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Underground mining method

Ore body shape is presented in Figure 4 and Figure 5 along with underground openings at the level L+1600m. Resources tonnage for the trial excavation can be satisfied by small portion of total resource that is illustrated in Figure 6.



Figure 4 Shape of total ore body; underground openings at the level L+1600m



Figure 5 Part of the ore body selected for the trial excavation



Figure 6 Part of the ore body selected for the trial excavation

 

Figure 7 and Figure 8 present the part of the ore body selected for trial excavation and the nearby underground drifts at the level L+1600m. Selected part of the ore body spreads up the level L+1610m at its top. It is divided into 4 parts with 2.5m height where trial excavation takes place.



Figure 7 Detailed overview of ore body portion selected for trial excavation



Figure 8 Detailed overview of ore body portion selected for trial excavation

 

Geotechnical conditions for underground mining are not favorable. Rock mass is weak and available geotechnical database is not reliable. Due to weak rock mass it is not possible to apply any open stoping mining method, and morphology of the ore body limits application of caving methods. Having all this in mind, it is necessary to apply mining method with backfilling. This mining method has to be adjusted to the conditions in deposit. Description of the method and stope formation is explained in following section.

First step towards creating basic condition for trial excavation is extension of the existing drifts at the level L+1600m to the location of the ventilation shaft and its excavation up to the surface (Figure 9).



Figure 9 Extension of the existing drift at the level L+1600m and ventilation shaft position

 

Next phase of development requires that directional drifts in hanging wall and footwall are excavated following the contour of the ore body (Figure 10). These drifts are mutually connected at their ends. By connecting the directional drifts main ventilation is created and next steps are excavation of backfill shafts and ore passes. Development of all levels is in same manner, directional drifts are following boundary between ore and waste rocks.



Figure 10 Directional drifts in hanging wall and footwall with necessary connection between them and existing openings at the level L+1600m

 

Figure 11 presents the formation of the stopes at the level L+1600m. Stopes are 2.5m and 3m wide. Between two adjacent stopes 4m wide strip pillar is left.



Figure 11 Stopes formation at the level L+1600m

 

Directional drifts footwall are excavated by following the ore-waste boundary, while hangingwall drifts are placed following the contour of the topmost level (due to the backfilling technology and safety). After reaching the end, place where waste rock is encountered, stope is formed by connecting the two directional drifts. Figure 12  and Figure 13 illustrate stope formation at the level L+1600m. Ore is blasted in drifting manner and hauled to the ore pass. Advancing direction is from footwall towards the hanging wall.



Figure 12 Stope formation at the level L+1600m



Figure 13 Haulage of ore at the level L+1600m

 

At the level L+1600m all stopes are excavated in previously explained manner. After complete excavation of the stopes at this level, hanging wall drift is excavated up to the next level (L+1602.5m). Since it is excavated in ore, same is loaded and hanging wall directional drift is backfilled for the height of 2.5m. Then, excavation of the next level begins (Figure 14 and Figure 15). Crushed rock is used as backfilling material.



Figure 14 Typical situation at the stope; drilling is done by standing on the rock backfill



Figure 15 Ore is loaded from the level of footwall drift



Figure 16 Backfilling from the level of hangingwall drift

 

In general, excavation takes place in 2 Sectors (Figure 17). First sector has two parts, first part between footwall and hangingwall directional drifts with 11 stopes at each level, and second part outwardly directed from hangingwall drift with different number of stopes per each level. Second sector has 7 stopes between directional drifts.

Stope 0 is stope always excavated first and has direct connection with ventilation shaft.



Figure 17 Stope sequencing and markup

 

Selected mining method assumes that all stopes and pillars are strictly vertical and therefore stope positions are spatially same at each level. Only difference between levels comes from the fact the shape of the ore body is changed and length of stopes is adjusted accordingly. This is mostly case in the Sector 1, while stopes and drifts in the Sector 2 do not change position and are strictly above each other. This is caused by the shape and dip of the assumed ore body.

 



Figure 18 Stopes at the level L+1600m



Figure 19 Stopes at the level L+1602.5m



Figure 20 Stopes at the level L+1605m



Figure 21 Stopes at the level L+1607.5m

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