Chemistry and water cycle of the groundwater in the Jurassic confined fissured aquifers at Ili No.1 Coal Mine,South Ili Coalfield,China
South Ili Jurassic Coalfield in Ili Basin is an important coalfield in China for having been early discovered sandstone-hosted U deposits.The active Ili No.1 Coal Mine and the neighbor uranium mines are all simultaneously influencing or destroying the groundwater systems of the Jurassic fissured confined aquifers.To coordinate mining the two types of syngenetic minerals with distinctly different attributes,the key issue is how to manage the impact of the coal mines and the uranium mines on the Jurassic groundwater systems.It is of necessary and imperative to investigate and predict the existing impacts of coal mines on the Jurassic coal aquifer.Ili No.1 Coal Mine now is the only and the largest active coal mine in South Ili Coalfield.The water samples were collected from the quaternary unconso-lidated aquifer,the roof sandstone confined aquifers of the No.3 coal seam and the No.5 coal seam,the floor sandstone confined aquifer of the No.5 coal seam,and the overall mixed mine water at the underground site of Ili No.l Coal Mine respectively.By testing the water chemistry,stable isotopes of D and 18O,and T & 14C dating,and adopting geochemistry analysis,we investigated how the mining and dewatering activities of Ili No.1 Coal Mine affect the water chemistry and water cycle of the Juras-sic fissured confined aquifers.It indicates that the groundwater is near-neutral,low mineralized HCO3-SO4 or HCO3-SO4 freshwater;δD and δ18O are-91‰--118‰ and-12.7‰--16.0‰ respectively.Except for the floor sandstone aquifer of the No.5 coal seam(U concentration of 11.1 μg/L),the ura-nium concentration in the Jurassic aquifers is only about 0.8 μg/L.The average age of the groundwater is 5 000-6 000 a,among which the age of groundwater in the roof aquifers of the No.3 coal seam and the No.5 coal seam is up to 12 500-25 000 a.The Jurassic groundwater at Ili No.1 Coal Mine has the remarkable characteristics of"three Lows,one Old,and one Less",i.e.,Low salinity,Low deute-rium,Low uranium,Older age,and Less pollution.It is owing to dewater the floor aquifer of the No.5 coal seam that the quicker local water cycle driven by dewatering has formed within Ili No.1 coal mine,while the vast cone of drawdown of the floor sandstone aquifer of the No.5 coal seam has been laterally and ceaselessly expanding and the local velocity of water cycle has been obviously accelerating along the aquifer.The roof sandstone aquifers of the No.3 coal seam and the No.5 coal seam are still ideally isolated and closed.Once being drained,it is hard to replenish the two roof aquifers.All the groundwater enriched in the roof aquifers of the No.3 coal seam and the No.5 coal seam is rare low-deuterium and high-quality.
South Ili Coalfieldthe Jurassic fissured aquifersstable hydrologic isotopesgroundwater agewater cycle
万方数据
维普
