(a) Environmental pollution in metal mines
Heavy metal pollution is common in metal mines in southwest China, especially in nonferrous metals such as mercury and thallium, especially in Wanshan mercury mine, Lanmuchang mercury mine and Danzhai mercury mine in Guizhou Province. Mercury and thallium enter the food chain, endangering human health and becoming invisible killers.
A large number of slag in mining, tailings and slag in smelting are ore components discarded after crushing, grinding and treatment by different methods. At the same time, many mine tailings, especially flotation tailings, contain chloride, cyanide, sulfide, pine oil, organic flocculant and surfactant. In the process of stacking, these substances are influenced by sunlight, rain, air and their interaction, which will produce harmful gas, liquid or acidic water, aggravate the loss of heavy metals, pollute groundwater and soil, and pollute crops growing in the surrounding and downstream soil. In this way, the content of heavy metals in some crops will increase exponentially or dozens of times, which will enter the human food chain, destroy the ecological balance and produce a series of environmental geological problems. The data show that the high incidence of lung cancer is obviously related to fine particles such as arsenic, cadmium, nickel, manganese, thallium and beryllium in the atmosphere. Lead, mercury and arsenic can lead to acute poisoning death, and cadmium, manganese and nickel can also induce cardiovascular diseases. It can be seen that these heavy metals, whether in the atmosphere, water or soil, can enter the human body through various channels and become terrible killers of human beings.
1. Mercury pollution of Wanshan mercury mine in Guizhou
Guizhou Wanshan mercury mine was originally a large central mining enterprise, and its mining time began in the first year of Hongwu in Ming Dynasty, with a history of more than 600 years. At present, the mine resources have been exhausted and the mine has been closed. However, hundreds of years of mining and smelting have caused mercury pollution to the environment and destroyed the virtuous circle of biological chain in this area. Due to mine air pollution, soil pollution, water pollution, farmland pollution and crop pollution, the health and living environment of residents in the mining area and its surrounding areas have been seriously damaged. It has caused serious economic and social problems. The average urine mercury of ordinary residents in Wanshan town exceeded the standard by 3.5 times, and the mercury smelting workers exceeded the standard by an order of magnitude. The prevalence of mercury poisoning accounts for 40% of smelting workers, and mercury smelting workers in township enterprises account for more than 50%. The total drainage area of the whole region is 338km2, of which 180km2 is endangered by mercury pollution in different degrees. The toxic paddy fields reached 433.29hm2, accounting for 27% of the total rice area. The mercury content in corn and rice exceeded the standard 10.25 times and 33./kloc-0 times, respectively, and the mercury content in Chinese cabbage exceeded the standard by 98./kloc-0 times. The total length of mining roadway in the mining area is 970km, which forms a large area of mined-out area, resulting in a large amount of surface water leakage, a significant drop in groundwater level, and much pollution, making it difficult for people and animals to drink water in many areas. The local SAR government spared no expense to take water from Xinmian County, Hunan Province, which is 0/7 km away from/kloc-to solve the drinking water problem in the mining area, but there are still 35,000 people drinking water contaminated by mercury. It can be seen that once water resources and soil are polluted, it is very difficult to restore the ecological environment, which seriously threatens the health of local people and forms economic and social problems in the mine and its surrounding areas. Guizhou is a big province of mercury mines, and similar situations have occurred in other mines, and the problem is quite serious.
2. Thallium pollution of mercury mine in Lanmuchang, Guizhou
Thallium (Tl) exists in the earth's crust in the form of isomorphism, isomorphism, colloid adsorption and independent minerals, mainly in the form of isomorphism under endogenous action and adsorption under exogenous action.
A few mercury, antimony and pyrite deposits in southwest Guizhou and northeast Guizhou and their adjacent soils all contain thallium, and thallium mainly exists in related deposits, especially closely related to mercury deposits. The thallium-bearing selenium mercury mine in Kezhai, Guizhou, the thallium-bearing antimony gold mine in Getang, Guizhou and the thallium-bearing mercury mine in Lanmuchang, Guizhou all contain thallium components. Especially the Lanmuchang Hg-Tl deposit has the highest thallium content.
