Solving a multi-stage mine sequencing model encompassing excavator allocation through Constraint Programming in a bauxite strip mining operation

Sedimentary mineral deposits are generally tabular and sub-horizontal, composed of one or multiple well-defined seams, arranged over large extensions, and when close to the surface, they are mined by surface mining methods. These geometric characteristics make it suitable for the application of the strip mining method as an alternative to the traditional open-pit mining method, which allows the reduction of the truck haulage fleet and the costs associated with waste disposal. Consequently, it reduces the greenhouse gas emissions and carbon footprint associated with excavation and transportation processes. This article presents a two-stage mathematical model based on Integer Linear Programming to address the mine sequencing problem of a strip mining operation in a bauxite deposit, encompassing the allocation of a heterogeneous fleet of excavators. The model is solved through Constraint Programming, an approach first used in strip mining problems. The first stage resulted in a near-optimal solution for panels that reached 94,80% of optimality in 639 seconds for the proposed mathematical model, which is an acceptable computational time. In turn, the second stage resulted in an optimal solution for strips that is more realistic and reached 94,87% of the first stage's objective function value in just 9 seconds.