Scientific and reasonable measures for the early stage of ferrous metal mines to open underground mining

At present, most black metal open pit mine will soon face problems caused by open underground mining. There are many new technical problems encountered in the transition from open pit mining to underground mining, and how to achieve a smooth transition during the transition is the main concern of enterprises. The main problem of a smooth transition is the convergence of production, including the integration of mining technology and technology, the transformation of safety management technology and the transformation of mining production management methods. Tangshan Iron and Steel Shirengou of iron ore is mined from open pit to underground iron ore mine earlier, from 2000 to proceed with the underground mining of the open-air building, after the construction of an underground turn, and the current second phase of construction to expand the scale Phase III Construction. During the transition to underground mining construction, the mine has basically achieved a smooth transition, and the output has remained basically stable. The main means to achieve this effect is that the mine has adopted a series of scientific and reasonable measures before and during the construction.

I. Introduction to Tangren Shirengou Iron Mine

Tangshi Shirengou Iron Mine is an open-pit iron mine that was completed and put into operation in 1975. The construction scale is 1.5 million t/a. Before the construction, the mine was planned to be divided into two phases according to open-air and underground, and the open-pit mining was carried out in the early stage. Underground mining. Open-pit mining until 1999, the ore reserves in the realm have been basically completed, and it is urgent to transfer to underground mining. Because the market price of iron ore was too low at the time, the optimal period of transfer to underground mining was delayed, and the mine faced an imbalance of production. Passive situation. In 1999, the amount of ore in the open-air boundary was only over 2 million tons, and the construction of underground engineering has not yet begun. The construction period of underground engineering construction is generally 4 to 5 years. It can be seen that the mine maintains a production scale of about 1 million t/a. difficult to realize.

At that time, the area of ​​the 18th to 28th lines of the open mining area of ​​the mine was over, and the open mining of the north area of ​​the north line of the 18th line to the 5th line was still in progress. The whole mine is 2. 8 km from south to north. It is divided into 3 mining areas during open pit mining, 28 lines to 18 lines for the south area, 18 lines to 8 lines for the middle area, and 8 lines to the north. There are mainly four layers of ore bodies in the mining area, which are distributed in strips in the north and south, and the M ₂ ore body is the main ore body. The geological reserves of the mine are 233.4 million tons, of which the industrial reserves are 94.05 million tons, and the prospective reserves are 139.34 million tons. The underground reserves are still very rich, but the underground construction has not yet been carried out. The mine ore mainly magnetite, average grade of TFe31.13%, easy to wear and easy ore selected from iron concentrate grade of 68%, low sulfur, phosphorus content. The mining area is a monoclinic structure, and the ore body is inclined to the west with an inclination of 50°-70°. The development of fault structure in the mining area has a great impact on the ore body. The main faults are three with F18, F19 and F8, which brings great difficulties to underground mining. The thickness of the M ₂ main ore body in the mining area is 3 to 40 m, the ore body in the southern area is thinner, and the ore body in the north area is thicker. The orientation of the ore body varies greatly along the strike and tendency, and there are many branches and complex and sudden pinch-out phenomena, and the occurrence situation is complicated.

Second, the level of transition measures

Under the situation that the production situation is very passive, the Shirengou iron ore mine has developed a series of measures to facilitate the production connection, balanced production, and smooth transition. The production balance has been achieved, and the open-air and underground mining have been initially connected and smoothly transitioned.

(1) Sub-stage underground mining

Under the passive situation that the open-pit mining is about to end the underground mining just started, it is impossible to achieve production balance and output convergence according to the underground mining in the whole mining area. Therefore, it is necessary to study and formulate a feasible underground construction plan.

The study believes that the construction of underground mining should be carried out first from the southern area, and it should be transferred to underground mining in stages. This will help avoid the interaction of open-pit mining and underground mining, and will help shorten the mining time in the initial stage of underground mining. The mode of development is the single-wing ventilation arrangement of the central shaft in the lower plate. The construction scale is set at 600,000 t/a. The open-pit bottom of the open-pit mining in the southern area ends at 17 to 24 m, and the first mid-section of the underground mining is determined to be -60 m for the first middle section, 0 m for the return air level, and the ore reserve in the middle section of the first mining is 5.87 million tons. The mining method adopts the empty field method. This method is mainly used to maintain the isolation layer between open pit and underground mining, that is, the boundary pillar and the safe roof pillar for underground mining. This is beneficial to avoid the interaction between the open and the underground. Make underground construction and mining safer. Because the ore body in the southern area is thin, it is not suitable for large-scale mechanical mining. At that time, the ore market price was very low, and the investment should be controlled as much as possible. Therefore, the shallow hole retention method with less investment, quick effect and lower cost was selected. The investment is 72 million yuan. The construction of the first phase of the underground project from July 2000 to August 2004, after four years of construction, reached the conditions for the production of mines. During the construction period, the middle section of the vein is used, and as much as by-produced ore is used as much as possible, and the first part is qualified in the conditional part.

