Using a custom-designed self-heating apparatus and procedure, activation energy (E(a)) was determined for four sulfide-bearing materials: two nickel concentrates, a copper concentrate and a sphalerite/pyrite mixture. The E(a) ranged from 22-29 kJ mol(-1), implying a common reaction. Comparing to literature, the E(a) values correspond to partial oxidation of hydrogen sulfide, supporting the contention that H(2)S may be an intermediate product in the self-heating of sulfide minerals. (C) 2011 Elsevier Ltd. All rights reserved.