The open-pit mining process is an important part of mining science and open-pit mining, mainly including three stages: stripping, mining, and trenching. The main production process procedures of these stages include drilling, blasting, loading of ore (rock), transportation of ore rock, and unloading of rocks.

Stripping

       Stripping is the first step in open-pit mining, with the main task of removing the rock covering the surface of the ore body to prepare for subsequent mining work. The stripping operation mainly includes three stages: drilling, blasting, and loading. Drilling uses a drill to create holes of a certain depth on the surface of the ore body to provide conditions for blasting operations. Blasting uses explosives to break the rock into pieces of a certain size, facilitating subsequent loading operations. The loading operation uses equipment such as excavators to load the blasted rock into transport vehicles, which are then taken to the dumping site for unloading.

Mining

       Mining is the core stage of open-pit mining, with the main task of extracting valuable minerals from the ore body. The mining operation mainly includes stages such as drilling, blasting, loading, and transportation. Drilling and blasting are similar to stripping operations, but the depth of drilling and the scale of blasting are adjusted according to the needs of the mining operation. The loading operation uses equipment such as excavators to load the blasted ore into transport vehicles, which are then taken to the processing plant for mineral processing.

Trenching

       Trenching is one of the important stages of open-pit mining, with the main task of excavating transport channels around the mined-out area to transport minerals to the processing plant for treatment. The trenching operation mainly includes stages such as drilling, blasting, and excavation. Drilling and blasting are similar to stripping and mining operations, but the depth of drilling and the scale of blasting are adjusted according to the needs of the trenching operation. The excavation operation uses equipment such as excavators to dig out the blasted rock and ore, forming channels of a certain width.

Drilling, blasting, loading, and transportation

       Drilling, blasting, loading, and transportation are important stages in the open-pit mining process, and the quality and efficiency of these stages directly affect the production efficiency and quality of the entire open-pit mine. Drilling operations are the foundation of open-pit mining, blasting operations are key, and loading and transportation operations are guarantees.

       Drilling operations involve using a drill to create holes of a certain depth on the surface of the ore body to provide conditions for blasting operations. There are many types of drills, including impact, rotary, and down-the-hole drills, which should be selected based on different terrain conditions and rock properties.

       Blasting operations involve using explosives to break rock or ore into pieces of a certain size, facilitating subsequent loading and transportation operations. Blasting operations need to consider factors such as the type of explosives, blasting parameters, and safety distances to ensure blasting effectiveness and safe production.

       Loading operations involve using equipment such as excavators to load the blasted rock or ore into transport vehicles, which are then taken to the processing plant for mineral processing. There are many types of loading equipment, including excavators, loaders, and conveyors, which should be selected based on different terrain conditions and rock properties.

       Transportation operations involve transporting the loaded rock or ore to the processing plant for treatment. There are many types of transportation equipment, including trucks, trains, and ships, which should be selected based on different terrain conditions and transportation distances. Additionally, transportation costs and environmental pollution should be considered to ensure a balance between economic and social benefits.

Unloading of rocks

       Unloading of rocks is one of the important stages of open-pit mining, with the main task of transporting the stripped rocks to the dumping site for unloading. The unloading of rocks needs to consider factors such as the site selection, design, and management of the dumping site to ensure that the rocks can be unloaded reasonably and effectively while meeting safety and environmental protection requirements. Additionally, the lifespan and reclamation of the dumping site should be considered to ensure the sustainable development of the open-pit mine.

6. Drilling operations and safety requirements

　　Drilling operations are the first step in open-pit mining, aimed at providing holes for placing explosives for blasting work. The quality of drilling directly affects the efficiency of subsequent blasting, loading, and crushing operations.

　　The drilling equipment commonly used in open-pit mines in China is divided into shallow hole drills and deep hole drills based on drilling depth. Shallow hole drilling equipment mainly includes rock drills and drilling vehicles. Deep hole drills mainly include roller drills and down-the-hole drills.

　　1. Rock drilling machinery

　　Rock drills can be divided into four types based on their power: pneumatic, electric, internal combustion, and hydraulic; based on weight, they are divided into light, medium, and heavy types; and based on working methods, they are divided into handheld, leg-type, and column guide rail types. The drilling equipment used in open-pit mines mainly includes:

　　(1) Roller drill. (2) Down-the-hole drill. (3) Fire drill. (4) Drilling vehicle. (5) Wire rope impact drill.

