ING THE OUTPUT.

Although the above argument can be academically defended, there
are, as said at the start, practical limitations to the maximum
intensity of production, arising out of many other considerations
to which weight must be given. In the main, there are five principal
limitations:--

1. Cost of equipment.
2. Life of the mine.
3. Mechanical inefficiency of patchwork plant.
4. Overproduction of base metal.
5. Security of investment.

COST OF EQUIPMENT.--The "saving of fixed charges" can only be obtained
by larger equipment, which represents an investment. Mining works,
shafts, machinery, treatment plants, and all the paraphernalia cost
large sums of money. They become either worn out or practically
valueless through the exhaustion of the mines. Even surface machinery
when in good condition will seldom realize more than one-tenth of its
expense if useless at its original site. All mines are ephemeral;
therefore virtually the entire capital outlay of such works must
be redeemed during the life of the mine, and the interest on it
must also be recovered.

The certain life, with the exception of banket and a few other
types of deposit, is that shown by the ore in sight, plus something
for extension of the deposit beyond exposures. So, against the
"savings" to be made, must be set the cost of obtaining them, for
obviously it is of no use investing a dollar to save a total of
ninety cents. The economies by increased production are, however,
of such an important character that the cost of almost any number
of added units (within the ability of the mine to supply them)
can be redeemed from these savings in a few years. For instance,
in a Californian gold mine where the working expenses are $3 and
the fixed charges are at the low rate of 30 cents per ton, one
unit of increased production would show a saving of over $10,000
per annum from the saving of fixed charges. In about three years
this sum would repay the cost of the additional treatment equipment.
If further shaft capacity were required, the period would be much
extended. On a Western copper mine, where the costs are $8 and the
fixed charges are 80 cents per ton, one unit of increased production
would effect a saving of the fixed charges equal to the cost of
the extra unit in about three years. That is, the total sum would
amount to $80,000, or enough to provide almost any type of mechanical
equipment for such additional tonnage.

The first res