Environmental geological problems in the development of metal minerals

The metal minerals in northwest China mainly include gold, lead, zinc, copper, nickel, molybdenum, mercury, antimony, iron, rare earth, rare metals and rare earth metals, and the main mines are located in Qinling, Qilian, Tianshan, Altai and Daqingshan. The famous metal mines in northwest China include Jinduicheng molybdenum mine in Shaanxi, Tongguan gold mine, Qiandongshan lead-zinc mine in Fengxian, Taibai double gold mine, Lueyang iron mine, Lueyang Jianchaling nickel mine and Xunyang mercury-antimony mine. Jinchuan copper-nickel mine, Baiyin copper mine, Changba lead-zinc mine and Jingtieshan iron mine in Gansu; Xitieshan lead-zinc mine in Qinghai; Xinjiang Craton Ke copper-nickel mine, Hami Yamansu iron mine, etc. Bayanobo iron mine and rare earth mine in Inner Mongolia.

The main environmental geological problems in the development of metal mines are: the destruction and waste of mineral resources, the destruction of land occupation and vegetation, the environmental pollution caused by "three wastes", and the geological disasters such as landslides, collapses, mudslides and dam breaks in mountain mine tailings ponds.

3.4.3. 1 Destruction and waste of mineral resources

The disorderly exploitation and predatory development of small and medium-sized mining enterprises, as well as the low utilization rate of associated components in enterprises, highlight the destruction and waste of mineral resources.

Most deposits in northwest China belong to multi-component associated minerals, but due to technical reasons, most mines are not comprehensively recycled or the utilization rate is very low, resulting in serious waste of resources. For example, the Huitong Mountain copper mine in Gansu Province is associated with arsenic and belongs to a large deposit. Because arsenic is not recovered in the process of copper mining, arsenic resources are wasted. The Tagouer tungsten mine in Gansu Province is associated with 2583 tons of beryllium, bismuth and arsenic. Because the ore is rich and the waste is poor, only wolframite is used, and the associated ore is not rationally utilized. Qinghai Chaerhan Potash Factory only extracts potash from brine, and the associated components such as sodium, magnesium and lithium are not utilized.

Like other mines in China, Jinduicheng Molybdenum Mine in Shaanxi Province has the problem of cherishing and rationally utilizing resources. According to the design provided by Beijing Metallurgical Design and Research Institute 1972, the ore body is delineated according to the cut-off grade of molybdenum ore of 0.03%, the lowest industrial grade of 0.06%, the reserved reserve of 1993 is 28,432.60×104t, and the average grade is 0.11. With the change of international market economy, in 1993, according to the spirit of approval from China Nonferrous Metals Industry Corporation, the grade index of this mine was raised from 0.03% ~ 0.06% to 0.06%, and the ore body boundary was re-delineated. The amount of new ore is 22 169.83× 104t, and the grade is. The difference between them is 6262.77× 104t, accounting for 18% of the total reserves of Xiaobei open-pit mine. As lean ores, these ores will change their physical and chemical properties over time, which makes it difficult to recover these resources in the future. According to the calculation, the recovery rate of Jinduicheng molybdenum mine is 83.5%, which is 7 percentage points lower than the international level. According to the calculation of 1998 19000t molybdenum concentrate, the annual loss of molybdenum resources is nearly 33x104t. The waste of resources will inevitably aggravate the exhaustion of resources. According to the current mining scale of Jinduicheng, the service life of Xiaobei open-pit mine will be shorter than the designed 50 years 10 years.

Land occupation and vegetation destruction in 3.4.3.2

The development of metal minerals is mostly concentrated in mountainous areas such as Qinling Mountains, where vegetation is relatively developed. The stacking of mining residues in metal mines, the occupation of tailings ponds, the stripping and dumping of open-pit mining sites and the collapse of mined-out areas have caused relatively serious damage to terrestrial vegetation.

Tongguan gold producing area in Xiaoqinling, Shaanxi Province is a rocky mountain area with thin soil layer and high vegetation coverage. The annual erosion amount is10.1×104t, and the erosion modulus is 573.8t/km2·a, which belongs to mild erosion area. Since the large-scale development in the 1970s, gold miners have swarmed in, and there are more than 2,000 mining pits in the mining area, with 800× 104m3 of mine waste rock and tailings discharged, occupying more than 200 hectares of land and vegetation. Due to long-term deforestation, most of the trees within 5 kilometers of Yushan Yukou were cut down, and a lot of land and vegetation were destroyed, which aggravated soil erosion. From 1982 to 1990, the soil erosion modulus in the mining area increased from 760.7 t/km2 a to 3448.7 t/km2 a, with an average annual increase of 24.4× 65430. Vegetation destruction and external drainage pressure caused by open-pit stripping of Jinduicheng Molybdenum Mine account for about 2km2 of terrestrial vegetation.