　　2. Technical performance of rock drills (1) Roller drill

　　The roller drill is a high-efficiency drilling equipment widely used in large open-pit mines in China. Based on drilling size, the drilling speed of roller drills is generally 4000~6000m/month, with a maximum of over 10000m/month; if calculated based on annual blasting volume, it is generally 4 million to 6 million tons, with a maximum of 12 million to 14 million tons, which is 4 to 5 times that of wire rope impact drills. The drilling speed of roller drills is about 40% to 100% higher than that of down-the-hole drills.

　　From an economic perspective, the cost of drilling with roller drills is also the lowest, approximately 75% of that of wire rope impact drills and 70% of that of down-the-hole drills.

　　(2) Down-the-hole drill

　　The down-the-hole drill is a drilling equipment that began to be used in China in the 1950s and replaced wire rope impact drills in the 1960s. Its main characteristics are:

　　The diameter is small (Φ150~200mm), allowing for the drilling of inclined holes, and the size of the blasted rock fragments is small, which facilitates loading by small excavators.

　　② The equipment has a simple structure, is easy to operate and maintain, is flexible, and is low in price.

　　③ The equipment performs well in efficiency, with a drilling efficiency of 2000m/(unit.month), and the annual blasting rock volume is about 600,000 to 1,500,000 tons. This type of equipment is mainly suitable for medium and small open-pit mines.

　　(3) Fire Drill

　　The fire drill uses high temperatures (1600~3000C) and high speeds (1100~1800m/s) to spray flames onto the rock surface, causing the rock to ignite, expand, fracture, and peel under thermal action. The mechanism of fire drilling is based on the uneven changes in the rock due to heating. Therefore, it is suitable for rocks with low heat capacity, poor thermal conductivity, and high expansibility, especially for rocks with high quartz content, such as quartzite, iron-containing quartzite, and quartz granite. The perforation efficiency of fire drills in hard quartz-type rocks is 6m/h, which can greatly exceed the perforation efficiency of wire rope impact drills.

　　(4) Rock Drilling Trolley

　　The rock drilling trolley is a perforation device that uses a rail-type heavy pneumatic rock drill. Due to its simple and flexible equipment and small aperture, it can drill blast holes at any angle, significantly improving labor productivity and working conditions, so it is widely used in small mines.

　　3. Rock Drilling Safety Requirements

　　(1) Rock drilling workers are special operation personnel and must undergo training and pass examinations to obtain special operation certificates before they can work.

　　(2) Before operation, the equipment should be carefully inspected, and the work site should be thoroughly checked for collapses, dangerous rocks, obstacles, etc. Only after confirming safety can the equipment be started for rock drilling operations.

　　(3) During the drilling process, the hole mouth and equipment operation should be observed frequently, and any abnormal phenomena should be dealt with in a timely manner; it is prohibited to drill dry holes.

　　(4) When stopping and starting the equipment, a call-and-response must be performed. Before moving the rock drill, check if there are people or obstacles under the machine, and ensure that there are no sliding objects on the machine. When lifting the drill rod, it is strictly prohibited for anyone to stand on the drill rig or platform.

　　(5) When bundling cables, power must be cut off, and safety warning signs should be hung or a dedicated person should be assigned to guard. Power should not be restored without the permission of repair personnel. During heavy rain, it is prohibited to stop or restore high voltage.

　　(6) When handling electrical faults, cleaning the distribution box, repairing or adjusting the electromagnetic brake, the power supply must be cut off.

　　(7) Cables must not be placed in mud or on metal objects. When vehicles pass over cables, they should be protected with wood or stones to prevent damage to the cables.

　　(8) When operating air switches and pulling cables, insulated gloves must be worn or insulated rods must be used. Before powering on the transformer switch, check and confirm that the transformer casing is not leaking electricity before operating.

　　(9) Cleaning, securing, lubricating, and repairing rotating parts must be done with the machine stopped and the power cut off.

　　(10) Before the first alarm signal of blasting in the mining area, the rock drill must be moved to a safe and reliable location to stop and avoid blasting, and all doors and windows must be closed. After blasting, the platform and top must be checked and cleaned before power can be restored.

