Optimization of combined mining of pits and dews in Dahongshan Iron Mine

Dahongshan iron ore reserves of geological exploration eligible 450,000,000 t, the ore body 71, the spatial position of the ore staggered form multilayer interbedded output. Mine at the end of December 2006 reached underground 4 million t / a mining scale, expand the overall planning and construction in 2007, a comprehensive open-air mining shallow lava iron ore, copper ore belt # 1, â…¢ ~ â…£ ore body, â…¡1 ore 720m Ore body above the elevation. After the completion of the end of 2010, a new pattern of resource development for multi-segment, time-space simultaneous mining and comprehensive utilization of low-poor ore bodies, such as open-pit mining and underground column-free sublevel caving, open field method, and upward stratified filling method, has been formed. The deep comprehensive utilization of resources has been realized, and the overall mining scale has reached more than 12 million t/a, but at the same time, the mining relationship has become very complicated, bringing many new mining problems.
Key issues of joint mining and pit mining
1.1 exposed mining pressure
The Dahongshan open-pit shallow lava iron ore is located on the northwest side of the upper part of the deep underground iron ore. With the expansion of the underground caving method, it will affect the upper open step and cause a large amount of resources to be recovered. According to the preliminary design plan, the 4 million t/a pit mining will transition to the 400 m elevation below the twelfth year after commissioning, and the shallow lava open-pit iron mine will complete the rescue mining of resources before this. But in the actual production process, due to the constraints and factors influencing the amount of capital investment and capital operation efficiency, so that the mining schedule subject to greater influence. At the same time, in order to meet the requirements of the steel market for raw material quality, the underground ore body has accelerated the mining speed, and the time for the transition of the 4 million t/a pit mining project to below 400 m elevation has been advanced by 2 to 3 years, resulting in a contradictory relationship between the originally tight pits. To stand out.
1.2 mining is not guaranteed to increase
Due to the restrictive influence of the pit dew, the safety pillars in the underground were determined according to the design of the 65° moving angle circle in the early stage. The northern part of the ore body below 420m was almost crushed in the deep part, and the continuous mining production of 300-400m of the mine was achieved. 25 million tons or so. As a result, the underground working face and output can be greatly restricted, and the mining is not guaranteed. According to the mining capacity of 4 million t/a or more, it will not be able to continue production after 3 to 4 years.
1.3 Deterioration of economic efficiency
Since 2014, the mining industry has faced a new situation in which the mining price has fallen and the market is sluggish, while the geological grade of open-pit mining iron ore in the shallow lava is about 20% (the marginal grade is 13%), which is lower than the national industrial use grade and the magnetic iron occupation rate. Less than 40%, the technical and economic indicators of mineral processing are not ideal, and the selection ratio is large, resulting in low output, high cost and deteriorating economic benefits.
1.4 Restricted waste sites
The waste rock yard in the early stage of the mine was basically full. The Xiaomiaogou waste rock yard planned in the early stage could not be invested and built due to the deterioration of operating efficiency. There is not enough waste rock site to meet the needs of open-air discharge, and the production and operation are worse.
2 pit and dew combined synchronous mining optimization
According to the monitoring data of the underground collapse and subsidence of the Changsha Mine Research Institute and the theoretical speculation of the interaction between the Maanshan Mine Research Institute on the contradiction of the pits, combined with the actual problems, the mining optimization ideas are proposed in four aspects: First, combined with self-production Since the surface movement caused by underground mining, the movement angle has been reasonably adjusted, the boundary of the underground mine is re-delineated, part of the ore is released, and the contradiction of the pit is relaxed; the second is to rationalize the relationship between underground mining and realize the safe mining of pits and the smooth transition in the future. Third, combined with the current market and dumping conditions, optimize the open-pit mining realm, while reducing the loss of mining operations, accelerate the progress of open-pit mining, and eliminate the conflicts as soon as possible;
The ore outside the realm is rationally planned and mined to ensure the comprehensive utilization of resources.
2.1 Underground mining movement angle adjustment
In combination with the “Pit and Lulian Mining Integrated Mining Technology” of Maanshan Mine Research Institute, by superimposing the current situation of underground empty space and surface cracking, it is inferred from the spatial relationship of each mining area and the mining situation that the surface cracking range covers the underground. The main mining area, the middle II mining area and the south wing mining area of ​​the caving method are directly above. At the same time, because the main mining area has been connected with the south wing mining area, the middle II mining area is also connected with the south wing mining area in the vertical direction. Combined with the surface subsidence monitoring data analysis, it is believed that the main impact on the surface cracking and sinking is Underground main mining area, south wing mining area and medium II mining area. Comprehensively analyze the mining status of the main mining area, the south wing mining area, the middle I and middle II mining areas and the distribution of the goafs, and compare the current surface cracking status. Select the typical horizontal and vertical profiles in the collapsed area, and compare the different sections. Crack angle (collapse angle). The angle between the underground area of ​​the subsided area and the surface crack affected by it is greater than 76° (especially near the side of the slope), which can be approximated as the underground goaf of the Dahongshan Iron Mine, causing the rock to expand and expand to The ground surface forms the collapse angle of the crack. The research indicates that the future 400m level and the second stage mining will mainly develop to the southwest direction, and the surface cracks and collapse areas will also develop to the southwest direction. The collapse status has gradually stabilized, and the 70° can be selected as the moving angle for the adjustment of the ore range. safety.
Therefore, combined with the actual further analysis, from the perspective of underground mining, in order to facilitate the coordination of production organization, ensure the integrity of the reserved pillars, and reduce the contact surface of the recovered pillars in the later stage of the pillar, it should be bounded by the A36' line, A36' The east ore body is relieved of pressure and mining restrictions. In the west of A36', a 20m protective belt is reserved for the upper top line of the open air, and the northern part of the main mining area is bounded by a 70° moving angle. According to this principle, the ore boundary of each section of the underground is re-circled, and the ore body of the underground A36' is released. The continuous release of mining area above 300m is about 12 million tons, which alleviates the restriction of open pit mining.
2.2 The rationalization of underground mining
In order to coordinate the relationship between pit and open mining during the restricted period of open pit mines and the relationship of underground mining after the release of open pit mines, the mining sequence of continuous production in underground mines is reasonably planned, and the mining relationship between crushed and uncompressed mines is coordinated.
From the space, the vertical height of the unpressed ore should be reasonably controlled to avoid the obvious ground pressure phenomenon. The north-south direction between the upper and lower sections is divided into strips staggered, and the mining is continued in sequence, which is beneficial to equipment and personnel. Coordination and production organization between sections, strips, and production efficiency and production balance requirements. Through analysis, the following sequence is used to refine the order of continuous production mining in the underground:
(1) Continuous production mining area should be left in the early stage of mining, and the unpressed part should be used in conjunction with the mining of other areas to ensure the overall output of the mine.
(2) Coordinating and arranging the mining relationship between the crushing part and the unpressed ore. With the decline of the mining section, the area of ​​the crushing part is getting larger and larger, and the area of ​​the unpressed part is getting smaller and smaller. The time of mining, the overall output of the mine will not be able to ensure, after the mining of the ore portion, the initial production is also small, therefore, planning mining part of the mining
The time is 2022, that is, the open pit mine must end mining within 6a.
(3) The ore-mining part should be strongly harvested according to the section, and the mining sequence of the upper and lower sections should be balancedly controlled (Fig. 1) to reduce the height difference of the ore-mining part, and also facilitate the coordination of equipment, personnel and the inlet and return air passages to achieve balanced production.

