We propose, implement, and test two approaches for dispatching trucks in an open-pit mining operation. The first approach relies on a nonlinear optimization model that incorporates queueing effects to set target average flow rates between mine locations. The second approach is based on a time-discretized mixed integer programming (MIP) model. The MIP model is difficult to solve exactly in real-time operations, so we present a heuristic that quickly produces high-quality feasible solutions. We give computational results demonstrating the effectiveness of the proposed heuristics and several key model components. We test the dispatching policies and model features by building a discrete-event simulation of an open-pit mine. We present a full computational study of the two policies in which we perform output analysis on key metrics of the open-pit mine simulation. Results indicate that the MIP-based dispatching policy consistently outperforms the more commonly-used average flow rate dispatching policy on open-pit mines in a wide variety of operational settings.