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constituents moving outward from the vein fractures. Some beds are
slightly silicified for a few feet from veins and some beds are much more
pyritized than others. Limestone beds are silicified outward for variable
distances, some are very siliceous throughout their known length, and
others for only a foot from the point where they are crossed by a quartz
vein. Another striking feature of the wall-rocks where veins traverse
fissile rocks, particularly fissile black argillites, is the presence of thin
wedges a few inches long of fine-grained pyrite tapering away from the
vein and lying parallel to the fissility. Such wedges are very numerous and
show very conclusively outward migration of vein constituents. Limestone
beds in the Cariboo Gold Quartz mine show fairly complete replacement by
fine-grained pyrite for variable distances from some veins. In some
places this replacement extends outward only an inch or two and then
gradually fades out, but supplies very good evidence that some limestones
may be replaced far enough to make good ore-bodies.

The largest pyrite replacement body in the Cariboo Gold Quartz mine
is in the area crossed by the Sanders zone of veins. In this case there is
good evidence that the replacement ore was made by constituents moving
outward from the quartz veins. The Island Mountain replacement body,
however, is cut by very few veins and those responsible for the replacement
ore are not evident. The body, however, is still imperfectly explored and
the writer believes that the ore was supplied by penetrating quartz veins
and that they will be found as development proceeds.

So far as is known the best ore-bodies lie in the base of the Baker
member or in the much fractured, underlying Rainbow member. There
is presumably a great difference in frangibility between the Rainbow
member and the Baker member, with which can be associated much of the
overlying Barkerville formation. Under the Rainbow member are rather
solid members and below the Basal member a great thickness of relatively
unyielding rock. The gold belt rocks as a whole would fracture more easily
than those above or below and most stresses causing fractures would be
relieved within the belt. Within the belt itself there are several members
that are comparatively solid and unyielding, so that stresses would be
relieved in a small part of the belt. This relief apparently took place in
the Rainbow member, in the lower part of the Baker member, and locally
in other members, particularly the Lowhee member. The Baker member
appears to be the cover or cap of the best part of the gold belt and mineral-
ization would be most prolific in the nearest rocks that permitted free circu-
lation or movement of ore solutions. The solutions presumably rose to the
Baker member which acted as a dam and forced them to remain in the
fractured rocks below.

RESUME AND POSSIBILITIES

The rocks of Cariboo district are mainly clastic sediments, some not
sheared and others sheared in varying degree. The oldest rocks, known as
the Cariboo series, are presumably Precambrian and have been divided into
three formations. The oldest formation is the Richfield and over this lie
the Barkerville and Pleasant Valley. formations. The whole has been
folded into a northwesterly trending anticline. The upper part of the