and
lead-zinc ores of Coeur d'Alene, Idaho, Butte, Mont., and Lead-ville,
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. 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 29,602,270
short tons in 1915 to 43,371,329 tons in 1916, mainly because of the
much greater activity at copper mines. 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 4,127,411 short tons in 1915 to 5,496,226
tons in 1916. Montana mills produced the largest quantity of
concentrates, or 40 per cent, followed by those of Arizona, Utah,
Nevada, and Idaho. The total recoverable gold content of all
concentrates : was 547,172 ounces in 1916, against 528,507 ounces in
1915, and came mainly from Alaska, California, Colorado, Utah, and
Nevada, in the order named. The total recoverable silver from
concentrates produced was 29,566,150 fine ounces in 1916, against
25,778,129 ounces in 1915, and came chiefly from Montana, Idaho, Utah,
Colorado, and Arizona.
The
fourth item covers the quantity and the recoverable precious-metal
content of crude ores shipped from the mines direct to the smelters,
and in general includes the richer gold, sdver, copper, lead, and mixed
ores from which the gold and silver is eventually recovered by refining
the copper or lead bullion that collects the precious metals in the
smelting. The total quantity shipped of this class of ore increased
from 7,018,379 short tons in 1915 to 8,894,609 tons in 1916. Tim output was notably from Arizona, followed by Utah, California, Montana,
Eastern or Appalachian States, and Colorado, in the order named. The
total yield of gold from crude ores smelted decreased from 728,132 fine
ounces in 1915 to 634,366 ounces in 1916, and came chiefly from
Colorado, Arizona, Utah, Montana, California, and Nevada, in the order
given. The total recoverable silver output increased from 29,074,428
fine ounces in 1915 to 33,161,551 ounces in 1916, and was notably from
Utah, Arizona, Colorado, Idaho, and Montana.
Under
the fifth item is given the quantity of old materials, principally
tailings and slags, re-treated, and their recoverable contents. These
are partly smelted, often for their fluxing as well as their metal
value; but considerable quantities of old tailings are now concentrated
and cyanided, and impounding of mill tailings for future treatment as
well as because of legal requirements has now become a general
practice. The total quantity of all old material treated as shown in
the table increased from 385,378 short tons in 1915 to 894,030 tons in
1916. Most of the gold and silver derived from old tailings is included
under recoveries by amalgamation and cyanidation at gold and silver
mills.
From
this table the output of ore from the Central States, producing small
quantities of silver and no gold, has been omitted. The output of zinc
ore from the Eastern States is also omitted, as this zinc ore is
reported to produce neither silver nor gold.
