Determining a Reasonable Mining Sequence for Ore Deposits

I. Introduction: The Importance of Ore Deposit Mining Sequence

In the field of mining engineering, determining the mining sequence of an ore deposit is akin to the foundation of a skyscraper—it is the critical link upon which the entire mining operation relies for efficient and safe execution. It profoundly influences not only production safety but also plays a decisive role in cost control and resource utilization efficiency.

From a production safety perspective, an unreasonable mining sequence can trigger a series of serious hazards. For example, in the mining of certain metal deposits, if the mining sequence is determined arbitrarily without fully considering the orebody’s occurrence conditions and the distribution patterns of ground pressure, it may lead to goaf instability, causing accidents such as roof collapses and rib spalling, severely threatening the lives of personnel. Relevant statistical data shows that personnel casualties and property losses in some mine accidents attributed to improper mining sequences are extremely severe.

Regarding cost control, the mining sequence directly affects the mine’s capital investment, operational costs, and equipment lifespan. A scientific and reasonable mining sequence can reduce unnecessary shaft and roadway construction, lowering the costs associated with frequent equipment relocation and maintenance. Taking a large coal mine as an example, by optimizing the mining sequence and concentrating the initial mining area near the main shaft, the length of haulage roadways and their associated maintenance workload were reduced, resulting in an annual transportation cost decrease of [X]% and a significant drop in equipment failure rates.

Resource utilization efficiency is also closely tied to the mining sequence. A reasonable sequence can maximize ore extraction, reducing ore loss and dilution rates. For instance, for deposits with multi-layered orebodies, mining in a sequence from top to bottom, from easy to difficult sections, can effectively prevent damage to lower layers caused by upper layer extraction, improving overall resource recovery. An unreasonable mining sequence may lead to the permanent loss of some ore underground, causing significant resource waste.

In practical mining operations, we frequently encounter various complex geological conditions and orebody occurrence states. Some orebodies have extensive strike lengths, others have significant thickness variations, and still others exhibit marked differences in stability compared to the surrounding rock. These factors make determining a reasonable mining sequence particularly complex and important. Therefore, in-depth research into ore deposit mining sequences, comprehensively considering the influence of various factors, holds immeasurable significance for achieving sustainable mine development.

II. Basic Concepts and Classification of Ore Deposit Mining Sequence

(I) Basic Concepts

The mining sequence of an ore deposit, simply put, refers to the specific order in which various mining units are extracted throughout the mining operation process, according to defined principles and patterns. Here, mining units can be mine fields, levels, blocks, or adjacent orebodies. It is like a meticulously planned battle layout, where each move affects the overall outcome.

In essence, determining the mining sequence is the result of a comprehensive trade-off among multiple complex factors. These factors encompass the orebody’s occurrence conditions, such as its shape, size, dip angle, thickness, and spatial distribution underground; the ore grade and value, where the optimal timing for mining high-grade ore significantly impacts economic benefits; the stability of geological structures, as faults, folds, and other structures alter the orebody’s mechanical state, thereby influencing the choice of mining sequence; and also the technical mining conditions, including the mining method employed and equipment performance, as different mining methods impose different requirements on the mining sequence.

Throughout the entire mining process, the ore deposit mining sequence occupies a core and pivotal position, playing a connecting role. From preliminary geological exploration to mine planning and design, to the implementation of specific mining operations and finally mine closure, the mining sequence runs through it all. A reasonable mining sequence ensures the continuity and stability of mine production, enabling mining operations to proceed in an orderly manner. For example, in some large metal mines, scientific planning of the mining sequence can ensure close coordination between different mining stages, avoiding production interruptions or delays caused by improper sequencing. It acts like an invisible bond, tightly linking all aspects of the mining process together, enabling the efficient operation of the entire mining system.

(II) Classification

1. Mining Sequence of Levels within a Mine Field

1. Descending (Top-Down) Mining: This refers to mining in sequence from top to bottom, extracting the upper levels first before moving to lower ones, or simultaneously mining several levels based on actual conditions. This sequence is relatively common in practice. For example, a large lead-zinc mine used descending mining, first mining the upper Level 1. During mining, the development workings from the upper level were used to further explore the occurrence of the orebody in the lower Level 2, providing accurate geological data for subsequent mining. Additionally, as mining the upper level is relatively easier to initiate with lower initial investment, it allows for rapid production startup and economic benefits. Moreover, in descending mining, the influence of upper goafs on lower mining is relatively small, production safety conditions are better, and a wider range of mining methods, such as open stoping and fill mining, are applicable.

However, simultaneous mining of multiple levels, while increasing the working line length and mine production capacity, also brings a series of problems. For instance, production management becomes decentralized, requiring more manpower and resources for coordination; roadway maintenance workload increases significantly; various pipelines and tracks cannot be recovered and reused promptly, causing resource waste; air contamination recirculation becomes more severe, affecting underground air quality and increasing ventilation costs; and operational management expenses also rise accordingly. Generally, the number of levels being mined simultaneously can be maintained at 1-2 and should not exceed 3-4 to balance production efficiency and management costs.

