0 Preface
The natural caving method is to change the stress in the ore body by means of the bottoming and weakening engineering, and form a fracture network by the development of joint fissures in the rock mass, and then naturally collapse under the action of self-weight, which is an independent High-strength, low-cost large-scale underground mining methods for rock drilling and blasting [1-2]. The natural caving method is often carried out for the nuggets or panels. The successful mining practice is influenced by many aspects. It can be divided into two major categories: natural factors and engineering factors. The natural factors mainly include geological factors and ore rock physical mechanics. Nature, mineral rock surface development, geostress and distribution, engineering factors are mainly engineering layout and construction methods. Due to many factors affecting natural caving mining, its engineering layout has its particularity. Failure to convert into other types of mining methods or remediation will result in great waste and loss of resources. Therefore, in order to effectively control risks, a large amount of preliminary feasibility studies and research work must be carried out before mining practice to reduce risks and ensure Successful mining practice of natural caving.
The 30# ore body of Huangshan Copper- Nickel Mine is a low-grade thick ore body. The original design mining method is a sub-column-free sublevel caving method. However, due to the development of the ore-rock structure surface in the area above 530m, the roadway is prone to occur during the actual construction process. deformation and collapse, supporting a high workload and the difficulty and cost of support, to the progress of the project and downhole operation caused serious security threat; in addition, due to the continued downturn in metal prices, using the original design of mining method is difficult to produce benefits, but also It is not conducive to the mine entering the normal production track. Therefore, the mine cooperated with the research institutes to carry out joint research to find a mining method that is more in line with safe and efficient requirements. Through multiple communication, it decided to carry out the feasibility of the natural caving mining method for the 30# ore body (above 530m). the study.
1 analysis of mining technical conditions
The Huangshan copper-nickel mine is a newly-built mine, and the No.30 ore body is in the basic-super-basic rock body, which is concealed. The ore body of the area above 530m is 240m long, with an average thickness of 43m and an ore body inclination of 50°. ~65 °, the average inclination angle is 61 °, the individual sections are slow, the average grade of ore is Cu 0.298%, Ni 0.461%, the overall ore body shape changes little, is a low grade thick ore body. Of roof of ore mainly amphibolite peridotite, gabbro norite, lithology floor hornblende gabbro, gabbro norite, partly in amphibolite peridotite. The geological structure of the mining area is relatively simple. Although the large-scale structural fracture zone is less developed, the small and medium-sized structural surface is relatively developed, which has brought certain adverse effects to the underground construction. This has been very much in the construction process of infrastructure projects in the past few years. Good proof [3].
In addition, the engineering geological type of the mining area is a hard and semi-hard non-stratified deposit, and the geological problems of bad engineering are relatively simple, and it is a simple-medium mining area with engineering geological conditions. There are no surface water systems and perennial rivers in the area. Only the dry valleys are not deeply cut. The rainy season forms a temporary flood. It disappears 3 to 5 days after the rain. The possibility of landslides, mudslides and landslides is small in the mining area. The source of recharge is atmospheric precipitation, and the alternating groundwater interaction is extremely weak, so the hydrogeology is generally simple.
In addition, the mining area is located on the Gobi Desert, and there are no roads, pipeline works and civil buildings on the surface above and below the area, so the surface is allowed to collapse.
On the basis of the mining technical conditions, combined with the actual situation on the site, it can be seen that due to the low grade of ore in the study area, the overall instability of the ore rock, and the low metal price, the original design mining method cannot be carried out normally, so it is necessary to The mining method is subject to corresponding changes and special studies to ensure the safety of mining operations and the rational use and recycling of resources. In addition, the surface above the area is allowed to collapse, which makes it possible to exploit the natural caving method. It is necessary to carry out a large number of experiments, investigations, tests and analysis on the natural factors affecting the successful exploitation of the natural caving method, thus causing natural collapse in the area. A reasonable comprehensive evaluation of the feasibility of the law.
2 related investigations, tests and tests
2.1 Experimental study on physical and mechanical properties of ore
The physical and mechanical properties of the ore rock directly affect the overall characteristics of the rock mass, and its properties play an important role in the formation and development of the rock mass collapse. Therefore, it is necessary to carry out corresponding physical and mechanical properties experiments on various types of rock in the study area. According to the on-site geological survey, the rocks in the range are mainly fine bismuth, olivine pyroxenite and some green talc talc in some sections. The physico-physical properties of fine bismuth and holorite are relatively good, so Sampling and processing into standard samples for indoor mechanical experiments, and some green mud talc kiln rock is not easy to process into a regular shape of rock samples, so the mechanical properties can be measured on-site by point load test.
