The distribution characteristics and its influencing factors of rare earth elements in the karst geothermal water in Pingdingshan Coalfield
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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