2. Ascending (Bottom-Up) Mining: In contrast to descending mining, this involves mining the lower levels first, then the upper ones, proceeding level by level from bottom to top. This sequence is used only in special circumstances. For instance, when mining gently dipping deposits and there is no suitable waste dump on the surface, waste rock from upper mining needs to be backfilled into lower goafs, making ascending mining a necessity. Another example is when deep goafs are intended to be used as water reservoirs. In a coal mine, due to scarce surface land resources and the inability to establish a waste dump, ascending mining was adopted, backfilling waste rock from upper coal seam mining into lower, mined-out spaces, solving both waste disposal and partial goaf backfilling.

The advantages of ascending mining include being able to develop to the economically optimal and technically feasible maximum depth in one go and conducting extraction at the deepest point, while simultaneously developing and preparing levels 1-2 above. This allows waste rock to be used to fill goafs, forming high-strength backfill that effectively prevents large-scale rock mass movement and overall failure, reducing the possibility of surface damage and subsidence. Furthermore, this mining method helps mitigate rockburst hazards induced by deep mining, as the backfill in lower goafs can act as a buffer and disperse stress.

However, ascending mining also has limitations. For example, in the early mining stages, the top levels experience less mining disturbance, but in later stages, as lower goafs expand, significant stress fluctuations can occur in upper levels, impacting safety and the stability of surface structures. Moreover, ascending mining demands higher mining technology and equipment, requiring more precise engineering control and management.

2. Block Mining Sequence within a Level

1. Advancing Mining: When the level haulage drift has been driven a certain distance, mining begins from blocks near the main development workings and then advances successively towards the mine field boundary. This is called advancing mining. Its significant advantage is the short initial mine construction period, enabling rapid production startup and early economic benefits. For example, a small gold mine used advancing mining, starting to extract blocks near the main shaft after the level haulage drift had been driven 500 meters. This allowed ore extraction and sales to commence quickly, facilitating rapid capital turnover.

However, advancing mining also has obvious disadvantages. Since mining starts near the main development workings, as mining advances, development workings gradually move farther away from the main workings, increasing the difficulty and cost of maintaining these development roadways. Furthermore, during mining, if the geological conditions of subsequent blocks are not accurately understood, it can easily lead to insufficient development and prepared reserves, creating passive situations in production. Its applicable conditions are deposits with simple conditions, stable ore and rock, and a requirement for early commencement of mining within the level. Under such conditions, advancing mining can fully utilize its advantage of rapid production startup, while the pressure of maintaining development roadways is relatively lower due to stable ground conditions.

2. Retreating Mining: After the level haulage drifts are driven to the mine field boundary, mining begins from blocks at the boundary and retreats successively towards the main development workings. This mining sequence is retreating mining. It can be further subdivided into double-wing, single-wing, and flank retreating mining. For example, a large copper mine used double-wing retreating mining, extracting blocks simultaneously from both east and west sides of the mine field boundary towards the main shaft.

The advantages of retreating mining include lower roadway maintenance costs because mining proceeds towards the main development workings, keeping development roadways close to the main workings for easier maintenance and management. Also, roadways can be driven in advance before mining, allowing for early exploration of seam conditions, aiding in mining planning and safety assurance.

However, retreating mining involves a long initial mine construction period and slow production startup, requiring relatively long haulage drifts to be driven to the mine field boundary before mining can begin. The advantage of low roadway maintenance costs is fully realized only with a central parallel shaft layout; with a central diagonal shaft layout, due to differences in the ventilation system, this advantage may not be as evident.

Combined Mining: Combined mining integrates features of both advancing and retreating methods. Initially, advancing mining is used; after the level haulage drift is fully driven, it switches to retreating mining, or both advancing and retreating mining proceed simultaneously during the operation. For example, an iron ore mine used advancing mining initially to quickly start production, extracting blocks near the main shaft. As the level haulage drift was completed, it switched to retreating mining to reduce roadway maintenance costs. This approach combines the advantages of both sequences, achieving early economic benefits while effectively controlling costs later.

However, combined mining introduces complexity in production management, requiring more precise scheduling and coordination to ensure smooth transitions between different mining methods. In practical application, the specific method and timing of combined mining need to be reasonably chosen based on the mine’s specific conditions, such as orebody occurrence, mining technology level, and production management capability.

3. Mining Sequence for Adjacent Orebodies

Determining the mining sequence for adjacent orebodies needs to follow certain basic principles. The primary principle is to achieve integrated mining of rich and poor ores, large and small orebodies, thick and thin sections, and easy and difficult parts, aiming to maximize resource utilization and avoid waste.

In actual mining, the mutual influence between orebodies must be fully considered. When the dip angle of the orebody is less than or equal to the angle of draw of the surrounding rock, the influence of the first-mined orebody on the later-mined one is relatively small, and the choice of mining sequence is more flexible. For example, in a lead-zinc ore field with two adjacent orebodies, Orebody 1 has a dip of 30°, Orebody 2 has a dip of 25°, and the angle of draw is 40°. In this case, the mining sequence can be determined based on factors like ore grade and mining difficulty. If Orebody 1 has higher grade and lower mining difficulty, it can be mined first.

