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Environmental geological problems of nonmetallic mines
Non-metallic minerals damage resources.
1. Impact and destruction of nonmetallic mines on landscape
Large-scale non-metallic mining activities, especially open-pit mining, and geological disasters induced by mining activities often cause great changes in the topography of mining areas, destroy the landscape and worsen the regional ecological environment. Mining activities along major roads and around rivers and lakes have a particularly prominent impact on topography and landscape. Most non-metallic mines such as building materials in southwest China are located along the highway, and the slope of goaf forms "white stubble mountain", which seriously affects the sight and landscape along the highway, and then affects the image of southwest tourist area. For example, there are dozens of phosphate rocks in Dianchi Lake Basin of Yunnan Province, such as Kunyang phosphate rock and Jinning phosphate rock, as well as dozens of quarries and sand yards. Mining activities not only destroy vegetation and form a large area of "bare mountain", but also a considerable number of mining sites are built on steep slopes with a slope of more than 35 degrees, with frequent landslides and serious soil erosion, which seriously affects the ecological environment of Dianchi Lake. The forest vegetation in Dianchi Lake Basin decreased from 25. 1% in 1975 to 26.5438+0.2% in 1988, and the average annual sediment deposition in Dianchi Lake was 33. 1× 104m3, which led to lake bottom uplift and lake surface elevation. In addition to the above situation, there are also many quarries in Puzhehei Scenic Area in Qiubei, Yunnan, which have obviously affected the landscape of the scenic spot. There used to be about 10 large and small mining enterprises in Laojunshan Nature Reserve of Wenshan County, including 3 arsenic plants, which caused great damage to forest vegetation. At an altitude of more than 2,500 meters in Cangshan, Dali, several quarries used to mine marble, which also formed a "white stubble mountain". The exploitation of waste rock also aggravated the frequency of debris flow in Cangshan gully and the sediment deposition in Erhai Lake.
The quarry in Guanyinxia area of Jialing River in Chongqing is located in Beibei District. There are beautiful geological landscapes and typical geological sections in this area. In recent decades, Jialing Cement Plant, Jiangbei Cement Plant and Huangfu Cement Plant have been built on both sides of Guanyin Gorge, mainly mining limestone mines of Lower Triassic Jialingjiang Formation and Feixianguan Formation on both sides of Jialing River. At present, there are three large-scale mining areas on both sides of Jialing River, with the areas of 0.66× 104m2, 0.6× 104m2 and 0.84×105.6×/kloc-0 and 42× respectively. Large-scale exploitation of limestone mine has exposed the bedrock of the mining area without vegetation coverage, and the former green hills have become today's barren hills and bald ridges, which have seriously damaged the natural geological landscape of Guanyin Gorge (photo 3- 13). At the same time, a steep slope with a height of 70 ~ 160 m is formed in the mining area, and the stability of some sections is poor, which poses a threat to Shuibei Highway, 2 12 National Highway and Jialing River waterway.
2. Non-metallic minerals occupy and destroy land resources.
Non-metallic mines in southwest China occupy and destroy land resources quite prominently, with a total area of 57855.92hm2, accounting for 30.67% of the total area. Among them, Yunnan Province is 25398.42hm2, Sichuan Province is 2094 1.43hm2, Guizhou Province is 2334.89hm2, Tibet is 3755hm2, and Chongqing is 5436.1.08hm2.. Yunnan and Sichuan have larger areas, while Chongqing, Tibet and Guizhou have smaller areas.
The flow length of Fujiang River in Youxian District of Mianyang is 37.5 kilometers. The Fujiang River bed is wide and gentle, and there are many gravels and pebbles. Therefore, this section has become an important producing area of building sand and gravel in Mianyang City. In recent 20 years, the amount of sand mining in Youxian District has reached 750× 104m3, the amount of reclaimed sand is about 7.5× 104g, and there are more than 10000 employees, forming 2 134 sand yards, with an average mining depth of 5m and the deepest part of/kloc-. It has caused the destruction of vegetation, soil erosion and river blockage in this area, and affected the urban safety of Mianyang City.
Figure 3- 13 Panorama of Guanyin Gorge
A large number of broken mountains and mountains of slag have been mined in Guangyuanbao Asbestos Mining Area, Shimian County, Sichuan Province, covering an area of 200hm2, which not only destroyed the ecological environment in this area, but also formed a great hidden danger of debris flow, which seriously threatened the national highway 108 and the safety of Shimian County (photo 3- 14).
