88

Very minute diamonds were discovered by R. A. A. Johnston! in the
laboratory tests to be associated with the Scottie Creek chrompicotite &
but owing to their small size they are of mineralogical interest only. 5

Eugene Poitevin of the Geological Survey, Canada, collected samples
of pinkish chromiferous chlorite and emerald green chromiferous garnet
uvarovite from this locality, in the summer of 1918. a |

‘The serpentine in which the chromite occucs, outcrops on both sides =
of Chrome creek, (Figure 14). At the southwest extremity of .this area :
are outcrops of Miocene basalts and augite andesites. The lavas outcrop
also in the bottom of Scottie creek one-quarter to half a mile to the south-
east and southwest. To the north and east, the country for long distances
is covered with glacial drift. The serpentine in places is a greenish black,
dense rock; in othér places, light yellow green, much sheared, with films
of white in the shear-planes; and in others it has a red colour. In the
field these three varieties of serpentine are in most places sharply differen-
tiated from each other by fracture planes, although in one or two exposures
they were seen to grade into each other. The dense serpentine has an
irregular almost conchoidal fracture and within it are forms with a well-
defined, platy cleavage which may be serpentine, pseudomorphous after
pyroxene, but of the original mineral matter from which the serpentine
was derived nothing was seen. Through the serpentine mass are scattered
black minerals with metallic lustre, which are secondary magnetite and, in
the case of the larger individuals, chromite. Under the microscope the
rock is seen to be made up practically wholly of sérpentine and iron ore.
There are larger individuals of the ore that are chromite, and smaller q

crystals of secondary magnetite lying parallel to the serpentine fibres in 4
small veins in the rock. The yellow-green variety of serpentine is seen 4
under the microscope to consist of iron ore, serpentine, and a carbonate. ;

The serpentine has a fibrous appearance, the fibres being at right angles to
central lines, giving them a feathery appearance. The carbonate lies in
veins along these lines which are often roughly parallel over a small area,
and from the main carbonate veins little arms project into the serpentine
and into adjacent cracks, so that the carbonate is evidently of later origin.
The red variety of serpentine found in certain places owes its colour to the
oxidation of the iron ore crystals that lie scattered through the rock which
consists of serpentine, iron ore, and carbonate, or areas that are a mosaic
of fine secondary quartz, carbonate, and iron ore partly altered. The red
variety apparently represents a further stage in the alteration of the
serpentine.
Intruded into the serpentine are dykes of diallage pyroxenite and
quartz diorite; one dyke of an acid, much altered rock was also noted.
Major fault planes were observed in the cliffs at the tunnel (Figure —
14, locality 2), in prospect holes just to the west of this, and in the cliffs east
of the valley. All these fault planes trend within 15 degrees of true north,
most of them slightly to the east of north. Some well-defined fault planes
in the serpentine occur farther west and trend northeast and northwest.
n most exposures of the serpentine, the whole mass is very much fractured
in an irregular manner into rounded, lens-shaped, and angular masses,
some only a few feet across. Figure 15, in which a section of the wall of
tunnel No. 2 is shown, illustrates the irregularity of the fracturing. The
best-defined fault plane ((A) in this figure) 1s warped and has a northerly

1Geol. Surv., Can., Sum. Rept., 1911, p. 360.

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