When the dip angle of the orebody is greater than the angle of draw of the surrounding rock, mining the first orebody may cause movement and deformation of the surrounding rock, significantly affecting the later-mined orebody. In this case, a reasonable mining sequence and measures need to be adopted to reduce this impact. For example, in a copper mine with two adjacent orebodies, Orebody A has a dip of 70°, Orebody B has a dip of 65°, and the angle of draw is 50°. If Orebody A is mined first, as it is extracted, the surrounding rock may move and collapse, potentially damaging the integrity of Orebody B, increasing its mining difficulty and risk. In this situation, after detailed geological analysis and mechanical calculations, it was decided to mine Orebody B first, then employ fill mining for Orebody A to control rock movement and reduce its impact on Orebody B. This approach effectively facilitated the smooth mining of both orebodies and improved resource recovery.

In some special geological conditions, such as the presence of faults or fractured zones, the mining sequence for adjacent orebodies requires even more careful determination. In a gold mine, a large fault existed between orebodies, with broken and unstable rock near the fault. To avoid fault activation during mining leading to safety accidents, after expert evaluation, it was decided to first mine the orebody farther from the fault, then mine the orebody near the fault using special mining methods and support measures. Through this flexible approach, difficulties posed by special geological conditions were successfully overcome, ensuring the safety and smooth progress of mining operations.

III. Factors Influencing Ore Deposit Mining Sequence

(I) Geological Factors

1. Orebody Occurrence Conditions

The dip angle, thickness, strike length, and other occurrence conditions of the orebody are crucial influences on the mining sequence.

When the orebody dip angle is small, such as in gently dipping orebodies, mining method choices and sequence selection are relatively limited. Taking a gently dipping medium-thick orebody with a dip angle less than 30° as an example, when using traditional open stoping methods, ore handling is difficult because ore cannot slide down by gravity. In such cases, fill mining might be prioritized, extracting parts near the surface or convenient for transportation first, using backfill to support the roof to ensure mining safety. In this situation, the mining sequence typically progresses from shallow to deep or from one end of the orebody to the other to reduce ore loss and guarantee extraction efficiency.

The difficulty of handling ore can be simply explained by the formula ：

is the gravitational force of the ore

is the dip angle of the orebody.

When θ is small, F is also small, which is unfavorable for the natural downward sliding of the ore.

For thick orebodies, sequence determination is more complex. Thick orebodies generally employ sublevel or slice mining. When determining the sequence, the influence of upper sublevel or slice mining on lower ones must be considered. For example, when using sublevel caving for thick orebodies, the upper sublevels are usually mined first, using the upper goaf as compensation space for lower caved ore. However, in this case, blasting parameters and draw control in the upper mining must be strictly managed to prevent premature and excessive mixing of upper ore into lower ore, causing dilution. Generally, during upper sublevel mining, the amount of ore blasted each time should not be too large, and the principle of “draw more, leave less” should be followed during drawing to ensure normal recovery of lower ore.

The orebody strike length also affects the mining sequence. Orebodies with great strike length can be divided into multiple mining panels based on actual conditions. When dividing panels, factors such as the orebody’s geological structure and ore grade variations must be considered. For instance, in a copper mine, the orebody strike length reached several kilometers. For ease of mining and management, the orebody was divided into 5 panels. Panel 1, located centrally with relatively simple geology and higher ore grade, was mined first. This allowed for quick economic benefits while utilizing the mining experience and data from Panel 1 as a reference for subsequent panels. For the sequence of later panels, based on the extension direction of geological structures and ore grade distribution, mining proceeded in order from high-grade to low-grade and from geologically simple to complex areas to improve resource recovery and mining efficiency.

Geological Structure

Faults, folds, and other geological structures are important factors influencing the mining sequence.

The presence of faults disrupts the integrity and continuity of the orebody, increasing mining difficulty and risk. When fault displacement is large, it may offset the orebody, making normal mining impossible. In a coal mine, encountering a fault with a displacement of 10 meters directly cut off the coal seam. To address this, when determining the mining sequence, detailed exploration of the orebody on both sides of the fault was conducted first to ascertain the fault’s extension direction and influence range. Then, based on the fault’s location and strike, the mining sequence was adjusted to mine other parts of the orebody by working around the fault. For the parts affected by the fault, special support measures and mining methods were adopted, such as using rock bolt support to enhance roadway stability and using the shortwall mining method to extract coal near the fault safely and as much as possible.

Fold structures alter the attitude of the orebody, leading to significant differences in mining conditions at different locations. In the fold hinge zone, the orebody often experiences greater compressive stress, with broken rock and poor stability; while on the fold limbs, the orebody is relatively more intact. In a lead-zinc mine, the orebody had obvious fold structures. When determining the mining sequence, the parts of the orebody on the fold limbs with better integrity and relatively easier mining conditions were mined first. For the orebody in the hinge zone, detailed ground pressure monitoring and analysis were conducted before mining, and targeted support measures were taken, such as increasing support density and using high-strength support materials, to ensure mining safety. Simultaneously, during mining, ground pressure changes were closely monitored, and mining techniques and sequence were adjusted promptly.

