The
ore treated in straight concentration mills decreased notably in 1919,
mainly because of less activity at copper mines in Montana, Arizona,
and other States. Arizona ranked first in quantity of ore concentrated,
followed by Utah, Montana, Nevada, New Mexico, and Idaho. These
quantities, except those of Montana and Idaho, represent largely
low-grade disseminated copper ores milled. Montana mills produced the
largest quantity of concentrates, followed by those of Arizona, Utah,
Nevada, Idaho, and New Mexico. The recoverable gold content of
concentrates came mainly from California, Alaska, Colorado, Utah,
Montana, and Nevada. About 68 per cent of the recoverable silver from
concentrates produced came from Montana and Idaho; and large
quantities came from Colorado, Utah, Arizona, Alaska, and Nevada. The
decrease was due largely to a smaller output in the silver in
concentrates derived from ores mined in Montana and Idaho.
The
quantity and the recoverable precious-metal content of crude ores
shipped from the mines direct to the smelters in general include the
richer gold, silver, copper, lead, and mixed ores from which the
f
old and silver is
eventually recovered by refining the copper or lead ullion that
collects the precious metals in the smelting. Arizona produced 50 per
cent of the ore directly smelted and was followed by Utah, Tennessee,
Montana, Colorado, Nevada, and California. The gold from crude ores
smelted came chiefly from Arizona, Utah, Colorado, Montana, Nevada, and
Washington. The recoverable silver output came notably from Utah,
Arizona, Colorado, Montana, Idaho, Nevada, California, and New Mexico.
Utah and Arizona produced more than 56 per cent of the silver recovered
from crude ore smelted.
The
old materials, principally tailings and slags, re-treated (with which
are included ore and tailings leached) 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 the
impounding of mill tailings for future treatment as well as because of
legal requirements has become a general practice. The decrease in
quantity of old material treated in 1919 was due mainly to the high
cost of labor and supplies, which made the treatment of tailings
unprofitable. Most of the gold and silver derived from old tailings is
included under recoveries by amalgamation and cyanidation at gold and
silver mills. The total quantity of ore leached in 1919 was 1,885,776
short tons, of which 1,543,373 tons was from Arizona mines, 68,137 from
Utah mines, 272,084 tons from Montana mines, and 1,182 tons from Nevada
mines.
