Abstract:

In closed mines, the rebounded and risen groundwater level and the changed groundwater level hydrodynamics influenced the evolution of groundwater hydrochemistry, leading to serious problems in groundwater environment. In this research, the SLW Mine, a typical closed mine in Qingyuan, Guangdong province was selected as the study area to elucidate the hydrochemical characteristics and origins of the closed mine, using a field survey, multivariate statistical analysis, stoichiometry analysis and isotope tracing technology. The results showed that (1) the hydrogen and oxygen isotope composition (δ¹⁸O and δD) analysis indicated that groundwater and mine drainage both had precipitation origins and a close hydraulic connection between groundwater and mine drainage was also found due to similar δ¹⁸O and δD signals, which was also approved by multivariate statistical analysis. (2) There were significant differences between background water, groundwater and mine drainage hydrochemic. The TDS values ranged from 44.18 to 138.86 mg·L^-1 in background water, from 43.39 to 6917.6 mg·L^-1 in the groundwater, and from 3329.22 to 4174.12 mg·L^-1 in the mine drainage; while, their pH values ranged from 4.39 to 8.2, from 2.75 to 7.9, and from 2.87 to 2.92, respectively. The hydrochemical patterns of background water, groundwater and AMD were Ca-Mg-HCO₃, Ca-SO₄-HCO₃, and Ca-SO₄. (3) The stoichiometric analysis showed that water-rock interaction was the main factor in controlling the evolution of hydrochemistry in the study area. In the background area, the weathering of silicate rock was the main controlling process. For groundwater in the mining area, the water-rock interaction was strengthened, and the neutral or slightly alkaline groundwater was formed by sulfide oxidation and the weathering of silicate and carbonate rocks. The dissolution of sulfide minerals was the main process forming typical acid mine drainage with low pH and high SO₄^2-. This study revealed the hydrochemical characteristics and main controlling factors of a closed mine, which is highly important for heavy metal pollution prevention and control in regional water environment.

Key words: hydrochemical characteristics, hydrochemical origins, environmental isotope, water-rock action, groundwater, mine closure

摘要：

矿山关闭后，水位迅速回弹升高，区域水动力场发生改变进而影响到水化学场的演变，并伴随着严重的区域水环境问题。为研究闭坑矿区水体水化学特征和成因，系统采集丰水期、枯水期背景点、地下水和矿井水样测定现场参数、δ¹⁸O和δD值、主量离子等，综合利用多元统计分析、同位素示踪和水化学计量分析等分析方法开展不同水体的水化学特征及成因分析。结果表明，（1）δ¹⁸O和δD组成说明研究区地下水和矿井水主要来源为大气降水，且受到了不同程度的蒸发影响；同一季节内背景点、地下水、矿井水同位素组成具有分区聚集性，丰水期同位素相对亏损，枯水期相对富集，表明不同水体水力联系密切；分层聚类分析和水化学同样揭示了不同含水层之间存在密切的水力联系。（2）研究区水化学具有较大差异。背景点、地下水、矿井水TDS取值范围分别为44.18-138.86、43.39-6917.6、3329.22-4174.20 mg·L^-1，从淡水到咸水均有分布；pH取值范围分别为4.39-8.2、2.75-7.9、2.87-2.92，呈酸性、弱酸性、中性、弱碱性。水化学类型沿补-径-排路径发生系统性演化，背景点、地下水、矿井水水型依次为Ca-Mg-HCO₃型、Ca-SO₄型、Ca-SO₄型。（3）水岩作用是控制研究区水化学演化的主要因素。背景区地下水受制于硅酸盐的溶解，水岩作用较弱；矿区地下水水岩作用增强，受硫化物氧化和硅酸盐、碳酸盐岩的溶解的共同影响，形成中性或偏碱性地下水；矿井水主控水岩反应为硫化矿物的氧化溶解，形成典型低pH、高SO₄^2-的酸性矿山排水。矿山闭坑后水文地球化学特征及主控因素的研究对区域水环境重金属污染防控具有重要意义。

关键词: 水化学特征, 水化学形成作用, 环境同位素, 水岩作用, 地下水, 闭坑矿区