Study on mining method of steep slope double-layer ore body in a phosphate mine

0 Preface
A phosphate ore body is composed of a, b ore layer and an intermediate layer of stone, wherein a layer is located in the lower plate of the shale layer, and layer b is located on the upper plate of the slate layer. The ore body is slow and steep, the upper ore body has an average inclination of about 60°, and the lower ore body has an average inclination of 85° to 90°. The design adopts the segmented empty field method for recovery, with a section height of 22 to 23 m and a mining width of 15 m. The stope is arranged along the ore body direction, leaving 6 to 8 m columns every 50 m. During the section mining, a 4.0m×4.2m rock drilling roadway was drilled along the a and b mineral layers. The YGZ90 drilling rig was used to drill the upper fan-shaped medium-deep hole collapse. The ore was dumped into the truck by loader. Surface. In the mining process of the mine, the direct top column, the upper plate and the stone of most of the stope collapsed, and the rock collapse between the a and b mine layers is the most serious. With the increase of mining depth, the pressure of ground pressure is intensified, and the collapse of mineral rock is intensifying. Affected by this, the actual mining height of the underground mining site is about 10m, and the remaining ore can not be produced, and the ore loss rate is as high as 50%. In addition, the safety of workers and equipment is seriously threatened. To this end, the mine commissioned Changsha Mining Research Institute Co., Ltd. to carry out research on mining methods, with a view to improving resource recovery rate, improving safety conditions for underground operations, and achieving safe, economical and efficient mining.
1 Mining engineering geological conditions
Nearly half of the ore body is located above the local erosion datum, and there is a rock pit river on the north west side of the mine. The distance between the surface water and the groundwater is not close, the groundwater recharge conditions are poor, and the water-filled rock formation of the deposit is light. The dolomite is rich in water and is a type of karst water-filled deposit with medium hydrogeological conditions, mainly composed of dissolution and fissures.
The direct roof of the ore body is light gray thin layered phosphorus-containing dolomite with stable thickness; the stone layer is light gray medium-layered phosphorus-containing particles dolomite, the top has unstable siliceous mass, or the phosphorus siliceous mass It is interspersed with unstable dolomitic phosphorite lens bodies; the bottom plate is light gray medium-thick layered fine-grained dolomite. According to the scene disclosure, the rock mass in the lower part of the a-mine layer is moderately stable, and the rock mass on the upper plate is moderately stable to unstable; the lower plate of the b-layer is a stone, medium-solid and unstable, and the upper plate is very weak and easy to fall. There is a muddy layer between the disc and the compartment.
2 Mining method design
2.1 Mining method primary selection
In the three methods of empty field method, caving method and filling method, the empty field method will be used to leave hidden dangers in a large number of goafs, and at the same time, it can not meet the requirements of processing tailings in the plant selection and selection, and the mining practice has proved the mine. Rock conditions are not suitable for mining by the open field method; the caving method is a safe, efficient and low-cost mining method , but its ore loss is depleted, and the surface collapse may cause a series of ecological problems, and the tailings of the plant are not treated. Therefore, the caving method is not suitable as the main mining method of the mine. Therefore, the mining method suitable for the technical and economic conditions of the mining technology is initially determined by the exclusion method as the filling method.
2.2 The design of mining method combined with the stability of the ore rock for analysis and demonstration, the final optimal mining method suitable for the mine is the upward horizontal layered filling mining method, in which the a layer is mined by conventional methods and the b layer is divided by way. Step back. Its typical scheme is shown in Figure 1.
According to the status quo of the mine development, the middle section is set at 46m, the segment height is 10~14m, and the segmentation is divided into 3~4 layers. The nuggets are arranged perpendicular to the ore body, with a length of 50-55 m along the strike and a width of the ore body. In order to control the exposed area of ​​the roof of the stope, a 4m wide permanent pillar is placed in the adjacent mining block and in the mining unit.
The main mining project include cutting the middle roadway transportation, mining area ramps, roadway segments, layered access road, filled ventilation shaft, chute, cutting flat Lane.
2.3 Recovery and filling process (1) Rock drilling. The rock was drilled with a YT-28 rock drill, and the depth of the blasthole was determined to be 2.5 to 3.0 m, and the diameter of the blasthole was 40 mm. When the mining body of each floor of the stope is recovered, 4 rows of horizontal blastholes are constructed: the first, second and third rows of blastholes are the main blasting holes, the row spacing is 0.9m, the hole spacing is 0.8~1.0m; the fourth The row of blasting holes is a smooth blasting control hole, which is 0.6m away from the third row of blastholes, and the hole spacing is 0.5-0.6m.
(2) Blasting. After the rock drilling is finished, the blasthole is cleaned, and the volumetric explosive is manually loaded, and the detonator of the millisecond differential detonator is detonated. Among them, the loading coefficient of the first, second and third rows of falling blastholes is 0.5-0.6, and the charging coefficient of the fourth row of smooth blasting control holes is 0.1-0.2.
(3) Ventilation. The fresh air flow enters the stope through the layered communication road from the sectioned roadway, and the dirty wind is filled back into the upper and middle section of the return airway. In order to enhance the ventilation effect, can fill in the return air shaft, respectively stope install auxiliary fans and local fan.
(4) Mining. The WJD-2 electric scraper is used for mining. Before the blasting of the stope, the scraper leaves the mining room and enters the sectioned alley. After the blasting and ventilation is completed, the scraper starts to mine from the entrance of the stratified contact road. In the initial stage, a small amount of ore is transported to the outside of the vein to release the ore. When the in-pulse well is cleaned out, the ore can be directly poured into the vein.
(5) Filling. After the end of the mining area is finished and the experience is accepted, the equipment is removed from the stope. The filling pipe, the smoothing steel chute, the pedestrian filtering well are built according to the design requirements, and the wall can be filled after the wall is built.
2.4 Main economic and technical indicators The main technical and economic indicators of the above-mentioned horizontal stratified mining method are shown in Table 1. 3 Conclusion
     Aiming at the problems of poor safety and serious resource loss in the mining of a steeply inclined double-layer ore body in a phosphate mine, combined with the actual mining technical and economic conditions of the mine, the selection of the upward horizontal stratified filling mining method is the best method. The method panel production capacity of 500.0t / d, ore comprehensive loss was 19.2% dilution rate of 5.0%, job security condition has been greatly improved over the original plan, while resource recovery rate has also been significantly improved.  

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