Candiota coalfield: a world class Brazilian coal deposit

Abstract

The Candiota coalfield is situated at the southwestern margin of the Sul-Riograndense shield in the State of Rio Grande do Sul, south Brazil. The coal seams and associated sedimentary rocks occur in the Rio Bonito Formation, Guatá Group, of Artinskian/Kungurian age (Lower Permian). The palynological assemblage found in the Candiota coals is characterized by the predominance of pteridophytic spores. Pollen grains from gymnospermic vegetation, as well as algae-related elements, are minor elements in the assemblage. Coal resources in the basin reach more than 12 billion t and the production of run-of-mine coal was about 1,500,000 t in 1989. Several coal beds occur in the basin. However, only the Candiota seam is exploited in an open-cast mine. The macroscopic seam section of the Candiota seam shows a predominance of banded and dull coal, which characterizes a mineral-rich and vitrain-poor coal. Vitrinite never reaches 50% and minerals vary from 36% to 50% under microscopic examination. The coal is poor in inertinite when compared with other Brazilian coals and the content of exinite is about 7%. The composition of samples collected in various areas of the basin is very uniform, as revealed by proximate analysis. The coal is very high in ash yield and even the hand picked vitrain present values of about 12%. The calorific value is very low (3,300 kcal/kg) for samples of run-of-mine coal with 52% ash. Based on data from both moisture and carbon contents of vitrain, the Candiota coal seam can be classified as equivalent to subbituminous A coal in the American Standards for Testing and Materials classification.