This paper presents a solution for scheduling open-pit mining operations and machinery affectation to meet production goals. The problem is complex due to various constraints such as operation sequencing, machinery compatibility, machinery availability, and accessibility to layers. The solution uses a disjunctive graph and a GRASP algorithm to solve the problem modeled as a flexible job shop problem with generic time-lags between operations. The algorithm performance has been benchmarked against a Mixed Integer Linear Program and provides high-quality solutions via numerical experiments.