Incorporation of Geometallurgical Attributes and Geological Uncertainty into Long-Term Open-Pit Mine Planning

Nelson Morales,Maximiliano Alarcón,Sebastián Seguel,Enrique Jélvez,Alejandro Cáceres

doi:10.3390/min9020108

Abstract

Long-term open-pit mine planning is a critical stage of a mining project that seeks to establish the best strategy for extracting mineral resources, based on the assumption of several economic, geological and operational parameters. Conventionally, during this process it is common to use deterministic resource models to estimate in situ ore grades and to assume average values for geometallurgical variables. These assumptions cause risks that may negatively impact on the planned production and finally on the project value. This paper addresses the long-term planning of an open-pit mine considering (i) the incorporation of geometallurgical models given by equiprobable scenarios that allow for the assessing of the spatial variability and the uncertainty of the mineral deposit, and (ii) the use of stochastic integer programming model for risk analysis in direct block scheduling, considering the scenarios simultaneously. The methodology comprises two stages: pit optimization to generate initial ultimate pit limit per scenario and then to define a single ultimate pit based on reliability, and stochastic life-of-mine production scheduling to define block extraction sequences within the reliability ultimate pit to maximize the expected discounted value and minimize the total cost of production objective deviations. To evaluate the effect of the geometallurgical information, both stages consider different optimization strategies that depend on the economic model to be used and the type of processing constraints established in the scheduling. The results show that geometallurgical data with their associated uncertainties can change the decisions regarding pit limits and production schedule and, consequently, to impact the financial outcomes.

Highlights

This paper addresses the long-term planning of an open-pit mine incorporating simulated geometallurgical models that allow to consider the spatial variability and the uncertainty of the mineral deposit, quantifying the risk and assessing the impact on mine planning decisions such as ultimate pit limit and life-of-mine production scheduling along a number of simulated scenarios by means of a stochastic Direct Block Scheduling approach, where the entire set of realizations are simultaneously used into a stochastic model to maximize the expected discounted value of the project, and simultaneously, to minimize the discounted total cost associated to deviation of the production objectives
The present study explores the practical uses of long-term geometallurgical models in the mine planning, incorporating simulated models that allow to consider the spatial variability and the uncertainty of the mineral deposit through a stochastic Direct Block Scheduling (DBS) approach, quantifying the risk and assessing the impact on mine planning decisions such as life-of-mine production scheduling along a number of simulated scenarios, serving as a guide for mining engineers to considers geometallurgical uncertainty in the mine planning decisions
Geological and geometallurgical scenarios are considered in one-run as input to the optimization process, the extraction period for each mining block is determined, the solution achieves the maximum discounted economic benefit of the mining business, the solution achieves the minimum risk of losses due to potential deviations from the production plan, the solution satisfies operational constraints, such as slope angles in pit walls and mining capacities

Summary

Introduction

For an open-pit mine, there are two important problems that strategic planning process must be addressed: the ultimate pit limit problem (it defines the mineable reserves) and the life-of-mine (LOM) production scheduling problem (it defines when the reserves should be extracted in order to maximize the net present value, or NPV). These problems depend considerably on the spatial variability of the deposit. Figure onmathematical mathematical programming and that aims to integrate integrate allthe thesteps stepspresented presented in 1 based is based on mathematical programming known as (DBS) This approach aims to generate optimal pit limits and known as. This approach aims to generate optimal pit limits production schedules, where a single optimization process determines the best block-support production schedules, where a single optimization best block-support block-support and production schedules, where a single optimizationprocess processdetermines determines the the best extraction period, sosothe scheduled volumes ofofmineral already comply with some constraints, such extraction period, the scheduled volumes mineral already comply with some constraints, such extraction period, so the scheduled volumes of mineral already comply with some constraints, such asasmining or plant capacities [33].

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