　　(11) For large and medium-sized blasting, the cables should be pulled out of the blasting area, and after blasting, checks should be made to confirm that if any cables are damaged, they should be bundled in a timely manner.

　　(12) When repairing the lifting electromagnetic brake, the rotating mechanism must be supported to prevent it from falling automatically after releasing the brake. It is prohibited to support the drill bit with hands when placing the drill tool.

　　(13) When repairing or replacing air pipes, the air supply must be stopped. When there are people working at the hole mouth, air must not be supplied to the impactor.

　　(14) When moving the rock drill, the protruding part must be kept more than 3m away from the edge of the step, and a dedicated person must direct the operation. If the brake is not functioning properly, the machine must not be started. When the drill is parked or in operation, the longitudinal axis should be vertical to the ground; if the step width is insufficient, the angle between the longitudinal axis of the drill and the top of the step should not be less than 45°, and the protruding part must be no less than 2.5m from the edge of the step. It is strictly prohibited to park on blasting piles or loose ground.

　　(15) The drill should not walk on a slope of 15°. If it is necessary to pass through this surface, the drill frame should be lowered, and anti-tipping measures should be taken.

　　(16) Before lifting the large frame, the drill rod and the rotating gearbox must be secured, and the lifting mechanism must be carefully checked for tightness. No one is allowed to linger or pass under the large frame. If any wire rope is found to be rusted or has broken wires (more than 10% broken wires), it must be replaced.

　　(17) The electric furnace cover must be complete, and the power must be cut off when leaving. It is strictly prohibited to use open flames for heating in the rock drill driver's operating room. There should be good lighting at night.

　　(18) The rock drill driver's cabin must be equipped with fire-fighting facilities to prevent electrical fires.

7. Blasting Operations and Safety Requirements

　　Blasting operations are an important procedure in open-pit mining, providing suitable rock materials for subsequent loading, transportation, and crushing. Therefore, the quality of blasting technology has a significant impact on subsequent work.

　　(1) Blasting Methods

　　In open-pit mining, the commonly used blasting methods are as follows:

　　1. Shallow Hole Blasting Method

　　Shallow hole blasting refers to blasting methods that are relative to deep hole blasting. In this blasting method, the borehole diameter is smaller (generally 28-75mm), and the hole depth is generally 5-8m. Due to the limitations of hole diameter and depth, the blasting volume is relatively small and cannot meet the requirements of large loading equipment. Therefore, this blasting method is mainly used in small open-pit mines or in cases where geological conditions are more complex, as well as when there are special geometric requirements for the blasted ore. Large and medium-sized open-pit mines only use this blasting method for secondary blasting of the base or floating boulders on the working face. (1) The main characteristics of the shallow hole blasting method are:

　　① It has mobility and flexibility, with a wide range of applicability.

　　② For deposits with complex burial conditions and high ore grade requirements, separate blasting and mining can be implemented to reduce the dilution rate.

　　The rock drilling tools are relatively simple and easy to master.

　　The amount of preparation work is small.

　　The size of the ore blocks after blasting is small, making it easy to meet the requirements for transportation and crushing.

　　Compared to chamber blasting and deep hole blasting, the amount of explosives consumed is less.

　　The shortcomings are: it cannot meet the needs of large-scale production, and there are often loopholes in the processes of loading, wiring, and detonation, leading to blasting accidents.

　　(2) Shallow hole classification and hole arrangement

　　Shallow holes are generally divided into vertical, inclined, and horizontal types. Several common arrangements of blast holes in shallow hole blasting are shown in Figure 4-7.

　　2. Overburden blasting method

　　The overburden blasting method refers to the method of secondary crushing of large blocks without drilling blast holes (commonly known as the paste blasting method). The blasting method is shown in Figure 4-8. The specific operation of this blasting method is to place explosive packages on the upper or side of the large block, preferably in the concave area of the blasted rock. The amount of explosives used depends on the strength of the explosives, the size of the block, the degree of fragmentation required, and the nature of the rock. The detonator should be pre-inserted into the explosive package. To improve blasting efficiency, cover the explosive package with a layer of loess, soil, sand, or fine rock powder that is thicker than the height of the charge, and then detonate.

