Discussion on Application of Natural Caving Mining Technology

0 Preface

Since the successful trial of the natural caving method in the United States in 1895, after more than 100 years of continuous development, it has been widely used in more than 50 mines in more than 20 countries including the United States, Canada, Chile, Indonesia, South Africa and the Philippines.

The natural caving method, including the mass collapse method, the panel caving method, the inclined ore caving method, and the front end caving method, is a large-scale and low-cost mining method. Its large production capacity, easy organization and management, safe operation and low mining cost are the only efficient underground mining methods that can compete with the economic benefits of open pit mining. In many countries, the mining process has matured and is widely used in the mining of large ore bodies. Mining with this method can achieve better economic benefits.

Different from other mining methods, this method can not carry out layered rock drilling and sub-step blasting to cause the ore body to collapse, and only rely on the bottom space at the bottom of the stope to make the ore body naturally collapse.

1 Nature and application background of natural caving mining law

The principle of natural caving method is: in the ore body which is easy to collapse naturally, using the joint distribution characteristics and low-strength characteristics inherent in the ore body itself, a certain area of ​​the bottom is made at the bottom of the ore block to form a free surface for the ore to fall. Under the necessary conditions, it is supplemented by roadway, deep hole cutting, weakening the connection between the ore and the surrounding ore and surrounding rock, etc., changing the distribution of stress in the ore body, causing the ore to gradually cause damage, instability and use of the ore body. The role of the gravitational field naturally collapses into a suitable ore block to achieve the ultimate purpose of falling. The mining model of the natural caving method is shown in Figure 1.

Figure 1 The apparent collapse mining model

Fig. 1 The model of present status of block

Caving mining method

The natural caving method has high requirements on the physical properties of the ore rock. The application conditions of the ore body mining are quite strict in application, which requires a high level of production management, and the application of this method is more risky than the use of other methods.

Before deciding to adopt the natural caving method, the following parameters and their influencing factors should be considered. These parameters are the same for all kinds of natural caving. Any form of natural caving needs to consider these parameters: ore collapse; one collapse block; ore or ore zone; ore height; Roadway layout (mining system); rockburst possibility; mining sequence; bottoming sequence; caving disturbance stress; bottoming rock blasting; mining system layout, mining order; mining system stability; tough support requirements Actual tapping system size; ore-mining method; ore-mining speed; mutual influence of ore-mining point; ore-like column stress; secondary block degree (block size reaching the ore discharge) distribution; secondary blasting; Maintenance and overhaul; ore recovery rate; surface subsidence.

How to use the rock mass's own characteristics, use the ground stress, and use the engineering control to carry out the natural collapse is the specific application of rock mechanics in mining, and also the technical key of the natural caving method.

2 The main problems in the natural caving mining method

In the past, ore bodies that were prone to caving and breaking were considered to be mined by natural caving. Due to the more accurate evaluation of the collapsibility and fragmentation of the ore body, the scraper became readily available and the law of the process of the ore control was understood. More in-depth, with appropriate secondary rock blasting equipment, and reliable cost data, the natural block large stable ore body can be mined by the natural caving method much lower than the rock blasting method.

Mining engineering practice shows that natural caving is a mining method with greater risk. Once the engineering layout of the natural caving method is completed, there is almost no room for change. Until now, the mining industry at home and abroad is still studying and exploring the mining method.

Mines using the natural caving method need to determine the following elements: ore body collapse, block distribution, ore-mining mode, ore-mining or ore zone spacing, ore system design, bottoming sequence and support Protection design. A detailed understanding of local and regional geological formations, the use of well-recognized rock mass classification methods that characterize rock mass, and understanding of regional and disturbance stress states are essential for the development of mining plans.

The main potential problems of the natural caving mining method are as follows:

1) Geological data. The limitations and inaccuracies of geological data are among the factors that contribute to the risk of natural caving mining.

2) Mineral rock data. The geological exploration drilling data reflects the “line” information of the whole ore body. Based on the comprehensive analysis of the “several holes” of a limited number of boreholes, it is the most critical step to establish a geological model that reflects the entire deposit.

3) Continuity of rock fall. The continuity of rock fragmentation depends mainly on the factors such as the bottom area of ​​the ore, the bottoming direction, the bottoming rate, the stability of the rock mass, the structural characteristics of the rock mass and the decision of the ore control.

4) Collapse block. The ore block size determines the size of the ore bin and the shape of the discharge body, which is directly related to the ore spacing, equipment selection and production capacity.

5) The bottom mining structure. The ore-mining work is completed well, the ore can be released smoothly, and the mine can make full use of the huge advantages of the natural caving method to obtain good economic benefits.

