Carbonaceous shales contain organic carbon that can react with air when either exposed during the mining process or when buried in waste rock dumps. However, at ambient mine temperatures their intrinsic reactivity is extremely low due to the presence of a high mineral matter content (often silicate, carbonate and sulfate minerals) acting as a diluent and heat sink. However, if pyrite is present in these rocks, in a reactive form (size and morphology), it can act as an initiator of self-heating to raise the temperature of a broken rock pile to the point where the organic carbon takes over the self heating process (generally > 120°C) leading to subsequent thermal runaway. A systematic approach has been used to assess this spontaneous combustion hazard across Fortescue iron ore operations in the Pilbara. A substantial database of adiabatic self-heating Incubation test results has enabled the development of a spontaneous combustion hazard potential chart based on the total sulfur and total organic carbon content of the shale. The chart can be used as a ready reckoner to classify whether thermal runaway or no thermal runaway is achievable assuming a critical pile thickness is present and from Mine Ambient conditions, which can then be used to make informed decisions on waste rock management to control the spontaneous combustion hazard. In addition, some fundamental differences between the carbonaceous shale units at the various mine sites has also been identified from the chart.