The
mine production of silver from the three most important sources of
silver—dry and siliceous ores, copper ores, and lead ores— was 87.90
per cent of the total output in 1920, against 89.16 per cent in 1919.
The percentage of the total output from dry and siliceous ores
decreased 0.47 per cent in 1920, following an increase of 5.01 per cent
in 1919; that from lead ores increased 2.54 per cent, that from
lead-zinc ores decreased 1.60 per cent, and that from copper ores 3.33
per cent. The combined yield of silver from placer bullion, zinc ores,
and copper-lead ores was only 3.54 per cent of the total.
PLACERS.
The
output of silver from the refining of placer gold was less than in 1919
or 1918. Of the total production 75 per cent came from Alaska and
California.
DRY AND SILICEOUS ORES.
About
34 per cent of the mine production of silver from dry and siliceous
ores was from Nevada (cniefly from the Tonopah district), 19 per cent
from Utah (mainly from the Tintic district), and nearly 18 per cent
from Colorado. There were increases in the quantity of silver from
siliceous ores in many of the States, especially in California, Nevada,
Utah, Montana, Alaska, and New Mexico. More than 99 per cent of the
silver produced in Texas came from siliceous silver ores.
A
large part of the silver from gold-silver siliceous ores is obtained
with the gold by amalgamation and cyanidation in the mills, and the
silver is then recovered by refining the mill bullion. The remainder is
produced by smelting the richer ores and refining the copper or lead
bullion produced. A small quantity of silver was also recovered from
the leaching of copper ores.
COPPER ORES.
The
silver produced from copper ores is obtained in the electrolytic
refining of Lake and blister copper produced by smelting. The copper
ores are mainly sulphides (except the Lake ores of Michigan, which are
native metal in amygdaloid and conglomerate matrix), and a greater
quantity contains chalcocite than chalcopyrite or cupriferous pyrite.
The silver tenor of the extensive disseminated deposits of the Santa
Rita district, N. Mex., and of Ely, Nev., is notably low, but similar
deposits elsewhere add considerable quantities of silver.
In
output of silver from copper ores Montana continued to lead with
6,030,507 ounces in 1920, against 6,341,825 ounces in 1919. Arizona
was next with 3,716,246 ounces in 1920, against 3,711,052 ounces in
1919; Alaska ranked third, with 682,033 ounces in 1920, against 488,034
ounces in 1919; and California produced only 179,752 ounces in 1920,
against 349,480 ounces in 1919. The production of Montana comes mainly
from Butte, that of Arizona chiefly from Bisbee and Jerome, that of
Utah from Tintic and Bingham, and that of California from Plumas
County. Of these districts Bisbee well represents the disseminated
type; Bingham produces from both lode and disseminated deposits; and
the remainder produce silver chiefly from copper ore mined from deep
lodes.
