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GOLD AND SILVER.
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271
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The
mills contributed over half the gold output in 1911 and 1912 and
increased the relative output of silver from 15.7 per cent of the total
in 1911 to 19 per cent in 1912. The placers, the amalgamation and the
cyanidation processes, and the smelters supplied practically all the
gold production in nearly equal parts, the recovery of gold by the
chlorination process having declined from 3.8 per cent of the total
output of gold m 1911 to 0.4 per cent in 1912. The placers and
amalgamation processes contribute very small percentages of the total
silver production. The bulk of the output remains from the smelters
treating crude ore, concentrates, and other material, the
E
percentage of total
output of silver from this source having declined, however, from 84 per
cent in 1911 to 80.8 per cent in 1912. This decline is explained by the
corresponding rise in relative recovery of silver by cyanidation, from
15.7 per cent of the total output in 1911 to 19 per cent in 1912.
The
following table shows in greater detail the tonnage treated and output
of precious metals by gold and silver mills, by States, in 1912:
Quantity
of ore treated at gold and silver mills in 1912, giving recoveries by
amalgamation and cyanidation and percentage of each to gold and silver
recovered from all sources.
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Figures
corresponding to those in this table were collected and compiled for
the United States for the first time in 1911 by the Survey, and
comparison for two years for the first time can therefore now be made.
The
total quantity of crude ore and old tailings treated in gold and silver
mills in 1912 was 9,677,360 short tons, against 9,670,483 tons in 1911.
The great bulk of the ore treated, as shown, was milled in California, South Dakota, Alaska, Colorado, and Nevada, and here the
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