97

The porphyrite east of the Paxton extends northwards as a spur from
the main body penetrating the limestone. East of the tip of the spur, a
rounded mass of magnetite about 90 feet across has formed in the lime-
stone, and several smaller lenses, one at the porphyrite-lime contact, occur
to the south. The mineralized area is here cut across by a large diorite-
porphyrite dyke.

A buried lens of magnetite about 30 feet in width was cut through in
the copper workings at the Lake mine, 250 feet northeast of the main
magnetite ore-body. The lens is overlain by crystalline limestones prac-
tically free from secondary minerals.

_A line of narrow magnetite lenses about 1,000 feet in length, simulating
an interrupted vein, occurs south of the Lake mine in the porphyrite at a
considerable distance from both lime and diorite contacts. The conditions
are unusual as the porphyrite near the magnetite shows little alteration
and non-metallic secondary minerals are rare. The most northerly lens,
the longest one, measures 220 feet in length with a width of from 10 feet
to 20 feet. Two other lenses measure respectively 84 feet and 50 feet in
length, with widths of from 10 to 20 feet. The other lenses are compara-
tively small. The magnetite in all the lenses is fine-grained and remarkably
pure. Some epidote and garnet occur scattered through it, but the
quantity is small and only occasional grains of pyrite were noted. ey

MODE OF ORIGIN

Dawson! at an early date recognized that the magnetite ore was one
of the results of the intrusion of the mass of quartz diorite and that the
bodies occurred variously within the diorite, the porphyrite, and the lime-
stone. Leith? states that the ores . . . .‘‘are obviously replacements
of limestone. In some instances the ore may be seen entirely surrounded
by igneous rock, evidently a replacement of limestone intruded by and
caught up in igneous rock near the contact” . . . . The same author?
cites the Texada ore-bodies as examples of the “pegmatite type” of iron
ore deposits. Ores of this type are defined by him as being such as
“are carried to or near the surface in magmas and are extruded from them,
in the manner of pegmatite dykes, after the remainder of the magma has
been partially cooled and crystallized. They are deposited from essentially
aqueous solutions mixed in varying proportions with solutions of quartz and
the silicates.”

McConnell! states that . . . . “the iron and associated copper
ores. _. are typical examples of contact metamorphic deposits.

They occur along the lime-diorite contacts, the lime-porphyrite contacts,
the porphyrite-diorite contacts, and enclosed in all three formations at
considerable distances from the boundaries. . . . They originated
during the closing stages of the Coast Range batholith invasion. :
While the main mass of the metallic minerals probably formed after the
non-metallic ones (epidote, garnet, pyroxene, ete.) there is reason to believe
that the deposition of both kinds was taking place at the same time In
different parts of the mineralized area, and that small quantities of non-
metallic minerals continued to form until deposition finally ceased”. . .

1 Dawson, G. M.: Geol. Surv., Canada, Ann. Rept., vol. I, pt. B, p. 37 (1887).
i y Geol. Surv., Bull. 285, p. 196 (1906).

GC. I our, Can. Min. Inst., vol. 11, pp. 92-98 (1908).

., pp. 77, 78, and 81.