The Wallace miner. [volume] (Wallace, Idaho) 1907-current, 1920-01-08
Mining Methods in Occur d'Alenes

Dupont Magazlne).
The characteristic geological forma-
ton of the Occur d'Alene district Is
sedimentary rock, known as quartzite
and slate. originally deposited in beds
or layers during the pre-Cambrian
period and afterward compressed and
folded into its present form. This
rock is extensively exposed through
out the district, runs to a depth OF
over five miles in many places, and
contains rich deposits Of lead, silver
ard zinc. The successive strata, be-
ginning with the oldest in point OF
time and the deepest below the sur
face. are as follows:
1st-Prichard slate stratum Of an
undetermined thickness composed Of
an accumulation Of sediment in the
fern of bluish-gray slate.
2nd-The Burke formation a STRAIT
um about 1000 feet in thickness, COM
posed Of sliceous rocks of fine grain
ranging from nearly pure white
quartzite to dark gray slate.
3rd--The Revett formation, a STRAIT
UNI about 1900 feet thick, composed
mainly Of white, hard -bedded quartz
lite
4th-The st. Regis formation, a
stratum about 100 feet in thickness
composed Of shale and sandstone re-
sembling the Burke formation, but
dark green or purple in contrast to
the light -colored Burke rock
5th-The Wallace formation, stra-
tum about 1000 feet thick, consisting
chiefly of thin -bedded shales and
sandstones
6th--The Striped Peak formation
the uppermost stratum, about 1000
feet in thickness, composed Of shady
siiceous sandstones
Although these various strata gen.
orally occur in the order mentioned,
they do not lie horizontally one on
top of the other. The original layers
have been shifted, tilted and folded by
volcanic activity which also forced up,
under high pressure, gases and heated
liquids, rich in metals, through the
cracks and assures of the rock. Thus
have been formed the rich veins Of
ore being mined today.
The first five strata named are the
mineral bearing rocks. They contain
the richest values of lead silver ore;
also the largest ore bodies occurring
in the Burke and Revett formations,
and the largest bodies of zinc ore in
the Prichard slate.
The principal ores found in this
district are galena or lead sulphide,
which Is by far the greatest source Of
lead and silver: lead carbonate which
occurs in the upper strata near the
surface workings; and zinc sulphide,
occurring in the lower strata Some
y very high silver values are found as
ISOLATED with gray copper ore, and in
some parts of the district low grade
copper ores of commercial value are
encountered.
In Fissure Veins.
The ores occur in assure veins that
usually lie in more or less vertical
position. The average dip varies from
70 degrees to vertical, but in one part
OF the district the veins run at an an
gle of about AZ or 43 degrees. The
width of the ore varies from about
~ inches to so or 60 feet, with a
probable average of approximately IL
feet. In exceptional instances ore
bodies of 100 feet in width have been
exposed
After a mineral lode is discovered
and proved by surface workings, the
next step is to get as much depth as
possible beneath the surface discov-
cry. This Is done either by sinking a
shaft or preferably, by driving a
tunnel from a lower elevation to
crpsscut the vein at the greatest
practical depth. Then, if ores of COM
mercial value are encountered, they
are extracted by stopping upward, fol-
lowing the veins. The obvious reason
for getting beneath the ore bodies is
to take advantage of gravity in
breaking and loading the ores,
The average tunnel, in rock that will
stand without timbering, is driven
about five feet wide and seven feet
high; but If timbers are necessary,
the section is enlarged sufficiently to
accommodate them. A tunnel of this
size requires an average of IL bore
holes; that Is, about three cut holes,
three breast holes, three back holes
and three lifters. In very hard rock,
possibly two or more additional holes
called helpers would be used.
The main work tunnels or drifts in
the larger mines are usually seven or
eight feet wide and nine feet high in
the clear, inside the timbers. tun-
mel or drift of this size accommodates
haulage track for the ore cars (pro-
PEELED by electric locomotives) carry
ing from one to five tons of material;
and also provides room for ore chutes
on the side, passing space for miners
afoot, air and ventilating pipes above
and drainage ditch along the side
Methods Of Stopping.
of, or beneath. the track.
The methods of stopping most gen.
orally employed are the "square-set,"