Mining method suitable for stoping open pit bottom gently inclined ore body

Abstract

The invention provides a mining method suitable for stoping an open pit bottom gently-inclined ore body, particularly relates to the technical field of mining of metal ore deposits from open pit to underground, and aims to overcome the technical defects in the prior art. The method is suitable for the gently inclined ore body with the open pit bottom exposed out of the ground surface and a vertical distance away from the open pit bottom, ore body stoping is achieved through the three steps of room supporting structure arrangement, stoping blasting and underground passage cooperation and ore removal filling linkage, and therefore the defects existing in the prior art are overcome.

Description

Technical Field

[0001] This invention relates to the field of open-pit to underground mining technology for metal deposits, and more specifically, to a mining method suitable for mining gently dipping ore bodies at the bottom of open-pit pits. Background Technology

[0002] In the mid-to-late stages of traditional open-pit mining of gently dipping ore bodies, those ore bodies exposed at the bottom of the pit and perpendicular to the pit bottom—due to their location being constrained by the slope of the pit bottom and their gently extending shape—become "difficult-to-mine bodies" for resource recovery. Traditional mining techniques have consistently failed to balance the relationship between "safety, efficiency, and resource utilization," resulting in four core technological bottlenecks:

[0003] First, continuing to use the open-pit mining model results in a dual imbalance between technical and economic efficiency and safety. Open-pit mining relies on a linear process of "stripping waste rock - exposing the ore body." However, the ore body at the bottom of the pit has a gentle dip angle. If the open-pit pit is extended along the dip of the ore body, a large amount of surrounding rock on the slope needs to be stripped to form an operating platform, leading to a sharp increase in the stripping ratio, far exceeding the economic stripping ratio threshold for mines, and a significant increase in the unit cost of ore mining. More importantly, open-pit equipment needs to operate on gently sloping surfaces, and the climbing angle of the equipment is prone to exceed the safety limit, significantly increasing the risk of slippage and overturning. At the same time, open-pit blasting operations will directly disturb the surrounding rock on the bottom slope, especially when there are joints, fissures or faults on the slope. Blasting vibrations can easily induce slope displacement exceeding the safety threshold, highlighting the risk of slope instability and collapse.

[0004] Secondly, the conventional underground mining method suffers from a combination of resource losses and safety hazards. When mining gently dipping ore bodies, permanent pillars must be installed inside the ore body to prevent roof collapse in the goaf. The high proportion of pillars results in a large amount of ore being unrecoverable. Furthermore, underground mining requires the excavation of independent preparatory works, leading to long construction periods and high upfront costs. More critically, the gently dipping ore body at the bottom of the pit is directly connected to the open-pit bottom, meaning the underground mining roof directly bears the load of the open-pit bottom. If traditional shallow-hole blasting is used, the exposed roof area is large, and when the roof rock strength is low, roof collapse is highly likely, posing a direct threat to underground workers and equipment.

[0005] Third, there is a lack of coordination in traditional open-pit to underground transition processes. Existing open-pit to underground mining often adopts an "independent open-pit and underground operation" model: open-pit equipment is only used in open-pit areas, while underground equipment is confined to underground spaces, resulting in low equipment utilization and serious resource waste. Furthermore, waste rock generated from open-pit mining needs to be transported separately to spoil heaps for storage, and backfill materials for underground goaf areas need to be purchased separately, leading to high backfill costs. In addition, there is a lack of a unified ventilation and drainage system between the open-pit pit bottom and the underground mining area, and the temperature and humidity conditions at the underground working face are harsh, resulting in decreased worker efficiency and further restricting mining capacity.

[0006] Fourth, the adaptability of stope layout to slope stability is insufficient. In traditional mining schemes, stopes are often arranged uniformly along the strike of the ore body with fixed dimensions, without considering the geological differences in different areas of the open-pit slope. In areas with poor geological conditions (such as the presence of faults and fissures), if the same stope size and column spacing are used as in areas with good geological conditions, the slope is prone to instability due to insufficient support strength. On the other hand, if the stope size is reduced too much in areas with good geological conditions, it will increase the amount of preparation work and reduce the mining efficiency, creating a dilemma of "either unsafe or uneconomical". Summary of the Invention

[0007] The purpose of this invention is to provide a mining method suitable for the mining of gently inclined ore bodies at the bottom of open pits, which can solve the technical defects existing in the prior art.