The experimental results of the physical and mechanical properties of typical ore rocks in the 30# ore body of the Huangshan Copper-Nickel Mine (above 530m) are shown in Table 1.
2.2 Engineering Geological Survey
The structural plane in the rock mass has an indispensable effect on the formation and development of the fracture network. At the same time, the characteristics of the structural plane also directly affect the overall mechanical properties of the rock mass. Therefore, on the basis of understanding the regional geology, it is necessary to study The detailed ore geological survey of the ore body within the scope to fully understand the development and distribution of the structural plane in the ore body provides a realistic basis for the feasibility analysis of natural caving.
The rock core structure surface inspection can generally adopt the core investigation method and the tunnel investigation method, and the tunnel investigation method is much more accurate, but its workload is also larger. This time, the tunnel investigation method was adopted to measure the base distance, occurrence, continuity, opening degree, roughness, filling or cementation, weathering or alteration degree, and water seepage of the structural surface one by one by arranging the measuring lines. Then based on mathematical statistics, the survey results are collated, statistically analyzed and analyzed to obtain the dominant structural surface occurrence, development and characteristics of the ore body. According to the actual situation and analysis needs of the 30# ore body of the Huangshan Copper-Nickel Mine (above 530m), combined with the occurrence of the ore body and the rock mass of the upper and lower plates, the investigation scope is determined to be between the 114 line and the 119 line. In the vein lane, a detailed survey of the outcropping and representative sections was carried out. In this survey, 15 survey lines were arranged. The total length of the survey was 402.2m, and the total number of structural planes surveyed was 1,378. The final survey results are shown in Figure 1.
According to the above investigation results, the structural plane in the ore body is generally developed, and the ore body is most developed, which has 198°∠80°, 101°∠77°, 54°∠33° and 139°∠78°4 The dominant structural plane of the group; the three dominant structural planes of 51°∠86°, 84°∠69° and 7°∠34° are developed in the upper disc rock mass; and 38°∠82° is developed in the lower disc rock mass. And 2 sets of structural planes of 10 ° ∠75 °. At the same time, according to the on-site investigation, the average structural noodle density in the ore body is 2.81 strips/m, the average spacing is 0.36m, and the structural plane is mostly slightly rough open, which is generally extended and the surface of the rock wall is dry. , moderate differentiation.
2.3 original rock stress test
The original rock stress is the natural stress in the earth's crust that is not disturbed by engineering. It is mainly composed of self-weight stress, tectonic stress and pore pressure. In the study of natural caving mining, the original rock stress is to promote the ore body to occur under the induced engineering. The intrinsic and fundamental factors of natural caving, the magnitude and distribution of geostress are decisive for the feasibility study of natural caving, but due to the complexity and variability of geostress state, its size is often difficult to pass analytical solutions. For calculations or simulations by models, the most effective way to obtain ground stress is to perform on-site measurements [4-5].
In order to clarify the magnitude and distribution of the in-situ stress in the area where the No.30 ore body of Huangshan Copper-Nickel Mine is located, the in-situ stress field test of the feasibility study area and its vicinity was carried out by using the hollow inclusion strain measurement technique, and the digital hollow inclusion body was used. The stress gauge successfully carried out the stress relief of the casing core, and the final test results are shown in Table 2.
According to the above test results, the general rule of stress distribution of the original rock in the middle section of 530m and the middle section of 450m is consistent. The maximum principal stresses are 24.9MPa and 29.5MPa, respectively, and the directions are near horizontal direction; the minimum principal stress is 9.6 MPa and 13.1 MPa, and the directions are all near vertical. The overall stress magnitude and distribution of the mine conform to the general stress distribution law, that is, the horizontal stress is generally greater than the vertical stress and the maximum principal stress is often more than twice the vertical stress, and the magnitude of each principal stress increases linearly with depth.
3 Feasibility analysis of natural caving mining in the study area
3.1 Technical feasibility analysis
(1) According to the results of typical petrophysical experiments, it is known that the overall physical and mechanical properties of the ore in the range are good, which can meet the needs of general engineering construction, but there are green mud talc Millennium rocks in some areas, although for the construction of the project It has a certain impact, but its existence is conducive to the natural fall of the ore body. In addition, the ore-bearing rock (olivine pyroxenite) has good mechanical properties and has a certain influence on the ore body's collapse into smaller ore blocks, but at the same time, the probability of occurrence of fines in the occurrence of caving is relatively small.
