Research and Practice on Recycling Process of Residual Large Ore in Caving Mining Method

0 Preface

Taibai Gold Mining Co., Ltd. The company's main ore body is KT8 ore body, mining using two Gold Deposit. After more than 20 years of mining, the mine is currently concentrated in the middle section of 1100 and the middle section of 1150. As the mining elevation continues to decline, the upper overburden becomes thicker and thicker, and the large blocks gradually accumulate during the ore-mining process. The ore is mixed, the decline of large ore is slow, the ore loss and depletion are severe; at the same time, the large blasting treatment not only delays the mining time, but also has safety risks, which directly affects the production and supply of minerals; Treatment will result in damage to the ramp and failure to mine. The author first studies the problems of ore mining under overburden, analyzes the causes and formation mechanism of large blocks, and determines the main factors affecting production. Then, the research on the law of ore-mining is carried out, and the reforming scheme of the bottom column and residual large ore recovery process is proposed. Finally, the transformation process was used in production tests and achieved good results.
1 caving method mining basic theory
1.1 Caving method of ore-out law The caving rock is frequently subjected to blasting, impact and collision in the stope, and the movement process collides with each other to form a large number of siltstones and small blocks. Due to the different selection of blasting parameters, rock drilling and blasting effects The difference causes the ore to break unevenly and form a certain amount of large pieces.
At the end of the ore mining, the particles of these caving ore bodies will continue to move down with the release of the ore deposits, and the movement speed is mainly related to the block size and the grain size ratio and in the sports field (loose body). Relative position.
There are many voids between the loose particles, large voids or medium-sized voids may be formed between the large particles, and small gaps may be formed between the small particles, and a medium size may be formed between the large particles and the small particles. The gap. Small particles may pass through large or medium-sized voids formed by large particles, fine particles may pass through the voids formed by the small particles, and the powder particles may pass through the void formed between almost all of the particles. Non-uniform bulk particles have a variety of motion characteristics. As shown in Figure 1, non-uniform bulk particles have different motion characteristics under self-weight.
During the process of ore-boring, the distribution of rock particles will change in reverse. Where it is far from the ore discharge, there are few small-sized particles and large particles. As the distance from the ore discharge is close, the proportion of small-sized particles is small. Increase, the proportion of large particles is reduced. In the vicinity of the ore discharge, a large accumulation of powdery rocks is produced.

According to the stochastic medium ore-mining theory, the equation of movement law of caving rock in the influence range of the ore discharge can be established [7]:

Particle moving trace equation:

Release the funnel equation:

Points equal to the amount of holes constitute the outer surface of the discharge body, from which the evolution equation can be derived:

Where Vx, Vy, Vz are the descending speeds of the bulk particles in the x, y, and z directions; P(x, y, z) is the probability density of the bulk movement; Qf is the volume of the discharge funnel.
The particle moving trace, the discharge funnel and the release body shape determined by the formulas (1) to (3) are shown in Fig. 2.

The axis of the waste rock funnel coincides with the long axis of the discharge body, and the upper boundary thereof coincides with the boundary of the loose body. The change process of the waste rock funnel is shown in Figure 3 throughout the mining process.

1.2 Determination of the cut-off grade of the ore discharge The cut-off grade of the ore discharge can be determined according to the principle of the maximum profit. The Taibai Company is the joint venture and the final product is the combined gold. The calculation is shown in (4):