　　The advantages of this blasting method are: it can be applied in situations where drilling is difficult or when there is an urgent need to crush large blocks. However, this method is rarely used in normal blasting operations in mines. The reason is that it is difficult to control the blasting effect, the consumption of explosives is large, and the distance of rock fragments flying is far, which can easily cause accidents, so this blasting method is used less in mines.

　　3. Deep hole blasting method

　　(1) Deep hole

　　Deep hole blasting is the most widely used blasting method in open-pit mines. The depth of the blast holes is generally 15 to 20 meters. The diameter ranges from 75 to 310 mm, with common diameters being 200 to 250 mm. Deep hole blasting is widely used in the production processes of large mines, such as trenching, stripping, and mining. The blasting volume accounts for more than 90% of the total blasting volume in large mines.

　　(2) Characteristics of deep hole blasting

　　① The amount of rock blasted in one operation is large, generally ranging from 200,000 to 1,000,000 tons.

　　② Advanced blasting technologies can be used in deep hole blasting, such as micro-delay blasting, squeeze blasting, and for special requirements, throwing blasting and directional blasting.

③ Blasting operations are relatively safe, management is simpler, and there are no special requirements for explosives except for deep holes with water; the detonation methods are also more flexible.

　　Deep holes can be classified into vertical deep holes and inclined deep holes. Vertical deep holes are mostly drilled by impact drilling machines. Inclined deep holes are mostly drilled by roller bit drilling machines or down-the-hole drilling machines. The inclination is generally between 75° and 80°, and compared to vertical deep holes, they have the following advantages:

　　① The blast holes are at an angle of 75° to 80° to the horizontal plane, significantly reducing the resistance line of the base, which is beneficial for eliminating the foundation.

　　② The explosives are distributed evenly in the inclined holes, and the fragmentation after blasting is also relatively uniform, reducing the large block rate.

　　③ The width and height of the blast pile after blasting are significantly reduced, the step shape is relatively neat, and there is less backflow, making it easier for the next drilling.

　　④ The angle of the face after blasting is relatively gentle, which is beneficial for the stability of the slope.

　　⑤ The cost of blasting is relatively low.

　　(3) Preparation work for deep hole blasting

　　The smooth progress of deep hole blasting and the quality of the blasting effect are closely related to the preparation work before blasting. Therefore, the following preparations must be made before deep hole blasting.

　　① Check and repair the equipment used for blasting (such as detonators, blasting electric bridges, ohm meters, etc.) and various tools (such as loading funnels, electrician's knives, pliers, shovels, etc.) to ensure that the equipment and tools are in good condition.

　　② When using electric detonation, the resistance values of the electric detonators should be measured and selected.

　　③ Carefully check the wires used for detonation to prevent the use of damaged wires that may cause electric shock accidents.

　　④ Check whether there is mud and standing water in the blast holes. If there is, use a wind pipe to blow it out to ensure that the explosives can fully exert their capabilities and achieve the expected blasting effect.

　　⑤ The technical performance of the explosives used should be tested.

　　⑥ Prepare the filling materials for plugging the blast holes.

　　⑦ Remove equipment and facilities from the blasting area.

　　4. Chamber blasting

　　Chamber blasting involves placing explosives in pre-drilled chambers for concentrated loading. The amount of explosives detonated each time is irregular, with some loading tens of tons, hundreds of tons, or even thousands of tons. Due to the large amount of blasting at one time, it is also called large-scale blasting. The chamber blasting method is shown in Figure 4-9.

　　The main characteristics of this blasting method are:

　　(1) The amount of preparation work is relatively small, allowing for a large amount of rock blasting to be completed in a short time.

　　(2) It is suitable for rocks of various hardness, especially in complex terrain where construction conditions are not restricted.

　　(3) No special drilling equipment is required; tunneling chambers can generally be done using tunneling drilling machines.

　　(4) There are no special requirements for the explosives used; any explosives used in deep hole blasting can also be used in chamber blasting. The shortcomings of chamber blasting are: the drilling conditions for tunneling operators are poor, and there are many large blocks blasted.

　　(2) Open-pit mining blasting.