Thallium pollution belongs to local pollution, but its toxicity is no less than arsenic, sulfur and mercury. A thallium-polluted area has been formed in the Hg-Tl mining area of Mu Lan Factory in Xingren, Guizhou, where the contents of soil, spring water, vegetables and animals exceed the standard. Thallium poisoning caused by mercury thallium mining in Mu Lan is the first case in the world (Zhang Tianfu et al., 2005). The symptoms of poisoning are headache, stomachache, general pain, blindness, hair loss and death. As long as the human body ingests T 12SO4 1g, it will die. There were 87 cases of villagers near Mu Lan factory who developed the above symptoms in 1960 and 1 year, and more than 200 people developed the above symptoms from 19 1 year to 1962, resulting in serious deaths. It was not until the study of 1986 to 1987 that it was known that the above patients might be thallium poisoning. Thallium poisoning of villagers in Lanmuchang is mainly due to drinking water polluted by thallium and eating food and vegetables with high thallium content.
The mining of mercury thallium mine in Lanmuchang, Guizhou Province began in the late Ming and early Qing dynasties. 1957 to 1960, which was identified as a large mercury mine by the geological prospecting team. Because the lean ore is a concealed ore body, it is difficult to further explore and mine, so it is put on hold. Since 1958, local villagers have been mining and smelting mercury, and accumulated mountains of ore and slag in Shan Ye. Due to the long-term exposure of primary ore and slag to the surface and weathering and leaching, thallium changed its occurrence state and entered soil, water, crops and human body from thallium sulfide and thallium arsenate. Due to the epigenetic geochemical cycle of thallium, soil, water, grain and vegetables are polluted. People drink water polluted by thallium and eat grain and vegetables polluted by thallium, which leads to thallium poisoning. But I didn't know it was thallium poisoning. It was1June, 1995. CCTV and China Youth Daily reported that Zhu Ling, a 2 1 year-old girl in Tsinghua University, was suffering from acute thallium poisoning, which was very similar to that of the villagers in Ruimu Factory. It was only then that the symptom of Ruimu Factory was thallium poisoning.
3. Environmental pollution of Danzhai mercury mine in Guizhou.
The Danzhai mercury mine in Guizhou produces about 2 1000t of solid wastes such as mercury smelting slag, tailings and mining waste rock every year, in which the mercury content is 0.005,438+0% ~ 0.06%. The concentration of mercury in tailings water, mercury washing water, slag washing water, furnace gas condensate water and other wastewater is 0.008 ~ 0.07 mg/L; The annual emission of waste gas is about 3500× 104dm3, and its mercury concentration is 50mg/dm3 (Lin Qiwei et al., 1998). Due to the discharge of "three wastes", the mercury content in the soil around the mine is 5.9 1 ~ 327.5 mg/kg, and the mercury pollution range carried by water and atmosphere reaches hundreds of square kilometers.
4. Environmental pollution of tin-lead mines in Yunnan Province
There are a total of concentrator 1 1 in Dulong tin mine in Yunnan, of which only about 6 such as Tong Jie, Xingfa, Manjiazhai, * * and Group have tailings ponds, while the other 5 do not. In addition, there are about 10 individual illegal workshop-type small washing plants, which discharge waste water and tailings at will. According to statistics, Dulong Tin Mine directly discharges the washing wastewater into the river every year to 120× 104m3, of which the tailings are about 27.8× 104t. According to the monitoring of Yunnan Geological Environment Monitoring Station, the content of sulfate ion in sewage is as high as 1 160mg/L, the suspended matter is over 200mg/L, and Zn is 5.30mg/L. Eight indicators exceed the GB 8978-96 Integrated Wastewater Discharge Standard. The Huogudu tailings pond 1965 of Gejiu tin mine in Yunnan was flooded. By 2003, there were still 8 hm ~ 2 "toxic fields" on the polluted land that could not be cultivated.
The total daily discharge of smelting wastewater from Huize lead-zinc mine in Yunnan is 7587m3, of which the acid-containing wastewater is about 1 163m3, and only lime is added and discharged into Shizui tiankeng and reservoir. Acid-containing wastewater contains 30 180mg/L, 4380mg/L of zinc, 200.0mg/L of fluorine and 200.0mg/L of nitrogen. Wastewater containing a large amount of toxic and harmful substances is directly discharged into Shizui tiankeng and discharged from Niulanjiang Blackfish Cave, which pollutes deep groundwater. In addition, acid-free smelting wastewater is injected into Niulan River at a flow rate of 882m3/d, which not only pollutes the river water, but also pollutes the phreatic water in the gravel layer on both sides of the river.
