四川沐川地区上二叠统宣威组底部稀土富集层地球化学特征及其成因  

GEOCHEMICAL CHARACTERISTICS AND GENESIS OF REE ENRICHMENT BEDS AT THE BOTTOM OF THE UPPER PERMIAN XUANWEI FORMATION IN MUCHUAN AREA,SICHUAN PROVINCE

作　　者：张航飞 文俊 竹合林[1] 陈东方 钟海仁 赵伟 张金元[1,2] Zhang Hangfei;Wen Jun;Zhu Helin;Chen Dongfang;Zhong Hairen;Zhao Wei;Zhang Jinyuan(No.207 Geological Team,Sichuan Bureau of Geology and Mineral Resources,Leshan,Sichuan 614000,China;Zhang Jinyuan Model Worker Innovation Studio Leshan,Sichuan 614000,China;Sichuan Jiayuanrongchuang Geological Technology Co.LTD,Chengdu,Sichuan 610000,China)

机构地区：[1]四川省地质矿产勘查开发局二零七地质队,四川乐山614000 [2]张金元劳模创新工作室,四川乐山614000 [3]四川嘉源蓉创地质科技有限公司,四川成都610000

出　　处：《矿物岩石》2021年第2期24-37,共14页Mineralogy and Petrology

基　　金：四川省自然资源厅2020年省政府性投资地质勘查项目(编号:510201202038652/1)。

摘　　要：扬子陆块西南缘滇、黔地区上二叠统宣威组(P3x)底部存在的稀土富集层已经有很多报导。采集四川沐川地区ZK15-3钻孔宣威组底部的16件黏土岩及玄武岩样品进行地球化学测试分析,通过矿物学和地球化学特征的研究探讨了稀土富集层的成因。测试结果表明,样品ΣREE为263.87~12 820.56×10-6,ΣLREE/ΣHREE为4.31~43.31;w(TiO2)为1.65%~14.6%, LaN/YbN比值介于7.73~130.26,属于轻稀土富集。δEu值介于0.26~0.92,Eu负异常明显,δCe值介于0.87~1.25,Ce丰度无明显异常。稀土富集层自下而上ΣREE先增长后降低,依层序变化曲线总体呈"中隆形",岩性上稀土元素显著富集于铁质、铝质黏土岩中。综合稀土富集层的地质特征、稀土分配模式、对峨眉山玄武岩钛元素高含量背景的继承性、主微量元素建立的物源性质图解判别结果以及Ce/La和Sm/Nd比值的DF判别结果等,认为稀土富集层下亚段铁质黏土岩的形成以高钛玄武岩风化淋滤作用为主,上亚段铝质黏土岩、深灰色黏土岩等为玄武岩风化剥蚀后搬运再沉积并混有上地壳中酸性火成岩提供的部分物源的产物。该项研究可为川南地区稀土矿的找矿工作提供重要线索,对构架整个西南峨眉山玄武岩地区黏土岩型稀土矿的成矿理论具有重要意义。The existence of rare earth enrichment layer in the Upper Permian Xuanwei Formation(P3x) in Yunnan and Guizhou area on the southwest margin of the Yangtze Block has been frequently discussed. Based on the mineralogical and geochemical characteristics of 16 claystone and basalt samples from the bottom of Xuanwei Formation in ZK15-3 drilling hole in Muchuan area, Sichuan Province, the researches on origin of rare earth enrichment layer have been made. The sample test results show that the ΣREE of the rock ranges from 263.87 to 12 820.56×10-6, and LREE/HREE ranges from 4.31 to 43.31. The w(TiO2) is 1.65% to 14.6%, and the LaN/YbN ratio is 7.73 to 130.26, indicating the enrichment of LREE. The δEu value ranges from 0.26 to 0.92, showing obvious negative Eu anomaly, and the δCe value ranges from 0.87 to 1.25, showing no obvious Ce abundance anomaly. It shows that the ΣREE of the REE enrichment layer increases first and then decreases from the bottom to the top, and the sequence change curve of the REE generally displays a "dome" shape. Lithologically, REE is significantly enriched in ferruginous and aluminum claystone. According to the geological characteristics of rare earth enriched layer, rare earth distribution patterns, inheritance of Emeishan basalt high titanium content in the background, the main source nature of trace element diagrams and Sm/Ce/La/Nd results as well as the ratio of DF discriminant results, it is considered that the formation of ferric claystone in the lower member of REE enrichment layer is mainly resulted from the weathering and leaching of high titanium basalt. Aluminium claystone and dark gray claystone in the upper submember are the products of weathering and denudation of basalt, which is transported and re-deposited, and mixed with acidic igneous rocks in the upper crust. This study provides an important clue for the prospecting of rare earth deposits in the southern Sichuan region, and is of great significance for metallogenic theory of the claystone type rare earth deposits in th

关 键 词：上二叠统宣威组 稀土富集层﹔地球化学 风化作用 四川 

分 类 号：P579[天文地球—矿物学]