161

no quartz, and a relatively high proportion of hornblende and _ biotite;
and a granodiorite consisting of orthoclase, oligoclase, quartz, and a
relatively low proportion of ferromagnesian minerals, chiefly biotite... .
: “In the northern part, however, these two types become so intimately
intermixed that it is impossible to map them separately on the scale adopted.
There is also a change in the colour of the rocks from light and dark greys
to pinks and reds” (28, pages 13-16).! ;

The only geological maps of the west coast that have been published
are those by Dawson (2) in 1886, showing the distribution of the forma-
tions from Quatsino sound to cape Scott, at the northwest extremity of
the island; and by Clapp (17) in 1908-1910, showing the geology from
the southeast shore of Barkley sound to Victoria. Of the intervening
stretch of about 175 miles, no geological map is yet available.

GEOLOGICAL OCCURRENCE OF THE IRON DEPOSITS

Occurrences of iron ore minerals, principally magnetite, are common
in the vicinity of the west coast of Vancouver island. As indicated above,
these occurrences occupy a belt, roughly parallel to the coast, but inset
a few miles from the outer margin of the island. They are frequently
referred to as occurring in the older sedimentary and voleanic rocks,
flanking on the southwest what is believed to be the igneous backbone or
core of the island.

As outlined in the table on page 163 they occur as a variety of types,
each with well-marked characteristics. With the exception of the limonite
deposits, that are recent surface concentrations, all of the others are
believed to be of contact metamorphic origin. Of the deposits of this
origin, there are three principal sub-classes: (a) contact deposits in lime-
stone, (b) contact deposits in volcanic rocks, and (ce) contact deposits of
copper sulphides and magnetite in voleanic rocks or limestone. In some
cases, as listed, the original petrographic character of the host rock could
not be deciphered, and these are listed under the heading of “Host rock of
unknown origin’. A small occurrence of hematite is also listed.

Contact metamorphic deposits in limestone (principally of the Nitinat
formation?) produced by the intrusion of hornblende diorite (Beale for-
mation) are more important as possible sources of iron ore than any other
type, since their magnetite is more massive, of better quality, and is as-
sociated with less gangue. Many of the individual deposits show clean-
cut boundaries with the limestone. They are usually unstratified, and the
garnet-epidote parts are usually segregated.

The deposits in voleanic rocks (andesitic tuff and andesite of the
Vancouver voleanics) are in some cases quite extensive, with respect to the
distance the mineralizing solutions have wandered, but they are. charac-
terized by a bedding structure, inherited from the tuffs, in which dis-
continuous flat lenses of magnetite are interbanded with layers of silicates
and gangue, with a consequent rarity of magnetite segregations. These
deposits are also believed to owe their origin to intrusive masses of diorite,

The copper sulphide-magnetite group contains, in addition to magne-
tite, chalcopyrite and bornite, and occurs in both limestone and volcanic
rocks. The individual deposits vary considerably in character, but they

1 In this and all succeeding references, the number cited is that used to designate individual articles in the Bib-
liography, p. 158.