of
deep mines increasing by 319 and the number of placer mines decreasing
by 412. For the last five years the number of placer mines reported has
been as follows: 2,316 in 1906; 2,586 in 1907; 2,599 in 1908; 2,187 in
1909; and 2,026 in 1910. The enumeration of placer mines presents
certain difficulties, as noted above, and it has been especially
difficult in Alaska in the earlier years. The figures show increases
for three years followed by decreases for the last two years. The
number of deep-mine producers, however, has steadilv increased, having
been 2,114 in 1906; 2,604 in 1907; 2,864 in 1908; 3,183 in 1909f and
3,299 in 1910.
In
Alaska the estimate for producing placer mines was 1,000 for 1909 and
650 for 1910, and there were 19 deep mines producing each year. In
Arizona the placer producers increased from 25 to 44 and the deep mines
from 243 to 329. In California the placer mines increased from 556 to
564, but the deep mines decreased from 571 to 515. In Colorado the
placer mines increased from 21 to 42 and the number of producing deep
mines decreased from 904 to 856. In Idaho, Nevada, Utah, and Washington
both placers and deep mines increased in number in 1910, and in Montana
both decreased.
ORE PRODUCTION AND AVERAGE VALUES.
The
best index of deep mining is, of course, the tonnage, content, and
value of ore mined, rather than the number of mines or of operators.
In the next following table is given the ore production, by classes of
ore and by States and Territories, of mines producing gold and silver,
and the average extraction value of precious metals per ton.
The
classification adopted is necessarily arbitrary in part. An ore is
generally understood to be worked at a profit for one or more metals.
The complex nature of western ores, especially, and the gradations from
one well-recognized class to another render essential some fixed
measures for the terminology used. The dry or siliceous ores comprise
gold and silver ores proper, as well as fluxing ores carrying
considerable quantities of iron and manganese oxides and very small
quantities of gold and silver, and precious-metal bearing ores carrying
ropper, lead, or zinc in quantities too low to classify them as copper,
lead, zinc, or mixed ores. The distinction between gold and silver ores
is not here made, although an attempt at such further classification
will be made in a forthcoming report. The total number of silver mines
and the total quantity of true silver ores are both relatively very
small. The copper ores include those containing over 2\ per
cent of copper, or less than this in the cases of the great
disseminated copper deposits of the West and of the Lake Superior ores;
the lead ores are those containing 4\ per cent or more of lead,
and the zinc ores are those containing 25 per cent or more of zinc,
both irrespective of their precious metal content. The mixed ores are
combinations of the ones enumerated.
