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GOLD AND SILVER.
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235
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in
a few instances platinum are recovered from gravels and sands, whether
by hand-washing, sluicing, hydraulicking, drifting (in frozen ground or
ancient buried river channels), or dredging. The deep mines are those
producing gold and silver mainly from underground workings, including
those whose ores are valuable chiefly for copper, lead, or zinc, but
which contribute precious metals as by-products. In addition to the
producing mines here enumerated, many mines were being prospected and
developed without making an output in 1911, and annual assessment work
(required by law to hold claims not patented) was done on a very much
greater number of new or old, worked-out, or indefinitely idle
properties, once productive or otherÂwise, and of mere mining claims,
which have not yet become "mines.' The enumeration of placer mines is
less satisfactory than that of deep mines, because some of the
operations are only temporary' and because the production is frequently
by transitory miners not reguÂlarly working placer ground. The unit, so
far as possible is, however, as for deep mines, not the operator, but
the mining claim, or group of claims.
Number of producing mines in 1911, by States and Territories.11
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o Illinois, Kentucky, Philippines, and Porto Rico not included, b Number of mines'contributing to silver production in 1911.
The
table shows the number and distribution of mines producing gold and
silver in the United States and Alaska. With the exception of (1) some
of the Michigan copper mines, (2) all zinc mines in the Eastern and
Central States and a few in the far West, and (3) all lead mines of the
Central States (except a few in Illinois and southeastern Missouri),
practically all mines producing copper, lead, and zinc in the United
States and Alaska yield gold and silver also. The table, therefore,
with these exceptions, is a table of mines producing gold, silver,
copper, lead, and zinc in the United States. It also includes certain
mines producing oxidized manganese-iron fluxing ores of Colorado, Utah,
and elsewhere, whose ores contain small quantities of precious metals,
especially silver, and are sold to western smelters as flux.
Comparisons
with corresponding figures for 1910 show a net total increase of 374
producing mines in 1911. The number of deep mines increased by 254 and
the number of placers by 120. In 1910 the
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