Hydrogeochemical formation and inverse simulation of limestone groundwater in Carboniferous Taiyuan formation of Huaibei coalfield

With the exhaustion of shallow coal resources, coal mining is gradually developing into the deeper part to the concealed coalfield in North China, which destroys the original balance of groundwater system, complicates the hydrogeological conditions, and changes the dynamic conditions and hydrochemical characteristics of deep groundwater. The main hydrogeochemical formation and the control factors for the aquifer of Carboniferous Taiyuan formation limestone in the Huaibei coalfield were investigated by the ion ratio analysis and the principal component analysis. Meanwhile, the aquifer of Carboniferous Taiyuan formation limestone in the Linhuan mining area in the south of Huaibei coalfield was studied, and the inverse hydrogeochemical simulation was carried out by PHREEQC. Results show that the main types of hydrogeochemical formation in the aquifer in the Huaibei coalfield are the leaching dissolution (including calcite, dolomite, gypsum dissolution and pyrite oxidation) and the cations alternate adsorption. The quantitative analysis results of inverse hydrogeochemical simulation are basically consistent with the qualitative analysis results of ion ratio and principal component. Affected by mining activities, the leaching dissolution in the aquifer in the south of Huaibei coalfield is gradually weakened with time, while the cation alternate adsorption is gradually strengthened. In contrast, the opposite phenomena are shown because the strata of Taiyuan formation limestone are generally shallow in the north of Huaibei coalfield. The hydrogeochemical formation of the aquifer in the south of Huaibei coalfield presents obvious spatial difference under the influence of structure, while the hydrogeochemical formation in the north of Huaibei coalfield is affected by its runoff, showing the characteristics of gradually increasing from east to west. The inverse hydrogeochemical simulation for the Linhuan mining area in the south of Huaibei coalfield verifies the hydrogeochemical processes and the spatial distribution difference in the aquifer of Carboniferous Taiyuan formation limestone.