(4) In order to avoid the safety problem and dust pollution of the upper and lower sections simultaneously using one slide unloading, the order of mining between the upper and lower sections should be divided into strips according to the joints of the horizontal north-south direction (divided from north to south) ), staggered back.
(5) In order to meet the production scale requirements, each section needs to be arranged with a cutting trough to arrange for multiple sections of the uncompressed ore part to be harvested at the same time.

(6) The strips of the segmented troughs under the upper section are subject to priority de-mining.

(7) In the process arrangement, it is necessary to realize deep hole drilling, blasting and mining to maintain a reasonable front-rear relationship, and the close operation of each process in the work area to avoid cross-influence and improve efficiency.
2.3 Optimization of open pit mining
2.3.1 Realm Optimization Program
The previous realm optimization program uses 3DMine mining software to establish a lava rock deposit model. According to the current technical and economic conditions, the economic value of each unit block in the model is calculated and selected according to the economics of mining. Mining realm.

Taking the average price of the company's iron concentrate products as the benchmark price in 2015, the calculation is based on the reduction of 5%, 10%, 15%, 20%, 25%, and 30%, respectively, and it is concluded that when the price decline is less than 20%, the optimization is made. The realm of the economy is feasible; when the price drops by 20% and above, it cannot be economically exploited under the current technical and economic indicators.
Under the benchmark price of economic optimization, the ore volume in the realm is about 31 million tons, and the amount of stripping is about 13 million m3. The ore in the boundary can be considered for one-time mining or staged mining according to the earth drain capacity. Among them, the production capacity is verified by the average descent speed and the number of excavators that can be arranged, and the one-time mining can reach 5.5 million t/a. Due to the small size of the transitional boundary, the staged mining can only reach 4 million t/a. In combination with the requirement of safe extraction time of pit dew, it should be considered as one-time mining.
By optimizing the open-pit mining boundary, it can meet the safety requirements for the end of open-pit mining in 6a, and basically coordinate with the underground arrangement in time, so that in the second half of 2022, the underground part of the underground can be recovered in time to adjust the moving angle, and the part of the ore is still pressed. 320,300m section of collaborative mining, 2027 pressure part of the mine fell to 320m elevation, and then with the uncompressed part of the coordination to a smooth transition below 300m.