Physical and Mechanical Properties of Ore and Rock

The hardness, stability, and other physical and mechanical properties of ore and rock significantly constrain the mining sequence.

Hard ore and rock present greater mining difficulty, requiring more powerful mining equipment and more efficient rock-breaking methods. In an iron ore mine, the ore and rock were hard, and conventional drilling and blasting methods were inefficient. When determining the mining sequence, areas with relatively lower hardness were prioritized for mining. The revenue from these areas was used to purchase more advanced mining equipment, such as high-power drill jumbos and high-power explosives, to improve the mining capability for harder ore and rock. For hard ore and rock, during the mining process, blasting parameters also need optimization, such as increasing hole depth and charge amount, and adopting reasonable initiation sequences to improve rock-breaking effectiveness.

The stability of ore and rock is directly related to safety during mining. Unstable ore and rock are prone to collapses, rib spalling, and other accidents, so in terms of mining sequence, priority should be given to taking measures for support and reinforcement. In a gold mine, the ore and rock stability was poor, with developed joints and fractures. Before mining, detailed geological investigation and stability assessment of the ore and rock were conducted, and the mining sequence was determined based on the assessment results. For areas with the poorest stability, rock bolt/cable support and shotcrete reinforcement were carried out first before mining. During mining, methods like short advance and controlled blasting were used to reduce disturbance to the ore and rock, while ground pressure monitoring was strengthened, and support measures and mining sequence were adjusted timely based on monitoring data.

Judging ore and rock stability can be aided by some empirical formulas and indices, such as the Rock Quality Designation (RQD):

is the total length of core pieces longer than 10cm

is the total drill run length.

A larger RQD value indicates better integrity and relatively higher stability of the ore and rock. Generally, when the RQD value is less than 50%, the ore and rock stability is poor, requiring special attention during mining sequence determination and the mining process.

Generally, when the RQD value is less than 50%, the ore and rock stability is poor, requiring special attention during mining sequence determination and the mining process.

(II) Technical Factors

Mining Method

Different mining methods impose specific requirements on the mining sequence.

Open stoping methods require relatively stable ore and rock. In terms of sequence, ore is typically mined first, followed by surrounding rock or pillars. Taking room and pillar mining as an example, rooms and pillars are first delineated within the block, and rooms are extracted in a certain order. Generally, starting from one end of the block, rooms are extracted row by row. After extracting one row of rooms, pillars are promptly supported and reinforced to ensure their stability, providing a guarantee for subsequent mining. When extracting rooms, the room dimensions and mining height should be reasonably controlled based on the stability of the ore and rock and the thickness of the orebody. If the ore and rock are stable, room dimensions can be appropriately increased; otherwise, room dimensions should be reduced, and pillar density increased.

Caving methods are suitable for orebodies with unstable ore and rock. Their mining sequence is generally top-down, from far to near. In the sublevel caving method without sill pillars, drilling and blasting are first conducted in the upper part of the sublevel to cave the ore, which is then transported out through the lower drawpoint drifts. In terms of sequence, upper sublevels are mined first. As ore from upper sublevels is extracted, the surrounding rock gradually caves to fill the goaf. To ensure drawing efficiency and ore quality, draw quantity and sequence must be strictly controlled during mining to avoid excessive waste rock mixing. The mining height and sublevel spacing for each sublevel should be determined based on the properties of the ore and rock and the performance of the mining equipment. Generally, sublevel height ranges from 10 to 20 meters, and sublevel spacing ranges from 15 to 30 meters.

Fill mining methods are often used for mining valuable ores or orebodies with strict requirements on surface subsidence. In terms of sequence, a part of the orebody is mined first, then backfilled promptly, followed by mining adjacent orebody parts. In a silver mine, the up-dip horizontal cut-and-fill mining method was used. Extraction started at the bottom of the block. After mining one layer, backfilling was done immediately using tailings-cement backfill material to form a stable backfill mass. After the backfill reached a certain strength, the next layer was mined, and so on. During backfilling, the mix proportion and quality of the backfill material must be strictly controlled to ensure the backfill can effectively support the surrounding rock and reduce the impact of ground pressure on mining.

Development System

The layout of development workings is closely related to the mining sequence. A reasonable development system can provide convenient conditions for implementing the mining sequence and improve mining efficiency.

Shaft hoisting systems are suitable for orebodies buried deep with limited strike length. When using shaft development, stage haulage drifts and development workings are generally arranged radially around the shaft. The mining sequence usually starts with blocks close to the shaft to reduce ore transport distance and lower transportation costs. In a lead-zinc mine shaft development system, the main shaft was located in the center of the orebody, with stage haulage drifts extending from the shaft to both sides. During initial mining, Block 1 near the shaft was mined first, utilizing the shaft for ore hoisting and transportation. As mining advanced, it gradually expanded to blocks farther from the shaft, while simultaneously improving systems like ventilation and drainage to ensure smooth mining operations.