(2) Geological disasters in metal mines
Environmental geological disasters in metal mines in southwest China are more prominent, especially in Yunnan Province.
1. Geological hazards of landslides in metal mines
Landslides often occur in mined-out areas, which are caused by the collapse of steep slopes on the surface. There are roughly two kinds: first, the mined-out area is located at the foot of the mountain, and the underground mined-out area is too large, which leads to roof caving under the action of gravity, rain or earthquake. In addition, the surface slope of the mined-out area is steep, the lower part of the mountain forms a free surface, and the upper part of the mountain cracks, resulting in collapse and landslide under the action of rainwater infiltration; Second, the mined-out area is located in the upper part of the mountain, and the surface of the mined-out area collapses to form a landslide.
Landslide is a common geological disaster in mines, especially in Laojinshan Gold Mine in Yuanyang, Yunnan. The mine has a mining history of more than 600 years. During the period of 1992, the group mining activities were fierce, with more than 7,000 miners at the peak. The rock mass structure in the mining area is broken, with strong weathering, steep slope, abundant rainfall and serious landslide disaster. According to the investigation of Yunnan Geological Environment Monitoring Station, there are 36 landslides and collapses with a volume greater than 500m3 within 27.6km2 of Fiona Fang. Among them, the "5.3 1" and "6.3" landslides in Laojinshan occurred in 1996, which caused the most serious damage. Two landslides in a few days caused 372 deaths or disappearances, resulting in direct economic losses of10.40 billion yuan. The landslide occurred in Damugang-Qi alloy mine section of Beidongpo Group mining area on the west bank of Laojinshan mining area, and it slipped twice in three days. Its landslide process and accumulation body are distributed in the north of Laojinshan, reaching Jinhe River, with a total length of 16 14.5m, a width of 120 ~ 300m and a total area of 26x14. The back wall of the landslide is an east-west wavy steep vertical plane with a slope of 70 ~ 88, a length of 120m, a height of 16 ~ 48m and an elevation of1400 ~1210m. West wall length 180m, height 7 ~ 10m, slope 55, east wall length 120m, height10 ~/5m, slope 55. The shear outlet is arc-shaped from northwest to southeast, and the front edge is a steep free surface with a width of 200. Landslide starts quickly, the slip distance is short, and it collapses quickly. After leaving the shear outlet and disintegrating, the sliding body has obvious characteristics of debris flow movement, and the sliding surface is a moderately weathered zone of Middle Silurian siliceous dolomite. At present, the back wall of landslide is still unstable, and small-scale collapse often occurs in rainy season.
Figure 3-5 Plan of Laojinshan Landslide in Yuanyang, Yunnan Province
(According to Wu Jun et al., 2003)
1- perimeter of sliding body; 2- landslide-debris flow boundary; 3- Cut-out; Four-walled scarp; 5- landslide zoning boundary; 6- secondary landslide; 7- secondary accumulation fan; 8— Bare bedrock; 9— Sliding direction; 10- spring; 1 1- dangerous rock mass boundary; 12- mining activity intensive area; 13- landslide zoning code; 14- section and number; 15- failure; 16- geological boundary; 17- false conformity geological boundary; 18-Middle Devonian Laojingzhai Formation limestone; 19 —— shale of Middle Songjiazhai Formation in Devonian with limestone; 20— Middle Devonian Maludong Formation limestone; 21-Silurian dolomite; 22— diorite; 23— Gabbro diabase; 24— Rivers
Figure 3-6 Longitudinal Profile of Laojinshan Landslide in Yuanyang, Yunnan (I-I')
(According to Wu Jun et al., 2003)
1-dolomite; 2- limestone; 3— Mud shale mixed with limestone; 4- diorite; 5- landslide boulder deposit; 6- Landslide gravel and clay deposits; 7— Songjiazhai Formation of Middle Devonian; 8— Maludong Formation of Middle Devonian; 9- zhongzhi will remain in the world; 10-diorite; 1 1- spring; 12- failure; 13- stratigraphic boundary; 14-rock occurrence; 15 —— Original topographic line of sliding area; 16— landslide zoning code: I— landslide source line, II— landslide disintegration and separation area, III— platform resistance and energy dissipation block stone accumulation area, IV— denudation trough ridge accumulation area, V— epidermis shovel tongue debris flow accumulation area, VI— Jinji River debris flow fan accumulation area.