In the formula, Cc, Cj and Cw are the ore grade, concentrate grade and tailing grade, g/t; Ak is the cost of ore, transportation, lifting and beneficiation of ore mined per ton, yuan/t; As For the transportation cost from mine to plant, Yuan/t; Ax is the ore dressing cost per ton of ore, yuan/t; Mz is the net income of sulfur, silver and other by-products per ton of ore mined, yuan/t; Lu is Sales revenue per gram of gold.
According to the formula, the final best-selling cut-off grade is 0.6g/t.
2 The main factors affecting mining Taibai Company is in the east of Line 16 of 8# and 9# ore body, and the middle section of 1150 is using the bottom-column stage caving mining. The upper part is collapsed with the surface and the lower part is discharged under the cover rock. The ore body is thick and has a low grade. The rock drilling construction is safe and the mining efficiency is high. However, some problems have arisen in the application of this method, such as high block rate, large loss of depletion, and serious damage to the ramp.
2.1 The change of the ore cover under the overburden is east of the 16th line of the 8# and 9# ore bodies, and the bottom section of the 1150 is used for the mining of the bottomed stage. The hole pattern is a fan-shaped cloth hole, and the fan-shaped cloth hole is characterized by The distribution of explosives is uneven, and the ore blasting effect close to the rocky roadway is often good, and the ore blasting effect at the bottom of the hole is poor. In addition, due to the different lithology of the ore, the loose ore of the blasting collapses in different sizes and shapes, generally with large blockiness and extremely uneven distribution. There is a gap between the rock ore bodies, which causes small-sized waste rock in the upper cover rock to be mixed, resulting in more ore remaining in the covered rock [8-9].
According to the ellipsoid theory, when the ore is discharged by electric shovel, the original position occupied by the sliding particles becomes a vacancy, and the particles in the upper part are transferred by gravity, and the new vacancies formed by these downwardly moving particles are The particles of the upper layer are transferred downward, and so on, the flow of the scattered ore is formed. In the process of the vacant vacancies of the particles, the small pieces are less pinned. If there is a gap, it may be preferentially moved down, causing the large pieces to lag in motion, which will cause the shovel to be a mixture of minerals and rocks. The large ore remaining in the middle reduces the ore recovery efficiency. The formation of ore blocks is mainly due to the following reasons:
(1) The geological conditions are relatively complicated, and the faults in some sections are relatively developed. As a result, some of the ore blocks have not been blasted and fallen, and the mining roadways have collapsed. Some sections have failed to mine according to the design intention, resulting in more large blocks. This point is obvious in the middle section of the company's 8# ore body 1150, line 34-36. The local section is affected by the 34-line large fault, resulting in the construction of the ore mining project. The rock passing through the faultway is relatively broken. The phenomenon of inner drum is more obvious, and the phenomenon of roadway subsidence occurs in the process of lowering the bottom. A large area of ​​landslide occurs in some sections, and the large blocks formed cannot be recovered. At the same time, the recovery of ore is also affected.
(2) The selection of design parameters is unreasonable, resulting in a high block rate.
It is extremely important to select the design parameters of the bottomed stage collapse method. In the process of selecting the design parameters, the geological structure and rock hardness of the design section should be fully considered. If the row spacing and hole bottom distance in the design of the blasthole are If the selection is too large, it will lead to problems such as insufficient extrusion, unsatisfactory secondary crushing, and high bulk rate.
(3) Construction management is not in place, and engineering errors are large, resulting in a large number of nuggets. The recovery of a ore ore, from mining to blasting, must be carried out in strict accordance with the quality requirements of the project. If there is a problem in one of the links, it will lead to unsatisfactory mining effect and high bulk rate. .
2.2 Under the overlying rock, the ore loss and depletion conditions are discharged under the cover rock. Due to the intrusion of waste rock, the ore grade decreases, resulting in depletion. The ore left after the mine is stopped is mixed with the cover rock, and some may be divided. The section is released in the form of mixed rock and rock, while the other part is permanently left in the stope as a permanent loss. For the caving method, there are many contact surfaces between ore and waste rock, and the caving ore and cover rock are affected by the end wall restraint and the degree of blasting. The morphology of the released body is large, and the loss of lean is difficult to control.
For the mining houses in the middle of the middle section of 1150, the modes of caving mining, cover rock mining, and electric mine mining are adopted. The following problems are found during the mining process:
(1) Part of the electric ramp is damaged, causing more ore to fail to mine normally and causing ore loss. The electric tunnel damage is mainly caused by the caving method. The upper pressure is concentrated on the bottom structure. The geological structure of some sections is complicated, the block rate is too high, and the guns are frequently changed, so that the masses have not been mass-produced after blasting. Mines, electric ramps can no longer be used, some ore can be placed in the next middle section for recycling, but in combination with the actual, 8#, 9# ore bodies belong to the upper rich and the lower, the upper width is narrower, if it is recycled in the lower part, it will inevitably lead to Part of the loss of ore.

