The mineral processing research community has devoted enormous efforts to the modeling of mineral separators. While many efforts have been made to use only fundamental physics as a basis for the models, fluid flow patterns in separators are complex and the motion of particle swarms through fluids is difficult to describe. Even though computer codes for computational fluid dynamics are now very powerful, a reliable means of calculating the hindered settling velocity of a specific particle type within a polydisperse and polydense particle mixture has proved to be elusive. It is however an absolutely fundamental prerequisite to almost all model structures. In an effort to test the extent to which fundamental fluid mechanics can provide a prediction of particle separation, a study on a simple parallel-sided sluice has been carried out using glass bead and ilmenite mixtures at various particle concentrations and flow rates. Great care was taken to devise a flow splitter at the end of the sluice that permitted accurate measurement of the fluid flow profile and collection of slurry samples, allowing evaluation of the particle species concentration profiles.