| Summary: | The geology, petrography and chemical variation of the Pecket coal sequence, Magellan Region (52_x0001_57VS, 71_x0001_10VW), the only Chilean coal used for electricity generation on a large scale, has been studied in order to predict their combustion behaviour, especially in coal blends. The depositional environment of formation of the coal seams was a swamp rarely exposed to subaerial conditions and was associated with the development of the folded foreland of the Magellan basin during the Tertiary (Oligo–Miocene). The general tectonic regime of the collision of the Antarctic and South American plates is reflected by a system of joints with 40_x0001_N–50_x0001_W strike. The maceral composition of all six seams studied indicates high contents of vitrinite ( > 90%), minor content of liptinite (4.7%) and inertinite ( < 2%). Occurrence of tonstein horizons altered to kaolinite indicates a distal volcanism during peat accumulation. Coal rank varies between lignite and subbituminous (Ro = 0.28–0.42%) with an average dry basis calorific value of 5450 kcal/kg, 17 wt.% moisture, 41 wt.% volatile matter, and sulphur content below 0.5 wt.%. The mineral matter (LTA) associated with the coal shows a dominance of kaolinite with quartz, smectite, and minor basanite. SiO2/Al2O3 and Fe2O3/CaO ratios of the ashes diminish towards the lower seams
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