Nechako River Map-Area

Molybdenite

Several molybdenite occurrences have been described north of the map-area
near Francois Lake (Armstrong, 1949, pp. 192-3), and small amounts of molyb-
denite have been noted in quartz veins in the Topley granites of the area. Molyb-
denite was also noted in a small quartz vein about 2 miles north of the west end
of Chelaslie Lake. None of these occurrences was of significant size or extent.

Perlite Deposits
References: Ann. Rept., Minister of Mines, B.C., 1953, pp. 194-5; 1958, pp. 97-8.

Perlitic rhyolite or perlite flows, 30 to 40 feet thick, form part of the Ootsa
Lake Group. Although it has not been possible to establish the stratigraphic
position of these flows (if, indeed they form a stratigraphic unit) in general it
is believed that they are near the top of the group, certainly in the rhyolite unit.

Perlite has been described as “... one variety of obsidian, characterized by
a perlitic or spherulitic texture, a waxy to pearly luster, a perlitic, splintery, or
columnar fracture, and the presence of a relatively large amount, 2 to 5 per
cent, of chemically combined water” (Barr, 1949, p. 749). When perlite is
crushed and heated to the softening point, the combined water is released as
fine bubbles of steam. The resulting product is a synthetic pumice used as a light
weight aggregate in cement.

Perlite flows in Nechako River area vary in colour from black to pearl
grey. Such flows have been noted south of Uncha Lake, south of Cheslatta Lake,
near the outlet of Ootsa Lake, and near the north end of Entiako Lake. Other
flows may occur within the area, as the Ootsa Lake Group is widespread. Although
none of the perlite from these occurrences was tested, it is probable that deposits
of commercial size and grade will be found when the demand is great enough;
commercial perlite from the Ootsa Lake Group is mined north of the area near
Francois Lake (Armstrong, 1949, pp. 198-199).

In 1953 perlite occurrences were staked by C. S. Powney and John Ras-
mussen of Fort St. James, on Dayeezcha Mountain south of Uncha Lake. These
claims were not visited subsequent to staking but presumably the occurrence is
the one mentioned in the preceding paragraph.

Asbestos

Asbestos is reported by local residents to occur on or near Sinkut Mountain,
which is east of the northeast corner of the area. This is in the area underlain by
ultrabasic rocks. Although no prospects or claims carrying asbestos were examined,
a fibrous mineral was noted along a forestry road. This mineral was identified by
X-ray analysis as anthophyllite. The mineral occurs in an anthophyllite-talc-
chlorite schist presumably derived from the metamorphism of ultrabasic rocks
within the contact zone of the Topley granites. The fibres observed in these
rocks are white and brittle.

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