Chuzhou Xin Copper Mining Co., Ltd. (hereinafter referred to as the Langyashan copper) located in Xicheng District Chuzhou City, Anhui Province, adjacent to the Class 4A State Forest Park Langya Mountain Scenic Spot is the core subsidiary of Anhui Langya Mountain Mining Corporation. In 1958, the mine was built. In 2002, it was restructured into a state-owned holding company. At present, it produces ore 300,000 t/a, with an annual output of more than 4,200 tons of copper, 150 kg of gold , 4.2 tons of silver , and more than 10,000 tons of iron .
The Minshan copper mine has small scale, dispersion and high value. With the deepening of mining and the structural adjustment of the production system, in order to ensure the stable production of the mine, the remaining top pillar of the upper middle section needs to be recovered as soon as possible. In recent years, many experts have carried out sufficient research on cementation and recovery of ore pillars [1-2], and have succeeded in most metal mines. For this reason, the Lushan Copper Mine has tested the horizontal approach classification tail according to its actual situation. The sand cementing method is used to recover the top column, which provides guarantee for closing the upper middle section and optimizing the system as soon as possible.
1 Geological overview and technical conditions for top column mining
1.1 Geological overview
The Lushan copper deposit is a typical skarn-type copper-rich deposit. The ore body is distributed in the contact zone between the quartz diorite porphyrite and the Upper Cambrian Lushan Formation in the upper reticulated or strip-like crystalline limestone. Leading edge. The size of the ore body is small and the number is large. The ore body is generally transparent, lenticular, saclike, etc. The plane is extended by tens of meters to more than 100 meters, generally extending from tens of meters to more than 200 m and thickness of 2 to 10 m. The maximum thickness is more than 30 m and the average thickness is 3.2 m. The length of the ore body is generally much longer than the strike and the length of the trend. It is long column-shaped to the northeast direction, and the side angle is 45°-60°. The strike is distributed along the location of the contact zone, and the dip angle is basically eastward.
The surrounding rock of the upper and lower plates of the ore body is basically quartz diorite porphyrite and metamorphic crystalline limestone. It is generally hard, but there is structural fracture phenomenon on the upper plate. It is generally a shrinkage crack after mineralization, and it is formed in the later stage. 2 to 5 m. In the middle of the orebodies with copper-bearing skarn ore types, there are often quartz diorite or veins interspersed with the late lamprophyre, which destroys the integrity of the skarn, especially the softer porphyry veins. There is a safety hazard of rock ore breaking and collapse, which poses a great hazard to the safety of ore mining.
1.2 Top column mining technical conditions
In order to recover mineral resources as much as possible and adapt to the geographical characteristics of the urban-type mines adjacent to the scenic area, the main mining method of the Lushan Copper Mine was changed from the empty field method to the upper layered tailings filling method. Due to the large number of ore bodies and complex structure, a single ore body is generally used as a recovery unit. At the mining level, the mining project is designed with a single ore body as the object. After the construction of the mining project is completed, the inner edge of the mine is constructed, and then the ore body is pulled open to the side (if the thickness of the ore body is large, according to the site situation, the mining site has It may be necessary to leave a security pillar.) After the mining of the first layer of the ore body, in order to recover the top column of the lower middle ore body, a 50cm thick reinforced concrete floor should be laid on the floor of the layered stope as the roof of the lower middle section. When the top column is recovered, the bottom column bottom is a stope filling body, and the top plate is a reinforced concrete false roof.
2 horizontal approach classification tailings cement filling method typical scheme
The mining top column can be fully harvested in one section by normal stratified mining mode, and the stripping cement can be used to fill the inlet type. Because the mining of the top and bottom sections of the ore body has been recovered, the original rock stress of the stope has been redistributed, and the stress state of the top column is more complicated. Following the principles of safety, reliability, economic rationality, and technical feasibility, and drawing on the successful experience of similar mines, the selected horizontal approach graded tailings cementing filling method was used to carry out the top column recovery test.
2.1 Approving arrangement
According to the occurrence state and safety condition of the ore body, the top column should be used as an extraction unit for the design after the last layer of mining. The mining time is mainly the engineering design of slope roads, mining roadways, filling small wells, especially the division of the road, including the width, length, direction and recovery sequence of the approach. Emphasis is placed on the use of original mining projects to reduce the number of new acquisitions. Among them, the division of the approach is particularly important. A reasonable approach to the division can not only ensure safe recovery, but also achieve good economic benefits. The route division should be considered from the following three aspects.
(1) Access geometry. According to the research of related scholars, the stability of the approach mainly depends on its own bearing strength. The false top is bent under the action of horizontal stress and vertical stress, and the damage occurs when the stress reaches the critical value of the strength [3]. The artificial false roof of the Lushan Copper Mine is a 50cm thick reinforced concrete with the designation C15. According to the relevant research data of the approaching mining method and the safe thickness of the top pillar roof [4], the access width should be within 5m (3, 4, 5m). The length should be within 30m.
(2) Route arrangement. The approach is generally arranged along the strike or vertical direction. According to the actual situation of the ore body and the existing available project, the stopway approach is flexible, with single approach, double approach and multiple approach. One or more of the ore bodies are less than 6m thick, and two or more are arranged larger than 6m.
(3) The order of recovery of the approach. Generally, the backward type is adopted, and the interval is adopted when paralleling each approach, and the way is generally numbered in numerical order (as shown in Fig. 1). According to the principle of pressure arch [5], firstly, the odd-numbered roads such as 1# and 3# are taken back. After the end of the mining, the graded tailings are filled and filled to fill the tapping top, so that the filling body has sufficient strength to ensure the subsequent recovery of mining, and then back mining 2# Even roads such as 4# are generally filled with tailings or waste rock, requiring full topping. This method returns to the top column, and each approach has support around the recovery, which is safe and reliable.