Incline/ramp systems are suitable for orebodies with gentle dip angles and shallow burial. When developing with inclines, the gradient and length of the incline should be determined based on the occurrence conditions of the orebody and the performance of the mining equipment. In a coal mine incline development, the incline had a gradient of 15° and a length of 500 meters. In terms of mining sequence, mining started from the coal seam near the incline and progressed along the strike. Due to the limited transport capacity of the incline, mining progress needed to be reasonably arranged during the process to avoid ore accumulation. Simultaneously, based on the incline’s location and coal seam distribution, the ventilation system was optimized to ensure good underground ventilation.

Adit systems are suitable for orebodies located near the surface with favorable terrain conditions. Adit development has advantages like low investment, fast construction, and convenient transport. In a copper mine adit development, the adit directly connected to the orebody, allowing ore to be transported directly to the surface via the adit. In terms of mining sequence, mining started with orebody parts near the adit, then expanded to both sides and deeper parts. As adits offer good ventilation conditions, mining intensity can be appropriately increased during the process, but stope scale should also be controlled to avoid excessive ground pressure.

Equipment Capability

The type and performance of mining equipment impose important limitations on the mining sequence.

Large mining equipment, such as large drill jumbos and large LHDs (Load-Haul-Dump machines), have high production capacity but demand larger working spaces and specific operational conditions. In a large iron ore mine, large drill jumbos and large LHDs were used. Due to the large size of this equipment, when determining the mining sequence, areas that could meet the equipment’s operational space requirements were prioritized for mining. For example, areas with larger room dimensions and more stable roofs were mined first to allow large equipment to conduct drilling and mucking operations smoothly. Simultaneously, based on the equipment’s production capacity and maintenance cycles, mining progress was reasonably arranged to ensure efficient equipment operation. Generally, the daily advance rate of a large drill jumbo can reach 50-100 meters, and the loading capacity of a large LHD can reach 100-200 cubic meters per hour. These parameters must be fully considered when arranging the mining sequence.

Small mining equipment offers high flexibility but relatively lower production capacity. In some small mines, due to funding and technical limitations, small mining equipment is used. When determining the mining sequence, based on the equipment characteristics, areas with higher ore grades and lower mining difficulty should be prioritized to improve economic returns. In a small gold mine, small pneumatic drills and small mine cars were used. Due to the limited rock-breaking capability of small pneumatic drills, areas of the orebody with relatively lower hardness were chosen for mining first, employing multiple drills operating simultaneously to improve mining efficiency. Small mine cars have limited transport capacity, so during mining, transport routes needed to be reasonably arranged to reduce the number of ore transfers and improve transport efficiency.

(III) Economic Factors

Capital Investment

Different mining sequences significantly impact capital investment.

When using a descending mining sequence, since upper levels are mined first, the development workings of the upper levels can facilitate exploration and development of lower levels, thereby reducing the capital investment for lower levels. For example, in a metal mine using descending mining, Level 1 in the upper part was developed first. During development, detailed geological exploration of Level 2 in the lower part was conducted through the workings of the upper level, understanding the occurrence of the lower orebody. When developing Level 2, based on prior exploration results, the layout of development workings was optimized, reducing unnecessary shaft and roadway construction.

When using an ascending mining sequence, development workings need to be driven to the deep part in one go initially, involving larger capital investment. However, if the deep orebody has high grade and can yield high economic benefits after mining, this sequence might also be reasonable in the long run. Therefore, when determining the mining sequence, capital investment and future economic benefits must be considered comprehensively. Through detailed cost accounting and benefit analysis, the optimal plan is selected.

Production Costs

The mining sequence significantly impacts costs like mining, transportation, and ventilation.

In terms of mining costs, a reasonable mining sequence can reduce ore loss and dilution during the mining process, lowering mining costs. For example, when mining multi-layered orebodies, mining in a top-down sequence can avoid damage to lower layers caused by upper layer extraction, reducing ore loss.

Mining cost can be calculated by the formula

is the quantity of ore mined

is the unit mining cost

is the ore loss rate.

In terms of transportation costs, the mining sequence affects ore transport distance and methods. If the mining sequence is unreasonable, it may lead to excessively long transport distances, increasing transportation costs. In an iron ore mine, due to improper mining sequence arrangement, some ore required multiple transfers to reach the main haulage drift, significantly increasing transportation costs.

The calculation formula for transportation cost is

is the transportation distance

is the quantity of ore transported

is the unit transportation cost.

Ventilation costs are also closely related to the mining sequence. An unreasonable sequence may lead to a complex ventilation system, increasing ventilation resistance and costs. In a coal mine, due to a disorganized mining sequence, the ventilation system had multiple air leakage points, increasing ventilation resistance and costs. Later, by optimizing the mining sequence and reasonably arranging ventilation roadways, air leakage points were reduced, and ventilation resistance decreased.

Ore Value

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

For higher-grade ore, it should be prioritized for mining to obtain economic benefits as soon as possible. In a gold mine, through detailed geological exploration, areas with higher grades within the orebody were identified. In terms of mining sequence, these high-grade areas were mined first. The extracted high-grade ore was prioritized for processing and smelting, yielding higher sales revenue. This not only quickly recouped funds but also allowed reinvestment into subsequent mining and production. Simultaneously, when mining high-grade ore, protecting the orebody is important, using reasonable mining methods and techniques to reduce ore loss and dilution, improving resource utilization.

