淮南朱集井田二叠纪煤中稀土元素地球化学特征及其地质解释

Characterization of REE Geochemistry of the Permian Coals from the Zhuji Coal Mine,Huainan Coalfield and Its Geological Implication

采用电感耦合等离子体-光学发射光谱仪(ICP-OES),系统测定了淮南朱集井田二叠纪3个沉积组11个煤层371个煤样品的稀土元素含量。通过对煤中稀土元素地球化学参数分析,得出以下认识:朱集煤中稀土元素总量位于86×10-6～143×10-6范围内,平均值为112×10-6;稀土元素具有指相意义,靠近物源区的上、下石盒子组煤中稀土元素总量比远离物源区受陆表海影响的山西组煤分别高出38%和25%;上、下石盒子组及山西组煤中稀土元素分配模式总体属于轻稀土富集、重稀土亏损型,轻稀土曲线段呈"右倾"趋势,重稀土曲线段则较为"平坦";样品δEu变化范围为0.52～0.80,平均值为0.59,Eu中度负异常,指示成煤沼泽受陆源碎屑影响较大;样品δCe变化范围为0.93～1.04,平均值为0.99,Ce含量无异常,指示成煤沼泽受海水影响较小;煤中稀土元素总量与煤中灰分呈不太显著的正相关关系(R=0.59),说明成煤过程中陆源碎屑物质所携带的部分稀土元素可能吸附在煤的有机质中。原煤X射线衍射图谱(XRD)和光学煤岩薄片显示煤中矿物以石英和粘土矿物为主,高岭石可能是稀土元素的无机载体。另外,稀土元素与陆源碎屑元素(Si、Al、Ti、Ni、Sc和Se等)相关性较好,而与海相元素(B、Sr和Ca)相关性不明显。

The concentrations of the rare earth elements （REEs） in 371 Permian coal samples taken from 11 coal seams of three depositional formations in Zhuji Coal Mine,Huainan Coalfield were determined by inductively coupled plasma-optical emission spectrometry （ICP-OES）.The geochemical characteristics of REEs in coal were discussed and its geological implication was investigated.The total concentration of REEs ranges from 86×10-6 to 143×10-6 with an average value of 112×10-6.On average,the REEs concentrations in coals of Upper and Lower Shihezi Formations are higher than Shanxi Formation by 38% and 25%,respectively,which is suggested to relate the difference of respective depositional environment.Coals in three formations show similar REEs distribution,and are characterized by enrichment of light REEs and depletion of heavy REEs.The distribution of light REEs is steep and heavy REEs is rather flat.Moderate Eu negative anomaly （an average of 0.59 for δ Eu in range of 0.52 ～ 0.80） and absence of Ce anomaly （an average value for δ Ce is 0.99 in range of 0.93 ～ 1.04） were observed for all the samples,which suggests weak influence of seawater on terrestrial detritals-dominated coal-forming swamp.Positive but insignificant correlation （R=0.59） of REEs vs.ash yields was seen in bivariate plot,demonstrating co-existence of inorganic and organic affinities for REEs.The XRD mineral analysis and petrographic observation show that REEs were possibly incorporated into the inorganic clays such as kaolinite.In addition,cluster analysis shows that REEs were grouped together with terrigenous elements such as Si,Al,Ti,Ni,Sc and Se rather than marine elements （B,Sr and Ca）.