大青山煤田煤系高岭岩稀土元素地球化学特征

Geochemical characteristics of rare earth elements in kaolin rock from Daqingshan coalfield

采用中子活化法对采自内蒙古大青山煤田石炭-二叠纪煤系的12个高岭岩样品进行了稀土元素（REE）含量测定。结果表明，样品的稀土元素含量变化很大，∑REE最低31．98×10^-6，最高616．3×10^-6，平均178．6×10^-6，与NASC的173．21×10^-6相近；∑LREE／∑HRgE介于6．32～46．14之间，平均17．5，明显高于NASC；中一弱Eu亏损，弱Ce正异常。通过不同对比样品（北美页岩、超基性岩、基性岩、中性岩、酸性岩以及偏碱性岩等）所作的标准化分析结果表明，研究样品不具有典型的沉积型泥岩特征；结合薄片鉴定及前人分析结果推论，高岭岩可能由中-基性或偏碱性火山碎屑物质原地蚀变而成，泥炭化所提供的酸性介质条件对火山灰向高岭岩转化以及稀土元素的分异提供了必要的条件。

The contents of the rare earth element （REE） in 12 samples of the kaolin rocks from the Daqingshan coalfield of Inner Mongolia are detected by neutron activation analysis （NAA）. The results show that the REE contents of the samples changes very greatly, the ∑REE ranges from 31.98 × 10^-6 to 616.3 × 10^-6, average 178.6 × 10^-6, approaching the content of NASC, and the ratios of ∑LREE/∑HREE is 6.32 - 46.14, average 17.5, obviously higher than that of NASC. The Eu is medium to weak negative abnormity, and Ce weak positive abnormity. The comparative study with the contrast samples （NASC, ultrabasic rock, basalt, intermediate rock, acid rock and alkalic rock） indicats that the samples, on the REE contents, are not of the typical characteristics of sedimentogenic mudstone, and combining with the results of the rock and mineral analyses and the early study, the kaolin rocks may be formed by the intermediate, basalt or alkalic volcanic ash altered in situ. The acid medium offered by the peatification is the necessary condition that the ash transformed into the kaolin rock and the REE produced difference.