Cut off Grade Optimizer Integrating Contaminant Constraints

APCOM 2009
Enrique Alfonso Rubio, Sebastián Horacio Troncoso, Patricio A. Prieto,
Abstract Open pit mine planning is normally based on the selection of an economic envelope that has been generated by the Lerchs & Grossman algorithm, which requires individual economic valuation of each block of a geological block model. The selected envelope, usually called Final Pit, is later discretized in pushbacks and benches, which correspond finally to the fractions that the production schedule will allocate in time. This planning methodology has been widely used by the mining industry in countless projects to exploit open-pit mines, however, in many of the deposits can be found some undesirable elements such as arsenic, phosphates, ash among other that tend to reduce the value of elements of economic interest, either by disrupting the processes of concentration or as deemed impurities that affect the quality of the final product. The existence of such elements makes the methodology described above become biased in the resultant economic valuation of the entire deposit, because any reduction in value by the presence of these undesirable elements is not directly attributable to the economic value of a block by itself because the economic result by process a set of blocks can differ from the result of processing each one individually. This paper proposes a methodology for the selection of an economic envelope, which discretized in pushbacks, benches and grade ranges, feeds an optimization model which supports the construction of a production schedule. The objective of the model is to maximize the net present value, considering contaminant constraints. Preliminary results show significant increases in value and reserves quantity, questioning the use of cut-off grades in generating a production schedule due to the reduction in the contaminant content in the processed ore allowed by block blending. Finally, it shows the importance of having adequate planning tools that will lead to the ability to look at the potential economic value of a mineral deposit.
Keywords: Mine planning, Arsenic, Production schedule, Open pit, pollutant constraints, Open pit, Mine planning, Arsenic, Production schedule, pollutant constraints, Mine planning, Arsenic, Production schedule, pollutant constraints, Open pit
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