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GENESIS OF THE DEPOSITS

This deposit is an excellent representative of the group described
above as contact metamorphic deposits. The magnetite is a replacement
of limestone, along its contact with fine-grained intrusive diorite; and
possibly also to some extent a replacement of the somewhat shattered
marginal parts of the diorite.

The actual contact of diorite and limestone cannot be observed at
this locality, as the two rocks are separated by the tabular sheet of magne-
tite; but the localization of the magnetite in relatively abrupt contact
with the diorite above the falls; its irregular width in the limestone, as
shown by its pinching in a northwesterly direction; the occurrence of
isolated lens-shaped or dyke-like bodies within the limestone; the garnet-
ization of the diorite, and its impregnation with pyrite, pyrrhotite, and
magnetite; the dissemination through the magnetite of grains and small
bunches of the typical contact metamorphic calcium silicates, garnet, and
epidote; and the fineness of grain of the diorite (a marginal phenomenon) ;
all these facts bespeak a contact metamorphic origin for the deposit.

Clapp attributes the origin of this deposit to hot concentrated magne-
tite solutions, ‘‘virtually magnetite magma”, that invaded and brecciated
both the diorite and the limestone; and he states further that “irregular
magnetite veins or apophyses extend from the magnetite body into the
pure marble, brecciating it and including blocks of marble much as apo-
physes of an igneous rock would brecciate and include fragments of an
invaded formation” (17, page 193). It is quite clear that masses of magne-
tite in the shape of dykes or sills occur in the limestone, and even surround
blocks of limestone; but it is also true that massive limestone in places
contains isolated solid masses of magnetite that could not have been
formed by rapid injection of magma. Besides, there is no evidence to
prove that the magnetite actually brecciated the limestone by its invasion,
indeed, it is more probable, in the opinion of the writer, that the brec-
ciation of the rocks was an accompaniment of the intrusion of the diorite,
and that the magnetite solutions took advantage of the already existing
or potentially existing channels, through the rocks, for their migration.
It is contended that this deposit, as well as most of the others along the
west coast of Vancouver island, does not owe its origin to magnetite magma
that did its work by a process similar to igneous intrusion; but to hot tenuous
iron solutions that had access to the country rock through pre-existent
fractures, and accomplished their work by replacement rather than dis-
placement.

ECONOMIC CONSIDERATIONS
Extent of Deposit

The greatest length of exposed magnetite parallel to the diorite-
limestone contact is 75 feet; the width of the nearly vertical sheet
varies from 45 to 60 fect. The two tail-like extensions running to the
southwest constitute what seems to be remnants of what was a nearly
flat blanket of magnetite overlying the intrusive diorite. The greatest
thickness of magnetite exposed now in these flat masses is 9 feet. Brewer
(21, page 15) quotes 100 feet as the maximum width exposed in the bed of
the creek, whereas Lindeman (16, page 11) cites 63 feet which, according to
the map and sections accompanying the present report, is very nearly
correct.

17135—12