The phenomenon of particle segregation during epoxy block preparation for characterisation studies by optical or SEM microscopy, and its potential detrimental effect on the results of such characterisation, is well known. However, the absence of a proper study showing the possible scale of errors caused by it, and the existing belief that in certain circumstances the effect can be neglected, result in the continuing practice where important characterisation is performed using traditional horizontally sectioned epoxy blocks. This article presents the results of optical image analysis of the particle segregation effect during epoxy block preparation for different size fractions of iron ore fines using the CSIRO Minera14/Recognition4 software. The differences in mineral abundances and liberation characteristics for different horizontal layers of vertical sections of epoxy blocks were analysed. Also the effects of particle layer thickness, epoxy block mixing techniques and the relative ratio of the iron ore sample to the epoxy during initial specimen preparation were investigated and discussed. The work performed shows that the difference between layers in the epoxy block due to density segregation can be unacceptably high for iron ore samples and, similarly, to any ore samples with significant density differences between particles of different texture. The traditional block preparation technique, with its random selection of the analysed horizontal layer, can therefore result in large errors in estimation of mineral abundances, mineral liberation and textural classification characteristics. It is suggested that vertical sections of epoxy blocks are used for image analysis where significant density difference between particles is suspected.