Fig. 3- 14 guangyuanbao asbestos mining area, Shimian county, Sichuan province
② Environmental pollution in nonmetallic mines.
Southwest China is a large area of phosphorus resources in China, and sulfur mineral resources are also rich. Sulfur and phosphorite are important sources of pollution in nonmetallic minerals.
1. Environmental pollution of phosphate rock in Yunnan
Yunnan is a major phosphorus-producing province. There are only 33 phosphate mining and dressing enterprises in five phosphate mining areas in Dianchi Lake Basin, and the stripped waste rocks and tailings are randomly piled up along the slopes and gullies near the stope. The annual total slag discharge of each mine is 640.28× 104t. These accumulated waste rocks and tailings are leached by atmospheric precipitation, and the main pollutants in the produced sewage are fluorine and total phosphorus. According to the data of Yunnan Geological Environment Monitoring Station, the leaching solution of phosphate rock tailings (phosphogypsum) contains Cd0. 1 18mg/L, Pb0.027mg/L, total phosphorus 14757mg/L and F5308mg/L, which pollutes the surrounding surface water and groundwater.
In the phosphate ore concentrator around Dianchi Lake, except for the wastewater from Shangsuan phosphate ore concentrator, which reaches the standard and is partially reused in Jinning phosphate ore concentrator, most of the wastewater from other concentrator is randomly discharged into the surrounding gullies or tailings ponds, and then scattered in the surrounding gullies and streams. Most of the phosphate rocks around Dianchi Lake are located in the recharge area and runoff area of Dianchi Lake. Randomly discharged mineral processing wastewater and pulp flow into nearby water bodies with surface runoff, polluting surface water. Or runoff seeps into the ground and pollutes the groundwater. Surface water and groundwater eventually flowed into Dianchi Lake, which aggravated the pollution of Dianchi Lake.
The water in Dianchi Lake contains high phosphorus, which promotes the growth of green algae. The green algae in Dianchi Lake are only a few meters thick at most. A large number of green algae consume oxygen in water, which makes it difficult for fish to survive, and the water stinks because of pollution. In recent years, the state has allocated a huge sum of money to control Dianchi Lake, but it has not achieved the expected results, only improving some water bodies. The reason is that the phenomenon of environmental deterioration is in Dianchi Lake, but its root is in mines.
2. Environmental pollution caused by pyrite in southern Sichuan.
The pollution problem of coal-bearing pyrite in southern Sichuan is also quite prominent. The pyrite in this area was built in 1950 ~ 1960, and the mining has caused serious deterioration of the mine and its surrounding ecological environment.
(1) Sulfur pollution caused by local smelting. The whole mine is full of sulfur-smelting loess kilns. The harmful gas after sulfur smelting is directly discharged into the air through the chimney. The concentration of hydrogen sulfide and sulfur dioxide in the atmosphere of the mining area is greatly increased, and the soil is acidified, which makes it difficult for plants around the mine to survive and crops nearby to grow. After sulfur smelting, tailings piled up like a mountain (only the tailings piled up in Dashu pyrite mine area in xuyong county were nearly 1000× 104m3), which filled the whole mining area, and the slag was directly discharged into the surface runoff, which seriously polluted the environment.
(2) Wastewater pollution. During the development of pyrite mine in southern Sichuan, untreated tunnel water, a large amount of mineral processing wastewater, tailings and sulfur smelting waste residue are often discharged into rivers through surface gullies, resulting in serious river pollution, yellow turbidity and rising riverbed, endangering downstream farmland and buildings. Nearly 10% sulfur in the ore in the furnace is dissolved by water and enters the river, which intensifies the pollution of the river.
