MECHANISMS OF THE NATURAL CONCENTRATION OF COAL MACERALS, PARTICULARLY CUTINITE, IN AMERICAN COALS

In humic coals the inertinite macerals, fusinite and semifusinite, are concentrated in the fusain lithotype and vitrinite is concentrated in the vitrain lithotype. Sporinite and alginite are concentrated in the cannel and boghead coals, respectively. These concentrations occur at the depositional stage of coalification and can yield concentrations as high as 90% or more. Resinite macerals usually occur as ovoid masses in minor amounts dispersed throughout coal seams. However, in the Cretaceous-Tertiary coals of the Wasatch Plateau in the western USA the resinites (type II) are slightly more abundant (up to10%) and some have been heated during the coalification process to the point of mobilization and then flowed throughout the coal to fill cleats. Cutinite macerals are derived from leaf and other plant cuticles and occur in minor amounts (usually 1% or less but occasional up to as much as 10%). However, in some coals, the cutinites are concentrated during weathering and the resulting coals are called paper coals. At two mid-western paper coal outcrops, one in Indiana and one in Kentucky, samples were taken and analyzed chemically and petrographically. In both cases the amount of cutinite in the fresh unweathered coal was less than 10% but at the outcrop edge cutinite and mineral matter were the only materials present. It appears that the massive, waxy, and planar nature of the cutinite allows it to resist weathering and to be concentrated. Thus, while most natural concentrations of macerals occur in lithotypes formed during coal deposition, natural concentrations of some resinite macerals are due to thermal mobilization during coalification and natural concentrations of cutinite are due to weathering.