Calculating ultimate pit limits and determining pushbacks in open-pit mining projects

Abstract

A very important part of any open-pit mining project is determining the ultimate pit limits and optimizing the pushbacks. Currently, block models are the most widely used for calculating mineral resources and reserves. Block models can define the ultimate pit limits through algorithms like floating cone, Lerchs-Grossmann, PseudoFlow, etc. However, only through an economic study will the best pits be selected, from most to least economically valuable, and the different possible pushbacks can then be defined.Based on pre-determined operating costs, all possible scenarios should be studied while varying the selling price in fixed increments between minimum and maximum values that cover all possible future prices. The starting selling price should be very low, and consequently, the only phase that will be economical is the one with adequate grade and a low stripping ratio. As the selling price increases, the ultimate pit limits do not vary or vary only slightly until the price reaches the point at which another of the ore bodies in the deposit becomes economical. This process is repeated as the price increases until the maximum price considered is reached; then, the project reaches the last phase that is economical if economic conditions are very favourable.The data obtained in each phase can be used to simulate different scenarios, since the different phases will not change because operating costs or economic conditions change. The ore is not going to move; what changes is the phase up to which mining will be economical and what profits will be obtained in each phase.