In the field of mining engineering, determining the sequence of mine extraction is like laying the cornerstone for a towering building—it is a critical step that enables the entire mining operation to proceed efficiently and safely. This sequence not only profoundly affects safety during the production process but also plays a decisive role in cost control and resource utilization efficiency.

From the perspective of production safety, an unreasonable mining sequence can trigger a series of serious safety hazards. For example, in the extraction of certain metallic ore deposits, if the occurrence conditions of ore bodies and the patterns of ground stress distribution are not adequately considered and the mining sequence is determined arbitrarily, it may lead to instability in mined-out areas, causing roof collapses, rib failures, and other accidents that pose a severe threat to the safety of workers. According to relevant statistical data, in some mine accidents caused by improper mining sequences, the resulting casualties and property losses have been extremely severe.

In terms of cost control, the mining sequence directly affects the mine’s capital investment in infrastructure, operational costs, and the service life of equipment. A scientifically sound and rational mining sequence can reduce unnecessary construction of shafts and tunnels, thereby lowering the frequency of equipment relocation and maintenance costs. Take a large coal mine as an example: by optimizing the mining sequence and concentrating initial mining activities near the main shaft, the length of transport roadways and the workload for maintenance were significantly reduced. As a result, annual transportation costs dropped by [X]%, and the equipment failure rate also declined markedly.

Resource utilization efficiency is closely linked to the mining sequence. A rational mining sequence can maximize the extraction of ore resources while minimizing ore loss and dilution rates. For example, in deposits with multi-layer ore bodies, mining should proceed from top to bottom and from easier-to-extract areas to harder-to-extract ones. This approach can effectively prevent the upper ore layers from damaging the lower ones, thereby improving the overall resource recovery rate. If the mining sequence is not properly planned, some ore may be permanently lost underground, resulting in significant resource wastage.

In actual mining operations, we often encounter a variety of complex geological conditions and diverse ore-body occurrences. Some ore bodies have great strike lengths, while others exhibit significant variations in thickness; still others show marked differences in stability between the ore body and its surrounding rock. All these factors make determining a rational mining sequence particularly challenging and crucial. Therefore, conducting an in-depth study of mine extraction sequences and comprehensively considering the impacts of various factors are of immeasurable importance for achieving sustainable development in mining operations.

II. Basic Concepts and Classification of Ore Deposit Mining Sequences

(1) Basic Concepts

Simply put, the mining sequence of a deposit refers to determining the order in which various mining units are exploited throughout the entire mining operation process, following specific principles and patterns. These mining units can include mine fields, stages, ore blocks, or even adjacent ore bodies. It’s akin to the carefully planned layout of a battle—every single step taken is critical to the outcome of the entire operation.

Essentially, determining the sequence of mine extraction is the result of a comprehensive trade-off among a variety of complex factors. These factors encompass the geological characteristics of ore bodies, such as their shape, size, dip angle, thickness, and spatial distribution underground; the grade and value of the ore—where the optimal timing for extracting high-grade ore significantly impacts economic benefits; the stability of geological structures—faults, folds, and other geological features can alter the mechanical state of ore bodies, thereby influencing the selection of the extraction sequence; and also the technical conditions for mining operations, including the mining methods employed and the performance of the equipment used. Different mining methods impose distinct requirements on the extraction sequence.

Throughout the entire mining process, the sequence of mine extraction occupies a central and pivotal position, playing a crucial role in linking upstream and downstream activities. From the initial geological exploration and mine planning and design through to the actual implementation of mining operations and the subsequent closure of the mine, the extraction sequence runs consistently throughout. A rational extraction sequence can ensure the continuity and stability of mine production, enabling mining operations to proceed smoothly and systematically. For example, in some large-scale metal mines, scientifically planned extraction sequences can guarantee seamless coordination among different mining stages, thereby avoiding production disruptions or delays caused by improper extraction sequencing. It acts like an invisible bond, tightly connecting all the various stages of the mining process and ensuring that the entire mining system operates efficiently.

(2) Classification

Mining sequence for the wellfield stage

Downward mining

Downward mining refers to a mining sequence in which the upper stages are mined first, followed by the lower stages, though it is also possible—in accordance with actual conditions—to simultaneously mine several stages. In practical production, this downward mining sequence is relatively common. Take, for example, a large lead-zinc mine that employs a downward mining sequence: The mine first mines the upper-stage No. 1. During the mining process, the development roadways established in the upper stage are utilized to further delineate the occurrence and characteristics of the ore body in the lower-stage No. 2, providing accurate geological data for subsequent mining operations. Meanwhile, since mining in the upper stage is relatively easier to carry out and requires less initial investment, the mine can quickly start production and reap economic benefits. Moreover, during downward mining, the voids created in the upper stage have relatively little impact on the mining operations in the lower stage, resulting in better safety conditions and allowing for a wider range of applicable mining methods, such as open-stope mining and backfilling mining. However, when multiple stages are mined simultaneously, although this approach can increase the length of working faces and enhance the mine’s production capacity, it also brings about a series of challenges. For instance, production management becomes more fragmented, requiring greater human and material resources for coordination and management; the workload for roadway maintenance increases significantly, and various pipelines and tracks cannot be promptly recovered and reused, leading to resource wastage; the phenomenon of contaminated air being circulated in series becomes more severe, adversely affecting underground air quality and increasing ventilation costs; and operational and management expenses also rise accordingly. Generally speaking, the number of stages mined simultaneously should be kept within 1–2, and should not exceed 3–4, in order to strike a balance between production efficiency and management costs.

