NSTON.

W. L. UGLOW AND Ww. A. JOH

556
es of minute
lets of

could have been formed only in zon
Gold crystals and leaves or vein
ones in quartz either near the sur-
ut the limitation of the free gold to
limonite occurs confines the

quartz breccias,
shattering of the quartz.
gold may be formed in shear z
face or at considerable depths ; b

those parts of the veins in which
possibilities of such occurrences in this area to fractured zones at

or near the surface. The free gold, therefore, has been formed
by processes which operated under conditions of oxidation near

the surface.

The hypothesis whic
the occurrence of the free go
unoxidized parts of the veirts W

h is here advocated as an explanation of

ld is that the gold content of the
as and still is largely, if not en-~-

tirely, confined to the sulphides, mainly arsenopyrite and pyrite;
that the oxidation of these sulphides under near-surface conditions
released the gold which passed into solution only to be precipitated

in crystal and leaf form at short distances below in the belts of

weathering and cementation.
eration of such processes

The conditions necessary for the op
1d in the veins to supply

and for production of sufficient free go
and disintegration of the

the placers would be (1) deep weathering
2) the presence of solvents and precipi-

veins and country rock, (
tants for gold, and (3) sluggish transportation by the streams.
These conditions are fulfilled in the Barkerville area, which con-
sists of a deeply dissected high-level plateau, the uplands being
composed of remnants of a plain-like surface of erosion. Streams
which formerly flowed at or somewhat below this plateau level
must have been sluggish, for they occupied broad shallow valleys.
The amount of material being carried by the streams was there-
fore small, and rock decomposition with solution of the constitu-
ents must have been the most important feature of the later phases
of that cycle of erosion.
There is little definite information available co
agents of solution and precipitation of the gold in the veins of this
area but it is certain that this action has taken place. As shown

ncerning the