Major and trace elements redistribution in weathered claystones from the Corumbataí Formation, Paraná Sedimentary Basin, São Paulo, Brazil

ABSTRACT: We studied 30 samples from 10 mining fronts of clayish rocks of the Corumbataí Formation, in the region of the Santa Gertrudes Ceramic Pole (São Paulo, Brazil), in order to evaluate the variation of rare earth elements (REE), mineralogy, weathering effects and provenance. The profiles show diagnostic geochemical signatures that are uniform across the Corumbataí Formation samples in the studied region and can be correlated from mine to mine, i.e.: 1) the constant MgO/K2O ratio and the variation of other oxides, which allow the identification of three main groups of samples; 2) similar groups of chemical index of weathering (CIW) and chemical index of alteration (CIA); 3) the immobile character of REE, Th, and Sc. The erosion/denudation processes were apparently the same among the studied profiles, allowing the identification of a similar weathering pattern among the mines, despite its location within the stratigraphic column. Mineralogical and geochemical data here reported suggest a dominant felsic source, but intermediate or mixed sources cannot be discarded. The chemical and mineralogical aspects observed are practically uniform along the studied profiles and mines, which allow them to be used as raw material by the industries of the Santa Gertrudes Ceramic Pole (SGCP) region.

摘要：我们于巴西圣保罗州圣赫尔特鲁德斯陶瓷产业集聚区（Santa Gertrudes Ceramic Pole）区域内，针对科鲁姆巴泰组（Corumbataí Formation）黏土岩的10个采矿工作面采集了30件样品，旨在探究稀土元素（Rare Earth Elements, REE）、矿物学特征、风化作用效应及物源的变化规律。各研究剖面均呈现特征性地球化学指纹，在本次研究区域内的科鲁姆巴泰组样品中均保持一致，且可在各矿山间进行对比，具体表现为：1）MgO/K₂O比值恒定，其余氧化物含量存在显著差异，据此可划分出三大样品集群；2）化学风化指数（Chemical Index of Weathering, CIW）与化学蚀变指数（Chemical Index of Alteration, CIA）的聚类特征高度相似；3）稀土元素、钍（Th）及钪（Sc）具备惰性不易迁移的特征。各研究剖面间的侵蚀与剥蚀过程基本一致，尽管各矿山所处的地层柱位置存在差异，但仍可识别出统一的风化模式。本研究获取的矿物学与地球化学数据显示，物源以长英质为主，但无法排除中性或混合物源的可能性。本次研究涉及的剖面与矿山的化学及矿物学特征整体均一，因此可作为圣赫尔特鲁德斯陶瓷产业集聚区（SGCP）相关产业的原材料加以利用。