Design of Recycling Scheme for Residual Ore in Xiaobaoshan Iron Mine

Hill iron ore parcel is located approximately 400m south of the Hubei Daye City of Hope township. The general elevation of the area is 80-150m, and the northward terrain is open and flat, belonging to the middle and low hills. The structure in the area is extremely developed.
The development of folds and rupture zones greatly affects the stability of the rock and strictly controls the hydrogeological conditions of the mine. This area is a subtropical climate with cold, hot, humid and rainy winters. The underground mining method adopts the room-column mining method of retaining part of the permanent pillar, and the designed mining capacity is 100,000 t/a. For a long time, the amount of residual minerals is large and the waste of resources is more serious. The proper method is adopted to deal with the goaf and open slope, and the recovery of residual ore can not only make full use of resources, but also have good economic benefits. As other infrastructures are relatively complete, there is not much need for additional investment, so the recovery of residual mines is more feasible.
1 Mine Overview
The geotectonic location of the Xiaobaoshan mining area is located in the west wing of the Huaiyang Mountain-shaped structure front arc, near the top of the arc, the Daye complex-type oblique south wing. The ore body is produced on the contact zone between the plagiotic diorite and the Daye limestone in the north wing of the Xiaobaoshan anticline. Its shape and occurrence are strictly controlled by structure and lithology. The strike is SEE-NWW and the length is about 350m. The ore body is inclined to the NE by about -90 m or more, and the inclination angle is 70°, and the inclination angle of the portion below -90 m is deflected toward the SW. The eastern end is exposed to the surface and the elevation is 65m. The west end is sloping underground and extends down to -145m. It is controlled by 7 exploration lines of 60, 0~2, 1, 2, 3, 3~2, 4, and the thickness of the ore body varies greatly, from 3 to 75m, with an average of 25m. The cross-section is shaped like a boot or a pipe, and the upper and lower sides are large. From the longitudinal section, the forks of the upper and lower branches are inserted into the rock mass from east to west. The upper part of the ore body is mainly marble , the lower part is plagiotic diorite, and the remaining marble in the ore body is the scorpion. The ore bodies available for mining mainly include 1#, 2# and 3# ore bodies, and the 2# and 3# ore bodies are very small in scale and have no mining value. The natural type of ore is single, and most of the main ore bodies are upper hematite and lower magnetite, which are densely packed, and fine ore is seen in the upper ore body. The open-pit mining part eventually formed an open pit with a width of 250m and a depth of 75m. A 10m thick boundary pillar is retained between the underground mining and the open pit. At present, only the -88m floor is completely retained, the -120m floor is mined, the -70m floor is 35%, the -50m floor is 80%, and the -50m roof column (ie the open-pit west pit floor) is worn up to 50m (Figure 1 ). Since the mine has been turned underground, the ore body below -35m has been basically recovered, and the volume of the entire goaf is about 88312.5m3. By accounting for the remaining ore of the section, the total ore content of the pillar is about 123,000 tons.

2 Feasibility analysis
2.1 Rock and rock stability analysis
The ore body is located in the contact zone between the plagiotic diorite and the marble in the north wing of the Xiaobaoshan anticline. Under the compression of the tectonic stress in the north-south direction and the east-west direction, the ore body folds and ruptures, forming a hillside Structures such as slant, fracture and joint. The shape and occurrence of the ore body are controlled by structure and lithology. The surrounding rock of the ore body is dominated by marble, followed by plagioling diorite, and the lower plate is dominated by porphyritic diorite, followed by marble and ore body. There is a marble inclusion in the middle. The porphyritic diorite is moderately stable. The marble has poor development stability in addition to local joint fissures, and is generally moderately stable. The ore is hematite and magnetite, which is dense and solid and relatively stable.
2.2 Stability analysis of goaf
According to the upper or lower ore body, the upper ore body is mined underground from top to bottom. The upper ore body is divided into sections of -50, -70, -89m3, and the lower ore body is divided into -120, -140m2 sections. Column housing mining method. At present, the overall goaf area remains basically stable.