3 Typical case analysis

In the mountains of non-ferrous metal mining company copper mine valley line of large porphyry copper deposit, ore body in the northern section of the upper Proterozoic drop Zhongtiaoshan county roadway group Tongkuangyu metamorphic volcanic rocks, volcanic - gas Liquid-induced sedimentary metamorphic copper deposits. Mine surrounding rock sericite quartz schist, sericite quartzite, quartz and chlorite schist ore-bearing rocks containing non-mine section. The ore-bearing rocks are metamorphic granodiorite porphyry and basic intrusive bodies. The ore body and the surrounding rock are roughly the same, and the northeast tends to the northwest, which is like a layered or lenticular output. The copper ore mine was once a “large and two poor” copper mine, and the mineral deposit type was a metamorphic porphyry copper deposit with volcanic gas-liquid genesis. The geological reserves of the mining area are 320 million tons, the metal reserves are more than 2 million tons, and the average geological copper grade is 0.67%. The associated gold and silver can only be partially recovered in the anode mud, and the other has no recycling economic value.

The copper ore mine began construction in February 1958 and was officially put into operation in 1975. The original method of forced collapse mining with bottom structure is adopted. The annual production capacity is only 800,000 tons, the mining cost is high, and the loss is serious.

Since 1985, the copper ore bismuth copper ore has been studied in the continuous and natural natural caving method in the medium-hard and joint-developed No. 5 ore body, and the finger hopper is used to extract the ore similar to the Climax molybdenum mine in the United States. The program is carried out in a natural caving mining test. After the scientific research of the project such as “Mineral Caving Technology and Equipment Research”, on-site trial production began in October 1989. The production practice shows that the natural caving performance of the ore body is better than expected, but the blockage of the caving is large, the phenomenon of mining and fighting is serious, and the recovery effect at the initial stage of trial production is ignored. (See Figure 2)

Figure 2 mining area recovery sequence

Fig. 2 The mining sequence

The bottoming work of the first mining area of ​​the copper ore mine was started in October 1989. In order to ensure the initial collapse and the continuous collapse, the bottoming strictly followed the principle of pushing from NE to SW. The part of the "opening" of the bottom was selected. The four types of rock masses with dense geological structures in the eastern part of the ore body and some three types of rock masses are carried out and gradually expanded.

Observation and analysis show that under the condition that the ore body joint fissure is not developed and moderately intensified, the mining scheme of using the funnel structure to extract the eel, the high block rate and the serious card fight are normal phenomena. If we learn from the successful experience of foreign countries and use the natural caving method of the trench-type structure and the unearthing equipment to produce ore, the area of ​​the ore-outing port will increase several times, which can increase the block size standard and reduce the block rate. At the same time, the non-track equipment is flexible in mining, which is conducive to controlling the mining and improving the production capacity of the stope.

After the copper ore mine has been continuously improved in technology and production management, and the first natural avalanche method has been applied in China to carry out large-area cover rock mining under high-altitude mining, and significant progress has been made. Since the natural caving mining area was put into operation at the end of 1989, the ore content of copper ore has increased by an average of 400,000 tons per year, and has reached an annual output of 4 million tons, although the world's largest production capacity is 112,000 tons per day. There is still a big gap in the Teigne mine in Chile, but it is the largest in China's underground metal mining, and it is also the only mine in China that successfully applied the natural caving method.

4 Application prospects

Caving method since 1895 in the United States since the advent of Pewabie iron ore, so far, 100 years of history, the international mining industry has accumulated rich experience.

In the 1960s, China began to use the application of natural caving mines. The application of the natural caving method in the copper ore mine to carry out the ore-mining management under the large-area cover of the high-altitude section is the first time in China. The only experience that can be used for the production management of some extra-large mines abroad is that this mining method is largely It also exists at the base of experience. This requires more people to explore and make it more rational and procedural, and people are more likely to master it. The experiment and production of the natural caving method is just beginning in China. In view of the lack of practical experience and the backwardness of management level, the mine cannot blindly choose to apply the natural caving method, but according to the actual situation of the mine, carefully study whether the method can be used. .

references

[1] Yang Dian. Underground mining of metal deposits [M]. Changsha: Central South University of Technology Press, 1999.

[2] Guo Jinfeng. The progress and development trend of mining methods in underground mines in China. Mining Research and Development [J] Metal Mine, 2000 (2): 4-7.

[3] Zhang Shumao. The initial practice of natural caving of copper ore mines [J] Metal Mine, 2003 (2): 12-14.

[4] Shen Yuanhong. The ore mining management of the natural caving method of copper ore mine [J]. Non-ferrous metals (mine part) 2007.59 (5): 14-17.

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