Upward mining

Upward mining, the opposite of downward mining, involves first extracting the lower stages and then proceeding to the upper stages, mining one stage at a time from bottom to top. This mining sequence is used only under certain special circumstances—for example, when mining gently inclined ore deposits. If there is no suitable waste-rock dump available on the surface, the waste rock generated from the upper-stage extraction must be backfilled into the previously mined voids in the lower stages; in such cases, upward mining becomes an inevitable choice. Another scenario where upward mining is employed is when deep-level mined-out areas are utilized as reservoirs for water storage. In a particular coal mine, due to the scarcity of surface land resources and the inability to establish a waste-rock dump, upward mining was adopted. Waste rock from the upper coal seams was backfilled into the previously mined-out spaces in the lower seams, thereby solving the problem of waste-rock disposal and partially filling the mined-out areas. The advantage of upward mining lies in its ability to develop mines to the economically optimal and technically feasible maximum depth in a single operation, allowing for extraction at the deepest level while simultaneously carrying out development and preparatory work at the 1–2 upper levels. This approach enables the use of waste rock to fill mined-out areas, forming high-strength backfill masses that effectively prevent large-scale rock movements and overall structural failure, thus reducing the likelihood of surface damage and subsidence. Moreover, this mining method helps mitigate the risk of rockbursts triggered by deep-level mining, as the backfill masses in the lower mined-out areas can act as buffers to absorb and distribute stress. However, upward mining also has certain limitations. For instance, during the early stages of mining, the upper levels experience relatively little disturbance from mining activities. But as mining progresses and the lower mined-out areas continue to expand, the upper levels will experience significant stress fluctuations, which may adversely affect safe production and the stability of surface structures. Furthermore, upward mining places higher demands on mining technology and equipment, requiring more precise engineering control and management.

Sequence of ore block mining in the stage

Progressive mining

Once the stage transport drift has been driven to a certain distance, mining begins from the ore blocks closest to the main development drifts and proceeds sequentially toward the boundaries of the mine field. This method is known as forward mining. A significant advantage of forward mining is that it shortens the initial construction period of the mine, enabling rapid commissioning and allowing the mine to realize economic benefits at an early stage. Take, for example, a small gold mine that adopted a forward mining sequence: after driving the stage transport drift 500 meters, the mine began extracting ore from the blocks nearest the main shaft. As a result, ore extraction and sales were achieved within a relatively short period, allowing funds to be recovered quickly. However, forward mining also has obvious drawbacks. Since mining operations start near the main development drifts, as the mining progresses, the preparatory drifts gradually move farther away from the main development drifts, thereby increasing the difficulty and cost of maintaining these preparatory drifts. Moreover, during the mining process, if the geological conditions of subsequent ore blocks are not accurately understood, it can easily lead to insufficient preparatory drifts and unmined reserves, putting the mine in a passive position in production. The conditions suitable for forward mining include simple ore deposit characteristics, stable ore and rock formations, and situations where mining operations need to be initiated relatively early in the mining stages. Under such circumstances, forward mining can fully leverage its advantage of rapid commissioning; moreover, given the stability of the ore and rock formations, the maintenance pressure on the preparatory drifts is relatively low.

Retreat mining

After the stage transport roadway has been driven to the boundary of the mining field, mining begins from the ore blocks at the boundary and proceeds sequentially toward the main development roadways. This mining sequence is known as retreat mining. Retreat mining can be further subdivided into three types: double-wing, single-wing, and side-wing mining. Taking a large copper mine as an example, this mine employs... Double-wing retreat mining Mining is carried out simultaneously from the east and west sides of the mine field boundary, advancing toward the main shaft. The advantage of retreat mining lies in its low roadway maintenance costs, as the mining operations proceed toward the primary development roadways, keeping the preparatory roadways consistently close to the main development roadways, thus facilitating maintenance and management. Moreover, before commencing actual mining, roadways can be excavated in advance, enabling early assessment of coal seam conditions and thereby aiding in the planning and safety assurance of mining operations. However, retreat mining requires a longer initial construction period for the mine, resulting in a slower time-to-production. Specifically, it necessitates the excavation of lengthy transport roadways along the mine field boundary before mining activities can begin. Only when using a central parallel development system can retreat mining fully leverage its advantage of low roadway maintenance costs. In contrast, if a central diagonal development system is employed, the advantages of retreat mining may not be fully realized due to differences in the ventilation system.

Hybrid mining

Hybrid mining combines the characteristics of both advancing and retreating mining methods. In the initial stage, advancing mining is adopted; once the stage transport drifts have been fully excavated, the mining method is switched to retreating mining. Alternatively, during the mining process, both advancing and retreating operations can be carried out simultaneously. Take a certain iron ore mine as an example: in the early stages of mining, in order to achieve rapid production, the mine employed advancing mining to extract ore from the sections closest to the main shaft. As the stage transport drifts were completed, to reduce tunnel maintenance costs, the mine switched to retreating mining. This hybrid approach leverages the advantages of both preceding mining sequences: it enables quick economic benefits in the early stage while effectively controlling costs in the later stage. However, hybrid mining also introduces complex challenges in production management, requiring more meticulous scheduling and coordination to ensure smooth transitions between different mining methods. In practical applications, the specific hybrid mining approach and timing must be carefully selected based on the mine’s particular conditions, including orebody occurrence, mining technology level, and production management capabilities.

Mining sequence of adjacent ore bodies

The determination of the mining sequence for adjacent ore bodies must adhere to certain fundamental principles. The primary principle is to achieve simultaneous extraction of both low-grade and high-grade ores, large and small ore bodies, thick and thin ore bodies, and easy and difficult-to-mine deposits. The goal is to maximize resource utilization and avoid waste. In actual mining operations, it is also essential to fully consider the mutual influences among ore bodies. When the dip angle of an ore body is less than or equal to the rock mass movement angle, the earlier-mined ore body has relatively little impact on the subsequently mined ore body, making the choice of mining sequence relatively flexible. For example, in a certain lead-zinc ore field, there are two adjacent ore bodies: Ore Body 1 has a dip angle of 30°, Ore Body 2 has a dip angle of 25°, and the rock mass movement angle is 40°. Under these circumstances, the mining sequence can be determined based on factors such as ore grade and mining difficulty. If Ore Body 1 has a higher ore grade and is easier to mine, it can be mined first.

