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GOLD AND SILVER.
133
silver
milling ores, and explains why the rise in value during the last few
years has failed to increase the production greatly. Nevada
p
roduced nearly
6,500,000 ounces of silver from siliceous ores, chiefly from Tonopah,
but even these contain 1 part of gold to 3 parts of silver, by value.
The Colorado production closely approaches the figures for Nevada; but
here again most of it came either from mixed ores, either pyritic or
siliceous, which are concentrated and smelted, and which also contain
lead, copper, or gold, or from the gold-silver ores, partly free
milling, from the Gilpin or San Juan regions. Montana has in Granite
County a district of purely silver ores, but the yield from this source
fell off in 1906, the largest quantity of silver in Montana being
derived from Butte copper ores; the output of the State from siliceous
ores is a little over 1,250,000 ounces. Arizona comes next with almost
600,000 ounces, but in no other State does the quantity reach half a
million ounces.
The
silver is recovered from siliceous ores by amalgation or cyanide
processes; from smelting ores by desilverization of lead bullion or by
electrolytic refining of copper.
Copper ores.—From
copper ores 15,880,870 fine ounces were recovered; the smallness of
the increase over 1905, in spite of heavily increased tonnage, is
explained by the low tenor of the copper ores in silver. The States
rank as follows: Montana, Utah, Arizona, California, Idaho, and
Colorado. Montana yielded nearly 10,000,000 ounces, the largest silver
production in any State from any one kind of ore. This represents a
decrease of about 100,000 ounces from the output of 1905 in spite of
heavily increased tonnage. Arizona, from a very heavy tonnage, produced
only 1,750,000 ounces. Utah, from a very much smaller tonnage, reported
over 2,000,000 ounces. None of the other States reached the
1,000,000-ounce mark. The extraction of gold and silver per ton from
the ores of the principal copper camps runs approximately as follows:
Yield of gold and silver per ton of copper ore from the principal copper camps, in 1906,
in fine ounces.
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Copper
ores shipped from the Coeur d'Alene district yielded a notable
addition of silver to the production of Idaho, which for this class of
ore was nearly 600,000 ounces. The silver from California copper ores
was nearly doubled in 1906, owing to greatly increased activity in
Shasta County, and approached 800,000 ounces.
About
85 per cent of the silver-bearing copper ores of the West are now
sulphides. Oxidized ores are still contributed by Arizona, New Mexico,
Idaho, and other States.
Lead ores.—The
lead ores have always been one of the most important sources of
silver, but a decided declining tendency in the output has been noted
during the last few years. The total is
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