PLACERS.
The
output of silver from the refining of placer gold was 89,494 fine
ounces in 1918, against 118,604 fine ounces in 1917, and 126,351 ounces
in 1916. Of the total production 76 per cent came from Alaska and
California.
DRY AND SILICEOUS ORES.
The
mine production of silver from dry and siliceous ores in 1918 was
21,564,982 fine ounces, against 21,489,465 fine ounces in 1917, and
24,593,656 ounces in 1916. About 42 per cent of this was from Nevada
(chiefly from the Tonopah district) and 22 per cent was from Colorado
(mainly from the Leadville, Upper San Miguel, and Sneffels districts).
The quantity of silver from siliceous ores mined in Utah increased from
2,340,537 ounces in 1917 to 3,987,068 ounces in 1918. There were
decreases in many of the States, especially in Nevada, where the
production in 1918 was 1,024,341 ounces less than in 1917, and
3,599,535 ounces less than in 1916. Arizona and Montana each produced
more than 900,000 ounces of silver from this source, and New Mexico
nearly 380,000 ounces. Nearly 99 per cent of the 576,565 ounces of
silver produced in Texas was 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 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
mine production of silver from domestic copper ores in 1918 was
20,462,597 fine ounces, against 20,314,233 fine ounces in 1917, and
24,541,234 ounces in 1916. The decrease in production of silver from
copper ores mined in Alaska was 320,794 ounces; Utah, 779,560 ounces;
Nevada, 49,136 ounces; Michigan, 179,084 ounces; and California,
212,769 ounces. Only two of the larger copper-producing States had any
increase in silver recovered from copper ores; Montana had an increase
of 1,609,830 ounces and Arizona of 133,207 ounces.
The
production of silver from copper ores is from 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 tonnage
contains chalcocite than cnalcopyrite or cupriferous
p
yrite. The great
disseminated copper deposits of Utah, Arizona, and few Mexico are of
increasing importance, and the lode deposits of Butte, Mont., have long
been famous. The silver tenor of the extensive disseminated deposits of
the Santa Rita district, N. Mex., and of Ely, Nev., are notably low,
but similar deposits elsewhere add considerable quantities of silver.
In Michigan 2,806,000 tons of copper ore yielded 509,467 ounces of silver, or slightly less than 0.2 ounce per top,
147566°—m b 1918—pt. 1------49
