The Ely miner. [volume] (Ely, Minn.) 1895-1986, 1924-02-29

peak, then falling much more slow
", the decline extending over many
years.
The Lake Superior life curve is
so far of the same general form,
except that the peak has not yet
been reached and the remainder of
the curve must be. projected. The
available data show the peak to lie
some ten years ahead. perhaps a
little more. It is Immediately
evident to any engineer that no
mine nor group of mines can ex-
pect to maintain an increasing out
put so that the last years ship
ments are the greatest. After the
maximum is reached, there in
evitably follows long period of de-
cline during which ends, sides and
bottom are cleaned up, pillars rob
bed, small tributaries followed, to
wind up finally as scram. When,
that the life of the Lake Superior
region is twenty to thirty years, it
really means that for so per cent to
go per cent of that period the in
creasing demands of the furnaces
can be met from known merchant
able ore. After that they cannot,
without resorting to shipments of con-
stantly lessening grade, or to the
adoption of benefciation methods
for raising the grade of the enor-
nous reserves of iron-bearing mat
erial mentioned above, but not now
considered ore at all.
Benefciation Movement.
It has never been the history of
the other metals that the adoption
of such methods has awaited full
depletion of the high grade ores,
nor is it so with iron. The eighteen
washing plants now in existence
show the movement has already be-
gun. 1t is only question as to
what methods are to come into use
first. This is almost entirely a
question of values and costs. The
value of an iron ore is dependent
primarily on the percentage of iron
contained, and sells regularly and
fairly on that basis, the sale price
rising quite uniformly as the assay
rises.
On a straight unit basis, ignoring
all premiums and penalties, a "a
per cent Aold range Bessemer ore
nets at the Minnesota mines about
$3.50 per ton more than does a So
per cent ore, and that $1.50 repre-
sents the additional cost that may
safely be put into raising the grade
to that point. This additional cost
must also include the metallurgical
losses. It should be kept in mind
that a figure Of this kind is for
illustration only. It will vary con-
with ore prices, freight
rates, labor schedules, metallurgical
skill, grade of raw material and
product, and many other factors.
1t should also be remembered that
any such figure is not the total cost,
but the marginal or extra cost of
benefciation, assuming such benefi-
citation to mean simply the raising
of a So per cent ore to "a per
cent grade. 4,
There are two general classes of
methods proposed for utilizing the
low grade ores. The first class
includes preliminary beneficiation
methods like washing, jigging, tab
ling, magnetic separation, drying
and sintering, the product in each
case being improved ore for blast
furnace use. The second class in
cludes direct reduction, electric
smelling and electralysis, the final
products being iron or steel and not
iron ore.
Washing is the best known and
most widely applied preliminary
method. For several years past it
has produced about 10 per cent of
all the Mesabi range Shipments
remarkable record, and one that
makes further comment or attempt
at description unnecessary. 1t may
be taken for granted that washing
plants will operate as long as wash
ores are available.
Juggling and Tabling Iron Ore.
Juggling and tabling of iron ores Is
an old story in other parts of the
world. There are large reserves of
material on the Mesabi range which
will sooner or later be brought to
market over jigs and tables. Elk
periments already completed show,
however, that extreme care will have
to be used in selecting the ores to
be utilized first. While construc-
ton and operating costs are moder-