| Metal mineral resources are the material basis for the development of the national economy.Nearly 60% of China's metal deposits are distributed in the area south of the Yangtze River,where karst is widely developed.The southwest mountainous area with widely developed karsts has experienced complex structural evolution history and formed rich mineral resources in this area,where the number of metal mines accounts for 20% of the total number of metal mines in China.Meanwhile,the humid climate in Southwest China is conducive to the development of karst,and the karst water system is a complex system composed of multiple media such as karst caves,pipes,cracks,pores,etc.The karst aquifer medium has a high degree of heterogeneity.Most metal mines in southwest China coexist with carbonate rocks,and the hydrogeological conditions are complex and changeable.The karst water inrush,which results in huge economic loss and human casualties,is easily induced in the process of deep mining.At present,the common difficulties encountered in the prevention and control of groundwater in karst metal mines in southwest China mainly include the extreme heterogeneity of karst aquifer medium,the development of several karst aquifers,multi-stage tectonic processes,diverse waterfilling sources,complex water-filling channels,the ore intercalation,long-term drainage mining,etc.The fundamental solution to these problems lies in identifying the hydrogeological conditions of the mining area,clarifying the hydraulic connections of different karst aquifers,and analyzing the internal structure of the karst water system.Maoping lead-zinc deposit,with a long mining history of more than 300 years,is located in Zhaotong City,Yunnan Province.It is a typical representative of karst metal mountain in southwest China,with high grade,large reserves,and the potential to become a super large lead-zinc deposit.At present,the mining area has formed five mining levels and a relatively complete mining system,and the ore body is divided into Hedong mining area and Hexi mining area with Luoze River as the boundary.The structure of the mining area is extraordinarily complex,and several sets of karst aquifers are developed.It belongs to a water-filling deposit through karst fissure under complex hydrogeological conditions,and currently,the method of strong drainage,depressurization and drainage is mainly adopted to ensure the safety of mining.With the development of deep mining,the head pressure of the ore body surrounding rock and the water inflow of the mine are significantly increased,and the deep mining is faced with hidden dangers caused by highpressure groundwater,which has become the main factor restricting the safe exploitation of deep mining.Meanwhile,the long-term drainage has constantly changed the waterfilling conditions of the mining area,so that the data obtained in the previous survey stage can not reveal the change of the water filling conditions under the long-term artificial strong disturbance,nor can it effectively guide the water prevention and control project in the mining area.At present,there are still great controversies and doubts about the main water-filling sources,channels and scope of influence in the mining area.Therefore,it is urgent to carry out the study on the structure identification of karst groundwater system in Maoping mining area,clarify the hydrogeological conditions and guide the work of water prevention and control project.This paper is based on the groundwater system theory.From the perspective of identifying the structural characteristics of karst water system,combined with the hydrogeological data accumulated in the original investigation stage and the mining process of Maoping lead-zinc mine,the internal structure of karst water system is studied by means of groundwater dynamic monitoring,dewatering test,tracer test and hydraulic calculation.This research ascertained the relationship among these groundwater systems,constructed the evolving hydrogeological conceptual model of this mining area,and preliminarily summarized a set of models suitable for identifying the structure of groundwater system in karst metal mines in southwest China,which could provide hydrogeological basis for the optimization of water control and deep mining engineering of Maoping lead-zinc mine and similar mines.This paper mainly has the following conclusions and understandings:1.Based on the theory and research methods of groundwater aquifer system and groundwater flow system,the karst aquifer system in the mining area is delineated,and the corresponding karst water flow system is defined.The delineation of the regional karst water system makes the research scope break through the limitation of the traditional mining area survey scope and helps to clarify the evolution of the hydrogeological conditions under the background of intense drainage.The regional karst aquifer system can be divided into Devonian,Carboniferous and Permian karst aquifer systems.The Permian Liangshan formation and Carboniferous Wanshoushan formation are used as aquifuge or impervious boundary to separate the three sets of karst aquifer systems.The Devonian karst aquifer system is mainly composed of the Chenjiawan spring flow system and the Devonian karst water flow system in the Hedong mining area,which can be divided into three sections: northern line 110-118,central line 90-94 and southern curtain.The Carboniferous karst aquifer system is mainly supplied by meteoric water,which can be divided into the Shuilu Power Station spring flow