The bottomless sublevel caving method is widely used when mining thick ore bodies of low value. The mining method has the advantages of large production capacity, high degree of mechanization of the equipment, and good safety of the mining operation. The disadvantage is that the ore is discharged under overburden, and the loss rate and depletion rate are large [1]. Therefore, how to reduce the two rates in the mining recovery process has become a key issue of this method. The method of reducing the loss depletion can be summarized into two categories: one is to optimize the structural parameters of the stope. According to the ore-mining theory, in order to obtain the best mining index, try to combine the structural parameters of the stope (ie, the section height, the approach The spacing and the step size of the collapse are consistent with the morphology of the discharge body. In the ellipsoid ore mining theory, the structural arrangement of high segmentation and large spacing is proposed [2]; the other is the implementation of ore management, through control The amount of ore-mining and the process of ore-mining control the morphology of the contact surface of the ore, so as to reduce the loss of depletion [3]. In actual production, these two methods are generally adopted at the same time. This paper intends to study the low-depletion ore-concentration scheme in the ore-mining management. 1.1 Ore rock movement process Compared with other mining methods, the biggest feature of the caving method is that the ore contact surface is constantly changing during the ore mining process. According to the theory of ore-delding ellipsoid, under the condition of no boundary limitation, the single funnel release body is an approximate ellipsoid, and the part that moves in the ore pile after release is called loose ellipsoid, and the horizontal ore in the loose range The contact surface has a concave funnel shape and is called a discharge funnel. Assume that the height of the discharge body is Hf and the height of the discharge funnel is h. At the initial stage of ore-mining, the ore-rock contact surface is above the ellipsoid (h>Hf), which is a moving funnel; as the ore is released, the discharge funnel gradually moves, flush with the top of the discharge body (h=Hf), which is the falling funnel. The ore continues to be released, the funnel level will be less than the top of the discharge body (h < Hf), which is the rupture funnel, and the appearance of the rupture funnel, which indicates that the ore begins to be depleted [4]. In the case of multiple leaking ore deposits, the ore-rock interface gradually moves down at the initial stage of ore-mining, and after a certain height, unevenness begins to appear. When the ore-mining continues, the unevenness becomes more and more obvious until the ore boundary reaches the ore-outing port. Depletion began to appear [5-6]. It can be seen that when the ore is discharged, it is released as pure ore. When a certain amount of ore is released, the waste rock begins to mix in, and the depletion rate gradually increases until all the last released are waste rock. In the actual production, the low-depleted ore-mining can be based on the specific conditions of the mine, and each section adopts different grade reduction levels to combine the optimal low-depletion ore-concentration scheme. When the mine funds can be used to allow a significant reduction in dilution and improve grade recovery program, funding is tight when the mine can be appropriate to reduce the use of depleted steadily increase the recovery grade programs in order to avoid the mine in the early application requires a lot of The funds are subject to a three-level mineral reserve. The numerical simulation of ore-preserving uses PFC2D software to establish a discrete model of ore-boring through programming, using its own fish language to servo-control the ore-mining process, and record the loss and depletion information in the process of ore-mining. The workflow of this simulation program is [10]: 1 establish the wall and set the wall parameters, including the stope boundary and the ore approach; 2 generate waste rock particles and middle ore particles, and set the particle parameters; The ore-mining simulation is carried out according to the cut-off grade of the ore discharge set by each mining plan, and the volume of waste rock and ore discharged is counted; 4 The output and analysis of the ore-out result. (1) Particle size. According to the particle size distribution of the ore measured in the field, in this simulation, the particle size of the waste rock is 0.3-0.5 m, and the ore particle size is 0.2-0.3 m, all of which are subject to uniform distribution. In this PFC2D simulation ore mining process, the ore is mainly based on the ore weight of the ore and rock particles. The ore-mining process and the cut-off conditions are written using the embedded fish language of PFC2D, and then the computer is guided to mine according to the written fish program [12]. The procedure for simulating the ore-mining process is as follows: 1 delete the segmented roofs and simulate blasting excavation; 2 run 30,000 steps to simulate the ore-rock movement process after blasting; 3 delete the ore in the approach, simulate the mining process, and simultaneously Calculate the number and volume of ore and waste stone particles deleted, and make a cumulative; 4 Calculate the ratio of the volume of waste rock to the ore volume of this mine, and compare it with the cutoff value of the ore discharge. If it is greater than the cutoff grade of the ore discharge, then this At the end of the road discharge, if it is less than the discharge cutoff value, return to the second step; in the 5th section, all the way to the end of the ore discharge will enter the lower section of the ore mining simulation. During the caving process, every time the ore is released, it is hoped that the recovery rate of the ore is as high as possible, and the depletion rate of the ore is as small as possible. However, in the actual process, blind pursuit of high recovery rate will often lead to an increase in ore depletion rate. In order to reduce the depletion rate of ore, it is necessary to sacrifice the recovery rate. Therefore, in order to comprehensively reflect the impact of the two indicators on the effect of ore-mining, the difference between the recovery rate and the depletion rate is generally used as a comprehensive indicator, that is, the poor return [13-14]. If D is used to indicate poor return difference, N is the ore recovery rate, and P is the depletion rate, then the poor return difference can be expressed as: D = N-P. (3) The comprehensive poverty alleviation of low-depleted ore deposits is better than the current cut-off grade ore mining method. The difference in returning poverty under different low-depletion ore-concentration schemes is also different. In this study, when the cut-off grade of the upper segment is higher, the difference in the return to poverty is larger. For example, in Scheme 1 and Scheme 8, respectively, 20% is depleted. When there is no depletion, the comprehensive poverty alleviation difference is 0.798. 0.791. Huizhou City Melors Plastic Products Co., Limited , https://www.evadecking.com
1 caving method mining ore movement process and cut-off grade mining
1.2 Current cut-off grade mining and its shortcomings
When the ore is released, if the ore grade drops to a certain value, the ore will be stopped. The grade at this time is called the cut-off grade. In order to release more ore, the current cut-off grades of mines have been relatively low, and the mining methods have the following problems [6-7]:
(1) Using the break-even method to determine the mine boundary line, the one-sided emphasis on the ore recovery rate of a single step, will inevitably lead to excessive waste rock mixing, high depletion rate; due to the bottomless sublevel caving method, the loss of ore in the middle section can be under The middle section is recycled, so the method of mining is not optimal.
