Basic knowledge of open-pit mining

I. Overview

1. Mineral resources

Refers to the aggregate of minerals or useful elements that are formed through geological mineralization, naturally occur in the crust or on the surface, buried underground or exposed on the surface, in solid, liquid or gaseous form, and have development and utilization value. Mineral resources are non-renewable resources and their reserves are limited. There are 168 known minerals in the world, of which more than 80 are widely used. According to their characteristics and

uses, they are usually divided into four categories: 11 energy minerals; 59 metal minerals; 92 non-metallic minerals; 6 water and gas minerals. Metallic minerals basically exist in solid form in nature. From the perspective of mining, metal ore deposits are mined regardless of metal varieties. Gold, silver, copper, iron, nickel, etc. are treated the same; only considering the occurrence state of the ore body, different mining processes will be selected.

2. Mining

In modern society, the mining industry has made great progress and has been more refined and subdivided. Generally refers to the exploration, mining, beneficiation, refining and other related businesses of minerals. The construction of a modern mine includes the hard work of professionals in mining geology, surveying, civil engineering, mining, mineral processing, safety, environmental protection, electromechanical, HVAC, water supply and drainage, automation, chemistry, etc.

3. Characteristics of mining and beneficiation industry

First, the labor object is the geological ore body discovered by geological survey and naturally occurring, and the mining and processing object cannot be freely selected;

Second, the mining object, mining tools and production personnel are constantly transferred with the mining, there is no fixed place, and the industrial conditions change at any time, which is different from the general processing industry;

Third, the mining geological conditions and mineral raw materials are very complex, making it difficult to standardize mining projects.

At the same time: ⒈ The occurrence conditions of the ore deposit are unstable; ⒉ The grade, composition and composition of the ore vary greatly; ⒊ The geological structure is complex; ⒋ The physical and mechanical properties of the ore and the surrounding rock vary greatly; ⒌ The water content of the ore deposit is complex. Therefore, no mining and beneficiation of a mine can be completely replicated.

2. Open-pit mining

1. Basic concepts of open-pit mining

The necessary prerequisite for open-pit mining is the presence of suitable ore deposits. Whether the ore deposit is suitable for open-pit mining is best evaluated in the early stage of geological exploration, and then a geological report (including hydraulic and environmental geological data) that meets the requirements of open-pit mine design is proposed after further exploration; after approval, the design department can carry out the design. Due to the occurrence conditions of the ore body exposed on the surface and shallow burial, all the work of mining the rock from the whole according to a certain process is collectively called open-pit mining engineering.

The essence of open-pit mining is to remove the topsoil and surrounding rocks covering the upper part of the ore body in an open space within a certain range, and mine the ore. Therefore, in order to mine the ore, waste rock must also be mined.

The ore body classified as an open-pit mine is called an open-pit mine. The place where open-pit mining engineering is carried out with mining equipment is called an open-pit mine. Open-pit mine: the sum of mining pits, steps and open-pit trenches formed during open-pit mining.

2. General steps for open-pit mine construction and production:

(1) Ground preparation. Bring traffic lines and transmission lines into the mining area, and remove or relocate natural and man-made obstacles in the mining area, such as trees, swamps, villages, factories, roads, canals, cemeteries, etc.

(2) Mine area water isolation and drainage. Cut off the river passing through the mining area or divert it, drain the water, and make the water level lower than the required level.

(3) Mine infrastructure engineering. Including digging ditches, building roads from the ground to the mining level; establishing working lines, carrying out infrastructure stripping to expose the mined ore body; establishing transportation lines, spoil dumps, bridges, etc.; building ground industrial facilities and necessary civil buildings.

(4) Daily production. Mine infrastructure engineering can be handed over to production after the necessary mining and stripping working lines are opened and a certain mining capacity is reached. Generally, it will take some time to reach the designed production capacity. The mined areas need to be reclaimed.

The construction and production of open-pit mines are very complex engineering projects. The purchase of land, the purchase, installation and commissioning of equipment, the training of personnel, the establishment of organizational management agencies, and the reclamation of land, etc., involve a wide range of aspects and are closely related to each other.

3. Open-pit mine development

Only road development is introduced, and the development of horizontal shafts and ramp hoists is not introduced.

(1) The stripping operation of hillside open-pit mines starts from the highest level of the mining area and proceeds downward layer by layer; while the development pit line is built from the lowest to the highest mining steps at one time. As the mining level decreases, the upper development pit line is gradually abandoned or disappears, and the ore and rock transportation distance is shortened accordingly.

(2) The road development pit line of the sunken open-pit mine is gradually formed as the mining steps extend downward. Pit line changes include fixed pit line development and mobile pit line development. Fixed pit line development: The development pit line is arranged on the final side wall within the mining boundary and does not change its position during the entire mining process of the mining area. It can be adopted in straight, return and spiral ways. Spiral pit line development: The development pit line is arranged in a spiral along the four sides of the mining area.

The development process of the fixed pit line development project: including the mining process of the steps, the advancement of the working wall and the development and deepening of the new level. At the final side of the open-pit mine, according to the determined entry and exit trench position, direction and slope, the inclined entry and exit trench is excavated from the surface (the upper flat plate of the step) to the lower flat plate of the step. After reaching the elevation of the lower flat plate, a new horizontal section trench is excavated from the end of the entry and exit trench to establish the initial working line of the mining step.

