Evening star. [volume] (Washington, D.C.) 1854-1972, 1929-08-18

increasing Strio partly because OF economic
factors, partly because of the comparative
simplicity of OF rations and partly because of
the great impro -ement in equipment which has
helped to reduce costs. Electric stripping shoves
Of capacity as high as II and Is yards. 3-yard
electric loading shovels, trains with Is to 40
dump cars, liquid oxygen explosive, modern
tipples and a daily production of up to 5000
tons of coal are some of the features of BIZ
luminous strip mines. The cover is Is to 60
feet in thickness. At one mine in Wyoming
the cover is removed successfully by hydraulick-
ing. In Illinois and Indiana part of the cover
at two mines is removed by drag lines and
Shovels In tandem. The coal beds are 10 to "a
inches in thickness, although % feet are being
mined in Montana and 70 feet in Wyoming.
Ignite is mined in North Dakota and Texas,
and stripping practice is reported to be i'm
proving, particularly in the former State, where
conditions are generally favorable
The stripping and mining of copper ore
represent highly developed and extensive
phase Of the mining industry In a recent
year 60 Shovels stripped at least 10000 600 yards
Of Gaping and 100000 tons of ore in 80 to
70 foot benches in mountainous country.
Iron ore has been stripped and mined for
years on an enormous scale. AS whole
operation is on o greater scale than that at
open-pit copper mines but the average produc-
VOA Va tAAC 1IAouy HUH ullIleS Is muC0 less. NO
iron mine handles by large tonnage as much
material as the benches at Bingham, Utah,
and few Of the iron mines handle as much as
the other copper mines. However. the removal
OF up to 100000 yards of Gaping and 35,-
OOU,OOO tons OF iron ore in season of eight
months with 300 to 400 power shovels in opera
tion and standard transportation systems is a
great feat
Well or churn drills are used in prospecting
and in blasting at stripping operations. The
type to be used depends upon the character of
the overburden or ore, the method of mining
and the equipment available. Piston drills or
hammer drills are used at the metal mines
particularly for hard rock and bench work.
and also at anthracite pits.
Blasting is necessary at all but pebble phos-
phate mires. Where well-drn holes have been
put down it Is necessary to chamber or spring
the holes one, two or three times, occasionally
more than that Holes are sprung by shooting
relatively small charge of say 40 per cent
low-freeZing dynamite at the bottom where q
chamber large enough for the charge required
to loosen the ground is formed. At each sue
ceeding stripping the quantity of explosive is
increased
For actual blasting black powder is generally
used at coal mines, and at copper and iron
mines both black powder and dynamite of
various strengths are used. Fuse and detonatorS
and electric decorators with blasting machines
are used to set of the charge. In general, air
drill holes are loaded with stick explosives.
tamped and stemmed with various materials.
Bulk explosives are sometimes used, but require
rather more attention in loading.
The use of liquid oxygen explosive for shoot
ing overburden is increasing, particularly at
coal mines. The Bureau of Mines has informal
ton of its use at five large strip coal lnines