| Karst water disaster is one of the major disasters that threaten the deep mining of north China type coal field.Huainan coalfield is located at the edge of the North China platform,and the carbonate rocks of Carboniferous,Ordovician and Cambrian under the Permian coal seam in Huainan coalfield have strong karst development.Most karst pipelines and caverns are located in the drainage area under carbonate rock above the water-resisting floor and Karst water has the characteristics of high water pressure,large flow rate and rapid flow.The disasters of karst water bursting have happened frequently and caused great losses as coal mining continues deeper and deeper.On the other hand,Karst water is an important source of water supply in the water-poor north China.Therefore,the study on the occurrence law and hydrochemical characteristics of deep karst water is of great significance for the safe mining of mines and the protection and utilization of water resources.On the basis of the previous research results and 567 samples of carbonate rocks collected from the Huainan coalfield,this paper has analyzed rock ore identification and chemical composition,has found out the chemical composition and microstructure of different lithofacies carbonate rocks of,the characteristics of karst development and the combined characteristics of water-bearing media,and has expounded the regional karst geological conditions in Huainan coalfield.In the meantime,the occurrence,recharge,runoff,discharge conditions and water-rich intensity of groundwater from the concealed bedrock outcrop to the deep are obtained,and this paper has divided the different types hydrogeological units of groundwater,obtained the spatial distribution law of water flow subsystem based on 4 surface pumping tests,9 drainage tests and 5 tracer tests in Huainan coalfield.Through the collection of 1267 samples and chemical analysis,this paper has discussed the hydrochemical field characteristics and genetic mechanism of karst aquifer,and carried out the hydrologic geochemistry simulation experiments in which seven hydrochemical reaction paths and six hydrologic geochemistry processes under temperature and pressure were simulated.Furthermore,this paper has predicted the evolution law of hydrochemical field,runoff field and temperature field.The following major achievements have been made.(1)The mineral composition and chemical composition of carbonate rocks in the Huainan coalfield are complex and the ratio of calcite to dolomite is 3:1.Iron is mainly concentrated in dolomite in the isomorphous way instead of magnesium as iron dolomite.The siliceous bands were formed and the transition from opal to chalcedony was observed.The phenomena of dissolution pore and silicification indicate that the hydrothermal,metasomatism and recrystallization of carbonate rocks in this area are strong.In addition,weathering and denudation in supergene process greatly promoted the development of karst in this area.The karst development of Xinzhuangzi mining area,Panji mining area,Xieqiao mining area,Zhangji mining area,Liuzhuang mining area and Kouziji mining area in Huainan coalfield decreases in turn.(2)NWW trending structural fissures and interlayer fissures are the main runoff channels of karst groundwater in Huainan coalfield.The boundary of regional karst groundwater flow system is Liufu fault in the north,yingshang-Dingyuan fault in the South,xinchengkou-Changfeng county fault in the East and kouzi-nanzhaoji fault in the West and all of them are water blocking fracture.The boundary of middle flow system is shangtang-minglongshan fault,Fufeng fault,Shungenshan fault,Shanwangji fault and Fuli fault and the limestone of Minglongshan mountain,Shangyaoshan mountain,Shungenshan mountain and Bagongshan mountain is the recharge area of karst water.The local flow system is composed of NWW trending medium and small sized water-conducting faults in the coal field which is in a wild-goose formation.(3)The average pH of karst water in Huainan coalfield is 8.41,which belongs to weak alkaline water,and the average water temperature is 31?,which is low temperature hot water.The evolution of hydrochemical types from east to west was HCO3·SO4?SO4·Cl?Cl,from south to North was HCO3?SO4·HCO3?SO4·Cl.TDS gradually increases from southeast and northwest to central which shows that the karst water in the south and east is in strong runoff,while the middle zone is in weak runoff-retention zone.Karst water from southwest to northeast developed recharge area,runoff area,detention area and discharge area in the whole mine field area.The results of R-type factor analysis of hydrochemistry show that the five principal components extracted by Taiyuan limestone water and Ordovician limestone water respectively can explain 87.24%and 83.85%of the information of the original variables and the factor that accounts for the largest proportion in the factor score is the factor of concentration,the secondary factors are lytic filtration and cation alternating adsorption,which shows that the natural water-rock interaction is the main control of the chemical composition of karst water.The shallow and deep mixing factors were also extracted as the main components that show that the mixing effect caused by the large-scale drainage of karst water plays an important role in controlling the chemical composition of karst water.