Dept. Geology, Shahid Beheshti University
The Alborz coal basin is located in northern part of Iran. The coal deposits of Shahrood in eastern Alborz, Zirab in central Alborz and Abyek in western Alborz were studied as typical coalfields of the basin. Shemshak Formation which is the main coal-bearing sequence was formed during the Triassic-Jurassic in the basin. It consists of sandstone, siltstone, shale and claystone, which variedly alternate with coal seams. The coal seams have relatively low quality because of highly disturbed and tectonized, having been subjected to multiple phases of orogenic deformation. The coals of Alborz basin are bituminous type and are dominated by macerals of vitrinite group and have relatively low proportions of exinite and fusinite. They contain different minerals such as clays (mostly argillite), pyrite and quartz as well as plant remains such as Cladophlebis, Marattia and Pachypteris. To compare the main geochemical characters of three typical coalfields of Alborz basin, we analyzed 18 samples for major oxides, ash and SO3 content. The geochemical data show that the enrichment factor for major elements is less than 2. The Ti, P and Mn are enriched with high enrichment factor of 3, 18 and 7, respectively. The mineralogical and petrographic characters of the samples indicate that the coals were formed in lagoons and peat-swamps, fluvial flood plain to lacustrine depositional systems that experienced subtropical to tropical climatic conditions.