③ Exhaust gas pollution. The air pollution of pyrite in southern Sichuan is mainly caused by sulfur smelting in a small earth furnace. Due to the original production mode of smelting sulfur, the resource utilization rate is very low, and the sulfur recovery rate is between 30% and 40%. Only 8% ~ 10% sulfur enters the slag, and the rest is discharged into the atmosphere in gaseous form. According to the survey data of industrial pollution, the annual emission of SO2 in the sulfur smelting waste gas of Dashu pyrite mine is as high as 9248t, which is only 4642t of pure sulfur, which not only wastes resources, but also seriously pollutes and destroys the surrounding environment and ecological balance of the mining area. In the physical examination of mine workers in 1985, the total number of patients was 60.8%, among which 90% of young and middle-aged earth furnace operators suffered from emphysema, bronchitis, hemoptysis, rhinitis and other diseases (Jiang Jun,1999; Li, 1980). This shows that a large amount of sulfur smelting waste gas is discharged out of order in this area, forming an air pollution zone dominated by sulfur dioxide and hydrogen sulfide, which seriously affects the health of employees.
At present, the only way to solve waste gas pollution is to stop indigenous sulfur smelting production as soon as possible and introduce smokeless sulfur smelting technology. This project is a new technology to develop pyrite resources and protect the environment. This technology can make the hourly emission of sulfur dioxide less than 34 kg, and the hourly emission of hydrogen sulfide less than 1.3 kg, and the operators of sulfur smelting will not feel the pungent smell of smoke, which is also very beneficial to the labor protection of employees. While adopting this new technology, it also reduces the pollution load of acid wastewater in this area, and will also receive good results in improving the acid rain situation in mining areas.
The slag in the pyrite mining area in southern Sichuan is still increasing at a rate of nearly one million tons per year, and the ecological environment of the mining area has been seriously damaged. Ecological restoration project is to compare mixed soil and unmixed soil in pure tailings environment, select plants that can grow and reproduce on pure tailings slag heap, such as water candle and leafless grass, restore vegetation, transform dust pollution and toxic substances, improve soil fertility, change community climate, make "mature" land available for planting and breeding, and fundamentally realize the social benefits of ecological restoration project; At the same time, through the study of sulfur smelting waste residue and sulfur concentrate tailings, the resources can be recycled, so that the iron content in the waste residue can be raised to the iron ore standard, which is of development value. In this way, the waste of resources is reduced, the benefits of enterprises are increased, and the environmental pollution load is reduced.
(3) Geological disasters in nonmetallic mines
Geological disasters of nonmetallic mines in southwest China are more prominent in Sichuan, followed by Guizhou, Yunnan, Chongqing and Tibet.
1. Geological hazards of landslides in nonmetallic mines
Limestone mine of Jinding Cement Plant in Emeishan, Sichuan Province is a large-scale mine with landslide geological disasters among nonmetallic mines. Since 1970 was put into production, large-scale blasting has been used in this mine until about 1990, and no shock absorption measures have been taken. Strong blasting vibration acts on the slope, which destroys the integrity and stability of the slope rock mass. In addition, due to the influence of rainfall, serious landslide geological disasters have developed (Table 3- 19).
Table 3- 19 Statistics of Geological Hazards in Limestone Mine of Emei Cement Plant
The landslide in the western mining area is a large-scale rock-pulled landslide, and the landslide body slides down as a whole with a sliding distance of160m (Li Yungui et al., 2004). According to the topographic map before landslide sliding, the front edge of the slope before sliding is a straight steep wall, and the steep wall facing the air is 20 ~ 25m high and 190m wide. It consists of thick massive limestone with a vertical thickness of 30 ~ 40m. There is a weak interlayer (argillaceous siltstone) under the thick limestone, which is exposed at the foot of the mining platform 720 meters below the slope. The east side of the slope is cut by the grove, and the west side is cut by the dissolving tank. There are structural cracks in the slope, with a tendency of 45 ~ 135, and the slope has been cut into blocks. The distance between the 720m platform and the steep wall plane on the slope is about120m, and high, steep and medium-high slopes with height difference exceeding100m are formed from the top. Therefore, after three days of continuous light rain on March 15, 2002, the upper slope suddenly fell, and a "3. 15" landslide occurred in the western mining area, killing 8 people and burying a large number of mining facilities. The sliding body slides down along the weak structural plane at high speed160m (horizontal distance) and lands on the 720m platform, with the leading edge reaching the 670m platform, and the plane is tongue-shaped. The landslide is triangular in plane, with an area of 12440m2 and a volume of 37.32× 104m3. The accumulation area of sliding body is 6.06× 104m2, the thickness of sliding body is 10~30m ~ 30m, and the volume is about 60×104m3. . The remaining volume after cleaning is about 40× 104m3 (Figure 3- 15).
