Enrichment characteristics of strategic metal elements in Late Paleozoic coal-bearing sequences in Renjiazhuang Mine Field

Coal-bearing sequences are important source for increasing strategic metal mineral reserves. There are abundant coal resources in Ningdong Coalfield,and strategic metals enrichment have been found in several coal-bearing sequences. The study selected coal-bearing sequences of Renjiazhuang Mine Field in Ningdong Coal Field as the research object, the coal samples, gangue, roof and floor plate of the main coal seam section were collected systematically. The mineralogical and geochemical tests were carried out by inductively coupled plasma mass spectrometry (ICP-MS), X-ray fluorescence spectroscopy and X-ray diffraction, and the distribution characteristics of major and trace elements were ascertained. The causes of strategic metal element enrichment and their provenance were analyzed.The results showed that the Permo-Carboniferous coal-bearing of late Paleozoic are the enrichment beds of strategic metal minerals in RenJiazhuang Mine Field. The enrichment of strategic metal elements in coal is common in Taiyuan and Shanxi formations, and the overall content of trace elements is high, which is characterized by Li-Ga-Zr(Hf)-Nb(Ta)-Th(U)-Pb,rare earth element and Yttrium(REY), co-enrichment. Moreover, strategic metal elements are more enriched in coal-bearing near the roof,floor and the gangue.Among them, Li and Ba are highly enriched, Rb and Zr are enriched in No.5 coal seam. Li is highly enriched in No.9 coal seam, while Zr, Hf and Th are enriched. The content of strategic metal elements in upper No.9 coal seam is relatively low and Cr is enriched. The concentration of trace elements in No.5 and No.9 coal is better than that in upper No.9 coal seam. Li and Ga of the ash foundation of No. 5 and No. 9 coal seam have reached the industrial grade, and REY of the ash foundation of No. 5 coal seam has also reached the industrial grade, which presenting a very promising potential for further exploration.Based on the comprehensive analysis of element occurrence characteristics, sedimentary environment and tectonic evolution, it is concluded that the strategic metal element enrichment in Renjiazhuang Mine Field is mainly influenced by the clastic supplying of the erosion source area, and the felsitic-neutral rock detrites from the northern Yinshan ancient landthe and the northwestern Alxa block in the western margin of Ordos Basin were transported into the peat swamp by palaeocurrent. It was enriched through interaction between organic matter and inorganic matter in specific sedimentary environment and geochemical environment, and formed the present distribution state and enrichment characteristics under the control of multi-stage tectonic evolution.