ment between 1933 and 1938. The Cariboo Gold Quartz mine began producing gold in
1933 and the Island Mountain mine in 1934, and have operated continuously since then.
The Cariboo Hudson mine produced gold in 1938 and 1939. From 1933 to the end of
1945 more than 1,000,000 tons of ore averaging 0.41 oz. of gold per ton have been
mined, resulting in a total production of 538,070 oz. of gold. This amount, however,
is only about one-fifth the total placer-gold production of the same region.

GEOLOGY.

The productive areas of the Cariboo are underlain by a thick succession of Pre-
cambrian sedimentary rocks called the Cariboo series, comprising the Richfield, Bar-
kerville, and Pleasant Valley formations. The oldest formation, the Richfield, contains
all the known gold-quartz veins of importance. The Richfield formation is com-
posed of quartzite, argillite, limestone, and various rock-types gradational between
them. All rocks have been metamorphosed to the corresponding kind of schist, such
as sericite schist, quartz sericite schist, graphitic schist, and slate. The Barkerville
and Pleasant Valley formations, which lie above the Richfield, are composed largely of
- limestone and black argillite respectively.

The Cariboo series has been folded into a major anticline whose axis runs from
Mount Borland on the east side of Cariboo Lake to Dragon Mountain, north-west of
Stanley. A synclinal fold axis lies parallel to it and about 12 miles to the north-east.
Jurassic voleanics and sediments of the Quesnel River group overlap the south-western
limb of the anticline along a line running from Wingdam south-eastward through to
Likely and Cedar Creek.

An important development in the knowledge of the Cariboo geology was the
recognition and mapping of the members which make up the upper part of the Rich-
field formation. From Island Mountain south-westward to Grouse Creek, five members
—the Baker, Rainbow, B.C., Lowhee, and Basal member—have been mapped. The
Rainbow member consists of interbedded argillite and dark quartzite. On the Hudson
claims and Roundtop Mountain. four members—the Lostway, Roundtop, Bee, and
Hudson—have been mapped. The middle part of the Hudson consists of impure
quartzite. These lithological subdivisions are important because most of the pro-
ductive veins between Island Mountain and Grouse Creek are found in the Rainbow
member, while on the Cariboo Hudson claims the productive veins are in the middle
part of the Hudson member.

On the north-east, late Paleeozoic sediments and volcanics of the Slide Mountain
series lie on the north-eastern limb of the anticline and in the trough of the north-
westerly-plunging syncline.

The intrusive rocks of the area mainly lie to the east of the Barkerville gold belt.
They are the Proserpine intrusives, quartz porphyry and felsite sills and dykes, which
cut the Cariboo series, but are older than the Slide Mountain series; the Mount
Murray diabase, gabbro, and diorite sills and dykes in the Slide Mountain series north
of Mount Murray; and one large and several small quartz monzonite and diorite stocks
intruding the Cariboo series east of Cariboo River.

The rock-types between Roundtop and Island Mountains undergo a lithologic
change along their strike, reflecting different conditions of sedimentation. Con-
sequently, it is not possible to correlate the members of the upper Richfield at Roundtop
Mountain with those north-west of Grouse Creek. Moreover, because of the changes
in lithology that are known to have taken place along strike, there is no reason for
believing that the Rainbow member will extend unchanged north-west of Island Moun-
tain, nor that the Hudson member will continue unchanged to the south-east of Cariboo
River. Nevertheless, rocks of similar character or competency may be found to the
north-west or to the south-east.

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