Fig. 3- 15 "3. 15" landslide in the west mining area of Sichuan Emei Jinding Cement Plant.
The steep wall at the trailing edge of the landslide is linear, and the strike is about NW45, which is composed of tensile structural planes with strong dissolution. After dissolution, the steep wall surface is uneven and stalactites are hung. The height of sliding wall is 15 ~ 30m. The sliding mode is bedding sliding, the landslide body slides down as a whole, the leading edge slide body rolls down, some blocks of the trailing edge slide body still retain the layered structure of the original rock, and the top of the slide body retains residual residual soil and vegetation. There are sliding and caving deposits between the sliding body and the east sliding wall, the sliding bed is exposed, the sliding surface is flat and smooth, and there is calcite film. The sliding surface is slightly arc-shaped, with the azimuth angle of 22 ~ 26 and the inclination angle of 27 ~ 365438+0. The top is gentle and the bottom is steep, and the scratches on the sliding surface are clearly visible. The direction of scratches is NE22, which is consistent with the dip angle of strata and slip surface. The sliding surface consists of the weak structural surface in the lower soft-hard rock group and the sliding zone under the steep cliff at the back wall of the landslide, and the groundwater overflows along the sliding surface after rainfall (Figure 3-7). The sliding surface of the landslide is complete, and no fracture surface is found. A shaft-like cave with a diameter of 30 meters was found at an altitude of 770 meters in the middle of the sliding surface. The cave is semi-circular, the vertical depth is 15m, and there are branches on the side wall of the cave bottom. In this landslide, the cave was exposed after the overlying rock mass slipped.
After the occurrence of geological disasters, the geological environment of the mine was explored and evaluated, the causes of geological disasters were found out, and the next safe mining plan was formulated.
In addition, the geological disasters of pyrite mountain landslide in Xuyong area of southern Sichuan are also serious. For example, at the end of March of Dashu pyrite mine in Xuyong1990, several surface cracks appeared at the foot of Yingying rock slope in Hexi section, and the cracks developed rapidly. Due to the surface cracking and sliding, more than 20 dormitories in the mine collapsed, and more than 0/00 houses, floors and walls of/kloc-were cracked and seriously tilted. At present, 443 buildings such as workers' houses and clubs in the Ministry of Mines have been damaged or threatened.
Fig. 3-7 Schematic diagram of landslide status in west mining area of Jinding Cement Plant in Emeishan, Sichuan.
1-the second weak layer (argillaceous layer); 2- the third weak layer (argillaceous layer); 3-dissolution ditch; 4- landslide accumulation; 5-limestone of the sixth member of Lower Permian; Limestone of the 6th-5th member of Lower Permian; 7— Water marl
The formation of geological disasters is not only related to the complex geological environment conditions such as topographic relief, soft and hard alternation of the Triassic Feixianguan Formation, soft sediments on the Quaternary slope, but also closely related to the human activity factor-underground mining. The deformation and collapse of underground mining (coal-bearing) roof leads to the destruction of overlying strata and surface subsidence, which is the most important active factor to trigger and induce various disasters. In 1990s, there were small coal wells in Dashu pyrite mine area. According to the estimation of daily output and mining time of small coal mines, the cumulative coal output of small coal mines is about 4× 104t, and the converted goaf area is 3.6× 104m2. According to the data of other coal mines in China, when the mined-out area reaches 1000 ~ 3000m2, the surface may move and deform. The positions of three cracks on the existing ground are basically consistent with the mined-out area. This shows that the surface cracks are caused by long-term mining in small coal mines and induce the movement and deformation of overlying strata.
At the same time, there are many types of disasters in this area. Besides collapses and landslides, there are also environmental geological problems such as mountain torrents and mudslides (water-bearing stone flows), environmental pollution, river blockage, river bed elevation, road pavement damage and tailings occupation (photo 3- 16).
Figure 3- 16 Dashu pyrite slag was washed into the river.
2. Geological hazards of debris flow in nonmetallic mines
The geological disasters of debris flow in nonmetallic mines in southwest China are mainly rainstorm, especially in old mines. For example, large-scale debris flow geological disasters have occurred in Kaiyang phosphate mine in Guizhou and asbestos mine in Sichuan.
