The Wallace miner. [volume] (Wallace, Idaho) 1907-current, 1914-09-03

shape and occurrence. They may oc.
eur in veins, beds. masses, shoots OF
irregular pockets; they may be flat
sloping or vertical. Gold bearing
quartz veins an inch wide are profit.
ably mined in the western part Of the
United States; on the other hand
some Of the iron ore deposits OF thu
Lake Superior district are 500 fec1
wide. Some classes Of ore deposits
are found only at or near the surface
Iothers extend mile or more under
ground.
In metal mines the ore may vary
from ore that Is as soft as mud te
ore so hard that sparks will fly wher
1t is drilled. and the same is true Of
the walls or rock surrounding the
ore.
In many mining districts faults OF
breaks in the rocks are numerous
and at such places there ds often a
marked change in the nature Of the
ground. II the fault is sharp and well
defined, there may be no change. but
where the rock has been crushed and
ground, blocky and heavy ground may
be expected Sudden changes are met
with when drifting into a dixie OF
through a contact. In either case the
rock may change from hard to soft
or from soft to hard rock.
In some metal mines work Is car
ried on in ground that must be sup
ported by rock walls several feet thick.
In other mines, when drifting in wet
and heavy ground, 1t is necessary to
spall or forepole and place heavy
timber sets with no space between
them.
The causes and Prevention Of Acct
dents from Falls.
Accidents from falls are many and
varied in their nature, depending on
the kind of ground worked. They in
clude accidents due to the dropping
of small pieces rock or ore as well
as those resulting from the caving Of
large masses Of ground. Miners have
been killed by being struck on the
head by piece of rock no larger than
"a baseball. Falls may occur at faces,
in timbered or untimbered workings,
In raises or slopes, in short, at almost
any point beneath or beyond the en-
trance to the mine.
Rock or ore falls because 1t lacks
support. Although hard firm ground
Is often self-supporting, there is a
limit to the size of the excavation that
may be made. even in the hardest
ground. without providing support.
The usual tendency, whether drifting
or stopping, Is to use too little timber,
or to wait too long before placing the
timber.
Although 1t is impossible in this cir
cular to consider In detail falls that
may occur in all Of the varied types
OF ore deposits, the most common
causes of falls that may occur in diff
ferent classes of ore deposits and the
precautions that should be taken to
prevent such falls are discussed in the
remainder Of this article.
Drifting or crosscutting Without Tim.
berino.
In driving without the use of timber
1t Is taken for granted that the ground
Is hard and firm enough to support IT.
self. In this class Of work falls &C.
cur when the opening is too large or
Is not Of proper shape. Ground that
will not stand If the drift is large may
hold well II small, well arched open
ing be carried II soft rib Of rock
is encountered when driving in hard
ground, the tendency Is to drift
through It without timbering, a fall
sometimes results.
Many accidents are caused by the
falling Of loose rock. All loose rock
should be removed from the face.
back and sides as driving progresses
This should be done Immediately on
returning to the face after blasting.
Drifting or crosseuttins With the Use
OF Timber.
In driving In ground where timber
ing Is required many varying condi-
tions are met In heavy ground where
the rock Is soft, mudsills must be used
for without them the posts (legs) of
the timber sets, whether they be large
enough or not, will be forced into the
floor If the timber is not large
or strong enough the caps and posts
will be crushed, provided they can not
be forced into the floor If the timber
sets are placed too far apart, the
weight Of the ground may cause it to |
break through the tagging.
In driving through heavy ground
1ext to a firm hanging wall the dam
ger Is from the foot wall side, and the
zap and the foot wall post will take
most Of the weight II the foot wall is
lrm and the ledge and hanging wall
weak, the pressure will be on the cap
md the hanging wall post If both
wallis are hard and the ledge is soft
he greatest weight will be from the
Jack. When the direction from which
he greatest pressure is coming is
nown, timber of sufficient strength
hould be opposed to this pressure.
he sets should be carefully placed
nd well blocked and enough tagging
hould be used 1t should be borne
IND nj 10