Comparison
of the figures for 1916 shows a net total decrease of 22 producing
mines, following decreases in 1912, 1913, 1914, and an increase of 344
mines in 1915. The total number of properties operated in 1916 was 27
in excess of the average for the last 11 years. The number of placer
properties worked in 1916 showed a decrease of 190 and was nearly 800
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 increased from 3,597 in 1915 to 3,765 in 1916, or 564
more than the average for 11 years. High prices for copper, lead, and
zinc in 1916 resulted in more deep mines being operated than in any
year for which data are available by the Survey.
In
total number of operating mines Colorado again ranked first with- 852,
followed in order by Nevada with 779, Alaska with 697, California with
589, Arizona with 527, Montana with 513, and Idaho with 418. In number
of placers Alaska lead with 650, followed by California with 292, and
Idaho with 162; and in deep mines Colorado led with 825, followed by
Nevada with 714, Arizona with 504, Montana with 393, Utah with 310,
and California with 297.
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 cases of the great disseminated, copper deposits
of the West and of 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 irrespective of
their precious-metal content; but ores of lower grades in lead and
especially in zinc are treated profitably in some places, and of course
they are then classified as lead or zinc ores, as the case may be. The
mixed ores are combinations of those enumerated.