(2) There will be a large amount of waste rock mixing in each section of the ore during mining, and the number of depletion increases with the number of segments.
(3) The cut-off grade is the core of the ore in each unit of the ore-mining step. Therefore, it is required to grasp the grade change of the stope at any time during the process of the ore-mining to guide the mining of the stope. However, due to the fact that there is no domestic grade analysis instrument that is efficient, timely and suitable for special conditions in the underground, it can meet this requirement, which makes it impossible to carry out effective related control during mine production.
In summary, due to the process characteristics of the cut-off grade itself, the ore mixing degree in the ore-mining process is high, the overall ore depletion rate is large, and it is difficult to control when the production site is limited by the detection instrument. In order to reduce the depletion of ore in actual production, it is recommended to implement low-depleted ore.
2 low depletion ore discharge principle
When the upper section is mined, the cut-off grade is higher, and the depletion rate is lower at the end of the mine release, allowing the appropriate ore to remain in the stope. The residual ore is not only to reduce the mixing of the ore, but also to obtain a higher grade. Ore is produced and can be used as a cover. When the last section is mined, the current cut-off grade is used to mine and release as much ore as possible. Compared with the current cut-off grade, the characteristics of low-depleted ore deposits are [7-9]: 1 the cut-off grade is higher, the current depletion rate is smaller, and the ore grade is higher in the early stage; 2 conscious pre- Part of the ore remains in the stope, reducing the degree of mineral mixing, and the overall depletion rate is small; 3 the ore reserved in the upper section is recycled in the lower section, increasing the amount of pure ore in the lower section; 4 according to the ton grade curve using controlled release embodiment ore low Dilution mine management, ease of management; layered mineral is temporarily remaining part empty area on ⑤, the delamination may not yet formed enough of roof falling of stone "cover layer Continue to carry out the mining, that is, to continue the lower layer mining under the cover layer composed of "ore + rock", providing sufficient time for the upper rock roof to fall; 6 in the final production index, the process is Keeping the recovery rate basically equal, it can significantly reduce the depletion rate of ore, improve product quality, reduce invalid costs, and improve mine operation.
3 Numerical simulation of low-depletion ore-concentrating PFC
3.1 Mine overview and low-depletion plan determination
A gold ore body is thick and has a low grade. The surrounding rock also contains ore. Therefore, it is mined by sublevel caving without a bottom column. The annual output is 1 million tons, the average grade of ore is 1.2g/t, and the average grade of waste rock is 0. 3g/t. The mine is now using the cut-off grade of 0.5g/t to mine, and the loss of ore is much depleted. It is often the case that the ore is not covered by waste rock. This topic takes the 1190m middle section of the mine as the research object. The upper section is as small as possible or no waste rock, and the bottom section is mined according to the current cut-off grade to study the optimal low-depletion ore-concentration scheme. According to the actual situation of the mine, eight kinds of ore-mining plans (see Table 1) were drawn up, and the optimal plan was selected through simulation analysis.
When the ore-mining model is generated, all the particles are generated within the boundary of the model according to the set porosity, and then the particles are separated by the extrusion exclusion method in the PFC. In order to avoid large-area particle overlap in the local region, an initial cycle is required. Calculate, make the kinetic energy of the particle zero, reach the initial stress environment and conditions, try to be the same as the actual situation of the mine [11]. The ore-mining power in this PFC simulation is mainly derived from the self-weight of ore and waste rock particles, and the friction between the ore-removing resistance particles. The cut-off conditions of the two ore-extracting methods can be based on the ratio of the released ore particles and waste rock particles. control. 
