low
extraction values. The lead ores of Utah showed an average recovery in
gold and silver of $16.04 a ton, and the lead ores of Idaho, the
leading State, only $4.52 a ton. Of the output of ore considered as
producing gold and silver, the proportion of dry and siliceous ore
decreased, whereas that of copper ore increased slightly as compared
with the output in 1919. The other classes of ore, except lead-zinc
ore, also increased. The average precious-metal extraction value per
ton of siliceous ores of the United States increased slightly, whereas
that of copper, lead, and lead-zinc ores decreased. There were
conspicuous increases in the extraction value of zinc and copper-lead
ores.
DISTRIBUTION OF MINE PRODUCTION OF GOLD IN 1920, BY
SOURCES.
As
shown in the following table, more than 89 per cent of the domestic
output of gold is obtained from dry and siliceous ore— normally gold
quartz and gold-silver quartzose ores—and from placers. The total
contribution of gold derived from the great copper, lead, and zinc
mines of the country is therefore relatively small, notwithstanding
their recent enormous development and production of ore.
The
contribution of gold from dry and siliceous ores, which had gradually
declined from about 69 per cent in 19-10 to about 66 per cent in 1914
and has fluctuated since then, was 63.93 per cent in 1920. The
contribution of gold from copper ores, which had increased from 6 per
cent in 1914 to 9.6 per cent in 1918 and decreased to 6.78 per cent in
1919, increased again to 7.18 per cent in 1920.
Mine production of gold in 1920, in fine ounces.
