Theory And Practice Of Karst Water Control And Prevention In Iron Mining Area,in South China

Metal ores is the backbone of the national economy’s development, more than half the metal ores distribute in the south of the Yangtze River in China, where karst development. Karst water is called "water tiger", in karst development mining area, because the huge amount of karst water; karst water dewatering damages groundwater resources, leaving endless troubles to geological environment. Metal ores generally has smaller distribution range, due to the control of the genesis of ore bodies. The investigation of metal mine are mostly in the seventies and eighties of the last century, in China. the depth of investigation is limited because of the survey and technical limitations at that time. Metal deposits mined expanding, with the increase of the needs of national economic development. Some mining areas, which were recognized not suited to mining before, for the karst water, are mining now; and some mining areas, that had been mined, are extending to the deep, to expand the scale of mining. The mining water prevention and control work become harder. Identification of the hydrogeological conditions is the critical to karst water prevention and control. The study of hydrogeological conditions in mining area almost stopped, because the large costly. Therefore, how to use of the hydrogeological data accumulated in the mining production process, to identify the hydrogeological condition in mining areas with karst water, with simple and practical theories and methods, becomes the critical work in karst water prevention and control work, in metal mining area with karst water, in China.Makeng Iron Mine locates in Longyan, Fujian province, is the largest one in East China, with an identified iron ore reserves of420million tons. Makeng IronMine covers an aera of4.5km2, and the buried depth of the ore body is from400m to800m. The main ore body is distributed from-200to200m above the mean sea level. Currently, the production of the Makeng Iron Mine is around1million tons per year. The mining level now extends to the level of+250m, and the infrastructure facilities reach to the level of+100m. According to the proved report in2010, it designed that the production will be increased to300million tons per year in 2017, and finally reach600million tons per year. The mining level is also planned to reach the levels of+200m,0m, and-200m, gradually. Because of the complicated geological structure in the Makeng Iron mining area, the average karst rate as discovered in the boreholes is as high as6.02%, and accidents due to groundwater flow into the tunnel during construction are encountered with high frequency. These are the typical characteristics of the Metal Mine areas in the karst area in South China. Therefore, it is necessary to carry out the research on the hydrogeological conditions of the area and guarantee the safety in production of mine. The research results can also play an important role in underground mine water prevention and control in the southern metal mine area.The author has been studied the hydrogeological conditions and the prevention methods in Makeng Mining area, since2006, and visited some iron mines like:Fankou Lead mine in Guangdong, White Xiangshan iron mine in Anhui, and Wushan Copper Mine in Jiangxi. This paper based on the experience gained in the process of collection and practice.The theory of groundwater system was used as a guide in this paper, analyzed the karst water system as a whole. Mining the information of karst water system from investigation data, mining and excavation expose data, water level, water temperature, water chemistry and groundwater tracer test, mining and excavation expose data. The boundaries of karst aquifer system were delineated in Makeng mining area; analyzed the structural characteristics of karst aquifer system; revealed the relationship between the karst aquifer system and karst flow system; identified the evolution of the karst flow system during mining period; found out the role in recharge and the concentrate recharge channel quantitative or semi-quantitative. Proposed measures of karst water prevention and control.Conclusions were got in in this paper are as follows:(1)The delineation of the groundwater system in Mining Area should be based on the groundwater system. It should be for the purpose that has a direct significance to the groundwater system of the pit. Making use of the accumulated hydrogeological data in the phase of exploration and drawing a hydrogeological profile which traverse the possible boundary is an effective method to determine the boundary of the karst water aquifer system. The boundaries of MaKeng Mine Area are the fault of XiMa River, F1, TianShanAo, Nameless, ChenKeng-QiLai.(2) The lithology outside the fault of the boundaries and the situation of its fracture development decide the boundaries’ properties. The upper boundary of MaKeng Mine Area is relative water insulation, and other boundaries are weakly permeable.(3)Internal faults and karst water-bearing in karst system are important factors causing karst aquifer heterogeneity. The use of remote sensing interpretation, surface structure investigation, track roadway fault investigation and surface geophysical exploration makes us have further understanding of the fault structure’s development in MaKeng Mine Area.we counted the karst rate in different working level during50meters, and we drew maps of the karst development in level+420, level+300, level+200and level+100meters. Besides, we found that the karst in the Mine Area mainly distributes along the fracture zone of F1, F2, F10and F15; Vertical karst development from the shallow and deep, developed from strong to weak, most of them are above level+200meters, and below+200meters, it merely develops around the fracture zone of high angle fault.