CHAPTER II—BEDROCK GEOLOGY.
REGIONAL.

The central part of the Cariboo region, a belt 15 to 20 miles wide and about 50
miles long, is underlain by a thick series of non-fossiliferous, metamorphosed sedi-
mentary rocks of Precambrian age. These rocks, known as the Cariboo series, are sub-
divided on the basis of lithology into three formations. The Richfield formation, which
is dominantly quartzitic, is overlain by the Barkerville formation, chiefly limestone and
calcareous sediments, which in turn is overlain by the Pleasant Valley formation,
chiefly argillaceous sediments. In the Little River area, south-east of Cariboo (Swamp)
River, the Cariboo series is overlain by fossiliferous Lower Cambrian rocks.

In the Barkerville Gold Belt the upper part of the Richfield formation has been sub-
divided (Hanson, 1935, p. 4), from the base of the Barkerville formation downward,
into the Baker, Rainbow, B.C., Lowhee, and Basal members. Later, detailed work in
Island Mountain mine (Benedict, 1945, p. 761) and at Cariboo Gold Quartz mine (Skerl,
1948a, p. 574) suggests that not only may this upper part of the succession be over-
turned and the Rainbow be younger than the Baker, but that the Rainbow and Lowhee
members, and the B.C. and Basal members, though originally mapped separately, may
be the same members on opposite limbs of a very close overturned fold.

The major structural element of the Cariboo series is a broad anticlinorium whose
axis trends north-westward. As a consequence, the central belt of Cariboo schists is
flanked on the north-east between Summit and Kimball Creeks by north-easterly dipping
Mississippian sediments and volcanics of the Slide Mountain series, and on the south-
west, between Wingdam and Likely, by south-westerly dipping Jurassic voleanics and
sediments of the Quesnel River group.

Igneous rocks are infrequent. They comprise sills and dykes of altered, difficultly-
identifiable, quartz and feldspar porphyry of the pre-Mississippian Proserpine intru-
Sives; sills and dykes of diorite and diabase of the Jurassic (?) Mount Murray intru-
Sives; stocks of Mesozoic quartz monzonite and diorite in the Little River area; and
stocks of post-Jurassic granite, diorite, and other types in the Quesnel Forks area.

DETAILED.

The Stanley area is underlain by a succession of metamorphosed sedimentary rocks
belonging to the Precambrian Richfield formation. The rocks cannot be correlated with
members of the Barkerville Gold Belt. The area straddles the regional anticlinal axis
which has been mapped previously (Johnston and Uglow, 1926, p. 31) as running
between Mount Amador and Mount Nelson.

Quartzite in almost bewildering variety is the predominating rock in the area.
It displays variations in colour from white and light grey, through medium grey, brown,
to black; in granularity from fine quartzite to coarse grits with interbeds of meta-
morphosed pebble conglomerate; in composition through admixture with varying
amounts of dark argillaceous material; and in fissility either through variations in
amount of mica developed in the rock or through the rocks’ relation to the axial planes
of minor folds. Individual beds, ranging from a fraction of an inch to several tens
of feet in thickness, are interbedded with others which may vary in colour, granularity,
and general composition.

Dominantly argillaceous rocks are considerably less common than quartzites. They
are present as black slate and dark schistose quartzitic argillite, grey argillaceous
schists, and as thin partings and interbeds of dark argillaceous material in a dominantly
quartzitic succession. The grey colours of most quartzites are due to the variable
content of dark argillaceous and, in some instances, graphitic material.

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