When the dip angle of a mineral body exceeds the movement angle of the surrounding rock, the mining of the earlier-extracted mineral body may induce movement and deformation in the surrounding rock, thereby significantly affecting the subsequent mining of the later-extracted mineral body. In such cases, it is essential to adopt a rational mining sequence and implement appropriate measures to mitigate these effects. As an example, consider a copper mine with two adjacent ore bodies: Ore Body A has a dip angle of 70°, Ore Body B has a dip angle of 65°, and the movement angle of the surrounding rock is 50°. If Ore Body A is mined first, as the voids created by the extraction of Ore Body A expand, the surrounding rock will move and collapse, potentially compromising the integrity of Ore Body B and increasing both the difficulty and risks associated with mining Ore Body B. Under these circumstances, after conducting detailed geological analysis and mechanical calculations, it was decided to mine Ore Body B first and then carry out backfilling mining of Ore Body A, thereby controlling the movement of the surrounding rock and minimizing its impact on Ore Body B. By adopting this approach, the smooth extraction of both ore bodies was effectively ensured, and the resource recovery rate was significantly improved.

Under certain special geological conditions—such as the presence of faults or fractured zones—the sequence of mining operations among adjacent ore bodies requires particularly careful determination. In a certain gold mine, a large fault runs between ore bodies, and the rock near the fault is highly fractured and unstable. To avoid triggering fault activation during mining operations and thereby preventing safety incidents, after expert deliberation, it was decided to first mine the ore body located farther from the fault, and then adopt special mining methods and support measures for the ore body situated closer to the fault. By adopting this flexible approach, the difficulties posed by the special geological conditions were successfully overcome, ensuring that the mining operations proceeded safely and smoothly.

III. Factors Influencing the Mining Sequence of Ore Deposits

(1) Geological Factors

Ore body occurrence conditions

The occurrence conditions of ore bodies—such as their dip angle, thickness, and strike length—have a critically important impact on the mining sequence.

When the dip angle of an ore body is relatively small—such as in gently inclined ore bodies—the choice of mining methods and their sequence is relatively limited. Taking a moderately thick, gently inclined ore body with a dip angle of less than 30° as an example, if the traditional open-pit mining method is employed, ore transportation becomes quite challenging because the ore cannot easily slide down by gravity. In such cases, it may be necessary to give priority to the backfilling mining method: first, mine the sections closer to the surface or those that are easier to transport, using backfill material to support the roof and ensure mining safety. Under these circumstances, the mining sequence typically proceeds from shallow to deep or gradually advances from one end of the ore body to the other, thereby minimizing ore loss and ensuring mining efficiency.

For ore bodies with greater thickness, determining the mining sequence becomes more complex. Thick ore bodies are typically mined using either a segmented or layered approach. When deciding on the mining sequence, it is essential to consider the impact of the upper segments or layers on the lower ones. For example, when using the segmented caving method to mine thick ore bodies, the upper segments are usually mined first, and the resulting voids in the upper sections serve as compensating spaces for the caved ore from the lower sections. However, under such circumstances, it is crucial to strictly control the blasting parameters and ore-handling practices in the upper sections to prevent excessive and premature mixing of upper ore into the lower sections, which could lead to dilution. Generally, during the mining of upper segments, the amount of ore blasted each time should not be too large, and the ore-discharge practice should follow the principle of "discharging more and leaving less," thereby ensuring the smooth recovery of ore from the lower sections.

The strike length of the ore body also influences the mining sequence. For ore bodies with longer strike lengths, it is possible to divide them into multiple mining sections based on actual conditions. When dividing the ore body into mining sections, factors such as its geological structure and variations in ore grade should be taken into account. For example, in a certain copper mine, the ore body has a strike length of several kilometers. To facilitate mining and management, the ore body was divided into five mining sections. First, Mining Section No. 1, located at the center of the ore body and characterized by relatively simple geological conditions and high ore grade, was mined. This approach allowed for rapid realization of economic benefits. At the same time, the mining experience and data obtained from Mining Section No. 1 provided valuable references for the subsequent mining of other sections. In the subsequent mining sequence, the mining sections were developed in accordance with the extension direction of the ore body’s geological structure and the distribution of ore grades—starting from areas with higher grades to those with lower grades, and progressing from sections with simpler geological conditions to those with more complex ones—thereby enhancing resource recovery rates and mining efficiency.

Geological structure

Geological structures such as faults and folds are important factors influencing the mining sequence of ore deposits.

The presence of faults can compromise the integrity and continuity of ore bodies, increasing mining difficulty and risks. When fault displacement is significant, it may cause the ore body to be offset, making normal mining operations impossible. In a certain coal mine, a fault with a displacement of up to 10 meters was encountered, directly severing the coal seam. To address this situation, when determining the mining sequence, detailed exploration was first conducted on the ore bodies on both sides of the fault to clarify the fault’s extension direction and its zone of influence. Then, based on the fault’s location and strike, the mining sequence was adjusted to bypass the fault and first extract ore from other areas. For the sections affected by the fault, special support measures and mining methods were adopted—for instance, using bolt supports to enhance roadway stability and employing short-wall mining techniques to ensure safety and maximize recovery of coal resources near the fault.

Fold structures can cause changes in the orientation of ore bodies, leading to significant differences in mining conditions across various parts of the ore body. At the axial zone of a fold, the ore body is often subjected to intense compressive stress, resulting in fractured rock and poor stability; whereas on the flanks of the fold, the ore body tends to remain relatively intact. In a certain lead-zinc mine, the ore body exhibits distinct fold structures. When determining the mining sequence, we first extract the portions of the ore body located on the flanks, where the integrity is better and mining conditions are relatively easier. For the ore body in the axial zone of the fold, we conduct detailed geostress monitoring and analysis prior to mining and implement targeted support measures—such as increasing support density and using high-strength support materials—to ensure mining safety. Meanwhile, during the mining process, we closely monitor changes in geostress and promptly adjust mining techniques and sequences accordingly.

Physical and Mechanical Properties of Ore and Rock

The physical and mechanical properties of ore and rock, such as hardness and stability, exert a significant influence on the mining sequence.