Geological Disasters of Collapse, Landslide and Debris Flow in 3.4.3.3

Mountainous metal mines have natural conditions and human factors that induce three kinds of geological disasters, such as collapse, landslide and debris flow, and are high-risk areas of collapse, landslide and debris flow disasters. A large number of mining waste rocks are piled up along hillsides and valleys, lacking engineering and technical measures such as slag retaining, slope protection, water guiding and biology, and the waste rocks on the slope are in an unstable state, which is easy to induce landslides when the goaf collapses or the mountain cracks. Geological disasters such as landslides and mudslides induced by heavy rains have caused the mining area to stop production and endangered people's lives and property.

Figure 3-4 Schematic Diagram of Debris Flow Gully in Dongtongyu, Tongguan County, Shaanxi Province

(According to the investigation and zoning report of geological disasters in Tongguan County, Shaanxi Province)

Tongguan Gold Mine is located in Xiaoqinling Mountains, with steep topography, elevation of 700 ~ 265,438+000 m, and relative height difference of 900m m m. Seven V-shaped valleys are developed from east to west (Figure 3-4), and the riverbed gradient is relatively large, with an average of 9.465,438+0% ~ 65,438+05.20%. Due to historical reasons, different enterprises in different heights and sections of the same ore body are mining, resulting in the so-called "upstairs and downstairs" mining. Today, the unreasonable mining layout of "upstairs and downstairs" can still be seen everywhere in narrow valleys. A similar situation also exists in Yindongliang lead-zinc mine area in Fengxian County, Shaanxi Province, where mining waste rocks are directly piled up on the hillside of Dongkou. These waste rocks with different sizes and loose structures are piled up along the slope, forming the debris flow source area. In July 1994, 1 1, a large amount of mining waste rock and tailings mixture accumulated in Xiyu River, Tongguan, which was handed over by Lingbao, Henan Province, formed a catastrophic geological disaster debris flow under the action of heavy rainfall, and mining facilities were destroyed, sheds and houses collapsed, washing away more than 300 mu of farmland, and traffic, electricity and communication were interrupted, resulting in 56544. From August 65438 to August 0996, a mudslide occurred in Dongtongyu, which washed away bridges and flooded farmland, causing serious economic losses and social impacts again.

Lead-copper lead-zinc mine in Fengxian County, Shaanxi Province is a large state-owned mine, which was built in 1985. At present, the ore output has reached 170× 104t. With the increase of mining area, the surrounding rock of the upper wall collapses, and two collapse pits are formed on the east and west sides of the surface, forming an erosion structure landform with high north and low south. The continuous rainfall of 1999 10 8 and 16 days caused two large landslides with a scale of 50000m3 and a slip distance of nearly 1000m, which led to the suspension of production in four middle mining areas to varying degrees, resulting in a direct economic loss of 300,000 yuan and159,000m. There are 12 ground fissures at the top of the caving zone in the footwall, with the maximum strike of 1000m and the crack width of nearly 2m, which constitute a potential collapse body, and the estimated earthwork volume is 70000m3, which has become the biggest factor threatening the safe production of the mine field and slag yard.

Land subsidence and ground fissures in 3.4.3.4.

Although the ground subsidence and ground fissures in metal mines are not as common and serious as those in coal mines, there are obvious geological disasters of ground subsidence and ground fissures in metal mines with thick ore bodies. For example, the Laoling Iron Mine in Lueyang, Shaanxi Province, with the development of mining, the ground subsidence center leads to the cracking and abandonment of the ventilation mine and the cracking of the mountain. In most metal mines, such as Tongguan Gold Mine, Fengxian Lead-zinc Mine and Chengxian Changba Lead-zinc Mine, with the continuous expansion of underground mined-out areas, ground cracks and mountain cracks have appeared on the surface to varying degrees. 200 1 A medium-sized geological disaster accident occurred in a mine in Fengxian County, Shaanxi Province, which resulted in the disappearance and death of five people due to the collapse of goaf. Goaf collapse not only induces geological disasters such as landslides and collapses, but also seriously threatens the normal production of mining enterprises. Underground mining has caused the danger of endangering the living safety of villagers on the ground, aggravated the contradiction between mines and local residents, and the number of petitions has been increasing. Therefore, it is particularly important to strengthen the prediction and prevention of ground fissures and potential subsidence areas induced by goaf in metal mines. At 200 1, the surface of the lead-zinc mine in Liuxiang, Dengjiashan, Xihe County, Gansu Province suddenly collapsed, forming a collapse pit with a diameter of about 10 meters, resulting in two people missing. In Bainaimiao copper mine area, Siziwangqi, Wulanchabu League, Inner Mongolia, 1996, the ground subsidence formed two large subsidence pits with a width of more than 70 meters from north to south, a length of more than 200 meters from east to west, a depth of 20-50 meters, a width of 50 meters, a length of 100 meters and a depth of more than 50 meters. In mid-July, the roof caving roadway in 1998 West 202 stope was about 20 meters long, resulting in direct economic loss of 380,000 yuan and indirect loss of 30-40 million yuan.

