Understanding free surface flow of mine tailings is necessary to plan deposition operations in tailings' storage facilities (TSF), and is important to predict the consequences of a dam break. Proper understanding of deposition operations has probably hindered adoption of alternative tailings technologies, wheras recent failures of tailings impoundments have had catastrophic consequences. Tailings exhibit thixotropic properties - their behavior is a function of the material's stress history. A thixotropic constitutive model has been implemented into an open-source Material Point Method (MPM) framework. The results were validated with previous experimental data at laboratory scale with good agreements. Large-scale simulations were done for 2D and 3D cases. The thixotropic model was able to model self-forming channels seen during field scale deposition. Dam break events also scaled differently from laboratory scale experiments with thixotropy. This can possibly be an element that explains longer runouts then initially predicted with standard rheology.