(4)The flow field and cross-sectional view of the karst water system is an importantmanifestation of the karst water flow system.Karst water aquifer system and the relationship of the flow system have a great significance to the prevention and control of underground mine water.Using maps and cross-sectional view of the flow field of karst water system under natural conditions,Ma Hang mine karst water flow system is layered,Spring1spring3should be the upper part of the mine karst water system the local stream excretion point,Qilai spring is karst water system areas excretion.(5) The flow field diagram of Karst water system Under different unwatering state illustrates Ma Hang mine karst water system is evolving. With the underground water points are emerging and karst water level dropped,The original level of the karst water flow system has been disrupted, The plane gradually showing a strong non-uniformity.(6) Karst water flow system is under control of the structure of the aquifer system, he flow field diagram, hydrogeological cross-sectional maps and leaking water points dynamic indicate, faults, karst, local impermeable belt control the strong runoff controls the flow system, espcially fault F15, F10fault; However, the blocking effect of the part impermeable belt fault F3,western igneous strength the non-uniformity of the karst water flow system and control the evolution of the karst water flow system. The part impermeable belt can be used as the basis for prevention and treatment of different stages of the mining area of karst water.(7)The condition of groundwater recharge in karst area is the main factor to decide whether or not karst water drainage in advance, while the boundary condition of karst system determines the characteristics of karst water supplies。The characteristic of water level dynamic in karst water system shows that groundwater recharge increased from the rainy season in2010, which mostly concentrated in the eastern mining area. Precipitation is the main replenishment source of groundwater in Makeng mining area. Surface caves exposed by excavation, fracture collapsed by mining, surface disturbance because of mining limonite and the plugs in the valley are the main reasons for the increase of precipitation infiltration recharge.(8)Water chemistry, water level and water temperature characteristics of water discharge point in Karst water system shows the features of replenishment source to some extent. The change of the karst aquifer system caused by mining engineering brought about karst water system replenishment conditions change, the characteristics of water chemistry, water level and water temperature shows:the upper jiafu group (Pj1) sandstone fissure water supplies karst water system through the fault fracture zone.Water chemistry simulation results shows that the mixed water point W100-1is made up with sandstone fissure water and karst water,its mixed ratio is1:2.W-40-2water point is mixed by the deep granite fissure water and karst water According to temperature characteristics, tracer test results reveal atmospheric rainfall near Tian Shan Ao fault concentrated into the exposed surface of the karst cave, then flow to W-40-2rapidly.(9)Karst water system flow chart displays that the Xima river supplied karst water system under mining conditions.Automatic monitoring system of surface water discharge reveals:river leakage existed among stations2,3,4.Tracer tests confirmed this leakage occurred in the intersection between Xima river and F2fault, it flew along F2fault and concentrated into ZK614direction.when the intersection between Xima river and F2fault disturbed, water level fluctuations nearby ZK557indicate leakage existed in the intersection between Xima river and F1fault.(10)Use the heterogeneity of karst water system and flow system, we need to drain the Makeng mining by stages and partition, for the fault,karst and any other karst water system structure, put the drainage hole and the ground hole; For the Identified atmospheric precipitation, upper sandstone fissure water, lower granite fissure and Xima river,to block them, which can effectively improve the efficiency of drainage of the karst water in mining area.The characteristic of this article is featured in:(1) the instruction is the Groundwater system theory, on the whole analyzing Makeng mining area of karst water system, and selecting the boundaries of the karst aquifer system.(2) Extracting the characteristics of water system and flow system of the mining area from the multi-source information,which has revealed the relation of karst water system and the flow system.(3) Comprehensive utilizating new technology, new methods, such as the underground water level, water temperature automatic monitoring technology, the surface water automatic monitoring technology, water chemistry and high-precision tracer test to find out the supply condition of karst water system that from the external water.(4) Design the project of karst water control and prevention, based on the structural features of karst water system and recharge condition of the karst water system, made the project much effective.