Method for working steeply dipping vein ores with vertically downwards propagating pillars

The invention relates to a cut-and fill method of a mine, where the working is done by pillar working, which propagates vertically downwards. The working is done by placing the stope and the pillars interlaced with each other when propagating downwards. The pillars are made by the hardening fill-method and likewise, at the bottom of the excavated stope, in the lower corners, a bed of hardening fill is made.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The invention relates to a cut-and fill method of a mine, where the working 
is done by pillar working, which propagates vertically downwards, the 
Working is done by placing the stope and the pillars interlaced with each 
other when propagating downwards. The pillars are made by the hardening 
fill-method. 
2. Description of Related Art 
The working of steeply dipping vein ores often includes expensive operating 
costs and low capacity. However, because the ore body might be valuable, 
different working methods have been developed. In these circumstances the 
vein mining method has been used as well as other cut-and fill methods. In 
one of these methods, which in a sense is a combined working method, the 
working is unrestricted in the longitudinal direction of the ore, but 
above it is left either a horizontal pillar of ore or a pillar made with 
the hardening fill-method. If the mechanical properties of the rock are 
poor, the horizontal pillars give insufficient support. This can lead to 
local collapses, collapses at the working site as well as make selective 
working impossible. In the case of a really valuable and, in terms of its 
strength, weak ore, a downward propagating cut and fill method has been 
used, but this method is very inefficient. 
SUMMARY OF THE INVENTION 
Now a new method in accordance with this invention has been developed, 
which is used for working steeply dipping vein ores and uses the hardening 
fill-method, whose efficiency is as good as the above mentioned vein 
mining or sublevel stoping, but without their above mentioned 
disadvantages. In this way the ore body can be fully worked when 
propagating downwards. In the method according to the invention, the 
propagating occurs vertically downwards, which makes it unnecessary to 
immediately make deep shafts, which in turn saves on the starting up 
costs. According to the method, the vertical pillars of the new stope are 
worked first and then filled with hardening fill. After this, safe working 
of the stopes between the hardened pillars is possible, either in two 
stages or one. The dimensioning however, is dependent on the strength 
characteristics of the ore as well as of the siderock, of the thickness of 
the ore vein, of the dip and of the regularity. 
The dimensioning of the pillars and the stopes has to be such, that the 
stopes remain open even after empty loading, which makes it possible to 
fill the stope and the pillars of the next level. A dimensioning which has 
been found good in practice, is to make the pillars approximately 12 m 
wide and the stopes 30-40 m wide. The height of the stope and the pillars 
is preferably in the order of magnitude of 50 m. 
In order to make it possible to open a new stope underneath a filled stope, 
a bed of hardening fill has to be made in the lower corners of the bottom 
part of the above lying stope, which prevents either filling from above or 
a possible cave in (if the filling is not done) from flowing downwards 
into the space that is being worked.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
FIG. 1 shows a principle drawing of a working that has proceeded to the 
third level. The working of the first level (I) is already completed, and 
as can be seen from the figure, the pillars 1 have been made of hardening 
fill, and a bed 2 of hardening fill has been made in the bottom part of 
the stop in its lower corners. At this stage the pillars of the second 
level (II) are also worked. Following this, stope 3 can at least partially 
be filled with dead rock (in the figure it has been completely filled). In 
the schematic drawing, working is preformed in two stages and the worked 
material is transported through loading openings 4 in the pillars to an 
inclined tunnel 5 in the side rock. In FIG. 1 on the second level, the 
upper part of the rightmost stope has been completely worked and the lower 
part has been partially worked. In the middle and the leftmost stope, the 
lower part has been completely worked and the upper part is either 
partially worked or completely unworked. When the lower part of level II 
has been worked, the pillars of level III can be worked and filled with 
hardening fill. As can be seen from the drawings, it is preferably to make 
the pillars in different places on different levels, which makes 
propagating downwards safe at all times. 
The advantages of the method according to the invention compared to methods 
in use now are at least the following: 
A cave of the roof rock in the area of the ore body can be stopped, i.e. 
local stability is under control. 
The stopes can be kept open during the whole working process, which 
guarantees selective working. In conjunction with the method, a wire 
bolting can be used as an additional support method, and therefore the 
size of the stope can be kept large enough to be efficient. 
The dilution of the stope with dead rock can be controlled and it 
decreases, which leads to a corresponding increase in the valuable ore 
content of the worked ore. The average content can rise by up to 0.5%. 
The decrease in the dead rock dilution also decreases the costs of the ore 
mill and lessens the load on the waste area. 
The dead rock derived from the preparing work can be placed in nearby 
stopes, which have been emptied of ore, thus decreasing the handling costs 
of the dead rock considerably. The dead rock can also be used as a main 
ingredient in the hardening fill. 
The ore can be worked systematically when propagating downwards and there 
is no need to leave any horizontal ore pillars. This means that the 
downwards-excavating speed of the mine decreases. 
By systematic controlled use of hardening fill a less risky production can 
be achieved and this way a more planned use of the mine can be achieved. 
As a result of this, there is e.g. no more need for emergency work and the 
high cost involved with it. 
The new method requires that the general preparing work is done one level 
below the working level, but through this it is possible to acquire, early 
enough, the necessary information that the planning of the excavation 
demands, and expensive faulty decisions, due to lack of geological 
information, become fewer. 
The rock pressure, which usually increases when propagating downwards, can 
be kept under control due to the filling of the mine, which is done after 
the working.