What are the main methods of metal mining?

Metal mining methods involve studying the methods of extracting ore from ore bodies.  This includes three main tasks: preparation, cutting, and extraction. The sum of these preparation, cutting, and extraction activities carried out within the ore body to facilitate better ore recovery is called the mining method. Currently, the main mining methods used are: open stope mining, backfill mining, and caving mining.

NO.1 Open Stope Mining

In open stope mining, the ore body is divided into stopes and pillars during the extraction process. The stopes are mined first, followed by the pillars. The basic conditions for applying open stope mining are that the ore and surrounding rock are stable, and the mined-out area can have a large exposed area for a certain period of time. Widely used mining methods within this category include: full-face mining, room-and-pillar mining, shrinkage stoping, and staged room-and-pillar mining.

01 Full-Face Mining
Full-face mining is used in thin and medium-thick, gently dipping (dip angle generally less than 30°) ore bodies where both the ore and surrounding rock are stable. Its characteristics are: the working face advances comprehensively along the strike or dip of the ore body, and during the extraction process, the interbedded waste rock or low-grade ore in the ore body is left behind as irregular pillars to support the mined-out area. These pillars are generally considered a permanent loss and are not recovered.
02 Room-and-Pillar Mining
Used for mining horizontal or inclined ore bodies, in which stopes and pillars are arranged alternately in the ore body or mined-out area. When mining the stopes, continuous or discontinuous regular pillars are left to support the roof rock. It has a wider range of application than full-face mining, and can be used to mine not only thin ore bodies but also thick and very thick ore bodies. Stable ore and surrounding rock in horizontal and gently dipping ore bodies are the basic conditions for the application of this mining method.
03 Shrinkage Stoping
Workers work directly on the pile of broken ore under the exposed face of the stope, extracting the ore in layers from bottom to top. Each time, about 1/3 of the extracted ore is released by gravity, and the rest is temporarily left in the stope as a working platform for continued upward mining. After all the stopes are mined out, the ore temporarily remaining in the stopes is then released in large quantities, which is called mass ore extraction. This mining method is suitable for steeply dipping ore deposits where the ore and surrounding rock are stable, the ore is not prone to spontaneous combustion, and the crushed ore easily re-cements.
04 Staged Stope Method
The ore block is divided into several sections in the vertical direction. Stopes and pillars are arranged horizontally in each section, and the ore mined from the middle section is transported out through the ore extraction roadways of each section. After the stope mining in a section is completed, the pillars in that section can be immediately mined, and the mined-out area can be simultaneously processed.
05 Stage Stope Method
This is an open-stope mining method using deep-hole mining.  Based on the method of ore extraction, it can be divided into horizontal deep-hole stage stope method and vertical deep-hole stage stope method. The former requires undercutting at the bottom of the stope, while the latter, in addition to undercutting, also requires opening a vertical cutting slot along the entire height of the stope.

NO.2 Caving Mining Method

Caving mining is a mining method that uses caving of the surrounding rock to manage ground pressure. That is, as the ore collapses, the surrounding rock is forcibly (or naturally) caved to fill the mined-out area, thereby controlling and managing ground pressure. It mainly includes single-layer caving method, layered caving method, sectional caving method, and stage caving method.
01 Single-Layer Caving Method
This method is mainly used to mine gently dipping ore seams with unstable roof rock and a thickness generally less than 3m. The ore seam between stages is divided into ore blocks, and the mining work of the ore blocks progresses along the strike of the ore body. After the mining face advances a certain distance, except for the space required for mining operations, the supports are systematically recovered, and the roof of the mined-out area is caved in. The caved roof rock fills the mined-out area to control the roof pressure. According to the form of the working face, it can be divided into longwall caving method, shortwall caving method, and entry caving method.
02 Layered Caving Method
The ore blocks are mined from top to bottom in layers. After the ore in each layer is extracted, the overlying caved rock moves down to fill the mining area. Layered mining is carried out under artificial roof protection, where the artificial roof separates the ore from the caved rock, thus ensuring minimal ore loss and dilution.
03 Sublevel Caving Method with Bottom Pillars
This method is also called the sublevel caving method with a bottom structure. Its main features are: firstly, mining is carried out section by section; secondly, a dedicated bottom structure for ore extraction is provided at the bottom of each section, and the section mining is carried out sequentially from top to bottom. It can be further divided into horizontal deep-hole blasting sublevel caving method with bottom pillars and vertical deep-hole blasting sublevel caving method with bottom pillars. 04 Sublevel Caving Method without Bottom Pillars
The bottom of the section does not have a bottom structure composed of dedicated ore extraction roadways.  All operations such as drilling, blasting, and ore extraction are carried out in the mining roadway. 05 Stage Caving Method
The mining height is equal to the full height of the stage. It can be divided into stage forced caving method and stage natural caving method. The stage forced caving method can be further divided into stage forced caving method with compensation space and continuous mining stage forced caving method.