[0008] The embodiments of the present invention are achieved through the following technical solutions: A mining method suitable for the extraction of gently dipping ore bodies at the bottom of open pits is applicable to gently dipping ore bodies where the bottom of the open pit is exposed on the surface and there is a vertical distance between the ore body and the bottom of the open pit. The ore body extraction is achieved through a three-stage process: arrangement of stope support structure, coordinated extraction blasting and underground passage, and linkage of ore extraction and backfilling. Specifically, the method includes the following steps: Step 1: Arrange the stopes and support structures along the ore body occurrence characteristics to construct a spatial support system adapted to the stability of the open-pit slope; Step 2: Initiate mining operations with risk management as the guiding principle, simultaneously design the blasting free face and lay out underground operation and ore extraction channels to achieve synergy between open-pit blasting and underground operations; specifically including the following steps: Step 2.1: Start and advance of mining operations; Step 2.2: Design of the blasting free face and open-pit downward medium-deep hole blasting; Step 2.3: Underground operations and ore extraction tunnel layout; Step 3: Complete the phased ore extraction according to the mining progress. After the entire stope has been mined, implement unified backfilling of the goaf to form a closed loop of mining and backfilling. This includes the following steps: Step 3.1: Step-by-step ore extraction operation; Step 3.2: Unified backfilling of the goaf.

[0009] In some embodiments, the arrangement of the mine and the supporting structure in step 1 includes the following steps: Step 1.1: The stopes are laid out along the natural occurrence direction of the ore body, and the extension trajectory is completely consistent with the ore body strike, ensuring that the stopes fully cover the area to be mined along the thickness direction of the ore body, and avoiding ore residue due to stope offset; Step 1.2: Interval columns are left in the ore room along the strike of the ore body to form a continuous structure in which the ore room and the interval columns are alternately distributed. The distribution range of the interval columns corresponds to the projection area of ​​the open slope at the bottom of the pit, so that the interval columns directly bear the lateral stress of the slope. Step 1.3: Dynamically adjust the structural parameters of the stope and columns based on the results of the open-pit slope stability test: in areas with poor slope geological conditions, reduce the width of the stope and increase the spacing between columns; in areas with good slope geological conditions, the width of the stope can be appropriately increased to ensure that the support system is compatible with the stress state of the slope.

[0010] In some embodiments, step 2.1, the initiation and advancement of the mining operation further includes the following steps: Step 2.1.1: Determine the starting point of mining: Take the side of the open-pit slope with poorer geological conditions as the starting point of mining. The horizontal distance between the stope on this side and the open-pit slope is smaller than that on the side with better geological conditions. Prioritize mining in this area to release stress in advance. Step 2.1.2: Plan the direction of mining advance: Advance continuously along the strike of the ore body towards the side of the open-pit slope with better geological conditions, and adopt the "retreat mining" sequence - first mine the marginal risk zone stope, and after the stope has been mined, mine the adjacent inner stope to ensure that the mined goaf is always below the stable slope. Step 2.1.3: Ensure the effectiveness of the support: During the mining process, the interstitial pillars remain intact and together with the unmined ore chambers, they form a "double support". The unmined ore chambers bear the pressure of the surrounding rock of the ore body, while the interstitial pillars bear the lateral thrust of the slope, thus avoiding slope instability caused by the failure of a single support.

[0011] In some embodiments, step 2.2, the design of the blasting free face and the open-pit downward medium-deep hole blasting include the following steps: Step 2.2.1: Excavating cutting slots to construct free faces: Pre-set cutting slots in each ore chamber to be returned to the mine. The cutting slots are excavated along the vertical direction of the ore chamber, and their sidewalls form vertical free faces perpendicular to the direction of the ore chamber, providing space for directional rock collapse. Step 2.2.2: Drilling medium-deep holes in the open pit: Drill medium-deep holes from the surface of the open pit bottom into the interior of the stope. The drilling path extends towards the top area of ​​the stope, ensuring that the holes penetrate the full thickness of the ore body and that the hole positions are arranged around the circumference of the cutting groove. Step 2.2.3: Implement top blasting: Trigger medium-deep hole blasting by detonating in rows, and use the vertical free face to guide the rock to collapse towards the cutting groove. At the same time, ensure that the top of the stope is completely connected to the bottom of the open pit after blasting, eliminate the exposed space on the top of the stope, and form a flat interface flush with the bottom of the open pit.

