ores, 342,550 ounces, or nearly 5 per cent; and the small remainder came from copper-lead and zmc ores.
IDAHO.
Gold.—The
gold production of Idaho in 1911 was $1,372,387, against $1,096,842 in
1910. The output from 152 deep mines in 1911 was $968,060, largely from
Owyhee and Elmore counties, and the production from 217 placers was
$404,327, principally from 7 dredges, but nearly one-third of the
placer output also came from 204 sluicing or hydraulicking operations.
Siliceous ore supplied 57.30 per cent of the gold output, placers 29.46
per cent, copper ores 6.76
g
ercent, and lead ores
5.78 per cent. Two new dredges, one at Idaho ity, with a rated capacity
of 8,000 cubic yards per day, and the other near Salmon, with a
capacity of 5,000 yards, contributed to the increased output of gold.
Boise County produced $265,767, a large increase, from placers in 1911
and $87,697 from deep mines. Elmore County produced $3,546 from placers
and $234,741 from deep mines. Owyhee County produced $1,368 from
placers and $320,835 from deep mines. The Boise Basin region, in Boise
County, whose output is largely from placers, including dredges,
produced $328,838 in gold in 1911, against $168,051 in 1910 and
$127,954 in 1909.
Silver.—The
silver output of Idaho increased from 7,369,742 fine ounces in 1910 to
8,196,136 ounces in 1911. Over 86 per cent of the silver output of
Idaho is from the lead mines, especially of the Coeur d'Alene, in
Shoshone County; and as production of lead ores largely increased, that
of silver did also. The silver output from lead and lead-zinc
concentrates was 5,221,406 ounces in 1911, and crude ore shipped to
smelters contained 2,689,807 ounces. Of the small remainder of the
silver production, 13,753 ounces were recovered by amalgamation and
266,319 ounces by cyanidation.
MICHIGAN.
Silver.—The
Michigan copper mines produced 497,281 fine ounces of silver in 1911,
against 330,500 ounces in 1910. The silver production is mainly from
the electrolytic refining of the copper produced, and, as refining may
proceed at a different rate from mining, increased output of silver in
general indicates only increased quantity of copper refined. The
average recovery per ton of "rock" (both conglomerate and amygdaloid)
was 0.04 ounce in 1911, against 0.03 ounce in 1910. Of the total output
in 1911, Houghton County supplied 459,715 ounces, Keweenaw County
37,053 ounces, and Ontonagon County 513 ounces. The increased
production was almost wholly from Houghton County.
MISSOURI, ILLINOIS, AND KENTUCKY.
Silver.—The
lead and zinc mines of the Central States contribute no gold and but
little silver as a by-product. The small production is mainly from the
lead ores of southeastern Missouri, where the silver content is only
about 1 ounce per ton of concentrates saved, and lead from only about
one-sixth of these ores is desilverized. The output of silver in
Missouri in 1911 was 49,867 fine ounces from 51,109 short
