The
Mint Bureau records the production of the precious metals from gold
bullion deposits in United States mints and assay offices, from the
fine bars reported by the refineries, and from the gold and silver
contained in ores and metallurgical products exported for reduction.
The
statistics of gold and silver collected from the mines by the
Geological Survey are obtained from the following four items: 1. Gold
and silver in placer bullion produced during calendar year. 2. Gold and
silver in mill bullion produced in mill of company during calendar
year. 3. Gold and silver in base bullion, matte, etc. (by assay
value),-produced in smelter of company during calendar year. 4. Gold
and silver in crude ore and concentrates (by assay value) shipped to
custom works in calendar year.
The
first item needs no explanation. The second and third items cover the
cases of mining companies which have their own reduction works; they
report the gold and silver bullion produced during the-year, or the
gold and silver contained in their metallurgical products sold to
refineries, as there are very few smelting works owned by mining
companies which also refine their base bullion. There is, as a rule, no
great interval of time before the ore sent to these mills and smelters
is reduced to gold and silver or base bullion, and, although there is
some overlap at the beginning and close of the year, the tonnage
shipped from the mine during the year corresponds with fair accuracy to
the quantity of fine or base bullion or matte produced.
The
greatest difficulties are found in the fourth item, comprising ores and
concentrates shipped to custom works—generally smelters, more rarely
mills—as a considerable interval of time, often thirty days or more,
elapses before the ore reaches the works, and often much more before it
is reduced and refined. It is mixed with other ores and loses its
identity, and the assay value is the only guide the miner has to the
quantity of metal produced. In these cases the miner is requested by
the Geological Survey to give the tonnage and assay value of ores and
concentrates shipped up to the end of the year.
It
should be emphasized that the table of mine production does not give
the contents of the ore mined during the year. Only the ore that is
treated or sold is recorded. Neither does this report give the assay
value of the total tonnage; for if this were the case the heavy losses
in concentration would be disregarded, and the results would be very
much larger and wholly misleading. As far as possible the report aims
to give the metals recovered from the tonnage sold or treated during
the year. In items 2 and 3 this is substantially correct, except for
the very small refining losses. In item 4 the amount given is
theoretically larger than the actual recovery of refined metals by the
combined smelting and refining losses, which in the case of gold and
silver are known to be very small. Practically, however, this is
counterbalanced by several factors: (1) Small quantities of gold and
silver are recovered from many ores, but not-paid for by the smelting
companies or recorded in the settlements. As a rule, payments are not
made on less than 2 ounces of silver or 0.05 ounce of gold per ton. (2)
Settlements are made on the basis of 95 per cent of New York price for
silver and of $19 to $20 per ounce of gold. Small producers, who often
report in terms of dollars alone, are very likely to give a
correspondingly smaller