Mineral rocks with higher hardness are more difficult to mine, requiring the use of more powerful mining equipment and more efficient rock-breaking methods. In a certain iron ore mine, the mineral rocks have relatively high hardness, and the conventional drilling-and-blasting method proves to be inefficient. When determining the mining sequence, priority is given to extracting areas with relatively lower rock hardness. The revenue generated from these areas will then be used to acquire more advanced mining equipment—such as high-power drilling rigs and high-explosive charges—to enhance the ability to extract harder rock formations. For mineral rocks with higher hardness, during the mining process, it is also necessary to optimize blasting parameters—for example, increasing borehole depth and charge weight, and adopting a rational detonation sequence—to improve the effectiveness of rock breaking.

The stability of mine rock directly affects safety during the mining process. Mine rock with poor stability is prone to accidents such as collapse and roof falls; therefore, in terms of mining sequence, priority should be given to implementing support and reinforcement measures. In a certain gold mine, the mine rock exhibits poor stability and well-developed joint fractures. Before mining begins, a detailed geological survey and stability assessment are conducted on the mine rock. Based on the assessment results, the mining sequence is determined. For areas with the worst stability, anchor bolts and cable supports, along with shotcrete reinforcement, are first applied before mining commences. During the mining process, short advancing lengths and mild blasting techniques are employed to minimize disturbance to the mine rock. At the same time, ground pressure monitoring is intensified, and support measures and the mining sequence are adjusted promptly according to the monitoring data.

Generally speaking, when the RQD value is less than 50%, the rock mass has poor stability and requires special attention during the determination of mining sequence and throughout the mining process.

(2) Technical Factors

Mining method

Different mining methods have specific requirements for the order of extraction.

The open-pit mining method requires that the ore and surrounding rock possess good stability. In terms of mining sequence, it is generally advisable to extract the ore first, followed by the surrounding rock or pillars. Taking the room-and-pillar mining method as an example, the mine block is first divided into rooms and pillars, and the rooms are mined sequentially according to a specific order. Typically, mining begins at one end of the block, with rooms being extracted row by row. After completing the extraction of one row of rooms, the pillars should be promptly supported and reinforced to ensure their stability and provide a reliable foundation for subsequent mining operations. When extracting the rooms, it is essential to rationally control the dimensions and extraction height of the rooms based on the stability of the ore and the thickness of the ore body. If the ore has good stability, the room dimensions can be appropriately increased; conversely, if the stability is poor, the room dimensions should be reduced and the density of the pillars increased.

The caving mining method is suitable for ore bodies with unstable rock and ore conditions. The typical mining sequence involves working from top to bottom and from distant areas toward closer ones. In the sublevel caving method without pillars, drilling and blasting are first carried out in the upper part of each sublevel, causing the ore to collapse. The mined ore is then transported out through underground ore-drawing tunnels located in the lower part of the sublevel. In terms of mining sequence, the upper sublevels are mined first. As the ore from the upper sublevels is extracted, the surrounding rock gradually collapses and fills the mined-out areas. To ensure efficient ore extraction and high ore quality, it is crucial to strictly control the amount and sequence of ore discharge during the mining process, thereby preventing excessive mixing of waste rock. The mining height of each sublevel and the spacing between sublevels should be determined based on the properties of the ore and rock as well as the performance of the mining equipment. Generally, the sublevel height ranges from 10 to 20 meters, and the sublevel spacing typically falls between 15 and 30 meters.

The backfill mining method is often used for extracting valuable ores or ore bodies that have strict requirements regarding surface subsidence. In terms of mining sequence, a portion of the ore body is typically mined first, followed immediately by backfilling, and then the adjacent ore body is mined. In a certain silver mine, the upward horizontal layer-by-layer backfill mining method was adopted. First, mining was carried out at the bottom of the ore block; after completing one layer, backfilling was performed right away, using tailings-cemented backfill material to form a stable backfill mass. Once the backfill mass had reached a certain strength, the next upper layer would be mined, and this process was repeated cyclically. During the backfilling process, it is crucial to strictly control the mix ratio of backfill materials and the quality of backfilling to ensure that the backfill mass can effectively support the surrounding rock and minimize the impact of ground pressure on mining operations.

Development System

The layout of development roadways is closely related to the mining sequence. A rational development system can provide favorable conditions for implementing the mining sequence and enhance mining efficiency.

The shaft development system is suitable for ore bodies that are buried relatively deep and have a relatively short strike length. When using the shaft development method, stage haulage tunnels and preparatory drifts are typically arranged radially around the shaft. The usual mining sequence involves first extracting ore blocks located closer to the shaft, which helps reduce the transportation distance of ore and lower transportation costs. In a certain lead-zinc mine’s shaft development system, the main shaft is situated at the center of the ore body, and stage haulage tunnels extend from the shaft in both directions. At the initial stage of mining, ore block No. 1, which is closest to the shaft, is mined first, with the shaft used for hoisting and transporting the ore. As mining progresses, the mining operations gradually expand toward ore blocks farther from the shaft, while the ventilation, drainage, and other supporting systems are continuously improved to ensure the smooth operation of the mining process.

The inclined shaft development system is suitable for ore bodies with relatively gentle dip angles and shallow burial depths. When developing an inclined shaft, the slope and length of the shaft must be determined based on the geological conditions of the ore body and the performance of the mining equipment. In a certain coal mine’s inclined-shaft development project, the shaft has a slope of 15° and a length of 500 meters. In terms of mining sequence, mining begins from the coal seams near the inclined shaft and gradually progresses along the strike of the coal seams. Given the limited transportation capacity of the inclined shaft, it is essential to carefully schedule the mining progress during the extraction process to avoid accumulation of mined ore. At the same time, the ventilation system should be optimized according to the location of the inclined shaft and the distribution of coal seams, ensuring adequate underground ventilation.

The adit development system is suitable for ore bodies located close to the surface and characterized by favorable topographical conditions. Adit development offers advantages such as low investment, rapid construction, and convenient transportation. In an adit development project at a certain copper mine, the adit is directly connected to the ore body, allowing ore to be transported directly to the surface via the adit. In terms of mining sequence, the ore bodies near the adit are mined first, and then the mining operations extend laterally and deeper. Due to the relatively good ventilation conditions in the adit, the mining intensity can be appropriately increased during the extraction process. However, it is also important to carefully control the size of the mining areas to avoid excessive ground pressure.

