Iron ore fines contain so-called slimes that act negatively on particle beneficiation due to elevated viscosity, leading to contamination of the final product, poor dewatering, and inferior materials handling. Cyclones provide a low-cost solution to removing the slimes, while also concentrating the coarser particles. The reality, however, is that there is significant misplacement of slimes into the underflow and significant loss of ultrafine iron ore that reports with the slimes to the tailings.This study investigated the application of a REFLUXTM Classifier, incorporating closely spaced inclined channels, to achieve beneficiation of iron ore fines less than 0.3 mm. The objective was to extend the separation to cover the full-size range below 0.3 mm, maximizing the Fe recovery and the product grade, while seeking to achieve complete removal of any slimes not removed by the cyclone. The impact of the presence of the slimes was investigated by performing experiments at different volumetric feed rates and pulp densities, recognising the impact of the viscosity due to the slimes could be reduced through dilution. Additional experiments were conducted using the REFLUXTM Graviton, exploiting G forces to remove the slimes below 0.015 mm, and then examining the performance of the REFLUXTM Classifier in the absence of the slimes. The results demonstrate the challenge faced by the industry in slimes removal and the prospects for significant advances in this area. CITATION:Carpenter, J L, Iveson, S M, Zhou, J, Sutherland, J and Galvin, K P, 2019. Influence of slimes on gravity separation of iron ore fines in a REFLUXTM Classifier, in Proceedings Iron Ore 2019, pp 685692 (The Australasian Institute of Mining and Metallurgy: Melbourne).