Geochemical characteristics of trace elements and sedimentary environment in coal from the XX Coal Mine, Turpan-Hami Basin, China

Abstract

As a significant coal resource base in China, the Turpan-Hami Basin hosts substantial coal reserves with notable potential for trace element enrichment and mineralization. This study investigates the restrictions imposed by the sedimentary environment on trace element distribution through geochemical analysis of coal and depositional settings in the No. 3-2 coal seam of the XX Coal Mine. The results indicated that the coal in the seam is rich in vitrinite and is classified as a low-rank coal with ultralow ash content, high volatility, and moderate fixed carbon. The average contents of vitrinite, moisture, ash, volatile matter and fixed carbon are 83.54%, 4.57%, 4.11%, 41.65%, and 55.96%, respectively. The average random vitrinite reflectance is 0.487%. Only the values for V, Co, Ni, Zn, Sr, In, and Ba are close to the average values for worldwide coals. The trace elements in coal are generally present at low concentrations and are depleted. The contents of major and trace elements in the roof of the vertical upward coal seam are generally greater than those in the coal. The rare earth elements and yttrium in coal are generally characterized by LREY enrichment, with negative Eu and Ce anomalies and positive Y anomalies. The predominant sediment source in the study area is identified as acid rock. The coal-forming plants consisted primarily of herbaceous plants. The coal-forming environment was interpreted as a freshwater phase, with moderate weathering, a dry and hot paleoclimate, and an oxidizing environment. Sediment source is identified as the dominant factor controlling trace element depletion, while insufficient hydrodynamic conditions suppress terrigenous debris input, further restricting element enrichment.

Graphical abstract

Keywords

trace elements / geochemical characteristics / sedimentary environment / Keyayi sag / Turpan-Hami Basin / Lower Jurassic

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