PLACER GOLD OF THE BARKERVILLE AREA. 559

cement gold is undoubted proof of the operation of the processes
of solution and deposition of gold ending with the healing of the
fractures. Where a rich supply of gold in its original form, as
in some of the arsenopyrite, is available, there seems to be no
reason why the continuous oxidation of the arsenopyrite and the
removal of part of the gold in solution should not result in the
gradual growth of fairly large single masses of cement gold.

A’ satisfactory hypothesis of the origin of large crystalline
masses and definite crystals of gold in the veins is based on the
reasonable assumption that the main part of the enrichment took
place prior to peneplanation, while the country was still somewhat
rugged and semi-arid. Under these conditions the belt of oxida-
tion above the ground-water table would have had a considerable
vertical extent, perhaps 100 feet or even more. On the oxidation
of the sulphides and the solution of the carbonates, solvents would
be provided for the fine gold. This gold, once in solution, would
travel downwards until reducing conditions were met with at
the level of ground-water or beneath it, and there would be de-
posited in crystalline form. Such conditions would provide a
relatively thick gathering ground for the gold solvents, and, on
the other hand, a restricted locality in which deposition would take
place. Were the level of the ground-water table to remain con-
stant until all the goldwere leached from the suggested thickness of
100 feet above the water table, the result would be the deposition
of all of this gold in a shallow horizontal belt near the water level.
During this process of deposition large crystals, groups and vein-
lets would develop by gradual accretion. The progressive lower-
ing of the water table with the reduction of the relief of the
country would bring lower and lower portions of the sulphide
zone into the belt of oxidation and release its content of gold. As
the larger pieces of this secondarily deposited gold came within
reach of surface erosive agencies through the mechanical removal
by drainage of the oxidized overburden, they gravitated into the
valleys of the early Tertiary streams, there to form the first
placers, which have since been worked over and concentrated to
form the placers that occur in the bottoms of the deep V-shaped
valleys of post-peneplain time.