Figures
corresponding to those in this table have been published for the entire
United States by the Geological Survey since 1911. The quantity of
crude ore treated and old and new tailings re-treated in gold and
silver mills reached a maximum in 1915 (11,878,287 tons). It exceeded
11,000,000 tons in 1916 and 1917 but has declined steadily since the
record year, except for a small increase in 1919.
The
great bulk of the ore treated was milled in Alaska, Colorado, South
Dakota, California, Nevada, and Arizona, and here the famous mines and
mills of the Homestake, Mother Lode, Grass Valley, Treadwell, Cripple
Creek, Tonopah, Goldfield, and San Francisco (Oatman) districts are
especially noteworthy. Large numbers of smaller mills, however, mark
the wide distribution of gold mining in these regions and in many other
scattered districts.
The
total yield of gold by amalgamation in the United States in 1920 was
679,409 fine ounces, against 839,761 fine ounces in 1919, and there has
been a decrease of about 285,200 ounces since 1916. Appreciable
decreases were shown in Colorado, California, Alaska, and Nevada, and
there were small increases in Oregon and South Dakota.
The
silver produced by amalgamation came mainly from California, South
Dakota, Alaska, Colorado, and Nevada, and consisted chiefly of silver
alloyed with gold.
The
output of gold by cyanidation decreased 105,125 ounces. It was derived
mainly from Colorado, Arizona, Nevada, South Dakota, California, and
Alaska. The principal decreases were in Colorado, 69,321 ounces;
Nevada, 32,983 ounces; and Montana, 10,465 ounces.
Nevada led in yield of silver by cyanidation and was followed by Texas, New Mexico, and Arizona. The most notable loss was in