1995 In the middle of the night of June 24, a torrential rain occurred in Jinzhong Town, Kaiyang County, Guizhou Province, causing mudslides and landslides, with a volume of about 200× 104m3. Jinzhong Town and Kaiyang Phosphate Mine were affected in a large area, which destroyed the factory building 1 1606 square meters, flooded the mine 27 179 square meters, flooded the mine 49 10 meters, 645 sets of equipment, 2 1800 meters of water supply pipeline and 7.6 power supply and communication trunk lines. 464 households were affected, accounting for 130 12, 25 people were killed and 18 people were injured, resulting in a direct economic loss of 205 million yuan.
Debris flow also occurred in Xinkang asbestos mine in Sichuan. The mine is located on the hillside downstream of Nanda Honggou, Shimian County, Ya 'an City, and Dahonggou is its dump and tailings pond. In order to separate water from rocks, a flood dam and a flood diversion tunnel were built on the upper part of the garbage dump. The downstream slag dam and spillway are built by directional blasting: slag and tailings are accumulated in the reservoir 2 100× 104m3. On April 6, 200 1 year, due to the maintenance of the upstream drainage tunnel, it rained and the water was temporarily discharged to the downstream, resulting in debris flow (water-rock flow). The debris flow partially washed out the slag dam and poured down 30× 104 ~ 50× 104m3, which made the silt in the downstream Zhujiang River 8m high, and damaged the enterprises along the river, which was directly economical. The Sichuan Provincial Party Committee and the provincial government attached great importance to it and invested 4.8 million yuan to complete the emergency response in September, 200 1. The main works include: ① the slag dam is repaired with lead wire gabion (spillway is built in the scouring section) (photo 3-17); (2) clean up the waterways in the reservoir; (3) heightening the upstream flood dam and repairing the spillway tunnel; ④ A grid dam is added upstream. Through the above treatment project, the threat of debris flow in tailings pond was initially alleviated.
Figure 3- 17 Spillway of the tailings pond of Xinkang asbestos mine in Shimian County, Sichuan Province
3. Geological disasters of non-metallic mine collapse
Geological disasters of non-metallic mine collapse are often related to irregular and unreasonable mining. On September 6th, 20001year, the Guangzhongtian Dapo quarry in Tangya Village, Xinyao Township, Liuzhi Special Zone, Guizhou Province collapsed, causing 15 deaths and 2 injuries. The collapse is about 73m long, 75m wide and 5 ~ 15m thick, with a total volume of 2× 104m3. The exposed stratum of this quarry is thin to medium layered limestone of Yongningzhen Formation of Lower Triassic, with several layers of 2 ~ 5 mm mudstone, and two groups of fractures, 143 and 225, are developed in the rock. The collapse occurred mainly because of unfavorable rock combination conditions, weak layers between layers, developed corrosion cracks and reduced rock strength due to water infiltration. At the same time, unreasonable human engineering activities caused some or most of the old slopes of simple highways built in the early 1990s to cut off the soft layers, and farmers themselves mined stones to form free surfaces, which destroyed the already fragile rock mass balance and caused geological disasters.
At 23: 30 on February 6, 2003, the dangerous rock mass on the east side of the cement plant jointly run by Group 7, Xunsi Village, Junlian Town, Bing Yi City, Sichuan Province suddenly collapsed, destroying 500 square meters of the cement plant, causing three deaths and 65,438 minor injuries. Damaged or buried a large number of mining equipment, resulting in direct economic losses of 2 million yuan. The collapse volume is about 500m3, and the caving rocks are irregular, with a diameter of about 3m and a maximum of 6m. The maximum rock volume at the collapse site is about1100m3. Xunsi Town is 14km away from Junlian County, and the landform is a low mountain with dissolution structure. The exposed stratum is the Permian Maokou Formation (P2m) medium-thick layered limestone with bioclastic limestone, and the rock mass occurrence is 2 15 ∠ 18. Limestone joints and cracks are developed, and the integrity of rock mass is poor. At 1992, when the patrol company built the cement plant, the slope of the local mountain was cut to some extent. The factory building of the cement plant is built on the edge of a steep cliff about 20 meters high. Three groups of joints and fissures are developed in limestone. Due to the influence of joint surface and rock stratum, rock mass is cut into dangerous rocks with different sizes. For a long time, groundwater moves in cracks and erodes rock masses, which reduces the shear strength between rock masses. Under the action of gravity, the dangerous rock mass is separated.