[0012] In some embodiments, the layout of underground operations and ore extraction channels in step 2.3 includes the following steps: Step 2.3.1: Determine the tunnel layout area: All underground tunnels are laid in the stable surrounding rock area of ​​the footwall of the ore body, avoiding the ore body and slope fracture zone, and avoiding areas at risk of tunnel excavation disturbance; Step 2.3.2: Establish channel connection relationships, including: Constructing ramps: extending from the bottom of the open pit into the underground, forming a transition passage between the open and underground areas; The ore exit route is laid out as follows: one end is directly connected to the goaf area of ​​the ore stope, and the other end is connected to the ramp at a preset angle, forming a continuous transportation path of "goaf area - ore exit route - ramp". Drilling tunnels are laid out: one end connects to the mine entrance or ramp, and the other end extends to the auxiliary operation area, forming a network connection system with other channels to meet the needs of equipment passage, ventilation and auxiliary operations.

[0013] In some embodiments, step 3.1, the step-by-step ore extraction operation includes the following steps: Step 3.1.1: Plan the ore extraction equipment route: The ore extraction equipment enters the ore extraction route from the bottom of the open pit via a ramp, and then goes directly to the mined-out area of ​​the ore stope. The entire route is a straight line or a gentle curve without turning back, to ensure transportation efficiency. Step 3.1.2: Control the ore extraction rhythm: Start ore extraction immediately after the mining of a single stope is completed, and empty the ore in the stope in a short period of time to avoid ore stagnation and oxidation; during the ore extraction process, monitor the surrounding rock condition of the goaf in real time, and suspend ore extraction and take support measures when an abnormality is found. Step 3.1.3: Ensure safety during mining: Use remote or semi-remote mining equipment to reduce the frequency of personnel entering the goaf and reduce operational risks.

[0014] In some embodiments, step 3.2, the unified backfilling of the goaf includes the following steps: Step 3.2.1: Determine the timing of backfilling: Start unified backfilling after all mines have finished producing ore, to avoid frequent equipment relocation and process interruption caused by "mining one and backfilling one". Step 3.2.2: Implement backfilling operation: Use open-pit equipment to take materials from the waste rock pile area at the bottom of the open pit, and push the waste rock into the underground goaf through the connecting opening formed by the top of the stope. The backfilling sequence is to gradually advance from the edge of the goaf to the center. Step 3.2.3: Control the quality of backfilling: Compact the waste rock by layered rolling to ensure that the density of the backfill meets the support requirements, so that the backfill, the mine pillars, and the bottom of the open pit form an integral load-bearing structure, further enhancing the stability of the open slope.

[0015] The technical solutions of the embodiments of the present invention have at least the following advantages and beneficial effects: 1. This invention effectively controls slope displacement and roof collapse risks throughout the entire process by dynamically adjusting the parameters of the stope and pillars to adapt to slope stability, adopting a retreat mining method "from the risk side to the safety side" and unified filling of the goaf, thus ensuring safe mining operations without accidents. 2. In this invention, there are no permanent pillars, and the stopes are arranged to cover the entire ore body, which greatly reduces the ore loss rate and significantly improves the resource recovery rate. 3. In this invention, open-pit blasting and underground ore extraction are coordinated, open-pit waste rock is directly used for backfilling, and adjacent mines share the same preparatory engineering, which effectively shortens the infrastructure cycle, reduces backfilling and equipment investment costs, and improves mining efficiency. 4. In this invention, the open-pit and underground equipment are efficiently linked, and the underground passages form a network connection system, which optimizes the working environment and improves equipment utilization, ultimately extending the service life of the mine and bringing significant economic benefits. It provides a safe, efficient, and economical replicable engineering model for the mining of similar open-pit gently dipping ore bodies. Attached Figure Description

[0016] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0017] Figure 1 This is a plan view of the gently sloping ore body at the bottom of an open pit provided in an embodiment of the present invention; Figure 2 This is a longitudinal cross-sectional view of the gently dipping ore body at the bottom of an open pit provided in an embodiment of the present invention; Figure 3 This is a top view of the gently sloping ore body mining at the bottom of an open pit, as provided in an embodiment of the present invention.

[0018] Explanation of the attached diagram labels: 1. Rock drilling tunnel; 2. Mine access road; 3. Access ditch; 4. Cutting groove; 5. Open pit bottom; 6. Drill hole; 7. Cutting riser; 8. Open pit boundary line; 9. Inclined ramp; 10. Goaf; 11. Stope and pillar; 12. Connecting tunnel. Detailed Implementation

[0019] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. The components of the embodiments of the present invention described and shown in the accompanying drawings can generally be arranged and designed in various different configurations.

[0020] Therefore, the following detailed description of the embodiments of the invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the invention without inventive effort are within the scope of protection of the invention.

[0021] It should be noted that similar labels and letters in the following figures indicate similar items. Therefore, once an item is defined in one figure, it does not need to be further defined and explained in subsequent figures.