2.2 Prepare the construction sequence before mining
After the end of the last layer of mining, the structure is normally raised and filled, and the space of about 2.5m is reserved. The preparation work for the top column is as follows: 1. Filling the small well according to the design and construction (for the filling of the road), the specification is 2.0m× 2.0m; 2 In order to improve the mining strength of the pillar, the WGD-1 electric scraper is generally used for mining. Therefore, the slope is leveled under the plane roadway in the upper middle section of the pillar, and the slope level is 3 .0m×2.5m, the slope is generally determined according to the performance parameters of the scraper (≤13°); 3 construction funnel, try to use the original mining hopper brush to clean, fill the ore after the brush is finished, such as using the original funnel, the funnel should The top of the shovel is about 1.5m, which is convenient for the pouring of the funnel. 4 The funnel that continues to be used rises normally to the height of the bottom of the top column. The unused sidewalks and funnels are closed with concrete. 5 pairs of empty areas are filled. After filling 1.5m tailings, 1m remains. The space is filled with graded tailings cement to make the cement body fully connected. The ratio of cement to sand and sand is 1:4, and the compressive strength of 28d is required to reach 5MPa. 6 After the filling is completed, the construction will continue from the slope to return to the mining lane (according to the approach) Layout settings
2.3 way back mining
After the mining project is in place, the approach is taken in accordance with the design sequence.
Generally, the odd-numbered approach is adopted first, and the conditions of the stope can be constructed at the same time: 1 Use the YT-28 rock drill to construct the 3.0m×2.5m section to cut the well until the end of the approach; 2 brush to The design boundary of the approach; 3 way to reduce the roof to the reinforced concrete false roof, pay attention to the false roof protection during construction, prevent the blasting damage to the roof; 4 use the WGD-1 electric scraper to quickly mine.
2.4 filling
After the ore is finished, it should be filled in time to shorten the empty roof time: 1 use reinforced concrete wall to close the approach, set the water filter tower in the middle of the approach; 2 use the graded tail sand cementation to fill, the cement body lime sand ratio is 1:4, 28d compressive strength requirement to reach 5MPa; 3 filling requirements to fully top, can be replenished after 24h after one filling; 4 according to design requirements and the actual situation of the top plate can be properly adjusted, even numbered approach after general recovery Fill the tailings with a single fill.
2.5 Security Management Work
Top of pillar recovery and security situation in the environment than mining stope recovery time difference, especially top slate stone complex mechanical state, the situation is unclear roof structure, in the construction process be careful. It is necessary to promptly consult the top board problem, analyze the reasons according to the actual situation, and determine the follow-up work.
2.6 ventilation
When the cutting of the road is not connected with the filling well, it is generally a single heading. If necessary, the local fan can be used to enhance the ventilation.
3 exploration in the mining of pillars
Due to years of mining, the upper middle section of the Lushan Copper Mine has entered the top column recovery stage. In order to safely and efficiently recover the top column, engineers and technicians conducted some useful explorations:
(1) The use of electric rafts and T2G mining, eliminating the construction of slopes. In the preparation work of the top column, choose the right position to pick the top, to ensure that there is enough working space when the top column is returned, to prepare for a large number of quick recovery of the post column, and save a lot of mining engineering.
(2) The problem of filling and topping has always been a difficult problem in the filling work. The filling is strengthened through the construction drilling to the approach, the small well is found on the uphill slope, and the position of the small well is higher than the top plate; after the completion of one filling, the measures are added after 24 hours. To ensure that the filling body is fully attached. By actually revealing the filling body, the filling top rate can generally reach more than 60%.
4 Conclusion
(1) The Lushan Copper Mine adopts horizontal approach classification tailings cementation filling method to recover the top column, and has safely recovered 200,000 tons of pillars, and the recovery rate of the top column is above 90%.
(2) In the top column recovery process, because the top column is in a complex stress state, it must be “fast”, strong, strong, and fast.

(3) The mining environment of the top column is complicated. Before the construction, the actual situation of the roof of the pillar should be mastered, and the mining design should be carried out according to the safety condition of the stope. According to the position map of the roof of the stope, when the two approaches are close to the upper and lower plates, the design cannot be designed to the side. As far as possible, the continuous pillar of about 1m is reserved as the roof support. According to the safety situation, some high-grade ore can be recovered at intervals. , grasp the order of the top column.

(4) Timely mining of the top column after the mining of the mining house is completed, which not only benefits the safety management work, but also saves the mining project. Timely recovery of the top column is conducive to the optimization of the mine system and the sustainable development of the mine.
references
[1] Wang Yunmin. Modern Mining Handbook [M]. Beijing: Metallurgical Industry Press, 2012.
[2] Wang Xinmin, Gu Desheng, Zhang Qinli. Deep well mine filling theory and pipeline transportation technology [M]. Changsha: Central South University Press, 2010.
[3] Zhao Fujun, Li Xibing, Zhao Guoyan, et al. Stability analysis of the artificial false roof of the top mining column with access method [J]. Metal Mine, 2002 (4): 27-29.
[4] Hu Wei, Zhou Aimin. Numerical analysis method for the safe thickness of the roof of the top mining column with access method [J]. Mining Research and Development, 2001, 21(2): 14-17.
[5] Zhang Chunfang. Feasibility demonstration of cement filling and mining method mining column [J]. Mining Technology, 2014, 14(1): 9-13.