摘要
目的 为了探究华北型煤田深部岩溶地热水中稀土元素地球化学行为的指示意义,方法 以平顶山煤田为例,通过野外调查取样,室内测试,再结合稀土元素配分模式分析和赋存形态模拟等手段,探究深层岩溶地热水中稀土元素(rare earth elements,REEs)的分布特征与迁移规律.结果 结果表明,寒武系灰岩含水层中REEs质量浓度较低(0.054～0.244 μg/L),沿径流路径呈下降趋势;稀土元素(post-archean Australian shale,PAAS)标准化配分模式表现为MREEs和HREEs相对富集,LREEs相对亏损,并且具有明显的Eu正异常和程度不一的Ce负异常,且Ce负异常程度和Eu正异常程度从补给区到排泄区呈降低趋势;水化学平衡软件MINTEQ 3.1模拟结果表明,地热水中REEs以Ln(CO3)2-和LnCO3+络合态为主,随原子序数增大或pH升高,Ln(CO3)2-摩尔分数明显增大,而LnCO3+摩尔分数依次递减,另外,地热水中还存在少量LnSO4+,Ln3+,LnHCO32+,LnF2+和Ln(SO4)2-,其摩尔分数随原子序数增大依次减小,同时受地热水pH和HCO3-,SO42-,F-浓度共同控制;此外,岩溶地热水中还表现出明显的Y正异常和高ρ(Y)/ρ(Ho),可能与地热水富集Ca2+有关.结论 研究结果拓展了稀土元素在煤田水文地球化学研究中的应用,可为揭示矿区深部岩溶地热水补径排过程提供重要依据.
Abstract
Objectives In order to understand the indicative significance of the geochemical behavior of rare earth elements(REEs)in deep karst geothermal water of the coalfield in North China.Methods Taking the Pingdingshan coalfield as an example,the distribution characteristics and migration pattern of REEs in the deep karst geothermal water were investigated through field sampling,laboratory testing,combined with analysis of rare earth element distribution patterns and simulation of occurrence forms.Results This study shows that the contents of REEs in the Cambrian reservoirs in Pingdingshan coalfield is raletively low(0.054～0.244 μg/L),and decrease along the flowing path.The standardized distribution pattern of rare earth elements(PAAS)shows a relative enrichment of MREEs and HREEs and a relative depletion of LREEs,and obvious Eu positive anomalies and varying degrees of Ce negative anomalies.The degree of Ce negative anomalies and Eu positive anomalies decreases from the recharge area to the discharge area.The simulation results of MINTEQ show that the REEs in the geothermal water are dominated by complex spe-cies of Ln(CO3)2-and LnCO3+,and the proportion of Ln(CO3)2-increases significantly with increasing atomic number or pH value,while the content of LnCO3+decreases sequentially.In addition,there are still small amount of LnSO4+,Ln3+,LnHCO32+,LnF2+,and Ln(SO4)2-species in the geothermal fluid,whose contents de-crease sequentially with the atomic number,controlled by the pH as well as HCO3-,SO42-,and F-contents of geothermal water.In addition,there are obvious Y positive anomalies and high ρ(Y)/ρ(Ho)in karst geothermal water,which is closely related to the enrichment of Ca2+in geothermal water.Conclusions The research results expand the application of REEs in the study of coalfield hydrogeochemistry,and can pro-vide a basis for revealing the recharge,runoff,and discharge processes of deep karst geothermal water in mining areas.
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