Comparison
of the figures for 1918 shows a net total decrease of 662 producing
mines, following decrease in 1912, 1913, 1914, and 1916, and an
increase of 344 mines in 1915 and 68 mines in 1917. The total number of
properties operated in 1918 was 531 less than the average for the last
13 years. The number of placer properties worked in 1918 showed a
decrease of 138, and the total was about 900 less than the number
operated in 1906. This is a natural result due to the exhaustion of the
rich gravels and to the acquisition of large areas of placer ground by
dredge mining companies. The number of deep mines operated decreased
from 3,811 in 1917 to 3,287 in 1918, or 33 more than the average for 13
years. High costs of labor and material in 1918 resulted in less deep
mines being operated than in any year since 1914.
In
total number of operating mines Alaska ranked first with 769, followed
in order by Nevada with 714, California with 703, Colorado with 588,
Montana with 493, Arizona with 469, and Idaho with 301. In number of
placers Alaska led with 727, followed by California with 315, Montana
with 86, and Idaho with 85; and in deep mines Nevada led with 660,
followed by Colorado with 576, Arizona with 456, Montana with 407,
California with 388, Utah with 248, and Idaho with 216.
ORE PRODUCTION, CLASSIFICATION, AND AVERAGE VALUE.
The
best index of deep mining is, of course, the quantity, metallic
content, and value of ore mined, rather than the number of mines or of
operators: In the next following table are given the production of ore
by classes of ore and by States and Territories from 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
copper, 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. The total number of silver mines and the total
production of true silver ores are both very small. The copper ores
include those containing 2.5 per cent or more of copper, or less than
this percentage in the great disseminated copper deposits of the West
and in the Lake Superior ores; in general, the lead ores are those
containing 4.5 per cent or more of lead and the zinc ores are those
containing 25 per cent or more of zinc, both irre-
