中国岩溶2025，Vol.44Issue(2)：283-299,339,18.DOI:10.11932/karst20250207
肥城安驾庄岩溶型地热氡泉水化学特征及成因机理
Chemical characteristics and genetic mechanism of karst geothermal radon spring in Anjiazhuang,Feicheng
摘要
Abstract
The Anjiazhuang geothermal field,the only karst geothermal radon spring discovered in Shandong Province,is located at the contact zone between the Wenkou depression and the Dongping uplift in Feicheng City.The geological framework of this geothermal field is based on a Neoarchean granite basement,which is overlain by Cambrian-Ordovician carbonate rock strata and Quaternary loose sediments.Geothermal water originates within the tectonic fracture zone at the intersection of the Anjiazhuang fault and its secondary faults.It surges upward along the fracture zone and is stored in the layered karst fractures,forming a belt-like and layered thermal reservoir controlled by the fracture structure. In this study,we systematically reveal the hydrochemical evolution characteristics of geothermal fluids and the genetic mechanisms of radon enrichment through the collection and analysis of groundwater and geothermal water samples.This includes measurements of soil radon gas,CSAMT measurement,and the application of hydrochemical diagram methods,ion component ratio characteristic methods,mineral saturation index methods and PHREEQC software simulations.The research findings show that the geothermal water is a weakly alkaline,medium-low temperature thermal mineral water,classified as a hydrochemical type of SO4·Cl-Na·Ca.The concentrations of fluorine(1.87-4.00 mg·L-1),metasilicic acid(32.50-68.45 mg·L-1),and radon(82.60-640.00 Bq·L-1)all meet the standards for designated mineral water,classified as a fluorine-metasilicic acid-radon composite therapeutic thermal mineral water,which possesses significant therapeutic value.The evolution of ion components in the geothermal water is mainly controlled by the dissolution of evaporite and carbonate minerals,followed by the dissolution of silicate minerals and cation exchange.The mineral saturation index shows that calcite and dolomite are supersaturated,anhydrite is nearly saturated,and halite is unsaturated.The enrichment of radon in geothermal water is closely related to the fracture structure:the radon in surface soil and the high anomalies of radon in groundwater are both distributed along the fracture zone.The low-resistance zone revealed by the inversion section of CSAMT measurement highly coincides with the fracture zone and the burial depthes(from 150 m to 350 m)of the karst thermal reservoir.Radon mainly originates from the uranium-rich S-type granite of the Neoarchean Aolaishan Sequence underlying the thermal reservoir and the radioactive decay of the uranium series in the uranium mineralization zone distributed along the fracture.Deep active faults,such as the Anjiazhuang fault,induce the development of micro-fracture networks in rocks.This process facilitates the transformation of radon from a closed and adsorbed state in granite into a free state,allowing it to dissolve in geothermal water.Consequently,radon migrates and accumulates along the fracture zone.Regional seismic activities and the release of tectonic stress help to intensify the damage and fracturing of rocks,enhancing the radon exhalation ability.The relationship between hydrogen and oxygen isotopes shows that geothermal water is mainly recharged by atmospheric precipitation and is formed following the deep circulation and heating of groundwater through the karst-fault system.Its heat source exhibits the characteristics of a four-element heat accumulation:deep-circulating hydrothermal convection in the fracture zone serves as the main heat source,supplemented by the conduction of terrestrial heat flow,heat generated by seismic friction,and heat generated by the decay of radioactive elements. In conclusion,the formation of the Anjiazhuang geothermal radon spring is the result of the synergistic effect of multiple factors including structure,hydrology and geochemistry,the structure system of the Anjiazhuang fault is not only the channel for radon migration and enrichment,but also provides the dynamic conditions for the exhalation of radon in rocks;the underlying uranium-rich granite and the uranium mineralization zone distributed along the fracture lay the material foundation,and deep-circulating hydrothermal convection and multi-source thermal effects jointly drive the evolution of geothermal water.This study systematically elucidates the multi-source synergistic genetic mechanism of radon enrichment in karst geothermal radon spring,providing a scientific basis for the exploration,development and utilization of similar geothermal resources.关键词
地热氡泉/复合型热矿水/四元聚热/断裂构造/S型花岗岩Key words
geothermal radon spring/compound hot ore water/four-element heat accumulation/fault structure/S-type granite分类
天文与地球科学引用本文复制引用
白新飞,宋亮,胡彩萍,宋津宇,杨时骄,郄亮,张军,于超,洪欢仁,王涛..肥城安驾庄岩溶型地热氡泉水化学特征及成因机理[J].中国岩溶,2025,44(2):283-299,339,18.基金项目
山东省地质矿产勘查开发局2022年度局地质勘查引领示范与科技攻关项目(鲁地字[2022]15号) （鲁地字[2022]15号）