The formulation and implementation of the above measures have realized the simultaneous development of open-air production and underground construction, shortening the construction period and achieving the purpose of early mining of underground mining.

(2) Measures to increase underground mining

In order to increase the production capacity of underground mining as soon as possible, and to achieve the connection between open-pit and underground mining production, the mine has studied and formulated the construction plan for increasing the number of wells during the construction of the underground project. A measure well was drilled at the 46 m level in the northern end. The measure well is a shaft, and the mining area is the ore body in the north of the 6th line and the slope in the north area. The ore body above -60 m level is designed and mined, and the ore reserve is 730,000 tons. The construction of the measure began in October 2003. By April 2004, it began to produce by-product ore. By August, it had officially produced ore, which achieved the short construction period and quick effect. The measure well project has an investment of 4.8 million yuan, and the annual mining capacity has reached more than 150,000 tons, effectively supplementing the ore output during the transition period.

(3) Arranging the second phase of underground construction in due course

The open-pit mining in the north of Shirengou Iron Mine was in 2003, and it has the conditions for underground construction in the North District. Therefore, the research and development plan for the underground development of the North District was developed.

In order to shorten the construction period, try to use favorable terrain and conditions to carry out underground construction in the north area. On the upper step formed in the open mining area, select the appropriate position to construct the inclined shaft, and adopt the inclined well development plan in the pit to mine the ore body between 16 and 6 lines in the north area, and the area of ​​the north area. The ore reserves are 6 million tons. The characteristics of the ore body in the northern area are relatively large, the hydrogeological conditions are simple, the amount of water inflow is small, and the impact of faults is small. The construction of the project has been completed and put into operation from October 2003 to August 2005, realizing the underground mining as soon as possible in the North District.

(4) Slope ore body mining

In order to supplement the ore production as much as possible during the underground mining construction, the mine research has developed a slope residual recovery plan.

There are still some residual ore bodies in the slope outside the open-air boundary. During the transition period, the part of the ore body can be recycled. The mine research developed a slope ore recovery program. The amount of ore remaining in the slope of the northern area is 1 million tons. This part of the ore is safely recovered, effectively supplementing the insufficient production of the open-air to underground over-current period.

(V) Expanding the scale of construction

According to the development of iron and steel raw materials by Tangshan Iron and Steel Co., Ltd., Shirengou Iron Mine started its three-stage expansion of mining capacity construction in 2005. The scale of mining capacity building is 2 million tons of iron ore per year, and the project is scheduled to be completed and put into operation in 2010.

Due to changes in engineering geological conditions, the construction of the third-phase expansion of mining capacity engineering is more difficult, resulting in the lag of the project. In order to complete the construction on time, the mine has optimized the construction soil, that is, prioritize the construction of major projects that affect the ability to form the system in the third phase, such as the main and auxiliary well lifting systems, underground power supply, drainage, ventilation, main transportation system, etc. So that the construction of the third phase of the project will reach the system capacity on schedule and realize the early production of mines.

In addition, the construction measures well plan was also developed. The program has increased the construction of two measure wells at the -60m level and the location of the bottom hole yard near the -180 m level in the north and south regions. Using these two measures wells, the speed can be accelerated. m well bottom yard and various diverticulum construction, and can make a 180 m level and -60m level through to form ventilation conditions. The two measures wells are the main construction measures to speed up the construction of the third phase.

After the construction of the three-phase expansion project and the overall optimization of the construction plan, the project can be completed and put into operation according to the predetermined target, and will reach 2 million tons in 2012 as planned.