Dam failure accident of tailings dam in 3.4.3.5.

Mine tailings ponds are mostly built in valleys, and ditches are blocked to build dams. Most tailings ponds in small and medium-sized mines are built by mountains and rivers, and some tailings ponds do not meet the specified requirements. Or, due to the extended service of tailings pond and heavy rain, the dam foundation is often unstable, which leads to dam break and collapse, which leads to tailings flooding farmland, washing away roads and causing serious environmental pollution. There are serious problems in this respect in Fengxian lead-zinc mine area in Shaanxi, Xunyang mercury-antimony lead-zinc mine area in Shaanxi, Tongguan gold mine area in Shaanxi and Changba mine area in Chengxian county in Gansu province. For example, a tailings pond with a daily concentration of 50 t in a concentrator in Fengxian County, Shaanxi Province was built in the middle of Anhe River at the source of Jialing River. The four walls made of cement can only stop the annual average flood. Once rainstorm causes flood, reservoir overflow or retaining wall is washed away, tailings containing lead, zinc, mercury and mineral processing chemicals will pollute Jialing River. In another small lead-zinc ore dressing plant, the tailings pond was built by the mountain and the river. In 2000 and 200 1, it was washed away by floods twice, and dozens of cubic meters of lead-zinc ore tailings were brought into Jialing River. Starting from 200 1, the clear river water swirls into Jialing River in a dam-break gap several tens of meters long. The seven main ditches in Tongguan gold mining area of Shaanxi Province are all gold mining areas, with narrow valleys and some tailings ponds along the river, which further narrows the river. In case of heavy rain, the river swells, and floods or dam accidents may occur. In the event of dam break, a large amount of tailings sand in the reservoir will pour down with the flood, which will lead to the blockage of downstream rivers, the destruction of houses and the serious damage to the ecological environment. 200 1, Makou gold mine tailings dam failure caused farmland pollution.

The disaster and environmental pollution caused by tailings dam break are very serious. For example, 1987, the spillway tunnel of Li Xi tailings pond of Shanxi Jinduicheng Molybdenum Company collapsed, which caused 136× 104m3 tailings and tailings water leakage, polluted the water sources of Shaanxi and Henan provinces 16 counties and cities, and caused direct economic losses of more than 32 million yuan. On June 5438+February, 2000, Tianzishan tailings dam in Chengxian County, Gansu Province broke, causing nearly 2× 104m3 tailings to flow into Donghe River.

Water and Soil Pollution in 3.4.3.6

Heavy metals in tailings slurry and mining dust pollute water and soil seriously. The main pollution source is tailings wastewater discharged from mineral processing, followed by solid waste leaching water and mine water. Among them, gold mine, mercury mine, lead-zinc mine and arsenic mine have the most serious environmental pollution. The wastewater discharged from ore flotation contains mineral processing reagents, non-beneficiated metal elements, heavy metals associated with * * * and ore particles. The wastewater discharged from cyanide gold extraction contains cyanide, a highly toxic substance, and the wastewater discharged from gold extraction with mixed mercury has a high mercury content. Mineral processing liquid containing toxic and harmful substances such as heavy metals, cyanide, petroleum and acidic mine water. If it is discharged into rivers and lakes, it will cause serious pollution of water and endanger aquatic life. If these polluted water is drunk by people and animals, it will affect health and endanger life. If it is used to irrigate farmland, it will lead to reduced production and no production, so that toxic and harmful substances can sneak into crops and endanger human health through the food chain.

The mining areas with serious pollution caused by disorderly discharge of mine water and tailings slurry mainly include Tongguan gold mining area in Shaanxi, Fengxian lead-zinc mining area, Lueyang iron mining area and Xunyang lead-zinc-mercury-antimony mining area. Chengchangba lead-zinc mine in Gansu province, Dengjiashan lead-zinc mine in Xihe county, etc.

