The
placers produced about 25.6 per cent of the total output of gold—an
increase of 2 per cent. The dredges produced a little more gold in 1919
than in 1918, and the combined placer yield from hydraulic, drift, and
other surface methods was about $994,000 less than in 1918. The
decrease from placers was largely due to a decrease of 45,000 ounces
in Alaska. The percentage of output of silver credited to the placers
is insignificant.
In
the mills the amalgamation process showed a large gain of 10.8 per cent
of the total recovery of gold in 1919. This was due entirely to
increases in Colorado, California, and Alaska, which produce ores more
amenable to treatment by amalgamation. The percentage of gold
recovered by cyanidation showed a decrease of 3.5 per cent, following
an increase of 1.4 per cent in 1917 and of 2.5 per cent in 1918.
Colorado, Nevada, Arizona, South Dakota, and Oregon ores yielded the
larger part of the gold recovered by cyanidation and the decrease was
due to much smaller recoveries by the cyanide process in Colorado. The
chlorination process was not used in California in 1919.
GOLD AND SILVER PRODUCED AT MILLS, BY STATES.
A
large quantity of concentrates from sulphide ores is now smelted, and
the increased application of the notation process has resulted in
decreased yield of gold and silver from cyanidation, as nearly all such
concentrates are shipped to smelters.
The
smelters, which had for two years been producing a slightlv greater
proportion of gold and silver, are to be credited in 1919 with about 19
per cent of the total output of gold and 84.85 per cent of the silver.
There was no appreciable decrease in the percentage of output of silver
recovered at smelters, but that of gold decreased 3.9 per cent.
The
bulk of the gold produced continues to come from the gold mills. As
shown in the table the proportion of gold recovered by amalgamation and
cyanidation has increased from 50.1 per cent in 1916 to 55.4 per cent
in 1919,
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