地下水水化学垂向分带特征及成因机制-以新街矿区为例

Vertical zoning characteristics and genesis mechanism of groundwater hydrochemistry:a case study of Xinjie Mining Area

矿井水作为煤矿矿区主要的潜在供水水源,具有较好的综合再利用潜力。然而,煤层顶板充水含水层与围岩发生的复杂多样的物理、化学反应共同影响煤矿矿井水水质。因此,确定不同充水含水层地下水水质状况及其成因机制,对矿井水的保护与综合利用具有至关重要的意义。本研究基于新街矿区一井田的地下水样本和岩石矿物成分数据,采用多元统计分析与水文地球化学方法,并通过PHREEQC软件对水化学平衡进行模拟,深入探讨了不同含水层地下水的化学特征及其矿物溶解/沉淀的垂直分带规律,旨在揭示其成因机制。研究发现:①矿区地下水的化学特征呈现出明显的垂直异质性,其中志丹群以HCO_(3)-Na·Ca、HCO_(3)-Mg·Ca型为主,而安定组至延安组则主要为SO_(2)-4Cl·SO_(4)-Na、SO_(4)-Na型,TDS、Na^(+)、可能是主导水质垂向分异的关键驱动因子。②关键水质指SO_(4)^(2-)标,如TDS、Na+和的浓度与含水层深度(从志丹群至延安组)呈线性关系,通过离子比值分析发现K^(+)、Na^(+)主要源于硅酸盐矿物溶解,Ca^(2+)、Mg^(2+)浓度受到碳酸盐、硫酸盐以及硅酸盐矿物溶解作用的共同影响。③矿物饱和指数的深度变化表明,白云石、斜长石和岩盐等矿物在不同含水层中存在未饱和与过饱和状态的交替,志丹群和安定组的地下水中,许多矿物显示出进一步溶解的趋势;而在直罗组和延安组,多数矿物已达到过饱和状态。④水岩相互作用控制不同深度矿井水的水化学组成,最上层的志丹群水化学组分主要受钠长石、钾长石、方解石、绿泥石等矿物溶解作用的影响,深部含水层硅酸盐矿物、石膏、岩盐和黄铁矿的溶解反应更强,并伴随着阳离子交替吸附作用,形成了高矿化的Cl·SO_(4)-Na、SO_(4)-Na型水。本研究深入探讨了煤矿区不同含水层地下水化学的垂直分带特征及其矿物溶解机制,为矿井水资源的精准管理、水质调控和环境保护提供了坚实的科学基础,具有重要的理论指导价值和实践应用前景。

Mine water,as the main potential water supply source for coal mine sites,has a good potential for comprehensive reuse.However,the complex and diverse physical and chemical reactions between the coal seam roof-filling aquifers and the surrounding rocks jointly affect the quality of mine water in coal mines.Therefore,it is of vital significance to determine the status of groundwater quality and its genesis mechanism in different water-filled aquifers for the protection and comprehensive utilization of mine water.Based on the groundwater samples and rock mineral composition data from a well field in Xinjie Taigemiao Mine,this study uses multivariate statistical analysis and hydrogeochemical techniques,and simulates the water chemical equilibrium by PHREEQC software,to explore in depth the chemical characteristics of the groundwater in different aquifers and its vertical zoning laws of mineral dissolution/precipitation,with the aim of revealing the causative mechanism.It is found that①the chemical characteristics of the groundwater in the mining area show obvious vertical heterogeneity,in which the Zhidan Group is dominated by HCO_(3)-Na-Ca and HCO_(3)-Mg·Ca types,while the Anding Formation to Yan’an Formation is dominated by Cl-SO_(4)-Na and SO_(4)-Na types,TDS,Na^(+),and SO_(4)^(2-) may be key drivers dominating vertical water quality differentiation.②The concentrations of key water quality indicators,such as TDS,Na^(+),and SO_(4)^(2-),show a linear relationship with the depth of the aquifer(from the Zhidan Group to the Yan'an Formation),and the analysis of the ionic ratios reveals that the K^(+)and Na^(+)mainly originate from the dissolution of silicate minerals,and that the concentrations of Ca^(2+)and Mg^(2+)are affected by the dissolution of carbonate,sulfate and silicate minerals.③The depth variation of the mineral saturation index shows that dolomite,plagioclase feldspar and rock salt alternate between unsaturated and oversaturated states in different aquifers.In the groundwater of the Zhidan Group and the Anding Formation,many minerals show a tendency of further dissolution,while in the Zhiluo Formation and the Yan’an Formation,the majority of the minerals have already reached the oversaturated state.④Water-rock interactions control the hydrochemical composition of mine water at different depths.The hydrochemical components of the uppermost Shidan Group are mainly affected by the dissolution of minerals such as sodium feldspar,potassium feldspar,calcite,chlorite,and so on,and the deeper aquifers show a stronger reaction to the dissolution of silicate minerals,gypsum,rock salts,and pyrite accompanied by alternating adsorption of cations,resulting in the formation of highly mineralized Cl-SO_(4)-Na,SO_(4)-Na type water.This study deeply explores the vertical zoning characteristics of groundwater chemistry in different aquifers in the coal mine area and its mineral dissolution mechanism,which provides a solid scientific foundation for the precise management of mine water resources,water quality regulation and environmental protection,and has important theoretical guidance value and practical application prospects.