The recovery of some of the pillars between the goaf and the bottom of the open pit will weaken the lateral support of the pillar, and the displacement or deformation of the side will affect the stability of the goaf. Therefore, while recovering the resources of the pillars, corresponding measures should be taken to reduce the lateral pressure of the side, and the gravel is used to fill the empty area to improve the bearing capacity of the surrounding rock.
2.3 Stability analysis of open slope
The north side of the open pit is dominated by marble, and local joint fissures are developed, which is prone to local landslides. An underground goaf is distributed around the 1# silt well on the east side of the former Xikeng original slope road and the west slope of the Xikeng slope road in the north, which is unfavorable to the stability of the side gang. The open pit is narrow and long, the width is not large, and the end gang is basically stable. The stability of the eastern end is better, and the height of the western end is smaller, but there is a goaf at the bottom of the slope, which is less stable than the east. Therefore, it is necessary to take measures such as cutting and reducing the load, and use gravel to fill the empty area, reduce the sliding force, increase the anti-sliding force, and improve the overall stability of the slope body. The height of the stepping step is 10 to 16 m, the step angle of the step is 60°, and the safety platform is 4 m wide.
3 recovery plan
From the perspective of mining technology, the eastern ore body selects the “open-air rock blasting and open-pit mining” mining scheme, and the volume of the goaf below -35m is about 88312.5m3. In order to ensure the safety of the pillar mining, it is -25~-35m. Before the horizontal pillar mining, it is necessary to fill the underground goaf area of ​​-50~-80m, the filling volume is about 56823m3. At the same time, in order to improve the safety of the pillar mining, consider leaving three pillars to support the surrounding rock of the upper and lower plates; After completion, the open-pit mining method is used to return to the mining column, that is, from the bottom of the open pit to the bottom of the pit, and the ore is transported from the open pit to the surface by the ramp. The western ore body (ie the ore body west of the III# pillar) is subjected to open-air rock blasting to a level of -50m horizontally loaded and transported to the surface through the original main inclined shaft.
4 mining process
Before the mining of the pillars, the main measures are completed, that is, the yellow mud cleaning at the bottom of the open pit, the slope cutting of the open slope and the filling of the underground goaf, and the construction of the open-air transport ramp. The pillar recovery project as a whole is divided by 3# pillars. The west ore body is to ensure the safety of the surrounding rock of the upper and lower plates. It is necessary to leave 3 pillars, first to expose the minerals at the bottom of the eastern pit, and to be partially and downhole. After wearing, start to expand backfill, and then mine the bottom of the mine.
Rock drilling and blasting is used in the recycling process. The convex slope of the 2#~3# exploration line on the north slope of the open pit is firstly treated for slope cutting. The rock in the east will be cut and the waste rock discharged from the slope during the previous mining. Fill together in the gob area (Figure 2). From the bottom of the open pit, stratify from top to bottom until the design elevation. First mining the bottom of the pit -27m or more, using the original
The upper slope is hoisted and raised; the ore below -27m is transported from the open pit to the eastern slope by the mine, raised to 20m, and then transported to the surface by car.

The amount of slope cutting in the west is 16067m3, and the amount of slope cutting in the east is 29587m3, totaling 45654m3. The slope cutting project adopts shallow hole rock blasting. The row of guns in the nearest slope must be smooth blasting. The diameter of the hole is 42mm, the resistance line of the chassis is 0.72m, the spacing of the blasthole is 0.6m, and the 2# rock is adopted. Explosives, 8# electric detonator millisecond blasting (Figure 3). The backfill volume of the slope is 57067 m3. Shallow hole blasting is used for the recovery of the bottom pillar. The diameter of the borehole is 42mm. The blasthole is arranged in 3 rows according to the plum blossom pattern. The first row and the third row are 29 blastholes, and the second row is 28 blastholes. The minimum resistance line is 1.2m; the hole spacing of the blasthole is 1.2m, the row spacing of the blasthole is 1m, and the 2# rock explosive and the 8# electric detonator blasting are used (Fig. 4). The mining is carried out by manual loading, 0.75m3 small-scale mine car transportation, manual cart; using open-air ramp transportation, manual cart to the ramp to the -25m level, and the hoist will raise the mine to 20m storage level. The surface is transported by car.

5 technical and economic indicators
5.1 pillar mining technology indicators
The main technical indicators of the single column recovery project are shown in Table 1.

5.2 Economic benefits

The newly added project of the pillar recovery system mainly includes infrastructure construction cost of 1.955 million yuan and safety and environmental protection expenses, etc., totaling 2,472,900 yuan. The research scope has a reserve of 123,000 tons and a mined amount of 92,000 tons. The normal annual output is 40,000 tons, the service period is 3a, and the infrastructure period is 0.5a. The unit cost of mining is 56.46 yuan / t, the total unit cost is 86.46 yuan / t, the normal total cost is 3,510,400 yuan / a. The total sales revenue of the project is 39.56 million yuan, the total profit is 2,806,410 yuan, and the input-output ratio of the project is 0.063. The economic benefit is good.
6 Conclusion
The Xiaobaoshan Iron Mine has long been exploited by the housing-pillar mining method, and the amount of residual ore is large, making it difficult to recover safely. Through the technical measures such as cutting slope, filling mining area and shallow hole blasting, the mining of the pillars becomes safe and feasible, and the ore is effectively recovered 92,000 tons. The total sales revenue of the project is estimated to be 39.56 million yuan, and the total profit is 2804.41. Ten thousand yuan, social benefits and economic benefits are significant, providing technical support for the sustainable production of mines, and also providing reference for similar conditions mine recovery projects.