Study On Geological Environment Evaluation Of Abandoned Ionized Rare Earth Mine

Ion-type rare earth minerals in southern Jiangxi are characterized by shallow burial,easy mining and high economic value.They are rich in medium and heavy rare earth elements,making them one of the most advantageous minerals in China.There are abundant rare earth resources in the south of Jiangxi,which not only brings great convenience to the economic development of the south of Jiangxi,but also has a serious impact on the ecological geological environment of the south of Jiangxi.Aiming at the abandoned rare earth mining area in Lingbei Town,Dingnan County,various geological environment problems caused by long-term in-situ leaching operation,the geological environment evaluation research is carried out by obtaining the geological environment information of the mining area,which provides reference for disaster control and environmental restoration of the abandoned ion-type rare earth mining area.In this paper,a small abandoned rare earth mining area in the north of Lingbei Town,Dingnan County is taken as the research object.Through remote sensing image processing and interpretation,the collection of mineral resource exploitation information is completed and the work plan of field geological survey is formulated.Complete the investigation and record of ammonia nitrogen pollution,collapse,landslide,soil and water loss,landform landscape damage and other geological environment problems in the mining area.The UAV photography technology is used to conduct a supplementary survey on the hard-to-reach areas,which is also a supplement and auxiliary to the remote sensing image of the mining area.Water and soil samples collected in the mining area were used for laboratory tests to test the ammonia nitrogen content and study the ammonia nitrogen pollution and its spatial distribution inside the mining area.Through indoor soil column leaching test and simulated rainfall conditions,the migration law and speed of ammonia nitrogen content in soil were studied,and the migration law of ammonia nitrogen pollution in soil in mining area was analyzed.Geological hazards such as landslide,collapse,debris flow and other geological hazards and hidden point data obtained from field geological survey are used to evaluate the risk of geological hazards.The evaluation results of geological hazard are taken as evaluation indexes to participate in the construction of an evaluation index system applicable to the abandoned ionic mining area,to conduct geological environment evaluation research in the study area,and to provide references for environmental restoration and control and geological disaster prevention and control.Through the research,the main conclusions are as follows:(1)Each small mining spot in Lingbei mining area is separated from each other,which has the characteristics of miniaturization and independence.Through the analysis of the investigation results in the whole Lingbei area,it can be seen that the geological environment problems in each small mining area are basically the same,but there are some interconnecting parts,and the geological environment problems are very similar.An abandoned rare earth mining area in Lingbei Mining area is selected as the research area to complete a more refined geological environment evaluation and restoration and treatment research,which can provide a theoretical basis for the geological environment evaluation of Lingbei Mining area.(2)Through the field geological survey,I have a clearer understanding of the geological environment problems in the mining area.There are serious surface water pollution,groundwater pollution and soil ammonia nitrogen pollution in the mining area.Site excavation,workshop building and in-situ leaching operation have caused serious damage to the landform landscape of the mining area,induced geological disasters such as landslide and collapse for many times,and formed a large number of geological disaster hidden points in the mining area.At the same time,six different scale debris flow gullies were found in the mining area,and there were relatively large gullies inside,which caused serious soil erosion.(3)The ammonia nitrogen content of water and soil samples was detected by spectrophotometry.There was widespread ammonia nitrogen pollution in soil within the study area,with the ammonia nitrogen content mostly within the range of 2-90 mg/kg and the highest content reaching 493.29 mg/kg,which was calculated as multiple of exceeding the standard.It is found that the pollution in the central area of the mining area is the most serious,and the ratio of exceeding the standard is nearly 500 times.The ammonia nitrogen content of water samples from mining area mostly exceeded the water quality limit of ClassⅤ,and the highest value was35.22mg/L.The proportion of ClassⅤwater quality exceeding the standard reached 78%,and the proportion meeting ClassⅢdrinking water standard only accounted for 11%.Most of the water sources in the mining area could not meet the demand of the surrounding residents for production and living water.(4)In order to explore the risk degree of landslide,collapse and debris flow disaster in the study area,the index extraction of debris flow gully in the study area was carried out to evaluate the risk of single gully of debris flow.The area of medium risk grade was 0.39km~2,accounting for 19.4%of the mining area.Nine indexes,including elevation,slope,NDVI,distance to road,distance to water system,profile curvature,plane curvature,TWI and land use type,were selected.By the method of index extraction,combined with the distribution of geological hazard points,the frequency ratio method was used to evaluate the geological hazard risk of landslide and collapse in the study area.The risk of the study area was divided into three levels:low risk area,medium risk area and higher risk area,with the area of 1.08 km~2,0.58 km~2 and0.35 km~2 respectively,accounting for 54.1%,28.7%and 17.2%.The overall risk degree of geological disaster is at a low level.(5)The evaluation index system was constructed with six indexes,including landform landscape,surface water pollution,groundwater pollution,soil ammonia nitrogen pollution,collapse,landslide risk and debris flow risk.The geological environment of the study area was evaluated by AHP,fuzzy comprehensive evaluation method and self-organizing feature mapping network(SOM network),and the evaluation results were divided into three levels.The areas of low,medium and high risk areas obtained by AHP were 1.11km~2,0.68km~2 and0.23km~2 respectively,accounting for 54.9%,33.9%and 11.2%.The area of low risk area,medium risk area and high risk area obtained by fuzzy comprehensive evaluation method were1.16km~2,0.69km~2 and 0.16km~2 respectively,accounting for 57.8%,34.1%and 8.1%.The sub-areas of low risk area,medium risk area and high risk area obtained by SOM network were0.58km~2,0.98km~2 and 0.45km~2 respectively,accounting for 28.7%,48.8%and 22.5%.