The mining area is located in the northern foot of the Wutai Mountain Range. The northern part of the Wutai Mountain Uplift Area, the Niangniang will be turned to the Gobi Ping Complex slant of the North Slope. The ore body is a thick continuous ore body with a thickness of 100m-250m and a strip length of 2680m. The Dahegou section is 780m, the width of the excavation is 46m, the average thickness is 109.77m, and the ore body elevation is 1940m~2140m. The control depth is 66m~80m. The ore body has an inclination of 50° to 60°. The ore body is not buried deeply, and the bed is exposed on the surface. The geological reserves are 135.504 million tons, the average geological grade is TF31.07%, and the mine design production capacity is 600,000 t/a.
A, mining conditions Mine ore mining rock is hard, dense and difficult to weathering magnetic iron quartzite, good stability properties. Ore body and surrounding rock with stone mainly amphibolite schist, green clay quartz schist, amphibolite rock, with its fresh and unweathered rock are among the dense rock hard, good solid performance. The hardness of the above-mentioned various types of rock is (10~12) degrees, and the ultimate compressive strength is more than 1000kg/cm2. According to the engineering geological survey norm, it can be classified as the second type of massive rock. According to its topography and landform, there are many steep slopes and cliffs in the area, and there is no large fault structure in the area. The ore body has large thickness and good continuity. Therefore, the engineering geological conditions of the mining area are simple. The mechanical properties of ore and surrounding rock are shown in Table 1.
Second, the program design
(1) Determination of the final slope angle of the open pit in the open-pit mining boundary: the design refers to the similar mine data and refers to the mining technical conditions, the final slope height, and the mining process to determine the final slope angle of the open pit by 50°. design. Determination of mining depth: The mining depth is mainly determined by reference to the reasonable economic stripping ratio of the mine, the exploration degree of the ore body and the amount of minerals delineated. Due to the low level of exploration in the mine, the open-pit mining boundary is mainly used to delineate the 122b and 333 ore bodies. The amount of minerals to be demarcated this time is within the range of 15 years or so. The reasonable economic stripping ratio of the mine is calculated to be 5t/t (4.1m3/m3). After delineation, it is determined that the lowest mining level of mine 3 line to 1 line is 1920m, and the lowest mining level of line 0 to 2 is l980m. The minimum mining level of the 4-line is 2000m. The height of the mining stage is 5m, and the two mining stages are in the final stage of open mining. The final stage height is 10m, the safety platform width is 5m, the stage slope angle is 70°, the highest mining level is 2120m, and the minimum mining level is 1920m. In the stage, the highest demolition level is 2190m, and the maximum height of the open slope is 230m.
(II) Exploring the mode of transportation According to the requirements of the “Design Power of Attorneyâ€, the mine production scale is 600,000 t/a, and the total annual mining and stripping is 950,000 tons. The amount of open pit mining is 13.354007 million tons, according to the ore recovery rate of 95%, the depletion rate is 5%, and the calculated ore can be 13.354 million tons. Calculated according to the production scale of 600,000/a, the mine service period is 23 years. The stable production period is 22 years, and the annual production of ore is 600,000 tons, the production period is reduced by 1 year, and the annual production of ore is 154,000 tons. According to the current existing conditions of the mine, there are two types of development methods that can be used in mines: road development and transportation, peace, roadway and road joint development. Highway development and transportation mode: The transportation line is arranged outside the open pit, and the branch line is connected with the working face of the stope. The transport road is designed according to the three-level road and two-way traffic. The maximum synthetic slope value of the line is less than 9%, and the average slope of the continuous 1 km line is not More than 6.5%. Pingyi slipping well and highway joint development and transportation mode: the plan is 1900m elevation, the flat length is 780m, the flat section is 5m×5m, the slip section is φ3m, the flat raft is transported by car, and the ore is discharged from the downhole to the 1900m level. Then transport the surface from Pingyi. Stripped rocks are transported directly to the waste rock yard by cars. With the slope topography, there are 4 slides from the inside to the periphery. The total length of the slipper is 500m, and the longest one is 200m long. It is also necessary to arrange the uppermost working platform of the uphill road leading to the open pit. Use adit and highway jointly developing the infrastructure investment significantly higher than the road to open up much larger, so use adit and highways jointly developing reduced modes of transport distance, reduce transportation costs, due to the mine infrastructure funds tight, do not plan to The power supply in the open pit was finally determined to be developed by road.