Device capability

The type and performance of mining equipment impose significant constraints on the order of extraction.

Large-scale mining equipment, such as large-scale rock-drilling rigs and large-scale loaders, boasts high production capacity but places stringent demands on mining space and operating conditions. In a certain large iron ore mine, large-scale rock-drilling rigs and large-scale loaders were employed. Given the considerable size of this equipment, when determining the mining sequence, priority should be given to areas that can meet the equipment’s operational space requirements. For example, mining areas with larger chamber dimensions and relatively stable roof conditions should be exploited first, enabling the large-scale equipment to carry out rock drilling and ore extraction smoothly. At the same time, the mining schedule should be carefully planned in accordance with the equipment’s production capacity and maintenance cycle to ensure its efficient operation. Generally speaking, a large-scale rock-drilling rig can advance 50 to 100 meters per day, while a large-scale loader can handle an excavation capacity of 100 to 200 cubic meters per hour. These parameters must be fully taken into account when arranging the mining sequence.

Although small-scale mining equipment boasts high flexibility, its production capacity is relatively low. In some small-scale mines, due to limitations in funding and technological capabilities, small-scale mining equipment is employed. When determining the mining sequence, it’s essential to take into account the characteristics of the equipment and prioritize mining areas with higher ore grades and lower mining difficulty, thereby enhancing the economic benefits of the operation. In a certain small gold mine, small pneumatic rock drills and small mine carts were utilized. Given the limited rock-breaking capacity of the small pneumatic rock drills, the mining process began by targeting sections of the ore body with lower rock hardness. Multiple rock drills were operated simultaneously to boost mining efficiency. Moreover, since the small mine carts have limited transport capacity, it’s crucial to carefully plan transportation routes during the mining process, minimizing the number of ore transfers and thereby improving overall transport efficiency.

(3) Economic Factors

Infrastructure investment

Different mining sequences can significantly impact infrastructure investment.

When adopting a downward mining sequence, since the upper stages are mined first, the development roadways in the upper stages can provide favorable conditions for exploration and development of the lower stages, thereby reducing capital investment in infrastructure for the lower stages. As an example, consider a certain metal mine that employs a downward mining method: First, the No. 1 stage in the upper part is developed. During this development process, detailed geological exploration of the No. 2 stage in the lower part is carried out via the roadways in the upper stage, allowing the mine to fully understand the occurrence and characteristics of the lower-stage ore body. When developing the No. 2 stage, based on the results of the earlier exploration, the layout of the development roadways is optimized, thus minimizing unnecessary underground roadway works.

When adopting an upward mining sequence, the initial stage requires excavating the development roadways all at once to reach deep levels, resulting in substantial capital investment for infrastructure. However, if the ore grade in the deep-level ore bodies is relatively high and mining them can yield significant economic benefits, this mining sequence may prove rational in the long run. Therefore, when determining the mining sequence, it is essential to take into account both the capital investment for infrastructure and the future economic benefits. By conducting detailed cost accounting and profitability analysis, we can select the optimal mining plan.

Production cost

The mining sequence has a significant impact on costs related to mining, transportation, ventilation, and other operations.

In terms of mining costs, a rational mining sequence can reduce ore loss and dilution during the mining process, thereby lowering overall mining costs. For example, when mining multi-layer ore bodies, adopting a mining sequence that proceeds from top to bottom can prevent the upper ore layers from damaging the lower ones, thus minimizing ore loss.

In terms of transportation costs, the mining sequence can affect both the distance and mode of ore transportation. If the mining sequence is not properly arranged, it may result in excessively long transportation distances and higher transportation costs. In a certain iron ore mine, due to improper scheduling of the mining sequence, some ore had to be transferred multiple times before reaching the main transport roadway, leading to a substantial increase in transportation costs.

Ventilation costs are also closely related to the mining sequence. An improper mining sequence can lead to a complex ventilation system, increasing ventilation resistance and ventilation costs. In one coal mine, due to a chaotic mining sequence, the ventilation system developed multiple air leakage points, resulting in increased ventilation resistance and higher ventilation costs. Later, by optimizing the mining sequence and rationally arranging ventilation roadways, the number of air leakage points was reduced, and ventilation resistance was lowered.

Ore value

Ore grade and reserve distribution are important economic factors that influence the mining sequence.

For ores with higher grades, priority should be given to their extraction in order to realize economic benefits as soon as possible. In a certain gold mine, detailed geological exploration identified areas within the ore body that have particularly high grades. In terms of mining sequence, these high-grade areas were mined first, and the extracted high-grade ore was prioritized for beneficiation and smelting, yielding substantial sales revenue. This approach not only enables rapid recovery of capital but also allows the recovered funds to be reinvested in subsequent mining and production activities. At the same time, when extracting high-grade ore, it is crucial to properly protect the ore body by employing rational mining methods and technologies, minimizing ore loss and dilution, and enhancing resource utilization efficiency.

For ore bodies with larger reserves, priority should also be given to them in the mining sequence. This is because large-scale mining of such ore bodies can achieve economies of scale and reduce per-unit mining costs. In a certain copper mine, there was a mineral section with substantial reserves. By carefully planning the mining sequence and prioritizing the extraction of this section first, the mine was able to employ large-scale mining equipment and highly efficient mining processes during the extraction phase, thereby achieving scaled production. As a result, the per-unit mining cost was reduced by [X]% compared to small-scale mining operations. When mining ore bodies with larger reserves, it is crucial to fully consider the compatibility between equipment capacity and mining scale, so as to avoid situations where equipment remains idle or underutilized due to insufficient production capacity, thus enhancing mining efficiency and economic benefits.

(4) Safety Factors

Ground Pressure Management

Ground pressure is a critical safety factor that influences the mining sequence. A rational mining sequence can effectively control ground pressure and ensure mining safety.

