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220
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MINERAL RESOURCES.
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material treated at the mines or shipped from them during the calendar year.
The
first item is the native gold (with silver in natural alloy) produced
from placer mines and sold to Government mints and assay offices, and
to refineries, banks, and traders. It is difficult to obtain accurate
figures for this item only in some parts of Alaska, or from transitory
miners elsewhere, or from miners who report only value received for
their output. The second and third items cover metal production by
mining companies whose mills and smelters treat their own ores and
whose products go to the mints and refineries and are covered by
confidential mine reports to the Survey. The fourth item, which covers
raw mine products shipped for treatment, gives rise to the main
apparent discrepancies between mine and mint-refinery reports on the
production of gold and silver for the same calendar year. The
discrepancies are due largely to the lapse of time between the disposal
by shipment of the ore as reported from the mines and its arrival and
metallurgical treatment at the mills or smelters, followed by the
refining of the products, an interval in which large quantities of
metals in ores reported from the mines as shipped in one year may be
reported from refineries as produced in marketable form in the
following year. For instance, ore shipped in November may be smelted in
the following January, and the metal content would be reported from the
mines for the calendar year preceding that for which it would be
reported in marketable form by the smelters and refineries. The miners
furnish the United States Geological Survey with confidential reports
on assay values and tonnages of ore and concentrates shipped as the
measure of their output, and the mine figures are reported by the
Survey so far as possible in terms of recoverable metal; and the
smelters and refineries report the metals eventually produced, first as
unrefined and finally as refined.
In
using the mines report it should be noted that tonnages and metal
output given are based not on ore mined but on ore treated or sold
during the year. Of course most of the ore treated or sold is also
mined during the same year, but some of it is necessarily mined during
the preceding year. It must not be overlooked also that the mines
report aims to give the recoverable content, not the assay content, of
ore treated or sold. A part of the actual recovery is of course made
during the early part of the following year for ores treated or sold
late in the year under review, but the basis of the report is
essentially metal recovered at whatever time from the tonnage treated
or sold during the year covered by the report. For the second and third
items enumerated the recovery figures are easily had, as the ore is
treated on the ground, and the metal content of the bullion, either
base or unrefined, is readily known. In the third item the refining
loss and in the fourth item the combined concentrating, smelting, and
refining losses must be considered. In the case of the precious metals
the concentrating losses may be large and must be allowed for, but the
smelting and refining losses are known to be very small and in ordinary
practice to be more than offset by certain gams. These gains are of
small quantities of precious metals (not paid for, but actually
recovered from ores of copper, lead, and zinc) and certain differences
in quantity of gold and silver between actual recovery and basis of
settlement—for
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