Tongguan gold mining area in Shaanxi Province is one of the typical water and soil environmental pollution areas. In the middle and late 1980s, towns and individual miners flocked to Tongguan Gold Mine, forming a scene of large-scale disorderly development. At the peak, there are 24 10 mining pits, and the annual waste rock discharge is 607× 104t, 1465438 mixed mercury mills and 654338+00 tailings water discharge. Direct discharge of mixed mercury mill wastewater causes lead pollution in the source water of the mining area to exceed the standard by 2.4 ~ 1 13 times, and suspended solids in the water to exceed the standard by 62 ~ 2 143 times (Table 3-9).

Table 3-9 1992 Monitoring average value of tailings water in Qigou 10: mg/l.

From the monitoring results and single factor evaluation (Table 3- 10) of the water quality of seven source water functional areas in 195 mining area, it can be seen that the lead in seven rivers exceeds the standard by 37-959 times, the mercury exceeds the standard by 0.2-3 1 times, and the cadmium exceeds the standard by 1-66 times, which is the largest oil.

Table 3- 10 Water Quality Monitoring and Exceeding Multiple of Seven Rivers in Tongguan County Unit: mg/L

sequential

Source: Ninth Five-Year Plan and 20 10 Long-term Plan for Environmental Treatment of Gold Producing Areas in Tongguan County (Tongguan County People's Government).

In August 2002, the Environmental Impact Assessment Office of Xi Institute of Geology and Mineral Resources monitored the pit water of Haochayu Gold Mine in Tongguan County (Table 3- 1 1). The results show that the mine water is discharged directly without treatment, and the Pb in the wastewater exceeds the standard by19.5438+0.5 times, and the SS exceeds the standard by 87 times.

Table 3- 1 1 Monitoring Results of Haochayu Mine Wastewater in Tongguan Gold Mining Area and Exceeding Multiple Unit: mg/L.

The monitoring results of three sections of Haochayu River show that the contents of Pb, Hg and Fe in the reach above the gully mouth are 282 ~ 345 times, 17 ~ 59 times and 10.7 ~ 15.6 times respectively. Pb and Hg in the downstream reach are 25.8 times and 0.7 times higher than the Class IV water standard, respectively (Table 3- 12). The water quality of Haochayu River has been seriously polluted, and the main pollutants are lead and mercury, which belong to heavy metal pollution. The reason is the wastewater discharge from the concentrator in the upper reaches of Haochayu River.

Table 3- 12 Water Quality Monitoring Results of Haochayu River in Tongguan Gold Mining Area Unit: mg/L

According to the water quality monitoring results of the upstream and downstream rivers in the concentrator of Lijia Gold Mine No.3 in Xiyu River (Table 3- 13), the heavy metals Pb, Cd and Hg in Xiyu River exceeded the standards by 879 ~1,8 ~1,and 23.2 ~ 43 respectively.

Table 3- 13 Water Quality Monitoring Results of Xiyu River in Tongguan Gold Mining Area Unit: mg/L

According to the investigation and monitoring results, from the development of Tongguan Gold Mine 1995 in Shaanxi Province to 2002, seven rivers in the area have basically become the discharge places of mine wastewater and tailings slurry of concentrator, with heavy metals Hg, Pb, Cd and Cr exceeding the standard seriously, the river water can not be irrigated and aquatic organisms are extinct. The metal elements in local soil and wheat are generally higher than the regional background values. Using mercury plate and steaming mercury to extract gold, the atmospheric mercury concentration in this area all exceeded the standard, with the highest exceeding 38 times. The root cause of river pollution lies in the direct discharge, illegal discharge and accidental discharge of mineral processing wastewater and pit water from most township individual enterprises, so that seven rivers in the jurisdiction are always in a state of serious over-standard pollution.

The heavy metal pollution in Dongfang Gou, where Yindongzi silver-lead mine is located in Zhashui, Shaanxi Province, is obvious. The Pb content in the downstream 1km of Yindongzi silver-lead mine (HS-003) is twice as high as that in the control point (HS-00 1) and 1 times higher than that in the pollution point of Ma 'erxia (downstream 1km). Pb in the soil around this area is nearly 70 times higher than the background value, and Cd is nearly 8 times higher.

