PLACER GOLD OF THE BARKERVILLE AREA.

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SUMMARY OF CONCLUSIONS.

(1) The placer gold of the region is undoubtedly derived from
the belt of auriferous quartz veins.

(2) The auriferous constituents of the unoxidized parts of the
veins are the sulphides, arsenopyrite and pyrite. There is no evi-
dence indicating that the eroded parts of the veins were richer in
primary free gold than the remaining parts. It is probable that
they contained minerals similar to those of the lower parts.

(3) Deep decomposition of the veins during Tertiary time re-
sulted in the oxidation of the sulphides and the removal of the
soluble constituents. Part of the fine gold thus set free from the
sulphides formed enrichments in the oxidized parts of the quartz
veins. Gold enrichment also took place by means of the solution
of the gold thus released followed by its deposition in the form of
crystals, crystal groups, plates, or veinlets and irregular masses, in
cracks and cavities in the veins and adjacent country rock near the
base of the zone of oxidation. The crystal groups, plates and
irregular masses‘thus formed and subsequently modified by the
action of the streams are the main source of the nuggets in the
gravels.

(4) The agencies by which solution and deposition of the gold
were effected are not definitely known, but it is probable that the
solvents were chiefly chloride solutions containing manganese.
Precipitating agencies are abundant in the veins and country rock
in the form of siderite, pyrite and carbonaceous material.

(5) During early and middle Tertiary time the area was being
reduced to a peneplain—probably under semi-arid conditions—
and, therefore, conditions were suitable for deep secular decay, for
slow removal of the products of decomposition, and for gold en-
richment in the oxidized parts of the quartz veins. In late
Tertiary time, uplift of the region caused rejuvenation of the
streams. Deep valleys which, for the most part, coincided with
the ancient valleys were cut and in them the gold, liberated in the
zone of Tertiary weathering and concentrated in the old stream
valleys, was reconcentrated.

(6) In Pleistocene time nearly stagnant ice-sheets covered the