Hydro-geochemical characteristics of burnt rocks aquifer in Shenfu Mining Area and its implications

The study of the hydro-chemical characteristics of burnt rock aquifers helps to distinguish the hydraulic connections between different aquifers. Taking Zhangjiamao Coal Mine in Shenfu Mining Area as an example, 29 groups of water samples were collected from weathered bedrock, bedrock, 2−2 coal burned rock and 3−1 coal burned rock aquifers, and the hydro-chemical characteristics and control factors in the study area were analyzed by comprehensive use of statistical analysis, Piper trilinear diagram, Gibbs model and hybrid model, and the source of main ions was determined, based on which the contact relationship of each aquifer was identified. The results indicated that the total dissolved solids (TDS) of the weathered bedrock and the 2−2 coal burnt rock aquifer were close, slightly lower than the TDS of the bedrock aquifer, while the TDS of the 3−1 coal burnt rock aquifer was the highest, showing a trend of gradually increasing TDS with the increase of aquifer depth. The cations in the weathered bedrock and the 2−2 coal burnt rock aquifer were mainly Ca2+, while the cations in the bedrock and 3−1 coal burnt rock aquifer were mainly Na+; the anions in the weathered bedrock, 2−2 coal burnt rock, and 3−1 coal burnt rock aquifers were mainly HCO3−, while the bedrock aquifers were mainly HCO3−, and SO42−. The hydro-chemical types of weathered bedrock, 2−2 coal burnt rock, and 3−1 coal burnt rock aquifers were mainly HCO3−Ca type, HCO3−Ca and HCO3−Ca·Mg type, HCO3−Ca and HCO3−Na·Mg type. The hydro-chemical composition of weathered bedrock and 2−2 coal burnt rock aquifer was mainly controlled by water rock interaction, while the hydro-chemical composition of bedrock and 3−1 coal burnt rock aquifer was mainly influenced by both water rock interaction and concentration. The main ions of 3−1 coal burned rock, bedrock, weathered bedrock and 2−2 coal burned rock aquifer were respectively from the dissolution of silicate rock salt, the dissolution of silicate rock and evaporite rock salt, and the weathering dissolution of silicate rock and carbonate rock salt. At the same time, the reverse cation exchange interaction effect occurred in the groundwater disasters of each aquifer. Multiple indicator results showed that the ion composition of the weathered bedrock and the aquifer of the 2−2 coal fired rock was similar, and there was a strong hydraulic connection. There may be a direct contact relationship locally, which is different from the ion composition of the aquifer of the 3−1 coal fired rock. There is a certain barrier layer between them, and the hydraulic connection between them is weak.