In general, the pressure is greatest in the central part of the ore body. Therefore, it is more rational to adopt a forward mining sequence that advances from the center toward both sides of the ore body. As an example, consider a certain metal mine that, during its mining operations, employed a forward mining sequence starting from the center and progressing toward both flanks of the ore body. In the early stages of mining, the central portion of the ore body was excavated first. As mining progressed, the ground pressure gradually shifted toward the two flanks. By adopting this mining sequence, the concentration of ground pressure was effectively controlled, thereby avoiding such hazards as mine collapse caused by excessive ground pressure. ## IV. Methods and Steps for Determining a Reasonable Mining Sequence for Ore Deposits

(1) Collecting data

Collecting comprehensive and accurate data is a crucial prerequisite for determining a rational mining sequence for ore deposits, covering multiple key aspects including geological, technical, economic, and safety considerations.

Geological data are the very foundation of all geological studies. To accurately characterize ore bodies, it is essential to obtain detailed information on their spatial distribution underground—including their shape, size, dip angle, thickness, and three-dimensional location. Data such as the strike length and burial depth of ore bodies play a crucial role in delineating mining areas and determining the sequence of mining operations. The data obtained through geological exploration enable us to assess the stability of ore bodies and estimate the difficulty of mining. Geological structural data are equally indispensable; the location, scale, and nature of geological structures such as faults, folds, and joints directly affect the integrity of ore bodies and the distribution of ground pressure during mining operations. In the mining of a certain metal deposit, insufficient preliminary data on a major fault led to the collapse of ore bodies near the fault during mining. This not only resulted in significant ore losses but also severely disrupted the mining schedule. Therefore, when collecting geological data, it is important to employ a variety of exploration methods—such as drilling and geophysical surveys—to ensure the accuracy and completeness of the data.

In terms of technical documentation, the selection of mining methods is closely linked to the mining sequence. Different mining methods—such as open-pit mining, caving mining, and backfilling mining—each have distinct requirements for the mining sequence. Collecting information on the types, performance, and production capacities of existing mining equipment can help us determine whether the equipment can meet production demands under various mining sequences. Understanding the mine’s existing development systems—including the locations and layouts of shafts, inclined shafts, and adits—as well as the conditions of auxiliary systems such as ventilation, drainage, and power supply, is crucial for developing a rational mining sequence. In one coal mine’s extraction operation, insufficient consideration was given to the capacity of the existing ventilation system when determining the mining sequence, resulting in inadequate ventilation in certain mining areas and jeopardizing safe production. Therefore, when collecting technical documentation, it is essential to conduct a comprehensive assessment of the mine’s overall technical condition.

Economic data covers multiple aspects, and infrastructure investment is one of them. Understanding the infrastructure investment requirements under different mining sequences—including costs associated with shaft and tunnel construction, equipment procurement, site preparation, and more—can help us minimize upfront investment costs while ensuring optimal mining performance. Production cost data is equally important; mining costs, transportation costs, ventilation costs, and other related expenses will vary depending on the specific mining sequence. In a certain iron ore mine, optimizing the mining sequence by shortening the distance for ore transportation significantly reduced transportation costs. Collecting data on market prices and sales prospects for the ore is also crucial for determining the optimal mining sequence. If the market price of a particular ore type is high and demand exceeds supply, prioritizing the extraction of that ore body can quickly yield economic benefits.

The collection of safety data is equally important. Ground pressure monitoring data can reflect changes in stress within underground rock masses, providing crucial reference for determining the optimal mining sequence. In a certain gold mine, real-time monitoring of ground pressure revealed that the central part of the ore body experienced significantly higher ground pressure. Consequently, the mining sequence was adjusted to first extract the peripheral areas of the ore body, where ground pressure was relatively lower, thereby ensuring mining safety. Data on the distribution and hazard assessment of disasters such as gas outbursts and water hazards are also key factors that must be considered when determining the mining sequence. In mines with high gas concentrations, priority should be given to extracting areas where gas is easier to manage, thus preventing gas-related accidents.

(2) Plan Development

Based on thorough data collection, multiple mining sequence plans should be developed, taking into account comprehensively various factors such as geological conditions, technological capabilities, economic considerations, and safety requirements, to ensure the feasibility and effectiveness of the plans.

Based on the occurrence conditions of ore bodies and geological structures, different mining sequence schemes should be developed. For ore bodies with considerable strike lengths, a segmented mining approach can be considered, with scheme designs varying according to sequences such as mining from the central area toward both flanks, from both flanks toward the central area, or through alternating segmented mining. If the ore body contains geological structures like faults, a reasonable avoidance or crossing plan should be formulated based on the location and extent of influence of these faults. In a certain lead-zinc mine, the ore body was divided into two parts by a fault. Considering the characteristics of the fault, a mining sequence was established: first, the part farther from the fault was mined, followed by special support measures for the part closer to the fault before proceeding with its extraction. Meanwhile, taking into account the thickness and dip angle of the ore body, for thick and large ore bodies, layered mining or segmented caving methods can be adopted, and appropriate mining sequence schemes for each layer or segment can be developed accordingly.

Based on the mine’s technical conditions, select appropriate mining methods and equipment, and develop a corresponding extraction sequence plan. If the mine adopts the open-stope mining method, the extraction sequence for ore rooms and ore pillars should be determined according to the stability of the ore and rock masses, as well as the timing for reclaiming the ore pillars. In a certain copper mine that employs the open-stope method, the ore rooms are reclaimed first; after the ore rooms have been fully reclaimed, the ore pillars will be reclaimed at an appropriate time, taking into account the stability of the ore pillars and the stress conditions of the surrounding rock mass. If the mine uses the caving mining method, the caving sequence and caving extent must be carefully considered to control ground pressure and ensure smooth recovery of the ore. In the sublevel caving method without bottom pillars, a typical extraction sequence involves working from top to bottom and from distant areas toward closer ones, ensuring that the ore caved from the upper levels can be smoothly transported out through the lower-level ore-drawing tunnels. Based on the existing equipment’s production capacity and operational scope, develop an extraction sequence plan that is well-suited to these capabilities, thereby avoiding situations where equipment remains idle or underutilized.

