Origin and Geochemical Characteristics of Cherts of Qiergusitao Formation in Southeastern of Dabancheng Area, Xinjiang

The cherts of Qiergusitao Formation show the addition of more foreign substances with high content of SiO₂,and great transformable content of Al₂O₃,and TiO₂.Also the high ratios of Si/(Al+Fe+Mn),Al/(Al+Fe+Mn),MnO/TiO₂,and Al₂O₃/(Al₂O₃+Fe3O₂) reflect that the cherts of Qiergusitao Formation are the biochemical cherts and formed in a continental margin.Moreover,the Fe₂O₃/TiO₂-Al₂O₃/(Al₂O₃+Fe₂O₃) diagram shows that Qiergusitao Formation formed in a continental margin as well.Meanwhile the cherts of Qiergusitao Formation have high content of REE,unobvious enrichment of HREE,low ratios of(La/Ce)shale,high values of δCeshale and typical NASC-normalized flat REE patterns without visible negative anomaly and visible leaning to the left.Furthermore the characteristics of the lanthanon element show that the cherts of Qiergusitao Formation are the biochemical cherts and formed in a continental margin.In addition,the(La/Ce)shale-Al₂O₃/(Al₂O₃+Fe₂O₃) diagram proves that Qiergusitao Formation formed in a continental margin.And the samples of Qiergusitao Formation have the high content of trance element Hf,low content of Li,Nb,Rb,Sr,Ta,Th,U,V and Zr;unobvious enrichment of Co and Ni,the high ratios of Co/Ni,and low ratios of U/Th.The characteristics of the trace element show that the cherts of Qiergusitao Formation is normal biochemical origin.