Study on Variation Characteristics of Rare Earth Elements in Sequential Metamorphic Coal

Rare earth elements are good carriers for tracing geological evolution. The study on the variation characteristics of rare earth elements in sequential metamorphic coals can provide valuable insights into the elemental and geochemical parameters during coalification process. The No. 2 coal seam in Handan-Xingtai coalfield is taken as the research object, and sequentially modified coals were constructed based on volatile yield. The rare earth elements content, rare earth elements distribution pattern, δCe, δEu and other parameters of sequentially modified coals were analyzed, and the relationship between rare earth elements content and metamorphism degree was explored. The results show that the distribution pattern of rare earth elements (REEs) remains unaffected by the degree of metamorphism, while the light rare earth elements (LREEs) predominantly content the variation characteristics of REEs with increasing metamorphic grade. With the gradual deepening of metamorphism, the cerium anomaly shows an obvious trend of decreasing and then increasing, and the inflection point is located in the third jump area of coalification. The europium anomaly firstly increases and then decreases as the change of metamorphism degree, attributed to the uneven heating of coal seam caused by the superposition of heat of bidirectional magmatic rocks in different periods. La_N/Yb_N values show a two-stage change with the gradual deepening of metamorphism degree, whereas the yttrium anomalies remain unaffected by metamorphic processes.