[0022] In the description of this invention, it should be noted that if terms such as "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," or "outer" are used to indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, or the orientation or positional relationship commonly used when the product is in use, they are only for the convenience of describing this invention and simplifying the description, and are not intended to indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this invention.

[0023] In the description of this invention, it should also be noted that, unless otherwise explicitly specified and limited, the terms "set," "install," "connect," and "link" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0024] Please see Figures 1-3 As shown, this embodiment addresses a residual ore body at the bottom of an open-pit mine during its later stages of mining. This ore body conforms to the characteristics of a gently dipping ore body that emerges from the surface of the open-pit bottom 5 and has a vertical distance from it. The ore body strikes approximately east-west, is about 800m long, 3-6m thick, and dips gently at an angle of 12°-18°. The hanging wall of the ore body is in direct contact with the bottom of the open pit (5), while the footwall is composed of stable marble. The vertical distance between the ore body and the bottom of the open pit (5) is 5-8m, and the exposed ore body at the bottom of the pit is continuously distributed along the strike. There are significant geological differences between the east and west sides of the open pit slope. The eastward direction is the direction of the ore body's strike extension. There is a normal fault on the west slope that strikes parallel to the ore body, with a fault fracture zone width of 1-2m, a uniaxial compressive strength of 25-30MPa, and a maximum historical monthly displacement of 4.2mm, indicating poor geological conditions. The east slope has no obvious structures, a uniaxial compressive strength of 55-60MPa, and a monthly displacement of ≤1.5mm, indicating good geological conditions.

[0025] To ensure the safe mining of the ore body, control the risk of slope instability, and reduce ore loss, open-pit waste rock will be used simultaneously to solve the problem of filling the goaf.

[0026] Specific implementation steps Step 1: Layout of the stope support structure: This is implemented strictly according to the three steps of "stope layout - interstitial column placement - parameter adjustment". The core is to construct a support system adapted to the slope stability. Step 1.1: The stopes are laid out along the strike of the ore body. 1. Strike Positioning: First, through geological drilling and 3D modeling, it was determined that the strike of the ore body is 30° northeast. The direction of the stope layout is completely consistent with this strike, ensuring that the extension trajectory of the stope coincides with the natural occurrence trajectory of the ore body. 2. Thickness Coverage: Each stope is fully covered along the thickness direction of the ore body perpendicular to the strike. The width of the stope is dynamically adjusted from 4 to 7 meters according to the thickness of the ore body, thereby avoiding the residue at the edge of the ore body due to stope offset. 3. Scope definition: The total layout of the mining stope extends from the western boundary of the open pit bottom 5 to the eastern boundary, completely matching the area of ​​the exposed ore body at the bottom of the pit, with a total coverage length of 650m, and is divided into 13 independent mining stops.

[0027] Step 1.2: Leave space for columns between mining rooms: Interstitial columns are evenly distributed between adjacent ore rooms along the strike of the ore body, forming a continuous structure with alternating distribution of ore rooms and interstitial columns. The distribution range of these interstitial columns precisely corresponds to the projection area of ​​the open-pit slope on the bottom of the pit. The interstitial columns within the projection range of the north slope are kept at a horizontal distance of 5-8m from the north slope, directly bearing the lateral thrust of the slope. The interstitial columns within the projection range of the south slope only need to bear the conventional surrounding rock pressure, and the horizontal distance from the south slope can be widened to 10-12m.

[0028] Step 1.3: Adjust structural parameters according to slope stability Stability testing: Stability testing was conducted using GNSS displacement monitoring and borehole stress testing. Twelve GNSS monitoring points were set up on the north slope with a spacing of 25m between adjacent monitoring points, and eight GNSS monitoring points were set up on the south slope with a spacing of 50m between adjacent monitoring points. Basic data were obtained through continuous monitoring for two months. Parameter adjustment plan: After the test is completed, the parameters are adjusted. The width of the stope on the north side is reduced to 4-5m, and the spacing between the columns is increased to 8-10m to enhance the support density and resist the lateral pressure of the fractured rock mass on the slope. The width of the stope on the south side is increased to 6-7m, and the spacing between the columns is adjusted to 12-15m to improve the mining efficiency while ensuring the safety of the support. Verification and optimization: The stress distribution of the adjusted chamber and inter-column 11 structure was verified through ANSYS mechanical simulation. If the support requirements are met, the parameter scheme is confirmed to be feasible.