At present, although the collapsed rock mass is basically stable, there are still thousands of dangerous rock masses on the other side of the collapse (next to the quarry of the cement plant). Under the inducement of quarrying and rainfall, it may collapse again, which directly threatens the safety of cement plants and workers and should be avoided.
Pangang limestone mine in Panzhihua City, Sichuan Province is located in the middle and upper part of the mountain on the right bank of Guankou River, which is the production base of Pangang's auxiliary raw materials. The mining area has steep terrain, complex structure and broken rock mass. The formation lithology is Permian limestone, which is monoclinic, and the dip angle is consistent with the slope direction, and the formation dip angle is 23. Open-pit mining is carried out by perforation blasting, and the annual limestone mining is about 120× 104t.
Within a short period of 8 years from 1980 to 1988, three large-scale collapses occurred on the west side of the stope, with a total amount of 398× 104m3. The first 1 collapse occurred on June 8th 1980, 165438+, located on the east side of++1400m platform. It mainly develops along joints and fissures and bedding planes, and the formed collapse is 46m long, 65m wide, 6-35m thick and 5× 104m3 in volume. The reason is that chamber blasting was used in the+1400m level of the stope, and the "root foot" of the coal seam was cut off along the horizontal step along the strike 1400m, which made the slope toe of the stope form a free surface with a height of about 245m, which led to the collapse of the upper broken rock mass. The second plunge occurred in June 198 1 day, which was mainly based on the plunge of 1 day. The volume of the collapse is 392× 104m3, and its formation reason is basically similar to that of 1 collapse. The third collapse occurred at the west side of F8 fault in the northwest of the stope, and the time was 1988 10 10/3. The collapse body is 100 m long from north to south and 350 m wide from east to west, and its volume is about 1.0× 104 cubic meter. Excessive blasting vibration and high slope excavation are still the causes.
Three caving accumulations covered one-third of the stope area, which stopped mining all the production steps in the west of the mine 1400 ~ 1363m4, reduced the east-west length of the stope by 450m, and covered 2,800×104t of high-quality ore, which brought great difficulties to mine traffic and mining. At present, a steep cliff with a height of about 100 meters is formed on the west side slope, and there is an obvious crack area on its upper part, so its stability is poor. In addition, due to the loose structure, large slope and poor stability of the collapsed accumulation body, it is easy to form landslide or debris flow disaster under the action of rain.
4. Geological disasters of ground subsidence in nonmetallic mines
The ground collapse of nonmetallic mines is similar to other types of mines and related to mined-out areas. Combined with the influence of hydrogeological conditions and blasting vibration.
1June 999 13 10: 50, the slope of Shuimogou, Group 5, Village 4, Hongbai Town, shifang city City, Sichuan Province suddenly collapsed, forming a circular collapse pit with a diameter of about 5 meters and a depth of about 6 meters, which led to the collapse of the house in Yuejiashan No.1 Mine of Jinhe Phosphate Mine and the burial of three foreigners living in it. In addition, there are still 4 villages and 5 groups 13 villagers living on the slope of Shuimogou collapse pit. There are cracks and cracks on the floor of most residents' houses. The crack width is 0.1~ 3cm, mostly 0.2 ~ 0.8cm, and the length varies from several meters to more than ten meters, mostly in the northeast-southwest direction, and some in the northwest-southeast direction. The concrete floor cracks and sinks, and cracks appear at the joints of vertical and horizontal walls of houses, doors and windows of walls and other structural weak parts. The reason of ground collapse is related to the roof deformation of goaf and the vibration of mining blasting.
To sum up, the environmental geological problems of energy mines in Southwest China are mainly water pollution, air pollution, landslide, debris flow, land subsidence and occupation of land resources, while the environmental geological problems of metal mines are mainly heavy metal pollution, landslide, debris flow and soil erosion. The environmental geological problems of nonmetallic mines are mainly the destruction of landscape resources, the destruction of land resources, the pollution of sulfur and phosphorus chemical raw materials, landslides, mudslides and other geological disasters, which shows that the environmental geological problems formed by different types of mines are different (Table 3-
Table 3-20 Environmental Geological Problems of Major Mines in Southwest China
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