鲁中南典型地热区地热水氟分布特征及其驱动机制

Characteristics and mechanisms of fluorine enrichment in the geothermal water of south central Shandong Province

山东省鲁中南典型地热区主要包括沂沭断裂带地热区和鲁中隆起地热区,为了探明研究区地热水氟分布特征及其富集规律,综合运用水化学图解、地球化学模拟和主成分分析等方法,分析沂沭断裂带地热区和鲁中隆起地热区地热水水化学数据。结果表明:研究区地热水以Na-Ca-Cl型、Na-Ca-SO_(4)-Cl型和Na-Cl^(-)SO 4型为主,基本为弱碱性水,优势阳离子为Na^(+),氟质量浓度在0.38~4.5 mg/L之间,富钠弱碱性环境有利于地热水中氟的富集。地热水中F-质量浓度与Na^(+)、Cl^(-)和总溶解固体(TDS)质量浓度呈显著正相关,而沂沭断裂带地热水样中F-质量浓度还与K^(+)、SO_(4)^(2-)质量浓度呈显著正相关,与Mg^(2+)和HCO_(3)质量浓度呈显著负相关;鲁中隆起地热区地热水中阳离子交换作用较沂沭断裂带地热区更为强烈,Na^(+)反应强度明显强于Mg^(2+)。鲁中隆起地热区和沂沭断裂带地热区均为裂隙型热储,热储岩性分别为石灰岩、灰岩热蚀变带和安山岩破碎带,水岩作用强烈。研究区地热水中氟离子的物质来源主要为萤石等含氟矿物的溶解沉淀,受控于阳离子交换等水岩相互作用影响,最终形成高氟地热水,其中高温和富钠对研究区地热水中氟离子富集影响较大。研究成果为地热资源开发利用提供了参考。

[Objective]Yishu fault zone geothermal field and central Shandong uplift geothermal field are typical geothermal fields in south central Shandong Province.In order to investigated the distribution characteristics and mechanisms of fluorine enrichment in the geothermal water of the this area,[Methods]hydrochemical diagrams,geochemical simulations and principal component analysis were employed.[Results]The results show that the geothermal water in the study area is mainly Na-Ca-Cl^(-),Na-Ca-SO_(4)-Cl^(-) and Na-Cl^(-)SO_(4)-type water,dominated by weakly alkaline water.The predominant cation is the sodium ion,with fluorine concentration between 0.38 and 4.5 mg/L.Sodium-rich and weakly alkaline environments are faciliated to the enrichment of fluorine in the geothermal water.The fluorine concentration has significant positive correlations with the Na^(+),Cl^(-) and TDS concentrations in the geothermal water.In addition,it has significant positive correlations with K^(+) and SO_(4)^(2-) concentrations and significant negative correlations with Mg^(2+) and HCO_(3)^(-) concentrations in the geothermal water in the Yishu fault zone.The cation exchange effect in the geothermal water of the central Shandong uplift zone is stronger than that in the Yishu fault zone,and the reaction strength of Na^(+)is significantly stronger than that of Mg^(2+).The geothermal field of the central Shandong uplift and Yishu fault zones are both fracturing types.The thermal storage lithologies are limestone,limestone in the thermal alteration zone and ansanite in the broken belt,with strong water-rock interactions.The provenance of fluorine in the geothermal water is the dissolution reprecipitation of fluorine-containing minerals,and the fluorine concentration in the geothermal water is further increased by cation exchange and other water-rock interactions.High temperature and sodium-rich have a great influence on fluorine enrichment.[Conclusion]This research provides a reference for the exploitation and utilization of geothermal resources.