Qualitative and quantitative descriptions of ‘refractoriness’ are proposed and discussed. Three types of problematic ores may be distinguished. These are described as “inherently refractory” (due to their complex mineralogical composition and texture), “economically refractory” (due to high cost of processing to meet required product grade specification, or waste handling procedures), or “environmentally refractory” (where processing is restricted due to chemicals required or generation of airborne, solid or liquid waste products). An example of a quantitative descriptor based on reported image analysis of different sulphide ores (Sutherland et al., 1989, 1991) is illustrated. The increased complexity of processing problematic ores is demonstrated with reference to typical process flow sheets for different types of sulphidic gold ores.