DRY AND SILICEOUS ORES.
In
1919 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 $36,807,594 in gold, against
$42,-284,130 in gold in 1918 and $49,963,518 in 1917. The largest
producers from ores of this class were Colorado, California, South
Dakota, Alaska, Nevada, and Arizona. In 1919 deep mines in the
Philippine Islands yielded $1,092,267 from siliceous ores, but the
output is not included in the table.
The
siliceous ores are in part free-milling (amalgamating), as in Alaska,
California, Arizona, and Oregon; both amalgamating and concentrating,
as in many States; simply concentrating ores, as in parts of Colorado
and Arizona; all-sliming and cyaniding ores; and finally smelting ores.
Tailings both from old dumps and from present millings are largely
reworked by concentration and subsequent cyani-dation. Owing to the
increase in the cost of labor and supplies in the last three or four
years, much of the old tailings could not be reworked at a profit.
The
material smelted consists mainly of concentrates and of siliceous and
pyritic ores, which are also valuable as fluxes. Exact figures of
relative output by methods and by States are given in another table.
As
most of the production of gold in the United States is derived from
placer gravels and dry or siliceous ores, including true gold,
gold-silver, and silver ores, the following table for certain States,
prepared by V. C. Heikes, of the United States Geological Survey, is of
special interest.
