Elk City mining news. (Elk City, Idaho) 1903-1913, 1904-05-07
ORE DELIVERY METHODS
Explaining the Advantages and Disadvantages of the Different
Kinds Of Mill Holes and Their CONSTRUCTION. Methods
Described bya Practical Mining Man.

The economical disposal of ore after
it is broken down in the Slopes is a
problem of great Importance and fire.
quently demands displays of high tech
nical knowledge from managers in or
der to bring the various items of timber
cost, labor and repairs within CERTAIN
limit of cost per ton of ore, beyond
which prudence demands halt. 1t is
matter of surprise, too, at the per-
functory way in which some managers
give directions for mill hole construc-
tion At variapce with all rules of eco
nomic mining. AS soon as the ore body
is opened up the problem of its econom-
ical handling at once becomes para
mount, and while it is true that hap
hazard selection of method of ore
delivery will, and frequently does, an
swer for the purpose, yet instances Of
injudicious adoption of faulty systems
are to common. The executive head of
mine, intent on producing results in
the best way at least cost, has a large
field before him when he takes up the
study of the timber problem of a big
mine, located usually at place where
timber is scarce article. The practi-
cal, expeditions and cheap delivery of
ore may be placed at the head of the
subdivisions of timbering and num-
ber of other things considered before a
general scheme of mill hole construc-
ton is finally adopted. Size of the ore
body, dip of the vein and character OF
the walls are the major items upon
which to base a decision. Physical
properties Of ore, distance between lev
els viewed with reference to the prob.
able wear of the timbers. proper spac.
ing in order to facilitate sfreveling, ant
an exact comparison of relative costs
of the various systems are other thing'
that influence the adoption or rejection
of general plan of ore delivery.
There are six meritorious systems O.
mill hole construction in general use
with slight notifications to fit individ
ual cases, furnish diversity Of plan
sufficient to meet the requirements o
any kind of an ore body. These are:
l. The crib Of tenoned mill timbers.
2. The stulled mill hole.
8. The stull and block mill hole.
A. The all-block mill hole.
S. The stone-faced mill hole.
6. The lined, square-set mill hole.
The first and most generally used
the crib built of tenoned timbers of fix
, ed pattern dimensions.
This form is to be recommended fo
all veins having rotten walls, where
is not necessary to use the square sc
and where the Slopes are filled wit
waste, as it furnishes the cheapest an
most practical method of sustaining ba
ground and affording an outlet for OF
at the same time. tits well to stat
that, no matter how great the dip {
the vein up to that angle where the OF
ceases to mechanically deliver into IL
hopper, the cribbed mill hole is by f;
the best sustainer of rotten ground v
have, where filled stope is used.
A number of things are to be consi
cred even after physical conditions SUI
gest the crib form of construction. IT
distance between levels, amount of or
character and size of broken ore al
average dip of vein are all determinir
factors in deciding upon the size. al
quality of timbers used. For exampl
it would be injudicious and wasteful
build mill hole three feet in the Gle
for narrow vein with levels 100 fe
apart, unless the dip was excessive a
the ore wet enough to block the hole
sticking to the sides. Not only wor
the timber cost be excessive, but lar
unnecessary expense would be incurr
in shooting out the walls IN order
secure the space to properly set the til
bers. On the other hand, have knoN
levels to be run 400 feet apart, usi
three foot mill holes spaced 60 fe
apart. The dip, of the vein was slig
and free from abrupt variation, with
stoping width averaging five feet a
fairly staple walls. In this particul
instance timber was an expensive ite
and the atmospheric conditions we
such that two years represented the |
of first quality drift set. A care.
scrutiny of the expense items convinc
the management that it was cheaper
line the mill holes with first class 2-ir
plank than to stand the staggering CT
of drift timbers for intermediate leve