Study On Hydrogeochemical Characteristics of Deeply Buried Mining Area In Inner Mongolia - Shaanxi Province, China

Abstract In order to distinguish the differences of hydrogeochemical characteristics between coal measures strata and aquifers on the roof of deep buried mining areas in Inner Mongolia-Shaanxi, China, this paper adopted inorganic components, environmental isotopes and organic components to study water quality comprehensively. The results show that the deep buried mining area in Inner Mongolia-Shaanxi belongs to Mu Us Desert, and the surface is covered by aeolian sand, so it has excellent precipitation infiltration capacity. Mineralization of surface water and Quaternary water < 500mg/L, the cation is mainly Ca2+, the anion is mainly HCO3−, which belongs to HCO3-Ca·Mg type water. The Cretaceous Zhidan Group is in unconformable contact with the Quaternary, and constitutes a unified water-bearing complex on the whole, which makes Zhidan Group have a better supply water source, and its inorganic water quality characteristics are close to the Quaternary water; The deep aquifer is affected by the Anding formation relative impermeable layer and its recharge runoff condition is weak. The salinity of Jurassic water is generally > 3500mg/L due to long-term water-rock action. The cation is dominated by Na+ and the anion is dominated by SO42−, which belongs to SO4-Na type water. According to the analysis of hydrochemical characteristics, there is no direct hydraulic connection between Luohe Formation and Zhiluo Formation. The characteristics of environmental isotopes show that the rainwater, surface water and Quaternary water in the study area belong to the modern groundwater, while Zhidan Group water is between the modern groundwater and the ancient water. The values of δD and δ18O in the deep Straight Rom Group and Yan’an Group are low, and the groundwater falls below the rainwater line of Ordos Basin with a deep circulation depth. Before mining, the groundwater is in the stagnant state with good closed conditions. The content of dissolved organic matter (TOC and UV254) in groundwater decreases gradually with the increase of aquifer depth; Fluorescence peaks in Area I and Area III mainly appeared in surface water and Quaternary water, and DOM sources in surface water were more abundant; The fluorescence peak in Area I also appears in the water of Zhidan Group, Straight Rom Group and Yan’an Group, and the fluorescence peak between Area I and Area II is a symbol; The fluorescence peak intensity of Cretaceous → Straight Rom Group in Area V area has an increasing trend, indicating that there are humus like DOM from other sources in the deep Straight Rom Group aquifer. In general, the comprehensive analysis of hydrochemical characteristics by various means can well distinguish the differences of hydrogeochemical characteristics among aquifers, which provides a scientific basis for the rapid and accurate discrimination of water situation and disaster in coal mines and the safe production.