Earth Day: Abandoned mines left alone? Mountains without mines can also be turned into treasures!

Today is World Earth Day. Our planet has a variety of natural resources, among which mineral resources are related to our daily food, clothing, housing and transportation. We can't help but ask, as the "mother" of mineral resources, are mines abandoned after being mined? In fact, "mineless" mountains can also be turned into treasures!

Open-pit mine in Holingol City, Inner Mongolia (copyright image from the gallery; reprinting may lead to copyright disputes)

01 What is an abandoned mine?

A mine is a man-made place in three-dimensional space where minerals are mined . Due to the non-renewable nature of mineral resources, almost all mines have their own "lifespan". Once the exploitable resources are exhausted, the mine faces the fate of being abandoned or closed, becoming an abandoned mine.

Generally speaking, mines are often abandoned due to resource depletion. However, in recent years, many mines have been closed due to environmental protection and ecological red lines, becoming a new form of mine abandonment. Different from mines abandoned due to resource depletion, in essence, this type of mine is more like a "dormant mine" - because this type of mine often has certain resources to be mined, and when the production process level and environmental protection technology are improved in the future, it can be converted into a production mine again.

A mine is a man-made place where minerals are mined in three-dimensional space. (Image copyrighted by the library; reprinting and use may cause copyright disputes)

Regardless of the reason for abandonment, once it becomes an abandoned mine, it means that the mine can no longer continue to provide the original mineral resources for mankind, that is, a "dormant mine" or a closed mine. However, some abandoned mines may be revived or mined again after being abandoned .

02 Hazards of Abandoned Mines

When a mine is in normal production, mining activities disrupt the original balance of the mountain or ore deposit. As mining and production progress, harmful gases will be released from the ore body or mountain, causing various geological problems such as water inrush and rock burst . Artificial ventilation, drainage and anchoring intervention are required to ensure the safety of mining operations.

When a mine is abandoned, the original mineral production is terminated, the original ventilation, drainage and other activities are terminated or even the related systems are dismantled, leaving only a hollowed-out cavity or tunnel in the three-dimensional space. However, since this cavity or tunnel is often lower than the surrounding non-mining area, a large amount of water and gas will accumulate in the hollow area over time .

Since the original mineral-bearing strata contain a large amount of elements such as sulfur and phosphorus or acidic organic salts, some of the accumulated water leaches over a long period of time to form acidic mine water, which overflows onto the ground or pollutes groundwater, causing water pollution.

Some abandoned mines, such as abandoned coal mines, produce a large amount of coal seam methane in the goaf. After accumulation, it overflows from the cracks on the surface of the coal mines, causing methane leaks, polluting the atmosphere, and even exploding when encountering open flames.

Some shallow and deep underground coal mines will have a large number of goaf collapses after abandonment, resulting in mining geological disasters such as ground fissures or surface subsidence, or underground coal fires.

After the open-pit mine is abandoned, the surface vegetation is destroyed, the strata are exposed to the surface for a long time, and suffer from weathering and erosion, causing geological disasters such as mudslides and landslides.

03 Abandoned mines are actually full of treasures

After a mine is abandoned, it often forms a variety of secondary resources:

Intangible and tangible resources

Intangible resources: refers to the mining culture contained therein, such as mining history, mining spirit and other intangible resources.

Tangible resources: abandoned tunnels, railroad tracks, buildings, squares, construction land, etc., as well as the three-dimensional space on the ground where mines are located and underground in mines.

Classification by the form of matter

Solids: tailings, surrounding rocks, residual minerals, etc.;

Liquid: mine water, water in underground goaf, water in ground subsidence area, etc.;

Gas: coal-bed methane (such as methane, carbon dioxide, etc.);

There are a large number of bauxite resources under the coal in the lower parts of many Carboniferous-Permian coal mines in North China . There are rich "three rare" mineral resources such as lithium and gallium in the roof and floor plates and interlayers of the coal mines, and there are large amounts of coalbed methane, mine water and other resources in the goafs.

03 Development and Utilization of Abandoned Mines

For abandoned mines, the best way to restore them is often not to abandon them, but to restore their natural ecology through secondary development and utilization. For example:

Land leveling and reclamation are carried out in abandoned open-pit mines to form new farmland .

Areas with heavy rainfall can be built into artificial lakes or lakeside parks according to local conditions . For example, the Pan'an Lake National Wetland Park in the Jiawang Mining Area in Xuzhou, China, has become a national 4A-level tourist attraction.

A corner of Pan'an Lake National Wetland Park (Source: Xinhua News Agency)

After a slight artificial leveling of the subsidence area of ​​abandoned coal mines produced by underground mining, a photovoltaic power generation base can be built on it , such as the first batch of domestic photovoltaic "leader" demonstration bases in Yungang District, Datong, which is well-known on the Internet.

Photovoltaic power generation project in Datong City (Source: Xinhua News Agency)

Abandoned mines near the edge of the city can also be transformed into mine hotels or competition venues . For example, the Wangping Mine in Mentougou District, Beijing, will build a cultural and tourism resort hotel with the theme of "coal industry culture + hotel leisure". The Xinqiu Open-pit Mine in Fuxin, Liaoning, was built into an international mountain car international racetrack city after its closure, becoming a new world for racers to gallop.

Some relics with a long history of ancient mining can be built into site museums. For example, the Tonglushan Ancient Copper Mine Site Museum in Daye, Hubei, where mining dates back to 4,000 years ago, is the oldest, largest, and best-preserved ancient mining site in China.

The new museum of Tonglushan ancient copper mine site (Source: Xinhua News Agency)

Abandoned underground salt caverns with good sealing conditions can be used as underground oil, gas and carbon dioxide storage. For example, in Jintan, Changzhou, Jiangsu, and Rongbing, Zhenjiang, my country, four abandoned salt cavern gas storage facilities have been built by the end of 2023, realizing the reuse of 1.2 million cubic meters of underground space.

Energy storage power stations can also be built in abandoned mine tunnels and goafs , such as:

Pumped-storage power station : It uses the three-dimensional underground space with height differences formed by underground mining or open-pit mining to form two water reservoirs with different height differences, and uses the natural gravitational potential energy formed by the height difference between the water bodies to generate electricity.

Compressed air energy storage : Utilize the space in coal mine tunnels or rock caves to convert electrical energy into air potential energy through compressed air during the peak period of power generation, and release the air into electrical energy during the peak period of electricity consumption, thereby reducing the peak and filling the valley and replenishing electrical energy.

Author: Liu Hanbin, Senior Engineer, Shanxi Coal Geology Bureau

Reviewer: Liu Qinjie, Professor of School of Mining Engineering, Anhui University of Science and Technology

Produced by: Science Popularization China

Produced by: China Science and Technology Press Co., Ltd., China Science and Technology Publishing House (Beijing) Digital Media Co., Ltd.