北京市密云水库上游金矿区土壤稀土元素的地球化学特征

Geochemical Characteristics of the Rare-earth Elements in the Gold Mine Soil in the Upstream Area of the Miyun Reservoir,Beijing

采集了密云水库上游金矿区的34个土壤表层样品,用电感耦合等离子体质谱法（ICP-MS）测定了土壤稀土元素含量,研究了土壤不同粒级中稀土元素的分布特征,并对土壤稀土元素含量分布的影响因素、累积效应、配分模式及分馏特征进行了分析和探讨。结果表明：金矿区土壤稀土元素总量∑REE略高于中国大陆土壤∑REE背景值。随着颗粒粒径的减少,稀土元素及总有机碳（TOC）含量均逐渐增加。相关性分析表明,各稀土元素均表现出相似的相关性,与全量元素Li、V、Co、Ga、Rb、Cs呈正相关,与Cu、Cd、Pb及pH呈负相关,与TOC呈显著正相关;土壤pH、有机质和矿物质成分与稀土元素含量分布密切相关。累积因子（AF）分析表明,稀土元素在粘粒级（0~2μm）、粉砂粒级（2~50μm）中表现出显著的累积效应,这是由于微细颗粒比表面积较大,次生矿物及有机质含量较高。经球粒陨石标准化后,各粒级稀土元素总体配分曲线相近,均表现为Ce无异常,Eu明显亏损,〉50μm的粗粒级Eu亏损较细粒级更为严重。土壤轻重稀土分馏程度关系为：砂粒级（50~350μm）〉粉砂粒级（2~50μm）〉粘粒级（0~2μm）。该研究结论将为选取稀土元素作为示踪剂提供科学依据,并为不同粒级中稀土元素的进一步研究提供一定的参考价值。

A total of 34 surface soil samples were collected in the gold mine soil in the upstream area of the Miyun Reservoir.The contents of REE in soil were determined by inductively coupled plasma mass spectrometry（ICP-MS）,and the distribution characteristics of REE in different particle size fractions were investigated.Then,the influencing factors,accumulation effect,distribution patterns and fractionation characteristics of REE were studied.The results showed that the average content of total REE in soil was just over the Chinese soil background value.The contents of REE and TOC in soil particle size fractions generally increase with decreasing particle size.Correlation analysis indicated that all REEs showed a similar correlation,REEs were positively correlated with Li,V,Co,Ga,Rb,Cs and TOC,while Cu,Cd,Pb and pH had a negative correlation with REE;pH,organic matter and mineral composition of soil were closely correlated with the distribution of REE contents.Accumulation factor（AF）analysis suggested that REEs were mainly accumulated in the fractions of clay（0-2μm）and silt（2-50μm）.The high concentrations of REE occurred in fine size fractions due to larger surface area,high clay minerals and organic matter amount associated with fine particles.The chondrite-normalized patterns of REEs showed that the different soil fractions had similar distribution patterns,exhibiting no Ce anomaly and a clear loss of Eu,which were more serious in the50μm fractions than in fine fractions.The LREE/HREE fractionation showed that the relationship of their fractionation degree was：sand fraction（50-350μm） silt fraction（2-50μm） clay fraction（0-2μm）.The results of this study provided a scientific basis for rare-earth elements being selected as tracers,and it also provided references for the further study of REEs in various particle size fractions internationally.