From an economic perspective, develop an extraction sequence plan that can reduce costs and enhance efficiency. Consider infrastructure investment and production costs under different scenarios, and select the plan with the lowest investment and cost. In a certain coal mine, by comparing the infrastructure investment and production costs of various extraction sequence options, it was found that adopting a downward extraction sequence—first mining the upper coal seam and then using the roadways in the upper seam to develop and prepare the lower seam—can significantly reduce infrastructure investment and transportation costs. Analyze the ore output and quality under different scenarios, and choose the plan that can improve both ore output and quality. If a particular extraction sequence can minimize ore loss and dilution, increase ore recovery rates, and enhance the grade of the concentrate, then this plan will be economically more advantageous.

Safety is the primary consideration in developing a mining sequence plan. Based on the collected safety data, a mining sequence plan should be formulated to effectively control ground pressure and prevent disasters such as gas outbursts and water hazards. In high-gas mines, areas with lower gas content or those that are easier to manage should be prioritized for extraction. By adopting a rational ventilation system and implementing appropriate gas-control measures, it is essential to ensure that gas concentrations remain within safe limits throughout the mining process. In one coal mine, a zoned mining approach was adopted to separate areas with varying gas contents: first, the areas with low gas content were mined, while gas drainage was simultaneously carried out in the areas with high gas content. Mining would then proceed once the gas concentration had been reduced to a safe level. For ore bodies threatened by water hazards, a well-planned drainage scheme and an appropriate mining sequence must be developed to prevent water-inrush accidents during mining operations.

When developing a mining sequence plan, it is essential to fully consider the mutual influences of various factors, conduct comprehensive analysis and trade-offs, and formulate multiple feasible and targeted plans to provide a basis for subsequent plan evaluation and selection.

(3) Scheme Evaluation

Technical Feasibility Assessment

Technical feasibility assessment is the evaluation of the rationality and feasibility of mining sequence plans in terms of mining methods, development systems, and other related aspects.

In terms of mining methods, different extraction sequence schemes must be matched with appropriate mining techniques. For schemes employing the open-stope mining method, it is essential to evaluate whether the arrangement of ore rooms and pillars is reasonable, and whether the span and height of ore rooms as well as the dimensions and spacing of pillars meet the stability requirements of the ore and rock mass. In a certain tungsten mine that employs the open-stope mining method, an assessment of various extraction sequence schemes revealed that if the span of ore rooms is too large, roof collapses are likely to occur during the mining process; conversely, if the pillar dimensions are too small, they will fail to provide adequate support for the roof, thereby jeopardizing subsequent mining operations. Therefore, based on the physical and mechanical properties of the ore and rock mass—such as hardness, strength, and the degree of joint and fracture development—it is necessary to use rock mechanics theories and empirical formulas to calculate and optimize the parameters of ore rooms and pillars. When evaluating schemes using the caving mining method, it is important to consider how the caving sequence and caving extent affect ore recovery and ground pressure control. In particular, when adopting the sublevel caving method without bottom pillars, it is crucial to ensure that the caved ore can be smoothly transported out through the ore-drawing tunnels, thus avoiding blockages or excessive dilution of the ore. By studying the movement trajectories of caved ore and the patterns of ore discharge, and by employing numerical simulation methods, the caving sequence and ore-drawing parameters can be optimized.

The development system represents another crucial aspect of technical feasibility assessment. It is necessary to evaluate whether the layout of development roadways under different mining sequence options is reasonable and capable of meeting production requirements such as ore transportation, ventilation, and drainage. In a certain gold mine, a shaft-based development system is employed. For various mining sequence options, it is essential to analyze whether the location of the shaft facilitates ore hoisting from each mining district and whether the slope and cross-sectional dimensions of the stage transport roadways can meet the operational demands of the transportation equipment. At the same time, the rationality of the ventilation system must be considered to ensure that fresh airflow can reach all working areas smoothly and that stale air can be promptly exhausted. By using methods such as ventilation network calculations, the ventilation resistance and airflow distribution under different mining sequence options can be evaluated, thereby optimizing the design of the ventilation system. Additionally, the drainage system must be assessed to determine whether it can adequately handle underground water inflows and prevent water accumulation that might compromise production safety.

Economic Rationality Assessment

Economic feasibility assessment involves evaluating the economic benefits of different mining sequence options through cost-benefit analysis to identify the optimal solution.

Cost-benefit analysis is the core method for evaluating economic feasibility. First, we need to calculate the costs associated with different mining sequence options, including capital investment, production costs, and operating costs. Capital investment covers expenses such as shaft and tunnel construction, equipment procurement, and site preparation; production costs include mining costs, transportation costs, and ore-processing costs; and operating costs encompass equipment maintenance, personnel wages, and energy consumption. In a certain iron ore mine, under Option A, the capital investment amounts to [X] ten thousand yuan, the production cost per ton of ore is [X] yuan, and the annual operating cost is [X] ten thousand yuan. Under Option B, the capital investment is [X] ten thousand yuan, the production cost per ton of ore is [X] yuan, and the annual operating cost is [X] ten thousand yuan. Through detailed cost accounting, we can accurately grasp the cost profile of each option. Next, we need to estimate the revenues generated by different options, primarily consisting of ore sales revenue and revenue from other by-products. Ore sales revenue is calculated based on the quantity of ore produced, its grade, and the market price. In a certain copper mine, Option A is expected to produce [X] ten thousand tons of ore annually, with an ore grade of [X]% and a market price of [X] yuan per ton, resulting in an ore sales revenue of [X] ten thousand yuan. Under Option B, the mine is expected to produce [X] ten thousand tons of ore annually, with an ore grade of [X]% and a market price of [X] yuan per ton, yielding an ore sales revenue of [X] ten thousand yuan. By conducting a cost-benefit analysis, we compare the costs and revenues of different options and calculate evaluation indicators such as net present value (NPV), internal rate of return (IRR), and payback period. Net present value refers to the algebraic sum of the present values of each year’s net cash flows over the project’s calculation period, discounted at a predetermined discount rate or benchmark rate of return. When the NPV is greater than zero, it indicates that the project is economically feasible; the larger the NPV, the better the option. The internal rate of return is the discount rate that makes the project’s NPV equal to zero. If the IRR exceeds the benchmark rate of return, the project is considered feasible. The payback period is the time required from the start of investment until the entire investment is recovered. The shorter the payback period, the better the option. By calculating and comparing these indicators, we can select the mining sequence option with the optimal economic benefits.