(2) When the mining is carried out by the mining method with the caving method, the ore grade is much lower than the geological grade, and the depletion rate of the ore is as high as 40% to 50%. The main reason for the increase of the depletion rate of the ore is the mine. The medium block rate is too high. Because the underground mine is a process of granules in the form of loose particles, under normal circumstances, the small pieces are less pinned. If there is a gap, the small pieces may move down preferentially, causing the large pieces to lag.
In the lower part of the underground caving area, the ore is discharged under the cover rock, and the upper part of the waste rock is small. At the edge of the waste rock funnel in the near-release ore section, the ore block is obviously mixed during the downward movement, resulting in the ore grade. The decline is obvious.
(3) Although some electric ramps have not been destroyed, the mining capacity of the mines is much lower than that of the geological mines. In the process of mining, due to the large blockiness of some bucket piercings, and the overhead of the bucket piercing, the outflow of the blockage and the treatment of the cannon, there are technical difficulties and safety risks, resulting in technical difficulties and safety risks. Some mining hoppers cannot be mined according to the design, which reduces the amount of ore mined.
2.3 Safety status of ore mining under overburden (1) The underground mining structure uses electric rafts for ore mining. It mainly undergoes three processes, firstly the stage of no depletion and ore, which is the stage of uniform ore release; the second is low poverty. The stage of demineralization; once again, the stage of cut-off grade. Fighting through ore is the use of electric smash to destroy the natural angle of repose of the rock of each bucket, which causes the upper rock to continue to slide and form a new angle of repose. However, no matter which stage of the ore-extracting stage, there is a phenomenon of blocking the passage of the bucket. In the process of sealing, there is a possibility that the rock suddenly slips due to the gap between the rocks, which causes a large safety risk in the sealing process.
(2) Due to the large number of large blocks in the mine, the problem of large blockage often occurs during the mining process, and it is necessary to carry out the operation of the bucket and “reordering” frequently. In this process, there is a great security risk due to the frequent operation of the bucket.
3 bottom column and residual large ore recovery process transformation plan

After analyzing the problems of ore mining under the cover rock, there are many large ore remains in the mine. How to recover these remaining large ore and damaged ramp is difficult. The original electric raft is mined - the bottom structure is to be recovered in the lower middle section, and the ore-mining mode of the lower end of the rock is covered. The ore-extracting process is changed from the original three-stage ore-mining to the end-stage demineralization. After the cut-off grade, the next cycle of ore mining is carried out [10-11].
3.1 Bottom structural transformation In order to reduce the loss rate and depletion rate of the ore block, shorten the sliding distance of the large block, and reduce the number of times the personnel wear the bucket during the mining operation. After research, it is decided to transform the bottom mining structure. .
Breaking the shackles of the original middle concept, based on the original bottom structure, the bottom structure is lowered by 8m. One is to minimize the sliding distance of large blocks. Second, according to different geological rock conditions, the retained pillars should be able to support the pressure of the upper cover rock to ensure the safety of personnel and equipment during the mining process.
In order to ensure the recovery effect, the groove is redrawn at the end of the nugget to form an extrusion blasting space. In order to ensure the blasting effect, when the conditions permit, the end uses the shallow hole slip method to pull the groove to form a relatively neat initial blasting surface, which creates favorable conditions for subsequent blasting.
3.2 Optimization of the ore-mining process According to the problem of high bulk rate and difficulty in mining during the mining process, the falling process is adjusted during the process of process modification.
(1) Optimize the parameters of the deep hole arrangement and reduce the block rate. Construction of the original 65mm aperture only Model YG-90 deep-hole rock drill, the replacement of DTH Type KQJ-100B may be 90mm aperture rig construction, the construction sector to sector level deep or deep, in order to increase the deep Charge per meter. In the aspect of deep hole arrangement, according to different rock properties, the hole bottom distance and the row spacing of the deep hole arrangement are adjusted in real time, and the hole bottom distance is adjusted from the original 2.8 to 3.0 m to 2.2 to 2.5 m; From the original 1.8 to 2.0 m, it is adjusted to 1.4 to 1.6 m.
(2) Adjust the blasting parameters and control the ore particle size. When the pillar is blasted, the lateral extrusion blasting is used, and the grooved space at the end is shallow, and the blasting is performed row by row. In order to ensure that the ore can be fully recovered, only one or two rows of charge are applied for each blasting. After blasting, the next blasting operation can be carried out after the completion of the blasting. The subsequent blasting is the loose rock blasting after the previous blasting. In the blasting process, the position, clogging mode and blasting step of the blasting charge were adjusted in the charging mode.
The primer bag is still placed in the orifice, but after loading the primer kit, it must be followed by 1 to 2 knots (30-60mm) of tubular explosives to enhance the detonation power; when the orifice is blocked, it must be blocked with the mud. 30mm or more, and screw it with wooden wedges to fully exert the rock breaking effect of gas expansion energy during blasting; since it is mined at the end, in order to ensure the mining effect of each cycle, as much as possible to recover resources, each The cycle of the blasting step is controlled at 2~4m, the charge of each row of blasting is 600~800kg, and the amount of collapse is 500~700t.
(3)Strongly grasp the construction quality and ensure the effect of falling mine. In deep hole rock drilling, the orientation, angle and hole depth of the blasthole must be controlled in strict accordance with the design requirements in order to achieve the best construction results. In the process of blasting charge, it is necessary to control the density of the charge, place the primer package, make the hole blocked, and lap the hole to detonate the network.
3.3 Adjustment of the mining method After the bottom structure is lowered by 8m, the electricity production by the electric raft can not meet the production requirements. In order to improve the mining efficiency and increase the ore supply, the original electric boring machine is converted into the shovel. Machine mining, by applying the flexibility of the scraper, can reduce the amount of equipment used and reduce the maintenance cost of the equipment.
According to the situation of the rock and the upper ore body, the ore approach (size 2.8m × 2.8m) is arranged every 10~12m to ensure the ore can be fully recovered. During the process of project layout, a slipping patio is set at each mining point, which enables the scraper to directly pour the ore out into the slip mine and directly load the mine car in the next middle section, which can greatly improve the treatment efficiency.
3.4 Production test The ore-bearing structure of the 1150 middle section 20-18 line 1142 is used as the test object. The ore-free ore-mining structure is re-arranged at a level below 8m (ie, 1142 level), and the vertical ore body is arranged with a north-south direction scraper discharge approach, and a cutting groove is arranged at the end of the ore body near the mine. The cutting groove is grooved by the shallow hole retention method. In the upper ore mining outburst and the outburst way, medium-deep hole drilling is carried out. After the completion of the mining route, the construction of the fan-shaped hole in the mining route can be started, and the mine collapses and retreats. Recycling ore.
According to the statistics in actual production, the daily mining volume of the site is about 600t, and the average grade is above 0.8g/t. As of the end of June 2016, a total of 63,000 tons of ore is produced (see Table 1).