(6) Recovery of pillars, treatment of empty areas and formation of overburden

The first and second underground works of Shirengou Iron Mine are developed according to a middle section, that is, from the 0 to -60 m level (south area) and the level of -16 to -60 m (north area) of the open bottom, mining-60 For ore bodies above the m level, the ore reserves in the total mining area of ​​the first and second phases are 12 million tons. The mining methods all use the shallow hole retention method, and all of them have a safety top column, that is, a boundary top column. The retention of the top pillars of the boundary is mainly to avoid the mutual interference between the open pit and the underground mining, so that the open air and the underground can be constructed at the same time, effectively preventing the flooding of the open air from flooding underground. The combined production capacity of Phase I and Phase II is 1.3 million tons, and the service period is 6 years, that is, the mining is completed by 2011. The third phase of the expansion of underground mining scale project development is based on two large and medium-sized sections, developing two large and medium-sized sections of -180 m and -300 m, designed according to the height of 120 m, and the industrial reserves within the scope of development are 45 million tons. The age is 20a. The third phase of construction selected advanced mining methods and completely changed the mode of miniaturization and artificialization of the first and second phases of construction. The mining method uses a bottomless column collapse method that requires the formation of an overburden. The problem of pillar recovery and empty area treatment in the first and second phases of mining should be considered in a unified manner with the formation of the three-stage caving method. From the time and space, it should be studied and formulated to solve the unified solution. At present, the national “Eleventh Five-Year” science and technology support project, which is based on the Shirengou iron ore mine, has been launched. The key technology research on the smooth transition from open pit to underground mining has been launched. The main content of the research is to solve the stone man The mine's pillar recovery, empty zone treatment and overburden formation problems. Formulate a practical plan to make the first and second phases of the mine’s underground mining and the third-stage expansion of mining scale

The convergence of the benefits to achieve safe and efficient mining. After the smooth transition and connection of the first, second and third phases of the Shirengou iron ore mine, it can be considered that the smooth transition between the open and the underground is realized, because the open and underground marked isolation layer, that is, the boundary pillar has not been processed. Only by dealing with this transitional layer can it be called a smooth transition from open-pit to underground mining in the true sense. Therefore, a lot of work needs to be done in the later stage, and its technical work will be more complicated and difficult. Therefore, the program measures that have been studied in this study are only the preliminary research of the smooth transition. In the later period, the research will continue through the “Eleventh Five-Year” science and technology support project, with a view to making the smooth transition problem finally solved.

Third, the implementation effect of the preliminary measures

The first phase and the second phase of the Shirengou iron ore mine transition to underground mining. From 2004 to 2007, through the implementation of the above measures, the ore production during the turning period was effectively supplemented, and the ore was avoided. The output dropped sharply, and the production and operation of the mine proceeded smoothly, and a smooth transition was achieved in the early stage (see Table 1).

Table 1 Ore production of Shirengou iron ore from 2004 to 2007

Through the analysis of Table 1, from 2004 to 2007, the first phase and the second phase of underground engineering mining accounted for 43.96% of the total mined amount in 4 years. If only relying on this to maintain mine production, it is not enough, it will cause The mine output has fallen sharply, and measures have been taken to mine, the slope is remnant and the open-air residuals have been used, so that the annual ore output of the mine is maintained above 850,000 tons, and the iron concentrate production is maintained above 300,000 tons. And slope mining has clearly played a very good role in supplementing minerals.

On the other hand, the first- and second-stage underground mining has not reached the designed annual output of 1.3 million tons in 2007, and the actual mining has just reached 710,800 tons. The root cause of the failure is the low level of equipment. The low efficiency is also the main reason for the decrease of the underground ore body. In order to improve the underground mining capacity, the mine adopted several important measures to increase the ore mining in 2008, so that the ore production in 2008 and beyond will be achieved. Gradually increase, it is expected to reach 200,000 tons in 2008, 1.4 million tons in 2009, and 1.6 million tons in 2010. According to the newly-developed five-year plan of the mine, the mine will reach a mining scale of 2 million tons after 2012. To achieve this goal, the mine still has to do a lot of work, mainly to solve the problem of recovery of pillars in the first and second phases of mining, the problem of empty area treatment, how the transition layer is mined and treated, and how the cover layer is formed. The national “Eleventh Five-Year” Science and Technology Support Research Project has started, and the research of this topic will help solve the problem of smooth transition of Shirengou Iron Mine in the later stage and the scale of production of 2 million tons of mining.

Fourth, the conclusion

(1) In the early stage of the Shirengou iron ore mine, the development of a series of measures was carried out in the open-air to underground mining, so that the mine achieved a balanced ore production and stable production and operation, and the measures were balanced and stable for the production of open-pit to underground mining. The transition is very important.

(2) Measures for open-pit mining to underground mining and implementation during the transition period can achieve less investment and quicker results.

(3) During the transition period from open-pit to underground mining, the potential of residual ore bodies outside the open-air boundary should be fully exploited, and measures to exploit open-pit mines and slope ore bodies can help solve the problem of insufficient ore during the transition period.

(IV) There are still a lot of problems waiting for research and solution in the later stage of Shirengou iron ore mine. The main problems are the recovery of pillars, the treatment of empty areas and the formation of rock formations, so that the mine can smoothly achieve a smooth transition.