The
total quantity of ore sold or treated and from which gold or silver was
produced increased from 43,050,703 short tons in 1914 to 50,513,452
short tons in 1915, which was the largest quantity of such ores ever
recorded. The quantity of copper ores sold or treated increased more
than 5,300,000 tons; that of dry or siliceous ores more than 1,720,000
tons; lead ores, 122,000 tons; and lead-zinc ores, 411,000 tons. Utah,
Arizona, and Montana continued to lead in quantity of ore, owing to the
largely increased output from copper mines, that from the first two
States being mainly from low-grade disseminated ores and that from
Montana mainly from the Butte vein deposits. Nevada ranked next in
output of ore, mainly from Ely copper ores, but also from siliceous
ores from Goldfield, Tonopah, and other districts. Alaska, California,
New Mexico, and Colorado come next, with an output mainly of dry or
siliceous ores from many districts in Alaska, California, and Colorado,
and of copper ores from the low-grade ore bodies in New Mexico.
The
large production of lead and lead-zinc ores in Idaho ranked that State
before South Dakota, which yielded ores which were all dry or siliceous
in character.
The
average gold and silver extraction values were high for the siliceous
ores of Colorado, New Mexico, Nevada, Montana, Oregon, Utah, Idaho, and
Washington, and low for the larger ore bodies of California, South
Dakota, and Alaska. Some of the States produced comparatively small
quantities of copper ore carrying high extraction values in gold and
silver, but the copper ores of the important copper-producing States
showed low extraction values. The average recovery in gold and silver
from the copper ores of Arizona was $0.42 a ton, that of Montana $1.05
a ton, that of Nevada $0.44, that of New Mexico $0.24, that of Utah
$0.33, and that of Michigan $0.15. The lead ores of Utah showed an
average recovery in gold and silver of $9.23 a ton, and the lead ores
of Idaho only about one-third as much. Montana produced the largest
quantity of gold and silver bearing lead ores, and also lead-zinc ores.
Idaho yielded the next largest quantity of these classes of ore, but
the gold and silver content of such ore was very much less than that of
Montana ores of similar character. About 25 per cent of the output of
ore considered as producing gold and silver was dry or siliceous ore,
against 26 per cent in 1914; 65 per cent was copper ore, against 64 per
cent in 1914; less than 5 per cent was lead ore; about 4 per cent was
lead-zinc ore; and 1 per cent was zinc ore. The average precious-metal
extraction value per ton of siliceous ores of the United States
decreased from $6.95 to $6.26, that of lead ores from $5.29 to $4.86,
and that of lead-zinc ores from $2.90 to $2.06. The average gold and
silver value of copper ores per ton increased from $0.49 to $0.51, and
that from zinc ores from $0.19 to $1.32.
DISTRIBUTION OP MINE PRODUCTION OF GOLD IN 1915, BY
SOURCES.
As
shown by the following table, the great bulk of the domestic output of
gold is from dry or siliceous ores—normally gold quartz and gold-silver
quartzose ores—and from placers, more than 90 per cent of the total
production of gold coming from these sources alone. The total
contribution of gold derived from the great copper, lead,
