长江沉积物稀土元素的粒度效应研究

Study of granularity effects of rare earth elements in the sediments of Yangtze River

依据Stokes定律,将小于63μm的长江沉积物分成小于2、2～4、4～8、8～16、16～32、32～63μm6个粒级,采用ICP-MS法分别测试了分粒级沉积物的REE含量,结果显示:长江沉积物REE的丰度遵循元素的"粒度控制律",即随粒度变细,∑REE含量依次增高;北美页岩标准化分布曲线均呈右倾的近"W"型,轻、重稀土分馏明显,相对富集LREE,明显的Ce负异常和弱Eu亏损。对长江沉积物不同粒级样品进行X射线衍射分析和体视镜下观测,结果表明:长江沉积物随粒度增大石英和长石含量逐步增加,碳酸盐和重矿物在各个粒级中含量甚微并且随粒级变化不大;长江沉积物REE随粒度变细逐渐增加的特征主要受控于沉积物随粒度变化而变化的矿物成分,黏土粒级及细粉砂中较高的∑REE主要是黏土矿物吸附作用的结果,粗粉砂中较低的∑REE主要为长石和石英的稀释作用结果,而碳酸盐和重矿物因其较低的含量对稀土元素含量影响较小。

Sediment of 〈 63 μm in the Yangtze River could be divided into six size fractions, i.e. 〈 2 μm, 2 - 4 μm, 4 - 8 μm, 8 - 16 μm, 16 -32 μm and 32 -63μm, according to Stoke＇s law. Using ICP-MS method to measure the REE content of various grade sediments, the resuh showed that the abundance of REE in the Yangtze River sediment was related to granular control law of element, i.e. the higher ~ REE content increased successively, the thinner the granularity was ; there existed all right-inclined ＂W＂ model, obvious fractionation of LREE and HREE, relative enriched LREE and clear Ce negative anomaly as well as weak Eu deficit in the curves of North America Shale-normalized patterns. The measurement of different grade samples according to X-ray diffraction analysis showed that the content of quartz and feldspar were raised gradually as granularity of sediment increase ; content and change of carbonate and heavy minerals were little as change of grade-size in sediment; the diminution and increase character of REE as grade-size change of sediment was controlled by mineral content as grade-size change of sediment in the Yangtze River. Higher; REE content in clay parti- cle and fine silt was caused mainly by adsorption of clay minerals and lower ∑REE content in coarse sih was caused by dilution of feldspar and quartz, rare earth elements were not itffluenced by carbonate influence and heavy minerals, because of their lower content. geywords