Geochemistry and origin of elements of Upper Triassic Olang coal deposits in northeastern Iran

Abstract

The Olang area is a part of Gheshlagh-Olang synclinal, which is a member of eastern Alborz coal basin and is situated at a distance of<br />70 km northeast of Shahroud city. Coal-bearing strata of this region are part of the Shemshak group (Upper Triassic to Lower Jurassic).<br />Samples from the 9 coal seams of the Olang coal deposits were collected and ashed. The aim of this study is to determine the<br />occurrence and distribution of major and trace elements in the coal ashes of Upper Triassic Olang coal deposits in northeastern Iran.<br />The concentration of the elements in the coal ashes of the Olang region is higher than the Clarke value and the average of World coal<br />ash. The coal ashes have been enriched in Zn, Mn, and P in comparison with the average of the World coal ash. The correlation<br />coefficient analysis on the major and trace elements in the ash yielded in four groups including: A (Rb, K, Cs, Si), B (Al), C (Tl, Ca,<br />Nb, Ta, V) and D (Cr, Hf, Sn, Zr, Th, Zn, Ti, Ba, W, Mg, Na, P, Sr, Co, Cu, Mo, Ni, U, Fe, Ca). The first two groups are strongly<br />correlated with ash yield and mainly have an inorganic affinity. C and D groups are negatively or less strongly correlated with ash<br />yield. The rare earth elements' abundances are negatively correlated with the ash yield and exhibit an organic affinity. Based on<br />correlation, cluster analyses, and rare earth elements' distribution characteristics, two separate modes of occurrence can be considered<br />for rare earth elements: 1) Accompanying phosphate minerals with organic origin (phosphorites) or phosphate organic materials, and 2)<br />Accompanying the vitrinite maceral group.