This
division necessarily includes a great variety of ores, which, briefly
enumerated, are as follows: The quartzose free-milling gold ores
include those of southeastern Alaska, and especially of Douglas Island,
where now 880 stamps are dropping; those of the Oregon and the
California gold belts; those of the central Arizona and the Yavapai
gold regions; those of the Telluride and Ouray belt in Colorado; those
of scattered Montana and Idaho mines, and those of the great Homestake
mines in the Black Hills of South Dakota, where 1,000 stamps are
dropping.
The
quartzose gold-silver ores, which ordinarily are only imperfectly
amenable to direct amalgamation, include the rich ores of western
Nevada, most of which are now smelted, but which can be treated also by
a combined amalgamation concentration and cyanide process. Scattered
ores from Arizona, from Colorado, from Silver City in Idaho, and from
other sources contribute also to this total.
The
quartzose gold ores formed by replacement of limestone add a fairly
large amount of gold. The metal occurs in these ores in fine
distribution, sometimes, indeed, as a telluride, and the cyanide
process is used for its recovery. The three most prominent localities
are the Camp Floyd (Mercur) district in Utah, the Black Hills of South
Dakota, and the Moccasin Mountains of Fergus County, Mont.
The
dry or siliceous ores further include the quartzose ores of Cripple
Creek, Colo., in which the prominent characteristic is the occurrence
of large quantities of gold tellurides. These ores are partly smelted,
partly chlorinated, and partly cyanided, all three processes being
applicable.
There
is, finally, a large class of dry ores which contain pyrite and other
sulphides and which are best treated by the smelting process, with or
without, concentration. Colorado contributes by far the largest
quantity of these ores, among which those of Leadville are of
particular importance.
Copper ores.—A
total of 255,568 ounces of gold were obtained from copper ores in 1905,
against 237,116 ounces in 1904. The increase is wholly due to the
development of the great copper mines from which gold is obtained as a
by-product in the refining of the copper. The richest of these ores
are obtained from Utah (Bingham, San Francisco, and Tintic districts),
in which State the gold from this source increased from 109,968 ounces
in 1904 to 125,897 in 1905.
The
Butte, Mont., copper ores are poorer in gold, but the increase in
copper production was here, too, felt in the yield of gold. The same
applies to Arizona, the copper ores of which are, as a rule, very poor
in gold and silver. In California alone the yield of gold from copper
ores decreased from 24,727 ounces in 1904 to 10,867 ounces in 1905,
owing to a temporary lull in the Shasta County industry. Idaho records
an increased but still small output from the Seven Devils and from the
Cceur d'Alene, and the same is to be said of Oregon, where the Takilma
mine was the principal producer. The quantity of gold obtained from
Colorado copper ores remained about stationary. Nearly all of the
copper ores are classed as sulphides.
Lead ores.—From
lead ores proper only 66,067 ounces of gold were obtained, chiefly from
Colorado, Utah, Arizona, Montana, and Nevada. The lead ores have been
further subdivided this year into lead ores proper and copper-lead
ores, but even the combined output of the two fails to come up to the
figures for 1904. The decrease is about 18,000 ounces and is most
strongly pronounced in Colorado. The decrease in this State is,
however, partly compensated by increases from the Tintic district in
Utah and from the Tombstone district in Arizona. Rich lead ores are
growing notably scarce. The copper-lead ores containing gold are, on
the whole, rare and are principally represented in the Tintic district.
Zinc ores.—Although
there is ordinarily but little gold in zinc ores and lead-zinc ores, a
total of about 7,500 ounces is credited to this source, an increase of
2,800 ounces over the figures for 1904. Most of this gold is associated
with a predominant amount of silver and is derived from Leadville and
many other localities in Colorado.