For parts of the orebody with larger reserves, they should also be given priority consideration in the mining sequence. Because large-scale orebody mining can achieve economies of scale, reducing unit mining costs. In a copper mine, there was a large reserve block. Through reasonable planning of the mining sequence, this block was mined first. During mining, large mining equipment and efficient mining techniques were used, achieving large-scale production. The unit mining cost compared to small-scale mining was reduced by [X]%. When mining large reserve orebodies, the matching of equipment production capacity and mining scale must be fully considered to avoid equipment idleness or insufficient production capacity, thereby improving mining efficiency and economic returns.

(IV) Safety Factors

Ground Pressure Management

Ground pressure is a key safety factor influencing the mining sequence. A reasonable sequence can effectively control ground pressure, ensuring mining safety.

Under general conditions, the pressure is greatest near the center of the orebody’s strike. Therefore, adopting an advancing mining sequence from the center towards the flanks is considered more reasonable. For example, in a metal mine, an advancing sequence from the center towards the flanks was used during mining. In the initial mining stage, the central part of the orebody was mined first. As mining advanced, ground pressure gradually dispersed towards the flanks. Through this sequence, ground pressure concentration was effectively controlled, avoiding stope collapses and other accidents caused by excessive ground pressure.

IV. Methods and Steps for Determining a Reasonable Ore Deposit Mining Sequence

(I) Data Collection

Collecting comprehensive and accurate data is an important prerequisite for determining a reasonable ore deposit mining sequence. It covers multiple key aspects including geology, technology, economics, and safety.

Geological data is the foundation. Detailed orebody occurrence conditions, including shape, size, dip angle, thickness, and spatial distribution underground, need to be accurately mastered. Data such as strike length and burial depth play a key role in dividing mining areas and determining the sequence. Data obtained through geological exploration helps assess orebody stability and mining difficulty. Data on geological structures is equally indispensable. The location, scale, and nature of faults, folds, joints, etc., directly affect orebody integrity and ground pressure distribution during mining. In a metal mine, due to insufficient preliminary data on a major fault, the orebody near the fault collapsed during mining, causing ore loss and severely impacting progress. Therefore, when collecting geological data, multiple exploration methods like drilling and geophysics should be used to ensure accuracy and completeness.

Regarding technical data, the choice of mining method is closely related to the sequence. Different methods like open stoping, caving, and fill mining impose different requirements. Collecting data on existing mining equipment types, performance, and production capacity helps determine if equipment can meet production needs under different sequences. Understanding the mine’s existing development system, including the location and layout of shafts, inclines, adits, and auxiliary systems like ventilation, drainage, and power supply, is crucial for formulating a reasonable sequence. In a coal mine, due to insufficient consideration of the existing ventilation system’s capacity when determining the sequence, some panels experienced poor ventilation, affecting safety. Therefore, when collecting technical data, the mine’s overall technical condition should be comprehensively assessed.

Economic data involves multiple aspects, with capital investment being one. Understanding the capital investment situation under different sequences, including costs for shaft/roadway construction, equipment purchase, site leveling, etc., helps minimize upfront investment costs while ensuring mining effectiveness. Production cost data should not be overlooked. Mining, transportation, and ventilation costs vary under different sequences. In an iron ore mine, by optimizing the sequence and shortening ore transport distance, transportation costs were significantly reduced. Collecting data on ore market prices and sales prospects is also important for determining the sequence. If a certain ore has high market price and demand, prioritizing that part can yield quick economic benefits.

Safety data collection is equally important. Ground pressure monitoring data reflects stress changes in underground rock masses, providing important reference for sequence determination. In a gold mine, through real-time monitoring of ground pressure data, it was found that pressure was higher in the central part of the orebody. Consequently, the sequence was adjusted to mine the peripheral parts with lower pressure first, ensuring safety. Data on the distribution and risk assessment of hazards like gas and water also need consideration when determining the sequence. In mines with high gas content, areas easier for gas control should be prioritized to avoid gas accidents.

(II) Scheme Formulation

Based on fully collected data, formulating multiple mining sequence schemes requires comprehensive consideration of geological conditions, technical level, economic factors, and safety requirements to ensure feasibility and effectiveness.

Based on the orebody’s occurrence conditions and geological structures, formulate different sequence schemes. For orebodies with great strike length, consider panel mining, designing schemes with different orders like center-to-flanks, flanks-to-center, or alternating panel mining. If the orebody has geological structures like faults, formulate reasonable avoidance or crossing schemes based on the fault’s location and influence range. In a lead-zinc mine, the orebody was divided by a fault. Based on the fault situation, a scheme was formulated to mine the part farther from the fault first, then mine the part near the fault after special support. Simultaneously, considering the orebody’s thickness and dip angle, for thick orebodies, layered or sublevel caving methods can be used, formulating sequences for different layers or sublevels.

