DRY AND SILICEOUS ORES.
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 cyanidation. Owing to the
increase in the cost of labor and supplies in the last five or six
years, much of the old tailings could not be reworked at a profit.
The
materialsmelted consists mainly of concentrates and of siliceous and
pyritic ores, whichare also valuable asfluxes. Exactfigures of
relative output by methods and by States are given in another table.
As
most of the gold produced in the United States is derived from placer
gravels and dry and siliceous ores, including true gold, gold-silver,
and silver ores, tbe following table for certain States, prepared by V.
C. Heikes, is of special interest.
