area of the accompanying figure.
The principal one, over which the creek falls, lies in the contact zone of
the fine-grained diorite with the limestone, and for the most part within
the limestone. This magnetite mass occupies a nearly vertical attitude
at the falls, but laps over the fine-grained diorite above the falls like ¢
blanket in nearly horizontal attitude. The creek has worn through this
blanket, thus exposing the underlying diorite, and leaving two tail-like
remnants of magnetite on each bank.

Below the falls are exposed two small masses of magnetite within the
limestone, one of which is about 7 feet wide, and the other about 24 feet
wide. The larger one is in the form of a pocket, lying against a dyke
of porphyrite, and expanding somewhat in size in a downward direction.
The smaller one is a tabular-shaped body with sharp walls against the
limestone and standing nearly vertical.

From 300 to 400 feet southeast of the falls, on a heavily overgrown,
nearly flat patch of country are two old open-cuts or pits 15 to 20 feet deep.
The sides are badly caved at the present time, but several large pieces of
magnetite, manifestly almost in place, were found in the bottom of one
of them. These pits are situated along a line that represents closely
the direction of continuation of the limestone- diorite contact; and this
fact lends weight to the inference that the loose magnetite mentioned
above is substantially in situ.

CHARACTER OF THE MAGNETITE

The magnetite is hard and of medium grain, and contains scattered
through it varying amounts of garnet, epidote, and actinolite, either in
small grains or small irregular-shaped masses. Pyrite and pyrrhotite oceur
sparingly within the magnetite, but pyrite isabundantly disseminated through
the masses and blocks of diorite or contact silicates, included within the
lode. Consequently it is expected that the sulphur content of the analyses
quoted below is lower than that of any large tonnage of minable ore.