The
figures show that fewer placer mines and more deep mines were reported
as producers in 1914 than the respective averages for the period.
In
total number of operating mines Colorado again ranked first with 866,
followed in order by Alaska with 768, Nevada with 731, California with
658, and Montana with 505. In number of placers Alaska led with 730,
followed by California with 340, and Idaho with 208; and in deep mines
Colorado led with 831, followed by Nevada with 620, Montana with 358,
Arizona with 338, and California with 318.
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 is 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 over 2$ per cent 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\ 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. 12793°—m r 1914—vol 1-----54
