陕西省子长矿区晚三叠世5号煤层的稀土元素和钇的地球化学特征

Geochemical features of REY in late Triassic No.5 coal seam in Zichang mining area in Shaanxi Province

对采自陕西省子长县枣林永胜煤矿的晚三叠世5号煤层剖面样品进行了详细的稀土元素地球化学研究,报道了我国北方晚三叠世陆相环境形成的煤层的稀土元素（rare earth element）和钇（yttrium）（简称 REY）的地球化学特征.研究成果显示,5号煤层（9个煤分层）的稀土元素和钇的总含量（REY）为51.8～172.6μg/g,平均103μg/g,略低于中国一般煤的稀土元素和钇的含量.在5号煤层的下部分层,稀土元素富集类型以重稀土类型为主,而在煤层上部的煤分层则以轻稀土类型为主.以上地壳（简称 UCC）中的稀土元素和钇含量作为标准,对子长5号煤层的稀土元素和钇含量作标准化比值的处理（即以5号煤层的稀土元素和钇的含量除以上地壳中相应的元素含量）后,显示5号煤层的大多数煤分层中存在明显的铕负异常（Eu/Eu＊＝0.67～0.76,平均0.71）,反映聚煤时期曾有较多的Eu＋2从Eu＋3中分馏丢失,从而造成铕的亏损.

This paper studies in detail the geochemistry of the rare earth elements in section samples from the late Triassic No.5 coal seam in Zaolin Yongsheng Mine in Zichang County,and reports the geochemical features of the REY in coal seam formed in late Triassic continental envi-ronment in Northern China. The results show that the total content of rare earth elements and yttrium （REY）is 51.8～172.6μg/g,103μg/g on average in No.5 coal seam （including 9 coal layers）is slightly lower than that in general Chinese coal. In the lower layers of No. 5 coal seam, the heavy rare earth is dominant,and in the upper layers,the light rare earth is dominant. Taking the content of REY in the upper continental crust（referred to as UCC）as the standard,the paper gets the normalized ratio of REY in No. 5 coal seam （i.e.,to divide the content of rare earth elements and yttrium in No. 5 coal seam by the corresponding elements content in UCC）, the results from which display there is obvious negative europium anomaly （Eu/Eu＊=0.6 7~0.76,average 0.71）in most of coal layers in No. 5 coal seam,which indicates in the coal accumulating period,more Eu＋2 fractionated from Eu＋3 and lost,resulting in the loss of europium.