Safety and Reliability Assessment

The safety and reliability assessment evaluates the mining sequence plan from aspects such as ground pressure management and ventilation conditions to ensure the safety and reliability of the mining process.

Ground pressure management is a critical component of safety and reliability assessment. To evaluate the distribution and variation patterns of ground pressure under different mining sequence schemes, it is essential to analyze whether potential safety hazards such as concentrated ground pressure, roof collapses, and rib spalling might occur. In a certain lead-zinc mine, numerical simulations and on-site monitoring were used to analyze the ground pressure conditions under various mining sequence schemes. The analysis revealed that in Scheme C, since the key supporting sections of the ore body were mined first, ground pressure became concentrated in the remaining ore body, making roof collapse accidents more likely. In contrast, Scheme D adopted a rational mining sequence that gradually released ground pressure, resulting in a more uniform distribution of ground pressure and lower safety risks. Therefore, it is crucial to employ ground pressure monitoring technologies and rock mechanics analysis methods to assess ground pressure conditions under different schemes and implement effective ground pressure control measures—such as rationally arranging pillars and conducting backfilling—to ensure the safety of ground pressure during the mining process.

Ventilation conditions are critical to the health and safety of underground workers. To assess whether ventilation systems under different mining sequence plans can meet underground ventilation requirements, it is essential to ensure an adequate supply of fresh airflow and effective removal of contaminated air. In a certain coal mine, during the implementation of Plan E, due to an improperly designed ventilation system, some mining areas experienced poor ventilation, leading to the accumulation of gas and posing significant safety risks. In contrast, Plan F, through optimization of the ventilation system—including the rational arrangement of ventilation roadways and the selection of appropriate ventilation equipment—guaranteed good ventilation in all mining areas. Therefore, it is necessary to conduct calculations of ventilation resistance, airflow distribution, and ventilation effectiveness for each plan, and to adopt effective ventilation measures, such as adding more ventilation equipment or optimizing the ventilation network, to ensure safe underground ventilation. Additionally, it is important to evaluate the safety of different plans in responding to hazards such as gas explosions, water inrushes, and fires, and to develop corresponding emergency response plans and safety measures. This will ensure that, in the event of a disaster, timely and effective actions can be taken to protect the lives of personnel and safeguard the mine’s assets.

(4) Option Selection

To select the optimal mining sequence plan by comprehensively considering various factors, it is necessary to follow certain methods and principles to ensure that the chosen plan enables safe, efficient, and economical mining operations.

When selecting a project plan, technical feasibility should be the primary consideration. A technically infeasible plan, no matter how attractive its economic indicators may be, cannot be implemented in actual production. It is essential to ensure that the mining method chosen is well-suited to the orebody’s occurrence conditions and geological structure, that the development system can meet the mine’s production requirements, and that the equipment can operate normally and comply with safety standards. In a certain gold mine, although Plan G had certain economic advantages, it was ruled out because its mining method placed high demands on the stability of the ore and rock mass, whereas the stability of this gold mine’s ore and rock mass was poor, posing significant safety risks if the plan were adopted. Only technically feasible plans provide a solid foundation for further consideration of other factors.

Economic rationality is an important basis for selecting among alternative options. Among technically feasible options, those with better economic benefits should be given priority. By conducting a cost-benefit analysis and comparing key economic indicators such as net present value, internal rate of return, and payback period across different options, we can choose the option that maximizes investment returns while minimizing costs. In a certain iron ore mining project, both Option H and Option I are technically feasible; however, Option H has a higher net present value and a shorter payback period, giving it a clear advantage in terms of economic rationality and making it the preferred choice. Nevertheless, while pursuing economic benefits, we must not overlook factors such as safety and environmental considerations. Instead, we need to strike a balance among economy, safety, and the environment.

Safety and reliability are the lifeline of mine production, and any proposed plan must ensure safe operations. A comprehensive assessment of safety factors—including ground pressure management, ventilation conditions, and disaster prevention—must be conducted for each alternative, and the option with the lowest safety risks and highest reliability should be selected. In a certain coal mine’s mining operation, although Plan J boasts favorable economic indicators, it poses significant safety risks due to its imperfect ventilation system, which can easily lead to the accumulation of gas. Therefore, Plan J cannot be considered the preferred choice. By contrast, Plan K excels in terms of safety and reliability; through a rational mining sequence and effective safety measures, it can substantially reduce safety risks and guarantee the safe and stable operation of the mine.

In addition to technical, economic, and safety factors, other relevant considerations must also be taken into account, such as environmental impacts, the integrated utilization of resources, and compliance with policies and regulations. When selecting a solution, efforts should be made to minimize environmental damage, enhance the comprehensive utilization of resources, and ensure that the chosen solution complies with national and local policies and regulations. In the mining of a certain nonferrous metal ore, although Option L is economically and technically feasible, it has significant environmental impacts and does not meet the requirements of environmental protection policies. In contrast, Option M not only satisfies the economic and technical requirements but also implements effective environmental protection measures that reduce pollution to the environment; therefore, Option M better aligns with the principles of sustainable development.

After comprehensively considering various factors and employing scientific decision-making methods—such as the Analytic Hierarchy Process and fuzzy comprehensive evaluation—different alternatives are quantitatively evaluated and ranked, ultimately leading to the selection of the optimal mining sequence plan. By adopting this integrated and systematic approach and principles, we can ensure that the chosen plan not only meets the mine’s current production needs but also promotes its long-term development.