a Other States that have produced gold, by dredges are Colorado, which yielded, 1901-1915, $3,408,384; Idaho, 1897-1915, $3,3^4,360; Montana,
1896-1915, $7,457,161; and Oregon, New Mexico, Nevada, South Dakota,
Wyoming, Alabama, Georgia, and North Carolina, with a combined yield,
1902-1915, of 51,514,563.
DRY AND SILICEOUS ORES.
In
1915 dry and siliceous ores, including true gold, gold-silver, and
silver ores, and precious metal ores not classed primarily as copper,
lead, zinc, or mixed ores, produced 866,404,089 in gold, against
$60,793,236 in 1914, or more than 67.5 per cent of the total output in
each year. The largest producers from this class of ore are in order of
rank: Colorado, California, Nevada, South Dakota, and Alaska.
The
siliceous ores are in part free-milling (amalgamating), as in Alaska,
California, and Oregon; in part both amalgamating and concentrating,
as in many States; in smaller part simply concentrating ores, as in
parts of Colorado and Arizona; in increasing part all-sliming and
cyaniding ores; and finally in some part smelting ores. Tailings both
from old dumps and from present millings are largely reworked by
concentration and subsequent cyanidation.
The
loss in tailings from gold mills is being constantly cut down, and the
most serious loss remains in tailings from concentrating plants. The
chlorination process is of decreasing relative importance, having been
used in only a few plants in California and Colorado in 1915. Smelting
is mainly of concentrates and of siliceous and pyritic ores, which are
also valuable as fluxes. Exact figures of relative output by methods
will appear in detail by States in another table.
COPPER ORES.
The
production of gold as a by-product of the smelting of copper ores sold
or treated in 1915 was $7,095,110, against $5,474,559 in 1914, an
increase from 6 per cent of the total gold yield in 1914 to 7.2 per
cent in 1915. The largest production was in Utah, followed by Arizona,
Nevada, and Montana, in the order given.
