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 of70 km northeast of Shahroud city. Coal-bearing strata of this region are part of the Shemshak group (Upper Triassic to Lower Jurassic).Samples from the 9 coal seams of the Olang coal deposits were collected and ashed. The aim of this study is to determine theoccurrence and distribution of major and trace elements in the coal ashes of Upper Triassic Olang coal deposits in northeastern Iran.The concentration of the elements in the coal ashes of the Olang region is higher than the Clarke value and the average of World coalash. The coal ashes have been enriched in Zn, Mn, and P in comparison with the average of the World coal ash. The correlationcoefficient 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,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 stronglycorrelated with ash yield and mainly have an inorganic affinity. C and D groups are negatively or less strongly correlated with ashyield. The rare earth elements' abundances are negatively correlated with the ash yield and exhibit an organic affinity. Based oncorrelation, cluster analyses, and rare earth elements' distribution characteristics, two separate modes of occurrence can be consideredfor rare earth elements: 1) Accompanying phosphate minerals with organic origin (phosphorites) or phosphate organic materials, and 2)Accompanying the vitrinite maceral group.