average values in gold and silver per ton are, as a rule, somewhat
lower than in 1904, indicating that the greater quantity of ore
produced hat- permitted the mining of a somewhat lower grade of ore.
Xevada still stands alone, with an average value of §21.25. Colorado
follows with an average of 812.73, which is only maintained at this
high point by reason of the high-grade Cripple Creek ores. Wherever
copper ores enter to large extent into the tonnage, as in Arizona,
Montana, Utah, and Tennessee, the average value per ton is greatly
depressed. California's gold quartz ores average only slightly higher
than the figures given for the whole State, $5.06, while those of
Alaska have only half of this average value. The free-milling and
cyaniding gold ores of South Dakota averaged $3.86.
of the most striking facts in the mining industry of the last few years
is the gradual development of the leasing system, by which a mine or a
part of a mine is worked by lessees upon the payment of a royalty or a
certain percentage per ton.
CLASSIFICATION OF ORES.
gold and silver product is divided according to its derivation from
placers, from dry or siliceous ores, copper ores, lead ores, zinc ores,
copper-lead or eopper-lead-zinc ores, and lead-zinc ores.
divisions of the ores from the deep mines are, of course, to a certain
degree arbitrary, and in many cases of complex ores doubt exists about
their proper classification.
general, ores which contain 2-1/2 per cent or more of copper are
considered as copper ores, while those with over 4-1/2 per cent of lead
are called lead ores. Special divisions of mixed ores, such as
copper-lead and lead-zinc, have been established. The bulk of the zinc
ores contain at least 25 per cent of that metal. The classification is
based on the quality of the ore ax mined.
DISTRIBUTION OF THE GOLD PRODUCT OF 1905.
The following table shows the source of gold in the United States in 1905, by kinds of ore and by States:
of gold in 1905 in States and Territories, as reported from the mines
to the United States Geological Survey, by kinds of ore and by States.