(III) Design of mining methods According to the conventional design, open-pit mining is generally carried out from the top to the bottom. For the mine, there are two problems: 1. From the top to the bottom, it is necessary to build the uphill road to the top working platform value="2190" unitname="m">2190m elevation. Height difference value="270" unitname="m">270m, calculated according to the average gradient of 6.5%, the trunk transportation road is about 4200m, plus the branch road leading to the mining operation surface, the total length is about 6,000m, and the investment is large. Mine infrastructure investment is difficult to meet. 2. To build a transportation road, it is necessary to apply for land acquisition. Since the hillside where the mining area is located is a forest land, there are many small trees planted, and it is very difficult to apply for land reclamation to the forestry department. Since the current simple transportation road has been repaired to the 1920m elevation, it can be used with a little modification. In order to reduce the amount of infrastructure stripping in the mine and reduce the production stripping ratio, after research, it was decided to break the conventional design idea and adopt the combined step type steep mining technology for low-to-high opening. The first mining location of the mine is l920m~2000m. The whole mine is divided into four inclined steep mining operation strips. The steep mining process parameters are: according to the position of the ore body, the mining operation strips are basically arranged along the topography, and the combined steps are pushed once to have a width of about 100m. Left and right, the step safety platform width is 5 m, the combined step working platform has a minimum width of 25 m to 30 m, the combined step is composed of 8 to 10 steps, the height of each step is 5 m, and the total height of the combined steps is 40 m to 50 m. The transport road is arranged in the open pit, and the moving pit line is adopted. After being pushed into the chassis, it is arranged on the open side to solve the problem of occupying land and cutting down trees. Due to the tight investment in the mine, the artificial shallow hole rock drill was used for rock drilling. The rock mass of the 7655-type shallow hole rock drill with a diameter of 42 mm was used to drill the hole with a bore diameter of 42 mm. The excavator was used for transportation and transported by car. Mining and stripping The layered height is 5m and the step slope angle is 700. Using artificial shallow hole rock drilling, chiseling to 900 vertical holes, the blastholes are arranged with a spacing of (0.8 ~ l × 0.8 ~ 1) m triangle, the blasthole is deep 0.2m, the blasthole packing length is not less than 0.5m, take Detonation tube differential blasting technology is used for blasting.
The main technical and economic indicators for open pit mining are: (1) working face length: (200 ~ 300) m; (2) minimum working platform width: (20 ~ 30) m; (3) mining stratification height: 5m; (4) Mining stage slope angle: 70°; (5) Final slope angle: 50°; (6) Borehole diameter: φ=42mm; (7) Blast hole blasting network: (0.8~1) m×(0.8～ 1) m (line spacing × spacing); (8) blasting safety warning distance: 300m; (9) blasting extension meter blasting capacity: 3.0t / m; (10) blasting blasthole filling minimum amount: 0.5m; (11) shallow Hole blasting blasthole ultra-deep: 0.2m; (12) open pit mining depletion rate: 5%; (13) open pit mining loss rate: 5%; (14) open pit mining block rate: 1%; (15) mining Ore grade: 32.94%; (16) The total amount of ore in the open pit is 13.554 million tons (17) The total amount of rock stripping in open pit is 5.526 million tons (18) The average stripping ratio of open pit is 0.41t/t. From the bottom up and down mining plan, the infrastructure construction will form a combined mining step between 1920 and 950m, and gradually form a mining combination step. At the time of production, one excavator was mined, and one excavator was engaged in a new level of mining work, with a mining scale of 600,000 t/a. The initial production stripping ratio is 0, and gradually increases from small to large to 0.58 t/t.
Open-pit mining is carried out according to the designed mining plan. The amount of each layered mining and the amount of rock-peeling are shown in Table 2. The use of combined step mining technology, after low to high mining, significantly reduced the mine's infrastructure rock stripping and production stripping ratio, and achieved good economic benefits.
III. Conclusion Hongjian Iron Mine in Daixian County, Shanxi Province has difficulty in land acquisition and deforestation to the forestry department due to the lack of infrastructure investment. According to the conventional design ideas, it is difficult to mine from the top to the bottom. Through the investigation of site survey and design methods, the open-pit mining design routine was broken, and the combined step-type steep-cut mining process was adopted to reduce the investment in the infrastructure construction and the practical problems of deforestation. At present, the open pit mine is in normal production and has reached a design production capacity of 600,000 tons. The design idea of ​​the mine can provide experience for similar open pit mines.
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