The Aznalcóllar mine-pond break is the most catastrophic mining accident registered in the Iberian Peninsula (April 1998), and caused a tailings spill that affected around 45 km of the Agrio and Guadiamar Rivers. The flood was well-documented through satellite images, gauge station data and field campaigns. However, the lack of some data, the uncertainties in the spilled volume and the kind of fluid (mud-like) did not allow to reproduce it after it happened. In this work, as a first approximation for the numerical modelling of the flood propagation, the new non-Newtonian module of Iber model was used. The model was calibrated testing several combination of the parameters of the Bingham friction model. The results show that the spilled volume should have been around twice of the volume indicated in the literature. The consideration of non-Newtonian fluid properties can be necessary to obtain suitable results in the flood propagation and extension, besides the retention of the flood.