Combining the mine’s technical conditions, select appropriate mining methods and equipment, and formulate corresponding sequence schemes. If the mine uses open stoping, determine the extraction sequence of rooms and pillars, and the timing of pillar recovery based on ore and rock stability. In a copper mine using open stoping, rooms were extracted first. After room extraction, based on pillar stability and surrounding rock stress, appropriate timing for pillar recovery was chosen. If the mine uses caving methods, consider the caving sequence and range to control ground pressure and ensure ore recovery. In sublevel caving without sill pillars, a top-down, far-to-near sequence is typically used to ensure caved ore from upper parts can be smoothly transported out through lower drawpoint drifts. Based on the production capacity and operational range of existing equipment, formulate sequence schemes that match them to avoid equipment idleness or insufficient capacity.

From an economic perspective, formulate schemes that can reduce costs and improve returns. Consider the capital investment and production costs under different schemes, selecting those with lower investment and costs. In a coal mine, by comparing these for different sequence schemes, it was found that using a descending sequence, mining upper seams first and utilizing their workings for developing lower seams, could reduce capital investment and transportation costs. Analyze the ore output and quality under different schemes, selecting those that can improve output and quality. If a certain sequence can reduce ore loss and dilution, improving ore recovery and concentrate grade, then that scheme is more advantageous economically.

Safety is the primary consideration when formulating sequence schemes. Based on collected safety data, formulate schemes that can effectively control ground pressure and prevent hazards like gas and water. In gassy mines, prioritize mining areas with lower gas content or easier control, using reasonable ventilation systems and gas management measures to ensure gas concentration remains within safe limits during mining. In a coal mine, a zoning approach was used, separating areas with different gas contents. Areas with low gas were mined first, while areas with high gas underwent gas drainage simultaneously, and were mined after concentration was lowered. For orebodies threatened by water hazards, formulate reasonable drainage plans and mining sequences to avoid water inrushes during mining.

When formulating sequence schemes, the interaction of various factors must be fully considered, conducting comprehensive analysis and trade-offs to develop multiple feasible and targeted schemes, providing a basis for subsequent scheme evaluation and selection.

(III) Scheme Evaluation

1. Technical Feasibility Evaluation

Technical feasibility evaluation assesses the rationality and feasibility of mining sequence schemes in terms of mining methods, development systems, etc.

Regarding mining methods, different sequence schemes need to match corresponding mining methods. For schemes using open stoping, evaluate if the layout of rooms and pillars is reasonable, and if room span, height, pillar size, and spacing conform to ore and rock stability requirements. In a tungsten mine using open stoping, by evaluating different sequence schemes, it was found that if room span was too large, roof collapses were likely during mining; while if pillar size was too small, effective roof support was impossible, affecting subsequent mining. Therefore, based on the physical and mechanical properties of ore and rock, like hardness, strength, joint/fracture development, use rock mechanics theory and empirical formulas to calculate and optimize room and pillar parameters. When evaluating schemes using caving methods, consider the influence of caving sequence and range on ore recovery and ground pressure control. When using sublevel caving without sill pillars, ensure caved ore can be smoothly transported out through drawpoint drifts, avoiding ore blockage or excessive dilution. By studying the movement trajectory and draw laws of caved ore, using methods like numerical simulation, optimize the caving sequence and draw parameters.

The development system is another important aspect of technical feasibility evaluation. Evaluate if the layout of development workings under different sequence schemes is reasonable and if it can meet production needs like ore transport, ventilation, and drainage. In a gold mine using a shaft system, for different sequence schemes, analyze if the shaft location facilitates ore hoisting from various panels, and if the gradient and cross-sectional dimensions of stage haulage drifts meet the operational requirements of transport equipment. Simultaneously, consider the rationality of the ventilation system, ensuring fresh air can smoothly reach all working places and contaminated air can be promptly exhausted. Using methods like ventilation network calculation, evaluate ventilation resistance and airflow distribution under different sequence schemes, optimizing ventilation system design. Also evaluate if the drainage system can meet the discharge requirements for underground water inflow, avoiding water accumulation affecting production safety.

2. Economic Rationality Evaluation

Economic rationality evaluation assesses the economic returns of different mining sequence schemes through cost-benefit analysis to determine the optimal scheme.

Cost-benefit analysis is the core method. First, calculate the costs of different schemes, including capital investment, production costs, and operating costs. Capital investment covers shaft/roadway construction, equipment purchase, site leveling, etc.; production costs include mining, transportation, processing costs, etc.; operating costs include equipment maintenance, personnel wages, energy consumption, etc. In an iron ore mine, for Scheme A, capital investment was [X] thousand yuan, production cost per ton of ore was [X] yuan, annual operating cost was [X] thousand yuan; for Scheme B, capital investment was [X] thousand yuan, production cost per ton was [X] yuan, annual operating cost was [X] thousand yuan. Through detailed cost accounting, accurately master each scheme’s cost situation. Then, estimate the revenue of different schemes, mainly including ore sales revenue and other by-product income. Calculate ore sales revenue based on ore output, grade, and market price. In a copper mine, Scheme A projected annual ore output [X] thousand tons, ore grade [X]%, market price [X] yuan/ton, so ore sales revenue [X] thousand yuan; Scheme B projected annual output [X] thousand tons, grade [X]%, price [X] yuan/ton, revenue [X] thousand yuan. Through cost-benefit analysis, compare costs and revenue of different schemes, calculating evaluation indicators like Net Present Value (NPV), Internal Rate of Return (IRR), and Payback Period. NPV is the algebraic sum of the present values of annual net cash flows during the project calculation period, discounted at a set rate or benchmark rate. When NPV > 0, the project is economically feasible, and a larger NPV indicates a better scheme. IRR is the discount rate that makes NPV = 0. When IRR > benchmark rate, the project is feasible. Payback Period is the time required from initial investment to full recovery. A shorter period indicates a better scheme. By calculating and comparing these indicators, select the economically optimal mining sequence scheme.

