Open-pit mining

Open-pit mining is a method of directly exposing and mining ore bodies. It is mainly suitable for the mining of ore deposits with shallow burial depth, large thickness and gentle inclination. Open-pit mining mainly includes three major production links: excavation, transportation and soil discharge.

I. Mining

The main purpose of mining and excavation is to separate the ore body from the surrounding rock and form transportable mineral and rock materials. The specific processes include steps such as perforation, blasting and shipment:

1. Perforation

Perforation mainly involves the use of drilling RIGS (such as down-the-hole drills and cone drills) to carry out drilling operations in mines and rocks, creating conditions for subsequent blasting. The conventional perforation process is as follows:

Drilling design: The conventional parameters of the mesh are calculated as hole spacing (a), row spacing (b), and ultra-depth (h), which are determined based on the nature of the ore and rock and the blasting method.

Drilling positioning: Use GPS or total stations to calibrate the hole positions to ensure that the drilling layout conforms to the design. Adjust the drilling rig to a horizontal position to avoid deviation.

Drilling: Use a rotary drill or down-the-hole drill to drill holes at the designed positions and depths. Generally, the diameter of the drill holes is usually 150 to 380mm, and they are arranged vertically or at an Angle.

In-hole treatment: Use high-pressure air ducts to remove residues in the holes to prevent blockage and affect the loading of reagents. Then cover the openings to prevent debris from falling in or rainwater from seeping in.

Data recording: Record information such as hole position coordinates, hole depth, and rock layer changes to optimize subsequent blasting designs.

The commonly used piercing equipment in open-pit mines is as follows:

Cone drilling rig: Suitable for drilling medium-hard to hard mineral and rock, with large drilling diameters (200 to 380mm), high efficiency, and suitable for large-scale mining

Down-the-hole drill: It is suitable for drilling in hard rock and ore bodies with well-developed fractures. It features impact crushing and rotary cutting, with high drilling accuracy and adaptability to complex rock strata

Top hammer drilling rig: Suitable for small open-pit mines or auxiliary operations, it is highly mobile and flexible, but has a smaller hole diameter (usually). "150mm

2. Blasting

Blasting is the process of breaking up ores and rocks by means of explosives or electric detonation to form ore blocks that are easy to load. The conventional operation procedures include: blasting design, drilling operation, charging and filling, layout of the detonation network, safety warning and blasting implementation, as well as disposal of the blast pile and effect evaluation, etc.

Blasting design: It is necessary to calculate the parameters of the mesh and the charge quantity. The calculation of hole mesh parameters includes hole spacing (the distance between the centers of adjacent blast holes, with a spacing of 8 to 15 meters), row spacing (the row spacing of blasting is 0.8 to 1.2 times the hole spacing), and ultra-depth (referring to the depth of the borehole beyond the step base plate). The calculation of the dosage should be determined based on the hardness of the rock.

Loading and packing: Loading includes continuous loading and sectional loading. Fill the orifice with drill cuttings or sand.

The layout of the detonation network: There are two types of detonation methods: electric detonators and non-conductive detonators. The row-by-row detonation method and the millisecond delay detonation method can be adopted.

Safety alert and blasting implementation: For a general boundary range of 300 meters or more, warning lines and sentries must be set up. When initiating the explosion, follow the initiation signal prompt, then conduct post-explosion inspection. After confirming that there are no blind guns, lift the alert. Blasting treatment and effect evaluation: Mainly for large blocks that have not been fully blasted, it is necessary to use a hydraulic hammer or secondary blasting treatment. Generally, a blasting particle size of 80% and a ore block size of ≤1m³ are considered qualified. At the same time, blasting vibration monitoring should be carried out, which should comply with national standards.

3. Shipment

Loading and unloading involves using mining and loading equipment to load the crushed ore into transport vehicles or other equipment to complete the initial processing of the ore.

Ii. Transportation

The main task of transportation is to transport the excavated ores and exfoliates from the mining site to the concentrator, storage site or waste dump. The choice of transportation mode directly affects production efficiency and cost. Common transportation modes are as follows:

Railway transportation: It is suitable for long-distance and large-scale open-pit mines and has the advantages of low transportation cost and large capacity.

Road transportation: It is suitable for small and medium-sized mines or mining areas with complex terrain, and has relatively high flexibility.

Belt conveyor: It is suitable for short-distance transportation, operates smoothly and has low energy consumption.

Combined transportation: It combines the advantages of railway and road transportation and is suitable for mines with complex terrain and long transportation distances.

Commonly used equipment includes:

Dump trucks: Widely used in road transportation, they have strong adaptability.

Belt conveyor: Suitable for short-distance and large-capacity continuous transportation.

Slope skip hoisting: Suitable for vertical transportation.

Iii. Soil Removal

The main task of soil discharge is to transport the stripped topsoil and rocks to the designated location for stacking. Common soil discharge methods are as follows:

Internal soil discharge: Directly discharge the exfoliated materials into the stope, suitable for flat terrain mining areas.

External soil discharge: Transport the stripped materials to a dedicated site outside the mining area for stacking, which is suitable for mining areas with complex terrain or restricted internal soil discharge.

Commonly used soil discharge equipment includes:

Soil plow: It is used to level the surface of the soil dump and improve the soil discharge efficiency.

Bulldozer: It is often used to level the debris and push it into the dump.

Cantilever soil discharge machine: Suitable for different terrain requirements of waste disposal sites.

Depending on the equipment used, open-pit mining processes can be classified into three types: intermittent operation, continuous operation and semi-continuous operation.

Intermittent operation: The characteristic is that the operation of equipment in each production stage has periodic interruptions. Its combined equipment includes single-bucket excavators, dump trucks, crushers, etc. During operation, the single-bucket excavator excavates and loads the blasting ore and rock at the mining and excavation face onto the dump truck. The truck then tranches the ore and rock along the pre-determined transportation route to the crushing station, mineral processing plant or waste disposal site. During the transportation process, the driving and loading/unloading of the truck are intermittent operations. After each transportation task is completed, it needs to return to the mining and excavation work face for loading again, and this cycle repeats itself. This process is mostly suitable for occasions where the ore body is large and periodic treatment is required.

Continuous operation: The characteristic is that the operation of equipment in each production link is continuous. Commonly used equipment includes bucket wheel excavators, belt conveyors, soil discharge machines, etc. During operation, the bucket wheel excavator continuously excavates the ore and rock at the mining site. The excavated ore and rock are directly conveyed to the belt conveyor, which continuously and without interruption conveys the ore and rock to the waste disposal site or crushing station. During the operation process, all the equipment is in continuous motion without any pause.

Semi-continuous operation: It combines the characteristics and equipment configuration of intermittent and continuous operations. At the initial stage of mining, single-bucket excavators load the ore and rock onto dump trucks, which then transport them to the crushing station. After crushing, the ore and rock are transported over long distances by belt conveyors. This operation mode combines intermittent transportation with continuous transportation, improving transportation efficiency while ensuring a certain degree of flexibility.