[0029] Step 2: Coordination of Mining Blasting and Underground Passages This step includes three parallel steps: initiation and advancement of mining operations, design of the blasting free face and roof-mounted blasting, and layout of underground passages. Step 2.1: Initiation and Advancement of Mining Operations: Strictly follow the three steps of determining the starting point, planning the direction of advancement, and ensuring the effectiveness of support. The core is to control the risks on the north slope. Step 2.1.1: Determine the starting point of the mining operation The outermost stope corresponding to the north slope is taken as the starting point for mining. The horizontal distance between this stope and the north slope is only 5m. The slope has well-developed joints and fissures. If mining is carried out later, it is easy to cause collapse due to disturbance. Prioritizing mining can release the stress in this area in advance and reduce subsequent risks.

[0030] Step 2.1.2: Plan the direction of the mining advance The ore body is continuously advanced along the south slope, employing a retreating mining sequence. Phase 1: Complete the mining and ore extraction of the No. 1 stope at the starting end, and then advance to the next adjacent No. 2 stope; Phase 2: Mining stopes 3 through 13 in sequence, always maintaining the layout of "mined goaf 10 in the south and unmined stopes in the north", ensuring that goaf 10 is always below the stable southern slope and avoiding disturbance to the northern slope. Path optimization: The mining equipment is an open-pit drilling rig, which moves from the north edge of the open pit bottom 5 to the south side. The operation path is consistent with the mining advance direction, reducing the round-trip distance of the equipment.

[0031] Step 2.1.3: Ensure support effectiveness: Support pillar protection: During the mining process, all supports must remain intact. Drilling blasting holes or excavating channels in the supports is prohibited to avoid damaging the supporting structure. Dual support verification: stress changes of the unrecovered ore chamber and the inter-pillar 11 are monitored in real time by stress sensors. The unrecovered ore chamber bears the pressure of the hanging wall of the ore body, and the inter-pillar bears the lateral thrust of the north slope. The dual support works in coordination and there is no single structure overload.

[0032] Step 2.2: Design of the blasting free face and open-pit downward medium-deep hole blasting: Follow the three steps of excavating cutting groove 4 - drilling medium-deep holes - implementing roof blasting to ensure blasting safety and the integrity of the stope roof: Step 2.2.1: Excavate cutting groove 4 to construct free surface Location of cutting groove 4: In the granite surrounding rock area slightly below the center of each ore-to-be-mined chamber, a cutting groove is first excavated. The cutting groove is arranged along the strike of the ore body and has a cross-sectional size of 3m×3m. Construction of the cutting well: Vertically excavate the cutting well 7 at both ends of the cutting groove. The top of the well extends to the bottom of the open pit 5. The bottom connects to the underground passage to be laid later and also serves as a ventilation well. Widening the groove to form a free face: Medium-deep hole blasting is used to widen the rock mass between the cutting groove and the riser to form a vertical free face along the vertical direction of the stope (the height of the free face is 4~7m, consistent with the thickness of the ore body, and the verticality deviation of the sidewall is ≤2°).

[0033] Step 2.2.2: Drilling an open-pit downward medium-deep hole Equipment selection: The CM351 crawler-type open-pit medium-deep hole drilling rig is adopted, with a drill rod length of 15m, which meets the requirements of ore body thickness and vertical distance. Drilling parameters: Drill hole 6 has a diameter of 110mm and is arranged around the cutting groove 4 in a circumferential direction. The spacing between the holes is 1.2~1.5m. The extension path of drill hole 6 is consistent with the dip angle of the ore body (10°~20°) to ensure that drill hole 6 penetrates the full thickness of the ore body (4~7m) and reaches the bottom of the footwall granite surrounding rock. Hole position verification: The trajectory of borehole 6 is detected by a borehole inclinometer to ensure that the hole position deviation is ≤5%, so as to avoid ore body residue or incomplete blasting due to borehole 6 offset.

[0034] Step 2.2.3: Implement roof blasting Charge scheme: Rock ammonium nitrate explosive is used, with a continuous charge structure. The charge length is 70% to 80% of the hole depth. The hole opening is plugged with stemming material with a plugging length of 2 to 3 meters. Detonation sequence: Using non-electric millisecond detonators, detonate row by row from cutting slot 4 to both sides of the mine, with an interval of 60ms between sections, and use the vertical free face to guide the rock to fall directionally towards cutting slot 4; Roof connection effect test: After blasting, the top of the mine and the bottom of the open pit 5 were completely connected by drone aerial photography and manual exploration of the underground passage (roof connection rate 100%), with no overhanging rocks or cavities, forming a flat interface that is flush with the bottom of the open pit 5, which meets the needs of subsequent ore extraction and backfilling.

