MINERAL PRODUCTS. 
19 
The actual gain in capacity is even more than is indicated by these 
figures, for in the earlier years a number of small, antiquated 
smelters that had been idle for several years were included in esti 
mating the total capacity, whereas in the later years almost all such 
smelters have been dismantled or abandoned completely, and there 
have been more new, modern additions than ever before in the same 
time. It is to be borne in mind that a certain portion of the capacity 
is taken up in the redistillation of zinc drosses, and that some plants 
do not yield full capacity because they treat lower-grade ores, so 
that the spelter produced from ore always falls much short of the 
maximum capacity. On the other hand, the new zinc oxide plant 
at Leadville, Colo., will take a great deal of the low-grade carbonate 
ore away from the zinc smelters, so that the capacity per retort will 
be increased because of the higher grade of the remaining supply; 
and the introduction of ore flotation in the Western States will 
probably raise the grade of zinc concentrates from that section, like 
wise increasing the capacity per retort. 
The following table shows that the production of zinc at the 
mines is steadily increasing: 
Joplin district 
Now Jersey 
Colorado 
Montana 
Upper Mississippi Valley 
Other States 
1911 
137,633 
77,445 
47,304 
21,905 
33,939 
27,034 
345,260 
152,465 
69,755 
66,111 
13,459 
37,115 
39,911 
378,816 
1913 
146,474 
84,122 
59,673 
44,337 
32,346 
51,430 
418,382 
The largest increase in sight is the result of the application of ore 
flotation concentration in Montana, but an increase due to the same 
cause is to be looked for in Idaho and possibly in Utah. In Mon 
tana the Butte & Superior mill is now producing at the rate of 
50,000 tons of zinc a year, and the new Pilot Butte mill, which has 
just gone into operation, should raise the State output to 70,000 tons 
a year, or if, as planned, another unit is added to this mill the State 
output may rise to 90,000 tons and more by 1915. In Colorado the 
new zinc-oxide plant at Leadville is reported to be purchasing 11 
per cent zinc carbonate ore, as against a minimum of about 20 per 
cent ore purchased by zinc smelters. As the Leadville carbonate ore 
is not amenable to concentration this means a large increase in the 
available zinc-ore resources of that region. Another source of zinc 
which will be made available in the future is zinc-bearing copper 
ore, the zinc content of which now either makes the ore unsalable 
or, when the ore is smelted for the copper, collects as flue and bag- 
house dusts, for the recovery of the zinc from which there is at 
present no satisfactory process. Much ore of this sort is mined in