Define ridge - tier operation?

Ridge-tier operation refers to a specific type of mining operation in which a ridge or a series of ridges is excavated to extract valuable minerals or resources. This method involves removing the overlying material, such as soil or rock, to expose the mineral deposit beneath the ridge. The excavation process typically follows a tiered approach, where each tier is sequentially removed to access the underlying mineral deposits. This technique is commonly used in open-pit mining operations, particularly for minerals like coal, iron ore, or gold, where the mineral deposits are located along the ridges or elevated areas.