(2) According to the analysis of engineering geological survey results, there are 3 groups of well-developed vertical structural planes in the ore body, and 1 group of slow-developing structural planes, which meet the requirements of a set of horizontal joints for natural caving, in engineering induction and Under the action of ground stress, it can develop into a three-dimensional fracture network, which is conducive to the continuous fall of the ore and provides a better and ideal geological environment for the effective implementation of the natural caving method. However, the structural plane in the lower rock mass is relatively weak, so it is suitable to arrange the bottom structure and other projects.
(3) According to the original rock stress test results, the maximum principal stress direction in the survey range is near horizontal direction, and the use of the clip during the bottoming process will hinder the ore caving to some extent, and at the same time due to the maximum principal stress direction and Partially dominant structural planes intersect at a large angle, and the normal stress effect on the structural plane is not conducive to the expansion and extension of the joint fissure during the caving process, but a certain weakening project is arranged at a suitable position on the ore body boundary to reduce The adverse effect of this part of the stress.
According to the basic experiments, investigations and test results analysis related to the feasibility analysis of the above natural caving method, it can be known that the geological and physical mechanics conditions of the study area can meet the basic conditions of natural caving, and in the case of reasonable engineering layout and construction, assistance is necessary. The weakening of the project, the study area using natural caving mining is technically safe, efficient and feasible.
3.2 Economic Benefit Analysis
After the secondary geological setting of the ore body within the research scope by the mine geological department, the 30# ore body (above 530m) can have a mining capacity of about 1.5 million tons, a nickel metal amount of 6900t, and a copper metal amount of 4950t, according to the current metal price and beneficiation. The recovery rate calculation shows that the value of the tonnage within the research scope is 211.2 yuan, and it is expected to create an output value of 316.8 million yuan. The cost calculation in the feasibility of this natural caving method includes excavation amortization, support cost, direct mining cost (including workshop expenses), secondary crushing, ore dressing cost, etc., according to the local unit price and the construction unit price provided by the mine. The cost is estimated. The unit cost of the unit ore mined by the natural caving method is 184.56 yuan/t. The total cost of all ore mining in the study area is 276.84 million yuan, which can realize a sales profit of 39.96 million yuan and a net profit of 3396. 60,000 yuan (after deducting 15% of profits and taxes), and can meet the mining needs of 2 to 3a of mines, which is a very important transitional role in ensuring that mines enter normal production.
4 Conclusion
A lot of basic research work has been carried out on the feasibility of the natural caving method of low-grade thick and large broken ore body in Huangshan Copper-nickel Mine 30# (above 530m area), including the analysis of mining technical conditions, physical and mechanical experiments of mineral rock, engineering geological survey and original Rock stress test, etc. According to the comprehensive analysis of the experiment, investigation and test results, the geological conditions in the study area are relatively simple, and the physical and mechanical properties and structural plane of the ore are in the case of reasonable engineering layout and construction, and with the necessary weakening of the project. The developmental conditions and the original rock stress conditions are generally technically suitable for the ore body to collapse. In addition, from the economic analysis, it can be known that mining with natural caving can create greater output value and profit, and has greater advantages than the original design mining method is difficult to profit. Therefore, in the case of low ore grades in the study area, overall instability of the ore, and low copper and nickel metal prices, it is feasible to use natural caving.
references:
[1] Wen Youdao, Li Xiangdong. Study on the collapseability of ore rock in Jinchuan III mining area [J]. Mining Research and Development, 2007, 27 (05): 4-5, 16.
[2] Zhang Bao, Li Yonghui, Wen Xing, et al. Study on the disintegration of ore rock in Huangshan copper-nickel-rich thick deposit[J]. Mining Research and Development, 2015, 35(7): 1-4
[3] Li Xiangdong, Li Yonghui, Wan Bing, et al. Feasibility study on the natural caving method of No. 30 ore body of Huangshan Copper-Nickel Mine (above 530) [R]. Changsha: Changsha Mining Research Institute Co., Ltd., Xinjiang Yax Resources Development Co., Ltd., 2014.
[4] Ma Chunde, Li Xibing, Chen Feng, et al. Test and study on the distribution law of deep geostress field in natural caving method mine [J]. Mining and metallurgy engineering. 2010, 30 (06): 10-14, 22.
[5] Cai Meifeng, He Manchao, Liu Dongyan. Rock Mechanics and Engineering [M]. Beijing: Science Press, 2002: 129-176.
Li Yonghui, Jiang Feifei; Changsha Mining Research Institute Co., Ltd., Changsha 410012, China; National Metal Mining Engineering Technology Research Center, Changsha 410012, China;
    Source: Mining Technology: 2016.16(1);
    Copyright:
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