The Geochemical Evolution Of Groundwater And The Influence On Regional Groundwater In Abandoned Mines In The Fengfeng Mining Area

With a large number of coal mines enter to the period of exhaustion of mining resources in China,there are more and more abandoned mines,resulting in some hydrogeological and environmental disasters which can not be ignored.Because of the good water-abundance of Ordovician limestone aquifer which underlying of deep coal layer in Fengfeng mining area,water-full of abandoned mine water will cause water pollution and water inrush in this area.Therefore,analyzing the hydrochemcial evolution,assessing the impact of mine water-inrush on region groundwater chemical composition have significant on reducing mine hazards and resource utilization of mine well after closed.This paper takes the abandoned mine and part of the production of mine as an example,using the method of Piper diagram and delta D and delta ¹⁸O for hydrochemical type and hydraulic connection analysis;based on Bayesian discriminant method and fuzzy comprehensive method,we build a water inrush source discriminating model to identify the source of abandoned mine water.By using multiple ways,such as strontium and strontium isotope analysis,iron and iron isotope analysis,ion ratio analysis,factor analysis and hydrogeochemical simulation,the process of mine water hydrogeochemical evolution was learned.Finally,combing with the collected data of regional groundwater quality,the process of hydrochemical evolution of groundwater quality in abandoned mine and region groundwater system was analyzed.The main conclusions are as follows:1.Piper diagram and isotopic characteristics shows that the source of water-full of abandoned mine water is Ordovician limestone water.2.Using the Bayesian discriminant model and fuzzy mathematical model,source of water-full of the abandoned mine was identified,the result show that the Ordovician limestone water is the major water-full source,with mixture of groundwater from the nearby limestone aquifers.3.The ⁸⁷Sr/⁸⁶Sr ratio of groundwater shows that the chemical components of the groundwater in the study area are the result of leaching of carbonate,sulfate and aluminum silicate.Abandoned mine water and Ordovician limestone water have the same source and with similar water-rock interaction,which indicate there may exist a hydraulic connection between the them.according to the iron isotope analysis,chemical oxidation,hydrolysis and oxidation of pyrite may occur in abandoned coal mine.4.Ion ratio analysis,,factor analysis and hydrogeochemical simulation all showed that dolomite,halite,gypsum dissolution,calcite precipitation,cation exchange interaction occurs during the mine water filling.5.The chemical composition of abandoned mine water and regional groundwater water have changed in comparing with the mine closed before,Ca²⁺,Mg²⁺,SO₄^2-concentration,salinity,total hardness and p H increases.The formation of chemical composition of groundwater is mainly due to the leaching and mixing effect.