ABSTRACT

The occurrence of instantaneous outbursting in the Bulli coal seam at the West Cliff Colliery, Appin, NSW can be correlated directly with an increase in concentration (0.5 to 75%) and a related decrease in the ¹³C content (δ¹³C +16 to -8‰ PDB) of the CO₂ in the seam gas. Two sources of CO₂ are required. The greater incidence of outbursting in CO₂-rich zones is explained by the conversion to bicarbonate of cleat and fracture filling calcite deep within the coal and the transport of this bicarbonate in water to mine openings. The weakening of the resistance of the coal to shear by this removal of carbonate is an additional factor to be considered in assessing outbursting situations.