The
dredges produced about $1,060,000 less gold in 1920 than in 1919, and
the combined placer yield from hydraulic, drift, and other surface
methods was about $1,035,900 less than in 1919. The decrease from
placers was largely due to a decrease of 53,000 ounces in Alaska and
47,000 ounces in California. The percentage of output of silver
credited to the placers is insignificant.
In
the mills the proportion of gold recovered by the amalgamation process
showed a loss of 3 per cent in 1920. The proportion of gold recovered
by cyanidation showed a decrease of 4.2 per cent, following a decrease
of 3.5per cent in 1919. Colorado, Arizona, Nevada, South Dakota, and
California 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 and Nevada. The chlorina-tion process
was not used in California in 1919 or 1920.
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 flotation 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 slightly greater
proportion of gold and silver, are to be credited in 1920 with about 22
per cent of the total output of gold and 86 per cent of the silver.
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 52.8 per
cent in 1920.
