The
quantity of siliceous ores treated in South Dakota in 1922 increased,
but the recovery of gold per ton was slightly smaller; the siliceous
ore in California increased 149,582 tons, and the gold recovery per ton
was the second largest recorded for 10 years.
COPPER ORES.
The
gold obtained as a by-product in the smelting of copper ores sold or
treated in 1922 showed an increase in quantity and a very large
increase in percentage of the total gold yield, though the percentage
was less than in 1920. The largest producer was Arizona, followed by
Utah, Montana, New Mexico, California, and Nevada.
LEAD ORES.
The
geld in lead ores sold or treated in 1922 came chiefly from Utah,
Colorado, Arizona, Nevada, Montana, and Idaho and showed a decrease
compared with the output in 1921.
LEAD-ZINC, ZINC, AND MIXED ORES.
The
production of gold from zinc, lead-zinc, copper-lead, and
copper-lead-zinc ores in 1922 was about six times as great as the
production in 1921. Utah and Montana produced nearly all the gold from
lead-zinc ores, and Montana and California produced most of the gold
from zinc ores. Idaho and Montana contributed nearly all the gold from
copper-lead ore.
PRODUCTION OF GOLD, BY SOURCES, 1905-1922.
As
shown in the following table, giving the source of the output of gold
in the United States during the period 1905-1922, dry and siliceous
ores yielded 65.7 per cent of the total, placer mining 25.4 per cent,
copper ores 6.4, and all other ores 2.5 per cent. It is evident that
there can be no great increase from the last-named ores. The yield from
copper ores may increase, but no probable gain will bring the output of
gold from copper ore to more than $5,000,000 or $6,000,000. The yield
of gold from placers in 1922 was less than half that of the average of
the years 1906-1916, and though there may be spasmodic increases during
the next few years, it is practically certain that the output from this
source will decline owing to the steady exhaustion of ground capable of
being worked with dredges. Apparently any large increases in the yield
of gold must come from dry and siliceous ores, which have yielded
two-thirds of the output in the last 18 years. As the production from
the dry and siliceous ores has decreased more than 50 per cent since
1915, as no new large bodies of ores of that class have been
discovered, and as some of the low-grade siliceous ore can not be
worked on account of the increased cost of mining and milling, there is
apparently no reason to expect that the annual yield of gold from mines
in the United States will exceed $50,000,000 to $55,000,000.
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