The
placer production 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 can still be
had on application to the Director, United States Geological Survey,
Washington, D. C.
DREDGING.
The
production of gold by dredging in the United States and Alaska from the
commercial beginning of the industry in 1896 to the record output of
1916, inclusive, has amounted in value according to best available
data to $120,103,117, of which $86,880,458 came from California,
$15,109,894 from Alaska, $8,099,733 from Montana, $4,103,649 from
Colorado, and $3,632,056 from Idaho. Oregon produced more gold from
dredging in 1916 than Montana or Idaho and nearly as much as Colorado.
Brief
details of dredging operations have been given in Mineral Eesources in
the mines reports on gold, silver, copper, lead, and zinc of the
Western States and also in earlier reports of the Director of the Mint.
A brief history of gold dredging in the United States was given in the
gold and silver (general) report for the year 1914, and the gold
production obtained by dredging in the United States and Alaska from
1896 to the end of 1914, and the number of dredges operated was given
by States for each year. 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, "Gold dredging in California," by
W. B. Winston and Charles Janin. Another valuable treatise is "Dredging
for gold in California," by D'Arcy Weatherbe, published by the Mining
and Scientific Press; and a recent valuable contribution is that on
"The history and development of gold dredging in Montana," by Hennen
Jennings, with a chapter on placer mining methods and costs, by Charles
Janin, published as Bulletin 121 of the Bureau of Mines.
The
gold recovered in the United States and Alaska by 113 gold dredges in
1916 was $12,786,614, against $12,483,125 by 114 dredges in 1915. Of the production in 1916 California yielded $7,769,227 from
60 dredges, Alaska $2,679,000 from 34 dredges, Montana $642,572 from 5
dredges, Colorado $695,265 from 6 dredges, and Idaho $327,696 from 4
dredges. Two dredges operating in Baker County and one in Josephine
County, Oreg., produced $670,415.
