Siderite ores of the Bakalskoe deposit contain iron, magnesium and manganese carbonates. Since the content of manganese in the ore is insignificant, its effect of the processes under consideration is not taken into account in the calculations. Siderite ores are roasted in shaft furnaces, resulting from which carbonate decomposition occurs at a high level of heat consumption. In order to optimize the operating parameters of the roasting process and to determine the required fuel consumption, a thermodynamic analysis has been carried out, which made it possible to determine the initial temperature range for the decomposition of pure iron carbonate and sideroplesite (an ore mineral containing from 70 to 95% of iron carbonate), as well as to calculate the specific and equivalent heat of the decomposition thereof with the use of an approximate solution to the phase transition problem and the data of thermographic analysis. The comparison of the results obtained in determining the specific heat has demonstrated quite a good agreement between the experimental values and the values obtained with the use of calculations. The results of this work are of interest for specialists engaged in the preparation of siderite ores for blast furnace processing.