in
the South, in New Mexico, and in California. There are other items,
however. which may easily escape the collector of statistics by this
method and which may result, for instance, from retreatment of slags or
of old metallurgical by-products. The gold from stolen ore in rich
camps, such as Cripple Creek, Goldfield, and Grass Valley, which is
believed by many to make a considerable sum in the aggregate, is
collected by small assay offices and naturally is not represented in
these tables of individual returns.
Further
errors may arise through mistakes in the replies, a common one being
the returning of the net smelter returns instead of the gross amount.
Willful misstatements have been traced in the returns from a few small
mines, but are very rare.
When
the metals are obtained as placer gold or from the mills at the mines
little difficulty is encountered. The case is somewhat different with
regard to custom-smelting ores, where the miner has no way of measuring
the bullion actually extracted except by the assay. The loss of gold in
lead smelting is extremely small, and the figures used are the ounces
calculated from the assay; but in the case of silver the loss is
commonly estimated at 5 per cent by the smelters, which rate probably
leaves them a safe margin. It has been noted that most frequently when
ounces are given in the replies the amounts corresponds to 95 per cent
of the assay value, and thus the returns should correspond closely with
the direct smelter returns for silver obtained by the Bureau of the
Mint.
Ordinarily
gold is not paid for in ores when below five one-hundredths part of an
ounce, but this in the aggregate amounts to a fairly large sum. As
examples may be cited some of the Leadville lead ores, for which a
separate estimate had to be given, and also some of the lead
concentrates from northern Idaho. The small amount of gold in
electrolytically refined copper is usually correctly obtained from the
producing mining companies.
Silver
is not as a rule paid for unless it runs above 2 ounces per ton, but as
the ores treated in custom smelters rarely contain less than this
quantity, there is very little from this source W'hich escapes this
method of collecting statistics. As an example may be cited the small
quantity of silver in the Cripple Creek smelting ores, for which a
separate estimate had to be made. The low silver values contained in
certain copper ores are, like the gold, recovered by the electrolytic
method and are directly reported by the mining companies.
Summing
up the comparative merits of the "mines report" method and the "smelter
and refinery " method, one notes that the first is dependent upon a
complete mine list and upon accurate returns from the mines, while the
latter is dependent upon the accuracy of the data from the smelters.
The smelter records are, however, not kept for the purpose of compiling
statistics for the whole country, so that in reference to special
districts wholly technical and, from point of view of the reduction
works, unavoidable errors may easily be introduced. Moreover, there is
the very important matter of the "stock on hand," which is almost sure
to make the smelter returns differ from the mines report. The miner in
his answer includes all smelter and mint returns which have been
received up to the last day of December, while the smelter reports
only the bullion which has been turned out up to that date. In
individual cases important differences between State and county reports
received by these two methods have been actually traced to this factor.
Special efforts will be made in future reports by the Geological
Survey, in cooperation with the Bureau of the Mint, to account strictly
for the discrepancies which may be found.
In
the West, gold and silver are so intimately connected with copper,
lead, and zinc that it was found desirable to include the latter in the
queries addressed to the mines. Here increased difficulties are met,
especially in States with extensive custom smelting, like Colorado.
Greater losses must be counted on in smelting these metals than in the
case of gold and silver. Lead is only paid for in the ores when it runs
over 5 per cent., except in special cases of large contracts.
Consequently a