3.2 Model establishment
The vertical profile of a mining face is selected to establish a mining model, as shown in Figure 1. The model has 5 sections, width 121m, height 83.5m, and waste stone cover thickness 33.4m. The mining structure parameters (height x width) were 16.7 m x 22 m, the access size (width x height) was 3 m x 3 m, and the side hole angle was 55. The boundary condition of the model: the lateral fixing requirement is achieved by limiting the horizontal movement, and the vertical movement is limited to achieve the fixing requirement of the bottom surface.
Due to the large size of the model, the average diameter of the caving rock is 30cm. If the whole area is generated all at once, there are about 112,328 spheres. The amount of calculation is too large and slow. Therefore, this study uses segmentation modeling and segmental ore mining. That is, Mr. became a waste rock and the first section of ore, and then carried out the ore mining procedure; after the completion of the one-stage ore release, the second-stage granules were generated and the ore-mining was performed; finally, the third-stage granules were generated and the ore-mining was performed. Until the end. Taking the calculation of scheme 1 as an example, the calculation model of the PFC for each section is shown in Fig. 2, and the information of the ore model is shown in Table 2.
3.3 Model parameter selection
(2) Particle density. The density of ore is 2.75×103 kg/m3, and the density of waste rock is 2.75×103 kg/m3.
(3) Bond strength between particles. According to the actual situation on the site, the ore and waste rock after blasting are loosely stacked, and the connection relationship between the ore particles and the waste rock particles has been destroyed, but there is still little friction. In order to add this factor to the numerical simulation, the normal stiffness between the ore particles and the wall is 108 N/m, the tangential stiffness is 108 N/m, the friction coefficient between the wall and the particles is 0.5, and the friction of the ore particles The coefficient is 0.1; the friction coefficient of the waste stone particles is 0.3, and the calculation parameters are shown in Table 3.
3.4 Calculation Process Control
4 mining results and analysis
4.1 mining simulation results
This project simulates the ore-mining process of each scheme, and carries out statistics and calculations on the ore-out results of each scheme (the space is limited and will not be displayed here). After the mine is released, the boundary of the ore rock is shown in Figure 3 (taking Option 1 as an example).
4.2 Analysis of results
By comparing the statistical results of the eight kinds of ore-mining schemes, the technical indexes of the ore recovery rate, the depletion rate and the returning poverty difference in the three ore-mining sections are respectively plotted, as shown in Figures 4-7.
From the figure you can get:
(1) Under the conditions of different ore-mining schemes, the ore recovery rate of the same segment is different; under the same scheme conditions, the ore recovery rate of each segment is quite different. In terms of the overall trend, the recovery rate of the first segment is higher. Small, the recovery rate of the ore to the second section has increased. When the last stage of ore mining, the ore recovery rate is very large, even exceeding the segment.
Blasting ore. This is because each segment uses a different cut-off grade, the first two segments have a higher cut-off grade, and the last segment uses the selected grade as the cut-off grade.
(2) Under the conditions of different ore-concentrating schemes, the ore depletion rate of the same segment is different; under the same scheme conditions, the ore depletion of each segment is different, and the overall trend, the first section of the ore mining The ore depletion rate is small, the ore depletion rate of the second stage is the second, and the ore depletion rate of the third stage is the largest. This is because the 1st and 2nd sections adopt a larger ore-cutting cut-off grade, which controls the mixing rate of ore during the ore-extraction, while the third-stage ore-mining adopts the selected grade, and the cut-off grade is lower, which increases. The incorporation of ore.
(3) Under the conditions of different ore-mining schemes, there is a certain fluctuation in the difference of the ore returning to the same segment; under the same scheme conditions, the difference in the returning poverty of each segment is quite different. In terms of the overall trend, the difference in the return to poverty in the first sub-segment is significantly smaller than that in the 2nd and 3rd sub-segments, and the difference in the regression of the 2nd and 3rd sub-segments is similar, both around 0.9.
(4) It can be seen from the comprehensive poverty alleviation curve of the scheme that the difference in returning poverty between schemes 1 and 8 is significantly larger than that of other schemes, and the difference in poverty reduction of scheme 7 is the smallest, followed by scheme 3, scheme 5, and scheme 6. Option 2, Option 4.
5 Conclusion
(1) The ore recovery rate of the low-depletion ore-off method is lower than the current cut-off grade ore method, but as the ore-mining section moves down, the gap between the two is gradually decreasing, which is due to low depletion. In the first section, the ore-mining method requires some ore to mix with the rock to form an ore-depleted layer. At a higher grade, the ore is stopped, and the remaining ore is released in the next section.
(2) The rate of waste rock mixing in low-depleted ore deposits is lower than the current cut-off grade ore method, and with the downward shift of the section, the rate of waste rock mixing in low-depleted ore-mining will continue to decrease, and the current deadline is The grade ore mining method is increasing with the segmentation of the waste rock mixing rate.
In summary, the low-depletion mine management method has a positive effect on reducing the depletion rate of ore on the basis of ensuring the recovery rate, and can be promoted and applied.
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Article source: "Modern Mine"; 2016.9;
Author: Wang DPRK, Zhou Xingyu; Xi'an, capital of Materials and Mining & Technology;
Zhang Wenge; Sifang Gold Mine Co., Ltd.;
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