Comparative study on geochemical characterization of the Carboniferousaluminous argillites from the Huainan Coal Basin, China

Aluminous argillites were widely deposited in the Taiyuan Formation at the Huainan Coalfield at the southeast margin of the North China Plate. However, knowledge about their formation conditions and geochemical characterizations is not presently known. We recovered underground aluminous argillites at depths of 485-610 m from a borehole in the Zhangji Coal Mine and characterized their geochemical parameters, including major and trace elements, by X-ray fluorescence, inductively coupled plasma optical emission spectrometry, and inductively coupled plasma mass spectrometry. The provenance, climatic conditions during the weathering process of parent rocks, weathering extent, and depositional environments of Huainan aluminous argillites were investigated. Results show that Huainan aluminous argillites are depleted in alkalis and alkaline earth elements and enriched in Al, Fe, and Ti. The ratios of immobile trace elements such as Nb/Ta and Zr/Hf are similar in all the argillite samples. The NASC-normalized rare earth element (REE) patterns of the argillites show an enrichment of heavy REEs and depletion of light REEs, with positive Ce and negative Eu anomalies. The provenance analysis indicates that the studied aluminous argillites probably derived from the common parent rocks composed of felsic to intermediate igneous rocks. These argillites were presumably deposited under anoxic environments.