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Open-pit mining, is a process of removing the overburden from the ore, obtaining the required minerals, and extracting useful minerals from open-pit stopes. Open-pit mining operations mainly include perforation, blasting, mining, transportation and dumping processes. According to the continuity of work, it can be divided into discontinuous, continuous and semi-continuous.
Compared with underground mining, open-pit mining has the advantages of full utilization of resources, low dilution rate, suitable for large-scale mechanical construction, fast mining construction, large output, high labor productivity, low cost, good labor conditions and safe production.
Open-pit mining is the earliest mining method for human to use minerals. It was originally the outcrop of ore deposits and shallow rich ore deposits. Since the power excavator was used at the end of the 19th century, open-pit mining technology has developed rapidly, and the scale of open-pit mine has become larger and larger.
Open-pit Mining Technology
1. Open-pit mining refers to the method of stripping rocks and extracting ores in a certain mining process and in a certain mining sequence. Open-pit mining technology, according to the continuity of operation, is divided into discontinuous, continuous and semi-continuous, according to the distribution of ore deposits, there are roughly two types of mining methods:
1.1. Mining methods for gentle deposits
It is suitable for gentle deposits whose dip angle is generally less than 12 degrees. Discontinuous mining technology is suitable for various geological, mineral and rock conditions; continuous mining technology has high labor efficiency and is easy to realize automation of production process, but can only be used for soft rock of typical loose-dry filling mining method scheme; semi-continuous mining technology has the characteristics of both above, but in hard rock, it is necessary to increase the link of mechanical breaking rock. Mining sequence is the coordination of mining and stripping in time and space.
1.2. Inverted heap mining method
The stripped material is dumped by mechanical shovel or rope bucket shovel directly in the goaf of the first mining zone, and the mining area is pushed forward closely with the stripped area. In the same case, the weight of the mechanical shovel is about 1.8 times that of the rope shovel. Therefore, when peeling the high steps, the rope shovel is often used. The higher step can be stripped by two or more stacking. In the scheme, one mechanical shovel cooperates with one rope bucket shovel, two rope bucket shovels cooperate with each other, or only one rope bucket shovel acts as a secondary dump, etc.
1.3 transverse mining method
The stripping material is transported to the goaf by dump bridge and cantilever dump along the direction perpendicular to the working line. The spatial relationship between stripping step and the advancing of mining step is also limited by the specifications of transportation equipment, but it is not as strict as the upside-down mining method. This method can be applied to larger stripping thickness. The stripping thickness of AFB-60 dump bridge in Democratic Germany is 60m.
1.4. Longitudinal mining method
The stripped material is transported longitudinally to the goaf along the working line, bypassing the end wall. This method is not limited by the specifications of mining and transportation equipment and the thickness of peeled rock, and has greater flexibility. It is suitable for single bucket - locomotive vehicle, single bucket - belt conveyor, single bucket - automobile, wheel bucket - locomotive vehicle - belt conveyor and other processes.
1.5. Mining methods of inclined mineral deposits
Essentially, the stripped material is transported to the outside dump. Only when the excavation reaches the final depth can be discharged in the goaf. The layout of working line is basically along the direction of ore and vertical direction of ore.
The selection of initial location and advancing direction should take into account the factors such as the topographic and geological conditions of the deposit, production capacity, transportation mode, the balance of capital stripping volume and production stripping ratio. The production-stripping ratio of inclined deposits varies during mining. In order to reduce the amount of capital stripping and delay the peak of stripping, balance production stripping ratio and improve economic effect, the following measures can be taken to steepen the working slope angle.
1.6. Combination Steps
There are other ways to excavate a group of adjacent steps sequentially with one equipment, and only a working platform is set up on the excavation steps .
1.7. Transverse mining belt
Horizontal excavation belt of automobile transportation, adjacent steps followed by excavation, horizontal layout of working line, longitudinal advance . There is only one working platform on any cross section, and 1 to 2 mining equipments can be installed on each step. Compared with the combined bench, this method can be arranged more mining equipments.
1.8. Divided and staged mining
For the mineral deposits with longer strike or larger area, the zoning and staged mining should be carried out. The areas with thick ore, high grade, thin coverage and small stripping ratio should be preferentially mined.
1.9. Types of equipment and processes:
II. Construction Method
2. Open-pit mining process mainly includes perforation blasting, mining, transportation and dumping. The order of open-pit mining is the coordination of mining and stripping in time and space. The quality of these four tasks and their coordination is the key to open-pit mining.
2.1. Perforation blasting is to drill directional blasting holes with a certain diameter and depth in open-pit stope to break and loosen ore and rock by explosive blasting. Perforation equipment mainly includes impact drilling rig, DTH drilling rig and rotary drilling rig. Ammonium oil explosive, slurry anti-water explosive, emulsified explosive and granular emulsified explosive are commonly used.
2.2. Mining and loading is the operation of loading ore and rock into transport equipment by manual or mechanical means or unloading them directly to designated locations. The commonly used equipment is excavator (with multiple buckets and single bucket), wheel bucket shovel and front-end loader, which is widely used as single bucket excavator.
2.3. Transportation work is to transport the ore and rock of open-pit stope to the unloading point (or concentrator) and dump respectively, and to transport the production personnel, equipment and materials to the stope at the same time. The main modes of transportation are railways, highways, conveyors, hoists, as well as hydraulic transport and ropeway transport for rugged mountainous areas. The selection of transportation mode must take into account the topography, geology and climate conditions, open pit production capacity, mining depth, physical and mechanical properties of ores and surrounding rocks, etc. After a comprehensive technical and economic comparison, a reasonable transportation mode should be determined.
2.4. Dumping refers to the removal of a large amount of topsoil and rock covering the upper part of the deposit and its surroundings from an open pit to a specially designed site (such as a dump or a waste rock yard) for disposal. According to the different dump equipment, the method of dump can be divided into bulldozer plow, bulldozer, front loader, tractor scraper or cable bucket shovel, etc. Bulldozers should be located as close as possible to the mining site and occupy less farmland. When conditions permit, they should be placed in valleys and depressions. Attention should be paid to environmental protection, land-making and returning.
III Skills
3. Open-pit mining is the most advantageous method when the orebody is buried shallowly or the surface is outcropped. With the development of mining technology, the scope of open-pit mining is becoming wider and wider, which can be used to mine low-grade ore deposits and some underground residual ore.
3.1. Ore and rock in open-pit stope are usually divided into layers of a certain height, each layer constitutes a step for stripping and mining. The production process consists of rock crushing, mining, loading, transportation and unloading (unloading and dumping). Loose ore and rock can be excavated directly with mining equipment without breaking up.
3.2. For gentle mineral deposits (generally the dip angle of the ore bed is less than 12 degrees), dump, transverse or vertical mining method is adopted. For inclined deposits, the method of combination step, cross mining zone or zoning and staged mining is adopted.
3.3. The upside-down method is usually the best, the transverse method is the second, and the longitudinal method is the worst. However, the applicable stripping thickness is the opposite. When the stripping thickness is large, the inverted stacking method or transverse transport method can be used on the lower step and the longitudinal transport method can be used on the upper step. In order to shorten the transportation distance, the ore field can be divided into several mining areas, mining in a certain order, and discharging the stripped material to the goaf of the mining area or the previous mining area.