广西姑婆山离子吸附型稀土矿床微量元素地球化学特征

Geochemical characteristics of trace elements of ion adsorption type rare earth elements deposit in Guposhan region,Guangxi,China

探讨广西姑婆山地区离子吸附型稀土矿床中微量元素的分布与富集规律。根据野外地质特征,将矿床的风化壳从上到下分为4层。姑婆山稀土矿床为轻稀土富集型;微量元素及稀土元素整体不同程度富集;垂向上从上到下ΣLREE/ΣHREE质量分数比值逐渐减小,ΣREE呈"低→高→低"的"抛物线"式分布。部分微量元素(如Sr等)与其他微量元素之间,轻、重稀土之间,Ce和Eu与其他稀土元素之间发生了明显的分异现象。风化壳中稀土元素的迁移分异行为可能与稀土元素自身性质差异、风化壳中矿物分布、氧化还原条件、pH值、微生物活动等有关。离子吸附型稀土矿床是开放系统中多次、多阶段的地质作用的产物,其分布规律受成矿母岩和风化条件的共同控制。

This paper approaches the vertical distribution and enrichment of the trace elements in an ion adsorption type REE deposit to understand the geochemical behavior of REEs.Based on the field geological works,the weathering crust of this deposit is divided into 4 layers.According to geochemical characteristics of the trace elements,the total amount of rare earth elements（ΣREE）in the weathered crust is higher than that in the parent rock.REE is distributed vertically in a parabolic form.Chondrite-normalized REE patterns are rich in LREE,with LREE/HREE decreasing vertically from the upper to the lower part of the profile.The REE distribution pattern of the weathering crust is similar to its original rocks.However,the differentiation of the trace elements is also very obvious.It occurs between some trace elements（such as Sr,etc.）and other trace elements,between LREE and HREE,and between Ce,Eu and other rare earth elements.The main effective factors of the mobility and fractionation of REE include the nature of REEs,the mineralogical assemblages of the weathering crust,the redox conditions,pH value,the microbial activities,and so on.The ion adsorption type rare earth elements deposit is a product of multistage and multiple metallogenetic processes in the open system.