Comment on “Influence of a basic intrusion on the vitrinite reflectance and chemistry of the Springfield (No. 5) coal, Harrisburg, Illinois” by Stewart et al. (2005)

In this communication, we demonstrate that the intrusion temperature of about 600 °C for the Cottage Grove dike provided by Stewart et al. [Stewart, A.K., Massey, M., Padgett, P.L., Rimmer, S.M., Hower, J.C., 2005. Influence of a basic intrusion on the vitrinite reflectance and chemistry of the Springfield (No. 5) coal, Harrisburg, Illinois. International Journal of Coal Geology 63, 58-67] is questionable, because their computation is based on an unrealistic heat flow model and the estimated contact temperature is derived from a geothermometer that is not calibrated for contact metamorphism. In order to obtain an accurate and reliable intrusion temperature based on the contact temperature of the intrusion, a reliable geothermometer in high temperature ranges should be used to calculate the peak temperature.