冀北蓟县系铁岭组古风化壳稀土元素富集规律及古环境意义  

REE enrichment and palaeoenvironmental significance of paleo-weathering crust of Tieling Formation of Jixian System,northern Hebei Province

作　　者：张运强 陈海燕 杨鑫朋 王志民 郝森 李朋伟 ZHANG YunQiang;CHEN HaiYan;YANG XinPeng;WANG ZhiMin;HAO Sen;LI PengWei(Langfang Center for General Survey of Natural Resources,China Geological Survey,Langfang 065000,Hebei,China;Hebei Regional Geological Survey Institute,Langfang 065000,Heibei,China)

机构地区：[1]中国地质调查局廊坊自然资源综合调查中心,河北廊坊065000 [2]河北省区域地质调查院,河北廊坊065000

出　　处：《矿床地质》2023年第5期1034-1047,共14页Mineral Deposits

基　　金：中国地质调查局地质调查项目(编号:DD20230383和DD20230060);河北省高层次人才资助项目(编号:A202001056);河北地矿局综合研究项目(编号:454-0502-JBN-G43D)共同资助。

摘　　要：冀北地区蓟县系铁岭组顶部普遍发育一套古风化壳,该层位轻稀土元素和Rb均出现显著的富集现象。为了进一步探讨风化过程中元素的迁移规律以及古环境特征,文章对该套古风化壳开展了详细的地球化学研究。结果表明,古风化壳中轻稀土元素、Rb和Ti等含量自下而上表现为“先升高,后降低”的分布规律,且随着风化层中黏土物质的增加而升高,在中上部黏土岩中达到富集的峰值,推测与黏土矿物的吸附作用相关;古风化壳δCe正异常、δEu明显的负异常等特征指示轻稀土元素主要富集于中上部的氧化环境,且氧化作用越强越富集;化学蚀变指数CIA介于53.54~79.50,风化淋滤指数BA变化范围为0.39~1.08,共同指示了风化壳形成于温暖湿润的气候环境。综合稀土元素、微量元素和La/Yb-∑REE图解显示,风化壳稀土元素和微量元素主要来源于下伏铁岭组碳酸盐岩以及火山岩浆活动。A set of paleo-weathering crust is widely developed on the top of Tieling Formation in the Middle Proterozoic in northern Hebei Province,it is found that both the light rare earth and the associated Rb have reached enrich-ment.The paper studies migration of elements during weathering and the characteristics of paleoenvironment based on detailed geochemistry study,the results show that the contents of LREE、Rb and Ti in the paleoweathering crust increase first and then decrease,and enhance with the increase of clay material in the paleo-weathering layer,in the middle and upper part of the clay rock reached the peak value,presumably related to the adsorp-tion of clay minerals.The light rare earths in the paleo-weathering crust begin to be enriched under the condition of oxidation,and enriched with the increase of oxidation.Positive abnormality ofδCe and obvious negative anomaly ofδEu indicate that the light rare earths are mainly enriched in the oxidation environment of the middle and upper part,and gradually reach mineralization with the increase of oxidation.The CIA of chemical alteration index is between 53.54 and 79.50,and the BA of weathering shower index varied from 0.39 to 1.08,indicating that the weathering crust was formed in a warm and humid climate conditions.The spider-web Diagram,REE dis-tribution curve and the diagram analysis of La/Yb-∑REE of the micronutrient indicate that the rare earth ele-ments and micronutrient are mainly derived from the carbonate rocks of the underlying Tieling Formation and volcanic magmatism during this geological period.

关 键 词：稀土元素 富集机理 古风化壳 铁岭组 冀北 

分 类 号：P618.7[天文地球—矿床学] P618.77[天文地球—地质学]