中国东部主要河流稀土元素地球化学特征

Geochemical Feature of Rare Earth Elements in Major Rivers of Eastern China

在2007年底至2008年初的枯水期间,系统采集了中国东部流域面积和径流量较大的33条河流沉积物、悬浮颗粒物和水样,采用等离子质谱法、X荧光光谱法等方法测定了14种稀土元素含量以及常量组分和水体pH值等理化指标。研究发现中国河流稀土元素浓度总体高于世界均值,且南方河流沉积物、悬浮物稀土元素含量高于北方河流,南方河流悬浮物态中稀土、重稀土呈现一定程度的相对富集,与我国上地壳稀土丰度和稀土矿产种类的南北分异相吻合。展示了以中国东部泥质岩稀土元素丰度标准化后的稀土配分模式及Ce、Eu异常特征,发现河流沉积物的中、重稀土元素相对富集,悬浮物轻稀土相对富集,溶解相重稀土富集的特征;北方河流溶解相稀土元素浓度明显大于南方河流,且除小清河外,溶解相Eu不同于沉积物与悬浮物而呈强烈的正异常,主要与河水理化性质影响下的稀土分异有关。研究发现小清河等少数河流沉积物中稀土元素为异常高值,经Al标准化处理、计算拟合剩余值后,认为小清河等河流稀土元素已受人为污染的影响。

River sediments（RS）,suspended particulate material（SPM） and water were systematically sampled for thirty-three major rivers in eastern China during dry season between the end of 2007 to early 2008.Rare Earth Element（REE）,macro elements and physico-chemical indicators such as pH were determined by ICP-MS,XRF and other methods.It was found that the REE concentrations in RS,SPM and water（i.e.dissolved form-DF） were generally greater than the average of other rivers in the world.The REE concentration of RS and SPM in south rivers was usually higher than that in north rivers and rich in MREE and HREE.This regional pattern of REE was coincident with the REE abundance of upper crust and REE mineralization in China.The clay-rock normalized distribution patterns of REE in RS,SPM and DF were illustrated.It presented that RS was relatively rich in MREE and HREE,SPM rich in LREE and DF rich in HREE.Dissolved concentration in north rivers were much higher than that in south rivers.Normalized Eu showed strong positive anomaly in DF except for Xiaoqinghe.This is quite different from the negative Eu anomaly normally appeared in RS and SPM,and can be explained as the results of fractionation under given physico-chemical condition of river water.The anoma-lous contents in some rivers such as Xiaoqinghe,after standardization and regression based on Al content,can be due to anthropogenic impact.