[0035] Step 2.3: Layout of underground operations and ore extraction channels Following the two steps of "determining the layout area - establishing channel connections", an efficient and interconnected underground channel network is constructed in the footwall of the ore body: Step 2.3.1: Determine the channel layout area All underground passages are located in the granite surrounding rock area of ​​the footwall of the ore body (2-3m from the footwall boundary). The rock in this area has good integrity and high compressive strength, which avoids disturbing the ore body or the fracture zone on the north slope during passage excavation and reduces the risk of passage collapse.

[0036] Step 2.3.2: Establish channel connection relationships 1. Constructing a ramp 9: extending underground from the south side of the open pit bottom 5 into the access ditch 3, intersecting the ore body at a 45° angle; its cross-sectional dimensions are 4.5m wide × 4m high, with a slope of 12° to accommodate the climbing ability of loader. The road surface is made of C30 concrete with a thickness of 200mm and a 1% drainage slope is provided; the ramp 9 serves as the main passage between the open pit and the underground, undertaking the tasks of equipment entry and exit and ore transportation.

[0037] 2. Layout of ore exit route 2: It is arranged perpendicular to the strike of the ore body, and each ore exit route 2 corresponds to 1 to 2 mining rooms; one end of it is directly connected to the goaf area 10 of the mining room, and the other end is connected to the ramp 9 at a 30° angle, forming a continuous transportation path from goaf area 10 to ore exit route 2 to ramp 9; its cross-sectional dimensions are 4m×3.5m, and it adopts shotcrete and anchor support.

[0038] 3. Drilling horizontal tunnel 1 is set up: its position is parallel to the ore body and located below the ore access road 2; one end of it is connected to the ore access road 2 through the connecting tunnel 12, and the other end extends to the bottom of the cutting well 7; the drilling horizontal tunnel 1 serves as an auxiliary channel for drilling operations and a supplementary ventilation channel. Fresh air enters from the inclined ramp 9, passes through the ore access road 2 and the connecting tunnel 12 and enters the drilling horizontal tunnel 1, while polluted air is discharged from the cutting well 7, forming a complete ventilation system.

[0039] Step 3: The integrated mining and backfilling process comprises two interconnected steps: phased mining and unified backfilling of the goaf. This forms a closed loop between mining and backfilling, ensuring coordinated resource recovery and ground pressure control. Step 3.1: Step-by-step ore extraction operation, following three steps: planned equipment path - controlled ore extraction rhythm - ensured safety, to achieve efficient and safe ore extraction. Step 3.1.1: Plan the route for the ore extraction equipment The ST3.5 type 3m³ underground remote-controlled loader is used to avoid personnel entering the goaf area 10. The loader enters from the bottom of the open pit 5 via the ramp 9 and goes directly to the goaf area 10 of the mine along the ore exit road 2. The entire route is a straight line with gentle curves and no turning back section. The single transport distance is controlled at 50~80m and the transport time is ≤12min. Path maintenance: Regularly clean up any loose ore in the ore access road 2 and ramp 9 to ensure a smooth road surface and prevent ore spillage or equipment malfunction caused by equipment bumps.

[0040] Step 3.1.2: Control the ore extraction rhythm Single-cell ore extraction: Ore extraction will begin within 24 hours after the blasting of a single ore cell is completed; Ore transfer: The loader transfers the ore from the goaf 10 to the temporary ore bin in the middle of the ramp 9, and then the mining trucks transport the ore from the temporary ore bin to the open-pit concentrator. Retention control: During the ore extraction process, the loader's built-in camera monitors the ore residue in the goaf in real time to ensure that the ore residue rate meets the standard and avoids oxidation or agglomeration caused by long-term retention.

[0041] Step 3.1.3: Ensure safety during ore extraction Personnel protection: The loader is operated remotely, and the operators work in the control room at the bottom of the open pit 5, without having to enter the underground passage; Surrounding rock monitoring: A stress sensor is installed every 10m on the roof of the ore access road 2 to monitor the roof pressure in real time. When the stress value exceeds 80% of the compressive strength of the granite, ore extraction is immediately suspended and anchor bolts are used for reinforcement. Emergency measures: A refuge chamber is set up every 50m along the ramp 9, equipped with emergency ventilation and communication equipment to deal with emergencies.

[0042] Step 3.2: Unified backfilling of goaf 10 By following three steps—determining the timing of backfilling, implementing backfilling operations, and controlling backfilling quality—low-cost backfilling can be achieved using open-pit waste rock. Step 3.2.1: Determine the timing of filling After all 13 mining rooms have completed mining, a unified backfilling operation will be started to avoid the frequent relocation of bulldozers and loaders caused by "mining one and backfilling one". At the same time, it will ensure that all mined-out areas 10 are in the same empty state, which will facilitate synchronous backfilling control.

