The Raniganj coalfield, located in West Bengal, is situated at a distance of 125 km from Calcutta, the total area being about 1500 sq. km. the mining towns of Raniganj and Asansol are located within this coalfield.
The Lower Gondwana rocks have been well preserved in this coalfield, the total thickness being about 3200 meters. The Barakar Measures containing yellowish sandstone, shale and coal seams, is overlaid with Ironstone Shale (365 meters thick), but devoid of coal seams. These are again overlain with the Raniganj Formation of rocks represented by fine-trained sandstone, shale and a few coal seams.
The Barakar Measures, in this coalfield, contain 14 coal seams varying in thickness from 5 ft to 8 ft (24 meters). The seams have been named after the localities where they are found, with the result that the same seam is known by different names in different parts of the field.
The coals of the Barakar Measures have relatively low moisture, from under 1 to about 3 per cent, the lower volatile-content ranking from 20 to 25 per cent and rarely over 30 per cent, while all the better quality coals exhibit coking characteristics.
The sulphur content of all the coals of the Raniganj field is low and usually below 1 per cent, while phosphorus content varies from about 0.02 to 0.025 per cent. Caloric values lie between 14500 to 14800 for coals from the Raniganj Measures and between 14700 and 15700 for the Barakar coals. A few coal seams, viz. Ramnagar, Laikdih and Begunia belonging to the Barakar Measures, are of good quality, while the Dishergar, Sanctoria and Poniati coal seams belonging to the Raniganj Measures are suitable for gasification and also for blending with the Jharia coals for blast-furnace works.
Raniganj was the first coalfield to be worked in India in 1877 and till today its total production has been more than 900 million tones.