The
first item consists of all classes of ores, tailings, and slags from
which gold and silver was produced in 1916. The grand total is
64,409,377 short tons in 1916, against 48,514,980 tons in 1915. This
takes no account of placer gravel but represents output of mines
producing ore only. The greatest output was. from Arizona, Utah,
Montana, Nevada, and Alaska, all notable for large yield of copper
ores.
In
reference to the second item many gold and. silver mills employ
concentrating apparatus, and the concentrates obtained are combined in
the table with those from straight concentrating mills under the
heading "Concentrates produced." The gold and silver recovery under
this item is mainly by amalgamation and cyanidation, as is shown in
detail in the last table of this report. The total quantity of crude
ore treated in gold and silver mills in 1916 was 11,249,436 short tons,
against 11,508,953 tons in 1915. The greatest quantities milled were
in Alaska, California, South Dakota, Colorado, and Nevada. The total
recovery of gold from the mills was 2,118,252 fine ounces in 1916,
against 2,416,590 ounces in 1915, and the production was, as usual,
chiefly from Colorado, California, South Dakota, and Nevada, in the
order named. The total silver recovery in mills was 14,724,426 fine
ounces, against 16,503,801 ounces in 1915, and came very largely from
Nevada (from Tonopah and Goldfield chiefly), but also in considerable
part from New Mexico, Arizona, Texas, and Colorado.
Under
the third item is given the quantity of ore treated by concentration
only, including 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., the lead