2. Geological hazards of debris flow in metal mines
Debris flow in metal mines in southwest China is mainly small, and there are few large and medium-sized ones. The main types are rainstorm debris flow (Lugu iron mine in Sichuan) and dam-break debris flow in tailings pond (Fumin titanium mine in Yunnan and Huogudu debris flow in Gejiu). Among them, rainstorm and debris flow can be divided into two types according to their sources: loose deposits such as landslides, collapses and soil erosion, and mining waste rock soil. Debris flow caused by improper stacking of mining spoil is common, accounting for more than 90% of the total; The proportion of debris flow caused by loose deposits such as landslides and collapses is small, accounting for about 5% of the total; Debris flow caused by dam break in tailings reservoir accounts for about 4% of the total.
(1) Debris flow caused by mining spoil and improper rock stacking.
Taking the geological disaster of debris flow in Lugu Iron Mine in Mianning County, Sichuan Province as an example, Lugu Iron Mine is located in Lugu Town, Mianning County, Liangshan Prefecture, Sichuan Province, and belongs to Zhongshan District. The mine is a state-owned medium-sized mine, which was built in 1960s and put into operation in 1970s. Since the mine was established, a large amount of waste residue has accumulated in the Yanjing ditch between Tiekuangshan mining area and Dadingshan mining area, resulting in many mudslides in the ditch during the period of 1970 ~ 1984, and the direct economic loss reached100000 yuan. Among them, on May 26th, mud-rock flow killed 104 people (Liu Xilin et al., 2004). At the same time, the chengdu-kunming railway-Lugu-Yuexi Highway stopped running due to a large amount of sediment transported downstream, causing huge economic losses.
The Sichuan provincial government attached great importance to this and 1982 invested 300,000 yuan in emergency treatment. 1986 started comprehensive treatment, and the treatment project was completed on may 1990. Specific projects include: ① construction of No.3 slag dam (photo 3-7); ② Building No.5 slag dam; (3) building a row of diversion dikes; (4) Planting trees on the hillside on both sides of Yanjinggou; ⑤ Add "Yu Zui" project to Yanjinggou Railway Bridge; The project cost is about 5 million yuan. After the project was put into production, No.2 slag dam and Dadingshan branch ditch dam were built. The governance project has achieved remarkable results. After years of heavy rain, especially the rain of 92.9mm in July 1987 and the rain of+1 10.4mm on October 8, although debris flow occurred in the ditch, the dam was successfully intercepted, the project operated normally and the dam was safe. The concrete results are as follows: ① The slope toe of iron ore dump tends to be stable; (2) controlling the downward movement of solid loose materials in the trench bed; Dam No.3, Dam No.5, Dadingshan Branch Gully Dam and other dams retain upstream materials, so the sedimentation line moves up greatly, the lost materials decrease, and the stone moving ability decreases. ③ The longitudinal slope of gully bed has been newly adjusted, the slope decreases and the flow velocity decreases; ④ The widening of the middle and lower reaches of the gully bed gradually weakens (Jiang Jianjun et al., 2000).
Figure 3-7 One of the debris flow control projects in Yanjinggou, Lugu Iron Mine, Mianning County, Sichuan Province
Nevertheless, due to the local villagers' mining and mineral processing in the iron mine dump, the stability of the dump has been destroyed, the sand and gravel in the slag dam has been almost filled, the slag dam is about to lose its function, and new debris flow hazards are forming.
(2) Geological hazards of dam-break debris flow
Dam-break debris flow mainly occurs in some private mines, which is caused by improper design of tailings pond, blind stacking of tailings and poor management. For example, Fumin County and Wuding County in central Yunnan Province have experienced two dam-breaking events of tailings ponds in recent years. Some state-owned mines have experienced dam-break and debris flow events due to unreasonable tailings dam design, such as Huotougou tailings pond of Gejiu tin mine in southern Yunnan.
