Mining method and practice of pillars in goaf of a gold mine

1 Mine Overview
1.1 Deposit geology
The gold mine is located in the eastern part of Qinghai-Tibet Plateau Snowy Mountains, a large tributary of leather Shenzha Jinchuan River, it is part of the mountains and canyons of western Sichuan. The geological structure of the mining area is complex, and the ore body belongs to the typical structurally controlled quartz vein type gold deposit, which occurs in the fault fracture zone. Most of the ore bodies are buried above the local erosion base (2720m elevation), the upper veins are thick and the flank is exposed along the slopes. The surrounding rock of the ore body is poor in permeability and weak in water content. The surrounding rock of the direct roof is mostly Eryun quartz schist, quartzite , quartz vein and tectonic breccia, rock anisotropy, rock mass f=7～10, stable Moderate sex. The No. 1 ore body is the main ore body of the gold ore. The length of the ore body is about 850m, the maximum depth is 625m, the minimum is 0m, the average true thickness is 5.04m, and the thickness variation coefficient is 65.94%. The whole body of the ore body leans westward, tending to 227°-306°, and the inclination angle is steeper overall, but the inclination angle changes greatly, showing a steep and gentle pattern. The slope angle is 75°-90° below the surface, and the inclination angle is 75°-90°. The downward trend is gradually slower, and the minimum inclination angle is 42°. The average grade of ore body gold is 4.38g/t, and the ore value is high.
1.2 Mining status and mining methods
The gold mine was put into operation in 2000, and the current mining scale has reached 1000t/d. The mine adopts the flat development method and has formed 6 middle sections such as 3188, 3155, 3113, 3075, 3035 and 3000m. At present, all the mining sites above the middle section of the mine 3113m have been fully recovered, and the middle section of 3035, 3075m is currently in the middle of production. For many years, the mine has been using the shallow hole retention method, and the down-draw mining method has adopted the vein-in-pulse development method. The mining project is arranged in the bottom column and the inter-column, and the 5~10m top column and the bottom column are reserved.
2 The situation of goaf and the technical conditions of mining pillar mining
(1) The remaining bottom column, point column and strip pillar in the middle section of 3155m and above total 20,000 tons. Most of the mined areas in the middle section and above have reached the surface. The volume of the goaf is about 200,000 m3, due to the surface of the mine. For forest landforms, it is not allowed to collapse. In order to prevent disturbance to the lower pillar recovery and ore body mining, it is considered to recycle some of the pillars and fill them as soon as possible.
(2) The remaining ore pillars in the middle section of 3113m are about 120,000 tons, located between the 11th and 19th lines. In the early stage, about 100,000 m3 of goaf was formed after mining the high-grade ore body, which was located between 13 and 17 lines. The goaf has a large span of 100m and is complex in shape. It has 8~10m bottom column and 10~15m top column. There is no column. The average gold grade of the pillar is 4.58g/t. The ore value is high and needs to be recovered.
(3) The middle section of 3075m belongs to the middle section of production. The middle section of the ore body is between line 3 and line 19, and the remaining ore volume is 160,000 tons. The amount of unmined mining field is 53,000 tons. The amount of column ore is 107,000 tons, and the goaf is located between 5 lines to 9 lines and 13 lines to 19 lines. The area of ​​the goaf is about 80,000 m3. The middle section of the goaf is similar to the middle section of 3113m. The span is large and the shape is complex. There are 6~10m bottom columns and 8~10m top columns (15th line and 3113m middle section are connected), no pillars, and the average gold grade of the pillars is 4. 39g/t.
(4) The 3035m and 3000m middle ore bodies are located between the 1st and 19th lines, and the remaining minerals in the middle and the middle sections are 690,000 tons. In the early stage, the mining of the rich ore also formed about 10,000 m3 of goaf, leaving 6~10m in the stope. Bottom column. In the two middle sections, only the existing mining methods are considered to be optimized, so that it is more convenient and convenient to recover the pillars later. The situation of the goaf and the position of the pillar are shown in Figure 1.

3 pillar recovery method
In order to recover more high-grade ore, it is necessary to recover as many pillars as possible in the goaf. Therefore, a detailed understanding of the distribution of each middle pillar is carried out, and the safety is passed and the mining of the lower section is not affected. Considering the whole situation, the work of recycling the pillars [1-3].
3.1 Recovery of the bottom column of the middle section of 3155m
Due to the large area of ​​the goaf above the middle section of 3155m, in the case where the surface subsidence is not allowed, according to the actual situation of the mine, some of the pillars are replaced by concrete artificial pillars, and the replacement method is to construct artificial false lanes in the middle section of 3155m (see the figure). 2) In the upper part of the artificial false bottom, the bottom column of the middle section of 3155m is harvested by shallow hole falling mine and scraper mining method. After the end of the mining, it is closed by bricklaying method, and then the goaf of the middle section is cemented. Filling. During the filling process, a high-strength cemented filling body of 10m thick in the middle part of the artificial section of 3155m is required. The cemented filling body can be used as the isolation layer of the upper and lower middle sections, so that the upper goaf does not affect the lower pillar and the mining area. Recycling.

