The
first item takes no account of placer gravel but represents output of
mines producing ore only. The greatest output was from Arizona, Utah,
Montana, Nevada, and New Mexico—all notable for large yield of copper
ores—and from Alaska.
Many
gold and silver mills employ concentrating apparatus, and the
concentrates they obtain are combined in the table with those from
straight concentrating mills under the heading "Concentrates produced.'
The gold and silver included in this item is recovered mainly by
amalgamation and cyanidation, as is shown in detail in the last table
of this report. The greatest quantities milled were in Alaska, South
Dakota, Colorado, California, and Nevada. The gold recovered in the
mills was, as usual, chiefly from Colorado, California, South Dakota,
Nevada, Alaska, and Arizona.
The
silver recovered came very largely from Nevada (Tonopah, Wonder, and
Rochester districts chiefly) and in much smaller quantities from
Texas, New Mexi"co, Colorado, and Arizona.
The
figures for the quantity of ore treated by concentration only include
the large quantities of copper, lead, zinc, and mixed ores whose
concentrates are smelted primarily for these metals, the gold and
silver being recovered in refining the copper and lead bullion and
smelting the zinc residues. Examples are the copper ores of the
disseminated deposits of Bingham, Utah, and of New Mexico and Nevada;
the copper ores of Butte, Mont.; and the lead and lead-zinc ores of
Coeur d'Alene, Idaho, Butte, Mont., and Leadville, Colo. The quantity
of concentrates produced and the recoverable gold and silver content
represent not only the concentrates from these straight concentrating
mills but also those from gold and silver mills, which form, however, a
very small part of the total quantity of concentrates and are derived
mainly from Alaska, California, and Colorado ores. These concentrates
are mainly smelted but are also treated in gold and silver mills by the
processes named.
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