change; but in Washington the number of producing placers fell from 24
to 12 and the deep mines from 36 to 34. In the Central States there are
no placers and the small number of deep mines producing precious
metals varies little from year to year. In the Eastern States the
numbers of producing placers and deep mines were the same in 1912 as in
total number of producing mines California led with 1,041, followed by
Colorado with 889, Alaska with 752, Nevada with 704, Montana with 604,
Arizona with 445, and Idaho with 408. The order was the same in 1911,
except that Montana preceded Nevada.
ORE PRODUCTION, CLASSIFICATION, AND AVERAGE VALUES.
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.
clasification 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 relatively very small. The
copper ores include those containing over 2-1/2 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 4-1/2 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