Through optimization, the amount of stripping and stripping is greatly reduced, avoiding the construction investment of new dumping sites, and achieving economic and rational mining under the conditions of sharp drop in international mining prices. In accordance with the requirements of the comprehensive utilization of national mineral resources, it is still not possible to abandon the ore outside the boundary, and more economic and rational mining plans must be considered.
2.3.2 Implementation steps for further downward price of the mineral price
As the price of iron ore continues to decline, according to the realm optimization plan, when the benchmark price falls by 20% or more, it cannot be economically exploited. In the early stage, the contract price negotiation with the outsourcing mining unit did not reach an agreement and the open-pit mining was suspended. The next step was to organize the implementation according to the optimization plan. When the open-pit mining was resumed, if the price dropped by 20% or more, the abandoned mining is not necessarily the optimal solution. The total amount of fixed assets sold in the previous period was compared with the total loss of abandoned investment, and the implementation steps were improved. In the first step, the analysis does not add new stripping, and the direct mining in the early stage. In the second step, according to the optimization realm, the slope angle is appropriately adjusted under the premise of ensuring safety, and the stripping is less, and the cut-off grade is re-circulated according to 20% or more, and the production operation is arranged. Plan, strive to improve the quality of the ore supply, and consider the waste stone pre-disposal treatment, crushing to form the sales of building materials; if the first step and the second step are not feasible, implement the third step, that is, further improve the cut-off grade and re-delineate The ore body, research and utilization of high-grade ore bodies according to the occurrence of ore bodies; if the above is not feasible, the fourth step will be considered to increase the scale of underground and low-grade ore, completely replace the production of low-grade iron ore in the open, and fully release the underground Partial production capacity of the ore.
2.4 The ore outside the boundary is planned and mined in advance

The mining plan for ore outside the boundary is based on the principle of ensuring simultaneous ore mining and non-influence of the ore inside and outside the boundary. The final optimized optimization boundary line is 30m to the southeast as a safety protection zone for the open-air steps, except for the 30m protective belt to the original underground mining III2- 3 The ore planning in the western section is to optimize the underground mining in the early stage outside the boundary, and the ore in the 30m protective belt will be used for mining later.
In order to make full use of the original underground mine ore body system engineering and channel planning to optimize the underground ore mining in the early stage to save investment and reduce mining costs, in the early stage, through the improvement of relevant geological data and raw goaf data, the surrounding tunnels will be supplemented on the flat section. Combined with on-site implementation of goaf, transportation and return air system, hydropower use conditions, etc., the initial mining plan is proposed, and the mining plan is completed by refining the relevant technical economy and cost indicators.
The ore mining plan outside the boundary is combined with the status of the abandoned mining area around the ore and the need for protection of the open-air steps. After many demonstrations, the house-column method is used for mining, and the deep mining range of the well in the next few years is planned, combined with the collapse of the previous downhole. The study analyzes the impact of underground mining on the ore outside the real estate in the next year and is expected to be affected to varying degrees after 2 years. In order to improve the comprehensive recycling level of resources, it is necessary to carry out rescue mining of ore outside the boundary. Combined with the underground mining system near the ore outside the boundary, the original II5 ore body 835,775 segment of the tunnel is complete and reliable, and the short-term analysis of the western section is not affected by the deep underground mining, planning to use the 775m section of the western section to the surface of the channel As the main channel for air intake and transportation, the passage from the west section of the 835m section to the surface is used as the return air passage. At the same time, it is convenient for each section to mine. The auxiliary slope of the mining area is set in the middle of the ore body as the vehicle, personnel, material in and out and The main transportation channel for ore and waste rock.
Through optimization, the amount of iron and copper ore that can be produced in the early stage is more than 25%, the copper grade is about 0.4%, and the ore mining cost is 42 yuan/t. The comprehensive cost of concentrate mining is 348 yuan. /t, still economically viable at current mine prices. At the same time, the implementation of ore mining planning outside the boundary is a necessary condition for realm optimization. Joint implementation can take into account the contradiction between the pits and the comprehensive utilization of resources, and promote the safe and sustainable production of open pits and underground wells.
3 safeguards
In order to ensure the effective implementation of the scheme, a 60m wide platform is reserved as a safety buffer platform in the open 1000m steps, and the rock mass quality characteristics and rock structural planes of the open upper east slope are tracked and analyzed, between the open slope and the underground collapse area. Set observation points, carry out mobile deformation monitoring, use the III2-3 ore body mining tunnel to set stress and displacement monitoring in the northeast side of the well, etc., to provide a guarantee for the rational implementation of pit and dew mining technology.
4 Conclusion
In view of the problems of the slow mining of open pit mining, the prominent contradiction of pits and the inadequate selection of mining in the Dahongshan Iron Mine, combined with the actual situation and overall consideration, four technical optimization ideas were proposed and the implementation plan was formulated, including the adjustment of underground mining movement. Angle, rationalize the relationship between underground mining, optimize the open-pit mining boundary, and plan the ore outside the boundary in advance. The system considers the time and space relationship of mining, economic and safety, and solves the key problems. It can realize the fastest to shallow lava open air. The implementation of rescue mining in iron ore can ensure that the mining volume of pit mining meets the production needs and maximize the comprehensive utilization of mineral resources.