The reaction of ammonium nitrate with pyrite was studied using a simultaneous differential scanning calorimetry and thermogravimetric analyser (TGA/DSC). When a mixture of pyrite and ammonium nitrate is heated at a constant heating rate of 10 K min(-1) from room temperature to 800 degrees C, two exothermic reactions occur at about 200 and 450 degrees C, respectively. The first exothermic reaction is considered to take place between ammonium nitrate and pyrite where NO, NH3, SO2 and N2O gases are produced. The second exothermic reaction is due to the oxidation of the remaining pyrite by atmospheric oxygen. Based on the quantitative analysis of the gaseous and solid products of the reaction, a new overall reaction is proposed at the first exothermic peak of interest, which is thermodynamically favourable. The results have significant implication in the understanding of stability of ammonium nitrate-based industrial explosives in reactive mining grounds containing pyritic minerals. (c) 2006 Elsevier Ltd. All rights reserved.