Antimony and arsenic anomalies in the coal seams from the Gokler coalfield, Gediz, Turkey

Abstract

The Gokler coalfield in the western part of Turkey mainly contains high sulphur (4.5% to 11.5% on a dry basis) bituminous (0.5% to 0.95% Rr) coals of Middle Miocene age. The Gokler coals from Buyuk, Kucuk and unnamed seams are in general characterised on a mineral matter-free basis by higher amounts of macerals of the vitrinite group (av. 95.5%) than liptinite (av. 2.5%) and inertinite (av. 2%) contents. Geochemical characterisation of 45 coal samples on a whole-coal dry basis was achieved using an energy dispersive, polarised X-ray fluorescence (EDP-XRF) spectrometer. The Gokler coals proved to be anomalously enriched in Sb (8.3–2347 ppm; av. 134 ppm) and As (170–3854 ppm; av. 833 ppm) in the samples in comparison with range values for most world coals. Sb and As are respectively associated with epigenetic stibnite and iron sulfides, both of which formed in microfractures and micropores in the Gokler coals. Stibnite occurs mainly as prismatic crystals and less radial crystals. Scanning electron microscopy (SEM) shows that some stibnites are chemically pure, while others contain minor Fe. Epigenetic Fe sulfides (pyrite and marcasite) typically include (in addition to Fe and S) minor amounts of As and trace amounts of Zn. As and Zn are below the SEM detection levels in syngenetic framboidal pyrites. Epigenetic calcites in the samples consist mainly of Mg and Fe and trace amounts of Sr. All epigenetic minerals, such as stibnite, iron sulfides, calcite and quartz, indicated that the Gokler coals were mainly effected by post-Miocene hydrothermal mineralisations.