decreased
from 3,287 in 1918 to 2,460 in 1919, or 737 less than the average for
14 years. Owing to the high cost of labor and material in 1919 fewer
deep mines were operated than in any other year since 1906.
In
total number of operating mines California ranked first, followed in
order by Alaska, Colorado, Montana, and Nevada. In number of placers
Alaska led, followed by California and Idaho; and in deep mines
Colorado led, followed by Montana, Nevada, and California.
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
from mines producing gold and silver and the average extraction value
of precious metals per ton.
The
classification adopted is necessarily arbitrary in part. The complex
nature of western ores, especially, and the gradations from one
well-recognized class to another render essential a fixed terminology.
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
irrespective of their precious-metal content ; but ores of lower
grades in lead and especially in zinc are treated profitably in many
districts, 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.
The
lead, zinc, and lead-zinc ores in many districts in the Eastern and
Central States carry no appreciable quantity of gold or silver, and
such ores are excluded from this report.
The
total quantity of ore sold or treated from which gold or silver was
produced decreased from 68,046,900 short tons in 1918, the largest
output ever recorded, to 42,509,072 short tons in 1919. The total of
such ores had increased more than 17,500,000 tons in the three years
prior to 1919. In 1919 the quantity of copper ores sold or treated
decreased more than 23,490,000 tons; zinc ores more than 121,600 tons;
dry or siliceous ores about 400,000 tons; lead-zinc ores, 986,400 tons;
and lead ores, 541,300 tons; but copper-lead ores increased about 2,000 tons. Arizona, Utah, Montana, Alaska, and Nevada
led in quantity of ore, owing to the large output from copper mines in
all the States other than Alaska, which yielded mainly siliceous ores;
the ore from Arizona and Utah was mainly low-grade disseminated ore,
and that from Montana came mainly from the Butte vein deposits. Nevada
ore was mainly Ely copper ores, but included also siliceous ores from
Goldfield, Tonopah, and other districts.