As can be seen from Table 1:
(1) With the increase of the number of collapses, the end face of the ore discharge gradually moves southward, and the middle part of the upper mine is close. The proportion of the large amount of ore in each approach is gradually increasing, reaching about 50%;
(2) With the decrease of the grade of the ore, the recovery rate of the large block is gradually increased, and the prolonged lean ore discharge time can increase the recovery rate of the large block;
(3) Among the ore, 0.8~1g/t ore accounts for about 40% of the total ore. It can be seen that the mining management measures adopted have reduced the depletion to a certain extent and delayed the mining. The overall depletion rate has extended the mining time and increased the recovery rate of large blocks.
4 Conclusions (1) The non-uniform dispersion of ore and rock in the caving mining method. When the ore is discharged, the velocity of the falling particles of these caving rocks is affected by two aspects: one is the block size and the grain ratio. Related; the second is related to its relative position in the sports field (loose body). Small particles of ore rock move faster; the ore rock in the center of the ore discharge moves faster. Therefore, after the collapse of the continuous stage, the fine-grained waste rock in the upper overburden will continue to mix, causing depletion and loss.
(2) According to the laws of rock movement and production practice, a technological transformation plan for large-scale treatment is proposed. This scheme reduces the falling distance of granular ore at all levels and reduces the mixing time; at the same time, it stops the lower part of the upper mining block and moves to the lower mining room, which terminates the fine-grained waste rock and further mixes into the lower mining room, thereby reducing the large block. Superposition, reducing waste rock mixing, theoretically in line with scientific principles.
(3) Production practice shows that the small particle waste rock mixing is reduced by 50%, the depletion rate is reduced, and the depletion is reduced; the best prospecting level is 0.6g/t, which reduces the loss; The crushing is about 10 times a day, the number of times is reduced, and the safety risk is reduced; the breakage step distance per cycle is better than 2 rows, and the adjacent two approaches are simultaneously mined. The sunrise ore volume can reach 600t, and the mining efficiency is obvious. Improve and improve production efficiency.
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