The development process of the mobile pit line development project: the entry and exit trench and the section trench are excavated horizontally from the upper plate or lower plate near the contact zone between the ore body and the surrounding rock in the mining field. When the section trench is excavated to a certain length, the section trench is excavated while the sides of the section trench are expanded to form the stripping working line. During the mining process, the entry and exit trench moves with the advancement of the working wall on one side until the working line is advanced to the final mining boundary, and then it is fixed on the final side.

4. Open-pit mining technology

The main production process of open-pit mines includes three important projects: trenching, stripping and mining; the production links include mining-transportation-discharge (soil discharge, ore discharge). Mining is the link that directly interacts with the rock layer, including drilling, blasting, mining and loading, transportation line relocation and other processes, and is the most important in open-pit mine production; transportation is the link between mining and discharge, and it is the link that occupies the most equipment, consumes the most energy and manpower in open-pit mine production; discharge is an indispensable requirement for the economic and reasonable discharge of materials produced in open-pit mines.

Around these three main production links, there are also a series of auxiliary production links, such as equipment maintenance, power supply, drainage, etc.

Open-pit mining process systems can be divided into: intermittent process, continuous process, and semi-continuous process.

(1) Intermittent process refers to the process in which the mining and transportation of ore and rock are carried out intermittently in the three main production links. For example: a mechanical shovel loads a truck one scoop at a time, and a train or car transports rock one truck at a time. For each scoop loaded or truck transported, the equipment completes a cycle or period accordingly. This process is also called a cyclic process or a periodic process.

(2) A continuous process refers to a process in which the mining and transportation of ore and rock are carried out continuously. This is the case with the ore and rock flow on a multi-bucket excavator and a belt conveyor. This ore and rock flow will continue uninterruptedly as long as the equipment is operating normally. Therefore, this process is also called a flow process.

(3) A semi-continuous process is a process in which some production links are operated continuously. For example, a process system in which a mechanical shovel loads ore and rock into a crusher and then transports it by a belt conveyor after crushing is a typical semi-continuous process system.

5. Professional terms

a. When mining on a step, the ore and rock are divided into horizontal layers of a certain thickness from top to bottom, and mined with independent

mining and transportation equipment. Each layer maintains a certain advance relationship, thus forming a step shape.

The step is composed of the following elements: upper plate, lower plate, slope, top line, bottom line, height, and slope angle. Step slope angle: the angle between the step slope and the horizontal plane.

Steps are divided into:

Working steps - working flat plates for arranging mining and transportation equipment.

Non-working steps - security platforms: used to buffer and intercept falling rocks and reduce the slope angle.

Clean-up platforms: intercept falling rocks and clean them with cleaning equipment.

Transportation platforms: serve as a connection channel between working steps and access trench transportation.

b. Working line - a well-prepared ore rock section.

c. Excavation zone: during mining, the steps are divided into several strips, which are mined one by one. Each strip of each mine is called an excavation zone. Width ... depends on the blasting method and parameters; electric shovel ... depends on the excavation and unloading radius of the electric shovel.

d. Each strip of the mining area can also be divided into several sections and equipped with independent mining and transportation equipment during mining. Length ... the length of the mining working line occupied by an electric shovel.

f. Open pit tunnels: divided by purpose:

(1) Access trench ... an inclined trench dug to establish transportation links between the ground and the working level and between each working level. According to the shape of the cross section: whole cross section, single side ditch.

(2) Open section ditch... horizontal ditch excavated to open up the mining working line and establish the first working line (initial step).

g. The area of the open-pit mine where open-pit mining has been carried out or is being carried out, formed by steps and open-pit tunnels.

Hillside open-pit: above the closed circle. Depression open-pit: below the closed circle.

Constituent elements:

(1) Side wall: the overall surface around the open-pit mine, divided into: top wall, bottom wall, and end wall.

(2) Working wall: the side wall composed of steps that are being mined and will be mined.

(3) Working wall slope and working wall slope angle.

(4) Final side slope angle: the angle between the final wall slope and the horizontal plane

(5) Final wall slope: the imaginary inclined plane made by the top line of the top step of the non-working wall and the bottom line of the bottom step.

(6) Final boundary of the open-pit mine: the position defined by the upper and lower final boundary lines.

6. Main technical and economic indicators: stripping ratio

The stripping ratio of open-pit mines is an important technical and economic indicator, which is related to the amount of ore mined, the amount of rock and soil stripping, and the production scale, service life, production cost, etc. of the mine.

Stripping ratio: the amount of rock required to strip per unit of ore mined.

The stripping ratio is variable. The open-pit mining boundary defined in the design is only a reasonable boundary under certain conditions in a certain period of time. The measurement unit is expressed in m3/m3 or m3/t or t/t.

Average stripping ratio: the ratio of the total amount of rock in the boundary to the total amount of ore.

Layered stripping ratio: the ratio of the amount of rock in a certain horizontal layer within the boundary to the amount of ore.

Production stripping ratio: the ratio of the amount of rock stripped in a certain period to the amount of ore mined.

Boundary stripping ratio: the ratio of the rock increment caused by the unit depth increase of the boundary to the ore increment.

Reserve stripping ratio: the stripping ratio is calculated based on the ore and rock quantities provided in the geological exploration report.

Stripping ratio of raw ore: the stripping ratio is calculated based on the amount of ore and rock obtained from ore loss and depletion during mining.

Economically reasonable stripping ratio: refers to the maximum amount of rock stripping economically allowed per unit ore volume in open-pit mining. The mining cost of the ore layer adjacent to the open-pit mining boundary is not greater than the underground mining cost.