The
first item consists of all classes of ores, tailings, and slag from
which gold and silver were produced in 1918. The grand total is
65,240,900 short tons in 1918, against 63,935,882 short tons in 1917,
and 64,409,377 tons in 1916. 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 New Mexico, 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 1918 was 8,121,428 short tons,
against 10,329,197 short tons in 1917, and 11,249,436 tons in 1916. The
greatest quantities milled were in Alaska, South Dakota, California,
Colorado, and Nevada. The total recovery of gold from the mills was
1,669,681 fine ounces in 1918, against 1,927,528 fine ounces in 1917,
and 2,118,252 ounces in 1916, and the production was, as usual, chiefly
from Colorado, South Dakota, California, Nevada, Arizona, and Alaska in
the order named. The total silver recovery in mills was 9,923,457 fine
ounces in 1918, against 11,753,827 fine ounces in 1917, and 14,724,426
ounces in 1916, and came very largely from Nevada (from Tonopah,
Wonder, and Rochester districts chiefly) but also in much smaller
quantities from Texas, Colorado, New Mexico, and Arizona.
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.; 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,
however, as already stated, 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 mainly derived from Alaska, California, South
Dakota, and Colorado ores. These concentrates are mainly smelted but
are also treated in gold and silver mills by the processes named.
The
ore treated in straight concentration mills increased from 42,905,807
short tons in 1917 to 45,135,544 tons in 1918, mainly because of
greater activity at copper mines in Montana and Arizona. Arizona ranked
first in quantity of ore concentrated, followed by Utah, Montana,
Nevada, New Mexico, and Idaho. These quantities, with the exception of
those of Montana and Idaho, represent largely low-grade disseminated
copper ores milled. The total quantity of gold and silver bearing
concentrates from all classes of milling ore increased from 5,244,959
short tons in 1917 to 5,357,214 tons in 1918. Montana mills produced
the largest quantity of concentrates, or 38 per cent, followed by those
of Arizona, Utah, Nevada, New Mexico,
