鄂尔多斯盆地煤中稀土元素分布与赋存特征及其地质意义

Ordos Basin is the main energy basin of China, which has great renown for the coexistence of multiple energy. A variety of energy minerals have been able to co-exist, which is bound to be controled by the geological factors of basin formation and evolution. Rare earth elements(REE) in coal are good geochemical indicators to the study of coal formation.The Ordos Basin has developed with four coal series, Carboniferous-Permian Taiyuan formation and Shanxi formation as well as late Triassic Wayaobao formation those existed before basin formed,Jurassic Yan'an formation that existed after basin formed. The research of REE content and distribution pattern in four sets of coal and shale is to discuss the material source and depositional environment.The study will improve the understanding of formation and evolution in the Ordos Basin, then the comprehending of multiple energy minerals reservoir (mine) mechanism.WaYaoBao formation deposited on the eve of the basin formation, it is the first time to study REE in coal in this formation. The north rim of the basin ZhunGeEr, Shenfu-Dongsheng and Wuhai mining areas are the nearest mining areas from sediment source rocks in north China coal accumulating areas, which are helpful to study material source and sedimentary environment. The basin has a series of low and high rank coal,and coal seam in Yan'an formation has macro components of coal and clear rock band structures.All these researches can provide appropriate conditions for studying the relationship between REE and coal rank,as well as the connect REE with organic composition these two problems,enrich the knowledge of trace elements in coal occurrence mechanism.

鄂尔多斯盆地是我国的主要能源基地，因多能源同盆共存而倍受关注。多种能源矿产之所以能够共存，必定受该盆地形成与演化的地质因素控制。煤中稀土元素是研究煤系形成的良好地球化学指示剂。在鄂尔多斯盆地发育有四组煤系，盆地形成前的石炭－二叠纪太原组和山西组和晚三叠世瓦窑堡组，盆地形成后的侏罗纪延安组。系统研究四组煤和泥岩中稀土元素的含量和分配模式，探讨其物质来源和沉积环境，必将加深和完善对鄂尔多斯盆地形成与演化的认识，以及对多种能源矿产共存成藏（矿）机理的认识。瓦窑堡组沉积于盆地形成的前夕，对该组煤中稀土元素的研究尚属首次。盆地北缘的准格尔、神府-东胜和乌海矿区是华北聚煤区离沉积物源岩最近的矿区，有利于研究物质来源和沉积环境。该盆地赋存有低中高系列煤阶的煤，延安组煤层内宏观煤岩组分条带结构明显，为研究稀土元素与煤阶和与有机组分关系两难题提供条件，有望取得新成果，丰富对煤中微量元素赋存机理的认识。

煤中稀土元素是研究煤系形成环境的良好地球化学指示剂，系统探讨煤中稀土元素含量、分布模式、赋存状态和地质影响因素，可加深和完善对鄂尔多斯盆地形成与演化的认识，同时可为多种能源矿产共存成藏（矿）机理、规律提供可靠地质依据。本研究综合运用煤岩学、矿物学、地球化学等多学科理论知识，采用煤的工业分析、X射线荧光光谱（XRF）、电感耦合等离子体质谱（ICP-MS）、X射线衍射（XRD）、扫描电镜-能谱（SEM-EDX）等分析测试方法，通过重点分析鄂尔多斯盆地东部准格尔煤田、河东煤田和渭北煤田中石炭系—二叠系煤以及侏罗系彬长矿区侏罗系煤的煤质煤岩特征，煤中矿物和稀土元素的分布规律、赋存状态及其富集的主控地质因素进行了系统研究。研究发现鄂尔多斯盆地石炭二叠系煤中稀土元素含量略低于中国煤均值，但远高于世界煤均值，侏罗系煤中稀土元素含量均低于中国煤与世界煤均值；三套地层煤中δEu多呈负异常，南部地区部分显示正异常，表现出了强烈的母岩继承性；煤中δCe多数显示弱负异常的特征，说明沉积环境偏向还原；煤中稀土元素的无机亲和性更强，主要赋存在黏土矿物和磷灰石中，稀土元素也可以赋存在有机质中，但含量较低，在一定的酸性还原条件下，重稀土更易被低煤阶煤中有机质吸附；距离物源远近控制了稀土元素的总含量，不同物源则会影响其配分模式；变质程度主要影响赋存在有机质中的稀土元素，随着煤变质程度的增强，有机质吸附稀土元素的能力也逐渐增大；海水侵入一般情况下仅影响稀土元素的配分模式，而地层水淋滤则可能带来稀土元素含量的增加。