Mineralogical and geochemical characterization of the Saray and Pınarhisar coals, Northwest Thrace Basin, Turkey Cemile Erarslan ⁎, Yüksel Örgün Istanbul Technical University, Faculty of Mines, Geological Engineering Department, Maslak, 34469 Istanbul, Turkey abstract article info Article history: Received 25 August 2016 Received in revised form 27 January 2017 Accepted 27 January 2017 Available online 5 February 2017 This study investigates the mineralogical and geochemical characteristics of coals from the Saray and Pınarhisar coalfields in the Northwest Thrace Basin, using optical microscopy, scanning electron microscopy, X-ray diffrac- tion and inductively coupled plasma mass spectrometry. The Saray and Pınarhisar coals were deposited in a limnic environment. The sulfur content of the coals ranges from 0.3 to 15.3% and high sulfur contents may orig- inate from both seawater and volcanism. Pyritic and organic sulfur are the dominant sulfur forms (1.2% and 2.7% on average, respectively). The mineral matter of the coals consists mainly of pyrite, barite, gypsum, muscovite and kaolinite, with minor amounts of quartz, butlerite, tamarugite and rozenite. The coals are enriched in trace elements, including V (61 ppm on average), Co (5.85 ppm on average), Ni (79 ppm on average), As (39.2 ppm on average), Th (3.6 ppm on average) and U (6.7 ppm on average). Based on Pearson correlation coefficients, Ti, V, Cr, Fe, Co, Ni, Cu, Se, Rb, Au, Hg, Pb and Th have mainly inorganic affinities (r ash-elements N +0.5) in the Pınarhisar coals; Fe, As and Au also have inorganic affinities (r ash-elements ≥ +0.5) in the Saray coals. The element contents and correlation coefficients indicate that the Strandja Massif, the Tethyan ophiolite belt and the oldest basement sediments were included in the sediment source region for both coalfields, while the Strandja Massif was the prevailing sediment source region for Pınarhisar coalfield. © 2017 Elsevier B.V. All rights reserved. Keywords: Sulfur forms Pyritic sulfur Sulfur origin Seawater Volcanism Trace elements Strandja Massif Northwest Thrace Basin 1. Introduction It is known that coal utilization and coal mining can cause significant environmental and health problems because of its complex mineralog- ical and chemical composition (Carlson and Adriano, 1993; Chen et al., 2011; Dai et al., 2012a; Finkelman, 1994, 2004; Finkelman and Gross, 1999; Finkelman et al., 2002; Goodarzi, 2006; Kolovos et al., 2002; Singh et al., 2011; Swaine and Goodarzi, 1995; Zhang et al., 2004; Zhao et al., 2008). However, due to increasing energy demand, many in- dustrialized and developing countries will continue to use coal for power generation in the decades to come (International Energy Agency, 2015). Identification and evaluation of the problems likely to be resulted from the utilization of coal and the possible measures to deal with them requires an understanding of the mineralogical, petrographic and geochemical properties of coal (e.g. Dai et al., 2008; Finkelman, 1994; Goodarzi, 2002). Also, the mineral matter and element composi- tion of the coal are important for interpretation of the depositional en- vironment (Moore and Esmaeili, 2012; Ren, 1996; Scott, 2002). Turkey has about 15 billion tons of coal reserves; about two billion tons of these reserves (≈10%) are found in the Thrace coal basin. The coals are generally low rank sub-bituminous coal and lignite, except for the Carboniferous bituminous coals of the Zonguldak region (on the Black Sea coast) (Toprak et al., 2015). The low-rank coal deposits formed during the Eocene to Pleistocene period in lacustrine environ- ments, with their formation controlled by either faults or volcanics (Toprak, 2009). The late Oligocene and Miocene Thrace Basin minable coal seams are located in Edirne (Demirhanlı, Meriç, Keşan and Uzunköprü), Kırklareli (Pınarhisar) and Tekirdağ (Topçular, Saray and Malkara) provinces and these coals have been mined for domestic fuel in general. The Saray and Pınarhisar coalfields have been exploited since the 1970s by the General Directorate of Turkish Coal Enterprises and private corporations. The earlier studies on these coals were just presented as raw data (MTA, 2010; Tuncalı et al., 2002). Some data are available for the Thrace region coals on the general and petrographic characteristics (Palmer et al., 2004; Toprak, 2009), but, up to now, there have been no detailed studies of sulfur species, mineralogical and petrographical characteristics, and trace element contents of these coals. Therefore, the purpose of this study is to examine the sulfur species, mineralogical and petrographic characteristics, and the major and trace elements in International Journal of Coal Geology 173 (2017) 9–25 ⁎ Corresponding author. E-mail address: erarslanc@itu.edu.tr (C. Erarslan). http://dx.doi.org/10.1016/j.coal.2017.01.015 0166-5162/© 2017 Elsevier B.V. All rights reserved. Contents lists available at ScienceDirect International Journal of Coal Geology journal homepage: www.elsevier.com/locate/ijcoalgeo