鄂尔多斯盆地东胜煤田侏罗系煤中元素地球化学特征及其古环境意义

本文以鄂尔多斯盆地东胜煤田塔然高勒矿区锡尼布拉格勘查区6 5号钻孔延安组煤为研究对象,在工业分析和元素分析的基础上,采用X 射线荧光光谱仪（XRF）和电感耦合等离子体质谱仪（ICP MS）测定了煤中常量元素及微量元素含量,对煤中元素的富集程度进行了分析,并利用煤相参数和地球化学参数对延安组不同煤层的沉积古环境进行了重建。结果表明：不同煤层样品以低水分含量、（特）低灰分产率、特低硫含量和中高挥发分产率为特征,煤中硫以有机硫为主;不同煤层煤中常量元素均以SiO2和Al2O3为主,其次为CaO、Fe2O3和Na2O;煤中微量元素富集程度不同,3#煤中富集Cr、Zr、Nb、Ta和Th,轻度富集V、Cu、Zn、Ga、Y、Ba、Yb、Hf、W、Pb和U,4#煤中富集Sb,轻度富集Ba、Be、Co,5#煤中轻度富集Be和Co,6#煤中轻度富集Cr和V;稀土元素结果表明,3#煤和6#煤以重稀土富集型为特征,4#煤和5#煤以中/重稀土富集型为特征,不同煤层均存在Eu正异常现象;不同煤层煤岩显微组分均以惰质组为主,其中4#煤中惰质组含量最低;各煤层沉积水体均为氧化环境占主导,其中3#、5#及6#煤形成于酸性、富氧—次富氧、水动力较弱的干燥森林沼泽相,而4#煤形成于酸性、富氧—次富氧、水动力较弱的干燥森林沼泽相与碱性、缺氧—极贫氧环境、水体环境波动较大的潮湿森林沼泽相,这两种环境交替出现。

Geochemical characteristics of Jurassic coal in the Dongsheng coalfield of Ordos basin and their paleoenvironmental implications

This study investigated the geochemical characteristics and sedimentary paleoenvironment of the Yanan Formation from borehole No.6- 5 in the Xinibulage exploration area of the Dongsheng coalfield, Ordos basin. Proximate and ultimate analyses, an X- ray fluorescence spectrometer (XRF), and an inductively coupled plasma- mass spectrometer (ICP- MS) were employed to determine the major and trace element compositions of coal. The results showed that coal samples from different seams exhibit low moisture content, (extra) low ash yield, extremely low sulfur content (with organic sulfur being the primary form), and medium to high volatile matter yield. Major elements are predominantly SiO2 and Al2O3, followed by CaO, Fe2O3, and Na2O. Trace element enrichment varies among seams: coal 3# is enriched in Cr, Zr, Nb, Ta, and Th, with slight enrichment in V, Cu, Zn, Ga, Y, Ba, Yb, Hf, W, Pb, and U;coal 4# is enriched in Sb and slightly enriched in Ba, Be, and Co; coal 5# shows slight enrichment in Be and Co;and coal 6# exhibits slight enrichment in Cr and V. Rare earth element analysis indicates that coal 3# and 6# are characterized by heavy rare earth element enrichment, while coal 4# and 5# are enriched in medium/heavy rare earth elements. All coal seams display a positive Eu anomaly. Inertinite is the dominant maceral in all seams, with coal 4# exhibiting the lowest inertinite content. Sedimentary paleoenvironmental reconstruction suggests that all coal seams formed in predominantly oxidative environments. Coal 3#, 5#, and 6# likely originated in oxidative, acidic, oxygen- rich to sub- oxygen- rich, and hydraulically weak dry forest swamp facies. Coal 4# experienced fluctuating conditions, alternating between oxidative, acidic, oxygen- rich to sub- oxygen- rich, and hydraulically weak dry forest swamp facies, and reducing, alkaline, highly fluctuating water body environments characteristic of anoxic to extremely hypoxic moist forest swamp facies.