STRUCTURE.

The major structural element of the area is a broad anticlinorium whose axis
trends north-west and runs from Mount Borland past the east side of Yanks Peak to
Mount Burdett; thence through Mounts Agnes, Pinkerton, Amador, and Nelson to
Dragon Mountain. In the section by Mount Pinkerton the anticlinal axis is nearly
horizontal, but farther to the north-west it plunges 10 degrees north-westward, and at
Dragon Mountain plunges 20 to 40 degrees north-westward. On the limbs are minor
drag-folds of varying amplitude whose axial planes are overturned. Generally higher
dips prevail on the north-east limb than on the south-west one.

Of minor importance is the synclinal axis, about 12 miles north-east of Mount Bor-
land, trending north-westward by Kimball and Limestone Creeks, east of Cariboo
River.

The rocks are cut by north-easterly-striking and north-westerly-dipping normal
faults, some of large displacement; e.g., the Willow River fault displaces the Cariboo-
Slide Mountain contact 4 miles. :

Strike-faults are the commonest type. They are parallel to the dip and strike of
the beds, are of the normal type, and generally have a throw of not more than 25 feet.

A number of northerly-striking faults cut the Cariboo series. These faults dip
about 60 degrees east and offset the beds to the right, as much as 1,300 feet in the case
of the Lowhee fault. Those recognized and named are the Aurum fault on Island
Mountain; the No. 1, Rainbow, Sanders, and Lowhee faults on Cow Mountain; the
Goldfinch, Marie, and Sirius faults on Barkerville Mountain; and the Pin Money, War-
spite, Tipperary, and Independence faults on Proserpine Mountain.

Cleavage is developed in the rocks for the most part parallel to the regional strike
and specifically parallel to the axial planes of the drag-folds.

Of most importance are premineral fractures, many of which are occupied by
quartz veins. The fractures are more abundant in certain of the more competent
rocks; e.g., the Rainbow member. These fractures are grouped in three sets: those
striking north-east, at right angles or transverse to the regional strike of the rocks;
those striking either east or north, diagonal to the strike of the rocks; and those
striking north-west, parallel to the strike of the rocks. All the fractures parallel to
and diagonally crossing the beds are occupied by quartz veins, whereas not all, but
many, transverse fractures are quartz-filled.

MINERAL DEPOSITS.

Mineral deposits in the Cariboo are of two types: quartz veins and replacement
deposits in limestone. At the Island Mountain mine a pyritic replacement in limestone
is mined; similar pyritic replacements in the Cariboo Gold Quartz mine have con-
tributed an insignificant amount of ore, and elsewhere replacement deposits in lime-
stone carrying mixed sulphides, such as galena, sphalerite, pyrrhotite, etc., have been
neither large enough nor valuable enough to be mined. Gold-bearing quartz veins
constitute the bulk of the minable mineral deposits of the Cariboo. A total of 1,299,419
tons of ore mined to the end of 1945 yielded 538,070 oz. of gold and 59,149 oz. of
silver, or an average recovered content of 0.415 oz. of gold and 0.045 oz. of silver
per ton.

The veins contain gold, pyrite, galena, arsenopyrite, scheelite, sphalerite pyrrho-
tite, and also cosalite (bismuth-lead sulphide) in a quartz and ankerite gangue. The
gold content is not directly proportional to the amount of pyrite, but higher values in
gold occur with the larger amounts of pyrite. Gold is especially abundant in and
around the nests of cosalite.

The quartz veins occupy fractures developed in Precambrian rocks (Richfield
formation of the Cariboo series) and are pre-Mississippian (older than the Slide

_ Mountain series) in age. Transverse veins are numerous; they range up to 6 feet

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