The siderite ores of the Bakal deposit contain iron, magnesium and manganese carbonates. Since the content of manganese in the ore is insignificant, its influence on the considered processes is not taken into account in the calculations. Roasting of siderite ores is carried out in shaft furnaces, as a result of which carbonates are decomposed with a large expenditure of heat. To optimize the operating parameters of the firing process and determine the required fuel consumption, a thermodynamic analysis was carried out, which made it possible to determine the initial decomposition temperatures of pure iron carbonate and sideroplesite (an ore mineral containing 70-95% iron carbonate), as well as to calculate the specific and equivalent heat of their decomposition using an approximate solution of the phase transition problem and thermographic analysis data. Comparison of the results obtained by determining the specific heat of decomposition of iron and magnesium carbonates was carried out, which showed a fairly good convergence of the experimental values and the values obtained by calculation. The results obtained in the work are of particular interest to specialists involved in the preparation of siderite ores for blast-furnace processing.