OO a

132

useful in determining the nature of the serpentinized material, are insig-
nificant in amount; they probably do not occupy a total of more than about
200 acres in the 25-square mile stock east of Polaris Creek.

No generally acceptable classification of the different varieties of
serpentine has yet come into general use. The terms used in this report
are essentially those proposed by Lodochnikow (1933), modified by Leech
(1953), and are used in a descriptive sense only. They include chrysotile,
the microscopically fine fibrous variety of serpentine, with fibres, of either
positive or negative elongation, usually oriented perpendicular to the walls

; of the veinlet or lens (See Plate VIII B); antigorite, in bladed or lamellar
grains, with positive elongation, commonly arranged in three mutually
perpendicular planes and presenting a reticulated appearance in thin section;
serpophite, the apparently structureless rounded masses that form the cores
im an interlacing network of chrysotile or antigorite; and bastite, the
product of pseudomorphous serpentinization of pyroxene. All of ‘these
types are represented in the serpentinized ultramafic rocks of the Lay
Range. Their occurrence and distribution is described in connection with
the discussion of the process of serpentinization (See pages 140-144).

Sepiolite (Meerschaum). Several of the fractures in the serpentine
and joint surfaces in the serpentinized peridotite contain fillings of a pale
greyish white or green, very compact, smooth textured, light, soft material,
which is probably mainly sepiolite. Much of this material shows a delicate,
scroll-like banding. The largest pieces seen in place were plate-like masses
about 1 inch thick and up to 3 feet long, but masses more than 1 foot thick
have been reported by prospectors, and the writer was shown a trimmed
fragment, about 3 inches cube, of pure white meerschaum from the stock
east of Polaris Creek.

Magnetite. Magnetite is a by-product of the process of serpentinization
of olivine and pyroxene, and as such occurs in all ultramafic rocks in the
Lay Range and near Wasi Lake, as minute grains along the grain boundaries
of olivine and pyroxene, and in the cleavage plane cracks and fractures of
the altered minerals. In the completely serpentinized rock the persistence
of trains of magnetite grains in such positions affords an indication of the
nature of the original minerals. In some otherwise fresh-appearing pyroxene
the first conspicuous indication of serpentinization is the development. of
plates of magnetite along cleavage planes in the interior of the crystal.

Corundum. Corundum is the principal constituent of some white
dykes cutting the pyroxenite and peridotite. It occurs as an aggregate of
fine, rounded masses, and as elongated grains with hexagonal cross-section,
up to 0-4 mm. in greatest dimension, which in places show a tendency to
form radiating groups. The grains are colourless, and almost isotropic,
with the high refractive index and length-fast character typical of corundum.
They are embedded in a serpentinous or clayey matrix and, as is common
with this mineral, appear deceptively soft; but a fragment of the corundum-
bearing rock will scratch quartz crystals.

Talc, Brucite. Some shear zones contain white, palpable material that
may be tale or brucite. It is noteworthy that, unlike many ultramafic
bodies, and unlike the type bodies of the Trembleur intrusions to the south
(Armstrong, 1949, p. 89), no known masses of ultramafic rock in Aiken
Lake map-area have altered to talc.