　　Due to the continuous development and updating of open-pit mining excavation machinery, there has been a significant increase in mining productivity. Therefore, it is necessary to adopt blasting methods with a large amount of initial blasting to meet the needs of new excavation machinery. Currently, the large initial blasting methods in China use multi-row hole micro-delay blasting and multi-row hole micro-delay squeezing blasting methods. These two methods can blast 5 to 10 rows of blast holes at once, with the amount of blasted rock reaching 300,000 to 500,000 tons.

　　1. Multi-row hole micro-delay blasting

　　Micro-delay blasting refers to a blasting method where the explosive packages in adjacent blast holes are detonated in a predetermined sequence within a very short time (measured in milliseconds).

　　(1) Characteristics of multi-row hole micro-delay blasting

　　1) The consumption of explosives is greatly reduced compared to other blasting methods.

　　2) The foundation of the blasting is minimal, and the fragmentation is uniform, which can improve the production efficiency of electric shovels.

　　3) The shock wave of the blasting is small, which is beneficial for the stability of the slopes.

　　(2) Detonation sequence of multi-row hole micro-delay blasting

　　1) There are various forms of detonation sequences for multi-row hole micro-delay blasting. The main factors determining which detonation sequence to use are:

　　① The requirements for this blasting; ② The conditions allowed at the blasting site; ③ The properties of the rock and geological structure characteristics; ④ The maximum allowable shock wave; ⑤ The control time intervals adopted; ⑥ The amount of preparatory work and the capabilities that production or engineering can achieve.

　　2) The commonly used detonation sequences for multi-row hole micro-delay blasting are as follows:

　　① Single-row hole micro-delay blasting detonation sequence

　　Single-row micro-delay blasting often uses inter-hole micro-delay detonation sequences. This method is simple and easy to master, and is often used in step working face mining blasting operations, with the detonation sequence shown in Figure 4-10.

　　② Inter-row micro-delay blasting detonation sequence for multi-row holes

　　This method is also relatively simple and generally has good results. The arrangement of blast holes in inter-row micro-delay blasting is mostly triangular. Sometimes it is arranged in a grid shape, with the detonation sequence shown in Figure 4-11.

　　③ Wavy micro-delay blasting detonation sequence

　　This detonation sequence combines the characteristics of the above two types of micro-delay blasting, with good rock fragmentation, small blasting width, and a more complex arrangement of blast holes. It is mostly used in working faces where the ore is difficult to blast or prone to large blocks. However, this detonation sequence has a more complex connection and is prone to leaving a foundation. The detonation sequence is shown in Figure 4-12.

　　④ Diagonal micro-delay blasting detonation sequence

　　This detonation sequence can ensure the minimum detonation pile width, with a smaller distance for rock fragments to scatter. Its detonation sequence is shown in Figure 4-13.

　　⑤ Wedge-shaped micro-delay blasting detonation sequence

　　Wedge-shaped detonation is often used in cases with a large number of blast holes, such as in the excavation of roadbeds. Due to its compressive and shock effects, the rock is well fragmented. The wedge-shaped detonation sequence is shown in Figure 4-14.

　　2. Multi-row hole micro-delay squeezing blasting

　　Multi-row hole micro-delay squeezing blasting refers to multi-row hole micro-delay blasting in the presence of residual blasting piles at the working face. The presence of the spoil pile creates conditions for squeezing, while also extending the effective action time of the blasting, improving the utilization of explosive energy and fragmentation effects, and controlling the width of the blasting pile to avoid scattering of rock fragments.

　　Based on practical experience in domestic mines using multi-row hole micro-delay squeezing blasting, the following points should be noted when implementing multi-row hole micro-delay squeezing blasting:

　　(1) The impact of spoil pile thickness on blasting pile width. To protect the lines of the step working face, the loading must refer to the requirements in Table 4-4.

　　(2) Unit explosive consumption and explosive allocation. The unit explosive consumption for multi-row hole micro-delay squeezing blasting is about 20% to 30% larger than that of general micro-delay blasting.

　　(3) Micro-delay interval time. Since squeezing blasting needs to push the front spoil pile, the detonation interval time is generally 50 to 100 ms.

　　(4) The number of blasting rows and the detonation sequence. The number of rows in squeezing blasting is generally more than four. The detonation sequence for each row can use several detonation sequences from ordinary micro-delay blasting, and there is also a circular detonation sequence, as shown in Figure 4-15.