3.2 mining the top pillar of the middle section of 3113m

Due to unreasonable mining in the early stage of the mine, the 3113m middle section left a pillar of about 10~15m thick. The goaf is more complicated. Now, in order to recover this part of the top column, it is unsafe to enter the goaf, so consider it under the ore body. The outer part of the disk is arranged along the vein roadway. The vein roadway is connected by a patio. The rocky roadway is arranged at the top of the courtyard, and the horizontal deep hole is placed on the top pillar of the ore body for mining (see Figure 3). The ore that has fallen from the goaf Put it out and use the scraper to mine the existing veins.

3.3 top bottom column simultaneous mining
Considering that the pillars will be filled after recovery, the 3075m middle section and the 3113m middle section can be combined in parallel, and the 3075m middle section and the 3113m bottom column are recovered, and the 3075m middle section is reserved as the upper and lower sections. The bottom column can be recovered by way of roadway excavation after the upper and lower goafs are filled. In the same way, the middle section of 3000m and the middle section of 3035m are processed in parallel, and the top column of the middle section of 3000m and the bottom column of 3035m are recovered.
For the recovery of the top and bottom columns of the stope [4-6], there are two cases, one is the recovery of the top and bottom columns of the unmining roof, and the Other is the recovery of the top and bottom columns in the goaf. . For the first case, the upper middle section of the mine is generally first recovered. After the mining of the upper middle section is completed, the lower middle section of the mine is returned, and then the top and bottom columns of the stop are recovered along with the mining of the lower middle section (see Figure 4). ). Under the condition of ensuring safety, the top column and the bottom column can be designed by adopting the method of segmented receding shallow hole falling mine. The method increases the recovery rate of the pillar from about 65% to over 90% in the past, greatly improving the ore recovery rate and increasing economic benefits. The technical requirement of the method is that the segment length is about 4.0 to 6.0 m, the segment height is about 3.0 to 4.0 m, and the upward or horizontal blast hole arrangement is adopted, and the blasthole length and the charge are strictly controlled during the operation. The amount is to prevent the occurrence of a suspended ceiling accident, so that the circulation operation goes smoothly. During the operation, appropriate wooden support is required for safety reasons. For the second case, it is necessary to use the pulsed roadway plus the communication patio for recycling, and the recovery method is similar to the recovery of the top column of the middle section of 3113m.

3.4 Mining the top column of the middle section of 3035m and the bottom column of the middle section of 3075m

The top pillar of the 3035m middle section and the bottom pillar of the 3075m middle section cannot be recovered at the same time. Considering the safety and stability of the entire stope, the middle section of 3075m plays a role of a compartment, so that the upper and lower goafs are not connected to each other, resulting in an excessively large area of ​​the goaf. Therefore, the recovery of the top column needs to be completed after the 3075 m middle section of the upper and lower goafs are filled. The design uses a down-stratified filling mining method to recover the top and bottom columns (see Figure 5) with a stratification height of 3 m. Technical requirements: Firstly, the slope is excavated in the vein. The layered roof is supported by concrete pillars and steel anchor nets, and the scraper is used for mining.

3.5 Mining of columns between the middle sections
First, the mining room will be cemented and filled after the ore is finished. In the recovery of the column, the shallow hole retention method is adopted. In order to solve the two export problems, a pedestrian ventilation well is arranged outside the ore body of the ore body, and the upper horizontal vein along the vein roadway is drilled to the upper horizontal vein, and the ventilation well is outside the vein. The middle excavation column contact channel is connected with the pedestrian ventilation shaft in the inter-column, and is filled after the completion of the post.
3.6 mining sequence of the pillar
From the perspective of the entire mining area, the down-draw mining method is adopted. Now, in order to recover the pillars as much as possible [7-9], a more detailed planning is needed for the recovery of the mine pillars. In the case of not affecting the recovery of the lower middle ore body, the bottom column of the middle section of 3155m and the top column of the middle section of 3113m are first recovered. For the middle section of 3075, 3035m and the middle section of 3000m, the three ore mine ore bodies are recovered first, and when the ore body is recovered, the top and bottom columns after the section are recovered. For the inter-pillars between the mines, the adjacent mines in each middle section need to be filled before they can be recovered. Finally, the bottom column of the middle section of 3075m and the top pillar of the middle section of 3035m are left as a compartment. Recycling the compartment ore body requires the mining of the corresponding upper and lower sections to be recovered. In order not to destroy the spatial continuity of the column between the bottom columns, the column and the bottom column are generally not recovered at the same time. The corresponding columns in the upper and lower sections cannot be recovered. The adjacent columns in the same middle section are not harvested at the same time.
4 mining practice of the pillar
Through the different mining processes, the pillars in the mined-out area of ​​the mine are recovered, and good economic and technical indicators are obtained, which greatly improves the ore recovery rate of the mine and increases the economic benefits of the mine. The recovery parameters of the pillars are shown in the table. 1.

5 Conclusion
According to the different types of pillars in the goaf, different mining techniques are adopted for mining. Under the premise of meeting the safe production of the mine, the mining volume of the pillars is 580,300 tons, which greatly increases the recovery rate of the mine. Increase the economic benefits of the mine. However, when recovering the sandwich pillar, the mine filling must be timely, and the goaf must be cemented and filled. For mines not affected by the goaf, it is recommended to reduce the size of the back to the mining room, control the filling volume of the cemented backfill, increase the size of the column, and increase the filling of the low-strength filling body to save the filling cost. .
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