Changba mining area in Chengchang County, Gansu Province is another typical area with serious environmental pollution. There are more than 20 lead-zinc ore dressing plants owned by towns and villages on both sides of the 2-kilometer-long Donghe River, and the phenomenon of direct and illegal discharge of tailings slurry is very common. Tailings from tailings ponds near mountains and rivers are higher than the dam surface, resulting in overflow and dam break. Thick gray tailings sand was deposited in Donghe River, which seriously reduced the water quality of Donghe River and completely destroyed the biological balance system of water body. According to the Special Environmental Impact Assessment Report of Changba Lead-zinc Mine Phase II Project compiled by Northwest Mining Research Institute in June, 20001year, the monitoring data of surface water in four sections of Donghe River are shown in Table 3- 14.

Table 3- 14 Statistical unit: mg/L Monitoring results of surface water quality in Donghe, Changba mining area, Chengxian County, Gansu Province

As can be seen from Table 3- 14, the surface water of Qijiagou in the mining area mainly comes from the leaching water from the tailings pond and waste rock field of the upstream factory dam, the overflow water from the surface of private mining pit and the spring water, which is perennial flow, and the lead exceeds the standard 1 times. Qijiagou section is located in the main channel of Donghe River. There are dozens of state-owned factories, dams, mineral processing plants and lead-zinc mines within 2 kilometers upstream of this section, with many pollution sources. The lead and zinc in the section exceed the standard by 44.66 times and 1.04 times respectively. Bijiazhuang section is located in the downstream of Changba mining area, with a linear distance of about 10km. Lead and zinc are the most serious elements exceeding the standard, which are 65.6 times and 5.53 times respectively.

Based on the data of Donghe sediments before the development of Changba lead-zinc mine area, after more than 20 years of development, the cumulative deposition multiples of the monitoring values of lead, zinc and cadmium in Donghe sediments are 25.7 ~ 4.4, 188.5 ~ 5.7 and 540.438+0 ~ 23.7, respectively, and the pollutants at the bottom of the river are becoming more and more serious (Table 3-6543).

Table 3- 15 Monitoring results of heavy metals in Donghe bottom mud in Changba lead-zinc mine area, Chengxian County, Gansu Province Unit:10-6 mg/L.

Xunyang section of Hanjiang River is a second-class protected area of drinking water source, and the water quality can reach the standard of direct drinking for people and animals. Because of its good water quality, it was selected as the water source of the middle route project of South-to-North Water Transfer. Danjiangkou reservoir is located about 300 kilometers downstream of Xunyang section of Hanjiang River, which is the water intake point of the middle route project of South-to-North Water Transfer Project. Before July 200 1 year, there were seven mineral processing plants on both sides of the Hanjiang River, which was more than 40 kilometers down from Xunyang County. A simple "tailings dam" about 2 meters high is built with sandbags and stones. After simple precipitation, the black sewage with pungent smell flows directly into the Han River along the ravine, and the gray-black sewage forms a long pollution zone. In July of 20001year, CCTV's "Focus Interview" column exposed this. In 2002, the project team conducted a follow-up investigation, and it was obvious that most of the concentrator beside Bai Han Highway had been demolished. However, some mineral processing plants and small lead-zinc smelting enterprises on the south bank of the Han River are still producing, and wastewater is still polluting the Han River.

Cyanide heap leaching technology is used in gold dressing and metallurgy. If the waste water is unqualified, it will cause serious pollution to the water and soil environment in the mining area. Cyanide is a highly toxic substance. Ordinary people will die of poisoning by inhaling 50 mg of cyanide or eating 120 mg of sodium cyanide by mistake. When the concentration of CN- in water is ≥ (0.05 ~ 1) mg/L, the fish will die. According to the monitoring of cyanide heap leaching process in Sifang Gold Mine in Fengxian County, Shaanxi Province, the untreated tailings slurry discharged directly into Bagua River will increase the CN- in the river water to 44.674mg/L, which is 893.5 times higher than the standard. Especially in some remote and economically backward areas, enterprises have a weak concept of environmental protection and excessively pursue short-term economic benefits, which leads to the direct discharge of toxic cyanide waste residue and wastewater during gold mining, causing pollution of rivers, grasslands, vegetation and crops in mining areas, which is potentially serious. The leakage of tail liquid of Inner Mongolia Liqingdi Silver Industry Co., Ltd. (silver mine) caused cyanide in water to reach 4 14.85mg/L/L, exceeding the standard by 424 times. Zinc is 140mg/L, which is 28 times higher than the standard. The copper content is 3.669mg/L, exceeding the standard 1.223 times. In the rainy season, these pollutants will cause serious pollution to the surrounding environment.