system and Linjiaping flow system.The Permian karst aquifer system in the mining area is mainly composed of two secondary flow systems,which are Tangfang spring flow system and Longdongshui spring flow system.As a whole,karst development characteristics show a weakening trend from the periphery to the inner circle and from high to low,that is,the karst development degree of Permian limestone is the highest,Carboniferous karst water system takes the second place,and Devonian karst water system is relatively poor.2.The dynamic response characteristics of karst groundwater system in mining area are analyzed by using rainfall events and the water inrush event.The dynamic response of water level is not only the main variable reflecting the state of karst groundwater,but also the concentrated embodiment of the structure and function of karst groundwater system.The different structures of karst groundwater system lead to different responses to the excitation of groundwater system,such as rainfall events and the water inrush event.The water level in north line 110-118 of the Devonian karst groundwater system in Hedong mining area responds quickly and increases greatly,and it is closely related to the Carboniferous karst groundwater system.The water level of the southern curtain section basically did not show a response to rainfall replenishment events,which is obviously laged.The response speed of the central line 90-94 section is slower than that of the northern line 110-118,and the water level increase is smaller.The Carboniferous karst groundwater system responds quickly and increases greatly to rainfall recharge events,which shows that it mainly receives rapid recharge.3.Combined with hydrogeological tests such as dewatering test and tracer test,supplemented by hydraulic calculations,the water-filling conditions of the mining area were ascertained.The information obtained by a single means is relatively isolated,while the organic combination of multiple means can more accurately determine the supply source and runoff channel.According to the results,the Permian karst groundwater does not constitute the main source of water-filling to the aquifer in the mining area.There is no large and concentrated water channel between the Permian and Carboniferous karst groundwater systems,and the stratified fissure runoff from the east side of the mining area is the main water source and channel of the Carboniferous system.At the same time,although there is a certain hydraulic connection between the Hexi and Hedong mining areas,it is mainly pressure transmission.And the degree of water-filling of the Carboniferous groundwater system in Hexi mining area is limited.In addition,there is a direct hydraulic connection between the Carboniferous and Devonian karst groundwater systems.The Carboniferous karst water system supplies runoff to the northern line 110-118 of the Devonian karst groundwater system in Hedong mining area via NE and NS channels.The groundwater in the southern curtain section of the Devonian karst groundwater system in Hedong mining area is mainly recharged by the deep slowly distant runoff,and the deep karst flow system has strong regulation and storage effect.The central line 90-94 section,located in the center of the draining cone of depression,receive mixed recharge from different sources.4.Based on the theory of groundwater system,the existing curtain roadway in the mining area is fully utilized to optimize and adjust the curtain water control project.Based on the discussion and research on the water-filling conditions of the northern and southern curtain areas,it is considered that the northern curtain project should take the Carboniferous shallow water-filling source on the east side of the mining area as the main prevention and control target.While the main prevention and control target of the southern curtain project is the deep filling water source in the south of the Devonian system.Therefore,it is not necessary to adopt a full-line closed curtain project.The water plugging efficiency can be effectively and greatly improved after effective prevention and treatment of shallow groundwater sources in the northeast section of the northern curtain and deep groundwater sources in the southern curtain.The major advances achieved in this study are given as follows:(1)Based on the theory and research methods of groundwater aquifer system and groundwater flow system,and using a variety of modern hydrogeological techniques,the spatial structure and evolution of highly heterogeneous karst groundwater system in the mining area under strong artificial disturbance were identified.This research preliminarily summarized a set of models suitable for identifying the structure of groundwater system in karst metal mines in southwest China.The research thinking and technical methods are of great theoretical and practical significance to the prevention and control of groundwater in deep mining of karst metal mines in our country.(2)The research results combined with dewatering test,tracer test and hydraulic calculation analysis,have explained the reasons for the mismatch between karst water level dynamics and water quality changes in the mining area,and analyzed the hydraulic connection mode between diffirent karst groundwater systems.It deepens the research on structure identification of karst groundwater system and enriches the application of using tracer technology to solve the problem of groundwater system structure identification. |
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