[0043] Step 3.2.2: Carry out the filling operation Waste rock source: Utilize the waste rock that was stockpiled on the north side of the pit bottom in the early stage of open-pit mining, so that there is no need to transport it from outside, thus reducing transportation costs; Filling equipment: SD22 type 220kW open-pit bulldozer and ZL50 type 5m³ loader are used in combination; Backfilling sequence: proceed gradually from the north side to the south side of goaf 10, first backfill goaf 10 of mined houses 1#~6#, then backfill goaf 10 of mined houses 7#~13#, to avoid backfilling dead corners caused by uneven accumulation of waste rock; Conveying route: The bulldozer takes material from the waste rock pile at the bottom of the open pit 5, and pushes the waste rock to the underground goaf 10 through the connection between the top of the mine and the bottom of the open pit 5. The loader assists in leveling the waste rock pile.

[0044] Step 3.2.3: Control the filling quality Layered compaction: Waste rock backfilling is carried out in layers with a thickness of 1.5m. After each layer is filled, it is compacted 3 times with bulldozer tracks to ensure that the backfill is dense. Compaction test: The compaction of the filling body is tested every 500m³ using the ring cutter method, and the compaction is required to be ≥90%. Overall stress verification: After the filling was completed, slope displacement monitoring showed that the monthly displacement of the north slope decreased to 1.3 mm and that of the south slope decreased to 0.9 mm. The filling body, the intercolumns, and the bottom of the open pit formed an integral stress structure, which further enhanced the stability of the slope.

[0045] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A mining method suitable for mining gently dipping ore bodies at the bottom of open pits, characterized in that, This method is suitable for gently dipping ore bodies that are exposed on the surface at the bottom of an open pit and are at a vertical distance from the pit bottom. Ore body recovery is achieved through a three-stage process: arrangement of the stope support structure, coordinated blasting and underground tunneling, and linked ore extraction and backfilling. Specifically, it includes the following steps: Step 1: Arrange the stopes and support structures along the ore body occurrence characteristics to construct a spatial support system adapted to the stability of the open-pit slope; Step 2: Initiate mining operations with a risk management focus, simultaneously designing blasting free faces and laying out underground operation and ore extraction channels to achieve synergy between open-pit blasting and underground operations; specifically including the following steps: Step 2.1: Start and advance of mining operations; Step 2.2: Design of the blasting free face and open-pit downward medium-deep hole blasting; Step 2.3: Underground operations and ore extraction tunnel layout; Step 3: Complete the phased ore extraction according to the mining progress. After the entire stope has been mined, implement unified backfilling of the goaf to form a closed loop of mining and backfilling. This includes the following steps: Step 3.1: Step-by-step ore extraction operation; Step 3.2: Unified backfilling of the goaf.

2. The mining method for mining gently dipping ore bodies at the bottom of open pits according to claim 1, characterized in that: In step 1, the arrangement of the mine and supporting structure includes the following steps: Step 1.1: The stopes are laid out along the natural occurrence direction of the ore body, and the extension trajectory is completely consistent with the ore body strike, ensuring that the stopes fully cover the area to be mined along the thickness direction of the ore body, and avoiding ore residue due to stope offset; Step 1.2: Interval columns are left in the ore room along the strike of the ore body to form a continuous structure in which the ore room and the interval columns are alternately distributed. The distribution range of the interval columns corresponds to the projection area of ​​the open slope at the bottom of the pit, so that the interval columns directly bear the lateral stress of the slope. Step 1.3: Dynamically adjust the structural parameters of the stope and columns based on the results of the open-pit slope stability test: in areas with poor slope geological conditions, reduce the width of the stope and increase the spacing between columns; in areas with good slope geological conditions, the width of the stope can be appropriately increased to ensure that the support system is compatible with the stress state of the slope.

