An application of 3-D modeling and optimization of the final pit limits for a lignite deposit

A number of algorithms have been developed in order to determine the optimal final limits of an open pit mine. Due to the complex nature of this problem, however, very few of them can offer a reliable and complete answer. The case of an actual lignite deposit was used in this study, which enabled an investigation into the capabilities of one of the most established optimizers (Whittle Three-D™). A three-dimensional block model of the deposit was first developed, based on the available drillhole data, with the use of the Digital Underground™, an integrated geostatistical modeling package. The largest possible utilization of the original geologic information was intended, and the modeling results were correlated with existing reserves calculations and past geologic observations on quality characteristics. A flexible methodology was then followed to transform the geologic reserves block model into an economic one, where each block is assigned a net value. Two alternative objective criteria formulations where introduced to facilitate this scope. A series of parametric regular 3-D fixed economic block models were constructed by varying the block size and also some basic mining and economic parameters. A number of case studies were then conducted, to form an extended sensitivity analysis of the various parameters that affect the total value, tonnage, and waste volume of the final optimal pit. The conclusions drawn can develop useful guidelines for the decision making of the mine operator. The optimization also provides a detailed ultimate open pit layout, that can enable a comprehensive mine planning and design.