Open Pit Optimization - Strategies For Improving Economics Of Mining Projects Through Mine Planning

17* International Mining Congress and Exhibition of Turkey- IMCET2001, © 2001, ISBN 975-395-417-4

Open Pit Optimization - Strategies for Improving Economics of Mining Projects Through Mine Planning
K.Dagdelen
Mining Engineering Department, Colorado School of Mines. Golden, Colorado, USA

ABSTRACT: The open pit design and scheduling problem is a large-scale optimization problem that hasattracted considerable attention during the last 40 years The development of the "know-how" to improve economics of open pit mining projects through the use of mathematical optimization techniques goes back to early 1960's. Unfortunately, up until recently, many of these "optimizing algorithms" could not be implemented due to the limited capacity of the computer hardware used in many miningoperations. During the last 10 years, advancements in the computer hardware technology along with developments in software technology allowed open pit mines to have powerful desktop computers that can solve complex optimization problems on site. Due to applications of optimization techniques developed in the early 1960*s, for example, Chuquicamata Open Pit Mine in Chile re-evaluated their cutoff gradestrategy and improved Net Present Value (NPV) of their ' operations by USS800M. Newmont Gold Corporations in Nevada, USA has implemented large scale Linear Programming Model mat was developed in early I980's to schedule their entire mine and mill production in the Carlin District, resulting in significant process costs savings. This presentation will outline open pit optimization techniques that areavailable today and how they can be used to improve overall economics of projects that are being planned or in production.

1 INTRODUCTION The current practice of planning of hard rock open pit mine begins with a geologic block model (see Figure 1) and involves determination of: 1) Whemer a given block in the model should be mined or not; 2) If it is to be mined when it should be mined; 3) Onceit is mined then how it should be processed. The answer to each of these questions, when combined within the whole block model, define the annual progression of the pit surface and the yearly cash flows that will be coming from the mining operations during the life of mine. There can be many different solutions to the scheduling problem depending on how the decision is made for each of the blocks.Decision as to which blocks should be mined in a given year, and how they should be processed (i.e. waste, run of mine leach, crushed ore leach or mill ore etc.) defines not only the cash flows for that year but also impacts the future annual schedules. What is decided today has long-term implications as to what can be done in the future and all these decisions link together in defining theoverall economics of the a given project. The objective of the planning process for an open pit mine is usually to find optimum annual schedules that will give the highest Net Present Value (NPV)

while meeting various production, blending, sequencing and pit slope constraints. Traditionally, the scheduling problem described above is solved by dividing the problem into sub problems similar to oneshown in Figure 2. The solution step starts with the assumption of initial production capacities in the raining system and the estimates for the related costs and commodity prices.

Figure I 3-D geologic block model representation of a copper deposit.

117

Once the economic parameters are known, the analysis of the ultimate pit limits of the mine İs undertaken to determine what portion of thedeposit can economically be mined. Within the ultimate pit limits, pushbacks are further designed so that deposit is divided into nested pits going from the smallest pit with highest value per ton of ore to largest pit with the lowest value per ton of ore. These pushbacks are designed with haul road access and act as a guide during the scheduling of yearly productions from different benches. The...