Full resolution (JPEG) - On this page / på denna sida - Second part - IX. Mining Industry and Metal Production - 1. The Iron Mines (together with information regarding other mines). By the late Prof. O. G. Nordenström - Technics of mining
<< prev. page << föreg. sida << >> nästa sida >> next page >>
Below is the raw OCR text
from the above scanned image.
Do you see an error? Proofread the page now!
Här nedan syns maskintolkade texten från faksimilbilden ovan.
Ser du något fel? Korrekturläs sidan nu!
This page has never been proofread. / Denna sida har aldrig korrekturlästs.
702
IX. MINING INDUSTRY AND METAL PRODUCTION OF SWEDEN.
workman and year of 300 days, amounts to 1,000 à 1,600 cubic meters, or,
estimated in weight, to 3,500 à 5,500 tons; and in driving galleries, the advance
by the use of drilling machines is generally twice as fast as by hand-drilling when
the same number of workmen are employed.
Methods of working. In regard to the working methods, as has
already been intimated, underhand stoping is in most common use.
Over 80 per cent of all the iron ore mined in Sweden is mined
according to this method. It is, moreover, always used in its original
form, or without filling. The excavations thus stand open, and their
walls are supported by röck pillars and, where necessary, by more or
less complicated timbering between the hanging-wall and the foot-wall
This method has been used since time immemorial, and it has always
given good results both technically and economically. This has, of
course, to a large extent depended upon the fact that both the iron
ores and their country generally are of a very compact nature.
In the mines where this is not the case, the filling method has been
resorted to during recent years; and the same change has also been
introduced in some mines where the ore and röck are compact, but where
the ore deposit has been very thick, and therefore mining in open places
has made it necessary to leave large quantities of ore, especially at
greater depths. Among the methods belonging to this class, overhand
and cross-working are exclusively used, and their adaptation does not,
on the whole, differ from the corresponding methods in use in other
countries. The only more notable difference is the width of the stope
when overhand working is used in mines with ores of a compact nature.
In such cases the width of the stopes can rise to 12 or 15 meters, and
sometimes, e. g. at Dannemora, up to 30 meters.
As to the general effect of blasting in our mines, experience shows
that in stoping, overhand, and cross-work, the amount of röck broken
down varies between 10 and 15 tons per kilogram of explosive, and
between 2 and 3 tons per meter drilled. In favourable circumstances
the former figure can rise to 20 or 25 tons, and the latter to 4 or 6 tons.
The coal-bedB in Skåne, which, as has already been mentioned, lie almost
horizontally, are intersected by stripes of schist, and, including these stripes, generally
have a thickness of, at the most, 1 to 1*6 meter. The superincumbent country
Ss composed of sandstone. The beds are generally worked by a combination of
the pillar and stall method and of the double stall method. In the coal-field at
Bjuf, long wall method has been exclusively used for several years. Now this
method is used only in a part of this coal-field.
According to the aforesaid combined method, the coal-bed is divided into a
series of pillars by a system of galleries, some of which are driven in the direction
of the strike and some along the rise. The main galleries are driven by means
of a stall 10—11 meters wide. As this advances, it is filled until only 2 meters of
the width of the stall is left. At distances of 80 to 100 meters, rising galleries
of the same width as the main gallery are driven from it, and from the rising
galleries, stalls parallel with the main stall, thus forming pillars 60 to 80 meters
wide and 80 to 100 meters in length.
<< prev. page << föreg. sida << >> nästa sida >> next page >>
