PLACEES.
GENERAL FEATURES.
The only States showing a considerable increase in placer gold were Oregon (3,409 ounces) and Nevada (984 ounces).
The
placer gold is derived chiefly from dredging, 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 was of
much importance in the past and had become 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 a small annual output
of gold from dry placers in the Southwest and also a 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 may still be
had on application to the Director, United States Geological Survey,
Washington, D. C.
DREDGING.
The
value of gold produced by dredging in the United States from the
commercial beginning of the industry in 1896 to the end of 1920 has
amounted, according to best available data, to $162,628,504, of which
$117,243,197 came from California, $21,524,826 from Alaska, $9,365,078
from Montana, $6,328,819 from Colorado, $4,287,798 from Idaho, and
$3,554,900 from Oregon.
Brief
details of dredging operations have been given in Mineral Resources in
the mines reports on gold, silver, copper, lead, and zinc in the
Western States and also in earlier reports of the Director of the Mint.
A brief history of gold dredging m the United States was given in the
general report on gold and silver for the year 1914, and the production
of gold obtained by dredging in the United States and the number of
dredges operated were given by States for each year from 1896 to the
end of 1914. Further information is to be found in reports of
geological surveys or mining officials of different States. A
comprehensive and very useful report is contained in Bulletin 57 of the
California State Mining Bureau. Other valuable treatises are "Dredging
for gold in California," by D'Arcy Weatherbe, published by the Mining
and Scientific Press, and Bulletins 121 and 127 of the oi Bureau Mines.