Dam-break debris flow of Luoshide Titanium Factory in Danqing, Fumin County, Yunnan Province: Danqing is located in the northeast of Fumin County, which is a U-shaped gully with a catchment area of 2.8km2 and a longitudinal slope drop of 8.5%. Luoshide Titanium Factory is a private enterprise, and its tailings pond is located in the upper reaches of Danqing, with a length of 150m and an average width of about 70m. The catchment area is 0.2km2, and the dam body is a mechanical roller compacted earth dam, with a dam height of 19m, a dam crest width of 12m, and a backwater slope ratio of 1: 1. Because the dam body is not designed, the tailings pile is unreasonable (there is no dry beach in front of the dam), the saturation line of the dam body is high, the storage capacity is small, the dam body increases too fast, and piping occurs when the degree of compaction fails to meet the requirements. 1July, 1999, piping with a diameter of about 2m appeared in the dam body, resulting in dam failure. Tailings and waste water accumulated in the reservoir after dam break, with the help of the height difference between the top and bottom of the dam and the steep longitudinal slope of the valley, instantly form a debris flow with great impact. About 4× 104m3 of sediment tailings and wastewater were quickly discharged into the tailings pond of another private enterprise at downstream 150m, and continued to drain after a gap was punched in the dam, and finally rushed out of the valley mouth and flowed into Sandan River, sweeping houses and farmland in ditches along the way. Eight people were killed in the disaster, four houses and drinking water projects in two downstream villages were washed away, and a large area of farmland about 3 kilometers long on both sides of the valley was blocked and buried. Agricultural irrigation reservoirs with storage capacity of about 1km and 12000m3 have silted up and burst their banks, and local gullies and beds have risen 1 ~ 2 m, resulting in direct economic losses of several million yuan.
Debris flow of Huogudu tailings dam in Gejiu tin mine, Yunnan Province: 1965, the dam burst in front of Huogudu tailings dam in Gejiu tin mine, resulting in a debris flow of about 370× 104m3, which washed away 575 houses in Zhadian farm, 35.53hm2 cultivated land and downstream 12 villages and killed 65,438 people. The grain loss was 67× 104kg, 37 cows were injured, and many roads, bridges, water conservancy and power transmission facilities were damaged, forcing Yunxi Company and local factories and mines to stop production 10 day, resulting in tens of millions of economic losses.
3. Geological disasters of ground subsidence in metal mines
The ground collapse of metal mines in southwest China is generally small in scale, and the main types are karst ground collapse and goaf ground collapse. Karst ground collapse mainly occurs in mining enterprises in semi-exposed carbonate areas in eastern Yunnan and Guizhou. The main reason is that the mine uses karst funnel or karst depression to accumulate tailings, and karst collapse occurs at the bottom of the reservoir under the action of tailings pressure and tail water scouring. Karst collapse is sudden, often causing casualties, property losses and groundwater pollution. Ground collapse occurred in Gejiu tin mine in Yunnan, Shangchang iron mine in Yuxi and Zunyi and Songtao manganese mines in Guizhou.
(1) Geological disaster of karst ground collapse in mine
Karst ground collapse of Gejiu tin mine: Gejiu tin mine has used 3/kloc-0 tailings ponds successively, with a total design capacity of 19550.7× 104 m3. Most tailings ponds are located in karst funnels or karst depressions, among which 27 tailings ponds have experienced karst collapse of different scales, and the karst collapse of tailings ponds such as Huoduyu, Niubahuang and Laochang is more harmful.
Karst ground collapse of Shangchang Iron Mine in Yuxi: The tailings pond of Shangchang Iron Mine in Yuxi chose karst depression near the concentrator. Karst depression is located in the axis of anticline and the watershed of the surface. A sinkhole and underground karst pipeline are developed on the west side of the depression. After the completion of the tailings pond, karst collapse occurred many times, and the most harmful one was 1, which occurred in198065438+February. This collapse caused nearly 10× 104m3 of mud and water to flow into the underground karst pipeline along the sinkhole, which blocked the underground river and provided nearly 10,000 mu of farmland irrigation and drinking water for people and animals for the three natural villages downstream.
(2) Geological disaster of ground collapse in goaf
Collapse of Yimen Copper Mine: All four ore sections collapsed, covering an area of 530hm2, of which Shizishan ore section covers an area of 400hm2. The collapse affected and destroyed the mountain forest 2 1 hm2, cultivated land 16.7hm2, threatened the safety of three villages, relocated some production and living facilities, and died 14 people.
Collapse of Dongchuan Copper Mine: The collapse area reached 1 1 1.5hm2, which seriously threatened the safety of production and life in the mining area.
Dulong tin mine collapse: the surface of six mined-out areas, such as Huashitou, collapsed, with a total area of more than 50hm2 ~ 2, and the maximum depth of the collapse pit was 40 m. Four people died, 42 houses were damaged and 28 hm 2 of cultivated land was destroyed.
