Geochemical properties of major and rare earth elements in the South Kouchek-Ali Coal Mine, Tabas

Abstract

Introduction The rare earth elements (REEs) are classified into light (La, Ce, Pr, Nd, and Sm), medium (Eu, Gd, Tb, Dy, and Y), and heavy (Ho, Er, Tm, Yb, and Lu) groups (Seredin and Dai, 2012). Goldschmidt (1933) was the first to study the REEs in coal in some detail. In recent years, REEs in coal have received much more attention owing to their stable geochemical characteristics and potential economic value (Seredin, 1996; Seredin and Dai, 2012; Rantitsch et al., 2003; Fu et. al., 2010). Coal deposits have since become an important alternative source for REEs (Seredin and Dai, 2012; Hower et al., 2016), However, unusual REE anomalies in coal basins have not attracted special attention, because it seems that there are sufficient resources of these metals in conventional deposits (e.g., carbonatites, alkaline granites, and weathering crusts) ( Seredin and Dai, 2012). The aim of this study is to assess REE content in the South Kouchek -Ali coal mine, located in the Central Iran Coal Basin, about 65 km southwest of the city of Tabas. Materials and methods Samples were collected from the South Kouchek-Ali coal mine that includes 3 coal samples, five coaly shales. The samples were analyzed by X-ray fluorescence spectrometry (XRF) for major elements. REEs were analyzed by inductively coupled plasma mass spectrometry (ICP-MS). Results The concentration of rare earth elements of the South Kouchek-Ali coal mine may have resulted in background rare earth elements in the primary mineral matter. The concentration of rare earth elements of south kouchek -Ali coal mine has been determined, and the range of these elements in representive studied samples is compared with the worldwide, Chinese and USA coals. Rare earth elements show positive correlation with major elements, indicating that these elements are mainly associated with clay mineral. Positive correlations of ∑REEs with Al2O3, SiO2, and TiO2 suggest that the REEs are mainly derived from detrital sources and occur dominantly in kaolinite and illite. The concentrations of ∑REEs in representative samples range from 69.54 to 113.06 ppm with an average value of 127.94 ppm, higher than the average ∑REE content of the USA (53.59 ppm) (Finkelman, 1993) and worldwide coals (68ppm) (Yudovich and Ketris, 2006), but lower than that of average Chinese coals (162.51 ppm) (Dai et. al., 2008). The abundance of light rare earth elements is higher relative to heavy rare earth elements. Light rare earth elements may have resulted in high background LREEs in primary mineral matter. Discussion The South Kouchek-Ali coal mine occurs in the Middle Jurassic Hojedk Formation, and is located in the western part of the Tabas coalfield. The Hojedk Formation mainly consists of shale, sandstone and carbonate rocks. The concentration of rare earth elements of the South Kouchek-Ali coal mine has been determined, and the range of these elements in coal samples studied is compared with the worldwide types of coal. The Ozbak-Kuh granites have been identified at the north of the Tabas Coal Basin, and Narigan, Zarigan, Chadormalou, and Saghand granites have been identified in the west of the Tabas Basin. During the accumulation of coal-bearing formations, the supply of terrigenous materials originated from here (Pazand, 2015). Acknowledgement We appreciate the help of Mr. Rafia, the director of Tabas Coal mining company, plus Mr. Zahedi and Mr. Gholami for taking samples. References Dai, S.F., Li, D., Chou, C.L., Zhao, L., Zhang, Y., Ren, D.Y., Ma, Y.W. and Sun, Y.Y., 2008. Mineralogy and geochemistry of boehmite-rich coals: new insights from the Haerwusu Surface Mine, Jungar Coalfield, Inner Mongolia, China. International Journal of Coal Geology, 74(3–4): 185–202. Finkelman, R.B., 1993. 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Keywords

• Coal
• Rare earth elements
• Major elements
• Kouchek –Ali
• Tabas Coalfield