Geochemical characteristics of groundwater about Zhiluo Formation in the north-ern Ordos Basin and its indicative significance

SUN Kui; FAN Limin; MA Wanchao; CHEN Jianping; PENG Jie; ZHANG Penghua; GAO Shuai; LI Cheng; MIAO Yanping; WANG Hongke

doi:10.13225/j.cnki.jccs.2023.0537

Abstract：Coal mine water disaster is the main disaster of the Jurassic coalfield in the northern Shaanxi and the groundwa-ter of the Zhiluo Formation is one of the main water inrush sources.Using the Durov diagram,Piper three-line diagram,Gibbs diagram,Stiff diagram and principal component analysis method,the geochemical characteristics of the Zhiluo Formation groundwater in the northern Ordos Basin and its indicative significance were investigated in this study.Also,it studied the geochemical characteristics of groundwater and explains its significance for the hydraulic connection between the Zhiluo Formation and overlying aquifer and the groundwater runoff conditions.The results show that the concentra-tions of the pH,TDS,K++Na+,SO4-and Cl-show a decreasing trend about the Zhiluo Formation groundwater from the western normal bedrock area to the eastern weathered bedrock area.And there are some differences about the Zhiluo Formation groundwater chemical types.For the deep buried area of the Zhiluo Formation in the west,the hydrochemical types of groundwater are mainly SO4-Na type,SO4·Cl-Na type and HCO3·SO4-Na type.For the bedrock weathering area of the Zhiluo Formation in the east,the groundwater type transitions to HCO3-Ca type and HCO3-Ca·Mg type.The hydrochemical formation of the Zhiluo Formation groundwater is controlled by rock weathering,alternating adsorption,desulfuration and leaching.Hydrogen isotope and oxygen isotope and hydro-chemical characteristics have obvious indicat-ive effects on the hydraulic connection between aquifers.The analysis of hydrogen isotope and oxygen isotope,chemical ion concentration of typical borehole groundwater and regional groundwater hydro-chemical characteristics shows that there is no hydraulic connection between the normal bedrock groundwater of the Zhiluo Formation and the groundwater of the Luohe Formation and the Salawusu Formation in the western part of the study area.The weathered bedrock groundwa-ter of the Zhiluo Formation in the eastern part is closely related to the Salawusu Formation groundwater.The halogen ele-ment(Cl-)has obvious indication effect on the runoff conditions of the Zhiluo Formation groundwater.,The normal bed-rock groundwater runoff of the Zhiluo Formation in the western is slow and the groundwater is mainly static reserves.For the bedrock weathering area,due to its development of pores and fissures,the water storage and permeability are signific-antly enhanced and there is a strong mixing effect with the Quaternary groundwater.So the groundwater runoff intensity is large and the groundwater is mainly dynamic reserves.