Study on hydro-geochemistry processes of deep Ordovician limestone water of Fengfeng coal mining area

In order to analyze the impact of high-intensity coal mining on the groundwater environment of Ordovician limestone, this paper analyzes the hydro-geochemistry data of Ordovician limestone water in five different periods from 1980 to 2017 in the Fengfeng coal-mining area, analyzes the development the hydro-geochemistry processes by using Pipper three line diagram, ions correlation analysis and principal component analysis.The results show that the chemical composition of Ordovician limestone water has been changed by high-intensity coal mining activities, the hydro-chemical type has developed from bicarbonate type to sulfate type, and the water quality tends to deteriorate.With the extension of mining life, except HCO^3-, the values of other hydro-chemical ions Ca²⁺, Mg²⁺, SO₄^2-, Na⁺+k⁺, Cl^- and TDS increase year by year.In the early stage, the anions dominated by HCO-3 gradually evolved into SO₄^2-, and the hydro-chemical types gradually evolved from Ca-HCO^3- or Ca-Mg-HCO^3- to Ca-Mg-HCO^3--SO₄^2-, Ca-Mg-SO₄^2--HCO^3-, Ca-SO₄^2--HCO^3-, and even Ca-SO₄^2-.Since 2012, the hydro-chemical ions Ca²⁺+Mg²⁺-HCO^3--SO₄^2- and Na⁺+k⁺-Cl^- have a strong correlation (R>0.85), which indicates that the water rock interaction of Ordovician limestone water has obvious ion exchange except for the dissolution of carbonatite minerals.The research results reveal the evolution law and driving mechanism of Ordovician limestone water chemistry driven by coal mining, and provide an important scientific reference for the protection and prevention of water resources, ecological environment protection and people's health and safety.