3. The mining method for mining gently dipping ore bodies at the bottom of open pits according to claim 1, characterized in that: In step 2.1, the initiation and advancement of the longwall mining operation also includes the following steps: Step 2.1.1: Determine the starting point of mining: Take the side of the open-pit slope with poorer geological conditions as the starting point of mining. The horizontal distance between the stope on this side and the open-pit slope is smaller than that on the side with better geological conditions. Prioritize mining in this area to release stress in advance. Step 2.1.2: Plan the direction of mining advance: Advance continuously along the strike of the ore body towards the side of the open-pit slope with better geological conditions, and adopt the "retreat mining" sequence - first mine the marginal risk zone stope, and after the stope has been mined, mine the adjacent inner stope to ensure that the mined goaf is always below the stable slope. Step 2.1.3: Ensure the effectiveness of the support: During the mining process, the interstitial pillars remain intact and together with the unmined ore chambers, they form a "double support". The unmined ore chambers bear the pressure of the surrounding rock of the ore body, while the interstitial pillars bear the lateral thrust of the slope, thus avoiding slope instability caused by the failure of a single support.

4. A mining method for mining gently dipping ore bodies at the bottom of open pits according to claim 1, characterized in that: Step 2.2, the design of the blasting free face and the open-pit downward medium-deep hole blasting include the following steps: Step 2.2.1: Excavating cutting slots to construct free faces: Pre-set cutting slots in each ore chamber to be returned to the mine. The cutting slots are excavated along the vertical direction of the ore chamber, and their sidewalls form vertical free faces perpendicular to the direction of the ore chamber, providing space for directional rock collapse. Step 2.2.2: Drilling medium-deep holes in the open pit: Drill medium-deep holes from the surface of the open pit bottom into the interior of the stope. The drilling path extends towards the top area of ​​the stope, ensuring that the holes penetrate the full thickness of the ore body and that the hole positions are arranged around the circumference of the cutting groove. Step 2.2.3: Implement top blasting: Trigger medium-deep hole blasting by detonating in rows, and use the vertical free face to guide the rock to collapse towards the cutting groove. At the same time, ensure that the top of the stope is completely connected to the bottom of the open pit after blasting, eliminate the exposed space on the top of the stope, and form a flat interface flush with the bottom of the open pit.

5. A mining method for mining gently dipping ore bodies at the bottom of open pits according to claim 1, characterized in that: In step 2.3, the layout of underground operations and ore extraction channels includes the following steps: Step 2.3.1: Determine the tunnel layout area: All underground tunnels are laid in the stable surrounding rock area of ​​the footwall of the ore body, avoiding the ore body and slope fracture zone, and avoiding areas at risk of tunnel excavation disturbance; Step 2.3.2: Establish channel connection relationships, including: Constructing ramps: extending from the bottom of the open pit into the underground, forming a transition passage between the open and underground areas; The ore exit route is laid out as follows: one end is directly connected to the goaf area of ​​the ore stope, and the other end is connected to the ramp at a preset angle to form a continuous transportation path of "goaf area - ore exit route - ramp". Drilling tunnels are laid out: one end connects to the mine entrance or ramp, and the other end extends to the auxiliary operation area, forming a network connection system with other channels to meet the needs of equipment passage, ventilation and auxiliary operations.

6. A mining method for mining gently dipping ore bodies at the bottom of open pits according to claim 1, characterized in that: In step 3.1, the step-by-step ore extraction operation includes the following steps: Step 3.1.1: Plan the ore extraction equipment route: The ore extraction equipment enters the ore extraction route from the bottom of the open pit via a ramp, and then goes directly to the mined-out area of ​​the ore stope. The entire route is a straight line or a gentle curve without turning back, to ensure transportation efficiency. Step 3.1.2: Control the ore extraction rhythm: Start ore extraction immediately after the mining of a single stope is completed, and empty the ore in the stope in a short period of time to avoid ore stagnation and oxidation; during the ore extraction process, monitor the surrounding rock condition of the goaf in real time, and suspend ore extraction and take support measures when an abnormality is found. Step 3.1.3: Ensure safety during mining: Use remote or semi-remote mining equipment to reduce the frequency of personnel entering the goaf and reduce operational risks.

7. A mining method for mining gently dipping ore bodies at the bottom of open pits according to claim 1, characterized in that: In step 3.2, the unified backfilling of the goaf includes the following steps: Step 3.2.1: Determine the timing of backfilling: Start unified backfilling after all mines have finished producing ore, to avoid frequent equipment relocation and process interruption caused by "mining one and backfilling one". Step 3.2.2: Implement backfilling operation: Use open-pit equipment to take materials from the waste rock pile area at the bottom of the open pit, and push the waste rock into the underground goaf through the connecting opening formed by the top of the stope. The backfilling sequence is to gradually advance from the edge of the goaf to the center. Step 3.2.3: Control the quality of backfilling: Compact the waste rock by layered rolling to ensure that the density of the backfill meets the support requirements, so that the backfill, the mine pillars, and the bottom of the open pit form an integral load-bearing structure, further enhancing the stability of the open slope.

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