certain
quantity, sometimes a large quantity, is reported from smelter returns,
for which no mine returns can be obtained. According to local
conditions such discrepancies are more or less easily traceable.
Copper, again, is only paid for when it runs over 1-1/2 per cent wet
assay, and 1-1/2 per cent or more is usually deducted from any wet
assay. Here, again, the answers most commonly record the pounds of
copper for which pay was obtained. Colorado, for instance, does not
haye a large production of copper, and yet it has been found that the
smelter returns, as recorded by the State authorities, the mint,
and the Geological Survey, greatly exceed the mines report. From the
mines the most careful canvass resulted in returns of about 6,000,000
pounds, while the actual output of copper from Colorado ores was
undobut-edly over 9,000,000 pounds.
The
mines report of copper and lead are thus apt to be somewhat lower than
the smelter reports in States with much custom smelting, but experience
has shown that serious errors may occur also where the latter are
exclusively relied on. The best results will be obtained from a
combination of the two methods, such as will be inaugurated by the
Geological Survey for the year 1906.
The
recently developed zinc industry of the West has proved difficult of
exact measurement. The ores vary so widely in character and tenor that
the Missouri Valley measure by tons of ore is practically useless. The
loss of metal in smelting is much greater than in case of lead and
copper, so that the spelter actually recovered from a given ore is
difficult to estimate. In this report the loss has been assumed to be
25 per cent, and the mines have been requested to give assay value and
tonnage from which the probable spelter has been calculated. A better
way probably is to count 8 per cent off on all percentages. Few ores
below 25 per cent are utilized; the majority of ores average about 35
per cent, while concentrates and exceptionally rich ores range from
this figure up toward 60 per cent. Sulphide ores prevail. New Mexico
still ships large quantities of oxidized ores, but these will soon be
exhausted and sulphides will take their place. A part of the zinc ores
are shipped to the Mississippi Valley smelters, the only reduction
plant in the West being that of the United States Zinc Company at
Pueblo, Colo. The United States Smelting Company at Pueblo makes
zinc-lead pigment from the zinc-lead ores of Aspen and other places.
In
marketing zinc ores for spelter, cobalt, nickel, antimony, and fluorine
are very objectionable constituents. Lead in such ores is usually not
paid for, and a large percentage is not desired. Lime above 4 per cent
and iron above 6 per cent are often penalized. It is difficult to give
average prices paid, as the schedules vary and are rather complicated.
A 40 per cent zinc ore otherwise satisfactory would probably be paid
for at the rate of $20 per ton, less freight to smelter. There is
seldom much gold in zinc ores, but silver is nearly always present. A
small payment is usually received for silver above 5 ounces per ton.
The cinders from the zinc retorts in the Mississippi Valley seldom
contain enough silver to warrant treatment, but the Pueblo plant
transfers its cinders from Colorado ores to the American Smelting and
Refining Company, which extracts a considerable quantity of silver and
a little gold from them.
It
is often difficult to ascertain whether, in a given zinc ore with low
tenor of silver, the latter metal has actually been recovered or not.
UNITS OF MEASUREMENT.
Gold
and silver are measured by the fine ounce. In the mines reportof the
United States Geological Survey gold is calculated at $20.671834 per
fine ounce, and the average commercial price of silver at New York for
1905 is taken as 60.4 cents per fine ounce. The average price of crude
platinum is $17 per ounce. As to the base metals, the average price of
copper in 1905 is taken as 15.6 cents per pound, that of lead as 4.7
cents per pound, and that of zinc as 5.9 cents per pound. These are the