Gejiu Mining Area Collapse: The total area of ground collapse is about 19.5× 104 m2, the area of damaged buildings is 4000m2, and the forest, farmland and cultivated land are damaged * * * about 10hm2. Only the old factory building collapsed, damaging more than 40 houses with an area of 8,000m2, resulting in property losses of about 20 million yuan. There are still more than 1000 residents and 40 million yuan of property threatened.
4. Geological disasters of water inrush in metal mines
Compared with energy mines, there are fewer geological disasters of water inrush in metal mines in southwest China, which are generally formed in broken zones or in tunnels with irregular and unplanned mining. For example, water inrush occurred at the contact zone elevation1and E2 1 2 between the main inclined shaft and the air shaft1789 ~18120m3/h in Heqing Beiya Gold Mine, Dali City, Yunnan Province, and the water inflow was 80 ~120m3/h. As a result, the middle parking lot of 1734m( 1760m), the northern vein of 1774m( 1800m) and the middle parking lot were flooded, the stope was flooded, and some pit sections collapsed, so the production was stopped for 40 days to deal with the accident. The reason of water gushing in this mine is that the main inclined shaft is close to Dongshan River, and the fractured zone is encountered in the process of excavation. Due to untimely support, the roof water-resisting layer is deformed and caving, which leads to river water leakage.
5. Geological disasters of ground fissures in metal mines
Ground fissures are generally related to mined-out areas, which are often caused by the collapse of mined-out areas. Ground cracking will damage houses, destroy cultivated land and threaten production safety in mining areas. For example, the southeast slope of Shizishan, the northwest slope of Fengshan, Dongpo and Qilalangding in Yimen Copper Mine, Yunnan Province, were all cracked with the collapse of mined-out areas. The length of the cracks ranges from 10 to 600 meters, and the width ranges from 0.5 meters to several meters, and the largest cracks are bottomless. Cracks mainly appear in the rainy season, which leads to instability of the surface mountain, collapse and landslide. Manjiazhai mining area of Dulong tin mine in Yunnan is mainly a private mining area. There are two adjacent villages, Manjiazhai and Dida Village, with 00 households with 5 1 17 people. There are 83 mining lanes near the two villages. Due to the large mined-out area formed by mining, the ground cracked due to uneven settlement, and there were 42 households in Manjiazhai and Dida villages. Among them, the walls of 16 houses are seriously cracked and tilted, and the hillside behind Manjiazhai village is cracked, forming a crack with a length of 200m and a width of 20 ~ 30 m, which seriously threatens the lives of villagers in the two villages. At present, villagers have moved one after another.
There are ground fissures in Luobusa chromite and Langxian chromite in Tibet. The former is 65,438+00 (photo 3-8), while the latter is 5,3-20m long, 0. 1-0.5m wide and 0.4- 1.0m deep (Li Zhen et al., 2005), with a wide bottom and a narrow bottom. The reason is related to the tensile stress of goaf collapse.
(c) Destruction of resources by metal mines
The area occupied and destroyed by metal mines in southwest China is smaller than that of energy mines and non-metal mines. According to the statistical data of Sichuan Province, the area of mines in Sichuan Province is 9 1720.72hm2, of which energy mines occupy the largest area, reaching 6825 1hm 2, followed by non-metal mines, reaching 19386.2hm2, and metal mines occupy the least area, reaching 41/kloc. Metal mines generally occupy a lot of land, such as stopes, solid wastes and tailings ponds. For example, Panzhihua Iron Mine, a mining company of Sichuan Pangang Group, is a famous large-scale iron mine in China, and the occupied area of stope and solid waste is 1.039 hm2.
The development of mining industry in Xizang Autonomous Region is relatively backward, and there are fewer mining enterprises, with 253 * * *. However, due to more open-pit mines, especially the mining of placer gold, a large amount of land is still occupied and destroyed. Mining development in Xizang Autonomous Region occupied and destroyed 9940.46hm2 of land, of which more than 50% was occupied by placer gold mines, resulting in serious consequences of grassland destruction in mining areas (photos 3-9 to 3- 12).
Figure 3-8 Ground fissures in Luobusa chromite mine area, Tibet.
Figure 3-9 Tibet Dacha placer gold concentrator
Photo 3- 10 Mayoumushan Gold Mine in Tibet
Photo 3- 1 1 Tibet Benna Zangbo placer gold concentrator
Photo 3- 12 Placer Gold Mine in Benna, Tibet