NEW DATA ON THE FORMATION OF CARBONIFEROUS COAL BALLS

Coal balls are formed from the precipitation of carbonate minerals, pr edominantly calcite, from water during or immediately post-peat format ion. Previous petrological studies suggest permineralization occurred at various stages during the peatification process by precipitation fr om a mixture of marine and meteoric freshwater. The geochemical studie s reported here aimed to test previous theories of coal ball formation . Coal balls studied here are from Upper Carboniferous and Carbonifero us/Permian coal seams in Britain, United States of America, Belgium an d China. Stable carbon isotopic values of calcites range from delta(13 )C of -5 to -35 parts per thousand indicating highly variable contribu tion of decayed organic matter to the carbonate cement. Oxygen isotopi c values of delta(18)O range from -3 to -15 parts per thousand suggest both marine and meteoric freshwater sources. The range, in the Britis h coal balls in particular, with delta(13)C ranging from -7 to -25 par ts per thousand indicates the complexity of carbonate generation. Isot opic data support at least four theories of carbonate coal ball format ion. This makes their absence from post-Permian coals the more puzzlin g and it is suggested that the overall structure of the peat may play a role.