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2 Underground Gold Mining Method

xinhai 2021-01-22(07:01:20) 568 0

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There are many types of primary gold deposits, and the conditions for the occurrence of ore bodies are complicated. For gold deposits with relatively deep ore body buried depth and extended depth, underground mining method is more suitable. Commonly used underground gold mining methods include open-stope method and filling method. This article will briefly introduce these two underground gold mining methods.

First of all, as an underground gold mining method, the open-stope method is widely used. According to the different specific operation schemes, it can be divided into the typical shallow hole retention method, the shallow hole retention method in the road courtyard and the comprehensive retention method.

1. Open-stope method

Open-stope method.jpg

(1) Typical shallow hole retention mining method

It refers to a underground mining method in which there is a pillar between each mine room, and the quasi patio and horizontal connecting road are excavated in the pillar, and connected with the stope. This method is generally used for thin ore bodies or very thin ore bodies with a thickness of less than 4-5 meters and an inclination of the ore body greater than 60 degrees.

When mining, the ore is mostly stratified horizontally. The rock drill is perpendicular to the blast hole at an angle of 45 degrees or nearly 90 degrees. In order to minimize the loss when mining fissure-filled thin veins or extremely thin veins, the blasthole should not be too deep, generally not exceeding 1.5 times the mining width.

The main disadvantage of this underground gold mining method is that the pillar ore accounts for a large proportion. This part of the ore volume is difficult to recover, the recovery rate is low, and it is easy to cause a lot of losses. The advantages of this method are good ventilation conditions, few factors affecting the stope, and higher stope productivity.

(2) The shallow hole retention mining method in the road courtyard

This underground gold mining method refers to that there is no pillar between each mine room, and it can be continuously mined along the entire length of the ore block. The road patio can be erected with pit wood every 40-60 meters, or metal circles can be installed. The tube is used as a road-way patio in the stope for pedestrian passage and erection of air and water pipelines.

When using pit wood to erect a road-way patio, the surrounding rock of the ore body is required to be relatively stable, and the ore body should not be too thick (generally less than 2.5-3m). When the vein is too thick, and the horizontal bracing is too long, which not only consumes a lot of wood, but also may cause accidents such as broken bracing and collapse along the way, affecting normal production and threatening personal safety.

(3) Comprehensive method of retaining ore

This kind of underground gold mining method can be divided into two types: horizontal harrow ore and vertical slope harrow ore.

When the inclination of the ore body is greater than 45 degrees, although the floor of the ore body is not necessarily smooth, the ore contains more muddy water and is highly oxidizing, one-third of the by-product ore during the mining process can generally be released by the ore's own weight.

However, a considerable part of the ore is difficult to release due to the uneven floor of the ore body and secondary cementation. At this time, the electric rake can be used to harrow the ore in the inclined direction of the ore body. After the end of mining, part of the ore still uses the bottom funnel to release the ore by its own weight.

The main advantage of this underground gold mining method is that the stope structure is relatively simple, and the stoping process is basically the same as the shallow hole retention method. For thin ore bodies or very thin ore bodies that have more muddy water with an inclination angle of 45-70 degrees, strong ore oxidation, and prone to secondary cementation, this method can achieve better technical and economic indicators.

When the inclination of the ore body is less than 35-45 degrees, the by-product ore during the stoping process must also be rake out. At this time, the horizontal rake ore retention method is usually adopted. When mining, the surplus by-product ore is generally raked out along the direction of the ore body using electric harrows.

2. Backfill mining method

Backfill mining method.jpg

(1) Dry filling mining method

Dry fill mining is mostly used in thick ore bodies of altered gold deposits, and some mines are used in thin ore bodies with relatively broken surrounding rocks. When the dry filling method is used for thick ore bodies, the ore houses are generally arranged perpendicular to the direction of the ore body, and the width of the ore houses is determined according to the stability of the ore body, which is generally 5-8 meters. The length of the ore house is the horizontal thickness of the ore body.

There are two plans for the mining sequence. One is a stepped continuous mining method, and the other is a two-step mining method, which means one step back to the mining room, and the filling body is used as the pillar of the second step back to the mining room. During stooping, the height difference between the mine houses should be higher than 5m. If it is too small, it will easily cause the roof of the stope to fall.The main advantage of this underground gold mining method is that it is relatively simple, the recovery rate is high, and the loss rate is low. The dilution rate of the mining house is about 5-10%, and the loss rate is about 3-8%. 

Its disadvantages are the low degree of mechanization and small stope production capacity. Most of the altered ore bodies in mines are not very stable, and roof fall often occurs in stopes, which poses a serious threat to safe production. This is also one of the problems that the law needs to solve urgently.

(2) Cutting wall and filling mining method

The cut-and-fill underground gold mining method is mostly used for extremely thin ore bodies with stable ore and obvious decomposition. Commonly used divisions include horizontal layered cutting and filling method, V-shaped working face and fan-shaped working face cutting and filling method.

The main advantage of cutting wall filling mining method is to reduce loss and dilution, which is more obvious for improving and enhancing the comprehensive economic benefits of mining enterprises. At present, most of the mines that use the cutting wall filling method have low mechanization, complicated mining techniques, low stope productivity, poor working conditions, and high labor intensity.

(3) Tailings (or cementation) filling mining method

With the continuous improvement of underground mining technology, the highly mechanized tailings-filling mining method used for gold mines has been developed rapidly in recent years. And the use of mechanized tailings-filling underground mining method greatly improves the production capacity of the stope, and can realize connected filling, reduce the labor intensity of workers, and reduce the footprint of the tailings dam.

The main shortcomings of this underground gold mining method are that the process is more complicated, there are many links, and it is prone to failures. It requires the mine to have a certain technical quality and management level. In addition, the underground production conditions are poor and the muddy water is difficult to handle.

To wrap up

The above is a brief introduction to the two underground gold mining techniques of open-stope method and filling method. At present, the most widely used method of underground mining in gold mines is still the shrinkage stoping method, but several other mining techniques have their own characteristics. In the actual production process, it is still necessary to determine the most suitable mining technology based on the geological analysis of the deposit.

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