San Juan is a large potential underground coal mine located in the La Guajira region in the northeast of Colombia. The regional geology is composed of a Cretaceous age basement rock overlain by the coal-bearing sequence of the Tertiary age Cerrejon Formation. The Cerrejon Formation (Middle-Late Paleocene) consist of bituminous coal fields that are an important economic resource. The coal seams within the Cerrejon Formation are numerous and are variable in thickness, ranging from a few centimeters 6 meters. The Cerrejon Formation has been divided into three groups (lower, middle, upper) based on the thickness and distribution of the coal beds. On the Tertiary deposits are Quaternary alluvial deposits of 400-700 m thickness, covering the San Juan mine area. The Cerrejon Formation was likely formed on a coastal plain, covered in a wet tropical rainforest and incised by a large river system. San Juan underground mine coal probable reserve is 671.7 million tons. Based on evaluation, 92% of the coal reserve is suitable as a PCI (pulverized coal injection) product to the steel industry (MPX, 2012). Proximate analyses of San Juan coals are moisture content (Wt. %) 16.2, ash content (Wt. %) 6.8, volatile matter (Wt. %) 35.2, fixed carbon (Wt. %) 41.9, total sulphur (Wt. %) 0.49 and calorific value (kcal/kg) 6289. The result of coal petrography analyses San Juan coals are composed of vitrinite (48.3-79.7 %), exinite (1.0-6.6 %), fusinite (0.3-5.6 %), semifusinite (5.5-25.9 %) and mineral matter (0.6-13.3 %). Based on vitrinite reflectance (0.5-07 Rm %), the coal of San Juan can classified as high volatile bituminous coal in rank.
Reference: MPX, 2012. San Juan Underground Preliminary Feasibility Study (Colombia-Guajira Thermal Coal Project). Project Number: 11514050003. R002, Golder Associates (1 copy/pdf), CCX Colombia.
Key words: Coal, geology, Cerrejon Formation, San Juan, Colombia