(4)The Cr,Co,Cu and As of micronutrient reflect the dissolution and filtration of karst water,Mn,Zr and Sb indicate that karst water receives shallow infiltration recharge,while Li,V,Cr,Mn,Ni and As represent that karst water is supplied by deep hot water;It is inferred that the karst water in this area is palaeo lixiviation and long range infiltration recharge water because the contents of ?D and ?18O in central coalfield are much higher than those in precipitation;The interval value of T content is 1.03-5.89 TU and less than 6 TU,and it shows that the karst water is more than 70 years old,the recent precipitation is poor,and is in a relatively closed environment,so it is palaeo-lytic water.(5)The temperature of karst water can be calculated based on the chemical temperature scale of SiO2.The circulation depth of karst water is calculated to be-800?-2100m according to the predicted water temperature and geothermal gradient.The deepest part of Karst water circulation is located in Dingji area and it is-2065m.So it is inferred that ordovician limestone water participates in deep circulation along the fault structure,flows from the West and east to the middle,and migrates to the shallow after deep circulation warming.According to the partial pressure test of CO2,the high solubility of deep hot water will occur at the depth of-900?-1200m in the Huainan coalfield,which will lead to deep carbonate dissolution and secondary precipitation and form deep karstification.(6)The calculated results show that the maximum saturation index of gypsum and rock salt is-1.43 and-3.92 respectively,and all of them are dissolved.The saturation index of calcite changes regularly in the region:the southeast is less than-0.85,which is in the recharge area;the middle is 1.48,which is in the detention area or discharge area;the west is between[-0.20,0.20],which is in the runoff area.As a result of large-scale drainage of karst water,the water in different karst aquifers in the depth of pan II mining area is mixed and re-diluted,and the water-rock interaction can not reach the equilibrium state in a short time.(7)The results from the mixing ratio calculation show that Taiyuan limestone water of number 2 in Zhangji is made up of 22.48%shallow coal measure water,Ordovician limestone water of number 1 in Xieqiao is composed of 66.15%shallow limestone water,Ordovician limestone water of number 2 in Xieqiao is composed of 66.15%shallow limestone water,Taiyuan limestone water of number 2 in Panbei is mixed with 45.72%deep Ordovician limestone water,Ordovician limestone water of number 4 in Panbei is composed of 60%deep Cambrian limestone water and Ordovician limestone water of number 2 in Pan II is composed of 22.35%deep Cambrian limestone water.The shallow vertical runoff of Xieqiao is stronger than Zhangji and the deep vertical runoff of Panbei is stronger than Pan II.(8)The reverse path simulation of karst water show that the eastern part of the coalfield mainly occurs dissolution and filtration and pyrite oxidation;the western part mainly occurs dissolution and filtration and cation alternating adsorption;the central part mainly occurs mixing,desulfurization and concentration due to continuous drainage of karst water.It is inferred that the eastern part belongs to the open system,the western part to the semi-open system and the central part to the closed system.(9)According to the dynamic state of Karst groundwater,there are four circulation models of karst groundwater,which are infiltration-runoff model,infiltration-mining model,runoff-retention model and runoff-mining model.The Huainan coalfield can be divided into three regional hydrogeological units according to the karst groundwater flow system and hydrochemical system,furthermore,six intermediate hydrogeological units can be divided which are infiltration-recharge area,runoff-recharge area,runoff area,weak runoff area,confluence-mining area and deep circulation area respectively.Figure[49]Table[28]Reference[184]... |
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