NO.3 Backfilling Mining Method

This is a mining method that gradually fills the mined-out area with backfill material as the mining face advances. Sometimes, supports are used in conjunction with backfill material to maintain the mined-out area. The main purpose of backfilling the mined-out area is to use the formed backfill body for ground pressure management to control surrounding rock collapse and surface subsidence, and to create safe and convenient conditions for mining. Sometimes it is also used to prevent internal fires in self-igniting ore. According to the ore block structure and the direction of the mining face advancement, it can be divided into single-layer backfilling mining method, upward layered backfilling mining method, downward layered backfilling mining method, and selective backfilling mining method. According to the different backfill materials and output methods used, it can be divided into dry backfilling mining method, hydraulic backfilling mining method, and cemented backfilling mining method.

 01 Single-Layer Backfilling Mining Method
This method is suitable for gently dipping thin ore bodies.  A wall-type mining face, extending the full length of the ore block, is used to mine the entire thickness of the ore body in one pass along the strike direction. As the working face advances, the mined-out area is systematically backfilled with hydraulic or cemented fill to control the roof.
02 Upward Horizontal Layered Backfilling Mining Method
This method is suitable for gently dipping thin ore bodies. A wall-type mining face, extending the full length of the ore block, is used to mine the entire thickness of the ore body in one pass along the strike direction. As the working face advances, the mined-out area is systematically backfilled with hydraulic or cemented fill to control the roof.
03 Upward Inclined Layered Backfilling Mining Method
The difference between this method and the upward horizontal layered backfilling method is that inclined layers are mined. The transportation of ore and backfill material in the stope mainly relies on gravity. This method can only use dry backfilling.
04 Downward Layered Backfilling Mining Method
This method is used for mining very unstable ore bodies or those where both the ore and surrounding rock are very unstable, and the ore grade is very high or the non-ferrous or rare metal ore body is of very high value. The essence of this mining method is: layered mining and backfilling from top to bottom, with the mining of each layer carried out under the protection of an artificial false roof from the previous layer. The mining layers are horizontal or inclined at an angle of 4°–10° or 10°–15° to the horizontal. Inclined layers are mainly for backfilling the immediate roof, and also facilitate ore transportation, but drilling and support operations are less convenient than in horizontal layers.
05 Selective Mining and Backfilling Method
When the thickness of the ore vein is less than 0.3–0.4m, miners cannot work in it by only mining the ore.  It is necessary to selectively mine the ore and surrounding rock separately to achieve a minimum working thickness (0.8–0.9m) in the mined-out area. The mined ore is transported out of the stope, while the excavated surrounding rock is used to backfill the mined-out area, creating conditions for continued upward mining. This mining method is called the selective mining and backfilling method. 06 Square-Set Timbering Mining Method
In the past, thin ore veins were mostly mined using cross-braced or timber-framed support methods.  Under conditions where the ore body is thick, the ore and surrounding rock are extremely unstable, the ore body shape is very complex, and the ore is valuable, this mining method remains an effective one.