The
remainder of the placer production is chiefly from drift mining (which
is of decreasing importance in Alaska in frozen ground at no great
depth, but of continued importance in California in ancient buried
river channels, often at considerable depth) and from hydraulic and
sluicing placers. In California, especially, hydraulic mining has been
of much importance in the past and a special branch of the industry in
itself, but restrictive laws relative to the debris and to disturbance
of navigable streams have in recent years greatly confined mining
activity of this kind. Finally, there is also a small annual output of
gold from dry placers of the Southwest, and a considerable production
of gold and platinum from ocean-beach mining in California and Oregon.
Some
interesting notes on beach mining in California and Oregon and on dry
placers in California, by Charles G. Yale, and on dry placers in
Arizona, Nevada, and New Mexico, by V. C. Heikes, were published in the
Survey report on gold and silver for 1912, copies of which can still be
had on application to the Director, United States Geological Survey,
Washington, D. C.
DRY AND SILICEOUS ORES.
In
1913 dry and siliceous ores, including true gold, gold-silver, and
silver ores, and precious metal-bearing ores not classed as copper,
lead, zinc, or mixed ores, produced $59,222,751, against $62,111,910 in
1912 and $66,369,199 in 1911. States producing over $1,000,000 in gold
from these ores in 1913 ranked as follows: Colorado, California,
Nevada, South Dakota, Alaska, Arizona, Montana, and Oregon.
Increased
output from this source for 1913 was recorded for Arizona, California,
and Oregon and decreased production from Alaska, Colorado, Montana,
Nevada, and South Dakota.
The
siliceous ores are in part free-milling (amalgamating), as in Alaska,
California, and Oregon; in part both amalgamating and concentrating,
as in many States; in smaller part simply concentrating