3. Safety and Reliability Evaluation

Safety and reliability evaluation assesses mining sequence schemes from aspects like ground pressure management and ventilation conditions to ensure safe and reliable mining processes.

Ground pressure management is a key content. Evaluate the ground pressure distribution and variation patterns under different schemes, analyzing if hazards like pressure concentration, roof collapse, or rib spalling may occur. In a lead-zinc mine, through numerical simulation and field monitoring, the ground pressure situations of different sequence schemes were analyzed. It was found that in Scheme C, because a key support part of the orebody was mined first, ground pressure concentrated on the remaining orebody, easily triggering roof collapse; while Scheme D used a reasonable sequence, gradually releasing pressure, resulting in a more uniform distribution and lower safety risk. Therefore, use ground pressure monitoring technology and rock mechanics analysis methods to assess the ground pressure situation of different schemes, taking effective control measures like reasonably arranging pillars or using fill mining to ensure ground pressure safety during mining.

Ventilation conditions are crucial for the health and safety of underground personnel. Evaluate if the ventilation system under different schemes can meet underground ventilation needs, ensuring sufficient fresh air supply and effective exhaust of contaminated air. In a coal mine, in Scheme E, due to unreasonable ventilation system design, some panels had poor ventilation, leading to gas accumulation and safety hazards; while Scheme F, by optimizing the ventilation system and reasonably arranging ventilation roadways and equipment selection, ensured good ventilation in all panels. Therefore, conduct ventilation resistance calculation, airflow distribution calculation, and ventilation effectiveness evaluation for different schemes’ ventilation systems, taking effective measures like adding ventilation equipment or optimizing the network to ensure underground ventilation safety. Also evaluate the safety of different schemes in responding to hazards like gas, water, and fire, formulating corresponding emergency plans and safety measures to ensure timely and effective response during disasters, protecting lives and mine property.

(IV) Scheme Selection

Comprehensively considering all factors to select the optimal mining sequence scheme requires following certain methods and principles to ensure the chosen scheme achieves safe, efficient, and economic mine extraction.

When selecting a scheme, consider technical feasibility as the primary factor. A technically infeasible scheme cannot be implemented in actual production, regardless of its attractive economic indicators. Ensure the chosen scheme’s mining method matches the orebody’s occurrence conditions and geological structures, the development system meets production needs, and equipment can operate normally and meet safety standards. In a gold mine, although Scheme G had certain economic advantages, because its mining method required high ore and rock stability while the mine’s stability was poor, implementing it posed significant safety risks, so it was excluded. Only technically feasible schemes form the basis for further considering other factors.

Economic rationality is an important basis for selection. Among technically feasible schemes, prioritize those with better economic returns. Through cost-benefit analysis, compare economic indicators like NPV, IRR, and Payback Period of different schemes, selecting those that maximize investment return and minimize costs. In an iron ore mine, both Scheme H and I were technically feasible, but Scheme H had higher NPV and shorter Payback Period, giving it more advantage economically, and was prioritized. However, while pursuing economic benefits, safety and environmental factors cannot be ignored. Seek balance among economy, safety, and environment.

Safety and reliability are the lifeline of mine production. Any scheme must ensure safe production. Comprehensively assess safety factors like ground pressure management, ventilation conditions, and hazard prevention of different schemes, selecting those with lower safety risks and higher reliability. In a coal mine, although Scheme J had good economic indicators, it had significant hidden safety dangers, like an imperfect ventilation system easily leading to gas accumulation, so it could not be the first choice. Scheme K performed excellently in safety and reliability. Through a reasonable mining sequence and effective safety measures, it could effectively reduce safety risks, ensuring safe and stable mine production.

Besides technical, economic, and safety factors, other relevant factors need consideration, like environmental impact, comprehensive resource utilization, and policy/regulatory requirements. When selecting a scheme, try to minimize environmental damage, improve comprehensive resource utilization, and ensure the scheme complies with national and local policies/regulations. In a non-ferrous metal mine, although Scheme L was economically and technically feasible, it had greater environmental impact, not meeting environmental protection requirements; while Scheme M, while meeting economic and technical requirements, also took effective environmental protection measures, reducing pollution, thus better aligning with sustainable development requirements.

After comprehensively considering all factors, use scientific decision-making methods like the Analytic Hierarchy Process (AHP) or Fuzzy Comprehensive Evaluation to quantitatively evaluate and rank different schemes, ultimately selecting the optimal mining sequence scheme. Through such comprehensive and systematic methods and principles, it can be ensured that the chosen scheme meets both the mine’s current production needs and benefits its long-term development.