Congo (King) Kamoa copper mine large-area gently inclined single-layer thin ore body room and pillar mining method

The room-column mining method has the advantages of simple process and low mining cost. It has strong adaptability to gently inclined thin ore bodies with ore inclination below 30°, and thus has been widely used [1-3]. With the improvement of the mechanization level of modern mines, the trackless mechanized house and pillar mining method can greatly increase the production capacity of the stope and reduce the unit mining cost, thus further broadening the application range of the room and column method. Congo (DRC) Kamoa copper mineral ore # 1 is gently inclined large single-ply ore for mining mechanized track-free room and pillar method. However, as the area of ​​the empty area and the depth of burial increase, the design size of the deep pillar increases and the loss rate increases.
To this end, this study optimizes the stope structure and mining sequence of the deep room and pillar method of the mine, minimizing the loss of the pillar and improving the economic benefits of the mine.
1I# ore body profile
The Kamoa copper deposit in the Congo is a layered copper deposit that is deposited in sedimentary rocks. Its main ore body is I# ore body, 1.2 to 1.7 km long from north to south, and 2 to 8.7 km wide from east to west. It gradually deepens from 30m to 1300m, and the production is gentle, generally 5°～20°, the thickness is 4～6m, the average copper grade is 2.57%, and the resource is 847 million tons. It is a gently inclined single-layer super-large thin mine. body. Ore powder containing ore rocks, sandstone, yellow iron mineralization sandstone roof, floor of feldspathic sandstone. The physical and mechanical parameters show that the surrounding rock of the ore-bearing rock and the top and bottom plates is dominated by hard rock, and the RQD values ​​are all greater than 62%, and the integrity is above medium integrity.
The deposits in the mining area are mainly composed of bedrock structural fissure water-filled deposits, and the hydrogeological conditions in the area are medium.
2 trackless mechanized room and pillar mining method
According to the occurrence conditions and resource conditions of the ore body, it is suitable for mining by the room and pillar mining method. Due to the large area of ​​the mining area and the large amount of resources, the production capacity of the ordinary ore dumping and mining stope is obviously small. Therefore, the use of the trackless mechanized room column method (Fig. 1) is more suitable for the mine. The 6m3 diesel scraper and the 50t downhole dump truck are selected for mining, and the production capacity of the stope can reach 1800t/d.

2.1 common room method
The trackless mechanized room-column mining method (general house-column method) adopts the structure of the stope, which increases with the increase of the area of ​​the empty area and the depth of the mining, which easily leads to an increase in ground pressure. Under the premise that the airspace is stable and does not collapse, the structural parameters of the stope determined in this study are shown in Table 1.

It can be seen from Table 1 that as the depth of the mining is increased, the size of the pillars in the ore block is getting larger and larger, and the recovery rate is getting smaller and smaller. Due to the large size of the mining column, the empty area is not easy to collapse. The mining method has a relatively flexible order of recovery. On the basis of meeting the requirements of developing transportation and ventilation, it can be freely recovered in principle. After the ore is finished, the empty area is closed and can be filled with waste rock or tailings to control the ground pressure.

2.2 Trackless mechanized room and pillar mining method (convergence)

Because the Kamoa copper mine is a large-area single-layer ore body, the surface is allowed to collapse. On the basis of selecting the appropriate mining sequence, ensuring the gradual release of ground pressure, avoiding rock accumulation and rapid release stress, the underground mine can be realized. Safely mine and increase recovery rates.
Drawing on the experience of the LGOM copper deposit in Poland using the trackless mechanized room-column mining method (convergence type), the room-column method is divided into two steps for recovery: the first step is to ensure the safety of the mining face through the large strip-shaped pillar, step 2 The strip-shaped pillars are dismantled into small pillars, and the pillars are uniformly withdrawn, and part of the pillars are recovered, so that the small pillars form a flexible support, and gradually collapse and release stress as the area of ​​the empty zone increases (Fig. 2). The theory of rock mass failure caused by this mining method has been verified in practice in the mining process of sedimentary ore bodies. The underground mining area is mainly divided into four states, namely, the undisturbed undisturbed zone, the initial disturbance zone, the strong failure zone, and the second equilibrium zone (Fig. 3). Because the pillar protection is in a stable state in the mining area, the dismantled pillar gradually enters the state of destruction as the working line advances. When the pillar breaks and releases the stress, the empty zone will enter the second equilibrium stable state. The stope structure of the trackless mechanized room and pillar mining method (convergence type) is less affected by the increase of the mining depth, and the permanent stability of the goaf cannot be guaranteed. The recovery of the ore column can improve the recovery rate of the room and column method. In particular, the deep mining recovery rate is significantly higher than the ordinary house column method. The mining structure parameters of the mining method are shown in Table 2. Since the disassembled pillar is in a state of flexible support, it will be gradually destroyed as time and space range expands, and eventually a cave (top curved) state will naturally form in the area of ​​the remaining pillar. Therefore, the mining method needs to strictly control the mining sequence, and uniformly withdraws in one direction, and controls the propulsion direction of the recovery and recovery columns to one propulsion line. The ground pressure formed by the underground empty area is gradually released with the destruction of the remaining pillars. Combined with some waste rock or tailings filling, the ground pressure can be effectively controlled to ensure the safety of mining.

3 Conclusion
For the large-area gently inclined single-layer thin ore body of the Kamoa copper mine, the trackless mechanized mining method can greatly improve the production efficiency and reduce the cost per ton. Since the size of the permanent pillars left by the room and column method directly affects the final mining recovery rate, this study uses a convergent deformation room-column mining scheme to effectively reduce the loss of permanent pillars, especially It can solve the problem of large deep pillars and low recovery rate. Compared with common room and column mining methods, the advantages are obvious and can be used as reference for similar mines.
references
[1] Beijing Nonferrous Metallurgy Design and Research Institute. Mining Design Manual [M]. Beijing: China Building Industry Press, 1987.
[2] He Guicheng. Research on prediction and control of mining subsidence in gently inclined layered ore body [D]. Changsha: Central South University, 2013.
[3] Gao Zhirong, Zhang Rui. Dipping thick orebody [J] using the room and pillar mining a deep lead zinc ore. Modern Mining, 2015 (6): 49-50.